Normalization of impaired response of platelets to prostaglandin E1/I2 and synthesis of prostacyclin by insulin in unstable angina pectoris and in acute myocardial infarction

Reduction of death rate due to acute myocardial infarction in subjects with cancers through systemic restoration of impaired nitric oxide

Introduction

Excessive aggregation of platelets at the site of plaque rupture on the coronary artery led to the formation of thrombus which is reported to precipitate acute myocardial infarction (AMI). Nitric oxide (NO) has been reported to inhibit platelet aggregation and induce thrombolysis through the in situ formation of plasmin. As the plasma NO level in AMI patients from two different ethnic groups was reduced to 0 µM (median) compared to 4.0 µM (median) in normal controls, the effect of restoration of the NO level to normal ranges on the rate of death due to AMI was determined.

Methods and Results

The restoration of plasma NO level was achieved by a sticking small cotton pad (10×25 mm) containing 0.28 mmol sodium nitroprusside (SNP) in 0.9% NaCl to the abdominal skin of the participants using non-toxic adhesive tape which was reported to normalize the plasma NO level. The participants (8,283) were volunteers in an independent study who had different kinds of cancers and did not wish to use any conventional therapy for their condition but opted to receive SNP “pad” for their condition for 3 years.

The use of SNP “pad” which normalized (≈4.0 µM) the plasma NO level that in consequence reduced the death rate due to AMI, among the participants, was found to be significantly reduced compared to the death due to AMI in normal population.

Conclusion

Our data suggested that the use of SNP “pad” significantly reduced the death due to AMI.

Trial Registration

www.ctri.nic.in004236

Isolation and study of insulin activated nitric oxide synthase inhibitory protein in acute myocardial infarction subjects

Insulin inhibits platelet aggregation through nitric oxide synthesis by stimulating platelet insulin activated nitric oxide synthase. Impaired platelet insulin activated nitric oxide synthase in acute myocardial infarction (AMI) patients had been reported and thus our aim was to identify and isolate the factors impairing insulin activated nitric oxide in acute myocardial infarction patients' plasma and study its effect on platelets aggregation in vitro. The insulin activated nitric oxide synthase inhibitor was identified as a protein and was purified from the plasma of AMI subjects using DEAE cellulose and Sephadex G-50 column, molecular weight determined by SDS-PAGE, nitric oxide quantified by methaemoglobin method, inhibitor protein quantified in plasma by immunoblot and ELISA, platelet aggregation studies done using an aggregometer, thromboxane-A2 in the platelets determined by radioimmunoassay, (125)I-insulin radioligand binding studies done using normal subject platelets. The purified nitric oxide synthase inhibitor protein was ~66 kDa, concentration in AMI subjects' plasma varied from 114 to 9,090 μM and was undetected in normal subjects' plasma. The inhibitor protein competes with insulin for insulin receptor binding sites. The Incubation of the normal subject PRP with 5.0 μM inhibitor for 30 min followed by 0.4 μM ADP addition caused platelet aggregation in vitro, 130 μM aspirin or 400 μU insulin/ml addition was able to abrogate 0.4 μM ADP induced platelet aggregation even in the presence of 5.0 μM inhibitor. A potent inhibitory protein against insulin activated nitric oxide synthase in platelets appears in circulation of AMI subjects impairing nitric oxide production, potentiating ADP induced platelet aggregation and increasing the thromboxane-A2 level in platelets.

Long-chain polyunsaturated fatty acids, endothelial lipase and atherosclerosis

Endothelial lipase (EL), a new member of the lipase gene family, was recently cloned and has been shown to have a significant role in modulating the concentrations of plasma high-density lipoprotein levels (HDL). EL is closely related to lipoprotein and hepatic lipases both in structure and function. It is primarily synthesized by endothelial cells, functions at the cell surface, and shows phospholipase A1 activity. Overexpression of EL decreases HDL cholesterol levels whereas blocking its action increases concentrations of HDL cholesterol. Pro-inflammatory cytokines suppress plasma HDL cholesterol concentrations by enhancing the activity of EL. On the other hand, physical exercise and fish oil (a rich source of eicosapentaenoic acid and docosahexaenoic acid) suppress the activity of EL and this, in turn, enhances the plasma concentrations of HDL cholesterol. Thus, EL plays a critical role in the regulation of plasma HDL cholesterol concentrations and thus modulates the development and progression of atherosclerosis. The expression and actions of EL in specific endothelial cells determines the initiation and progression of atherosclerosis locally explaining the patchy nature of atheroma seen, especially, in coronary arteries. Both HDL cholesterol and EPA and DHA enhance endothelial nitric oxide (eNO) and prostacyclin (PGI2) synthesis, which are known to prevent atherosclerosis. On the other hand, pro-inflammatory cytokines augment free radical generation, which are known to inactivate eNO and PGI2. Thus, interactions between EL, pro- and anti-inflammatory cytokines, polyunsaturated fatty acids, and the ability of endothelial cells to generate NO and PGI2 and neutralize the actions of free radicals may play a critical role in atherosclerosis.

