- Email: [email protected]
RETRACTED: Long-term oxygen administration reduces plasma adrenomedullin levels in patients with obstructive sleep apnea syndrome
Sleep Medicine 9 (2007) 80–87 www.elsevier.com/locate/sleep
Original Article
D
Long-term oxygen administration reduces plasma adrenomedullin levels in patients with obstructive sleep apnea syndrome
AC TE
Hiroshi Yamamoto, Shinji Teramoto *, Yasuhiro Yamaguchi, Yoko Hanaoka, Masaki Ishii, Shinichiro Hibi, Yasuyoshi Ouchi Department of Geriatric Medicine, Faculty of Medicine, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan Received 7 December 2006; received in revised form 17 January 2007; accepted 11 February 2007 Available online 18 May 2007
Abstract
R ET
R
Background and purpose: Obstructive sleep apnea syndrome (OSAS) is recognized as one of the risk factors of hypertension and cardiovascular disorders. In the current study, we hypothesized that the hypoxic stress caused by obstructive sleep apnea would increase circulating adrenomedullin (ADM) levels in untreated OSAS patients compared to an age-matched control group. We further hypothesized that oxygen administration treatment may decrease OSAS-induced hypoxic stress and ADM levels. Methods: We examined short-term and long-term oxygen administration effects on circulating ADM in 48 OSAS patients. Results: The circulating levels of ADM in untreated OSAS patients were significantly greater than those in the controls. We did not observe a significant effect inU:/AP/DTD501/SLEEP/896 2 weeks of oxygen administration on the circulating ADM in the patients, but we observed a significant effect in long-term oxygen administration for more than 3 months on plasma ADM levels. Long-term oxygen therapy decreased both the magnitude of arterial oxygen desaturation and plasma ADM levels in patients but did not decrease blood pressure. Conclusions: These observations suggest that long-term oxygen therapy could reduce OSAS-induced nocturnal hypoxemia and plasma ADM levels in patients with OSAS. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Adrenomedullin; Sleep apnea; Hypertension; Cardiovascular disorders; Oxyhemoglobin desaturation intensity; Hypoxic stress
1. Introduction
It has been recognized that obstructive sleep apnea syndrome (OSAS) is an important risk factor of cardiovascular disorders, including hypertension, ischemic heart disease and cerebrovascular diseases [1–5]. Although obstructive sleep apnea (OSA) itself, OSArelated autonomic dysfunction and OSA-induced hypoxic stress may be dependently or independently *
Corresponding author. Tel.: +81 3 5800 8652; fax: +81 3 5800 6530. E-mail address: [email protected] (S. Teramoto). 1389-9457/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.sleep.2007.02.002
involved in the development of cardiovascular disorders, the exact mechanism remains to be elucidated [6,7]. One of the potential mechanisms is that OSASinduced hypoxic stress and oxidative stress increase circulating inflammatory mediators, including adhesion molecules, inflammatory cytokines, and high-sensitivity C-reactive protein (hsCRP), leading to hypertension and cardiovascular events [8–12]. In addition, it has been reported that endothelium-dependent vasorelaxation is impaired in patients with OSA, with changes in the balance of endothelium-derived vasoactive factors in favor of vasoconstriction [13]. Whereas vasoconstrictors have been reported to be elevated in patients with
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
2. Methods
R
2.1. Subjects
D
sity Hospital, and all patients gave written informed consent. Characteristics of the subjects in the OSAS and normal groups are shown in Table 1. There were no significant differences in age and body mass index (BMI) between the two groups, while AHI in the OSAS group was markedly greater than that in the control. There are no significant differences in blood pressure and metabolic indices. Following the polysomnography study, OSAS patients underwent therapeutic nasal continuous positive airway pressure (nCPAP) treatment, while 48 subjects continued to receive nCPAP successfully for 6 months and more. The Epworth sleepiness scale (ESS) was used to investigate changes in subjective daytime sleepiness. Blood pressure and heart rate measurements were measured three times per day during the hospital stay. The mean values of these three daytime measurements were obtained before the initial polysomnography.
AC TE
OSAS, hypoxia, oxidative stress, inflammatory cytokines, endothelin, shear stress, and other changes induced by OSA are implicated in the production of adrenomedullin (ADM), which is a potent endothelialderived vasodilator [14]. Nocturnal chronic hypoxia caused by OSA, which is one of the major causes of pulmonary vascular remodeling, may induce the production of both reactive oxygen species (ROS) and ADM. Recent studies have indicated that hypoxia upregulates expression of ADM, which is not only a potent vasodilator but also an antioxidant [15,16]. Because OSAS causes hypoxia, vasoconstriction, endothelin production, oxidative stress, shear stress, and inflammatory cytokines, we hypothesized that circulating ADM is increased in patients with OSAS. In the treatment of OSAS, oxygen administration effectively reduces hypoxic episode and oxidative stress. We then examined the effects of oxygen administration on the production of ADM in patients with OSAS. In the current study, we applied two protocols for oxygen administration. The first is a short-period time trial of oxygen, for comparing with compressed air administration. The second trial is the long-term oxygen administration at home for more than 6 months. We measured physiological parameters including blood pressure and plasma ADM levels before and after oxygen administration in OSAS patients.
81
R ET
Among patients diagnosed as OSAS in our department, 48 male subjects participated in the current study. As age-matched controls, 48 male subjects were chosen and studied. No subjects had any history of cardiovascular, pulmonary, metabolic or neuromuscular diseases. We excluded the co-morbidities of the participants by using their medical histories. We also checked the office blood pressure more than twice, fasting blood samples before entry into the trials. Furthermore, to be eligible, all 48 patients had to fulfill the following criteria: absence of (1) renal and renovascular hypertension, (2) blood pressure >160/90 mm Hg, (3) chronic renal and hepatic diseases, and (4) diabetes mellitus. Patients who smoked or had systemic infections at the time of the study or within 2 weeks of the study were excluded. No patients were being treated with antihypertensive agents, and all subjects were in stable condition for one month prior to the study. These subjects were examined with polysomnography and classified as obese control subjects according to the apnea–hypopnea index (AHI) data. The diagnosis of OSAS was also established with polysomnography. The study was approved by the Institutional Review Board of the Ethics Committee at the Tokyo Univer-
2.2. Polysomnography
The subjects underwent polysomnography for two consecutive nights, which included an electroencephalogram (EEG), an electro-oculogram (EOG), an electromyogram (EMG) of the chin, and an electrocardiogram (ECG; DG Compact32, Medelec, UK). Surface electrodes were used to record two channels of EEG (C3A2, C4A1), right and left EOG, and submental EMG. We monitored ventilation and airflow using inductive plethysmography (Respitrace, Ambulatory Monitoring, Ardsley, NY) and thermistors (Fukuda-Sangyo, Chiba, Japan) placed at the nostril and mouth. Arterial oxygen saturation (SaO2) was continuously measured by pulse oximeter (Datex, Helsinki, Finland). Data acquisition was performed overnight from 9:00 pm to 7:00 am the next morning [17,18]. Apnea was defined as continuous cessation of airflow for >10 s, and hypopnea
Table 1 The characteristics of the subjects Group
OSAS group
Control group
Age (years) BMI Systolic BP Diastolic BP HR Total cholesterol (mg/dL) High-density lipoprotein cholesterol (mg/dL) Low-density lipoprotein cholesterol (mg/dL) Triglyceride (mg/dL) Total sleep time (min) ESS
49.8 ± 2.2 32.4 ± 0.9 145.1 ± 8.7 84.1 ± 3.2 74.1 ± 3.2 202.9 ± 10.9 41.0 ± 2.4
49.6 ± 2.1 30.7 ± 1.4 142.1 ± 10.7 82.1 ± 2.9 72.1 ± 2.9 198.3 ± 12.5 39.6 ± 2.9
128.7 ± 5.2
130.1 ± 5.8
150.1 ± 12.7 348.1 ± 20.3 14.6 ± 0.9*
148.0 ± 11.8 424.3 ± 22.2 3.6 ± 1.9
%TST, percentage of total sleep time. * P < 0.001 vs control group. Data are presented as means ± SE.
