Plasma homocysteine levels in obstructive sleep apnea: association with cardiovascular morbidity

Association between elevated homocysteine levels and obstructive sleep apnea hypopnea syndrome: a systematic review and updated meta-analysis

Objective

This study aimed to distinguish between healthy controls and patients with OSAHS regarding homocysteine (HCY) levels and investigate how individuals with OSAHS respond to continuous positive airway pressure ventilation (CPAP) in terms of serum and plasma HCY levels.

Methods

To ascertain published articles about OSAHS, an exhaustive search was performed across medical databases, encompassing PubMed, Web of Science, EMBASE, CNKI, and Cochrane Library, until January 2, 2024. This study reviewed the literature regarding HCY levels in individuals with OSAHS and control groups, HCY levels under pre- and post-CPAP treatment, the Pearson/Spearman correlation coefficients between HCY levels and apnea-hypopnea index (AHI), and the hazard ratio (HR) of HCY levels concerning the occurrence of major adverse cerebrocardiovascular events (MACCEs) in patients with OSAHS. Meta-analyses were performed using weighted mean difference (WMD), correlation coefficients, and HR as effect variables. The statistical analysis was conducted using the R 4.1.2 and STATA 11.0 software packages.

Results

In total, 33 articles were selected for the final analysis. The OSAHS group exhibited significantly higher serum/plasma HCY levels than the control group (WMD = 4.25 μmol/L, 95% CI: 2.60-5.91, P< 0.001), particularly among individuals with moderate and severe OSAHS. Additionally, subgroup analysis using mean age, ethnicity, mean body mass index, and study design type unveiled significantly elevated levels of HCY in the serum/plasma of the OSAHS group compared to the control group. CPAP treatment can significantly decrease serum/plasma HCY levels in patients with OSAHS. Moreover, elevated HCY levels in individuals with OSAHS could be one of the risk factors for MACCEs (adjusted HR = 1.68, 95% CI = 1.10-2.58, P = 0.017). AHI scores show a positive correlation with serum/plasma HCY levels.

Conclusion

Patients with OSAHS had elevated serum/plasma HCY levels compared to healthy controls; however, CPAP therapy dramatically decreased HCY levels in patients with OSAHS. In patients with OSAHS, elevated HCY levels were linked with an increased risk of MACCEs, and HCY was positively connected with AHI values. HCY levels may serve as a useful clinical indicator for determining the severity and efficacy of OSAHS treatments.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42024498806.

Homocysteine as a predictor of apnea-hypopnea index in obstructive sleep apnea: a longitudinal epidemiological study (EPISONO)

BACKGROUND

Obstructive sleep apnea (OSA) affects nearly 1 billion people globally, and has established links with cardiovascular and neurocognitive complications. Although it has some limitations, the apnea-hypopnea index (AHI) is commonly used to gauge OSA severity and therapeutic response. Homocysteine (Hcy) metabolism, when impaired, can elicit cellular senescence mechanisms that may be shared with OSA. Hence, our objective was to explore the role of Hcy concentrations both as a predictor of AHI values and as a potential risk factor for OSA.

METHODS

Involving 1042 volunteers aged 20 to 80 years, the initial study (2007) included polysomnographic evaluations, questionnaires on sleep and general health, as well as biochemical analyses. After an 8-year interval, 715 participants from the initial study were invited for a follow-up assessment in 2015.

RESULTS

Our findings showed that Hcy was a predictor for an increased AHI, and AHI increased over time. Individuals with plasma Hcy concentrations ≥ 15 µmol/L experienced an average AHI increase of 7.43 events/hour ([beta coefficient] β = 7.43; 95%CI 2.73 to 12.13) over time, compared to those with plasma concentrations < 10 µmol/L. A similar trend was apparent in those with plasma Hcy concentrations between 10 ≥  and  < 15 µmol/L, who had an AHI increase with an average beta coefficient of 3.20 events/hour (95%CI 1.01 to 5.39) compared to those with plasma Hcy concentrations < 10 µmol/L.

CONCLUSIONS

In summary, our study suggests that increased plasma Hcy concentrations could be considered a risk factor for the development of OSA. These findings highlight that elevated plasma Hcy concentrations can predict the severity of OSA, underscoring their correlation with the AHI.

Prognostic implications of obstructive sleep apnea in patients with acute coronary syndrome stratified by homocysteine level: a prospective cohort study

BACKGROUND

Sporadic studies have examined the impact of OSA on ACS patients by homocysteine (Hcy) level. This study attempted to comprehensively evaluate the effects of the interaction between Hcy and OSA on long-term cardiovascular outcomes in ACS patients.

METHODS

In this prospective, large-scale cohort study, 2160 patients admitted for ACS were recruited to undergo overnight sleep monitoring. OSA was diagnosed when apnea-hypopnea index ≥ 15 events/h. Patients with normohomocysteinemia (NHcy) were defined as having serum Hcy ≤ 15 μmol/L, and the others had hyperhomocysteinemia (HHcy). The primary endpoint was major adverse cerebrocardiovascular event (MACCE), a composite of cardiovascular death, myocardial infarction, stroke, ischemia-driven revascularization and hospitalization for unstable angina and heart failure.

RESULTS

A total of 1553 eligible ACS patients (average age: 56.3 ± 10.5 years) were enrolled, among which 819 (52.7%) had OSA, and 988 (63.6%) were with NHcy. OSA did not significantly affect the level of Hcy. During a median follow-up of 2.9 (1.6, 3.5) years, after adjustment for clinical confounders, OSA was associated with increased risk for MACCE occurrence versus non-OSA ones in ACS patients with NHcy (adjusted hazard ratio [HR] = 1.36, 95% confidence interval [CI] 1.02-1.83, P = 0.039), but not in those with HHcy (adjusted HR = 0.92, 95%CI 0.62-1.36, P = 0.668). There was an absence of interaction between homocysteine level and OSA in relation to MACCE (interaction P = 0.106).

CONCLUSIONS

OSA was independently associated with worse prognosis in ACS patients with NHcy. Our study emphasized the necessity to identify potential presence of OSA in such a population.

TRIAL REGISTRATION

ClinicalTrials.gov; Number: NCT03362385; URL: www.

CLINICALTRIALS

gov .

Risk Factors and Brain Metabolic Mechanism of Sleep Disorders in Autoimmune Encephalitis

Background

Sleep disorders (SDs) in autoimmune encephalitis (AE) have received little attention and are poorly understood. We investigated the clinical characteristics, risk factors, and cerebral metabolic mechanism of SD in AE.

Methods

Clinical, laboratory, and imaging data were retrospectively reviewed in 121 consecutively patients with definite AE. The risk factors for SD in AE were estimated by logistic regression analysis. Group comparisons based on ¹⁸F-fluorodeoxy-glucose positron emission tomography (¹⁸F-FDG-PET) data were made between patients with and without SD, to further analyze potential brain metabolic mechanism of SD in AE.

Results

A total of 52.9% patients (64/121) with SD were identified. The multivariate logistic model analysis showed that smoking [odds ratio (OR), 6.774 (95% CI, 1.238-37.082); p = 0.027], increased Hamilton Depression scale (HAMD) score [OR, 1.074 (95% CI, 1.002-1.152); p = 0.045], hyperhomocysteinemia [OR, 2.815 (95% CI, 1.057-7.496); p = 0.038], elevated neuron-specific enolase (NSE) level [OR, 1.069 (95% CI, 1.007-1.135); p = 0.03] were independently correlated with higher risk of SD in AE patients. Contrastingly, high MoCA score [OR, 0.821 (95% CI, 0.752-0.896); p < 0.001] was associated with lower risk of SD in AE subjects. Compared to controls, AE patients had less total sleep time, less sleep efficiency, longer sleep latency, more wake, higher percent of stage N1, lower percent of stage N3 and rapid eye movement, and more arousal index in non-rapid eye movement sleep (p < 0.05 for all). Voxel-based group comparison analysis showed that, compared to patients without SD, patients with SD had increased metabolism in the basal ganglia, cerebellum, brainstem, median temporal lobe, thalamus, and hypothalamus [p < 0.05, false discovery rate (FDR) corrected]; decreased metabolism in superior frontal gyrus, medial frontal gyrus, and posterior cingulate cortex (p < 0.001, uncorrected). These results were confirmed by region of interest-based analysis between PET and sleep quality.

