Innovative detection methods for aquatic algal toxins and their presence in the food chain

Detection of aquatic algal toxins has become critical for the protection of human health. During the last 5 years, techniques such as optical, electrochemical, and piezoelectric biosensors or fluorescent-microsphere-based assays have been developed for the detection of aquatic algal toxins, in addition to optimization of existing techniques, to achieve higher sensitivities, specificity, and speed or multidetection. New toxins have also been incorporated in the array of analytical and biological methods. The impact of the former innovation on this field is highlighted by recent changes in legal regulations, with liquid chromatography–mass spectrometry becoming the official reference method for marine lipophilic toxins and replacing the mouse bioassay in many countries. This review summarizes the large international effort to provide routine testing laboratories with fast, sensitive, high-throughput, multitoxin, validated methods for the screening of seafood, algae, and water samples.     

基于金属有机骨架材料的生物传感器在食源性致病菌或毒素检测中的应用

食源性致病菌或其产生的毒素污染的食物会给人体健康带来严重威胁,并造成巨大的经济损失。近年来,金属有机骨架材料(MOFs)作为一种新型的多孔晶体材料,因其具有大的表面积、高的孔隙率等特点,受到人们的广泛关注。将MOFs与生物传感器结合用于食源性致病菌或毒素的检测引起了研究者的兴趣。基于此,本文介绍了MOFs用于生物传感器的优势,概述了MOFs在不同的电化学和光学生物传感器的应用,综述了基于MOFs的生物传感器在致病菌或毒素的研究进展,讨论了基于MOFs的生物传感器在致病菌或毒素所面临的挑战和展望。     

The role of chromatography in the hunt for red tide toxins

An overview is given of the different approaches that have been used to identify toxins responsible for seafood poisoning incidents, to investigate the origins of toxins, and to monitor seafood on a routine basis. It is shown that advancements in our knowledge of toxins and our ability to protect the public have often followed key developments in separation and analysis technologies. Specific examples of research in this field are presented to illustrate the significant role that chromatographic methods play. The presentation will be given in an order that reflects the typical sequence of investigations that follow a new toxin episode.     

Characterisation of botulinum toxins type A and B,by matrix-assisted laser desorption ionisation and electrospray mass spectrometry

A method earlier developed for the mass spectrometric (MS) identification of tetanus toxin (TTx) was applied to botulinum toxins type A and B (BTxA and BTxB). Botulinum toxins are extremely neurotoxic bacterial toxins, likely to be used as biological warfare agent. Biologically active BTxA and BTxB are comprised of a protein complex of the respective neurotoxins with specific haemagglutinins (HAs) and non-toxic non-haemagglutinins (NTNHs). These protein complexes are also observed in mass spectrometric identification. The particular BTxA complex, from Clostridium botulinum strain 62A, almost completely matched database data derived from genetic sequences known for this strain. Although no such database information was available for BTxB, from C. botulinum strain okra, all protein sequences from the complex except that of HA-70 were found to match proteins known from other type B strains. It was found that matrix-assisted laser desorption ionisation MS provides provisional identification from trypsin digest peptide maps and that liquid chromatography electrospray (tandem) mass spectrometry affords unequivocal identification from amino acid sequence information of digest peptides obtained in trypsin or pepsin digestion.     

Analysis of acidic drugs in the effluents of sewage treatment plants using liquid chromatography-electrospray ionization tandem mass spectrometry

Azaspiracid poisoning (AZP) is a new human toxic syndrome that is caused by the consumption of shellfish that have been feeding on harmful marine microalgae. A liquid chromatography–mass spectrometry (LC–MS) method has been developed for the determination of the three most prevalent toxins, azaspiracid (AZA1), 8-methylazaspiracid (AZA2) and 22-demethylazaspiracid (AZA3) as well as the isomeric hydroxylated analogues, AZA4 and AZA5. Separation of five azaspiracids was achieved on a C₁₈ column (Luna-2, 150×2 mm, 5 μm) with isocratic elution using acetonitrile–water containing trifluoroacetic acid and ammonium acetate as eluent modifiers. Using an electrospray ionisation (ESI) source with an ion-trap mass spectrometer, the spectra showed the protonated molecules, [M+H]⁺, with most major product ions due to the sequential loss of two water molecules. A characteristic fragmentation pathway that was observed in each azaspiracid was due to the cleavage of the A-ring at C₉–C₁₀ for each toxin. It was possible to select unique ion combinations to distinguish between the isomeric azaspiracids, AZA4 and AZA5. Highly sensitive LC–MS³ analytical methods were compared and the detection limits were 5–40 pg on-column. Linear calibrations were obtained for AZA1 in shellfish in the range 0.05–1.00 μg/ml (r²=0.9974) and good reproducibility was observed with a relative standard deviation (%RSD) of 1.8 for 0.9 μg AZA1/ml (n=5). The %RSD values for the minor toxins, AZA4 and AZA5, using LC–MS³ (A-ring fragmentation) were 12.3 and 8.1 (0.02 μg/ml; n=7), respectively. The selectivity of toxin determination was enhanced using LC–MS–MS with high energy WideBand activation.     

