Activity and gene expression profile of certain antioxidant enzymes to microcystin-LR induced oxidative stress in mice

Comparative Analysis of Tentacle Extract and Nematocyst Venom: Toxicity, Mechanism, and Potential Intervention in the Giant Jellyfish Nemopilema nomurai

The giant jellyfish Nemopilema nomurai sting can cause local and systemic reactions; however, comparative analysis of the tentacle extract (TE) and nematocyst venom extract (NV), and its toxicity, mechanism, and potential intervention are still limited. This study compared venom from TE and NV for their composition, toxicity, and efficacy in vitro and in vivo used RAW264.7 cells and ICR mice. A total of 239 and 225 toxin proteins were identified in TE and NV by proteomics, respectively. Pathological analysis revealed that TE and NV caused heart and liver damage through apoptosis, necrosis, and inflammation, while TE exhibited higher toxicity ex vivo and in vivo. Biochemical markers indicated TE and NV elevated creatine kinase, lactatedehydrogenase, and aspartate aminotransferase, with the TE group showing a more significant increase. Transcriptomics and Western blotting indicated both venoms increased cytokines expression and MAPK signaling pathways. Additionally, 1 mg/kg PACOCF3 (the phospholipase A2 inhibitor) improved survival from 16.7% to 75% in mice. Our results indicate that different extraction methods impact venom activities, tentacle autolysis preserves toxin proteins and their toxicity, and PACOCF3 is a potential antidote, which establishes a good extraction method of jellyfish venom, expands our understanding of jellyfish toxicity, mechanism, and provides a promising intervention.

Pubertal exposure to Microcystin-LR arrests spermatogonia proliferation by inducing DSB and inhibiting SIRT6 dependent DNA repair in vivo and in vitro

The reproduction toxicity of pubertal exposure to Microcystin-LR (MC-LR) and the underlying mechanism needs to be further investigated. In the current study, pubertal male ICR mice were intraperitoneally injected with 2 μg/kg MC-LR for four weeks. Pubertal exposure to MC-LR decreased epididymal sperm concentration and blocked spermatogonia proliferation. In-vitro studies found MC-LR inhibited cell proliferation of GC-1 cells and arrested cell cycle in G2/M phase. Mechanistically, MC-LR exposure evoked excessive reactive oxygen species (ROS) and induced DNA double-strand break in GC-1 cells. Besides, MC-LR inhibited DNA repair by reducing PolyADP-ribosylation (PARylation) activity of PARP1. Further study found MC-LR caused proteasomal degradation of SIRT6, a monoADP-ribosylation enzyme which is essential for PARP1 PARylation activity, due to destruction of SIRT6-USP10 interaction. Additionally, MG132 pretreatment alleviated MC-LR-induced SIRT6 degradation and promoted DNA repair, leading to the restoration of cell proliferation inhibition. Correspondingly, N-Acetylcysteine (NAC) pre-treatment mitigated the disturbed SIRT6-USP10 interaction and SIRT6 degradation, causing recovered DNA repair and subsequently restoration of cell proliferation inhibition in MC-LR treated GC-1 cells. Together, pubertal exposure to MC-LR induced spermatogonia cell cycle arrest and sperm count reduction by oxidative DNA damage and simultaneous SIRT6-mediated DNA repair failing. This study reports the effect of pubertal exposure to MC-LR on spermatogenesis and complex mechanism how MC-LR induces spermatogonia cell proliferation inhibition.

Integration of Multi-Omics, Histological, and Biochemical Analysis Reveals the Toxic Responses of Nile Tilapia Liver to Chronic Microcystin-LR Exposure

Microcystin-LR (MC-LR) is a cyanobacterial metabolite produced during cyanobacterial blooms and is toxic to aquatic animals, and the liver is the main targeted organ of MC-LR. To comprehensively understand the toxicity mechanism of chronic exposure to environmental levels of MC-LR on the liver of fish, juvenile Nile tilapia were exposed to 0 μg/L (control), 1 μg/L (M1), 3 μg/L (M3), 10 μg/L (M10), and 30 μg/L (M30) MC-LR for 60 days. Then, the liver hepatotoxicity induced by MC-LR exposure was systematically evaluated via histological and biochemical determinations, and the underlying mechanisms were explored through combining analysis of biochemical parameters, multi-omics (transcriptome and metabolome), and gene expression. The results exhibited that chronic MC-LR exposure caused slight liver minor structural damage and lipid accumulation in the M10 group, while resulting in serious histological damage and lipid accumulation in the M30 group, indicating obvious hepatotoxicity, which was confirmed by increased toxicity indexes (i.e., AST, ALT, and AKP). Transcriptomic and metabolomic analysis revealed that chronic MC-LR exposure induced extensive changes in gene expression and metabolites in six typical pathways, including oxidative stress, apoptosis, autophagy, amino acid metabolism, primary bile acid biosynthesis, and lipid metabolism. Taken together, chronic MC-LR exposure induced oxidative stress, apoptosis, and autophagy, inhibited primary bile acid biosynthesis, and caused fatty deposition in the liver of Nile tilapia.

Microcystin-LR accelerates follicular atresia in mice via JNK-mediated adherent junction damage of ovarian granulosa cells

Microcystin-LR (MC-LR), one of aquatic environmental contaminants with reproductive toxicity produced by cyanobacterial blooms, but its toxic effects and mechanisms on the ovary are not fully understood. Here, proteomic techniques and molecular biology experiments were performed to study the potential mechanism of MC-LR-caused ovarian toxicity. Results showed that protein expression profile of ovarian granulosa cells (KK-1) was changed by 17 μg/mL MC-LR exposure. Comparing with the control group, 118 upregulated proteins as well as 97 downregulated proteins were identified in MC-LR group. Function of differentially expressed proteins was found to be enriched in pathways related to adherent junction, such as cadherin binding, cell-cell junction, cell adhesion and focal adherens. Furthermore, in vitro experiments, MC-LR significantly downregulated the expression levels of proteins associated with adherent junction (β-catenin, N-cadherin, and α-catenin) as well as caused cytoskeletal disruption in KK-1 cells (P < 0.05), indicating that the adherent junction was damaged. Results of in vivo experiments have shown that after 14 days of acute MC-LR exposure (40 μg/kg), damaged adherent junction and an increased number of atretic follicles were observed in mouse ovaries. Moreover, MC-LR activated JNK, an upstream regulator of adherent junction proteins, in KK-1 cells and mouse ovarian tissues. In contrast, JNK inhibition alleviated MC-LR-induced adherent junction damage in vivo and in vitro, as well as the number of atretic follicles. Taken together, findings from the present study indicated that JNK is involved in MC-LR-induced granulosa cell adherent junction damage, which accelerated follicular atresia. Our study clarified a novel mechanism of MC-LR-caused ovarian toxicity, providing a theoretical foundation for protecting female reproductive health from environmental pollutants.

State-of-the-art review on the ecotoxicology, health hazards, and economic loss of the impact of microcystins and their ultrastructural cellular changes

Cyanobacteria are ubiquitously globally present in both freshwater and marine environments. Ample reports have been documented by researchers worldwide for pros and cons of cyanobacterial toxins. The implications of cyanobacterial toxin on health have received much attention in recent decades. Microcystins (MCs) represent the unique class of toxic metabolites produced by cyanobacteria. Although the beneficial aspects of cyanobacterial are numerous, the deleterious effect of MCs overlooked. Several studies on MCs evidently reported that MCs exhibit a plethora of harmful effect on animals, plants, and cell lines. Accordingly, numerous histopathological studies have also found that MCs cause detrimental effects to cells by damaging cellular organelles, including nuclear envelope, Golgi apparatus, endoplasmic reticulum, mitochondria, plastids, flagellum, pilus membrane structures and integrity, vesicle structures, and autolysosomes and autophagosomes. Such ultrastructural cellular damages holistically influence the morphological, biochemical, physiological, and genetic status of the host. Indeed, MCs have also been found to cause the deleterious effect to different animals and plants. Such deleterious effects of MCs have greater impact on agriculture, public health which in turn influences ecotoxicology and economic consequences. The impairments correspond to oxidative stress, organ failure, carcinogenesis, aquaculture loss, with an emphasis for blooms and respective bioaccumulation prospects. The preservation of mortality among life forms is addressed in a critical cellular perspective for multitude benefits. The comprehensive cellular assessment could provide opportunity to develop strategy for therapeutic implications.

