Synergistic Potentials of Coffee on Injured Pancreatic Islets and Insulin Action via KATP Channel Blocking in Zebrafish

Coffee prevents IQ-induced liver damage by regulating oxidative stress, inflammation, endoplasmic reticulum stress, autophagy, apoptosis, and the MAPK/NF-κB signaling pathway in zebrafish

2-Amino-3-methylimidazole[4,5-f]quinoline (IQ), one of heterocyclic amines (HCAs) produced in proteinaceous foods upon heating, is recognized as a carcinogen. Previous studies have confirmed that IQ intake can cause liver damage in zebrafish. In the current study, we revealed the protective effects of coffee against IQ-induced liver damage. We exposed one-month-old wild-type zebrafish to IQ (80 ng/mL) and coffee at 50 mg/L, 100 mg/L, and 300 mg/L for 35 days. Markers of oxidative stress, inflammation, endoplasmic reticulum stress (ERS), autophagy, and apoptosis in the liver were assessed to explore the potential mechanisms of the protective effects. The results showed that coffee effectively improved IQ-induced liver damage by reducing ALT, AST, TC, TG, and LDL-C levels, increasing HDL-C level, and restoring hepatic morphology. Moreover, coffee showed an antioxidative effect by increasing GSH, GSH-Px, GST, CAT, and SOD levels and attenuating ROS and MDA contents. Additionally, coffee reduced the NO, iNOS, TNF-α, IL-6, IL-1β, and IL-12 expression levels, presenting an anti-inflammatory effect. Furthermore, coffee protected against ERS, autophagy dysfunction, and apoptosis by decreasing the GRP78, CHOP, and p62 while increasing the Atg5-Atg12, Beclin1, LC3-II, and Bcl-2 expression levels. TUNEL results showed that coffee rescued IQ-induced hepatocyte apoptosis. In addition, coffee interrupted the MAPK/NF-κB signaling pathway by suppressing the phosphorylation expressions of JNK, ERK, p38, p65, and IκB. These findings indicated that coffee prevents IQ-induced liver damage with antioxidative, anti-inflammatory, anti-ERS, anti-apoptotic, and pro-autophagic effects, thus to serve as a functional beverage with potential health benefits.

Erigeron annuus Extract Alleviates Insulin Resistance via Regulating the Expression of Mitochondrial Damage and Endoplasmic Reticulum Stress-Related Genes

Diabetes is a prevalent and debilitating metabolic disorder affecting a large population worldwide. The condition is characterized by insulin resistance and impaired function of pancreatic β-cells, leading to elevated blood glucose levels. In this study, the antidiabetic effects of Erigeron annuus extract (EAE) on zebrafish with damaged pancreatic islets caused by insulin resistance were investigated. The study utilized the zebrafish model to monitor live pancreatic islets. RNA sequencing was also conducted to determine the mechanism by which EAE exerts its antidiabetic effect. The results showed that EAE was effective in recovering reduced islets in excess insulin-induced zebrafish. The effective concentration at 50% (EC₅₀) of EAE was determined to be 0.54 μg/mL, while the lethal concentration at 50% (LC₅₀) was calculated as 202.5 μg/mL. RNA sequencing indicated that the mode of action of EAE is related to its ability to induce mitochondrial damage and suppress endoplasmic reticulum stress. The findings of this study demonstrate the efficacy and therapeutic potential of EAE in treating insulin resistance in zebrafish. The results suggest that EAE may offer a promising approach for the management of diabetes by reducing mitochondrial damage and suppressing endoplasmic reticulum stress. Further research is required to establish the clinical application of EAE in diabetic patients.

