Adverse effects of BDE-47 on life cycle parameters, antioxidant system, and activation of MAPK signaling pathway in the rotifer Brachionus koreanus

Establishment of a comprehensive method to derive seawater quality criteria of BDE-47 in China

2,2',4,4'-tetrabromodiphenyl ether (BDE-47) is an emerging toxic organic pollutant widely detected in territorial waters. Accordingly, establishing the seawater quality criteria (SWQC) for BDE-47 is of significant importance to protect the marine ecosystems. In this study, published ecotoxicity data of BDE-47 to aquatic species in China were collected, and acute and chronic toxicity tests were carried out on saltwater aquatic organisms from 5 phyla and 8 families widely existed in the Chinese marine environment. Static acute toxicity tests and renewed chronic toxicity tests were adopted. The scientific theories and technical methods of the United States Environmental Protection Agency (US EPA), Canada, the European Union (EU), and the Netherlands on water quality criteria guidelines, as well as the Chinese freshwater quality criteria guidelines were compared. Then an integrated method of SWQC derivation was introduced through comprehensive consideration. Afterward, the SWQC of BDE-47 was derived based on the ecotoxicity data. The SWQC includes short-term seawater quality criteria (S-SWQC), long-term seawater quality criteria (L-SWQC), and serious risk concentration for the ecosystem (SRC_eco). And they were derived and recommended as 7.90 μg/L, 0.217 μg/L, and 3.65 μg/L, respectively. This study served as a specific example to quantitatively studies the differences between different scientific theories and technique methods. The derivation process and improvement of SWQC for BDE-47 provide support for the future revision of water quality criteria in China.

In vitro immunotoxicity and possible mechanisms of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on Ruditapes philippinarum hemocytes

Marine bivalves can accumulate large amounts of pollutants from sea water, sediments and microalgae due to their filter-feeding habits. BDE-47 is often the most highly concentrated congener in bivalves. BDE-47 has been found to have toxic effects on bivalves, however, the immunotoxicity and the underlying mechanisms of BDE-47 on bivalves are not well understood yet. In this study, isolated hemocytes of Manila clam Ruditapes philippinarum were exposed to five concentrations of BDE-47 (6.25 μM, 12.5 μM, 25 μM, 50 μM, 100 μM), the effects of BDE-47 on hemocyte survival rate, cell viability, granulocyte ratio, phagocytosis, bacteriolytic activity, reactive oxygen species (ROS), lysosomal membrane permeability (LMP), superoxide dismutase (SOD), and phosphorylation state of extracellular regulated protein kinase (ERK) and p38 at 2 h, 6 h and 12 h were studied. The results indicated that BDE-47 exposure declined the hemocyte cell viability, reduced the granulocyte ratio, hampered the hemocyte phagocytosis and bacteriolytic activity, elevated the ROS levels, increased the LMP, significantly changed SOD expression and depressed the phosphorylation levels of ERK and p38. Taken together, the results demonstrated that BDE-47 had significant toxic effects on the immune function, and the immunotoxicity may partly via the overproduction of ROS and the alteration of MAPK signaling pathways.

Micro- and nano-plastics activation of oxidative and inflammatory adverse outcome pathways

Microplastics (MPs) and nanoplastics (NPs) have attracted considerable attention in the recent years as potential threats to the ecosystem and public health. This review summarizes current knowledge of pathological events triggered by micro- and nano-plastics (MP/NPs) with focus on oxidative damages at different levels of biological complexity (molecular, cellular, tissue, organ, individual and population). Based on published information, we matched the apical toxicity endpoints induced by MP/NPs with key event (KE) or adverse outcomes (AO) and categorized them according to the Adverse Outcome Pathway (AOP) online knowledgebase. We used existing AOPs and applied them to highlight formal mechanistic links between identified KEs and AOs in two possible scenarios: first from ecological, and second from public health perspective. Ecological perspective AOP based literature analysis revealed that MP/NPs share formation of reactive oxygen species as their molecular initiating event, leading to adverse outcomes such as growth inhibition and behavior alteration through oxidative stress cascades and inflammatory responses. Application of AOP on literature data related to public health perspective of MP/NPs showed that oxidative stress and its responding pathways, including inflammatory responses, could play the role of key events. However insufficient information prevented precise definitions of AOPs at this level. To overcome this knowledge gap, further mammalian model and epidemiological studies are necessary to support development and construction of detailed AOPs with public health focus.

