Noise exposure levels predict blood levels of the inner ear protein prestin

Serum Levels of Stereocilin as a Hearing Biomarker

Noise-induced hearing loss (NIHL) often presents with an insidious onset, resulting from the cumulative effect of chronic, high-level noise exposure regardless of etiology. Stereocilin (STRC) is a protein that supports stereocilia attachment and cochlear hair cell function, 2 common targets of noise trauma. In this study, we explored the relationship between STRC and daily noise exposure in young, healthy adults. We found that higher noise exposure levels were associated with lower serum levels of STRC, as was the case for another inner-ear protein, prestin. There was a statistically significant positive correlation between serum STRC and prestin levels. These results support a biomarker approach for the diagnosis and monitoring of NIHL. The ability to detect and measure STRC in the blood also has implications for targeted gene therapy. STRC mutations are known to be associated with autosomal recessive deafness, a condition that is now amenable to targeted gene therapy.

Prestin in Human Perilymph, Cerebrospinal Fluid, and Blood as a Biomarker for Hearing Loss

OBJECTIVE

Determining the concentration of prestin in human blood, cerebrospinal fluid (CSF), and perilymph (PL), and evaluating its suitability as a clinical biomarker for sensori-neural hearing loss (SNHL).

STUDY DESIGN

Human blood, CSF, and PL samples were intraoperatively collected from 42 patients with tumors of the internal auditory canal or with intracochlear tumors undergoing translabyrinthine or middle fossa tumor removal. Prestin concentration was measured using enzyme-linked immunosorbent assay and linear regression analyses were performed to investigate its associations with audiological as well as vestibular test results.

SETTING

Tertiary referral center.

RESULTS

The median prestin concentration in blood samples of the 42 study participants (26 women, mean ± standard deviation age, 52.7 ± 12.5 years) was 1.32 (interquartile range, IQR, 0.71-1.99) ng/mL. CSF prestin levels were significantly higher with 4.73 (IQR, 2.45-14.03) ng/mL (P = .005). With 84.74 (IQR, 38.95-122.00) ng/mL, PL prestin concentration was significantly higher compared to blood (P = .01) and CSF (P = .03) levels. Linear regression analyses showed significant associations of CSF prestin concentration with preoperative hearing levels (pure-tone average and word recognition; P = .008, R2 = 0.1894; P = .03, R2 = 0.1857), but no correlations with blood or PL levels.

CONCLUSION AND RELEVANCE

This study's findings highlight the volatile nature of prestin levels and provide the first insights into this potential biomarker's concentrations in body fluids apart from blood. Future investigations should comprehensively assess human prestin levels with different etiologies of SNHL, prestin's natural homeostasis and systemic circulation, and its temporal dynamics after cochlear trauma. Finally, clinically approved detection kits for prestin are urgently required prior to considering a potential translational implementation of this diagnostic technique.

Verification of Outer Hair Cell Motor Protein, Prestin, as a Serological Biomarker for Mouse Cochlear Damage

The motor protein prestin, found in the inner ear's outer hair cells (OHCs), is responsible for high sensitivity and sharp frequency selectivity in mammalian hearing. Some studies have suggested that prestin could be a serological biomarker for cochlear damage, as OHCs are highly vulnerable to damage from various sources. However, the reported data are inconsistent and lack appropriate negative controls. To investigate whether prestin can be used as a serological biomarker for cochlear damage or stress, we measured prestin quantities in the bloodstreams of mice using ELISA kits from different companies. Wildtype (WT) mice were exposed to different ototoxic treatments, including noise exposure and ototoxic reagents that rapidly kill OHCs. Prestin-knockout (KO) mice were used as a negative control. Our data show that some ELISA kits were not able to detect prestin specifically. The ELISA kit that could detect the prestin protein from cochlear homogenates failed to detect prestin in the bloodstream, despite there being significant damage to OHCs in the cochleae. Furthermore, the optical densities of the serum samples, which correlate to prestin quantities, were significantly influenced by hemolysis in the samples. In conclusion, Prestin from OHCs is not a sensitive and reliable serological biomarker for detecting cochlear damage in mice using ELISA.