Ameliorative Effects of Flavonoids from Platycodon grandiflorus Aerial Parts on Alloxan-Induced Pancreatic Islet Damage in Zebrafish

Platycodon grandiflorus (balloon flower), used as a food reserve as well as in traditional herbal medicine, is known for its multiple beneficial effects. In particular, this plant is widely used as a vegetable in Republic of Korea. We examined the ameliorative effects of P. grandiflorus on alloxan-induced pancreatic islet damage in zebrafish. The aerial part treatment led to a significant recovery in pancreatic islet size and glucose uptake. The efficacy of the aerial part was more potent than that of the root. Eight flavonoids (1-8) were isolated from the aerial part. Structures of two new flavone glycosides, designated dorajiside I (1) and II (2), were elucidated to be luteolin 7-O-α-L-rhamno-pyranosyl (1 → 2)-(6-O-acetyl)-β-D-glucopyranoside and apigenin 7-O-α-L-rhamnopyranosyl (1 → 2)-(6-O-acetyl)-β-D-glucopyranoside, respectively, by spectroscopic analysis. Compounds 1, 3, 4 and 6-8 yielded the recovery of injured pancreatic islets in zebrafish. Among them, compound 7 blocked K_ATP channels in pancreatic β-cells. Furthermore, compounds 3, 4, 6 and 7 showed significant changes with respect to the mRNA expression of GCK, GCKR, GLIS3 and CDKN2B compared to alloxan-induced zebrafish. In conclusion, the aerial part of P. grandiflorus and its constituents conferred a regenerative effect on injured pancreatic islets.

Research Progress on the Construction and Application of a Diabetic Zebrafish Model

Diabetes is a metabolic disease characterized by high blood glucose levels. With economic development and lifestyle changes, the prevalence of diabetes is increasing yearly. Thus, it has become an increasingly serious public health problem in countries around the world. The etiology of diabetes is complex, and its pathogenic mechanisms are not completely clear. The use of diabetic animal models is helpful in the study of the pathogenesis of diabetes and the development of drugs. The emerging vertebrate model of zebrafish has many advantages, such as its small size, large number of eggs, short growth cycle, simple cultivation of adult fish, and effective improvement of experimental efficiency. Thus, this model is highly suitable for research as an animal model of diabetes. This review not only summarizes the advantages of zebrafish as a diabetes model, but also summarizes the construction methods and challenges of zebrafish models of type 1 diabetes, type 2 diabetes, and diabetes complications. This study provides valuable reference information for further study of the pathological mechanisms of diabetes and the research and development of new related therapeutic drugs.

β-cells regeneration by WL15 of cysteine and glycine-rich protein 2 which reduces alloxan induced β-cell dysfunction and oxidative stress through phosphoenolpyruvate carboxykinase and insulin pathway in zebrafish in-vivo larval model

BACKGROUND

Pancreatic β-cells are susceptible to oxidative stress, leading to β-cell death and dysfunction due to enhanced ROS levels and type 2 diabetes. To inhibit the β-cells damages induced by the oxidative stress, the present study investigates the beneficial effect of various peptides (WL15, RF13, RW20, IW13 and MF18) of immune related proteins (cysteine and glycine-rich protein 2, histone acetyltransferase, vacuolar protein sorting associated protein 26B, serine threonine-protein kinase and CxxC zinc finger protein, respectively). Also, the molecular mechanism of WL15 from cysteine and glycine-rich protein 2 on β-cell regeneration was identified through PEPCK and insulin pathway.

MATERIALS AND METHODS

In this study, a total of five peptides including WL15, RF13, RW20, IW13, and MF18 were derived from immune-related proteins such as cysteine and glycine-rich protein 2, histone acetyltransferase, vacuolar protein sorting associated protein 26B, serine threonine-protein kinase and CxxC zinc finger protein, respectively. These protein sequences were obtained from an earlier constructed transcriptome database of a teleost Channa striatus. The identified peptides were evaluated for their antioxidant as well as antidiabetic activity. Based on the in silico analysis and in-vitro screening experiments, WL15 was predicted to have better antioxidant and antidiabetic activity among the five different peptides. Therefore, WL15 alone was further analyzed for apoptosis, antioxidant capacity, glucose metabolism, and gene expression performance, which was investigated on the alloxan (500 µM) induced zebrafish in vivo larval model.

