A Randomized, Placebo-Controlled, Double-Blind, Phase IIa Study of Amiloride in the Treatment of Acute Autoimmune Optic Neuritis

Recent studies have shown that the acid-sensing ion channel 1 (ASIC1) contributes to the axonal degeneration in CNS lesions Physiologically, ASIC1 has been described as a postsynaptic proton receptor on hippocampal neurons influencing the intracellular Ca2+ concentration. In MS, ASIC1 seems to activate under acidic conditions predominating in the inflammatory CNS lesions leading to a Na+ and Ca2+ overload and consecutive damage and apoptosis of axons. Consecutively, in a MS mousemodel axonal damage was significantly less pronounced after administering amiloride, a clinically safe blocker of ASICs. So ASIC1 seems to play a major role in axonal degeneration in MS. To our knowledge no clinical studies have tested those promising in vitro results in humans so far.

Only one retrospective registry-based cohort study was performed. This study showed no difference in the risk of incident MS or hospitalization and death among MS patients using amilorid compared to those using thiazide diuretics. However, this study has numerous limitations with respect to it's retrospective designone and the fact that amilorid users were at the vast majority older individuals. Such a late stage of the MS course does not seem to be the best window of opportunity for interventions with neuroprotective agents. Moreover, death may be a too multifactorial parameter to correspond with axonal damage alone. Consequently, a more sensitive parameter for axonal damage in MS is needed to test the impact of amiloride on neuroprotection and repair.Based on the findings described above we intend to assess the potential neuroprotective effect of amiloride hydrochlorothiazide (Amilostad HCT®) in patients with optic neuritis (ON), which has already been demonstrated in a mouse model. ON is one of the most common manifestations of MS and has already been proven appropiate to test neuroprotective agents.