PI3K and Inhibitor of Apoptosis Proteins Modulate Gentamicin- Induced Hair Cell Death in the Zebrafish Lateral Line

Zebrafish neuromast sensory system: Is it an emerging target to assess environmental pollution impacts?

Environmental pollution poses risks to ecosystems. Among these risks, one finds neurotoxicity and damage to the lateral line structures of fish, such as the neuromast and its hair cells. Zebrafish (Danio rerio) is recommended as model species to be used in ecotoxicological studies and environmental biomonitoring programs aimed at assessing several biomarkers, such as ototoxicity. However, little is known about the history of and knowledge gaps on zebrafish ototoxicity. Thus, the aim of the current study is to review data available in the scientific literature about using zebrafish as animal model to assess neuromast toxicity. It must be done by analyzing the history and publication category, world production, experimental design, developmental stages, chemical classes, neuromasts and hair cell visualization methods, and zebrafish strains. Based on the results, number, survival and fluorescence intensity of neuromasts, and their hair cells, were the parameters oftentimes used to assess ototoxicity in zebrafish. The wild AB strain was the most used one, and it was followed by Tübingen and transgenic strains with GFP markers. DASPEI was the fluorescent dye most often applied as method to visualize neuromasts, and it was followed by Yo-Pro-1 and GFP transgenic lines. Antibiotics, antitumorals, metals, nanoparticles and plant extracts were the most frequent classes of chemicals used in the analyzed studies. Overall, pollutants can harm zebrafish's mechanosensory system, as well as affect their behavior and survival. Results have shown that zebrafish is a suitable model system to assess ototoxicity induced by environmental pollution.

6'-sialyllactose ameliorates the ototoxic effects of the aminoglycoside antibiotic neomycin in susceptible mice

Sialic acids are terminal sugars of the cellular glycocalyx and are highly abundant in the nervous tissue. Sialylation is sensed by the innate immune system and acts as an inhibitory immune checkpoint. Aminoglycoside antibiotics such as neomycin have been shown to activate tissue macrophages and induce ototoxicity. In this study, we investigated the systemic subcutaneous application of the human milk oligosaccharide 6'-sialyllactose (6SL) as a potential therapy for neomycin-induced ototoxicity in postnatal mice. Repeated systemic treatment of mice with 6SL ameliorated neomycin-induced hearing loss and attenuated neomycin-triggered macrophage activation in the cochlear spiral ganglion. In addition, 6SL reversed the neomycin-mediated increase in gene transcription of the pro-inflammatory cytokine interleukin-1β (Il-1b) and the apoptotic/inflammatory kinase Pik3cd in the inner ear. Interestingly, neomycin application also increased the transcription of desialylating enzyme neuraminidase 3 (Neu3) in the inner ear. In vitro, we confirmed that treatment with 6SL had anti-inflammatory, anti-phagocytic, and neuroprotective effects on cultured lipopolysaccharide-challenged human THP1-macrophages. Thus, our data demonstrated that treatment with 6SL has anti-inflammatory and protective effects against neomycin-mediated macrophage activation and ototoxicity.

Hepatocyte growth factor mimetic confers protection from aminoglycoside-induced hair cell death in vitro

Loss of sensory hair cells from exposure to certain licit drugs, such as aminoglycoside antibiotics, can result in permanent hearing damage. Exogenous application of the neurotrophic molecule hepatocyte growth factor (HGF) promotes neuronal cell survival in a variety of contexts, including protecting hair cells from aminoglycoside ototoxicity. HGF itself is not an ideal therapeutic due to a short half-life and limited blood-brain barrier permeability. MM-201 is a chemically stable, blood-brain barrier permeable, synthetic HGF mimetic that serves as a functional ligand to activate the HGF receptor and its downstream signaling cascade. We previously demonstrated that MM-201 robustly protects zebrafish lateral line hair cells from aminoglycoside ototoxicity. Here, we examined the ability of MM-201 to protect mammalian sensory hair cells from aminoglycoside damage to further evaluate MM-201's clinical potential. We found that MM-201 exhibited dose-dependent protection from neomycin and gentamicin ototoxicity in mature mouse utricular explants. MM-201's protection was reduced following inhibition of mTOR, a downstream target of HGF receptor activation, implicating the activation of endogenous intracellular substrates by MM-201 as critical for the observed protection. We then asked if MM-201 altered the bactericidal properties of aminoglycosides. Using either plate or liquid growth assays we found that MM-201 did not alter the bactericidal efficacy of aminoglycoside antibiotics at therapeutically relevant concentrations. We therefore assessed the protective capacity of MM-201 in an in vivo mouse model of kanamycin ototoxicity. In contrast to our in vitro data, MM-201 did not attenuate kanamycin ototoxicity in vivo. Further, we found that MM-201 was ototoxic to mice across the dose range tested here. These data suggest species- and tissue-specific differences in otoprotective capacity. Next generation HGF mimetics are in clinical trials for neurodegenerative diseases and show excellent safety profiles, but neither preclinical studies nor clinical trials have examined hearing loss as a potential consequence of pharmaceutical HGF activation. Further research is needed to determine the consequences of systemic MM-201 application on the auditory system.