RESULTS

The results showed alloxan exposure to zebrafish larvae for a day, the ROS was generated in the β-cells. Interestingly, WL15 treatment showed a protective effect by reducing the toxicity of alloxan exposed zebrafish larvae by increasing their survival and heart rate. Moreover, WL15 reduced the intracellular ROS level and apoptosis in alloxan-induced larvae. The superoxide anion and lipid peroxidation levels are also reduced by improving the glutathione content after the WL15 treatment. Besides, WL15 treatment increased the proliferation rate of β-cells and decreased the glucose level. Further, the gene expression studies revealed that WL15 treatment normalized the PEPCK expression while upregulating the insulin expression in alloxan exposed larvae.

CONCLUSION

Overall, the findings indicate that WL15 of cysteine and glycine-rich protein 2 can act as a potential antioxidant for type 2 diabetes patients in respect of improving β-cell regeneration.

Zebrafish: A New Promise to Study the Impact of Metabolic Disorders on the Brain

Zebrafish has become a popular model to study many physiological and pathophysiological processes in humans. In recent years, it has rapidly emerged in the study of metabolic disorders, namely, obesity and diabetes, as the regulatory mechanisms and metabolic pathways of glucose and lipid homeostasis are highly conserved between fish and mammals. Zebrafish is also widely used in the field of neurosciences to study brain plasticity and regenerative mechanisms due to the high maintenance and activity of neural stem cells during adulthood. Recently, a large body of evidence has established that metabolic disorders can alter brain homeostasis, leading to neuro-inflammation and oxidative stress and causing decreased neurogenesis. To date, these pathological metabolic conditions are also risk factors for the development of cognitive dysfunctions and neurodegenerative diseases. In this review, we first aim to describe the main metabolic models established in zebrafish to demonstrate their similarities with their respective mammalian/human counterparts. Then, in the second part, we report the impact of metabolic disorders (obesity and diabetes) on brain homeostasis with a particular focus on the blood-brain barrier, neuro-inflammation, oxidative stress, cognitive functions and brain plasticity. Finally, we propose interesting signaling pathways and regulatory mechanisms to be explored in order to better understand how metabolic disorders can negatively impact neural stem cell activity.

Metabolic study of cafestol using in silico approach, zebrafish water tank experiments and liquid chromatography high-resolution mass spectrometry analyses

Coffee is one of the most consumed beverages worldwide. Cafestol is an endogenous coffee diterpene present in raw coffee beans and also found in hot beverages, with several biological activities. However, there is still little information on this molecule after ingestion of coffee infusion. Zebrafish (Danio rerio) is a promising in vivo model for metabolic studies due to the annotation of mammalian orthologs to encode enzymes related to drug metabolism. Experiments using Zebrafish Water Tank (ZWT) model produce more significant number of metabolites for molecular investigation in a cleaner matrix than other classical models, such as purified hepatocytes. This work aimed to investigate the biotransformation of cafestol by the ZWT model using ultra-performance liquid chromatography coupled to hybrid quadrupole-orbitrap high-resolution mass spectrometry equipped with electrospray ionization (UPLC-HRMS) supported by in silico approach using SMARTCyp, Way2Drug and XenoSite Softwares. Twenty-five metabolites of cafestol were proposed by in silico analysis, in which 5 phase I metabolites were confirmed in the ZWT by UPLC and MS/HRMS investigation: 6-hydroxy-cafestol, 6,12-dihydroxy-cafestol, 2-oxo-cafestol, 6-oxo-cafestol and one isomer whose position in the carboxyl group was not determined. These metabolites were observed during 9 h of the experiment, whose contents were associated with the behavioral responses of the fish.

Recovery Effect of a Rutin-Enriched Fraction Prepared From Forsythia koreana Flowers on Alloxan-Induced Pancreatic Islets in Zebrafish Larvae (Danio rerio)

A simple method to prepare a high-content rutin fraction from Forsythia koreana flowers (HRFK) is described. Rutin, isolated for the first time from the flowers, was identified from spectroscopic data including nuclear magnetic resonance, mass spectrometry, and infrared. As a result of HPLC quantitative analysis, the content of rutin was found to be 80.0 ± 0.02% in HRFK. Our previous study reported that F koreana MeOH extract (FK) significantly recovered alloxan-induced pancreatic islets in zebrafish. However, HRFK as well as rutin exhibited an enhanced anti-diabetic effect compared to FK in our latest experiments. In conclusion, HRFK, as well as rutin and FK, have potential as anti-diabetic agents.

