The Role of Quinols in Estrogen Neuroprotection

描述（由申请人提供）：越来越多的证据表明，雌激素主要通过其直接的自由基清除活性抑制神经毒性刺激来表达神经保护作用。该资助申请的目的是通过关注基础化学来了解这种活性，其中该过程的分子机制以及自由基清除反应产生的产物的化学性质和命运被认为是关键要素。我们的假设中心的作用，雌激素衍生的醌醇作为特定的反应产物，其参与已牵连的初步数据。通过系统地改变酚A环化合物的2-和/或4-位上的取代基，我们应该了解苯氧基自由基（ArO*）稳定性、ArO* 在C-110位上的电子密度以及其对羟基自由基（-OH）的反应性的影响。芬顿反应，导致OH的形成，将被用作化学模型。我们推测，羟基化将涉及 * OH暴露作为一个重要的过程，产生非自由基产物的雌激素。在将用于研究通过内源性化合物的系统修饰获得的合成雌激素的命运的模型系统中，预期只有一种类型的（单）羟基化物质，即醌醇结构，通过两步羟基自由基清除机制。预计醌醇形成的速率不仅与甾体化合物的空间和电子元素相关，而且与它们的神经保护作用相关。苯酚-对苯二酚途径可能增强雌激素清除自由基的功效，并对神经保护做出关键贡献。还将研究还原性醌醇至苯酚的转化（因此，雌激素“再循环”），其防止体内可用的神经保护性雌激素的耗尽。将在体外无细胞和细胞系统中以及通过实验动物的体内微透析研究这种再活化（在动力学和A环取代基的影响方面）。将寻求支持的假设，减少醌醇是不伴随着活性氧物种的形成增加。通过使用谷氨酸诱导的氧化应激在HT 22细胞作为一个实验范例，我们将研究雌激素的酚A-环衍生物的神经保护作用。除了结构-活性关系研究之外，还将寻求化合物在-OH暴露时形成其醌醇产物的倾向与其在该模型系统中用于神经保护的有效剂量之间的相关性。预期基于机理研究和体外筛选选择的新雌激素类似物将在短暂性大脑中动脉闭塞（脑缺血模型）中显示出体内神经保护作用。因此，它们将作为新的先导化合物用于开发具有改善功效的神经保护剂。

DESCRIPTION (provided by applicant): There has been mounting evidence that estrogens express neuroprotective effects by the suppression of neurotoxic stimuli largely via their direct radical-scavenging activity. The objective of this grant application is to understand this activity by focusing on the underlying chemistry in which the molecular mechanism of the process and the chemical nature and fate of the products derived from the radical-scavenging reaction are considered the key elements. Our hypotheses center on the role of estrogen-derived quinols as specific reaction products whose involvement has been implicated by preliminary data. By systematically varying substituents in the 2- and/or 4-positions of the phenolic A-ring compounds, we should gain insight into the influence of phenoxy-radical (ArO*) stability, electron density of ArO* at the C-1i0 position and, thus, its reactivity towards hydroxyl radical (-0H). The Fenton-reaction, which leads to 0H formation, will be employed as a chemical model. We hypothesize that hydroxylation will be involved upon *0H exposure as an important process that produces non-radical products from estrogens. In the model system that will be used to study the fate of the synthetic estrogens obtained by the systematic modification of the endogenous compounds, only one type of (mono)hydroxylated species, of a quinol structure, is anticipated via a two-step hydroxyl-radical scavenging mechanism. The rate of quinol formation is expected to correlate not only with the steric and electronic elements of the steroidal compounds, but also with their neuroprotective effect. The phenol to quinol pathway may augment the estrogens' free-radical scavenging efficacy, and make a pivotal contribution to neuroprotection. A reductive quinol to phenol transformation (hence, estrogen "recycling") that prevents the depletion of the available neuroprotective estrogens in vivo will also be investigated. This reactivation (in terms of kinetics and influence by the A-ring substituents) will be studied in vitro in cell-free and cellular systems, and by in vivo microdialysis in experimental animals. Support will be sought for the hypothesis that the reduction of quinols is not accompanied by an increased formation of reactive oxygen species. By using glutamate-induced oxidative stress in HT22 cells as an experimental paradigm, we will study the neuroprotective effects of the phenolic A-ring derivatives of estrogens. In addition to structure - activity relationship studies, a correlation between the propensity of the compound to form its quinol product upon -OH exposure and its effective dose in this model system for neuroprotection will be sought. It is anticipated that the new estrogen analogs selected based on mechanistic studies and in vitro screening will show in vivo neuroprotective effects in a transient middle cerebral artery occlusion, a model for cerebral ischemia. Hence, they will serve as new lead compounds for the development of neuroprotective agents with improved efficacy.