The capability of fish to synthesize vitamin D on exposure to ultraviolet (UV) light was examined. Purposeful exposure of the freshwater fish Tilapia mossambica (Tilapia) to artificial UV light (300 nm) resulted in a significant increase of vitamin D3 with a concomitant decrease in provitamin D3 [7-dehydrocholesterol (7-DHC) ], indicating that provitamin D3 was coverted to vitamin D3. However, only 0.13% of the intraperitoneally injected 4-14C cholesterol was recovered in the vita-min D3 and 25-hydroxyvitamin D3 (25-OH-D3) fractions after 15 h of irradiation. Thus, although fish is capable of photosynthesizing vitamin D through constant, prolonged exposure to UV light of appropriate wave-length, the contribution of this mode of synthesis is unlikely to be of any significance in its natural habitat.
An important event in the pathogenesis of atherosclerosis is believed to be the oxidative modification of low-density lipoprotein (LDL) initiated by a free radical-driven lipid peroxidation process. Vitamin E acts as a lipophilic chain-breaking antioxidant, while water-soluble chain-breaking antioxidants such as vitamin C or uric acid suppress the oxidation of LDL initiated by aqueous radicals. In this study, we established a new method of measuring the lag time of inhibited lipid peroxidation using the lipophilic azo radical initiator V-70: 2-2'-azobis(4-methoxy-2, 4-dimethylvaleronitrile) and investigated in vitro the suscepti-bility of LDL to oxidation using this method when lipid- and water-soluble antioxidants were added. When the lipid-soluble antioxidant, vitamin E, was added to LDL, the lag time was extended whereas a higher dose of vitamin E led to a shortened lag time of V-70-induced lipid peroxidation in LDL. These results suggest that vitamin E radicals (tocopheroxyl radicals) act as prooxidants during the autoxidation of LDL. It was also shown that the shortened lag time induced by higher doses of vitamin E was restored when lipid- and water-soluble antioxidants were added simultaneously, which suggests that vitamin E radicals derived from vitamin E are subsequently reduced by vitamin C to regenerate vitamin E. Thus, the interaction between lipid- and water-soluble antioxidants provides an important function in maintaining LDL resistance to oxi-dation.
The response of the bowel mucosa to enteral formula supplemented with dietary fiber was examined in rats with 30% full-thickness burns. The rats were fed a standard enteral formula without fiber or with one of two types of fiber (insoluble soy fiber or soluble guar gum fiber). Seventy-two hours after burn injury, the mesenteric lymph nodes were excised aseptically for bacterial culturing. Samples of the jejunum, ileum and cecum were also collected for histological examination. There were significantly fewer bacterial colonies in the lymph node cultures from rats given soy fiber compared to those from rats fed no fiber. In rats given soy fiber, the integrity of the bowel mucosa was maintained in the jejunum, ileum and cecum. In rats given guar gum fiber, however, the repair of mucosal erosions was observed in the jejunum and ileum as well as flattening of the cecal mucosa. These findings indicate that soy fiber is superior to guar gum fiber for maintaining bowel mucosal integrity and preventing bacterial translocation in burned rats receiving enteral feeding.
The anti-tumor activity of a new type of peptidoglycan isolated from squid ink was shown to have a cure rate of 64% for Meth A tumor from BALB/c mice. The ink delipidated in acetone, which con-tained the peptidoglycan at 0.1% (w/w), was administered to tumor-transplanted mice so as to examine the anti-tumor activity. One-fifth of the tumor-bearing mice was cured with 3 injections (1 mg/head) of the acetone delipidated squid ink or a prolongation of survival was observed in the treated animals. Heat treatment at 100°C for 10 min did not affect the anti-tumor activity of the delipidated ink, its potentiality being pre-served. The acetone-extractable fraction of the ink also brought about a similar cure rate for Meth A tumor. The delipidated ink enhanced the phagocytic activity of macrophages but no direct cytotoxicity was observed for the Meth A tumor cells. Hence it may be said that the anti-tumor activity of the delipidated ink was mainly due to the aug-mented cellular immunity in vivo.
