Deafness in cochlear and auditory nerve disorders

Bio-piezoelectricity: fundamentals and applications in tissue engineering and regenerative medicine

In recent years, smart materials have piqued the interest of scientists and physicians in the biomedical community owing to their ability to modify their properties in response to an external stimulation or changes in their surroundings. Biocompatible piezoelectric materials are an interesting group of smart materials due to their ability to produce electrical charges without an external power source. Electric signals produced by piezoelectric scaffolds can renew and regenerate tissues through special pathways like that found in the extracellular matrix. This review summarizes the piezoelectric phenomenon, piezoelectric effects generated within biological tissues, piezoelectric biomaterials, and their applications in tissue engineering and their use as biosensors.

Distortion Product Otoacoustic Emission Test is Not the Test to Use in Nonclinical Safety Assessment

Ototoxicity and ocular toxicity screening are but two examples of specialty product lines that are often employed as Tier II or III nonclinical safety/hazard screening assessments. Compared to the regulatory guidelines that govern over standard toxicology or neurotoxicology programs, there is a paucity of regulatory strategies to address these specialized product lines. With respect to ototoxicity testing, we argue for the inclusion of the "least burdensome principles" adopted by the US FDA in providing the most pragmatic, efficient, and directed identification of potential harm to auditory function in the nonclinical safety arena. We argue for the exclusive use of the auditory brainstem response and the exclusion of the distortion product otoacoustic emissions (DPOAEs) in these Tiered II safety assessment programs. The inclusion of both are a burden on operational staff and, due to the extended episodes of anesthesia required to conduct both assays, this strategy poses a health and welfare concern for the selected animal species to be used. The DPOAE does not provide any sufficiently valid or reliable data above and beyond the gold standard ABR data, followed by complete oto-histopathology and cytocochleogram combination designs.

Age-related Hearing Loss and Dementia

Dementia is a devastating disease and global health challenge that is highly prevalent worldwide. A growing body of research has shown an independent association between age-related hearing loss (ARHL) and dementia, identifying ARHL as a compelling potential target in preventive strategies for dementia. However, a causal linkage between ARHL and dementia needs to be investigated before making definitive clinical guidelines and treatment recommendations regarding ARHL as a modifiable risk factor. In this review, we discuss the association between ARHL and dementia, the importance of addressing this finding, as well as common mechanisms (eg, microvascular disease) and causal mechanisms (eg, depletion of cognitive reserve and social isolation) that may explain the nature of this relationship. Future directions for research are also highlighted, including randomized controlled trials, developing high-resolution microvascular imaging, and further refining audiometric testing.

Short-term NAD+ supplementation prevents hearing loss in mouse models of Cockayne syndrome

Age-related hearing loss (ARHL) is one of the most common disorders affecting elderly individuals. There is an urgent need for effective preventive measures for ARHL because none are currently available. Cockayne syndrome (CS) is a premature aging disease that presents with progressive hearing loss at a young age, but is otherwise similar to ARHL. There are two human genetic complementation groups of CS, A and B. While the clinical phenotypes in patients are similar, the proteins have very diverse functions, and insight into their convergence is of great interest. Here, we use mouse models for CS (CSA -/- and CSB m/m ) that recapitulate the hearing loss in human CS patients. We previously showed that NAD+, a key metabolite with various essential functions, is reduced in CS and associated with multiple CS phenotypes. In this study, we report that NAD+ levels are reduced in the cochlea of CSB m/m mice and that short-term treatment (10 days) with the NAD+ precursor nicotinamide riboside (NR), prevents hearing loss, restores outer hair cell loss, and improves cochlear health in CSB m/m mice. Similar, but more modest effects were observed in CSA -/- mice. Remarkably, we observed a reduction in synaptic ribbon counts in the presynaptic zones of inner hair cells in both CSA -/- and CSB m/m mice, pointing to a converging mechanism for cochlear defects in CS. Ribbon synapses facilitate rapid and sustained synaptic transmission over long periods of time. Ribeye, a core protein of synaptic ribbons, possesses an NAD(H) binding pocket which regulates its activity. Intriguingly, NAD+ supplementation rescues reduced synaptic ribbon formation in both CSA -/- and CSB m/m mutant cochleae. These findings provide valuable insight into the mechanism of CS- and ARHL-associated hearing loss, and suggest a possible intervention.

Is Sensorineural Hearing Loss Related to Chronic Rhinosinusitis Caused by Outer Hair Cell Injury?

Background

Sensorineural hearing loss is caused by defects in the inner ear. In the present study, associations between chronic rhinosinusitis, outer hair cell injury, and sensorineural hearing loss were investigated.

Material/Methods

A total of 103 patients who met the inclusion criteria were recruited and allocated into a chronic rhinosinusitis group (n=82) and a simple deviated nasal septum group (n=21). Degree and type of hearing loss, including distortion product otoacoustic emissions, were used to assess the status of cochlear outer hair cells.

Results

The rate of hearing loss in the simple deviated nasal septum group was significantly lower than in the chronic rhinosinusitis group (4.76%, 1/21 vs. 24.39%, 20/82, P<0.05), among which 15 chronic rhinosinusitis patients (75%, 15/20) had hearing loss in the high frequency range. Acoustic stapedial reflexes were elicited in all patients of the 2 groups, while positive Metz was found in 3 chronic rhinosinusitis patients (15%, 3/20). The pass rate of distortion product otoacoustic emissions (DPOAEs) for chronic rhinosinusitis patients was significantly lower than in simple deviated nasal septum patients (88.10% vs. 70.73%, P<0.05). Moreover, the signal-to-noise ratio of DPOAE test results at 704 Hz, 3991 Hz, and 5649 Hz in the chronic rhinosinusitis group were significantly lower than in the simple deviated nasal septum group (P<0.05). Logistic regression analysis revealed a correlation between severity of chronic rhinosinusitis and sensorineural hearing loss (OR=1.39, P<0.05).

Conclusions

Outer hair cell injury and sensorineural hearing loss may have a common cause in chronic rhinosinusitis patients.