Hexavalent chromium is cytotoxic and genotoxic to American alligator cells

Hexavalent chromium damages intestinal cells and coelomocytes and impairs immune function in the echiuran worm Urechis unicinctus by causing oxidative stress and apoptosis

Hexavalent chromium (Cr(VI)) is a common pollutant in the marine environment, which impairs immunity and causes reproductive and heredity disorders in organisms. To clarify the immunotoxic effects of Cr (VI) on the marine worm Urechis unicinctus, we analyzed tissue damage and immune dysfunction caused by Cr (VI) in this organism at histopathologic, zymologic, apoptotic and molecular levels. The results indicated that the bioaccumulation of Cr (VI) bioaccumulation levels in coelomocytes was significantly higher than in the intestines and muscles. Pathological observation showed that Cr (VI) caused damage to the respiratory intestine, stomach and midgut. Cr (VI) also increased the replication of goblet cells and a reduction in the replication of epithelial cells. Meanwhile, Cr (VI) induced apoptosis of intestinal cells and coelomocytes, accompanied by an increase in the expression of Caspase-3, COX-2, and MyD88 in the intestine and coelomocytes. At the same time, Cr (VI) significantly affected the activities of antioxidant enzymes such as SOD, ACP, CAT, CAT, and GST, and increased H2O2 and MDA contents in U. unicinctus. Moreover, Cr (VI) exposure also up-regulated the transcription of hsc70, mt and jnk genes but decreased that of sod in the intestines. In contrast, Cr (VI) down-regulated the expression of sod, hsc70, mt, and jnk genes in coelomocytes. Collectively, Cr (VI) bioaccumulated in U. unicinctus cells and tissues, causing several histopathological changes, oxidative stress, and apoptosis of several cells in the organism, resulting in intestinal and coelomocyte damage and immune dysfunctioning.

Heavy Metals in the Blood Serum and Feces of Mugger Crocodile (Crocodylus palustris) in Sistan and Baluchistan Province, Iran

This study was conducted to measure concentrations of cadmium (Cd), lead (Pb), arsenic (As), mercury (Hg), copper (Cu), chromium (Cr), and iron (Fe) in blood serum and feces of mugger crocodile (Crocodylus palustris) and in water and sediment of their habitat (Negour site, Chabahar County in Sistan and Baluchistan Province, Iran). Heavy metal contents in crocodile serum and feces, water, and sediments were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES spectrometer-Spectro Genesis). The highest levels of heavy metals in the mugger crocodile's serum were Fe > Hg > Pb > Cr > Cu > Cd > As, respectively. The total metal concentrations in the feces exhibited the following decreasing order from Fe > As > Pb = Cr > Hg > Cd > Cu. The highest average levels of heavy metals in water were Hg > Fe > As > Pb > Cu > Cr > Cd respectively and As > Fe > Pb > Cu > Hg > Cd > Cr in the sediment of lagoons. A significant difference was observed in the concentration of Fe and Pb between male and female crocodiles. Moreover, correlation analysis indicated significant negative correlations between sex and bioconcentrations of Cd, Fe, Pb, As, and Hg in the serum. In conclusion, this study showed that the environmental conditions of Negour lagoons are not suitable for crocodiles regarding habitat health and water quality. Furthermore, since these lagoons and fish are the most important sources of drinking water and seafood for the residents of the area, contamination of these pools with heavy metals can also threaten people's health.

Transcriptome analysis reveals antioxidant defense mechanisms in the red swamp crayfish Procambarus clarkia after exposure to chromium

