Therapeutic activity of lipoxin A₄ in TiO₂-induced arthritis in mice: NF-B and Nrf2 in synovial fluid leukocytes and neuronal TRPV1 mechanisms

BackgroundLipoxin A4 (LXA(4)) has anti-inflammatory and pro-resolutive roles in inflammation. We evaluated the effects and mechanisms of action of LXA4 in titanium dioxide (TiO2) arthritis, a model of prosthesis-induced joint inflammation and pain. MethodsMice were stimulated with TiO2 (3mg) in the knee joint followed by LXA(4) (0.1, 1, or 10ng/animal) or vehicle (ethanol 3.2% in saline) administration. Pain-like behavior, inflammation, and dosages were performed to assess the effects of LXA(4) in vivo. ResultsLXA(4) reduced mechanical and thermal hyperalgesia, histopathological damage, edema, and recruitment of leukocytes without liver, kidney, or stomach toxicity. LXA(4) reduced leukocyte migration and modulated cytokine production. These effects were explained by reduced nuclear factor kappa B (NF & kappa;B) activation in recruited macrophages. LXA(4) improved antioxidant parameters [reduced glutathione (GSH) and 2,2-azino-bis 3-ethylbenzothiazoline-6-sulfonate (ABTS) levels, nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA and Nrf2 protein expression], reducing reactive oxygen species (ROS) fluorescent detection induced by TiO2 in synovial fluid leukocytes. We observed an increase of lipoxin receptor (ALX/FPR2) in transient receptor potential cation channel subfamily V member 1 (TRPV1)(+) DRG nociceptive neurons upon TiO2 inflammation. LXA(4) reduced TiO2-induced TRPV1 mRNA expression and protein detection, as well TRPV1 co-staining with p-NF & kappa;B, indicating reduction of neuronal activation. LXA(4) down-modulated neuronal activation and response to capsaicin (a TRPV1 agonist) and AITC [a transient receptor potential ankyrin 1 (TRPA1) agonist] of DRG neurons. ConclusionLXA(4) might target recruited leukocytes and primary afferent nociceptive neurons to exert analgesic and anti-inflammatory activities in a model resembling what is observed in patients with prosthesis inflammation.