Metabolomic Characterizations of Liver Injury Caused by Acute Arsenic Toxicity in Zebrafish

Copper, Iron, Cadmium, and Arsenic, All Generated in the Universe: Elucidating Their Environmental Impact Risk on Human Health Including Clinical Liver Injury

Humans are continuously exposed to various heavy metals including copper, iron, cadmium, and arsenic, which were specifically selected for the current analysis because they are among the most frequently encountered environmental mankind and industrial pollutants potentially causing human health hazards and liver injury. So far, these issues were poorly assessed and remained a matter of debate, also due to inconsistent results. The aim of the actual report is to thoroughly analyze the positive as well as negative effects of these four heavy metals on human health. Copper and iron are correctly viewed as pollutant elements essential for maintaining human health because they are part of important enzymes and metabolic pathways. Healthy individuals are prepared through various genetically based mechanisms to maintain cellular copper and iron homeostasis, thereby circumventing or reducing hazardous liver and organ injury due to excessive amounts of these metals continuously entering the human body. In a few humans with gene aberration, however, liver and organ injury may develop because excessively accumulated copper can lead to Wilson disease and substantial iron deposition to hemochromatosis. At the molecular level, toxicities of some heavy metals are traced back to the Haber Weiss and Fenton reactions involving reactive oxygen species formed in the course of oxidative stress. On the other hand, cellular homeostasis for cadmium and arsenic cannot be provided, causing their life-long excessive deposition in the liver and other organs. Consequently, cadmium and arsenic represent health hazards leading to higher disability-adjusted life years and increased mortality rates due to cancer and non-cancer diseases. For unknown reasons, however, liver injury in humans exposed to cadmium and arsenic is rarely observed. In sum, copper and iron are good for the human health of most individuals except for those with Wilson disease or hemochromatosis at risk of liver injury through radical formation, while cadmium and arsenic lack any beneficial effects but rather are potentially hazardous to human health with a focus on increased disability potential and risk for cancer. Primary efforts should focus on reducing the industrial emission of hazardous heavy metals.

Sustained effects of developmental exposure to inorganic arsenic on hepatic gsto2 expression and mating success in zebrafish

The impacts of exposure to the pervasive environmental toxicant, inorganic arsenic (iAs), on human and fish health are well characterized and several lines of evidence suggest that some impacts can manifest years after exposure cessation. Using a developmental exposure protocol whereby zebrafish embryos were exposed to 0.5 and 1.5 mM iAs from 4-120 hours post fertilization (hpf) and then removed, we investigated the sustained effects of iAs on gene expression in the liver, survival, reproductive success, and susceptibility to iAs toxicity in the subsequent generation. Persistent exposure to iAs during development had substantial effects on the hepatic transcriptome, with 23% of all expressed genes significantly changed following developmental exposure. The gsto2 gene is involved in iAs metabolism and this gene was significantly downregulated in female livers 9 months after iAs was removed. Developmental exposure to 1.5 mM iAs, but not 0.5 mM, decreased survival by over 50% at 3 months of age. Adults that were developmentally exposed to 0.5 mM iAs had reduced mating success, but their offspring had no differences in observable aspects of development or their susceptibility to iAs toxicity. This demonstrates that developmental exposure of zebrafish to iAs reduces long-term survival, reproductive success and causes sustained changes to gsto2 expression in the liver.

Zebrafish facilitate non-alcoholic fatty liver disease research: Tools, models and applications

Non-alcoholic fatty liver disease (NAFLD) has become an increasingly epidemic metabolic disease worldwide. NAFLD can gradually deteriorate from simple liver steatosis, inflammation and fibrosis to liver cirrhosis and/or hepatocellular carcinoma. Zebrafish are vertebrate animal models that are genetically and metabolically conserved with mammals and have unique advantages such as high fecundity, rapid development ex utero and optical transparency. These features have rendered zebrafish an emerging model system for liver diseases and metabolic diseases favoured by many researchers in recent years. In the present review, we summarize a series of tools for zebrafish NAFLD research and the models established through different dietary feeding, hepatotoxic chemical treatments and genetic manipulations via transgenic or genome editing technologies. We also discuss how zebrafish models facilitate NAFLD studies by providing novel insights into NAFLD pathogenesis, toxicology research, and drug evaluation and discovery.