Toxins as Tools in Neurochemistry

Neurotoxins have evolved as molecules targeted specifically against molecules with an important function in the nervous system. Because of their selectivity they have been used as probes for detecting and characterizing key proteins of the nerve cell. Ion channels involved in the propagation of the action potential, proteins of presynaptic neurotransmitter exocytosis, and most importantly, neurotransmitter receptors have been and are presently being analyzed, in some cases already at atomic level by a combination of the tools of neurotoxins, molecular biology, and patch clamp electrophysiology. In this review a selection of these toxins is presented, together with their targets in the nervous system. Special emphasis is given to the recent breakthroughs in our understanding of the mechanism of action of tetanus and botulinum toxins and to the neurotoxins ranging from the plant alkaloid strychnine to the peptide toxins from poisonous snakes, which were fundamental in elucidating ligand-gated ion channels like the glycine and nicotinic acetylcholine receptors.     

Simultaneous determination of toxins in algae and water samples by high-performance liquid chromatography with triple quadrupole mass spectrometry

A facile method based on liquid chromatography coupled with electrospray ionization tandem triple quadrupole mass spectrometry working in selected reaction monitoring mode has been established to analyze toxins in the algae and water samples. Twelve types of toxins (anatoxin, cylindrospermopsin, dinophysistoxin-1, nodularin, okadaic acid, microcystins) were efficiently separated under optimized liquid chromatography coupled with mass spectrometry conditions in the selected reaction monitoring mode. Correlation coefficients of the calibration curves, all felt in the range of 0.9958-0.9998, indicated good linearity. The detection limits of toxins in this method were all lower than 0.20 ng/mL and the quantification limits were in the range from 0.04 to 0.60 ng/mL. Except for anatoxin, cylindrospermopsin, and nodularin, the other toxins' recoveries varied from 55.45 to 140.85%. And the relative standard deviations of interday and intraday precision were at 8.61% (n = 5). The high-performance liquid chromatography (HPLC)/electrospray ionization (ESI)-mass spectrometery (MS) method was also successfully applied to analyze the algae and water samples. Owing to its exclusive selectivity and excellent sensitivity, the developed method is a tool for comprehensive analyses of the 12 types of toxins at nanogram levels.     

A strategy to study genotoxicity: application to aquatic toxins, limits and solutions

Humans can be exposed to aquatic toxins mainly through contamination of food and water (drinking and recreational). Among these toxins, contamination by both phycotoxins occurring in shellfish and cyanotoxins mostly involved in freshwater bodies are of concern for public health. Whereas regulations exist to evaluate the genotoxicity of most compounds to which humans are exposed, including drugs and chemicals, no regulations have been established for these compounds. In this paper, we show that the same strategy including both in vitro and in vivo tests can be followed to evaluate the genotoxicity of aquatic toxins (phycotoxins and cyanotoxins). However, this strategy encountered different limits which arise when completing an overview of the genotoxic potential of toxins. The most restrictive one is undoubtedly the low amount (even the lack sometimes) of purified toxins available. Solutions and recommendations for testing the genotoxicity of aquatic toxins are suggested to overcome the specific problems encountered with these compounds. It must be kept in mind that recent developments in drug toxicology should be considered and that experiments must be conducted in respect of the 3Rs principle of refinement, reduction and replacement for animal experimentation.     

Discovery of fatty acid ester metabolites of spirolide toxins in mussels from Norway using liquid chromatography/tandem mass spectrometry

