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Abstract
The goal of this project was to develop NMR spectroscopy techniques to provide nondestructive and noninvasive determinations of cartilage structural and functional integrity.
Because glycosaminoglycans (GAGs) have a net charge under physiological conditions, GAG concentration in the tissue is directly related to tissue fixed charge density (FCD). Using NMR sodium measurements in calf articular cartilage, we have calculated FCD on the order of that measured using other techniques. For calf epiphyseal cartilage, FCD varied with the position of the sample within the tissue, in a manner consistent with tissue GAG content determined using a biochemical assay. Results demonstrate the ability of sodium NMR to nondestructively measure FCD in cartilage and to follow changes in FCD with changes in matrix charge and composition.
To examine collagen, an NMR experiment known as magnetization transfer (MT) was performed. The amount of relative signal decrease, expressed as Ms/Mo, provides an indication of the amount of macromolecules present and of the interaction between macromolecular and water protons. We have shown that the MT effect is dependent on collagen concentration in collagen suspensions, collagen gels, soluble collagen suspensions, and cartilage, with an approximately logarithmic relationship. However, at concentrations on the order of those seen in vivo, MT is relatively insensitive to changes in concentration. In addition, we have demonstrated that factors other than concentration affect the MT signal in collagen suspensions and cartilage. We have also shown that an intact triple helix is important for MT; loss of the triple helix with thermal denaturation of soluble collagen suspensions resulted in substantially increased Ms/Mo. Furthermore, treatment with enzymes or low pH led to measurable differences in Ms/Mo which were not explained by differences in collagen concentration. They may be attributable to changes in matrix charge, structure and/or collagen fibril hydration (although changes in fibril hydration with trypsin and low pH produced conflicting results). These data demonstrate the ability of MT to detect changes in collagen concentration and collagen structure. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.) (Abstract shortened by UMI.)
