In vitro metabolism of the new insecticide flupyrazofos by rat liver microsomes

Abstract

1. The in vitro metabolism of the new insecticide flupyrazofos was studied using rat liver microsomes. Two metabolites were produced and identified as O,O-diethyl O-(1-phenyl-3-trifluoromethyl-5-pyrazoyl) phosphoric acid ester (flupyrazofos oxon) and 1-phenyl-3-trifluoromethyl-5-hydroxypyrazole (PTMHP) based on UV and mass spectral analysis. 2. Cytochrome P450 oxidatively converted flupyrazofos to flupyrazofos oxon, a major metabolite and phenobarbital-induced microsomes increased this desulphuration by 8-fold. 3. Flupyrazofos oxon was converted to PTMHP with a half-life of 47.8 min by chemical hydrolysis and this conversion also proceeded non-enzymatically under our microsomal incubation conditions.

Metabolism of flupyrazofos in the isolated perfused rat liver

“…From HPLC analysis of outflow perfusate and bile samples, PTMHP was identified as a major metabolite of flupyrazofos in the isolated perfused rat liver. However, flupyrazofos oxon, previously identified as a major metabolite following rat liver microsomal incubation,5 was not detected in outflow perfusate or bile. On incubation of the outflow perfusate and bile samples with β‐glucuronidase or sulfatase, the amount of PTMHP increased, indicating that hepatically generated PTMHP was conjugated to form PTMHP–glucuronide and PTMHP–sulfate in the liver.…”

“…The concentrations of flupyrazofos in the inflow perfusate and of flupyrazofos, flupyrazofos oxon and PTMHP in the outflow perfusate were determined by HPLC, using a method based on that described by Lee et al 5 Perfusate (1 ml) and bile samples (50 µl) were adjusted to pH 3.0 with phosphoric acid, extracted with methylene chloride (2 ml) and centrifuged. The organic phase was evaporated to dryness under nitrogen gas, and the residue was dissolved in mobile phase (100 µl).…”

“…Flupyrazofos [KH‐502; O,O ‐diethyl O ‐(1‐phenyl‐3‐trifluoromethylpyrazol‐5‐yl) phosphorothioate] is a new insecticide developed by Korea Research Institute of Chemical Technology (KRICT, Taejeon, Korea) in 1987 and is particularly effective against the diamond‐back moth Plutella xylostella (L), acting as an acetylcholinesterase inhibitor. The safety of flupyrazofos in animals and the environment has been assessed using both in vitro and in vivo systems 1–6…”

“…In vitro metabolism study using rat liver microsomes found flupyrazofos to be a good substrate for oxidative metabolism by cytochrome P450, and flupyrazofos oxon and 1‐phenyl‐3‐trifluoromethyl‐5‐hydroxypyrazole (PTMHP) were identified as major metabolites (see Fig 1). 5 After intravenous injection of flupyrazofos to rats, flupyrazofos and PTMHP were determined in the plasma samples 6. Although these studies identified PTMHP as a metabolite of flupyrazofos, the subsequent metabolism and biliary excretion of flupyrazofos and hepatically formed PTMHP are not known.…”

In vitro metabolism of a new H+/K+ ATPase inhibitor DBM‐819 in liver microsomes using HPLC and electrospray mass spectrometry

“…injection of BNF (40 mg/kg) in corn oil for 4 days, daily oral administration of ethanol (5 ml/kg) in saline for 3 days, or daily oral dosing of DEX (300 mg/kg) in corn oil for 3 days. Liver microsomes (control, PB, BNF, ethanol and DEX microsomes) were prepared from untreated, PB-, BNF-, ethanol-or DEX-treated rats, respectively, after a 24 h fasting period as previously described (Lee et al, 1997). Microsomal protein content was determined according to the method of Bradford (1976) …”