Review: Current understanding on biological filtration for the removal of microcystins

Harmful algal blooms (HABs) have become a global problem not only in aquatic habitats but also in public health and safety due to the production of cyanotoxins as their secondary metabolites. Among the various identified cyanotoxin groups, microcystins (MCs) are one of the most prevalent cyanotoxin detected during HABs. Different strategies including advanced physical and chemical treatment processes have been developed to mitigate the threat of cyanotoxins in water utilities, but these have revealed certain limitations in terms of high operational costs, low removal efficacy, and harmful by-products formation. Recently, biological filtration systems (BFS) have gained attention for safe drinking water production as they can treat various natural organic matter (NOM) and emerging contaminants through a highly efficient and environmentally sustainable process. However, limited attention has been given to understand the current research progress, research challenges, and knowledge gaps for the successful implementation of BFS for MC removal. Therefore, in this review, currently identified MC biodegradation pathways and MC-degrading microorganisms with their degradation rates are summarized, which may be pivotal for studying bioaugmented BFS to enhance the MC removal during HABs. Moreover, both laboratory and field studies on BFS for MC removal are reviewed, followed by a discussion of current challenges and future research needs for the practical application of BFS.

Impacts of algal organic matter and humic substances on microcystin-LR removal and their biotransformation during the biodegradation process

The application of bioaugmentation (i.e., injection of contaminant-degrading microorganisms) has shown its potential to remove harmful cyanotoxins like microcystin-LR (MC-LR) from drinking water sources. However, the natural organic matter (NOM) present in both natural and engineered water systems might affect the bacterial biodegradation of MC-LR. Therefore, for the successful application of bioaugmentation for MC-LR removal in water treatment, it is important to understand NOM effects on MC-LR biodegradation. In this study, the impact of NOM [algal organic matter (AOM) and humic substances (HS)] on MC-LR biodegradation was evaluated in the presence of varying concentrations of NOM by monitoring MC-LR biodegradation kinetics. The changes in NOM composition during MC-LR biodegradation were also characterized by a five-component Parallel factor (PARAFAC) model using 336 excitation-emission matrix (EEM) spectra collected at different sampling points. Our results showed decreases in MC-LR biodegradation rate of 1.6-and 3.4-fold in the presence of AOM and HS, respectively. The expression of the functional mlrA gene exhibited a similar trend to the MC-LR degradation rate at different NOM concentrations. EEM-PARAFAC analyses and NOM molecular size fractionation results indicated a relatively greater production of terrestrial humic-like components (57%) and a decrease of protein-like components. Two-dimensional correlation spectroscopy (2D-COS) analyses further confirmed that low molecular weight protein-like components were initially utilized by bacteria, followed by the formation of higher molecular weight humic-like components, likely due to microbial metabolism.

Antioxidant Therapy Significantly Attenuates Hepatotoxicity following Low Dose Exposure to Microcystin-LR in a Murine Model of Diet-Induced Non-Alcoholic Fatty Liver Disease

We have previously shown in a murine model of Non-alcoholic Fatty Liver Disease (NAFLD) that chronic, low-dose exposure to the Harmful Algal Bloom cyanotoxin microcystin-LR (MC-LR), resulted in significant hepatotoxicity including micro-vesicular lipid accumulation, impaired toxin metabolism as well as dysregulation of the key signaling pathways involved in inflammation, immune response and oxidative stress. On this background we hypothesized that augmentation of hepatic drug metabolism pathways with targeted antioxidant therapies would improve MC-LR metabolism and reduce hepatic injury in NAFLD mice exposed to MC-LR. We chose N-acetylcysteine (NAC, 40 mM), a known antioxidant that augments the glutathione detoxification pathway and a novel peptide (pNaKtide, 25 mg/kg) which is targeted to interrupting a specific Src-kinase mediated pro-oxidant amplification mechanism. Histological analysis showed significant increase in hepatic inflammation in NAFLD mice exposed to MC-LR which was attenuated on treatment with both NAC and pNaKtide (both p ≤ 0.05). Oxidative stress, as measured by 8-OHDG levels in urine and protein carbonylation in liver sections, was also significantly downregulated upon treatment with both antioxidants after MC-LR exposure. Genetic analysis of key drug transporters including Abcb1a, Phase I enzyme-Cyp3a11 and Phase II metabolic enzymes-Pkm (Pyruvate kinase, muscle), Pklr (Pyruvate kinase, liver, and red blood cell) and Gad1 (Glutamic acid decarboxylase) was significantly altered by MC-LR exposure as compared to the non-exposed control group (all p ≤ 0.05). These changes were significantly attenuated with both pNaKtide and NAC treatment. These results suggest that MC-LR metabolism and detoxification is significantly impaired in the setting of NAFLD, and that these pathways can potentially be reversed with targeted antioxidant treatment.

Effects of chronic exposure to environmental levels of tributyltin on the lined seahorse (Hippocampus erectus) liver: Analysis of bioaccumulation, antioxidant defense, and immune gene expression

Tributyltin (TBT), an organotin compound frequently detected in the coastal environments, poses a threat to aquatic organisms. The lined seahorse (Hippocampus erectus) is a vulnerable species found in nearshore water habitats. The mechanisms by which this fish responds to TBT exposure are not yet fully understood. Histological, biochemical, and transcriptional analyses were conducted, and the results showed that 60 days of exposure to 50 and 500 ng/L TBT caused significant tin accumulation and liver damage to seahorses. Antioxidant defenses and immune responses to TBT exposure in the livers of seahorses were further investigated. The enzymatic activity of superoxide dismutase and malondialdehyde content increased, while catalase activity decreased. Transcriptomic analysis revealed that a series of genes involved in the antioxidant defense system were highly induced to protect the hepatic cells from oxidative damage. TBT exposure also resulted in the induction of genes associated with immune and inflammatory processes, representing a stress response to combat the adverse environmental conditions in the exposed seahorses. Furthermore, seahorses showed an increased health risk, according to the elevation of the expression of genes with tumor-promoting effects, when exposed to TBT. These findings contribute to our understanding of the adverse effects of TBT exposure on seahorses, and their potential defense mechanisms.

Repeated exposure to microcystin-leucine-arginine potentiates excitotoxicity induced by a low dose of kainate

Microcystin-leucine-arginine (MLCR) is a cyanobacterial toxin, and has been demonstrated to cause neurotoxicity. In addition, MCLR has been identified as an inhibitor of protein phosphatase (PP)1 and PP2A, which are known to regulate the phosphorylation of various molecules related to synaptic excitability. Thus, in the present study, we examined whether MCLR exposure affects seizures induced by a low dose of kainic acid (KA; 0.05 μg, i.c.v.) administration. KA-induced seizure occurrence and seizure score significantly increased after repeated exposure to MCLR (2.5 or 5.0 μg/kg, i.p., once a day for 10 days), but not after acute MCLR exposure (2.5 or 5.0 μg/kg, i.p., 2 h and 30 min prior to KA administration), and hippocampal neuronal loss was consistently facilitated by repeated exposure to MCLR. In addition, repeated MCLR significantly elevated the membrane expression of kainate receptor GluK2 subunits, p-pan-protein kinase C (PKC), and p-extracellular signal-related kinase (ERK) at 1 h after KA. However, KA-induced membrane expression of Ca²⁺/calmodulin-dependent kinase II (CaMKII) was significantly reduced by repeated MCLR exposure. Consistent with the enhanced seizures and neurodegeneration, MCLR exposure significantly potentiated KA-induced oxidative stress and microglial activation, which was accompanied by increased expression of p-ERK and p-PKCδ in the hippocampus. The combined results suggest that repeated MCLR exposure potentiates KA-induced excitotoxicity in the hippocampus by increasing membrane GluK2 expression and enhancing oxidative stress and neuroinflammation through the modulation of p-CaMKII, p-PKC, and p-ERK.

