Ototoxic effects of carboplatin in organotypic cultures in chinchillas and rats

Abstract

Carboplatin, a second-generation platinum chemotherapeutic drug, is considerably less ototoxic than cisplatin. While common laboratory species such as mice, guinea pigs and rats are highly resistant to carboplatin ototoxicity, the chinchilla stands out as highly susceptible. Moreover, carboplatin causes an unusual gradient of cell death in chinchillas. Moderate doses selectively damage type I spiral ganglion neurons (SGN) and inner hair cells (IHC) and the lesion tends to be relatively uniform along the length of the cochlea. Higher doses eventually damage outer hair cells (OHC), but the lesion follows the traditional gradient in which damage is more severe in the base than the apex. While carboplatin ototoxicity has been well documented in adult animals in vivo, little is known about its in vitro toxicity. To elucidate the ototoxic effects of carboplatin in vitro, we prepared cochlear and vestibular organotypic cultures from postnatal day 3 rats and adult chinchillas. Chinchilla cochlear and vestibular cultures were treated with carboplatin concentrations ranging from 50 µM to 10 mM for 48 h. Consistent with in vivo data, carboplatin selectively damaged IHC at low concentrations (50–100 µM). Surprisingly, IHC loss decreased at higher doses and IHC were intact at doses exceeding 500 µM. The mechanisms underlying this nonlinear response are unclear but could be related to a decrease in carboplatin uptake via active transport mechanisms (e.g., copper). Unlike the cochlea, the carboplatin dose-response function increased with dose with the highest dose destroying all chinchilla vestibular hair cells. Cochlear hair cells and auditory nerve fibers in rat cochlear organotypic cultures were unaffected by carboplatin concentrations <10 µM; however, the damage in OHC were more severe than IHC once the dose reached 100 µM. A dose at 500 µM destroyed all the cochlear hair cells, but hair cell loss decreased at high concentrations and nearly all the cochlear hair cells were present at the highest dose, 5 mM. Unlike the nonlinear dose-response seen with cochlear hair cells, rat auditory nerve fiber and spiral ganglion losses increased with doses above 50 µM with the highest dose destroying virtually all SGN. The remarkable species differences seen in vitro suggest that chinchilla IHC and type I SGN posse some unique biological mechanism that makes them especially vulnerable to carboplatin toxicity.

Low, but Not High, Doses of Cisplatin Damage Cochlear Hair Cells in C57 Mouse Organotypic Cultures

“…Our results suggest that a peak concentration of cisplatin induces the most severe damage to hair cells, and that hair cells are able to resist damage at higher concentrations which coincides with the reports performed on rats and chinchilla [14,24,25,26]. This unexpected finding may be related to the mechanism of cisplatin resistance, which involves transport of the compound into cells.…”

Kanamycin Damages Early Postnatal, but Not Adult Spiral Ganglion Neurons

“…Our procedures for preparing organotypic cultures from postnatal and adult animals have been described in prior publications (Ding et al, 2012, Ding et al, 2013b, Wei et al, 2010). In brief, animals were euthanized with an overdose of CO 2 , decapitated and the cochleae quickly removed.…”

“…Our procedures for preparing and culturing adult whole cochlear explants have been described previously (Ding et al, 2012). In adult rats, the bony cochlea was removed from the temporal bone after decapitation, and perforations were carefully made along the bony surface of cochlear spiral shell in order to permit the flow of culture medium into the tissue.…”

Audiological Monitoring in Children Treated with Platinum Chemotherapy

“…On the contrary, there are significant differences in carboplatin ototoxicity among different animal species: higher doses of carboplatin damage OHCs in mice, rats and guinea pigs, while in chinchillas it preferentially destroys inner hair cells and type-I spiral ganglion neurons [Ding et al, 1999;Dalian et al, 2012]. However, in clinical studies, carboplatin affects OHCs, as shown by the loss of distortion product otoacoustic emissions (OAEs) [Reavis et al, 2008].…”