DIFFERENTIAL-EFFECTS OF GLUTATHIONE AND CYSTEINE ON FE2-INDUCED PROXIMAL TUBULAR CELL ATTACK(, FE3+, H2O2 AND MYOGLOBIN)

Glutathione (GSH) is widely advocated as a cytoprotectant for preventi ng oxidant forms of renal damage. However, in the case of myoglobinuri c tubular injury, both beneficial and adverse effects have been noted. The purpose of this study was to help elucidate this seeming paradox by assessing the impact on thiol supplementation on normal tubules and on tubules subjected to individual components of heme protein-induced oxidant attack (Fe2+, Fe3+, and H2O2). Isolated mouse proximal tubula r segments (PTS) were exposed to either GSH or cysteine under normal c onditions or in the presence of exogenous Fe2+, Fe3+, or H2O2 Lethal c ell injury (LDH release) and lipid peroxidation (malondialdehyde) were then assessed. GSH and cysteine exerted iron dependent, H2O2 independ ent, pro-oxidant effects on normal PTS. Both were also pro-oxidant in the presence of an exogenous Fe3+ challenge. In contrast, each attenua ted Fd(2+) cytotoxicity. The importance oi iron's redox status on the expression of tubular injury was further underscored by the fact that Fe3+ partially blocked Fe2+'s cytotoxic effects. GSH mitigated H2O2 to xicity (consistent with a fueling of GSH peroxidase activity). Convers ely, cysteine promoted H2O2's injurious effects. To assess the impact of thiol supplementation on a fully integrated model of heme protein t oxicity, proximal tubular (HK-2) cells were cultured with myoglobin x 24 hours +/- test reactants. Exogenous GSH worsened, while GSH depleti on (BSO) protected, against myoglobin toxicity (indicating a predomina nce of GSH's pro-oxidant effects). Conversely, cysteine (but not homoc ysteine) decreased myoglobin toxicity. These GSH/cysteine effects were confirmed in LLC-PK1 cells subjected to iron attack. We conclude that : (I) GSH and cysteine can exert pro-and anti-oxidant effects, dependi ng on the nature of the oxidant challenge and iron's redox status; (2) Fe3+ can function as a cytoprotectant, partially offsetting Fe2+ toxi city; and (3) cysteine, although potentially pro-oxidant, can mitigate heme protein-induced injury. Since the kidney rapidly catabolizes GSH to cysteine, the latter may be at least partially responsible for GSH 's reported cytoprotective actions against myoglobinuric acute renal f ailure.