Beneficial effect of yam on the amyloid β-protein, monoamine oxidase B and cognitive deficit in mice with accelerated senescence

This study was designed to evaluate the effect of yam tuber material [Dioscorea alata L. var. purpurea (M.) Pouch.] on the amyloid beta-protein (A beta) accumulation, monoamine oxidase (MAO) activity, cognitive ability and antioxidative defense system in senescence-accelerated mice (SAMP8). Three-month-old male mice were fed with four different diets for 12 weeks: a casein diet (control group) and a casein diet supplemented with either 100, 200 or 400 g kg(-1) lyophilized yam. The results of the active shuttle avoidance test showed that the mice fed with the yam-containing diets had significantly better learning and memory ability than the control group. All yam-containing diet groups had lower A beta levels and MAO B activities than the control, whereas the MAO A activity did not differ among the four diet groups. At the 400 g kg(-1) level, the yam-containing diet group showed significantly lower concentration of thiobarbituric acid-reactive substances (TBARS), higher total thiol level and superoxide dismutase (SOD) activity in the hippocampus than the control, but these values were not altered by the 100 and 200 g kg(-1) yam-containing diet groups. The addition of 200 or 400 g kg(-1) yam also lowered the triglyceride levels but not the total cholesterol concentration. These results indicate that lyophilized yam could reduce brain A beta accumulation, MAO B activity and cognitive deficits and promote the antioxidative defense system in SAMP8 mice. The improvements were in a dose-dependent manner, possibly because the 400 g kg(-1) yam-containing diet might contain more antioxidative phytochemicals. (c) 2006 Society of Chemical Industry.