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

M. Tomita et al., The role of nitric oxide in paraquat-induced cytotoxicity in the human A549 lung carcinoma cell line, FREE RAD RE, 34(2), 2001, pp. 193-202
Citations number
Categorie Soggetti
Biochemistry & Biophysics
Journal title
ISSN journal
1071-5762 → ACNP
Year of publication
193 - 202
SICI code
Paraquat (PQ) is a well-known pneumotoxicant that exerts its toxic effect b y elevating intracellular levels of superoxide. In addition, production of pro-inflammatory cytokines has possibly been linked to PQ-induced inflammat ory 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 expo sing them to the exogenous NO donor NOC18 or to cytokines; tumor necrosis f actor-alpha, interleukin-1 beta and interferon-gamma, as well as PQ. Althou gh the exogenous NO donor on its own had no effect on the release of lactat e 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 muM NOC18 added into the medium i mproved the MTT reduction activity of mitochondria, suggesting a beneficial effect of NO on the cells. Incubation of A549 cells with cytokines increas ed in inducible NO synthase (iNOS) expression and nitrite accumulation, res ulting 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 t hem. On the other hand, ROS scavenging enzymes, superoxide dismutase and ca talase, inhibited the leakage of LDH, whereas they had no effect on the inc rease in the nitrite level. These results indicate that superoxide, not NO, played a kev role in the cellular damage caused by PQ/cytokines. Our in vi tro models demonstrate that NO has both beneficial and deleterious actions, depending on the concentrations produced and model system used.