Addition of Exogenous NAD+ Prevents Mefloquine-Induced Neuroaxonal and Hair Cell Degeneration through Reduction of Caspase-3-Mediated Apoptosis in Cochlear Organotypic Cultures

Abstract

BackgroundMefloquine is widely used for the treatment of malaria. However, this drug is known to induce neurological side effects including depression, anxiety, balance disorder, and sensorineural hearing loss. Yet, there is currently no treatment for these side effects.Principal FindingsIn this study, we show that the coenzyme NAD+, known to play a critical role in maintaining the appropriate cellular redox environment, protects cochlear axons and sensory hair cells from mefloquine-induced degeneration in cultured rat cochleae. Mefloquine alone destroyed hair cells and nerve fiber axons in rat cochlear organotypics cultures in a dose-dependent manner, while treatment with NAD+ protected axons and hair cells from mefloquine-induced degeneration. Furthermore, cochlear organs treated with mefloquine showed increased oxidative stress marker levels, including superoxide and protein carbonyl, and increased apoptosis marker levels, including TUNEL-positive nuclei and caspases-3. Treatment with NAD+ reduced the levels of these oxidative stress and apoptosis markers.Conclusions/SignificanceTaken together, our findings suggest that that mefloquine disrupts the cellular redox environment and induces oxidative stress in cochlear hair cells and nerve fibers leading to caspases-3-mediated apoptosis of these structures. Exogenous NAD+ suppresses mefloquine-induced oxidative stress and prevents the degeneration of cochlear axons and sensory hair cells caused by mefloquine treatment.

Effects of Long-Term Exercise on Age-Related Hearing Loss in Mice

“…In agreement with these reports, elevated levels of CRP, polymorphisms of TNF receptors, and genes involved in immunity were associated with the incidence of hearing impairment among older adults. (Dong et al, 2014;Nash et al, 2014;Uchida et al, 2014), whereas elevated markers of inflammatory status such as white blood cell count, neutrophil count, IL-6, and CRP were associated with degree of hearing loss in older people in the United Kingdom (Verschuur et al, 2012). In laboratory mice, an age-related elevation of the proinflammatory markers TNF-␣ and IL-1b was observed in the cochlea of SAMP8 mice, a mouse model of early-onset AHL (Menardo et al, 2012).…”

“…The number of IHC, first-row OHCs (OHC1), secondrow OHCs (OHC2), and third-row OHCs (OHC3) were counted over 0.24 mm intervals along the entire length of the cochlea under the microscope at 400ϫ magnification as described previously Ding et al, 2013). The counting results were then entered into a custom computer program designed to compute a cochleogram that shows the number of missing IHC and OHC1-3 as a function of percentage distance from the apex of the cochlea.…”

“…The counting results were then entered into a custom computer program designed to compute a cochleogram that shows the number of missing IHC and OHC1-3 as a function of percentage distance from the apex of the cochlea. A frequency-place map for mouse cochlea is shown on the abscissa in the figures as described previously (Müller et al, 2005;Ding et al, 2016).…”

“…To visualize capillaries in the SV, endomucin, a marker of endothelial cells, was stained on paraffin-embedded cochlear sections as described previously (Doebele et al, 2010;Zahr et al, 2016). Briefly, cochlear sections were rehydrated and subjected to antigen retrieval (0.01 M Na citrate, pH 6.0, for 30 min at 60°C) and then incubated with rat anti-mouse endomucin antibodies (dilution 1:250; Santa Cruz Biotechnology).…”

G6pd Deficiency Does Not Affect the Cytosolic Glutathione or Thioredoxin Antioxidant Defense in Mouse Cochlea

“…At 3-5 months of age, ABRs were measured with a tone burst stimulus at 4,8,16,32,48, and 64 kHz using the TDT neurophysiology workstation (Tucker-Davis Technologies) in a sound isolation booth as previously described (Han et al, 2016). Mice were anesthetized with a mixture of xylazine hydrochloride (10 mg/kg, i.m.)…”