Hydrogen Gas Inhalation Attenuates Acute Impulse Noise Trauma: A Preclinical In Vivo Study

Abstract

Objective: Molecular hydrogen (H₂) has shown therapeutic potential in several oxidative stress-related conditions in humans, is well-tolerated, and is easily administered via inhalation.The aim of this preclinical in vivo study was to investigate whether impulse noise trauma can be prevented by H₂ when inhaled immediately after impulse noise exposure.

Methods: Guinea pigs (n = 26) were subjected to impulse noise (n = 400; 156 dB SPL; 0.33/s; n = 11; the Noise group), to impulse noise immediately followed by H₂ inhalation (2 mol%; 500 ml/min; 1 hour; n = 10; the Noise + H₂ group), or to H₂ inhalation (n = 5; the H₂ group). The acoustically evoked ABR threshold at 3.15, 6.30, 12.5, 20.0, and 30.0 kHz was assessed before and 4 days after impulse noise and/or H₂ exposure. The cochleae were harvested after the final ABR assessment for quantification of hair cells.

Results: Noise exposure caused ABR threshold elevations at all frequencies (median 35, 35, 30, 35, and 35 dB SPL, the Noise group; 20, 25, 10, 13, and 20 dB SPL, the Noise + H₂ group; P < .05) but significantly less so in the Noise + H₂ group (P < .05). Outer hair cell (OHC) loss was in the apical, mid, and basal regions 8.8%, 53%, and 14% in the Noise group and 3.5%, 22%, and 1.2% in the Noise + H₂ group. The corresponding inner hair cell (IHC) loss was 0.1%, 14%, and 3.5% in the Noise group and 0%, 2.8%, and 0% in the Noise + H₂ group. The difference between the groups was significant in the basal region for OHCs (P = .003) and apical (P = .033) and basal (P = .048) regions for IHCs.

Conclusions: Acute acoustic trauma can be reduced by H₂ when inhaled immediately after impulse noise exposure.

Keywords: auditory brainstem response; auditory hair cell; guinea pig; hearing loss; molecular hydrogen; noise-induced; otoprotection.

Figure 1.

Guinea pigs were exposed to unilateral (left-side) impulse noise (400 short sound impulses; ~156 dB SPL; rate 0.33/s) only (the Noise group; n = 11) or followed by 1-hour H₂ inhalation (Noise + H₂; n = 10). Frequency specific acoustically evoked auditory brainstem response (ABR) thresholds of the left ear at 3.15, 6.30, 12.5, 20.0, and 30.0 kHz were determined before and 4 days after the exposure. The frequency specific ABR threshold shifts in each group are shown. The horizontal line in the middle of the boxes represents the median, and the bottom and the top of the boxes represent the first and third quartiles, respectively. The bottom and top whiskers extend to the minimum and maximum values, respectively, that are within 1.5 times the height of the box. The empty circles are outliers, that is, values that are without 1.5 times the height of the box. p is the P value for the inter-group difference in frequency specific ABR threshold shift (2-sided Mann-Whitney U test). n = 10 in the Noise + H₂ group and n = 11 in the Noise group at each frequency.

Figure 2.

A micrograph of a surface preparation derived from the left cochlea of a guinea pig in the Noise + H₂ group that shows a remaining (top) and a lost (bottom) outer hair cell (OHC) of the first (OHC1), second (OHC2), and third (OHC3) rows.

Figure 3.

Loss of OHCs in the first (A), second (B), and third (C) rows and loss of inner hair cells (IHCs; (D)) per mm distance from the round window in the left cochlea of the Noise + H₂ group (n = 10) and the Noise group (n = 11). The circles represent the median, while the bottom and top error bars extend to Q1 and Q3, respectively. The number of observations is 9 at 18 to 10 mm, 8 at 9 and 8 mm, 9 at 7 to 4 mm, 8 at 3 mm, 5 at 2 mm, and 1 at 1 mm in the Noise + H₂ group and 10 at 18–4 mm, 8 at 3 mm, 4 at 2 mm, 0 at 1 mm in the Noise group.

Figure 4.

Mean loss of OHCs (A) and IHCs (B) in the apical (15-18 mm), mid (9-14 mm), and basal (1-8 mm) parts of the cochlea in the Noise + H₂ (n = 10) group and the Noise group (n = 11). The horizontal line in the middle of the boxes represents the median, and the bottom and the top of the boxes represent Q1 and Q3, respectively. The bottom and top whiskers extend to the minimum and maximum values, respectively, that are within 1.5 times the height of the box. The empty circles are outliers, that is, values that are without 1.5 times the height of the box. The grey star is an extreme outlier, that is, a value that is without 3 times the height of the box. P is the significant P value for the difference in hair cell loss between the treatment groups (2-sided Mann–Whitney U test). n = 9 in each region for the Noise + H₂ group and n = 10 in each region for the Noise group.