Alpha1antitrypsine (AAT) in sputum: is it a useful biomarker in Bronchiectasis (BE)?

<b>Background:</b> Protease-antiprotease impaired balance is crucial in the pathophysiology of BE, contributing to airways (AW) inflammation. AAT represents one of the main protease inhibitors, contrasting the effect of proteases such as Neutrophil Elastase, but little is known about its concentration in AW or its role in BE as a biomarker. We hypothesize that AAT levels in sputum (AATs) could correlate with BE severity, and represent a marker of airways disease activity. <b>Methods:</b> We collected spontaneous sputum and blood from stable BE patients, along with most relevant clinical data. AAT levels were measured in sputum supernatant by ELISA, and in blood with nephelometry. AATs was also measured in 9 healthy non-smokers controls. <b>Results:</b> We recruited 34 patients, mostly women(74%), mean age 63±11.9 years old, mean FEV1 86±20.5%. Significantly lower values of AATs were observed in BE compared with healthy controls (0.086mg/dl versus 0.126mg/dl, p=0.005). Level of AATs had inverse correlation with radiological extension (number of involved lobes, r=-0.45, p=0.016; Reiff score, r=-0.58; p=0.001). No correlation was found with severity (BSI and FACED), FEV1, dyspnoea, age or BMI. We calculated the ratio between AATs and AAT in blood (SBAAT) in 24 patients: correlation with Reiff index was confirmed (p=0.016). Lower SBAAT was associated with chronic <i>Pseudomonas</i> infection (p= 0.039) and sputum purulence (p=0.040). <b>Conclusions:</b> Our results suggest a possible correlation between AATs and disease extension. SBAAT and its correlation with sputum characteristics (purulence and chronic infection) seems to indicate higher consumption of AAT in airways that could correspond to an increased disease activity and&nbsp;protease&nbsp;imbalance.