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
was defined as a reduction in airflow for >10 s with oxygen desaturation of 4% or an EEG arousal from sleep. Apneas were classified as obstructive, mixed or central according to standard criteria of the American Academy of Sleep Medicine. AHI was calculated as the total number of episodes of apnea and hypopnea per hour of sleep. An AHI of 5 was considered diagnostic of OSAS. 2.3. Oxygen administration trials
We obtained peripheral blood from the subjects between 7:30 and 8:00 am before and after the 1–6 months of treatment with oxygen therapy. Blood samples were stored in chilled polypropylene tubes containing ethylene-diamine-tetraacetic acid (EDTA) (1 mg/mL of blood) and aprotinin (Sigma Co.) (500 kU/mL1 of blood). Blood samples were centrifuged at 250g and 4 °C for 10 min. The plasma samples were then stored at 80 °C until measurement. ADM was measured by a specific and sensitive radioimmunoassay using the kit from Phoenix Pharmaceuticals (Mountain View, CA, USA). The range of the standard curve was 0.5–128 pg/mL. Interassay and intra-assay variability was 10.6 ± 2.8% and 10.1 ± 1.9%, respectively.
R ET
R
AC TE
We examined the effects of oxygen administration on the levels of circulating ADM in patients with OSAS. We used two protocols: (i) Short-term oxygen administration trial. After nocturnal oxygen administration (1–2 l/min) by nasal prong for 2 weeks, sleep studies were repeated to assess the effects of oxygen supplement on the severity of nocturnal apneas and arterial oxygen desaturation in OSAS patients. For the control arm of the study, the same group received nocturnal administration of compressed air by nasal prong for 2 weeks, and the sleep study was repeated to assess the effects of air administration on the ADM levels, severity of nocturnal apneas, and arterial oxygen desaturation in these patients. The flow rate of oxygen/air administration was determined by the nadir SaO2; 2 l/min of oxygen/air was administered when the nadir SaO2 was less than 80%. Oxygen and air were randomly administered using a crossover protocol with a week-long washout period. Forty-eight patients completed the short-term oxygen/air administration trials. (ii) Long-term oxygen administration trial. After the short-term oxygen administration trial, patients received oxygen by nasal prong at home for more than 6 months. One to six months after the introduction of oxygen supplementation therapy at home, the patients were admitted and polysomnography was re-performed as oxygen therapy was given. Forty patients completed the long-term oxygen administration trial for 6 months.
2.5. Measurements of circulating ADM
D
82
2.4. Assessment of hypoxic episodes and arterial oxygen desaturation magnitude
To assess OSAS-induced hypoxia quantitatively, we used several parameters, including the number of nocturnal apneas and the number of oxyhemoglobin desaturations. The number of significant oxyhemoglobin desaturations (SDS) was determined by drops in oxyhemoglobin saturation of more than 2%, 4%, and 6%. Drops in SaO2 lasting more than 5 s were counted. We also applied oxyhemoglobin desaturation index (ODI) in this study as previously described [8,9]. Desaturation episodes were defined as hypoxia of SaO2 90%. We defined ODI as DI = R(90 SaO2)t, where t is time of desaturation (h) [8,9]. As shown in the equation, ODI expresses the severity of hypoxic stress quantitatively.
2.6. Data analysis
Comparisons of data between each experimental group were carried out with the Student’s t-test. Data are expressed as means ± standard error (SE). P values less than 0.05 were interpreted as significant. The significance of differences within groups was analyzed with the Student’s paired t-test, and the significance of differences between groups was performed by analysis of variance, followed by t-tests with Bonferroni correction. The correlation was analyzed with a Spearman rank correlation. Data are expressed as means ± standard deviation (SD); P < 0.05 was considered significant. 3. Results
3.1. Assessment of hypoxic episodes There were significant differences in baseline ODI between the OSAS and normal groups (2.41 ± 0.36 and 0.02 ± 0.01, respectively, P < 0.001), suggesting that the OSAS patients were exposed to a significantly greater degree of hypoxia compared to the control subjects (Table 2). Table 2 Assessment of apnea and hypoxic episodes in both OSAS group and control group Group AHI (events/h) SaO2 < 90% (%TST) Lowest SaO2 (%) ODI SDS (2%) (events/h) SDS (4%) (events/h) SDS (6%) (events/h) Arousal index (per h)
OSAS group *
51.1 ± 3.2 34.1 ± 6.2* 68.9 ± 3.0* 2.41 ± 0.36* 58.2 ± 4.1* 34.4 ± 4.2* 18.8 ± 6.2* 41.9 ± 3.2*
Control group 4.1 ± 0.4 0 96.8 ± 0.5 0.02 ± 0.01 8.6 ± 2.4 1.1 ± 0.2 0±0 8.3 ± 3.1
ODI, oxyhemoglobin desaturation index; SDS, the number of significant oxyhemoglobin desaturation. SDS was determined by drops in oxyhemoglobin saturation of more than 2%, 4%, and 6%. * P < 0.001 vs control group. Data are presented as means ± SE.
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
ADM and hypoxic episodes (ODI) rather than apnea episodes (AHI). Table 3 summarizes correlations between ADM and sleep apnea-related variables, including nocturnal hypoxia and oxidant stress in OSAS patients. The circulating ADM levels are significantly associated with the nocturnal hypoxic variables rather than apnea itself.
circulating ADM levels (pg/mL) p< 0.01
60
83
50 40 30
3.4. Effects of short-term oxygen administration on physiological indices and circulating ADM
10 0 Obese Obese CTRL with OSAS
AC TE
Fig. 1. The baseline levels of circulating adrenomedullin (ADM) levels in obese control subjects (CTRL) and obese subjects in OSAS groups. OSAS, obstructive sleep apnea syndrome.
Following 2 weeks administration of air or oxygen, improvement in sleepiness was observed in the patients with O2 administration. Although the AHI parameters were slightly improved by short-term oxygen administration, the AHI was not affected by short-term air administration. Oxygen administration, hypoxic episode and arterial oxygen desaturation magnitude as indicated by ODI were markedly improved by short-term oxygen administration but not by short-term air administration (Table 4). However, there were no obvious effects of short-term oxygen administration on the plasma level of ADM. There was no difference in ADM levels between short-term oxygen administration and shortterm air administration (Fig. 3).
D
20
3.2. Baseline measurements of circulating ADM
Fig. 1 summarizes the ADM levels in the baseline. The levels of both ADM in the OSAS group were significantly greater than those in the normal group (Fig. 1). Baseline ADM levels were significantly greater than those in the control groups (49.1 ± 4.7 vs 23.9 ± 5.2 pg/mL, respectively).
R
3.3. Relationships between ADM and sleep apnea-related variables
R ET
Fig. 2 demonstrates the relationships between ADM and AHI or arterial oxygen desaturation magnitude as indicated by ODI in OSAS patients. As shown, significant correlation is observed between
3.5. Effects of long-term oxygen administration on physiological indices and circulating ADM Fig. 4 summarizes the effects of long-term oxygen administration on circulating ADM levels. Long-term oxygen administration clearly decreases the plasma ADM levels dependent on treatment duration. The ADM levels after 6 months of treatment with oxygen were less than those after one month of treatment with oxygen. Although the physiological parameters were
a
b
circulating ADM levels (pg/mL)
circulating ADM levels (pg/mL)
60
60
50
50
40
40
30
30
20
20
r = 0.428, p< 0.01
10
r = 0.658, p< 0.01
10 0
0 0
20
40
AHI (/ hour)
60
80
0
1
2
3
ODI
Fig. 2. Correlation between circulating ADM and sleep apnea-associated parameters, i.e., (a) apnea index (AHI) and (b) oxygen desaturation magnitude as indicated by oxyhemoglobin desaturation index (ODI).
84
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
Table 3 Correlations between ADM and sleep apnea-related variables in OSAS group Variables
r
p
AHI (events/h) SaO2 < 90% (%TST) Lowest SaO2 (%) ODI SDS (2%) (events/h) SDS (4%) (events/h) SDS (6%) (events/h) Arousal index (per h)
0.378 0.364 0.512 0.598 0.312 0.357 0.298 0.344
<0.05 <0.05 <0.05 <0.01 0.09 <0.05 0.12 0.08
circulating ADM levels (pg/mL) 60 50 40
* *
30 20
D
10 0
Before
Systolic BP Diastolic BP HR Total sleep time (min) ESS AHI (events/h) SaO2 < 90% (%TST) Lowest SaO2 (%) ODI SDS (2%) (events/h) SDS (4%) (events/h) SDS (6%) (events/h) Arousal index (per h)
After 2 weeks administration of
144.1 ± 8.7 81.1 ± 3.2 73.1 ± 3.2 350.1 ± 20.3 14.4 ± 0.9 50.3 ± 3.2 36.4 ± 6.2 69.7 ± 2.8 2.43 ± 0.34 59.3 ± 3.9 36.2 ± 4.2 18.1 ± 6.2 41.6 ± 3.2
Air
Oxygen
142.1 ± 7.4 80.9 ± 2.9 73.2 ± 2.9 351.3 ± 19.2 12.4 ± 1.9 49.1 ± 2.9 34.1 ± 5.2 70.9 ± 2.7 2.36 ± 0.26* 54.6 ± 2.4 34.0 ± 0.2 17.1 ± 0.1 38.3 ± 2.6
141.5 ± 7.8 80.2 ± 3.2 73.6 ± 2.8 352.3 ± 19.7 11.9 ± 1.6 44.3 ± 0.4* 4.1 ± 0.3* 90.8 ± 0.5* 0.19 ± 0.03* 16.3 ± 2.0* 5.9 ± 0.2* 1.2 ± 0.1* 29.4 ± 2.2*
R ET
R
* P < 0.05 vs the same value before treatment. Data are presented as means ± SE.
circulating ADM levels (pg/mL)
ns
ns
60 50 40 30 20 10
0
Before
Before 1 3 6 months after O2 administration
Fig. 4. Effects of long-term oxygen administration on circulating ADM levels. *P < 0.05 vs baseline value before treatment with oxygen.
