Are little brown bats (Myotis lucifugus) impacted by dietary exposure to microcystin?✰.

The cyanobacterium, Microcystis aeruginosa, can produce the hepatotoxin microcystin. When toxic M. aeruginosa overwinters in the sediments of lakes, it may be ingested by aquatic insects and bioaccumulate in nymphs of Hexagenia mayflies. When volant Hexagenia emerge from lakes to reproduce, they provide an abundant, albeit temporary, food source for many terrestrial organisms including bats. Little brown bats, Myotis lucifugus, feed opportunistically on aquatic insects including Hexagenia. To determine if microcystin moves from aquatic to terrestrial ecosystems via trophic transfer, we combined a dietary analysis with the quantification of microcystin in bat livers and feces. In June 2014, coincident with the local Hexagenia emergence, bat feces were collected from underneath a maternity roost near Little Traverse Lake (Leelanau County, Michigan, USA). Insects in the diet were identified via molecular analyses of fecal pellets from the roost and from individual bats. Livers and feces were collected from 19 female M. lucifugus, and the concentrations of microcystin in these liver tissues and feces were measured using an enzyme-linked immunosorbent assay (ELISA) and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). We show that the majority of the bats' diets consisted of aquatic insects and that microcystin was detected in high concentrations (up to 129.9 µg/kg dw) in the bat feces by ELISA. Histopathological examination of three bat livers with the highest concentrations of microcystin showed no evidence of phycotoxicosis, indicating that M. lucifugus may not be immediately affected by the ingestion of microcystin. Future work could examine whether bats suffer delayed physiological effects from ingestion of microcystin.

Limnological Differences in a Two-Basin Lake Help to Explain the Occurrence of Anatoxin-a, Paralytic Shellfish Poisoning Toxins, and Microcystins.

Chautauqua Lake, New York, is a two-basin lake with a deeper, cooler, and less nutrient-rich Northern Basin, and a warmer, shallower, nutrient-replete Southern Basin. The lake is populated by a complex mixture of cyanobacteria, with toxigenic strains that produce microcystins, anatoxins, and paralytic shellfish poisoning toxins (PSTs). Samples collected from 24 sites were analyzed for these three toxin classes over four years spanning 2014-2017. Concentrations of the three toxin groups varied widely both within and between years. During the study, the mean and median concentrations of microcystins, anatoxin-a, and PSTs were 91 and 4.0 µg/L, 0.62 and 0.33 µg/L, and 32 and 16 µg/L, respectively. Dihydro-anatoxin was only detected once in Chautauqua Lake, while homo-anatoxin was never detected. The Northern Basin had larger basin-wide higher biomass blooms with higher concentrations of toxins relative to the more eutrophied Southern Basin, however blooms in the North Basin were infrequent. Chlorophyll concentrations and toxins in the two basins were correlated with different sets of environmental and physical parameters, suggesting that implementing controls to reduce toxin loads may require applications focused on more than reductions in cyanobacterial bloom density (e.g., reduction of phosphorus inputs), and that lake limnological factors and morphology are important determinants in the selection of an appropriate management strategy. Chautauqua Lake is a drinking water source and is also heavily used for recreation. Drinking water from Chautauqua Lake is unlikely to be a significant source of exposure to cyanotoxins due to the location of the intakes in the deeper North Basin, where there were generally low concentrations of toxins in open water; however, toxin levels in many blooms exceeded the US Environmental Protection Agency's recreational guidelines for exposure to cyanotoxins. Current cyanotoxin monitoring in Chautauqua Lake is focused on microcystins. However, the occurrence of blooms containing neurotoxic cyanotoxins in the absence of the microcystins indicates this restricted monitoring may not be sufficient when aiming to protect against exposure to cyanotoxins. The lake has a large number of tourist visitors; thus, special care should be taken to prevent recreational exposure within this group.

Effects of microcystins-LR on genotoxic responses in human intestinal epithelial cells (NCM460).

