Aprotinin reduces nitric oxide production in vitro and in vivo in a dose-dependent manner.

1. Cardiopulmonary bypass is associated with an increase in nitric oxide concentrations, and plasma levels of tumour necrosis factor and interleukin-1. Aprotinin, a serine protease inhibitor, commonly used during cardiopulmonary bypass to reduce blood loss, has been demonstrated to exhibit significant anti-inflammatory effects during and after cardiopulmonary bypass. 2. Airway nitric oxide was measured during cardiopulmonary bypass in 10 controls (Group 1), 10 subjects receiving half-dose aprotinin (Group 2) and 10 patients receiving full-dose aprotinin (Group 3). In vitro, a murine bronchial epithelial cell line (LA-4) was cultured with cytomix (a combination of tumour necrosis factor, interleukin-1, and (gamma-interferon) with and without aprotinin in increasing concentrations. Nitrite concentrations, the stable and measureable end-product of nitric oxide oxidative metabolism, were measured in the culture supernatant by chemiluminescence. 3. Airway nitric oxide concentrations were increased after 50 min cardiopulmonary bypass compared with that measured at 5 min in controls (53 +/- 5 versus 29 +/- 3 ppb, P < 0.05) but not in the aprotinin-treated groups (25 +/- 4 versus 14 +/- 5, Group 2; 21 +/- 6 versus 15 +/- 3 ppb, Group 3). 4. In a dose-dependent manner, nitrite levels (means +/- S.E.M.) were significantly reduced by aprotinin at 500 and 1000 units/ml when compared with cells cultured in the presence of cytomix alone (P < 0.05). 5. These data demonstrate that aprotinin, in a dose-responsive manner, reduces nitric oxide production in vivo and reduces cytokine-induced nitrite production by murine bronchial epithelial cells in vitro. Since increased airway nitric oxide is found in inflammatory lung diseases, like asthma, and anti-inflammatory therapy reduces the concentration of airway nitric oxide, these data support the concept that aprotinin is anti-inflammatory during cardiopulmonary bypass.