Toxicological Sciences

Acetaminophen (APAP) overdose is a leading cause of acute liver failure worldwide. The RNA-binding protein Human antigen R (HuR) is a multifunctional post-transcriptional regulator that plays a pivotal role in cellular stress responses, including those triggered by APAP toxicity. This study investigated the mechanisms by which HuR protects against APAP-induced hepatotoxicity in male mice. Hepatocyte-specific HuR-deficient (HuRHep-/-) male mice on a C57BL/6N background and wild-type (WT) littermates were treated with 200 mg/kg APAP, and liver tissues were collected at 2, 6, and 24 hours post-treatment. APAP administration increased hepatic HuR mRNA expression and induced HuR cleavage and the formation of a higher-molecular weight HuR-immunoreactive band, with the latter two correlating with injury severity. Compared with WT controls, HuRHep-/- mice exhibited markedly increased susceptibility to hepatotoxicity at both 2 and 6 hours. Metabolite profiling revealed altered APAP metabolism and reduced glutathione S-transferase (Gst) expression in HuRHep-/- livers, consistent with impaired APAP detoxification and increased APAP-protein adduct formation. Fourier-transform infrared (FTIR) spectroscopy further identified early biochemical differences between WT and HuRHep-/- livers as early as 2 hours after APAP exposure. Additionally, HuR deficiency resulted in pronounced mitochondrial structural abnormalities and dysfunction at 2 and 6 hours, accompanied by reduced expression of the mitochondrial fission and fusion proteins Drp1 and Mfn2, increased mitochondrial protein release, and enhanced hepatocyte death. Although pro-inflammatory cytokine levels were elevated in HuRHep-/- mice relative to WT controls at 24 hours, hepatocyte proliferation was similarly blunted in both genotypes, consistent with severe liver injury and delayed recovery. Collectively, these findings identify hepatocyte HuR as a critical regulator of xenobiotic metabolism and mitochondrial integrity and establish its essential role in early protection against APAP-induced hepatotoxicity in male mice.

Ethylene glycol monomethyl ether (EGME) is a testicular germ cell toxicant that selectively targets spermatocytes. In rats, male-only EGME exposure reduces mating success and can lead to an increase in resorbed fetuses. In a previous study, five-day exposure to 50, 60, or 75 mg/kg/d EGME in male rats led to a decrease in sperm motility and increase in retained spermatid heads with a LOAEL of 75 mg/kg/d. At 60 mg/kg/d, EGME exposure altered the proportion of sperm small RNA reads mapped to different small RNA categories and the distribution of read lengths. Because there is evidence that small non-coding RNAs (sncRNAs) in sperm regulate embryonic development, we analyzed sperm sncRNA data from EGME-treated male rats to identify differential expression at the individual RNA level. EGME treatment resulted in dose-dependent increases in the expression levels of microRNAs (miRNAs), piRNAs, and tRNA-derived small RNAs (tsRNAs). We identified 12 miRNAs that were differentially expressed at all EGME doses, with a monotonic, dose-dependent increase. High-confidence targets of these 12 miRNAs are known to be expressed in pre-implantation embryos and statistically enriched for Gene Ontology (GO) biological processes related to early development, such as cell fate commitment and regulation of developmental growth. These results demonstrated that the EGME-induced changes in sperm sncRNA levels were reproducible, dose-dependent, and provided a putative mechanism of paternal EGME effects on embryonic development, which will be investigated in future studies.

