We investigated the digestion of cerebrosides of plant origin prepared from maize, focusing especially on the digestive fates of trans-4, cis-8- and trans-4, trans-8-sphingadienine, which are common in higher plants. In the small intestinal mucosa and cecal contents of rats, the cerebrosidase activity at pH 5.2 toward the glucosyl linkage in maize cerebrosides (glucosylceramides) was similar to that in cerebrosides of mammalian origin. Similarly, the ceramidase activity toward the amide linkage in ceramides prepared from maize cerebrosides at pH 7.0 was the same as that toward ceramides of mammalian origin. In addition, maize cerebrosides were hydrolyzed to ceramide and free sphingoid bases in the digestive tract of rats after oral administration. To further evaluate the uptake by enterocytes of 4,8-sphingadienine, we used differentiated Caco-2 cells, derived from human colonic carcinoma, as a model of intestinal epithelial cells. The accumulation of sphingoid bases in Caco-2 cells incubated with each isomer of sphingadienine was lower than that after incubation with sphingosine (P < 0.05). Verapamil, a P-glycoprotein inhibitor, increased the accumulation of each sphingadienine but not of sphingosine, suggesting that the efflux of sphingadienine of plant origin, but not sphingosine of mammalian origin, was affected by P-glycoprotein. The digestibility of maize cerebrosides appears similar to that of cerebrosides of mammalian origin, but the metabolic fate of sphingoid bases of plant origin within enterocytes differs from that of sphingosine. Isomers of 4,8-sphingadienine degraded from dietary plant cerebrosides appear to be poorly absorbed from the digestive tract.
In a previous study, we found that the extent of dietary n-3 docosahexaenoic acid (DHA)-stimulated tissue lipid peroxidation was less than expected from the relative peroxidizability index of the total tissue lipids in rats with adequate vitamin E nutritional status. This suppression of lipid peroxidation was especially prominent in the liver. To elucidate whether this phenomenon was unique to DHA, we compared the peroxidation effects of n-3 a-linolenic acid (a-LN) and n-3 eicosapentaeonic acid (EPA) with those of DHA in rats. Either a-LN (8·6 % of total energy), EPA (8·2 %), or DHA (8·0 %) and one of two levels of dietary vitamin E (7·5 and 54 mg/kg diet) were fed to rats for 22 d. Levels of conjugated diene, chemiluminescence emission and thiobarbituric acid (TBA)-reactive substance in the liver, kidney, and testis were determined as indicators of lipid peroxidation. In rats fed the DHA diet deficient in vitamin E (7·5 mg/ kg diet), TBA values in the liver, kidney, and testis correlated well with the tissues' relative peroxidizability indices. In rats fed the a-LN diet with an adequate level of vitamin E (54 mg/kg diet), a close association between relative peroxidizability indices and lipid peroxide levels was observed in all the tissues analysed. However, in rats fed either the EPA diet or the DHA diet with an adequate level of vitamin E, the extent of lipid peroxidation in each tissue was less than expected from the relative peroxidizability index. This suppression was particularly marked in the liver. We concluded that suppression of lipid peroxidation below the relative peroxidizability index was not unique to DHA, but was also seen with EPA, which has five double bonds, in rats with adequate vitamin E nutritional status, but not with a-LN, which has three double bonds.
The aim of this study was to determine whether sphingoid bases that originated from various dietary sources, such as mammals, plants, and fungi, are substrates for P-glycoprotein in differentiated Caco-2 cells, which are used as a model of intestinal epithelial cells. In Caco-2 cells, the uptake of sphingosine, the most common sphingoid base found in mammals, was significantly higher at physiological temperatures than those of cis/trans-8-sphingenine, trans-4, cis/trans-8-sphingadienine, 9-methyl-trans-4, trans-8-sphingadienine, or sphinganine. Verapamil, a potent P-glycoprotein inhibitor, increased the cellular accumulation of sphingoid bases, except for sphingosine, in a dose-dependent manner. Incubation with 1 microM digoxin for 48 h caused up-regulation of multidrug-resistance (MDR)1 mRNA and decreased the accumulation of sphingoid bases in Caco-2 cells, except for sphingosine. Thus P-glycoprotein probably contributes to the selective absorption of sphingosine from dietary sphingolipids in the digestive tract.
The design of removable partial dentures (RPDs) is an important factor for good prognostication. The purpose of this study was to clarify the effectiveness of denture designs and to clarify the component that had high rates of failure and complications. A total of 91 RPDs, worn by 65 patients for 2-10 years, were assessed. Removable partial dentures were classified into four groups: telescopic dentures (TDs), ordinary clasp dentures (ODs), modified clasp dentures (MDs) and combination dentures (CDs). The failure rates of abutment teeth were the highest and those of retainers were the second highest. The failure rates of connectors were generally low, but they increased suddenly after 6 years. Complication and failure rates of denture bases and artificial teeth were generally low. Complication and failure rates of TDs were high at abutment teeth and low level at retainers. Complication and failure rates of ODs were high at retainers.
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