Sensory systems and ionocytes are targets for silver nanoparticle effects in fish

In vivo toxicological assessment of silver nanoparticle in edible fish, Oreochromis mossambicus

Silver nanoparticles are the extensively utilized among all nanoparticles due to their antibacterial and wound healing properties making them highly suitable for medical and pharmaceutical applications. The field of nanoparticle toxicity is an emerging field and the present study aims to assess the biochemical, hematological and genotoxicity in Oreochromis mossambicus exposed to different concentrations of silver nanoparticles for 7 and 14 days. Silver nanoparticles were synthesized by reduction of silver nitrate using trisodium citrate and was characterized using X-ray diffraction, SEM, HRTEM and DLS. Hematological parameters like RBC, WBC, Hb, HCT and MCV and for biochemical analysis, antioxidant enzymes SOD, CAT and GPX and serum enzymes AST, ALT, ACP, ALP and LDH were analyzed. Genotoxicity was studied using comet assay. Results obtained showed decrease in erythrocytes, HCT, Hb and MCV while an increase was noted in WBC on day 7 and 14. The antioxidant enzymes SOD, CAT and GPx showed a decrease and the lipid peroxidation product MDA was elevated. The serum enzymes AST, ALT, ACP ALP and LDH showed an increased activity when compared to control. DNA damage was evident by an increase in % TDNA. The results indicate hematological, biochemical and genotoxicity of silver nanoparticles that might be mediated through ROS generation in O. mossambicus.

Toxicity assessment of poultry-waste biosynthesized nanosilver in Anabas testudineus (Bloch, 1792) for responsible and sustainable aquaculture development-A multi-biomarker approach

The current study investigates the potential utilization of poultry intestines for the synthesis of stable silver nanoparticles (AgNPs) and their impact on fish physiology. The AgNPs were synthesized and characterized using various analytical techniques. The toxicity of AgNPs on Anabas testudineus was evaluated, determining a 96-h LC50 value of 25.46 mg l-1. Subsequently, fish were exposed to concentrations corresponding to 1/10th, 1/25th, 1/50th, and 1/100th of the estimated LC50 for a duration of 60 days in a sub-acute study. A comprehensive range of biomarkers, including haematological, serum, oxidative stress, and metabolizing markers, were analyzed to assess the physiological responses of the fish. Additionally, histopathological examinations were conducted, and the accumulation of silver in biomarker organs was measured. The results indicate that silver tends to bioaccumulate in all biomarker organs in a dose- and time-dependent manner, except for the muscle tissue, where accumulation initially increased and subsequently decreased, demonstrating the fish's inherent ability for natural attenuation. Analysis of physiological data and integrated biomarker responses reveal that concentrations of 1/10th, 1/25th, and 1/50th of the LC50 can induce stress in the fish, while exposure to 1/100th of the LC50 shows minimal to no stress response. Overall, this study provides valuable insights into the toxicity and physiological responses of fish exposed to poultry waste biosynthesized AgNPs, offering potential applications in aquaculture while harnessing their unique features.

Mortality and histopathology in sheepshead minnow (Cyprinodon variegatus) larvae exposed to pectenotoxin-2 and Dinophysis acuminata

Toxic species of the dinoflagellate genus Dinophysis can produce diarrheic toxins including okadaic acid (OA) and dinophysistoxins (DTXs), and the non-diarrheic pectenotoxins (PTXs). Okadaic acid and DTXs cause diarrheic shellfish poisoning (DSP) in human consumers, and also cause cytotoxic, immunotoxic and genotoxic effects in a variety of mollusks and fishes at different life stages in vitro. The possible effects of co-produced PTXs or live cells of Dinophysis to aquatic organisms, however, are less understood. Effects on an early life stage of sheepshead minnow (Cyprinodon variegatus), a common finfish in eastern USA estuaries, were evaluated using a 96-h toxicity bioassay. Three-week old larvae were exposed to PTX2 concentrations from 50 to 4000 nM, live Dinophysis acuminata culture (strain DAVA01), live cells resuspended in clean medium or culture filtrate. This D. acuminata strain produced mainly intracellular PTX2 (≈ 21 pg cell^-1), with much lower levels of OA and dinophysistoxin-1. No mortality or gill damages were observed in larvae exposed to D. acuminata (from 5 to 5500 cells mL^-1), resuspended cells and culture filtrate. However, exposure to purified PTX2 at intermediate to high concentrations (from 250 to 4000 nM) resulted in 8 to 100% mortality after 96 h (24-h LC₅₀ of 1231 nM). Histopathology and transmission electron microscopy of fish exposed to intermediate to high PTX2 concentrations revealed important gill damage, including intercellular edema, necrosis and sloughing of gill respiratory epithelia, and damage to the osmoregulatory epithelium, including hypertrophy, proliferation, redistribution and necrosis of chloride cells. Tissue damage in gills is likely caused by the interaction of PTX2 with the actin cytoskeleton of the affected gill epithelia. Overall, the severe gill pathology observed following the PTX2 exposure suggested death was due to loss of respiratory and osmoregulatory functions in C. variegatus larvae.

