Effect of aprotinin on smooth muscle cell proliferation, migration, and extracellular matrix synthesis

Aprotinin (AP) is a plasmin inhibitor commonly used to limit bleeding during reoperative coronary bypass surgery. The effect on smooth muscle cell (SMC) behavior and the development of intimal hyperplasia has not been evaluated. This study examines the effect of AP on SMC proliferation, migration, and extracellular matrix synthesis. Bovine aortic SMCs (three to five passages) plated at 5 x 10(4) cells/ml were treated with 1.0, 10, 100, and 1000 microg/ml AP. Proliferation was measured as micrograms of DNA per well, after 3 days in culture. SMC migration was measured after treatment with mitomycin C (20 microg/ml, to study migration in the absence of proliferation) by means of a fence assay. Extracellular matrix was quantitated utilizing a tritiated proline assay and corrected for cell density (cpm/microg DNA). Data are presented as means +/- SEM; ANOVA and post hoc Tuckey test were used to test for significant differences. AP stimulated SMC proliferation at dosages of 100 microg/ml (353 +/- 6 microg DNA, SMC control vs 440 +/- 11, 100 microg/ml; P < 0.05) and 1000 microg/ml (353 +/- 6, SMC control vs 503 +/- 14, 1000 microg/ml; P < 0.01). AP concentrations less than 100 microg/ml had no effect on SMC proliferation. A dose-response relationship existed between AP and SMC migration. AP doses as low as 10 microg/ml increased SMC migration from 66 +/- 4 mm2 (control SMC) to 90 +/- 4 mm2 (P < 0.02) while the maximal dose of AP (1000 microg/ml) produced an almost twofold increase in migration (66 +/- 4, SMC control vs 113 +/- 3, 1000 microg/ml group; P < 0.0001). AP had no effect on extracellular matrix synthesis. AP stimulated vascular SMC migration and proliferation but not matrix synthesis in vitro. These data suggest that AP could augment the development of intimal hyperplasia following bypass surgery.