Evaluation of Effects of Ractopamine on Cardiovascular, Respiratory, and Locomotory Physiology in Animal Model Zebrafish Larvae

Short- and Long-Term Neurobehavioral Effects of Developmental Exposure to Valproic Acid in Zebrafish

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impairments in social interaction and communication, anxiety, hyperactivity, and interest restricted to specific subjects. In addition to the genetic factors, multiple environmental factors have been related to the development of ASD. Animal models can serve as crucial tools for understanding the complexity of ASD. In this study, a chemical model of ASD has been developed in zebrafish by exposing embryos to valproic acid (VPA) from 4 to 48 h post-fertilization, rearing them to the adult stage in fish water. For the first time, an integrative approach combining behavioral analysis and neurotransmitters profile has been used for determining the effects of early-life exposure to VPA both in the larval and adult stages. Larvae from VPA-treated embryos showed hyperactivity and decreased visual and vibrational escape responses, as well as an altered neurotransmitters profile, with increased glutamate and decreased acetylcholine and norepinephrine levels. Adults from VPA-treated embryos exhibited impaired social behavior characterized by larger shoal sizes and a decreased interest for their conspecifics. A neurotransmitter analysis revealed a significant decrease in dopamine and GABA levels in the brain. These results support the potential predictive validity of this model for ASD research.

Zebrafish mutants in egln1 display a hypoxic response and develop polycythemia

AIMS

Prolyl hydroxylase domain 2 (PHD2), encoded by the Egln1 gene, serves as a pivotal regulator of the hypoxia-inducible factor (HIF) pathway and acts as a cellular oxygen sensor. Somatic inactivation of Phd2 in mice results in polycythemia and congestive heart failure. However, due to the embryonic lethality of Phd2 deficiency, its role in development remains elusive. Here, we investigated the function of two egln1 paralogous genes, egln1a and egln1b, in zebrafish.

MAIN METHODS

The egln1 null zebrafish were generated using the CRISPR/Cas9 system. Quantitative real-time PCR assays and Western blot analysis were employed to detect the effect of egln1 deficiency on the hypoxia signaling pathway. The hypoxia response of egln1 mutant zebrafish were assessed by analyzing heart rate, gill agitation frequency, and blood flow velocity. Subsequently, o-dianisidine staining and in situ hybridization were used to investigate the role of egln1 in zebrafish hematopoietic function.

KEY FINDINGS

Our data show that the loss of egln1a or egln1b individually has no visible effects on growth rate. However, the egln1a; egln1b double mutant displayed significant growth retardation and elevated mortality at around 2.5 months old. Both egln1a-null and egln1b-null zebrafish embryo exhibited enhanced tolerance to hypoxia, systemic hypoxic response that include hif pathway activation, increased cardiac activity, and polycythemia.

SIGNIFICANCE

Our research introduces zebrafish egln1 mutants as the first congenital embryonic viable systemic vertebrate animal model for PHD2, providing novel insights into hypoxic signaling and the progression of PHD2- associated disease.

Environmental concentrations of tire rubber-derived 6PPD-quinone alter CNS function in zebrafish larvae

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-quinone) is a degradation product of 6PPD, an antioxidant widely used in rubber tires. 6PPD-quinone enters aquatic ecosystems through urban stormwater runoff and has been identified as the chemical behind the urban runoff mortality syndrome in coho salmon. However, the available data suggest that the acute effects of 6PPD-quinone are restricted to a few salmonid species and that the environmental levels of this chemical should be safe for most fish. In this study, larvae of a "tolerant" fish species, Danio rerio, were exposed to three environmental concentrations of 6PPD-quinone for only 24 h, and the effects on exploratory behavior, escape response, nonassociative learning (habituation), neurotransmitter profile, wake/sleep cycle, circadian rhythm, heart rate and oxygen consumption rate were analyzed. Exposure to the two lowest concentrations of 6PPD-quinone resulted in altered exploratory behavior and habituation, an effect consistent with some of the observed changes in the neurotransmitter profile, including increased levels of acetylcholine, norepinephrine, epinephrine and serotonin. Moreover, exposure to the highest concentration tested altered the wake/sleep cycle and the expression of per1a, per3 and cry3a, circadian clock genes involved in the negative feedback loop. Finally, a positive chronotropic effect of 6PPD-quinone was observed in the hearts of the exposed fish. The results of this study emphasize the need for further studies analyzing the effects of 6PPD-quinone in "tolerant" fish species.

