Effects of saxitoxins exposure on oligodendrocyte development in mouse neonates.

Saxitoxins (STXs) are neurotoxins produced by cyanobacteria and dinoflagellates, and they are primarily known to block voltage-gated sodium channels in neurons. The present study aimed to obtain further information regarding the effects of these toxins on neurodevelopment by investigating the responses of murine subventricular zone (SVZ) neural progenitors to STXs. An in vitro neonatal mouse SVZ explant model was exposed to different concentrations of toxic cyanobacterial extracts to evaluate the migration and differentiation of SVZ-derived progenitor cells. To test the ability of STX to cross the placental barrier, pregnant mice received a single intraperitoneal injection of STXs (7.5 µg/kg body weight) on gestational day fifteen. Immunocytochemistry was performed to detect proliferating and differentiating progenitors, including oligodendrocyte progenitor cells (OPCs). It was found that specific proliferation of OPCs was significantly increased, but there was no corresponding increase in the number of differentiated oligodendrocytes, which may indicate a negative effect on the maturation process of these cells. Additionally, the data showed that STXs crossed the placental barrier. Thus, STXs can be considered a potential risk to fetal neurodevelopment.

Molecular effects of Microcystin-LA in tilapia (Oreochromis niloticus).

Nile tilapia (Oreochromis niloticus) is a freshwater phytoplanktivorous fish species reported to accumulate and tolerate large amounts of cyanotoxins such as microcystins (MCs). The present study aimed to investigate molecular responses to the acute exposure of Nile tilapia to the Microcystin-LA analogue (MC-LA). Thus, the specimens were sublethally exposed to 1000 µg kg-1 of MC-LA for 12, 24, 48, and 96 h. Gene expression of PP1, PP2A, GST, GPX and actin was analyzed by quantitative PCR. The protein abundance profile of PP2A was determined by immunoblotting, while the integrity of its biological function was assessed by a phosphatase enzymatic assay. PP2A activity was significantly and strongly reduced by MC-LA. A resulting feedback mechanism significantly increased PP2A gene expression and protein abundance in all assessed times. However, a recovery of that phosphatase activity was not observed. In this study, the observed increase in GPX gene expression was the only response that could be directly related to the unknown factors associated to the fish survival to such high dose exposure.

Oxidative imbalance in mice intoxicated by microcystin-LR can be minimized.

Microcystins-LR (MC-LR) is a cyanotoxin produced by cyanobacteria. We evaluated the antioxidant potential of LASSBio-596 (LB-596, inhibitor of phosphodiesterases 4 and 5), per os, and biochemical markers involved in lung and liver injury induced by exposure to sublethal dose of MC-LR. Fifty male Swiss mice received an intraperitoneal injection of 60 µL of saline (CTRL group, n = 20) or a sublethal dose of MC-LR (40 µg/kg, TOX group, n = 20). After 6 h the animals received either saline (TOX and CTRL groups) or LB-596 (50 mg/kg, TOX + LASS group, n = 10) by gavage. At 6 h after exposure, respiratory mechanics was evaluated in 10 CTRL and 10 TOX mice: there was a significant increase of all lung mechanics parameters (static elastance, viscoelastic component of elastance and lung resistive and viscoelastic/inhomogeneous pressures) in TOX compared to CTRL. 8 h after saline or MC-LR administration, i.e., 2 h after treatment with LB-596, blood serum levels of alanine aminotransferase and aspartate aminotransferase, activity of superoxide dismutase, catalase, and content of malondialdehyde and carbonyl in lung and liver, NADPH oxidase 2 and 4 mRNA expressions, dual oxidase enzyme activity and H2O2 generation were analyzed in lung homogenates. All parameters were significantly higher in TOX than in the other groups. There was no significant difference between CTRL and TOX + LASS. MC-LR deteriorated lung and liver functions and induced redox imbalance in them, which was prevented by oral administration of LB-596.

Repeated intranasal exposure to microcystin-LR affects lungs but not nasal epithelium in mice.

