title: Cellular mechanisms in intermittent hypoxia-induced cardiac damage in vivo.
abstract: Obstructive sleep apnea (OSA), characterized by intermittent hypoxia (IH) during sleep, is increasingly recognized as an independent risk factor of cardiovascular diseases. OSA is associated with changes in the levels of circulating oxidative stress/inflammatory markers and dyslipidemia, supporting their mediating roles in cardiovascular pathogenesis. Our aims were to investigate the effect of IH on heart tissue using an IH-exposed rat model and to explore the potential mechanisms involved in the occurrence of cardiac damage. Male Sprague-Dawley rats were exposed to IH and intermittent normoxia as control and sacrificed after 2 or 4 weeks. IH for 4 weeks caused elevation in serum malondialdehyde and cytokine-induced neutrophil chemoattractant-1 and reduction in serum adiponectin levels. In contrast, cardiac oxidative stress and pro-inflammatory markers were suppressed while cardiac adiponectin and cholesterol levels were elevated after IH exposure for 4 weeks. In parallel, there was an increase in apoptosis in the heart of IH-exposed rats, demonstrated by elevations of Bax and cleaved caspase-3 protein and TUNEL staining. Cardiac damage was further evident with decreased arterial vessel and capillary densities, increased cardiac fibrosis, and the loss of troponin I. Our data demonstrated that IH exposure paradoxically caused systemic oxidative and inflammatory responses and cardioprotective responses, i.e., anti-oxidative and anti-inflammatory responses. Despite such a local compensatory protective mechanism, cardiac damage was observed that might be due to IH-induced cholesterol accumulation in the heart and caspase-dependent apoptosis.
authors.affiliation: Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Han
authors.forename: Sze C
authors.initials: SC
authors.lastname: Yeung
authors.forename: Mary S M
authors.initials: MS
authors.lastname: Ip
authors.forename: Judith C W
authors.initials: JC
authors.lastname: Mak
mesh_terms: D052242:Adiponectin / Q000097:blood; D000818:Animals; D017209:Apoptosis; D015687:Cell Hypoxia; D054360:Chemokine CXCL1 / Q000097:blood; D051547:Heme Oxygenase-1 / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D008297:Male; D008315:Malondialdehyde / Q000097:blood; D009206:Myocardium / Q000378:metabolism / Q000473:pathology*; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020181:Sleep Apnea, Obstructive / Q000097:blood / Q000473:pathology; D019210:Troponin I / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D052242:Adiponectin; D054360:Chemokine CXCL1; C513297:Cxcl1 protein, rat; D015850:Interleukin-6; D051267:NF-E2-Related Factor 2; C495637:Nfe2l2 protein, rat; D019210:Troponin I; D014409:Tumor Necrosis Factor-alpha; D008315:Malondialdehyde; D051547:Heme Oxygenase-1