Embryotoxicity characterization of the flame retardant tris(1-chloro-2-propyl)phosphate (TCPP) in the invertebrate chordate Ciona intestinalis

Tris(2-chloroisopropyl) phosphate (TCPP) decreases CYP1A1, CYP1A2, and CYP1B1/CYP2B expression and activities through potential interactions between AhR and NRF2 pathways in the HepG2 cell line

Tris(2-chloropropyl) phosphate (TCPP) is a flame retardant used in various products. Since it is not chemically bound to polymers, it easily migrates into the environment and has been detected in water, soil, and air. Additionally, TCPP can bioaccumulate in living organisms. Although suspected to be a carcinogen and endocrine disruptor, its cytotoxic properties and potential carcinogenic mechanisms remain largely unknown. This study aimed to elucidate the effects of TCPP on the HepG2 cell line, particularly its impact on CYP enzyme expression and activity. Cells were exposed to increasing TCPP concentrations (1 nM-100 μM) for 24 and 48 h. Our results show that TCPP, at any tested concentration, did not affect lactate dehydrogenase release or resazurin reduction. However, at 50 and 100 μM, it increased reactive oxygen species production. Moreover, after 48 h, TCPP (100 nM-100 μM) enhanced caspase-3 activity. This is the first study suggesting that, despite probable aryl hydrocarbon receptor (AhR) pathway activation, TCPP (1-10 μM) decreases CYP1A1, CYP1A2, and CYP1B1/CYP2B expression and activity in HepG2 cells after 48 h. Given the crucial role of CYP enzymes in detoxification, their inhibition may have serious health implications. AhR, PPARγ, and CYP enzymes regulate fatty acid, steroid hormone, vitamin, and melatonin synthesis. Our findings also indicate that TCPP increases lipid accumulation in HepG2 cells, likely due to CYP disruption. Therefore, TCPP may function as an endocrine disruptor.

Ecotoxicological responses of marine fish to the organophosphate flame-retardant tris (2-chloroisopropyl) phosphate (TCPP) dietary exposure: Juvenile gilthead seabream (Sparus aurata) as a case study

High Production Volume Chemicals (HPVCs) are contaminants that pose serious threats to aquatic environments and species that inhabit them, given their massive production and ubiquitous distribution across biological compartments. Among them, organophosphate esters (OPEs) are of particular concern, as they are widely used as plasticizers and flame-retardants, and linked to various forms of toxicity in marine organisms. In this study, we investigated the ecotoxicological response of juvenile gilthead seabream Sparus aurata to the OPE tris (2-chloroisopropyl) phosphate (TCPP) following chronic dietary exposure to three different concentrations (low, D1: 0.2 mg kg-1; ecologically relevant, D2: 2 mg kg-1; and high, D3: 10 mg kg-1). Different biomarkers indicative of antioxidant defence mechanisms (catalase, CAT, glutathione S-transferase, GST, activities), metabolism (citrate synthase, CS, lactate dehydrogenase, LDH, activities) and endocrine disruption (vitellogenin content, VTG), as well as cell (lipid peroxidation levels, LPO) and protein damage (ubiquitin content, UBI) were analyzed in liver and muscle to assess TCPP toxicity. High concentrations of TCPP affected S. aurata growth, but not overall fitness condition. Furthermore, metabolic disruption and severe oxidative damages were observed, regardless of exposure dose. VTG content significantly decreased after exposure to all TCPP dosages, indicating a possible masculinization effect. These findings provide new insights to the scientific knowledge on TCPP ecotoxicological attributes and impacts on marine ichthyofauna. In addition, our results confirm the relevance of conducting integrated multi-biomarker approaches to disclose the ecotoxicological effects of poorly studied chemical contaminants and, ultimately, implement wastewater treatment strategies and legislation to protect marine ecosystems from pollution.

