Platelet insulin receptor determination in non-insulin dependent diabetes mellitus

Effect of <i>Ocimum gratissimum</i> Leaf-extract on Hematological Indices and Lipid Profile of Streptozotocin-induced Diabetic Wistar Rats

BACKGROUND AND OBJECTIVE

Ocimum gratissimum (OG) has been used in ethnopharmacology for the treatment of diabetes. The aim of the study was to evaluate the effect of Ocimum gratissimum leaf-extract on hematological indices and lipid profile of Streptozotocin-induced diabetic Wistar rats.

MATERIALS AND METHODS

Twenty-four rats weighing 100-160 g were randomly assigned to four treatment groups, the normal and diabetic controls, received a placebo treatment, while groups three and four were administered glibenclamide and OG leaf-extract (400 mg kg-1 b.wt.), respectively. The extracts were administered twice daily for 28 days. The rats were sacrificed and whole blood was collected for hematological and serum lipid profile assays. Data were analyzed using one-way ANOVA.

RESULTS

Diabetes induction resulted in decreases (p<0.05) in Red Blood Cell (RBC), Hemoglobin (Hb), White Blood Cell (WBC) and increases in Mean Corpuscular Hemoglobin and Blood platelets compared to the normal control. Treatment with O. gratissimum extract reversed RBC (7.74±0.39 μL), WBC (16.57±3.02) and Platelet (804.33±194.02) levels, but not Hb, towards normal levels (7.99±0.04, 11.27±0.69, 839.67±10.17 respectively). Diabetes induction also resulted in increases (p<0.05) in Triglyceride (TG) and Very-Low-Density Lipoprotein (VLDL), decreases (p<0.05) in High-Density Lipoprotein (HDL) and Low-Density Lipoprotein (LDL) compared to normal control with no significant change in Total Cholesterol (TC). After administration with Ocimum gratissimum TC, LDL and VLDL and HDL levels were significantly (p<0.05) reduced relative to the diabetic control. TG was however increased relative to the diabetic control.

CONCLUSION

Overall, data suggests the plant holds great potential in amelioration of diabetes-induced dyslipidemia and hematological disorders.

Enhanced Platelet Sensitivity to IGF-1 in Patients with Type 2 Diabetes Mellitus

Diabetes mellitus is characterized by increased platelet activation which is determined by many factors including changes in the expression of membrane proteins. The aim of this study was to investigate the sensitivity of human platelets to the insulin-like growth factor (IGF) system in patients with poorly controlled type 2 diabetes mellitus (DM2). Ligand binding was analyzed using ¹²⁵I-labelled IGF-1 and insulin, and relative expression of insulin-like growth factor 1 receptor (IGF-1R) and insulin receptor (IR) was evaluated by Western blotting. Platelet aggregation in the presence of IGF-1 was studied by the plate aggregometry assay. We found that platelets from DM2 patients exhibited significantly higher IGF-1 binding and upregulation of IGF-1R expression in comparison with healthy individuals. Both insulin binding and IR expression were lower in the DM2 group, but the differences with the healthy control were statistically insignificant. The potentiating effect of IGF-1 on the thrombin-induced activation of platelets was detected in both groups but was significantly more pronounced in the DM2 patients. The initial rate of platelet activation in the presence of IGF-1 positively correlated with the concentration of glycated hemoglobin. Platelets isolated from DM2 patients displayed elevated expression of the IGF-1R subunits, which might have contributed to the higher sensitivity of these cells to IGF-1 in thrombin-initiated aggregation by increasing the rate of platelet activation. However, further experiments are needed to investigate the role of IGF-1 in thrombotic complications that usually accompany diabetes.

