The developmental toxicity and apoptosis in zebrafish eyes induced by carbon-ion irradiation

Visual toxicity in zebrafish larvae following exposure to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), triphenyl phosphate (TPhP), and isopropyl phenyl diphenyl phosphate (IPPP)

TPhP and IPPP, alternatives to PBDEs as flame retardants, have been studied for their developmental toxicity, but their visual toxicities are less understood. In this study, zebrafish larvae were exploited to evaluate the potential ocular impairments following exposure to BDE-47, TPhP, and IPPP. The results revealed a range of ocular abnormalities, including malformation, vascular issues within the eyes, and histopathological changes in the retina. Notably, the visually mediated behavioral changes were primarily observed in IPPP and TPhP, indicating that they caused more severe eye malformations and vision impairment than BDE-47. Molecular docking and MD simulations showed stronger binding affinity of TPhP and IPPP to RAR and RBP receptors. Elevated ROS and T3 levels induced by these compounds led to apoptosis in larvae eyes, and increased GABA levels induced by TPhP and IPPP hindered retinal repair. In summary, our results indicate TPhP and IPPP exhibit severer visual toxicity than BDE-47, affecting eye development and visually guided behaviors. The underlying mechanism involves disruptions in RA signaling, retinal neurotransmitters imbalance, thyroid hormones up-regulation, and apoptosis in larvae eyes. This work highlights novel insights into the need for cautious use of these flame retardants due to their potential biological hazards, thereby offering valuable guidance for their safer applications.

N-nitrosodimethylamine exposure to zebrafish embryos/larvae causes cardiac and spinal developmental toxicity

N-nitrosodimethylamine (NDMA), one of the new nitrogen-containing disinfection by-products, is potentially cytotoxic, genotoxic, and carcinogenic. Its potential toxicological effects have attracted a wide range of attention, but the mechanism is still not sufficiently understood. To better understand the toxicological mechanisms of NDMA, zebrafish embryos were exposed to NDMA from 3 h post-fertilization (hpf) to 120hpf. Mortality and malformation were significantly increased, and hatching rate, heart rate, and swimming behavior were decreased in the exposure groups. The result indicated that NDMA exposure causes cardiac and spinal developmental toxicity. mRNA levels of genes involved in the apoptotic pathway, including p53, bax, and bcl-2 were significantly affected by NDMA exposure. Moreover, the genes associated with spinal and cardiac development (myh6, myh7, nkx2.5, eph, bmp2b, bmp4, bmp9, run2a, and run2b) were significantly downregulated after treatment with NDMA. Wnt and TGF-β signaling pathways, crucial for the development of diverse tissues and organs in the embryo and the establishment of the larval spine, were also significantly disturbed by NDMA treatment. In summary, the disinfection by-product, NDMA, exhibits spinal and cardiac developmental toxicity in zebrafish embryos, providing helpful information for comprehensive analyses and a better understanding the mechanism of its toxicity.

Synergetic effects of polyethylene microplastic and abamectin pesticides on the eyes of zebrafish larvae and adults through activation of apoptosis signaling pathways

Although the toxicity of microplastics (MPs) and pesticides has recently been described, the possible effects of combining these pollutants are poorly understood. Thus, we evaluated the potential impact of exposure to polyethylene MP (PE-MP) and abamectin (ABM) (alone and combined) in zebrafish. After five days, the combined exposure to MP and ABM decreased the survival rate compared to exposures to individual pollutants. A significant increase in reactive oxygen species (ROS), lipid peroxidation, apoptosis, and impairment in antioxidant response was observed in zebrafish larvae. Morphological changes in the eyes of zebrafish significantly increased in the combined exposure group than in the individual exposure. Furthermore, the bax and p53 expression (specific apoptotic genes) was significantly upregulated after the combined exposure to PE-MP and ABM. So, the synergetic effect of MP and ABM cannot be ignored, and further research on other higher models is required to confirm its consequences.

