ARTICLE
Auteur(s) : Hanna
Suchanek1, Jolanta Myśliwska1, Janusz
Siebert2, Joanna Więckiewicz1, Łukasz
Hak1, Krzysztof Szyndler3, Dorota
Kartanowicz4
1Department of Immunology, Medical University of
Gdańsk, Ul. Dębinki 1, 80-210 Gdańsk, Poland
2Department of Family Medicine
3Department of Cardiac Surgery
4Department of Histology, Medical University of Gdańsk,
Poland
accepté le 19 Juillet 2005
Patients with coronary artery disease and type 2 diabetes are
different from those without diabetes. CAD among patients with
diabetes attracts more attention because of the high mortality
rates. Although in the United States, there has been a decline of
13% in CAD mortality in diabetic men and an increase of 23% for
diabetic women [1], this is in the contrast with trends observed in
the general CAD population. In all patients with CAD, and in
non-diabetic CAD individuals, mortality rates have decreased by
36%-62% in men and by 27%-45% in women respectively [1, 2]. This
decrease has been attributed to reductions in population risk
factors [2]. Diabetic patients tend to have similar CAD risk
factors, but at higher rates [3], an increased risk of recurrent
disease, an increased likelihood of angiographic restenosis [4], an
increased short-term (7 days) and post-CABG adverse outcome [5], in
addition to a poorer overall prognosis. A long-term response to
CABG in diabetics was found to be poorer as well [6].At present,
the prevailing hypothesis suggests that the inflammation reflecting
responses of innate and acquired immunity plays a crucial role in
the development and progression of atherosclerosis and type 2
diabetes [7-12]. Circulating markers of inflammation such as
C-reactive protein (CRP), interleukin-6 (IL-6), fibrinogen,
sVCAM-1, sICAM-1 have been shown to predict cardiovascular risk in
initially healthy people across different populations [7-9, 13].
The elevated levels of CRP and IL-6 predict the development of
type 2 diabetes in healthy women and men [10, 11, 13]. Their
application to clinical practice has recently been discussed [14],
but only hs-CRP was recommended as a useful predictor of coronary
events in the healthy population, however not for secondary
prevention clinical practice.Interleukin-18 (IL-18), as a
pro-inflammatory cytokine, is involved in the development and
progression of both atherosclerosis and type 2 diabetes. IL-18
induces atherogenesis by stimulating the IL-18 receptors on
endothelial and smooth muscle cells, releasing IL-6 and IL-8 from
these cells, as well as by up-regulating an expression of adhesion
molecules and matrix metalloproteinases [15]. Moreover, the
inhibition of IL-18 signalling has been shown to reduce lesion
progression and to change the plaque composition towards
stable forms [16]. IL-18-deficient, apolipoprotein E-knockout
mice exhibited substantially reduced atherosclerotic lesion size,
in spite of increased serum cholesterol [17]. Increased
inflammatory activity predisposes atherosclerotic plaques to
destabilization [18, 19]. IL-18 concentrations tend to be higher in
the patients with unstable angina [20] and acute coronary
syndrome [21]. Moreover, patients with documented coronary disease
and a high serum level of IL-18 had a 3.3–fold increase in
subsequent fatal cardiovascular events, compared to those with a
low level of IL-18 [22].The Prospective Epidemiological Study of
Myocardial Infarction (PRIME Study) has claimed a strong
association between inflammatory biomarkers and classical risk
factors (body mass index, smoking status, diabetes, hypertension,
lipid status) [7, 23]. Since the concentration of IL-18 was
independent of either classical or inflammatory factors, this
cytokine was identified as a predictor of coronary events in
healthy, middle-aged, European men [23]. In patients with
established CAD, IL-18 has been recognised as a strong predictor of
cardiovascular death in the AtheroGene Study [22]. IL-18 is also
implicated in promoting a low-grade, systemic inflammation in
patients with type 2 diabetes. Newly diagnosed, type 2 diabetic
patients without micro and macrovascular complications [24, 25],
and those with long-lasting diabetes [26, 27] presented higher
circulating concentrations of IL-18 compared with non-diabetic
subjects. In patients with diabetes and a high level of IL-18, the
early atherosclerosis changes were more pronounced [26].We have not
encountered a study analysing serum IL-18 level in patients with
established, multi-vessel coronary artery disease and long-lasting,
type 2 diabetes. Therefore, it was interesting to look at the
concentration of IL-18 in such patients and to find out whether
IL-18 may be a discriminating marker for secondary prevention in
CAD patients.
