Salivary Gland Ligation Inhibited The Antipyroptotic Effect Of Inorganic Nitrate

The aim of this study is to determine the effect of salivary gland function on the anti-inflammatory and anti-pyroptotic effects of inorganic nitrate in collagen-induced arthritis (CIA). The CIA model was established in male Wistar rats by injection of a mixture of type II collagen and Freund's adjuvant emulsion and salivary duct ligation was performed. Clinical phenotypes of CIA rats were evaluated by monitoring foot volume and arthritis scores. Degenerative changes in hard tissues were analyzed by safranin O-fast green staining and micro-CT. Serum nitrate and nitrite levels were measured using the Griess method and fluorescence assay. The expressions of inflammatory and pyroptosis relative protein in serum and synovial tissue were detected using ELISA, Western blotting, immunohistochemistry, and fluorescence staining. Salivary gland duct ligation did not significantly affect serum nitrate levels but significantly reduced serum nitrite levels, indicating that duct ligation suppressed the process of nitrate reduction. The ligation significantly weakened the inhibitory effect of nitrate intervention on synovial cell infiltration and hard tissue damage. Immunofluorescence and Western blotting results showed that salivary gland duct ligation significantly reduced the inhibitory effects of nitrate intervention on the expression of NLRP3, caspase-1, GSDMD, and IL-1β. Salivary gland duct ligation inhibited the anti-inflammatory and anti-pyroptotic effects of inorganic nitrate in CIA by impairing the bioconversion of nitrate to nitrite.