Quantification and profiling of lipophilic marine toxins in microalgae by UHPLC coupled to high-resolution orbitrap mass spectrometry

Current Research Status of Azaspiracids

The presence and impact of toxins have been detected in various regions worldwide ever since the discovery of azaspiracids (AZAs) in 1995. These toxins have had detrimental effects on marine resource utilization, marine environmental protection, and fishery production. Over the course of more than two decades of research and development, scientists from all over the world have conducted comprehensive studies on the in vivo metabolism, in vitro synthesis methods, pathogenic mechanisms, and toxicology of these toxins. This paper aims to provide a systematic introduction to the discovery, distribution, pathogenic mechanism, in vivo biosynthesis, and in vitro artificial synthesis of AZA toxins. Additionally, it will summarize various detection methods employed over the past 20 years, along with their advantages and disadvantages. This effort will contribute to the future development of rapid detection technologies and the invention of detection devices for AZAs in marine environmental samples.

Effects of the toxic dinoflagellate Protoceratium reticulatum and its yessotoxins on the survival and feed ingestion of Argopecten purpuratus veliger larvae

The effects of yessotoxins (YTXs) produced by the dinoflagellate Protoceratium reticulatum in the early stages of bivalves have not been studied in detail. The present study evaluates the effects of P. reticulatum and YTXs on the survival and feed ingestion of veliger larvae of Argopecten purpuratus. Larvae were 96 h-exposed to 500, 1000 and 2000 P. reticulatum cells mL-1, and their equivalent YTX extract was prepared in methanol. Results show a survival mean of 82 % at the highest density of dinoflagellate, and 38 % for larvae with the highest amount of YTX extract. Feed ingestion is reduced in the dinoflagellate exposure treatments as a function of cell density. Therefore, the effect of YTXs on A. purpuratus represents a new and important area of study for investigations into the deleterious effects of these toxins in the early stages of the life cycle of this and, potentially, other bivalves.

Phycotoxin-Enriched Sea Spray Aerosols: Methods, Mechanisms, and Human Exposure

To date, few studies have examined the role of sea spray aerosols (SSAs) in human exposure to harmful and beneficial marine compounds. Two groups of phycotoxins (brevetoxins and ovatoxins) have been reported to induce respiratory syndromes during harmful algal blooms. The aerosolization and coastal air concentrations of other common marine phycotoxins have, however, never been examined. This study provides the first (experimental) evidence and characterization of the aerosolization of okadaic acid (OA), homoyessotoxin, and dinophysistoxin-1 using seawater spiked with toxic algae combined with the realistic SSA production in a marine aerosol reference tank (MART). The potential for aerosolization of these phycotoxins was highlighted by their 78- to 1769-fold enrichment in SSAs relative to the subsurface water. To obtain and support these results, we first developed an analytical method for the determination of phycotoxin concentrations in SSAs, which showed good linearity (R² > 0.99), recovery (85.3-101.8%), and precision (RSDs ≤ 17.2%). We also investigated natural phycotoxin air concentrations by means of in situ SSA sampling with concurrent aerosolization experiments using natural seawater in the MART. This approach allowed us to indirectly quantify the (harmless) magnitude of OA concentrations (0.6-51 pg m^-3) in Belgium's coastal air. Overall, this study provides new insights into the enriched aerosolization of marine compounds and proposes a framework to assess their airborne exposure and effects on human health.

Monitoring Lipophilic Toxins in Seawater Using Dispersive Liquid-Liquid Microextraction and Liquid Chromatography with Triple Quadrupole Mass Spectrometry

The use of dispersive liquid–liquid microextraction (DLLME) is proposed for the preconcentration of thirteen lipophilic marine toxins in seawater samples. For this purpose, 0.5 mL of methanol and 440 µL of chloroform were injected into 12 mL of sample. The enriched organic phase, once evaporated and reconstituted in methanol, was analyzed by reversed-phase liquid chromatography with triple-quadrupole tandem mass spectrometry. A central composite design multivariate method was used to optimize the interrelated parameters affecting DLLME efficiency. The absence of any matrix effect in the samples allowed them to be quantified against aqueous standards. The optimized procedure was validated by recovery studies, which provided values in the 82–123% range. The detection limits varied between 0.2 and 5.7 ng L⁻¹, depending on the analyte, and the intraday precision values were in the 0.1–7.5% range in terms of relative standard deviation. Ten water samples taken from different points of the Mar Menor lagoon were analyzed and were found to be free of the studied toxins.

