Aging and retinoid X receptor agonists on masculinization of female Pomacea canaliculata, with a critical appraisal of imposex evaluation in the Ampullariidae

Transcriptomic analysis reveals the endocrine toxicity of tributyltin and triphenyltin on the whelk Reishia clavigera and mechanisms of imposex formation

Organotin compounds (OTs) are endocrine disruptors that induce imposex in hundreds of gastropods, but little is known about their underlying molecular mechanisms. This study aimed to investigate the endocrine toxicity and molecular responses to tributyltin (TBT) and triphenyltin (TPT) exposure in the whelk Reishia clavigera, which often serves as a biomonitor for OT contamination. Over a 120-day exposure to environmentally relevant concentrations of TBT (1000 ng L-1) and TPT (500 ng L-1), we observed a significant increase in penis length in both male and female whelks. Notably, TPT exhibited a stronger potency in inducing pseudo-penis development and female sterility, even at a half dose of TBT. Bioaccumulation analysis also revealed higher persistence and accumulation of TPT in whelk tissues compared to TBT. Differential expression analysis identified a substantial number of differentially expressed genes (DEGs), with TPT exposure eliciting more DEGs than TBT. Our results demonstrated that OTs induced xenobiotic metabolism and metabolic dysregulation in the digestive gland, impaired multiple cellular functions and triggered neurotoxicity in the nervous system, and disrupted lipid homeostasis and oxidative stress in the gonads. Furthermore, imposex was possibly associated with disturbances in retinoic acid metabolism, nuclear receptor signaling, and neuropeptide activity. When compared to TBT, TPT exhibited a more pronounced endocrine-disrupting effect, attributable to its higher bioaccumulation and substantial interruption of transcriptional regulation, OT detoxification, and biosynthesis of retinoic acids in R. clavigera. Our results, therefore, highlight the importance of considering the differences in bioaccumulation and molecular toxicity between TBT and TPT in future risk assessments of these contaminants. Overall, our study provided molecular insights into the toxicity and transcriptome profiles in R. clavigera exposed to TBT and TPT, shedding light on the endocrine-disrupting effects and reproductive impairment in female gastropods.

The organotin triphenyltin disrupts cholesterol signaling in mammalian ovarian steroidogenic cells through a combination of LXR and RXR modulation

Organotins, a chemical family with over 30 congeners to which humans are directly exposed to through food consumption, are a chemical class widely used as stabilizers in polyvinyl chloride, and biocides in antifouling products. Aside from tributyltin (TBT), toxicological information on other organotin congeners, such as triphenyltin (TPT), remains scarce. Our previous work has demonstrated that TBT can interfere with cholesterol trafficking in steroidogenic cells. Given their structural similarities, we hypothesized that TPT, similar to TBT, disrupts intracellular cholesterol transport and impairs steroidogenesis in ovarian theca cells. To test this, human and ovine primary ovarian theca cells were isolated, purified and exposed to TPT at environmentally relevant doses (1 or 10 ng/ml) in pre-luteinized (48 h exposure) or luteinizing cells (72 h exposure). Intracellular cholesterol levels, progesterone, and testosterone secretion and gene expression of nuclear receptors, cholesterol transporters, and steroidogenic enzymes were evaluated. In ovine cells, TPT upregulated StAR, ABCA1, and SREBF1 mRNA and ABCA1 protein in both pre-luteinized and luteinized stages. TPT did not alter intracellular cholesterol or testosterone synthesis, but upregulated progesterone production. Inhibitor and shRNA knockdown approaches were then used to evaluate the role of retinoid X receptor (RXR) and liver X receptor (LXR) on TPT's effects. TPT upregulated ABCA1 and StAR expression was blocked by both LXR and RXR antagonists. TPT's effect on ABCA1 expression was reduced in LXRβ and RXRβ knockdown theca cells. Similar findings were obtained with primary human theca cells. No synergistic effect of TBT and TPT was observed. In conclusion, at an environmentally relevant dose, TPT upregulates theca cell cholesterol transporter ABCA1 expression via RXR and LXR pathways. Similar effects of TPT on human and sheep theca cells supports its conserved mechanism across mammalian theca cells.

