Evaluation of Lipids and Lipid-Related Transcripts in Human and Ovine Theca Cells and an in Vitro Mouse Model Exposed to the Obesogen Chemical Tributyltin

BACKGROUND

Exposure to obesogenic chemicals has been reported to result in enhanced adipogenesis, higher adipose tissue accumulation, and reduced ovarian hormonal synthesis and follicular function. We have reported that organotins [tributyltin (TBT) and triphenyltin (TPT)] dysregulate cholesterol trafficking in ovarian theca cells, but, whether organotins also exert lipogenic effects on ovarian cells remains unexplored.

OBJECTIVE

We investigated if environmentally relevant exposures to organotins [TBT, TPT, or dibutyltin (DBT)] induce lipid dysregulation in ovarian theca cells and the role of the liver X receptor (LXR) in this effect. We also tested the effect of TBT on oocyte maturation and neutral lipid accumulation, and lipid-related transcript expression in cumulus cells and preimplantation embryos.

METHODS

Primary theca cell cultures derived from human and ovine ovaries were exposed to TBT, TPT, or DBT (1, 10, or 50   ng / ml ). The effect of these chemical exposures on neutral lipid accumulation, lipid abundance and composition, lipid homeostasis-related gene expression, and cytokine secretion was evaluated using liquid chromatography-mass spectrometry (LC-MS), inhibitor-based methods, cytokine secretion, and lipid ontology analyses. We also exposed murine cumulus-oocyte complexes to TBT and evaluated oocyte maturation, embryo development, and lipid homeostasis-related mRNA expression in cumulus cells and blastocysts.

RESULTS

Exposure to TBT resulted in higher intracellular neutral lipids in human and ovine primary theca cells. In ovine theca cells, this effect was dose-dependent, independent of cell stage, and partially mediated by LXR. DBT and TPT resulted in higher intracellular neutral lipids but to a lesser extent in comparison with TBT. More than 140 lipids and 9 cytokines were dysregulated in TBT-exposed human theca cells. Expression of genes involved in lipogenesis and fatty acid synthesis were higher in theca cells, as well as in cumulus cells and blastocysts exposed to TBT. However, TBT did not impact the rates of oocyte maturation or blastocyst development.

DISCUSSION

TBT induced dyslipidemia in primary human and ovine theca cells, which may be responsible for some of the TBT-induced fertility dysregulations reported in rodent models of TBT exposure. https://doi.org/10.1289/EHP13955.

Low-dose tributyltin triggers human chondrocyte senescence and mouse articular cartilage aging

Tributyltin (TBT) is known as an endocrine-disrupting chemical. This study investigated the effects and possible mechanisms of TBT exposure on inducing human articular chondrocyte senescence in vitro at the human-relevant concentrations of 0.01-0.5 μM and mouse articular cartilage aging in vivo at the doses of 5 and 25 μg/kg/day, which were 5 times lower than the established no observed adverse effect level (NOAEL) and equal to NOAEL, respectively. TBT significantly increased the senescence-associated β-galactosidase activity and the protein expression levels of senescence markers p16, p53, and p21 in chondrocytes. TBT induced the protein phosphorylation of both p38 and JNK mitogen-activated protein kinases in which the JNK signaling was a main pathway to be involved in TBT-induced chondrocyte senescence. The phosphorylation of both ataxia-telangiectasia mutated (ATM) and histone protein H2AX (termed γH2AX) was also significantly increased in TBT-treated chondrocytes. ATM inhibitor significantly inhibited the protein expression levels of γH2AX, phosphorylated p38, phosphorylated JNK, p16, p53, and p21. TBT significantly stimulated the mRNA expression of senescence-associated secretory phenotype (SASP)-related factors, including IL-1β, TGF-β, TNF-α, ICAM-1, CCL2, and MMP13, and the protein expression of GATA4 and phosphorylated NF-κB-p65 in chondrocytes. Furthermore, TBT by oral gavage for 4 weeks in mice significantly enhanced the articular cartilage aging and abrasion. The protein expression of phosphorylated p38, phosphorylated JNK, GATA4, and phosphorylated NF-κB-p65, and the mRNA expression of SASP-related factors were enhanced in the mouse cartilages. These results suggest that TBT exposure can trigger human chondrocyte senescence in vitro and accelerating mouse articular cartilage aging in vivo.

