The role of deferoxamine in the prevention of gentamicin ototoxicity: a histological and audiological study in guinea pigs

Nanodelivery of antioxidant Agents: A promising strategy for preventing sensorineural hearing loss

Sensorineural hearing loss (SNHL), often stemming from reactive oxygen species (ROS) generation due to various factors such as ototoxic drugs, acoustic trauma, and aging, remains a significant health concern. Oxidative stress-induced damage to the sensory cells of the inner ear, particularly the non-regenerating hair cells, is a critical pathologic mechanism leading to SNHL. Despite the proven efficacy of antioxidants in mitigating oxidative stress, their clinical application for otoprotection is hindered by the limitations of conventional drug delivery methods. This review highlights the challenges associated with systemic and intratympanic administration of antioxidants, including the blood-labyrinthine barrier, restricted permeability of the round window membrane, and inadequate blood flow to the inner ear. To overcome these hurdles, the application of nanoparticles as a delivery platform for antioxidants emerges as a promising solution. Nanocarriers facilitate indirect drug delivery to the cochlea through the round and oval window membrane, optimising drug absorption while reducing dosage, Eustachian tube clearance, and associated side effects. Furthermore, the development of nanoparticles carrying antioxidants tailored to the intracochlear environment holds immense potential. This literature research aimed to critically examine the root causes of SNHL and ROS overproduction in the inner ear, offering insights into the application of nanoparticle-based drug delivery systems for safeguarding sensorineural hair cells. By focusing on the intricate interplay between oxidative stress and hearing loss, this research aims to contribute to the advancement of innovative therapeutic strategies for the prevention of SNHL.

Protective Effects of Deferoxamine on Vestibulotoxicity in Gentamicin-Induced Bilateral Vestibulopathy Rat Model

Introduction: Administration of aminoglycoside (AG) antibiotics is one of the most common causes of ototoxicity. This study aimed to determine the protective effects of deferoxamine, an iron-chelating agent, on vestibulotoxicity using an intratympanic gentamicin injection (ITGM)-induced bilateral vestibulopathy rat model.

Methods: Fifteen Sprague-Dawley rats were randomly assigned to the ITGM only (n = 5), the ITGM combined with intramuscular deferoxamine (DFO) injection (ITGM+DFO, n = 5), or the intratympanic normal saline (control, n = 5) group. The rats in the ITGM+DFO group received intramuscular injection of 150 mg/kg of deferoxamine at 30, 90, and 150 min after the ITGM. The vestibular function was evaluated using the rotarod and open field test every 3 days after the injection until Day 16 when the rats were subjected to histological changes.

Results: The rats in the ITGM only group began to show significantly impaired vestibular function 2 days after ITGM into both ears. In contrast, the vestibular function was maintained in the control and ITGM+DFO groups without a difference throughout the experiments. The rats in the ITGM only group showed a near-complete loss of the type I and II hair cells and a collapse of the sensory epithelium in both the saccule and utricle. In contrast, the rats in the ITGM+DFO and control groups showed a relatively well-preserved sensory epithelium including the hair cells, cilia, and otolith layer.

Conclusion: This study provides experimental evidence for preventive effects of iron-chelating agents on AG-induced vestibulotoxicity. Simultaneous administration of iron-chelating agents may be considered when using ototoxic agents, especially in those considered to be vulnerable to toxic damage of the inner ear.

Adverse outcome pathway for aminoglycoside ototoxicity in drug-resistant tuberculosis treatment

