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The effect of (N-hydroxymethyl)-2-propylpentamide (HPP), a novel valproic acid(VPA) derivatives possessing anticonvulsant activity, on rat hepatic cytochrome P450 was studied in ex vivo and in vitro system. In ex vivo study, HPP at doses of 100 and 200 mg/kg/day or VPA at 250 mg/kg/day were given intraperitoneally to male Wistar rats once daily for 7 days. On the day after, rat liver microsomes were prepared and determined for total CYP contents as well as CYP activities (ethoxyresorufin O-dealkylation for CYP1A1, methoxyresorufin O-dealkylation for CYP1A2, benzyloxy- & pentoxyresorufin O-dealkylation for CYP2B1/2B2 and aniline 4-hydroxylation for CYP2E1). In in vitro study, inhibitory effects of HPP at final concentrations of 0.1, 1, 10, 100 and 1000 μM on β-napthoflavone-induced CYP1A1/1A2, phenobarbital-induced CYP2B1/2B2 and ethanol-induced CYP2E1 activities were studied. The results showed that VPA at the dose studied did not have any effect on total CYP contents and all CYP activities. However, HPP at 100 and 200 mg/kg/day significantly induced CYP1A1 and CYP2B1/2B2 activities. In addition, HPP at 100 and 1000 μM significantly inhibited CYP2B1/2B2 activities in vitro with IC50 of about 752 μM. These results suggested that the inhibitory effect of HPP on CYP2B1/2B2 activities may be, in part, responsible for the prolongation of barbiturate sleeping time after single dose administration of HPP. The induction effect of HPP, but not VPA, on CYP1A1 and CYP2B1/2B2 activities after being administered for 7 days may be resulted from the direct effect of HPP or its metabolites. Further studies are needed to clarify the metabolic pathways of HPP and the CYPs involved as well as the effect of HPP on human CYPs. In vivo studies to verify the potential of drug interaction and carcinogenic risk are also needed.
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