Use of freshly prepared rat hepatocytes to study toxicity of blooms of the blue-green algae Microcystis aeruginosa and Oscillatoria agardhii

In vitro and in vivo toxicity assessment of alginate/eudragit S 100-enclosed chitosan-calcium phosphate-loaded iron saturated bovine lactoferrin nanocapsules (Fe-bLf NCs)

Lactoferrin has been known to have antimicrobial properties. This research was conducted to investigate the toxicity of Alginate/EUDRAGIT^® S 100-enclosed chitosan-calcium phosphate-loaded Fe-bLf nanocapsules (NCs) by in vitro and in vivo assays. Brine shrimp lethality assay showed that the LC₅₀ value of NCs was more than 1mg/mL which indicated that NCs was not toxic to Brine shrimp. However, the LC₅₀ values for the positive control potassium dichromate at 24h is 64.15μg/mL, which was demostrated the toxic effect against the brine shrimp. MTT cytotoxicity assay also revealed that NCs was not toxic against non-cancerous Vero cell line with IC₅₀ values of 536μg/mL. Genotoxicity studies by comet assay on Vero cells revealed that NCs exerted no significant genotoxic at 100μg/mL without tail or shorter comet tail. Allium cepa root assay carried out at 125, 250, 500 and 1000μg/mL for 24h revealed that the NCs was destitute of significant genotoxic effect under experimental conditions. The results show that there is no significant difference (p>0.05) in mitotic index between the deionized water and NCs treated Allium cepa root tip cells. In conclusion, no toxicity was observed in NCs in this study. Therefore, nontoxic NCs has the good potential to develop as a therapeutic agent.

A comparison of in vivo and in vitro assays to assess the toxicity of algal blooms

The toxicity of purified microcystin-LR (MC-LR) and algal material collected during the winter and summer seasons (2005/2006) from the Hartebeespoort dam, South Africa, was investigated using the enzyme-linked immunosorbent assay (ELISA), mouse bioassay, catfish primary hepatocytes (in vitro assay) and protein phosphatase inhibition (PPi) assays. Microcystis aeruginosa, known producer of microcystins, was the dominant cyanobacteria present in the water samples. Exceptionally high cell numbers per millilitre were observed, especially with the summer samples (approximately 1.442 x 10(8)cells/ml), indicating a severe algal bloom in the dam. The toxin concentration as detected by ELISA and PPi assay in the winter and summer extracts was at least 1000 times more than the provisional guideline value (1 microg/l) set by the World Health Organization (WHO) for MC-LR in drinking water. Hepatotoxic effects and death of mice were observed after dosing with the summer extracts, while no hepatotoxic effects were observed with winter extracts. The EC(50) values obtained after exposure of the catfish primary hepatocytes for 72h to MC-LR, winter and summer extracts was about 0.091, 0.053 and 0.014 mg/l, respectively. Similar toxicity results were obtained when the mouse bioassay and primary hepatocytes were used.

Acute and subacute toxic effects produced by microcystin-YR on the fish cell lines RTG-2 and PLHC-1

Approximately 80 microcystins (MCs) variants have been isolated in surface water worldwide. The toxicity of the most frequently MCs are encountered, MC-LR and MC-RR, has been extensively studied in humans and animals. However, studies dealing with MC-YR toxicity are still scarce. In this work, the toxic effects of MC-YR were investigated in the fish cell line PLHC-1, derived from a hepatocellular carcinoma of the topminnow Poeciliopsis lucida, and RTG-2 fibroblast-like cells derived from the gonads of rainbow trout Oncorhynchus mykiss. After 48 h, morphological and biochemical changes (total protein content, neutral red uptake and methylthiazol tetrazolium salt metabolization) were determined. The most sensitive endpoint for both cell lines was the reduction of total protein content, with EC(50) values of 35 microM for PLHC-1 cells and 67 microM for the RTG-2 cell line. Lysosomal function and methylthiazol tetrazolium salt metabolization were stimulated at low concentrations, while they decreased at high doses. Increase of piknotic cells, rounding effects, reduction in cell number and cell size, hydropic degeneration, and death mainly by necrosis but also by apoptosis were observed in the morphological study. Furthermore, PLHC-1 cells are more sensitive than RTG-2 cells to MC-YR exposure. These results were similar to those obtained when both cell lines were exposed for 24h to a Microcystis aeruginosa isolated strain extract containing MC-LR.