Acute exposure to microcystin-LR induces hepatopancreas toxicity in the Chinese mitten crab (Eriocheir sinensis)

The Chinese mitten crab is an important economic species in the Chinese aquaculture industry due to its rich nutritional value and distinct flavor. The hepatopancreas is a popular edible part of the Chinese mitten crab, and therefore, hepatopancreatic health directly determines its quality. However, a large-scale outbreak of hepatopancreatic necrosis syndrome ("Shuibiezi" disease in Chinese), which is caused by abiotic agents correlated with cyanobacteria bloom outbreaks, adversely affects the Chinese mitten crab breeding industry. Cyanobacterial blooms that occur in high-density farming ponds can produce microcystin-LR (MC-LR), which is hepatotoxic in fish and mammals. Hepatopancreas toxicity of MC-LR (0, 25, 50 and 75 μg/kg) was investigated after 48 h of exposure. The MC-LR can cause hepatopancreatic injury by inducing hepatopancreatic structural damage, subcellular structural changes, and cell apoptosis, followed by enhanced lipid peroxidase, reactive oxygen species, and apoptosis-related enzyme (Caspase 3, 8, and 9) activities. These in turn promote gene and protein expression of apoptosis-associated proteases (Caspase 3, 7, and 8, Bcl-2, and Bax), and alter antioxidant system responses (superoxide dismutase, glutathione S-transferase, glutathione peroxidase, glutathione reductase activities, and glutathione content). The present study is the first report on MC-LR hepatotoxicity in the Chinese mitten crab and confirms hepatopancreas toxicity, providing a theoretical basis for enhancing MCs resistance and developing preventive and curative measures against hepatopancreatic disease in the Chinese mitten crab breeding industry.

Hydrogen peroxide-induced oxidative stress impairs redox status and damages aerobic metabolism of breast muscle in broilers

Oxidative stress has always been a hot topic in poultry science. However, studies concerning the effects of redox status and glucose metabolism induced by hydrogen peroxide (H₂O₂) in the breast muscle of broilers have been rarely reported. This study was aimed to evaluate the impact of intraperitoneal injection of H₂O₂ on oxidative damage and glycolysis metabolism of breast muscle in broilers. We also explored the activation of the nuclear factor erythroid 2–related factor 2 (Nrf2) signaling pathway to provide possible mechanism of the redox imbalance. Briefly, a total of 320 one-day-old Arbor Acres chicks were randomly divided into 5 treatments with 8 replicates of 8 birds each (noninjected control, 0.75% saline-injected, 2.5, 5.0, and 10.0% H₂O₂-injected treatments). Saline group was intraperitoneally injected with physiological saline (0.75%) and H₂O₂ groups received an intraperitoneal injection of H₂O_2. The dosage of the injection was 1.0 mL/kg BW. All birds in the saline and H₂O₂ groups were injected on days 16 and 37 of the experimental period. At 42 d of age, 40 birds (8 cages per group and one chicken per cage) were selected to be stunned electrically (50 V, alternating current, 400 Hz for 5 s each one), and then immediately slaughtered via exsanguination. The results showed that broilers in the H₂O₂ injection group linearly exhibited higher contents of reactive oxygen species, carbonyl and malondialdehyde, and lower total antioxidant capacity and glutathione peroxidase activities. With the content of H₂O₂ increased, the H₂O₂ groups linearly downregulated the mRNA expressions of GPX, CAT, HMOX1, NQO1, and Nrf2 and its downstream target genes. In addition, H₂O₂ increased serum activities of creatine kinase and lactate dehydrogenase. Meanwhile, in the pectoral muscle, the glycogen content was linearly decreased, and the lactate content was linearly increased in muscle of broilers injected with H₂O₂. In addition, the activities of glycolytic enzymes including pyruvate kinase, hexokinase, and lactate dehydrogenase were linearly increased after exposure to H₂O₂. In conclusion, H₂O₂ injection could impair antioxidant status and enhance anaerobic metabolism of breast muscle in broilers.

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.

α-Lipoic acid protects against microcystin-LR induced hepatotoxicity through regeneration of glutathione via activation of Nrf2

Microcystins (MCs), as the most dominant bloom-forming strains in eutrophic surface water, can induce hepatotoxicity by oxidative stress. Alpha-lipoic acid (α-LA) is a super antioxidant that can induce the synthesis of antioxidants, such as glutathione (GSH), by nuclear factor erythroid 2-related factor 2 (Nrf2). However, the potential molecular mechanism of α-LA regeneration of GSH remains unclear. The present study aimed to investigate whether α-LA could reduce the toxicity of MCs induced in human hepatoma (HepG2), Bel7420 cells, and BALB/c mice by activating Nrf2 to regenerate GSH. Results showed that exposure to 10 μM microcystin-leucine arginine (MC-LR) reduced viability of HepG2 and Bel7402 cells and promoted the formation of reactive oxygen species (ROS) compared with untreated cells. Moreover, the protection of α-LA included reducing the level of ROS, increasing superoxide dismutase activity, and decreasing malondialdehyde. Levels of reduced glutathione (rGSH) and rGSH/oxidized glutathione were significantly increased in cells cotreated with α-LA and MC-LR compared to those treated with MC-LR alone, indicating an ability of α-LA to attenuate oxidative stress and MC-LR-induced cytotoxicity by increasing the amount of rGSH. α-LA can mediate GSH regeneration through the Nrf2 pathway under the action of glutathione reductase in MC-LR cell lines. Furthermore, the data also showed that α-LA-induced cytoprotection against MC-LR is associated with Nrf2 mediate pathway in vivo. These findings demonstrated the potential of α-LA to resist MC-LR-induced oxidative damage of liver.

Epigenetic modification of H3K4 and oxidative stress are involved in MC-LR-induced apoptosis in testicular cells of SD rats

Microcystin-leucine arginine (MC-LR) is a cyclic heptapeptide, produced by aquatic cyanobacteria such as microcystis, with strong reproductive toxicity which poses greater threat to the reproductive abilities of humans and animals. By exploring the role of trimethylation of histone H3 at lysine 4 (H3K4me3) and the role of oxidative stress in MC-LR-induced apoptosis in testicular Sertoli cells in Sprague-Dawley (SD) rats, this study indicated that MC-LR increased the expression levels of apoptosis-related genes by raising the levels of H3K4me3. 5'-Deoxy-5'-methylthioadenosine (MTA), the inhibitor of H3K4me3, reduced apoptosis, indicating for the first time that epigenetic modification is closely related to the testicular reproductive toxicity induced by MC-LR. MC-LR also induced oxidative stress by stimulating the generation of reactive oxygen species (ROS), and subsequently triggering mitochondria-mediated apoptotic pathway by decreasing mitochondrial membrane potential and increasing the levels of Bax, Bcl-2, Caspase-3, and so on. MC-LR-induced apoptosis of testicular cells could be decreased after pretreatment with oxidative stress inhibitor N-acetyl-cysteine (NAC). Furthermore, the pathological damage to mitochondria and testes were observed in SD rats. These results show that MC-LR can induce apoptosis by raising the levels of H3K4me3, and pretreatment with MTA can ameliorate the MC-LR-induced apoptosis of cocultured cells by lowering the levels of H3K4me3. Furthermore, NAC has a protective effect on MC-LR-induced apoptosis of testicular cells in SD rats by inhibiting the oxidative stress.

Antioxidant Activity of Silymarin in Microcystin-LR Cardiac and Pulmonary Induced Injuries on Mice

BACKGROUND AND OBJECTIVES

Microcystin-LR has a toxic effect on several organs causing the destruction and fibrosis of these organs. This study was done to evaluate the antioxidant activity of silymarin on some oxidative stress parameters on heart and lung injuries induced by microcystin-LR in mice.

