Although soy foods have been consumed for more than 1000 y, it is only in the past 20 y that they have made inroads into Western diets. We investigated the effect of dietary supplementation with natto extracts produced from fermented soybeans on intimal thickening of arteries after vessel endothelial denudation. Natto extracts include nattokinase, a potent fibrinolytic enzyme having four times greater fibrinolytic activity than plasmin. Intimal thickening was induced in the femoral arteries by intravenous infusion of rose bengal followed by focal irradiation with a transluminal green light. Dietary natto extract supplementation was started 3 wk before endothelial injury and continued for another 3 wk after. In ex vivo studies, euglobulin clot lysis times were measured 3 wk after the initial supplementation. Neointima formation and thickening were also initiated successfully. The intima media ratio 3 wk after endothelial injury was 0.15 ± 0.03 in the control group. Dietary natto extract supplementation suppressed intimal thickening (0.06 ± 0.01; P < 0.05) compared with the control group. Natto extracts shortened euglobulin clot lysis time, suggesting that their thrombolytic activities were enhanced. These findings suggest that natto extracts, because of their thrombolytic activity, suppress intimal thickening after vascular injury as a result of the inhibition of mural thrombi formation.
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