Alteration of intracellular GSH levels and its role in microcystin-LR-induced DNA damage in human hepatoma HepG2 cells

The cytotoxicity of microcystin-LR: ultrastructural and functional damage of cells

Microcystin-LR (MC-LR) is a toxin produced by cyanobacteria, which is widely distributed in eutrophic water bodies and has multi-organ toxicity. Previous cytotoxicity studies have mostly elucidated the effects of MC-LR on intracellular-related factors, proteins, and DNA at the molecular level. However, there have been few studies on the adverse effects of MC-LR on cell ultrastructure and function. Therefore, research on the cytotoxicity of MC-LR in recent years was collected and summarized. It was found that MC-LR can induce a series of cytotoxic effects, including decreased cell viability, induced autophagy, apoptosis and necrosis, altered cell cycle, altered cell morphology, abnormal cell migration and invasion as well as leading to genetic damage. The above cytotoxic effects were related to the damage of various ultrastructure and functions such as cell membranes and mitochondria. Furthermore, MC-LR can disrupt cell ultrastructure and function by inducing oxidative stress and inhibiting protein phosphatase activity. In addition, the combined toxic effects of MC-LR and other environmental pollutants were investigated. This review explored the toxic targets of MC-LR at the subcellular level, which will provide new ideas for the prevention and treatment of multi-organ toxicity caused by MC-LR.

Involvement of reactive oxygen species (ROS) in the hepatopancreatic cytotoxicity, oxidative stress, and apoptosis induced by microcystin-LR in Eriocheir sinensis

There is limited knowledge about the toxicity of Microcystin-LR (MC-LR) in crustaceans, despite its high toxicity to aquatic organisms. This research aimed to explore the effects of MC-LR on cytotoxicity, oxidative stress, and apoptosis in the hepatopancreas of Eriocheir sinensis, as well as elucidate the involvement of reactive oxygen species (ROS) and potential mechanisms of toxicity. In vivo and in vitro exposures of crabs to MC-LR and N-acetylcysteine (NAC) were performed, followed by assessments of cell morphology, viability, tissue pathology, biochemical indicators, gene expression, and hepatopancreatic transcriptome. Results revealed that MC-LR facilitated the entry of the MC-LR transporter oatp3a into hepatopancreatic cells, leading to upregulated expression of phase I detoxification enzyme genes (cyp4c, cyp2e1, and cyp3) and downregulated the phase II enzyme genes (gst1, gpx, gsr2, gclc, and nqo1), resulting in increased ROS levels and cytotoxic effects. MC-LR exhibited cytotoxicity, reducing cell viability and inducing abnormal nuclear morphology with a 48 h-IC50 value of approximately 120 μm. MC-LR exposure caused biochemical changes indicative of oxidative stress damage and evident hepatopancreatic lesions. Additionally, MC-LR exposure regulated the levels of bax and bcl-2 expression, activating caspase 3 and 6 to induce cell apoptosis. Intervention with NAC attenuated MC-LR-induced ROS production and associated toxic effects. Transcriptome analysis revealed enrichment of differentially expressed genes in pathways related to cytochrome P450-mediated xenobiotic metabolism and the FoxO signaling pathway. These findings shed light on the potential mechanisms underlying MC-LR toxicity and provide valuable references for further research and conservation efforts regarding the health of aquatic animals.

The presence of polystyrene nanoplastics enhances the MCLR uptake in zebrafish leading to the exacerbation of oxidative liver damage

The accumulation of diminutive plastic waste in the environment, including microplastics and nanoplastics, has threatened the health of multiple species. Nanoplastics can adsorb the pollutants from the immediate environment, and may be used as carriers for pollutants to enter organisms and bring serious ecological risk. To evaluate the toxic effects of microcystin-LR (MCLR) on the liver of adult zebrafish (Danio rerio) in the presence of 70 nm polystyrene nanoplastics (PSNPs), zebrafish were exposed to MCLR alone (0, 0.9, 4.5 and 22.5 μg/L) and a mixture of MCLR + PSNPs (100 μg/L) for three months. The results indicated that groups with combined exposure to MCLR and PSNPs further enhanced the accumulation of MCLR in the liver when compared to groups only exposed to MCLR. Cellular swelling, fat vacuolation, and cytoarchitectonic damage were observed in zebrafish livers after exposure to MCLR, and the presence of PSNPs exacerbated these adverse effects. The results of biochemical tests showed the combined effect of MCLR + PSNPs enhanced MCLR-induced hepatotoxicity, which could be attributed to the altered levels of reactive oxygen species, malondialdehyde and glutathione, and activities of catalase. The expression of genes related to antioxidant responses (p38a, p38b, ERK2, ERK3, Nrf2, HO-1, cat1, sod1, gax, JINK1, and gstr1) was further performed to study the mechanisms of MCLR combined with PSNPs aggravated oxidative stress of zebrafish. The results showed that PSNPs could improve the bioavailability of MCLR in the zebrafish liver by acting as a carrier and accelerate MCLR-induced oxidative stress by regulating the levels of corresponding enzymes and genes.

Allium sativum mitigates oxidative damages induced by Microcystin-LR in heart and liver tissues of mice

Microcystins (MCs) are hepatotoxic cyanotoxins implicated in several incidents of human and animal toxicity. Microcystin-(Lysine, Arginine) or MC-LR is the most toxic and encountered variant of MCs where oxidative stress plays a key role in its toxicity. This study investigated the oxidative damages induced in the liver and heart of Balb/C mice by an intraperitoneal injected acute dose of MC-LR. Thereafter, the potential protective effect of garlic (Allium sativum) extract supplementation against such damages was assessed through the evaluation of oxidative stress and cytotoxicity markers. Lipid peroxidation (LPO), carbonyl content (CC), glutathione content (GSH), alkaline phosphatase activity (ALP), lactate dehydrogenase (LDH) and sorbitol dehydrogenase (SDH) activities were measured. Results showed important oxidative damages in hepatic and cardiac cells of mice injected with the toxin. However, these damages have been significantly reduced in mice supplemented with garlic extract. Thus, this study demonstrated for the first time the effective use of garlic as an antioxidant agent against oxidative damages induced by MC-LR. As well, this study supports the use of garlic as a potential remedy against pathologies related to toxic agents.

Harmful algal blooms and their eco-environmental indication

Harmful algal blooms (HABs) in freshwater lakes and oceans date back to as early as the 19th century, which can cause the death of aquatic and terrestrial organisms. However, it was not until the end of the 20th century that researchers had started to pay attention to the hazards and causes of HABs. In this study, we analyzed 5720 published literatures on HABs studies in the past 30 years. Our review presents the emerging trends in the past 30 years on HABs studies, the environmental and human health risks, prevention and control strategies and future developments. Therefore, this review provides a global perspective of HABs and calls for immediate responses.

Supplementation with asiatic acid during in vitro maturation improves porcine oocyte developmental competence by regulating oxidative stress

Asiatic acid is a natural triterpene found in Centella asiatica that acts as an effective free radical scavenger. Our previous research showed that asiatic acid delayed porcine oocyte ageing in vitro and improved preimplantation embryo development competence in vitro; however, the protective effects of asiatic acid against oxidative stress in porcine oocyte maturation are still unclear. Here, we investigated the effects of asiatic acid on porcine oocyte in vitro maturation (IVM) and subsequent embryonic development competence after parthenogenetic activation (PA) and in vitro fertilization (IVF). The results of the present research showed that 10 μM asiatic acid supplementation did not affect the expansion of cumulus cells or polar body extrusion of porcine oocytes, while asiatic acid application significantly increased the subsequent blastocyst formation rate and quality of porcine PA and IVF embryos. Hydrogen peroxide (H₂O₂) is a reactive oxygen species (ROS) that induces oxidative stress in porcine oocytes. As expected, asiatic acid supplementation not only decreased intracellular ROS levels but also attenuated H₂O₂-induced intracellular ROS generation. Further analysis revealed that asiatic acid supplementation enhanced intracellular glutathione production, mitochondrial membrane potential, and ATP generation at the end of IVM. In summary, our results reveal that asiatic acid supplementation exerts beneficial effects on porcine oocytes by regulating oxidative stress during the IVM process and could act as a potential antioxidant in porcine oocytes matured in vitro production systems.

