The binding of riboflavin to rat small intestinal brush border membrane at equilibrium was formerly shown to have a saturable, specific component, prevailing at the intraluminal physiological concentrations of the vitamin. In this study, the specificity of riboflavin binding to rat small intestinal brush border vesicles was further investigated using structural analogues of riboflavin. The vesicles, prepared by Ca²⁺-precipitation, were incubated at 25°C, for 20min, in the presence of [³H]-riboflavin at physiological intraluminal concentrations for rat, and each analogue, at appropriate concentrations. Three groups of analogues were used, that were derived from the riboflavin molecule by modifying one of the following positions: the ribityl side chain, position 3, and position 8 of the isoalloxazine moiety. Group specificity was assessed by determining the inhibition potency of each analogue on the saturable component of riboflavin binding to the vesicles. Inhibition constants were calculated, according to Dixon, for lumiflavin, lumichrome, and for analogues substituted at position 8. Specific riboflavin binding was inhibited competitively by most of the analogues used. Substitutions at the ribityl side chain or at position 3 of the isoalloxazine moiety reduced the inhibition power. Substitutions at position 8 enhanced the inhibition power in direct proportion to the bulk of the substituents. We conclude that the ribityl side-chain and the NH group at position 3 are essential for recognition by the specific binding sites, whereas the methyl group at position 8 is important but not essential. The analogues that bind to specific membrane sites for riboflavin share specificity requirements with many riboflavin binding proteins, and are also good substrates for the intracellular phosphorylating enzyme flavokinase. Thus, the riboflavin-binding component in the membrane is likely to be a protein with high specificity. Cellular internalization of the membrane bound vitamin is probably achieved by phosphorylation of the vitamin bound to the inner side of the membrane.

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To study the effect of palm fruit carotene intake on skin lipid peroxidation, hairless mice were given ad libitum palm fruit caro-tene, β-carotene, or vehicle emulsions for 15 weeks in which the carotene (0.005%, w/w) was suspended in drinking water, and then their dorsal skin was exposed to ultraviolet ray (UV). The carotene content of the skin was increased by the oral intake of palm fruit carotene or β-carotene. In carotene-drinking mice, before the UV irradiation, the amount of thiobarbituric acid-reacting substances (TBARS) in the skin was lower than that of control (carotene untreated) mice. The skin TBARS immediately after the UV irradiation was lower in carotene-treated mice than in control mice. At 24h after irradiation, the skin TBARS of mice that orally received palm fruit carotene was lower than that of β-carotene mice. Immediately after the UV irradiation, the skin carotene content transiently decreased but gradual recovery was observed at 48 h. In palm fruit carotene-treated mice, the rate of carotene recovery after UV irradiation was higher than in β-carotene-treated mice. Retinol found in the skin had also decreased after UV irradiation, and recovered gradually in both carotene-drinking groups within 48 h. These results suggested that the carotene intake, especially palm fruit carotene, prevented skin lipid peroxidation in hairless mice.

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To study the antioxidant effect of palm fruit carotene on skin lipid peroxidation, the guinea pigs were orally fed ad libitum palm fruit carotene, β-carotene, or vehicle emulsions, in which carotene (0.05%, w/w) was suspended in drinking water. After treatment of carotene for 12 weeks, animals were exposed to ultraviolet ray (UV), and squalene monohydroperoxide (SqOOH)/squalene (Sq) ratios in the skin lipid were analyzed using the chemiluminescence-HPLC method. Carotene accumulation was found in the skin of guinea pigs that were orally administered palm fruit carotene or β-carotene. After UV irradiation, especially immediately after, the rise in the SqOOH/Sq ratio was effectively suppressed in both carotene-drinking groups in contrast with the control (carotene-untreated) group. An inverse correlation between the carotene content and the SqOOH/Sq ratio in the skin was also observed. The results suggested that palm fruit carotene intake prevents skin lipid peroxidation caused by UV irradiation.

