Which Hyperglycemic Model of Zebrafish (Danio rerio) Suites My Type 2 Diabetes Mellitus Research? A Scoring System for Available Methods

Fish-hunting cone snail disrupts prey's glucose homeostasis with weaponized mimetics of somatostatin and insulin

Venomous animals have evolved diverse molecular mechanisms to incapacitate prey and defend against predators. Most venom components disrupt nervous, locomotor, and cardiovascular systems or cause tissue damage. The discovery that certain fish-hunting cone snails use weaponized insulins to induce hypoglycemic shock in prey highlights a unique example of toxins targeting glucose homeostasis. Here, we show that, in addition to insulins, the deadly fish hunter, Conus geographus, uses a selective somatostatin receptor 2 (SSTR2) agonist that blocks the release of the insulin-counteracting hormone glucagon, thereby exacerbating insulin-induced hypoglycemia in prey. The native toxin, Consomatin nG1, exists in several proteoforms with a minimized vertebrate somatostatin-like core motif connected to a heavily glycosylated N-terminal region. We demonstrate that the toxin's N-terminal tail closely mimics a glycosylated somatostatin from fish pancreas and is crucial for activating the fish SSTR2. Collectively, these findings provide a stunning example of chemical mimicry, highlight the combinatorial nature of venom components, and establish glucose homeostasis as an effective target for prey capture.

Progress in experimental models to investigate the in vivo and in vitro antidiabetic activity of drugs

Diabetes mellitus is one of the world's most prevalent and complex metabolic disorders, and it is a rapidly growing global public health issue. It is characterized by hyperglycemia, a condition involving a high blood glucose level brought on by deficiencies in insulin secretion, decreased activity of insulin, or both. Prolonged effects of diabetes include cardiovascular problems, retinopathy, neuropathy, nephropathy, and vascular alterations in both macro- and micro-blood vessels. In vivo and in vitro models have always been important for investigating and characterizing disease pathogenesis, identifying targets, and reviewing novel treatment options and medications. Fully understanding these models is crucial for the researchers so this review summarizes the different experimental in vivo and in vitro model options used to study diabetes and its consequences. The most popular in vivo studies involves the small animal models, such as rodent models, chemically induced diabetogens like streptozotocin and alloxan, and the possibility of deleting or overexpressing a specific gene by knockout and transgenic technologies on these animals. Other models include virally induced models, diet/nutrition induced diabetic animals, surgically induced models or pancreatectomy models, and non-obese models. Large animals or non-rodent models like porcine (pig), canine (dog), nonhuman primate, and Zebrafish models are also outlined. The in vitro models discussed are murine and human beta-cell lines and pancreatic islets, human stem cells, and organoid cultures. The other enzymatic in vitro tests to assess diabetes include assay of amylase inhibition and inhibition of α-glucosidase activity.

Transcriptome Analysis Reveals the Molecular Basis of Overfeeding-Induced Diabetes in Zebrafish

Diabetes has gradually become a serious disease that threatens human health. It can induce various complications, and the pathogenesis of diabetes is quite complex and not yet fully elucidated. The zebrafish has been widely acknowledged as a useful model for investigating the mechanisms underlying the pathogenesis and therapeutic interventions of diabetes. However, the molecular basis of zebrafish diabetes induced by overfeeding remains unknown. In this study, a zebrafish diabetes model was established by overfeeding, and the molecular basis of zebrafish diabetes induced by overfeeding was explored. Compared with the control group, the body length, body weight, and condition factor index of zebrafish increased significantly after four weeks of overfeeding. There was a significant elevation in the fasting blood glucose level, accompanied by a large number of lipid droplets accumulated within the liver. The levels of triglycerides and cholesterol in both the serum and liver exhibited a statistically significant increase. Transcriptome sequencing was employed to investigate changes in the livers of overfed zebrafish. The number of up-regulated and down-regulated differentially expressed genes (DEGs) was 1582 and 2404, respectively, in the livers of overfed zebrafish. The DEGs were subjected to KEGG and GO enrichment analyses, and the hub signaling pathways and hub DEGs were identified. The results demonstrate that sixteen genes within the signal pathway associated with fatty acid metabolism were found to be significantly up-regulated. Specifically, these genes were found to mainly participate in fatty acid transport, fatty acid oxidation, and ketogenesis. Furthermore, thirteen genes that play a crucial role in glucose metabolism, particularly in the pathways of glycolysis and glycogenesis, were significantly down-regulated in the livers of overfed zebrafish. These results indicate insulin resistance and inhibition of glucose entry into liver cells in the livers of overfed zebrafish. These findings elucidate the underlying molecular basis of zebrafish diabetes induced by overfeeding and provide a model for further investigation of the pathogenesis and therapeutics of diabetes.

