High-performance liquid chromatographic separation of microcystins and nodularin, cyanobacterial peptide toxins, on C18 and amide C16 sorbents

Comprehensive insights into the occurrence and toxicological issues of nodularins

The occurrence of cyanobacterial toxins is being increasingly reported. Nodularins (NODs) are one of the cyanotoxins group mainly produced by Nodularia spumigena throughout the world. NODs may exert adverse effects on animal and human health, and NOD-R variant is the most widely investigated. However, research focused on them is still limited. In order to understand the realistic risk well, the aim of this review is to compile the available information in the scientific literature regarding NODs, including their sources, distribution, structural characteristics, physicochemical properties, biosynthesis and degradation, adverse effects in vitro and vivo, and toxicokinetics. More data is urgently needed to integrate the cumulative or synergistic effects of NODs on different species and various cells to better understand, anticipate and aggressively manage their potential toxicity after both short- and long-term exposure in ecosystem, and to minimize or prevent the adverse effects on human health, environment and the economy.

Biosensing of microcystins in water samples; recent advances

Safety and quality of water are significant matters for agriculture, animals and human health. Microcystins, as secondary metabolite of cyanobacteria (blue-green algae) and cyclic heptapeptide cyanotoxin, are one of the main marine toxins in continental aquatic ecosystems. More than 100 microcystins have been identified, of which MC-LR is the most important type due to its high toxicity and common detection in the environment. Climate change is an impressive factor with effects on cyanobacterial blooms as source of microcystins. The presence of this cyanotoxin in freshwater, drinking water, water reservoir supplies and food (vegetable, fish and shellfish) has created a common phenomenon in eutrophic freshwater ecosystems worldwide. International public health organizations have categorized microcystins as a kind of neurotoxin and carcinogen. There are several conventional methods for detection of microcystins. The limitations of traditional methods have encouraged the development of innovative methods for detection of microcystins. In recent years, the developed sensor techniques, with advantages, such as accuracy, reproducibility, portability and low cost, have attracted considerable attention. This review compares the well-known of biosensor types for detection of microcystins with a summary of their analytical performance.

Synthesis of magnetic core–shell Fe3O4@PDA@Cu-MOFs composites for enrichment of microcystin-LR by MALDI-TOF MS analysis

The synthetic route of the Fe₃O₄@PDA@Cu-MOFs microspheres and enrichment process of MC-LR.

Inhibition equivalency factors for microcystin variants in recombinant and wild-type protein phosphatase 1 and 2A assays

In this work, protein phosphatase inhibition assays (PPIAs) have been used to evaluate the performance of recombinant PP1 and recombinant and wild-type PP2As. The enzymes have been compared using microcystins-LR (MC-LR) as a model cyanotoxin. Whereas PP2ARec provides a limit of detection (LOD) of 3.1 μg/L, PP1Rec and PP2AWild provide LODs of 0.6 and 0.5 μg/L, respectively, lower than the guideline value proposed by the World Health Organization (1 μg/L). The inhibitory potencies of seven MC variants (-LR, -RR, -dmLR, -YR, -LY, -LW and -LF) have been evaluated, resulting on 50 % inhibition coefficient (IC50) values ranging from 1.4 to 359.3 μg/L depending on the MC variant and the PP. The PPIAs have been applied to the determination of MC equivalent contents in a natural cyanobacterial bloom and an artificially contaminated sample, with multi-MC profiles. The inhibition equivalency factors (IEFs) have been applied to the individual MC quantifications determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, and the estimated MC-LR equivalent content has been compared to PPIA results. PPIAs have demonstrated to be applicable as MC screening tools for environmental applications and to protect human and animal health.

Account: characterization and identification of microcystins by mass spectrometry

In this brief overview, the authors describe mass spectral techniques for the detection and identification of microcystin toxins. Microcystins are secondary metabolites produced by cyanobacteria. Determination of these toxic compounds and discovery of new variants is very important as they pose a great danger to the human food chain. Cyanobacterial blooms frequently occur in many areas worldwide and have the potential to contaminate the water via cyanotoxin release, especially microcystins. Among the various analytical techniques used for analysis, mass spectrometry has become the most important method as it allows simultaneous quantification and structural characterization of multiple microcystin variants. This brief overview article focuses on mass spectrometry techniques for identification of microcystins, including ionization methods, mass spectral fragmentation routes, profiling techniques, tandem and high-resolution mass spectrometry as well as typing of cyanobacterial strains.