A comprehensive pharmacological analysis of fenoterol and its derivatives to unravel the role of β2-adrenergic receptor in zebrafish

β-adrenergic receptors (βARs) belong to a key molecular targets that regulate the most important processes occurring in the human organism. Although over the last decades a zebrafish model has been developed as a model complementary to rodents in biomedical research, the role of β₂AR in regulation of pathological and toxicological effects remains to elucidate. Therefore, the study aimed to clarify the role of β₂AR with a particular emphasis on the distinct role of subtypes A and B of zebrafish β₂AR. As model compounds selective β₂AR agonists - (R,R)-fenoterol ((R,R)-Fen) and its new derivatives: (R,R)-4'-methoxyfenoterol ((R,R)-MFen) and (R,R)-4'-methoxy-1-naphtylfenoterol ((R,R)-MNFen) - were tested. We described dose-dependent changes observed after fenoterols exposure in terms of general toxicity, cardiotoxicity and neurobehavioural responses. Subsequently, to better characterise the role of β₂-adrenergic stimulation in zebrafish, we have performed a series of molecular docking simulations. Our results indicate that (R,R)-Fen displays the highest affinity for subtype A of zebrafish β₂AR and β_2AAR might be involved in pigment depletion. (R,R)-MFen shows the lowest affinity for zebrafish β₂ARs out of the tested fenoterols and this might be associated with its cardiotoxic and anxiogenic effects. (R,R)-MNFen displays the highest affinity for subtype B of zebrafish β₂AR and modulation of this receptor might be associated with the development of malformations, increases locomotor activity and induces a negative chronotropic effect. Taken together, the presented data offer insights into the functional responses of the zebrafish β₂ARs confirming their intraspecies conservation, and support the translation of the zebrafish model in pharmacological and toxicological research.

The N-Substituted-4-Methylbenzenesulphonyl Hydrazone Inhibits Angiogenesis in Zebrafish Tg(fli1: EGFP) Model

One of the most important therapies of malignant neoplasms, which are the second cause of death worldwide, is focused on the inhibition of pathological angiogenesis within the tumor. Therefore, the searching for the efficacious and relatively inexpensive small-molecule inhibitors of this process is essential. In this research, the anti-angiogenic potential of N-substituted-4-methylbenzenesulphonyl hydrazone, possessing antiproliferative activity against cancer cells, was tested. For this purpose, an intersegmental vessel (ISV) angiogenesis assay was performed using 6 hpf (hours post fertilization), 12 hpf and 24 hpf embryos of zebrafish transgenic strain, Tg(fli1: EGFP). They were incubated with different concentrations of tested molecule and after 24 h the development of intersegmental vessels of the trunk was analysed. In turn, the acute toxicity study in the zebrafish model was mainly conducted on strain AB, using the OECD-approved and recommended fish embryo acute toxicity test (FET) procedure. The results showed the moderate toxicity of N-[(3-chloro-4-methoxyphenyl)methylidene]-4-methylbenzenesulphonohydrazide in above-mentioned model with the LC₅₀ value calculated at 23.04 mg/L. Moreover, newly synthesized molecule demonstrated the anti-angiogenic potential proved in Tg(fli1: EGFP) zebrafish model, which may be promising for the therapy of neoplastic tumors as well as other diseases related to pathological angiogenesis, such as age-related macular degeneration and diabetic retinopathy.

Ractopamine at the Center of Decades-Long Scientific and Legal Disputes: A Lesson on Benefits, Safety Issues, and Conflicts

Ractopamine (RAC) is a synthetic phenethanolamine, β–adrenergic agonist used as a feed additive to develop leanness and increase feed conversion efficiency in different farm animals. While RAC has been authorized as a feed additive for pigs and cattle in a limited number of countries, a great majority of jurisdictions, including the European Union (EU), China, Russia, and Taiwan, have banned its use on safety grounds. RAC has been under long scientific and political discussion as a controversial antibiotic as a feed additive. Here, we will present significant information on RAC regarding its application, detection methods, conflicts, and legal divisions that play a major role in controversial deadlock and why this issue warrants the attention of scientists, agriculturists, environmentalists, and health advocates. In this review, we highlight the potential toxicities of RAC on aquatic animals to emphasize scientific evidence and reports on the potentially harmful effects of RAC on the aquatic environment and human health.

Detrimental impact of fine dust on zebrafish: Investigating a protective agent against ocular-damage using in vitro and in vivo models

Pollution caused by fine dust is becoming a global problem in the aquatic environment. Many studies have investigated the hazards that fine dust may pose to terrestrial organisms; however, information on the effects on aquatic environments remain limited. In this study, the physicochemical characteristics of the fine dust associated with the captured powder or liquid state were compared using scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). Raw fine dust (RFD), in the captured powder state, was suspended in water (SFD), and the elemental composition, morphology, and size distribution of both were analyzed. Zebrafish were used as a model to study the effects of SFD-exposure on aquatic organisms. A fatal malformation was observed in the integuments of zebrafish exposed to SFD, specifically in the exterior and interior eye tissues. Furthermore, the exposure of SFD to Tg (flk; EGFP) zebrafish remarkably increased ocular vessel diameter expansion along with blood flow velocity. Regarding vessel diameter expansion, EA.hy926 cells exposed to SFD were adversely affected, with a significant increase in cell migration and capillary-like structure formation, which are angiogenic markers. The SFD-induced angiogenesis in vitro and in vivo was dramatically restored to normal via α/β-adenosine isolated from the anti-angiogenic brown algae Ishige okamurae extract. Taken together, the current study presents solid evidence of the altered physicochemical characteristics of SFD compared to RFD, and the detrimental impact of SFD in an aquatic in vivo zebrafish model. In addition, the protective effect of α/β-adenosine, a marine natural product, on SFD-induced angiogenesis suggests that it can be used as an agent to reduce the adverse effects of SFD on aquatic animals.