Effects Of microcystin-LR Research Articles

Increased Prorenin Expression in the Kidneys May Be Involved in the Abnormal Renal Function Caused by Prolonged Environmental Exposure to Microcystin-LR.

Toxic algae in eutrophic lakes produce cyanotoxic microcystins. Prior research on the effect of microcystin-LR in the kidney utilized intraperitoneal injections, which did not reflect natural exposure. Oral microcystin-LR research has focused on renal function and histopathology without examining the molecular mechanisms. The present study aimed to evaluate the mechanism of microcystin-LR in the kidneys via oral administration in WKAH/HkmSlc rats over 7 weeks, alongside stimulation of the proximal tubular cells. Although there were no differences in the concentrations of plasma albumin, blood urea nitrogen, and creatinine, which are parameters of renal function, between the control and microcystin-LR-administrated rats, prorenin expression was significantly increased in the renal cortex of the rats administered microcystin-LR and the microcystin-LR-treated proximal tubular cells. The expression levels of (pro)renin receptor (PRR), transforming growth factor-β1 (TGFβ1), and α-smooth muscle actin (α-SMA) in the renal cortex did not differ significantly between the control and microcystin-LR-administered rats. However, the expression levels of prorenin were significantly positively correlated with those of PRR, TGFβ1, and α-SMA in the renal cortex of rats administered microcystin-LR. Additionally, a significant positive correlation was observed between the expression levels of TGFβ1 and α-SMA. Collectively, increased prorenin expression caused by the long-term consumption of microcystin-LR may initiate a process that influences renal fibrosis and abnormal renal function by regulating the expression levels of PRR, TGFβ1, and α-SMA.

Exposure to microcystin-LR promotes the progression of colitis-associated colorectal cancer by inducing barrier disruption and gut microbiota dysbiosis

Microcystins (MCs) are secondary metabolites generated by cyanobacterial blooms, among which microcystin-LR (MC-LR) stands out as the most widely distributed variant in aquatic environments. However, the effects of MC-LR on the colorectum and its role in promoting colorectal tumor progression remain unclear. Therefore, this study aims to scrutinize the impact of MC-LR on a mice model of colitis-associated colorectal cancer and elucidate the potential underlying molecular mechanisms. In this study, we used AOM/DSS mice and orally administered MC-LR at doses of 40 µg/kg or 200 µg/kg. Exposure to MC-LR increased tumor burden, promoted tumor growth, shortened colon size, and decreased goblet cell numbers and tight junction protein levels in intestinal tissues. Additionally, exposure to MC-LR induced alterations in the structure of gut microbiota in the mouse colon, characterized by an increase in the relative abundance of Escherichia_coli and Shigella_sonnei, and a decline in the relative abundance of Akkermansia_muciniphila. Transcriptomic analysis revealed that MC-LR exposure activated the IL-17 signaling pathway in mouse colorectal tissues and participated in inflammation regulation and immune response. Immunofluorescence results demonstrated an increase in T-helper 17 (Th17) cell levels in mouse colorectal tumors following MC-LR exposure. The results from RT-qPCR revealed that MC-LR induced the upregulation of IL-6, IL-1β, IL-10, IL-17A, TNF-α, CXCL1, CXCL2, CXCL5 and CCL20. The novelty of this study lies in its comprehensive approach to understanding the mechanisms by which MC-LR may contribute to CRC progression, offering new perspectives and valuable reference points for establishing guidance standards regarding MC-LR in drinking water. Our findings suggest that even at guideline value, MC-LR can have profound effects on susceptible mice, emphasizing the need for a reevaluation of guideline value and a deeper understanding of the role of environmental toxins in cancer progression.

