Thrombosis |
From the Laboratory of Hematology (I.J.-V., P.E.M., M.C.A.), Centre de Détection et de Prévention de lAthérosclerose (I.J.-V., J.F.R.), Statistics Department (J.G.), CHU Timone, Marseille, and Serbio Genevilliers (M.G.) and Stago Asnières (Y.G.), Asnières, France.
Correspondence to Prof I. Juhan-Vague, Laboratory of Hematology, CHU Timone, 13385 Marseille cedex 5, France. E-mail ijuhan{at}ap-hm.fr
| Abstract |
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Key Words: thrombin-activatable fibrinolysis inhibitor cardiovascular risk fibrinogen plasminogen activator inhibitor-1
| Introduction |
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The importance of the hemostatic system in predisposing to or precipitating coronary heart disease has gained increasing recognition over the past several years. The published results from prospective studies are remarkably consistent for fibrinogen, indicating a highly statistically association with coronary artery disease.14 A rise in the circulating level of the fibrinolytic inhibitor, plasminogen activator inhibitor (PAI)-1, has also been shown to predict the occurrence of myocardial infarction.15 Interestingly, both of these factors are related to lifestyle.16 17 Thus, conventional cardiovascular risk factors may be involved in atherosclerosis through modifications of the plasma levels of hemostatic factors. Therefore, it is of importance to analyze the associations between hemostatic parameters and conventional cardiovascular risk factors to determine whether they could be affected by modification of lifestyle.
The physiological relevance of TAFI is not known, but it might be involved in pathways regulating the balance between fibrin formation and deposition within and in the vicinity of the vascular bed. Thus, TAFI could represent a candidate gene for thrombosis and atherogenesis. The quantity of TAFIa generated during coagulation could not be easily measured, but in small populations, its level has been shown to be positively correlated with the level of circulating TAFI antigen.18
Our aim was to determine the interindividual variability of the TAFI antigen in a large population of subjects attending an outpatient clinic for primary prevention of cardiovascular disease. We then analyzed the association of conventional cardiovascular risk factors with TAFI antigen plasma levels. Results were compared with those obtained for fibrinogen and PAI-1.
| Methods |
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Patients were submitted to a standardized examination. Height and weight were recorded, and the body mass index (BMI) was calculated as kilograms per square meter. The waist and the hip circumferences were measured, with patients in a standing position, midway between the lower rib margin and the iliac crest and at the greatest circumference, respectively; the former divided by the latter is reported as the waist-to-hip circumference ratio (WHR) and is a measure of fat distribution.
While the patient was in the sitting position, systolic blood pressure (SBP) and diastolic blood pressure (DBP) measurements were taken on the left arm by an automated device (OMRON 705 CP); the mean of 3 measurements was used for analysis. A 12-lead ECG was recorded.
Noninvasive arterial explorations were performed with a B-mode ultrasound imager (High Definition Imaging, Advanced Technologies Laboratories). Left and right common carotid arteries were examined with a 5- to 10-MHz linear probe. Artery images were obtained in the anteroposterior projection and were perpendicular to the far wall of the vessel. The measurement of the intima-media thickness (IMT) was performed by the same physician with the built-in software from 3 images of each carotid artery. The mean of these 6 measures was used for analysis.
The interview included questions on health status, personal and familial history of cardiovascular disease, socioprofessional factors, and drug use, including hormonal therapy. Patients were graded as nonsmokers, exsmokers, and current smokers, with a quantification in packs per year.
Total energy and nutrient intakes were calculated by recording 3 days of nutrition and analyzed by use of nutritional software (GENI). Alcohol consumption (kilocalories per day) was automatically calculated from self-report.
Anxiety and physical activity were assessed by self-administered questionnaires.
Laboratory Methods
Blood samples were obtained from the antecubital vein, after an
overnight fasting, between 8:00 and 10:00 AM, collected on
citrate (3.8% citrate, 0.129 mol/L), and centrifuged
(2500g for 30 minutes at 4°C). Platelet-poor plasma
was kept frozen at <-80°C until analysis. Antigen
determination of TAFI was performed with a commercially available kit
from Milan Analytica. This assay is based on affinity-purified sheep
anti-TAFI IgG raised against TAFI purified from plasma. These
antibodies do not recognize carboxypeptidase N and are able to
recognize the proenzyme as well as the active form of TAFI. Results are
expressed as a percentage of a control pooled plasma from 30 healthy
volunteers. Fibrinogen concentration was determined by the
Clauss thrombin clotting method. PAI-1 antigen was assayed by a
commercially available kit (Asserachrom PAI-1, Stago).
