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To date there are only pirfenidone (PFD) and nintedanib to be given conditional recommendation in idiopathic pulmonary fibrosis (IPF) therapies with slowing disease progression, but neither has prospectively shown a reduced mortality. It is one of the urgent topics to find effective drugs for pulmonary fibrosis in medicine. Previous studies have demonstrated that microcystin-RR (MC-RR) effectively alleviates bleomycin-induced pulmonary fibrosis, but the mechanism has not been fully elucidated yet. We further conducted a comparison of therapeutic effect on the model animals of pulmonary fibrosis between MC-RR and PFD with histopathology and the expression of the molecular markers involved in differentiation, proliferation and metabolism of myofibroblasts, a major effector cell of tissue fibrosis. The levels of the enzyme molecules for maintaining the stability of interstitial structure were also evaluated. Our results showed that MC-RR and PFD effectively alleviated pulmonary fibrosis in model mice with a decreased signaling and marker molecules associated with myofibroblast differentiation and lung fibrotic lesion. In the meantime, both MC-RR and PFD treatment are beneficial to restore molecular dynamics of interstitial tissue and maintain the stability of interstitial architecture. Unexpectedly, MC-RR, rather than PFD, showed a significant effect on inhibiting PKM2-HIF-1α signaling and reducing the level of p-STAT3. Additionally, MC-RR showed a better inhibition effect on FGFR1 expression. Given that PKM2-HIF-1α and activated STAT3 molecular present a critical role in promoting the proliferation of myofibroblasts, MC-RR as a new strategy for IPF treatment has potential advantage over PFD. [Display omitted] • Low toxicity microcystin-RR effectively alleviates pulmonary fibrosis as pirfenidone. • The medicinal application of microcystin-RR in pulmonary fibrosis could have better safety. • Microcystin-RR suppresses pyruvate kinase M2 signaling but pirfenidone does not. • Microcystin-RR impedes markedly the augment of fibroblast growth factor receptor 1. [ABSTRACT FROM AUTHOR]

Coupling different energy harvesting technologies to obtain an excellent output signal is essential for the development of high-performance self-powered electrochemical sensors. Herein, a novel hydrovoltaic-photothermal coupling self-powered electrochemical aptasensing platform was designed for sensitive detection of microcystin (MC-RR) with a digital multimeter as a direct visual readout strategy. The straightforward ultrasonic method was employed to synthesize polyaniline (PANI) and bismuth oxybromide (BiOBr) nanosheets, which were then integrated as active components in a hydrovoltaic device. The unique layer structure of two-dimensional (2D) nanomaterials BiOBr can create flexible interlayer spaces to accommodate various ions and water molecules, which was beneficial to construct evaporation-driven channels. Meanwhile, the exceptional photothermal characteristics of polyaniline could accelerate the water evaporation rate, consequently boosting the migration speed of charge carriers and increasing output signal. Moreover, a digital multimeter was connected to the constructed sensor for real-time displaying the output signal. With the assistance of aptamer, a novel self-powered electrochemical aptasensing platform was constructed for sensitive detection of MC-RR. Under optimum conditions, the output signal of the hydrovoltaic-photothermal coupling cell was linearly related to the logarithm of MC-RR concentration in the range of 1 fM to 1 nM with a detection limit of 0.31 fM (S/N = 3). Furthermore, this sensor also exhibited many advantages such as high selectivity, good repeatability and portability. Such novel strategy not only offers a completely new general approach to construct high-performance self-powered devices for the detection of MC-RR, but also provides a new strategy for advancing the miniaturization and field application of self-powered electrochemical sensors., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Microcystins (MC)-RR is a significant analogue of MC-LR, which has been identified as a hepatotoxin capable of influencing lipid metabolism and promoting the progression of liver-related metabolic diseases. However, the toxicity and biological function of MC-RR are still not well understood. In this study, the toxic effects and its role in lipid metabolism of MC-RR were investigated in hepatoblastoma cells (HepG2cells). The results demonstrated that MC-RR dose-dependently reduced cell viability and induced apoptosis. Additionally, even at low concentrations, MC-RR promoted lipid accumulation through up-regulating levels of triglyceride, total cholesterol, phosphatidylcholines and phosphatidylethaolamine in HepG2 cells, with no impact on cell viability. Proteomics and transcriptomics analysis further revealed significant alterations in the protein and gene expression profiles in HepG2 cells treated with MC-RR. Bioinformatic analysis, along with subsequent validation, indicated the upregulation of CD36 and activation of the AMPK and PI3K/AKT/mTOR in response to MC-RR exposure. Finally, knockdown of CD36 markedly ameliorated MC-RR-induced lipid accumulation in HepG2 cells. These findings collectively suggest that MC-RR promotes lipid accumulation in HepG2 cells through CD36-mediated signal pathway and fatty acid uptake. Our findings provide new insights into the hepatotoxic mechanism of MC-RR. MC-RR exposure promotes up-regulation of CD36 and activates the AMP-activated protein kinase (AMPK) and the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway, resulting in a significant augmentation of cellular triglycerides (TG), total cholesterol (T-CHO), phosphatidylethanolamine (PE), and phosphatidylcholine (PC), thus driving the observed lipid accumulation. [Display omitted] • Low concentration of MC-RR retains cell viability but promotes lipid accumulation. • MC-RR leads to augmentation of triglycerides, total cholesterol, phosphatidylethanolamine, and phosphatidylcholine. • MC-RR exposure induces significant up-regulation of CD36. • MC-RR activates AMPK and PI3K/AKT/mTOR pathway. [ABSTRACT FROM AUTHOR]