Effects of microcystin-LR on immune function, lipid metabolism and intestinal microbial structure in Eriocheir sinensis

To investigate the potential toxic mechanism of Microcystin-LR (MC-LR) on juvenile Eriocheir sinensis (E. sinensis), a toxicity test was conducted by injecting MC-LR into the 3rd pereiopod. Following injection, we evaluated alterations in immune response biomarkers, antioxidant status, lipid metabolism-related genes expression, and intestinal microbiota composition in the hepatopancreas and intestinal tissues of E. sinensis. The results of immune response showed that after injection of MC-LR, the serum complement C3 level in E. sinensis significantly decreased at 48 hours (P < 0.05), whereas complement C4 level increased considerably from 12 to 96 hours (P < 0.01). The phenoloxidase system (PO) showed an increasing trend from 6 to 96 hours (P < 0.05 or P < 0.01). The levels of TNF-α, IL-6 significantly increased at 6 and 12 hours (P < 0.05 or P < 0.01). Gene expression analysis showed that FASN gene in the hepatopancreatic tissue displayed a higher expression at both 6 and 12 hours post-exposure (P < 0.01), while ALDH and ACAA2 gene exhibited a consistent downward trend from 6 to 48 hours (P < 0.05), Additionally, the mRNA levels of MECR and ACSL demonstrated a pattern of initial downregulation, followed by an upregulation, and subsequent downregulation. The antioxidant status results revealed that the levels GSH and CAT increased first and then decreased, while the activity of SOD decreased first and then increased. Meanwhile, the MDA content showed an increasing trend. 16 S rDNA analysis showed that the intestinal microbial diversity in MC-LR treatment group was significantly higher relative to the control group (P < 0.01). Compared with the control group, the MC-LR group had a significantly higher relative abundance of Proteobacteria, Fusobacteria, and Actinobacteria (P < 0.05) and a significantly lower relative abundance of Firmicutes (P < 0.01). At genus level, the relative abundance of Acinnetobacter, Flavobacterium, Acidovorax, Paracoccus, Cloacibacterium, Gemmobacter, Aeromonas, and Dechloromonas in the intestine of MC-LR-treated group was significantly increased relative to the control group (P < 0.05 or P < 0.01), but the relative abundance of Lachnospiraceae_NK4A136_group was significantly decreased (P < 0.01). The results of the study demonstrated that MC-LR could induced oxidative stress, hepatopancreas tissue damage, and intestinal microbial imbalance in E. sinensis.

Effects of microcystin-LR on purification efficiency of simulating drinking water source by Hydrocharis dubia (Bl.) backer

The safety of drinking water source directly affects human health. Microcystin-LR (MC-LR), a toxic and common pollutant in drinking water source, is released by algae and can impede the in-situ remediation effect of aquatic plant. Finding out the effect mechanism of MC-LR on the purification of drinking water by aquatic plant is the key to its application. This study aims to explore the performance and mechanism of MC-LR on drinking water source purification by Hydrocharis dubia (Bl.) backer. The optimum removal efficiency of NH4+-N, TP and COD were 90.7%, 93.2% and 77.3% at MC-LR concentration of 0.5 μg L−1, respectively. With the increase of MC-LR concentration, the pollutants removal rate was obviously inhibited causing by concentration-dependent. Furthermore, the growth and development of the Hydrocharis dubia (Bl.) backer roots were significantly promoted at the concentration of 0.1 μg L−1. The length, tips, surface area, and average diameter of the root increased by 71.3%, 271.4%, 265.5%, and 113.0%, respectively. Chlorophyll contents under low-concentration MC-LR show a 14.5%–15.7% promoting effect compared with the control group. The activities of POD and CAT were also stimulated with the MC-LR increasing (<1.0 μg L−1). Notably, the MDA contents increased with increasing MC-LR concentration (p < 0.01). This study indicates the effect mechanism of MC-LR on Hydrocharis dubia (Bl.) backer purification performance relies on the increased growth and enzyme activity of Hydrocharis dubia (Bl.) backer.

