The toxic effects of microcystin-LR on the reproductive system of male rats in vivo and in vitro

Probiotic Lactobacillus rhamnosus modulates MCLR-induced oogenesis disorders in zebrafish: Evidence from the transcriptome

Microcystin-LR (MCLR) produced by cyanobacterial blooms have received global attention. MCLR has been recognized as a reproductive toxin to fish and poses a threat to ecosystem stability. It has been proven that probiotic dietary management can improve reproductive performance of fish. It is worth paying attention to exploring whether probiotic management can alleviate the reproductive toxicity caused by MCLR. In this investigation, adult zebrafish were exposed to different doses of MCLR solution (0, 2.2, and 22 μg/L) with or without the Lactobacillus rhamnosus GG supplementation for a duration of 28 days. The results showed that female zebrafish spawning was reduced after exposure to MCLR, but this reduction was reversed when L. rhamnosus GG was added. To elucidate how L. rhamnosus GG mitigates reproductive toxicity caused by MCLR, we examined a series of indicators of MCLR accumulation, ovarian histology, hormones, and transcriptome levels. Our study showed that L. rhamnosus GG could alleviate oogenesis disorders and ultimately attenuate MCLR-induced reproductive toxicity by reducing MCLR accumulation in the gonads, modulating the expression of endocrine system and auto/paracrine factors. The transcriptome results revealed that single or combined exposure of MCLR and L. rhamnosus GG mainly affected the endocrine system, energy metabolism, and RNA degradation and translation. Overall, our results provide new insights for alleviating MCLR-induced reproductive toxicity and help promote healthy aquaculture.

Mediation of association between semen microcystin exposure and semen quality by sex hormones in Chinese men

Numerous studies have shown microcystins (MCs) inducing male reproductive toxicity, but the underlying mechanisms in humans are unclear. Therefore, this study aimed to evaluate the mediating role of serum sex hormones in the association between MC exposure and semen quality. In this study, we measured the levels of semen MCs and serum sex hormones in Chinese men [sample 1 (n = 649); sample 2 (n = 924)]. The results showed that there was a non-significant dose-dependent relationship between semen MCs and semen volume reduction (p for trend = 0.079) in sample 1, and semen MCs were significantly negatively associated with total motility, progressive motility, curvilinear velocity, mean angular displacement and acrosome integrity (p < 0.05) in sample 2. We also found that semen MCs were significantly positively associated with serum follicle stimulating hormone (FSH) (β = 0.151; 95% CI: 0.065, 0.236), but negatively associated with serum inhibin B (INHB) (β = -0.605; 95% CI: -0.944, -0.265), and these linear associations were confirmed in restricted cubic spline (RCS) models (all pnon-linearity > 0.1). Furthermore, mediation analysis revealed that serum INHB mediated 19.86% of the adverse effect of MC exposure on acrosome integrity. In conclusion, this study reveals the mediating roles of serum sex hormones in the relationship between MC exposure and decreased semen quality in men.

Effects of sub-chronic exposure to microcystin-LR on the endocrine system of male rats

Microcystins (MCs) can cause reproductive and developmental toxicity and disrupt endocrine homeostasis in mammals. In the present study, male, Sprague-Dawley (SD) rats were administrated 3 or 30 μg MC-LR/kg, body mass (bm) per day via intraperitoneal (i.p.) injections for 6 weeks. Effects of MC-LR on histology, hormone concentrations, gene transcriptional profiles and protein expressions along the hypothalamic-pituitary-adrenal (HPA), -gonad (HPG) and -thyroid (HPT) axes were assessed. Sub-chronic administration with MC-LR caused histological damage to hypothalamus, pituitary, adrenal, testes and thyroid and affected relative masses of pituitary, adrenal and testes. The HPA axis was activated and serum concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were significantly augmented. Along the HPG axis, serum concentrations of gonadotropin-releasing hormone (GnRH) and dihydrotestosterone (DHT) were diminished, while concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T) and estradiol (E2) were augmented. For the HPT axis, only concentrations of free tetra-iodothyronine (fT4) were significantly diminished, while concentrations of thyrotropin-releasing hormone (TRH), thyroid-stimulating hormone (TSH) or free tri-iodothyronine (fT3) were not significantly changed. Also, several genes and proteins related to synthesis of steroid hormones were significantly altered. Findings of the present study illustrate that MC-LR can cause endocrine-disrupting effects through the disruption of synthesis and secretion of hormones along the HPA, HPG and HPT axes and negative feedback regulation. Also, there could be crosstalk among HPA, HPG and HPT axes. These findings elucidate mechanisms of endocrine-disrupting effects of MCs.

Potential risk of estrogenic compounds produced by water blooms to aquatic environment

Some freshwater phytoplankton species have been suggested to produce estrogenic compounds in concentrations which could cause adverse effects to aquatic biota, while other studies showed no estrogenic effects after exposure to phytoplankton extracts or pointed out possible sources of the overestimation of the estrogenic activity. This study aimed to clarify these research inconsistencies by investigating estrogenicity of biomass extracts from both environmental freshwater blooms and laboratory cyanobacterial and algae cultures by in vitro reporter bioassay. Biomasses of 8 cyanobacterial and 3 algal species from 7 taxonomic orders were extracted and tested. Next to this, samples of environmental water blooms collected from 8 independent water bodies dominated by phytoplankton species previously assessed as laboratory cultures were tested. The results showed undetectable or low estrogenicity of both freshwater blooms and laboratory cultures with E2 equivalent concentration (EEQ) in a range from LOQ up to 4.5 ng EEQ/g of dry mass. Moreover, the co-exposure of biomass extracts with environmentally relevant concentration of model estrogen (steroid hormone 17β-estradiol; E2), commonly occurring in surface waters, showed simple additive interaction. However, some of the biomass extracts elicited partially anti-estrogenic effects in co-exposure with higher E2 concentration. In conclusion, our study documents undetectable or relatively low estrogenic potential of biomass extracts from both environmental freshwater blooms and studied laboratory cultured cyanobacterial and algae species. Nevertheless, in case of very high-density water blooms, even this low estrogenicity (detected for two cyanobacterial species) could lead to EEQ content in biomass reaching effect-based trigger values indicating potential risk, if recalculated per water volume at field sites. However, these levels would not occur in water under realistic environmental scenarios and the potential estrogenic effects would be most probably minor compared to other toxic effects caused by massive freshwater blooms of such high densities.

Co-occurrence of marine and freshwater phycotoxins in oysters, and analysis of possible predictors for management

Oysters (Crassostrea virginica) were screened for 12 phycotoxins over two years in nearshore waters to collect baseline phycotoxin data and to determine prevalence of phycotoxin co-occurrence in the commercially and ecologically-relevant species. Trace to low concentrations of azaspiracid-1 and -2 (AZA1, AZA2), domoic acid (DA), okadaic acid (OA), and dinophysistoxin-1 (DTX1) were detected, orders of magnitude below seafood safety action levels. Microcystins (MCs), MC-RR and MC-YR, were also found in oysters (maximum: 7.12 μg MC-RR/kg shellfish meat wet weight), warranting consideration of developing action levels for freshwater phycotoxins in marine shellfish. Oysters contained phycotoxins that impair shellfish health: karlotoxin1-1 and 1-3 (KmTx1-1, KmTx1-3), goniodomin A (GDA), and pectenotoxin-2 (PTX2). Co-occurrence of phycotoxins in oysters was common (54%, n = 81). AZAs and DA co-occurred most frequently of the phycotoxins investigated that are a concern for human health (n = 13) and PTX2 and KmTxs co-occurred most frequently amongst the phycotoxins of concern for shellfish health (n = 9). Various harmful algal bloom (HAB) monitoring methods and tools were assessed for their effectiveness at indicating levels of phycotoxins in oysters. These included co-deployed solid phase adsorption toxin tracking (SPATT) devices, toxin levels in particulate organic matter (POM, >1.5 μm) and whole water samples and cell concentrations from water samples as determined by microscopy and quantitative real-time PCR (qPCR). The dominant phycotoxin varied between SPATTs and all other phycotoxin sample types, and out of the 11 phycotoxins detected in oysters, only four and seven were detected in POM and whole water respectively, indicating phycotoxin profile mismatch between ecosystem compartments. Nevertheless, there were correlations between DA in oysters and whole water (simple linear regression [LR]: R² = 0.6, p < 0.0001, n = 40), and PTX2 in oysters and SPATTs (LR: R² = 0.3, p = 0.001, n = 36), providing additional monitoring tools for these phycotoxins, but oyster samples remain the best overall indicators of seafood safety.

