Protection by 4-methylthiobenzoic acid against cisplatin-induced ototoxicity: antioxidant system

Quinoxaline protects zebrafish lateral line hair cells from cisplatin and aminoglycosides damage

Hair cell (HC) death is the leading cause of hearing and balance disorders in humans. It can be triggered by multiple insults, including noise, aging, and treatment with certain therapeutic drugs. As society becomes more technologically advanced, the source of noise pollution and the use of drugs with ototoxic side effects are rapidly increasing, posing a threat to our hearing health. Although the underlying mechanism by which ototoxins affect auditory function varies, they share common intracellular byproducts, particularly generation of reactive oxygen species. Here, we described the therapeutic effect of the heterocyclic compound quinoxaline (Qx) against ototoxic insults in zebrafish HCs. Animals incubated with Qx were protected against the deleterious effects of cisplatin and gentamicin, and partially against neomycin. In the presence of Qx, there was a reduction in the number of TUNEL-positive HCs. Since Qx did not block the mechanotransduction channels, based on FM1-43 uptake and microphonic potentials, this implies that Qx’s otoprotective effect is at the intracellular level. Together, these results unravel a novel therapeutic role for Qx as an otoprotective drug against the deleterious side effects of cisplatin and aminoglycosides, offering an alternative option for patients treated with these compounds.

A kinase inhibitor library screen identifies novel enzymes involved in ototoxic damage to the murine organ of Corti

Ototoxicity is a significant side effect of a number of drugs, including the aminoglycoside antibiotics and platinum-based chemotherapeutic agents that are used to treat life-threatening illnesses. Although much progress has been made, the mechanisms that lead to ototoxic loss of inner ear sensory hair cells (HCs) remains incompletely understood. Given the critical role of protein phosphorylation in intracellular processes, including both damage and survival signaling, we screened a library of kinase inhibitors targeting members of all the major families in the kinome. Micro-explants from the organ of Corti of mice in which only the sensory cells express GFP were exposed to 200 μM of the ototoxic aminoglycoside gentamicin with or without three dosages of each kinase inhibitor. The loss of sensory cells was compared to that seen with gentamicin alone, or without treatment. Of the 160 inhibitors, 15 exhibited a statistically significant protective effect, while 3 significantly enhanced HC loss. The results confirm some previous studies of kinase involvement in HC damage and survival, and also highlight several novel potential kinase pathway contributions to ototoxicity.

Mitochondria-Targeted Antioxidant Mitoquinone Reduces Cisplatin-Induced Ototoxicity in Guinea Pigs

Objective To determine if mitoquinone (MitoQ) attenuates cisplatin-induced hearing loss in guinea pigs. Study Design Prospective and controlled animal study. Setting Academic, tertiary medical center. Subjects and Methods Guinea pigs were injected subcutaneously with either 5 mg/kg MitoQ (n = 9) or normal saline (control, n = 9) for 7 days and 1 hour before receiving a single dose of 10 mg/kg cisplatin. Auditory brainstem response thresholds were measured before MitoQ or saline administration and 3 to 4 days after cisplatin administration. Results Auditory brainstem response threshold shifts after cisplatin treatment were smaller by 28 to 47 dB in guinea pigs injected with MitoQ compared with those in the control group at all tested frequencies (4, 8, 16, and 24 kHz, P = .0002 to .04). Scanning electron microscopy of cochlear hair cells showed less outer hair cell loss and damage in the MitoQ group. Conclusion MitoQ reduced cisplatin-induced hearing loss in guinea pigs. MitoQ appears worthy of further investigation as a means of preventing cisplatin ototoxicity in humans.

Protective Effect of Selenium Against Cisplatin-Induced Ototoxicity in an Experimental Design

Cisplatin is an effective chemotherapeutic agent in the treatment of several types of malignant solid tumors but its clinical use is associated with ototoxicity. In the present study, we investigated the effect of selenium administration on lipid peroxidation (malondialdehyde [MDA]) and cisplatin-induced ototoxicity in rats. Healthy wistar albino rats (n = 21) were randomly divided into 3 groups: control (C), cisplatin (Cis), cisplatin and selenium (Cis+Se). Cisplatin was administered for 3 days to Cis and Cis+Se groups. Cis+Se group received selenium 5 days before cisplatin injection and continued for 11 consecutive days. Hearing thresholds and lipid peroxidation (MDA) levels of the rats were recorded before injections and at the end of experimental protocol. The cochleas of animals were harvested for histologic and immunuhistochemical examinations. In biochemichal analyses, pretreatment with selenium prevented the elevation of MDA levels in Cis+Se group rats. Moreover, animals in Cis+Se group had better hearing threshold levels than animals in cis group. Samples obtained from the animals in Cis group revealed extensive loss of the normal microarchitecture of the organ of Corti. On the other hand, animals in Cis+Se group exhibited a preservation of the morphology of the organ of Corti and outer hair cells. In the immunohistochemical examinations of cochlear tissues stained with anti-caspase-3, a higher degree of immunopositivity was found in the Cis group. When Cis+Se group and Cis group were compared, significantly less immunopositivity occurred in the Cis+Se group (P < 0.05). Thus, it appears that pretreatment with selenium may reduce cisplatin-induced ototoxicity in rats.

Protective effect of polyphenols on presbycusis via oxidative/nitrosative stress suppression in rats

Age-related hearing loss (AHL) -presbycusis- is the number one neurodegenerative disorder and top communication deficit of our aged population. Experimental evidence suggests that mitochondrial dysfunction associated with reactive oxygen species (ROS) plays a central role in the aging process of cochlear cells. Dietary antioxidants, in particular polyphenols, have been found to be beneficial in protecting against the generation of ROS in various diseases associated with oxidative stress, such as cancer, neurodegenerative diseases and aging.

OBJECTIVES

This study was designed to investigate the effects of polyphenols on AHL and to determine whether oxidative stress plays a role in the pathophysiology of AHL.

METHODS

Sprague-Dawley rats (n=100) were divided into five groups according to their age (3, 6, 12, 18 and 24months old) and treated with 100mg/kg/day body weight of polyphenols dissolved in tap water for half of the life of the animal. Auditory steady-state responses (ASSR) threshold shifts were measured before sacrificing the rats. Then, cochleae were harvested to measure total superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities, reactive oxidative and nitrogen species levels, superoxide anions and nitrotyrosine levels.

