Micronucleus test in mussels Perna perna fed with the toxic dinoflagellate Prorocentrum lima

Fate and effects of graphene oxide alone and with sorbed benzo(a)pyrene in mussels Mytilus galloprovincialis

Graphene oxide (GO) has gained a great scientific and economic interest due to its unique properties. As incorporation of GO in consumer products is rising, it is expected that GO will end up in oceans. Due to its high surface to volume ratio, GO can adsorb persistent organic pollutants (POPs), such as benzo(a)pyrene (BaP), and act as carrier of POPs, increasing their bioavailability to marine organisms. Thus, uptake and effects of GO in marine biota represent a major concern. This work aimed to assess the potential hazards of GO, alone or with sorbed BaP (GO+BaP), and BaP alone in marine mussels after 7 days of exposure. GO was detected through Raman spectroscopy in the lumen of the digestive tract and in feces of mussels exposed to GO and GO+BaP while BaP was bioaccumulated in mussels exposed to GO+BaP, but especially in those exposed to BaP. Overall, GO acted as a carrier of BaP to mussels but GO appeared to protect mussels towards BaP accumulation. Some effects observed in mussels exposed to GO+BaP were due to BaP carried onto GO nanoplatelets. Enhanced toxicity of GO+BaP with respect to GO and/or BaP or to controls were identified for other biological responses, demonstrating the complexity of interactions between GO and BaP.

A simple method to evaluate the toxic effects of Prorocentrum lima extracts to fish (sea bass) kidney cells

The diarrhetic shellfish toxins (DSTs) okadaic acid (OA) and its analogues - the dinophysistoxins (DTXs) - are produced by dinoflagellates such as Prorocentrum lima and can bioaccumulate in filter-feeding organisms as they are transferred through the food web. Although there is no assessment of the harmful effects of these toxins on the fish's immune system, this study developed a primary culture protocol for kidney cells from marine fish Centropomus parallelus and evaluated the immunotoxic effects to P. lima extracts containing DSTs. The cells were obtained by mechanical dissociation, segregated with Percoll gradient, and incubated for 24 h at 28 °C in a Leibovitz culture medium supplemented with 2% fetal bovine serum and antibiotics. The exposed cells were evaluated in flow cytometry using the CD54 PE antibody. We obtained >5.0 × 10⁶ viable cells per 1.0 g of tissue that exhibited no cell differentiation. Exposure to 1.2 or 12 ng DST mL^-1 stimulated the immune system activation and increased the proportion of activated macrophages and monocytes in 48 to 52% and in 127 to 146%, respectively. The protocol proved to be an alternative tool to assess the immunotoxic effects of DST exposure on fish's anterior kidney cells.

Invasive clams (Ruditapes philippinarum) are better equipped to deal with harmful algal blooms toxins than native species (R. decussatus): evidence of species-specific toxicokinetics and DNA vulnerability

This study aims to assess and compare the kinetics (accumulation/elimination) of the marine biotoxins okadaic acid (OA) and dinophysistoxin-1 (DTX1), between native (Ruditapes decussatus) and invasive (Ruditapes philippinarum) clam species, and their genotoxic effects and DNA recover capacity after, exposure to toxic dinoflagellates Prorocentrum lima. Clams were fed with P. lima for 5 days and then to non-toxic algae (post-exposure) during other 5 days. Toxin concentrations determined in clams by LC-MS/MS were related with DNA damage and repair assessment through the comet and base excision repair (BER) assays, respectively. Differential accumulation patterns were observed between the invasive and native species. The invasive species consistently and progressively accumulated the toxins during the first 24 h of exposure, while the native clams showed drastic variations in the toxin accumulation. Nevertheless, at the end of a 5 days of exposure period, the native clams presented higher toxin concentrations, nearly reaching the legal regulatory limit for human consumption. In addition, native clams were vastly affected by OA and DTX1, presenting an increment in the DNA damage since the first day, with a correspondent increase in the repair activity. On the other hand, invasive clams were not affected by the dinoflagellate toxins, exhibiting only some signs of the challenge, namely an increase in the DNA repair mechanisms in the post-exposure period. Invasive clams R. philippinarum are better adapted to cope with harmful algal blooms and OA-group toxins than native species. These results may increase farming interest and may lead to new introductions of the invasive clams. In sympatry sites, exposure to OA-group toxins may unbalance clams species biomass and distribution as exposure to toxic dinoflagellates affects the native clams from cellular to a population level, representing a significant threat to development and maintenance of R. decussatus populations.

