阻塞性睡眠呼吸中止症的臨床表型、分子機轉及治療性介入

Study on Clinical Phenotyping, Molecular Mechanism, and Therapeutic Intervention of Obstructive Sleep Apnea

李佩玲(Peilin Lee)

指導教授 ： 陳健尉 ； 余忠仁

國立臺灣大學/醫學院/臨床醫學研究所/博士(2012年)

https://doi.org/10.6342/NTU.2012.03410

摘要

阻塞性睡眠呼吸中止症 (obstructive sleep apnea，OSA)是一個常見疾病，其機制為睡眠時肌肉張力下降，造成上呼吸道塌陷，氣流阻滯以及血氧降低，進而引起慢性間歇性缺氧及睡眠片段。其臨床症狀包括打鼾，睡不飽，目睹性呼吸停止，高血壓以及日間嗜睡。整夜睡眠多項生理檢查(overnight polysomnography，PSG) 為目前OSA 診斷標準，以每小時呼吸停止次數(apnea-hypopnea index，AHI)為評量OSA 嚴重度的指標，但其與OSA 臨床嚴重度無法有很好的關聯。具有相同的AHI的病患，其症狀可以從很輕微到很嚴重。OSA 併發症包括心血管疾病、神經認知異常，及代謝異常。而且常合併肥胖引起的併發症。OSA 引起心血管疾病的可能機制包括自由基(reactive oxidative stress ，ROS)、內皮細胞功能失調、胰島素抗性、全身性發炎以及肥胖。ROS 能活化白血球，促進發炎物質如TNF-α及hsCRP 的分泌，以及傷害內皮細胞，最後引起動脈粥狀硬化以及血管病變。
愈來愈多證據顯示基因影響OSA 的形成與併發症的產生。許多研究嘗試釐清候選基因，如ACE gene I/D polymorphism，與OSA 的關聯，但研究結果卻不一致。OSA 是一個複雜性基因疾病，其phenotyping 包括高度表型及中度表型。前者為呼吸相關的障礙如AHI，後者則分為髗顏特徵及上呼吸道解剖位置、呼吸驅動力及上呼吸道塌陷度、醒睡週期的控制及嗜睡感受力，以及體脂肪堆積及代謝症候群。為了釐清基因型對表型的影響，我們探討台灣家族congenital central hypoventilationsyndrome (CCHS) 的多變臨床表型，從新生兒因呼吸衰竭致死，到成人從無症狀到清醒及睡眠時皆有換氣低下。存活家族成員的基因篩檢，確認在三位成人發作的CCHS，具有PHOX2B gene 25 repeat polyalanine expansions (20/25 genotype)。為釐清ACE I/D polymorphism 跟OSA 關聯，我們整合分析10 個研究，結果顯示ACEI/D polymorphism 跟罹患OSA 風險無顯著關聯，即使去除掉種族、OSA 患者來源、及高血壓的干擾，ACE I/D genotype 和allele frequency 與OSA 風險仍無顯著關聯。連續陽壓呼吸器(continuous positive airway pressure，CPAP)目前為OSA 治療首選，可以改善嗜睡、血壓、代謝異常以及生活品質。CPAP 治療後可降低OSA 患者心血疾管風險，然而經由何種分子機制卻未明。為釐清CPAP 對全身性發炎的效果，我們利用一雙盲、隨機、安慰劑控制，平行的試驗，來檢驗在重度OSA 病患，12 星期CPAP 治療對TNF-α、hsCRP，及內臟脂肪的效果。結果顯示即使CPAP可以改善嗜睡，卻無法改變TNF-α和hsCRP 濃度以及內臟脂肪量。本實驗結果暗示CPAP 減低OSA 心血管併發症的機制，應該非經由影響TNF-α、hsCRP，及內臟脂肪的量。
迄今有幾個研究利用基因微陣列技術像RNA oligomicroarray 來尋找與分子機制相對應的基因表現。結果顯示一些表現差異的基因，與發炎、ROS 的調控以及細胞週期等生物路徑相關。為了進一步找出其他與OSA 相關的候選基因以及生物路徑，我們利用oligomicroarray 技術，比較重度OSA 病患CPAP 治療前後，表現差異的基因以及牽涉的生物路徑，並利用此候選基因來建立基因模式以預測OSA病患的預後。最後我們確認了37 個牽涉在6 個生物路徑的基因。此6 個生物路徑包括包括氧化還原、 細胞訊息傳導、 細胞凋亡、細胞沾接及能動性、 細胞週期，及細胞激素。我們進一步用此37 基因表現量，建立三個模式分別來預測基準線時OSA 相關併發症，以及對4 星期 CPAP 及12 星期CPAP 治療反應。
總結目前的研究到達了以下目標: (1) 釐清基因型對表型的影響; (2) 釐清候選基因與OSA的關聯; (3)釐清CPAP 治療對全身性發炎與內臟脂肪的效果; (4)找出牽涉在OSA 生物路徑的的候選基因，並且利用這些候選基因來建立了基因模式以預測OSA 的預後。