Patients and methods
One hundred and thirty consecutive patients admitted between
October 2002 and November 2003, to The Clinic of Cardiac
Surgery of Medical University in Gdańsk and scheduled for initial,
elective, coronary artery bypass surgery, were enrolled in the
study. Coronary angiography was performed in all patients. The
patients with two or three vessel disease qualified for surgery.
They had at least 75% stenosis in two [left anterior descending
coronary artery (LAD) + circumflex coronary artery (CX) or
LAD+ right coronary artery (RCA)] or three of the major (LAD +
CX + RCA) coronary arteries. The clinical data were entered into a
computerized database. Written informed consent was obtained from
all participants. The present study was approved by the Ethics
Committee of the Medical University of Gdańsk. The investigation
conforms to the principles outlined in the Declaration of Helsinki
[27]. All patients with CAD were divided in two groups: with
type 2 diabetes and without diabetes. Diagnosis of type 2
diabetes was based on the criteria of the American Diabetes
Association [28]. Diabetic patients were tested for diabetic
nephropathy. None of them had an albumin excretion rate above
30 mg/24h.
Hypertension was defined as systolic blood pressure ≥
140 mmHg or diastolic blood pressure ≥ 90 mmHg, or the
self-reported use of anti-hypertensive medication. Information
concerning the first diagnosis, smoking history and medication use
was obtained by interview. Subjects who reported smoking at least 1
cigarette per day during the year prior to the examination were
classified as current smokers. The angina pectoris was graded
according to the Canadian Cardiovascular Society Classification for
Angina Pectoris (CCS). Unstable angina was defined according
to the Braunwald criteria [29]. The New York Heart Association
(NYHA) functional classification of patients with heart disease was
applied for description of the patient’s state. The control group
consisted of 31 individuals as presented in table 1( Table 1 ). They were non-diabetic (fasting
plasma glucose < 110mg/dL and negative 75 g oral glucose
tolerance test), and without CAD (absence of chest pain at rest and
on exertion, no ECG changes at rest, negative exercise stress
test). They were recruited from the staff of the Medical University
of Gdańsk. They had not suffered from any acute or chronic disease
during the 3 months prior to examination.
Blood collection
Blood was drawn from the ante cubical vein the day before surgery,
between 7 and 8 o’clock, was frozen in aliquots (-70°C) and used no
later than 3 months thereafter.
Table 1 Characteristics of the control group and the
group with coronary artery disease
|
Characteristics
|
|
|
|
Men/women
|
16/15
|
96/36
|
|
Age (years)
|
61.2 ± 7.6
|
62.5 ± 9.0
|
|
BMI, kg/m2
|
28.7 ± 4.7
|
28.4 ± 4.3
|
|
Total cholesterol (mg/dL)
|
221.4 ± 46.3
|
217.0 ± 51.0
|
|
LDL cholesterol (mg/dL)
|
143.2 ± 40.1
|
133.3 ± 40.7
|
|
HDL cholesterol (mg/dL)
|
48.5 ± 15.7
|
43.4 ± 11.8
|
|
Triglycerides (mg/dL)
|
168.1 ± 105.3
|
172.0 ± 118,.0
|
|
FPG (mg/dL)
|
93.6 ± 12.6
|
116.1 ± 47.4
|
|
Smoking status (n (%))
|
|
|
|
current smoking
|
7 (25.6)
|
31 (23.8)
|
|
ex-smokers
|
16 (48.4)
|
60 (46.2)
|
|
never smoked
|
8 (25.8)
|
39 (30.0)
|
|
Duration of smoking (years)
|
26 (2.0-51.0)
|
27 (1.0-54.0)
|
|
Serum level of IL-18 (pg/mL)
|
- 248.99 ± 103.69
- 276.6 (102.5-540.3)
|
- 463.48 ± 111.7*
- 445.0 (262.0-688.0)
|
Laboratory examinations
Fasting plasma glucose (FPG) and lipid were measured by enzymatic
tests (Roche Diagnostics GmbH, Germany) and Comray-Chol, Comray-HDL
Direct and Comray-TG (P.Z. Comray, Poland). Urinary albumin
excretion had been measured in triplicate, timed and overnight, at
least twice a year, by immuno-turbidometric assay using
Tina-quant® (Boehringer Mannheim GmbH, Germany). Urinary
albumin excretion was expressed as the mean of all 24h collections
obtained during the 6 months prior to our examination.
