Reactive oxygen species mediate a cellular 'memory' of high glucose stress signalling.

AIMS/HYPOTHESIS: A long-term 'memory' of hyperglycaemic stress, even when glycaemia is normalised, has been previously reported in endothelial cells. In this report we sought to duplicate and extend this finding. MATERIALS AND METHODS: HUVECs and ARPE-19 retinal cells were incubated in 5 or in 30 mmol/l glucose for 3 weeks or subjected to 1 week of normal glucose after being exposed for 2 weeks to continuous high glucose. HUVECs were also treated in this last condition with several antioxidants. Similarly, four groups of rats were studied for 3 weeks: (1) normal rats; (2) diabetic rats not treated with insulin; (3) diabetic rats treated with insulin during the last week; and (4) diabetic rats treated with insulin plus alpha-lipoic acid in the last week. RESULTS: In human endothelial cells and ARPE-19 retinal cells in culture, as well as in the retina of diabetic rats, levels of the following markers of high glucose stress remained induced for 1 week after levels of glucose had normalised: protein kinase C-beta, NAD(P)H oxidase subunit p47phox, BCL-2-associated X protein, 3-nitrotyrosine, fibronectin, poly(ADP-ribose) Blockade of reactive species using different approaches, i.e. the mitochondrial antioxidant alpha-lipoic acid, overexpression of uncoupling protein 2, oxypurinol, apocynin and the poly(ADP-ribose) polymerase inhibitor PJ34, interrupted the induction both of high glucose stress markers and of the fluorescent reactive oxygen species (ROS) probe CM-H(2)DCFDA in human endothelial cells. Similar results were obtained in the retina of diabetic rats with alpha-lipoic acid added to the last week of normalised glucose. CONCLUSIONS/INTERPRETATION: These results provide proof-of-principle of a ROS-mediated cellular persistence of vascular stress after glucose normalisation.

Effects of S21403 (mitiglinide) on postprandial generation of oxidative stress and inflammation in type 2 diabetic patients.

AIM/HYPOTHESIS: Evidence suggests that postprandial hyperglycaemia may be a cardiovascular risk factor in diabetes. Oxidative stress and inflammation are involved in the pathogenesis of diabetic complications and previous studies have shown increased oxidative stress and inflammation in the postprandial phase in diabetic patients. The aim of the present study was to evaluate whether controlling postprandial hyperglycaemia with S21403 (mitiglinide) is accompanied by a reduced generation of oxidative stress and inflammation. SUBJECTS AND METHODS: Forty type 2 diabetic patients participated in the study. Two different breakfast-tests were performed in each patient, with placebo or S21403. Plasma nitrotyrosine, plasma malondialdehyde (MDA), oxidised LDL (oxLDL), plasma total radical-trapping antioxidant parameter (TRAP), IL-6, IL-18, TNF-alpha, plasma glucose and insulin were measured. RESULTS: After the administration of S21403, 40 mg, a rapid stimulation of insulin secretion was observed, accompanied by a reduction of postprandial hyperglycaemia. With S21403, a significant decrease of either nitrotyrosine, MDA and oxLDL levels, and a preservation of plasma TRAP compared with placebo was found. Significant decreases of IL-6, IL-18 and TNF-alpha were also observed with S21403 compared with placebo. CONCLUSIONS/INTERPRETATION: This study shows that controlling postprandial hyperglycaemia with S21403 significantly improves the cluster of oxidative stress and inflammation markers that are increased in the postprandial state in diabetic patients.

Intermittent high glucose enhances ICAM-1, VCAM-1, E-selectin and interleukin-6 expression in human umbilical endothelial cells in culture: the role of poly(ADP-ribose) polymerase.

