Recombinant Kunitz protease inhibitor ameliorates reperfusion injury in rat lung transplantation

Background. Recombinant Kunitz protease inhibitor (rKPI-BG022) is more homologous to human Kunitz protease inhibitor than is aprotinin. Because aprotinin has been reported to inhibit free radicals, we hypothesized that rKPI would ameliorate reperfusion injury caused by free radicals. We examined its effect and the timing of administration in an in vivo rat lung transplantation model. Methods. All lungs were flushed with low-potassium dextran-1% glucose solution and stored for 24 hours at 4°C, then orthotopic left lung transplantations were performed. Rats were divided into 4 groups (n = 6) as follows: group 1 served as control; in Group 2, rKPI was added to the flush solution (10 μmol/L); in group 3, rKPI (5 mg/kg) was administered intravenously to the recipient just after reperfusion; and in group 4, rKPI was added to the flush solution (10 μmol/L) and rKPI (5 mg/kg) was administered intravenously to the recipient just after reperfusion. Twenty- four hours after transplantation, the right main pulmonary artery and right main bronchus were ligated, and the rats were ventilated with 100% O₂ for 5 minutes. Peak airway pressure, blood gas analysis, serum lipid peroxide level, tissue myeloperoxidase activity, and wet-dry weight ratio were measured. Results. The partial oxygen tension values of group 2 were higher than those of groups 1 and 4 (groups 1, 2, and 4: 104.8 ± 15.8, 245.1 ± 49.0, 101.4 ± 4.5 mm Hg, respectively; p < 0.01). The partial carbon dioxide tension values of groups 3 and 4 were lower than those of group 1 (groups 1, 3, and 4:74.5 ± 5.7, 42.0 ± 11.0, 46.0 ± 8.4 mm Hg, respectively; p < 0.05). Peak airway pressures were lower in groups 2 and 3 than in groups 1 and 4 (groups 1, 2, 3, and 4:22.5 ± 0.5, 18.2 ± 0.5, 19.2 ± 0.8, 22.5 ± 1.1 mm Hg; p < 0.01). Serum lipid peroxide levels in groups 2 and 3 were lower than those of groups 1 and 4 (groups 1, 2, 3, and 4: 0.793 ± 0.037, 0.577 ± 0.069, 0.560 ± 0.029, and 0.785 ± 0.053 nmol/mL, respectively; groups 2 and 3 vs group 1, and group 3 vs group 4: p < 0.01; group 2 vs group 4: p < 0.05). There were no differences in wet-dry weight ratio and tissue myeloperoxidase activity between the groups. Conclusion. Recombinant Kunitz protease inhibitor ameliorates reperfusion injury caused by free radicals in an in vivo rat lung transplantation model. Administration of rKPI through the flush solution and intravenous injection after reperfusion were effective separately, but the combination of the two administrations was not effective.