Cultured mussels sampled in the spring of 2002 and 2003 from Skjer, a location in the Sognefjord, Norway, tested positive in the mouse bioassay for lipophilic toxins. In a previous report, it was established that a number of spirolides, cyclic imine toxins produced by the phytoplankton Alexandrium ostenfeldii, were present in the mussels and were responsible for the observed toxicity. The main toxin proved to be a new compound named 20-methyl spirolide G. In subsequent studies, a delayed onset of spirolide-like symptoms in the mouse bioassay exceeding the usual time limit of 20 min was observed in some samples, with symptoms and death appearing as long as 45-50 min after injection. It is well known that shellfish can extensively metabolize other toxins, such as okadaic acid and the dinophysistoxins, to fatty acid acyl esters and it is also known that a delayed onset of toxic symptoms with such metabolites can occur. Analyses performed with liquid chromatography/tandem mass spectrometry (LC/MS/MS) have revealed a complex mixture of esters of 20-methyl spirolide G in the contaminated mussels. Precursor ion scanning has delineated the range of fatty acid esters involved, while product ion scanning has provided information on structure. Identity was also supported through reaction of 20-methyl spirolide G with palmitic anhydride, which produced a derivative with a retention time and spectrum identical with one putative metabolite, 17-O-palmitoyl-20-methyl spirolide G.     

Analysis of cyanobacterial toxins by hydrophilic interaction liquid chromatography-mass spectrometry

The combination of hydrophilic interaction liquid chromatography with electrospray mass spectrometry (HILIC-MS) has been investigated as a tool for the analysis of assorted toxins produced by cyanobacteria. Toxins examined included saxitoxin and its various analogues (1-18), anatoxin-a (ATX-a, 19), cylindrospermopsin (CYN, 20), deoxycylindrospermopsin (doCYN, 21), and microcystins-LR (22) and -RR (23). The saxitoxins could be unequivocally detected in one isocratic analysis using a TSK gel Amide-80 column eluted with 65% B, where eluent A is water and B is a 95% acetonitrile/water solution, both containing 2.0 mM ammonium formate and 3.6 mM formic acid. The analysis of ATX-a, CYN and doCYN required 75% B isocratic. Simultaneous determination of 1-21 was also possible by using gradient elution. HILIC proved to be suitable for the analysis of microcystins, but peak shape was not symmetric and it was concluded that these compounds are best analysed using existing reversed-phase methods. The HILIC-MS method was applied to the analysis of field and cultured samples of Anabaena circinalis and Cylindrospermopsis raciborskii. In general, the method proved quite robust with similar results obtained in two different laboratories using different instrumentation.     

Biofilm formation and extracellular microvesicles—The way of foodborne pathogens toward resistance

Almost all known foodborne pathogens are able to form biofilms as one of the strategies for survival under harsh living conditions, to ward off the inhibition and the disinfection during food production, transport and storage, as well as during cleaning and sanitation of corresponding facilities. Biofilms are communities where microbial cells live under constant intracellular interaction and communication. Members of the biofilm community are embedded into extracellular matrix that contains polysaccharides, DNA, lipids, proteins, and small molecules that protect microorganisms and enable their intercellular communication under stress conditions. Membrane vesicles (MVs) are produced by both Gram positive and Gram negative bacteria. These lipid membrane-enveloped nanoparticles play an important role in biofilm genesis and in communication between different biofilm members. Furthermore, MVs are involved in other important steps of bacterial life like cell wall modeling, cellular division, and intercellular communication. They also carry toxins and virulence factors, as well as nucleic acids and different metabolites, and play a key role in host infections. After entering host cells, MVs can start many pathologic processes and cause serious harm and cell death. Prevention and inhibition of both biofilm formation and shedding of MVs by foodborne pathogens has a very important role in food production, storage, and food safety in general. Better knowledge of biofilm formation and maintaining, as well as the role of microbial vesicles in this process and in the process of host cells’ infection is essential for food safety and prevention of both food spoilage and host infection.     

Determination of Toxins Using Enzyme-Amplified Receptor Assay

Abstract

A new receptor based assay is described for the determination of toxins which have high affinities for the acetylcholine receptor. The method is based upon the hindrance of the normal binding of a synthetic enzyme-drug conjugate with a high affinity for the acetylcholine receptor protein by the presence of toxins acting as antagonists. The activity of the enzyme marker system, glucose-6-phosphate dehydrogenase covalently conjugated to desipramine, is monitored by colorimetric detection of the rate for NADH formation at 340 nm. The procedure proposed is designed to provide a simple toxin screen which can be done in a minimally equipped laboratory while achieving the required sensitivity. The technique is illustrated for snake venoms from Bungarus multicintus, Naja naja, and the alkaloid tubocurarine. Aspecific binding responses are shown to have minimal effect on the assay.     