Environmentally relevant concentrations of F-53B induce eye development disorders-mediated locomotor behavior in zebrafish larvae

The perfluorooctane sulfonate alternative, F-53B, induces multiple physiological defects but whether it can disrupt eye development is unknown. We exposed zebrafish to F-53B at four different concentrations (0, 0.15, 1.5, and 15 μg/L) for 120 h post-fertilization (hpf). Locomotor behavior, neurotransmitters content, histopathological alterations, morphological changes, cell apoptosis, and retinoic acid signaling were studied. Histology and morphological analyses showed that F-53B induced pathological changes in lens and retina of larvae and eye size were significantly reduced as compared to control. Acridine orange (AO) staining revealed a dose-dependent increase in early apoptosis, accompanied by upregulation of p53, casp-9 and casp-3 genes. Genes related to retinoic acid signaling (aldh1a2), lens developmental (cryaa, crybb, crygn, and mipa) and retinal development (pax6, rx1, gant1, rho, opn1sw and opn1lw) were significantly downregulated. In addition, behavioral responses (swimming speed) were significantly increased, while no significant changes in the neurotransmitters (dopamine and acetylcholine) level were observed. Therefore, in this study we observed that exposure to F-53B inflicted histological and morphological changes in zebrafish larvae eye, induced visual motor dysfunctions, perturbed retinoid signaling and retinal development and ultimately triggering apoptosis.

Zebrafish as an Animal Model for Ocular Toxicity Testing: A Review of Ocular Anatomy and Functional Assays

Xenobiotics make their way into organisms from diverse sources including diet, medication, and pollution. Our understanding of ocular toxicities from xenobiotics in humans, livestock, and wildlife is growing thanks to laboratory animal models. Anatomy and physiology are conserved among vertebrate eyes, and studies with common mammalian preclinical species (rodent, dog) can predict human ocular toxicity. However, since the eye is susceptible to toxicities that may not involve a histological correlate, and these species rely heavily on smell and hearing to navigate their world, discovering visual deficits can be challenging with traditional animal models. Alternative models capable of identifying functional impacts on vision and requiring minimal amounts of chemical are valuable assets to toxicology. Human and zebrafish eyes are anatomically and functionally similar, and it has been reported that several common human ocular toxicants cause comparable toxicity in zebrafish. Vision develops rapidly in zebrafish; the tiny larvae rely on visual cues as early as 4 days, and behavioral responses to those cues can be monitored in high-throughput fashion. This article describes the comparative anatomy of the zebrafish eye, the notable differences from the mammalian eye, and presents practical applications of this underutilized model for assessment of ocular toxicity.

Radiosensitivity enhancement by Co-NMS-mediated mitochondrial impairment in glioblastoma

We investigated the radiosensitizing effects of Co-NMS, a derivative of nimesulide based on a cobalt carbonyl complex, on malignant glioma cells. In the zebrafish exposed to Co-NMS ranging from 5 to 20 μM, cell death and heat shock protein 70 expression in the brain and neurobehavioral performance were evaluated. Our data showed that Co-NMS at 5 μM did not cause the appreciable neurotoxicity, and thereby was given as a novel radiation sensitizer in further study. In the U251 cells, Co-NMS combined with irradiation treatment resulted in significant inhibition of cell growth and clonogenic capability as well as remarkable increases of G2/M arrest and apoptotic cell population compared to the irradiation alone treatment. This demonstrated that the Co-NMS administration exerted a strong potential of sensitizing effect on the irradiated cells. With regard to the tumor radiosensitization of Co-NMS, it could be primarily attributed to the Co-NMS-derived mitochondrial impairment, reflected by the loss of mitochondrial membrane potential, the disruption of mitochondrial fusion and fission balance as well as redox homeostasis. Furthermore, the energy metabolism of the U251 cells was obviously suppressed by cotreatment with Co-NMS and irradiation through repressing mitochondrial function. Taken together, our findings suggested that Co-NMS could be a desirable drug to enhance the radiotherapeutic effects in glioblastoma patients.

Embryotoxicity assessment and efficient removal of naphthalene from water by irradiated graphene aerogels

Naphthalene has remained a challenge how to eradicate it from the water because of its carcinogenic risk to humans. In the present study, naphthalene prominently increased the rates of embryonic mortality and malformation, and decreased the hatchability of zebrafish which have a high developmental similarity to humans. Moreover, multiple-organ toxicity were notably found in naphthalene-treated zebrafish. Here, irradiated graphene aerogel (IGA) was successfully prepared from high-energy electron beam to generate more wrinkles, folds, defects and a strong absorption capability for naphthalene, compared with the non-irradiated graphene aerogel. IGA was outstandingly found to remove naphthalene from the embryo culture medium, and subsequently inhibit the embryotoxicity and maintain tissue integrity by restoring cardiac function, attenuating apoptosis signals, recovering eye morphology and structure, reducing expression of heat shock protein 70 in the tissues and promoting behavioral capacity. Meanwhile, no obvious negative impact of IGA was found in the developing zebrafish from embryo to larvae. Consequently, reduction in the toxicity of naphthalene during zebrafish embryogenesis was mediated by IGA as an advanced strategy.