Chromium (Cr) as a chromate anion has a strong redox capacity that seriously threatens the ecological environment and human health. Cr can contaminate water and impart toxicity to aquatic species. Procambarus clarkii is an important food source that once represented a large proportion of the aquaculture industry due to its rapid reproduction and high economic value. However, there have been reports on the death of P. clarkii due to heavy metal pollution. The underlying mechanism regarding heavy metal toxicity was studied in this paper. The transcriptome data of hemocytes extracted from P. clarkii injected with Cr were analyzed by high-throughput sequencing and compared to the control group. In total, 48,128,748 clean reads were obtained in the treatment group and 56,480,556 clean reads were obtained in the control group. The reads were assembled using Trinity and the identified unigenes were then annotated. Then, 421 differentially-expressed genes (DEGs) were found, 170 of which were upregulated and 251 downregulated. Many of these genes were found to be related to glutathione metabolism and transportation. The glutathione metabolic pathway of P. clarkii was thus activated by Cr exposure to detoxify and maintain body function. Validation of DEGs with quantitative real-time PCR confirms the changes in gene expression. Thus, this study provides data supporting a glutathione-focused response of P. clarkii to exposure to heavy metals.

Biomarkers of geno- and cytotoxicity in the native broad-snouted caiman (Caiman latirostris): Chromosomal aberrations and mitotic index

We evaluated the sensitivity of the chromosomal aberration (CA) and mitotic index (MI) assays on peripheral blood lymphocytes (PBLs) of Caiman latirostris, following ex vivo exposure to the alkylating agent, MMS. Two concentrations of MMS were tested in cultured peripheral blood. Relative to controls, MMS exposure reduced the number of metaphases observed, but both the numbers of cells with MN and the percentages of aberrant metaphases increased. The types of CA identified were chromosome and chromatid breaks, chromosomal rearrangements, monosomies, and nullisomies, with significantly higher values in the MMS-exposed groups. The incorporation of the MI and CA tests in C. latirostris can provide information on damage caused by xenobiotic exposures.

Hexavalent chromium induced heart dysfunction via Sesn2-mediated impairment of mitochondrial function and energy supply

Hexavalent chromium (Cr(VI)), the most toxic valence state of chromium, is widely present in industrial effluents and wastes. Although previous study has reported that Cr(VI) can cause cytomembrane structure impairment by aggravating lipid peroxidation in the heart, the detailed mechanism of Cr(VI)-induced heart dysfunction is still unclear. Sesn2, a novel antioxidant and stress-inducible molecule, is evidenced to protect against various cardiometabolic diseases such as atherosclerosis and cardiomyopathy. To define the potential mechanism of heart dysfunction induced by chronic Cr(VI) exposure, Wistar rats were intraperitoneal injected with potassium dichromate (K₂Cr₂O₇) for 35 d in the present study. The data showed that chronic K₂Cr₂O₇ exposure caused dose-dependently hematological variations, oxidative stress, dysfunction, and disorganized structure of heart, cardiomyocyte apoptosis, ATP depletion, and mitochondria impairment in rats. In addition, the expressions of Drp1 and Bax were increased by K₂Cr₂O₇. However, the suppression of Mfn2, PGC-1α, Sesn2, nuclear Nrf2, HO-1, and NQO1 protein levels was observed in K₂Cr₂O₇-treated rat hearts. In conclusion, these results demonstrate that chronic K₂Cr₂O₇ exposure dose-dependently causes heart dysfunction, and the molecular mechanism of this event is associated with the loss of Sesn2 mediated mitochondrial function and energy supply impairment.

New insight into the molecular basis of chromium exposure of Litopenaeus vannamei by transcriptome analysis

Heavy metal pollution arising from agricultural and industrial activities poses a significant threat to the aquatic environment, especially the increasing levels of chromium (Cr) that is exacerbating marine pollution. Given the economic importance of the Pacific white shrimp Litopenaeus vannamei (L. vannamei), understanding the impact of marine Cr pollution is deemed to be significant. In this study, we used the transcriptome sequencing (RNA-seq) technique to characterize the molecular mechanism of Cr exposure in L. vannamei. Gene ontology enrichment analysis showed substrate-specific and ion transport-related functions were mainly influenced by Cr exposure. We further identified genes involved in protein digestion and absorption (PEPT1, BAT1, MDU1), chemical carcinogenesis (GST and UGTs), ABC transporters (ABCC2), apoptosis (CAPN1, CASP10, PARP), implying the potentially Cr disintoxication mechanisms in L. vannamei. Genes within pancreatic secretion (ALT, LDH), lysosome (CTSL and HEXB), and peroxisome (ACOX1, ECI2, NUDT12) pathways implied the potentially Cr toxicity mechanisms in L. vannamei.