Toxic effects produced by microcystins from a natural cyanobacterial bloom and a Microcystis aeruginosa isolated strain on the fish cell lines RTG-2 and PLHC-1

Toxic cyanobacterial blooms are a worldwide problem, causing serious water pollution and public health hazard to humans and livestock. The intact cells as well as the toxins released after cellular lysis can be responsible for toxic effects in both animals and humans and are actually associated with fish kills. Two fish cell lines-PLHC-1 derived from a hepatocellular carcinoma of the topminnow Poeciliopsis lucida and RTG-2 fibroblast-like cells derived from the gonads of rainbow trout Oncorhynchus mykiss were exposed to several concentrations of extracts from a natural cyanobacterial bloom and a Microcystis aeruginosa-isolated strain. After 24 hours, morphologic and biochemical changes (total protein content, lactate dehydrogenase leakage, neutral red uptake, methathiazole tetrazolium salt metabolization, lysosomal function, and succinate dehydrogenase [SDH] activity) were investigated. The most sensitive end point for both cyanobacterial extracts in PLHC-1 cells was SDH activity, with similar EC(50) values (6 microM for the cyanobacterial bloom and 7 microM for the isolated strain). RTG-2 cells were less susceptible according to SDH activity, with their most sensitive end point lysosomal function with an EC(50) of 4 microM for the M. aeruginosa-isolated strain and 72 microM for the cyanobacterial bloom. The lysosomal function was stimulated at low concentrations, although SDH activity increased at high doses, indicating lysosomal and energetic alterations. Increased secretion vesicles, rounding effects, decreased cell numbers and size, hydropic degeneration, esteatosis, and apoptosis were observed in the morphologic study. Similar sensitivity to the M. aeruginosa-isolated strain was observed in both cell lines, whereas the cyanobacterial bloom was more toxic to the PLHC-1 cell line.

Microcystin production in benthic mats of cyanobacteria in the Nile River and irrigation canals, Egypt

The present study describes for the first time the species composition and toxicity of benthic cyanobacteria forming mats on the Nile River and irrigation canal sediments in Egypt. A total of 19 species of cyanobacteria were isolated from these mats during this study. The toxicity of the extracts of these species was investigated using Artemia salina assay, mouse bioassay and enzyme linked immunosorbent assay (ELISA). The results showed that all the 19 benthic species isolated from cyanobacterial mats, were toxic to A. salina. Two of these species, namely Calothrix parietina and Phormidium tenue, caused toxicity to mice with neurotoxic signs appeared within 12 h after injection. Whereas, five species showed hepatotoxic effects to mice within 6 h after injection. The results of ELISA showed that all the extracts which had hepatotoxic effects to mice, contained high levels of microcystins with concentrations ranging from 1.6 to 4.1 mg g(-1) dry weight. HPLC analysis for heptotoxic extracts revealed that these extracts contained two peaks corresponding to microcystin-YR and -LR with different proportions. This study suggests that benthic species should be considered along with planktonic species during monitoring of toxic cyanobacteria in water sources, particularly the Nile river which is the main source of drinking water in Egypt.

The freshwater cyanobacterium Lyngbya aerugineo-coerulea produces compounds toxic to mice and to mammalian and fish cells

Despite a growing awareness of the presence of cyanobacterial toxins, knowledge about the ability of specific species to produce toxic compounds is still rather limited. It was the overall goal of the current work to investigate if probes derived from the freshwater species Lyngbya aerugineo-coerulea (Kutz.) Gomont, a cyanobacterium frequently found in southern Europe and not previously investigated for the presence of bioactive compounds, were capable of eliciting in vivo and in vitro toxicity. The cyanobacterial extract revealed signs of neuro- as well as hepatotoxicity in mice, although these signs could not be explained by the well-known respective cyanobacterial neuro- and hepatotoxins saxitoxin and microcystin. Cytotoxicity was elicited by the cyanobacterial extract in all mammalian cell lines tested. As well, the rainbow trout liver cell line, RTL-W1, was found to be susceptible to the cytotoxic effects of the extract, although the cytotoxicity was dependent on temperature. In contrast, the cyanobacterial growth medium elicited cytotoxicity independent of temperature, leading to morphological changes indicative of alterations to the cytoskeleton. Overall, the results suggest that Lyngbya aerugineo-coerulea is an important cyanobacterium to be considered for its potential to cause health risks on environmental exposure of it to mammals and fish. Applying a combination of mammalian and piscine cell line bioassays is a unique approach that, combined with chemical analysis, could be used in the future to identify the structure and cellular mechanisms of the as-yet-unknown toxic Lyngbya aerugineo-coerulea metabolites in particular and to screen cyanobacterial extracts for their toxicity in general.