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive interstitial pulmonary disease characterized with radiographically evident pulmonary infiltrates and extracellular matrix deposition with limited treatment options. We previously described that microcystin-LR (MC-LR) reduces transforming growth factor (TGF)-β1/Smad signaling and ameliorates pulmonary fibrosis in bleomycin (BLM)-induced rat models. In the present study, we further demonstrate that microcystin-RR (MC-RR), an MC congener with lower toxicity than MC-LR, exerted an anti-fibrotic effect on BLM-induced pulmonary fibrosis rodent models and compared it with MC-LR. Our data show that MC-RR treatment attenuated BLM-associated pulmonary inflammation and collagen deposition in both therapeutic and preventive models. MC-RR reduced the expression of fibrotic markers, including vimentin, α-smooth muscle actin, collagen 1α1, and fibronectin, in rat pulmonary tissues. Furthermore, the core features of BLM-induced pulmonary fibrotic lesions were better alleviated by MC-RR than by MC-LR. MC-RR treatment substantially decreased the number of pulmonary M2 macrophages. In vitro, MC-RR attenuated the epithelial-mesenchymal transition and fibroblast-myofibroblast transition triggered by M2 macrophages. Therefore, we highlight MC-RR as a promising molecule for developing therapeutic and prophylactic strategies against IPF, a refractory lung disease.

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive interstitial pulmonary disease characterized with radiographically evident pulmonary infiltrates and extracellular matrix deposition with limited treatment options. We previously described that microcystin-LR (MC-LR) reduces transforming growth factor (TGF)-β1/Smad signaling and ameliorates pulmonary fibrosis in bleomycin (BLM)-induced rat models. In the present study, we further demonstrate that microcystin-RR (MC-RR), an MC congener with lower toxicity than MC-LR, exerted an anti-fibrotic effect on BLM-induced pulmonary fibrosis rodent models and compared it with MC-LR. Our data show that MC-RR treatment attenuated BLM-associated pulmonary inflammation and collagen deposition in both therapeutic and preventive models. MC-RR reduced the expression of fibrotic markers, including vimentin, α-smooth muscle actin, collagen 1α1, and fibronectin, in rat pulmonary tissues. Furthermore, the core features of BLM-induced pulmonary fibrotic lesions were better alleviated by MC-RR than by MC-LR. MC-RR treatment substantially decreased the number of pulmonary M2 macrophages. In vitro , MC-RR attenuated the epithelial-mesenchymal transition and fibroblast-myofibroblast transition triggered by M2 macrophages. Therefore, we highlight MC-RR as a promising molecule for developing therapeutic and prophylactic strategies against IPF, a refractory lung disease. [ABSTRACT FROM AUTHOR]