Male subjects in animal and human studies are disproportionately used for toxicological testing. This discrepancy is evidenced in clinical medicine where females are more likely than males to experience liver-related adverse events in response to xenobiotics. While previous work has shown gene expression differences between the sexes, there is a lack of systems-level approaches to understand the direct clinical impact effect of these differences. Here, we integrate gene expression data with metabolic network models to characterize the impact of transcriptional changes of metabolic genes in the context of sex differences and drug treatment. We used Tasks Inferred from Differential Expression (TIDEs), a reaction-centric approach to analyzing differences in gene expression, to discover that androgen, ether lipid, glucocorticoid, tryptophan, and xenobiotic metabolism have more activity in the male liver, and serotonin, melatonin, pentose, glucuronate, and vitamin A metabolism have more activity in the female liver. When TIDEs is used to compare expression differences in treated and untreated hepatocytes, we see little response in those sex-altered subsystems, and the largest differences are in subsystems related to lipid metabolism. Finally, using sex-specific transcriptomic data, we create individual and averaged male and female liver models and find differences in the import of bile acids and salts. This result suggests that the sexually dimorphic behavior of the liver may be caused by differences in enterohepatic recirculation, and we suggest an investigation into sex-specific microbiome composition as an avenue of further research. Author SummaryMale-bias in clinical testing of drugs has led to a disproportionate number of hepatotoxic events in women. Previous works use gene-by-gene differences in biological sex to explain this discrepancy, but there is little focus on the systematic interactions of these differences. To this end, we use a combination of gene expression data and metabolic modeling to compare metabolic activity between the male and female liver and treated and untreated hepatocytes. We find several subsystems with differential activity in each sex; however, when comparing these subsystems with those pathways altered by hepatotoxic agents, we find little overlap. To explore these differences on a reaction-by-reaction basis, we use the same sex-specific transcriptomic data to contextualize the previously published Human1 human cell metabolic model. In these models we find a difference in flux for the import of bile acids and salts, suggesting a potential difference in enterohepatic circulation. These findings can help guide future drug design, toxicological testing, and sex-specific research to better account for the entire human population.

Single doses of perfluoro-n-decanoic acid (PFDA) cause wasting, a progressive loss of 30 to 50% body weight, increasing liver/body weight ratios, and death within several weeks (Olson and Andersen, 1983). Repeat high doses of perfluorooctane sulfonate (PFOS) produce a subset of these responses in rats and monkeys. The mode of action (MOA) of these wasting-like syndromes is not clear, nor is it understood if these responses are limited to a subset of perfluoroacid substances (PFAS) or a common response to high dose exposure with a larger number of PFAS. To identify pathway perturbations in liver caused by PFAS, we analyzed published in vitro gene expression studies from human primary liver spheroids treated with various PFAS for treatment times up to 14 days (Rowan-Carroll et al., 2021). With treatment times of 10 to 14 days, longer-chain PFAS compounds, specifically PFOS, perfluorodecane sulfonate (PFDS) and higher doses of perfluorooctanoic acid (PFOA), downregulated large numbers of genes in pathways for steroid metabolism, fatty acid metabolism and biological oxidations. Shorter chain PFAS compounds upregulated genes in pathways for fatty acid metabolism. Although PFDA was more toxic and could only be examined at 1-day of treatment, it also downregulated genes for lipid metabolism, steroid metabolism, and biological oxidations. Shorter chain PFAS, both carboxylic and sulfonic acids, did not lead to downregulation of pathways for fatty acid or steroid metabolism. TCDD is also known to cause wasting responses in rodents and humans. In intact rats, high dose responses of longer chain PFAS produce downregulation of batteries of genes associated with fatty acid oxidation and lipogenesis similar to those seen with TCDD. Based on our results, when combined with other literature, we propose that the longer-chain PFAS impair lipogenic pathways through inhibitory interactions between PPAR{beta}, PPAR and PPAR{gamma}.

Background and AimsThe constitutive androstane receptor (CAR) is a nuclear receptor able to recognize a large panel of xenobiotics leading to the modulation of the expression of its target genes involved in xenobiotic detoxication and energy metabolism. While CAR hepatic activity is thought to be higher in women than in men, its response to an acute pharmacological activation has never been investigated in both sexes. MethodsHepatic transcriptome, plasma and hepatic metabolome, have been analyzed in Car+/+ and Car-/- male and female mice treated either with the CAR-specific agonist, 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP), or with vehicle. ResultsWhile 90% of TCPOBOP-sensitive genes were modulated in a sex- independent way, the remaining 10% were almost exclusively impacted in female liver specifically. These female-specific CAR-sensitive genes were mainly involved in xenobiotic metabolism, inflammation and extracellular matrix organization. CAR activation also induced higher hepatic oxidative stress and hepatocyte cytolysis in females than in males. Data mining on human data confirmed that CAR activation may be involved in sexually-dimorphic drug-induced liver injury. Hepatic expression of flavin monooxygenase 3 (Fmo3) was almost abolished and associated with a decrease of hepatic trimethylamine-N-oxide (TMAO) concentration in TCPOBOP-treated females. In line with a possible role in the control of TMAO homeostasis, CAR activation decreased platelet hyperresponsiveness in female mice supplemented with dietary choline. ConclusionsOur results demonstrate that more than 10% of CAR-sensitive genes are sex-specific and influence hepatic and systemic response such as platelet aggregation. Also, CAR activation may be an important mechanism of sexually- dimorphic drug-induced liver injury.

