In the spinal cord, the nucleus pulposus (NP) is the collagen rich core of the intervertebral discs. Intervertebral disc degeneration (IDD) is thought to be a major contributor to lower back pain, which the majority of people will experience in their lifetime. Lumbar disc herniation (LDH) (displacement) is also one of the major causes of lower back pain. Changes in the NP leading to IDD could potentiate herniation, however changes in the NP of herniated patients is not well characterized.
Tao Zhang of Tianjin First Central Hospital, China, and colleagues, used Raman spectroscopy to determine compositional and structural changes in the NP from patients with LDH. They also investigated the biochemical mechanisms of IDD. The results were published in the journal Experimental and Therapeutic Medicine.
Between June 2016 and June 2018, NP samples were obtained from 30 patients with a mean age of 52 years, who were diagnosed with LDH and received spinal fusion surgery. A grading system (I-V) proposed by Pfirrmann can be used to quantify disc degeneration from MRI T2 spin-echo weighted images. No discs were evaluated as the least severe grades I or II, the remaining were evenly distributed between grades III-V.
Raman intensity increased with the Pfirrmann grade, with grade V displaying a distinctive Raman shift peak profile. Glycosaminoglycans were degraded in Pfirrmann grades IV and V, compared with grade III. Judging from the amide content, collagen content appeared to increase and become more disordered as the Pfirrmann grade increased.
The authors speculate that the changes in Raman shift at higher Pfirrmann grades may indicate a transition to a more brittle, fibrotic composition containing less water with less cushioning capacity.
The authors noted that the Raman spectrometry of the study could be made more reliable by assessing a greater number of points within the sample. It could also be beneficial to have positive controls of collagen in various states of disorder.
“In conclusion, the results of the present study provided a step towards the potential use of ex vivo Raman spectroscopy for the investigation of biomarkers in IDD. A higher relative intensity of the ratio of two peaks (I1670/I1640; amide I) indicated a higher fractional content of disordered collagen, which provides evidence of the defective collagen structure leading to abnormalities of the NP,” stated the authors.