Increased levels of serum cholesterol (CHO) are associated with a risk of coronary artery disease. The beneficial effect of various dietary components on hypercholesterolemia and atherosclerosis was reviewed based on our animal experiments. Exogenously hypercholesterolemic (ExHC) rats, a strain susceptible to dietary CHO, show increased secretion of β-very-low-density lipoproteins (VLDL) and reduced uptake of lipoproteins by the liver. Exposure of ExHC rats to a high-cholesterol diet in early life exerted a long-lasting effect leading to transient suppression of hypercholesterolemia in later life. Dietary polyunsaturated fats, particularly those containing docosahexaenoic acid (DHA), were effective in lowering serum lipid levels in comparison with saturated fats, but stearic acid-containing fats were less hypercholesterolemic because they interrupted the intestinal absorption of CHO. The hypocholesterolemic action of dietary phosphatidylethanolamine was attributed to the ethanolamine constituent, which prevented methylation of the phospholipid to phosphatidylcholine in primary cultured hepatocytes, consequently leading to suppression of VLDL-CHO secretion. Soybean protein and DHA were found to be beneficial for reducing atherosclerosis in both ExHC rats and apo E-deficient mice.
We investigated the metabolism of n-6 and n-3 fatty acids and their effect on lipid metabolism. Rat hepatocytes were a good model for the study of Δ5-desaturation, while HepG2 cells did not have this activity. We found that sesamin, a lignan of sesame seed, inhibited the activity of Δ5-desaturation in n-6 fatty acids but not in n-3 fatty acids. This result was confirmed in vivo using rats fed diets rich in n-6 and n-3 fatty acids. Sesamin also inhibited the increase of n-3 fatty acids in the liver caused by a n-3 fatty acid-rich diet. Sesamin had a unique function in changing the balance of intermediate metabolites of n-6 and n-3 fatty acids. We also examined the effect of fatty acids on lipid metabolism in HepG2 cells. Linolenic acid (LLA) decreased the synthesis and secretion of TG from HepG2 cells while linoleic acid (LA) and γ-linolenic acid (GLA) reduced only the secretion of TG. LA increased the binding and uptake of LDL. LLA had a strong effect in promoting the catabolism of cholesterol. These results suggest that a change in n-6/n-3 balance caused by a dietary component such as sesamin can affect lipid metabolism.
We investigated effects of astaxanthin on antitumor effector activities of immunocytes including NK cells suppressed by stress in mice in order to define the immunological significance of astaxanthin when combined with restraint stress treatment. When the mice given restraint stress alone, the total number of spleen cells, and NK cell activities per spleen were reduced to the lowest level on day 3, and restraint stress also caused a significant increase in lipid peroxidation of liver tissue. On the other hand, metastatic nodules were observed in the liver of syngenic DBA/2 mice on day 12 after inoculation with mastocytoma P815. The hepatic metastasis was promoted further by restraint stress when it was applied on day 3 before P815 inoculation. When astaxanthin was consecutively administered orally prior to the restraint stress treatment, asthaxanthin greatly reduced both the metastatic nodules and lipid peroxidation, and improved the NK cell activity that should have been reduced by restraint stress. These results suggest that astaxanthin may improve antitumor immune responses via inhibition of lipid peroxidation in the oxidation process caused by stress.
Standard reference ranges for all laboratory test values are mandatory. This study was designed to establish a reference range for blood vitamin B1 levels, since the normal range has not been determined in the Japanese population. We founded the Japan Committee for Vitamin Laboratory Standards, which was incorporated with the Vitamin Society of Japan and the Japanese Society of Nutrition and Food Science. We standardized whole blood vitamin B1 levels using three HPLC techniques (post-calumn reverse-phase HPLC, pre-column reverse-phase HPLC, and precolumn GP-HPLC). The reference range was obtained in 54 volunteers administered a 1, 800 kcal diet with 2mg of vitamin B1 (1.74mg measured) daily to avoid marginat vitamin B1 deficiency in the population. The range for each assay was 26-47ng/ ml, 28-51ng/ml, and 28-56ng/ml, respectively. Our data suggest that 26-28ng/ml is the lower limit of normal for whole blood vitamin B1, but further studies in a larger population are needed in order to obtain more definitive results.