The influence of microcystin-LR on fish phagocytic cells

A Review of Common Cyanotoxins and Their Effects on Fish

Global warming and human-induced eutrophication drive the occurrence of various cyanotoxins in aquatic environments. These metabolites reveal diversified mechanisms of action, encompassing cyto-, neuro-, hepato-, nephro-, and neurotoxicity, and pose a threat to aquatic biota and human health. In the present paper, we review data on the occurrence of the most studied cyanotoxins, microcystins, nodularins, cylindrospermopsin, anatoxins, and saxitoxins, in the aquatic environment, as well as their potential bioaccumulation and toxicity in fish. Microcystins are the most studied among all known cyanotoxins, although other toxic cyanobacterial metabolites are also commonly identified in aquatic environments and can reveal high toxicity in fish. Except for primary toxicity signs, cyanotoxins adversely affect the antioxidant system and anti-/pro-oxidant balance. Cyanotoxins also negatively impact the mitochondrial and endoplasmic reticulum by increasing intracellular reactive oxygen species. Furthermore, fish exposed to microcystins and cylindrospermopsin exhibit various immunomodulatory, inflammatory, and endocrine responses. Even though cyanotoxins exert a complex pressure on fish, numerous aspects are yet to be the subject of in-depth investigation. Metabolites other than microcystins should be studied more thoroughly to understand the long-term effects in fish and provide a robust background for monitoring and management actions.

Microcystin-Induced Immunotoxicity in Fishes: A Scoping Review

Cyanobacteria (blue-green algae) have been present on Earth for over 2 billion years, and can produce a variety of bioactive molecules, such as cyanotoxins. Microcystins (MCs), the most frequently detected cyanotoxins, pose a threat to the aquatic environment and to human health. The classic toxic mechanism of MCs is the inhibition of the protein phosphatases 1 and 2A (PP1 and PP2A). Immunity is known as one of the most important physiological functions in the neuroendocrine-immune network to prevent infections and maintain internal homoeostasis in fish. The present review aimed to summarize existing papers, elaborate on the MC-induced immunotoxicity in fish, and put forward some suggestions for future research. The immunomodulatory effects of MCs in fish depend on the exposure concentrations, doses, time, and routes of exposure. Previous field and laboratory studies provided strong evidence of the associations between MC-induced immunotoxicity and fish death. In our review, we summarized that the immunotoxicity of MCs is primarily characterized by the inhibition of PP1 and PP2A, oxidative stress, immune cell damage, and inflammation, as well as apoptosis. The advances in fish immunoreaction upon encountering MCs will benefit the monitoring and prediction of fish health, helping to achieve an ecotoxicological goal and to ensure the sustainability of species. Future studies concerning MC-induced immunotoxicity should focus on adaptive immunity, the hormesis phenomenon and the synergistic effects of aquatic microbial pathogens.

Immunotoxic Effects Induced by Microcystins and Cylindrospermopsin: A Review

Cyanotoxin occurrence is gaining importance due to anthropogenic activities, climate change and eutrophication. Among them, Microcystins (MCs) and Cylindrospermopsin (CYN) are the most frequently studied due to their ubiquity and toxicity. Although MCs are primary classified as hepatotoxins and CYN as a cytotoxin, they have been shown to induce deleterious effects in a wide range of organs. However, their effects on the immune system are as yet scarcely investigated. Thus, to know the impact of cyanotoxins on the immune system, due to its importance in organisms’ homeostasis, is considered of interest. A review of the scientific literature dealing with the immunotoxicity of MCs and CYN has been performed, and both in vitro and in vivo studies have been considered. Results have confirmed the scarcity of reports on the topic, particularly for CYN. Decreased cell viability, apoptosis or altered functions of immune cells, and changed levels and mRNA expression of cytokines are among the most common effects reported. Underlying mechanisms, however, are still not yet fully elucidated. Further research is needed in order to have a full picture of cyanotoxin immunotoxicity.

