The effect of initiating doses of benzo[a]pyrene and 7,12-dimethylbenz[a]anthracene on the expression of PAH activating enzymes and its modulation by plant phenols.

Polycyclic aromatic hydrocarbons (PAHs) including benzo[a]pyrene (B[a]P) and 7,12-dimethylbenz[a]anthracene (DMBA) are environmental pollutants, which undergo metabolic activation to exert their carcinogenic effects. Our earlier studies showed that naturally occurring plant phenols, protocatechuic, chlorogenic, tannic acids and resveratrol, besides inhibiting B[a]P and DMBA binding to DNA, modulate the activity of the enzymes involved in PAHs activation. The aim of the present study was further examination of the effect of these compounds on the expression and activities of CYP1A1/1A2, CYP1B1, CYP2B, and phase 2 enzymes in female BALB/C mouse epidermis treated with an initiating dose of B[a]P or DMBA. Application of a single 400 nmol dose of B[a]P alone significantly (by 119-127%) increased the activities of ethoxy- (EROD) and methoxy- (MROD) resorufin dealkylases and to lesser extent penthoxyresorufin depentylase (PROD) (by 32%). Western blot analysis with CYP1A1/1A2, CYP1B1 and CYP2B-specific antibodies showed the increase of CYP1A1/1A2 and CYP2B levels in B[a]P-treated animals. Phase 2 enzymes, gluthatione S-transferase and NAD(P)H:quinone oxidoreductase-1 (NQO1) were also significantly increased. In contrast to B[a]P, application of the initiating dose of DMBA (10 nmol) on mouse skin did not change the activities or protein levels of cytochrome P450, however increased the activities of NQO1 and GST. Pretreatment of mice with phenolic compounds one hour before B[a]P application significantly decreased the activities of all alkoxyresorufin dealkylases in comparison with the group of mice treated only with B[a]P. The sole exception was tannic acid which did not affect the PROD activity. This polyphenol, however, decreased the protein level of CYP1A1/1A2 and CYP1B1 isozymes enhanced by B[a]P. All phenolics, particularly resveratrol, significantly (by 129-174%) increased the activity of NQO1 in comparison with B[a]P-treated animals. On the other hand, pretreatment with phenolic compounds significantly diminished NQO1 activity in comparison with DMBA-treated group. These results indicate that the reduction of B[a]P-DNA adducts observed in our earlier studies may result from the decreased B[a]P activation by investigated plant phenols. In case of DMBA-DNA adducts, the scavenging or masking the binding sites to be occupied by DMBA reactive metabolites is more probable. Moreover, the lack of cytochrome P450 induction by the initiating dose of DMBA suggests that the constitutive expression of P450, particularly CYP1B1 is sufficient for DMBA activation and subsequent DNA adducts formation.