Advs Exp. Medicine, Biology - Neuroscience and Respiration (2015) 8: 55–60 DOI 10.1007/5584_2014_44 # Springer International Publishing Switzerland 2014 Published online: 15 October 2014
Soluble Ligand CD40 and Uric Acid as Markers of Atheromatosis in Patients with Obstructive Sleep Apnea M. Kosacka, A. Brzecka, P. Piesiak, A. Korzeniewska, and R. Jankowska Abstract
The aim of the study was to evaluate the risk of atheromatosis in patients with obstructive sleep apnea (OSA), as based on the concentration of the pro-atherogenic soluble CD40L ligand (sCD40L) in relation to the level of uric acid. The serum levels of sCD40L and uric acid were measured in 79 OSA patients (mean apnea/hypopnea index – AHI 34.4 20.9) and in 40 healthy controls. We found that sCD40L was higher in the OSA patients with hyperuricemia than that in the patients with uric acid in the normal range (sCD40L: 9.0 ng/ml vs. 8.0 ng/ml, respectively, p < 0.05). There was a positive association of sCD40L with AHI (p ¼ 0.01) and a negative one with the mean minimal nocturnal SaO2 (p < 0.05). Uric acid correlated negatively with the mean and minimal SaO2 and positively with the oxygen desaturation index (p < 0.05). OSA patients with hyperuricemia also had a higher prevalence of hypertension and ischemic heart disease. We conclude that OSA patients with increased uric acid concentration have increased risk of atheromatosis, as indicated by a higher level of soluble pro-atherogenic ligand CD40, and a higher prevalence of cardiovascular adverse events. Keywords
Atherosclerosis • sCD40L • Sleep apnea syndrome • CRP • Uric acid
1
Introduction
In the obstructive sleep apnea (OSA) syndrome there is a high incidence of cardiovascular M. Kosacka (*), A. Brzecka, P. Piesiak, A. Korzeniewska, and R. Jankowska Department of Pulmonology and Lung Cancer, Wroclaw Medical University, 105 Grabiszynska St., Wroclaw 53-439, Poland e-mail: [email protected]
diseases (McNicholas and Bonsigore 2007). Different mechanisms have been postulated to explain this relationship, including increased sympathetic activity, oxidative stress, inflammation, abnormal coagulation, and endothelial and metabolic dysfunction (Lavie and Lavie 2009; McNicholas and Bonsigore 2007). CD40 and its ligand (CD40L) are transmembrane proteins and the members of the tumor necrosis factor (TNF) superfamily (Mavroudi and Papadaki 2011). 55
56
Expression of these molecules has been described in a variety of cell types, including Tand B-lymphocytes, monocytes, macrophages, endothelial cells, epithelial cells, smooth-muscle cells, platelets, fibroblasts, and adipocytes (Seijkens et al. 2013; Mavroudi and Papadaki 2011). The main source of soluble CD40L (sCD40L) in the circulation consists of activated platelets and T-cells. The exact biological function of CD40 remains unclear; however CD40–CD40L interactions are described in numerous immune and non-immune processes (Seijkens et al. 2013; Rizvi et al. 2008). Many studies indicate that CD40–CD40L interactions participate in the development and progression of atherosclerosis (Rizvi et al. 2008; Lutgens et al. 2007; Chakrabarti et al. 2005). CD40 and its ligand play a role in oxidative stress and inflammation (Rizvi et al. 2008). Soluble CD40 (sCD40) stimulates platelet activation, aggregation, and platelet-leukocyte conjugation (Chakrabarti et al. 2005). Moreover, binding of CD40L to CD40 stimulates the release and expression of many pro-inflammatory mediators as cytokines IL-1, IL-6, IL-8 IL-12, TNF-alpha, and matrix metalloproteinases (Kobayashi et al. 2006; Lutgens and Daemen 2002). This may lead to destabilization of the atherosclerotic plaques (Rizvi et al. 2008). Hyperuricemia is associated with the metabolic syndrome and many cardiovascular diseases (Kanbay et al. 2013; Schachter 2005). It has been shown that elevated uric acid increases the risk of cardiovascular events and mortality in patients with hypertension, heart failure, and diabetes (Alderman and Aiver 2004). However, the exact pathways by which uric acid participate in progression of atherosclerosis are not obvious. It is postulated that hyperuricemia plays a role in endothelial dysfunction and oxidative stress, enhances vasoconstriction and inflammatory process, and in addition has an influence on platelet function, especially its adhesiveness and aggregation (Kanbay et al. 2013; Alderman and Aiver 2004). Repetitive hypoxia during episodes of apnea or hypopnea, which is a main feature of OSA, has an influence on the concentration of uric acid and on the inflammatory effects exerted by CD40L.