Consumption and activity decline in Northern Pike (Esox lucius) during and after silver nanoparticle addition to a lake

Silver nanoparticles (AgNPs) are antimicrobial additives in many consumer products with high potential for release into aquatic ecosystems. Though AgNPs have been shown to have negative impacts on fish in laboratory experiments, these effects are rarely observed at ecologically relevant concentrations or in situ in field settings. To evaluate ecosystem-level effects of this contaminant, AgNPs were added to a lake at the IISD Experimental Lakes Area (IISD-ELA) during 2014 and 2015. Mean total silver (TAg) concentrations in the water column were 4 µg L^-1 during additions. The growth of Northern Pike (Esox lucius) declined, and their primary prey, Yellow Perch (Perca flavescens) became less abundant after AgNP exposure. Here, we used a combined contaminant-bioenergetics modeling approach to show that individual activity and both individual and population-level consumption of Northern Pike declined significantly in the lake dosed with AgNPs, which, combined with other evidence, suggests that observed declines in body size were likely a result of indirect effects (i.e., reduced prey availability). Further, we found the contaminant-bioenergetics approach was sensitive to modelled elimination rates of mercury, overestimating consumption and activity by 43% and 55%, respectively, when using the mercury elimination rate commonly used in these models versus field-derived estimates for this species. This study contributes to the growing evidence of potentially long-term negative impacts on fish from chronic exposure to environmentally relevant concentrations of AgNPs in a natural setting.

Developmental neurotoxicity of silver nanoparticles: the current state of knowledge and future directions

The increasing production and use of silver nanoparticles (AgNPs) as an antimicrobial agent in an array of medical and commercial products, including those designed for infants and children, poses a substantial risk of exposure during the developmental period. This review summarizes current knowledge on developmental neurotoxicity of AgNPs in both pre- and post-natal stages with a focus on the biological specificity of immature organisms that predisposes them to neurotoxic insults as well as the molecular mechanisms underlying AgNP-induced neurotoxicity. The current review revealed that AgNPs increase the permeability of the blood-brain barrier (BBB) and selectively damage neurons in the brain of immature rats exposed pre and postnatally. Among the AgNP-induced molecular mechanisms underlying toxic insult is cellular stress, which can consequently lead to cell death. Glutamatergic neurons and NMDAR-mediated neurotransmission also appear to be a target for AgNPs during the postnatal period of exposure. Collected data indicate also that our current knowledge of the impact of AgNPs on the developing nervous system remains insufficient and further studies are required during different stages of development with investigation of environmentally-relevant doses of exposure.

Microbiota-dependent TLR2 signaling reduces silver nanoparticle toxicity to zebrafish larvae

Many host-microbiota interactions depend on the recognition of microbial constituents by toll-like receptors of the host. The impacts of these interactions on host health can shape the hosts response to environmental pollutants such as nanomaterials. Here, we assess the role of toll-like receptor 2 (TLR2) signaling in the protective effects of colonizing microbiota against silver nanoparticle (nAg) toxicity to zebrafish larvae. Zebrafish larvae were exposed to nAg for two days, from 3 to 5 days post-fertilization. Using an il1ß-reporter line, we first characterized the accumulation and particle-specific inflammatory effects of nAg in the total body and intestinal tissues of the larvae. This showed that silver gradually accumulated in both the total body and intestinal tissues, yet specifically caused particle-specific inflammation on the skin of larvae. Subsequently, we assessed the effects of microbiota-dependent TLR2 signaling on nAg toxicity. This was done by comparing the sensitivity of loss-of-function zebrafish mutants for TLR2, and each of the TLR2-adaptor proteins MyD88 and TIRAP (Mal), under germ-free and microbially-colonized conditions. Irrespective of their genotype, microbially-colonized larvae were less sensitive to nAg than their germ-free siblings, supporting the previously identified protective effect of microbiota against nAg toxicity. Under germ-free conditions, tlr2, myd88 and tirap mutants were equally sensitive to nAg as their wildtype siblings. However, when colonized by microbiota, tlr2 and tirap mutants were more sensitive to nAg than their wildtype siblings. The sensitivity of microbially-colonized myd88 mutants did not differ significantly from that of wildtype siblings. These results indicate that the protective effect of colonizing microbiota against nAg-toxicity to zebrafish larvae involves TIRAP-dependent TLR2 signaling. Overall, this supports the conclusion that host-microbiota interactions affect nanomaterial toxicity to zebrafish larvae.

