Inhibition of adenylate-cyclase-coupled G protein complex by ototoxic diuretics and cis-platinum in the inner ear of the guinea pig

Cisplatin-Induced Stria Vascularis Damage Is Associated with Inflammation and Fibrosis

The stria vascularis (SV) generates the endocochlear potential (EP) in the inner ear and is necessary for proper hair cell (HC) mechanotransduction and hearing. Cell junctions are indispensable for the establishment of compositionally distinct fluid compartments in the inner ear. Ototoxic drug cisplatin can damage SV and cause sensorineural hearing loss; however, the underlying mechanisms behind such injury are unclear. In this study, after the intraperitoneal injection of cisplatin (3 mg/kg/day for 7 days) in mice, we determined the auditory function by EP recording and auditory brainstem response (ABR) analysis, observed the ultrastructure of SV by transmission electron microscopy (TEM), and examined the expression and distribution of cell junction proteins by western blot, PCR, and immunofluorescence staining. We discovered that the EP was significantly reduced while ABR thresholds were significantly elevated in cisplatin-treated mice; cisplatin induced ultrastructural changes in marginal cells (MCs), endothelial cells (ECs), pericytes, etc. We found that cisplatin insulted auditory function not only by reducing the expression of zonula occludens protein-1 (ZO-1) in MCs of the SV but also by decreasing the expression of connexin 26 (Cx26) and connexin 43 (Cx43) in MCs and basal cells (BCs). More importantly, cisplatin induced activations of perivascular-resident macrophage-like melanocytes (PVM/Ms) and interleukin-1beta (IL-1β) as well as increased expressions of profibrotic proteins such as laminin and collagen IV in SV. Thus, our results firstly showed that cisplatin induced fibrosis, inflammation, and the complex expression change of cell junctions in SV.

Hearing status in children with frequently relapsing and steroid resistant nephrotic syndrome

BACKGROUND

Children with idiopathic nephrotic syndrome (INS) are at risk of hearing impairment due to nephrotoxic drugs and biochemical impairments.

METHODS

Forty children with INS aged 5-16 years [20 patients with frequently relapsing nephrotic syndrome (FRNS)/steroid dependent nephrotic syndrome (SDNS) and 20 with steroid resistant nephrotic syndrome (SRNS)] and 20 normal healthy controls were enrolled in this study. Pure tone audiometry was done using the ALPS AD 2000 audiometer. Sensorineural hearing loss was diagnosed when the bone conduction level was >20 dB and the difference in air to bone gap was ≤15 dB. Based on the air conduction (AC) threshold, deafness was graded into the following categories: mild (26-40 dB), moderate (41-55 dB), moderately severe (56-70 dB), severe (71-91 dB) and profound (>91 dB).

RESULTS

Children with FRNS/SDNS had a higher threshold for hearing at frequencies of 250 and 500 Hz, respectively, than the controls. Of the children in the FRNS/SDNS category, three (15 %) had mild sensorineural hearing impairment. These children had a low serum calcium level (P < 0.03) and received higher cumulative doses of furosemide (P < 0.04). Children with SRNS had a higher threshold for hearing at frequencies of 250, 500, 1,000, and 2,000 Hz, respectively, than the controls. Of the 20 children with SRNS, ten (50 %) had sensoineural hearing impairment (8 mild, 2 moderate). Children with SRNS with a hearing defect had received a higher cumulative dose of furosemide (P < 0.03).

CONCLUSIONS

Children with FRNS/SDNS and SRNS are at risk of sensorineural hearing impairment. The risk factors associated with this impairment were higher cumulative doses of furosemide and hypocalcemia. Larger prospective cohort studies are required to evaluate this association.

Detection of cisplatin-induced ototoxicity with transient evoked otoacoustic emission test before pure tone audiometer

Our aim was to investigate cisplatin ototoxicity with transient evoked otoacoustic emission (TEOAE) test before it is seen with pure tone audiometer. In our study, we compared the hearing of the patients who are receiving 100 mg/m(2) 4-cycle cisplatin for lung cancer, with pure tone audiometer and transient evoked otoacoustic emission test in 1,000, 2,000 and 4,000 Hz. We found 55% hearing decrease with pure tone audiometer in patients that are receiving 100 mg/m(2) 4-cycle cisplatin for lung cancer. We also established emission amplitude decrease with TEOAE test in 85% of the patients. When we compare the patients' pure tone audiometer in 1,000, 2,000 and 4,000 Hz and TEOAE amplitude changes we did not find statistically significant results (P > 0.05), but when we compare the patients' TEOAE amplitude changes in 1,000, 2,000 and 4,000 Hz with control group we found statistically significant results (P < 0.05). Our results show that cisplatin ototoxicity could be find out with TEOAE test before it is seen with pure tone audiometer.

