[Possible participation of advanced glycation endproducts and their receptor system in the development of diabetic vascular complications]

Role of advanced glycation end products with oxidative stress in resistance artery dysfunction in type 2 diabetic mice

OBJECTIVE

Type 2 diabetes is associated with increased advanced glycation end product (AGE) formation and vasculopathy. We hypothesized that AGEs contribute to resistance artery dysfunction.

METHODS AND RESULTS

Type 2 diabetic db(-)/db(-) (diabetic) and nondiabetic db(-)/db(+) (control) mice were treated with the AGE inhibitor (aminoguanidine: 50 mg/Kg/d) for 3 months. Isolated mesenteric resistance arteries (MRAs) were mounted in an arteriograph. Pressure-induced myogenic tone (MT) was increased in diabetic mice but was unaffected by aminoguanidine treatment. Phenylephrine-induced contraction and nitric oxide donor-induced endothelium-independent relaxation were similar in all groups. In diabetic mice, endothelium-dependent relaxation in response to shear-stress or acetylcholine was altered and was associated with reduced eNOS protein and mRNA expression. Aminoguanidine treatment improved endothelial function and restored eNOS expression. AGE formation and hypoxia markers (plasminogen activator inhibitor 1 and Bnip3) were increased in MRA from diabetic mice and normalized with Aminoguanidine. Primary cultured endothelial cells (ECs) isolated from resistance arteries subjected to high glucose for 48 hours showed decreased eNOS expression and phosphorylation in response to calcium ionophore. High glucose decreased antioxidant protein (MnSOD) and increased prooxidant proteins (gp91phox) expression leading to increased oxidative stress generation, as assessed by DHE staining and endothelial NADH/NADPH oxidase activity. The preincubation of ECs with aminoguanidine restored eNOS-phosphorylation and expression as well as the balance between pro- and antioxidant factors induced by high glucose.

CONCLUSIONS

We provide evidence of a link between AGEs, oxidative stress, and resistance artery EC dysfunction in type 2 diabetic mice. Thus, AGEs and oxidative stress may be a potential target for overcoming diabetic microvessels complications.

Retinopathy is related to the angiographically detected severity and extent of coronary artery disease in patients with type 2 diabetes mellitus

Diabetic retinopathy (DR) is an early and frequent marker of other vascular complications of diabetes and its relation with coronary ischemia is known. The aim of the present study was to evaluate the association between DR and indices of coronary artery disease (CAD) severity and extent determined by coronary angiography. Sixty-nine diabetic patients undergoing coronary angiography for suspected CAD were evaluated. The severity and extent of CAD were scored from coronary angiograms by using 3 scores. Retinopathy was graded by fundus examination. There were differences in the severity score, extent score, number of vessels with disease, duration of diabetes, diabetes therapy, history of previous myocardial infarction (MI), and serum creatinine level among patients with and without DR. CAD severity was associated with the presence of DR (r: 0.53, P < 0.001), grade of DR (r: 0.52, P < 0.001), duration of diabetes (r: 0.28, P: 0.019), history of previous MI (r: 0.36, P: 0.002); and serum creatinine level (r: 0.24, P: 0.049) where the presence of DR was the only independent factor related to the severity score in multivariate analysis (r: 0.48, P < 0.001). The parameters related to the extent score were the presence of DR (r: 0.50, P < 0.001); grade of DR (r: 0.48, P < 0.001); previous MI (r: 0.37, P: 0.002) and age of the patient (r: 0.26, P: 0.033). Factors independently related to the extent score in multivariate analysis were the presence of DR (r: 0.37, P: 0.001), previous MI (r: 0.30, P: 0.006), and age of the patient (r: 0.22, P: 0.003). Among diabetics who are suspected of having CAD, those with retinopathy have more diffuse and severe coronary atherosclerosis, compared with diabetics without retinopathy. This cannot be explained by a longer duration or inferior control of the disease.

Reduction of retinal albumin leakage by the antioxidant calcium dobesilate in streptozotocin-diabetic rats

Calcium dobesilate stabilizes blood-retinal barrier in patients with diabetic retinopathy and possesses antioxidant properties in the retinas of rats with streptozotocin-induced diabetes, exposed ex vivo to ischemia-reperfusion. Here we investigated the action of calcium dobesilate on retinal albumin leakage in streptozotocin-diabetic rats, together with relevant in vivo retinal antioxidant and permeability markers, i.e., carboxymethyl-lysine-advanced glycation end product (CML-AGE) formation and vascular endothelial cell growth factor (VEGF) overexpression. Twenty days after streptozotocin administration, diabetic rats were treated for 10 days with calcium dobesilate (100 mg/kg/day per os) or vehicle. Retinal albumin leakage, CML-AGE formation, and VEGF overexpression were evaluated by immunohistochemistry of frozen eye sections. Diabetic rats exhibited dramatic increases in: (i) retinal albumin leakage (31% of positive vessels vs. 0.2% in nondiabetic rats, P<0.008), (ii) CML-AGE retinal occurrence (40+/-3% vs. undetectable positive vessels), and (iii) retinal VEGF protein expression (14.6+/-1.1 vs. 3.5+/-0.5 VEGF-positive spots/field, P<10(-4)). Calcium dobesilate significantly reduced: (i) retinal albumin leakage (by 70%, P<0.008), (ii) retinal CML-AGEs contents (by 62%, P<0.008), and (iii) retinal VEGF expression (by 69.4%, P<0.008). In conclusion, calcium dobesilate orally given to diabetic rats markedly reduced retinal hyperpermeability, CML-AGE contents, and VEGF overexpression. These results strongly suggest that calcium dobesilate stabilizes blood-retinal barrier in diabetic retinopathy via an in situ antioxidant action. Further studies in patients are required to confirm such view.