ABNORMAL CANCELLOUS BONE-COLLAGEN METABOLISM IN OSTEOARTHRITIS

Biochemical investigations into the pathogenesis of osteoarthritis hav e, for the last two decades, concentrated on the mechanisms involved i n the destruction of the articular cartilage. Although bone changes ar e known to occur, the biochemistry of the collagenous matrix within os teoarthritic bone has received scant attention. We report that bone co llagen metabolism is increased within osteoarthritic femoral heads, wi th the greatest changes occurring within the subchondral zone. Collage n synthesis and its potential to mineralize were determined by the car boxy-terminal propeptide content and alkaline phosphatase activity, re spectively. These data supported elevated new matrix formation. Our fi nding of a three- to fourfold increase in TGF-beta in osteoarthritic b one indicates that this might represent a stimulus for the increased c ollagen synthesis observed. Of additional significance is the hypomine ralization of deposited collagen in the subchondral zone of osteoarthr itic femoral heads, supporting a greater proportion of osteoid in the diseased tissue. The cross-linking of collagen was similar to that obs erved for controls. In addition, the degradative potential of osteoart hritic bone was considerably higher as demonstrated by increased matri x metalloproteinase 2 activity, and again the greater activity was ass ociated with the subchondral bone tissue. The polarization exhibited i n the metabolism of bone collagen from osteoarthritic hips might exace rbate the processes involved in joint deterioration by altering joint morphology. This in turn may alter the distribution of mechanical forc es to the various tissues, to which bone is a sensitive responder. Bon e collagen metabolism is clearly an important factor in the pathogenes is of osteoarthritis and certainly warrants further biochemical study.