Antioxidant responses of triangle sail mussel Hyriopsis cumingii exposed to toxic Microcystis aeruginosa and thermal stress

Harmful planktonic Microcystis and benthic Oscillatoria-induced toxicological effects on the Asian clam (Corbicula fluminea): A survey on histopathology, behavior, oxidative stress, apoptosis and inflammation

Cyanobacterial blooms are worldwide distributed and threaten aquatic ecosystems and public health. The current studies mainly focus on the adverse impacts of planktonic cyanobacteria or pure cyanotoxins, while the benthic cyanobacteria-induced ecotoxic effects are relatively lacking. The cyanobacterial cell-induced toxic effects on aquatic organisms might be more serious and complex than the pure cyanotoxins and crude extracts of cyanobacteria. This study explored the chronic effects of toxin-producing planktonic Microcystis aeruginosa (producing microcystin) and benthic Oscillatoria sp. (producing cylindrospermopsin) on the behaviors, tissue structures, oxidative stress, apoptosis, and inflammation of the Asian clams (Corbicula fluminea) under 28-d exposure. The data showed that both M. aeruginosa and Oscillatoria sp. can decrease the behaviors associated with the feeding activity and induce tissue damage (i.e. gill and digestive gland) in clams. Furthermore, two kinds of cyanobacteria can alter the antioxidant enzyme activities and increase antioxidant, lipid oxidation product, and neurotransmitter degrading enzyme levels in clams. Moreover, two kinds of cyanobacteria can activate apoptosis-related enzyme activities and enhance the proinflammatory cytokine levels of clams. In addition, two kinds of cyanobacteria can disturb the transcript levels of genes linked with oxidative stress, apoptosis, and inflammation. These results suggested harmful cyanobacteria can threaten the survival and health of clams, while the benthic cyanobacteria-induced adverse effects deserve more attention. Our finding also indicated that it is necessary to focus on the entire algal cell-induced ecotoxicity when concerning the ecological impacts of cyanobacterial blooms.

Insights into the combined toxicity and mechanisms of BDE-47 and PFOA in marine blue mussel: An integrated study at the physiochemical and molecular levels

The coexistence of multiple emerging contaminants imposes a substantial burden on the ecophysiological functions in organisms. The combined toxicity and underlying mechanism requires in-depth understanding. Here, marine blue mussel (Mytilus galloprovincialis L.) was selected and exposed to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and perfluorooctanoic acid (PFOA) individually and in combination at environmental related concentrations to elucidate differences in stress responses and potential toxicological mechanisms. Characterization and comparison of accumulation, biomarkers, histopathology, transcriptomics and metabolomics were performed. Co-exposure resulted in differential accumulation patterns, exacerbated histopathological alterations, and different responses in oxidative stress and biomarkers for xenobiotic transportation. Moreover, the identified differentially expressed genes (DEGs) and differential metabolites (DEMs) in mussels were found to be annotated to different metabolic pathways. Correlation analyses further indicated that DEGs and DEMs were significantly correlated with the above biomarkers. BDE-47 and PFOA altered the genes and metabolites related to amino acid metabolism, energy and purine metabolism, ABC transporters, and glutathione metabolism to varying degrees, subsequently inducing accumulation differences and combined toxicity. Furthermore, the present work highlighted the pivotal role of Nrf2-keap1 detoxification pathway in the acclimation of M. galloprovincialis to reactive oxygen species (ROS) stress induced by BDE-47 and PFOA. This study enabled more comprehensive understanding of combined toxic mechanism of multi emerging contaminants pollution.

Cyanobacteria and Macroinvertebrate Relationships in Freshwater Benthic Communities beyond Cytotoxicity

Cyanobacteria are harmful algae that are monitored worldwide to prevent the effects of the toxins that they can produce. Most research efforts have focused on direct or indirect effects on human populations, with a view to gain easy accurate detection and quantification methods, mainly in planktic communities, but with increasing interest shown in benthos. However, cyanobacteria have played a fundamental role from the very beginning in both the development of our planet's biodiversity and the construction of new habitats. These organisms have colonized almost every possible planktic or benthic environment on earth, including the most extreme ones, and display a vast number of adaptations. All this explains why they are the most important or the only phototrophs in some habitats. The negative effects of cyanotoxins on macroinvertebrates have been demonstrated, but usually under conditions that are far from natural, and on forms of exposure, toxin concentration, or composition. The cohabitation of cyanobacteria with most invertebrate groups is long-standing and has probably contributed to the development of detoxification means, which would explain the survival of some species inside cyanobacteria colonies. This review focuses on benthic cyanobacteria, their capacity to produce several types of toxins, and their relationships with benthic macroinvertebrates beyond toxicity.

