In vitro cytochrome P450 monooxygenase and prostaglandin H-synthase mediated aflatoxin B1 biotransformation in guinea pig tissues: Effects of β-naphthoflavone treatment

Abstract

In the present study, we examined the effects of treating guinea pigs with beta-naphthoflavone (BNF) on aflatoxin B1 (AFB1) metabolism by microsomal cytochrome P450 monooxygenase (P450) and prostaglandin H synthase (PHS) in liver, lung and kidney tissues. After BNF treatment, microsomal 7-ethoxyresorufin O-deethylase activity was induced 13-, 25- and 11-fold in lung, kidney and liver, respectively, confirming that the BNF treatment protocol was effective at inducing monooxygenase activity. Treatment of guinea pigs with BNF did not change [3H]AFB1-DNA binding catalyzed by microsomal PHS or P450 in lung, kidney or liver. In contrast, AFM1 formation by P450 was significantly increased in microsomes from all three organs. The data indicate that BNF-inducible P450 isozymes of the P4501A class are responsible for the biotransformation of AFB1 to non-toxic metabolites. Guinea pig kidney microsomes could also catalyze NADPH-dependent formation of aflatoxicol (AFL), a metabolite usually produced by a cytosolic steroid dehydrogenase. Renal microsomal AFL formation was not altered by prior BNF treatment. The results in the present study suggest that BNF may alter the bioactivation of AFB1 in guinea pig tissues by inducing P450 activity, leading to the formation of less reactive metabolite.

2-Aminoacetophenone Is the Main Volatile Phase I Skatole Metabolite in Pietrain × Baden-Württemberg Hybrid Type Boars

“…This sort of negative control is referred to as a boiled blank in literature papers. 38 On the other hand, CYP activity was suppressed by omission of the reducing agent NADPH. To verify whether product formation arises solely from skatole conversion or also from metabolism of other compounds, an additional third type of negative control was implemented by omitting skatole addition.…”

“…On the one hand, protein inactivation was achieved by heating mixtures of microsomal protein and buffer to 90 °C for 5 min before the actual incubation experiment. This sort of negative control is referred to as a boiled blank in literature papers . On the other hand, CYP activity was suppressed by omission of the reducing agent NADPH.…”

Aflatoxin B1 Alters the Expression of p53 in Cytochrome P450-Expressing Human Lung Cells

“…Aflatoxin B 1 (AFB 1 ) is a potent immunotoxicant and hepatocarcinogen in animals and probably in humans (Bondy and Pestka, 2000;Klein et al, 2000). The liver is the primary target organ, because AFB 1 requires metabolic activation to form the reputed carcinogenic species AFB 1 -8,9-epoxide (AFBO) (Mace et al, 1994(Mace et al, , 1997, but other organs are also affected by AFB 1 exposures (Ball and Coulombe, 1991;Ball et al, 1995;Coulombe et al, 1991;Imaoka et al, 1992;Kato et al, 1994;Kelly et al, 1997;Liu et al, 1990Liu et al, , 1993Liu and Massey, 1992). In human liver, CYPs 1A2 and 3A4 have been shown to be the principle enzymes responsible for AFB 1 activation (Ramsdell et al, 1991;Shimada and Guengerich, 1989) and have also been detected in human lung tissues and cultured lung cells (Mace et al, 1998;Van Vleet et al, 2001;Wei et al, 2001).…”