Polychlorinated biphenyls (PCBs) are persistent environmental toxicants that bioaccumulate in the food chain and readily cross the placenta, raising concerns for developmental toxicity. While PCB exposure has been associated with metabolic and neurodevelopmental disorders, its cell type-specific effects on liver development remain poorly understood. This study aimed to investigate how maternal exposure to an environmentally relevant Fox River PCB mixture affects liver development in female offspring at single-cell resolution. We hypothesized that early-life PCB exposure disrupts hepatic metabolic and immune function in a cell type-specific manner. Using single-cell RNA sequencing (scRNA-seq) on liver tissue from postnatal day 28 female mice perinatally exposed to PCBs, we identified major hepatic and immune cell populations and assessed cell-specific transcriptional responses. PCB exposure significantly altered the proportions of endothelial cells and Kupffer cells and reduced neutrophil abundance. Transcriptomic analysis revealed that PCBs dysregulated key pathways in hepatocytes and non-parenchymal cells, including ER stress responses, drug metabolism, and glucose/insulin signaling. Notably, hepatocytes exhibited upregulation of phase-I drug-metabolizing enzymes and uptake transporters, but downregulation of phase-II enzymes and efflux transporters. Kupffer cells and endothelial cells had altered immune and metabolic gene expression, and intercellular communication analysis predicted disrupted fibronectin, collagen, and chemokine signaling due to PCB exposure. RT-qPCR validation confirmed increased hepatic ER stress marker expression. Together these findings demonstrate that perinatal PCB exposure induces persistent, cell type-specific transcriptomic reprogramming in the liver, impairing metabolic and immune functions. This study highlights the utility of single-cell transcriptomics for revealing toxicant effects with cellular precision during critical windows of development.

AO_SCPLOWBSTRACTC_SCPLOWPeripubertal exposure to the phthalate metabolite mono-(2-ethylhexyl) phthalate (MEHP) in rodents causes testicular inflammation, spermatocyte apoptosis, and disruption of the blood-testis barrier. The MEHP-induced inflammation response includes an infiltration of macrophages and neutrophils to the testes, although the cause and purpose of this response is unknown. Recently, a population of testicular macrophages phenotypically distinct from those resident in the interstitium was described in mice. Testicular peritubular macrophages aggregate near the spermatogonial stem cell niche and are believed to stimulate their differentiation. We hypothesized that if testicular peritubular macrophages do indeed stimulate spermatogonial differentiation, MEHP exposure would result in an increase of peritubular macrophages to stimulate the replacement of lost spermatocytes. Male rats were exposed to 700 mg/kg MEHP or corn oil (vehicle control) via oral gavage at PND 28 and euthanized at 48 hours, 1 week, or 2 weeks later. Tubules were stained with immunofluorescent markers for macrophages and undifferentiated spermatogonia. Peritubular macrophages were observed in rat testis similar to those previously described in mice: MHC-II+ cells on the surface of seminiferous tubules with heterogeneous morphology. Quantification of MHC-II+ cells revealed that, unlike in the mouse, their numbers did not increase through puberty. MEHP increased macrophage presence by six-fold 48-hours after exposure and remained elevated by two-fold two weeks after exposure. An increase of differentiating spermatogonia occurred two weeks after MEHP exposure. Taken together, our results suggest that peritubular macrophages play a crucial role in the testis response to acute injury and the subsequent recovery of spermatogenesis.\n\nSummary SentencePhthalate-induced testicular injury results in an increase of specialized peritubular macrophages that may assist in the recovery of spermatogenesis.

Monolayer cultures of hepatocytes lack many aspects of the liver sinusoid, including a tissue-level organization that results from extracellular matrix interactions and gradients of soluble molecules that span from the portal triad to the central vein. We measured the activity and transcript levels of drug-metabolizing enzymes in HepaRG cells maintained in three different culture configurations: as monolayers, seeded onto paper scaffolds that were pre-loaded with a collagen matrix, and when seeded directly into the paper scaffolds as a cell-laden gel. Drug metabolism was significantly decreased in the presence of the paper scaffolds compared to monolayer configurations when cells were exposed to standard culture conditions. Despite this decreased function, transcript levels suggest the cells undergo increased polarization and adopt a biliary-like character in the paper scaffolds, including the increased expression of transporter proteins (e.g., ABCB11 and SLOC1B1) and the KRT19 cholangiocyte marker. When exposed to representative periportal or perivenous culture conditions, we observed in vivo zonal-like patterns, including increased cytochrome P450 (CYP) activity and transcript levels in the perivenous condition. This increased CYP activity is more pronounced in the laden configuration, supporting the need to include multiple aspects of the liver microenvironment to observe the post-differentiation processing of hepatocytes. TOC Figure O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=77 SRC="FIGDIR/small/524330v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@17eb8dorg.highwire.dtl.DTLVardef@69a430org.highwire.dtl.DTLVardef@19a78a8org.highwire.dtl.DTLVardef@679f0a_HPS_FORMAT_FIGEXP M_FIG C_FIG

