Exogenous Ca2+ mitigates the toxic effects of TiO2 nanoparticles on phagocytosis, cell viability, and apoptosis in haemocytes of a marine bivalve mollusk, Tegillarca granosa

Titanium Dioxide Nanoparticles Negatively Influence Gill Metabolism in Pinctada fucata martensii

BACKGROUND

In recent years, titanium dioxide (TiO2) nanoparticles (NPs) have been widely used in various industries due to their favorable chemical properties, and their contamination of the environment has attracted much attention, especially to aquatic animals.

METHODS

Therefore, we assessed the impact of TiO2 NPs (5 mg/L) on the marine bivalve, pearl oyster (Pinctada fucata martensii), especially gill metabolism. Pearl oysters were exposed to seawater containing 5 mg/L TiO2 NPs for 14 days, followed by 7 days of recovery in untreated seawater. Gill tissues and hepatopancreatic tissues were sampled on days 0, 14, and 21 of the experiment named C0, E14, and R7, respectively.

RESULTS

Metabolomic analysis identified 102 significantly different metabolites (SDMs) on gills tissue in pearl oysters following exposure to TiO2 NPs (C0 vs. E14). Compared with group C0, group E14 had 76 SDMs (such as acetylcholine, itaconic acid, citric acid, and taurine) with higher concentrations and 26 (including L-arginine and isobutyryl-L-carnitine) with lower concentrations. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis showed that these SDMs enriched 28 pathways, including glycine, serine, and threonine metabolism, neuroactive ligand-receptor interaction, and taurine and hypotaurine metabolism. In addition, 116 SDMs were identified in E14 and R7 pearl oysters. Compared with group E14, group R7 had 74 metabolites (such as acetylcholine, 6-phosphogluconic acid, isocitric acid, and itaconic acid) with higher concentrations and 42 (including uracil, glycerophosphocholine, N-Acetyl-D-glucosamine) with lower concentrations. The SDMs identified between E14 and R7 enriched 25 pathways, including the pentose phosphate pathway, glutathione metabolism, and citrate cycle (TCA cycle). In addition, analysis of the energy metabolism-associated enzymes revealed that exposure to TiO2 NPs reduced Ca2+/Mg2+-ATPase, Na+/K+-ATPase, and Total-ATPase activities.

CONCLUSIONS

These findings suggested that TiO2 NPs may inhibit the energy metabolism function of gill and hepatopancreas of pearl oysters. Meanwhile, TiO2 NPs may affect the normal functioning of immune and osmoregulatory functions of pearl oysters gill and even may lead to oxidative stress and neurotoxicity. Therefore, this study may provide a reference for analyzing the bioadaptation of marine bivalves to TiO2 NPs and the potential negative effects of TiO2 NPs on bivalves.

The involvement of CaMKKI in activating AMPKα in yesso scallop Patinopecten yessoensis under high temperature stress

Calcium/calmodulin dependent protein kinase kinase (CaMKK), a highly conserved protein kinase, is involved in the downstream processes of various biological activities by phosphorylating and activating 5'-AMP-activated protein kinase (AMPK) in response to the increase of cytosolic-free calcium (Ca2+). In the present study, a CaMKKI was identified from Yesso scallop Patinopecten yessoensis. Its mRNA was ubiquitously expressed in haemocytes and all tested tissues with the highest expression level in mantle. The expression level of PyCaMKKI mRNA in adductor muscle was significantly upregulated at 1, 3 and 6 h after high temperature treatment (25 °C), which was 3.43-fold (p < 0.05), 5.25-fold (p < 0.05), and 5.70-fold (p < 0.05) of that in blank group, respectively. At 3 h after high temperature treatment (25 °C), the protein level of PyAMPKα, as well as the phosphorylation level of PyAMPKα at Thr170 in adductor muscle, and the positive co-localized fluorescence signals of PyCaMKKI and PyAMPKα in haemocyte all increased significantly (p < 0.05) compared to blank group (18 °C). The pull-down assay showed that rPyCaMKKI and rPyAMPKα could bind each other in vitro. After PyCaMKKI was silenced by siRNA, the mRNA and protein levels of PyCaMKKI and PyAMPKα, and the phosphorylation level of PyAMPKα at Thr170 in adductor muscle were significantly down-regulated (p < 0.05) compared with the negative control group receiving an injection of siRNA-NC. These results collectively suggested that PyCaMKKI was involved in the activation of PyAMPKα in response to high temperature stress and would be helpful for understanding the function of PyCaMKKI-PyAMPKα pathway in maintaining energy homeostasis under high temperature stress in scallops.