Effects of microcystin-LR on behavior, histopathology, oxidative stress, non-specific immunity and gene expression of red claw crayfish (Cherax quadricarinatus)

Microcystin-LR (MC-LR), the most prevalent cyanobacterial toxin, poses a serious threat to the survival of aquatic animals. Herein, crayfish (Cherax quadricarinatus) were treated with MC-LR at 33.06 μg kg−1 for 48 h, and the effects of MC-LR on behavior, histomorphology, oxidative stress, non-specific immunity, and gene expression were investigated to elucidate the molecular mechanisms underlying antioxidation and detoxification in crayfish. MC-LR caused vacuolation and disruption of crayfish hepatopancreatic cells, although no significant effect was observed on the structure of intestinal cells. Moreover, MC-LR increased the activity of antioxidant enzymes (SOD, CAT, GPx, GST) and up-regulated the expression of genes encoding antioxidant enzymes (ecCu,Zn-SOD, SOD, Se-GPx, GPx3P, GST). In addition, GSH was found depleted in the hepatopancreas and plasma. MC-LR activated the immune system, enhanced immunoenzyme activity (ACP, AKP) and induced the expression of immunity-related genes (C-LZM, proPO, hemocyanin). Furthermore, caspase and HSP70 genes were induced in the hepatopancreas of crayfish under MC-LR stress. Taken together, MC-LR was shown to cause a positive response in crayfish, and our findings suggested that the antioxidant activity and immune system play an important role in protecting crayfish from MC-LR stress by regulating gene expression and activities of antioxidant and immune enzymes.

Effects of microcystin-LR on mammalian ovaries

The ovaries play critical roles in regulating oocyte maturation and sex steroid hormone production and thus are critical for female reproduction. Ovarian function relies on hormone receptors and signaling pathways, making the ovaries potential targets for environmental factors, such as microcystins (MCs). MCs are a diverse group of cyanobacterial toxins generally found in eutrophic water or algal blooms. Here, we review relevant research on the associations between MC exposure and ovarian dysfunction, including their effects on ovarian morphology, folliculogenesis, steroid production, oxidative stress, endoplasmic reticulum stress, apoptosis, autophagy, and fertility. This review covers the most recent in vitro and in vivo studies in mammals. We also discuss important gaps in the literature. Overall, current evidence indicates that MC exposure causes impairments in ovarian function, but further studies are needed to elucidate the mechanisms through which MCs affect ovarian function and other female endocrine functions.

Integration of metagenomic and metabolomic insights into the effects of microcystin-LR on intestinal microbiota of Litopenaeus vannamei.

Microcystin-LR (MC-LR) is a hazardous substance that threaten the health of aquatic animals. Intestinal microbes and their metabolites can interact with hosts to influence physiological homeostasis. In this study, the shrimp Litopenaeus vannamei were exposed to 1.0 μg/l MC-LR for 72 h, and the toxic effects of MC-LR on the intestinal microbial metagenomic and metabolomic responses of the shrimp were investigated. The results showed that MC-LR stress altered the gene functions of intestinal microbial, including ABC transporter, sulfur metabolism and riboflavin (VB2) metabolism, and induced a significant increase of eight carbohydrate metabolism enzymes. Alternatively, intestinal metabolic phenotypes were also altered, especially ABC transporters, protein digestion and absorption, and the biosynthesis and metabolism of amino acid. Furthermore, based on the integration of intestinal microbial metagenomic and metabolome, four bacteria species (Demequina globuliformis, Demequina sp. NBRC 110055, Sphingomonas taxi and Sphingomonas sp. RIT328) and three metabolites (yangonin, α-hederin and soyasaponin ii) biomarkers were identified. Overall, our study provides new insights into the effects of MC-LR on the intestinal microbial functions of L. vannamei.

Effects of microcystin-LR on the colony formation of Chlorella vulgaris induced by the submerged macrophyte Potamogetom crispus

Interspecifically induced phytoplankton colony formation, which is accompanied by increased particle size and sedimentation, plays important roles in enhancing anti-predation capability and alleviating competition among photosynthetic organisms. Induced morphological changes may indirectly affect the structure of food webs and thus influence ecosystem functions. In this study, the effects of microcystin-LR (MC-LR) on colony formation of Chlorella vulgaris under induction by the submerged macrophyte Potamogetom crispus were evaluated. The growth of C. vulgaris was significantly inhibited under P. crispus stress (10g FW L−1), and the adverse influences of extracts were considerably greater than those of exudates. In addition, the cell numbers per colony and colony proportion of C. vulgaris were significantly increased with the presence of P. crispus extracts. However, in contrast to our expectation, the addition of MC-LR exerted no significant effects on the growth and morphological changes of C. vulgaris under P. crispus induction. The present research results provide additional knowledge on interspecific interactions between submerged macrophyte and green algae in the eutrophic cyanotoxin-contaminated ecosystems.