Cyanobacteria Microcystis aeruginosa Contributes to the Severity of Fish Diseases: A Study on Spring Viraemia of Carp

Fish are exposed to numerous stressors in the environment including pollution, bacterial and viral agents, and toxic substances. Our study with common carps leveraged an integrated approach (i.e., histology, biochemical and hematological measurements, and analytical chemistry) to understand how cyanobacteria interfere with the impact of a model viral agent, Carp sprivivirus (SVCV), on fish. In addition to the specific effects of a single stressor (SVCV or cyanobacteria), the combination of both stressors worsens markers related to the immune system and liver health. Solely combined exposure resulted in the rise in the production of immunoglobulins, changes in glucose and cholesterol levels, and an elevated marker of impaired liver, alanine aminotransferase (ALT). Analytical determination of the cyanobacterial toxin microcystin-LR (MC-LR) and its structurally similar congener MC-RR and their conjugates showed that SVCV affects neither the levels of MC in the liver nor the detoxification capacity of the liver. MC-LR and MC-RR were depurated from liver mostly in the form of cysteine conjugates (MC-LR-Cys, MC-RR-Cys) in comparison to glutathione conjugates (LR-GSH, RR-GSH). Our study brought new evidence that cyanobacteria worsen the effect of viral agents. Such inclusion of multiple stressor concept helps us to understand how and to what extent the relevant environmental stressors co-influence the health of the fish population.

Hepatotoxicity and immunotoxicity of MC-LR on silver carp

Microcystins produced by some cyanobacteria can cause damages to the liver and kidneys of aquatic animals. In the natural water with cyanobacterial blooms, silver carp may suffer from the most serious affect of the bloom due to their filtering these cyanobacteria and ingesting them as food. In the present study, silver carp was exposed to microcystin-LR by using the method of intraperitoneal injection first to determine the acute toxicity of microcystin-LR on silver carp and then to determine the activity of inflammatory protein and content of inflammatory factors from the serum of silver carp following a subacute exposure of microcystin-LR at doses of 104.9 μg kg^-1 (1/5 of LD₅₀) or 262.1 μg kg^-1 (1/2 of LD₅₀). The results showed that MC-LR exposure increased fish liver index and promoted the activities of fish serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST), indicating the hepatotoxicity of MC-LR on the fish. Moreover, MC-LR exposure also increased the number of leukocytes, complement C3 level, lysozyme activity (at the first 9 h of exposure), and the contents of cytokines TNF-α, IL-1β and IFN-γ in fish serum. In addition, a significant increase in IgM level was observed in the serum and head kidney of silver carp following MC-LR exposure. This result suggests that semi-lethal doses of MC-LR exposure is not only hepatotoxic but also immunotoxic to silver carp.

Effects of dietary toxic cyanobacteria and ammonia exposure on immune function of blunt snout bream (Megalabrama amblycephala)

Cyanobacterial blooms caused by water eutrophication have become a worldwide problem. During the degradation of toxic cyanobacterial blooms, elevated ammonia and microcystins concentrations co-occur and exert toxicity on fish. Up to now, the combined effect of microcystins and ammonia on fish immunotoxicity has not been reported. The present study investigated immune responses of blunt snout bream (Megalabrama amblycephala) to dietary toxic cyanobacteria and ammonia exposure. Megalobrama amblycephala were exposed to solutions with different concentrations of NH₃-N (0, 0.06, 0.12 mg/L) and fed with diets containing 15% and 30% of toxic cyanobacteria lyophilized powder for 30 d. The microcystins concentration in different organs of Megalobrama amblycephala was in the following sequence: head kidney > liver > intestine > gonad > spleen > gill > trunk kidney > brain > muscle > heart. In both head kidney and spleen, the MC-LR and MC-RR concentration increased significantly with increasing NH₃-N concentration. It indicates that NH₃-N maybe promote the accumulation of microcystins in immune organs of Megalobrama amblycephala. Meanwhile, broadened peripheral interspace of lymphocytes, nucleus shrivel and edematous mitochondria were observed in head kidney lymphocyte of toxic treatment fish. Moreover, there were significant interactions between dietary toxic cyanobacteria and ammonia exposure on head kidney macrophage phagocytosis activity, respiratory burst activities, total number of white blood cells and the transcriptional levels of sIgM, mIgD and sIgZ genes. Our data clearly demonstrated that dietary toxic cyanobacteria combined with ammonia exposure showed a synergistic effect on Megalobrama amblycephala immunotoxicity.

