Human lung is a major target organ for all inhaled drugs, environmental toxicants and carcinogens. Recent hypotheses suggesting a role for environmental toxicants in the pathogenesis of lung diseases, such as lung cancer and chronic obstructive pulmonary disease have stimulated interest in research on the xenobiotic metabolizing capability of the lung. Many of the compounds associated with these diseases require enzymatic activation to exert their deleterious effects on pulmonary cells. Interindividual differences in in situ activation and inactivation of xenobiotics may contribute to the risk of developing of lung diseases associated with these compounds. The major xenobiotic metabolizing enzymes, including both phase I and phase II enzymes, have been detected in animal and human lung tissues. Although the lung cytochrome P450 (CYP) and other xenobiotic metabolizing enzymes share many common features with those present in other tissues such as liver, kidney and gut, there are some distinctive differences. It is evident from the studies carried out to date CYP1A1, 1B1, 2A13, 2F1, 2S1 and 4B1 are preferentially expressed in the lung together with CYP2E1 and 3A5. This review provides a detailed picture of major xenobiotic-metabolizing phase I (CYPs, epoxide hydrolases, flavin monooxygenases, etc.) and phase II enzymes (conjugation enzymes, including several transferases) expressed in human lung. The roles of individual metabolizing enzymes and their genetic polymorphisms are also discussed.

ABSTRACT:Valdecoxib is a potent and specific inhibitor of cyclooxygenase-2, which is used for the treatment of rheumatoid arthritis, osteoarthritis, and the dysmenorrhea pain. Eight male human subjects each received a single 50-mg oral dose of [

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This article is available online at http://dmd.aspetjournals.org ABSTRACT:The pharmacokinetics and metabolism of valdecoxib, a potent cyclooxygenase-2 selective inhibitor, were investigated in mice. Valdecoxib, 4-(5-methyl-3-phenylisoxazol-4-yl)benzenesulfonamide, is a new anti-inflammatory drug that is highly selective for inhibition of the inducible form of cyclooxygenase (COX-2 1 ) in in vitro enzymatic assays (Talley et al., 2000). This drug (BEXTRA, Pharmacia Corporation) was approved recently by the U.S. Food and Drug Administration for the treatment of rheumatoid arthritis, osteoarthritis, and primary dysmenrrhea (Camu et al., 2002;Fricke et al., 2002). Valdecoxib is the second generation COX-2 inhibitor developed by Pharmacia after celecoxib, the first approved COX-2 inhibitor. These new types of anti-inflammatory drugs are developed based on the hypothesis that selective inhibition of COX-2 should decrease inflammation without the adverse gastrointestinal effects associated with inhibition of the constitutive cyclooxygenase (COX-1) (Donnelly and Hawkey, 1997;Pennisi, 1998;Vane et al., 1998). Clinical studies have demonstrated that COX-2 inhibitors lead to a significant reduction in joint pain, joint tenderness/pain, and joint swelling with a statistically-significantly lower incidence of gastric ulceration Simon et al., 1998). Additionally, recent studies demonstrated that COX-2 inhibitors appear to provide some relief for preventing colon cancer and Alzheimer's disease (Elder and Paraskeva, 1998;Hecker, 1998;Pennisi, 1998;Ziegler, 1998).We have recently reported the absorption, distribution, metabolism, and excretion of valdecoxib in humans (Yuan et al., 2002). The primary oxidative metabolic pathways of valdecoxib in humans involved in hydroxylation at either the methyl group to form a hydroxymethyl metabolite or N-hydroxylation at the sulfonamide moiety to form an N-hydroxy metabolite. Further oxidation of the hydroxymethyl metabolite led to the formation of several other phase I metabolites. Oxidative breakdown of the N-hydroxy sulfonamide functional group in the N-hydroxy metabolite led to the formation of corresponding sulfinic acid and sulfonic acid metabolites. The Oglucuronidation of the hydroxymethyl metabolite and N-glucuronidation of valdecoxib were the major metabolites in human urine. The objectives of this study were to determine the total radioactivity recovery in male and female mice following a single oral administration of [ 14 C]valdecoxib at 5 mg/kg, to obtain metabolic profiles in selected mouse plasma RBC, urine, and fecal samples, to identify the major metabolites of valdecoxib, to estimate plasma and RBC pharmacokinetic parameters for total radioactivity, and to examine gender difference in pharmacokinetics of valdecoxib and major metabolites. Materials and Methods Chemicals. Valdecoxib and [14 C]valdecoxib (uniformly labeled at the six carbons of 3-phenyl ring) were synthesized at Pharmacia Corporation (Skokie, IL). The specific activity of [ 14 C]valdecoxib was approximately 5...