Serum Prestin Level May Increase Following Music Exposure That Induces Temporary Threshold Shifts: A Pilot Study

OBJECTIVES

To determine if blood prestin level changes after exposure to music at high sound pressure levels, and if this change is associated with temporary threshold shift (TTS) and/or changes in distortion product (DP) amplitude.

DESIGN

Participants were exposed to pop-rock music at 100 dBA for 15 min monaurally through headphones. Pure-tone audiometry, DP amplitude, and blood prestin level were measured before and after exposure.

RESULTS

Fourteen adults (9 women; age range: 20 to 54 years, median age = 31 [Interquartile ratio = 6.75]) with normal hearing were included in the study. Mean prestin level increased shortly after exposure to music, then returned to baseline within 1 week, although this trend was not observed in all participants. All participants presented TTS or a decrease in DP amplitude in at least one frequency after music exposure. There was a statistically significant average threshold elevation at 4 min postexposure. Statistically significant DP amplitude shifts were observed at 4 and 6 kHz, 2 min following exposure. Mean baseline serum prestin level (mean: 140.00 pg/mL, 95% confidence interval (CI): 125.92 to 154.07) progressively increased following music exposure, reaching a maximum at 2 hr (mean: 158.29 pg/mL, 95% CI: 130.42 to 186.66) and returned to preexposure level at 1 week (mean: 139.18 pg/mL, 95% CI: 114.69 to 163.68). However, after correction for multiple comparisons, mean prestin level showed no statistically significant increase from baseline at any timepoint. No correlation between maximum blood prestin level change and average TTS or distortion product otoacoustic emission amplitude shift was found. However, in an exploratory analysis, TTS at 6 kHz (the frequency at which maximum TTS occurred) decreased significantly as baseline blood prestin level increased.

CONCLUSIONS

The results suggest that blood prestin level may change after exposure to music at high sound pressure levels, although statistical significance was not reached in this relatively small sample after correction. Baseline serum prestin level may also predict the degree of TTS. These findings thus suggest that the role of baseline serum prestin level as a proxy marker of cochlear susceptibility to intense music exposure should be further explored.

Serum Prestin After Ototoxin Exposure Is Not Dependent on Outer Hair Cell Loss

HYPOTHESIS

Cyclodextrin (CDX)-induced serum prestin burst is not dependent on outer hair cell (OHC) loss.

BACKGROUND

Serum prestin has been proposed as a biomarker for ototoxicity. We recently used an automated Western approach to quantify serum prestin changes in a newly introduced model of CDX ototoxicity. To gain insights into prestin as a biomarker, here we further characterize serum prestin in the CDX model.

METHODS

Guinea pigs were treated with 750, 3,000, or 4,000 mg/kg CDX, and serum samples were obtained through up to 15 weeks after exposure. Serum prestin levels were quantified using automated Western, and hair cell counts were obtained.

RESULTS

All three doses induced an N -glycosylated ~134-kDa prestin burst; however, only the 3,000 and 4,000 mg/kg resulted in robust OHC loss. Prestin levels returned to baseline where they remained up to 15 weeks in the absence of OHCs.

CONCLUSION

The ~134-kDa prestin burst induced after CDX administration is N -glycosylated, representing a posttranslational modification of prestin. Serum prestin seems to be a promising biomarker when using therapeutics with ototoxic properties because it is not dependent on OHC loss as a necessary event, thus affording the opportunity for early detection and intervention.

Evaluation of inner ear damage by mastoid drilling with measurement of serum prestin (SLC26A5) levels

OBJECTIVE

The objective of this study is to demonstrate any inner ear injury caused by drilling in mastoid surgery with prestin, outer hair cell motor protein specific to the cochlea.

METHODS

The patients with chronic otitis media requiring mastoidectomy (n = 21) and myringoplasty (n = 21) were included. Serum prestin level obtained from blood samples was measured before surgery and on postoperative days 0, 3, and 7 using Human Prestin (SLC26A5) ELISA Kit. All patients underwent the Pure Tone Audiometry (PTA) test before surgery and on the postoperative 7th day. The drilling time was also recorded for all patients who underwent mastoidectomy.

