Facile detection of anatoxin-a in algal material by thin-layer chromatography with Fast Black K salt

Analytical Methods for Anatoxin-a Determination: A Review

Anatoxin-a (ATX-a) is a potent neurotoxin produced by several species of cyanobacteria whose exposure can have direct consequences, including neurological disorders and death. The increasing prevalence of harmful cyanobacterial blooms makes the detection and reliable assessment of ATX-a levels essential to prevent the risk associated with public health. Therefore, the aim of this review is to compile the analytical methods developed to date for the detection and quantification of ATX-a levels alone and in mixtures with other cyanotoxins and their suitability. A classification of the analytical methods available is fundamental to make an appropriate choice according to the type of sample, the equipment available, and the required sensitivity and specificity for each specific purpose. The most widely used detection technique for the quantification of this toxin is liquid chromatography-tandem mass spectrometry (LC-MS/MS). The analytical methods reviewed herein focus mainly on water and cyanobacterial samples, so the need for validated analytical methods in more complex matrices (vegetables and fish) for the determination of ATX-a to assess dietary exposure to this toxin is evidenced. There is currently a trend towards the validation of multitoxin methods as opposed to single-ATX-a determination methods, which corresponds to the real situation of cyanotoxins' confluence in nature.

DNA aptamers selection and characterization for development of label-free impedimetric aptasensor for neurotoxin anatoxin-a

High affinity DNA aptamers against anatoxin-a (ATX), the smallest potent neurotoxin (Mol. Wt, 165.23 Da) were selected and identified in vitro using the systematic evolution of ligands by exponential enrichment (SELEX) approach. Aptamers with dissociation constants (Kd) of nanomolar range were isolated. The aptamer sequence of highest affinity was used to design a label-free impedance based aptasensor to assay ATX, for which there are no reported biosensors so far. The aptamer self assembled monolayer is formed on a gold electrode using the disulfide modified aptamer. The assembly process of the aptasensor was characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Upon ATX binding to the immobilized aptamer, a significant decrease in the electron-transfer resistance was observed as a result of the aptamer conformation change, which is used as the sensor signal. The aptasensor showed a limit of detection of 0.5 nM and a wide linear range for ATX concentrations between 1 nM and 100 nM. The Kd of anti-ATX aptamer was calculated by electrochemical methods as well as the fluorescence. Interestingly, the Kd that was calculated from the aptasensor signal showed a lower value implying that the anchoring of the aptamer on the Au surface enhanced its affinity to ATX. The ATX aptasensor showed high stability as well as high specificity against common cynaobacterial toxins. Further development of biosensors that use anatoxin-a binding aptamers as a new recognition receptors could provide potential alternatives to the traditional assays for fast and simple monitoring of anatoxin-a.

Analysis of the toxicity and histopathology induced by the oral administration of Pseudanabaena galeata and Geitlerinema splendidum (cyanobacteria) extracts to mice

Cyanobacteria are common members of the freshwater microbiota in lakes and drinking water reservoirs, and are responsible for several cases of human intoxications in Brazil. Pseudanabaena galeata and Geitlerinema splendidum are examples of the toxic species that are very frequently found in reservoirs in Sao Paulo, which is the most densely populated area in Brazil. In the search for toxic strains collected from water reservoirs and maintained in the Cyanobacterial Culture Collection (CCIBt) of the Institute of Botany of Brazil, the acetic acid extracts (AE) of P. galeata CCIBt 3082 and G. splendidum CCIBt 3223 were analyzed by planar chromatography, which indicated the absence of cyanotoxins. Animal tests were then carried out, and both extracts were found to induce toxic effects in mice when administered intraperitoneally. The present study aimed to investigate whether the oral ingestion of the above mentioned cyanobacteria extracts would also induce toxic effects in mice. Necropsy and histopathological studies were conducted using tissue samples from the animals, which were euthanized one week after the administration of the extracts. The AE of P. galeata did not cause death but did induce transient symptoms, including eyebrow ptosis, straub tail, and pain. The euthanized animals presented hemorrhage in the liver, whereas the histological analysis showed disorganization of the hepatic parenchyma, necrosis, hyperemia, and proximity of the centrilobular vein in the liver. In addition, alterations in the convoluted tubules of the kidneys were observed, and the lungs were unaffected. The AE of G. splendidum caused only one death, and induced transient symptoms, such as dyspnea, paralysis, and pain, in the other mice. The necropsy of the euthanized mice showed hemorrhage in the lungs and liver. The lungs presented hemorrhagic focuses, alveolar collapse, and granulomatous foci. The liver presented hemorrhagic and enlarged sinusoids, hyperemia, proximity of the centrilobular vein, and disorganization of the hepatic parenchyma. Some areas also exhibited an inflammatory infiltrate and calcified tissue inside blood vessels. Necrosis and rupture of the convoluted tubule cells were observed in the kidneys. Further analysis of the both extracts indicated the lack of hemolytic activity, and the presence of two unknown anti-AChE substances in the AE of G. splendidum. Thus, P. galeata and G. splendidum are producers of novel toxins that affect mammals when administered orally.

