[An experimental model of osteoarthritis. II.- Biochemical study of collagen and proteoglycans]

We investigated biochemical modifications of the initial phase of cartilage degradation in an osteoarthritic model developed in the rabbit by intraarticular papain injection. The amino-acid composition of the collagen did not differ significantly between control and papain-treated groups. After 3H-proline in vivo incorporation, the absence of radioactivity in peaks beta 12 and alpha 2 shows that cartilage did not synthesize type I collagen in noticeable quantity during the labelling period. The study of proteoglycans by the use of the "fixed charges density" (FCD) shows that in our model they decreased rapidly and substantially, as in human disease. The decrease was measurable from 1 h after injection with a minimum at about 24 h (54% of the normal level). However, increased 35SO4 incorporation was observed, beginning very soon after injection and passing through a maximum (500% of the normal level) around the 3rd day. The rates of 3H-proline incorporation and 3H-hydroxyproline formation were decreased in the treated cartilage in a similar way as for the proteoglycans, with a minimum (55% of the normal level) at about 24 h. The "turn-over" of 3H-hydroxyproline and "non collagen" 3H-proline were increased in the treated cartilage. The half-lives of both amino-acids went respectively from 26 to 15 days and from 14 to 10 days. Injection of papain in the rabbit knee-joint produced a major loss of ground substance and a reaction of the chondrocytes. The cells metabolism seemed modified with especially a catabolism stimulation.