Conclusion

Smoking, increased HAMD score, hyperhomocysteinemia, and elevated NSE level were correlated with higher risk of SD. High MoCA score was associated with lower risk of SD in AE subjects. Moreover, a widespread metabolic network dysfunction may be involved in the pathological mechanism of SD in AE.

[The role of biomarkers in the detection of the OSA syndrome. A narrative review of the literature]

INTRODUCTION

Obstructive sleep apnoea (OSA) is a common sleep-related breath disorder associated with cardiovascular and cerebrovascular complications, such as hypertension, arrhythmia, coronary artery disease and stroke. Unfortunately, OSA is underdiagnosed.

BACKGROUND

Because of its clinical and therapeutic variability, OSA could benefit a personalized medicine approach. Diagnosis with polysomnography is expensive and access is limited. Clinical scoring systems allow screening of OSA, but many limitations exist. Because of this, biomarkers could be useful for the detection of OSA.

OUTLOOK

Biomarkers specific to OSA would allow for better mass screening and more personalized treatment of the disease. This narrative review of the literature aims to summarize the biomarkers already described for the diagnosis of OSA and clarify both their advantages and limitations in daily practice.

CONCLUSIONS

Our review of the literature did not actually identify an ideal biomarker even if promising research is ongoing.

Advances and challenges in pursuing biomarkers for obstructive sleep apnea: Implications for the cardiovascular risk

Obstructive sleep apnea (OSA) is a common clinical condition associated with increased cardiovascular morbidity and mortality. Recent evidence from clinical studies and animal models suggest that OSA can promote cardiovascular disease by inducing autonomic, hemodynamic, inflammatory and metabolic dysregulation. However, most of the evidence addressing hard endpoints in humans is derived from observational studies. Several challenges have been noted in the pursuit of a comprehensive knowledge base about the impact of OSA including: 1) the precise mechanisms by which OSA causes metabolic and cardiovascular consequences are not clear, which limits our current ability to address potential targets in OSA; 2) several patients with OSA, even with severe forms, present with no or mild daytime symptoms. Beyond the obvious challenges for obtaining good adherence for conventional OSA treatments, there is evidence that symptomatic vs. asymptomatic patients with OSA do not necessarily have the same metabolic and cardiovascular outcomes; and 3) the cardiovascular response to OSA treatment may vary even in those patients with good adherence. In this scenario, there is an obvious need to develop biomarkers in the OSA research area. This review focuses on describing the advances that have occurred so far in exploring potential OSA biomarkers with clear emphasis for the cardiovascular risk. Particular attention will be devoted to discuss molecular biomarkers including the potential role of microRNAs, proteomics and metabolomics. We also discuss the major challenges and perspectives in this growing research field.

Sleep apnea and risk of traumatic brain injury and associated mortality and healthcare costs: a population-based cohort study

Background

The objective of this study was aimed to investigate whether sleep apnea patients had a higher risk of traumatic brain injury.

Methods

Data were collected from the Taiwan Longitudinal Health Insurance Database during the period of 2000-2012. The study cohort comprised 6,456 patients aged ≥20 years with a first diagnosis of sleep apnea. The primary outcome was the incidence of traumatic brain injury. Kaplan-Meier survival analysis and Cox proportional-hazards modeling were used.

Results

After adjustments for associated comorbidities and hypnotic medications, sleep apnea patients were associated with a 1.19-fold higher risk of traumatic brain injury (95% CI, 1.07-1.33) compared with patients without sleep apnea. Sleep apnea patients who took benzodiazepine (BZD) had a 1.30-fold increased risk of traumatic brain injury compared with patients without sleep apnea (95% CI, 1.14-1.49). However, this risk was not statistically significant, with a 1.03-fold risk of traumatic brain injury in sleep apnea patients without BZD use (95% CI, 0.84-1.25) compared with patients without sleep apnea. Compared with patients without sleep apnea, the risk of traumatic brain injury in sleep apnea patients aged 65-79 years old was higher (adjusted hazard ratio, 1.36; 95% CI, 1.06-1.74).

Conclusions

Sleep apnea patients, regardless of hypnotic use, had a higher risk of traumatic brain injury compared with patients without sleep apnea.

Concurrent Presence of Obstructive Sleep Apnea and Elevated Homocysteine Levels Exacerbate the Development of Hypertension: A KoGES Six-year Follow-up Study

Accumulating evidence has revealed that obstructive sleep apnea (OSA) and high homocysteine (Hcy) levels play important roles in the increased risk of hypertension and cardiovascular disease. We investigated whether the presence of elevated Hcy levels among individuals with OSA increase the risk of hypertension in a cohort study. A total of 1825 participants were selected from the cohort study. A high homocysteine level (Hcy) was defined as those in the 75th percentile of Hcy levels of the study cohort. The prevalence of hypertension was higher among subjects with OSA and high Hcy levels than among the other groups stratified by the presence of OSA and high Hcy levels. The incidence of hypertension at 6-year follow-up was: Hcy[-]/OSA[-] vs. Hcy[+]/OSA[-] vs. Hcy[-]/OSA[+] vs. Hcy[+]/OSA[+], 14.2% vs. 19.8% vs. 24.2% vs. 36.1%. After adjusting for confounding factors, subjects with OSA and high Hcy levels had a 1.86-fold risk of developing hypertension compared to those without OSA and high Hcy levels. Moderate to severe OSA group with the highest tertile of Hcy levels had a 2.31-fold increased risk of developing hypertension. Interaction between Hcy and OSA on development of hypertension was significant, suggesting that these conditions may constitute an important determinant.

Effects of positive airway pressure therapy on cardiovascular and metabolic markers in males with obstructive sleep apnea

INTRODUCTION

Obstructive sleep apnea syndrome (OSAS) is associated with cardiovascular/metabolic complications. Some analytical parameters (homocysteine, glycemic and lipidic profiles) are recognized markers of these consequences. Limited data is available on the association of these markers and OSAS's severity/response to positive airway pressure therapy (PAP).

MATERIAL AND METHODS

In this prospective study we analyzed polysomnographic and analytical data of male patients admitted to sleep laboratory. The aim was to evaluate metabolic/cardiovascular markers in snorers and OSAS patients, to relate with sleep parameters and PAP response. One-hundred and three patients were included, and 73 (71%) were OSAS patients. OSAS patients were similar to snorers except for higher body mass index (BMI) and dyslipidemia. Severe OSAS patients showed higher glycemia, HbA1c, insulin, and insulin resistance, and lower HDL cholesterol in comparison to mild-moderate (p<0.05, p<0.05, p<0.001, p<0.001, p<0.05, respectively). Glycemic profile and triglycerides were slightly correlated with OSAS severity. 46 OSAS patients were submitted to 6 months of PAP, with a statistical decrease in mean values of homocysteine, glycemia, total and LDL cholesterol (p<0.05, p<0.05, p<0.05, respectively), and in glycemia and LDL cholesterol in severe group only (p<0.05, p<0.05, respectively).