Characteristics of the New Insulin-Resistant Zebrafish Model

Insulin resistance, which occurs when insulin levels are sufficiently high over a prolonged period, causing the cells to fail to respond normally to the hormone. As a system for insulin resistance and diabetes drug development, insulin-resistant rodent models have been clearly established, but there is a limitation to high-throughput drug screening. Recently, zebrafish have been identified as an excellent system for drug discovery and identification of therapeutic targets, but studies on insulin resistance models have not been extensively performed. Therefore, we aimed to make a rapid insulin-resistant zebrafish model that complements the existing rodent models. To establish this model, zebrafish were treated with 10 μM insulin for 48 h. This model showed characteristics of insulin-resistant disease such as damaged pancreatic islets. Then we confirmed the recovery of the pancreatic islets after pioglitazone treatment. In addition, it was found that insulin-resistant drugs have as significant an effect in zebrafish as in humans, and these results proved the value of the zebrafish insulin resistance model for drug selection. In addition, RNA sequencing was performed to elucidate the mechanism involved. KEGG pathway enrichment analysis of differentially expressed genes showed that insulin resistance altered gene expression due to the MAPK signaling and calcium signaling pathways. This model demonstrates the utility of the zebrafish model for drug testing and drug discovery in insulin resistance and diabetes.

Anti-insulin resistance effect of constituents from Senna siamea on zebrafish model, its molecular docking, and structure-activity relationships

Senna siamea has been used as an antidiabetic drug since antiquity. With regard to traditional Thai medicine, the use of S. siamea was described for diabetes therapy. To understand the molecular mechanism regarding insulin resistance. Pure compounds were isolated from wood extract. We studied their biological activities on insulin-resistance using an in vivo zebrafish model. We also performed an in silico study; molecular docking, and in vitro study by taking advantage of the enzyme inhibitory activities of α-glucosidase, PTP1B, and DPP-IV. Based on the preliminary investigation that ethyl acetate and ethanol extracts have potent effects against insulin resistance on zebrafish larvae, five compounds were isolated from two fractions following: resveratrol, piceatannol, dihydropiceatannol, chrysophanol, and emodin. All of the isolated compounds had anti-insulin resistance effects on zebrafish larvae. Resveratrol, piceatannol, and dihydropiceatannol also demonstrated inhibitory effects against α-glucosidase. Chrysophanol and emodin inhibited PTP1B activity, while resveratrol showed a DPP-IV inhibition effect via the molecular docking. The results of enzyme assay were similar. In conclusions, S. siamea components demonstrated effects against insulin resistance. The chemical structure displayed identical biological activity to that of the compounds. Therefore, S. siamea wood extract and their components are potential therapeutic options in the treatment of diabetes.

Wild-Type Zebrafish (Danio rerio) Larvae as a Vertebrate Model for Diabetes and Comorbidities: A Review

Zebrafish have become a popular alternative to higher animals in biomedical and pharmaceutical research. The development of stable mutant lines to model target specific aspects of many diseases, including diabetes, is well reported. However, these mutant lines are much more costly and challenging to maintain than wild-type zebrafish and are simply not an option for many research facilities. As an alternative to address the disadvantages of advanced mutant lines, wild-type larvae may represent a suitable option. In this review, we evaluate organ development in zebrafish larvae and discuss established methods that use wild-type zebrafish larvae up to seven days post fertilization to test for potential drug candidates for diabetes and its commonly associated conditions of oxidative stress and inflammation. This provides an up to date overview of the relevance of wild-type zebrafish larvae as a vertebrate antidiabetic model and confidence as an alternative tool for preclinical studies. We highlight the advantages and disadvantages of established methods and suggest recommendations for future developments to promote the use of zebrafish, specifically larvae, rather than higher animals in the early phase of antidiabetic drug discovery.

