Xenobiotic Transporter Regulation and IRIP Function

描述（由申请人提供）：外源转运体在药物处置和反应中起关键作用。在公认的例子中，有机阳离子转运体1 （OCT1）已被我们证明是二甲双胍治疗反应的关键决定因素，二甲双胍是美国十大处方药之一。尽管具有临床意义，但许多外源转运蛋白，特别是包括OCT1在内的摄取转运蛋白，在其调控方面的特征尚不明确。最近发现的缺血/再灌注诱导蛋白（IRIP）在体外调节多种转运蛋白，介导内源性代谢物和外源物的膜运输。因此，IRIP可能代表了转运体活性的一种新的调节机制，对临床药物治疗有重大影响，研究非常有必要描述目前尚不清楚的IRIP在体内的功能。我们令人兴奋的初步结果表明，在服用二甲双胍的小鼠中，肝脏中IRIP的过表达与肝脏中二甲双胍积累的显著减少有关。我们还观察到肥胖小鼠和内毒素脂多糖（LPS）小鼠肝脏中二甲双胍积累和IRIP表达的改变。利用基因靶向，我们已经产生了一个敲入小鼠品系，可用于产生全局和条件IRIP敲除小鼠。这些敲除小鼠，以及我们建立的细胞模型和基因传递技术，提供了一个强大的系统来验证我们的中心假设，即IRIP表达影响临床重要药物的处置和反应，这些药物是由IRIP调节的外源转运体的底物。我们提出了三个具体的研究目标。在Aim 1中，通过在细胞模型中使用遗传操作和模型化合物，我们将在蛋白质活性，细胞和分子水平上描述IRIP转运体调控的机制。

DESCRIPTION (provided by applicant): Xenobiotic transporters play a critical role in drug disposition and response. Among recognized examples, the organic cation transporter 1 (OCT1) has been demonstrated by us as a key determinant of the therapeutic response to metformin, one of top ten prescription drugs in the United States. Despite their clinical significance, many xenobiotic transporters, particularly those uptake transporters including OCT1, are poorly characterized in their regulation. The recently identified ischemia/reperfusion-inducible protein (IRIP) regulates a variety of transporters in vitro mediating membrane transport of endogenous metabolites and xenobiotics. Therefore, IRIP may represent a novel regulatory mechanism for transporter activity with a substantial effect on clinical drug therapy, and studies are highly warranted to characterize the, as of yet unknown, IRIP function in the body. Our exciting preliminary results indicate that hepatic overexpression of IRIP is associated with a strikingly reduced hepatic accumulation of metformin in the mice administrated with the drug. We also observed altered metformin accumulation and IRIP expression in the livers of obese mice and those received the endotoxin lipopolysaccharide (LPS). Using gene targeting, we have generated a knockin mouse strain that can be used to generate global and conditional IRIP knockout mice. These knockout mice, along with our established cell models and gene delivery techniques, provide a powerful system to test our central hypothesis that IRIP expression affects the disposition and response of clinically important drugs which are substrates of the xenobiotic transporters regulated by IRIP. We propose three specific research aims. In Aim 1, by using genetic manipulation and model compounds in cell models, we will delineate the mechanism of transporter regulation by IRIP at the protein activity, cellular and molecular levels. In Aim 2, we will determine how liver- specific and ubiquitous alteration in IRIP expression affects transporter function and metformin disposition. Hepatic conditional IRIP knockout (mIRIP?hep) mice, hepatic IRIP overexpression (mIRIP+hep), global IRIP knockout (mIRIP-/-), and their corresponding control mice will be employed to perform the studies in Aim 2. In addition, as transporter activities and drug disposition are significantly changed during pathophysiological conditions, in Aim 3 we will use the mouse and in vitro cellular models to define the role of IRIP in regulation of drug disposition during fatty liver disease, lipopolysaccharide-induced endotoxemia and ischemia/ reperfusion injury. The proposed research will characterize the first function of mammalian IRIP in the body. The results will significantly aid in our understanding of xenobiotic transporter regulation and provide a target for improvement of drug efficacy and avoidance of drug side effects for patients.