The canonical mode of action (MOA) of microcystins (MC) is the inhibition of protein phosphatases, but complete characterization of toxicity pathways is lacking. The existence of over 200 MC congeners complicates risk estimates worldwide. This work employed RNA-seq to provide an unbiased and comprehensive characterization of cellular targets and impacted cellular processes of hepatocytes exposed to either MC-LR or MC-RR congeners. The human hepatocyte cell line, HepaRG, was treated with three concentrations of MC-LR or -RR for 2 h. Significant reduction in cell survival was observed in LR1000 and LR100 treatments whereas no acute toxicity was observed in any MR-RR treatment. RNA-seq was performed on all treatments of MC-LR and -RR. Differentially expressed genes and pathways associated with oxidative and endoplasmic reticulum (ER) stress, and the unfolded protein response (UPR) were highly enriched by both congeners as were inflammatory pathways. Genes associated with both apoptotic and inflammatory pathways were enriched in LR1000. We present a model of MC toxicity that immediately causes oxidative stress and leads to ER stress and the activation of the UPR. Differential activation of the three arms of the UPR and the kinetics of JNK activation ultimately determine whether cell survival or apoptosis is favored. Extracellular exosomes were enrichment of by both congeners, suggesting a previously unidentified mechanism for MC-dependent extracellular signaling. The complement system was enriched only in MC-RR treatments, suggesting congener-specific differences in cellular effects. This study provided an unbiased snapshot of the early systemic hepatocyte response to MC-LR and MC-RR congeners and may explain differences in toxicity among MC congeners.

A novel biological material named activated carbon fibers-sodium alginate@Sphingopyxis sp. YF1 (ACF-SA@YF1) was synthesized for microcystin-RR (MC-RR) and nutrient pollutant degradation in eutrophic water. The synthesized biomaterial was characterized by scanning electron microscopy (SEM). Box-Behnken design and response surface methodology (RSM) were utilized for the optimization of conditions during the MC-RR degradation. The degradation of MC-RR and nutrient pollutants was dynamically detected. The results revealed that the optimal conditions were temperature 32.51 °C, pH 6.860, and inoculum 14.97%. The removal efficiency of MC-RR, nitrogen, phosphorus, and chemical oxygen demand were 0.76 μg/mL/h, 32.45%, 94.57%, and 64.07%, respectively. In addition, ACF-SA@YF1 also performed satisfactory cyclic stability, while the MC-RR removal efficiency was 70.38% after seven cycles and 78.54% of initial activity after 20 days of storage. Therefore, it is reasonable to believe that ACF-SA@YF1 is an effective material which has a great prospect in removing MC-RR and nutrients from freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Microcystins (MCs) are toxins produced by several cyanobacterial species found worldwide. While MCs have a common structure, the variation of two amino acids in their structure affects their toxicity. As toxicodynamics are very similar between the MC variants, their differential toxicity could rather be explained by toxicokinetic parameters. Microcystin-RR (MC-RR) is the second most abundant congener and induces toxicity through oral exposure. As intestinal permeability is a key parameter of oral toxicokinetics, the apparent permeability of MC-RR across a differentiated intestinal Caco-2 cell monolayer was investigated. We observed a rapid and large decrease of MC-RR levels in the donor compartment. However, irrespective of the loaded concentration and exposure time, the permeabilities were very low from apical to basolateral compartments (from 4 to 15 × 10−8 cm·s−1) and from basolateral to apical compartments (from 2 to 37 × 10−8 cm·s−1). Our results suggested that MC-RR would be poorly absorbed orally. As similar low permeability was reported for the most abundant congener microcystin-LR, and this variant presented a greater acute oral toxicity than MC-RR, we concluded that the intestinal permeability was probably not involved in the differential toxicity between them, in contrast to the hepatic uptake and metabolism.

Toxic cyanobacteria (TCB) are well-known worldwide for their adverse impacts on humans. Species compositions and seasonal variations of TCB in reservoirs depend on interactions between physical and chemical factors. This study was conducted to evaluate the water quality in the Aha Reservoir, Southwest China, focusing on cyanobacteria and cyanotoxins. Water samples were collected weekly or biweekly from May to September of 2015 and used to delineate temporal variations in density and distribution of toxic cyanobacteria and cyanotoxins in the reservoir. Toxic cyanobacteria identified consisted of Aphanizomenon flos-aquae, Pseudanabaena limnetica, Cylindrospermopsis sp., and Microcystis sp., with Aphanizomenon flos-aquae and Pseudanabaena limnetica being the most common and significant toxic genera. The total biomass of cyanobacteria was 17.0 mg/L. Identification and quantification of microcystin variants were conducted by high performance liquid chromatography (HPLC) using a system equipped with a photodiode array detector. Microcystin levels were between 0–3.0 μg/L, MC-RR was around 0–3.0 μg/L and MC-LR was approximately 0–0.9 μg/L. Overall, the results of this study indicate that the investigated reservoirs should be monitored regularly to minimize potential health risks to the human population. [ABSTRACT FROM AUTHOR]