Timosaponin AIII attenuates inflammatory injury in AGEs-induced osteoblast and alloxan-induced diabetic osteoporosis zebrafish by modulating the RAGE/MAPK signaling pathways

BACKGROUND

Advanced glycation end products (AGEs) deposition causes inflammatory injury in osteoblasts and contributes to diabetic osteoporosis. The receptor for advanced glycation end product/mitogen-activated protein kinase pathway (RAGE/MAPK) signaling pathway is closely linked to the pathogenesis of diabetic osteoporosis. Timosaponin AIII, a steroidal saponin isolated from Anemarrhena asphodeloides Bunge (Asparagaceae), shows anti-inflammatory and anti-osteoporosis effects.

PURPOSE

The present study was aimed to investigate the therapeutic effects of timosaponin AIII on diabetic osteoporosis and whether its effect is dependent on protecting osteoblasts against AGEs-induced injury via RAGE/MAPK signaling suppression.

METHODS

An alloxan-induced diabetic osteoporosis zebrafish model was applied to investigate the effects of timosaponin AIII in vivo, and alendronate was used as a positive control. Moreover, related mechanisms were explored in primary rat osteoblasts. Molecular docking was applied to investigate the interactions between timosaponin AIII and RAGE.

RESULTS

Timosaponin AIII treatment reversed alloxan-induced reduction in the mineralized area of the larvae head skeleton, accompanied by a decreased level of triglyceride and total cholesterol in the zebrafish. Additionally, AGEs significantly influenced RAGE expression, alkaline phosphatase activity, interleukin 1β expression, interleukin 6 expression, and tumor necrosis factor-α expression, and increased cell apoptosis. Timosaponin AIII significantly downregulated AGEs-induced interleukin 1β, interleukin 6, and tumor necrosis factor-α levels, and upregulated alkaline phosphatase and osteocalcin levels. Timosaponin AIII also significantly reduced the expression of RAGE and had additive effects on downstream P38, extracellular signal-regulated kinase and c-Jun N-terminal kinase in AGEs-induced osteoblast. Molecular docking predicted that hydrogen and hydrophobic interactions occurred between timosaponin AIII and RAGE.

CONCLUSION

These data clarified that timosaponin AIII attenuates diabetic osteoporosis via a novel mechanism involved suppressing the RAGE/MAPK signaling pathway. Our finding highlights the potential value of timosaponin AIII as an anti-diabetic osteoporosis agent.

Steamed Ginger May Enhance Insulin Secretion through KATP Channel Closure in Pancreatic β-Cells Potentially by Increasing 1-Dehydro-6-Gingerdione Content

Ginger (Zingiber officinale Roscoe) and its active compounds (gingerols, shogaols and paradols) have been reported as having beneficial functions for several diseases, including diabetes. In this study, we revealed that the steaming process could enhance the anti-diabetic potential of ginger. To confirm the anti-diabetic effect of steamed ginger extract (GG03), we assessed pancreatic islets impaired by alloxan in zebrafish and demonstrated anti-hyperglycemic efficacy in a mouse model. The EC50 values of ginger extract (GE) and GG03 showed that the efficacy of GG03 was greater than that of GE. In addition, LC50 values demonstrated that GG03 had lower toxicity than GE, and the comparison of the Therapeutic Index (TI) proved that GG03 is a safer functional food. Furthermore, our data showed that GG03 significantly lowered hyperglycemia in a diabetic mouse model. HPLC was performed to confirm the change in the composition of steamed ginger. Interestingly, GG03 showed a 375% increase in 1-dehydro-6-gingerdione (GD) compared with GE. GD has not yet been studied much pharmacologically. Thus, we identified the protective effects of GD in the damaged pancreatic islets of diabetic zebrafish. We further assessed whether the anti-diabetic mechanism of action of GG03 and GD involves insulin secretion. Our results suggest that GG03 and GD might stimulate insulin secretion by the closure of KATP channels in pancreatic β-cells.

Panax ginseng (Korea Red Ginseng) repairs diabetic sensorineural damage through promotion of the nerve growth factor pathway in diabetic zebrafish

Background

Diabetic sensorineural damage is a complication of the sensory neural system, resulting from long-term hyperglycemia. Red ginseng (RG) has shown efficacy for treatment of various diseases, including diabetes mellitus; however, there is little research about its benefit for treating sensorineural damage. Therefore, we aim to evaluate RG efficacy in alloxan-induced diabetic neuromast (AIDN) zebrafish.

