Evidence of nitric oxide synthase 2 activity in swine naturally infected with Actinobacillus pleuropneumoniae

Expression of Nitric Oxide Synthase 2 and Cyclooxygenase-2 in Swine Experimentally Infected with Actinobacillus pleuropneumoniae

The expression of inflammatory mediators was examined in pigs experimentally infected with Actinobacillus pleuropneumoniae. The activity of nitric oxide synthase 2 (NOS2) and cyclooxygenase-2 (COX-2) was determined by measuring nitric oxide (NO) and prostaglandin E2 (PGE2) in bronchoalveolar lavage fluid in response to A. pleuropneumoniae in vivo. By in situ hybridization and immunohistochemistry, both NOS2 and COX-2 enzymes were detected in neutrophils and macrophages that had infiltrated into alveolar spaces. The sharp increase in PGE2 concentration preceded the increase in the concentrations of NO. NO levels were highly correlated with PGE2 level ( rs = 0.7218, P < 0.05). The NO levels were positively correlated with lung lesion scores ( rs = 0.9087, P < 0.05) until 24 hours postinoculation (hpi) as were the lung lesion scores and PGE2 levels ( rs = 0.925, P < 0.01). High levels of PGE2 produced by COX-2 are generated in early infection (6 hpi). However, in later stages of infection (12–36 hpi), there is participation of NO and PGE2 accompanied by coinduction of both NOS2 and COX-2.

NOS-2 Inhibition in Phosgene-Induced Acute Lung Injury

Phosgene exposure via an industrial or warfare release produces severe acute lung injury (ALI) with high mortality, characterized by massive pulmonary edema, disruption of epithelial tight junctions, surfactant dysfunction, and oxidative stress. There are no targeted treatments for phosgene-induced ALI. Previous studies demonstrated that nitric oxide synthase 2 (NOS-2) is upregulated in the lungs after phosgene exposure; however, the role of NOS-2 in the pathogenesis of phosgene-induced ALI remains unknown. We previously demonstrated that NOS-2 expression in lung epithelium exacerbates inhaled endotoxin-induced ALI in mice, mediated partially through downregulation of surfactant protein B (SP-B) expression. Therefore, we hypothesized that a selective NOS-2 inhibitor delivered to the lung epithelium by inhalation would mitigate phosgene-induced ALI. Inhaled phosgene produced increases in bronchoalveolar lavage fluid protein, histologic lung injury, and lung NOS-2 expression at 24 h. Administration of the selective NOS-2 inhibitor 1400 W via inhalation, but not via systemic delivery, significantly attenuated phosgene-induced ALI and preserved epithelial barrier integrity. Furthermore, aerosolized 1400 W augmented expression of SP-B and prevented downregulation of tight junction protein zonula occludens 1 (ZO-1), both critical for maintenance of normal lung physiology and barrier integrity. We also demonstrate for the first time that NOS-2-derived nitric oxide downregulates the ZO-1 expression at the transcriptional level in human lung epithelial cells, providing a novel target for ameliorating vascular leak in ALI. Our data demonstrate that lung NOS-2 plays a critical role in the development of phosgene-induced ALI and suggest that aerosolized NOS-2 inhibitors offer a novel therapeutic strategy for its treatment.

Changes in the expression pattern of the nitrergic system of ovine cerebellum affected by scrapie

The constitutive and inducible isoforms of nitric oxide synthase (NOS) and the end-product of nitration, nitrotyrosine, were analyzed by immunohistochemistry, Western blotting, and enzymatic activity in sheep at different stages of the prion disease, scrapie. Four groups were studied: 1) nonaffected (control), 2) preclinical, 3) clinical, and 4) terminal. Constitutive neuronal NOS (nNOS) was the most abundant isoform present in cerebellar neurons of the sheep. Expression of nNOS increased in preclinical animals but diminished in the late stages of the disease. The Purkinje cells that usually are not immunoreactive for this protein became immunopositive in the clinical phase. In unaffected sheep, the inducible isoform (iNOS) was slightly positive in the Purkinje cells. As the disease progressed, the immunoreactivity of Purkinje neurons for iNOS increased. At the final stages, numerous iNOS-positive microglial cells were found in the molecular layer. There was a basal level of protein nitration in the cerebellum of unaffected sheep, especially in the molecular layer. As the disease progressed, the distal prolongations of the Purkinje cells and the astroglia became immunoreactive for nitrotyrosine. Our results suggest that the nitrergic system reacts to the progression of spongiform diseases and may be part of their pathogenesis mechanism.

Distribution and expression pattern of the nitrergic system in the cerebellum of the sheep

The nitrergic system produces nitric oxide as an atypical neurotransmitter in the nervous system. Nitric oxide is produced from l-arginine through specific enzymes known as nitric oxide synthases. Of these, the more abundant form in neurons is the constitutive neuronal nitric oxide synthase, although the inducible isoform can be expressed as well, especially following stress or other injuries. The excessive formation of nitric oxide results in protein nitration, particularly at tyrosine residues, thus the presence of nitrotyrosine can be used as a marker of nitric oxide production. In previous studies we have shown the distribution of the components of the nitrergic system in the cerebellum of rodents, where neuronal nitric oxide synthase immunoreactivity was present in stellate and basket cells, and occasionally in granule cells. Here, we present evidence that in the sheep, as a model of larger mammals, most cerebellar neurons display an intense immunostaining for neuronal nitric oxide synthase, including unipolar brush cells, and Lugaro and Golgi neurons, which are not immunoreactive in rodents. In addition, weak immunoreactivity for inducible nitric oxide synthase and nitrotyrosine was found in particular cell types, indicating a basal expression for these markers. Our results suggest a larger dependence on the nitrergic system for the cerebella of larger mammals. Since this increase happens in both activating and inhibitory neurons of the cerebellar circuitry, we propose that in these animals there is a higher steady-state regulation of the cerebellum based on nitric oxide.

Expression of cyclooxygenase-2 and nitric oxide synthase 2 in swine ulcerative colitis caused by Salmonella typhimurium

Cyclooxygenase-2 (COX-2) and nitric oxide synthase 2 (NOS2) were detected and localized in 20 pigs with ulcerative colitis caused by natural infection with Salmonella typhimurium. Evidence of NOS2 activity was determined by the formation of nitrotyrosine, a reaction product of peroxynitrite, in NOS2-expressing ulcerative colons by immunohistochemistry. Transcript RNA of COX-2 and NOS2 was consistently detected in colonic tissues from the 20 pigs with ulcerative colitis by using reverse transcription-polymerase chain reaction. Immunohistochemical signals for COX-2 and NOS2 were detected in the ulcerated area of all 20 pigs. Expression of COX-2 and NOS2 was identified continuously within inflammatory intestinal lesions but was minimal in unaffected regions of the colon of S. typhimurium-infected pigs. The immunohistochemistry of serial sections of intestine indicated that the majority of colons containing numerous COX-2-positive cells also had numerous NOS2-positive cells. Localization of NOS2 and a nitrotyrosine antigen was prominent in neutrophils and macrophages in the periphery of the lesions. Simultaneous detection of COX-2 and NOS2 RNA and protein indicated functional activity of prostaglandin and NO production in vivo. This study suggested that COX-2 and NOS2 expression may play a role in the pathophysiologic processes in ulcerative colitis caused by S. typhimurium.