Nontarget Screening and Toxicity Evaluation of Diol Esters of Okadaic Acid and Dinophysistoxins Reveal Intraspecies Difference of Prorocentrum lima

High-resolution mass spectrometry (HRMS) analysis with the assistance of molecular networking was used to investigate intracellular toxin profiles of five Prorocentrum lima (P. lima) strains sampled from the north Yellow Sea and South China Sea. Mice were used as a model species for testing the acute toxicity of intracellular okadaic acid (OA) and dinophysistoxins (DTXs) in free and esterified states. Results showed that OA and DTX1 esterified derivatives were detected in all P. lima samples, accounting for 55%-96% of total toxins in five strains. A total of 24 esters and 1 stereoisomer of DTX1 (35S DTX1) were identified based on molecular networking and MS data analysis, 15 esters of which have been reported first. All P. lima strains displayed specific toxin profiles, and preliminary analysis suggested that toxin profiles of the five P. lima strains might be region-related. Moreover, acute toxicity in mice suggested higher toxicity of esters compared with free toxins, which highlights the importance and urgency of attention to esterified toxins in P. lima.

Establishment of double probes rolling circle amplification combined with lateral flow dipstick for rapid detection of Chattonella marina

Chattonella marina is one of the main algae that could cause harmful algal blooms. It has killed a large number of cultured fish in coastal areas of many countries, causing serious economic losses. Therefore, it is necessary to establish a method that can specifically detect C. marina at pre-bloom abundance, so that timely measures can be taken before this alga causes harm. In this study, a long probe, a short probe and a pair of amplification primers were first designed by using the internal transcribed spacer (ITS) sequence of C. marina as the target gene and using the CD74 gene of a distant species Gallus gallus as the base sequence. The double probes rolling circle amplification (dpRCA) system was then established with the designed probes and amplification primers. A novel detection protocol referred to as dpRCA-LFD by combining the dpRCA products and lateral flow dipstick (LFD) was finally established, which can make the detection results visible to the naked eyes. The reaction conditions of dpRCA were optimized and the optimal conditions were as follows: cycle number of ligation reaction, 12; ligation temperature, 58 °C; amplification temperature, 60 °C; and amplification time, 60 min. The specificity test that was performed using the optimized dpRCA conditions indicated that dpRCA-LFD was exclusively specific for the target alga. The tests with the genomic DNA of C. marina and the recombinant plasmid containing the ITS sequence of C. marina showed that the sensitivity of dpRCA-LFD was 100 times higher than that of conventional PCR. The detection limit (DL) for the genomic DNA was 8.3 × 10^-3 ng µL^-1 (8.3 × 10^-3 ng per reaction), and the DL for the recombinant plasmid DNA was 7.8 copies µL^-1 (7.8 copies per reaction). The practicality of the developed dpRCA-LFD was further validated by test with the spiked samples containing C. marina and field samples. The simulative test showed that the dpRCA-LFD has a DL of 10 cells mL^-1. The dpRCA-LFD could successfully recognize the target cells from the field samples. In summary, the dpRCA-LFD established in this study has advantages of good specificity, high sensitivity, and easily visible detection results, and therefore is promising for the analysis of C. marina in field samples.

A Screening Tool for the Direct Analysis of Marine and Freshwater Phycotoxins in Organic SPATT Extracts from the Chesapeake Bay

