A synovial amidase acting on tissue kallikrein-selective substrate in clinical and experimental arthritis.

Increased levels of amidase acting on a tissue-kallikrein selective substrate, Val.Leu.Arg.pNA, with an activity optimum at pH9, were detected in blood-free inflamed tissues from adjuvant arthritic rats (p less than 0.01). The component of this activity resistant to inhibition by soybean trypsin inhibitor (SBTI) also greatly increased (p less than 0.05). Both the SBTI-sensitive and SBTI-resistant components were inhibited by aprotinin (93% and 72% respectively). Kallikrein-like amidase also increased in inflamed synovia from seropositive rheumatoid, and osteoarthritic dogs when compared with healthy canine synovia. This increase was parallelled by an increase in kinin-forming enzyme which was also measured in rheumatoid and healthy animals and this activity was inhibited 72% by aprotinin. Total kallikrein-like amidase also increased 989% (p less than 0.05) in synovia from seropositive rheumatoid human patients, compared with healthy synovial tissue. Evidence is presented indicating that the origin of this enzymic activity may be plasma kallikrein.