Circulating ICAM-1 and VCAM-1 Levels in Patients with Obstructive Sleep Apnea SyndromeUrsavaş A.a · Karadağ M.a · Rodoplu E.a · Yılmaztepe A.b · Oral H.B.c · Gözü R.O.a
Departments of aPulmonary Medicine and Tuberculosis, bBiochemistry, and cMicrobiology and Infectious Diseases, Immunology Unit, Medical Faculty, Uludag University, Bursa, Turkey Corresponding Author
Background: Obstructive sleep apnea syndrome (OSAS)-induced hypoxic stress modulates circulating inflammatory mediators causing accelerated atherogenesis. Objectives: We hypothesized that OSAS-induced hypoxia might result in cardiovascular disease due to increased expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on the endothelial surface. Methods: Thirty-nine subjects with moderate-to-severe OSAS and 34 non-apneic controls matched for age, gender, body mass index (BMI), smoking history, and cardiovascular disease were included in this prospective study. Overnight polysomnography was performed. Circulating ICAM-1 and VCAM-1 levels in the serum were measured by enzyme-linked immunosorbent assay. Results: Circulating levels of both ICAM-1 (480.1 ± 216.7 vs. 303.4 ± 98.6 ng/ml, p < 0.0001) and VCAM-1 (1,156.6 ± 79.8 vs. 878.8 ± 71.1 ng/ml, p = 0.002) were significantly increased in the OSAS group compared to the control group. For an ICAM-1 cutoff level of 375 ng/ml, predictive sensitivity and specificity for OSAS were 69.2% (95% confidence interval, CI: 52.4–83.0%) and 82.4% (95% CI: 65.5–93.2%), respectively. For a VCAM-1 cutoff level of 859 ng/ml, predictive sensitivity and specificity for OSAS were 74.4% (95% CI: 57.9–86.9%) and 64.7% (95% CI: 46.5–80.2%), respectively. There was a significant positive correlation between circulating levels of ICAM-1 and ln of AHI (r = 0.276, p = 0.018). Multiple logistic regression analyses showed that OSAS was associated with high ICAM-1 and high VCAM-1 levels independent of age, gender, BMI, smoking status and cardiovascular disease. Conclusion: We conclude that OSAS can independently increase circulating levels of adhesion molecules.
Copyright © 2006 S. Karger AG, Basel
The obstructive sleep apnea syndrome (OSAS) is defined as intermittent, complete or partial, upper airway obstruction during sleep with subsequent excessive daytime sleepiness . These episodes of sleep apnea are often accompanied by nocturnal intermittent hypoxia and repetitive action of the sympathetic nervous system . The prevalence rates of OSAS in adults aged 20–100 years reported in a community-based study are 3.9% in males and 1.2% in females . Several studies have demonstrated that OSAS may be one of the most important risk factors of cardiovascular disorders, including hypertension and ischemic heart disease [4,5,6,7].
The exact mechanism of the development of cardiovascular disease in patients with OSAS remains to be elucidated. One of the potential mechanisms suggested to explain the association between OSAS and cardiovascular events postulates that OSAS-induced hypoxic stress modulates circulating inflammatory mediators causing accelerated atherogenesis. The role of inflammation in the atherosclerotic disease process has been well established over the past decade. Initiation, growth, and complications of atherosclerotic plaques might be considered as an inflammatory response to injury. Major injurious factors that promote atherogenesis, e.g. cigarette smoking, hypertension, dyslipidemia and hyperglycemia, are well known [8, 9]. OSAS is associated with repetitive hypoxia, sympathetic nervous system activation, hypertension, obesity, insulin resistance and dyslipidemia, all of which might also contribute to accelerated atherosclerosis . These injurious factors induce the release of primary proinflammatory cytokines (e.g. interleukin-1 and tumor necrosis factor-α). Primary proinflammatory cytokines stimulate the production of adhesion molecules, procoagulants and other mediators by endothelial and other cells. Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) are responsible for leukocyte adhesion to the endothelium .
ICAM-1 is both an 80- to 110-kDa glycoprotein consisting of five immunoglobulin-like domains and a ligand for lymphocyte function associated antigen-1α. ICAM-1 has been reported to play an important role in leukocyte migration to inflamed area . VCAM-1 belongs to the immunoglobulin superfamily of adhesion molecules and is a ligand for very late antigen-4, which is present on monocytes and lymphocytes but not on neutrophils . In animal and human models of atherosclerosis, the first sign of disease activity is an upregulation of adhesion molecules .
In the present study, we hypothesized that OSAS-induced intermittent hypoxia might elevate ICAM-1, and VCAM-1 levels on the endothelial surface, and this damage might result in cardiovascular disease. In order to test this hypothesis, we compared circulating ICAM-1 and VCAM-1 levels between OSAS patients and age-matched controls.
