Phosphate Binding Materials and Their Uses
Field of the Invention
The present invention relates to phosphate binding materials and
their uses in the treatment of hyperphosphatemia and for removing
phosphate from materials, for in vitro and in vivo applications.
More particularly, the present invention relates to phosphate
binding materials which are ligand-modified ferric poly oxo-
hydroxy materials.
Background of the Invention
Phosphate levels are regulated predominantly by the kidneys and
in healthy people phosphate homeostasis is maintained by urinary
excretion. Phosphate concentrations in serum can increase
dramatically in patients with chronic renal failure and lead to
secondary hyperthyroidism and soft tissue calcification. This
calcification results in atherosclerosis of the coronary arteries
and premature heart disease, which is the major cause of death in
end-stage renal disease (ESRD). Dietary phosphate restriction
alone is usually insufficient to control hyperphosphatemia in
haemodialysis patients and the oral intake of phosphate binders
is required to reduce intestinal absorption.
Aluminium and calcium compounds have been widely used to bind
dietary phosphate, but there are concerns regarding their long-
term safety. The use of aluminium-based phosphate binders
results in tissue accumulation of this element and may result in
systemic toxicity. The administration of large quantities of
calcium-based phosphate binders can result in hypercalcemia and
subsequently aggravate tissue calcification.
Sevelamer (polyallylamine hydrochloride) , a synthetic polymer
commercialised under the name of Renagel, is an anion exchange
resin used to bind dietary phosphate. However, the binding
action of this resin is not specific to phosphate and large doses
have to be administered to control serum phosphate in ESRD
patients, which can lead to low patient compliance.
Lanthanum carbonate is an approved phosphate binder
commercialised under the name of Fosrenol. However, concerns
exist about the long-term accumulation and toxicity of lanthanum
in tissues.
US 6,903,235 describes the use of ferric citrate, a soluble iron
compound, to bind dietary phosphate. However, the long-term use
of a soluble iron compound is likely to lead to gastrointestinal
side-effects due to the redox activity of free iron in the gut
lumen, which may subsequently result in low compliance.
WO 2007/088343 describes a phosphate binder formed from the
reaction of aqueous solutions of magnesium sulphate and ferric
sulphate in the presence of sodium hydroxide and sodium
carbonate, probably leading to an iron magnesium hydroxy
carbonate with an hydrotalcitic structure. This phosphate binder
is known as "Alpharen", but suffers from the disadvantage that it
binds relatively small amounts of phosphate and moreover releases
Mg2+ in the stomach, leading to frequent side-effects.
The ability to bind phosphate by iron oxo-hydroxides is known in
the art. For example, US 6,174,442 describes an adsorbent for
phosphate using ß-iron hydroxide stabilized by carbohydrates
and/or humic acid. However, its binding ability is limited and
the manufacturing process is unsuitable for the preparation of
large quantities of material. WO 2008/071747 describes an
adsorbent for phosphate containing -iron oxide-hydroxide
stabilized by insoluble and soluble carbohydrates. However, the
phosphate binding activity of the materials described therein is
limited to very low pH, limiting its effectiveness as a phosphate
binder.
In summary, there is no ideal phosphate binder in current use and
existing materials have one or many flaws, most commonly toxicity
or accumulation, cost, efficacy of phosphate removal, acidosis
and/or patient intolerance.
Accordingly, there remains a continuing need in the art to
develop further phosphate binders that overcome or ameliorate
some of the drawbacks of existing treatments.
Summary of the Invention
Broadly, the present invention relates to phosphate binding
materials and compositions comprising them which are solid
ligand-modified poly oxo-hydroxy metal ion materials. The
compositions disclosed herein are based on ferric iron oxo-
hydroxides modified with carboxylic acid ligands, or ionised
forms thereof,- such as adipate. These materials are made and
tested in the examples provided in the application to demonstrate
that they can bind phosphate in in vitro and in in vivo studies.
Accordingly, in a first aspect, the present invention provides a
ferric iron composition for use in a method of treating
hyperphosphatemia, wherein the ferric iron composition is a solid
ligand-modified poly oxo-hydroxy metal ion material represented
by the formula (MxLy(OH)n), wherein M represents one or more metal
ions that comprise Fe3+ ions, L represents one or more ligands
that comprise a carboxylic acid ligand, or an ionised form
thereof, and OH represents oxo or hydroxy groups and
wherein the material has a polymeric structure in which the
ligands L are substantially randomly substituted for the oxo or
hydroxy groups. It is preferred that the solid ligand-modified
poly oxo-hydroxy metal ion material has one or more reproducible
physico-chemical properties, for example dissolution profile
and/or phosphate binding characteristics. As discussed further
below, the ferric iron materials of the present invention
preferably have structures which are consistent with ligand-
modif ied ferrihydrite. It is also preferred that the ferric iron
materials of the present invention have demonstrable M-L bonding
using physical analysis, such as infrared spectroscopy.
In a further aspect, the present invention provides the use of a
ferric iron composition of the present invention for the
preparation of a medicament for the treatment of
In a further aspect, the present invention provides a method of
treating hyperphosphatemia, the method comprising administering
. to a patient in need of treatment a therapeutically effective
amount of a ferric iron composition of the present invention.
In a further aspect, the present invention provides a method for
removing phosphate from a medium, the method comprising (a)
contacting a medium containing phosphate with a ferric iron
composition of the present invention under conditions in which
the phosphate is capable of binding to the ferric iron
composition and (b) separating the bound phosphate from the
composition. This method may be used in vitro or in vivo.
Accordingly, the materials described herein are capable of
selectively removing phosphate from solutions or suspensions
containing this anion. The removal might take place in vivo, for
example where the materials described herein are capable of
removing phosphate from the liquid or sludge-like contents of the
gastrointestinal tract following oral administration. However,
the materials of the present invention may find other
applications, for example where the materials are capable of
removing phosphate from food-stuffs prior to consumption, or are
capable of selectively removing phosphate from dialysis fluids,
plasma and/or whole blood. One particular application of the
phosphate binders of the present invention is in dialysis where
they may be used for the extracorporeal removal of phosphate from
dialysis fluids during haemodialysis processes. In this aspect,
the present invention provides compositions such as a food-stuff
or dialysis fluid that comprise a phosphate binding material of
the present invention.
Accordingly, the present invention provides a method to treat
high plasma phosphorus levels, hyperphosphatemia arising from any
level of renal insufficiency, acute renal failure, chronic renal
failure, and/or end-stage renal disease, including conditions
that require haemodialysis. The clinical management of these
conditions using the present invention may help to ameliorate
complications associated with these conditions, such as secondary
hyperthyroidism, soft tissue calcification, osteodystrophy,
hypercalcaemia, hyperparathyroidism reduction, cardiovascular
morbidity or mortality, renal osteodystrophy and/or
calciphylaxis.
In one aspect, the present invention provides a process
comprising the steps of producing a ferric iron material and
testing it to determine whether, or' to what extent it is capable
of binding phosphate. By way of example, the process may
comprise:
(a) mixing the solution comprising Fe3+ and carboxylic acid
ligand (e.g. adipic acid), and any additional ligands or other
components, in a reaction medium at a first pH(A) at which the
components are soluble;
(b) changing the pH(A) to a second pH(B) to cause a solid
precipitate or a colloid of the ligand-modified poly oxo-hydroxy
metal ion material to be formed;
(c) separating, and optionally drying and/or formulating,
the solid ligand-modified poly oxo-hydroxy metal ion material
produced in s'tep (b) .
Embodiments of the present invention will now be described by way
of example and not limitation with reference to the accompanying
figures and examples.
Brief Description of the Figures
Figure 1: Evolution of FeOH AdlOO precipitation with increasing
pH, expressed as the percentage of total iron in the starting
solution. A fully precipitated and agglomerated phase is
achieved at pH 4.5.
Figure 2: (a) In vitro phosphate binding. When iron hydroxide is
ligand-modified as described (e.g. FeOH AdlOO) there is clearly
superior phosphate binding to unmodified ferrihydrite (Fe(OH)3) or
Renagel (polyallylamine hydrochloride) and at least equivalence
to the effective, but potentially toxic, lanthanum carbonate.