De novo transcriptome analysis of the mussel Perna viridis after exposure to the toxic dinoflagellate Prorocentrum lima

Diarrheic shellfish poisoning (DSP) toxins are produced by harmful microalgae and accumulate in bivalve mollusks, causing various toxicity. These toxic effects appear to abate with increasing DSP concentration and longer exposure time, however, the underlying mechanisms remain unclear. To explore the underlying molecular mechanisms, de novo transcriptome analysis of the digestive gland of Perna viridis was performed after Prorocentrum lima exposure. RNA-seq analysis showed that 1886 and 237 genes were up- and down-regulated, respectively after 6 h exposure to P. lima, while 265 genes were up-regulated and 217 genes were down-regulated after 96 h compared to the control. These differentially expressed genes mainly involved in Nrf2 signing pathways, immune stress, apoptosis and cytoskeleton, etc. Combined with qPCR results, we speculated that the mussel P. viridis might mainly rely on glutathione S-transferase (GST) and ABC transporters to counteract DSP toxins during short-term exposure. However, longer exposure of P. lima could activate the Nrf2 signaling pathway and inhibitors of apoptosis protein (IAP), which in turn reduced the damage of DSP toxins to the mussel. DSP toxins could induce cytoskeleton destabilization and had some negative impact on the immune system of bivalves. Collectively, our findings uncovered the crucial molecular mechanisms and the regulatory metabolic nodes that underpin the defense mechanism of bivalves against DSP toxins and also advanced our current understanding of bivalve defense mechanisms.

Responses of CYP450 in the mussel Perna viridis after short-term exposure to the DSP toxins-producing dinoflagellate Prorocentrum lima

Diarrhetic shellfish poisoning (DSP) toxins are key shellfish toxins that cause diarrhea, vomiting and even tumor. Interestingly, bivalves such as Perna viridis have been reported to exhibit some resistances to alleviate toxic effects of DSP toxins in a species-specific manner. Nevertheless, the molecular mechanisms underlying the resistance phenomenon to DSP toxins, particularly the mechanistic role of CYP450 is scant despite its crucial role in detoxification. Here, we exposed P. viridis to Prorocentrum lima and examined the expression pattern of the CYP450 and our comprehensive analyses revealed that P. lima exposure resulted in unique expression pattern of key CYP450 genes in bivalves. Exposure to P. lima (2 × 10⁵ cells/L) dramatically orchestrated the relative expression of CYP450 genes. CYP2D14-like mRNA was significantly down-regulated at 6 h in gill, but up-regulated at 2 h in digestive gland compared with control counterparts (p < 0.05), while CYP3A4 mRNA was increased at 12 h in gill. After exposure to P. lima at 2 × 10⁶ cells/L, the expression of CYP3A4 mRNA was significantly increased in digestive gland at 2 h and 12 h, while CYP2D14-like was up-regulated at 6 h. Besides, CYP3L3 and CYP2C8 also exhibited differential expression. These data suggested that CYP3A4, CYP2D14-like, and even CYP3L3 and CYP2C8 might be involved in DSP toxins metabolism. Besides, provision of ketoconazole resulted in significant decrement of CYP3A4 in digestive gland at 2 h and 12 h, while the OA content significantly decreased at 2 h and 6 h compared to control group without ketoconazole. These findings indicated that ketoconazole could depress CYP3A4 activity in bivalves thereby altering the metabolic activities of DSP toxins in bivalves, and also provided novel insights into the mechanistic role of CYP3A4 on DSP toxins metabolism in bivalves.

Impacts of the toxic benthic dinoflagellate Prorocentrum lima on the brown mussel Perna perna: Shell-valve closure response, immunology, and histopathology

