| Globally, over 1.5 billion people have some form of hearing loss. Hearing loss has no cure, but evidence suggests that enhancing the Medial Olivocochlear (MOC) system, an efferent pathway controlling auditory gain, may significantly protect hair cells from noise exposure.
Gain-of-function mutations in mice MOC α9α10 nicotinic acetylcholine receptors (nAChRs) protected against noise-related hearing loss. The α9 and α10 subunits, found mainly in inner ear hair cells, are a promising therapeutic target due to their role in auditory processing.
Increasing α9α10 receptor response with positive allosteric modulators (PAMs) may enhance auditory sensitivity and protect hearing from noise-induced damage. Only two PAMs
for the α9α10 receptor are known: the diterpenoid ryanodine (Ry) and L-ascorbic acid (AA, Vitamin C). Of these, AA is more effective than Ry, suggesting greater promise for selective ligand design.
AA is a polyhydroxylated chiral synthon known for its antioxidant properties and essential roles in biological pathways. Recently, it was shown to potentiate acetylcholine (ACh) responses at the α9α10 nAChR at millimolar concentrations. These receptors are selectively expressed on efferent postsynaptic hair cells of the inner ear, where their potentiation is hypothesized to provide neuroprotective effects against acoustic trauma (AT).
This work aimed to identify AA structural features responsible for α9α10 potentiation by synthesizing a targeted library of AA-derived analogs. These analogs enabled systematic structure–activity relationship (SAR) exploration and facilitated the discovery of novel
2 potentiators. Antioxidant capacity was evaluated with the ferric reducing antioxidant power (FRAP) assay to assess the correlation between electron-donating ability and receptor activity.
Potentiation of α9α10 nAChRs was measured using two-electrode voltage clamp (TEVC) electrophysiology in Xenopus laevis oocytes. Ligand-based virtual screening (LBVS) also
identified scaffolds with similar physicochemical properties and predicted allosteric potential.
Through these strategies, several α9α10 potentiators were identified. Notably, antioxidant capacity did not predict receptor modulation, highlighting that structural, rather than redoxdriven, determinants are responsible for activity. The key pharmacophoric elements of AA
required for α9α10 potentiation were identified. Together, these findings offer new insights into receptor–ligand interactions and guide future medicinal chemistry efforts to develop modulators that protect auditory function.
Keywords: L-ascorbic acid, chiral pool, positive allosteric modulator, nicotinic acetylcholine
receptor, structure-activity relationship, ligand-based virtual screening, hearing loss |