The citrus flavanone naringenin attenuates zymosan-induced mouse joint inflammation: induction of Nrf2 expression in recruited CD45+ hematopoietic cells

Background Naringenin is a biologically active analgesic, anti-inflammatory, and antioxidant flavonoid. Naringenin targets in inflammation-induced articular pain remain poorly explored. Methods The present study investigated the cellular and molecular mechanisms involved in the analgesic/anti-inflammatory effects of naringenin in zymosan-induced arthritis. Mice were pre-treated orally with naringenin (16.7-150 mg/kg), followed by intra-articular injection of zymosan. Articular mechanical hyperalgesia and oedema, leucocyte recruitment to synovial cavity, histopathology, expression/production of pro- and anti-inflammatory mediators and NF kappa B activation, inflammasome component expression, and oxidative stress were evaluated. Results Naringenin inhibited articular pain and oedema in a dose-dependent manner. The dose of 50 mg/kg inhibited leucocyte recruitment, histopathological alterations, NF kappa B activation, and NF kappa B-dependent pro-inflammatory cytokines (TNF-alpha, IL-1 beta, and IL-33), and preproET-1 mRNA expression, but increased anti-inflammatory IL-10. Naringenin also inhibited inflammasome upregulation (reduced Nlrp3, ASC, caspase-1, and pro-IL-1 beta mRNA expression) and oxidative stress (reduced gp91(phox) mRNA expression and superoxide anion production, increased GSH levels, induced Nrf2 protein in CD45(+) hematopoietic recruited cells, and induced Nrf2 and HO-1 mRNA expression). Conclusions Naringenin presents analgesic and anti-inflammatory effects in zymosan-induced arthritis by targeting its main physiopathological mechanisms. These data highlight this flavonoid as an interesting therapeutic compound to treat joint inflammation, deserving additional pre-clinical and clinical studies.