Study on the cytotoxicity of microcystin-LR on cultured cells

The toxicity of purified blue-green algal toxin, microcystin-LR, on permanent cell lines KB, NIH/3T3, H-4-II-E, HeLa, Vero, Hep G2, Caco-2 and HL-60 was studied. Assessment of cell viability using colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays indicated that purified microcystin-LR induced toxic effect on KB and H-4-II-E cell lines after 96 h incubation at toxin concentrations greater than 18.75 microg/ml. KB cell line was selected for further study when reproducibility, consistency and sensitivity were considered. Significant amounts of lactate dehydrogenase (LDH) were released from KB cells when incubation durations were 72 and 96 h with toxin concentrations of 18.75 microg/ml and higher. Although previous studies suggested that microcystin-LR had no cytotoxic effect on permanent cell lines, LDH release assay performed on KB cells indicated that exposure to microcystin-LR could result in damage to the cell membrane.

First report of microcystins in Taiwan

This is the first report on microcystins from Microcystis aeruginosa Kützing in Taiwan. A total of nine strains of cyanobacteria have been isolated from eutrophic aquaculture ponds and water reservoirs. By mouse toxicity assay, six of the nine strains had LD100 in the range of 25-100 mg per kg mouse for dried bacterial mass. Microcystin-LR and -RR were found in all toxic strains and their contents ranged from 0.11-10.06 microg and 0.08 2.21 microg per mg of dried bacteria, respectively. Microcystin-RA, a minor component found only in M. TN-2 and M. CY-1 strains, was identified as a new microcystin. All three toxins were isolated by a serial separation on an LH-20 column, Si-flash column chromatography and reverse phase HPLC. Toxins were further identified by comparing their FABMS, 1H and 1H-1H COSY NMR spectra with the authentic microcystin-LR. Several other microcystin-like compounds were also found in the cultured strains and their structures are being determined.

Liver slice culture for assessing hepatotoxicity of freshwater cyanobacteria

1. A modified mouse liver slice culture technique was established and the viability of the system was assessed on the basis of leakage of cytosolic enzymes viz. lactate dehydrogenase (LDH), alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartic aminotransferase (AST) and slice histology. 2. This system was employed for toxicity screening of five algal species of Indian origin on the basis of the EC50 for LDH leakage (dose of cyanobacteria resulting in leakage of 50% of enzyme) of a known toxic cyanobacterial strain Microcystis aeruginosa (PCC 7820). On the basis of both in vitro and in vivo toxicity none of the five species screened exhibited toxicity. 3. The toxicity of PCC 7820 was compared with a purified cyanobacterial hepatotoxin, Microcystin-LR. Various biochemical indices and histological changes confirm the hepatotoxic nature of the toxins. 4. The toxins did not induce glutathione-mediated lipid peroxidation but they did cause significant mitochondrial damage based on an MTT assay. 5. The study illustrates the utility of this in vitro system in identifying naturally occurring toxic cyanobacteria, particularly hepatotoxic species.

Light and scanning electron microscopic studies on effects of marine algal toxins toward freshly prepared hepatocytes

Mussels exposed to dinoflagellates may represent a human health risk due to accumulation of a variety of algal toxins. In several parts of the world, algal toxins leading to diarrhea (diarrhetic shellfish poisons, DSP) are found in mussels for extended periods of the year. Routine monitoring of these toxins involves ip injections in mice. Chemical analytical methods have been developed for only some of the toxins in question, namely, those giving diarrhea. Other toxins in the DSP complex are not easily detected by analytical methods. In this report we show that freshly prepared hepatocytes from rats are a convenient means to differentiate between the toxins that give diarrhea and those that do not. Consequently, hepatocytes can be useful in both screening and as a tool in the process of developing analytical methods. Freshly prepared hepatocytes might be useful in combination either with the mouse bioassay or with chemical analytical methods.

