Porphyrin biosynthesis in normal and disease states

正常和疾病状态下的卟啉生物合成

• 批准号: 7891080
• 负责人: JAMES P KUSHNER
• 金额: $ 8.7万
• 依托单位: UNIVERSITY OF UTAH
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-17 至 2010-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7891080
• 关键词: Address; Alcohol abuse; Animals; Bacteria; Binding; Biopsy Specimen; Blood; Carbon; Complex; Crystallization; Cytochrome P450; Decarboxylation; Disease; Embryo; Enzyme Inhibitor Drugs; Enzyme Inhibitors; Enzymes; Estrogens; Face; Fibroblasts; Gene Expression Profiling; Generations; Genetic; Genetic Polymorphism; Heme; Hepatic; Hepatitis C; Hormones; Human; In Vitro; Incidence; Iron; Iron Overload; Light; Liver; Measures; Mediating; Methods; Modeling; Molecular; Mus; Mutation; Palladium; Pathogenesis; Patients; Phenotype; Porphyria Cutanea Tarda; Porphyrias; Porphyrins; Pyrroles; Reaction; Relative (related person); Risk Factors; Role; Serum; Siderosis; Skin; Stream; Structure; System; Testing; Tetrapyrroles; The Sun; Uroporphyrinogen Decarboxylase; Uroporphyrinogens; Uroporphyrins; Yeasts; enzyme activity; enzyme mechanism; hepcidin; hydroxymethylbilane; inhibitor/antagonist; liver biopsy; mouse model; mutant; novel; oxidation; particle; porphyrin biosynthesis; protonation; public health relevance; research study

DESCRIPTION (provided by applicant): Porphyria cutanea tarda (PCT), the most common form of porphyria in humans, is associated with excess liver iron stores, alcohol abuse, hepatitis C and medicinal estrogen use. PCT is due to a reduction in the specific activity of the heme biosynthetic enzyme uroporphyrinogen decarboxylase (URO-D) in the liver. We have determined that impaired catalytic activity of URO-D is caused by a competitive inhibitor designated uroporphomethene, an octacarboxylic tetrapyrrole macrocycle with a single oxidized bridge carbon between two of the pyrrole rings. Oxidation of the bridge carbon is mediated by P450 and iron dependent reactions. Our first specific aim is to determine if the porphomethene is generated by oxidation of hydroxymethyl bilane which then cyclizes non- enzymatically or by oxidation of uroporphyrinogen, the fully reduced substrate of URO-D. We will test the hypothesis that specific P450s and iron are required to generate the porphomethene by transfecting wild type and mutant yeast with functional human P450 systems and by altering cytosolic iron concentrations. Our second specific aim will utilize a structural approach to define the mechanism of porphomethene mediated inhibition and to confirm our model of the URO-D reaction. Our third specific aim will address the cause of iron loading in PCT. We will test the hypothesis that suppression of hepcidin expression is responsible for the excess liver iron stores. Collectively, these studies will define the molecular mechanisms involved in the pathogenesis of PCT and explain the relative rarity of PCT in face of the high incidence of disease associated risk factors. PUBLIC HEALTH RELEVANCE: Porphyria cutanea tarda (PCT) is characterized by accumulation in the liver of a compound that moves through the blood stream to the skin. The compound, called uroporphyrin, absorbs light from the sun and liberates energy particles that damage the skin. The disease is due to deficient activity of an enzyme in the liver. We have determined that deficient enzyme activity is caused by an inhibitor generated when excess iron is present in the liver. Many patients with PCT have liver damage from alcohol abuse, hepatitis C or from use of certain hormones. We propose to determine how environmental and genetic factors combine to allow the enzyme inhibitor to develop.

描述(申请人提供)：迟发性皮肤卟啉病(PCT)是人类最常见的一种卟啉病，与肝脏铁储备过多、酗酒、丙型肝炎和药物雌激素的使用有关。PCT是由于肝脏中的血红素生物合成酶尿卟啉原脱羧酶(Uro-D)的比活性降低所致。我们已经确定，Uro-D的催化活性减弱是由一种名为尿膦甲烷的竞争性抑制剂引起的，这是一种八碳酸四吡咯大环，在两个吡咯环之间有一个氧化的桥碳。桥碳的氧化是由P450和铁依赖的反应介导的。我们的第一个具体目标是确定卟啉是由羟甲基丙烷氧化生成的，然后羟甲基丙烷在非酶条件下环化，还是通过尿卟啉原氧化生成，尿卟啉原是尿素-D的完全还原底物。我们将通过将具有功能的人类P450系统导入野生型和突变酵母，并通过改变胞液中铁的浓度来检验这一假设，即特定的P450和铁是产生卟甲烷所必需的。我们的第二个具体目标将利用结构方法来定义卟啉介导的抑制机制，并确认我们的Uro-D反应模型。我们的第三个具体目标将解决PCT中铁负荷的原因。我们将检验这一假说，即抑制海普西丁的表达是导致肝脏铁储存过剩的原因。总而言之，这些研究将确定PCT发病的分子机制，并解释PCT在疾病相关危险因素高发的情况下相对罕见的原因。与公共卫生相关：迟发性皮肤卟啉病(PCT)的特征是一种化合物在肝脏中积聚，该化合物通过血液流向皮肤。这种名为尿卟啉的化合物能吸收太阳光，并释放出损害皮肤的能量粒子。这种疾病是由于肝脏中一种酶的活性不足所致。我们已经确定，酶活性不足是由肝脏中存在过量铁时产生的一种抑制物引起的。许多PCT患者因酗酒、丙型肝炎或使用某些激素而导致肝脏损伤。我们建议确定环境和遗传因素如何结合起来允许酶抑制剂的发展。