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Arteriosclerosis, Thrombosis, and Vascular Biology. 2000;20:251-258

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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2000;20:251.)
© 2000 American Heart Association, Inc.


Thrombosis

Intravascular Free Tissue Factor Pathway Inhibitor Is Inversely Correlated With HDL Cholesterol and Postheparin Lipoprotein Lipase but Proportional to Apolipoprotein A-II

Akito Kawaguchi; Yuji Miyao; Teruo Noguchi; Hiroshi Nonogi; Masakazu Yamagishi; Kunio Miyatake; Yuichi Kamikubo; Kousuke Kumeda; Motoo Tsushima; Akira Yamamoto; Hisao Kato

From the National Cardiovascular Center Research Institute (A.K., A.Y., H.K.) and Hospital (Y.M., T.N., H.N., M.Y., K.M., M.T.) and Chemo-Sera Therapeutics Research Institute (Y.K., K.K.), Osaka, Japan.

Correspondence to Akito Kawaguchi, MD, Department of Etiology and Pathophysiology, National Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita-shi, Osaka 565-8565, Japan. E-mail akitok{at}ri.ncvc.go.jp


*    Abstract
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Abstract—To elucidate the distribution and clinical implications of tissue factor pathway inhibitor (TFPI) concentrations, we measured TFPI levels consisting of preheparin free, lipoprotein-bound (Lp-bound), and endothelial cell–anchor pools in 156 patients with coronary artery disease (average age, 61.2±9.1 years; range, 32 to 78 years) by heparin infusion (50 IU/kg) and compared them with the preheparin TFPI levels of 229 healthy subjects (average age, 59.6±9.4 years; range, 41 to 80 years). The patients had lower preheparin free TFPI and lower HDL cholesterol (HDL-C) levels than the healthy subjects with equivalent Lp-bound forms (free TFPI, 15.9±6.5 versus 19.2±8.1 ng/mL). In a partial correlation analysis, the preheparin free TFPI levels were shown to be inversely correlated with the HDL-C concentrations in both the patients (r=-0.454, P<0.001) and the healthy subjects (r=-0.136, P<0.05). As determined by comparison of preheparin and postheparin plasma, the patients generally showed preheparin free TFPI <10%, Lp-bound TFPI at 30%, and endothelial cell–anchor TFPI at 60%. When the patients were divided into 4 categories by their LDL cholesterol (LDL-C, 130 mg/dL) and HDL-C (40 mg/dL) levels to specify their coronary risks, the low–HDL-C groups had significantly increased preheparin and postheparin free TFPI levels and decreased postheparin LPL levels, whereas the high–LDL-C groups showed increased levels of Lp-bound TFPI. In a partial correlation analysis, we found a proportional relation between postheparin free TFPI and apolipoprotein A-II (r=0.5327) and between HDL-C and LPL (r=0.4906), whereas postheparin free TFPI was inversely correlated with HDL-C (r=-0.4280) and postheparin LPL (r=-0.4791). The inverse relationship between TFPI and LPL suggests that increased free TFPI concentrations as a compensatory response of the endothelium to prevent atherothrombotic processes compete with and displace LPL on endothelial surface, resulting in reduced LPL and low HDL-C.


Key Words: TFPI • HDL cholesterol • lipoprotein lipase • apolipoprotein A-II • coronary artery disease


*    Introduction
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Tissue factor pathway inhibitor (TFPI) plays an important role in the antithrombotic properties of vessel walls by inhibiting extrinsic coagulation processes.1 2 Intravascular TFPI consists of free and lipoprotein-bound (Lp-bound) forms.3 The free form includes 2 subfractions except in platelets,4 ie, a circulating free TFPI fraction without carrier in preheparin plasma and a heparin-releasable TFPI fraction from endothelial cells.5 Exogenous administration of recombinant TFPI to experimental animals prevents thrombosis,6 whereas increased TFPI levels have been observed in patients with acute myocardial infarction.7 Although the alteration of serum lipids by cholesterol-lowering therapy influences Lp-bound TFPI profiles,8 9 10 11 little is known about the clinical implications of the TFPI level and its regulation in relation to lipid risk profiles.