Patients and Methods
Thirty-nine patients with newly diagnosed moderate-to-severe OSAS, and 34 non-apneic controls matched for age, gender, body mass index (BMI) and smoking (pack-years) were recruited for this study. A questionnaire was administered to each patient. The questionnaire inquired about any history of snoring, witnessed apnea, and excessive daytime sleepiness, and included the Epworth Sleepiness Scale. Demographic information (age, gender, and smoking habits) and anthropometric measurements (height, weight, and BMI) were obtained at presentation to the sleep center. No subject had cancer, or pulmonary or neuromuscular disease.
The study protocol was approved by the Ethics Committee of the Uludag University. All patients gave written informed consent regarding participation in this study.
Overnight polysomnography was performed in all patients using the Compumedics Sleepwatch System (Compumedics p-series: Compumedics, Melbourne, Australia). All participants reported to the sleep laboratory at approximately 8.30 p.m., and polysomnography was initiated at approximately 10.30 p.m. Polysomnographic recordings included two electroencephalography channels (C3/A2 and O2/A1), two electrooculogram channels, one submental electromyogram channel, and one electrocardiography channel. Ventilatory monitoring included recording of oronasal airflow (with an oronasal thermistor), hemoglobin oxygen saturation by pulse oximetry (SaO2 was measured via a finger oximeter), respiratory movement of the chest (with an inductive plethysmography) and abdomen, and body posture.
Staging of sleep was performed according to the standard criteria of Rechtschaffen and Kales . Nasal airflow was carefully analyzed in order to assess ventilation during sleep. Apnea was defined as an episode of airflow cessation that lasts at least 10 s. Hypopnea was defined as an episode of reduced thermistor signal amplitude of at least 50% and an associated fall in oxygen saturation of at least 3% or an arousal lasting 10 s or longer, respectively. The sum of the time for apnea and hypopnea periods was divided by the total sleep time to obtain the apnea-hypopnea index (AHI). Patients with AHI ≥5 were considered to have OSAS. Subjects with AHI <5 were included in the control group.
Blood samples were drawn between 08.00 and 09.00 a.m. after the sleep study. Blood samples were centrifuged at 3,000 g at 4°C for 10 min. Centrifugation was performed during the hour following blood sampling. Serum samples were stored at –80°C until assayed. Serum levels of circulating ICAM-1 and VCAM-1 were measured by enzyme-linked immunosorbent assay (Biosource International, Camarillo, Calif., USA), according to the manufacturer’s instructions.
Statistical analysis was performed using the SPSS package for Windows, version 13.0. Comparisons of data between the OSAS and control groups were carried out using Student’s t, χ2 and Mann-Whitney U tests. We performed logistic regression analyses to identify any significant relations between parameters of sleep disorders and circulating adhesion molecules. A p value <0.05 was considered statistically significant.
Baseline characteristics of the OSAS and control groups are shown in table 1. There were no significant differences between age, gender, BMI, smoking habits, snoring, hypertension and coronary heart disease between the two groups. Excessive daytime sleepiness and the Epworth sleepiness score were significantly higher in the OSAS group compared to the control group (p < 0.001).
|Table 1. Baseline characteristic of the OSAS and control groups|
Polysomnographic characteristics of the OSAS and control groups are summarized in table 2. There were no significant differences in total sleeping time, sleep efficiency and baseline oxygen saturation between the two groups. Sleep stages of 3 and 4, arousal (per hour), AHI, duration of apnea-hypopnea periods, average oxygen saturation during sleep, average oxygen desaturation and length of time spent at an oxygen saturation <90% were significantly different between the OSAS group and the control group (p < 0.001).
|Table 2. Polysomnographic characteristics of the OSAS and control groups|
Results of measurements of circulating ICAM-1 and VCAM-1 levels are presented in table 3. Circulating ICAM-1 levels of the OSAS group were significantly higher than those of the control group (480.1 ± 216.7 vs. 303.4 ± 98.6 ng/ml, p < 0.0001); similarly, circulating VCAM-1 levels were also significantly higher in the OSAS group compared to the control group (1,156.6 ± 79.8 vs. 878.8 ± 71.1 ng/ml, p = 0.002).
|Table 3. Circulating ICAM-1 and VCAM-1 levels|
We used receiver-operating curve (ROC) analysis to determine the most meaningful ICAM-1 and VCAM-1 levels that can predict OSAS. In OSAS, the area under the ROC curve was 0.808 (p < 0.001) for ICAM-1 and 0.683 (p = 0.007) for VCAM-1. For the ICAM-1 cutoff of 375 ng/ml, predictive sensitivity and specificity for OSAS were 69.2% (95% confidence interval, CI: 52.4–83.0%) and 82.4% (95% CI: 65.5–93.2%), respectively; for the VCAM-1 cutoff of 859 ng/ml, predictive sensitivity and specificity for OSAS were 74.4% (95% CI: 57.9–86.9%) and 64.7% (95% CI: 46.5–80.2%), respectively. Results of the ROC analyses are summarized in figures 1 and 2.
