Mariella Trovati

Postprandial blood glucose predicts cardiovascular events and all-cause mortality in type 2 diabetes in a 14-year follow-up: lessons from the San Luigi Gonzaga Diabetes Study.

OBJECTIVE To evaluate whether postprandial blood glucose predicts cardiovascular events and all-cause mortality in type 2 diabetes in a long-term follow-up taking into account A1C and the main cardiovascular risk factors. RESEARCH DESIGN AND METHODS Consecutive type 2 diabetic patients (n = 505) followed up at our diabetes clinic were evaluated at baseline (1995) for the main cardiovascular risk factors and for five glycemic control parameters (fasting blood glucose, blood glucose 2 h after breakfast, blood glucose 2 h after lunch, blood glucose before dinner, and A1C); all-cause mortality and the first cardiovascular events occurring during the 14-year follow-up were measured. RESULTS We observed 172 cardiovascular events (34.1% of the population) and 147 deaths (29.1% of the population). Using the Cox analysis with the backward method, we categorized the variables according to the therapeutic targets of the American Diabetes Association. Our observations were as follows. When the five glycemic control parameters were considered together, the predictors were 1) for cardiovascular events, blood glucose 2 h after lunch (hazard ratio 1.507, P = 0.010) and A1C (1.792, P = 0.002); and 2) for mortality, blood glucose 2 h after lunch (1.885, P < 0.0001) and A1C (1.907, P = 0.002). When blood glucose 2 h after lunch and A1C were considered together with the main cardiovascular risk factors, the following glycemic control parameters were predictors: 1) for cardiovascular events, blood glucose 2 h after lunch (1.452, P = 0.021) and A1C (1.732, P = 0.004); and 2) for mortality, blood glucose 2 h after lunch (1.846, P = 0.001) and A1C (1.896, P = 0.004). CONCLUSIONS In type 2 diabetes, both postprandial blood glucose and A1C predict cardiovascular events and all-cause mortality in a long-term follow-up.

Influence of Physical Training on Blood Glucose Control, Glucose Tolerance, Insulin Secretion, and Insulin Action in Non-insulin-dependent Diabetic Patients

This study has been designed to investigate, in five non-insulin-dependent diabetic patients, the influence of physical training (1 h a day, 7 days a wk for 6 wk, at 50–60% maximum oxygen uptake) on blood glucose control, glucose tolerance, insulin secretion, and insulin action. Physical training resulted in a significant improvement in blood glucose control, glucose tolerance, and insulin action. These results suggest that short-term intense physical training ameliorates the main metabolic derangements of non-insulin-dependent diabetes mellitus.

Role of catecholamines in platelet function: pathophysiological and clinical significance

Platelets are involved in the pathogenesis of vascular damage in both atherosclerosis and arterial hypertension. Their reactivity in vivo is influenced by different factors, including sympathoadrenal activation, plasma levels of atherogenic lipoproteins and haemorrheological changes. In the present review, we examine the modulation of platelet function by the sympathoadrenal system and concentrate on the role of circulating catecholamines in the control of platelet responses. Human platelets exhibit both adrenergic and dopaminergic receptors that are influenced by different catecholamines. α2‐Adrenoceptors of α2A subtype prevail on platelet membrane; through their stimulation, catecholamines potentiate the effects of other agonists and, at higher concentrations, initiate platelet responses, including aggregation, secretion and arachidonate pathway activation. Physiological and pathological conditions causing sympathoadrenal activation in vivo, i.e. physical activity, mental stress, insulin‐induced hypoglycaemia, acute coronary ischaemia and heart failure, modify the circulating platelet populations and modulate platelet reactivity through an increase in circulating catecholamines. A sympathoadrenal hyperactivation modifies the function of circulating platelets through direct catecholamine effects, catecholamine‐induced changes of haemodynamic factors and lipid pattern and inhibition of the vascular eicosanoid synthesis. The catecholamine effects on platelet function can be involved in the interplay among stress, adrenomedullary system activation and cardiovascular diseases.