In Vivo and In Vitro Toxicity Testing of Cyanobacterial Toxins: A Mini-Review

Harmful cyanobacterial blooms are increasing and becoming a worldwide concern as many bloom-forming cyanobacterial species can produce toxic metabolites named cyanotoxins. These include microcystins, saxitoxins, anatoxins, nodularins, and cylindrospermopsins, which can adversely affect humans, animals, and the environment. Different methods to assess these classes of compounds in vitro and in vivo include biological, biochemical, molecular, and physicochemical techniques. Furthermore, toxic effects not attributable to known cyanotoxins can be observed when assessing bloom material. In order to determine exposures to cyanotoxins and to monitor compliance with drinking and bathing water guidelines, it is necessary to have reliable and effective methods for the analysis of these compounds. Many relatively simple low-cost methods can be employed to rapidly evaluate the potential hazard. The main objective of this mini-review is to describe the assessment of toxic cyanobacterial samples using in vitro and in vivo bioassays. Newly emerging cyanotoxins, the toxicity of analogs, or the interaction of cyanobacteria and cyanotoxins with other toxicants, among others, still requires bioassay assessment. This review focuses on some biological and biochemical assays (MTT assay, Immunohistochemistry, Micronucleus Assay, Artemia salina assay, Daphnia magna test, Radionuclide recovery, Neutral red cytotoxicity and Comet assay, Enzyme-Linked Immunosorbent Assay (ELISA), Annexin V-FITC assay and Protein Phosphatase Inhibition Assay (PPIA)) for the detection and measurement of cyanotoxins including microcystins, cylindrospermopsins, anatoxin-a, saxitoxins, and nodularins. Although most bioassay analyses often confirm the presence of cyanotoxins at low concentrations, such bioassays can be used to determine whether some strains or blooms of cyanobacteria may produce other, as yet unknown toxic metabolites. This review also aims to identify research needs and data gaps concerning the toxicity assessment of cyanobacteria.

Protective effects of melatonin and N-acetyl cysteine against oxidative stress induced by microcystin-LR on cardiac muscle tissue

Microcystin Leucine-Arginine (MC-LR) is a toxin produced by the cyanobacteria Microcystis aeruginosa. It is the most encountered and toxic type of cyanotoxins. Oxidative stress was shown to play a role in the pathogenesis of microcystin LR by the induction of intracellular reactive oxygen species (ROS) formation that oxidize and damage cellular macromolecules. In the present study we examined the effect of acute MC-LR dose on the cardiac muscle of BALB/c mice. Afterwards, melatonin and N-acetyl cysteine (NAC) were assayed and evaluated as potential protective and antioxidant agents against damages generated by MC-LR. For this purpose, thirty mice were assigned into six groups of five mice each. The effect of MC-LR was first compared to the control group supplied with distilled water, then compared to the other groups supplied with melatonin and NAC. The experiment lasted 10 days after which animals were euthanized. Biomarkers of toxicity such as alkaline phosphatase activity, lipid peroxidation, protein carbonyl content, reduced glutathione content, serum lactate dehydrogenase and serum sorbitol dehydrogenase were assayed. Results showed that toxin treated mice have experienced significant oxidative damage in their myocardial tissue as revealed by noticeable levels of oxidative stress biomarkers and by the reduction in alkaline phosphatase activity. Whereas, melatonin and NAC treated mice manifested lesser oxidative damages. Our findings suggest a potential therapeutic use of melatonin and N-acetyl cysteine as antioxidant protective agents against oxidative damage induced by MC-LR.

Genotoxic stress-triggered β-catenin/JDP2/PRMT5 complex facilitates reestablishing glutathione homeostasis

The mechanisms underlying how cells subjected to genotoxic stress reestablish reduction-oxidation (redox) homeostasis to scavenge genotoxic stress-induced reactive oxygen species (ROS), which maintains the physiological function of cellular processes and cell survival, remain unclear. Herein, we report that, via a TCF-independent mechanism, genotoxic stress induces the enrichment of β-catenin in chromatin, where it forms a complex with ATM phosphorylated-JDP2 and PRMT5. This elicits histone H3R2me1/H3R2me2s-induced transcriptional activation by the recruitment of the WDR5/MLL methyltransferase complexes and concomitant H3K4 methylation at the promoters of multiple genes in GSH-metabolic cascade. Treatment with OICR-9429, a small-molecule antagonist of the WDR5-MLL interaction, inhibits the β-catenin/JDP2/PRMT5 complex-reestablished GSH metabolism, leading to a lethal increase in the already-elevated levels of ROS in the genotoxic-agent treated cancer cells. Therefore, our results unveil a plausible role for β-catenin in reestablishing redox homeostasis upon genotoxic stress and shed light on the mechanisms of inducible chemotherapy resistance in cancer.

It is known that genotoxic stress induces high levels of ROS and deplete cellular glutathione stores. Here, Cao et al. uncover a β-catenin-dependent TCF/LEF-independent mechanism that promotes histone-mediated transcriptional activation of glutathione synthesis.

Highly sensitive detection of microcystin-LR under visible light using a self-powered photoelectrochemical aptasensor based on a CoO/Au/g-C3N4 Z-scheme heterojunction

Based on the unique photoelectrochemical properties of a CoO/Au/g-C₃N₄ Z-scheme heterojunction, a self-powered photoelectrochemical (PEC) aptasensor was constructed for the detection of microcystin-leucine arginine (MC-LR). Z-scheme heterojunctions can promote the separation of a photo-induced electron-hole pair, and the surface plasmonic resonance (SPR) of Au nanoparticles can significantly enhance the adsorption of visible light. Importantly, MC-LR molecules were captured by aptamers initially immobilized on the modified electrode due to their high affinity, and then oxidized by the photogenerated holes, which caused an amplified photocurrent signal, allowing the quantitative analysis of MC-LR by measuring the photocurrent intensity change. This PEC MC-LR aptasensor showed high sensitivity and selectivity within a wide linear response range from 0.1 pM to 10 nM and a detection limit of 0.01 pM. The application of this sensor in the analysis of lake water samples provided accurate results with a relative standard deviation (RSD) of 2.6%-4.2%.

Cyanobacterial bioactive metabolites-A review of their chemistry and biology

Cyanobacterial blooms occur when algal densities exceed baseline population concentrations. Cyanobacteria can produce a large number of secondary metabolites. Odorous metabolites affect the smell and flavor of aquatic animals, whereas bioactive metabolites cause a range of lethal and sub-lethal effects in plants, invertebrates, and vertebrates, including humans. Herein, the bioactivity, chemistry, origin, and biosynthesis of these cyanobacterial secondary metabolites were reviewed. With recent revision of cyanobacterial taxonomy by Anagnostidis and Komárek as part of the Süβwasserflora von Mitteleuropa volumes 19(1-3), names of many cyanobacteria that produce bioactive compounds have changed, thereby confusing readers. The original and new nomenclature are included in this review to clarify the origins of cyanobacterial bioactive compounds. Due to structural similarity, the 157 known bioactive classes produced by cyanobacteria have been condensed to 55 classes. This review will provide a basis for more formal procedures to adopt a logical naming system. This review is needed for efficient management of water resources to understand, identify, and manage cyanobacterial harmful algal bloom impacts.

