Okara ameliorates glucose tolerance in GK rats.

Okara, a food by-product from the production of tofu and soy milk, is rich in three beneficial components: insoluble dietary fiber, ß-conglycinin, and isoflavones. Although isoflavones and ß-conglycinin have recently been shown to improve glucose tolerance, the effects of okara have not yet been elucidated. Therefore, we herein investigated the effects of okara on glucose tolerance in Goto-Kakizaki (GK) rats, a representative animal model of Japanese type 2 diabetes. Male GK rats were fed a 10% lard diet with or without 5% dry okara powder for 2 weeks and an oral glucose tolerance test was performed. Rats were then fed each diet for another week and sacrificed. The expression of genes that are the master regulators of glucose metabolism in adipose tissue was subsequently examined. No significant differences were observed in body weight gain or food intake between the two groups of GK rats. In the oral glucose tolerance test, increases in plasma glucose levels were suppressed by the okara diet. The mRNA expression levels of PPARγ, adiponectin, and GLUT4, which up-regulate the effects of insulin, were increased in epididymal adipose tissue by the okara diet. These results suggest that okara provides a useful means for treating type 2 diabetes.

Nutritional and hormonal regulation of uncoupling protein gene expression in rat adipocytes.

Nutritional and hormonal regulation of the expression of uncoupling protein (UCP)-1, -2, and -3 mRNA and protein was investigated in primary cultured adipocytes of rats. The UCP-1, -2, -3 mRNA and protein induction in the adipocytes reached maximal levels at 4 h in the presence of glucose with or without insulin. Moreover, the UCP induction was accelerated by triiodothyronine (T3) or epinephrine, and reached a maximum at 2 h. It appeared that the induction of UCP mRNA and protein was rapid. UCP-1 mRNA expression was stimulated by the presence of T3 or epinephrine in the culture medium. UCP-2 mRNA expression was more markedly increased by glucose, unsaturated fatty acids, insulin and T3 than UCP-1 or -3 mRNA expression. UCP-3 expression was more markedly increased by epinephrine than by T3. The protein expression of the UCPs was induced by glucose and the hormones nearly parallel to the UCP mRNA expression. Thus, UCP-2 expression appears to be stimulated by energy sources such as glucose and fat, and by regulators of thermogenesis and basal metabolic rate such as T3 and insulin, in contrast to UCP-1 and -3 expression.

Labeled acetate incorporation into lipids and lipid elimination after oral administration in rat liver and adipose tissue.

To investigate the incorporation of acetate into fatty acids and their turnover, the time courses for the incorporation of labeled acetate into lipids in the liver and epididymal adipose tissue (adipose tissue) after the oral administration to rats were examined for 10 d. The labeled acetate was abundantly incorporated into lipids, mainly into triacylglycerols (TAG) in the liver, reached a maximum at 2 h after the administration and then quickly decreased. In the adipose tissue, the incorporation of the acetate reached a maximum after 8 h and began to decrease slowly after 2 d. The acetate incorporation into the lipids was markedly lower in the liver, plasma and adipose tissue of rats fed the corn oil diet than in those fed the fat-free diet. However, the half-lives of esterified fatty acids were similar in both dietary groups. The half-lives of esterified C16:0 and C18:1 in the decreasing phase were 5.4 and 8.9 h, respectively, in the liver, and 4.3 and 5.6 d, in the adipose tissue. The time courses for incorporation into plasma lipids were parallel to those in the liver. Thus the fatty acids synthesized in the liver appeared to be transported to adipose tissues and to stay there longer. Moreover, it is remarkable that 30% of the acetate radioactivities administered were found after 2 h in the whole liver: 75% of the products from the acetate at the maximum were lipids and 61%, of the lipids, TAG. The major products from acetate in the liver were lipids.

Dietary diacylglycerol-rich oil stimulation of glucose intolerance in genetically obese rats.

The effects of dietary 1,3-diacylglycerol-rich oil (DG oil) on glucose and lipid metabolism were investigated in comparison with triacylglycerol (TG) oil in female genetically obese Wistar fatty rats. The obese rats and their lean littermates (8 wk old) were fed a synthetic diet containing 10%, (w/w) DG or TG oil for 5 wk. The body weights, abdominal fat weights, and the plasma and liver TG concentrations were not significantly different due to dietary fat type in the obese and lean rats. The plasma glucose concentrations were significantly elevated by dietary DG oil as compared to TG oil in the portal vein and inferior vena cava of obese and lean rats. The plasma free fatty acid concentrations were markedly elevated by dietary DG oil as compared to TG oil in the portal vein and inferior vena cava of both genotype rats, particularly in the obese rats. In the glucose tolerance test, the obese rats fed DG oil showed glucose intolerance, possibly due to the markedly elevated plasma free fatty acids. Thus, the effects of dietary DG oil on lipid-lowering effects and anti-obesity were not observed in either genotype in the present study. Moreover, it is remarkable that glucose intolerance was induced by dietary DG oil in the genetically obese rats. dietary

Comparisons of glucose and lipid metabolism in rats fed diacylglycerol and triacylglycerol oils.