SIRT1/P53 pathway is involved in the Arsenic induced aerobic glycolysis in hepatocytes L-02 cells

Arsenic is a known human carcinogen. Low doses of arsenic can induce cell proliferation, but the mechanism remains elusive. Aerobic glycolysis, also known as the Warburg effect, is one of the characteristics of tumour cells and rapidly proliferating cells. P53 is a tumour suppressor gene that has been shown to be a negative regulator of aerobic glycolysis. SIRT1 is a deacetylase that inhibits the function of P53. In this study, we found that P53 was involved in low dose of arsenic-induced aerobic glycolysis through regulating HK2 expression in L-02 cells. Moreover, SIRT1 not only inhibited P53 expression but also decreased the acetylation level of P53-K382 in arsenic-treated L-02 cells. Meanwhile, SIRT1 influenced the expression of HK2 and LDHA, which then promoted arsenic-induced glycolysis in L-02 cells. Therefore, our study demonstrated that the SIRT1/P53 pathway is involved in arsenic-induced glycolysis, thereby promoting cell proliferation, which provides theoretical basis for enriching the mechanism of arsenic carcinogenesis.

HIF-1α Mediates Arsenic-Induced Metabolic Reprogramming in Lung Bronchial Epithelial Cells

Arsenic is a common environmental pollutant that can cause damage to multiple systems and organs in the body. The lungs are particularly sensitive to arsenic exposure, and respiratory disease is thought to be the leading cause of death from arsenic poisoning. Our previous study found that human bronchial epithelial (HBE) cells treated with NaAsO₂ exhibited mitochondrial dysfunction accompanied by elevated HIF-1α; however, the molecular mechanism was unclear. The aim of the current study was to confirm the role of HIF-1α in arsenic-induced mitochondrial damage. The results of this study indicated that NaAsO₂ treatment induced mitochondrial ultrastructure impairment and depolarization of the mitochondrial membrane potential. Furthermore, NaAsO₂ induced a significant decrease in basal respiration, maximal respiration, spare respiratory capacity, ATP (adenosine-triphosphate)-associated mitochondrial respiration and proton leakage in HBE cells (P < 0.05), while promoting an increase in ECAR (extracellular acidification rate) values. To clarify the role of HIF-1α, the effect of HIF-1α siRNA on NaAsO₂-induced glycolysis in HBE cells was examined, and the results showed that HIF-1α siRNA reversed the NaAsO₂-induced elevation in PKM2 (Tyr105), HIF-1α, GLUT1 and HK2 protein expression and decreased the NaAsO₂-mediated glycolysis level, glycolytic capacity and glycolytic reserve. These findings suggest that targeting metabolic dysregulation has significant implications for targeting arsenic-induced lung injury and that HIF-1α is an exciting new therapeutic target for the treatment of arsenic-induced lung injury.

Fisetin Attenuates Arsenic-Induced Hepatic Damage by Improving Biochemical, Inflammatory, Apoptotic, and Histological Profile: In Vivo and In Silico Approach

Arsenic (As) is a toxic metalloid and human carcinogen that may cause hepatotoxicity. Fisetin (3, 3′, 4′, 7-tetrahydroxyflavone) is a phytoflavonoid, which shows diverse therapeutic activities. This study aimed to examine the remedial potential of fisetin against As-instigated hepatotoxicity in adult male rats. To accomplish this aim, albino rats (N = 48) were evenly classified into 4 groups: control group, As (10 mg/kg) group, fisetin (2.5 mg/kg) + As (10 mg/kg) group, and fisetin (2.5 mg/kg) group. After one month of treatment, biochemical assay, total protein content (TPC), hepatic serum enzymes, inflammatory as well as pro- or anti-apoptotic markers, and histopathological profile of hepatic tissues were estimated. As administration disordered the biochemical profile by decreasing activities of antioxidant enzymes i.e., catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GSR), and glutathione (GSH) content while escalating the levels of reactive oxygen species (ROS), and thiobarbituric acid reactive substances (TBARS). TPC was also considerably reduced after exposure to As. Furthermore, As markedly raised the levels of liver serum enzymes such as aspartate transaminase (AST), alkaline phosphatase (ALP), and alanine transaminase (ALT) as well as the levels of inflammatory markers, i.e., nuclear factor- κB (NF-κB), tumor necrosis- α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and cyclo-oxygenase-2 (COX-2) activity. Besides, it lowered the level of antiapoptotic markers (Bcl-2) and upregulated the levels of proapoptotic markers (Bax, Caspase-3, and Caspase-9). Additionally, As exposure led to histopathological damage in hepatic tissues. However, fisetin administration remarkably alleviated all the depicted hepatic damages. For further verification, the screening of several dock complexes was performed by using the GOLD 5.3.0 version. Based on docking fitness and GOLD score, the ranking order of receptor proteins with fisetin compound is superoxide dismutase, interleukin, aspartate aminotransferase, alkaline phosphatase, TNF-alpha, alanine transaminase, cyclo-oxygenase 2, antiapoptotic, and glutathione reductase. Out of these three receptor proteins superoxide dismutase, interleukin, and aspartate aminotransferase showed the best interaction with the fisetin compound. In vivo and in silico outcomes of the current study demonstrated that fisetin could potentially ameliorate As-instigated hepatotoxicity.