Microcystin-LR in peripheral circulation worsens the prognosis partly through oxidative stress in patients with hepatocellular carcinoma

Prognostic significance of serum microcystin in hepatocellular carcinoma has not been well investigated. The aim of the study was to reveal the relationship between serum microcystin-LR and prognosis in these patients. There were 650 early-stage hepatitis B-induced hepatocellular carcinoma patients, who were not affected by hepatitis C, cirrhosis, heavy drinking or excessive aflatoxin exposure. All of them underwent hepatectomy and were followed up for 5 years. Tumor relapse and overall death were recorded. Blood specimens were collected on admission and at the time of relapse. Serum levels of microcystin-LR and fluorescent oxidation products (FlOP_360, FlOP_320 and FlOP_400) were measured separately using enzyme-linked immunosorbent assay and fluorescence spectrometry. Multifactorial COX regression analysis suggested that serum microcystin-LR ≥ 0.97 ng/ml was associated with the increased risk of the tumor relapse (HR: 1.53, 95% CI: 1.35-1.77) and serum microcystin-LR ≥ 1.09 ng/ml was related to the higher risk of the overall death (HR: 1.58, 95% CI: 1.35-1.84) in the follow-up period. Furthermore, there was a linear relationship between serum level of microcystin-LR and serum levels of FlOP_360, FlOP_320 and FlOP_400 (P = 0.001, P = 0.023, P = 0.047). Serum levels of these fluorescent oxidation products were also higher in the patients with tumor relapse (P < 0.001, P < 0.001, P = 0.001) or overall death (P < 0.001, P = 0.001, P = 0.002) compared with the remaining patients. Serum microcystin-LR independently worsens the prognosis partly through promoting oxidative stress in patients with hepatocellular carcinoma.

Cytotoxic and morphological effects of microcystin-LR, cylindrospermopsin, and their combinations on the human hepatic cell line HepG2

Cylindrospermopsin (CYN) and Microcystin-LR (MC-LR) are toxins produced by different cyanobacterial species, which are found mainly in freshwater reservoirs. Both of them can induce, separately, toxic effects in humans and wildlife. However, little is known about the toxic effects of the combined exposure, which could likely happen, taking into account the concomitant occurrence of the producers. As both cyanotoxins are well known to induce hepatic damage, the human hepatocellular HepG2 cell line was selected for the present study. Thus, the cytotoxicity of both pure cyanotoxins alone (0-5 μg/mL CYN and 0-120 μg/mL MC-LR) and in combination for 24 and 48 h was assayed, as long as the cytotoxicity of extracts from CYN-producing and nonproducing cyanobacterial species. The potential interaction of the combination was evaluated by the isobologram or Chou-Talalay's method, which provides a combination index as a quantitative measure of the two cyanotoxins interaction's degree. Moreover, a morphological study of the individual pure toxins and their combinations was also performed. Results showed that CYN was the most toxic pure cyanotoxin, being the mean effective concentrations obtained ≈4 and 90 μg/mL for CYN and MC-LR, respectively after 24 h. However, the simultaneous exposure showed an antagonistic effect. Morphologically, autophagy, at low concentrations, and apoptosis, at high concentrations were observed, with affectation of the rough endoplasmic reticulum and mitochondria. These effects were more pronounced with the combination. Therefore, it is important to assess the toxicological profile of cyanotoxins combinations in order to perform more realistic risk evaluations.

Cyanobacterial bioactive metabolites-A review of their chemistry and biology

Cyanobacterial blooms occur when algal densities exceed baseline population concentrations. Cyanobacteria can produce a large number of secondary metabolites. Odorous metabolites affect the smell and flavor of aquatic animals, whereas bioactive metabolites cause a range of lethal and sub-lethal effects in plants, invertebrates, and vertebrates, including humans. Herein, the bioactivity, chemistry, origin, and biosynthesis of these cyanobacterial secondary metabolites were reviewed. With recent revision of cyanobacterial taxonomy by Anagnostidis and Komárek as part of the Süβwasserflora von Mitteleuropa volumes 19(1-3), names of many cyanobacteria that produce bioactive compounds have changed, thereby confusing readers. The original and new nomenclature are included in this review to clarify the origins of cyanobacterial bioactive compounds. Due to structural similarity, the 157 known bioactive classes produced by cyanobacteria have been condensed to 55 classes. This review will provide a basis for more formal procedures to adopt a logical naming system. This review is needed for efficient management of water resources to understand, identify, and manage cyanobacterial harmful algal bloom impacts.

Genotoxicity and cytotoxicity of three microcystin-LR containing cyanobacterial samples from Antioquia, Colombia

The presence of cyanobacterial blooms and cyanotoxins in water presents a global problem due to the deterioration of ecosystems and the possibility of poisoning in human and animals. Microcystin LR is the most widely distributed cyanotoxin and liver cells are its main target. In the present study, HepG2 cells were used to determine DNA damage of three crude extracts of cyanobacterial blooms containing MC-LR, through comet assay. The results show that all extracts at a concentration of 500 μg mL^-1 caused low damage in hepatocytes exposed for 24 h, but produced total mortality even at low concentrations at 48 h. Moreover, balloons corresponding to cell apoptosis were found. Through HPLC/MS, MC-LR was detected in all samples of cyanobacterial blooms at concentrations of (5,65 μg ml^-1) in sample 1, (1,24 μg ml^-1) in sample 2 and (57,29 μg ml^-1) in sample 3. In addition, in all samples high molecular weights peaks were detected, that may correspond to other microcystins. Besides, the cytotoxic effect of a cyanobacterial bloom and some of its chromatographic fractions from the crude extracts were evaluated in U-937, J774, Hela and Vero cell lines, using the enzymatic micromethod (MTT). The highest toxicity was detected in U-937 cells (LC₅₀ = 29.7 μg mL^-1) and Vero cells (LC₅₀ = 39.7 μg mL-¹). Based on these results, it is important to remark that genotoxic and cytotoxicity assays are valuable methods to predict potential biological risks in waters contaminated with blooms of cyanobacteria, since chemical analysis can only describe the presence of cyanotoxins, but not their biological effects.

Tumor-promoting cyanotoxin microcystin-LR does not induce procarcinogenic events in adult human liver stem cells

HL1-hT1 cell line represents adult human liver stem cells (LSCs) immortalized with human telomerase reverse transcriptase. In this study, HL1-hT1 cells were found to express mesenchymal markers (vimentin, CD73, CD90/THY-1 and CD105) and an early hepatic endoderm marker FOXA2, while not expressing hepatic progenitor (HNF4A, LGR5, α-fetoprotein) or differentiated hepatocyte markers (albumin, transthyretin, connexin 32). In response to microcystin-LR (MC-LR), a time- and concentration-dependent formation of MC-positive protein bands in HL1-hT1 cells was observed. Cellular accumulation of MC-LR occurred most likely via mechanisms independent on organic anion transporting polypeptides (OATPs) or multidrug resistance (MDR) proteins, as indicated (a) by a gene expression analysis of 11 human OATP genes and 4 major MDR genes (MDR1/P-glycoprotein, MRP1, MRP2 and BCRP); (b) by non-significant effects of OATP or MDR1 inhibitors on MC-LR uptake. Accumulation of MC-positive protein bands in HL1-hT1 cells was associated neither with alterations of cell viability and growth, dysregulations of ERK1/2 and p38 kinases, reactive oxygen species formation, induction of double-stranded DNA breaks nor modulations of stress-inducible genes (ATF3, HSP5). It suggests that LSCs might have a selective, MDR1-independent, survival advantage and higher tolerance towards MC-induced cytotoxic, genotoxic or cancer-related events than differentiated adult hepatocytes, fetal hepatocyte or malignant liver cell lines. HL1-hT1 cells provide a valuable in vitro tool for studying effects of toxicants and pharmaceuticals on LSCs, whose important role in the development of chronic toxicities and liver diseases is being increasingly recognized.

Oxidative stress-mediated p53/p21WAF1/CIP1 pathway may be involved in microcystin-LR-induced cytotoxicity in HepG2 cells

A previous study showed that microcystin-LR (MC-LR) exerted cytotoxicity and induced apoptosis in HepG2 cells. In the present study, we investigated whether oxidative stress-mediated p53/p21^WAF1/CIP1 is involved in this process to further elucidate the mechanism of cytotoxicity induced by MC-LR. Morphological evaluation showed that MC-LR induced time- and dose-dependent cytotoxicity in HepG2 cells. Biochemical assays revealed that MC-LR exposure altered the protein levels of HSP70 and HSP90, generally inhibited superoxide dismutase and catalase, reduced glutathione content, and increased the cellular malondialdehyde level of HepG2 cells, suggesting that MC-LR may induce biochemical disturbance and oxidative stress in HepG2 cells. The protein levels of p-p53 and p21 were markedly increased by MC-LR exposure in a concentration-dependent manner, suggesting that p53 and p21 may be involved in the process. Moreover, we also found that the proto-oncogene c-myc was significantly activated in HepG2 cells following MC-LR exposure, indicating that c-myc in HepG2 cells was potentially involved in response to MC-LR-induced apoptosis. These findings may contribute to further understanding the in vitro molecular mechanism of MC-LR hepatotoxicity.

