Advances in investigating microcystin-induced liver toxicity and underlying mechanisms

Chronic exposure to low-dose MC-LR induces ileal inflammation in mice through the PI3K/AKT/mTOR pathway

The global phenomenon of cyanobacterial bloom pollution is spreading globally due to climate change and eutrophication. It is well established that harmful cyanobacteria produce a wide range of toxins including microcystin-LR (MC-LR), a cyclic heptapeptide toxin known to damage various organs. The intestinal tract is the main site of MC-LR absorption and one of the targets susceptible to toxicity. Currently, studies on the enterotoxic effects of MC-LR predominantly focused on the colorectum, with limited investigations addressing the impact of microcystins on the small intestine. Therefore, the aim of our study was to examine the impact of chronic 9-month exposure of mice to low-dose 120 μg/L MC-LR in drinking water on ileal inflammation and potential mechanisms underlying these effects. Our findings showed that in mice chronically administered with low-dose MC-LR disorganized intestinal epithelial cells, lymphocytic infiltration and disturbed crypt arrangement were detected. The results of qPCR and Western blot demonstrated that, in comparison to control, the mRNA expression levels of pro-inflammatory factors IL-6, IL-17, IL-18, and IFN-γ were markedly elevated in the ileal tissue of mice treated with MC-LR, associated with significant increases in protein expression levels of p-PI3K, p-AKT, and p-mTOR. Taken together, evidence indicates that MC-LR induces ileal inflammation and histopathological damage involved activation of the PI3K/AKT/mTOR signaling pathway.

Microcystin-LR induces lung injury in mice through the NF-κB/NLRP3 pathway

Microcystin-LR (MC-LR) a cyclic toxin produced by cyanobacterial species is known to exert detrimental effects on various organs, including lung. Several investigators demonstrated that MC-LR exerts pulmonary toxicity, but the underlying mechanisms remain unclear. This study aimed to investigate whether exposure to MC-LR-induced lung inflammation and examine the underlying mechanisms. Thirty specific pathogen-free (SPF) male mice were allocated into control and MC-LR treatment groups. Mice were intraperitoneally injected with physiological saline or MC-LR (20 μg/kg) daily for a total of 21 days. Our findings indicated that exposure to MC-LR-produced histopathological changes in lung tissue, including thickening of alveolar walls and inflammatory infiltration. MC-LR was found to upregulate mRNA expression levels of pro-inflammatory cytokines TNFα, IL-6, IL-1β, and IL-18. Further, MC-LR significantly elevated the expression levels of proteins associated with the NF-κB/NLRP3 pathway p-NF-κB, NLRP3, Caspase-1, ASC. The activation of NF-κB/NLRP3 pathway further promoted the release of inflammatory cytokine IL-1β and cleavage of pyroptosis-associated GSDMD protein. These findings indicate that MC-LR may induce lung inflammation by promoting cell pyroptosis via the activation of the NF-κB/NLRP3 pathway.

Simultaneous determination of twelve microcystins in algal supplements on the Chinese market and possible risks to exposed populations

Algae supplements are widely recognized for their nutritional benefits and are commonly marketed as natural health products. However, concerns regarding contamination with cyanobacterial toxins have been raised. Moreover, there is very little data regarding the potential contamination of algal supplements on the Chinese market by these toxins. In this study, we employed a validated solid-phase extraction ultra-high-performance liquid chromatography-tandem mass spectrometry (SPE-UHPLC-MS/MS) method to analyze algal supplements available in China. Therefore, this study optimized the extraction conditions for twelve microcystins (MCs) simultaneously using response surface methodology (RSM) and analyzed via UHPLC-MS/MS. Method validation was conducted in four supplement matrices (capsule, liquid, powder, and tablet) to ensure the method's accuracy, sensitivity, and reproducibility. Analysis of nineteen commercial algae products available in China using the validated method revealed the presence of four MCs: microcystin-LF (MC-LF), microcystin-LR (MC-LR), microcystin-LA (MC-LA), and microcystin-YR (MC-YR). Furthermore, seven products were found to contain one or more of the MCs, with two products exceeding the 1 μg/g MC limit. These findings underscore the effectiveness of the validated method in assessing MC contamination of algae supplements and consequently identifying consumers expected to be at risk from prolonged exposure to recommended daily algal supplements.