Effects of azithromycin on feeding behavior and nutrition accumulation of Daphnia magna under the different exposure pathways

Antibiotics had been paid more and more attention to their toxicity to non-target aquatic organisms in the aquatic environment. As azithromycin (AZI) was an important antibiotic pollutant in water, its toxicity to aquatic organisms had been investigated. In this study, the potential aquatic ecological risk of AZI was identified by assessing the toxicity on the feeding behavior and physiological function of Daphnia magna (D. magna) under the different exposure pathways (aqueous phase exposure vs. food phase exposure). For the food Chlorella pyrenoidosa (C. pyrenoidosa), AZI could inhibit the growth and nutrition accumulation with concentration- and time-response relationship. For D. magna, the feeding behavior was inhibited by AZI under the aqueous phase exposure pathway. However, the feeding behavior was inhibited firstly and then reversed into promotion in the low and medium concentration groups and was continually promoted in the high concentration group under the food phase exposure pathway. The accumulation of polysaccharides and total protein were decreased in D. magna n the high concentration group under the aqueous phase exposure pathway, while the accumulation of polysaccharides and crude fat were decreased in the high concentration group under the food phase exposure pathway. The activity of amylase (AMS) and trypsin in D. magna were decreased after exposure to AZI under the aqueous phase exposure pathway. On the other hand, the activity of AMS in the medium and high concentration groups was decreased under the food phase exposure pathway, but the activity of trypsin was decreased in the medium concentration group and increased in the high concentration group. The levels of ROS in D. magna were also measured and increased in both exposure pathways except in the low concentration group under the food phase exposure pathway, indicating the oxidative stress injury of D. magna. Our results showed that AZI could affect the digestive enzyme activities and oxidative stress-antioxidative system, ultimately leading to the change of D. magna's feeding behavior and nutrition accumulation. These results also provided a comprehensive perspective to evaluate the toxic effects of non-lethal dose antibiotics to non-target aquatic organisms via different exposure pathways.

The glutathione S-transferase genes in marine rotifers and copepods: Identification of GSTs and applications for ecotoxicological studies

Various xenobiotics are constantly being released and accumulated into the aquatic environments and consequently, the aquatic organisms are continuously being exposed to exogenous stressors. Among various xenobiotic detoxifying enzymes, Glutathione S-transferase (GST) is one of the major xenobiotic detoxifying enzyme which is widely distributed among living organisms and thus, understanding of the nature of GSTs is crucial. Previous studies have shown GST activity in response to various xenobiotics yet, full identification of GSTs in marine invertebrates is still limited. This review covers information on the importance of GSTs as a biomarker for emerging chemicals and their response to wide ranges of environmental pollutants as well as in-depth phylogenetic analysis of marine invertebrates, including recently identified GSTs belonging to rotifers (Brachionus spp.) and copepods (Tigriopus japonicus and Paracyclopina nana), with unique class-specific features of GSTs, as well as a new suggestion of GST evolutionary pathway.

Effects of temperature changes on life parameters, oxidative stress, and antioxidant defense system in the monogonont marine rotifer Brachionus plicatilis

Global warming is a big concern for all organisms and many efforts have been made to reveal the potential effects of temperature elevation on aquatic organisms. However, limited studies on molecular mechanistic approaches on physiological effects due to temperature changes are available. Here, we investigated the effects of temperature changes on life parameters (e.g., population growth [total number of rotifers], and lifespan), oxidative stress levels and antioxidant activities (e.g., glutathione S-transferase [GST], catalase [CAT], superoxide dismutase [SOD]) with expression levels in the monogonont marine rotifer Brachionus plicatilis. The changes in temperatures led to significant reduction (P < 0.05) in lifespan, possibly due to significant decrease (P < 0.05) in antioxidant activities, reducing the potential to cope with significant elevation in the temperature-induced oxidative stress in B. plicatilis. To further assess the actual induction and clearance of reactive oxygen species (ROS), N-acetyl-L-cysteine was used to examine whether the temperature-induced oxidative stress could be successfully scavenged. Furthermore, expression patterns of the antioxidant-related genes (GSTs, SODs, and CATs) were down- or upregulated (P < 0.05) in response to different temperatures in B. plicatilis. Overall, these findings indicate that ROS-mediated oxidative stress led to cellular damage and antioxidant defense system, resulting in deleterious effects on life parameters in rotifer.

