Acute effects of microcystins exposure on the transcription of antioxidant enzyme genes in three organs (liver, kidney, and testis) of male Wistar rats

Visualization of microcystin-LR and sulfides in plateau lakes

In eutrophic water bodies, sulfides are closely related to the growth of cyanobacteria and the production of microcystin-LR (MC-LR). To date, the underlying interaction mechanism between a sulfides and MC-LR remains controversial. Thus, visually presenting the distribution characteristics of sulfides and MC-LR in contaminated water is crucial. Here, we propose a novel and expeditious practical approach, utilizing fluorescence probe technology, to assess the distribution characteristics of MC-LR and sulfur in natural lakes. We have developed novel probes, pib2, to detect HSO3- and HS-, and pib18, to simultaneously identify MC-LR and sulfides. Through correlation analysis of fluorescence data and physicochemical indicators at sampling points, it is found that fluorescence data has good correlation with sulfides and MC-LR, and speculated that pib2 and pib18 may be able to detect sulfides and MC-LR in lakes. Using this method, we rapidly obtained the distribution of MC-LR and sulfur in Qilu and Erhai Lakes. Notably, for the first time, we rapidly displayed the distributions of sulfides and MC-LR across lakes by the fluorescent probe technology.

The Abnormal Proliferation of Hepatocytes is Associated with MC-LR and C-Terminal Truncated HBX Synergistic Disturbance of the Redox Balance

Background

Microcystin-LR (MC-LR) and hepatitis B virus (HBV) are associated with hepatocellular carcinoma (HCC). However, the concentrations of MC-LR in drinking water and the synergistic effect of MC-LR and HBV on hepatocellular carcinogenesis through their disturbance of redox balance have not been fully elucidated.

Methods

We measured the MC-LR concentrations in 168 drinking water samples of areas with a high incidence of HCC. The relationships between MC-LR and both redox status and liver diseases in 177 local residents were analyzed. The hepatoma cell line HepG2 transfected with C-terminal truncated hepatitis B virus X gene (Ct-HBX) were treated with MC-LR. Reactive oxygen species (ROS), superoxide dismutase (SOD), glutathione (GSH) and malondialdehyde (MDA) were measured. Cell proliferation, migration, invasion, and apoptosis were assessed with cell activity assays, scratch and transwell assays, and flow cytometry, respectively. The mRNA and protein expression-related redox status genes were analyzed with qPCR and Western blotting.

Results

The average concentration of MC-LR in well water, river water and reservoir water were 57.55 ng/L, 76.74 ng/L and 132.86 ng/L respectively, and the differences were statistically significant (P < 0.05). The MC-LR levels in drinking water were correlated with liver health status, including hepatitis, clonorchiasis, glutamic pyruvic transaminase abnormalities and hepatitis B surface antigen carriage (all P values < 0.05). The serum MDA increased in subjects who drank reservoir water and were infected with HBV (P < 0.05). In the cell experiment, ROS increased when Ct-HBX-transfected HepG2 cells were treated with MC-LR, followed by a decrease in SOD and GSH and an increase in MDA. MC-LR combined with Ct-HBX promoted the proliferation, migration and invasion of HepG2 cells, upregulated the mRNA and protein expression of MAOA gene, and downregulated UCP2 and GPX1 genes.

Conclusion

MC-LR and HBV may synergistically affect redox status and play an important role in hepatocarcinoma genesis.

Microcystins in Water: Detection, Microbial Degradation Strategies, and Mechanisms

Microcystins are secondary metabolites produced by some cyanobacteria, a class of cyclic heptapeptide toxins that are stable in the environment. Microcystins can create a variety of adverse health effects in humans, animals, and plants through contaminated water. Effective methods to degrade them are required. Microorganisms are considered to be a promising method to degrade microcystins due to their high efficiency, low cost, and environmental friendliness. This review focuses on perspectives on the frontiers of microcystin biodegradation. It has been reported that bacteria and fungi play an important contribution to degradation. Analysis of the biodegradation mechanism and pathway is an important part of the research. Microcystin biodegradation has been extensively studied in the existing research. This review provides an overview of (1) pollution assessment strategies and hazards of microcystins in water bodies and (2) the important contributions of various bacteria and fungi in the biodegradation of microcystins and their degradation mechanisms, including mlr gene-induced (gene cluster expressing microcystinase) degradation. The application of biodegradable technology still needs development. Further, a robust regulatory oversight is required to monitor and minimize MC contamination. This review aims to provide more references regarding the detection and removal of microcystins in aqueous environments and to promote the application of biodegradation techniques for the purification of microcystin-contaminated water.

Advances in the toxicology research of microcystins based on Omics approaches

Microcystins (MCs) are the most widely distributed cyanotoxins, which can be ingested by animals and human body in multiple ways, resulting in a threat to human health and the biodiversity of wildlife. Therefore, the study on toxic effects and mechanisms of MCs is one of the focuses of attention. Recently, the Omics techniques, i.e. genomics, transcriptomics, proteomics and metabolomics, have significantly contributed to the comprehensive understanding and revealing of the molecular mechanisms about the toxicity of MCs. This paper mainly reviews current literature using the Omics approaches to explore the toxicity mechanism of MCs in liver, gonad, spleen, brain, intestine and lung of multiple species. It was found that MCs can exert strong toxic effects on various metabolic activities and cell signal transduction in cell cycle, apoptosis, destruction of cell cytoskeleton and redox disorder, at protein, transcription and metabolism level. Meanwhile, it was also revealed that the alteration of non-coding RNAs (miRNA, circRNA and lncRNA, etc.) and gut microbiota plays an essential regulatory role in the toxic effects of MCs, especially in hepatotoxicity and reproductive toxicity. In addition, we summarized current research gaps and pointed out the future directions for research. The detailed information in this paper shows that the application and development of Omics techniques have significantly promoted the research on MCs toxicity, and it is also a valuable resource for exploring the toxic mechanism of MCs.