RESULTS

This study demonstrated an association between glucose metabolism parameters and triglycerides with OSAS severity underlying the complexity of the process leading to cardiovascular/metabolic complications in this disorder. Moreover, homocysteine, glycemic and lipidic profiles changed significantly after 6 months of PAP therapy in OSAS, supporting its cardiovascular and metabolic protective effect.

CONCLUSION

Our study has reinforced the importance of analytical cardiovascular/metabolic evaluation as complementary tool of diagnosis/treatment response in OSAS.

Predictors of obstructive sleep apnoea in patients admitted for acute coronary syndrome

Identifying undiagnosed obstructive sleep apnoea (OSA) patients in cardiovascular clinics could improve their management. Aiming to build an OSA predictive model, a broad analysis of clinical variables was performed in a cohort of acute coronary syndrome (ACS) patients.

Sociodemographic, anthropometric, life-style and pharmacological variables were recorded. Clinical measures included blood pressure, electrocardiography, echocardiography, blood count, troponin levels and a metabolic panel. OSA was diagnosed using respiratory polygraphy. Logistic regression models and classification and regression trees were used to create predictive models.

A total of 978 patients were included (298 subjects with apnoea–hypopnoea index (AHI) <15 events·h−1and 680 with AHI ≥15 events·h−1). Age, BMI, Epworth sleepiness scale, peak troponin levels and use of calcium antagonists were the main determinants of AHI ≥15 events·h−1(C statistic 0.71; sensitivity 94%; specificity 24%). Age, BMI, blood triglycerides, peak troponin levels and Killip class ≥II were determinants of AHI ≥30 events·h−1(C statistic of 0.67; sensitivity 31%; specificity 86%).

Although a set of variables associated with OSA was identified, no model could successfully predict OSA in patients admitted for ACS. Given the high prevalence of OSA, the authors propose respiratory polygraphy as a to-be-explored strategy to identify OSA in ACS patients.

Daytime sleepiness is associated with hyperhomocysteinemia in rural area of China: A cross-sectional study

OBJECTIVE

To ascertain whether sleep abnormalities including daytime sleepiness, snoring, apnea, sleep disruption and sleep duration abnormity are significantly associated with hyperhomocysteinemia (Hhcy).

METHODS

A total of 5992 participants were involved in the cross-sectional study. Sleep abnormalities were evaluated by a structured questionnaire. Hhcy was defined as plasma levels of homocysteine ≥15μm/L.

RESULTS

After adjustment for age, gender, education, current smoking status and current drinking status, daytime sleepiness (OR, 1.597; 95%CI, 1.210-2.110, P=0.001), sleep duration <6h (OR, 1.273; 95%CI, 1.063-1.524, P=0.009) and sleep duration >8h (OR, 1.205; 95%CI, 1.065-1.364, P=0.003) were significantly associated with Hhcy. While snoring (OR, 1.065; 95%CI, 0.950-1.195, P=0.279), apnea (OR, 1.170; 95%CI, 0.924-1.482, P=0.193), and sleep disruption (OR, 1.065; 95%CI, 0.852-1.331, P=0.580) were not. After further adjustment for body mass index, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglyceride, total cholesterol, physical activity, diabetes, coronary heart disease, stroke, depression, glomerular filtration rate, hypertension and hyperuricemia, still the increased OR could be found in the daytime sleepiness group (OR, 1.569; 95%CI, 1.145-2.150, P=0.005). However, sleep duration <6h (OR, 1.067; 95%CI, 0.788-1.445, P=0.676) and sleep duration >8h groups (OR, 1.080; 95%CI, 0.883-1.320, P=0.453) were no longer significantly associated with Hhcy.

CONCLUSIONS

Daytime sleepiness, but not sleep duration abnormity, snoring, apnea and sleep disruption was an independent risk factor for Hhcy.

Quality of life, depression and dietary intake in Obstructive Sleep Apnea patients

BACKGROUND

The aim of this study was to analyze the association between depression, quality of life and dietary intake in newly diagnosed Obstructive Sleep Apnea (OSA) patients.

METHODS

From 153 eligible patients suffering from sleep disturbances, 64 met inclusion and exclusion criteria. The polysomnography was used for OSA diagnosis. The quality of life (QOL) was assessed by WHOQOL-BREF questionnaire, self-reported chronotype by morningness-eveningness questionnaire and level of depression by Beck's Depression Inventory. Blood pressure and parameters of glucose and lipid metabolism were assessed by routine methods. The dietary intake was evaluated by 24-hr dietary recalls.

RESULTS

Significantly negative associations were found between depression inventory and QOL. Better QOL for physical health and social relationships was observed in the "definitely morning" chronotype. The "morning type" of patients was positively related to the intake of fat, monounsaturated fatty acids and vitamin B12. Correlations between QOL and diastolic blood pressure, HDL-cholesterol, TG, fasting glucose, as well as protein and vitamin B6 intake were found.

CONCLUSIONS

In conclusion, both chornotype and depression influence QOL in OSA patients where morning type is associated with better physical health and social relationships and increase in depression index deteriorate physical health, psychological and social relationship QOL domains. QOL as well as depression and chornotype are also influenced by selected cardio-metabolic factors and dietary intake.

Sleepiness, inflammation and oxidative stress markers in middle-aged males with obstructive sleep apnea without metabolic syndrome: a cross-sectional study

BACKGROUND

The simultaneous occurrence of metabolic syndrome and excessive daytime sleepiness are very common in obstructive sleep apnea (OSA) patients. Both conditions, if present in OSA, have been reported to be associated with inflammation and disruption of oxidative stress balance that impair the cardiovascular system. To verify the impact of daytime sleepiness on inflammatory and oxidative stress markers, we evaluated OSA patients without significant metabolic disturbance.

METHODS

Thirty-five male subjects without diagnostic criteria for metabolic syndrome (Adult Treatment Panel III) were distributed into a control group (n = 10) (43 ± 10.56 years, apnea-hypopnea index - AHI 2.71 ± 1.48/hour), a non-sleepy OSA group (n = 11) (42.36 ± 9.48 years, AHI 29.48 ± 22.83/hour) and a sleepy OSA group (n = 14) (45.43 ± 10.06 years, AHI 38.20 ± 25.54/hour). Excessive daytime sleepiness was considered when Epworth sleepiness scale score was ≥ 10. Levels of high-sensitivity C-reactive protein, homocysteine and cysteine, and paraoxonase-1 activity and arylesterase activity of paraoxonase-1 were evaluated.

RESULTS

Patients with OSA and excessive daytime sleepiness presented increased high-sensitivity C-reactive protein levels even after controlling for confounders. No significant differences were found among the groups in paraoxonase-1 activity nor arylesterase activity of paraoxonase-1. AHI was independently associated and excessive daytime sleepiness tended to have an association with high-sensitivity C-reactive protein.

CONCLUSIONS

In the absence of metabolic syndrome, increased inflammatory response was associated with AHI and daytime sleepiness, while OSA was not associated with abnormalities in oxidative stress markers.

Serum nutritional biomarkers and their associations with sleep among US adults in recent national surveys

Background

The associations between nutritional biomarkers and measures of sleep quantity and quality remain unclear.

Methods

Cross-sectional data from the National Health and Nutrition Examination Surveys (NHANES) 2005–2006 were used. We selected 2,459 adults aged 20–85, with complete data on key variables. Five sleep measures were constructed as primary outcomes: (A) Sleep duration; (B) Sleep disorder; (C) Three factors obtained from factor analysis of 15 items and labeled as “Poor sleep-related daytime dysfunction” (Factor 1), “Sleepiness” (Factor 2) and “Sleep disturbance” (Factor 3). Main exposures were serum concentrations of key nutrients, namely retinol, retinyl esters, carotenoids (α-carotene, β-carotene, β-cryptoxanthin, lutein+zeaxanthin, lycopene), folate, vitamin B-12, total homocysteine (tHcy), vitamin C, 25-hydroxyvitamin D (25(OH)D) and vitamin E. Main analyses consisted of multiple linear, logistic and multinomial logit models.

