Hepatotoxicity and metabolic effects of cellular extract of cyanobacterium Radiocystis fernandoi containing microcystins RR and YR on neotropical fish (Hoplias malabaricus)

The toxicological effect of cellular extract of cyanobacterium Radiocystis fernandoi strain R28 containing RR and YR microcystins was analyzed in the fish Hoplias malabaricus with emphasis on the liver structure and energetic metabolism, after short-term exposure. Fish were intraperitoneally (i.p.) injected with 100 μg of equivalent MC-LR kg^-1 body mass containing in the cellular extract of R. fernandoi strain R28. Twelve and 96 h post-injection, the plasma, liver and white muscle were sampled for biochemical analyses and liver was also sampled for morphological analyses. After i.p. injection, the activity of acid phosphatase (ACP), alanine aminotransferase (ALT) and direct bilirubin increased in the plasma, while ALT and aspartate aminotransferase (AST) decreased in the liver. Glucose, lactate and pyruvate increased while protein decreased in the plasma; glycogen, pyruvate and lactate decreased in the liver; and glycogen and glucose increased in the muscle. Ammonia increased in the plasma, liver and muscle. The hepatocyte cell shape changed from polyhedral to round after cellular extract injection; there was loss of biliary canaliculus organization, but the biliary duct morphology was conserved in the liver parenchyma. In conclusion, microcystins present in the cellular extract of R. fernandoi strain R28 affect the liver structure of H. malabaricus, but the liver was able to continuously produce energy by adjusting its intermediate metabolism; glycogenolysis and gluconeogenesis maintained glucose homeostasis and energy supply.

Combined toxic effects and mechanisms of microsystin-LR and copper on Vallisneria Natans (Lour.) Hara seedlings

Microcystin-LR (MCLR) and copper are commonly found in eutrophic water bodies because of eutrophic run-offs, cyanobacterial blooms, and copper algicide applications. However, the ecotoxicological risk of their combination remains unknown. This study investigated the effect of MCLR, Cu, and their mixture on the growth and physiological responses of Vallisneria natans. Results showed that the combined toxicity of them was concentration dependent. Synergistic effects were elicited at low concentrations of MCLR and Cu exposure (≤0.25+0.64mg/L). Additive or antagonistic effects were induced at higher concentrations. Single and combined exposures could induce oxidative stress, such as increased superoxide anion radical levels. To cope with oxidative stress, V. natans could activate their antioxidant defense systems, such as enhanced superoxide dismutase production and changes in peroxidase activities. Exposure to combined MCLR and Cu (even only with 0.005+0.041mg/L) adversely affected their antioxidant defense systems. As a consequence, malondialdehyde levels significantly increased. The interaction of MCLR and Cu could also significantly increase the bioaccumulations of MCLR and Cu. This increase could be accounted for their synergistic toxic effects on V. natans. Our results suggested that the exacerbated ecological hazard of MCLR and Cu with environmental concentrations may harm aquatic ecosystems.

Overexpression of carboxylesterase contributes to the attenuation of cyanotoxin microcystin-LR toxicity

Microcystin-LR is a hepatotoxin produced by several cyanobacteria. Its toxicity is mainly due to a inhibition of protein phosphatase, PP1 and PP2A. Previously, we used a cell line stably expressing uptake transporter for microcystin-LR, OATP1B3 (HEK293-OATP1B3 cells). In this study, to determine whether overexpression of carboxylesterase (CES), which degrades ester-group and amide-group, attenuates the cytotoxicity of microcystin-LR, we generated the HEK293-OATP1B3/CES2 double-transfected cells. HEK293-OATP1B3/CES2 cells showed high hydrolysis activity of p-nitrophenyl acetate (PNPA), which is an authentic substrate for esterase. CES activity in HEK293-OATP1B3/CES2 cells was approximately 3-fold higher than that in the HEK293-OATP1B3 cells. HEK293-OATP1B3/CES2 cells (IC₅₀: 25.4±7.7nM) showed approximately 2.1-fold resistance to microcystin-LR than HEK293-OATP1B3 cells (IC₅₀: 12.0±1.5nM). Moreover, the CES inhibition assay and microcystin-agarose pull down assay showed the possibility of the interaction between CES2 and microcystin-LR. Our results indicated that the overexpression of CES2 attenuates the cytotoxicity of microcystin-LR via interaction with microcystin-LR.

