Salivary SLPI and disease severity in bronchiectasis

<b>Introduction:</b> Sputum Secretory Leukocyte Protease Inhibitor (SLPI) and LL-37 are antimicrobial peptides related to disease severity in bronchiectasis. However, spontaneous sputum samples are not as easy to obtain as saliva samples in clinical practice. Therefore, we aimed to determine salivary SLPI and LL-37 levels to assess their association with disease severity and their relationship with sputum levels in patients with bronchiectasis. <b>Methods:</b> Unstimulated saliva samples from 157 adult patients with clinically stable bronchiectasis [mean age 69 ± 12, FEV₁ 72 ± 23%, Bronchiectasis Severity Index (BSI) 6.4 ± 3.7] were collected. At the same time, spontaneous sputum was obtained from 66 patients. SLPI and LL-37 levels were measured in supernatants of saliva and sputum by ELISA. Saliva total protein was determined using Qubit fluorometer to adjust salivary levels by the total protein content. <b>Results:</b> Patients with severe BSI showed lower salivary SLPI levels compared to patients with moderate and mild disease [0.4 (0.2-1.2) vs 1.4 (0.3-2.7) vs 0.8 (0.4-2.6), p=0.02]. Lowest levels were observed in patients with chronic <i>Pseudomona aeruginosa</i> infection, although differences were not statistically significant [0.6 (0.2-1.6) vs 1.4 (0.4-3.2), p=0.1]. No relationship among salivary LL-37 levels and disease severity was observed. A weak but statistically significant correlation between salivary and sputum SLPI (rho=0.28, p=0.03) and LL-37 (rho=0.25, p=0.04) were found. <b>Conclusions:</b> Salivary SLPI levels are related with disease severity in bronchiectasis. In addition, a weak correlation among salivary and sputum antimicrobial peptides are found. Further studies are needed to determine the role of salivary biomarkers in bronchiectasis