Genetic Variation in Human Stromelysin Gene Promoter
and Common Carotid Geometry in Healthy Male Subjects
Agostino Gnasso, Corradino Motti, Concetta Irace, Claudio Carallo, Laura Liberatoscioli,
Sergio Bernardini, Renato Massoud, Pier Luigi Mattioli,† Giorgio Federici, Claudio Cortese
Downloaded from http://atvb.ahajournals.org/ by guest on June 14, 2017
Abstract—A common variant in the promoter of the human stromelysin gene, causing reduced enzyme expression, has
been associated with the progression of coronary atherosclerosis. On the other hand, increased stromelysin activity may
promote plaque rupture. The present study was undertaken to investigate the relationship between the genetic variation
in the human stromelysin gene promoter and common carotid geometry. Forty-two healthy male subjects without major
coronary heart disease risk factors were investigated. The polymorphism in the stromelysin gene promoter was studied
through polymerase chain reaction amplification with the use of mutagenic primers. Age, blood pressure, lipids, glucose,
viscosity, and body mass index were similar in homozygotes for the 5A allele (5A/5A), heterozygotes (5A/6A), and
homozygotes for the 6A allele (6A/6A). Serum matrix metalloproteinase-3 levels did not differ significantly among
genotypes. Common carotid diameters and intima-media thickness, measured by noninvasive ultrasonography, were
significantly larger in 6A/6A subjects (for respective 6A/6A, 5A/6A, and 5A/5A subjects, diameter at the R wave was
0.63⫾0.09, 0.55⫾0.06, and 0.53⫾0.04 cm [mean⫾SD], P⬍0.005 by ANOVA; intima-media thickness was 765⫾116,
670⫾116, and 630⫾92 ␮m [mean⫾SD], P⬍0.05 by ANOVA). Wall shear stress, calculated as blood velocity⫻blood
viscosity/internal diameter, was significantly lower in 6A/6A subjects (for respective 6A/6A, 5A/6A, and 5A/5A
subjects, mean wall shear stress was 10.4⫾2.9, 13.5⫾3.5, and 12.6⫾1.9 dyne/cm2 [mean⫾SD], P⬍0.05 by
ANOVA).The results demonstrate that the gene polymorphism in the promoter region of stromelysin is associated with
structural and functional characteristics of the common carotid artery in healthy male subjects without major risk factors
for atherosclerosis. Individuals with the 6A/6A genotype (associated with lower enzyme activity) show a triad of events,
namely, increased wall thickness, enlarged arterial lumen, and local reduction of wall shear stress, which might
predispose them to atherosclerotic plaque localization. (Arterioscler Thromb Vasc Biol. 2000;20:1600-1605.)
Key Words: carotid arteries 䡲 atherosclerosis 䡲 ultrasonics 䡲 metalloproteinases 䡲 polymerase chain reaction
S
tromelysin is a metalloproteinase (MMP-3) involved in
the turnover of the extracellular matrix components. This
enzyme exhibits a wide spectrum of activity: it is able to
degrade proteoglycans, collagens III, IV, V, and IX, laminin,
fibronectin, gelatin, and elastin. Furthermore, stromelysin
activates other members of the MMP family, such as the
collagenases. Thus, it can play a pivotal role in the physiological and pathological events associated with connective
tissue metabolism, including changes in arterial wall composition and/or function.1,2
Stromelysin production is regulated in response to several
stimuli.3–5 A common variant in the promoter region of the
human stromelysin gene with 1 allele having a run of 5
adenosines (5A) and the other having 6 adenosines (6A) has
been recently reported.6 In in vitro experiments, it has been
demonstrated that the 6A allele has a lower promoter activity,
which is probably attributable to preferential binding of a
putative transcriptional repressor protein.7 Therefore, subjects
carrying the 6A allele accumulate extracellular matrix because of decreased degradation.