Effects of acute exposure to microcystins on hypothalamic-pituitary-adrenal (HPA), -gonad (HPG) and -thyroid (HPT) axes of female rats.

Microcystins (MCs) are common, well-known cyanobacterial toxins that can affect health of humans. Recently, it has been reported that MCs affect endocrine functions. In the present study, for the first time, histopathology, concentrations of hormones and transcription of genes along the hypothalamic-pituitary-adrenal (HPA), hypothalamic-pituitary-gonad (HPG) and hypothalamic-pituitary-thyroid (HPT) axes were examined in rats exposed to microcystin-LR (MC-LR). Female, Sprague-Dawley (SD) rats were exposed acutely to MC-LR by a single intraperitoneal (i.p.) injection at doses of 0.5, 0.75, or 1 median lethal dose (LD50), i.e. 36.5, 54.75, or 73μg MC-LR/kg body mass (bm) then euthanized 24 hours after exposure. Acute exposure to MC-LR significantly increased relative mass of adrenal in a dose-dependent manner, but relative mass of hypothalamus, pituitary, ovary and thyroid were not significantly different from respective mass in controls. However, damage to all these tissues was observed by histology. Along the HPA axis, lesser concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were observed in blood serum of exposed individuals, relative to controls. For the HPG axis, concentrations of gonadotropin-releasing hormone (GnRH) and estradiol (E2) were significantly less in rats treated with MC-LR, but greater concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone (T) were observed. Along the HPT axis, MC-LR caused greater concentrations of thyroid-stimulating hormone (TSH), but lesser concentrations of thyrotropin-releasing hormone (TRH), free tetra-iodothyronine (fT4) and tri-iodothyronine (fT3). Significant positive/negative correlations of concentrations of hormones were observed among the HPA, HPG and HPT axes. In addition, profiles of transcription of genes for synthesis of hormones along the endocrine axes and nuclear hormone receptors in adrenal, ovary and thyroid were significantly altered. Therefore, these results suggested that MC-LR affected HPA, HPG and HPT axes and exerted endocrine-disrupting effects. Effects of MC-LR on crosstalk among these three axes need further studies.

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

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

Effects of microcystin-LR and nitrite on the lifespan, reproduction, and heat shock responses of rotifer Brachionus calyciflorus at different temperatures

Cyanobacterial blooms aggravate with increasing temperature, and the increased concentrations of toxicants such as cyanotoxins and nitrite during bloom decay adversely affect the growth of aquatic animals. Heat-shock proteins (Hsps) are induced by a wide range of environmental stressors, including temperature and toxicants. In this study, Brachionus calyciflorus Pallas was exposed to different combined solutions of microcystin-LR (0, 10, 30, and 100 µg L−1) and nitrite (0, 1, 3, and 5 mg L−1) to evaluate their effects on the rotifer lifespan, the reproductive rate (R), and the responses of four Hsp genes at 20 °C, 25 °C, and 30 °C. Results revealed that single high doses of microcystin-LR (100 µg L−1) and nitrite (5 mg L−1) were harmful to the lifespan and reproduction of rotifers. Hormesis was induced by low doses of microcystin-LR (10–30 µg L−1) and nitrite (1–3 mg L−1). At different toxicant concentrations, the expression levels of Hsp40, Hsp60, Hsp70, and Hsp90 fluctuated, whereas reactive oxygen species (ROS) levels increased regardless of temperature. The two toxicants induced high levels of ROS production, which negatively affected the lifespan, R, and Hsp gene expression at 30 °C (p 0.05). Temperature, microcystin-LR, and nitrite had interactive effects on the lifespan, R, ROS levels, and Hsp gene expression levels (p < 0.05). The expression levels of Hsp genes are useful biomarkers of high-temperature exposure, and Hsp-mediated heat shock responses are important in microcystin-LR and nitrite stress tolerance of B. calyciflorus.

