Meconium induces expression of inducible NO synthase and activation of NF-kappa B in rat alveolar macrophages

Meconium aspiration causes intensive inflammatory reactions in the lungs, a nd may lead to neonatal respiratory disorder. Infiltrated inflammatory cell s, particularly macrophages, play an important role in such an inflammation . A rat alveolar macrophage cell line (ATCC8383) was exposed to meconium al one or in combination with dexamethasone, budesonide, or interferon-gamma, Nitric oxide MO) accumulation in the supernatant of the cell culture was de tected by Griess reaction, and mRNA of inducible NO synthase (iNOS) express ion was detected by reverse transcriptase-PCR. Nuclear factor-kappa B was a nalyzed by electrophoretic mobility shift assay, and iNOS location and nucl ear factor-kappa B transactivation were determined by immunostaining. Our r esults showed that meconium was capable of inducing production of NO and ex pression of iNOS in alveolar macrophages in a dose- (1-25 mg/mL, p < 0.05) and time(4-48 h, p < 0.05) dependent manner. This capability of meconium co uld be further enhanced in the presence of interferon-gamma (100 IU/mL, p < 0.05). Budesonide (10(-4)-10(-10) M) or dexamethasone (10(-4)-10(-6) M) el ectively inhibited the meconium-induced NO production (p < 0.05). Using the protein synthesis inhibitor cycloheximide, we demonstrated that meconium d irectly induced iNOS in macrophages. Furthermore, meconium also triggered n uclear factor-kappa B activation, a mechanism possibly responsible for the iNOS expression. Our findings suggest that meconium is a potent inflammator y stimulus, resulting in iNOS expression, leading to overproduction of NO f rom the macrophages, which may be of pathogenic importance in meconium aspi ration syndrome. In vitro steroids down-regulated the iNOS expression, thus suggesting a potential to down-regulate NO-mediated inflammation in neonat es with meconium aspiration syndrome.