Differential Effects of Combined Soluble Epoxide Hydrolase inhibitor t ‐TUCB and n‐3 Epoxide in Diet‐Induced Obesity

Abstract

Brown adipose tissue (BAT) is a promising target for obesity treatment and prevention by increasing energy expenditure through nonshivering thermogenesis. N-3 epoxides, such as epoxyeicosatetraenoic acids (EEQs) and epoxydocosapentaenoic acids (EDPs), are produced by cytochrome P-450 epoxygenases from n-3 polyunsaturated fatty acids, which have shown many beneficial effects in vascular dilation, inflammation, and cell growth/differentiation. However, the epoxides are unstable and quickly metabolized to less active diols by soluble epoxide hydrolase (sEH), a cytosolic enzyme encoded by the Ephx2 gene. We have previously demonstrated that t-TUCB, a potent sEH inhibitor, decreased serum triglycerides (TG) level by increasing protein expression of lipid metabolic genes in the BAT of diet-induced obese mice. This study aims to investigate the preventive effects of t-TUCB alone or combined with 19,20-EDP or 17,18-EEQ on BAT activation in the development of diet-induced obesity and associated metabolic disorders. 8-week old male C57BL6/J mice were fed a high-fat diet (45% kcal from fat) and received either of the following treatment: the vehicle control, t-TUCB alone (T) (3 mg/kg/day), or t-TUCB combined with 19,20-EDP (0.05 mg/kg/day) (T+EDP) or 17,18-EEQ (0.05 mg/kg/day) (T+EEQ) (n=5-6 per group) via osmotic minipump delivery at the subcutaneous area near the interscapular BAT for 6 weeks. Mice were examined for changes in bodyweight, food intake, glucose and insulin tolerance tests, cold tolerance tests, and indirect calorimetry before the mice were euthanized for further biochemical analysis. Although there were no differences in food intake among groups, there were small but significant increases in bodyweight in both T and T+EDP groups. While there were no differences in insulin tolerance tests among groups, the T+EEQ group showed a trend of improvement in glucose tolerance tests, and both T+EEQ and T+EDP groups showed significant improvement in fasting glucose compared to the controls (208.8 ± 36.43 mg/dl vs. 214 ± 10.81 mg/dL vs. 262.8 ± 8.9 mg/dL). The core body temperature was not changed by t-TUCB (37.34 ± 0.08 °C), but were significantly increased in the T+EDP (37.85±0.06 °C) and T+EEQ (38.1± 0.09 °C) groups compared to the controls (37.30±0.14°C). Consistently, both T+EDP and T+EEQ groups showed significantly better cold tolerance in the cold tolerance tests. Furthermore, heat production measured by indirect calorimetry was significantly increased in the T+EEQ group but not in the T and T+EDP groups compared to the controls. In addition, there were no differences in serum total cholesterol and non-esterified free fatty acids levels among all groups, but serum TG levels were significantly decreased in the T+EDP (45.75± 2.23 mg/dL) and T+EEQ (38.32± 6.67 mg/dL) groups compared to the controls (69.73± 7.2 mg/dL). Our results suggest that sEH pharmacological inhibition by t-TUCB combined with n-3 epoxide may prevent high-fat diet-induced glucose and lipid disorders, in part through increased thermogenesis.