Opposite behavior of plasma levels surfactant protein type B and receptor for advanced glycation end products in pulmonary sarcoidosis

Background No biological marker is currently available for evaluating pulmonary involvement and/or for monitoring the clinical course of sarcoidosis. The present pilot study focused on possible relationships between circulating plasma levels of surfactant protein type B (SP-B) and plasma receptor for advanced glycation end products (RAGE) and lung function abnormalities in patients with pulmonary sarcoidosis, since both SP-B and RAGE have been previously suggested as lung injury markers. The plasmatic levels of these two proteins were also investigated with respect to functional capacity, as assessed by a cardiopulmonary exercise test (CPET). Methods Thirty pulmonary sarcoidosis outpatients and fifteen volunteers (Control Group) underwent lung function tests and CPET. Resting SP-B and RAGE plasma levels were also determined. Patients were then categorized according to the severity of their pulmonary involvement, as assessed in terms of lung diffusion for carbon monoxide (DL CO) values. Results Group B showed SP-B levels higher and RAGE levels lower than Group A and Control Group (p < 0.01). Group A showed lower RAGE levels than Control Group (p < 0.01), whereas SP-B levels did not differ between these two groups. A significant univariate relationship was found between both SP-B and RAGE and several lung function data, particularly with DLCO (SP-B Vs DLCO: r: -0.437, p = 0.016; RAGE Vs DL CO: r: -0.451, p = 0.012). Conclusions Circulating plasma levels of SP-B and RAGE showed an opposite behavior in patients with pulmonary sarcoidosis. SP-B values are directly related to alveolar unit damage, supporting a possible role of SP-B as a marker of disease severity in these patients. Differently, RAGE decreases in severe sarcoidosis, suggesting more complex underlying mechanisms.