The Combined Effects of Toxic Microcystis aeruginosa and Thermal Stress on the Edible Clam (Corbicula fluminea): Insights into Oxidative Stress Responses and Molecular Networks

Cyanobacterial blooms (CYBs) have become a global environmental issue, posing risks to edible bivalves. Toxic cyanobacteria and thermal stress represent the two key co-occurring stressors to bivalves experiencing CYBs. To investigate the combined effects of these stressors on the edible bivalve Corbicula fluminea, the responses to oxidative stress and the molecular mechanisms of physiological adaptations in C. fluminea were examined under co-exposure to toxic Microcystis aeruginosa and thermal stress. The activity of antioxidant enzymes, including GST, SOD, CAT, GPx and GR, was significantly influenced by the interaction between temperature and M. aeruginosa (p < 0.05). A positive correlation was observed between toxic M. aeruginosa exposure and elevated SOD and GPx activities at 30 °C, demonstrating that SOD and GPx may help C. fluminea defend effectively against MCs under thermal stress. Furthermore, significant interactive effects between toxic M. aeruginosa and temperature were also observed in ROS and MDA (p < 0.05). The results of the PCA and IBR index also evidenced the apparent influence of toxic M. aeruginosa and thermal stress on oxidative stress responses of C. fluminea. The eggNOG and GO annotations confirmed that a substantial portion of differentially expressed genes (DEGs) exhibited associations with responses to oxidative stress and transporter activity. Additionally, KEGG analysis revealed that abundant DEGs were involved in pathways related to inflammatory responses, immune functions and metabolic functions. These findings improve our understanding of the mechanism of the physiological adaptation in bivalves in response to cyanotoxins under thermal conditions, potentially enabling the evaluation of the viability of using bivalves as a bioremediation tool to manage CYBs in eutrophic waters.

Combined effects of salinity and polystyrene microplastics exposure on the Pacific oysters Crassostrea gigas: Oxidative stress and energy metabolism

Microplastics (MPs) pollution and salinity variation are two environmental stressors, but their combined effects on marine mollusks are rarely known. Oysters (Crassostrea gigas) were exposed to 1 × 10⁴ particles L^-1 spherical polystyrene MPs (PS-MPs) of different sizes (small polystyrene MPs (SPS-MPs): 6 μm, large polystyrene MPs (LPS-MPs): 50-60 μm) under three salinity levels (21, 26, and 31 psu) for 14 days. Results demonstrated that low salinity reduced PS-MPs uptake in oysters. Antagonistic interactions between PS-MPs and low salinity mainly occurred, and partial synergistic effects were mainly induced by SPS-MPs. SPS-MPs induced higher lipid peroxidation (LPO) levels than LPS-MPs. In digestive glands, low salinity decreased LPO levels and glycometabolism-related gene expression, which was related to salinity levels. Low salinity instead of MPs mainly affected metabolomics profiles of gills through energy metabolism and osmotic adjustment pathway. In conclusion, oysters can adapt to combined stressors through energy and antioxidative regulation.

A meta-analysis on the toxicity of microcystin-LR to fish and mammals

Microcystin-leucine arginine (MC-LR), the most prevalent and dangerous microcystin, poses high risks to living organisms, especially fish and mammals. Although many studies have focused on the toxic effect on fish and mammals exposed to MC-LR, works that incorporate published data into a comprehensive comparison and analysis are still limited. Here, the adverse effects of oxidative stress markers, health, functional traits, and performance traits in fish and mammals were systematically verified by collecting data from 67 studies for the first time. Notably, we first found that the activities of malondialdehyde (MDA) (p < 0.05) and lactoperoxidase (LPO) always showed increases, whereas the growth (performance traits) always had a significant decrease (p < 0.001) under all variables of MC-LR exposure, i.e., exposure time, exposure concentration, exposure route, and even life stage. Additionally, our study first verified that the activities of MDA and LPO can be employed as oxidative stress indicators of MC-LR effects in fish and mammals instead of other biomarkers of oxidative stress, such as superoxide dismutase (SOD) and catalase (CAT), considered by previous studies. Growth may be regarded as a highly sensitive indicator of MC-LR toxicity in mammals and fish. At the same time, we first found that the impact of MC-LR exposure concentration on LPO, MDA, and growth is higher than that of exposure time, exposure route, and different life stages using the random forest (RF) model. In short, this work sheds light on the potential biochemical and individual toxicity of MC-LR exposure in fish and mammals.