MMP-3 has been found to be extensively expressed in
atherosclerotic plaques by foam cells of macrophage origin
and smooth muscle cells in the plaque cap, intima, and
adventitia. This finding has led to the hypothesis that MMP-3
might be involved in plaque rupture, followed by platelet
activation and initiation of the coagulation cascade.8 –12 However, data from studies involving MMP-3 5A/6A promoter
polymorphism indicate that a condition associated with reduced enzyme activity (6A allele) predisposes the subject to
the progression of atherosclerotic lesions in the coronary
district.6 Indeed, matrix accumulation is a major feature of
atheromatous lesions.
Received August 12, 1999; revision accepted November 26, 1999.
From the Department of Experimental and Clinical Medicine (A.G., C.I., C. Carallo, P.L.M.), Atherosclerosis Unit, University of Catanzaro “Magna
Græcia,” Catanzaro, Italy; the Institute of Biochemistry and Molecular Biology (C.M.), University of Teramo, Teramo, Italy; and the Clinical
Biochemistry Laboratory (G.F.), IRCCS Bambino Gesù, and the Department of Internal Medicine (L.L., S.B., R.M., C. Cortese), University of Tor
Vergata, Rome, Italy.
†Dr Mattioli died June 23, 1999.
Correspondence to Prof Claudio Cortese, Dipartimento di Medicina Interna, Università di Tor Vergata, Via di Tor Vergata 135, 00133 Roma, Italy.
E-mail [email protected]
© 2000 American Heart Association, Inc.
Arterioscler Thromb Vasc Biol. is available at http://www.atvbaha.org
1600
Gnasso et al
MMP-3 Gene Polymorphism and Carotid Geometry
1601
A rearrangement of the arterial wall, involving cellular and
matrix elements, is triggered by hemodynamic factors, such
as shear stress and tensile stress. Variations in these forces
cause the endothelium-mediated release of active substances,
such as NO and endothelin, which in the short term modulate
the vascular tone by restoring basal stress levels and in the
long term induce vascular remodeling.13–19
The present study was designed to investigate the relationships between the MMP-3 polymorphism, vessel geometry,
and shear stress in the common carotid artery of healthy male
subjects selected for the absence of major risk factors for
atherosclerosis.
Methods
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One hundred nine presumed healthy male subjects were selected
among hospital staff and their relatives for participation in the study.
Subsequently, 62 subjects were excluded from the study because of
the presence of major risk factors for atherosclerosis (36 subjects
with hyperlipidemia, defined as plasma cholesterol and/or triglycerides ⬎6.46 and 2.66 mmol/L, respectively; 4 subjects with diabetes,
defined as fasting blood glucose ⬎6.11 mmol/L; 18 subjects who
were current smokers; and 4 subjects with elevated blood pressure
level, defined as ⬎140/90 mm Hg). Of the remaining 47 subjects, 5
refused blood withdrawal. Finally, 42 healthy male subjects, who
were nonsmokers with an absence of hyperlipidemia, blood hypertension, or diabetes and not currently using any drug, gave informed
consent and were enrolled.
Systolic blood pressure (SBP) and diastolic blood pressure (DBP)
were measured on the right arm after the participant had been resting
for at least 5 minutes; a standardized Hawksley zero-random
sphygmomanometer was used. The average of the second and third
of 3 readings was computed. Height and weight were measured by
routine methods. Body mass index (BMI) was computed as weight
(in kilograms) divided by height squared (in meters). Blood lipids
and glucose were measured by commercially available kits. LDL
cholesterol was calculated by the Friedewald formula (LDL cholesterol⫽total cholesterol⫺HDL cholesterol⫺[triglycerides/5]).
