The role of nitric oxide in paraquat-induced cytotoxicity in the human A549 lung carcinoma cell line

Abstract

Paraquat (PQ) is a well-known pneumotoxicant that exerts its toxic effect by elevating intracellular levels of superoxide. In addition, production of pro-inflammatory cytokines has possibly been linked to PQ-induced inflammatory processes through reactive oxygen species (ROSs) and nitric oxide (NO). However, the role of NO in PQ-induced cell injury has been controversial. To explore this problem, we examined the effect of NO on A549 cells by exposing them to the exogenous NO donor NOC18 or to cytokines; tumor necrosis factor-alpha, interleukin-1 beta and interferon-gamma, as well as PQ. Although the exogenous NO donor on its own had no effect on the release of lactate dehydrogenase (LDH), remarkable release was observed when the cells were exposed to high concentrations of NOC18 and PQ. This cellular damage caused by 1 mM NOC18 plus 0.2 mM PQ was ascertained by phase contrast microscopy. On the other hand, NO derived from 25-50 microM NOC18 added into the medium improved the MTT reduction activity of mitochondria, suggesting a beneficial effect of NO on the cells. Incubation of A549 cells with cytokines increased in inducible NO synthase (iNOS) expression and nitrite accumulation, resulting in LDH release. PQ further potentiated this release. The increase in nitrite levels could be completely prevented by NOS inhibitors, while the leakage of LDH was not attenuated by the inhibition of NO production with them. On the other hand, ROS scavenging enzymes, superoxide dismutase and catalase, inhibited the leakage of LDH, whereas they had no effect on the increase in the nitrite level. These results indicate that superoxide, not NO, played a key role in the cellular damage caused by PQ/cytokines. Our in vitro models demonstrate that NO has both beneficial and deleterious actions, depending on the concentrations produced and model system used.

Nitric oxide in paraquat‐mediated toxicity: A review

“…•− 2 , not NO, play a key role in the cellular damage caused by PQ [26]. However, in PQ models of lung injury, injury that was previously attributed to the generation of reactive oxygen species was found to be related to the induction of NO synthesis and was totally preventable by inhibition of NO synthesis [60,61].…”

“…Human lung epithelial cells treated with PQ also express significant amounts of iNOS mRNA [23]. Similarly, human-derived cell lines such as A549 lung carcinoma [26] or the human neuroblastoma-derived cell line SH-SY5Y [27] show upregulation of iNOS expression after PQ exposure.…”

Nitric Oxide Mediates Lung Injury Induced by Ischemia-Reperfusion in Rats

“…Chang et al [3] demonstrated that the L-arginine-NO pathway contributes to LI induced by hyperoxia, and Tomita et al [21] also showed that an NO donor has deleterious effects in a lung carcinoma cell line. In contrast, the production of NO has been shown to be protective in tissue injury [1,5,19,27].…”

Oxidative and Inflammatory Pathways in Parkinson’s Disease

“…Because NO is a vasodilator, increased production may benefit the brain after injury [111]. On the other hand, excess production of NO can cause neurodegeneration manifesting as stroke, PD and HIV dementia [101,112]. NO can form adducts with mitochondrial enzymes and dysregulate mitochondrial function.…”