Ophthalmic Intervention of Naringenin Decreases Vascular Endothelial Growth Factor by Counteracting Oxidative Stress and Cellular Damage in In Vivo Zebrafish

Diabetes Mellitus is a metabolic disease that leads to microvascular complications like Diabetic retinopathy (DR), a major cause of blindness worldwide. Current medications for DR are expensive and report multiple side effects; therefore, an alternative medication that alleviates the disease condition is required. An interventional approach targeting the vascular endothelial growth factor (VEGF) remains a treatment strategy for DR. Anti-VEGF medicines are being investigated as the main therapy for managing vision-threatening complications of DR, such as diabetic macular oedema. Therefore, this study investigated the effect of flavonoid naringenin (NG) from citrus fruits on inhibiting early DR in zebrafish. When exposed to 130 mM glucose, the zebrafish larvae developed a hyperglycaemic condition accompanied by oxidative stress, cellular damage, and lipid peroxidation. Similarly, when adult zebrafish were exposed to 4% Glucose, high glucose levels were observed in the ocular region and massive destruction in the retinal membrane. High glucose upregulated the expression of VEGF. In comparison, the co-exposure to NG inhibited oxidative stress and cellular damage and restored the glutathione levels in the ocular region of the zebrafish larvae. NG regressed the glucose levels and cellular damage along with an inhibition of macular degeneration in the retina of adult zebrafish and normalized the overexpression of VEGF as a promising strategy for treating DR. Therefore, intervention of NG could alleviate the domestication of alternative medicine in ophthalmic research.

Improvement in Zebrafish with Diabetes and Alzheimer's Disease Treated with Pasteurized Akkermansia muciniphila

Diabetes and Alzheimer's disease (AD) are associated with specific changes in the composition of the intestinal flora. Studies have shown that the supplementation with pasteurized Akkermansia muciniphila has therapeutic and preventive effects on diabetes. However, it is not clear whether there is any association with improvement in and prevention of Alzheimer's disease and diabetes with Alzheimer's disease. Here, we found that pasteurized Akkermansia muciniphila can significantly improve the blood glucose, body mass index, and diabetes indexes of zebrafish with diabetes mellitus complicated with Alzheimer's disease and also alleviate the related indexes of Alzheimer's disease. The memory, anxiety, aggression, and social preference behavior of zebrafish with combined type 2 diabetes mellitus (T2DM) and Alzheimer's disease (TA zebrafish) were significantly improved after pasteurized Akkermansia muciniphila treatment. Moreover, we examined the preventive effect of pasteurized Akkermansia muciniphila on diabetes mellitus complicated with Alzheimer's disease. The results showed that the zebrafish in the prevention group were better in terms of biochemical index and behavior than the zebrafish in the treatment group. These findings provide new ideas for the prevention and treatment of diabetes mellitus complicated with Alzheimer's disease. IMPORTANCE The interaction between intestinal microflora and host affects the progression of diabetes and Alzheimer's disease. As a recognized next-generation probiotic, Akkermansia muciniphila has been shown to play a key role in the progression of diabetes and Alzheimer's disease, but whether A. muciniphila can improve diabetes complicated with Alzheimer's disease and its potential mechanism are unclear. In this study, a new zebrafish model of diabetes mellitus complicated with Alzheimer's disease was established, and the effect of Akkermansia muciniphila on diabetes mellitus complicated with Alzheimer's disease is discussed. The results showed that Akkermansia muciniphila after pasteurization significantly improved and prevented diabetes mellitus complicated with Alzheimer's disease. Treatment with pasteurized Akkermansia muciniphila improved the memory, social preference, and aggressive and anxiety behavior of TA zebrafish and alleviated the pathological characteristics of T2DM and AD. These results provide a new prospect for probiotics in the treatment of diabetes and Alzheimer's disease.