State of knowledge and concerns on cyanobacterial blooms and cyanotoxins

Cyanobacteria are ubiquitous microorganisms considered as important contributors to the formation of Earth's atmosphere and nitrogen fixation. However, they are also frequently associated with toxic blooms. Indeed, the wide range of hepatotoxins, neurotoxins and dermatotoxins synthesized by these bacteria is a growing environmental and public health concern. This paper provides a state of the art on the occurrence and management of harmful cyanobacterial blooms in surface and drinking water, including economic impacts and research needs. Cyanobacterial blooms usually occur according to a combination of environmental factors e.g., nutrient concentration, water temperature, light intensity, salinity, water movement, stagnation and residence time, as well as several other variables. These environmental variables, in turn, have promoted the evolution and biosynthesis of strain-specific, gene-controlled metabolites (cyanotoxins) that are often harmful to aquatic and terrestrial life, including humans. Cyanotoxins are primarily produced intracellularly during the exponential growth phase. Release of toxins into water can occur during cell death or senescence but can also be due to evolutionary-derived or environmentally-mediated circumstances such as allelopathy or relatively sudden nutrient limitation. Consequently, when cyanobacterial blooms occur in drinking water resources, treatment has to remove both cyanobacteria (avoiding cell lysis and subsequent toxin release) and aqueous cyanotoxins previously released. Cells are usually removed with limited lysis by physical processes such as clarification or membrane filtration. However, aqueous toxins are usually removed by both physical retention, through adsorption on activated carbon or reverse osmosis, and chemical oxidation, through ozonation or chlorination. While the efficient oxidation of the more common cyanotoxins (microcystin, cylindrospermopsin, anatoxin and saxitoxin) has been extensively reported, the chemical and toxicological characterization of their by-products requires further investigation. In addition, future research should also investigate the removal of poorly considered cyanotoxins (β-methylamino-alanine, lyngbyatoxin or aplysiatoxin) as well as the economic impact of blooms.

Monitoring approaches for a toxic cyanobacterial bloom

Cyanobacterial blooms, dominated by Microcystis sp. and associated microcystin variants, have been implicated in illnesses of humans and animals. Little is known regarding the formation of blooms and the presence of cyanotoxin variants in water bodies. Furthermore, the role played by ecological parameters, in regulating Microcystis blooms is complicate and diverse. Local authorities responsible for water management are often faced with the challenging task of dealing with cyanobacterial blooms. Therefore, the development of suitable monitoring approaches to characterize cyanobacterial blooms is an important goal. Currently, various biological, biochemical and physicochemical methods/approaches are being used to monitor cyanobacterial blooms and detect microcystins in freshwater bodies. Because these methods can vary as to the information they provide, no single approach seemed to be sufficient to accurately monitor blooms. For example, immunosensors are more suited for monitoring the presence of toxins in clear water bodies while molecular methods are more suited to detect potentially toxic strains. Thus, monitoring approaches should be tailored for specific water bodies using methods based on economic feasibility, speed, sensitivity and field applicability. This review critically evaluates monitoring approaches that are applicable to cyanobacterial blooms, especially those that focus on the presence of Microcystis, in freshwater bodies. Further, they were characterized and ranked according to their cost, speed, sensitivity and selectivity. Suggested improvements were offered as well as future research endeavors to accommodate anticipated environmental changes.