Effects of Microcystis on Hypothalamic-Pituitary-Gonadal-Liver Axis in Nile Tilapia (Oreochromis niloticus)

In the present study, Nile tilapia (Oreochromis niloticus) were used to assess the endocrine disruption potential of Microcytis aeruginosa. Male Nile tilapia were exposed to lyophilized M. aeruginosa or purified microcystin-LR (8.3 μg/L) for 28 days. The levels of serum hormones (17β-estradiol and testosterone) and transcripts of selected genes in the hypothalamus-pituitary-gonadal-liver axis were analyzed. The results showed that serum hormones were significantly up-regulated, and transcripts of 13 genes (GHRH, PACAP, GH, GHR1, GHR2, IGF1, IGF2, CYP19a, CYP19b, 3β-HSD1, 20β-HSD, 17β-HSD1 and 17β-HSD8) were significantly altered after Microcytis exposure. These results indicate that fish reproduction can be altered in a Microcystis bloom-contaminated aquatic environment.

Impairment of endoplasmic reticulum is involved in β-cell dysfunction induced by microcystin-LR

Microcystins (MCs) widely distributed in freshwaters have posed a significant risk to human health. Previous studies have demonstrated that exposure to MC-LR impairs pancreatic islet function, however, the underlying mechanisms still remain unclear. In the present study, we explored the role of endoplasmic reticulum (ER) impairment in β-cell dysfunction caused by MC-LR. The result showed that MC-LR modified ER morphology evidenced by increased ER amount and size at low doses (15, 30 or 60 μM) and vacuolar and dilated ER ultrastructure at high doses (100 or 200 μM). Also, insulin content showed increased at 15 or 30 μM but declined at 60, 100, or 200 μM, which was highly accordant with ER morphological alteration. Transcriptomic analysis identified a number of factors and several pathways associated with ER protein processing, ER stress, apoptosis, and diabetes mellitus in the cells treated with MC-LR compared with non-treated cells. Furthermore, MC-LR-induced ER stress significantly promoted the expression of PERK/eIF2α and their downstream targets (ATF4, CHOP, and Gadd34), which indicates that PERK-eIF2α-ATF4 pathway is involved in MC-LR-induced insulin deficiency. These results suggest that ER impairment is an important contributor to MC-LR-caused β-cell failure and provide a new insight into the association between MCs contamination and the occurrence of human diseases.

Toxic effects of microcystin-LR on the development of prostate in mice

Although it is well known that microcystin-LR (MC-LR) may cause male reproductive toxicity, less is known on its potential impact on the development of prostate. In this study, from the 12th day in the embryonic period to the 21st day after birth, 4 randomly assigned groups of pregnant mice were exposed to 0, 1, 10, and 50μg/L of MC-LR through drinking water followed by the analyses of their 30- and 90-day-old male offspring. The result showed that MC-LR could enter and be accumulated in the offsprings prostate. Using serological, morphological, and immunohistochemical analysis, we explored the effect of perinatal MC-LR exposure on the prostate development of male offspring. With increasing MC-LR concentrations, the 30 day-old male offspring experienced decreased prostate index, increased serum testosterone levels, decreased serum estradiol levels, and increased the serum androgen/estrogen ratio. Morphological findings showed a significant acini branching defect in both the10 and 50μg/L group and increasing MC-LR exposures induced augmented expression of androgen receptor (AR) and estrogen receptor α (ERα). For the 90-day group, MC-LR exposure resulted in decreased physiological indexes including prostate index and the serum androgen/estrogen ratio. Pathological changes could be observed in prostate tissues of mice treated with MC-LR. Increased expression of AR and ERα was also observed. Taken together, our results demonstrated that perinatal MC-LR exposure interfered with the development of the prostate in the offspring, evidenced by prostatic necrosis, hyperplasia, inflammation, and fibrosis, anddisordered hormone conversion of androgen to estrogen inducing imbalance of androgen and estrogen in the prostate may be one of the potential mechanisms of MC-LR disrupting prostate development.