Actin filament alterations in rat hepatocytes induced in vivo and in vitro by microcystin-LR, a hepatotoxin from the blue-green alga, Microcystis aeruginosa

The morphologic effects of microcystin-LR (MCLR) were examined in vitro and in vivo to identify the specific cell type(s) affected and to characterize the actin filament changes occurring in hepatocytes. Male Sprague Dawley rats were used for all studies. For in vitro studies, hepatic cells were isolated by collagenase perfusion of liver, while parenchymal cells (hepatocytes) and nonparenchymal cells were prepared by pronase digestion and metrimazide gradient centrifugation. Cell suspensions and and primary hepatocyte monolayer cultures were treated with MCLR at doses up to 10 micrograms/ml; cultured hepatocytes were also treated with phalloidin or cytochalasin B at a dose of 10 micrograms/ml; and rats were treated intraperitoneally with MCLR at 180 mg/kg. Cultured hepatocyte preparations and frozen liver sections were stained with rhodamine-labeled phalloidin for filamentous actin. In cell suspensions, MCLR did not affect nonparenchymal cells but caused rapid, progressive, blebbing of the plasma membrane in hepatocytes. In cultured hepatocytes, MCLR caused plasma membrane blebbing as well as marked reorganization of actin microfilaments. These alterations were dose and time dependent. Cultured hepatocytes treated with phalloidin or cytochalasin B also showed extensive plasma membrane blebbing and actin filament alterations; however, actin filament changes were morphologically distinct from those induced by MCLR. In vivo, MCLR-induced hepatocyte actin alterations occurred at the same time as, or slightly preceded, histologic changes that began 30 minutes after dosing. These studies suggest that early MCLR-induced morphologic changes occurring both in vivo and in vitro are due to alterations in hepatocyte actin filaments.

Evaluation of potential chemoprotectants against microcystin-LR hepatotoxicity in mice

Microcystin-LR (MCLR) is a potent cyclic heptapeptide hepatotoxin produced by the blue-green algae, Microcystis aeruginosa. Toxic blooms of this cyanobacteria have been reported throughout the temperate world. In spite of the potential economic loss and health hazard posed by this toxin, few studies on the development of an antidote have been conducted. Thus, a number of biologically active compounds were tested in mice for effectiveness in preventing the toxicity of a lethal dose of MCLR (100 micrograms kg-1). Efficacy was evaluated based upon the percentage of surviving mice, time to death and serum lactate dehydrogenase activity 45 min after treatment with the toxin. The biologically active compounds were separated into groups based upon proposed mechanisms of action. Enzyme induction by phenobarbital but not by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in partial protection against toxicity. Calcium channel blockers, free-radical scavengers and water-soluble antioxidants produced little protection against toxicity. The membrane-active antioxidants vitamin E and silymarin, as well as glutathione and the monoethyl ester of glutathione, produced significant protection from lethality. Rifampin and cyclosporin-A, both immunosuppressive and membrane-active agents, which also block the bile acid uptake system of hepatocytes, produced complete protection from the toxicity of MCLR. Thus, lipophilic antioxidants provide partial protection against MCLR toxicity while cyclosporin-A and rifampin are highly effective and potentially useful antidotes. The toxicity of MCLR may depend upon stimulation of the immune system and may be mediated by membrane alterations.

Use of a rapid bioluminescence assay for detecting cyanobacterial microcystin toxicity

The recent rise in the awareness of the occurrence of toxic cyanobacterial blooms in aquatic environments, with associated human health problems and animal deaths, has increased the need for rapid, reliable and sensitive methods of determining cyanobacterial toxicity. A luminescent bacterial toxicity test was assessed as a complement to the established mouse bioassay. Seventeen samples including pure cyanobacterial microcystin-LR hepatotoxin, laboratory isolates and natural blooms of cyanobacteria were tested and toxicity data compared with mouse LD50 values. Microcystin-LR and all five microcystin-containing cyanobacterial samples, hepatotoxic by mouse test gave EC50 values of less than 0.46 mg/ml in bioluminescence-based Microtox assays. Of 11 samples non-toxic by mouse bioassay, only two gave an EC50 of less than 0.98 mg/ml by bioluminescence assay. It is suggested that the Microtox bioluminescence assay may prove useful in the preliminary screening of cyanobacterial blooms for microcystin-based toxicity.