Echo-Doppler examination for the measurement of arterial diameter, intima-media thickness (IMT), and blood flow velocity was
performed by using an ECG-triggered high-resolution ATL Ultramark 9 HDI Instrument (Advanced Technology Laboratories, Inc)
equipped with a 5- to 10-MHz multifrequency linear probe, as
previously described.20 All measurements were performed in the left
common carotid artery, 1 to 2 cm proximal to the bulb. The left
carotid artery was chosen because it was 2 to 2.5 cm longer than the
right carotid artery, thus allowing the blood flow to develop a nearly
parabolic profile of velocity. This is particularly relevant when
measuring blood flow velocity and calculating wall shear stress. The
common carotid artery was studied in longitudinal and transverse
planes with anterior, lateral, and posterior approaches. A sonographer measured blood flow velocities and recorded the examination
on a videotape. A reader, blinded with regard to the Doppler and
physical examination results, performed the measurement of diameters and IMT. Reader and sonographer were unchanged during
the course of the study. Internal diameter (ID) was defined as the
distance between the leading edge of the echo produced by the
intima-lumen interface of the near wall and the leading edge of
the echo produced by the lumen-intima interface of the far wall. ID
was measured at the R wave (IDR) and T wave (IDT) of the ECG.
IDR, obtained just before the systolic wave passage, is the narrowest
luminal diameter, whereas IDT, obtained during the systolic wave
passage, is the largest one. IMT was measured from images
displayed on a computer screen by the use of a Video Maker Card
(Vitec) and analyzed by software that allows quantitative evaluation
of the IMT. For each participant, 3 measurements pertaining to
anterior, lateral, and posterior projections of the far wall were
performed. The average of the 3 measurements was used to calculate
the IMT. Blood flow velocity was detected with the sample volume
reduced to the smallest possible size (1 mm) and placed in the center
of the vessel. The angle between the ultrasound beam and the
Detection of the stromelysin polymorphism after PCR amplification and restriction analysis with Tth111I in 3 subjects. Digested
products are separated by electrophoresis on 2% agarose gel
and visualized with use of ethidium bromide. M denotes DNA
molecular weight marker V (Boehringer-Mannheim). The 6A/6A
subject exhibits a unique undigested 130-bp band, whereas the
5A/5A subject exhibits one 97-bp digestion fragment. The 5A/6A
subject displays 130- and 97-bp bands.
longitudinal vessel axis was kept between 44° and 56°. Systolic peak
velocity (VSP) and mean velocity (VM) were recorded as the mean of
3 cardiac cycles.
Blood viscosity at a shear rate of 225/s (␩) was measured in vitro,
at 37°C, on the same day as the echo-Doppler examination with the
use of a cone/plate viscometer (Wells-Brookfield DV III).
Peak (␶P) and mean (␶M) wall shear stress were calculated
according to the following formulas:
␶P⫽4␩VSP/IDT
␶M⫽4␩VM/IDR
where ␶P and ␶M are expressed in dynes per centimeter squared; VSP
and VM, in centimeters per second; IDT and IDR, in centimeters, and
␩, in poise.
The common polymorphism in the stromelysin gene promoter
(5A/6A) was studied through polymerase chain reaction (PCR)
amplification with the use of mutagenic primers (Figure). A 130-bp
fragment was amplified from genomic DNA with use of the
following primers (in parentheses, the exact positions within the
promoter follow the numbering in Reference 21): forward primer
(⫺1201 to ⫺1172, mismatch at nucleotide ⫺1173), 5⬘GGTTCTCCATTCCTTTGATGGGGGGAAAgA-3⬘; reverse
primer (⫺1072 to ⫺1101), 5⬘-CTTCCTGGAATTCACATCACTGCCACCACT-3⬘. Thus, a recognition site for the enzyme Tth111I
(GACN/NNGTC) is created in the case of a 5A allele. The PCR
reaction mixture contained 1 ␮g DNA, 0.8 ␮mol/L of each primer,
1.5 mmol/L MgCl2, 0.2 mmol/L 4dNTP, and 1 U Taq DNA
polymerase. After denaturing the DNA for 5 minutes at 95°C, the
reaction mixture was subjected to 30 cycles of denaturing for 30
seconds at 94°C, 30-second annealing at 65°C, and 1-minute
extension at 72°C. The PCR product was digested with 5 U Tth111I
(Promega) for 3 hours at 65°C, and the digested products were
separated by electrophoresis on 2% agarose gel and visualized with
the use of ethidium bromide. The 5A genotype contains a unique
Tth111I restriction site that results in 97- and 32-bp products. The
method was validated by genotype confirmation through direct
sequencing according to described methods.21
The frequency of the genetic polymorphism was also assessed in
155 unrelated healthy subjects participating in a study reported
elsewhere.22
1602
Arterioscler Thromb Vasc Biol.