RESULTS

In both mastoidectomy and myringoplasty groups, the postoperative serum prestin levels increased on days 0 and 7 (pday-0 = 0.002, pday-7 = 0.001 and pday-0 = 0.005, pday-7 = 0.001, respectively). There was no significant difference in the serum prestin levels between the two groups, postoperatively. The PTA thresholds at day 7 did not change in either group. A significant decline at 2000 Hz of bone conduction hearing threshold in both groups and a decline at 4000 Hz in the myringoplasty group were found. There was no correlation between the drilling time and the increase of prestin levels in the postoperative day 0, 3, and 7.

CONCLUSION

Our results showed that mastoid drilling is not related to a significant inner ear injury. Although the myringoplasty group was not exposed to drill trauma, there was a similar increase in serum prestin levels as the mastoidectomy group. Also, a significant decline at 2000 Hz of bone conduction hearing threshold in both groups and a decline at 4000 Hz in the myringoplasty group were found. These findings suggest that suction and ossicular manipulation trauma can lead to an increase in serum prestin levels and postoperative temporary or permanent SNHL at 2000 and 4000 Hz.

LEVEL OF EVIDENCE

Level-4.

Serum Prestin and Otolin-1 Levels in Pilots of Helicopter-Based Emergency Medical Services: Potential Markers for Ear Injury

INTRODUCTION

Occupational noise exposure is a major public health concern, impacting a large workforce worldwide. In this study, we sought to evaluate the serum concentrations of prestin, a cochlear protein that diminishes following noise exposure, and otolin-1, a protein secreted into the bloodstream subsequent to inner ear damage, among three diverse professional categories, each exposed to varying degrees of noise. Helicopter emergency medical service (HEMS) pilots and construction workers were considered high-risk groups due to their elevated exposure to occupational noise, whereas office workers were regarded as a low-risk group, reflecting their comparatively minimal noise exposure.

METHODS

The study sample included 60 males, encompassing helicopter pilots, construction laborers, and office workers (n=20, each). Recruitment occurred during standard occupational health visits, with all participants presenting normal clinical audiograms. Serum levels of prestin and otolin-1 were measured in duplicate using commercially available immunoassays and compared across the three professional categories.

RESULTS

HEMS pilots had the lowest mean serum prestin level at 211±27 pg/mL, followed by construction workers at 234±29 pg/mL, and office workers at 269±42 pg/mL (p<0.001, one-way analysis of variance), with all inter-group differences statistically significant (p<0.05, Tukey's post hoc tests). For otolin-1, HEMS pilots showed the highest mean at 216±20 pg/mL, with construction workers at 196±22 pg/mL, and office workers at 181±20 pg/mL (p<0.001, one-way analysis of variance). Statistically significant differences were found between HEMS pilots and both other groups for otolin-1 levels (p<0.05, Tukey's post hoc tests), but not between construction workers and office workers.

CONCLUSIONS

 Serum concentrations of prestin and otolin-1 may differ among healthy individuals according to their occupational noise exposure and have the potential to act as indicators of subclinical inner ear injury. To substantiate these preliminary observations, incorporating exposure assessment, especially via direct measurements of noise and vibration exposure, would markedly improve the reliability of our findings.

Heightened OAEs in young adult musicians: Influence of current noise exposure and training recency

Otoacoustic emissions (OAEs) are a non-invasive metric of cochlear function. Studies of OAEs in musicians have yielded mixed results, ranging from evidence of diminished OAEs in musicians-suggesting noise-induced hearing loss-to no difference when compared to non-musicians, or even a trend for stronger OAEs in musicians. The goal of this study was to use a large sample of college students with normal hearing (n = 160) to compare OAE SNRs in musicians and non-musicians and to explore potential effects of training recency and noise exposure on OAEs in these cohorts. The musician cohort included both active musicians (who at the time of enrollment practiced at least weekly) and past musicians (who had at least 6 years of training). All participants completed a questionnaire about recent noise exposure (previous 12 months), and a subset of participants (71 musicians and 15 non-musicians) wore a personal noise dosimeter for one week to obtain a more nuanced and objective measure of exposure to assess how different exposure levels may affect OAEs before the emergence of a clinically significant hearing loss. OAEs were tested using both transient-evoked OAEs (TEOAEs) and distortion-product OAEs (DPOAEs). As predicted from the literature, musicians experienced significantly higher noise levels than non-musicians based on both subjective (self-reported) and objective measures. Yet we found stronger TEOAEs and DPOAEs in musicians compared to non-musicians in the ∼1-5 kHz range. Comparisons between past and active musicians suggest that enhanced cochlear function in young adult musicians does not require active, ongoing musical practice. Although there were no significant relations between OAEs and noise exposure as measured by dosimetry or questionnaire, active musicians had weaker DPOAEs than past musicians when the entire DPOAE frequency range was considered (up to ∼16 kHz), consistent with a subclinical noise-induced hearing loss that only becomes apparent when active musicians are contrasted with a cohort of individuals with comparable training but without the ongoing risks of noise exposure. Our findings suggest, therefore, that separate norms should be developed for musicians for earlier detection of incipient hearing loss. Potential explanations for enhanced cochlear function in musicians include pre-existing (inborn or demographic) differences, training-related enhancements of cochlear function (e.g., upregulation of prestin, stronger efferent feedback mechanisms), or a combination thereof. Further studies are needed to determine if OAE enhancements offer musicians protection against damage caused by noise exposure.

