Disposition of Flavonoids via Metabolic Interplay

描述(由申请人提供)： 众所周知，饮食中的类黄酮具有多种健康益处，从抗癌、抗氧化、抗骨质疏松症、降低胆固醇到抗衰老。然而，这些化合物的生物利用度很低，这阻碍了将它们开发为药物的努力。我们研究的长期目标是确定关键元素的协调相互作用如何决定类黄酮类化合物的整体处置，并对它们在体内的生物学命运做出贡献。本研究建议的一般假设是，通过干扰黄酮类药物处置的关键成分之间的相互作用，将提高黄酮类药物的生物利用度。我们以前的研究表明，类黄酮类化合物的关键成分是结合酶(即磺基转移酶和UDP-葡萄糖醛酸基转移酶)和外排转运体(例如BCRP和MRP2)。我们以前的研究也表明，黄酮类化合物经历了肠道和肠道-肝脏的双重循环过程，这增加了它们在体内的结合浓度和明显的生物半衰期。结合形式的黄酮类化合物可能是生物可利用的，因为结合的黄酮类化合物被葡萄糖醛酸酶和硫酸酯酶局部和系统地水解为苷元是向靶器官提供苷元的一种可行的方法。因此，这一假说超越了经典假说，即如果苷元AUC增加，生物利用度就会增加。这也是对我们最初的假设的一步，即识别和抑制处置过程中的一个关键元素将导致更高的生物利用度，当我们专注于确定相关的酶亚型时，我们发现这是不正确的。然而，我们确实发现染料木素在BCRP-/-(基因敲除)小鼠中的生物利用度提高，尽管我们也观察到sULT活性的下降。这项持续提案的具体目的是：(1)确定负责选定的黄酮类化合物代谢的关键UGT和SULT异构体，以及负责黄酮类化合物II相结合物排泄的关键外流转运体；(2)确定目标1中确定的关键UGT和相关关键外流转运体如何弥补彼此的功能缺陷；(3)确定目标1中确定的关键硫化物和相关关键外流转运体如何弥补彼此的功能缺陷；以及(4)确定葡萄糖醛酸化和硫酸盐化途径如何弥补彼此的功能缺陷。通过这些新的研究，我们试图确定如何有效地中断类黄酮代谢的关键成分之间的相互作用，以提高它们的局部和系统生物利用度。拟议研究的成功应该会导致开发对人类具有更高生物利用度的剂型。 公共卫生相关性： 基于使用人类细胞的体外研究和使用动物模型的体内研究，类黄酮类化合物已被证明具有多种有益效果。然而，目前还没有明确的临床数据来证明这类化合物对人类的有效性。黄酮类最终临床研究的一个主要障碍在于，临床试验昂贵(由于黄酮类化合物的生物利用度较低)，而且没有可吸引私人资本进行临床试验的专利剂型。拟议的基础机制研究应有助于开发生物利用度更高的新剂型，并从长远来看有利于美国人的健康。

DESCRIPTION (provided by applicant): Dietary flavonoids are known to have a variety of health benefits, ranging from anticancer, antioxidant, antiosteoperosis and cholesterol lowering to anti-aging. However, these compounds are poorly bioavailable which impedes the effort to develop them as drugs. The long-term goal of our study is to determine how coordinated interplay of key elements determines the overall disposition of flavonoids and contributes to their biological fate in vivo. The general hypothesis for the present research proposal is that the flavonoid bioavailability will be improved by interrupting interplays between key components of their disposition. Our previous research has shown that key components of flavonoid disposition are conjugating enzymes (i.e., sulfotransferases and UDP-glucuronosyltransferases) and efflux transporters (e.g., BCRP and MRP2). Our previous research also showed that flavonoids undergo the dual enteric and enterohepatic recycling processes, which increase their conjugate concentrations and apparent biological half- lives in vivo. The conjugated form of flavonoids may be bioavailable since local and systemic hydrolysis of conjugated flavonoids to aglycones by glucuronidases and sulfatases is a viable means of providing aglycone to target organs. Therefore, this present hypothesis is a step beyond the classical hypothesis that bioavailabilities are increased if aglycone AUC is increased. It is also a step beyond our original hypothesis that identification and inhibition of one key element in the disposition processes will lead to higher bioavailabilities, which we found to be untrue when we focused on identifying the enzyme isoform responsible. However, we did find that bioavailability of genistein improved in BCRP-/- (knockout) mice, although we observed a decrease in SULT activities as well. The Specific Aims of this continuing proposal are to: (1) determine the key UGT and SULT isoforms responsible for the metabolism of selected flavonoids, and key efflux transporters responsible for the excretion of phase II conjugates of flavonoids; (2) determine how key UGTs and relevant key efflux transporters identified in aim 1 compensate for each other's functional deficiency; (3) determine how key SULTs and relevant key efflux transporters identified in aim 1 compensate for each other's functional deficiency; and (4) determine how glucuronidation and sulfation pathways will compensate for each other's functional deficiency. Through these new studies, we seek to determine how interplay between key components of flavonoid metabolism can be effectively interrupted to improve their local and systematic bioavailabilities. The success of the proposed studies should lead to the development of dosage forms with improved bioavailability for humans. PUBLIC HEALTH RELEVANCE: Flavonoids have been shown to have a variety of beneficial effects based on in vitro studies using human cells and in vivo studies using animal models. However, there are no definitive clinical data to prove the effectiveness of this class of compounds in humans. A major impediment to definitive clinical studies of flavonoids lies with the facts that clinical trials are expensive (as the result of flavonoid's poor bioavailability) and there is no patentable dosage form that will attract private capital to enable the clinical trials. The proposed basic mechanistic studies should facilitate the development of new dosage forms with improved bioavailability, and benefit the health of American in the long run.