Peroxiredoxin 6 Alone or in Combination with Fingolimod Ameliorates EAE.

Introduction: Multiple Sclerosis (MS) is characterized by the infiltration of leukocytes into the nervous tissue, and disruption of the Blood-Brain Barrier (BBB) is one of the main factors in the progression of MS and its model, Experimental Autoimmune Encephalomyelitis (EAE). Furthermore, some anti-lymphocytic drugs against MS may inherently produce BBB disruption as their side effect. This study hypothesized that drugs restoring the BBB may be useful for the treatment of MS and EAE, as well as for ameliorating the side effects of modern anti-lymphocytic drugs.

Methods: EAE was induced in SJL/J mice. EAE progression was evaluated by a severity score and a plasma cytokine profile, while a BBB condition was evaluated by the Evans dye method, Tight Junction Proteins (TJPs) content, and leukocyte infiltration.

Results: The mice with EAE demonstrated neurological symptoms, a cytokine response, and BBB deterioration, which was associated with upregulation of the NADPH oxidases NOX1 and NOX4 in the brain. Administration of the anti-lymphocyte drug fingolimod to EAE mice caused lymphopenia, improved animal health, enhanced the BBB function during the administration period, and decreased the pro-inflammatory response, but it was accompanied by a "withdrawal effect," defined as a sharp increase in the IL-17 and IFN-gamma to levels higher than those in untreated animals, lymphocyte hyperactivation, worsening symptoms, and increasing BBB permeability after discontinuation of fingolimod. Administration of peroxiredoxin 6 (Prdx6) to EAE mice also improved BBB, decreased lymphocyte infiltration and NADPH oxidase expression, and ameliorated symptoms. Preliminary administration of Prdx6 before the fingolimod treatment eliminated the "withdrawal effect" of fingolimod and led to full recovery of the EAE mice. This Prdx6 effect was associated with the activation of anti-proliferative and pro-apoptotic signaling cascades in lymphocytes.

Discussion and conclusion: Both fingolimod and Prdx6 produced beneficial effects, while Prdx6 may be useful for ameliorating the side effects of anti-lymphocytic drugs. Accounting for literature data that discontinuation of MS treatment is very likely to lead to a severe MS rebound, a drug that prevents the rebound should be useful.