Abstract
BackgroundNapsin A, an aspartic protease, is mainly expressed in alveolar type-II cells and renal proximal tubules and is a putative immunohistochemical marker for pulmonary adenocarcinomas. This study sought to determine whether napsin A could be measured in the serum to evaluate its relationship to idiopathic pulmonary fibrosis (IPF) and determine whether renal dysfunction might affect serum napsin A levels.MethodsSerum levels of napsin A were measured in 20 patients with IPF, 34 patients with lung primary adenocarcinoma, 12 patients with kidney diseases, and 20 healthy volunteers. Surfactant protein (SP)-A, SP-D, and Krebs von den Lungen-6 (KL-6) levels in serum and pulmonary function tests were also evaluated in IPF patients.ResultsCirculating levels of napsin A were increased in patients with IPF, as compared with healthy controls, and they correlated with the severity of disease. Moreover, the serum napsin A levels were not elevated in patients with pulmonary adenocarcinoma or renal dysfunction. The distinguishing point between IPF and the controls was that the area under the receiver operating characteristic curve (ROC) of napsin A was larger than that of KL-6, SP-A, or SP-D.ConclusionThese findings suggest that serum napsin A may be a candidate biomarker for IPF.
Highlights
Napsin A, an aspartic protease, is mainly expressed in alveolar type-II cells and renal proximal tubules and is a putative immunohistochemical marker for pulmonary adenocarcinomas
The diagnostic values for serum napsin A, Krebs von den Lungen-6 (KL-6), Surfactant protein A (SP-A), and Surfactant protein D (SP-D) for idiopathic pulmonary fibrosis (IPF) vs control subjects were evaluated from the receiver operating characteristic curve (ROC) curves (Figure 2)
The areas under the ROC curves for IPF patients in comparison with control subjects were 0.988 for napsin A, 0.938 for KL-6, 0.931 for Surfactant protein (SP)-A, and 0.940 for SP-D, with serum napsin A levels showing the greatest area, there were no significant differences in AUC values between serum napsin A and the other markers
Summary
Napsin A, an aspartic protease, is mainly expressed in alveolar type-II cells and renal proximal tubules and is a putative immunohistochemical marker for pulmonary adenocarcinomas. Identification of peripheral blood biomarkers may facilitate the diagnosis, estimation of prognosis, and selection and evaluation of a treatment as well as the Napsin A, an aspartic proteinase, is expressed in type II pneumocytes and in alveolar macrophages presumably secondary to phagocytosis [10,11]. It is abundant and active in the alveolar space, correlating with the levels of SP-B, proSP-B, and SP-C [11]. Its local expression is reported to be useful both for classifying primary lung tumors as adenocarcinoma and for identifying lung origin in the setting of a metastatic adenocarcinoma [12,13]
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