Insulin Stimulates Nitric Oxide Synthesis in Human Platelets and, Through Nitric Oxide, Increases Platelet Concentrations of Both Guanosine-3′, 5′-Cyclic Monophosphate and Adenosine-3′, 5′-Cyclic Monophosphate

The insulin-induced platelet anti-aggregating effect is attributed to a nitric oxide (NO)-mediated increase of cyclic guanosine monophosphate (cGMP). The aim of this work, carried out in human platelets, is to show whether insulin increases NO synthesis in platelets and whether it enhances not only cGMP but also cyclic adenosine monophosphate (cAMP) in these cells. We observed that 1) insulin dose-dependently increases NO production, evaluated as citrulline synthesis from Larginine (n = 4, P = 0.015); 2) insulin dose-dependently increases not only cGMP but also cAMP: for instance, after 8 min of insulin incubation at 1,920 pmol/l, cAMP increased from 39.8 ± 1.4 to 121.3 ± 12.6 pmol/l/109platelets (in = 16, P = 0.0001);3) when insulin is incubated for 120 min, the increase of cGMP and cAMP shows a plateau between 2 and 20 min, and while the effect on cGMP is significant until 120 min, the effect on cAMP is no more significant at 60 and 120 min; 4) insulin increases the effects on cAMP of the adenylate cyclase agonists Iloprost and forskolin (n = 5, P = 0.0001) and enhances their platelet anti-aggregating effects (n = 6 and 8, respectively; P = 0.0001); and 5) the inhibition of NO synthase by NG-monomethyl-L-arginine blunts both the insulin effects on basal cGMP and cAMP (n = 4) and those on the Iloprost- and forskolin-induced cAMP increase (n = 5). Thus, insulin increases NO synthesis in human platelets, and, through NO, enhances both cGMP and cAMP. The platelet antiaggregating effect exerted by insulin is, therefore, a NO-mediated phenomenon involving both cGMP and cAMP.

Insulin Directly Reduces Platelet Sensitivity to Aggregating Agents: Studies In Vitro and In Vivo

The aim of this study was to investigate the influence of insulin on platelet function, both in vitro and in vivo. For the in vitro investigation, we evaluated whether insulin affects platelet function at a physiological hormone concentration by incubating the platelet-rich plasma (PRP) of fasting subjects with human regular insulin at the final concentration of 40 μU/ml for 30 min; we observed a significant reduction of platelet sensitivity to all the aggregating agents employed, i.e., ADP, platelet-activating factor (PAF), epinephrine, collagen, and Na+ arachidonate. To investigate whether the insulin effect on platelets is dose dependent, we incubated the PRP of fasting subjects with different concentrations of human regular insulin (40, 80, 120, and 160 μU/ml) for 5 min, and we observed that the insulin-induced reduction of platelet sensitivity to aggregating agents is a dose-dependent phenomenon. Furthermore, the comparison between the platelet responses after 5 and 30 min of incubation with insulin showed that the insulin effect on platelet aggregation is time dependent. The lack of specificity of its inhibiting activity suggests that insulin does not interfere with the initial binding of each aggregating agent at specific sites but does influence a common step of platelet aggregation. Our study rules out the possibility that insulin reduces platelet-function–modifying intraplatelet cAMP levels or thromboxane A2 production, because this hormone decreases the platelet concentrations of cAMP–a phenomenon that, per se, promotes platelet aggregation–and does not modify collagen or Na+ arachidonate–induced platelet production of thromboxane A2, measured by radioimmunoassay of its stable-metabolite thromboxane B2. Insulin seems to help in modifying platelet membrane properties, as has already been shown for erythrocytes. The in vivo investigation comprised three studies of the influence of insulin on platelet function in male volunteers: 1) a euglycemic-hyperinsulinemic (40-μU/ml) clamp for 90 min followed by 60 min of euglycemia; 2) a euglycemic-hyperinsulinemic (160-μU/ml) clamp for 30 min followed by 60 min of euglycemia; and 3) an intravenous bolus of human regular insulin (3.84 U/m2). Throughout the three studies, we serially measured platelet sensitivity to ADP, PAF, epinephrine, collagen, and Na+ arachidonate. We observed that insulin in vivo and at the physiologic concentration of 40 μU/ml reduced platelet aggregation. For some aggregating agents, we demonstrated a dose and time dependence of the insulin effect. The latter was reversed after the insulin infusion. When insulin was administered as an intravenous bolus and platelet aggregation was studied before the appearance of hypoglycemia, we observed that insulin influence on platelets can be detected after only 10 min. In conclusion, this study suggests that insulin may have a role in the physiological modulation of platelet function and that the long-term insulin deficiency might account for the enhanced platelet aggregability frequently observed in diabetic patients.