Effects of toxic cyanobacteria and ammonia on flesh quality of blunt snout bream (Megalobrama amblycephala)

BACKGROUND

Toxic cyanobacterial blooms result in the production of an organic biomass containing cyanotoxins (e.g. microcystins) and an elevated ammonia concentration in the water environment. The ingestion of toxic cyanobacteria and exposure to ammonia are grave hazards for fish. The present study assessed the effects of dietary toxic cyanobacteria and ammonia exposure on the flesh quality of blunt snout bream (Megalobrama amblycephala).

RESULTS

Dietary toxic cyanobacteria and ammonia exposure had no impact on fish growth performance, fillet proximate composition and drip loss, whereas it significantly decreased fillet total amino acids, total essential amino acids, hardness and gumminess, and increased fillet ultimate pH as well as malondialdehyde content. However, there was no significant interaction between dietary toxic cyanobacteria and ammonia exposure on these parameters. Additionally, dietary toxic cyanobacteria significantly increased fillet initial pH, thaw loss and protein carbonyl content, whereas ammonia exposure did not.

CONCLUSION

The results of the present study indicate that dietary toxic cyanobacteria and ammonia exposure reduced the quality of blunt snout bream fillet. © 2016 Society of Chemical Industry.

Protein phosphatase 2A inhibition and subsequent cytoskeleton reorganization contributes to cell migration caused by microcystin-LR in human laryngeal epithelial cells (Hep-2)

The major toxic mechanism of Microcystin-LR is inhibition of the activity of protein phosphatase 2A (PP2A), resulting in a series of cytotoxic effects. Our previous studies have demonstrated that microcystin-LR (MCLR) induced very different molecular effects in normal cells and the tumor cell line SMMC7721. To further explore the MCLR toxicity mechanism in tumor cells, human laryngeal epithelial cells (Hep-2) was examined in this study. Western blot, immunofluorescence, immunoprecipitation, and transwell migration assay were used to detect the effects of MCLR on PP2A activity, PP2A substrates, cytoskeleton, and cell migration. The results showed that the protein level of PP2A subunits and the posttranslational modification of the catalytic subunit were altered and that the binding of the AC core enzyme as well as the binding of PP2A/C and α4, was also affected. As PP2A substrates, the phosphorylation of MAPK pathway members, p38, ERK1/2, and the cytoskeleton-associated proteins, Hsp27, VASP, Tau, and Ezrin were increased. Furthermore, MCLR induced reorganization of the cytoskeleton and promoted cell migration. Taken together, direct covalent binding to PP2A/C, alteration of the protein levels and posttranslational modification, as well as the binding of subunits, are the main pattern for the effects of MCLR on PP2A in Hep-2. A dose-dependent change in p-Tau and p-Ezrin due to PP2A inhibition may contribute to the changes in the cytoskeleton and be related to the cell migration in Hep-2. Our data provide a comprehensive exposition of the MCLR mechanism on tumor cells. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 890-903, 2017.

New insights into cytotoxicity induced by microcystin-LR, estradiol, and ractopamine with mathematical models: Individual and combined effects

Humans are most likely to be exposed to microcystins (MCs) combined with other water pollutants rather than to individual compounds through the consumption of contaminated drinking water or through recreational activities, such as swimming. However, the combined effects of MC-LR, estradiol (EST), and ractopamine (RAC) have not been extensively researched. The goal of this study was to investigate the combined effects of these compounds. For this purpose, cytotoxicity was evaluated in HepG2 cells treated with single or combined doses of MC-LR, EST, and RAC based on concentration addition (CA), independent action (IA), and Chou-Talalay's combination-index (CI) methods. Singly applied MC-LR and EST induced HepG2 cellular proliferation at low-concentration levels (1 × 10^-12-1 × 10^-9 M), and decreased viability at higher doses of exposure (1 × 10^-9-1 × 10^-6 M). Exposure to binary or ternary mixtures of MC-LR, EST, and RAC exhibited synergistic effects at high concentrations, irrespective of the models used. In contrast, antagonism was observed for the mixture of MC-LR and EST at relatively low concentrations. A synergistic effect on reactive oxygen species (ROS) generation was observed for the combined drugs at high concentrations. Additionally, the ratio of apoptotic cells was increased more by the combined drugs than the single drugs, consistent with the inhibition of cell viability. The ROS increase after treatment with the combined drugs may enhance cytotoxicity and subsequently lead to cell apoptosis. Given the interactions between MC-LR, EST, and RAC, government regulatory standards for MC-LR should consider the toxicological interactions between MC-LR and other environment pollutions.