Biochemical investigations of the hepatoprocarcinogen N-acetyl-2-aminofluorene (AAF) have shown that normal adult rat hepatocytes in primary culture express two sets of pharmacokinetic constants - designated Systems I and II, and Sites I and II - associated respectively with the metabolism (System I [high-affinity Km[APPARENT] and low-velocity VMAX[APPARENT]] and System II [low-affinity Km APPARENT] and high-velocity VMAX[APPARENT]]), and the macromolecular binding (Site I [high-affinity KD[APPARENT] and low capacity BMAX[APPARENT]] and Site II ([low-affinity KD[APPARENT] and high-capacity BMAX[APPARENT]]) of AAF. Additional findings - that genomically saturating levels of AAF-DNA adducts form far below reported extracellular AAF concentrations required to block replicative and repair DNA synthesis; and, that biphasic Site I and Site II BMAX[APPARENT] and KD[APPARENT] expression curves varied inversely with respect to time and magnitude during hepatocyte growth - led us to wonder how macromolecular binding constants are expressed during chemical hepatocarcinogenesis. These questions were addressed by Scatchard analysis measurements through five consecutive AAF feeding cycles. Notably, cultured premalignant hepatocytes displayed reduced and elevated BMAX[APPARENT] and KD[APPARENT] levels, respectively, akin to the Site I and Site II expression curves observed during hepatocyte growth transitions in vitro. In contrast, prominent hepatocellular functions such as N-OH-AAF production, DNA replication, cell aggregation and resistance to AAF toxicity displayed different temporal trajectories. Impact StatementStriking similarities are observed between both Site I and Site II BMAX and KD expression curves during in vitro and in vivo premalignant growth transitions. These new findings fit earlier ones that hepatocytes growing during carcinogen exposure manifest fewer intranuclear AAF-DNA adducts. How this phenomenon leads to malignancy remains unclear.

Benzo[a]pyrene (BaP) is a prototypical polycyclic aromatic hydrocarbon (PAH) produced during combustion processes and when grilling foods. Epidemiological studies indicate exposure to PAHs during pregnancy lead to learning and memory deficits as well as behavioral problems that persist into adolescence. Studies in rodents and zebrafish have frequently reported anxiolytic effects of BaP exposure in adult animals and in developmental studies. We conducted sequential experiments of Cyp1a1(-/-) and Cyp1b1(-/-) knockout mice compared with wild type C57BL/6J mice to determine if genotype changes the response to developmental BaP exposure. We treated pregnant dams from gestational day 10 to postnatal day 25 (P25) with BaP in corn oil-soaked cereal or the corn oil vehicle and tested one male and one female offspring beginning at P60. We found increased exploratory behavior in the elevated zero maze for Cyp1a1(-/-) knockout mice, but no significant differences in Cyp1b1(-/-) knockouts. In contrast, Cyp1b1(-/-) knockout mice buried fewer marbles in a second test of anxiety-like behavior. There were no significant differences when Cyp1a1(-/-) knockout mice were tested. BaP decreased immobility time in Cyp1a1(-/-) knockouts in the forced swim test, but increased immobility time in wild type and Cyp1b1(-/-) knockout mice. We measured plasma corticosterone levels at baseline and following the forced swim test and monoamine neurotransmitters at the end of behavioral testing. BaP treatment increased corticosterone in wild type mice, but decreased it in Cyp1a1(-/-) knockout mice. Both BaP-exposed and corn oil control Cyp1b1(-/-) knockout mice had higher corticosterone levels compared with wild type mice. Dopamine and serotonin signaling were altered in the hypothalamus dependent on genotype, treatment and sex. Together, these data suggest that both CYP1A1 and CYP1B1 have a normal role in brain functioning or development, and that CYP1 genotype alters the response to developmental BaP exposure in behavioral and biochemical tests related to stress, anxiety and depression. HighlightsO_LIBaP-exposed Cyp1a1(-/-) mice had lower corticosterone and decreased immobility in the forced swim test C_LIO_LIBaP exposure increased FST immobility in wild type and Cyp1b1(-/-) mice C_LIO_LICyp1a1(-/-) and Cyp1b1(-/-) knockout mice showed less anxiety-like behavior C_LIO_LIDevelopmental BaP exposure altered corticosterone levels dependent on Cyp1 genotype C_LIO_LIGenotype, treatment and sex all impacted neurotransmitter levels in the hypothalamus C_LIO_LIGenetic differences in CYP enzymes altered susceptibility to developmental BaP exposure C_LI

