Effects of 17,18-Epoxyeicosatetraenoic Acid and 19,20-Epoxydocosapentaenoic Acid Combined with Soluble Epoxide Hydrolase Inhibitor t-TUCB on Brown Adipogenesis and Mitochondrial Respiration

<b>Background/Objectives</b>: 17,18-epoxyeicosatetraenoic acid (17,18-EEQ) and 19,20-epoxydocosapentaenoic acid (19,20-EDP) are bioactive metabolites produced from eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), respectively, by CYP450s. These metabolites are unstable and quickly metabolized by auto-oxidation, esterification, β-oxidation, or hydrolysis by soluble epoxide hydrolase (sEH). 17,18-EEQ or 19,20-EDP combined with a potent sEH inhibitor <i>t</i>-TUCB differentially activated brown adipose tissue in diet-induced obesity. In the current study, we investigated whether these <i>n</i>-3 epoxy fatty acids with <i>t</i>-TUCB directly promote brown adipocyte differentiation and their thermogenic capacities. <b>Methods</b>: Murine brown preadipocytes were treated with 17,18-EEQ or 19,20-EDP with <i>t</i>-TUCB during and post differentiation. Brown marker protein expression and mitochondrial respiration were measured. In addition, the activation of PPARγ and suppression of NFκB reporter by 17,18-EEQ or 19,20-EDP alone or with <i>t</i>-TUCB were assessed, and the roles of PPARγ were evaluated with PPARγ knockdown and GW9662. <b>Results</b>: 17,18-EEQ or 19,20-EDP with <i>t</i>-TUCB promoted brown adipogenesis and mitochondrial respiration and uncoupling. Moreover, with <i>t</i>-TUCB, both epoxides improved mitochondrial respiration, but only 17,18-EEQ with <i>t</i>-TUCB significantly increased mitochondrial uncoupling (and heat production) in the differentiated adipocytes. PPARγ may be required for the effects of epoxides on differentiation but not on the thermogenic function post differentiation. <b>Conclusions</b>: The results demonstrate that, with <i>t</i>-TUCB, 17,18-EEQ and 19,20-EDP promote brown adipogenesis and mitochondrial respiration and uncoupling. 17,18-EEQ also promotes thermogenesis in differentiated brown adipocytes. Together, the results suggest thermogenic potentials of tested <i>n</i>-3 epoxides, especially 17,18-EEQ with <i>t</i>-TUCB. Translational studies of these <i>n</i>-3 epoxides on human brown adipocyte differentiation and functions are warranted.