In the present study, we compared TFPI subfractions in preheparin plasmas of normal healthy subjects and patients with coronary artery disease (CAD). Significant negative correlations were observed between the preheparin free TFPI and HDL cholesterol (HDL-C) concentrations in both of these groups. Accordingly, we studied the TFPI distribution further, including endothelial cell–anchor TFPI (EC-TFPI) levels in CAD patients divided according to their different phenotypes of dyslipidemia, especially hypercholesterolemia (raised LDL cholesterol, LDL-C) and low HDL-C to evaluate the patients’ coronary risks. Although Lp-bound TFPI constitutes most of the circulating TFPI before heparin infusion, EC-TFPI released by heparin is still the greater pool in postheparin plasma, which is detected in free form. The free form of TFPI inhibits tissue factor–induced coagulation more effectively than Lp-bound TFPI.12 13 Consequently, EC-TFPI is physiologically the more important pool, mediating the major antithrombotic activity on the endothelial surface. EC-TFPI is believed to bind to heparan sulfate on the cell surface, as does lipoprotein lipase (LPL).14 LPL regulates the LDL and HDL fractions because it contributes to the ultimate formation of LDL particles by hydrolyzing triglyceride (TG)-rich lipoproteins and also mediates the transfer of phospholipids and free cholesterol together with apolipoproteins to HDL particles.15 The endothelial cell surface, therefore, may play an important role in the interactive function between lipid metabolism and antithrombotic properties. We therefore measured the generation of TFPI in patients with CAD and in normal subjects to test the hypothesis that the low–HDL-C state associated with endothelial dysfunction16 17 18 19 20 leads to an increased production of TFPI to reduce the risk of thrombosis on the endothelial surface.

We first documented the inverse relationship between TFPI and LPL on the endothelial cell surface. Our results suggest a close relation between the antithrombotic aspect and lipid metabolism on vascular beds, giving new insight into risk profiles and mechanism of low HDL-C for atherothrombosis in vivo.


*    Methods
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Subjects
Patients with CAD (n=156), 32 to 78 years old, were recruited for the study. These patients were referred to and admitted to the National Cardiovascular Center Hospital (Osaka, Japan) because of stable symptoms or suspected CAD. No patients had hepatic or renal dysfunction, but antianginal drugs, such as nitrates (47.4%), calcium antagonists (46.1%), ß-blockers (28.8%), and aspirin (44.1%), had been administered. When the patients were divided into subgroups (see below), there was no significant difference of the distribution of therapies among the subgroups. The patients who had been given lipid-lowering drugs, those with a TG level >4.5 mmol/L (400 mg/dL), and those with familial hypercholesterolemia or type III hyperlipidemia were excluded from this study. All patients were examined by coronary angiography to evaluate the severity of coronary atherosclerosis. Blood samples were obtained during the diagnostic catheterization procedure in the early morning. Preheparin plasma samples were collected from a femoral artery just after the insertion of the sheath for catheter manipulation. Postheparin plasma samples were obtained 10 minutes after an intravenous injection of unfractionated standard heparin (Novo-Nordisk A/S) with a bolus of 50 IU/kg body wt. The blood samples were drawn into evacuated tubes containing 0.38% trisodium citrate (1:9 vol/vol) and disodium EDTA (0.1%), immediately placed in a refrigerator, and centrifuged at 3000g at 4°C within 1 hour to obtain platelet-poor plasma. Aliquots were stored at -80°C until assay.

As control subjects, 229 normal volunteers 40 to 81 years old were selected from the population-based prospective cohort in the district of Ise (Kisei-cho, Mie Prefecture in Japan). Serum lipids and TFPI were measured without heparin infusion. After the subjects had fasted overnight, blood samples were obtained from an antecubital vein into evacuated tubes. Informed consent was obtained from all patients and healthy subjects for the blood sampling and measurements.

