Development and Validation of a Liquid Chromatography-Tandem Mass Spectrometry Method for the Quantitation of Microcystins in Blue-Green Algal Dietary Supplements.

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous detection and quantitation of seven microcystin congeners (1-7) and nodularin-R (8) in blue-green algal dietary supplements. Single-laboratory method validation data were collected in four supplement matrices (capsule, liquid, powder, and tablet) fortified at toxin concentrations from 0.25-2.00 µg/g (ppm). Average recoveries and relative standard deviations (RSD) using matrix-corrected solvent calibration curves were 101% (6% RSD) for all congeners and supplements investigated. Limits of detection (0.006-0.028 µg/g) and quantitation (0.018-0.084 µg/g) were sufficient to confirm the presence of microcystin contamination at the Oregon-mandated guidance concentration of 1.0 µg of microcystin-LReq/g. Quantitated concentrations of microcystin contamination in market-available Aphanizomenon flos-aquae blue-green algal supplements ranged from 0.18-1.87 µg of microcystin-LReq/g for detected congeners microcystin-LR, microcystin-LA, and microcystin-LY (3-5). Microcystin-RR, -YR, -LW, and -LF and nodularin-R (1, 2, and 6-8) were not detected in the supplements examined.

First report of a direct surface plasmon resonance immunosensor for a small molecule seafood toxin.

Tetrodotoxin (TTX), a small molecular weight neurotoxin, is responsible for poisoning events that traditionally occur from consumption of contaminated puffer fish. Recent studies have shown a growing number of foods contaminated with TTX and a larger number of waters and associated countries where the toxin may occur. The apparent expanding prevalence of TTX supports a growing need for screening assays that can be used to detect potentially harmful food. In the past few years, surface plasmon resonance (SPR) biosensors have been developed for rapid, robust detection of TTX; however, these assays focus on detection of unbound antibody from an inhibition reaction with the toxin. This manuscript introduces the first direct immunoassay for a seafood toxin, specifically TTX. Major advantages of this assay compared to indirect assays include increased speed of analysis, decreased use of biological reagents, and improved confidence in the detection of the toxin, along with the ability to characterize the antibody/toxin interaction. The analytical method introduced in this paper could be applied to other seafood toxins, as well as to a wide range of low molecular weight targets.

Surface plasmon resonance biosensor for detection of feline calicivirus, a surrogate for norovirus.

The human noroviruses are the most common non-bacterial cause of gastroenteritis and are responsible for as much as 50% of all gastroenteritis outbreaks worldwide. Norovirus (NoV), a single stranded RNA virus, is highly contagious with an infectious dose of less than 100 viral particles. While techniques exist for the identification of NoV, the lack of a reliable cell culture system, NoV genetic variability, and time-consuming sample preparation steps required to isolate the virus (or its genome) prior to molecular based methods has hindered rapid virus detection. To better protect the public from virus-contaminated food and enable better detection in clinical and environmental samples, sensitive and selective methods with simple sample preparation are needed. Surface plasmon resonance (SPR) biosensors represent an emerging detection platform, and this approach has been applied to the rapid detection of foodborne small molecule toxins, protein toxins, and bacteria. This analytical technique, however, has yet to be fully investigated for rapid virus detection, especially for intact viral particles extracted from food matrices. For this study, the culturable, non-human pathogen feline calicivirus (FCV), which has similar morphology and is genetically related to NoV, was chosen as a surrogate virus for designing and evaluating an SPR assay. An antibody-based assay was performed by first immobilizing anti-FCV to an SPR chip surface and then directly measuring virus binding and subsequent secondary antibody binding. The resulting biosensor directly detected intact FCV particles with limits of detection of approximately 10(4)TCID50FCV/mL from purified cell culture lysates. In addition, intact virus detection in FCV-spiked oyster matrix was possible when using a simple extraction procedure and employing a secondary antibody to FCV for quantitation. The results from these preliminary studies show promise for the development of a rapid assay for detecting intact viruses, such as NoV, using an SPR biosensor. While the current level of sensitivity achieved with this SPR biosensor may be more applicable to virus detection in clinical specimens, broader application and increased sensitivity of this method for foodborne viruses may be achieved when performed in conjunction with efficient virus extraction and concentration methods.

First report of the use of a saxitoxin-protein conjugate to develop a DNA aptamer to a small molecule toxin.