Hepatoprotective, antioxidant, anti-inflammatory, and antiviral activities of silymarin against mayaro virus infection

Infection caused by Mayaro virus (MAYV) is responsible for causing acute nonspecific fever, in which the majority of patients develop incapacitating and persistent arthritis/arthralgia. Mayaro fever is a neglected and underreported disease without treatment or vaccine, which has gained attention in recent years after the competence of Aedes aegypti to transmit MAYV was observed in the laboratory, coupled with the fact that cases are being increasingly reported outside of endemic forest areas, calling attention to the potential of an urban cycle arising in the near future. Thus, to mitigate the lack of information about the pathological aspects of MAYV, we previously described the involvement of oxidative stress in MAYV infection in cultured cells and in a non-lethal mouse model. Additionally, we showed that silymarin, a natural compound, attenuated MAYV-induced oxidative stress and inhibited MAYV replication in cells. The antioxidant and anti-MAYV effects prompted us to determine whether silymarin could also reduce oxidative stress and MAYV replication after infection in an immunocompetent animal model. We show that infected mice exhibited reduced weight gain, hepatomegaly, splenomegaly, anaemia, thrombocytopenia, leukopenia, increased liver transaminases, increased pro-inflammatory cytokines and liver inflammation, increased oxidative damage biomarkers, and reduced antioxidant enzyme activity. However, in animals infected and treated with silymarin, all these parameters were reversed or significantly improved, and the detection of viral load in the liver, spleen, brain, thigh muscle, and footpad was significantly reduced. This work reinforces the potent hepatoprotective, antioxidant, anti-inflammatory, and antiviral effects of silymarin against MAYV infection, demonstrating its potential against Mayaro fever disease.

Update on the adverse effects of microcystins on the liver

Microcystins (MCs) are the most common cyanobacteria toxins in eutrophic water, which have strong hepatotoxicity. In the past decade, epidemiological and toxicological studies on liver damage caused by MCs have proliferated, and new mechanisms of hepatotoxicity induced by MCs have also been discovered and confirmed. However, there has not been a comprehensive and systematic review of these new findings. Therefore, this paper summarizes the latest advances in studies on the hepatotoxicity of MCs to reveal the effects and mechanisms of hepatotoxicity induced by MCs. Current epidemiological studies have confirmed that symptoms or signs of liver damage appear after human exposure to MCs, and a long time of exposure can even lead to liver cancer. Toxicological studies have shown that MCs can affect the expression of oncogenes by activating cell proliferation pathways such as MAPK and Akt, thereby promoting the occurrence and development of cancer. The latest evidence shows that epigenetic modifications may play an important role in MCs-induced liver cancer. MCs can cause damage to the liver by inducing hepatocyte death, mainly manifested as apoptosis and necrosis. The imbalance of liver metabolic homeostasis may be involved in hepatotoxicity induced by MCs. In addition, the combined toxicity of MCs and other toxins are also discussed in this article. This detailed information will be a valuable reference for further exploring of MCs-induced hepatotoxicity.

Antioxidant responses of triangle sail mussel Hyriopsis cumingii exposed to toxic Microcystis aeruginosa and thermal stress

Harmful algal blooms (HABs) and thermal stress as climate changes become more common in global water ecosystem, especially under eutrophic habitats. Here our study examined the combined impacts of bloom forming cyanobacteria Microcystis aeruginosa and thermal stress on the antioxidant responses of the ecologically important species triangle sail mussel Hyriopsis cumingii. The differential responses of a series of enzymes, e.g. superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione-S-transferase (GST), as well as signal metabolites including reactive oxygen species (ROS), malondialdehyde (MDA) and glutathione (GSH) involved in antioxidant defense mechanisms were analyzed during 14 d exposure to toxic cyanobacterium M. aeruginosa and 7 d depuration period. The activities of SOD and GPx as well as the content of ROS and MDA in H. cumingii increased, while CAT activity reduced due to M. aeruginosa exposure. Thermal stress resulted in decrease of CAT, the accumulation of GSH and the enhance of GST and SOD. Meanwhile, the interactive effects among M. aeruginosa, thermal stress and time were also observed on most parameters except for GST activity. The total amount of microcystins (MC) in sail mussels increased with concentrations of exposed M. aeruginosa, independently of the presence or absence of thermal stress. Although around 50% of MC in mussels dropped in the depuration period, most parameters showed alterations because of cyanobacteria exposure and thermal stress. Overall, these findings suggested that toxic cyanobacteria or thermal stress induces oxidative stress and severely affects the enzymes activities and intermediates level associated with antioxidant defense mechanisms in sail mussels respectively. More importantly, the toxic impacts on sail mussels could be intensified by their combination.