Classification
To evaluate their coronary risk according to their lipid profiles, the CAD patients were divided into 4 categories according to their LDL-C and HDL-C levels (Figure 1Down): the normal group (a), low–HDL-C group (b), low–HDL-C and high–LDL-C group (c), and high–LDL-C group (d). The cutoff value for LDL-C (3.34 mmol/L [130 mg/dL]) is the point above which drug therapy is recommended to patients with established atherosclerotic disease (Adult Treatment Panel II),21 and that for HDL-C (1.03 mmol/L [40 mg/dL]) is the diagnostic level for low HDL-C in the guidelines of the Japanese Atherosclerosis Society.22 HDL-C was plotted as reciprocal values (1/HDL-C) as a negative risk factor. This classification according to lipid risk profiles can be used to evaluate the independent contributions of the 2 confounding variables of HDL-C and LDL-C. A simple factorial ANOVA (2-way ANOVA) was applied to determine the separate abilities of HDL-C and LDL-C levels to affect the dependent variables.



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Figure 1. Relation between LDL cholesterol and 1/HDL cholesterol in 229 healthy subjects ({circ}) and 156 patients with CAD ({blacktriangleup}). All subjects were divided according to their LDL and HDL cholesterol levels into 4 categories: (a) normal lipid profile, (b) low-HDL cholesterolemia, (c) low-HDL cholesterolemia and high-LDL cholesterolemia, and (d) high-LDL cholesterolemia. The cutoff levels (dotted lines) of LDL cholesterol and HDL cholesterol were 130 mg/dL (3.34 mmol/L) and 40 mg/dL (1.03 mmol/L), respectively.

Measurements of Lipids and Risk
The serum total cholesterol and TG levels of preheparin and postheparin plasma samples were determined by enzymatic methods23 24 with reagents commercially supplied by Daiichi Kagaku for cholesterol and by Nihon Shoji for TG and with an autoanalyzer (COBAS MIRA plus, Nihon Roche). HDL-C was determined in the supernatant after heparin-manganese precipitation of the apolipoprotein (apo) B–containing lipoproteins.25 Apo A-1, A-II, B, C-II, C-III, and E were measured immunoturbidimetrically with kits (Daiichi Kagaku).26 LDL-C was calculated by Friedewald’s formula.27 In the patients, blood pressure and body mass index (BMI: body weight divided by height in square meters) were measured, and alcohol and smoking habits were also documented on the basis of a standard questionnaire.

TFPI and LPL Antigen Determination
Both the total and free TFPI concentrations were measured by a 1-step sandwich ELISA method using "total" and "free" TFPI reagent kits (Kaketsuken) in both preheparin and postheparin plasma.28 Monoclonal anti-TFPI antibodies for the Kunitz 3 domain (K9) and for the tertiary structure of the first and second Kunitz domains (K270) were prepared to detect the free and total TFPI levels, respectively. Because heparin-releasable TFPI from the EC-TFPI pool is detected as free after a heparin infusion, EC-TFPI was calculated by subtracting the total TFPI concentration in the preheparin plasma from total TFPI concentration in the postheparin plasma. The amounts of preheparin and postheparin Lp-bound TFPI were calculated by subtracting the free TFPI concentration from the total TFPI concentration in both preheparin and postheparin plasmas, respectively. Preheparin Lp-bound TFPI is different from postheparin Lp-bound TFPI, because a part of the heparin-releasable TFPI from endothelium newly binds to lipoprotein, as described in the Results. The plasma LPL mass was measured by a sandwich ELISA with commercial reagent kits (Daiichi Kagaku).29 The EC-LPL level was calculated by subtraction of the preheparin LPL concentration from the postheparin LPL concentration.

