Oxidation of glutathione and cysteine in human plasma associated with smoking.

Cigarette smoking contributes to the development or progression of numerous chronic and age-related disease processes, but detailed mechanisms remain elusive. In the present study, we examined the redox states of the GSH/GSSG and Cys/CySS couples in plasma of smokers and nonsmokers between the ages of 44 and 85 years (n = 78 nonsmokers, n = 43 smokers). The Cys/CySS redox in smokers (-64 +/- 16 mV) was more oxidized than nonsmokers (- 76 +/- 11 mV; p <.001), with decreased Cys in smokers (9 +/- 5 microM) compared to nonsmokers (13 +/- 6 microM; p <.001). The GSH/GSSG redox was also more oxidized in smokers (-128 +/- 18 mV) than in nonsmokers (-137 +/- 17 mV; p =.01) and GSH was lower in smokers (1.8 +/- 1.3 microM) than in nonsmokers (2.4 +/- 1.0; p <.005). Although the oxidation of GSH/GSSG can be explained by the role of GSH in detoxification of reactive species in smoke, the more extensive oxidation of the Cys pool shows that smoking has additional effects on sulfur amino acid metabolism. Cys availability and Cys/CySS redox are known to affect cell proliferation, immune function, and expression of death receptor systems for apoptosis, suggesting that oxidation of Cys/CySS redox or other perturbations of cysteine metabolism may have a key role in chronic diseases associated with cigarette smoking.

Increased oxidant-induced apoptosis in cultured nondividing human retinal pigment epithelial cells.

PURPOSE: To determine whether long-term cultured nondividing human retinal pigment epithelial (hRPE) cells are sensitive to oxidant-induced apoptosis and whether the Fas pathway is involved in the process. METHODS: Confluent hRPE cells were maintained for 2 to 3 months in the basal medium (DMEM containing 2% fetal bovine serum) with one medium change per week. DNA synthesis was measured by incorporation of bromodeoxyuridine (BrdU) and the cell cycle was analyzed by flow cytometry. Intracellular glutathione (GSH) and glutathione disulfide (GSSG) were measured by HPLC. Apoptosis was triggered with the oxidant tert-butylhydroperoxide (tBH), recombinant soluble Fas ligand (sFasL), or agonistic anti-Fas antibody (CH-11). Cell viability was assessed by tetrazolium salt (WST-1) assay, and apoptosis was determined by measuring DNA cleavage or phosphatidylserine exposure. FasL and Fas proteins were detected by flow cytometry and Western blot. FasL and Fas transcripts were analyzed by RT-PCR. RESULTS: After incubation in basal medium for more than 2 months, hRPE cells were largely nondividing and accumulated autofluorescent granules identified by electron microscopy to be lysosomes. Compared with proliferating hRPE cells, the nondividing cells had lower intracellular GSH, GSSG, and GSH/GSSG and a more oxidized redox potential (E(h)). Downregulation of Fas but upregulation of FasL was observed in these cells. The nondividing hRPE cells appeared more susceptible to tBH-induced apoptosis. Similar to proliferating hRPE cells, the apoptosis induced by tBH was preceded by induction of FasL, and antioxidants inhibited both FasL increase and apoptosis. Apoptosis was also inhibited with the antagonistic anti-Fas antibody ZB4. However, the nondividing hRPE cells had decreased sensitivity to apoptosis triggered by sFasL or CH-11. CONCLUSIONS: Long-term hRPE culture created cells that were nondividing and accumulated autofluorescent granules. The increased sensitivity to tBH-induced apoptosis in these cells was associated with intracellular oxidation and upregulation of FasL. These results suggest that an increase in FasL may contribute to the vulnerability of nondividing hRPE cells to oxidant-induced apoptosis.