Circulating microRNA profiles altered in mice after 28 d exposure to perfluorooctanoic acid

Perfluorooctanoic acid (PFOA) is a stable man-made compound with many industrial and commercial uses. Recently, however, concern has been raised that it may induce various toxicological effects such as hepatotoxicity, immunotoxicity, and developmental toxicity. Because levels of circulating microRNAs (miRNAs) can be altered in several clinical diseases, they may serve as potential novel biomarkers. Here, we explored differences in the profiles of circulating miRNAs in mice after PFOA exposure. Using TaqMan miRNA arrays, we determined that the levels of 24 circulating miRNAs were altered in mice dosed with PFOA at 1.25 mg/kg/d and 73 were altered in mice dosed with 5 mg/kg/d. Eight miRNAs were further validated using TaqMan Real-Time PCR assays. Results were consistent with those obtained from the TaqMan miRNA arrays, except for miR-199a-3p. The most remarkable of the circulating miRNAs (miR-26b-5p and miR-199a-3p) were also up-regulated in the serum of occupational workers in our previous epidemiological study. We also found similar patterns in mice exposed to PFOS. These results demonstrated that circulating miRNA profiles were altered after exposure to high concentrations of PFOA and miR-28-5p, miR-32-5p, miR-122-5p, miR-192-5p, and miR-26b-5p in serum may be linked to effects of PFOA, especially in occupationally exposed people.     

Identification of urinary microRNA profiles in rats that may diagnose hepatotoxicity

Circulating microRNAs (miRNAs) have emerged as novel noninvasive biomarkers for several diseases and other types of tissue injury. This study tested the hypothesis that changes in the levels of urinary miRNAs correlate with liver injury induced by hepatotoxicants. Sprague-Dawley rats were administered acetaminophen (APAP) or carbon tetrachloride (CCl(4)) and one nonhepatotoxicant (penicillin/PCN). Urine samples were collected over a 24 h period after a single oral dose of APAP (1250 mg/kg), CCl(4) (2000 mg/kg), or PCN (2400 mg/kg). APAP and CCl(4) induced liver injury based upon increased serum alanine and aspartate aminotransferase levels and histopathological findings, including liver necrosis. APAP and CCl(4) both significantly increased the urinary levels of 44 and 28 miRNAs, respectively. In addition, 10 of the increased miRNAs were in common between APAP and CCl(4). In contrast, PCN caused a slight decrease of a different nonoverlapping set of urinary miRNAs. Cluster analysis revealed a distinct urinary miRNA pattern from the hepatotoxicant-treated groups when compared with vehicle controls and PCN. Analysis of hepatic miRNA levels suggested that the liver was the source of the increased urinary miRNAs after APAP exposure; however, the results from CCl(4) were equivocal. Computational analysis was used to predict target genes of the 10 shared hepatotoxicant-induced miRNAs. Liver gene expression profiling using whole genome microarrays identified eight putative miRNA target genes that were significantly altered in the liver of APAP- and CCl(4)-treated animals. In conclusion, the patterns of urinary miRNA may hold promise as biomarkers of hepatotoxicant-induced liver injury.     

Evaluation of an in vitro toxicogenetic mouse model for hepatotoxicity

Numerous studies support the fact that a genetically diverse mouse population may be useful as an animal model to understand and predict toxicity in humans. We hypothesized that cultures of hepatocytes obtained from a large panel of inbred mouse strains can produce data indicative of inter-individual differences in in vivo responses to hepato-toxicants. In order to test this hypothesis and establish whether in vitro studies using cultured hepatocytes from genetically distinct mouse strains are feasible, we aimed to determine whether viable cells may be isolated from different mouse inbred strains, evaluate the reproducibility of cell yield, viability and functionality over subsequent isolations, and assess the utility of the model for toxicity screening. Hepatocytes were isolated from 15 strains of mice (A/J, B6C3F1, BALB/cJ, C3H/HeJ, C57BL/6J, CAST/EiJ, DBA/2J, FVB/NJ, BALB/cByJ, AKR/J, MRL/MpJ, NOD/LtJ, NZW/LacJ, PWD/PhJ and WSB/EiJ males) and cultured for up to 7 days in traditional 2-dimensional culture. Cells from B6C3F1, C57BL/6J, and NOD/LtJ strains were treated with acetaminophen, WY-14,643 or rifampin and concentration-response effects on viability and function were established. Our data suggest that high yield and viability can be achieved across a panel of strains. Cell function and expression of key liver-specific genes of hepatocytes isolated from different strains and cultured under standardized conditions are comparable. Strain-specific responses to toxicant exposure have been observed in cultured hepatocytes and these experiments open new opportunities for further developments of in vitro models of hepatotoxicity in a genetically diverse population.     