Toxicity of organophosphate flame retardant in marine rotifers: Evidence from the population, individual, biochemical and molecular levels

Tris (1-chloro-2-propyl) phosphoric acid (TCPP), a widely used organophosphate flame retardant, has been detected in various aquatic environments due to its extensive industrial application. TCPP is well-known to negatively impact large aquatic organisms. However, the effects of TCPP on zooplankton remain poorly understood. This study explored the ecological risk of TCPP in low-trophic marine organisms by evaluating the marine rotifer Brachionus plicatilis at the molecular, biochemical, individual, and population levels after exposure to TCPP concentrations of 14.79, 44.37, and 73.94 μM. Results showed that exposure to TCPP inhibited body size, feeding behavior, life expectancy, generation time, net reproductive rate, reproduction rate, and population growth rate of rotifers, thus impairing their growth, survival, reproduction, and population expansion. Environmental concentrations surpassing 0.031 μM and 0.23 μM adversely impact rotifer reproduction and survival, respectively. Biochemically, TCPP induced oxidative stress, increased amylase activity, decreased lipase activity, and total protein content. Transcriptome analysis revealed that TCPP could induce abnormal mitochondrial function, impaired energy metabolism, programmed cell death by generating excessive reactive oxygen species, and affect cellular DNA replication. Results indicate that TCPP disrupts homeostasis in rotifers by inducing oxidative stress, significantly suppressing individual and population parameters. These findings provide critical insights for assessing the ecological risk posed by TCPP to zooplankton and the stability of aquatic ecosystems.

A tiered toxicity testing strategy for assessing early life stage toxicity in estuarine fish (Mugilogobius chulae): A case study on tris (1-chloro-2-propyl) phosphate ester

The estuarine ecological environment faces significant threats from contaminants of emerging concern (CECs); yet, the risk posed by CECs to resident organisms remains poorly understood. Here, we employed tiered toxicity testing to investigate the adverse effects and potential mechanisms of tris (1-chloro-2-propyl) phosphate (TCPP) on the early life stages of an estuarine fish, Mugilogobius chulae. TCPP affected the development of M. chulae embryos, including survival, morphology, hatching, and behavior. A concentration-dependent transcriptomic analysis showed that TCPP disrupted 12 neurodevelopment-related KEGG pathways in M. chulae embryos, with five of the 30 % top-ranked pathways related to neurotransmitter signaling. Besides the cholinergic synapse signaling pathway, the glutamatergic signaling pathway (including NMDAR and AMPAR subtypes) may also mediate TCPP-induced neurodevelopmental toxicity. The NMDAR subtype GRIN2B was downregulated at high concentrations. Molecular dynamics simulations revealed a strong interaction between TCPP and GRIN2B, with TCPP binding to the residues Ile153 and Ile188. The results suggest that NMDARs play a crucial role in TCPP-induced neurodevelopmental toxicity toward M. chulae. AOP network analysis predicted that TCPP may impact cognitive functions and memory. Our study provides a novel testing strategy for identifying the mechanisms of toxicity of CECs, a crucial component of ecological risk assessment.

Integrated biomarker-based ecological risks assessment of tadpole responses to tris(2-chloroethyl) phosphate, tris(1-chloro-2-propyl) phosphate, and their combined environmental exposure

Tris(2-chloroethyl) phosphate (TCEP) and tris(1-chloro-2-propyl) phosphate (TCPP) are common chlorinated organophosphorus flame retardants (OPFRs) used in industry. They have been frequently detected together in aquatic environments and associated with various hazardous effects. However, the ecological risks of prolonged exposure to these OPFRs at environmentally relevant concentrations in non-model aquatic organisms remain unexplored. This study investigated the effects of long-term exposure (up to 25 days) to TCEP and TCPP on metamorphosis, hepatic antioxidants, and endocrine function in Polypedates megacephalus tadpoles. Exposure concentrations were set at 3, 30, and 90 μg/L for each substance, conducted independently and in equal-concentration combinations, with a control group included for comparison. The integrated biomarker response (IBR) method developed an optimal linear model for predicting the overall ecological risks of TCEP and TCPP to tadpoles in potential distribution areas of Polypedates species. Results showed that: (1) Exposure to environmentally relevant concentrations of TCEP and TCPP elicited variable adverse effects on tadpole metamorphosis time, hepatic antioxidant enzyme activity and related gene expression, and endocrine-related gene expression, with their combined exposure exacerbating these effects. (2) The IBR value of TCEP was consistently greater than that of TCPP at each concentration, with an additive effect observed under their combined exposure. (3) The ecological risk of tadpoles exposed to the combined presence of TCEP and TCPP was highest in China's Taihu Lake and Vietnam's Hanoi than in other distribution locations. In summary, prolonged exposure to environmentally relevant concentrations of TCEP and TCPP presents potential ecological risks to amphibian tadpoles, offering insights for the development of policies and strategies to control TCEP and TCPP pollution in aquatic ecosystems. Furthermore, the methodology employed in establishing the IBR prediction model provides a methodological framework for assessing the overall ecological risks of multiple OPFRs.

