S-[(1 and 2)-Phenyl-2-hydroxyethyl]-cysteine-Induced Cytotoxicity to Rat Renal Proximal Tubules

Abstract

S-[(1 and 2)-Phenyl-2-hydroxyethyl]-glutathione is nephrotoxic in rats through its metabolic conversion to corresponding cysteine-S-conjugate, e.g.,S-[(1 and 2)-phenyl-2-hydroxyethyl]-cysteine (PHEC). The present study was carried out to determine the mechanism of PHEC-induced toxicity in isolated rat renal proximal tubules. PHEC decreased tubule viability in concentration (0–2 mM)- and time (0–3 hr)-dependent manner, with initial decreases occurring 2 hr after exposure. Tubule basal and nystatin-stimulated oxygen consumption decreased before cell death following exposure to 0.5 and 1 mMPHEC. Assessment of direct mitochondrial function within the proximal tubules showed that respiration was reduced in the absence and presence of a phosphate acceptor using site II (succinate) and site I (malate/glutamate) respiratory substrates 30 and 45 min after exposure to 0.5 and 1 mMPHEC. Exposure of proximal tubules to 1 mMPHEC caused a time-dependent decline of mitochondrial membrane potential (as measured by the uptake of the cationic fluorescent dye, rhodamine 123 by the proximal tubules) and depletion of ATP content with initial decrease occurring as early as 30 min after the exposure. Glutathione depletion and lipid peroxidation occurred within 90 min clearly preceding cell death after exposure to 0.5 and 1 mMPHEC. Pretreatment with 1 mMdeferoxamine prevented PHEC-induced lipid peroxidation but did not prevent PHEC-induced cytotoxicity, whereas deferoxamine pretreatment prevented lipid peroxidation, mitochondrial dysfunction, and cytotoxicity after exposure to 0.5 mMtertiary-butyl hydroperoxide, suggesting that iron-mediated lipid peroxidation does not contribute to PHEC-induced proximal tubule cell death. Pretreatment of renal proximal tubules with 10 mMfructose failed to prevent the change in mitochondrial membrane potential, the ATP depletion and cytotoxicity caused by 1 mMPHEC, indicating that the glycolytic pathway is not important in renal proximal tubule respiration and cell injury. Pretreatment of renal tubules with aminooxyacetic acid failed to prevent the mitochondrial dysfunction induced by 1 mMPHEC, indicating an absence of further metabolism of PHEC by a β-lyase-dependent pathway. It is therefore proposed that the alteration of mitochondrial functions and the consequent loss of cellular energy supplies can represent the mechanisms by which PHEC expressed its acute cytotoxicity.