Effects of selective dopamine D1-like and D2-like agonists on prepulse inhibition of startle in inbred C3H/HeJ,SPRET/EiJ,and CAST/EiJ mice

Rationale Prepulse inhibition (PPI) and locomotor activity have been used to investigate the effects of antipsychotic and stimulant drugs and their underlying dopaminergic mechanisms. Whereas D2-like agonists consistently decreased PPI and increased locomotion in rats in previous studies, we recently reported that these hallmark behavioral effects were not observed in several mouse strains. Nevertheless, we recently identified three mouse strains (C3H/HeJ, SPRET/EiJ, and CAST/EiJ) that exhibited locomotor hyperactivity after administration of a selective D2-like agonist. Objectives We hypothesized that, similar to rats, C3H/HeJ, SPRET/EiJ, and CAST/EiJ mice would exhibit decreased PPI after administration of a D2-like agonist. Results Administration of the D2-like agonist quinelorane dose-dependently decreased PPI in C3H/HeJ and SPRET/EiJ mice. In agreement with previous reports in rats and other strains of mice, the D1-like agonist R-6-Br-APB also decreased PPI in C3H/HeJ and SPRET/EiJ mice. In contrast, CAST/EiJ mice had low levels of baseline PPI in our standard test session and quinelorane and R-6-Br-APB had no effect on PPI under those conditions. Through the optimization of session parameters, we obtained higher baseline PPI in CAST/EiJ mice and found that quinelorane but not R-6-Br-APB decreased PPI. In summary, similar to rats and unlike previous published reports on several strains of mice, we have now identified three strains of mice in which a D2-like agonist decreased PPI. Conclusions The C3H/HeJ, SPRET/EiJ, and CAST/EiJ mice may more closely mirror the Sprague Dawley rat than most other mouse strains and may confer advantages in cross-species behavioral pharmacology studies related to D2 receptor function.     

MicroRNA changes in rat mesentery and serum associated with drug-induced vascular injury

Regulatory miRNAs play a role in vascular biology and are involved in biochemical and molecular pathways dysregulated during vascular injury. Collection and integration of functional miRNA data into these pathways can provide insight into pathogenesis at the site of injury; the same technologies applied to biofluids may provide diagnostic or surrogate biomarkers. miRNA was analyzed from mesentery and serum from rats given vasculotoxic compounds for 4 days. Fenoldopam, dopamine and midodrine each alter hemodynamics and are associated with histologic evidence of vascular injury, while yohimbine is vasoactive but does not cause histologic evidence of vascular injury in rat. There were 38 and 35 miRNAs altered in a statistically significant manner with a fold change of 2 or greater in mesenteries of fenoldopam- and dopamine-dosed rats, respectively, with 9 of these miRNAs shared. 10 miRNAs were altered in rats given midodrine; 6 were shared with either fenoldopam or dopamine. In situ hybridization demonstrated strong expression and co-localization of miR-134 in affected but not in adjacent unaffected vessels. Mesenteric miRNA expression may provide clarity or avenues of research into mechanisms involved in vascular injury once the functional role of specific miRNAs becomes better characterized. 102 miRNAs were altered in serum from rats with drug-induced vascular injury. 10 miRNAs were commonly altered in serum from dopamine and either fenoldopam or midodrine dosed rats; 18 of these 102 were also altered in mesenteries from rats with drug-induced vascular injury, suggesting their possible utility as peripheral biomarkers.     

Targeted Stage-Specific Inflammatory microRNA Profiling in Urine During Disease Progression in Experimental Autoimmune Encephalomyelitis: Markers of Disease Progression and Drug Response

Recently, microRNAs (miRNAs) have been implicated in regulating neuroinflammatory and demyelinative responses in multiple sclerosis (MS) and its mouse model of experimental autoimmune encephalomyelitis (EAE). miRNAs have also been studied as biomarkers of disease pathology and drug-response in MS. However, no complete miRNA profiling at various stages of EAE disease has been examined, especially in the urine. We carried out a systematic analysis of miRNAs in the urine exosomes as well as in the plasma and spinal cord at pre-onset, onset and peak stages of EAE established in the chronic B6 mice model. For the first time, we provide evidence that urine exosomes can be a specific and sensitive source of miRNA biomarkers for all 3 stages of EAE disease. In a significant observation, we observed that miR-155-5p expression increased in urine exosomes, plasma and spinal cord 6 days before the onset of disease, suggesting its early involvement in the pathology of EAE disease. We also analyzed the effect of Glatiramer acetate (GA; copaxone) treatment, an approved treatment for MS patients, in modulating miRNA expression at the peak of EAE disease. We identified miR-155-5p, miR-27a-3p, miR-9-5p and miR-350-5p as putative GA-treatment responsive miRNA biomarkers. Since, EAE is a mainly CD4 cells mediated disease, we also examined the above set of miRNAs and found to be significantly altered in T cells polarized to Th1 and Th17 phenotype, similar to urine exosomes. Thus, urine exosome miRNAs hold the potential to be defined as novel accessible stage-specific biomarkers of EAE (MS) disease as well as treatment response.     

