Correlation of HR-MAS spectroscopy derived metabolite concentrations with collagen and proteoglycan levels and Thompson grade in the degenerative disc

Study Design. A quantitative high-resolution magic angle spinning (HR-MAS) NMR study of human lumbar discs was conducted to determine biomarkers of disc degeneration. Objectives. To correlate HR-MAS quantification of compounds relevant to human lumbar disc degeneration to conventional methods of disc grading such as Thompson grading and biochemical analysis. Summary of Background Data. It has been shown that there is poor correlation between MRI and CT morphologic findings, spinal biomechanics, and patient symptoms in degenerative disc disease and low back pain. There is a need for an objective, quantitative measurement of biochemical status, morphology, and function. Methods. A total of 17 cadaveric human lumbar intervertebral discs were harvested from patients ranging from 20 to 85 years of age. Quantitative HR-MAS data were acquired, and proteoglycan and collagen biochemical analyses were conducted on 3-mm biopsy punches taken from the anulus fibrosus and nucleus pulposus of each sample. HR-MAS data were fitted and analyzed for hydroxyproline (3.42 ppm), glycine (3.56 ppm), and the N-acetyl peak (2.04 ppm) associated with proteoglycans in comparison with an internal standard. These concentrations were then compared directly to biochemical analyses and Thompson grade. Results. HR-MAS data correlated well with Thompson grade (P < 0.001). An increase was seen in the levels of unbound hydroxyproline and glycine in anular tissue, which is directly associated to collagen breakdown. This trend also correlates with the changes of total collagen measured by a collagen biochemical assay. HR-MAS also detected a decrease in concentration of nucleus pulposus proteoglycans with degeneration. This proteoglycan decrease was verified by a standard proteoglycan biochemical assay. Conclusions. Changes in disc chemical composition can be accurately quantified using quantitative HR-MAS NMR spectroscopy ex vivo. This noninvasive method of qualitatively and quantitatively assessing disc degeneration supports the utility of these biomarkers and underlines the need for developing in vivo magnetic resonance spectroscopic imaging (MRSI) for characterizing intervertebral disc degeneration.