石墨烯表面官能团种类多样性对诱导大型溞氧化应激的影响

Effect of different surface functional groups of graphene on oxidative stress in Daphnia magna

石墨烯纳米材料进入到环境后,可能通过一系列转化形成表面官能化衍生物.因此,研究表面修饰的石墨烯纳米材料对水生生物造成的毒性效应对于评价其生态风险具有重要意义.本研究考察了石墨烯(u-G)、羧基化石墨烯(G-COOH)、氨基化石墨烯(G-NH_2)、羟基化石墨烯(G-OH)及巯基化石墨烯(G-SH)对大型溞(Daphnia magna)体内活性氧物种(ROS)、抗氧化酶、抗氧化剂及脂质过氧化水平的影响,评价了其诱导大型溞氧化应激的程度.结果表明:相同暴露条件下(24h,2mg/L),u-G,G-COOH和G-OH诱导大型溞体内丙二醛含量显著升高,且u-G诱导产生的丙二醛含量显著高于G-COOH和G-OH,表明u-G造成大型溞氧化损伤的程度高于G-COOH和G-OH.此外,这3种材料也导致大型溞体内ROS升高和谷胱甘肽(GSH)含量显著变化,其中u-G和G-OH还诱导超氧化物歧化酶(SOD)、过氧化氢酶(CAT)活性显著降低.在24h暴露期间内,G-SH在不影响大型溞体内ROS水平的情况下,诱导SOD和CAT活性降低,可能是由于G-SH破坏了这些抗氧化酶的结构.G-NH_2暴露没有影响大型溞体内的氧化应激标志物.综上,石墨烯及其表面官能化衍生物对大型溞造成氧化应激的能力:u-G>G-COOH≈G-OH>G-SH>G-NH_2.

Graphene could be modified by functional groups through a series of transformation processes after being released into environment. Meanwhile, the properties of graphene, such as solubility and biotoxicity, could be altered by surface modification. It is important to investigate the aquatic toxicity of graphene and its surface functionalized derivatives for assessing their ecological risks. Oxidative stress is one of the main toxicity mechanisms of graphene nanomaterials, but the effect mechanism of different surface functional groups(amino and thiol) on the oxidative stress induced by graphene is still unclear. In order to illuminate the toxicity mechanism and evaluate the extent of oxidative stress, a series of graphene nanomaterials including unfunctionalized grapheme(u-G), carboxylated grapheme(G-COOH), aminated grapheme(G-NH2), hydroxylated grapheme(G-OH) and sulfydryl grapheme(G-SH) were selected to determine the levels of reactive oxygen species(ROS), antioxidant enzymes, antioxidant and lipid peroxidation in Daphnia magna induced by these graphene nanomaterials. Daphnia magna were exposed to graphene and its surface functionalized derivatives during 24 h period. Following treatment, the parameters reflecting oxidative stress such as ROS, superoxide dismutase(SOD), catalase(CAT), glutathione(GSH) and malondialdehyde in Daphnia magna were measured. The results showed that malondialdehyde, a marker of lipid peroxidation in Daphnia magna, was significantly increased by u-G, G-COOH and G-OH, respectively. The level of malondialdehyde was significantly higher under u-G exposure than that under G-COOH or G-OH exposure. It is indicated that the degree of oxidative damage induced by u-G in Daphnia magna was more serious than that of G-COOH and G-OH. In addition, the three nanomaterials also caused the changes in ROS and glutathione(GSH) levels, and activities of superoxide dismutase(SOD) and catalase(CAT) were decreased by u-G and G-OH. However, G-SH and G-NH2 did not cause oxidative damage within 24 h exposure period. Marked inactivation of antioxidant enzymes in an ROS-independent manner was observed in response to G-SH, suggesting that G-SH may cause a structural change in enzymes, leading to functional inactivity. G-NH2 did not affect the levels of ROS, antioxidant enzymes, antioxidant and lipid peroxidation. At 24 h after stopping exposure, Daphnia magna can alleviate the oxidative damage induced by u-G, G-COOH and G-OH to a certain extent by its own regulation. The ability of graphene nanomaterials to cause oxidative stress in Daphnia magna is as follows: u-G>G-COOH≈G-OH>G-SH>G-NH2. The main reasons of oxidative stress in Daphnia Magna induced by u-G, G-COOH and G-OH were the generation of ROS, which led to the imbalance of antioxidant defense system and lipid peroxidation. G-SH mainly inhibited the activities of SOD and CAT antioxidant enzymes and affected the antioxidant defense system. However, there were no significant changes in ROS levels and antioxidant enzymes in Daphnia magna under G-NH2 exposure.