Hair cell toxicology: With the help of a little fish

Hearing or balance loss are disabling conditions that have a serious impact in those suffering them, especially when they appear in children. Their ultimate cause is frequently the loss of function of mechanosensory hair cells in the inner ear. Hair cells can be damaged by environmental insults, like noise or chemical agents, known as ototoxins. Two of the most common ototoxins are life-saving medications: cisplatin against solid tumors, and aminoglycoside antibiotics to treat infections. However, due to their localization inside the temporal bone, hair cells are difficult to study in mammals. As an alternative animal model, zebrafish larvae have hair cells similar to those in mammals, some of which are located in a fish specific organ on the surface of the skin, the lateral line. This makes them easy to observe in vivo and readily accessible for ototoxins or otoprotective substances. These features have made possible advances in the study of the mechanisms mediating ototoxicity or identifying new potential ototoxins. Most importantly, the small size of the zebrafish larvae has allowed screening thousands of molecules searching for otoprotective agents in a scale that would be highly impractical in rodent models. The positive hits found can then start the long road to reach clinical settings to prevent hearing or balance loss.

Identification of Target Proteins Involved in Cochlear Hair Cell Progenitor Cytotoxicity following Gentamicin Exposure

Given the non-labile, terminal differentiation of inner-ear sensory cells, preserving their function is critical since sensory cell damage results in irreversible hearing loss. Gentamicin-induced cytotoxicity is one of the major causes of sensory cell damage and consequent sensorineural hearing loss. However, the precise molecular mechanisms and target proteins involved in ototoxicity are still unknown. The objective of the present study was to identify target proteins involved in gentamicin-induced cytotoxicity to better characterize the molecular pathways involved in sensory cell damage following ototoxic drug administration using House Ear Institute-Organ of Corti 1 (HEI-OC1) cells and high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). We identified several unique proteins involved in gentamicin-induced cytotoxicity, expression of which were further confirmed using confocal microscopy. Further investigation of these pathways can inform the design and discovery of novel treatment modalities to prevent sensory cell damage and preserve their function.

The Protective Effect of Rutin against the Cisplatin-induced Cochlear Damage in vitro

Rutin is a natural flavonoid, with typical effects including interaction with enzymes and scavenging of free radicals. However, the role of rutin in the auditory system is still unclear. In the present study, we used neonatal organ of Corti explants in vitro to investigate the effects of rutin in cisplatin-induced ototoxicity. The TUNEL assay and the cleaved caspase-3 immunohistochemistry were used to detect the apoptosis of hair cell (HCs) in cochlear explants, and the MitoSox-Red staining was used to detect the difference in mitochondrial superoxide among different groups. Western blot was used to investigate the expression of genes. Confocal microscopy showed that after pretreatment with rutin, the accumulation of reactive oxygen species in HCs caused by cisplatin exposure was significantly reduced. Furthermore, the expression levels of p-P38 and p-JNK were significantly decreased, while ratio of p-AKT/AKT was significantly upregulated. Our study showed that rutin reduced cisplatin-induced HCs death in neonatal cochlear explants in vitro. The potential mechanism involved the alleviation of mitochondrial damage, the scavenging of reactive oxygen species (ROS), the suppression of MAPK signaling pathway, and the activation of PI3K/AKT signaling pathway. DATA AVAILABILITY STATEMENT: The datasets during and/or analyzed during the current study available from the corresponding author on reasonable request.

