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

Evaluation of the wound healing properties of South African medicinal plants using zebrafish and in vitro bioassays

ETHNOPHARMACOLOGICAL RELEVANCE

In South Africa, medicinal plants have a history of traditional use, with many species used for treating wounds. The scientific basis of such uses remains largely unexplored.

AIM OF THE STUDY

To screen South African plants used ethnomedicinally for wound healing based on their pro-angiogenic and wound healing activity, using transgenic zebrafish larvae and cell culture assays.

MATERIALS AND METHODS

South African medicinal plants used for wound healing were chosen according to literature. Dried plant material was extracted using six solvents of varying polarities. Pro-angiogenesis was assessed in vivo by observing morphological changes in sub-intestinal vessels after crude extract treatment of transgenic zebrafish larvae with vasculature-specific expression of a green fluorescent protein. Subsequently, the in vitro anti-inflammatory, fibroblast proliferation and collagen production effects of the plant extracts that were active in the zebrafish angiogenesis assay were investigated using murine macrophage (RAW 264.7) and human fibroblast (MRHF) cell lines.

RESULTS

Fourteen plants were extracted using six different solvents to yield 84 extracts and the non-toxic (n=72) were initially screened for pro-angiogenic activity in the zebrafish assay. Of these plant species, extracts of Lobostemon fruticosus, Scabiosa columbaria and Cotyledon orbiculata exhibited good activity in a concentration-dependent manner. All active extracts showed negligible in vitro toxicity using the MTT assay. Lobostemon fruticosus and Scabiosa columbaria extracts showed noteworthy anti-inflammatory activity in RAW 264.7 macrophages. The acetone extract of Lobostemon fruticosus stimulated the most collagen production at 122% above control values using the MRHF cell line, while all four of the selected extracts significantly stimulated cellular proliferation in vitro in the MRHF cell line.

CONCLUSIONS

The screening of the selected plant species provided valuable preliminary information validating the use of some of the plants in traditional medicine used for wound healing in South Africa. This study is the first to discover through an evidence-based pharmacology approach the wound healing properties of such plant species using the zebrafish as an in vivo model.

Assessment of resveratrol on diabetes of zebrafish (Danio rerio)

Purpose

Zebrafish (Danio rerio) is an established model for studying various metabolic diseases. The aim of this study was to evaluate the effect of resveratrol as a natural polyphenol on reducing inflammation caused by hyperglycemia (diabetes) and its effect on digestive tissue as well as TNF-α, IFN-γ, and INL1β genes in zebrafish.

Methods

Within a 20-day period, the research was performed on 120 adult zebrafish, which were randomly classified into eight groups: two experimental treatments (induced glucose = +G) and (without glucose = -G), where each main group was as follows: CTRL = control and RSV resveratrol with doses 10, 20, and 30 μmol/L. At the end of the period, the blood glucose level was measured using glucose test strip, staining of intestinal tissue was done by hematoxylin and eosin (H&E), and expression of INF-γ, IL1-β, and TNF-α genes extracted from the intestinal was measured via internal method RT-PCR. Data analysis in this study was performed using SPSS software version 21. One-way ANOVA and mean comparison of treatments by Duncan test were used for data analysis. All statistical analyses were performed at a significant level (P < 0.5) where the mean data were presented with standard deviation.

Results

According to the results, the lowest blood sugar level at the end of the experiment belonged to the group (G-RSV20) where no significant difference was observed between treatments (P > 0.05). The highest expression of IL1-β gene belonged to the (G + CTRL) group (P < 0.05), while the (G + RSV20) group showed the lowest expression of the INF-γ gene and had a significant difference with other groups (P < 0.05). In (G + RSV10) treatment, the lowest expression of TNF-α gene was observed and there was no significant difference with other treatments (P > 0.05). Resveratrol would improve the absorption of nutrients in the intestinal tissue by increasing the number of goblet cells as well as the width and height of the villi.

Conclusion

Collectively, this study indicated that treatment with resveratrol could improve metabolic-mediated performances by reducing blood glucose, increasing food absorption in the intestine tissue, and reducing the expression of inflammatory genes in type 2 diabetic zebrafish model.

