Presence of dipeptidyl peptidase II, dipeptidyl peptidase IV, and prolyl endopeptidase in effusion from patients with serous otitis media

We have measured for the first time, using specific substrates and specific fluorometric analyses, activities of three pathophysiologically important peptidases, i.e., dipeptidyl peptidase II, dipeptidyl peptidase IV, and prolyl endopeptidase in effusions from 45 patients with chronic otitis media with effusion. In 20 patients, DPP II and DPP IV were assayed simultaneously in effusions and sera. Activity of PEP was also estimated in effusions and sera from 25 patients. The mean values (±SD) of DPP II and DPP IV ( n = 45) and PEP ( n = 25) in effusion from patients with OME were 0.020 ± 0.007, 0.66 ± 0.04, and 0.040 ± 0.006 nmole/min/mg protein, and 0.21 ± 0.01, 16.2 ± 1.87, and 1.90 ± 0.23 nmole/min/ml of effusion, respectively. The mean values (±SD) for DPP II, DPP IV, and PEP in sera were 2.82 ± 0.18, 54.8 ± 1.23, and 3.73 ± 0.33 nmole/min/ml of serum, respectively, which were similar to our previously reported values. Activities of DPP II, DPP IV, and PEP of serous effusions were comparable to those in serum. However, there was no significant correlation between their activities in serum and effusion. This may suggest that the major source of these enzymes in effusions may not be serum but the cells in the middle ear.