What do changes in concentrations of serum surfactant proteins A and D in OSA mean?

Previous studies have shown that surfactant proteins are affected by oxygen concentration and mechanic stretches, although the alteration of serum surfactant proteins in individuals with obstructive sleep apnea (OSA) is still unclear. Therefore, the aim of this study is to examine whether serum concentrations of surfactant proteins A and D are altered and related to hypopnea index (HI) in OSA.

This is a cross-sectional study. Consecutive 140 males, suspicious of OSA, were studied. OSA was determined by PSG and polysomnographic data examined. Subjects with HI ≥ 10.1/h were classified as higher HI group and those with HI < 10.1/h as lower HI group. Hs-CRP, HbA1C, and FBG were determined by standard methods and Krebs von den Lungen-6 (KL-6), surfactant protein-A (SP-A), and surfactant protein-D (SP-D) by ELISA.

OSA was diagnosed in 110 patients (78.5%). Mild, moderate, and severe OSA constitutes 26.4, 27.8, and 24.3%, respectively. Mean age was 44.6 ± 7.65 years. Subjects with higher HI had lower SP-A (139.54. ± 32.94 vs 158.2 ± 38.9 ng/L, p = 0.005) and SP-D (16.54 ± 3.67 vs 18.10 ± 3.48 ng/L, p = 0.014) compared to those with lower HI. Nocturnal HI was strongly correlated with serum levels of SP-A (r = 0.343, p = 0.012) and SP-D (r = 0.504, p < 0.001) and are inversely associated with circulating SP-A and SP-D levels, even after adjusting for age and body mass index in nonsmoking subjects.

Circulating SP-A and SP-D levels are decreased in some individuals with higher HI in OSA, possibly reflecting severity of hypoxia in OSA.