Benzene is a ubiquitous environmental pollutant. Recent population-based studies suggest that benzene exposure is associated with an increased risk for cardiovascular disease. However, it is unclear whether benzene exposure is sufficient to induce cardiovascular toxicity. We examined the effects of benzene inhalation (50 ppm, 6 h/day, 5 days/week, 6 weeks) or HEPA-filtered air exposure on the biomarkers of cardiovascular toxicity in male C57BL/6J mice. Benzene inhalation significantly increased the biomarkers of endothelial activation and injury including endothelial microparticles, activated endothelial microparticles, endothelial progenitor cell microparticles, lung endothelial microparticles, and activated lung and endothelial microparticles while having no effect on circulating levels of endothelial adhesion molecules, endothelial selectins, and biomarkers of angiogenesis. To understand how benzene may induce endothelial injury, we exposed human aortic endothelial cells to benzene metabolites. Of metabolites tested, trans,trans-mucondialdehyde (10 M, 18h) was most toxic. It induced caspases-3, -7 and -9 (intrinsic pathway) activation, and enhanced microparticle formation by 2.4-fold. Levels of plateletleukocyte aggregates, platelet macroparticles, and proportion of CD4+ and CD8+ T-cells were also significantly elevated in the blood of the benzene-exposed mice. We also found that benzene exposure increased the transcription of genes associated with endothelial cell and platelet activation in the liver; and induced inflammatory genes and suppressed cytochrome P450s in the lungs and the liver. Together, these data suggest that benzene exposure induces endothelial injury, enhances platelet activation and inflammatory processes; and circulatory levels of endothelial cell and platelet-derived microparticles and platelet-leukocyte aggregates are excellent biomarkers of cardiovascular toxicity of benzene. HighlightsO_LIInhaled benzene exposure increases the levels of blood endothelial microparticles. C_LIO_LIIn vitro, benzene metabolite trans, trans-mucondialdehyde induces endothelial cell apoptosis and microparticles formation. C_LIO_LIInhaled benzene exposure decreases the levels of hematopoietic progenitor cells in the bone marrow. C_LIO_LIInhaled benzene exposure augments the circulating levels of platelet-leukocyte adducts. C_LI

Single, high doses of TCDD in rats caused wasting, a progressive loss of 30 to 50% body weight and death within several weeks. To identify pathway perturbations at or near doses causing wasting, we examined differentially gene expression (DGE) and pathway enrichment in centrilobular (CL) and periportal (PP) regions of female rat livers following 6 dose levels of TCDD - 0, 3, 22, 100, 300, and 1000 ng/kg/day, 5 days/week for 4 weeks. At the higher doses, rats lost weight, had increased liver/body weight ratios and nearly complete cessation of liver cell proliferation, signs consistent with wasting. DGE curves were left shifted for the CL versus the PP regions. Canonical Phase I and Phase II genes were maximally increased at lower doses and remained elevated at all doses. At lower doses, < 22 ng/kg/day in the CL and < 100 ng/kg/day, upregulated genes showed transcription factor (TF) enrichment for AHR and ARNT. At the mid- and hi-dose doses, there was a large number of downregulated genes and pathway enrichment for DEGs showed downregulation of many cellular metabolism processes including those for steroids, fatty acid metabolism, pyruvate metabolism and citric acid cycle. There was significant TF enrichment of the hi-dose downregulated genes for RXR, ESR1, LXR, PPARalpha. At the highest dose, there was also pathway enrichment with upregulated genes for extracellular matrix organization, collagen formation, hemostasis and innate immune system. TCDD demonstrates most of its effects through binding the aryl hydrocarbon receptor (AHR) while the downregulation of metabolism genes at higher TCDD doses is known to be independent of AHR binding to DREs. Based on our results with DEG, we provide a hypothesis for wasting in which high doses of TCDD shifts circadian processes away from the resting state leading to greatly reduced synthesis of steroids and complex lipids needed for cell growth and producing gene expression signals consistent with an epithelial-to-mesenchymal transition in hepatocytes.