Aluminum, Arsenic, Beryllium, Cadmium, Chromium, Cobalt, Copper, Iron, Lead, Mercury, Molybdenum, Nickel, Platinum, Thallium, Titanium, Vanadium, and Zinc: Molecular Aspects in Experimental Liver Injury

Experimental liver injury with hepatocelluar necrosis and abnormal liver tests is caused by exposure to heavy metals (HMs) like aluminum, arsenic, beryllium, cadmium, chromium, cobalt, copper, iron, lead, mercury, molybdenum, nickel, platinum, thallium, titanium, vanadium, and zinc. As pollutants, HMs disturb the ecosystem, and as these substances are toxic, they may affect the health of humans and animals. HMs are not biodegradable and may be deposited preferentially in the liver. The use of animal models can help identify molecular and mechanistic steps leading to the injury. HMs commonly initiate hepatocellular overproduction of ROS (reactive oxygen species) due to oxidative stress, resulting in covalent binding of radicals to macromolecular proteins or lipids existing in membranes of subcellular organelles. Liver injury is facilitated by iron via the Fenton reaction, providing ROS, and is triggered if protective antioxidant systems are exhausted. Ferroptosis syn pyroptosis was recently introduced as mechanistic concept in explanations of nickel (Ni) liver injury. NiCl₂ causes increased iron deposition in the liver, upregulation of cyclooxygenase 2 (COX-2) protein and mRNA expression levels, downregulation of glutathione eroxidase 4 (GPX4), ferritin heavy chain 1 (FTH1), nuclear receptor coactivator 4 (NCOA4) protein, and mRNA expression levels. Nickel may cause hepatic injury through mitochondrial damage and ferroptosis, defined as mechanism of iron-dependent cell death, similar to glutamate-induced excitotoxicity but likely distinct from apoptosis, necrosis, and autophagy. Under discussion were additional mechanistic concepts of hepatocellular uptake and biliary excretion of mercury in exposed animals. For instance, the organic anion transporter 3 (Oat3) and the multidrug resistance-associated protein 2 (Mrp2) were involved in the hepatic handling of mercury. Mercury treatment modified the expression of Mrp2 and Oat3 as assessed by immunoblotting, partially explaining its impaired biliary excretion. Concomitantly, a decrease in Oat3 abundance in the hepatocyte plasma membranes was observed that limits the hepatic uptake of mercury ions. Most importantly and shown for the first time in liver injury caused by HMs, titanium changed the diversity of gut microbiota and modified their metabolic functions, leading to increased generation of lipopolysaccharides (LPS). As endotoxins, LPS may trigger and perpetuate the liver injury at the level of gut-liver. In sum, mechanistic and molecular steps of experimental liver injury due to HM administration are complex, with ROS as the key promotional compound. However, additional concepts such as iron used in the Fenton reaction, ferroptosis, modification of transporter systems, and endotoxins derived from diversity of intestinal bacteria at the gut-liver level merit further consideration.

Identification of novel lipid biomarkers in xmrk- and Myc-induced models of hepatocellular carcinoma in zebrafish

BACKGROUND

Hepatocellular carcinoma (HCC) is the predominant form of liver cancer and is accompanied by complex dysregulation of lipids. Increasing evidence suggests that particular lipid species are associated with HCC progression. Here, we aimed to identify lipid biomarkers of HCC associated with the induction of two oncogenes, xmrk, a zebrafish homolog of the human epidermal growth factor receptor (EGFR), and Myc, a regulator of EGFR expression during HCC.

METHODS

We induced HCC in transgenic xmrk, Myc, and xmrk/Myc zebrafish models. Liver specimens were histologically analyzed to characterize the HCC stage, Oil-Red-O stained to detect lipids, and liquid chromatography/mass spectrometry analyzed to assign and quantify lipid species. Quantitative real-time polymerase chain reaction was used to measure lipid metabolic gene expression in liver samples. Lipid species data was analyzed using univariate and multivariate logistic modeling to correlate lipid class levels with HCC progression.