June 2000
TABLE 1. Clinical and Biochemical Characteristics of Participants, According to Stromelysin
5A/6A Polymorphism
5A/5A (n⫽8)
5A/6A (n⫽24)
6A/6A (n⫽10)
F
P
49.9⫾11.5
48.3⫾14.8
49.9⫾10.5
0.073
ⱕ0.929
SBP, mm Hg
117.6⫾10.0
116.7⫾13.9
124.1⫾13.3
1.149
ⱕ0.327
DBP, mm Hg
79.2⫾6.0
76.1⫾6.8
80.6⫾10.9
1.349
ⱕ0.271
BMI, kg/m2
27.1⫾3.8
25.6⫾2.5
27.3⫾3.1
1.562
ⱕ0.222
HR, bpm
60.0⫾4.9
64.7⫾9.4
66.4⫾4.2
1.618
ⱕ0.211
Chol, mmol/L
4.51⫾0.61
5.11⫾0.77
5.21⫾0.91
2.117
ⱕ0.134
HDL-C, mmol/L
1.10⫾0.26
1.19⫾0.31
1.32⫾0.36
1.101
ⱕ0.342
Trig, mmol/L
0.94⫾0.60
1.33⫾0.62
1.49⫾0.69
1.725
ⱕ0.191
LDL-C, mmol/L
2.98⫾0.58
3.31⫾0.76
3.20⫾0.66
0.691
ⱕ0.506
Gluc, mmol/L
5.49⫾1.24
5.18⫾0.70
4.85⫾0.65
1.391
ⱕ0.260
4.6⫾0.5
4.6⫾0.4
4.6⫾0.3
0.233
ⱕ0.793
Age, y
␩225, cP
Values are mean⫾SD. HR indicates heart rate; Chol, total cholesterol; HDL-C, HDL cholesterol; Trig, triglycerides;
LDL-C, LDL cholesterol; Gluc, glucose; and ␩225, blood viscosity.
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Total serum MMP-3 concentrations were measured by a Biotrak
ELISA assay (Amersham International), based on a 2-site “sandwich” format. All tests were performed in duplicate. The sensitivity
of the assay was reported as 2.35 ng/mL. According to the data
provided by the manufacturer, the assay specifically recognizes total
MMP-3 (active MMP-3, pro-MMP-3, and MMP-3 complexed with
tissue inhibitors ), and there is no cross-reaction with other MMPs.
In the determination of MMP-3 polymorphism, Hardy-Weinberg
equilibrium was assessed by ␹2 analysis. All considered variables
had normal distribution. ANOVA and Bonferroni-Dunn post hoc
tests were used to compare continuous variables among subjects with
different MMP-3 polymorphisms. Multiple regression analyses were
performed to adjust carotid geometry and hemodynamic parameters
for age, blood pressure, blood lipids, glucose, and heart rate.
Results
Of the 42 subjects participating in the study, 8 subjects
(19.1%) were homozygous for the 5A allele, 10 (23.8%) were
homozygous for the 6A allele, and 24 (57.1%) were heterozygous. The frequencies of the 5A and 6A alleles were 0.476
(95% CI 0.367 to 0.587) and 0.524 (95% CI 0.413 to 0.633),
respectively. Although obtained in a highly selected sample,
the frequencies were not significantly different from those
found in a control sample of 155 unrelated healthy Italian
individuals (5A 0.471, 6A 0.529). The genotype distribution
was not significantly different from the Hardy-Weinberg
prediction.