Differential toxic effects of nano-titanium dioxide on clams (Meretrix meretrix) with various individuality

Nano-TiO2 is inevitably released into aquatic environment with increasing of nanotechnology industries. Study pointed that different individuality showed divergent behavioral and physiological response when facing environmental stress. However, the effects of nano-TiO2 on tolerance of bivalves with different individualities remain unknown. In the study, clams were divided into two types of individuality - proactive and reactive by post-stress recovery method. It turned out that proactive individuals had quicker shell opening level, stronger burrowing behavior, faster feeding recovery, higher standard metabolic rate and more rapid ammonia excretion ability than reactive individuals after exposed to air. Then, the survival rate, hemocytes response and oxidase activity of classified clams were evaluated after nano-TiO2 exposure. Results showed that after 30 d exposure, proactive individuals accelerated burrowing behavior with higher survival rate. Moreover, proactive clams had better adaptability and less hemocytes response and oxidative damage than reactive clams. The study highlights the individualities of marine shell fish determine individual capacity to adapt to environmental changes, play important roles in aquaculture and coastal ecosystem health.

Novel 3D printed polysaccharide-based materials with prebiotic activity for potential treatment of diaper rash

Diaper rash, mainly occurring as erythema and itching in the diaper area, causes considerable distress to infants and toddlers. Increasing evidence suggests that an unequal distribution of microorganisms on the skin contributes to the development of diaper dermatitis. Probiotic bacteria, like Staphylococcus epidermidis, are crucial for maintaining a healthy balance in the skin's microbiome, among others, through their fermentative metabolites, such as short-chain fatty acids. Using a defined prebiotic as a carbon source (e.g., as part of the diaper formulation) can selectively trigger the fermentation of probiotic bacteria. A proper material choice can reduce diaper rash incidence by diminishing the skin exposure to wetness and faeces. Using 3D printing, we fabricated carbon-rich materials for the top sheet layer of baby diapers that enhance the probiotic activity of S. epidermidis. The developed materials' printability, chemical composition, swelling ability, and degradation rate were analysed. In addition, microbiological tests evaluated their potential as a source of in situ short-chain fatty acid production. Finally, biocompatibility testing with skin cells evaluated their safety for potential use as part of diapers. The results demonstrate a cost-effective approach for producing novel materials that can tailor the ecological balance of the skin microflora and help treat diaper rash.

Titanium dioxide nanoparticles induce apoptosis through ROS-Ca2+-p38/AKT/mTOR pathway in TM4 cells

Titanium dioxide nanoparticles (TiO2 NPs) can cause apoptosis in TM4 cells; however, the underlying mechanism has not been entirely elucidated. The purpose of this study was to investigate the effects of TiO2 NPs on ROS, Ca2+ level, p38/AKT/mTOR pathway, and apoptosis in TM4 cells and to evaluate the role of Ca2+ in p38/AKT/mTOR pathway and apoptosis. After exposure to different concentrations (0, 50, 100, 150, and 200 μg/mL) of TiO2 NPs for 24 h, cell viability, ROS, Ca2+ level, Ca2+-ATPase activity, p38/AKT/mTOR pathway-related proteins, apoptosis rate, and apoptosis-related proteins (Bax, Bcl-2, Caspase 3, Caspase 9, and p53) were detected. The ROS scavenger NAC was used to determine the effect of ROS on Ca2+ level. The Ca2+ chelator BAPTA-AM was used to evaluate the role of Ca2+ in p38/AKT/mTOR pathway and apoptosis. TiO2 NPs significantly inhibited cell viability, increased ROS level, and elevated Ca2+ level while suppressing Ca2+-ATPase activity. TiO2 NPs regulated the p38/AKT/mTOR pathway via increasing p-p38 level and decreasing p-AKT and p-mTOR levels. TiO2 NPs significantly enhanced the apoptosis. NAC attenuated Ca2+ overload and reduction in Ca2+-ATPase activity caused by TiO2 NPs. BAPTA-AM alleviated TiO2 NPs-induced abnormal expression of p38/AKT/mTOR pathway-related proteins. BAPTA-AM assuaged the apoptosis caused by TiO2 NPs. Altogether, this study revealed that TiO2 NPs elevated intracellular Ca2+ level through ROS accumulation. Subsequently, the heightened intracellular Ca2+ level was observed to exert regulation over the p38/AKT/mTOR pathway, ultimately culminating in apoptosis. These results provides a complementary understanding to the mechanism of TiO2 NPs-induced apoptosis in TM4 cells.

Intrinsic and extrinsic pathways of apoptosis induced by multiple antibiotics residues and ocean acidification in hemocytes of scallop Argopecten irradians irradians: An interactionist perspective