Psychomotor stimulation by dopamine D₁-like but not D₂-like agonists in most mouse strains

Many neurological and psychiatric disorders are treated with dopamine modulators. Studies in mice may reveal genetic factors underlying those disorders or responsiveness to various treatments, and species and strain differences both complicate the use of mice and provide valuable tools. We evaluated psychomotor effects of the dopamine D?-like agonist R-6-Br-APB and the dopamine D?-like agonist quinelorane using a locomotor activity procedure in 15 mouse strains (inbred 129S1/SvImJ, 129S6/SvEvTac, 129X1/SvJ, A/J, BALB/cByJ, BALB/cJ, C3H/HeJ, C57BL/6J, CAST/EiJ, DBA/2J, FVB/NJ, SJL/J, SPRET/EiJ, outbred Swiss Webster, and CD-1) and Sprague-Dawley rats, using groups of both females and males. Both D? and D? stimulation produced hyperactivity in the rats, and surprisingly, only two mouse strains were similar in that regard (C3H/HeJ, SPRET/EiJ). In contrast, the majority of mouse strains exhibited hyperactivity only with D? stimulation, whereas D? stimulation had no effect or decreased activity. BALB substrains, A/J and FVB/NJ mice showed only decreased activity after either D? or D? stimulation. CAST/EiJ mice exhibited hyperactivity exclusively with D? stimulation. Sex differences were observed but no systematic trend emerged: For example, of the five strains in which a main factor of sex was identified for the stimulant effects of the D? agonist, responsiveness was greatest in females in three of those strains and in males in two of those strains. These results should aid in the selection of mouse strains for future studies in which D? or D? responsiveness is a necessary consideration in the experimental design.     

围生期缺血缺氧性脑病的微 RNA生物标志物筛选研究

目的研究围生期缺血缺氧性脑病( HIE)的微 RNA(miRNA)生物标志物的筛选情况。方法通过动态队列研究法获取 2020年 1月至 2021年 1月深圳市龙华区中心医院 144例 HIE病儿作为受试者。将其根据病情严重程度的差异分作轻度 HIE组 42例、中度 HIE组 62例以及重度 HIE组 40例,另取同期该院 50例健康新生儿作为对照组。分别采集所有新生儿脐带血进行测序比较分析差异表达 miRNA,筛选 3个和 HIE相关的 miRNA作为早期预测 HIE的生物标志物,并分析各组新生儿上述 3个 miRNA表达情况的差异。采用 Spearman相关性分析明确 HIE病情严重程度和 miRNA表达的关系。此外,将所有 HIE病儿按照是否合并脏器损伤分为合并脏器损伤组 102例以及未合并脏器损伤组 42例,比较两组上述 3个 miRNA表达情况的差异。此外,检测并比较 HIE组和对照组血清诱导型一氧化氮合酶( iNOS)、内皮素 -1水平。结果 miRNA芯片通过扫描、分析以及标准化处理,结果发现 miRNA芯片共检测 miRNA达 921种。相较于对照组, HIE病儿血浆中有 29种 miRNA表达异常升高, 26种 miRNA表达异常下降,选择差异有统计学意义的 miRNA实施生物学信息分析,发现了 miR-4472、miR-5195-3p以及 miR6794-5p可能具有潜在的预测 HIE作用。重度 HIE组 miR-4472、miR-5195-3p以及 miR-6794-5p表达水平分别为 0.71±0.12、2.34±0.28、2.24±0.24,均高于对照组的 0.20±0.04、0.78±0.15、0.47±0.11和轻度 HIE组的 0.37±0.08、0.92±0.18、0.89±0.15以及中度组的 0.55±0.09、1.45±0.23、1.46±0.20,且轻度 HIE组、中度 HIE组 miR-4472、miR-5195-3p以及 miR-6794-5p表达水平均高于对照组,中度 HIE组 miR-4472、miR-5195-3p以及 miR-6794-5p表达水平均高于轻度 HIE组(均 P<0.05)。 HIE病儿病情严重程度和 miR-4472、miR-5195-3p、miR-6794-5p表达均呈正相关关系(均 P<0.05)。合并脏器损伤 HIE病儿 miR-4472、miR-5195-3p、 miR-6794-5p表达水平分别为 0.60±0.09、2.05±0.18、1.70±0.31,均高于未合并脏器损伤组的 0.46±0.03、1.58±0.12、1.37±0.23(均 P<0.05)。 HIE组血清 iNOS及内皮素 -1水平均高于对照组(均 P<0.05)。结论 HIE的 miRNA生物标志物包括 miR-4472、miR5195-3p、miR-6794-5p,且上述 miRNA表达水平和病儿病情严重程度以及脏器损伤有关,值得临床重点关注。     

