In vivo effect of insulin to decrease matrix metalloproteinase-2 and -9 activity after arterial injury

In vitro, insulin has both growth-promoting and vasculoprotective effects. In vivo, the effect of insulin is mainly protective. Insulin treatment (3 U/day) decreases smooth muscle cell (SMC) migration and neointimal growth after carotid angioplasty in normal rats maintained at normoglycemia by oral glucose. SMC migration requires limited proteolysis of the extracellular matrix, which is mediated by matrix metalloproteinases (MMPs). In this study, we investigated the effects of normoglycemic hyperinsulinemia on MMP activity after balloon angioplasty. Rats were divided into three groups: (1) control implants and tap water; (2) control implants and oral glucose, and (3) insulin implants (3 U/day) and oral glucose.

Gelatin zymography revealed that insulin reduced the gelatinolytic activity of pro-MMP-2 by 46% (p < 0.05), MMP-2 by 44% (p < 0.05) and MMP-9 by 51% (p < 0.05) compared to controls after arterial injury. Insulin also reduced mRNA levels of MMP-2 (p < 0.05) and MMP-9 (p < 0.05) and protein levels of MMP-2 (p < 0.05). In contrast, there were no significant changes in membrane-type 1 MMP protein and tissue inhibitors of MMP activity after insulin treatment. Thus, these results suggest a mechanism by which insulin inhibits SMC migration and supports a vasculoprotective role for insulin in vivo.