Moreover, the ligand chosen is advantageous with others, for
example histidine, which unlike adipate does not lead to the
marked increase in phosphate binding (i.e. FeOH HislOO versus
Fe(OH)3) . White bars are pH 3 and grey bars are pH 5. (b) A
second example of in vitro phosphate binding: pH3 (white), pH5
(grey) and also at pH 7 (black). The effectiveness of Fe OH
Adl00 SiO2 (i.e. silicate modified FeOH Ad100) is also shown. In
both figures (a and b) the solution was 10 mM phosphate and the
amount of binder used was 53.6 mg in a total volume of 20 ml. In
these experiments the binder was first exposed to the lower pH
for 60 minutes then the higher pH(s) for 60 minutes, all
sequentially.
Figure 3: Lanthanum carbonate appears only effective where low pH
'pre-conditioning' occurs unlike for FeOHAdlOO and FeOH AdlOO
Si02. Experimental conditions were as in Figure 2a/b except that
the phosphate binders were only exposed to the phosphate solution
at pH 5 and not sequentially and thus no acidic (gastric) pre-
conditioning of the binders occurred at the higher pHs.
Figure 4: Dissolution profile for FeOH AdlOO (diamonds),
FeOHAdlOO Si02 (triangles), and unmodified 2-line ferrihydrite
(squares) at pH 1.2. See materials and methods for detailed
description of methodology.
Figure 5: Particle size of FeOHAdlOO freshly prepared (a); upon
drying(b); and after basic milling (c).
Figure 6: Infrared analysis of FeOH AdlOO.
Figure 7: Infrared analysis of FeOH AdlOO Si02.
Figure 8: Infrared analysis of unmodified ferrihydrite (Fe(OH)3)
for reference.
Figure 9: Infrared analysis of unmodified adipic acid for
reference.
Figure 10: a) The primary particles (crystallites) of FeOH AdlOO
show up as 2-3 nm, dark, mottled particles in a high resolution
TEM image of the powder, and appear less crystalline than
unmodified ferrihydrite (not shown). b) The underlying
ferrihydrite-like structure is apparent from electron diffraction
with plane spacings at 2.5 and 1.5 A. c)EDX spectrum shows major
elements of FeOH AdlOO to be C, 0 and Fe with minor contributions
from Cl (~ 1.4 at.%), K (~1.2 at.%), and possibly Na. The Cu
signal is due to the support grid.
Figure 11. Mean (SEM) Urinary Phosphorus Excretion (mg in 8
hours) from 13 Volunteers Following a Meal plus FeOH Ad100 or
placebo.
Figure 12. In vitro phosphate binding of various ligand-modified
ferric hydroxides. The solution was 10 mM phosphate and the
amount of binder used was 214 mg in a total volume of 80 ml. The
binder was first exposed to the lower pH for 60 minutes then the
higher pH(s) for 60 minutes, all sequentially.
Figure 13. In vitro phosphate binding of various ligand-modified
ferric oxo-hydroxides. Different amounts of binder were added to
a 10 mM phosphate solution to obtain 1:1, 1:3 and 1:10 phosphate-
to-iron molar ratios. Phosphate binding occurred for 120 min at
37°C.
Figure 14. In vitro phosphate binding of FeOH AdlOO recovered
using different production methods. The solution was 10 mM
phosphate and the amount of binder used was 214 mg in a total
volume of 80 ml. The binder was first exposed to the lower pH
for 60 minutes then the higher pH(s) for 60 minutes, all
sequentially. (ND= Not determined).
Detailed Description
The Metal Ion (M)
The production and characterisation of solid ligand-modified poly
oxo-hydroxy metal ion materials is disclosed in our earlier
application PCT/GB2008/000408 (WO 2008/096130) filed on 6
February 2008. These materials, including those that comprise
ferric iron (Fe3+), that are used to form the phosphate binding
materials disclosed herein, may be represented by the formula
(MxLy(OH)n), where M represents one or more metal ions. Normally,
the metal ion will originally be present in the form of a salt
that in the preparation of the materials may be dissolved and
then induced to form poly oxo-hydroxy co-complexes with ligand
(L). In some embodiments, the metal ions substantially comprise
ferric iron (Fe3+), as opposed to a combination of metal ions
being present, or the metal ions including iron in other
oxidation states, such as Fe2+. Preferably, some of the ligand
used is integrated into the solid phase through formal M-L
bonding, i.e. not all of the. ligand (L) is simply trapped or
adsorbed in the bulk material. The bonding of the metal ion in
the materials can be determined using physical analytical
techniques such as infrared spectroscopy where the spectra will
have peaks characteristic of the bonds between the metal ion and
the ligand (L), as well as peaks characteristic of other bonds
present in the material such as M-O, O-H and bonds in the ligand
species (L). The phosphate binders disclosed herein use ferric
iron (Fe3+) to provide compositions that are biologically
compatible under the conditions for which the materials are used,
for example to ameliorate some of the drawbacks of the prior art
phosphate binding compositions which tend to be systemically
toxic or have binding properties that are not specific to
phosphate.
By way of background, it is well known in the art that iron
oxides, hydroxides and oxo-hydroxides are composed of Fe together
with 0 and/or OH and are collectively referred to in this patent
and known in the art as iron oxo-hydroxides. Different iron oxo-
hydroxides possess different structures and elemental
compositions which in turn determine their physicochemical
properties (see Cornell & Schwertmann, The Iron Oxides Structure,
Properties, Reactions, Occurrence and Uses. 2nd ed, 1996, VCH
Publishers, New York). For example, Akageneite (ß- or beta-iron
oxo-hydroxide) contains chloride or fluoride in its intrinsic
structure and forms spindle or rod-shaped crystals. Maghemite
(?- or gamma-iron oxide) contains cation deficient sites and
typically shows ferromagnetic properties. This material tends to
produce cubic crystals. Ferrihydrite is a further example of an
iron oxo-hydroxide material that shows a lower level of
structural order than the akageneite and maghemite and produces
spherical crystals. The experiments disclosed herein demonstrate
that the phosphate binders disclosed herein, such as FeOH Ad100,
preferably have a ferrihydrite-like structure and preferably a
structure consistent with 2-line ferrihydrite. By way of
example, the skilled person can assess whether a material has a
2-line ferrihydrite structure using a diffraction technique,
preferably using electron diffraction, a technique in which
electrons that bombard a sample in an electron microscope are
scattered in a fashion that reflects the internal order of the
primary particle of the material, and produces a spectrum that is
similar to that of 2-line ferrihydrite, as opposed to other forms
of iron oxo-hydroxide. Alternatively or additionally, the size
and morphology of particles of the phosphate binders of the
present invention, when viewed with electron microscopy, is
similar to that of 2-line ferrihydrite. However, it should be
noted that although from electron studies the size, morphology
and atomic ordering of the primary particle appears similar to
that of 2-line ferrihydrite, the material is not 2-line
ferrihydrite, rather a ligand modified form of it. This is
apparent firstly from in vitro phosphate binding studies where
the materials claimed herein consistently and significantly show
an enhancement of phosphate binding ability in relation to
unmodified 2-line ferrihydrite. Secondly, dissolution studies
show that at an acidic pH, typically at or below pH 1.2, the
materials of the present invention have rapid dissolution, a
physico-chemical parameter that is not observed with 2-line
ferrihydrite.
Similarly, it is preferred that the materials of the present
invention have a significantly higher phosphate binding capacity
than 2-line ferrihydrite at a range of pHs that may be
experienced post prandially in the gastrointestinal tract, for
example from pH 3-7. An exemplary assay for determining
phosphate binding is reported in the example 2.1 in which equal
masses of ferrihydrite (e.g. 53.6 mg), or indeed any other binder
used as a comparison, and a phosphate binder of the present
invention were assayed to determine the percentage of phosphate
they are capable of binding under physiological conditions. In
general, the mass of the materials used in the assay may be
between 10mg and 80mg inclusive in a 20 mL assay. These results
show that ferrihydrite binds about 30% of phosphate from 10 mM
phosphate solution. In contrast, it is preferred that the
phosphate binders of the present invention bind at least 50% of
the phosphate, more preferably at least 60%, more preferably at
least 70%, and most preferably 80% to 85% or more of the
phosphate, illustrating the significant improvements to the
properties of the phosphate binders of the present invention as
compared to unmodified ferrihydrite.