BACKGROUND AND AIMSBiliary atresia is a fibrosing cholangiopathy affecting neonates that is thought to be caused by a prenatal environmental insult to the bile duct. Biliatresone, a plant toxin with an -methylene ketone group, was previously implicated in toxin-induced biliary atresia in Australian livestock, but is found in a limited location and is highly unlikely to be a significant human toxin. We hypothesized that other molecules with -methylene ketone groups, some with the potential for significant human exposure, might also be biliary toxins. APPROACH AND RESULTSWe focused on the family of microcystins, cyclic peptide toxins from blue-green algae that have an -methylene ketone group and are found worldwide, particularly during harmful algal blooms. We found that microcystin-RR, but not 6 other microcystins, caused damage to cell spheroids made using cholangiocytes isolated from 2-3-day-old mice, but not from adult mice. We also found that microcystin- RR caused occlusion of extrahepatic bile duct explants from 2-day-old mice, but not 18-day-old mice. Microcystin-RR caused elevated reactive oxygen species in neonatal cholangiocytes, and treatment with N-acetyl cysteine partially prevented microcystin-RR- induced lumen closure, suggesting a role for redox homeostasis in its mechanism of action. CONCLUSIONSThis study highlights the potential for environmental toxins to cause neonatal biliary disease and identifies microcystin-RR acting via increased redox stress as a possible neonatal bile duct toxin.

BACKGROUNDEgg development has unique features that render it vulnerable to environmental perturbation. The herbicide atrazine is an endocrine disruptor shown to have detrimental effects on reproduction across a number of vertebrate species. OBJECTIVESTo determine whether exposure to low levels of atrazine impairs meiosis in female mammals using a mouse model; in particular, whether and how the fidelity of oocyte chromosome segregation is affected, and whether the aging-related aneuploidy is exacerbated. METHODSFemale C57BL/6J mice were exposed to two levels of atrazine in drinking water, with the lower level corresponding to detected environmental contamination. To model exposure during development, atrazine was ingested by pregnant females at 0.5 days post coitum and continued until pups were weaned at 21 days post-partum. For adult exposure, 2-month-old females ingested atrazine for 3 months. For each exposure group, various indicators of oocyte quality were determined, including developmental capacity and chromosomal abnormalities during the two meiotic divisions. RESULTSDevelopmental exposure caused only minor effects on the fetal events of meiotic prophase-I and establishment of initial follicle pools. However, ovulation was enhanced while oocyte quality was significantly reduced. At the chromosome level, misalignment and numerical and structural abnormalities were increased at both meiotic divisions. Furthermore, fertilization efficiency was impaired in vitro, and apoptosis was elevated in blastocysts derived from the eggs of atrazine-exposed females. Similar levels of chromosomal defects were seen in oocytes following both developmental and adult exposure regimens suggesting that quiescent primordial follicles may be the consequential targets of atrazine. Importantly, defects were observed long after exposure was terminated. Moreover, dramatic increases in chromosomally abnormal oocytes were seen in older mice indicating that atrazine exposure during development exacerbates the effects of maternal aging on oocyte quality. Indeed, analogous to the effects of maternal age, atrazine exposure resulted in weakened cohesion between sister chromatids. CONCLUSIONLow-level atrazine exposure causes persistent changes to the female mammalian germline with potential consequences for reproductive lifespan and congenital disease.