Developmental exposure window influences silver toxicity but does not affect the susceptibility to subsequent exposures in zebrafish embryos

Silver is a non-essential, toxic metal widespread in freshwaters and capable of causing adverse effects to wildlife. Its toxic effects have been studied in detail but less is known about how sensitivity varies during development and whether pre-exposures affect tolerance upon re-exposure. We address these knowledge gaps using the zebrafish embryo (Danio rerio) model to investigate whether exposures encompassing stages of development prior to mid-blastula transition, when chorion hardening and epigenetic reprogramming occur, result in greater toxicity compared to those initiated after this period. We conducted exposures to silver initiated at 0.5 h post fertilisation (hpf) and 4 hpf to determine if toxicity differed. In parallel, we exposed embryos to the methylation inhibitor 5-azacytidine as a positive control. Toxicity increased when exposures started from 0.5 hpf compared to 4 hpf and LC50 were significantly lower by 1.2 and 7.6 times for silver and 5-azacyitidine, respectively. We then investigated whether pre-exposure to silver during early development (from 0.5 or 4 hpf) affected the outcome of subsequent exposures during the larvae stage, and found no alterations in toxicity compared to naïve larvae. Together, these data demonstrate that during early development zebrafish embryos are more sensitive to silver when experiments are initiated at the one-cell stage, but that pre-exposures do not influence the outcome of subsequent exposures, suggesting that no long-lasting memory capable of influencing future susceptibility was maintained under our experimental conditions. The finding that toxicity is greater for exposures initiated at the one-cell stage has implications for designing testing systems to assess chemical toxicity.

Silver Nanoparticles in Zebrafish (Danio rerio) Embryos: Uptake, Growth and Molecular Responses

Silver nanoparticles (AgNPs) are widely used in commercial applications as antimicrobial agents, but there have recently been increasing concerns raised about their possible environmental and health impacts. In this study, zebrafish embryos were exposed to two sizes of AgNP, 4 and 10 nm, through a continuous exposure from 4 to 96 h post-fertilisation (hpf), to study their uptake, impact and molecular defense responses. Results showed that zebrafish embryos were significantly impacted by 72 hpf when continuously exposed to 4 nm AgNPs. At concentrations above 0.963 mg/L, significant in vivo uptake and delayed yolk sac absorption was evident; at 1.925 mg/L, significantly reduced body length was recorded compared to control embryos. Additionally, 4 nm AgNP treatment at the same concentration resulted in significantly upregulated hypoxia inducible factor 4 (HIF4) and peroxisomal membrane protein 2 (Pxmp2) mRNA expression in exposed embryos 96 hpf. In contrast, no significant differences in terms of larvae body length, yolk sac absorption or gene expression levels were observed following exposure to 10 nm AgNPs. These results demonstrated that S4 AgNPs are available for uptake, inducing developmental (measured as body length and yolk sac area) and transcriptional (specifically HIF4 and Pxmp2) perturbations in developing embryos. This study suggests the importance of particle size as one possible factor in determining the developmental toxicity of AgNPs in fish embryos.

Xenobiotic transporter activity in zebrafish embryo ionocytes

Ionocytes are specialized cells in the epidermis of embryonic zebrafish (Danio rerio) that play important roles in ion homeostasis and have functional similarities to mammalian renal cells. Here, we examined whether these cells might also share another functional similarity with renal cells, which is the presence of efflux transporter activities useful for elimination of toxic small molecules. Xenobiotic transporters (XTs), including the ATP-Binding Cassette (ABC) family, are a major defense mechanism against diffusible toxic molecules in aquatic embryos, including zebrafish, but their activity in the ionocytes has not previously been studied. Using fluorescent small molecule substrates of XT, we observed that specific populations of ionocytes uptake and efflux fluorescent small molecules in a manner consistent with active transport. We specifically identified a P-gp/ABCB1 inhibitor-sensitive efflux activity in the H⁺-ATPase-rich (HR) ionocytes, and show that these cells exhibit enriched expression of the ABCB gene, abcb5. The results extend our understanding of the functional significance of zebrafish ionocytes and indicate that these cells could play an important role in protection of the fish embryo from harmful small molecules.

