INHIBITION OF BENZO[A]PYRENE METABOLISM BY INSULIN, FITC-INSULIN AND AN FITC-INSULIN-ANTIBODY CONJUGATE IN THE HUMAN HEPATOMA-CELL LINE HEPG2

Benzo[a]pyrene (BaP) can be metabolically activated to an ultimate car cinogen, (+)-anti-BaP-7, 8-dihydrodiol-9,10-epoxide [(+)-anti-BaPDE] b y cells in culture. This activation involves oxidation by specific iso forms of cytochrome P450s such as CYP1A1. The human hepatoma cell line , HepG2, was used to examine the effect of inhibition of CYP1A1 activi ty by anti CYP1A1 specific antibodies on BaP metabolism. Metabolism of BaP to water-soluble metabolites by HepC2 cells in culture was 50% lo wer in fluorescein isothiocyanate (FITC)-insulin-CYP1A1-antibody-conju gate-treated cells than in control cells. However, FITC-insulin (lacki ng anti CYP1A1 conjugates) or insulin alone also decreased BaP metabol ism by 50%. This insulin-induced inhibition of BaP metabolism was obse rved for cultures treated with a concentration range of FITC-insulin f rom 50-1000 nM. FITC-conjugated gamma-globulin showed no significant b inding to HepG2 cells by fluorescence microscopy, however, FITC-insuli n-antibody conjugates bound extensively, suggesting that FITC-insulin conjugates still retain the ability to bind insulin receptors. These r esults demonstrate that free insulin, FITC-insulin or FITC-insulin con jugated to antibodies are effective inhibitors of BaP metabolism in ce lls in culture.