Relationship of Serum Prestin Levels to the Severity of Sensorineural Hearing Loss

OBJECTIVE

Prestin is an outer hair cell (OHC) protein responsible for increasing cochlear sensitivity and has been proposed as a biomarker. We aimed to evaluate whether the serum prestin level is related to the severity of chronic sensorineural hearing loss (SNHL).

METHODS

Ninety subjects were recruited from the patient base at Samarra public hospitals and clinics in Iraq from January to October of 2022. They were divided into three groups equally: a group of healthy people without hearing loss (G0), a group with moderate SNHL (G1), and a group with severe SNHL (G2). The subjects ranged from 20 to 80 years of age and included 51 males and 39 females. Blood samples were collected, then serum was separated, and enzyme-linked immunosorbent assays were performed to quantify the levels of prestin.

RESULTS

Hearing thresholds were sequentially statistically higher across the three groups. While prestin levels were significantly higher in G1 and G2 than that in G0, there were no differences between the G1 and G2 levels. Serum prestin levels were positively correlated with hearing thresholds in G1, but not G2.

CONCLUSION

Our results suggest that in the clinical setting, prestin is sensitive to chronic mild to moderate SNHL (i.e., up to 40-60 dB), not more severe loss. This range is consistent with the added sensitivity provided by OHCs in the cochlea and provides support for prestin as a biomarker of OHC-mediated SNHL.

Automated Western Blot Analysis of Ototoxin-Induced Prestin Burst in the Blood after Cyclodextrin Exposure

HYPOTHESIS

Ototoxin cyclodextrin (CDX) will induce a burst in serum prestin when quantified with automated Western blot analysis.

BACKGROUND

In the clinical realm, we primarily rely on audiological measures for diagnosis and surveillance of sensorineural hearing loss (SNHL) and have limited therapeutic options. We have proposed a blood-based biomarker approach to overcome this challenge by measuring the outer hair cell's (OHC) electromotile protein, prestin, in the blood. Previously, we demonstrated a burst in serum prestin after cisplatin exposure using enzyme-linked immunosorbent assayELISA.

METHODS

Guinea pigs were treated with either 3,000 or 4,000 mg/kg CDX, and serum samples were obtained through 3 days after exposure. Serum prestin levels were quantified using automated blot analysis, western and hair cell counts were obtained.

RESULTS

Both 3,000 and 4,000 mg/kg resulted in robust OHC loss, although more variability was seen at the lower dose. Automated Western blot analysis demonstrated that the prestin profile after CDX exposure is different than baseline. Specifically, a new ~134- kDa band accounted for the prestin burst after ototoxin ablation of OHCs at both doses.

CONCLUSIONS

We reproduced the prestin burst seen after cisplatin administration using CDX. Automated Western blot western analysis revealed that a ~a ~ 134- kDa species of prestin is responsible for the burst. We suggest that the induced band may be a prestin dimer, which could serve as a biomarker for early detection of ototoxicity in the clinical setting. These results add further promise to the potential of serum prestin to serve as an ototoxicity biomarker when using therapeutics with ototoxic properties.