Bioreactor-grown exo- and endo-β-glucan from Malaysian Ganoderma lucidum: An in vitro and in vivo study for potential antidiabetic treatment

This study aims to identify the roles of exo-β-glucan (EPS-BG) and endo-β-glucan (ENS-BG) extracted from Ganoderma lucidum (GL) in inhibiting the alpha-glucosidase enzyme, a target mechanism for postprandial hyperglycaemia regulation. Upscale production of GL was carried out using a 10 L bioreactor. The zebrafish embryo toxicity test (ZFET) was carried out based on OECD guidelines. The hatching rate, survival rate, heart rate, morphological malformation, and teratogenic defects were observed and determined every 24 h from 0–120 h of post-exposure (hpe). For diabetes induction, adult zebrafish (3–4 months of age) were overfed and induced with three doses of 350 mg/kg streptozotocin (STZ) by intraperitoneal injection (IP) on three different days (days 1, 3, and 5). The oral sucrose tolerance test (OSTT) and anti-diabetic activity of EPS-BG and ENS-BG were evaluated (day 7) using the developed model (n = 15). This study showed that EPS is the most potent compound with the highest inhibitory effect toward the alpha-glucosidase enzyme with an IC₅₀ value of 0.1575 mg/ml compared to ENS extracts (IC₅₀ = 0.3479 mg/ml). Both EPS-BG and ENS-BG demonstrated a strong inhibition of alpha-glucosidase activity similar to the clinically approved alpha-glucosidase inhibitor, acarbose (IC₅₀ = 0.8107 mg/ml). ENS-BG is non-toxic toward zebrafish embryos with LC₅₀ of 0.92 mg/ml and showed no significant changes in ZE hatching and normal heart rate as compared to untreated embryos (161 beats/min). Teratogenic effects of ENS-BG (<1.0 mg/ml) on zebrafish embryonic development were not observed. The DM model of zebrafish was acquired after the third dose of STZ with a fasting BGL of 8.98 ± 0.28 mmol/L compared to the normal healthy group (4.23 ± 0.62 mmol/L). The BGL of DM zebrafish after 30 min treated with EPS-BG and ENS-BG showed a significant reduction (p < 0.0001). Both EPS-BG and ENS-BG significantly reduced DM zebrafish’s peak blood glucose and the area under the curve (AUC) in OSTT. Hence, EPS-BG and ENS-BG extracted from GL showed promising inhibition of the alpha-glucosidase enzyme and are considered non-toxic in ZE. Moreover, EPS-BG and ENS-BG reduced blood glucose levels and inhibited hyperglycemia in DM zebrafish.

Thiosulfate sulfurtransferase prevents hyperglycemic damage to the zebrafish pronephros in an experimental model for diabetes

Thiosulfate sulfurtransferase (TST, EC 2.8.1.1), also known as Rhodanese, was initially discovered as a cyanide detoxification enzyme. However, it was recently also found to be a genetic predictor of resistance to obesity-related type 2 diabetes. Diabetes type 2 is characterized by progressive loss of adequate β-cell insulin secretion and onset of insulin resistance with increased insulin demand, which contributes to the development of hyperglycemia. Diabetic complications have been replicated in adult hyperglycemic zebrafish, including retinopathy, nephropathy, impaired wound healing, metabolic memory, and sensory axonal degeneration. Pancreatic and duodenal homeobox 1 (Pdx1) is a key component in pancreas development and mature beta cell function and survival. Pdx1 knockdown or knockout in zebrafish induces hyperglycemia and is accompanied by organ alterations similar to clinical diabetic retinopathy and diabetic nephropathy. Here we show that pdx1-knockdown zebrafish embryos and larvae survived after incubation with thiosulfate and no obvious morphological alterations were observed. Importantly, incubation with hTST and thiosulfate rescued the hyperglycemic phenotype in pdx1-knockdown zebrafish pronephros. Activation of the mitochondrial TST pathway might be a promising option for therapeutic intervention in diabetes and its organ complications.