Inhibition to crucial enzymes in the lethal effects of the dinoflagellate Karenia mikimotoi on the rotifer Brachionus plicatilis

Blooms of the dinoflagellate Karenia mikimotoi have cause great financial losses to the marine aquaculture industry. However, the toxicity mechanism of this species is still not fully known. In this study, we evaluated the short-term effects of K. mikimotoi on the rotifer Brachionus plicatilis by micro and sub micro observing and by measuring inhibition of crucial enzymes. Behaviour disorder, mucus production, corona and cilium damage, vesical production, and body shrinkage occurred within 1 h after rotifers were treated with K. mikimotoi at a density of 3 × 10⁴ cells/mL. Enzyme activity assays showed that K. mikimotoi at low densities significantly inhibited multiple enzymes within 3 h, and obvious density-effect trends were also observed. For instance, activity of esterase and acetylcholinesterase of rotifers significantly decreased to 94.3/83.3% and 82.8/66.9% of control treatment values in 30 and 1000 cells/mL algal treatment, respectively. Total ATPase and Na⁺-K⁺-ATPase activities of rotifers also decreased to 82.3% and 68.6% of control values in 1000 cells/mL treatment. The LDH releasement test and MDA tests showed no significant difference between algae treatment and control. It suggested that K. mikimotoi might not cause significant cytolysis and oxidative damage to rotifers, but may cause mortality by inhibiting the activity of crucial enzymes, which may lead to cell permeability disorder and body shrinkage.

The genome of the marine rotifer Brachionus koreanus sheds light on the antioxidative defense system in response to 2-ethyl-phenanthrene and piperonyl butoxide

BRACHIONUS: spp. (Rotifera: Monogononta) have been introduced as ecotoxicological model-organisms that are widely distributed in aquatic environments. Among the Brachionus spp., the monogonont rotifer Brachionus koreanus has been widely used for ecology, ecotoxicology, and evolution, thus, providing the whole genome data of B. koreanus is important for further understandings of in-depth molecular mechanisms. In this study, the completed assembly and characterization of the B. koreanus genome resulted in a total length of 85.7 Mb with 14,975 annotated genes. The final number of scaffolds was 567 with an N50 value and a GC content of 1.86 Mb and 24.35 %, respectively. Based on the fully constructed genome database, a total of 24 CYPs, 23 GSTs, two SODs, and a single CAT genes were identified and analyzed antioxidant activities (CAT, SOD, and GST), and transcriptional regulation of the entire CYPs, GSTs, SODs, and CAT in response to 2-ethyl-phenanthrene (2-ethyl-PHE) and piperonyl butoxide (PBO), to demonstrate the usefulness of the whole genome library of B. koreanus in response xenobiotic-induced oxidative stress. The assembled B. koreanus genome will provide a better understanding on the molecular ecotoxicology in the view of molecular mechanisms underlying toxicological responses, particularly on xenobiotic detoxification processes in the rotifer B. koreanus.

Embryo bioassays with aquatic animals for toxicity testing and hazard assessment of emerging pollutants: A review

This review article gathers the available information on the use of embryo-tests as high-throughput tools for toxicity screening, hazard assessment and prioritization of new and existing chemical compounds. The approach is contextualized considering the new legal trends for animal experimentation, fostering the 3R policy, with reduction of experimental animals, addressing the potential of embryo-tests as high-throughput toxicity screening and prioritizing tools. Further, the current test guidelines, such as the ones provided by OECD and EPA, focus mainly in a limited number of animal lineages, particularly vertebrates and arthropods. To extrapolate hazard assessment to the ecosystem scale, a larger diversity of taxa should be tested. The use of new experimental animal models in toxicity testing, from a representative set of taxa, was thoroughly revised and discussed in this review. Here, we critically review current tools and the main advantages and drawbacks of different animal models and set researcher priorities.

