Cisplatin-induced vestibular hair cell lesion-less damage at high doses

Three-dimensional cultured ampullae from rats as a screening tool for vestibulotoxicity: Proof of concept using styrene

Numerous ototoxic drugs, such as some antibiotics and chemotherapeutics, are both cochleotoxic and vestibulotoxic (causing hearing loss and vestibular disorders). However, the impact of some industrial cochleotoxic compounds on the vestibular receptor, if any, remains unknown. As in vivo studies are long and expensive, there is considerable need for predictive and cost-effective in vitro models to test ototoxicity. Here, we present an organotypic model of cultured ampullae harvested from rat neonates. When cultured in a gelatinous matrix, ampulla explants form an enclosed compartment that progressively fills with a high-potassium (K+) endolymph-like fluid. Morphological analyses confirmed the presence of a number of cell types, sensory epithelium, secretory cells, and canalar cells. Treatments with inhibitors of potassium transporters demonstrated that the potassium homeostasis mechanisms were functional. To assess the potential of this model to reveal the toxic effects of chemicals, explants were exposed for either 2 or 72 h to styrene at a range of concentrations (0.5-1 mM). In the 2-h exposure condition, K+ concentration was significantly reduced, but ATP levels remained stable, and no histological damage was visible. After 72 h exposure, variations in K+ concentration were associated with histological damage and decreased ATP levels. This in vitro 3D neonatal rat ampulla model therefore represents a reliable and rapid means to assess the toxic properties of industrial compounds on this vestibular tissue, and can be used to investigate the specific underlying mechanisms.

Progress in protecting vestibular hair cells

Vestibular hair cells are mechanosensory receptors that are capable of detecting changes in head position and thereby allow animals to maintain their posture and coordinate their movement. Vestibular hair cells are susceptible to ototoxic drugs, aging, and genetic factors that can lead to permanent vestibular dysfunction. Vestibular dysfunction mainly results from the injury of hair cells, which are located in the vestibular sensory epithelium. This review summarizes the mechanisms of different factors causing vestibular hair cell damage and therapeutic strategies to protect vestibular hair cells.

Cisplatin ototoxicity histopathology

This study investigates the histopathological changes of the cochlea and vestibular end organs of a patient who received cisplatin for Hodgkin's lymphoma. He experienced acute high-frequency sensorineural hearing loss and tinnitus after receiving treatment. Using histopathological analysis of his temporal bones after he unfortunately succumbed to his disease, we found that the ototoxic effect of cisplatin is primarily within the cochlea, with significant damage located at the organ of Corti at the base-hook region, consistent with findings in animal models. The effects of cisplatin were minimal when reviewing the vestibular end organs.

Roles of Bak and Sirt3 in Paraquat-Induced Cochlear Hair Cell Damage

Paraquat, a superoxide generator, can damage the cochlea causing an ototoxic hearing loss. The purpose of the study was to determine if deletion of Bak, a pro-apoptotic gene, would reduce paraquat ototoxicity or if deletion of Sirt3, which delays age-related hearing loss under caloric restriction, would increase paraquat ototoxicity. We tested these two hypotheses by treating postnatal day 3 cochlear cultures from Bak^±, Bak^-/-, Sirt3^±, Sirt3^-/-, and WT mice with paraquat and compared the results to a standard rat model of paraquat ototoxicity. Paraquat damaged nerve fibers and dose-dependently destroyed rat outer hair cells (OHCs) and inner hair cells (IHCs). Rat hair cell loss began in the base of the cochlea with a 10 μM dose and as the dose increased from 50 to 500 μM, the hair cell loss increased near the base of the cochlea and spread toward the apex of the cochlea. Rat OHC losses were consistently greater than IHC losses. Unexpectedly, in all mouse genotypes, paraquat-induced hair cell lesions were maximal near the apex of the cochlea and minimal near the base. This unusual damage gradient is opposite to that seen in paraquat-treated rats and in mice and rats treated with other ototoxic drugs. However, paraquat always induced greater OHC loss than IHC loss in all mouse strains. Contrary to our hypothesis, Bak deficient mice were more vulnerable to paraquat ototoxicity than WT mice (Bak^-/- > Bak^± > WT), suggesting that Bak plays a protective role against hair cell stress. Also, contrary to expectation, Sirt3-deficient mice did not differ significantly from WT mice, possibly due to the fact that Sirt3 was not experimentally upregulated in Sirt3-expressing mice prior to paraquat treatment. Our results show for the first time a gradient of ototoxic damage in mice that is greater in the apex than the base of the cochlea.

