Platelets, aspirin, and cardiovascular disease

Aspirin was first synthesised 100 years ago and its preparation and marketing is generally reckoned to have been the foundation of the pharmaceutical industry. For most of the time since then it has been used for the relief of pain and fever. The modern phase of aspirin use commenced with the reporting in 1974 of a randomised controlled trial in the secondary prevention of death by low-dose aspirin given to patients who had suffered a myocardial infarct. Reports of other trials followed and an overview of the first six trials was presented to the inaugural meeting of the Society for Clinical Trials in Philadelphia in 1980. There have been two further major overviews and the most recent, based on 145 trials, established that low-dose aspirin reduces vascular events by around one third. It has been estimated that, used appropriately, aspirin could prevent 100,000 premature deaths each year worldwide, at a cost of about 250 Pounds ($400) per life saved, and about 80 Pounds ($130) per cardiovascular event prevented. The evidence indicates that it is seriously underused at present. The aspirin story continues and trials are in progress to test other possible uses of aspirin, in vascular dementia, colorectal cancer, and cataract.

Anti-glycoprotein Ib causes platelet aggregation: different effects of blocking glycoprotein Ib and glycoprotein IIb/IIIa in the high shear filterometer

In 1987 we reported that when blood was forced through a fine filter under pressure in the filterometer the platelets aggregated and blocked the filter. von Willebrand factor (vWF) and glycoprotein (Gp) IIb/IIIa and calcium were involved. Results with anti-GpIb were equivocal. We now report that all the anti-GpIb antibodies studied, glycocalicin, as well as some concentrations of aurin tricarboxylic acid caused platelet aggregation in the pre-filter blood and therefore could not be used in the filterometer. Using two different molecules that prevent vWF binding to GpIb and two anti-GpIIb/IIIa antibodies at two pressures it has now been shown that GpIb, vWf and high shear are primarily responsible for platelet retention at 0-5 s. Progressive platelet retention studied between 20 and 40 s required high shear and GpIIb/IIIa after the calcium influx mediated by GpIb/vWF binding. When GpIb was inhibited, GpIIb/Ila could not function normally, so GpIb inhibition resulted in decreased aggregation both at 0-5 s and at 20-40 s. Anti-GpIIlb/IIIa caused a minimal decrease in retention at 0-5 s and marked inhibition at 20-40 s. These findings fit and amplify concepts derived from other high shear methodologies. A diagram is presented of the events leading up to the final 'passivation' of the 'thrombus' in the filter when the surface of the aggregated platelets becomes unattractive.

The relative power of heat-precipitation nephelometric and clottable (Clauss) fibrinogen in the prediction of ischaemic heart disease: the Caerphilly and Speedwell studies

The Caerphilly and Speedwell studies have previously reported the predictive power of heat-precipitation, nephelometric, fibrinogen for 10-year incidence of ischaemic heart disease. A Clauss, clotting time, fibrinogen was also measured at baseline, but has not previously been reported. The predictive power of the two assays is compared. Both methods were employed on fasting blood samples from a total of 4391 men aged 45-63 years. Over the following 10 years 533 (12%) developed major ischaemic heart disease. Nephelometric fibrinogen was higher by 0.33 g/l among the men who developed disease; clottable fibrinogen was higher by 0.20 g/l. This difference is statistically significant (P=0.01). Relative odds of developing heart disease increased steadily to 3.53 (P<0.0001) in the 20% of men with the highest nephelometric fibrinogen; for clottable fibrinogen the corresponding relative odds increased to 2.24 (P<0.0001). When both measures of fibrinogen were included in logistic regression models together with age and smoking habit, the trend for incidence to increase with increasing nephelometric fibrinogen remained highly significant (P<0.0001), whereas for the Clauss fibrinogen the trend almost entirely disappeared (P = 0.37). We conclude that functional assays of clottable fibrinogen may not reflect all of the mechanisms which mediate the association between fibrinogen and cardiovascular disease and that assays of both 'heat precipitable' and 'clottable' fibrinogen should be included in all future prospective studies.

