Differential effects of silver nanoparticles on two types of mitochondrion-rich ionocytes in zebrafish embryos

Investigation of verapamil-induced cardiorenal dysfunction and compensatory ion regulation in zebrafish embryos

The purpose of the present study was to investigate the development of verapamil-induced cardiorenal failure and the response of epidermal ionocytes in zebrafish embryos to this syndrome. Zebrafish embryos were exposed to verapamil for 24 h at different developmental stages (48, 72, and 96 h post-fertilization). The exposure resulted in the generation of edema in the pericardial and yolk sac regions, with more-pronounced effects observed in later-stage embryos. Cardiac parameters showed a suppressed heart rate at all stages, with a more-significant effect appearing in later stages. Verapamil also affected cardiac parameters including the end-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), and cardiac output (CO), indicating negative overall effects on cardiac performance. mRNA levels of heart failure markers (nppa and nppb genes) were upregulated in verapamil-exposed embryos at all stages. Renal function was impaired as FITC-dextran excretion was suppressed. A whole-embryo ion content analysis revealed significant increases in sodium and calcium contents in verapamil-exposed embryos. The density of epidermal ionocytes increased, and the apical membrane of ionocytes was enlarged, indicating upregulation of ion uptake. In addition, mRNA levels of several ion transporter genes (rhcg1, slc9a3, atp6v1a, atp2b1a, trpv6, and slc12a10.2) were significantly upregulated in verapamil-exposed embryos. In summary, prolonged exposure to verapamil can induce cardiorenal failure which triggers compensatory upregulation of ionocytes in zebrafish embryos.

Acidified water promotes silver-induced toxicity in zebrafish embryos

Freshwater acidification is a global environmental challenge, yet the effects of acidic water on fish resistance to toxic Ag+ remain an unexplored area. To address this knowledge gap, zebrafish embryos were exposed to different concentrations (0 (control), 0.1, and 0.25 mg/L) of AgNO3 under pH 5 or 7 for 7 days. Notably, AgNO3 at 0.25 mg/L resulted in 100 % mortality in both pH conditions, while AgNO3 at 0.1 mg/L resulted in higher mortality at pH 5 (85 %) compared to pH 7 (20 %), indicating that acidic water enhanced Ag+ toxicity. Several parameters, including body length, inner ear (otic vesicle and otolith) and yolk sac areas, lateral line hair cell number and morphology, the number of ionocytes (H+-ATP-rich cells and Na+/K+-ATP-rich cells), and ion contents (Ag+, Na+, and Ca2+) were assessed at 96 h (day 4) to investigate individual and combined effects of Ag+ and acid on embryos. Acid alone did not significantly alter most parameters, but it decreased the yolk sac area and increased the ionocyte number. Conversely, Ag+ alone caused reductions in most parameters, including body length, the inner ear area, hair cell number, and ionocyte number. Combining acid and Ag+ resulted in greater suppression of the otolith area, hair cell number, and Na+/Ca2+ contents. In conclusion, acidification of freshwater poses a potential risk to fish embryo viability by increasing their susceptibility to silver toxicity, specifically affecting sensory function and ion regulation.

Zebrafish Insights into Nanomaterial Toxicity: A Focused Exploration on Metallic, Metal Oxide, Semiconductor, and Mixed-Metal Nanoparticles

Nanomaterials are widely used in various fields, and ongoing research is focused on developing safe and sustainable nanomaterials. Using zebrafish as a model organism for studying the potentially toxic effects of nanomaterials highlights the importance of developing safe and sustainable nanomaterials. Studies conducted on nanomaterials and their toxicity and potential risks to human and environmental health are vital in biomedical sciences. In the present review, we discuss the potential toxicity of nanomaterials (inorganic and organic) and exposure risks based on size, shape, and concentration. The review further explores various types of nanomaterials and their impacts on zebrafish at different levels, indicating that exposure to nanomaterials can lead to developmental defects, changes in gene expressions, and various toxicities. The review also covers the importance of considering natural organic matter and chorion membranes in standardized nanotoxicity testing. While some nanomaterials are biologically compatible, metal and semiconductor nanomaterials that enter the water environment can increase toxicity to aquatic creatures and can potentially accumulate in the human body. Further investigations are necessary to assess the safety of nanomaterials and their impacts on the environment and human health.