Effects of microcystin-LR and cylindrospermopsin on plant-soil systems: A review of their relevance for agricultural plant quality and public health

Toxic cyanobacterial blooms are recognized as an emerging environmental threat worldwide. Although microcystin-LR is the most frequently documented cyanotoxin, studies on cylindrospermopsin have been increasing due to the invasive nature of cylindrospermopsin-producing cyanobacteria. The number of studies regarding the effects of cyanotoxins on agricultural plants has increased in recent years, and it has been suggested that the presence of microcystin-LR and cylindrospermopsin in irrigation water may cause toxic effects in edible plants. The uptake of these cyanotoxins by agricultural plants has been shown to induce morphological and physiological changes that lead to a potential loss of productivity. There is also evidence that edible terrestrial plants can bioaccumulate cyanotoxins in their tissues in a concentration dependent-manner. Moreover, the number of consecutive cycles of watering and planting in addition to the potential persistence of microcystin-LR and cylindrospermopsin in the environment are likely to result in groundwater contamination. The use of cyanotoxin-contaminated water for agricultural purposes may therefore represent a threat to both food security and food safety. However, the deleterious effects of cyanotoxins on agricultural plants and public health seem to be dependent on the concentrations studied, which in most cases are non-environmentally relevant. Interestingly, at ecologically relevant concentrations, the productivity and nutritional quality of some agricultural plants seem not to be impaired and may even be enhanced. However, studies assessing if the potential tolerance of agricultural plants to these concentrations can result in cyanotoxin and allergen accumulation in the edible tissues are lacking. This review combines the most current information available regarding this topic with a realistic assessment of the impact of cyanobacterial toxins on agricultural plants, groundwater quality and public health.

Microcystin accumulation and potential effects on antioxidant capacity of leaves and fruits of Capsicum annuum

Surface water, often used for irrigation purposes, may sometimes be contaminated with blooming cyanobacteria and thereby may contain their potent and harmful toxins. Cyanotoxins adversely affect many terrestrial plants, and accumulate in plant tissues that are subsequently ingested by humans. Studies were undertaken to (1) examine the bioaccumulation of microcystins (MCs) in leaves and fruits of pepper Capsicum annuum and (2) examine the potential effects of MCs on antioxidant capacity of these organs. Plants were irrigated with water containing MCs for a period of 3 mo. Data showed that MCs did not accumulate in leaves; however, in fruits the presence of the MC-LR (0.118 ng/mg dry weight) and dmMC-LR (0.077 ng/mg dry weight) was detected. The concentrations of MC-LR in fruit approached the acceptable guideline values and tolerable daily intake for this toxin. Lipid peroxidation levels and flavonoids content were significantly enhanced in both organs of treated plants, while total phenolic concentrations were not markedly variable between control and treated plants. Significant decrease in 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging capacity was noted for both organs. The levels of superoxide anion in fruits and hydroxyl radical in leaves were markedly reduced. Data suggest that exposure to MCs significantly reduced antioxidant capacity of experimental plants, indicating that MCs affected antioxidant systems in C. annuum.

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

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

Responses of the Proteome and Metabolome in Livers of Zebrafish Exposed Chronically to Environmentally Relevant Concentrations of Microcystin-LR

In this study, for the first time, changes in expressions of proteins and profiles of metabolites in liver of the small, freshwater fish [Formula: see text] (zebrafish) were investigated after long-term exposure to environmentally relevant concentrations of microcystin-LR (MC-LR). Male zebrafish were exposed via water to 1 or 10 μg MC-LR/L for 90 days, and iTRAQ-based proteomics and ¹H NMR-based metabolomics were employed. Histopathological observations showed that MC-LR caused damage to liver, and the effects were more pronounced in fish exposed to 10 μg MC-LR/L. Metabolomic analysis also showed alterations of hepatic function, which included changes in a number of metabolic pathways, including small molecules involved in energy, glucose, lipids, and amino acids metabolism. Concentrations of lactate were significantly greater in individuals exposed to MC-LR than in unexposed controls. This indicated a shift toward anaerobic metabolism, which was confirmed by impaired respiration in mitochondria. Proteomics revealed that MC-LR significantly influenced multiple proteins, including those involved in folding of proteins and metabolism. Endoplasmic reticulum stress contributed to disturbance of metabolism of lipids in liver of zebrafish exposed to MC-LR. Identification of proteins and metabolites in liver of zebrafish responsive to MC-LR provides insights into mechanisms of chronic toxicity of MCs.