The role of insulin as an antithrombotic humoral factor

Insulin is well known for its essential role in carbohydrate metabolism: insulin deficiency results in the development of diabetes mellitus. It has been known for many years that people with diabetes mellitus are predisposed to develop thrombotic diseases including myocardial infarction. It was thought that the thrombus formation was the consequence of impaired carbohydrate metabolism. In recent years, it has become apparent that insulin is capable of ameliorating several pathophysiological events, leading to the inhibition and dissolution of the formed thrombus in the system. These insulin-induced events include inhibition of platelet aggregation by prompting the synthesis of NO in platelet and prostacyclin in endothelial cells. Furthermore, insulin upregulates prostacyclin receptors and downregulates alpha(2) adrenergic receptor in platelets, thereby amplifying the inhibition of platelet aggregation. Insulin also releases tissue plasminogen activator, a potent thrombolytic enzyme, from the platelet membrane which dissolves the formed thrombus leading to the resumption of normal blood circulation. In effect, insulin could be an essential tool in the control of thrombotic disorders.

Neointimal hyperplasia after arterial injury is increased in a rat model of non-insulin-dependent diabetes mellitus

BACKGROUND

The key biological determinants that promote restenosis in the setting of diabetes have not been elucidated. There is no accepted animal model to study restenosis in diabetes.

METHODS AND RESULTS

We evaluated 2 models of diabetes mellitus: (1) streptozotocin (STZ)-treated Sprague-Dawley rats (type I diabetes) versus regular Sprague-Dawley rats and (2) obese Zucker rats (type II diabetes) versus lean Zucker rats. Neointimal hyperplasia was assessed after carotid balloon injury at 21 days by computerized morphometry. There was no difference in neointimal area in the STZ-treated rats compared with controls, irrespective of insulin administration or dose of STZ. Neointimal area was increased >2-fold in obese Zucker rats compared with lean Zucker rats (0.21+/-0.06 versus 0.08+/-0.03 mm(2), P<0.01). The neointimal area was markedly increased in the obese Zucker rats 7 days after injury (0.058+/-0.024 versus 0.033+/-0.009 mm(2), P<0.05) and persisted through 21 days. In both obese and lean Zucker rats, cell proliferation peaked in the media at 3 days (118.66+/-84.28 versus 27.50+/-12.75 bromodeoxyuridine-labeled cells per cross section). In the intima, cell proliferation markedly increased beginning at day 3 and persisted through day 14 in the obese and lean Zucker rats (202.27+/-98.86 versus 35.71+/-20.54 bromodeoxyuridine-labeled cells at 7 days).

CONCLUSIONS

The type II diabetic rat model, typifying insulin resistance, is associated with a propensity for neointima. The obese Zucker rat model may be an ideal diabetic model to further characterize the diabetic vascular response to injury.

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.

Markedly reduced insulin-like growth factor-1 in the acute phase of myocardial infarction

OBJECTIVES

We investigated whether insulin-like growth factor-1 (IGF-1) is reduced in the early phase of acute myocardial infarction (AMI) and whether such a decrease might influence prognosis.

BACKGROUND

Insulin-like growth factor-1 protects against insulin resistance and apoptosis. Although insulin resistance has been reported in AMI, IGF-1 levels have not been investigated.

METHODS

We measured serum IGF-1 in 23 patients with AMI within 24 h of symptom onset and in 11 matched controls. In the first 12 patients and controls, we also measured fasting insulin, diurnal growth hormone (GH) and insulin sensitivity (assessed as glucose disappearance or T/2 after an insulin bolus), and repeated IGF-1, insulin and GH after one year. In all patients, 90-day cardiovascular death, recurrent ischemia, reinfarction, revascularization and late malignant arrhythmias were assessed.