In Situ-Grown Cdot-Wrapped Boehmite Nanoparticles for Cr(VI) Sensing in Wastewater and a Theoretical Probe for Chromium-Induced Carcinogen Detection

In modern society, massive industrialization escalates environmental degradation by liberating various contaminants into the environment. Hexavalent chromium is a heavy metal that is being discharged from tannery and other industries, resulting in various carcinogenic diseases. This study reports a carbon dot (cdot)-based fluorometric probe for detecting hexavalent chromium in water. This is the very first time that cdots are tailored over the boehmite nanoparticle's surface using an in situ approach. Validation of formation of the nanocomposite has been discussed in detail employing the Rietveld refinement-based X-ray crystallography method. Vibrational spectroscopy and electron microscopy of the sample authenticate the nucleation process and the growth mechanism. The Stern-Volmer approach and time-resolved fluorescence measurements justify the sensitivity of the sensor (∼58 nM), and selectivity is analyzed by exposing the material to different ionic environments. Density functional theory (DFT) is applied herein to analyze the origin of fluorescence and the sensing mechanism of the probe, which shows that photoinduced electron transfer is responsible for the turn-off-based sensing of Cr(VI). The molecular docking simulation is carried out to ensure the binding of cdots to the binding pocket of the glutathione enzyme, which is responsible for treating reactive oxygen species-mediated DNA damage due to elements such as hexavalent chromium. Time-dependent density functional calculations show that the fluorometric probe is capable of detecting Cr(VI) in living cells making it an early stage chromium-mediated carcinogen detector.

Sulforaphane attenuates hexavalent chromium-induced cardiotoxicity via the activation of the Sesn2/AMPK/Nrf2 signaling pathway

Hexavalent chromium (Cr(vi)), the most toxic valence state of chromium, is widely present in industrial effluents and wastes. Sulforaphane (SFN), rich in Brassica genus plants, bears multiple biological activity. Wistar rats were used to explore the protective role of SFN against the cardiotoxicity of chronic potassium dichromate (K2Cr2O7) exposure and reveal the potential molecular mechanism. The data showed that SFN alleviated hematological variations, oxidative stress, heart dysfunction and structure disorder, and cardiomyocyte apoptosis induced by K2Cr2O7. Moreover, SFN reduced p53, cleaved caspase-3, Bcl2-associated X protein, nuclear factor kappa-B, and interleukin-1β levels, and increased Sesn2, nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1, NAD(P)H quinone oxidoreductase-1, and phosphorylated adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) levels. This study demonstrates that SFN ameliorates Cr(vi)-induced cardiotoxicity via activation of the Sesn2/AMPK/Nrf2 signaling pathway. SFN may be a protector against Cr(vi)-induced heart injury and a novel therapy for chronic Cr(vi) exposure.

Towards the development of standardised sea turtle primary cell cultures for toxicity testing

Chemical contaminants are known to accumulate in marine megafauna globally, but little is known about how this impacts animal health. In vitro assays offer an ethical, reproducible and cost-effective alternative to live animal toxicity testing on large, long-lived or threatened species, such as sea turtles. However, using a cell culture from a single animal raise the question of whether the toxicity observed adequately represents the toxicity in that species. This study examined variation in the cytotoxic response of primary skin fibroblasts established from seven green (Chelonia mydas) and five loggerhead (Caretta caretta) sea turtles. Cell viability using resazurin dye was examined in response to exposure to five contaminants. The variation in cytotoxicity was generally low (within a factor of five) for both independent analyses of the same cell culture, and cell cultures from different individuals. This low within and between cell culture variation indicates that primary sea turtle cell cultures can provide a suitable approach to understanding toxicity in sea turtles. In addition, green and loggerhead turtle cells showed similar toxicity to the compounds tested, indicating that only subtle differences in chemical sensitivity may exist between sea turtle species. This study provides a framework for using species-specific cell cultures in future toxicological studies on sea turtles. Although in vivo studies are the gold standard for toxicological studies and species-specific risk assessments, the development of in vitro tools can provide important information when in vivo studies are not possible or practical. For large, endangered species such as sea turtles that are exposed to, and accumulate, a large number of contaminants, using validated cell cultures may facilitate the rapid assessment of chemical risk to these animals.

