Enrico Motz

Is Oxidative Stress the Pathogenic Mechanism Underlying Insulin Resistance, Diabetes, and Cardiovascular Disease? The Common Soil Hypothesis Revisited

Type 2 diabetes is a worldwide increasing disease resulting from the interaction between a subjects genetic makeup and lifestyle. In genetically predisposed subjects, the combination of excess caloric intake and reduced physical activity induces a state of insulin resistance. When beta cells are no longer able to compensate for insulin resistance by adequately increasing insulin production, impaired glucose tolerance appears, characterized by excessive postprandial hyperglycemia. Impaired glucose tolerance may evolve into overt diabetes. These 3 conditions, ie, insulin resistance, impaired glucose tolerance, and overt diabetes, are associated with an increased risk of cardiovascular disease. Because all these conditions are also accompanied by the presence of an oxidative stress, this article proposes oxidative stress as the pathogenic mechanism linking insulin resistance with dysfunction of both beta cells and endothelium, eventually leading to overt diabetes and cardiovascular disease. This hypothesis, moreover, may also contribute to explaining why treating cardiovascular risk with drugs, such as calcium channel blockers, ACE inhibitors, AT-1 receptor antagonists, and statins, all compounds showing intracellular preventive antioxidant activity, results in the onset of new cases of diabetes possibly being reduced.

Evidence for an Independent and Cumulative Effect of Postprandial Hypertriglyceridemia and Hyperglycemia on Endothelial Dysfunction and Oxidative Stress Generation Effects of Short- and Long-Term Simvastatin Treatment

Background—Postprandial hypertriglyceridemia and hyperglycemia are considered risk factors for cardiovascular disease. Evidence suggests that postprandial hypertriglyceridemia and hyperglycemia induce endothelial dysfunction through oxidative stress; however, the distinct role of these two factors is a matter of debate. Methods and Results—Thirty type 2 diabetic patients and 20 normal subjects ate 3 different meals: a high-fat meal; 75 g glucose alone; and high-fat meal plus glucose. Glycemia, triglyceridemia, nitrotyrosine, and endothelial function were assayed during the tests. Subsequently, diabetics took 40 mg/d simvastatin or placebo for 12 weeks. The 3 tests were performed again at baseline, between 3 to 6 days after the start, and at the end of each study. High-fat load and glucose alone produced a decrease of endothelial function and an increase of nitrotyrosine in normal and diabetic subjects. These effects were more pronounced when high fat and glucose were combined. Short-term simvastatin treatment had no effect on lipid parameters but reduced the effect on endothelial function and nitrotyrosine observed during each different test. Long-term simvastatin treatment was accompanied by a lower increase in postprandial triglycerides, which was followed by smaller variations of endothelial function and nitrotyrosine during the tests. Conclusions—This study shows an independent and cumulative effect of postprandial hypertriglyceridemia and hyperglycemia on endothelial function, suggesting oxidative stress as common mediator of such effect. Simvastatin shows a beneficial effect on oxidative stress and endothelial dysfunction, which may be ascribed to a direct effect as well as the lipid-lowering action of the drug.

Detection of nitrotyrosine in the diabetic plasma: evidence of oxidative stress.

Aims/hypothesis. Oxidative stress plays an important role in diabetic vascular complications. It has been shown that an imbalance in the ratio of nitric oxide: superoxide anion, because of a prevalence of superoxide anion, leads to an alteration in vascular reactivity. In this condition peroxynitrite production, resulting from the reaction between nitric oxide and superoxide, could increase. Peroxynitrite is responsible for nitration of tyrosine residues in proteins. Therefore, the presence of nitrotyrosine in plasma proteins is considered indirect evidence of peroxynitrite production. The aim of this study was to demonstrate the presence of nitrotyrosine in the plasma of patients with Type II (non-insulin-dependent) diabetes mellitus and to correlate its concentrations with the plasma concentrations of glucose and antioxidant defenses. Methods. A total of 40 Type II diabetic patients and 35 healthy subjects were enrolled, and glycaemia, plasma nitrotyrosine, total antioxidant parameter and glycated haemoglobin were measured. Nitrotyrosine was detected by ELISA with a detection limit of 10 nmol/l. Results. Nitrotyrosine was found in the plasma of all diabetic patients (means ± SD = 0.251 ± 0.141 μmol/l), whereas it was not detectable in the plasma of healthy control subjects. Nitrotyrosine plasma values were correlated with plasma glucose concentrations (r = 0.38, p < 0.02) but not with total antioxidant parameter or glycated haemoglobin. Total antioxidant parameter was reduced in diabetic patients (p < 0.01). Conclusions. The presence of nitrotyrosine in the plasma of diabetic patients indicates that peroxynitrite is generated in diabetes, suggesting a possible involvement of peroxynitrite in the development of diabetic complications. [Diabetologia (2001) 44: 834–838]

