No association between the ApoE ε2 and ε4 alleles and the risk of obstructive sleep apnea: A systematic review and meta-analysis

Relationships between apolipoprotein E and insulin resistance in patients with obstructive sleep apnoea: a large-scale cross-sectional study

BACKGROUND

Obstructive sleep apnoea (OSA) is commonly associated with insulin resistance (IR) and dyslipidaemia. Apolipoprotein E (APOE) plays important roles in lipid metabolism. The study aimed to disentangle the multifactorial relationships between IR and APOE based on a large-scale population with OSA.

METHODS

A total of 5,591 participants who underwent polysomnography for OSA diagnosis were finally enrolled. We collected anthropometric, fasting biochemical and polysomnographic data for each participant. Linear regression analysis was performed to evaluate the relationships between APOE, IR, and sleep breathing-related parameters. Logistic regression, restricted cubic spline (RCS) and mediation analyses were used to explore relationships between APOE and IR in patients with OSA.

RESULTS

Increasing OSA severity was associated with greater obesity, more obvious dyslipidaemia, and higher levels of APOE and IR. APOE was positively correlated with the apnoea-hypopnoea index (AHI), oxygen desaturation index (ODI) and microarousal index (MAI) even after adjusting for age, sex, body mass index, and smoking and drinking levels (β = 0.107, β = 0.102, β = 0.075, respectively, all P < 0.001). The risks of IR increased from the first to fourth quartiles of APOE (odds ratio (OR) = 1.695, 95% CI: 1.425-2.017; OR = 2.371, 95% confidence interval (CI): 2.009-2.816; OR = 3.392, 95% CI: 2.853-4.032, all P < 0.001) after adjustments. RCS analysis indicated non-linear and dose response relationships between APOE, AHI, ODI, MAI and insulin resistance. Mediation analyses showed that HOMA-IR explained 9.1% and 10% of the association between AHI, ODI and APOE. The same trends were observed in men, but not in women.

CONCLUSIONS

This study showed that APOE is a risk factor for IR; moreover, IR acts as a mediator between OSA and APOE in men. APOE, IR, and OSA showed non-linear and multistage relationships. Taken together, these observations revealed the complex relationships of metabolic disorders in patients with OSA, which could lead to the development of new treatment modalities and a deeper understanding of the systemic impact of OSA.

Respiratory Dysfunction in Alzheimer's Disease-Consequence or Underlying Cause? Applying Animal Models to the Study of Respiratory Malfunctions

Alzheimer's disease (AD) is a neurodegenerative brain disease that is the most common cause of dementia among the elderly. In addition to dementia, which is the loss of cognitive function, including thinking, remembering, and reasoning, and behavioral abilities, AD patients also experience respiratory disturbances. The most common respiratory problems observed in AD patients are pneumonia, shortness of breath, respiratory muscle weakness, and obstructive sleep apnea (OSA). The latter is considered an outcome of Alzheimer's disease and is suggested to be a causative factor. While this narrative review addresses the bidirectional relationship between obstructive sleep apnea and Alzheimer's disease and reports on existing studies describing the most common respiratory disorders found in patients with Alzheimer's disease, its main purpose is to review all currently available studies using animal models of Alzheimer's disease to study respiratory impairments. These studies on animal models of AD are few in number but are crucial for establishing mechanisms, causation, implementing potential therapies for respiratory disorders, and ultimately applying these findings to clinical practice. This review summarizes what is already known in the context of research on respiratory disorders in animal models, while pointing out directions for future research.

Variants of candidate genes associated with the risk of obstructive sleep apnea

BACKGROUND

The researches on the associations between different candidate genes and obstructive sleep apnea (OSA) are inconsistent. Here, we performed a comprehensive qualitative and quantitative analysis to estimate the contribution of variants from candidate genes to the risk of OSA.

METHODS

Qualitative analysis was conducted to find the relationships for all included genes. Then, quantitative analysis of both allele models and genotype models was applied to evaluate the risk variants for OSA. Furthermore, a similar analysis was performed in different ethnic groups.