Individuals treated for multidrug-resistant tuberculosis (MDR-TB) with aminoglycosides (AGs) in resource-limited settings often experience permanent hearing loss. However, AG ototoxicity has never been conceptually integrated or causally linked to MDR-TB patients' pre-treatment health condition. We sought to develop a framework that examines the relationships between pre-treatment conditions and AG-induced hearing loss among MDR-TB-infected individuals in sub-Saharan Africa. The adverse outcome pathway (AOP) approach was used to develop a framework linking key events (KEs) within a biological pathway that results in adverse outcomes (AO), which are associated with chemical perturbation of a molecular initiating event (MIE). This AOP describes pathways initiating from AG accumulation in hair cells, sound transducers of the inner ear immediately after AG administration. After administration, the drug catalyzes cellular oxidative stress due to overproduction of reactive oxygen species. Since oxidative stress inhibits mitochondrial protein synthesis, hair cells undergo apoptotic cell death, resulting in irreversible hearing loss (AO). We identified the following pre-treatment conditions that worsen the causal linkage between MIE and AO: HIV, malnutrition, aging, noise, smoking, and alcohol use. The KEs are: (1) nephrotoxicity, pre-existing hearing loss, and hypoalbuminemia that catalyzes AG accumulation; (2) immunodeficiency and antioxidant deficiency that trigger oxidative stress pathways; and (3) co-administration of mitochondrial toxic drugs that hinder mitochondrial protein synthesis, causing apoptosis. This AOP clearly warrants the development of personalized interventions for patients undergoing MDR-TB treatment. Such interventions (i.e., choosing less ototoxic drugs, scheduling frequent monitoring, modifying nutritional status, avoiding poly-pharmacy) will be required to limit the burden of AG ototoxicity.

Toward Cochlear Therapies

Sensorineural hearing impairment is the most common sensory disorder and a major health and socio-economic issue in industrialized countries. It is primarily due to the degeneration of mechanosensory hair cells and spiral ganglion neurons in the cochlea via complex pathophysiological mechanisms. These occur following acute and/or chronic exposure to harmful extrinsic (e.g., ototoxic drugs, noise...) and intrinsic (e.g., aging, genetic) causative factors. No clinical therapies currently exist to rescue the dying sensorineural cells or regenerate these cells once lost. Recent studies have, however, provided renewed hope, with insights into the therapeutic targets allowing the prevention and treatment of ototoxic drug- and noise-induced, age-related hearing loss as well as cochlear cell degeneration. Moreover, genetic routes involving the replacement or corrective editing of mutant sequences or defected genes are showing promise, as are cell-replacement therapies to repair damaged cells for the future restoration of hearing in deaf people. This review begins by recapitulating our current understanding of the molecular pathways that underlie cochlear sensorineural damage, as well as the survival signaling pathways that can provide endogenous protection and tissue rescue. It then guides the reader through to the recent discoveries in pharmacological, gene and cell therapy research towards hearing protection and restoration as well as their potential clinical application.

Ototoxicity: The Radical Drum Beat and Rhythm of Cochlear Hair Cell Life and Death

The function and structure of the auditory information processing system establishes a unique sensory environment for the "perfect storm." The battle between life and death pits the cascade of an apoptotic storm, programmed cell death cascades, against simple cell death (necrosis) pathways. Live or die, the free radical biology of oxygen and hydroxylation, and the destruction of transition metal migration through the mechanical gate sensory processes of the hair cell lead to direct access to the cytoplasm, cytoplasmic reticulum, and mitochondria of the inner workings of the hair cells. These lead to subsequent interactions with nuclear DNA resulting in permanent hearing loss. The yin and yang of pharmaceutical product development is to document what kills, why it kills, and how do we mitigate it. This review highlights the processes of cell death within the cochlea.

Protective role of intratympanic nigella sativa oil against gentamicin induced hearing loss

OBJECTIVE

Aminoglycosides, used to combat with life-threatening infections, have a substantial risk of hearing loss. Nigella sativa is an annual herbaceous plant and used for treatment of many diseases for ages. We aimed to investigate the protective role of intratympanic nigella sativa oil against gentamicin induced hearing loss in an animal model.

METHODS AND MATERIALS

Twenty eight guinea pigs were randomly divided into four groups: i-control, ii- Intratympanic nigella sativa oil (IT-NSO), iii- Intraperitoneal gentamicin (IP-G) and iv- Intraperitoneal gentamicin and intratympanic nigella sativa oil (IP-G + IT-NSO). Preoperative and postoperative hearing thresholds were determined with auditory brainstem response with click and 8 kHz tone-burst stimuli. Histological analysis of the cochlea specimens were performed under light microscope. Semiquantitative grading of the histological findings was carried out and compared between the groups.