Microcystin-LR (MC-LR), a cyclic heptapeptide toxin produced by cyanobacteria, was found to induce genotoxic actions in various types of cells. Some investigators reported that microcystin-LR acted as tumor initiator in the observed genotoxic action mediated by this cyanotoxin. However, the underlying mechanisms underlying MC-induced DNA damage in the human intestine epithelium cell line (NCM460) are not known. The purpose of this study was to examine the influence of 24 hr exposure to 5 or 10 µM MC-LR on intestinal DNA damage using NCM460 intestine cell line as a model. Data showed that MC-LR increased Olive tail moment (OTM) as evidenced by the comet assay, inhibited protein phosphatase 2A (PP2A) activity, elevated reactive oxygen species levels (ROS) and enhanced γ-H2AX and p-p53 protein expression levels. Results indicated that MC-LR produced intestinal DNA damage by inhibiting PP2A activity, activating p53 protein and subsequently initiating excess generation of ROS. These observations suggest that MC-LR-induced intestinal DNA damage involves a complex series of events that include oxidant stress, PP2A enzymic inhibition and activation of p53 protein.

Circular RNA expression profiles following MC-LR treatment in human normal liver cell line (HL7702) cells using high-throughput sequencing analysis.

Microcystin-LR (MC-LR), a frequently occurring hepatotoxic cyanotoxin produced by cyanobacterial blooms, poses a great threat to human health. However, the precise molecular mechanisms underlying MC-LR-induced hepatotoxicity remain to be determined. Recent investigators found that in many human diseases circular RNAs (circRNAs) a class of endogenous non-coding RNAs played critical roles in disease outcomes. The aim of this study was to investigate whether circRNAs were involved in MC-LR-mediated hepatotoxicity using human normal liver cell line (HL7702). Using high-throughput sequencing analysis data demonstrated that expression levels of 3250, 3111, 3097, 3253 circRNAs were significantly altered at concentrations ranging from 1 to 10 µM MC-LR. Expression levels of hsa_circRNA_0000657 and hsa_circRNA_0000659 were down-regulated while hsa_circRNA_0003247 and hsa_circRNA_0001535 were up-regulated in all MC-LR-exposed groups. The high-throughput sequencing results of selected circRNAs differential expression genes (DEGs) levels were verified by real-time fluorescent quantitative PCR (qRT-PCR). Gene Ontology (GO) enrichment analysis showed that the functions of circRNAs significantly altered in HL7702 cells were predominantly associated with metabolism, systems development, and protein binding. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis data revealed that the target genes of differentially expressed circRNAs in HL7702 cells were involved in FoxO signaling pathway, protein processing in endoplasmic reticulum, Ras signaling pathway, cell cycle, PI3K-Akt signaling pathway, MAPK signaling pathway and pathways in cancer. In summary, evidence indicates that a correlation may exist between circRNAs and MC-LR-induced hepatotoxicity.

Desmodesmus subspicatus co-cultured with microcystin producing (PCC 7806) and the non-producing (PCC 7005) strains of Microcystis aeruginosa.

Although microcystins (MCs) are the most commonly studied cyanotoxins, their significance to the producing organisms remains unclear. MCs are known as endotoxins, but they can be found in the surrounding environment due to cell lysis, designated as extracellular MCs. In the present study, the interactions between MC producing and the non-producing strains of Microcystis aeruginosa, PCC 7806 and PCC 7005, respectively, and a green alga, Desmodesmus subspicatus, were studied to better understand the probable ecological importance of MCs at the collapse phase of cyanobacterial blooms. We applied a dialysis co-cultivation system where M. aeruginosa was grown inside dialysis tubing for one month. Then, D. subspicatus was added to the culture system on the outside of the membrane. Consequently, the growth of D. subspicatus and MC contents were measured over a 14-day co-exposure period. The results showed that Microcystis negatively affected the green alga as the growth of D. subspicatus was significantly inhibited in co-cultivation with both the MC-producing and -deficient strains. However, the inhibitory effect of the MC-producing strain was greater and observed earlier compared to the MC-deficient strain. Thus, MCs might be considered as an assistant factor that, in combination with other secondary metabolites of Microcystis, reinforce the ability to outcompete co-existing species.

Effects of microcystin-LR on the immune dysfunction and ultrastructure of hepatopancreas in giant freshwater prawn Macrobrachium rosenbergii.

