β-Alanine-oxoglutarate aminotransferase (β-AIaAT I) and β-alanine-pyru-vate aminotransferase (β-AlaAT II) catalyze the transamination reaction of ω-amino acids such as β-alanine, β-aminoisobutyrate, and γ-aminobutyrate, amino acids that are not pro-tein constituents. The influence of dietary protein levels on the expression and activities of these enzymes was investigated by using male rats. Both, β-AIaAT I and β-AIaAT II activities in the liver were increased with the level of protein in the diet in accordance with changes in their mRNA levels. However, the β-AlaAT I activity in the kidney was increased by protein-free and low-protein diets in relation to changes in its mRNA level. On the other hand, the level of β-AIaAT II activity in the kidney was slightly decreased by a protein-free diet. Neither β-AIaAT I nor β-AIaAT II activities in the kidney were affected by a high-protein diet. These results suggested that β-alanine may be used efficiently in animals fed a protein-free or low-protein diet because the kidney provides β-alanine by means of the hydrolysis of β-alanyl-L-histidine (carnosine). The addition of, β-alanine to the diet significantly activatedβ-AIaAT I in the kidneys of rats in accordance with changes in its mRNA level. In the rat brain, β-AIaAT I activity was not altered by the dietary protein level or by the β-alanine diet, and β-AIaAT II activity was not detected.
We determined the effects of soy protein isolate (SPI) intake on remnant-like particles (RLP), lipolytic enzymes, lipid transfer protein, transaminases, sex hormones, iron, calcium, and vitamin E in healthy men. In the first randomized, crossover experiment, 14 men were given either 20 g per day of SPI or nothing (control) for each 4-week segment. After 3 weeks of SPI intake, TG and RLP cholesterol levels were significantly lower than the baseline by 13.4% (p<0, 05) and 9.8% (p<0.05), respectively. However, no significant change was found in total and low-density lipoprotein (LDL) cholesterol levels or the activi-ties of lipoprotein lipase, hepatic lipase, cholesterol ester transfer protein, and lecithin cho-lesterol acyltransferase. Although the levels of transaminases, testosterone, iron, and cal-cium did not change, the vitamin E level was reduced from the baseline by 9.7%, a signifi-cant decrease (p<0.01). In the second study, we attempted to determine the effect of vita-min E supplement taken with SPI. For each 3-week segment, 12 men were given 20 g per day of SPI, either with or without 200 mg per day of vitamin E, in a randomized crossover design. The vitamin E level was reduced by 9.2%, a significant decrease (p<0.05), after SPI intake for 3 weeks, and vitamin E supplement increased vitamin E level significantly (p<0.05). These results demonstrate that SPI intake reduces remnant lipoproteins, TG, and the plasma level of vitamin E, although vitamin E supplementation compensates for the re-duction of vitamin E. Therefore the supplementation of vitamin E may be required in sub-jects with long-term and abundant intake of soy protein.
The association between nutrient intake and bone mineral density (BMD) at calcaneus was cross-sectionally examined in 243 pre- (aged 29-60 years) and 137 post-menopausal (aged 39-60 years) Japanese women who participated in a BMD checkup and have kept a stable diet for at least 3 previous years and had no dietary therapy. Nutrient in-takes were assessed with a self administered diet history questionnaire. BMD at calcaneus was measured with dual-energy X-ray absorptiometry. In a multiple regression analysis with adjustments for nondietary factors such as age, body height, fat body weight, nonfat body weight, and number of deliveries, calcium (p<0.01) and niacin (p<0.05) significantly and positively, and phosphorus and dietary fiber (p<0.05 for both) significantly and nega-tively correlated in premenopausal women, and only potassium (p<0.05) significantly and positively correlated in postmenopausal women with BMD. The results suggest that several nutrients correlate with BMD, and the associations differ depending on menopausal status.
We investigated the effect of CH-19 Sweet, a nonpungent cultivar of red pep-per, and capsiate, a nonpungent capsaicin analog found in CH-19 Sweet on body tempera-ture in mice. The body temperature was recorded from conscious and unrestrained mice by use of a telemetry system. The body temperature in the mice administered CH-19 Sweet was higher than in the mice administered California-Wandar, which contains no capsiate or capsaicin. The body temperature in the mice administered capsiate was higher than in the mice administered the vehicle. Furthermore, we injected capsazepine, a specific antagonist of vanilloid receptors, into the peritoneal cavity and orally administered capsiate via a stom-ach tube to mice. The body temperature in the mice pretreated with capsazepine was lower than in the mice injected with the vehicle. This result suggested that capsazepine sup-pressed the rise in body temperature induced by capsiate administration. In conclusion, CH-19 Sweet increased body temperature, and this effect may be induced by the vanilloid recep-tors' stimulation of capsiate.