Prorocentrum lima is a widely distributed marine benthic dinoflagellate that produces diarrhetic toxins, okadaic acid (OA) and its analogs, that may promote damage on bivalve tissues and cellular responses. Cultivation of the brown mussel Perna perna represents an important economic activity in the tropical and subtropical regions, where mussels may co-occur with P. lima. This study aimed to assess the behavioral, cellular immune responses, and pathological condition of P. perna following a short-term experimental exposure to P. lima. The toxic dinoflagellate treatment was compared to a non-toxic exposure to the chlorophyte Tetraselmis sp. at similar concentrations. The prevalence of pathological conditions and parasites were assessed, and a pathological index was applied by scoring the prevalences into four levels. Reaction time and the number of stimuli necessary for shell-valve closure response significantly increased after 72 h of P. lima exposure. Circulating hemocyte concentration was significantly lower in P. lima exposed mussels than in control mussels at 48- and 96 h of incubation, while hemocyte relative size in exposed mussels was significantly higher than that in control mussels. Comparatively, phagocytic activity and ROS production by hemocytes was significantly higher in mussels exposed to P. lima at 48- and 96 h of incubation, respectively. In addition, exposed mussels significantly presented exacerbated hemocytic infiltration in digestive organs, higher prevalence of moderate to severe atrophy in digestive tubules, and higher pathological index which suggests an impairment of mussel immunologic responses. A lower prevalence of Rickettsia-like organisms (RLOs), trematodes and copepods in P. lima exposed mussels suggests a direct toxic effect of OA on parasites. The exposure of mussels to P. lima is likely to occur frequently and may lead to constraints on mussel behavior, physiology, and pathological condition.

Environmental genotoxicity and risk assessment in the Gulf of Riga (Baltic Sea) using fish, bivalves, and crustaceans

Environmental genotoxicity in the Gulf of Riga was assessed using different bioindicators (fish, clams, and isopods) collected from 14 study stations. Comparison of genotoxicity responses (micronuclei (MN) and nuclear buds (NB)) in blood erythrocytes of herring (Clupea harengus), eelpout (Zoarces viviparous), and flounder (Platichthys flesus) revealed the species- and site-specific differences. For the first time, the analysis of genotoxicity was carried out in gill cells of isopods Saduria entomon. The highest inductions of MN and NB in gill cells of investigated S. entomon and clams (Macoma balthica) were evaluated in specimens from station 111A (offshore zone). In fish, the highest incidences of MN were measured in eelpout and in herring collected in the southern part of Gulf of Riga (station GOR3/41S). Moreover, in the southern coastal area, the assessment of genotoxicity risk (according to micronuclei levels) indicated exceptionally high risk for flounder, eelpout, and clams.

Transcriptional and biochemical analysis of antioxidant enzymes in the mussel Mytilus galloprovincialis during experimental exposures to the toxic dinoflagellate Prorocentrum lima

The genotoxic and cytotoxic effects of Diarrhetic Shellfish Poisoning (DSP) toxins have been widely investigated in bivalve molluscs, representing the main vectors of these compounds in the Atlantic coast of Europe. DSP toxins are produced by Harmful Algal Blooms (HABs) of Dinophysis and Prorocentrum dinoflagellates, being subsequently accumulated by marine organisms and biomagnified throughout trophic webs. Yet, bivalves display increased resistance to the harmful effects of these toxins during HAB episodes. While previous reports have suggested that such resilience might be the result of an increased activity in the bivalve antioxidant system, very little is still known about the specific mechanism underlying the protective effect observed in these organisms. The present work aims to fill this gap by studying transcriptional expression levels and biochemical activities of antioxidant enzymes in different tissues the mussel Mytilus galloprovincialis during experimental exposures to DSP toxins produced by the dinoflagellate Prorocentrum lima. Results are consistent with the presence of a compensatory mechanism involving a down-regulation in the expression of specific genes encoding antioxidant enzymes [i.e., SuperOxide Dismutase (SOD) and CATalase (CAT)] which is counterbalanced by the up-regulation of other antioxidant genes such as Glutathione S-Transferase pi-1 (GST-pi) and Selenium-dependent Glutathione PeroXidase (Se-GPx), respectively. Enzymatic activity analyses mirror gene expression results, revealing high antioxidant activity levels (consistent with a protective role for the antioxidant system) along with reduced lipid peroxidation (increasing the defense against oxidative stress).

Crassostrea gigas exposure to the dinoflagellate Prorocentrum lima: Histological and gene expression effects on the digestive gland

Bivalve mollusks bioaccumulate toxins via ingestion of toxic dinoflagellates. In this study, Crassostrea gigas was used to investigate the effects related to Prorocentrum lima exposure. Oysters were fed with three diets Isochrysis galbana (2 × 10(6) cell mL(-1)) control treatment; algal mix of I. galbana (2 × 10(6)) and P. lima (3 × 10(3) cell mL(-1)); and P. lima alone (3 × 10(3) cell mL(-1)). Feeding behavior changes, histopathological alterations, and expression patterns changes of genes involved in cell cycle (p21, cafp55, p53), cytoskeleton (tub, act), and inflammatory process (casp1) were evaluated. Results indicated that the presence of diarrheic shellfish poisoning by P. lima cells decreased the clearance rate (p < 0.05), induced structural loss, significantly decreased tubule area of the digestive gland (p < 0.05), and up-regulated in expression all gene (p < 0.05), suggesting that toxic cells might trigger inflammatory tissue process, disturb cell cycle and cytoskeleton representing a risk to oysters integrity.