Effects of MC-LR on histological structure and cell apoptosis in the kidney of grass carp (Ctenopharyngodon idella)

Microcystin-LR (MC-LR) is a well-known hepatotoxin; however, increasing evidence suggests that it might induce kidney injury. Grass carp (Ctenopharyngodon idella) is one of the most important farmed species and may be affected by MC-LR releasing into waterbody during cyanobacterial bloom. Here, this present study aimed to explore the nephrotoxicity of grass carp by MC-LR. The grass carp received a single intraperitoneal injection of different doses of MC-LR (0, 25, 75, and 100 μg/kg body weight (BW)), and the kidneys were isolated at 24 and 96 h post-injection (hpi). Histopathological examination revealed kidney lesions, with severe hemorrhage, necrosis of the interstitium, and dilation of Bowman's capsule in the 75 and 100 μg MC-LR/kg BW groups. Under transmission electron microscopy, a larger number of swelling and vacuolated degeneration of mitochondria were observed; moreover, apoptotic features, such as condensed chromatin and shrinkage of cells, were observed in the 75 and 100 μg MC-LR/kg BW groups at 96 hpi. MC-LR significantly upregulated the number of apoptotic cells in the 75 and 100 μg/kg BW groups at 96 hpi as indicated by terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) assay (P < 0. 05). The results of quantitative assays showed that the mRNA expression of Bax, caspase-9, and caspase-3 in grass carp kidney were significantly increased at 96 hpi in the 75 and 100 μg MC-LR/kg BW groups compared with that in the control group, but Bcl-2 mRNA expression was significantly decreased in all the treatment groups at 24 and 96 hpi. Taken together, these results indicated that MC-LR damaged the kidney structure and resulted in renal apoptosis which may occur via the mitochondrial pathway.

Effects of Microcystin-LR on Metabolic Functions and Structure Succession of Sediment Bacterial Community under Anaerobic Conditions.

Microcystins (MCs), which are produced by harmful cyanobacteria blooms, pose a serious threat to environmental health. However, the effect of MCs on the bacterial community under anaerobic conditions is still unclear. This study examined the dynamic changes of MC-degrading capacity, metabolic activity, and structure of the bacterial community in lake sediment repeatedly treated with 1 mg/L microcystin-LR (MC-LR) under anaerobic conditions. The results showed that the MC-degrading capacity of the bacterial community was increased nearly three-fold with increased treatment frequency. However, the metabolic profile behaved in exactly opposite trend, in which the overall carbon metabolic activity was inhibited by repeated toxin addition. Microbial diversity was suppressed by the first addition of MC-LR and then gradually recovered. The 16S amplicon sequencing showed that the dominant genera were changed from Exiguobacterium and Acinetobacter to Prosthecobacter, Dechloromonas, and Agrobacterium. Furthermore, the increase in the relative abundance of Dechloromonas, Pseudomonas, Hydrogenophaga, and Agrobacterium was positively correlated with the MC-LR treatment times. This indicates that they might be responsible for MC degradation under anaerobic conditions. Our findings reveal the relationship between MC-LR and the sediment bacterial community under anaerobic conditions and indicate that anaerobic biodegradation is an effective and promising method to remediate MCs pollution.