Adverse effects of microcystins on sperm: A systematic review

Eutrophication of water bodies can lead to cyanobacterial blooms, with the resultant release of microcystins (MCs), posing a threat to the ecosystem and human health. MCs are environmental toxins with male reproductive toxicity. However, there is a dearth of reviews focusing on sperm or spermatogenesis. In this paper, studies on sperm toxicity caused by MCs in recent 20 years were collected and summarized, aiming at revealing the toxic effects and potential mechanisms of MCs on sperm. Based on the previous findings, MCs can decline sperm quality and count, and cause malformation in vertebrates and invertebrates. The reason might be that MCs cause indirect damage to sperm through impairing the structure and function of the testis. The mechanisms of MCs-induced sperm toxicity mainly result from alterations in genetic material, abnormalities in the structure and function of sperm. The epigenetic modifications such as miRNA and piRNA were also involved in MC-LR-induced sperm damage. In conclusion, MCs exposure is harmful to sperm, but its direct effects and mechanisms on sperm are still not known, which remains a significant research direction. Our review will provide a basis for the protection of male reproductive health damage caused by microcystins.

Microcystin leucine arginine induces human sperm damage: Involvement of the Ca2+/CaMKKβ/AMPK pathway

As a common pollutant in the water environment, microcystin leucine arginine (MC-LR) can enter semen and damage the sperm in animals. However, the mechanism by which MC-LR damages human sperm is unclear. Therefore, human sperm samples were obtained from the Henan Provincial Sperm Bank and exposed to different concentrations (0, 1, 10, and 100 μg/L) of MC-LR for 1, 2, 4, and 6 h, to invegest the effects and potential mechanism of MC-LR on sperm. The results showed that MC-LR mainly accumulated in the neck and flagellum of human sperm. Compared to the control group, the sperm capacitation rate and motility were significantly decreased in the 100 μg/L group. After exposure of 100 μg/L of MC-LR, the central microtubule and microtubule doublet of sperm flagellum were blurred, asymmetrical, or even lost. Furthermore, the expression levels of flagellin DNAH17, SPEF2, SPAG16, SPAG6, and CFAP44 in human sperm were reduced. Also, the phosphorylation levels of CaMKKβ and AMPK can be inhibited by MC-LR. These findings revealed that MC-LR can induce functional and structural damage in human sperm, and the Ca²⁺/CaMKKβ/AMPK pathway may be involved in this process. This study will provide a basis for prevention and treatment of male fertility declines caused by MC-LR.

Microcystin-LR-induced autophagy regulates oxidative stress, inflammation, and apoptosis in grass carp ovary cells in vitro

MC-LR is one of the cyanotoxins produced by fresh water cyanobacteria. Previous studies showed that autophagy played an important role in MC-LR-induced reproduction toxicity. However, information on the toxicological mechanism is limited. In this study, MC-LR could induce autophagy and apoptosis in GCO cells in vitro. In GCO cells that had been exposed to MC-LR, the inhibitor of 3-MA effectively decreased cell viability and damaged cell ultrastructure. Oxidative stress was significantly increased in the 3-MA + MC-LR group, accompanied by significantly increased MDA content and decreased CAT activity and GST, SOD1, GPx, and GR expression levels (P < 0.05). Inflammation was more serious in the 3-MA + MC-LR group than that of MC-LR group, which was evidenced by increasing expression levels of TNFα, IL11, MyD88, TNFR1, TRAF2, JNK, CCL4, and CCL20 (P < 0.05). Interestingly, the significant decrease of Caspase-9, Caspase-7, and Bax expression and significant increase of Bcl-2 and Bcl-2/Bax ratio in 3-MA + MC-LR group compared to MC-LR group, suggesting that extent of apoptosis were reduced. Taken together, these results indicated that MC-LR induced autophagy and apoptosis in GCO cells, however, the inhibition of autophagy decreased the extent of apoptosis, induced more serious oxidative stress and inflammation, which eventually induced cell death. Our findings provided some information for exploring the toxicity of MC-LR, however, the role of autophagy require further study in vivo.

Acute exposure to microcystins affects hypothalamic-pituitary axes of male rats

Microcystins (MCs) produced by some cyanobacteria can cause toxicity in animals and humans. In recent years, growing evidence suggests that MCs can act as endocrine disruptors. This research systematically investigated effects of microcystin-LR (MC-LR) on endocrine organs, biosynthesis of hormones and positive/negative feedback of the endocrine system in rats. Male, Sprague-Dawley rats were acutely administrated MC-LR by a single intraperitoneal injection at doses of 45, 67.5 or 90 μg MC-LR/kg body mass (bm), and then euthanized 24 h after exposure. In exposed rats, histological damage of hypothalamus, pituitary, adrenal, testis and thyroid were observed. Serum concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and corticosterone (CORT), expressions of genes and proteins for biosynthesis of hormones were lesser, which indicated an overall suppression of the hypothalamus-pituitary-adrenal (HPA) axis. Along the hypothalamus-pituitary-gonadal (HPG) axis, lesser concentrations of gonadotropin-releasing hormone (GnRH) and testosterone (T), but greater concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and estradiol (E2) were observed. Except for greater transcription of cyp19a1 in testes, transcriptions of genes and proteins for T and E2 biosynthesis along the HPG axis were lesser. As for the hypothalamus-pituitary-thyroid (HPT) axis, after MCs treatment, greater concentrations of thyroid-stimulating hormone (TSH), but lesser concentrations of free tri-iodothyronine (fT3) were observed in serum. Concentrations of free tetra-iodothyronine (fT4) were greater in rats dosed with 45 μg MCs/kg, bm, but lesser in rats dosed with 67.5 or 90 μg MCs/kg, bm. Transcripts of genes for biosynthesis of hormones and receptors along the HPT axis and expressions of proteins for biosynthesis of tetra-iodothyronine (T4) and tri-iodothyronine (T3) in thyroid were significantly altered. Cross-talk among the HPA, HPG and HPT axes probably occurred. It was concluded that MCs caused an imbalance of positive and negative feedback of hormonal regulatory axes, blocked biosynthesis of key hormones and exhibited endocrine-disrupting effects.

Potential Endocrine Disruption of Cyanobacterial Toxins, Microcystins and Cylindrospermopsin: A Review

Microcystins (MCs) and cylindrospermopsin (CYN), although classified as hepatotoxins and cytotoxins, respectively, have been shown to also induce toxic effects in many other systems and organs. Among them, their potential endocrine disruption (ED) activity has been scarcely investigated. Considering the increasing relevance of ED on humans, mammals, and aquatic organisms, this work aimed to review the state-of-the-art regarding the toxic effects of MCs and CYN at this level. It has been evidenced that MCs have been more extensively investigated than CYN. Reported results are contradictory, with the presence or absence of effects, but experimental conditions also vary to a great extent. In general, both toxins have shown ED activity mediated by very different mechanisms, such as estrogenic responses via a binding estrogen receptor (ER), pathological changes in several organs and cells (testis, ovarian cells), and a decreased gonad-somatic index. Moreover, toxic effects mediated by reactive oxygen species (ROS), changes in transcriptional responses on several endocrine axes and steroidogenesis-related genes, and changes in hormone levels have also been reported. Further research is required in a risk assessment frame because official protocols for assessment of endocrine disrupters have not been used. Moreover, the use of advanced techniques would aid in deciphering cyanotoxins dose-response relationships in relation to their ED potential.