Sensitivity of aerobic spore-forming species of the genus Bacillus to the pteridine compound O129

Discs containing the pteridine compound O129 at various concentrations may be useful in differentiating the following closely related species belonging to the genus Bacillus, viz. B. subtilis, B. licheniformis and B. pumilus; B. polymyxa and B. macerans; together with B. cereus and its subspecies B. cereus var. mycoides. At concentrations of 10 micrograms O129, the ATCC type strain of B. subtilis was resistant whereas B. licheniformis and B. pumilus were sensitive. However, B. subtilis was sensitive to O129 at 150 micrograms. Similar reactions differentiated the ATCC type strains of B. polymyxa and B. macerans. The ATCC type strain of B. cereus was resistant to O129 at both 150 micrograms and 10 micrograms, but its subspecies B. cereus var. mycoides (ATCC 28) was partially sensitive at 150 micrograms concentration. When clinical isolates of B. cereus var. mycoides were subsequently tested, this partial sensitivity was found to be a variable characteristic.

High shear-induced platelet activation and inactivation: the importance of methodology

High shear platelet activation may be conveniently studied by forcing blood through a fine filter in the filterometer. To achieve haemostasis in vivo platelets are activated. When haemostasis is achieved, inactivation must follow. In the filterometer, activation occurs with filter blocking (first phase) and after 100s inactivation ('rebleeding') may occur (second phase). We report the effect of different pressures, temperatures, incubation times, anticoagulants and aspirin in this system. Most 'rebleeding' occurred in citrate, followed by native blood, r-hirudin and low-molecular-weight heparin. Unfractionated heparin inhibited 'rebleeding' whereas aspirin potentiated it. These and other findings are technically and clinically relevant and contribute to an understanding of the mechanisms involved in 'rebleeding' and hence perhaps in thrombogenesis.

Decreased platelet function in aortic valve stenosis: high shear platelet activation then inactivation

OBJECTIVE

To elucidate the mechanism of the bleeding tendency observed in patients with aortic valve stenosis.

DESIGN

A prospective study of high and low shear platelet function tests in vitro in normal controls compared with that in patients with severe aortic valve stenosis with a mean (SD) systolic gradient by Doppler of 75 (18) mm Hg before and at least 4 months after aortic valve replacement.

SETTING

District general hospital.

RESULTS

The patients showed reduced retention in the high shear platelet function tests. (a) Platelet retention in the filter test was 53.6 (12.6)% in patients with aortic valve stenosis and 84.8 (9.6)% in the controls (P < 0.001). (b) Retention in the glass bead column test was 49.8 (19.2) in the patients and 87.4 (8.7) in the controls (P < 0.001). (c) The standard bleeding time was longer in the patients (P < 0.06). Results of the high shear tests (a, b, and c) after aortic valve replacement were within the normal range. The platelet count was low but within the normal range before surgery and increased postoperatively (P < 0.01). There were no differences in the results of standard clotting tests, plasma and intraplatelet von Willebrand's factor, or in 15 platelet aggregation tests using five agonists between patients with aortic valve stenosis and controls.

CONCLUSIONS

The high shear haemodynamics of aortic valve stenosis modify platelet function in vivo predisposing to a bleeding tendency. This abnormality of platelet function is detectable only in vitro using high shear tests. The abnormal function is reversed by aortic valve replacement. High shear forces in vitro activate and then inactivate platelets. By the same mechanisms aortic valve stenosis seems to lead to high shear damage in vivo, resulting in a clinically important bleeding tendency in some patients.

Temperature and risk factors for ischaemic heart disease in the Caerphilly prospective study

OBJECTIVE

To examine the associations between air temperature and risk factors for ischaemic heart disease.

METHOD

Data on risk factors are available from up to 2036 men in the Caerphilly Prospective Heart Disease Study. Daily temperatures were obtained from the Meteorological Office. Relations between these were examined by regression.

