Visceral Fat Accumulation Is an Important Determinant of
PAI-1 Levels in Young, Nonobese Men and Women
Modulation by Cross-Sex Hormone Administration
E.J. Giltay, J.M.H. Elbers, L.J.G. Gooren, J.J. Emeis, T. Kooistra, H. Asscheman, C.D.A. Stehouwer
Downloaded from http://atvb.ahajournals.org/ by guest on June 16, 2017
Abstract—Increased plasminogen activator inhibitor type-1 (PAI-1) levels, leading to impaired fibrinolysis, are associated
with increased visceral fat in middle-aged and obese subjects. It is unknown, however, whether this association is
independent of other disturbances clustered in the insulin resistance syndrome. We analyzed this association in young,
nonobese transsexual men and women before and after administration of cross-sex steroids, which potentially influence
many elements of the insulin resistance syndrome, including PAI-1 levels and visceral fat accumulation. We assessed
the visceral fat area (by MRI); total body fat; insulin sensitivity (with a glucose clamp technique); and plasma levels of
PAI-1, insulin, and triglycerides in young (,37 years old), nonobese (body mass index ,28 kg/m2), healthy men
(n518) and women (n515) before and after 12 months of cross-sex hormone administration. Men were treated with
ethinyl estradiol 100 mg/d plus cyproterone acetate 100 mg/d, and women were treated with testosterone esters 250 mg
IM every 2 weeks. At baseline, only visceral fat area was significantly correlated with plasma PAI-1 levels in both men
(r50.57, P50.03) and women (r50.59, P50.03). In multivariate linear regression analysis, this association was
independent of total body fat, insulin sensitivity, and plasma levels of triglycerides and insulin. After 12 months of
cross-sex hormone administration, the plasma PAI-1 levels were no longer correlated with visceral fat (which had
increased).We conclude that in young, nonobese men and women, visceral fat area is an important determinant of
plasma PAI-1 levels. After cross-sex hormone administration, this association was no longer demonstrable. (Arterioscler
Thromb Vasc Biol. 1998;18:1716-1722.)
Key Words: plasminogen activator inhibitor type-1 n visceral fat accumulation n insulin sensitivity n sex hormones
I
mpaired fibrinolysis is a risk factor for cardiovascular disease
(CVD).1–3 Fibrinolysis is activated by tissue plasminogen
activator (tPA) and urokinase-type plasminogen activator
(uPA).4 Plasmatic type 1 plasminogen activator inhibitor (PAI-1)
inhibits the action of both tPA and uPA.4 The exact origin of
plasmatic PAI-1 is unknown, but in vitro studies show that it is
produced by a wide variety of cell types,4 including endothelial
cells, vascular smooth muscle cells, hepatocytes,5 and adipocytes.6 – 8 Correlations have been found between plasma PAI-1
levels and visceral fat accumulation measured by means of the
waist-to-hip ratio (WHR),9–14 ultrasonographic techniques,15 or
CT.7,16 It is unknown, however, whether this association already
exists in young, nonobese subjects, since previous studies
included middle-aged subjects,7,9–16 obese subjects,9–16 or subjects with essential hypertension.14 Associations of plasma PAI-1
levels have also been described with other disturbances that are
clustered in the insulin resistance syndrome, ie, insulin resistance, hyperinsulinemia, glucose intolerance, dyslipidemia, and
hypertension.17 Therefore, it is unknown whether the association
between plasma PAI-1 levels and visceral fat accumulation is
independent of these disturbances.18 Previous studies either did
not include all of these elements of the insulin resistance
syndrome in one statistical model7,9,10 or used indirect or crude
estimates, such as WHR, to estimate fat distribution,9,11–14,19 and
insulin levels after a glucose tolerance test,12,15,16 the minimalmodel method,11,13 or a hyperglycemic clamp14 to estimate
insulin sensitivity.