Next generation planar waveguide detection of microcystins in freshwater and cyanobacterial extracts, utilising a novel lysis method for portable sample preparation and analysis

The study details the development of a fully validated, rapid and portable sensor based method for the on-site analysis of microcystins in freshwater samples. The process employs a novel lysis method for the mechanical lysis of cyanobacterial cells, with glass beads and a handheld frother in only 10 min. The assay utilises an innovative planar waveguide device that, via an evanescent wave excites fluorescent probes, for amplification of signal in a competitive immunoassay, using an anti-microcystin monoclonal with cross-reactivity against the most common, and toxic variants. Validation of the assay showed the limit of detection (LOD) to be 0.78 ng mL(-1) and the CCβ to be 1 ng mL(-1). Robustness of the assay was demonstrated by intra- and inter-assay testing. Intra-assay analysis had % C.V.s between 8 and 26% and recoveries between 73 and 101%, with inter-assay analysis demonstrating % C.V.s between 5 and 14% and recoveries between 78 and 91%. Comparison with LC-MS/MS showed a high correlation (R(2)=0.9954) between the calculated concentrations of 5 different Microcystis aeruginosa cultures for total microcystin content. Total microcystin content was ascertained by the individual measurement of free and cell-bound microcystins. Free microcystins can be measured to 1 ng mL(-1), and with a 10-fold concentration step in the intracellular microcystin protocol (which brings the sample within the range of the calibration curve), intracellular pools may be determined to 0.1 ng mL(-1). This allows the determination of microcystins at and below the World Health Organisation (WHO) guideline value of 1 μg L(-1). This sensor represents a major advancement in portable analysis capabilities and has the potential for numerous other applications.

Development of an analytical method for the unambiguous structure elucidation of cyclic peptides with special appliance for hepatotoxic desmethylated microcystins

The periodical occurrence of harmful algal blooms (HABs) in freshwater lakes requires the determination of potential cyanobacterial toxins, especially microcystins (MCs). On demand of an adequate risk assessment, the high diversity of these hepatotoxic cyclic heptapeptides implicates the need of an unambiguous detection of their specific structural variants. Therefore, LC-MS and LC-MS/MS methods are the approaches of choice for determination of MCs. In contrast, even tandem mass spectromic fragmentation patterns are not even sufficient in any kind of structural determination requirements, whereas NMR methods require very high amounts of MCs. In this study, we present a novel method for chromatographic separation of desmethylated microcystins (dm-MCs). Based on the isolation of the specific structural variants using semi-preparative HPLC, a method was developed for the structure elucidation of cyclic peptides with special appliance for the determination of dm-MCs via analysis of the specific amino acid composition after peptide hydrolysis followed by stereospecific detection of the amino acids and resulting keto acids. On the basis of this method it is demonstrated that dm-MC-RR with the structure [Dha(7)]MC-RR represented the major compound in the microcystin pattern of Microcystis aeruginosa bloom events in 2005 and 2006 in Lake Senftenberg, Germany.

Toxins of cyanobacteria

Blue-green algae are found in lakes, ponds, rivers and brackish waters throughout the world. In case of excessive growth such as bloom formation, these bacteria can produce inherent toxins in quantities causing toxicity in mammals, including humans. These cyanotoxins include cyclic peptides and alkaloids. Among the cyclic peptides are the microcystins and the nodularins. The alkaloids include anatoxin-a, anatoxin-a(S), cylindrospermopsin, saxitoxins (STXs), aplysiatoxins and lyngbyatoxin. Both biological and chemical methods are used to determine cyanotoxins. Bioassays and biochemical assays are nonspecific, so they can only be used as screening methods. HPLC has some good prospects. For the subsequent detection of these toxins different detectors may be used, ranging from simple UV-spectrometry via fluorescence detection to various types of MS. The main problem in the determination of cyanobacterial toxins is the lack of reference materials of all relevant toxins. In general, toxicity data on cyanotoxins are rather scarce. A majority of toxicity data are known to be of microcystin-LR. For nodularins, data from a few animal studies are available. For the alkaloids, limited toxicity data exist for anatoxin-a, cylindrospermopsin and STX. Risk assessment for acute exposure could be relevant for some types of exposure. Nevertheless, no acute reference doses have formally been derived thus far. For STX(s), many countries have established tolerance levels in bivalves, but these limits were set in view of STX(s) as biotoxins, accumulating in marine shellfish. Official regulations for other cyanotoxins have not been established, although some (provisional) guideline values have been derived for microcystins in drinking water by WHO and several countries.