Sublethal effects on the hard clam Mercenaria mercenaria after exposure to Aureococcus anophagefferens Chinese strain isolates

Brown tides caused by Aureococcus anophagefferens occur frequently worldwide and have contributed to the collapse of Mercenaria mercenaria farming in the United States. This economically valuable hard clam has been used in China for more than 20 years. To date, it has remained unknown whether A. anophagefferens Chinese strain has an impact on hard clam cultivation in the coastal areas of China or other sea areas worldwide if it enters through ship ballast water and other ways. In this study, a Chinese strain of A. anophagefferens isolated from the brown tide waters of Bohai Bay, China, was selected to explore its influence on the feedback of hard clams. After being fed with A. anophagefferens, hard clams showed characteristics similar to starvation. The reduced feeding efficiency of hard clams leads to reduced energy intake. However, the immune response and oxidative stress, result in increased energy consumption. An imbalance in the energy budget may be an important reason for hard clam starvation. This study has described the response characteristics of the A. anophagefferens Chinese strain to M. mercenaria, explored the reasons for the negative impact of A. anophagefferens on hard clams, and provides ideas for reducing shellfish aquaculture caused by brown tides.

4-tert-butylphenol triggers common carp hepatocytes ferroptosis via oxidative stress, iron overload, SLC7A11/GSH/GPX4 axis, and ATF4/HSPA5/GPX4 axis

4-tert-butylphenol (4-tBP) is a toxic environmental pollutant with moderate bioaccumulation, environmental persistence, and long-term toxicity. Its toxicity to aquatic organisms has become an issue of concern. However, the molecular mechanism of 4-tBP toxicity to aquatic organisms remained unclear. Liver is a target organ for environmental pollutants. Here, we established 4-tBP-exposed toxicity model in vivo and primary hepatocyte model in vitro in common carp (Cyprinus carpio L.). We found increased hepatic-somatic index (HSI) and abnormal serum biochemical indexes (ALT, AST, and LDH) after 4-tBP exposure, indicating liver damage. We further revealed that 4-tBP damaged the structural integrity of the livers with typical features of ferroptosis. Based on toxicogenomics analysis, we found ferroptosis is likely to be involved in the mechanism of 4-tBP-induced liver damage. Moreover, our in vivo and in vitro experiment provided evidences that 4-tBP-exposure led to excess oxidative stress, iron overload, decreased MMP, and abnormal expression of ferroptosis-related factors. Interestingly, ferrostatin-1 (Fer-1, a ferroptosis inhibitor) pretreatment alleviated above changes. In summary, we demonstrated that 4-tBP triggered hepatocytes ferroptosis via oxidative stress, iron overload, SLC7A11/GSH/GPX4 axis, and ATF4/HSPA5/GPX4 axis. For the first time, we discovered that Fer-1 can ameliorate the toxicity of 4-tBP, which needs more investigations. Our results provided a scientific basis of molecular mechanism of 4-tBP-induced fish poisoning.

Histopathology, antioxidant responses, transcriptome and gene expression analysis in triangle sail mussel Hyriopsis cumingii after bacterial infection

Bacterial disease outbreaks in filter feeder bivalve Hyriopsis cumingii as water contamination become more frequent in the water ecosystem, especially in intensive aquaculture habitats. To characterize host-pathogen interactions between H. cumingii and bacterial infection, we investigated the effects of Stenotrophomonas maltophilia HOP3 and Aeromonas veronii GL1 on the antioxidant response, tissue invasion and transcriptome expression of H. cumingii by infectivity trials. We showed that bacterial infections resulted in tubular necrosis of the hepatopancreas and induced the acute immune response in H. cumingii. The transcriptomic study identified a total of 5957 differentially expressed genes (DEGs) after A. veronii challenge. These DEGs were implicated in 302 KEGG pathways, notably in Apoptosis, Phagosome and Lysosome. The results showed that the relative expressions of all six immune-related DEGs were effectively stimulated with A. veronii, accompanied by tissue differences. Overall, these findings will contribute to an analysis of the immune response of H. cumingii to bacterial infection at the transcriptomic level and its genomic resource for research.