Hepatic lipid peroxidation, sulfhydryl status, and toxicity of the blue-green algal toxin microcystin-LR in mice

Microcystin-LR (MCLR), a cyclic heptapeptide produced by the blue-green algae Microcystis aeruginosa, produces death in female mice treated with 100 micrograms MCLR/kg. Kupffer-cell hyperplasia was observed histologically after treatment with 50 or 100 micrograms MCLR/kg. No other changes or lethality were observed with the 50 micrograms MCLR/kg, while 100% lethality occurred in less than 2 h in mice treated with 100 micrograms/kg. In these animals liver weights increased by 45% and hepatic hemoglobin content increased 106% at 60 min posttreatment. Liver histology showed loss of hepatic architecture and necrosis 30 min after treatment, and congestion with blood became evident at 45 min after treatment. Serum enzymes were significantly increased 45 min posttreatment. Hepatic nonprotein sulfhydryl content decreased 19% when calculated on the basis of cytosolic protein and 39% when based upon the total protein content, respectively. The sulfhydryl content of the liver cytoskeletal fraction decreased 26% by 30 min after treatment. Decreased enzyme-mediated and increased non-enzyme-mediated lipid peroxidation were observed in hepatic microsomes following both in vivo and in vitro exposure of hepatic microsomes to MCLR. The toxicity of MCLR may be related to alterations in the sulfhydryl content of the cytoskeletal protein. Furthermore, MCLR may either directly or indirectly affect microsomes, suggesting alterations in structure and function of smooth endoplasmic reticulum.

Toxicity of microcystin LR, a cyclic heptapeptide hepatotoxin from Microcystis aeruginosa, to rats and mice

Rats (Sprague-Dawley) and mice (Balb/c) were given microcystin LR intraperitoneally and were killed at intervals up to 24 hr (rats) or 90 min (mice) and necropsied. The lowest consistently lethal dose was 160 micrograms/kg in rats and 100 micrograms/kg in mice. Rats that were clinically unaffected had no lesion. All clinically affected rats in all dose groups died (from 20 to 32 hr after toxin) and had similar hepatic lesions. Livers were enlarged and dark red beginning 40 to 60 min after toxin. Mild disassociation and rounding of centrilobular hepatocytes developed within 20 min. By 60 min after toxin, degeneration and necrosis of hepatocytes involved most of the lobules except for small periportal zones. Weights of livers and kidneys were significantly increased. Eosinophilic fibrillar material filled renal glomerular capillaries as early as 9 hr after toxin. At 18 to 24 hr there was moderate vacuolation of proximal tubular epithelium with mild tubular dilatation. Beginning at 1 hr, intact hepatocytes and hepatic debris were present in pulmonary vessels. Analysis of serum revealed an increase in alanine aminotransferase 40 min after toxin; at 6 to 12 hr there were significant increases in alkaline phosphatase, total bilirubin, blood urea nitrogen, and creatinine. Mice survived only 60 to 90 min after toxin. Hepatic lesions were similar to those in rats, but renal and pulmonary lesions were not seen.

In vitro screens from CNS, liver and kidney for systemic toxicity

The development and evaluation of in vitro systems from target organs for preliminary assessments of the potential for systemic toxic effects has been receiving increased attention. This review presents a synopsis of progress made in developing toxicity screens for three common target organs and identifies further work needed for more complete validation.

Comparison of in vivo and in vitro toxic effects of microcystin-LR in fasted rats

The toxic effects of microcystin-LR, a cyclic heptapeptide isolated from the cyanobacterium Microcystis aeruginosa, were studied in the fasted rat model and in subcellular fractions from fasted, toxin-treated and control rats. Hepatotoxic effects of a lethal dose (100 micrograms/kg) were examined 15-90 min post-injection. Elevations of serum enzymes, particularly sorbitol dehydrogenase, specific for liver mitochondria, correlated with hepatic damage. Electron micrographs showed progressive cellular disruption, including dilation of rough endoplasmic reticulum, incorporation of cellular components into cytolysosomes, hydropic mitochondria devoid of electron-opaque deposits, loss of desmosome-associated intermediate filaments, disruption of sinusoidal architecture and, ultimately, lysis of hepatocytes. The appearance of hydropic mitochondria correlated with loss of coupled electron transport. Changes in plasma membrane-associated cytoskeletal filaments correlated with loss of desmosome tonofilaments. In contrast to in vivo exposure to microcystin-LR, in vitro exposure to toxin had no effect on mitochondria or cytoskeletal filaments, suggesting that the toxic effects observed in vivo were indirect and may be dependent on bioactivation of the toxin or a cascade of events not supported in in vitro models.