Background & AimsLongitudinal animal models are essential for understanding the temporal dynamics of liver injury and recovery. While drinking water-based administration is ideal for sustained exposure in high feasibility, available compounds are limited, with thioacetamide (TAA) being the primary option. Here, we aimed to establish a novel drinking water-induced mouse model of cholestatic liver injury using 4,4-methylenedianiline (MDA), and to characterize its pathological trajectory in comparison to the TAA model. MethodsMice were administered MDA via drinking water for 28 Days. To elucidate the early events that give rise to chronic pathological divergence, we conducted a multi-layered analysis comprising plasma biochemical assays, immune cell profiling by flow cytometry, and hepatic transcriptomics at five time points during the early phase. The MDA model was evaluated against the established TAA model. ResultsMDA administration induced sustained ALT elevation, peribiliary fibrosis, and spatially irregular focal hepatocellular necrosis, distinguishing it from the centrilobular injury observed with TAA. Additionally, the MDA model showed significant elevations in ALP, TBIL, and TCHO, indicating cholestatic liver dysfunction. Early-phase analyses revealed model-specific differences in immunological and molecular responses, including increased CD8 T cell populations and enrichment of fibrinolysis-related gene expression in MDA-DW mice. ConclusionsWe present the MDA-DW model as a novel, longitudinally tractable liver injury model that complements existing systems by capturing alternative spatial, immunological, and transcriptional patterns of injury. This model offers a valuable platform for dissecting the temporal dynamics of liver disease progression in experimental settings. Significance StatementWe developed a cost-effective, non-invasive mouse model of cholestatic liver injury using drinking-water administration of 4,4-methylenedianiline (MDA). This model exhibits periportal-predominant damage, peribiliary fibrosis, and spatially irregular focal hepatocellular necrosis, distinct from conventional centrilobular models. Early-phase multi-omics analysis revealed immunological and transcriptomic differences, including increased CD8 T cells and activation of fibrinolysis-related pathways. The low mortality rate and ease of implementation enable long-term studies and cross-sectional comparisons across time points or interventions. This study provides not only a practical model for investigating chronic liver injury, but also a rich time-series, multi-view dataset, offering a valuable resource for advancing research on liver pathophysiology and toxicological mechanisms.

Inter-individual and population variability in susceptibility to chemical exposures confounds determination of threshold exposure levels to protect the most vulnerable. Current risk assessment frameworks, in the absence of empiric chemical-specific data, generally recommend default or probabilistic adjustment factors to account for such variability. We present an experimental approach to incorporate common genetic variants potentially impacting population-level differences in toxicant susceptibility into human cell-based models for any cellular apical endpoint of interest. We focus on the genes with the most common aggregate loss-of-function (LoF) alleles in the gnomAD v3.0 data which we designated as the PopVarLoF set. Unexpectedly, enrichment analysis of these genes found significant overrepresentation of gene products playing important functional roles in toxicology. Interrogation of GWAS and PheWAS databases found that these genes are associated with diverse metabolic phenotypes consistent with the relevance of the PopVarLoF set in studying variability of toxicant response in human populations. We further characterized the PopVarLoF set by developing custom lentiviral CRISPR knockout libraries targeting the PopVarLoF genes to assess their functional essentiality in the HepG2/C3A cell line. Functional disruption of 14 of the PopVarLoF genes ([~]1 %) without toxicant exposure resulted in significant growth defects in this cell line, consistent with the majority of PopVarLoF gene products having non-essential roles. The development of human cell-based toxicity assays or other NAMs which include the empiric assessment of common genetic sources of population variability in susceptibility to chemical exposure could contribute to more robust risk assessment which protects vulnerable populations while reducing uncertainty. Impact statementWe characterize common loss of function genetic variants which could impact toxicant susceptibility and describe an approach to incorporate them into NAMs to enable empiric estimates of the contribution of genetic variability to diverse toxicity endpoints.

BackgroundHepatocytes are an important tool for in vitro toxicology testing. In addition to primary cultures, a limited number of immortalized cell lines have been developed. We here describe a new cell line, designated as HepaMN, which has been established from a liver associated with biliary atresia.\n\nMethodsHepatocytes were isolated from a liver of 4-year-old girl with biliary atresia and immortalized by inoculation with CSII-CMV-TERT, CSII-CMV-Tet-Off, CSII-TRE-Tight-cyclin D1 and CSII-TRE-Tight-CDK4R24C (mutant CDK4: an INK4a-resistant form of CDK4) lentiviruses at the multiplicity of infection of 3 to 10.\n\nResultsHepaMN cells exhibited morphological homogeneity, displaying hepatocyte-like phenotypes. Phenotypic studies in vivo and in vitro revealed that HepaMN cells showed polarized and functional hepatocyte features along with a canalicular cell phenotype under defined conditions, and constitutively expressed albumin and carbamoyl phosphate synthetase I in addition to epithelial markers. Since HepaMN cells are immortal and subcloned, kinetics and expression profiles were independent of population doublings.\n\nConclusionsHepaMN cells showed increased CYP3A4 expression after exposure to rifampicin, implying that their close resemblance to normal human hepatocytes makes them suitable for research applications including drug metabolism studies.