It has been previously reported that endothelial cells exposed to constant high concentrations of glucose upregulate the expression of adhesion molecules. Moreover, it has been suggested that this phenomenon is related to generation of oxidative stress. It has also been suggested that oxidative injuries, related to high glucose, induce the activation of the enzyme poly ADP ribose polymerase (PARP), which can promote the expression of adhesion molecules and the generation of inflammation. Recent in-vivo and in-vitro evidence suggests that oscillation of glucose may play an autonomous and direct role in favoring the development of cardiovascular complications in diabetes. In this study we have investigated the effects of constantly high and intermittently high glucose on nitrotyrosine formation (a marker of nitrosative stress) and adhesion molecule (ICAM-1, VCAM-1 and E-selectin), as well as on interleukin (IL)-6 expression in human umbilical vein endothelial cells, either in the presence or in the absence of PJ34, a potent inhibitor of PARP. We found that oscillating glucose was more effective in triggering the generation of nitrotyrosine and inducing the expression of adhesion molecules and IL-6 than stable high glucose. Pharmacological inhibition of PARP suppressed both nitrotyrosine formation, adhesion molecule expression and IL-6 to the levels seen in the normal glucose conditions. Thus, PARP activation appears to be involved in both promoting nitrosative stress and upregulating adhesion molecules and inflammation in endothelial cells exposed to oscillating high glucose conditions.

Effect of irbesartan on nitrotyrosine generation in non-hypertensive diabetic patients.

AIMS/HYPOTHESIS: Oxidative stress is involved in the pathogenesis of microangiopathic and macroangiopathic diabetic complications. The results of recent trials suggest that type 1 angiotensin II (AT-1) receptor blockers may prevent or delay nephropathy and cardiovascular disease in diabetic patients, independently of their anti-hypertensive action. There is evidence that AT-1 receptor blockers can work as intracellular antioxidants. This study investigated whether the AT-1 receptor blocker irbesartan is able to reduce nitrotyrosine formation in non-hypertensive diabetic patients under fasting conditions and during acute hyperglycaemia. METHODS: A total of 40 non-hypertensive, non-microalbuminuric Type 2 diabetic patients and 20 healthy, normotensive subjects were recruited for this study. Diabetic patients followed a randomised, double-blind, placebo-controlled, crossover protocol, taking either irbesartan (150 mg orally, twice daily) or placebo for 60 days. Fasting glucose and nitrotyrosine were measured at baseline and at the end of each treatment period. An OGTT was also performed at the same time intervals, during which plasma glucose and nitrotyrosine levels were monitored. RESULTS: Compared with baseline measurements, treatment with irbesartan (0.57+/-0.4 vs 0.35+/-0.3 micromol/l, p<0.01) but not placebo (0.58+/-0.3 vs 0.59+/-0.2 micromol/l) significantly reduced fasting nitrotyrosine levels. Irbesartan also significantly reduced nitrotyrosine formation during the OGTT. CONCLUSIONS/INTERPRETATION: . This study demonstrates that irbesartan reduces plasma levels of nitrotyrosine in diabetic patients and is effective in counterbalancing nitrotyrosine formation during acute hyperglycaemia. Our results may help to elucidate how AT-1 receptor blockers exert their beneficial effect independently of their BP-lowering activity.

The post-prandial state in Type 2 diabetes and endothelial dysfunction: effects of insulin aspart.

OBJECTIVE: Recently, much attention has been focused on the possibility that the post-prandial state may be a cardiovascular risk factor in diabetes. The aim of the present study was to evaluate whether the post-prandial state is associated with endothelial dysfunction in patients with diabetes and to explore the effect on this aspect of managing post-prandial hyperglycaemia by insulin aspart. RESEARCH DESIGN AND METHODS: Twenty-three patients with Type 2 diabetes and 10 normal controls were recruited. In the diabetic patients two different tests were performed in each subject: a standard meal preceded by subcutaneous injection of soluble insulin (0.15 U/kg body weight) or of short-acting insulin aspart (0.15 U/kg body weight). These tests were designed to achieve different levels of post-prandial hyperglycaemia. Controls received a single standard meal test. Immediately before, and 1, 2, 4 and 6 h after each meal, blood glucose, triglycerides, free fatty acids and flow-mediated vasodilation were measured. RESULTS: Compared with regular insulin, insulin aspart significantly reduced the area under the curve for post-prandial hyperglycaemia (58.3 +/- 17.6 vs. 68.1 +/- 17.7; P<0.04), and preserved flow-mediated vasodilation, which was decreased in the post-prandial state (39.4 +/- 2.9 vs. 34.1 +/- 2.2; P<0.01). Triglyceride and free fatty acid levels were not differentially affected by the treatment. In normal controls the meal did not affect flow-mediated vasodilation. CONCLUSION: This study shows that the post-prandial state is accompanied by endothelial dysfunction in Type 2 diabetic patients and that insulin aspart improved endothelial function.