EFFECT OF BACTERIAL LIPOPOLYSACCHARIDES ON SULFATED GLYCOSAMINOGLYCANMETABOLISM AND PROSTAGLANDIN E(2) SYNTHESIS IN EQUINE CARTILAGE EXPLANT CULTURES

The metabolic responses of equine articular cartilage to incubation wi th bacterial lipopolysaccharide (LPS) were studied, using explant cult ures of articular cartilage obtained from the metatarsophalangeal join ts of 15 horses, age of which ranged from 3 months to 20 years. For co mparison, explants were also established from the metatarsophalangeal joints of 3 calves. Explants were cultured for 3 days in medium contai ning various concentrations of LPS from 0 (control) to 100 mu g/ml. Gl ycosaminoglycan (GAG) released during the 3-day incubation was determi ned by a spectrophotometric assay, using the dye 1,9-dimethylmethylene blue. Newly synthesized GAG content was assayed by measuring [S-35]su lfate incorporation during a S-hour pulse labeling period. In addition , prostaglandin E(2) (PGE(2)) synthesis was quantified, using a [H-3]P GE(2) radioimmunoassay kit and magnetic separation. Finally, explants from 3 animals were used to evaluate the effect of supple menting cult ure medium with 5% serum on the re sponse of explants to LPS, and expl ants from 1 horse were used to compare responses to stimulation with L PS derived from 2 bacterial sources. Equine explants cultured with bac terial LPS had a dose-dependent decrease in synthesis and increase in release of GAG, and these responses were significantly (P < 0.0001) gr eater in explants from younger horses. In addition, equine explants ha d a significant (P = 0.0001) dose-dependent increase in concentration of PGE(2) released into the culture medium in response to incubation w ith LPS. Comparison of data for GAG synthesis from equine and bovine e xplants revealed a significant (P = 0.025) difference in responsivenes s to LPS between the 2 species. Equine explants tended to have a great er suppression of GAG synthesis in response to incubation with increas ing concentrations of LPS than did age-corrected bovine samples. Howev er, similar analysis of data on GAG release did not indicate any diffe rence in sensitivity between the 2 species for this response. There wa s no evidence that the presence or absence of serum supplementation or the use of LPS derived from different bacterial sources made a signif icant difference in the response of explants to incubation with LPS.