HPLC and HPCE analysis of microcystins RR, LR and YR present in cyanobacteria and water by using immunoaffinity extraction

Microcystins, which have their origin in species of cyanobacteria present in freshwaters, have recently been found to be important contaminants of the aquatic environment at trace levels. HPLC and HPCE with UV detection have been applied in the determination of such toxic compounds. Immunoaffinity chromatography for the selective extraction and clean-up of microcystins has been successfully applied to different matrices. Simple protocols for unambiguous determination of these toxins are presented and the immunoaffinity clean-up is compared with conventionally used solid phase extraction procedures. The development and optimisation of an on-line preconcentration procedure based on field amplified sample stacking for the analysis of microcystins by HPCE in the micellar electrokinetic chromatography mode is also described, using borate buffer with the anionic surfactant SDS, as separation electrolyte. Results indicate that sub-nanogram/gram content of microcystins can be detected in water samples, while sub-microgram/gram concentrations can be determined in algae samples.     

Electrochemical detection of microcystins, cyanobacterial peptide hepatotoxins, following high-performance liquid chromatography

A novel amperometric HPLC detection method for the cyanobacterial (blue–green algal) peptide toxins microcystin-LR, -YR and -RR was developed. Purified microcystins and cyanobacterial extracts were chromatographed using an internal surface reversed-phase column with acetate- and phosphate-based mobile phase systems. Electrochemical oxidation reactions at 1.20 V vs. Ag/AgCl (glassy carbon working electrode) were shown to originate in arginine and tyrosine residues of microcystins.     

Application of molecularly imprinted polymers for electrochemical detection of some important biomedical markers and pathogens

The determination of biomedical markers and pathogens using electrochemical sensors is a well-established technique in which the transducer and the recognition element are used to detect the target molecule. There is a growing interest in molecularly imprinted polymer (MIPs) applications as promising recognition elements. The use of MIPs as recognition elements in electrochemical sensors offers the advantages of being fast, low cost, and, at the same time, provides accurate and selective results compared with other commonly applied routine methods for biomedical markers and pathogen detection. Compared with other nanomaterials and aptamer-based biosensors, MIP-based sensors offered excellent selectivity for low-priced reagents to be used. The aim of the current review is to discuss the most recent applications of MIP-based electrochemical sensors (2019–2021) as promising detection devices for some important biomarkers, enzymes, and pathogens, such as viruses, bacteria, and toxins.     

水产品中有害物质分析样品前处理技术研究进展

水产品含有丰富的蛋白、维生素和多种微量元素,是人们摄取动物性蛋白质的重要来源之一,我国是世界上最大的水产品消费国,其质量安全问题一直备受关注。但水产样品基质复杂,有害物质的含量低,须对其进行分离富集后才能进行检测,传统的液-液萃取、固相萃取和快速固相分散萃取等样品前处理技术在水产品分析中得到广泛应用,同时针对一些挥发性和超痕量有害物质检测时,固相微萃取同样体现出巨大优势。这些样品前处理技术可以有效去除基体对分析对象的干扰,提高检测方法的灵敏度和准确度。根据目标分析物性质的不同,选择合适的样品前处理技术,是水产品中有害物质分析的关键步骤。该文以水产品中有害物的来源不同,将其分为3类:(1)水产品中环境污染物的分析;(2)养殖运输和加工过程中有害物的分析;(3)水产品中生物毒素的分析。以这3类有害物质的分析为主线,综述了近10年水产品中有害物质分析的样品前处理技术,包括液-液萃取、固相萃取、固相微萃取、快速固相分散萃取和磁性固相萃取等。此外,还对各种技术的优缺点进行了探讨,并对其未来发展方向进行了展望。     

水产品中微囊藻毒素检测方法的研究进展

微囊藻毒素是蓝藻暴发中出现频率最高、产生量最大和造成危害最严重的藻毒素,具有多器官毒性、遗传毒性和致癌性。水产品中微囊藻毒素的残留会对人体产生危害,并对我国公众健康构成巨大威胁。因此,水产品中微囊藻毒素的检测和控制变得非常重要,迫切需要建立一种简便、快速、灵敏度较高的检测方法,以对水产品中的微囊藻毒素进行监控。为加强水产品中微囊藻毒素的痕量分析技术研究,对水产品中残留的微囊藻毒素开展监测,综述了国内外有关水产品中微囊藻毒素污染检测的提取、净化及分析技术进展。     

Computer modeling of binding of diverse weak toxins to nicotinic acetylcholine receptors