Microcystin-LR (MC-LR) is a harmful cyanotoxin able to induce adverse outcomes in the respiratory system. We aimed to examine the lungs and nasal epithelium of mice following a sub-chronic exposure to MC-LR. Swiss mice were intranasally instilled with 10 µL of distilled water (CTRL, n = 10) or 6.7 ng/kg of MC-LR diluted in 10 µL of distilled water (TOX, n = 8) during 30 consecutive days. Respiratory mechanics was measured in vivo and histology measurements (morphology and inflammation) were assessed in lungs and nasal epithelium samples 24 h after the last intranasal instillation. Despite the lack of changes in the nasal epithelium, TOX mice displayed an increased amount of PMN cells in the lungs (× 10(-3)/µm(2)), higher lung static elastance (cmH2O/mL), resistive and viscoelastic/inhomogeneous pressures (cmH2O) (7.87 ± 3.78, 33.96 ± 2.64, 1.03 ± 0.12, 1.01 ± 0.08, respectively) than CTRL (5.37 ± 4.02, 26.65 ± 1.24, 0.78 ± 0.06, 0.72 ± 0.05, respectively). Overall, our findings suggest that the nasal epithelium appears more resistant than lungs in this model of MC-LR intoxication.

Sublethal microcystin exposure and biochemical outcomes among hemodialysis patients.

Cyanobacteria are commonly-occurring contaminants of surface waters worldwide. Microcystins, potent hepatotoxins, are among the best characterized cyanotoxins. During November, 2001, a group of 44 hemodialysis patients were exposed to microcystins via contaminated dialysate. Serum microcystin concentrations were quantified with enzyme-linked immunosorbent assay which measures free serum microcystin LR equivalents (ME). We describe serum ME concentrations and biochemical outcomes among a subset of patients during 8 weeks following exposure. Thirteen patients were included; 6 were males, patients' median age was 45 years (range 16-80), one was seropositive for hepatitis B surface antigen. The median serum ME concentration was 0.33 ng/mL (range: <0.16-0.96). One hundred thirty nine blood samples were collected following exposure. Patients' biochemical outcomes varied, but overall indicated a mixed liver injury. Linear regression evaluated each patient's weekly mean biochemical outcome with their maximum serum ME concentration; a measure of the extrinsic pathway of clotting function, prothrombin time, was negatively and significantly associated with serum ME concentrations. This group of exposed patients' biochemical outcomes display evidence of a mixed liver injury temporally associated with microcystin exposure. Interpretation of biochemical outcomes are complicated by the study population's underlying chronic disease status. It is clear that dialysis patients are a distinct 'at risk' group for cyanotoxin exposures due to direct intravenous exposure to dialysate prepared from surface drinking water supplies. Careful monitoring and treatment of water supplies used to prepare dialysate is required to prevent future cyanotoxin exposure events.

Thyroid hormone and estradiol have overlapping effects on kidney glutathione S-transferase-α gene expression.

α-Class GST (Gsta) represents an essential component of cellular antioxidant defense mechanisms in both the liver and the kidney. Estrogens and thyroid hormones (TH) play central roles in animal development, physiology, and behavior. Evidence of the overlapping functions of thyroid hormones and estrogens has been shown, although the molecular mechanisms are not always clear. We evaluated an interaction between TH and estradiol in regulating kidney Gsta expression and function. First, we observed that female mice expressed greater amounts of Gsta compared with males and showed an opposite pattern of expression in TRß knock-in mice. To further investigate these sex differences, hypothyroidism was induced by a 5-propyl-2-thiouracil diet, and hyperthyroidism was induced by daily T3 injections. Hypothyroidism increased kidney Gsta expression in male mice but not in female mice, indicating that sex hormones could be influencing the regulation of Gsta by thyroid hormones. To analyze this hypothesis, ovariectomized females were subjected to hypo- and hyperthyroidism, which led to a male profile of Gsta expression. When hypo- or hyperthyroid ovariectomized mice were treated with 17ß-estradiol benzoate, we were able to confirm that estradiol was interfering with TH modulation; Gsta expression is increased by T3 when estradiol is present and decreased by T3 when estradiol is absent. Using proximal tubule cells, we also showed that estradiol and T3 worked together to modulate Gsta expression in an overlapping fashion. In summary, 1) the sex difference in the basal expression of Gsta impacts the detoxification process, 2) kidney Gsta expression is regulated by TH in males and females but in opposite directions, and 3) T3 and estradiol interact directly in renal proximal cells to regulate Gsta expression in females.

LASSBio 596 per os avoids pulmonary and hepatic inflammation induced by microcystin-LR.

