The Effect of Phytochemicals on Biochemical Mechanisms R

大量证据表明，富含水果和蔬菜的饮食可以预防或减缓各种癌症，包括乳腺癌、前列腺癌和肾癌。然而，对此负责的植物成分(植物化学物质)及其作用机制仍有待阐明。在这一组的主要项目中，我们研究了一些植物化学物质对与致癌相关的各种生化机制的影响。研究的植物化学物质包括类黄酮，它存在于所有水果和蔬菜中。其中包括柑橘类水果中的Diosmin，所有食用植物中含量最丰富的类黄酮类化合物栎素，以及槲皮素的代谢物高良姜素和山奈酚。其他植物化学物质包括b-二酮、姜黄素和二苯甲酰甲烷，以及白藜芦醇，白藜芦醇是一种存在于葡萄皮中的植物保卫素，因此存在于葡萄汁和葡萄酒中。在癌症的动物模型中，所有这些化合物都被证明是化学预防的，流行病学研究表明，含有大量这些化合物的食物与降低癌症风险有关。 有许多生化和分子事件与癌症的发展有关。其中最重要的途径之一是由芳烃受体(AhR)介导的。AhR是一种细胞质转录因子，在与配体结合后移位到细胞核，在那里与其蛋白伙伴Arnt相互作用，与存在于许多基因启动子区域的外源反应元件(XRE)相互作用。对AhR配体最具特征性的分子反应是诱导细胞色素P450 1A1(CYP1A1)的表达。CYP1A1是一种1相代谢酶，可激活环境致癌物，使其最终具有遗传毒性。除了细胞色素P1A1，AhR还控制着许多其他基因，这些基因被称为“AhR电池”，影响致癌物的激活和解毒。我们已经集中在第一阶段，或激活，酶，包括CYP1A1，CYP1B1和CYP1A2。我们还研究了植物化学物质对苯醌还原酶的影响，这是一种2相解毒酶，是AhR电池的一部分。在进行这项研究时，我们既在各种细胞系上进行了体外实验，也在啮齿动物身上进行了体内实验。我们研究了某些植物化学物质如何影响AhR的活性，包括它结合致癌配体和与XRE相互作用的能力。我们检测了细胞色素P1A1的转录活性，并确定了化学预防化合物对细胞色素P1A1、细胞色素P1B1和细胞色素P1A2的表达和活性的影响。我们已经研究了一些与AhR结合的环境致癌物质，例如苯并[a]芘(BP)，一种多环芳烃(PAH)，是一种存在于熟肉、香烟和工业废物副产品中的强有力的环境致癌物质。我们还检测了2，3，5，7-四氯二苯并-对二恶英(TCDD)，它是二恶英家族中的一员，也是典型的AhR配体。我们发现，许多饮食中的植物化学物质通过影响AhR来调节细胞对环境致癌物的反应。例如，我们证明了白藜芦醇抑制了通常由TCDD或BP等致癌物诱导的CYP1A1的活性和表达。它通过阻断配体激活的AhR与CYP1A1启动子的XRE的结合来实现这一点，阻止转录的上调。此外，它还通过竞争机制直接抑制酶的活性。因此，这种在大多数组织中抑制主要致癌物激活酶的双重机制为其被证实的化学预防作用提供了一种生化机制。我们还发现，AhR的活性受姜黄素、二苯甲酰甲烷、栎素、Diosmin和其他一些植物化学物质的调节。我们目前正在研究这些化合物对其他致癌机制的影响，包括调节g-谷氨酰转肽酶和端粒酶的表达。为了进一步确定植物化学物质的分子靶标，我们还利用了微阵列技术。我们还研究了非植物化学物质的其他化学预防化合物对AHR的影响。这些药物包括类固醇激素脱氢表雄酮和非类固醇消炎药舒林酸。

Numerous lines of evidence have shown that diets rich in Numerous lines of evidence have shown that diets rich in fruits and vegetables prevent or slow various types of cancers, including breast, prostate, and kidney cancers. However, the plant constituents (phytochemicals) responsible for this, and their mechanisms of action, remain to be elucidated. In this, the major project of the Section, we have examined the effect of a number of phytochemicals on various biochemical mechanisms relevant to carcinogenesis. The phytochemicals studied include the flavonoids, which are present in all fruits and vegetables. These include diosmin, from citrus fruit, quercetin, the most abundant flavonoid which is present in all dietary plants, and galangin and kaempferol, metabolites of quercetin. Other phytochemicals include the b-diketones curcumin and dibenzoylmethane, and resveratrol, a phytoalexin present in grape skins and therefore in grape juice and wine. All of these compounds have been shown to be chemopreventive in animal models of cancer, and epidemiologic studies have shown that food items containing large amounts of these compounds are associated with a reduced risk of cancer. There are many biochemical and molecular events associated with the development of cancer. One of the most important pathways is mediated by the aryl hydrocarbon receptor (AhR). The AhR is a cytoplasmic transcription factor which, upon ligand binding, translocates to the nucleus, where, with its protein partner ARNT, it interacts with the xenobiotic responsive