RESULTS

Increased levels of ROS and RNS in cochlea observed with age decreases with polyphenol treatment. In addition, the activity of SOD and GPx enzymes in older rats recovered after the administration of polyphenols.

CONCLUSION

The reduction in oxidative and nitrosative stress in the presence of polyphenols correlates with significant improvements in ASSR threshold shifts.

The protective effect of intratympanic dexamethasone on cisplatin-induced ototoxicity in guinea pigs

Objective

The purpose of this study was to investigate the effectiveness of intratympanic dexamethasone injection as a protection agent against cisplatin-induced ototoxicity.

Study Design and Setting

The four groups of guinea pigs were injected as follows: 1) cisplatin, 2) intratympanic dexamethasone, 3) cisplatin following intratympanic dexamethasone, and 4) cisplatin after intratympanic saline. Before and 3 days following injections, the ototoxic effect was measured with distortion product otoacoustic emissions (DPOAEs).

Results

The DPOAEs amplitudes and signal-to-noise ratio (SNR) values at 1 to 6 kHz frequencies for group 1 animals after injections significantly decreased over those before injections ( P < 0.05). In group 2, there were no significant differences in DPOAE amplitude and SNR values between before and after intratympanic dexamethasone injections ( P > 0.05). Considering group 3, there were also no significant differences in DPOAEs amplitudes and SNR values before and after of dexamethasone and cisplatin injections ( P > 0.05).

Conclusions

Intratympanic dexamethasone injection did not cause any ototoxic effect; in contrast, it might have a significant protective effect after cisplatin injection.

Efficacy of topotecan treatment on antioxidant enzymes and TBA-RS levels in submandibular glands of rabbits: An experimental study

OBJECTIVE:

The aim of this study was to investigate the effects of topotecan (Hycamtin), a topoisomerase I inhibiting anticancer agent, on antioxidant enzymes (SOD, CAT, and GSH-Px) and TBA-RS values of the submandibular glands of the rabbits.

STUDY DESIGN AND SETTING:

The study was conveyed in two groups (Group I, II) and control with a total of 24 rabbits. Eight rabbits in group I received intravenous (i.v.) topotecan (0.25 mg/kg once daily) for 3 days. Eight rabbits in group II received i.v. topotecan (0.5 mg/kg once daily) for 3 days. On the 15th day after administration of topotecan, sub-mandibular glands were removed and levels of the SOD, CAT, and GSH-Px and the TBA-RS in the sub-mandibular glands of the rabbits were examined.

RESULTS:

SOD, CAT, and GSH-Px values were significantly higher in high-dose topotecan group compared to control group ( P < 0.05). SOD and TBA-RS values were significantly higher in high-dose topotecan group compared to low-dose topotecan group ( P < 0.05).

CONCLUSION:

It was concluded that, to prevent the hazardous effects of oxygen free radicals due to topotecan, antioxidant enzymes SOD, CAT, and GSH-Px were increased. The higher levels of the TBA-RS values in group II showed that permanent damage was present because of high-dose topotecan administration in the submandibular glands of the rabbits.

Bucillamine prevents cisplatin-induced ototoxicity through induction of glutathione and antioxidant genes

Bucillamine is used for the treatment of rheumatoid arthritis. This study investigated the protective effects of bucillamine against cisplatin-induced damage in auditory cells, the organ of Corti from postnatal rats (P2) and adult Balb/C mice. Cisplatin increases the catalytic activity of caspase-3 and caspase-8 proteases and the production of free radicals, which were significantly suppressed by pretreatment with bucillamine. Bucillamine induces the intranuclear translocation of Nrf2 and thereby increases the expression of γ-glutamylcysteine synthetase (γ-GCS) and glutathione synthetase (GSS), which further induces intracellular antioxidant glutathione (GSH), heme oxygenase 1 (HO-1) and superoxide dismutase 2 (SOD2). However, knockdown studies of HO-1 and SOD2 suggest that the protective effect of bucillamine against cisplatin is independent of the enzymatic activity of HO-1 and SOD. Furthermore, pretreatment with bucillamine protects sensory hair cells on organ of Corti explants from cisplatin-induced cytotoxicity concomitantly with inhibition of caspase-3 activation. The auditory-brainstem-evoked response of cisplatin-injected mice shows marked increases in hearing threshold shifts, which was markedly suppressed by pretreatment with bucillamine in vivo. Taken together, bucillamine protects sensory hair cells from cisplatin through a scavenging effect on itself, as well as the induction of intracellular GSH.

Gene expression changes for antioxidants pathways in the mouse cochlea: relations to age-related hearing deficits

Age-related hearing loss - presbycusis - is the number one neurodegenerative disorder and top communication deficit of our aged population. Like many aging disorders of the nervous system, damage from free radicals linked to production of reactive oxygen and/or nitrogen species (ROS and RNS, respectively) may play key roles in disease progression. The efficacy of the antioxidant systems, e.g., glutathione and thioredoxin, is an important factor in pathophysiology of the aging nervous system. In this investigation, relations between the expression of antioxidant-related genes in the auditory portion of the inner ear - cochlea, and age-related hearing loss was explored for CBA/CaJ mice. Forty mice were classified into four groups according to age and degree of hearing loss. Cochlear mRNA samples were collected and cDNA generated. Using Affymetrix® GeneChip, the expressions of 56 antioxidant-related gene probes were analyzed to estimate the differences in gene expression between the four subject groups. The expression of Glutathione peroxidase 6, Gpx6; Thioredoxin reductase 1, Txnrd1; Isocitrate dehydrogenase 1, Idh1; and Heat shock protein 1, Hspb1; were significantly different, or showed large fold-change differences between subject groups. The Gpx6, Txnrd1 and Hspb1 gene expression changes were validated using qPCR. The Gpx6 gene was upregulated while the Txnrd1 gene was downregulated with age/hearing loss. The Hspb1 gene was found to be downregulated in middle-aged animals as well as those with mild presbycusis, whereas it was upregulated in those with severe presbycusis. These results facilitate development of future interventions to predict, prevent or slow down the progression of presbycusis.

Gene therapy for cisplatin-induced ototoxicity: a systematic review of in vitro and experimental animal studies

OBJECTIVE

Ototoxicity is a frequent adverse event of cisplatin treatment. No therapy is currently available for cisplatin-induced ototoxicity. A systematic review of experimental animal studies and in vitro experiments was conducted to evaluate gene therapy as a potential future therapeutic option.