In the present study, to explore the beneficial effect of dietary galactoglyc-erolipids on the lower digestive tract environment, male BALB/c mice were fed a 5% wheat glycolipid, fiber-free diet, or the standard AIN diet for 3 wk. The wheat glycolipid composi-tion was digalactosyldiacylglycerol 51.6%, ceramide monohexoside 6.6%, acylated steryl-glucoside 3.4%, and other lipids 22.2% (mostly phospholipids). Cecum and colon weights and colonic crypt depth were significantly greater in the glycolipid-diet mice relative to groups fed the other two diets. Furthermore, in the cecum, propionate, butyrate, and total short-chain fatty acids, concentrations were significantly greater in the glycolipid-diet mice than others were, and correlated with the observed increased lower digestive tract (cecum and colon) weights and colonic crypt depth. The cecal lithocholic acid/deoxycholic acid ratio, a risk index for colorectal cancer, was significantly lower in the glycolipid-diet mice than in the other two dietary groups. These results suggest that the dietary supplementa-tion of plant-source galactoglycerolipids may contribute to improving the lower digestive tract environment.
Vitamin B6 deficiency increases the lipid peroxidation and the synthesis of xanthurenic acid from tryptophan. Antioxidant properties of xanthurenic acid were exam-ined in relation to the coordination of transition metals. Xanthurenic acid inhibited the for-mation of thiobarbituric acid-reactive substances as a marker of iron-mediated lipid peroxi-dation and copper-dependent oxidation of low density lipoprotein. NADP-isocitrate dehydro-genase (EC 220.127.116.11), a principal NADPH-generating enzyme for the antioxidant defense system, was inactivated by reduced iron and copper, and xanthurenic acid protected the en-zyme from the Fe2+-mediated inactivation. Xanthurenic acid may participate in the en-hanced regeneration of reduced glutathione by stimulating the NADPH supply. Xanthurenic acid further enhanced the autooxidation of Fe2+ ion. Other tryptophan metabolites such as kynurenic acid and various quinoline compounds did not inhibit the lipid peroxidation and the inactivation of NADP-isocitrate dehydrogenase, and they showed little or no effect on the Fe2+ autooxidation. The antioxidant properties of xanthurenic acid are related to the metal-chelating activity and probably to the enhanced oxidation of reduced transition met-als as a prooxidant, and this action may be due to the electron deficient nature of this com-pound.
The purpose of the current study was to assess the involvement of the branched-chain amino acid leucine in the regulation of translation initiation in the liver and to compare the time course of leucine action on the translation initiation in the liver and skeletal muscle of rats. The phosphorylation of the eukaryotic initiation factor (eIF)4E-binding protein 1 (4E-BP 1) frees eIF4E and stimulates protein synthesis by accelerating translation initiation. Phosphorylation of the 70-kDa ribosomal protein S6 kinase (S6K1) is thought to be involved in regulating the synthesis of certain ribosomal proteins and other selected proteins with polypyrimidine clusters near the transcription start site. Food-de-prived (18 h) male rats were orally administered 135 mg/ 100 g body weight L-leucine and sacrificed at 0, 1, 3, or 6 h after administration. The oral administration of leucine resulted in an enhanced phosphorylation of 4E-BP1 and S6K1 in both the liver and skeletal muscle. A time-dependent change in the phosphorylation state of 4E-BP1 and S6K1 was more acute in the skeletal muscle than in the liver and closely paralleled the changes in plasma leucine concentration. Our results indicate that the primary mediator in 4E-BP1 phosphorylation and S6K1 phosphorylation by the oral administration of leucine is an increase in the plasma concentration of leucine. Furthermore, our findings suggest differential sensitivity in the tissue response to oral administration of leucine.
A reduction of dehydroerythorbic acid (DERA) to erythorbic acid (ERA) in vitamin C-deficient guinea pigs was evaluated and compared with that of dehydroascorbic acid (DASA). Thirty-six guinea pigs were fed with vitamin C-deficient diets for 18 days. On day 19, the guinea pigs were divided into four groups for the administration of 100 mg of DERA, ERA, ascorbic acid (ASA), or DASA every day. After 12 days of oral administration, the concentration of DERA, ERA, ASA, and DASA in the liver, adrenal, spleen, kidney, and plasma of guinea pigs was determined by HPLC. A recovery from scurvy was measured in terms of weight gain and serum alkaline phosphatase activity. All four groups showed simi-lar recovery, indicating that the oral administration of relatively high concentrations of DERA reversed the effects of scurvy in vitamin C-deficient guinea pigs. In spite of DERA or DASA administration, ERA or ASA was mainly detected in the tissues. The reduction ratios of DEAR and DASA were similar (approximately 80%) in all tissues except spleen. These re-sults suggest that both DASA and DERA are taken up and reduced to ASA or ERA in vivo.