Infrared analysis shows that unlike with 2-line ferrihydrite the
material claimed herein shows bonding consistent with the
presence of the added ligand, namely adipate in this particular
example.
In summary, the structure of the phosphate binding materials of
the present invention is preferably based upon 2-line
ferrihydrite, but has been chemically modified in such a way that
it has significantly different and novel properties.
Accordingly, the materials of the present invention may be
described as having structures that are consistent with 2-line
ferrihydrite, as determined using TEM imaging and/or electron
diffraction (see the examples).
Moreover, by way of comparison with the ferric iron compositions
disclosed herein, the presence of formal bonding is one aspect
that helps to distinguish the materials of the present invention
from other products such as "iron polymaltose" (Maltofer) in
which particulate crystalline ß-iron oxo-hydroxide (akageneite)
is surrounded by a sugar shell formed from maltose and thus is
simply a mixture of iron oxo-hydroxide and sugar at the nano-
level (Heinrich (1975); Geisser and Muller (1987); Nielsen et al
(1994; US Patent No: 3,076,798); US20060205691). In addition,
the materials of the present invention are metal poly oxo-hydroxy
species modified by non-stoichiometric ligand incorporation and
should therefore not be confused with the numerous metal-ligand
complexes that are well reported in the art (e.g., see WO
2003/092674, WO 2006/037449). Although generally soluble, such
complexes can be precipitated from solution at the point of
supersaturation, for example ferric trimaltol, Harvey et al.
(1998), WO 2003/097627; ferric citrate, WO 2004/074444 and ferric
tartrate, Bobtelsky and Jordan (1947) and, on occasions, may even
involve stoichiometric binding of hydroxyl groups (for example,
ferric hydroxide saccharide, US Patent No: 3,821,192). The use
of hydroxyl groups to balance the charge and geometry of metal-
ligand complexes is, of course, well reported in the art (e.g.
iron-hydroxy-malate, WO 2004./050031) and unrelated to the solid
ligand-modified poly oxo-hydroxy metal ion materials reported
herein.
Similarly, WO 2008/071747 describes an adsorbent for phosphate
containing gamma-iron oxide-hydroxide (maghemite) stabilized by
an insoluble and soluble carbohydrates. The production of the
material described therein requires the presence of an insoluble
carbohydrate, such as starch, which only acts as a physical
support for material and does not significantly interact with the
iron oxo-hydroxide. The production of the material described
therein may also include an optional addition of a soluble
carbohydrate, such as sucrose, in the final stages of production.
The sole purpose of addition of the soluble carbohydrate
described therein is to prevent phase changes due to ageing of
the material. In contrast, the ferric iron compositions of the
present invention preferably have 2-line ferrihydrite-like
structure and do not employ an insoluble carbohydrate as a
support material and/or do not modify the properties of the
starting material using a soluble carbohydrate.
Without modification, the primary particles of the materials used
herein have metal oxide cores and metal hydroxide surfaces and
within different disciplines may be referred to as metal oxides
or metal hydroxides. The use of the term 'oxo-hydroxy' or 'oxo-
hydroxide' is intended to recognise these facts without any
reference to proportions of oxo or hydroxy groups. Hydroxy-oxide
could equally be used therefore. As described above, the
materials of the present invention are altered at the level of
the primary particle of the metal oxo-hydroxide with at least
some of the ligand L being introduced into the structure of the
primary particle, i.e. leading to doping or contamination of the
primary particle by the ligand L. This may be contrasted with
the formation of nano-mixtures of metal oxo-hydroxides and an
organic molecule, such as iron saccharidic complexes, in which
the structure of the primary particles is not so altered.
The primary particles of the ligand-modified poly oxo-hydroxy
metal ion materials described herein are produced by a process
referred to as precipitation. The use of the term precipitation
often refers to the formation of aggregates of materials that do
separate from solution by sedimentation or centrifugation. Here,
the term "precipitation" is intended to describe the formation of
all solid phase material, including aggregates as described above
and solid materials that do not aggregate but remain as non-
soluble moieties in suspension, whether or not they be
particulate or nanoparticulate {colloidal or sub-colloidal).
These latter solid materials may also be referred to as aquated
particulate solids.
In the present invention, reference may be made to the modified
metal oxo-hydroxides having polymeric structures that generally
form above the critical precipitation pH. As used herein, this
should not be taken as indicating that the structures of the
materials are polymeric in the strict sense of having a regular
repeating monomer unit because, as has been stated, ligand
incorporation is, except by co-incidence, non-stoichiometric.
The ligand species is introduced into the solid phase structure
by substituting for oxo or hydroxy groups leading to a change in
solid phase order. In some cases, for example the production of
the ferric iron materials exemplified herein, the ligand species
L may be introduced into the solid phase structure by the
substitution of oxo or hydroxy groups by ligand molecules in a
manner that decreases overall order in the solid phase material.
While this still produces solid ligand modified poly oxo-hydroxy
metal ion materials that in the gross form have one or more
reproducible physico-chemical properties, the materials have a
more amorphous nature compared, for example, to the structure of
the corresponding metal oxo-hydroxide. The presence of a more
disordered or amorphous structure can readily be determined by
the skilled person using techniques well known in the art. One
exemplary technique is Transmission electron microscopy (TEM).
High resolution transmission electron microscopy allows the
crystalline pattern of the material to be visually assessed. It
can indicate the primary particle size and structure (such as d-
spacing), give some information on the distribution between
amorphous and crystalline material, and show that the material
possesses a structure consistent with a 2-line ferrihydrite-like
structure. Using this technique, it is apparent that the
chemistry described above increases the amorphous phase of our
described materials compared to corresponding materials without
the incorporated ligand. This may be especially apparent using
high angle annular dark field aberration-corrected scanning
transmission electron microscopy due to the high contrast
achieved while maintaining the resolution, thus allowing the
surface as well as the bulk of the primary particles of the
material to be visualised.
The reproducible physico-chemical property or characteristic of
the materials of the present invention will be dependent on the
application for which the material is intended. Examples of the
properties that can be usefully modulated using the present
invention include: dissolution (rate, pH dependence and pM
dependence), disaggregation, adsorption and absorption
characteristics, reactivity-inertness, melting point, temperature
resistance, particle size, magnetism, electrical properties,
density, light absorbing/reflecting properties, hardness-
softness, colour and encapsulation properties. Examples of
properties that are particularly relevant to the field of
supplements, fortificants and mineral therapeutics are physico-
chemical properties selected from one or more of a dissolution
profile, an adsorption profile or a reproducible elemental ratio.
In this context, a property or characteristic may be reproducible
if replicate experiments are reproducible within a standard
deviation of preferably ± 10%, and more preferably ± 5%, and even
more preferably within a limit of ± 2%. In the present
invention, the phosphate binding materials preferably have
reproducible phosphate binding properties and/or dissolution
profiles. In addition to the physiological phosphate binding
assay discussed above and exemplified in section 2.1, additional
properties of the materials of the present invention, such as
phosphate binding affinity or capacity, or dissolution profiles,
may be also determined using techniques disclosed herein, see for
example sections 2.2 and 3. In preferred embodiments, the
capacity (K2) of the phosphate binders of the present invention
is at least 1.5 mmol P/g binder, more preferably at least 2.0
mmol P/g binder, and most preferably at least 2.5 mmol P/g
binder.
The dissolution profile of the solid ligand-modified poly oxo-
hydroxy metal ion materials can be represented by different
stages of the process, namely disaggregation and dissolution.
The term dissolution is used to describe the passage of a
substance from solid to soluble phase. More specifically,
disaggregation is intended to describe the passage of the
materials from a solid aggregated phase to an aquated phase that
is the sum of the soluble phase and the aquated particulate phase
(i.e. solution plus suspension phases). Therefore, the term
dissolution as opposed to disaggregation more specifically
represents the passage from any solid phase (aggregated or
aquated) to the soluble phase.