Cyanobacterial blooms that generate microcystins (MCYSTs) are increasingly recognized as an important health problem in aquatic ecosystems. We have previously reported the impairment of pulmonary structure and function by microcystin-LR (MCYST-LR) exposure as well as the pulmonary improvement by intraperitoneally injected (i.p.) LASSBio 596. In the present study, we aimed to evaluate the usefulness of LASSBio 596 per os on the treatment of pulmonary and hepatic injuries induced by MCYST-LR. Swiss mice received an intraperitoneal injection of 40 µl of saline (CTRL) or a sub-lethal dose of MCYST-LR (40 µg/kg). After 6 h the animals received either saline (TOX and CTRL groups) or LASSBio 596 (50 mg/kg, LASS group) by gavage. Eight hours after the first instillation, lung impedance (static elastance, elastic component of viscoelasticity and resistive, viscoelastic and total pressures) was determined by the end-inflation occlusion method. Left lung and liver were prepared for histology. In lung and hepatic homogenates MCYST-LR, TNF-α, IL-1ß and IL-6 were determined by ELISA. LASSBio 596 per os (LASS mice) kept all lung mechanical parameters, polymorphonuclear (PMN) cells, pro-inflammatory mediators, and alveolar collapse similar to control mice (CTRL), whereas in TOX these findings were higher than CTRL. Likewise, liver structural deterioration (hepatocytes inflammation, necrosis and steatosis) and inflammatory process (high levels of pro-inflammatory mediators) were less evident in the LASS than TOX group. LASS and CTRL did not differ in any parameters studied. In conclusion, orally administered LASSBio 596 prevented lung and hepatic inflammation and completely blocked pulmonary functional and morphological changes induced by MCYST-LR.

Can LASSBio 596 and dexamethasone treat acute lung and liver inflammation induced by microcystin-LR?

The treatment of microcystin-LR (MCYST-LR)-induced lung inflammation has never been reported. Hence, LASSBio 596, an anti-inflammatory drug candidate, designed as symbiotic agent that modulates TNF-alpha levels and inhibits phosphodiesterase types 4 and 5, or dexamethasone were tested in this condition. Swiss mice were intraperitoneally (i.p.) injected with 60 microl of saline (CTRL) or a sub-lethal dose of MCYST-LR (40 micrg/kg). 6 h later they were treated (i.p.) with saline (TOX), LASSBio 596 (10 mg/kg, L596), or dexamethasone (1 mg/kg, 0.1 mL, DEXA). 8 h after MCYST-LR injection, pulmonary mechanics were determined, and lungs and livers prepared for histopathology, biochemical analysis and quantification of MCYST-LR. TOX showed significantly higher lung impedance than CTRL and L596, which were similar. DEXA could only partially block the mechanical alterations. In both TOX and DEXA alveolar collapse and inflammatory cell influx were higher than in CTRL and L596, being LASSBio 596 more effective than dexamethasone. TOX showed oxidative stress that was not present in CTRL and L596, while DEXA was partially efficient. MCYST-LR was detected in the livers of all mice receiving MCYST-LR and no recovery was apparent. In conclusion, LASSBio 596 was more efficient than dexamethasone in reducing the pulmonary functional impairment induced by MCYST-LR.

Effects of microcystin-LR on mouse lungs.

Toxic cyanobacteria blooms in drinking water supplies have been an increasing public health concern all over the world. Human populations can be exposed to microcystins, an important family of cyanotoxins, mainly by oral ingestion. However, inhalation from recreational water and hemodialysis can represent other routes. This study investigated changes in respiratory mechanics, histology, protein phosphatase (PP) 1 and 2A activity and microcystin in lung of adult mice injected intraperitoneally (i.p.) with microcystin-LR. Thirty-six mice were divided into control (CTRL) and test (CYANO) groups. CTRL group received an i.p. injection of saline and the CYANO group received 40 microg MCYST-LR/kg i.p. After 2 and 8 h, and 1, 2 and 4 days after toxin injection, six mice from each group were sampled for analyses. Resistive and viscoelastic pressures, static and dynamic elastances augmented at 2 h in CYANO and so remained until day 4. Alveolar collapse and inflammatory cell infiltration were found 2h after the injection, reaching peak values at 8 h. However, no microcystin or inhibition of PPases could be detected in mice lungs. In conclusion, MCYST-LR led to a rapid increase in lung impedance and an inflammatory response with interstitial edema and inflammatory cell recruitment in mice.

Sublethal exposure from microcystins to renal insufficiency patients in Rio de Janeiro, Brazil.