A Review of Nephrotoxicity of Microcystins

Cyanobacterial blooms triggered by eutrophication and climate change have become a global public health issue. The toxic metabolites microcystins (MCs) generated by cyanobacteria can accumulate in food chain and contaminate water, thus posing a potential threat to human and animals health. Studies have suggested that aside liver, the kidney may be another target organ of MCs intoxication. Therefore, this review provides various evidences on the nephrotoxicity of MCs. The review concludes that nephrotoxicity of MCs may be related to inhibition of protein phosphatases and excessive production of reactive oxygen species, cytoskeleton disruption, endoplasmic reticulum stress, DNA damage and cell apoptosis. To protect human from MCs toxic consequences, this paper also puts forward some directions for further research.

Microcystin-LR exposure results in aberrant spindles and induces apoptosis in porcine oocytes

Microcystin-LR (MC-LR), as a well-known hepatotoxin, was recently found to accumulate in gonads and induce a variety of reproductive damages in zebrafish, mice and other model organisms, however, little information is available on whether MC-LR has toxic effects on the mammalian oocytes, especially in livestock species. In this study, the effects of MC-LR on meiotic maturation of porcine oocytes were investigated, and the potential mechanism of MC-LR toxicity was explored. Germinal vesicle (GV)-stage oocytes were exposed to 0, 20, 40 and 60 μM MC-LR, respectively, during the in vitro maturation for 44 h, and the results showed that the first polar body (PbI) extrusion rate of the oocytes decreased significantly when the MC-LR concentration reached 40 (P < 0.01) or 60 μM (P < 0.001). After treated with 60 μM MC-LR for 44 h, a significant higher percentage of the oocytes arrested at anaphase-telophase I (ATI) stage (P < 0.01). Laser scanning confocal results further confirmed that a significantly larger proportion of the 60 μM MC-LR-treated oocytes exhibited aberrant spindles and misaligned chromosomes, suggesting a failure of spindle assembly and homologous chromosome segregation during the ATI stage. Furthermore, the ROS levels in the 60 μM MC-LR-exposed oocytes were significantly higher than the control group (P < 0.01), while the expression of antioxidant related genes (SOD1, CAT and GPX) were much lower compared with control group, indicating that oxidative stress was induced and the antioxidant capacity of oocytes was depleted by 60 μM MC-LR treatment. Additionally, markedly decreased mitochondrial membrane potential (MMP) (P < 0.01) and significantly higher incidence of early apoptosis (P < 0.01) were observed in the 60 μM MC-LR-treated oocytes, suggesting that MC-LR exposure induced apoptosis in porcine oocytes. Moreover, the protein expression of PP2A was remarkably inhibited, whereas the expression of p53, BAX, Caspase3 and Cleaved-caspase3 were prominently increased in the 60 μM MC-LR-exposed oocytes. Together, these results suggested that 60 μM of MC-LR exposure can induce oxidative stress, and lead to aberrant spindles, impaired MMP, and trigger apoptosis, which eventually result in failure of porcine oocyte maturation.

Novel Microcystins from Planktothrix prolifica NIVA-CYA 544 Identified by LC-MS/MS, Functional Group Derivatization and 15N-labeling

Microcystins are cyclic heptapeptides from cyanobacteria that are potent inhibitors of protein phosphatases and are toxic to animals and humans. At present, more than 250 microcystin variants are known, with variants reported for all seven peptide moieties. While d-glutamic acid (d-Glu) is highly-conserved at position-6 of microcystins, there has been only one report of a cyanobacterium (Anabaena) producing microcystins containing l-Glu at the variable 2- and 4-positions. Liquid chromatography–mass spectrometry analyses of extracts from Planktothrix prolifica NIVA-CYA 544 led to the tentative identification of two new Glu-containing microcystins, [d-Asp³]MC-ER (12) and [d-Asp³]MC-EE (13). Structure determination was aided by thiol derivatization of the Mdha⁷-moiety and esterification of the carboxylic acid groups, while ¹⁵N-labeling of the culture and isotopic profile analysis assisted the determination of the number of nitrogen atoms present and the elemental composition of molecular and product-ions. The major microcystin analog in the extracts was [d-Asp³]MC-RR (1). A microcystin with an unprecedented high-molecular-mass (2116 Da) was also detected and tentatively identified as a sulfide-linked conjugate of [d-Asp³]MC-RR (15) by LC–HRMS/MS and sulfide oxidation, together with its sulfoxide (16) produced via autoxidation. Low levels of [d-Asp³]MC-RW (14), [d-Asp³]MC-LR (4), [d-Asp³,Mser⁷]MC-RR (11), [d-Asp³]MC-RY (17), [d-Asp³]MC-RF (18), [d-Asp³]MC-RR–glutathione conjugate (19), and [d-Asp³]MC-RCit (20), the first reported microcystin containing citrulline, were also identified in the extract, and an oxidized derivative of [d-Asp³]MC-RR and the cysteine conjugate of 1 were partially characterized.