Total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides, apoB, glucose, creatinine, and microalbuminuria were determined by routine clinical chemical procedures.
Statistical Analysis
Statistical analyses were performed by use of Statview
and SPSS software. Values are expressed as mean±SD. Distribution of
BMI, PAI-1 antigen, lipid parameters, and
microalbuminuria values were skewed, and logarithmically
transformed values were used. The Mann-Whitney test was used to
determine differences in mean values between men and women. One-way
ANOVA was computed to compare the hemostatic parameter
levels according to the presence or absence of the
cardiovascular risk factors and was substituted by the
Kruskal-Wallis test for small subpopulations. Spearman correlation
coefficients were calculated to study the associations between
hemostatic parameters and other variables. When the
influence of the hormonal status was evaluated, the interaction with
age was tested. Stepwise multiple linear regression analysis
was performed to evaluate independent correlates of hemostatic
parameters. A value of P<0.05 was considered
statistically significant.
| Results |
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TAFI Antigen, Clottable Fibrinogen, and PAI-1 Antigen Distribution
in the Population
Table 2
shows the distribution of
the hemostatic parameters according to the study
participants. TAFI antigen levels presented a wide range of
values in men and in women, with a 2.5- to 3-fold increase between the
10th and 90th percentiles. The distribution was gaussian in men and
women. However, a small population (13.4%) with low values (<60%)
was identified (Figure 1
). Compared with
the rest of the population, this small population did not exhibit
differences in all the variables studied, nor did it present
any difference in familial history of thrombosis or the use of blood
pressurelowering or lipid-lowering agents. In contrast to fibrinogen
and PAI-1, no sex difference was observed in TAFI antigen levels. A
significant correlation was observed between age and TAFI, fibrinogen,
and PAI-1 levels in women (r=0.17, 0.16, and 0.15,
respectively; P<0.01) but not in men. To evaluate further
the association between TAFI levels and age in women, we compared
levels of TAFI antigen according to quartiles of age (Figure 2
). It appears that the oldest women were
more likely to have high levels of TAFI antigen (P<0.01).
The same trend was observed for men, without reaching significance
(P=0.09).
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Associations Between Hemostatic Variables and
Cardiovascular Risk Factors
By univariate analysis, in men, TAFI antigen
was significantly and positively correlated with BMI
(P<0.03), WHR (P<0.05), SBP
(P<0.02), DBP (P<0.01), and fibrinogen
(P<0.03), whereas in women, it was correlated with age
(P<0.01), SBP (P<0.02), total
cholesterol (P<0.05), apoB
(P<0.01), fibrinogen (P<0.03), and IMT
(P<0.01). After adjustment for age, the correlations
between TAFI and other parameters disappeared in women, but
TAFI remained significantly correlated with WHR and blood pressure in
men (Table 3
). No change related to the
use of blood pressurelowering or lipid-lowering agents was
observed.
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After adjustment for age, in men, fibrinogen was significantly and
positively correlated with BMI, WHR, SBP, DBP, smoking, and glycemia
and significantly and negatively correlated with HDL
cholesterol and alcohol intake, whereas in women,
fibrinogen levels were correlated with BMI, DBP, and
microalbuminuria (Table 2
). PAI-1 was strongly
correlated with variables related to insulin resistance state (BMI,
WHR, blood pressure, HDL cholesterol,
triglycerides, and glucose) in both sexes. It was also
significantly correlated with IMT in men but not in women (Table 3
).
Interestingly, in the whole population, the TAFI antigen levels were significantly higher in patients with a self-reported familial history of cardiovascular disease than in those without (106±35% versus 100±35% [mean±SD], respectively; P=0.05).