Widespread dispersal and bio-accumulation of toxic microcystins in benthic marine ecosystems

Freshwater cyanobacteria produce toxic microcystins (MCs), which travel from freshwater areas into the sea. The MCs produced by cyanobacteria in a freshwater reservoir were discharged frequently into the adjacent Isahaya Bay, remained in the surface sediments, and then accumulated in various macrobenthic animals on the seafloor. The MCs were transported further outside of Isahaya Bay (Ariake Bay), and the median values of the MC contents in the sediments were in the same levels in both bays, while their temporal variations were also similar during the study period. Therefore, the fluctuations of the MC contents in the surface sediments were physically controlled by the timing of the discharge from the reservoir. The MC contents in polychaetes and oysters collected in Isahaya Bay increased markedly during winter. The median values of the carbon-based MC contents in the sediments, primary consumers, and secondary consumers in the bay were 87, 160, and 250 ngMC gC^-1, respectively. These results demonstrated bio-accumulation at lower trophic levels in benthic marine ecosystems. An understanding of the processes occurring between sediments and macrobenthic animals is important for clarifying MC dynamics in ecosystems.

HEK293 cells exposed to microcystin-LR show reduced protein phosphatase 2A activity and more stable cytoskeletal structure when overexpressing α4 protein

Microcystin-LR (MC-LR) is one of the most toxic members of microcystins released by freshwater cyanobacterial. The major mechanism of MC-LR toxicity has been attributed to its inhibition of protein phosphatases 1 (PP1) and 2A (PP2A). In our prior research, α4 protein, a regulator of PP2A, was found not only crucial for PP2A regulation but also for the overall response of HEK 293 cells encountering MC-LR. To explore the role of α4 in MC-LR toxicity via PP2A regulation, here, HEK 293 cells overexpressing α4 protein were exposed to MC-LR and PP2A, cytoskeletal organization, and cytoskeleton-related proteins were investigated. The results showed that PP2A activity decreased and PP2A/C subunit expression and phosphorylation at Tyr307 increased significantly in the group exposed to high MC-LR. Vimentin IF became concentrated and formed perinuclear bundles. However, the assembly of actin filament and microtubules remained unchanged and the expression and phosphorylation of the cytoskeleton-related proteins HSP27 and VASP did not increase significantly. Some of these results differ from those of our previous study in which normal HEK293 cells were exposed to MC-LR. Our results indicate that elevated α4 expression confers some resistance to MC-LR-induced cytoskeletal change These new findings provide helpful insights into the mechanism of MC-LR toxicity and the role of α4 in regulating PP2A function. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 255-264, 2017.

Analysis of the use of microcystin-contaminated water in the growth and nutritional quality of the root-vegetable, Daucus carota

Toxic cyanobacterial blooms are often observed in freshwaters and may reflect the increased eutrophication of these environments and alterations in climate. Cyanotoxins, such as microcystins (MCs), are an effective threat to many life forms, ranging from plants to humans. Despite the research conducted to date on cyanotoxins, the risks associated to the use of contaminated water in agriculture require further elucidation. To tackle this aim, a research was conducted with the root-vegetable Daucus carota. The specific aims of this work were the following: (i) to evaluate the effects of MC-LR on the plant growth and photosynthesis; (ii) to evaluate the nutritional quality of carrot roots; and (iii) to measure bioaccumulation. To this purpose, young carrots were grown in soil during 1 month in natural conditions and exposed to Mycrocystis aeruginosa aqueous extracts containing environmentally realistic concentrations of MC-LR (10 and 50 MC-LR μg/L). The results showed that MC-LR may decrease root growth after 28 days of exposure to 50 μg/L and increase photosynthetic efficiency. We also observed changes in mineral and vitamin content in carrots as a result of the exposure to contaminated water. Moreover, MC-LR was detected in carrot roots by ELISA at very low concentration 5.23 ± 0.47 ng MC eq./g FW. The soil retained 52.7 % of the toxin potentially available for plants. This result could be attributed to MC-LR adsorption by soil particles or due to microbial degradation of the toxin. We conclude that the prolonged use of MC-LR-contaminated water may affect crop growth, alter the nutritional value of vegetable products, and potentiate contamination.

