Temporomandibular Joint Osteoarthritis: Regenerative Treatment by a Stem Cell Containing Advanced Therapy Medicinal Product (ATMP)-An In Vivo Animal Trial

Abstract

Temporomandibular joint osteoarthritis (TMJ-OA) is a chronic degenerative disease that is often characterized by progressive impairment of the temporomandibular functional unit. The aim of this randomized controlled animal trial was a comparative analysis regarding the chondroregenerative potency of intra-articular stem/stromal cell therapy. Four weeks after combined mechanical and biochemical osteoarthritis induction in 28 rabbits, therapy was initiated by a single intra-articular injection, randomized into the following groups: Group 1: AB Serum (ABS); Group 2: Hyaluronic acid (HA); Group 3: Mesenchymal stromal cells (STx.); Group 4: Mesenchymal stromal cells in hyaluronic acid (HA + STx.). After another 4 weeks, the animals were euthanized, followed by histological examination of the removed joints. The histological analysis showed a significant increase in cartilage thickness in the stromal cell treated groups (HA + STx. vs. ABS, p = 0.028; HA + ST.x vs. HA, p = 0.042; STx. vs. ABS, p = 0.036). Scanning electron microscopy detected a similar heterogeneity of mineralization and tissue porosity in the subchondral zone in all groups. The single intra-articular injection of a stem cell containing, GMP-compliant advanced therapy medicinal product for the treatment of iatrogen induced osteoarthritis of the temporomandibular joint shows a chondroregenerative effect.

Keywords: TMJD; osteoarthritis; regenerative medicine; regenerative therapy; stem cell therapy; temporomandibular joint.

Figure 1

To objectify the cartilage thickness measurements, a line grid (black) was used to define random measuring points on the cartilage surface. At these points the thickness measurement (yellow) was finally taken, each right angled to an imaginary tangent (dotted).

Figure 2

Boxplot analysis showing the underlying distribution of final cartilage thickness vs. the four treatment groups. Circles represent outliers with more than 1.5 times interquartile range. Significant group differences are marked (***).

Figure 3

(A–D). Histological analysis 4 weeks after intra-articular injection therapy (1 = Safranin-O, 2 = Picrosirius red, 3 = Picrosirius red (polarized)). (A1–A3) representing group 1 (ABS), (B1–B3) group 2 (HA), (C1–C3) group 3 (STx.), and (D1–D3) group 4 (STx. + HA). Collagen I on cartilage surface could be visualized much better in group 3 (STx.) than in the other groups (Picrosirius red: red; Picrosirius red (polarized): yellow-orange), indicating a comparatively higher cartilage regeneration. A statistical significance analysis was not performed. Overall, no significant increased or decreased GAG accumulation could be detected in any of the groups using Safranin-O staining.

Figure 4

Representative back-scattered images of temporomandibular joint (TMJ) specimens of all groups. (A–D) The images show a cross-sectional view of the TMJ, whereby darker pixels correspond to a low degree of mineralization and brighter pixels correspond to higher degree of mineralization. The articular cartilage (AC) is located on top of the subchondral mineralized zone (SMZ) which is composed of calcified cartilage containing chondrocyte lacunae and subchondral bone containing osteocyte lacunae. (E) In the calcified cartilage zone, the ratio of mineralized area per tissue area, an inverse measure of tissue porosity, was similar between the groups. (F) The heterogeneity of mineralization, assessed as the full-width-half-maximum of the gray value histogram, was similar between groups.