RESULTS

We found that induction of xmrk, Myc and xmrk/Myc caused different stages of HCC. Lipid deposition and class levels generally increased during tumor progression, but triglyceride levels decreased. Myc appears to control early HCC stage lipid species levels in double transgenics, whereas xmrk may take over this role in later stages. Lipid metabolic gene expression can be regulated by either xmrk, Myc, or both oncogenes. Our computational models showed that variations in total levels of several lipid classes are associated with HCC progression.

CONCLUSIONS

These data indicate that xmrk and Myc can temporally regulate lipid species that may serve as effective biomarkers of HCC progression.

Effects of arsenic and heavy metals on metabolic pathways in cells of human origin: Similarities and differences

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There are distinctive overlaps in different heavy metal affected metabolic pathways.

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Affected pathways vary according to the tissue origin and maturity of the cell.

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Arsenic appears to have relatively more pleiotropic effects on metabolic pathways.

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Some of the arsenic affected pathways are associated with diabetes.

Various anthropogenic and natural events over the years have gradually increased human exposure to various heavy metals. Several of these heavy metals including cadmium, mercury, nickel, chromium, and the metalloid arsenic among others, have created major public health concerns for their high level of toxicities. Identification of the general as well as the differentially affected cellular metabolic pathways will help understanding the molecular mechanism of different heavy metal-induced toxicities. In this study, we analyzed 25 paired (control vs. treated) transcriptomic datasets derived following treatment of various human cells with different heavy metals and metalloid (arsenic, cadmium, chromium, iron, mercury, nickel and vanadium) to identify the affected metabolic pathways. The effects of these metals on metabolic pathways depend not only on the metals per se, but also on the nature of the treated cells. Tissue of origin, therefore, must be considered while assessing the effects of any particular heavy metal or metalloid. Among the metals and metalloid, arsenic appears to have relatively more pleiotropic influences on cellular metabolic pathways including those known to have association with diabetes. Although only two stem cell derived datasets are included in the current study, effects of heavy metals on these cells appear to be different from other mature cells of similar tissue origin. This study provides useful information about different heavy metal affected pathways, which may be useful in further exploration using wet-lab based techniques.

Coenzyme Q10 protected against arsenite and enhanced the capacity of 2,3-dimercaptosuccinic acid to ameliorate arsenite-induced toxicity in mice

BACKGROUND

Arsenic poisoning affects millions of people. The inorganic forms of arsenic are more toxic. Treatment for arsenic poisoning relies on chelation of extracellularly circulating arsenic molecules by 2,3-dimecaptosuccinic acid (DMSA). As a pharmacological intervention, DMSA is unable to chelate arsenic molecules from intracellular spaces. The consequence is continued toxicity and cell damage in the presence of DMSA. A two-pronged approach that removes extracellular arsenic, while protecting from the intracellular arsenic would provide a better pharmacotherapeutic outcome. In this study, Coenzyme Q10 (CoQ10), which has been shown to protect from intracellular organic arsenic, was administered separately or with DMSA; following oral exposure to sodium meta-arsenite (NaAsO2) - a very toxic trivalent form of inorganic arsenic. The aim was to determine if CoQ10 alone or when co-administered with DMSA would nullify arsenite-induced toxicity in mice.

METHODS

Group one represented the control; the second group was treated with NaAsO2 (15 mg/kg) daily for 30 days, the third, fourth and fifth groups of mice were given NaAsO2 and treated with 200 mg/kg CoQ10 (30 days) and 50 mg/kg DMSA (5 days) either alone or in combination.

RESULTS

Administration of CoQ10 and DMSA resulted in protection from arsenic-induced suppression of RBCs, haematocrit and hemoglobin levels. CoQ10 and DMSA protected from arsenic-induced alteration of WBCs, basophils, neutrophils, monocytes, eosinophils and platelets. Arsenite-induced dyslipidemia was nullified by administration of CoQ10 alone or in combination with DMSA. Arsenite induced a drastic depletion of the liver and brain GSH; that was significantly blocked by CoQ10 and DMSA alone or in combination. Exposure to arsenite resulted in significant elevation of liver and kidney damage markers. The histological analysis of respective organs confirmed arsenic-induced organ damage, which was ameliorated by CoQ10 alone or when co-administered with DMSA. When administered alone, DMSA did not prevent arsenic-driven tissue damage.

CONCLUSIONS

Findings from this study demonstrate that CoQ10 and DMSA separately or in a combination, significantly protect against arsenic-driven toxicity in mice. It is evident that with further pre-clinical and clinical studies, an adjunct therapy that incorporates CoQ10 alongside DMSA may find applications in nullifying arsenic-driven toxicity.