Silver nanoparticles: An integrated view of green synthesis methods, transformation in the environment, and toxicity

Nowadays, silver nanoparticles (AgNPs) are the most widely used nanoparticles (NPs) in the industry due to their peculiar biocidal features. However, the use of these NPs still runs into limitations mainly because of the low efficiency of environmental friendly synthesis methods and lack of size standardization. When NPs are release in the environment, they can be transformed by oxidation, adsorption or aggregation. These modification shows a dual role in toxic response of AgNPs. The adsorption of natural organic matter from environment on AgNPs, for example, can decrease their toxicity. Otherwise oxidation occurred in the environment is also able to increase the release of toxic Ag⁺ from NPs. Thus, the current review proposes an integrated approach of AgNP synthetic methods using bacteria, fungi, and plants, AgNP cytotoxic and genotoxic effects as well as their potential therapeutic applications are also presented.

The Olfactory System of Zebrafish as a Model for the Study of Neurotoxicity and Injury: Implications for Neuroplasticity and Disease

The olfactory system, composed of the olfactory organs and the olfactory bulb, allows organisms to interact with their environment and through the detection of odor signals. Olfaction mediates behaviors pivotal for survival, such as feeding, mating, social behavior, and danger assessment. The olfactory organs are directly exposed to the milieu, and thus are particularly vulnerable to damage by environmental pollutants and toxicants, such as heavy metals, pesticides, and surfactants, among others. Given the widespread occurrence of olfactory toxicants, there is a pressing need to understand the effects of these harmful compounds on olfactory function. Zebrafish (Danio rerio) is a valuable model for studying human physiology, disease, and toxicity. Additionally, the anatomical components of the zebrafish olfactory system are similar to those of other vertebrates, and they present a remarkable degree of regeneration and neuroplasticity, making it an ideal model for the study of regeneration, reorganization and repair mechanisms following olfactory toxicant exposure. In this review, we focus on (1) the anatomical, morphological, and functional organization of the olfactory system of zebrafish; (2) the adverse effects of olfactory toxicants and injury to the olfactory organ; and (3) remodeling and repair neuroplasticity mechanisms following injury and degeneration by olfactory toxicant exposure.

Developmental exposure to silver nanoparticles at environmentally relevant concentrations alters swimming behavior in zebrafish (Danio rerio)

Silver nanoparticles (Ag-NPs) are ubiquitous in household and medical products because of their antimicrobial activity. A consequence of the high volume of Ag-NP production and usage is increased amounts of Ag-NPs released into the environment. Their small size (1-100 nm) results in unique physiochemical properties that may increase toxicity relative to their bulk counterpart. Therefore, the goal of the present study was to assess the potential toxicity of environmentally relevant concentrations of Ag-NPs in zebrafish (Danio rerio). Wild-type tropical 5D zebrafish embryos were exposed to Ag-NPs from 4 to 120 h postfertilization at 0.03, 0.1, 0.3, 1, and 3 ppm (mg/L). Inductively coupled plasma-mass spectrometry confirmed concentration-dependent uptake of Ag into zebrafish as well as bioaccumulation over time. A morphological assessment revealed no significant hatching impairment, morphological abnormalities, or mortality at any concentration or time point examined. However, assessment of photomotor behavior at 3 d postfertilization (dpf) revealed significant hyperactivity in the 0.3, 1, and 3 ppm Ag-NP treatment groups. At 4 dpf, significant hyperactivity was observed only in the 3 ppm treatment group, whereas 5 dpf larvae exposed to Ag-NPs displayed no significant abnormalities in photomotor behavior. These findings suggest that nonteratogenic concentrations of Ag-NPs are capable of causing transient behavioral changes during development. Environ Toxicol Chem 2018;37:3018-3024. © 2018 SETAC.

Iron metabolism gene expression and prognostic features of hepatocellular carcinoma

Iron metabolism is crucial to hepatocellular carcinoma progression and is a key determinant of prognosis. Protein-protein interactions within the iron metabolism gene network were analyzed using the European Molecular Biology Laboratory's Search Tool for Recurring Instances of Neighbouring Genes/Proteins database. We obtained 423 liver hepatocellular carcinoma gene expression profiles from the Cancer Genome Atlas database. The expression and pathway enrichment of representative iron intake genes (TFRC and DMT1), utilization genes (FTH1, FTL, HIF1A, HMOX1, SLC25A37, and SLC25A38), and efflux genes (FLVCR1 and SLC40A1) was investigated in tumor and adjacent tissues. We determined the relationship between iron metabolism and the prognostic features of liver hepatocellular carcinoma. The liver metabolism genes TFRC and FLVCR1 were related to survival, disease status, and prognosis in patients with hepatocellular carcinoma. Our results provide novel insight into liver cancer therapy.

