Effects of Intratympanic Dexamethasone on High-Dose Radiation Ototoxicity In Vivo

Reactive Oxygen Species-Related Disruptions to Cochlear Hair Cell and Stria Vascularis Consequently Leading to Radiation-Induced Sensorineural Hearing Loss

Aims: Radiation-induced sensorineural hearing loss (RISNHL) is one of the major side effects of radiotherapy for head and neck cancers. At present, no effective clinical treatment or prevention is available for RISNHL. This study thus aimed to investigate the cochlear pathology so that the underlying mechanisms of RISNHL may be elucidated, consequently paving the way for potential protective strategies to be developed. Results: Functional and morphological impairment in the stria vascularis (SV) was observed after irradiation (IR), as indicated by endocochlear potential (EP) reduction, hyperpermeability, and SV atrophy. The expression of zonulae occludins-1 was found to have decreased after IR. The loss of outer hair cells (OHCs) occurred later than SV damage. The disruption to the SV and OHCs could be attributed to reactive oxygen species (ROS)-related damage. In addition, EP shifts and the loss of OHCs were reduced when ROS was reduced by N-acetylcysteine (NAC) in C57BL/6 mice, attenuating auditory threshold shifts. Innovation: The damage to the SV was found to occur before OHC loss. ROS-related damage accounted for SV damage and OHC loss. The incidences of SV damage and OHC loss were decreased through ROS modulation by NAC, subsequently preventing RISNHL, suggesting the possible role of NAC as a possible protective agent against RISNHL. Conclusion: The findings from this study suggest oxidative stress-induced early SV injury and late OHC loss to be the key factors leading to RISNHL. NAC prevents IR-induced OHC loss, and attenuates auditory brainstem response and EP shifts by regulating the level of oxidative stress. Antioxid. Redox Signal. 40, 470-491.

Single Fraction and Hypofractionated Radiation Cause Cochlear Damage, Hearing Loss, and Reduced Viability of Merlin-Deficient Schwann Cells

BACKGROUND

Vestibular schwannomas (VS) are benign intracranial tumors caused by loss of function of the merlin tumor suppressor. We tested three hypotheses related to radiation, hearing loss (HL), and VS cell survival: (1) radiation causes HL by injuring auditory hair cells (AHC), (2) fractionation reduces radiation-induced HL, and (3) single fraction and equivalent appropriately dosed multi-fractions are equally effective at controlling VS growth. We investigated the effects of single fraction and hypofractionated radiation on hearing thresholds in rats, cell death pathways in rat cochleae, and viability of human merlin-deficient Schwann cells (MD-SC).

METHODS

Adult rats received cochlear irradiation with single fraction (0 to 18 Gray [Gy]) or hypofractionated radiation. Auditory brainstem response (ABR) testing was performed for 24 weeks. AHC viabilities were determined using immunohistochemistry. Neonatal rat cochleae were harvested after irradiation, and gene- and cell-based assays were conducted. MD-SCs were irradiated, and viability assays and immunofluorescence for DNA damage and cell cycle markers were performed.

RESULTS

Radiation caused dose-dependent and progressive HL in rats and AHC losses by promoting expression of apoptosis-associated genes and proteins. When compared to 12 Gy single fraction, hypofractionation caused smaller ABR threshold and pure tone average shifts and was more effective at reducing MD-SC viability.

CONCLUSIONS

Investigations into the mechanisms of radiation ototoxicity and VS radiobiology will help determine optimal radiation regimens and identify potential therapies to mitigate radiation-induced HL and improve VS tumor control.