Enantiomeric environmental behavior, oxidative stress and toxin release of harmful cyanobacteria Microcystis aeruginosa in response to napropamide and acetochlor

Harmful algal blooms have emerged as a worldwide issue. After concentrations of herbicides entering water, herbicides in water may pose ecological effects on them. The present study investigates the toxicity and environmental behavior of the herbicides, napropamide and acetochlor as enantiomers and as racemates on Microcystis aeruginosa which is the main specie known to produce hepatotoxins. S-napropamide/acetochlor are degraded faster than their corresponding isomer R-napropamide/acetochlor, with the latter more prone to accumulate in algal cells. Moreover, all the enantiomers did not undergo measurable racemization in the medium and algal cells. S-napropamide/acetochlor exhibited much higher toxicity than R-napropamide/acetochlor, with the S-enantiomer inducing a much greater production of antioxidant defense enzymes (superoxide dismutase (SOD) and malondialdehyde (MDA)) and microcystins (MC). SOD and MC increased after treatment with the herbicides and these increases were dependent on the exposure time, whereas MDA showed no apparent change. The information provided in this work will be useful for understanding the toxicity mechanism and environmental behaviors of different amide herbicides (napropamide and acetochlor) in aquatic environments at the enantiomeric level. Additionally, analysis of chiral herbicides in aquatic system needs more attention to aide in the environmental assessment of chiral herbicides.

Effect of pure microcystin-LR on activity and transcript level of immune-related enzymes in the white shrimp (Litopenaeus vannamei)

Microcystins (MCs) in freshwater and marine waters released by toxin-producing cyanobacteria have negative impacts to the aquatic environment. This study aimed to investigate the effect of pure microcystin-LR on activity and transcript level of immune-related enzymes in the white shrimp Litopenaeus vannamei. After exposed to varying concentrations of pure microcystin-LR (MC-LR) for 30 days, the activity of superoxide dismutase (SOD), lysozyme (LZM), glutathione peroxidase (GPx), peroxidase (POD), acid phosphatase (ACP), alkaline phosphatase (AKP) and transcript level of cMn-sod, lzm, gpx were investigated in the hepatopancreas of white shrimp (L. vannamei). Immune-related enzyme activities responded differently to MC-LR exposure. SOD, GPx, and POD activity in the hepatopancreas were activated in a concentration-dependent manner while LZM activity was significantly inhibited in the treatment groups. ACP and AKP activity showed an increase, followed by a decrease. The transcript levels of cMn-sod, lzm, and gpx were consistent with changes in their encoding enzyme activity. These results demonstrated that sub-chronical exposure to MC-LR induced the alteration of immune-related enzymes and corresponding genes in the hepatopancreas, which may help explain the presence of detoxification mechanisms in crustaceans and how they were protected from MC-LR stress for a long period of time.

Agaricus brasiliensis (sun mushroom) affects the expression of genes related to cholesterol homeostasis

PURPOSE

The sun mushroom (Agaricus brasiliensis) is considered a major source of bioactive compounds with potential health benefits. Mushrooms typically act as lipid-lowering agents; however, little is known about the mechanisms of action of A. brasiliensis in biological systems. This study aimed to determine the underlying mechanism involved in the cholesterol-lowering effect of A. brasiliensis through the assessment of fecal and serum lipid profiles in addition to gene expression analysis of specific transcription factors, enzymes, and transporters involved in cholesterol homeostasis.

METHODS

Twenty-four albino Fischer rats approximately 90 days old, with an average weight of 205 g, were divided into four groups of 6 each and fed a standard AIN-93 M diet (C), hypercholesterolemic diet (H), hypercholesterolemic diet +1 % A. brasiliensis (HAb), or hypercholesterolemic diet +0.008 % simvastatin (HS) for 6 weeks. Simvastatin was used as a positive control, as it is a typical drug prescribed for lipid disorders. Subsequently, blood, liver, and feces samples were collected for lipid profile and quantitative real-time polymerase chain reaction gene expression analyses.

RESULTS

Diet supplementation with A. brasiliensis significantly improved serum lipid profiles, comparable to the effect observed for simvastatin. In addition, A. brasiliensis dietary supplementation markedly promoted fecal cholesterol excretion. Increased expression of 7α-hydroxylase (CYP7A1), ATP-binding cassette subfamily G-transporters (ABCG5/G8), and low-density lipoprotein receptor (LDLR) was observed following A. brasiliensis administration.

CONCLUSIONS

Our results suggest that consumption of A. brasiliensis improves the serum lipid profile in hypercholesterolemic rats by modulating the expression of key genes involved in hepatic cholesterol metabolism.

A review of reproductive toxicity of microcystins

Animal studies provide strong evidence of positive associations between microcystins (MCs) exposure and reproductive toxicity, representing a threat to human reproductive health and the biodiversity of wild life. This paper reviews current knowledge of the reproductive toxicity of MCs, with regard to mammals, fishes, amphibians, and birds, mostly in males. Toxicity of MCs is primarily governed by the inhibition of protein phosphatases 1 and 2A (PP1 and PP2A) and disturbance of cellular phosphorylation balance. MCs exposure is related to excessive production of reactive oxygen species (ROS) and oxidative stress, leading to cytoskeleton disruption, mitochondria dysfunction, endoplasmic reticulum (ER) stress, and DNA damage. MCs induce cell apoptosis mediated by the mitochondrial and ROS and ER pathways. Through PP1/2A inhibition and oxidative stress, MCs lead to differential expression/activity of transcriptional factors and proteins involved in the pathways of cellular differentiation, proliferation, and tumor promotion. MC-induced DNA damage is also involved in carcinogenicity. Apart from a direct effect on testes and ovaries, MCs indirectly affect sex hormones by damaging the hypothalamic-pituitary-gonad (HPG) axis and liver. Parental exposure to MCs may result in hepatotoxicity and neurotoxicity of offspring. We also summarize the current research gaps which should be addressed by further studies.

