Interaction of diabetes and hypertension on determinants of endothelial adhesiveness

Epidemiological studies have established that diabetes mellitus and hypertension are independent risk factors for atherosclerosis. One of the earliest abnormalities seen in atherogenesis is enhanced monocyte adherence to the endothelium. The mechanisms by which diabetes mellitus or hypertension enhances monocyte-endothelial cell interactions are incompletely characterized. It is not known whether there are additive interactions between these risk factors on endothelial adhesiveness for monocytes. Male Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats were fed a normal or fructose-enriched diet. In some cases, animals were injected with streptozotocin (35 mg/kg body weight) to induce diabetes. After 2 weeks, plasma was drawn for biochemical measurements, and thoracic aortas were harvested, opened longitudinally, and exposed to fluorescently labeled mouse monocytoid cells (WEHI 78/24, 2 x 10(6)/mL) for 30 minutes on a rocking platform. Adherent cells were counted by epifluorescence microscopy. WEHI 78/24 binding to aortic segments from SHR animals was elevated compared with segments from WKYs. Fructose feeding alone had no effect on endothelial adhesiveness. When WKYs were made hyperglycemic by STZ injection, monocyte binding was 160% of the control value. Elevated monocyte binding was also observed in aortas derived from SHR animals injected with STZ, indicating an additive effect of hypertension and hyperglycemia. To determine whether alterations in oxidative state played a role in the endothelial adhesiveness, aortic segments were exposed to lucigenin (250 micromol/L) for measurement of superoxide anion. Aortic segments from SHR elaborated 120% more superoxide anion than did controls. Elevated free-radical production was also observed in aortas from diabetic WKYs. Furthermore, thoracic aortas derived from diabetic SHR animals elaborated more superoxide anion than did any of the other groups (374%, P<0.05). Immunohistochemical staining for monocyte chemotactic protein-1 demonstrated increased expression in aortas isolated from diabetic WKY and SHR compared with control vessels. These studies demonstrate that both diabetes and hypertension lead to increased monocyte adherence to the endothelium. This abnormality is associated with increased vascular superoxide production and monocyte chemotactic protein-1 expression. Furthermore, there appears to be an additive interaction between hyperglycemia and hypertension in their effects on endothelial adhesiveness and its determinants.