Monitoring glycosaminoglycan replenishment in cartilage explants with gadolinium-enhanced magnetic resonance imaging

We previously devised a magnetic resonance imaging method. that allows for the nondestructive and quantitative determination of glycosaminoglycan conc entration in excised cartilage. The technique measures the concentration of the charged contrast agent Gd-DTPA(2-) (gadolinium diethylenetriamine pent aacetic,acid) equilibrated within cartilage, from which the tissue distribu tion of glycosaminoglycan can be calculated. The goals of our study were to determine the practicality pf nondestructively monitoring glycosaminoglyca n concentration in cartilage explants over a long-term culture period and t o determine if glycosaminoglycan could be restored to glycosaminoglycan-dep leted cartilage explants maintained in longterm culture. To meet our object ives, we harvested bovine cartilage explants, treated them initially with t rypsin to reduce the glycosaminoglycan concentration, and cultured them for as long as 8 weeks. Images depicting glycosaminoglycan concentration were calculated from magnetic resonance images acquired at selected intervals du ring the trypsinization process and the subsequent culture period. The resu lts indicate that gadolinium-enhanced magnetic resonance imaging can follow the reduction of glycosaminoglycan concentration over the course of enzyma tic digestion and the replenishment of glycosaminoglycan over several weeks of culture and that cultured cartilage explants are, capable of restoring glycosaminoglycan to 85% of its initial concentration.: Of particular inter est, samples cultured for 5 weeks indicated a depth dependence of glycosami noglycan regeneration to values similar to the-initial physiologic distribu tion. Thus, this magnetic resonance imaging method may be a very powerful m eans for exploring the spatial and temporal evolution of glycosaminoglycan in cartilage.