The Effects And Mechanisms Of Thymol On Oxidative Metabolism And Fiber Type Transformation Of Skeletal Muscle

Animal skeletal muscle fiber type is closely related to energy metabolism and meat quality.Different kinds of skeletal muscle fiber have different metabolic characteristics.The differences and transformation of muscle fiber type were mainly affected by genetic factors,but nutritional factors and environmental factors such as exercise had an important effect.Thymol,which is the main active ingredients of thyme,basil and oregano,has powerful capacity for antioxidant and anti-inflammatory.In recent years,thymol has also been confirmed to have therapeutic effect on metabolic diseases.Up to now,whether thymol can regulate the oxidative metabolism and muscle fiber type of skeletal muscle has not been reported.Therefore,this study was carried out in vivo and in vitro to explore the effects of thymol on oxidative metabolism and fiber type switch of skeletal muscle,and to investigate its undergoing mechanism.In vitro,C2C12 cell line was used.After differentiation for 6 d with 2%horse serum,0,10,20 or 40?M thymol was adden into C2C12 myotubes culture medium to study the effects of thymol on oxidative metabolism and transformation of muscle fiber type of C2C12 cells.Western Blot was used to detect the expression of myosin heaven chain in C2C12 cells;colorimetric method was used to detect the activity of succinate dehydrogenase?SDH?,hexokinase?HK?and lactate dehydrogenase?LDH?in C2C12 cells.The results show that after treating with thymol for 2 d,the protein expression of MyHC I and MyHC IIa was significantly increased?P<0.05?in C2C12 myotubes,the activity of enzyme related oxidation metabolism was also incrased by thymol administration?P<0.05?.Thymol can increase the number of oxidative fibers and promote oxidative metabolism in C2C12 myotubes.In vivo,firstly,a total of 32 4-weeks-old male SD rats were randomly divided into 4groups,feeding with 0%,0.01%,0.025%or 0.5%thymol in the diet for 4 weeks.Immunohistochemistry,Western Blot and quantitative PCR were carried out to detect the expression of metabolism and muscle fiber type related genes and proteins of rats'gastrocnemius;colorimetric method was used to detect the activity of succinate dehydrogenase?SDH?,hexokinase?HK?and lactate dehydrogenase?LDH?of rats'gastrocnemius.The results show that after feeding with thymol for 4 weeks,the oxidative muscle fiber ratio was significantly improved in the rats'gastrocnemius?P<0.05?and oxidative metabolism of rats'gastrocnemius muscle was strengthened?P<0.05?.Then we selected 36 150-days-old fattening Pigs?Duroc*Landrace*Yorkshire?to explore to effects of thymol on meat quality.According to the principle of weight,sex ratio is consistent between groups;pigs were randomly divided into 3 groups feeding with 0%or0.01%thymol for 6 weeks,each group of 3 repeats,every repeat 6 pigs?3 castrated males and 3 females?.Colorimetric method was used to detect the activity of succinate dehydrogenase?SDH?,hexokinase?HK?and lactate dehydrogenase?LDH?of longissimus dorsi of pigs,and quantitative PCR was carried out to detect the expression of muscle fiber type related genes of longissimus dorsi of pigs.The results show that:After feeding with thymol for 6 weeks,muscle water loss rate was significantly reduced?P<0.05?,mRNA level of MyHC I was significantly improved in the longissimus muscle?P<0.05?.Meat quality was improved to a certain extent.In order to further reveal the mechanism of thymol on oxidative metabolism and muscle fiber type transformation of skeletal muscle,calcium chelating agent was pretreated in C2C12 cells to detect the effects of thymol on muscle fiber types.The results show that chelating intracellular calcium reversed the effect of thymol on the myosin heaven chain and oxidative metabolism related genes in C2C12 cells.To sum up,thymol can promote the transformation of glycolytic muscle fibers to the oxidative muscle fibers through the Ca²⁺/Calcineurin pathway.