Rapid analysis of peptide toxins in cyanobacteria

A quick and easy-to-perform method for routine analysis of cyanobacterial (blue-green algal) peptide toxins is proposed. The toxins are analysed by means of high-performance liquid chromatography using a recently developed internal surface reversed-phase column. The sample clean-up work is minimized and the total analysis time is thus shortened considerably compared to previously described methods.

Isolated rat liver perfusion studies with cyclic heptapeptide toxins of Microcystis and Oscillatoria (freshwater cyanobacteria)

Isolated perfused rat livers were used to study the dose-dependent effects of three cyclic heptapeptide toxins isolated from Norwegian freshwater bloom samples containing Microcystis aeruginosa, Oscillatoria agardhii var. and Oscillatoria agardhii var. isothrix. The high pressure liquid chromatography (HPLC) purified toxins had an i.p. LD50 in the rat and mouse of approximately 50, 500 and 1000 micrograms/kg, respectively. Hepatic insult of the toxins at concentrations of 0.5-4.0 times the rat i.p. lethal dose were assessed by monitoring bile flow, accumulation of total protein in the perfusate, release of intracellular enzymes and histopathologic examination of perfused liver tissue. One hundred micrograms of Microcystis toxin produced cessation of bile flow during a 1 hr perfusion period, while the two Oscillatoria toxins required 1000 and 2000 micrograms of toxin, consistent with their lower LD50 values. Hepatic cell membranes remained intact during the perfusion since release of enzymes and proteins into the perfusate was similar for toxin treated and control livers, and histopathologic examination of Trypan Blue infused livers revealed exclusion of the dye from the intracellular compartment of the parenchyma. Histopathologic findings for all three toxins showed hepatocellular disassociation that increased with toxin concentration. At the ultrastructural level, all three toxins caused dose-dependent vesiculation of rough endoplasmic reticulum, formation of concentric whorls composed of rough-ER, mitochondrial swelling, large cytoplasmic vacuoles and altered bile canaliculi. These changes were similar to those found for previous in vivo studies using Microcystis cyclic heptapeptides from Scotland and Australia. The Oscillatoria toxins required five to ten times more toxin to produce similar effects as the Microcystis toxin. At the higher concentrations, the Oscillatoria toxins also caused a proliferation of smooth-ER. The isolated perfused rat liver was found to be a good model for studying the hepatocellular effects of different cyclic peptide toxins from cyanobacteria.

Correspondence of results from hepatocyte studies with in vivo response

Isolated hepatocyte systems are being examined in our laboratory for a number of applications, including alternatives to animal testing. This report summarizes findings from studies with chlorinated aliphatics, acetaminophen, nitrotoluenes, and cyanide and its antidotes that relate to in vivo toxicity and validation of these systems for cytotoxicity screening.

Testing for Algal Toxins In Vitro

Toxic blooms of several strains of blue-green algae are found in both natural and man-made freshwater lakes. Furthermore, mussels may accumulate toxic marine dinoflagellates, rendering them toxic to humans.

Traditionally, the presence of algal toxins is tested by intraperitoneal injections of extracts in mice. However, toxic waterblooms and mussels can both be detected by means of freshly prepared rat hepatocytes in suspension.

Freshly prepared rat hepatocytes used in screening the toxicity of blue-green algal blooms

The acute toxicity of extracts of blue-green algae was tested in freshly prepared rat hepatocytes in suspension. The results were compared with the traditional in vivo mouse bioassay. Sixty samples of natural algal blooms from freshwater lakes in Norway, Sweden, and Finland and 14 samples cultured in the laboratory were tested. The mouse bioassay revealed hepatotoxins in a large number of the algae, while neurotoxins were not found. Acute hepatotoxicity in vitro was scored by measurement of leakage of the enzyme lactate dehydrogenase (LDH) from damaged cells and of morphological changes of the cells. The correlation coefficients between mouse toxicity and LDH, mouse toxicity and morphological cell damage, and between LDH and morphological cell damage were 0.812, 0.735, and 0.882, respectively. Consequently, the rat hepatocyte toxicity test seems to be well suited for screening blooms of blue-green algae for the presence of hepatotoxins.