Platelet function in male diabetics with and without macrovascular complications

Platelet aggregation is not altered among men with diabetes mellitus

AIMS

Platelets are pivotal in arterial thrombosis, and platelet hyperresponsiveness may contribute to the increased incidence of cardiovascular events in diabetes mellitus. Consequently, we hypothesized that increased in vitro platelet aggregation responses exist in men with diabetes mellitus.

METHODS

The Danish Cardiovascular Screening Trial (DANCAVAS) is a community-based cardiovascular screening trial including men aged 65-74 years. Platelet aggregation was tested using 96-well light transmission aggregometry with thrombin receptor-activating peptide (TRAP), adenosine diphosphate, collagen type 1, arachidonic acid and protease-activated receptor-4 in three concentrations. Further, cardiovascular risk factors and coronary artery calcification (CAC), estimated by CT scans and ankle-brachial index, were obtained.

RESULTS

Included were 720 men aged 65-74 years, 110 with diabetes mellitus. Overall, there was no difference in platelet aggregation among men with versus without diabetes mellitus when adjusting for or excluding platelet inhibitor treatment and men with established cardiovascular disease (CVD). This was true for all agonists, e.g., 10 µM TRAP-induced platelet aggregation of median 69% (IQR 53-75) versus 70% (IQR 60-76) in men with versus without diabetes mellitus. Platelet aggregation did not correlate with HbA_1c or CAC. Men with diabetes mellitus displayed higher CAC, median 257 Agatston units (IQR 74-1141) versus median 111 Agatston units (IQR 6-420) in the remaining individuals, p < 0.0001.

CONCLUSIONS

Among outpatients with diabetes mellitus, but no CVD and no platelet inhibitor treatment, neither are platelets hyperresponsive in diabetes mellitus, nor is platelet aggregation associated with glycemic status or with the degree of coronary atherosclerosis.

TRIAL REGISTRATION

ISRCTN12157806.

Urinary albumin excretion is correlated to fibrinogen levels and protein S activity in patients with type 1 diabetes mellitus without overt diabetic nephropathy

The aim of the study was to test the hypothesis that in diabetic patients without overt nephropathy there may be a correlation between the activity of natural anticoagulant proteins and glomerular dysfunction. Assays for functional activity of proteins S and C, measurements of urinary albumin excretion, lipid parameters and haemoglobin A1c were performed in 91 patients with type 1 diabetes mellitus and 85 patients with type 2. Patients with type 1 diabetes and microalbuminuria had significantly higher mean age (44.1 +/- 10.9 vs. 37.9 +/- 12.7 years; p<0.05), fibrinogen level (3.75 +/- 1.0 vs. 3.21 +/- 0.8 g/l; p<0.01), protein S activity (92.3 +/- 17.6 vs. 84.5 +/- 15.5%; p<0.05) and higher prevalence of retinopathy (p<0.01) and macrovascular disease (p<0.01) than those with normoalbuminuria. Albumin excretion was significantly correlated to age (r=0.25, p<0.05), fibrinogen level (r=0.39, p<0.01), protein S activity (r=0.27; p<0.05), total cholesterol (r=0.23; p<0.05), apoprotein B (r=0.22; p<0.05), retinopathy (r=0.33; p<0.01) and macrovascular disease (r=0.33; p<0.01). Patients with type 2 diabetes mellitus and microalbuminuria had significantly higher apoprotein B levels (1.17 +/- 0.3 vs. 1.06 +/- 1.2 mg/dl; p<0.05) than those with normoalbuminuria, and apoprotein B was significantly correlated to albumin excretion (r=0.22; p<0.05). In a multivariate model of type 1 diabetes mellitus with fibrinogen, protein S and C activity, cholesterol, triglycerides, haemoglobin A1c, retinopathy, and macrovascular disease as independent parameters (r=0.53; p<0.003), there was significant independent correlation of fibrinogen (beta=0.28; p<0.01), protein S activity (beta=0.27; p<0.05) and retinopathy (beta=0.21; p<0.01) with albumin excretion. We conclude that in type 1 diabetes, relative elevation of fibrinogen level and protein S activity appear in the early stages of development of diabetic nephropathy, and may be related to the pathogenesis of diabetic kidney disease.