Proteomic evidences for microcystin-RR-induced toxicological alterations in mice liver

This study deals with the isolation and purification of an important variant of microcystins namely microcystin-RR (MCYST-RR) from Microcystis aeruginosa and reports its effects on mice liver protein profile and cellular functions. Protein profiling by 2-dimensional gel electrophoresis revealed changes in the number and accumulation of protein spots in liver of mice treated with different concentrations of MCYST-RR. Untreated (control) mice liver showed 368 protein spots while the number was 355, 348 and 332 in liver of mice treated with 200, 300 and 400 µg kg body wt⁻¹ of MCYST-RR respectively. Altogether 102, 97, and 92 spots were differentially up-accumulated and 93, 91, and 87 spots were down- accumulated respectively with the treatment of 200, 300, 400 µg kg body wt⁻¹. Eighteen differentially accumulated proteins present in all the four conditions were identified by MALDI-TOF MS. Of these eighteen proteins, 12 appeared to be involved in apoptosis/toxicological manifestations. Pathway analysis by Reactome and PANTHER database also mapped the identified proteins to programmed cell death/apoptosis clade. That MCYST-RR induces apoptosis in liver tissues was also confirmed by DNA fragmentation assay. Results of this study elucidate the proteomic basis for the hepatotoxicity of MCYST-RR which is otherwise poorly understood till date.

Genotoxic potential of the binary mixture of cyanotoxins microcystin-LR and cylindrospermopsin

Increased eutrophication of water bodies promotes cyanobacterial blooming that is hazardous due to the production of various bioactive compounds. Microcystin-LR (MCLR) is among the most widespread cyanotoxins classified as possible human carcinogen, while cylindrospermopsin (CYN) has only recently been recognized as health concern. Both cyanotoxins are genotoxic; however, the mechanisms of their action differ. They are ubiquitously present in water environment and are often detected together. Therefore, we studied genotoxic potential of the binary mixture of these cyanotoxins. Human hepatoma cells (HepG2) were exposed to a single dose of MCLR (1 μg/mL), graded doses of CYN (0.01-0.5 μg/mL), and their combinations. Comet and Cytokinesis block micronucleus assays were used to detect induction of DNA strand breaks (sb) and genomic instability, respectively, along with the transcriptional analyses of the expression of selected genes involved in xenobiotic metabolism, immediate/early cell response and DNA-damage response. MCLR induced DNA sb that were only transiently present after 4 h exposure, whereas CYN, after 24 h exposure, induced DNA sb and genomic instability. The MCLR/CYN mixture induced DNA sb after 24 h exposure, but to lesser extent as CYN alone. On the other hand, induction of genomic instability by the MCLR/CYN mixture was comparable to that induced by CYN alone. In addition, patterns of changes in the expression of selected genes induced by the MCLR/CYN mixture were not significantly different from those induced by CYN alone. Our results indicate that CYN exerts higher genotoxic potential than MCLR and that genotoxic potential of the MCLR/CYN mixture is comparable to that of CYN alone.

Serum microcystin levels positively linked with risk of hepatocellular carcinoma: A case-control study in southwest China

Microcystins have been reported to be carcinogenic by animal and cell experimentation, but there are no data on the linkage between serum microcystins and hepatocellular carcinoma (HCC) risk in humans. We conducted a clinical case-control study to investigate the association between serum microcystins and HCC risk after controlling several known risk factors, such as hepatitis B virus, alcohol, and aflatoxin. From December 2013 to May 2016, 214 patients newly diagnosed with HCC along with 214 controls (frequency-matched by age and sex) were recruited from three hospitals in Chongqing, southwest China. Basic information on lifestyle and history of disease was obtained by questionnaire. Blood samples were collected and analyzed for serum microcystin-LR (MC-LR) and aflatoxin-albumin adduct by enzyme-linked immunosorbent assay and for hepatitis B surface antigen status by chemiluminescence assay. Binary logistic regression analyses were performed to assess the independent effects of MC-LR and its joint effects with other factors on HCC risk. The adjusted odds ratio for HCC risk by serum MC-LR was 2.9 (95% confidence interval [CI], 1.5-5.5) in all patients. Notably, a clear relationship between increased MC-LR level (Q2, Q3, and Q4) and HCC risk was observed with elevated adjusted odds ratios (1.3, 2.6, and 4.0, respectively). Positive interactions with the additive model were investigated between MC-LR and hepatitis B virus infection (synergism index = 3.0; 95% CI, 2.0-4.5) and between MC-LR and alcohol (synergism index = 4.0; 95% CI, 1.7-9.5), while a negative interaction was found between MC-LR and aflatoxin (synergism index = 0.4; 95% CI, 0.3-0.7). Additionally, serum MC-LR was significantly associated with tumor differentiation (r = -0.228, P < 0.001).

CONCLUSION

We provide evidence that serum MC-LR was an independent risk factor for HCC in humans, with an obvious positive interaction with hepatitis B virus and alcohol but a negative interaction with aflatoxin. (Hepatology 2017;66:1519-1528).

Amelioratory effect of coenzyme Q10 on potential human carcinogen Microcystin-LR induced toxicity in mice

Microcystins are a group of cyclic heptapeptide toxins produced by cyanobacteria. More than 100 microcystin analogues have been detected, among which microcystin-LR is the most abundant and toxic variant. Present study was designed to reveal whether potential human carcinogen microcystin-LR could imbalance the glycolytic-oxidative-nitrosative status of heart, kidney and spleen of mice and also to explore the amelioratory effect of coenzyme Q10 on microcystin-LR induced toxicity. Microcystin-LR was administered at a dose of 10 μg/kg bw/day, ip for 14 days in male mice. In microcystin-LR treated mice as compared to control, significant increase in the level of lipid peroxidation, hydrogen peroxide, lactate dehydrogenase, nitric oxide with a concomitant decrease in the level of glutathione was observed, suggesting microcystin-LR induced toxicity via induction of oxidative-nitrosative-glycolytic pathway. Although several studies have evaluated numerous antioxidants but still there is no effective chemoprotectant against microcystin-LR induced toxicity. When microcystin-LR treated mice were co-administered coenzyme Q10 (10 mg/kg bw/day, im) for 14 days, it was observed that coenzyme Q10 ameliorates microcystin-LR induced toxicity via modulation of glycolytic-oxidative-nitrosative stress pathway. Thus, the results suggest that coenzyme Q10 has a potential to be developed as preventive agent against microcystin-LR induced toxicity.

Analysis of MicroRNA Expression Profiling Involved in MC-LR-Induced Cytotoxicity by High-Throughput Sequencing

In recent years, microRNAs (miRNAs) in toxicology have attracted great attention. However, the underlying mechanism of miRNAs in the cytotoxicity of microcystin-LR (MC-LR) is lacking. The objective of this study is to analyze miRNA profiling in HepG2 cells after 24 h of MC-LR-exposure to affirm whether and how miRNAs were involved in the cytotoxicity of MC-LR. The results showed that totally 21 and 37 miRNAs were found to be significantly altered in the MC-LR treated cells at concentrations of 10 and 50 μM, respectively, when compared to the control cells. In these two groups, 37,566 and 39,174 target genes were predicted, respectively. The further analysis showed that MC-LR-exposure promoted the expressions of has-miR-149-3p, has-miR-449c-5p, and has-miR-454-3p while suppressed the expressions of has-miR-4286, has-miR-500a-3p, has-miR-500a-5p, and has-miR-500b-5p in MC-LR-treated groups when compared to the control group. Moreover, the result of qPCR confirmed the above result, suggesting that these miRNAs may be involved in MC-LR-hepatotoxicity and they may play an important role in the hepatitis and liver cancer caused by MC-LR. The target genes for differentially expressed miRNAs in MC-LR treatment groups were significantly enriched to totally 23 classes of GO, in which three were significantly enriched in both 10 and 50 μM MC-LR groups. Moreover, the results of KEGG pathway analysis showed that MC-LR-exposure altered some important signaling pathways such as MAPK, biosynthesis of secondary metabolites, and pyrimidine and purine metabolism, which were possibly negatively regulated by the corresponding miRNAs and might play important role in MC-LR-mediated cytotoxicity in HepG2 cells.