RESULTS

Highest posttreatment hearing thresholds were detected in IP-G group. Posttreatment mean hearing threshold of the IP-G group with click stimulus was significantly higher than the IP-G + IT-NSO group (p = 0.004). whereas the difference was not significant with 8 kHz tone-burst stimulus (p = 0.137). Both IP-G and IP-G + IT-NSO groups had significantly higher hearing thresholds compared to control and IT-NSO groups (p > 0.05). Histological examination of the control and IT-NSO groups demonstrated normal appearance of cochlear nerve, stria vascularis and organ of Corti. IP-G group showed the most severe histological alterations including hydropic and vacuolar degenerations, hair cell damage and deformation of the basilar mambrane. Histological evidence of damage was significantly reduced in IP-G + IT-NSO group compared to IP-G group.

CONCLUSION

Addition of intratympanic NSO to systemic gentamicin was demonstrated to have beneficial effects in hearing thresholds which was supported by histological findings.

Protective role of misoprostol in prevention of gentamicin ototoxicity

OBJECTIVES

To demonstrate potential protective effect of misoprostol on cochlear toxicity caused by gentamicin with electrophysiological tests and histopathological studies.

MATERIALS AND METHODS

The study included 80 ears of 40 rats with normal hearing threshold and DPOAE value in both ears. Animals were assigned into 4 groups. The rats were randomized into 4 groups. Group I (n = 10): Gentamicin, Group II (n = 10): Gentamicin plus misoprostol, Group III (n = 10): Saline; Group IV (n = 10): Misoprostol. All drugs used in the study were given once daily for 15 days. DPOAE and ABR measurements were repeated after drug administration. Subsequently, the rats' cochleae were examined histopathologically. Baseline DPOAE and ABR values were compared to those obtained after drug exposure and cochlear toxicity was evaluated in electrophysiological manner.

RESULTS

When At baseline, there were no significant differences in DPOAE responses at frequencies of 1001, 1501, 2002, 3003, 4004, 6006 and 7996 Hz among groups. However In DPOAE test, statistically significant difference was observed between the pre-study basal values and post-study results in groups other than gentamicin + misoprostol group. Additionally, It was found that there was a significant difference in DPOAE response at frequency of 4004 Hz obtained at baseline and after drug exposure according to measurements of epithelial vacuolization in stria vascularis. While ABR threshold values were compared at baseline, there were no significant difference in ABR threshold values of left and right ear between groups. Histopathologically it was also found that there were significant differences measurements of epithelial vacuolization in stria vascularis and inflammation among groups (p < 0.05).

CONCLUSION

By these results, misoprostol, a potent antioxidant, has protective effect against cochlear damage, and that may be a safe alternative.

Quercetine attenuates the gentamicin-induced ototoxicity in a rat model

OBJECTIVES

The aim of this study is to evaluate the protective role of quercetin in gentamicin-induced ototoxicity through an auditory brainstem response (ABR) test and a histopathological evaluation of the cochlea.

METHODS

In this study, 48 female adult Sprague-Dawley rats aged 20-22 weeks and weighing 200-250g were used. An ABR test was carried out on all rats prior to drug administration, after which, the rats were divided into four groups of 12 animals each. Drug administration was gentamicin 120mg/kg plus ethanol in group one; gentamicin 120mg/kg plus quercetin 15mg/kg in group two; quercetin 15mg/kg in group three; and ethanol in group four. The drugs were administered intraperitoneally once a day for two weeks, and the ABR test was repeated after drug administration. Subsequently, the rats were sacrificed and their cochleae were dissected and examined histopathologically.

RESULTS

There was no significant difference between the pre-treatment ABR measurement values of the groups. However, a significant increase was detected in the ABR values in the group of rats that were administered gentamicin plus ethanol, while no statistically significant increase was found in the ABR values in the groups administered with gentamicin plus quercetin; quercetin alone; and ethanol alone. The number of TUNEL positive cells in the inner and outer hair cells in the Corti organ was found to be fewer, and Caspase 3 and 9 expressions were found to be weaker in the group receiving gentamicin plus quercetin than in the group receiving gentamicin plus ethanol.

CONCLUSIONS

Auditory function was detected to be significantly protected and apoptotic cells were found to be decreased when quercetin was administered together with gentamicin. From these results it was concluded that quercetin, a powerful antioxidant, attenuates ABR thresholds and histopathological lesions in the cochlea in gentamicin-induced ototoxicity in rats.