The increasing prevalence of antibiotics in seawater across global coastal areas, coupled with the ocean acidification induced by climate change, present a multifaceted challenge to marine ecosystems, particularly impacting the key physiological processes of marine organisms. Apoptosis is a critical adaptive response essential for maintaining cellular homeostasis and defending against environmental threats. In this study, bay scallops Argopecten irradians irradians were exposed to multiple antibiotics (sulfamethoxazole, tetracycline, oxytetracycline, norfloxacin, and erythromycin, each at a concentration of 1 μg/L) combined with/without acidic seawater (pH 7.6) for 35 days. The single and interactive effects of the two stressors on apoptosis and the underlying mechanisms in hemocytes of A. irradians irradians were determined through flow cytometry analysis, comet assay, oxidative stress biomarkers analysis, and transcriptome analysis. Results showed that apoptosis could be triggered by either AM exposure or OA exposure, but through different pathways. Exposure to AM leads to mitochondrial dysfunction and oxidative damage, which in turn triggers apoptosis via a series of cellular events in both intrinsic and extrinsic pathways. Conversely, while OA exposure similarly induced apoptosis, its effects are comparatively subdued and are predominantly mediated through the intrinsic pathway. Additionally, the synergistic effects of AM and OA exposure induced pronounced mitochondrial dysfunction and oxidative damages in the hemocytes of A. irradians irradians. Despite the evident cellular distress and the potential initiation of apoptotic pathways, the actual execution of apoptosis appears to be restrained, which might be attributed to an energy deficit within the hemocytes. Our findings underscore the constrained tolerance capacity of A. irradians irradians when faced with multiple environmental stressors, and shed light on the ecotoxicity of antibiotic pollution in the ocean under prospective climate change scenarios.

Nanomaterials in sunscreens: Potential human and ecological health implications

Inorganic nanomaterials such as TiO2 and ZnO provide significant benefits in terms of UV protection, and their use generally has increased in commercial sunscreens. However, more recently there have been concerns about their potential human and ecological health implications, mostly driven by perception rather than by formal assessments. The large and increasing body of literature on these nanomaterials indicates that in most circumstances their risk are minimal. Penetration of the human epidermis is minimal for these nanomaterials, significantly reducing the potential effects that these nanomaterials may pose to internal organs. The excess Zn ion dose is very small compared to normal dietary consumption of Zn, which is a necessary element. The levels of residual nanomaterials or released ions in public swimming pools is also low, with minimal effect in case this water is ingested during swimming or bathing. In natural environments with significant water flow due to wind and water currents, the concentrations of nanomaterials and released ions are generally well below levels that would cause effects in aquatic organisms. However, sensitive habitats with slow currents, such as coral reefs, may accumulate these nanomaterials. The number of studies of the levels and effects of nanomaterials in these sensitive habitats is very small; more research is needed to determine if there is an elevated risk to these ecosystems from the use of sunscreens with these nanomaterials.

Impact of polyethylene microplastics on the clam Ruditapes decussatus (Mollusca: Bivalvia): examination of filtration rate, growth, and immunomodulation

The present study was conducted to assess, for the first time, the effects of a 14 days experimental exposure to polyethylene (PE) based MPs (40-48 µm) on the clam Ruditapes decussatus. Clams were exposed to three different concentrations of MPs in controlled laboratory conditions: 10 µg/L (low), 100 µg/L (medium), and 1000 µg/L (high). The effects of MPs were assessed using a multi-marker approach, including the filtration rate, growth, and the integrity of immune cells (such as haemocyte numbers, viability, and lysosomal membrane destabilization). The results revealed that as the concentration of PE-MPs increased, the filtration rate decreased, indicating that PE-MPs hindered the clams' ability to filter water. Furthermore, there was a noticeable decrease in the overall weight of the clams, particularly in the group exposed to 1000 µg/L. This decrease could be attributed to the impairment of their nutrient filtration function. In terms of immune system biomarkers, exposure to PE-MPs led to immune system disruption, characterized by a significant increase in the number of haemocytic cells, especially in the group exposed to the high concentration. Additionally, there was a notable reduction in the viability of haemocytes, resulting in the destabilization of their lysosomal membranes, particularly in the groups exposed to medium and high PE-MPs concentrations. The findings of this study indicate that the sensitivity of hemolymph parameter changes and filtration rate in R. decussatus exposed to PE-MPs (100 and 1000 µg/L), surpasses that of growth performance and can serve as reliable indicators to assess habitat conditions and contaminant levels.

Ocean acidification enhances the embryotoxicity of CuO nanoparticles to Oryzias melastigma

Concerns are raised towards individual effects of ocean acidification (OA) and engineered nanoparticles (NPs) on marine organisms. However, there are scarce studies regarding nanotoxicity under OA conditions. We investigated the combined effects of OA (pHs, 7.70 and 7.40) and CuO NPs on the embryotoxicity of marine medaka Oryzias melastigma and the bioavailability of CuO NPs in embryos. The results showed that OA alleviated the aggregation of CuO NPs and promoted the dissolution of CuO NPs in seawater (increased by 0.010 and 0.029 mg/L under pHs 7.70 and 7.40, respectively). Synergistic effects of OA with CuO NPs on medaka embryos were observed as indicated by much higher mortality and oxidative damage. Importantly, the enhanced toxicity of CuO NPs to medaka embryos under OA conditions mainly originated from the higher bioavailability of particulate CuO (e.g., 30.28 mg/kg at pH 7.40) rather than their released Cu²⁺ ions (e.g. 3.04 mg/kg at pH 7.40). The weaker aggregation of NPs under OA conditions resulted in higher penetration of individual particles (or small aggregates) into embryos through the micropyle and chorionic pores, causing enhanced bioavailability of NPs. The obtained results provided underlying insights into understanding the risk of NPs to marine ecosystem under OA conditions.