Protective effects of a cocktail of lactic acid bacteria on microcystin-LR-induced hepatotoxicity and oxidative damage in BALB/c mice

The aim of this study was to investigate the effects of mixed lactic acid bacteria (LAB) against microcystin-LR-exposed hepatotoxicity and oxidative stress in BALB/c mice.

Chemical proteomic analysis of the potential toxicological mechanisms of microcystin-RR in zebrafish (Danio rerio) liver

Microcystins (MCs) are common toxins produced by freshwater cyanobacteria, and they represent a potential health risk to aquatic organisms and animals, including humans. Specific inhibition of protein phosphatases 1 and 2A is considered the typical mechanism of MCs toxicity, but the exact mechanism has not been fully elucidated. To further our understanding of the toxicological mechanisms induced by MCs, this study is the first to use a chemical proteomic approach to screen proteins that exhibit special interactions with MC-arginine-arginine (MC-RR) from zebrafish (Danio rerio) liver. Seventeen proteins were identified via affinity blocking test. Integration of the results of previous studies and this study revealed that these proteins play a crucial role in various toxic phenomena of liver induced by MCs, such as the disruption of cytoskeleton assembly, oxidative stress, and metabolic disorder. Moreover, in addition to inhibition of protein phosphate activity, the overall toxicity of MCs was simultaneously modulated by the distribution of MCs in cells and their interactions with other target proteins. These results provide new insight into the mechanisms of hepatotoxicity induced by MCs. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1206-1216, 2016.

The role of GSH in microcystin-induced apoptosis in rat liver: Involvement of oxidative stress and NF-κB

Microcystins (MCs) are potent and specific hepatotoxins produced by cyanobacteria in eutrophic waters, representing a health hazard to animals and humans. The objectives of this study are to determine the relationship between oxidative stress and NF-κB activity in MC-induced apoptosis in rat liver and the role of glutathione (GSH). Sprague-Dawley rats were intraperitoneally (i.p.) injected with microcystin-LR (MC-LR) at 0.25 and 0.5 LD50 with or without pretreatment of buthionine-(S,R)-sulfoximine (BSO), a specific GSH synthesis inhibitor. MC-LR induced time-dependent alterations of GSH levels in rat liver. Increased malondialdehyde (MDA) and significant changes of antioxidant enzymes including GSH peroxidase (GPX) and GSH reductase (GR) were also observed, particularly at 24 h post-exposure. The results indicated that acute exposure to MC-LR induced oxidative stress, and GSH depletion (BSO pretreatment) enhanced the level of oxidative stress. Furthermore, the modulation of pro-apoptotic gene p53 and Bax and anti-apoptotic gene Bcl-2 was observed in 0.5 LD50 group at 24 h, and the alteration was more pronounced by BSO injection before MC-LR treatment, suggesting that GSH played a protective role against MC-induced toxicity. Additionally, electrophoretic mobility shift assay (EMSA) showed that NF-κB was induced at 0.25 LD50 but inhibited at 0.5 LD50 . The above results indicated that the possible crosstalk of oxidative stress and NF-κB activity was associated with MC-LR-induced hepatocytes apoptosis in vivo. Our data will provide a new perspective for understanding the mechanisms of MC-induced liver injury.

Quantitatively evaluating detoxification of the hepatotoxic microcystin-LR through the glutathione (GSH) pathway in SD rats

Glutathione (GSH) plays crucial roles in antioxidant defense and detoxification metabolism of microcystin-LR (MC-LR). However, the detoxification process of MC-LR in mammals remains largely unknown. This paper, for the first time, quantitatively analyzes MC-LR and its GSH pathway metabolites (MC-LR-GSH and MC-LR-Cys) in the liver of Sprague-Dawley (SD) rat after MC-LR exposure. Rats received intraperitoneal (i.p.) injection of 0.25 and 0.5 lethal dose 50 (LD50) of MC-LR with or without pretreatment of buthionine-(S,R)-sulfoximine (BSO), an inhibitor of GSH synthesis. The contents of MC-LR-GSH were relatively low during the experiment; however, the ratio of MC-LR-Cys to MC-LR reached as high as 6.65 in 0.5 LD50 group. These results demonstrated that MC-LR-GSH could be converted to MC-LR-Cys efficiently, and this metabolic rule was in agreement with the data of aquatic animals previously reported. MC-LR contents were much higher in BSO + MC-LR-treated groups than in the single MC-LR-treated groups. Moreover, the ratio of MC-LR-Cys to MC-LR decreased significantly after BSO pretreatment, suggesting that the depletion of GSH induced by BSO reduced the detoxification of MCs. Moreover, MC-LR remarkably induced liver damage, and the effects were more pronounced in BSO pretreatment groups. In conclusion, this study verifies the role of GSH in the detoxification of MC-LR and furthers our understanding of the biochemical mechanism for SD rats to counteract toxic cyanobacteria.

The role of glutathione detoxification pathway in MCLR-induced hepatotoxicity in SD rats

In the present study, we investigated the role of glutathione (GSH) and its related enzymes in Sprague Dawley (SD) rats subjected to microcystin-leucine-arginine (MCLR)-induced hepatotoxicity. SD rats were intraperitoneally (i.p.) injected with MCLR after pretreating with or without buthionine-(S,R)-sulfoximine (BSO), an inhibitor of GSH synthesis. The depletion of GSH with BSO enhanced MCLR-induced oxidative stress, resulting in more severe liver damage and higher MCLR accumulation. Similarly, the contents of malondialdehyde (MDA), total GSH (T-GSH), oxidized GSH (GSSG) and GSH were significantly enhanced in BSO pretreated rats following MCLR treatment. The study showed that the transcription of GSH-related enzymes such as glutathione-S-transferase (GST), γ-glutamylcysteine synthetase (γ-GCS), glutathione reductase (GR) varied in different ways (expect for glutathione peroxidase (GPx), whose gene expression was induced in all treated groups) with or without BSO pretreatment before MCLR exposure, suggesting an adaptative response of GSH-related enzymes at transcription level to combat enhancement of oxidative stress induced by MCLR when pretreated with BSO. These data suggested the tissues with low GSH concentration are highly vulnerable to MCLR toxicity and GSH was critical for the detoxification in MCLR-induced hepatotoxicity in vivo.

Involvement of oxidative stress and cytoskeletal disruption in microcystin-induced apoptosis in CIK cells

The outbreak of cyanobacterial blooms induces the production and release of microcystins (MCs) into water, representing a health hazard to aquatic organisms and even humans. Some recent studies have suggested that kidney is another important target organ of MCs except liver, however, the potential toxicity mechanisms are still unclear. In this study, we first investigated the collaborative effect of oxidative stress and cytoskeletal disruption in microcystin-induced apoptosis in CIK (Ctenopharyngodon idellus kidney) cells in vitro. CIK cells were treated with 0, 1, 10, and 100μg/L microcystin-LR (MC-LR) for 24 and 48h. Cell viability was increased by MC-LR in 1μg/L group, while decreased in 100μg/L group at 48h. Cell cycle assay showed that 1 and 10μg/L MC-LR induced cell cycle through G1 into S and G2/M phases, while 100μg/L MC-LR reduced G2/M phase population. MC-LR markedly induced apoptosis in 10 and 100μg/L groups. Elevated reactive oxygen species (ROS) production, increased malondialdehyde (MDA) contents, decreased glutathione (GSH) levels, and modulated antioxidant enzymes including catalase (CAT) and superoxide dismutase (SOD) were observed in CIK cells exposed to MC-LR. These alterations were more pronounced at higher doses (10 and 100μg/L), indicating that oxidative stress was induced by MC-LR. Laser scanning confocal microscope observation showed aggregation and collapse of microfilaments (MFs) and microtubules (MTs) in CIK cells, and even loss of some cytoskeleton structure. Moreover, transcriptional changes of cytoskeletal genes (β-actin, lc3a, and keratin) were also determined, which have a high probability with cytoskeleton structure damage. Our data suggest that oxidative stress and cytoskeletal disruption may interact with each other and jointly lead to apoptosis and renal toxicity induced by MCs.