Microcystins (MCs), produced by cyanobacteria, can strongly inhibit the activity of protein phosphatase, and exhibit strong hepatotoxicity. Macrobrachium rosenbergii is an important aquaculture economic species. Cyanobacterial blooms occur frequently during the culture of M. rosenbergii. However, the effects of MCs on the M. rosenbergii immune function have not been studied. In the present study, M. rosenbergii were exposed to environment-related concentrations of MC-LR type (0.5 and 5 µg/L) for 3 weeks. Hepatopancreatic histology was investigated, and antioxidant enzymes activity, acid phosphatase, alkaline phosphatase and lysozyme activity in hepatopancreas were also analyzed. Results showed that MC-LR could damage M. rosenbergii hepatopancreas, induce hepatopancreatic apoptosis and antioxidant dysfunctions. The expression profiles of major immune-related genes after MC-LR exposure were also detected. Some genes with antibacterial functions were suppressed, and the expression of apoptosis-related genes were up-regulated. After MC-LR exposure, the cumulative mortality of M. rosenbergii infected with Vibrio vulnificus and Aeromonas hydrophila were much higher than the control in a time-dose dependent manner. These results indicated the potential negative influence of MC-LR on the immune function of M. rosenbergii.

Molecular characterization of caspase-8-like and its expression induced by microcystin-LR in grass carp (Ctenopharygodon idella).

Caspase-8, an initiator caspase, plays a vital role in apoptosis. In this study, caspase-8-like (named as Cicaspase-8-like), a homologue of caspase-8, was identified in grass carp (Ctenopharygodon idella). The full-length cDNA sequence of CiCaspase-8-like was 1409 bp and contained a 162 bp 5'-UTR, a 239 bp 3'-UTR and a 1008 bp coding sequence. The putative amino acids sequence was 335 residues long, including a large subunit (P20) and a small subunit (P10), but lacking conserved death effector domains. A histidine active site DHSQMDAFVCCVLSHG and a cysteine active-site motif KPKLFFIQACQG were found in P20. Phylogenetic analysis showed that Cicaspase-8-like clustered with the caspase-8 and caspase-8-like of other fish and grouped closely with Carassius auratus caspase-8-like. Quantitative real-time PCR revealed that the Cicaspase-8-like mRNA were expressed constitutively in all tested tissues from healthy grass carp, with high expression level in the blood, spleen, liver and gill, indicating its role in immune reaction. The expression of Cicaspase-8-like mRNA was decreased significantly in the liver because of the stress caused by microcystin-LR (MC-LR) (75 and 100 µg MC-LR/kg BW) at 24 h and 96 h post injection (P < 0.05), but it was increased significantly in grass carp treated with 25 µg MC-LR/kg BW at 24 h (P < 0.05) post injection. Cleaved fragments of Cicaspase-8-like were observed using western blot analysis, and the expression of Cicaspase-8-like protein was increased after MC-LR treatments. Moreover, the expression of both caspase-9 and caspase-3 mRNA increased significantly after treatment with the three doses of MC-LR. TUNEL assay results showed remarkable changes in apoptosis after the MC-LR treatment. These results suggest that Cicaspase-8-like is an important caspase and plays an essential role in MC-LR-induced apoptosis.

piRNA-DQ722010 contributes to prostate hyperplasia of the male offspring mice after the maternal exposed to microcystin-leucine arginine.

BACKGROUND: Microcystin-leucine arginine (MC-LR) could disrupt prostate development and cause prostate hyperplasia. But whether and how maternal and before-weaning MC-LR exposure causes prostate hyperplasia in male offspring by changing expression profile of P-element-induced wimpy (PIWI)-interacting RNAs (piRNAs) have not yet been reported. METHODS: From the 12th day in the embryonic period to the 21st day after offspring birth, three groups of pregnant mice that were randomly assigned were exposed to 0, 10, and 50 µg/L of MC-LR through drinking water followed by the analyses of their male offspring. Abortion rate and litter size of maternal mice were recorded. The prostate histopathology was observed. Differential expressed piRNAs of prostate were screened by piRNA microarray analysis. Murine prostate cancer cell line (RM-1) was used for further mechanism study. Luciferase report assay was used to determine the relationship between piRNA-DQ722010 and polypeptide 3 (Pik3r3). RESULTS: The downregulated expression of piRNA-DQ722010 was the most significant in piRNA microarray analysis in 10 µg/L MC-LR treated group, while Pik3r3 was significantly upregulated, consistent with the results that a distinct prostatic epithelial hyperplasia was observed and phosphoinositide-3-kinase (PI3K)/protien kinase B (AKT) signaling pathway was activated. Pik3r3 was verified as the target gene of piRNA-DQ722010. In addition, we found MC-LR decreased the expression of PIWI-like RNA-mediated gene silencing 2 (Piwil2) and 4 (Piwil4) both in vivo and in vitro, and both Piwil4 and Piwil2 could regulate the expression of DQ722010. CONCLUSION: MC-LR caused downregulation of piRNA-DQ722010 and PIWI proteins, while piRNA-DQ722010 downregulation promoted activation of PI3K/AKT signaling pathway inducing prostate hyperplasia by upregulating the expression of Pik3r3. In contrast, piRNA-DQ722010 downregulation may be attributed to PIWI proteins downregulation.