Effects of microcystin-producing and non-microcystin-producing Microcystis on the behavior and life history traits of Chironomus pallidivittatus

Species of the genus Microcystis are among the most notorious cyanobacteria in eutrophic lakes worldwide, with ability present adverse effects on many aquatic organisms. In the surface sediments, Microcystis can be ingested by benthic macroinvertebrates such as Chironomus. However, the potential negative effects of Microcystis on Chironomus life history traits remain unclear. In the present study, we investigated the effect of different Microcystis diets on specific behaviors (burrowing activity, locomotion ability) and life history traits of Chironomus pallidivittatus (Diptera, Chironomidae). We also studied the interactive effects of microcystin-producing M. aeruginosa and temperature (15, 20, and 25 °C) stress on chironomid larvae. The results showed that the inhibitory effect on the cumulative emergence and burrowing activity of larvae was more severe when they were fed M. aeruginosa among the three Microcystis diets groups. Locomotion ability (i.e., locomotor distance and velocity) and adult dry weight decreased significantly in the group fed M. aeruginosa. Locomotion was significantly inhibited and mortality increased when the larvae were fed a mixture of M. aeruginosa and M. wesenbergii, which may have been the result of additive or synergistic effect of the toxins. Under the stress of lower temperature, C. pallidivittatus larvae exhibited weaker locomotion and growth ability, and the emerging adults were mostly male. At both the lower and higher temperature conditions, M. aeruginosa cause cumulative emergence decreased, and sex ratio imbalance, which inhibited the reproduction of larvae from the population perspective. The fourth-instar larvae showed better adaption to Microcystis than did the other instars. This study thus highlights the adverse effects of microcystin-producing M. aeruginosa on Chironomus. It also provides a novel perspective on how environmental factors may influence the behavior and life history traits of chironomid larvae, and how they may respond to cyanobacterial blooms and global warming.

Protective effects of Schisandrin B against D-GalN-induced cell apoptosis in human hepatocyte (L02) cells via modulating Bcl-2 and Bax

Schisandrin B is a dibenzocyclooctadiene derivative extracted fromSchisandra chinensis (Turcz.) Baill., that exhibits anti-oxidation, anti-inflammation, anti-tumor and hepatoprotective activities. To understand the hepatoprotective mechanism of schisandrin B, this study investigated the efficacy of schisandrin B on L02 cells after treatment with D-GalN. Following pretreatment with 40 μM schisandrin B, L02 cells were stimulated with 40 mM D-GalN. Cell viability, apoptosis, the expression levels of genes associated with apoptosis, and the intracellular oxidative stress indexes were measured. The viability of L02 cells was determined using MTT assay, and the Annexin V-FITC/PI assay kit was utilized for the assessment of apoptosis. The activities of GSH-Px and SOD, the level of MDA were assessed, separately, using relative detection kits. Moreover, RT-PCR as well as Western blot was applied to measure the mRNA and protein expression of Bax and Bcl-2. The results indicated that schisandrin B significantly prevented D-GalN‑induced oxidative damage in L02 cells (P<0.05), decreased GSH-Px and SOD activities (P<0.05), increased MDA content (P<0.05). Furthermore, schisandrin B inhibited D-GalN-induced apoptosis in L02 cells (P<0.05), regulated the expression of Bax and Bcl-2 (P<0.05). The results indicated that schisandrin B decreased the D-GalN-induced intracellular oxidative stress indexes generation, and inhibited the down-regulation of Bcl-2 and up-regulation of Bax induced by D-GalN. In conclusion, schisandrin B was shown to exert protective effect against oxidative damage of L02 cells, which, in part, was achieved by regulating the mRNA and protein levels of Bax and Bcl-2.

Thermal tolerance, metabolic scope and performance of meagre, Argyrosomus regius, reared under high water temperatures

This article reports on the thermal tolerance, metabolic capacity and performance of juvenile meagre (Argyrosomus regius) reared under three high water temperatures (24, 29 and 34 °C) for three months. The analysis includes the thermal effects on the growth performance, metabolism and physiology of meagre, including a range of molecular, haematological, metabolic, enzymatic and hormonal indicators, as well as the effects on the proximate composition and ingestion speed. Meagre performs best between 24 and 29 °C while the temperature of 34 °C is very close to the upper end of its temperature tolerance range. At 34 °C meagre exhibits a poor growth performance and physiological status, increased blood clotting, high mortality rates and a diminished capacity for aerobic metabolism, as indicated by its low aerobic scope (129 mg kg^-1 h^-1). Meagre may tolerate short exposures to high temperatures after sufficient acclimation (Critical thermal maximum of 37.5 °C after acclimation to 29 °C) but its overall performance declines under prolonged exposure, suggesting that this emerging aquaculture species may be vulnerable to global warming. Our work corroborates previous findings on the thermal preferences of the species, identifies critical biological thresholds, and provides insights into the effects of prolonged exposure to high temperature regimes.

