Sulfoxides as Urinary Metabolites of S-Allyl-l-Cysteine in Rats: Evidence for the Involvement of Flavin-Containing Monooxygenases

Abstract

ABSTRACT:S-Allyl-L-cysteine (SAC), a component of garlic and a metabolite of allyl halides, is a known substrate for multiple flavin-containing monooxygenases (FMOs). In the current study, we characterize the in vivo SAC metabolism by investigating the presence of SAC, N-acetyl-S-allyl-L-cysteine (NASAC), and their corresponding sulfoxides in the urine of rats given SAC (200 or 400 mg/kg i.p.). In some experiments, rats were given aminooxyacetic acid (AOAA), an inhibitor of cysteine conjugate ␤-lyase, or methimazole, an alternative FMO substrate, 30 min prior to treatment with 200 mg/kg SAC. Nearly 40 to 50% of the dose was recovered in the 24-h collection period. In all treatment groups, the majority of the metabolites were excreted within 8 h. The major metabolites detected were NASAC and NASAC sulfoxide (NASACS; nearly 30-40% and 5-10% of the dose, respectively). Only small amounts of the dose (approximately 1.5%) were recovered as SAC and SAC sulfoxide (SACS). Methimazole pretreatment significantly reduced amounts of both SACS and NASACS detected in the urine when compared with rats given SAC only, whereas AOAA pretreatment had no effect. In vitro assays using rat liver microsomes were also carried out to compare the sulfoxidation rates of SAC and NASAC. The results showed that SAC was much more readily oxidized than NASAC. Collectively, the results provide evidence for the involvement of FMOs in the in vivo metabolism of SAC and that SAC is a much better substrate for FMOs than its corresponding mercapturic acid. (SAC 1 ) is a significant water-soluble allyl sulfur component in garlic preparations (Weinberg et al., 1993), a component which has been shown to have antioxidant and anticancer properties in animals (Sumiyoshi and Wargovich, 1990;Hatono et al., 1996;Ho et al., 2001). SAC has been shown to have antiproliferative effects on neuroblastoma (Welch et al., 1992), melanoma (Takeyama et al., 1993), and prostate carcinoma cells (Pinto et al., 1997). However, the mechanisms of the anticancer properties of SAC are unclear. S-Allyl-L-cysteineSAC is also a known metabolite of allyl halides and allyl esters, including allyl chloride, allyl bromide, sodium allyl sulfate, and allyl nitrate (Kaye et al., 1972;Kaye, 1973). It results from the formation of the glutathione conjugate of the allyl halide or ester. The glutamate and glycine moieties of S-allyl-glutathione are then cleaved by ␥-glutamyl transpeptidase and dipeptidases to yield SAC.Our laboratory has previously shown that SAC is a substrate for multiple rabbit and human flavin-containing monooxygenases (FMOs). FMOs are microsomal enzymes that catalyze the NADPHdependent oxidation of many compounds that contain sulfur, nitrogen, selenium, and phosphorus (Ziegler, 1993). Previously, we have shown that SAC is metabolized to the greatest extent by cDNA-expressed rabbit FMO3 followed by FMO1 and then FMO2, but SAC showed no activity with rabbit FMO5 (Ripp et al., 1997). More recently and using cDNA-expressed human FMOs, SAC has been shown to be a good substr...

The Pharmacological Effects of S-Propargyl-Cysteine, a Novel Endogenous H2S-Producing Compound

“…The major metabolite in rat biomatrices, which was identified by MRM information-dependent, acquisition-enhanced product ion (MRM-IDA-EPI) scans on API 4000 QTRAP system, was N-acetylation (Zheng et al 2012). These pharmacokinetic properties of SPRC were observed similar in previous pharmacokinetic SAC study (Nagae et al 1994;Krause et al 2002).…”

S-(1,2,2-Trichlorovinyl)-l-cysteine Sulfoxide, a Reactive Metabolite of S-(1,2,2-Trichlorovinyl)-l-cysteine Formed in Rat Liver and Kidney Microsomes, Is a Potent Nephrotoxicant

“…When rats were pretreated with AOAA before TCVC, they exhibited severe toxicity and two rats of four died during the course of the 24-h experiment, whereas all rats given the equimolar dose of TCVC did not exhibit severe toxicity signs or death during the course of the experiment. This was unexpected, because this AOAA dosing protocol had been found previously protective with other nephrotoxic cysteine S-conjugates (Lash et al, 1994;Elfarra, 1997;Krause et al, 2002). Because of the jpet.aspetjournals.org potent nephrotoxicity of TCVCS compared with TCVC, the data suggest that inhibiting the ␤-lyase pathway results in increased toxicity, possibly due to increased formation of TCVCS in rats given AOAA and TCVC.…”

Preclinical assessment of the distribution, metabolism, and excretion of S-propargyl-cysteine, a novel H2S donor, in Sprague-Dawley rats

“…Neither the parent drug nor the N-acetyl metabolite was found in rat feces. Previous studies demonstrated that S-allyl-L-cysteine sulfoxide and N-allyl-L-cysteine sulfoxide were the expected metabolites of SAC in rat urine [18] . However, these sulfoxide metabolites of SPRC were not observed in our experiment.…”