Dualistic immunomodulation of sub-chronic microcystin-LR exposure on the innate-immune defense system in male zebrafish

Microcystins (MCs), produced by toxic cyanobacterial blooms that appeared world wildly in eutrophication waters, have often caused fish illness and even massive death cases. Among at least 90 structural variants, microcystin-LR (MC-LR) is the most common and toxic variant. In order to better understand innate immune responses in fish disrupted by environmental concentrations of MC-LR, male zebrafish (Danio rerio) were exposed to 0, 0.3, 1, 3, 10 and 30 μg/L MC-LR for 30 d, and the changes in splenic pathology and immunological gene expression as well as serum immune parameters were studied. In the low concentration groups (0.3, 1 and 3 μg/L), zebrafish displayed splenic inflammatory changes including the formation of melano-macrophage centers and the increase of macrophage pseudopodia, remarkable elevation of serum C3 levels, and significantly upregulated expression of innate immune-related genes (c3b, lyz, il1β, tnfα and ifnγ). In contrast, high concentrations of MC-LR (10 and 30 μg/L) resulted in the degeneration of splenic lymphocytes and macrophages, and down-regulation of immune-related genes as well as significant decreases in the level of serum C3. Furthermore, significant increases in the activity of serum ACP and ALP suggested that high concentrations of MC-LR increased permeability of macrophage plasma membrane or cellular necrosis, and subsequently decreased innate immune function. Our findings illustrated that sub-chronic exposure of MC-LR has dualistic influences on fish innate immune system with inflammatory activation at low exposure concentrations but turned to immune inhibition with the increases of exposure concentration.

New insights into cytotoxicity induced by microcystin-LR, estradiol, and ractopamine with mathematical models: Individual and combined effects

Humans are most likely to be exposed to microcystins (MCs) combined with other water pollutants rather than to individual compounds through the consumption of contaminated drinking water or through recreational activities, such as swimming. However, the combined effects of MC-LR, estradiol (EST), and ractopamine (RAC) have not been extensively researched. The goal of this study was to investigate the combined effects of these compounds. For this purpose, cytotoxicity was evaluated in HepG2 cells treated with single or combined doses of MC-LR, EST, and RAC based on concentration addition (CA), independent action (IA), and Chou-Talalay's combination-index (CI) methods. Singly applied MC-LR and EST induced HepG2 cellular proliferation at low-concentration levels (1 × 10^-12-1 × 10^-9 M), and decreased viability at higher doses of exposure (1 × 10^-9-1 × 10^-6 M). Exposure to binary or ternary mixtures of MC-LR, EST, and RAC exhibited synergistic effects at high concentrations, irrespective of the models used. In contrast, antagonism was observed for the mixture of MC-LR and EST at relatively low concentrations. A synergistic effect on reactive oxygen species (ROS) generation was observed for the combined drugs at high concentrations. Additionally, the ratio of apoptotic cells was increased more by the combined drugs than the single drugs, consistent with the inhibition of cell viability. The ROS increase after treatment with the combined drugs may enhance cytotoxicity and subsequently lead to cell apoptosis. Given the interactions between MC-LR, EST, and RAC, government regulatory standards for MC-LR should consider the toxicological interactions between MC-LR and other environment pollutions.

