Research Paper: The Effect of Orally Administered Probiotics on the Behavioral, Cellular, and Molecular Aspects of Adjuvant-Induced Arthritis

Rheumatoid Arthritis (RA) is a chronic autoimmune disease, which is accompanied with pain, hyperalgesia, and edema. Overproduction of pro-inflammatory cytokines and activation of intracellular signaling pathways sustain the RA symptoms considerably. There is a strong correlation between the expression of cytokines and opioid receptors in the arthritis process. Studies have shown that probiotics via different pathways such as reducing the levels of pro-inflammatory cytokines can alleviate inflammatory symptoms. Therefore, based on the crucial role of cellular and humoral immunity in induction of RA symptoms and potency of probiotics in modulation of immune responses, the purpose of this study was to investigate the effect of orally administered probiotics on the behavioral, cellular and molecular aspects of adjuvant-induced arthritis in male Wistar rats. Complete Freund’s Adjuvant (CFA)-induced arthritis was caused by single subcutaneous injection of CFA into the rat’s hind paw on day 0. Different doses of probiotics (1/250, 1/500 and 1/1000 [109 CFU/g]) were administered daily (gavage) after CFA injection. Hyperalgesia, edema, serum IL-1β levels, μ-Opioid Receptor (MOR) expression, and p38MAPK (Mitogen-Activated Protein Kinase) activities were assessed on days 0, 7, 14 and 21 of the study. The results of this study indicated the efficacy of probiotics in reducing hyperalgesia, edema, serum levels of Interleukin-1β, and p38MAPK pathway activity during different phases of arthritis as well as increasing the expression of MORs during chronic phase of CFA-induced arthritis. It seems that probiotics can effectively reduce inflammatory symptoms by inhibiting the intracellular signaling pathway and cytokine production