Correlation between As, Cd, Hg, Pb and Sn concentration in human milk and breastfeeding mothers' food consumption: a systematic review and infants' health risk assessment

Mothers' food and water consumption appear to be determining factors for infants' potentially toxic elements exposure through human milk. Therefore, this systematic review aimed to assess correlations between As, Cd, Hg, Pb and/or Sn concentration in human milk and breastfeeding mothers' food consumption, with later infants' health risk assessment. Estimated Daily Intakes of such elements by infants were also calculated and compared with reference values (RfD or BMDL01). Among 5.663 identified studies, 23 papers remained for analysis. Potentially toxic elements concentration in human milk presented positive correlation with seafood (As, Hg), fresh vegetables (Hg, Cd), cereals (Hg, Cd), cheese, rice, potatoes, private and well-water supply (Pb), wild meat (Pb, Cd) and milk, dairy products, dried fruits and oilseeds (Cd) mothers' consumption. Red meat, caffeinated drinks, and dairy products consume presented negative correlations (Pb). No correlations were found for Sn. Infants from three studies presented high Hg exposition through human milk (> 0. 1 μg/kg PC-1 day-1), as well as observed for Pb in one study (> 0. 5 μg/kg PC-1 day-1). Potentially toxic elements can damage infants' health when they are present in mothers' diet due to the infants' high vulnerability. Therefore, these results raise important issues for public health.Supplemental data for this article is available online at https://doi.org/10.1080/10408398.2022.2056869 .

Effects of exposure to triphenyltin (TPT) contaminant on sperm activity in adulthood of Calomys laucha exposed through breastfeeding

Triphenyltin (TPT) is an organotin compound (OT), primarily used in agriculture and in the composition of antifouling paints for ships worldwide. Studies have showed its effects as an endocrine disrupter in several organisms by preventing enzymatic expression and causing reproductive toxicity. This study aimed to evaluate the effects of exposure to TPT, via breastfeeding, on reproductive physiology in the Calomys laucha species. The experimental design was compound of five groups, two controls and three with different doses of TPT. Moreover, females were exposed by gavage to the TPT for 20 days, from the 1st day postpartum to the 21st postnatal day (PND). Then, the pups were euthanized and the kinetics, organelles, and biochemistry of the sperm were evaluated. The results presented a reduction in total motility in the groups exposed to TPT. Regarding cellular organelles analysis, a loss in membrane integrity was evidenced; the functionality of mitochondria showed diminution followed by increased acrosome reaction. In conclusion, the TPT causes alteration of the reproductive parameters, decreasing the activity and sperm quality in individuals exposed in the breastfeeding phase.

Tributyltin induces distinct effects on cortical and trabecular bone in female C57Bl/6J mice

The retinoid X receptors (RXR), peroxisome proliferator activated receptor gamma (PPARγ), and liver X receptors (LXR) all have been shown to regulate bone homeostasis. Tributyltin (TBT) is an environmental contaminant that is a dual RXRα/β and PPARγ agonist. TBT induces RXR, PPARγ, and LXR-mediated gene transcription and suppresses osteoblast differentiation in vitro. Bone marrow multipotent mesenchymal stromal cells derived from female C57BL/6J mice were more sensitive to suppression of osteogenesis by TBT than those derived from male mice. In vivo, oral gavage of 12 week old female, C57Bl/6J mice with 10 mg/kg TBT for 10 weeks resulted in femurs with a smaller cross-sectional area and thinner cortex. Surprisingly, TBT induced significant increases in trabecular thickness, number, and bone volume fraction. TBT treatment did not change the Rankl:Opg RNA ratio in whole bone, and histological analyses showed that osteoclasts in the trabecular space were minimally reduced. In contrast, expression of cardiotrophin-1, an osteoblastogenic cytokine secreted by osteoclasts, increased. In primary bone marrow macrophage cultures, TBT marginally inhibited the number of osteoclasts that differentiated, in spite of significantly suppressing expression of osteoclast markers Nfatc1, Acp5, and Ctsk and resorptive activity. TBT induced expression of RXR- and LXR-dependent genes in whole bone and in vitro osteoclast cultures. However, only an RXR antagonist, but not an LXR antagonist, significantly inhibited TBTs ability to suppress osteoclast differentiation. These results suggest that TBT has distinct effects on cortical versus trabecular bone, likely resulting from independent effects on osteoblast and osteoclast differentiation that are mediated through RXR.