Loss of vacuolar-type H+-ATPase induces caspase-independent necrosis-like death of hair cells in zebrafish neuromasts

The vacuolar-type H+-ATPase (V-ATPase) is a multi-subunit proton pump that regulates cellular pH. V-ATPase activity modulates several cellular processes, but cell-type-specific functions remain poorly understood. Patients with mutations in specific V-ATPase subunits can develop sensorineural deafness, but the underlying mechanisms are unclear. Here, we show that V-ATPase mutations disrupt the formation of zebrafish neuromasts, which serve as a model to investigate hearing loss. V-ATPase mutant neuromasts are small and contain pyknotic nuclei that denote dying cells. Molecular markers and live imaging show that loss of V-ATPase induces mechanosensory hair cells in neuromasts, but not neighboring support cells, to undergo caspase-independent necrosis-like cell death. This is the first demonstration that loss of V-ATPase can lead to necrosis-like cell death in a specific cell type in vivo. Mechanistically, loss of V-ATPase reduces mitochondrial membrane potential in hair cells. Modulating the mitochondrial permeability transition pore, which regulates mitochondrial membrane potential, improves hair cell survival. These results have implications for understanding the causes of sensorineural deafness, and more broadly, reveal functions for V-ATPase in promoting survival of a specific cell type in vivo.

Key Signaling Pathways Regulate the Development and Survival of Auditory Hair Cells

The loss of auditory sensory hair cells (HCs) is the most common cause of sensorineural hearing loss (SNHL). As the main sound transmission structure in the cochlea, it is necessary to maintain the normal shape and survival of HCs. In this review, we described and summarized the signaling pathways that regulate the development and survival of auditory HCs in SNHL. The role of the mitogen-activated protein kinase (MAPK), phosphoinositide-3 kinase/protein kinase B (PI3K/Akt), Notch/Wnt/Atoh1, calcium channels, and oxidative stress/reactive oxygen species (ROS) signaling pathways are the most relevant. The molecular interactions of these signaling pathways play an important role in the survival of HCs, which may provide a theoretical basis and possible therapeutic interventions for the treatment of hearing loss.

Identification of a series of hair-cell MET channel blockers that protect against aminoglycoside-induced ototoxicity

To identify small molecules that shield mammalian sensory hair cells from the ototoxic side effects of aminoglycoside antibiotics, 10,240 compounds were initially screened in zebrafish larvae, selecting for those that protected lateral-line hair cells against neomycin and gentamicin. When the 64 hits from this screen were retested in mouse cochlear cultures, 8 protected outer hair cells (OHCs) from gentamicin in vitro without causing hair-bundle damage. These 8 hits shared structural features and blocked, to varying degrees, the OHC's mechano-electrical transducer (MET) channel, a route of aminoglycoside entry into hair cells. Further characterization of one of the strongest MET channel blockers, UoS-7692, revealed it additionally protected against kanamycin and tobramycin and did not abrogate the bactericidal activity of gentamicin. UoS-7692 behaved, like the aminoglycosides, as a permeant blocker of the MET channel; significantly reduced gentamicin-Texas red loading into OHCs; and preserved lateral-line function in neomycin-treated zebrafish. Transtympanic injection of UoS-7692 protected mouse OHCs from furosemide/kanamycin exposure in vivo and partially preserved hearing. The results confirmed the hair-cell MET channel as a viable target for the identification of compounds that protect the cochlea from aminoglycosides and provide a series of hit compounds that will inform the design of future otoprotectants.

XIAP inhibits gentamicin-induced hair cell damage and ototoxicity through the caspase-3/9 pathway