MATERIALS AND METHODS

Total 72 Balb/c male mice aged between five to seven weeks were grouped into 6; Group 1 contained twelve mice which were assigned as the healthy control group (C). Two microcystin-LR control groups assigned M6 and M12 contain 12 mice each. A fourth group contains twelve mice called the silymarin control group(S). The fifth and sixth groups contain twenty-four mice assigned as microcystin-LR silymarin groups SM6 and SM12. A blood sample was collected for estimation of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST). The homogenates of heart and lungs were extracted for estimation of protein carbonyl content (CC), lipid peroxidation products (LPO), reduced glutathione (GSH), methylglyoxal (MG) and activity of protein phosphatase I (PPI).

RESULTS

Significant statistical differences in both ALT and AST were observed between all groups (P>0.01). In cardiac homogenate, a significant statistical difference was observed in PPI, LPO and CC between all groups (P<0.05). Furthermore, methylglyoxal showed a significant statistical difference between all groups (p<0.01).

CONCLUSION

The findings suggested a potential therapeutic role of using silymarin as an antioxidant agent against cardiac and pulmonary injuries induced by MC-LR.

Microcystin-LR exposure decreased the fetal weight of mice by disturbance of placental development and ROS-mediated endoplasmic reticulum stress in the placenta

The placenta is essential for sustaining the growth of the fetus. The aim of this study was to investigate the role of the placenta in MCLR-induced significant reduction in fetal weight, especially the changes in placental structure and function. Pregnant mice were intraperitoneally injected with MCLR (5 or 20 μg/kg) from gestational day (GD) 13 to GD17. The results showed MCLR reduced fetal weight and placenta weight. The histological specimens of the placentas were taken for light and electron microscopy studies. The internal space of blood vessels decreased obviously in the placental labyrinth layer of mice treated with MCLR. After the ultrastructural examination, the edema and intracytoplasmic vacuolization, dilation of the endoplasmic reticulum and corrugation of the nucleus were observed. In addition, maternal MCLR exposure caused a reduction of 11β-hydroxysteroid dehydrogenase type 2 (HSD11B2) expression in placentae, a critical regulator of fetal development. Several genes of placental growth factors, such as Vegfα and Pgf and several genes of nutrient transport pumps, such as Glut1 and Pcft were depressed in placentas of MCLR-treated mice, however nutrient transporters Fatp1 and Snat4 were promoted. Moreover, significant increases in malondialdehyde (MDA) revealed the occurrence of oxidative stress caused by MCLR, which was also verified by remarkable decrease in the glutathione levels, total antioxidant capacity (T-AOC) as well as the activity of antioxidant enzymes. Real-time PCR and western blot analysis revealed that GRP78, CHOP, XBP-1, peIF2α and pIRE1 were remarkable increased in placentas of MCLR-treated mice, indicating that endoplasmic reticulum (ER) stress pathway was activated by MCLR. Furthermore, oxidative stress and ER stress consequently triggered apoptosis which contributed to the impairment of placental development. Collectively, these results suggest maternal MCLR exposure results in reduced fetal body weight, which might be associated with ROS-mediated endoplasmic reticulum stress and impairment in placental structure and function.

A Review of Cardiovascular Toxicity of Microcystins

The mortality rate of cardiovascular diseases (CVD) in China is on the rise. The increasing burden of CVD in China has become a major public health problem. Cyanobacterial blooms have been recently considered a global environmental concern. Microcystins (MCs) are the secondary products of cyanobacteria metabolism and the most harmful cyanotoxin found in water bodies. Recent studies provide strong evidence of positive associations between MC exposure and cardiotoxicity, representing a threat to human cardiovascular health. This review focuses on the effects of MCs on the cardiovascular system and provides some evidence that CVD could be induced by MCs. We summarized the current knowledge of the cardiovascular toxicity of MCs, with regard to direct cardiovascular toxicity and indirect cardiovascular toxicity. Toxicity of MCs is mainly governed by the increasing level of reactive oxygen species (ROS), oxidative stress in mitochondria and endoplasmic reticulum, the inhibition activities of serine/threonine protein phosphatase 1 (PP1) and 2A (PP2A) and the destruction of cytoskeletons, which finally induce the occurrence of CVD. To protect human health from the threat of MCs, this paper also puts forward some directions for further research.

Microcystin-LR promotes necroptosis in primary mouse hepatocytes by overproducing reactive oxygen species

Microcystin-LR (MC-LR) is a type of cyclic heptapeptide toxin produced by cyanobacteria during bloom events. MC-LR-induced cell death is critically involved in its potent specific hepatotoxicity. Many studies have demonstrated that prototypical apoptosis as a form of programmed cell death after MC-LR is associated with liver injury. However, whether another form of programmed cell death exists and the underlying mechanism have not been reported. Here, we demonstrate that MC-LR can induce necroptosis via ROS overactivation in primary mouse hepatocytes. Various potential pathways of programmed cell death induced by MC-LR were evaluated by annexin V/PI dual staining for flow cytometric analysis, image-based PI staining analysis and western blot analysis. Cell viability was determined by the CCK8 assay. Rupture of the plasma membrane was indicated by lactate dehydrogenase release. ROS was evaluated with the carboxy-H2DCFDA fluorescent probe. It was found that in MC-LR-treated cells, as the plasma membrane was damaged, annexin V/PI-stained double-positive cells were significantly induced and PI-stained nuclei were more diffuse. Western blot analysis showed that MC-LR treatment significantly upregulated the expression of necroptotic and apoptotic proteins. Mechanistically, MC-LR induced ROS overproduction by dysregulating the expression and activity of the pro-oxidants SOD1, MAOA, and NOX4 and the antioxidant GPX1. These results indicate the presence of a novel mechanism for MC-LR-mediated liver injury and present a novel target in the treatment of MC-LR-exposed patients.

Heat-induced protein oxidation of soybean meal impairs growth performance and antioxidant status of broilers

This study aimed to evaluate the impact of oxidative modification on soybean meal (SBM) proteins after exposure to different heating times, and the effects of the oxidized SBM on the growth performance [average daily feed intake (ADFI), average daily gain (ADG), and feed to gain ratio (F: G)], oxidative redox status [(reactive oxygen species (ROS), total antioxidant capacity (TAC), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), malondialdehyde (MDA), and protein carbonyl (PC)]. A total of 400 one-day-old Arbor Acres chicks were randomly divided into 5 treatment groups with 8 replicates of 10 birds each. Birds in the control group (CON) were fed diet containing non-heated SBM, and those in the treatment groups were fed SBM heated at 100°C for 1, 2, 4, and 8 h, for 42 d. Heated SBM (HSBM) showed a relatively higher PC content in vitro. The ADG decreased, whereas the F:G increased linearly with an increase in heating time during the starter (days 1 to 21), grower (days 22 to 42), and the overall growth phases (days 1 to 42; P < 0.05). However, the ADFI decreased linearly only during the grower phase (P < 0.05). The plasma, liver, and jejunum ROS levels, MDA concentrations, and PC contents increased linearly (P < 0.05) in broilers fed HSBM. Furthermore, the TAC in the plasma and jejunum, and the total SOD and GSH-Px activities in the plasma, liver, and jejunum decreased linearly (P < 0.05) in broilers when feeding HSBM. (P < 0.05). The mRNA level of Nrf2 in the liver and jejunum was lower (P < 0.05) in broilers fed diet containing the SBM after 8 h heat-treatment than in those fed the CON diet at days 42. This study suggested that heat-induced protein oxidation of SBM could decrease growth performance and impair antioxidant status of broilers.