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.

Antioxidant responses of triangle sail mussel Hyriopsis cumingii exposed to harmful algae Microcystis aeruginosa and hypoxia

Bloom forming algae and hypoxia are considered to be two main co-occurred stressors associated with eutrophication. The aim of this study was to evaluate the interactive effects of harmful algae Microcystis aeruginosa and hypoxia on an ecologically important mussel species inhabiting lakes and reservoirs, the triangle sail mussel Hyriopsis cumingii, which is generally considered as a bio-management tool for eutrophication. A set of antioxidant enzymes involved in immune defence mechanisms and detoxification processes, i.e. glutathione-S-transferases (GST), glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), lysozyme (LZM) in mussel haemolymph were analyzed during 14days exposure along with 7days depuration duration period. GST, GSH, SOD, GPX and LZM were elevated by toxic M. aeruginosa exposure, while CAT activities were inhibited by such exposure. Hypoxia influenced the immune mechanisms through the activation of GSH and GPX, and the inhibition of SOD, CAT, and LZM activities. Meanwhile, some interactive effects of M. aeruginosa, hypoxia and time were observed. Independently of the presence or absence of hypoxia, toxic algal exposure generally increased the five tested enzyme activities of haemolymph, except CAT. Although half of microcystin could be eliminated after 7days depuration, toxic M. aeruginosa or hypoxia exposure history showed some latent effects on most parameters. These results revealed that toxic algae play an important role on haemolymph parameters alterations and its toxic effects could be affected by hypoxia. Although the microcystin depuration rate of H. cumingii is quick, toxic M. aeruginosa and/or hypoxia exposure history influenced its immunological mechanism recovery.

Hypercholesterolemic diet induces hepatic steatosis and alterations in mRNA expression of NADPH oxidase in rat livers

OBJECTIVE

This study aimed to determine whether a hypercholesterolemic diet induces hepatic steatosis, alterations in mRNA expression of NADPH oxidase subunits, and antioxidant defenses.

MATERIALS AND METHODS

Fischer rats were divided into two groups of eight animals according to the treatment, control (C) and hypercholesterolemic diet (H). Those in group C were fed a standard diet (AIN-93M), and those of the group H were fed a hypercholesterolemic diet (25% soybean oil and 1% cholesterol).

RESULTS

The hypercholesterolemic diet did not affect body weight, but resulted in the accumulation of lipids in the liver, increased serum activities of aminotransferases and cholesterol levels. Biomarker of lipid peroxidation (TBARS) and mRNA expression of NADPH oxidase subunits p22(phox) and p47(phox) were increased in the liver of animals in group H. Besides, the activity and expression of antioxidant enzymes were altered.

CONCLUSION

The results show increased mRNA expression of NADPH oxidase subunits and changes in antioxidant enzyme activities in diet-induced hepatic steatosis.

Role of nitric oxide in the genotoxic response to chronic microcystin-LR exposure in human-hamster hybrid cells

Microcystin-LR (MC-LR) is the most abundant and toxic microcystin congener and has been classified as a potential human carcinogen (Group 2B) by the International Agency for Research on Cancer. However, the mechanisms underlying the genotoxic effects of MC-LR during chronic exposure are still poorly understood. In the present study, human-hamster hybrid (AL) cells were exposed to MC-LR for varying lengths of time to investigate the role of nitrogen radicals in MC-LR-induced genotoxicity. The mutagenic potential at the CD59 locus was more than 2-fold higher (p<0.01) in AL cells exposed to a cytotoxic concentration (1 μmol/L) of MC-LR for 30 days than in untreated control cells, which was consistent with the formation of micronucleus. MC-LR caused a dose-dependent increase in nitric oxide (NO) production in treated cells. Moreover, this was blocked by concurrent treatment with the NO synthase inhibitor NG-methyl-L-arginine (L-NMMA), which suppressed MC-LR-induced mutations as well. The survival of mitochondrial DNA-depleted (ρ0) AL cells was markedly decreased by MC-LR treatment compared to that in AL cells, while the CD59 mutant fraction was unaltered. These results provided clear evidence that the genotoxicity associated with chronic MC-LR exposure in mammalian cells was mediated by NO and might be considered as a basis for the development of therapeutics that prevent carcinogenesis.

Iron dextran increases hepatic oxidative stress and alters expression of genes related to lipid metabolism contributing to hyperlipidaemia in murine model

The objective of this study was to investigate the effects of iron dextran on lipid metabolism and to determine the involvement of oxidative stress. Fischer rats were divided into two groups: the standard group (S), which was fed the AIN-93M diet, and the standard plus iron group (SI), which was fed the same diet but also received iron dextran injections. Serum cholesterol and triacylglycerol levels were higher in the SI group than in the S group. Iron dextran was associated with decreased mRNA levels of pparα, and its downstream gene cpt1a, which is involved in lipid oxidation. Iron dextran also increased mRNA levels of apoB-100, MTP, and L-FABP indicating alterations in lipid secretion. Carbonyl protein and TBARS were consistently higher in the liver of the iron-treated rats. Moreover, a significant positive correlation was found between oxidative stress products, lfabp expression, and iron stores. In addition, a negative correlation was found between pparα expression, TBARS, carbonyl protein, and iron stores. In conclusion, our results suggest that the increase observed in the transport of lipids in the bloodstream and the decreased fatty acid oxidation in rats, which was promoted by iron dextran, might be attributed to increased oxidative stress.

