Green tea polyphenols alter lipid metabolism in the livers of broiler chickens through increased phosphorylation of AMP-activated protein kinase

<div><p>Our previous results showed that green tea polyphenols (GTPs) significantly altered the expression of lipid-metabolizing genes in the liver of chickens. However, the underlying mechanism was not elucidated. In this study, we further characterized how GTPs influence AMP-activated protein kinase (AMPK) in the regulation of hepatic fat metabolism. Thirty-six male chickens were fed GTPs at a daily dose of 0, 80 or 160 mg/kg of body weight for 4 weeks. The results demonstrated that oral administration of GTPs significantly reduced hepatic lipid content and abdominal fat mass, enhanced the phosphorylation levels of AMPKα and ACACA, and altered the mRNA levels and enzymatic activities of lipid-metabolizing enzymes in the liver. These results suggested that the activation of AMPK is a potential mechanism by which GTPs regulate hepatic lipid metabolism in such a way that lipid synthesis is reduced and fat oxidation is stimulated.</p></div

Phosphorylation of hepatic AMPKα and ACACA in broilers treated with green tea polyphenols.

<p>Broilers were treated with vehicle (distilled water), 80 mg/kg GTPs, or 160 mg/kg GTPs for 2 or 4 weeks. Western blots were probed with antibodies targeting phosphorylated version of ACACA, acetyl-CoA carboxylase and AMPK, AMP-activated protein kinase or unphosphorylated version of ACACA and GAPDH, glyceraldehyde-3-phosphate dehydrogenase. Values are represented as the means ± SEM (n = 6); statistical significance was determined by ANOVA with Duncan's multiple-range test, with *<i>p</i> < 0.05 and **<i>p</i> < 0.01 compared with control.</p

Effects of GTPs on lipid-related enzyme activities in the liver.

<p>Broilers were treated with vehicle (distilled water), 80 mg/kg GTPs, or 160 mg/kg GTPs for 2 or 4 weeks: A, fatty acid synthase (FASN); B, acetyl-CoA carboxylase (ACACA); C, carnitine palmitoyl transferase I (CPT1A); and D, AMP-activated protein kinase (AMPK). Values are represented as the means ± SEM (n = 6). Statistical significance was determined by ANOVA with Duncan's multiple-range test, with * <i>p</i> < 0.05, ** <i>p</i> < 0.01, and *** <i>p</i> < 0.001 representing significant differences compared with control.</p

Effects of green tea polyphenols on feed intake, body weight, liver-to-body weight ratio, and abdominal fat mass in broiler chickens.

<p>Effects of green tea polyphenols on feed intake, body weight, liver-to-body weight ratio, and abdominal fat mass in broiler chickens.</p

Effects of green tea polyphenols on the fat profile and malonyl-CoA content in the liver of broilers.

<p>Effects of green tea polyphenols on the fat profile and malonyl-CoA content in the liver of broilers.</p

Gene-specific primers for mRNA amplification of key lipid metabolism genes.

<p>Gene-specific primers for mRNA amplification of key lipid metabolism genes.</p

Effects of GTPs on the mRNA expression levels of representative fatty acid synthesis genes in the liver.

<p>Broilers were treated with vehicle (distilled water), 80 mg/kg GTPs, or 160 mg/kg GTPs for 2 or 4 weeks: A, fatty acid synthase (FASN); B, acetyl-CoA carboxylase (ACACA); C, stearoyl-coenzyme A desaturase 1 (SCD1); D, Sterol regulatory element-binding protein-1c (SREBP-1c). Values are represented as the means ± SEM (n = 6). Statistical significance was determined by ANOVA with Duncan's multiple-range test, with levels of significance at *<i>p</i> < 0.05, **<i>p</i> < 0.01, and ***<i>p</i> < 0.001 compared with the control.</p

Effects of GTPs on mRNA expression levels of representative lipolysis genes in the liver.

<p>Broilers were treated with vehicle (distilled water), 80 mg/kg GTPs, or 160 mg/kg GTPs for 2 or 4 weeks: A, carnitine palmitoyl transferase I (CPT1A); B, acyl-CoA oxidase 1 (ACOX); and C, peroxisome proliferator-activated receptor-alpha (PPARα). Values are represented as the means ± SEM (n = 6). Any statistical significance was determined by ANOVA with Duncan’s multiple-range test, with levels of significance at ** <i>p</i> < 0.01 and *** <i>p</i> < 0.001 compared with the control.</p