Cisplatin-induced ototoxicity: Updates on molecular mechanisms and otoprotective strategies

Cisplatin is a highly effective antitumor drug generally used in the treatment of solid malignant tumors. However, cisplatin causes severe side effects such as bone marrow depression, nephrotoxicity, and ototoxicity, thus limiting its clinical application. The incidence of ototoxicity induced by cisplatin ranges from 20% to 70%, and it usually manifests as a progressive, bilateral and irreversible hearing loss. Although the etiology of cisplatin-induced ototoxicity remains unclear, an increasing body of evidence suggests that the ototoxicity of cisplatin is mainly related to the production of reactive oxygen species and activation of apoptotic pathway in cochlear tissues. Many drugs have been well proved to protect cisplatin-induced hearing loss in vitro and in vivo. However, the anti-tumor effect of cisplatin is also weakened by systemic administration of those drugs for hearing protection, especially antioxidants. Therefore, establishing a local administration strategy contributes to the otoprotection without affecting the effect of cisplatin. This review introduces the pathology of ototoxicity caused by cisplatin, and focuses on recent developments in the mechanisms and protective strategies of cisplatin-induced ototoxicity.

Cochlear spiral ganglion neuron degeneration following cyclodextrin-induced hearing loss

Because cyclodextrins are capable of removing cholesterol from cell membranes, there is growing interest in using these compounds to treat diseases linked to aberrant cholesterol metabolism. One compound, 2-hydroxypropyl-beta-cyclodextrin (HPβCD), is currently being evaluated as a treatment for Niemann-Pick Type C1 disease, a rare, fatal neurodegenerative disease caused by the buildup of lipids in endosomes and lysosomes. HPβCD can reduce some debilitating symptoms and extend life span, but the therapeutic doses used to treat the disease cause hearing loss. Initial studies in rodents suggested that HPβCD selectively damaged only cochlear outer hair cells during the first week post-treatment. However, our recent in vivo and in vitro studies suggested that the damage could become progressively worse and more extensive over time. To test this hypothesis, we treated rats subcutaneously with 1, 2, 3 or 4 g/kg of HPβCD and waited for 8-weeks to assess the long-term histological consequences. Our new results indicate that the two highest doses of HPβCD caused extensive damage not only to OHC, but also to inner hair cells, pillar cells and other support cells resulting in the collapse and flattening of the sensory epithelium. The 4 g/kg dose destroyed all the outer hair cells and three-fourths of the inner hair cells over the basal two-thirds of the cochlea and more than 85% of the nerve fibers in the habenula perforata and more than 80% of spiral ganglion neurons in the middle of basal turn of the cochlea. The mechanisms that lead to the delayed degeneration of inner hair cells, pillar cells, nerve fibers and spiral ganglion neurons remain poorly understood, but may be related to the loss of trophic support caused by the degeneration of sensory and/or support cells in the organ of Corti. Despite the massive damage to the cochlear sensory epithelium, the blood vessels in the stria vascularis and the vestibular hair cells in the utricle and saccule remained normal.

Hydroxypropyl-β-cyclodextrin causes massive damage to the developing auditory and vestibular system

2-hydroxypropyl-β-cyclodextrin (HPβCD), a cholesterol chelator used to treat Niemann-Pick C1 (NPC1) lysosomal storage disease, causes hearing loss in mammals by preferentially destroying outer hair cells. Because cholesterol plays an important role in early neural development, we hypothesized that HPβCD would cause more extensive damage to postnatal cochlear and vestibular structures in than adult rats. This hypothesis was tested by administering HPβCD to adult rats and postnatal day 3 (P3) cochlear and vestibular organ cultures. Adult rats treated with HPβCD developed hearing impairment and outer hair cell loss 3-day post-treatment; damage increased with dose from the high frequency base toward the low-frequency apex. The HPβCD-induced histopathologies were more severe and widespread in cochlear and vestibular cultures at P3 than in adults. HPβCD destroyed both outer and inner hair cells, auditory nerve fibers and spiral ganglion neurons as well as type I and type II vestibular hair cells and vestibular ganglion neurons. The early stage of HPβCD damage involved disruption of hair cell mechanotransduction and destruction of stereocilia. HPβCD-mediated apoptosis in P3 cultures was most-strongly initiated by activation of the extrinsic caspase-8 cell death pathway in cochlear and vestibular hair cells and neurons followed by activation of executioner caspase-3. Thus, HPβCD is toxic to all types of postnatal cochlear and vestibular hair cells and neurons in vitro whereas in vivo it only appears to destroy outer hair cells in adult cochleae. The more severe HPβCD-induced damage in postnatal cultures could be due to greater drug bioavailability in vitro and/or greater vulnerability of the developing inner ear.

