Oral exposure to arsenic causes hearing loss in young people aged 12-29 years and in young mice

Abstract

There is no information on the association between oral exposure to arsenic (As) and hearing loss in humans or mice. In this combined epidemiological study and experimental study, the association of oral exposure to As with hearing loss in people aged 12-29 years and young mice was examined. Subjects in the exposure group (n = 48), who were drinking tube well water contaminated with As, showed significantly higher risks of hearing loss at 4 kHz [odds ratio (OR) = 7.60; 95% confidence interval (CI): 1.56, 57.88], 8 kHz (OR = 5.00; 95% CI: 1.48, 18.90) and 12 kHz (OR = 8.72; 95% CI: 2.09, 47.77) than did subjects in the control group (n = 29). We next performed an experiment in which young mice were exposed to As via drinking water at 22.5 mg/L, which is a much greater concentration than that in human studies. The exposure group showed hearing loss and accumulation of As in inner ears. Ex vivo exposure of the organ of Corti from mice exposed to As significantly decreased the number of auditory neurons and fibers. Thus, our combined study showed that oral exposure to As caused hearing loss in young people and young mice.

Figure 1

As levels in biological samples in from people aged 12–29 years drinking As-contaminated water and control group. As levels (means ± SD) in the control group (control; n = 29) and exposure group (exposure; n = 48) in toenails (A), hair (B) and urine (C) were measured. Significant differences (***p < 0.0001) were determined by the Mann-Whitney U test.

Figure 2

Hearing loss in people aged 12–29 years drinking As-contaminated water. Hearing thresholds (means ± SD) in the control group (control; n = 29) and the exposure group (exposure; n = 48) at 1, 4, 8 and 12 kHz were measured. Significant differences (**p < 0.01; ***p < 0.0001) were determined by the Mann-Whitney U test.

Figure 3

Oral exposure to As causes hearing loss in young mice aged 3 months. ABR thresholds (means ± SD) at 4, 12, 20 and 32 kHz in the control group (ctrl, closed squares, n = 9) and exposure group (As, open trianglers, n = 8) before (A) and after exposure to As (B) are presented. Significant differences (*p < 0.05; **p < 0.01) were determined by the Mann-Whitney U test.

Figure 4

Accumulation of As in inner ears of young mice aged 3 months after oral exposure to As. As levels (means ± SD) in the control (closed bar, n = 5) and exposure (open bar, n = 7) group in inner ears are presented. Significant differences (***p < 0.0001) were determined by the Mann-Whitney U test.

Figure 5

Ex vivo exposure of the organ of Corti to As at 0.3 µg/mL. (A,B) After ex vivo exposure of the organ of Corti to As at 0.3 µg/mL and no exposure (cont) for 48 and 72 hours, (A) inner hair cells (arrowhead) and outer hair cells (arrows) were stained with phalloidin and (B) spiral ganglion neurons (SGNs) and auditory neuron fibers (ANFs) were stained with anti-neurofilament 200 antibody. Scale bars: 50 µm. (C–F) Densities (means ± SD) of (C) inner hair cells, (D) outer hair cells, (E) auditory nerve fibers and (F) SGNs from the organ of Corti exposed to As (+, black bars, n = 10) and no exposure (−, white bars, n = 10) are presented. Significant difference (*p < 0.05, **p < 0.01, ***p < 0.0001) from the control was analyzed by the unpaired t-test.