A short-term incubation with high glucose impairs VASP phosphorylation at serine 239 in response to the nitric oxide/cGMP pathway in vascular smooth muscle cells: role of oxidative stress.

A reduction of the nitric oxide (NO) action in vascular smooth muscle cells (VSMC) could play a role in the vascular damage induced by the glycaemic excursions occurring in diabetic patients; in this study, we aimed to clarify whether a short-term incubation of cultured VSMC with high glucose reduces the NO ability to increase cGMP and the cGMP ability to phosphorylate VASP at Ser-239. We observed that a 180 min incubation of rat VSMC with 25 mmol/L glucose does not impair the NO-induced cGMP increase but reduces VASP phosphorylation in response to both NO and cGMP with a mechanism blunted by antioxidants. We further demonstrated that high glucose increases radical oxygen species (ROS) production and that this phenomenon is prevented by the PKC inhibitor chelerythrine and the NADPH oxidase inhibitor apocynin. The following sequence of events is supported by these results: (i) in VSMC high glucose activates PKC; (ii) PKC activates NADPH oxidase; (iii) NADPH oxidase induces oxidative stress; (iv) ROS impair the signalling of cGMP, which is involved in the antiatherogenic actions of NO. Thus, high glucose, via oxidative stress, can reduce the cardiovascular protection conferred by the NO/cGMP pathway via phosphorylation of the cytoskeleton protein VASP in VSMC.

Oleic acid increases synthesis and secretion of VEGF in rat vascular smooth muscle cells: role of oxidative stress and impairment in obesity.

Obesity is characterized by poor collateral vessel formation, a process involving vascular endothelial growth factor (VEGF) action on vascular smooth muscle cells (VSMC). Free fatty acids are involved in the pathogenesis of obesity vascular complications, and we have aimed to clarify whether oleic acid (OA) enhances VEGF synthesis/secretion in VSMC, and whether this effect is impaired in obesity. In cultured aortic VSMC from lean and obese Zucker rats (LZR and OZR, respectively) we measured the influence of OA on VEGF-A synthesis/secretion, signaling molecules and reactive oxygen species (ROS). In VSMC from LZR we found the following: (a) OA increases VEGF-A synthesis/secretion by a mechanism blunted by inhibitors of Akt, mTOR, ERK-1/2, PKC-beta, NADPH-oxidase and mitochondrial electron transport chain complex; (b) OA activates the above mentioned signaling pathways and increases ROS; (c) OA-induced activation of PKC-beta enhances oxidative stress, which activates signaling pathways responsible for the increased VEGF synthesis/secretion. In VSMC from OZR, which present enhanced baseline oxidative stress, the above mentioned actions of OA on VEGF-A, signaling pathways and ROS are impaired: this impairment is reproduced in VSMC from LZR by incubation with hydrogen peroxide. Thus, in OZR chronically elevated oxidative stress causes a resistance to the action on VEGF that OA exerts in LZR by increasing ROS.

Effects of high glucose on vascular endothelial growth factor synthesis and secretion in aortic vascular smooth muscle cells from obese and lean Zucker rats.

Type 1 diabetes is characterized by insulin deficiency, type 2 by both insulin deficiency and insulin resistance: in both conditions, hyperglycaemia is accompanied by an increased cardiovascular risk, due to increased atherosclerotic plaque formation/instabilization and impaired collateral vessel formation. An important factor in these phenomena is the Vascular Endothelial Growth Factor (VEGF), a molecule produced also by Vascular Smooth Muscle Cells (VSMC). We aimed at evaluating the role of high glucose on VEGF-A(164) synthesis and secretion in VSMC from lean insulin-sensitive and obese insulin-resistant Zucker rats (LZR and OZR). In cultured aortic VSMC from LZR and OZR incubated for 24 h with d-glucose (5.5, 15 and 25 mM) or with the osmotic controls l-glucose and mannitol, we measured VEGF-A(164) synthesis (western, blotting) and secretion (western blotting and ELISA). We observed that: (i) d-glucose dose-dependently increases VEGF-A(164) synthesis and secretion in VSMC from LZR and OZR (n = 6, ANOVA p = 0.002-0.0001); (ii) all the effects of 15 and 25 mM d-glucose are attenuated in VSMC from OZR vs. LZR (p = 0.0001); (iii) l-glucose and mannitol reproduce the VEGF-A(164) modulation induced by d-glucose in VSMC from both LZR and OZR. Thus, glucose increases via an osmotic mechanism VEGF synthesis and secretion in VSMC, an effect attenuated in the presence of insulin resistance.

