Tadasu Furusho

Administration of beta-carotene Suppresses Lipid Peroxidation in Tissues and Improves the Glucose Tolerance Ability of Streptozotocin-Induced Diabetic Rats

The present study attempted to examine the antioxidative effect of dietary beta-carotene (BC) on lipid peroxidation (LPO) in the streptozotocin (STZ)-induced diabetic rats. Male Sprague-Dawley (SD) rats were fed on the AIN76 standard diet with or without 0.1% BC. On the 21st day after introduction of these diets, STZ was intraperitoneally injected in half the subjects of both groups. All animals were sacrificed seven days after the STZ injection. Glucose tolerance and thiobarbituric acid reactive substance (TBARS) in the tissues or serum were measured. Body weight gain in the BC + STZ group was significantly higher than that in the STZ group (p < 0.05). Blood glucose and TBARS concentrations of the liver, pancreas, and serum in the BC + STZ group were significantly lower than those in the STZ group. The blood insulin concentration in the BC + STZ group was significantly higher than that in the STZ group. The hepatic and serum beta-carotene concentrations in the BC + STZ group were significantly lower than those in the BC group. Moreover, the synthesis and oxidation of glutathione (GSH) in the BC + STZ group were reduced when compared to the STZ group. These results suggest that the administration of beta-carotene suppresses the elevation of LPO and reduces the symptoms of diabetes mellitus (DM) in the STZ-induced diabetic rats.

Retinol Equivalence of Carotenoids Can be Evaluated by Hepatic Vitamin A Content

The present study demonstrates a new method to evaluate the bioavailability of carotenoids based on the calculation of the hepatic retinol contents. Weaning male rats of Wistar strain were divided into 5 groups. Each group respectively received retinol acetate (2000-10,000 IU per kg diet), alpha-carotene (2400-6000 micrograms per kg diet), beta-carotene (2400-6000 micrograms per kg diet), mixture of alpha- and beta-carotenes in the ratio of 1:2 (2400 and 4800 micrograms per kg dit), and palm-carotene oil (2400-6000 micrograms per kg diet). The derived retinol equivalences of each carotenoid calculated according to the hepatic retinol contents were almost constant regardless of the volume of respective intake (alpha-carotene: 1.25 micrograms per IU; beta-carotene: 0.59 microgram per IU; mixture of alpha- and beta-carotene in the ratio of 1:2: 0.96 microgram per IU; Palm-carotene oil: 1.23 micrograms per IU). The results suggest that the hepatic retinol contents can be used as a new measure to evaluate the vitamin A bioavailability of carotenoids.

Jew's mellow leaves (Corchorus olitorius) suppress elevation of postprandial blood glucose levels in rats and humans.

The study was performed to explore the suppressive effect of Jews mellow leaves (JML) on postprandial blood glucose levels in rats and humans. A soluble dietary fiber (SDF) was extracted from the freeze-dried JML powder. An elevation of the postprandial blood glucose level in rats given 1% or 2% JML-SDF solution orally together with 20% glucose solution was significantly suppressed as compared with that observed in the control rats given only glucose solution. When seven healthy young male adults ingested 225 mL of JML mixed juice containing 15 g of freeze-dried powder with 75 g of glucose in the fasting state in the morning, the elevation of the postprandial blood glucose level was significantly suppressed as compared with the control subjects. The diffusion rate of glucose and the permeation rate of glucose in the cultured Caco-2 cells were both significantly reduced by the addition of appropriate amounts of JML-SDF when compared to the controls. These results indicate that the effective substance in JML for suppressing blood glucose elevation is a kind of mucilaginous SDF. The mechanism by which this suppression occurs may be largely attributable to the delayed absorption of glucose from the intestinal membrane in the upper digestive tract by viscous SDF.

Dose-responsive alteration in hepatic lipid peroxidation and retinol metabolism with increasing dietary beta-carotene in iron deficient rats.

Phosphatidylcholine hydroperoxide (PCOOH) levels are increased in the iron-deficient rat liver. We investigated the antioxidative effect of dietary beta-carotene and altered retinol metabolism in iron-deficient rats. Experiment 1: Male Wistar-strain rats were divided into six groups and fed a control diet, an iron-deficient diet, and iron-deficient diets with four different levels of dietary beta-carotene. The PCOOH concentration in the iron-deficient rat liver was decreased by supplementation with dietary beta-carotene. However, the beta-carotene dose response was not related to antioxidative potency. Hepatic and plasma beta-carotene concentrations were increased by iron deficiency. The hepatic retinol concentration was increased while the plasma retinol concentration was decreased in iron-deficient rats. Experiment 2: Male Wistar-strain rats were divided into two groups, with one group receiving a control diet with beta-carotene and the other an iron-deficient diet with beta-carotene. Intestinal iron was decreased and intestinal beta-carotene was unchanged in iron-deficient rats. The intestinal beta-carotene conversion ratio and beta-carotene cleavage enzyme activity were decreased in iron-deficient rats. Dietary beta-carotene played the role of an antioxidant in hepatic lipid peroxidation in the iron-deficient state, but there was no dose dependency. Moreover, intestinal beta-carotene cleavage and hepatic retinol release appear to be altered in iron-deficient rats.