The Ligand (L)
In the solid phase ligand-modified poly oxo-hydroxy metal ion
species represented by the formula (MxLy(OH)n) , L represents one
or more ligands or anions, such as initially in its protonated or
alkali metal form, that can be incorporated into the solid phase
ligand-modified poly oxo-hydroxy metal ion material. In the
materials described herein, at least one of the ligands is a
carboxylic acid ligand, or an ionised form thereof (i.e., a
carboxylate ligand), such as adipic acid or adipate. Preferably,
the ligand is a dicarboxylic acid ligand, and may be represented
by the formula HOOC-R1-COOH (or an ionised form thereof) , where R1
is an optionally substituted C1-10 alkyl, C1-10 alkenyl or C1-10
alkynyl group. In general, the use of ligands in which R1 is a
C1-10 alkyl group, and more preferably is a C2-6 alkyl group, is
preferred. Preferred optional substituents of the R1 group
include one or more hydroxyl groups, for example as present in
malic acid. In preferred embodiments, the R1 group is a straight
chain alkyl group. A more preferred group of carboxylic acid
ligands include adipic acid (or adipate), glutaric acid (or
glutarate), pimelic acid (or pimelate) , succinic acid (or
succinate) , and malic acid (or malate). Whether the carboxylic
acid ligand is present as the acid or is partially or completely
ionised and present in the form of a carboxylate anion will
depend on a range of factors such as the pH at which the material
is produced and/or recovered, the use of post-production
treatment or formulation steps and how the ligand becomes
incorporated into the poly oxo-hydroxy metal ion material. In
some embodiments, at least a proportion of the ligand will be
present in the carboxylate form as the material are typically
recovered at pH>4 and because the interaction between the ligand
and the positively charged iron would be greatly enhanced by the
presence of the negatively charged carboxylate ion. For the
avoidance of doubt, the use of carboxylic acid ligands in
accordance with the present invention covers all of these
possibilities, i.e. the ligand present as a carboxylic acid, in a
non-ionised form, in a partially ionised form (e.g., if the
ligand is a dicarboxylic acid) or completely ionised as a
carboxylate ion, and mixtures thereof.
Typically, ligands are incorporated in the solid phase poly oxo-
hydroxy metal ion materials to aid in the modification of a
physico-chemical property of the solid material, e.g. as compared
to a poly oxo-hydroxylated metal ion species in which the
ligand(s) are absent. In some embodiments of the present
invention, the ligand(s) L may also have some buffering capacity.
Examples of ligands that may be employed in the present invention
include, but are by no means limited to: carboxylic acids such as
adipic acid, glutaric acid, tartaric acid, malic acid, succinic
acid, aspartic acid, pimelic acid, citric acid, gluconic acid,
lactic acid or benzoic acid; food additives such as maltol, ethyl
maltol or vanillin; 'classical anions' with ligand properties
such as bicarbonate, sulphate and phosphate; mineral ligands such
as silicate, borate, molybdate and selenate; amino acids such as
tryptophan, glutamine, proline, valine, or histidine; and
nutrient-based ligands such as folate, ascorbate, pyridoxine or
niacin or nicotinamide. Typically ligands may be well recognised
in the art as having high affinity for a certain metal ion in
solution or as having only low affinity or not be typically
recognised as a ligand for a given metal ion at all. However, we
have found that in poly oxo-hydroxy metal ion materials, ligands
may have a role in spite of an apparent lack of activity in
solution. Typically, two ligands of differing affinities for the
metal ion are used in the production of these materials although
one, two, three, four or more ligands may be useful in certain
applications.
For many applications, ligands need to be biologically compatible
under the conditions used and generally have one or more atoms
with a lone pair of electrons at the point of reaction. The
ligands include anions, weak ligands and strong ligands. Ligands
may have some intrinsic buffering capacity during the reaction.
Without wishing to be bound by a particular explanation, the
inventors believe that the ligands have two modes of interaction:
(a) substitution of oxo or hydroxy groups and, therefore,
incorporation with a largely covalent character within the
material and (b) non-specific adsorption (ion pair formation).
These two modes likely relate to differing metal-ligand
affinities (i.e. strong ligands for the former and weak
ligands/anions for the latter). There is some evidence in our
current work that the two types of ligand are synergistic in
modulating dissolution characteristics of the materials and,
perhaps, therefore, in determining other characteristics of the
material. In this case, two ligand types are used and at least
one (type (a)) is demonstrable as showing metal binding within
the material. Ligand efficacy, probably especially for type (b)
ligands, may be affected by other components of the system,
particularly electrolyte.
The ratio of the metal ion(s) to the ligand(s) (L) is also a
parameter of the solid phase ligand-modified poly oxo-hydroxy
metal iron material that can be varied according to the methods
disclosed herein to vary the properties of the materials.
Generally, the useful ratios of M:L will be between 10:1, 5:1,
4:1, 3:1, 2:1 and 1:1 and 1:2, 1:3, 1:4, 1:5 or 1:10.
Producing and processing the phosphate binders
Generally, the phosphate binders of the present invention may be
produced by a process comprising:
(a) mixing the solution comprising Fe3+ and a carboxylic
acid ligand, and optionally any further ligands or other
components, in a reaction medium at a first pH(A) at which the
components are soluble;
(b) changing the pH(A) to a second pH(B) to cause a solid
precipitate or a colloid of the ligand-modified poly oxo-hydroxy
metal ion material to be formed;
(c) separating, and optionally drying and/or formulating,
the solid ligand-modified poly oxo-hydroxy metal ion material
produced in step (b).
Examples of conditions that may be employed include the following
using a first pH(A) which is less than 2.0 and the second pH(B)
which is between 3.0 and 12.0, preferably between 3.5 and 8.0,
and more preferably between 4.0 and 6.0, and carrying out the
reaction at room temperature (20-25°C). In general, it is
preferred that in step (a), the solution contains 20 to 100mM Fe3+
and 50 to 250mM of a suitable carboxylic acid ligand, and more
preferably about 40mM Fe3+ and about lOOmM of the ligand. A
preferred ligand is adipic acid.
The separation of a candidate material may then be followed by
one or more steps in which the material is characterised or
tested. By way of example, the testing of the phosphate binding
material may be carried out in vitro or in vivo to determine one
or more properties of the material, most notably its dissolution
profile and/or one or more phosphate binding properties.
Alternatively or additionally, the process may comprise
chemically, e.g. through a titration process, or physically, e.g.
through a micronizing process, altering the final particle size
of the ferric iron composition and/or subjecting the ferric iron
phosphate binder to one or more further processing steps on the
way to producing a final composition, e.g. for administration to
a subject. Examples of further steps include, but are not
limited to: washing, centrifugation, filtration, spray-drying,
freeze-drying, vacuum-drying, oven-drying, dialysis, milling,
granulating, encapsulating, tableting, mixing, compressing,
nanosizing and micronizing.
In some embodiments, additional steps may be carried out between
the initial production of the material and any subsequent step in
which it is formulated as a medicament. These additional post-
production modification steps may include the step of washing the
material, for example with water or a solution containing a
further ligand such as nicotinamide, that the inventors have
found to remove impurities or replace an incorporated ligand with
the further ligand, thereby increasing the Fe3+ content of the
material and its phosphate binding capacity and/or providing the
material with one or more further properties because of the
presence of the further ligand. The effect of this is
demonstrated in the examples and is discussed further in the
section below.
Hydroxy and oxo groups
The present invention may employ any way of forming hydroxide
ions at concentrations that can provide for hydroxy surface
groups and oxo bridging in the formation of these poly oxo-
hydroxy materials. Examples include but are not limited to,
alkali solutions such as sodium hydroxide, potassium hydroxide
and sodium bicarbonate, that would be added to increase [OH] in
an ML mixture, or acid solutions such as mineral acids or organic
acids, that would be added to decrease [OH] in an ML mixture.
The conditions used to produce the phosphate binding compositions
of the present invention may be tailored to control the physico-
chemical nature of the precipitate, or otherwise assist in its
collection, recovery or formulation with one or more excipients.