M. Kosacka et al.
Hypoxia stimulates the degradation of adenosine triphosphatase into xanthine, which, in turn, increases the level of uric acid (Mentzer et al. 1975). Hypoxia could also enhance the inflammatory effects of CD40L in the endothelial and monocytic cells through increased reactive oxygen species (ROS) and intercellular adhesion molecule (ICAM-1) production (Chakrabarti et al. 2009). The aim of the present study was to evaluate the risk of atheromatosis based on the concentrations of the pro-atherogenic sCD40L in relation with the serum uric acid in patients with OSA syndrome.
2
Methods
The study was approved by the Bioethics Committee of the Medical University of Wroclaw, Poland. A total of 79 patients with OSA syndrome (F/M – 21/58; mean age 54 9 years) and 40 healthy age-matched controls were included into the study. The majority of patients were overweight or obese (BMI 25–30 and >30, respectively); the mean BMI amounted to BMI 34.1 7.9 kg/m2. There were 13 patients with mild (apnea/hypopnea index – AHI 5–15), 26 with moderate (AHI 15–30) and 40 with severe OSA (AHI >30). The control group consisted of healthy persons (mean BMI 30.1 5.5), without any sleep breathing disorders (mean AHI 2.2 1.9). All subjects underwent nocturnal respiratory polygraphy using a Grass Aura PSG Lite (Warwick, USA). The following parameters were evaluated during 8 h of nocturnal sleep: AHI, desaturation index – DI, the mean and minimal SaO2 at the end of sleep apnea/hypopnea episodes. Apnea was defined as a cessation of airflow for more than 10 s and hypopnea as a reduction in airflow of 50 % from its baseline value during wakefulness for at least 10 s followed by a 4 % or more decrease in oxyhemoglobin saturation. An oxygen desaturation event was defined as a drop in SaO2 by 4 %. AHI and DI were expressed as the number of events per hour of sleep. Blood samples were collected from fasting subjects in the morning. After centrifugation for
Soluble Ligand CD40 and Uric Acid as Markers of Atheromatosis in Patients. . .
10 min at 1,467 relative centrifugal force (RCF), the serum was removed and stored at 80 C. The serum levels of sCD40L were measured using the enzyme-linked immunosorbent assay (ELISA) method (Human CD40 Ligand/TNFSF5 Quantikine; R & D Systems, Minneapolis, USA). The tests were performed according to the manufacturer’s specifications. The ELISA microplate reader from MRXe Dynex Technologies (Chantilly, USA) was used. Additionally, in the sample of blood serum the following biochemical parameters were measured: uric acid, CRP, total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides. The group of OSA patients was divided into two subgroups with elevated and normal uric acid concentration. The cut-off value for uric acid, separating normal from elevated, was 7 mg/dl for males and 6 mg/dl for females. There were 53 hyperuricemic and 26 normouricemic patients. Values were given as means SD. Spearman’s r correlation coefficient was used to assess the relationship between two variables and the Mann-Whitney U test to compare values between two groups. Differences between samples were considered significant at p < 0.05. Statistical analysis was performed using the CSS Statistica software ver. 5.0 for Windows.
