Transtympanic Ringer's lactate application in the prevention of cisplatinum-induced ototoxicity in a chinchilla animal model

Intraperitoneal curcumin and vitamin E combination for the treatment of cisplatin-induced ototoxicity in rats

INTRODUCTION

Cisplatin ototoxicity is characterized by irreversible, progressive, bilateral sensorineural hearing loss at high frequencies, accompanied by tinnitus. The aim of this study is to demonstrate the protective action of curcumin alone or in combination with vitamin E against cisplatin-induced ototoxicity in animal models.

MATERIAL AND METHODS

The study included 42 rats. Experimental animals were randomized into 6 groups. In the first group, intra-peritoneal cisplatin was administered alone. In the second group, intra-peritoneal cisplatin and curcumin were administered together. In the third group, intra-peritoneal cisplatin and vitamin E were administered together. In the fourth group, intra-peritoneal cisplatin was administered together with curcumin in combination with vitamin E. In the fifth group, intra-peritoneal curcumin was administered alone. The sixth group was sacrificed directly without administration of any drugs. A distortion product otoacoustic emission (DPOAE) test was applied to both ears of all experimental animals. Curcumin was administered 1 h before cisplatin treatment continued for three successive days. Vitamin E was administered only as a single dose 30 min prior to cisplatin. All animals were sacrificed following DPOAE testing on the 5th day of cisplatin administration. Histopathological findings included a TUNEL (TdT-mediated deoxyuridine triphosphate nick end-labeling) assay, and the percentage of apoptotic cells was calculated. DPOAE values and the percentage of apoptotic cells were compared before and after treatment and between experimental groups.

RESULTS

In Group 1, DPOAE values were significantly decreased at all frequencies (3000 Hz, 4000 Hz and 6000 Hz; P < 0.05). In Groups 2, 3, 4 and 5 there was no significant difference between the pre- and post-treatment DPOAE results (p > 0.05). Apoptotic index values were lower in all treatment groups compared to the cisplatin group, however the difference was only statistically significant in group 3 (p = 0.009).

CONCLUSION

In rats, cisplatin ototoxicity can be prevented with curcumin or curcumin-vitamin E combination.

Comparison of the protective effects of intratympanic dexamethasone and methylprednisolone against cisplatin-induced ototoxicity

OBJECTIVE

This study aimed to compare the efficacies of intratympanic dexamethasone and methylprednisolone in preventing in cisplatin-induced ototoxicity in rats.

METHODS

Experimental groups of rats (n = 8 each) received intratympanic isotonic saline, intraperitoneal cisplatin and intratympanic isotonic saline, intraperitoneal cisplatin and intratympanic dexamethasone, or intraperitoneal cisplatin and intratympanic methylprednisolone. Distortion product otoacoustic emission thresholds were compared on days 0 and 10 in all rats, and correlations between drug effects and changes in cochlear histology were evaluated.

RESULTS

Distortion product otoacoustic emission thresholds were comparable in groups III and IV (p > 0.05). Significant protection against cisplatin-induced ototoxicity was seen in groups III and IV compared with group II (p < 0.05). Dexamethasone and, to a lesser extent, methylprednisolone protected against cellular apoptosis in cisplatin-induced ototoxicity.

CONCLUSION

Dexamethasone (and possibly methylprednisolone) may be clinically useful as an intratympanic chemopreventive agent to treat cisplatin ototoxicity. Future clinical studies should investigate the use of dexamethasone for this purpose in adult patients.

The Safety Pharmacology of Auditory Function

Safety pharmacology satisfies a key requirement in the process of drug development. Safety pharmacology studies are required to assess the impact of a new chemical entity (NCE) or biotechnology-derived product for human use on vital systems, such as those subserving auditory function. Safety pharmacology studies accordingly are defined as those studies that investigate the potential undesirable effects of a substance on auditory functions in relation to exposure in and above the therapeutic range. Auditory safety studies should be designed with the primary objective of determining how administration of a compound influences normal hearing. If an effect on hearing is identified, then it is necessary to determine through histopathology the underlying mechanism for the observed hearing loss. Since the auditory system contains a heterogeneous mixture of structural and cellular components that are organized in a very complex and integrated manner, it is necessary to clearly identify the underlying primary mechanism or target of the new chemical entity that produced the hearing loss. This chapter will highlight major components of auditory function with regard to potential opportunities for drug interaction. Aspects of designing ototoxicity studies will be discussed with an emphasis on standards deemed necessary by the US Food and Drug Administration. Additionally, classes of ototoxic compounds and their proposed mechanisms of action are described in depth.

Early investigational drugs for hearing loss

INTRODUCTION

Sensorineural hearing loss (HL) is becoming a global phenomenon at an alarming rate. Nearly 600 million people have been estimated to have significant HL in at least one ear. There are several different causes of sensorineural HL included in this review of new investigational drugs for HL. They are noise-induced, drug-induced, sudden sensorineural HL, presbycusis and HL due to cytomegalovirus infections.

AREAS COVERED

This review presents trends in research for new investigational drugs encompassing a variety of causes of HL. The studies presented here are the latest developments either in the research laboratories or in preclinical, Phase 0, Phase I or Phase II clinical trials for drugs targeting HL.

EXPERT OPINION

While it is important that prophylactic measures are developed, it is extremely crucial that rescue strategies for unexpected or unavoidable cochlear insult be established. To achieve this goal for the development of drugs for HL, innovative strategies and extensive testing are required for progress from the bench to bedside. However, although a great deal of research needs to be done to achieve the ultimate goal of protecting the ear against acquired sensorineural HL, we are likely to see exciting breakthroughs in the near future.