Antioxidative responses in zebrafish liver exposed to sublethal doses Aphanizomenon flos-aquae DC-1 aphantoxins

Aphanizomenon flos-aquae secretes paralytic shellfish poisons (PSPs), termed aphantoxins, and endangers environmental and human health via eutrophication of water worldwide. Although the molecular mechanism of neuronal PSP toxicity has been well studied, several issues remain unresolved, notably the in vivo hepatic antioxidative responses to this neurotoxin. Aphantoxins extracted from a natural isolate of A. flos-aquae DC-1 were resolved by high performance liquid chromatography. The primary components were gonyautoxins 1 and 5 and neosaxitoxin. Zebrafish (Danio rerio) were treated intraperitoneally with either 5.3 or 7.61 (low and high doses, respectively) μg saxitoxin (STX) equivalents (eq)/kg of A. flos-aquae DC-1 aphantoxins. Antioxidative responses in zebrafish liver were examined at different timepoints 1-24h post-exposure. Aphantoxin administration significantly enhanced hepatic malondialdehyde (MDA) content 1-12h post-exposure, indicative of oxidative stress and lipid peroxidation. By contrast, levels of reduced glutathione (GSH) in zebrafish liver declined significantly after 3-24h exposure, suggesting that GSH participates in MDA metabolism. A significant upregulation of the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) was observed, suggesting that aphantoxins induce lipid peroxidation in zebrafish liver and are likely to be hepatotoxic. Hepatic levels of MDA and GSH, and of the three enzymes (SOD, CAT, and GPx), therefore provide potential biomarkers for studying environmental exposure to aphantoxins/PSPs from cyanobacterial blooms.

Differences in copper bioaccumulation and biological responses in three Mytilus species

Mytilus species are important organisms in marine systems being highly abundant and widely distributed along the coast of Europe and worldwide. They are typically used in biological effects studies and have a suite of biological effects endpoints that are frequently measured and evaluated for stress effects in laboratory experiments and field monitoring programmes. Differences in bioaccumulation and biological responses of the three Mytilus species following exposure to copper (Cu) were investigated. A laboratory controlled exposure study was performed with three genetically confirmed Mytilus species; M. galloprovincialis, M. edulis and M. trossulus. Chemical bioaccumulation and biomarkers were assessed in all three Mytilus species following a 4 day and a 21 day exposure to waterborne copper concentrations (0, 10, 100 and 500μg/L). Differences in copper bioaccumulation were measured after both 4 and 21 days, which suggests some physiological differences between the species. Furthermore, differences in response for some of the biological effects endpoints were also found to occur following exposure. These differences were discussed in relation to either real physiological differences between the species or merely confounding factors relating to the species natural habitat and seasonal cycles. Overall the study demonstrated that differences in chemical bioaccumulation and biomarker responses between the Mytilus spp. occur with potential consequences for mussel exposure studies and biological effects monitoring programmes. Consequently, the study highlights the importance of identifying the correct species when using Mytilus in biological effects studies.

Ochratoxin A promotes porcine circovirus type 2 replication in vitro and in vivo

Ochratoxin A (OTA), a worldwide mycotoxin found in food and feeds, is a potent nephrotoxin in animals and humans. Porcine circovirus-associated disease (PCVAD), including porcine dermatitis and nephropathy syndrome, is a worldwide swine disease. To date, little is known concerning the relationship between OTA and porcine circovirus type 2 (PCV2), the primary causative agent of PCVAD. The effects of OTA on PCV2 replication and their mechanisms were investigated in vitro and in vivo. The results in vitro showed that low doses of OTA significantly increased PCV2 DNA copies and the number of infected cells. Maximum effects were observed at 0.05 μg/ml OTA. The results in vivo showed that PCV2 replication was significantly increased in serum and tissues of pigs fed 75 μg/kg OTA compared with the control group and pigs fed 150 μg/kg OTA. In addition, low doses of OTA significantly depleted reduced glutathione and mRNA expression of NF-E2-related factor 2 and γ-glutamylcysteine synthetase; increased reactive oxygen species, oxidants, and malondialdehyde; and induced p38 and ERK1/2 phosphorylation in PK15 cells. Adding N-acetyl-L-cysteine reversed the changes induced by OTA. Knockdown of p38 and ERK1/2 by their respective specific siRNAs or inhibition of p38 and ERK1/2 phosphorylation by their respective inhibitors (SB203580 and U0126) eliminated the increase in PCV2 replication induced by OTA. These data indicate that low doses of OTA promoted PCV2 replication in vitro and in vivo via the oxidative stress-mediated p38/ERK1/2 MAPK signaling pathway. This suggests that low doses of OTA are potentially harmful to animals, as they enhance virus replication, and partly explains why the morbidity and severity of PCVAD vary significantly in different pig farms.

Comparative study of the cytotoxic and genotoxic potentials of zinc oxide and titanium dioxide nanoparticles

Nanoparticles (NPs) of zinc oxide (ZnO) and titanium dioxide (TiO₂) are receiving increasing attention due to their widespread applications. The aim of this study was to evaluate the toxic effect of ZnO and TiO₂ NPs at different concentrations (50, 100, 250 and 500 ppm) and compare them with their respective salts using a battery of cytotoxicity, and genotoxicity parameters. To evaluate cytotoxicity, we have used human erythrocytes and for genotoxic studies human lymphocytes have been used as in vitro model species. Concentration dependent hemolytic activity to RBC's was obtained for both NPs. ZnO and TiO₂ NPs resulted in 65.2% and 52.5% hemolysis at 250 ppm respectively indicating that both are cytotoxic to human RBCs. Antioxidant enzymes assays were also carried out in their respective hemolysates. Both nanoparticles were found to generate reactive oxygen species (ROS) concomitant with depletion of glutathione and GST levels and increased SOD, CAT and lipid peroxidation in dose dependent manner. ZnO and TiO₂ NPs exerted roughly equal oxidative stress in terms of aforementioned stress markers. Genotoxic potential of both the NPs was investigated by in vitro alkaline comet assay. DNA damage induced by the NPs was concentration dependent and was significantly greater than their ionic forms at 250 and 500 ppm concentrations. Moreover, the nanoparticles of ZnO were significantly more genotoxic than those of TiO₂ at higher concentrations. The toxicity of these NPs is due to the generation of ROS thereby causing oxidative stress.

Toxicopathology induced by microcystins and nodularin: a histopathological review

Cyanobacteria are present in all aquatic ecosystems throughout the world. They are able to produce toxic secondary metabolites, and microcystins are those most frequently found. Research has displayed a negative influence of microcystins and closely related nodularin on fish, and various histopathological alterations have been observed in many organs of the exposed fish. The aim of this article is to summarize the present knowledge of the impact of microcystins and nodularin on the histology of fish. The observed negative effects of cyanotoxins indicate that cyanobacteria and their toxins are a relevant medical (due to irritation, acute poisoning, tumor promotion, and carcinogenesis), ecotoxicological, and economic problem that may affect both fish and fish consumers including humans.