Sex differences have been found in the interrelations
between fibrinolytic variables and elements of the insulin
resistance syndrome,14 many of which are influenced by
administration of sex steroids. Oral estrogen administration
increases triglyceride and HDL cholesterol levels20 and decreases insulin sensitivity.21,22 Exogenous estrogens are also
known to reduce plasma PAI-1 levels.23–25 Testosterone administration has no effect on triglyceride26 –28 and insulin28
levels but decreases HDL cholesterol levels,26,27 decreases22,29
or has no effect28 on insulin sensitivity, reduces total body
fat28 and abdominal subcutaneous fat depots,30,31 and increases
Received February 26, 1998; revision accepted April 24, 1998.
From the Institute of Endocrinology, Reproduction and Metabolism (E.J.G., J.M.H.E., L.J.G.G., H.A.), the Department of Internal Medicine (C.D.A.S.),
and the Institute for Cardiovascular Research (C.D.A.S.), Hospital Vrije Universiteit, Amsterdam, and the Gaubius Laboratory (J.J.E., T.K.), TNO-PG,
Leiden, The Netherlands.
Correspondence to Prof Dr Louis J.G. Gooren, MD, Department of Endocrinology, Division of Andrology, Hospital Vrije Universiteit, PO Box 7057,
1007 MB, Amsterdam, Netherlands. E-mail [email protected]
© 1998 American Heart Association, Inc.
Arterioscler Thromb Vasc Biol. is available at http://www.atvbaha.org
1716
Giltay et al
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visceral fat depots.30,31 It is unknown whether the shifts in
PAI-1 levels during sex-steroid administration are partly
mediated by quantitative changes in visceral fat accumulation
or by other elements of the insulin resistance syndrome.
The aim of this study was to examine the association
between plasma PAI-1 levels and visceral fat accumulation in
young, nonobese subjects. We aimed particularly to examine
whether this association was independent of other variables
clustered in the insulin resistance syndrome. Furthermore,
because we selected transsexual subjects for these studies, we
were able to reassess this association after 12 months of
cross-sex hormone administration, which is known to influence many elements of the insulin resistance syndrome,
including PAI-1 levels and visceral fat accumulation. Transsexuals, being no different from members of their own genital
sex from an endocrine32–34 or metabolic22,27,31 viewpoint, provide us with the opportunity to study the effects of high-dose
sex steroid administration in young, nonobese subjects. We
therefore consider transsexuals as a valid model for a study of
the regulation of PAI-1 levels.
Methods
Patients
Eighteen male-to-female (M3 F) transsexuals with a median age of
27 years (range, 18 to 37) and 15 female-to-male (F3 M) transsexuals with a median age of 23 years (range, 16 to 33) were recruited
between October 1993 and April 1996 and agreed to participate in
the study. Subjects with a body mass index (BMI) (weight/height2)
.28 kg/m2 were excluded. All subjects were judged to be clinically
healthy on the basis of medical history, physical examination, and
routine laboratory tests. In particular, hypertension, diabetes mellitus, and evidence of cardiovascular, liver, or endocrine diseases were
not noted. None reported intake of hormones (such as oral contraceptives) or medications known to affect sex-steroid or lipid metabolism or insulin sensitivity. Ten M3 F transsexuals and 7 F3 M
transsexuals were smokers. Before the start of hormone therapy, all
F3 M transsexuals had regular menstrual cycles (28 to 31 days).
We measured the variables reflecting insulin resistance (glucose
and insulin levels and glucose utilization), plasma lipids (triglyceride
and HDL cholesterol levels), fat distribution (BMI, WHR, total body
fat, abdominal subcutaneous fat, and visceral fat area), and mean
arterial pressure at baseline and again after 12 months of cross-sex
hormone administration. For logistical reasons, some measurements
were not obtained in all subjects. Mean arterial pressure was
measured directly, not calculated, with an automatic device (BP8800, Colin) at baseline and after 12 months of cross-sex hormone
administration after the patient had rested for at least 15 minutes
(mean of 4 recordings repeated every 3 minutes). M3 F transsexuals
were treated with ethinyl estradiol 100 mg/d (Lynoral, Organon) in
combination with the antiandrogen cyproterone acetate 100 mg/d
(Androcur, Schering) to counteract the effects of testosterone. F3 M
transsexuals were treated with testosterone esters (Sustanon, Organon) 250 mg every 2 weeks intramuscularly. Informed consent
was obtained from all subjects, and the study was approved by the
Ethical Review Board of the Hospital Vrije Universiteit.