A new identity of microcystins: Environmental endocrine disruptors? An evidence-based review

Microcystins (MCs) are widely distributed cyanobacterial toxins in eutrophic waters. At present, the endocrine-disrupting effects of MCs have been extensively studied, but whether MCs can be classified as environmental endocrine disruptors (EDCs) is still unclear. This review is aimed to evaluate the rationality for MCs as to be classified as EDCs based on the available evidence. It has been identified that MCs meet eight of ten key characteristics of chemicals that can be classified as EDCs. MCs interfere with the six processes, including synthesis, release, circulation, metabolism, binding and action of natural hormones in the body. Also, they are fit two other characteristics of EDC: altering the fate of producing/responding cells and epigenetic modification. Further evidence indicates that the endocrine-disrupting effect of MCs may be an important cause of adverse health outcomes such as metabolic disorders, reproductive disorders and effects on the growth and development of offspring. Generally, MCs have endocrine-disrupting properties, suggesting that it is reasonable for them to be considered EDCs. This is of great importance in understanding and evaluating the harm done by MCs on humans.

Chronic exposure to low concentration of MC-LR caused hepatic lipid metabolism disorder

Microcystin-LR (MC-LR), a potent hepatotoxin can cause liver damages. However, research on hepatic lipid metabolism caused by long-term exposure to environmental concentrations MC-LR is limited. In the current study, mice were exposed to various low concentrations of MC-LR (0, 1, 30, 60, 90, 120 μg/L in the drinking water) for 9 months. The general parameters, serum and liver lipids, liver tissue pathology, lipid metabolism-related genes and proteins of liver were investigated. The results show that chronic MC-LR exposure had increased the levels of triglyceride (TG) and total cholesterol (TC) in serum and liver. In addition, histological observation revealed that hepatic lobules were disordered with obvious inflammatory cell infiltration and lipid droplets. More importantly, the mRNA and proteins expression levels of lipid synthesis-related nuclear sterol regulatory element binding protein-1c (nSREBP-1c), SREBP-1c, cluster of differentiation 36 (CD36), acetyl-CoA-carboxylase1 (ACC1), stearoyl-CoA desaturase1 (SCD1) and fatty acid synthase (FASN) were increased in MC-LR treated groups, the expression levels of fatty acids β-oxidation related genes peroxisomal acyl-coenzyme A oxidase 1 (ACOX1) was decreased after exposure to 60-120 μg/L MC-LR. Furthermore, the inflammatory factors interleukin 6 (IL-6) and tumor necrosis factor-α (TNF-α) were higher than that in the control group. All the findings indicated that mice were exposed to chronic low concentrations MC-LR caused liver inflammation and hepatic lipid metabolism disorder .

Water Blooms-A Potential Threat to Male Reproduction: Clues From Aquatics and Rodents

Toxic cyanobacteria blooms are a potential threat to global aquatic ecosystems and human health. Microcystin-leucine-arginine (MC-LR) is the most toxic variant of microcystins (MCs), and exposure to MCs can damage the male reproductive system. Two electronic databases were searched for controlled studies of rodents and fishes published before September 2020. Effect sizes were calculated for eight main reproductive parameters, including sperm count, sperm motility, sperm morphology, serum testosterone, testis weight, serum follicle stimulating hormone (FSH), serum luteinising hormone (LH) and serum estradiol. Nine meta-analyses of individual parameters were conducted using R version 4.0.2. Fifteen studies were included in the meta-analysis. In the studies of rodents, exposure to MC-LR by intraperitoneal injection or intragastric administration yielded statistically significant effects on sperm count (standardised mean difference (SMD) = -1.7426 (95% CI: -2.2098 to -1.2754)), abnormal sperm rate (SMD = 1.6714 (95% CI: 0.9702 to 2.3726)), sper5% CI: -3.9811 to -1.7834)), testis weight (SMD = -2.8822 (95% CI: -3.9811 to -1.7834)) and serum FSH (SMD = 0.4707 (95% CI: 0.0659 to 0.8756) changes in serum testosterone (SMD = 0.5521 (95% CI: 0.1652; 0.9391)) and estradiol (SMD = 0.6398 (95% CI: 0.1896 to 1.0900)) concentrations are considered to be statistically significant. Dose-response analysis reflected the dynamic changes of male reproductive function caused by MC. Short-term exposure to MC-LR can affect the function of the male reproductive system in rodents and fish. Elevated dosage or extended exposure time may worsen the damage. Human-related research on MC-LR exposure is very necessary to protect health and the water environment.

Long-term exposure to low concentrations of MC-LR induces blood-testis barrier damage through the RhoA/ROCK pathway

Microcystin-leucine arginine (MC-LR), an emerging water pollutant, produced by cyanobacteria, has an acute testicular toxicity. However, little is known about the chronic toxic effects of MC-LR exposure on the testis at environmental concentrations and the underlying molecular mechanisms. In this study, C57BL/6 J mice were exposed to different low concentrations of MC-LR for 6, 9 and 12 months. The results showed that MC-LR could cause testis structure loss, cell abscission and blood-testis barrier (BTB) damage. Long-term exposure of MC-LR also activated RhoA/ROCK pathway, which was accompanied by the rearrangement of α-Tubulin. Furthermore, MC-LR reduced the levels of the adherens junction proteins (N-cadherin and β-catenin) and the tight junction proteins (ZO-1 and Occludin) in a dose- and time-dependent way, causing BTB damage. MC-LR also reduced the expressions of Occludin, ZO-1, β-catenin, and N-cadherin in TM4 cells, accompanied by a disruption of cytoskeletal proteins. More importantly, the RhoA inhibitor Rhosin ameliorated these MC-LR-induced changes. Together, these new findings suggest that long-term exposure to MC-LR induces BTB damage through RhoA/ROCK activation: involvement of tight junction and adherens junction changes and cytoskeleton disruption. This study highlights a new mechanism for MC-LR-induced BTB disruption and provides new insights into the cause and treatment of BTB disruption.

Repeated exposure to microcystin-leucine-arginine potentiates excitotoxicity induced by a low dose of kainate

Microcystin-leucine-arginine (MLCR) is a cyanobacterial toxin, and has been demonstrated to cause neurotoxicity. In addition, MCLR has been identified as an inhibitor of protein phosphatase (PP)1 and PP2A, which are known to regulate the phosphorylation of various molecules related to synaptic excitability. Thus, in the present study, we examined whether MCLR exposure affects seizures induced by a low dose of kainic acid (KA; 0.05 μg, i.c.v.) administration. KA-induced seizure occurrence and seizure score significantly increased after repeated exposure to MCLR (2.5 or 5.0 μg/kg, i.p., once a day for 10 days), but not after acute MCLR exposure (2.5 or 5.0 μg/kg, i.p., 2 h and 30 min prior to KA administration), and hippocampal neuronal loss was consistently facilitated by repeated exposure to MCLR. In addition, repeated MCLR significantly elevated the membrane expression of kainate receptor GluK2 subunits, p-pan-protein kinase C (PKC), and p-extracellular signal-related kinase (ERK) at 1 h after KA. However, KA-induced membrane expression of Ca²⁺/calmodulin-dependent kinase II (CaMKII) was significantly reduced by repeated MCLR exposure. Consistent with the enhanced seizures and neurodegeneration, MCLR exposure significantly potentiated KA-induced oxidative stress and microglial activation, which was accompanied by increased expression of p-ERK and p-PKCδ in the hippocampus. The combined results suggest that repeated MCLR exposure potentiates KA-induced excitotoxicity in the hippocampus by increasing membrane GluK2 expression and enhancing oxidative stress and neuroinflammation through the modulation of p-CaMKII, p-PKC, and p-ERK.

