Effect Of Lipoic Acid On Skeletal Muscle Development And Its Protective Effects Against Aflatoxicosis In Broiler Chickens

This study was designed to evaluate the effect of alpha lipoic acid (ALA) on skeletal muscle development, transformation of myofiber type and antioxidant ability in vovo and in vitro in broiler chickens. In addition, the protective mechanisms of lipoic acid on aflatoxicosis were investigated in broiler chickens, based on the characteristics of its antioxidant and anti-inflammatory.In Exp.l, the experiment was conducted to study the effects of dietary ALA on the growth performance, the expression of skeletal muscle development-related genes, transformation of myofibre type and antioxidant ability of skeletal muscle in broiler chickens. A total of80male broilers were randomly divided into2groups and assigned different diets:basal diet (Control),300mg/kg ALA supplementation in basal diet, for3weeks. Results showed that LA significantly decreased the average daily weight gain (ADWG), have a decrease tend on the average daily feed intake (ADFI). ALA had no marked change on the relative percentage of breast and thigh muscle, but significantly decreased the breast muscle weight. Triglyceride, glucose, and triiodothyronine were significantly decreased among chickens in the treatment group. In ALA treated broiler chickens, a decrease in the breast muscle malondialdehyde (MDA) level, an increase in the activities of glutathionereductase (GR), Na+-K+-ATPase and Ca2+-Mg2+-ATPase (P<0.05) and a deletion of the glutathione (GSH) in in breast and thigh muscle, while had an increase in total superoxide disumutase (T-SOD) activity in thigh muscle. LA increased the expression of breast muscle slow myofiber (SM)(P<0.05), thigh muscle SM (P <0.05), thigh muscle fast red myofiber (FRM) MyHC mRNA (P<0.05), and decreased the expression of breast muscle fast white myofiber (FWM)(P<0.05), thigh muscle FWM MyHC mRNA (P<0.05) in broilers. ALA administration down-regulated the mRNA expression of myogenic determining factor (MyoD), myogenic factor5(Myf5) and myostatin in breast muscle, and down-regulated the mRNA expression of MyoD, Myf5, insulin-like growth factor I and insulin-like growth factor I receptor in thigh muscle. Results indicated that ALA decreased the growth performance and breast muscle weight, inhibited the expression of skeletal muscle development-related genes, but enhance the antioxidant ability of chicken muscle and regulated the transformation of myofibre type, and then might improve meat quality.In Exp.2, this study was designed to evaluate the effect of lipoic acid on skeletal myoblasts proliferation, the activities of Na+-K+-ATPase and Ca2+-Mg2+-ATPase, the expression of skeletal muscle cell transcription factors (involved in proliferation and differentiation) and MyHC genes. The results by MTT method showed that, the value of myoblast absorbance in the ALA-treated group was significantly decreased than the control group, especially high doses (P<0.05). Similar with the results by the cell morphology, beside that, we also found that a large number of cells were shed after72h in1000μmol/L ALA treated group. Results of cell cycle showed that ALA (exceed to100umol/L) significantly increased the number of cells in G1/G0phase, and significantly reduced the number of cells in the S phase. The fusion index was inhibited in the200umol/L ALA group as compared to the control group.500μmol/L ALA down-regulated the expression of the myoblast Pax7gene in the proliferation period.200μmol/L ALA up-regulated the expression of MyoD, myogenin (MyoG) and Myf5in the later stages of ALA treatment, however, the expression of MyoG was down-regulated in24h. With the increasing ALA level, significantly increased the expression of skeletal cell myofibre SM, FRM MyHC mRNA, and decreased the relative expression of FWM MyHC mRNA. In addition, ALA inhibited the activities of myoblast Na+-K+-ATP and Ca2+-Mg2+-ATPase. Results suggest that a high dose of ALA can inhibit the myoblast proliferation, maybe have a tendency of decreasing firstly and then increasing with treatment time, and alter the transformation of myofiber type.In Exp.3, LA, an antioxidant and anti-inflammatory compound, is evaluated in this study for its ability to protect the body from Aflatoxin B1(AFB1) caused injury in broiler chickens. A total of160male broilers were randomly divided into4groups and assigned different diets:basal diet,300mg/kg ALA supplementation in basal diet, diet containing74μg/kg AFB1, and300mg/kg ALA supplementation in diet containing74μg/kg AFB1, for3weeks. The results revealed that AFB1(74ppb) had no change on growth performance, however, the addition of300mg/kg ALA to the AFB1diet significantly decreased the ADWG and had a decrease trend on ADFI in broilers. Addition of300mg/kg ALA protected against the liver function damage of broilers induced by chronic low dose of AFB1as estimated by significantly (P<0.05) change in levels of plasma total protein, albumin, alkaline phosphatase and the activities of liver glutamic-oxalacetic transaminase and glutamic-pyruvic transaminase, and histological morphology. After fed diet containing AFB1, MDA (P<0.05) and nitric oxide (NO) levels (P<0.05) increased; the activity of glutathione peroxidase (GSH-Px)(P<0.05) decreased and GSH (P<0.05) content depleted in the chicken liver, while the expression of GSH-Px (P <0.05) mRNA was also down-regulated, but these negative effects were inhibited by the addition of300mg/kg ALA. Meantime, ALA alone can decrease the levels of MDA and NO, increase the activities of T-SOD, GR and GSH-Px and GSH level. AFB1significantly up-regulated the expression of the hepatic CYP1A1and CYP2H1, down-regulated the expression of the hepatic glutathione S-transferase (GSTa), and had no any change on the expression of epoxide hydrolase (P>0.05). However, the supplementation of ALA in AFB1-diet down-regulated the expression of the CYP1A1and CYP2H1, and tended to up-regulate the expression of GSTa gene. The pro-inflammatory factor IL-6(P<0.05) mRNA level increased in the AFB1group as compare to the control group. Additionally, the protein expression of the nuclear factor kappa B (NF-κB) p65and inducible nitric oxide synthase increased significantly (P<0.05) in the AFB1group compared to the corresponding control group. In addition, the increased expressions of IL-6, TNFa and IFNy were observed in birds exposed to the AFB1-contaminated diet. However, these negative effects were inhibited by treatment of ALA. The results suggest that ALA inhibits the performance in broiler chickens exposed to AFB1, but improves birds health, alleviates AFB1induced liver damage, enhance liver antioxidant ability, modulates the liver biotransformation, inhibits the inflammatory response in liver and spleen, and reduce the protein expression of NF-κB.