Investigation of ammonia-induced lethal toxicity toward ion regulation in zebrafish embryos

Ammonia is an environmental pollutant that is toxic to all aquatic animals. However, the mechanism of ammonia toxicity toward the ion regulatory function of early-stage fish has not been fully documented. We addressed this issue using zebrafish embryos as a model. We hypothesized that ammonia might impair ion regulation by inducing oxidative stress, mitochondrial dysfunction, and cell death of epidermal ionocytes and keratinocytes in zebrafish embryos. After exposure to various concentrations (10- 30 mM) of NH4Cl for 96 h, mortality increased up to 50 % and 100 % at 25 and 30 mM, respectively. Whole-embryo sodium, potassium, and calcium contents decreased at ≥10 mM, suggesting dysfunction of ion regulation. Numbers of H+-ATPase-rich (HR) cells and Na+/K+-ATPase-rich (NaR) cells (two ionocyte subtypes) were not significantly altered at 15 or 20 mM, while the mitochondrial abundance significantly decreased and reactive oxygen species (ROS) levels significantly increased in ionocytes. Moreover, caspase-3-dependent apoptosis was found in epidermal keratinocytes. Whole-embryo transcript levels of several genes involved in ion regulation, antioxidation, and apoptosis were upregulated after ammonia exposure. In conclusion, ammonia exposure was shown to induce oxidative stress and mitochondrial dysfunction in ionocytes and apoptosis in keratinocytes, thereby impairing ion regulation and ultimately leading to the death of zebrafish embryos.

Comparison of toxicity of silver nanomaterials and silver nitrate on developing zebrafish embryos: Bioavailability, osmoregulatory and oxidative stress

The mechanisms of toxicity of engineered nanomaterials (ENMs) to the early life stages of freshwater fish, and the relative hazard compared to dissolved metals, is only partially understood. In the present study, zebrafish (Danio rerio) embryos were exposed to lethal concentrations of silver nitrate (AgNO₃) or silver (Ag) ENMs (primary size 42.5 ± 10.2 nm). The 96 h-LC₅₀ for AgNO₃ was 32.8 ± 0.72 μg Ag L^-1 (mean ± 95% CI) compared to 6.5 ± 0.4 mg L^-1 of the whole material for Ag ENMs; with the ENMs being orders of magnitude less toxic than the metal salt. The EC₅₀ for hatching success was 30.5 ± 1.4 μg Ag L^-1 and 6.04 ± 0.4 mg L^-1 for AgNO₃ and Ag ENMs, respectively. Further sub-lethal exposures were performed with the estimated LC₁₀ concentrations for both AgNO₃ or Ag ENMs over 96 h where about 3.7% of the total Ag as AgNO₃ was internalised, as measured by Ag accumulation in the dechorionated embryos. However, for the ENMs exposures, nearly all (99.8%) of the total Ag was associated with chorion; indicating the chorion as an effective barrier to protect the embryo in the short term. Calcium (Ca²⁺) and sodium (Na⁺) depletion was induced in embryos by both forms of Ag, but hyponatremia was more pronounced in the nano form. Total glutathione (tGSH) levels declined in embryos exposed to both Ag forms, but a superior depletion occurred with the nano form. Nevertheless, oxidative stress was mild as superoxide dismutase (SOD) activity stayed uniform and the sodium pump (Na⁺/K⁺-ATPase) activity had no appreciable inhibition compared to the control. In conclusion, AgNO₃ was more toxic to the early life stage zebrafish than the Ag ENMs, still differences were found in the exposure and toxic mechanisms of both Ag forms.