High dietary fat-induced obesity in Wistar rats and type 2 diabetes in nonobese Goto-Kakizaki rats differentially affect retinol binding protein 4 expression and vitamin A metabolism

Obesity is a major risk factor for type 2 diabetes, which is caused mainly by insulin resistance. Retinol binding protein 4 (RBP4) is the only specific transport protein for retinol in the serum. RBP4 level is increased in the diabetic state and high-fat condition, indicating that retinol metabolism may be affected under these conditions. However, the precise effect of diabetes and high fat-induced obesity on retinol metabolism is unknown. In this study, we examined differences in retinol metabolite levels in rat models of diet-induced obesity and type 2 diabetes (Goto-Kakizaki [GK] rat). Four-week-old male Wistar and GK rats were given either a control diet (AIN-93G) or a high-fat diet (HFD, 40% fat kJ). After 15 weeks of feeding, the RBP4 levels increased by 2-fold in the serum of GK rats but not HFD-fed rats. The hepatic retinol concentration of HFD-fed rats was approximately 50% that of the controls (P < .01). In contrast, the renal retinol concentrations of GK rats increased by 70% (P < .01). However, expression of RARβ in the kidney, which was induced in a retinoic acid-dependent manner, was downregulated by 90% (P < .01) in GK rats. In conclusion, diabetes and obesity affected retinol metabolism differently, and the effects were different in different peripheral tissues. The impact of HFD may be limited to the storage of hepatic vitamin A as retinyl palmitate. In particular, our data indicate that renal retinoic acid production might represent an important target for the treatment of type 2 diabetes mellitus.

Elevation of urinary methylmolonic acid induces the suppression of megalin-mediated endocytotic cycles during vitamin B12 deficiency

Megalin is a scavenger receptor that serves in the endocytosis of a highly diverse group of ligands that includes Vitamin B12. We found an accumulation of megalin closed to apical region in renal proximal tubule cells of Vitamin B12-deficient rats. Interestingly, Vitamin B12 levels also controlled resorption of renal retinol binding protein. Using L2 yolk sac cells, megalin localized to the submembrane compartment by methylmalonic acid (MMA), which accumulates during vitamin B12 deficiency. In addition, MMA inhibited megalin-mediated endocytosis via YWTD repeats motif in an ectodomain of megalin. Therefore, megalin endocytosis may be regulated by MMA.

A Nuclear Factor Involved in Transcriptional Regulation of the AREBP Gene

The AICAR responsive element binding protein (AREBP) suppresses transcription of the gluconeogenic enzyme genes in response to AICAR treatment. Moreover, overexpression of AREBP also suppresses gluconeogenic gene expressions in animals, indicating that AREBP plays an important role in gluconeogenesis. Through a combination of systematic analyses of the AREBP gene promoter and assays for DNA-protein interaction, we identified a nuclear factor involved in tissue-specific expression of AREBP. By targeting this nuclear factor, pharmacological or nutraceutical induction of AREBP gene expression is expected to reduce blood glucose levels in patient with insulin resistance.

Data on the weights, specific gravities and chemical compositions of potato (Solanum tuberosum) tubers for food processing from different areas of Hokkaido, Japan

This data article provides the weights, specific gravities and chemical compositions (moisture, protein, fat, ash, and carbohydrate) of potato tubers, for food processing use, from the Tokachi, Kamikawa and Abashiri areas of Hokkaido, Japan. Potato tubers of four cultivars (‘Toyoshiro’, ‘Kitahime’, ‘Snowden’ and ‘Poroshiri’) were employed in the current study. The weights and specific gravities of potato tubers from each cultivar, harvested from three areas, were measured, and those of near average weight and specific gravity from each group were analyzed for their chemical composition. In this article, weight, specific gravity, and chemical composition data are provided in tables.

Data on the sensory evaluation of potatoes (Solanum tuberosum) from different areas of Hokkaido, Japan, performed by untrained young adults

This data article describes a sensory evaluation of potatoes used in food processing from the Tokachi, Kamikawa, and Abashiri geographic areas of Hokkaido, Japan, performed by untrained young adults. We gathered sensory data on potatoes from the four cultivars ‘Toyoshiro,’ ‘Kitahime,’ ‘Snowden,’ and ‘Poroshiri.’ The sensory evaluation was performed on steamed potatoes from each cultivar; these potatoes were harvested from each of the three geographic areas. Table 1 provides the data from the evaluation of the five basic tastes (sweet, salty, sour, bitter, and umami), as well as the evaluation of the egumi taste, which is a Japanese term indicating a taste that is acrid, astringent, and slightly bitter.