title: Metabolic fate of glutathione conjugate of benzo[a]pyrene-(7R,8S)-diol (9S,10R)-epoxide in human liver.
abstract: Benzo[a]pyrene-(7R,8S)-diol (9S,10R)-epoxide [(+)-anti-BPDE] is believed to be the activated form of the widely spread environmental pollutant benzo[a]pyrene. Glutathione (GSH) S-transferase (GST)-catalyzed conjugation of (+)-anti-BPDE with GSH is an important mechanism in its cellular detoxification. Here, we report that the GSH conjugate of (+)-anti-BPDE [(-)-anti-BPD-SG] is a potent inhibitor (K(i) 15 microM) of class Mu human GST isoenzyme, which, among human liver GSTs, is a highly efficient detoxifier of (+)-anti-BPDE. Thus, the inhibition of GST activity by (-)-anti-BPD-SG may hinder GSH conjugation of (+)-anti-BPDE, unless the conjugate is metabolized and/or eliminated. The results of the present study show that gamma-glutamyltranspeptidase (gamma-GT) can metabolize (-)-anti-BPD-SG at a rate of about 0.29 nmol/min/mg protein. Our studies also show that (-)-anti-BPD-SG is transported across the human canalicular liver plasma membrane (cLPM) in an ATP-dependent manner at a rate of about 0.33 nmol/min/mg protein. The ATP-dependent transport of (-)-anti-[(3)H]BPD-SG across human cLPM follows Michaelis-Menten kinetics (K(m) 84 microM; V(max) 0.33 nmol/min/mg). In conclusion, the results of the present study suggest that both gamma-GT-mediated metabolism and ATP-dependent canalicular transport may be important steps in overall detoxification of (+)-anti-BPDE in the human liver.
authors.affiliation: Cancer Research Laboratory, Mercy Hospital of Pittsburgh, Pittsburgh, Pennsylvania 15219, USA.
authors.forename: S K
authors.initials: SK
authors.lastname: Srivastava
authors.forename: X
authors.initials: X
authors.lastname: Hu
authors.forename: H
authors.initials: H
authors.lastname: Xia
authors.forename: S
authors.initials: S
authors.lastname: Awasthi
authors.forename: S
authors.initials: S
authors.lastname: Amin
authors.forename: S V
authors.initials: SV
authors.lastname: Singh
mesh_terms: D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D001648:Bile Canaliculi / Q000378:metabolism; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism*; D005982:Glutathione Transferase / Q000037:antagonists & inhibitors; D006801:Humans; D008658:Inactivation, Metabolic; D007527:Isoenzymes / Q000037:antagonists & inhibitors; D008099:Liver / Q000378:metabolism*; D005723:gamma-Glutamyltransferase / Q000378:metabolism
chemical_list: D007527:Isoenzymes; C113118:glutathione-BPDE conjugate; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; D000255:Adenosine Triphosphate; D005723:gamma-Glutamyltransferase; D005982:Glutathione Transferase; D005978:Glutathione