Effects of phytoplankton extracts containing the toxin microcystin-LR on the survival and reproduction of cladocerans

The use of ecotoxicological techniques for the evaluation of the quality of limnetic waters allows the early detection of toxic agents that pose risks to human health. In this study Moina micrura (two clones), Daphnia laevis (two clones) and Daphnia similis, a temperate species, were used to evaluate the toxicity of six Microcystis extracts from two Colombian reservoirs. Toxin was detected and quantified by HPLC. Microcystin-LR was found in all extracts with the highest concentrations in one sample from each reservoir (434 μg g(-1) and 538 μg g(-1)). The extracts that had the highest toxin concentration also had the highest toxicities to cladocerans. Measurement of 48-h LC50 showed consistent differences between cladoceran species but not clones, Also, reproduction data in two species were consistent with the MC-LR content of one sample tested, with decreased reproduction and disruption of egg production. However, only some growth results of neonates exposed to extracts were consistent with the acute response. In conclusion, Daphnia species are a good model for monitoring cyanotoxins as they respond in a sensitive way to natural phytoplankton samples containing microcystin-LR.

Agents of earthy-musty taste and odor in water: evaluation of cytotoxicity, genotoxicity and toxicogenomics

Considering the limited number of studies on the biological effects on human health of cyanobacterial compounds that cause taste and odor, the present study assessed the cytotoxic and genotoxic potentials of 2-methylisoborneol (2-MIB) and geosmin (GEO) using the MTT assay and the in vitro comet and cytokinesis-block micronucleus (CBMN-Cyt) assays in human HepG2 cells. The toxicogenomics of genes responsive to DNA damage and metabolization by the exposure of cells to 2-MIB and GEO were also investigated. The results showed that concentrations of 2-MIB and GEO above 100 and 75 μg/mL, respectively, were cytotoxic to HepG2 cells. Doses of 2-MIB (12.5, 25, 50, 75 and 100 μg/mL) and GEO (12.5, 25, 50, and 75 μg/mL) were unable to induce neither DNA damage nor events associated with chromosomal instability. Similarly, no concentration of each compound induced increments in the expression of CDKN1A, GADD45α, MDM2 and TP53 DNA damage responsive genes as well as in CYP1A1 and CYP1A2 metabolizing genes. Although cytotoxicity was observed, concentrations that caused it are much higher than those expected to occur in aquatic environments. Thus, environmentally relevant concentrations of both compounds are not expected to exhibit cytotoxicity or genotoxicity to humans.

Genotoxicity of microcystin-LR in in vitro and in vivo experimental models

Microcystin-LR (MCLR) is a cyanobacterial toxin known for its acute hepatotoxicity. Despite being recognized as tumour promoter, its genotoxicity is far from being completely clarified, particularly in organs other than liver. In this work, we used the comet and/or the micronucleus (MN) assays to study the genotoxicity of MCLR in kidney- (Vero-E6) and liver-derived (HepG2) cell lines and in blood cells from MCLR-exposed mice. MCLR treatment (5 and 20 μM) caused a significant induction in the MN frequency in both cell lines and, interestingly, a similar positive effect was observed in mouse reticulocytes (37.5 μg MCLR/kg, i.p. route). Moreover, the FISH-based analysis of the MN content (HepG2 cells) suggested that MCLR induces both chromosome breaks and loss. On the other hand, the comet assay results were negative in Vero-E6 cells and in mouse leukocytes, with the exception of a transient increase in the level of DNA damage 30 minutes after mice exposure. Overall, the present findings contributed to increase the weight of evidence in favour of MCLR genotoxicity, based on its capacity to induce permanent genetic damage either in vitro or in vivo. Moreover, they suggest a clastogenic and aneugenic mode of action that might underlie a carcinogenic effect.

Lipid peroxidation and antioxidant responses in zebrafish brain induced by Aphanizomenon flos-aquae DC-1 aphantoxins

Aphanizomenon flos-aquae is a cyanobacterium that is frequently encountered in eutrophic waters worldwide. It is source of neurotoxins known as aphantoxins or paralytic shellfish poisons (PSPs), which present a major threat to the environment and human health. The molecular mechanism of PSP action is known, however the in vivo effects of this neurotoxin on oxidative stress, lipid peroxidation and the antioxidant defense responses in zebrafish brain remain to be understood. Aphantoxins purified from a natural isolate of A. flos-aquae DC-1 were analyzed using high performance liquid chromatography. The major components of the toxins were gonyautoxins 1 and 5 (GTX1 and GTX5, 34.04% and 21.28%, respectively) and neosaxitoxin (neoSTX, 12.77%). Zebrafish (Danio rerio) were injected intraperitoneally with 7.73 μg/kg (low dose) and 11.13 μg/kg (high dose) of A. flos-aquae DC-1 aphantoxins. Oxidative stress, lipid peroxidation and antioxidant defense responses in the zebrafish brain were investigated at various timepoints at 1-24h post-exposure. Aphantoxin exposure was associated with significantly increased (>1-2 times) reactive oxygen species (ROS) and malondialdehyde (MDA) in zebrafish brain compared with the controls at 1-12h postexposure, suggestive of oxidative stress and lipid peroxidation. In contrast, reduced glutathione (GSH) levels in the zebrafish brain exposed to high or low doses of aphantoxins decreased by 44.88% and 41.33%, respectively, after 1-12h compared with the controls, suggesting that GSH participated in detoxification to ROS and MDA. Further analysis showed a significant increase in the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) compared with the controls, suggesting elimination of oxidative stress by the antioxidant response in zebrafish brain. All these changes were dose and time dependent. These results suggested that aphantoxins or PSPs increased ROS and MDA and decreased GSH in zebrafish brain, and these changes induced oxidative stress. The increased activity of SOD, CAT and GPx demonstrated that these antioxidant enzymes could play important roles in eliminating excess ROS and MDA. These results also suggest that MDA, ROS, GSH and these three antioxidant enzymes in the brain of zebrafish may act as bioindicators for investigating A. flos-aquae DC-1 aphantoxins or PSPs and algal blooms in nature.

Increased glutathione and mitogen-activated protein kinase phosphorylation are involved in the induction of doxorubicin resistance in hepatocellular carcinoma cells

AIM

  The human hepatocellular carcinoma (HCC) cell line HepG2 can easily acquire resistance to doxorubicin. However, the mechanism of action is unclear.

METHODS

  In the present study, we used confocal microscopy, flow cytometry and other methods to reveal the mechanisms by which HepG2 cells acquire doxorubicin resistance.

RESULTS

  Our results showed that R-HepG2 cells, a doxorubicin-resistant sub-line of HepG2, exhibited decreased intracellular accumulation of doxorubicin and increased expression of P-glycoprotein (P-gp) and multidrug resistance-associated protein 1 when compared with HepG2 cells. R-HepG2 cells also harbored higher levels of glutathione and increased expression of glutathione peroxidase. Furthermore, we demonstrated that the phosphorylation of mitogen-activated protein kinases (p38 and c-jun-N-terminal kinases), IkBα and CREB were increased in R-HepG2 cells. Specific p38 inhibitor SB203580 decreased P-gp expression. The multi-kinase inhibitor sorafenib tosylate also significantly suppressed the phosphorylation of these proteins and inhibited the expression of P-gp.

CONCLUSION

  These findings reveal that the drug resistance could be acquired through mitogen-activated protein kinase-dependent upregulation of P-gp. This mechanism protects R-HepG2 cells from the anticancer action of doxorubicin.

Toxic effects of microcystin-LR on the reproductive system of male Rana nigromaculata in vitro

This study aims to demonstrate that microcystin-LR (MC-LR) has toxic effects on the reproductive system of male Rana nigromaculata in vitro. R. nigromaculata were treated with 0, 0.1, 1, 10, and 100 nmol/L of MC-LR for 6 h. Results show that exposure to 1 nmol/L to 100 nmol/L of MC-LR decreased sperm motility and number of sperm cells and increased the sperm abnormality rate, whose values were significantly different from those of the control (P<0.01). Moreover, the same dosage of MC-LR increased reactive oxygen species production and malondialdehyde content. At the same time, antioxidant enzyme (catalase and glutathione S-transferase) activity and glutathione reduced content rapidly increased, whereas antioxidant enzyme superoxide dismutase activity significantly decreased. These results imply that the defense system of the testes quickly responds to oxidative stress. Ultrastructural observation shows distention of the mitochondria, endoplasmic reticulum, and Golgi apparatus and changes in the mitochondrial matrix color, cristae number, and morphology. Moreover, using real-time PCR, increased relative expressions of P450 aromatase and SF-1 genes were observed. The results demonstrate for the first time that MC-LR could induce toxicity in the male reproductive system of R. nigromaculata. The findings in this research will provide more insights into the relationships between aquatic microcystins and amphibians.