Effects of dietary toxic cyanobacteria and ammonia exposure on immune function of blunt snout bream (Megalabrama amblycephala).

Cyanobacterial blooms caused by water eutrophication have become a worldwide problem. During the degradation of toxic cyanobacterial blooms, elevated ammonia and microcystins concentrations co-occur and exert toxicity on fish. Up to now, the combined effect of microcystins and ammonia on fish immunotoxicity has not been reported. The present study investigated immune responses of blunt snout bream (Megalabrama amblycephala) to dietary toxic cyanobacteria and ammonia exposure. Megalobrama amblycephala were exposed to solutions with different concentrations of NH3-N (0, 0.06, 0.12 mg/L) and fed with diets containing 15% and 30% of toxic cyanobacteria lyophilized powder for 30 d. The microcystins concentration in different organs of Megalobrama amblycephala was in the following sequence: head kidney > liver > intestine > gonad > spleen > gill > trunk kidney > brain > muscle > heart. In both head kidney and spleen, the MC-LR and MC-RR concentration increased significantly with increasing NH3-N concentration. It indicates that NH3-N maybe promote the accumulation of microcystins in immune organs of Megalobrama amblycephala. Meanwhile, broadened peripheral interspace of lymphocytes, nucleus shrivel and edematous mitochondria were observed in head kidney lymphocyte of toxic treatment fish. Moreover, there were significant interactions between dietary toxic cyanobacteria and ammonia exposure on head kidney macrophage phagocytosis activity, respiratory burst activities, total number of white blood cells and the transcriptional levels of sIgM, mIgD and sIgZ genes. Our data clearly demonstrated that dietary toxic cyanobacteria combined with ammonia exposure showed a synergistic effect on Megalobrama amblycephala immunotoxicity.

Something in the Water: Hospital Responds to Water Crisis.

Early on August 2, 2014, in the city of Toledo, Ohio, a media alert informed the public that traces of microcystin, a hazardous toxin, had been detected in the drinking water. The warning stated that residents should not drink, boil, or even touch the contaminated water. A water crisis of this magnitude was recognized to pose a potentially serious and significant impact on patient care and safety in health care environments. ProMedica Toledo Hospital's Emergency Operation Plan addressed 3 critical issues: safe water availability, alternate cleaning solutions, and preparations for a prolonged crisis. This report details some of the lessons learned throughout the response to the crisis: particularly, because the impact was county-wide which affected other hospitals who used the same vendors, alternate water sources should have been secured in advance; the courier service was vital to delivery of supplies and moving equipment to alternate areas for sterilization processes; and finally, communication with staff and patients was jeopardized by external media outlets. Changes to the emergency plan considering these unanticipated aspects proved useful in a later incident and should be considered by all health care facilities as water emergency policies and procedures are created and reviewed. (Disaster Med Public Health Preparedness. 2018;12:666-668).

Cyanobacterial Toxins of the Laurentian Great Lakes, Their Toxicological Effects, and Numerical Limits in Drinking Water.