Potential Role of Protein Disulfide Isomerase in Metabolic Syndrome-Derived Platelet Hyperactivity

Metabolic Syndrome (MetS) has become a worldwide epidemic, alongside with a high socioeconomic cost, and its diagnostic criteria must include at least three out of the five features: visceral obesity, hypertension, dyslipidemia, insulin resistance, and high fasting glucose levels. MetS shows an increased oxidative stress associated with platelet hyperactivation, an essential component for thrombus formation and ischemic events in MetS patients. Platelet aggregation is governed by the peroxide tone and the activity of Protein Disulfide Isomerase (PDI) at the cell membrane. PDI redox active sites present active cysteine residues that can be susceptible to changes in plasma oxidative state, as observed in MetS. However, there is a lack of knowledge about the relationship between PDI and platelet hyperactivation under MetS and its metabolic features, in spite of PDI being a mediator of important pathways implicated in MetS-induced platelet hyperactivation, such as insulin resistance and nitric oxide dysfunction. Thus, the aim of this review is to analyze data available in the literature as an attempt to support a possible role for PDI in MetS-induced platelet hyperactivation.

Loss of the insulin receptor in murine megakaryocytes/platelets causes thrombocytosis and alterations in IGF signalling

Aims

Patients with conditions that are associated with insulin resistance such as obesity, type 2 diabetes mellitus, and polycystic ovary syndrome have an increased risk of thrombosis and a concurrent hyperactive platelet phenotype. Our aim was to determine whether insulin resistance of megakaryocytes/platelets promotes platelet hyperactivation.

Methods and results

We generated a conditional mouse model where the insulin receptor (IR) was specifically knocked out in megakaryocytes/platelets and performed ex vivo platelet activation studies in wild-type (WT) and IR-deficient platelets by measuring aggregation, integrin α_IIbβ₃ activation, and dense and α-granule secretion. Deletion of IR resulted in an increase in platelet count and volume, and blocked the action of insulin on platelet signalling and function. Platelet aggregation, granule secretion, and integrin α_IIbβ₃ activation in response to the glycoprotein VI (GPVI) agonist collagen-related peptide (CRP) were significantly reduced in platelets lacking IR. This was accompanied by a reduction in the phosphorylation of effectors downstream of GPVI. Interestingly, loss of IR also resulted in a reduction in insulin-like growth factor-1 (IGF-1)- and insulin-like growth factor-2 (IGF-2)-mediated phosphorylation of IRS-1, Akt, and GSK3β and priming of CRP-mediated platelet activation. Pharmacological inhibition of IR and the IGF-1 receptor in WT platelets recapitulated the platelet phenotype of IR-deficient platelets.

Conclusions

Deletion of IR (i) increases platelet count and volume, (ii) does not cause platelet hyperactivity, and (iii) reduces GPVI-mediated platelet function and platelet priming by IGF-1 and IGF-2.

Platelet hemostasis in patients with metabolic syndrome and type 2 diabetes mellitus: cGMP- and NO-dependent mechanisms in the insulin-mediated platelet aggregation

Patients with metabolic syndrome (MetS) and type 2 diabetes mellitus (T2DM) have high risk of microcirculation complications and microangiopathies. An increase in thrombogenic risk is associated with platelet hyperaggregation, hypercoagulation, and hyperfibrinolysis. Factors leading to platelet activation in MetS and T2DM comprise insulin resistance, hyperglycemia, non-enzymatic glycosylation, oxidative stress, and inflammation. This review discusses the role of nitric oxide (NO) in the regulation of platelet adhesion and aggregation processes. NO is synthesized both in endotheliocytes, smooth muscle cells, macrophages, and platelets. Modification of platelet NO-synthase (NOS) activity in MetS patients can play a central role in the manifestation of platelet hyperactivation. Metabolic changes, accompanying T2DM, can lead to an abnormal NOS expression and activity in platelets. Hyperhomocysteinemia, often accompanying T2DM, is a risk factor for cardiovascular accidents. Homocysteine can reduce NO production by platelets. This review provides data on the insulin effects in platelets. Decrease in a number and sensitivity of the insulin receptors on platelets in T2DM can cause platelet hyperactivation. Various intracellular mechanisms of anti-aggregating insulin effects are discussed. Anti-aggregating effects of insulin are mediated by a NO-induced elevation of cGMP and upregulation of cAMP- and cGMP-dependent pathways. The review presents data suggesting an ability of platelets to synthesize humoral factors stimulating thrombogenesis and inflammation. Proinflammatory cytokines are considered as markers of T2DM and cardiovascular complications and are involved in the development of dyslipidemia and insulin resistance. The article provides an evaluation of NO-mediated signaling pathway in the effects of cytokines on platelet aggregation. The effects of the proinflammatory cytokines on functional activity of platelets are demonstrated.