Characterization of oxidative damage induced by nanoparticles via mechanism-driven machine learning approaches

The wide application of TiO₂-based engineered nanoparticles (nTiO₂) inevitably led to release into aquatic ecosystems. Importantly, increasing studies have emphasized the high risks of nTiO₂ to coastal environments. Bivalves, the representative benthic filter feeders in coastal zones, acted as important roles to assess and monitor the toxic effects of nanoparticles. Oxidative damage was one of the main toxic mechanisms of nTiO₂ on bivalves, but the experimental variables/nanomaterial characteristics were diverse and the toxicity mechanism was complex. Therefore, it was very necessary to develop machine learning model to characterize and predict the potential toxicity. In this study, thirty-six machine learning models were built by nanodescriptors combined with six machine learning algorithms. Among them, random forest (RF) - catalase (CAT), k-neighbors classifier (KNN) - glutathione peroxidase (GPx), neural networks - multilayer perceptron (ANN) - glutathione s-transferase (GST), random forest (RF) - malondialdehyde (MDA), random forest (RF) - reactive oxygen species (ROS), and extreme gradient boosting decision tree (XGB) - superoxide dismutase (SOD) models performed good with high accuracy and balanced accuracy for both training sets and external validation sets. Furthermore, the best model revealed the predominant factors (exposure concentration, exposure periods, and exposure matrix) influencing the oxidative stress induced by nTiO₂. These results showed that high exposure concentrations and short exposure-intervals tended to cause oxidative damage to bivalves. In addition, gills and digestive glands could be vulnerable to nTiO₂-induced oxidative damage as tissues/organs differences were the important factors controlling MDA activity. This study provided insights into important nano-features responsible for the different indicators of oxidative stress and thereby extended the application of machine learning approaches in toxicological assessment for nanoparticles.

Two common nanoparticles exert immunostimulatory and protective effects in Tegillarca granosa against Vibrio parahaemolyticus

There are many studies revealed that metal-based nanoparticles (NPs) possess excellent bactericidal effect on multitudinous bacteria and fungi. However, the control effect of NPs as antimicrobial agents to against Vibrio parahaemolyticus infection remain in poorly understood for blood clam, Tegillarca granosa. In order to evaluate the effect, the changes in six physiological parameters and the immune-related genes expression of clams exposed to V. parahaemolyticus alone or along with NPs (nZnO or nCuO) were investigated in present study. Results showed that both tested NPs exerted prominent redemptive or mitigative effect in an inverse dose-dependent way on physiological indexes of clam, especially in the total counts, phagocytosis and the cell viability of haemocytes, as well as the concentration and activity of lysozymes, when co-exposed with Vibrio. Gene expression analysis showed NPs at a concentration of 0.1 mg/L generally mitigated the downregulation of immune-related genes after clam exposure to V. parahaemolyticus. The combination of 0.1 mg/mL nZnO and nCuO additives has been shown to significantly enhance the humoral immunity of blood clam, suggesting its potential as a protective measure against V. parahaemolyticus infection in T. granosa.

Transcriptome analysis of gene expression profiling from the deep sea in situ to the laboratory for the cold seep mussel Gigantidas haimaensis

Background

The deep-sea mussel Gigantidas haimaensis is a representative species from the Haima cold seep ecosystem in the South China Sea that establishes endosymbiosis with chemotrophic bacteria. During long-term evolution, G. haimaensis has adapted well to the local environment of cold seeps. Until now, adaptive mechanisms responding to environmental stresses have remained poorly understood.

Results

In this study, transcriptomic analysis was performed for muscle tissue of G. haimaensis in the in situ environment (MH) and laboratory environment for 0 h (M0), 3 h (M3) and 9 h (M9), and 187,368 transcript sequences and 22,924 annotated differentially expressed genes (DEGs) were generated. Based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, these DEGs were enriched with a broad spectrum of biological processes and pathways, including those associated with antioxidants, apoptosis, chaperones, immunity and metabolism. Among these significantly enriched pathways, protein processing in the endoplasmic reticulum and metabolism were the most affected metabolic pathways. These results may imply that G. haimaensis struggles to support the life response to environmental change by changing gene expression profiles.

Conclusion

The present study provides a better understanding of the biological responses and survival strategies of the mussel G. haimaensis from deep sea in situ to the laboratory environment.

The effect of ocean warming on accumulation and cellular responsiveness to cobalt in Mytilus galloprovincialis

Cobalt (Co) is among the hazardous substances identified in aquatic environments. Industrialization and population growth have also contributed to climate change, namely in what concerns ocean temperature rise. The aim of the present study was to evaluate the influence of temperature rise on the impacts caused by Co on Mytilus galloprovincialis. To this end, mussels were exposed for 28 days to 17 °C and 21 °C, without and with 200 μg L^-1 of Co. Results showed no significant differences in Co bioaccumulation by the organisms between temperatures. A significant interaction between temperature and Co contamination was observed in terms of oxidative damage, detoxification capacity, and neurotoxicity, with a synergistic effect particularly evident in terms of biotransformation enzymes' activity. The obtained results point out that population survival and distribution may be limited in the long term, highlighting the need for future research on the combined effects of both stressors.