Glycated cytosolic aspartate aminotransferase was detected in the liver and kidney of streptozotocin diabetic rats using a boronate affinity column for adjacent cis.hydroxyl groups and an iunoblotting technique. The enzymatic activity and amount of immunoreactive subb stance were determined in the liver, kidney, and erythrocytes of diabetic and control rats. The ratio of enzymatic activity to the amount of enzyme was lower in diabetic rat tissue than in that in the control rats. It has been suggested that there is an inactive aspartate aminotransferase molecule in the tissues of diabetic rats. We therefore suggest that the cytosolic aspartate aminotransferase was inactivated in the diabetic rat tissues by a glycation reaction, accompanied by an impairment in glucose utilization.
It is known that change in the arachidonic acid metabolism plays an important role in the development of tumors. This study was undertaken to understand the relationship of changes in lipoxygenase, cyclooxygenase and ornithine decarboxylase (ODC) to the inhibitory effect of vitamin E on urethane-induced lung tumorigenesis in mice. We analyzed the inhibitory effect of vitamin E on ornithine decarboxylase, cyclooxygenase and lipoxygenase activities at a promotion phase of lung tumorigenesis in mice. An increase in the ODC of urethane treated-mice and no significant change in the ODC of VE-treated mice were observed. An increase in the production of PGE2 and all HETES tested in the lungs of the urethane-treated mice was observed at week 8 after injection (promotion phase), showing a significant difference compared to the control group. Excessive vitamin E feeding during the initiation or promotion phases inhibited the increase in PGE2 and HETES produced by urethane treatment. These results suggest that the suppression of prostagrandin metabolism and ODC may be associated with the in-hibitory effect of vitamin E against urethane-induced lung tumorigenesis.
The effect of a vitamin B1-free diet on the conversion ratio of tryptophan to niacin in rats was investigated using the current methods for determination of the intermediate metabolites. Rats were fed with diets with or without B1 for 33 days. The body weight gain and food intake in the B1-free group were almost the same as the control group for 10 days, but, they steeply dropped after that time and the conversion ratio of tryptophan to niacin began to increase. The ratio reached 7-fold that of the control group on the last day of the experiment. This finding seriously differed from the previous reports, which described that B 1 was needed in the first part of tryptophan conversion to niacin and that the conversion ratio of tryptophan to niacin decreased in B1-deficient rats. Furthermore, the activity of tryptophan oxygenase, in which it was reported that B 1 is required for the tryptophan catalytic reaction, did not decrease but increased even when the B1-free diet was fed. These results suggest that there is a very small possibility of the direct involvement of B 1 in the conversion of tryptophan to niacin.
Using [35S] PAPS as the sulfate donor, we have detected a sulfotransferase from bovine heart which catalyzes the sulfation of tyro-sine-containing peptides. The enzyme displayed optimal activity at pH 5.75 and 35°C in a one-hour reaction. The addition of 10 mM Mn2+ or Co2+ to the reaction mixture increased the sulfotransferase activity by 3.4-and 3.5-fold, respectively. In contrast, the maximum increment stimu-lated by Mg2+ was only 1.75-fold at 15 mM concentration, and instead of exerting an enhancement effect, Ca2+ was found to be a potent inhibitor. The addition of 50 mM NaF to the reaction mixture resulted in an increase in sulfotransferase activity of 3.3-fold. The Km for 3'-phosphoadenosine 5'-phosphosulfate (PAPS) was determined to be 2 μM at a constant 0.5 mM Boc-Glu-Asp-Tyr-Val. Among the 10 peptides tested as substrates, Boc-Glu-Asp-Tyr-Val and Boc-Asp-Asp-Tyr-Val provided the highest activities.