Age-related decrease in the responsiveness of rat articular chondrocytes to EGF is associated with diminished number and affinity for the ligand of cell surface binding sites.

The effect of age on the responsiveness of articular chondrocytes (AC) to epidermal growth factor (EGF) was examined. Cells were isolated by digesting cartilage fragments from the humeral and femoral heads of 21-day old, 8- and 14-month old rats with collagenase. The cells were cultured under standard conditions, as monolayers.

The mechanism of inhibition of endothelin-1-induced stimulation of DNA synthesis in rat articular chondrocytes.

Endothelin-1 (ET-1) is a potent mitogen for rat articular chondrocytes (AC) in short term culture (24 h). Prolonged incubation (72 h) of AC with ET-1 resulted in inhibition of [3H]thymidine incorporation. This inhibition seemed to be mediated by prostaglandins (PGs) released in response to ET-1, since indomethacin (INDO) enhanced ET-1-induced [3H]thymidine incorporation.

Mitogenic and metabolic actions of epidermal growth factor on rat articular chondrocytes: modulation by fetal calf serum, transforming growth factor-beta, and tyrphostin.

The effects of human recombinant epidermal growth factor (EGF) on rat articular chondrocytes from humeral and femoral head cartilage of 21-day-old Wistar rats were analyzed. The cells were cultured under standard conditions as monolayers. Cell proliferation was studied by [3H]thymidine incorporation and determination of DNA content, proteoglycan synthesis by [35S]sulfate incorporation, and collagen synthesis by [3H]proline incorporation.

Effect of reactive oxygen species on the biosynthesis and structure of newly synthesized proteoglycans.

The effect of reactive oxygen species (ROS) generated by a xanthine oxidase hypoxanthine system (mainly H2O2) on proteoglycan (PG) metabolism and structure was investigated in vitro, using cell monolayers of cultured rabbit articular chondrocytes and purified resident and newly synthesized proteoglycans. It was shown that ROS generated in this system frequently stimulate (at low concentrations), and consistently inhibit (at higher concentrations), the incorporation of 35SO4 and 3H-glucosamine into PG molecules synthesized by cultured chondrocytes. The inhibition of isotopes' incorporation at higher enzyme concentrations was suppressed completely by heating xanthine oxidase and allopurinol with superoxide dismutase (SOD) and catalase.

Metabolic and structural changes in newly synthesized proteoglycans induced by implantation of a polyethylene sheet in the rabbit knee joint.

A sheet of polyethylene was surgically implanted in a rabbit right patello-femoral joint and changes in the structure and chemical composition of newly synthesized articular cartilage proteoglycans (PGs) were studied 1 month after surgery. The articular cartilage from implanted and sham-operated control knee joints was labeled in vitro with 3H-glycine and 35S-SO4 and then extracted with 4 M guanidinium chloride (GuHCl) solution. Labeled extracts were analyzed by dissociative CsCl gradient centrifugation and by Sepharose CL-2B column chromatography.