Roles of hemocyte subpopulations in silver nanoparticle transformation and toxicity in the oysters Crassostrea hongkongensis

Hemocytes are the main immune cells in bivalve mollusks and one of the sensitive targets for nanoparticle toxicity. Bivalve hemocytes consist of multiple functional heterogeneous cell types, but their different roles in immune system against foreign particles remain largely unknown. In order to clarify the different immune responses of hemocyte subpopulations to silver nanoparticles (AgNPs) and Ag ions, in this study, the Hong Kong oyster (Crassostrea hongkongensis) hemocytes were employed and separated into three subpopulations based on their cell size and granularity, including agranulocytes (R1), semigranulocytes (R2), and granulocytes (R3). We first demonstrated that AgNPs could rapidly enter into the oyster hemocytes within 3 h by phagocytosis process and resulted in different immune responses in hemocyte subpopulations. The most affected cell subtype by AgNPs was the granulocytes, followed by semigranulocytes, whereas agranulocytes were not affected following exposure to AgNPs. Interestingly, AgNPs induced the granule formation in semigranulocytes and further increased the proportion of granulocytes, whereas their ionic counterparts had no such effects on hemocyte composition, indicating the different detoxification mechanisms for nanoparticulate and ionic form. Following AgNP exposure, the dissolved Ag ions were accumulated in lysosomes and caused lysosomal dysfunction, indicating that lysosomes were the main targets for AgNP toxicity and the dissolved Ag ions were the main contributor of AgNP toxicity. Furthermore, AgNP exposure induced reactive oxygen production and impeded the lysosome function and phagocytosis in granulocytes, with impaired immunity system in oysters. Our study identified the different immune responses of oyster hemocyte subpopulations to AgNPs based on the in vitro short-term exposure assays, which may be applied to rapidly evaluate the ecotoxicological risks of different nanoparticles in aquatic systems.

Influence of Titanium Dioxide Nanoparticles on Human Health and the Environment

Nanotechnology has enabled tremendous breakthroughs in the development of materials and, nowadays, is well established in various economic fields. Among the various nanomaterials, TiO₂ nanoparticles (NPs) occupy a special position, as they are distinguished by their high availability, high photocatalytic activity, and favorable price, which make them useful in the production of paints, plastics, paper, cosmetics, food, furniture, etc. In textiles, TiO₂ NPs are widely used in chemical finishing processes to impart various protective functional properties to the fibers for the production of high-tech textile products with high added value. Such applications contribute to the overall consumption of TiO₂ NPs, which gives rise to reasonable considerations about the impact of TiO₂ NPs on human health and the environment, and debates regarding whether the extent of the benefits gained from the use of TiO₂ NPs justifies the potential risks. In this study, different TiO₂ NPs exposure modes are discussed, and their toxicity mechanisms—evaluated in various in vitro and in vivo studies—are briefly described, considering the molecular interactions with human health and the environment. In addition, in the conclusion of this study, the toxicity and biocompatibility of TiO₂ NPs are discussed, along with relevant risk management strategies.

The toxic impacts of microplastics (MPs) and polycyclic aromatic hydrocarbons (PAHs) on haematic parameters in a marine bivalve species and their potential mechanisms of action

Microplastics (MPs) and polycyclic aromatic hydrocarbons (PAHs) are universally detected in the marine ecosystem and may exert adverse impacts on marine species. Although under realistic pollution scenarios, PAH pollution usually occurs as a mixture of different PAH compounds, the toxic impacts of PAH mixtures on marine organisms remain largely unknown to date, including their interactions with other emergent pollutants such as MPs. In this study, the single and combined toxic impacts of polystyrene MPs and a mixture of PAHs (standard mix of 16 representative PAHs) on haematic parameters were evaluated in the blood clam Tegillarca granosa. Our data demonstrated that blood clams treated with the pollutants examined led to decreased total haemocyte count (THC), changed haematic composition, and inhibited phagocytosis of haemocytes. Further analyses indicated that MPs and a mixture of PAHs may exert toxic impacts on haematic parameters by elevating the intracellular contents of reactive oxygen species (ROS), giving rise to lipid peroxidation (LPO) and DNA damage, reducing the viability of haemocytes, and disrupting important molecular signalling pathways (indicated by significantly altered expressions of key genes). In addition, compared to clams treated with a single type of pollutant, coexposure to MPs and a mixture of PAHs exerted more severe adverse impacts on all the parameters investigated, indicating a significant synergistic effect of MPs and PAHs.

