Cysteine conjugate beta-lyase-dependent biotransformation of the cysteine S-conjugates of the sevoflurane degradation product compound A in human, nonhuman primate, and rat kidney cytosol and mitochondria.

BACKGROUND

2-(Fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (compound A) is a fluorinated alkene formed by the degradation of sevoflurane in the anesthesia circuit. Compound A is toxic to the kidneys in rats and undergoes glutathione-dependent metabolism in vivo. Several nephrotoxic halogenated alkenes also undergo cysteine conjugate beta-lyase-dependent biotransformation. These experiments were designed to test the hypothesis that cysteine S-conjugates of compound A undergo beta-lyase-dependent biotransformation.

METHODS

S-[2-(Fluoromethoxy)-1,1,3,3,3-pentafluoropropyl]-L-cysteine 4, S-[2-(fluoromethoxy)-1,3,3,3-tetrafluoro-1-propenyl]-L-cysteine 5, and S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine 11 were incubated with rat, human, and nonhuman primate (cynomolgus, rhesus, and marmoset) kidney cytosol and mitochondria. beta-Lyase activity was determined by measuring pyruvate formation.

RESULTS

Compound A-derived conjugates 4 and 5 as well as conjugate 11, a positive control, were substrates for cytosolic and mitochondrial beta-lyase from human, nonhuman primate, and rat kidney. For all substrates, beta-lyase activity was highest in the rat and lowest in the human and was higher in cytosol than in mitochondria. Conjugate 11 was a much better substrate than conjugates 4 or 5. The biotransformation of conjugates 4, 5, and 11 was inhibited by the beta-lyase inhibitor (aminooxy)acetic acid and was stimulated by the amino group acceptor 2-keto-4-methylthiolbutyric acid, indicating a role for beta-lyase.

CONCLUSIONS

These data confirm the presence of beta-lyase activity in human and rat kidney and show that activity is also present in kidney tissue from nonhuman primates. The data also show that compound A-derived conjugates 4 and 5 undergo beta-lyase-catalyzed biotransformation. beta-Lyase activity in rat and nonhuman primate kidney tissue was 8 to 30 times and one- to three times, respectively, higher than in human kidney tissue.