Effect of treatment of chum salmon Oncorhynchus keta (Walbaum) eggs with 1,3;1,6-β-D-glucans on their development and susceptibility to Saprolegnia infection

The effects of six 1,3;1,6-β-D-glucooligo- and polysaccharides with different structures (ranging from 1 to 10 kDa in molecular mass and containing 10-25% of β-1,6-linked glucose residues) from brown algae, Saccharina cichorioides, on development of the chum salmon, Oncorhynchus keta (Walbaum), were evaluated. Exposure of chum salmon eggs to 1,3;1,6-β-D-glucans with a molecular mass of more than 2 kDa increased the survival of embryos and juveniles and their resistance to Saprolegnia infection by up to 2.5-fold, leading to a weight gain in juveniles of 40-55% compared with The control chum salmons. The 1,3;1,6-β-D-glucans with molecular mass of 6-8 kDa and used at a at concentration of 0.5 mg mL(-1) rendered the best stimulative effect.

Distribution of microcystin-LR to testis of male Sprague-Dawley rats

Microcystins (MCs) are a group of cyclic heptapeptide toxins produced by naturally freshwater cyanobacteria. Among more than 90 identified analogues of microcystins, microcystin-LR (MC-LR) is the most abundant and toxic. Our previous investigations indicated that MC-LR displays male reproductive toxicity, but the target of MC-LR in testes remains unclear. To this end, the present study is designed to elucidate whether microcystin-LR could be distributed to testes and explore the target cells in testes. In the in vivo study, male Sprague-Dawley rats were injected intraperitoneally with MC-LR at a dose of 300 μg/kg per day for 6 days. MC-LR was detected in testes, mainly within seminiferous tubules, which was further validated by Western blot. The concentrations of MC-LR were determined by LC-MS analysis, with a result of 0.0252 ± 0.0037 and 0.0056 ± 0.0012 μg/g dry weight in liver and testis respectively. In the in vitro study, Primary cultured spermatogonia, Sertoli cells and Leydig cells were exposed to MC-LR respectively, and MC-LR was observed to enter spermatogonia and Sertoli cells, but not Leydig cells. These results suggested that the reproductive toxicity of MC-LR were induced by its distribution in testis. Spermatogonia and Sertoli cells are important target cells.

Cytotoxic effects and changes in cytokine gene expression induced by microcystin-containing extract in fish immune cells--an in vitro and in vivo study

Blooms of cyanobacteria producing very toxic secondary metabolites (especially microcystins) are potent environmental stressors, hazardous not only to aquatic animals but also to public health. The purpose of this study was to investigate the effects of an extract containing microcystins on immune cells isolated from the common carp (Cyprinus carpio L.). In the present study it has been found that the extract induced apoptosis and inhibited in vitro lymphocyte proliferation. In addition, the results indicated the possible role of oxidative stress in this cytotoxicity and apoptosis. The in vivo investigations showed that the extract containing microcystins had greater suppressive effects on the essential functions of immune cells (intracellular reactive oxygen species production and lymphocyte proliferation) than the pure toxin alone. Moreover, immersion of fish in the toxic extract caused changes in the mRNA levels of various pro- and anti-inflammatory cytokines in carp leukocytes, while after exposure to the pure toxin, only IL1-β expression was markedly up-regulated. The observed modulatory effects on immune cells could have important implications for the health of planktivorous fish, which feed more frequently on toxic cyanobacteria.

