Role of Cytochrome P4503A in Cysteine S-Conjugates Sulfoxidatıon and the Nephrotoxicity of the Sevoflurane Degradatıon Product Fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl Ether (Compound A) in Rats

Abstract

The volatile anesthetic sevoflurane is degraded to fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether (FDVE) in anesthesia machines. FDVE is nephrotoxic in rats. FDVE undergoes glutathione conjugation, subsequent conversion to cysteine and mercapturic acid conjugates, and cysteine conjugate metabolism by renal beta-lyase, which is a bioactivation pathway mediating nephrotoxicity in rats. Recent in vitro studies revealed cytochrome P4503A-catalyzed formation of novel sulfoxide metabolites of FDVE cysteine-S and mercapturic acid conjugates in rat liver and kidney microsomes. FDVE-mercapturic acid sulfoxides were more toxic than other FDVE conjugates to renal proximal tubular cells in culture. Nevertheless, the occurrence and toxicological significance of FDVE sulfoxides formation in vivo remain unknown. This investigation determined, in rats in vivo, the existence, role of P4503A, and nephrotoxic consequence of FDVE conjugates sulfoxidation. Rats were pretreated with dexamethasone, phenobarbital, troleandomycin, or nothing (controls) before FDVE, and then, nephrotoxicity, FDVE-mercapturate sulfoxide urinary excretion, and FDVE-mercapturate sulfoxidation by liver microsomes were assessed. The formation of FDVE-mercapturic acid sulfoxide metabolites in vivo and their urinary excretion were unambiguously established by mass spectrometry. Dexamethasone and phenobarbital increased, and troleandomycin decreased (i) liver microsomal FDVE-mercapturic acid sulfoxidation in vitro, (ii) FDVE-mercapturic acid sulfoxide urinary excretion in vivo, and (iii) FDVE nephrotoxicity in vivo assessed by renal histology, blood urea nitrogen concentrations, and urine volume and protein excretion. Urine 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid, reflecting beta-lyase-dependent FDVE-cysteine S-conjugates metabolism, was minimally affected by the pretreatments. These results demonstrate that FDVE S-conjugates undergo P4503A-catalyzed sulfoxidation in rats in vivo, and this sulfoxidation pathway contributes to nephrotoxicity. FDVE S-conjugates sulfoxidation constitutes a newly discovered mechanism of FDVE bioactivation and toxicification in rats, in addition to beta-lyase-catalyzed metabolism of FDVE-cysteine S-conjugates.

Influence of Sevoflurane on the Metabolism and Renal Effects of Compound A in Rats

“…The dose of compound A used in these experiments (0.25 mmol/kg) was based on the threshold dose for nephrotoxicity observed in previous experiments. 4 Renal effects (urine volume, protein excretion and osmolality, serum creatinine and urea nitrogen, and necrosis; table 1) were similar to those seen previously at this intraperitoneal dose 4,9 and at approximately 350 -400 ppm-h inhaled compound A. 5,28 Coadministration of compound A with 3 h of sevoflurane increased some but not all measures of renal toxicity (table 1).…”

“…Urinary excretion of compound A metabolites is described in table 2 and was similar to that reported previously. 9 Both major mercapturic acid conjugates (N-Ac-DFEC and (E, Z)-N-Ac-FFVC) and the sulfoxide of N-Ac-DFEC (N-Ac-DFEC-SO) were observed. The sulfoxide of (E, Z)-N-Ac-FFVC was not observed, presumably because its greater reactivity precludes escape from the kidney.…”

“…Urine concentra-tions of compound A-mercapturic acid conjugates, their corresponding sulfoxides, and 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid in urine were determined by high-pressure liquid chromatography-mass spectrometry as described previously. 9 Formalin-treated kidney sections were embedded in paraffin, and sections were stained with hematoxylin and eosin. They were examined by a veterinary pathologist who was unaware of the animal treatments.…”

“…1, 10 -13). Compound A sulfoxides are also thought to contribute to nephrotoxicity, because induction (or inhibition) of sulfoxidation in vivo increased (or decreased) compound A nephrotoxicity, 8,9 and the sulfoxide conjugates were more toxic than other compound A conjugates to renal proximal tubular cells in culture. 10 Compound A undergoes qualitatively similar biotransformation in humans.…”

Characterization of the chemical reactivity and nephrotoxicity of N-acetyl-S-(1,2-dichlorovinyl)-l-cysteine sulfoxide, a potential reactive metabolite of trichloroethylene

“…Evidence for the possible formation of NA-DCVCS is based on a number of observations: (1) the precursor mercapturic acid NA-DCVC can be oxidized by CYP3A1/2 to NA-DCVCS in rat liver microsomes in vitro (Werner et al, 1996), (2) CYP3A-mediated sulfoxidation is an established β-lyase independent bioactivating pathway for nephrotoxic mercapturic acids (Sheffels et al, 2004; Birner et al, 1995), and (3) NA-DCVCS-derived hemoglobin adducts have been detected in rats given doses of DCVC relevant to blood concentrations of DCVG in humans exposed to TCE (Barshteyn and Elfarra, 2009). The present study demonstrates that NA-DCVC and NA-DCVCS were nephrotoxic to rats under the in vivo experimental conditions utilized.…”