The protective effect of metformin against the noise-induced hearing loss.

OBJECTIVE: To test the protective effect of metformin against noise-induced hearing loss. METHODS: 24 rats were included in the study. The first group was exposed to noise only, the second group took metformin, the third group was exposed to noise and took metformin, and the fourth group was neither exposed to noise nor took metformin as control group. After measurement of baseline DPOAE and ABR of rats, the metformin group and the metformin + noise group received 300 mg/kg/day metformin via gavage for 10 days. On the 11th day, group 1 and group 3 were exposured to white noise at 105 dB SPL for 15 h. After noise exposure, DPOAE and ABR measurements of all rats were repeated on days 1st, 7th, and 21st. At the end of the study, all animals were sacrificed and cochlear tissues were separated for immunohistochemical assessments. RESULTS: ABR threshold values and DPAOE measurements of groups 1 and 3 were deteriorated on the 1st day after noise, while deterioration in group 1 continued on 7th and 21st days, but normalized on 7th day in group 3. After immune staining, a significant immunoreaction was observed in the noise group, while the reaction in the noise + metformin group was close to the control group. CONCLUSION: Metformin has a protective effect on noise-induced hearing loss in rats. As a conclusion, it is determined that metformin protects from permanent threshold shift in rats. It can be considered a good alternative for protecting noise-induced hearing loss.

The protective effect of adrenocorticotropic hormone treatment against noise-induced hearing loss.

OBJECTIVE: NIHL is a common problem, and steroids are the most effective treatment option. In this study, we aimed to evaluate the protective effects of the synthetic adrenocorticotropic hormone (ACTH) analogues, which induce endogenous steroid secretion, against noise-induced hearing loss (NIHL) and to compare their effectiveness with that of steroid treatment. METHODS: Twenty-four male Sprague-Dawley albino rats were divided into four subgroups as follows: group 1 (n=6) control, group 2 (n=6) saline, group 3 (n=6) dexamethasone (2mg/kg/day intramuscularly [IM]), group 4 (n=6) ACTH analogue (0,4mg/kg/day IM), respectively. Three groups (groups 2-4) were exposed to white noise (105dB SPL, 12h). All the rats were evaluated for hearing thresholds of 10kHz, 20kHz, and 32kHz via acoustic brainstem responses (ABR) measurement. After the basal threshold measurements, measurements were repeated immediately after the noise and on day 7 and day 21. RESULTS: Both steroid and ACTH analogue groups showed significantly better hearing outcomes than the saline group on day 7 (p<0.001) and day 21 (p<0.001) after the noise exposure. No superior treatment effect was demonstrated in either the steroid or ACTH analogue group. None of the related intervention groups reached the basal hearing thresholds. CONCLUSION: Steroids were effective drugs for the treatment of NIHL. ACTH analogues also demonstrated promising therapeutic effects for NIHL. Further studies to establish ACTH analogues as an alternative NIHL treatment option to steroids are needed.