Blood Sampling and Analysis
In F3 M transsexuals, blood was drawn at baseline between days 3
and 9 of the menstrual cycle during the follicular phase, and during
hormone treatment, within 5 to 9 days after the most recent
testosterone injection. Blood samples were obtained between 9:30
and 10:30 AM after a 12-hour fast. Standardized radioimmunoassays
were used to measure serum levels of 17b-estradiol and testosterone.
Serum levels of luteinizing hormone (LH) and follicle-stimulating
hormone (FSH) were measured by immunometric luminescence
assays. Immunoradiometric assays were used to measure serum
November 1998
1717
levels of sex hormone– binding globulin (SHBG) and insulin (Biosource Diagnostics). Plasma levels of glucose, triglycerides, and
HDL cholesterol were measured by using standard laboratory methods. Blood was also collected into evacuated tubes (Diatube H
CTAD, Becton Dickinson). Samples were immediately placed on ice
and centrifuged at 3500g for 30 minutes at 4°C. Plasma was
separated and snap-frozen within 1 hour and stored at 270°C until
analysis. Plasma levels of tPA and PAI-1 antigen were measured by
using commercially available enzyme immunoassay kits (Thrombonostika tPA and Thrombonostika PAI-1, Organon Teknika), and uPA
antigen was evaluated by using an in-house enzyme immunoassay.35
Measurement of Fat Distribution
The lean body mass (LBM) and the total body fat were estimated at
baseline and after 12 months of cross-sex hormone treatment by
bioelectrical impedance analysis (BIA 101/S, RJL Systems).36 In
addition, body circumferences were measured in duplicate with a
flexible plastic tape at the level of the abdomen (midway between the
lower rib margin and the iliac crest) and the hip (over the greater
trochanters) to calculate the WHR. Areas of abdominal subcutaneous
and visceral fat depots were assessed by MRI technique in 15 M3 F
and 14 F3 M transsexuals. The procedure of image analysis has
been described in detail elsewhere.31 Repeated measurements were
obtained by using the same MRI and scanning parameters. An
inversion recovery pulse sequence was used, and appropriate scanning parameters were chosen to obtain good image contrast between
adipose and other tissues. Three transverse images were taken at the
abdominal level: 1 at the anatomic marker (lower edge of the
umbilicus) and 1 above and 1 below this position (slice thickness, 10
or 12 mm, depending on the imager used). The image-analyzing
computer program (developed by our Department of Biomedical
Engineering) is based on a “seed-growing” procedure. In short, after
a seed point is placed in the abdominal subcutaneous or the visceral
fat depot, it can be circumscribed by selection of a pixel intensity
range. The intensity range is selected for each image separately
according to the pixel intensity histogram. The areas of the circumscribed abdominal subcutaneous and visceral fat depots were calculated by converting the number of pixels to square centimeters, and
the mean of the 3 abdominal images was taken. To reduce variability,
all measurements were performed by a single experienced observer.
The intraobserver coefficients of variation were 2.3% for abdominal
subcutaneous fat and 9.8% for visceral fat.
