Hydroxamic acid-containing hydrogels for nonabsorbed iron chelation therapy: synthesis, characterization, and biological evaluation.

Iron overload is a severe clinical condition and can be largely prevented by the use of iron-specific chelating agents. A successful iron chelator needs to be orally active, nontoxic, and selective. In this study, hydrogels containing pendant hydroxamic acid groups have been synthesized as potential nonabsorbed chelators for iron in the gastrointestinal tract. The synthetic method employed to introduce hydroxamic acid groups to polymer chains involved reaction of polymer gels based on N-acryloxysuccinimide, acryloyl chloride, and (2-hydroxyethyl)acrylate monomers with hydroxylamine. These hydroxamic acid-functionalized polymer gels swell favorably in water and effectively sequester iron. In vitro iron-binding properties of these hydrogels were evaluated from their binding isotherms by use of iron(II) alone and in the presence of other competing metal ions. These polymers bind iron over a broad pH range. The iron-binding properties of the polymers were found to depend on the concentration of hydroxamate groups on polymer chains. The in vivo iron-binding efficacy of the polymers was evaluated in rat as the animal model. The polymers prevented an increase in serum hemoglobin and hematocrit levels in the animals, thus suggesting the prevention of systemic absorption of dietary iron from the gastrointestinal tract. The animals also maintained normal body weight during the treatment period, indicating the absence of any apparent toxicity associated with these polymers.

Effect of RenaGel, a non-absorbable, cross-linked, polymeric phosphate binder, on urinary phosphorus excretion in rats.

BACKGROUND: Normalization of serum phosphorus is critical in the treatment of End Stage Renal Failure patients. Aluminum or calcium based phosphate binders, while efficacious, are associated with potential adverse side effects and toxicities. We have developed RenaGel, a novel, non-absorbed hydrogel which binds dietary phosphate leading to increased fecal excretion, decreased absorption and decreased serum phosphorus levels. In this paper, we present results from both in vitro and in vivo studies in which we examined the efficacy of this novel phosphate binder. METHODS: In vitro, RenaGel was suspended in the test solution, and the mixture was stirred for 1 hour at room temperature. The solid was then filtered off, and the residual liquid analyzed for phosphate. In vivo, RenaGel was mixed in rodent feed at different concentrations and fed to normal rats for up to 4 days. Urine was collected and analysed for phosphate content. RESULTS AND CONCLUSIONS: In vitro binding studies demonstrate that RenaGel has an extremely high phosphate binding capacity. At an estimated physiological concentration of 5 mM phosphate, RenaGel binds 2.6 mmole phosphate/g of phosphate binder. The in vivo binding study shows that RenaGel mixed into the diet decreased urinary phosphorus excretion in a dose dependent manner. RenaGel particles with a 23 microns mean diameter are more efficacious than the larger ones. In conclusion, the above studies indicate that RenaGel is a potent phosphate binder. RenaGel contains no calcium or aluminum and offers an alternative to existing phosphate binder treatments.

Calcium deficiency in fluoride-treated osteoporotic patients despite calcium supplementation.

