The purpose of this study was to discover the effects of
soybean beta-conglycinin (7S-globulin) and
glycinin (11S-globulin) on serum
lipid levels and metabolism in the livers of normal and genetically obese mice. Male normal (ICR) and obese (KK-Ay) mice were fed ad libitum high fat diets for two weeks, followed by a 2-week restriction of diet (2 g diet/mouse/day) containing 20%
casein,
soybean beta-conglycinin, or soybean
glycinin, and then sacrificed immediately. Serum
triglyceride (TG),
glucose, and
insulin levels of
beta-conglycinin-fed mice were lower than in
casein- and
glycinin-fed mice of both strains. In order to analyze the related events to these effects,
enzyme activities and relative
mRNA levels of lipid metabolism-related
proteins were measured. The activities of two
enzymes related to
fatty acid beta-oxidation were higher while that of
fatty acid synthase was lower in livers of
beta-conglycinin-fed mice than of
casein-fed both mice.
Messenger RNA levels of
acyl-CoA oxidase (fatty acid beta-oxidation related
enzyme) were significantly higher in livers of
beta-conglycinin-fed mice than of both
casein-fed mice. On the contrary,
mRNA levels of SREBP-1 and 2 tended to be lowered in livers of
soy protein-fed mice than of both
casein-fed mice. Fecal excretion of TG was higher in
beta-conglycinin-fed mice than in
casein-fed mice. Our results demonstrated that the soy
beta-conglycinin diet reduced serum TG levels by acceleration of beta-oxidation, suppression of
fatty acid synthase and/or increased TG fecal excretion, and also diminished serum
glucose and
insulin levels. Some of these events might be caused at the transcriptional levels, judged from the result that relative
messenger RNA levels of lipid metabolism-related
proteins were altered. These results suggest that soy
beta-conglycinin could be a potentially useful
dietary protein source for the prevention of
hypertriglyceridemia,
hyperinsulinemia, and
hyperglycemia, which are recognized as risk factors for
atherosclerosis.