Hyperinsulinemic Euglycemic Clamp
Insulin sensitivity was measured at baseline and after 12 months of
cross-sex hormone treatment by using a glucose clamp technique.37
Two intravenous catheters were placed in contralateral antecubital or
antebrachial veins of each arm, 1 for blood withdrawal and the other
for insulin and glucose infusion. The insulin solution for intravenous
infusion was prepared by adding 0.5 mL human insulin (100 IU/mL;
Velosulin, Novo Nordisk A/S) and 4.5 mL human albumin (20%)
(Central Blood Transfusion Laboratory, Amsterdam, Netherlands) to
45 mL of 0.9% NaCl to a final insulin concentration of 1 IU/mL. The
insulin infusion rate was calculated per kilogram of LBM. The
procedure consisted of a 2-hour period with the insulin infusion rate
at 62.5 mU/kg LBM per hour. The clamp procedure was started 30
minutes after cannulation (0 minutes). After the start of the insulin
infusion, arterial blood glucose levels were measured every 5
minutes with the use of a Yellow Springs Instruments glucose
analyzer (glucose oxidase method), and the 20% glucose infusion
rate was adjusted to maintain blood glucose concentration at the
fasting level (ie, mean blood glucose level from 230 to 0 minutes).
Blood samples for the determination of insulin levels were collected
every half hour. In the second hour, the glucose disposal rate was
calculated from the steady-state glucose infusion rate, the LBM, and
the mean insulin level, ie, M/I value5(1003mg glucose/kg LBM per
min per pmol insulin per L).
Statistical Analysis
Data are given as mean6SD. Variables with a skewed distribution
(abdominal subcutaneous fat area, total body fat, and plasma levels
1718
PAI-1, Visceral Fat, and Insulin Sensitivity
TABLE 1.
Baseline Characteristics in Men and Women
Variable
PAI-1 antigen, ng/mL
2
Men
(n518)
Women
(n515)
19.0613.6
28.8619.5
interrelationships between the logarithmically transformed plasma
PAI-1 level and elements of the insulin resistance syndrome.
Interaction terms were included to test whether the associations of
the plasma PAI-1 level and the visceral fat area differed between
men and women or before and after cross-sex hormone administration. When endocrine measurements were below the lower limit of
detection, the value of that lower limit was used for statistical
calculations (for LH 0.3 IU/L, for FSH 0.5 IU/L, for 17b-estradiol 90
pmol/L, and for testosterone 1.0 nmol/L). Two-sided P,0.05 was
considered statistically significant. The software used was SPSS for
Windows 7.0.
BMI, kg/m
20.962.7
21.563.0
WHR
0.8260.04
0.7960.05
LBM, kg
57.269.0
43.466.0
Total body fat, kg
9.562.6
19.864.9
Abdominal subcutaneous fat area, cm2
85640
163690
Visceral fat area, cm2
41616
38613
Glucose, mmol/L
5.060.7
5.060.6
Determinants of PAI-1 Levels at Baseline
Insulin, pmol/L
39615
47624
2.2860.72
2.4760.97
Triglycerides, mmol/L
0.860.6
0.860.5
HDL cholesterol, mmol/L
1.160.2
1.360.3
Mean arterial pressure, mm Hg
8869
8167
All subjects were eugonadal at baseline by clinical and
laboratory criteria. Baseline characteristics are presented in
Table 1. Plasma PAI-1 levels were statistically significantly
higher in women than in men (P50.049), a difference that
disappeared (P50.93) after controlling for total body fat
(higher in women) in an ANCOVA. Plasma tPA and uPA
levels were not statistically significantly different between
men and women (P50.63 and P50.50). Plasma PAI-1 levels
were positively and significantly correlated with plasma tPA
levels in men (r50.72, P50.001) and women (r50.63,
P50.01), negatively with serum SHBG levels in men
(r520.50, P50.05), and negatively with serum 17bestradiol levels in women (r520.55, P50.03).