Future Directions for the Discovery of Natural Product-Derived Immunomodulating Drugs

Drug discovery from natural sources is going through a renaissance, having spent many decades in the shadow of synthetic molecule drug discovery, despite the fact that natural product-derived compounds occupy a much greater chemical space than those created through synthetic chemistry methods. With this new era comes new possibilities, not least the novel targets that have emerged in recent times and the development of state-of-the-art technologies that can be applied to drug discovery from natural sources. Although progress has been made with some immunomodulating drugs, there remains a pressing need for new agents that can be used to treat the wide variety of conditions that arise from disruption, or over-activation, of the immune system; natural products may therefore be key in filling this gap. Recognising that, at present, there is no authoritative article that details the current state-of-the-art of the immunomodulatory activity of natural products, this in-depth review has arisen from a joint effort between the International Union of Basic and Clinical Pharmacology (IUPHAR) Natural Products and Immunopharmacology, with contributions from a Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation number of world-leading researchers in the field of natural product drug discovery, to provide a "position statement" on what natural products has to offer in the search for new immunomodulatory argents. To this end, we provide a historical look at previous discoveries of naturally occurring immunomodulators, present a picture of the current status of the field and provide insight into the future opportunities and challenges for the discovery of new drugs to treat immune-related diseases.

Optimization of ultrasonic-assisted extraction of polyphenols from the polyherbal formulation of Cinnamomum verum, Origanum majorana, and Origanum vulgare and their anti-diabetic capacity in zebrafish (Danio rerio)

The Cinnamomum verum (CV), Origanum majorana (CM), and Origanum vulgare (OV) have been used in traditional medicine in several regions of México for their anti-diabetic properties. In this study investigated the variables of ultrasound-assisted extraction for the polyphenolic compounds from the combination of these plants and explore their potential antidiabetic activities on glucose-induced-diabetic zebrafish. Determined the optimum conditions for ultrasonic-assisted extraction (UAE) to maximum recovery amounts of phenolic compounds from the extract of these plants. Polyphenols were detected in the extracts using HPLC-DAD-analysis. Extracts were evaluated on zebrafish exposed to high glucose concentration (110 mM) for two weeks. Results showed second-order polynomial mathematical models with a high coefficient of determination (R2 > 0.9564). Optimized extraction conditions for UAE from the combination of the 3 plants (COV) were as follows: 66.03%, ethanol, 28.87 min, and 21.51 mL/g for maximal flavonoids extraction. Used the same optimal extraction conditions for CV, CM, and OV. Results from LC-MS/MS indicated 9 polyphenolic compounds in CV, 12 in CM, and 6 in OV, the content of total polyphenols was 310.28, 90.42, and 126.74 mg GAE 100 g-1 dry weight, respectively. However, hyperglycemic fish showed an increase in cholesterol and triglyceride levels whereas extracts completely prevented these metabolic alterations. COV showed higher anti-diabetic ability than CV, CM, and OV, suggesting a synergistic effect between them. Our investigation developed a new herbal formulation of Cinnamomum verum; Origanum majorana; Origanum vulgare that has proven effective in animals with type 2 diabetes will form a new class of supplements to treat diabetic complications.

Metabolism in the Zebrafish Retina

Retinal photoreceptors are amongst the most metabolically active cells in the body, consuming more glucose as a metabolic substrate than even the brain. This ensures that there is sufficient energy to establish and maintain photoreceptor functions during and after their differentiation. Such high dependence on glucose metabolism is conserved across vertebrates, including zebrafish from early larval through to adult retinal stages. As the zebrafish retina develops rapidly, reaching an adult-like structure by 72 hours post fertilisation, zebrafish larvae can be used to study metabolism not only during retinogenesis, but also in functionally mature retinae. The interplay between rod and cone photoreceptors and the neighbouring retinal pigment epithelium (RPE) cells establishes a metabolic ecosystem that provides essential control of their individual functions, overall maintaining healthy vision. The RPE facilitates efficient supply of glucose from the choroidal vasculature to the photoreceptors, which produce metabolic products that in turn fuel RPE metabolism. Many inherited retinal diseases (IRDs) result in photoreceptor degeneration, either directly arising from photoreceptor-specific mutations or secondary to RPE loss, leading to sight loss. Evidence from a number of vertebrate studies suggests that the imbalance of the metabolic ecosystem in the outer retina contributes to metabolic failure and disease pathogenesis. The use of larval zebrafish mutants with disease-specific mutations that mirror those seen in human patients allows us to uncover mechanisms of such dysregulation and disease pathology with progression from embryonic to adult stages, as well as providing a means of testing novel therapeutic approaches.

