Lysosomal Thiol Proteases (Cathepsin B-like Proteases) in Serous Middle Ear Effusions from Adult Patients

Abstract

Hydrolytic activity of cathepsins B, H and trypsin-like proteases was measured in 38 serous middle ear effusion (MEE) samples. The concentrations of (alpha 1-AT) and alpha 2-macroglobulin (alpha 2-M) were also quantitated. The mean value of cathepsin B activity was 25.0 +/- 20.7 RFU and that of cathepsin H was 14.3 +/- 3.0--both significantly higher than those in plasma (1.8 +/- 0.4 RFU, 1.2 +/- 0.3 RFU, p less than 0.005). Very low trypsin-like protease activity could be observed. The mean concentrations of alpha 1-AT and alpha 2-M were 368 +/- 94.8 mg/dl and 57.5 +/- 57.3 mg/dl. The bulk of alpha 1-AT in MEEs was occupied by free alpha 1-AT, which can saturate exogenous trypsin. Due to the very low molar concentration of alpha 2-M in MEEs, thiol proteases (mainly cathepsin B) could be a possible major factor inflicting proteolytic injury on the middle ear mucosa and reflecting the severity of the inflammatory process.

Association of Reflux With Otitis Media in Children

“…The potential endogenous production of pepsinogen in the middle ear mucosa also needs to be ruled out in order to establish reflux as the mechanism for finding pepsin or pepsinogen in middle ear fluid. Several groups of investigators have established that the production of enzymes may be induced in the middle ear during acute infections and with chronic effusions, 18–20 so that it is possible that the production of pepsinogen may also be inducible in the middle ear. Isozymogens of pepsinogen have been identified in other tissues in the body other than the stomach, including intestine, lung, pancreas, prostate, and some malignancies 21 .…”

Endotoxin and Lysosomal Protease Activity in Acute and Chronic Otitis Media with Effusion

“…Several investigators have reported that the endotoxin level in MEE is one of the parameters reflecting the chronicity of OME in children.>:" Lysosomal proteases in the middle ear mucosa and MEE have been shown to play significant roles during the disease processes of OME, because their proteolytic activity causes tissue damage and prolongs middle ear inflammation by activating proenzymes (kininogen and plasminogen) and the complement system. [9][10][11] Lysosomal proteases seem to suppress the recovery from acute OME unless they are inactivated by protease inhibitors. 12 .…”