A single-cell survey unveils cellular heterogeneity and sensitive responses in mouse cortices induced by oral exposure to triphenyl phosphate

Developmental immunotoxicity study of tris(chloropropyl) phosphate in Hsd:Sprague Dawley SD rats exposed through dosed feed

Tris(chloropropyl) phosphate (TCPP) is a member of organophosphate flame retardants used commonly as a replacement for polybrominated diphenyl ethers in consumer and commercial products. Flame retardants have been shown to modulate immune function in vivo and in vitro and there is evidence that at least some related compounds such as organophosphate pesticides can cause developmental immunotoxicity. Developmental immunotoxicology studies were conducted by administering 0, 2500, 5000, or 10,000 ppm TCPP in feed to pregnant Hsd:Sprague Dawley SD rats from gestation day 6 through weaning on postnatal day 28. Feed exposure to TCPP was continued in the F1 offspring until terminal euthanasia at ∼16 to 21 weeks of age when assessments for developmental immunotoxicity were conducted. Innate, humoral, and cell-mediated immune function were assessed in the F1 adults. The antibody-forming cells (AFCs) response to sheep red blood cells was reduced in male and female F1 rats in the 10,000 ppm treatment group but coincided with reduced bodyweights. The AFC response was also significantly reduced in male rats exposed to 5000 ppm where only moderate effects on bodyweights occurred. TCPP exposure affected baseline T-cell proliferation without stimulation; however, the relevance of this change for immunotoxicity risk is unknown. TCPP exposure did not affect cytotoxic T-lymphocyte activity. Only minor and inconsistent treatment-related effects on hematology, innate NK cell function, and immune cell population distributions in the spleen were observed. Taken together, these data indicate that TCPP has the potential to impact humoral immune responses following developmental exposure.

Environmental factors ultraviolet a and ozone exacerbate the repeated inhalation toxicity of 6PPD in mice via accelerating the aging reaction

The burden of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its oxidized products on human health can no longer be ignored due to the detection types and concentrations in the environment continue to increase. Environmental ozone (O3) and ultraviolet A (UVA) may induce ozonation and photoaging of 6PPD to produce toxic products. However, the impact of specific environmental conditions on the aging and toxic effects of 6PPD is unclear. This study investigated the aging effects of O3 and UVA on 6PPD, and compared the repeated inhalation toxicity of differently aging 6PPDs in C57BL/6 male mice. The result showed that UVA and O3 accelerated 6PPD aging, and the aging products varied depending on the O3 and irradiation conditions. After 10 weeks of inhalation intoxication at human comparable level, mice exhibited significant neurobehavior alterations, respiratory dysfunction, and DNA damage in the blood, showing significant heterogeneity among groups. Notably, 6PPD treated with perozonation and UVA aging may be the most toxic. The study suggests inhalation health risks of transportation derived tire pollutants under the influence of ground-level ozone and ultraviolet light need more attention, and provides new insights into risk assessment and pollution control of 6PPD and other pollutants from the perspective of environmental factors.

Prenatal exposure to low doses of benzophenone-3 elicits disruption of cortical vasculature in fetuses through perturbations in Wnt/β-catenin signaling correlating with depression-like behavior in offspring mice

Benzophenone-3 (BP-3), commonly used in personal care products, is routinely detected in environmental and human matrices. Evidence delineates a correlation between gestational BP-3 exposure and emotional and social disorders in children and adolescents. However, sensitive target cells and the mode of action underlying the early responses to environmentally relevant level of BP-3 exposure remain unclear. In this study, 0.3 and 3 mg/kg of BP-3 were administered to pregnant mice. Compared with the control group, the cortical blood vessel development process manifested the highest susceptibility to BP-3 exposure using transcriptomic sequencing at embryonic day 14 (E14). Notably, the diminution in vascular density and tight junction proteins presence was observed in the fetal cortex at E14, concomitant with the suppressed transcriptional activity of genes essential to angiogenesis and barrier formation. Strikingly, the investigation revealed that BP-3 exposure impeded vascular sprouting in aortic ring explants and neuroendothelial migration, implicating the Wnt/β-catenin signaling pathway. Moreover, BP-3 exposure compromised perivascular neural stem cell differentiation. Cortical vascular injury correlated with the exhibition of depression-like behavior in four-week postnatal progeny. These insights underscore the cerebrovasculature as an early sensitive target for low doses of BP-3 exposure, fostering the development of biomarkers and the establishment of the adverse outcome pathway framework for BP-3 hazard evaluation.

Embryonic Exposure to Organophosphate Flame Retardants (OPFRs) Differentially Induces Cardiotoxicity in Rare Minnow (Gobiocypris rarus)

Organophosphorus flame retardants (OPFRs) such as triphenyl phosphate (TPHP) and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) were reported to impair cardiac function in fish. However, limited information is available regarding their cardiotoxic mechanisms. Using rare minnow (Gobiocypris rarus) as a model, we found that both TPHP and TDCIPP exposures decreased heart rate at 96 h postfertilization (hpf) in embryos. Atropine (an mAChR antagonist) can significantly attenuate the bradycardia caused by TPHP, but only marginally attenuated in TDCIPP treatment, suggesting that TDCIPP-induced bradycardia is independent of mAChR. Unlike TDCIPP, although TPHP-induced bradycardia could be reversed by transferring larvae to a clean medium, the inhibitory effect of AChE activity persisted compared to 96 hpf, indicating the existence of other bradycardia regulatory mechanisms. Transcriptome profiling revealed cardiotoxicity-related pathways in treatments at 24 and 72 hpf in embryos/larvae. Similar transcriptional alterations were also confirmed in the hearts of adult fish. Further studies verified that TPHP and TDCIPP can interfere with Na+/Ca2+ transport and lead to disorders of cardiac excitation-contraction coupling in larvae. Our findings provide useful clues for unveiling the differential cardiotoxic mechanisms of OPFRs and identifying abnormal Na+/Ca2+ transport as one of a select few known factors sufficient to impair fish cardiac function.

Application of Single Cell Gene Expression Technologies to Neurotoxicology

Neurotoxicological research faces the challenge of linking biological changes resulting from exposures to neuronal function. An additional challenge is understanding cell-type specific differences and selective vulnerabilities of distinct neuronal populations to toxic insults. Single cell RNA-sequencing (scRNA-seq) allows for measurement of the transcriptome of individual cells. This makes it a valuable tool for validating and characterizing cell types present in multicell type samples in complex tissue or cell culture models, but also for understanding how different cell types respond to toxic insults. Pathway analysis of differentially expressed genes can provide in depth insights into underlying cell type-specific mechanisms of neurotoxicity. Toxicological data often has to be translated to outcomes for human health which requires an understanding of inter-species differences. Transcriptomic data aids in understanding these differences, including understanding developmental timelines of different species. We believe that scRNA-seq holds exciting promises for future neurotoxicological research.