This may involve purposeful inhibition of agglomeration, or the
used drying or grinding steps to subsequently affect the material
properties. However, these are general variables to any such
system for solid extraction from a solution phase. After
separation of the precipitated material, it may optionally be
dried before use or further formulation. The dried product may,
however, retain some water and be in the form of a hydrated solid
phase ligand-modified poly oxo-hydroxy metal ion material. It
will be apparent to those skilled in the art that at any of the
stages described herein for recovery of the solid phase,
excipients may be added that mix with the ligand-modified poly
oxo-hydroxy metal ion material but do not modify the primary
particle and are used with a view to optimising formulation for
the intended function of the material. Examples of these could
be, but are not limited to, glycolipids, phospholipids (e.g.
phosphatidyl choline), sugars and polysaccharides, sugar alcohols
(e.g. glycerol), polymers (e.g. polyethyleneglycol (PEG)) and
taurocholic acid.
In other embodiments, further ligands may be included in the
reaction for producing the ligand-modified poly oxo-hydroxy metal
ion materials, so that these ligands become incorporated into the
material. Examples of ligands that may be included in this way
include phosphate uptake inhibitors and/or a substance capable of
providing additional therapeutic or physiological properties such
as protection of the gut mucosa, for example to ameliorate
potential gastric side effects that may occur on administration
of the phosphate binding material to a subject. Alternatively or
additionally a phosphate uptake inhibitor and/or a substance
capable of ameliorating gastric side effects may be formulated in
a composition with the solid ligand-modified poly oxo-hydroxy
metal ion material, i.e. mixed with the material as described in
the section below.
By way of illustration, phosphate uptake inhibitors are well
known in the art and include nicotinamide, niacin or the
inhibitors described in US 2004/0019113, US 2004/0019020 and WO
2004/085448. Examples of substances capable of ameliorating
gastric side effects include retinol and/or riboflavin, see Ma et
al., J. Nutr. Sci., 138(10): 1946-50, 2008.
Formulations and Uses
The solid phase materials of the present invention may be
formulated for use as phosphate binding materials and may be used
to treat hyperphosphatemia, in vitro and/or in vivo. Accordingly,
the compositions of the present invention may comprise, in
addition to one or more of the solid phase materials of the
invention, a pharmaceutically acceptable excipient, carrier,
buffer, stabiliser or other materials well known to those skilled
in the art. Such materials should be non-toxic and should not
significantly interfere with the efficacy of the solid phase
materials for the application in question.
The precise nature of the carrier or other component may be
related to the manner or route of administration of the
composition. These compositions may be delivered by a range of
delivery routes including, but not limited to: gastrointestinal
delivery, especially orally and nasogastric delivery; parenteral
delivery, including injection; or by implant at specific sites,
including prosthetics that may be used for this purpose or mainly
for another purpose but have this benefit. The compositions
described herein may also be employed for removing phosphate from
food-stuffs prior to consumption or for selectively removing
phosphate from dialysis fluids, plasma and whole blood. In
particular, the compositions can be used in dialysis fluids to
enhance phosphate removal during haemodialysis processes.
Pharmaceutical compositions for oral administration may be in a
tablet, capsule, powder, gel, liquid form, sprinkle or a suitable
food-stuff. A tablet may include a solid carrier such as gelatin
or an adjuvant. Capsules may have specialised properties such as
an enteric coating. Liquid pharmaceutical compositions generally
include a liquid carrier such as water, petroleum, animal or
vegetable oils, mineral oil or synthetic oil. Physiological
saline solution, dextrose or other saccharide solution or glycols
such as ethylene glycol, propylene glycol or polyethylene glycol
may be included. Where the solid ligand-modified poly oxo-hydroxy
ferric ion material of the present invention needs to be
maintained in a solid form, e.g. to control the delivery of a
component of the material, it may be necessary to select
components of the formulation accordingly, e.g. where a liquid
formulation of the material is made. Where the material is
administered with a food-stuff, the formulation components will be
chosen to be compatible with the phosphate binder material and to
provide suitable physicochemical and organoleptic characteristics.
For intravenous, cutaneous or subcutaneous injection, or injection
at the site of affliction, the active ingredient will be in the
form of a parenterally acceptable aqueous solution or suspension
which is pyrogen-free and has suitable pH, isotonicity and
stability. Those of relevant skill in the art are well able to
prepare suitable solutions using, for example, isotonic vehicles
such as Sodium Chloride Injection, Ringer's Injection, Lactated
Ringer's Injection. Preservatives, stabilisers, buffers,
antioxidants and/or other additives may be included, as required.
The materials and compositions used in accordance with the
present invention that are to be given to an individual are
preferably administered in a "prophylactically effective amount"
or a "therapeutically effective amount" (as the case may be,
although prophylaxis may be considered therapy), this being
sufficient to show benefit to the individual clinical state. The
actual amount administered, and rate and time-course of
administration, will depend on the nature and severity of what is
being treated. By way of example, phosphate binders of the
present invention may be administered in amounts between about 1
and 20 g/day per patient, more preferably between about 2 and 10
g/day per patient and most preferably 3 to 7 g/day per patient.
Prescription of treatment, e.g. decisions on dosage etc, is
within the responsibility of general practitioners and other
medical doctors, and typically takes account of the disorder to
be treated, the condition of the individual patient, the site of
delivery, the method of administration and other factors known to
practitioners. Examples of the techniques and protocols
mentioned above can be found in Remington's Pharmaceutical
Sciences, 20th Edition, 2000, Lippincott, Williams & Wilkins. A
composition may be administered alone or in combination with
other treatments, either simultaneously or sequentially,
dependent upon the condition to be treated.
The phosphate binders disclosed herein may be employed for the
treatment of hyperphosphatemia. This condition often arises in
renal disease, especially in patients undergoing haemodialysis
and/or patients having chronic or end stage renal disease. As
mentioned in the introduction, current therapies for
hyperphosphatemia suffer from a number of serious disadvantages,
most significantly that the prior art compositions have non-
specific modes of action not restricted to phosphate or cause
side effects or have long term safety issues.
The conditions that may be treated with the compositions of the
present invention include high plasma phosphorus levels,
hyperphosphatemia arising from any level of renal insufficiency,
acute renal failure, chronic renal failure, and/or end-stage
renal disease, including conditions that require haemodialysis.
The clinical management of these conditions using the present
invention may help to ameliorate complications associated with
these conditions, such as secondary hyperthyroidism, soft tissue
calcification, osteodystrophy, hypercalcaemia,
hyperparathyroidism reduction, cardiovascular morbidity or
mortality, renal osteodystrophy and/or calciphylaxis.
Materials and methods
In vitro phosphate binding assay
a) Phosphate binding at physiological concentration
A solution containing 10 mM phosphate, a physiologically relevant
concentration, and 0.9% NaCl was adjusted to pH 3, pH 5 and
finally pH 7. The mass of binder was kept constant. The
percentage of phosphate binding was calculated according to:
Phosphate binding=(1-([P]t0-[P]ti)/ [P]ti)x100
Where [P]t0 is the concentration of phosphorus in the initial
solution and [P]ti is the concentration of phosphorus in filtrate
at different time points.
b) Langmuir isotherms
The Langmuir isotherms were obtained using the same methodology
as in Autissier et al. (2007), except in vitro solutions also
contained 0.9% NaCl to make the assay better simulate
physiological conditions. These Langmuir isotherms were
generated at pH 5 and experimental conditions were similar to
those in "Phosphate binding at physiological concentration"
except the mass of binders was varied from 13.4-80.4 mg.
In vitro gastrointestinal digestion assay
An amount of the solid ligand-modified poly oxo-hydroxy ferric
ion materials or unmodified ferric oxo-hydroxide, equivalent to
60mg elemental iron, were added to a synthetic gastric (stomach)
solution (50 mL of 2g/L NaCl, 0.15 M HCl and 0.3mg/mL porcine
pepsin) and incubated at 37°C for 30 minutes with radial shaking.