Maternal repeated oral exposure to microcystin-LR affects neurobehaviors in developing rats

Microcystins are toxic peptides secreted by certain water blooms of toxic cyanobacteria. The most widely studied microcystin is microcystin-LR (MC-LR), which exhibits hepatotoxicity and neurotoxicity. However, limited information is available regarding the effects on offspring following maternal exposure. The present study was conducted to observe the effects of progestational exposure to MC-LR on postnatal development in rats. Female Sprague-Dawley rats (28 d old) were randomly divided into a control group and 3 treatment groups (1.0 µg MC-LR/kg body wt, 5.0 µg MC-LR/kg body wt, and 20.0 µg MC-LR/kg body wt), with 7 rats per group. The MC-LR was administered through gavage once every 48 h for 8 wk. Pure water was used as control. Each female rat was mated with an unexposed adult male rat. Motor development, behavioral development, and learning ability of pups were detected using surface righting reflex, negative geotaxis, and cliff avoidance tests on postnatal day 7. Open-field and Morris water maze tests were performed on postnatal day 28 and day 60. The levels of lipid peroxidation products and antioxidant indices in the rat hippocampus were also detected. Pups from the MC-LR-treated groups had significantly lower scores than controls in the cliff avoidance test (p < 0.05). Cognitive impairment, malondialdehyde level, and total superoxide dismutase activity significantly increased in MC-LR-exposed pups compared with controls (p < 0.05). Therefore, the present study reveals that maternal exposure to MC-LR has adverse effects on neurodevelopment in rat offspring.

Protective effect of Baccharis trimera extract on acute hepatic injury in a model of inflammation induced by acetaminophen

BACKGROUND

Acetaminophen (APAP) is a commonly used analgesic and antipyretic. When administered in high doses, APAP is a clinical problem in the US and Europe, often resulting in severe liver injury and potentially acute liver failure. Studies have demonstrated that antioxidants and anti-inflammatory agents effectively protect against the acute hepatotoxicity induced by APAP overdose.

METHODS

The present study attempted to investigate the protective effect of B. trimera against APAP-induced hepatic damage in rats. The liver-function markers ALT and AST, biomarkers of oxidative stress, antioxidant parameters, and histopathological changes were examined.

RESULTS

The pretreatment with B. trimera attenuated serum activities of ALT and AST that were enhanced by administration of APAP. Furthermore, pretreatment with the extract decreases the activity of the enzyme SOD and increases the activity of catalase and the concentration of total glutathione. Histopathological analysis confirmed the alleviation of liver damage and reduced lesions caused by APAP.

CONCLUSIONS

The hepatoprotective action of B. trimera extract may rely on its effect on reducing the oxidative stress caused by APAP-induced hepatic damage in a rat model. General Significance. These results make the extract of B. trimera a potential candidate drug capable of protecting the liver against damage caused by APAP overdose.

Spatial learning and memory impairment and pathological change in rats induced by acute exposure to microcystin-LR

Microcystin-LR (MCLR) is a commonly encountered blue-green algal hepatotoxin and a known inhibitor of cellular protein phosphatase. However, little is known about its neurotoxicity. By using Morris water maze, histopathological and biochemical analysis, we investigated MCLR-induced neurotoxicity on the hippocampus of rat brain. After rats were intrahippocampally injected with MCLR (1 and 10 μg/L), their learning and memory function was greatly impaired, suggesting the neurotoxic potential of MCLR. Meanwhile, obvious histological and ultrastructural injuries and serious oxidative damage were also observed in the hippocampus. These results suggested that oxidative stress might be involved in the MCLR-induced pathological damage in hippocampus, subsequently leading to the spatial learning and memory deficit of rat. Taken together, our results highlighted the MCLR-induced neurotoxicity in the rat, as well as the importance of oxidative stress and pathological impairment in this procedure.

β-Carotene, α-tocopherol and ascorbic acid: differential profile of antioxidant, inflammatory status and regulation of gene expression in human mononuclear cells of diabetic donors

BACKGROUND

Diabetic patients are exposed to increased oxidative stress due to several mechanisms, mainly hyperglycaemia. Pathological processes, such as those in type 1 diabetes, include diminished activity of the antioxidant defense system(s) or excessive oxidative generation resulting in an oxidative/antioxidant imbalance and development of oxidative stress.