RESULTS

The coldest month of the year has a mean temperature that is 16 degrees C lower than that in the warmest month. A fall in temperature of this magnitude is associated with higher blood pressures (by 3-5 mm Hg) and a lower concentration of high density lipoprotein cholesterol (by 0.08 mmol/l). The most important effects however, seem to be on the haemostatic system. Fibrinogen is 0.34 g/l higher in the coldest month than in the warmest (p < 0.001) and alpha 2 macroglobulin, a protein that inhibits fibrinolysis, is also raised. Platelet count is increased by 30% of a standard deviation and the sensitivity of platelets in whole blood to adenosine diphosphate is increased by cold.

CONCLUSIONS

These effects on haemostasis, together with the effect on blood pressure, could explain a large part of the increase in ischaemic heart disease in the winter but are unlikely to explain much of the difference in mortality within different areas of England and Wales.

Gender and employment grade differences in blood cholesterol, apolipoproteins and haemostatic factors in the Whitehall II study

In the first Whitehall study, plasma cholesterol was a strong predictor of coronary heart disease (CHD) but it showed a positive association with grade of employment: the higher the grade the higher the level. Because it could not explain the higher rate of CHD in lower employment grades, further investigation of biochemical CHD risk factors has been conducted with data from the baseline examination of the Whitehall II cohort in 1985-88. These data also allow investigation of gender differences and the effect of menopause. Serum cholesterol (6860 men and 3374 women) and apolipoproteins A-I and B (apo AI and apo B) were measured in those aged 35-55 working in the London offices of twenty Civil Service departments. Plasma fibrinogen and factor VII were determined in 45-55 year olds. The apo B/apo AI ratio (95% confidence interval) after age adjustment is lowest in premenopausal women: 0.557 (0.549-0.565), intermediate in postmenopausal women: 0.601 (0.589-0.613) and highest in men: 0.703 (0.698-0.709). After age adjustment fibrinogen is higher in postmenopausal (2.90 (2.85-2.95) g/l) than in premenopausal women (2.78 (2.71-2.84) g/l), who have higher levels than men (2.64 (2.62-2.67) g/l). A positive association with employment grade is seen for apo AI and a negative association is seen for fibrinogen, apo B (women only) and the apo B/apo AI ratio, after age adjustment. These patterns are consistent with the higher rates of CHD in lower grades. Cholesterol and factor VII show no gradient with our sensitive measure of social position. After adjusting for the effects of smoking rates, alcohol consumption, exercise and dietary pattern, as well as age, ethnicity, body mass index and report of symptoms, the regression coefficient for apo AI on employment grade is reduced by 43% in men and 70% in women. Corresponding reductions for fibrinogen are 53% and 65%. These attenuations suggest that a considerable part of the social gradients in apo AI and fibrinogen are explained by variations in health related behaviours. The remaining gradients may represent effects independent of these behaviours.

Inter-relationships between haemostatic tests and the effects of some dietary determinants in the Caerphilly cohort of older men

Inter-relationships between fibrinogen, platelets and other haemostatic factors were examined in 1030 men aged 55-99 years. Fasting blood was taken and used for cell counts, platelet counts and platelet parameters, aggregation of platelets to ADP by a whole blood method and a filter test of platelet activation. Plasma fibrinogen, von Willebrand factor, factor VII and plasma viscosity were measured by standard methods. A stressed bleeding time was conducted on the forearm of the arm not used for venepuncture. Variability within the laboratory and short-term intra-subject variation were examined and found to be acceptably small. The effect of age on the tests was modest, except for von Willebrand factor which increased by about 50% of a SD for every 10 years of age. Cholesterol and triglyceride levels had small effects on the platelet tests and a large effect on factor VII. A number of dietary and life-style determinants were examined: smokers had increased levels of fibrinogen, viscosity and white cell count and reduced bleeding times. Alcohol drinkers showed reduced platelet activity and have lower levels of fibrinogen, von Willebrand factor and white cell count. Men who took fish oil capsules had substantially increased bleeding times and lower levels of von Willebrand factor and men who took capsules containing an extract of garlic showed reduced platelet retention in the filter test.

Exercise, fibrinogen, and other risk factors for ischaemic heart disease. Caerphilly Prospective Heart Disease Study

OBJECTIVE

To examine the associations between physical activity and a wide range of risk factors for ischaemic heart disease including fibrinogen concentration and viscosity.

