Department of Biology, Faculty of Arts and Science, Karaelmas University, 67100, Zonguldak, Turkey.
Comp Biochem Physiol A Mol Integr Physiol. 2010 Jun;156(2):176-83. doi: 10.1016/j.cbpa.2010.01.020. Epub 2010 Feb 4.
Antioxidant enzymes play a major role in the defense against pro-oxidative effects of xenobiotics and pro-oxidant plant allelochemicals in insects. We posed the hypothesis that eicosanoids also mediate antioxidant enzymatic defense reactions to pro-oxidant challenge. To test this idea, we reared first-instar larvae of Galleria mellonella (L.) with the lypoxygenase inhibitor, esculetin (0.001%), the phospholipase A(2) inhibitor, dexamethasone (0.001%) and the dual inhibitor of cyclooxygenase and lipoxygenase, phenidone (0.1%) to seventh-instars. Newly ecdysed seventh-instars were then fed on artificial diet containing 0.05% xanthotoxin (XA) for 2 days. Treating seventh-instar larvae of G. mellonella with XA induced lipid peroxidation and protein carbonylation as evident from the increased content of malondialdehyde (MDA) and protein carbonyls respectively, and antioxidative enzymatic response in a dose-dependent manner. High dietary XA concentrations (0.005 and 0.1%) were associated with increasing MDA and carbonyl content (by 3-fold) and antioxidant enzyme activities, superoxide dismutase (SOD) (by 3-fold) and catalase (CAT) (by 4-fold), and glutathione-dependent enzymes, glutathione S-transferase (GST) (by 15-fold) and glutathione peroxidase (GPx) (by 7-fold). Relative to control, eicosanoid biosynthesis inhibitors (EBIs) esculetin, dexamethasone and phenidone also resulted in impaired MDA content and antioxidant enzyme activities. However, carbonyl content did not differ between control- and EBIs-feeding larvae. Finally, MDA and carbonyl content, and antioxidant enzymes SOD, GST and GPx activities exhibited an incremental increase while CAT activity was decreased in the experimental larvae that had been reared on media amended with esculetin, dexamethasone and phenidone and then challenged with our standard XA challenge dose. Two of the markers indicated that significantly higher levels of oxidative stress were produced in the hemolymph tissue of larvae fed diets supplemented with EBIs and then challenged with XA. This oxidative stress was associated with elicited antioxidative responses by increasing SOD, GST and GPx and decreasing CAT activities in hemolymph. We infer from these findings that eicosanoids mediate insect antioxidant enzymatic responses to dietary pro-oxidants.
抗氧化酶在防御外来生物和植物化感物质的促氧化作用以及昆虫中的抗氧化酶防御反应中起着重要作用。我们假设类二十烷酸也介导了抗氧化酶防御反应以应对促氧化剂的挑战。为了验证这一观点，我们用脂氧合酶抑制剂 esculetin（0.001%）、磷脂酶 A2 抑制剂地塞米松（0.001%）和环加氧酶和脂加氧酶双重抑制剂 phenidone（0.1%）饲养大蜡螟（Galleria mellonella）的第一龄幼虫，并饲养至第七龄。新蜕皮的第七龄幼虫然后用含有 0.05%黄杉毒素（XA）的人工饲料喂养 2 天。用 XA 处理大蜡螟的第七龄幼虫诱导脂质过氧化和蛋白质羰基化，分别表现为丙二醛（MDA）和蛋白质羰基含量增加，并且抗氧化酶反应呈剂量依赖性。高膳食 XA 浓度（0.005 和 0.1%）与 MDA 和羰基含量增加（增加 3 倍）和抗氧化酶活性增加相关，超氧化物歧化酶（SOD）（增加 3 倍）和过氧化氢酶（CAT）（增加 4 倍）以及谷胱甘肽依赖性酶，谷胱甘肽 S-转移酶（GST）（增加 15 倍）和谷胱甘肽过氧化物酶（GPx）（增加 7 倍）。与对照组相比，类二十烷酸生物合成抑制剂（EBIs） esculetin、地塞米松和 phenidone 也导致 MDA 含量和抗氧化酶活性受损。然而，羰基含量在对照和 EBIs 喂养的幼虫之间没有差异。最后，在用 esculetin、地塞米松和 phenidone 改良的培养基中饲养的实验幼虫中，MDA 和羰基含量以及抗氧化酶 SOD、GST 和 GPx 活性呈递增增加，而 CAT 活性降低，然后用我们的标准 XA 挑战剂量进行挑战。两种标记物表明，用补充了 EBIs 的饮食喂养的幼虫的血液组织中产生了显著更高水平的氧化应激。这种氧化应激与血液中 SOD、GST 和 GPx 活性增加和 CAT 活性降低引起的抗氧化反应有关。从这些发现中，我们推断类二十烷酸介导了昆虫对膳食促氧化剂的抗氧化酶反应。
