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Hepatocyte growth factor mimetic protects lateral line hair cells from aminoglycoside exposure.

Uribe PM, Kawas LH, Harding JW, Coffin AB - Front Cell Neurosci (2015)

Bottom Line: We found that a Dihexa concentration of 1 μM confers optimal protection from acute treatment with either ototoxin.Pretreatment with Dihexa does not affect the amount of fluorescently tagged gentamicin that enters hair cells, indicating that Dihexa's protection is likely mediated by intracellular events and not by inhibiting aminoglycoside entry.Our data suggest that Dihexa confers protection of hair cells through an HGF-mediated mechanism and that Dihexa holds clinical potential for mitigating chemical ototoxicity.

View Article: PubMed Central - PubMed

Affiliation: Department of Integrative Physiology and Neuroscience, Washington State University Pullman, WA, USA.

ABSTRACT
Loss of sensory hair cells from exposure to certain licit drugs (e.g., aminoglycoside antibiotics, platinum-based chemotherapy agents) can result in permanent hearing loss. Here we ask if allosteric activation of the hepatocyte growth factor (HGF) cascade via Dihexa, a small molecule drug candidate, can protect hair cells from aminoglycoside toxicity. Unlike native HGF, Dihexa is chemically stable and blood-brain barrier permeable. As a synthetic HGF mimetic, it forms a functional ligand by dimerizing with endogenous HGF to activate the HGF receptor and downstream signaling cascades. To evaluate Dihexa as a potential hair cell protectant, we used the larval zebrafish lateral line, which possesses hair cells that are homologous to mammalian inner ear hair cells and show similar responses to toxins. A dose-response relationship for Dihexa protection was established using two ototoxins, neomycin and gentamicin. We found that a Dihexa concentration of 1 μM confers optimal protection from acute treatment with either ototoxin. Pretreatment with Dihexa does not affect the amount of fluorescently tagged gentamicin that enters hair cells, indicating that Dihexa's protection is likely mediated by intracellular events and not by inhibiting aminoglycoside entry. Dihexa-mediated protection is attenuated by co-treatment with the HGF antagonist 6-AH, further evidence that HGF activation is a component of the observed protection. Additionally, Dihexa's robust protection is partially attenuated by co-treatment with inhibitors of the downstream HGF targets Akt, TOR and MEK. Addition of an amino group to the N-terminal of Dihexa also attenuates the protective response, suggesting that even small substitutions greatly alter the specificity of Dihexa for its target. Our data suggest that Dihexa confers protection of hair cells through an HGF-mediated mechanism and that Dihexa holds clinical potential for mitigating chemical ototoxicity.

No MeSH data available.


Related in: MedlinePlus

Dihexa treatment prevents neomycin-induced hair cell loss in Brn3c:mGFP transgenic larvae. (A) DMSO-treated control, (B) 400 μM neomycin treated neuromast shows a reduction in hair cells, and (C) neuromasts treated with 1 μM Dihexa plus 400 μM neomycin remain mostly intact. (D) 1 μM Dihexa provides protection from neomycin-induced hair cell loss across the neomycin dose-response curve (Two-way ANOVA; Dihexa: F(1,456) = 50.77 p < 0.001). Asterisks indicate significant difference from neomycin control (**p < 0.01, ****p < 0.001). N = 8–10 animals per treatment, error bars represent ± s.e.m.
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Figure 3: Dihexa treatment prevents neomycin-induced hair cell loss in Brn3c:mGFP transgenic larvae. (A) DMSO-treated control, (B) 400 μM neomycin treated neuromast shows a reduction in hair cells, and (C) neuromasts treated with 1 μM Dihexa plus 400 μM neomycin remain mostly intact. (D) 1 μM Dihexa provides protection from neomycin-induced hair cell loss across the neomycin dose-response curve (Two-way ANOVA; Dihexa: F(1,456) = 50.77 p < 0.001). Asterisks indicate significant difference from neomycin control (**p < 0.01, ****p < 0.001). N = 8–10 animals per treatment, error bars represent ± s.e.m.

Mentions: To verify DASPEI scores, fish from the same treatment groups were fixed and immunohistochemically processed with anti-parvalbumin (Millipore) to visualize hair cells (see Coffin et al., 2013b for details) (data not shown). Direct hair cell counts were also obtained from Brn3c:mGFP fish, further demonstrating that Dihexa robustly protects hair cells from neomycin damage (Figure 3).These results indicate that Dihexa only modulates targets responsible for the acute phase of aminoglycoside ototoxicity.