The PAI-I level was correlated significantly with the
visceral fat area in men (r50.57, P50.03) and with the
visceral fat area and total body fat in women (r50.59,
P50.03 and r50.70, P50.006) but not with WHR or insulin
sensitivity (Figure 1). Also, no significant correlations were
found with levels of glucose, insulin, triglycerides, HDL
Insulin sensitivity
(1003mg glucose per kg LBM
per min per pmol insulin/L)
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Data are mean6SD.
of PAI-1, uPA, and triglycerides) were logarithmically transformed
before analysis to normalize their distributions. Student’s t test for
independent samples and an ANCOVA was used to compare
baseline differences between men and women. In the M3 F and
F3 M groups separately, the ANOVA test for repeated measurements or the t test for paired samples were used to explore the effects
of cross-sex hormones on plasma PAI-1 levels and other variables of
interest. Baseline values, values after 12 months of treatment, and
proportional changes between baseline and 12 months were correlated by using Spearman’s correlation coefficient. Both groups were
pooled in a multiple linear regression analysis to further explore
Results
Figure 1. Scatterplots of data for 16
men and 14 women at baseline with
plasma PAI-1 levels on a logarithmic
scale. The visceral fat area (using an MRI
technique) was significantly correlated
with plasma PAI-I levels in men (r50.57,
P50.03) and women (r50.59, P50.03).
The logarithmically transformed total
body fat was significantly correlated with
plasma PAI-I levels in women (r50.70,
P50.006). No correlations were found
between PAI-1 levels and WHR or insulin
sensitivity for men and women separately or when the data were pooled in
the analysis.
Giltay et al
November 1998
1719
TABLE 2. Standardized Regression Coefficients From Multiple
Linear Regression Analysis of Plasma PAI-1 Levels in Relation
to Visceral Fat Area and Possible Confounding Variables in
Pooled Data for Men and Women at Baseline
TABLE 3. Endocrine and Fibrinolytic Variables Before and
After 4 and 12 Months of Cross-Sex Hormone Administration in
Transsexual Subjects
Dependent
Variable
M3 F (n518)
Plasma PAI-1
level, ng/mL
Independent Variables
Biological sex, men/women
Standardized
Coefficient, b*
0.47
P
0.15
17b-Estradiol, pmol/L
Baseline
4 Months
12 Months
99615
*
*
P
Testosterone, nmol/L
2366
160
160
,0.001
LH, IU/L
3.362.2
0.360.1
0.360.0
,0.001
FSH, IU/L
2.862.4
0.560.1
0.660.1
,0.001
SHBG, IU/L
36612
237652
250641
,0.001
20.08
0.74
20.18
0.41
19.0613.6
6.462.8
7.361.2
,0.001
Plasma triglyceride level, mmol/L
0.01
0.95
tPA antigen, ng/mL
9.763.7
4.862.3
4.661.3
,0.001
Total body fat, kg
0.07
0.84
uPA antigen, ng/mL
1.0160.27
0.5560.16
0.6460.13
,0.001
Visceral fat area, cm2
0.59
0.03
Multiple R 2 (F53.4, P50.02)
0.52
Plasma insulin level, pmol/L
Insulin sensitivity
(1003glucose per kg LBM
per min per pmol insulin/L)
PAI-1 antigen, ng/mL
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zzz
*Standardized coefficients (b) are given to enable comparison of the relative
strengths of associations. These are partial regression coefficients when all
variables are expressed in standardized (z score) form. Unstandardized
coefficients (B) are not given because of their complex interpretation due to the
use of logarithmically transformed plasma PAI-1, plasma triglyceride, and total
body fat values.
cholesterol, BMI, abdominal subcutaneous fat area, and mean
arterial pressure (data not shown).
A multiple linear regression analysis was performed on
pooled data from all subjects, with the plasma PAI-1 level as
the dependent variable and biological sex, age, total body fat,
and the visceral fat area forced into the model. The visceral
fat area was the only variable that added significantly to the
model (b50.53, P50.02). Interaction analysis showed that
the relationship of plasma PAI-1 level and the visceral fat
area was not significantly different between men and women
(P50.84). To further analyze the relationship between
plasma PAI-1 level and the visceral fat area, the biological
sex, insulin level, insulin sensitivity, triglyceride levels, total
body fat, and the visceral fat area were forced into the model.