A comparison of particulate hexavalent chromium cytotoxicity and genotoxicity in human and leatherback sea turtle lung cells from a one environmental health perspective

Evaluating health risks of environmental contaminants can be better achieved by considering toxic impacts across species. Hexavalent chromium [Cr(VI)] is a marine pollutant and global environmental contaminant. While Cr(VI) has been identified as a human lung carcinogen, health effects in marine species are poorly understood. Little is known about how Cr(VI) might impact humans and marine species differently. This study used a One Environmental Health Approach to compare the cytotoxicity and genotoxicity of particulate Cr(VI) in human and leatherback sea turtle (Dermochelys coriacea) lung fibroblasts. Leatherbacks may experience prolonged exposures to environmental contaminants and provide insight to how environmental exposures affect health across species. Since humans and leatherbacks may experience prolonged exposure to Cr(VI), and prolonged Cr(VI) exposure leads to carcinogenesis in humans, in this study we considered both acute and prolonged exposures. We found particulate Cr(VI) induced cytotoxicity in leatherback cells comparable to human cell data supporting current research that shows Cr(VI) impacts health across species. To better understand mechanisms of Cr(VI) toxicity we assessed the genotoxic effects of particulate Cr(VI) in human and leatherback cells. Particulate Cr(VI) induced similar genotoxicity in both cell lines, however, human cells arrested at lower concentrations than leatherback cells. We also measured intracellular Cr ion concentrations and found after prolonged exposure human cells accumulated more Cr than leatherback cells. These data indicate Cr(VI) is a health concern for humans and leatherbacks. The data also suggest humans and leatherbacks respond to chemical exposure differently, possibly leading to the discovery of species-specific protective mechanisms.

Sustaining the efficiency of the Fe(0)/H2O system for Cr(VI) removal by MnO2 amendment

This study aims to provide new knowledge regarding the effect of MnO₂ co-presence on efficiency of Cr(VI) removal with Fe(0). Non-disturbed batch experiments (≤40 days) were conducted using two types of Fe(0) (milli- and micro-sized), two Cr(VI) concentrations (5 and 100 mg/L), in three different systems ("Fe(0) only", "MnO₂ only", and "Fe(0) + MnO₂"), at an initial pH value of 6.9. Compared to "Fe(0) only" system, the efficiency and rate of Cr(VI) removal were highly promoted in "Fe(0) + MnO₂" system; moreover, while for the "Fe(0) only" system removal of Cr(VI) was severely hindered by increasing Cr(VI) concentration, in "Fe(0) + MnO₂" system comparable high efficacies were noticed both at low and high concentration. Recycling experiments indicated that total Cr(VI) removal capacity of "Fe(0) + MnO₂" system was up to 48.1 times greater than of the "Fe(0) only" system. Enhanced removal of Cr(VI) with Fe(0) was achieved at low doses of MnO₂, with an optimal mass ratio Fe(0):MnO₂ of 4:1. The favorable synergistic effect observed in "Fe(0) + MnO₂" system was ascribed to capacity of MnO₂ to accelerate Fe(0) oxidative dissolution, and to generate supplementary amounts of secondary adsorbents/reductants with removal ability towards Cr(VI). This study provides compelling evidence that "Fe(0) + MnO₂" system could represent a highly efficient and cost-effective alternative for the abatement of Cr(VI) aqueous pollution.