Genotoxicity of microcystin-LR in mammalian cells: Implication from peroxynitrite produced by mitochondria

Microcystin-LR (MC-LR) is a widely known hepatotoxin which could induce the occurrence and metastasis of hepatocellular carcinoma. In recent years, with the frequent outbreak of cyanobacteria, the harm of MC-LR has gradually attracted more attention. Hence, this study focused on the effect of MC-LR on DNA damage in HepG2 cells, identifying the types and sources of free radicals that make an important function on this issue. Our data suggested that MC-LR induced concentration- and time-dependent increasement of DNA double-strand breaks (DSBs). After exposure to 1μM MC-LR for 3 days, the protein expression and immunofluorescence staining of γ-H2AX was significantly increased. Using a scavenger of mitochondrial O2.- (4-hydroxy-tempo), a inhibitor of mitochondrial NOS (7-nitroindazole), and a scavenger of ONOO- (uric acid), it was revealed that ONOO- originated from mitochondria made a significant contribution to the genotoxicity of MC-LR. Moreover, a significant decreasement of mitochondrial membrane potential (MMP) was observed. These findings suggested that peroxynitrite targeting mitochondria plays a vital role in the MC-LR-induced genotoxic response in mammalian cells.

Oral Microcystin-LR Does Not Cause Hepatotoxicity in Pigs: Is the Risk of Microcystin-LR Overestimated?

The global increase of toxin-producing cyanobacteria poses a serious risk to humans. Many investigations have shown that the cyanotoxin microcystin-LR induces hepatotoxicity in rodents. However, many of these studies applied the toxin intraperitoneally or used high oral concentrations, leading to an unrealistically high bioavailability of the toxin. Such approaches have put into question how these results translate to human exposure scenarios. Epidemiology studies have linked microcystin-LR with hepatotoxicity and liver cancer in humans, though by design these investigations cannot provide direct evidence. The present work investigated the effect of microcystin-LR exposure on pigs closely mimicking real-life human conditions. In two animal experiments, pigs were administered microcystin-LR daily by oral gavage for 35 days. Metabolomic and lipidomic tools were used to analyse blood and liver samples. In addition, blood biochemistry parameters indicative of liver function and health were studied to further investigate the potential hepatotoxic effects of microcystin-LR. Results indicated that the metabolomic and lipidomic analyses did not show a gross treatment effect in blood and liver. Furthermore, no significant alterations were found in the tested blood biochemistry parameters. No evidence of hepatotoxicity was found. These results shed more light onto the effects (or lack of effects) of low-dose oral microcystin-LR exposure. The data suggests that the risk of oral microcystin-LR exposure may be overestimated.

Effects of Microcystin-LR on the Microstructure and Inflammation-Related Factors of Jejunum in Mice.

The increasing cyanobacterial blooms have recently been considered a severe environmental problem. Microcystin-leucine arginine (MC-LR) is one of the secondary products of cyanobacteria metabolism and most harmful cyanotoxins found in water bodies. Studies show MC-LR negatively affects various human organs when exposed to it. The phenotype of the jejunal chronic toxicity induced by MC-LR has not been well described. The aim of this paper was to investigate the effects of MC-LR on the jejunal microstructure and expression level of inflammatory-related factors in jejunum. Mice were treated with different doses (1, 30, 60, 90 and 120 μg/L) of MC-LR for six months. The microstructure and mRNA expression levels of inflammation-related factors in jejunum were analyzed. Results showed that the microstructure of the jejunum was destroyed and expression levels of inflammation-related factors interleukin (IL)-1β, interleukin (IL)-8, tumor necrosis factor alpha, transforming growth factor-β1 and interleukin (IL)-10 were altered at different MC-LR concentrations. To the best of our knowledge, this is the first study that mice were exposed to a high dose of MC-LR for six months. Our data demonstrated MC-LR had the potential to cause intestinal toxicity by destroying the microstructure of the jejunum and inducing an inflammatory response in mice, which provided new insight into understanding the prevention and diagnosis of the intestinal diseases caused by MC-LR.

