4. Oxidative stress as a new paradigm in hearing loss at high frequencies in different etiologies

The hearing losses under study are examples of pathological conditions in the inner ear that are clinically distinct, and often accumulate over a lifetime. Final expression is determined by molecular mechanisms based on oxidative stress. Assessing the different aspects such as etiology, clinical picture and treatment of these hearing disorders should not be restricted to pre-established immutable models that treat each of them separately without including the intrinsic and extrinsic factors that significantly influence auditory damage.

Prevention possibilities and rehabilitation perspectives for these hearing disorders have been discussed for decades. It is important to prevent NIHL by non-exposure to damaging sound levels, but this is not enough, since factors such as genetic predisposition to hearing loss and the use of ototoxic drugs may exacerbate the final audiological clinical condition. Presbycusis

is the final product of different factors that are harmful to hearing during an individual's lifetime, such that its prevention is hindered by the limits in controlling these factors from childhood onward. Avoiding hearing loss caused by the use of ototoxic drugs is a challenge, since they cannot always be substituted by non-cochleotoxic medication due to the greater efficacy of the former in treating serious diseases, such as cancer. Maintaining good auditory acuity in chronic kidney patients is essential, since hearing loss becomes one more disorder for patients who depend on care and need good communication. Hearing loss related to CKD leads to restricted participation, as well as social and emotional impacts; however, the physiopathology of CKD causes progressive and irreversible cochlear damage.

loss. As such, preventing, treating, and avoiding exacerbations are possibilities to be investi-

Hearing Loss at High Frequencies and Oxidative Stress: A New Paradigm for Different Etiologies

http://dx.doi.org/10.5772/intechopen.76325

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gated in order to guarantee efficient communication and quality of life for individuals.

p38MAPK the release of cytochrome and mitochondria and procaspase activation

Conflict of interest

There is no conflict of interest.

List of the technical terms

CKD chronic kidney disease

dBHL decibel hearing level

GPx glutathione peroxidase

GSH-Red glutathione reductase

GST glutathione S-transferase

JNK c-Jun N-terminal kinase

L length of the ear canal

NOX noise increases oxidase

ROS reactive oxygen species

SHT systemic hypertension

mtDNA mitochondrial DNA

NIHL noise-induced hearing loss

DM diabetes mellitus

GSH glutathione

Hz hertz

kHz kilo hertz

dBA decibel weighting curve A

Some cell factors characterize the basal turn of the cochlea as a risk zone, justifying selective hearing loss at high frequencies in NIHL, presbycusis, ototoxic hearing loss, and CKD. The lower number of ciliated cells and their greater susceptibility in the basal turn make it a risk zone under aggressor conditions (noise, aging, ototoxic, CKD).

Furthermore, the acoustic reflex is efficient in protecting at frequencies below 2 kHz, leaving high frequencies under unfavorable conditions [52]. This reflex is defined as the contraction of middle ear muscles induced by intense acoustic stimulation. The tensor tympani muscle pulls the malleus (hammer) away from the eardrum and the stapedius muscle exerts force behind the stirrup, causing greater stiffness in the system and reducing sound transmission, primarily at low frequencies, that is, below 1 kHz. Thus, changes in middle-ear impedance, due to the aforementioned contractions, have little or no effect on frequencies above 2 kHz [53].

Studying hearing loss using a new model based on oxidative stress leads to new perspectives on how to prevent this disorder. Several factors display important limitations with respect to preventing auditory damage. However, when oxidative stress is present, understanding how it occurs and devising therapies to minimize it is a new prevention strategy that could be applied to workers exposed to intense noise, individuals with a family history of presbycusis, patients using ototoxic drugs and chronic kidney patients. Adjuvant antioxidant therapies represent a new method to help prevent hearing loss. This model serves as a potential alternative to treat the forms of hearing loss under study, and should be assessed more thoroughly for these and other hearing disorders.