DATA SOURCES

Eligible studies were identified through searches of electronic databases Ovid MEDLINE, Ovid MEDLINE In-Process, Embase, PubMed, Biosis Previews, Scopus, ISI Web of Science, and The Cochrane Library.

STUDY SELECTION

Articles obtained from the search were independently reviewed by 2 authors using specific criteria to identify experimental animal studies and in vitro experiments conducted to evaluate gene therapy for cisplatin-induced ototoxicity. No restriction was applied to publication dates or languages.

DATA EXTRACTION

Data extracted included experiment type, cell type, species, targeted gene, gene expression, method, administration, inner ear site evaluated, outcome measures for cytotoxicity, and significant results.

RESULTS

Fourteen articles were included in this review. In vitro and in vivo experiments have been performed to evaluate the potential of gene expression manipulation for cisplatin-induced ototoxicity. Twelve different genes were targeted including NTF3, GDNF, HO-1, XIAP, Trpv1, BCL2, Otos, Nfe2l2, Nox1, Nox3, Nox4, and Ctr1. All of the included articles demonstrated a benefit of gene therapy on cytotoxicity caused by cisplatin.

CONCLUSION

Experimental animal studies and in vitro experiments have demonstrated the efficacy of gene therapy for cisplatin-induced ototoxicity. However, further investigation regarding safety, immunogenicity, and consequences of genetic manipulation in the inner ear tissues must be completed to develop future therapeutic options.

Protective effects of vitamins E, B and C and l-carnitine in the prevention of cisplatin-induced ototoxicity in rats

Objective:

This experimental study aimed to investigate the effects of vitamins E, B and C and l-carnitine in preventing cisplatin-induced ototoxicity.

Methods:

Twenty-five adult, male, Wistar albino rats were randomly allocated to receive intraperitoneal cisplatin either alone or preceded by vitamins B, E or C or l-carnitine. Auditory brainstem response (i.e. hearing thresholds and wave I–IV intervals) and distortion product otoacoustic emissions (i.e. signal-to-noise ratios) were recorded before and 72 hours after cisplatin administration.

Results:

The following statistically significant differences were seen: control group pre- vs post-treatment wave I–IV interval values (p < 0.05); control vs vitamin E and B groups' I–IV interval values (p < 0.05); control vs other groups' hearing thresholds; vitamin E vs vitamin B and C and l-carnitine groups' hearing thresholds (p < 0.05); and vitamin B vs vitamin C and l-carnitine groups' hearing thresholds (p < 0.05). Statistically significant decreases were seen when comparing the initial and final signal-to-noise ratios in the control, vitamin B and l-carnitine groups (2000 and 3000 Hz; p < 0.01), and the initial and final signal-to-noise ratios in the control group (at 4000 Hz; p < 0.01).

Conclusion:

Vitamins B, E and C and l-carnitine appear to reduce cisplatin-induced ototoxicity in rats. The use of such additional treatments to decrease cisplatin-induced ototoxicity in humans is still under discussion.

Protective effects of apocynin on cisplatin-induced ototoxicity in an auditory cell line and in zebrafish

Cisplatin is a very effective anticancer drug and generates reactive oxygen species (ROS) such as superoxide anions that can deplete antioxidant protective molecules in the cochlea. These processes result in the death of cochlear hair cells by induction of apoptosis. Apocynin, which is used as a specific nicotinamide adenine dinucleotide phosphate oxidase inhibitor, has a preventive effect for intracellular ROS generation. In this study, the effect of apocynin was investigated in a cochlear organ of Corti-derived cell line, HEI-OC1 cells, and in transgenic zebrafish (Brn3C: EGFP). To investigate the protective effects of apocynin, HEI-OC1 cells were treated with various concentrations of apocynin and a 20 µm concentration of cisplatin, simultaneously. An in vivo study of transgenic zebrafish (Brn3C: EGFP) was used to investigate the protective effects of apocynin on cisplatin-induced hair cell death. In an in vitro study, apocynin appeared to protect against cisplatin-induced apoptotic features on Hoechst 33258 staining in the HEI-OC1 cells. Treatment of the HEI-OC1 cells with 100 µm of apocynin, significantly decreased caspase-3 activity. Treatment of the cells with a 100 µm concentration of apocynin and a 20 µm concentration of cisplatin significantly decreased the intracellular ROS production. In the in vivo study, apocynin significantly decreased the TUNEL reaction and prevented cisplatin-induced hair cell loss of the neuromasts in the transgenic zebrafish at low concentrations (125 and 250 µm). These findings suggest that apocynin has antioxidative effects and prevents cisplatin-induced apoptotic cell death in HEI-OC1 cells as well as in zebrafish.

No hearing loss after repeated courses of tobramycin in cystic fibrosis patients

CONCLUSION

Our results indicate that repeated treatment courses with tobramycin 10 mg/kg (twice daily for 3 weeks) may be safely applied in cystic fibrosis (CF) patients with respect to ototoxicity. The risk of hearing loss in this patient group is less than expected, which could be explained by either unfavourable baseline audiometry or the use of unidentified protective medication, or both. However, due to large inter-individual variations, audiometry screening remains important with respect to the detection of individual outliers.

OBJECTIVES

Tobramycin is frequently prescribed for CF patients. In this study, hearing loss due to cumulative tobramycin exposure in adult CF patients was investigated.

PATIENTS AND METHODS

We retrospectively investigated 19 patients with both baseline and follow-up audiometry before and after repeated courses of intravenous tobramycin (10 mg/kg/day in twice daily administrations for 3 weeks). Pure tone audiometry was performed at 0.250-16 kHz.

RESULTS

After repeated courses of tobramycin (median 3, range 1-8), the mean increase per frequency was 2.1 dB (median 0.5 dB, SD 12.6) with large (inter-individual) variations (range -23.5 to 34.5 dB). The pure tone averages (PTA) at 1-2-4 kHz and 8-10-12 kHz increased 1.4 dBHL and 2.3 dBHL, respectively, but were neither statistically significant, nor correlated with the cumulative tobramycin exposure.