Ototoxicity of aluminum acetate/benzethonium chloride otic solution in the chinchilla animal model

OBJECTIVES/HYPOTHESIS

To determine the ototoxic potential of aluminum acetate (0.5%)/benzethonium chloride (0.03%) otic solution in the chinchilla animal model.

STUDY DESIGN

A randomized, prospective, controlled study was conducted in the chinchilla animal model.

METHODS

Fourteen female chinchillas were used. After an incision was made in each tympanic membrane, baseline auditory brainstem response measurements were performed at 16, 20, and 25 kHz. One ear was randomized to receive aluminum acetate (0.5%)/benzethonium chloride (0.03%), whereas the other ear served as the control and received 0.9% NaCl. Solutions were applied transtympanically once a day for 3 consecutive days. Postapplication auditory brainstem response measurements were done at day 7 and day 30. In half of the animals, scanning electron microscopy was done following the last auditory brainstem response measurement.

RESULTS

A statistically significant difference was found between the mean threshold shifts in the experimental and control ears at all frequencies on both 7 and 30 days postapplication (P < .02). Increased ossification of the cochleae was seen in experimental ears (n = 12). Scanning electron microscopy study demonstrated outer hair cell damage and/or loss in the experimental ears. No significant morphological changes were detected on scanning electron microscopy obtained from the control ears.

CONCLUSIONS

Application of aluminum acetate (0.5%)/benzethonium chloride (0.03%) otic solution causes hearing loss in chinchillas when a tympanic membrane perforation exists. Further studies are needed to test the effect of this otic solution on hearing.

LEVEL OF EVIDENCE

4.

In vitro and in vivo models of drug ototoxicity: studying the mechanisms of a clinical problem

INTRODUCTION

Drug ototoxicity represents one of the main preventable causes of deafness. Ototoxicity is a trait shared by aminoglycoside and macrolide antibiotics, antimalarial medications, loop diuretics, platinum-based chemotherapeutic agents, some NSAIDs and most recently described, acetaminophen when abused with narcotic medication. These medications are prescribed despite their side effects, which includes inner ear toxicity, because they are life-saving drugs or there is a lack of better treatment.

AREAS COVERED

This review will discuss in vitro and in vivo models of ototoxicity highlighting recently published ototoxicity research. The reader will learn the strengths and limitations of different ototoxicity models and what molecular insights have been gained from their application. A better understanding of the cellular mechanisms of these ototoxins will help in the discovery of ways to prevent and treat hearing loss associated with ototoxic medications.

EXPERT OPINION

There are benefits to both in vitro and in vivo models of ototoxicity. Research of a particular medication and its ototoxic mechanisms should draw from several models, enabling a better answer to the clinical question of prevention and treatment of inner ear drug toxicity.

The design and screening of drugs to prevent acquired sensorineural hearing loss

INTRODUCTION

Sensorineural hearing loss affects a high percentage of the population. Ototoxicity is a serious and pervasive problem in patients treated with cisplatin. Strategies to ameliorate ototoxicity without compromising on antitumor activity of treatments are urgently needed. Similar problems occur with aminoglycoside antibiotic therapy for infections. Noise-induced hearing loss affects a large number of people. The use of ear protection is not always possible or effective. The prevention of hearing loss with drug therapy would have a huge impact in reducing the number of people with hearing loss from these major causes.

AREAS COVERED

This review discusses significant research findings dealing with the use of protective agents against hearing loss caused by cisplatin, aminoglycoside antibiotics and noise trauma. The efficacy in animal studies and the application of these protective agents in clinical trials that are ongoing are presented.

EXPERT OPINION

The reader will gain new insights into current and projected future strategies to prevent sensorineural hearing loss from cisplatin chemotherapy, aminoglycoside antibiotic therapy and noise exposure. The future appears to offer numerous agents to prevent hearing loss caused by cisplatin, aminoglycoside antibiotics and noise. Novel delivery systems will provide ways to guide these protective agents to the desired target areas in the inner ear and circumvent problems with therapeutic interference of antitumor and antibiotics agents as well as minimize undesired side effects.

Effect of nystatin on Guinea Pigs' inner ear

Nystatin is a topical antifungal agent. Its wide spectrum of action and low cost make it a treatment of choice. Though it is safe for external ear use, no study has proven its safety in cases of tympanic membrane perforation (TMP). We aim to test the safety of Nystatin when applied directly to the middle ear of a Guinea Pig model. We performed an experimental study with 18 Hartley Guinea Pigs that were divided into two groups. All tympanic membranes were perforated at the beginning of the study. Exposing one group to Nystatin and the other to the ototoxic Neomycin, we compared results of auditory brainstem response testing at three intervals. Each animals' contralateral ear was used as a negative control. At the end, we performed a histological analysis of the animals' cochleae using a scanning electron microscope (SEM). Average hearing loss in the Nystatin group was 13.0 dB which was similar to the results obtained in the negative control group (13.1 dB). Average hearing loss in the Neomycin group was 39.3 dB, which represents a statistically significant difference (P < 0.001). SEM evaluation revealed intact cochlear hair cell architecture in the Nystatin and normal saline groups, whereas significant hair cell losses were noted in the Neomycin group was noted. Nystatin does not cause hearing impairment or cochlear hair cell damage when exposed directly to the middle ear of a Guinea Pig model. It is therefore a safe treatment option for otomycosis with presence of TMP.