Results

Among key findings, independent inverse associations were found between serum vitamin B-12 and sleep duration, 25(OH)D and sleepiness (as well as insomnia), and between folate and sleep disturbance. Serum total carotenoids concentration was linked to higher odds of short sleep duration (i.e. 5–6 h per night) compared to normal sleep duration (7–8 h per night).

Conclusions

A few of the selected serum nutritional biomarkers were associated with sleep quantity and quality. Longitudinal studies are needed to ascertain temporality and assess putative causal relationships.

The differences in homocysteine level between obstructive sleep apnea patients and controls: a meta-analysis

BACKGROUND

Studies have reported inconsistent findings regarding the relationship between obstructive sleep apnea (OSA) and homocysteine (HCY) level. This study aimed to assess the difference in plasma HCY level between OSA patients and controls by conducting a meta-analysis of published studies.

METHODS

Database of PubMed, SCI, and China National Knowledge Internet (CNKI) were comprehensively searched. Eligible studies regarding plasma HCY level in OSA patients were identified by two independent reviewers. RevMan (version 5.2) and STATA (version 12.0) were employed for data synthesis.

RESULTS

A total of 10 studies involving 432 subjects were included. Meta-analysis showed that plasma HCY levels in OSA group were 3.11 µmol/l higher than that in control group (95% confidence interval: 2.08 to 4.15, P<0.01). Subgroup analysis revealed a more significant differences between OSA patients and controls when average body mass index ≥ 30 (the total weighted mean difference (WMD) was 3.64), average age<50 (the total WMD was 3.96) and average apnea hypopnea index ≥ 35 (the total WMD was 4.54).

CONCLUSIONS

In this meta-analysis, plasma HCY levels were found to be higher in OSA patients compared to control subjects.

Circadian rhythm of homocysteine is hCLOCK genotype dependent

Homocysteine (Hcy) is known to be a prognostic marker for neurological, cardiovascular and cerebrovascular diseases and several other pathophysiological conditions. A sudden surge in Hcy can increase cardiovascular events. Hemodynamic modulations are known to be associated with individual's chronotype. Therefore, precise monitoring of Hcy is crucial for evaluating its impact on risk. The aim of the present study was to investigate the rhythmicity of Hcy under controlled dietary conditions and whether this rhythmicity is under the genetic control of circadian rhythm. Five subjects were selected from 200 Malayalam speaking healthy ethnic individuals who were screened for functionally critical variants of MTHFR and hCLOCK genes. MTHFR is the rate-limiting enzyme in the methionine cycle and critical for regulating Hcy levels while hCLOCK is a critical gene responsible in regulating the day and night cycles. Rhythmicity in Hcy levels were observed in all the subjects with a consensus on a morning nadir and an evening peak. Gender specific stratification of Hcy levels were observed among similar genotypes of MTHFR and hCLOCK genes. Variations from the conventional rhythmicity of Hcy were observed among similar genotypes of MTHFR and dissimilar hCLOCK genotypes. A reduced plasma Hcy in hCLOCK rs1801260 CC genotype individuals were observed in contrast to CT genotype individuals. The study tends to suggest that Hcy and body time are genetically interdependent and throws light on some of the previously unexplained reasons for variability in Hcy levels. A population specific variation of MTHFR and hCLOCK genes also highlights ethnicity specific risk management.

Association of plasma homocysteine with self-reported sleep apnea is confounded by age: results from the national health and nutrition examination survey 2005-2006

High levels of plasma homocysteine are implicated in the pathogenesis of cardiovascular diseases especially if accompanied by sleep apnea, but a direct pathogenetic link between plasma homocysteine levels and obstructive sleep apnea is debatable. This association can have far-reaching public health implications considering the inverse association between folate and plasma homocysteine. We used data from the 2005-2006 cycle of the National Health and Nutrition Examination Survey (NHANES) to test the hypothesized associations. Of the 4490 subjects included in analysis, 177 reported sleep apnea. Age-standardized and design-effect-corrected prevalence rates were differential across gender, plasma homocysteine, and red cell folate status. Plasma homocysteine was positively correlated with age (r = 0.38, P < 0.0001). Multivariate analyses using sociodemographic and clinical covariates demonstrated that plasma homocysteine levels retained their respective associations with self-reported sleep apnea in all models except when age was included as a covariate. Our results demonstrate that the claimed association of plasma homocysteine with sleep apnea may be confounded by age.

Association between plasma homocysteine levels and obstructive sleep apnoea in patients with ischaemic stroke

We aimed to investigate the association between plasma homocysteine and obstructive sleep apnoea (OSA) syndrome in patients with ischaemic stroke. A total of 102 patients with ischaemic stroke were classified into four OSA groups based on their apnoea-hypopnoea index (AHI): absent (AHI < 5/hour); mild (5-14/hour); moderate (15-30/hour); and severe (> 30/hour). The mean (± standard deviation) homocysteine levels in the four OSA groups were: absent, 8.98 ± 3.74 μmol/L; mild, 11.46 ± 3.31 μmol/L; moderate, 14.18 ± 4.36 μmol/L; and severe, 18.57 ± 4.56 μmol/L; and these differences were statistically significant (p < 0.001). The Pearson correlation analysis revealed a positive correlation between homocysteine levels and the severity of AHI (r = 0.482, p < 0.001). Multiple linear regression analysis showed that AHI and folate were independent predictors of homocysteine levels (R(2) = 0.539, p < 0.001, β for AHI = 0.259, β for folate = -0.400). In conclusion, the severity of OSA is significantly associated with elevated homocysteine levels in patients with ischaemic stroke, and this association is independent of other factors that cause elevation in homocysteine.

Metabolic syndrome, insulin resistance, fibrinogen, homocysteine, leptin, and C-reactive protein in obese patients with obstructive sleep apnea syndrome

OBJECTIVE

The prevalence of obstructive sleep apnea syndrome (OSAS) and metabolic syndrome is increasing worldwide, in part linked to epidemic of obesity. The purposes of this study were to establish the rate of metabolic syndrome and to compare fibrinogen, homocysteine, high-sensitivity C-reactive protein (hsCRP), leptin levels, and homeostasis model assessment insulin resistance (HOMA-IR) in the obese patients with and without OSAS.

METHODS

The study population included 36 consecutive obese patients with OSAS (23 males; mean age, 50.0 ±19.7 years), and 34 obese patients without OSAS (17 males; mean age, 49.7±11.1 years) were enrolled as control group. Metabolic syndrome was investigated; fibrinogen, homocysteine, CRP, and leptin levels were measured, and IR was assessed.

RESULTS

Metabolic syndrome was found in 17 (47.2%) obese OSAS patients, whereas only 29.4% of obese subjects had metabolic syndrome (P > 0.05). Obese patients with OSAS had significantly higher mean levels of triglyceride (P < 0.001), total-cholesterol (P = 0.003), low-density lipoprotein-cholesterol (P = 0.001), fasting glucose (P = 0.01), HOMA-IR (P <0.001), thyroid-stimulating hormone (P = 0.03), fibrinogen (P < 0.003), hsCRP (P <0.001), and leptin (P = 0.03) than control group . Besides, leptin level was positively correlated with waist (r = 0.512, P = 0.03) and neck circumferences (r = 0.547, P = 0.03), and fasting glucose (r = 0.471, P = 0.04) in OSAS patients, but not in obese subjects.

