Early morphofunctional alterations induced by cisplatin in the cochlea. A quantitative and electrocochleographic study

Review: ototoxic characteristics of platinum antitumor drugs

Cisplatin, carboplatin, nedaplatin, and oxaliplatin are widely used in contemporary oncology; however, their ototoxic and neurotoxic side effects are quite different as discussed in this review. Cisplatin is considered the most ototoxic, but despite its reputation, the magnitude of hair cell loss that occurs with a single, large drug bolus is limited and confined to the base of the cochlea. For all of these platinum compounds, a major factor limiting damage is drug uptake from stria vascularis into the cochlear fluids. Disrupting the blood-labyrinth barrier with diuretics or noise exposure enhances drug uptake and significantly increases the amount of damage. Combined treatment with ethacrynic acid (a loop diuretic) and cisplatin results in rapid apoptotic hair cell death characterized by upregulation of initiator caspase-8 and membrane death receptor, TRADD, followed by downstream executioners, caspase-3 and caspase-6. Unlike cisplatin, nedaplatin and oxaliplatin are highly neurotoxic when applied to cochlear cultures preferentially damaging auditory nerve fibers at low concentrations and hair cells at high concentrations. Carboplatin, considered far less ototoxic than cisplatin, is paradoxically highly toxic to chinchilla inner hair cells and type I spiral ganglion neurons; however, at high doses it also damages outer hair cells. Hair cell death from cisplatin and carboplatin is characterized in its early stages by upregulation of p53; blocking p53 expression with pifithrin-α prevents hair cell death. Major differences in the toxicity of these four platinum compounds may arise from several different metal transporters that selectively regulate the influx, efflux, and sequestration of these drugs.

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

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.

Cisplatin-induced ototoxicity: morphological evidence of spontaneous outer hair cell recovery in albino guinea pigs?

Cisplatin is frequently used in the treatment of various forms of malignancies. Its therapeutic efficacy, however, is limited by the occurrence of sensorineural hearing loss. Little is known about the course of hearing loss over longer time intervals after cessation of cisplatin administration. Infrequently, recovery of hearing has been described in animals and humans. Stengs et al. (1997) treated guinea pigs with cisplatin at a daily dose of 1.5 mg/kg for 8 consecutive days and subsequently studied cochlear function after survival times varying from 1 day to 16 weeks. Spontaneous improvement of the hair cell-related potentials (cochlear microphonics and summating potentials) was observed starting 2 weeks after cessation of treatment. In the present study we examined light microscopically the cochleas used in the study of Stengs et al. (1997). One day after cessation of cisplatin administration outer hair cell (OHC) loss in the basal cochlear turn averaged 66%. In the 1-week survival group, OHC counts were similar to those of the 1-day survival group. In the 4-week survival group, however, a relatively small loss of OHCs was found in the basal cochlear turn; OHC loss averaged only 15%. A similar loss was found after 8 weeks. In the 16-week survival group, OHC loss in the basal turn increased to 48%, but this was not statistically significant. Our histological observations are in line with the electrophysiological data from the same animals. Our findings suggest that OHCs recover from cisplatin-induced damage 1-4 weeks after treatment. However, the results do not allow a conclusion as to whether the observed recovery is due to the formation of new OHCs or to (self-)repair of damaged OHCs.

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).

Experimental model of cisplatin ototoxicity in chinchillas

Cisplatin is an important antineoplastic agent. Its ototoxicity has been well defined, both in human and animal studies. However, animal models of systemic cisplatin administration have been complicated by multiple toxic effects. We studied cisplatin ototoxicity in an animal model involving topical application of cisplatin to the round-window membrane. Adult chinchillas were anesthetized with ketamine and pentobarbital, and auditory function was tested with the use of auditory brain-stem responses to various stimuli (clicks and 8-and 16-kHz tone bursts). Each animal was used as its own control. The middle-ear cavity was exposed through the bulla. In the experimental ear, a 25-microl solution of 0.25 mg cisplatin/1.0 ml normal saline solution was applied to the round-window membrane. In the control ear, 25 microl normal saline solution was applied to the round-window membrane. Follow-up auditory brain-stem response testing was conducted 7 days after treatment. A significant increase in threshold in the experimental ears was seen on comparison with the control ears. This finding suggests that application of cisplatin to the round-window membrane is a useful animal model in which to study cisplatin ototoxicity.

Co-administration of the neurotrophic ACTH(4-9) analogue, ORG 2766, may reduce the cochleotoxic effects of cisplatin

In this study the effect of the neurotrophic ACTH(4-9) analogue, ORG 2766, on cisplatin cochleotoxicity was investigated with both light- and transmission electron microscopy. Guinea pigs were treated with either cisplatin+ORG 2766 (n = 11) or cisplatin + physiological saline (n = 9). All animals treated with cisplatin + physiological saline showed complete loss of outer hair cells (OHC) and degeneration of the organ of Corti in the basal cochlear turns, while partial OHC loss was found in the middle and apical turns. The inner hair cells (IHC) and other cochlear tissues were not affected. Eight animals from the group treated with cisplatin + ORG 2766 demonstrated similar pathological changes, but to a lesser degree, especially in the middle turns. The three remaining animals demonstrated no cochlear alterations at all, light-microscopically, and only minor subcellular changes in the OHCs at the ultrastructural level. Electrophysiologically, these three animals showed normals compound action potential (CAP) amplitudes at stimulus frequencies from 0.5 to 16 kHz and normal cochlear microphonics (CM) in the frequency range from 0.5 to 8 kHz. The other animals treated with cisplatin + ORG 2766 showed a severe loss in their CAPs and CM, except for one showing intermediate loss. All animals from the group treated with cisplatin alone showed a severe loss in their CAPs and CM. Endolymphatic hydrops was present in all animals from the cisplatin- and the cisplatin + ORG 2766-treated groups. These data indicate that daily, concomitant administration of ORG 2766 may reduce OHC loss and subsequent degeneration of the organ of Corti in cisplatin-treated guinea pig cochleas.

Pantothenic acid and coenzyme A in experimental cisplatin-induced ototoxia

We have observed that pantothenic acid (PA) prevents deafness induced by cisplatin (CP) in the guinea pig if both drugs are administered jointly. When deafness was previously produced, recovery was sometimes obtained after the administration of PA; so, we studied the effects of PA on cisplatian-induced ototoxia in guinea pigs, both as a prophylactic agent in healthy animals, and as a therapeutic agent in animals previously made deaf by the drug. To elucidate why PA protects the ear from the toxic effects of CP, we used coenzyme A (CoA) instead of PA-since PA is a component of CoA-to test the hypothesis that the action of PA is due to CoA. The results were practically the same in both experiences, the compound action potential of the auditory nerve (CAP) was tested and cochleas were examined by scanning electron microscopy (SEM). Our results suggest that the protective effect of PA takes place through CoA. Both substances had the same effect on CP ototoxicity, but CoA appears to be much more active, since the dose tested here was much lower than that of PA.