Genetic resistance of mice to persistent infection with Mycobacterium lepraemurium in vitro: association with macrophage bactericidal responsiveness to lymphokines and dissociation from production of hydrogen peroxide by macrophages

Peritoneal and splenic adherent macrophages (SAC) from M. lepraemurium susceptible (C3H/HeJ) and resistant (C57B1/6J) mice were studied for their abilities to generate H2O2 in vitro. Unexpectedly, SAC from the susceptible C3H/HeJ strain produced more H2O2 than those of the resistant C57BL/6J. In vivo sensitization with M. bovis (BCG), or C. parvum increased production of H2O2 by SAC from both strains, whereas in vivo sensitization with M. lepraemurium enhanced H2O2 production only in the C3H/HeJ susceptible strains. In vitro addition of a crude lymphokine enhanced H2O2 production by C3H/HeJ SAC more than by C57BL/6J SAC. In vitro addition of M. lepraemurium caused an inhibition of H2O2 production by SAC from both strains but the inhibition was greater for the resistant C57BL/6J strain. M. lepraemurium phagocytosed in vitro by untreated peritoneal macrophages of both mouse strains were morphologically altered to the same extent. However, the addition of lymphokine dramatically increased the degree of bacterial lysis in only the C57BL/6J strain. These results, support the view that H2O2 plays a limited, if any, role in the protection of the host from M. lepraemurium and may even contribute to susceptibility by inhibiting the host's immune response.     

Rhein lysinate decreases inflammation and adipose infiltration in KK/HlJ diabetic mice with non-alcoholic fatty liver disease

The objective of this study was to investigate the protective effects of rhein lysinate (RHL) on the liver. Mice were divided into four groups: C57BL/J control, the KK/HlJ diabetic model, and 25 and 50 mg/kg/day RHL-treated KK/HlJ groups. The KK/HlJ diabetic mouse model was made by injecting STZ and feeding mice diabetic food. At 16 weeks, mice were sacrificed and their livers were harvested. The results indicated that compared with the C57BL/J control group, the body weights, liver weights and liver weight-to-body weight ratio were increased in KK/HlJ diabetic mice; however, these values were decreased following treatment with RHL. Compared with the C57BL/J control, KK/HlJ diabetic mice had a significantly lower level of SOD and GSH-px in their livers, but had a significantly higher level of MDA. However, these effects were ameliorated by RHL. Hepatic adipose infiltration was observed in KK/HlJ mice, but not in C57BL/J mice. RHL decreased the incidence of hepatic adipose infiltration and significantly decreased the expression of TNF-α, IL-6, NF-κB, SREBP-1c, and Fas, as well as the phosphorylation of NF-κB in the liver. In conclusion, RHL can improve hepatic function by decreasing hepatic adipose infiltration and the expression of inflammatory factors.     

Mitochondrial bioenergetics and drug-induced toxicity in a panel of mouse embryonic fibroblasts with mitochondrial DNA single nucleotide polymorphisms

Mitochondrial DNA (mtDNA) variations including single nucleotide polymorphisms (SNPs) have been proposed to be involved in idiosyncratic drug reactions. However, current in vitro and in vivo models lack the genetic diversity seen in the human population. Our hypothesis is that different cell strains with distinct mtDNA SNPs may have different mitochondrial bioenergetic profiles and may therefore vary in their response to drug-induced toxicity. Therefore, we used an in vitro system composed of four strains of mouse embryonic fibroblasts (MEFs) with mtDNA polymorphisms. We sequenced mtDNA from embryonic fibroblasts isolated from four mouse strains, C57BL/6J, MOLF/EiJ, CZECHII/EiJ and PERA/EiJ, with the latter two being sequenced for the first time. The bioenergetic profile of the four strains of MEFs was investigated at both passages 3 and 10. Our results showed that there were clear differences among the four strains of MEFs at both passages, with CZECHII/EiJ having a lower mitochondrial robustness when compared to C57BL/6J, followed by MOLF/EiJ and PERA/EiJ. Seven drugs known to impair mitochondrial function were tested for their effect on the ATP content of the four strains of MEFs in both glucose- and galactose-containing media. Our results showed that there were strain-dependent differences in the response to some of the drugs. We propose that this model is a useful starting point to study compounds that may cause mitochondrial off-target toxicity in early stages of drug development, thus decreasing the number of experimental animals used.     