Liver Lesions in Estuarine Dolphins in the Indian River Lagoon, Florida: Does Microcystin Play a Role?

Microcystin (MC), a hepatotoxin produced by cyanobacteria, was introduced into the Indian River Lagoon (IRL), Florida, in 2005 through freshwater outflows. Since then, MC has been detected in humans, domestic animals, and wildlife in the lagoon. Potential public health effects associated with MC exposure along the IRL include an increased risk of non-alcoholic liver disease among area residents. Yet, there are limited studies characterizing liver disease, as well as the potential role of MC, in humans and animals in this region. Thus, histopathology reports (n = 133) were reviewed in the stranded common bottlenose dolphin (Tursiops truncatus truncatus) (n = 156, 2005-2024) to describe liver lesions in this important IRL sentinel. Liver and fecal samples (n = 161) from stranded individuals were screened for MC via an enzyme immunoassay (ELISA). These samples were then confirmed via the 2-methyl-3-methoxy-4-phenylbutyric acid technique (MMPB) to evaluate whether liver histopathologic lesions were linked to MC exposure. Minimally invasive MC screening methods were also assessed using respiratory swabs and vapor. Inflammation (24%, n = 32), fibrosis (23%, n = 31), lipidosis/vacuolation (11%, n = 15), and necrosis (11%, n = 14) were the most common liver anomalies observed. These non-specific lesions have been reported to be associated with MC exposure in numerous species in the peer-reviewed literature. Ten bottlenose dolphins tested positive for the toxin via ELISA, including two individuals with hepatic lipidosis, but none were confirmed by MMPB. Thus, this study did not provide evidence for MC-induced liver disease in IRL bottlenose dolphins. Other causes should be considered for the lesions observed (e.g., heavy metals, metabolic disease, and endoparasites). Respiratory swabs require further validation as a pre-mortem MC screening tool in free-ranging wildlife.

Hepatocyte apoptosis is triggered by hepatic inflammation in common carp acutely exposed to microcystin-LR or chronically exposed to Microcystis

Cyanobacterial blooms pose a serious threat to the survival of fish because of the hepatotoxicity of microcystins produced by toxic cyanobacteria such as Microcystis. Many studies have investigated the hepatotoxicity of microcystins in common carp, a freshwater fish distributed worldwide, but the hepatotoxicity mechanism has not been fully clarified. The present study aimed to investigate the mechanism underlying the hepatic inflammatory response and hepatocyte apoptosis induced by acute microcystin-LR exposure via intraperitoneal injection (71 μg/kg and 119 μg/kg) or gavage (357.08 μg/kg) and chronic exposure to toxic Microcystis blooms. The results of acute exposure revealed that microcystin-LR caused an increase in serum transaminase activity and increased the levels of inflammatory factors and inflammatory mediators, inducing a significant inflammatory response in the liver of common carp. Moreover, biochemical detection revealed that hepatocyte apoptosis occurred in the fish. Moreover, chronic toxic Microcystis exposure also caused hepatic inflammation and subsequent apoptosis mediated by the tumour necrosis factor-α (TNF-α) pathway and the mitochondrial pathway similar to acute exposure. Therefore, our study suggests that the inflammatory response induced by microcystin-LR exacerbates apoptosis, likely mediated by TNF-α. In summary, both acute microcystin-LR exposure and chronic toxic Microcystis exposure can cause inflammation in the liver of common carp, which subsequently triggers hepatocyte apoptosis mediated by the TNF-α pathway and the mitochondrial pathway. This study helps elucidate the mechanism of liver damage induced by cyanobacterial blooms in natural water.