Then 5 mL of the resulting gastric mixture was added to 30 mL of
synthetic duodenal solution (containing 10g/L pancreatin and 2g/L
NaCl in 50mM bicarbonate buffer pH 9.5). The final volume was 35
mL and the final pH was 7.0. The mixture was incubated at 37°C
for 60 min with radial shaking. Homogeneous aliquots (1mL) were
collected at different time points during the process and
centrifuged at 13,000 rpm for 10 minutes to separate the
aggregate and aquated disaggregated phases. The supernatant was
analysed for iron content by ICPOES. At the end of the
experiment, the remaining solution was centrifuged at 4,500 rpm
for 15 min and the supernatant analysed for the Fe content by
ICPOES. The mass of remaining material (i.e. the wet pellet) was
recorded. Concentrated HNO3 was added to this wet pellet and the
new mass recorded. The tubes were left at room temperature until
all the pellet dissolved and an aliquot was collected for ICPOES
analysis to determine the quantity of iron that did not
disaggregate / dissolve. The starting amount of iron was
calculated from the iron in the wet pellet plus the iron in the
supernatant.
To differentiate between soluble iron and aquated particulate
iron in the supernatant, at each time point, this fraction was
also ultrafiltered (Vivaspin 3,000 Da molecular weight cut-off
polyethersulfone membrane, Cat. VS0192, Sartorius Stedium Biotech
GmbH, Goettingen, Germany) and again analysed by ICPOES.
Inductively Coupled Plasma Optical Emission Spectrometry analysis
(ICPOES)
Iron and phosphorus contents of solutions or solids (including
wet solids) were measured using a JY2000-2 ICPOES (Horiba Jobin
Yvon Ltd., Stanmore, U.K.) at the iron specific wavelength of
259.940 nm, and at the phosphorus wavelengths of 177.440 and/or
214.914 nm . Solutions were diluted in 1-7.5% nitric acid prior
to analysis while solids were digested with concentrated HN03.
The percentage of iron in solution or solid phase was determined
by the difference between the starting iron content and either
the iron in the soluble phase or the iron in the solid phase
depending on the assay.
Determination of particle size
The size distribution of micron-sized particles was determined
using a Mastersizer 2000 with a Hydro-uP dispersion unit (Malvern
Instruments Ltd, Malvern, UK) and nano-sized particles was
determined with a Zetasizer Nano ZS (Malvern Instruments Ltd,
Malvern, UK). Mastersizer measurements required no sample pre-
treatment whereas centrifugation was needed to remove large
particles prior to Zetasizer measurements.
Infrared Analysis (IR)
IR spectra were collected using a DurasamplIR diamond ATR
accessory with a Nicolet Avatar 360 spectrometer with a
wavelength range of 4000-650cm-1 and resolution of 4cm-1. Analysis
were undertaken by ITS Testing Services (UK) Ltd Sunbury on
Thames, UK.
Transmission Electron Microscopy and Energy Dispersive X-ray
Analysis (EDX)
Powder samples were analysed by first dispersing the powder in
methanol and then drop-casting on standard holey carbon TEM
support films. Analyses were undertaken by the Institute for
Materials Research, University of Leeds, UK.
Exploratory Human Study to Assess Phosphate Binding of FeOH Ad100
As part of a study assessing markers of oxidative damage and
antioxidant status after oral iron supplementation, a study was
carried out to determine whether dietary phosphate (PO4) binding
could be observed for phosphate binders of the present invention
(893 mg) when given with a meal (containing 781.5 mg phosphorus
(P)). Briefly 13 volunteers, each received a high-P breakfast on
3 occasions with either placebo or the phosphate binder or
ferrous sulphate - these being given in random order. Urine was
collected pre-meal (spot urine), at 0-3 hours post meal (expect
little or no urinary phosphate derived from the meal) and at 3-8
hours post meal (expect ˜ 45% of absorbed phosphate that was
derived from the meal to be excreted.
Results
1. Production of phosphate binder
Broadly, the phosphate binders described herein were produced by
totally, or partially, neutralising an acidic solution, typically
at pH<2.5, containing, at least, soluble ferric and one or more
ligands. Subsequently, a ligand-modified oxo-hydroxide material
was formed once a suitable pH was achieved, typically at pH>3.5,
which could be recovered using a range of strategies (e.g.
centrifugation). Note that the production of phosphate binders
described below does not include any post-production
modifications, such as washing.
1.1 FeOH Ad100
To a 500 mL beaker containing 400 mL ddH2O, 4.5g KCl and 7.3g
adipic acid were added. The mixture was stirred until all of the
components dissolved. Then 100 mL of a ferric iron solution was
added (200mM FeCl3.6H2O, 1.7mL conc. HCl in 100 mL ddH2O) . The
final concentration of iron in the solution was 40 mM and KCl was
0.9% w/v. The pH of the final solution to which ferric iron was
added is generally below <2 and usually about 1.5. To this
mixture, NaOH was added drop-wise (from a 5M NaOH solution
prepared in ddH2O) with constant stirring until pH 4.5 ± 0.2 (see
Figure 1). The process was carried out at room temperature (20-
25°C). The solution was then centrifuged and the agglomerate was
air-dried in an oven at 45°C. The dried material was milled by
hand or micronized with a ball mill.
1.2 FeOH Ad100 SiO2
The procedure for producing FeOH Ad100 SiO2 was the same as for
FeOH Ad100 except a sodium silicate solution (SiO2.NaOH) was used
instead of NaOH to raise the pH. This solution contains 27% Si.
1.3 FeOH Glutaric100
The procedure for producing FeOH Glutaric100 was the same as for
FeOH Ad100 except 6.6 g glutaric was used instead of adipic acid
and NaOH was added until pH 5.0± 0.2 was reached.
1.3 FeOH Pimelic100
The procedure for producing FeOH Pimelic100 was the same as for
FeOH Ad100 except 8.0 g pimelic was used instead of adipic acid
and NaOH was added until pH 4.2 ± 0.2 was reached.
2. In vitro phosphate-binding
2.1 P-binding at physiological concentration
The iron oxide ferrihydrite is well known to bind phosphate. For
example, following incubation at pH 3 for 60 minutes and then pH
5 for 60 minutes, 54 mg ferrihydrite will bind about 30% of
phosphate from a 20 mL, 10 mM phosphate solution (Figure 2a). On
a small scale this may mimic physiological conditions in the use
of phosphate binders. A preferred amount of binding is ˜ 50%
under identical conditions as seen for the commercial phosphate
binder Renagel, polyallylamine hydrochloride (Figure 2a/b). A
yet more preferred amount is 70-85 % under identical conditions,
as seen in the high affinity phosphate binding agent lanthanum
carbonate(Figure 2a/b). FeOHAd100 and FeOHAd100 SiO2 achieve a
phosphate binding of 80-85% binding under these conditions
(Figure 2a/b) illustrating significant beneficial modification in
relation to ferrihydrite alone. In Figure 2a and 2b, white bars
relate to experiments carried out at pH 3 and grey bars pH5, and
black bars are at pH7 (in Figure 2b only), and in all cases the
binder was first exposed to the lower pH for 60 minutes and then
the higher pH(s) for 60 minutes, all sequentially.
Interestingly, when assay conditions were changed such that the
exposure of binder was made directly to the solution at pH 5 for
1 hour, but without pre-conditioning' at pH 3 for 1 hour, the
phosphate binding fell sharply for lanthanum carbonate from 70-
85% (Figure 2) to ˜ 30% (Figure 3). In contrast phosphate binding
by FeOHAd100 and FeOHAd100 SiO2 fell only from 80-85% (Figure 2)
to 65-75% (Figure 3), indicating superior binding by the latter
binder under conditions that may exist physiologically (e.g.
post-prandial gastric pH). In the context of superiority, it is
also worth noting that lanthanum carbonate can be toxic and
Renagel is a non-specific binder.
2.2 Langmuir plots - Determination of affinity and capacity-
Vie further compared the phosphate binding abilities of FeOH
Ad100, FeOH Ad100 SiO2, and lanthanum using Langmuir isotherms.
The Langmuir equation relates the adsorption of molecules on a
solid surface to a concentration and was adapted to determine the
affinity and capacity of the above noted phosphate binders:

C = concentration of adsorbate unbound in mM
Cad/m = mmol of adsorbate bound per g binder
Kl = affinity; K2 = capacity
It was not possible to determine these values for Renagel because
its low affinity required a higher concentration of phosphate
than the physiologically relevant concentration (10mM)that was
tested in this experiment. Langmuir isotherms were generated at
pH 5 and experimental conditions were similar to those in Figure
2a/b, except the mass of binders was varied from 13.4-80.4 mg.