Methods

In this study, we developed and validated an AIDN zebrafish model. To assess RG effectiveness, we observed morphological changes in live neuromast zebrafish. Also, zebrafish has been observed to have an ultrastructure of hair-cell cilia under scanning electron microscopy. Thus, we recorded these physiological traits to assess hair cell function. Finally, we confirmed that RG promoted neuromast recovery via nerve growth factor signaling pathway markers.

Results

First, we established an AIDN zebrafish model. Using this model, we showed via live neuromast imaging that RG fostered recovery of sensorineural damage. Damaged hair cell cilia were recovered in AIDN zebrafish. Furthermore, RG rescued damaged hair cell function through cell membrane ion balance.

Conclusion

Our data suggest that RG potentially facilitates recovery in AIDN zebrafish, and its mechanism seems to be promotion of the nerve growth factor pathway through increased expression of topomyosin receptor kinase A, transient receptor potential channel vanilloid subfamily type 1, and mitogen-activated protein kinase phosphorylation.

Zebrafish as a Model for Obesity and Diabetes

Obesity and diabetes now considered global epidemics. The prevalence rates of diabetes are increasing in parallel with the rates of obesity and the strong connection between these two diseases has been coined as “diabesity.” The health risks of overweight or obesity include Type 2 diabetes mellitus (T2DM), coronary heart disease and cancer of numerous organs. Both obesity and diabetes are complex diseases that involve the interaction of genetics and environmental factors. The underlying pathogenesis of obesity and diabetes are not well understood and further research is needed for pharmacological and surgical management. Consequently, the use of animal models of obesity and/or diabetes is important for both improving the understanding of these diseases and to identify and develop effective treatments. Zebrafish is an attractive model system for studying metabolic diseases because of the functional conservation in lipid metabolism, adipose biology, pancreas structure, and glucose homeostasis. It is also suited for identification of novel targets associated with the risk and treatment of obesity and diabetes in humans. In this review, we highlight studies using zebrafish to model metabolic diseases, and discuss the advantages and disadvantages of studying pathologies associated with obesity and diabetes in zebrafish.

Flavonoid 8-O-Glucuronides from the Aerial Parts of Malva verticillata and Their Recovery Effects on Alloxan-Induced Pancreatic Islets in Zebrafish

Malva verticillata (Cluster mallow), a leafy vegetable that has been popular in East Asia for a long time, has also been used in herbal teas and medicines. The aqueous fraction of the aerial parts of Malva verticillata, exhibiting a very high quantity of flavonoids compared to the EtOAc and n-BuOH fractions, exhibited significant recovery effects on pancreatic islets damaged by alloxan in zebrafish larvae. Thus, the bioactive components responsible for this anti-diabetic activity were investigated. A new flavonoid glucuronide (1) and five known flavonoids were isolated from the aqueous fraction. Based on several spectroscopic methods, compound 1 was identified to be nortangeretin-8-O-β-D-glucuronide, and was named malvaflavone A. The A-ring of compound 1 had a 5,6,7,8-tetrahydroxy moiety, which rarely occurs in plant systems. Also 8-O-glucuronide attached to the flavonoid moiety was rarely occurred in plant system. Compounds 1, 3, 4, and 6 significantly improved the pancreatic islet size in zebrafish at 0.1 μM, and compounds 1 and 6 were found to block β-cell K⁺ channels in experiments with diazoxide. In ABTS, ORAC, and SOD assays, compounds 1-5 exhibited high anti-oxidant activities compared with quercetin and BHA (positive controls), indicating that the 8-O-glucuronide attached to the flavonoid moiety is a key structure for the expression of anti-oxidant activity. This is the first report of the isolation of compounds 1-6 from M. verticillata as well evaluated for anti-diabetic and anti-oxidant ativities.