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.

Curcumin Sensitizes Kidney Cancer Cells to TRAIL-Induced Apoptosis via ROS Mediated Activation of JNK-CHOP Pathway and Upregulation of DR4

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), is a selective anticancer cytokine capable of exerting a targeted therapy approach. Disappointingly, recent research has highlighted the development of TRAIL resistance in cancer cells, thus minimising its usefulness in clinical settings. However, several recent studies have demonstrated that cancer cells can be sensitised to TRAIL through the employment of a combinatorial approach, utilizing TRAIL in conjunction with other natural or synthetic anticancer agents. In the present study, the chemo-sensitising effect of curcumin on TRAIL-induced apoptosis in renal carcinoma cells (RCC) was investigated. The results indicate that exposure of kidney cancer ACHN cells to curcumin sensitised the cells to TRAIL, with the combination treatment of TRAIL and curcumin synergistically targeting the cancer cells without affecting the normal renal proximal tubular epithelial cells (RPTEC/TERT1) cells. Furthermore, this combination treatment was shown to induce caspase-dependent apoptosis, inhibition of the proteasome, induction of ROS, upregulation of death receptor 4 (DR4), alterations in mitogen-activated protein kinase (MAPK) signalling and induction of endoplasmic reticulum stress. An in vivo zebrafish embryo study demonstrated the effectiveness of the combinatorial regime to inhibit tumour formation without affecting zebrafish embryo viability or development. Overall, the results arising from this study demonstrate that curcumin has the ability to sensitise TRAIL-resistant ACHN cells to TRAIL-induced apoptosis.

Glycogen storage in a zebrafish Pompe disease model is reduced by 3-BrPA treatment

Pompe disease (PD) is an autosomal recessive muscular disorder caused by deficiency of the glycogen hydrolytic enzyme acid α-glucosidase (GAA). The enzyme replacement therapy, currently the only available therapy for PD patients, is efficacious in improving cardiomyopathy in the infantile form, but not equally effective in the late onset cases with involvement of skeletal muscle. Correction of the skeletal muscle phenotype has indeed been challenging, probably due to concomitant dysfunctional autophagy. The increasing attention to the pathogenic mechanisms of PD and the search of new therapeutic strategies prompted us to generate and characterize a novel transient PD model, using zebrafish. Our model presented increased glycogen content, markedly altered motor behavior and increased lysosome content, in addition to altered expression of the autophagy-related transcripts and proteins Beclin1, p62 and Lc3b. Furthermore, the model was used to assess the beneficial effects of 3-bromopyruvic acid (3-BrPA). Treatment with 3-BrPA induced amelioration of the model phenotypes regarding glycogen storage, motility behavior and autophagy-related transcripts and proteins. Our zebrafish PD model recapitulates most of the defects observed in human patients, proving to be a powerful translational model. Moreover, 3-BrPA unveiled to be a promising compound for treatment of conditions with glycogen accumulation.

Optimization of Hyperglycemic Induction in Zebrafish and Evaluation of Its Blood Glucose Level and Metabolite Fingerprint Treated with Psychotria malayana Jack Leaf Extract

A standard protocol to develop type 1 diabetes in zebrafish is still uncertain due to unpredictable factors. In this study, an optimized protocol was developed and used to evaluate the anti-diabetic activity of Psychotria malayana leaf. The aims of this study were to develop a type 1 diabetic adult zebrafish model and to evaluate the anti-diabetic activity of the plant extract on the developed model. The ability of streptozotocin and alloxan at a different dose to elevate the blood glucose levels in zebrafish was evaluated. While the anti-diabetic activity of P. malayana aqueous extract was evaluated through analysis of blood glucose and LC-MS analysis fingerprinting. The results indicated that a single intraperitoneal injection of 300 mg/kg alloxan was the optimal dose to elevate the fasting blood glucose in zebrafish. Furthermore, the plant extract at 1, 2, and 3 g/kg significantly reduced blood glucose levels in the diabetic zebrafish. In addition, LC-MS-based fingerprinting indicated that 3 g/kg plant extract more effective than other doses. Phytosterols, sugar alcohols, sugar acid, free fatty acids, cyclitols, phenolics, and alkaloid were detected in the extract using GC-MS. In conclusion, P. malayana leaf aqueous extract showed anti-diabetic activity on the developed type 1 diabetic zebrafish model.