Weak toxins are the "three-fingered" snake venoms toxins grouped together by having an additional disulfide in the N-terminal loop I. In general, weak toxins have low toxicity, and biological targets have been identified for some of them only, recently by detecting the effects on the nicotinic acetylcholine receptors (nAChR). Here the methods of docking and molecular dynamics simulations are used for comparative modeling of the complexes between four weak toxins of known spatial structure (WTX, candoxin, bucandin, gamma-bungarotoxin) and nAChRs. WTX and candoxin are those toxins whose blocking of the neuronal alpha7- and muscle-type nAChR has been earlier shown in binding assays and electrophysiological experiments, while for the other two toxins no such activity has been reported. Only candoxin and WTX are found here to give stable solutions for the toxin-nAChR complexes. These toxins appear to approach the binding site similarly to short alpha-neurotoxins, but their final position resembles that of alpha-cobratoxin, a long alpha-neurotoxin, in the complex with the acetylcholine-binding protein. The final spatial structures of candoxin and WTX complexes with the alpha7 neuronal or muscle-type nAChR are very similar and do not provide immediate answer why candoxin has a much higher affinity than WTX, but both of them share a virtually irreversible mode of binding to one or both these nAChR subtypes. Possible explanation comes from docking and MD simulations which predict fast kinetics of candoxin association with nAChR, no gross changes in the toxin conformation (with smaller toxin flexibility on alpha7 nAChR), while slow WTX binding to nAChR is associated with slow irreversible rearrangement both of the tip of the toxin loop II and of the binding pocket residues locking finally the toxin molecule. Computer modeling showed that the additional disulfide in the loop I is not directly involved in receptor binding of WTX and candoxin, but it stabilizes the structure of loop I which plays an important role in toxin delivery to the binding site. In summary, computer modeling visualized possible modes of binding for those weak toxins which interact with the nAChR, provided no solutions for those weak toxins whose targets are not the nAChRs, and demonstrated that the additional disulfide in loop I cannot be a sound criteria for joining all weak toxins into one group; the conclusion about the diversity of weak toxins made from computer modeling is in accord with the earlier phylogenetic analysis.     

Structure and stereochemistry of a new cytotoxic polychlorinated sulfolipid from Adriatic shellfish

A detailed analysis of the causative toxins contained in the hepatopancreas of toxic mussels from the northern Adriatic sea has been carried out. Along with some DSP (diarrhetic shellfish poisoning) type toxins, such as okadaic acid, yessotoxin, and their derivatives, which are involved in a number of human intoxications throughout the world, we have now isolated a new cytotoxin, a polychlorinated sulfolipid 1, whose gross structure has been elucidated by spectral analysis, including various 2D NMR techniques. The relative stereochemistry of 1 was elucidated by successful application of the J-based configuration analysis developed for acyclic compounds using carbon-proton spin-coupling constants ((2,3)J(C,H)) and proton-proton spin-coupling constants ((3)J(H,H)); its absolute stereochemistry was established by the Mosher method. Compound 1 possesses in vitro cytotoxicity against WEHI 164 and RAW 264.7 cells.     

Anthrax fusion protein therapy of cancer

Most patients with cancer are treated with chemotherapy but die from progressive disease or toxicities of therapy. Current chemotherapy regimens primarily use cytotoxic drugs which damage cell DNA or impair cell proliferation in both malignant and normal tissues. After several treatment courses, the patients' tumor cells often overexpress multi-drug resistance genes which prevent further tumor cytoreduction. Novel agents which can kill such resistant tumor cells are needed. One such class of agents are targeted peptide toxins. Targeted peptide toxins consist of peptide toxins covalently linked to tumor selective peptide ligands. These molecules bind tumor cell surface receptors, internalize, and facilitate transfer of the toxin catalytic domains to the cytosol. Once in the cytosol, the enzyme activity leads to cell death. A number of plant, bacterial and fungal toxins have been used, and clinical trials with several of these have produced complete remissions in chemoresistant neoplasms. Nevertheless, there is a continuing need for novel targeted toxins. Many patients have pre-existing antibodies against the currently clinically used toxins and many toxins are inactive when used for myeloid malignancies where internalized proteins are rapidly routed and degraded in lysosomes. Anthrax toxins are the cytotoxic components of Bacillus anthracis. While the bacteria has been the source of serious illness, deaths and global anxieties related to past or future bioterrorism, the isolated toxins do not pose public health hazards. In fact, toxin treated patients will likely develop protective antibodies. Anthrax toxin is an excellent choice for tumor cell surface targeting. Other than U.S. military personnel immunized during the Gulf War, most people lack pre-existing antibodies. This may change in the future due to threats of additional terrorist acts, but for the present few patients will have antibodies to anthrax proteins. The separate subunits for binding, translocation and cell killing facilitate genetic engineering to yield tumor-specific cell killing. The toxins are more potent than most of the other peptide toxins and may yield highly efficacious targeted molecules. This essay will review anthrax toxin structure-function, preliminary experiments with re-targeted anthrax toxin and potential designs for new ligand-anthrax therapeutics.