Marine Toxin Okadaic Acid Affects the Immune Function of Bay Scallop (Argopecten irradians)

Okadaic acid (OA) is produced by dinoflagellates during harmful algal blooms and is a diarrhetic shellfish poisoning toxin. This toxin is particularly problematic for bivalves that are cultured for human consumption. This study aimed to reveal the effects of exposure to OA on the immune responses of bay scallop, Argopecten irradians. Various immunological parameters were assessed (total hemocyte counts (THC), reactive oxygen species (ROS), malondialdehyde (MDA), glutathione (GSH), lactate dehydrogenase (LDH), and nitric oxide (NO) in the hemolymph of scallops at 3, 6, 12, 24, and 48 h post-exposure (hpe) to different concentrations of OA (50, 100, and 500 nM). Moreover, the expression of immune-system-related genes (CLT-6, FREP, HSP90, MT, and Cu/ZnSOD) was also measured. Results showed that ROS, MDA, and NO levels and LDH activity were enhanced after exposure to different concentrations of OA; however, both THC and GSH decreased between 24-48 hpe. The expression of immune-system-related genes was also assessed at different time points during the exposure period. Overall, our results suggest that exposure to OA had negative effects on immune system function, increased oxygenic stress, and disrupted metabolism of bay scallops.

Early Genotoxic and Cytotoxic Effects of the Toxic Dinoflagellate Prorocentrum lima in the Mussel Mytilus galloprovincialis

Okadaic acid (OA) and dinophysistoxins (DTXs) are the main toxins responsible for diarrhetic shellfish poisoning (DSP) intoxications during harmful algal blooms (HABs). Although the genotoxic and cytotoxic responses to OA have been evaluated in vitro, the in vivo effects of these toxins have not yet been fully explored. The present work fills this gap by evaluating the in vivo effects of the exposure to the DSP-toxin-producing dinoflagellate Prorocentrum lima during the simulation of an early HAB episode in the mussel Mytilus galloprovincialis. The obtained results revealed that in vivo exposure to this toxic microalgae induced early genotoxicity in hemocytes, as a consequence of oxidative DNA damage. In addition, the DNA damage observed in gill cells seems to be mainly influenced by exposure time and P. lima concentration, similarly to the case of the oxidative damage found in hemocytes exposed in vitro to OA. In both cell types, the absence of DNA damage at low toxin concentrations is consistent with the notion suggesting that this level of toxicity does not disturb the antioxidant balance. Lastly, in vivo exposure to growing P. lima cell densities increased apoptosis but not necrosis, probably due to the presence of a high number of protein apoptosis inhibitors in molluscs. Overall, this work sheds light into the in vivo genotoxic and cytotoxic effects of P. lima. In doing so, it also demonstrates for the first time the potential of the modified (OGG1) comet assay for assessing oxidative DNA damage caused by marine toxins in marine invertebrates.

P-glycoprotein and its inducible expression in three bivalve species after exposure to Prorocentrum lima

P-glycoprotein (P-gp or ABCB1) belongs to the family of ATP-binding cassette (ABC) transporters responsible for multixenobiotic resistance (MXR) in aquatic organisms. To provide more information of P-gp in shellfish, in this study, complete cDNA of P-gp in three bivalve species including Ruditapes philippinarum, Scapharca subcrenata and Tegillarca granosa were cloned and its expressions in gill, digestive gland, adductor muscle and mantle of the three bivalves were detected after exposure to Prorocentrum lima, a toxogenic dinoflagellate. The complete sequences of R. philippinarum, S. subcrenata and T. granosa P-gp showed high homology with MDR/P-gp/ABCB proteins from other species, having a typical sequence organization as full transporters from the ABCB family. Phylogenetic analyses revealed that the amino acid sequences of P-gp from S. subcrenata and T. granosa had a closest relationship, forming an independent branch, then grouping into the other branch with Mytilus californianus, Mytilus galloprovincialis and Crassostrea gigas. However, P-gp sequences from R. philippinarum were more similar to the homologs from the more distantly related Aplysia californica than to homologs from S. subcrenata and T. granosa, suggesting that bivalves P-gp might have different paralogs. P-glycoprotein expressed in all detected tissues but there were large differences between them. After exposure to P. lima, the expression of P-gp changed in the four tissues in varying degrees within the same species and between different species, but the changes in mRNA and protein level were not always synchronous.