Toxic effects of nano-TiO2 in bivalves-A synthesis of meta-analysis and bibliometric analysis

Since the beginning of the 21st century, the increasing production and application of nano-TiO₂ in consumer products have inevitably led to its release into aquatic systems and therefore caused the exposure of aquatic organisms, resulting in growing environmental concerns. However, the safety of nano-TiO₂ in aquatic environments has not been systematically assessed, especially in coastal and estuary waters where a large number of filter-feeding animals live. Bivalves are considered around the world to be a unique target group for nanoparticle toxicity, and numerous studies have been conducted to test the toxic effects of nano-TiO₂ on bivalves. The aim of this review was to systematically summarize and analyze published data concerning the toxicological effects of nano-TiO₂ in bivalves. In particular, the toxicity of nano-TiO₂ to the antioxidant system and cell physiology was subjected to meta-analysis to reveal the mechanism of the toxicological effects of nano-TiO₂ and the factors affecting its toxicological effects. To reveal the cooperation, hot keywords and co-citations in this field, bibliometric analysis was conducted, and the results showed that the toxicological molecular mechanisms of nano-TiO₂ and the combined effects of nano-TiO₂ and other environmental factors are two major hot spots. Finally, some perspectives and insights were provided in this review for future research on nano-TiO₂ toxicology in bivalves.

Microplastics aggravate the bioaccumulation of three veterinary antibiotics in the thick shell mussel Mytilus coruscus and induce synergistic immunotoxic effects

Marine bivalves living in pollution-prone coastal areas may be simultaneously coexposed to veterinary antibiotic residuals and microplastics (MPs). However, the synergistic effects of these two types of emergent pollutants have not been fully elucidated in mussel species. Therefore, the immunotoxic effects of the three representative antibiotics, oxytetracycline (OTC, 270 ng/L), florfenicol (FLO, 42 ng/L), and sulfamethoxazole (SMX, 140 ng/L), with and without the copresence of polystyrene MPs (0.26 mg/L, dimeter: 500 nm), were investigated in the thick shell mussel. Our data showed that the immunity was significantly hampered by exposure to the pollutants and MP-antibiotic coexposure induced synergistic immunotoxicity. For instance, compared to those treated with antibiotics (OTC, FLO, and SMX) alone, mussels coexposed to antibiotic and MPs had significantly lower phagocytic rate (further decline by approximately 28.80%, 34.21%, and 11.22%, respectively) and total hemocyte count (further reduced by approximately 37.45%, 61.67%, and 46.32%, respectively). Exposure to the pollutants tested also led to inductions in intracellular reactive oxygen species (ROS), decreases in the F-actin cytoskeleton, declines in the cell viability of hemocytes, and downregulation of cytoskeleton- and immune-related genes. In addition, mussels coexposed to antibiotic-MP accumulated significantly greater amounts of antibiotics, which may partially explain the synergic immunotoxic effect detected. Exposure to pollutants tested also led to suppression in the activity of glutathione-S-transferase (GST) and downregulation of detoxification-related genes whereas induction in the level of lipid peroxidation (indicated by MDA content) in gills, which may facilitate the entry whereas constrain the exclusion of antibiotics and therefore result in an elevation in accumulation of antibiotics.

Fine polystyrene microplastics render immune responses more vulnerable to two veterinary antibiotics in a bivalve species

Living in close proximity to the sediment of coastal areas, bivalves may be exposed to veterinary antibiotic residuals and microplastics (MPs) simultaneously. However, the immunotoxic impacts of veterinary antibiotics remain unknown in bivalves, let alone their interactions with MPs. Therefore, the immune responses of two representative veterinary antibiotics, oxytetracycline and florfenicol, was investigated in a bivalve species, the blood clam (Tegillarca granosa). The effects of the copresence of MPs on the immune responses triggered by these antibiotics were also analyzed. Results showed that exposure to antibiotics investigated led to significant alteration in hematic parameters and reduction in lectin content in serum. In addition to inducing ROS production, aggravating lipid peroxidation and DNA damage, and suppressing the hemocyte viability, antibiotic treatments also downregulated the expression of immune- and detoxification-related genes but upregulated apoptosis-related Caspase-3. Furthermore, the toxic impacts of antibiotics were found to be significantly increased by the copresence of MPs.

Modulatory function of calmodulin on phagocytosis and potential regulation mechanisms in the blood clam Tegillarca granosa

Unlike vertebrate species, invertebrates lack antigen-antibody mediated immune response and mainly rely on haemocyte phagocytosis to fight against pathogen infection. Recently, studies conducted in model vertebrates demonstrated that the multifunctional protein calmodulin (CaM) plays an important role in regulating immune responses. However, the intrinsic relation between CaM and phagocytosis process remains poorly understood in invertebrate species such as bivalve mollusks. Therefore, in the present study, the immunomodulatory function of CaM on haemocyte phagocytosis was verified in the blood clam, Tegillarca granosa, using the CaM-specific inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7). Results obtained show that CaM inhibition significantly suppressed the phagocytic activity of haemocytes. In addition, CaM inhibition constrained intracellular Ca²⁺ elevation, hampered actin cytoskeleton assembly, suppressed calcineurin (CaN) activity, and disrupted NF-κB activation in haemocytes upon LPS induction. Furthermore, expression of seven selected genes from the actin cytoskeleton regulation- and immune-related pathways were significantly downregulated whereas those of CaM and CaN from the Ca²⁺-signaling pathway were significantly upregulated by in vitro incubation of haemocytes with W-7. For the first time, the present study demonstrated that CaM play an important role in phagocytosis modulation in bivalve species. In addition, the intracellular Ca²⁺ and downstream Ca²⁺-signaling-, actin cytoskeleton regulation-, and immune-related pathways offer candidate routes through which CaM modulates phagocytosis.

