Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB073

Poster Communications

Apocynin reduces apnoea index in a mouse model of chronic intermittent hypoxia in a non-NADPH oxidase 2 dependent manner

S. E. Drummond1, D. P. Burns1, V. Healy1, K. D. O'Halloran1

1. Department of Physiology, University College Cork, Cork, Ireland.

Chronic intermittent hypoxia (CIH) is a hallmark feature of obstructive sleep apnoea syndrome (OSAS) as a consequence of repetitive upper airway occlusions in patients during sleep. These recurring hypoxia-reoxygenation cycles result in the overproduction of reactive oxygen species (ROS). Excessive ROS are associated with aberrant plasticity at multiple levels of the respiratory system including impaired respiratory control, which manifests as destabilised breathing during sleep. NADPH oxidase (NOX) enzymes are implicated in CIH-induced respiratory plasticity. We hypothesize that NOX-derived ROS underlie CIH-induced respiratory maladaptation, which perturbs respiratory homeostasis and exacerbates the pathology of OSAS. A mouse model of CIH was generated by the cycling of gas from normoxia (21% O2) for 210 seconds to hypoxia (5% O2 at the nadir) over 90 seconds for 8hr/day for 2 weeks. 10-11 week old male (C57BL/6J) mice were assigned to one of 3 groups: normoxic controls (sham; n=12), CIH exposed (n=12) and CIH+apocynin (NADPH oxidase 2 inhibitor, 2mM; n=12) given in the drinking water throughout the CIH exposure. In separate studies, 10-11 week old NOX2 null (B6.129S-Cybbtm1Din/J) male mice were assigned to sham (n=12) or CIH (n=12) exposure. On day 15, whole body plethysmography was used to measure breathing parameters in unrestrained, unaesthetized mice on a breath-by-breath basis in room air. Flow signals recorded from the plethysmograph were analysed offline for the determination of apnoea count. An apnoea was defined as ≥ 2 missed breaths. All values are expressed as mean ± SD and data were statistically compared by unpaired Student t-test. Mice exposed to 2 weeks of CIH showed almost double the number of apnoeas per hour compared with sham exposed mice (11.2 ± 10.3 vs. 19.0 ± 12.5; p=0.11), although this increase was not statistically significant. Apocynin intervention significantly reduced the frequency of apnoeas compared with the CIH group (19.0 ± 12.5 vs. 9.5 ± 5.9; p=0.03). Apnoea index was increased in NOX2 null mice exposed to CIH compared with NOX2 null sham mice (12.0 ± 12.5 vs. 19.5 ± 13.8; p=0.18) reminiscent of that observed in wild-type mice. CIH-induced increase in the propensity for apnoea may be of biological relevance as it may underpin progression in the severity of OSAS pathology (i.e. mild to moderate OSA). The reduction in apnoea frequency following treatment with apocynin implicates ROS in the manifestation of CIH-induced respiratory disturbances. However, these ROS do not appear to be NOX2-derived as apnoea index in NOX2 null mice largely mirrors that of wild type mice. Our results reveal the proclivity for CIH to perpetuate respiratory maladaptation perhaps relevant to ‘complex' apnoea in OSAS patients, and point to antioxidant intervention as a potential therapeutic strategy in OSAS.

Where applicable, experiments conform with Society ethical requirements