Many detection methods for phycotoxins, bioactive compounds produced by harmful algae, focus on one compound or a class of related compounds. Multiple harmful algal species often co-occur in the environment, however, emphasizing the need to analyze for the presence of multiple groups of marine and freshwater phycotoxins in environmental samples, e.g., extracts from solid phase adsorption toxin tracking (SPATT). Two methods were developed to screen for 13 phycotoxins (microcystin-RR, -LR, -YR, azaspiracid-1, -2, karlotoxin 3, goniodomin A, brevetoxin-2, yessotoxin, pectenotoxin-2, dinophysistoxin-1, -2, and okadaic acid) in organic SPATT extracts using ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) equipped with a trapping dimension (trap) and at-column dilution (ACD). The performance of each compound under 36 combinations of chromatographic conditions was characterized, and two final methods, acidic and basic, were selected based on peak shapes, signal intensities, resolution, and the separation in time of positive and negative MS ionization modes. Injection volumes of up to 1 mL were possible through trap/ACD technology, resulting in limits of detection between 0.001 and 0.05 µg/L across the analytes. Benefits highlighted in this study, beyond the improved detection limits and co-detection of multiple toxin groups, include the ability to inject samples of 100% organic solvent, ensuring analyte stability and streamlining workflow through the elimination of laborious sample preparation steps.

Aerosolizable Marine Phycotoxins and Human Health Effects: In Vitro Support for the Biogenics Hypothesis

Respiratory exposure to marine phycotoxins is of increasing concern. Inhalation of sea spray aerosols (SSAs), during harmful Karenia brevis and Ostreopsis ovata blooms induces respiratory distress among others. The biogenics hypothesis, however, suggests that regular airborne exposure to natural products is health promoting via a downregulation of the mechanistic target of rapamycin (mTOR) pathway. Until now, little scientific evidence supported this hypothesis. The current explorative in vitro study investigated both health-affecting and potential health-promoting mechanisms of airborne phycotoxin exposure, by analyzing cell viability effects via cytotoxicity assays and effects on the mTOR pathway via western blotting. To that end, A549 and BEAS-2B lung cells were exposed to increasing concentrations (ng·L⁻¹–mg·L⁻¹) of (1) pure phycotoxins and (2) an extract of experimental aerosolized homoyessotoxin (hYTX). The lowest cell viability effect concentrations were found for the examined yessotoxins (YTXs). Contradictory to the other phycotoxins, these YTXs only induced a partial cell viability decrease at the highest test concentrations. Growth inhibition and apoptosis, both linked to mTOR pathway activity, may explain these effects, as both YTXs were shown to downregulate this pathway. This proof-of-principle study supports the biogenics hypothesis, as specific aerosolizable marine products (e.g., YTXs) can downregulate the mTOR pathway.

Structure Elucidation and Relative Toxicity of (24R)-24-Hydroxyyessotoxin from a Namibian Isolate of Gonyaulax spinifera

Liquid chromatography-high-resolution mass spectrometry (LC-HRMS) analysis of a Namibian strain of Gonyaulax spinifera showed the presence of a number of yessotoxins (YTXs). Principal among these were YTX (1), homoYTX (2), and a tentative hydroxylated analogue that did not correspond to any previously confirmed YTX structures. Culturing the G. spinifera strain afforded sufficient biomass for purification of the new analogue through a series of solvent partitioning and chromatographic steps, yielding ∼0.9 mg as a solid. NMR spectroscopy, ion-trap mass spectrometry, and HRMS identified the new analogue as 24-hydroxyYTX (7). Purified 24-hydroxyYTX was quantitated by NMR, and its relative toxicity evaluated using two embryonic zebrafish toxicity assays. 24-HydroxyYTX demonstrated reduced toxicity compared to YTX.

Profiling of Extracellular Toxins Associated with Diarrhetic Shellfish Poison in Prorocentrum lima Culture Medium by High-Performance Liquid Chromatography Coupled with Mass Spectrometry

Extracellular toxins released by marine toxigenic algae into the marine environment have attracted increasing attention in recent years. In this study, profiling, characterization and quantification of extracellular toxin compounds associated with diarrhetic shellfish poison (DSP) in the culture medium of toxin-producing dinoflagellates were performed using high-performance liquid chromatography–high-resolution mass spectrometry/tandem mass spectrometry for the first time. Results showed that solid-phase extraction can effectively enrich and clean the DSP compounds in the culture medium of Prorocentrum lima (P. lima), and the proposed method achieved satisfactory recoveries (94.80%–100.58%) and repeatability (relative standard deviation ≤9.27%). Commercial software associated with the accurate mass information of known DSP toxins and their derivatives was used to screen and identify DSP compounds. Nine extracellular DSP compounds were identified, of which seven toxins (including OA-D7b, OA-D9b, OA-D10a/b, and so on) were found in the culture medium of P. lima for the first time. The results of quantitative analysis showed that the contents of extracellular DSP compounds in P. lima culture medium were relatively high, and the types and contents of intracellular and extracellular toxins apparently varied in the different growth stages of P. lima. The concentrations of extracellular okadaic acid and dinophysistoxin-1 were within 19.9–34.0 and 15.2–27.9 μg/L, respectively. The total concentration of the DSP compounds was within the range of 57.70–79.63 μg/L. The results showed that the proposed method is an effective tool for profiling the extracellular DSP compounds in the culture medium of marine toxigenic algae.

