Protective Efficacy of T-type, Calcium Channel Antagonist on Auditory Function in Cdh23 Erl/Erl Mice.

Abstract

Context: In normal physiological conditions, calcium ions (Ca2+) have an important effect in terms of the regulation of hair cell (HC) functions, and T-type calcium antagonists may be protective against hearing loss. However, no studies have occurred related to a T-type calcium-channel antagonist with regard to otoprotection in a Cdh23 mouse model.

Objective: The study intended to examine the protective efficacy of ethosuximide-a T-type calcium-channel antagonist-against age-related hearing loss in a Cadherin 23 (Cdh23) erl/erl mouse model, to potentially offer an insight and foundation for therapy in the near future for patients in clinical practice who suffer from age-related hearing loss.

Design: The research team conducted an animal study.

Animals: The animals were 12 male and 12 female, Cdh23 erl/erl mice.

Intervention: The research team randomly divided the mice into two groups, with 12 mice in each group: (1) the control group, the saline group, which received saline at 10 mL/kg of body weight, and (2) the intervention group, the ethosuximide group, which received ethosuximide at 10 mL/kg of body weight. Both groups received the treatments intraperitoneally every other day, beginning postnatally at 7 days until the mice were 8 weeks old.

Outcome measures: For both groups, the research team: (1) measured auditory brainstem response (ABR); (2) measured distortion product otoacoustic emission (DPOAE) at 4, 6, and 8 weeks of age; (3) separated the basilar membrane from the modiolus and lateral tissues and determined the percentage of inner-and-outer hair-cell (IHC and OHC) loss; (4) investigated relative levels of apoptosis-related gene mRNA using reverse transcription polymerase chain reaction (PCR); and (5) examined relative levels of apoptosis-related protein, using immunofluorescent (IF) staining.

Results: Compared to the saline group, the ethosuximide group: (1) had significantly lower ABR thresholds for click at 8 weeks, for 8 KHz at 6 and 8 weeks, and for 16 KHz and 32 KHz (all P < .01); (2) had significantly higher DPOAE amplitudes at 4 weeks at 15.4 KHz and 17.7 KHz (both P < .01); at 6 weeks at 8.8 KHz (P < .05), 10.1 KHz (P < .01), 11.7 KHz (P < .01), 13.4 KHz (P < .01), 15.4 KHz (P < .01), and 17.7 KHz (P < .01); and at 8 weeks at 6.7 KHz (P < .05), 7.7 KHz (P < .05), 10.1 KHz (P < .01), 11.7 KHz (P < .01), 13.4 KHz (P < .01), 15.4 KHz (P < .01), and 17.7 KHz (P < .01); (3) had significantly lower OHC loss in the middle and basal turns of the cochlea's surface (both P < .05); (4) at the age of 2 months, had significantly lower mRNA relative levels of apoptosis-related genes, including caspase-3, caspase-9, caspase-12, m-calpain and u-calpain, as found using a polymerase chain reaction (PCR); and (5) had weaker protein levels of caspase-3 and caspase-9 in the inner ears, as found using immunofluorescent (IF) staining.

Conclusions: T-type calcium-channel antagonists can exert protective efficacy in terms of the hearing function among cdh23 erl/erl mouse.