The visceral fat area maintained a positive, independent
association with plasma PAI-1 levels after controlling for
these possible confounding variables (Table 2). The use of the
M value instead of the M/I value did not lead to different
conclusions in any of the analyses (data not shown).
Effects of Cross-Sex Hormone Administration
After estrogen and antiandrogen administration to M3 F
transsexuals, serum levels of testosterone decreased to undetectable levels. The ethinyl estradiol administered could not
be detected by the assay used, but the biological effects of
estrogens were reflected in a large increase of serum levels of
SHBG. After testosterone administration to F3 M transsexuals, serum levels of testosterone increased markedly while
serum 17b-estradiol levels decreased. In 2 F3 M subjects the
serum 17b-estradiol levels decreased to below the lower limit
of detection. The serum level of SHBG decreased, reflecting
the biological effects of androgens. Serum levels of LH and
FSH were not significantly suppressed (Table 3).
Ethinyl estradiol plus cyproterone acetate administration to
men during a 12-month period was associated with decreases
in plasma levels of PAI-1 by 62% (Figure 2), tPA by 53%,
F3M (n515)
17b-Estradiol, pmol/L
160663
129634
129633
0.04
Testosterone, nmol/L
1.560.5
29610
34612
,0.001
LH, IU/L
3.761.5
2.562.9
2.362.1
0.17
FSH, IU/L
4.661.5
3.762.0
3.362.2
0.14
63631
28613
25610
,0.001
28.8619.5
24.8612.0
24.3613.3
0.49
tPA antigen, ng/mL
8.963.1
10.064.1
10.163.8
0.45
uPA antigen, ng/mL
0.9760.33
0.9860.29
1.2460.27
,0.001
SHBG, IU/L
PAI-1 antigen, ng/mL
Data are mean6SD.
*M3 F transsexuals were treated with ethinyl estradiol, which is not
detected by the 17b-estradiol assay used.
and uPA by 37% (Table 3). Testosterone treatment of women
during the same 12 months was not associated with changes
in PAI-1 (Figure 2) or tPA levels; however, uPA levels
increased by 28% (Table 3). This increase in uPA level was
only apparent after 12 months. There was a positive correlation between the proportional changes in plasma levels of
PAI-1 and tPA in the men (r50.77, P,0.001) and in the
women (r50.70, P50.004). After 12 months of treatment,
the plasma levels of PAI-1 and tPA were significantly
correlated in M3 F (r50.58, P50.01) and F3 M (r50.69,
P50.005) transsexuals, similar to the situation before hormone administration.
In men treated with ethinyl estradiol plus cyproterone
acetate, significant increases were found in the fasting insulin
levels (by 38%), the triglyceride levels (by 88%), the HDL
cholesterol level (by 18%), the BMI (by 5%), the WHR (by
1%), the total body fat (by 38%), the abdominal subcutaneous
fat area (by 54%), and the visceral fat area (by 17%). Insulin
sensitivity (M/I value) and mean arterial pressure did not
change significantly. In women treated with testosterone,
plasma levels of glucose, insulin, and triglycerides; insulin
sensitivity; and mean arterial pressure did not change significantly. The HDL cholesterol level decreased by 23%. The
BMI did not change significantly, but the LBM increased by
9%, the WHR increased by 3%, the total body fat decreased
by 24%, the abdominal subcutaneous fat area decreased by
18%, and the visceral fat area increased by 18%, all
significantly.
Proportional changes in plasma PAI-1 levels were not
correlated with any of the proportional changes of the
1720
PAI-1, Visceral Fat, and Insulin Sensitivity
area was weakened significantly in M3 F (P,0.001) and
nonsignificantly in F3 M (P50.16; Figure 3) transsexuals.
