Cystinuria therapy by ascorbic acid (author's transl)

Abstract

At the beginning of the four chapters on phenomena, analysis, pathophysiology and therapy of cystinuria the essentials of the published literature are summarized. The frequency of cystinuria is in the order of 1:10,000. Besides the cystine lithiasis occurring in nine tenths of all cystinuria patients neurological diseases may also be observed. All commonly applied methods to analyze cystine detect the sum of cystine and cysteine. Cystinuria is characterized by a higher cystine excretion, up to the 100-fold of the normal. Also the concentrations of lysine, arginine and ornithine in the urine of cystinuria patients are elevated, caused by intestinal and renal transport defects. Inevitable damage of renal parenchyma by multiple operations can drastically be reduced by the therapy with D-penicillamine or alpha-mercaptopropionylglycine. The disadvantages of that formation of soluble asymmetric disulfides are the side effects, such as nausea, gastric difficulties and dermatosis, occurring in up to 50% of the patients. Using the especially developed method with HPLC separation and electrochemical detector with a mercury electrode, cystine and cysteine are analyzed simultaneously. In the urine of healthy persons the molar concentration of cysteine is in the same order as cystine. But in cystinuria the cysteine concentration in urine is about a thousand times less than that of cystine. These results are evidence that a shifted redox-equilibrium of cystine-cysteine is also typical of cystinuria. The molar cysteine percentage of cysteine in healthy persons is increased from 30 to 50% by oral ascorbic acid administration. Therefore a vitamin C therapy for cystinuria is developed. 31 cystinuria patients who receive 5 g of vitamin C a day show a decrease in the cystine concentration of about 40%. Up to now, no side effects have been observed. The most obvious sign of the positive effect of the proposed vitamin C therapy for cystinuria is the missing cystine sediment in fresh urine.