Platelet Resistance to Nitrates in Obesity and Obese NIDDM, and Normal Platelet Sensitivity to Both Insulin and Nitrates in Lean NIDDM

OBJECTIVE Previous studies in our laboratory showed that the platelet anti-aggregating effect exerted by insulin, mediated by a nitric oxide (NO)-induced increase of guanosine-3′,5′-cyclic monophosphate (cGMP), is lost in the insulin-resistant of obesity and obese NIDDM. It is not clear 1) whether the alterations observed in obese NIDDM patients are attributable to the obesity-related insulin resistance or to diabetes per se and 2) whether insulin-resistant states present a normal or a blunted response to NO. This study has been conducted to investigate 1) the platelet sensitivity to insulin in lean NIDDM and 2) the platelet sensitivity to an NO donor, glyceryl trinitrate (GTN), in obesity and in both lean and obese NIDDM. RESEARCH DESIGN AND METHODS We determined 1) ADP-induced platelet aggregation and platelet cGMP content in platelet-rich plasma (PRP) obtained from 11 lean NIDDM patients, after a 3-min incubation with insulin (0, 240, 480, 960, 1,920 pmol/l) and 2) ADP-induced platelet aggregation and platelet cGMP content in PRP obtained from 9 obese subjects, 11 lean and 8 obese NIDDM patients, and 18 control subjects, after a 3-min incubation with 0, 20, 40, and 100 μmol/l GTN. RESULTS Insulin dose-dependently decreased platelet aggregation in lean NIDDM patients (P = 0.0001): with 1,920 pmol/l of insulin, ADP ED50 was 141.5 ± 6.4% of basal values (P = 0.0001). Furthermore, insulin increased platelet cGMP (P = 0.0001) from 7.5 ± 0.2 to 21.1 ± 3.7 pmol/109 platelets. These results were similar to those previously described in healthy subjects. GTN reduced platelet aggregation in all the groups (P = 0.0001) at all the concentrations tested (P = 0.0001), but GTN IC50 values were much higher in insulin-resistant patients: 36.3 ± 5.0 μmol/l in healthy control subjects, 26.0 ± 6.0 μmol/l in lean NIDDM patients (NS vs. control subjects), 123.6 ± 24.0 μmol/l in obese subjects (P = 0.0001 vs. control subjects), and 110.1 ± 19.2 μmol/l in obese NIDDM patients (P = 0.0001 vs. control subjects). GTN dose-dependently increased platelet cGMP in all the groups (P = 0.0001 in control subjects, lean NIDDM patients, and obese subjects; P = 0.04 in obese NIDDM patients). Values reached by obese subjects and obese NIDDM patients, however, were lower than those reached by control subjects (with 100 μmol/l of GTN, P = 0.001 and P = 0.0001, respectively). In healthy control subjects and in obese subjects, the insulin:glucose ratio, used as an indirect measure of insulin sensitivity, was positively correlated to GTN IC50 (r = 0.530, P = 0.008), further suggesting that the sensitivity to NO is reduced in the presence of insulin resistance. CONCLUSIONS The insulin anti-aggregating effect is preserved in lean NIDDM; platelet sensitivity to GTN in preserved in lean NIDDM but is reduced in the insulin-resistant states of obesity and obese NIDDM. Resistance to nitrates, therefore, could be considered another feature of the insulin-resistance syndrome.

Platelet dysfunction in central obesity.

Central obesity is a relevant risk factor for major cardiovascular events due to the atherosclerotic involvement of coronary, cerebral and lower limb arterial vessels. A major role in the increased cardiovascular risk is played by platelets, which show an increased activation and a reduced sensitivity to the physiological and pharmacological antiaggregating agents. This review focuses on platelet dysfunction in central obesity. The mechanisms involved are related to: i) the reduced sensitivity to insulin and other substances acting via intracellular cyclic nucleotides, such as nitrates and prostacyclin; ii) the altered intracellular ionic milieu with elevated cytosolic Ca(2+); and iii) the increased oxidative stress, which elicits isoprostane production from arachidonic acid. Therapeutic guidelines recommend a multifactorial prevention of cardiovascular disease including antiplatelet drugs in high risk patients, even though, at present, the protective effect of antiplatelet therapy in obese, insulin resistant subjects has not been evaluated by specific trials. Some reports, however, suggest a decreased sensitivity to the antiaggregating effects of both acetylsalicylic acid (aspirin) and thienopyridines in human obesity. Platelet defects may play a pivotal role in the reduced efficacy of antiplatelet therapy in obese subjects in the setting of cardiovascular prevention and acute coronary syndrome treatment. Thus, a specifically tailored antiaggregating therapy is likely necessary in obese, insulin resistant subjects, especially in the presence of type 2 diabetes mellitus.

