Beta-carotene is a carotenoid with a range of reported health benefits besides vitamin A activity. If the enzymatic conversion of beta-carotene to retinal is suppressed in the digestive tract, residual beta-carotene that reaches the tissues increases. We evaluated the function of quercetin and rutin (quercetin-3-rutinoside) to increase the accumulation of beta-carotene in vitro and in vivo in BALB/c mice. When the conversion of beta-carotene by a preparation of the murine small intestine was measured in vitro, the addition of quercetin or rutin considerably inhibited the conversion. When the levels of hepatic beta-carotene and retinoids were measured among three groups of mice fed a diet supplemented with beta-carotene plus quercetin or rutin or beta-carotene alone (four to six mice per group), quercetin increased the level of beta-carotene and decreased the level of retinol, whereas rutin did not. These results demonstrate that quercetin can suppress the conversion of beta-carotene which develops in the cytosol of small intestinal epithelial cells, and that rutin whose rutinose-moiety prevents being absorbed in the small intestine cannot suppress the conversion in vivo. This study offers a novel insight into the interaction between flavonoids and carotenoids with respect to the health benefits from the latter.
The development of automobile emission reduction technologies has decreased dramatically the particle concentration in emissions; however, there is a possibility that unexpected harmful chemicals are formed in emissions due to new technologies and fuels. Therefore, we attempted to develop new and efficient toxicity prediction models for the myriad environmental pollutants including those in automobile emissions. We chose 54 compounds related to engine exhaust and, by use of the DNA microarray, examined their effect on gene expression in human lung cells. We focused on IL-8 as a proinflammatory cytokine and developed a prediction model with quantitative structure-activity relationship (QSAR) for the IL-8 gene expression by using an in silico system. Our results demonstrate that this model showed high accuracy in predicting upregulation of the IL-8 gene. These results suggest that the prediction model with QSAR based on the gene expression from toxicogenomics may have great potential in predictive toxicology of environmental pollutants.
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