Stress granule-related genes during embryogenesis of an invertebrate chordate

Controlling global protein synthesis through the assembly of stress granules represents a strategy adopted by eukaryotic cells to face various stress conditions. TIA 1-related nucleolysin (TIAR), tristetraprolin (TTP), and Ras-GTPase-activating protein SH3-domain-binding protein (G3BP) are key components of stress granules, allowing the regulation of mRNA stability, and thus controlling not only stress responses but also cell proliferation and differentiation. In this study, we aimed at investigating the roles of tiar, ttp, and g3bp during embryogenesis of the solitary ascidian Ciona robusta under both physiological and stress conditions. We carried out CRISPR/Cas9 to evaluate the effects of gene knockout on normal embryonic development, and gene reporter assay to study the time and tissue specificity of gene transcription, together with whole-mount in situ hybridization and quantitative real time PCR. To induce acute stress conditions, we used iron and cadmium as "essential" and "non-essential" metals, respectively. Our results highlight, for the first time, the importance of tiar, ttp, and g3bp in controlling the development of mesendodermal tissue derivatives during embryogenesis of an invertebrate chordate.

A feather star is born: embryonic development and nervous system organization in the crinoid Antedon mediterranea

Crinoids belong to the Echinodermata, marine invertebrates with a highly derived adult pentaradial body plan. As the sister group to all other extant echinoderms, crinoids occupy a key phylogenetic position to explore the evolutionary history of the whole phylum. However, their development remains understudied compared with that of other echinoderms. Therefore, the aim here was to establish the Mediterranean feather star (Antedon mediterranea) as an experimental system for developmental biology. We first set up a method for culturing embryos in vitro and defined a standardized staging system for this species. We then optimized protocols to characterize the morphological and molecular development of the main structures of the feather star body plan. Focusing on the nervous system, we showed that the larval apical organ includes serotonergic, GABAergic and glutamatergic neurons, which develop within a conserved anterior molecular signature. We described the composition of the early post-metamorphic nervous system and revealed that it has an anterior signature. These results further our knowledge on crinoid development and provide new techniques to investigate feather star embryogenesis. This will pave the way for the inclusion of crinoids in comparative studies addressing the origin of the echinoderm body plan and the evolutionary diversification of deuterostomes.

Bisphenol A affects the development and the onset of photosymbiosis in the acoel Symsagittiferaroscoffensis

Photosymbiosis indicates a long-term association between animals and photosynthetic organisms. It has been mainly investigated in photosymbiotic cnidarians, while other photosymbiotic associations have been largely neglected. The acoel Symsagittifera roscoffensis lives in obligatory symbiosis with the microalgal Tetraselmis convolutae and has recently emerged as alternative model to study photosymbiosis. Here, we investigated the effects of Bisphenol A, a common plastic additive, on two pivotal stages of its lifecycle: aposymbiotic juvenile development and photosymbiogenesis. Based on our results, this pollutant altered the development of the worms and their capacity to engulf algae from the environment at concentrations higher than the levels detected in seawater, yet aligning with those documented in sediments of populated areas. Data provide novel information about the effects of pollutants on photosymbiotic associations and prompt the necessity to monitor their concentrations in marine environmental matrices.

Ciona spp. and ascidians as bioindicator organisms for evaluating effects of endocrine disrupting chemicals: A discussion paper

In context of testing, screening and monitoring of endocrine-disrupting (ED) type of environmental pollutants, tunicates could possibly represent a particularly interesting group of bioindicator organisms. These primitive chordates are already important model organisms within developmental and genomics research due to their central position in evolution and close relationship to vertebrates. The solitary ascidians, such as the genus Ciona spp. (vase tunicates), could possibly be extra feasible as ED bioindicators. They have a free-swimming, tadpole-like larval stage that develops extremely quickly (<20 h under favorable conditions), has a short life cycle (typically 2-3 months), are relatively easy to maintain in laboratory culture, have fully sequenced genomes, and transgenic embryos with 3D course data of the embryo ontogeny are available. In this article, we discuss possible roles of Ciona spp. (and other solitary ascidians) as ecotoxicological bioindicator organisms in general but perhaps especially for effect studies of contaminants with presumed endocrine disrupting modes of action.