Tributyltin engages multiple nuclear receptor pathways and suppresses osteogenesis in bone marrow multipotent stromal cells

Organotins are members of the environmental obesogen class of contaminants because they activate peroxisome proliferator-activated receptor γ (PPARγ), the essential regulator of adipogenesis. Exposure to thiazolidinediones (PPARγ ligands used to treat type 2 diabetes) is associated with increased fractures. Diminished bone quality likely results from PPARγ's role in promoting adipogenesis while suppressing osteogenesis of bone marrow multipotent mesenchymal stromal cells (BM-MSC). We hypothesized that tributyltin (TBT) would be a potent modifier of BM-MSC differentiation and a negative regulator of bone formation. Organotins interact with both PPARγ and retinoid X receptors (RXR), suggesting that they activate multiple nuclear receptor pathways. To investigate the role of RXR in the actions of TBT, the effects of PPARγ (rosiglitazone) and RXR (bexarotene, LG100268) agonists were compared to the effects of TBT in BMS2 cells and primary mouse BM-MSC cultures. In BMS2 cells, TBT induced the expression of Fabp4, Abca1, and Tgm2 in an RXR-dependent manner. All agonists suppressed osteogenesis in primary mouse BM-MSC cultures, based on decreased alkaline phosphatase activity, mineralization, and expression of osteoblast-related genes. While rosiglitazone and TBT strongly activated adipogenesis, based on lipid accumulation and expression of adipocyte-related genes, the RXR agonists did not. Extending these analyses to other RXR heterodimers showed that TBT and the RXR agonists activated the liver X receptor pathway, whereas rosiglitazone did not. Application of either a PPARγ antagonist (T0070907) or an RXR antagonist (HX531) significantly reduced rosiglitazone-induced suppression of bone nodule formation. Only the RXR antagonist significantly reduced LG100268- and TBT-induced bone suppression. The RXR antagonist also inhibited LG100268- and TBT-induced expression of Abca1, an LXR target gene, in primary BM-MSC cultures. These results provide novel evidence that TBT activates multiple nuclear receptor pathways in BM-MSCs, activation of RXR is sufficient to suppress osteogenesis, and TBT suppresses osteogenesis largely through its direct interaction with RXR.

Development, validation, and application of an ultra-performance liquid chromatography-sector field inductively coupled plasma mass spectrometry method for simultaneous determination of six organotin compounds in human serum

Organotin compounds (OTCs) are heavily employed by industry for a wide variety of applications, including the production of plastics and as biocides. Reports of environmental prevalence, differential toxicity between OTCs, and poorly characterized human exposure have fueled the demand for sensitive, selective speciation methods. The objective of this investigation was to develop and validate a rapid, sensitive, and selective analytical method for the simultaneous determination of a suite of organotin compounds, including butyl (mono-, di-, and tri-substituted) and phenyl (mono-, di-, and tri-substituted) species in human serum. The analytical method utilized ultra-performance liquid chromatography (UPLC) coupled with sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). The small (sub-2 µm) particle size of the UPLC column stationary phase and the sensitivity of the SF-ICP-MS enabled separation and sensitive determination of the analyte suite with a runtime of approximately 3 min. Validation activities included demonstration of method linearity over the concentration range of approximately 0.250-13.661 ng mL(-1), depending on the species; intraday precision of less than 21%, interday precision of less than 18%, intraday accuracy of -5.3% to 19%, and interday accuracy of -14% to 15% for all species; specificity, and matrix impact. In addition, sensitivity, and analyte stability under different storage scenarios were evaluated. Analyte stability was found to be limited for most species in freezer, refrigerator, and freeze-thaw conditions. The validated method was then applied for the determination of the OTCs in human serum samples from women participating in the Snart-Foraeldre/MiljØ (Soon-Parents/Environment) Study. The concentration of each OTC ranged from below the experimental limit of quantitation to 10.929 ng tin (Sn) mL(-1) serum. Speciation values were confirmed by a total Sn analysis.

Association of placenta organotin concentrations with growth and ponderal index in 110 newborn boys from Finland during the first 18 months of life: a cohort study

BACKGROUND

Humans are exposed to tributyltin (TBT), previously used as an antifouling paint in ships, mainly through fish consumption. As TBT is a known obesogen, we studied the association of placenta TBT and other organotin compounds (OTCs) with ponderal index (PI) and growth during the first 18 months of life in boys.

METHODS

In a prospective Finnish study, 110 placenta samples were collected from mothers of boys born in 1997-1999 with (n = 55) and without (n = 55) cryptorchidism. To account for the original study design, linear regression, weighted for sampling fractions of boys with (121/55) and without (5677/55) cryptorchidism from the total cohort, was used to study the association between placenta OTCs and children's weight, length, growth rates and PI up to 18 months of age.

