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Anti-apoptotic effect of dexamethasone in an ototoxicity model

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


Cochlea histology in mice exposed to 0.3 mM GM and dose-dependence of DEX treatment. Phalloidin stained cochlear explant cultures of postnatal day-4-old mice pretreated with PBS (a), 0.3 mM GM only (b), 1 μg/mL DEX (c), 5 μg/mL DEX (d), 10 μg/mL DEX (e), 30 μg/mL DEX (f), 50 μg/mL DEX (g), and 300 μg/mL DEX (h) (400x magnification)
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Fig2: Cochlea histology in mice exposed to 0.3 mM GM and dose-dependence of DEX treatment. Phalloidin stained cochlear explant cultures of postnatal day-4-old mice pretreated with PBS (a), 0.3 mM GM only (b), 1 μg/mL DEX (c), 5 μg/mL DEX (d), 10 μg/mL DEX (e), 30 μg/mL DEX (f), 50 μg/mL DEX (g), and 300 μg/mL DEX (h) (400x magnification)

Mentions: Cochlear cultures from postnatal mice were pretreated with medium containing DEX at concentrations of 0, 1, 5, 10, 30, 50, and 100 μg/mL and then exposed to a medium containing 0.3 mM GM for 24 h. The specific concentration of GM (0.3 mM) to affect inner or outer HC loss was determined from our previous works [1, 14]. Compared with the control group, IHCs and OHCs of the organ of Corti in the GM-only group were destroyed. Viable phalloidin-labeled hair cells were counted and shown in Fig. 1. A dose-dependent protective effect of DEX was evident. Compared to use of GM alone, pretreatment with DEX concentrations exceeding 5 ug/mL were significantly protective (p < 0.005; Fig. 1). The images of phalloidin stained cochlear explant also showed that DEX pretreatment reduced the GM-induced ototoxicity in a dose-dependent manner. GM alone group severely distorted the anatomy of the organ of corti, compared with untreated controls. However, above 5 ug/mL of DEX effectively provided protection against GM-induced ototoxicity. The alignment of bundles in the organ of Corti was retained their shape by the highest DEX (300 μg/mL) pretreatment in GM-induced ototoxicity (Fig. 2). Taken together, these results indicated that DEX was significantly protective against GM-induced hair cell loss.Fig. 1


Anti-apoptotic effect of dexamethasone in an ototoxicity model
Cochlea histology in mice exposed to 0.3 mM GM and dose-dependence of DEX treatment. Phalloidin stained cochlear explant cultures of postnatal day-4-old mice pretreated with PBS (a), 0.3 mM GM only (b), 1 μg/mL DEX (c), 5 μg/mL DEX (d), 10 μg/mL DEX (e), 30 μg/mL DEX (f), 50 μg/mL DEX (g), and 300 μg/mL DEX (h) (400x magnification)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5383979&req=5

Fig2: Cochlea histology in mice exposed to 0.3 mM GM and dose-dependence of DEX treatment. Phalloidin stained cochlear explant cultures of postnatal day-4-old mice pretreated with PBS (a), 0.3 mM GM only (b), 1 μg/mL DEX (c), 5 μg/mL DEX (d), 10 μg/mL DEX (e), 30 μg/mL DEX (f), 50 μg/mL DEX (g), and 300 μg/mL DEX (h) (400x magnification)
Mentions: Cochlear cultures from postnatal mice were pretreated with medium containing DEX at concentrations of 0, 1, 5, 10, 30, 50, and 100 μg/mL and then exposed to a medium containing 0.3 mM GM for 24 h. The specific concentration of GM (0.3 mM) to affect inner or outer HC loss was determined from our previous works [1, 14]. Compared with the control group, IHCs and OHCs of the organ of Corti in the GM-only group were destroyed. Viable phalloidin-labeled hair cells were counted and shown in Fig. 1. A dose-dependent protective effect of DEX was evident. Compared to use of GM alone, pretreatment with DEX concentrations exceeding 5 ug/mL were significantly protective (p < 0.005; Fig. 1). The images of phalloidin stained cochlear explant also showed that DEX pretreatment reduced the GM-induced ototoxicity in a dose-dependent manner. GM alone group severely distorted the anatomy of the organ of corti, compared with untreated controls. However, above 5 ug/mL of DEX effectively provided protection against GM-induced ototoxicity. The alignment of bundles in the organ of Corti was retained their shape by the highest DEX (300 μg/mL) pretreatment in GM-induced ototoxicity (Fig. 2). Taken together, these results indicated that DEX was significantly protective against GM-induced hair cell loss.Fig. 1

View Article: PubMed Central - PubMed

ABSTRACT

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&ndash;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 &mu;g/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.

No MeSH data available.