Information on the catalytic role of mlrA gene-encoded enzyme (MlrA) in microcystin-RR (MC-RR) biodegradation was limited. This study succeeded in expressing mlrA homolog of Novosphingobium sp. THN1 in heterologous host for the first time, by constructing a recombinant bacterium. Mass spectrometric analysis showed that the recombinant MlrA hydrolyzed MC-RR into linear intermediate product by cleaving the peptide bond between Adda and arginine residue, greatly detoxifying MC-RR. This finding clearly manifested that the MlrA homolog of THN1 strain possesses its original catalytic function, and ring-opening constituted the first step in MC-RR biodegradation pathway of THN1 strain. Moreover, MC-RR degradation by intact recombinant cells and cell-free crude enzyme (CE) from recombinant was compared. Results exhibited that intact recombinant was able to degrade 20 μg mL −1 MC-RR more quickly than CE, with the maximum rate of 9.22 μg mL −1 h −1 in the first 8 h. Thus, this study provided new insights on the catalytic activity and roles of MlrA originated from THN1 strain in MC-RR biodegradation process, which lay a foundation for efficiently removing and detoxifying MC-RR, and exploring downstream steps in MC-RR biodegradation pathway of THN1 strain. [ABSTRACT FROM AUTHOR]

Microcystins (MCs) are a group of monocyclic heptapeptide toxins that have been shown to act as potent hepatotoxins. However, the observed symptoms of water metabolism disruption induced by microcystin-RR (MC-RR) or MCs have rarely been reported, and a relatively clear mechanism has not been identified. In the present study, male mice were divided into 4 groups (A: 140 μg/kg, B: 70 μg/kg, C: 35 μg/kg, and D: 0 μg/kg) and administered MC-RR daily for a month. On day 8 of treatment, an increase in water intake and urine output was observed in the high-dose group compared with the control, and the symptoms worsened with the repeated administration of the toxin until day 30. In addition, the urine specific gravity decreased and serum enzymes that can reflect hepatic damage increased in the high-dose group compared with the control ( P < 0.05 ). The mRNA level of angiotensinogen (AGT) in hepatocytes was upregulated to approximately 150% of the control ( P < 0.05 ), and the serum renin-angiotensin system (RAS) was activated in the high-dose group; however, signs of renal injury were not observed throughout the experiment. After the toxin treatment was completed, the high levels of the RAS and vasopressin in group A returned to normal levels within 1 week. As expected, the symptoms of polyuria and polydipsia also disappeared. Therefore, we propose that water metabolism dysfunction occurs via RAS activation caused by liver damage because the increased serum RAS levels in the experiment were consistent with the increased urine output and water intake in the mice during the observation period. In addition, we found for the first time that a RAS blocker could alleviate the observed polyuria and polydipsia and inactivate the high level of the RAS induced by MC-RR in a dose-dependent manner, which further supported our hypothesis. [ABSTRACT FROM AUTHOR]

Microcystins produced during the outbreak of cyanobacteria are a serious threat to human beings and the ecological environment, so it's important to remove microcystins from water. In this study, the magnetic metal-organic framework (MOFs) Fe 3 O 4 @ZIF-8 was prepared to adsorb microcystins. The characterization of the structure, morphology and properties of the material showed that the material had high specific surface area, great paramagnetism and obvious core-shell structure. At the same time, the effects of pH, contact time, initial concentration of microcystin-RR, temperature, coexisting ions, real water and reusability were investigated and the kinetic models and isotherm models were established. The results showed that the adsorption processes were well described by the pseudo-second-order kinetic model and Freundlich isotherm model, indicating that the adsorption process was chemical heterogeneous multi-layer adsorption process. In addition, when pH = 6.0 and temperature was 298 K, the theoretical maximum adsorption capacity of Fe 3 O 4 @ZIF-8 was calculated to be 6.055 mg·g−1 for microcystin-RR. Most importantly, Fe 3 O 4 @ZIF-8 could be separated from aqueous solution under external magnetic field easily, and maintained good adsorption performance after three cycles. The adsorption mechanism analyzed by FTIR and XPS showed that the adsorption process involved π-π accumulation, complexation reaction and electrostatic interaction. Therefore, the Fe 3 O 4 @ZIF-8 is a kind of potential material which aims to provide a new idea in the field of removing microcystins. [Display omitted] • Fe 3 O 4 @ZIF-8 adsorbed microcystin-RR(MC-RR) rapidly. • Fe 3 O 4 @ZIF-8 can be rapidly separated from water under magnetic field. • The adsorption capacities for MC-RR was 6.1 mg·g−1. [ABSTRACT FROM AUTHOR]

