Biochemical characterization of cartilage degradation in embryonic chick tibial explant cultures.

The growth plates of birds reared for meat production are susceptible to diseases such as tibial dyschondroplasia (TD). We have modified a tibial explant culture system to study the regulation of growth plate cartilage turnover. The purpose of these experiments was to characterize some of the biochemical changes that occur in cultured tibiae as the cartilage is degraded. Tibiae were dissected from 12-d-old embryos and cultured in medium formulated for chondrocytes. Proteoglycan and nitric oxide concentrations as well as metalloproteinase and lactate dehydrogenase activities were measured in recovered media. Metalloproteinase activity was also measured in cartilage extracts from tibiae collected every 2 d during the culture period. Proteoglycan and nitric oxide concentrations in recovered media increased after 8 d in culture and peaked on Day 14. Lactate dehydrogenase (LDH), an indicator of cell death, increased in media after 10 d in culture. Metalloproteinase activity in the cartilage increased after 6 d, whereas activity in recovered media did not increase until after Day 10. These results suggest that chondrocytes in the tibiae undergo hypertrophy, degrade the extracellular matrix, and die. Further experiments demonstrated that pyrrolidine dithiocarbamate (PDTC), which is from a family of molecules that induce TD, inhibited both nitric oxide production and proteoglycan degradation. Thus, we think our tibial explant culture system can be useful in elucidating molecules that regulate growth plate cartilage turnover as well as predicting what conditions or molecules might lead to bone growth problems in birds.