D-methionine pre-loading reduces both noise-induced permanent threshold shift and outer hair cell loss in the chinchilla

This study tested multiple dosing epochs of pre-loaded D-methionine (D-met) for otoprotection from noise-induced hearing loss (NIHL).Auditory brainstem response (ABR) thresholds were measured at baseline, 1 day, and 21 days following a 6-hour 105 dB sound pressure level (SPL) octave band noise (OBN) exposure. Outer hair cell (OHC) counts were measured after day 21 sacrifice.Three groups of five Chinchillas laniger each were given a 2-day regimen comprising five doses of D-met (200 mg/kg/dose) intraperitoneally (IP) starting 2, 2.5, or 3 days prior to noise exposure. A control group (n = 5) received five doses of equivalent volume saline IP starting 2.5 days prior to noise exposure.ABR threshold shifts from baseline to day-21 post-noise exposure were reduced in all D-met groups versus controls, reaching significance (p0.05) in the 3-day group. D-met groups showed reduced OHC loss relative to controls at day-21 post-noise exposure, reaching significance (p0.05) at all frequency regions in the 3-day group and at the 2, 4, and 8 kHz frequency regions in the 2.5-day group.D-met administration in advance of noise-exposure, without further administration, significantly protects from noise-induced ABR threshold shift and OHC loss.