Screening sufficient Fermi level differentiation of photoeletrodes is significantly meaningful for developing high-performance self-powered photoelectrochemical (PEC) sensors. In this work, a dual-photoelectrode self-powered system was fabricated for sensitive detection of Microcystin-RR (MC-RR) by integration of the TiO 2 /S-doped Ti 3 C 2 photoanode and MoS 2 /S-doped Ti 3 C 2 photocathode. The introduction of S-doped Ti 3 C 2 nanosheets synergistically integrated with semiconductors (TiO 2 and MoS 2) could generate the unique Schottky junctions, which could adjust the Fermi energy levels, facilitate the separation of electron-hole pairs and broaden light absorption, leading to high photoelectric conversion efficiency. The electric output of self-powered sensing systems was increased by the substantial inherent bias between the Fermi energy levels of various photoelectrodes and the complementary functions of Schottky junctions, which provided a necessary foundation for the development of sensitive sensors. After the immobilization of the MC-RR aptamer, a novel signal-off dual-photoelectrode self-powered sensor was constructed for sensitive detection of MC-RR based on steric hindrance effect. Moreover, the as-fabricated sensor exhibited prominent analytical performance including wide detection range (10−16 M to 10−9 M), low detection limit (3.4 × 10−17 M), good selectivity, stability and reproducibility, so as to be successfully applied to real sample analysis. The designing ideas of the proposed S-doped Ti 3 C 2 MXene-based Schottky junctions can provide a foothold for the innovative construction of dual-photoelectrode internal-driven self-powered sensing platforms with satisfactory performance. [Display omitted] • S-doping Ti 3 C 2 and Schottky junctions construction were realized simultaneously by one step method. • TiO 2 /S–Ti 3 C 2 and MoS 2 /S–Ti 3 C 2 were applied to construct a dual-photoelectrode self-powered sensor for MC-RR assay. • The introduction of S-doped MXene could enhance photoelectric performance and provide sufficient Fermi level differentiation. • The proposed sensor exhibited excellent analytical performance for MC-RR assay. • The sensing platform was successfully applied to evaluate MC-RR in real samples. [ABSTRACT FROM AUTHOR]

ABSTRACT 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. [ABSTRACT FROM AUTHOR]

Bench-scale tests were conducted to investigate the ozonation of Microcystin (MC)-RR obtained from cyanobacterial blooms in this study. The effects of ozone dose, initial MC-RR concentration, solution pH, and coexisting anions on the MC-RR ozonation kinetics were evaluated. Results showed that the MC-RR ozonation well followed the pseudo-first-order degradation kinetics under different experimental conditions. At pH 7 and 461.5 μg/L MC-RR, the degradation rate constant dramatically increased from 0.0125 to 0.0623 min−1with the increase of the ozone dose from 0.31 to 1.35 mg/L, but was not significantly affected by the initial MC-RR concentration. Typically, an acidic condition favored the MC-RR degradation. As the pH increased from 3.1 to 10.1, the rate constant decreased from 0.1906 to 0.0102 min−1at an O3dose of 0.82 mg/L. Different inorganic anions exhibited different behaviors in the MC-RR degradation.slightly enhanced the decomposition, while, Cl−, andslowed the degradation to different degrees. Particularly, the inhibiting effect ofwas significant, probably due to its scavenging effect. These results demonstrated that ozonation appears to be a promising treatment method in the removal of MC-RR from water sources. [ABSTRACT FROM PUBLISHER]

