The role of metabolism in N-methylthiobenzamide-induced pneumotoxicity

Penney, David A.; Gottschall, David W.; Hanzlik, Robert P.; Traiger, George J.

doi:10.1016/0041-008x(85)90237-6

Cited by 12 publications

(1 citation statement)

References 14 publications

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“…Ortho substitution, which sterically blocks the ability of the S , S -dioxide intermediate to acylate nucleophiles, also blocks covalent binding and toxicity without blocking metabolism . In contrast, N -methylation increases potency considerably, but the toxicity is directed to the lung rather than the liver – . This latter example illustrates a potential liability of perturbational approaches to investigating mechanism, namely, that the perturbation may change the mechanism qualitatively rather than simply modulating it quantitatively.…”

Section: Introductionmentioning

confidence: 98%

Protein Targets of Reactive Metabolites of Thiobenzamide in Rat Liver in Vivo

Ikehata

Duzhak

Galeva

et al. 2008

Chem. Res. Toxicol.

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Thiobenzamide (TB) is a potent hepatotoxin in rats, causing dose-dependent hyperbilirubinemia, steatosis, and centrolobular necrosis. These effects arise subsequent to and appear to result from the covalent binding of the iminosulfinic acid metabolite of TB to cellular proteins and phosphatidylethanolamine lipids [ Ji et al. ( 2007) Chem. Res. Toxicol. 20, 701- 708 ]. To better understand the relationship between the protein covalent binding and the toxicity of TB, we investigated the chemistry of the adduction process and the identity of the target proteins. Cytosolic and microsomal proteins isolated from the livers of rats treated with a hepatotoxic dose of [ carboxyl- (14)C]TB contained high levels of covalently bound radioactivity (25.6 and 36.8 nmol equiv/mg protein, respectively). These proteins were fractionated by two-dimensional gel electrophoresis, and radioactive spots (154 cytosolic and 118 microsomal) were located by phosphorimaging. Corresponding spots from animals treated with a 1:1 mixture of TB and TB- d 5 were similarly separated, the spots were excised, and the proteins were digested in gel with trypsin. Peptide mass mapping identified 42 cytosolic and 24 microsomal proteins, many of which appeared in more than one spot on the gel; however, only a few spots contained more than one identifiable protein. Eighty-six peptides carrying either a benzoyl or a benzimidoyl adduct on a lysine side chain were clearly recognized by their d 0/ d 5 isotopic signature (sometimes both in the same digest). Because model studies showed that benzoyl adducts do not arise by hydrolysis of benzimidoyl adducts, it was proposed that TB undergoes S-oxidation twice to form iminosulfinic acid 4 [PhC(NH)SO 2H], which either benzimidoylates a lysine side chain or undergoes hydrolysis to 9 [PhC(O)SO 2H] and then benzoylates a lysine side chain. The proteins modified by TB metabolites serve a range of biological functions and form a set that overlaps partly with the sets of proteins known to be modified by several other metabolically activated hepatotoxins. The relationship of the adduction of these target proteins to the cytotoxicity of reactive metabolites is discussed in terms of three currently popular mechanisms of toxicity: inhibition of enzymes important to the maintenance of cellular energy and homeostasis, the unfolded protein response, and interference with kinase-based signaling pathways that affect cell survival.

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