Chronic intermittent hypoxia aggravates cardiomyocyte apoptosis in rat ovariectomized model

The prevalence of obstructive sleep apnea (OSA) increases after menopause in women, but remains under diagnosed because of social or lifestyle factors. It is important to evaluate the hazards of OSA on cardiovascular disease in menopausal women. We tested the hypothesis that chronic intermittent hypoxia (CIH) may aggravate cardiomyocyte apoptosis in ovariectomized (OVX) Sprague Dawley (SD) rats; the changes of anti-oxidation ability in cardiac muscles may be one of the reasons for cardiomyocyte apoptosis.

Forty-eight 60-day old female SD rats were randomly divided into a CIH group, OVX group, OVX+CIH (OC) group, and handled control (HC) group, and the rats were exposed either to CIH (nadir O2 6%) or handled normoxic controls. The changes of body weight and whole heart weight were measured. Super oxide dismutase (SOD) and malonaldehyde (MDA) were used to evaluate the level of oxidative stress. TdT-mediated dUTP nick end labeling (TUNEL) was used to measure apoptosis in each rat. Western blotting was used to measure apoptosis associated proteins in cardiac muscle samples from each rat.

When compared with the HC and CIH groups, the levels of oxidative stress in the OC and OVX groups were significantly higher. The levels of SOD in the HC, CIH, OC, and OVX groups were (47.99 ± 4.89), (53.60 ± 4.47), (20.99 ± 2.72), and (30.64 ± 3.79) mmol/mg protein; significantly increased in the CIH group (P < 0.05) and significantly decreased in the OC (P < 0.01) and OVX (P < 0.05) groups. The levels of MDA in the HC, CIH, OVX, and OC groups were (1.63 ± 0.20), (1.93 ± 0.77), (3.30 ± 0.39), and (1.95 ± 0.20) mmol/mg protein; it significantly increased in the CIH (P < 0.05), OC (P < 0.01), and OVX (P < 0.05) groups compared with the HC group. Bax protein expression was significantly increased and bcl-2 protein expression was significantly reduced after CIH compared with HC rats (P < 0.05). The protein expression of bax and bcl-2 in the OC group was not significantly different from the CIH group, but the ratio of bax/bcl-2 was significantly increased in the OC group (P < 0.05); this was associated with severe cardiomycyte apoptosis in the OC group. TUNEL confirmed this observation.

This study found that CIH may induce oxidative stress in OVX rats but not in CIH rats, and cause more severe cardiomyocyte apoptosis in OVX rats compared with CIH rats. This means that OVX rats exposed to CIH suffered more severe cardiac injury compared with CIH rats due to reduced antioxidation. These findings may partly explain the reason why OSA has a worse cardiovascular impact on menopausal women, and emphasize the importance of detection and early treatment of OSA in menopausal patients.