The protective role of thymoquinone in the prevention of gentamicin ototoxicity

OBJECTIVE

To investigate the potential protective effect of thymoquinone in gentamicin-induced ototoxicity through auditory brain stem responses (ABR) testing and histomorphological evaluation of the cochlea.

METHODS

This study was conducted on 48 adult female Sprague-Dawley rats that were randomized into 4 groups. Group 1 received intraperitoneal gentamicin; group 2 received intraperitoneal gentamicin plus corn oil solution; group 3 received intraperitoneal thymoquinone; and group 4 received intraperitoneal gentamicin plus thymoquinone. All groups received the drugs (once daily) in the above-mentioned protocols over 15 days. After conducting repeated ABR measurements, the rats were sacrificed, and their cochleae were isolated.

RESULTS

ABR thresholds were preserved in the gentamicin plus thymoquinone group when compared with the group receiving gentamicin alone. There were fewer TUNEL-positive cells and caspase-3 and caspase-9 expressions were weaker in the inner and outer hairy cells of the organ of Corti in the gentamicin plus thymoquinone group compared with the group receiving gentamicin alone.

CONCLUSION

The ABR values and number of apoptotic cells did not significantly increase in the group receiving gentamicin plus thymoquinone when compared to the group receiving gentamicin alone. Again, the cochlear histomorphological findings were supportive of the auditory findings. In light of these findings, we conclude that gentamicin-induced ototoxicity may be prevented by thymoquinone use in rats.

A novel use of gentamicin in the ROS-mediated sensitization of NCI-H460 lung cancer cells to various anticancer agents

Aminoglycosides are broad-spectrum antibiotics that are used for the treatment of severe Gram-negative and Gram-positive bacterial infections. While bactericidal effects of aminoglycosides are due to binding to the 30S subunit of the bacterial ribosome, aminoglycosides can affect protein synthesis, intracellular calcium levels, and levels of reactive oxygen species (ROS) in eukaryotic cells. While aminoglycosides can be cytotoxic at high concentrations, our results show that at much lower doses, gentamicin can be implemented as a sensitizing agent for the NSCLC cell line NCI-H460, increasing the efficacy of camptothecin, digitoxin, and vinblastine in vitro. We have also established that this sensitization is reliant on the ROS response generated by gentamicin.

Protective effect of pentoxifylline on amikacin-induced ototoxicity in rats

PURPOSE

This experimental study was performed to investigate the possible protective effect of pentoxifylline (PTX) on amikacin-induced ototoxicity in rats.

MATERIALS AND METHODS

In this study, 21 healthy female rats were randomly assigned to 1 of 3 groups: the amikacin group (n = 8), the amikacin + PTX group (n = 8), and the control group (n = 5). The amikacin group received amikacin (200 mg·kg(-1)·day(-1)) intramuscularly once daily for 14 days. The amikacin + PTX group received intramuscular injections of amikacin (200 mg·kg(-1)·day(-1)) once daily for 14 days and PTX (25 mg·kg(-1)·day(-1)) once daily via gastric gavage for 14 days. The control group received saline solution (1 mL·day(-1) intraperitoneal injections) once daily for 14 days. The hearing levels of the rats were evaluated using distortion product otoacoustic emissions before and after treatment.

RESULTS

The distortion product otoacoustic emissions' amplitude levels (decibel, sound pressure levels) measured before and after treatment at frequencies of 4000, 6000, and 8000 Hz revealed that values of the amikacin group dropped significantly at the end of treatment (P < .01). In contrast, the amikacin + PTX and the control groups showed no significant difference at the end of the treatment compared with the initial measurements (P > .05).

CONCLUSION

The results showed that PTX has protective effects on hearing functions in amikacin-induced ototoxicity in rats.

Relationship between serum ferritin level and amikacin ototoxicity

OBJECTIVES

Aminoglycosides are highly effective against bacteria but have serious side-effects including ototoxicity and nephrotoxicity. One of the theories in aminoglycosides ototoxicity is that Iron-aminoglycoside complex causes ototoxicity by creating free radicals. Based on this theory, the relationship between serum iron level and amikacin ototoxicity was studied to determine whether more iron results in more ototoxcity.