RESULTS

We included 152 publications containing 75 genes for qualitative analysis. Among them, we included 93 articles containing 28 variants from 16 genes for quantitative analysis. Through allele models, we found 10 risk variants for OSA (rs1801133 of MTHFR, ɛ4 of ApoE, -1438G/A of 5-HT2A, -308G/A of TNF-α, Pro1019Pro of LEPR, rs1130864 and rs2794521 of CRP, D/I of ACE, LPR and VNTR of 5-HTT) with the ORs of 1.21-2.07 in global population. We found that the variant of ɛ2 of ApoE could uniquely decrease the risk of OSA in the East Asian subgroup, while the other 6 variants, including ɛ4 in ApoE, -308G/A in TNF-α, Pro1019Pro in LEPR, D/I in ACE, LPR and VNTR in 5-HTT, could increase the risk of OSA. As for the European subpopulation, we only found that -308G/A in TNF-α could increase the risk for OSA.

CONCLUSIONS

Eleven variants from the candidate genes are associated with the risk of OSA, which also show ethnicity differences in East Asian and European subgroups.

Obstructive Sleep Apnea and Its Treatment in Aging: Effects on Alzheimer's disease Biomarkers, Cognition, Brain Structure and Neurophysiology

Here we review the impact of obstructive sleep apnea (OSA) on biomarkers of Alzheimer's disease (AD) pathogenesis, neuroanatomy, cognition and neurophysiology, and present the research investigating the effects of continuous positive airway pressure (CPAP) therapy. OSA is associated with an increase in AD markers amyloid-β and tau measured in cerebrospinal fluid (CSF), by Positron Emission Tomography (PET) and in blood serum. There is some evidence suggesting CPAP therapy normalizes AD biomarkers in CSF but since mechanisms for amyloid-β and tau production/clearance in humans are not completely understood, these findings remain preliminary. Deficits in the cognitive domains of attention, vigilance, memory and executive functioning are observed in OSA patients with the magnitude of impairment appearing stronger in younger people from clinical settings than in older community samples. Cognition improves with varying degrees after CPAP use, with the greatest effect seen for attention in middle age adults with more severe OSA and sleepiness. Paradigms in which encoding and retrieval of information are separated by periods of sleep with or without OSA have been done only rarely, but perhaps offer a better chance to understand cognitive effects of OSA than isolated daytime testing. In cognitively normal individuals, changes in EEG microstructure during sleep, particularly slow oscillations and spindles, are associated with biomarkers of AD, and measures of cognition and memory. Similar changes in EEG activity are reported in AD and OSA, such as "EEG slowing" during wake and REM sleep, and a degradation of NREM EEG microstructure. There is evidence that CPAP therapy partially reverses these changes but large longitudinal studies demonstrating this are lacking. A diagnostic definition of OSA relying solely on the Apnea Hypopnea Index (AHI) does not assist in understanding the high degree of inter-individual variation in daytime impairments related to OSA or response to CPAP therapy. We conclude by discussing conceptual challenges to a clinical trial of OSA treatment for AD prevention, including inclusion criteria for age, OSA severity, and associated symptoms, the need for a potentially long trial, defining relevant primary outcomes, and which treatments to target to optimize treatment adherence.

Obstructive sleep apnea and hypertriglyceridaemia share common genetic background: Results of a twin study

Obstructive sleep apnea is associated with an increased risk of hypertension, diabetes and dyslipidaemia. Both obstructive sleep apnea and its comorbidities are at least partly heritable, suggesting a common genetic background. Our aim was to analyse the heritability of the relationship between obstructive sleep apnea and its comorbidities using a twin study. Forty-seven monozygotic and 22 dizygotic adult twin pairs recruited from the Hungarian Twin Registry (mean age 51 ± 15 years) attended an overnight diagnostic sleep study. A medical history was taken, blood pressure was measured, and blood samples were taken for fasting glucose, total cholesterol, triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol and lipoprotein (a). To evaluate the heritability of obstructive sleep apnea and its comorbidities bivariate analysis was performed with an adjustment for age, gender, body mass index (BMI) and smoking after false discovery rate correction and following exclusion of patients on lipid-lowering and antidiabetic medications. There was a significant correlation between indices of obstructive sleep apnea severity, such as the apnea-hypopnea index, oxygen desaturation index and percentage of sleep time spent with oxygen saturation below 90%, as well as blood pressure, serum triglyceride, lipoprotein (a) and glucose levels (all p < .05). The bivariate analysis revealed a common genetic background for the correlations between serum triglyceride and the oxygen desaturation index (r = .63, p = .03), as well as percentage of sleep time spent with oxygen saturation below 90% (r = .58, p = .03). None of the other correlations were significantly genetically or environmentally determined. This twin study demonstrates that the co-occurrence of obstructive sleep apnea with hypertriglyceridaemia has a genetic influence and heritable factors play an important role in the pathogenesis of dyslipidaemia in obstructive sleep apnea.