Mitochondrial and endoplasmic reticulum pathways involved in microcystin-LR-induced apoptosis of the testes of male frog (Rana nigromaculata) in vivo

Previous studies have shown that toxins produced by toxic cyanobacterial blooms are hazardous materials. In the present study, 1 μg/L microcystin-LR (MC-LR) was observed to induce apoptosis in the testes of male Rana nigromaculata via the mitochondrial and endoplasmic reticulum (ER) pathways at exposure times ranging from 7 d to 14 d. The results showed that reactive oxygen species production and malondialdehyde content were positively correlated with exposure time. Antioxidant enzyme contents, such as reduced glutathione and glutathione peroxidase rapidly decreased, implying that the defense system of the testes induces oxidative damage. MC-LR significantly stimulated the release of cytochrome c in the testes, thereby improving the protein expressions of Bax and caspases-3, 8, and 9 (p<0.01) and inhibiting the protein expression of Bcl-2 with prolonged exposure (p<0.01). Ultrastructural observations showed distention of the mitochondria and endoplasmic reticulum and deformation of the nucleolus. Moreover, prolonged exposure times strengthened and weakened the relative expression levels of C/EBP homologous protein and GRP78, respectively. These results indicate that MC-LR-induced apoptosis of the testes in male frogs in vivo may occur through the mitochondrial and ER pathways. It also further proves our previous findings that MC-LR can induce toxicity in the male reproductive system of R. nigromaculata in vitro. The findings show that MC-LR is highly hazardous to frogs and that the accepted drinking water limit of 1 μg/L MC-LR exerts significant toxicity to amphibians.

Toxic effects of microcystin-LR on the reproductive system of male Rana nigromaculata in vitro

This study aims to demonstrate that microcystin-LR (MC-LR) has toxic effects on the reproductive system of male Rana nigromaculata in vitro. R. nigromaculata were treated with 0, 0.1, 1, 10, and 100 nmol/L of MC-LR for 6 h. Results show that exposure to 1 nmol/L to 100 nmol/L of MC-LR decreased sperm motility and number of sperm cells and increased the sperm abnormality rate, whose values were significantly different from those of the control (P<0.01). Moreover, the same dosage of MC-LR increased reactive oxygen species production and malondialdehyde content. At the same time, antioxidant enzyme (catalase and glutathione S-transferase) activity and glutathione reduced content rapidly increased, whereas antioxidant enzyme superoxide dismutase activity significantly decreased. These results imply that the defense system of the testes quickly responds to oxidative stress. Ultrastructural observation shows distention of the mitochondria, endoplasmic reticulum, and Golgi apparatus and changes in the mitochondrial matrix color, cristae number, and morphology. Moreover, using real-time PCR, increased relative expressions of P450 aromatase and SF-1 genes were observed. The results demonstrate for the first time that MC-LR could induce toxicity in the male reproductive system of R. nigromaculata. The findings in this research will provide more insights into the relationships between aquatic microcystins and amphibians.

Effect of cyanobacteria on immune function of crucian carp (Carassius auratus) via chronic exposure in diet

Cyanobacterial blooms caused by water eutrophication have become a worldwide problem. Microcystins (MCs) released during cyanobacterial blooms exert toxicity on fish. Up to now, immunotoxicity of MCs on fish has been rarely reported. The present study investigated immune response of crucian carp (Carassius auratus) to cyanobacteria via chronic exposure in diet. Fish were fed with diets containing 20% (low dose group) and 40% (high dose group) of cyanobacteria lyophilized powder. After exposure of 30 d, a batch of assays was determined for assessing immunotoxicity of MCs. The head kidney and spleen indexes significantly increased in high dose group. Blood nitroblue tetrazolium activity in high dose group was nearly twice as much as that in control group with no cyanobacteria additive. Marked haemorrhage and hyperemia were observed in kidney and spleen in high dose group. The edematous mitochondria, deformation of the nucleus and compaction of chromatin occurred in lymphocytes of head kidney and spleen in both cyanobacteria groups. Lysozyme activity showed an obvious increase in low dose group but a sharp decrease in high dose group. Significant increase of macrophage bactericidal activity was detected in low dose group. The present findings indicate that via chronic diet exposure of different cyanobacteria levels, fish exhibit various immune responses. Fish immunity tends to proceed toward the direction of immunostimulative response at low MCs concentrations but toward the trend of immunosuppressive answer at high MCs concentrations.