Arsenic induced redox imbalance triggers the unfolded protein response in the liver of zebrafish

Inorganic arsenic (iAs) is one of the most endemic toxicants worldwide and oxidative stress is a key cellular pathway underlying iAs toxicity. Other cellular stress response pathways, such as the unfolded protein response (UPR), are also impacted by iAs exposure, however it is not known how these pathways intersect to cause disease. We optimized the use of zebrafish larvae to identify the relationship between these cellular stress response pathways and arsenic toxicity. We found that the window of iAs susceptibility during zebrafish development corresponds with the development of the liver, and that even a 24-h exposure can cause lethality if administered to mature larvae, but not to early embryos. Acute exposure of larvae to iAs generates reactive oxygen species (ROS), an antioxidant response, endoplasmic reticulum (ER) stress and UPR activation in the liver. An in vivo assay using transgenic larvae expressing a GFP-tagged secreted glycoprotein in hepatocytes (Tg(fabp10a:Gc-EGFP)) revealed acute iAs exposure selectively decreased expression of Gc-EGFP, indicating that iAs impairs secretory protein folding in the liver. The transcriptional output of UPR activation is preceded by ROS production and activation of genes involved in the oxidative stress response. These studies implicate redox imbalance as the mechanism of iAs-induced ER stress and suggest that crosstalk between these pathways underlie iAs-induced hepatic toxicity.

Use of Zebrafish in Drug Discovery Toxicology

Unpredicted human safety events in clinical trials for new drugs are costly in terms of human health and money. The drug discovery industry attempts to minimize those events with diligent preclinical safety testing. Current standard practices are good at preventing toxic compounds from being tested in the clinic; however, false negative preclinical toxicity results are still a reality. Continual improvement must be pursued in the preclinical realm. Higher-quality therapies can be brought forward with more information about potential toxicities and associated mechanisms. The zebrafish model is a bridge between in vitro assays and mammalian in vivo studies. This model is powerful in its breadth of application and tractability for research. In the past two decades, our understanding of disease biology and drug toxicity has grown significantly owing to thousands of studies on this tiny vertebrate. This Review summarizes challenges and strengths of the model, discusses the 3Rs value that it can deliver, highlights translatable and untranslatable biology, and brings together reports from recent studies with zebrafish focusing on new drug discovery toxicology.

Manganese attenuates the effects of arsenic on neurobehavioral and biochemical changes in mice co-exposed to arsenic and manganese

An unsafe level of manganese (Mn) was detected in the drinking water in some arsenic (As)-contaminated areas in Bangladesh. Mn is an essential trace element; however, the intake of a higher level of Mn through the drinking water is associated with the development of toxicity in humans. This study was designed to evaluate the effects of As and Mn co-exposure on neurobehavioral and biochemical alterations in a mouse model. Sodium arsenite (10 mg/kg body weight) and manganese chloride tetrahydrate (10 mg/kg body weight) were given to mice individually and in combination with drinking water for 90 days. Results showed that individual As and Mn exposure as well as co-exposure of As and Mn significantly (p < 0.05) reduced the percent of time spent in the open arms when compared with that of control mice. In addition, percent of time spent in open arms significantly (p < 0.05) increased in co-exposed mice compared with As exposure in elevated plus maze (42.05 ± 1.10 versus 38.94 ± 0.66). In the Morris water maze test, the mean time latency to find the platform was longer in metal-treated mice in comparison to that of control mice (p < 0.05). Importantly, the co-exposed group had shorter time when compared with the As-exposed group during the training periods (p < 0.05). Moreover, co-exposed mice stayed significantly (p < 0.05) more time in the target quadrant in the probe trial in comparison with that of As-exposed mice (27.25 ± 1.21 versus 23.83 ± 0.87 s) but less time than control mice (27.25 ± 1.21 versus 43.17 ± 1.49 s). In addition, a significant (p < 0.05) alteration of biochemical parameters such as ALT, AST, ALP, BChE, and SOD as well as urea and creatinine levels were noted in the As-exposed group compared with the control group and Mn significantly (p < 0.05) attenuated the effects of As in co-exposed mice. Therefore, the results of this study suggest that As and Mn may have some antagonistic effect and Mn could attenuate the As-induced neurobehavioral and biochemical alterations in co-exposed mice.