Therapeutic Potential of Lactiplantibacillus plantarum FB091 in Alleviating Alcohol-Induced Liver Disease through Gut-Liver Axis

Alcoholic liver disease (ALD) poses a significant global health burden, often requiring liver transplantation and resulting in fatalities. Current treatments, like corticosteroids, effectively reduce inflammation but carry significant immunosuppressive risks. This study evaluates Lactiplantibacillus plantarum FB091, a newly isolated probiotic strain, as a safer alternative for ALD treatment. Using an in vivo mouse model, we assessed the effects of L. plantarum FB091 on alcohol-induced liver damage and gut microbiota composition. Alcohol and probiotics administration did not significantly impact water/feed intake or body weight. Histopathological analysis showed that L. plantarum FB091 reduced hepatocellular ballooning and inflammatory cell infiltration in liver tissues and mitigated structural damage in colon tissues, demonstrating protective effects against alcohol-induced damage. Biomarker analysis indicated that L. plantarum FB091 decreased aspartate aminotransferase levels, suggesting reduced liver damage, and increased alcohol dehydrogenase activity, indicating enhanced alcohol metabolism. Additionally, cytokine assays revealed a reduction in pro-inflammatory TNF-α and an increase in anti-inflammatory IL-10 levels in colon tissues of the L. plantarum FB091 group, suggesting an anti-inflammatory effect. Gut microbiota analysis showed changes in the L. plantarum FB091 group, including a reduction in Cyanobacteria and an increase in beneficial bacteria such as Akkermansia and Lactobacillus. These changes correlated with the recovery and protection of liver and colon health. Overall, L. plantarum FB091 shows potential as a therapeutic probiotic for managing ALD through its protective effects on liver and colon tissues, enhancement of alcohol metabolism, and beneficial modulation of gut microbiota. Further clinical studies are warranted to confirm these findings in humans.

Microcystin-LR induces histopathological injury and cell apoptosis in the hepatopancreas of white shrimp, Litopenaeus vannamei

Microcystin-LR (MC-LR), a common hepatotoxin produced by bloom-forming cyanobacteria, presents a serious threat to the health of aquatic animals. In this study, we studied the impact of MC-LR on hepatopancreas histopathology, enzyme activity, transcriptome, and apoptosis of Litopenaeus vannamei. Thus, shrimp postlarvae (1.63 ± 0.5 g) exposed to MC-LR at 500 μg/kg caused morphological lesions in the histology of the shrimp hepatopancreas, which exhibited swollen, lighter coloration and unclear edges. Moreover, MC-LR significantly altered the hepatopancreas enzyme activities such as the levels of glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), acid phosphatase (ACP), alkaline phosphatase (AKP) and lysozyme (LZM), including the state of apoptosis in hepatopancreas. From the RNA-seq analysis of the hepatopancreas, a total of 728 differentially expressed genes (DEGs) were identified, and their functions in MC-LR treatment group were involved in cellular processes, metabolic processes, biological regulation, cellular components, catalytic activity and binding. The metabolic pathways primarily associated with the DEGs included reactive oxygen species, glycerophospholipid metabolism and the phospholipase D signaling pathway. Overall, q-PCR results indicated that MC-LR led to significant changes in multiple apoptosis genes of shrimp hepatopancreas. This study expand the understanding of the effect of microcystin-LR on commercially farmed crustaceans.

Potential (co-)contamination of dairy milk with AFM1 and MC-LR and their synergistic interaction in inducing mitochondrial dysfunction in HepG2 cells

Several toxic metabolites, such as aflatoxin M1 (AFM1), are known to contaminate dairy milk. However, as mentioned in an external EFSA report, there is a knowledge gap regarding the carry-over of certain emerging toxins such as microcystin-LR (MC-LR). Therefore, this work aimed to develop an LC-MS/MS method for MC-LR quantification in dairy milk. Also, the method included AFM1 as a common fungal metabolite and applied to analyze 113 dairy milk samples collected directly after the end of the summer peak. Both toxins were below their LODs, keeping the question on MC-LR carry-over still unanswered. Moreover, an in silico analysis, using a 3D molecular modeling was performed, pointing to a possible interaction between MC-LR and milk proteins, especially β-lactoglobulin. Since AFM1 and MC-LR are hepatotoxic, their interaction in inducing mitochondrial dysfunction in HepG2 cells was investigated at low (subcytotoxic) concentrations. Live cell imaging-based assays showed an inhibition in cell viability, without involvement of caspase-3/7, and a hyperpolarization in the mitochondrial membrane potential after the exposure to a mixture of 100 ng mL-1 AFM1 and 1000 ng mL-1 MC-LR for 48h. Extracellular flux analysis revealed inhibitions of several key parameters of mitochondrial function (basal respiration, ATP-linked respiration, and spare respiratory capacity).

