Purpose/Objectives: Rheumatoid Arthritis (RA) is an autoimmune disease characterized by chronic inflammation and destruction of synovial joints that affects approximately 7.5 million people worldwide. Disease pathology, while multifactorial in etiology, is driven by an imbalance in the ratio of pro-inflammatory vs. anti-inflammatory immune cells, especially macrophages. Modulation of macrophage phenotype, specifically an M1 to M2, pro- to anti-inflammatory transition, can be induced by biologic scaffold materials composed of extracellular matrix (ECM). The ECM-based immunomodulatory effect is thought to be mediated in part through recently identified matrix-bound nanovesicles (MBV) embedded within ECM. While it is known that an M1:M2 disequilibrium contributes to RA disease progression, there are no therapies available that specifically modulate macrophage phenotype to promote disease remission through an M2, anti-inflammatory phenotype. There is thus a clear unmet need for developing approaches to modulate rather than suppress the immune response for the treatment of autoimmune diseases such as RA. The evidence supporting ECM- and MBV-mediated immunomodulation of macrophage phenotype, combined with the clinical evidence of pro-inflammatory M1 macrophages as a key mediator of RA, provides the premise of the present research. Using the pristane-induced, pre-clinical rat model of RA, it was hypothesized that MBV would reduce inflammatory arthritis disease development, decrease synovial inflammatory cell infiltration, prevent adverse cartilage remodeling, modulate synovial and systemic macrophage populations from a pro-inflammatory M1 phenotype towards an anti-inflammatory M2 phenotype, and thus promote disease resolution.
Methodology: Isolated MBV were delivered via intravenous (i.v.) or peri-articular (p.a.) injection to rats with pristane-induced arthritis (PIA). The results of MBV administration were compared to those following intraperitoneal (i.p.) administration of methotrexate (MTX), the clinical standard of care, using disease scoring, microCT imaging, histopathology, multiplex cytokine analysis, and multi-parameter flow cytometry.
Results: Relative to the vehicle treated animals, i.p. MTX, i.v. MBV, and p.a. MBV reduced arthritis scores in both acute and chronic phases of pristane-induced arthritis, decreased synovial inflammation, decreased adverse joint remodeling, and reduced the ratio of synovial and splenic pro-inflammatory M1 macrophages to anti-inflammatory M2 macrophages (p<.05). Both p.a. and i.v. MBV, but not MTX, reduced the serum concentration of RA and PIA biomarkers CXCL10 and MCP-3 in the acute and chronic phases of disease (p<.05). Flow cytometry dimensional data reduction with Uniform Manifold Approximation and Projection (UMAP) revealed the presence of a systemic CD43hi/His48lo/CD206+, immunoregulatory monocyte population unique to p.a. and i.v. MBV treatment associated with disease resolution.
Conclusion/Significance: The results show that the therapeutic efficacy of both systemic and local administration of MBV is equal to that of MTX for the management of acute and chronic, pristane-induced arthritis, and further, this effect is associated with modulation, not suppression, of local synovial macrophages and systemic myeloid populations. The findings suggest that the immunomodulatory properties of ECM-based materials, specifically the MBV component of ECM-based materials, have therapeutic potential for diseases driven by a dysregulated immune system such as RA. The anti-inflammatory effects of ECM-based products have been well documented, and the expanded clinical applications made possible by MBV are worthy of further investigation.