CHONDROGENESIS IN PERIOSTEAL EXPLANTS - AN ORGAN-CULTURE MODEL FOR IN-VITRO STUDY

Periosteal grafts have chondrogenic potential and have been used to re pair defects in articular cartilage. We studied the effects of the cul ture conditions and of transforming growth factor-beta 1 on chondrogen esis in rabbit periosteal explants that were cultured in vitro. A tota l of 390 periosteal explants were obtained from the anteromedial sides of the proximal parts of the tibiae of eleven rabbits that were two w eeks, two months, or six months old. The culture medium (alpha minimum essential medium or Dulbecco minimum essential medium) contained feta l calf serum, with or without transforming growth factor-beta 1, at a concentration of one or ten nanograms per milliliter for the first two weeks of culture. Three hundred and twenty-one explants were submerge d in liquid medium and sixty-nine were suspended in an agarose gel; th ey were then evaluated histochemically, histomorphometrically, and by collagen-typing. In the media without agarose, in the presence of ten nanograms of transforming growth factor-beta 1 per milliliter, chondro genesis was commonly seen after two to four weeks with use of safranin -O staining and histomorphometry. In the agarose gels, chondrogenesis from the periosteum was observed at four and six, weeks and was enhanc ed by the presence of one or ten nanograms of transforming growth fact or-beta 1 per milliliter. The combination of agarose, with transformin g growth factor-beta 1 most favored the formation of cartilage, which was maximum at six weeks in the presence of ten nanograms of transform ing growth factor-beta 1 per milliliter. Under these conditions, chond rogenesis occurred in almost every explant, with 50 +/- 30 per cent of the tissue being composed of cartilage. Type-II collagen was present in the explants that had undergone chondrogenesis. CLINICAL RELEVANCE: The finding that transforming growth factor-beta 1 ran induce chondro genesis in the periosteum, particularly when the explant had been cult ured in an agarose gel, confirms the potential of the periosteum to fo rm cartilage. With use of in vitro methodology to define the optimum c onditions that enhance chondrogenesis, it should be possible to elicit chondrogenesis, when periosteal grafts are used to repair cartilage d efects in vivo.