[Effect of niacin on nitric oxide synthase expression in rat lung exposed to silica]

To evaluate the effects of niacin supplemented in diet on temporal expression of nitric oxide synthase in rat lung exposed to silica by tissue array technology.

Wistar rats were randomly divided into three experimental groups: saline-treated group, silica-treated group, niacin-treated group. There are 48 animals in each group. Animal models were established by direct tracheal instillation of silica into the rat lungs. Plasma level of niacin was measured by high performance liquid chromatography (HPLC). The expression of iNOS protein in the paraffin-embedded lung sections was measured with streptavidin/peroxidase (SP) immunohistochemistry on tissue microarray and quantified by Image-Pro Plus.

Plasma level of niacin in niacin-treated group were significantly elevated by 5.946 4, 17.422 0, 21.398 0, 16.091 0, 4.414 3 and 7.130 5 mg/L at 1, 3, 7, 14, 21 and 28 days after instillation of silica, as compared to control and silica-treated groups. Seven days after instillation of silica, iNOS integrated optical density (IOD) of the lung, total NOS and iNOS activities in bronchial alveolar lavage fluid (BALF) supernatant in silica-treated group significantly elevated by 273 421, 2.61 kU/L and 1.89 kU/L, respectively, in the saline-treated group, with statistical significance. Niacin treatment could significantly decrease silica-elevated iNOS integrated optical density (IOD) of the lung, total NOS and iNOS activities in BALF supernatant by 248.292, 1.50 kU/L and 0.91 kU/L in the silica-treated group, respectively, with statistical significance.

It is suggested that treatment with niacin could effectively attenuate the over expression of nitric oxide synthase in the rat lung induced by silica particles in our study.