Microcystin-LR induces cytotoxicity and affects carp immune cells by impairment of their phagocytosis and the organization of the cytoskeleton

Microcystin-LR (MC-LR) is the main isoform of hepatotoxin produced by cyanobacteria, which occur worldwide in the aquatic environment. The present study investigated the in vitro toxic MC-LR effects on immune cells isolated from the blood of carp. Cells were exposed to different MC-LR concentrations ranging from 0.01 to 1 µg ml(-1) for 2, 6 and 24 h. In addition, the effect of the toxin on the phagocytic activity of leukocytes and on actin and tubulin re-organization in phagocytic cells was studied. We observed that MC-LR induces apoptosis in lymphocytes 2 h after incubation, whereas high toxin concentrations induced necrosis in lymphocytes in a time- and concentration-dependent manner. Incubation of the cells for 2 h with 0.1 and 1 µg ml(-1) MC-LR inhibited phagocytosis without affecting apoptosis or glutathione (GSH) levels. Moreover, at this time point and with these concentrations, the toxin also induced a significant re-organization of the actin cytoskeleton in phagocytes, which subsequently collapsed around the nucleus leading to cell shrinkage and the disappearance of filopodia. These results suggest that both phagocytes and lymphocytes are targets for MC-LR and the disturbances of phagocytosis may impair the balance of the immune system.

Effects of microcystin-containing cyanobacterial extract on hematological and biochemical parameters of common carp (Cyprinus carpio L.)

The aim of the study was to assess the effects of a cyanobacterial extract containing microcystins (MCs) on selected hematological and biochemical parameters in common carp (Cyprinus carpio L.), as well as to determine the accumulation of toxins in fish tissues. The fish were immersed for 5 days in water containing toxins at a final concentration of 12 μg/L of microcystin LR equivalent. Microcystin LR residues were detected in fish liver, reaching 207, 238 and 260 ng/g f.w. of the tissues taken 24 h, 72 h and 5 days after the end of intoxication, respectively. The most substantial changes were found in fish plasma, including increases in creatine kinase, lactate dehydrogenase, ammonia, glucose, aspartate aminotransferase and alanine aminotransferase levels. A decline of about 50% in lysozyme activity was observed by the end of the experimental period. Moreover, a marked increase in ceruloplasmin activity was detected 24 h after the end of intoxication with a subsequent decrease in its activity after 72 h and 5 days. This study concludes that not only consumption of food containing toxins but also MCs dissolved in water may pose a threat to fish health. Additionally, detected changes in lysozyme and ceruloplasmin activity may have distinct effects in fish resistance against pathogens or oxidative stress, which should be taken into account in the future studies.

Microcystin-LR causes cytotoxicity effects in rat testicular Sertoli cells

Microcystins (MCs) are produced by cyanobacteria. The most toxic and widely distributed MC is microcystin-LR (MC-LR). The aim of this study was to investigate whether exposure to MC-LR could induce oxidative stress, leading the further toxicity effects on Sertoli cells in vitro. Sertoli cells obtained from rats were cultured with a medium containing 0, 0.5, 5, 50 or 500 nM/l MC-LR. We examined the decrease of mitochondrial membrane potential (MMP), the increase of reactive oxygen species (ROS) production, the increase of lipid peroxidation and decrease of superoxide dismutase (SOD) activity in Sertoli cells after treatment with MC-LR in vitro, and higher expression of caspase-9 and caspase-3, the increase of apoptosis rate. Therefore, we deduced that direct exposure to microcystin-LR could induce oxidative stress generation in Sertoli cells, and subsequently depressed cellular viability and caused cells to undergo apoptosis, resulting in the reproductive toxicity in male rats.