Assessment of uptake and phytotoxicity of cyanobacterial extracts containing microcystins or cylindrospermopsin on parsley (Petroselinum crispum L.) and coriander (Coriandrum sativum L)

Blooms of harmful cyanobacteria that synthesize cyanotoxins are increasing worldwide. Agronomic plants can uptake these cyanotoxins and given that plants are ultimately ingested by humans, this represents a public health problem. In this research, parsley and coriander grown in soil and watered through 7 days with crude extracts containing microcystins (MCs) or cylindrospermopsin (CYN) in 0.1-1 μg mL^-1 concentration range were evaluated concerning their biomass, biochemical parameters and uptake of cyanotoxins. Although biomass, chlorophylls (a and b), carotenoids and glutathione-S-transferase of parsley and coriander exposed to the crude extracts containing MC or CYN had shown variations, these values were not statistically significantly different. Protein synthesis is not inhibited in coriander exposed to MC or CYN and in parsley exposed to MC. Also, glutathione reductase (GR) and glutathione peroxidase (GPx) in parsley and coriander was not affected by exposure to MC, and in coriander, the CYN did not induce statistically significant differences in these two antioxidative enzymes. Only parsley showed statistically significant increase in protein content exposed to 0.5 μg CYN mL^-1 (3.981 ± 0.099 mg g^-1 FW) compared to control (2.484 ± 0.145 mg g^-1 FW), statistically significant decrease in GR exposed to 0.1 μg CYN mL^-1 (0.684 ± 0.117 nmol min^-1 mg^-1 protein) compared to control (1.30 ± 0.06 nmol min^-1 mg^-1 protein) and statistically significant increase in GPx exposed to 1 μg CYN mL^-1 (0.054 ± 0.026 nmol min^-1 mg^-1 protein) compared to 0.5 μg CYN mL^-1 (0.003 ± 0.001 nmol min^-1 mg^-1 protein). These changes may be due to the induction of defensive mechanisms by plants by the presence of toxic compounds in the soil or probably to a low generation of reactive oxygen species. Furthermore, the parsley and coriander leaves and stems after 10 days of exposure did not accumulate microcystins or cylindrospermopsin.

The organic anion transporting polypeptide 1a5 is a pivotal transporter for the uptake of microcystin-LR by gonadotropin-releasing hormone neurons

Microcystins (MCs) are widely distributed hepatotoxic polypeptides produced by cyanobacteria. Microcystin-LR (MC-LR) has the broadest distribution and strongest toxicity among more than 80 isoforms of hepatotoxic MCs. MC-LR suppresses the expression of gonadotropin-releasing hormone (GnRH) that is critically required for the release of testosterone, resulting in the induction of male reproductive toxicity. However, the specific mechanisms of the uptake of MC-LR by GnRH-secreting neurons still remain unclear. In this study, GT1-7 cells were exposed to MC-LR in order to determine whether the GnRH-secreting neurons were the target of MC-LR that could induce male reproductive toxicity. Our data demonstrated that at least four organic anion transporting polypeptides (Oatp1a4, Oatp1a5, Oatp5a1, Oatp2b1) were expressed in GnRH neurons at the mRNA level, but only Oatp1a5 was expressed at the protein level. Furthermore, we demonstrated that MC-LR could not be transported into Oatp1a5-deficient GT1-7 cells which were protected from cell viability loss induced by MC-LR. These data suggest that Oatp1a5 may play an important role in the toxic effect of MC-LR on GnRH neurons.

Microcystins affect zooplankton biodiversity in oxbow lakes

The authors tested the hypothesis that zooplankton diversity and density are affected by the presence of cyanotoxins in the water. The authors focused on 4 oxbow lakes of the Vistula River in southern Poland, which are subjected to mass cyanobacterial development. In 2 of the oxbows (Piekary and Tyniec), microcystins released into the water were found. The highest concentration of microcystins (0.246 μg/L) was observed for microcystins LR. Zooplankton diversity showed a weak response to the presence of microcystins released into the water. The Shannon index (H') of total zooplankton diversity decreased in the Piekary and Tyniec oxbows during periods when the microcystin concentrations were highest. The same trend was noted for diversity of rotifers in both oxbows and for diversity of copepods in Piekary, but not for copepods in Tyniec. No such trends were found for the diversity of cladocerans in any of the oxbows, nor was a relationship found between density of zooplankton and microcystins. Statistical analyses showed that the number of species in individual samples was negatively correlated with the levels of sulfates, phosphates, and ammonia, but the microcystin concentration was positively related to those levels. This points to the complexity of the interactions and synergies among toxins, abiotic factors, and zooplankton biodiversity. In focusing on the problem of cyanotoxins, conservation studies should pay attention to this complexity. Environ Toxicol Chem 2017;36:165-174. © 2016 SETAC.

