In Vivo Antifatigue Activity of Spirulina Peptides Achieved by Their Antioxidant Activity and by Acting on Fat Metabolism Pathway in Mice

Spirulina are multicellular and filamentous cyanobacteria that have achieved considerable popularity in the health sector, food industry, and aquaculture. In the present study, we aimed to evaluate the antifatigue effects of Spirulina-derived peptides on Institute for Cancer Research mice and explore the association between antifatigue activity and fat metabolism involving the adenosine monophosphate-activated protein kinase (AMPK) signaling pathway. We extracted the peptides from Spirulina by enzymatic hydrolysis and ultrafiltration. The mice were orally administered with Spirulina peptides (0.125, 0.5, and 2 mg/g bw/day) daily for 4 weeks. We found that Spirulina peptides, especially the high-dose group, significantly prolonged the swimming time by 126.1%, increased the activities of antioxidant enzymes, and decreased the content of malondialdehyde by 60.2% compared with the glutathione (GSH) group. The levels of some indicators of exercise fatigue, including lactic dehydrogenase, blood lactic acid, and creatine phosphokinase, were reduced. In the high-dose group, these indicators were reduced by 40.7%, 22.3%, and 11.3% compared with the GSH group. Spirulina peptides did not excessively consume blood sugar or glycogen in the liver and muscle to produce energy. However, the triglyceride level was reduced, and the level of free fatty acids was increased. Besides, the proteins in the AMPK signaling pathway were activated. Taken together, these findings indicated that Spirulina peptides could effectively alleviate physical fatigue by reducing the production of lactic acid and improving antioxidant capacity. Spirulina peptides also helped increase the energy resources by activating the AMPK signaling pathway to utilize fat metabolism.