Immunotoxicity and neurotoxicity of bisphenol A and microplastics alone or in combination to a bivalve species, Tegillarca granosa

Though invertebrates are one of the largest groups of animal species in the sea and exhibit robust immune and neural responses that are crucial for their health and survival, the potential immunotoxicity and neurotoxicity of the most produced chemical bisphenol A (BPA), especially in conjunction with microplastics (MPs), still remain poorly understood in marine invertebrate species. Therefore, the impacts of exposure to BPA and MPs alone or in combination on a series of immune and neural biomarkers were investigated in the invertebrate bivalve species blood clam (Tegillarca granosa). Evident immunotoxicity as indicated by alterations in hematic indexes was observed after two weeks of exposure to BPA and MPs at environmentally realistic concentrations. The expression of four immune-related genes from the NFκB signaling pathway was also found to be significantly suppressed by the BPA and MP treatment. In addition, exposure to BPA and MPs led to an increase in the in vivo contents of three key neurotransmitters (GABA, DA, and ACh) but a decrease in the expression of genes encoding modulatory enzymes and receptors for these neurotransmitters, implying the evident neurotoxicity of BPA and MPs to blood clam. Furthermore, the results demonstrated that the toxic impacts exerted by BPA were significantly aggravated by the co-presence of MPs, which may be due to interactions between BPA and MPs as well as those between MPs and clam individuals.

Immunotoxicities of microplastics and sertraline, alone and in combination, to a bivalve species: size-dependent interaction and potential toxication mechanism

Although coexposure to pharmaceuticals and microplastics (MPs) may frequently occur, the synergistic impact of MPs and antidepressants on marine species still remains poorly understood. In this study, the immunotoxicities of polystyrene MPs (diameters 500 nm and 30 μm) and sertraline (Ser), alone and in combination, were investigated in a bivalve mollusk Tegillarca granosa. Results showed that both MPs and Ser significantly suppressed the immune responses of T. granosa. In addition, though the toxic effect of Ser was not affected by microscale MPs, an evident synergistic immuno-toxic effect was observed between Ser and nanoscale MPs, which indicates a size-dependent interaction between the two. To further ascertain the underlying toxication mechanisms, the intracellular content of reactive oxygen species, apoptosis status, ATP content, pyruvate kinase activity, plasma cortisol level, and in vivo concentrations of neurotransmitters and cytochrome P450 1A1 were analysed. A transcriptomic analysis was also performed to reveal global molecular alterations following Ser and/or MPs exposure. The obtained results indicated that the presence of nanoscale MPs may enhance the immunotoxicity of Ser by (i) inducing apoptosis of haemocytes and, hence, reducing the THC; (ii) constraining the energy availability for phagocytosis; and (iii) hampering the detoxification of Ser.

Rethinking Nano-TiO2 Safety: Overview of Toxic Effects in Humans and Aquatic Animals

Titanium dioxide nanoparticles (nano-TiO₂ ) are widely used in consumer products, raising environmental and health concerns. An overview of the toxic effects of nano-TiO₂ on human and environmental health is provided. A meta-analysis is conducted to analyze the toxicity of nano-TiO₂ to the liver, circulatory system, and DNA in humans. To assess the environmental impacts of nano-TiO₂ , aquatic environments that receive high nano-TiO₂ inputs are focused on, and the toxicity of nano-TiO₂ to aquatic organisms is discussed with regard to the present and predicted environmental concentrations. Genotoxicity, damage to membranes, inflammation and oxidative stress emerge as the main mechanisms of nano-TiO₂ toxicity. Furthermore, nano-TiO₂ can bind with free radicals and signal molecules, and interfere with the biochemical reactions on plasmalemma. At the higher organizational level, nano-TiO₂ toxicity is manifested as the negative effects on fitness-related organismal traits including feeding, reproduction and immunity in aquatic organisms. Bibliometric analysis reveals two major research hot spots including the molecular mechanisms of toxicity of nano-TiO₂ and the combined effects of nano-TiO₂ and other environmental factors such as light and pH. The possible measures to reduce the harmful effects of nano-TiO₂ on humans and non-target organisms has emerged as an underexplored topic requiring further investigation.

