Metformin Protects Against Noise-Induced Hearing Loss in Male Mice

Hypothesis Metformin treatment will protect mice from noise-induced hearing loss (NIHL). Background We recently identified metformin as the top-ranking, Food and Drug Administration-approved drug to counter inner ear molecular changes induced by permanent threshold shift-inducing noise. This study is designed to functionally test metformin as a potential otoprotective drug against NIHL. Methods Male and female B6CBAF1/J mice were obtained at 7 to 8 weeks of age. A cohort of the females underwent ovariectomy to simulate menopause and eliminate the effect of ovarian-derived estrogens. At 10 weeks of age, mice underwent a permanent threshold shift-inducing noise exposure (102.5 or 105 dB SPL, 8-16 kHz, 2 h). Auditory brainstem response (ABR) thresholds were obtained at baseline, 24 h after noise exposure, and 1 week after noise exposure. Mice were administered metformin (200 mg/kg/d) or a saline control in their drinking water after the baseline ABR and for the remainder of the study. After the 1-week ABR, mice were euthanized and cochlear tissue was analyzed. Results Metformin treatment reduced the 1-week ABR threshold shift at 16 kHz (p < 0.01; d = 1.20) and 24 kHz (p < 0.01; d = 1.15) as well as outer hair cell loss in the 32-45.5 kHz range (p < 0.0001; d = 2.37) in male mice. In contrast, metformin treatment did not prevent hearing loss or outer hair cell loss in the intact or ovariectomized female mice. Conclusions Metformin exhibits sex-dependent efficacy as a therapeutic for NIHL. These data compel continued investigation into metformin's protective effects and demonstrate the importance of evaluating the therapeutic efficacy of drugs in subjects of both sexes.