Seawater carbonate chemistry and enzymatic antioxidant defense, protein repair and removal of temperate shark (Scyliorhinus canicula)

Ocean acidification is a consequence of chemical changes driven mainly by a continuous uptake of carbon dioxide, resulting in pH decrease. This phenomenon represents an additional threat to marine life, with expected effects ranging from changes in behavioral responses and calcification rates to the potential promotion of oxidative stress. To unravel the impacts of ocean acidification on the antioxidant system of sharks, we performed a long-term exposure (9 months, since early embryogenesis) to high CO2 conditions (pCO2 900 μatm) on a temperate shark (Scyliorhinus canicula). The following biomarkers were measured: enzymatic antioxidant defense (superoxide dismutase, catalase and glutathione peroxidase), protein repair and removal (heat shock proteins and ubiquitin), and oxidative damage on lipids (malondialdehyde) and DNA (8-hydroxy-2′-deoxyguanosine). Changes in the antioxidant enzyme defense were restricted to an increase in catalase activity in the muscle, an enzyme that plays a major role in oxidative stress mitigation. On the other hand, no evidence of oxidative damage was found, indicating that the observed increase in catalase activity may be enough to neutralize the effects of potentially higher reactive oxygen species. These results further indicate that these sharks' antioxidant system can successfully cope with the levels of carbon dioxide projected for the end of the century. Nonetheless, the interaction between ocean acidification and the rise in temperature expected to occur in a near future may disturb their antioxidant capacity, requiring further investigation.

海洋酸化（ocean acidification）是主要由二氧化碳持续吸收驱动的化学变化所导致的结果，会引起pH值下降。这一现象对海洋生物构成额外威胁，预期影响范围从行为反应（behavioral responses）和钙化速率（calcification rates）的改变，到潜在促进氧化应激（oxidative stress）。为揭示海洋酸化对鲨鱼抗氧化系统（antioxidant system）的影响，我们对一种温带鲨鱼（Scyliorhinus canicula）进行了长期暴露（9个月，自胚胎发生早期起）于高CO₂条件（pCO₂ 900 μatm）的实验。测定的生物标志物包括：酶促抗氧化防御（enzymatic antioxidant defense）（超氧化物歧化酶（superoxide dismutase）、过氧化氢酶（catalase）和谷胱甘肽过氧化物酶（glutathione peroxidase））、蛋白质修复与清除（protein repair and removal）（热休克蛋白（heat shock proteins）和泛素（ubiquitin）），以及脂质氧化损伤（oxidative damage on lipids）（丙二醛（malondialdehyde））和DNA（8-羟基-2'-脱氧鸟苷（8-hydroxy-2′-deoxyguanosine））的氧化损伤。抗氧化酶防御的变化仅限于肌肉中过氧化氢酶活性的升高，该酶在缓解氧化应激中发挥主要作用。另一方面，未发现氧化损伤的证据，表明观察到的过氧化氢酶活性升高可能足以中和潜在更高水平的活性氧。这些结果进一步表明，这些鲨鱼的抗氧化系统能够成功应对本世纪末预计的二氧化碳水平。然而，海洋酸化与未来预期的温度升高之间的相互作用可能会干扰其抗氧化能力，需要进一步研究。