BackgroundObesity is a major risk factor for insulin resistance, type 2 diabetes, and stroke. Flavonoids are effective antioxidants that protect against these chronic diseases. In this study, we evaluated the effects of sudachitin, a polymethoxylated flavonoid found in the skin of the Citrus sudachi fruit, on glucose, lipid, and energy metabolism in mice with high-fat diet-induced obesity and db/db diabetic mice. In our current study, we show that sudachitin improves metabolism and stimulates mitochondrial biogenesis, thereby increasing energy expenditure and reducing weight gain.MethodsC57BL/6 J mice fed a high-fat diet (40% fat) and db/db mice fed a normal diet were treated orally with 5 mg/kg sudachitin or vehicle for 12 weeks. Following treatment, oxygen expenditure was assessed using indirect calorimetry, while glucose tolerance, insulin sensitivity, and indices of dyslipidemia were assessed by serum biochemistry. Quantitative polymerase chain reaction was used to determine the effect of sudachitin on the transcription of key metabolism-regulating genes in the skeletal muscle, liver, and white and brown adipose tissues. Primary myocytes were also prepared to examine the signaling mechanisms targeted by sudachitin in vitro.ResultsSudachitin improved dyslipidemia, as evidenced by reduction in triglyceride and free fatty acid levels, and improved glucose tolerance and insulin resistance. It also enhanced energy expenditure and fatty acid β-oxidation by increasing mitochondrial biogenesis and function. The in vitro assay results suggest that sudachitin increased Sirt1 and PGC-1α expression in the skeletal muscle.ConclusionsSudachitin may improve dyslipidemia and metabolic syndrome by improving energy metabolism. Furthermore, it also induces mitochondrial biogenesis to protect against metabolic disorders.

BackgroundPacific saury is a common dietary component in East Asia. Saury oil contains considerable levels of n-3 unsaturated fatty acids (PUFA) and long-chain monounsaturated fatty acids (LCMUFA) with aliphatic tails longer than 18 carbons. In our previous study, consumption of saury oil for 4 to 6 wk improved insulin sensitivity and the plasma lipid profile in mice. However, the long-term effects of saury oil on metabolic syndrome (MetS) risk factors remain to be demonstrated. In the current study, we examined the long-term effects of saury oil on mice fed a high-fat diet, and compared the effect of n-3 PUFA EPA and LCMUFA on MetS risk factor in diet-induced obese mice.Methods and ResultsIn Experiment 1, male C57BL/6 J mice were fed either a 32 % lard diet (control) or a diet containing 22 % lard plus 10 % saury oil (saury oil group) for 18 weeks. Although no differences were found in body weight and energy expenditure between the control and saury oil groups, the saury oil diet decreased plasma insulin, non–HDL cholesterol, hepatic steatosis, and adipocyte size, and altered levels of mRNA transcribed from genes involved in insulin signaling and inflammation in adipose tissue. Organ and plasma fatty acid profile analysis revealed that consumption of saury oil increased n-3 PUFA and LCMUFA (especially n-11 LCMUFA) levels in multiple organs, and decreased the fatty acid desaturation index (C16:1/C16:0; C18:1/C18:0) in liver and adipose tissue. In Experiment 2, male C57BL/6 J mice were fed a 32 % lard diet (control), a diet containing 28 % lard plus 4 % EPA (EPA group), or a diet containing 20 % lard plus 12 % LCMUFA concentrate (LCMUFA group) for 8 weeks. EPA or LCMUFA intake increased organ levels of EPA and LCMUFA, respectively. Consumption of EPA reduced plasma lipid levels and hepatic lipid deposition, and decreased the fatty acid desaturation index in liver and adipose tissue. Consumption of LCMUFA decreased plasma non–HDL cholesterol, improved hyperinsulinemia, and decreased the fatty acid desaturation index in adipose tissue. EPA accumulated mainly in liver, and LCMUFA (especially n-11 LCMUFA) accumulated mainly in white adipose tissue, suggesting their possible individual biological effects for improving MetS.ConclusionOur results suggest that saury oil-mediated improvement of metabolic syndrome in diet-induced obese mice may possibly be due to a combined effect of n-3 PUFA and LCMUFA.Electronic supplementary materialThe online version of this article (doi:10.1186/s12944-015-0161-8) contains supplementary material, which is available to authorized users.

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