Intracellular catabolin-like activity in cultured synovial tissue

What's happened to catabolin?

Unlike other areas of research into arthritis, it is pleasing to record independent work leading to convergence of ideas instead of divergence and increasing complexity. Catabolin is now identified with interleukin-1, although there is case for the retention of the original name to describe its chondrocyte-stimulating function with subsequent matrix degradation. In 10 years, catabolin/interleukin-1 research has yielded much information about cellular interactions within the arthritic joint and has provided a probe with which the intricacies of matrix metabolism are being unravelled. In future, there are prospects of characterizing the naturally occurring inhibitors and developing new compounds which influence the actions of catabolin/IL-1 to the benefit of the patient with arthritis.

In vivo studies of articular tissue damage mediated by catabolin/interleukin 1

A partially purified porcine synovial catabolin interleukin 1 (CF) preparation was injected intra-articularly into rabbit stifle (knee) joints. Radiolabelled CF was rapidly cleared from the joint (0.4 h). Repeated injections of CF caused a marked loss of articular cartilage glycosaminoglycan (GAG) and a great increase in synovial fluid GAG. 35SO4 uptake was inhibited. Time course experiments after a single injection produced similar loss of GAG from knee cartilages, which was maximal three days after injection. The above changes were significantly less with heat inactivated preparations. Loss of articular cartilage metachromasia was found histologically, and an acute synovitis occurred together with lymphocytic foci and plasma cell infiltration.

Production of cartilage degrading activity by human synovial tissues

Human synovial tissues have been assayed for the production of cartilage degrading activity (CDA). This activity is thought to be homologous with catabolin/interleukin 1 (IL1) produced by porcine synovium and leucocytes and by human leucocytes. The CDA of 26 rheumatoid (RA) and 41 non-rheumatoid synovia was measured on a dry weight basis. The rheumatoid synovia showed a threefold increase in activity over the non-rheumatoid, but there was no significant overall difference on a deoxyribonucleic acid (DNA) basis. The rheumatoid synovia appeared to consist of two populations; in over half the samples CDA was not related to cellularity, but eight patients had a high CDA and a high cellularity.

Porcine heart valves produce a protein that induces cell-mediated connective tissue degradation: I. Biological properties

Cultured porcine heart valves secrete a factor that induces cells to degrade their extracellular matrix. This activity was routinely monitored by measuring the release of glycosaminoglycans from proteoglycan in cultured bovine nasal cartilage. It was observed that factor-mediated matrix degradation was dose dependent and required live target cells, while factor production by valves was inhibited by cycloheximide and declined with reduced cell viability. The effect of various steroidal and nonsteroidal anti-inflammatory drugs on the production and activity of the factor is discussed with reference to similar cytokines. It is concluded that there is a close similarity between the cardiac catabolic factor described here and catabolin, a protein isolated from porcine synovia and leukocytes, as shown by the neutralization of biological activity with antisera raised to porcine catabolin (interleukin-1).

Release of interleukin-1 from human synovial tissue in vitro

During the enzymatic disaggregation of human synovium, used in the process of isolating synoviocytes, a factor was liberated into the culture medium that exhibited the thymocyte mitogenic properties of interleukin-1. Like interleukin-1, this synovial-derived mitogen could be isolated using an affinity column of antihuman leukocytic pyrogen. By gel filtration and isoelectric focusing, the mitogen cofractionated with human monocyte-derived interleukin-1. Finally, the isolated mitogen was shown to exhibit other properties of interleukin-1: stimulation of the secretion of interleukin-2, enhancement of the titer of acute-phase proteins in vivo, and stimulation of the release of prostaglandin E2 from human synoviocyte cultures. These observations suggest that interleukin-1 can be derived from the human synovium.

A catabolin-like factor from porcine kidney

Explants of pig kidney cortex and medulla release a catabolin-like factor (CLF). The CLF of both kidney cortex and medulla can be precipitated with ammonium sulphate, mainly in the 60-95 per cent fraction. By gel chromatography the kidney CLF showed a major active fraction at a molecular weight of around 22 500. Whole glomeruli and dissociated glomerular cells in culture also released into the medium a CLF that could be bioassayed in live cartilage but displayed no effect on dead cartilage. The possible role of such a local hormone is discussed.