Expression profile of eight glutathione S-transferase genes in Crassostrea ariakensis after exposure to DSP toxins producing dinoflagellate Prorocentrum lima

In this study, changes in eight GSTs mRNA level including GST-α, GST-σ, GST-ω, GST-π, GST-μ, GST-ρ, GST-θ and microsomal GST (mGST) in the oyster Crassostrea ariakensis after exposure to Prorocentrum lima have been evaluated by quantitative real-time PCR. Additionally, the contents of five GST isoforms were detected by ELISA. After exposure to P. lima at density of 2 × 10(5) cells/L, mGST mRNA significantly increased in gill, while GST-σ was induced in digestive gland. After exposure to P. lima at density of 2 × 10(6) cells/L, GST-ω and mGST expressions increased in gill, whereas GST-α and GST-σ were induced in digestive gland. The GST content and activity in oysters exposed to P. lima also showed a different pattern when the different isoforms and organs were compared. After exposure to P. lima (2 × 10(6) cell/L), GST-π increased in gill but decreased in digestive gland. The total GST enzyme activity increased in gill, while remained unchanged in digestive gland. These various regulation of GST gene expressions indicated that the GSTs isoenzymes might play divergent physiological roles in the detoxification of DSP toxins in C. ariakensis.

Proteomic profile in Perna viridis after exposed to Prorocentrum lima, a dinoflagellate producing DSP toxins

In the current study, we compared protein profiles in gills of Perna viridis after exposure to Prorocentrumlima, a dinoflagellate producing DSP toxins, and identified the differential abundances of protein spots using 2D-electrophoresis. After exposure to P. lima, the level of okadaic acid (a main component of DSP toxins) in gills of P. viridis significantly increased at 6 h, but mussels were all apparently healthy without death. Among the 28 identified protein spots by MALDI TOF/TOF-MS, 12 proteins were up-regulated and 16 were down-regulated in the P. lima-exposed mussels. These identified proteins were involved in various biological activities, such as metabolism, cytoskeleton, signal transduction, response to oxidative stress and detoxification. Taken together, our results indicated that the presence of P. lima caused DSP toxins accumulation in mussel gill, and might consequently induce cytoskeletonal disorganization,oxidative stress, a dysfunction in metabolism and ubiquitination/proteasome activity.

Does the marine biotoxin okadaic acid cause DNA fragmentation in the blue mussel and the pacific oyster?

Two bivalve species of global economic importance: the blue mussel, Mytilus edulis and the pacific oyster, Crassostrea gigas were exposed in vivo, to the diarrhoetic shellfish toxin okadaic acid (OA), and impacts on DNA fragmentation were measured. Shellfish were exposed using two different regimes, the first was a single (24 h) exposure of 2.5 nM OA (∼0.1 μg/shellfish) and algal feed at the beginning of the trial (T0), after which shellfish were only fed algae. The second was daily exposure of shellfish to two different concentrations of OA mixed with the algal feed over 7 days; 1.2 nM OA (∼0.05 μg OA/shellfish/day) and 50 nM OA (∼2 μg OA/shellfish/day). Haemolymph and hepatopancreas cells were extracted following 1, 3 and 7 days exposure. Cell viability was measured using the trypan blue exclusion assay and remained above 85% for both cell types. DNA fragmentation was examined using the single-cell gel electrophoresis (comet) assay. A significant increase in DNA fragmentation was observed in the two cell types from both species relative to the controls. This increase was greater in the pacific oyster at the higher toxin concentration. However, there was no difference in the proportion of damage measured between the two cell types, and a classic dose response was not observed, increasing toxin concentration did not correspond to increased DNA fragmentation.

