Serum surfactant protein D is a potential biomarker of lung damage in systemic sclerosis

Abstract

Background: Interstitial lung disease (ILD) complicates the course of systemic sclerosis (SSc) up to two-third of the cases, representing the main cause of death in these patients. Assessment of lung involvement by HRCT and close monitoring of lung function are mandatory. At present no serologic biomarkers are validated for the assessment for lung damage in SSc. The current study was designed to test the hypothesis that the levels of surfactant are altered in SSc compared to healthy controls. To this aim serum levels of SP-A (Surfactant Protein A) and SP-D (Surfactant Protein-D) in serum were assessed.

Methods: We enrolled 12 consecutive patients (M/F: 2/10) affected by scleroderma referred to our Respiratory Clinic by the Rheumatology Unit of the University Hospital of Palermo. Ten healthy subjects served as controls. All patients underwent clinical, lung functional and biological assessments. Serum levels of SP-A and SP-D were measured by enzyme immunoassay/ELISA.

Results: The surfactant analysis of plasma proteins showed a significant increase in protein SP-D levels in SSc than in control subjects (92.7±58.5 ng/ml vs 32±11.9 ng/ml, p=0.004). Conversely, the concentrations of protein SP-A were not different between the two groups (50.3±27.1 ng/ml vs 37.5±24.9 ng/ml, p=0.26). As expected, the degree of diffusion capacity was significantly lower in the scleroderma subjects (58.4±9.9% vs 73.6±4.6% respectively, p = 0.0002). In addition, in the SSc group, SP-D in serum was significantly and inversely correlated with DLCO% predicted.

Conclusions: Serum SP-D is proposed as a candidate biomarker in the assessment of lung damage in SSc complicated by ILD.