Hepatocyte growth factor mimetic protects lateral line hair cells from aminoglycoside exposure.

Uribe PM, Kawas LH, Harding JW, Coffin AB - Front Cell Neurosci (2015)

Dihexa treatment prevents neomycin-induced hair cell loss in Brn3c:mGFP transgenic larvae. (A) DMSO-treated control, (B) 400 μM neomycin treated neuromast shows a reduction in hair cells, and (C) neuromasts treated with 1 μM Dihexa plus 400 μM neomycin remain mostly intact. (D) 1 μM Dihexa provides protection from neomycin-induced hair cell loss across the neomycin dose-response curve (Two-way ANOVA; Dihexa: F(1,456) = 50.77 p < 0.001). Asterisks indicate significant difference from neomycin control (**p < 0.01, ****p < 0.001). N = 8–10 animals per treatment, error bars represent ± s.e.m.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4309183&req=5

Figure 3: Dihexa treatment prevents neomycin-induced hair cell loss in Brn3c:mGFP transgenic larvae. (A) DMSO-treated control, (B) 400 μM neomycin treated neuromast shows a reduction in hair cells, and (C) neuromasts treated with 1 μM Dihexa plus 400 μM neomycin remain mostly intact. (D) 1 μM Dihexa provides protection from neomycin-induced hair cell loss across the neomycin dose-response curve (Two-way ANOVA; Dihexa: F(1,456) = 50.77 p < 0.001). Asterisks indicate significant difference from neomycin control (**p < 0.01, ****p < 0.001). N = 8–10 animals per treatment, error bars represent ± s.e.m.
Mentions: To verify DASPEI scores, fish from the same treatment groups were fixed and immunohistochemically processed with anti-parvalbumin (Millipore) to visualize hair cells (see Coffin et al., 2013b for details) (data not shown). Direct hair cell counts were also obtained from Brn3c:mGFP fish, further demonstrating that Dihexa robustly protects hair cells from neomycin damage (Figure 3).These results indicate that Dihexa only modulates targets responsible for the acute phase of aminoglycoside ototoxicity.

Bottom Line: We found that a Dihexa concentration of 1 μM confers optimal protection from acute treatment with either ototoxin.Pretreatment with Dihexa does not affect the amount of fluorescently tagged gentamicin that enters hair cells, indicating that Dihexa's protection is likely mediated by intracellular events and not by inhibiting aminoglycoside entry.Our data suggest that Dihexa confers protection of hair cells through an HGF-mediated mechanism and that Dihexa holds clinical potential for mitigating chemical ototoxicity.

View Article: PubMed Central - PubMed

Affiliation: Department of Integrative Physiology and Neuroscience, Washington State University Pullman, WA, USA.

ABSTRACT
Loss of sensory hair cells from exposure to certain licit drugs (e.g., aminoglycoside antibiotics, platinum-based chemotherapy agents) can result in permanent hearing loss. Here we ask if allosteric activation of the hepatocyte growth factor (HGF) cascade via Dihexa, a small molecule drug candidate, can protect hair cells from aminoglycoside toxicity. Unlike native HGF, Dihexa is chemically stable and blood-brain barrier permeable. As a synthetic HGF mimetic, it forms a functional ligand by dimerizing with endogenous HGF to activate the HGF receptor and downstream signaling cascades. To evaluate Dihexa as a potential hair cell protectant, we used the larval zebrafish lateral line, which possesses hair cells that are homologous to mammalian inner ear hair cells and show similar responses to toxins. A dose-response relationship for Dihexa protection was established using two ototoxins, neomycin and gentamicin. We found that a Dihexa concentration of 1 μM confers optimal protection from acute treatment with either ototoxin. Pretreatment with Dihexa does not affect the amount of fluorescently tagged gentamicin that enters hair cells, indicating that Dihexa's protection is likely mediated by intracellular events and not by inhibiting aminoglycoside entry. Dihexa-mediated protection is attenuated by co-treatment with the HGF antagonist 6-AH, further evidence that HGF activation is a component of the observed protection. Additionally, Dihexa's robust protection is partially attenuated by co-treatment with inhibitors of the downstream HGF targets Akt, TOR and MEK. Addition of an amino group to the N-terminal of Dihexa also attenuates the protective response, suggesting that even small substitutions greatly alter the specificity of Dihexa for its target. Our data suggest that Dihexa confers protection of hair cells through an HGF-mediated mechanism and that Dihexa holds clinical potential for mitigating chemical ototoxicity.

No MeSH data available.


Related in: MedlinePlus