Contaminant Exposure and Liver and Kidney Lesions in North American River Otters in the Indian River Lagoon, Florida

The harmful algal bloom (HAB) liver toxin microcystin (MC) and trace element biomagnification were previously detected in organisms in the Indian River Lagoon (IRL), Florida. Since there are no routine screening programs for these contaminants, liver tissue from North American river otters (Lontra canadensis), an important sentinel species in the IRL, was screened for MC via enzyme-linked immunoassay (ELISA), followed by confirmatory analyses via liquid-chromatography/mass spectrometry methods (LC-MS/MS). Liver and kidney samples were evaluated for trace element (As, Cd, Co, Cu, Fe, Hg, Mn, Mo, Pb, Se, Tl, and Zn) bioaccumulation via inductively coupled plasma mass spectrometry (ICP-MS). Histopathologic evaluation of the liver and kidney was conducted to assess possible correlation with toxic insults. Forty-three river otters were evaluated (2016-2022). Microcystin was not detected in any river otter sample (n = 37). Of those tested for trace element bioaccumulation (n = 22), no sample measured above provided reference ranges or estimated toxic thresholds for this species. There were no statistically significant patterns observed based on season, year, or age class, but sex had a small influence on trace element levels in the kidney. One individual had a kidney Cu level (52 μg/g dry weight) higher than any previously reported for this species. Trace elements were detected at presumed background levels providing baselines for future monitoring. For otters with available histopathologic evaluation (n = 28), anomalies indicative of contaminant exposure (non-specific inflammation, necrosis, and/or lipidosis) were present in the liver and kidney of 18% and 4% of individuals, respectively. However, since these lesions were not linked to abnormal trace element bioaccumulation or MC exposure, other causes (e.g., infectious disease) should be considered.

Cyanobacterial Cyclic Peptides Can Disrupt Cytoskeleton Organization in Human Astrocytes-A Contribution to the Understanding of the Systemic Toxicity of Cyanotoxins

The systemic toxicity of cyclic peptides produced by cyanobacteria (CCPs) is not yet completely understood. Apart from the most known damages to the liver and kidneys, symptoms of their neurotoxicity have also been reported. Hepatotoxic CCPs, like microcystins, as well as non-hepatotoxic anabaenopeptins and planktopeptins, all exhibit cytotoxic and cytostatic effects on mammalian cells. However, responses of different cell types to CCPs depend on their specific modes of interaction with cell membranes. This study demonstrates that non-hepatotoxic planktopeptin BL1125 and anabaenopeptins B and F, at concentrations up to 10 µM, affect normal and tumor human astrocytes (NHA and U87-GM) in vitro by their almost immediate insertion into the lipid monolayer. Like microcystin-LR (up to 1 µM), they inhibit Ser/Thr phosphatases and reorganize cytoskeletal elements, with modest effects on their gene expression. Based on the observed effects on intermediate filaments and intermediate filament linkage elements, their direct or indirect influence on tubulin cytoskeletons via post-translational modifications, we conclude that the basic mechanism of CCP toxicities is the induction of inter- and intracellular communication failure. The assessed inhibitory activity on Ser/Thr phosphatases is also crucial since the signal transduction cascades are modulated by phosphorylation/dephosphorylation processes.