Gentamicin (GM), an aminoglycoside antibiotic, is one commonly used clinical drugs with ototoxic side effects. One of the most principal mechanisms of its ototoxicity is that GM can activate caspase-mediated cell death pathways in the cochlea. Since the anti-apoptotic protein known as X-linked Inhibitor of Apoptosis Protein (XIAP) has been reported to directly bind to activated caspase protein and inhibit their activities, we hypothesized that it might protect cochlea hair cells from GM ototoxicity. To evaluate this hypothesis, postnatal day 2-3 (P2-3) transgenic (TG) mice, in which XIAP gene is over-expressed under a pure C57BL/6J genetic background was constructed. We first extracted the cochlea tissue of normal mice and treated them with different concentrations of GM, and the number of hair cells were observed to determine the concentration of GM used in subsequent experiments. Next, we used Western Blot experiment to examine the effect of GM on XIAP protein expression in normal mouse cochlea, and then Western Blot and RT-PCR experiments were used to identify the transgenic mice. Finally, immunofluorescence assays were used to detect the effect of GM on the expression of caspase protein and verify the protective effect of XIAP. We found that GM at a concentration of 0.5 mM significantly affected the function of cochlea hair cells, up-regulating the expression of cleaved-caspase-3 and cleaved-caspase-9 protein but down-regulating XIAP protein. In the cochlea tissues of TG mice, this effect of GM was suppressed, and the destruction of hair cells was significantly reduced, and the cleaved-caspase-3 and cleaved-caspase-9 proteins were significantly suppressed. These results suggested that XIAP reduces GM-induced ototoxicity and caspase-3/9 pathway is associated with this process.

Using the Zebrafish Lateral Line to Understand the Roles of Mitochondria in Sensorineural Hearing Loss

Hair cells are the mechanosensory receptors of the inner ear and can be damaged by noise, aging, and ototoxic drugs. This damage often results in permanent sensorineural hearing loss. Hair cells have high energy demands and rely on mitochondria to produce ATP as well as contribute to intracellular calcium homeostasis. In addition to generating ATP, mitochondria produce reactive oxygen species, which can lead to oxidative stress, and regulate cell death pathways. Zebrafish lateral-line hair cells are structurally and functionally analogous to cochlear hair cells but are optically and pharmacologically accessible within an intact specimen, making the zebrafish a good model in which to study hair-cell mitochondrial activity. Moreover, the ease of genetic manipulation of zebrafish embryos allows for the study of mutations implicated in human deafness, as well as the generation of transgenic models to visualize mitochondrial calcium transients and mitochondrial activity in live organisms. Studies of the zebrafish lateral line have shown that variations in mitochondrial activity can predict hair-cell susceptibility to damage by aminoglycosides or noise exposure. In addition, antioxidants have been shown to protect against noise trauma and ototoxic drug–induced hair-cell death. In this review, we discuss the tools and findings of recent investigations into zebrafish hair-cell mitochondria and their involvement in cellular processes, both under homeostatic conditions and in response to noise or ototoxic drugs. The zebrafish lateral line is a valuable model in which to study the roles of mitochondria in hair-cell pathologies and to develop therapeutic strategies to prevent sensorineural hearing loss in humans.

Berbamine Analogs Exhibit Differential Protective Effects From Aminoglycoside-Induced Hair Cell Death

Hearing loss is the third most common chronic health condition in the United States and largely results from damage to sensory hair cells. Major causes of hair cell damage include aging, noise exposure, and medications such as aminoglycoside antibiotics. Due to their potent antibacterial properties and low cost, aminoglycosides are often used for the treatment of gram-negative bacterial infections, surpassing expensive antibiotics with fewer harmful side effects. However, their use is coupled with permanent hearing loss in over 20% of patients requiring these life-sustaining antibiotics. There are currently no FDA-approved drugs that prevent hearing loss from aminoglycosides. A previous study by our group identified the plant alkaloid berbamine as a strong protectant of zebrafish lateral line hair cells from aminoglycoside damage. This effect is likely due to a block of the mechanotransduction channel, thereby reducing aminoglycoside entry into hair cells. The present study builds on this previous work, investigating 16 synthetic berbamine analogs to determine the core structure underlying their protective mechanisms. We demonstrate that nearly all of these berbamine analogs robustly protect lateral line hair cells from ototoxic damage, with ED₅₀ values nearing 20 nM for the most potent analogs. Of the 16 analogs tested, nine strongly protected hair cells from both neomycin and gentamicin damage, while one conferred strong protection only from gentamicin. These data are consistent with prior research demonstrating that different aminoglycosides activate somewhat distinct mechanisms of damage. Regardless of the mechanism, protection required the entire berbamine scaffold. Phenolic alkylation or acylation with lipophilic groups appeared to improve protection compared to berbamine, implying that these structures may be responsible for mitigating damage. While the majority of analogs confer protection by blocking aminoglycoside uptake, 18% of our analogs also confer protection via an uptake-independent mechanism; these analogs exhibited protection when delivered after aminoglycoside removal. Based on our studies, berbamine analogs represent a promising tool to further understand the pathology of aminoglycoside-induced hearing loss and can serve as lead compounds to develop otoprotective drugs.

