LIPOPOLYSACCHARIDE ALTERS AGGRECAN METABOLISM IN THE GROWTH-PLATE

In this study, we examined the influence of lipopolysaccharide (LPS) o n aggrecan metabolism and structure in the growth plate, Two experimen tal approaches were used: (i) in vivo administration of LPS to 10-day- old chicks; and (ii) in vitro addition of LPS to explant culture of no rmal chick growth plate, Twelve-day-old male broiler chicks were kille d 48 hr after intravenous injection of LPS (3 mg/kg) or saline (contro l), and growth plate from the femur or tibia was cultured or frozen, T issue for explant culture was (i) cultured for 5 days with daily mediu m change (glycosaminoglycan release into the medium estimates proteogl ycan breakdown rates), or (b) incubated with (SO4)-S-35 to determine t he rate of proteoglycan synthesis, Proteoglycan structure was determin ed by associative (0.5 M sodium acetate) and dissociative (4 M guanidi ne HCl) Sepharose CL2B chromatography. Explant culture of growth plate from LPS-injected chicks (in vivo) showed a decrease (P <0.05) in the rate of proteoglycan synthesis, There were a greater proportion of sm all monomers and a reduced ability to aggregate in growth plate from L PS-injected chicks, In vitro addition of LPS (100 mu g/ml) to explant culture medium reduced proteoglycan synthesis (P <0.02), and the rate of release was increased (P <0.001). In addition, the total and newly synthesized proteoglycans released into the medium from LPS-treated ex plant culture had a reduced aggregation and a majority of monomers tha t were smaller than control, These results demonstrate that LPS disrup ts the normal metabolism and structure of growth plate aggrecan, and w e hypothesize that this may adversely influence longitudinal growth.