Complex Mechanical Loading and Pro-Inflammatory Cytokines in Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration is a major contributor to low back pain, yet its initiating factors remain unclear. While the individual effects of pro-inflammatory cytokines and mechanical loading on IVDs have been studied, their combined impact is poorly understood. This study investigated how dynamic compression and torsion interact with interleukin-1 beta (IL-1β) and its inhibitor, interleukin-1 receptor antagonist (IL-1Ra), using bovine IVDs in an ex vivo organ culture system.

Whole bovine caudal IVDs were cultured for one week in a custom bioreactor applying diurnal dynamic compression (0.1-0.5 MPa) and torsion (±6°) under three media conditions: physiological, catabolic (10 ng/mL IL-1β), and inhibitory (10 ng/mL IL-1Ra). Static compression (0.1 MPa) served as control. 3 T magnetic resonance imaging (MRI) was used pre- and post-culture for imaging and segmentation using 3DSlicer. Subject-personalized finite element (FE) models were generated via morphing algorithms and coupled with a parallel network (PN) model to analyze metabolite transport and its impact on gene expression. Outcomes included disc height, glycosaminoglycan (GAG) content, qPCR, and cell metabolic activity.

Degenerative changes were detected in all treatment groups. Results of decreased disc height, hydration, and ACAN expression, alongside increased MMP-13, indicated that the applied loading was supraphysiological and induced catabolic responses. IL-1Ra, at the given dose, did not counteract degeneration. MRI-based FE modeling effectively captured patterns of tissue consolidation and degeneration, providing valuable insights into IVD responses under combined mechanical and inflammatory stress. This integrative platform highlights the importance of modeling complex IVD environments and may inform the design of improved anti-catabolic therapies.