Statistical Analysis
Statistical analysis was performed with SPSS software (SPSS Inc). A 2-tailed Student’s t test was applied for the differences between the control subjects and CAD patients, except for the sex distribution ({chi}2 test). Comparisons of the dyslipidemic categories were made by a simple factorial ANOVA (2-way ANOVA) to determine the differences in clinical parameters, where HDL and LDL cholesterol were the 2 independent factors. Significant differences of the main effect of each factor were examined after that of their interaction. Partial correlation coefficients were also calculated for the preheparin and postheparin TFPI, LPL, lipid, and apolipoprotein levels. The TG concentrations were logarithmically transformed because of their skewed distribution. Values of P<0.05 were considered significant.


*    Results
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*Results
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Comparison of Serum Lipid, Apolipoprotein, and TFPI Levels in Control Subjects and Patients
Figure 1Up shows a scattergram of the LDL-C and HDL-C levels of the healthy subjects and CAD patients. The HDL-C levels of the patients were clearly shifted to the lower range, characterizing lipid profiles of patients at risk for atherosclerosis; 80 patients (51%) had HDL-C levels <1.03 mmol/L (40 mg/dL). The CAD patients had significantly lower serum lipid and apolipoprotein levels than the control subjects, with the exception of apo C-II levels (Table 1Down). However, the apo A-II level divided by HDL-C was higher in the patient group than in the healthy subjects, indicating a relative abundance of apo A-II–rich HDL particles in the CAD patients.


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Table 1. Comparison Between Patients With CAD and Healthy Control Subjects

Both the preheparin free and total TFPI concentrations were significantly lower in the patients than in the control subjects. The Lp-bound TFPI concentrations were not significantly different between the patients and control subjects. The preheparin free TFPI/total TFPI ratios and Lp-bound TFPI/total TFPI ratios showed that the TFPI in the control group was {approx}25% in the free form and 75% in the Lp-bound form. The TFPI of the patients was {approx}20% in the free form and 80% in the Lp-bound form. In the healthy group, male subjects had significantly higher Lp-bound TFPI (67.9±19.1 ng/mL versus 59.5±18.7 ng/mL; P<0.005) and lower HDL-C (1.37±0.30 mmol/L versus 1.48±0.33 mmol/L; P<0.05) levels than female subjects, but no sex difference was found in the patient group.

Partial Correlation Coefficients in Control Subjects and Patients
The preheparin free TFPI levels were inversely correlated with the HDL-C levels (Table 2Down) in both the healthy subjects (r=-0.1358; P<0.05) and the CAD patients (r=-0.4540; P<0.001; Figure 2Down). In the control subjects, HDL-C was correlated with apo A-I (r=0.7895; P<0.001) and apo A-II (r=0.3054; P<0.001), whereas in the patients, HDL-C was weakly correlated with apo A-I (r=0.1898; P=0.026) and not at all with the apo A-II level (r=-0.0638). Despite the negative correlation of preheparin free TFPI with HDL-C, the preheparin free TFPI concentration was positively correlated with the apo A-II level in both groups, more so in the patients. Although the preheparin free TFPI was related to apo A-II rather than apo A-I in both the patients and the control subjects, the patients who had low HDL-C levels had a stronger correlation between preheparin free TFPI and apo A lipoproteins (apo A-I and apo A-II). Only in the control group was preheparin free TFPI correlated with the TG level (r=0.254; P<0.001) and LDL-C level (r=0.1669; P<0.01).


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Table 2. Partial Correlation Coefficients



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Figure 2. HDL cholesterol and preheparin free TFPI in the 156 CAD patients. An inverse relation (r=-0.4587) was revealed between the HDL cholesterol concentration and preheparin free TFPI level (Table 2Up).

Lp-bound TFPI was found in the LDL fraction as the major constituent in the control subjects (r=0.4587; P<0.001) and in the patients (r=0.4623; P<0.001). In the control group, the HDL fraction (r=0.3152; P<0.001) also contributed significantly to the level of Lp-bound TFPI. In the patients, by contrast, a linkage between Lp-bound TFPI and HDL was not observed.

