ascorbic-acid and Cystinosis

Important insights have recently been derived from studies of inborn human defects of sulfur metabolism. Metabolic lesions responsible for homocystinuria have been elucidated, with possible implications for understanding atherogenesis in the general population. The cause of cystinosis remains enigmatic, but important information has been gained on the origin of some stored cystine from degraded protein. Cysteamine and ascorbic acid deplete the cystine content of cystinotic fibroblasts in vitro, and clinical trials with these agents have been undertaken. Studies of patients with glutathione synthetase deficiency have provided new understanding of the roles of glutathione as in antioxidant and as a modulator of microtubule-related processes. Studies of patients with this disorder and glucose-6-phosphate dehydrogenase deficiency, in which the capacity to maintain glutathione in the reduced state is compromised, indicate that pharmacologic doses of vitamin E can correct certain functional consequences of an inadequate supply of reduced glutathione both in erythrocytes and polymorphonuclear leukocytes. Much remains to be learned about the mechanisms of membrane damage in these states of enhanced oxidative susceptibility.

Topics: Amino Acid Metabolism, Inborn Errors; Amino Acids, Sulfur; Ascorbic Acid; Cysteamine; Cystinosis; Erythrocytes; Glucosephosphate Dehydrogenase Deficiency; Glutathione; Glutathione Synthase; Homocystinuria; Humans; Leukocytes; Vitamin E

Topics: Adolescent; Ascorbic Acid; Cystine; Cystinosis; Female; Fetus; Fibroblasts; Heterozygote; Homozygote; Humans; Hybridization, Genetic; Infant; Kidney; Leukocytes; Male; Pedigree; Pregnancy; Prenatal Diagnosis

Metabolic studies were performed on two HLA identical 9 1/2-year-old twins with nephropathic cystinosis during 14 months' participation in a double-blind study to evaluate ascorbic acid treatment for cystinosis. Replacement therapy was identical in both children throughout the study except for the use of ascorbic acid. Leukocyte cystine content was markedly abnormal and elevated in both children prior to, during, and after the ascorbic acid study. We postulate that the lack of improvement in growth or chemical parameters in the twin treated with ascorbic acid was due to the ineffectiveness of ascorbic acid in decreasing intracellular cystine content.

Topics: Amino Acids; Ascorbic Acid; Child; Cystine; Cystinosis; Diseases in Twins; Double-Blind Method; Growth; Humans; Leukocytes; Male; Thyrotropin

Because high concentrations of ascorbic acid (0.57 mM) lower the free (nonprotein) cystine content of cultured cystinotic skin fibroblasts by over 50 per cent, we did a double-blind clinical trial to establish whether this drug would benefit cystinotic children. Sixty-four patients were randomized into the study; 32 received ascorbic acid (200 mg per kilogram of body weight per day), and 32 placebo. The study was terminated after approximately two years because there was no indication that vitamin C was beneficial and accumulating evidence that it might be harmful. Of 11 patients who left the study because of death or the requirement for dialysis or renal transplantation, eight were receiving ascorbic acid. The estimated relative risk (treatment vs. control) of an adverse event was R = 2.7, with a 90 per cent confidence interval of (0.8, 11.5). The serum creatinine concentration increased 0.53 mg per deciliter per year in patients receiving vitamin C and 0.24 mg per deciliter per year in patients receiving placebo (P = 0.08).

Topics: Ascorbic Acid; Blood Urea Nitrogen; Child; Child, Preschool; Clinical Trials as Topic; Creatinine; Cystine; Cystinosis; Double-Blind Method; Drug Evaluation; Female; Hematocrit; Humans; Leukocytes; Male; Risk

The present study shows that homocysteine depleted cystine from cystinotic fibroblasts in vitro. No toxic effects were noted as judged by morphology and growth patterns. Efflux of radioactivity from cystinotic cells prelabeled with [35S]cystine was greater in homocysteine-treated cystinotic cells than in untreated controls. This radioactivity was found, by high voltage electrophoresis separation of effluxed products, to consist mainly of [35S]cystine, along with smaller amounts of [35S]homocysteine-cysteine mixed disulfide. When homocysteine and cysteamine were presented together to cystinotic cells at dose levels individually ineffective in removing cystine from these cells, a marked synergistic effect was observed and cystine content fell to 10% of that seen in untreated cystinotic fibroblasts. Similarly, synergistic effects of cystine depletion from cystinotic cells were demonstrated when cells were treated with a combination of cysteamine and dithiothreitol or glutathione. Incubation of cystinotic cells with homocysteine, dithiothreitol, or cysteamine in combination with vitamin C did not yield synergistic effects. The above findings suggest a novel way to probe metabolic processes in these mutant cells. Exploration of these synergistic effects may lead to more efficacious therapeutic protocols for cystinosis.

Topics: Ascorbic Acid; Cells, Cultured; Cysteamine; Cystine; Cystinosis; Fibroblasts; Glutathione; Homocysteine; Humans

After loading isolated normal and cystinotic white blood cell lysosomes with radioactive amino acid methyl esters, egress of the corresponding amino acids was measured in the presence or absence of reducing agents. Cysteamine greatly enhanced disposal of cystine- and, to a lesser extent, cysteine-loaded lysosomes, resulting in final similar rates of radioactive clearance. Cysteamine did not alter leucine egress. Cysteamine comparably accelerated cystine egress from normal and cystinotic lysosomes. Reduced glutathione, ascorbic acid, coenzyme A and acetylcoenzyme A, which are much less effective cystine-depleting agents on intact cystinotic cells than cysteamine, failed to increase egress rates from isolated lysosomes loaded with cystine. We believe this in vitro system can help in the future in evaluating drug efficacy in reducing cystine content in cystinotics in addition to the already existing tissue culture technique.

Topics: Amino Acids; Ascorbic Acid; Cysteamine; Cystine; Cystinosis; Glutathione; Half-Life; Humans; In Vitro Techniques; Leukocytes; Lysosomes; Sulfhydryl Compounds

Topics: Adult; Animals; Ascorbic Acid; Child; Cystine; Cystinosis; Fibroblasts; Glutathione; Humans; Kidney; Leukocytes; Skin

Topics: Amino Acids, Sulfur; Ascorbic Acid; Aspirin; Cysteamine; Cystinosis; Dipyridamole; Glutathione; Glutathione Synthase; Homocystinuria; Humans; Metabolism, Inborn Errors; Pyridoxine; Vitamin E

The 100-fold increase in free cystine content characteristic of cultured skin fibroblasts from patients with nephropathic cystinosis was decreased more than 50 percent by addition of L-ascorbic acid to the culture medium at concentrations of 0.29 to 2.9 millimolar. Fresh ascorbic acid must be added to the culture medium daily to produce a progressive decrease of the free cystine content of the cells over a 3-day period. Upon removal of ascorbic acid from the medium, the free cystine content returns to its initial value.

Topics: Ascorbic Acid; Cells, Cultured; Cystine; Cystinosis; Dithiothreitol

Topics: Ascorbic Acid; Butyrates; Chemistry, Clinical; Chromatography, Thin Layer; Cystinosis; Glyoxylates; Humans; Hydrazines; Keto Acids; Ketoglutaric Acids; Levulinic Acids; Methods; Oxaloacetates; Phenylketonurias; Phenylpyruvic Acids; Pyruvates