Liquid Chromatography−Tandem Mass Spectrometry Application, for the Determination of Extracellular Hepatotoxins in Irish Lake and Drinking Waters

A novel method for the determination of hepatotoxins; microcystins (MCs), and nodularin (Nod) in lake water and domestic chlorinated tap water has been developed using liquid chromatography hyphenated with electrospray ionization triple quadrupole mass spectrometry (LC-ESI-MS/MS). Optimization of the mass spectrometer parameters and mobile-phase composition was performed to maximize the sensitivity and reproducibility of the method. Detection of the hepatotoxins was carried out using multiple reaction monitoring experiments, thus improving the selectivity of the method. A total ion chromatogram and a precursor ion scan on ion m/z 135 was also applied to all samples to detect unknown microcystins or microcystins for which there are no standards available. A comprehensive validation of the LC-ESI-MS/MS method was completed that took into account matrix effects, specificity, linearity, accuracy, and precision. Good linear calibrations were obtained for MC-LR (1-200 microg/L; R2=0.9994) in spiked lake and tap water samples (1-50 microg/L; R2=0.9974). Acceptable interday repeatability was achieved for MC-LR in lake water with RSD values (n=9) ranging from 9.9 (10 microg/L) to 5.1% (100 microg/L). Excellent limits of detection (LOD) and limits of quantitation (LOQ) were achieved with spiked MCs and Nod samples; LOD=0.27 microg/L and LOQ=0.90 microg/L for MC-LR in the "normal linear range" and LOD=0.08 microg/L and LOQ=0.25 microg/L in the "low linear range" in both lake and chlorinated tap water. Similar results were obtained for a suite of microcystins and nodularin. This sensitive and rapid method does not require any sample preconcentration, including the elimination of solid-phase extraction (SPE) for the effective screening of hepatotoxins in water below the 1 microg/L WHO provisional guideline limit for MC-LR. Furthermore, SPE techniques are time-consuming, nonreproducible at trace levels, and offer poor recoveries with chlorinated water. The application of this LC-ESI-MS/MS method for routine screening of hepatotoxins in lake and chlorinated tap water (average Cl2=0.23 mg/L) is achieved and this study represents the first direct method for the screening of hepatotoxins in chlorinated tap water.

Methods for determining microcystins (peptide hepatotoxins) and microcystin-producing cyanobacteria

Episodes of cyanobacterial toxic blooms and fatalities to animals and humans due to cyanobacterial toxins (CBT) are known worldwide. The hepatotoxins and neurotoxins (cyanotoxins) produced by bloom-forming cyanobacteria have been the cause of human and animal health hazards and even death. Prevailing concentration of cell bound endotoxin, exotoxin and the toxin variants depend on developmental stages of the bloom and the cyanobacterial (CB) species involved. Toxic and non-toxic strains do not show any predictable morphological difference. The current instrumental, immunological and molecular methods applied for determining microcystins (peptide hepatotoxins) and microcystin-producing cyanobacteria are reviewed.

Summer changes in cyanobacterial bloom composition and microcystin concentration in eutrophic Czech reservoirs

In mid-July and August 2003 and 2004, 18 reservoirs in the Czech Republic were sampled for phytoplankton species composition and concentration of intracellular microcystins (MCs). As a consequence of high nutrient loading, most of the reservoirs experienced cyanobacterial blooms of various intensities, with the prevalence of cyanobacteria increasing markedly in August, along with a conspicuous shift in species composition toward dominance of Microcystis spp. Microcystins were detected in 90% of the samples, and their amount also increased considerably in August, reflecting the cyanobacterial biomass. In Microcystis-dominated samples, a significantly higher amount of MCs (p < 0.001) occurred than in samples in which other taxa prevailed. Microcystins were positively correlated with chlorophyll a and cyanobacterial biovolume (p < 0.05, R2 = 0.61 and 0.66, respectively), with the strongest correlation found for Microcystis spp. biovolume (p < 0.001, R2 = 0.87). This taxon was the most important producer of MCs in Czech reservoirs. The main structural variants of MCs were MC-LR, MC-RR, and MC-YR. This study's data also indicate that the relative share of MC variants (MC-LR and MC-RR) varies considerably with time, most likely as a consequence of different species and strain compositions during the summer. This study clearly demonstrates a high prevalence of MC-producing cyanobacteria in Czech reservoirs. Therefore, regular monitoring of these reservoirs is highly desirable in an effort to minimize potential health risks to the human population.