Combination of Vinpocetine and Dexamethasone Alleviates Cognitive Impairment in Nasopharyngeal Carcinoma Patients following Radiation Injury

BACKGROUND

Nasopharyngeal carcinoma (NPC) originates in the nasopharyngeal epithelium. The most common treatments for NPC rT1-4 are radiotherapy and surgery. The pathogenesis of radiation-induced cognitive impairment is complex and includes oxidative stress, mitochondrial dysfunction, neuro-inflammation, and even apoptosis and cell death. Principally, toll-like receptors (TLRs) could regulate the inflammatory/anti-inflammatory balance in patients with radiation-induced brain injury. Vinpocetine has an anti-inflammatory effect as shown in both animal and in vitro studies. Also, dexamethasone is a widely used anti-inflammatory drug. Thus, it is important to test whether addition of vinpocetine could improve the anti-inflammatory properties of dexamethasone for the treatment of NPC patients with radiation-induced brain injuries.

METHODS

A total of 60 NPC patients with radiation-related brain injury were recruited for this study. All subjects were randomly and blindly assigned to the following groups: the dexamethasone group (D group, n = 30) and the vinpocetine and dexamethasone group (VD group, n = 30). Both medicine treatments were uninterrupted for 14 days of administration.

RESULTS

Combined administration of vinpocetine and dexamethasone lowered the expression levels of serum inflammatory cytokines, including TLR2, TLR4, interleukin (IL)-20, IL-8, tumor necrosis factor-α, interferon-γ, monocyte chemoattractant protein 2, and interferon-induced protein 20, when compared to dexamethasone monotherapy. Notably, combination therapy increased antioxidants (superoxide dismutase, glutathione, glutathione peroxidase, and glutathione reductase) and decreased oxidants (thiobarbituric acid reactive substances). Furthermore, combination therapy significantly increased the Mini Mental State Examination score, when compared to dexamethasone monotherapy.

CONCLUSION

Administration of a combination of vinpocetine and dexamethasone may enhance the anti-inflammatory and anti-oxidative effects when compared to dexamethasone monotherapy, which leads to alleviated cognitive impairment in NPC patients with radiation injury.

Efficacy of 2 Different Intratympanic Steroid Regimen on Prevention of Cisplatin Ototoxicity: An Experimental Study

Ototoxicity is the general name of cochlear and vestibular organ injury resulting from encountering various therapeutic agents and chemical substances. Cisplatin is commonly used in the treatment of many cancers. In this study, the efficacy of intratympanic steroids was compared for preventing cisplatin ototoxicity. In this study, 32 (64 ears) rats were used by separating into 4 groups. Cisplatin was administered intraperitoneally to the first group (n = 8). Methylprednisolone and then cisplatin were administered intratympanically to the second group (n = 8). On the third group (n = 8), dexamethasone and then cisplatin were administered intratympanically. To the fourth group (n = 8), 0.9% NaCl and then cisplatin were given intratympanically. Otoacoustic emission (OAE) measurements and auditory brainstem responses (ABRs) tests were performed on all groups before and 72 hours after the procedure. Pretreatment of ABR-IV values were 4.29 ± 0.19 milliseconds in group 2 and 4.27 ± 0.16 milliseconds in group 3, whereas posttreatment ABR-IV values were 4.95 ± 0.35 milliseconds in group 2 and 4.65 ± 0.26 milliseconds in group 3. The ABR-IV values were measured significantly shorter in the rats given dexamethasone and methylprednisolone, according to control and cisplatin groups (P < .001). Pretreatment of ABR I-IV interval values were 2.98 ± 0.34 milliseconds and 3.03 ± 0.42 milliseconds in group 1 and group 4, respectively, and ABR I-IV interval values in group 1 and group 4 posttreatment were 3.49 ± 0.39 milliseconds and 3.5 ± 0.39 milliseconds in group 1 and group 4, respectively. Auditory brainstem responses I-IV interval was significantly longer in the cisplatin and control group than in the rats given dexamethasone and methylprednisolone (P < .001). After cisplatin treatment, OAE amplitudes decreased significantly in group 1 and group 4 for all frequencies, while OAE values were protected in methylprednisolone and dexamethasone group (P < .001). In conclusion, it has been shown that both agents have protective effects on cisplatin ototoxicity, with dexamethasone slightly more than methylprednisolone.