Effects of microcystin-LR on the metal bioaccumulation and toxicity in Chlamydomonas reinhardtii

Microcystin-LR (MC-LR) is one of the most notorious toxins liberated from cyanobacteria in eutrophicated freshwater ecosystems. Its effects on the bioaccumulation and toxicity of Cd(2+), CrO(4)(2-), Cu(2+), and Zn(2+) in a green alga Chlamydomonas reinhardtii were investigated in the present study. The metal bioaccumulation in the alga was unaffected by MC-LR. The surface-adsorbed and intracellular metal concentrations in the treatments with and without the addition of MC-LR could be well simulated by a single Freundlich isotherm for each metal with their accumulation ability following the order of Cu(2+) > Cd(2+) > Zn(2+) > CrO(4)(2-). The bioavailable metal concentrations measured by diffusion gradients in thin-films remained unchanged when MC-LR was applied. Accordingly, the growth of C. reinhardtii was similarly inhibited at the same metal concentration regardless of the addition of MC-LR. The metal toxicity could also be well delineated with the classic free ion activity and biotic ligand models. However, the intracellular metal concentration was found to have the best predictability suggesting its more direct relationship with metal toxicity. Metal exposure induced the accumulation of MC-LR in the alga, which was leveled off at high metal levels. The underlying uptake mechanisms need to be further examined.

Microcystin-LR modulates selected immune parameters and induces necrosis/apoptosis of carp leucocytes

Microcystins (MCs) are potent hepatotoxins acting by the inhibition of protein phosphatase 1 and 2A, and may promote liver tumors. Moreover, studies also suggest they are nephrotoxic. The aim of the present study was to assess possible in vitro effects of microcystin-LR (which contains the amino acids leucine and arginine, the most widely studied and distributed variant of all microcystins) on the selected immune functions of the cells isolated from the head kidney of carp. In the experiments, pure microcystin-LR (MC-LR), was used at concentrations of 0.01, 0.1, 0.5, and 1 microg/ml RPMI-1640 medium. Leucocytes (lymphocytes and phagocytes) were isolated by centrifugation on a density gradient. Lymphocyte proliferation, intracellular production of reactive oxygen species by phagocytes, and the presence of apoptotic and/or necrotic cells were assessed. The respiratory burst activity of phagocytic cells was increased at the lowest toxin concentration used in the study, but it was decreased at higher concentrations. Using a sensitive luminescent immunoassay, MC-LR was observed to have no influence on the T-cell proliferation but decreased the proliferation of B lymphocytes. Moreover, it was noted that MC-LR induced necrosis to a higher degree than apoptosis in fish leucocytes. The results of the present study suggest the modulatory potency of microcystin-LR on fish leucocytes.

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

The aim of this study was to investigate whether microcystin-LR, one of the most common cyanobacterial toxins has toxic effects on reproductive system in vivo or Leydig cells in vitro. Male rats were treated with MC-LR (i.p.) at a dose of 0, 5, 10 or15 microg/(kgday) for 28 days. Leydig cells were cultured with a culture medium including 0, 0.5, 5, 50 or 500 nM MC-LR. In vivo study, we observed exposure to 5 microg/(kgday) of MC-LR decreased the sperm motility, increasing the sperm abnormality rate, 15 microg/(kgday) of MC-LR led to the decrease of testis weight and sperm concentration, decreased the levels of serum testosterone, FSH and LH. The histological findings showed that the seminiferous tubules atrophied and obstructed. In vitro study evaluated MC-LR-induced toxicity and oxidative stress in Leydig cells. It was observed 50 and 500 nM MC-LR significantly decreased the cell viability, increasing the apoptotic DNA fragmentation, and increasing the ratio of necrotic cells. The Leydig cells exposed to MC-LR decreased testosterone production. 500 nM MC-LR increased ROS production, 50 or 500 nM MC-LR enhanced the lipid peroxidation. All Leydig cells exposed to MC-LR showed decreased SOD activity. The results of this study showed that the oxidative stress of MC-LR might lead to cytotoxicity, which may play an important role in cell apoptosis. Then could reduce the production of testosterone in Leydig cells and result in reproductive toxicity.