3
Results
Concentrations of both sCD40L and uric acid were higher in the OSA patients than those in the control subjects (mean group sCD40L: 8.30 3.70 vs. 7.10 3.54 ng/ml, respectively; p < 0.05, and mean group uric acid: 6.30 1.49 vs. 5.70 1.20 mg/dl, respectively; p < 0.05). There was a positive correlation between sCD40L and AHI (r ¼ 0.24; p ¼ 0.01) and a negative correlation between sCD40L and the mean minimal SaO2 at the end of sleep apnea/ hypopnea episodes (r ¼ 0.18; p < 0.05). sCD40L correlated positively also with uric acid (r ¼ 0.32; p < 0.001) and C-reactive protein – CRP (r ¼ 0.21; p < 0.005). There were no correlations between sCD40L and age, BMI, DI,
57
Table 1 Correlations between the serum level of sCD40L and selected parameters
Age BMI AHI DI Mean SaO2 Mean of min. SaO2 CRP Uric acid Total cholesterol LDL cholesterol HDL cholesterol Triglycerides
Serum sCD40L r-Spearman’s 0.12 0.16 0.24 0.17 0.13 0.18 0.21 0.32 0.02 0.05 0.08 0.15
p ns ns 0.01 ns ns
Soluble Ligand CD40 and Uric Acid as Markers of Atheromatosis in Patients with Obstructive Sleep Apnea M. Kosacka, A. Brzecka, P. Piesiak, A. Korzeniewska, and R. Jankowska Abstract
The aim of the study was to evaluate the risk of atheromatosis in patients with obstructive sleep apnea (OSA), as based on the concentration of the pro-atherogenic soluble CD40L ligand (sCD40L) in relation to the level of uric acid. The serum levels of sCD40L and uric acid were measured in 79 OSA patients (mean apnea/hypopnea index – AHI 34.4 20.9) and in 40 healthy controls. We found that sCD40L was higher in the OSA patients with hyperuricemia than that in the patients with uric acid in the normal range (sCD40L: 9.0 ng/ml vs. 8.0 ng/ml, respectively, p < 0.05). There was a positive association of sCD40L with AHI (p ¼ 0.01) and a negative one with the mean minimal nocturnal SaO2 (p < 0.05). Uric acid correlated negatively with the mean and minimal SaO2 and positively with the oxygen desaturation index (p < 0.05). OSA patients with hyperuricemia also had a higher prevalence of hypertension and ischemic heart disease. We conclude that OSA patients with increased uric acid concentration have increased risk of atheromatosis, as indicated by a higher level of soluble pro-atherogenic ligand CD40, and a higher prevalence of cardiovascular adverse events. Keywords
Atherosclerosis • sCD40L • Sleep apnea syndrome • CRP • Uric acid
1
Introduction
In the obstructive sleep apnea (OSA) syndrome there is a high incidence of cardiovascular M. Kosacka (*), A. Brzecka, P. Piesiak, A. Korzeniewska, and R. Jankowska Department of Pulmonology and Lung Cancer, Wroclaw Medical University, 105 Grabiszynska St., Wroclaw 53-439, Poland e-mail: [email protected]
diseases (McNicholas and Bonsigore 2007). Different mechanisms have been postulated to explain this relationship, including increased sympathetic activity, oxidative stress, inflammation, abnormal coagulation, and endothelial and metabolic dysfunction (Lavie and Lavie 2009; McNicholas and Bonsigore 2007). CD40 and its ligand (CD40L) are transmembrane proteins and the members of the tumor necrosis factor (TNF) superfamily (Mavroudi and Papadaki 2011). 55
56
Expression of these molecules has been described in a variety of cell types, including Tand B-lymphocytes, monocytes, macrophages, endothelial cells, epithelial cells, smooth-muscle cells, platelets, fibroblasts, and adipocytes (Seijkens et al. 2013; Mavroudi and Papadaki 2011). The main source of soluble CD40L (sCD40L) in the circulation consists of activated platelets and T-cells. The exact biological function of CD40 remains unclear; however CD40–CD40L interactions are described in numerous immune and non-immune processes (Seijkens et al. 2013; Rizvi et al. 2008). Many studies indicate that CD40–CD40L interactions participate in the development and progression of atherosclerosis (Rizvi et al. 2008; Lutgens et al. 2007; Chakrabarti et al. 2005). CD40 and its ligand play a role in oxidative stress and inflammation (Rizvi et al. 2008). Soluble CD40 (sCD40) stimulates platelet activation, aggregation, and platelet-leukocyte conjugation (Chakrabarti et al. 2005). Moreover, binding of CD40L to CD40 stimulates the release and expression of many pro-inflammatory mediators as cytokines IL-1, IL-6, IL-8 IL-12, TNF-alpha, and matrix metalloproteinases (Kobayashi et al. 2006; Lutgens and Daemen 2002). This may lead to destabilization of the atherosclerotic plaques (Rizvi et al. 2008). Hyperuricemia is associated with the metabolic syndrome and many cardiovascular diseases (Kanbay et al. 2013; Schachter 2005). It has been shown that elevated uric acid increases the risk of cardiovascular events and mortality in patients with hypertension, heart failure, and diabetes (Alderman and Aiver 2004). However, the exact pathways by which uric acid participate in progression of atherosclerosis are not obvious. It is postulated that hyperuricemia plays a role in endothelial dysfunction and oxidative stress, enhances vasoconstriction and inflammatory process, and in addition has an influence on platelet function, especially its adhesiveness and aggregation (Kanbay et al. 2013; Alderman and Aiver 2004). Repetitive hypoxia during episodes of apnea or hypopnea, which is a main feature of OSA, has an influence on the concentration of uric acid and on the inflammatory effects exerted by CD40L.