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 73 μg 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-leucine arginine induced the apoptosis of GnRH neurons by activating the endoplasmic reticulum stress resulting in a decrease of serum testosterone level in mice

Microcystin-leucine arginine (MC-LR) is a kind of toxin produced by cyanobacterial, resulting in decrease of testosterone levels in serum and leading to impaired spermatogenesis. Gonadotropin-releasing hormone (GnRH) neurons play crucial roles in the regulation of testosterone release. Meanwhile, it has been demonstrated that MC-LR is capable of entering the GnRH neurons and inducing apoptosis. Nevertheless, the molecular mechanism of MC-LR induced apoptosis of GnRH neurons remains elusive. In present study, we found that MC-LR inhibited the cell viability of GT1-7 cells. In addition, we discovered apoptosis of GnRH neurons and GT1-7 cells treated with MC-LR. And increased intracellular ROS production and the release of intracellular Ca²⁺ were all observed following exposure to MC-LR. Furthermore, we also found the endoplasmic reticulum stress (ERs) and autophagy were activated by MC-LR. Additionally, pretreatment of the ERs inhibitor (4-Phenyl butyric acid) reduced the apoptotic rate of GT1-7 cells comparing with MC-LR exposure alone. Comparing with MC-LR treatment alone, apoptotic cell death was increased by pretreatment of GT1-7 cells with an autophagy inhibitor (3-methyladenine). Together, our data implicated that the treatment of MC-LR induced the apoptosis of GnRH neurons by activating the ERs resulting in a decrease of serum testosterone level in mice. Autophagy is a protective cellular process which was activated by ER stress and thus protected cells from apoptosis upon MC-LR exposure.

The latest advances in the reproductive toxicity of microcystin-LR

Microcystin-LR (MC-LR) is an emerging environmental pollutant produced by cyanobacteria that poses a threat to wild life and human health. In recent years, the reproductive toxicity of MC-LR has gained widespread attention, a large number of toxicological studies have filled the gaps in past research and more molecular mechanisms have been elucidated. Hence, this paper reviews the latest research advances on MC-LR-induced reproductive toxicity. MC-LR can damage the structure and function of the testis, ovary, prostate, placenta and other organs of animals and then reduce their fertility. Meanwhile, MC-LR can also be transmitted through the placenta to the offspring causing trans-generational and developmental toxicity including death, malformation, growth retardation, and organ dysfunction in embryos and juveniles. The mechanisms of MC-LR-induced reproductive toxicity mainly include the inhibition of protein phosphatase 1/2 A (PP1/2 A) activity and the induction of oxidative stress. On the one hand, MC-LR triggers the hyperphosphorylation of certain proteins by inhibiting intracellular PP1/2 A activity, thereby activating multiple signaling pathways that cause inflammation and blood-testis barrier destruction, etc. On the other hand, MC-LR-induced oxidative stress can result in cell programmed death via the mitochondrial and endoplasmic reticulum pathways. It is worth noting that epigenetic modifications are also involved in reproductive cell apoptosis, which may be an important direction for future research. Furthermore, this paper proposes for the first time that MC-LR can produce estrogenic effects in animals as an environmental estrogen. New findings and suggestions in this review could be areas of interest for future research.

IRE1 and CaMKKβ pathways to reveal the mechanism involved in microcystin-LR-induced autophagy in mouse ovarian cells

Microcystin-LR (MC-LR) is an emerging water pollutant produced by blooming cyanobacteria. It could be absorbed into human body via contaminated food and drinking water causing severe reproductive toxicity. Previous studies showed that MC-LR could regulate autophagy by inducing endoplasmic reticulum (ER) stress thereby causing female reproductive toxicity. However, the molecular mechanisms of MC-LR-induced autophagy remain to be elucidated. It is known that IRE1 and CaMKKβ pathways are two important pathways involved in autophagy induced by ER stress. Hence, this study investigated the roles of both pathways in MC-LR-induced autophagy in mouse ovarian cells. The results showed that MC-LR significantly up-regulated the expression of autophagy marker proteins LC3Ⅱ and BECLIN1 and down-regulated the expression of P62 in vivo and in vitro. MC-LR-caused increase of autophagosomes could be observed in KK-1 cells by MDC staining. MC-LR induced the formation of autolysosomes as indicated by the overlap of LAMP1 and LC3. Meanwhile, MC-LR significantly activated the proteins in IRE1 pathway (IRE1, XBP1 and JNK) and in CaMKKβ pathway (CaMKKβ, AMPK, mTOR). Furthermore, MC-LR caused weight loss and ovarian histopathological damage in mice. In contrast, after the expression and function of IRE1 and CaMKKβ were inhibited with siRNA in vitro and by inhibitors (4μ8C and STO-609, respectively) in vivo, the up-regulation of LC3Ⅱ and BECLIN1 and the degradation of P62 induced by MC-LR were significantly suppressed. MC-LR-induced autophagosomes in KK-1 cells and autolysosomes in mouse ovarian cells were also decreased. Moreover, the knockdown of IRE1 and CaMKKβ relieved MC-LR-induced histopathological injury to mouse ovaries. These results indicated that MC-LR induced ovarian cell autophagy and ovarian injury via IRE1 and CaMKKβ pathways. This study is the first study revealing the molecular mechanisms of MC-LR-induced autophagy of ovarian cells and providing new insights into the female reproductive toxicity of MC-LR.

Vitamin C Protects Porcine Oocytes From Microcystin-LR Toxicity During Maturation

Microcystin-leucine arginine (MC-LR) is the most toxic cyanotoxin found in water bodies. Microcystins are produced as secondary products of cyanobacteria metabolism. They have a stable structure, and can bioaccumulate in living organisms. Humans and livestock who drink fresh water containing MC-LR can be poisoned. However, few studies have reported the effects of MC-LR exposure on livestock or human reproduction. In this study, we used porcine oocytes as a model to explore the effects of MC-LR on oocyte maturation, and studied the impact of vitamin C (VC) administration on MC-LR-induced meiosis defects. Exposure to MC-LR significantly restricted cumulus cell expansion and decreased first polar body extrusion. Further studies showed that MC-LR exposure led to meiosis arrest by disturbing cytoskeleton dynamics with MC-LR exposed oocytes displaying aberrant spindle organization, low levels of acetylate α-tubulin, and disturbed actin polymerization. Additionally, MC-LR exposure impaired cytoplasmic maturation by inducing mitochondria dysfunction. Moreover, MC-LR also produced abnormal epigenetic modifications, and induced high levels of oxidative stress, caused DNA damage and early apoptosis. The administration of VC provided partial protection from all of the defects observed in oocytes exposed to MC-LR. These results demonstrate that MC-LR has a toxic effect on oocyte meiosis through mitochondrial dysfunction-induced ROS, DNA damage and early apoptosis. Supplementation of VC is able to protect against MC-LR-induced oocyte damage and represents a potential therapeutic strategy to improve the quality of MC-LR-exposed oocytes.

Microcystins: Biogenesis, Toxicity, Analysis, and Control

Microcystins are cyclic peptide toxins formed by cyanobacteria. These toxins are recognized for their association with algal blooms, posing a significant threat to ecosystems and drinking water quality. Due to the growing environmental concerns they raise, a comprehensive review on microcystins' genesis, toxicity, and analytical methods for their quantitative determination is outlined. Genes, including the mcyABC cluster, regulate microcystin biogenesis. Bioanalytical experiments have identified key environmental factors, such as temperature and nitrogen availability, that promote microcystin production. Microcystin toxicity is explored based on its modulatory effects on protein phosphatases 1 and 2A in specific tissues and organs. Additionally, biochemical mechanisms of chelation, transportation, resultant oxidative stress, and tumor promotion abilities of microcystins are also discussed. Various analytical methods to separate, detect, and quantify microcystins, including the quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, nuclear magnetic resonance spectroscopy, and chromatographic platforms-linked tandem mass spectrometry (LC-MS) for unequivocal structural identification, are also reviewed. Since control of microcystins in water is of great necessity, both water treatment and mechanisms of abiotic transformation and microbial degradation are also discussed.

Aberrant Expressional Profiling of Known MicroRNAs in the Liver of Silver Carp (Hypophthalmichthys molitrix) Following Microcystin-LR Exposure Based on samllRNA Sequencing

Microcystin-LR (MC-LR) poses a serious threat to human health due to its hepatotoxicity. However, the specific molecular mechanism of miRNAs in MC-LR-induced liver injury has not been determined. The aim of the present study was to determine whether miRNAs are regulated in MC-LR-induced liver toxicity by using high-throughput sequencing. Our research demonstrated that 53 miRNAs and 319 miRNAs were significantly changed after 24 h of treatment with MC-LR (50 and 200 μg/kg, respectively) compared with the control group. GO enrichment analysis revealed that these target genes were related to cellular, metabolic, and single-organism processes. Furthermore, KEGG pathway analysis demonstrated that the target genes of differentially expressed miRNAs in fish liver were primarily involved in the insulin signaling pathway, PPAR signaling pathway, Wnt signaling pathway, and transcriptional misregulation in cancer. Moreover, we hypothesized that 4 miRNAs (miR-16, miR-181a-3p, miR-451, and miR-223) might also participate in MC-LR-induced toxicity in multiple organs of the fish and play regulatory roles according to the qPCR analysis results. Taken together, our results may help to elucidate the biological function of miRNAs in MC-LR-induced toxicity.

