Poor Indicator of Course and Prognosis in Sarcoidosis
A proportion (20 percent) of patients who present with sarcoidosis develop chronic pulmonary disease, which is characterized by impaired pulmonary function and eventual fibrosis. Early identification of these patients could ensure more informed clinical decisions aimed at preventing permanent lung injury. Pulmonary fibrosis is characterized by an increase in fibroblast numbers and altered collagen metabolism in the lung. Although end-stage fibrosis is marked by an increased proportion of type 1 collagen in the alveolar interstitium, several studies indicate that during the early phase of fibrosis, there is a temporary increase in the production of type 3 collagen. Bateman et al, in a study of lung biopsy samples from patients with cryptogenic fibrosing alveolitis, found that type 3 collagen was associated with active fibro-genesis in this disease.
Type 3 collagen is produced and secreted by fibroblasts in a precursor form. Following secretion, specific N-terminal and C-terminal procollagen peptides are cleaved from the precursor. The mature collagen molecule is then deposited in fibrillar form in the extracellular matrix. Several investigators have indicated that levels of procollagen peptides in body fluids reflect altered collagen synthesis and that these peptides may serve as markers of fibrotic changes in the tissues. Low et al found that concentrations of N-terminal type 3 procollagen peptide were elevated in bronchoalveolar lavage fluids from patients with idiopathic pulmonary fibrosis and sarcoidosis and indicated that lavage type 3 procollagen peptide levels might reflect changes in collagen production in lung disease. More recently, Bjermer et al observed an association between lavage type 3 procollagen peptide concentrations and clinical symptoms of lung impairment in patients with sarcoidosis. These authors suggest that lavage type 3 procollagen peptide levels might reflect fibrotic activity in the sarcoid lung, and hence, be useful in assessing disease severity and outcome. In the present study, we measured type 3 procollagen peptide levels in bronchoalveolar lavage fluids from a group of sarcoid patients and monitored disease progress in those patients for a minimum of 12 months to determine whether lavage procollagen peptide levels might serve to identify patients who develop functional impairment and chronic disease.