Meal-Generated Oxidative Stress in Type 2 Diabetic Patients

OBJECTIVE Free radical production has been reported to be increased in diabetic patients and to be involved in the pathogenesis of diabetic complications. In this study, a standardized meal was administered to 10 type 2 diabetic patients and 10 healthy matched normal subjects to evaluate its effects on plasma oxidative stress generation. RESEARCH DESIGN AND METHODS In diabetic patients, at baseline and after the meal, plasma malondialdehyde (MDA), vitamin C, protein SH groups, uric acid, vitamin E, and total plasma radical-trapping parameter, which evaluates plasma antioxidant capacity due to known and unknown antioxidants present in the plasma as well as their mutual cooperation, were measured. RESULTS After the meal, plasma MDA and vitamin C increased, while protein SH groups, uric acid, vitamin E, and total plasma radical-trapping parameter decreased more significantly in the diabetic subjects than in control subjects. CONCLUSIONS This finding shows that in the absorptive phase, free radicals are produced in diabetic patients. Since plasma glucose, but not insulin, rose significantly more in diabetic subjects than in control subjects, hyperglycemia may play an important role in the generation of postprandial oxidative stress in diabetic patients.

Meal-induced oxidative stress and low-density lipoprotein oxidation in diabetes: The possible role of hyperglycemia

Oxidative stress and its contribution to low-density lipoprotein (LDL) oxidation have been implicated in the pathogenesis of vascular diabetic complications. However, the relationship between hyperglycemia, hyperinsulinemia, hyperlipidemia, and oxidative stress is still debated. If plasma glucose and/or insulin and/or lipid are some of the most important determinants of oxidative stress in diabetes, then their typical postprandial elevations in diabetes would be expected to favor oxidative stress and LDL oxidation. To test this hypothesis, in type 2 diabetic patients, we evaluated the effects of two different standard meals designed to produce different levels of postprandial hyperglycemia on the plasma oxidative status and LDL oxidation. The meals were administered in randomized order to each of 10 type 2 diabetic patients. Blood samples were collected at baseline and 60 and 120 minutes after the meals. In every sample, plasma levels of glucose, insulin, cholesterol, triglycerides, nonesterified fatty acids (NEFAs), malondialdehyde (MDA), and the total radical-trapping antioxidant parameter (TRAP) were measured. LDL susceptibility to oxidation was evaluated at baseline and after 120 minutes. Plasma glucose, insulin, triglycerides, and MDA increased and NEFAs and TRAP significantly decreased after either meal. The variations in plasma glucose, MDA, and TRAP were significantly greater and LDL was more susceptible to oxidation after the meal that produced a significantly higher degree of hyperglycemia. These results suggest that postprandial hyperglycemia may contribute to oxidative stress in diabetic patients, providing a mechanistic link between hyperglycemia and diabetic vascular disease.

Hyperglycemia-Induced Thrombin Formation in Diabetes: The Possible Role of Oxidative Stress

Diabetes is characterized by the existence of a thrombosis-prone condition, possibly related to hyperglycemia. However, the mechanism linking hyperglycemia to the activation of the coagulation cascade is still unclear. It has been recently suggested that diabetes is accompanied by increased oxidative stress. In this work, the possibility that oxidative stress may be involved in the hyperglycemia-induced coagulation activation has been evaluated. Prothrombin fragment 1 + 2 (F1+2), which represents a reliable marker of the amount of thrombin released in the circulation, has been chosen for studying thrombin formation in vivo. In nine type II diabetic patients and in seven healthy control subjects, matched for age and body mass index, three different experiments were performed: oral glucose tolerance test (OGTT), intravenous antioxidant glutathione (GSH) administration for 2 h, and OGTT plus intravenous GSH administration. Samples were drawn at −15 min and every 30 min from 0 to 180 min. During the OGTT, F1+2 significantly increased in both diabetic and healthy subjects. GSH administration during OGTT normalized this phenomenon. GSH administered alone significantly decreased F1+2 in diabetic patients, while no effect was observed in the normal subjects. These data suggest that hyperglycemia may induce thrombin activation, possibly inducing an oxidative stress, and that antioxidant GSH may counterbalance this effect.