The mechanism of Oatp1a5-mediated microcystin-leucine arginine entering into GnRH neurons

Microcystin-leucine arginine (MC-LR) enters into gonadotropin-releasing hormone (GnRH) neurons and induces decline of serum GnRH levels resulting in male reproductive toxicity via hypothalamic-pituitary-testis axis. The organic anion transporting polypeptide 1a5 (Oatp1a5) is a critical transporter for the uptake of MC-LR by GnRH neurons. However, the underlying molecular mechanisms of the transport process are still elusive. In this study, we found that the transmembrane domains 2, 8, and 9 played important roles in transporting function of Oatp1a5. In addition, our data demonstrated that N-linked glycosylation was involved in the transport of MC-LR by Oatp1a5. Moreover, we showed that N-linked glycosylation sites Asn483 and Asn492 were vital for the transport function of Oatp1a5. In summary, the study furthered our understanding of mechanisms that the uptake of MC-LR by GnRH neurons and laid a theoretical foundation for preventing MC-LR from injuring male reproductive health.

Microcystin-LR disturbs testicular development of giant freshwater prawn Macrobrachium rosenbergii

Microcystins (MCs) are produced by cyanobacterial blooms and known for their hepatotoxicity. They could cause serious damage to the reproduction of higher vertebrate mice and fish. However, few studies have focused on the reproductive toxicity of MCs to invertebrates. Giant freshwater prawn Macrobrachium rosenbergii are highly cultivated in China. During their breeding process, M. rosenbergii are often infested by cyanobacteria blooms. In the present study, to investigate the toxic effect of MCs on the testicular development of M. rosenbergii. Male M. rosenbergii were exposed to environmental relevant concentration of MC-LR for 1, 2 and 3 weeks. Results showed that MC-LR entered M. rosenbergii testis, down-regulated hemolymph testosterone (T) levels, and damaged testicular germ cells, mitochondria and cell junctions, and inhibited testicular development. Moreover, MC-LR could significantly induce the expression of gonadal development related genes in testis and eyestalk). The present results indicate that MC-LR can disrupt the testicular development of M. rosenbergii by affecting T levels and gonadal development related genes in the testis and eyestalk.

Pharmacological inhibition of TLR4/NF-κB with TLR4-IN-C34 attenuated microcystin-leucine arginine toxicity in bovine Sertoli cells

This study investigated the pharmacological inhibition of the toll-like receptor 4 (TLR4) genes as a measure to attenuate microcystin-LR (MC-LR) reproductive toxicity. Bovine Sertoli cells were pretreated with TLR4-IN-C34 (C34) for 1 hour. Thereafter the pretreated and non-pretreated Sertoli cells were cultured in medium containing 10% heat-activated fetal bovine serum + 80 μg/L MC-LR for 24 hours to assess the ability of TLR4-IN-C34 to attenuate the toxic effects of MC-LR. The results showed that TLR4-IN-C34 inhibited MC-LR-induced mitochondria membrane damage, mitophagy and downregulation of blood-testis barrier constituent proteins via TLR4/nuclear factor-kappaB and mitochondria-mediated apoptosis signaling pathway blockage. The downregulation of the mitochondria electron transport chain, energy production and DNA replication related genes (mt-ND2, COX-1, COX-2, ACAT, mtTFA) and upregulation of inflammatory cytokines (interleukin [IL]-6, tumor necrosis factor-α, IL-1β, interferon-γ, IL-4, IL-10, IL-13 and transforming growth factor β1) were modulated by TLR4-IN-C34. Taken together, we conclude that TLR4-IN-C34 inhibits MC-LR-related disruption of mitochondria membrane, mitophagy and downregulation of blood-testis barrier proteins of the bovine Sertoli cell via cytochrome c release and TLR4 signaling blockage.

Subcellular localization of microcystin in the liver and the gonads of medaka fish acutely exposed to microcystin-LR

Among the diverse toxic components produced by cyanobacteria, microcystins (MCs) are one of the most toxic and notorious cyanotoxin groups. Besides their potent hepatotoxicity, MCs have been revealed to induce potential reproductive toxicity in various animal studies. However, little is still known regarding the distribution of MCs in the reproductive organ, which could directly affect reproductive cells. In order to respond to this question, an acute study was conducted in adult medaka fish (model animal) gavaged with 10 μg.g^-1 body weight of pure MC-LR. The histological and immunohistochemical examinations reveal an intense distribution of MC-LR within hepatocytes along with a severe liver lesion in the toxin-treated female and male fish. Besides being accumulated in the hepatocytes, MC-LR was also found in the connective tissue of the ovary and the testis, as well as in oocytes and degenerative spermatocyte-like structures but not spermatocytes. Both liver and gonad play important roles in the reproductive process of oviparous vertebrates. This observation constitutes the first observation of the presence of MC-LR in reproductive cells (female, oocytes) of a vertebrate model with in vivo study. Our results, which provide intracellular localization of MC-LR in the gonad, advance our understanding of the potential reproductive toxicity of MC-LR in fish.

Sodium Selenite inhibits mitophagy, downregulation and mislocalization of blood-testis barrier proteins of bovine Sertoli cell exposed to microcystin-leucine arginine (MC-LR) via TLR4/NF-kB and mitochondrial signaling pathways blockage

This study was conducted to investigate the ameliorative effect of selenium on microcystin-LR induced toxicity in bovine Sertoli cells. Bovine Sertoli cells were pretreated with selenium (Na₂SeO₃) for 24 h after which selenium pretreated and non-pretreated Sertoli cells were cultured in medium containing 10% heat activated fetal bovine serum FBS+ 80 µg/L MC-LR to assess its ameliorative effect on MC-LR toxicity. The results show that selenium pretreatment inhibited the MC-LR induced mitophagy, downregulation and mislocalization of blood-testis barrier constituent proteins in bovine Sertoli cells via NF-kB and cytochrome c release blockage. The observed downregulation of electron transport chain (ETC) related genes (mt-ND2, COX-1, COX-2) and upregulation of inflammatory cytokines (IL-6, TNF-α, IL-1β, IFN-γ, IL-4, IL-10, 1 L-13, TGFβ1) in non-pretreated cells exposed to MC-LR were ameliorated in selenium pretreated cells. There was no significant difference (P > 0.05) in the protein levels of blood-testis barrier constituent proteins (ZO-1, occludin, connexin-43, CTNNB1, N-cadherin) and mitochondria related genes (mt-ND2, COX-1, COX-2, ACAT1, mtTFA) of selenium pretreated Sertoli cell compared to the control. Taken together, we conclude that selenium inhibits MC-LR caused Mitophagy, downregulation and mislocalization of blood-testis barrier proteins of bovine Sertoli cell via mitochondrial and TLR4/NF-kB signaling pathways blockage.

Microcystin-LR reduces the synthesis of gonadotropin-releasing hormone by activating multiple signaling pathways resulting in decrease of testosterone in mice

We previously reported Microcystin-LR (MC-LR) could enter the hypothalamus, reduce the expression of gonadotropin-releasing hormone (GnRH), and induce male reproductive barriers. However, the molecular mechanisms underlying in the hypothalamus have not been elucidated in detail. In this study, we further showed that MC-LR inhibited the synthesis of GnRH in GnRH neurons via activating protein kinase a (PKA), cAMP-response element binding protein (Creb), protein kinase c (PKC), nuclear factor kappa B (NF-κB), extracellular regulated protein kinases (Erk) and P38 protein, and thus resulted in the change of activity of transcriptional enhancers or suppressors such as Oct-1, Otx-2, Pbx1a, Dlx-2, c-Jun and c-Fos. Following exposure, MC-LR-treated mice exhibited decreased GnRH level. Our data demonstrated that MC-LR can stimulate intracellular Ca²⁺ and cAMP to activate PKC, PKA and MAPK signaling pathways in GnRH neurons, and then inhibit Pbx1a, Oct-1, Dlx-2, Otx-2 and upregulate c-Jun and c-Fos to initiate the transcription of GnRH, which provides novel insights to explore the mechanism associated with MC-LR-induced male reproductive barriers.

