Oxidation of articular cartilage glyceraldehyde-3-phosphate dehydrogenase (G3PDH) occurs in vivo during carrageenin-induced arthritis.

Articular cartilage proteoglycan biosynthesis was substantially inhibited by the competitive glycolytic inhibitor 2-deoxyglucose (approximately 65% at 100 mM), but to a much lesser degree (approximately 10%) by the oxidative phosphorylation uncoupler, 2,4-dinitrophenol. These results confirm that articular cartilage proteoglycan synthesis mostly utilises ATP which is generated by glycolysis. In addition, we have utilised the loss of the relatively specific labelling of glyceraldehyde-3-phosphate dehydrogenase (G3PDH) by [3H]-iodoacetic acid to show that rabbit articular G3PDH is oxidised in vivo during the animal model of acute arthritis, carrageenin-induced arthritis, in the same way as we have previously shown that cartilage G3PDH is oxidised after in vitro exposure to sublethal doses of H2O2. The oxidation of rabbit G3PDH in vivo (18 hr post-injection) corresponds with the maximal influx of PMNL cells into the arthritic synovial fluid and with substantial inhibition of proteoglycan core protein synthesis. We propose that H2O2 released from "activated" PMNLs and macrophages is responsible for the "down-regulation" of biosynthetic processes found in cartilage during acute inflammation.

The role of serine proteinase in cartilage damage.

Arthritic cartilage from experimental animals has been shown to have a decreased proteoglycan content, a decreased rate of proteoglycan synthesis, and a marked increase in an active serine proteinase when compared with normal articular cartilage. The serine proteinase is transferred from PMN cells into cartilage during the inflammatory response where it increased the rate of proteoglycan degradation and is eventually removed by interaction with the chondrocyte surface. The interaction also results in an inhibition of proteoglycan synthesis by the chondrocytes. Both these factors contribute to the loss of proteoglycan from arthritic cartilage.

Carrageenin-induced arthritis. VI. Alterations in amino acid transport by articular cartilage in acute inflammatory arthritis.

The mechanism of transport of alanine and aminoisobutyric acid into chondrocytes in rabbit articular cartilage was shown to be mediated by transport systems similar to that described for other eukaryotic cells namely the A, ASC, and L systems. Three days after the initiation of an acute inflammatory arthritis by the intra-articular injection of carrageenin into one knee joint the rate of transport of both these amino acids was decreased. Although all three transport systems were depressed, it appeared that the A and ASC systems were partially susceptible to damage by the induced inflammation. The rate of amino acid transport by the affected cartilage had recovered by 28 days after carrageenin treatment. This depression in amino acid transport is discussed in relation to a decrease in general metabolic processes in chondrocytes as a consequence of inflammation.

Evidence for polymorphonuclear-leucocyte-derived proteinases in arthritic cartilage.

1. An enzyme that degrades proteoglycan at neutral pH was extracted with 4 M-guanidine hydrochloride from the articular cartilage of rabbits with antigen-induced arthritis. 2. The enzyme had an apparent molecular weight on Ultrogel AcA 54 of about 8000 and was optimally active at pH 7.5 in Tris/HCl buffer containing 0.2 M-NaCl. The partially purified preparation was totally inhibited by 0.01 mM-N-acetyldialanylprolylvalylchloromethane, severely inhibited by 2 mM-phenylmethanesulphonyl fluoride and soya-bean trypsin inhibitor (200 microgram/ml) and slightly inhibited by 10 mM-EDTA. Marked inhibition was also obtained with a cytosolic fraction prepared from rabbit polymorphonuclear leucocytes. 3. All properties of the enzyme were virtually identical with those of an 'elastase-like' proteinase that was isolated from rabbit polymorphonuclear-leucocyte granules. 4. The results are consistent with the idea that cartilage proteoglycan degradation in acute joint inflammation is due at least partly to the diffusion into the cartilage of proteinases derived from synovial-fluid polymorphonuclear leucocytes.

Antigen-induced arthritis. Studies on the inhibition of proteoglycan synthesis observed in articular cartilage during short-term joint inflammation.

During the acute phase of antigen-induced arthritis, cartilage was obtained from five different sites within the joint, and chondrocyte activity was assessed by autoradiography of sections labeled with 35S-sulfate. There was a marked inhibition of chondrocyte proteoglycan synthesis in all weight-bearing areas; in addition, the complete superficial layer of cells and many mid-zone cells in these areas were completely inactive. Electron microscopy showed that the inactive surface cells had degenerated completely, and that many mid-zone cells contained an accumulation of intracytoplasmic filaments and were depleted in biosynthetic organelles. A biochemical study of the inhibition showed that: 1) the incorporation of 35S-sulfate and 3H-acetate into glycosaminoglycans was inhibited to a similar extent; 2) the inhibition of glycosaminoglycan synthesis could not be reversed either by the addition of benzyl-beta-D-xyloside to incubations or by maintenance of the cartilage in organ culture for 6 days; 3) the inhibited chondrocytes exhibited a decreased ability to secrete proteoglycans into the extracellular fraction of the cartilage.

Antigen-induced arthritis. Decreased proteoglycan content and inhibition of proteoglycan synthesis in articular cartilage.

An arthritis was induced in rabbits immunized with human serum albumin by injection of antigen into the hind knee joint. Histological changes in the synovial membrane and an increase in polymorphonuclear granulocytes in the synovial fluid indicated an inflammatory response similar to that described with fibrin as antigen (1). The arthritis was accompanied by no significant change in the collagen content, but a marked decrease in the proteoglycan content of the cartilage was noted. Cartilage from inflamed joints generally exhibited a decreased ability to synthesize proteoglycan in vitro.

Manganese levels and the morphology of the epiphyseal plate in broilers with slipped tendons.

Manganese deficiency in chickens results in perosis and a higher incidence of slipped tendon. Perosis is associated with a disorganization of the epiphyseal growth plates and changes in the chemical composition of the cartilage matrix. Male broilers with slipped tendons were selected from a commercial broiler farm over a 9 week growing period. Their growth rates, epiphyseal cartilage histology and tissue manganese concentrations were examined and compared with (a) normal broilers from the same farm, and (b) similar broilers raised on control and manganese deficient diets. Field broilers with slipped tendons showed no evidence of abnormality in the histological appearance of the proximal tibial growth plate at any of the ages examined. The manganese content of liver and epiphyseal cartilage from field broilers showing slipped tendon was comparable with that present in tissue from normal broilers wither from the field or raised on a chemically defined diey supplemented with managese. The slightly retared growth rate seen in the field broilers was attributed to feeding problems associated with the lameness condition. These results provide conclusive evidence that slipped tendon in field broilers is not dur to a manganese deficiency in the tissues, nor does it appear to be associated with abnormal proliferation of the chondrocytes in the epiphyseal plate.