Impact of Microcystin-LR on Liver Function Varies by Dose and Sex in Mice

Microcystin (MC) exposure is an increasing concern because more geographical locations are covered with cyanobacterial blooms as eutrophication and bloom-favoring environmental factors become more prevalent worldwide. Acute MC exposure has been linked to gastrointestinal distress, liver toxicity, and death in extreme circumstances. The goal of this study was to provide an accurate and comprehensive description of MC-LRs impacts on liver pathology, clinical chemistry, and gap junction intercellular communication (GJIC) in CD-1 male and female mice. Mice were exposed to 0, 3000, and 5000/4000 µg/kg/day MC-LR, daily for 7 days, and were necropsied on Day 8. Blood samples for clinical chemistry analysis were processed to serum, while liver sections were fixed for histopathology or evaluated for GJIC using fluorescent cut-load dye. Results show a dose-dependent relationship with MC-LR exposure and hepatocellular hypertrophy, degradation, and necrosis. Clinical chemistry parameters alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, total bilirubin, and cholesterol increased significantly in MC-LR exposed mice. Clinical chemistry parameter analysis showed significantly increased susceptibility to MC-LR in females compared to males. Changes in GJIC were not noted, but localization of hepatotoxicity near the central veins and midlobular areas was seen. Future toxicity studies involving MCs should consider response differences across sexes, differing MC congeners, and combinatorial exposures involving other cyanotoxins.

Glutathione peroxidase-1 overexpressing transgenic mice are protected from neurotoxicity induced by microcystin-leucine-arginine

Although it has been well-recognized that microcystin-leucine-arginine (MCLR), the most common form of microcystins, induces neurotoxicity, little is currently known about the underlying mechanism for this neurotoxicity. Here, we found that MCLR (10 ng/μL/mouse, i.c.v.) induces significant neuronal loss in the hippocampus of mice. MCLR-induced neurotoxicity was accompanied by oxidative stress, as shown by a significant increase in the level of 4-hydroxynonenal, protein carbonyl, and reactive oxygen species (ROS). Superoxide dismutase-1 (SOD-1) activity was significantly increased, but glutathione peroxidase (GPx) level was significantly decreased following MCLR insult. In addition, MCLR significantly inhibited GSH/GSSG ratio, and significantly induced NFκB DNA binding activity. Because reduced activity of GPx appeared to be critical for the imbalance between activities of SODs and GPx, we utilized GPx-1 overexpressing transgenic mice to ascertain the role of GPx-1 in this neurotoxicity. Genetic overexpression of GPx-1 or NFκB inhibitor pyrrolidine dithiocarbamate (PDTC) significantly attenuated MCLR-induced hippocampal neuronal loss in mice. However, PDTC did not exert any additive effect on neuroprotection mediated by GPx-1 overexpression, indicating that NFκB is a neurotoxic target of MCLR. Combined, these results suggest that MCLR-induced neurotoxicity requires oxidative stress associated with failure in compensatory induction of GPx, possibly through activation of the transcription factor NFκB.

Effect of crude extracts from Nodularia spumigena on round goby (Neogobius melanostomus)

Nodularia spumigena is a nitrogen-fixing filamentous cyanobacteria in the Baltic Sea. Nodularin (NOD), the hepatotoxic peptide produced by this cyanobacterium, accumulates in the organisms from different trophic levels. In this paper, the effects of N. spumigena cell extract on the round goby (Neogobius melanostomus) was investigated under laboratory conditions. This benthic fish species feed on mussels in which nodularin accumulation was well documented. In current study a sharp increase in the NOD concentration in analyzed organs was observed after 24 h (PPIA) after 72 h of exposure (LC/MS). To determine the direction and strength of the changes induced in the fish by the toxin, several biochemical markers of exposure such as concentration of glutathione and activities of catalase, guaiacol peroxidase and glutathione S-transferase were used. In analyzed organs (liver, gills and muscle) of the round goby, the activity of these enzymes were suppressed. Higher GSH/protein amount and CAT and POD activity in gills than in liver reflects the importance of gills in NOD entering into analyzed fish body when exposed to toxin. The results indicate that the round goby (Neogobius melanostomus) exposed to extracts from N. spumigena cells triggered a defense system in a time-dependent manner. The obtained results contribute to a better understanding of fish response to the presence of compounds produced by N. spumigena.

Electrochemical Biosensing of Algal Toxins in Water: The Current State-of-the-Art

Due to increasing stringency of water legislation and extreme consequences that failure to detect some contaminants in water can involve, there has been a strong interest in developing electrochemical biosensors for algal toxin detection during the past decade, evidenced by literature increasing from 2 journal papers pre-2009 to 24 between 2009 and 2018. In this context, this review has summarized recent progress of successful algal toxin detection in water using electrochemical biosensing techniques. Satisfactory detection recoveries using real environmental water samples and good sensor repeatability and reproducibility have been achieved, along with some excellent limit-of-detection (LOD) reported. Recent electrochemical biosensor literature in algal toxin detection is compared and discussed to cover three major design components: (1) biorecognition elements, (2) electrochemical read-out techniques, and (3) sensor electrodes and signal amplification strategy. The recent development of electrochemical biosensors has provided one more step further toward quick in situ detection of algal toxins in the contamination point of the water source. In the end, we have also critically reviewed the current challenges and research opportunities regarding electrochemical biosensors for algal toxin detection that need to be addressed before they attain commercial viability.

Terminalia arjuna bark extract attenuates picrotoxin-induced behavioral changes by activation of serotonergic, dopaminergic, GABAergic and antioxidant systems

Stress and emotion are associated with several illnesses from headaches to heart diseases and immune deficiencies to central nervous system. Terminalia arjuna has been referred as traditional Indian medicine for several ailments. The present study aimed to elucidate the effect of T. arjuna bark extract (TA) against picrotoxin-induced anxiety. Forty two male Balb/c mice were randomly divided into six experimental groups (n = 7): control, diazepam (1.5 mg·kg^-1), picrotoxin (1 mg·kg^-1) and three TA treatemt groups (25, 50, and 100 mg/kg). Behavioral paradigms and PCR studies were performed to determine the effect of TA against picrotoxin-induced anxiety. The results showed that TA supplementation increased locomotion towards open arm (EPM) and illuminated area (light-dark box test), and increased rearing frequency (open field test) in a dose dependent manner, compared to picrotoxin (P < 0.05). Furthermore, TA increased number of licks and shocks in Vogel's conflict. PCR studies showed an up-regulation of several genes, such as BDNF, IP₃, D₂L, CREB, GABA_A, SOD, GPx, and GR in TA administered groups. In conclusion, alcoholic extract of TA bark showed protective activity against picrotoxin in mice by modulation of genes related to synaptic plasticity, neurotransmitters, and antioxidant enzymes.

Genetic overexpression of glutathione peroxidase-1 attenuates microcystin-leucine-arginine-induced memory impairment in mice

Microcystin-leucine-arginine (MCLR) is the most common form of microcystins, which are environmental toxins produced by cyanobacteria, and its hepatotoxicity has been well-documented. However, the neurotoxic potential of MCLR remains to be further elucidated. In the present study, we investigated whether intracerebroventricular (i.c.v.) infusion of MCLR induces mortality and neuronal loss in the hippocampus of mice. Because we found that MCLR impairs memory function in the hippocampus at a low dose (4 ng/μl/mouse, i.c.v.) without a significant neuronal loss, we focused on this dose for further analyses. Results showed that MCLR (4 ng/μl/mouse, i.c.v.) significantly increased oxidative stress (i.e., malondialdehyde, protein carbonyl, and synaptosomal ROS) in the hippocampus. In addition, MCLR significantly increased superoxide dismutase (SOD) activity without corresponding induction of glutathione peroxidase (GPx) activity, and thus led to significant decrease in the ratio of GPx/SODs activity. The GSH/GSSG ratio was also significantly reduced after MCLR treatment. GPx-1 overexpressing transgenic mice (GPx-1 Tg) were significantly protected from MCLR-induced memory impairment and oxidative stress. The DNA binding activity of nuclear factor erythroid-derived 2-related factor 2 (Nrf2) in these mice was significantly enhanced, and the ratios of GPx/SODs activity and GSH/GSSG returned to near control levels in the hippocampus. Importantly, memory function exhibited a significant positive correlation with the ratios of GPx/SODs activity and GSH/GSSG in the hippocampus of MCLR-treated non-transgenic (non-Tg)- and GPx-1 Tg-mice. Combined, our results suggest that MCLR induces oxidative stress and memory impairment without significant neuronal loss, and that GPx-1 gene constitutes an important protectant against MCLR-induced memory impairment and oxidative stress via maintaining antioxidant defense system homeostasis, possibly through the induction of Nrf2 transcription factor.

