Flavin-containing monooxygenases (FMO) oxygenate numerous drugs and other xenobiotics. Caucasians and Asians do not express functional pulmonary FMO2 but up to 50% of African individuals and 3-10% of Hispanics express at least one allele coding for catalytically active enzyme (FMO2.1). Mycobacterium tuberculosis, the causative agent in tuberculosis (TB), possesses a similar flavin monooxygenase (EtaA) that catalyzes S-oxygenation of second-line anti-tuberculosis drugs to the metabolite toxic to the bacteria. Ethionamide (ETA) is one of a class of drugs increasingly used due to development of resistance to first-line therapeutic regimens. FMO2.1 is more efficient in the firstS-oxygenation of ETA to the sulfenic acid than EtaA, but bacterial enzyme is more efficient in the second S-oxygenation to the sulfinic acid having bactericidal activity. The sulfenic acid is capable of redox-cycling with glutathione producing oxidative/nitrative stress and toxicity. There is a fundamental knowledge gap in understanding the role of human FMO2 in ETA action. The highest incidence of individuals with active FMO2.1 and the highest incidence of TB co-occur in Sub-Saharan Africa where resistance to front-line TB drugs is of great importance. Our central hypothesis is that individuals having active FMO2.1 will have reduced ETA efficacy in inhibition and killing of M. tuberculosis and enhanced oxidative/nitrative stress and pulmonary toxicity, issues not previously considered. Understanding the effect of genotype on ETA metabolism and thus on M. tuberculosis will enable improved drug selection and utilization. The central hypothesis will be tested by three integrated specific aims employing innovative tools under the guidance of a powerful investigative team: 1) Test, in vitro, the efficacy of FMO and EtaA in metabolism of ETA, bacterial killing and lung cell damage employing bacterial cell culture and transfected human lung cells;2) Employ a newly developed Fmo1/2/4 triple knockout mouse to assess in vivo the contribution of FMO and EtaA in ETA metabolism, therapeutic efficacy and lung toxicity;and 3) Construct and utilize a transgenic humanized FMO2.1 mouse to better model human response. The approach is innovative: it creates a highly unique environment capitalizing on FMO and TB expertise and facilities, uses the first Fmo knockout mouse available and extends and enhances the model by creation of the first humanized FMO mouse;for the first time absolute quantification by mass spectrometry is used to quantify individual FMOs. The proposed research is significant with the potential for high impact: it will lead to better matching of individuals with appropriate drug therapy. Relevance to Public Health: The WHO has termed TB a global health emergency. Two billion people (1/3 the world's population) are infected with M. tuberculosis;in the next 12 years another billion will be infected and 30 million will die. The outcome of the studies and work facilitated by this grant is expected to provide guidance for physicians seeking to identify and administer the drug most likely to maximize individual drug response and minimize TB drug toxicity.

Public Health Relevance

One-third of the world's population is infected by the bacterium causing tuberculosis (TB) with over 9 million infected and 2 million deaths every year. This project investigates metabolism of an anti-TB drug by a lung enzyme found in many people from Sub-Saharan Africa, a region that has one of the highest incidence rates of TB in the world. The knowledge gained will improve treatment approaches in combating TB.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Special Emphasis Panel (ZRG1-DKUS-E (03))
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Peavy, Hannah H
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Oregon State University
Public Health & Prev Medicine
Schools of Earth Sciences/Natur
United States
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Siddens, Lisbeth K; Krueger, Sharon K; Henderson, Marilyn C et al. (2014) Mammalian flavin-containing monooxygenase (FMO) as a source of hydrogen peroxide. Biochem Pharmacol 89:141-7
Henderson, Marilyn C; Siddens, Lisbeth K; Krueger, Sharon K et al. (2014) Flavin-containing monooxygenase S-oxygenation of a series of thioureas and thiones. Toxicol Appl Pharmacol 278:91-9
Palmer, Amy L; Leykam, Virginia L; Larkin, Andrew et al. (2012) Metabolism and Pharmacokinetics of the Anti-Tuberculosis Drug Ethionamide in a Flavin-Containing Monooxygenase Null Mouse. Pharmaceuticals (Basel) 5:1147-1159
Celius, Trine; Pansoy, Andrea; Matthews, Jason et al. (2010) Flavin-containing monooxygenase-3: induction by 3-methylcholanthrene and complex regulation by xenobiotic chemicals in hepatoma cells and mouse liver. Toxicol Appl Pharmacol 247:60-9
Krueger, Sharon K; Henderson, Marilyn C; Siddens, Lisbeth K et al. (2009) Characterization of sulfoxygenation and structural implications of human flavin-containing monooxygenase isoform 2 (FMO2.1) variants S195L and N413K. Drug Metab Dispos 37:1785-91
Siddens, Lisbeth K; Henderson, Marilyn C; Vandyke, Jonathan E et al. (2008) Characterization of mouse flavin-containing monooxygenase transcript levels in lung and liver, and activity of expressed isoforms. Biochem Pharmacol 75:570-9
Henderson, Marilyn C; Siddens, Lisbeth K; Morre, Jeffrey T et al. (2008) Metabolism of the anti-tuberculosis drug ethionamide by mouse and human FMO1, FMO2 and FMO3 and mouse and human lung microsomes. Toxicol Appl Pharmacol 233:420-7
Krueger, Sharon K; Siddens, Lisbeth K; Henderson, Marilyn C et al. (2005) Haplotype and functional analysis of four flavin-containing monooxygenase isoform 2 (FMO2) polymorphisms in Hispanics. Pharmacogenet Genomics 15:245-56
Krueger, Sharon K; Williams, David E (2005) Mammalian flavin-containing monooxygenases: structure/function, genetic polymorphisms and role in drug metabolism. Pharmacol Ther 106:357-87