CHONDROCYTE TRANSPLANTATION TO ARTICULAR-CARTILAGE EXPLANTS IN-VITRO

The transplantation of chondrocytes has shown promise for augmenting t he repair of defects in articular cartilage. This in vitro study exami ned the efficiency of the transplantation of bovine chondrocytes onto articular cartilage disks and the ability of the transplanted chondroc ytes to subsequently synthesize and deposit proteoglycan. The radiolab eling of chondrocyte cultures with [H-3]thymidine, followed by 4 days of chase incubation, resulted in the incorporation of 98% of the radio label into DNA (as assessed by susceptibility to DNase). At the end of the culture period, the [H-3]DNA was stable, with a half-life of radi oactivity loss into the medium of 73 days. With use of radiolabeled ch ondrocytes for quantitation, the efficiency of transplantation onto a cartilage substrate was 93 +/- 4% for seeding densities of as much as 650,000 cells per cm(2) and a seeding duration of 1 hour. These findin gs were confirmed both by tracking cells stained with 5-chlormethylflu orescein diacetate and by quantitating DNA. During the 16 hours after seeding onto a cartilage substrate (in which the endogenous cells had been lysed by lyophilization), the transplanted cells synthesized sulf ated proteoglycan in direct proportion to the number of cells seeded. Most (83%) of the newly synthesized proteoglycan was released into the medium rather than retained within the layer of transplanted cells an d the recipient cartilage substrate. Comparative studies with lyophili zed-rehydrated or live cartilage as the recipient substrate indicated a similar efficiency of chondrocyte seeding and proteoglycan synthesis by the seeded chondrocytes. The transplanted cells retained the chond rocyte phenotype, as judged by a high proportion of the [S-35]macromol ecules being in the form of aggrecan that was capable of aggregating w ith hyaluronan and link protein, as well as by immunostaining within a nd around the transplanted cells for type-II, but not type-I, collagen . These results indicate that the number of chondrocytes transplanted onto a cut cartilage surface greatly affects the level of matrix synth esis; this in turn may affect repair.