Neutral proteases capable of proteoglycan digesting activity in osteoarthritic and normal human articular cartilage

Abstract

Proteases have been postulated to account for the progressive disappearance of matrix proteoglycans in osteoarthritic (OA) cartilage. The digestion of endogenous proteoglycans by neutral proteases in human OA cartilage homogenates has been measured and compared with that of normal age-matched controls. Cartilage was obtained from 16 patients at the time of knee arthroplasty and from 7 accident victims. Tissue blocks were cut from the tibia1 plateau; part was used for histologic grading of the severity of OA and part was homogenized for the quantification of neutral metalloand serine protease activities, based on the release of digested products from endogenous proteoglycans. Total metalloprotease activity (latent plus active forms) was elevated 3-to 10-fold in all diseased cartilage. This elevation was already significant in mild disease, but was greatest in samples of moderate to severe disease. The active form of the enzyme was highest at the center of erosions and decreased in the margins of the plateau. The digestion of proteoglycans, as distinct from their mere release from the tissue, was demonstrated by chromatography on Sepharose-CL2B and by large pore electrophoresis. Serine protease activity on proteoglycans was much lower than that of metalloprotease. The mean activity was highest in mild disease and declined in the severe disease samples, but the difference between these 2 groups and the controls was not statistically significant. The results of this study are consistent with the hypothesis that the neutral metalloproteases of cartilage are involved in the degradation of proteoglycans in osteoarthritis.Although the etiologic mechanisms of osteoarthritis remain unknown, one fundamental finding is always the progressive degeneration and erosion of articular cartilage. In early stages of the disease there is a consistent loss of matrix proteoglycans, as evaluated by histochemical and biochemical means (1-5).Accompanying this loss is an increase in water content, as well as disturbances in the chemistry of the remaining proteoglycans (1,(6)(7)(8)(9)(10) In the present study we have measured the activity of neutral proteases in human OA cartilage by their action on endogenous proteoglycans using a micromethod modified from the procedure of Sapolsky et a1 (15). We havc demonstrated a significant elevation of neutral metalloprotease activity in OA specimens, particularly in the modcrate-severe stages of the disease. A second protease activity of the serine type appeared to be quantitatively less important. Serine activity tended to rise in OA, but the elevation was not statistically significant. MATERIALS AND METHODS Chemicals. The chemicals used were either AmericanChemical Society certified or the best grade commercially available. DNA calf thymus type I, chondroitin sulfate, and phenylmethylsulfonyl fluoride (PMS-F) were purchased from Sigma Chemical Co., St. Louis, MO; bovine trypsin inhibitor from Boehringer Mannheim, Indianapolis, IN; paminophenylmercuric acetate (APMA), cetylpyridinium chloride, and ...

Role of synovial membrane inflammation in cartilage matrix breakdown in the Pond‐Nuki dog model of osteoarthritis

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Adenosine triphosphate pyrophosphohydrolase and neutral inorganic pyrophosphatase in pathologic joint fluids. Elevated pyrophosphohydrolase in calcium pyrophosphate dihydrate crystal deposition disease

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