AC TE
Table 4 Effects of 2 weeks administration of oxygen or air on physiological indices and sleep apnea-related variables (n = 48)
Air O2 2 weeks administration
Fig. 3. Effects of 2 weeks administration of compressed air or oxygen on circulating ADM levels.
not significantly changed for 6 months of treatment with oxygen, nocturnal hypoxic episodes and arterial oxygen desaturation magnitude as indicated by ODI were mark-
edly improved by long-term oxygen administration in patients with OSAS (Table 5).
4. Discussion
The results of the current study demonstrate that circulating ADM levels are significantly increased in OSAS patients compared to the normal subjects. In addition, 6 months of treatment with oxygen administration decreased arterial oxyhemoglobin desaturation, and circulating ADM in the OSAS patients. At baseline, levels of ADM in the OSAS group were significantly greater than those in the control group. ADM levels are positively correlated with the severity of hypoxia as indexed by ODI. These observations suggest that long-term oxygen therapy could reduce OSAS-induced nocturnal hypoxia and levels of ADM. Several issues warrant consideration before arguing the results. First, we measured circulating levels of ADM but not tissue levels of ADM in OSAS patients. Because the plasma levels of ADM and tissue and vascular endothelium levels of ADM may not be the same, we do not have real evidence for the significant relationship between the OSAS-induced hypoxic stress and the functional ADM levels in endothelium. However, exogenous ADM has been reported to act as the vasodilator effectively. Thus, the increased levels of circulating ADM may have a significant effect on the vasodilation in OSAS patients. Although the ADM is known as a potent vasodilator, the recent data suggest that ADM may also act as an antioxidant [15,16]. The increased levels of ADM may be an adaptive mechanism against the severe oxidative stress due to intermittent hypoxia and increased production of reactive oxygen species. Second, the mean value of blood pressure in patients with OSAS is slightly greater than normal values.
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
85
Table 5 Effects of long-term O2 administration on physiological indices and sleep apnea-related variables (n = 40)
Systolic BP Diastolic BP HR TST (min) ESS AHI (events/h) SaO2 < 90% (%TST) Lowest SaO2 (%) ODI SDS (2%) (events/h) SDS (4%) (events/h) SDS (6%) (events/h) Arousal index (per h)
1
3
6
143.1 ± 7.4 82.9 ± 2.9 73.2 ± 2.9 355.3 ± 21.2 10.4 ± 1.9 44.1 ± 1.4* 3.1 ± 0.2* 90.8 ± 0.4* 0.13 ± 0.06* 14.6 ± 2.4* 4.0 ± 0.2* 0.1 ± 0.1* 18.3 ± 2.1*
144.5 ± 7.8 82.2 ± 3.1 73.6 ± 2.8 354.3 ± 20.2 9.9 ± 1.6* 44.3 ± 0.4* 2.9 ± 0.3* 91.8 ± 0.5* 0.12 ± 0.04* 14.3 ± 2.0* 3.9 ± 0.2* 0.2 ± 0.1* 16.4 ± 2.0*
142.1 ± 7.9 82.6 ± 2.9 72.4 ± 2.6 360.3 ± 21.9* 10.1 ± 2.1* 41.6 ± 0.8* 1.7 ± 0.1* 92.1 ± 0.5* 0.10 ± 0.02* 13.9 ± 1.9* 3.8 ± 0.2* 0.1 ± 0.1* 16.8 ± 2.2*
P < 0.05 vs the same value before treatment. Data are presented as means ± SE.
AC TE
*
144.1 ± 8.7 83.1 ± 3.2 73.1 ± 3.2 349.1 ± 20.3 14.5 ± 0.9 50.1 ± 3.2 36.1 ± 6.2 69.2 ± 2.8 2.42 ± 0.34 59.6 ± 3.9 36.4 ± 4.2 18.8 ± 6.2 42.1 ± 3.2
After treatment with O2 administration (months)
D
Before
R ET
R
Therefore, the increase of blood pressure may affect the plasma ADM levels in the patients. It has been recently reported that OSA does not exert any significant acute or chronic effects on plasma ADM levels [19]. However, the study sample is very small, and the magnitude of hypoxic stress was not examined. Therefore, the effect of OSA itself on the ADM levels can be speculated on, but the effects of hypoxic stress and/or oxidative stress induced by OSA on the ADM levels in OSAS patients requires further attention. Furthermore, only 15 OSAS patients and 10 control subjects were studied. At 2:00 am, the levels of ADM in the OSAS group (28.2 ± 5.9 pg/ml) were slightly greater than those in the normal group (23.3 ± 5.1 pg/ml) in their study [19]. Thus, the results did not completely deny the increase of ADM level in OSAS with nocturnal hypoxemia. They indicated no association of OSA with the levels of ADM in the patients, nor did they indicate the relationship between oxyhemoglobin desaturation induced by OSAS and levels of ADM. Our study indicates that ADM levels are not correlated with apnea numbers but are well correlated with the magnitude of hypoxia as indicated by ODI. This may be supported by the recent data by Schulz et al. [20]. In their study, it was also shown that ADM is increased in OSAS when compared to controls. In addition, the treatment of OSAS with CPAP significantly decreased the circulating ADM levels. It has been recently postulated that inflammatory process has a crucial role in the pathogenesis of atherosclerosis, leading to the various cardiovascular disorders [21–23]. We have previously reported that the circulating ICAM-1 level is significantly increased compared to the control group, suggesting that OSAS-induced hypoxia may induce the activation of ICAM-1 and the inflammation of endothelium in patients with OSAS [8,9]. Furthermore, we have also demonstrated that the
circulating IL-8 and MCP-1 levels increased in the OSAS patients compared to the normal subjects. There was a significant correlation between circulating ICAM1 and IL-8 in the OSAS patients [9]. In addition, we also found that the serum level of nitrite/nitrates (NOx), which are stable metabolites of NO, was lower in patients with OSAS than in control subjects [24]. There is a significant negative correlation between serum nitrites/nitrates and the magnitude of oxygen desaturation. Furthermore, nocturnal oxygen supplementation increased the NOx level but did not affect the apneas, suggesting that repeated episodes of nocturnal hypoxemia are a mechanism of the impaired NO production in patients with OSAS. Because the measurements of brachial artery diameter are obtained under baseline conditions, during reactive hyperemia and after sublingual administration of nitroglycerin (an endotheliumindependent vasodilator), patients with OSAS have an impairment of resistance-vessel endothelium-dependent vasodilation, and the vascular endothelial function in OSAS may be disturbed [25,26]. Because ADM is reported to induce cell surface expression of the adhesion molecules E-selectin, VCAM-1, and ICAM-1 on human endothelial cells, an increase in levels of ADM serves as a mechanism of increased levels of ICAM-1 in OSAS patients. [11,27] It has also been reported that ADM inhibits VEGFstimulated ICAM-1 and VCAM-1 expression through a phosphatidylinositol 3 0 -kinase/Akt pathway [28]. Although circulating VEGF levels are elevated in OSAS patients, ADM may have an anti-inflammatory role in controlling VEGF-induced adhesion molecular gene expression and adhesiveness toward leukocytes in endothelial cells [29]. To treat patients with OSAS, oxygen therapy is one choice for patients who do not tolerate nCPAP therapy. We did not find any significant effect of short-term oxy-
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