Inner ear protection and regeneration: a 'historical' perspective

PURPOSE OF REVIEW

In evaluating strategies to preserve or regenerate the cochlea, understanding the process of labyrinthine injury on a cellular and molecular level is crucial. Examination of inner ear injury reveals mechanism-specific types of damage, often at specific areas within the cochlea. Site-specific interventions can then be considered.

RECENT FINDINGS

The review will briefly summarize the historical perspective of advancements in hearing science through 2006. Areas of research covered include hair cell protection, hair cell regeneration, spiral ganglion cell regeneration, and stria vascularis metabolic regulation.

SUMMARY

The review will briefly summarize the early development of a few such site-specific interventions for inner ear functional rehabilitation, for work done prior to 2006. The outstanding reviews of cutting edge research from this year's and last year's Hearing Science section of Current Opinion in Otolaryngology - Head and Neck Surgery can then be understood and appreciated in a more informed manner.

The protective role of tiopronin in cisplatin ototoxicity in Wistar rats

The purpose of this study was to evaluate cisplatin-induced ototoxicity and the protective effects of tiopronin. Twenty-four adult Wistar rats served as subjects and were divided into three groups. Eight rats receiving only saline (group A) were used as controls. Eight rats received cisplatin (2 mg/kg) injections (group B) and eight rats received cisplatin and tiopronin (300 mg/kg) (group C) for 8 consecutive days. Both ears of all animals were tested by DPOAE before treatment and on the 4th and 9th days. Seventy-two hours after the final recording session, all animals were killed, and the left cochleas were prepared for electron microscopy and analysed. DPOAE responses were significantly reduced in group B compared to controls (p<0.05). When tiopronin was added, DPOAE responses were significantly increased compared to those obtained with the administration of cisplatin alone (p<0.05). The cochleogram showed that tiopronin had a significant protective effect in the basal half and in the lower half of the middle turn. We conclude that tiopronin, a drug effective in protecting against cisplatin nephrotoxicity, is also effective in protecting against cisplatin ototoxicity.

Epicatechin protects auditory cells against cisplatin-induced death

Cisplatin, a chemotherapeutic drug that is widely used to treat various cancers, promotes ototoxicity at higher doses. In this study, the effect of epicatechin (EC) on cisplatin-induced hair cell death was investigated in a cochlear organ of Corti-derived cell line, HEI-OC1, and in vivo in zebrafish. Cisplatin promoted apoptosis and altered mitochondrial membrane potential (MMP) in HEI-OC1 cells. EC inhibited cisplatin-induced apoptosis and intracellular reactive oxygen species (ROS) generation. Labeling of zebrafish lateral line hair cells by the fluorescent dye YO-PRO1 was lost upon exposure to cisplatin, and EC protected against this cisplatin-induced loss of labeling in a dose-dependent manner. Scanning and transmission electron micrographs showed that treatment with EC protected against cisplatin-induced loss of kinocilium and stereocilia in zebrafish neuromasts. These results suggest that EC prevents cisplatin-induced ototoxicity by blocking ROS generation and by preventing changes in MMP.

Immunoreactivities for glutathione S-transferases and glutathione peroxidase in the lateral wall of pigmented and albino guinea pig cochlea

Dark-skinned people are known to be more tolerant of ototraumatic noise than are light-skinned people, and pigmented animals are more tolerant of ototraumatic noise and aminoglycoside ototoxicity than are albino animals. Such tolerance may be dependent on the local ability of detoxification and antioxidant enzymes, including glutathione S-transferase (GST) and glutathione peroxidase (GSPx). In the present study, we examined the difference in GST/GSPx expression in the lateral wall of the cochlea between pigmented and albino guinea pigs. Eight-week-old male pigmented and albino guinea pigs were killed by transcardiac perfusion with 2% paraformaldehyde. The cochlear ducts were isolated, further fixed with 4% paraformaldehyde, decalcified, and then embedded in paraffin. Sections prepared at 5-microm thickness were incubated with anti-GST-alpha,-mu,-pi, or anti-GSPx antibody, reacted with Alexa Fluorconjugated secondary antibody, and examined under a Carl Zeiss Axioskop 2 plus fluorescence microscope. The cochlea ducts were also subjected to immunoelectron microscopy for GST-pi by the postembedment method. The stria vascularis of pigmented guinea pigs was strongly immunoreactive for GST-alpha,-mu,-pi, and GSPx, whereas no or only weak immunoreactivities were seen in the stria vascularis of albino guinea pigs. The spiral ligament showed positive but different immunoreactivities for these enzymes between the strains. Double-stained immunofluorescence micrographs for GST-pi and GSPx showed a close resemblance of localization between the two enzymes in both pigmented and albino guinea pigs. At the ultrastructural level, immunoreactivity for GST-pi was localized preferentially in the melanin cells of pigmented guinea pigs. These results suggest that correlation between pigmentation and inner ear susceptibility is, at least partially, attributed to the different distribution of GST/GSPx in the stria vascularis.

Cisplatin-induced hair cell loss in zebrafish (Danio rerio) lateral line

We have used time-lapse imaging to study cisplatin-induced hair cell death in lateral line neuromasts of zebrafish larvae in vivo. We found that cisplatin-induced hair cell death occurred much more slowly than had been shown to occur in aminoglycoside-induced hair cell death. By prelabeling hair cells with FM1-43FX, and assessing hair cell damage, it was established that cisplatin causes hair cell loss in the lateral line in a dose-dependent fashion. The kinetics of hair cell loss during exposure to different concentrations of cisplatin was also assessed and it was found that the onset of hair cell loss correlated with the accumulated dose of cisplatin. These data demonstrate the feasibility and repeatability of cisplatin damage protocols in the zebrafish lateral line and set the stage for future evaluations of modulation of cisplatin-induced hair cell death.

Understanding drug ototoxicity: molecular insights for prevention and clinical management

Ototoxicity is a trait shared by aminoglycoside and macrolide antibiotics, loop diuretics, platinum-based chemotherapeutic agents, some NSAIDs and antimalarial medications. Because their benefits in combating certain life-threatening diseases often outweigh the risks, the use of these ototoxic drugs cannot simply be avoided. In this review, the authors discuss some of the most frequently used ototoxic drugs and what is currently known about the cell and molecular mechanisms underlying their noxious effects. The authors also provide suggestions for the clinical management of ototoxic medications, including ototoxic detection and drug monitoring. Understanding the mechanisms of drug ototoxicity may lead to new strategies for preventing and curing drug-induced hearing loss, as well as developing new pharmacological drugs with less toxic side effects.