RESULTS

Placenta TBT concentrations were above the limit of quantification (LOQ) in 99% of the samples. However, monobutyltin (MBT), dibutyltin (DBT) and triphenyltin (TPhT) concentrations were below LOQ in 90%, 35% and 57% of samples, respectively. Placenta TBT was positively associated (p = 0.024) with weight gain during the first three months of life, but no other significant associations were observed for weight or length gain. Also, no significant associations between placenta OTC concentrations and child length, weight or PI at any time point were found.

CONCLUSIONS

We observed a trend towards higher weight gain from birth to 3 months of age with increasing placenta TBT concentration. These results should be interpreted with caution because obesogenic effects in animal experiments were seen after in-utero TBT exposures to doses that were orders of magnitude higher. Also the number of study subjects included in this study was limited.

What Are We Putting in Our Food That Is Making Us Fat? Food Additives, Contaminants, and Other Putative Contributors to Obesity

The "chemical obesogen" hypothesis conjectures that synthetic, environmental contaminants are contributing to the global epidemic of obesity. In fact, intentional food additives (e.g., artificial sweeteners and colors, emulsifiers) and unintentional compounds (e.g., bisphenol A, pesticides) are largely unstudied in regard to their effects on overall metabolic homeostasis. With that said, many of these contaminants have been found to dysregulate endocrine function, insulin signaling, and/or adipocyte function. Although momentum for the chemical obesogen hypothesis is growing, supportive, evidence-based research is lacking. In order to identify noxious synthetic compounds in the environment out of the thousands of chemicals that are currently in use, tools and models from toxicology should be adopted (e.g., functional high throughput screening methods, zebrafish-based assays). Finally, mechanistic insight into obesogen-induced effects will be helpful in elucidating their role in the obesity epidemic as well as preventing and reversing their effects.

Butyltins degradation by Cunninghamella elegans and Cochliobolus lunatus co-culture

Organotin compounds are ubiquitous in environment. However, biodegradation of tributyltin (TBT) and dibutyltin (DBT) to non toxic metabolites by fungi has been seldom observed. In this study we constructed a fungal co-culture with an efficient ability of TBT and its metabolites removal. The microscopic fungus strain Cunninghamella elegans degraded TBT via hydroxybutyldibutyltin (OHBuDBT) to its metabolites: DBT and monobutyltin (MBT), which were then transformed by Cochliobolus lunatus. The sequential biodegradation resulted in a 10-fold decrease in samples toxicity to Artemia franciscana larvae. With an initial TBT concentration of 5 mg l(-1), the co-culture of both fungi almost completely eliminated butyltins during 12 days of incubation in synthetic medium. To our knowledge, this is the first report that the mixed fungal co-culture could efficiently degrade TBT. This process was associated with glucose utilization, and a cometabolic nature of butyltins removal by selected strains has been suggested.

Organotin compounds, including butyltins and octyltins, in house dust from Albany, New York, USA

Organotin compounds (OTs) have been used in a wide variety of consumer products. Despite this, very few studies have reported the occurrence of OTs in house dust or exposure of humans to OTs through the ingestion of house dust. In the present study, concentrations of monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), monooctyltin (MOT), dioctyltin (DOT), trioctyltin (TOT), diphenyltin (DPT), and triphenyltin (TPT) were measured in dust collected from 24 houses in Albany, New York, USA. In addition, a few household products, such as wallpaper, floor tile, vinyl window blinds, and handbags were analyzed for the presence of OTs. Organotins were found in all of the house dust samples analyzed, and total OT concentrations varied from 390 to 28,000 ng/g (mean +/- SD: 6700 +/- 6200; median: 5000). Relative abundances of OTs in house dust were in the order MBT >MOT >DBT >DOT >TBT. TOT, DPT, and TPT were not found in any of the samples at concentrations above their corresponding detection limits. MBT accounted for, on average, 51% of the total OT concentrations. Mean concentrations of total OTs found in house dust samples from our study were two to five times higher than concentrations that have been reported for dust samples from several European countries. Calculations indicate that dust ingestion by children account for, on average, 15-18% of the tolerable daily intake proposed by the World Health Organization (WHO). The estimated rates of OT intake by children via dust ingestion were, on average, eightfold higher than the intake rates calculated for adults. Household products, such as wallpaper, contained total OT concentrations as high as 780,000 ng/g.