ROLE OF RENAL CYSTEINE CONJUGATE BETA-LYASE IN THE MECHANISM OF COMPOUND-A NEPHROTOXICITY IN RATS

Background: The sevoflurane degradation product compound A is nephroto xic in rats, in which it undergoes extensive metabolism to glutathione and cysteine S-conjugates. The mechanism of compound A nephrotoxicity in rats is unknown. Compound A nephrotoxicity has not been observed i n humans. The authors tested the hypothesis that renal uptake of compo und A S-conjugates and metabolism by renal cysteine conjugate beta-lya se mediate compound A nephrotoxicity in rats. Methods: Compound A (0-0 .3 mmol/kg in initial dose-response experiments and 0.2 mmol/kg in sub sequent inhibitor experiments) was administered to Fischer 344 rats by intraperitoneal injection. Inhibitor experiments consisted of three g roups: inhibitor (control), compound A, or inhibitor plus compound A. The inhibitors were probenecid (0.5 mmol/kg, repeated 10 h later), an inhibitor of renal organic anion transport and S-conjugate uptake; aci vicin (10 mg/kg and 5 mg/kg 10 h later), an inhibitor of gamma-glutamy l transferase, an enzyme that cleaves glutathione conjugates to cystei ne conjugates; and aminooxyacetic acid (0.5 mmol/kg and 0.25 mmol/kg 1 0 h later), an inhibitor of renal cysteine conjugate beta-lyase, Urine was collected for 24 h and then the animals were killed, Nephrotoxici ty was assessed by light microscopic examination and biochemical marke rs (serum urea nitrogen and creatinine concentration, urine volume and urine excretion of protein, glucose, and alpha-glutathione-S-transfer ase [(alpha GST], a marker of tubular necrosis). Results: Compound A c aused dose-related nephrotoxicity, as shown by selective proximal tubu lar cell necrosis at the corticomedullary junction, diuresis, proteinu ria, glucosuria, and increased alpha GST excretion. Probenecid pretrea tment significantly (P < 0.05) diminished compound A-induced increases (mean +/- SE) in urine excretion of protein (45.5 +/- 3.8 mg/24 h vs. 25.9 +/- 1.7 mg/24 h), glucose (28.8 +/- 6.2 mg/24 h vs. 10.9 +/- 3.2 mg/24 h), and alpha GST (6.3 +/- 0.8 mu g/24 h vs. 1.0 +/- 0.2 mu g/2 4 h) and completely prevented proximal tubular cell necrosis, Aminooxy acetic acid pretreatment significantly diminished compound A-induced i ncreases in urine volume (19.7 +/- 3.5 ml/24 h vs. 9.8 +/- 0.8 ml/24 h ), protein excretion (37.2 +/- 2.7 mg/24 h vs. 22.2 +/- 1.8 mg/24 h), and alpha GST excretion (5.8 +/- 1.5 vs. 2.3 mu g/24 h +/- 0.8 mu g/24 h) but did not significantly alter the histologic pattern of injury, In contrast, acivicin pretreatment increased the compound A-induced hi stologic and biochemical markers of injury. Compound A-related increas es in urine fluoride excretion, reflecting compound A metabolism, were not substantially altered by any of the inhibitor treatments, Conclus ions: Intraperitoneal compound A administration provides a satisfactor y model of nephrotoxicity, Aminooxyacetic acid and probenecid signific antly diminished histologic and biochemical evidence of compound A nep hrotoxicity, whereas acivicin potentiated toxicity. These results sugg est that renal uptake of compound A-glutathione or compound A-cysteine conjugates and cysteine conjugates metabolism by renal beta-lyase med iate, in part, compound A nephrotoxicity in rats.