The ecotoxicology of marine tributyltin (TBT) hotspots: A review

Tributyltin (TBT) was widely used as a highly efficient biocide in antifouling paints for ship and boat hulls. Eventually, TBT containing paints became globally banned when TBT was found to cause widespread contamination and non-target adverse effects in sensitive species, with induced pseudohermaphroditism in female neogastropods (imposex) being the best-known example. In this review, we address the history and the status of knowledge regarding TBT pollution and marine TBT hotspots, with a special emphasis on the Norwegian coastline. The review also presents a brief update on knowledge of TBT toxicity in various marine species and humans, highlighting the current understanding of toxicity mechanisms relevant for causing endocrine disruption in marine species. Despite observations of reduced TBT sediment concentrations in many marine sediments over the recent decades, contaminant hotspots are still prevalent worldwide. Consequently, efforts to monitor TBT levels and assessment of potential effects in sentinel species being potentially susceptible to TBT in these locations are still highly warranted.

A nuclear receptor heterodimer, CgPPAR2-CgRXR, acts as a regulator of carotenoid metabolism in Crassostrea gigas

Nuclear receptors (NRs) are mostly ligand-activated transcription factors in animals and play essential roles in metabolism and homeostasis. The NR heterodimer composed of PPAR/RXR (peroxisome proliferator-activated receptor/retinoid X receptor) is considered a key regulator of lipid metabolism in vertebrate. However, in molluscs, how this heterodimer is involved in carotenoid metabolism remains unclear. To elucidate how this heterodimer regulates carotenoid metabolism, we identified a PPAR gene in C. gigas, designated as CgPPAR2 (LOC105323212), and functionally characterized it using two-hybrid and reporter systems. CgPPAR2 is a direct orthologue of vertebrate PPARs and the second PPAR gene identified in C. gigas genome in addition to CgPPAR1 (LOC105317849). The results demonstrated that CgPPAR2 protein can form heterodimer with C. gigas RXR (CgRXR), and then regulate carotenoid metabolism by controlling carotenoid cleavage oxygenases with different carotenoid cleavage efficiencies. This regulation can be affected by retinoid ligands, i.e., carotenoid derivatives, validating a negative feedback regulation mechanism of carotenoid cleavage for retinoid production. Besides, organotins may disrupt this regulatory process through the mediation of CgPPAR2/CgRXR heterodimer. This is the first report of PPAR/RXR heterodimer regulating carotenoid metabolism in mollusks, contributing to a better understanding of the evolution and conservation of this nuclear receptor heterodimer.

iTRAQ-derived quantitative proteomics uncovers the neuroprotective property of bexarotene in a mice model of cerebral ischemia-reperfusion injury

Bexarotene, a FDA-approved drug for cutaneous lymphoma, has been shown to exert brain protective effects. In previous study, we demonstrated that Bexarotene protects against cerebral ischemic stroke by suppressing the JNK/Caspase-3 signaling pathway. However, the molecular mechanisms by which Bexarotene-mediated neuroprotective are not fully understood. Based on the isobaric tags for relative and absolute quantification (iTRAQ)-derived proteomics and bioinformatics analysis, 4,454 differentially expressed proteins (DEPs) were identified in upstream of the JNK signaling pathway. Among them, 149 DEPs showed aberrant expression in the vehicle-versus Bexarotene-treated mice. DEPs were primarily enriched in the metabolism, calcium, and MAPK signaling pathways. The largest DEP increase was seen with heat shock protein HSP 70, whereas the largest DEP decrease was seen with JNK scaffold protein JIP3, both of which are involved in the MAPK network. Furthermore, we illustrated the Bexarotene obviously abolished oxygen and glucose deprivation/reperfusion (OGD/R)- induced LDH leakage, cells apoptosis, and the protein expression level of the JIP3,p-ASK1, p-JNK, and Cleaved Caspase3. Together, these results suggest a potential neuroprotective role of Bexarotene via inhibition of the JIP3/ASK1/JNK/Caspase 3 signaling pathway.