Saxitoxin (STX) is a low molecular weight neurotoxin mainly produced by certain marine dinoflagellates that, along with its family of similarly related paralytic shellfish toxins, may cause the potentially fatal intoxication known as paralytic shellfish poisoning. Illness and fatality rates are low due to the effective monitoring programs that determine when toxins exceed the established regulatory action level and effectuate shellfish harvesting closures accordingly. Such monitoring programs rely on the ability to rapidly screen large volumes of samples. Many of the screening assays currently available employ antibodies or live animals. This research focused on developing an analytical recognition element that would eliminate the challenges associated with the limited availability of antibodies and the use of animals. Here we report the discovery of a DNA aptamer that targets STX. Concentration-dependent and selective binding of the aptamer to STX was determined using a surface plasmon resonance sensor. Not only does this work represent the first reported aptamer to STX, but also the first aptamer to any marine biotoxin. A novel strategy of using a toxin-protein conjugate for DNA aptamer selection was successfully implemented to overcome the challenges associated with aptamer selection to small molecules. Taking advantage of such an approach could lead to increased diversity and accessibility of aptamers to low molecular weight toxins, which could then be incorporated as analytical recognition elements in diagnostic assays for foodborne toxin detection. The selected STX aptamer sequence is provided here, making it available to any investigator for use in assay development for the detection of STX.

Developing improved immunoassays for paralytic shellfish toxins: the need for multiple, superior antibodies.

Paralytic shellfish toxins (PSTs) are a risk to humans upon consumption of contaminated seafood. The PST family is comprised of more than twenty congeners, with each form having a different potency. In order to adequately protect consumers yet reduce unnecessary closures of non-contaminated harvesting areas, a rapid method that allows for analysis of sample toxicity is needed. While a number of PST immunoassays exist, the outstanding challenge is linking quantitative response to sample toxicity, as no single antibody reacts to the PST congeners in a manner that correlates with potency. A novel approach, then, is to combine multiple antibodies of varying reactivity to create a screening assay. This research details our investigation of three currently available antibodies for their reactivity profiles determined using a surface plasmon resonance biosensor assay. While our study shows challenges with detection of the R1-hydroxylated PSTs, results indicate that using multiple antibodies may provide more confidence in determining overall toxicity and the toxin profile. A multiplexed approach would not only improve biosensor assays but could also be applied to lateral flow immuno-chromatographic platforms, and such a theoretical device incorporating the three antibodies is presented. These improved assays could reduce the number of animal bioassays and confirmatory analyses (e.g., LC/MS), thereby improving food safety and economic use of shellfish resources.

Endangered North Atlantic right whales (Eubalaena glacialis) experience repeated, concurrent exposure to multiple environmental neurotoxins produced by marine algae.

The western North Atlantic population of right whales (Eubalaena glacialis) is one of the most critically endangered of any whale population in the world. Among the factors considered to have potentially adverse effects on the health and reproduction of E. glacialis are biotoxins produced by certain microalgae responsible for causing harmful algal blooms. The worldwide incidence of these events has continued to increase dramatically over the past several decades and is expected to remain problematic under predicted climate change scenarios. Previous investigations have demonstrated that N. Atlantic right whales are being exposed to at least two classes of algal-produced environmental neurotoxins-paralytic shellfish toxins (PSTs) and domoic acid (DA). Our primary aims during this six-year study (2001-2006) were to assess whether the whales' exposure to these algal biotoxins occurred annually over multiple years, and to what extent individual whales were exposed repeatedly and/or concurrently to one or both toxin classes. Approximately 140 right whale fecal samples obtained across multiple habitats in the western N. Atlantic were analyzed for PSTs and DA. About 40% of these samples were attributed to individual whales in the North Atlantic Right Whale Catalog, permitting analysis of biotoxin exposure according to sex, age class, and reproductive status/history. Our findings demonstrate clearly that right whales are being exposed to both of these algal biotoxins on virtually an annual basis in multiple habitats for periods of up to six months (April through September), with similar exposure rates for females and males (PSTs: ∼70-80%; DA: ∼25-30%). Notably, only one of 14 lactating females sampled did not contain either PSTs or DA, suggesting the potential for maternal toxin transfer and possible effects on neonatal animals. Moreover, 22% of the fecal samples tested for PSTs and DA showed concurrent exposure to both neurotoxins, leading to questions of interactive effects. Targeted studies employing both in vivo and in vitro model systems represent the next logical step in assessing how and to what extent these algal biotoxins might compromise the health and reproduction of this endangered population.

Comparison of biosensor platforms for surface plasmon resonance based detection of paralytic shellfish toxins.