Toxic potential of five freshwater Phormidium species (Cyanoprokaryota)

Among the Cyanoprokaryota (blue-green algae), the genus Phormidium has thus far rarely been studied with respect to toxin production and potentially resulting human and environmental health effects. We here show that five previously unexplored freshwater species of this genus (Ph. bijugatum, Ph. molle, Ph. papyraceum, Ph. uncinatum, Ph. autumnale) are indeed capable of producing bioactive compounds. Phormidium extracts caused weight loss as well as neuro/hepatotoxic symptoms in mice, and in the case of Ph. bijugatum even death. Very low levels of saxitoxins and microcystins, as confirmed by ELISA, were insufficient to explain this toxicity and the differing toxic potencies of the Phormidium species. Qualitative HPLC analyses confirmed different substance patterns and in the future could aid in the separation of fractions for more detailed substance characterisation. The results in vivo were confirmed in vitro using cells of human, mouse and fish. The fish cells responded least sensitive but proved useful in studying the temperature dependence of the toxicity by the Phormidium samples. Further, the human cells were more sensitive than the mouse cells thus suggesting that the former may be a more appropriate choice for studying the impact of Phormidium to man. Among the human cells, two cancer cell lines were more responsive to one of the samples than a normal cell line, thereby indicating a potential anti-tumour activity. Thus, the five freshwater Phormidium species should be considered in environmental risk assessment but as well, as a source of therapeutic agents.

Microcystin-producing blooms--a serious global public health issue

The investigation on microcystin topics is increasing due to the related ecological and public health risks. Recent investigation confirms a gap in establishing global patterns relating a particular environment to the bloom occurrence of a species and the production of certain microcystin variants. All the results concerning the environmental effects on the microcystin synthesis of one species must be checked in the light of genome diversity. Thus, the poisoning risks of a bloom depend on the strain causing toxicity. To be more effective, specific water treatment methods are required for blooms of different microcystin producing species (such as colonial and filamentous cyanobacteria found in stratified and unstratified water bodies, respectively). With the increasing number of new microcystin variants discovered, the development of new rapid, inexpensive and sensitive enough monitoring methods to promptly screen simultaneously a great diversity of toxins and also check their toxic effects is becoming necessary.

Effects of phosphate and light on growth of and bioactive peptide production by the Cyanobacterium anabaena strain 90 and its anabaenopeptilide mutant

Cyanobacteria synthesize several types of bioactive secondary metabolites. Anabaena strain 90 produces three types of bioactive peptides, microcystins (inhibitors of protein phosphatases 1 and 2A), anabaenopeptilides, and anabaenopeptins (serine protease inhibitors). To investigate the role of the anabaenopeptilides in Anabaena, wild-type strain 90 (WT) and its anabaenopeptilide deficient mutant (MU) were cultured with various light and phosphate levels to evaluate the effects and coeffects of these growth factors on the concentrations of the three classes of peptides and the growth characteristics. WT and MU grew in comparable ways under the different growth conditions. The total peptide concentration in WT was significantly higher than that in MU (2.5 and 1.4 microg/mg [dry weight], respectively). Interestingly, the average concentration of anabaenopeptins was significantly higher in MU than in WT (0.59 and 0.24 microg/mg [dry weight], respectively). The concentration of microcystins was slightly but not statistically significantly higher in MU than in WT (1.0 and 0.86 microg/mg [dry weight], respectively). In WT, the highest peptide concentrations were usually found after 13 days in cultures grown at medium light intensities (23 micromol m(-2) s(-1)) and with the highest phosphate concentrations (2,600 microg liter(-1)). In MU, the highest peptide concentrations were found in 13-day-old cultures grown at medium light intensities (23 micromol m(-2) s(-1)) and with phosphate concentrations greater than 100 microg liter(-1). The higher concentrations of anabaenopeptins in MU may compensate for the absence of anabaenopeptilides. These findings clearly indicate that these compounds may have some linked function in the producer organism, the nature of which remains to be discovered.