Microcystis bloom containing microcystin-LR induces type 2 diabetes mellitus

Epidemiological data from Lake Taihu showed significantly higher incidences of type 2 diabetes mellitus (T2DM) than in other areas of China. This may be related to the occurrence of a Microcystis bloom in Lake Taihu in the summer and autumn every year. The objective of this study is to investigate whether the contaminated water from the Microcystis bloom and the derivative pollutant microcystin-LR (MC-LR) can explain the higher incidences of T2DM. Healthy male mice were fed with water from different regions of Lake Taihu, and were either acutely or chronically exposed to MC-LR through oral administration or intraperitoneal injection. Serum lipid profiles were determined, and the effects on T2DM-related gene expression and insulin receptor signaling pathway were investigated. Intraperitoneal glucose tolerance (IPGTT) and insulin resistance (IRT) tests were implemented, and the functions of pancreatic islet and β-cell were also evaluated. The results showed that both water sampled from the region with a Microcysis bloom and those containing MC-LR altered the serum glucide and lipid profiles in mice after exposure. The exposure to a Microcysis bloom water affected the expression T2DM-related genes: up-regulated the mRNA levels of FASn, ACACA, G6pc, LPL, and Insig2, and down-regulated the mRNA level of PEPCK and Gsk-3β. Both acute and chronic exposure of MC-LR, even at very low concentrations (1 μg/L), impaired the insulin receptor signalling pathway and induced hyperinsulinemia and insulin resistance in mice. In this study, the most important intracellular target of MC-LR was found to be hetapocellular mitochondria. Thus, exposure to Microcystis bloom water containing microcystin-LR can induce the incidence of T2DM, by impairing the function of mitochondria by microcystin-LR. The study suggests a review of the risk assessment concerning 1 μg/L MC-LR as the reference dose in surface water.

Oxidative imbalance in mice intoxicated by microcystin-LR can be minimized

Microcystins-LR (MC-LR) is a cyanotoxin produced by cyanobacteria. We evaluated the antioxidant potential of LASSBio-596 (LB-596, inhibitor of phosphodiesterases 4 and 5), per os, and biochemical markers involved in lung and liver injury induced by exposure to sublethal dose of MC-LR. Fifty male Swiss mice received an intraperitoneal injection of 60 μL of saline (CTRL group, n = 20) or a sublethal dose of MC-LR (40 μg/kg, TOX group, n = 20). After 6 h the animals received either saline (TOX and CTRL groups) or LB-596 (50 mg/kg, TOX + LASS group, n = 10) by gavage. At 6 h after exposure, respiratory mechanics was evaluated in 10 CTRL and 10 TOX mice: there was a significant increase of all lung mechanics parameters (static elastance, viscoelastic component of elastance and lung resistive and viscoelastic/inhomogeneous pressures) in TOX compared to CTRL. 8 h after saline or MC-LR administration, i.e., 2 h after treatment with LB-596, blood serum levels of alanine aminotransferase and aspartate aminotransferase, activity of superoxide dismutase, catalase, and content of malondialdehyde and carbonyl in lung and liver, NADPH oxidase 2 and 4 mRNA expressions, dual oxidase enzyme activity and H₂O₂ generation were analyzed in lung homogenates. All parameters were significantly higher in TOX than in the other groups. There was no significant difference between CTRL and TOX + LASS. MC-LR deteriorated lung and liver functions and induced redox imbalance in them, which was prevented by oral administration of LB-596.

Microcystin-leucine-arginine Modulates the Expression Patterns of Proinflammatory Cytokines and an Apoptotic Gene in Chicken Liver

Microcystins (MCs) are included in drinking water and a family of cyclic heptapeptide hepatotoxins that have been implicated in the impairment of liver function in various animals. There is scarce information on the effect of MCs on cytokines and apoptotic gene expression and on whether MCs can induce inflammation and apoptosis in avian hepatic tissue. This study investigated the expression of genes related to proinflammatory interleukins, apoptosis, and antioxidant function in chicken liver tissues cultured in the presence of different doses of microcystin-leucine-arginine (MC-LR). Livers were collected from five hens and liver slices were placed in sterile tubes containing Dulbecco's medium supplemented with 0, 1, 10, or 100 ng/mL of MC-LR. After 6 h of cultivation, total RNA was extracted and quantitative PCR analysis was performed for interleukin genes (IL-1β, IL-6, and IL-8), TNF sf15, an apoptotic gene (caspase-3), and genes involved in antioxidant function ([catalase [CAT ], glutathione peroxidase [GSH-PX ], and superoxide dismutase [SOD]). Liver tissues in each group were fixed for histopathology. MC-LR downregulated the mRNA levels of IL-1β, IL-8, and TNF sf15 as compared to the control (0 ng/mL) in dose-dependent patterns; however, the differences were not significant. The expression of IL-6 in liver tissues exposed to 100 ng/mL of MC-LR was significantly (P<0.05) lower than that in tissues exposed to 1 ng/mL. In contrast, MC-LR upregulated the mRNA expression of caspase-3 and genes involved in antioxidant function in the liver tissues after 6 h, without the difference reaching statistical significance. Hepatocytes showed vacuolar degeneration and focal necrosis according to the dose of MC-LR. This study highlighted the risk of low doses of MC-LR in chicken liver. Moreover, MC-LR could modulate the transcriptional patterns of at least IL-6 in liver-tissue culture of chicken after 6 h of exposure.

Modulatory effects of Terminalia arjuna against domoic acid induced toxicity in Caco-2 cell line

Domoic acid is a potent marine algal toxin produced by diatomic genus of Pseudo-nitzschia causing amnesic shell fish poisoning. Domoic acid toxicosis mainly involves excitotoxic effects coupled with oxidative stress. The present study was aimed to evaluate the protective effects of hydro-alcoholic extract of Terminalia arjuna (TA) against domoic acid induced toxic effects in Caco-2 cell line. It was observed that the toxicity induced by domoic acid in Caco-2 cells was mediated by oxidative insult leading to morphological changes, DNA damage and apoptosis. In our study pre-treatment of the cells with TA (10, 20 and 30 μg/ml) showed significant protection against domoic acid induced morphological, oxidative and apoptotic damages in a dose dependent manner. The effect of phytocompounds present in TA viz., kaempferol and arjungenin showed significant protection against domoic acid induced toxicity in Caco-2 cell line. Hence, it could be inferred that the protective effect of TA extract against domoic acid induced toxicity could be due to the individual or synergistic effects of kaempferol and argungenin. However, further clinical studies are warranted to consider TA as a natural remedy to prevent amnesic shell fish poisoning.

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.

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.

Evaluation of chemopreventive potential of Strobilanthes crispus against colon cancer formation in vitro and in vivo

Background

With cancer being one of the major causes of death around the world, studies are ongoing to find new chemotherapeutic leads. There are common mechanisms for colorectal cancer (CRC) formation. Several are connected with oxidative stress-induced cell apoptosis and others are related to imbalanced homeostasis or intake of drugs/toxins. Plants that have been used for decades in folk and traditional medicine have been accepted as one of the commonest sources of discovered natural agents of cancer chemotherapy and chemoprevention. The aim was to study the antioxidant and chemopreventive effects of Strobilanthes crispus on colorectal cancer formation.