Trigonelline promotes auditory function through nerve growth factor signaling on diabetic animal models

BACKGROUND

Protection of cochlear function and reconstruction of neuronal networks in damaged auditory sensory structures is crucial for therapeutic treatment of diabetic hearing loss. Nerve growth factor (NGF) has been used as a novel therapeutic target to protect against the neurodegenerative effects of Diabetes Mellitus (DM).

PURPOSE

We aimed to evaluate the potential effect of trigonelline (TRG) on reducing auditory damage produced by DM using NGF as a potential marker.

METHOD

Docking simulations were carried out using Autodock Vina software and visualized using Discovery Studio. Morphological analysis of hair cells and neuromasts was performed on alloxan-induced diabetic zebrafish by fluorescence and scanning electron microscopy. Blockage of NGF receptor phosphorylation with K-252a was used to evaluate TRG and NGF action. Further assessment of NGF by ELISA on a primary culture of spiral ganglion cells was performed as a marker of neuronal function on the hearing system. Finally, auditory function was assessed in LepR(^db/db) mice using auditory brainstem response (ABR) and transient evoked otoacoustic emission (TEOAE) during 8 weeks.

RESULTS

Docking simulations showed that TRG binds to the active site of NGF through molecular interactions with Lysine88 (Lys88) and Tyrosine52 (Tyr52). TRG treatment significantly reduced hair cell loss and neuromast damage in diabetic zebrafish (P < .05). Further evaluation revealed a significant increase in the number of neuromasts after NGF administration (P < .001). TRG and NGF action was suppressed during blockage of NGF receptor phosphorylation. Moreover, spiral ganglion cells revealed significant elevation on NGF values after TRG treatment (P < .05). In vivo evaluation of LepR(^db/db) mice revealed a significant reduction in the auditory damage produced under diabetic progression, characterized by reduced ABR hearing threshold shifts and increased signal-to-noise ratio in TEOAE (P < .05).

CONCLUSIONS

This study suggests that the enhanced hearing function produced by TRG may be mediated by NGF, providing a potential therapeutic strategy for diabetic hearing loss.

A synthetic Nitraria alkaloid, isonitramine protects pancreatic β-cell and attenuates postprandial hyperglycemia

OBJECTIVE

The extracts of Nitraria genus are composed of Nitraria alkaloids and have been used traditionally as a hypoglycemic medicine. However, the efficacy and precise mechanism of Nitraria alkaloids remain largely unknown.

METHODS

Previously, we reported the total synthesis of (+)-isonitramine, one of Nitraria alkaloids. In this study, we investigated the anti-diabetic potential of isonitramine in diabetes mellitus and its underlying molecular mechanism in carbohydrate catabolism in vitro and in vivo.

RESULTS

Isonitramine exerted significant inhibitory effect on α-glucosidases but not α-amylase in vitro. In zebrafish, isonitramine alleviated the streptozotocin (STZ)-induced postprandial hyperglycemia and protected the pancreatic damages against alloxan-induced oxidative stress in vivo. Also, isonitramine induced insulin without any toxicities and downregulated phosphoenolpyruvate carboxykinase (PEPCK), which catalyzes the first committed step in gluconeogenesis.

CONCLUSION

Taken together, isonitramine inhibited α-glucosidase activity and PEPCK expression, while increased insulin expression, resulting in attenuating the postprandial hyperglycemia. Also, isonitramine protected the pancreas from ROS-mediated toxicities. Therefore, isonitramine may be a new drug candidate for the treatment of diabetes mellitus.

Expression and function of ATP-dependent potassium channels in zebrafish islet β-cells

ATP-sensitive potassium channels (KATP channels) are critical nutrient sensors in many mammalian tissues. In the pancreas, KATP channels are essential for coupling glucose metabolism to insulin secretion. While orthologous genes for many components of metabolism-secretion coupling in mammals are present in lower vertebrates, their expression, functionality and ultimate impact on body glucose homeostasis are unclear. In this paper, we demonstrate that zebrafish islet β-cells express functional KATP channels of similar subunit composition, structure and metabolic sensitivity to their mammalian counterparts. We further show that pharmacological activation of native zebrafish KATP using diazoxide, a specific KATP channel opener, is sufficient to disturb glucose tolerance in adult zebrafish. That β-cell KATP channel expression and function are conserved between zebrafish and mammals illustrates the evolutionary conservation of islet metabolic sensing from fish to humans, and lends relevance to the use of zebrafish to model islet glucose sensing and diseases of membrane excitability such as neonatal diabetes.