Trimethyltin chloride induces reactive oxygen species-mediated apoptosis in retinal cells during zebrafish eye development

Trimethyltin chloride (TMT), one of the most widely used organotin compounds in industrial and agricultural fields, is widespread in soil, aquatic systems, foodstuffs and household items. TMT reportedly has toxic effects on the nervous system; however, there is limited information about its effects on eye development and no clear associated mechanisms have been identified. Therefore, in the present study, we investigated eye morphology, vison-related behavior, reactive oxygen species (ROS) production, apoptosis, histopathology, and gene expression to evaluate the toxicity of TMT during ocular development in zebrafish embryos. Exposure to TMT decreased the axial length and surface area of the eye and impaired the ability of zebrafish to recognize light. 2',7'-dichlorofluorescein diacetate and acridine orange assays revealed dose-dependent increases in ROS formation and apoptosis in the eye. Furthermore, pyknosis of retinal cells was confirmed through histopathological analysis. Antioxidative enzyme-related genes were downregulated and apoptosis-inducing genes were upregulated in TMT-treated zebrafish compared to expression in controls. Retinal cell-specific gene expression was suppressed mainly in retinal ganglion cells, bipolar cells, and photoreceptor cells, whereas amacrine cell-, horizontal cell-, and Müller cell-specific gene expression was enhanced. Our results demonstrate for the first time the toxicity of TMT during eye development, which occurs through the induction of ROS-mediated apoptosis in retinal cells during ocular formation.

Toxic effects of 56Fe ion radiation on the zebrafish (Danio rerio) embryonic development

All living organisms and ecosystems are permanently exposed to ionizing radiation. Of all the types of ionizing radiation, heavy ions such as ⁵⁶Fe have the potential to cause the most severe biological effects. We therefore examined the effects and potential mechanisms of iron ion irradiation on the induction of developmental toxicity and apoptosis in zebrafish embryos. Zebrafish embryos at 4h post-fertilization (hpf) were divided into five groups: a control group; and four groups irradiated with 0.5, 1, 2, and 4Gy radiation, respectively. Mortality and teratogenesis were significantly increased, and spontaneous movement, heart rate, and swimming distance were decreased in the irradiated groups, accompanied by increased apoptosis. mRNA levels of genes involved in the apoptotic pathway, including p53, bax, bcl-2, and caspase-3, were significantly affected by radiation exposure. Moreover, protein expression levels of P53 and Bcl-2 changed in accordance with the corresponding mRNA expression levels. In addition, we detected the protein expression levels of γ-H2AX, which is a biomarker for radiation-induced DNA double-strand breaks, and found that γ-H2AX protein levels were significantly increased in the irradiated groups. Overall, the results of this study improve our understanding of the mechanisms of iron ion radiation-induced developmental toxicity and apoptosis, potentially involving the induction of DNA damage and mitochondrial dysfunction. The findings of this study may aid future impact assessment of environmental radioactivity in fish.

Effect of PMA-induced protein kinase C activation on development and apoptosis in early zebrafish embryos

Protein kinase C (PKC) isoforms have been implicated in several key steps during early development, but the consequences of xenobiotic-induced PKC activation during early embryogenesis are still unknown. In this study, zebrafish embryos were exposed to a range of phorbol 12-myristate 13-acetate (PMA) concentrations (0-200μg/L) at different time points after fertilization. Results showed that 200μgPMA/L caused development of yolk bags, cardiac edema, slow blood flow, pulsating blood flow, slow pulse, elongated heart, lack of tail fins, curved tail, and coagulation. PMA exposure decreased survival rate of the embryos starting within the first 24h and becoming more pronounced after prolonged exposure (96h). PMA increased the number of apoptotic cells in the brain region as demonstrated by acridine orange staining and caused up-regulation of caspase 9 (casp9) and p53 up-regulated modulator of apoptosis (puma) mRNA in whole embryos. PMA caused oxidative stress in the embryos as demonstrated by decreased mRNA expression of catalase and superoxide dismutase 2. Inhibition of Pkc with GF109203X improved overall survival rate, reduced apoptosis in the brain and decreased expression of casp9 and puma in the PMA-exposed embryos. However, Pkc inhibition neither prevented development of deformities nor reversed oxidative stress in the PMA-exposed embryos. These data suggest that direct over-activation of Pkc during early embryogenesis of zebrafish is associated with apoptosis and decreased survival rate of the embryos.