References [1] Chhajed PN, Tamm M, Strobel W. Sleep apnea and heart disease. N Engl J Med 2006;354:1086–9. [2] Can M, Acikgoz S, Mungan G, Bayraktaroglu T, Kocak E, Guven B, et al. Serum cardiovascular risk factors in obstructive sleep apnea. Chest 2006;129:233–7. [3] Suzuki YJ, Jain V, Park AM, Day RM. Oxidative stress and oxidant signaling in obstructive sleep apnea and associated cardiovascular diseases. Free Radic Biol Med 2006;40:1683–92. [4] Teramoto S, Kume H, Matsuse T. Ambulatory blood pressure after sleep apnoea treatment. Lancet 2002;360:341–2. [5] Teramoto S, Ohga E, Ouchi Y. Obstructive sleep apnoea. Lancet 1999;354(9185):1213–4. [6] Teramoto S, Kume H, Matsuse T, Fukuchi Y. The risk of future cardiovascular diseases in the patients with OSAS is dependently or independently associated with obstructive sleep apnoea. Eur Respir J 2001;17:573–4. [7] Teramoto S, Yamamoto H, Yamaguchi Y, Namba R, Ouchi Y. Obstructive sleep apnea causes systemic inflammation and metabolic syndrome. Chest 2005;127:1074–5. [8] Ohga E, Nagase T, Tomita T, Teramoto S, Matsuse T, Katayama H, et al. Increased levels of circulating ICAM-1, VCAM-1, and L-selectin in obstructive sleep apnea syndrome. J Appl Physiol 1999;87:10–4. [9] Ohga E, Tomita T, Wada H, Yamamoto H, Nagase T, Ouchi Y. Effects of obstructive sleep apnea on circulating ICAM-1, IL-8, and MCP-1. J Appl Physiol 2003;94:179–84. [10] Caples SM, Gami AS, Somers VK. Obstructive sleep apnea. Ann Intern Med 2005;142:187–97. [11] Teramoto S, Yamamoto H, Ouchi Y. Increased plasma interleukin-6 is associated with the pathogenesis of obstructive sleep apnea syndrome. Chest 2004;125:1964–5. [12] Teramoto S, Yamamoto H, Ouchi Y. C-reactive protein and increased plasma interleukin-6 may synergistically affect the progression of coronary atherosclerosis in obstructive sleep apnea syndrome. Circulation 2003;107:E40. [13] Wolk R, Kara T, Somers VK. Sleep-disordered breathing and cardiovascular disease. Circulation 2003;108:9–12. [14] Sugo S, Minamino N, Kangawa K, Miyamoto K, Kitamura K, Sakata J, et al. Endothelial cells actively synthesize and secrete adrenomedullin. Biochem Biophys Res Commun 1994;201:1160–6. [15] Saito T, Itoh H, Chun TH, Fukunaga Y, Yamashita J, Doi K, et al. Coordinate regulation of endothelin and adrenomedullin secretion by oxidative stress in endothelial cells. Am J Physiol Heart Circ Physiol 2001;281:H1364–71. [16] Yoshimoto T, Gochou N, Fukai N, Sugiyama T, Shichiri M, Hirata Y. Adrenomedullin inhibits angiotensin II-induced oxidative stress and gene expression in rat endothelial cells. Hypertens Res 2005;28:165–72. [17] Teramoto S, Sudo E, Matsuse T, Ohga E, Ishii T, Ouchi Y, et al. Impaired swallowing reflex in patients with obstructive sleep apnea syndrome. Chest 1999;116:17–21. [18] Teramoto S, Kume H, Yamamoto H, Ishii T, Miyashita A, Matsuse T, et al. Effects of oxygen administration on the circulating vascular endothelial growth factor (VEGF) levels in patients with obstructive sleep apnea syndrome. Intern Med 2003;42:681–5. [19] Wolk R, Svatikova A, Otto ME, Hoffmann MS, Duenwald CJ, Somers VK. Plasma adrenomedullin and obstructive sleep apnea. Am J Hypertens 2004;17:74–6. [20] Schulz R, Flototto C, Jahn A, Eisele HJ, Weissmann N, Seeger W, et al. Circulating adrenomedullin in obstructive sleep apnoea. J Sleep Res 2006;15:89–95. [21] Ferrario CM, Strawn WB. Role of the renin–angiotensin–aldosterone system and proinflammatory mediators in cardiovascular disease. Am J Cardiol 2006;98:121–8.
R ET
R
AC TE
gen therapy on physiological parameters and ADM levels. However, we observed that long-term oxygen therapy was effective to improve nocturnal apnea and oxyhemoglobin desaturation and the circulating ADM levels. One possible explanation is that long-term oxygen therapy decreases hypoxic episodes, resulting in the reduction of hypoxia-induced oxidative stress in patients. Schulz et al. [20] demonstrated that CPAP therapy provoked a decrease in circulating ADM, which was more pronounced at long-term follow-up. Their observations are very similar to those made in the current study after oxygen administration. The novel aspect of the current study is that it is indeed nocturnal hypoxia which seems to be responsible for the elevation of ADM in OSAS patients. To assess the severity of hypoxia induced by OSAS, we used desaturation magnitude, that is, ODI. This parameter may reflect OSAS-induced hypoxic stress more quantitatively than AHI or nadir SaO2, alone. The conventional way to assess the degree of OSAS counted the number of apnea episodes alone, while ODI could reflect both decreases in SaO2 and time spent below 90%. However, in order to accurately analyze the hypoxic stress, exploring other indices of hypoxic stress may be important and helpful. The ODI is significantly correlated with the levels of ADM. Although the AHI is also correlated with both parameters, the relationship is more significant with ODI rather than AHI or nadir SaO2. We have previously reported that increased levels of pro-inflammatory cytokines and C-reactive protein in plasma are decreased by nCPAP in patients with OSAS [11,12]. The reduction of hypoxic stress and oxidant stress by the long-term oxygen therapy may contribute to decrease the inflammatory mediators. These results also support that there are beneficial effects of long-term oxygen therapy on circulating ADM in patients with OSAS. In summary, circulating ADM levels were increased in the OSAS patients compared to the control obese subjects. The long-term, but not short-term, oxygen therapy for OSAS significantly decreased the levels of ADM in patients with OSAS. Because the magnitude of ODI is significantly associated with levels of ADM, the amelioration of hypoxic stress and oxidant stress by long-term oxygen therapy may be a mechanism of the reduced levels of ADM.
D
86
Acknowledgments This work was supported in part by Grant for Mitsui Life Social Welfare Foundation Japan fund in Japan and by Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture, Japan (17590781).
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
D
[26] Ip MS, Tse HF, Lam B, Tsang KW, Lam WK. Endothelial function in obstructive sleep apnea and response to treatment. Am J Respir Crit Care Med 2004;169:348–53. [27] Hagi-Pavli E, Farthing PM, Kapas S. Stimulation of adhesion molecule expression in human endothelial cells (HUVEC) by adrenomedullin and corticotrophin. Am J Physiol Cell Physiol 2004;286:C239–46. [28] Hagi-Pavli E, Farthing PM, Henshaw FN, Kapas S. Adrenomedullin reduces VEGF-induced endothelial adhesion molecules and adhesiveness through a phosphatidylinositol 3 0 -kinase pathway. Arterioscler Thromb Vasc Biol 2003;23: 1377–83. [29] Lavie L, Kraiczi H, Hefetz A, Ghandour H, Perelman A, Hedner J, et al. Plasma vascular endothelial growth factor in sleep apnea syndrome: effects of nasal continuous positive air pressure treatment. Am J Respir Crit Care Med 2002;165:1624–8.
R ET
R
AC TE
[22] Yoshii T, Iwai M, Li Z, Chen R, Ide A, Fukunaga S, et al. Regression of atherosclerosis by amlodipine via anti-inflammatory and anti-oxidative stress actions. Hypertens Res 2006;29:457–66. [23] Toba H, Shimizu T, Miki S, Inoue R, Yoshimura A, Tsukamoto R, et al. Calcium channel blockers reduce angiotensin II-induced superoxide generation and inhibit lectin-like oxidized low-density lipoprotein receptor-1 expression in endothelial cells. Hypertens Res 2006;29:105–16. [24] Teramoto S, Kume H, Matsuse T, Ishii T, Miyashita A, Akishita M, et al. Oxygen administration improves the serum level of nitric oxide metabolites in patients with obstructive sleep apnea syndrome. Sleep Med 2003;4:403–7. [25] Kato M, Roberts-Thomson P, Phillips BG, Haynes WG, Winnicki M, Accurso V, et al. Impairment of endothelium-dependent vasodilation of resistance vessels in patients with obstructive sleep apnea. Circulation 2000;102:2607–10.