High glucose inhibits the aspirin-induced activation of the nitric oxide/cGMP/cGMP-dependent protein kinase pathway and does not affect the aspirin-induced inhibition of thromboxane synthesis in human platelets.

Since hyperglycemia is involved in the "aspirin resistance" occurring in diabetes, we aimed at evaluating whether high glucose interferes with the aspirin-induced inhibition of thromboxane synthesis and/or activation of the nitric oxide (NO)/cGMP/cGMP-dependent protein kinase (PKG) pathway in platelets. For this purpose, in platelets from 60 healthy volunteers incubated for 60 min with 5-25 mmol/L d-glucose or iso-osmolar mannitol, we evaluated the influence of a 30-min incubation with lysine acetylsalicylate (L-ASA; 1-300 µmol/L) on 1) platelet function under shear stress; 2) aggregation induced by sodium arachidonate or ADP; 3) agonist-induced thromboxane production; and 4) NO production, cGMP synthesis, and PKG-induced vasodilator-stimulated phosphoprotein phosphorylation. Experiments were repeated in the presence of the antioxidant agent amifostine. We observed that platelet exposure to 25 mmol/L d-glucose, but not to iso-osmolar mannitol, 1) reduced the ability of L-ASA to inhibit platelet responses to agonists; 2) did not modify the L-ASA-induced inhibition of thromboxane synthesis; and 3) prevented the L-ASA-induced activation of the NO/cGMP/PKG pathway. Preincubation with amifostine reversed the high-glucose effects. Thus, high glucose acutely reduces the antiaggregating effect of aspirin, does not modify the aspirin-induced inhibition of thromboxane synthesis, and inhibits the aspirin-induced activation of the NO/cGMP/PKG pathway. These results identify a mechanism by which high glucose interferes with the aspirin action.

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.

Lipoprotein(a) and family history of cardiovascular disease in children with familial dyslipidemias.

OBJECTIVE: To investigate in children and adolescents with familial dyslipidemias the association between lipoprotein(a) [Lp(a)] level and family history of cardiovascular disease (CVD), and whether this association is independent of the disturbed lipid profile. STUDY DESIGN: Lp(a) level, lipid profile, and a 2-generation genealogic tree to detect cardiovascular events were evaluated in 231 patients with familial dyslipidemias. Lp(a) levels were stratified according to presence, age of occurrence, and number and type of cardiovascular events in the patient's kindreds. RESULTS: Lp(a) and other plasma lipid fractions did not differ between patients with and those without a family history of cardiovascular events. However, the percentage of patients with elevated Lp(a) level (≥85th percentile) was higher in those with a positive family history for early cardiovascular events (P = .01). Lp(a) level was a significant independent predictor of the number of premature cardiovascular events (ß = 0.17; P = .01) and of cerebrovascular events in kindreds (OR, 2.5; 95% CI, 1.05-6.03; P = .039), independent of plasma lipid fractions and other cardiovascular risk factors. CONCLUSIONS: In children and adolescents with familial dyslipidemias, the overall association between Lp(a) level and family history of early CVD may be due to a threshold effect in those with the highest Lp(a) levels. However, multiple cardiovascular events and cerebrovascular events are predicted by any increase in plasma Lp(a) level, independent of other cardiovascular risk factors.

Nitric oxide activates PI3-K and MAPK signalling pathways in human and rat vascular smooth muscle cells: influence of insulin resistance and oxidative stress.