Screening and functional identification of antioxidant microRNA-size sRNAs from Spirulina platensis using high-throughput sequencing

MiRNA-size small RNAs, abbreviated as sRNAs, are increasingly being discovered as research progresses and omics technologies development in prokaryotes. However, there is a paucity of data concerning whether or not sRNAs exist in cyanobacteria and regulate the resistance to oxidative stress. In this investigation, small RNA libraries were constructed from the control, 50-nM and 100-nM H2O2 treatments of Spirulina platensis. By high-throughput sequencing, 23 candidate sRNAs showed significantly differential expression under oxidative stress, among which eight sRNAs were identified with the similar expression patterns as the sequencing results by real-time qPCR. By nucleic acid hybridisation, the corresponding expression changes also demonstrated that sequencing results of sRNAs were feasible and credible. By bioinformatics prediction and structure identification, 43 target genes were predicted for 8 sRNAs in plant miRNA database, among which 29 were annotated into the genome and related metabolic pathways of S. platensis. By COG functional classification and KEGG pathway analysis, 31 target genes were predicted to be directly or indirectly involved in the defence mechanism of H2O2 stress. Thirteen target genes displayed reversely changing patterns compared with those of their sRNAs under H2O2 treatment. These findings provide compelling evidence that these sRNAs in S. platensis play a crucial role in oxidative stress responses, and thus provide a theoretical reference for improving the stress-triggering physiological regulation.

Bioaccumulation, Metabolism, and Biomarker Responses in Hyriopsis cumingii Exposed to 4-Mono-Chlorinated Dibenzothiophene

Polychlorinated dibenzothiophenes (PCDTs) are sulfur analogues of polychlorinated dibenzofurans with prevalent occurrence in aquatic environments and potential ecological risks. However, data on the behavior and toxicity of PCDTs in aquatic organisms remain scarce. In the present study, the bioaccumulation, metabolism, and oxidative damage of 4-mono-chlorinated dibenzothiophene (4-mono-CDT) in freshwater mussel (Hyriopsis cumingii) were investigated after exposure to 4-mono-CDT in semistatic water. The uptake rates, depuration rates, half-lives, and bioconcentration factors of 4-mono-CDT in hepatopancreas, gill, and muscle tissues ranged from 0.492 to 1.652 L d^-1  g^-1 dry weight, from 0.117 to 0.308 d^-1 , from 2.250 to 5.924 d, and from 2.903 to 8.045 × 10³  L kg^-1 dry weight, respectively. A dechlorinated metabolite (dibenzothiophene) was detected in hepatopancreas tissue, indicating that dechlorination was the main metabolic pathway of 4-mono-CDT. As the exposure time increased, the activities of superoxide dismutase, catalase, and glutathione peroxidase were induced or inhibited in the different experimental groups. The malondialdehyde content increased with increasing 4-mono-CDT dose and exposure time. A higher concentration of 4-mono-CDT corresponded to a greater integrated biomarker response in each tissue and greater oxidative damage. The antioxidant enzymes in hepatopancreas were more sensitive to 4-mono-CDT than those in gill. The results provide useful information on the behavior and ecotoxicity of PCDTs in freshwater mussels. Environ Toxicol Chem 2021;40:1873-1882. © 2021 SETAC.

Acacetin Protects Myocardial Cells against Hypoxia-Reoxygenation Injury through Activation of Autophagy

Ischemic heart disease is a leading cause of mortality and morbidity worldwide. We previously demonstrated that acacetin protects against myocardial ischemia reperfusion injury in rats, although the underlying mechanism remains to be elucidated. In the present study, we investigated the effects of acacetin on autophagy during hypoxia/reoxygenation (H/R) injury by exposing H9c2 myocardial cells to H/R with or without acacetin pretreatment during hypoxia. Our results show that acacetin significantly increased cell viability in a dose-dependent manner, enhanced antioxidant capacity, and suppressed protein apoptosis of rat cardiomyocytes H9c2 cells following H/R injury. In addition, lentiviral infection of H9c2 cardiomyocytes revealed that acacetin pretreatment significantly enhanced the fluorescence intensity of autophagy proteins Beclin 1, LC3-II, and p62. These results indicate that acacetin protected H9c2 cardiomyocytes from H/R damage by enhancing autophagy. Moreover, we found that application of acacetin increased activation of the PI3K/Akt signaling pathway, whereas cotreatment with the PI3K inhibitor LY294002 reversed the inhibition of apoptosis and autophagy induced by acacetin. In conclusion, acacetin mitigated H/R injury by promoting autophagy through activating the PI3K/Akt/mTOR signaling pathway.