Determination of IL-18
Serum IL-18 was measured by ELISA using commercial antibodies
purchased from R&D System (Minneapolis, Minn., USA). The
sensitivity limit of the assay was 12.5 pg/mL. The intra-assay and
inter-assay coefficients of variation were 6.25% and 9.92%,
respectively.
Statistical analysis
The results were analysed using the Statistica, version 6 program
(StatSoft, Pl). Continuous variables were tested for normality by
the Kolmogorov-Smirnov test. Normally distributed variables were
analyzed with the ANOVA test. The results of the ANOVA test were
presented as arithmetic means ± SD. For comparison of the
skew-distributed variables, the non-parametric Mann Whitney U test
was employed. The results of the Mann Whitney U test were presented
as median (min-max). Nominal variables were analyzed by the
χ2 Pearson test. Correlation was determined by linear
and multivariate regression analyses. The non-normally distributed
values were log-transformed before performing multivariate
regression. In all analyses, a two-tailed significance level <
0.05 was regarded as statistically significant.
Results
Baseline characteristics
Characteristics of the control group in relation to all 130
patients with CAD are presented in table 1. The control group
was matched with CAD patients with respect to: age, BMI, total
cholesterol, LDL-cholesterol, triglycerides, fasting plasma glucose
and smoking status.
Baseline characteristics of the CAD diabetics and CAD
non-diabetics are reported in table 2( Table 2 ). As expected, there was a higher
percentage of men than women only in the non-diabetic group (p =
0.03). Duration of DM was eight years (0.25-30.0). The diabetic and
non-diabetic patients were similar with respect to age, BMI,
duration of CAD, history of myocardial infarction and PTCA,
instability of angina, numbers of affected vessels, grade of heart
failure and ejection fraction. Clinical examinations showed that
the diabetic patients had more advanced symptoms of CAD according
to CSS classification (p = 0.023), and a higher prevalence of
hypertension (p = 0.012) with longer duration (p = 0.008). The
diabetic patients had a lower total cholesterol (p = 0.008) and LDL
cholesterol levels (p < 0.001) than the non-diabetics.
Medications taken by both groups were similar, except for calcium
antagonists (p = 0.048), which were more common in diabetic
patients. A similar proportion of patients in the diabetic and
non-diabetic groups were current smokers at the time, with the same
smoking habit duration. There were no differences in the number of
ex-smokers and patients who had never smoked in those groups.
