Centro de Ciências Naturais e Exatas, Departamento de Química, Universidade Federal de Santa Maria, Santa Maria, RS 97105-900, Brazil.
Arch Toxicol. 2010 Feb;84(2):89-97. doi: 10.1007/s00204-009-0482-3. Epub 2009 Nov 10.
The hypothesis that methylmercury (MeHg) potently induces formation of reactive oxygen species (ROS) in the brain is supported by observations on the neuroprotective effects of various classes of antioxidants. Flavonoids have been reported to possess divalent metal chelating properties, antioxidant activities and to readily permeate the blood-brain barrier. They can also provide neuroprotection in a wide array of cellular and animal models of neurological diseases. Paradoxically, in vivo administration of quercetin displays unexpected synergistic neurotoxic effect with MeHg. Considering this controversy and the limited data on the interaction of MeHg with other flavonoids, the potential protective effect of quercetin and two of its glycoside analogs (i.e., rutin and quercitrin) against MeHg toxicity were evaluated in rat cortical brain slices. MeHg (100 microM) caused lipid peroxidation and ROS generation. Quercitrin (10 microg/mL) and quercetin (10 microg/mL) protected mitochondria from MeHg (5 microM)-induced changes. In contrast, rutin did not afford a significant protective effect against MeHg (100 microM)-induced lipid peroxidation and ROS production in cortical brain slices. MeHg-generated ROS in cortical slices was dependent upon an increase in intracellular Ca(2+) levels, because the over-production of MeHg-induced H(2)O(2) in mitochondria occurred with a concomitant increase in Ca(2+) transient. Here, we have extended the characterization of mechanisms associated with the neuroprotective effects of quercetin against MeHg-induced toxicity in isolated mitochondria, by performing an array of parallel studies in brain slices. We provide novel data establishing that (1) Ca(2+) plays a central role in MeHg toxicity and (2) in brain slices MeHg induces mitochondrial oxidative stress both via direct interaction with mitochondria (as previously reported in in vitro studies) as well as via mitochondria-independent (or indirect) mechanisms.
该假说认为，甲基汞（MeHg）在大脑中强烈诱导活性氧（ROS）的形成，这一假说得到了各种抗氧化剂类别的神经保护作用的观察结果的支持。类黄酮已被报道具有二价金属螯合特性、抗氧化活性，并且容易穿透血脑屏障。它们还可以在广泛的细胞和动物神经疾病模型中提供神经保护作用。矛盾的是，槲皮素在体内给药时与 MeHg 表现出出乎意料的协同神经毒性作用。考虑到这一争议以及关于 MeHg 与其他类黄酮相互作用的有限数据，我们评估了槲皮素及其两种糖苷类似物（即芦丁和槲皮苷）对 MeHg 毒性的潜在保护作用在大鼠皮质脑片中。MeHg（100 microM）引起脂质过氧化和 ROS 生成。槲皮苷（10 μg/mL）和槲皮素（10 μg/mL）保护线粒体免受 MeHg（5 microM）诱导的变化。相比之下，芦丁对皮质脑片中 MeHg（100 microM）诱导的脂质过氧化和 ROS 产生没有显著的保护作用。皮质切片中 MeHg 产生的 ROS 依赖于细胞内 Ca(2+)水平的增加，因为 MeHg 诱导的 H(2)O(2)在线粒体中的过度产生伴随着 Ca(2+)瞬变的增加。在这里，我们通过在脑片中进行一系列平行研究，扩展了槲皮素对 MeHg 诱导的毒性的神经保护作用相关机制的特征描述。我们提供了新的数据，证明（1）Ca(2+)在 MeHg 毒性中起核心作用，（2）在脑片中，MeHg 通过直接与线粒体相互作用（如先前在体外研究中报道的）以及通过线粒体独立（或间接）机制诱导线粒体氧化应激。