Discussion
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Figure 2. Plots showing the individual plasma PAI-1 levels on a
logarithmic scale in 18 M3 F transsexuals receiving estrogens
plus antiandrogens (F) and 15 F3 M transsexuals receiving
androgens (M) at baseline, after 4 months, and after 12 months
of cross-sex hormone administration. P values were assessed
by ANOVA for repeated measurements.
elements of the insulin resistance syndrome, including visceral fat area. For values obtained after 12 months of
cross-sex hormone treatment, plasma PAI-1 levels were not
correlated with any of these variables except for mean arterial
pressure, which was correlated positively with plasma PAI-1
levels in M3 F transsexuals (r50.70, P50.004). A multiple
linear regression analysis in data pooled from all subjects with
the plasma PAI-1 level as the dependent variable and the
biological sex and the visceral fat area forced into the model
showed that the visceral fat area had lost the association with the
plasma PAI-1 (b50.16, P50.13). When 12-month values were
compared with baseline values in a linear regression analysis, the
association between the plasma PAI-1 level and the visceral fat
An increased plasma PAI-1 level, an important cause of
impaired fibrinolysis, is a risk factor for CVD.1–3 We studied
the relation between plasma PAI-1 levels and the visceral fat
area. The strengths of our study are the inclusion of only
healthy, nonobese men and women under the age of 37 years
and the use of “gold standard” techniques to assess the
visceral fat mass and insulin sensitivity. In previous studies,
correlations have been found between plasma PAI-1 levels
and the visceral fat area measured by means of CT in
middle-aged men and women7 and in middle-aged men
including obese subjects.16 Our findings show this association
to exist even in healthy, young, nonobese subjects by the use
of an accurate MRI technique. This raises the possibility that
visceral fat accumulation is directly connected to CVD
through increased PAI-1 levels.1–3 Indeed, increasing mortality due to CVD is already apparent with increasing BMI in
nonobese and mildly overweight women (BMI ,29 kg/m2)38
and is also apparent in obesity, especially if the depot of fat
is visceral.38 – 42
The insulin resistance syndrome includes a cluster of
metabolic and hemodynamic disturbances, ie, insulin resistance, hyperinsulinemia, glucose intolerance, dyslipidemia
including hypertriglyceridemia, visceral fat accumulation,
hypertension, and hypofibrinolysis, which increase the risk of
CVD.17 Many studies in healthy subjects have suggested that
beside visceral fat accumulation, other elements of the insulin
resistance syndrome are associated with increased plasma
PAI-1 levels. PAI-1 levels were reported to be positively
correlated with increased insulin levels,9,10,12–14,16,43 decreased
insulin sensitivity,10,13,14,19,43 increased plasma triglyceride levels,11,12,14,15,43 and increased blood pressure.16,43 However, these
associations could well be indirect and, at least in part,
depend on the relationship between PAI-1 and visceral fat,
because visceral fat is associated with insulin resistance44 and
increased glucose, insulin, and triglyceride levels.40,41 This
concept is supported by our data showing that the association
between plasma PAI-1 levels and visceral fat area was
independent of insulin sensitivity and plasma levels of insulin
and triglycerides. Moreover, some previous studies may have
lacked sufficient sensitivity to show the influence of visceral
Figure 3. Scatterplots of data for 16 M3 F
transsexuals and 14 F3 M transsexuals with
plasma PAI-1 levels on a logarithmic scale. The
visceral fat area (using an MRI technique) was
significantly correlated with plasma PAI-I levels
in either group at baseline (r50.57, P50.03 and
r50.59, P50.03, respectively) but not after
cross-sex hormone administration for 12
months (r50.19, P50.51 and r50.27, P50.35,
respectively).
Giltay et al
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fat, because WHR or BMI was used in multivariate analysis
as an estimate of intra-abdominal fat.9,11–14,19 These measures
are reasonable but imprecise estimates of visceral fat, as
illustrated by our finding of no relation between PAI-1 and
WHR or BMI in the face of a strong relation between PAI-1
and MRI-estimated visceral fat mass.
