Relaxin in Obstructive Sleep Apnea: Relationship with Blood Pressure and Inflammatory Mediators

Significance of plasma relaxin-2 levels in patients with primary hypertension and type 2 diabetes mellitus

BACKGROUND

This study aimed to evaluate plasma relaxin‑2 (RLN-2) levels in patients with arterial hypertension (AH) and their relationships with clinical and laboratory parameters.

METHODS

The study involved 106 hypertensive patients, including 55 with type 2 diabetes mellitus (T2DM), and 30 control subjects. Plasma RLN-2 levels were measured using an enzyme-linked immunosorbent assay kit.

RESULTS

RLN-2 levels were reduced in patients with AH compared to healthy volunteers (p < 0.001), and hypertensive patients with T2DM had lower RLN-2 levels than those without impaired glucose metabolism (p < 0.001). RLN‑2 was negatively correlated with systolic blood pressure (SBP) (p < 0.001) and anthropometric parameters such as body mass index (BMI; p = 0.027), neck (p = 0.045) and waist (p = 0.003) circumferences, and waist-to-hip ratio (p = 0.011). RLN‑2 also had inverse associations with uric acid levels (p = 0.019) and lipid profile parameters, particularly triglycerides (p < 0.001) and non-HDL-C/HDL‑C (p < 0.001), and a positive relationship with HDL‑C (p < 0.001). RLN‑2 was negatively associated with glucose (p < 0.001), insulin (p = 0.043), HbA1c (p < 0.001), and HOMA-IR index (p < 0.001). Univariate binary logistic regression identified RLN‑2 as a significant predictor of impaired glucose metabolism (p < 0.001).

CONCLUSIONS

Decreased RLN-2 levels in patients with AH and T2DM and established relationships of RLN‑2 with SBP and parameters of glucose metabolism and lipid profile suggest a diagnostic role of RLN‑2 as a biomarker for AH with T2DM.

Matrix metalloproteinase-9 as a messenger in the cross talk between obstructive sleep apnea and comorbid systemic hypertension, cardiac remodeling, and ischemic stroke: a literature review

STUDY OBJECTIVES

OSA is a common sleep disorder. There is a strong link between sleep-related breathing disorders and cardiovascular and cerebrovascular diseases. Matrix metalloproteinase-9 (MMP-9) is a biological marker for extracellular matrix degradation, which plays a significant role in systemic hypertension, myocardial infarction and postmyocardial infarction heart failure, and ischemic stroke. This article reviews MMP-9 as an inflammatory mediator and a potential messenger between OSA and OSA-induced comorbidities.

METHODS

We reviewed the MEDLINE database (PubMed) for publications on MMP-9, OSA, and cardiovascular disease, identifying 1,592 studies and including and reviewing 50 articles for this work.

RESULTS

There is strong evidence that MMP-9 and tissue inhibitor of metalloproteinase-1 levels are elevated in patients with OSA (mainly MMP-9), systemic hypertension, myocardial infarction, and postmyocardial infarction heart failure. Our study showed variable results that could be related to the sample size or to laboratory methodology.

CONCLUSIONS

MMP-9 and its endogenous inhibitor, tissue inhibitor of metalloproteinase-1, are a common denominator in OSA, systemic hypertension, myocardial infarction, and heart failure. This characterization makes MMP-9 a target for developing novel selective inhibitors that can serve as adjuvant therapy in patients with OSA, which may ameliorate the cardiovascular and cerebrovascular mortality associated with OSA.

Elevation of CD40/CD40L Inflammatory Pathway Molecules in Carotid Plaques from Moderate-and-Severe Obstructive Sleep Apnea Patients