Evidence for a contribution of the APOE (but not the ACE) gene to the sleep profile of non-demented elderly adults

This study aims to investigate alleles of the human apolipoprotein E (APOE) and of the angiotensin-converting enzyme (ACE) genes as risk factors for poor quality of sleep in elderly individuals with no major cognitive decline. This cross-sectional, analytical study was conducted with 163 participants aged 75 years in average and 85% female. Sociodemographic, anthropometric and clinical data were gathered, and sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) and the Epworth scale, with patient followed for years prior to these evaluations to rule out onset of major mental disorders. Genotyping of classic polymorphic sites for the ApoE (rs429358 and rs7412) and the ACE (rs4646994) genes used peripheral DNA. A total of 63% of the subjects reported poor quality of sleep assessed by the PSQI whereas 54 (33%) reported daytime sleepiness through the Epworth scale. A significant correlation was observed between APOE and PSQI, with a greater frequency of the poor nighttime sleep quality phenotype among ε2 carriers, whereas no correlation was found among any of the sleep scores and the ACE genotypes. Thus, we suggest a correlation between APOE alleles and scale-assessed sleep quality scores in older adults, with no implications for ACE alleles, in a context devoid of cognitive impairment.

Biomarkers of dementia in obstructive sleep apnea

Epidemiologic and mechanistic evidence is increasingly supporting the notion that obstructive sleep apnea is a risk factor for dementia. Hence, the identification of patients at risk of cognitive decline due to obstructive sleep apnea may significantly improve preventive strategies and treatment decision-making. Cerebrospinal fluid and blood biomarkers obtained through genomic, proteomic and metabolomic approaches are improving the ability to predict incident dementia. Therefore, fluid biomarkers have the potential to predict vulnerability to neurodegeneration in individuals with obstructive sleep apnea, as well as deepen our understanding of pathophysiological processes linking obstructive sleep apnea and dementia. Many fluid biomarkers linked to Alzheimer's disease and vascular dementia show abnormal levels in individuals with obstructive sleep apnea, suggesting that these conditions share common underlying mechanisms, including amyloid and tau protein neuropathology, inflammation, oxidative stress, and metabolic disturbances. Markers of these processes include amyloid-β, tau proteins, inflammatory cytokines, acute-phase proteins, antioxydants and oxidized products, homocysteine and clusterin (apolipoprotein J). Thus, these biomarkers may have the ability to identify adults with obstructive sleep apnea at high risk of dementia and provide an opportunity for therapeutic intervention. Large cohort studies are necessary to establish a specific fluid biomarker panel linking obstructive sleep apnea to dementia risk.

Apolipoprotein E ɛ2/ɛ3/ɛ4 variant in association with obstructive sleep apnoea and lipid profile: A meta-analysis

Objective

A meta-analysis of the association between haplotypical variants of the apolipoprotein E (APOE) gene (ɛ2/ɛ3/ɛ4) and obstructive sleep apnoea (OSA) risk and changes in lipid profile.

Methods

Electronic databases were searched to retrieve articles that provided data on APOE gene ɛ2/ɛ3/ɛ4 variants in patients with OSA and healthy controls. Data were extracted from eligible articles and statistical analyses were performed.

Results

The meta-analysis included 14 articles involving 19 study populations (3198 patients and 6031 controls). There was no significant association between the presence of the ɛ4 allele and OSA risk. The presence of ɛ4 was associated with significantly increased total cholesterol and decreased high-density lipoprotein cholesterol, compared with ɛ4 allele negative individuals. There was a low probability of publication bias but significant heterogeneity.

Conclusions

There was no association between APOE ɛ2/ɛ3/ɛ4 and OSA susceptibility. The presence of APOE ɛ4 was associated with changes in lipid profile.