Avaliação da alanilglutamina e choque térmico na indução de HSP70 na cóclea como potencial terapêutico em ratos

Abstract

Hearing loss is the most prevalent sensory disorder, with global growth and impact on people's lives, with Noise-Induced Hearing Loss (NIHL) being the major preventable cause of sensorineural hearing loss. In situations of cochlear stress, such as exposure to noise and ototoxicity, there is an increase in the expression of 70kDa heat shock proteins (HSP70) in several cells of the inner ear, with the aim of cytoprotection and reduction of cochlear oxidative stress, in order to prevent hearing damage. Some agents have been shown as potential otoprotection agents due to the cochlear induction capacity of HSP70, such as heat shock, sound conditioning and geranylgeranylacetone. In this sense, alanylglutamine potentiates the induction of HSP70 in various tissues, demonstrating anti-inflammatory mechanisms in cochleas after exposure to noise. This study aimed to assess whether alanylglutamine and heat shock induce HSP70 in different cochlear regions and to assess whether alanylglutamine has hearing protection effects as assessed by Auditory Brainstem Response (ABR) and cochlear histology. For this, we developed two experimental studies. The first experimental study carried out the evaluation of cochlear induction of HSP70 by alanylglutamine and heat shock, using 6 Wistar rats, divided equally into three groups: control, subjected to heat shock throughout the body at 42 °C and treated with a single administration of alanylglutamine at 1.5 g/kg. After 6 hours, the animals were euthanized and their cochleas were collected for immunohistochemical analysis of HSP70. The second experimental study demonstrated the effect of alanylglutamine on hearing protection against noise exposure, using 15 Wistar rats divided into control groups, exposed to noise, and treated with alanylglutamine and exposed to noise. After 6 hours of treatment, the animals were exposed to white noise at 124 dB SPL for 2 hours (Noise and Alanylglutamine groups). ABR was performed before any intervention, 1 day (assessment of temporary hearing loss) and 14 days (assessment of permanent hearing loss) after noise exposure. After the last ABR, the animals were euthanized for histological analysis of the inner ear. Alanylglutamine and heat shock demonstrated increased expression of HSP70 in hair cells of the cochlea, spiral ganglion and stria vascularis compared to the Control group. In addition, in the group treated with alanylglutamine and exposed to noise, hearing recovery between the first and 14th. day after noise exposure was higher compared to the noise-exposed group without intervention (22.5 dB HL vs. 9 dB HL, respectively). Additionally, ABR showed lower P4 wave latency in the group treated with alanylglutamine when compared to the group exposed to noise, and in the histological analysis, the density of spiral ganglion neurons in the Alanylglutamine group was higher than in the Noise group. In view of this, we conclude that alanylglutamine and heat shock may be potential therapeutic agents in otoprotection, via induction of HSP70, creating a field for future studies in hearing preservation.