PDK1 regulates the survival of the developing cortical interneurons

Inhibitory interneurons are critical for maintaining the excitatory/inhibitory balance. During the development cortical interneurons originate from the ganglionic eminence and arrive at the dorsal cortex through two tangential migration routes. However, the mechanisms underlying the development of cortical interneurons remain unclear. 3-Phosphoinositide-dependent protein kinase-1 (PDK1) has been shown to be involved in a variety of biological processes, including cell proliferation and migration, and plays an important role in the neurogenesis of cortical excitatory neurons. However, the function of PDK1 in interneurons is still unclear. Here, we reported that the disruption of Pdk1 in the subpallium achieved by crossing the Dlx5/6-Cre-IRES-EGFP line with Pdk1^fl/fl mice led to the severely increased apoptosis of immature interneurons, subsequently resulting in a remarkable reduction in cortical interneurons. However, the tangential migration, progenitor pools and cell proliferation were not affected by the disruption of Pdk1. We further found the activity of AKT-GSK3β signaling pathway was decreased after Pdk1 deletion, suggesting it might be involved in the regulation of the survival of cortical interneurons. These results provide new insights into the function of PDK1 in the development of the telencephalon.

Comparative analysis of cutaneous bacterial communities of farmed Rana dybowskii after gentamycin bath

Introduction

Pathogenic bacteria limit the success of Rana dybowskii breeding. Gentamicin is used to treat R. dybowskii disease. To understand the effects of gentamicin on the composition and structure of the cutaneous bacterial community of R. dybowskii, three groups (control, gentamicin and recovery) were established in this study.

Materials & Methods

The V3-V4 hypervariable region of the 16S rRNA gene was analyzed in samples by high-throughput sequencing. Alpha diversity and beta diversity were evaluated to compare the cutaneous bacterial community diversity.

Results

A total of 1,159,668 valid sequences and 3,132 operational taxonomic units (OTUs) were obtained from these three experimental groups. The number of OTUs obtained in the control group, gentamicin group and recovery group were 2,194, 2,288, and 2,047, respectively, and the number of shared OTUs was 1,313. The alpha diversity of the cutaneous bacterial community was not significantly affected by gentamicin, while beta diversity was significantly affected.

Discussion & Conclusions

The effect of a gentamicin bath on relative species abundance was greater than the effect on the species composition. The changes in Proteobacteria, Acinetobacter, and Chryseobacterium were significant, and reductions were observed after the recovery period. Six potentially pathogenic genera were detected, including Aeromonas, Citrobacter, Chryseobacterium, Pseudomonas, Staphylococcus, and Streptococcus. Among them, Aeromonas and Chryseobacterium were significantly inhibited by the gentamicin bath. The results of this study provide a theoretical basis for the application of gentamicin in R. dybowskii breeding.

Use of zebrafish larvae lateral line to study protection against cisplatin-induced ototoxicity: A scoping review

AIM

The present review aimed to consolidate and analyze the recent information about the use of zebrafish in studies concerning cisplatin-induced ototoxicity and otoprotection.

MATERIAL AND METHODS

The PubMed, Web of Science, and Scopus databanks were searched using the following MESH terms: zebrafish, cisplatin, ototoxicity. The identified publications were screened according to inclusion and exclusion criteria and the 26 qualifying manuscripts were included in the full-text analysis. The experimental protocols, including cisplatin concentrations, the exposure duration and the outcome measurements used in zebrafish larvae studies, were evaluated and the reported knowledge was summarized.

RESULTS

Twenty-six substances protecting from cisplatin-induced toxicity were identified with the use of zebrafish larvae. These substances include quinine, salvianolic acid B, berbamine 6, benzamil, quercetin, dexmedetomidine, dexamethsanone, quinoxaline, edaravone, apocynin, dimethyl sulfoxide, KR-22335, SRT1720, ORC-13661, 3-MA, D-methionine, mdivi-1, FUT-175, rapamycin, Z-LLF-CHO, ATX, NAC, CYM-5478, CHCP1, CHCP2 and leupeptin. The otoprotective effects of compounds were attributed to their anti-ROS, anti-apoptotic and cisplatin uptake-blocking properties. The broadest range of protection was achieved when the experimental flow used preconditioning with an otoprotective compound and later a co-incubation with cisplatin. Protection against a high concentration of cisplatin was observed only in protocols using short exposure times (4 and 6 h).