Methods

Five groups of rats were injected subcutaneously with AOM, 15 mg/kg body weight, each once weekly for 2 weeks. The cancer group was continued on 10 % Tween-20 feeding for 8 weeks. The standard drug group was continued on 35 mg/kg 5-fluorouracil intraperitoneal injection twice a week for 8 weeks, and the experimental groups were continued on 250 and 500 mg/kg S. crispus extract oral feeding for 8 weeks, respectively. The normal group was injected subcutaneously with normal saline once a week for 2 weeks, followed by oral administration of 10 % Tween-20 for 8 weeks. All the rats were sacrificed after 10 weeks. The colons were evaluated grossly and histopathologically for aberrant crypt foci (ACF). Gene expression was performed for Bax, Bcl2, Defa24, Slc24a3, and APC genes by real-time PCR. S. crispus and its fractions were evaluated for their chemopreventive effects against human colorectal adenocarcinoma cell line HT29 and cytotoxicity for normal human colon epithelial cell line CCD 841, and the active fraction was assessed for its components.

Results

We observed significant decrease in total colonic ACF formation, malonaldehyde (MDA) and lactate dehydrogenase (LDH), increase in superoxide dismutase (SOD), up-regulation of APC, Bax and Slc24a3, and down-regulation of Defa24 and Bcl-2 in rats treated with Strobilanthes crispus.

Conclusion

Our results support the in vivo protection of S. crispus against CRC formation (azoxymethane-induced aberrant crypt foci) and suggest that the mechanism is highly specific to protect from oxidative insults and the following apoptotic cascade.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-015-0926-7) contains supplementary material, which is available to authorized users.

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.

Resveratrol ameliorates cisplatin-induced oxidative injury in New Zealand rabbits

This study investigated the preventive role of resveratrol in cisplatin-induced nephrotoxicity. The study used groups of New Zealand rabbits that were treated as follows: group C (cisplatin treated), group R (resveratrol treated), group R+C (resveratrol + cisplatin treatment), and group E (control group). Kidney levels of glutathione were significantly lower in group C than in groups E and R, whereas glutathione levels in group R+C were found to be similar to the control values. Malondialdehyde levels in group C were significantly higher than in groups E and R. However, malondialdehyde levels in group R+C were similar to group E. Kidney levels of nitric oxide were significantly higher in the cisplatin group than in the control, whereas nitric oxide levels were at basal values in group R+C. Cisplatin treatment significantly reduced kidney levels of glutathione peroxidase, superoxide dismutase, and catalase activity compared with those of group E, whereas resveratrol treatment significantly increased levels of glutathione peroxidase, superoxide dismutase, and catalase activity in group R+C. However, cisplatin injection did not affect mRNA levels of glutathione peroxidase, superoxide dismutase, or catalase enzymes. Histopathological and immunohistochemical analyses indicated that cisplatin caused kidney damage, which was mostly prevented by resveratrol treatment. In conclusion, resveratrol ameliorates cisplatin-induced oxidative injury in the kidney of rabbit.

Recognizing the importance of exposure-dose-response dynamics for ecotoxicity assessment: nitrofurazone-induced antioxidase activity and mRNA expression in model protozoan Euplotes vannus

The equivocality of dose-response relationships has, in practice, hampered the application of biomarkers as a means to evaluate environmental risk, yet this important issue has not yet been fully recognized or explored. This paper evaluates the potential of antioxidant enzymes in the ciliated protozoan Euplotes vannus for use as biomarkers. Dose-response dynamics, together with both the enzyme activity and the gene expression of the antioxidant enzymes, superoxide dismutase, and glutathione peroxidase, were investigated when E. vannus were exposed to graded doses of nitrofurazone for several discrete durations. Mathematical models were explored to characterize the dose-response profiles and, specifically, to identify any equivocality in terms of endpoint. Significant differences were found in both enzyme activity and messenger RNA (mRNA) expression in the E. vannus treated with nitrofurazone, and the interactions between exposure dosage and duration were significant. Correlations between enzyme activity, mRNA expression, and nitrofurazone dose varied with exposure duration. Particularly, the dose-responses showed different dynamics depending on either endpoint or exposure duration. Our findings suggest that both the enzyme activity and the gene expression of the tested antioxidant enzymes can be used as biomarkers for ecotoxicological assessment on the premise of ascertaining appropriate dosage scope, exposure duration, endpoint, etc., which can be achieved by using dose-response dynamics.

Alteration in the expression of cytochrome P450s (CYP1A1, CYP2E1, and CYP3A11) in the liver of mouse induced by microcystin-LR

Microcystins (MCs) are cyclic heptapeptide toxins and can accumulate in the liver. Cytochrome P450s (CYPs) play an important role in the biotransformation of endogenous substances and xenobiotics in animals. It is unclear if the CYPs are affected by MCs exposure. The objective of this study was to evaluate the effects of microcystin-LR (MCLR) on cytochrome P450 isozymes (CYP1A1, CYP2E1, and CYP3A11) at mRNA level, protein content, and enzyme activity in the liver of mice the received daily, intraperitoneally, 2, 4, and 8 µg/kg body weight of MCLR for seven days. The result showed that MCLR significantly decreased ethoxyresorufin-O-deethylase (EROD) (CYP1A1) and erythromycin N-demthylase (ERND) (CYP3A11) activities and increased aniline hydroxylase (ANH) activity (CYP2E1) in the liver of mice during the period of exposure. Our findings suggest that MCLR exposure may disrupt the function of CYPs in liver, which may be partly attributed to the toxicity of MCLR in mice.

Effect of hydroalcoholic extract of Aegle marmelos fruit on radical scavenging activity and exercise-endurance capacity in mice

CONTEXT

Aegle marmelos L. Corr (Rutaceae) is an important Indian Ayurvedic medicinal plant used for the treatment of various ailments. However, little information is available on the anti-fatigue properties of its fruit.

OBJECTIVE

Evaluation of the physical endurance and exercise-induced oxidative stress modulating properties of A. marmelos fruit in mice.

MATERIAL AND METHODS

Radical scavenging activity of the fruit hydroalcoholic extract was evaluated using in vitro systems. The extract was further evaluated for its endurance-enhancing properties at three oral doses (100, 200 and 400 mg/kg b.wt) in BALB/c mice for 21 d using a swimming test.

RESULTS AND DISCUSSION

The extract exhibited significant scavenging activity against DPPH (IC₅₀, 351 ± 37 µg/ml) and ABTS radicals (IC₅₀, 228 ± 25 µg/ml), respectively, with the polyphenol content of 95 µg/mg extract. It also inhibited AAPH radical-induced oxidation of biomolecules such as BSA protein (63%), plasmid DNA (81%) and lipids (80.5%). Administration of extract resulted in an increase in the duration of swimming time to exhaustion by 23.4 and 47.5% for medium and higher doses, respectively. The extract significantly normalized the fatigue-related biochemical parameters and also down-regulated the swim stress-induced over-expression of heat shock protein-70 and up-regulated the skeletal muscle metabolic regulators (GLUT-4 and AMPK1-α) by 2- and 3-fold, respectively, at the higher dose in muscle tissues.

CONCLUSION

Our study demonstrates the anti-fatigue properties of A. marmelos fruit, most probably manifested by delaying the accumulation of serum lactic acid, increasing the fat utilization and up-regulating the skeletal muscle metabolic regulators.

