ANTIOXIDANT MODULATION OF FREE RADICAL GENERATION IN CIRRHOSIS

本研究明确了氧化剂损伤在介导酒精摄入和病毒感染引起的肝损伤中所起的作用，并确定抗氧化剂维生素是否调节这一作用。具体地说，我利用了一种最近表征的方法来定量评估体内自由基的产生--测量异前列腺素--来解决这样的假设，即自由基(FR)的产生发生在酒精诱导的肝损伤的公开模型中，并被抗氧化剂维生素的摄入抑制。我将这一体内生成FRS的标记物与已建立的体外氧化损伤检测方法--共轭双烯的测定--进行了比较。此外，我还探讨了血栓素A(2)介导的血管收缩导致肝脏损伤加重的理论，即尽管给予阿司匹林减少了酶促产生的血栓素A2的代谢产物，但异前列腺素的排泄没有变化。我们最近发现，与年龄和性别匹配的健康对照组相比，酒精诱导的肝病和丙型肝炎诱导的肝硬变患者的氧化应激水平都有所增加，这是通过尿8-epi PGF(2a)的形成来衡量的。8-epi PGF(2a)生物合成增加的来源尚不清楚。传统上，人们认为酗酒者的饮食缺乏抗氧化性维生素。这项研究探讨了抗氧化剂维生素对已确诊的肝硬变患者氧化损伤标记物的影响。供肝血管收缩导致肝内缺氧被认为是酒精性肝病的发病机制之一。其他研究人员提出，血栓烷通过血栓烷/PGH2受体发挥作用，通过引起血管收缩来促进酒精喂养的大鼠的肝脏损伤。我测量了同一组确诊肝病患者服用阿司匹林前后的11-脱氢TxB2水平，这是血栓素A2的尿液代谢物。自由基是在酶的更替过程中产生的，细胞色素P450亚型--细胞色素P450亚型--细胞色素P450-1的诱导被认为是饮酒过程中产生细胞色素P450的一个来源。类似地，FRS可能是细胞刺激时酶激活的副产物。血小板和中性粒细胞的激活是肝硬变的一个特征，两者都可能导致FR的产生。8-epi PGF(2a)除了由自由基催化生成外，还可能是环氧合酶周转的次要产物。这项研究提出的假设是，这一途径对化合物在体内的整体生物合成没有影响，因为在既往的肝病患者中，服用环氧合酶抑制剂阿司匹林后，尿8-epi PGF(2a)排泄或共轭二烯的形成没有改变。

This study defines the role oxidant injury plays in mediating hepatic injury caused by alcohol ingestion and viral infection, and to determine whether antioxidant vitamins modulate this effect. Specifically, I took advantage of a recently characterized approach to the quantitative assessment of free radical generation in vivo - measurement of isoprostanes - to address the hypothesis that free radical(FR) generation occurs in overt models of alcohol induced liver injury and is suppressed by antioxidant vitamin intake. I compared this marker of in vivo generation of FRs with an established ex vivo assay of oxidative injury - measurement of conjugated dienes. In addition, I explored the theory that vasoconstriction mediated by thromboxane A(2) results in exacerbation of hepatic injury and that while the enzymatically produced metabolite of thromboxane A2 is reduced by aspirin administration there is no alteration in isoprostane excretion. We have recently shown that patients with both alcohol induced liver disease and hepatitis C induced cirrhosis have increased levels of oxidative stress as measured by urinary 8-epi PGF(2a) formation when compared with age and gender matched healthy controls. The source of the increased 8-epi PGF(2a) biosynthesis is unclear. Alcoholics are traditionally thought to consume a diet deficient in antioxidant vitamins. This study addressed the effect of antioxidant vitamin administration on this marker of oxidative injury in patients with established cirrhosis. Vasoconstriction of blood vessels supplying the liver leading to intrahepatic hypoxia has been proposed as one mechanism involved in the pathogenesis of alcoholic liver disease. Other investigators have proposed that thromboxanes acting via the thromboxane/ PGH2 receptors, promote liver injury in the ethanol fed rats by causing vasoconstriction. I measured levels of 11 - dehydro - TxB2, the urinary metabolite of thromboxane A2 in the same group of patients with established liver disease both before and after dosing with aspirin. Free radicals are generated during enzyme turnover and the induction of the cytochrome P450 isoform, CYP2E1, has been implicated as a source of FR generation during alcohol consumption. Similarly, FRs may be generated as a byproduct of enzyme activation upon cellular stimulation. Activation of platelets and neutrophils is a feature of cirrhosis and both may result in FR generation. Additional to its generation by a free radical catalyzed process, 8-epi PGF(2a) may also be formed as a minor product of cyclooxygenase turnover. This study addresses the hypothesis that this pathway contributes trivially to overall biosynthesis of the compound in vivo by showing no alteration in urinary 8-epi PGF(2a) excretion or conjugated diene formation following the administration of aspirin, a cyclooxygenase inhibitor, to patients with established liver disease.