Crude extract of cyanobacteria (Radiocystis fernandoi, strain R28) induces liver impairments in fish

Radiocystis fernandoi R28 strain is a cyanobacterium which produces mostly the RR and YR microcystin variants (MC-RR and MC-YR, respectively). The effects of crude extract of the R. fernandoi strain R28 were evaluated on the protein phosphatases and on the structure and ultrastructure of the liver of the Neotropical fish, Hoplias malabaricus, after acute and subchronic exposure. Concomitantly, the accumulation of the majority of MCs was determined in the liver and muscle. The fish were exposed to 120.60 MC-RR+MC-LR kg-fish^-1 (=100μg MC-LReq kg-fish^-1) for 12 and 96h (one single dose, acute exposure) and 30days (one similar dose every 72h, subchronic exposure). MCs did not accumulate in the muscle but, in the liver, MC-YR accumulated after acute exposure and MC-RR and MC-YR accumulation occurred after subchronic exposure. Protein phosphatase 2A (PP2A) activity was inhibited only after subchronic exposure. Acute exposure induced liver hyperemia, hemorrhage, changes in hepatocytes and cord-like disorganization. At the ultrastructural level, the decreasing of glycogen and lipid levels, the swelling of mitochondria and whirling of endoplasmic reticulum suggested hepatocyte necrosis. Subchronic exposure resulted in a complete disarrangement of cord-like hepatocytes, some recovery of mitochondria and whirling endoplasmic reticulum and extensive connective tissues containing fibrous materials in the liver parenchyma. Despite microcystin toxicity and liver alterations, no tumor was induced by MCs. In conclusion, the increased algal mass of R. fernandoi in tropical freshwater, producing mainly MC-RR and MC-YR variants, results in fish liver impairments.

An integrated omic analysis of hepatic alteration in medaka fish chronically exposed to cyanotoxins with possible mechanisms of reproductive toxicity

Cyanobacterial blooms threaten human health as well as the population of other living organisms in the aquatic environment, particularly due to the production of natural toxic components, the cyanotoxin. So far, the most studied cyanotoxins are microcystins (MCs). In this study, the hepatic alterations at histological, proteome and transcriptome levels were evaluated in female and male medaka fish chronically exposed to 1 and 5 μg L^-1 microcystin-LR (MC-LR) and to the extract of MC-producing Microcystis aeruginosa PCC 7820 (5 μg L^-1 of equivalent MC-LR) by balneation for 28 days, aiming at enhancing our understanding of the potential reproductive toxicity of cyanotoxins in aquatic vertebrate models. Indeed, both MC and Microcystis extract adversely affect reproductive parameters including fecundity and egg hatchability. The liver of toxin treated female fish present glycogen storage loss and cellular damages. The quantitative proteomics analysis revealed that the quantities of 225 hepatic proteins are dysregulated. In particular, a notable decrease in protein quantities of vitellogenin and choriogenin was observed, which could explain the decrease in reproductive output. Liver transcriptome analysis through Illumina RNA-seq reveals that over 100-400 genes are differentially expressed under 5 μg L^-1 MC-LR and Microcystis extract treatments, respectively. Ingenuity pathway analysis of the omic data attests that various metabolic pathways, such as energy production, protein biosynthesis and lipid metabolism, are disturbed by both MC-LR and the Microcystis extract, which could provoke the observed reproductive impairment. The transcriptomics analysis also constitutes the first report of the impairment of circadian rhythm-related gene induced by MCs. This study contributes to a better understanding of the potential consequences of chronic exposure of fish to environmental concentrations of cyanotoxins, suggesting that Microcystis extract could impact a wider range of biological pathways, compared with pure MC-LR, and even 1 μg L^-1 MC-LR potentially induces a health risk for aquatic organisms.

