Icariin ameliorates the progression of experimental autoimmune encephalomyelitis by down-regulating the major inflammatory signal pathways in a mouse relapse-remission model of multiple sclerosis

This study aimed at investigating whether treatment with icariin (ICA) could modulate the progression of experimental autoimmune encephalomyelitis (EAE) and its potential mechanisms in SJL/J mice. Female SJL/J mice were immunized with PLP139-151 peptide to induce relapse-remitting EAE and the immunized mice were treated with vehicle alone (EAE) or ICA (12.5 or 25 mg/body weights) by gavage daily for 42 days. Compared with the control, the EAE mice developed relapse-remitting EAE and reduced body weights (15.76 ± 0.61 vs. 17.60 ± 0.98 g on day 13; 17.35 ± 0.44 vs. 18.46 ± 0.66 g on day 26), accompanied by severe inflammation with many microglia infiltrates and obvious demyelination in the spinal cord tissues. Conversely, ICA treatment significantly reduced the clinical scores (on day 13, 1.00 ± 0.16 and 1.10 ± 0.33 for ICA 12.5 and 25 mg/kg group, respectively vs. 1.62 ± 0.41 in the EAE group; on day 26, 0.50 ± 0.23 and 0.40 ± 0.24 for ICA 12.5 and 25 mg/kg group, respectively, vs. 1.56 ± 0.29 in the EAE group), mitigated the body weight reduction, spinal cord inflammation and demyelination in EAE mice (pathological scores of 2.33 ± 0.82 and 1.11 ± 0.57 for ICA 12.5 and 25 mg/kg, respectively; vs. 4.78 ± 1.13, P < 0.0001). Furthermore, ICA treatment significantly mitigated the EAE-increased iNOS, TNF-α, CD206 and TGF-β1, but further reduced IL-10 mRNA transcripts in the brain mice. More importantly, ICA treatment significantly mitigated the inflammation-related NF-κB, AKT, ERK1/2, p38, c-Jun and MEK phosphorylation in the brain of EAE mice. ICA treatment ameliorates the progression of EAE by down-regulating the major inflammation-related signal pathways in mice.