gms | German Medical Science

Objective: Spinal cord injury (SCI) induces heterogeneous cellular and biochemical alterations of nervous tissue. SCI regeneration therapies still require comprehensive basic research, which include direct identification of the biochemical components of SCI and of their temporal changes. Vibrational spectroscopy, based on intrinsic interaction between light and molecular vibrations, offers label-free high resolution imaging with chemical contrast. This method is of potential use in vivo and in clinical situation since minute biochemical alterations of tissue composition as well as of implants can be monitored. Here, we applied infrared (IR) optical spectroscopy to evaluate its use for assessment of alginate implants in a rat hemimyelonectomy model of SCI.

Method: 28 rats underwent a hemimyelonectomy at the level of Th9. 14 rats received alginate gel into the lesion, 14 rats served as controls. The rats were sacrificed one or six months after hemisection-induced injury. The unstained spinal cord sections were investigated by FT-IR optical spectroscopy imaging. Spectroscopic data was mathematically processed and colour-coded biochemical images of spinal cord lesion and of surrounding tissue were obtained. Reference immunohistochemistry of adjacent sections was performed using antibodies for GFAP, Ki67, NeuN, β3Tubulin, iba1, CD61, and vWF.

Results: Selected vibrational markers were addressed to generate chemical images and allowed the identification of biochemical tissue alterations that followed injury of both control and alginate-treated spinal cords. Intensity images of 1380, 1465, 1375 cm^-1 bands, which probe lipid concentration, clearly identified: (i) the intact nervous tissue and white matter fiber tracts; (ii) the demyelination around the lesion; (iii) the lipid-depleted lesion core. Alginate implant with a specific spectral signature of polysaccharide molecular vibrations (950–1180 cm^-1) could be evaluated. Of interest, that alginate would not decompose within the first 30 days and did not show significant cellular or axonal infiltrations. Increase of the band intensity of collagen (1340 cm^-1) showed formation of a fibrous scar in the lesion core of control animals and around the implant in treated animals.

Conclusions: The tissue components critical to identify changes after SCI were classified by label-free IR optical spectroscopy. The detailed biochemical mapping correlated with changes of the implant and related structural changes of the regenerating spinal cord.