Injection of human umbilical tissue-derived cells into the nucleus pulposus alters the course of intervertebral disc degeneration in vivo

Abstract

Background context: Patients often present to spine clinic with evidence of intervertebral disc degeneration (IDD). If conservative management fails, a safe and effective injection directly into the disc might be preferable to the risks and morbidity of surgery.

Purpose: To determine whether injecting human umbilical tissue-derived cells (hUTC) into the nucleus pulposus (NP) might improve the course of IDD.

Design: Prospective, randomized, blinded placebo-controlled in vivo study.

Patient sample: Skeletally mature New Zealand white rabbits.

Outcome measures: Degree of IDD based on magnetic resonance imaging (MRI), biomechanics, and histology.

Methods: Thirty skeletally mature New Zealand white rabbits were used in a previously validated rabbit annulotomy model for IDD. Discs L2-L3, L3-L4, and L4-L5 were surgically exposed and punctured to induce degeneration and then 3 weeks later the same discs were injected with hUTC with or without a hydrogel carrier. Serial MRIs obtained at 0, 3, 6, and 12 weeks were analyzed for evidence of degeneration qualitatively and quantitatively via NP area and MRI Index. The rabbits were sacrificed at 12 weeks and discs L4-L5 were analyzed histologically. The L3-L4 discs were fixed to a robotic arm and subjected to uniaxial compression, and viscoelastic displacement curves were generated.

Results: Qualitatively, the MRIs demonstrated no evidence of degeneration in the control group over the course of 12 weeks. The punctured group yielded MRIs with the evidence of disc height loss and darkening, suggestive of degeneration. The three treatment groups (cells alone, carrier alone, or cells+carrier) generated MRIs with less qualitative evidence of degeneration than the punctured group. MRI Index and area for the cell and the cell+carrier groups were significantly distinct from the punctured group at 12 weeks. The carrier group generated MRI data that fell between control and punctured values but failed to reach a statistically significant difference from the punctured values. There were no statistically significant MRI differences among the three treatment groups. The treated groups also demonstrated viscoelastic properties that were distinct from the control and punctured values, with the cell curve more similar to the punctured curve and the carrier curve and carrier+cells curve more similar to the control curve (although no creep differences achieved statistical significance). There was some histological evidence of improved cellularity and disc architecture in the treated discs compared with the punctured discs.

Conclusions: Treatment of degenerating rabbit intervertebral discs with hUTC in a hydrogel carrier solution might help restore the MRI, histological, and biomechanical properties toward those of nondegenerated controls. Treatment with cells in saline or a hydrogel carrier devoid of cells also might help restore some imaging, architectural, and physical properties to the degenerating disc. These data support the potential use of therapeutic cells in the treatment of disc degeneration.

Copyright © 2013 Elsevier Inc. All rights reserved.

Figures

Figure 1

Lumbar spine magnetic resonance images (MRIs). Sample T2-weighted midsagittal lumbar MRI images of L1–L2 through L5–L6 at time-points 0, 3, 6, and 12 weeks. Rabbits have six lumbar vertebrae. The punctured discs (L2–L3, L3–L4, and L4–L5) are outlined by the red boxes. The adjacent unpunctured discs for each rabbit (L1–L2 and L5–L6) do not show any qualitative evidence of degeneration. The discs of the (A) control group did not degenerate, as expected. (B) The punctured discs became smaller and darker across time-points, suggesting degeneration. (C) The discs that were punctured and then treated with carrier, (D) human umbilical tissue–derived cells (hUTC)+buffer, and (E) hUTC+carrier demonstrate less evidence of degeneration across time-points compared with the (B) punctured discs. Each group consisted of six rabbits (18 discs).

Figure 2

Quantitative MRI analysis. Average data for (Top) NP area and (Bottom) MRI Index combining L2–L3, L3–L4, and L4–L5 (the treated discs) for each rabbit group, expressed as a percent of the Time 0 value, demonstrates that the punctured group undergoes the largest decrease in area and MRI Index across time-points. The groups that were punctured and subsequently treated with carrier or cells+buffer undergo lesser decrease in area and Index, whereas the group treated with cells+carrier undergoes the least decrease in area and Index. Error bars represent standard error. Each group consisted of six rabbits (18 discs).

Figure 3

Creep curves. Average normalized total displacement (ramp phase+creep) curves of potted L3–L4 functional spinal units after 12 weeks were generated for each condition. Axial testing generates distinct appearing creep curves in the early phase of testing (time, 0–200 seconds). Dotted boundaries represent standard error of measurement. The curves generated for puncture and buffer+cells appear similar, as do curves for control and carrier+cells. Each of these groups appears distinct from the curve generated for the carrier group. Each group consisted of six rabbits (six discs). Post-op, postoperative.

Figure 4

Histology. Sagittal slices of disc L4–L5 obtained after sacrifice at 12 weeks for each treatment group ([A] Control, [B] Puncture, [C] Carrier, [D] Buffer + Cells, [E] Carrier + Cells), stained with hematoxylin and eosin, and magnified ×20 and ×100. Treatment helps restore some aspects of cellularity and architecture. Each group consisted of six rabbits (six discs).