Diurnal blood pressure variations in incipient and end stage diabetic renal disease

Our aim was to compare the diurnal blood pressure patterns of people with Type 1 diabetes on continuous ambulatory peritoneal dialysis (CAPD, n=9) or haemodialysis (n=10) to diabetic patients with normo-albuminuria (n=12) or micro-albuminuria (n=15). Blood pressure was measured with an ABPM02 Meditech oscillometric blood pressure monitor. The micro-albuminuric group had significantly higher nocturnal diastolic and mean arterial pressures than the normo-albuminuric group. CAPD and haemodialysis patients had significantly higher day time, nocturnal mean systolic, diastolic and mean arterial blood pressures. Micro-albuminuric and end-stage renal failure patients displayed a loss of the physiological drop of systolic blood pressure, which was only significant in the normo-albuminuric group. Nocturnal drop of blood pressure characterised by diurnal indices were 7.4% in the CAPD, 8.8% in the haemodialysis, 10.0% in the micro-albuminuric and 16.5% in the normo-albuminuric group. These results suggest, that pathological circadian blood pressure variation is common in diabetic patients on dialysis, and ambulatory blood pressure monitoring can be a useful tool both in its the detection and its adequate treatment.

Pine bark extract reduces platelet aggregation

The effects of long-term consumption of the bioflavonoid mixture, French maritime pine bark extract (Pycnogenol(R)), were assessed on aggregation of platelets from cigarette smokers and nonsmokers. Previously we showed that a single dose of Pycnogenol(R) reduced platelet aggregation in cigarette smokers in a dose-response fashion. Cigarette smoking increased platelet reactivity aggregation when measured 2 h after smoking the first cigarette of the day. Blood was collected immediately before and 5 min after smoking three cigarettes each. Smoking increased platelet aggregation (1.17 +/- 0.04). However 200 mg Pycnogenol(R)/day, taken 3 h prior to first cigarette for the day for 2 months, significantly (p <.0023) reduced smoke-induced platelet aggregation (0.98 +/- 0.05) to the level of nonsmokers. In a group of 19 nonsmokers, platelet aggregation was measured during in vitro stimulation by platelet aggregation factor (PAF) after 4 or 8 weeks of 200 mg/day of Pycnogenol(R) consumption. Platelet aggregation was significant when induced in vitro by PAF. However, Pycnogenol(R) consumption did not change platelet aggregation, suggesting that Pycnogenol(R)'s regulation of aggregation is by another mechanism. Thromboxane A2 (TxA2) is increased in smokers by release from platelets and rapidly becomes thromboxane B2 (TxB2). Smoking increased TxB2, which was prevented by Pycnogenol(R), lowering TxB2 levels to those of nonsmokers. However, Pycnogenol(R) had no effect on the lower levels of TxB2 in nonsmokers. These observations suggest that Pycnogenol(R) supplementation reduces a risk factor for cardiovascular diseases, that is, platelet aggregation in smokers. The bioflavonoids in Pycnogenol(R) reduced platelet aggregation stimulated by tobacco smoke.

Inhibition of smoking-induced platelet aggregation by aspirin and pycnogenol

The effects of a bioflavonoid mixture, Pycnogenol, were assessed on platelet function in humans. Cigarette smoking increased heart rate and blood pressure. These increases were not influenced by oral consumption of Pycnogenol or Aspirin just before smoking. However, increased platelet reactivity yielding aggregation 2 hours after smoking was prevented by 500 mg Aspirin or 100 mg Pycnogenol in 22 German heavy smokers. In a group of 16 American smokers, blood pressure increased after smoking. It was unchanged after intake of 500 mg Aspirin or 125 mg Pycnogenol. In another group of 19 American smokers, increased platelet aggregation was more significantly reduced by 200 than either 150 mg or 100 mg Pycnogenol supplementation. This study showed that a single, high dose, 200 mg Pycnogenol, remained effective for over 6 days against smoking-induced platelet aggregation. Smoking increased platelet aggregation that was prevented after administration of 500 mg Aspirin and 125 mg Pycnogenol. Thus, smoking-induced enhanced platelet aggregation was inhibited by 500 mg Aspirin as well as by a lower range of 100-125 mg Pycnogenol. Aspirin significantly (p<0.001) increased bleeding time from 167 to 236 seconds while Pycnogenol did not. These observations suggest an advantageous risk-benefit ratio for Pycnogenol.