CONCLUSION

This study demonstrated that obese OSAS patients may have an increased rate of metabolic syndrome and higher levels of serum lipids, fasting glucose, IR, leptin, fibrinogen, and hsCRP than obese subjects without sleep apnea. Thus, clinicians should be encouraged to systematically evaluate the presence of metabolic abnormalities in OSAS and vice versa.

Distribution of common methylenetetrahydrofolate reductase gene mutations in patients with obstructive sleep apnoea

Homocysteine levels have been investigated in patients with obstructive sleep apnoea syndrome (OSAS), a syndrome associated with a high level of comorbid cardiovascular disease (CVD). While significant increases in homocysteine levels have been observed in OSAS patients with CVD, no increases have been noted in OSAS patients without CVD. This study was designed to investigate the methylenetetrahydrofolate reductase (MTHFR) gene, which is essential for homocysteine metabolism and has been shown to have a causal role in the development of CVD. Eighty subjects, 30 diagnosed with OSAS by polysomnography and 50 controls (healthy volunteers with no symptoms of OSAS) were enrolled. Two mutations in the MTHFR gene were investigated using polymerase chain reactions and restriction fragment length polymorphisms. No significant differences were found in mean age, body mass index, homocysteine levels, or MTHFR allele or genotype distributions between patient and control groups.

Association between serum homocysteine and oxidative stress in elderly patients with obstructive sleep apnea/hypopnea syndrome

OBJECTIVE

Elderly patients with obstructive sleep apnea/hypopnea syndrome (OSAHS) has a higher risk of cardiovascular and cerebrovascular disease. However, changes of homocysteine (Hcy) as markers of cardiovascular and cerebrovascular disease associated with OSAHS and their mechanism have not been elucidated so far. This study aims to investigate the changes of both serum Hey and oxidative stress and their possible links with OSAHS in elderly patients.

METHODS

Based on polysomnogram (PSG) and age, 83 patients with OSAHS were recruited and divided into elderly-OSAHS (n=32) and non-elderly OSAHS groups (n=51). Fifty two subjects without OSAHS were divided into elderly control (n=29) and non-elderly control groups (n=23). A total of 135 subjects were included in the present study. All subjects were recorded for PSG variables and the contents of homocysteine (Hcy), malonaldehyde (MDA), and glutathione (GSH) which were detected after sleep. Serum homocysteine was measured by cyclophorase. MDA and GSH were measured by spectrophotometer.

RESULTS

(1) The serum levels of Hcy showed significant difference among the four groups (P < 0.05). The concentrations of Hey in elderly OSAHS patients were higher than in other groups, while those in the elderly control group were higher than in the non-elderly control; the concentrations in the non-elderly OSAHS group were higher than in the non-elderly control. (2) The concentrations of MDA and GSH changed at an equal pace with Hey in the four groups. (3) Multielement linearity regression analysis indicated a statistically significant relationship between Hcy concentration and age, MDA, GSH, and apnea hypopnea index (AHI).

CONCLUSIONS

(1) The concentrations of Hey and oxidative stress have increased with advancing age. (2) The concentrations of Hey and oxidative stress have further increased in the elderly patients with OSAHS. (3) Oxidative stress might cause high-level serum Hey in the elderly patients with OSAHS.

Sleep apnea, respiratory cooling and thermoregulation

This article will suggest that moderate sleep apnea may have an adaptive benefit, the reduction of nocturnal, respiratory heat loss, that may have caused it to be selected for despite the associated disadvantages. Sleep apnea is caused by the collapse of the throat, specifically the pharyngeal airway, during sleep and can result in discomfort and hypoxia. The large size of the fleshy structures in the pharynx and hypotonicity of the pharyngeal musculature are what cause humans, and many other species of mammals, to be susceptible to apnea. There are many functional and anatomical parallels between sleep apnea and a well known, thermoregulatory response that minimizes respiratory cooling in the lower airways known as reflex bronchoconstriction. Bronchoconstriction involves the constriction of the inner airways, the bronchioles, in response to cold air, a reaction that acts to warm inspired air before it makes contact with the more sensitive lower airways and alveoli. Because air is colder at night and body temperature drops severely during sleep, sleep apnea may represent a similar protective, thermoregulatory adaptation. When the pharynx is collapsed, the diameter of the pharyngeal airway decreases, allowing increased intermolecular collisions between inspired air and the epithelial walls of the upper airway. An increase in the number of collisions facilitates the transference of both warmth and humidity to inspired air before it reaches the more sensitive lower airway resulting in the maintenance of internal, core temperature and alveolar heat retention. In fact, sleep apnea can be conceptualized as a functional reversal of the thermoregulatory process of panting, where the pharynx is highly dilated instead of collapsed. Given the disorder associated with sleep apnea, the absence of a disease state secondary to surgical correction, the fact that the disorder is exclusive to warm-blooded animals, the high proclivity for collapse documented in pregnant mothers, and the functional similarities between collapse and reflex bronchoconstriction, it appears that the phenomenon may represent an evolutionary trade-off that helped to minimize respiratory cooling.

A 1H magnetic resonance spectroscopy study in patients with obstructive sleep apnea

BACKGROUND AND PURPOSE

Repeated episodes of hypoxia, hypercapnia and transient blood pressure elevation in obstructive sleep apnea syndrome (OSAS) may damage neutral structures and induce cerebral metabolic impairment. This study aimed to determine the impact of OSAS on cerebral metabolites measured by (1)H magnetic resonance spectroscopy ((1)H -MRS).

METHODS

Twenty OSAS patients underwent standard overnight polysomnography and (1)H-MRS separately. Proton volumes of interest (VOIs) were placed in frontal and midtemporal regions bilaterally.

RESULTS

Significantly lower values of the N-acetylaspartate (NAA)/creatine (Cr) ratio were found in frontal regions (P < 0.004) compared with 20 age-matched control subjects. A significant increase in the myo-inositol (Ins)/Cr ratio was evident bilaterally in temporal and frontal regions (P < 0.00002 and P < 0.04). Choline (Cho)/Cr ratio values were also significantly greater in temporal regions (P < 0.00001). A significant negative correlation (r = -0.51, P < 0.03) was found between the apnea-hypopnea index (AHI) and NAA/Cr ratio in the frontal regions of OSAS patients.

CONCLUSIONS

Reduction in the NAA/Cr ratio in frontal regions of OSAS patients could be related to neural loss. Increase in the Cho/Cr ratio in temporal regions and Ins/Cr ratio in both frontal and temporal regions could be interpreted as evidence of membrane breakdown and reactive gliosis, respectively, consequent to repeated episodes of hypoxia in OSAS.

Increased erythrocyte adhesiveness and aggregation in obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea (OSA) is associated with an increased incidence of stroke and myocardial infarction as well as increased prothrombotic and inflammatory processes. Although erythrocyte adhesiveness/aggregation is known to be elevated in cardiovascular diseases, it has never been evaluated in OSA. The aim of this study was to examine the possible association of OSA and erythrocyte adhesiveness/aggregation.

METHODS

The study was conducted in the Sleep Laboratory of a tertiary university-affiliated medical center in 79 patients (age 57.1+/-12.9 years) with a diagnosis of OSA (apnea hypopnea index 41.2+/-25.9). Findings were compared with data on 1079 controls without clinical symptoms of OSA, matched for sex, age, and body mass index. Overnight polysomnography and blood sampling for erythrocyte sedimentation rate, levels of fibrinogen, high-sensitivity C-reactive protein, and erythrocyte adhesion/aggregation test consisting of measures of erythrocyte percentage and vacuum range on image analysis.

