Cleavage Products of Dietary Carotenoids: Occurrence & Nutritional Function

描述（由申请人提供）：膳食类胡萝卜素的消耗与心血管疾病和癌症的风险降低有关。人类通过摄取水果和蔬菜从饮食中获得类胡萝卜素。历史上，人们认为某些类胡萝卜素最重要的作用是它们通过在中心双键处裂解而代谢转化为必需的微量营养素维生素A（视黄醇）。最近，人们对膳食类胡萝卜素向脱胡萝卜素醛的“偏心裂解”及其可能氧化为脱胡萝卜酸产生了浓厚的兴趣。这些类胡萝卜素代谢产物可能在类胡萝卜素的非维生素A活性中起重要作用。目前还没有对这些化合物在人类食物和组织中的含量进行定量分析。完整的类胡萝卜素代谢这些化合物的程度和他们的作用机制的研究缺乏证明。我们将填补这些知识空白。(1)我们确定的底物特异性和表征的两个已知的人类类胡萝卜素代谢酶（BCO 1和BCO 2）的产品。这些研究也将建立细胞视黄醇结合蛋白和类胡萝卜素裂解酶在这些酶的代谢功能中的关系。(2)我们将证明相关的apo-carotenoids在人类使用分析化学来表征的存在和量化的apo-carotenals和apo-carotenoic酸在人体血浆和组织和食物中的量。这将通过在受试者食用单份含有营养相关量的β-胡萝卜素或番茄红素的番茄汁后立即定量母体类胡萝卜素和代谢物的餐后血浆浓度以及通过定量每日食用4周后血浆中的稳态浓度来实现。(3)我们将使用LNCaP细胞，一种表现出番茄红素依赖性生长抑制并表达BCO 2的人前列腺癌细胞，在番茄红素处理的细胞中寻找脱辅基酸和脱辅基酸，以解决番茄红素是否以及在多大程度上在这些细胞中代谢。我们将使用人单核细胞/巨噬细胞U937来寻找母体类胡萝卜素的代谢，该细胞在类胡萝卜素处理下生长受到抑制并被诱导分化。(4)我们将以多种方式探索类胡萝卜素代谢物的生物（营养）功能：（a）我们将使用我们已经显示出对膳食类胡萝卜素治疗具有特征性功能反应的细胞系，并询问这些反应是否是通过用裂解产物直接治疗获得的，以及（B）我们将询问这些裂解产物和代谢物是否直接激活或拮抗配体依赖性转录因子。(c)我们将向BCO 1基因敲除小鼠同时喂食β-胡萝卜素和番茄红素，以评估BCO 2代谢这些类胡萝卜素的程度以及类胡萝卜素代谢产物在整个动物中的代谢作用。研究结果将加强我们对富含水果和蔬菜的饮食对健康促进作用的分子基础的理解。 公共卫生相关性：增加膳食类胡萝卜素的消耗与降低心血管疾病和某些癌症的风险有关。这项拟议中的研究将记录人类膳食类胡萝卜素（水果和蔬菜中促进健康的有色色素）代谢的新途径。这项研究还将探索可能的机制，解释这些饮食成分促进健康的作用的基础。

DESCRIPTION (provided by applicant): Consumption of dietary carotenoids is associated with a decreased risk of cardiovascular disease and cancer. Humans obtain carotenoids in the diet by ingesting fruits and vegetables. Historically, it was thought that the most important role of some carotenoids was their metabolic conversion via cleavage at the central double bond to the essential micronutrient, vitamin A (retinol). There is intense recent interest in the "eccentric cleavage" of dietary carotenoids to apocarotenals and their possible oxidation to apocarotenoic acids. These metabolites of carotenoids may play important roles in the non-vitamin A activities of carotenoids. There are no quantitative analyses of the levels of these compounds in human foods and tissues. Demonstrations of the extent of metabolism of intact carotenoids to these compounds and studies of their mechanisms of action are lacking. We will address these gaps in knowledge. (1) We determine the substrate specificity and characterize the products of the two known human carotenoid-metabolizing enzymes (BCO1 & BCO2). These studies will also establish the relationship of cellular retinol-binding proteins and carotenoid cleavage enzymes in the metabolic function of these enzymes. (2) We will demonstrate the relevance of apocarotenoids in humans using analytical chemistry to characterize the presence and quantify the amounts of apo-carotenals and apocarotenoic acids in human plasma and tissues and in foods. This will be accomplished by quantitation of the immediate post- prandial plasma concentrations of parent carotenoids and metabolites after subjects consume a single serving of tomato juice containing nutritionally relevant amounts of beta-carotene or lycopene as well as by quantitation of steady state concentrations in plasma after 4 weeks of daily consumption. (3) We will use the LNCaP cell, a human prostate cancer cell that demonstrates lycopene-dependent growth inhibition and expresses BCO2 to look for apolycopenals and apolycopenoic acids in lycopene-treated cells to address whether and to what extent lycopene is metabolized in these cells. We will use the human monocyte/macrophage cell, U937, which is growth inhibited and induced to differentiate with carotenoid treatment, to look for metabolism of the parent carotenoids. (4) We will probe the biological (nutritional) function of carotenoid metabolites in multiple ways: (a) we will use cell lines that we have shown have characteristic functional responses to treatment with dietary carotenoids and ask whether these responses are obtained by direct treatment with the cleavage products and (b) we will ask whether these cleavage products and metabolites directly activate or antagonize ligand-dependent transcription factors. (c) We will feed the BCO1 knockout mouse both beta-carotene and lycopene to assess the extent of the metabolism of these carotenoids by BCO2 and the metabolic effects of carotenoid metabolites in the whole animal. The results will enhance our understanding of the molecular basis for the health-promoting effects of diets rich in fruits and vegetables. PUBLIC HEALTH RELEVANCE: Increased consumption of dietary carotenoids is associated with decreased risk of both cardiovascular disease and certain cancers. The proposed research will document the occurrence of new pathways of metabolism of dietary carotenoids (the health-promoting, colored pigments in fruits and vegetables) in humans. The research will also explore possible mechanisms that may explain the basis of the health-promoting effects of these components of the diet.