Overexpression of Nrf2 protects against microcystin-induced hepatotoxicity in mice

Oxidative stress and glutathione (GSH) depletion are implicated in mycocystin hepatotoxicity. To investigate the role of nuclear factor erythroid 2-related factor 2 (Nrf2) in microcystin-induced liver injury, Nrf2-null, wild-type, and Keap1-hepatocyte knockout (Keap1-HKO) mice were treated with microcystin (50 μg/kg, i.p.). Blood and liver samples were collected 8 h thereafter. Microcystin increased serum alanine aminotransferase and aspartate aminotransferase activities, and caused extensive inflammation and necrosis in Nrf2-null and wild-type mice, but not in Keap1-HKO mice. Oxidative stress and inflammation are implicated in microcystin-induced hepatotoxicity, as evidenced by increased lipid peroxidation and increased expression of pro-inflammatory genes, such as neutrophil-specific chemokines mKC and MIP-2, and pro-inflammatory cytokines IL-1β and IL-6. The increased expression of these pro-inflammatory genes was attenuated in Keap1-HKO mice. Nrf2 and Nqo1 mRNA and protein were higher in Keap1-HKO mice at constitutive levels and after microcystin. To further investigate the mechanism of the protection, hepatic GSH and the mRNA of GSH-related enzymes were determined. Microcystin markedly depleted liver GSH by 60–70% in Nrf2 and WT mice but only 35% in Keap1-HKO mice. The mRNAs of GSH conjugation and peroxide reduction enzymes, such as Gstα1, Gstα4, Gstμ, and Gpx2 were higher in livers of Keap1-HKO mice, together with higher expression of the rate-limiting enzyme for GSH synthesis (Gclc). Organic anion transport polypeptides were increased by microcystin with the most increase in Keap1-HKO mice. In conclusion, this study demonstrates that higher basal levels of Nrf2 and GSH-related genes in Keap1-HKO mice prevented microcystin-induced oxidative stress and liver injury.

Gene expression profiles in zebrafish (Danio rerio) liver after acute exposure to okadaic acid

Okadaic acid (OA), a main component of diarrheic shellfish poisoning (DSP) toxins, is a strong and specific inhibitor of the serine/threonine protein phosphatases PP1 and PP2A. However, not all of the OA-induced effects can be explained by this phosphatase inhibition, and controversial results on OA are increasing. To provide clues on potential mechanisms of OA other than phosphatase inhibition, here, acute toxicity of OA was evaluated in zebrafish, and changes in gene expression in zebrafish liver tissues upon exposure to OA were observed by microarray. The i.p. ED50 (6 h) of OA on zebrafish was 1.54 μg OA/g body weight (bw). Among the genes analyzed on the zebrafish array, 55 genes were significantly up-regulated and 36 down-regulated in the fish liver tissue upon exposure to 0.176 μg OA/g bw (low-dose group, LD) compared with the low ethanol control (LE). However, there were no obvious functional clusters for them. On the contrary, fish exposure to 1.760 μg OA/g bw (high-dose group, HD) yielded a great number of differential expressed genes (700 up and 285 down) compared with high ethanol control (HE), which clustered in several functional terms such as p53 signaling pathway, Wnt signaling pathway, glutathione metabolism and protein processing in endoplasmic reticulum, etc. These genes were involved in protein phosphatase activity, translation factor activity, heat shock protein binding, as well as transmembrane transporter activity. Our findings may give some useful information on the pathways of OA-induced injury in fish.

Characterizing dose-responses of catalase to nitrofurazone exposure in model ciliated protozoan Euplotes vannus for ecotoxicity assessment: enzyme activity and mRNA expression

In environmental studies, some biological responses, known as biomarkers, have been used as a powerful bioassay tool for more than four decades. Disparity between enzyme activity and mRNA abundance leads to correlation equivocality, which makes the application of biomarkers for environmental risk assessment more complicated. This study investigates this disparity in the case of catalase when used as a biomarker for detecting ecotoxicity induced by antibiotics in aquatic ecosystems. In particular, dose-responses for catalase activity and mRNA expression abundance were investigated in Euplotes vannus which were exposed to graded doses of nitrofurazone for several discrete durations, and dose-response models were developed to characterize the dose-response dynamics. Significant differences were found in both catalase activity and mRNA expression abundance among the E. vannus treated with nitrofurazone. Catalase activity showed a hormetic-like effect in terms of dose-response, characterized by a biphasic relationship which was more clearly evident after a longer exposure period, while mRNA expression abundance increased linearly with the exposure duration. Additionally, the correlation between catalase activity and mRNA expression abundance reversed along with the duration of exposure to nitrofurazone. Taken together, our results demonstrate that catalase mRNA expression offers a more straightforward dose-response model than enzyme activity. Our findings suggest that both catalase enzyme activity and mRNA expression abundance can be used jointly as bioassay tools for detecting ecotoxicity induced by nitrofurazone in aquatic ecosystems.

Microcystins in potable surface waters: toxic effects and removal strategies

In freshwater, harmful cyanobacterial blooms threaten to increase with global climate change and eutrophication of surface waters. In addition to the burden and necessity of removal of algal material during water treatment processes, bloom-forming cyanobacteria can produce a class of remarkably stable toxins, microcystins, difficult to remove from drinking water sources. A number of animal intoxications over the past 20 years have served as sentinels for widespread risk presented by microcystins. Cyanobacterial blooms have the potential to threaten severely both public health and the regional economy of affected communities, particularly those with limited infrastructure or resources. Our main objectives were to assess whether existing water treatment infrastructure provides sufficient protection against microcystin exposure, identify available options feasible to implement in resource-limited communities in bloom scenarios and to identify strategies for improved solutions. Finally, interventions at the watershed level aimed at bloom prevention and risk reduction for entry into potable water sources were outlined. We evaluated primary studies, reviews and reports for treatment options for microcystins in surface waters, potable water sources and treatment plants. Because of the difficulty of removal of microcystins, prevention is ideal; once in the public water supply, the coarse removal of cyanobacterial cells combined with secondary carbon filtration of dissolved toxins currently provides the greatest potential for protection of public health. Options for point of use filtration must be optimized to provide affordable and adequate protection for affected communities.

In situ studies on growth, oxidative stress responses, and gene expression of juvenile bighead carp (Hypophthalmichthys nobilis) to eutrophic lake water dominated by cyanobacterial blooms

Cyanobacterial blooms have received increasing attention as a public biohazard for human and animal health. To assess the effect of cyanobacteria-dominant lake water on juvenile fish, we measured the responses of specific growth rate, condition factor, body weight and body length, oxidative stress, and related gene expression of juvenile bighead carp Hypophthalmichthys nobilis exposed to in situ eutrophic lake (Chl a was around 7.0μgL(-1)). Results showed in situ cyanobacteria-dominant lake water had no effect on the growth performance, but significantly elevated the contents of malondialdehyde, the expression of heat shock protein 70, and the activity of superoxide dismutase, indicating that oxidative stress occurred. Meanwhile in situ lake water significantly decreased the expression of catalase and glutathione S-transferase genes. We conclude that in situ cyanobacteria-dominated lake water was harmful to juvenile bighead carp based on the oxidative stress and changes in the related gene expression levels.

Regulation of nodularin-induced apoptosis by epigallocatechin-3-gallate on fish lymphocytes in vitro

Nodularin is one of the most conspicuous and widespread pollutants that elicit water ecological hazards to fish, causing serious damage on the immune system and physiological functions. Nodularin can cause oxidative stress-induced apoptosis on fish lymphocytes. The regulatory effects of epigallocatechin-3-gallate (EGCG) at 10, 100, and 1000 μg/L levels on the antioxidant defense system and apoptosis of Carassius auratus lymphocytes exposed to a high dose of nodularin (100 μg/L) were quantified in vitro. EGCG reduced nodularin-induced oxidative damage on fish immune cells. This compound significantly increased the activities of superoxide dismutase and catalase and the level of glutathione but decreased the levels of intracellular reactive oxygen species and malondialdehyde. Flow cytometry results showed that the percentages of apoptotic cells after treatment with 10, 100, and 1000 μg/L EGCG for 12 h reached 27.9%, 19.1%, and 13.7%, respectively. By contrast, the nodularin alone-induced group showed a high percentage of apoptosis (44.2%). Western blot analysis showed the increased expression of bcl-2 and the decreased expression of bax and caspase-3 in EGCG-treated fish lymphocytes. EGCG also inhibited the potential collapse of the mitochondrial membrane. Overall, EGCG can inhibit nodularin-induced apoptosis and protect the normal immunity of fish by regulating bax/bcl-2 and blocking the downstream of mitochondrial apoptosis pathway with increased intracellular antioxidant enzyme activity.