Sex differences in response to kanamycin-induced ototoxicity in C57BL/6 J mice

Sensorineural hearing loss (SNHL) is caused mainly by irreversible damage to sensory hair cells after noise exposure, ototoxic medication, and ageing, with men being more prone to developing SNHL than women are. For animal models, sex-related susceptibility to develop SNHL needs to be taken into account. Ototoxic trauma can be modeled in mice via the systemic administration of furosemide and kanamycin. Several other deafening models have shown differences in response to ototoxic medication between female and male mice. Differences in response to kanamycin-induced ototoxicity in male and female mice have not been studied. Here, we examined sex differences in susceptibility to kanamycin plus furosemide-induced ototoxicity in adult C57BL/6 J mice. Adult (postnatal day 40) female and male C57BL/6 J and Lgr5GFP (C57BL/6 J background) mice were used. The animals were deafened with a single dose of furosemide (100 mg/kg, i.v.) in combination with kanamycin (700 or 900 mg/kg, s.c.). Before deafening, seven and twenty-eight days after deafening, auditory brainstem responses (ABRs) to click stimuli were recorded to evaluate hearing performance. The cochleae were harvested seven or twenty-eight days after the induction of ototoxicity and processed for histology to evaluate hair cell loss. Male mice presented large ABR threshold shifts after ototoxic treatment with 700 mg/kg kanamycin (50 dB median hearing loss). In males, 9/12 mice had threshold shifts greater than 40 dB. However, female mice presented significantly less hearing loss in response to 700 mg/kg kanamycin, as observed via ABRs after ototoxic treatment (32 dB median hearing loss), and only 8/22 female mice presented threshold shifts greater than 40 dB. When treated with 900 mg/kg kanamycin, female mice presented large ABR threshold shifts after ototoxic treatment (50 dB median), and 11/16 mice presented threshold shifts greater than 40 dB. Female C57BL/6 J mice are less susceptible to kanamycin-induced hearing loss than males are and hence need higher doses of kanamycin to reach the same level of hearing loss. This finding is in line with the prevalence of disabling hearing loss in humans, which is 7.3% in males and 4.8% in females, where estrogens have been linked to increased hearing performance and protection against hearing loss.