Ex vivo and in vivo effects of arsenite on GST and ABCC2 activity and expression in the middle intestine of the rainbow trout Oncorhynchus mykiss

In fish of freshwaters environments, the accumulation and toxic effects of arsenite (AsIII) can be attenuated by detoxification proteins such as GST and ABCC transporters. We studied the effects of AsIII on the middle intestine of O. mykiss in ex-vivo and in vivo/ex vivo assays. For the ex vivo assays, we measured the transport rate of the ABCC substrate DNP-SG and GST activity in intestinal strips and everted sacs. AsIII inhibited DNP-SG transport in a concentration-dependent manner, specifically when we applied it on the basolateral side. GST activity increased when we applied a maximum concentration of AsIII. For the in vivo/ex vivo assays, we kept fish in water with or without 7.7 μmol L−1 of AsIII for 48 h. Then, we measured DNP-SG transport rate, GST activity, and PP1 activity in intestine strips during one hour. For PP1 activity, we incubated the strips with or without microcystin-LR (MCLR), a toxin excreted through ABCC2 proteins. We also analyzed Abcc2 and Gst-π mRNA expression in intestine and liver tissue. In the group exposed in vivo to AsIII, DNP-SG transport rate and GST activity were higher and the effect of MCLR over PP1 activity was attenuated. AsIII significantly induced only Abcc2 mRNA expression in both middle intestine and liver. Our results suggest that, in the middle intestine of O. mykiss, AsIII is absorbed mainly at the basolateral side of the enterocytes, excreted to the lumen by ABCC2 transporters, and is capable of modulating Abcc2 mRNA expression by a transcriptional mechanism.

Microcystin-LR: Effects on Freshwater Catfish Heteropneustes fossilis Prolactin Cells

Background: Previous studies have been reported on the toxicity of Microcystin-LR, which is produced by cyanobacterial growth in fish, such as Heteropneustes fossilis (H. fossilis). However, no studies have been conducted on the effects of Microcystin-LR on the prolactin cells of H. fossilis. Methods: H. fossilis fish were intraperitoneally injected with Microcystin-LR (2.5μg/25g) and sacrificed after 1, 3, 5, 10 and 15 days. The blood samples were analyzed for the calcium levels. Histological slides of the pituitary prolactin cells were stained with Herlant’s tetrachrome and Heidenhan’s azan techniques, and examined under light microscopy. Results: The prolactin cells exposed to Microcystin-LR exhibited no structural changes on day 1. However, hyperactive prolactin cells exhibited cellular degranulation from day 3 to day 5. On days 10 and 15, degenerated and vacuolated prolactin cells were also observed. The nuclear volume of prolactin cells exposed to MC-LR increased progressively from day 3 to day 10 but on day 15 the nuclear volume returned to normal. The serum calcium level of MC-LR injected specimens showed hypocalcemia from day 3 to day 10. On day 15, the level became normal. Conclusions: Our results indicated that the serum calcium levels and prolactin cells were altered after exposure to microcystin-LR.

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.

Estrogenic potency of MC-LR is induced via stimulating steroidogenesis: In vitro and in vivo evidence

Waterborne microcystin-LR (MC-LR) has been reported to disrupt sex hormones, while its estrogenic potency remains controversial. We hypothesized that MC-LR could induce estrogenic effects via disrupting sex hormone synthesis, and verified this hypothesis by in vitro and in vivo assays. Effects of MC-LR (1, 10, 100, 500, 1000 and 5000 μg/L) on steroidogenesis were assessed in the H295R cells after 48 h. The contents of 17β-estradiol (E2) and testosterone (T) increased in a non-dose-dependent manner, which showed positive correlations with the expression of steroidogenic genes. In the in vivo assay, adult male zebrafish were exposed to 0.3, 1, 3, 10 and 30 μg/L MC-LR for 30 d. Similarly, E2 and T contents in the testis were increased, accompanied by extensive up-regulation of steroidogenic genes, especially cyp19a. Meanwhile, the percentage of spermatid in the testis declined. In the liver, the vtg1 gene was significantly up-regulated while both the transcriptional and protein levels of the estrogenic receptor (ER) declined. These results indicate that MC-LR induced non-dose-dependent estrogenic effects at environmental concentrations, which may result from steroidogenesis stimulation via a non-ER-mediated pathway. Our findings support a paradigm shift in the risk assessment of MC-LR from traditional toxicity to estrogenic risk, particularly at low concentrations, and emphasize the potential threat to the male reproductive capacity of wildlife in bloom areas.