Prevalence and Predictors of Frailty in Childhood Cancer Survivors and Siblings: A Report From the Childhood Cancer Survivor Study

PURPOSE

To estimate the prevalence of frailty among childhood cancer survivors and to determine the direct and indirect effects of treatment exposures, lifestyle factors, and severe, disabling, and life-threatening chronic condition on frailty.

METHODS

Childhood cancer survivors (≥ 5 years since diagnosis), treated between 1970 and 1999 when < 21 years old (n = 10,899; mean age, 37.6 ± 9.4 years; 48% male, 86% white) and siblings were included (n = 2,097; mean age, 42.9 ± 9.4 years). Frailty was defined as ≥ 3 of the following: low lean mass, exhaustion, low energy expenditure, walking limitations, and weakness. Generalized linear models were used to evaluate direct and indirect associations between frailty and treatment exposures, sociodemographic characteristics, lifestyle factors, and chronic condition.

RESULTS

The overall prevalence of frailty among survivors was 3 times higher compared with siblings (6.4%; 95% CI, 4.1% to 8.7%; v 2.2%; 95% CI, 1.2% to 3.2%). Survivors of CNS tumors (9.5%; 95% CI, 5.2% to 13.8%) and bone tumors (8.1%; 95% CI, 5.1% to 11.1%) had the highest prevalence of frailty. Survivors exposed to cranial radiation, pelvic radiation ≥ 34 Gy, abdominal radiation > 40 Gy, cisplatin ≥ 600 mg/m², amputation, or lung surgery had increased risk for frailty. These associations were partially but not completely attenuated when sociodemographic characteristics, lifestyle factors, and chronic conditions were added to multivariable models. Cranial radiation (prevalence ratio [PR], 1.47; 95% CI, 1.20 to 1.76), pelvic radiation ≥ 34 Gy (PR, 1.46; 95% CI, 1.01 to 2.11), and lung surgery (PR, 1.75; 95% CI, 1.28 to 2.38) remained significant after sociodemographic, lifestyle, and chronic conditions were accounted for.

CONCLUSION

Childhood cancer survivors reported a higher prevalence of frailty compared with siblings. Radiation and lung surgery exposures were associated with increased risk for frailty. Interventions to prevent, delay onset, or remediate chronic disease and/or promote healthy lifestyle are needed to decrease the prevalence of frailty and preserve function in this at-risk population.

Antioxidative stress-induced damage in cochlear explants

The imbalance of reactive oxygen species and antioxidants is considered to be an important factor in the cellular injury of the inner ear. At present, great attention has been placed on oxidative stress. However, little is known about fighting oxidative stress. In the current study, we evaluated antioxidant-induced cochlear damage by applying several different additional antioxidants. To determine whether excessive antioxidants can cause damage to cochlear cells, we treated cochlear explants with 50 μM M40403, a superoxide dismutase mimetic, 50 μM coenzyme Q-10, a vitamin-like antioxidant, or 50 μM d-methionine, an essential amino acid and the important antioxidant glutathione for 48 h. Control cochlear explants without the antioxidant treatment maintained their normal structures after incubation in the standard serum-free medium for 48 h, indicating the maintenance of the inherent oxidative and antioxidant balance in these cochlear explants. In contrast, M40403 and coenzyme Q-10-treated cochlear explants displayed significant hair cell damage together with slight damage to the auditory nerve fibers. Moreover, d-methiodine-treated explants exhibited severe damage to the surface structure of hair cells and the complete loss of the spiral ganglion neurons and their peripheral fibers. These results indicate that excessive antioxidants are detrimental to cochlear cells, suggesting that inappropriate dosages of antioxidant treatments can interrupt the balance of the inherent oxidative and antioxidant capacity in the cell.