Modulation of the In Vivo Inflammatory Response by Pro- Versus Anti-Inflammatory Intervertebral Disc Treatments

Abstract

Inflammation is central in intervertebral disc (IVD) degeneration/regeneration mechanisms, and its balance is crucial to maintain tissue homeostasis. This work investigates the modulation of local and systemic inflammatory response associated with IVD degeneration/herniation by administration of PRO-versus ANTI-inflammatory treatments. Chitosan/poly-γ-glutamic acid nanocomplexes, known as pro-inflammatory (PRO), and soluble diclofenac, a non-steroidal anti-inflammatory drug (ANTI), were intradiscally administered in a rat IVD injury model, 24 h after lesion. Two weeks after administration, a reduction of disc height accompanied by hernia formation was observed. In the PRO-inflammatory treated group, IL-1β, IL-6 and COX-2 IVD gene expression were upregulated, and loss of nucleus pulposus (NP) structure and composition was observed. Systemically, lower T-cell frequency was observed in the lymph nodes (LN) and spleen (SP) of the PRO group, together with an increase in CD4+ T cells subset in the blood (BL) and LN. In contrast, the ANTI-group had higher proteoglycans/collagen ratio and collagen type 2 content in the NP, while an increase in the frequency of myeloid cells, M1 macrophages and activated macrophages (MHCII+) was observed at the systemic level. Overall, this study illustrates the dynamics of local and systemic inflammatory and immune cell responses associated with intradiscal therapies, which will contribute to designing more successful immunomodulatory treatments for IVD degeneration.Several in vivo models of IVD degeneration are described in the literature, with murine tail models of mechanical injury by needle puncture commonly used [4,5]. Depending on the needle size, the puncture may induce annulus fibrosus (AF) disruption while causing depressurization of the nucleus pulposus (NP) [6,7]. Needle calibers, varying between 16 to 22 G, often lead to significant pressure failure, decreased cell viability, increased expression of pro-inflammatory/degenerative factors and alterations in extracellular matrix (ECM) composition in IVDs from both large (e.g., bovine [8]) and small animals (e.g., rabbit [9] and rat [10]), resembling human IVD degeneration. Our group has previously established and validated an IVD herniation/degeneration model of rat caudal needle puncture, using a 21 G needle [10,11], in which IVD herniation and infiltration of macrophages were observed [10]. This model is relatively simple to manipulate and presents cost-effectiveness [12]. Moreover, it allows the study of local and systemic immune response, crucial in human IVD degeneration and difficult to analyze in vitro or ex vivo [13]. Only a few studies, mainly in bone, address the dialogue/interplay between local/systemic immune responses and how this can be linked with tissue remodeling [14,15]. Despite this, it is important to consider the limitations of small animal models of IVD degeneration when compared to humans, such as differences in spine biomechanics, IVD size and cellular composition, which may be critical for clinical trans...

Decellularized Disc Hydrogels for hBMSCs tissue-specific differentiation and tissue regeneration

“…These hydrogels are mainly derived from non-degradable polyacrylates and polyacrylamides [ 10 , 11 ] and degradable hyaluronic acid, collagen in the extracellular matrix and chitosan [ 8 , 12 ]. However, these implanted materials often failed to regulate the post-injury microenvironment, and tissue degeneration, water loss and inflammatory reaction often appeared in situ [ 13 , 14 ]. Regarding AF, structural repair is a hot spot.…”

The nucleus pulposus microenvironment in the intervertebral disc: the fountain of youth?

“…Therefore, in the context of cell therapy, restoring the hypoxic microenvironment may favour the use of NP progenitor cells. E x c e s s i v e m e c h a n i c a l l o a d i n g a n d impaired biomechanics can be another crucial microenvironmental factor influencing NP progenitor behaviour (Chu et al, 2018;Desmoulin et al, 2020). For example, several studies showed an essential correlation between the presence and the severity of disc degeneration in obese or overweight adults (Lidar et al, 2012;Samartzis et al, 2012).…”

“…One aspect is the application of drugs. In addition to analgesics, which with their low molecular weight are often used as a first resort to relieve LBP associated with IVD degeneration, various novel treatments are also being evaluated in preclinical models (Cherif et al, 2020;Cunha et al, 2020;Hu et al, 2019;Wang et al, 2020a). Among these, inflammatory cytokine and enzyme inhibitors are frequently used as therapeutic agents, but so far these agents have shown no or only limited effectiveness and an increased risk of adverse events (Tryfonidou et al, 2020).…”

Advanced Strategies for the Regeneration of Lumbar Disc Annulus Fibrosus

“…A decrease in the AF cell density, as frequently observed in degenerated IVDs, alters the balance of anabolism:catabolism ratio in the extracellular matrix (ECM), changing the AF mechanical, biological, and structural properties [ 69 , 70 , 71 ]. Therefore, regenerative strategies aim to repopulate a degenerated IVD with healthy cells (cell therapy) or stimulating the existing cells to regulate the ECM reaching an enhanced composition, quantity, and structure (biomolecule and gene therapy) [ 81 , 82 , 83 , 84 , 85 ]. ECM remodeling is crucial to control the action of biochemical mediators such as cytokines (interleukins), growth factors, and enzymes (metalloproteinases and heparanase) to ultimately stop or reverse the IVD degeneration process [ 86 , 87 , 88 , 89 ].…”