RESULTS

The study group had significantly higher values than controls of all three markers of inflammation (p<0.001 for erythrocyte sedimentation rate and fibrinogen; p=0.037 for C-reactive protein). Erythrocyte percentage was significantly lower in the sleep apnea group (84.05+/-15.97 vs. 90.79+/-11.23%, p<0.001), and vacuum range was significantly higher (8.22+/-7.98 vs. 4.63+/-4.05 microm, p<0.001), indicating stronger erythrocyte adhesion/aggregation. Both these factors were significantly correlated with erythrocyte sedimentation rate and to hs-CRP (percentage: r=-0.630; 0.258, p=0.005; 0.031; vacuum range: r=0.494; -0.328, p=0.001; 0.005 respectively).

CONCLUSION

OSA is associated with increased erythrocyte aggregation/adhesion, which is correlated with an increase in inflammation markers. These findings might help explain the increased cardiovascular morbidity in OSA.

Effect of continuous positive airway pressure treatment on serum cardiovascular risk factors in patients with obstructive sleep apnea-hypopnea syndrome

BACKGROUND

Serum levels of circulating markers associated with cardiovascular morbidity are elevated in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS). These factors are studied in patients mainly before the application of therapy with continuous positive airway pressure (CPAP), and the effects of CPAP treatment on them have not been thoroughly studied. Therefore, the aim of the study was to examine the effect of compliance to CPAP therapy on these factors.

METHODS

Patients with newly diagnosed OSAHS, nonsmokers, without comorbidities or medication use, at baseline and during the follow-up period, were included. Serum cardiovascular risk factors (ie, high-sensitivity C-reactive protein [hs-CRP], homocysteine, total cholesterol, triglycerides, high-density lipoprotein cholesterol [HDL-C], low-density lipoprotein cholesterol, apolipoprotein A-I [ApoA-I], and apolipoprotein B [ApoB]) were measured at baseline and 6 months after CPAP application. Patients were classified into the following three groups according to CPAP use: group 1 (n = 20), good compliance (>or= 4 h use per night); group 2 (n = 19), poor compliance (< 4 h use per night); and group 3 (n = 14), refusal of CPAP treatment.

RESULTS

Fifty-three patients (47 male patients and 6 female patients; mean [+/- SD] age, 46.09 +/- 10.87 years) were included in the study. In all groups, body mass index remained stable. In group 1, significant decreases in the levels of hs-CRP (p = 0.03), homocysteine (p = 0.005), total cholesterol (p = 0.021), total cholesterol/HDL-C ratio (p = 0.018), and ApoB/ApoA-I ratio (p = 0.021) was observed. The patients in group 2 showed a decrease in homocysteine levels (p = 0.021) only, while no significant changes were observed in the patients in group 3.

CONCLUSIONS

Good compliance to CPAP treatment lowers the serum levels of cardiovascular risk factors, indicating a beneficial effect on the overall cardiovascular risk.

High frequency of vitamin B12 deficiency in asymptomatic individuals homozygous to MTHFR C677T mutation is associated with endothelial dysfunction and homocysteinemia

The aim of this study was to examine the association of homozygosity for the methylenetetrahydrofolate reductase (MTHFR) C677T mutation and vitamin B12 deficiency in 360 asymptomatic individuals and to investigate forearm endothelial function in C677T homozygotes. MTHFR C677T mutation and levels of vitamin B12, folic acid, and homocysteine were measured in study participants. Frequency of homozygosity for the C677T mutation was 67/360 (18.6%). Homocysteine levels were elevated in homozygous compared with heterozygous subjects or those without the mutation (20.6 +/- 18.8 vs. 9.4 +/- 3.2 mumol/l; P < 0.0001). The number of subjects with vitamin B12 deficiency (<150 pmol/l) was significantly higher among the homozygote than the heterozygote subjects or subjects without mutation [20/67 (29.8%) vs. 27/293 (9.2%); P < 0.0001]. Homozygote subjects had 4.2 times higher probability of having B12 deficiency (95% confidence interval = 2.1-8.3). Forearm endothelial function was assessed in 33 homozygote and 12 control subjects. Abnormal endothelial function was observed in homozygous subjects and was worse in homozygote subjects with vitamin B12 deficiency. Endothelial function was normalized after B12 and folic acid treatment. We found that homozygosity for the C677T mutation is strongly associated with B12 deficiency. Coexistence of homozygosity for the C677T mutation and B12 deficiency is associated with endothelial dysfunction and can be corrected with vitamin B12 and folic acid treatment.

Elevated plasma homocysteine in older shift-workers: a potential risk factor for cardiovascular morbidity

There is evidence supporting an association between shift work and cardiovascular morbidity, but the underlying mechanisms are unknown. The present paper investigated the levels of cardiovascular biochemical risk factors in shift-workers both with (n=26) and without (n=103) sleep complaints, and in day-workers (n=173) working in the same plant. Blood samples were taken in the morning after an overnight fast and analyzed for homocysteine, C-reactive protein, and lipid profile. Biochemical data were compared among groups after stratifying workers by age (i.e., <40 and > or = 40 yrs). Shift-workers who complained about sleep disturbances and who were > or = 40 years of age had significantly higher levels of homocysteine than did their younger counterparts - shift-workers who did not complain of sleep disturbances and day-workers. There were no other between-group differences in any of the biochemical variables. The results of this investigation demonstrate an association between sleep disturbances in older shift-workers and mild hyperhomocysteinemia. The elevated homocysteine levels may play a role in the increased rates of cardiovascular morbidity in shift-workers, and they may have practical implications regarding the nutrition of shift-workers.

Cardiovascular risk markers in obstructive sleep apnoea syndrome and correlation with obesity

BACKGROUND

High C-reactive protein (CRP) and homocysteine levels are risk factors for cardiovascular disease. Some, but not all, previous studies have reported increased levels of CRP and homocysteine in patients with obstructive sleep apnoea syndrome (OSAS). A study was undertaken to investigate the levels of these factors in carefully selected patients with OSAS and matched normal controls.

METHODS

CRP and homocysteine levels were measured in 110 subjects following polysomnography (PSG). Non-OSAS patients (group 1) were compared with two patient groups (mild/moderate OSAS (group 2) and severe OSAS (group 3)) group-matched for body mass index (BMI), and a fourth group of patients with severe OSAS who were more obese (group 4). All were free of other disease and similar in age, smoking habits and cholesterol levels. 50 suitable patients were commenced on continuous positive airway pressure (CPAP) treatment after PSG and 49 were reassessed 6 weeks later.

RESULTS

CRP levels were similar in groups 1, 2 and 3 (median (interquartile range (IQR)) 1.11 (0.76-2.11) mg/l vs 1.82 (1.20-3.71) mg/l vs 2.20 (1.16-3.59) mg/l; p=0.727, Kruskal-Wallis test), but were significantly higher in group 4 than in the other groups (5.36 (2.42-9.17) mg/l, p<0.05 by individual group comparisons). In multivariate analysis of all subjects, BMI was an independent predictor for CRP levels (beta=0.221; p=0.006) but apnoea-hypopnoea index and other measures of OSAS were not. There was no difference in homocysteine levels between all four groups (p=0.1). CPAP did not alter CRP (2.29 (1.32-4.10) vs 2.84 (1.13-5.40) mg/l; p=0.145) or homocysteine levels (8.49 (3.66) vs 9.90 (4.72) micromol/l; p=0.381).

CONCLUSION

CRP and homocysteine levels are not associated with OSAS severity in men but CRP is independently associated with obesity.