High glucose-induced ROS-accumulation in embryo-larval stages of zebrafish leads to mitochondria-mediated apoptosis

In recent decades, diabetes mellitus has become a major chronic disease threatening human health worldwide, and the age of patients tends to be younger; however, the pathogenesis remains unclear, resulting in many difficulties in its treatment. As an ideal model animal, zebrafish can simulate the processes of human diabetes well. In this study, we successfully established a model of diabetic zebrafish larvae in a previous work. Furthermore, transcriptome analysis was completed, and the results suggested that 10.59% of differentially expressed genes (DEGs) related to the apoptosis pathway need to be considered. Then, glucose-induced developmental toxicity, reactive oxygen species (ROS) accumulation, antioxidant system function, apoptosis and mitochondrial dysfunction were measured in zebrafish larvae. We hope that this study will provide valuable reference information for type 2 juvenile diabetes treatment.

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.

Vitamin D regulates insulin pathway and glucose metabolism in zebrafish (Danio rerio)

1,25-dihydroxyvitamin D₃ [1,25(OH)₂ D₃ ], the most active vitamin D (VD) metabolite, is a steroid hormone playing an important role in many physiological functions in addition to maintaining mineral homeostasis. In this study, we explored the mechanism that the VD regulated insulin pathway and glucose metabolism in zebrafish in vitro and in vivo. Our results show that 1,25(OH)₂ D₃  significantly enhances the expression of insulin receptor a (insra), insulin receptor substrate 1 (irs1) and glucose transporter 2 (glut2), and promotes glycolysis and glycogenesis, while suppressing gluconeogenesis in zebrafish liver cell line (ZFL) under the condition of high glucose (20 mM), instead of the normal glucose (10 mM). Moreover, consistent results were obtained from the zebrafish fed with VD₃ -deficient diet, as well as the cyp2r1^-/- zebrafish, in which endogenous VD metabolism is blocked. Furthermore, results from dual-luciferase reporting system exhibited that 1,25(OH)₂ D₃ directly activated the transcription of insra, rather than insrb in zebrafish by binding to vitamin D response element (VDRE) located at -181 to -167 bp in the promoter region of insra. Importantly, the 1,25(OH)₂ D₃ treatment significantly alleviated the symptoms of hyperglycemia in diabetic zebrafish. In conclusion, our study demonstrated that VD activates VDRE located in the promoter area of insra in zebrafish to promote insulin/insra signaling pathway, thereby contributing to the maintenance of glucose homeostasis.

The endocannabinoid system in zebrafish and its potential to study the effects of Cannabis in humans

Zebrafish is considered an unprecedented animal model in drug discovery. A review of the literature presents highlights and elucidates the biological effects of chemical components found in Cannabis sativa. Particular attention is paid to endocannabinoid system (eCB) and its main receptors (CB1 and CB2). The zebrafish model is a promising one for the study of cannabinoids because of the many similarities to the human system. Despite the recent advances on the eCB system, there is still the need to elucidate some of the interactions and, thus, the zebrafish model can be used for that purpose as it respects the 3Rs concept and reduced time and costs. In view of the relevance of cannabinoids in the treatment and prevention of diseases, as well as the importance of the zebrafish animal model in elucidating the biological effects of new drugs, the aim of this study was to bring to light information on the use of the zebrafish animal model in testing C. sativa-based medicines.

Functional Validation of Osteoporosis Genetic Findings Using Small Fish Models

The advancement of human genomics has revolutionized our understanding of the genetic architecture of many skeletal diseases, including osteoporosis. However, interpreting results from human association studies remains a challenge, since index variants often reside in non-coding regions of the genome and do not possess an obvious regulatory function. To bridge the gap between genetic association and causality, a systematic functional investigation is necessary, such as the one offered by animal models. These models enable us to identify causal mechanisms, clarify the underlying biology, and apply interventions. Over the past several decades, small teleost fishes, mostly zebrafish and medaka, have emerged as powerful systems for modeling the genetics of human diseases. Due to their amenability to genetic intervention and the highly conserved genetic and physiological features, fish have become indispensable for skeletal genomic studies. The goal of this review is to summarize the evidence supporting the utility of Zebrafish (Danio rerio) for accelerating our understanding of human skeletal genomics and outlining the remaining gaps in knowledge. We provide an overview of zebrafish skeletal morphophysiology and gene homology, shedding light on the advantages of human skeletal genomic exploration and validation. Knowledge of the biology underlying osteoporosis through animal models will lead to the translation into new, better and more effective therapeutic approaches.

