Biochemical evaluation of organ cultures from primate flexor tendons

Recently our laboratory has reported, in a lacerated flexor tendon model, that the "early turnover" phase of the repair process extends for a longer period of time in vivo than previously documented. The extensive turnover of the collagenous matrix was consistent with the presence of collagenolytic activity in repairing tendon tissue and suggested a possible regulatory role for neutral metalloproteinases in flexor tendon repair. However, these in vivo observations could not distinguish the relative contribution by the tendon fibroblasts from that of the surrounding sheath and vascular tissue elements. To further define these interrelationships, the present study investigates the repair process of the flexor tendon in an in vitro tissue culture environment. The sequential changes in matrix formation were defined (i.e., proteoglycans/glycosaminoglycans, glycoproteins, and collagenous proteins). The concomitant production of neutral metalloproteinases as well as prostaglandin E2 was determined in relation to net tissue repair. Profundus flexor tendon segments were obtained from young adult Macaca nemestrina monkeys and maintained in organ culture for periods from 4 days through 9 weeks. Initially (at 2 wks) there was an increase in both sulfated and nonsulfated glycosaminoglycans, which preceded the onset of maximal collagen protein formation. By 6 and 9 weeks of in vitro repair, of the lacerated tendon segments, there was a significant increase in net collagen formation. Neutral metalloproteinase activity increased early in the repair period, from the 4th to 9th day, and decreased thereafter through the 9th week of culture. Functionally the enzyme appeared to be a gelatinase. The temporal pattern of in vitro collagen synthesis in relation to the gelatinase activity support the hypothesis that regulation of this enzyme(s) may be a critical factor in mediating the flexor tendon response to injury.