Liver Fatty Acid Binding Protein Deficiency Provokes Oxidative Stress, Inflammation, and Apoptosis-Mediated Hepatotoxicity Induced by Pyrazinamide in Zebrafish Larvae

Pyrazinamide (PZA) is an essential antitubercular drug, but little is still known about its hepatotoxicity potential. This study examined the effects of PZA exposure on zebrafish (Danio rerio) larvae and the mechanisms underlying its hepatotoxicity. A transgenic line of zebrafish larvae that expressed enhanced green fluorescent protein (EGFP) in the liver was incubated with 1, 2.5, and 5 mM PZA from 72 h postfertilization (hpf). Different endpoints such as mortality, morphology changes in the size and shape of the liver, histological changes, transaminase analysis and apoptosis, markers of oxidative and genetic damage, as well as the expression of certain genes were selected to evaluate PZA-induced hepatotoxicity. Our results confirm the manner of PZA dose-dependent hepatotoxicity. PZA was found to induce marked injury in zebrafish larvae, such as liver atrophy, elevations of transaminase levels, oxidative stress, and hepatocyte apoptosis. To further understand the mechanism behind PZA-induced hepatotoxicity, changes in gene expression levels in zebrafish larvae exposed to PZA for 72 h postexposure (hpe) were determined. The results of this study demonstrated that PZA decreased the expression levels of liver fatty acid binding protein (L-FABP) and its target gene, peroxisome proliferator-activated receptor α (PPAR-α), and provoked more severe oxidative stress and hepatitis via the upregulation of inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) and transforming growth factor β (TGF-β). These findings suggest that L-FABP-mediated PPAR-α downregulation appears to be a hepatotoxic response resulting from zebrafish larva liver cell apoptosis, and L-FABP can be used as a biomarker for the early detection of PZA-induced liver damage in zebrafish larvae.

Effects of Ru(CO)3Cl-glycinate on the developmental toxicities induced by X-ray and carbon-ion irradiation in zebrafish embryos

The inhibitory effects of carbon monoxide (CO), generated by Ru(CO)₃Cl-glycinate [CO-releasing molecule (CORM-3)], on developmental toxicity in zebrafish embryos induced by ionizing radiation with different linear energy transfer (LET) were studied. Zebrafish embryos at 5h post-fertilization were irradiated with X-ray (low-LET) and carbon-ion (high-LET) with or without pretreatment of CORM-3 1h before irradiation. CORM-3 pre-treatment showed a significant inhibitory effect on X-ray irradiation-induced developmental toxicity, but had little effect on carbon-ion irradiation-induced developmental toxicity. X-ray irradiation-induced significant increase in ROS levels and cell apoptosis could be modified by CORM-3 pretreatment. However, embryos exposed to carbon-ion irradiation showed significantly increase of cell apoptosis without obvious ROS generation, which could not be attenuated by CORM-3 pretreatment. CORM-3 could inhibit apoptosis induced by ionizing radiation with low-LET as an effective ROS scavenger. The expression of pro-apoptotic genes increased significantly after X-ray irradiation, but increased expression was reduced markedly when CORM-3 was applied before irradiation. Moreover, the protein levels of P53 and γ-H2AX increased markedly after X-ray irradiation, which could be modified by the presence of CORM-3. The protective effect of CORM-3 on X-ray irradiation occurred mainly by suppressing ROS generation and DNA damage, and thus inhibiting the activation of P53 and the mitochondrial apoptotic pathway, leading to the attenuation of cell apoptosis and consequently alleviating X-ray irradiation-induced developmental toxicity at lethal and sub-lethal levels.