METHODS

This prospective cohort study was conducted from August 2005 to October 2008. Patients with amikacin prescription and different serum-ferritin levels were examined. Burned patients with amikacin prescription were divided into Group1 (89 patients; serum-ferritin >150) and Group2 (92 patients, serum-ferritin <150). Their hearing thresholds and red-blood-cells indices were compared using t- and paired t-test.

RESULTS

In comparing the two groups, thresholds of Group1 were higher than Group2 at all frequencies, and the difference was statistically significant (p<0.001). The maximum threshold shift in Group1 was greater than 20 dB and in Group2, it was less than 10 dB, at 8000Hz. Again, this result was statistically and clinically significant (p<0.001). Finally, the mean corpuscular volume (MCV)was higher in Group1 than Group2, and (p=0.001).

CONCLUSION

The results suggest that the level of iron is related to aminoglycoside ototoxicity. More iron can create more ototoxicity, and iron deficiency may inhibit aminoglycoside ototoxicity. An increase in MCV may be due to higher serum ferritin and an indication of more ototoxicity.

Intracellular mechanisms of aminoglycoside-induced cytotoxicity

Since introduction into clinical practice over 60 years ago, aminoglycoside antibiotics remain important drugs in the treatment of bacterial infections, cystic fibrosis and tuberculosis. However, the ototoxic and nephrotoxic properties of these drugs are still a major clinical problem. Recent advances in molecular biology and biochemistry have begun to uncover the intracellular actions of aminoglycosides that lead to cytotoxicity. In this review, we discuss intracellular binding targets of aminoglycosides, highlighting specific aminoglycoside-binding proteins (HSP73, calreticulin and CLIMP-63) and their potential for triggering caspases and Bcl-2 signalling cascades that are involved in aminoglycoside-induced cytotoxicity. We also discuss potential strategies to reduce aminoglycoside cytotoxicity, which are necessary for greater bactericidal efficacy during aminoglycoside pharmacotherapy.

Disruption of gap junctional intercellular communication by antibiotic gentamicin is associated with aberrant localization of occludin, N-cadherin, connexin 43, and vimentin in SerW3 Sertoli cells in vitro

Spermatogenesis is a very complex process by which male germ cells differentiate into mature spermatozoa. The sophisticated communication network that controls spermatogenesis can be derailed so that dysfunction of one cell type propagates to all types as a cascade. This accounts for the particular vulnerability of the testis to environmental factors such as drugs and xenobiotics. Sertoli cells play an important role in protecting developing germ cells by forming a physiological barrier, limiting exposure to potentially toxic substrates, or conversely, facilitating uptake of xenobiotics within the testis. In this study, cells from the rat Sertoli line (SerW3) were incubated for 3, 6 and 9 subsequent days in serum free DMEM (SFDM) composed of DMEM supplemented with three different concentrations of antibiotic gentamicin (10, 30, and 100 μg). The effect of the three different concentrations of this antibiotic was determined on Sertoli cell-cell interaction through impaired expression of their constitutive tight junction proteins as early targets for different toxicants in vitro by immunochemistry analysis. The Sertoli SerW3 cell line illustrated the cytotoxicity of GS, as the intercellular junction proteins such as occludin, N-cadherin, connexin 43, and vimentin were delocalized from the membrane to the cytoplasmic compartment during exposure to the antibiotic. This study underlines the potential deleterious effects of the routine use of antibiotics during continuous cell culture.

[Protection and regeneration of sensory epithelia of the inner ear]

Dysfunctions of the inner ear such as hearing impairment due to noise exposure or presbycusis and vertigo are often caused by loss of hair cells in the sensory epithelium. There is still no specific therapy, just technical aids. Options for protecting and regenerating hair cells are explained here. The inhibition of apoptosis via caspases is presently the main target of research. They are involved in damage caused by aminoglycosides, cisplatin, or noise exposure. Bcl-2, growth factors, and oxidative stress are discussed. In regeneration the transdifferentiation of supporting cells to hair cells is explained. This can be achieved with local gene therapy using math1. Approach and media for the application are discussed, while viral vectors such as the adenovector seem the most promising in research.