Correlation of increased activities of Na+, K+-ATPase and Ca2+-ATPase with the reversal of cisplatin ototoxicity induced by d-methionine in guinea pigs

Na(+), K(+)-ATPase and Ca(2+)-ATPase in the cochlear lateral wall play an important role in maintaining ionic homeostasis and physiologic function of the cochlea. The present study was designed to test whether the changes of Na(+), K(+)-ATPase and Ca(2+)-ATPase activities of the cochlear lateral wall and the brainstem of guinea pigs after receiving cisplatin for seven consecutive days were correlated with the altered auditory brainstem responses (ABR). Furthermore, whether a chemoprotective agent, D-methionine reversed the increased ABR threshold induced by cisplatin accompanied with the increased ATPase activities was also evaluated. The results obtained showed that cisplatin exposure caused not only a significant increase of threshold but also altered various absolute wave and interwave latencies of ABR. In addition, cisplatin significantly decreased the Na(+), K(+)-ATPase and Ca(2+)-ATPase activities in the cochlear lateral wall with a good dose-response relationship. Regression analysis indicated that an increase of ABR threshold was well correlated with a decrease of both Na(+), K(+)-ATPase and Ca(2+)-ATPase activities in the cochlear lateral wall. A chemoprotectant, D-methionine indeed reversed both abnormalities of ABR and ATPase activities in a well correlation function. The selectivity of these observed changes induced by cisplatin and D-methionine was revealed by the findings that cisplatin-treated guinea pigs had normal III-V interwave latency of ABR and no reduction of Na(+), K(+)-ATPase and Ca(2+)-ATPase specific activities in the brainstem, which is in accordance with the nonpenetrable cisplatin across the blood brain barrier. Taken all together, the present findings suggest that biochemical damage and ionic disturbance may contribute to cisplatin-induced ototoxicity to some extent, which can be reversed by d-methionine.

Acceleration of cisplatin ototoxicity by perilymphatic application of 4-methylthiobenzoic acid

The antitumor agent cisplatin has dose-limiting side effects such as ototoxicity. Systemical co-treatment with anti-oxidants like 4-methylthiobenzoic acid (MTBA) and sodium thiosulfate (STS) provides protection against cisplatin ototoxicity. However, systemically administered protective agents may reduce the chemotherapeutic effect of cisplatin. Local application of the protective agents could avoid this undesirable effect. In the present study, we aimed at suppressing cisplatin-induced ototoxicity in guinea pigs by administering MTBA or STS perilymphatically through cochlear perfusion. Guinea pig cochleas were perfused for 10 min with artificial perilymph (ArtP) containing cisplatin at 0.3 mg/ml, either alone, or in combination with MTBA (0.1 or 1.0 mg/ml) or STS (0.75 or 3.0 mg/ml). The compound action potential (CAP) and the summating potential (SP), evoked by 8 kHz tone bursts, and the endocochlear potential (EP; MTBA only) were measured just before and 1, 2, 3 and 4 h after perfusion. Cisplatin gradually reduced the CAP amplitude in time. Adding MTBA only accelerated this ototoxic effect. After cisplatin treatment a decline was found in the EP, irrespective of co-treatment, i.e., addition of MTBA did not accelerate the EP decrease. In contrast to MTBA, STS ameliorated the ototoxic effect of cisplatin. In conclusion, local application of anti-oxidants can ameliorate cisplatin ototoxicity but this is not a feature of all anti-oxidants.

Antioxidant protection in a new animal model of cisplatin-induced ototoxicity

Mortality is a major complication in animal models of cisplatin-induced hearing loss due to the systemic toxicity of the drug. Here we report on a novel two-cycle treatment in rats, each cycle consisting of four days of cisplatin injections (1 mg/kg, i.p., twice daily) separated by 10 days of rest. This regimen, similar to clinical courses of cancer chemotherapy, produced significant hearing loss without mortality. Auditory brain stem evoked responses were unchanged after the first cycle but were elevated by 40-50 dB at 16 and 20 kHz after the second. Loss of outer hair cells occurred after the second cycle, predominantly in the base of the cochlea. Total cochlear antioxidants declined progressively during drug treatment and were reduced to 60% of control values after the second cisplatin cycle. Co-administration of salicylate (100 mg/kg, s.c., twice daily) during both cycles or during the second cycle restored antioxidant levels and reduced cisplatin-induced threshold shifts. This model of cisplatin ototoxicity without mortality eliminates potentially confounding factors that may determine the survival of a special cohort of animals. The results also support the notion that reactive oxygen species are involved in cisplatin ototoxicity and show the potential usefulness of antioxidant treatment.

Sodium benzoate attenuates iminodipropionitrile-induced behavioral syndrome in rats

This study reports the effects of the antioxidant sodium benzoate (SB) on iminodipropionitrile (IDPN)-induced excitation with choreiform and circling (ECC) syndrome in adult female Wistar rats. Rats in four different groups (n=8) received i.p. injections of SB (0, 50, 100 and 200 mg/kg) daily for 10 days. IDPN (100 mg/kg, i.p.) was administered daily 30 min before SB for the first 8 days. Two additional groups served as control (vehicle) and SB alone (200 mg/kg) groups. The animals were observed daily for neurobehavioral abnormalities, including dyskinetic head movements, circling, tail hanging, righting reflex and contact inhibition of the righting reflex, characterized as the ECC syndrome. In the IDPN-alone treated group, the onset of ECC syndrome occurred on day 9 (2 out of 8 rats), whereas none of the animals treated with IDPN plus SB (100 or 200 mg/kg) showed any signs of ECC syndrome on that day. All the animals in the IDPN-alone group developed severe dyskinesia on day 11. Treatment of rats with SB significantly and dose-dependently attenuated IDPN-induced behavioral deficits.