87
Original Article
D
Long-term oxygen administration reduces plasma adrenomedullin levels in patients with obstructive sleep apnea syndrome
AC TE
Hiroshi Yamamoto, Shinji Teramoto *, Yasuhiro Yamaguchi, Yoko Hanaoka, Masaki Ishii, Shinichiro Hibi, Yasuyoshi Ouchi Department of Geriatric Medicine, Faculty of Medicine, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan Received 7 December 2006; received in revised form 17 January 2007; accepted 11 February 2007 Available online 18 May 2007
Abstract
R ET
R
Background and purpose: Obstructive sleep apnea syndrome (OSAS) is recognized as one of the risk factors of hypertension and cardiovascular disorders. In the current study, we hypothesized that the hypoxic stress caused by obstructive sleep apnea would increase circulating adrenomedullin (ADM) levels in untreated OSAS patients compared to an age-matched control group. We further hypothesized that oxygen administration treatment may decrease OSAS-induced hypoxic stress and ADM levels. Methods: We examined short-term and long-term oxygen administration effects on circulating ADM in 48 OSAS patients. Results: The circulating levels of ADM in untreated OSAS patients were significantly greater than those in the controls. We did not observe a significant effect inU:/AP/DTD501/SLEEP/896 2 weeks of oxygen administration on the circulating ADM in the patients, but we observed a significant effect in long-term oxygen administration for more than 3 months on plasma ADM levels. Long-term oxygen therapy decreased both the magnitude of arterial oxygen desaturation and plasma ADM levels in patients but did not decrease blood pressure. Conclusions: These observations suggest that long-term oxygen therapy could reduce OSAS-induced nocturnal hypoxemia and plasma ADM levels in patients with OSAS. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Adrenomedullin; Sleep apnea; Hypertension; Cardiovascular disorders; Oxyhemoglobin desaturation intensity; Hypoxic stress
1. Introduction
It has been recognized that obstructive sleep apnea syndrome (OSAS) is an important risk factor of cardiovascular disorders, including hypertension, ischemic heart disease and cerebrovascular diseases [1–5]. Although obstructive sleep apnea (OSA) itself, OSArelated autonomic dysfunction and OSA-induced hypoxic stress may be dependently or independently *
Corresponding author. Tel.: +81 3 5800 8652; fax: +81 3 5800 6530. E-mail address: [email protected] (S. Teramoto). 1389-9457/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.sleep.2007.02.002
involved in the development of cardiovascular disorders, the exact mechanism remains to be elucidated [6,7]. One of the potential mechanisms is that OSASinduced hypoxic stress and oxidative stress increase circulating inflammatory mediators, including adhesion molecules, inflammatory cytokines, and high-sensitivity C-reactive protein (hsCRP), leading to hypertension and cardiovascular events [8–12]. In addition, it has been reported that endothelium-dependent vasorelaxation is impaired in patients with OSA, with changes in the balance of endothelium-derived vasoactive factors in favor of vasoconstriction [13]. Whereas vasoconstrictors have been reported to be elevated in patients with
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
2. Methods
R
2.1. Subjects
D
sity Hospital, and all patients gave written informed consent. Characteristics of the subjects in the OSAS and normal groups are shown in Table 1. There were no significant differences in age and body mass index (BMI) between the two groups, while AHI in the OSAS group was markedly greater than that in the control. There are no significant differences in blood pressure and metabolic indices. Following the polysomnography study, OSAS patients underwent therapeutic nasal continuous positive airway pressure (nCPAP) treatment, while 48 subjects continued to receive nCPAP successfully for 6 months and more. The Epworth sleepiness scale (ESS) was used to investigate changes in subjective daytime sleepiness. Blood pressure and heart rate measurements were measured three times per day during the hospital stay. The mean values of these three daytime measurements were obtained before the initial polysomnography.
AC TE
OSAS, hypoxia, oxidative stress, inflammatory cytokines, endothelin, shear stress, and other changes induced by OSA are implicated in the production of adrenomedullin (ADM), which is a potent endothelialderived vasodilator [14]. Nocturnal chronic hypoxia caused by OSA, which is one of the major causes of pulmonary vascular remodeling, may induce the production of both reactive oxygen species (ROS) and ADM. Recent studies have indicated that hypoxia upregulates expression of ADM, which is not only a potent vasodilator but also an antioxidant [15,16]. Because OSAS causes hypoxia, vasoconstriction, endothelin production, oxidative stress, shear stress, and inflammatory cytokines, we hypothesized that circulating ADM is increased in patients with OSAS. In the treatment of OSAS, oxygen administration effectively reduces hypoxic episode and oxidative stress. We then examined the effects of oxygen administration on the production of ADM in patients with OSAS. In the current study, we applied two protocols for oxygen administration. The first is a short-period time trial of oxygen, for comparing with compressed air administration. The second trial is the long-term oxygen administration at home for more than 6 months. We measured physiological parameters including blood pressure and plasma ADM levels before and after oxygen administration in OSAS patients.
81
R ET
Among patients diagnosed as OSAS in our department, 48 male subjects participated in the current study. As age-matched controls, 48 male subjects were chosen and studied. No subjects had any history of cardiovascular, pulmonary, metabolic or neuromuscular diseases. We excluded the co-morbidities of the participants by using their medical histories. We also checked the office blood pressure more than twice, fasting blood samples before entry into the trials. Furthermore, to be eligible, all 48 patients had to fulfill the following criteria: absence of (1) renal and renovascular hypertension, (2) blood pressure >160/90 mm Hg, (3) chronic renal and hepatic diseases, and (4) diabetes mellitus. Patients who smoked or had systemic infections at the time of the study or within 2 weeks of the study were excluded. No patients were being treated with antihypertensive agents, and all subjects were in stable condition for one month prior to the study. These subjects were examined with polysomnography and classified as obese control subjects according to the apnea–hypopnea index (AHI) data. The diagnosis of OSAS was also established with polysomnography. The study was approved by the Institutional Review Board of the Ethics Committee at the Tokyo Univer-
2.2. Polysomnography
The subjects underwent polysomnography for two consecutive nights, which included an electroencephalogram (EEG), an electro-oculogram (EOG), an electromyogram (EMG) of the chin, and an electrocardiogram (ECG; DG Compact32, Medelec, UK). Surface electrodes were used to record two channels of EEG (C3A2, C4A1), right and left EOG, and submental EMG. We monitored ventilation and airflow using inductive plethysmography (Respitrace, Ambulatory Monitoring, Ardsley, NY) and thermistors (Fukuda-Sangyo, Chiba, Japan) placed at the nostril and mouth. Arterial oxygen saturation (SaO2) was continuously measured by pulse oximeter (Datex, Helsinki, Finland). Data acquisition was performed overnight from 9:00 pm to 7:00 am the next morning [17,18]. Apnea was defined as continuous cessation of airflow for >10 s, and hypopnea
Table 1 The characteristics of the subjects Group
OSAS group
Control group
Age (years) BMI Systolic BP Diastolic BP HR Total cholesterol (mg/dL) High-density lipoprotein cholesterol (mg/dL) Low-density lipoprotein cholesterol (mg/dL) Triglyceride (mg/dL) Total sleep time (min) ESS
49.8 ± 2.2 32.4 ± 0.9 145.1 ± 8.7 84.1 ± 3.2 74.1 ± 3.2 202.9 ± 10.9 41.0 ± 2.4
49.6 ± 2.1 30.7 ± 1.4 142.1 ± 10.7 82.1 ± 2.9 72.1 ± 2.9 198.3 ± 12.5 39.6 ± 2.9
128.7 ± 5.2
130.1 ± 5.8
150.1 ± 12.7 348.1 ± 20.3 14.6 ± 0.9*
148.0 ± 11.8 424.3 ± 22.2 3.6 ± 1.9
%TST, percentage of total sleep time. * P < 0.001 vs control group. Data are presented as means ± SE.
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
was defined as a reduction in airflow for >10 s with oxygen desaturation of 4% or an EEG arousal from sleep. Apneas were classified as obstructive, mixed or central according to standard criteria of the American Academy of Sleep Medicine. AHI was calculated as the total number of episodes of apnea and hypopnea per hour of sleep. An AHI of 5 was considered diagnostic of OSAS. 2.3. Oxygen administration trials
We obtained peripheral blood from the subjects between 7:30 and 8:00 am before and after the 1–6 months of treatment with oxygen therapy. Blood samples were stored in chilled polypropylene tubes containing ethylene-diamine-tetraacetic acid (EDTA) (1 mg/mL of blood) and aprotinin (Sigma Co.) (500 kU/mL1 of blood). Blood samples were centrifuged at 250g and 4 °C for 10 min. The plasma samples were then stored at 80 °C until measurement. ADM was measured by a specific and sensitive radioimmunoassay using the kit from Phoenix Pharmaceuticals (Mountain View, CA, USA). The range of the standard curve was 0.5–128 pg/mL. Interassay and intra-assay variability was 10.6 ± 2.8% and 10.1 ± 1.9%, respectively.
