PT  - JOURNAL ARTICLE
AU  - Bjarte Furnes
AU  - Daniel Schlenk
TI  - EXTRAHEPATIC METABOLISM OF CARBAMATE AND ORGANOPHOSPHATE THIOETHER COMPOUNDS BY THE FLAVIN-CONTAINING MONOOXYGENASE AND CYTOCHROME P450 SYSTEMS
AID  - 10.1124/dmd.104.000984
DP  - 2005 Feb 01
TA  - Drug Metabolism and Disposition
PG  - 214--218
VI  - 33
IP  - 2
4099  - http://dmd.aspetjournals.org/content/33/2/214.short
4100  - http://dmd.aspetjournals.org/content/33/2/214.full
SO  - Drug Metab Dispos2005 Feb 01; 33
AB  - The cytochrome P450 (P450) and flavin-containing monooxygenase (FMO) enzymes are the major oxidative enzymes in phase I metabolism. Many organophosphate and carbamate thioether compounds are excellent substrates for these enzymes. Stereoselective sulfoxidation of fenthion and methiocarb by human liver, kidney, and microsomes was investigated. A high level of stereoselectivity in the formation of fenthion (+)-sulfoxide was observed in kidney and intestinal microsomes. This activity was not inhibited by the P450 inhibitor 1-aminobenzotriazole but was dramatically reduced following mild heat treatment. In liver, fenthion was metabolized to its sulfoxide in a nonstereoselective manner, and the activity was sensitive to both 1-aminobenzotriazole and heat treatment. The carbamate pesticide methiocarb also was sulfoxidated with a high degree of stereoselectivity in human kidney microsomes. Human liver microsomes formed both stereoisomers in equal amounts. Sulfoxide formation in kidney was not inhibited by 1-aminobenzotriazole but was abolished in liver microsomes. Formation of methiocarb sulfoxides was not observed in intestinal microsomes. The relative contribution of FMO1 and FMO3 to the sulfoxidation of carbophenothion, demeton-O, ethiofencarb, fonofos, and methiocarb also was investigated by using baculovirus-expressed recombinant proteins. FMO1 showed the highest catalytic activity for all pesticides. This study indicates that FMO1 may have a bigger role in extrahepatic metabolism than previously thought. The American Society for Pharmacology and Experimental Therapeutics