NDT Advance Access originally published online on June 14, 2005
Nephrology Dialysis Transplantation 2005 20(9):1828-1832; doi:10.1093/ndt/gfh932
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Altered status of glutathione and its metabolites in cystinotic cells
1 Department of Paediatric Nephrology and 2 Laboratory of Paediatrics and Neurology, Radboud University Nijmegen Medical Centre, The Netherlands
Correspondence and offprint requests to: E. N. Levtchenko, Department of Paediatric Nephrology, Radboud University Nijmegen Medical Centre, PO 9101, 6500 HB Nijmegen, The Netherlands. Email: e.levtchenko{at}cukz.umcn.nl
Background. Cystinosis is an autosomal recessive disorder, caused by mutations of the lysosomal cystine carrier cystinosin, encoded by the CTNS gene (17p13). The concomitant intralysosomal cystine accumulation leads to multi-organ damage, with kidneys being the first affected. Altered mitochondrial oxidative phosphorylation has been demonstrated in animal proximal tubules loaded with cystine dimethyl ester, mimicking cystine accumulation in cystinosis, but has not been confirmed in cells of patients with cystinosis. Furthermore, the link between cystine accumulation and mitochondrial damage is also missing. We hypothesized that cytosolic cysteine deficiency resulting in intracellular glutathione (GSH) shortage might be involved in cellular dysfunction in cystinosis.
Methods. Components of the 
-glutamyl cycle were measured in cultured skin fibroblasts (n = 9) and polymorphonuclear (PMN) leukocytes (n = 15) derived from patients with cystinosis and compared with the values in cultured fibroblasts (n = 9) and PMN cells (n = 18) of healthy controls.
Results. Cystine content in cystinotic fibroblasts and PMN cells was significantly elevated compared with the controls, consistent with the lysosomal cystine accumulation in these cells. Although no reduction of total intracellular GSH content was found in cystinotic cells, it inversely correlated with cystine levels. Furthermore, GSH disulfide (GSSG) was elevated in cystinotic cells, resulting in an increased GSSG/total GSH (%) ratio. No relationship between intracellular cystine and GSH was found in control fibroblasts and PMN cells.
Conclusion. An elevated GSSG/total GSH (%) ratio might indicate increased oxidative stress present in cystinotic cells. Inverse correlation between cystine accumulation and intracellular GSH content indicates that under stress conditions such as intensive energy demand or increased oxidative insult, cystinotic cells may be more prone to GSH depletion.
Keywords: cystinosis; fibroblasts; glutathione; glutathione disulfide; polymorphonuclear cells
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