關鍵字

心血管疾病 ； 連續陽壓呼吸器 ； 睡眠呼吸中止症 ； 睡眠多項生理檢查 ； 基因型

並列摘要

Obstructive sleep apnea (OSA) is characterized with recurrent collapse of upper airway during sleep resulting in hypoxia and sleep fragmentation. Patients of OSA might have symptoms like snoring, non-restorative sleep, witnessed apnea, hypertension and excessive daytime sleepiness. Currently, polysomnography is the gold standard for diagnosing OSA and the apnea-hypopnea index (AHI) is the parameters to indicate the severity of OSA. However, AHI poorly correlated with clinical severity of OSA, where the symptoms of patients with the identical AHI could vary from minimal to striking. The sequels of OSA include cardiovascular diseases, metabolic disorders, and neurocognitive dysfunctions. Untreated moderate-severe OSA is associated with increased risk of fatal and non-fatal cardiovascular events. Several mechanisms have been linked to the cardiovascular sequel and OSA, which included the production of reactive oxidative stress (ROS), endothelial dysfunction, insulin resistance, systemic inflammation, and obesity. ROS could activate leukocytes and promote productions of pro-inflammatory mediators, like TNF-α, hsCRP, and injure the endothelium, which eventually led to the progressions of atherosclerotic plaques and vasculopathy.

The growing evidence showed that genetic basis contributed the development of OSA and its sequel. Currently, many studies tried to determine the association of candidate genes, like angiotensin converting enzyme insertion and deletion (ACE I/D) polymorphism, with OSA through association studies. However, the results were conflicting. The OSA is complex genetic disease and its phenotyping include high level and intermediate level. The former indicates the AHI, and later includes craniofacial morphology, ventilator control, obesity, and sleepiness vulnerability. To clarify the influence of genotyping on phenotyping, we reported a Chinese family with congenital central hypoventilation syndrome (CCHS) that had a clinical spectrum ranging from newborn fatality (secondary to respiratory failure) to adulthood that was either asymptomatic or with hypoventilation while awake. Genetic analysis was used to confirm the presence of the PHOX2B expansion mutation. Moreover, to clarify the association between ACE I/D polymorphisms and OSA, we undertook a meta-analysis on all studies published in this area. The meta-analysis has not demonstrated an association between the ACE I/D polymorphism and OSA susceptibility irrespective of ethnicity, population sample or the presence/absence of co-morbid hypertension. Till now, continuous positive airway pressure (CPAP) is the best treatment for OSA. CPAP can effectively improve daytime sleepiness, functional status, blood pressure, metabolic abnormalities, and quality of life. CPAP treatment has been demonstrated to reduce the risk of cardiovascular sequel of OSA. However, the exact mechanism has not been fully uncovered. To investigate the impact of CPAP on the systemic inflammation, we conducted a double-blind, randomised, placebo-controlled trial to investigate the effects of 12-week CPAP treatment on TNF-α, hsCRP, and visceral fat. The results showed 12-week CPAP treatment does not modify TNF-α and hsCRP levels, and visceral fat in typical patients with severe OSA, despite significant improvement in objective sleepiness. The results suggested CPAP may improve cardiovascular consequences of OSA through mechanism other than modifying the level of TNF-α and hsCRP, and visceral fat.

Nowadays, a couple of studies tried to genome-wide profiled the candidate genes involved in the biologic pathway of OSA. Biologic pathways corresponding to the candidate genes ever identified included pathway of inflammation, ROS, and cell cycle. To further exploring other candidate genes and biologic pathways involved, we profiled genes differentially expressed before and after CPAP treatment with oligomicroarray. Furthermore, the expressions of candidate genes were used to construct the gene-signature model to predict outcome of OSA. Finally, 37 candidate genes involved in six biologic pathways of OSA including oxidative phosphorylation, cell signaling, apoptosis, cellular adhesion and motility, cell cycle, and cytokine/chemokine were identified. Three models were constructed to predict the sequel and response to 4-week and 12-week CPAP treatment, respectively.

In conclusion, the results of the present studies achieves a couple of aims, including (1) Investigating the influence of genotyping on phenotyping; (2) Clarifying the association between candidate genes and OSA; (3) Investigating the CPAP effect on systemic inflammation and visceral obesity; (4) Genome-wide identifying the candidate genes involved in the biologic pathways and construction of the outcome-prediction model.

並列關鍵字

Cardiovascular disease ； Continuous positive airway pressure ； Genotyping ； Phenotyping ； Sleep Apnea

參考文獻

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