Cyanobacteria are ubiquitous phototrophic bacteria that inhabit diverse environments across the planet. Seasonally, they dominate many eutrophic lakes impacted by excess nitrogen (N) and phosphorus (P) forming dense accumulations of biomass known as cyanobacterial harmful algal blooms or cyanoHABs. Their dominance in eutrophic lakes is attributed to a variety of unique adaptations including N and P concentrating mechanisms, N2 fixation, colony formation that inhibits predation, vertical movement via gas vesicles, and the production of toxic or otherwise bioactive molecules. While some of these molecules have been explored for their medicinal benefits, others are potent toxins harmful to humans, animals, and other wildlife known as cyanotoxins. In humans these cyanotoxins affect various tissues, including the liver, central and peripheral nervous system, kidneys, and reproductive organs among others. They induce acute effects at low doses in the parts-per-billion range and some are tumor promoters linked to chronic diseases such as liver and colorectal cancer. The occurrence of cyanoHABs and cyanotoxins in lakes presents challenges for maintaining safe recreational aquatic environments and the production of potable drinking water. CyanoHABs are a growing problem in the North American (Laurentian) Great Lakes basin. This review summarizes information on the occurrence of cyanoHABs in the Great Lakes, toxicological effects of cyanotoxins, and appropriate numerical limits on cyanotoxins in finished drinking water.

Eutrophication and Warming Boost Cyanobacterial Biomass and Microcystins.

Eutrophication and warming are key drivers of cyanobacterial blooms, but their combined effects on microcystin (MC) concentrations are less studied. We tested the hypothesis that warming promotes cyanobacterial abundance in a natural plankton community and that eutrophication enhances cyanobacterial biomass and MC concentrations. We incubated natural seston from a eutrophic pond under normal, high, and extreme temperatures (i.e., 20, 25, and 30 °C) with and without additional nutrients added (eutrophication) mimicking a pulse as could be expected from projected summer storms under climate change. Eutrophication increased algal- and cyanobacterial biomass by 26 and 8 times, respectively, and led to 24 times higher MC concentrations. This effect was augmented with higher temperatures leading to 45 times higher MC concentrations at 25 °C, with 11 times more cyanobacterial chlorophyll-a and 25 times more eukaryote algal chlorophyll-a. At 30 °C, MC concentrations were 42 times higher, with cyanobacterial chlorophyll-a being 17 times and eukaryote algal chlorophyll-a being 24 times higher. In contrast, warming alone did not yield more cyanobacteria or MCs, because the in situ community had already depleted the available nutrient pool. MC per potential MC producing cell declined at higher temperatures under nutrient enrichments, which was confirmed by a controlled experiment with two laboratory strains of Microcystis aeruginosa. Nevertheless, MC concentrations were much higher at the increased temperature and nutrient treatment than under warming alone due to strongly promoted biomass, lifting N-imitation and promotion of potential MC producers like Microcystis. This study exemplifies the vulnerability of eutrophic urban waters to predicted future summer climate change effects that might aggravate cyanobacterial nuisance.

[Health Risk Assessment of Microcystins from Drinking Water Source by Monte Carlo Simulation Method].

To investigate the microcystins(MCs:MC-RR, MC-LR and MC-YR) exposure from drinking water source and to assess the health risk using Monte Carlo simulation method. 90 samples randomly collected from five sample points set along the river were determined using the national standard method (GB/T 20466-2006) during the period of January to June 2016. Professional risk assessment software@Risk7.0 was used to evaluate the dietary intake (exposure) risk of MCs based on building a nonparametric probabilistic evaluation model. First, 90 samples with the MCs were collected for fitting of distribution and the optimal fitting distribution model was selected from the results of three statistical test methods:the Chi-Squared test, the Anderson-Darling test and the Kolmogorov-Smirnov test. Of the 90 water samples tested, the most frequently detectable MCs was MC-RR with the detectable rate of up to 51.11% within the content range of 0.0017-0.3863 µg·L-1, followed by 47.78% of MC-LR within the range of 0.0285-0.2796 µg·L-1, and 21.11% of MC-YR within 0.0030-0.1362 µg·L-1. These results indicated that vast majority of MCs in testing samples were at relatively low levels with the highest concentration of MC-RR at 0.3863 µg·L-1 and MC-YR concentration was the lowest from drinking water source. The fit distribution of MC-LR concentration was the ExtValueMin(0.11391, 0.098462) and that of MC-RR was Logistic(0.058064, 0.053044)(the first number was µ as the position parameter, the second number was σ as the scale parameter). The result indicated that health risks of MC-LR from drinking water source were higher than those of MC-RR and MCs pollution and would lead to high potential health risks especially for children. The health risks caused by the MC-LR from drinking water source for children were significantly higher than the maximum allowance levels recommended by USEPA(1×10-4), and the health risks caused by the MC-LR from drinking water source for adults were significantly higher than the maximum allowance levels recommended by ICRP(5×10-5). Therefore, it is necessary to strengthen the protection and monitoring of drinking water source for effective control of water pollution and protection of human health.