Microcystin-leucine arginine inhibits gonadotropin-releasing hormone synthesis in mice hypothalamus

Microcystin-leucine arginine (MC-LR) causes serum testosterone declines and male reproductive disorders. However, the molecular mechanisms underlying the pathological changes are still unclear. In the present study, we aimed to investigate the toxic effects of MC-LR on gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus. Our results demonstrated that MC-LR could enter GnRH neurons and inhibit GnRH synthesis, resulting in the decrease of serum GnRH and testosterone levels. The inhibitory effects of MC-LR on GnRH synthesis were identified to be associated with activation of the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/cAMP response element-binding protein (CREB)/c-Fos signaling pathway. With miRNA microarray analyses, we found that miR-329-3p was down-regulated most dramatically in MC-LR-treated GT1-7 cells. We then further identified that miR-329-3p regulated PRKAR1A and PRKACB expression and thus influenced GnRH synthesis. This is the first study to explore the molecular mechanism underlying the inhibitory effects of MC-LR on GnRH synthesis in the hypothalamus. Our data have provided a new perspective in the development of diagnosis and treatment strategies for male infertility as a result of dysfunction of the hypothalamic-pituitary-gonadal axis.

Single and combined exposure of microcystin-LR and nitrite results in reproductive endocrine disruption via hypothalamic-pituitary-gonadal-liver axis

Microcystin-LR (MC-LR) released by Microcystis blooms degradation usually co-exists with a chemical called nitrite, posing a serious harm to aquatic organisms. To assess the single and combined effects of MC-LR and nitrite on the reproductive endocrine system, a fully factorial experiment was designed and adult male zebrafish (Danio rerio) were exposed to 9 treatment combinations of MC-LR (0, 3, 30 μg/L) and nitrite (0, 2, 20 mg/L) for 30 d. The results showed that both MC-LR and nitrite caused concentration-dependent effects including the growth inhibition, decreased gonad index as well as testicular injuries with widen intercellular spaces and seminiferous epithelium deteriorations. And testicular pathological changes in the co-exposure groups of MC-LR and nitrite were similar but more serious than those in single-factor exposure groups. Concurrently, exposure to MC-LR or nitrite alone could significantly decrease T levels by downregulating gene expressions (gnrh2, lhβ, ar, lhr) in the hypothalamic-pituitary-gonadal-liver-axis (HPGL-axis), and there were significant interactions between MC-LR and nitrite on them. In contrast, E2 levels as well as transcriptional levels of cyp19a1b, cyp19a1a and vtg1 showed significant inductions with increasing MC-LR concentrations, indicating an estrogen-like effect of MC-LR. Our findings illustrated that co-exposure of MC-LR and nitrite synergistically cause reproductive dysfunction by interfering with the HPGL axis in male fish, which prompt us to focus more on the potential risks in fish reproduction and even population dynamics due to the wide occurrence of toxic cyanobacterial blooms.

Glutathione peroxidase-1 overexpressing transgenic mice are protected from neurotoxicity induced by microcystin-leucine-arginine

Although it has been well-recognized that microcystin-leucine-arginine (MCLR), the most common form of microcystins, induces neurotoxicity, little is currently known about the underlying mechanism for this neurotoxicity. Here, we found that MCLR (10 ng/μL/mouse, i.c.v.) induces significant neuronal loss in the hippocampus of mice. MCLR-induced neurotoxicity was accompanied by oxidative stress, as shown by a significant increase in the level of 4-hydroxynonenal, protein carbonyl, and reactive oxygen species (ROS). Superoxide dismutase-1 (SOD-1) activity was significantly increased, but glutathione peroxidase (GPx) level was significantly decreased following MCLR insult. In addition, MCLR significantly inhibited GSH/GSSG ratio, and significantly induced NFκB DNA binding activity. Because reduced activity of GPx appeared to be critical for the imbalance between activities of SODs and GPx, we utilized GPx-1 overexpressing transgenic mice to ascertain the role of GPx-1 in this neurotoxicity. Genetic overexpression of GPx-1 or NFκB inhibitor pyrrolidine dithiocarbamate (PDTC) significantly attenuated MCLR-induced hippocampal neuronal loss in mice. However, PDTC did not exert any additive effect on neuroprotection mediated by GPx-1 overexpression, indicating that NFκB is a neurotoxic target of MCLR. Combined, these results suggest that MCLR-induced neurotoxicity requires oxidative stress associated with failure in compensatory induction of GPx, possibly through activation of the transcription factor NFκB.

Microcystin-leucine arginine (MC-LR) induced inflammatory response in bovine sertoli cell via TLR4/NF-kB signaling pathway

Sertoli cells were treated with 0, 20, 40, 60 and 80 μg/L of MC-LR to investigate its toxic effects, mechanism of action and immune response of the cells. Our results revealed that treatment containing 20 μg/L of MC-LR was non-toxic to the cells. Treatments containing 40, 60 and 80 μg/L of MC-LR reduced the cell viability, induced nuclear morphological changes and downregulated the blood-testis barrier constituent proteins within 48 h after treatment. The toll-like receptor 4 (TLR4) and nuclear factor-kappaB (NF-kB) were activated and significantly (P < 0.05) upregulated in cells treated with 40, 60 and 80 μg/L of MC-LR compared to the control. The pro-inflammatory cytokines were upregulated within 48 h after treatment. However commencing from 72 h, upregulation of anti-inflammatory cytokines and expression of blood-testis barrier constituent proteins was observed. This study indicates that MC-LR induced inflammatory response in bovine Sertoli cell via activation of TLR4/NF-kB signaling pathway.

The differential effects of microcystin-LR on mitochondrial DNA in the hippocampus and cerebral cortex

Microcystin-LR (MC-LR) is the most abundant toxicant among microcystin variants produced by cyanobacteria. MC-induced toxicity is broadly reported to pose a threat to aquatic animals and humans and has been associated with the dysfunction of some organs such as liver and kidney. However, MC-induced neurotoxicity has not been well characterized after long-term exposure. This study was designed to investigate the neurotoxic effects after chronic oral administration of MC-LR. In our trial, C57/BL6 mice received MC-LR at 0, 1, 5, 10, 20 and 40 μg/L in drinking water for twelve months. Our data demonstrated that mitochondrial DNA (mtDNA) damage was evident in the damaged neurons as a result of chronic exposure. Histopathological abnormalities and mtDNA damage were observed in the hippocampus and cerebral cortex. Furthermore, MC-LR exerted distinct effects on these two brain regions. The hippocampus was more susceptible to the treatment of MC-LR compared with the cerebral cortex. However, no strong relationships were observed between the genotoxic effects and exposure doses. In conclusion, this study has provided a mtDNA-related mechanism for underlying chronic neurotoxicity of MC-LR and suggested the presence of differential toxicant effects on the hippocampus and cerebral cortex.