OBJECTIVE: Vascular smooth muscle cells (VSMCs) from the animal model of insulin resistance obese Zucker rats (OZR) show impaired ability of nitric oxide (NO) to increase cGMP and of cGMP to activate its specific kinase PKG, these defects being attributable to oxidative stress. We aimed to investigate the intracellular signalling downstream PKG in human and rat VSMC, and to clarify whether it is modified by insulin resistance and oxidative stress. METHODS: In aortic VSMC from humans, lean Zucker rats (LZR) and OZR, we measured by Western blots the activation induced by NO and cGMP of signalling molecules of PI3-K and MAPK pathways, with or without PKG inhibition, hydrogen peroxide and antioxidants. We explored the mechanism of the increased oxidative stress in VSMC from OZR by measuring superoxide anion concentrations (luminescence method) with or without inhibition of NADPH oxidase, xanthine oxidase, and mitochondrial electron transport chain complex and by measuring superoxide dismutase (SOD) expression (Western blot) and activity. RESULTS: In VSMC from humans and LZR, the NO/cGMP/PKG pathway activates both PI3-K (Akt, mTOR) and MAPK (ERK-1/2, p38MAPK) signalling. This effect is attenuated in VSMC from OZR, in which the greater oxidative stress is mediated by NADPH oxidase and mitochondrial complex and by a reduced synthesis/activity of SOD. Impairment of the NO/cGMP/PKG signalling is reproduced in VSMC from LZR by hydrogen peroxide and reverted in VSMC from OZR by antioxidants. CONCLUSIONS: In VSMC from an animal model of insulin resistance the NO/cGMP/PKG intracellular signalling is impaired due to an increased oxidative stress.

Adipocytokines in atherothrombosis: focus on platelets and vascular smooth muscle cells.

Visceral obesity is a relevant pathological condition closely associated with high risk of atherosclerotic vascular disease including myocardial infarction and stroke. The increased vascular risk is related also to peculiar dysfunction in the endocrine activity of adipose tissue responsible of vascular impairment (including endothelial dysfunction), prothrombotic tendency, and low-grade chronic inflammation. In particular, increased synthesis and release of different cytokines, including interleukins and tumor necrosis factor-alpha (TNF-alpha), and adipokines-such as leptin-have been reported as associated with future cardiovascular events. Since vascular cell dysfunction plays a major role in the atherothrombotic complications in central obesity, this paper aims at focusing, in particular, on the relationship between platelets and vascular smooth muscle cells, and the impaired secretory pattern of adipose tissue.

The cardiovascular effects of metformin: further reasons to consider an old drug as a cornerstone in the therapy of type 2 diabetes mellitus.

Cardiovascular events occurring in type 2 diabetes (T2DM) are a major problem in clinical practice. In particular, the risk of myocardial infarction (MI) presented by patients affected by T2DM without previous cardiac events is similar to that of non-diabetic patients with previous MI. To reduce the elevated cardiovascular risk associated with T2DM, tight glycemic control and aggressive therapy against all known cardiovascular risk factors are strictly required. Despite the role played by hyperglycemia in the pathogenesis of cardiovascular events, studies showing an improvement of cardiovascular outcomes by anti-hyperglycemic or hypoglycemic agents are not conclusive. The United Kingdom Prospective Diabetes Study (UKPDS) demonstrated that in obese type 2 diabetic patients metformin reduces the risk of MI more than sulphonylureas or insulin. This observation identified metformin as the first-line treatment for T2DM. The vasoprotective role of metformin is largely independent of its hypoglycemic action and has been ascribed to pleiotropic effects. The present review considers the putative beneficial action exerted by metformin on arterial vessels by evaluating its effects on lipids, inflammation, hemostasis, endothelial and platelet function and vessel wall abnormalities. Furthermore, the molecular mechanisms of the beneficial metabolic and vascular effects of metformin will be considered, with a particular attention for its ability to activate AMP-activated protein kinase.

