DIETARY CAROTENOIDS - LIPOPROTEIN/CELL INTERACTIONS

人类从水果和蔬菜中获得饮食中的类胡萝卜素。类胡萝卜素作为抗氧化剂的作用一直是我们在脂蛋白氧化方面工作的重点。虽然脂蛋白是类胡萝卜素运输的主要载体，但对类胡萝卜素在肠道中的吸收机制知之甚少。我们现在试图定义肠道吸收类胡萝卜素的机制(S)及其在血细胞中的分布。我们关注类胡萝卜素与人类单核/巨噬细胞的相互作用，因为这种相互作用可能在动脉粥样硬化的发展中发挥作用。具体目标是：1.培养的CACO-2细胞中类胡萝卜素在肠道中的吸收及其掺入乳糜粒的机制。我们将测试其他脂溶营养素抑制β-胡萝卜素进入乳糜粒的假设。我们将检验这一假设，即SRB1、CD-36、FAT和其他假定的脂质转运体介导了β-胡萝卜素进入细胞的摄取。我们将检验这一假设，即增加β-胡萝卜素15，15‘双加氧酶的表达会增加β-胡萝卜素通过细胞的总流量。2.人体对β-胡萝卜素的肠道吸收。我们将使用稳定同位素方法来研究人体对β-胡萝卜素的肠道吸收机制。正在调查的一般问题是，各种脂溶饮食营养素的吸收是否存在共同的机制。我们将检验这一假设，即肠道吸收胆固醇的效率与肠道吸收β-胡萝卜素的效率正相关。我们将检验这一假设，即β-胡萝卜素仅在肠道内转化为维生素A。我们将对β-胡萝卜素向维生素A的转化进行量化，以检验以下假设：β-胡萝卜素的吸收增加与维生素A的转化增加有关。3.饮食中类胡萝卜素对巨噬细胞功能的调节。我们将使用U937细胞系以及人类外周血单核-巨噬细胞来检测类胡萝卜素在血源性细胞中的分配以及类胡萝卜素浓缩对单核-巨噬细胞功能的影响。我们将检验血浆类胡萝卜素分配给各种血细胞以及血浆脂蛋白的假设。我们将检验这一假说，即类胡萝卜素的富集会改变单核巨噬细胞的表型，增强或抑制潜在的动脉粥样硬化方面的细胞功能，包括对化学趋化刺激的反应，与内皮细胞的黏附，向巨噬细胞的分化，氧化低密度脂蛋白的能力，以及形成泡沫细胞的能力。

Humans obtain carotenoids in the diet from fruits and vegetables. The role of carotenoids as antioxidants has been the focus of our work on lipoprotein oxidation. While it is clear that lipoproteins are the main vehicles for transport of carotenoids, little is known about mechanisms of intestinal absorption of carotenoids. We now seek to define the mechanism(s) of intestinal absorption of carotenoids and their distribution into blood cells. We focus on the interaction of carotenoids and the human monocyte/macrophage since this interaction may play a role in the development of atherosclerosis. Specific aims are: 1. Mechanisms of intestinal absorption of carotenoids and their incorporation into chylomicrons in CACO-2 cells in culture. We will test the hypothesis that other fat-soluble nutrients inhibit the incorporation of beta-carotene into chylomicrons. We will test the hypothesis that SRB1, CD-36, FAT, and other putative lipid transporters mediate the uptake of beta-carotene into the cell. We will test the hypothesis the increasing the expression of beta-carotene 15,15' dioxygenase increases the total flux of beta-carotene through the cell. 2. Intestinal absorption of beta-carotene in humans. We will use stable isotope methodology to study the mechanisms of the intestinal absorption of beta- carotene in humans. The general question under investigation is whether there are common mechanisms for the absorption of various fat-soluble dietary nutrients. We will test the hypothesis that the efficiency of intestinal absorption of cholesterol is positively correlated with the efficiency of the intestinal absorption of beta-carotene. We will test the hypothesis that beta-carotene is converted to vitamin A solely in the intestine. We will quantify the conversion of beta-carotene to vitamin A to test the hypothesis that increased absorption of beta-carotene is associated with increased conversion to vitamin A. 3. Modulation of macrophage function by dietary carotenoids. We will use the U937 cell line as well as human peripheral blood monocyte- macrophages to examine the partitioning of carotenoids into blood-borne cells and the effects of carotenoid enrichment on monocyte-macrophage function. We will test the hypothesis that plasma carotenoids partition into various blood cells as well as into plasma lipoproteins. We will test the hypothesis that carotenoid enrichment alters monocyte-macrophage phenotype, either enhancing or inhibiting potentially pro-atherosclerotic aspects of cell function including response to chemotactic stimuli, adhesion to endothelial cells, differentiation into macrophages, ability to oxidize LDL, and ability to form foam cells.