Prophylactic effects of sporoderm-removed Ganoderma lucidum spores in a rat model of streptozotocin-induced sporadic Alzheimer's disease

Ganoderma lucidum (G. lucidum, Lingzhi), also known as "immortality mushroom" has been broadly used to improve health and longevity for thousands of years in Asia. G. lucidum and its spores have been used to promote health, based on its broad pharmacological and therapeutic activity. This species is recorded in Chinese traditional formula as a nootropic and has been suggested to improve cognitive dysfunction in Alzheimer's disease. However, little is known about the nootropic effects and molecular mechanism of action of G. lucidum spores. The present study investigated the protective effects of sporoderm-deficient Ganoderma lucidum spores (RGLS) against learning and memory impairments and its mechanism of action. In the Morris water maze, the effects of RGLS on learning and memory impairments were evaluated in a rat model of sporadic Alzheimer's disease that was induced by an intracerebroventricular injection of streptozotocin (STZ). Changes in amyloid β (Aβ) expression, Tau expression and phosphorylation, brain-derived neurotrophic factor (BDNF), and the BDNF receptor tropomyosin-related kinase B (TrkB) in the hippocampus were evaluated by Western blot. Treatment with RGLS (360 and 720 mg/kg) significantly enhanced memory in the rat model of STZ-induced sporadic Alzheimer's disease and reversed the STZ-induced increases in Aβ expression and Tau protein expression and phosphorylation at Ser199, Ser202, and Ser396. The STZ-induced decreases in neurotrophic factors, including BDNF, TrkB and TrkB phosphorylation at Tyr816, were reversed by treatment with RGLS. These findings indicate that RGLS prevented learning and memory impairments in the present rat model of STZ-induced sporadic Alzheimer's disease, and these effects depended on a decrease in Aβ expression and Tau hyperphosphorylation and the modulation of BDNF-TrkB signaling in the hippocampus.