Effects of pretreatment of Hep G2 Cells with β-naphthoflavone on cytotoxicity of propranolol and its active metabolite 4-hydroxypropranolol

Cytotoxicities of propranolol (PL) and its active metabolite, 4-hydroxypropranolol (4-OH-PL), were examined in a human hepatoma cell line, Hep G2. Hep G2 cells were cultured in the presence of β-naphthoflavone (BNF, 25 or 50 μM), lansoprazole (LPZ, 25 or 50 μM) or 0.5% dimethylsulfoxide (vehicle) for 48 hr. The cells were harvested, and microsomal and cytosolic fractions were prepared by differential centrifugation methods. Various enzyme activities were determined as follows: microsomal 7-ethoxyresorufin (ER) O-deethylation as a CYP1A1 index, microsomal phenacetin (PN) O-deethylation as a CYP1A2 index, microsomal and cytosolic p-nitrophenyl acetate (NPA) hydrolysis as a carboxylesterase index and cytosolic 4-OH-PL sulfation as a sulfotransferase index. The pretreatment of Hep G2 cells with LPZ or BNF increased microsomal ER O-deethylase activities, and the potency of BNF was much higher than that of LPZ. Cytosolic 4-OH-PL sulfation was also elevated by the pretreatment with BNF but not with LPZ. Microsomal PN O-deethylase activity was not detectable in either the control or BNF-pretreated group under the conditions used. Microsomal and cytosolic NPA hydrolase activities were similar between the control and the BNF-pretreated groups. Cytotoxicities of PL and 4-OH-PL were attenuated in BNF-pretreated Hep G2 cells compared to non-pretreated Hep G2 cells. These results suggest that increased activities of microsomal CYP1A1 and cytosolic sulfotransferases by pretreatment with BNF may contribute to the attenuating the cytotoxicity of PL and 4-OH-PL in Hep G2 cells, at least in part.