Articles |
From the Department of Internal Medicine, Awaji-Hokudan Public Clinic (K.K.), and the Department of Internal Medicine (K.K., T. Matsuo) and Central Laboratory (H.K., M.M.), Hyogo Prefectural Awaji Hospital, Hyogo, and the Clinical Laboratory (T.S.) and Research Institute (T. Miyata), National Cardiovascular Center, Suita, Japan.
Correspondence to Dr Kazuomi Kario, 480-2, Ikuha, Hokudan, Tsuna, Hyogo, 656-16, Japan.
| Abstract |
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Key Words: noninsulin-dependent diabetes mellitus microalbuminuria endothelial cell dysfunction tissue factorinduced coagulation activated factor VII
| Introduction |
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FVII plays an important role in the initiation of TF-induced coagulation.11 FVII is the single-chain zymogen form of a serine protease that is converted to the two-chain active form (FVIIa) by various coagulation proteases, including factor Xa, factor IXa, factor XIIa, thrombin, and FVIIa. At sites of vascular injury and on exposure of the subendothelium to circulating blood, an integral membrane protein known as TF comes in contact with circulating FVII to form a bimolecular complex. The formation of this complex is widely believed to be the initial event in the extrinsic blood coagulation pathway. TF-producing cells have also been identified in atherosclerotic plaques, where they may play a significant role in thrombosis-associated plaque rupture.12 Healthy individuals have trace levels of circulating FVIIa (0.5% to 1% of the total FVII:Ag level), which may initially activate FVII complexed with cell-surface TF.13 14 15 Thus, an elevated plasma level of FVIIa may indicate hypercoagulability.
An increase of FVIIc has been proposed as an independent cardiovascular risk factor and has been observed in various atherosclerotic diseases, including diabetes mellitus.16 In addition, we recently reported that patients with cardiovascular disease had an increased FVIIa level and proposed that FVIIa may be an independent risk factor for cardiovascular disease.15 Furthermore, our preliminary study indicated that FVIIa levels were also increased in diabetic patients with microalbuminuria.17
The aim of the present study was to clarify the relationship between microalbuminuria, FVII activation, endothelial cell dysfunction, and activation of the coagulation pathway in NIDDM. We found that the generation of FVIIa in NIDDM patients was associated with increases in the urinary AER and endothelial cell damage, resulting in the activation of coagulation. This increased FVIIa level may partly account for the hypercoagulable state in NIDDM patients.
| Methods |
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To avoid the confounding influence of daily physical activity and to facilitate precise specimen collection, we asked the patients to collect urine on two consecutive days between 7 PM and 7 AM, and then we determined the mean urinary albumin level. The 67 diabetic subjects were divided into the following three groups on the basis of their AER: a normoalbuminuria group (AER <15 µg/min, n=31), a microalbuminuria group (AER =15 to 200 µg/min, n=25), and an overt albuminuria group (AER >200 µg/min, n=11).
After a minimum 12-hour fast, blood samples for hemostatic determinations were collected into disposable, siliconized, evacuated glass tubes containing 0.1 vol 3.8% trisodium citrate, and blood from the second tube was used for the coagulation assay. The samples were centrifuged at 3000g for 15 minutes at room temperature within 1 hour of collection. Plasma was subsequently separated and stored in several plastic tubes at -80°C until laboratory determinations were performed. The thawed samples were used to determine the levels of TPAPAI-1 complex, PAI-1, FVII, TAT, and D-dimer.
Assay Procedures
FVIIa levels were measured by our previously described
fluorogenic assay15 using a fluorogenic peptide substrate
for thrombin
(N-tert-butoxycarbonyl-Val-Pro-Arg-7-amido-4-methylcoumarin,
Peptide Institute Inc), congenital human FVII-deficient plasma (George
King Bio-Medical), and recombinant, soluble, human TF expressed in
yeast and purified.18 Human plasma FVIIa for use as a
standard was kindly provided by Dr Tomohiro Nakagaki of the
Chemo-Sero-Therapeutic Research Institute (Kumamoto, Japan). The FVIIc
level was measured with a chromogenic assay
autoanalyzer (Behring Chromotimer, Behringwerke) using a
human placental calcified thromboplastin reagent (Chromoquick,
Behringwerke) and immunoadsorbed FVII-deficient plasma (Behringwerke
AG) as described previously.19 The FVII:Ag level was
determined with an ELISA kit (Diagnostica Stago).