Role of NMDA receptor in homocysteine-induced activation of mitogen-activated protein kinase and phosphatidyl inositol 3-kinase pathways in cultured human vascular smooth muscle cells.

INTRODUCTION: Exposure of vascular smooth muscle cells (VSMC) to homocysteine, at concentrations associated with an increased risk of cardiovascular events, enhances synthesis and secretion of Matrix Metalloproteinase-2 (MMP-2), which is involved in atherosclerotic plaque instabilization. This effect was prevented by inhibitors of Mitogen Activated Protein Kinase (MAPK) and Phosphatidylinositol 3-Kinase (PI3-K) pathways, allowing to hypothesize that homocysteine activates both these pathways, likely via a receptor-mediated mechanism. One possible receptor is N-methyl-D-aspartate receptor (NMDAr), which is expressed in VSMC and is involved in homocysteine effects in other cell types. MATERIALS AND METHODS: VSMC exposed to DL-homocysteine or NMDA (100 micromol/L for both; 5 min-8 hours), were investigated by measuring: i) phosphorylation of ERK1/2, p38MAPK (signaling molecules of MAPK pathway) and Akt and p70S6K (signaling molecules of PI3-K pathway) by western blot; ii) synthesis and secretion of MMP-2 (western blot); iii) activation of MMP-2 (gelatin zimography). To evaluate NMDAr involvement in the homocysteine effects, the experiments were repeated in the presence of a non-competitive NMDAr-antagonist MK-801 (50 micromol/L) or L-glycine (10 micromol/L), which inhibits NMDAr function by promoting its internalization. RESULTS: DL-homocysteine and NMDA time-dependently increased: i) the phosphorylation of ERK1/2, p38 MAPK, Akt and p70S6K (ANOVA, p<0.0001); ii) the synthesis, secretion and activation of MMP-2. DL-homocysteine and NMDA effects were prevented by VSMC pre-incubation with MK-801 or high L-glycine concentrations. CONCLUSIONS: In human VSMC homocysteine-at concentrations associated with increased cardiovascular risk- activates MAPK and PI3-K pathways and MMP-2 synthesis and secretion through NMDA receptor, a potential mechanism involved in intracellular signaling in response to homocysteine in VSMC.

Evaluation of a simple policy for pre- and post-prandial blood glucose self-monitoring in people with type 2 diabetes not on insulin.

BACKGROUND AND AIMS: Since there is no agreement on regimens of self-monitoring of blood glucose (SMBG) in type 2 diabetes not on insulin, we evaluated the effects of a simple SMBG policy taking into account compliance. METHODS AND RESULTS: 273 type 2 diabetic patients not on insulin with HbA1c >7% attending our Diabetes Clinic and already using SMBG were randomized as follows: Group A, one BG profile/month with fasting and post-prandial values; Group B, one BG profile every 2 weeks with pre- and post-prandial values. Patients were followed-up by the same team every 3 months with the same education and treatment policies. At 3 and 6 months, SMBG profiles were evaluated and HbA1c measured. SMBG was carried out as recommended by 73% of Group A and 44% of Group B patients. In compliant patients, HbA1c and BG were unchanged in Group A whereas in Group B fasting, pre-prandial and two out of three post-prandial BG values were reduced and HbA1c decreased from 8.09+/-0.84% to 7.60+/-0.73% (p<0.001). The influence on BG control was similar for the two policies when compliance was not considered. CONCLUSIONS: The more intensive SMBG policy considered is associated with improvements in glycaemic control in compliant subjects.

In central obesity, weight loss restores platelet sensitivity to nitric oxide and prostacyclin.