Oxidative stress and oxidant signaling in obstructive sleep apnea and associated cardiovascular diseases

Obstructive sleep apnea (OSA) has emerged as a major public health problem and increasing evidence indicates that untreated OSA can lead to the development of various cardiovascular disorders. One important mechanism by which OSA may promote cardiovascular diseases is intermittent hypoxia, in which patients are subjected to repeated episodes of brief oxygen desaturation in the blood, followed by reoxygenation. Such cycles of hypoxia/reoxygenation may result in the generation of reactive oxygen species. Some studies have demonstrated the presence of oxidative stress in OSA patients as well as in animals subjected to intermittent hypoxia. Further, modulations of nitric oxide and biothiol status might also play important roles in the pathogenesis of OSA-associated diseases. Reactive oxygen species and redox events are also involved in the regulation of signal transduction for oxygen-sensing mechanisms. This review summarizes currently available information on the evidence for and against the occurrence of oxidative stress in OSA and the role of reactive oxygen species in cardiovascular changes associated with OSA.

Serum cardiovascular risk factors in obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) patients have increased cardiovascular morbidity and mortality. The cardiovascular markers associated with OSA are currently not defined.

OBJECTIVES

The aims of this study were to determine whether OSA is associated with serum cardiac risk markers and to investigate the relationship between them.

METHODS

Sixty-two male patients were classified into two groups with respect to apnea-hypopnea index (AHI): group 1, sleep apnea (n = 30), with AHI > 5; and group 2 (n = 32), with AHI < 5. We compared cardiovascular risk factors in both groups with control subjects (n = 30) without OSA (AHI < 1). Serum cholesterol, triglyceride, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), apolipoprotein A-I, apolipoprotein B, lipoprotein (a), C-reactive protein (CRP), and homocysteine were measured. Statistical significance was assessed with analysis of variance at p < 0.05. In correlation analysis, Pearson correlation was used.

RESULTS

There was no significant difference between group 1 and group 2 in total cholesterol, LDL-C, HDL-C, triglyceride, apolipoprotein A-I, apolipoprotein B, and lipoprotein (a). All of the M-mode echocardiographic parameters were in the normal reference range. Serum homocysteine and CRP levels were significantly increased in group 1 compared to group 2 (p < 0.05). Serum CRP values were increased in both group 1 and group 2 when compared with control subjects (p < 0.05). Serum homocysteine values were higher in group 1 than in control subjects (p < 0.05).

CONCLUSIONS

Our results show that OSA syndrome is associated not only with slight hyperhomocysteinemia but also with increased CRP concentrations. Increased plasma concentrations of homocysteine and CRP can be useful in clinical practice to be predictor of long-term prognosis for cardiovascular disease and the treatment of OSA.

Serum homocysteine levels and cardiovascular morbidity in obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is associated with cardiovascular morbidity and mortality. Elevated levels of serum homocysteine are also associated with cardiovascular morbidity and mortality. We aimed to investigate serum homocysteine levels and conventional cardiovascular risk factors (cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglycerides) in OSAS patients with and without cardiovascular diseases (CVD).

METHODS AND RESULTS

Levels of homocysteine, cholesterol, LDL, HDL and triglycerides were measured in 114 obese, male participants after overnight fasting. The presence of OSAS was determined by standard overnight polysomnography. The cases included OSAS patients (apnea-hypopnea index: AHI5) with CVD (OSAS+CVD group) (n:25) and without CVD (OSAS-CVD group) (n:47). Control group was patients without OSAS (AHI<5) with CVD (CVD group) (n:42). The serum homocysteine levels were significant.

Antioxidant nutrient intake and supplements as potential moderators of cognitive decline and cardiovascular disease in obstructive sleep apnea

Cognitive deficits and cardiovascular disease (CVD) are comorbid conditions frequently associated with obstructive sleep apnea (OSA). Oxygen free radical release and its differential regulation of cytokine synthesis and immune modulation resulting from OSA-related hypoxic events have been hypothesized as the underlying mechanism(s) for the cognitive deficits and CVD in OSA. A number of studies have suggested that increased levels of oxidative stress and/or antioxidant deficiencies may also be risk factors in cognitive decline and CVD. The influence of antioxidant nutrients and supplements, such as Vitamins B6, B12, C, E, folic acid, alpha-lipoic acid and Coenzyme Q(10) on cognitive decline and CVD have been investigated. The influence of antioxidant nutrients or supplements on OSA remains to be investigated. Even if dietary or supplemental antioxidants do not prove to be effective therapies for OSA, dietary assessment and prescription to increase dietary intake of neuro- and cardio-protective nutrients may make it possible to reduce some of the cognitive and cardiovascular sequelae associated with OSA.

Circulating cardiovascular risk factors in obstructive sleep apnoea: data from randomised controlled trials

BACKGROUND

Obstructive sleep apnoea (OSA) is associated with high cardiovascular morbidity and mortality and is an independent risk factor for hypertension. Novel circulating cardiovascular risk markers enabling a more accurate prediction of cardiovascular risk have been identified. Examination of these markers may clarify the increased risk in OSA and contribute to an analysis of the benefits of treatment.

METHODS

Plasma levels of total cholesterol and triglyceride and activated coagulation factors XIIa and VIIa, factors VII, VIII, XII, fibrinogen, thrombin-antithrombin (TAT), von Willebrand factor antigen (vWFAg), soluble P-selectin (sP-sel), and homocysteine were measured before and after treatment for 1 month with therapeutic or subtherapeutic (control) continuous positive airways pressure (CPAP) in 220 patients with OSA.

RESULTS

Levels of activated coagulation factors XIIa, VIIa, TAT and sP-sel were higher in OSA patients at baseline than in unmatched controls, but did not fall with 1 month of therapeutic CPAP treatment. The raised sP-sel levels correlated only with body mass index (p = 0.002). There was a trend towards a significant fall in total cholesterol with therapeutic CPAP (p = 0.06) compared with the control group. In the therapeutic group there was a clinically significant mean fall in total cholesterol of 0.28 mmol/l (95% confidence interval 0.11 to 0.45, p = 0.001) which may reduce cardiovascular risk by about 15%.

CONCLUSION

A number of activated coagulation factors are increased in untreated OSA patients, potentially contributing to vascular risk, but they do not fall with 1 month of CPAP treatment. Nasal CPAP may produce a clinically relevant fall in total cholesterol level, potentially reducing cardiovascular risk, but this needs to be verified in a larger prospective study.

Daily rhythms in plasma levels of homocysteine

BACKGROUND: There is accumulated evidence that plasma concentration of the sulfur-containing amino-acid homocysteine (Hcy) is a prognostic marker for cardiovascular morbidity and mortality. Both fasting levels of Hcy and post methionine loading levels are used as prognostic markers. The aim of the present study was to investigate the existence of a daily rhythm in plasma Hcy under strictly controlled nutritional and sleep-wake conditions. We also investigated if the time during which methionine loading is performed, i.e., morning or evening, had a different effect on the resultant plasma Hcy concentration. METHODS: Six healthy men aged 23-26 years participated in 4 experiments. In the first and second experiments, the daily rhythm in Hcy as well as in other amino acids was investigated under a normal or an inverse sleep-wake cycle. In the third and fourth, Hcy concentrations were investigated after a morning and evening methionine loading. To standardize food consumption in the first two experiments, subjects received every 3 hours 150 ml of specially designed low-protein liquid food (Ensure(R) formula). RESULTS: In both the first and second experiments there was a significant daily rhythm in Hcy concentrations with a mid-day nadir and a nocturnal peak. Strikingly different 24-h patterns were observed in methionine, leucine, isoleucine and tyrosine. In all, the 24-h curves revealed a strong influence of both the sleep-wake cycle and the feeding schedule. Methionine loading resulted in increased plasma Hcy levels during both morning and evening experiments, which were not significantly different from each other. CONCLUSIONS: There is a daily rhythm in plasma concentration of the amino acid Hcy, and this rhythm is independent of sleep-wake and food consumption. In view of the fact that increased Hcy concentrations may be associated with increased cardiovascular risks, these findings may have clinical implications for the health of rotating shift workers.

