Serum matrix metalloproteinase-9 as a potential biomarker for obstructive sleep apnea severity

Purpose We aimed to investigate the associations between serum matrix metalloproteinase (MMP)-2 and MMP-9 levels and obstructive sleep apnea (OSA) severity with a focus on nocturnal hypoxemia. Methods The OSA patients (n = 105) were recruited from a prospective sleep apnea cohort after polysomnography, with 27 healthy volunteers as the controls. OSA severity was assessed via the apnea-hypopnea index (AHI) and percent night time with SpO2 < 90% (T90). Results The serum MMP-9 levels were significantly higher in the OSA patients (AHI >= 5/h, 68.8 +/- 44.9 ng/mL) than the controls (49.0 +/- 18.6 ng/mL, p < 0.001). The MMP-2 levels showed no significant differences. When grouped into T90 quartiles, the MMP-9 levels were higher in the OSA patients in the highest quartile compared to those in the lowest quartile or the controls (90.6 +/- 56.3 ng/mL vs. 56.9 +/- 31.9 ng/mL, p = 0.022; 90.6 +/- 56.3 ng/mL vs. 49.0 +/- 18.6 ng/mL, p = 0.002, respectively). The MMP-9 levels correlated with T90 and the AHI (r = 0.36, p < 0.001; r = 0.35, p < 0.001, respectively). Multiple linear regression confirmed a significant association between MMP-9 and T90 after adjusting for body mass index, smoking status, and comorbidities (beta = 0.53, p = 0.013). A similar association was observed for the AHI (beta = 0.48, p = 0.019). Conclusion We concluded that serum MMP-9 levels are independently associated with OSA severity, particularly with T90 and the AHI, which suggests that MMP-9 could be a biomarker for OSA severity.