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Original Investigation |

Association of Caffeine and Hearing Recovery After Acoustic Overstimulation Events in a Guinea Pig Model

Faisal Zawawi, MD, FRCSC1; Aren Bezdjian, MSc1; Mario Mujica-Mota, MD, MSc1; Jamie Rappaport, MD, FRCSC1; Sam Joseph Daniel, MD, MSc, FRCSC1
[+] Author Affiliations
1Department of Otolaryngology–Head and Neck Surgery, McGill University, Montreal, Quebec, Canada
JAMA Otolaryngol Head Neck Surg. 2016;142(4):383-388. doi:10.1001/jamaoto.2015.3938.
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Importance  Noise-induced hearing loss is an increasingly worrisome problem. Although caffeine intake is common in people involved in noise-related environments, the effect of caffeine on the recovery of hearing after a temporary threshold shift requires further understanding.

Objectives  To determine whether caffeine impairs hearing recovery in a guinea pig model exposed to acoustic overstimulation.

Design, Setting, and Subjects  This experiment at the McGill University Auditory Sciences Laboratory used 24 female albino guinea pigs (age, 6 months; weight, 500-600 g) divided randomly into 3 groups of 8 animals each. Group 1 was exposed to caffeine; group 2, acoustic overstimulation events (AOSEs); and group 3, both. Data were collected from July 1, 2013, to March 30, 2014, and analyzed from April 1 to August 1, 2014.

Interventions  Daily caffeine dose for groups 1 and 3 consisted of 25 mg/kg administered intraperitoneally for 15 days. The AOSEs were administered on days 1 and 8 and consisted of 1 hour of 110-dB pure-tone sound.

Main Outcomes and Measures  Serial auditory brainstem response (ABR) tests to determine the audiological threshold shift and recovery were obtained at baseline and on days 1 (1 hour after the first AOSE), 4, 8 (before and 1 hour after the second AOSE), 11, and 15. Scanning electron and light microscopy of the cochleas were performed to determine morphologic changes.

Results  The day 1 post-AOSE measurement resulted in a similar threshold shift in all animals in groups 2 and 3 at all frequencies tested (8, 16, 20, and 25 kHz). The maximum threshold shift was at 16 kHz, with a mean of 66.12 dB. By day 8, the threshold shift in group 2 recovered completely at all frequencies except 20 kHz, where a mean threshold shift of 20.63 dB of sound pressure level (SPL) was present. Hearing impairment in group 3 persisted in 8-, 16-, and 25-kHz frequencies with thresholds of 21.88, 28.13, and 26.25 dB SPL, respectively (P = .001). After a second AOSE at day 8, similar threshold shift and outcome were recorded on day 15 compared with day 8, with a mean threshold shift at 20 kHz of 29.38 dB SPL in group 2 and mean threshold shifts at 8, 16, 20, and 25 kHz of 29.38, 35.63, 40.63, and 38.75 dB SPL, respectively, in group 3. The difference in ABR threshold recovery was in concordance with scanning electronic and light microscopy findings for each group.

Conclusions and Relevance  A daily dose of caffeine was found to impair the recovery of hearing after an AOSE.

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Figure 1.
Auditory Brainstem Response (ABR) Threshold Shifts

Thresholds are shown 1 hour after the first exposure to acoustic overstimulation events (AOSEs) on day 1, days 4 and 8, day 8 1 hour after the second exposure to AOSEs, and days 11 and 15. Group 1 received an intraperitoneal injection of caffeine, 25 mg/kg, each study day; group 2, AOSE exposure on days 1 and 8; and group 3, both protocols. We used the Mann-Whitney test to compare groups 2 and 3 at each interval. A, B, and D, Impairment in recovery in group 3 was statistically significant on days 4, 8, 11, and 15. C, Impairment in recovery was not statistically different at any time. SPL indicates sound pressure level.

aIndicates 1 hour after exposure to an AOSE.

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Figure 2.
Scanning Electron Microscopy of the Apex of the Cochlea

The image is from a guinea pig from group 3 (intraperitoneal injection of caffeine, 25 mg/kg, each study day and exposure to acoustic overstimulation events on days 1 and 8) and demonstrates a grade 2 damage to the outer hair cells (count of <50%) (hematoxylin-eosin stain, original magnification ×200).

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