Silver nanoparticles have lethal and sublethal adverse effects on development and longevity by inducing ROS-mediated stress responses

Silver nanoparticles (AgNPs) are widely used in the household, medical and industrial sectors due to their effective bactericidal activities and unique plasmonic properties. Despite the promising advantages, safety concerns have been raised over the usage of AgNPs because they pose potential hazards. However, the mechanistic basis behind AgNPs toxicity, particularly the sublethal effects at the organismal level, has remained unclear. In this study, we used a powerful in vivo platform Drosophila melanogaster to explore a wide spectrum of adverse effects exerted by dietary AgNPs at the organismal, cellular and molecular levels. Lethal doses of dietary AgNPs caused developmental delays and profound lethality in developing animals and young adults. In contrast, exposure to sublethal doses, while not deadly to developing animals, shortened the adult lifespan and compromised their tolerance to oxidative stress. Importantly, AgNPs mechanistically resulted in tissue-wide accumulation of reactive oxygen species (ROS) and activated the Nrf2-dependent antioxidant pathway, as demonstrated by an Nrf2 activity reporter in vivo. Finally, dietary AgNPs caused a variety of ROS-mediated stress responses, including apoptosis, DNA damage, and autophagy. Altogether, our study suggests that lethal and sublethal doses of AgNPs, have acute and chronic effects, respectively, on development and longevity by inducing ROS-mediated stress responses.

Adoption of in vitro systems and zebrafish embryos as alternative models for reducing rodent use in assessments of immunological and oxidative stress responses to nanomaterials

Assessing the safety of engineered nanomaterials (NMs) is paramount to the responsible and sustainable development of nanotechnology, which provides huge societal benefits. Currently, there is no evidence that engineered NMs cause detrimental health effects in humans. However, investigation of NM toxicity using in vivo, in vitro, in chemico, and in silico models has demonstrated that some NMs stimulate oxidative stress and inflammation, which may lead to adverse health effects. Accordingly, investigation of these responses currently dominates NM safety assessments. There is a need to reduce reliance on rodent testing in nanotoxicology for ethical, financial and legislative reasons, and due to evidence that rodent models do not always predict the human response. We advocate that in vitro models and zebrafish embryos should have greater prominence in screening for NM safety, to better align nanotoxicology with the 3Rs principles. Zebrafish are accepted for use by regulatory agencies in chemical safety assessments (e.g. developmental biology) and there is growing acceptance of their use in biomedical research, providing strong foundations for their use in nanotoxicology. We suggest that investigation of the response of phagocytic cells (e.g. neutrophils, macrophages) in vitro should also form a key part of NM safety assessments, due to their prominent role in the first line of defense. The development of a tiered testing strategy for NM hazard assessment that promotes the more widespread adoption of non-rodent, alternative models and focuses on investigation of inflammation and oxidative stress could make nanotoxicology testing more ethical, relevant, and cost and time efficient.

The role of metals in mammalian olfaction of low molecular weight organosulfur compounds

Covering: up to the end of 2017While suggestions concerning the possible role of metals in olfaction and taste date back 50 years, only recently has it been possible to confirm these proposals with experiments involving individual olfactory receptors (ORs). A detailed discussion of recent experimental results demonstrating the key role of metals in enhancing the response of human and other vertebrate ORs to specific odorants is presented against the backdrop of our knowledge of how the sense of smell functions both at the molecular and whole animal levels. This review emphasizes the role of metals in the detection of low molecular weight thiols, sulfides, and other organosulfur compounds, including those found in strong-smelling animal excretions and plant volatiles, and those used in gas odorization. Alternative theories of olfaction are described, with evidence favoring the modified "shape" theory. The use of quantum mechanical/molecular modeling (QM/MM), site-directed mutagenesis and saturation-transfer-difference (STD) NMR is discussed, providing support for biological studies of mouse and human receptors, MOR244-3 and OR OR2T11, respectively. Copper is bound at the active site of MOR244-3 by cysteine and histidine, while cysteine, histidine and methionine are involved with OR2T11. The binding pockets of these two receptors are found in different locations in the three-dimensional seven transmembrane models. Another recently deorphaned human olfactory receptor, OR2M3, highly selective for a thiol from onions, and a broadly-tuned thiol receptor, OR1A1, are also discussed. Other topics covered include the effects of nanoparticles and heavy metal toxicants on vertebrate and fish ORs, intranasal zinc products and the loss of smell (anosmia).