Effect Of Nrf2 Activated By SFN On LDH Expression And Activity In Skeletal Muscle Of Acute Hypoxic Exercise Mice

Nuclear factor erythroid 2-related factor 2(Nrf2)plays an important role in antioxidant and aerobic metabolism of skeletal muscle.Sulforaphane(SFN)is a recognized activator of Nrf2,which is widely found in cruciferous plants.In this study,SFN was given to investigate the effects of hypoxia on endurance exercise ability and lactate metabolism of skeletal muscle in mice to provide theoretical basis for the application of altitude workers and athletes.Methods:male C57BL/6J mice were randomly divided into:SFN exercise,PBS exercise,SFN quiet control and PBS quiet control,with 9 mice in each group.The SFN exercise and PBS exercise groups were subjected to an incremental load treadmill exercise in hypoxic chambers with an oxygen concentration of 11.2%(simulating an altitude of 4500 m).Intraperitoneal injection of SFN(25 mg/kg body weight)or equal-volume PBS at 72,48,24 and 3 h before exercise was performed,respectively.Immediately after the exercise was executed,eyeball blood and anterior tibial muscle tissue were taken.The serum lactic acid concentration was determined by EKF lactic acid analyzer,and the protein expressions of Nrf2,phosphorylated Nrf2(p-Nrf2,ser 40),lactate dehydrogenase A(LDH-A)and LDH-B in skeletal muscle were determined by Western Blotting.The LDH activities of catalyzing pyruvate to lactic acid conversion and catalyzing lactate to pyruvate conversion were respectively determined by the kit.Results:(1)the distance and duration of movement were significantly higher in SFN exercise group than in PBS exercise group,and the serum lactic acid concentration was significantly lower in SFN exercise group than in PBS exercise group.(2)The expression levels of Nrf2 and p-Nrf2 in SFN exercise and SFN quiet control groups were significantly higher than those in PBS exercise and PBS quiet control groups.(3)The LDH-B protein expression and LDH activity of the SFN exercise group were significantly higher than those of the PBS exercise group.The LDH-A protein expression level of SFN exercise group was not significantly changed,but the LDH activity of catalyzing pyruvate into lactic acid was significantly lower than that of PBS exercise group.Conclusion:SFN administration before hypoxic exercise can significantly activate the protein of Nrf2 in mice skeletal muscle,increase LDH expression and activity of LDH catalyzing lactic acid to pyruvate in skeletal muscle,promote the metabolism of lactic acid of skeletal muscle,and thus reduce the blood lactate concentration,which may be an important factor to improve the exercise endurance of mice under hypoxic condition.