Environmental transformation of n-TiO2 in the aquatic systems and their ecotoxicity in bivalve mollusks: A systematic review

Over the past decades, titanium dioxide nanoparticles (n-TiO₂) have been extensively used in several industrial applications and the manufacture of novel consumer products. Although strict regulations have been put in place to limit their release into the aquatic environment, these nanoparticles can still be found at elevated levels within the environment, which can result in toxic effects on exposed organisms and has possible implications in term of public health. Bivalve mollusks are a unique and ideal group of shellfish for the study and monitoring the aquatic pollution by n-TiO₂ because of their filter-feeding behaviour and ability to accumulate toxicants in their tissues. In these animals, exposure to n-TiO₂ leads to oxidative stress, immunotoxicity, neurotoxicity, and genotoxicity, as well as behavioral and physiological changes. This review summarizes the uptake, accumulation, and fate of n-TiO₂ in aquatic environments and the possible interactions between n-TiO₂ and other contaminants such as heavy metals and organic pollutants. Moreover, the toxicological impacts and mechanisms of action are discussed for a wide range of bivalve mollusks. This data underlines the pressing need for additional knowledge and future research plans for the development of control strategies to mitigate the release of n-TiO₂ to the aquatic environment to prevent the toxicological impacts on bivalves and protect public health.

Immunotoxicity of petroleum hydrocarbons and microplastics alone or in combination to a bivalve species: Synergic impacts and potential toxication mechanisms

Both the frequent occurrence of accidental petroleum spills and the ubiquitous presence of microplastics (MPs) in the sea may pose severe threats to marine species. However, the immunotoxic impacts of these two types of pollutants and the underlying toxication mechanisms still remain largely unknown in sessile filter-feeding bivalve mollusks. Therefore, the impacts of exposure to petroleum hydrocarbons and MPs alone or in combination on the total count, cell type composition, and phagocytic activity of hemocytes were investigated in the blood clam, Tegillarca granosa. In addition, the intracellular ROS content, cell viability, degree of DNA damage, and expression levels of genes from immune-, apoptosis-, and immunotoxicity-related pathways were analyzed to reveal the potential toxication mechanisms. The results demonstrated that exposure to petroleum hydrocarbons and MPs alone or in combination at environmentally realistic concentrations could exert significant immunotoxic impacts on the blood clam, which may be caused by alterations in a series of physiological and molecular processes. In addition, the immunotoxicity of petroleum hydrocarbons could be significantly aggravated by the copresence of MPs, which suggests that coexposure to these two pollutants deserves closer attention.

Acetylcholine suppresses phagocytosis via binding to muscarinic- and nicotinic-acetylcholine receptors and subsequently interfering Ca2+- and NFκB-signaling pathways in blood clam

Though immunomodulation via cholinergic neurotransmitter acetylcholine (ACh), an important part of neuroendocrine-immune (NEI) regulatory network, has been well established in vertebrate species, the mechanisms remain poorly understood in invertebrates. In the present study, the immunomodulatory effect of ACh on haemocyte phagocytosis was investigated in an invertebrate bivalve species, Tegillarca granosa. Data obtained showed that in vitro ACh incubation suppressed phagocytic activity of haemocytes along with a significant elevation in intracellular Ca²⁺. In addition, the expressions of genes from Ca²⁺ signaling pathway were significantly induced whereas those from NF-κB signaling pathway were significantly down-regulated by ACh incubation. Furthermore, these adverse impacts of ACh were significantly relieved by the blocking of muscarinic acetylcholine receptors (mAChRs) or nicotinic acetylcholine receptors (nAChRs) using corresponding antagonists. Our study suggests that ACh suppresses phagocytosis via binding to both mAChRs and nAChRs, which disrupts intracellular Ca²⁺ homeostasis and subsequently interferes with downstream Ca²⁺ and NF-κB signaling pathways.

Specific dynamic action of mussels exposed to TiO2 nanoparticles and seawater acidification

Both nanoparticles (NPs) and ocean acidification (OA) pose threats to marine animals as well as marine ecosystems. The present study aims to evaluate the combined effects of NPs and OA on specific dynamic action (SDA) of mussels. The thick shell mussels Mytilus coruscus were exposed to two levels of pH (7.3 and 8.1) and three concentrations of TiO₂ NPs (0, 2.5, and 10 mg L^-1) for 14 days followed by a 7-day recovery period. The SDA parameters, including standard metabolic rate, peak metabolic rate, aerobic metabolic scope, SDA slope, time to peak, SDA duration and SDA, were measured. The results showed that TiO₂ NPs and low pH significantly affected all parameters throughout the experiment. When the mussels were exposed to seawater acidification or TiO₂ NPs conditions, standard metabolic rate, aerobic metabolic scope, SDA slope and SDA significantly decreased, whereas peak metabolic rate, time to peak and SDA duration significantly increased. In addition, interactive effects between TiO₂ NPs and pH were observed in SDA parameters except time to peak and SDA. Therefore, the synergistic effect of TiO₂ NPs and low pH can adversely affect the feeding metabolism of mussels.