Chronic lead exposure induces cochlear oxidative stress and potentiates noise-induced hearing loss

Abstract

Acquired hearing loss is caused by complex interactions of multiple environmental risk factors, such as elevated levels of lead and noise, which are prevalent in urban communities. This study delineates the mechanism underlying lead-induced auditory dysfunction and its potential interaction with noise exposure. Young-adult C57BL/6 mice were exposed to: 1) control conditions; 2) 2 mM lead acetate in drinking water for 28 days; 3) 90 dB broadband noise 2 h/day for two weeks; and 4) both lead and noise. Blood lead levels were measured by inductively coupled plasma mass spectrometry analysis (ICP-MS) lead-induced cochlear oxidative stress signaling was assessed using targeted gene arrays, and the hearing thresholds were assessed by recording auditory brainstem responses. Chronic lead exposure downregulated cochlear Sod1, Gpx1, and Gstk1, which encode critical antioxidant enzymes, and upregulated ApoE, Hspa1a, Ercc2, Prnp, Ccl5, and Sqstm1, which are indicative of cellular apoptosis. Isolated exposure to lead or noise induced 8–12 dB and 11–25 dB shifts in hearing thresholds, respectively. Combined exposure induced 18–30 dB shifts, which was significantly higher than that observed with isolated exposures. This study suggests that chronic exposure to lead induces cochlear oxidative stress and potentiates noise-induced hearing impairment, possibly through parallel pathways.

Environmental Exposures and Hearing Loss

“…Particularly, exposure to cadmium and lead damages the sensory receptor cells in the cochlea [15,16] and induces oxidative stress in several other organs [17][18][19]. As simultaneous exposures to multiple ototoxicants have a synergistic effect in the inner ear, the co-exposure of heavy metals with other ototraumatic agents can exacerbate the hearing loss [20][21][22][23]. Sources of lead include lead-based paints in older homes, batteries, solder, pipes, pottery, roofing materials, and some cosmetics.…”

Tinnitus and Self-Perceived Hearing Handicap in Firefighters: A Cross-Sectional Study

“…If four pollutants were involved the risk increased fourfold [17]. Because of the old housing stock and the auto industry in Detroit firefighters are probably exposed to higher levels of heavy metals such as lead and cadmium, which can cause auditory dysfunction [18,19]. The length of occupational exposure to environmental pollutants appears to be a predictor of hearing problems in firefighters, as indicated by the association of hearing handicap with the number of years in service.…”

Experimental animal models of drug-induced sensorineural hearing loss: a narrative review

“…Mice treated with 1.0 mg/kg mercuric sulfide per day through gastric gavage for 7 consecutive days demonstrated in an elevation of ABR threshold and prolongation of interwave latencies I-V (155). C57BL/6 mice given 2 mM Pb in water for 28 days presented 8-12 dB shifts in ABR thresholds (156). Rats subjected to 4.0 mg/kg Pb acetate by gavage for 30 days demonstrated prolonged latencies of waves I-V and increased wave amplitudes, implying the deterioration of the neural reflex and damaged hearing (157).…”