Role of bronchial hyperresponsiveness in patients with obstructive sleep apnea with asthma-like symptoms

BACKGROUND

Obstructive sleep apnea (OSA) is one of the major co-morbidities and aggravating factors of asthma. In OSA-complicated asthma, obesity, visceral fat, and systemic inflammation are associated with its severity, but the role of bronchial hyperresponsiveness (BHR) is unclear. We investigated the involvement of BHR and mediastinal fat width, as a measure of visceral fat, with OSA severity in patients with OSA and asthma-like symptoms.

METHODS

Patients with OSA who underwent BHR test and chest computed tomography scan for asthma-like symptoms were retrospectively enrolled. We evaluated the relationship between apnea-hypopnea index (AHI) and PC20 or anterior mediastinal fat width, stratified by the presence or absence of BHR.

RESULTS

OSA patients with BHR (n = 29) showed more obstructive airways and frequent low arousal threshold and lower mediastinal fat width, and tended to show fewer AHI than those without BHR (n = 25). In the overall analysis, mediastinal fat width was significantly positively correlated with AHI, which was significant even after adjustment with age and gender. This was especially significant in patients without BHR, while in OSA patients with BHR, there were significant negative associations between apnea index and airflow limitation, and hypopnea index and PC20.

CONCLUSIONS

Risk factors for greater AHI differed depending on the presence or absence of BHR in OSA patients with asthma-like symptoms. In the presence of BHR, severity of asthma may determine the severity of concomitant OSA.

Non-genomic inhibitory effect of glucocorticoids on activated peripheral blood basophils through suppression of lipid raft formation

We investigated the non-genomic effects of glucocorticoids (GCs) on inhibition of plasma membrane lipid raft formation in activated human basophils. Human basophils obtained from house dust mite (HDM)-sensitive volunteers were pretreated with hydrocortisone (CORT) or dexamethasone (Dex) for 30 min and then primed with phorbol 12-myristate 13-acetate (PMA, 10 ng/ml) or HDM (10 µg/ml). The expression of CD63, a basophil activation marker, was assessed by flow cytometry. Membrane-bound GC receptors (mGCRs) were analysed by flow cytometry and confocal laser microscopy. Lipid rafts were assessed using a GM1 ganglioside probe and visualization by confocal laser microscopy. Pretreatment of basophils with CORT (10(-4) M and 10(-5) M) and Dex (10(-7) M) significantly inhibited CD63 expression 20 min after addition of PMA or HDM. The inhibitory effects of GCs were not altered by the nuclear GC receptor (GCR) antagonist RU486 (10(-5) M) or the protein synthesis inhibitor cycloheximide (10(-4) M) (P < 0·05). CORT coupled to bovine serum albumin (BSA-CORT) mimicked the rapid inhibitory effects of CORT, suggesting the involvement of mGCRs. mGCRs were detectable on the plasma membrane of resting basophils and formed nanoclusters following treatment with PMA or HDM. Pretreatment of cells with BSA-CORT inhibited the expression of mGCRs and nanoclustering of ganglioside GM1 in lipid rafts. The study provides evidence that non-genomic mechanisms are involved in the rapid inhibitory effect of GCs on the formation of lipid raft nanoclusters, through binding to mGCRs on the plasma membrane of activated basophils.