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Background: Dietary polyphenols including anthocyanins target multiple organs.Objective: We aimed to assess the involvement of glucagon-like peptide 1 (GLP-1), leptin, insulin and fibroblast growth factor 21 (FGF21) in mediating metabolic beneficial effects of purified anthocyanin cyanidin-3-glucoside (Cy3G).Methods: Intestinal proglucagon gene (Gcg; encoding GLP-1) and liver Fgf21 expression were assessed in 6-wk-old male C57BL-6J mice fed a low-fat-diet (LFD; 10% of energy from fat), alone or with 1.6 mg Cy3G/L in drinking water for 3 wk [experiment (Exp.) 1; n = 5/group]. Similar mice were fed the LFD or a high-fat diet (HFD; 60% energy from fat) with or without Cy3G for 20 wk. Half of the mice administered Cy3G also received 4 broad-spectrum antibiotics (ABs) in drinking water between weeks 11 and 14, for a total of 6 groups (n = 8/group). Metabolic tolerance tests were conducted between weeks 2 and 16. Relevant hormone gene expression and plasma hormone concentrations were assessed mainly at the end of 20 wk (Exp. 2).Results: In Exp. 1, Cy3G administration increased ileal but not colonic Gcg level by 2-fold (P < 0.05). In Exp. 2, Cy3G attenuated HFD-induced body-weight gain (20.3% at week 16), and improved glucose tolerance (26.5% at week 15) but not insulin tolerance. Although Cy3G had no effect on glucose tolerance in LFD mice, LFD/Cy3G/AB mice showed better glucose tolerance than LFD/Cy3G mice (23%). In contrast, HFD/Cy3G/AB mice showed worse glucose tolerance compared with HFD/Cy3G mice (15%). Beneficial effects of Cy3G in HFD mice were not associated with changes in plasma leptin, insulin or GLP-1 concentrations. However, Cy3G increased hepatic Fgf21 expression in mice in Exp. 1 by 4-fold and attenuated Fgf21 overexpression in HFD mice (Exp. 2, 22%), associated with increased expression of genes that encode FGFR1 and β-klotho (>3-fold, P < 0.05).Conclusions: Dietary Cy3G may reduce body weight and exert metabolic homeostatic effects in mice via changes in hepatic FGF21. [ABSTRACT FROM AUTHOR]

Background: Long-term dietary curcumin (>12 wk) improves metabolic homeostasis in obese mice by sensitizing insulin signaling and reducing hepatic gluconeogenesis. Whether these occur only secondary to its chronic anti-inflammatory and antioxidative functions is unknown.Objective: In this study, we assessed the insulin sensitization effect of short-term curcumin gavage in a rapid dexamethasone-induced insulin resistance mouse model, in which the chronic anti-inflammatory function is eliminated.Methods: Six-week-old male C57BL/6 mice received an intraperitoneal injection of dexamethasone (100 mg/kg body weight) or phosphate-buffered saline every day for 5 d, with or without simultaneous curcumin gavage (500 mg/kg body weight). On day 7, insulin tolerance tests were performed. After a booster dexamethasone injection and curcumin gavage on day 8, blood glucose and insulin concentrations were measured. Liver tissues were collected on day 10 for quantitative polymerase chain reaction and Western blotting to assess gluconeogenic gene expression, insulin signaling, and the expression of fibroblast growth factor 21 (FGF21). Primary hepatocytes from separate, untreated C57BL/6 mice were used for testing the in vitro effect of curcumin treatment.Results: Dexamethasone injection impaired insulin tolerance (P < 0.05) and elevated ambient plasma insulin concentrations by ~2.7-fold (P < 0.01). Concomitant curcumin administration improved insulin sensitivity and reduced hepatic gluconeogenic gene expression. The insulin sensitization effect of curcumin was demonstrated by increased stimulation of S473 phosphorylation of protein kinase B (P < 0.01) in the dexamethasone-treated mouse liver, as well as the repression of glucose production in primary hepatocytes (P < 0.001). Finally, curcumin gavage increased FGF21 expression by 2.1-fold in the mouse liver (P < 0.05) and curcumin treatment increased FGF21 expression in primary hepatocytes.Conclusion: These observations suggest that the early beneficial effect of curcumin intervention in dexamethasone-treated mice is the sensitization of insulin signaling, involving the stimulation of FGF21 production, a known insulin sensitizer. [ABSTRACT FROM AUTHOR]