Plasma levels of PAI-1 and TPAPAI-1 complex were determined by using ELISA kits (TDC-88, Teijin Co Ltd)20 and were expressed in nanograms per milliliter. In brief, for measurement of TPAPAI-1 complex, 100 µL plasma was diluted, mixed, and incubated with a monoclonal antiPAI-1 antibodycoated polystyrene ball and peroxidase-conjugated monoclonal anti-TPA antibody. After being washed, the ball was immersed in a substrate solution containing H2O2. Then the reaction was stopped by the addition of oxalic acid, and the absorbance of the solution was measured spectrophotometrically. Plasma PAI-1 antigen levels were determined by ascertaining the capacity of plasma to form additional TPAPAI-1 complexes. Fifty microliters of plasma was preincubated for 30 minutes at 37°C with 50 µL exogenous TPA (500 ng/mL), and the concentration of TPAPAI-1 complexes was determined. Addition of this amount of TPA resulted in complete saturation of PAI-1.
vWF and D-dimer levels were determined by using ELISA kits (Diagnostica Stago). TAT and TFPI antigen levels were determined by using ELISA kits obtained from Behringwerke and American Diagnostica, respectively. For FVIIc, FVII:Ag, and vWF assays, commercially available pooled plasma (CTS Standard Plasma, Behringwerke AG) was taken as 100%. The FVIIa to FVII:Ag ratio was calculated as an indicator of FVII zymogen activation to FVIIa by taking the mean plasma FVIIa level in young Japanese control subjects (2.1 ng/mL) as 100%.15
Serum total cholesterol and triglyceride levels were determined by using commercial enzyme assay kits (Wako), whereas serum HDL cholesterol was determined by an enzymatic procedure after precipitation with phosphotungstic acid (Wako). Serum glucose was determined by the glucose oxidase method using a commercial enzymatic assay kit (Kanto Chemicals). HbA1c was determined by high-performance liquid chromatography. BUN, creatinine, and uric acid levels were also measured with routine enzyme assay kits. Urinary creatinine was measured by a method based on the Jaffe reaction. The AER was determined by a nephelometric method and expressed as micrograms per minute.
In our laboratory, the interassay coefficient of variation was 4.2% for vWF, 2.3% for TPAPAI-1 complex, 5.4% for PAI-1, 4.2% for TFPI, 4.2% for FVIIa, 2.8% for FVIIc, 4.4% for FVII:Ag, 3.3% for TAT, 3.0% for D-dimer, and 5.2% for AER.
Statistical Analysis
Data are shown as the mean (with the 95% confidence interval).
The distribution of vWF, TPAPAI-1 complex, PAI-1, TFPI, FVIIa, FVIIc,
FVII:Ag, FVIIa-FVII:Ag ratio, TAT, D-dimer, and
triglyceride levels was examined, and a logarithmic
transformation (to base 10) was performed to reduce the skewness and
kurtosis of the distribution curve prior to statistical
analysis. The geometric mean of each parameter was
determined. One-way ANOVA and unpaired t test were used for
comparison of mean values between any two groups. In addition,
Pearson's correlation coefficients were calculated for the different
variables. Differences with a value of P<.05 were
considered significant.
| Results |
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Table 2
shows plasma levels of FVII-related
activity/antigen, endothelial cellderived molecular
markers (vWF, TPAPAI-1 complex, PAI-1, and TFPI), and markers of
coagulation activation (TAT and D-dimer) in the three NIDDM
groups and control subjects. The normoalbuminuria group
had significantly higher FVIIa, PAI-1, and TAT levels than the control
subjects, whereas FVIIc and FVII:Ag were not significantly different.
The microalbuminuria group showed a further increase in
the FVIIa level accompanied by a significant increase in the
FVIIa-FVII:Ag ratio (indicating activation of FVII zymogen to FVIIa).
Both increases were significant compared with not only the control
subjects but also the normoalbuminuric group. In addition,
FVIIc and FVII:Ag levels were significantly increased in the
microalbuminuria group compared with the control
subjects. Furthermore, the microalbuminuria group had
higher levels of vWF, TPAPAI-1 complex, and PAI-1 but did not show a
significant increase in TFPI compared with the control group. The
albuminuria group had the highest levels of FVIIa, FVIIc,
FVII:Ag, FVIIa-FVII:Ag ratio, TAT, and endothelial
cellderived markers, including TFPI. D-Dimer levels also
tended to be increased in the albuminuria group, but the
change was not statistically significant.
