Disposition of Flavonoids via Metabolic Interplay

描述（由申请人提供）： 众所周知，膳食类黄酮具有多种健康益处，从抗癌、抗氧化、抗骨质疏松和降低胆固醇到抗衰老。然而，这些化合物的生物利用度差，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黄酮类化合物的总体分布，并有助于它们在体内的生物命运。本研究建议的一般假设是，类黄酮的生物利用度将通过中断其处置的关键成分之间的相互作用来提高。我们以前的研究表明，类黄酮处置的关键组分是缀合酶（即，磺基转移酶和UDP-葡萄糖醛酸基转移酶）和外排转运蛋白（例如，BCRP和MRP 2）。我们以前的研究也表明黄酮类化合物经历肠和肝肠的双重循环过程，这增加了它们的结合物浓度和体内表观生物半衰期。类黄酮的缀合形式可以是生物可利用的，因为通过葡糖醛酸苷酶和硫酸酯酶将缀合类黄酮局部和全身水解为糖苷配基是向靶器官提供糖苷配基的可行手段。因此，本假设超越了经典假设，即如果糖苷配基AUC增加，则生物利用度增加。这也超出了我们最初的假设，即识别和抑制处置过程中的一个关键因素将导致更高的生物利用度，当我们专注于识别负责的酶亚型时，我们发现这是不真实的。然而，我们确实发现染料木黄酮在BCRP-/-（敲除）小鼠中的生物利用度提高，尽管我们也观察到SULT活性降低。该持续提案的具体目的是：（1）确定负责所选类黄酮代谢的关键UGT和SULT亚型，以及负责类黄酮II相缀合物排泄的关键外排转运蛋白;（2）确定目标1中鉴定的关键UGT和相关关键外排转运蛋白如何补偿彼此的功能缺陷;（3）确定目标1中确定的关键SULT和相关关键外排转运蛋白如何补偿彼此的功能缺陷;（4）确定葡萄糖醛酸化和硫酸化途径如何补偿彼此的功能缺陷。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组分之间的相互作用，以提高其局部和系统的生物利用度。拟议研究的成功应导致开发具有改善的人类生物利用度的剂型。 公共卫生相关性： 基于使用人细胞的体外研究和使用动物模型的体内研究，已显示黄酮类化合物具有多种有益效果。然而，没有明确的临床数据来证明这类化合物在人类中的有效性。对类黄酮进行确定性临床研究的一个主要障碍在于临床试验费用昂贵（由于类黄酮的生物利用度低），并且没有可专利的剂型可以吸引私人资本进行临床试验。这些基础机制研究将有助于开发生物利用度更高的新剂型，并从长远来看有益于美国人的健康。

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.