The increased apoptosis plays an important role in bacterial invasion. In addition, LPS can induce inflammation and apoptosis of leukocytes via the production of reactive oxygen and nitrogen species. In the present study, we investigated the potential protective role of l-arginine (L-Arg) against the apoptosis of fish leukocytes in vitro. The results of Annexin V-FITC/PI staining and TUNEL assay indicated that L-Arg significantly alleviated the apoptosis of fish leukocytes induced by LPS at 24 h and 72 h post incubation (hpi). High caspase-3 activities induced by LPS at 72 hpi were significantly inhibited by L-Arg. Moreover, L-Arg supplementation also significantly decreased the mRNA expression levels of caspases at most time points, which contributed to the anti-apoptotic roles of L-Arg. Further analysis showed that L-Arg significantly inhibited the expression of several pro-inflammatory cytokines including IL-8 and TNF-α, partially via the down-regulation of the genes involved in NF-κB/MyD88 including NF-κB, IKKα and IKKγ. The down-regulation of these pro-inflammatory cytokines by L-Arg supplementation led to the further decrease in the expression of death receptor FasL, contributing to the anti-apoptotic effect of L-Arg. In addition, L-Arg supplementation increased both iNOS mRNA expression and NO production. The mRNA expressions of several anti-oxidant enzymes including SOD, CAT and GSHPx were also significantly increased after L-Arg supplementation, which accelerated the clearance of reactive oxygen species. In all, L-Arg inhibited apoptosis of fish leukocytes both via the increased NO production and antioxidant capacity and via the inhibition of inflammation mediated by NF-κB/MyD88 pathway.

凋亡增加在细菌入侵中起重要作用。另外，LPS可通过产生活性氧和氮来诱导白细胞的炎症和凋亡。在本研究中，我们调查了l-精氨酸（L-Arg）对鱼白细胞体外凋亡的潜在保护作用。Annexin V-FITC / PI染色和TUNEL分析的结果表明，L-Arg显着减轻了LPS孵育后24 h和72 h时LPS诱导的鱼白细胞凋亡。L-Arg显着抑制LPS在72 hpi诱导的高caspase-3活性。此外，补充L-Arg还可以显着降低胱天蛋白酶的mRNA表达水平在大多数时间点，这有助于L-Arg的抗凋亡作用。进一步的分析表明，L-精氨酸显著抑制几种促炎性细胞因子，包括表达IL-8和TNF-α，通过参与基因的下调部分NF-κB/ MyD88的包括NF-κB，IKKα和IKKγ。L-Arg补充剂对这些促炎性细胞因子的下调导致死亡受体FasL的表达进一步降低，从而有助于L-Arg的抗凋亡作用。此外，补充L-Arg可以增加iNOS mRNA的表达和NO的产生。SOD，CAT和Cd等几种抗氧化酶的mRNA表达补充L-Arg后GSHPx也显着增加，这加速了活性氧的清除。总之，L-Arg通过增加NO的产生和抗氧化能力以及通过抑制由NF-κB/ MyD88途径介导的炎症来抑制鱼白细胞的凋亡。