Critical Role of Endoplasmic Reticulum Stress in Cognitive Impairment Induced by Microcystin-LR.

Recent studies showed that cyanobacteria-derived microcystin-leucine-arginine (MCLR) can cause hippocampal pathological damage and trigger cognitive impairment; but the underlying mechanisms have not been well understood. The objective of the present study was to investigate the mechanism of MCLR-induced cognitive deficit; with a focus on endoplasmic reticulum (ER) stress. The Morris water maze test and electrophysiological study demonstrated that MCLR caused spatial memory injury in male Wistar rats; which could be inhibited by ER stress blocker; tauroursodeoxycholic acid (TUDCA). Meanwhile; real-time polymerase chain reaction (real-time PCR) and immunohistochemistry demonstrated that the expression level of the 78-kDa glucose-regulated protein (GRP78); C/EBP homologous protein (CHOP) and caspase 12 were significantly up-regulated. These effects were rescued by co-administration of TUDCA. In agreement with this; we also observed that treatment of rats with TUDCA blocked the alterations in ER ultrastructure and apoptotic cell death in CA1 neurons from rats exposed to MCLR. Taken together; the present results suggested that ER stress plays an important role in potential memory impairments in rats treated with MCLR; and amelioration of ER stress may serve as a novel strategy to alleviate damaged cognitive function triggered by MCLR.

Effect of Environmental Factors on Cyanobacterial Abundance and Cyanotoxins Production in Natural and Drinking Water, Bangladesh.

Cyanobacterial blooms commonly appear during the summer months in ponds, lakes and reservoirs in Bangladesh. In these areas, fish mortality, odorous water and fish and human skin irritation and eye inflammation have been reported. The influence of physicochemical factors on the occurrence of cyanobacteria and its toxin levels were evaluated in natural and drinking water in Bangladesh. A highly sensitive immunosorbent assay was used to detect microcystins (MCs). Cyanobacteria were found in 22 of 23 samples and the dominant species were Microcystis aeruginosa, followed by Microcystisflosaquae, Anabeana crassa and Aphanizomenon flosaquae. Cyanobacterial abundance varied from 39 to 1315 x 10(3) cells mL(-1) in natural water and 31 to 49 x 10(3) cells mL(-1) in tap water. MC concentrations were 25-82300 pg mL(-1) with the highest value measured in the fish research pond, followed by Ishakha Lake. In tap water, MC concentrations ranged from 30-32 pg mL(-1). The correlation between nitrate-nitrogen (NO3-N) concentration and cyanobacterial cell abundance was R2 = 0.62 while that between cyanobacterial abundance and MC concentration was R2 = 0.98. The increased NO3-N from fish feed, organic manure, poultry and dairy farm waste and fertilizer from agricultural land eutrophicated the water bodies and triggered cyanobacterial bloom formation. The increased amount of cyanobacteria produced MCs, subsequently reducing the water quality.

Freshwater harmful algal blooms: toxins and children's health.

Massive accumulations of cyanobacteria (a.k.a. "blue-green algae"), known as freshwater harmful algal blooms (FHABs), are a common global occurrence in water bodies used for recreational purposes and drinking water purification. Bloom prevalence is increased due to anthropogenic changes in land use, agricultural activity, and climate change. These photosynthetic bacteria produce a range of toxic secondary metabolites that affect animals and humans at both chronic and acute dosages. Children are especially at risk because of their lower body weight, behavior, and toxic effects on development. Here we review common FHAB toxins, related clinical symptoms, acceptable concentrations in drinking water, case studies of children's and young adults' exposures to FHAB toxins through drinking water and food, methods of environmental and clinical detection in potential cases of intoxication, and best practices for FHAB prevention.

Global effects of subchronic treatment of microcystin-LR on rat splenetic protein levels.