A chronic inflammatory process characteristic of obstructive sleep apnea promotes vascular endothelial dysfunction and atherogenesis. This process can lead to destabilization and rupture of cardiovascular plaques, which clinically manifests as an acute coronary syndrome or stroke. The aim of this study was to investigate the inflammatory pathway leading to plaque destabilization in non-to-mild and moderate-to-severe groups of OSA patients. This prospective study involved enrollment of patients scheduled for endarterectomy. A sleep study was performed prior to surgery. Immunohistochemistry was performed on atherosclerotic plaques from carotid arteries obtained during standard open endarterectomy to determine levels of CD40, CD40L receptors, MCP-1, and MMP-9. The 46 patients included 14 controls, 13 with mild, 11 with moderate, and 8 with severe OSA. Increased expression of CD40, CD40L receptors, MCP-1, and MMP-9 were found to be proportionate with OSA severity. However, significant differences among groups were observed only for MCP-1 (p = 0.014). Increased expression of inflammatory markers (CD40, CD40L, MCP-1, MMP-9) is associated with increasing OSA severity. This suggests the CD40-CD4-L inflammatory pathway may contribute to plaque instability and rupture in OSA patients.

Serum matrix metalloproteinase-2 as a predictor of level of hypoxemia and severity of obstructive sleep apnea

PURPOSE

Intermittent hypoxia in obstructive sleep apnea (OSA) resembles ischemia/reperfusion. Oxidative stress during ischemia/reperfusion increases matrix metalloproteinase-2 (MMP-2) activity and leads to adverse cardiovascular consequences in animal models, but there is scarce information about MMP-2 in humans with OSA. The aim of this study was to determine if serum MMP-2 levels of patients with OSA differ from controls and if MMP-2 activity correlates with the severity of OSA and level of hypoxemia.

METHODS

Patients with OSA (n = 124) were recruited from the Sleep Disorders Center (Saskatoon City Hospital, Canada) after in-lab polysomnography (PSG). Controls (n = 26) were subjects referred for PSG who did not have OSA. Severity of OSA was categorized according to American Academy of Sleep Medicine criteria. Level of hypoxemia was expressed as oxygen desaturation index (ODI; 3% desaturation). Gelatin zymography was performed to measure serum MMP-2 activity.

RESULTS

Serum MMP-2 activity was significantly higher in patients with OSA than in controls (p = 0.029). MMP-2 activity in patients with severe OSA was significantly higher than in those with mild/moderate OSA and controls (p = 0.002). Linear regression showed positive associations with MMP-2 activity in serum for AHI (p < 0.001) and ODI (p = 0.003). The associations persisted after adjustment for multiple confounders, including age, sex, BMI, and cardiovascular disease.

CONCLUSIONS

Serum MMP-2 activity was associated with OSA severity, and level of hypoxemia in patients with OSA, suggesting MMP-2 is worth considering as a potential biomarker to be included in future studies on sets of biomarkers for hypoxemic insult in OSA.

Matrix Metalloproteinase-9 Is a Predictive Factor for Systematic Hypertension and Heart Dysfunction in Patients with Obstructive Sleep Apnea Syndrome

Patients with obstructive sleep apnea syndrome (OSAS) showed higher prevalence in cardiovascular diseases due to aberrant hypoxia and oxidative stress. However, not all OSAS patients end up with cardiovascular disorders, and identification of novel biomarker will be invaluable for differentiating patients at risk. Here we tested the serum matrix metalloproteinase-9 (MMP-9) levels in 47 untreated OSAS patients and found that the MMP-9 level was positively correlated with severity of OSAS, which was consistent with hypoxia degree and duration. Besides, the MMP-9 level was higher in patients complicated with systematic hypertension (P < 0.001). Furthermore, we selected those OSAS patients without any cardiovascular dysfunction (n = 35) and followed up for up to five years. By the end of follow-up, 12 patients had hypertension onset and 3 patients had left ventricular hypertrophy. By analyzing the clinical outcomes with MMP-9 expression, we demonstrated that high serum MMP-9 in OSAS patients was a risk factor for occurrence of cardiovascular diseases. In addition, we cultured the vascular endothelial cells (VEC) from rat aorta in hypoxia condition to investigate whether MMP-9 was elevated due to hypoxia in OSAS patients. Cellular results revealed that the expression, secretion, and activity of MMP-9 were all upregulated by hypoxia and can cleave the beta2-adrenergic receptor (β2AR) on VEC surface. Our results not only determined MMP-9 as a risk factor for cardiovascular diseases in OSAS patients, but also showed the possible involvement of hypoxia-MMP-9-β2AR signaling axis.