Diarylamidines: High potency inhibitors of acid-sensing ion channels

Abstract

Acid-sensing ion channels (ASICs) are proton-gated cation channels that are predominantly expressed in the nervous system. ASICs are involved in a number of neurological diseases such as pain, ischemic stroke and multiple sclerosis but limited tools are available to target these channels and provide probes for their physiological functions. Here we report that the anti-protozoal diarylamidines, 4′,6-diamidino-2-phenylindole (DAPI), diminazene, hydroxystilbamidine (HSB) and pentamidine potently inhibit ASIC currents in primary cultured hippocampal neurons with apparent affinities of 2.8 µM, 0.3 µM, 1.5 µM and 38 µM, respectively. These four compounds (100 µM) failed to block ENaC channels expressed in oocytes. Sub-maximal concentrations of diminazene also strongly accelerated desensitization of ASIC currents in hippocampal neurons. Diminazene blocked ASIC1a, -1b -2a, and -3 currents expressed in CHO cells with a rank order of potency 1b > 3 > 2a ≥ 1a. Patchdock computational analysis suggested a binding site of diarylamidines on ASICs. This study indicates diarylamidines constitute a novel class of non-amiloride ASIC blockers and suggests that diarylamidines may be developed as therapeutic agents in treatment of ASIC-involved diseases.

The role of acid-sensing ion channels (ASICs) in epithelial Na+ uptake in adult zebrafish (Danio rerio).

“…DAPI is a diarylamidine, a class of drugs that have been recently shown to block ASIC Na + currents in cultured mice hippocampal neurons, but do not block other epithelial Na + channels, such as ENaCs (Chen et al, 2010). Recently, DAPI has also been demonstrated to inhibit Na + uptake in rainbow trout exposed to ultra-low ionic strength/low pH water (Dymowska et al, 2014).…”

“…To determine whether DAPI, an ASIC selective inhibitor (Chen et al, 2010) displayed a similar dose-response inhibition effect on Na + uptake in zebrafish to that of rainbow trout, flux experiments using 22 Na + were performed on adult zebrafish exposed to low-Na + medium (∼500 µmol l −1 Na + ; Table 1). After 90 min, zebrafish showed reduced Na + uptake with increasing concentrations of DAPI (Fig.…”

“…In the recent study by Dymowska et al (2014) asic1 and asic4 were cloned from the gill cDNA of the adult rainbow trout, and using immunohistochemistry, ASIC4 was apically localized to MRCs rich in Na + /K + -ATPase (NKA) (Dymowska et al, 2014). Additionally, ASIC-specific inhibitors 4′,6-diamidino-2-phenylindole (DAPI) and diminazene (Chen et al, 2010), were demonstrated to decrease Na + uptake in a dose-dependent manner in juvenile rainbow trout acclimated to a low-Na + (∼50 μmol l −1 ) environment (Dymowska et al, 2014).…”

Binding Site and Inhibitory Mechanism of the Mambalgin-2 Pain-relieving Peptide on Acid-sensing Ion Channel 1a

“…This is in good agreement with our data showing that the toxin/palm contact is determinant to explain inhibition of the peak current or stimulation when this interaction is modified. Domain P has also been proposed to constitute part of the binding site of diarylamidines, which are inhibitors of ASICs (36).…”

Ion Channels as Drug Targets in Central Nervous System Disorders

“…The application of aromatic diamidines is not limited to anti-parasitics. Recently, it was found that aromatic diamidines such as pentamidine, hydroxystilbamidine, and diminazene potently block ASICs [305]. Each of these compounds inhibited ASIC currents, indicating that the linker in each of these diamidines can be variable, while the amidine group linked with an aromatic moiety appears to be essential.…”