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.

Induction of mitochondrial fusion by cysteine-alkylators ethacrynic acid and N-ethylmaleimide

Mitochondrial fusion and fission are important aspects of eukaryotic cell function that permit the adoption of varied mitochondrial morphologies depending upon cellular physiology. We previously observed that ethacrynic acid (EA) induced mitochondrial fusion in cultured BSC-1 and CHO/wt cells. However, the mechanism responsible for it was not clear since EA has a number of known cellular effects including glutathione (GSH) depletion and alkylation of cysteine residues. To gain insight, we have tested the effects of a variety of compounds on EA induced cellular toxicity and mitochondrial fusion. N-acetyl cysteine (NAC), a GSH precursor, was found to abrogate both the toxic and fusion-inductive effects, whereas diethylmaleate (dEM), a GSH depletor, potentiated both these effects in a dose-dependent manner. However, treatment with dEM alone, which depleted GSH to the same degree as EA, did not induce mitochondrial fusion. These results indicate that although detoxification of EA via formation of GSH conjugates is dependant upon GSH levels, the depletion of GSH by EA is not responsible for its effect on mitochondrial fusion. Dihydro-EA (DH-EA), a saturated EA analogue, lacked EA's toxicity and effect on fusion, indicating that the alpha,beta-unsaturated ketone is central to its observed effects. N-ethylmaleimide (NEM), another well-known cysteine-alkylator, also induced mitochondrial fusion at near toxic concentrations. These data suggests that cysteine-alkylation is the causative factor for fusion and toxicity. In live BSC-1 cells, EA induced fusion of mitochondria occurred very rapidly (<20 min), which suggests that it is inducing fusion by modifying certain critical cysteine residue(s) in proteins involved in the process.

Time sequence of degeneration pattern in the guinea pig cochlea during cisplatin administration. A quantitative histological study

We investigated the key tissues that are implicated in cisplatin ototoxicity within the time window during which degeneration starts. Guinea pigs were treated with cisplatin at a dose of 2 mg/kg/day for either 4, 6, or 8 consecutive days. Histological changes in the organ of Corti, the stria vascularis and the spiral ganglion were quantified at the light microscopical level. Outer hair cell (OHC) loss started between 4 and 6 days of cisplatin administration, but is only significantly different from the non-treated group after 8 days of treatment. Midmodiolar OHC counts were comparable to the cytocochleogram data. The cross-sectional area of the stria vascularis did not differ from the non-treated group, nor did an endolymphatic hydrops develop during the course of treatment. Spiral ganglion cell (SGC) densities did not decrease. After 6 days, however, detachment of the myelin sheath of the type-I SGCs was seen in the lower basal turn, whereas after 8 days it was also present in the more apically located turns. Myelin sheath detachment is the result of perikaryal shrinkage and swelling of the myelin sheath. The present study confirms that cisplatin at a daily dose of 2 mg/kg has a detrimental effect on the OHCs as well as on the type-I SGCs. These intracochlear effects occur simultaneously; OHC loss and SGC shrinkage start between the fourth and sixth day of cisplatin administration and appear to develop in parallel. At this dose, no histological effect on the stria vascularis could be observed, although previous electrophysiological experiments demonstrated a clear effect on the endocochlear potential

Ethacrynic acid rapidly and selectively abolishes blood flow in vessels supplying the lateral wall of the cochlea