Clinical and biochemical characteristics of participants,
divided according to MMP-3 polymorphism, are shown in
Table 1. Age, DBP, BMI, and blood viscosity were similar in
the 3 groups. SBP, total cholesterol, triglycerides, and HDL
cholesterol were slightly higher in those homozygous for the
6A allele, but the difference did not reach statistical significance at the conventional 5% level. Blood glucose was
slightly, but again not significantly, lower in 6A homozygotes. Serum MMP-3 levels (mean⫾SD) were not significantly different among genotypes: 88.9⫾8.1 ng/mL in 5A/
5A, 93.3⫾15.3 ng/mL in 5A/6A, and 92.8⫾12.8 ng/mL in
6A/6A (F⫽0.317 and P⫽0.73 by ANOVA).
Common carotid artery diameter, at the R and T waves of
the ECG, and IMT were significantly larger in 6A/6A
subjects compared with heterozygotes or homozygotes for the
5A allele. No difference was observed between these last 2
groups. Mean blood flow velocity was slightly but significantly lower in 6A homozygotes. Increased arterial diameter
and reduced flow velocity yielded significantly lower values
of wall shear stress in 6A/6A subjects. Again, no difference
between 5A/6A and 5A/5A subjects was observed (Table 2).
Table 3 reports the same variables illustrated in Table 2
after adjustment for possible confounding variables by multiple regression analysis. Although slightly attenuated, the
differences between homozygotes for the 6A allele and
heterozygotes or homozygotes for the 5A allele persisted
even after adjustment.
Discussion
The results of the present study suggest that a genetic
polymorphism of an MMP, namely, stromelysin, which
TABLE 2. ANOVA of Left Common Carotid IDs, IMT, and Blood Velocity Among Participants
With Different Stromelysin 5A/6A Genotypes
5A/5A (n⫽8)
5A/6A (n⫽24)
6A/6A (n⫽10)
F
P
IDR, cm
0.53⫾0.04
0.55⫾0.06
0.63⫾0.09*†
6.671
ⱕ0.003
IDT, cm
0.57⫾0.03
0.60⫾0.06
0.67⫾0.10*†
8.108
ⱕ0.001
IMT, ␮m
630⫾92
670⫾116
765⫾116*
3.711
ⱕ0.03
VSP, cm/s
76.4⫾8.9
84.3⫾17.2
71.7⫾19.8
2.207
ⱕ0.12
VM, cm/s
36.2⫾4.3
39.7⫾6.0
34.2⫾5.8†
3.570
ⱕ0.03
2
␶P, dyne/cm
24.7⫾3.1
26.2⫾7.0
19.9⫾7.3*
3.157
ⱕ0.05
␶M, dyne/cm2
12.6⫾1.9
13.5⫾3.5
10.4⫾2.9*
3.375
ⱕ0.04
Values are mean⫾SD.
*P⬍0.167 vs 5A/5A; †P⬍0.0167 vs 5A/6A (Bonferroni-Dunn test).
Gnasso et al
MMP-3 Gene Polymorphism and Carotid Geometry
1603
TABLE 3. ANOVA of Left Common Carotid IDs, IMT, and Blood Velocity Among Participants
With Different Stromelysin 5A/6A Genotypes, After Adjustment for Possible Confounding
Variables by Multiple Regression Analyses
5A/5A (n⫽8)
5A/6A (n⫽24)
6A/6A (n⫽10)
F
P
IDR, cm
0.53⫾0.04
0.55⫾0.05
0.60⫾0.07*
3.972
ⱕ0.02
IDT, cm
0.58⫾0.04
0.60⫾0.05
0.66⫾0.08*†
5.210
ⱕ0.01
ⱕ0.04
IMT, ␮m
657⫾68
668⫾91
748⫾93*
3.374
VSP, cm/s
77.9⫾11.8
82.7⫾8.8
74.2⫾10.6
2.811
ⱕ0.07
VM, cm/s
36.8⫾3.8
38.9⫾4.3
35.4⫾2.5
3.075
ⱕ0.05
␶P, dyne/cm2
25.1⫾4.2
25.5⫾3.6
21.3⫾3.9*†
4.470
ⱕ0.02
␶M, dyne/cm
12.9⫾1.6
13.1⫾2.5
11.1⫾1.3†
3.165
ⱕ0.05
2
Values are mean⫾SD. All variables were adjusted for age, SBP, DBP, BMI, HR, blood glucose, and LDL-C.