In our young, nonobese subjects, PAI-1 levels were higher
in women than in men. However, this sex difference disappeared after adjustment for total body fat. Previous large
population-based studies in healthy men and premenopausal
women found similar PAI-1 activity levels45 and higher PAI-1
levels in men versus women.46 The assumption, based on
previous studies,23–25,47,48 that oral estrogen plus antiandrogen
administration would decrease PAI-1 levels and that testosterone administration would not change PAI-1, was indeed
confirmed by our data. Furthermore, uPA levels had increased after 12, but not after 4, months of testosterone
administration in women.
In both groups, the correlation between the visceral fat area
and plasma PAI-1 level at baseline had disappeared after 12
months of sex-steroid hormone administration. This was
especially clear in M3 F transsexuals, but in this group the
administered sex steroids had a substantially larger effect.
What might explain this dissociation? First, sex steroid–
induced shifts in metabolic variables that are included in the
insulin resistance syndrome could be involved in PAI-1
metabolism. This concept is not supported by our data,
because proportional changes in PAI-1 levels were not
correlated with proportional changes in insulin sensitivity or
plasma levels of insulin, glucose, triglycerides, and HDL
cholesterol. Second, changes in hepatic clearance might be
relevant. The parallel decrease in PAI-1, tPA, and uPA in
M3 F transsexuals is consistent with a clearance effect,
because PAI-1, tPA, and uPA share a major hepatic clearance
pathway.49,50 This idea is further supported by the observation
that oral, but not transdermal, administration of estrogens
reduces plasma PAI-1 levels.24,25 A clearance effect, however,
appears less likely to explain the changes in the testosteronetreated F3 M transsexuals. Third, sex steroids could have
altered adipocyte metabolism.51 PAI-1 synthesis can take
place in hepatocytes5 and adipocytes.6 – 8 Therefore, shifts
could have occurred directly in the secretion of PAI-1 by
adipocytes or indirectly in the secretion of substances influencing the hepatic secretion of PAI-1.8,52 In this respect, it is
noteworthy that the cytokines interleukin-6 and tumor necrosis factor-a and the acute-phase reactant C-reactive protein
were not associated with plasma PAI-1 levels either before or
after 12 months of hormone administration (data not shown).
We have, however, not studied portal concentrations of these
cytokines or free fatty acids, because the topography of the
portal vein makes these studies difficult.40
Our data indicate that in young, nonobese men and women,
the visceral fat area is an important determinant of plasma
PAI-1 level, independent of insulin sensitivity and plasma
levels of insulin and triglycerides. Visceral fat may be
directly linked to a low fibrinolytic activity and thereby to an
increased risk of CVD. After oral estrogen and antiandrogen
administration to men, plasma levels of PAI-1, tPA, and uPA
decreased substantially, and after testosterone administration
November 1998
1721
to women, only plasma uPA levels increased. After administration of cross-sex hormones, the association between
plasma PAI-1 and the ensuing increases in visceral fat area
was no longer demonstrable. This dissociation could not be
explained by changes in elements of the insulin resistance
syndrome, but whether it should be ascribed to changes in
hepatic clearance of PAI-1 or changes in adipocyte metabolism directly or indirectly involved in PAI-1 synthesis remains to be elucidated.
Acknowledgments
Dr Stehouwer is supported by a Clinical Research Fellowship from
the Diabetes Fonds Nederland and the Netherlands Organization for
Scientific Research (NWO). We are indebted to J.A.J. Megens and
Dr P.J.M. van Kesteren for assistance in the logistics of this study.
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Visceral Fat Accumulation Is an Important Determinant of PAI-1 Levels in Young,
Nonobese Men and Women: Modulation by Cross-Sex Hormone Administration
E. J. Giltay, J. M. H. Elbers, L. J. G. Gooren, J. J. Emeis, T. Kooistra, H. Asscheman and C. D.
A. Stehouwer
Arterioscler Thromb Vasc Biol. 1998;18:1716-1722
doi: 10.1161/01.ATV.18.11.1716
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