Differing effects of aprotinin and ε-aminocaproic acid on cytokine-induced inducible nitric oxide synthase expression

Background. Cell expression of inducible nitric oxide synthase (iNOS) is increased by cytokines, resulting in high endogenous levels of nitric oxide. Expression of iNOS has been implicated in organ injury, including myocardial reperfusion injury. Serine protease inhibitors reduce cytokine-induced iNOS expression. The protease inhibitors aprotinin and ε-aminocaproic acid (EACA), used to reduce blood loss after cardiac operations, were evaluated in vitro on cytokine-induced iNOS expression and nitric oxide production. Methods. A murine bronchial epithelial cell line was stimulated with a mixture of cytokines (tumor necrosis factor-α, interleukin-1β, and interferon-γ) with or without aprotinin or EACA. The resultant iNOS expression was measured by northern blot analysis, and nitric oxide production was assessed by cell supernatant nitrite levels. Results. Nitrite concentrations in the supernatant were significantly increased after cytokine stimulation; they were not affected by any concentration of EACA but were significantly (p < 0.05) reduced by aprotinin. Aprotinin significantly (p < 0.05) reduced cytokine-induced iNOS expression, whereas EACA had no effect. Conclusions. Aprotinin, but not EACA, reduces cytokine-induced nitric oxide production by inhibition of iNOS expression. Because increased endogenous nitric oxide levels secondary to iNOS activation have been implicated in organ injury, aprotinin may have clinical benefit compared with EACA when used for cardiac operations.