R ET
R
AC TE
We examined the effects of oxygen administration on the levels of circulating ADM in patients with OSAS. We used two protocols: (i) Short-term oxygen administration trial. After nocturnal oxygen administration (1–2 l/min) by nasal prong for 2 weeks, sleep studies were repeated to assess the effects of oxygen supplement on the severity of nocturnal apneas and arterial oxygen desaturation in OSAS patients. For the control arm of the study, the same group received nocturnal administration of compressed air by nasal prong for 2 weeks, and the sleep study was repeated to assess the effects of air administration on the ADM levels, severity of nocturnal apneas, and arterial oxygen desaturation in these patients. The flow rate of oxygen/air administration was determined by the nadir SaO2; 2 l/min of oxygen/air was administered when the nadir SaO2 was less than 80%. Oxygen and air were randomly administered using a crossover protocol with a week-long washout period. Forty-eight patients completed the short-term oxygen/air administration trials. (ii) Long-term oxygen administration trial. After the short-term oxygen administration trial, patients received oxygen by nasal prong at home for more than 6 months. One to six months after the introduction of oxygen supplementation therapy at home, the patients were admitted and polysomnography was re-performed as oxygen therapy was given. Forty patients completed the long-term oxygen administration trial for 6 months.
2.5. Measurements of circulating ADM
D
82
2.4. Assessment of hypoxic episodes and arterial oxygen desaturation magnitude
To assess OSAS-induced hypoxia quantitatively, we used several parameters, including the number of nocturnal apneas and the number of oxyhemoglobin desaturations. The number of significant oxyhemoglobin desaturations (SDS) was determined by drops in oxyhemoglobin saturation of more than 2%, 4%, and 6%. Drops in SaO2 lasting more than 5 s were counted. We also applied oxyhemoglobin desaturation index (ODI) in this study as previously described [8,9]. Desaturation episodes were defined as hypoxia of SaO2 90%. We defined ODI as DI = R(90 SaO2)t, where t is time of desaturation (h) [8,9]. As shown in the equation, ODI expresses the severity of hypoxic stress quantitatively.
2.6. Data analysis
Comparisons of data between each experimental group were carried out with the Student’s t-test. Data are expressed as means ± standard error (SE). P values less than 0.05 were interpreted as significant. The significance of differences within groups was analyzed with the Student’s paired t-test, and the significance of differences between groups was performed by analysis of variance, followed by t-tests with Bonferroni correction. The correlation was analyzed with a Spearman rank correlation. Data are expressed as means ± standard deviation (SD); P < 0.05 was considered significant. 3. Results
3.1. Assessment of hypoxic episodes There were significant differences in baseline ODI between the OSAS and normal groups (2.41 ± 0.36 and 0.02 ± 0.01, respectively, P < 0.001), suggesting that the OSAS patients were exposed to a significantly greater degree of hypoxia compared to the control subjects (Table 2). Table 2 Assessment of apnea and hypoxic episodes in both OSAS group and control group Group AHI (events/h) SaO2 < 90% (%TST) Lowest SaO2 (%) ODI SDS (2%) (events/h) SDS (4%) (events/h) SDS (6%) (events/h) Arousal index (per h)
OSAS group *
51.1 ± 3.2 34.1 ± 6.2* 68.9 ± 3.0* 2.41 ± 0.36* 58.2 ± 4.1* 34.4 ± 4.2* 18.8 ± 6.2* 41.9 ± 3.2*
Control group 4.1 ± 0.4 0 96.8 ± 0.5 0.02 ± 0.01 8.6 ± 2.4 1.1 ± 0.2 0±0 8.3 ± 3.1
ODI, oxyhemoglobin desaturation index; SDS, the number of significant oxyhemoglobin desaturation. SDS was determined by drops in oxyhemoglobin saturation of more than 2%, 4%, and 6%. * P < 0.001 vs control group. Data are presented as means ± SE.
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
ADM and hypoxic episodes (ODI) rather than apnea episodes (AHI). Table 3 summarizes correlations between ADM and sleep apnea-related variables, including nocturnal hypoxia and oxidant stress in OSAS patients. The circulating ADM levels are significantly associated with the nocturnal hypoxic variables rather than apnea itself.
circulating ADM levels (pg/mL) p< 0.01
60
83
50 40 30
3.4. Effects of short-term oxygen administration on physiological indices and circulating ADM
10 0 Obese Obese CTRL with OSAS
AC TE
Fig. 1. The baseline levels of circulating adrenomedullin (ADM) levels in obese control subjects (CTRL) and obese subjects in OSAS groups. OSAS, obstructive sleep apnea syndrome.
Following 2 weeks administration of air or oxygen, improvement in sleepiness was observed in the patients with O2 administration. Although the AHI parameters were slightly improved by short-term oxygen administration, the AHI was not affected by short-term air administration. Oxygen administration, hypoxic episode and arterial oxygen desaturation magnitude as indicated by ODI were markedly improved by short-term oxygen administration but not by short-term air administration (Table 4). However, there were no obvious effects of short-term oxygen administration on the plasma level of ADM. There was no difference in ADM levels between short-term oxygen administration and shortterm air administration (Fig. 3).
D
20
3.2. Baseline measurements of circulating ADM
Fig. 1 summarizes the ADM levels in the baseline. The levels of both ADM in the OSAS group were significantly greater than those in the normal group (Fig. 1). Baseline ADM levels were significantly greater than those in the control groups (49.1 ± 4.7 vs 23.9 ± 5.2 pg/mL, respectively).
R
3.3. Relationships between ADM and sleep apnea-related variables
R ET
Fig. 2 demonstrates the relationships between ADM and AHI or arterial oxygen desaturation magnitude as indicated by ODI in OSAS patients. As shown, significant correlation is observed between
3.5. Effects of long-term oxygen administration on physiological indices and circulating ADM Fig. 4 summarizes the effects of long-term oxygen administration on circulating ADM levels. Long-term oxygen administration clearly decreases the plasma ADM levels dependent on treatment duration. The ADM levels after 6 months of treatment with oxygen were less than those after one month of treatment with oxygen. Although the physiological parameters were
a
b
circulating ADM levels (pg/mL)
circulating ADM levels (pg/mL)
60
60
50
50
40
40
30
30
20
20
r = 0.428, p< 0.01
10
r = 0.658, p< 0.01
10 0
0 0
20
40
AHI (/ hour)
60
80
0
1
2
3
ODI
Fig. 2. Correlation between circulating ADM and sleep apnea-associated parameters, i.e., (a) apnea index (AHI) and (b) oxygen desaturation magnitude as indicated by oxyhemoglobin desaturation index (ODI).
84
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
Table 3 Correlations between ADM and sleep apnea-related variables in OSAS group Variables
r
p
AHI (events/h) SaO2 < 90% (%TST) Lowest SaO2 (%) ODI SDS (2%) (events/h) SDS (4%) (events/h) SDS (6%) (events/h) Arousal index (per h)
0.378 0.364 0.512 0.598 0.312 0.357 0.298 0.344
<0.05 <0.05 <0.05 <0.01 0.09 <0.05 0.12 0.08
circulating ADM levels (pg/mL) 60 50 40
* *
30 20
D
10 0
Before
Systolic BP Diastolic BP HR Total sleep time (min) ESS AHI (events/h) SaO2 < 90% (%TST) Lowest SaO2 (%) ODI SDS (2%) (events/h) SDS (4%) (events/h) SDS (6%) (events/h) Arousal index (per h)
After 2 weeks administration of
144.1 ± 8.7 81.1 ± 3.2 73.1 ± 3.2 350.1 ± 20.3 14.4 ± 0.9 50.3 ± 3.2 36.4 ± 6.2 69.7 ± 2.8 2.43 ± 0.34 59.3 ± 3.9 36.2 ± 4.2 18.1 ± 6.2 41.6 ± 3.2
Air
Oxygen
142.1 ± 7.4 80.9 ± 2.9 73.2 ± 2.9 351.3 ± 19.2 12.4 ± 1.9 49.1 ± 2.9 34.1 ± 5.2 70.9 ± 2.7 2.36 ± 0.26* 54.6 ± 2.4 34.0 ± 0.2 17.1 ± 0.1 38.3 ± 2.6
141.5 ± 7.8 80.2 ± 3.2 73.6 ± 2.8 352.3 ± 19.7 11.9 ± 1.6 44.3 ± 0.4* 4.1 ± 0.3* 90.8 ± 0.5* 0.19 ± 0.03* 16.3 ± 2.0* 5.9 ± 0.2* 1.2 ± 0.1* 29.4 ± 2.2*
R ET
R
* P < 0.05 vs the same value before treatment. Data are presented as means ± SE.
circulating ADM levels (pg/mL)
ns
ns
60 50 40 30 20 10
0
Before
Before 1 3 6 months after O2 administration
Fig. 4. Effects of long-term oxygen administration on circulating ADM levels. *P < 0.05 vs baseline value before treatment with oxygen.