Stem Cell Research Tools in Human Metabolic Disorders: An Overview

Metabolic disorders are very common in the population worldwide and are among the diseases with the highest health utilization and costs per person. Despite the ongoing efforts to develop new treatments, currently, for many of these disorders, there are no approved therapies, resulting in a huge economic hit and tension for society. In this review, we recapitulate the recent advancements in stem cell (gene) therapy as potential tools for the long-term treatment of both inherited (lysosomal storage diseases) and acquired (diabetes mellitus, obesity) metabolic disorders, focusing on the main promising results observed in human patients and discussing the critical hurdles preventing the definitive jump of this approach from the bench to the clinic.

Glucose inhibits haemostasis and accelerates diet-induced hyperlipidaemia in zebrafish larvae

Hyperglycaemia damages the microvasculature in part through the reduced recruitment of immune cells and interference with platelet signalling, leading to poor wound healing and accelerated lipid deposition in mammals. We investigated the utility of zebrafish larvae to model the effect of exogenous glucose on neutrophil and macrophage recruitment to a tail wound, wound-induced haemostasis, and chicken egg yolk feed challenge-induced hyperlipidaemia by supplementing larvae with exogenous glucose by immersion or injection. Neither method of glucose supplementation affected the recruitment of neutrophils and macrophages following tail transection. Glucose injection reduced thrombocyte retention and fibrin plug formation while only thrombocyte retention was reduced by glucose immersion following tail transection. We observed accelerated lipid accumulation in glucose-injected larvae challenged with high fat chicken egg yolk feeding. Our study identifies conserved and divergent effects of high glucose on inflammation, haemostasis, and hyperlipidaemia in zebrafish larvae compared to mammals.

Zebrafish Model in Ophthalmology to Study Disease Mechanism and Drug Discovery

Visual impairment and blindness are common and seriously affect people’s work and quality of life in the world. Therefore, the effective therapies for eye diseases are of high priority. Zebrafish (Danio rerio) is an alternative vertebrate model as a useful tool for the mechanism elucidation and drug discovery of various eye disorders, such as cataracts, glaucoma, diabetic retinopathy, age-related macular degeneration, photoreceptor degeneration, etc. The genetic and embryonic accessibility of zebrafish in combination with a behavioral assessment of visual function has made it a very popular model in ophthalmology. Zebrafish has also been widely used in ocular drug discovery, such as the screening of new anti-angiogenic compounds or neuroprotective drugs, and the oculotoxicity test. In this review, we summarized the applications of zebrafish as the models of eye disorders to study disease mechanism and investigate novel drug treatments.

Advancing Diabetic Retinopathy Research: Analysis of the Neurovascular Unit in Zebrafish

Diabetic retinopathy is one of the most important microvascular complications associated with diabetes mellitus, and a leading cause of vision loss or blindness worldwide. Hyperglycaemic conditions disrupt microvascular integrity at the level of the neurovascular unit. In recent years, zebrafish (Danio rerio) have come into focus as a model organism for various metabolic diseases such as diabetes. In both mammals and vertebrates, the anatomy and the function of the retina and the neurovascular unit have been highly conserved. In this review, we focus on the advances that have been made through studying pathologies associated with retinopathy in zebrafish models of diabetes. We discuss the different cell types that form the neurovascular unit, their role in diabetic retinopathy and how to study them in zebrafish. We then present new insights gained through zebrafish studies. The advantages of using zebrafish for diabetic retinopathy are summarised, including the fact that the zebrafish has, so far, provided the only animal model in which hyperglycaemia-induced retinal angiogenesis can be observed. Based on currently available data, we propose potential investigations that could advance the field further.

Zebrafish and Flavonoids: Adjuvants against Obesity

Obesity is a pathological condition, defined as an excessive accumulation of fat, primarily caused by an energy imbalance. The storage of excess energy in the form of triglycerides within the adipocyte leads to lipotoxicity and promotes the phenotypic switch in the M1/M2 macrophage. These changes induce the development of a chronic state of low-grade inflammation, subsequently generating obesity-related complications, commonly known as metabolic syndromes. Over the past decade, obesity has been studied in many animal models. However, due to its competitive aspects and unique characteristics, the use of zebrafish has begun to gain traction in experimental obesity research. To counteract obesity and its related comorbidities, several natural substances have been studied. One of those natural substances reported to have substantial biological effects on obesity are flavonoids. This review summarizes the results of studies that examined the effects of flavonoids on obesity and related diseases and the emergence of zebrafish as a model of diet-induced obesity.