Augmentation of Arterial Endothelial Cell Expression of the Plasminogen Activator Inhibitor Type-1 (PAI-1) Gene by Proinsulin and Insulinin vivo

Diabetes mellitus is associated with an increased incidence and greater severity of primary atherosclerosis as well as restenosis after angioplasty for reasons not yet clear. We have shown previously that insulin and proinsulin—typically elevated in blood in patients with type II diabetes—increase plasma activity of plasminogen activator inhibitor type 1 (PAI-1)in vivo. Others have demonstrated that increased PAI-1 activity is associated with coronary heart disease. Accordingly, the present study was performed to identify sites of increased expression of the PAI-1 gene within the vessel wall. Equimolar concentrations of insulin, proinsulin, or vehicle alone as a control, were administered intravenously over 1 h to conscious rabbits that were kept euglycemic throughout by the use of glucose clamping. Within 3 h plasma PAI-1 activity increased from 1.15±1.34 to 11.33±4.30 AU/ml with insulin (mean± ,P=0.015) and from 2.83±0.74 to 15.43±4.70 AU/ml with proinsulin (P=0.035). This was found to be in contrast to the controls where the increase in plasma PAI-1 activity was of lesser degree (2.43±1.86 to 6.80±1.10 AU/ml,P= ,n=4 each). As judged from the results ofin situhybridization, the site of prominent aortic expression of the PAI-1 gene was the endothelium. Furthermore, expression increased further in this site after administration of insulin or proinsulin. As judged from results of immunohistochemistry, PAI-1 protein in the aorta was also prominent in endothelium. These results suggest that “hyper(pro)insulinemia”, increases PAI-1 not only in blood but also in arterial endothelium. Thus, attenuation of vasculopathy and especially of restenosis after angioplasty in type II diabetes may be possible with somatic gene therapy targeting PAI-1 expression in endothelial cells.