The results are shown in the Table below and demonstrate that the
affinity is similar for the three compounds, but capacity is
inferior for lanthanum carbonate.
3. In vitro gastro-intestinal dissolution
While the phosphate binding ability provides one example of how
ferrihydrite has been modified herein to alter its
physicochemical properties, a second example is with the
dissolution profile at very acidic pH. At pH 1.2 the iron in
FeOHAd100 and FeOH Ad100SiO2 is rapidly dissolved while that from
unmodified ferrihydrite is slowly dissolved. For beneficial
application FeOHAd100 and FeOH Ad100SiO2 will be ingested with
food and will largely remain particulate at post-prandial pHs
(pH>2.5), but these laboratory dissolution data are simply shown
to illustrate that the agents claimed differ markedly from
ferrihydrite (Figure 4).
4. Particle size determination
Figure 5 shows that the agents claimed herein have an aggregated
particle diameter spanning 10-100 µm with a median diameter
around 40 µm (a); upon drying the range is increased (b),
especially to larger sizes (median then > 100 µm) but can be
restored with basic milling for example (c) or even reduced
further with micronisation or nanosizing (not shown).
5. Chemical characterisation
5.1 IR characterisation
The infrared spectra of FeOH Ad100 (Figure 6) and FeOH Ad100 SiO2
(Figure 7) were obtained and showed the presence of two bands at
1583-1585 cm-1 and 1524-1527 cm-1. These are absent in either
unmodified ferrihydrite (Figure 8) or adipic acid (Figure 9) and
indicate the presence of some bonding between the carboxylate
group of adipic acid (at 1684 cm-1) and a cation, which can
include iron in the FeOH Ad100 and FeOH Ad100 SiO2 materials.
5.2 TEM
FeOH Ad100
Electron diffraction gave 2 diffuse rings (plane spacings at 2.5
and 1.5 Angstroms respectively); these are diagnostic for the
presence of a ferrihydrite-like structure (Figure 10b). All other
forms of iron oxide such as Akageneite (ß- or beta-iron oxo-
hydroxide) or maghemite (?- or gamma-iron oxide) give completely
different plane spacings (see Cornell & Schwertmann, The Iron
Oxides Structure, Properties, Reactions, Occurrence and Uses. 2nd
ed, 1996, VCH Publishers, New York).
The general composition by EDX shows the presence of low levels
of Na, Cl, and K with significant levels of Fe, 0 and C (Figure
10c). The amount of C is greater than can be attributed to the
carbon support film, and it is concluded that this additional C
is from adipic acid. High magnification images indicate a
mottled structure where the darker spots of 2-3 nm indicate a
primary grain size (Figure 10a). This structure is still
consistent with 2-line ferrihydrite (Janney et al, 2000),
although in general is more disordered than unmodified 2-line
ferrihydrite. Thus, the phosphate binding materials described
herein are agglomerated particles with a ferrihydrite-like
structure of a primary crystallite size of 2-3 nm and containing
Fe, 0 and C, and low levels of Cl, Na and K. They are therefore
ligand-modified structures leading to some markedly different
and, with respect to phosphate binding, beneficial properties
compared to ferrihydrite alone.
6. Exploratory Human Study to Assess Phosphate Binding of FeOH
Ad100
As part of a study assessing markers of oxidative damage and
antioxidant status after oral iron supplementation, a study was
carried out to determine whether dietary phosphate (PO4) binding
could be observed for phosphate binders of the present invention
(893 mg) when given with a meal (containing 781.5 mg phosphorus
(P)). This study was used to test the hypothesis that urinary
phosphate excretion would be greater in a placebo period than the
phosphate binder period and this was tested using a 1 tailed,
paired T test.
First, following ingestion of the breakfast alone (i.e. just with
placebo), urinary excretion of phosphorus, corrected for
creatinine concentration, was used to identify the period in
which there was a rise in excreted phosphate concentration. This
was seen at 3-8 hours post ingestion of the meal as anticipated
(data not shown). Next, at the 3-8 hour time point, phosphorus
excretion was compared following the breakfast plus placebo
versus breakfast plus treatment with a binder of the present
invention, and a difference of 49.4 mg phosphorus was observed in
excretion (p = 0.01; Figure 11).
To provide some context around these figures, the in vivo data
for phosphorus binding of one material of the present invention
were compared with known literature. Calculations suggest that
the binder of the present invention, under these dietary
conditions, binds 514 mg PO4 per g of binder, once the urinary
data are extrapolated from 8h to 24 h excretion and phosphorus is
converted to phosphate. This extrapolation accounts for the
remaining absorbed phosphate to be excreted over the following 16
hours and assumes 70% gut absorption of phosphate from the
meal(Anderson, J.J.B, Watts M.L., Garner, S.A., Calvo, M.S., and
Klemmer, P.J. Phosphorus. In: Bowman, B., and Russell, R., ed.
Present Knowledge in Nutrition, 9th ed. ILSI Press, 2006) . This
compares to known in vivo values for Sevelamer hydrochloride of
262 mg phosphate per g of binder (Sherman RA: Seminars in
dialysis -Vol. 20(1), 2007, 16-18).
It should be also noted that the meal used here is, purposefully,
extremely high in P (to enable a movement in urinary P to be
observed), but therefore does not represents typical P intakes
from a single meal by renal patients. Thus, under more typical
conditions, the percentage of P bound by a phosphate binder of
the present invention (or indeed any of the binders) will be
higher.
7. Further comparative experiments with different ligands
Further phosphate binding materials of the present invention that
include a range of different carboxylic acid ligands (pimelic
acid and glutaric acid) were made and compared with materials
that comprise other types of ligand. These results are
summarised in Figures 12 and 13 and show that the carboxylic acid
ligands enhanced the phosphate binding capacity of the starting
material, while other types of ligand either had no effect on the
phosphate binding capacity of FeOH or else reduced it (see FeOH-
MOPS 50 and FeOH Boric 50).
8. Modelling pill burden
A major disadvantage of current therapeutic treatments for the
removal of phosphate is the pill burden placed on patients, where
the need to ingest large quantities of pills adversely affects
side effects and patient compliance. Accordingly, the pill
burden for some of the exemplified materials was compared to
Renagel and Fosrenol using a mathematical model based on in vitro
data and typical gastrointestinal conditions, such as pH, average
dietary phosphorus concentration under clinical conditions, and
competing anions, and the results are shown in the Table below.
formulation adds less than 10% mass as is true for Renagel; c Data from
literature; dA 3.1 g pill contains 750 mg elemental lanthanum (1.45g
lanthanum carbonate). eValues estimated by linear extrapolation of
unwashed material based on the 15% increase in phosphate binding that
washing produces, see below for production method.
9. Pre-formulation strategies: enhancement of iron content
The FeOH Ad100 produced and characterised as described above was
tested to determine the effect of pre-formulation processing
steps, such as washing. In these experiments potassium chloride,
the reaction medium used in the production of the materials, was
removed from the synthesis procedure (FeOH Ad100 - KC1) and a
washing step of the precipitated material has been added (FeOH
Ad100 -KCl+washed). Both of these steps resulted in an increase
in iron content in the materials produced, see the results in the
Table below.
-KCl: witnout KCl; +wasned: addition or a washing step
Excluding KCl from the synthesis and adding a washing step also
resulted in an increase in the phosphate binding ability as shown
in Figure 14.
When FeOH Ad100-KCl and FeOH Ad100-KCl+washed were tested and
their phosphate binding under a range of phosphate: binder ratios
was compared, the results were consistent with those shown in
Figure 14 and confirmed the increase in phosphate binding due to
the washing step.
10. Ligand replacement
Work in which the adipic acid of FeOH Ad100 was replaced by a
different ligand was also carried out. This consisted in either
washing FeOH Ad100 with a nicotinamide solution (FeOH Ad100
+nicotinamide wash) or adding nicotinamide during the
precipitation process, after the formation of FeOH Ad100 primary
particles (producing FeOH Ad100 +nicotinamide agglomeration
instead of FeOH Ad100 +adipate agglomeration). Both strategies
resulted in a decrease of adipic acid content (below) and,
although there was a reduction in phosphate binding, these
materials may be useful for the treatment of hyperphosphatemia by
combining phosphate binding with the release of nicotinamide,
which is known to reduce active uptake of phosphate in the gut.
