Cystinosis is an inherited disorder due to mutations in the CTNS gene which encodes cystinosin, a lysosomal transmembrane protein involved in cystine export to the cytosol. Both accumulation of cystine in the lysosome and decreased cystine in the cytosol may participate in the pathogenic mechanism underlying the disease. We observed that cystinotic cell lines have moderate decrease of glutathione content during exponential growth phase. This resulted in increased solicitation of oxidative defences of the cell denoted by concurrent superoxide dismutase induction, although without major oxidative insult under our experimental conditions. Finally.. decreased glutathione content in cystinotic cell lines could be counterbalanced by a series of exogenous precursors of cysteine. denoting that lysosomal cystine export is a natural source of cellular cysteine in the studied cell lines. (C) 2004 Elsevier Inc. All rights reserved.