Predictive value of serum proteomic biomarkers for noise-induced hearing loss

Early detection of noise-induced hearing loss (NIHL) in patients with long-term noise exposure is vital for improving public health and reducing social burden. However, at present, the diagnosis of NIHL mainly depends on audiometric testing, and the primary test is pure-tone audiometry. Moreover, testing requires professional operators and complex equipment; thus, NIHL is often diagnosed at a later disease stage. Using a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based proteomic approach, we identified 9 differentially expressed proteins (DEPs), namely, 6 upregulated serum proteins and 3 downregulated serum proteins, in samples from 50 ground crew personnel working at an air force station. Then, according to the results, we predicted that caldesmon (CALD1), myocilin (MYOC), zyxin (ZYX), creatine kinase M-type (CKM), insulin-like growth factor-binding protein 2 (IGFBP2), complement factor H-related protein 4 (CFHR4), prenylcysteine oxidase 1 (PCYOX1), heat shock cognate 71 kDa protein (HSPA8), and immunoglobulin lambda variable 3-21 (IGLV3-21) were associated with NIHL. We selected these DEPs as variables to perform logistic regression. Finally, a logistic regression model was constructed based on IGFBP2, ZYX, CKM, and CFHR4. The area under the curve was 0.894 (95% CI = 0.812 to 0.977). These findings suggested that IGFBP2, ZYX, CKM, and CFHR4 in serum are differentially expressed in NIHL patients and have the potential to be biomarkers for predicting the risk for NIHL. Further experiments in mice showed that ZYX and IGFBP2 in the cochlear were increased after noise exposure. ZYX and IGFBP2 may be involved in the occurrence and development of NIHL.

Conditional Ablation of Glucocorticoid and Mineralocorticoid Receptors from Cochlear Supporting Cells Reveals Their Differential Roles for Hearing Sensitivity and Dynamics of Recovery from Noise-Induced Hearing Loss

Endogenous glucocorticoids (GC) are known to modulate basic elements of cochlear physiology. These include both noise-induced injury and circadian rhythms. While GC signaling in the cochlea can directly influence auditory transduction via actions on hair cells and spiral ganglion neurons, evidence also indicates that GC signaling exerts effects via tissue homeostatic processes that can include effects on cochlear immunomodulation. GCs act at both the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). Most cell types in the cochlea express both receptors sensitive to GCs. The GR is associated with acquired sensorineural hearing loss (SNHL) through its effects on both gene expression and immunomodulatory programs. The MR has been associated with age-related hearing loss through dysfunction of ionic homeostatic balance. Cochlear supporting cells maintain local homeostatic requirements, are sensitive to perturbation, and participate in inflammatory signaling. Here, we have used conditional gene manipulation techniques to target Nr3c1 (GR) or Nr3c2 (MR) for tamoxifen-induced gene ablation in Sox9-expressing cochlear supporting cells of adult mice to investigate whether either of the receptors sensitive to GCs plays a role in protecting against (or exacerbating) noise-induced cochlear damage. We have selected mild intensity noise exposure to examine the role of these receptors related to more commonly experienced noise levels. Our results reveal distinct roles of these GC receptors for both basal auditory thresholds prior to noise exposure and during recovery from mild noise exposure. Prior to noise exposure, auditory brainstem responses (ABRs) were measured in mice carrying the floxed allele of interest and the Cre recombinase transgene, but not receiving tamoxifen injections (defined as control (no tamoxifen treatment), versus conditional knockout (cKO) mice, defined as mice having received tamoxifen injections. Results revealed hypersensitive thresholds to mid- to low-frequencies after tamoxifen-induced GR ablation from Sox9-expressing cochlear supporting cells compared to control (no tamoxifen) mice. GR ablation from Sox9-expressing cochlear supporting cells resulted in a permanent threshold shift in mid-basal cochlear frequency regions after mild noise exposure that produced only a temporary threshold shift in both control (no tamoxifen) f/fGR:Sox9iCre+ and heterozygous f/+GR:Sox9iCre+ tamoxifen-treated mice. A similar comparison of basal ABRs measured in control (no tamoxifen) and tamoxifen-treated, floxed MR mice prior to noise exposure indicated no difference in baseline thresholds. After mild noise exposure, MR ablation was initially associated with a complete threshold recovery at 22.6 kHz by 3 days post-noise. Threshold continued to shift to higher sensitivity over time such that by 30 days post-noise exposure the 22.6 kHz ABR threshold was 10 dB more sensitive than baseline. Further, MR ablation produced a temporary reduction in peak 1 neural amplitude one day post-noise. While supporting cell GR ablation trended towards reducing numbers of ribbon synapses, MR ablation reduced ribbon synapse counts but did not exacerbate noise-induced damage including synapse loss at the experimental endpoint. GR ablation from the targeted supporting cells increased the basal resting number of Iba1-positive (innate) immune cells (no noise exposure) and decreased the number of Iba1-positive cells seven days following noise exposure. MR ablation did not alter innate immune cell numbers at seven days post-noise exposure. Taken together, these findings support differential roles of cochlear supporting cell MR and GR expression at basal, resting conditions and especially during recovery from noise exposure.