Is Subclinical Hypothyroidism Associated With Hyperhomocysteinemia?

OBJECTIVE

To evaluate whether subclinical hypothyroidism is associated with hyperhomocysteinemia, in an attempt to determine whether hyperhomocysteinemia may explain the observed increased risk of coronary artery disease in patients with subclinical hypothyroidism, as has been shown in patients with overt hypothyroidism.

METHODS

We prospectively enrolled consecutive patients with newly diagnosed subclinical hypothyroidism and a parallel group of euthyroid control subjects in this study. Subclinical hypothyroidism was defined as high thyrotropin and normal free thyroxine levels. Fasting plasma total homocysteine, thyrotropin, and free thyroxine levels were measured in all participants, and persistent subclinical hypothyroidism was confirmed at least once.

RESULTS

Forty-seven patients (42 women and 5 men; mean age, 38 +/- 15 years) with subclinical hypothyroidism and 50 control subjects (46 women and 4 men; mean age, 34 +/- 10 years) were enrolled in the study. The manufacturer's reference range for the total homocysteine assay was 5 to 15 micromol/L, and we defined our own reference range as 3.9 to 10.8 micromol/L. The mean values (+/-SE) for total homocysteine in patients and control subjects were 7.44 +/- 0.5 micromol/L and 7.22 +/- 0.2 micromol/L, respectively (P = 0.68).

CONCLUSION

In this study, we found no association between subclinical hypothyroidism and hyperhomocysteinemia. Other contributing factors, such as associated hyperlipidemia, may explain the observed increased risk of coronary artery disease in patients with subclinical hypothyroidism.

Obstructive sleep apnea and cardiovascular disease

Obstructive sleep apnea (OSA) is a common medical condition that occurs in approximately 5% to 15% of the population. The pathophysiology of OSA is characterized by repetitive occlusions of the posterior pharynx during sleep that obstruct the airway, followed by oxyhemoglobin desaturation, persistent inspiratory efforts against the occluded airway, and termination by arousal from sleep. Obstructive sleep apnea is associated with daytime sleepiness and fatigue, likely due to fragmented sleep from recurrent arousals. Substantial evidence shows that patients with OSA have an increased incidence of hypertension compared with individuals without OSA and that OSA is a risk factor for the development of hypertension. Recent studies show that OSA may be implicated in stroke and transient ischemic attacks. Obstructive sleep apnea appears to be associated with coronary heart disease, heart failure, and cardiac arrhythmias. Pulmonary hypertension may be associated with OSA, especially in patients with preexisting pulmonary disease. Although the exact cause that links OSA with cardiovascular disease is unknown, there is evidence that OSA is associated with a group of proinflammatory and prothrombotic factors that have been identified to be important in the development of atherosclerosis. Obstructive sleep apnea is associated with increased daytime and nocturnal sympathetic activity. Autonomic abnormalities seen in patients with OSA include increased resting heart rate, decreased R-R interval variability, and increased blood pressure variability. Both atherosclerosis and OSA are associated with endothelial dysfunction, increased C-reactive protein, interleukin 6, fibrinogen, and plasminogen activator inhibitor, and reduced fibrinolytic activity. Obstructive sleep apnea has been associated with enhanced platelet activity and aggregation. Leukocyte adhesion and accumulation on endothelial cells are common in both OSA and atherosclerosis. Clinicians should be aware that OSA may be a risk factor for the development of cardiovascular disease.

Plasma cytokine levels in patients with obstructive sleep apnea syndrome: a preliminary study

The levels of some pro- and anti-inflammatory cytokines [interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, IL-6, IL-10, and transforming growth factor (TGF)-beta], were measured by enzyme-linked immunosorbent assay (ELISA) method in the plasma of patients affected by obstructive sleep apnea syndrome (OSAS) at 22:00 hours before polysomnographic recording and immediately after the first obstructive apnea causing an SaO2 below 85%. Significantly higher levels of TNF-alpha were found in OSAS patients assessed before polysomnography compared with the control group (P < 0.01). A slight but significant increase in the plasma levels of IL-6 was also present (P < 0.05). Conversely, a significant decrease in the plasma levels of IL-10 was evident at baseline in OSAS patients (P < 0.04). No significant difference emerged between the mean values of IL-1alpha and TGF-beta between OSAS patients and controls. The present data support a prevailing activation of the Th1-type cytokine pattern in OSAS patients, which is not associated with the severity and duration of OSAS. This can have important consequences for the outcome of OSAS patients, especially with regard to the increased risk for developing atherosclerosis and cardiovascular and cerebrovascular diseases. Immediately after the first obstructive apnea causing an SaO2 <85%, a significant variation was observed in the plasma levels of TNF-alpha in OSAS patients compared with those measured before the beginning of polysomnographic recording (P < 0.001). The role played by this further increase in TNF-alpha levels after the obstructive apnea in OSAS patients remains to be established in the light of the pathogenic mechanisms of this sleep disorder.

Sleep-disordered breathing and stroke

Sleep-related breathing disorders are strongly associated with increased risk of stroke independent of known risk factors. The direction of causation favors sleep-disordered breathing leading to stroke rather than the other way around, although definitive proof of this awaits the results of prospective cohort studies. If causal, even a moderately elevated risk of stroke coupled with the high prevalence of sleep-disordered breathing could have significant public health implications. The relationship between sleep-disordered breathing and stroke risk factors is complex, and likely part of the risk for cerebrovascular events is because of higher cardiovascular risk factors in patients with increased RDI. The mechanisms underlying this increased risk of stroke are multi-factorial and include reduction in cerebral blood flow, altered cerebral autoregulation, impaired endothelial function, accelerated atherogenesis, thrombosis, and paradoxic embolism. Because of the effects of sleep-disordered breathing on vascular tone, hypertension is believed to be a major mechanism by which sleep-disordered breathing might influence risk of stroke. Because sleep-related breathing disorders are treatable patients with stroke/TIA should undergo investigation, with a thorough sleep history interview, physical examination, and polysomnography. Treatment of sleep apnea has been shown to improve quality of life, lower blood pressure, improve sleep quality, improve neurocognitive functioning, and decrease symptoms of excessive daytime sleepiness [98]. Further treatment trials are needed to determine whether treatment improves outcome after stroke and whether treatment may serve as secondary prophylaxis and modify the risk of recurrent stroke or death.

Obstructive sleep apnoea syndrome--an oxidative stress disorder

Obstructive sleep apnoea syndrome (OSA) is associated with increased cardiovascular morbidity and mortality. However, the underlying mechanisms are not entirely understood. This review will summarize the evidence that substantiates the notion that the repeated apnoea-related hypoxic events in OSA, similarly to hypoxia/reperfusion injury, initiate oxidative stress. Thus, affecting energy metabolism, redox-sensitive gene expression, and expression of adhesion molecules. A limited number of studies substantiate this hypothesis directly by demonstrating increased free radical production in OSA leukocytes and increased plasma-lipid peroxidation. A great number of studies, however, support this hypothesis indirectly. Increase in circulating levels of adenosine and urinary uric acid in OSA are implicated with increased production of reactive oxygen species (ROS). Activation of redox-sensitive gene expression is suggested by the increase in some protein products of these genes, including VEGF, erythropoietin, endothelin-1, inflammatory cytokines and adhesion molecules. These implicate the participation of redox-sensitive transcription factors as HIF-1 AP-1 and NFkappaB. Finally, adhesion molecule-dependent increased avidity of OSA monocytes to endothelial cells, combined with diminished NO bioavailability, lead to exaggerated endothelial cell damage and dysfunction. Cumulatively, these processes may exacerbate atherogenic sequelae in OSA.