Table 2 Demographic and clinical data of patients with
coronary heart disease with or without type 2 diabetes
|
Characteristics
|
|
|
p
|
|
Men/women (%)
|
26/17 (60.5/39.5)
|
68/19 (78.2/21.8)
|
0.03*
|
|
Age (years)
|
65 (48-77)
|
63 (45-82)
|
0.9
|
|
Duration of DM (years)
|
8 (0.25 –30.0)
|
-
|
|
|
Duration of CAD (years)
|
5 (0.125-30.0)
|
5 (0.25-30.0)
|
0.9
|
|
History of MI (n (%))
|
27 (62.8)
|
55 (63.2)
|
0.9
|
|
Previous PTCA (n (%))
|
4 (9.3)
|
4 (4.6)
|
0.3
|
|
CSS I-II/III-IV (n (%))
|
9/34 (20.9/79.1)
|
35/52 (40.2/59.8)
|
0.023*
|
|
Unstable angina (n (%))
|
7 (19)
|
19 (21,8)
|
0,5
|
|
Triple-vessel disease (n (%))
|
30 (69.8)
|
49 (57.0)
|
0.2
|
|
NYHA 1/2/3/4 (n (%))
|
19/5/12/7
|
50/8/17/12
|
|
|
(44.2/11.6/27.9/16.3)
|
(57.5/9.2/19.5/13.8)
|
0,5
|
|
EF (%)
|
51.1±11.1
|
52.4±11.0
|
0,5
|
|
Hypertension (n (%))
|
36 (83.7)
|
54 (62.1)
|
0.012*
|
|
Duration of hypertension (years)
|
15 (0.25-40)
|
5 (0.25-40)
|
0.008*
|
|
BMI (kg/m2)
|
29.0 ± 4.8
|
28.2 ± 4.2
|
0.3
|
|
Total cholesterol (mg/dL)
|
196.5 (116.0-357.0)
|
221.5 (129.0-355.0)
|
0.008*
|
|
LDL cholesterol (mg/dL)
|
106.0 (55.0-194.0)
|
140.5 (74.0-255.0)
|
0.001*
|
|
HDL cholesterol (mg/dL)
|
38.0 (28.0-70.0)
|
44.5 (12.0-94.0)
|
0.1
|
|
Triglycerides (mg/dL)
|
155.0 (64.0-982.0)
|
140.0 (57.0-660.0)
|
0.6
|
|
FPG (mg/dL)
|
141.0 (45.0-329.0)
|
95.0 (71.0-158.0)
|
0.001*
|
|
Medication
|
|
|
|
|
Nitrates (n (%))
|
37 (86.1)
|
75 (86.2)
|
0.98
|
|
ß-blockers (n (%))
|
35 (81.4)
|
70 (81.4)
|
1.00
|
|
Calcium antagonists (n (%))
|
14 (32.6)
|
15 (17.2)
|
0.048*
|
|
Statins (n (%))
|
31 (73.8)
|
66 (75.9)
|
0.6
|
|
ACE inhibitors (n (%))
|
31 (73.8)
|
52 (60.5)
|
0.1
|
|
Aspirin (n (%))
|
39 (90.7)
|
77 (88.5)
|
0.7
|
|
Diuretics (n (%))
|
11 (29.7)
|
21 (25.9)
|
0.7
|
|
Diabetes treatment
|
|
|
|
|
Oral hypoglycemic agents (n (%))
|
29 (67.4)
|
|
|
|
Insulin
|
14 (32.6)
|
|
|
|
Smoking status (n (%))
|
|
|
|
|
current smoking
|
10 (23.3)
|
21 (25.3)
|
0.8
|
|
ex-smokers
|
21(48.8)
|
39 (47.0)
|
0.8
|
|
never smoked
|
12 (27.9)
|
27(31.7)
|
0.7
|
|
Duration of smoking (years)
|
30.0 (1.0-54.00)
|
25.0 (2.0-50.0)
|
0.8
|
IL-18 in patient serum
As shown in table 1, IL-18 serum concentration was
significantly higher in CAD patients compared to healthy, control
individuals (p = 0.0001).
As can be seen from table 3( Table
3 ), IL-18 levels were found to be significantly higher
when diabetic CAD patients were compared to non-diabetic CAD
patients(p = 0.04), and when a subgroup of the triple-vessel
disease CAD diabetics was compared to the triple-vessel disease CAD
non-diabetics (p = 0.02). Diabetic men showed significantly higher
concentrations of IL-18 than non-diabetic men (p = 0.05).
