The contribution of nitric oxide to the paraquat-induced cell injury.

本研究首先研究了百草枯（PQ）对培养的A549肺腺癌细胞一氧化氮（NO）生物合成的影响。PQ与细胞因子联合使用可协同提高亚硝酸盐含量（NOS活性指标），与诱导型NO合成酶（iNOS） mRNA的表达水平一致。此外，这种内源性NO对PQ中毒具有保护作用，而外源性大量NO可能与PQ衍生的超氧化物相互作用，从而刺激细胞损伤。接下来，我们利用RT-PCR技术，研究了亚致死和致死百草枯暴露对大鼠肝、肾和肺组织iNOS和白细胞介素-1 β基因表达的影响。肾和肺的iNOS信号未受影响，但在致死剂量暴露的肝脏中观察到iNOS信号的明显抑制和显著刺激。而肝脏中il -1 β信号在整个实验过程中呈下降趋势，提示暴露于致死剂量下肝脏iNOS表达的变化与il -1 β无关。在致死剂量组中，肾脏il -1 β信号在1小时达到峰值，3小时下降，而肺il -1 β信号在整个实验过程中升高。这些结果表明，PQ在体内对肝脏iNOS表达有直接的双相影响，从而为一氧化氮的产生可能参与PQ诱导的损伤提供了证据。另一方面，它们也表明，肺，受影响最严重的器官，可能是由il -1 β或其他促炎细胞因子调节，而不是由NO。

In the present study, we first investigated the effect of paraquat (PQ) on nitric oxide (NO) biosynthesis in cultured A549 lung adenocarcinoma cells. A combination of PQ with cytokines synergistically increased the amount of nitrite, as an index of NOS activity, which paralleled the expression of inducible NO synthase (iNOS) mRNA.In addition, this endogenous NO showed a protective effect against PQ poisoning, while larger exogenous amounts of NO stimulated cell injury, probably because of interaction with superoxide derived from PQ.Next, using RT-PCR,we studied the effect of sub-lethal and lethal paraquat exposure on iNOS and interleukin (IL)-1beta gene expression in rat liver, kidney and lung. The iNOS signals in kidney and lung were unaffected, but a marked suppression and then a significant stimulation of the signals was observed in liver exposed to a lethal dose. The IL-1beta signal in liver, however, decreased throughout the experiment, suggesting that the changes in liver iNOS expression exposed to a lethal dose was not relevant to IL-1beta. In the lethal dose group, the IL-1beta signal in kidney reached a peak at 1 hr, declining by 3 hr, whereas that in lung increased throughout the experiment. These results demonstrate that PQ has a direct biphasic effect on iNOS expression in liver in vivo, thus providing evidence of possible involvement of nitric oxide generation in PQ-induced injury. On the other hand, they also indicate that the lung, the most severely affected organ, may be regulated by IL-1beta or other proinflammatory cytokines and not by NO.