Microcystin-RR (MC-RR) is a dominant variant of microcystin (MC) worldwide. We previously isolated Sphingopyxis sp. USTB-05, which can efficiently biodegrade MC-RR. At least three enzymes encoded by MC-degrading genes are involved. Based on the successful expression of the first gene USTB- 05- A, the second ( USTB- 05- B, KC513423) and third ( USTB- 05- C, KC573527) genes involved in the biodegradation of MC-RR were further cloned from Sphingopyxis sp. USTB-05 and expressed in Escherichia coli BL21 (DE3). After purification, the MC-degrading enzymes encoded by these genes were used for the catalytic degradation of MC-RR. The results demonstrated that the second enzyme encoded by USTB- 05- B could convert linear MC-RR to a tetrapeptide by breaking the Ala-Arg bond. The third enzyme encoded by USTB- 05- C could cleave Adda-Glu peptide bonds of both linear MC-RR and the tetrapeptide of Adda-Glu-Mdha-Ala, producing Adda as their common product. These findings will help better understand the biodegradation mechanism of MCs by Sphingopyxis sp. USTB-05. [ABSTRACT FROM AUTHOR]

Cyanobacterial bloom, a common phenomenon nowadays often results in the depletion of dissolved oxygen (hypoxia) and releases microcystin-RR (MC-RR) in the water. Information on the combined effects of MC-RR and hypoxia on the goldfish is lacking, therefore, this study is aimed at evaluating the effect of two doses of MC-RR on the antioxidants and globin mRNA of goldfish under normoxia, hypoxia and reoxygenation. The result showed that MC-RR at both doses (50 and 200μgkg−1 body weight) significantly (p<0.05) induced superoxide dismutase activities in the liver and kidney but catalase activities and total antioxidant capacity were low in these organs during hypoxia and reoxygenation compared to normoxia and control. Myoglobin and neuroglobin mRNAs in MC-RR group were significantly induced in the brain only and are believed to protect the brain from oxidative damage. However, other organs were unprotected and extensive damage was observed in the liver cells. Our results clearly demonstrated that MC-RR and hypoxia-reoxygenation transitions were synergistically harmful to the goldfish and could impair its adaptation to hypoxia, especially during reoxygenation. [ABSTRACT FROM AUTHOR]

Microcystins (MCs) are toxins produced by several cyanobacterial species found worldwide. While MCs have a common structure, the variation of two amino acids in their structure affects their toxicity. As toxicodynamics are very similar between the MC variants, their differential toxicity could rather be explained by toxicokinetic parameters. Microcystin-RR (MC-RR) is the second most abundant congener and induces toxicity through oral exposure. As intestinal permeability is a key parameter of oral toxicokinetics, the apparent permeability of MC-RR across a differentiated intestinal Caco-2 cell monolayer was investigated. We observed a rapid and large decrease of MC-RR levels in the donor compartment. However, irrespective of the loaded concentration and exposure time, the permeabilities were very low from apical to basolateral compartments (from 4 to 15 × 10−8 cm·s−1) and from basolateral to apical compartments (from 2 to 37 × 10−8 cm·s−1). Our results suggested that MC-RR would be poorly absorbed orally. As similar low permeability was reported for the most abundant congener microcystin-LR, and this variant presented a greater acute oral toxicity than MC-RR, we concluded that the intestinal permeability was probably not involved in the differential toxicity between them, in contrast to the hepatic uptake and metabolism. [ABSTRACT FROM AUTHOR]

Microcystins (MCs), produced by Microcystis sp, are the most commonly detected cyanotoxins in freshwater, and due to their toxicity, worldwide distribution, and persistence in water, an improvement in the monitoring programs for their early detection and removal from water is necessary. To this end, we investigate the performance of three covalent organic frameworks (COFs), TpBD-(CF 3 ) 2 , TpBD-(NO 2 ) 2 , and TpBD-(NH 2 ) 2 , for the adsorption of the most common and/or toxic MC derivatives, MC-LR, MC-RR, MC-LA, and MC-YR, from water. While MC-LR and MC-YR can be efficiently adsorbed using all three COF derivatives, high adsorption efficiencies were found for the most lipophilic toxin, MC-LA, with TpBD-(NH 2 ) 2 , and the most hydrophilic one, MC-RR, with TpBD-(NO 2 ). Theoretical calculations revealed that MC-LA and MC-RR have a tendency to be located mainly on the COF surface, interacting through hydrogen bonds with the amino and nitro functional groups of TpBD-(NH 2 ) 2 and TpBD-(NO 2 ) 2 , respectively. TpBD-(NO 2 ) 2 outperforms the adsorbent materials reported for the capture of MC-RR, resulting in an increase in the maximum adsorption capacity by one order of magnitude. TpBD-(NH 2 ) 2 is reported as the first efficient adsorbent material for the capture of MC-LA. Large differences in desorption efficiencies were observed for the MCs with different COFs, highlighting the importance of COF-adsorbate interactions in the material recovery. Herein we show that efficient capture of these toxins from water can be achieved through the proper selection of the COF material. More importantly, this study demonstrates that by careful choice of COF functionalities, specific compounds can be targeted or excluded from a group of analogues, providing insight into the design of more efficient and selective adsorbent materials.