Hypertension and unstable angina did not affect IL-18
concentrations in diabetic and non-diabetic patients. The diabetic
patients who had received nitrates, β-blockers, calcium
antagonists, statins, ACE-inhibitors, and aspirin had still higher
concentration of IL-18 compared to the non-diabetic individuals
receiving these drugs. The differences were significant for
nitrates (p = 0.05), statins (p = 0.03), ACE-inhibitors (p =
0.015), aspirin (p = 0.05). IL-18 levels were found to be
significantly higher in the group of diabetics who received ACE
inhibitors (p = 0.05) compared to diabetics who did not receive
them. Smoking status affected only the diabetic patients. Those who
had never smoked had the lowest levels of IL-18 compared with
ex-smokers (p = 0.05) and current smokers (p = 0.04). There were no
differences in the concentrations of IL-18 between ex-smokers and
current smokers.
IL-18 levels in CAD patients with and without DM, together with
healthy, controls are presented in ( figure 1 ). The IL-18
levels found in CAD patients were in a higher range as compared to
the controls. IL-18 concentrations were significantly higher in CAD
DM+ patients than in the CAD DM- ones (p =
0.04).
Table 3 Serum IL-18 concentrations in patients with
coronary artery disease with or without type 2 diabetes
|
Characteristics
|
|
|
p1
|
|
Patients
|
500.0 (274.0-684.0)
|
430.0 (262.0-688.0)
|
0.04*
|
|
Men
|
510.0 (310.0-684.0)
|
433.5 (262.0-688.0)
|
0.05*
|
|
Women
|
451.0 (274.0-652.0)
|
430.0 (293.0-680.0)
|
0.2
|
|
p2
|
0.2
|
0.3
|
|
|
Hypertension
|
|
|
|
|
yes
|
487.0 (274.0-684.0)
|
430.0 (274.0-688.0)
|
0.07
|
|
no
|
531.0 (274.0-684.0)
|
424.0 (262.0-680.0)
|
0.3
|
|
p2
|
0.6
|
0.7
|
|
|
Unstable angina
|
|
|
|
|
yes
|
524.0 (420.0-680.0)
|
472.0 (293.0-680.0)
|
0.3
|
|
no
|
482.0 (274.0-684.0)
|
424.0 (262.0-688.0)
|
0.07
|
|
p2
|
0.3
|
0.3
|
|
|
Triple-vessel disease
|
|
|
|
|
yes
|
513.0 (344.0-684.0)
|
432.0 (274.0-688.0)
|
0.02*
|
|
no
|
445.0 (274.0-652.0)
|
424.0 (262.0-680.0)
|
0.5
|
|
p2
|
0.2
|
0.6
|
|
|
Smoking status
|
|
|
|
|
1. never smoked
|
441.0 (274.0-556.0)
|
429.0 (284.0-680.0)
|
0.8
|
|
2. ex-smokers
|
551.0 (529.0-577.0)
|
495.0 (390.0-531.0)
|
0.2
|
|
3. current smoking
|
510.0 (333.0-684.0)
|
435.0 (262.0-688.0)
|
0.07
|
|
p2 1-2
|
0.05*
|
0.2
|
|
|
1-3
|
0.04*
|
0.4
|
|
|
2-3
|
0.7
|
0.9
|
|
|
Medication
|
|
|
|
|
Nitrates
|
|
|
|
|
yes
|
508.0 (274.0-684.0)
|
430.0 (262.0-688.0)
|
0.05*
|
|
no
|
452.0 (360.0-570.0)
|
440.0 (293.0-636.0)
|
0.7
|
|
p2
|
0.6
|
0.9
|
|
|
β-blockers
|
|
|
|
|
yes
|
502.7 ± 90.7
|
464.9 ± 116.8
|
0.07
|
|
no
|
437.6 ± 118.5
|
408.9 ± 95.4
|
0.5
|
|
p2
|
0.09
|
0.06
|
|
|
Calcium antagonists
|
|
|
|
|
yes
|
452.0 (274.0-684.0)
|
404.0 (293.0-633.0)
|
0.5
|
|
no
|
524.0 (310.0 –680.0)
|
433.0 (262.0-688.0)
|
0.03*
|
|
p2
|
0.2
|
0.6
|
|
|
Statins
|
|
|
|
|
yes
|
500.0 (310.0-684.0)
|
430.0 (262.0-688.0)
|
0.03*
|
|
no
|
482.0 (274.0-580.0)
|
429.0 (302.0-680.0)
|
0.8
|
|
p2
|
0.2
|
0.8
|
|
|
ACE inhibitors
|
|
|
|
|
yes
|
524.0 (310.0-684.0)
|
437.0 (274.0-668.0)
|
0.015*
|
|
no
|
451.0 (274.0-577.0)
|
426.5 (262.0-688.0)
|
0.9
|
|
p2
|
0.05*
|
0.8
|
|
|
Aspirin
|
|
|
|
|
yes
|
500.0 (310.0-684.0)
|