Influence of Hormonal Status on Hemostatic Parameter
Levels
TAFI antigen was evaluated in the 198 premenopausal and 151
menopausal women according to the use of hormonal therapy. The use of
oral contraceptives (n=20 women) did not affect TAFI or fibrinogen
levels, whereas PAI-1 levels in women not receiving oral contraceptives
(n=178) were significantly higher (data not shown). When women were
studied according to menopausal status, postmenopausal women receiving
hormonal substitution (n=43), compared with postmenopausal women not
receiving hormonal substitution (n=108), had 6.6% lower levels of TAFI
antigen (103±41% versus 111±35%, respectively; P<0.01),
and the mean level was not significantly different from that of
premenopausal women (data not shown). The same evolution was observed
for fibrinogen and PAI-1 (data not shown). However, except for PAI-1,
this difference disappeared after age adjustment.
Contribution of Environmental Factors and Age to the Variability of
Hemostatic Parameters
Results of the multivariate
step-by-step analysis are reported in Table 4
. Results showed a low contribution of
the parameters studied to the variability of TAFI antigen
levels. Indeed, WHR explained only 2% of the variability of the TAFI
antigen values in men, and age explained only 3% of the variability in
women. On the other hand, the environmental factors studied could
account for
16% of the fibrinogen variance in men and 9.5%
of the variance in women. The influence of metabolic
factors on PAI-1 antigen was even more pronounced, because it could
account for
36% of the variance in men and 32% of the variance in
women. Multivariate analysis was also
performed, restricted to the upper part of the distribution (TAFI
antigen >60%), and did not lead to different results.
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| Discussion |
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The finding of a positive association between levels of
fibrinogen, PAI-1, and cardiovascular risk factors is
consistent with previous studies. In accordance with the
Prospective Epidemiological Study of Myocardial Infarction
(PRIME),20 the traditional cardiovascular
risk factors accounted for
10% and 30% of the total variance of
circulating fibrinogen and PAI-1, respectively. Whereas the same
percentage was obtained in men and women for PAI-1, this was not the
case for fibrinogen. Cardiovascular risk factors are
implicated differently in men than in women. These data are highly
consistent with those previously reported by the second
Monitoring Trends and Determinants in Cardiovascular
Disease (MONICA) survey.16 Indeed, in men, the relation
between fibrinogen and BMI was less strong than in women, and WHR was
consistently included before BMI in the stepwise procedure in
men but not in women.
Another difference between men and women was the absence of any effect of smoking on fibrinogen levels in women. These results also illustrate the discrepancy between fibrinogen and PAI-1 in regard to lifestyle. Whereas fibrinogen levels are moderately affected, their contribution to circulating PAI-1 levels is strong and unique among the hemostatic parameters. This difference likely reflects the high proportion of insulin-resistant obese patients included in this population. Indeed, in contrast to fibrinogen, PAI-1 levels are dramatically increased in the insulin-resistant state.21 Moreover, the predictive effect of plasma PAI-1 for myocardial infarction has been shown to disappear after adjustment for parameters of the insulin resistance syndrome,15 which is not the case for fibrinogen.22
In contrast to fibrinogen and PAI-1 levels, a weak or no relationship was found between TAFI antigen levels and all the variables studied. The percentage of TAFI variance that could be accounted for was very low, 2% and 3% in men and women, respectively. The association between age and TAFI antigen values confirms previous results,19 but in the present study, this relationship was restricted to women. The observation that TAFI antigen levels were mainly elevated in the oldest women and that postmenopausal women exhibited higher levels of TAFI antigen raises questions about the role of estrogen in controlling circulating TAFI levels. As previously reported,23 postmenopausal women receiving estrogen replacement therapy had lower levels of PAI-1 than did postmenopausal women not receiving therapy; this difference was maintained after age adjustment.
Altogether, these observations did not attribute an important role to lifestyle in the control of TAFI antigen levels. This was different from the results observed for fibrinogen and PAI-1 levels. Thus, the plasma levels of PAI-1 and TAFI, 2 circulating fibrinolytic inhibitors, are differently regulated. Because of the large interindividual variability of TAFI antigen levels and the weak relationship with environment, it is possible that TAFI antigen levels are mainly under genetic control. This awaits further confirmation.
| Acknowledgments |
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Received October 20, 1999; accepted April 25, 2000.
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