Z Demirel, A Sukatar
anatoxin-a, cyanobacteria blue-green algae, cylindrospermopsin, lipopolysaccharides, microcystins, saxitoxins
Z Demirel, A Sukatar. Cyanobacterial Toxin. The Internet Journal of Toxicology. 2012 Volume 8 Number 2.
Cyanobacteria which are known as blue-green algae can be found widespread around the world such as in lakes, ponds, rivers and brackish waters. Both toxin and non-toxin producing cyanobacterial species have been reported to make blooms. In the case of cyanobacterial toxins (cyanotoxins), there are two known groups as cytotoxins and biotoxins. The biotoxins comprise the alkaloids such as anatoxin-a, anatoxin-a(s), saxitoxins, cylindrospermopsin or lipopolysaccharides, and the cyclic peptides such as microcystins and nodularins. Cyanotoxins are shown to cause acute lethal, acute, chronic and sub-chronic poisoning in wild and domestic animals, and human. In studies both biological and chemical methods are used to determine cyanotoxins. The specific methods for toxin classification can be summarized as; bioassays, ELISA (enzyme linked immunosorbent assay), PPIA (Protein phosphatase inhibition assay), and MMPB (2-Methoxy-1- methyl-3-phenylbuturic acid). Additionally, the methods that are used to determine of toxins are can be classified as follow; NMR (Nuclear magnetic Resonance, MS (Mass Spectrometry), HPLC (high performance liquid chromatography) coupled with either photodiode array (PDA), HPLC-UV (High-performance liquid chromatography), TLC (Thin layer chromatography), MALDI-TOF-MS (matrix assisted laser/desorption ionization- time-of-flight-mass spectrometry), LC-MS (Liquid chromatography hyphenated with electrospray ionization triple quadrupole mass spectrometry).
Cyanobacteria, which are known as blue-green algae, are prokaryotic microorganisms that live in both freshwater, such as; in lakes, ponds, rivers, and reservoir, and in marine systems (Ouellette and Wilhelm, 2003). While cyanobacteria are one of the very few special groups that can perform oxygenic photosynthesis and respiration simultaneously in the same compartment; many cyanobacterial species are known to be able to fix nitrogen (Carmichael, 2001; Vermaas, 2001). Most of the references describe cyanobacteria as Gram-negative and Gram-negative cell wall of cyanobacteria has been previously shown by the electron microscopy (Stewart
Cyanobacteria can be seen in single-celled form or colonial form such as filaments, sheets or even hollow balls. The light responses exhibited by cyanobacteria apparently are the adaptation mechanisms for maintaining optimal light regimens to support photosynthesis, as well as to avoid from burial caused by sedimentation. In addition to light responses, there have been three reports related with cyanobacterial chemotaxis, or chemotaxis-related behaviours (Costa
Cyanobacteria “Blooms”, which can be seen as blue-green, milky blue, green, reddish, or dark brown blooms, and scum, typically occur in freshwater (Richardsont and Castenholz 1989; Rivasseau
Cyanotoxins have two groups as; cytotoxins and biotoxins and they are both known to be responsible for acute lethal, chronic and sub-chronic poisoning of wild and domestic animals and human (Molica
Microcystin and nodularin
Microcystins are non-ribosomally synthesized via peptide synthetases, polyketide synthetases, and additional modifying enzyme system called microcystin synthetase (Harada
Microcystins are the group of monocyclic heptapeptide (7 amino acids) hepatotoxins, containing a characteristic -amino acid residue, 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-deca-4,6-dienoic acid (Adda), N- methyldehydroalanine (Mdha), D-alanine (Ala), -linked D-erythro--methylaspartic acid (-Me-Asp), and -linked D-glutamic acid (Glu) which is most notably produced in both freshwater colonial cyanobacteria
Microcystin and nodularin have variable components such as arginine or N-methyldehydroalanine (Mdha) (Pyo and Shin, 2001). Adda appears to have great importance in hepatotoxicity of microcystin and nodularins (Furukawa
Additionally a halotolerant organism,
Cyanobacterial hepatotoxin nodularins (
Both nodularin and microcystins are relatively stable compounds that are not easily degraded by light, temperature or microwaves (Karjalainen, 2005). Intracellular cyanotoxins use freeze-drier or freeze-thawing for disruption of cell wall which is enhanced by ultrasonicator. While microcystins are soluble in polar solvents (methanol and water); they cannot be dissolved in non-polar solvents. Extraction of microcystin has been achieved by using 100% methanol, methanol–water solutions, methanol–n-butanol–water, 5% acetic acid solutions -eliminate proteins and pigments in the material for chromatograph-, and supercritical fluid CO2 modified with acetic acid. Similar extraction results were obtained with 25% methanol, n-butanol–methanol–water (5:20:75), n-butanol–methanol–acetic acid–water (5:20:1:74), methanol–acetic acid–water (25:1:74), and 5% acetic acid (Anjos
