Metabolism and Toxicity of Thioacetamide and Thioacetamide S-Oxide in Rat Hepatocytes

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• 作者：Heather Hajovsky ; Gang Hu ; Yakov Koen ; Diganta Sarma ; Wenqi Cui ; David S. Moore ; Jeff L. Staudinger ; Robert P. Hanzlik
• 刊名：Chemical Research in Toxicology
• 出版年：2012
• 出版时间：September 17, 2012
• 年：2012
• 卷：25
• 期：9
• 页码：1955-1963
• 全文大小：460K
• 年卷期：v.25,no.9(September 17, 2012)
• ISSN：1520-5010

文摘

The hepatotoxicity of thioacetamide (TA) has been known since 1948. In rats, single doses cause centrolobular necrosis accompanied by increases in plasma transaminases and bilirubin. To elicit these effects, TA requires oxidative bioactivation, leading first to its S-oxide (TASO) and then to its chemically reactive S,S-dioxide (TASO₂), which ultimately modifies amine-lipids and proteins. To generate a suite of liver proteins adducted by TA metabolites for proteomic analysis and to reduce the need for both animals and labeled compounds, we treated isolated hepatocytes directly with TA. Surprisingly, TA was not toxic at concentrations up to 50 mM for 40 h. On the other hand, TASO was highly toxic to isolated hepatocytes as indicated by LDH release, cellular morphology, and vital staining with Hoechst 33342/propidium iodide. TASO toxicity was partially blocked by the CYP2E1 inhibitors diallyl sulfide and 4-methylpyrazole and was strongly inhibited by TA. Significantly, we found that hepatocytes produce TA from TASO relatively efficiently by back-reduction. The covalent binding of [¹⁴C]-TASO is inhibited by unlabeled TA, which acts as a 鈥渃old-trap鈥?for [¹⁴C]-TA and prevents its reoxidation to [¹⁴C]-TASO. This in turn increases the net consumption of [¹⁴C]-TASO despite the fact that its oxidation to TASO₂ is inhibited. The potent inhibition of TASO oxidation by TA, coupled with the back-reduction of TASO and its futile redox cycling with TA, may help explain phenomena previously interpreted as 鈥渟aturation toxicokinetics鈥?in the in vivo metabolism and toxicity of TA and TASO. The improved understanding of the metabolism and covalent binding of TA and TASO facilitates the use of hepatocytes to prepare protein adducts for target protein identification.