Adverse effects, expression of defense-related genes, and oxidative stress-induced MAPK pathway in the benzo[α]pyrene-exposed rotifer Brachionus rotundiformis

To examine the adverse effects of the benzo[α]pyrene (B[α]P), the monogonont rotifer Brachionus rotundiformis was exposed to various concentration of B[α]P (0 [control], 1, 10, and 100 μg/L) and measured life cycle parameters (e.g., mortality, fecundity [cumulated number of offspring], and lifespan), reactive oxygen species (ROS), antioxidant enzymatic activity of glutathione S-transferase (GST). In addition, defense-related transcripts (e.g., glutathione S-transferases [GSTs], ATP binding cassette [ABCs] transporters) and Western blot analysis of mitogen-activated protein kinase (MAPK) signaling pathway were investigated in B[α]P-exposed rotifer. In this study, the total intracellular ROS level and GST activity were significantly increased (P < 0.05), while fecundity and lifespan were also significantly (P < 0.05) reduced in a concentration dependent manner in B[α]P-exposed B. rotundiformis. In addition, transcriptional regulation of GSTs and ABC transporters were significantly upregulated and downregulated (P < 0.05), respectively, suggesting that B[α]P can induce oxidative stress leading to induction of antioxidant system and detoxification mechanism. In addition to detoxification-related genes, B[α]P-exposed B. rotundiformis showed the increased levels of the p-JNK and p-p38, suggesting that B[α]P can activate MAPK signaling pathway in B. rotundiformis.

Responses of antioxidant defenses in the clam Mactra veneriformis to 2,2',4,4'‑tetrabromodiphenyl ether exposure

Antioxidant enzymes play essential roles against oxidative stress caused by 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), which is ubiquitous in marine environment and organisms. However, research on antioxidant responses to BDE-47 in marine bivalves is scarce. In this study, we identified the full-length cDNA of catalase (CAT), and glutathione peroxidase (GPx) in the clam Mactra veneriformis. Subsequently, the responses of CAT, GPx, and copper, zinc-superoxide dismutase (Cu, Zn-SOD) were investigated in the clams exposed to 0.1, 1, and 10 μg/L BDE-47 for 7 days, and then depurated in natural seawater for 3 days. MvCAT and MvGPx contained conserved sequences. The deduced amino acid sequences shared high similarity with CATs and GPxs in other mollusks. M. veneriformis accumulated BDE-47 in a dose-dependent manner and eliminated BDE-47 poorly. BDE-47 induced a time- and dose-dependent increase of malondialdehyde content. Both the dose and the duration had significant effect on mRNA expressions and activities of the three antioxidants. Cu, Zn-SOD responded to BDE-47 earlier than CAT and GPx. The antioxidant responses could recover after depuration. These results suggested that M. veneriformis could accumulate BDE-47 efficiently. Antioxidant enzymes were triggered to counter the oxidative stress generated by BDE-47. Cu, Zn-SOD acted as the first defense against oxidative stress, while CAT and GPx intervened later. This study is therefore helpful in understanding the antioxidant responses to PBDEs in marine bivalves.

Adverse effects of two pharmaceuticals acetaminophen and oxytetracycline on life cycle parameters, oxidative stress, and defensome system in the marine rotifer Brachionus rotundiformis

To investigate the adverse effect of two widely used pharmaceuticals, paracetamol (acetaminophen [APAP]) and oxytetracycline (OTC) on the marine rotifer Brachionus rotundiformis (B. rotundiformis), the animals were exposed to various environmentally-relevant concentrations. Up to date, acetaminophen and oxytetracycline have been considered as toxic, if used above threshold concentration, i.e. overdosed. However, this study demonstrated these two pharmaceuticals even at low concentration (i.e., μg/L scale) elicited oxidative stress through the generation of reactive oxygen species (ROS) along with the increased glutathione S-transferase activity, despite no-observed effect in in-vivo population growth. To validate the adverse effects of the two pharmaceuticals at relatively low concentrations, mRNA expression analysis was performed of the entire set of genes encoding 26 cytochrome P450s (CYPs) of phase I and 19 glutathione S-transferases (GSTs) of phase II of the rotifer B. rotundiformis. The mRNA expression analysis suggested specific genes CYP3045A2 and GSTσ1, GSTσ4, and GSTω1 take part in detoxification of APAP and OTC, resulting in no significant changes in the population growth and undetermined no observed effect concentration (NOEC) in the marine rotifer B. rotundiformis.