Different Forms of TFPI Associated With Dyslipidemic Profiles
The patients were divided by their LDL-C and HDL-C levels into 4 categories (Table 3Down). The low–HDL-C groups (b and c) had higher BMI and lower alcohol consumption values than the patients with normal HDL-C (a and d). There was no significant difference in smoking status and drug administration among the groups. LDL-C and HDL-C contributed to the significant differences of total cholesterol, apo A-I, and apo B between the patients with low HDL-C (b and c) and high LDL-C (c and d) without any secondary interaction. Although the apo A-II levels were lower in the high–LDL-C groups, the apo A-II/HDL-C ratio was significantly elevated in the low–HDL-C groups. Apo C-II levels were also higher in the low–HDL-C patients than in the patients with normal HDL-C.


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Table 3. Clinical Characteristics of the CAD Patients by Dyslipidemic Classification

The heparin infusion (50 IU/kg) caused marked increases in the free TFPI levels, from 7.7- to 11.1-fold, and in LPL concentrations, from 12- to 16-fold, compared with preheparin plasma (Table 4Down). The low–HDL-C groups were characterized by significantly higher preheparin and postheparin free TFPI and reduced LPL levels compared with the normal HDL-C groups. Accordingly, the calculated EC-TFPI values were also increased in the low–HDL-C groups compared with the normal–HDL-C groups, whereas the EC-LPL levels were significantly lower in the low–HDL-C groups (P<0.005) and higher in the high–LDL-C groups (P<0.01) than in the other groups.


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Table 4. TFPI Profile of the Preheparin and Postheparin Plasma of the CAD Patients by Dyslipidemic Classification

As expected, the Lp-bound TFPI levels in both the preheparin and postheparin plasma were increased in the groups with high LDL-C. However, the total TFPI level in postheparin plasma was higher in the low–HDL-C groups than in the high–LDL-C groups, because more EC-TFPI was released by heparin infusion in the low–HDL-C groups. Interestingly, the Lp-bound form in the postheparin plasma was increased by {approx}10 to 20 ng/mL compared with that in the preheparin plasma in all groups. Newly detected Lp-bound TFPI represented by {delta}-Lp-TFPI was significantly more abundant in the high–LDL-C groups (P<0.005). As determined by comparison of preheparin and postheparin plasmas, the patients generally showed <10% preheparin free TFPI, 30% Lp-bound TFPI, and 60% EC-TFPI, regardless of the dyslipidemia. The preheparin free TFPI level was {approx}10% to 14% the EC-TFPI level.

Partial Correlation Coefficients Among TFPI, LPL, and Lipids in the Patient Group
On the basis of the partial correlation analysis among the patients (Table 5Down), the preheparin free TFPI levels were shown to be significantly related to the postheparin free TFPI concentration (r=0.6748; P<0.001), whereas preheparin LPL showed a weak association with postheparin LPL levels (r=0.3473; P<0.001). Like the results shown by the dyslipidemic classification, the HDL-C concentration was inversely correlated with the preheparin and postheparin free TFPI levels and positively correlated with preheparin and postheparin LPL. Although the apo A-I and apo A-II levels were well correlated with each other (r=0.6458; P<0.001), only apo A-I was associated with the HDL-C level (r=0.2009; P<0.01). These 2 types of apolipoproteins were positively correlated with preheparin and postheparin free TFPI levels and were negatively correlated with postheparin LPL levels, whereas apo A-II was much more strongly correlated than was apo A-I in both cases.


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Table 5. Partial Correlation Coefficients Among TFPI, LPL, Lipids, and Apolipoproteins

Significant correlations were observed between postheparin free TFPI and apo A-II (r=0.5327; P<0.001) (Figure 3ADown) and between postheparin LPL and HDL-C (r=0.4906; P<0.001), whereas significant inverse correlations were documented between intravascular free TFPI and postheparin LPL (r=-0.4791; P<0.001) (Figure 3BDown), between intravascular free TFPI and HDL cholesterol (r=-0.4280; P<0.001), and between postheparin LPL and apo A-II (r=-0.3678; P<0.001).