Serotonin Receptors and Their Involvement in Melanization of Sensory Cells in Ciona intestinalis

Serotonin (5-hydroxytryptamine (5-HT)) is a biogenic monoamine with pleiotropic functions. It exerts its roles by binding to specific 5-HT receptors (5HTRs) classified into different families and subtypes. Homologs of 5HTRs are widely present in invertebrates, but their expression and pharmacological characterization have been scarcely investigated. In particular, 5-HT has been localized in many tunicate species but only a few studies have investigated its physiological functions. Tunicates, including ascidians, are the sister group of vertebrates, and data about the role of 5-HTRs in these organisms are thus important for understanding 5-HT evolution among animals. In the present study, we identified and described 5HTRs in the ascidian Ciona intestinalis. During development, they showed broad expression patterns that appeared consistent with those reported in other species. Then, we investigated 5-HT roles in ascidian embryogenesis exposing C. intestinalis embryos to WAY-100635, an antagonist of the 5HT1A receptor, and explored the affected pathways in neural development and melanogenesis. Our results contribute to unraveling the multifaceted functions of 5-HT, revealing its involvement in sensory cell differentiation in ascidians.

Genotoxic and Toxic Effects of The Flame Retardant Tris(Chloropropyl) Phosphate (TCPP) in Human Lymphocytes, Microalgae and Bacteria

Tris(chloropropyl) phosphate (TCPP) is a characteristic and widely used organophosphorus flame retardant. TCPP is comprised of four isomers and the most abundant is tris(1-chloro-2-propyl) phosphate. TCPP can be released into the environment, with potential impacts on living organisms and humans due to its extensive industrial use. Aiming to assess the potential risks of TCPP on human health and the environment, its toxic and genotoxic effects-using organisms from different trophic levels, i.e., bacteria, green microalgae, and human cells-were investigated. TCPP exposure at nominal concentrations of 10, 20, 30 and 40 μg mL^-1 was studied to identify the potential risk of inducing genotoxic effects in cultured human lymphocytes. Treatment with 30 and 40 μg mL^-1 of TCPP induced marginally significant micronuclei (MN) frequencies as well as cytotoxic effects. Freshwater microalgae species treated with TCPP (0.5, 1, 10, 20 and 50 μg L^-1) showed different growth rates over time. All the tested microalgae species were adversely affected after exposure to TCPP during the first 24 h. However, differences among the microalgae species' sensitivities were observed. In the case of the freshwater species, the most sensitive was found to be Chlorococcum sp. The marine algal species Dunaliella tertiolecta and Tisochrysis lutea were significantly affected after exposure to TCPP. The effects of TCPP on Aliivibrio fischeri that were observed can classify this flame retardant as a "harmful" compound. Our results suggest a potential risk to aquatic organisms and humans from the wide utilization of TCPP and its consequent release into the environment. These results highlight that further research should be conducted to investigate the effects of TCPP individually and in combination with other organophosphorus flame retardants in various organisms. In addition, the concern induced by TCPP points out that measures to control the introduction of TCPP into the environment should be taken.

Morphological Study and 3D Reconstruction of the Larva of the Ascidian Halocynthia roretzi

The swimming larva represents the dispersal phase of ascidians, marine invertebrates belonging to tunicates. Due to its adhesive papillae, the larva searches the substrate, adheres to it, and undergoes metamorphosis, thereby becoming a sessile filter feeding animal. The larva anatomy has been described in detail in a few species, revealing a different degree of adult structure differentiation, called adultation. In the solitary ascidian Halocynthia roretzi, a species reared for commercial purposes, embryogenesis has been described in detail, but information on the larval anatomy is still lacking. Here, we describe it using a comparative approach, utilizing 3D reconstruction, as well as histological/TEM observations, with attention to its papillae. The larva is comparable to those of other solitary ascidians, such as Ciona intestinalis. However, it displays a higher level of adultation for the presence of the atrium, opened outside by means of the atrial siphon, and the peribranchial chambers. It does not reach the level of complexity of the larva of Botryllus schlosseri, a phylogenetically close colonial ascidian. Our study reveals that the papillae of H. roretzi, previously described as simple and conform, exhibit dynamic changes during settlement. This opens up new considerations on papillae morphology and evolution and deserves to be further investigated.