*P⬍0.167 vs 5A/5A; †P⬍0.0167 vs 5A/6A (Bonferroni-Dunn test).
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modulates its enzymatic activity, is associated with structural
and functional characteristics of the common carotid artery in
healthy male subjects without major risk factors for atherosclerosis. Individuals homozygous for the 6A allele show a
triad of events, namely, increased wall thickness, enlarged
arterial lumen, and local reduction of wall shear stress, which
might predispose them to atherosclerotic plaque localization.
The relationship between MMP-3 polymorphism and the
observed triad of vascular events might be explained in
several ways. The reduced activity of stromelysin in 6A
subjects could lead to matrix accumulation and thickening of
the arterial wall. This would cause the lumen of the artery to
narrow, thereby subjecting the endothelium to an increase in
wall shear stress. The arterial enlargement to restore basal
hemodynamic forces would overcompensate, thus leading to
the observed arterial dilation and reduced wall shear stress.
Such a mechanism has been postulated by several authors to
explain the compensatory enlargement of carotid as well as
coronary arteries in response to atherosclerosis.23–25
An alternative hypothesis would consider the impairment
in elastic properties of the arterial wall, consequent to the
uncoordinated matrix accumulation, as a primary event. This
would cause reduced resistance to the dilating effect of blood
pressure, arterial dilation, and reduction of wall shear stress.
The thickening of the arterial wall could be an adaptive
process, subsequent to the changes in hemodynamic load.24
Enlarged common carotid diameter has been observed in
different physiological and pathological situations. Two
population-based studies have reported an increasing common carotid artery diameter with aging.26,27 Likewise, we
have observed increasing common carotid diameter with age
in normal subjects without major coronary heart disease risk
factors.20 Body weight and height are other situations in
which a correlation with arterial diameter has been described27; we also found in previous studies a correlation
between BMI and common carotid diameters. However, there
are also pathological conditions associated with enlarged
common carotid diameters. We have recently reported that
male subjects with non–insulin-dependent diabetes mellitus
have significantly larger common carotid diameters compared with age- and sex-matched controls.28 Furthermore, the
presence of atherosclerotic plaque, in the coronary and
carotid circulation, is often associated with larger arterial
diameter.29 Whether this enlargement is primary or secondary
to the presence of plaque is still a matter of debate.
As a whole, data in the literature indicate that increases
in the arterial lumen and wall thickness are constant
findings that accompany the process of aging as well as
clinical conditions associated with atherosclerosis.30 Our
present study demonstrates that middle-aged subjects homozygous for the 6A allele, although healthy and free of
the major risk factors for atherosclerosis, exhibit alterations in the common carotid artery resembling those
observed in aging and atherosclerosis.
Present knowledge about the influence of MMP-3 polymorphism on atherosclerosis provides evidence of a link
between the presence of the 6A allele and progression of
coronary lesions. In a report on 72 patients with coronary
heart disease defined by angiography participating in the St.
Thomas Atherosclerosis Regression Study (STARS), Ye et
al6 found that those homozygous for the 6A allele showed
more rapid progression of global and focal atherosclerotic
stenoses over the 3-year study period; this was particularly
evident in patients with mild baseline stenoses or with higher
LDL cholesterol concentration. Reports from the Regression
Growth Evaluation Statin Study (REGRESS), investigating
symptomatic patients over a 2-year period, and data from the
Lopid Coronary Angiography Trial (LOCAT) involving men
after coronary bypass with low HDL cholesterol show similar
results in the placebo groups, whereas no difference in vessel
diameter change was observed in the groups treated with
pravastatin (REGRESS) or gemfibrozil (LOCAT).31,32 The
findings of the present study, which was targeted to investigate the relationship between MMP-3 polymorphism and the
carotid artery in a prelesional stage, are in agreement with the
results of the above-mentioned studies. The design of the present
study makes difficult a direct comparison of our results with the
data published so far. To our knowledge, the present study is the
first to report on the effects of MMP-3 polymorphism in a
selected sample of healthy and relatively young male subjects
free of the symptoms and signs of atherosclerosis. The extracranial carotid district has been chosen because it can be easily and
reproducibly studied by noninvasive techniques.