Proteomic Analysis of Zebrafish (Danio rerio) After Chemical Exposure

Traditional toxicological screens based on the zebrafish model use observable phenotypic endpoints during their development to determine the toxicity of teratogens. Yet toxicity does not always translate to obvious phenotypic changes and the criteria used to score the toxicity of a teratogen are frequently subjected to human perception. The advancement in omics-based technologies has allowed us to quantitatively and objectively determine the toxicity of a teratogen based on biomolecular changes. The field of proteomics has been gaining popularity as a valuable tool in toxicology. Hence, in this chapter, we described a protocol for both label-free and label-based proteomic methods to analyse proteomic changes in both embryos and adult livers of zebrafish exposed to the teratogen TCDD (tetrachlorodibenzo-p-dioxin) as an example.

Dissecting metabolism using zebrafish models of disease

Zebrafish (Danio rerio) are becoming an increasingly powerful model organism to study the role of metabolism in disease. Since its inception, the zebrafish model has relied on unique attributes such as the transparency of embryos, high fecundity and conservation with higher vertebrates, to perform phenotype-driven chemical and genetic screens. In this review, we describe how zebrafish have been used to reveal novel mechanisms by which metabolism regulates embryonic development, obesity, fatty liver disease and cancer. In addition, we will highlight how new approaches in advanced microscopy, transcriptomics and metabolomics using zebrafish as a model system have yielded fundamental insights into the mechanistic underpinnings of disease.

Hepatotoxicity in Zebrafish Larvae

Zebrafish (Danio rerio) larvae are a uniquely powerful model system which investigate the effects of toxicant exposure on liver development and function. Manufacturing processes and development of new synthetic compounds increased rapidly since the middle of the twentieth century, resulting in widespread exposure to environmental toxicants. This is compounded by the shift in the global burden of disease from infectious agents to chronic disease, particularly in industrialized nations, which increases the need to investigate the long-term and transgenerational effects of environmental exposures on human health. Zebrafish provide an excellent model to investigate the mechanisms of action of environmental pollutants given their large-scale embryo production and rapid development, which allow for short-term assessment of toxicity in a whole animal system. Here we describe methods for the use of zebrafish to study hepatotoxicity and liver disease induced by chemical toxicants. Many of the genetic, molecular, and cellular processes are conserved between zebrafish and mammals, enabling translation to human populations and diseases.

Nux Vomica Exposure Triggered Liver Injury and Metabolic Disturbance in Zebrafish Larvae

Zebrafish larvae were used to further understand the liver toxicity of nux vomica. The histopathology, protein expression, and gene expression were assessed to confirm apoptosis in the liver, and then, profiles of the metabolites in zebrafish were investigated by untargeted metabolomic assessment to understand the potential toxicity mechanism of nux vomica. Histopathological observations showed that nux vomica caused damage to liver cells. Western blot results indicated increased expression of activated caspase3, and the result of real-time polymerase chain reaction showed a significant increase in the expression level of caspase-3, caspase-8, and caspase-9 genes (p < 0.05) compared with the control group. The liver injury from nux vomica was linked to the downregulation of amino acid (e.g., proline and alanine) and fatty acid (e.g., palmitoleic acid) metabolism and upregulation of some other fatty acid (e.g., arachidic acid) and purine (e.g., xanthine and uric acid) metabolism. The hepatotoxicity of nux vomica resulted from metabolic pathway disturbances, including small molecules involved in energy, purine, lipids, and amino acid metabolism.

Stress-responsive genes (hsp70 and mt) and genotoxicity elicited by roxarsone exposure in Carassius auratus

In this study, comet assay (single-cell gel electrophoresis), real-time quantitative PCR (qPCR) and proteomics approach were used to comprehensively assess toxicity elicited by roxarsone exposure in C. auratus at 50, 150 and 300 μg/L for 7, 14 and 21 days. Results of comet assay showed that DNA were seriously damaged under the pressure of roxarsone, especially the concentration of 50 μg/L that always maintained a sustained and increased damage effect to fish liver cell during the 21 days experiment. The expressions of biomarker genes showed that hsp70 gene expressions raised significantly and the group of 50 μg/L also showed a continued increased response effect, whereas mt gene was only slightly increased. Results of proteomics for the concentration of 300 μg/L found that thirty six significantly changed proteins were identified by MALDI-TOF/TOF-MS. They are involved in many important processes including energy producing, cytoskeleton stabilization, substance metabolism and stress response. Among these metabolites, carbohydrate metabolism (mainly occurred during day 1-14) and cytoskeleton proteins (mainly occurred during day 14-21) were the most identified proteins. These results revealed that the low levels of 50 μg/L probably led to a continuous damage than the higher groups during the experiment time. Furthermore, proteomics results might implied that though cell system expected to mobilize almost all the functional proteins to quickly establish a new homeostasis together when facing the roxarsone at first, but in the end the destroyed cell cytoskeleton structure might burst the bubble.

