Protective effect of hexane and ethanol extract of piper longum L. On gentamicin-induced hair cell loss in neonatal cultures

The Inner Ear Heat Shock Transcriptional Signature Identifies Compounds That Protect Against Aminoglycoside Ototoxicity

Mechanosensory hair cells of the inner ear transduce auditory and vestibular sensory input. Hair cells are susceptible to death from a variety of stressors, including treatment with therapeutic drugs that have ototoxic side effects. There is a need for co-therapies to mitigate drug-induced ototoxicity, and we showed previously that induction of heat shock proteins (HSPs) protects against hair cell death and hearing loss caused by aminoglycoside antibiotics in mouse. Here, we utilized the library of integrated cellular signatures (LINCS) to identify perturbagens that induce transcriptional profiles similar to that of heat shock. Massively parallel sequencing of RNA (RNA-Seq) of heat shocked and control mouse utricles provided a heat shock gene expression signature that was used in conjunction with LINCS to identify candidate perturbagens, several of which were known to protect the inner ear. Our data indicate that LINCS is a useful tool to screen for compounds that generate specific gene expression signatures in the inner ear. Forty-two LINCS-identified perturbagens were tested for otoprotection in zebrafish, and three of these were protective. These compounds also induced the heat shock gene expression signature in mouse utricles, and one compound protected against aminoglycoside-induced hair cell death in whole organ cultures of utricles from adult mice.

Autophagy-related protein 12 associates with anti-apoptotic B cell lymphoma-2 to promote apoptosis in gentamicin-induced inner ear hair cell loss

The aim of the present study was to investigate the underlying mechanisms of autophagy in a gentamicin (GM)-induced ototoxic model, and to establish whether the blocking of autophagy significantly increases the survival of inner ear hair cells. Cochleae were carefully dissected from four day‑old C57BL/6J mice and randomly divided into three groups prior to explant culture: Control (culture medium), GM‑treated (culture medium + GM) and GM + 3-methyladenine (3-MA; culture medium + GM + 3‑MA). Transmission electron microscopy, immunofluorescence and western blotting were performed to observe the expression of the autophagy protein microtubule‑associated protein 1A/B‑light chain 3 in explant cultures treated with GM and the autophagy inhibitor 3‑MA. Administration of GM in in vitro mouse cochlear culture induced apoptosis and the formation of autophagic vesicles and autophagosomes in hair cells. Notably, combined treatment with GM and 3‑MA to block autophagy significantly increased the survival of inner ear hair cells. Furthermore, it was indicated that the simultaneous expression and interaction of Atg12 with Bcl‑2 following GM treatment co‑integrated autophagy with apoptosis in the cochlea. The results of the present study demonstrated that autophagy was involved in GM-induced ototoxicity. Additionally, Atg12 may serve a protective role by binding to Bcl‑2. Therefore, Atg12 may be a potential therapeutic target for the treatment of GM-induced cochlear hair loss.

Anti-apoptotic effect of dexamethasone in an ototoxicity model

Background

Dexamethasone (DEX) is used for the treatment of various inner ear diseases. However, the molecular mechanism of DEX on gentamicin induced hair cell damage is not known. Therefore, this study investigated the protective effect of DEX on gentamicin (GM)-induced ototoxicity and the effect of GM on the expression of apoptosis related genes.

Methods

The protective effects of DEX were measured by phalloidin staining of explant cultures of organ of Corti from postnatal day 2–3 mice with GM-induced hair cell loss. Terminal deoxynucleotidyl transferase dUTP nick end labeling staining was used to detect apoptosis and immunofluorescence was done to analyze the effect of DEX on the expression of apoptosis related genes.

Results

Cochlear explant cultures of postnatal day-4-old mice were exposed to 0, 1, 5, 10, 30, 50, and 100 μg/ml DEX and GM during culture. DEX protected from GM-induced hair cell loss in the inner ear of postnatal day 4 mice. To understand the molecular mechanisms by which DEX pre-treatment decreased hair cell loss, the testes of cochlear explant cultures of postnatal day 4 mice were examined for changes in expression of cochlear apoptosis mediators. The pro-apoptotic protein Bax was significantly down-regulated and numbers of apoptotic hair cells were decreased.

Conclusions

DEX has a protective effect on GM-induced hair cell loss in neonatal cochlea cultures and the protective mechanism may involve inhibition of the mitochondrial apoptosis pathway. The combination with scaffold technique can improve delivery of DEX into the inner ear to protect GM-induced ototoxicity.

Histone deacetylase inhibitor sodium butyrate attenuates gentamicin-induced hearing loss in vivo

OBJECTIVE

Although histone deacetylase (HDAC) inhibition has been shown to protect against gentamicin (GM)-induced hearing loss in vitro, its protective effect has not been proven in vivo. In the present study, the aim was to investigate the protective effect of sodium butyrate (NaB), a specific HDAC inhibitor, on GM-induced ototoxicity in vivo.

METHODS

Forty 8-week-old albino guinea pigs were divided into two experimental groups. Group 1 (n=10) underwent bilateral ear surgery to place sponges (0.3mm(3)) permeated with NaB (10μl, 100mg/ml) and physiological saline (10μl; control) in the right and left round window niches, respectively. The sponges were left in place for 15days to evaluate the effects of NaB at the applied concentration. Group 2 (n=30) underwent the same bilateral ear surgery described for Group 1, except three days after surgery, the animals received intramuscular GM injections (200mg/kg/day) for 5 consecutive days. Seven days after the final GM injection, the protective effects of NaB were examined.

RESULTS

After 15days of NaB treatment (10μl, 100mg/ml), an increase in histone acetylation was detected in Corti organ samples. Auditory brainstem response (ABR) threshold shifts and hair cell loss were also reduced in NaB-treated ears after GM administration. Furthermore, GM treatment increased HDAC1 expression in outer hair cells (OHCs) in vivo, and NaB blocked this action.

CONCLUSION

GM increases HDAC1 expression in OHCs, and NaB is able to block this action. Thus, it appears that the HDAC inhibitor, NaB, attenuates GM-induced hearing loss in guinea pigs.