CONCLUSIONS

The data extracted from the selected papers confirm that despite the differences between the human and the zebra fish hearing thresholds (as affected by cisplatin), the sensory cells of zebrafish and larval zebrafish are a valuable tool which could be used: (i) for the discovery of novel otoprotective substances and compounds; (ii) to screen their side effects and (iii) to extend the knowledge on the mechanisms of cisplatin-induced inner ear damage. For future studies, the development of a consensus experimental protocol is highly recommended.

Material basis and molecular mechanisms of Dachengqi decoction in the treatment of acute pancreatitis based on network pharmacology

BACKGROUND

Dachengqi decoction (DCQD) is a classical prescription in traditional Chinese medicine (TCM). It has been used to treat abdominal pain and acute pancreatitis (AP) for thousands of years in China.

OBJECTIVE

To predict the active components and signaling pathway of DCQD and to further explore the potential molecular mechanism of DCQD as a treatment of AP using network pharmacology.

METHODS

Network pharmacology and bioinformatics were used to determine the active components of DCQD and its potential target in the treatment of AP. The AP model was induced by Cerulein (Cer) combined with lipopolysaccharide (LPS). The pharmacodynamic basis of DCQD in the treatment of AP was evaluated in vitro and in vivo and Western blot analysis and immunofluorescence were used to determine the molecular mechanism of DCQD.

RESULTS

Screening using relevant databases and topological analysis revealed 71 active components and 535 potential target proteins in DCQD. In addition, 445 differential genes for AP were also screened. Pathway enrichment analysis, PPI network analysis and transcription factor prediction showed that DCQD played an important role in the PI3K-Akt signal pathway, and 17 DCQD monomers were found in this signal pathway. In the AP model, DCQD promoted pancreatic acinar cell apoptosis, reduction in inflammation, and regulation of the PI3K-AKT signaling pathway. DCQD inhibited the expression of p-AKT and p- NF-kB proteins in pancreatic tissue of the AP model both in vitro and in vivo.

CONCLUSION

This study reveals that 17 active components of DCQD improve AP by regulating the PI3K/AKT signaling pathway and promoting apoptosis and suppressing pathological injury and inflammation.

Dietary α-Mangostin Provides Protective Effects against Acetaminophen-Induced Hepatotoxicity in Mice via Akt/mTOR-Mediated Inhibition of Autophagy and Apoptosis

Acetaminophen overdose-induced hepatotoxicity is the most common cause of acute liver failure in many countries. Previously, alpha-mangostin (α-MG) has been confirmed to exert protective effects on a variety of liver injuries, but the protective effect on acetaminophen-induced acute liver injury (ALI) remains largely unknown. This work investigated the regulatory effect and underlying cellular mechanisms of α-MG action to attenuate acetaminophen-induced hepatotoxicity in mice. The increased serum aminotransferase levels and glutathione (GSH) content and reduced malondialdehyde (MDA) demonstrated the protective effect of α-MG against acetaminophen-induced hepatotoxicity. In addition, α-MG pretreatment inhibited increases in tumor necrosis factor (TNF-α) and interleukin-1β (IL-1β) caused by exposure of mice to acetaminophen. In liver tissues, α-MG inhibited the protein expression of autophagy-related microtubule-associated protein light chain 3 (LC3) and BCL2/adenovirus E1B protein-interacting protein 3 (BNIP3). Western blotting analysis of liver tissues also proved evidence that α-MG partially inhibited the activation of apoptotic signaling pathways via increasing the expression of Bcl-2 and decreasing Bax and cleaved caspase 3 proteins. In addition, α-MG could in part downregulate the increase in p62 level and upregulate the decrease in p-mTOR, p-AKT and LC3 II /LC3 I ratio in autophagy signaling pathways in the mouse liver. Taken together, our findings proved novel perspectives that detoxification effect of α-MG on acetaminophen-induced ALI might be due to the alterations in Akt/mTOR pathway in the liver.