The mechanisms underlying the ototoxicity of ethacrynic acid (EA) are not fully understood. Previous studies have focused on morphologic and enzymatic changes in the stria vascularis. The current experiment shows that one of the earliest effects of EA is ischemia, resulting from impaired blood flow in vessels supplying the lateral wall of the cochlea. Inner ear microcirculation, endocochlear potentials, compound action potentials (CAP), cochlear microphonics (CM) and summating potentials (SP) were monitored over time in chinchillas following a single injection of EA (40 mg/kg i.v.). At all times after EA injection, blood vessels supplying the spiral lamina, modiolus, and vestibular end organs appeared normal. In contrast, lateral wall (spiral ligament and stria vascularis) vessels were poorly stained with eosin 2 min after EA injection, and devoid of red blood cells at 30 min post EA. Decline, but not recovery, of CAP, CM and SP followed the microcirculation changes in the lateral wall. Reperfusion was delayed in stria vascularis arterioles relative to other lateral wall vessels. The ischemia-reperfusion caused by EA would be expected to generate large quantities of free radicals, which may trigger or contribute to the cellular, enzymatic, and functional pathologies that have been described in detail previously.

Dose-dependent effect of 8-day cisplatin administration upon the morphology of the albino guinea pig cochlea

Numerous studies investigating cisplatin ototoxicity in animals have been performed, but it is difficult to derive a clear dose-effect relation from these studies. The degree of cisplatin-induced ototoxicity depends on a multitude of factors. Many parameters, such as dose, mode of administration, dosage schedule and concomitant administration of protective additives, vary among the published studies. Therefore, we performed a basic dose-effect study on cisplatin ototoxicity in the guinea pig. Albino guinea pigs were treated with cisplatin at daily doses of either 0.7, 1.0, 1.25, 1.5 or 2.0 mg/kg for 8 consecutive days. Electrocochleography was performed on day 10 after which the cochleas were removed and processed for histological examination. The electrophysiological results showed a marked transition from almost no ototoxic effect to a large effect between a daily dose of 1.25 and 1.5 mg/kg (Stengs et al., 1998). Outer hair cell (OHC) counts corresponded well with the electrophysiological results. At daily doses of 0.7, 1.0 and 1.25 mg/kg no statistically significant OHC loss was observed, whereas OHC loss averaged 60% and 65% in the basal turns at daily doses of 1. 5 and 2.0 mg/kg, respectively. Morphological changes in the stria vascularis were present only in cochleas from animals treated with cisplatin doses of 1.0, 1.25 and 1.5 mg/kg/day. Cochleas from animals treated with a daily cisplatin dose of 2.0 mg/kg for 8 consecutive days showed an endolymphatic hydrops. The present study shows that cisplatin, administered at a daily dose of 1.5 mg/kg for 8 consecutive days, provides a degree of OHC loss that is well suited to study the effects of putative protective agents and possible hair cell recovery.

Histological effects of co-administration of an ACTH((4-9)) analogue, ORG 2766, on cisplatin ototoxicity in the albino guinea pig

Cisplatin is one of the most potent antineoplastic drugs presently known, but its therapeutic efficacy is seriously limited by several side effects such as ototoxicity. Several compounds that are known for their nephroprotective effects also seem to reduce the incidence and severity of cisplatin-induced ototoxicity. Hamers et al. (1994) and De Groot et al. (1997) investigated the possibly protective effect of concomitant administration of the ACTH((4-9)) analogue ORG 2766 upon cisplatin ototoxicity in guinea pigs. Animals were treated with cisplatin at a daily dose of 2.0 mg/kg for 8 consecutive days and ORG 2766 at a daily dose of 75 mcg/kg for 9 days. Concomitant administration of cisplatin plus ORG 2766 resulted in a bimodal distribution of the electrophysiological data (compound action potential and cochlear microphonics amplitudes) and the histological data (outer hair cell (OHC) counts). It was surmised that this dichotomy might occur at a certain cisplatin dose. We investigated whether this protective effect of ORG 2766 could be enhanced by reducing the daily dose of cisplatin while maintaining the same dose of ORG 2766. Thirty-six animals were treated with daily i.p. injections of cisplatin at a dose of 1.0 mg/kg (n=18) or 1.5 mg/kg (n=18) for 8 consecutive days. When comparing the mean OHC counts of the different experimental groups, treatment with cisplatin at a daily dose of 1.5 mg/kg for 8 consecutive days resulted in a considerable loss of OHCs, which was significantly reduced after co-administration of ORG 2766. Co-treatment with ORG 2766 did not result in a change in the volume of the scala media. The present results are in agreement with the electrophysiological results published earlier (Stengs et al., 1998b).

