Cystine accumulation and loss in normal, heterozygous, and cystinotic fibroblasts.

Abstract

Cystinotic fibroblasts contain approximately 100 times more free cystine than do normal control fibroblasts. When cystinotic fibroblasts were placed in the presence of 30 mM cysteine-glutathione mixed disulfide (CSSG) for 24 h, their cystine content increased about 3-fold. Similar treatment of normal fibroblasts and fibroblasts from patients heterozygous for cystinosis resulted in a 6- to 7-fold increase in cystine content. In all 3 cell types, the intracellular free cystine is located within lysosomes. When placed in cystine-free medium after 24 h in CSSG-containing medium, the normal and heterozygous fibroblasts rapidly lost their lysosomal cystine (t1/2 [half-time] = 20 min), but the cystine content of the cystinotic cells remained stable for over 90 min. In contrast to the findings in intact fibroblasts, cystine loss could not be demonstrated from isolated, cystine-loaded lysosomes from any of the 3 cell types.