Toxicology and detection methods of the alkaloid neurotoxin produced by cyanobacteria, anatoxin-a

Freshwater resources are under stress due to naturally occurring conditions and human impacts. One of the consequences is the proliferation of cyanobacteria, microphytoplankton organisms that are capable to produce toxins called cyanotoxins. Anatoxin-a is one of the main cyanotoxins. It is a very potent neurotoxin that was already responsible for some animal fatalities. In this review we endeavor to divulgate much of the internationally published information about toxicology, occurrence and detection methods of anatoxin-a. Cyanobacteria generalities, anatoxin-a occurrence and production as well as anatoxin-a toxicology and its methods of detection are the aspects focused in this review. Remediation of anatoxin-a occurrence will be addressed with a public health perspective. Final remarks call the attention for some important gaps in the knowledge about this neurotoxin and its implication to public health. Alterations of aquatic ecosystems caused by anatoxin-a is also addressed. Although anatoxin-a is not the more frequent cyanotoxin worldwide, it has to be regarded as a health risk that can be fatal to terrestrial and aquatic organisms because of its high toxicity.

Analysis of anatoxin-a in biological samples using liquid chromatography with fluorescence detection after solid phase extraction and solid phase microextraction

Anatoxin-a is a naturally occurring, potent neurotoxin produced by some species of cyanobacteria in freshwaters. This toxin, which is a potential health hazard, especially to animals, has been determined in different biological matrices such as several cyanobacterial cultures and water samples and carps and mussels tissue using a sensitive High Performance Liquid Chromatography with Fluorescence detection method. Sonication was the technique selected for the extraction of intracellular anatoxin-a and solid phase extraction using weak cation exchange was used for the concentration and purification of the samples. 4-Fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was used to convert anatoxin into a highly fluorescent derivative. Recovery experiments were performed for each type of matrix used in this work, and adequate values were obtained (71-87%). Limits of detection for anatoxin-a were estimated to be in the ng/L and ng/g level for water and cyanobacterial samples, respectively. The results obtained were also compared with those obtained after using solid phase microextraction, as an alternative for the extraction and purification of the samples. Advantages and disadvantages regarding to the efficiency for impurities removal, simplicity and rapidity and the potential for concentration enhancement of using both methodologies have been also discussed.

Identification of anatoxins in blue-green algae food supplements using liquid chromatography-tandem mass spectrometry

Blue-green algae (cyanobacteria) in tablets and capsules, which are marketed as health food supplements, were investigated for the presence of neurotoxins related to anatoxin-a. These neurotoxins, which are nicotinic agonists, were investigated using isocratic micro-liquid chromatograph-tandem mass spectrometry (micro-LC-MS-MS). The investigated compounds were anatoxin-a and homoanatoxin-a, together with their degradation products, dihydroanatoxin-a, epoxyanatoxin-a, dihydrohomoanatoxin-a and epoxyhomoanatoxin-a which were synthesized from the parent toxins. The analytes were extracted with methanol followed by isocratic chromatography on a micro C18 reversed-phase column using acetonitrile-water, 50:50 (v/v), containing 20 mm acetic acid at 30 microl min(-1). The toxins were ionized in an ionspray (IS) interface operating in the positive ion mode, where the intact protonated molecules, [M + H]+, were generated at m/z 166, m/z 168, m/z 182, m/z 180, m/z 182 and m/z 196, for anatoxin-a, dihydroanatoxin-a, epoxyanatoxin-a, homoanatoxin-a, dihydrohomoanatoxin-a and epoxyhomoanatoxin-a, respectively. These served as precursor ions for collision-induced-dissociation (CID) and diagnostic product ions for these anatoxins were identified to carry out toxin confirmation by selected reaction monitoring (SRM) LC-MS-MS analysis. Dihydrohomoanatoxin-a and a novel isomer of epoxyanatoxin-a were identified in blue-green algae tablets. This finding suggests that a potential human health hazard could be associated with the consumption of these food supplements.