Insulin, insulin resistance and platelet function: similarities with insulin effects on cultured vascular smooth muscle cells

The relationships between insulin, insulin resistance and atherosclerosis are still a matter of intense debate [1±4] even though it was suggested as long as 30 years ago that insulin is involved in the pathogenesis of atherosclerosis [5]. It is not clear whether insulin plays the role of a culprit, an innocent bystander, a factor involved in the attenuation of some steps in the atherogenic process or an agent with multifaceted actions having different and possibly contrasting effects. The question is: is the prevalence of atherosclerosis in the insulin-resistant states due to hyperinsulinaemia or to the presence of cellular resistance to some anti-atherogenic insulin actions? To answer we need to know the mechanisms by which insulin influences the cells involved in the pathogenesis of atherosclerosis. In this review we examine the way in which insulin affects platelet function. Platelets are essential elements in the thrombotic and atherosclerotic processes because of their own functional properties and their ability to interact with endothelial and vascular smooth muscle cells (VSMC) [6]. As VSMC share common features in their contractile structure and its regulation with platelets [7] we also compare the effect of insulin and insulin resistance on these two types of cells. In particular we lay emphasis on the modulation of calcium fluxes, cyclic nucleotide concentrations, nitric oxide and prostacyclin actions.

Metformin reduces insulin requirement in Type 1 (insulin-dependent) diabetes

SummaryThe effect of metformin on Type 1 (insulin-dependent) diabetes has been assessed with the artificial pancreas. Fourteen Type 1 diabetic patients of normal body weight received in addition to their usual insulin therapy 850 mg metformin or placebo three times a day for 4–6 weeks. The sequence was placebo-metformin in eight patients and metformin-placebo in the other six. On the last day of metformin or placebo treatment, an artificial pancreas was used for about 36 h to assess insulin requirement. There was a 25.8% reduction in insulin requirement during metformin management despite slightly lower blood glucose levels (5.25±0.20 versus 5.98±0.18 mmol/l, P<0.01). Maximum reduction (about 50%) occurred 2 h after both lunch and dinner. There was no nocturnal effect. A marked decrease in specific insulin binding before metformin was found (0.56 + 0.27% to 107 monocytes versus 2.82±0.75 of control subjects) and significant increase after metformin (1.36±0.36%, p<0.05). There were no significant changes in blood lactate, total and HDL-cholesterol, triglycerides and C-peptide levels.These results show that insulin receptor binding is diminished in Type 1 diabetes, perhaps as a consequence of higher peripheral blood insulin levels and that metformin can improve binding, and so reduce the amount of insulin needed to reach euglycaemia. The insulin sparing effect is greatest after meals, and interference with intestinal absorption of sugars may also be important. It follows that metformin could be usefully administered to Type 1 diabetic patients with unimpaired liver and renal function to reduce their insulin requirement.

Studies on Mechanisms Involved in Hypoglycemia-Induced Platelet Activation

The aim of our study was to investigate the mechanisms involved in hypoglycemia-induced platelet activation. Sixteen healthy male subjects received a 60-min intravenous infusion of human regular insulin at the rate of 64 mU · m−2 · min−1: throughout 150 min, we serially measured plasma concentrations of glucose, insulin, and counterregulatory hormones; platelet sensitivity to ADP, thrombin and platelet-activating factor; plasma concentrations of platelet markers for specific proteins of in vivo release reaction (β-thromboglobulin and platelet factor 4). Our study showed that insulin-induced hypoglycemia causes a significant increase in platelet sensitivity to aggregating agents in vitro and a platelet release reaction in vivo. Hypoglycemia-induced platelet activation was not correlated with plasma glucose concentrations at nadir and occurred before the increase of plasma growth hormone and cortisol. To further elucidate the mechanisms of hypoglycemia-induced platelet activation, we incubated in vitro platelet-rich plasma (PRP) of seven fasting healthy subjects with the same concentrations of insulin, epineph-rine, glucagon, growth hormone, and cortisol measured in vivo during insulin-induced hypoglycemia. Only epinephrine was able to increase platelet sensitivity to aggregating agents. To investigate the role of α-adrenergic receptors in this phenomenon, we also studied four healthy subjects on another occasion, repeating the above-described insulin infusion together with intravenous infusion of phentolamine (–15 to + 150 min), 5 mg over 2 min followed by 500 μg/min. α-Blockade was able to suppress hypoglycemia-induced increase of platelet sensitivity to aggregating agents. A further study in vitro confirmed these results obtained in vivo, showing that incubation with phentolamine is able to inhibit the epinephrine-induced increase of platelet aggregation in response to ADP, thrombin, and platelet-activating factor. In conclusion, insulin-induced hypoglycemia deeply influences platelet function, causing an increase of platelet sensitivity to aggregating agents in vitro and a release reaction in vivo. Through α-adrenoreceptors, epinephrine is responsible for the hypoglycemia-induced increase of platelet aggregation in response to ADP, thrombin, and platelet-activating factor.