Enhanced breakdown in vitro of bovine articular cartilage proteoglycans by conditioned synovial medium: The Effect of Phenylglyoxal

Abstract

Addition of conditioned medium derived from fragment cultures of synovial tissue dissected from bovine knee joints (SM) to cultures of articular cartilage derived from the same animal resulted in enhanced breakdown of cartilage proteoglycans, measured as the release of [³⁵S] sulphate from pieces of prelabelled cartilage. Addition of conditioned medium from synovial tissue that had been cultured with 50 μg/ml dextran sulphate (DS-SM) to the cartilage cultures greatly enhanced cartilage degradation.

Phenylglyoxal is an arginine-specific reagent which has been shown to destroy the activity of interleukin 1 (former called LAF, lymphocyte-activating factor). The addition of phenylglyoxal (0.01, 0.1 or 1.0 mM) to the cartilage cultures did not affect cartilage degradation, whereas the addition of 2.5 mM phenylglyoxal seemed to inhibit cartilage breakdown. However, the cartilage degradation induced by SM was inhibited in a dose-dependent manner by the addition of phenylglyoxal (0.1, 1.0 and 10.0 mM). Also culturing the synovial tissue with phenylglyoxal (1.0 mM) inhibited the synovial-enhanced cartilage degradation. The addition of phenylglyoxal (1.0 mM) together with DS-SM to the cartilage cultures reduced cartilage degradation to that exerted by SM. Culturing the synovial tissue with both dextran sulphate (50 μg/ml) and phenylglyoxal (0.1, 1.0 and 10.0 mM) also dose-dependently reduced cartilage degradation to that exerted by SM.

It is therefore suggested that the cytokines produced by synovial tissue in culture may be related to interleukin 1. However, the role of other proteins, such as degradative enzymes, cannot be completely ruled out.