P-glycoprotein expression in Perna viridis after exposure to Prorocentrum lima, a dinoflagellate producing DSP toxins

Bivalves naturally exposed to toxic algae have mechanisms to prevent from harmful effects of diarrhetic shellfish poisoning (DSP) toxins. However, quite few studies have examined the mechanisms associated, and the information currently available is still insufficient. Multixenobiotic resistance (MXR) is ubiquitous in aquatic invertebrates and plays an important role in defense against xenobiotics. Here, to explore the roles of P-glycoprotein (P-gp) in the DSP toxins resistance in shellfish, complete cDNA of P-gp gene in the mussel Perna viridis was cloned and analyzed. The accumulation of okadaic acid (OA), a main component of DSP toxins, MXR activity and expression of P-gp in gills of P. viridis were detected after exposure to Prorocentrum lima, a dinoflagellate producing DSP toxins in the presence or absence of P-gp inhibitors PGP-4008, verapamil (VER) and cyclosporin A (CsA). The mussel P. viridis P-gp closely matches MDR/P-gp/ABCB protein from various organisms, having a typical sequence organization as full transporters from the ABCB family. After exposure to P. lima, OA accumulation, MXR activity and P-gp expression significantly increased in gills of P. viridis. The addition of P-gp-specific inhibitors PGP-4008 and VER decreased MXR activity induced by P. lima, but had no effect on the OA accumulation in gills of P. viridis. However, CsA, a broad-spectrum inhibitor of ABC transporter not only decreased MXR activity, but also increased OA accumulation in gills of P. viridis. Together with the ubiquitous presence of other ABC transporters such as MRP/ABCC in bivalves and potential compensatory mechanism in P-gp and MRP-mediated resistance, we speculated that besides P-gp, other ABC transporters, especially MRP might be involved in the resistance mechanisms to DSP toxins.

Genetic and genotoxic impacts in the oyster Crassostrea gigas exposed to the harmful alga Alexandrium minutum

Genotoxic, genetic and behavioral impacts of the paralytic shellfish toxin (PST)-producing alga Alexandrium minutum on the oyster Crassostrea gigas were assessed using RAPD-PCR, qPCR and valve activity recording. Oysters were exposed to a dose mimicking an algal bloom (≈1600 cells ml(-1)) for 48 h. Results indicate a rapid and sustained behavioral disturbance. Animals remained open but exhibited reduced valve-opening amplitude, correlated to the amount of toxin accumulated in the digestive gland. They also exhibited increased micro-closures. In the gills, gene transcription levels were modified: a transcriptional repression of genes involved in oxidative and mitochondrial metabolism, endogenous clock, immunity and detoxification processes was observed. DNA impacts, both quantitative and qualitative, were observed as well. Indeed, both the PCR product profile and the number of hybridization sites for the RAPD probe OPB7 were modified. These results indicate genotoxic effects and gene repression in C. gigas following behavioral disturbance by A. minutum.

Okadaic acid meet and greet: an insight into detection methods, response strategies and genotoxic effects in marine invertebrates

Harmful Algal Blooms (HABs) constitute one of the most important sources of contamination in the oceans, producing high concentrations of potentially harmful biotoxins that are accumulated across the food chains. One such biotoxin, Okadaic Acid (OA), is produced by marine dinoflagellates and subsequently accumulated within the tissues of filtering marine organisms feeding on HABs, rapidly spreading to their predators in the food chain and eventually reaching human consumers causing Diarrhetic Shellfish Poisoning (DSP) syndrome. While numerous studies have thoroughly evaluated the effects of OA in mammals, the attention drawn to marine organisms in this regard has been scarce, even though they constitute primary targets for this biotoxin. With this in mind, the present work aimed to provide a timely and comprehensive insight into the current literature on the effect of OA in marine invertebrates, along with the strategies developed by these organisms to respond to its toxic effect together with the most important methods and techniques used for OA detection and evaluation.

The CHROMEVALOA database: a resource for the evaluation of Okadaic Acid contamination in the marine environment based on the chromatin-associated transcriptome of the mussel Mytilus galloprovincialis

Okadaic Acid (OA) constitutes the main active principle in Diarrhetic Shellfish Poisoning (DSP) toxins produced during Harmful Algal Blooms (HABs), representing a serious threat for human consumers of edible shellfish. Furthermore, OA conveys critical deleterious effects for marine organisms due to its genotoxic potential. Many efforts have been dedicated to OA biomonitoring during the last three decades. However, it is only now with the current availability of detailed molecular information on DNA organization and the mechanisms involved in the maintenance of genome integrity, that a new arena starts opening up for the study of OA contamination. In the present work we address the links between OA genotoxicity and chromatin by combining Next Generation Sequencing (NGS) technologies and bioinformatics. To this end, we introduce CHROMEVALOAdb, a public database containing the chromatin-associated transcriptome of the mussel Mytilus galloprovincialis (a sentinel model organism) in response to OA exposure. This resource constitutes a leap forward for the development of chromatin-based biomarkers, paving the road towards the generation of powerful and sensitive tests for the detection and evaluation of the genotoxic effects of OA in coastal areas.

