Lipopolysaccharide causes NFĸB-mediated induction of inducible nitric oxide synthase gene and more production of nitric oxide in air-breathing catfish, Clarias magur (Hamilton)

The magur catfish (Clarias magur) is a facultative air-breather and regularly encounters with various environmental changes along with exposure to various bacterial pathogens in its natural habitats. Occurrence of various biochemical adaptational strategies related to nitrogen metabolism in magur catfish is already known. The present investigation aimed at determining the possible induction of inducible nitric oxide synthase (inos) gene and stimulation of nitric oxide (NO) production in this catfish while challenging with lipopolysaccharide (LPS, a bacterial endotoxin) treatment, and also to determine the involvement of nuclear factor kappa B (NFkB) in induction of inos gene. Intra-peritoneal injection of LPS led to more production and accumulation of NO in different body tissues of magur catfish as a consequence of induction of iNOS activity. The induction of iNOS activity was associated with the induction of inos gene as evidenced by more expression of inos mRNA and more abundance of iNOS enzyme protein in different tissues of magur catfish with certain variations in zonal specific expression patterns. Similar observations related to more production of NO and induction of inos gene were also made when the isolated hepatocytes were treated with LPS in vitro condition. LPS treatment also led to activation of NFĸB in hepatic cells. However, in presence of a specific inhibitor of NFkB, the LPS-mediated induction of inos gene and extra production of NO were almost blocked, thereby suggesting that the induction of inos gene due to LPS treatment was mediated via the NFkB in magur catfish. It is hypothesized that the induction of iNOS activity, and more synthesis and accumulation of NO could serve as indicators to determine the pathophysiological conditions of the fish living in bacterial contaminated water bodies. Further, it can be contemplated that more synthesis of NO through iNOS enzyme probably serves as an important pharmacological tool against fish pathogen and also plays an important role in host defense mechanisms in this unique group of magur catfish.