Insulin-like growth factor 1 and corticosteroid modulation of chondrocyte metabolic and mitogenic activities in interleukin 1-conditioned equine cartilage

Abstract

Objective - To evaluate potential stimulatory or matrix-sparing effects of insulin-like growth factor 1 (IGF-1), alone or in combination with a corticosteroid, in an interleukin 1 (IL-1)-induced model of cartilage degradation. Samples - Cartilage from the weightbearing surfaces of trochlea and condyles of clinically normal 2-year-old male horses. Procedure - Triamcinolone acetonide and IGF-1 effects were evaluated by assessing: matrix responses by sulfated glycosaminoglycan (GAG) assay and [35S]sulfated GAG synthesis; collagen content by hydroxyproline assay; and mitogenic response by [3H]thymidine incorporation into DNA and fluorometric assay of total DNA concentration. Results - Conditioning of cartilage explants with 10 ng of human recombinant IL-1α increased degradation and decreased synthesis of matrix proteoglycans (PG), without affecting matrix collagen content. Human recombinant IGF-1 decreased PG loss and reversed the reduction of PG synthesis in cartilage explants conditioned with IL-1. Given alone, steroids decreased PG concentration and synthetic rate in normal cartilage. However, the previously diminished PG content, attributable to IL-1 conditioning, was not further exacerbated by steroid administration in IL-1-conditioned explants. Combined treatment of normal cartilage explants with IGF-1 and steroids resulted in PG preservation and increase in collagen content. Similar PG and collagen effects were not evident when treating IL-1-conditioned cartilage with IGF-1/steroid combinations. Decrease in chondrocyte proliferation was associated with steroid administration. Exposure to IGF and steroids prevented the decrease in mitogenesis that could lead to cellular loss, particularly in IL-1-conditioned explants. Conclusion - Combination IGF-1 and steroid treatment of normal cartilage cultures indicated substantial ability to override the anabolic suppression associated with steroids alone. Potentially, administration of corticosteroids, followed by IGF-1, may act to decrease propagation of detrimental mediator release while allowing appreciation of the chondroenhancing effects of IGF-1. These beneficial effects were considerably reduced in IL-1-induced cartilage damage.