Effects of water‐soluble low‐molecular‐weight β‐1, 3‐D‐glucan (branch β‐1, 6) isolated from Aureobasidium pullulans 1A1 strain black yeast on restraint stress in mice

Abstract It is well known that different stress paradigms are able to rapidly induce corticosterone production and immune function through the activation of the hypothalamic‐pituitary‐adrenal axis. It has been reported that glucocorticoids suppress natural killer (NK) activity and interleukin (IL)‐1 production and, on the other hand, that IL‐1 and IL‐6 stimulate the release of corticotrophin‐releasing‐hormone from the rat hypothalamus. Moreover, it has been reported that IL‐12 plays a central role in the initiation of cell‐mediated immunity, directly and via its induction of interferon (IFN)‐γ and activation of NK cells. In this study, we examined the effects of water‐soluble low‐molecular‐weight β‐glucan isolated from Aureobasidium pullulans 1A1 strain on the corticosterone levels and immune function, such as NK activity and IL‐6 and IL‐12 production, using a restraint stress‐induced mouse model. The water‐soluble low‐molecular‐weight β‐glucan at a dose of 50 or 100 mg kg −1 inhibited the increases in the blood corticosterone level and the reduction of NK activity induced by restraint stress. Furthermore, the water‐soluble low‐molecular‐weight β‐glucan (100 mg kg −1 ) prevented the reduction of IL‐6 and IL‐12 production by splenocytes caused by restraint stress. These findings suggest that the inhibitory actions of water‐soluble low‐molecular‐weight β‐glucan on the increase in corticosterone level and reduction of NK activity induced by restraint stress may be associated with the abrogation of the IL‐6 and IL‐12 reduction caused by the stress. Thus, water‐soluble low‐molecular‐weight β‐glucan may be an effective dietary supplement for the prevention of stress.