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

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

Oxidative stress responses in the animal model, Daphnia pulex exposed to a natural bloom extract versus artificial cyanotoxin mixtures

In the natural environment, Daphnia spp. are constantly exposed to a complex matrix of biomolecules, especially during cyanobacterial bloom events. When cyanobacterial cells decay, not only are toxic secondary metabolites known as cyanotoxins released, but also multiple other secondary metabolites, some of which act as enzyme inhibitors. The present study examined the effects of such a natural toxin matrix (crude extract from a bloom) versus artificial toxin mixtures in terms of oxidative stress in Daphnia pulex. The results indicate that there is no significant effect on the survival of D. pulex. However, exposure to the bloom extract resulted in increased lipid peroxidation over a shorter exposure period and reduced antioxidative enzyme activities when compared to the artificial mixtures. The daphnids also needed a longer recovery time to reduce the increased cellular hydrogen peroxide concentration associated with the exposure to the crude extract than with the artificial mixtures. The results indicate a significant difference between the bloom crude extract and the two synthetic mixtures for all stress markers tested, indicating enhanced toxicity of the bloom extract.

Community Needs Assessment After Microcystin Toxin Contamination of a Municipal Water Supply - Lucas County, Ohio, September 2014

On August 1, 2014, routine testing at the Collins Park Water Treatment Plant in Lucas County, Ohio, revealed microcystin toxin levels in drinking water had reached 3.19 μg/L, surpassing the Ohio Environmental Protection Agency (EPA) drinking water advisory threshold of 1.0 μg/L. Microcystin is a hepatoxin released by cyanobacteria in certain harmful algal blooms. Exposure to microcystin has been associated with gastrointestinal and hepatic illness in both humans and animals (1-3). On August 2, a do-not-drink advisory was issued, warning community members not to drink, boil, or use the water for cooking or brushing teeth. Public health officials used traditional and social media outlets to disseminate public health messages to affected communities. On August 4, 2014, the advisory was lifted after multiple water samples confirmed microcystin toxin levels had dropped below the advisory threshold. To assess communication strategies, water exposure, and household needs, the Ohio Department of Health (ODH) and Toledo-Lucas County Health Department (TLCHD) conducted a Community Assessment for Public Health Emergency Response (CASPER) in Lucas County. Most households (88.1%) reported hearing about the advisory the morning it was issued, but 11% reported drinking and 21% reported brushing teeth with municipal water during the advisory. Household members reported physical (16%) and mental (10%) health concerns that they believed were related to the advisory and activity disruptions including temporarily staying outside of the home (6%) during the advisory and continued use of alternative water sources after the advisory was lifted (82%). During a do-not-drink advisory, governmental agencies and community partners need to engage in joint prevention and response efforts to decrease water exposure and prevent activity disruptions.

Comprehensive insights into microcystin-LR effects on hepatic lipid metabolism using cross-omics technologies

Microcystin-LR (MC-LR) can induce hepatic tissue damages and molecular toxicities, but its effects on lipid metabolism remain unknown. This study investigated the effects of MC-LR exposure on mice lipid metabolism and uncovered the underlying mechanism through metabonomic, transcriptomic and metagenomic analyses after administration of mice with MC-LR by gavage for 28 d. Increased liver weight and abdominal fat weight, and evident hepatic lipid vacuoles accumulation were observed in the mice fed with 0.2mg/kg/d MC-LR. Serum nuclear magnetic resonance analysis showed that MC-LR treatment altered the levels of serum metabolites including triglyceride, unsaturated fatty acid (UFA) and very low density lipoprotein. Digital Gene Expression technology was used to reveal differential expression of hepatic transcriptomes, demonstrating that MC-LR treatment disturbed hepatic UFA biosynthesis and activated peroxisome proliferator-activated receptor (PPAR) signaling pathways via Pparγ, Fabp1 and Fabp2 over-expression. Metagenomic analyses of gut microbiota revealed that MC-LR exposure also increased abundant ratio of Firmicutes vs. Bacteroidetes in gut and altered biosynthetic pathways of various microbial metabolic and pro-inflammatory molecules. In conclusion, oral MC-LR exposure can induce hepatic lipid metabolism disorder mediated by UFA biosynthesis and PPAR activation, and gut microbial community shift may play an important role in the metabolic disturbance.