The methods specific for toxin classification, can be summarized as; bioassays, ELISA (enzyme linked immunosorbent assay), PPIA (protein phosphatase inhibition assay), and MMPB (2-Methoxy-1- methyl-3-phenylbuturic acid). It is known that the toxicity of microcystis and nodularin are due to the inhibition of eukaryotic serine/threonine protein phosphatises (PPs), specifically PP1, PP2A and PP2B. Toxin specific methods, which are NMR (Nuclear magnetic Resonance, MS (Mass Spectrometry), HPLC (high performance liquid chromatography) coupled with either photodiode array (PDA) or high-performance capillary electrophoresis (HPCE), have been widely used for detection and quantitation of microcystins in water and in cyanobacterial cells (Hotto
In 2003 a method was reviewed by the International Standards Organization (ISO/ CD 20179) and in this method an extraction procedure was recommended, that consist of three sequential extractions with 75% MeOH and sonication for 5 min. The most recent recommendation from 2004 included the sonication for 2 min on ice. According to the World Health Organization (WHO) guideline, the microcystin value in prohibited drinking water is 1 μg/L (ppb), which is based on microcystin-LR which is a specific microcystin toxin (Saker
Five pathways of microcystin detoxification can be considered for contributing to the natural routes as follow; 1. Dilution, 2. Absorption, 3. Thermal decomposition aided by temperature and pH, 4. Photolysis, and 5. Biological degradation (Watanabe
Cylindrospermopsin [C15H21N5O7S] (MW= 415.43), a sulfate ester of a tricyclic guanidine substituted with a hydroxymethyluracil, is a cyanobacterial alkaloid toxin (
As a toxin, cylindrospermopsin mainly targets liver but it has also effect on other organs. While cylindrospermopsin is a hepatocytes inhibitor of protein synthesis that causes widespread necrotic injury in human such as in liver, kidneys, lungs, spleen and intestine; it is also a hepatocytes inhibitor of glutathione (GSH) that leads to cell death. Glutathione (GSH) is an important non-protein thiol in the cell which has protective feature against oxidative damage and has important role in the detoxification. The mechanism of the decrease in GSH caused by cylindrospermopsin was assigned to the inhibition of GSH synthesis rather than to altered consumption (Reisner
Cylindrospermopsin is a glassy solid and highly water-soluble toxin. The stability of cylindrospermopsin has been studied in different extreme conditions and cylindrospermopsin has been found to be relatively stable at very high temperatures (100 0C for 15 minutes) and pH (pH of 4, 7, and 10 for 8 weeks). Cylindrospermopsin is not commercially produced and is not used as a compound (Masten and Carson, 2000).
The analytical determination of cylindrospermopsin involves purification of cylindrospermopsin from purified extracts of cyanobacterial isolates with HPLC or over silica gel and characterization with mass spectrometry (MS) or NMR. In previous studies cylindrospermopsin was measured by HPLC using PDA detection and the results were confirmed by HPLC–MS (Runnegar
Anatoxins [C10H15NO] (MW = 165) are the group of low molecular weight neurotoxic alkaloids described in Table 1. They were found in the freshwater cyanobacteria
Anatoxin-a(S) similarly has action through synthetic organophosphonate nerve agents, such as sarin, soman or VX, which inhibit cholinesterases by phosphorylating their active site. While toxin is an acetylcholinesterase inhibitor; anatoxin-a(s) is not a homotropane (Wonnacott and Gallagher, 2006). Table 2 shows the different LD50 values for cyanobacterial toxins.
Extraction of anatoxin-a has been performed by using water adjusted to pH 5 with HCL, 0.05 M acetic acid, or methanol. Anatoxin–a has been determined by HPLC after derivatization with 7– fluoro–4–nitro–2,1,3–benzoxadiazole (NBD–F) and the results were confirmed by HPLC–MS of the free or NBD–derivatized toxin (Runnegar
Saxitoxins [C10H17N7O4] (MW = 299) are the carbamate alkaloids that block mammalian sodium channels and about 21 structural variants of sanitoxins have been found in cyanobacteria such as the strains of A
Saxitoxins are known as the products of three marine dinoflagellate genera (
The paralytic shellfish toxins (PSTs) are classified into carbamoyl or carbamate toxins, which are saxitoxin, neosaxitoxin, and gonyautoxins 1–4; and their N-sulfocarbamoyl derivatives as gonyautoxins 5, and 6, and C1–4; and finally decarbamoyl toxins. Small modifications of those elements are known as the result of sulfatation at positions of R2 and R3. PSTs are measured by HPLC with fluorescent detection after either chemical or electrochemical post–column derivatization (Runnegar
Lipopolysaccharides (LPS) endotoxins are determined in several species or strains of cyanobacteria, including
Cyanobacterial LPS is known to cause a range of pathological effects in human, such as gastro-intestinal illness, cutaneous signs and symptoms, allergy, respiratory disease, headache, and fever (Stewart
In conclusion, natural water has been used as fresh water, for example as drinking water, aquapark water, and bath water. This review emphasizes that fresh water is a habitat for toxic cyanobacteria which make blooms and produces different toxins. While legal regulations about chemical analysis, such as heavy metals and pesticides, monitor water quality; also cyanobacterial toxin analysis must be taken into consideration for human health around the world.
We also thank Odul Karayazi Atici, M.Sc. for editing the grammar of this review.