The PPAR-Platelet Connection: Modulators of Inflammation and Potential Cardiovascular Effects

Historically, platelets were viewed as simple anucleate cells responsible for initiating thrombosis and maintaining hemostasis, but clearly they are also key mediators of inflammation and immune cell activation. An emerging body of evidence links platelet function and thrombosis to vascular inflammation. peroxisome proliferator-activated receptors (PPARs) play a major role in modulating inflammation and, interestingly, PPARs (PPARβ/δ and PPARγ) were recently identified in platelets. Additionally, PPAR agonists attenuate platelet activation; an important discovery for two reasons. First, activated platelets are formidable antagonists that initiate and prolong a cascade of events that contribute to cardiovascular disease (CVD) progression. Dampening platelet release of proinflammatory mediators, including CD40 ligand (CD40L, CD154), is essential to hinder this cascade. Second, understanding the biologic importance of platelet PPARs and the mechanism(s) by which PPARs regulate platelet activation will be imperative in designing therapeutic strategies lacking the deleterious or unwanted side effects of current treatment options.

Insensitivity to the α2-adrenergic receptor blocker yohimbine hydrochloride and occurrence of spontaneous platelet macroaggregation (SPMA) in diabetes

We report here a study of platelet aggregation in diabetes, induced by epinephrine and its inhibition by yohimbine hydrochloride (YH), an alpha(2)-adrenergic receptor-blocking agent. Interestingly, emergence of spontaneous platelet macroaggregation (SPMA) was observed in six out of 75 cases in the absence of any agonist. The SPMA cases were strongly associated with insensitivity to YH (in contrast with non-SPMA cases) when epinephrine was used as an agonist. We suggest that the observed correlation is a result of over expression of platelet alpha(2)-adrenoceptors in such subjects. The quantitative nature of the effect is supported by the observation that addition of YH at higher concentration (more than 5 microM) led to restoration of the adrenergic receptor-blocking activity of the said agent. Eventually for non-SPMA subjects YH exhibited blocking activity even at lower concentration. The aggregation profile and the platelet morphology of the SPMA cases had distinctive features as compared to microaggregates formed in other diabetic subjects (non-SPMA cases).

Platelet signalling abnormalities in patients with type 2 diabetes mellitus: a review

The hyperactivation of platelets is involved in the cardiovascular complications associated with type 2 diabetes mellitus. Altered platelet behavior contributes to the angiopathies associated with diabetes. A number of mechanisms involved in platelet activation are altered in diabetes. Platelets from type 2 diabetic patients show an enhanced endogenous reactive oxygen species production and a reduced antioxidant capability, which increase the activity of several tyrosine kinases, such as the Bruton's tyrosine kinase, MAP kinases or proteins of the SRC family. Oxidative stress is also involved in the abnormal intracellular calcium homeostasis observed in platelets from type 2 diabetics, including an enhanced resting cytosolic calcium concentration and calcium release and entry in response to agonists. Moreover, diabetes alters the bioavailability of nitric oxide in platelets. Basal nitric oxide synthase activity is reduced in homogenates of platelets obtained from patients with type 2 diabetes mellitus. The study of these abnormalities might be helpful in the development of new pharmacological strategies to reduce platelet activation in type 2 diabetes mellitus.