DESIGN

Cross sectional evidence from the 2398 men aged 50-64 years in the Caerphilly Prospective Heart Disease Study.

METHODS

Validated questionnaires were used to quantify energy expenditure on leisure activities and to grade activities related to occupation. Risk factors for heart disease examined included blood pressure, lipids, fibrinogen, and plasma viscosity. Possible confounding variables included smoking, employment, and prevalent heart disease (angina, previous myocardial infarction, and electrocardiographic evidence of ischaemia).

RESULTS

Fibrinogen concentration was lower by 0.24 g/l and viscosity by 0.026 cP in the third of men who were most active in leisure activities (about 0.25 x 1 SD). A weak positive relation was found with high density lipoprotein cholesterol, but none with total cholesterol or fasting glucose concentrations or blood pressure. Triglyceride concentrations seem to be substantially lower in the most active men, although the evidence for this is not consistent. Work related activity showed relation with the lipid concentration but not with the haemostatic tests.

CONCLUSIONS

Leisure activities of all levels seem to affect haemostatic and lipid factors beneficially. These effects correspond to a difference in the risk of heart disease for an active man and a sedentary man of at least 7% or 8%. Fasting triglyceride concentrations have already been shown to be strongly predictive of heart disease in this cohort of men, and the effect of exercise on this factor is also likely to confer benefit.

Identification and growth characteristics of pink pigmented oxidative bacteria, Methylobacterium mesophilicum and biovars isolated from chlorinated and raw water supplies

Pink pigmented bacteria were isolated from a blood bank water purification unit, a municipal town water supply (tap water), and an island (untreated) ground water source. A total of thirteen strains including two reference strains of pink pigmented bacteria were compared in a numerical phenotypic study using 119 binary characters. Three clusters were derived, one major cluster of eleven strains was subdivided into two sub-clusters on the basis of methanol utilization. Five strains were facultative methylotrophs and were classified as Methylobacterium mesophilicum biovar 1. The other six strains did not utilize methanol, but on the basis of high phenotypic similarity of 83.6% were classified as M. mesophilicum biovar 2. The single reference strain comprising cluster 2 Pseudomonas extorquens NCIB 9399 was assigned to the genus Methylobacterium and classified as M. extorquens. Cluster 3 was the single reference strain Rhizobium CB 376.

Platelet responses to cardiopulmonary bypass. Assessment by a shear stress activation technique

Platelet responses before and during cardiopulmonary bypass were studied using a shear stress activation technique. Whole blood was passed through a 10 microns micro-porous filter and the percentage of platelets retained was determined. Retention in control subjects (n = 20, age 62 +/- 11 years) was 65.2 +/- 15.1%. Patients with ischaemic heart disease (n = 20, age 61 +/- 9 years) had significantly higher retention at 82.6 +/- 13.2%, p less than 0.001. In valvular heart disease (n = 15, age 57 +/- 14 years) the retention rate was 43.5 +/- 15.4%, lower than both controls and ischaemic heart disease patients (p less than 0.001). In vitro haemodilution had no significant effect on platelet retention. High retention rates were maintained in patients undergoing coronary artery surgery. During valve surgery retention increased before aortic cross-clamp removal (83.5 +/- 13.4%) compared with baseline values (p less than 0.001) and remained high 24 hours postoperatively (79.6 +/- 9.4%). Platelet retention also increased within 20 minutes of thoracotomy without cardiopulmonary bypass (n = 10, age 57 +/- 8 years, 79.3 +/- 11.6% versus 61.6 +/- 10.9% baseline, p less than 0.01) and remained high 24 hours postoperatively. Significant differences in platelet responses, assessed by shear stress activation, were demonstrated between healthy controls and patients with ischaemic and valvular heart disease. Surgery, with or without extracorporeal circulation, caused a significant increase in platelet retention.

Fibrinogen, viscosity, and white blood cell count are major risk factors for ischemic heart disease. The Caerphilly and Speedwell collaborative heart disease studies

BACKGROUND

Recent studies have suggested that hemostatic factors and white blood cell count are predictive of ischemic heart disease (IHD). The relations of fibrinogen, viscosity, and white blood cell count to the incidence of IHD in the Caerphilly and Speedwell prospective studies are described.