Protection against cisplatin ototoxicity by adenosine agonists

Cisplatin is a commonly used antineoplastic agent that causes ototoxicity through the formation of reactive oxygen species (ROS). Previous studies have shown that cisplatin causes an upregulation of A(1) adenosine receptor (A(1)AR) in the cochlea, and that application of the adenosine agonist, R-phenylisopropyladenosine (R-PIA), to the round window (RW) results in significant increases in cochlear glutathione peroxidase and superoxide dismutase. These data suggest that adenosine receptors (ARs) are an important part of the cytoprotective system of the cochlea in response to oxidative stress. The purpose of the current study was to investigate the effect of various adenosine agonists on cisplatin ototoxicity using RW application. Auditory brainstem response (ABR) thresholds were recorded in anesthetized chinchillas at 1, 2, 4, 8 and 16kHz. The auditory bullae were surgically opened, and 1mM R-PIA, 10microM 8-cyclopentyl-1,3-dipropylxanthine (DPCPX)/R-PIA (1mM) cocktail, 100microM 2-chloro-N-cyclopentyladenosine (CCPA), 2-[4-(2-p-carboxy-ethyl)phenylamino]-5'-N-ethylcarboxamidoadenosine (CGS) or vehicle were applied to the RW. After 90min, the remaining solution was removed and cisplatin was applied to the RW. The bullae were closed and the animals recovered for 72h, after which, follow-up ABRs were performed. Cochleae were harvested for scanning electron microscopy (SEM) and for lipid peroxides. Pre-administration of the A(1)AR agonists R-PIA or CCPA significantly reduced cisplatin-induced threshold changes at all but the highest test frequency. In addition, A(1)AR agonists protected against cisplatin-induced hair cell damage and significantly reduced cisplatin-induced lipid peroxidation. Co-administration of the A(1)AR antagonist, DPCPX, completely reversed the protective effects of R-PIA. In contrast, pretreatment with CGS-21680, an A(2A) adenosine receptor (A(2A)AR) agonist, significantly increased cisplatin-induced threshold changes. Our findings are consistent with the notion that the A(1)AR contributes significantly to cytoprotection in the cochlea, and thereby protects against hearing loss.

Time response of carboplatin-induced hearing loss in rat

Carboplatin is currently being used as an anticancer drug against human cancers. However, high dose of carboplatin chemotherapy resulted in hearing loss in cancer patients. We have shown that carboplatin-induced hearing loss was related to dose-dependent oxidative injury to the cochlea in rat model. However, the time response of ototoxic dose of carboplatin on hearing loss and oxidative injury to cochlea has not been explored. The aim of the study was to evaluate the time response of carboplatin-induced hearing loss and oxidative injury to the cochlea of the rat. Male Wistar rats were divided into two groups of 30 animals each and treated as follows: (1) control (normal saline, i.p.) and (2) carboplatin (256 mg/kg, a single i.p. bolus injection). Auditory brain-evoked responses (ABRs) were recorded before and 1-5 days after treatments. The animals (n = 6) from each group were sacrificed on day 1, 2, 3, 4, and 5 and cochleae were isolated and analyzed. Carboplatin significantly elevated the hearing thresholds to clicks and to 2, 4, 8, 16, and 32 kHz tone burst stimuli only 3-5 days post-treatment. Carboplatin significantly increased nitric oxide (NO), malondialdehyde (MDA) levels and manganese superoxide dismutase (Mn-SOD) activity in the cochlea 4-5 and 3-5 days post-treatment, respectively, indicating enhanced influx of free radicals and oxidative injury to the cochlea. Carboplatin significantly depressed the reduced to oxidized glutathione (GSH/GSSG) ratio, antioxidant enzyme activities such as copper/zinc-superoxide dismutase (CuZn-SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) as well as enzyme protein expressions in the cochlea 3-5 days after treatment. The data suggest that carboplatin-induced hearing loss involves oxidative injury to the cochlea of the rat in a time-dependent manner.

Cisplatin ototoxicity in the guinea pig: vestibular and cochlear damage

The aim of the present study was to investigate both vestibular and cochlear cisplatin toxicity. Twelve albino guinea pigs were divided into an experimental (n=8) and a control saline group (n=4) and were treated with cisplatin at a daily dose of 2.5 mg/kg for 6 consecutive days. Vestibular dysfunction was evaluated by computing the gain of the vestibular ocular reflex (VOR) evoked by stimulation in the horizontal (HVOR) and vertical (VVOR) planes. Changes in cochlear function were characterised as compound action potential threshold shifts. After the functional testing, tympanic bullae were removed and processed for morphological examination of the sensorineural epithelium. The onset of vestibular functional impairment was observed on the third day, although the VOR gain decrease was not significant. The impairment of the vestibular function progressed until the sixth day becoming statistically significant particularly at VVOR mid frequencies of stimulation. At these frequencies both macula and crista ampullaris functions are involved. Concomitantly a progressive auditory threshold shift was observed at all stimulus frequencies. The decline of the auditory function was statistically significant from the third day of treatment and it was more evident at high frequencies. Morphological observations showed a massive loss of outer hair cells and a degeneration of the organ of Corti in the basal/middle turns and only a slight loss of hair cells of the cristae ampullares and maculae. In conclusion, functional and morphological data provide evidence that the toxic effect of cisplatin is more pronounced in the organ of Corti than in the vestibular epithelium.

Effects of trolox, locally applied on round windows, on cisplatin-induced ototoxicity in guinea pigs

OBJECTIVE

Cisplatin (CDDP), an antitumor agent widely used in the treatment of pediatric solid tumors, has dose-limiting side effects such as ototoxicity and nephrotoxicity. Recently, evidence has been accumulated to demonstrate that these side effects are closely related to oxidative stress. In the present study, we attempted to suppress CDDP-induced ototoxicity in guinea pigs by administering trolox, a water-soluble analogue of alpha-tocopherol which is a natural lipid-soluble antioxidant, locally on round windows.

METHODS

Hartley albino guinea pigs (250-300 g) were treated with CDDP (0.3 mg/ml) in the presence or absence of a combined treatment of trolox (5 mM). Both drugs were administered locally on round windows.

RESULTS

The combined treatment of trolox distinctly improved the ototoxic side effects induced by CDDP. These were: elevation of auditory brain stem response threshold at 4, 8 and 16 kHz and substantial losses of outer hair cells with the base-to-apex gradient.

CONCLUSION

Trolox, locally applied on round windows, showed a suppression on CDDP-ototoxicity. The results obtained in the present study suggest that a local application of trolox in the tympanic cavity can be a promising candidate to prevent the CDDP-ototoxicity in the future.

