Microcystin-LR causes sexual hormone disturbance in male rat by targeting gonadotropin-releasing hormone neurons

In silico and in vitro evaluation of potential agonistic and antagonistic estrogenic and androgenic activities of pure cyanotoxins, microcystin-LR and cylindrospermopsin

The potential endocrine disruption activity of cyanotoxins, particularly their effects on estrogen and androgen receptors (ER, AR), remains poorly understood. In the present study, the potential agonistic/antagonistic estrogenic and androgenic activities of MC-LR and CYN have been determined for the first time with validated OECD Test Guidelines No. 455 and 458, respectively. The data show that only MC-LR demonstrated weak estrogenic agonistic effects (LogPC10 value of -9.85 M), while both toxins displayed antagonistic effects on the ER, with LogIC30 values of -4.4 and -6.4 for MC-LR and CYN, respectively. In addition, neither MC-LR nor CYN exhibited agonistic/antagonistic activities in AR. Docking studies revealed potential interactions between both toxins and AR, with CYN showing a higher predicted affinity for this receptor. In vivo studies, particularly those investigating androgen disruption, are warranted to confirm the endocrine disrupting potential of MC-LR and CYN.

Microcystin-LR Induces Estrogenic Effects at Environmentally Relevant Concentration in Black-Spotted Pond Frogs (Pelophylax nigromaculatus): In Situ, In Vivo, In Vitro, and In Silico Investigations

Harmful cyanobacterial blooms are frequent and intense worldwide, creating hazards for aquatic biodiversity. The potential estrogen-like effect of Microcystin-LR (MC-LR) is a growing concern. In this study, we assessed the estrogenic potency of MC-LR in black-spotted frogs through combined field and laboratory approaches. In 13 bloom areas of Zhejiang province, China, the MC-LR concentrations in water ranged from 0.87 to 8.77 μg/L and were correlated with sex hormone profiles in frogs, suggesting possible estrogenic activity of MC-LR. Tadpoles exposed to 1 μg/L, an environmentally relevant concentration, displayed a female-biased sex ratio relative to controls. Transcriptomic results revealed that MC-LR induces numerous and complex effects on gene expression across multiple endocrine axes. In addition, exposure of male adults significantly increased the estradiol (E2)/testosterone (T) ratio by 3.5-fold relative to controls. Downregulation of genes related to male reproductive endocrine function was also identified. We also showed how MC-LR enhances the expression of specific estrogen receptor (ER) proteins, which induce estrogenic effects by activating the ER pathway and hypothalamic-pituitary-gonadal (HPG) axis. In aggregate, our results reveal multiple lines of evidence demonstrating that, for amphibians, MC-LR is an estrogenic endocrine disruptor at environmentally relevant concentrations. The data presented here support the need for a shift in the MC-LR risk assessment. While hepatoxicity has historically been the focus of MC-LR risk assessments, our data clearly demonstrate that estrogenicity is a major mode of toxicity at environmental levels and that estrogenic effects should be considered for risk assessments on MC-LR going forward.

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.

Co-exposure to polystyrene microplastics and microcystin-LR aggravated male reproductive toxicity in mice

Microplastics (MPs) are plastic pollutants with a diameter of less than 5 mm and microcystins (MCs) are natural toxins produced by cyanobacteria. In recent years, the pollution of MPs and MCs attracted widespread attention. However, our understanding about the toxic effects of co-exposure of MPs and MCs on male reproduction is limited. Mice were continuously exposed to 0.04mg/(kg*bw) microcystin-leucine-arginine (MC-LR) or 45 mg/(kg*bw) polystyrene microplastics (PS-MPs) or a mixed solution of 0.04mg/(kg*bw) MC-LR and 45 mg/(kg*bw) PS-MPs by gavage for 28 days in this study. The results showed that PS-MPs could absorb MC-LR in ddH2O and MC-LR content in testis was increased in the group with combined exposure when compared to the group only exposed to MC-LR. Exposure to PS-MPs or MC-LR individually could destroy testis structure, increase the level of tissue apoptosis and decrease the quality of sperm, while the co-exposure enhanced the toxic effects. Furthermore, PS-MPs could carry MC-LR into testis Leydig cells, reduce testosterone levels and mRNA expression levels of key molecules involved in testosterone synthesis (StAR, P450scc, P450c17,3β-HSD and 17β-HSD). Among them, the combined effect of PS-MPs-MC-LR was the most severe. In summary, this study provides new insights into the toxicity of MPs and MCs in mammals.

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.

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.

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.

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.

Microcystin-leucine-arginine induced neurotoxicity by initiating mitochondrial fission in hippocampal neurons

Microcystin-leucine-arginine (MC-LR) can cross the blood-brain barrier (BBB) and demonstrate potent acute hippocampal neurotoxicity. Chronic exposure to MC-LR has been confirmed to cause learning and memory deficits in mice, but the potential molecular mechanism of MC-LR-caused neurotoxicity is still unclear. In this research, we observed that MC-LR induced oxidative stress, mitochondrial fission and apoptosis in HT-22 hippocampal neurons. Moreover, further studies identified that MC-LR induced mitochondrial fragmentation via activating Dynamin-related protein 1 (Drp1) and Mitochondrial fission factor (Mff), contributing to apoptosis of hippocampal neuronal cells. The observed effects were associated with increased intracellular Ca²⁺ and reduced activity of protein phosphatases 2A (PP2A) as results of MC-LR exposure in hippocampal neuron cells. Ca²⁺ activates CaMK II and Akt to enhance phosphorylation of Drp1 at Ser616 residue. Inhibition of PP2A activity increased AMPK activity to mediate phosphorylation of Mff. Our data proved that MC-LR can cause mitochondrial fragmentation in hippocampal neurons, which provides novel perception to explore the underlying molecular mechanism associated with MC-LR-induced neurotoxicity and Alzheimer's disease-like changes.

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 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.

Impact of Microcystin-LR on Liver Function Varies by Dose and Sex in Mice

Microcystin (MC) exposure is an increasing concern because more geographical locations are covered with cyanobacterial blooms as eutrophication and bloom-favoring environmental factors become more prevalent worldwide. Acute MC exposure has been linked to gastrointestinal distress, liver toxicity, and death in extreme circumstances. The goal of this study was to provide an accurate and comprehensive description of MC-LRs impacts on liver pathology, clinical chemistry, and gap junction intercellular communication (GJIC) in CD-1 male and female mice. Mice were exposed to 0, 3000, and 5000/4000 µg/kg/day MC-LR, daily for 7 days, and were necropsied on Day 8. Blood samples for clinical chemistry analysis were processed to serum, while liver sections were fixed for histopathology or evaluated for GJIC using fluorescent cut-load dye. Results show a dose-dependent relationship with MC-LR exposure and hepatocellular hypertrophy, degradation, and necrosis. Clinical chemistry parameters alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, total bilirubin, and cholesterol increased significantly in MC-LR exposed mice. Clinical chemistry parameter analysis showed significantly increased susceptibility to MC-LR in females compared to males. Changes in GJIC were not noted, but localization of hepatotoxicity near the central veins and midlobular areas was seen. Future toxicity studies involving MCs should consider response differences across sexes, differing MC congeners, and combinatorial exposures involving other cyanotoxins.

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.