Total Radical-Trapping Antioxidant Parameter in NIDDM Patients

OBJECTIVE The existence of an oxidative stress in diabetes is still debated. This is largely due to the lack of good tools to assay the level of oxidative stress. The use of total radical-trapping antioxidant parameter (TRAP) has recently been proposed to explore the antioxidant property of a plasma sample. TRAP may be either directly measured by a fluorescence-based method (TRAPm) or calculated (TRAPc) by a mathematical formula, taking into account the serum levels of four natural antioxidants: protein-bound SH (thiol) groups, uric acid, vitamin E, and vitamin C. The difference between TRAPm and TRAPc is due to antioxidants, which are still unidentified, and to the possible synergism among the antioxidants. RESEARCH DESIGN AND METHODS In this study, we evaluated malondialdehyde (MDA), TRAPm, TRAPc, protein-bound SH groups, uric acid, vitamin E, and vitamin C in 40 NIDDM patients and 40 matched normal control subjects. RESULTS TRAPm and TRAPc were significantly lower in diabetic patients. A good correlation between TRAPm and TRAPc was found in both NIDDM patients (r = 0.68, P < 0.0001) and control subjects (r = 0.74, P < 0.0001). Protein-bound SH groups and uric acid were significantly lower in diabetic subjects, while MDA and vitamin E level were significantly higher. After correction for serum triglycerides (MDA) and cholesterol (vitamin E), MDA lost significance, while vitamin E did not. Vitamin C was not different in the two groups. CONCLUSIONS These data show decreased TRAP levels in NIDDM patients, suggesting the existence of lower antioxidant defenses in diabetes. The decrease appears to be due to various antioxidants, some of them not yet clearly defined. TRAP may represent a more reliable estimation of serum antioxidant capacity than the measurement of each known antioxidants. The correlation found between TRAPm and TRAPc values suggests that TRAPc, easier to measure than TRAPm, might be adequately reliable for routine assessment of oxidative stress in diabetic patients.

Post-meal coagulation activation in diabetes mellitus: the effect of acarbose

SummaryIt has been previously demonstrated that hyperglycaemia activates haemostasis; diabetes mellitus is considered a thrombosis-prone state. Acarbose, by inhibiting dietary carbohydrate absorption, reduces post-meal hyperglycaemia. In this study we evaluated the effect of post-meal hyperglycaemia on two markers of coagulation activation: prothrombin fragments 1 + 2 and D-dimer. Seventeen non-insulin-dependent diabetic patients maintained on diet therapy alone were randomly assigned to receive — with a cross-over study design — acarbose (100 mg orally) or placebo before a standard meal. Blood samples for measurement of plasma glucose, insulin, prothrombin fragments 1 + 2 and D-dimer were drawn at 0, 60, 120 and 240 min. After both placebo and acarbose, hyperglycaemia and hyperinsulinaemia which followed a standard meal were accompanied by a significant increase of plasma concentration of prothrombin fragments 1 + 2 and D-dimer in comparison to their baseline values. Acarbose administration significantly reduced the rise of glucose, insulin, prothrombin fragments 1 + 2 and D-dimer from 0 to 240 min in comparison to placebo. We conclude that post-meal hyperglycaemia, at the level reached by many diabetic patients on diet therapy alone, induces a coagulation activation. Acarbose, by decreasing post-meal hyperglycaemia, may be useful in reducing meal-induced activation of haemostasis in diabetic patients.

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.

Increased Circulating Intercellular Adhesion Molecule-1 Levels in Type II Diabetic Patients: The Possible Role of Metabolic Control and Oxidative Stress

Blood levels of the circulating form of the integrin intercellular adhesion molecule-1 (ICAM-1), malondialdehyde (MDA), and hemoglobin A1c (HbA1c) were studied at baseline and 3 months after improved metabolic control in 25 type II diabetic patients without signs of macroangiopathy, and were compared with those in 15 matched healthy normal controls. Circulating ICAM-1 and MDA levels were increased in diabetic patients, both at baseline and 3 months later. However, with improving metabolic control HbA1c, circulating ICAM-1, and MDA significantly decreased. A significant correlation between circulating ICAM-1, HbA1c, and MDA was found in diabetic patients at each time. Multiple regression analysis considering circulating ICAM-1 as the dependent variable and HbA1c and MDA as independent variables, showed a significant correlation between the three variable at each time. Similar correlations were found in control subjects. These data show increased levels of circulating ICAM-1 in type II diabetic patients, independent of the presence of macroangiopathy. Moreover, these results suggest that oxidative stress and metabolic control might participate in determining increased circulating ICAM-1 levels in both type II diabetic patients and normal subjects.