Effect of the culture extract of Lentinus edodes mycelia on splenic sympathetic activity and cancer cell proliferation

The spleen is an important organ for tumor immunity, and the splenic sympathetic nerve has a suppressive effect on splenic natural killer (NK) cytotoxicity. On the basis of this and reports that Lentinus edodes (Shiitake mushroom) has tumor-inhibitory effects, the authors hypothesized that an extract of a mycelial culture of L. edodes grown in a solid medium of sugar-cane bagasse and defatted rice bran–L·E·M–might affect the sympathetic splenic sympathetic nerve activity (Splenic-SNA) and thus inhibit tumor proliferation. Thus, the effect of L·E·M on Splenic-SNA and human cancer cell proliferation was examined. Splenic-SNA was found to be suppressed by an intraduodenal L·E·M injection in urethane-anesthetized rats, which significantly inhibited increases in the tumor volume of human colon and breast cancer cells implanted in athymic nude mice. These findings suggest that L·E·M has an inhibitory effect on tumor proliferation possibly via a reduction in NK cytotoxicity through the suppression of Splenic-SNA.