Effects of insulin on in vitro vascular cell adhesion molecule-1 expression and in vivo soluble VCAM-1 release

Aims/hypothesis. To evaluate the effects of insulin on vascular cell adhesion molecule-1 expression by cultured human vascular endothelial cells and soluble vascular cell adhesion molecule-1 release in vivo. Methods. Human vascular endothelial cells derived from umbilical cord veins were incubated with either insulin (from 10(-6) to 10(-9) mol/l) or tumour necrosis factor-alpha (5 ng/ml) for 6 to 24 h. Plasma soluble vascular cell adhesion molecule-1 concentrations were evaluated in 12 non-insulin-dependent diabetic patients (8 men, 3 women, mean age 47.1 +/- 7.7 years) and 12 healthy volunteers matched for age, sex and weight (7 men, 5 women, mean age 42.2 +/- 7.2 years) before and after a 2-h euglycaemic hyperinsulinaemic clamp. Results. Transcriptional activities of nuclear factor-xB luciferase and vascular adhesion molecule-1 luciferase statistically significantly increased after incubation with tumour necrosis factor-ct. By contrast, a slight increment of nuclear factor-xB luciferase (mean: 1.8 +/- 0.3 fold) but not of vascular cell adhesion molecule-1 luciferase transcriptional activities were detected in cells stimulated with insulin. Soluble vascular cell adhesion molecule-1 concentrations in cell supernatants increased after tumour necrosis factor-a but not insulin stimulation. In vivo, baseline plasma soluble vascular cell adhesion molecule-1 concentrations were higher (p = 0.03) in non-insulin-dependent patients (708.7 +/- 97.4 mu g/l) than controls (632.1 +/- 65.2 mu g/l) but were not related to fasting insulin concentrations and did not change during insulin infusion. Conclusion/interpretation. The increased concentrations of circulating soluble vascular cell adhesion molecule-1 indicates that the vascular endothelium is activated in non-insulin dependent diabetic patients. Our in vitro and in vivo findings show that vascular cell adhesion molecule-1 activation cannot be due to hyperinsulinaemia.