biostudies-literatureMoon SHNational Institutes of Health100611https://www.ebi.ac.uk/biostudies/studies/S-EPMC11402452biostudies-literatureUnknown65(9)Mitochondrial fatty acid oxidation serves as an essential process for cellular survival, differentiation, proliferation, and energy metabolism. Numerous studies have utilized etomoxir (ETO) for the irreversible inhibition of carnitine palmitoylcarnitine transferase 1 (CPT1), which catalyzes the rate-limiting step for mitochondrial long-chain fatty acid β-oxidation to examine the bioenergetic roles of mitochondrial fatty acid metabolism in many tissues in multiple diverse disease states. Herein, we demonstrate that intact mitochondria robustly metabolize ETO to etomoxir-carnitine (ETO-carnitine) prior to nearly complete ETO-mediated inhibition of CPT1. The novel pharmaco-metabolite, ETO-carnitine, was conclusively identified by accurate mass, fragmentation patterns, and isotopic fine structJournal of lipid researchEtomoxir-carnitine, a novel pharmaco-metabolite of etomoxir, inhibits phospholipases A<sub>2</sub> and mitochondrial respiration.PMC11402452R01HL118639R01HL133178Liu XJenkins CMDilthey BGPatti GJMoon SHGross RWfalseEtomoxir-carnitine, a novel pharmaco-metabolite of etomoxir, inhibits phospholipases A<sub>2</sub> and mitochondrial respiration.Mitochondrial fatty acid oxidation serves as an essential process for cellular survival, differentiation, proliferation, and energy metabolism. Numerous studies have utilized etomoxir (ETO) for the irreversible inhibition of carnitine palmitoylcarnitine transferase 1 (CPT1), which catalyzes the rate-limiting step for mitochondrial long-chain fatty acid β-oxidation to examine the bioenergetic roles of mitochondrial fatty acid metabolism in many tissues in multiple diverse disease states. Herein, we demonstrate that intact mitochondria robustly metabolize ETO to etomoxir-carnitine (ETO-carnitine) prior to nearly complete ETO-mediated inhibition of CPT1. The novel pharmaco-metabolite, ETO-carnitine, was conclusively identified by accurate mass, fragmentation patterns, and isotopic fine struct2024-01-01T00:00:00Z2024 Sep2025-04-21T14:49:12.424Z2025-04-21T14:49:12.424ZS-EPMC114024523909477310.1016/j.jlr.2024.100611