BRAIN OXIDATIVE STRESS--A SIGN OF AGING OR EMINENT DEATH

据报道，脑氧化应激在衰老及衰老相关神经退行性疾病的发生过程中起着重要作用。然而，使用传统的标记物，研究产生了关于老年动物大脑氧化损伤水平的相互矛盾的数据。本研究的目的是利用反映不同脑区和细胞类型的不同贡献的新的敏感标记物，进一步研究大脑氧化应激与衰老的关系。最近，花生四烯酸和二十二碳六烯酸的非酶氧化产物F2-异前列腺素和F4-神经前列腺素分别被确定为氧化损伤的新的敏感标志物。初步数据显示，在所有被研究的动物组(4、10、50和100周龄的雄性Fischer 344只大鼠)中，只有一组50周龄的大鼠(8只中有4只)表现出高水平的脑神经前列腺素水平。根据这些数据，我们假设大脑氧化损伤与死亡有关，而不是与衰老有关。支持这一假设的事实是，在50%的研究动物中观察到的高脑神经前列腺素水平与该菌株在这个年龄段报告的死亡率相同，100周龄大鼠的平均脑神经前列腺素水平显著低于50周龄大鼠组。我们的假设将通过追求以下特定目标来验证：(1)确认不同年龄的雄性Fischer 344大鼠中高水平脑神经前列腺素的确切发生率，(2)确定与传统标志物相比，异前列腺素和神经前列腺素是否是更准确和更灵敏的大脑“氧化状态”指标，以及(3)确定大脑中氧化应激介质的来源。游离和酯化的脑内异前列腺素和神经前列腺素将通过质谱学进行定量。脑部常规氧化标记物的水平以及抗氧化酶活性将通过既定的生化方法进行评估。由于异前列腺素和神经前列腺素的前体花生四烯酸和二十二碳六烯酸的水平在大脑不同区域(白质和灰质)以及不同细胞类型(神经元、星形胶质细胞、少突胶质细胞)和亚细胞部分(髓鞘、突触体)之间存在显著差异，这两种标志物可能有助于定位暴露于氧化损伤的脑区和/或细胞类型。此外，证实大脑氧化应激发生在生命中的时间比之前报道的更早，这表明衰老的动物确实可能来自中年组中抗氧化损伤的亚群。因此，这种情况的早期诊断可能提供了进行干预以减缓或阻止神经元退化和老化的机会。

Brain oxidative stress is reported to play an important role in the process of aging and aging-related neurodegenerative diseases. Using conventional markers however, studies have produced conflicting data concerning the level of brain oxidative injury in aged animals. The purpose of this study is to further investigate the relationship between brain oxidative stress and aging, using novel sensitive markers which reflect differential contribution of various brain regions and cell types. Recently, F2-isoprostanes and F4-neuroprostanes, nonenzymatic oxidative products of arachidonic and docosahexaenoic acids, respectively, have been identified as novel and sensitive markers of oxidative injury. Preliminary data show that among all animal groups studied (Male Fischer 344 rats of 4,10,50, and 100 weeks old), only a subpopulation (4 out of 8) of 50 week old rats exhibited high brain neuroprostane levels. Based on these data, we hypothesize that brain oxidative damage is linked to death than to aging. This hypothesis is supported by the fact that the incidence of high brain neuroprostanes observed in 50 percent of studied animals is identical to the death rates reported for this strain at this age, and that mean brain neuroprostane levels were significantly lower in the 100 week old rats, compared with the 50 week old rat group. Our hypothesis will be tested by pursuing the following specific aims: (1) Confirm the exact incidence of high brain neuroprostane levels among male Fischer 344 rats of various ages, (2) Establish whether isoprostanes and neuroprostanes are more accurate and sensitive indicators, compared with conventional markers, of brain "oxidative status", and (3) Localize sources of oxidative stress mediators in the brain. Free and esterified brain isoprostanes and neuroprostanes will be quantified by mass spectroscopy. Levels of brain conventional oxidative markers as well as antioxidant enzyme activities will be assessed by established biochemical methods. Since the levels of arachidonic and docosahexaenoic acids, the precursors of isoprostanes and neuroprostanes, respectively, vary significantly between different regions of the brain (white vs gray matter), as well as among different cell types (neurones, astrocytes, oligodendrocytes) and subcellular fractions (myelin, synaptosomes), these two markers may help localize brain region and/or cell types exposed to oxidative injury. Furthermore, confirming that brain oxidative stress occurs earlier in life than previously reported would suggest that senescent animals may indeed arise from an oxidative damage-resistant subpopulation of the middle age group. Consequently, early diagnosis of this condition may present the opportunity to intervene to slow or halt neuronal degeneration and aging.