Pre-clinical Pharmacokinetic and Metabolomic Analyses of Isorhapontigenin, a Dietary Resveratrol Derivative

Background: Isorhapontigenin (trans-3,5,4'-trihydroxy-3'-methoxystilbene, ISO), a dietary resveratrol (trans-3,5,4'-trihydroxystilbene) derivative, possesses various health-promoting activities. To further evaluate its medicinal potentials, the pharmacokinetic and metabolomic profiles of ISO were examined in Sprague-Dawley rats. Methods: The plasma pharmacokinetics and metabolomics were monitored by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS), respectively. Results: Upon intravenous injection (90 μmol/kg), ISO exhibited a fairly rapid clearance (CL) and short mean residence time (MRT). After a single oral administration (100 μmol/kg), ISO was rapidly absorbed and showed a long residence in the systemic circulation. Dose escalation to 200 μmol/kg resulted in higher dose-normalized maximal plasma concentrations (C_max/Dose), dose-normalized plasma exposures (AUC/Dose), and oral bioavailability (F). One-week repeated daily dosing of ISO did not alter its major oral pharmacokinetic parameters. Pharmacokinetic comparisons clearly indicated that ISO displayed pharmacokinetic profiles superior to resveratrol as its C_max/Dose, AUC/Dose, and F were approximately two to three folds greater than resveratrol. Metabolomic investigation revealed that 1-week ISO administration significantly reduced plasma concentrations of arachidonic acid, cholesterol, fructose, allantoin, and cadaverine but increased tryptamine levels, indicating its impact on metabolic pathways related to health-promoting effects. Conclusion: ISO displayed favorable pharmacokinetic profiles and may be a promising nutraceutical in view of its health-promoting properties.

Inorganic arsenic causes fatty liver and interacts with ethanol to cause alcoholic liver disease in zebrafish

The rapid increase in fatty liver disease (FLD) incidence is attributed largely to genetic and lifestyle factors; however, environmental toxicants are a frequently overlooked factor that can modify the effects of more common causes of FLD. Chronic exposure to inorganic arsenic (iAs) is associated with liver disease in humans and animal models, but neither the mechanism of action nor the combinatorial interaction with other disease-causing factors has been fully investigated. Here, we examined the contribution of iAs to FLD using zebrafish and tested the interaction with ethanol to cause alcoholic liver disease (ALD). We report that zebrafish exposed to iAs throughout development developed specific phenotypes beginning at 4 days post-fertilization (dpf), including the development of FLD in over 50% of larvae by 5 dpf. Comparative transcriptomic analysis of livers from larvae exposed to either iAs or ethanol revealed the oxidative stress response and the unfolded protein response (UPR) caused by endoplasmic reticulum (ER) stress as common pathways in both these models of FLD, suggesting that they target similar cellular processes. This was confirmed by our finding that arsenic is synthetically lethal with both ethanol and a well-characterized ER-stress-inducing agent (tunicamycin), suggesting that these exposures work together through UPR activation to cause iAs toxicity. Most significantly, combined exposure to sub-toxic concentrations of iAs and ethanol potentiated the expression of UPR-associated genes, cooperated to induce FLD, reduced the expression of as3mt, which encodes an arsenic-metabolizing enzyme, and significantly increased the concentration of iAs in the liver. This demonstrates that iAs exposure is sufficient to cause FLD and that low doses of iAs can potentiate the effects of ethanol to cause liver disease.

This article has an associated First Person interview with the first author of the paper.

Summary: Using zebrafish, the authors show that exposure to a common environmental contaminant, inorganic arsenic, increases the risk of alcoholic liver disease.

Combination of HPLC with organic and inorganic mass spectrometry to study the metabolic response of the clam Scrobicularia plana to arsenic exposure

Arsenic is a toxic element extensively studied in the marine environment due to differential toxicological effects of inorganic and organic species. In the present work, the bivalve Scrobicularia plana was exposed to As^V (10 and 100 μg/L) for 14 days to evaluate the metabolic perturbations caused by this element. Arsenic speciation and metabolomic analysis were performed in the digestive gland of the bivalve using two complementary analytical platforms based on inorganic and organic mass spectrometry. It has been observed the greater presence of the innocuous specie arsenobetaine produced in this organism as defense mechanism against arsenic toxicity, although significant concentrations of methylated and inorganic arsenic were also present, depending on the level of arsenic in aqueous media. Complementarily, a metabolomic study based on mass spectrometry and statistical discriminant analysis allows a good classification of samples associated to low and high As(V) exposure in relation to controls. About 15 metabolites suffer significant changes of expression by the presence of As(V): amino acids, nucleotides, energy-related metabolites, free fatty acids, phospholipids and triacylglycerides, which can be related to membrane structural and functional damage. In addition, perturbation of the methylation cycle, associated with the increase of homocysteine and methionine was observed, which enhance the methylation of toxic inorganic arsenic to less toxic dimethylarsenic.