432.0 (262.0-688.0)
|
0.05*
|
|
no
|
484.0 (274.0-552.0)
|
395.5 (302.0-680.0)
|
0.7
|
|
p2
|
0.4
|
0.3
|
|
Relationship between IL-18 and clinical parameters
Linear regression analysis revealed, as presented in table 4(
Table 4 ), that the concentration of
IL-18 in the CAD DM+ group did not to correlate with: age,
BMI, fasting plasma glucose, HDL cholesterol, LDL cholesterol and
total cholesterol, triglycerides, EF, duration of CAD and DM,
hypertension, or smoking.
A low but significant inverse correlation was only found between
IL-18 and LDL cholesterol values in the non-diabetic, CAD group (r
= -0.28, p = 0.05).
To identify independent factors that might have affected serum
concentrations of IL-18, a multivariate regression analysis
controlling for selected variables (age, BMI, lipid status,
duration of CAD, angina status, EF, FPG, DM, duration of DM,
hypertension, duration of hypertension, number of affected vessels,
smoking, medications) was performed. In a model that explained only
16% of variation of serum IL-18 levels (table 5)( Table 5 ), triglycerides (β= 0.29, p = 0.01),
type 2 diabetes (β= 0.19, p = 0.03) and smoking
(β= 0.22, p = 0.01) were independent determinants of serum
IL-18 concentration in patients with coronary heart disease.
Table 4 Correlations between serum IL-18 concentrations
and clinical parameters in patients with coronary artery disease
with or without type 2 diabetes
|
Different factors
|
CAD DM+
|
CAD DM-
|
|
Age (years) ‡
|
0.12
|
-0.01
|
|
BMI (kg/m2) †
|
0.04
|
-0.08
|
|
FPG (mg/dL) †
|
-0.14
|
-0.09
|
|
Total cholesterol (mg/dL) †
|
-0.16
|
-0.13
|
|
LDL cholesterol (mg/dL) †
|
-0.25
|
-0.28*
|
|
HDL cholesterol (mg/dL) †
|
-0.01
|
-0.06
|
|
Triglycerides (mg/dL) †
|
0.01
|
0.21
|
|
EF (%) †
|
0.08
|
-0.11
|
|
Duration of CAD (years) ‡
|
0.14
|
-0.02
|
|
Duration of DM (years) ‡
|
-0.01
|
|
|
Duration of hypertension (years) ‡
|
0.18
|
-0.03
|
|
Duration of smoking (years) ‡
|
0.18
|
0.12
|
Table 5 Multivariate analysis of relationships between
serum IL-18 concentrations and selected variables in patients with
coronary artery disease
|
Variables
|
β
|
p
|
|
Age (years)
|
0.03
|
0.75
|
|
BMI (kg/m2)
|
-0.09
|
0.35
|
|
Total cholesterol (mg/dL)
|
-0.14
|
0.38
|
|
LDL cholesterol (mg/dL)
|
-0.23
|
0.11
|
|
HDL cholesterol (mg/dL)
|
0.03
|
0.76
|
|
Triglycerides (mg/dL)
|
0.29
|
0.01*
|
|
Duration of CAD (years)
|
0.01
|
0.45
|
|
Unstable angina (n)
|
0.17
|
0.06
|
|
Ejection fraction (%)
|
-0.01
|
0.94
|
|
FPG (mg/dL)
|
-0.01
|
0.96
|
|
DM (n)
|
0.19
|
0.03*
|
|
Duration of DM (years)
|
-0.03
|
0.78
|
|
Hypertension (n)
|
-0.05
|
0.60
|
|
Duration of hypertension (years)
|
0.10
|
0.32
|
|
Triple-vessel disease (n)
|
0.10
|
0.28
|
|
Smoking (n)
|
0.22
|
0.01*
|
|
Duration of smoking (years)
|
0.13
|
0.16
|
|
β-blockers (n)
|
0.01
|
0.97
|
|
Calcium antagonists (n)
|
-0.19
|
0.06
|
|
Statins (n)
|
0.01
|
0.96
|
|
ACE inhibitors (n)
|
0.13
|
0.17
|
|
Aspirin (n)
|
0.10
|
0.25
|
Discussion
In our study and for the first time, IL-18 serum concentrations
were measured in patients with advanced coronary heart disease with
at least two stenoses, with > 75% diagnosed in the major
coronary artery. In all studies conducted so far, a high level of
