Disposition of a low dose of 14C-bisphenol A in male rats and its main biliary excretion as BPA glucuronide

Bisphenol A (BPA) is a weak xenoestrogen mass-produced with potential human exposure. The disposition of bisphenol A in male Fischer-344 (F344) rats dosed orally (100 or 0.10 mg/kg) or intravenously (0.10 mg/kg) was determined. Smaller amounts of the dose appeared in the urine. The main excretion route was feces in rats irrespective of dose and administration route. The biliary excretion during 6 h was 58-66% after iv dosing and 45-50% after oral dosing at 0.10 mg C-14-BPA/kg. Toxicokinetic parameters obtained from C-14-BPA-derived radioactivity in blood were the terminal elimination half-life, t(1/2beta) = 39.5 h, and total body clearance, CLtot = 0.52 l/h/kg after iv dosing of 0.10 mg C-14-BPA/kg to male rats. The blood concentration reached its maximum of 5.5 ng-eq/ml at 0.38 h after oral dose. AUC((0-6 h)), AUC((0-48 h)), and AUC(inf) of C-14-BPA-derived radioactivity, were 34, 118, and 192 ng-eqh/ml for the iv dose and 18, 102, and 185 ng-eqh/ml for the oral dose, respectively. The oral bioavailability of F(0-6 h), F(0-48 h), and F-inf were 0.54, 0.86, and 0.97, respectively. The C-14-BPA-derived radioactivity was strongly bound to plasma protein (free fraction, fu = 0.046) and preferentially distributed to the plasma with a blood/plasma ratio of 0.67. From the bile of male rats orally dosed at 100 mg/kg, we have isolated and characterized BPA glucuronide (BPA-gluc) by ESI/MS, H-1 and C-13 NMR spectroscopy. HPLC analysis showed that BPA-gluc was the predominant metabolite in bile and urine. Unchanged BPA was mostly detected in feces. These results suggest that BPA is mainly metabolized to BPA-gluc and excreted into feces through the bile and subject to enterohepatic circulation in rats irrespective of dose and administration route.