Central obesity shows impaired platelet responses to the antiaggregating effects of nitric oxide (NO), prostacyclin, and their effectors--guanosine 3',5'-cyclic monophosphate (cGMP) and adenosine 3',5'-cyclic monophosphate (cAMP). The influence of weight loss on these alterations is not known. To evaluate whether a diet-induced body-weight reduction restores platelet sensitivity to the physiological antiaggregating agents and reduces platelet activation in subjects affected by central obesity, we studied 20 centrally obese subjects before and after a 6-month diet intervention aiming at reducing body weight by 10%, by measuring (i) insulin sensitivity (homeostasis model assessment of insulin resistance (HOMA(IR))); (ii) plasma lipids; (iii) circulating markers of inflammation of adipose tissue and endothelial dysfunction, and of platelet activation (i.e., soluble CD-40 ligand (sCD-40L) and soluble P-selectin (sP-selectin)); (iv) ability of the NO donor sodium nitroprusside (SNP), the prostacyclin analog Iloprost and the cyclic nucleotide analogs 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP) and 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) to reduce platelet aggregation in response to adenosine-5-diphosphate (ADP); and (v) ability of SNP and Iloprost to increase cGMP and cAMP. The 10 subjects who reached the body-weight target showed significant reductions of insulin resistance, adipose tissue, endothelial dysfunction, and platelet activation, and a significant increase of the ability of SNP, Iloprost, 8-Br-cGMP, and 8-Br-cAMP to reduce ADP-induced platelet aggregation and of the ability of SNP and Iloprost to increase cyclic nucleotide concentrations. No change was observed in the 10 subjects who did not reach the body-weight target. Changes of platelet function correlated with changes of HOMA(IR). Thus, in central obesity, diet-induced weight loss reduces platelet activation and restores the sensitivity to the physiological antiaggregating agents, with a correlation with improvements in insulin sensitivity.

Contribution of insulin resistance to vascular dysfunction.

Insulin is a vascular hormone, able to influence vascular cell responses. In this review, we consider the insulin actions on vascular endothelium and on vascular smooth muscle cells (VSMC) both in physiological conditions and in the presence of insulin resistance. In particular, we focus the relationships between activation of insulin signalling pathways of phosphatidylinositol-3 kinase (PI3-K) and mitogen-activated protein kinase (MAPK) and the different vascular actions of insulin, with a particular attention to the insulin ability to activate the pathway nitric oxide (NO)/cyclic GMP/PKG via PI3-K, owing to the peculiar relevance of NO in vascular biology. We also discuss the insulin actions mediated by the MAPK pathway (such as endothelin-1 synthesis and secretion and VSMC proliferation and migration) and by the interactions between the two pathways, both in insulin-sensitive and in insulin-resistant states. Finally, we consider the influence of free fatty acids, cytokines and endothelin on vascular insulin resistance.

Resistance to aspirin and thienopyridines in diabetes mellitus and metabolic syndrome.

Platelets from patients affected by diabetes mellitus and metabolic syndrome show an impaired sensitivity to physiological antiaggregating agents and an enhanced activation state, mirrored by an increased expression of membrane activation markers; furthermore, they are more prone to form spontaneous microaggregates with ADP receptor involvement. These abnormalities are responsible for a pro-thrombotic condition, contributing to a high cardiovascular risk. This pattern of platelet abnormalities provides a strong rationale for aggressive antiplatelet therapy strongly recommended by guidelines both in diabetes mellitus and in metabolic syndrome, not only in the setting of acute coronary syndromes, but also for the long-term prevention of the cardiovascular events. Antiplatelet therapy in these pathological conditions, however, is still a matter of intense debate, especially because a high prevalence of "resistance" to these drugs (and to aspirin in particular) has been described in these patients. This may result in non-significant reductions in cardiovascular events. Different factors seem to be involved, including: i) genetic polymorphisms; ii) hyperglycemia and poor metabolic control; iii) reduced sensitivity to nitric oxide; iv) a pro-inflammatory and/or pro-thrombotic status, and, v) increased oxidative stress. This review will take into consideration: i) the results of the most relevant studies addressing the effects of the anti-aggregating treatment in patients affected by diabetes mellitus and/or metabolic syndrome, and, ii) the biochemical mechanisms accounting for the impaired sensitivity to aspirin and thienopyridines in the above mentioned clinical conditions.