element (XRE) present in the promoter region of a number of genes. The best characterized molecular response to ligands of the AhR is the induction of expression of cytochrome P450 1A1 (CYP1A1). CYP1A1 is a Phase 1 metabolic enzyme which activates environmental procarcinogens to their ultimate genotoxic forms. In addition to CYP1A1, the AhR controls a number of other genes, termed the "AhR battery", which affect both the activation and detoxification of carcinogens. We have concentrated on the Phase 1, or activating, enzymes, including CYP1A1, CYP1B1, and CYP1A2. We have also examined the effect phytochemicals on quinone reductase, a Phase 2, or detoxifying, enzyme, that is part of the AhR battery. In carrying out this research, we have done both in vitro experimentation in a variety of cell lines, as well as in vivo experimentation in rodents. We have examined how certain phytochemicals affect the activity of the AhR, including its ability to bind carcinogenic ligands and to interact with the XRE. We have examined the transcriptional activation of CYP1A1 and determined the effect of chemopreventive compounds on the expression and enzymatic activity of CYP1A1, CYP1B1, and CYP1A2. We have studied a number of environmental carcinogens which bind to the AhR, such as benzo[a]pyrene (BP), a polycyclic aromatic hydrocarbon (PAH) that is a potent environmental carcinogen present in cooked meat, cigarettes, and as by-products of industrial waste. We have also examined 2,3,5,7-tetrachlorodibenzo-p-dioxin(TCDD), a member of the dioxin family of potent carcinogens and the prototypical AhR ligand. We have found that many dietary phytochemicals modulate the cellular response to environmental carcinogens by affecting the AhR. For example, we demonstrated that resveratrol inhibits both the activity and expression of CYP1A1 that is normally induced by carcinogens such as TCDD or BP. It does this by blocking the binding of the ligand-activated AhR with the XRE of the CYP1A1 promoter, preventing the up-regulation of transcription. In addition, it directly inhibits enzymatic activity by a competitive mechanism. Thus, this dual mechanism of inhibiting the major carcinogen activating enzyme in most tissues provides a biochemical mechanism for its proven chemopreventive effect. We have also found that AhR activity is modulated by curcumin, dibenzoylmethane, quercetin, diosmin, and a number of other phytochemicals. We are currently investigating the effect of these compounds on other mechanisms involved in carcinogenesis, including the modulation of expression of g-glutamyltranspeptidase and telomerase. In order to identify further molecular targets of phytochemicals, we are also utilizing microarray technology. We have also examined the effects of other chemopreventive compounds which are not phytochemicals, on the AhR. These include the steroid hormone dehydroepiandrosterone and the nonsteroidal anti-inflammatant drug, sulindac.