Integrating pharmacogenomics into clinical trials of hearing disorders

In 2019, the U.S. Food and Drug Administration issued guidance to increase the efficiency of drug development and support precision medicine, including tailoring treatments to those patients who will benefit based on genetic variation even in the absence of a documented mechanism of action. Although multiple advancements have been made in the field of pharmacogenetics (PGx) for other disease conditions, there are no approved PGx guidelines in the treatment of hearing disorders. In studies of noise-induced hearing loss (NIHL), some progress has been made in the last several years associating genomic loci with susceptibility to noise damage. However, the power of such studies is limited as the underlying physiological responses may vary considerably among the patient populations. Here, we have summarized previous animal studies to argue that NIHL subtyping is a promising strategy to increase the granularity of audiological assessments. By coupling this enhanced phenotyping capability with genetic association studies, we suggest that drug efficacy will be better predicted, increasing the likelihood of success in clinical trials when populations are stratified based on genetic variation or designed with multidrug combinations to reach a broader segment of individuals suffering or at risk from NIHL.

Subclinical diagnosis of cisplatin-induced ototoxicity with biomarkers

A mouse model with cisplatin-induced ototoxicity was used in addition to human samples from the ITMAT Biobank at the University of Pennsylvania. Mouse auditory brainstem responses (ABR), inner ear histology, perilymph cisplatin sampling, and measurement of serum prestin via ELISA were performed. Human serum prestin level was measured via ELISA in patients with otological issues after cisplatin treatment and compared to matched controls. Serum prestin was significantly elevated before ABR threshold shifts in mice exposed to cisplatin compared to control mice. Prestin concentration also correlated with the severity of hearing threshold shifts in mice. After an extended rest post-cisplatin treatment, prestin returned to baseline levels in mice and humans. Prestin was significantly elevated in the serum before the onset of objective hearing loss and correlated with the severity of hearing damage indicating that prestin may function as an effective biomarker of cisplatin-induced ototoxicity. Human serum prestin levels responded similarly to mice > 3 weeks from ototoxic exposure with decreased levels of prestin in the serum.

Acute Noise Causes Down-Regulation of ECM Protein Expression in Guinea Pig Cochlea

Proteomics technology reveals the marker proteins, potential pathogenesis, and intervention targets after noise-induced hearing loss. To study the differences in cochlea protein expression before and after noise exposure using proteomics to reveal the pathological mechanism of noise-induced hearing loss (NIHL). A guinea pig NIHL model was established to test the ABR thresholds before and after noise exposure. The proteomics technology was used to study the mechanism of differential protein expression in the cochlea by noise stimulation. The average hearing threshold of guinea pigs on the first day after noise exposure was 57.00 ± 6.78 dB Sound pressure level (SPL); the average hearing threshold on the seventh day after noise exposure was 45.83 ± 6.07 dB SPL. The proteomics technology identified 3122 different inner ear proteins, of which six proteins related to the hearing were down-regulation: Tenascin C, Collagen Type XI alpha two chains, Collagen Type II alpha one chain, Thrombospondin 2, Collagen Type XI alpha one chain and Ribosomal protein L38, and are enriched in protein absorption, focal adhesion, and extracellular matrix receptor pathways. Impulse noise can affect the expression of differential proteins through focal adhesion pathways. This data can provide an experimental basis for the research on the prevention and treatment of NIHL.