Immunohistochemical localization of adenylyl cyclase isoforms in the lateral wall of the rat cochlea

The enzymatic activity of adenylyl cyclase (AC) is attributable to nine isoforms with individual pharmacology and tissue distribution. Polyclonal antibodies for AC isoforms I-IV, VII and VIII were applied to sections of cochlear lateral wall, a tissue involved in ion transport contributing to the unique ion content of endolymph and electrical potential of scala media. Within the stria vascularis, immunoreactivity primarily to Ca(2+)/calmodulin-independent isoforms II, IV and VII was localized to sites consistent in position to the basolateral extensions of marginal cells. Little immunoreactivity was observed in the stria vascularis for Ca(2+)/calmodulin-dependent isoforms I, III and VIII. Within the spiral ligament, type II and type IV fibrocytes exhibited moderate staining for ACII, IV and VII, less staining for VIII and little for I and III. Immunoreactivity to ACII, IV, VII and VIII was observed in type I fibrocytes. The outer sulcus cells and root processes were highly immunoreactive for isoforms I and VIII, but not for III or the Ca(2+)/calmodulin-independent isoforms. The differential pattern of immunoreactivity in the lateral wall overall appears to reflect subfamily-specific expression with Ca(2+)/calmodulin-independent isoforms expressed in the stria vascularis and Ca(2+)/calmodulin-dependent isoforms expressed in the outer sulcus cells and root processes. cAMP-mediated modulation of ion transport by marginal cells is predicted to exhibit, in the microenvironment of basolateral membrane infoldings, pharmacological characteristics of the AC type II subfamily (II, IV and VII), including activation by protein kinase C (II and VII).

Partial cDNAs encoding G-protein alpha subunits in the rat vestibular periphery

To begin understanding what G-proteins are involved in signal transduction in the vestibular periphery, the expression of Galpha subunits in rat primary afferent neurons (Scarpa's ganglia) and end-organs was studied. Reverse transcription-polymerase chain reaction (RT-PCR) with degenerate primers corresponding to two conserved regions of the Galpha protein coding sequence produced partial cDNAs encoding two distinct forms of Galpha(s) subunit (Galpha(s2) and anove) Galpha(s2) subunit,GenBank accession number AF1841510); and two forms of Galpha(i2) subunits. A novel truncated form of Galpha(i2) (designated Galpha(i2(vest)),Gen Bank accession number AF189020) was detected in the vestibular periphery. Galpha(i2(vest)) was also expressed in rat cerebellum and heart. The possible role of the identified Galpha protein cDNAs in the function of the vestibular periphery is discussed.

Protection and spontaneous recovery from cisplatin-induced hearing loss

Cisplatin [cis-diamminechloroplatinum(II)] has proved itself as a potent antineoplastic agent. However, nephrotoxicity, neurotoxicity, gastrointestinal toxicity, myelosuppression, and ototoxicity interfere with its therapeutical efficacy. Forced diuresis reduces nephrotoxicity, effectively leaving neurotoxicity and ototoxicity as the major side effects of concern, and gastrointestinal toxicity and myelosuppression as the secondary side effects. So far, attempts to reduce these side effects by developing equally potent platinum analogs have been unsuccessful. Some success has been achieved, however, by co-treatment with protective agents. Nearly all these agents are sulfur- or sulfhydryl-containing compounds (thio compounds), known as antioxidants and potent heavy metal chelators. These thio compounds may provide protection from cisplatin toxicity either (1) by direct interaction between the cisplatin and the thio moiety, (2) by displacing platinum from its site of toxic action, (3) by preventing platinum from interfering with superoxide dismutase, or (4) by scavenging of cisplatin-induced free radicals. In particular the first two protective mechanisms bear the risk of reducing the antineoplastic activity of cisplatin. Since nephrotoxicity can be controlled effectively by forced diuresis, a more specific approach of coping with ototoxicity by focusing on protection at the sensorineural level was chosen. Being familiar with the neuro-protective and neurotrophic properties of ACTH-related neuropeptides, specifically against cisplatin-induced peripheral neuropathies, it was judged expedient to test for a possible otoprotective action of these neuropeptides. The results were positive, although tainted with high interanimal variability. When testing for the possibility that the neuropeptides would merely delay cisplatin-induced ototoxicity rather than reduce it, it was discovered in control series without neuropeptide co-treatment that the ear can recover spontaneously from cisplatin-induced hearing loss. This was found both electrophysiologically and in outer hair cell (OHC) counts. Although these preliminary findings require further investigation, they strongly suggest that spontaneous recovery of cochlear injury can occur in the mature mammalian cochlea. Moreover, the otoprotective action of the ACTH-related neuropeptides suggests that it may be possible to stimulate recovery from acute hearing loss using neuropeptides.

