This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Add to Saved Citations Download to citation manager Add to My Marked Citations Citing Articles Citing Articles via Google Scholar Citing Articles via Scopus Google Scholar Articles by Sajan, M. Articles by Kulkarni, A. P. Search for Related Content PubMed Articles by Sajan, M. Articles by Kulkarni, A. P. Social Bookmarking                         What's this?

In Vitro Inhibition of Mammalian Glutathione Transferases by Selected Nitrobenzenes

Florida Toxicology Research Center, Department of Environmental and Occupational Health, University of South Florida, Tampa, Florida, USA

Gunda Reddy

U.S. Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, Maryland, USA

Arun P. Kulkarni

Florida Toxicology Research Center, Department of Environmental and Occupational Health, University of South Florida, Tampa, Florida, USA

Five structurally related nitrobenzenes (1,2-dinitrobenzene, 1,3-dinitrobenzene, 1,4-dinitrobenzene, 1,3,5-trinitrobenzene, and picric acid) and Meisenheimer complex [1-(S-glutathionyl)-2,4,6-trinitrocyclohexadienate] were evaluated as possible inhibitors of affinity purified mammalian glutathione transferases (GSTs) isolated from human liver or human term placenta and rat fiver. The results suggest that the degree of GST inhibition depends upon both the chemical in question and the enzyme source. Among the nitrobenzenes tested, 1,3,5-trinitrobenzene (TNB) was found to be the most potent inhibitor of GST activity toward 1-chloro-2,4-dinitrobenzene (CDNB) from all the sources, whereas 1,3-dinitrobenzene (1,3-DNB) was the least effective. TNB-caused inhibition of GST activity toward CDNB appeared to be isozyme specific in that compared to the enzyme from human term placenta (GSTP1–1), the degree of inhibition of the mixture of GST isozymes present in the fivers of adult rats and humans was low. The enzyme assays conducted with 3,4-dichloro-1-nitrobenzene (DCNB), ethacrynic acid (EA), and 4-nitropyridinei N-oxide also suggested the isozymespecific inhibition of rat fiver GST activity by TNB. The nature of TNB-caused inhibition of GSTP1–1 was competitive with respect to CDNB and yielded a Ki value of 12.5 M. With EA, a specific substrate for GSTP1–1, an IC₅₀ value of 16 M was estimated for the GSTP1–1 inhibition by TNB. The Meisenheimer complex, the product of nonenzymatic GSH conjugation with TNB by different GSTs, was found to be the most potent inhibitor of mammalian GSTs, and IC₅₀ values ranged between 1 and 4 M when the enzyme activity was assayedusing CDNB. The nature of GSTP1–1 inhibition was noncompetitive with respect to CDNB, with a Ki value of 1 M for Meisenheimer complex. Although a precise mechanism was not identified, it is postulated that GSH depletion and/or GST inhibition may contribute, at least partly, to the target organ toxicity caused by exposures of animals to different nitrobenzenes reported in the literature.

Key Words: 1,3-Dinitrobenzene • In Vitro Inhibition • Mammalian Glutathione Transferases • Nitrobenzenes • 1,3,5-Trinitrobenzene

International Journal of Toxicology, Vol. 19, No. 4, 285-292 (2000)
DOI: 10.1080/10915810050202097


CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?