Platelet activation in type 2 diabetes mellitus

The abnormal metabolic state that accompanies diabetes renders arteries susceptible to atherosclerosis, being capable of altering the functional properties of multiple cell types, including endothelium and platelets. In particular, an altered platelet metabolism and changes in intraplatelet signaling pathways may contribute to the pathogenesis of atherothrombotic complications of diabetes. A variety of mechanisms may be responsible for enhanced platelet aggregation. Among them, hyperglycemia may represent a causal factor for in vivo platelet activation, and may be responsible for nonenzymatic glycation of platelet glycoproteins, causing changes in their structure and conformation, as well as alterations of membrane lipid dynamics. Furthermore, hyperglycemia-induced oxidative stress is responsible for enhanced peroxidation of arachidonic acid to form biologically active isoprostanes, which represents an important biochemical link between impaired glycemic control and persistent platelet activation. Finally, increased oxidative stress is responsible for activation of transcription factors and expression of redox-sensitive genes leading to a phenotypic switch of endothelium toward an adhesive, pro-thrombotic condition, initial platelet activation, adhesion and subsequent platelet aggregate formation. All this evidence is strengthened by the results of clinical trials documenting the beneficial effects of metabolic control on platelet function, and by the finding that aspirin treatment may even be more beneficial in diabetic than in high-risk non-diabetic patients. Attention to appropriate medical management of diabetic patients will have great impact on long-term outcome in this high-risk population.

Platelet dysfunction in type 2 diabetes

Insulin resistance is a uniform finding in type 2 diabetes, as are abnormalities in the microvascular and macrovascular circulations. These complications are associated with dysfunction of platelets and the neurovascular unit. Platelets are essential for hemostasis, and knowledge of their function is basic to understanding the pathophysiology of vascular disease in diabetes. Intact healthy vascular endothelium is central to the normal functioning of smooth muscle contractility as well as its normal interaction with platelets. What is not clear is the role of hyperglycemia in the functional and organic microvascular deficiencies and platelet hyperactivity in individuals with diabetes. The entire coagulation cascade is dysfunctional in diabetes. Increased levels of fibrinogen and plasminogen activator inhibitor 1 favor both thrombosis and defective dissolution of clots once formed. Platelets in type 2 diabetic individuals adhere to vascular endothelium and aggregate more readily than those in healthy people. Loss of sensitivity to the normal restraints exercised by prostacyclin (PGI(2)) and nitric oxide (NO) generated by the vascular endothelium presents as the major defect in platelet function. Insulin is a natural antagonist of platelet hyperactivity. It sensitizes the platelet to PGI(2) and enhances endothelial generation of PGI(2) and NO. Thus, the defects in insulin action in diabetes create a milieu of disordered platelet activity conducive to macrovascular and microvascular events.

Transient decrease of binding of insulin to platelets in acute ischemic heart disease

The specific binding sites of 125I-insulin in platelets from nondiabetic patients with acute myocardial infarction and unstable angina pectoris was significantly decreased (192 +/- 84/cell) during the acute ischemic condition when compared with normal platelets (496 +/- 76/cell; p < 0.001, n = 9). A relatively low mean plasma insulin level (20 microU/mL) with an elevated mean glucose level (130 mg/dL) was noted. The decreased binding of insulin and the relatively low mean plasma insulin level during the acute ischemic condition improved into the normal range during 8 to 12 weeks of recuperation. The decrease of insulin binding sites in the acute phase and their subsequent increase during recovery were directly related to the hormone-induced increase in sensitivity to prostaglandin E1 through the stimulation of adenosine 3',5'-cyclic monophosphate formation in platelets by the prostanoid.

Platelet sodium-hydrogen antiport in obese and diabetic black women

In this investigation we correlated platelet Na-H antiport parameters with blood pressure and serum lipids in a sample population of non-insulin-dependent diabetic obese, nondiabetic obese, and nondiabetic nonobese black women. Parameters of the Na-H antiport were examined in aspirin-treated platelets. These parameters were not altered in resting or in thrombin-stimulated platelets of diabetic patients. The activity index of platelet Na-H antiport after thrombin stimulation was positively correlated with the blood pressure (systolic blood pressure, r = 0.5320 and p = 0.0001; diastolic blood pressure, r = 0.5123 and p = 0.0017). Lower high density lipoprotein cholesterol levels were associated with an alkaline shift in the cytosolic pH set point for activation of the Na-H antiport. Highly significant correlations were also observed between the total cholesterol/high density lipoprotein cholesterol ratio and the cytosolic pH set point for activation of the Na-H antiport. These correlations were independent of diabetes or the body mass index. Together, these observations indicate that parameters of platelet Na-H antiport are altered with an increase in blood pressure and a decrease in serum high density lipoprotein cholesterol.