Sodium azide, a bacteriostatic preservative contained in commercially available laboratory reagents, influences the responses of human platelets via the cGMP/PKG/VASP pathway.

OBJECTIVE: The bacteriostatic preservative sodium azide (NaN(3)) activates soluble guanylate cyclase (sGC) in vascular tissues, thus elevating cellular 3',5'-cyclic guanosine monophosphate (cGMP). Because the sGC/cGMP pathway is involved in the control of platelet aggregation, we investigated whether in human platelets NaN(3) influences the responses to agonists, cGMP levels and cGMP-regulated pathways. DESIGN AND METHOD: Concentration- and time-dependent effects of NaN(3) (1-100 micromol/L; 5-60 min incubation) on ADP- and collagen-induced aggregation, NO synthase (NOS) activity, cGMP synthesis and vasodilator-stimulated phosphoprotein (VASP) phosphorylation at Ser239 were investigated in platelets from 21 healthy individuals. RESULTS: NaN(3) exerted concentration- and time-dependent antiaggregatory effects starting from 1 micromol/L (IC(50) with 5-min incubation: 2.77+/-0.35 micromol/L with ADP and 4.64+/-0.48 micromol/L with collagen) and significantly increased intraplatelet cGMP levels and phosphorylation of VASP at Ser239 at 1-100 micromol/L; these effects were prevented by sGC inhibition, but not by NOS inhibition. CONCLUSIONS: NaN(3) exerts antiaggregatory effects in human platelets via activation of the sGC/cGMP/VASP pathway. This biological effect must be considered when azide-containing reagents are used for in vitro studies on platelet function.

Platelet resistance to the antiaggregatory cyclic nucleotides in central obesity involves reduced phosphorylation of vasodilator-stimulated phosphoprotein.

BACKGROUND: Impairment of platelet response to antiaggregatory agents is seen in individuals with central obesity and may play a role in the increased cardiovascular risk associated with obesity. In this study we evaluated whether this impairment involves the antiaggregatory pathways regulated by cAMP and cGMP. METHODS: We obtained platelet-rich plasma from 12 obese individuals and 12 controls. We investigated the effects of the cyclic nucleotide analogs 8-pCPT-cAMP (10-500 micromol/L) and 8-pCPT-cGMP (10-500 micromol/L) on ADP-induced platelet aggregation as assessed by decreased light scattering. We assessed the activation of cAMP- and cGMP-dependent protein kinases by measuring phosphorylation of the vasodilator-stimulated phosphoprotein (VASP) at Ser157 and Ser239. RESULTS: The antiaggregatory effect of both cyclic nucleotide analogs was impaired in obese individuals compared to controls, with mean (SE) half-maximal inhibitory concentrations (IC(50)) (after 20-min incubation) of 123 (33) micromol/L vs 5 (1) micromol/L, respectively, for 8-pCPT-cAMP (P <0.01) and of 172 (43) micromol/L vs 17 (8) micromol/L, respectively, for 8-pCPT-cGMP (P <0.01). The Homeostasis Model Assessment Index of Insulin Resistance was independently correlated with cyclic nucleotide analog IC(50). In obese individuals, VASP phosphorylation at Ser157 and Ser239 in response to cyclic nucleotides was significantly lower than in controls. CONCLUSIONS: In central obesity the reduced ability of cyclic nucleotides to inhibit platelet aggregation is associated with reduced activation of their specific kinases. Because cyclic nucleotides help regulate platelet antiaggregation, alteration of this ability is consistent with platelet hyperactivity in obesity.

Relevance of the vascular effects of insulin in the rationale of its therapeutical use.