To test the hypothesis that the osteogenic response to fluoride can increase the skeletal requirement for calcium, resulting in a general state of calcium deficiency and secondary hyperparathyroidism, we assessed calcium deficiency, spinal bone density, by quantitative computed tomography, and serum PTH in three groups of osteoporotic subjects. Two of the three groups had been treated with fluoride and calcium (at least 1500 mg/day) for 32 +/- 19 months. Group 1 consisted of 16 fluoride-treated subjects who had shown rapid increases in spinal bone density (+ 3.8 +/- 2.6 mg/cm2 month), group II consisted of 10 fluoride-treated subjects who had shown decreases or only slow increases in spinal bone density (-0.05 +/- 0.6 mg/cm3 month), and group III consisted of 10 age-matched untreated osteoporotic controls. Calcium deficiency was assessed by measurement of calcium retention after calcium infusion. The results of our studies showed that 1) 94% of the subjects in Group I were calcium deficient compared with only 30% in groups II and III (P < 0.01 for each); 2) the subjects in group I retained more calcium (79%) than the subjects in group II (60%, P < 0.001) or the subjects in group III (64%, P < 0.005); 3) calcium retention was proportional to serum PTH (r = 0.37, n = 36, P < 0.03); and 4) calcium retention was proportional to the (previous) fluoride-dependent increase in quantitative computed tomography spinal bone density (in groups I and II, r = 0.48, n = 26, P < 0.02). To test the hypothesis that the calcium deficiency and the secondary hyperparathyroidism that were associated with the positive response to fluoride would respond to concomitant calcitriol treatment, a subgroup of 7 calcium-deficient subjects were selected from group I and treated with calcitriol (plus fluoride and calcium) for an average of 7 months. The calcitriol therapy reduced the calcium deficit in all 7 subjects, decreasing calcium retention from 80% to 62% (P < 0.02), and decreasing PTH from 50 to 28 pg/mL (P < 0.02). Together, these data indicate that fluoride-treated osteoporotic subjects may develop calcium deficiency in proportion to the effect of fluoride to increase bone formation, and this calcium deficit is responsive to calcitriol therapy.

Lack of a high prevalence of the BB vitamin D receptor genotype in severely osteoporotic women.

Studies of twins strongly suggest that more than 50% of the peak spinal bone density is determined by genetics. It was reported recently that this genetic effect is primarily determined by vitamin D receptor (VDR) alleles; specifically, a VDR genotype termed BB has been highly associated with low peak bone density. Homozygotes for the second VDR allele, bb, are associated with high peak bone density. If peak bone density is an important determinant of osteoporosis and if the VDR genotype is an important determinant of peak bone density, then patients with severe osteoporosis should have a high prevalence of the BB VDR genotype compared with that of control subjects. To test this hypothesis, we used Southern blot analysis to determine the VDR genotype of 41 Caucasian patients (72 +/- 14 yr) with severe osteoporosis (27 women with spinal bone densities below 50 mg/cm3 as determined by quantitative computed tomography; 14 women with spinal bone densities below 0.75 g/cm2 as determined by dual energy x-ray absorptiometry) and 23 Caucasian control subjects (68 +/- 7 yr) without osteoporosis (quantitative computed tomography values at or above the fracture threshold of 100 mg/cm3). Only 6 of the 41 individuals in the group with severe osteoporosis had the BB genotype, whereas 16 had the bb genotype. In the control group comprising 23 individuals, 7 had the BB genotype and only 6 had the bb genotype. We conclude that the BB VDR genotype is not a good predictor of risk for developing severe osteoporosis in our population.

The effect of fluoride therapy on blood chemistry parameters in osteoporotic females.

To determine the potential adverse effects, if any, of long-term fluoride ingestion in humans, samples were collected from 25 adult females taking daily doses of fluoride (mean, 23 mg elemental F) for the treatment of osteoporosis and from 38 osteoporotic female controls. Patients in the fluoride group had been receiving therapy for approximately 18 months with a mean duration of 4.2 years and had serum fluoride values of at least 10 mumol/l. Laboratory analyses for fluoride were conducted on plasma, urine and drinking water samples collected from each panelist. Blood was also collected for blood chemistry analyses and plasma lymphocytes were examined for the frequency of sister chromatid exchange (SCE). Plasma and urine fluoride levels were significantly different between the two groups, while water fluoride was not. The SCE frequency, a measurement of potential genotoxicity, did not differ between the two groups. Of the blood chemistry parameters measured, albumin, alkaline phosphatase, sodium, chloride, the albumin/globulin (A/G) ratio, indirect bilirubin, lactate dehydrogenase (LDH), and gamma-glutamyl transferase (GGT) were found to be significantly different between the two groups (P < or = 0.05). However, none of the mean group values were outside stated normal ranges for any of these parameters. We conclude that the risk of developing adverse systemic effects from the ingestion of fluoride, at dosages and for a duration comparable with that of our panel, is minimal.