The cytotoxicity and genotoxicity of particulate and soluble hexavalent chromium in leatherback sea turtle lung cells

Hexavalent chromium [Cr(VI)] is a marine pollution of concern as recent studies show it has a global distribution, with some regions showing high Cr concentrations in marine animal tissue, and it is extensively used. Leatherback sea turtles (Dermochelys coriacea) are an endangered marine species that may experience prolonged exposures to environmental contaminants including Cr(VI). Human activities have led to global Cr(VI) contamination of the marine environment. While Cr(VI) has been identified as a known human carcinogen, the health effects in marine species are poorly understood. In this study, we assessed the cytotoxic and genotoxic effects of particulate and soluble Cr(VI) in leatherback sea turtle lung cells. Both particulate and soluble Cr(VI) induced a concentration-dependent increase in cytotoxicity. Next, using a chromosome aberration assay, we assessed the genotoxic effects of Cr(VI) in leatherback sea turtle lung cells. Particulate and soluble Cr(VI) induced a concentration-dependent increase in clastogenicity in leatherback sea turtle lung cells. These data indicate that Cr(VI) may be a health concern for leatherback sea turtles and other long-lived marine species. Additionally, these data provide foundational support to use leatherback sea turtles as a valuable model species for monitoring the health effects of Cr(VI) in the environment and possibly as an indicator species to assess environmental human exposures and effects.

Transcriptome Analysis of Hepatopancreas from the Cr (VI)-Stimulated Mantis Shrimp ( Oratosquilla oratoria) by Illumina Paired-End Sequencing: Assembly, Annotation, and Expression Analysis

Cr (VI), the pathogenicity factor, is widely known to cause toxic effects in living organisms. Given the economic importance of the mantis shrimp ( Oratosquilla oratoria), the understanding of impacts by Cr (VI) is considered important. In this study, transcriptome of mantis shrimp was characterized by a comparison between control and Cr (VI)-treated samples using RNA-seq approach. Totally, 88 234 826 bp and 13.24G clean reads were obtained. The total length and number of unigenes were 68 411 206 bp and 100 918, respectively. The maximal and average length of unigenes was 24 906 bp and 678 bp, respectively (N50, 798 bp). 7115 of these unigenes accounted for 7.05% of the total that were annotated in all databases. After annotation of assembled unigenes, 35 619 of them were assigned into 3 functional categories and 56 subcategories using Gene Ontology; 18 580 of them were assigned into 26 functional categories using Clusters of Orthologous Groups of proteins; 16 864 of them were assigned into 5 major categories and 32 subclasses using KEGG. Finally, 1730 genes were differentially expressed (DGEs), 9 up-regulated pathways (protein digestion and absorption, neuroactive ligand-receptor interaction, pancreatic secretion, tyrosine metabolism, amoebiasis, ECM-receptor interaction, riboflavin metabolism, amino sugar and nucleotide sugar metabolism and AGE-RAGE signaling pathway in diabetic complications) were significantly enriched ( q < 0.05), and one down-regulated pathway ( Staphylococcus aureus infection) was significantly enriched ( q < 0.05). Up-regulation of genes in pathways of protein digestion/absorption ( PepT1/SLC15A and ATP1B) and environment information processing ( COL1AS, COL4A; LAMA3_5, LAMB3; FN1 and TN) may imply the potentially positive toxicity resistance mechanisms.

Characterization of Penicillium oxalicum SL2 isolated from indoor air and its application to the removal of hexavalent chromium

Removal of toxic Cr(VI) by microbial reduction is a promising approach to reducing its ecotoxicological impact. To develop bioremediation technologies, many studies have evaluated the application of microorganisms isolated from Cr(VI)-contaminated sites. Nonetheless, little attention has been given to microbes from the environments without a history of Cr(VI) contamination. In this study, we aimed to characterize the Cr(VI) tolerance and removal abilities of a filamentous fungus strain, SL2, isolated from indoor air. Based on phenotypic characterization and rDNA sequence analysis, SL2 was identified as Penicillium oxalicum, a species that has not been extensively studied regarding Cr(VI) tolerance and reduction abilities. SL2 showed high tolerance to Cr(VI) on solid and in liquid media, facilitating its application to Cr(VI)-contaminated environments. Growth curves of SL2 in the presence of 0, 100, 400, or 1000 mg/L Cr(VI) were well simulated by the modified Gompertz model. The relative maximal colony diameter and maximal growth rate decreased as Cr(VI) concentration increased, while the lag time increased. SL2 manifested remarkable efficacy of removing Cr(VI). Mass balance analysis indicated that SL2 removed Cr(VI) by reduction, and incorporated 0.79 mg of Cr per gram of dry biomass. In electroplating wastewater, the initial rate of Cr(VI) removal was affected by the initial contaminant concentration. In conclusion, P. oxalicum SL2 represents a promising new candidate for Cr(VI) removal. Our results significantly expand the knowledge on potential application of this microorganism.

