Alginate vs. Hyaluronic Acid as Carriers for Nucleus Pulposus Cells: A Study on Regenerative Outcomes in Disc Degeneration

Abstract

Intervertebral disc degeneration is a leading cause of chronic low back pain, affecting millions globally. Regenerative medicine, particularly cell-based therapies, presents a promising therapeutic strategy. This study evaluates the comparative efficacy of two biomaterials-hyaluronic acid (HA) and alginate-as carriers for nucleus pulposus (NP) cell transplantation in a beagle model of induced disc degeneration. NP cells were isolated, cultured, and injected with either HA or alginate into degenerated discs, with saline and non-cell-loaded carriers used as controls. Disc height index, T2-weighted MRI, and histological analyses were conducted over a 12-week follow-up period to assess reparative outcomes. Imaging revealed that both carrier and cell-loaded treatments improved outcomes compared to degenerative controls, with cell-loaded carriers consistently outperforming carrier-only treated discs. Histological assessments supported these findings, showing trends toward extracellular matrix restoration in both treatment groups. While both biomaterials demonstrated reparative potential, HA showed greater consistency in supporting NP cells in promoting disc regeneration. These results underscore HA's potential as a superior carrier for NP cell-based therapies in addressing disc degeneration.

Keywords: alginate; animal model; back pain; biomaterials; cell therapy; disc degeneration; hyaluronic acid; intervertebral disc.

Figure 1

Overview of results pertaining to induced disc degeneration. (A) Radiographic images showing central needle placement in the disc (top; dorsal view, bottom; sagittal view), following the method described by Hiraishi et al. [66]. Magenta arrowheads point to the needle. (B) Assessment of NP tissue weight extracted from discs showed no significant differences in the amount of tissue extracted between conditions. (C) Overview of the relative disc height index (DHI) and (D) MRI-observed hydration loss 2 weeks after induced degeneration (i.e., at the time of transplantation) indicated no significant differences in normalized sagittal T2-relaxation times per group. For all conditions, a sample size of six was involved. Bars represent mean values, dots indicate individual outcomes per disc, and error bars denote standard deviations.

Figure 2

Overview of disc height index (DHI) outcomes. (A) Relative DHI measurements were tracked over time for each condition, with values calculated relative to baseline DHI (i.e., before disc degeneration induction). (B) The measured change in relative DHI at the final time point (12 weeks) was compared to the time of transplantation. * p < 0.05; * (red) indicates significant differences to the healthy controls at the same time point, * (blue) indicates significant differences to the sham controls at the same time point, and * (black) indicates significant differences between the indicated comparisons. Statistical analysis was performed using (A) 2-way ANOVA with Geisser-Greenhouse correction and (B) the Kruskal-Wallis test. For all conditions except the healthy controls (n = 10), a sample size of six was involved. Bars represent mean values, dots indicate individual outcomes per disc, and error bars denote standard deviations.

Figure 3

Overview of MRI results. (A,D) Relative and normalized T2-relaxtion time measurements of (A) sagittal and (D) axial images calculated as fold-change to measurements taken just prior to transplantation (thus already degenerated). (B,E) The measured change in relative normalized T2 relaxation time of (B) sagittal and (E) Axial images at the final time point (12 weeks) compared to the time of transplantation. (C) Representative images of axial T2 maps images obtained at 0, 1, 2, and 3 months post-transplantation. * p < 0.05; * (red) indicates significant differences to the healthy controls at the same time point, * (blue) indicates significant differences to the sham controls at the same time point, and * (black) indicates significant differences between the indicated comparisons. Statistical analysis was performed using (A,D) 2-way ANOVA with Geisser-Greenhouse correction and (B,E) the Kruskal-Wallis test. For all conditions except the healthy controls (n = 10), a sample size of six was involved. Bars represent mean values, dots indicate individual outcomes per disc, and error bars denote standard deviations.

Figure 4

Overview of macroscopic examination. (A) Overview of macroscopic pictures of discs explanted of two representative samples for each condition. Scale bar represents 0.5 cm. (B) Thompson scores [76] given to all explanted discs 12 weeks following transplantation. (C) Overview of histological images of explanted discs stained with hematoxylin/eosin (left) and Safranin-O/Fast green (right). Scale bars represent 500 µm. (D) ORS Spine histological scores [75] given to explanted discs 12 weeks following transplantation. For all conditions except the healthy controls (n = 10), a sample size of six was used. Bars represent mean values, dots indicate individual outcomes per disc, and error bars denote standard deviation. Statistical assessment made by Kruskal-Wallis test. * p < 0.05, ** p < 0.01.