METHODS AND RESULTS

The two studies have a common core protocol and are based on a combined cohort of 4,860 middle-aged men from the general population. The first follow-up was at a nearly constant interval of 5.1 years in Caerphilly and 3.2 years in Speedwell; 251 major IHD events had occurred. Age-adjusted relative odds of IHD for men in the top 20% of the distribution compared with the bottom 20% were 4.1 (95% confidence interval, 2.6-6.5) for fibrinogen, 4.5 (95% confidence interval, 2.8-7.4) for viscosity, and 3.2 (95% confidence interval, 2.0-4.9) for white blood cell count. Associations with IHD were similar in men who had never smoked, exsmokers, and current smokers, and the results suggest that at least part of the effect of smoking on IHD is mediated through fibrinogen, viscosity, and white blood cell count. Multivariate analysis shows that white blood cell count is an independent risk factor for IHD as is either fibrinogen or viscosity, or possibly both. Jointly, these three variables significantly improve the fit of a logistic regression model containing all the main conventional risk factors. Further, a model including age, smoking habits, fibrinogen, viscosity, and white blood cell count predicts IHD as well as one in which the three hemostatic/rheological variables are replaced by total cholesterol, diastolic pressure, and body mass index.

CONCLUSION

Jointly, fibrinogen, viscosity, and white blood cell count are important risk factors for IHD.

Ischemic heart disease and platelet aggregation. The Caerphilly Collaborative Heart Disease Study

The Caerphilly Collaborative Heart Disease Study is based on a large cohort of men (2,398) aged 49-66 years at the time of study. Platelet aggregation induced by collagen, thrombin, and ADP was measured in fasting blood samples and was related to prevalent angina, past myocardial infarction, and electrocardiographic evidence of ischemic heart disease. A number of subjects had taken aspirin, other nonsteroidal anti-inflammatory drugs, or other drugs affecting platelet aggregation 7 days before blood sample collection; after the exclusion of these subjects, data were available for 1,811 men. No relations were demonstrated with angina, but significant relations were shown between past myocardial infarctions and electrocardiographic evidence of ischemia and ADP-induced aggregation (both primary and secondary) and between electrocardiographic evidence of ischemia and thrombin-induced aggregation. The strongest relation indicated more than a twofold increase in the odds of a past myocardial infarction in subjects of the highest fifth of ADP-induced primary platelet aggregation compared with the lowest fifth. No significant relations were detected with collagen-induced aggregation. Accounting for a number of possible confounding factors had a relatively small impact on the relations between platelet aggregation and ischemic heart disease. Other evidence, including the well-established effect of aspirin on reducing the incidence of ischemic heart disease, indicates that the relations we describe are unlikely to be simply an effect of IHD on platelets.

The association of platelet and red cell count with platelet impedance changes in whole blood and light-scattering changes in platelet rich plasma: evidence from the Caerphilly Collaborative Heart Disease Study

This epidemiological study was undertaken to explore possible relationships among various haematological indices, prevalent ischaemic heart disease and platelet "function" as measured by two rather different methods. ADP-induced platelet impedance changes in whole blood were strongly associated with prevalent ischaemic heart disease in a general population of 49-66 year men at increased risk. Adenosine diphosphate (ADP) induced platelet aggregation in platelet rich plasma (PRP) at a constant platelet count and also the whole blood platelet count and red cell (RBC) count were strongly and independently related to ADP-induced platelet impedance changes. Both platelet count and platelet aggregation in PRP assessed by changes in optical density were directly related to increasing platelet "sensitivity" as measured by impedance changes in whole blood but RBC count was inversely related. Positive independent relationships between platelet impedance changes and plasma viscosity and fibrinogen were markedly attenuated when platelet count was taken into account, but this finding does not discount a role for these factors in platelet aggregation. No relationship was noted between white blood cell (WBC) count and platelet impedance changes; however, a significant inverse relationship was noted with platelet aggregation in PRP. These findings indicate that laboratory-based experimental findings can be observed in population based studies, and that these haematological factors may be important indicators of ischaemic disease in the population.