Genome-wide identification of the entire 90 glutathione S-transferase (GST) subfamily genes in four rotifer Brachionus species and transcriptional modulation in response to endocrine disrupting chemicals

Genome-wide identification of glutathione S-transferase (GST), a major phase II detoxification enzyme, was investigated in four different aquatic model rotifer species Brachionus koreanus, B. plicatilis, B. rotundiformis, and B. calyciflorus. GSTs are ubiquitous antioxidant enzymes that play versatile function including cellular detoxification, stress alleviation, and production of the radical conjugates. Among the four rotifers, B. rotundiformis was found with the least number of GST genes (total 19 GST genes), whereas the other three species shared 23 to 24 GST genes. Among the identified GST genes, belonging to the cytosolic GST superfamily, the expansion of GST sigma classes mainly occurs through tandem duplication, resulting in tandem-arrayed gene clusters on the chromosomes. Overall, the number of genes discovered in this study was highest in the sigma class, zeta, alpha, and omega in descending order. With integration of phylogenetic analysis and xenobiotic-mediated GST mRNA expression patterns along with previous enzymatic activities, the functional divergence among species-specific GST genes was clearly observed. This study covers full identification of GST classes in three marine rotifer and one fresh-water rotifer species and their important role in marine environmental ecotoxicology.

Nanoplastic Ingestion Enhances Toxicity of Persistent Organic Pollutants (POPs) in the Monogonont Rotifer Brachionus koreanus via Multixenobiotic Resistance (MXR) Disruption

Among the various materials found inside microplastic pollution, nanosized microplastics are of particular concern due to difficulties in quantification and detection; moreover, they are predicted to be abundant in aquatic environments with stronger toxicity than microsized microplastics. Here, we demonstrated a stronger accumulation of nanosized microbeads in the marine rotifer Brachionus koreanus compared to microsized ones, which was associated with oxidative stress-induced damages on lipid membranes. In addition, multixenobiotic resistance conferred by P-glycoproteins and multidrug resistance proteins, as a first line of membrane defense, was inhibited by nanoplastic pre-exposure, leading to enhanced toxicity of 2,2',4,4'-tetrabromodiphenyl ether and triclosan in B. koreanus. Our study provides a molecular mechanistic insight into the toxicity of nanosized microplastics toward aquatic invertebrates and further implies the significance of synergetic effects of microplastics with other environmental persistent organic pollutants.

Effects of bisphenol A and its analogs bisphenol F and S on life parameters, antioxidant system, and response of defensome in the marine rotifer Brachionus koreanus

To understand the adverse outcome in response to bisphenol A and its analogs bisphenol F and S (BPA, BPF, and BPS), we examined acute toxicity, life parameter, and defensome in the marine rotifer Brachionus koreanus. Among the bisphenol analogs, BPA showed the highest acute toxicity and then BPF and BPS, accordingly in the view of descending magnitude of toxicity. In life parameters including life span and reproduction, BPA, BPF, and BPS were found to cause adverse effect. Both intracellular ROS level and GST activity were significantly increased (P < 0.05) in response to each dosage of bisphenol analogs exposures. In response to bisphenol analogs, defensomes of phase I, II, and III detoxification mechanism demonstrated inverse relationship between the lipophilicity of bisphenol analogs and the expression patterns of defensomes. BPA and BPF were found to have significant modulation (P < 0.05) in the expression of cytochrome P450 (CYP) and GST genes. In phase III, BPS with comparatively lower lipophilicity demonstrated highly diversified expressional pattern, suggesting that BPS is likely caused less toxicity compared to BPA and BPF. In this study, via phase I, II, and III detoxification mechanism, bisphenol A and its analogs F and S demonstrated specific detoxification mechanism in rotifer.