Basic fibroblast growth factor (FGF-2) protects rat cochlear hair cells in organotypical culture from aminoglycoside injury

Given the evidence that basic fibroblast growth factor (FGF-2) can protect neural and retinal cells from degeneration, we evaluated the potential of this growth factor to protect sensory cells in the inner ear. When sensory cells of the organ of Corti are exposed to aminoglycoside antibiotics such as neomycin either in vivo or in vitro, significant ototoxicity is observed. The in vitro cytotoxic effects of neomycin are dose and time dependent. In neonatal rat organ of Corti cultures, complete inner and outer hair cell destruction is observed at high (mM) concentrations of neomycin while inner hair cell survival and severely damaged outer hair cells are noted at moderate (microM) concentrations, with a maximal effect observed after 2 days of culture. Approximately 50% of cochlear outer hair cells are lost at a dose of 35 microM neomycin, and most surviving cells show disorganized stereocilia. Inner hair cells show primarily disorganization of their stereocilia. A significant protective effect is observed when the organ of Corti is pre-treated with FGF-2 (500 ng/ml) for 48 hours, and then FGF-2 is included with neomycin in the culture medium. A greater extent of outer hair cell survival and a significant decrease in stereociliary damage are noted with FGF-2. However, disorganization of inner hair cell stereocilia is unaffected by FGF-2. The protective effect of FGF-2 is specific, since interleukin-1B, nerve growth factor, tumor necrosis factor, and epidermal growth factor are ineffective, while retinoic acid and transforming growth factor alpha show only a moderate protective effect. These results confirm the potential of molecules like FGF-2 for preventing cell death due to a variety of causes.

Ultrastructural localization of G-protein GS in the lateral wall of the guinea pig cochlear duct

Immunocytochemical localization of a GTP-binding protein, Gs, in the various cells of the lateral wall of guinea pig cochlear duct was investigated using a post-embedding immunogold method with antibody raised against a synthetic decapeptide (RMHLRQYELL) encoding the C-terminus of the alpha-subunit of Gs. In the stria vascularis, labeling was observed on the basolateral membrane infoldings of marginal cells, on the juxtaposed membrane of intermediate cells, and on the cell membrane of basal cell. In contrast, no significant labeling was observed on the luminal membrane of marginal cells. Immunoreactivity also was detected on the cell membranes of various other cells. These include spiral prominence epithelial cells, fibrocytes of spiral ligament, external sulcus cells, and epithelial and mesothelial cells of Reissner's membrane. Adenylylcyclase has been functionally implicated in some of the cell types with membranes labeled in this study. The significance of these findings is briefly discussed.

Ultrastructural localization of G-protein Gs in the organ of Corti

Immunocytochemical localization of a stimulatory GTP-binding protein Gs in the organ of Corti in the inner ear was examined with a post-embedding immunogold technique, using antibodies raised against a synthetic decapeptide (RMHLRQYELL) of the C-terminus of the alpha subunit of Gs. Immunoreactivity was strong on the membranes of supporting cells in the reticular lamina, including inner and outer pillar cells and the phalangeal process of Deiters' cells. Immunolabeling also was seen on the membranes of cell bodies of those cells which surround nerve fibers, basilar fibers, outer spiral fibers and afferent nerve endings at outer hair cells. Gold particles also labeled the membrane of inner phalangeal cells and border cells. In contrast, outer and inner hair cells were not labeled. Possible roles of Gs in the organ of Corti are discussed.

Effects of ototoxins on quinuclidinyl benzylate binding in the rat cochlea

Ototoxins inhibit the muscarinic receptor-activated inositol phosphate synthesis in the rat cochlea. In order to study this inhibitory mechanism, we investigated the effects of the ototoxins ethacrynate, cisplatin, HgCl2 and neomycin on [3H]quinuclidinyl benzylate binding to muscarinic receptors in adult and 12-day-old rat cochleas. The results are similar whatever the age: at concentrations that inhibit the inositol phosphate synthesis, ethacrynate is without effect. Neomycin only reduces [3H]quinuclidinyl benzylate binding at concentrations in the millimolar range. Cisplatin and HgCl2 block the binding in a dose-dependent way. These results suggest that the block of the transduction system by cisplatin and HgCl2 is due to direct interactions with muscarinic binding sites. Moreover, considering these data together with previous results, ethacrynate and neomycin may affect the phosphoinositide signalling pathway at targets including phosphoinositides and G proteins.