RESULTS

The AMI patients versus controls showed markedly reduced IGF-1 (115 +/- 112 vs. 615 +/- 300 ng/ml, p < 0.0001) and slower T/2 (-0.98 +/- 1.5 vs. -2.57 +/- 1.0 mg/dl/min, p = 0.01). Low IGF-1 often preceded the rise of myocardial necrosis markers. Patients with 90-day events (n = 12) versus those without had lower IGF-1 (47 +/- 54 vs. 189 +/- 110 ng/ml, p < 0.0001). Acute phase GH and insulin concentrations did not differ significantly from controls. After one year, the patients' IGF-1 values had risen to 460 +/- 242 ng/ml (p = 0.1 vs. controls, p < 0.0005 vs. acute phase), whereas GH levels were lower (0.2 +/- 0.2 vs. 2.5 +/- 2.3 ng/ml, p = 0.01) and insulin levels higher (12.5 +/- 0.2 vs. 3.9 +/- 2.6 microU/ml, p < 0.0001) compared with controls.

CONCLUSIONS

In the early phase of AMI, serum IGF-1 levels are markedly reduced and may contribute to adverse outcomes. Reduced IGF-1 preceding the rise of myocardial necrosis markers suggests a possible pathogenetic role. A compensatory increase in IGF-1 appears to occur by one year.

Stenting of stenosed aortopulmonary collaterals and shunts for palliation of pulmonary atresia/ventricular septal defect

Patients with unrepaired pulmonary artery atresia and ventricular septal defect (PA/VSD) depend on aortoplumonary collaterals and surgically created shunts for pulmonary blood flow. These vessels frequently develop stenoses with time, leading to hypoperfusion of lung segments and systemic hypoxemia. The purpose of this article is to describe catheter palliation of hypoxemic patients with PA/VSD who were not candidates for surgical repair. We present our experience with stent implantation for stenosis of aortopulmonary collaterals and shunts in these patients. Three patients with hypoplastic pulmonary arteries underwent stent placement in aortopulmonary collateral arteries (APCAs) or their shunts. Technical aspects of the interventional catheterization procedure are discussed in detail. Case 1 underwent placement of five stents in collateral vessels and one stent in the Blalock-Taussig shunt (BT) with dramatic increase in vessel size and improvement in saturations from 70% to 89%. Case 2 underwent placement of two overlapping stents in a collateral vessel with an increase in diameter of the collateral vessel from 2.3 to 6 mm and an improvement in saturation from 68% to 88%. Case 3 underwent placement of three overlapping stents in a BT shunt with an increase in diameter of the shunt from 2.2 to 6.6 mm and an improvement in saturation from 71% to 89%. All three patients had excellent clinical improvement and stable saturation at follow-up. Stent placement for maintaining patency of APCAs and aortopulmonary shunts is feasible and safe.

Stimulation of nitric oxide synthesis and protective role of insulin in acute thrombosis in vivo

Administration of physiologic amounts of insulin in mice (200 microunits/g body weight) resulted in 9 fold increase of basal nitric oxide level from 0.51+/-0.1224 nmol/ml (mean+/-SD, n=12) to 4.45+/-0.645 nmol/ml after 30min of the injection of the hormone. Since NO is a potent inhibitor of platelet aggregation both in vitro and in vivo, we tested the possibility whether the administration of the hormone would result in the in vivo inhibition of thrombosis through the increase of NO level in the circulation. It was found that administration of insulin (200 microunits/g body weight) in mice protected >90%(p<0.00001, n=500) of these animals from death due to thrombosis in the coronary arteries induced by ADP injection in the heart. This effect of insulin in vivo was found to be directly related to the hormone induced increase of NO level in the system. The thromboprotective effect of insulin could not be achieved by using either prostacyclin, a well known antithrombotic agent or its stable probe prostaglandin E1 instead of insulin. The efficacy of insulin was neither related to the blood glucose level nor was the consequence of the hypoglycemic effect of the hormone. In contrast, inhibition of insulin induced increase of NO level resulted in the complete loss of the thromboprotective effect of the hormone. These results suggest that insulin besides being a hypoglycemic hormone could also be a potent antithrombotic humoral factor.

Platelet-stimulated thrombin and PDGF are normalized by insulin and Ca2+ channel blockers

Coronary artery disease is accelerated in chronic spinal cord injury (SCI). Because prostacyclin (PGI2) may retard atherogenesis through its inhibitory effects on platelet function, the role of PGI2 on SCI platelets was determined. The SCI platelets were neither hypersensitive to aggregating agonists nor resistant to the inhibitory effect of PGI2, but PGI2 failed to inhibit platelet-stimulated thrombin generation and the release of platelet-derived growth factor (PDGF) in SCI. Because thrombin and PDGF are atherogenic mitogens, the generation of these mitogens was investigated. Both the release of PDGF and thrombin generation in SCI platelets were higher when compared with control (n = 12). Treatment of non-SCI platelets with 100 nM PGE1 (a stable probe of PGI2) inhibited the release of the mitogens by 90% (P < 0.001), with no effect on SCI platelets. Scatchard analysis of prostaglandin E1 (PGE1) binding showed a 70% decrease of PGI2 receptors on the SCI platelet surface. Treatment of SCI platelets with insulin or Ca2+ channel blockers restored the PGI2-receptor number and "normalized" the inhibition of PDGF release and thrombin generation by PGI2.