AC TE
Table 4 Effects of 2 weeks administration of oxygen or air on physiological indices and sleep apnea-related variables (n = 48)
Air O2 2 weeks administration
Fig. 3. Effects of 2 weeks administration of compressed air or oxygen on circulating ADM levels.
not significantly changed for 6 months of treatment with oxygen, nocturnal hypoxic episodes and arterial oxygen desaturation magnitude as indicated by ODI were mark-
edly improved by long-term oxygen administration in patients with OSAS (Table 5).
4. Discussion
The results of the current study demonstrate that circulating ADM levels are significantly increased in OSAS patients compared to the normal subjects. In addition, 6 months of treatment with oxygen administration decreased arterial oxyhemoglobin desaturation, and circulating ADM in the OSAS patients. At baseline, levels of ADM in the OSAS group were significantly greater than those in the control group. ADM levels are positively correlated with the severity of hypoxia as indexed by ODI. These observations suggest that long-term oxygen therapy could reduce OSAS-induced nocturnal hypoxia and levels of ADM. Several issues warrant consideration before arguing the results. First, we measured circulating levels of ADM but not tissue levels of ADM in OSAS patients. Because the plasma levels of ADM and tissue and vascular endothelium levels of ADM may not be the same, we do not have real evidence for the significant relationship between the OSAS-induced hypoxic stress and the functional ADM levels in endothelium. However, exogenous ADM has been reported to act as the vasodilator effectively. Thus, the increased levels of circulating ADM may have a significant effect on the vasodilation in OSAS patients. Although the ADM is known as a potent vasodilator, the recent data suggest that ADM may also act as an antioxidant [15,16]. The increased levels of ADM may be an adaptive mechanism against the severe oxidative stress due to intermittent hypoxia and increased production of reactive oxygen species. Second, the mean value of blood pressure in patients with OSAS is slightly greater than normal values.
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
85
Table 5 Effects of long-term O2 administration on physiological indices and sleep apnea-related variables (n = 40)
Systolic BP Diastolic BP HR TST (min) ESS AHI (events/h) SaO2 < 90% (%TST) Lowest SaO2 (%) ODI SDS (2%) (events/h) SDS (4%) (events/h) SDS (6%) (events/h) Arousal index (per h)
1
3
6
143.1 ± 7.4 82.9 ± 2.9 73.2 ± 2.9 355.3 ± 21.2 10.4 ± 1.9 44.1 ± 1.4* 3.1 ± 0.2* 90.8 ± 0.4* 0.13 ± 0.06* 14.6 ± 2.4* 4.0 ± 0.2* 0.1 ± 0.1* 18.3 ± 2.1*
144.5 ± 7.8 82.2 ± 3.1 73.6 ± 2.8 354.3 ± 20.2 9.9 ± 1.6* 44.3 ± 0.4* 2.9 ± 0.3* 91.8 ± 0.5* 0.12 ± 0.04* 14.3 ± 2.0* 3.9 ± 0.2* 0.2 ± 0.1* 16.4 ± 2.0*
142.1 ± 7.9 82.6 ± 2.9 72.4 ± 2.6 360.3 ± 21.9* 10.1 ± 2.1* 41.6 ± 0.8* 1.7 ± 0.1* 92.1 ± 0.5* 0.10 ± 0.02* 13.9 ± 1.9* 3.8 ± 0.2* 0.1 ± 0.1* 16.8 ± 2.2*
P < 0.05 vs the same value before treatment. Data are presented as means ± SE.
AC TE
*
144.1 ± 8.7 83.1 ± 3.2 73.1 ± 3.2 349.1 ± 20.3 14.5 ± 0.9 50.1 ± 3.2 36.1 ± 6.2 69.2 ± 2.8 2.42 ± 0.34 59.6 ± 3.9 36.4 ± 4.2 18.8 ± 6.2 42.1 ± 3.2
After treatment with O2 administration (months)
D
Before
R ET
R
Therefore, the increase of blood pressure may affect the plasma ADM levels in the patients. It has been recently reported that OSA does not exert any significant acute or chronic effects on plasma ADM levels [19]. However, the study sample is very small, and the magnitude of hypoxic stress was not examined. Therefore, the effect of OSA itself on the ADM levels can be speculated on, but the effects of hypoxic stress and/or oxidative stress induced by OSA on the ADM levels in OSAS patients requires further attention. Furthermore, only 15 OSAS patients and 10 control subjects were studied. At 2:00 am, the levels of ADM in the OSAS group (28.2 ± 5.9 pg/ml) were slightly greater than those in the normal group (23.3 ± 5.1 pg/ml) in their study [19]. Thus, the results did not completely deny the increase of ADM level in OSAS with nocturnal hypoxemia. They indicated no association of OSA with the levels of ADM in the patients, nor did they indicate the relationship between oxyhemoglobin desaturation induced by OSAS and levels of ADM. Our study indicates that ADM levels are not correlated with apnea numbers but are well correlated with the magnitude of hypoxia as indicated by ODI. This may be supported by the recent data by Schulz et al. [20]. In their study, it was also shown that ADM is increased in OSAS when compared to controls. In addition, the treatment of OSAS with CPAP significantly decreased the circulating ADM levels. It has been recently postulated that inflammatory process has a crucial role in the pathogenesis of atherosclerosis, leading to the various cardiovascular disorders [21–23]. We have previously reported that the circulating ICAM-1 level is significantly increased compared to the control group, suggesting that OSAS-induced hypoxia may induce the activation of ICAM-1 and the inflammation of endothelium in patients with OSAS [8,9]. Furthermore, we have also demonstrated that the
circulating IL-8 and MCP-1 levels increased in the OSAS patients compared to the normal subjects. There was a significant correlation between circulating ICAM1 and IL-8 in the OSAS patients [9]. In addition, we also found that the serum level of nitrite/nitrates (NOx), which are stable metabolites of NO, was lower in patients with OSAS than in control subjects [24]. There is a significant negative correlation between serum nitrites/nitrates and the magnitude of oxygen desaturation. Furthermore, nocturnal oxygen supplementation increased the NOx level but did not affect the apneas, suggesting that repeated episodes of nocturnal hypoxemia are a mechanism of the impaired NO production in patients with OSAS. Because the measurements of brachial artery diameter are obtained under baseline conditions, during reactive hyperemia and after sublingual administration of nitroglycerin (an endotheliumindependent vasodilator), patients with OSAS have an impairment of resistance-vessel endothelium-dependent vasodilation, and the vascular endothelial function in OSAS may be disturbed [25,26]. Because ADM is reported to induce cell surface expression of the adhesion molecules E-selectin, VCAM-1, and ICAM-1 on human endothelial cells, an increase in levels of ADM serves as a mechanism of increased levels of ICAM-1 in OSAS patients. [11,27] It has also been reported that ADM inhibits VEGFstimulated ICAM-1 and VCAM-1 expression through a phosphatidylinositol 3 0 -kinase/Akt pathway [28]. Although circulating VEGF levels are elevated in OSAS patients, ADM may have an anti-inflammatory role in controlling VEGF-induced adhesion molecular gene expression and adhesiveness toward leukocytes in endothelial cells [29]. To treat patients with OSAS, oxygen therapy is one choice for patients who do not tolerate nCPAP therapy. We did not find any significant effect of short-term oxy-
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