Relative molar response of lipophilic marine algal toxins in liquid chromatography/electrospray ionization mass spectrometry

RATIONALE

Accurate quantitative analysis of lipophilic toxins by liquid chromatography/mass spectrometry (LC/MS) requires calibration solution reference materials (RMs) for individual toxin analogs. Untargeted analysis is aimed at identifying a vast number of compounds and thus validation of fully quantitative untargeted methods is not feasible. However, a semi-quantitative approach allowing for profiling is still required and will be strengthened by knowledge of the relative molar response (RMR) of analogs in LC/MS with electrospray ionization (ESI).

METHODS

RMR factors were evaluated for toxins from the okadaic acid (OA/DTXs), yessotoxin (YTX), pectenotoxin (PTX), azaspiracid (AZA) and cyclic imine (CI) toxin groups, in both solvent standards and environmental sample extracts. Since compound ionization and fragmentation influences the MS response of toxins, RMRs were assessed under different chromatographic conditions (gradient, isocratic) and MS acquisition modes (SIM, SRM, All-ion, target MS/MS) on low- and high-resolution mass spectrometers.

RESULTS

In general, RMRs were not significantly impacted by chromatographic conditions (isocratic vs gradient), with the exception of DTX1. MS acquisition modes had a more significant impact, with PnTX-G and SPX differing notably. For a given toxin group, response factors were generally in the range of 0.5 to 2. The cyclic imines were an exception.

CONCLUSIONS

Differences in RMRs between toxins of a same chemical base structure were not significant enough to indicate major issues for non-targeted semi-quantitative analysis, where there is limited or no availability of standards for many compounds, and where high degrees of accuracy are not required. Differences in RMRs should be considered when developing methods that use a standard of a single analogue to quantitate other toxins from the same group.

Separation and purification of two minor typical diarrhetic shellfish poisoning toxins from harmful marine microalgae via combined liquid chromatography with mass spectrometric detection

A novel method was developed for the purification of two typical diarrhetic shellfish poisoning toxins from toxin-producing marine microalgae using macroporous resin, high-speed countercurrent chromatography-mass spectrometry, and semipreparative high-performance liquid chromatography-mass spectrometry. Analytical high-performance liquid chromatography-mass spectrometry was used for identification and purity analysis of okadaic acid and dinophysistoxin-1 because they exhibit no visible or ultraviolet absorption. First, four kinds of macroporous resins were investigated, and HP-20 macroporous resin was selected for the preenrichment and cleanup of the two target toxins. Second, the resin-purified sample was further purified using high-speed countercurrent chromatography coupled with a mass spectrometer. The purities of the obtained okadaic acid and dinophysistoxin-1 were 89.0 and 83.0%, respectively, as determined through analytical high-performance liquid chromatography-mass spectrometry. Finally, further purification was carried out using semipreparative high-performance liquid chromatography with mass spectrometry, and the purities of the final okadaic acid and dinophysistoxin-1 products were both over 98.0% based on the analytical high-performance liquid chromatography-mass spectrometry chromatograms and fraction spectra. This work demonstrates that the proposed purification process is a powerful method for the preparation of high-purity okadaic acid and dinophysistoxin-1 from toxin-producing marine microalgae. Moreover, it is particularly important for the purification and preparation of minor toxins that exhibit no visible or ultraviolet absorption from harmful marine algae.