Effects of okadaic acid on haemocytes from Mytilus galloprovincialis: a comparison between field and laboratory studies

Individuals of Mytilus galloprovincialis, contaminated with Diarrheic Shellfish Poisoning (DSP) toxins, were studied with the aim to correlate the okadaic acid (OA) body burden and the percentage of damaged haemocytes by quantifying annexin V positive cells by flow cytometry. Results showed less percentage of damaged haemocytes in high OA contaminated samples. These data were compared with results of in vitro assays of mussel haemocytes exposed to increased concentrations of OA. Similarly, haemocytes exposed to the most concentrated OA solution were less damaged.

The structures of three metabolites of the algal hepatotoxin okadaic acid produced by oxidation with human cytochrome P450

Four metabolites of okadaic acid were generated by incubation with human recombinant cytochrome P450 3A4. The structures of two of the four metabolites have been determined by MS/MS experiments and 1D and 2D NMR methods using 94 and 133 μg of each metabolite. The structure of a third metabolite was determined by oxidation to a metabolite of known structure. Like okadaic acid, the metabolites are inhibitors of protein phosphatase PP2A. Although one of the metabolites does have an α,β unsaturated carbonyl with the potential to form adducts with an active site cysteine, all of the metabolites are reversible inhibitors of PP2A.

Environmental genotoxicity and cytotoxicity studies in mussels before and after an oil spill at the marine oil terminal in the Baltic Sea

Environmental genotoxicity and cytotoxicity effects in the gills of mussels Mytilus edulis, from the Baltic Sea areas close to the Būtingė oil terminal (Lithuania) before and after accidental oil spill in 31 January 2008 were studied. Mussels from the oil spillage zones were collected in 12 days, in 3 and 6 months after the spill to determine the effects of the spill. Mussels sampled in 2006-2007 were used for the assessment of the background levels of genotoxicity and cytotoxicity in the Būtingė oil terminal area. Comparison of the responses in M. edulis before and after the oil spill revealed significant elevation of frequencies of micronuclei (MN), nuclear buds (NB) and fragmented-apoptotic (FA) cells. Environmental genotoxicity and cytotoxicity levels in mussels from the Palanga site before the accident (in June 2007) served as a reference. Six months after the accident, in July 2008, 5.6-fold increase of MN, 2.9-fold elevation of NB, and 8.8-fold elevation of FA cells were observed in mussels from the same site.

GENE EXPRESSION PROFILING OF HUMAN LIVER CARCINOMA (HepG2) CELLS EXPOSED TO THE MARINE TOXIN OKADAIC ACID

The marine toxin, okadaic acid (OA) is produced by dinoflagellates of the genera Prorocentrum and Dinophysis and is the causative agent of the syndrome known as diarrheic shellfish poisoning (DSP). In addition, OA acts as both a tumor promoter, attributed to OA-induced inhibition of protein phosphatases as well as an inducer of apoptosis. To better understand the potentially divergent toxicological profile of OA, the concentration dependent cytotoxicity and alterations in gene expression on the human liver tumor cell line HepG2 upon OA exposure were determined using RNA microarrays, DNA fragmentation, and cell proliferation assays as well as determinations of cell detachment and cell death in different concentrations of OA. mRNA expression was quantified for approximately 15,000 genes. Cell attachment and proliferation were both negatively correlated with OA concentration. Detached cells displayed necrotic DNA signatures but apoptosis also was broadly observed. Data suggest that OA has a concentration dependent effect on cell cycle, which might explain the divergent effects that at low concentration OA stimulates genes involved in the cell cycle and at high concentrations it stimulates apoptosis.

Investigation of animal and algal bioassays for reliable saxitoxin ecotoxicity and cytotoxicity risk evaluation

Contamination of water bodies by saxitoxin can result in various toxic effects in aquatic organisms. Saxitoxin contamination has also been shown to be a threat to human health in several reported cases, even resulting in death. In this study, we evaluated the sensitivity of animal (Neuro-2A) and algal (Chlamydomonas reinhardtii) bioassays to saxitoxin effect. Neuro-2A cells were found to be sensitive to saxitoxin, as shown by a 24 h EC50 value of 1.5 nM, which was obtained using a cell viability assay. Conversely, no saxitoxin effect was found in any of the algal biomarkers evaluated, for the concentration range tested (2-128 nM). These results indicate that saxitoxin may induce toxic effects in animal and human populations at concentrations where phytoplankton communities are not affected. Therefore, when evaluating STX risk of toxicity, algal bioassays do not appear to be reliable indicators and should always be conducted in combination with animal bioassays.

