Increased activity of serum angiotensin-converting enzyme in progressive silicosis

The serum activity of angiotensin-converting enzyme (ACE, EC 3.4.15.1) in 135 male silicosis patients was analyzed. Twenty-eight of the patients had referents matched for silica dust exposure and age but without roentgenographic signs of silicosis. A reference group not exposed to silica dust comprised 34 lumberjacks. The serum mean activity of ACE was higher in silicosis patients (46.6 +/- 12.1 units/L) than in the referents exposed to silica (38.5 +/- 8.1 units/L) or in the lumberjacks (36.6 +/- 9.7 units/L). There was an association between the serum ACE level and the roentgenographic severity of fibrosis. A retrospective side-by-side assessment of roentgenographic progression was made in 49 silicosis patients. The ACE was higher in the 18 patients with progression (50.5 +/- 16.4 units/L) than in those with no progression (41.5 +/- 9.5 units/L). According to the multivariate regression analysis, progression of fibrosis explained the elevation of ACE better than profusion. The results confirm that the serum ACE activity is elevated in silicosis and suggest that the elevation is associated with progression of the disease.