Modified, optimized method of determination of Tributyltin (TBT) contamination in coastal water, sediment and biota in Sri Lanka

Tributyltin (TBT) is a toxic organotin compound that belongs to the group of Persistent Organic Pollutants (POPs) and it is documented to cause severe sexual disorders development in aquatic fauna. According to the present study, The TBT concentration in coastal water ranged from 303 ± 7.4 ngL^-1 to 25 ± 4.2 ngL^-1 wherein sediment was from 107 ± 4.1 ngKg^-1 to 17 ± 1.4 ngKg^-1. TBT in Perna viridis was found to range from 4 ± 1.2 ngKg^-1 to 42 ± 2.2 ngKg^-1 wet weight and in ascending order of the body weight. The highest TBT level in water and sediment was found in the Colombo port where the highest level of TBT in P. viridis (42 ± 2.2 ngKg^-1) was recorded from the Dikkowita fishery harbor. A positive correlation between the number of male P. viridis and TBT level (p < 0.05) suggests possible reproductive impairment in aquatic animals exposed continuously to a high concentration of TBT.

RXR Expression in Marine Gastropods with Different Sensitivity to Imposex Development

The superposition of male sexual characteristics in female marine gastropods (imposex) represents one of the clearest ecological examples of organotin-mediated endocrine disruption. Recent evidences suggest that signaling pathways mediated by members of the nuclear receptor superfamily, RXR and PPARγ, are involved in the development of this pseudohermaphroditic condition. Here, we identified significant differences in RXR expression in two caenogastropod species from Nuevo Gulf, Argentina, Buccinanops globulosus and Trophon geversianus, which present clear contrast in imposex incidence. In addition, B. globulosus males from a polluted and an unpolluted area showed differences in RXR expression. Conversely, PPARγ levels were similar between both analyzed species. These findings indicate specie-specific RXR and PPARγ expression, suggesting a major role of RXR in the induction of imposex.

Current understanding of potential ecological risks of retinoic acids and their metabolites in aquatic environments

In animals, retinoic acids (RAs), one of the main derivatives of vitamin A, are crucial for a variety of physiological processes. RAs, including all-trans-RA, 9-cis-RA, 13-cis-RA, and their corresponding metabolites (i.e., all-trans-4-oxo-RA, 9-cis-4-oxo-RA and 13-cis-4-oxo-RA) can be excreted through urination from humans and animals. Sewage treatment plants (STPs) are a significant source of RAs and 4-oxo-RAs into aquatic environments. RAs and 4-oxo-RAs can be identified and quantified by use of liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). RAs and 4-oxo-RAs have been reported in various environmental matrices including rivers, lakes, reservoirs and coastal marine environments as well as in sewage effluents discharged from STPs. Greater concentrations of RAs and 4-oxo-RAs have been observed during blooms of cyanobacteria and microalgae, suggesting that cyanobacteria and microalgae are natural sources of RAs and 4-oxo-RAs in aquatic environments. These potential sources of RAs and 4-oxo-RAs raise concerns about their concentrations and risks in aquatic environments because excessive intake of these chemicals can result in abnormal morphological development in animals. Teratogenic effects were observed in amphibians, fish embryos, gastropods, mammals and birds when exposed to RAs. This review summarizes sources, concentrations, adverse effects and ecological risks of RAs and 4-oxo-RAs in aquatic environments. An interim, predicted no-effect concentration (PNEC) of RAs (in terms of at-RA) for freshwater environments was determined to be 3.93 ng/L at-RA equivalents. Based on limited data on concentrations of RAs in freshwater ecosystems, their hazard quotients were found to range from zero to 16.41, depending on the environmental conditions of receiving waters. Ecological risks of RAs in marine environments are yet to be explored due to the paucity of data related to both their concentrations in marine environment and toxic potencies to marine species. This review updates current knowledge of RAs and 4-oxo-RAs in aquatic environments and calls for more studies on their concentrations and fate in aquatic environments, especially estuarine and coastal marine environments with a view to enabling a comprehensive assessment of their ecological risks around the globe.