Evaluation of genotoxicity in gills and hemolymph of clam Ruditapes decussatus fed with the toxic dinoflagellate Prorocentrum lima

Diarrheic shellfish poisoning (DSP) is a gastrointestinal (GIT) disease that appears a few hours after ingesting okadaic acid (OA)-contaminated mollusks; okadaic acid is present in dinoflagellates of the genera Dinophysis and Prorocentrum. Toxic manifestations occur all year round at a higher or lesser intensity, and as a consequence, extractive production factories need to be closed during these periods which affects the economy of aquaculture industries. Although the concentration of harmful algae is usually found at high levels in clam digestive gland, bivalve mortality was not increased. In this study, the genotoxic effects produced by OA in clam Ruditapes decussatus were determined using the comet assay. In vitro (exposing hemocytes to different concentrations of OA) and in vivo (feeding clams with toxic dinoflagellate Prorocentrum lima) experiments were conducted in order to determine the genotoxic effects of OA on bivalve cells. Hemocytes and gill cells were analyzed by in vivo and in vitro approaches. While the in vitro study showed a rapid effect of OA on hemocytes, data obtained in the in vivo experiment reflected contradictory results dependent upon the concentration of OA and cell type evaluated. An increase in DNA damage was observed at the lower concentration and only in gill tissue. The results obtained may contribute to a better understanding of the mechanisms underlying genotoxic effects induced by OA on bivalves.

Superoxide dismutase activity in juvenile Litopenaeus vannamei and Nodipecten subnodosus exposed to the toxic dinoflagellate Prorocentrum lima

The toxic effect of the dinoflagellate Prorocentrum lima on juvenile American whiteleg shrimp Litopenaeus vannamei and giant lion-paw scallop Nodipecten subnodosus was evaluated. Organisms were exposed to three densities (500, 2000, or 5000 cells mL(-1)), superoxide dismutase activity and soluble protein in the hepatopancreas and muscle were determined at 1, 6, 24 and 48 h after challenge. Shrimp exposed at 5000 cells mL(-1) significantly increased SOD activity in the hepatopancreas at 1 h post-challenge, whereas enzymatic activity in muscle significantly increased at 24 h at all densities. Scallops exposed to 500 and 2000 cells mL(-1) showed significant SOD activity increase in hepatopancreas at 24 and 12 h, respectively. Mortality at 48 h was 100% in scallops exposed to 5000 cells mL(-1). Shrimp showed higher levels of SOD activity than scallops. Soluble protein content in the shrimp hepatopancreas was significantly higher at densities of 500 and 2000 cells mL(-1) at 6 and 1 h, respectively. Soluble protein content in the scallop hepatopancreas was higher than control values at 1 h after challenge. In this study, 500 cells mL(-1) was enough to trigger SOD activity in two benthic species exposed to the toxic dinoflagellate P. lima.

Combined cytotoxicity and genotoxicity of a marine toxin and seafood contaminant metal ions (chromium and cadmium)

Algal bloom with consequent production of marine toxins contaminating bivalves is increasing in costal regions worldwide because of sea water quality worsening. Contamination of seafood by diarrheic shellfish poisoning toxins (DSP) together with metals is frequently reported, a phenomenon not fully explained yet. In this context, metal ions were assayed in clams collected from the banned area of Boughrara, Tunisia, contaminated by Gymnodinium and other algae such as Dinophysis sp, accumulated by these bivalves. The presence of toxic metals ions such as Chromium (Cr) and Cadmium (Cd) in meat, shells, and water released by the clams prompted us to experiment in Caco-2 intestinal cell line toxic effects of these heavy metals ions in combination with okadaic acid, one DSP present in clams to assess the potential global toxicity. Cr and Cd produce additive effects in (i) reactive oxygen species production, (ii) cytotoxicity as assessed by the mitochondrial activity testing method (MTT test), and (iii) DNA lesions evaluated by agarose gel electrophoresis and acridine orange staining. Exaggerated DNA fragmentation is observed, suggesting an overloading of repair capacity of Caco-2 cells. The apoptosis suggested by a DNA fragment sizing (180-200 bp) in agarose gel and mechanisms underlying these additive effects in Caco-2 cells still need to be more comprehensively explained.