this cytokine has been observed in patients with early
atherosclerosis [26] and in patients with at least one stenosis,
> 30% [22] or > 75% [21]. We have chosen IL-18 as an
inflammatory marker because it seems to be independent of the
well-known classical risk factors and other inflammatory markers
such as CRP, IL-6 and fibrinogen [22]. We have demonstrated that
patients with at least two-vessel CAD had a significantly elevated
level of IL-18 compared with the control group. A slightly lower
level of IL-18 in a much smaller group of patients with acute
coronary syndrome was found in one previous study [21]. In our
study, we concentrated on the IL-18 serum levels among patients
with advanced CAD and long-lasting type 2 diabetes. The IL-18
concentration appeared to be significantly higher in the diabetic
CAD group compared to the non-diabetic CAD individuals.
The differences in the IL-18 concentrations in the diabetic and
non-diabetic patients were more pronounced when patients with
triple-vessel disease were compared. The mechanisms responsible for
this elevation of the IL-18 serum level in diabetic patients have
not been fully clarified. However, conditions such as poor
glycaemic control, diabetic nephropathy, obesity and inflammation
must be taken into consideration as possible reasons for the high
serum IL-18 concentrations. Recently, a pivotal role for acute
hyperglycaemia in the induction of adhesion molecules and
pro-inflammatory cytokines has been identified [30, 31]. An
elevated glucose level has been blamed for an enhanced expression
of vascular cell adhesion molecule (VCAM-1), expressed on human
endothelial cells [30]. Through the oxidative mechanism, glycaemia
regulates the serum concentrations of IL-6, TNF-α and IL-18 in
subjects with normal and impaired glucose tolerance [31]. In
non-diabetic patients with a first myocardial infarction,
hyperglycaemic stress may contribute to the increased levels of
IL-18, CRP and of T-cell activation markers [32]. Some authors have
observed that in patients with long-lasting type 2 diabetes, the
serum level of IL-18 correlates with glycaemic control [33].
Furthermore, others have found distinctly higher IL-18 serum levels
in patients with microalbuminuria or clinical albuminuria than in
those without microalbuminuria [33]. An enhanced IL-18 level found
in non-diabetic CAD individuals may be regarded as a result of
obesity and insulin resistance. It has recently been reported that
serum IL-18 concentrations tend to increase in healthy, obese women
and decrease after a weight loss [34, 35]. Interestingly, the
impact of obesity on the IL-18 concentration was studied only
within the female group. Moreover, there was no correlation between
the BMI and the IL-18 concentration in the apparently healthy male
group [23]. In our study, we did not see any correlation between
the IL-18 serum level, fasting plasma glucose (FPG) and BMI in the
diabetic patients. However, we could not exclude the role of acute
hyperglycaemia in inducing an IL-18 increase in our diabetic
patients, because post-prandial hyperglycaemia was thought to be a
better marker of plasma glucose level oscillations than FPG
[31].