Ferroptosis is a form of regulated cell death closely associated with glutathione depletion and accumulation of reactive lipid peroxides. In the present study, we seek to determine whether 2-hydroxyestrone (2-OH-E1) and 2-hydroxyestradiol (2-OH-E2), two major metabolites of endogenous estrone and 17{beta}-estradiol formed in liver by cytochrome P450 enzymes, can strongly protect against erastin- and RSL3-induced ferroptosis in hepatoma cells (H-4-II-E and HuH-7) in vitro and acetaminophen-induced mouse liver injury in vivo. We find that 2-OH-E1 and 2-OH-E2 can protect, in a dose-dependent manner, H-4-II-E hepatoma cells against erastin/RSL3-induced ferroptosis. Similar protective effect of 2-OH-E1 and 2-OH-E2 against RSL3-induced ferroptosis is also observed in HuH-7 hepatoma cells. These two estrogen metabolites strongly reduce the levels of erastin- and/or RSL3-induced accumulation of cellular NO, ROS and lipid-ROS. Mechanistically, 2-OH-E1 and 2-OH-E2 protect cells against chemically-induced ferroptosis mainly by binding to cellular protein disulfide isomerase (PDI), and then inhibit its catalytic activity and reduce PDI-catalyzed formation of iNOS dimer, thereby abrogating cellular NO, ROS and lipid-ROS accumulation. Animal studies show that 2-OH-E1 and 2-OH-E2 can also exert a strong protection against acetaminophen-induced liver injury in mice. Interestingly, while estrone and 17{beta}-estradiol display a very weak protective effect in cultured hepatoma cells, they exert a similarly-strong protective effect as 2-OH-E1 and 2-OH-E2 in vivo, suggesting that the metabolic conversion of estrone and 17{beta}-estradiol to 2-OH-E1 and 2-OH-E2 contributes importantly to their hepatoprotective effect. The results of this study reveal that 2-OH-E1 and 2-OH-E2 are important endogenous factors for protection against chemically-induced liver injury in vivo.

ABSTRACTAcetaminophen (APAP) overdose causes hepatic injury and is major contributor to acute liver injury cases. To investigate potential roles of gut microbiota in APAP-induced liver injury, C57BL/6 mice from Jackson (JAX) or Taconic (TAC) were challenged with APAP. TAC mice were more susceptible to APAP toxicity, and this disappeared upon co-housing of JAX and TAC mice. When the cecum contents from JAX and TAC mice were transplanted to germ-free mice, the mice that received TAC gut microbiota exhibited more significant hepatotoxicity after APAP administration. Non-targeted metabolomic analysis using portal vein serum and liver tissue of the mice led to identification of 19 metabolites the levels of which are associated with JAX or TAC gut microbiota. A gut bacteria-derived metabolite phenylpropionic acid (PPA) levels in cecum contents and blood were higher in mice harboring JAX gut microbiota. PPA supplementation in drinking water alleviated APAP-induced hepatotoxicity in TAC mice. This was accompanied by reduced hepatic protein levels of cytochrome P450 (CYP) 2E1, the enzyme responsible for APAP bioactivation to a toxic metabolite. This illustrates a gut microbe-liver interaction mediated by a gut bacteria-derived metabolite in modulating drug-induced liver injury.Competing Interest StatementThe authors have declared no competing interest.View Full Text

Environmental chemicals play a significant role in the development of metabolic disorders, especially when exposure occurs early in life. We have recently demonstrated that benzene exposure, at concentrations relevant to a cigarette smoke, induces a severe metabolic imbalance in a sex-specific manner affecting male but not female mice. However, the roles of benzene in the development of aberrant metabolic outcomes following gestational exposure, remain largely unexplored. In this study, we exposed pregnant C57BL/6JB dams to benzene at 50 ppm or filtered air for 5 days/week (6h/day from gestational day 1 to birth) and studied male and female offspring metabolic phenotypes in their adult life. While no changes in body weight or body composition were observed between groups, 4-month-old male and female offspring exhibited reduced parameters of energy homeostasis (VO2, VCO2, and heat production). However, only male offspring from benzene-exposed dams were glucose intolerant and insulin resistant at this age. By six months of age, both male and female offspring displayed glucose and insulin intolerance, associated with elevated expression of hepatic gluconeogenesis and inflammatory genes. Additionally, this effect was accompanied by elevated insulin secretion and increased beta-cell mass only in male offspring. Thus, gestational benzene exposure can reprogram offspring for increased susceptibility to the metabolic imbalance in adulthood with differential sensitivity between sexes.