Diabetes-induced alterations in platelet metabolism

OBJECTIVES

This review summarizes the recent findings on some aspects of platelet metabolism that appear to be affected as a consequence of diabetes mellitus. The metabolites include glutathione, L-Arginine/nitric oxide, as well as the ATP-dependent exchange of Na+/K+ and Ca2+.

CONCLUSIONS

Several aspects of platelet metabolism are altered in diabetics. These metabolic events give rise to a platelet that has less antioxidants, and higher levels of peroxides. The direct consequence of this is the overproduction platelet agonists. In addition, there is evidence for altered Ca2+ and Na+ transport across the plasma membrane. Recent evidence indicates that plasma ATPases in diabetic platelets are not damaged instead their activities are likely to be modulated by oxidized LDL. Finally, platelet inhibitory mechanisms regulated by NO appear to be perturbed in the diabetes disease-state. The combined production of NO and superoxide by NOS isoforms in the platelet could be a major contributory factor to platelet pathogenesis in diabetes mellitus.

Platelet-dependent thrombin generation in patients with diabetes mellitus: effects of glycemic control on coagulability in diabetes

OBJECTIVES

This study sought to assess the usefulness of platelet-dependent thrombin generation as an index of coagulability in diabetes and to determine the effect of glycemic control on coagulability in diabetes.

BACKGROUND

It is important to investigate the interaction of platelets and the coagulation factors to clarify the processes of the coagulation system in detail.

METHODS

Platelet-rich plasma (150 X 10(9)/liter), 0.5 ml, was prepared, and 40 mmol/liter of calcium chloride was added to initiate clotting. S-2238 was added to each sample in a microtiter plate every 10 min, and the absorbance of the released color product at 2 min was measured spectrophotometrically at a wavelength of 405 nm using a microtiter plate reader as thrombin generation. We measured the platelet-independent thrombin generation in patients with non-insulin-dependent diabetes mellitus grouped according to glycemic control.

RESULTS

Platelet-dependent thrombin generation at 30 min after calcium chloride addition was significantly higher in 23 patients with poorly glycemic-controlled non-insulin-dependent diabetes mellitus without complications, such as diabetic retinopathy, nephropathy and neuropathy (hemoglobin [Hb] A1c >/= 9.0%) than in 46 healthy normal subjects (448 +/- 75 vs. 165 +/- 28 mU/min, p < 0.001). Thrombin generation in 31 well controlled diabetic patients without complications (Hb A1c < 9.0%) was intermediate (240 +/- 72 mU/min) between those of the poorly controlled group and healthy normal subjects. Platelet-poor plasma from diabetic patients increased platelet-dependent thrombin generation in normal subjects.

CONCLUSIONS

Coagulability is evidently enhanced in patients with non-insulin-dependent diabetes mellitus compared with that in healthy normal subjects on the basis of assessments of the platelet-dependent thrombin generation, and good glycemic control may help to correct a hypercoagulable state in diabetic patients.

Metabolic control in insulin-dependent diabetes mellitus, as reflected in the in vitro effects of platelets on endothelial cell proliferation and prostacyclin production

We tested the hypothesis that the degree of metabolic control in diabetes mellitus may be a determinant of the ability of platelets to stimulate proliferation of endothelial cells (ECs) and smooth muscle cells (SMCs). Platelets were obtained from 24 patients (two groups of 12 patients each) with insulin-dependent diabetes mellitus (IDDM) and increased blood glucose concentrations (HbA1c > 10% Hb), duration of disease 2-45 years, on no other medication than insulin at the time of blood sampling or during the preceding 6 months, and with no signs of coronary artery disease, nephropathy, hypertension or retinopathy. The patients served as their own controls, platelets being obtained from them again 2-4 months later when their mean glucose values were lower (HbA1c < 6.5% Hb). EC proliferation was significantly reduced after exposure to platelets obtained from the patients when their metabolic control had improved, whereas no significant differences were seen in either SMC proliferation or prostacyclin production. There was no correlation between changes in insulin dosage and either cell proliferation or prostacyclin production, or between changes in lipid values and cell proliferative capacity. It is concluded that, EC proliferation will be greater, owing to the platelet effects found in vitro, when metabolic control in diabetics is poor than when it is good, which may be of importance regarding the repair of endothelial lesions.