Involvement of endoplasmic reticulum and autophagy in microcystin-LR toxicity in Vero-E6 and HepG2 cell lines

This work investigates the involvement of the endoplasmic reticulum (ER) and autophagy in microcystin-LR (MCLR) toxicity in Vero-E6 and HepG2 cell lines. Additionally, morphological alterations induced by MCLR in lysosomes and mitochondria were studied. Cytotoxicity evaluation showed that pure MCLR and MCLR from LMECYA110 extract induce concentration dependent viability decays after 24h exposure. HepG2 cells showed an increased sensitivity to MCLR than Vero cells, with lower cytotoxic thresholds and EC(50) values. Conversely, LC3B immunofluorescence showed that autophagy is triggered in both cell lines as a survival response to low MCLR concentrations. Furthermore, MCLR induced a MCLR concentration-dependent decrease of GRP94 expression in HepG2 cells while in Vero cells no alteration was observed. This suggests the involvement of the ER in HepG2 apoptosis elicited by MCLR, while in Vero cells ER destructuration could be a consequence of cytoskeleton inflicted damages. Additionally, in both cell lines, lysosomal destabilization preceded mitochondrial impairment which occurred at high toxin concentrations. Although not an early cellular target of MCLR, mitochondria appears to serve as central mediators of different signaling pathways elicited by the organelles involved in MCLR toxicity. As a result, kidney and hepatic cell lines exhibit cell type and dose-dependent mechanisms to overcome MCLR toxicity.

Transcriptomic comparison of cyanotoxin variants in a human intestinal model revealed major differences in oxidative stress response: effects of MC-RR and MC-LR on Caco-2 cells

Microcystins (MCs) are cyclic hepatotoxins produced by various species of cyanobacteria. Their structure includes two variable amino acids (AA) giving rise to more than 90 MC variants, however most of the studies to date have focused on the most toxic variant: microcystin LR (MC-LR). Ingestion is the major route of human exposure to MCs and several in vivo studies have demonstrated macroscopic effects on the gastro-intestinal tract. However, little information exists concerning the pathways affected by MC variants on intestinal cells. In the current study, we have investigated the effects of MC-RR and MC-LR on the human intestinal cell line Caco-2 using a non-selective method and compared their response at the pangenomic scale. The cells were incubated for 4h or 24h with a range of non-toxic concentrations of MC-RR or MC-LR. Minimal effects were observed after short term exposures (4h) to either MC variant. In contrast, dose dependent modulations of gene transcription levels were observed with MC-RR and MC-LR after 24h. The transcriptomic profiles induced by MC-RR were quite similar to those induced by MC-LR, suggestive of a largely common mechanism of toxicity. However, changes in total gene expression were more pronounced following exposure to MC-LR compared to MC-RR, as revealed by functional annotation. MC-LR affected two principal pathways, the oxidative stress response and cell cycle regulation, which did not elicit significant alteration following MC-RR exposure. This work is the first comparative description of the effects of MC-LR and MC-RR in a human intestinal cell model at the pangenomic scale. It has allowed us to propose differences in the mechanism of toxicity for MC-RR and MC-LR. These results illustrate that taking into account the toxicity of MC variants remains a key point for risk assessment.

Alterations of GSH and MDA levels and their association with bee venom-induced DNA damage in human peripheral blood leukocytes

Bee venom (BV) has toxic effects in a variety of cell systems and oxidative stress has been proposed as a possible mechanism of its toxicity. This study investigated the in vitro effect of BV on glutathione (GSH) and malondialdehyde (MDA) levels, and their association with BV-induced DNA strand breaks and oxidative DNA damage in human peripheral blood leukocytes (HPBLs). Blood samples were treated with BV at concentrations ranging from 0.1 to 10 μg/ml over different lengths of time, and DNA damage in HPBLs was monitored with the alkaline and formamidopyrimidine glycoslyase (FPG)-modified comet assays, while GSH and MDA levels were determined in whole blood. Results showed a significant increase in overall DNA damage and FPG-sensitive sites in DNA of HPBLs exposed to BV compared with HPBLs from controls. An increase in DNA damage (assessed with both comet assays) was significantly associated with changes in MDA and GSH levels. When pretreated with N-acetyl-L-cysteine, a source of cysteine for the synthesis of the endogenous antioxidant GSH, a significant reduction of the DNA damaging effects of BV in HPBLs was noted. This suggests that oxidative stress is at least partly responsible for the DNA damaging effects of BV.

Microcystin-LR induced DNA damage in human peripheral blood lymphocytes

Human exposure to microcystins, which are produced by freshwater cyanobacterial species, is of growing concern due to increasing appearance of cyanobacterial blooms as a consequence of global warming and increasing water eutrophication. Although microcystins are considered to be liver-specific, there is evidence that they may also affect other tissues. These substances have been shown to induce DNA damage in vitro and in vivo, but the mechanisms of their genotoxic activity remain unclear. In human peripheral blood lymphocytes (HPBLs) exposure to non-cytotoxic concentrations (0, 0.1, 1 and 10μg/ml) of microcystin-LR (MCLR) induced a dose- and time-dependent increase in DNA damage, as measured with the comet assay. Digestion of DNA from MCLR-treated HPBLs with purified formamidopyrimidine-DNA glycosylase (Fpg) displayed a greater number of DNA strand-breaks than non-digested DNA, confirming the evidence that MCLR induces oxidative DNA damage. With the cytokinesis-block micronucleus assay no statistically significant induction of micronuclei, nucleoplasmic bridges and nuclear buds was observed after a 24-h exposure to MCLR. At the molecular level, no changes in the expression of selected genes involved in the cellular response to DNA damage and oxidative stress were observed after a 4-h exposure to MCLR (1μg/ml). After 24h, DNA damage-responsive genes (p53, mdm2, gadd45a, cdkn1a), a gene involved in apoptosis (bax) and oxidative stress-responsive genes (cat, gpx1, sod1, gsr, gclc) were up-regulated. These results provide strong support that MCLR is an indirectly genotoxic agent, acting via induction of oxidative stress, and that lymphocytes are also the target of microcystin-induced toxicity.

The apoptotic effect of oral administration of microcystin-RR on mice liver

Microcystin produced by cyanobacteria in diverse water systems is a potent hepatotoxin that has been documented to induce hepatocyte apoptosis and liver injury. There are more than eighty reported microcystins. The present work aimed at investigating the apoptotic effect of MC-RR (a common member of microcystin family), and its related mechanism. MC-RR was administered orally to ICR mice for 7 days with different dosages. Apoptotic cell death in liver was detected by TUNEL assay, and the expression levels of Bcl-2, Bax and p53, GRP 78 and CHOP which have been reported to be related to apoptosis and ER stress were determined via western-blot. The activity of PP2A was measured using the serine-threonine phosphatase assay system and PP2A A subunit expression at both transcription and protein levels was measured by RT-PCR and western blot, respectively. A significant difference was observed on the number of TUNEL positive liver cells between the control and MC-RR-treated groups. The expression levels of Bcl-2, Bax, p53, and GRP 78 in MC-RR-treated groups were altered significantly compared to the control, but no obvious alteration was found in CHOP expression. The PP2A activity and A subunit expression did not manifest any obvious change at both transcription and protein levels. The results indicated that oral exposure to MC-RR can cause apoptosis as well as moderate ER stress in mice liver. The mitochondrial pathway via Bcl-2 family members may contribute to the apoptosis. However, PP2A may not be involved in the regulation of apoptotic process under the current conditions.