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Figure 3. A, Relation between apo A-II and postheparin free TFPI in the 156 CAD patients (r=0.5327) (Table 5Up). B, Inverse relation between postheparin LPL and postheparin free TFPI in the 156 CAD patients (r=-0.4791) (Table 5Up).


*    Discussion
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*Discussion
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To elucidate the intravascular TFPI distribution in the present study, it was necessary to differentiate the free form from the Lp-bound form of TFPI because of their different anticoagulant properties.12 13 The heparin infusion allowed us to measure the total intravascular TFPI levels, including the EC-TFPI concentration, which was 7.7 to 11.2 times greater than the preheparin free TFPI level, as previously reported.5 As determined by comparison of preheparin and postheparin plasmas, the distribution of intravascular TFPI in the CAD patients studied consisted of <10% as the circulating preheparin free fraction (6% to 9%), 30% as the Lp-bound form (27% to 32%), and 60% as the EC-TFPI fraction (60% to 64%) regardless of the patients’ dyslipidemic profiles. The postheparin free TFPI was strongly correlated with preheparin free TFPI (r=0.6748), indicating a certain physiological equilibrium of free TFPI between the EC-TFPI pool and the preheparin circulating pool. In contrast, the preheparin LPL concentration was not a good predictor of the postheparin LPL levels (r=0.3709).

In our study, the patients with CAD had serum lipid levels that were lower than those in the healthy subjects. Dietary control during hospitalization might have affected the lipid profiles of the patients. However, a critical difference between the healthy subjects and patients was present in the HDL-C level, which may be a better indicator for CAD risk rather than hypercholesterolemia, in the Japanese population. We observed the inverse correlation between preheparin free TFPI and HDL cholesterol (r=-0.1358) in the healthy subjects and in the preheparin (r=-0.4547; Figure 2Up) and postheparin (r=-0.4280) plasmas of the CAD patients. In the dyslipidemic classification, the preheparin free TFPI and EC-TFPI levels were significantly increased in the patients with low HDL-C concentration compared with the other groups (Table 4Up). Hansen et al10 reported that preheparin plasma TFPI activity in 14 patients with familial hypercholesterolemia was not correlated with HDL-C or apo A-I, although they did not discriminate between TFPI activity and antigen, and their small group was highly heterogeneous. Cella et al30 reported a positive relationship between HDL-C and total TFPI antigen in postheparin plasma (20 IU/kg of heparin), analyzing a small number of heterogeneous subjects (12 hospitalized patients with marked obesity [mean BMI, 41.4] and 14 normal subjects). The reason for the difference in findings between that study and ours is unclear. We demonstrated that symptomatic CAD patients had lower preheparin free TFPI levels than did normal healthy subjects. This result indicates a reduction of intravascular (preheparin and postheparin) free TFPI in the atherogenic vascular milieu, except for the Lp-bound form, which is dependent on cholesterol levels. However, the fact that the (preheparin and postheparin) free TFPI concentrations rose most in those with low HDL-C suggests a compensatory augmentation of TFPI levels produced by endothelial cells against the atherogenic vascular milieu. Increased TFPI levels in patients with acute myocardial infarction7 may also be evidence of such an endothelial compensation, although the inflammatory response after myocardial infarction complicates interpretation.

Lesnik et al31 reported elevated TFPI activity in small, dense LDL and HDL fractions. Moor et al32 also described that HDL3b was associated with TFPI in patients with CAD. A low HDL-C concentration is generally associated with the presence of small and dense HDL particles, because HDL2 is transformed to HDL3.15 Small and dense HDL particles are enriched in apo A-II. Although apo A-I was positively correlated with HDL-C in the CAD patients in this study, apo A-II was inversely correlated with HDL-C among the patients with low HDL-C (80 patients; r=-0.291; P=0.009), indicating that at lower HDL-C concentrations, HDL-C becomes enriched with apo A-II. The apo A-II/HDL-C ratio was significantly higher in the CAD patients than in the healthy subjects (Table 1Up), and the apo A-II/HDL-C ratio of the patients with low HDL-C was higher than that of the patients with normal HDL-C (Table 3Up). Thus, both the apo A-II and (preheparin and/or postheparin) free TFPI levels were inversely correlated with HDL-C levels in both control subjects and patients, especially in the postheparin plasma of the patients. The precise relevance of this is uncertain. However, it has been reported that apo A-II is a discriminator for myocardial infarction,33 and apo A-II transgenic mice are atherogenic.34