Screening for cyanobacterial hepatotoxins, microcystins and nodularin in environmental water samples by reversed-phase liquid chromatography–electrospray ionisation mass spectrometry

Water samples taken from 93 freshwater and brackish water locations in Aland (SW Finland) in 2001 were analysed for biomass-bound microcystins and nodularin, cyanobacterial peptide hepatotoxins, by liquid chromatography-mass spectrometry (LC-MS) in selected ion recording (SIR) and multiple reaction monitoring modes, HPLC-UV, and enzyme-linked immunosorbent assay (ELISA). The extracted toxins were separated on a short C18 column with a gradient of acetonitrile and 0.5% formic acid, and quantified on a Micromass Quattro Micro triple-quadrupole mass spectrometer with an electrospray ion source operated in the positive SIR or scan mode. An injection of 50 pg of microcystin-LR, m/z 995.5, on column gave a signal-to-noise ratio of 17 (peak-to-peak) at the chosen SIR conditions. In-source or MS-MS fragmentation to m/z 135.1, a fragment common to most microcystins and nodularin, was used for confirmatory purposes. Microcystins with a total toxin concentration equal to or higher than 0.2 microg l(-1) were confirmed by all three methods in water samples from 14 locations. The highest toxin concentration in a water sample was 42 microg l(-1). The most common toxins found were microcystins RR, LR and YR with different degrees of demethylation (non-, mono- or didemethylated). Parallel results achieved with ELISA and HPLC-UV were generally in good agreement with the LC-MS SIR results.

Extraction of 15 microcystins and nodularin using immunoaffinity columns

Microcystins (MCYSTs) were isolated from surface water using reusable immunoaffinity columns. Individual MCYST were determined by high performance liquid chromatography equipped with a photo-diode array detector (HPLC-PDA, 200-300 nm). Subsequent analysis of the samples by liquid chromatography-electrospray ionization mass spectrometry (LC-ESMS) provided molecular weight information, which was used to tentatively identify individual MCYST variants for which standards were not available. Results obtained using immunoaffinity columns (IAC)-HPLC-PDA were compared to those obtained using solid phase extraction (SPE) Oasis HLB-HPLC-PDA. This is the first report of the extraction of 15 microcystins and nodularin using immunoaffinity columns. Whereas previous reports demonstrates the use of IAC for four microcystins, we found that IAC selectively extracted the following microcystins: MCYST-RR, [D-Asp3]MCYST-RR, MCYST-YR, MCYST-LR, 3 MCYST-LR variants, MCYST-AR, MCYST-FR, MCYST-WR, MCYST-LA, MCYST-LA variant, the less polar microcystins such as MCYST-LF, MCYST-LW and nodularin. The IAC extracts were free of interferences which enabled better detection and identification of MCYSTs. Based on the amount loaded to the cartridges, the method detection limit was 10-14 ng when using IAC and 25 ng for SPE of each MCYST-RR, MCYST-YR and MCYST-LR. Reproducibilities expressed as relative standard deviation were 6-10% for SPE and 4-17% for IAC.

Rapid separation of microcystins and nodularin using a monolithic silica C18 column

A monolithic C18-bonded silica rod column (Merck Chromolith) was compared to particle-based C18 and amide C16 sorbents in the HPLC separation of eight microcystins and nodularin-R. Two gradient mobile phases of aqueous trifluoroacetic acid modified with acetonitrile or methanol, different flow-rates and different gradient lengths were tested. The performance of the Chromolith column measured as the resolution of some microcystin pairs, the selectivity, efficiency (peak width) and peak asymmetry equalled, or exceeded, the performance of traditional particle-based columns. The Chromolith column allowed a shortening of the total analysis time to 4.3 min with a flow-rate 4 ml min(-1).