METHODS

The purpose of this study was to evaluate the production of reactive oxygen species (ROS) (chemiluminescence) and reduction capacity (MTT dye reduction), the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits, superoxide dismutase and catalase using quantitative reverse-transcriptase polymerase chain reaction, and the levels of cytokines [interleukin (IL)-6, tumour necrosis factor-α, IL-8, IL-10 and IL-4] by sandwich enzyme-linked immunosorbent assay in mononuclear cells from non-diabetic and diabetic donors treated with a vitamin complex (ascorbic acid, β-carotene and α-tocopherol) in two different concentrations ([A] = ascorbic acid = 0.08 µM, α-tocopherol = 0.04 µM, β-carotene = 0.0008 µM and [20A] = ascorbic acid = 1.6 µM, α-tocopherol = 0.82 µM, β-carotene = 0.016 µM).

RESULTS

Concentration [A] was antioxidant reducing ROS production, expression of NADPH oxidase subunits and pro-inflammatory cytokines while raising the expression of antioxidant enzymes and reducing pro-inflammatory cytokines in both groups. Concentration [20A] was pro-oxidant by raising ROS production, NADPH oxidase subunits and pro-inflammatory cytokines and reducing antioxidant enzymes and anti-inflammatory cytokines in the non-diabetic group but antioxidant in cells of type 1 diabetic patients by raising antioxidant enzymes and anti-inflammatory cytokines and reducing pro-inflammatory cytokines.

CONCLUSION

The vitamin complex has a dual effect, pro-oxidant and antioxidant, being also dose dependent with different profiles of cells of non-diabetic and type 1 diabetic patients.

The interactive effects of cytoskeleton disruption and mitochondria dysfunction lead to reproductive toxicity induced by microcystin-LR

The worldwide occurrence of cyanobacterial blooms evokes profound concerns. The presence of microcystins (MCs) in waters and aquatic food increases the risk to human health. Some recent studies have suggested that the gonad is the second most important target organ of MCs, however, the potential toxicity mechanisms are still unclear. For a better understanding of reproductive toxicity of MCs on animals, we conducted the present experimental investigation. Male rats were intraperitoneally injected with MC-LR for 50 d with the doses of 1 and 10 µg/kg body weight per day. After prolonged exposure to MC-LR, the testes index significantly decreased in 10 µg/kg group. Light microscope observation indicated that the space between the seminiferous tubules was increased. Ultrastructural observation showed some histopathological characteristics, including cytoplasmic shrinkage, cell membrane blebbing, swollen mitochondria and deformed nucleus. Using Q-PCR methods, the transcriptional levels of some cytoskeletal and mitochondrial genes were determined. MC-LR exposure affected the homeostasis of the expression of cytoskeletal genes, causing possible dysfunction of cytoskeleton assembly. In MC-LR treatments, all the 8 mitochondrial genes related with oxidative phosphorylation (OXPHOS) significantly increased. The reactive oxygen species (ROS) level significantly increased in 10 µg/kg group. The mitochondria swelling and DNA damage were also determined in 10 µg/kg group. Hormone levels of testis significantly changed. The present study verified that both cytoskeleton disruption possibly due to cytoskeletal reorganization or depolymerization and mitochondria dysfunction interact with each other through inducing of reactive oxygen species and oxidative phosphorylation, and jointly result in testis impairment after exposure to MC-LR.

The hypocholesterolemic activity of açaí (Euterpe oleracea Mart.) is mediated by the enhanced expression of the ATP-binding cassette, subfamily G transporters 5 and 8 and low-density lipoprotein receptor genes in the rat

Previous studies have demonstrated that the ingestion of açaí pulp can improve serum lipid profile in various animal models; therefore, we hypothesized that açaí pulp (Euterpe oleracea Mart.) may modulate the expression of the genes involved in cholesterol homeostasis in the liver and increase fecal excretion, thus reducing serum cholesterol. To test this hypothesis, we analyzed the expression of 7α-hydroxylase and ATP-binding cassette, subfamily G transporters (ABCG5 and ABCG8), which are genes involved with the secretion of cholesterol in the rat. We also evaluated the expression of sterol regulatory element-binding protein 2, 3-hydroxy-3-methylglutaryl CoA reductase, low-density lipoprotein receptor (LDL-R), and apolipoprotein B100, which are involved in cholesterol biosynthesis. Female Fischer rats were divided into 4 groups: the C group, which was fed a standard AIN-93 M diet; the CA group, which was fed a standard diet supplemented with 2% açaí pulp; the H group, which was fed a hypercholesterolemic diet (25% soy oil and 1% cholesterol); and the HA group, which was fed a hypercholesterolemic diet supplemented with 2% açaí pulp. At the end of the experimental period, the rats were euthanized, and their blood and livers were collected. The HA group exhibited a significant decrease in serum total cholesterol, low-density lipoprotein cholesterol, and atherogenic index and also had increased high-density lipoprotein cholesterol and cholesterol excretion in feces compared with the H group. In addition, the expression of the LDL-R, ABCG5, and ABCG8 genes was significantly increased by the presence of açaí pulp. These results suggest that açaí pulp promotes a hypocholesterolemic effect in a rat model of dietary-induced hypercholesterolemia through an increase in the expression of ATP-binding cassette, subfamily G transporters, and LDL-R genes.

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.