References [1] Chhajed PN, Tamm M, Strobel W. Sleep apnea and heart disease. N Engl J Med 2006;354:1086–9. [2] Can M, Acikgoz S, Mungan G, Bayraktaroglu T, Kocak E, Guven B, et al. Serum cardiovascular risk factors in obstructive sleep apnea. Chest 2006;129:233–7. [3] Suzuki YJ, Jain V, Park AM, Day RM. Oxidative stress and oxidant signaling in obstructive sleep apnea and associated cardiovascular diseases. Free Radic Biol Med 2006;40:1683–92. [4] Teramoto S, Kume H, Matsuse T. Ambulatory blood pressure after sleep apnoea treatment. Lancet 2002;360:341–2. [5] Teramoto S, Ohga E, Ouchi Y. Obstructive sleep apnoea. Lancet 1999;354(9185):1213–4. [6] Teramoto S, Kume H, Matsuse T, Fukuchi Y. The risk of future cardiovascular diseases in the patients with OSAS is dependently or independently associated with obstructive sleep apnoea. Eur Respir J 2001;17:573–4. [7] Teramoto S, Yamamoto H, Yamaguchi Y, Namba R, Ouchi Y. Obstructive sleep apnea causes systemic inflammation and metabolic syndrome. Chest 2005;127:1074–5. [8] Ohga E, Nagase T, Tomita T, Teramoto S, Matsuse T, Katayama H, et al. Increased levels of circulating ICAM-1, VCAM-1, and L-selectin in obstructive sleep apnea syndrome. J Appl Physiol 1999;87:10–4. [9] Ohga E, Tomita T, Wada H, Yamamoto H, Nagase T, Ouchi Y. Effects of obstructive sleep apnea on circulating ICAM-1, IL-8, and MCP-1. J Appl Physiol 2003;94:179–84. [10] Caples SM, Gami AS, Somers VK. Obstructive sleep apnea. Ann Intern Med 2005;142:187–97. [11] Teramoto S, Yamamoto H, Ouchi Y. Increased plasma interleukin-6 is associated with the pathogenesis of obstructive sleep apnea syndrome. Chest 2004;125:1964–5. [12] Teramoto S, Yamamoto H, Ouchi Y. C-reactive protein and increased plasma interleukin-6 may synergistically affect the progression of coronary atherosclerosis in obstructive sleep apnea syndrome. Circulation 2003;107:E40. [13] Wolk R, Kara T, Somers VK. Sleep-disordered breathing and cardiovascular disease. Circulation 2003;108:9–12. [14] Sugo S, Minamino N, Kangawa K, Miyamoto K, Kitamura K, Sakata J, et al. Endothelial cells actively synthesize and secrete adrenomedullin. Biochem Biophys Res Commun 1994;201:1160–6. [15] Saito T, Itoh H, Chun TH, Fukunaga Y, Yamashita J, Doi K, et al. Coordinate regulation of endothelin and adrenomedullin secretion by oxidative stress in endothelial cells. Am J Physiol Heart Circ Physiol 2001;281:H1364–71. [16] Yoshimoto T, Gochou N, Fukai N, Sugiyama T, Shichiri M, Hirata Y. Adrenomedullin inhibits angiotensin II-induced oxidative stress and gene expression in rat endothelial cells. Hypertens Res 2005;28:165–72. [17] Teramoto S, Sudo E, Matsuse T, Ohga E, Ishii T, Ouchi Y, et al. Impaired swallowing reflex in patients with obstructive sleep apnea syndrome. Chest 1999;116:17–21. [18] Teramoto S, Kume H, Yamamoto H, Ishii T, Miyashita A, Matsuse T, et al. Effects of oxygen administration on the circulating vascular endothelial growth factor (VEGF) levels in patients with obstructive sleep apnea syndrome. Intern Med 2003;42:681–5. [19] Wolk R, Svatikova A, Otto ME, Hoffmann MS, Duenwald CJ, Somers VK. Plasma adrenomedullin and obstructive sleep apnea. Am J Hypertens 2004;17:74–6. [20] Schulz R, Flototto C, Jahn A, Eisele HJ, Weissmann N, Seeger W, et al. Circulating adrenomedullin in obstructive sleep apnoea. J Sleep Res 2006;15:89–95. [21] Ferrario CM, Strawn WB. Role of the renin–angiotensin–aldosterone system and proinflammatory mediators in cardiovascular disease. Am J Cardiol 2006;98:121–8.
R ET
R
AC TE
gen therapy on physiological parameters and ADM levels. However, we observed that long-term oxygen therapy was effective to improve nocturnal apnea and oxyhemoglobin desaturation and the circulating ADM levels. One possible explanation is that long-term oxygen therapy decreases hypoxic episodes, resulting in the reduction of hypoxia-induced oxidative stress in patients. Schulz et al. [20] demonstrated that CPAP therapy provoked a decrease in circulating ADM, which was more pronounced at long-term follow-up. Their observations are very similar to those made in the current study after oxygen administration. The novel aspect of the current study is that it is indeed nocturnal hypoxia which seems to be responsible for the elevation of ADM in OSAS patients. To assess the severity of hypoxia induced by OSAS, we used desaturation magnitude, that is, ODI. This parameter may reflect OSAS-induced hypoxic stress more quantitatively than AHI or nadir SaO2, alone. The conventional way to assess the degree of OSAS counted the number of apnea episodes alone, while ODI could reflect both decreases in SaO2 and time spent below 90%. However, in order to accurately analyze the hypoxic stress, exploring other indices of hypoxic stress may be important and helpful. The ODI is significantly correlated with the levels of ADM. Although the AHI is also correlated with both parameters, the relationship is more significant with ODI rather than AHI or nadir SaO2. We have previously reported that increased levels of pro-inflammatory cytokines and C-reactive protein in plasma are decreased by nCPAP in patients with OSAS [11,12]. The reduction of hypoxic stress and oxidant stress by the long-term oxygen therapy may contribute to decrease the inflammatory mediators. These results also support that there are beneficial effects of long-term oxygen therapy on circulating ADM in patients with OSAS. In summary, circulating ADM levels were increased in the OSAS patients compared to the control obese subjects. The long-term, but not short-term, oxygen therapy for OSAS significantly decreased the levels of ADM in patients with OSAS. Because the magnitude of ODI is significantly associated with levels of ADM, the amelioration of hypoxic stress and oxidant stress by long-term oxygen therapy may be a mechanism of the reduced levels of ADM.
D
86
Acknowledgments This work was supported in part by Grant for Mitsui Life Social Welfare Foundation Japan fund in Japan and by Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture, Japan (17590781).
H. Yamamoto et al. / Sleep Medicine 9 (2007) 80–87
D
[26] Ip MS, Tse HF, Lam B, Tsang KW, Lam WK. Endothelial function in obstructive sleep apnea and response to treatment. Am J Respir Crit Care Med 2004;169:348–53. [27] Hagi-Pavli E, Farthing PM, Kapas S. Stimulation of adhesion molecule expression in human endothelial cells (HUVEC) by adrenomedullin and corticotrophin. Am J Physiol Cell Physiol 2004;286:C239–46. [28] Hagi-Pavli E, Farthing PM, Henshaw FN, Kapas S. Adrenomedullin reduces VEGF-induced endothelial adhesion molecules and adhesiveness through a phosphatidylinositol 3 0 -kinase pathway. Arterioscler Thromb Vasc Biol 2003;23: 1377–83. [29] Lavie L, Kraiczi H, Hefetz A, Ghandour H, Perelman A, Hedner J, et al. Plasma vascular endothelial growth factor in sleep apnea syndrome: effects of nasal continuous positive air pressure treatment. Am J Respir Crit Care Med 2002;165:1624–8.
R ET
R
AC TE
[22] Yoshii T, Iwai M, Li Z, Chen R, Ide A, Fukunaga S, et al. Regression of atherosclerosis by amlodipine via anti-inflammatory and anti-oxidative stress actions. Hypertens Res 2006;29:457–66. [23] Toba H, Shimizu T, Miki S, Inoue R, Yoshimura A, Tsukamoto R, et al. Calcium channel blockers reduce angiotensin II-induced superoxide generation and inhibit lectin-like oxidized low-density lipoprotein receptor-1 expression in endothelial cells. Hypertens Res 2006;29:105–16. [24] Teramoto S, Kume H, Matsuse T, Ishii T, Miyashita A, Akishita M, et al. Oxygen administration improves the serum level of nitric oxide metabolites in patients with obstructive sleep apnea syndrome. Sleep Med 2003;4:403–7. [25] Kato M, Roberts-Thomson P, Phillips BG, Haynes WG, Winnicki M, Accurso V, et al. Impairment of endothelium-dependent vasodilation of resistance vessels in patients with obstructive sleep apnea. Circulation 2000;102:2607–10.
87