We also measured the total serum MMP-3 levels to
identify any possible relationship with the genotype. No
significant association was evidenced, even though the limited sample size does not allow an adequate statistical power.
Tissue MMPs may leach into the blood stream in increased
amounts in several pathological conditions (eg, cancer and
inflammatory disease).33 However, an increased local produc-
1604
Arterioscler Thromb Vasc Biol.
June 2000
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tion of MMPs may not necessarily be associated with
increased circulating levels, because MMPs are capable of
binding to the connective matrix.34 Our data suggest that
changes in vessel wall MMP-3 expression as determined by
gene promoter polymorphism are not reflected in blood
MMP-3 levels.
The hypothesis of a genetically determined reduced expression of stromelysin as associated with the progression of
atherosclerosis is somehow in contrast to the present view
that an increased activity in matrix-degrading enzymes is a
potential source of plaque instability.35 Recently, Terashima
et al36 reported a significantly higher prevalence of the
5A/6A⫹5A/5A genotype among patients with acute myocardial infarction compared with control subjects. In this ethnic
group, however, the 5A allele frequency was much lower
than that observed in other European populations. Further
investigation is therefore required to clarify this point.
Furthermore, one has to consider that plaque progression
and plaque rupture are 2 distinct processes that recognize
different pathogenetic mechanisms and moments.37 One can
hypothesize that an imbalance in stromelysin expression in
the arterial wall in either direction can have deleterious
effects, depending on the stage of the atheromatous lesions. A
reduced enzyme activity leads to the accumulation of extracellular matrix and the progression of atherosclerosis.6 Accordingly, Tyagi et al38 have reported that weight for weight,
atherosclerotic vessels contain more collagen and less MMP
activity than do normal arteries. On the other hand, focal
overexpression of matrix-degrading activity in crucial plaque
sites can trigger the rupture of the fibrous cap and acute
thrombotic events.12
The relatively low number of enrolled subjects requires a
comment. Subjects with no major coronary heart disease risk
factors were selected. Although a larger number of presumed
healthy subjects were initially considered, only 42 individuals
fulfilled the enrollment criteria. The distribution of the
MMP-3 genotypes, however, allowed us to have a sufficient
number of subjects in each group. The power of the study,
calculated on the basis of the difference observed in IDs and
in the sample size investigated, was indeed at least 80%.
Thus, the findings reported in the present study may be
considered substantial, although studies with larger sample
sizes are certainly needed for a confirmation.
In conclusion, the present study identifies the MMP-3
promoter polymorphism as a major genetic determinant of
wall thickness and vessel dilation of the common carotid
artery in the absence of confounding risk factors for atherosclerosis. Future longitudinal studies are warranted to verify
the impact of this gene polymorphism on atherosclerosisrelated clinical end points.
Acknowledgments
This study was supported partly by a grant from MURST-CNR
Biotechnology Program L95/95 and partly by a grant from MURSTCofin ’98.
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Genetic Variation in Human Stromelysin Gene Promoter and Common Carotid Geometry
in Healthy Male Subjects
Agostino Gnasso, Corradino Motti, Concetta Irace, Claudio Carallo, Laura Liberatoscioli,
Sergio Bernardini, Renato Massoud, Pier Luigi Mattioli, Giorgio Federici and Claudio Cortese
Arterioscler Thromb Vasc Biol. 2000;20:1600-1605
doi: 10.1161/01.ATV.20.6.1600
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