| An experimental study was conducted to investigate anti-hyperglycemic activities and mechanism of quercetin in AA broilers without and with streptozotocin.The 2×4 factorial design [two factors(no streptozotocin and streptozotocin)and four levels(0.00%,0.02%,0.04% and 0.06% quercetin)] was adopted,480 one-day-old healthy Arbor Acre(AA)broilers with similar body weights were randomly divided in to 8 treatments with 6 replicates and 10 chicks in each replicate.Experimental diets were formulated with 4 different levels of quercetin: 0%,0.02%,0.04% and 0.06% quercetin.These 4 experimental diets were assigned to 8 treatments for 6 weeks.At the end of experiment,2 birds per replicate with similar body weight were selected,slaughtered,serum and organ samples were collected and stored for further analysis.Streptozotocin(STZ)significantly increased fasting blood glucose(FBG)(P<0.01)and significantly decreased fasting serum insulin(FINS)level(P<0.01)in AA broilers,supplementation of 0.06% quercetin significantly decreased FBG(P<0.01)and increased FINS(P<0.01),however,no significant difference was observed in interaction between STZ and quercetin(P>0.05).STZ and quercetin significantly decreased serum content of total cholesterol(TC),triglyceride(TG)and low density lipoprotein cholesterol(LDL-C)(P<0.01),significantly increased high density lipoprotein cholesterol(HDL-C)(P<0.01),interaction in serum lipid profile between STZ and quercetin was significant(P<0.01,P<0.01),except for LDL-C(P>0.05)in AA broilers.The effect of quercetin on serum lipid profile in AA broilers without STZ was more significant than that in AA broilers with STZ(P<0.05).STZ significantly decreased average daily gain(ADG)and average daily feed intake(ADFI)in AA broilers(P<0.01).No significant difference was observed in supplementation of quercetin and interaction between STZ and quercetin(P>0.05).Dressing percentage(DP),eviscerated percentage(EP),half eviscerated percentage(HEP)and breast muscle percentage(BMP)were not statistically different in groups supplemented with quercetin in AA broilers with STZ and without STZ groups(P>0.05).However,supplementation of 0.04% quercetin significantly increased thigh muscle percentage(TMP)(P<0.05)and decreased abdominal fat percentage(AFP)(P<0.01)in AA broilers with STZ.No significant difference was observed in interaction between STZ and quercetin(P>0.05).STZ significantly increased serum aspartate aminotransferase(AST)(P<0.01)and alanine aminotransferase(ALT)(P<0.01)in AA broilers,supplementation of 0.06% quercetin significantly increased ALT in AA broilers without STZ and with STZ(P<0.01).STZ and quercetin significantly affected serum nitric oxide(NO)level(P<0.01)and liver NO level(P<0.05)in AA broilers,respectively.Meanwhile,interaction between STZ and quercetin in serum NO level(P<0.05)and liver NO level(P<0.01)was observed in AA broilers.Supplementation of quercetin more effectively decreased serum and liver NO level in AA broilers without STZ than those in AA broiler with STZ(P<0.05)and this effect was STZ-dependent.STZ significantly increased lipid peroxide(LPO)content in pancreas of AA broilers(P<0.05),however,supplementation of quercetin didn’t affect LPO content in liver and pancreas of AA broilers(P>0.05).In liver and pancreas,STZ significantly affected activity of superoxide dismutase(SOD)(P<0.01),glutathione peroxidase(GSH-Px)(P<0.01)and catalase(CAT)(P<0.05)in AA broilers,supplementation of quercetin also significantly influenced activity of SOD(P<0.05),GSH-Px(P<0.01)and CAT(P<0.01),interaction between STZ and quercetin in activity of GSH-Px and CAT was observed in liver and pancreas of AA broilers(P<0.01,P<0.01).In serum,STZ significantly increased malondialdehyde(MDA)content(P<0.01),supplementation of quercetin significantly decreased MDA content in AA broiler without STZ and with STZ(P<0.01),however,the decrease of MDA content was more significant in AA broilers without STZ than that in AA broilers with STZ(P<0.01).In serum,STZ significantly decreased tumor necrosis factor-α(TNF-α)level(P<0.01),quercetin significantly increased TNF-α level(P<0.01),however,there was no interaction between STZ and quercetin(P>0.05).The effect of quercetin was more significant in AA broilers without STZ than that in AA broilers with STZ(P<0.05).In adipose tissues,STZ significantly impacted interleukines-6(IL-6)level(P<0.05)and TNF-α level(P<0.01),quercetin significantly increased monocyte chemoattractant protein-1(MCP-1)(P<0.01),IL-6(P<0.05)and TNF-α level(P<0.01),moreover,there was significant interaction between STZ and quercetin in MCP-1 and IL-6 level(P<0.05),TNF-α level(P<0.01).STZ significantly affected mRNA expression of IR,IRS-1 and PKB/AKT(P<0.01),there was no significant difference in mRNA expression of PI3 K and GSK-3β(P>0.05).Supplementation of quercetin significantly decreased mRNA expression of IR and GSK-3β(P<0.01,P<0.05),significantly increased mRNA expression of PI3 K and PKB/AKT(P<0.01),however,there was no significant difference in mRNA expression of IRS-1(P>0.05).In addition,significant interaction between STZ and quercetin was observed in mRNA expression of IR,IRS-1,PI3 K and PKB/AKT(P<0.01).In conclusion,hyperglycemic AA broilers was successfully induced by STZ.STZ significantly decreased ADG and ADFI in AA broilers with STZ,but supplementation of quercetin significantly increased thigh muscle percentage(TMP)and decreased abdominal fat percentage(AFP)in AA broilers with STZ.SZT induced oxidative stress in AA broilers,resulting in increased MDA and blood glucose levels,decreased insulin level and activities of antioxidant enzymes.Meanwhile,supplementation of quercetin improved redox status by enhancing the decreased activities of antioxidant enzymes,decreasing inflammatory cytokine levels and MDA content.Moreover,quercetin strengthened insulin signaling by activating key proteins of PI3K/PKB signaling pathway that modulated glucose and lipid metabolism,thereby decreased FBG and abdominal fat.Quercetin improved immune status of AA broilers by decreasing production of NO and regulating production of inflammatory cytokines.In a word,STZ increased blood glucose,decreased insulin secretion,induced oxidative stress,however,supplementation of quercetin relieved the detrimental effect via improving antioxidation and immunity,activating PI3K/PKB signaling pathway in AA broilers. |
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