High resolution mass spectrometry-based screening reveals lipophilic toxins in multiple trophic levels from the North Sea

Lipophilic marine biotoxins, which are mainly produced by small dinoflagellates, are increasingly detected in coastal waters across the globe. As these producers are consumed by zooplankton and shellfish, the toxins are introduced, bioaccumulated and possibly biomagnified throughout marine food chains. Recent research has demonstrated that ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS) is an excellent tool to detect marine toxins in algae and seafood. In this study, UHPLC-HRMS was used to screen lipophilic marine biotoxins in organisms from different trophic levels of the Belgian coastal zone ecosystem. A total of 20 tentatively identified lipophilic compounds was detected. Hereby, the trophic transfer of lipophilic marine biotoxins to the upper trophic level was considered to be rather limited. Furthermore, 36% of the compounds was clearly transferred between different organisms. A significant biotransformation of compounds from the okadaic acid and spirolide toxin groups was observed (64%), mainly in filter feeders. Through a multi-targeted approach, this study showed that marine organisms in the Belgian coastal zone are exposed to a multi-toxin mixture. Further research on both single compound and interactive toxic effects of the frequently detected lipophilic marine toxin ester metabolites throughout the food chain is therefore needed. As a future perspective, confirmatory identification of potential toxins by studying their fragmentation spectra (using new tools such as hybrid quadrupole Q-Exactive™ Orbitrap-MS) is designated.

Screening of lipophilic marine toxins in marine aquaculture environment using liquid chromatography-mass spectrometry

This study aimed to develop an exact mass suspect screening approach to perform finding of multiple lipophilic marine toxins (LMTs) in seawater, suspended particulate matter (SPM), and marine sediment from marine aquaculture area using liquid chromatography-time of flight mass spectrometry (LC-TOF/MS). The method was validated and proven to be reliable for the screening of various LMTs. Then, the method was applied to screen LMTs in marine environmental samples collected from mariculture area of Jiaozhou Bay, China. Okadaic acid (OA), pectenotoxin 2 (PTX2), etc were detected and tentatively identified. Positive detection results were confirmed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and contents of OA and PTX2 in seawater, SPM and marine sediment were also quantified. The mean concentration of OA ranged from 2.71 to 14.06 ng L^-1 in seawater and from 0.78 to 3.34 ng g^-1 dry weight in marine sediment. The mean concentration of PTX2 ranged from 0.86 to 7.90 ng L^-1 in seawater, from 1.56 to 10.67 ng in SPM obtained from 1 L seawater sample and from 0.95 to 2.23 ng g^-1 dry weight in marine sediment. The above results suggested that the proposed method was convenient and reliable for the screening of LMTs in different marine environmental samples. In addition, typical LMTs exist in different marine environmental media of the mariculture area of Jiaozhou Bay, China. Follow-up studies should focus on improving current understanding on the environmental behavior of these LMTs in the marine aquaculture environment.

Occurrence and Seasonal Variations of Lipophilic Marine Toxins in Commercial Clam Species along the Coast of Jiangsu, China

Recent studies have examined lipophilic marine toxins (LMTs) in shellfish and toxic algae worldwide, but the occurrence and seasonal variations of LMTs in commercial clams (including Mactra veneriformis, Ruditapes philippinarum, Meretrix meretrix, and Cyclina sinensis) at their major culturing area in Jiangsu, China, remain largely unexplored. In this study, a new solid phase extraction (SPE) in combination with an ultra-fast liquid chromatography and triple-quadrupole linear ion trap mass spectrometry (UFLC-TQ-MS) method was developed to determine the presence of 10 typical LMTs (okadaic acid (OA), yessotoxins (YTXs), azaspiracids (AZA1-3), pectenotoxins (PTX2), gymnodimine (GYM), dinophysistoxins (DTX1&2), and spirolides (SPX1)) in the aforementioned four clam matrices. After confirmation of its sensitivity and precision, this method was used to evaluate the amounts of LMTs in clam samples harvested in five aquaculture zones of the Jiangsu coastal area. Monthly variations of GYM, PTX2, OA, and DTX1&2 in 400 clam samples from the sample areas were determined from January 2014 through August 2015. Peak values were observed during May and August. This is the first systematic report of LMTs detected in clam samples harvested in Jiangsu. Follow-up research and the implementation of protective measures are needed to ensure the safety of clams harvested in this area.