Coupling gene-based and classic veterinary diagnostics improves interpretation of health and immune function in the Agassiz's desert tortoise (Gopherus agassizii)

The analysis of blood constituents is a widely used tool to aid in monitoring of animal health and disease. However, classic blood diagnostics (i.e. hematologic and plasma biochemical values) often do not provide sufficient information to determine the state of an animal's health. Field studies on wild tortoises and other reptiles have had limited success in drawing significant inferences between blood diagnostics and physiological and immunological condition. However, recent research using gene transcription profiling in the threatened Mojave desert tortoise (Gopherus agassizii) has proved useful in identifying immune or physiologic responses and overall health. To improve our understanding of health and immune function in tortoises, we evaluated both standard blood diagnostic (body condition, hematologic, plasma biochemistry values, trace elements, plasma proteins, vitamin A levels) and gene transcription profiles in 21 adult tortoises (11 clinically abnormal; 10 clinically normal) from Clark County, NV, USA. Necropsy and histology evaluations from clinically abnormal tortoises revealed multiple physiological complications, with moderate to severe rhinitis or pneumonia being the primary cause of morbidity in all but one of the examined animals. Clinically abnormal tortoises had increased transcription for four genes (SOD, MyD88, CL and Lep), increased lymphocyte production, biochemical enzymes and organics, trace elements of copper, and decreased numbers of leukocytes. We found significant positive correlations between increased transcription for SOD and increased trace elements for copper, as well as genes MyD88 and Lep with increased inflammation and microbial insults. Improved methods for health assessments are an important element of monitoring tortoise population recovery and can support the development of more robust diagnostic measures for ill animals, or individuals directly impacted by disturbance.

Accumulation and effects of Cr(VI) in Japanese medaka (Oryzias latipes) during chronic dissolved and dietary exposures

Chromium (Cr) is an essential metal and a nutritional supplement for both human and agricultural uses. It is also a pollutant from a variety of industrial uses. These uses can lead to elevated Cr levels in aquatic environments, where it can enter and affect aquatic organisms. Its accumulation and subsequent effects in fish have received relatively little attention, especially for chronic exposure. In the present study, Japanese medaka were chronically exposed to dissolved or dietary Cr(VI) for 3 months. Cr accumulation in liver, gills, intestine, and brain was evaluated. Effects on the antioxidant system, nervous system (acetylcholinesterase, AChE), digestive system (α-glucosidase, α-Glu), and tissue histology (liver and gills) were also assessed. Cr accumulation was observed in the intestine and liver of fish exposed to Cr-contaminated brine shrimp. However, chronic dissolved Cr exposure led to significant Cr accumulation in all organs tested. Analysis of the subcellular distribution of Cr in medaka livers revealed that 37% of the Cr was present in the heat stable protein fraction. The dissolved Cr exposure had pronounced effects on the antioxidant system in the liver, with an elevated ratio of reduced glutathione/oxidized glutathione (GSH/GSSG) and decreases in GSH and glutathione S-transferase (GST). The α-Glu activity in the intestine was significantly inhibited. In addition, Cr exposure caused histopathological alterations in the gills and liver. In general, the effects of dietary Cr were relatively minor, possible due to the much lower accumulation in the fish. Our results imply that Japanese medaka accumulate Cr mainly via uptake of dissolved Cr(VI).