Maternal/fetal metabolomes appear to mediate the impact of arsenic exposure on birth weight: A pilot study

Arsenic exposure has been associated with low birth weight. However, the underlying mechanisms are not well understood. Alterations to metabolites may act as causal mediators of the effect of arsenic exposure on low birth weight. This pilot study aimed to explore the role of metabolites in mediating the association of arsenic exposure on infant birth weight. Study samples were selected from a well-established prospectively enrolled cohort in Bangladesh comprising 35 newborns and a subset of 20 matched mothers. Metabolomics profiling was performed on 35 cord blood samples and 20 maternal peripheral blood samples collected during the second trimester of pregnancy. Inorganic arsenic (iAs) exposure was evaluated via cord blood samples and maternal toenail samples collected during the first trimester. Multiple linear regression and mediation analyses were used to explore the relationship between iAs exposure, metabolite alterations, and low birth weight. Cord blood arsenic level was correlated with elevated levels of 17-methylstearate, laurate (12:0) and 4-vinylphenol sulfate along with lower birth weight. Prenatal maternal toenail iAs level was associated with two peripheral blood metabolites (butyrylqlycine and tartarate), which likely contributed to higher cord blood iAs levels both independently and interactively. Findings of this pilot study indicate that both intrauterine and maternal peripheral blood metabolites appear to influence the toxic effect of inorganic arsenic exposure on low birth weight.

Using silver and bighead carp cell lines for the identification of a unique metabolite fingerprint from thiram-specific chemical exposure

Conservation biology often requires the control of invasive species. One method is the development and use of biocides. Identifying new chemicals as part of the biocide registration approval process can require screening millions of compounds. Traditionally, screening new chemicals has been done in vivo using test organisms. Using in vitro (e.g., cell lines) and in silico (e.g., computer models) methods decrease test organism requirements and increase screening speed and efficiency. These methods, however, would be greatly improved by better understanding how individual fish species metabolize selected compounds. We combined cell assays and metabolomics to create a powerful tool to facilitate the identification of new control chemicals. Specifically, we exposed cell lines established from bighead carp and silver carp larvae to thiram (7 concentrations) then completed metabolite profiling to assess the dose-response of the bighead carp and silver carp metabolome to thiram. Forty one of the 700 metabolomic markers identified in bighead carp exhibited a dose-response to thiram exposure compared to silver carp in which 205 of 1590 metabolomic markers exhibited a dose-response. Additionally, we identified 11 statistically significant metabolomic markers based upon volcano plot analysis common between both species. This smaller subset of metabolites formed a thiram-specific metabolomic fingerprint which allowed for the creation of a toxicant specific, rather than a species-specific, metabolomic fingerprint. Metabolomic fingerprints may be used in biocide development and improve our understanding of ecologically significant events, such as mass fish kills.

Zebrafish in Toxicology and Environmental Health

As manufacturing processes and development of new synthetic compounds increase to keep pace with the expanding global demand, environmental health, and the effects of toxicant exposure are emerging as critical public health concerns. Additionally, chemicals that naturally occur in the environment, such as metals, have profound effects on human and animal health. Many of these compounds are in the news: lead, arsenic, and endocrine disruptors such as bisphenol A have all been widely publicized as causing disease or damage to humans and wildlife in recent years. Despite the widespread appreciation that environmental toxins can be harmful, there is limited understanding of how many toxins cause disease. Zebrafish are at the forefront of toxicology research; this system has been widely used as a tool to detect toxins in water samples and to investigate the mechanisms of action of environmental toxins and their related diseases. The benefits of zebrafish for studying vertebrate development are equally useful for studying teratogens. Here, we review how zebrafish are being used both to detect the presence of some toxins as well as to identify how environmental exposures affect human health and disease. We focus on areas where zebrafish have been most effectively used in ecotoxicology and in environmental health, including investigation of exposures to endocrine disruptors, industrial waste byproducts, and arsenic.