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Male mice were fed cholesterol-supplemented diets contain-ing short-necked clams or defatted short-necked clams for 2 weeks under the dietary regimen of the same dietary level of protein (20%), fat (5%), and cholesterol (0.5%). Casein was used as a control protein. Similar results were obtained in two separate experiments with either boiled (Exp. 1) or steamed (Exp. 2) short-necked clams. The concentration of serum cholesterol in mice fed a clam diet was lower than in those fed control and defatted clam diets. Delipidation of clam raised the concentration of serum triglyceride. Both clams and defatted clams markedly reduced the concentration of hepatic cholesterol. Fecal excretion of neutral steroids was significantly increased by clam but not defatted clam, whereas the excretion of acidic steroids was stimulated by both specimens, in particu-lar defatted clam. The results suggest that the hypocholesterolemic effect of short-necked clams is attributed to its lipid fraction, whereas non-lipid components contribute to the reduction of hepatic cholesterol and in-creased fecal excretion of bile acids.

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Tritium-labeled antitumor β-D-glucan derivative (T-labeled glucan) was prepared from the branched β-1, 3-D-glucan of an edible mushroom, Volvariella volvacea, by its periodate oxidation followed by reduction with NaBT₄. Twenty-three hours after T-labeled glucan had been injected into the mouse peritoneal cavity, about 3% of the total radioactivity injected was found in the mouse serum. In spite of the fact that T-labeled glucan had no affinity to the anion-exchange column before injection, about 50% of the labeled β-D-glucan in the serum thus obtained was adsorbed onto the column. The labeled β-D-glucan fraction eluted from the column by salt gradient showed antitumor activity in vivo.

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We recently reported that cholestyramine (a bile acid sequestrant) lowered ileal apolipoprotein A-I mRNA level in rats. To obtain further information about this phenomenon, in this study, we investigated whether bile diversion lowers apolipoprotein A-I mRNA level in the ileum of rats. Bile-diverted rats were fed a diet with no added Na taurocholate (control diet) or with 0.4% Na taurocholate for 7 days. Sham-operated rats were also fed the control diet for the same period. Northern blot analysis revealed that the relative concentrations of jejunal apolipoprotein A-I and A-IV mRNA at the end of experimental period did not differ between groups while ileal apolipoprotein A-I and A-IV mRNA concentrations were significantly lower in bile-diverted rats fed the control and Na taurocholate-containing diets than in sham-operated rats. Plasma total and HDL cholesterol concentrations were the same in all groups. Relative concentration of apolipoprotein A-I in plasma also did not change. These results suggest that the bile plays an important role in ileal apolipoprotein gene expression at the pretranslational stage, but it is still unclear whether the effector is the bile acid or not. The unchanged concentration of plasma apolipoprotein A-I may have resulted from the constant secretion independent of synthesis in the intestine or the larger contribution from the liver which is another principal site for apolipoprotein A-I expression.

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The differential effects of dietary proteins on the metabolic process of eicosapentaenoic acid (EPA, 20:5n-3) via docosapentaenoic acid (DPA, 22:5n-3) to docosahexaenoic acid (DHA, 22:6n-3) were studied using parameters calculated from the proportion of n-3 polyenoic acid in liver phospholipid (PL) of rats. Rats were given casein or soy-protein isolate (SPI) diet containing 3% EPA with or without methi-onine (Met) supplementation for 3 weeks. The (22:5+22:6)/20:5 and 22:5/20:5 ratios of the PL fractions in the liver of rats given SPI were evidently elevated compared with those given casein. These ratios were also elevated when linoleic acid (LA, 18:2n-6) was added to the diet. There were no significant differences in the 22:6/22:5 ratio of the same PL fractions between the casein and SPI groups without the addition of LA, but the ratio was lowered by the addition of LA. It was found that these parameters for metabolic conversion were not affected by supple-mentation of Met or by a decrease in body weight. The above results suggest that the elongation step from EPA to DPA is affected by the type of protein, i. e., it is accelerated by SPI and is not affected by the presence of LA, while the metabolic process from DPA to DHA is not affected by the type of proteins without the addition of LA but is suppressed when LA is added.

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The frequency of apoptosis after treatment with 1, 2-di-methylhydrazine (DMH) was counted in the descending colonic and rectal crypts of food-deprived and fed rats. Food-deprived or fed rats were subcutaneously injected with DMH (100 mg/kg body weight). Six hours after the injection, apoptosic cells were observed in crypt regions by light microscopy. The incidence of DMH-induced apoptosis in food-deprived rats was significantly higher than in fed rats. The incidence appeared to be higher in descending colon than in rectum. PAS staining revealed that DMH treatment lowered mucin secretion in crypts, which was substantially lowered by food deprivation. The effect of food depri-vation on apoptosis induced by DMH may be due to the decrease in mucus barrier against DMH.

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