Chlorogenic acid rescues sensorineural auditory function in a diabetic animal model

Recently, many studies have reported that sensorineural hearing impairment related to neurological disorders may be caused by diabetes mellitus. However, to date, only a small number of studies have investigated the treatment of sensorineural hearing impairment. In the present study, the effects of chlorogenic acid on diabetic auditory pathway impairment were evaluated by neuro-electrical physiological measurements and morphological investigations. We have shown that CA efficiently prevents the progression of auditory pathway dysfunction caused by DM using auditory brainstem responses and auditory middle latency responses in mice. Additionally, using transient-evoked otoacoustic emissions measurement and scanning electron microscope observation of hair cells in DM mice, we found that CA may aid in the recovery from outer hair cell and otic hair cell damage. In conclusion, CA has beneficial effects for the management of diabetic sensorineural auditory dysfunction.

Enhanced antidiabetic efficacy and safety of compound K⁄β-cyclodextrin inclusion complex in zebrafish

Background

20(S)-Protopanaxadiol 20-O-D-glucopyranoside, also called compound K (CK), exerts antidiabetic effects that are mediated by insulin secretion through adenosine triphosphate (ATP)-sensitive potassium (K_ATP) channels in pancreatic β-cells. However, the antidiabetic effects of CK may be limited because of its low bioavailability.

Methods

In this study, we aimed to enhance the antidiabetic activity and lower the toxicity of CK by including it with β-cyclodextrin (CD) (CD-CK), and to determine whether the CD-CK compound enhanced pancreatic islet recovery, compared to CK alone, in an alloxan-induced diabetic zebrafish model. Furthermore, we confirmed the toxicity of CD-CK relative to CK alone by morphological changes, mitochondrial damage, and TdT-UTP nick end labeling (TUNEL) assays, and determined the ratio between the toxic and therapeutic dose for both compounds to verify the relative safety of CK and CD-CK.

Results

The CD-CK conjugate (EC₅₀ = 2.158μM) enhanced the recovery of pancreatic islets, compared to CK alone (EC₅₀ = 7.221μM), as assessed in alloxan-induced diabetic zebrafish larvae. In addition, CD-CK (LC₅₀ = 20.68μM) was less toxic than CK alone (LC₅₀ = 14.24μM). The therapeutic index of CK and CD-CK was 1.98 and 9.58, respectively.

Conclusion

The CD-CK inclusion complex enhanced the recovery of damaged pancreatic islets in diabetic zebrafish. The CD-CK inclusion complex has potential as an effective antidiabetic efficacy with lower toxicity.

Fishing for Nature's Hits: Establishment of the Zebrafish as a Model for Screening Antidiabetic Natural Products

Diabetes mellitus affects millions of people worldwide and significantly impacts their quality of life. Moreover, life threatening diseases, such as myocardial infarction, blindness, and renal disorders, increase the morbidity rate associated with diabetes. Various natural products from medicinal plants have shown potential as antidiabetes agents in cell-based screening systems. However, many of these potential "hits" fail in mammalian tests, due to issues such as poor pharmacokinetics and/or toxic side effects. To address this problem, the zebrafish (Danio rerio) model has been developed as a "bridge" to provide an experimentally convenient animal-based screening system to identify drug candidates that are active in vivo. In this review, we discuss the application of zebrafish to drug screening technologies for diabetes research. Specifically, the discovery of natural product-based antidiabetes compounds using zebrafish will be described. For example, it has recently been demonstrated that antidiabetic natural compounds can be identified in zebrafish using activity guided fractionation of crude plant extracts. Moreover, the development of fluorescent-tagged glucose bioprobes has allowed the screening of natural product-based modulators of glucose homeostasis in zebrafish. We hope that the discussion of these advances will illustrate the value and simplicity of establishing zebrafish-based assays for antidiabetic compounds in natural products-based laboratories.