Surfactant protein A as a biomarker of outcomes of anti-fibrotic drug therapy in patients with idiopathic pulmonary fibrosis

BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is a progressive and fibrosing lung disease with poor prognosis. Pirfenidone and nintedanib are anti-fibrotic drugs used for patients with IPF. These drugs reduce the rate of decline in forced vital capacity (FVC). Serum surfactant protein (SP)-A, SP-D, and Krebs von den Lungen-6 (KL-6) are monitoring and prognostic biomarkers in patients with IPF; however, their relationship with the therapeutic outcomes of anti-fibrotic drugs has not been investigated. We aim to clarify whether serum SP-A, SP-D, and KL-6 reflect therapeutic outcomes of pirfenidone and nintedanib administration in patients with IPF. METHODS: We retrospectively investigated patients with IPF who were initiated on pirfenidone or nintedanib administration between January 2014 and June 2018 at our hospital. Changes in clinical parameters and serum SP-A, SP-D, and KL-6 levels were evaluated. Patients with ≥10% decline in FVC or ≥ 15% decline in diffusing capacity of the lung for carbon monoxide (DLco) from baseline to 6 months were classified as progression group, while the other patients were classified as stable group. RESULTS: Forty-nine patients were included (pirfenidone, 23; nintedanib, 26). Stable group comprised 32 patients, while progression group comprised 17 patients. In the stable group, changes in SP-A and KL-6 from baseline to 3 and 6 months significantly decreased compared with the progression group (SP-A: 3 months - 6.0% vs 16.7%, 6 months - 10.2% vs 20.2%, KL-6: 3 months - 9.2% vs 6.7%, 6 months - 15.0% vs 12.1%, p < 0.05). Changes in SP-A and SP-D levels showed significant negative correlations with the change in %FVC (r = - 0.46 and r = - 0.39, p < 0.01, respectively) and %DLco (r = - 0.67 and r = - 0.54, p < 0.01, respectively). Similar results were also seen in subgroup analysis for both pirfenidone and nintedanib groups. On logistic regression analysis, decrease in SP-A from baseline to 3 months and 6 months was found to predict the outcomes at 6 months (odds ratios: 0.89 and 0.88, respectively). CONCLUSIONS: Changes in serum SP-A reflected the outcomes of anti-fibrotic drug therapy. Serum SP-A has a potential as a biomarker of therapeutic outcomes of anti-fibrotic drugs.