Prevalence of the neurotoxin domoic acid in the aquatic environments of the Bohai and Northern Yellow seas in China

Abundance of non-toxic and low-level toxic Pseudo-nitzschia explains the low levels of neurotoxin domoic acid in Chinese coastal waters

Domoic acid (DA), a well-known marine neurotoxin, is produced by toxic Pseudo-nitzschia species. However, the knowledge of DA in Chinese coastal waters remains limited, and the primary biological sources in these waters are still unknown. In this study, 200 surface phytoplankton samples were collected during summer and spring, covering the entire Chinese coastline. Particulate DA (pDA) was detected in 41 samples, and among these, 34 were from summer, particularly nearshore. The peak content, 230 ng L-1, was in the southern Yellow Sea, followed by 116.6 ng L-1 in the Taiwan Strait, both in July. Multiple methods were employed to trace the biological sources of pDA. The results indicated that the primary producer was P. multistriata in the southern Yellow Sea, but P. cuspidata Clade III in the Taiwan Strait. Temperature was the key factor affecting the composition of Pseudo-nitzschia community, and both primary DA producers showed warm temperature preferences. The levels of pDA in this study was comparatively low, which may be explained by the prevalence of non-toxic Pseudo-nitzschia species and the low DA-production capacity of toxic species under the prevailing environmental conditions. This study represents the first exploration of pDA along the entire Chinese coastline, identifying primary producers and thus enhancing our understanding of DA and toxic Pseudo-nitzschia.

Seasonal monitoring of dissolved and particulate algal biotoxins in the northern Salish Sea using high performance liquid chromatography and tandem mass spectrometry

Harmful algae are present in the coastal waters of British Columbia, Canada yet little is known about the spatial and temporal distributions of the biotoxins produced by these organisms. We describe a method for profiling dissolved and particulate algal biotoxins in sea water including those associated with amnesic, paralytic, and diarrhetic shellfish poisoning (ASP, PSP and DSP). Surface sea water was filtered and biotoxins recovered from filters and filtrate using solvent extraction and solid phase extraction, respectively. Extracts were analyzed by high-performance liquid chromatography and tandem mass spectrometry using hydrophilic interaction liquid chromatography for ASP and PSP toxins and reversed-phased liquid chromatography for DSP and other lipophilic toxins. The method was applied to samples collected in the northern Salish Sea in April, June and October 2022. Highest total concentrations of domoic acid and saxitoxin were found above a shallow sill in the eastern Juan de Fuca Strait whereas those of dinophysistoxin 1, pectenotoxin 2, yessotoxin, and PSP toxins C1 and C2 were measured near the southern end of Malaspina Strait. These maximum concentrations were observed in June when surface salinity was lowest, temperature highest, and harmful algae most abundant, as reflected in the relative high proportion of particulate biotoxins. In contrast, the high proportion of dissolved biotoxins observed in April when temperature and algal abundance were relatively low suggests that certain biotoxins may persist in surface waters and that the risk of biotoxin exposure does not necessarily correlate with the abundance of harmful algae.

A High-Throughput Biosensing Approach for Rapid Screening of Compounds Targeting the hNav1.1 Channel: Marine Toxins as a Case Study

Voltage-gated sodium (Nav) channels play a crucial role in initiating and propagating action potentials throughout the heart, muscles and nervous systems, making them targets for a number of drugs and toxins. While patch-clamp electrophysiology is considered the gold standard for measuring ion channel activity, its labor-intensive and time-consuming nature highlights the need for fast screening strategies to facilitate a preliminary selection of potential drugs or hazards. In this study, a high-throughput and cost-effective biosensing method was developed to rapidly identify specific agonists and inhibitors targeting the human Nav1.1 (hNav1.1) channel. It combines a red fluorescent dye sensitive to transmembrane potentials with CHO cells stably expressing the hNav1.1 α-subunit (hNav1.1-CHO). In the initial screening mode, the tested compounds were mixed with pre-equilibrated hNav1.1-CHO cells and dye to detect potential agonist effects via fluorescence enhancement. In cases where no fluorescence enhancement was observed, the addition of a known agonist veratridine allowed the indication of inhibitor candidates by fluorescence reduction, relative to the veratridine control without test compounds. Potential agonists or inhibitors identified in the initial screening were further evaluated by measuring concentration-response curves to determine EC50/IC50 values, providing semi-quantitative estimates of their binding strength to hNav1.1. This robust, high-throughput biosensing assay was validated through comparisons with the patch-clamp results and tested with 12 marine toxins, yielding consistent results. It holds promise as a low-cost, rapid, and long-term stable approach for drug discovery and non-target screening of neurotoxins.

Prevalence of lipophilic phycotoxins with different forms in the benthic environments of a typical mariculture bay