M. Kosacka et al.
Hypoxia stimulates the degradation of adenosine triphosphatase into xanthine, which, in turn, increases the level of uric acid (Mentzer et al. 1975). Hypoxia could also enhance the inflammatory effects of CD40L in the endothelial and monocytic cells through increased reactive oxygen species (ROS) and intercellular adhesion molecule (ICAM-1) production (Chakrabarti et al. 2009). The aim of the present study was to evaluate the risk of atheromatosis based on the concentrations of the pro-atherogenic sCD40L in relation with the serum uric acid in patients with OSA syndrome.
2
Methods
The study was approved by the Bioethics Committee of the Medical University of Wroclaw, Poland. A total of 79 patients with OSA syndrome (F/M – 21/58; mean age 54 9 years) and 40 healthy age-matched controls were included into the study. The majority of patients were overweight or obese (BMI 25–30 and >30, respectively); the mean BMI amounted to BMI 34.1 7.9 kg/m2. There were 13 patients with mild (apnea/hypopnea index – AHI 5–15), 26 with moderate (AHI 15–30) and 40 with severe OSA (AHI >30). The control group consisted of healthy persons (mean BMI 30.1 5.5), without any sleep breathing disorders (mean AHI 2.2 1.9). All subjects underwent nocturnal respiratory polygraphy using a Grass Aura PSG Lite (Warwick, USA). The following parameters were evaluated during 8 h of nocturnal sleep: AHI, desaturation index – DI, the mean and minimal SaO2 at the end of sleep apnea/hypopnea episodes. Apnea was defined as a cessation of airflow for more than 10 s and hypopnea as a reduction in airflow of 50 % from its baseline value during wakefulness for at least 10 s followed by a 4 % or more decrease in oxyhemoglobin saturation. An oxygen desaturation event was defined as a drop in SaO2 by 4 %. AHI and DI were expressed as the number of events per hour of sleep. Blood samples were collected from fasting subjects in the morning. After centrifugation for
Soluble Ligand CD40 and Uric Acid as Markers of Atheromatosis in Patients. . .
10 min at 1,467 relative centrifugal force (RCF), the serum was removed and stored at 80 C. The serum levels of sCD40L were measured using the enzyme-linked immunosorbent assay (ELISA) method (Human CD40 Ligand/TNFSF5 Quantikine; R & D Systems, Minneapolis, USA). The tests were performed according to the manufacturer’s specifications. The ELISA microplate reader from MRXe Dynex Technologies (Chantilly, USA) was used. Additionally, in the sample of blood serum the following biochemical parameters were measured: uric acid, CRP, total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides. The group of OSA patients was divided into two subgroups with elevated and normal uric acid concentration. The cut-off value for uric acid, separating normal from elevated, was 7 mg/dl for males and 6 mg/dl for females. There were 53 hyperuricemic and 26 normouricemic patients. Values were given as means SD. Spearman’s r correlation coefficient was used to assess the relationship between two variables and the Mann-Whitney U test to compare values between two groups. Differences between samples were considered significant at p < 0.05. Statistical analysis was performed using the CSS Statistica software ver. 5.0 for Windows.
3
Results
Concentrations of both sCD40L and uric acid were higher in the OSA patients than those in the control subjects (mean group sCD40L: 8.30 3.70 vs. 7.10 3.54 ng/ml, respectively; p < 0.05, and mean group uric acid: 6.30 1.49 vs. 5.70 1.20 mg/dl, respectively; p < 0.05). There was a positive correlation between sCD40L and AHI (r ¼ 0.24; p ¼ 0.01) and a negative correlation between sCD40L and the mean minimal SaO2 at the end of sleep apnea/ hypopnea episodes (r ¼ 0.18; p < 0.05). sCD40L correlated positively also with uric acid (r ¼ 0.32; p < 0.001) and C-reactive protein – CRP (r ¼ 0.21; p < 0.005). There were no correlations between sCD40L and age, BMI, DI,
57
Table 1 Correlations between the serum level of sCD40L and selected parameters
Age BMI AHI DI Mean SaO2 Mean of min. SaO2 CRP Uric acid Total cholesterol LDL cholesterol HDL cholesterol Triglycerides
Serum sCD40L r-Spearman’s 0.12 0.16 0.24 0.17 0.13 0.18 0.21 0.32 0.02 0.05 0.08 0.15
p ns ns 0.01 ns ns