|Fig. 1.a,b Critical circulating ICAM-1 (1) and VCAM-1 (2) levels for OSAS. b The line indicates the cutoff level of ICAM-1 (375.0 ng/ml; 1) and the cutoff of VCAM-1 (859.0 ng/ml; 2). Sensitivity: 69.2% for ICAM-1 and 74.4% for VCAM-1, and specificity: 82.4% for ICAM-1 and 64.7% for VCAM-1.|
|Fig. 2.a,b Critical circulating ICAM-1 (1) and VCAM-1 (2) levels for OSAS. b The line indicates the cutoff level of ICAM-1 (375.0 ng/ml; 1) and the cutoff of VCAM-1 (859.0 ng/ml; 2). Sensitivity: 69.2% for ICAM-1 and 74.4% for VCAM-1, and specificity: 82.4% for ICAM-1 and 64.7% for VCAM-1.|
There was a significant positive correlation between circulating levels of ICAM-1 and ln of AHI (r = 0.276, p = 0.018) and between circulating levels of VCAM-1 and the ln of AHI (r = 0.423, p < 0.001). Results of the correlation analyses are summarized in figure 3.
|Fig. 3. Scatter plot of circulating ICAM-I (a) and VCAM-1 (b) levels and the ln of AHI. a r = 0.276, p = 0.018. b r = 0.423, p = 0.001.|
Results of multiple logistic regression analyses including age, gender, BMI, smoking status, cardiovascular disease (coronary heart disease and hypertension), and OSAS are summarized in tables 4 and 5. Multiple logistic regression analyses showed that OSAS was a risk factor for high ICAM-1 (>375 ng/ml) and high VCAM-1 (>859 ng/ml) levels independent of age, gender, BMI, smoking status and cardiovascular disease.
|Table 4. Result of multivariate analysis for high circulating ICAM-1 level|
|Table 5. Results of multivariate analysis for high circulating VCAM-1 level|
OSAS is associated with several cardiovascular diseases. Several studies have demonstrated a strong association between sleep-related breathing disorders and cardiovascular disease independent of shared risk factors (e.g. obesity, age, and male sex) [4,5,6,7]. More than half of the patients with OSAS have systemic hypertension, and approximately 25% of the patients with hypertension have OSAS [16, 17]. A greater risk of coronary artery disease in OSAS is suggested by several retrospective and cross-sectional studies. The prevalence of OSAS was 37% among men and 30% among women with angiographically verified coronary artery disease [18, 19]. Mechanisms proposed to explain this relationship have included sympathetic nervous system activation and systemic endothelial dysfunction [20, 21].
In recent years, the inflammatory process has been indicated as an important risk factor for the development of coronary heart disease [8,9,10]. Adhesion molecules mediate attachment of circulating leukocytes to the endothelium, in addition to their subsequent transmigration and accumulation in the arterial intima. Particularly ICAM-1 has been reported to play an important role in the transmigration of leukocytes across the vascular endothelial wall [11,12,13,14]. Expression of adhesion molecules is an indicator of endothelial inflammation and is likely to be involved in the causal pathway leading to atherosclerosis. A number of clinical studies examined the causal importance of adhesion molecules in the development of coronary heart disease [22,23,24,25]. ICAM-1 levels were significantly associated with death from cardiovascular disease . They have also been reported to be associated with risk factors of cardiovascular disease and subclinical cardiovascular disease findings [27, 28]. Jenny et al.  examined the association of circulating ICAM-1 with subclinical cardiovascular disease findings and the risk of incident cardiovascular disease in older men and women in their Cardiovascular Health Study. They reported that circulating ICAM-1 was associated with risk factors for cardiovascular disease and fatal events in older men and women. ICAM-1 and death were more significantly associated in women.