Lipophilic phycotoxins (LPTs) are toxic and lipophilic secondary metabolites produced by toxic microalgae, which pose a serious threat to marine shellfish culture industries. LPTs were systematically investigated in bottom seawater, suspended particulate matter (SPM), sediment, and sediment porewater of Laizhou Bay, a typical mariculture bay in China, to understand the chemical diversity and environment behaviors of LPTs in the benthic environments. Okadaic acid (OA), pectenotoxin-2 (PTX2), dinophysistoxin-1 (DTX1), azaspiracid-2 (AZA2), gymnodimine (GYM), pectenotoxin-2 seco acid (PTX2 SA), 7-epi- pectenotoxin-2 seco acid (7-epi-PTX2 SA), 13-desmethylspirolide C (SPX1), yessotoxin (YTX) and homo YTX (h-YTX) were detected in the benthic environment of Laizhou Bay in spring, indicating that LPTs are rich in chemical diversity. OA and PTX2 were dominant in bottom seawater and porewater; PTX2 and PTX2 SA were dominant in SPM; and PTX2 and AZA2 were dominant in sediments, but AZA2 was present in sediments only. At the bottom seawater-SPM interface, the average proportion of LPTs in the dissolved phase (DP) (84.35%) was significantly higher than in the particulate phase (PP) (15.65%), indicating that LPTs were mainly distributed to the DP in the bottom seawater. At the sediment-porewater interface, a considerable variation exists in the partitioning behavior of different groups of LPTs, with abundant PTX2 and OA in DP, while the AZA2 and YTX group of LPTs were present in PP. The concentration of total lipophilic phycotoxins (∑LPTs) in the bottom seawater ranged from 8.07 ng L-1 to 37.11 ng L-1, with an average of 22.63 ng L-1, showing that the spatial distribution characteristics of ∑LPTs of the northern farshore are higher than in the southern nearshore. Concentrations of ∑LPTs in sediment and porewater ranged from 1.51 ng kg-1-32.67 ng kg-1 (mean: 17.32 ng kg-1) and 17.32 ng L-1-226.54 ng L-1 (mean: 88.72 ng L-1), respectively. Notably, the concentration of ∑LPTs in porewater is significantly higher than in bottom and surface seawater, indicating that the potential harm of LPTs to benthos needs more attention.

Spatiotemporal variations of domoic acid: New findings in the sedimentary environment of a typical nearshore mariculture bay, China

Domoic acid (DA) is a neurotoxin produced by marine microalgae. It tends to accumulate in marine shellfish and fish, posing a threat to aquaculture and seafood consumers' health. In this study, DA in the surface and bottom seawater, sediment, and porewater of the Jiaozhou Bay, a typical mariculture bay in China, was systematically investigated for the first time over different seasons. Surprisingly, a high concentration of DA was discovered in the marine sediment porewater (maximum detected concentration: 289.49 ng/L) for the first time. DA was found to be extensively distributed in the water body and sedimentary environment of the Jiaozhou Bay. DA in the surface and bottom seawater of Jiaozhou Bay in spring was uniformly distributed, whereas DA showed obvious spatial variations in summer and winter. The high concentration areas of DA are located in the north of Jiaozhou Bay and decreased to the south areas. DA was also distributed in the sediment (spring mean: 316.57 ng/kg; summer mean: 10.22 ng/kg; winter mean: 237.08 ng/kg) and porewater (spring mean: 129.70 ng/L; summer mean: 53.54 ng/L; winter mean: 19.90 ng/L) of Jiaozhou Bay. The DA concentrations in the surface sediment and porewater were higher in the spring than in the winter and summer, contrary to the seasonal variation pattern observed in the surface and bottom seawater. The DA concentration in porewater was significantly higher than in the surface and bottom seawater, indicating that the risk of pollution contamination from DA to benthic fishery organisms may be underestimated. Overall, DA is widely distributed in the seawater and also in the benthic environment of Jiaozhou Bay and exhibited potential harm to fishery organisms varied greatly with seasons. It is an important discovery for marine algae toxins and has important guiding significance and important indicative role for the routine monitoring and management of DA pollution in water and benthic environment.

Simultaneous determination of trace marine lipophilic and hydrophilic phycotoxins in various environmental and biota matrices

An efficient and sensitivity approach, which combines solid-phase extraction or ultrasonic extraction for pretreatment, followed by ultra-performance liquid chromatography-tandem mass spectrometry, has been established to simultaneously determine eight lipophilic phycotoxins and one hydrophilic phycotoxin in seawater, sediment and biota samples. The recoveries and matrix effects of target analytes were in the range of 61.6-117.3 %, 55.7-121.3 %, 57.5-139.9 % and 82.6 %-95.0 %, 85.8-106.8 %, 80.7 %-103.3 % in seawater, sediment, and biota samples, respectively. This established method revealed that seven, six and six phycotoxins were respectively detected in the Beibu Gulf, with concentrations ranging from 0.14 ng/L (okadaic acid, OA) to 26.83 ng/L (domoic acid, DA) in seawater, 0.04 ng/g (gymnodimine-A, GYM-A) to 2.75 ng/g (DA) in sediment and 0.01 ng/g (GYM-A) to 2.64 ng/g (domoic acid) in biota samples. These results suggest that the presented method is applicable for the simultaneous determination of trace marine lipophilic and hydrophilic phycotoxins in real samples.

Occurrence and distribution of phycotoxins in the Antarctic Ocean

Lipophilic phycotoxins (LPTs) and domoic acid (DA) in Antarctic seawater, as well as parts of the South Pacific and the Southern Indian Oceans were systematically investigated. DA and six LPTs, namely pectenotoxin-2 (PTX2), okadaic acid (OA), yessotoxin (YTX), homo-yessotoxin (h-YTX), 13-desmethyl spirolide C (SPX1), and gymnodimine (GYM), were detected. PTX2, as the dominant LPTs, was widely distributed in seawater surrounding Antarctica, whereas OA, YTX, and h-YTX were irregularly distributed across the region. The total concentration of LPTs in surface seawater ranged from 0.10 to 13.57 ng/L (mean = 2.20 ng/L). ∑LPT levels were relatively higher in the eastern sea areas of Antarctica than in the western sea areas. PTX2 was the main LPT in the vertical profiles, and the PTX2 concentration was significantly higher in the epipelagic zone than water depths below 200 m. The predominant sources of PTX2 and OA in Antarctic sea areas are likely to be Dinophysis.