In our studies, the gradation of IL-18 levels was noticeable;
the lowest levels were seen in the control group, intermediate
levels in the non-diabetic CAD patients, and higher levels in the
diabetic CAD ones. The highest levels were found in the diabetic
CAD patients with triple-vessel disease. This implies that the type
2 DM patients with CAD, especially with multi-vessel disease, are
characterized by the highest score of systemic inflammation. This
group is at great risk of further cardiovascular events, and
therefore secondary prevention should be taken particularly
seriously. The use of statins is highly recommended in this group.
The fact that type 2 DM patients are susceptible to statins has
been demonstrated in a randomised CARDS trial in the primary
prevention model [36]. In 2 838 diabetic patients without high LDL
cholesterol, the rates of first cardiovascular events were
significantly reduced after four years of treatment with a low dose
of atorvastatin. High doses of atorvastatin produced a marked
decrease of the high sensitivity to C-reactive protein seen in
diabetic patients, after 30 weeks of treatment [37]. Statins have
been shown to reduce the circulating, pro-inflammatory marker
levels (CRP, IL-6, sICAM-1, sVCAM-1) in hypercholesterolemic and
hypertriglyceridemic patients [38-40]. Results of large clinical
trials involving patients with coronary artery disease (the PRINCE
trial and the MIRACL study) have demonstrated that statins strongly
decrease the circulating level of CRP [41, 42]. Pleiotropic
vascular effects of statins are mediated by inhibition of
isoprenoid synthesis and increase in nitric oxide release or its
bioavailability [43]. So far, there are only limited data focused
on the effects of statins on IL-18 production [44-47]. Although the
benefit of statins as anti-inflammatory therapy is well documented,
it is noteworthy that other drugs such as angiotensin-converting
enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs),
β-blockers, tioglitazones are thought to possess an
anti-inflammatory activity as well [48-53].
In our study, we could not show any differences in IL-18 serum
concentrations between recipients and non-recipients of statins,
β-blockers or aspirin. Also, the multivariate regression analysis
did not show any effect of medical treatment on IL-18 serum levels.
This probably was due of the unequal distribution of the recipients
versus non-recipients (about 80% were recipients).
Interestingly, our results relating smoking to IL-18
concentrations lend support to the notion of the particularly
hazardous effects of smoking on diabetic patients. The IL-18
concentrations were still high in the diabetic patients who had
been smokers in the past. Smoking, as well diabetes, promote
endothelial dysfunction through an excessive generation of reactive
oxygen species (ROS), resulting in a decreased nitric oxide (NO)
production [54-56]. Endothelium-derived nitric oxide (NO) is not
only the major mediator of endothelium-dependent vasodilatation,
but it also has important anti-inflammatory, anti-thrombotic and
pro-fibrinolytic properties that are relevant at all stages of the
disease. However, the differences between the influence of smoking
and diabetes on endothelium exist [54, 55]. There are no
experimental data focused on both smoking and hyperglycaemia with
relation to endothelial injury. However, an association between
smoking and type 2 diabetes has recently been reported, which
points to a strong and consistent increase in the incidence of type
2 diabetes in heavy smokers in different populations [57, 58].
Smoking status did not affect the serum level of IL-18 in
apparently healthy men [23]. Further studies are needed to
establish the influence of smoking on diabetic patients.
A limitation of the present study is that the determination of
IL-18 was performed only once. It was impossible to measure the
IL-18 level twice because the patients were admitted to hospital
the day before surgery, and they came from a large area of north
Poland.
The current study provides support for an important role of
IL-18 in type 2 diabetes mellitus patients. Type 2
diabetes mellitus predisposes patients, especially those with
multi-vessel CAD and with a smoking habit, to high serum levels of
IL-18, which may help explain their vulnerability to fatal,
secondary cardiovascular events. These patients should be in the
first line for stringent secondary cardiovascular prevention.
Acknowledgements
This work was supported by The State Committee of Scientific
Research (project 3P05B17522).
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