Iron overload potentiates diet-induced hypercholesterolemia and reduces liver PPAR-α expression in hamsters

Iron stores and lipids are related to the development of cardiovascular disease. Given that peroxisome proliferator-activated receptor alpha (PPAR-α) regulates important physiological processes that impact lipid and glucose homeostasis, we decided to investigate the effects of iron overload on serum lipids and the liver expression of PPAR-α, 3-hydroxy-3-methylglutaryl coenzyme A reductase, and cholesterol 7α-hydroxylase. Hamsters were divided into four groups. The standard group (S) was fed the AIN-93M diet, the SI group was fed the diet and iron injections, the hypercholesterolemic group (H) was fed a standard diet containing cholesterol, and the HI group was fed a high-cholesterol diet and iron injections. Serum cholesterol in the HI group was higher than in the H group. Gene expression analysis of PPAR-α showed that the HI group had a lower PPAR-α expression than H. These data show that iron, when associated with a high-fat diet, can cause increased serum cholesterol levels, possibly due to a reduction in PPAR-α expression.

Expression and activity of glutathione S-transferases and catalase in the shrimp Litopenaeus vannamei inoculated with a toxic Microcystis aeruginosa strain

Microcystin (MC) produced during cyanobacteria blooms is notably toxic to human and wildlife. Conjugation with reduced glutathione (GSH) by glutathione S-transferase (GST) and the antioxidant enzymes defenses (e.g. catalase, CAT) are important biochemical defense mechanisms against MCs toxicity. We investigated the enzymatic activity of CAT and GST and the gene expression levels of CAT and eight GST isoforms in the hepatopancreas of the globally farmed shrimp Litopenaeus vannamei 48-h after injection with a sub-lethal dose of 100 μg kg⁻¹ of a toxic Microcystis aeruginosa extract. MCs caused up-regulation for GSTΩ, μ and a MAPEG isoform, by 12-, 2.8- and 1.8-fold, respectively, and increases in the total GST enzyme activity and CAT enzyme activity. The study points to the importance of further characterization for the L. vannamei GST isoforms and GST/CAT post-translational regulation processes to better understand the key mechanisms involved in the shrimp's defense against MC exposure.

Dietary açai modulates ROS production by neutrophils and gene expression of liver antioxidant enzymes in rats

Açai (Euterpe oleracea Mart.) has recently emerged as a promising source of natural antioxidants. Because increased oxidative stress and impaired antioxidant defense mechanisms are important factors in the development of diabetic complications and many health claims have been reported for açai, the present study was undertaken to evaluate the possible protective effects of açai on the production of reactive oxygen species by neutrophils and on the liver antioxidant defense system in control and streptozotocin-induced diabetic rats. Diet supplementation with 2% açai was found to increase mRNA levels for gamma-glutamylcysteine synthetase and glutathione peroxidase in liver tissue and to decrease reactive oxygen species production by neutrophils. Compared to control animals, diabetic rats exhibited lower levels of mRNA coding for Zn-superoxide dismutase, glutathione peroxidase and gamma-glutamylcysteine synthetase and higher levels of reactive oxygen species production by neutrophils, thiobarbituric acid-reactive substances and carbonyl proteins in hepatic tissues. Although açai supplementation was not effective in restore gene expression of antioxidant enzymes in diabetic rats, it showed a protective effect, decreasing thiobarbituric acid-reactive substances levels and increasing reduced glutathione content in the liver. These findings suggest that açai can modulate reactive oxygen species production by neutrophils and that it has a significant favorable effect on the liver antioxidant defense system under fisiological conditions of oxidative stress and partially revert deleterious effects of diabetes in the liver.

Human glutathione transferases catalyzing the conjugation of the hepatoxin microcystin-LR

Many cyanobacterial species are able to produce cyanotoxins as secondary metabolites. Among them, microcystins (MC) are a group of around 80 congeners of toxic cyclic heptapeptides. MC-LR is the most studied MC congener, in view of its high acute hepatotoxicity and tumor promoting activity. Humans may be exposed to cyanotoxins through several routes, the oral one being the most important. The accepted pathway for MC-LR detoxication and excretion in the urine is GSH conjugation. The GSH adduct (GS-MCLR) formation has been shown to occur spontaneously and enzymatically, catalyzed by glutathione transferases (GSTs). The enzymatic reaction has been reported but not characterized both in vitro and in vivo in animal and plant species. No data are available on humans. In the present work, the MC-LR conjugation with GSH catalyzed by five recombinant human GSTs (A1-1, A3-3, M1-1, P1-1, and T1-1) has been characterized for the first time. All GSTs are able to catalyze the reaction; kinetic parameters K(m), k(cat), and their relative specific activities to form GS-MCLR were derived (T1-1 > A1-1 > M1-1 > A3-3 ≫ P1-1). In the range of MC tested concentrations used (0.25-50 μM) GSTT1-1 and A1-1 showed a typical saturation curve with similar affinity for MC-LR (≈80 μM; k(cat) values 0.18 and 0.10 min(-1), respectively), A3-3 and M1-1 were linear, whereas GSTP1-1 showed a temperature-dependent sigmoidal allosteric curve with a k(cat) = 0.11 min(-1). The enzymes mainly expressed in the liver and gastrointestinal tract, GSTA1-1, T1-1, and M1-1, seemed to be mainly involved in the MC-LR detoxification after oral exposure, whereas P1-1 kinetics and location in the skin suggest a role related to dermal exposure. Considering the high frequency of some GST polymorphism, especially M1 and T1 gene deletion, with complete loss in activity, this information could be the first step to identify groups of individual at higher risk associated with MC exposure.