Paralytic shellfish poisoning (PSP) toxins are produced by certain marine dinoflagellates and may accumulate in bivalve molluscs through filter feeding. The Mouse Bioassay (MBA) is the internationally recognised reference method of analysis, but it is prone to technical difficulties and regarded with increasing disapproval due to ethical reasons. As such, alternative methods are required. A rapid surface plasmon resonance (SPR) biosensor inhibition assay was developed to detect PSP toxins in shellfish by employing a saxitoxin polyclonal antibody (R895). Using an assay developed for and validated on the Biacore Q biosensor system, this project focused on transferring the assay to a high-throughput, Biacore T100 biosensor in another laboratory. This was achieved using a prototype PSP toxin kit and recommended assay parameters based on the Biacore Q method. A monoclonal antibody (GT13A) was also assessed. Even though these two instruments are based on SPR principles, they vary widely in their mode of operation including differences in the integrated µ-fluidic cartridges, autosampler system, and sensor chip compatibilities. Shellfish samples (n=60), extracted using a simple, rapid procedure, were analysed using each platform, and results were compared to AOAC high performance liquid chromatography (HPLC) and MBA methods. The overall agreement, based on statistical 2×2 comparison tables, between each method ranged from 85% to 94.4% using R895 and 77.8% to 100% using GT13A. The results demonstrated that the antibody based assays with high sensitivity and broad specificity to PSP toxins can be applied to different biosensor platforms.

Antibody characterization and immunoassays for palytoxin using an SPR biosensor.

Palytoxin (PLTX), a polyether marine toxin originally isolated from the zoanthid Palythoa toxica, is one of the most toxic non-protein substances known. Fatal poisonings have been linked to ingestion of PLTX-contaminated seafood, and effects in humans have been associated with dermal and inhalational exposure to PLTX containing organisms and waters. Additionally, PLTX co-occurrence with other well-characterized seafood toxins (e.g., ciguatoxins, saxitoxins, tetrodotoxin) has hindered direct associations of PLTX to seafood-borne illnesses. There are currently no validated methods for the quantitative detection of PLTX(s). As such, a well-characterized, robust, specific analytical technique is needed for the detection of PLTX(s) in source organisms, surrounding waters, and clinical samples. Surface plasmon resonance (SPR) biosensors are ideally suited for antibody characterization and quantitative immunoassay detection. Herein, we describe a newly developed SPR assay for PLTX. An anti-mouse substrate was used to characterize the kinetic values for a previously developed monoclonal anti-PLTX. The characterized antibody was then incorporated into a sensitive, rapid, and selective PLTX assay. Buffer type, flow rate, analyte-binding time, and regeneration conditions were optimized for the antibody-PLTX system. Cross-reactivity to potentially co-occurring seafood toxins was also evaluated. We show that this optimized assay is capable of measuring low- to sub-ng/mL PLTX levels in buffer and two seafood matrices (grouper and clam). Preliminary results indicate that this SPR biosensor assay allows for (1) rapid characterization of antibodies and (2) rapid, sensitive PLTX concentration determination in seafood matrices. Method development information contained herein may be broadly applied to future PLTX detection and/or antibody characterization efforts.

Evaluation of surface plasmon resonance biosensors for detection of tetrodotoxin in food matrices and comparison to analytical methods.

Tetrodotoxin (TTX) is a low molecular weight neurotoxin found in a number of animal species, including pufferfish. One emerging method for TTX detection employs surface plasmon resonance (SPR) immunosensors. SPR, an optical technique that allows for label-free, real-time, multiplexed analysis, can have detection limits that rival many of the conventional transduction methods. Preliminary SPR approaches for TTX were successful, yet suffered from low throughput and used noncommercial instrumentation. To advance this method for broader use, the immunoassay was transferred to a commercial instrument and optimized for improved detection. This manuscript outlines the assay development and results for complex matrices relevant to seafood safety (pufferfish) and food adulteration (milk, apple juice). In addition, results are compared to those obtained using receptor binding assay, ELISA, HPLC-FD, and LC/MS/MS detection techniques. Results highlight the advantages of SPR assays, including rapid screening capability with low reagent consumption and low- to subppb detection limits.

Pre- versus post-column oxidation liquid chromatography fluorescence detection of paralytic shellfish toxins.

Both pre- and post-column oxidation liquid chromatography methods with fluorescence detection are available for detecting paralytic shellfish toxins. Each method has been evaluated in multiple laboratories and validated as a potential alternative to the mouse bioassay. This communication compares the advantages and limitations of both methods. For a given laboratory, the selection of either method may be based primarily on practicality and less on any deficiencies in scientific merit.

Solid core column technology applied to HPLC-FD of paralytic shellfish toxins.

Pre-column oxidation liquid chromatography with fluorescence detection is a chemical method for analyzing paralytic shellfish toxins. In order to improve the sample throughput and efficiency of AOAC Method 2005.06, solid core particle column technology was evaluated. We demonstrate that supplanting the original fully porous particle column with a solid core particle column reduces sample analysis time from 15 to 5 min per sample and improves resolution.