Influence of interleukin-1 beta and hyaluronan on proteoglycan release from equine navicular hyaline cartilage and fibrocartilage

Proteoglycan (PG) release, in response to recombinant human interleukin-1 b eta (rh-IL-1 beta), was measured in cartilage explants obtained from the eq uine distal sesamoid bone (navicular bone). Fibrocartilage from the surface of the navicular bone apposing the deep digital flexor tendon and hyaline cartilage from the surface of the navicular bone articulating with the midd le phalanx were labelled with (SO4)-S-35. Hyaline cartilage from the distal metacarpus was used as a control tissue. Following radiolabel incorporatio n, the three cartilage types were treated with rh-IL-1 beta (100 U/mL) in t he presence of hyaluronan (0.2, 2, 20, 200 and 2000 mu g/mL). rh-IL-1 beta- Induced PG release was measured by scintillation assay of PG-bound radiolab el. Increases in PG release of 94% (P < 0.01), 101% (P < 0.05) and 122% (P < 0.05), in response to rh-IL-1 beta, were noted in fibrocartilage, navicul ar hyaline cartilage and metacarpal hyaline cartilage, respectively. Hyalur onan (0.2 mu g/mL) significantly reduced rh-IL-1 beta-induced PG release in metacarpal hyaline cartilage (P < 0.01). In fibrocartilage and navicular h yaline cartilage, hyaluronan did not reduce PG release and at some concentr ations appeared to increase PG release, although this was not statistically significant. These experiments show that (i) fibrocartilage and hyaline ca rtilage of the navicular bone release PGs in response to rh-IL-1 beta, and (ii) hyaluronan does not prevent rh-IL-1 beta-induced breakdown of navicula r bone cartilage.