Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PE, C1A 4P3, Canada; Department of Veterinary Obstetrics and Reproductive Diseases. Faculty of Veterinary Medicine, University of Nigeria, Nsukka, Nigeria.
Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PE, C1A 4P3, Canada.
Free Radic Biol Med. 2021 Feb 20;164:439-456. doi: 10.1016/j.freeradbiomed.2020.12.234. Epub 2020 Dec 28.
Oxygen (O) deprivation and metals are common environmental stressors and their exposure to aquatic organisms can induce oxidative stress by disrupting cellular reactive oxygen species (ROS) homeostasis. Mitochondria are a major source of ROS in the cell wherein a dozen sites located on enzymes of the electron transport system (ETS) and substrate oxidation produce superoxide anion radicals (O˙‾) or hydrogen peroxide (HO). Sites located on ETS enzymes can generate ROS by forward electron transfer (FET) and reverse electron transfer (RET) reactions; however, knowledge of how exogenous stressors modulate site-specific ROS production is limited. We investigated the effects of anoxia-reoxygenation and cadmium (Cd) on HO emission in fish liver mitochondria oxidizing glutamate-malate, succinate or palmitoylcarnitine-malate. We find that anoxia-reoxygenation attenuates HO emission while the effect of Cd depends on the substrate, with monotonic responses for glutamate-malate and palmitoylcarnitine-malate, and a biphasic response for succinate. Anoxia-reoxygenation exerts a substrate-dependent inhibition of mitochondrial respiration which is more severe with palmitoylcarnitine-malate compared with succinate or glutamate-malate. Additionally, specific mitochondrial ROS-emitting sites were sequestered using blockers of electron transfer and the effects of anoxia-reoxygenation and Cd on HO emission were evaluated. Here, we find that site-specific HO emission capacities depend on the substrate and the direction of electron flow. Moreover, anoxia-reoxygenation alters site-specific HO emission rates during succinate and glutamate-malate oxidation whereas Cd imposes monotonic or biphasic HO emission responses depending on the substrate and site. Contrary to our expectation, anoxia-reoxygenation blunts the effect of Cd. These results suggest that the effect of exogenous stressors on mitochondrial oxidant production is governed by their impact on energy conversion reactions and mitochondrial redox poise. Moreover, direct increased ROS production seemingly does not explain the increased adverse effects associated with combined exposure of aquatic organisms to Cd and low dissolved oxygen levels.
缺氧和金属是常见的环境应激源，它们会通过破坏细胞内活性氧（ROS）稳态来诱导氧化应激。线粒体是细胞内 ROS 的主要来源，其中十几个位于电子传递系统（ETS）酶和底物氧化的位点产生超氧阴离子自由基（O˙‾）或过氧化氢（HO）。位于 ETS 酶上的位点可以通过正向电子传递（FET）和反向电子传递（RET）反应产生 ROS；然而，关于外源性应激源如何调节特定于位点的 ROS 产生的知识有限。我们研究了缺氧-复氧和镉（Cd）对鱼肝线粒体氧化谷氨酸-苹果酸、琥珀酸或棕榈酰肉碱-苹果酸时 HO 发射的影响。我们发现缺氧-复氧会减弱 HO 的发射，而 Cd 的影响取决于底物，谷氨酸-苹果酸和棕榈酰肉碱-苹果酸呈单调响应，琥珀酸呈双相响应。缺氧-复氧对线粒体呼吸有底物依赖性抑制作用，与琥珀酸或谷氨酸-苹果酸相比，棕榈酰肉碱-苹果酸的抑制作用更为严重。此外，使用电子转移抑制剂隔离了特定的线粒体 ROS 发射位点，并评估了缺氧-复氧和 Cd 对 HO 发射的影响。在这里，我们发现特定于位点的 HO 发射能力取决于底物和电子流的方向。此外，缺氧-复氧改变了琥珀酸和谷氨酸-苹果酸氧化过程中特定于位点的 HO 发射速率，而 Cd 则根据底物和位点施加单调或双相的 HO 发射反应。与我们的预期相反，缺氧-复氧削弱了 Cd 的作用。这些结果表明，外源性应激源对线粒体氧化剂产生的影响取决于它们对能量转换反应和线粒体氧化还原平衡的影响。此外，直接增加 ROS 产生似乎并不能解释与水生生物同时暴露于 Cd 和低溶解氧水平相关的不良影响增加的原因。