Enhanced secretion of insulin plays a role in the development of atherosclerosis and restenosis of coronary arteries: elective percutaneous transluminal coronary angioplasty in patients with effort angina

OBJECTIVES

We investigated the relation between insulin and coronary atherosclerosis and restenosis of the coronary arteries, by performing elective percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Insulin is known to promote atherosclerosis of the arteries and has been implicated in the development of restenosis after PTCA.

METHODS

Of 210 angina patients who underwent PTCA, newly detected lesions in 35 consecutive nondiabetic subjects without previous intervention on the same main coronary arteries were analyzed after a 75-g oral glucose tolerance test (OGTT) and follow-up coronary angiography. Atherosclerotic lesions were evaluated by pattern, severity and extent. Restenosis was defined as loss of gain, the percentage of loss of the initial gain in the coronary diameter achieved by PTCA > or = 50%.

RESULTS

Patients with restenosis had a significantly higher extent index (a marker of atherosclerosis), insulin area, ratio of insulin area to glucose area, insulinogenic index and minimal lumen diameter after PTCA than those without restenosis (p=0.001, 0.011, 0.002, 0.016 and 0.041, respectively). Simple regression analysis revealed that only the ratio of insulin area to glucose area (a relative marker of enhanced insulin secretion) significantly correlated with the extent index (p=0.035). Extent index, insulin area, the ratio of insulin area to glucose area and insulinogenic index significantly correlated with loss of gain (p=0.001, 0.010, 0.002 and 0.032, respectively). Stepwise multiple regression analyses revealed that extent index and the ratio of insulin area to glucose area significantly correlated with loss of gain.

CONCLUSIONS

Enhanced secretion of insulin during the OGTT might be useful as a predictor of coronary atherosclerosis and of restenosis after elective PTCA in nondiabetic patients with effort angina.

Relation of restenosis after excimer laser angioplasty to fasting insulin levels

Several studies have shown that diabetes mellitus increases the risk of restenosis after coronary intervention, but the role of insulin in restenosis has not been defined. The relation between fasting insulin levels and restenosis was evaluated prospectively at 6-month angiographic follow-up in 70 patients undergoing excimer laser coronary angioplasty of 75 lesions. Restenosis (> 50% diameter narrowing on quantitative angiography) was observed at 37 of 75 treated sites (49%). Although patients with glucose intolerance and noninsulin-dependent diabetes mellitus showed a trend toward increased restenosis (restenosis rate 69%; odds ratio for restenosis 2.7 [95% confidence interval 0.76, 9.82]; p = 0.124), those with increased fasting insulin levels > 15 muU/ml had reduced restenosis (restenosis rate 24%; odds ratio 0.22 [0.07, 0.67]; p = 0.008). Other factors including fasting serum glucose, glycated hemoglobin and lipoprotein fraction were not predictive of restenosis. The relation between insulin levels and restenosis after excimer laser angioplasty may provide insights into the biology of vascular injury and repair after coronary intervention.

Prostaglandin-E1-binding sites in rabbit erythrocyte membranes

Prostaglandin E1 (PGE1) binding sites have been identified on rabbit erythrocyte membranes. The binding of PGE1 to the membranes was found to be highly specific, reversible, and saturable. The high-affinity binding sites had a dissociation constant (Kd.1) of 5.6 +/- 1.2 nM with a binding capacity of 210 +/- 51 fmol/mg protein, whereas the low-affinity binding sites had a dissociation constant (Kd.2) of 22 +/- 6.4 microM, and a binding capacity of 321 +/- 78 pmol/mg protein. Incubation with PGE1 did not activate adenylate cyclase in the membranes. Preincubation of rabbit erythrocyte membranes with physiological amounts of insulin (1.5 nM) resulted in an increase of PGE1 binding to the membranes from 241 +/- 65 to 429 +/- 85 fmol/mg protein. The insulin-induced increase in PGE1 binding was due to an increase in binding sites (both high-affinity and low-affinity binding sites) rather than to an increase in the affinity of the binding sites. Treatment of erythrocyte membranes with PGE1 at concentrations (4.0-7.5 nM) which were within the Kd.1 value of the high-affinity binding sites, resulted in a significant reduction in membrane fluorescence anisotropy (0.27 +/- 0.005-0.21 +/- 0.003). Use of higher concentrations (> 15 nM) of PGE1 reversed the effect of its lower concentration on the membrane anisotropy.