Beyond carbohydrate, lipid and protein metabolism, insulin influences hemostasis, vascular tone and angiogenesis. Insulin per se causes a slow-acting vasodilation selectively occurring in skeletal muscle tissue, mainly related to an endothelium-dependent mechanism. Insulin-induced vasodilation is attenuated by the secretion of endothelin-1 and by the stimulation of sympathetic activity. The direct vasodilating effect of insulin is deeply reduced in the insulin-resistant states. The insulin effects on platelet aggregation and inflammatory response are attributable to increased synthesis of nitric oxide, and are deeply reduced in the insulin-resistant states. Furthermore, insulin reduces oxidative stress and promotes angiogenesis and proliferation of vascular smooth muscle cells. The involvement of insulin signalling pathways in these different insulin actions both in insulin sensitive and in insulin resistant states and the concept of "selective insulin resistance" are discussed. The vascular effects of insulin are generally ignored in the clinical practice, despite the evidences that insulin infusion with algorithms aiming to provide an optimal blood glucose control improves the clinical outcomes of patients with severe acute illness and myocardial infarction. Aim of this review is to clarify whether the vascular effects of insulin could represent a new "rationale" for its therapeutical use, independently of the well known metabolic actions.

Pathophysiology of platelet resistance to anti-aggregating agents in insulin resistance and type 2 diabetes: implications for anti-aggregating therapy.

The insulin resistance syndrome, which presents among its many facets obesity and type 2 diabetes mellitus, is a major risk factor for cardiovascular events. Thus, therapeutic guidelines recommend multifactorial treatment programs including, especially in the presence of type 2 diabetes, antiplatelet drugs. Few data, however, are available about the protective effect of antiplatelet therapy in both obese and type 2 diabetic patients. Furthermore, some reports showed a decreased sensitivity to the platelet antiaggregating effect of acetylsalicylic acid in diabetic patients. In the first part of this review, we focused our attention to alterations of platelets from insulin resistant subjects with or without type 2 diabetes, underlining that platelet hyperactivation is explained, at least in part, by: i) a reduced sensitivity to agents exerting an inhibitory modulation of platelet responses, ii) an altered intracellular milieu with elevated cytosolic Ca2+, iii) an enhanced thromboxane A2 synthesis, and iv) an increased number and/or function of GPIIb/IIIa complexes on platelet membranes. Furthermore, oxidative stress, which increases isoprostane production from arachidonic acid, may be involved in platelet hyperactivation, since isoprostanes activate platelets by interplaying with thromboxane receptors. These defects explain why antiplatelet therapy for both chronic atherosclerotic vascular disease and acute coronary syndromes should be specifically tailored in obese, insulin resistant subjects, especially in the presence of type 2 diabetes mellitus. Thus, in the second part of this review we carried out a critical overview of the clinical trials in subjects with metabolic syndrome and type 2 diabetes mellitus with or without macroangiopathy.

Platelet resistance to the anti-aggregating agents in the insulin resistant states.

Insulin resistance is a relevant risk factor for the major cardiovascular events, caused by severe atherosclerotic involvement of coronary, cerebral and lower limb blood vessels. One of the alterations accounting for this increased cardiovascular risk is the impairment of platelet function, explained, at least in part, by the reduced sensitivity to the physiological and pharmacological anti-aggregating agents. In the first part of this review, we will focus our attention on the physiological mechanisms involved in the attenuation of platelet response and on their impairment in insulin resistance, considering in particular: i) the reduced sensitivity to insulin and other substances acting via intracellular cyclic nucleotides; ii) the altered intracellular ionic milieu with elevated cytosolic Ca(2+), iii) the increase of oxidative stress, which elicits isoprostane production from arachidonic acid. Therapeutic guidelines recommend a multifactorial prevention including antiplatelet drugs, even though the protective effect of antiplatelet therapy in both obese and type 2 diabetic patients has not been completely clarified so far. Furthermore, some reports show a decreased sensitivity to the platelet antiaggregating effect of acetylsalicylic acid in obesity and type 2 diabetes mellitus. These defects explain why antiplatelet therapy for both chronic atherosclerotic vascular disease and acute coronary syndromes should be specifically tailored in obese, insulin resistant subjects, especially in the presence of type 2 diabetes mellitus. Thus, in the second part of this review we performed a critical overview of the clinical trials on anti-aggregating agents carried out in subjects with metabolic syndrome and type 2 diabetes mellitus.