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Fig 1
shows the relation of AER with vWF, FVIIa,
FVIIa-FVII:Ag ratio, and TAT in all 67 NIDDM patients. AER showed a
strong positive correlation with FVIIa (Fig 1B
, r=.574,
P<.0001). AER also showed a significant correlation with
the FVIIa-FVII:Ag ratio (Fig 1C
, r=.365, P<.01)
and weaker but still significant correlations with FVIIc
(r=.261, P<.05), FVII:Ag (r=.301,
P<.05), vWF (Fig 1A
, r=.319, P<.01),
and TAT (Fig 1D
, r=.323, P<.01). In addition,
vWF and FVIIa levels showed a slight but significant correlation (Fig 2
, r=.244, P<.05).
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HbA1c had a strong, positive correlation with FVII:Ag (r=.455, P<.0001), FVIIa (r=.373, P<.01), FVIIc (r=.306, P<.05), and TFPI (r=.380, P<.01) but showed no correlation with the FVIIa-FVII:Ag ratio (not shown). In contrast, fasting glucose levels did not show any correlations with these factors. Total cholesterol showed positive correlations with TFPI (r=.418, P<.001) and FVII:Ag (r=.305, P<.05), whereas triglycerides were correlated with FVII:Ag (r=.253, P<.05) (not shown).
Because 14 of 20 (70%) hypertensive diabetic patients were receiving antihypertensive therapy, the office blood pressure was not adequate to assess the correlation between blood pressure and other parameters. Accordingly, we divided the 67 NIDDM subjects into normotensive and hypertensive groups. In the hypertensive group, AER was higher than in the normotensive group (69 [28 to 150] versus 18 [12 to 29] µg/min, P<.01). The levels of FVIIa, FVIIc, vWF, TPAPAI-1 complex, and PAI-1 also tended to be increased in the hypertensive group, but the difference was not significant (P<.2).
Table 3
shows various factors in the NIDDM
patients with or without abnormal Q waves on the ECG. Those with
intercurrent illness and/or a history of coronary artery
disease were excluded. The FVIIa, FVIIa-FVII:Ag ratio, and vWF levels
were all significantly higher in patients with abnormal Q waves than in
those without this finding, but FVIIc and FVII:Ag levels did not differ
between these two groups.
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| Discussion |
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As most previous studies on hypercoagulability did not classify
diabetic patients on the basis of AER, it has remained unclear whether
or not normoalbuminuric patients have
endothelial damage and/or hypercoagulability. Several
recent articles have indicated that the levels of vWF,9
thrombomodulin (a marker of endothelial
damage),21 and factor XIa
1-antitrypsin
complex (a marker of activation of the contact phase of
coagulation)22 are not increased in
normoalbuminuric NIDDM patients, suggesting that systemic
endothelial damage and hypercoagulability do not pose a
problem for these patients. In contrast, our data indicated that FVIIa,
PAI-1, and TAT levels were significantly increased in
normoalbuminuric patients compared with healthy control
subjects. Thus, hemostatic abnormalities were present even in our
NIDDM patients with normoalbuminuria. However, the
FVIIc and FVII:Ag levels of this group were not significantly different
from those of control subjects. Thus, measurement of FVIIc seems to be
less sensitive for assessing FVII hyperactivity than does measurement
of FVIIa.
FVIIc has previously been shown to be increased in diabetic subjects,23 24 and a positive correlation between FVIIc and glucose levels has been observed in large population studies.25 26 Some authors have reported significantly higher FVIIc levels in microalbuminuric than normoalbuminuric subjects,27 28 but others have not found this difference.29 30 Our study indicated that FVIIc as well as FVII:Ag levels were slightly but significantly different in the microalbuminuria group compared with those from the healthy control subjects. These discrepancies may be partly attributable to the assays used for FVIIc, because the sensitivity of an FVIIc assay for detecting FVIIa is markedly influenced by the thromboplastin and FVII-deficient plasma preparations that are employed.31 32
To assess endothelial function, we measured plasma levels of vWF as well as other endothelial cellderived factors, including TPAPAI-1 complex, PAI-1, and TFPI. vWF is a glycoprotein secreted by the vascular endothelium,33 and an increased plasma vWF level is now accepted as an indicator of systemic endothelial dysfunction in NIDDM patients, with the endothelial damage suggested by the increase in this factor possibly explaining the linkage between microalbuminuria and cardiovascular death in these patients.8 9 Other endothelial cellderived factors are not well characterized in terms of their release from the endothelium as a result of vascular dysfunction. In the present study, we found that only the PAI-1 level was statistically increased in the normoalbuminuria group compared with the healthy control group, whereas the levels of PAI-1, vWF, and TPAPAI-1 complex were increased in the microalbuminuria group, suggesting a hyperfibrinolytic state and endothelial cell damage as described previously.8 9 10 21 An increase in TFPI was detected in the overt albuminuria group.