In November 2001, a cyanobacterial bloom dominated by Microcystis and Anabaena occurred in the Funil Reservoir and the Guandu River, both of which supply drinking water to Rio de Janeiro, Brazil. Using ELISA, microcystins were detected at a concentration of 0.4 microg/L in the drinking water, whereas a concentration of 0.32 microg/L was detected in activated carbon column-treated water for use at the renal dialysis center of Clementino Fraga Filho Hospital (HUCFF) at the Federal University of Rio de Janeiro. A total of 44 hemodialysis patients who received care at this center were believed to be exposed. Initial ELISA analyses confirmed the presence of serum microcystin concentrations > or = 0.16 ng/mL in 90% of serum samples collected from these patients. Twelve patients were selected for continued monitoring over the following 2-month period. Serum microcystin concentrations ranged from < 0.16 to 0.96 ng/mL during the 57 days after documented exposure. ELISA-positive samples were found throughout the monitoring period, with the highest values detected 1 month after initial exposure. ESI LC/MS analyses indicated microcystins in the serum; however, MS/MS fragmentation patterns typical of microcystins were not identified. LC/MS analyses of MMPB for control serum spiked with MCYST-LR. and patient sera revealed a peak at retention time of 8.4 min and a mass of 207 m/z. These peaks are equivalent to the peak observed in the MMPB standard analysis. Taken together ELISA, LC/MS, and MMPB results indicate that these renal dialysis patients were exposed to microcystins. This documents another incident of human microcystin exposure during hemodialysis treatment.

Influence of drinking water composition on quantitation and biological activity of dissolved microcystin (cyanotoxin).

Toxic cyanobacteria in aquatic environments have been implicated in many poisoning incidents of livestock, wildlife, and domestic animals. Microcystins (MCYSTs) in water supplies represent a risk to public health. This work investigated the effect of water composition on the quantitation and biological activity of MCYSTs analyzed by different methods (HPLC, ELISA, and protein phosphatase 1 inhibition assay). Different MCYST concentrations were added to deionized water and quantified, confirming the efficiency of these analytical methods. MCYST concentrations diluted in drinking water had reduced detection by all methods tested. The drinking water used contained a free chlorine concentration of 2.5 mg/L and an Fe concentration of 0.45 mg/L, and the conductivity was 69.8 microS cm(-1), whereas in deionized water, free chlorine and Fe were not detectable, and the conductivity was 1.6 microS cm(-1). Drinking water also interfered with the biological activity of MYCSTs, as these toxins showed reduced protein phosphatase-1 inhibition. A free chlorine concentration of 2.5 mg/L in deionized water was completely effective in preventing any detection of 10 microg/L of added MCYSTs. Fe and Al ions also were very effective in reducing MCYST detection. The chemical composition of drinking water thus affected MCYST detection, indicating a significant reduction in quantitation of this molecule either because of its decomposition or through complexation with metal ions.

Accumulation and depuration of microcystins (cyanobacteria hepatotoxins) in Tilapia rendalli (Cichlidae) under laboratory conditions.

In order to understand accumulation and depuration of microcystins (MCYSTs) in Tilapia rendalli, three experiments with juveniles were done. The experiments simulated the fish diet during a Microcystis aeruginosa bloom in three different situations. In the first one each fish received daily, during 15 days, fish food plus toxic cells of M. aeruginosa (20.4 microg MCYSTs fish(-1) day(-1)). In the following 15 days they were fed without toxic cells. In the second experiment, fish were fed only with toxic cells during 28 days (14.6 microg MCYSTs fish(-1) day(-1)) and in the third experiment, during 42 days, fish were fed with fish food plus toxic cells (29.2 microg MCYSTs fish(-1) day(-1)) previously disrupted (to simulate a senescent bloom). MCYSTs analyses were done by enzyme-linked immunosorbent assay (ELISA) in liver and muscle samples in all experiments and in faeces in the first one (only in the depuration period). The results demonstrated different profiles of MCYSTs accumulation in liver and muscle of T. rendalli. Comparing the experiments, the highest MCYSTs accumulation in the liver (2.8 microg g(-1)) occurred in the second one, where fish had only toxic cells as feeding source. In the first experiment, the highest MCYSTs accumulation in liver (0.6 microg MCYSTs g(-1)) was observed during the accumulation period, while in muscle, interestingly, the highest concentration (0.05 microg MCYSTs g(-1)) occurred in the depuration period. In this same period, it was also observed elimination of toxins through faeces. The second and third experiments showed almost the same average concentrations in tissues although fish have received more MCYSTs in third one. With respect to implications of the fish comsumption, MCYSTs accumulation in muscle of T. rendalli in all three experiments reached concentrations that would represent an intake of these toxins above the tolerable limit for humans and these results confirmed our previous observations from a field study. In conclusion, in this study it was observed that T. rendalli is able to accumulate MCYSTs and the availability of other feeding sources, besides toxic cells, probably interferes with the accumulation rate. Therefore, the occurrence of toxic cyanobacterial blooms produncing MCYSTs in aquaculture ponds could represent a risk to the quality of fish to the consumers.