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filed with this application, including references filed as part
of an Information Disclosure Statement are incorporated by
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WO 2007/088343.
WO 2008/071747.
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we claim:
1. A ferric iron composition for use in the treatment of
hyperphosphatemia, wherein the ferric iron composition is a solid
ligand-modified poly oxo-hydroxy metal ion material represented
by the formula (MxLy(OH)n), wherein M represents one or more metal
ions that comprise Fe3+ ions, L represents one or more ligands
that comprise a carboxylic acid ligand, or an ionised form
thereof, and OH represents oxo or hydroxy groups and wherein the
material has a polymeric structure in which the ligands L are
non-stoichiometrically substituted for the oxo or hydroxy groups
and wherein the solid ligand-modified poly oxo-hydroxy metal ion
material having one or more reproducible physico-chemical
properties.
2. The ferric iron composition for use in a method of treating
hyperphosphatemia according to claim 1, wherein the carboxylic
acid ligand is a linear dicarboxylic acid ligand.
3. The ferric iron composition for use in the treatment of
hyperphosphatemia according to claim 1 or claim 2, wherein the
carboxylic acid ligand is represented by the formula HOOC-R1-COOH,
where R1 is an optionally substituted alkyl, alkenyl or alkynyl
group, or an ionised form thereof.
4. The ferric iron composition for use in the treatment of
hyperphosphatemia according to any one of the preceding claims,
wherein R1 is a C1-10 alkyl group, wherein R1 is optionally
substituted with one or more hydroxyl group.
5. The ferric iron composition for use in the treatment of
hyperphosphatemia according to any one of the preceding claims,
wherein the carboxylic acid ligand is succinic acid, malic acid,
adipic acid, glutaric acid or pimelic acid, or an ionised form
thereof.
6. The ferric iron composition for use in the treatment of
hyperphosphatemia according to any one of the preceding claims,
wherein the material has a structure that is consistent with
ferrihydrite.
7. The ferric iron composition for use in the treatment of
hyperphosphatemia according to any one of the preceding claims,
wherein the one or more reproducible physico-chemical properties
comprise a dissolution profile and/or phosphate binding
properties.
8. The ferric iron composition for use in the treatment of
hyperphosphatemia according to claim 7, wherein the phosphate
binding properties comprise specificity for phosphate, affinity
for phosphate and/or binding capacity for phosphate.
9. The ferric iron composition for use in the treatment of
hyperphosphatemia according to claim 7, wherein the phosphate
binding capacity of 53.6 mg of the material is at least 50% of
the 10 mM phosphate in a sample at a pH between 3 and 7, in a
volume of 20 mL.
10. The ferric iron composition for use in the treatment of
hyperphosphatemia according to any one of the preceding claims,
wherein the material has demonstrable M-L bonding as determined
using infrared spectroscopy.
11. The ferric iron composition for use in the treatment of
hyperphosphatemia according to any one of the preceding claims,
wherein M is Fe3+ ions.
12. The ferric iron composition for use in the treatment of
hyperphosphatemia according to any one of the preceding claims,
wherein the composition further comprises a phosphate uptake
inhibitor and/or a substance capable of ameliorating gastric side
effects.
13. The ferric iron composition for use in the treatment of
hyperphosphatemia according to claim 12, wherein the phosphate
uptake inhibitor and/or the substance capable of ameliorating
gastric side effects is a further ligand incorporated into the
solid ligand-modified poly oxo-hydroxy metal ion material, or is
formulated in a composition with the solid ligand-modified poly
oxo-hydroxy metal ion material.
14. The ferric iron composition for use in the treatment of
hyperphosphatemia according to any one of the preceding claims,
wherein the material is FeOH Ad100, FeOH Ad100 SiO2, FeOH Glutaric
100, or FeOH Pimelic 100.
15. The ferric iron composition for use in the treatment of
hyperphosphatemia according to any one of claims 1 to 14, wherein
the patient having hyperphosphatemia has renal disease.
16. The ferric iron composition for use in the treatment of
hyperphosphatemia according to claim 15, wherein the renal
disease is chronic renal disease, end stage renal disease,
hyperphosphatemia arising from any level of renal insufficiency
or acute renal failure.
17. The composition for use in the treatment of hyperphosphatemia
or the use according to any one of claims 1 to 15, wherein the
patient having hyperphosphatemia is undergoing haemodialysis.
18. The ferric iron composition for use in the treatment of
hyperphosphatemia or the use according to any one of claims 1 to
15, wherein the patient having hyperphosphatemia has high plasma
phosphorus levels.
19. The ferric iron composition for use in the treatment of
hyperphosphatemia according to any one of claims 1 to 15, wherein
administration of the material is for treating a complication or
secondary condition of the patient that results from
hyperphosphatemia.
20. The ferric iron composition for use in the treatment of
hyperphosphatemia according to claim 19, wherein the complication
or secondary condition is secondary hyperthyroidism, soft tissue
calcification, osteodystrophy, hypercalcaemia,
hyperparathyroidism reduction, cardiovascular morbidity or
mortality, renal osteodystrophy and/or calciphylaxis.
21. The ferric iron composition for use in a method of treatment
according to any one of claims 1 to 20, wherein the composition
is formulated for oral or nasogastric administration.
22. The ferric iron composition for use in the treatment of
hyperphosphatemia according to any one of claims 1 to 20, wherein
the treatment comprises removing phosphate from dialysis fluids,
plasma and/or whole b100d.
23. A food-stuff or dialysis fluid comprising a phosphate
binding material as defined in any one of claims 1 to 14.
24. An ex vivo method for removing phosphate from a medium, the
method comprising (a) contacting a medium containing phosphate
with a ferric iron composition as defined in any one of claims 1
to 14 under conditions in which the phosphate is capable of
binding to the ferric iron composition and (b) separating the
bound phosphate from the composition.
25. The method of claim 24, wherein the medium is a solution or
suspension.
26. The method of claim 24 or claim 25, wherein the method is
for removing phosphate from food-stuffs prior to consumption.
27. A process for producing a phosphate binding material
according to any one of claims 1 to 14, the process comprising:
(a) mixing the solution comprising Fe3+ and a carboxylic
acid ligand, and optionally one or more further ligands or
reaction components, in a reaction medium at a first pH(A) at
which the components are soluble;
(b) changing the pH(A) to a second pH(B) to cause a solid
precipitate or a colloid of the ligand-modified poly oxo-hydroxy
metal ion material to be formed;
(c) separating, and optionally drying and/or formulating,
the solid ligand-modified poly oxo-hydroxy metal ion material
produced in step (b).
28. The process of claim 27, further comprising testing the
phosphate binding material in vitro or in vivo to determine one
or more properties of the material.
29. The process of claim 28, wherein the one or more properties
is a dissolution profile and/or a phosphate binding properties.
30. The process of any one of claims 27 to 29, wherein the first
pH(A) is less than 2.0 and the second pH(B) is between 3.0 and
12.0.
31. The process of any one of claims 27 to 30, wherein the
process is carried out room temperature (20-25°C).
32. The process of any one of claims 27 to 31, wherein in step
(a), the solution contains 20 to 100mM Fe3+ and 50 to 250mM adipic
acid.
34. The process of any one of claims 27 to 32, further
comprising chemically or physically altering the final particle
size of the ferric iron composition.
35. The process of any one of claims 27 to 34, further
comprising formulating the ferric iron composition.

Phosphate binding materials and compositions
comprising them which are solid ligand-modif ied poly
oxo-hydroxy metal ion materials are disclosed that
are based on ferric iron oxo- hydroxides modified
with carboxylic acid ligands, or ionised forms
thereof. These materials are made and tested in the
examples provided in the application to demonstrate
that they can bind phosphate in "in vitro" an in "in
vivo" studies. They are useful for treating
hyperphosphatenia or for removing phosphate from a
medium.