Genetic overexpression of glutathione peroxidase-1 attenuates microcystin-leucine-arginine-induced memory impairment in mice

Microcystin-leucine-arginine (MCLR) is the most common form of microcystins, which are environmental toxins produced by cyanobacteria, and its hepatotoxicity has been well-documented. However, the neurotoxic potential of MCLR remains to be further elucidated. In the present study, we investigated whether intracerebroventricular (i.c.v.) infusion of MCLR induces mortality and neuronal loss in the hippocampus of mice. Because we found that MCLR impairs memory function in the hippocampus at a low dose (4 ng/μl/mouse, i.c.v.) without a significant neuronal loss, we focused on this dose for further analyses. Results showed that MCLR (4 ng/μl/mouse, i.c.v.) significantly increased oxidative stress (i.e., malondialdehyde, protein carbonyl, and synaptosomal ROS) in the hippocampus. In addition, MCLR significantly increased superoxide dismutase (SOD) activity without corresponding induction of glutathione peroxidase (GPx) activity, and thus led to significant decrease in the ratio of GPx/SODs activity. The GSH/GSSG ratio was also significantly reduced after MCLR treatment. GPx-1 overexpressing transgenic mice (GPx-1 Tg) were significantly protected from MCLR-induced memory impairment and oxidative stress. The DNA binding activity of nuclear factor erythroid-derived 2-related factor 2 (Nrf2) in these mice was significantly enhanced, and the ratios of GPx/SODs activity and GSH/GSSG returned to near control levels in the hippocampus. Importantly, memory function exhibited a significant positive correlation with the ratios of GPx/SODs activity and GSH/GSSG in the hippocampus of MCLR-treated non-transgenic (non-Tg)- and GPx-1 Tg-mice. Combined, our results suggest that MCLR induces oxidative stress and memory impairment without significant neuronal loss, and that GPx-1 gene constitutes an important protectant against MCLR-induced memory impairment and oxidative stress via maintaining antioxidant defense system homeostasis, possibly through the induction of Nrf2 transcription factor.

Microcystin-leucine arginine mediates apoptosis and engulfment of Leydig cell by testicular macrophages resulting in reduced serum testosterone levels

Microcystin-leucine arginine (MC-LR) causes decline of serum testosterone levels resulting in impaired spermatogenesis; however, the underlying molecular mechanisms are not fully understood. In this study, we aimed to investigate the effects of MC-LR exposure on the number of Leydig cells (LCs) in testis. Following chronic low dose exposure to MC-LR, the number of LCs was markedly decreased while macrophages were significantly increased. Then, we established a co-culture system to study the interaction between macrophages and LCs in the presence of MC-LR. No significant apoptosis of LCs cultured alone was observed after MC-LR (< 5 000 nM) treatment; however, apoptosis was robustly increased when LCs were co-cultured with macrophages in the presence of MC-LR. Further studies identified that MC-LR could stimulate macrophage to produce TNF-α, and secreted TNF-α induced LC apoptosis by binding to the tumor necrosis factor receptor 1 (TNFR1) on the LCs and thus activating reactive oxygen species (ROS)-p38MAPK signaling pathway. Furthermore, we also examined increased expression of Axl receptor and growth arrest-specific 6 (Gas6) in macrophages after MC-LR treatment. GAS6 mediates phagocytosis of apoptotic LCs by binding to the Axl receptor on macrophages and phosphatidylserine (PtdSer) on apoptotic LCs. Together, these results suggested that reduced serum testosterone levels may be associated with decrease of LCs as a result of LC apoptosis and phagocytosis by immune cells in MC-LR-treated mice.

Effects of MCLR exposure on sex hormone synthesis and reproduction-related genes expression of testis in male Rana nigromaculata

Microcystin-leucine-arginine (MCLR) is the most popular and toxic variant among microcystins, which can cause severe reproductive toxicity to animals. However, the mechanisms of reproductive toxicity induced by MCLR in amphibians are still not entirely clear. In the current study, toxicity mechanisms of MCLR on the reproductive system of male Rana nigromaculata followed by low concentration (0, 0.1, 1, and 10 μg/L) and short-term (0, 7, and 14 days) MCLR exposure were shown. It was observed that MCLR could be bioaccumulated in the testes of male frogs, and the theoretical bioaccumulation factor values were 0.24 and 0.19 exposed to 1 μg/L and 10 μg/L MCLR for 14 days, respectively. MCLR exposure significantly decreased testosterone (T) concentrations and increased estradiol (E2) concentrations exposed to 1 and 10 μg/L MCLR for 14 days. The mRNA levels of HSD17B3 were downregulated, and HSD17B1 and CYP19A1 mRNA expression levels were upregulated, respectively. Only 10 μg/L MCLR group showed significant induction of follicle-stimulating hormone (FSH) levels and cyclic adenosine monophosphate (cAMP) content. Moreover, AR and ESR1 mRNA expression levels were significantly upregulated exposed to 1 and 10 μg/L MCLR for 14 days, respectively. Our results suggested that low-concentration MCLR induced transcription changes of CYP19A1, HSD17B3, and HSD17B1 led to endocrine disorders, and caused interference of spermatogenesis by the decrease of T and abnormal gene expressions of AR and ESR1 in the testes of R. nigromaculata.

Microcystin-leucine-arginine causes blood-testis barrier disruption and degradation of occludin mediated by matrix metalloproteinase-8

Microcystin-leucine-arginine (MC-LR) can cause male reproductive disorders. However, the underlying mechanisms are not yet fully understood. In this study, we aimed to investigate the effects of MC-LR on the integrity of blood-testis barrier (BTB) and the related molecular mechanisms. Both transepithelial electrical resistance measurement in vitro and electron microscope observation ex vivo revealed that MC-LR caused disruption of the tight junction between Sertoli cells, which was paralleled by the degradation of occludin. We observed increased expression of matrix metalloproteinase-8 (MMP-8) upon exposure to MC-LR, and confirmed that abrogation of MMP-8 activity by specific inhibitors as well as transfection with MMP-8 shRNA could abolish the degradation of occludin. Our data demonstrated that MC-LR up-regulated nuclear levels of c-Fos and c-Jun through activating ERK and JNK, and increased NF-κB levels by activating the phosphatidylinositol 3-kinase (PI3K)/AKT cascades. Enhanced binding of c-Fos and NF-κB to the promoter of MMP-8 promoted the transcription of MMP-8 gene. Furthermore, miR-184-3p was significantly downregulated in SC following exposure to MC-LR through targeting MMP-8 expression. Together, these results confirmed that MC-LR-induced MMP-8 expression was regulated at both transcriptional and post-transcriptional levels, which was involved in MC-LR-induced degradation of occludin and BTB destruction. This work may provide new perspectives in developing new diagnosis and treatment strategies for MC-induced male infertility.

Microcystin-leucine arginine exhibits immunomodulatory roles in testicular cells resulting in orchitis

Microcystin-leucine arginine (MC-LR) causes testicular inflammation and hinders spermatogenesis. However, the molecular mechanisms underlying the immune responses to MC-LR in the testis have not been elucidated in detail. In this study, we show that MC-LR induced immune responses in Sertoli cells (SC), germ cells (GC), and Leydig cells (LC) via activating phosphatidylinositol 3-kinase (PI3K)/AKT/nuclear factor kappa B (NF-κB), resulting in the production of pro-inflammatory cytokines and chemokines including tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), and chemokine (C-X-C motif) ligand 10 (CXCL10). The observed effects were attributed to reduced activity of protein phosphatases 2A (PP2A) as a result of binding of MC-LR to the catalytic subunit of PP2A in SC and GC. By contrast, innate immune responses were triggered by Toll-like receptor 2 (TLR2) in LC because MC-LR could not enter into the LC and subsequently inhibit the PP2A activity. PI3K/AKT/NF-κB were also activated in SC, GC, and LC in vivo, with the enrichment of TNF-α, IL-6, MCP-1, and CXCL10 in the testis. Following chronic exposure, MC-LR-treated mice exhibited decreased sperm counts and abnormal sperm morphology. Our data demonstrate that MC-LR can activate innate immune responses in testicular cells, which provides novel insights to explore the mechanism associated with MC-LR-induced orchitis.

Roles of piRNAs in microcystin-leucine-arginine (MC-LR) induced reproductive toxicity in testis on male offspring

In the present study, we evaluated the toxic effects on the testis of the male offspring of MC-LR exposure during fetal and lactational periods. Pregnant females were distributed into two experimental groups: control group and MC-LR group which were exposed to 0 and 10 μg/L of MC-LR, respectively, through drinking water separately during fetal and lactational periods. At the age of 30 days after birth, the male offspring were euthanized. The body weight, testis index, and histomorphology change were observed and the global changes of piwi-interacting RNA (piRNA) expression were evaluated. The results revealed that MC-LR was found in the testis of male offspring, body weight and testis index decreased significantly, and testicular tissue structure was damaged in the MC-LR group. In addition, the exposure to MC-LR resulted in an altered piRNA expression profile and an increase of the cell apoptosis and a decrease of the cell proliferation in the testis of the male offspring. It was reasonable to speculate that the toxic effects on reproductive system of the male offspring in MC-LR group might be mediated by piRNAs through the regulation of the target genes. As far as we are aware, this is the first report showing that MC-LR could play a role in disorder of proliferative and cell apoptosis in the testis of the male offspring by the maternal transmission effect of toxicity.

