[3H]proline incorporation and hydroxyproline concentration in articular cartilage during the development of osteoarthritis caused by immobilization. A study in vivo with rabbits

Abstract

Proline metabolism in vivo was studied during the development of immobilization osteoarthritis in rabbits. Collagen content was measured as the hydroxyproline concentration of the tissue in question. The incorporation of [3H]proline was used as the indicator for total protein synthesis; collagen synthesis rate was estimated from measurements of the specific radioactivity of hydroxyproline. Cartilage samples from knee and hip joints were analysed after 3, 7, 11, 18, 35 and 56 days of immobilization. The total protein and collagen synthesis rates of the immobilized legs increased and reached a maximum after 11-35 days. Although they decreased thereafter, these rates remained elevated to the end of the experiment. A slight increase in the synthetic activity of the non-immobilized contralateral legs was also detected after 7--18 days of immobilization. The isotope incorporation was markedly higher in tibial marginal tissue than in weight-bearing cartilage. In spite of the increased synthesis, no clear changes were found in the collagen content of the tissues studied during the experiment.

The Role of Changes in Extracellular Matrix of Cartilage in the Presence of Inflammation on the Pathology of Osteoarthritis

“…Unlike the decreased production of proteoglycan, collagen synthesis rate increases in the early stages of OA and remains elevated [8]. In addition to the increased ratio of collagen/aggrecan synthesis, the composition of collagen type has been also shown to change from collagen type II to type I [9].…”

Changes of articular cartilage after immobilization in a rat knee contracture model

“…Data for histological scores were analyzed statistically using the Kruskal-Wallis test, and data for thickness, number of 16 weeks, (E) control group at 16 weeks, and (F) a standardized sagittal section of the medial midcondylar region of the knee after 8 weeks immobilization. The articular cartilage lost luster only after 1 week of immobilization, and the surface became rough and a protrusion was observed after 4 weeks.…”

“…3 Biochemical changes of the articular cartilage after immobilization have been reported as increased hydration, [4][5][6][7] decreased proteoglycan (PG) content, 5,6,[8][9][10][11][12][13][14] altered PG aggregate structure, 7,9,[12][13][14] increased collagen synthesis, 15,16 and maintained or elevated collagen content. 6,[14][15][16] Histological examination revealed decreased PG staining intensity, 11,17 decreased thickness, 5,17,18 and progression of degenerative changes by histological grading scheme. 19 Though a large number of experimental studies regarding the articular cartilage after immobilization have been reported, changes occurring in a joint cavity after joint immobilization have not been fully clarified.…”

Altered swelling behavior of femoral cartilage following joint immobilization in a canine model

“…These changes have been widely studied in rabbit and canine models, and include alterations in cartilage composition, such as reduced proteoglycan content, measured as decreases in hexuronic acid content [5,16,21,35,38,41] Safranin 0 staining [15,25], as well as decreases in the ratio of proteoglycan to water content [45]. Also, periods of joint immobilization may induce changes in the conformation of cartilage proteoglycans [21,35,38,41,42,47,481, increased hydration [5,21,38,45] and changes in chondrocyte biosynthesis [5,38,46,47,49,50]. Several studies reported cartilage thinning [15,22,26,37,38], while others have not reported any change in cartilage thickness following immobilization [14, 25,45,48].…”