Analysis of anatoxin-a in freshwaters by automated on-line derivatization-liquid chromatography-electrospray mass spectrometry

Anatoxin-a is a toxin produced from cyanobacterial blooms in freshwaters. In order to determine trace anatoxin-a in freshwaters, an automated on-line derivatization procedure with fluorenyl methylchloroformate using liquid chromatography-electrospray ionization mass spectrometry was developed. Anatoxin-a was extracted using solid-phase extraction with adequate recovery (75.7+/-7.2%, n=6) at 20 ng/l. The limits of quantification and detection were calculated to be 15.2 ng/l and 2.1 ng/l, respectively, using selected ion monitoring.

Sensitive determination of anatoxin-a, homoanatoxin-a and their degradation products by liquid chromatography with fluorimetric detection

Cyanobacterial neurotoxins have been implicated in animal deaths resulting from drinking contaminated water. Anatoxin-a (AN) and homoanatoxin-a (HMAN) have previously been analysed using high-performance liquid chromatography (HPLC) with UV detection, but this procedure is insufficiently sensitive and is subject to interferences. A sensitive fluorimetric (FL) method for determining AN was recently developed using derivatisation with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) and this has been applied to the simultaneous determination of AN, HMAN and their epoxy and dihydro degradation products. Microscale syntheses were used to prepare the dihydro and epoxy derivatives from AN and HMAN. These compounds were produced in high yields, as confirmed by electrospray MS and HPLC-FL of their benzoxadiazole derivatives. All six NBD derivatives were readily separated using isocratic reversed-phase HPLC. The recoveries of these compounds from spiked water samples, using weak cation-exchange (WCX) solid-phase extraction (SPE), were 83.2-84.9% at concentrations of 10 micrograms/l. The R.S.D. values were 1.7-3.9% (n = 8) and the limits of detection were better than 10 ng/l for all six compounds, illustrating the high sensitivity of the method. This methodology was successfully applied to the analysis toxin degradation products in natural samples. Dihydroanatoxin-a (0.8 mg/g) was isolated from a benthic Oscillatoria bloom from Caragh Lake, Ireland, and was found to contain two isomers but their ratio was different from that found in the synthetic material.

Anatoxin-a in Irish freshwater and cyanobacteria, determined using a new fluorimetric liquid chromatographic method

A new sensitive high-performance liquid chromatographic (HPLC) method was used to determine anatoxin-a in freshwater, following blooms of cyanobacteria (blue-green algae). Anatoxin-a was converted into a highly fluorescent derivative using 4-fluoro-7-nitro-2,1,3-benzoxadiazole and HPLC analysis gave good linear calibrations even at low concentration ranges (1-10 micrograms/liter, r = 0.997). The detection limit for anatoxin-a was 0.02 ng/ml, and this new HPLC method should prove useful for the routine analysis of potable waters. Anatoxin-a was discovered in three major lakes in Ireland using this method and identification was confirmed using gas chromatraphy-mass spectrometry (GC-MS), following acetylation. Anatoxin-a was found in Anabaena, a planktonic cyanobacterium, as well as in a benthic Oscillatoria species. This is the first identification of anatoxin-a in Irish freshwater and this toxin was also implicated as the causative agent in incidents of fatal canine neurotoxicosis.

Determination of the cyanobacterial neurotoxin, anatoxin-a, by derivatisation using 7-fluoro-4-nitro-2,1,3-benzoxadiazole (NBD-F) and HPLC analysis with fluorimetric detection

A sensitive HPLC analysis has been developed for the determination of anatoxin-a in cyanobacterial bloom material and in raw and treated waters. Efficient extraction of this toxin from its matrix can be achieved using solid-phase extraction with a weak cation exchanger. HPLC analysis with fluorimetric detection (lambda ex 470 nm, lambda em 530 nm) was possible after derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F). This new analytical protocol permits the detection of anatoxin-a at low concentrations (0.1 micrograms/L) and gave a good linear calibration (1-20 micrograms/L, r = 0.997).