Submerged culture mycelium and broth of Grifola frondosa improve glycemic responses in diabetic rats

Grifola frondosa, an edible fungus with a large fruiting body and overlapping caps, has been demonstrated to be a natural source of health-promoting substances, mainly due to its polysaccharides beta-glucan. By using male Wistar rats injected with saline (normal rats) or nicotinamide plus streptozotocin (diabetic rats), we investigated the effects of an orally ingested placebo (CON and STZ groups), culture mycelium (CGM and SGM groups), broth (CGB and SGB groups), and mycelium plus broth (CGX and SGX groups) of Grifola frondosa on glycemic responses. During the experimental period (from day 0 to day 15), the STZ group had significantly lower body weight compared to the CON group (one-way ANOVA, p < 0.05). Moreover, the STZ group had significantly higher blood glucose concentrations at 2 hour-postprandial periods on days 0, 7, and 14 and in an oral glucose tolerance test (OGTT) on day 10, as well as significantly higher serum fructosamine and triglyceride on day 15 compared to the CON group. These diabetes-induced increases were significantly attenuated by administrations of mycelium and/ or broth, i.e., the SGM, SGB, and SGX groups. The results of repeated-measures analysis and three-way ANOVA indicated that diabetes mellitus significantly increases, and mycelium administration significantly decreases postprandial blood glucose; diabetes mellitus significantly increases, and mycelium and broth administrations significantly decrease serum triglyceride, fructosamine, and blood glucose concentrations; moreover, in the area under the curve in OGTT, p < 0.05. Our results revealed that submerged-culture mycelia and broth of Grifola frondosa have bioactivities for improving glycemic responses.