M40403, a superoxide dismutase mimetic, protects cochlear hair cells from gentamicin, but not cisplatin toxicity

Gentamicin, an aminoglycoside antibiotic, and cisplatin, a platinum-based anticancer drug, are two commonly used clinical drugs with ototoxic side effects. The ototoxicity of gentamicin and cisplatin has been linked to the production of reactive oxygen species (ROS), although the specific ROS pathways have not been identified. One ROS that might play a role in ototoxicity is the superoxide radical, which is enzymatically dismutated to molecular oxygen and hydrogen peroxide by endogenous superoxide dismutase (SOD) enzymes. M40403, a manganese-based nonpeptidyl molecule that mimics the activity of SOD, was tested for its ability to protect against gentamicin and cisplatin toxicity in cochlear organotypic cultures from neonatal C57BL/10J mice. Cultures were treated with gentamicin or cisplatin alone or in combination with M40403. M40403 alone had no effect on outer hair cell (OHC) or inner hair cell (IHC) survival at doses of 1, 5, and 10 microM, but a high dose of 30 microM reduced hair cell numbers by approximately 30%. Gentamicin alone and cisplatin alone killed OHCs and IHCs in a dose-dependent manner. The addition of M40403 to gentamicin-treated cultures significantly increased OHC and IHC survival in a dose-dependent manner, whereas M40403 failed to protect hair cells in cisplatin-treated cultures at any dose. The results suggest that the toxicity of gentamicin and cisplatin to cochlear hair cells are mediated by different pathways. Clinically, increased levels of SOD or SOD mimetics might provide significant protection against aminoglycoside ototoxicity.

Oxidative DNA damage is associated with intense noise exposure in the rat

Increasing evidence suggests that noise-induced hearing loss may be reduced or prevented with antioxidant therapy. Biochemical markers of reactive oxygen species (ROS)-induced damage can help elucidate possible treatment timing constraints. This study examined the time course of ROS damage following a 2-h, broad-band noise exposure resulting in permanent threshold shift in 35 Long-Evans rats. Cochlea, brain, liver, serum and urine were analyzed at 1, 3, 8, 72, and 672 h (28 days) after exposure. Oxidative DNA damage was assessed by measuring 8-hydroxy-2'-deoxyguanosine (8OHdG) by high performance liquid chromatography with electrochemical detection. Lipid peroxidation was measured via the thiobarbituric acid-reactive substances (TBARS) colorimetric assay for detection of aldehydes (e.g., malondialdehyde). Auditory brainstem response and distortion product otoacoustic emission thresholds showed progressive elevation for the 3- and 8-h groups, then notable recovery for the 72-h group, and some worsening for the 672-h group. 8OHdG was significantly elevated in cochlea in the 8-h group, and in brain and liver for the 72-h group. TBARS were significantly elevated in serum for the 72-h group. Based upon oxidative DNA damage present in cochlea following intense noise, we postulate that the first 8 h following exposure might be a critical period for antioxidant treatment.

TEOAE monitoring of Cisplatin induced ototoxicity in guinea pigs: the protective effect of vitamin B treatment

OBJECTIVE

To evaluate Cisplatin (CP) induced ototoxicity and the effects of vitamin B treatment on ototoxicity in guinea pigs by using the Transient Evoked Otoacoustic Emission (TEOAE) technique.

METHODS

Eleven guinea pigs were divided into two groups and they were tested by TEOAE before and after the experiment. A TEOAE response was regarded as positive when all of the following criteria were met: 1. The mean amplitude of the cochlear response in dB pe SPL should be greater than that of the noise in the external auditory canal; 2. The reproducibility rate of the response should be greater than 50%; 3. The stimulus stability rate should be greater than 65%; 4. The signal to noise ratio of the response in 1, 2, 3, 4 and 5 kHz band frequencies should be greater than 3 dB pe SPL in at least two bands. The first group included five animals that had only CP injections. Six animals in the second group received additional 0.2 ml/kg combined vitamin B preparations for 7 consecutive days. Thereafter, the right and left ears of all animals in both groups were tested by TEOAE.

RESULTS

TEOAE responses recorded from 22 ears of 11 guinea pigs before drug administrations showed that the responses with maximum amplitude were originated from the mid-frequency region. Positive TEOAE responses were significantly reduced after CP administrations in both groups when compared with their respective pretreatment results (P<0.01). However, vitamin B injections, in addition to a single large dose of CP, resulted in significantly better TEOAE responses than those obtained after only CP injections (P<0.05).

CONCLUSIONS

The routine use of TEOAE monitoring is recommended in clinical CP treatment protocols for the early detection and follow up of ototoxicity. Also, prospective clinical trials are needed in order to validate the protective effects of vitamin B treatment against ototoxicity.

Effects of alpha-tocopherol on cisplatin-induced ototoxicity in guinea pigs

Cisplatin (CDDP), an antitumor agent widely used in the treatment of head and neck cancers, has dose-limiting side effects such as ototoxicity and nephrotoxicity. Recently, evidence has been accumulated to demonstrate that these side effects are closely related to oxidative stress. In the present study, we attempted to suppress CDDP-induced ototoxicity and nephrotoxicity in guinea pigs by administering alpha-tocopherol, a naturally occurring antioxidant. Hartley albino guinea pigs (250 approximately 300 g) were treated with CDDP (4 mg/kg intraperitoneally (I.P.)) for 3 days in the presence and absence of alpha-tocopherol (50 mg/kg I.P.) injection for 6 days. The combined treatment of animals with alpha-tocopherol distinctly improved the CDDP-induced side effects. These were: loss of Preyer's reflex at high frequencies; distinct elevation of auditory brain stem response threshold at 16 kHz; increased lipid peroxidation in the cochlea determined by the malondialdehyde-thiobarbituric acid method; substantial losses of outer hair cells in the basal and second turns of the cochlea; fragmentation of nuclear DNA detected by the TUNEL method in cochlear hair cells and cells in the stria vascularis; and increases in serum BUN and Cr. These results strongly suggest that alpha-tocopherol suppresses CDDP-induced ototoxicity and nephrotoxicity via the suppression of the increased production of reactive oxygen species.