When the thrombotic process is activated and/or the augmentation of antithrombotic activity is required, endothelial cells may be forced to generate TFPI and compensate for the consumption of free TFPI in response to certain signals, such as thrombin35 or other inflammatory mediators.36 It has been elucidated that HDL improves endothelial function by opposing oxidation16 17 18 and expression of adhesion molecules.19 We postulate that the inverse relationship between HDL-C and preheparin and postheparin free TFPI in the present CAD patients also reflects compensatory augmentation of antithrombotic properties of the vascular wall to maintain normal endothelial function.

The HDL-C concentration is known to be proportional to LPL levels,37 as in the present study. LPL, like HDL-C, was negatively correlated with preheparin and postheparin free TFPI. It is possible that EC-TFPI shares common binding sites of heparan sulfate proteoglycans and that LPL was replaced by the increased production of TFPI, resulting in the negative correlation between the 2 parameters (Figure 3BUp). Therefore, some of the reduction of HDL-C may reflect diminished LPL anchoring, and it is likely to aggravate endothelial dysfunction and stimulate further TFPI generation.

The present study also revealed the novel finding that {approx}10% (8% to 15%) of EC-TFPI (10 to 20 ng/mL) was bound to lipoproteins, a level that was significantly higher in the patients with high LDL-C, suggesting an instant interaction between TFPI and lipoproteins. TFPI synthesized in the endothelium is believed to bind to heparan sulfate proteoglycans on the cell surface, where LPL also enhances the binding of lipoproteins.38 It is possible that part of the EC-TFPI is physiologically bound to lipoproteins mediated by LPL on the cell surface. The preheparin free TFPI levels were positively correlated with the TG concentrations only in the control group39 and not in the patients with CAD, as previously reported.7 This means that the contribution of TGs to TFPI levels may depend on the metabolic lipid state in a given population.

Taken together, the present findings indicate that the levels of intravascular free and Lp-bound TFPI are interrelated with lipid metabolism involving HDL-C, LDL-C, LPL, and apo A-II levels. The lower the HDL cholesterol concentration is, the higher the intravascular (preheparin and postheparin) free TFPI level. This may reflect a protective and stabilizing effect on the endothelial surface in the presence of normal HDL concentrations. Subclinical and/or clinical atherothrombotic events may cause increased TFPI as an endothelial compensation in response to atherothrombotic substances. Increased free TFPI may compete with and displace LPL, resulting in reduced LPL and low HDL-C. Thus, endothelial cell surface has the physiological significance to play a crucial role in the risk profiles not only of antithrombotic properties but also the lipoprotein metabolism through heparan sulfate proteoglycans.


*    Acknowledgments
 
We would like to thank Dr Paul Nestel (Baker Medical Research Institute, Melbourne, Australia) for his critical reading of the manuscript and constructive discussion. We also thank Akiko Makino and Eiko Saitoh for their expert technical assistance in performing ELISA and using the autoanalyzer.

Received August 20, 1999; accepted August 27, 1999.


*    References
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up arrowAbstract
up arrowIntroduction
up arrowMethods
up arrowResults
up arrowDiscussion
*References
 
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4. Novotny WF, Girard TJ, Miletich JP, Broze GL Jr. Platelets secrete a coagulation inhibitor functionally and antigenically similar to the lipoprotein associated coagulation inhibitor. Blood. 1988;72:2020–2025.[Abstract/Free Full Text]

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