The effects of dietary 1,3-diacylglycerol-rich oil (DG oil) on biochemical findings related to glucose and lipid metabolisms were investigated in comparison with triacylglycerol oil (TG oil) in normal rats. Young (7 wk-old) and old (8 mo-old) rats were fed a synthetic diet containing 10% (by weight) DC or TG oil for 1, 4, 8, or 12 wk. The body weights, epididymal and perirenal adipose tissue weights, and feed efficiency were not significantly different in the dietary oil groups during any feeding period. The plasma and liver triacylglycerol concentrations were not different in the dietary groups, except that the plasma triacylglycerol concentrations were rather lower only in the portal vein of rats fed DG oil. The plasma glucose and free fatty acid concentrations were significantly higher in rats fed DG oil as compared to TG oil. In the old rats fed DG oil for 8 wk, the fasted plasma glucose and insulin concentrations were elevated and glucose intolerance was observed. The insulin receptor expression was not different due to dietary oil, but was markedly reduced with aging. Thus, the anti-obesity and lipid-lowering effects of dietary DG oil were not found. Moreover, it appeared that the glucose intolerance might be induced by dietary DG oil, particularly in the old rats.

Changes in UCP family expressions in rat tissues due to diet and aging.

Regulation of the gene expressions of uncoupling proteins (UCP)-1, 2 and 3 was investigated in the white and brown adipose tissues and skeletal muscle of young and old rats (8-wk- and 8-mo-old, respectively) fed diets containing various fats (hydrogenated fat, corn oil or fish oil) and proteins (casein or soybean) for 1 wk. The mRNA expressions of UCP-1, 2 and 3 were elevated in the white adipose tissues of the young rats fed soybean protein as compared to those fed casein, and that of UCP-2 was also elevated in the brown adipose tissue. The effects of dietary fat type on the expressions were not clear. The UCP-1, 2 and 3 mRNA expressions were markedly reduced in the tissues of the old rats. The UCP-2 expressions were more markedly elevated by dietary soybean protein and reduced by aging than the others, particularly in the white adipose tissue. The expressions of leptin involved in thermogenesis were also reduced by aging. Moreover, in a fasted-refed experiment conducted for the young rats, UCP-2 mRNA induction in the white adipose tissues reached maximal levels at 1 or 2 h and was stimulated by dietary fat or soybean protein. Thus, UCP-2 mRNA expression was markedly affected by diet and aging, particularly in white adipose tissue.

Comparison of labeled acetate and glucose incorporations into lipids in the liver and adipose tissue after intravenous injection in rats.

To compare incorporations of acetate and glucose in tissue total lipids and triacylglycerols (TAG), incorporations of labeled acetate and glucose in livers and epididymal adipose tissues (adipose tissue) were followed after their intravenous injection in the tail vein of individual rat fed a fat-free or 10% corn oil diet. The incorporation of acetate into total lipids (mostly TAG) in the liver reached maximum 2 h after the injection, while the incorporation of glucose decreased more quickly. Incorporation of glucose into total lipids and TAG was more greatly suppressed by dietary corn oil than that of acetate in the liver. In the adipose tissues, the incorporation of labeled acetate or glucose into total lipids was maximum 2-8 h after the injection, while the incorporation of glucose was very low, especially in rats fed the corn oil diet. Moreover, the time courses for labeled acetate and glucose incorporations into total lipids in the liver were parallel to those in plasma, but opposite to those in adipose tissue. TAG synthesized from acetate and glucose in the liver appeared to be mostly transported to adipose tissue. Thus, it is suggested that as the labeled glucose rapidly decreased in the liver, plasma and adipose tissue, TAG should be less derived from dietary carbohydrate than from dietary fat.

Differences in labelled triolein turnover after oral administration between liver and adipose tissue of rats.

To investigate exogenous triacylglycerol turnover, the time courses for labelled triolein in the liver, plasma and epididymal adipose tissue (adipose tissue) after oral administration to rats fed a fat-free or 10 % corn oil diet for 3 d after fasting overnight were examined for 10 d. After the administration of labelled triolein to rats fed the fat-free diet, the incorporation (dpm/g) into total lipids of the liver and adipose tissue each reached the maximum in 8 h and was seven times higher in the adipose tissue than in the liver. The half-lives of total lipid radioactivities during the decreasing phases were 0.39 and 2.58 d, respectively, in the rapid and slow phases of the decay curve in the liver, and 4.78 d in only one phase of the adipose tissue. Radioactivity after administration of labelled triolein was mostly found in the oleic acid in the tissues. The half-life of oleic acid was 3.92 d in the adipose tissues. These half-lives were similar in both dietary groups. Thus, although dietary corn oil reduced the triolein incorporation to cellular lipids in comparison to the fat-free diet, it did not affect these half-lives. The labelled triacylglycerol-oleic acid stayed abundantly intact for a long time in the adipose tissue and was scarcely changed to other fatty acids, whereas it was slightly incorporated into total lipids and quickly metabolized in the liver. Non-essential fatty acids may be mostly endogenous in the liver but may be exogenous and endogenous in adipose tissue.