The effects of microcystin-RR (MC-RR) on water metabolism were studied on Sprague-Dawley (SD) rats and KunMing (KM) mice. In the single dose toxicity test, polydipsia, polyuria, hematuria and proteinuria were found in group of rats receiving a MC-RR dose of 574.7 μg/kg, and could be relieved by dexamethasone (DXM). Gradient damage was observed in kidney and liver in rats with gradient MC-RR doses of 574.7, 287.3, and 143.7 μg/kg. No significant water metabolic changes or kidney injuries were observed in mice treated with MC-RR doses of 210.0, 105.0, and 52.5 μg/kg. In the continuous exposure test, in which mice were administrated with 140.0, 70.0, and 35.0 μg/kg MC-RR for 28 days, mice in the 140.0 μg/kg group presented increasing polydipsia, polyuria, and liver damage. However, no anatomic or histological changes, including related serological and urinary indices, were found in the kidney. In summary, abnormal water metabolism can be induced by MC-RR in rats through kidney injury in single dose exposure; the kidney of SD rats is more sensitive to MC-RR than that of KM mouse; and polydipsia and polyuria in mice exposed to MC-RR for 28 days occurred but could not be attributed to kidney damage.

The canonical mode of action (MOA) of microcystins (MC) is the inhibition of protein phosphatases, but complete characterization of toxicity pathways is lacking. The existence of over 200 MC congeners complicates risk estimates worldwide. This work employed RNA-seq to provide an unbiased and comprehensive characterization of cellular targets and impacted cellular processes of hepatocytes exposed to either MC-LR or MC-RR congeners. The human hepatocyte cell line, HepaRG, was treated with three concentrations of MC-LR or -RR for 2 h. Significant reduction in cell survival was observed in LR1000 and LR100 treatments whereas no acute toxicity was observed in any MR-RR treatment. RNA-seq was performed on all treatments of MC-LR and -RR. Differentially expressed genes and pathways associated with oxidative and endoplasmic reticulum (ER) stress, and the unfolded protein response (UPR) were highly enriched by both congeners as were inflammatory pathways. Genes associated with both apoptotic and inflammatory pathways were enriched in LR1000. We present a model of MC toxicity that immediately causes oxidative stress and leads to ER stress and the activation of the UPR. Differential activation of the three arms of the UPR and the kinetics of JNK activation ultimately determine whether cell survival or apoptosis is favored. Extracellular exosomes were enrichment of by both congeners, suggesting a previously unidentified mechanism for MC-dependent extracellular signaling. The complement system was enriched only in MC-RR treatments, suggesting congener-specific differences in cellular effects. This study provided an unbiased snapshot of the early systemic hepatocyte response to MC-LR and MC-RR congeners and may explain differences in toxicity among MC congeners., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2020 Published by Elsevier Ltd.)

• Two fish species bioaccumulate microcystin analogues at different concentrations. • Mean microcystin-LR concentration significantly higher in C. gariepinus. • The hepatic response was more severe in C. gariepinus than O. mossambicus. • No significant positive correlation between microcystin levels and liver index. The Roodeplaat Dam and its three inflowing rivers are highly impacted by surrounding anthropogenic activities. The system is hyper-eutrophic and characterized by seasonal algal blooms and previous studies have reported levels of the hepatotoxin microcystin in the water of the impoundment. Limited information is available on the microcystin concentrations in the inflowing rivers and no information is available on the bioaccumulated levels and potential health effects in fish inhabiting these rivers. The aim of this study was to do a histopathological assessment and to determine the concentrations of bioaccumulated microcystins in the livers of two indicator fish species Clarias gariepinus and Oreochromis mossambicus. The results showed that the two species bioaccumulate microcystins at different concentrations and that their hepatic health response varied. The liver index was significantly higher for C. gariepinus compared to O. mossambicus. No significant positive correlation was found between the bioaccumulated microcystin levels and the liver histology index. It is recommended that this pilot study be followed by a controlled exposure study to confirm a possible cause and effect relationship between microcystin exposure and the specific liver alterations identified. [ABSTRACT FROM AUTHOR]