The ELISA used in this study enabled us to specifically measure the plasma level of active PAI-1 antigen that could form complexes with TPA.20 The mechanism of PAI-1 release is quite different from that for vWF. vWF can be released from an organelle of endothelial cells, known as the Weibel-Palade body, by various stimuli.34 PAI-1 is an acute-phase reactant that can be detected when lipopolysaccharide or cytokines are added to cultured endothelial cells; it is also found in patients with sepsis, trauma, or a postoperative state.35 An increase of PAI-1 levels has been reported in NIDDM, although the underlying mechanism remains controversial. In vitro studies have suggested that insulin, its precursors, or hyperglycemia itself stimulates PAI-1 synthesis by hepatocytes or endothelial cells.36 37 The different release mechanisms of these substances would explain the different behavior of vWF and PAI-1 in NIDDM patients with normoalbuminuria.
In NIDDM patients with microalbuminuria or overt
albuminuria, markedly elevated FVIIa levels were observed,
indicating an increase in the early phase of TF-induced coagulation. It
is noteworthy that the increase in FVIIa was far higher than that of
FVIIc or FVII:Ag, indicating that activation of FVII was markedly
enhanced. Factor Xa,
-thrombin, and possibly FVIIa are thought to
catalyze the initial activation of FVII in complex with a cell-surface
procoagulant protein, TF, under various pathological
conditions.11 There were significant correlations between
AER and FVIIa level (Fig 1B
, r=.574), vWF and AER (Fig 1A
,
r=.319), or vWF and FVIIa (Fig 2
, r=.244).
Elevated levels of plasma vWF have been reported to reflect systemic
endothelial cell damage and to be related to AER in
diabetes.8 9 At the present time, it remains uncertain
whether FVIIa generation in diabetes is due to systemic
endothelial cell damage or localized renal
endothelial damage in a TF-dependent manner. To address
this issue, TF expression in the kidneys of diabetic patients must be
studied by an in situ hybridization method or immunohistochemistry
technique.
The albuminuria group had the highest levels of endothelial cellderived factors, FVII, and TAT among the three patient groups. In our previous study of patients with arterial cardiovascular disease, a mean FVIIa level of 3.3 ng/mL was obtained.15 Thus, the mean FVIIa levels of 3.9 ng/mL in the microalbuminuria group and of 4.7 ng/mL in the overt albuminuria group were both much higher than those that are typically found in healthy young subjects (2.1 ng/mL) or in patients with cardiovascular disease. Such findings could explain the worse clinical outcome in these groups. In addition, FVIIc and FVII:Ag levels were also significantly increased along with AER, suggesting that proteinuria stimulates the hepatic synthesis of FVII. Concerning coagulation inhibitors, the levels of antithrombin III, protein C, and protein S have been reported to be decreased in albuminuric patients, probably due to urinary loss.38 On the contrary, TFPI levels were increased in the overt albuminuric group. Although the precise mechanism that underlies increases in TFPI levels in the overt albuminuria group remains uncertain, more extensive vascular damage might release TFPI from endothelial cell glycosaminoglycans.
In the present study, we excluded those patients with a history of
coronary artery disease, but we still found nine
asymptomatic patients with abnormal Q waves on the ECG.
In these patients with myocardial ischemia, vWF, FVIIa, and the
FVIIa-FVII:Ag ratio were higher, but FVII:Ag levels did not differ when
compared with those with no abnormal ECG findings (Table 3
). Thus, endothelial cell damage and
FVII activation were present in these patients.
In conclusion, generation of FVIIa increases along with AER in NIDDM patients. This FVIIa generation is probably due to endothelial cell damage, with subsequent activation of coagulation, and might explain the higher risk of cardiovascular disease in NIDDM patients with microalbuminuria. To confirm the predictive value of increased FVIIa levels in these patients for the hypercoagulable state and subsequent cardiovascular episodes, further studies are needed in a prospective cohort setting.
| Selected Abbreviations and Acronyms |
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| Acknowledgments |
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Received February 28, 1995; accepted May 30, 1995.
| References |
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1-antitrypsin complex
levels in NIDDM patients with diabetic nephropathy.
Diabetes. 1993;42:233-238. [Abstract]
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