Flavin monooxygenase isoforms

Albendazole is variably absorbed after oral administration. A fatty meal enhances absorption. After a 400-mg oral dose, albendazole cannot be detected in plasma, because the drug is rapidly metabolized in the liver to its sulfoxide, which has potent anthelmintic activity. Both the (-t-) and (-) enantiomers of albendazole sulfoxide are formed the (-t-) enantiomer reaches much higher peak plasma concentrations and is cleared much more slowly. Albendazole sulfoxide is -70% bound to plasma proteins and has a variable plasma tj (-4-15 hours). It is well distributed into various tissues including hydatid cysts, probably explaining its greater efficacy for tissue-dwelling helminths. Formation of albendazole sulfoxide is catalyzed by both microsomal flavin monooxygenase and CYP isoforms in the liver. Albendazole metabolites are excreted mainly in the urine. 

Flavin-containing monooxygenases (FMOs) are a class of flavin monooxygenases that contain tightly boxmd FAD and require NADPH as coenzyme. These enzymes catalyze the monooxygenation of different heteroatoms, with the natural role of participating in the detoxification of drugs and xenobiotics [22,53]. Most of the FMOs are membrane associated, which makes it difficult to obtain them for further application. The human proteome contains five FMO isoforms, FMOl-5. FMOS seems to be the dominant enzyme in the himian body. 

Tam TW, Liu R, Amason IT et al (2009) Actions of ethnobotanicaUy selected Cree antidiabetic plants on human cytochrome P450 isoforms and flavin-containing monooxygenase 3. 1 Ethnopharmacol 126 119-126... 

Tertiary amines such as trimethylamine and dimethylamine had long been known to be metabolized to A -oxides by a microsomal amine oxidase that was not dependent on CYP. This enzyme, now known as the microsomal flavin-containing monooxygenase (FMO), is also dependent on NADPH and 02, and has been purified to homogeneity from a number of species. Isolation and characterization of the enzyme from liver and lung samples provided evidence of clearly distinct physicochemical properties and substrate specificities suggesting the presence of at least two different isoforms. Subsequent studies have verified the presence of multiple forms of the enzyme. 

Phase I oxidation generally is described as the addition of an oxygen atom (e.g., as an hydroxyl moiety) to the parent molecule. Phase I oxidation is carried out by multiple enzyme pathways, including the various isoforms of the cytochrome P450 (CYP) family and the non-P450 biotransformation enzymes such as flavin-containing monooxygenase (FMO) and monamine oxidase (MAO). 

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