The exact mechanism of the development of cardiovascular disease in patients with OSAS remains to be elucidated. Some studies have suggested that OSAS-induced repetitive hypoxia may be involved in the pathogenesis of cardiovascular disorders by stimulating inflammatory responses via elevated levels of cytokines and adhesion molecules [30,31,32,33]. In vitro studies have demonstrated that hypoxia causes an increase in the level of adhesion molecules in cell cultures [12, 34]. However, other studies have found no significant changes . Arnould et al.  examined the effects of hypoxia on human umbilical vein endothelial cells in culture. They noted a very strong activation of polymorphonuclear neutrophils (PMN) and increased adherence of PMN to endothelial cells. This adherence was mediated by platelet activating factor, ICAM-1 on umbilical vein endothelial cells, and CD18/CD11b on PMN. They suggested that hypoxia itself could activate endothelial cells, and this activation could account for the increased PMN adherence observed in ischemic tissue. Lattimore et al.  investigated the effect of repetitive hypoxia on lipid loading in foam cells and monocyte adhesion to endothelial cells. They reported that repetitive hypoxia increased cholesteryl ester uptake by macrophages. By contrast, adhesion of monocytes and expression of adhesion molecules were unchanged with exposure to repetitive hypoxia compared to controls. In our study, we found that average oxygen desaturation and the length of time with an oxygen saturation <90% were significantly greater in the OSAS group compared to the control group.
Few previous studies have suggested that OSAS is associated with a rise in circulating levels of adhesion molecules. Ohga et al.  measured circulating ICAM-1, VCAM-1 and L-selectin levels before and after sleep in 7 OSAS patients and 6 age-matched controls. They found that the levels of circulating adhesion molecules were increased in OSAS patients before sleep compared with normal subjects. After sleep, however, significantly greater levels of ICAM-1 and L-selectin but not VCAM-1 were observed in the OSAS group. However, the study group was too small, and the study did not establish a correlation between the degree of hypoxia and levels of adhesion molecules; instead, they suggested that OSAS-induced hypoxia activated adhesion molecules, resulting in the development of cardiovascular disorders. El-Solh et al.  investigated 61 subjects with angiographically proven coronary artery disease. They compared age, gender, BMI, and severity of coronary artery disease of 15 moderate-to-severe OSAS patients with a matched control group. ICAM-1, VCAM-1 and E-selectin levels were significantly higher in the OSAS group. Results of our study also indicate that circulating ICAM-1 and VCAM-1 levels are elevated in patients with moderate-to-severe OSAS compared to normal subjects.
Repetitive apnea and hypopnea episodes in OSAS result in hypoxia with arousals and increased sympathetic nerve activity. Ohga et al.  measured circulating ICAM-1 and IL-8 levels before and after nasal continuous positive airway pressure in OSAS patients. They reported that a significant correlation existed between ICAM-1, IL-8, and oxygen desaturation and additional nasal continuous positive airway pressure therapy, which decreased apnea, desaturation, and levels of circulating ICAM-1 and IL-8.
Previously, an association has been reported between adhesion molecules and factors such as age, gender, smoking status, BMI, habitual exercise and blood pressure [23, 39, 40]. Demerath et al.  reported that male and female smokers had higher ICAM-1 and E-selectin levels than nonsmokers, and adhesion molecules were correlated with the pack-years of cigarette smoking. They demonstrated that obesity was related with increased concentrations of ICAM-1 and E-selectin. In the present study, there were no significant differences between the two groups regarding age, gender, BMI, smoking habits, snoring, hypertension and coronary heart disease. In addition, OSAS is an independent risk factor for high circulating ICAM-1 and VCAM-1 levels according to the multiple logistic regression analyses.
Potential limitations of this study merit consideration. First, we measured circulating ICAM-1 and VCAM-1 levels to assess the expression of cell-associated adhesion molecules, although this approach has been widely used in several previous studies. Second, subjects of the two groups were evaluated for coexisting cardiac disease by medical history, physical examination, measurement of blood pressure, and electrocardiography. However, no other information was provided regarding their cardiac function; therefore certain asymptomatic coronary artery diseases may be present in either group.
Consequently, OSAS increases the circulating levels of adhesion molecules independent of age, gender, BMI, smoking status and cardiovascular disease. Long-term monitoring of OSAS subjects with high levels of adhesion molecules but no known cardiovascular disease may provide important information regarding the predictive value of adhesion molecules and features of nasal continuous positive airway pressure therapy to prevent cardiovascular risks. Further studies are warranted to elucidate the exact role of adhesion molecules in cardiovascular disease.
Ahmet Ursavaş, MD
Uludağ Üniversitesi Tıp Fakültesi
Göğüs Hastalıkları ve Tüberküloz AD
TR–16059 Görükle, Bursa (Turkey)
Tel. +90 224 442 8400 1103, Fax +90 224 442 8149, E-Mail email@example.com
Received: May 10, 2006
Accepted after revision: August 30, 2006
Published online: December 4, 2006
Number of Print Pages : 8
Number of Figures : 3, Number of Tables : 5, Number of References : 41
Respiration (International Journal of Thoracic Medicine)
Vol. 74, No. 5, Year 2007 (Cover Date: August 2007)
Journal Editor: Bolliger, C.T. (Cape Town)
ISSN: 0025–7931 (print), 1423–0356 (Online)
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