Human carboxylesterases: a comprehensive review

Mammalian carboxylesterases (CEs) are key enzymes from the serine hydrolase superfamily. In the human body, two predominant carboxylesterases (CES1 and CES2) have been identified and extensively studied over the past decade. These two enzymes play crucial roles in the metabolism of a wide variety of endogenous esters, ester-containing drugs and environmental toxicants. The key roles of CES in both human health and xenobiotic metabolism arouse great interest in the discovery of potent CES modulators to regulate endobiotic metabolism or to improve the efficacy of ester drugs. This review covers the structural and catalytic features of CES, tissue distributions, biological functions, genetic polymorphisms, substrate specificities and inhibitor properties of CES1 and CES2, as well as the significance and recent progress on the discovery of CES modulators. The information presented here will help pharmacologists explore the relevance of CES to human diseases or to assign the contribution of certain CES in xenobiotic metabolism. It will also facilitate medicinal chemistry efforts to design prodrugs activated by a given CES isoform, or to develop potent and selective modulators of CES for potential biomedical applications.

Protective effect of Uncaria tomentosa extract against oxidative stress and genotoxicity induced by glyphosate-Roundup® using zebrafish (Danio rerio) as a model

Oxidative stress and DNA damage are involved in the glyphosate-based herbicide toxicity. Uncaria tomentosa (UT; Rubiaceae) is a plant species from South America containing bioactive compounds with known beneficial properties. The objective of this work was to evaluate the antioxidant and antigenotoxic potential of UT extract in a model of acute exposure to glyphosate-Roundup® (GR) in zebrafish (Danio rerio). We showed that UT (1.0 mg/mL) prevented the decrease of brain total thiols, the increase of lipid peroxidation in both brain and liver, and the decrease of liver GPx activity caused after 96 h of GR (5.0 mg/L) exposure. In addition, UT partially protected against the increase of micronucleus frequency induced by GR exposure in fish brain. Overall, our results indicate that UT protects against damage induced by a glyphosate-based herbicide by providing antioxidant and antigenotoxic effects, which may be related to the phenolic compounds identified in the extract.

Identification of Novel Melanin Synthesis Inhibitors From Crataegus pycnoloba Using an in Vivo Zebrafish Phenotypic Assay

Zebrafish has emerged as a powerful model organism for high throughput drug screening. Several morphological criteria, transgenic lines and in situ expression screens have been developed to identify novel bioactive compounds and their mechanism of action. Here, we used the inhibition of melanogenesis during early zebrafish embryo development to identify natural compounds that block melanogenesis. We identified an extract from the Greek hawthorn Crataegus pycnoloba as a potent inhibitor of melanin synthesis and used activity based subfractionation to identify active subfractions and eventually three single compounds of the same family (dibenzofurans). These compounds show reversible inhibition of melanin synthesis and do not act via inhibition of tyrosinase. We also showed that they do not interfere with neural crest differentiation or migration. We identified via in silico modeling that the compounds can bind to the aryl hydrocarbon receptor (AHR) and verified activation of the Ahr signaling pathway showing the induction of the expression of target genes.

Re-education begins at home: an overview of the discovery of in vivo-active small molecule modulators of endogenous stem cells

INTRODUCTION

Degenerative diseases, such as Alzheimer's disease, heart disease and arthritis cause great suffering and are major socioeconomic burdens. An attractive treatment approach is stem cell transplantation to regenerate damaged or destroyed tissues. However, this can be problematic. For example, donor cells may not functionally integrate into the host tissue. An alternative methodology is to deliver bioactive agents, such as small molecules, directly into the diseased tissue to enhance the regenerative potential of endogenous stem cells. Areas covered: In this review, the authors discuss the necessity of developing these small molecules to treat degenerative diseases and survey progress in their application as therapeutics. They describe both the successes and caveats of developing small molecules that target endogenous stem cells to induce tissue regeneration. This article is based on literature searches which encompass databases for biomedical research and clinical trials. These small molecules are also categorized per their target disease and mechanism of action. Expert opinion: The development of small molecules targeting endogenous stem cells is a high-profile research area. Some compounds have made the successful transition to the clinic. Novel approaches, such as modulating the stem cell niche or targeted delivery to disease sites, should increase the likelihood of future successes in this field.