Amelioratory effect of coenzyme Q10 on potential human carcinogen Microcystin-LR induced toxicity in mice

Microcystins are a group of cyclic heptapeptide toxins produced by cyanobacteria. More than 100 microcystin analogues have been detected, among which microcystin-LR is the most abundant and toxic variant. Present study was designed to reveal whether potential human carcinogen microcystin-LR could imbalance the glycolytic-oxidative-nitrosative status of heart, kidney and spleen of mice and also to explore the amelioratory effect of coenzyme Q10 on microcystin-LR induced toxicity. Microcystin-LR was administered at a dose of 10 μg/kg bw/day, ip for 14 days in male mice. In microcystin-LR treated mice as compared to control, significant increase in the level of lipid peroxidation, hydrogen peroxide, lactate dehydrogenase, nitric oxide with a concomitant decrease in the level of glutathione was observed, suggesting microcystin-LR induced toxicity via induction of oxidative-nitrosative-glycolytic pathway. Although several studies have evaluated numerous antioxidants but still there is no effective chemoprotectant against microcystin-LR induced toxicity. When microcystin-LR treated mice were co-administered coenzyme Q10 (10 mg/kg bw/day, im) for 14 days, it was observed that coenzyme Q10 ameliorates microcystin-LR induced toxicity via modulation of glycolytic-oxidative-nitrosative stress pathway. Thus, the results suggest that coenzyme Q10 has a potential to be developed as preventive agent against microcystin-LR induced toxicity.

Variable Cyanobacterial Toxin and Metabolite Profiles across Six Eutrophic Lakes of Differing Physiochemical Characteristics

Future sustainability of freshwater resources is seriously threatened due to the presence of harmful cyanobacterial blooms, and yet, the number, extent, and distribution of most cyanobacterial toxins—including “emerging” toxins and other bioactive compounds—are poorly understood. We measured 15 cyanobacterial compounds—including four microcystins (MC), saxitoxin (SXT), cylindrospermopsin (CYL), anatoxin-a (ATX) and homo-anatoxin-a (hATX), two anabaenopeptins (Apt), three cyanopeptolins (Cpt), microginin (Mgn), and nodularin (NOD)—in six freshwater lakes that regularly experience noxious cHABs. MC, a human liver toxin, was present in all six lakes and was detected in 80% of all samples. Similarly, Apt, Cpt, and Mgn were detected in all lakes in roughly 86%, 50%, and 35% of all samples, respectively. Despite being a notable brackish water toxin, NOD was detected in the two shallowest lakes—Wingra (4.3 m) and Koshkonong (2.1 m). All compounds were highly variable temporally, and spatially. Metabolite profiles were significantly different between lakes suggesting lake characteristics influenced the cyanobacterial community and/or metabolite production. Understanding how cyanobacterial toxins are distributed across eutrophic lakes may shed light onto the ecological function of these metabolites, provide valuable information for their remediation and removal, and aid in the protection of public health.

Expression analysis of microRNAs and mRNAs in ovarian granulosa cells after microcystin-LR exposure

Microcystin is a cyclic heptapeptide compounds which could cause female mammals' reproductive toxicity. Ovarian granulosa cells (GCs) are essential for the growth and development of follicles. In this study, after mouse granulosa cells (mGCs) treated with microcystin-LR (MC-LR) for 48 h, microRNAs (miRNAs) and mRNAs microarray technology were adopted to detect the expression of miRNAs and mRNAs. The results showed that 125 miRNAs and 283 mRNAs changed significantly, including 50 miRNAs down-regulated (fold change < -1.2), 75 miRNAs up-regulated (fold change > 1.2), 162 mRNAs down-regulated (fold change < -1.15) and 121 mRNAs up-regulated (fold change > 1.15) in treated group compared with the control group. Functional analysis showed that significant changed miRNAs and mRNAs are mainly involved in proliferation, apoptosis, immunity, metabolism and other biological processes of mGCs. By KEGG pathways analysis, we found that differentially expressed miRNAs and mRNAs mainly participated in apoptosis, formation of cancer, proliferation, production of hormones and other related signal pathways. miRNA-gene network analysis indicated that miR-29b-3p, miR-29a-3p, miR-29c-3p, miR-1906, miR-182-5p, growth factor receptor bound protein 2-associated protein 2 (Gab2), FBJ osteosarcoma oncogene (Fos), insulin-like growth factor 1 (Igf1), mannosidase 1, alpha (Man1a) are key miRNAs and genes. The microarray results were validated by real-time fluorescent quantitative PCR (qRT-PCR).

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

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

Transfer, tissue distribution and bioaccumulation of microcystin LR in the phytoplanktivorous and carnivorous fish in Anzali wetland, with potential health risks to humans

This study was conducted to determine Microcystin LR concentration in the aquatic ecosystem of the Anzali wetland in Iran. Extraction and detection of MC-LR from the water and fish samples was conducted by the SPE and HPLC-UV apparatus. Our results showed that among toxic cyanobacteria, Anabaena was the dominant genera during the study period. The results indicated that MC-LR content in water ranged from 0.18 to 3.02μg/L in dissolved fraction and undetectable level to 1.13μg/L in cellular fraction, in all three seasons. The results of PCA revealed that the environmental parameters including EC, Chl-a, PO₄^3-, pH and temperature were the most effective factors influencing the MC-LR production. Results further showed the mean concentration of MC-LR in muscle and liver of silver carp ranged from 10.12 to 40.98 and from undetectable to 44.34μg/kg w.w, respectively. The mean concentration of MC-LR in northern pike was 15.18 to 35.1μg/kg w.w in muscle and undetectable to 51.91μg/kg w.w in liver samples. Our results suggest that consumption of fish harvested from the Anzali wetland seems to be unsafe for humans, based on obtained estimated daily intake values which were higher than the tolerable daily intake value recommended by WHO. In addition, bioaccumulation factor of MC-LR in edible tissues of fish was estimated based on lipid normalization. The results showed that the BAF of MC-LR in silver carp (1047±185L/kg of lipid) was lower than the northern pike (1272±185L/kg of lipid), although the difference was not significant.

Microcystin-Leucine Arginine Causes Cytotoxic Effects in Sertoli Cells Resulting in Reproductive Dysfunction in Male Mice

Microcystin-leucine arginine (MC-LR) is a potent toxin for Sertoli cells. However, the specific molecular mechanisms of MC-induced cytotoxicity still remain unclear. In this study, we performed a comprehensive analyses of changes of miRNAs and mRNAs in Sertoli cells treated with MC-LR. Through computational approaches, we showed the pivotal roles of differentially expressed miRNAs that were associated with cell metabolism, cellular growth and proliferation, cell-to-cell signaling and interaction and cellular movement. Ingenuity Pathway Analyses (IPA) revealed some differentially expressed miRNAs and mRNAs that may cause reproductive system diseases. Target gene analyses suggested that destruction in tight junctions (TJ) and adherens junctions (AJ) in testes may be mediated by miRNAs. Consistent with a significant enrichment of chemokine signaling pathways, we observed numerous macrophages in the testes of mice following treatment with MC-LR, which may cause testicular inflammation. Moreover, miR-98-5p and miR-758 were predicted to bind the 3′-UTR region of the mitogen-activated protein kinase 11 (MAPK11, p38 β isoform) gene which stimulates tumor necrosis factor-α (TNF-α) expression in Sertoli cells. TNF-α could interact with the tumor necrosis factor receptor 1 (TNFR1) on germ cells leading to induction of germ cell apoptosis. Collectively, our integrated miRNA/mRNA analyses provided a molecular paradigm, which was experimentally validated, for understanding MC-LR-induced cytotoxicity.