Reactive Intermediates of Oxidative Lipid Fragmentation

描述(由申请人提供)：该项目的总体目标是为合理设计治疗措施提供一个基本的机械基础，以防止或改善脂质氧化的病理后果，例如通过阻止某些有毒产品的形成来损害视网膜，导致老年性黄斑变性。目前的目标是了解多不饱和脂肪酰基衍生物的氧化裂解反应，这些反应产生氧化截断的磷脂和脂类片段的复杂混合物。这些裂解产物表现出不同的、往往是病理性的生物活性。特别令人感兴趣的是诱变环氧烯类化合物和细胞毒性羟基烯类化合物的生产。了解参与其生成的活性中间体的化学知识对于了解环境或遗传因素如何促进它们的形成是重要的。例如，我们鉴定的所有中间体都需要在生物条件下进行催化活性金属离子的碎裂。我们尚未研究的一种中间体被认为是自发断裂的，不需要催化。然而，这些中间体还没有得到彻底的表征。我们将通过化学合成来制备纯的、表征良好的样品。如果我们证实了我们的假设，即这些中间体也需要金属离子催化，那么一种治疗策略将是去除或解毒这些金属离子。了解初级裂解产物在生物条件下发生的进一步转化是重要的，包括氧化、脱酰和蛋白质加成，因为这些过程产生具有生物活性的次级产物。例如，我们已经证明，从二十二碳六烯酸衍生的羟基烯醛磷脂的蛋白质加合物启动黄斑变性，并促进毛细血管病理性地发芽进入视网膜。该项目重点研究在氧化裂解反应条件下不稳定的关键中间体。讨论了三个基本问题：(1)假定的中间体是否确实参与其中，如果是，(2)它们的分解产生了什么产物，(3)它们是通过什么机制(S)分解的？在某些情况下，它们将被困为稳定的衍生品，以确认它们参与其中。为了提供大量的活性中间体，明确的全合成被设计和执行。真实样品被用作建立检测和量化氧化反应产物混合物中中间体水平的方法的标准。正在对它们的产生和转化为有毒或无害的最终产品进行调查。我们正在确定(1)环境的影响，例如在不同细胞器中发现的环境或与病理条件有关的环境，(2)辅助因子的水平，或(3)氧化启动系统和抑制剂，对活性中间体的产生以及对其后续转化的各种途径的相对重要性的影响。 与公共健康相关：磷脂是人体组织的主要组成部分，会被产生有毒的氧气碎片攻击和分解。例如，其中一些碎片会修改视网膜中的蛋白质，导致免疫系统攻击并摧毁视网膜。为了为治疗策略的设计提供合理的基础，该项目将确切地确定这种磷脂的氧化碎裂是如何发生的，这些碎片是什么，以及它们的毒性涉及哪些化学反应。

DESCRIPTION (provided by applicant): The overall objective of the project is to provide a fundamental mechanistic basis for the rational design of therapeutic measures to prevent or ameliorate the pathological consequences of lipid oxidation, for example, by blocking the formation of certain toxic products that damage the retina resulting in age-related macular degeneration. The immediate goal is to understand oxidative fragmentation reactions of polyunsaturated fatty acyl derivatives that generate a complex mixture of oxidatively truncated phospholipids and aliphatic lipid fragments. These fragmentation products exhibit diverse and often pathological biological activities. Of particular interest is the production of mutagenic epoxyalkenals and cytotoxic hydroxyalkenals. Knowledge of the chemistry of the reactive intermediates involved in their generation is important for understanding how environmental or genetic factors can promote their formation. For example, all of the intermediates that we have identified require catalytically active metal ions to undergo fragmentation under biological conditions. One type of intermediate that we have yet to study is believed to spontaneously fragment, without the need for catalysis. However, such intermediates have not been thoroughly characterized. We will prepare pure well characterized samples by chemical synthesis. If we confirm our hypothesis that metal ion catalysis is also required for such intermediates, then one therapeutic strategy would be to remove or detoxify such metal ions. Knowledge of the further transformations of the primary fragmentation products that occur under biological conditions, including oxidation, deacylation, and protein adduction is important because these processes produce biologically active secondary products. For example, we have shown that the protein adducts of hydroxyalkenal phospholipids derived from docosahexaenoic acid initiate macular degeneration and also promote the pathological sprouting of capillaries into the retina. The project focuses on studying key intermediates that are not stable under the oxidative fragmentation reaction conditions. Three basic questions are being addressed: (1) are the putative intermediates actually involved, and if so (2) what products are generated by their decomposition and (3) by what mechanism(s) do they fragment? In some cases, they will be trapped as stable derivatives to confirm their involvement. To provide ample quantities of some reactive intermediates, unambiguous total syntheses are designed and executed. The authentic samples are being used as standards for establishing methods for detecting and quantifying levels of the intermediates in oxidation reaction product mixtures. Their generation and conversion into toxic or innocuous end products is being investigated. We are determining the influences of (1) environments such as those found in different organelles or associated with pathological conditions, (2) levels of cofactors, or (3) oxidation initiating systems and inhibitors, on the production of the reactive intermediates and on the relative importance of various pathways for their subsequent transformations. PUBLIC HEALTH RELEVANCE: Phospholipids, major building blocks human tissue, are attacked and broken apart by oxygen producing fragments that can be toxic. For example, some of these fragments modify proteins in the retina causing the immune system to attack and destroy the retina. To provide a rational basis for the design of therapeutic strategies, this project will determine exactly how such oxidative fragmentation of phospholipids occurs, what the pieces are, and what are some of the chemical reactions involved in their toxicity.