Cytochrome P450 2C8 and Flavin-containing Monooxygenases are Involved in the Metabolism of Tazarotenic Acid in Humans

Abstract

This article is available online at http://dmd.aspetjournals.org ABSTRACT:Upon oral administration, tazarotene is rapidly converted to tazarotenic acid by esterases. The main circulating agent, tazarotenic acid is subsequently oxidized to the inactive sulfoxide metabolite. Therefore, alterations in the metabolic clearance of tazarotenic acid may have significant effects on its systemic exposure. The objective of this study was to identify the human liver microsomal enzymes responsible for the in vitro metabolism of tazarotenic acid. Tazarotenic acid was incubated with 1 mg/ml pooled human liver microsomes, in 100 mM potassium phosphate buffer (pH 7.4), at 37°C, over a period of 30 min. The microsomal enzymes that may be involved in tazarotenic acid metabolism were identified through incubation with microsomes containing cDNA-expressed human microsomal isozymes. Chemical inhibition studies were then conducted to confirm the identity of the enzymes potentially involved in tazarotenic acid metabolism. Reversed-phase high performance liquid chromatography was used to quantify the sulfoxide metabolite, the major metabolite of tazarotenic acid. Upon incubation of tazarotenic acid with microsomes expressing CYP2C8, flavin-containing monooxygenase 1 (FMO1), or FMO3, marked formation of the sulfoxide metabolite was observed. The involvement of these isozymes in tazarotenic acid metabolism was further confirmed by inhibition of metabolite formation in pooled human liver microsomes by specific inhibitors of CYP2C8 or FMO. In conclusion, the in vitro metabolism of tazarotenic acid to its sulfoxide metabolite in human liver microsomes is mediated by CYP2C8 and FMO.

Mammalian flavin-containing monooxygenases: structure/function, genetic polymorphisms and role in drug metabolism

“…Compounds containing a single positive charge (e.g., tertiary amines) are excellent substrates. Many compounds containing a negative charge are excluded entirely or are poor substrates with exceptions such as sulindac sulfide and lipoic acid (Taylor & Ziegler, 1987;Hvattum et al, 1991;Attar et al, 2003). Zwitterions and compounds with more than 1 positive charge are typically not substrates, although some, like methionine, can be oxygenated, but the apparent K m is above physiological levels (Park et al, 1992(Park et al, , 1994Duescher et al, 1994;Elfarra, 1995;Krause et al, 1996, Ripp et al, 1997, 1999.…”

“…Unfortunately, antibodies directed toward FMOs typically inhibit catalytic activity weakly, if at all, and the only chemical inhibitors are competitive substrates. The most commonly used alternative substrate to inhibit FMO in vitro (Mani et al, 1993;Narimatsu et al, 1999;Rawden et al, 2000;Pike et al, 2001;Attar et al, 2003;Wynalda et al, 2003;Virkel et al, 2004) and in vivo (Ruse & Waring, 1991;Nace et al, 1997;Wang et al, 2000) has been methimazole (see next section for further discussion of methimazole). FMO activity is unaffected by non-ionic detergent or carbon monoxide, but most FMOs are readily inhibited by short incubations at temperatures of 45-50 °C.…”

Role of Cytochrome P450 2C8 in Drug Metabolism and Interactions

“…For instance, CYP2C8 catalyzes dealkylation of both enantiomers of the calcium channel blocker verapamil and its metabolite norverapamil (Busse et al, 1995;Tracy et al, 1999). Tazarotenic acid, the active moiety of the antipsoriatic agent tazarotene, is mainly metabolized by CYP2C8 and flavin-containing monooxygenases in vitro (Attar et al, 2003). When tazarotenic acid was incubated with 10 individual recombinant CYP enzymes, only CYP2C8 markedly catalyzed sulfoxidation, which is the main metabolic pathway of tazarotenic acid.…”

Identification of Tazarotenic Acid as the First Xenobiotic Substrate of Human Retinoic Acid Hydroxylase CYP26A1 and CYP26B1

“…To assess the relative contribution of CYP26A1 and CYP26B1 to the in vitro oxidative metabolism of tazarotenic acid, metabolite formation was monitored across a panel of drug-metabolizing enzymes. Previously reported studies that characterized the enzymes responsible for the metabolism of tazarotenic acid were conducted at substrate concentrations of 1-200 mM (Attar et al, 2003). As total circulating plasma concentrations of tazarotenic acid are approximately 1-280 nM following typical doses of tazarotene, current studies were conducted using clinically relevant substrate concentrations.…”

“…Tazarotene is a prodrug whose activity is attributed to an active metabolite, tazarotenic acid, which binds with high affinity to retinoic acid receptors (Chandraratna, 1996). The active metabolite shares key structural features with at-RA and has been reported to be metabolized by a number of drugmetabolizing enzymes, including CYP2C8, CYP3A4, FMO1, and FMO3 (Madhu et al, 1997;Tang-Liu et al, 1999;Attar et al, 2003Attar et al, , 2005. Whether tazarotenic acid is a substrate of CYP26A1 and CYP26B1 is currently unknown.…”