Depletion of cystine in cystinotic fibroblasts by drugs enclosed in liposomes.

Abstract

Summary and degradable by lysosomal enzymes after their uptake by phagocytic cells. Lysosomally compartmentalized cystine can be removed from cystinotic cells by the use of reducing agents. In further investigation of means for converting cystine to a form or forms cystinosis is a recessive, autosomally inherited disease, the capable of penetrating the l~sosomal membrane, a number of fundamental cause of which remains unknown. There is an chemical agents either enclosed in phospholipid vesicles (li~o- accumulation of cystine in lysosomes, with particularly heavy wmes) or free in solution were presented to c~stinotic cells in concentrations in actively endocytic or phagocytic tissues such tissue culture. After a 2-hr incubation, cystine content of as kidney, liver, spleen, and white blood cells (25-27). These cultured cystinotic cells was generally reduced more effectively elevated cystine concentrations are apparently toxic to certain by such agents in liposomes than in the medium. The most cellular functions. During the first few years of life, the principal effective combination was cysteamine (MEA) in liposomes: a effects of abnormal cystine storage are growth retardation, 0-5 mM dose of MEA rduced the cystine content of cystinotic photophobia, hypothyroidism, and, most importantly, the renal cells 86% more when enclosed in liposomes than when dissolved Fanconi syndrome with subsequent renal failure (classic nephroat the equivalent dose in the medium. This observation could phathic cystinosis) (24). Adolescent onset and benign adult not be repeated when serum was omitted from the incubation cystinosis also shows intracellular accumulation of cystine but medium, indicating that serum binds or otherwise inactivates generally of lesser magnitude, with clinical symptoms correcystearnine and that the li~some-en~losed cystearnine is Pro- spondingly less severe or absent altogether. The existence of tected from this action. Other liposome-entra~~ed com~ounds these variant forms of cystinosis suggests that a partial reduction tested showed little if any depletion of intracellular cystine of intracellular cystine content in the nephropathic cystinotic beyond that caused by non-liposome-enciosed drug action. Some patient might therefore prove to be of clinical value. agents increased the intracellular cystine content. Others of low Cystine can be removed from cystinotic fibroblasts by agents molecular weight proved to be poorly retained by li~osomes, a such as MEA, cystamine, DTT, and vitamin C (4, 7, 11, 15, factor which may have been responsible for their relative 32). The first three compounds have known toxicity in vivo (13). ineffectiveness. Cysteamine, which is positively charged at neU- we have explored the action of these and other compounds on tral pH, was retained effectively when enclosed in negative cystinotic cells in tissue culture and the distribution of liposomes made by inclusion of phosphatidic acid in the lipid [35slcysteamine in normal mice, the free drug to its