Sulphhydryl-modifying reagents alter ototoxin block of muscarinic receptor-linked phosphoinositide turnover in the cochlea

In the 12-day-old rat cochlea, the synthesis of inositol phosphates (IPs) can be activated via M3 cholinoceptors. This stimulation is blocked by ototoxins (mercury, ethacrynate, cisplatin, neomycin), drugs with side effects that lead to damage of hair cells and strial cells. As these toxic effects can be reversed in vivo by thiol molecules, we investigated whether modifications of thiol compounds could be involved in ototoxin-induced inhibition of the IP turnover in the cochlea. For this purpose, we assessed whether the sulphhydryl-modifying reagents N-ethylmaleimide and cadmium modify the carbachol-stimulated formation of IPs in the 12-day-old rat cochlea. Both molecules inhibit the carbachol effect on a dose-dependent way without altering the basal metabolism of IPs. As cadmium may block some calcium channels, the effect of verapamil, another calcium channel antagonist, was tested. Verapamil (1-50 microM) does not alter carbachol-evoked IP formation, suggesting that the inhibitory effect of cadmium is not due to a calcium influx block. Binding experiments with the muscarinic ligand quinuclidinyl benzylate (QNB) showed that the sulphhydryl-modifying reagents do not displace QNB from binding sites. Combining ototoxins and reagents shows that N-ethylmaleimide acts synergistically with all ototoxins but ethacrynate while cadmium does so only with mercury. Both N-ethylmaleimide and cadmium have additive effects with ethacrynate. As a supplement, disulphide bond-modifying agents do not alter the carbachol-enhanced metabolism of IPs. These results suggest that molecules having thiol-modifying properties inhibit the carbachol-induced turnover of IPs without acting at the muscarinic sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of the carbachol-evoked synthesis of inositol phosphates by ototoxic drugs in the rat cochlea

The ability of amikacin, neomycin, ethacrynate, mercuric chloride and cisplatin to alter the inositol phosphate (IP) signalling pathway was assessed in the 12-day-old rat cochlea, where the turnover of IPs is coupled to muscarinic receptors. This study was motivated by: (1) the demonstration of neomycin binding to phosphatidylinositol 4,5-biphosphate, the precursor of IPs, and (2) the fact that ototoxic drugs induce some common symptoms in outer hair cells. At concentrations below 1 mM, none of the compounds changed the control 3H-IP formation. Mercuric chloride, cisplatin and ethacrynate inhibited the carbachol-induced formation of IPs in a dose-dependent manner with IC50 values of 74,340 and 430 microM, respectively. The aminoglycosides were less efficient in reducing the carbachol-stimulated accumulation of IPs, since neither amikacin nor neomycin, both at 1 mM, had any significant effect. However, neomycin applied at 15 and 30 microM induced 29% and 43% of inhibition of the stimulated IP response. Finally, additive effects are obtained between some of the toxic drugs. The results suggest that a block of the IP transduction system, associated with the cholinergic efferent innervation of the organ of Corti, is a feature that may be involved in some types of ototoxicity. The inefficiency of aminoglycosides and the putative targets of the ototoxic agents are discussed.

Evoked otoacoustic emissions and pure tone threshold audiometry in patients receiving cisplatinum therapy

Eight children and young adults with cancer were evaluated serially using pure tone audiometry as well as registration of click-evoked otoacoustic emissions (EOAE) 1 day prior to therapy as well as after various numbers of doses of cisplatinum. A reduction of EOAE-amplitudes following cisplatinum therapy was observed in all patients. This reduction tended to recover after the end of cisplatinum administration. Since EOAE are believed to result from cochlear bio-mechanical processes, the reduced emissions are interpreted as signs of cochlear dysfunction. We conclude, that EOAE testing may be a simple, non-invasive method that may detect early, transient functional impairment of hearing due to ototoxic agents such as cisplatinum, even in children. Further controlled trials are needed.