Microcystin-LR (MCLR), released by toxic cyanobacterial blooms, has received worldwide concerns in the past decades for its hepatotoxicity. Recent studies show that microcystins (MCs) can be accumulated in immune organs and exert notable immunotoxicity. In order to better understand cellular responses in immune tissues disrupted by MCLR treatment, this work mainly focuses on the spleen impairments of rats. After a subchronic 50 d exposure (1 or 10 µg/kg body weight per day), spleen index, MCLR accumulation, histological change and plasma lysozyme activity were detected in MCLR-treated rat. Results indicated that prolonged exposure of MCLR led to toxin accumulation and caused severe damage in spleen of rats, and eventually impaired the immune functions. To further our understanding of the toxic effects of MCLR on the spleen and the mechanisms behind it, a proteomic analysis was performed to determine the global effects of MCLR on splenetic protein levels. In total, 48 proteins were identified and showed a significant increase or decrease in abundance compared to the control after MCLR exposure. These proteins are mainly involved in immune response, oxidative stress, energetic metabolism and the cytoskeleton assembly, indicating that MCLR exerts complex toxic effects in rat spleen and jointly results in immunotoxicity.

Oxidative stress and detoxification biomarker responses in aquatic freshwater vertebrates exposed to microcystins and cyanobacterial biomass.

Cyanobacterial blooms represent a serious threat to the aquatic environment. Among other effects, biochemical markers have been studied in aquatic vertebrates after exposures to toxic cyanobacteria. Some parameters such as protein phosphatases may serve as selective markers of exposure to microcystins, but under natural conditions, fish are exposed to complex mixtures, which affect the overall biomarker response. This review aims to provide a critical summary of biomarker responses in aquatic vertebrates (mostly fish) to toxic cyanobacteria with a special focus on detoxification and oxidative stress. Detoxification biomarkers such as glutathione (GSH) and glutathione-S-transferase (GST) showed very high variability with poor general trends. Often, stimulations and/or inhibitions and/or no effects at GSH or GST have been reported, even within a single study, depending on many variables, including time, dose, tissue, species, etc. Most of the oxidative stress biomarkers (e.g., superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase) provided more consistent responses, but only lipid peroxidation (LPO) seemed to fulfill the criteria needed for biomarkers, i.e., a sufficiently long half-life and systematic response. Indeed, reviewed papers demonstrated that toxic cyanobacteria systematically elevate levels of LPO, which indicates the important role of oxidative damage in cyanobacterial toxicity. In summary, the measurement of biochemical changes under laboratory conditions may provide information on the mode of toxic action. However, comparison of different studies is very difficult, and the practical use of detoxification or oxidative stress biomarkers as diagnostic tools or early warnings of cyanobacterial toxicity is questionable.

Survivals of D. galeata in sub-tropical reservoirs: harmful effects of toxic cyanobacteria in food source.

In the present study, we tested the hypothesis that massive occurrence of cyanobacteria as food source is one of the factors limiting the distribution of the zooplankton Daphnia galeata in the warm water reservoirs of South China. D. galeata was fed with Chlorella pyrenoidosa, 4 strains of cyanobacteria (three strains of Microcystis aeruginosa: MC1, MC2 and MC3, and one strain of Pseudoanabaena sp. :PA), a mixture of C. pyrenoidosa and cyanobacterial strains, and natural particles from the reservoir where the animal was initially collected. On medium and high food levels (1 and 1.5 mg C L(-1)) of C. pyrenoidosa, D. galeata showed a typical Type III of survivorship, and had a high intrinsic rate of population increase (0.37-0.41). On low food levels, the intrinsic rate of population increase declined but lifespan largely increased (84 days). When feeding with natural particles, the intrinsic rate of increase was evidently reduced (0.19), but the maximal body length (2 mm) was much longer than that of individuals observed in the fields implying that D. galeata was strongly preyed upon by size-selective predators. Applying a mixture of Chlorella and cyanobacteria, the strain and proportion of cyanobacteria significantly affected life history variables of the animal and its somatic growth. On the sole diet of each stain of cyanobacteria, D. galeata failed to reproduce. Microcystin and colonial morphology of Microcystis strains reduced clutch size and somatic growth rate. In comparison, the less negative effect of the strain MC3 indicates that the morphology was critical for actual ingestion of toxic cyanobacteria by the zooplanktons. Pseudoanabaena sp. had a short filament (15 µm), can be easily used as a food by D. galeata. Composition of phytoplankton community plays a significant role in survival and population sizes of D. galeata and massive occurrence of cyanobacterial blooms limits the distribution of D. galeata in the reservoirs of South China.