N-acetylcysteine attenuates noise-induced permanent hearing loss in diabetic rats. - GreenMedInfo Summary
N-acetylcysteine attenuates noise-induced permanent hearing loss in diabetic rats.
Hear Res. 2010 Aug;267(1-2):71-7. Epub 2010 Apr 27. PMID: 20430080
Institute of Occupational Medicine and Industrial Hygiene, National Taiwan University, Taipei, Taiwan.
The purpose of this study is to investigate whether repeated noise exposure aggravates the level of permanent noise-induced hearing loss (NIHL) in diabetic rats and whether N-acetylcysteine (NAC), a precursor of glutathione, attenuates the level of noise-induced permanent hearing loss in diabetic rats. Fifty male Wistar rats were divided into four groups: 12 non-diabetic control rats with saline injection (Control-Saline), 11 non-diabetic control rats with NAC injection (Control-NAC), 13 streptozotocin-induced diabetic rats with saline injection (Diabetes-Saline) and 14 streptozotocin-induced diabetic rats with NAC injection (Diabetes-NAC). NAC (325mg/kg) was given by intraperitoneal injection twice per day (b.i.d.) for 14 days starting 2 days before noise exposure. All rats were exposed to noise for 8hours per day for 10 consecutive days to develop noise-induced permanent hearing loss. The hearing status of all animals was evaluated with auditory brainstem responses (ABR) evoked by clicks and tone bursts. ABRs were measured before and at 1hour, 1 week, 2 weeks and 4 weeks after noise exposure. After a recovery time of 4 weeks, animals were decapitated, and the loss of hair cells was assessed microscopically. In all groups, ABR thresholds failed to return to pre-exposure values throughout the experimental period. The ABR threshold to clicks was markedly elevated in the Diabetes-Saline group (36.9+/-2.3dB SPL), less elevated in the Control-Saline and Diabetes-NAC groups and least in the Control-NAC group (19.5+/-2.0dB SPL) at 4 weeks after noise exposure. Diabetes caused increased susceptibility to noise-induced hearing loss, and NAC treatment reduced the loss in both control and diabetic rats. Cochleograms revealed no gross destruction of hair cells in the non-diabetic groups or the Diabetes-NAC group; however, a significant number of outer hair cells (OHCs) were lost in the Diabetes-Saline group. This study demonstrated that diabetics were prone to developing more severe NIHL than non-diabetics and that NAC could preserve most OHCs and attenuate the permanent noise-induced hearing loss in both groups.