Transport properties of the human cartilage endplate in relation to its composition and calcification

Study Design. The transport properties of solutes of different sizes and conformations were studied in cartilage endplates. Objectives. The results were correlated with the composition of the cartilage matrix to determine if a relationship existed between this and the movement of molecules within it. Summary of Background Data. Solute transport through the hyaline cartilage endplate is important not only for the physiologic and metabolic processes of that tissue, but also for those of the adjacent intervertebral disc. Movement of solutes depends on solute size, shape or charges, and the composition of the matrix itself. Change in composition of the cartilage endplate, such as those that occur in degeneration or scoliosis, may affect transport. Methods. Partition and diffusion coefficients of solutes ranging in molecular weight from 115 to 70,000 d have been measured on cores of cartilage endplate. Transport properties were assessed in relation to core composition. Results. The shape and size of the solutes were found to affect their transport through cartilage matrix, with larger molecules being more highly excluded and diffusing more slowing. Long-chain polymers were able to penetrate the matrix less readily than the more globular molecules. The more hydrated the matrix, the higher the degree of penetration and the mor easily solutes could move, in contrast to the inverse relationship between the other components of the matrix and solute transport. With increased proteoglycan, collagen, or calcification in the tissue, there was greater restriction of solute movement. Conclusions. The proteoglycans normally found in the endplate regulate movement of solutes into and out of the disc. It has been shown previously that removal of proteoglycans from the endplate accelerates the loss of proteoglycans from the nucleus. Hence, a major function of the cartilage endplate may be to prevent fragments of osmotically active proteoglycans from leaving the disc.