Oxidative stress-induced apoptosis of cochlear sensory cells: otoprotective strategies

Apoptosis is an important process, both for normal development of the inner ear and for removal of oxidative-stress damaged sensory cells from the cochlea. Oxidative-stressors of auditory sensory cells include: loss of trophic factor support, ischemia-reperfusion, and ototoxins. Loss of trophic factor support and cisplatin ototoxicity, both initiate the intracellular production of reactive oxygen species and free radicals. The interaction of reactive oxygen species and free radicals with membrane phospholipids of auditory sensory cells creates aldehydic lipid peroxidation products. One of these aldehydes, 4-hydroxynonenal, functions as a mediator of apoptosis for both auditory neurons and hair cells. We present several approaches for the prevention of auditory sensory loss from reactive oxygen species-induced apoptosis: 1) preventing the formation of reactive oxygen species; (2) neutralizing the toxic products of membrane lipid peroxidation; and 3) blocking the damaged sensory cells' apoptotic pathway.

A radical demise. Toxins and trauma share common pathways in hair cell death

The pathologic similarities noted after ototoxic and/or traumatic injury to the cochlea as well as the key features of the cochlea that make it susceptible to reactive oxygen species (ROS) damage are reviewed. Recent evidence linking ROS to cochlear damage associated with both ototoxins and/or trauma are presented. Mechanisms of generation of ROS in the cochlea and how these metabolites damage the cochlea and impair function are also reviewed. Finally, examples of novel therapeutic strategies to prevent and reverse hearing loss due to noise and/or ototoxins are presented to illustrate the clinical relevance of these new findings.

Maturation of cochlear glutathione-S-transferases correlates with the end of the sensitive period for ototoxicity

The developing mammalian cochlea is especially sensitive to chemical toxins. In rats, the period of increased sensitivity falls roughly between postnatal days (P) 8 and 28. One unexplored hypothesis for this 'sensitive period' is that young cochleas may have immature complements of detoxification enzymes. Glutathione-S-transferases (GSTs) are a family of detoxification enzymes which catalyze the conjugation of many xenobiotics to glutathione. Using high performance liquid chromatography (HPLC), we measured the concentrations of soluble GST isoforms in cochleas of developing Fischer 344 rats. At P1, the concentration of isoform rGSTP1 was 9 pmol/mg protein. That of the remaining isoforms studied was low, <2 pmol/mg protein, and, except for rGSTA3, remained so throughout the period of study. At P2, immunolabelling visualized rGSTP1 in the stria vascularis, Reissner's membrane, spiral limbus and organ of Corti. From P1 to P28, rGSTP1 increased to 15 pmol/mg protein and was detected additionally in satellite cells of the spiral ganglion and in the spiral ligament. From P7 to P28, rGSTA3 increased 8-fold (3-24 pmol/mg protein), became the predominant isoform in the adult organ and localized to pillar cells, the limbus and the spiral ligament. In the vestibule, rGSTP1 predominated, although rGSTA3 increased slightly over time. These observations suggest that biochemical immaturity in detoxification enzymes in the cochlea may contribute to the increased sensitivity to ototoxins during development and that differences in detoxification enzymes between cells in the cochlea and between inner ear organs may underlie differences in susceptibility to ototoxins.

Application of antioxidants and other agents to prevent cisplatin ototoxicity

OBJECTIVE/HYPOTHESIS

To review the recent data from experiments performed in this laboratory to test the hypothesis that cisplatin ototoxicity is related to depletion of glutathione and antioxidant enzymes in the cochlea and that the use of antioxidants or protective agents would protect the cochlea against cisplatin damage and prevent hearing loss.

STUDY DESIGN/METHODS

Data were reviewed from experiments performed in this laboratory. Control rats were treated intraperitoneally with cisplatin 16 mg/kg. Experimental rats were given cisplatin in combination with one of the following protective agents: diethyldithiocarbamate, 4-methylthiobenzoic acid, ebselen, or lipoic acid. Animals in each group underwent auditory brainstem response (ABR) threshold testing before and 3 days after treatment. Cochleae were removed after final ABR testing and analyzed for glutathione and activities of the enzymes superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and malondialdehyde.

RESULTS

Rats in the control group receiving cisplatin were found to have significant ABR threshold shifts. This was accompanied by a reduction of glutathione and the activity of antioxidant enzymes (superoxide dismutase, glutathione peroxidase, catalase, and glutathione reductase) and an elevation of malondialdehyde. Experimental animals had preservation of ABR thresholds and levels of glutathione, antioxidant enzyme activity, and malondialdehyde that were similar to untreated animals.

CONCLUSION

Cisplatin ototoxicity appears to be initiated by fee-radical production, which causes depletion of glutathione and antioxidant enzymes in the cochlea, and lipid peroxidation, manifested by an increase in malondialdehyde. These effects were blocked by each of a series of antioxidant compounds given in combination with cisplatin. A mechanism for cisplatin ototoxicity is elaborated with a proposed plan of chemoprevention using agents with different mechanisms of action. These substances could be used alone or in combination to reduce the severity of cisplatin ototoxicity in patients.

Effect of 4-methylthiobenzoic acid on cisplatin-induced ototoxicity in the rat

The purpose of this study was to investigate the effectiveness of 4-methylthiobenzoic acid (MTBA) as a protection agent against cisplatin (CDDP)-induced changes in organ of Corti surface structure, compared to electrophysiological changes. Electrophysiological change was assessed using auditory brainstem response (ABR) and morphological changes were assessed using scanning electron microscopy (SEM). Male Wistar rats underwent pre-treatment ABRs in response to clicks, and tone bursts at 2, 4, 8, 16, and 32 kHz. The three groups of rats were injected as follows: (1) MTBA (250 mg/kg, i.p.), (2) CDDP (16 mg/kg, i.p.), (3) CDDP+MTBA (16 mg/kg, i.p. + 250 mg/kg, i.p.). Post-treatment ABRs were performed 3 days after drug administration and rats were sacrificed. Their cochleae were harvested and SEM was used to examine the surface of the organ of Corti, specifically the number of inner hair cells (IHCs) and outer hair cells (OHCs) in the apical, middle and basal turns of the cochlea. Animal weight was measured on the first and final days. There was a good correlation between ABR threshold changes and hair cell loss in the high frequency region of the cochlea (basal turn), while threshold changes in the lower test frequencies (middle turn) appeared to be the result of more subtle changes in the cochlea. MTBA provided effective protection against cisplatin-induced ABR threshold changes at all test frequencies as well as hair cell loss. MTBA also protected against body weight loss.