Histology and transcriptomic analysis reveal the inflammation and affected pathways under 2-methylisoborneol (2-MIB) exposure on grass carp

2-Methylisoborneol (2-MIB) is a common and widely distributed off-flavor compound in water. However, the toxic mechanisms of 2-MIB on aquatic organisms remain largely unexplored. In this study, grass carp larvae were exposed to different concentrations (0, 5, and 20 μg L-1) of 2-MIB for 96 h. The accumulation of 2-MIB in the dorsal muscle was measured. Histological analysis, ultrastructure observations, and transcriptomic sequencing were conducted on the liver tissues. The results showed that 2-MIB accumulated significantly in the fish muscle, with the accumulation increasing as the exposure concentration increased through gas chromatography-mass spectrometry (GC-MS) detection. Histological and ultrastructure observations indicated that 2-MIB caused concentration-dependent inflammatory infiltration and mitochondrial damage in the liver. Transcriptomic analysis revealed lipid metabolism disorders induced by exposure to 2-MIB in grass carp. Additionally, 5 μg L-1 2-MIB affected the neurodevelopment and cardiovascular system of grass carp larvae through extracellular matrix (ECM)-receptor interaction and focal adhesion pathway. Furthermore, several pathways related to the digestive system were significantly enriched, implying that 2-MIB may impact pancreatic secretion function, protein digestion and absorption processes. These findings provide new insights into the potential toxicological mechanisms of 2-MIB.

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.

Magnetic recyclable visible light-driven Bi2WO6/Fe3O4/RGO for photocatalytic degradation of Microcystin-LR: Mechanism, pathway, and influencing factors

Photocatalysis was an attractive strategy that had potential to tackle the Microcystin-LR (MC-LR) contamination of aquatic ecosystems. Herein, magnetic photocatalyst Fe3O4/Bi2WO6/Reduced graphene oxide composites (Bi2WO6/Fe3O4/RGO) were employed to degrade MC-LR. The removal efficiency and kinetic constant of the optimized Bi2WO6/Fe3O4/RGO (Bi2WO6/Fe3O4-40%/RGO) was 1.8 and 2.3 times stronger than the pure Bi2WO6. The improved activity of Bi2WO6/Fe3O4-40%/RGO was corresponded to the expanded visible light adsorption ability and reduction of photogenerated carrier recombination efficiency through the integration of Bi2WO6 and Fe3O4-40%/RGO. The MC-LR removal efficiency exhibited a positive tendency to the initial density of algae cells, fulvic acid, and the concentration of MC-LR decreased. The existed anions (Cl-, CO3-2, NO3-, H2PO4-) reduced MC-LR removal efficiency of Bi2WO6/Fe3O4-40%/RGO. The Bi2WO6/Fe3O4-40%/RGO could degrade 79.3% of MC-LR at pH = 7 after 180 min reaction process. The trapping experiments and ESR tests confirmed that the h+, ∙OH, and ∙O2- played a significant role in MC-LR degradation. The LC-MS/MS result revealed the intermediates and possible degradation pathways.

Transgenerational effects of extracts containing Microcystin-LR exposure on reproductive toxicity and offspring growth inhibition in a model organism zebrafish

Cyanobacteria cell lysates release numerous toxic substances (e.g., cyanotoxins) into the water, posing a serious threat to human health and aquatic ecosystems. Microcystins (MCs) are among the most abundant cyanotoxins in the cell lysates, with microcystin-LR (MC-LR) being one of the most common and highly toxic congeners. In this study, zebrafish (Danio rerio) were exposed to different levels MC-LR that from extracts of Microcystis aeruginosa. Changes in the MC-LR accumulations, organ coefficients, and antioxidant enzyme activities in the zebrafish were analyzed. Transgenerational reproductive toxicity of MC-LR in the maternal and paternal generations was further investigated, as well as the influences of extracts containing MC-LR exposures of the F1 on the growth of zebrafish. The study found that high levels of MC-LR could be detected in the major organs of adult zebrafish, particularly in spleen. Notably, concentration of MC-LR in the spermary was significantly higher than that in the ovarium. MC-LR could induce oxidative damage by affecting the activities of catalase and superoxide dismutase. Inherited from F0, MC-LR led to impaired development in the F1 generation. Difference in offspring survival rates could be observed in the groups with different MC-LR levels of maternal and paternal exposures. This study reveals transgenerational effects of MC-LR on the reproductive toxicity and offspring growth inhibition to the aquatic organisms, which should be emphasized in the future ecological risk assessment.