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基本的机制基础，以预防或改善脂质氧化的病理后果，例如，通过阻断某些损害视网膜的毒性产物的形成，从而导致年龄相关性黄斑变性。当前的目标是了解多不饱和脂肪酰基衍生物的氧化断裂反应，产生氧化截断磷脂和脂肪族脂质片段的复杂混合物。这些片段化产物表现出多种多样的且常常是病理性的生物活性。特别令人感兴趣的是产生诱变性环氧烯醛和细胞毒性羟基烯醛。了解其生成过程中所涉及的活性中间体的化学性质对于了解环境或遗传因素如何促进其形成非常重要。例如，我们已经确定的所有中间体都需要催化活性金属离子在生物条件下进行断裂。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，这样的中间体尚未被彻底表征。我们将通过化学合成制备纯的表征良好的样品。如果我们证实了我们的假设，即金属离子催化也需要这样的中间体，那么一种治疗策略将是去除或解毒这样的金属离子。了解在生物条件下发生的初级片段化产物的进一步转化，包括氧化、脱酰和蛋白质加合，是很重要的，因为这些过程产生具有生物活性的次级产物。例如，我们已经表明，来自二十二碳六烯酸的羟基烯醛磷脂的蛋白加合物引发黄斑变性，并且还促进毛细血管的病理性发芽进入视网膜。该项目的重点是研究在氧化裂解反应条件下不稳定的关键中间体。三个基本的问题正在解决：（1）假定的中间体实际上涉及，如果是这样的话，（2）什么产品是由他们的分解和（3）通过什么机制（S）他们的碎片？在某些情况下，它们将被困为稳定的衍生品，以确认它们的参与。为了提供足够数量的一些活性中间体，设计并执行明确的全合成。真实样品被用作标准品，用于建立检测和定量氧化反应产物混合物中中间体水平的方法。目前正在调查这些物质的产生和转化为有毒或无害的最终产品的情况。我们正在确定（1）环境，如在不同细胞器中发现的或与病理条件相关的环境，（2）辅因子水平，或（3）氧化引发系统和抑制剂对活性中间体产生的影响，以及对各种途径的相对重要性。 公共卫生相关性：磷脂是人体组织的主要组成部分，它会受到氧气的攻击，并被分解成有毒的碎片。例如，这些片段中的一些修饰视网膜中的蛋白质，导致免疫系统攻击并破坏视网膜。为了为治疗策略的设计提供合理的基础，该项目将确定磷脂的氧化断裂是如何发生的，碎片是什么，以及参与其毒性的一些化学反应是什么。

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.