Insulin induced phosphorylation and activation of the cGMP-inhibited cAMP phosphodiesterase in human platelets

Insulin induced phosphorylation and activation of the cGMP inhibited cAMP phosphodiesterase (cGI-PDE) in human platelets were demonstrated after isolation of the enzyme with specific polyclonal cGI-PDE antibodies. The demonstration of this insulin effect required suppression of basal cGI-PDE phosphorylation, through the use of the protein kinase inhibitor H-7 (1-(5-isoquinolinylsulfonyl)-2-methylpiperazine). The human platelet insulin receptor beta-subunit, previously identified as a 97 kDa polypeptide, was detected with the use of wheat germ agglutinin chromatography and anti-phosphotyrosine antibodies. These results suggest that insulin, through phosphorylation/activation of cGI-PDE, could decrease cAMP/cAMP dependent protein kinase (cAMP-PK) activity and thereby make the platelets more sensitive towards aggregating agents.

Interaction of receptors for prostaglandin E1/prostacyclin and insulin in human erythrocytes and platelets

Prostaglandin E1/I2 and insulin receptors of human erythrocyte and platelet are capable of modulating each other's activity. This modulation of the receptor activity and number in one system by a second receptor system in human platelet and erythrocyte seems to be beneficial. Insulin increases the PGE1 binding to platelets and thereby enhances the platelet antiaggregatory action of prostaglandin by increasing cyclic AMP levels. Similarly, PGE1 increases insulin binding to human erythrocyte, and thereby reduces the optimum concentration of insulin for a maximal reduction in membrane microviscosity. During ischemia the reduced response of platelets to the inhibitory effect of PGE1 or PGI2 relates to the impaired PGE1/I2 receptor activity. Treatment of these platelets with insulin at physiological concentrations can normalise the PGE1/I2 receptor activity. This review focuses on the relationship between the two receptor systems in human blood cells.

Glucose intolerance and insulin resistance with aging--studies on insulin receptors and post-receptor events

The oral glucose tolerance test and immune reactive insulin level determination were performed on 100 non-obese healthy elderly and 40 young and middle-aged non-obese healthy subjects. In about 60% of the elderly an altered glucose tolerance test was found, but the insulin level was increased in the whole group of elderly subjects. This means an insulin-resistant state with aging. Further investigations were carried out to determine some possible causes of this insulin resistance. The chromium level in sera and granulocytes of elderly was significantly decreased as well as the insulin receptor numbers and the affinity to erythrocytes. In contrast, when the cyclic nucleotide levels were investigated in granulocytes under in vitro stimulation, an age-dependent increase of cAMP level was found and an unresponsiveness of cGMP, which ranged between mild and severe degrees. Concomitantly, all these changes found could contribute to the insulin resistance at the receptor and post-receptor levels with aging.

Insulin stimulates a novel GTPase activity in human platelets

Insulin stimulated the activity of a high-affinity GTPase activity in human platelet membranes some 62% over that of the basal activity. Half-maximal stimulation (Ka) was achieved with 3.1 nM insulin. The Km for GTP of the insulin-stimulated GTPase was 0.6 microM GTP. Treatment of isolated platelet membranes with cholera toxin, but not pertussis toxin, blocked insulin's ability to stimulate GTPase activity. Cholera toxin acted as a more potent inhibitor of the insulin-stimulated GTPase activity than that of the GTPase activity of the stimulatory guanine nucleotide regulatory protein, Gs, as monitored by stimulation using prostaglandin E1 (PGE1). Mixed ligand experiments showed that insulin stimulated GTPase activity in an additive fashion to GTPase activity stimulated by PGE1, due to Gs; by adrenaline (+ propranolol), due to the inhibitory guanine nucleotide regulatory protein, G1 and by vasopressin, which stimulates the putative 'Gp', a G-protein suggested to control the stimulation of inositol phospholipid metabolism. Insulin thus appears to stimulate a novel high-affinity GTPase activity in human platelet membranes. This may reflect the functioning of the putative Gins, a guanine nucleotide regulatory protein which has been suggested to mediate certain of insulin's actions on target tissues.