The changes of miRNA expression in rat hippocampus following chronic lead exposure

miRNAs have been found to contribute to normal brain functions, nervous system diseases, as well as neurotoxicities induced by external agents. However, whether they are involved in lead-induced neurotoxicities is still not clear. To identify that, a lead-induced chronic neurotoxicity model of rats was built. Both miRNA microarray analysis and qRT-PCR were performed to determine the change of miRNA expression in hippocampus. Then 3 bioinformatics databases were used to analyze the relative target genes of these miRNA, which were further confirmed by qRT-PCR and Western blot. In the present study, lead exposure resulted in the changed expression of 7 miRNAs: miR-204, miR-211, miR-448, miR-449a, miR-34b, and miR-34c were greatly up-regulated while miR-494 was greatly down-regulated. Bioinformatics analysis results showed that the target genes of 6 up-regulated miRNAs were related to neural injury and neurodegeration, axon and synapse function, neural development and regeneration. Correspondingly, the expression levels of mature mRNAs and proteins of three target genes (Bcl-2, Itpr1, and Map2k1) were greatly repressed, verifying the results of bioinformatics analysis. Taken together, our results showed that the expression of several miRNAs reported to be associated with neurophysiological pathways and neurodegenerative diseases changed in rat hippocampus following chronic lead exposure. These miRNAs may play important roles in lead-induced neurotoxicity.     

Psychomotor stimulant effects of cocaine in rats and 15 mouse strains

Relative to intravenous drug self-administration, locomotor activity is easier to measure with high throughput, particularly in mice. Therefore its potential to predict differences in self-administration between genotypes (e.g., targeted mutations, recombinant inbred strains) is appealing, but such predictive value is unverified. The main goal of this study was to evaluate the utility of the locomotor assay for accurately predicting differences in cocaine self-administration. A second goal was to evaluate any correlation between activity in a novel environment, and cocaine-induced hyperactivity, between strains. We evaluated locomotor activity in male and female Sprague-Dawley rats and 15 mouse strains (129S1/SvImJ, 129S6/SvEvTac, 129X1/SvJ, A/J, BALB/cByJ, BALB/cJ, C3H/HeJ, C57BL/6J, CAST/EiJ, DBA/2J, FVB/NJ, SJL/J, SPRET/EiJ, and outbred Swiss Webster and CD-1/ICR), as well as cocaine self-administration in BALB substrains. All but BALB/cJ mice showed locomotor habituation and significant cocaine-induced hyperactivity. BALB/cJ mice also failed to self-administer cocaine. BALB/cByJ mice showed modest locomotor habituation, cocaine-induced locomotion, and cocaine self-administration. As previously reported, female rats showed greater cocaine-induced locomotion than males, but this was only observed in one of 15 mouse strains (FVB/NJ), and the reverse was observed in two strains (129X1/SvJ, BALB/cByJ). The intriguing phenotype of the BALB/cJ strain may indicate some correlation between all-or-none locomotion in a novel environment, and stimulant and reinforcing effects of cocaine. However, neither novelty- nor cocaine-induced activity offered a clear prediction of relative reinforcing effects among strains. Additionally, these results should aid in selecting mouse strains for future studies in which relative locomotor responsiveness to psychostimulants is a necessary consideration.     

The relationship between the contents of 13 amino acids in brain tissues and the progression of NAFLD via C57BL/6 model mice

Non-alcoholic fatty liver disease (NAFLD) is the steatosis of liver parenchyma unrelated to alcoholism, autoimmunity, and viral infection. It is also a metabolism-related syndrome, which has an unseparated relationship with adipose tissue dysfunction and obesity. Hepatic encephalopathy (HE) is one of the severe complications of chronic liver disease and one of the end-stage syndromes of liver disease. Some researchers have suggested that NAFLD, like other forms of liver injury, may be related to the metabolic disorder of branched-chain amino acids (BCAAs), which have been approved to be associated with HE influencing ammonia and energy metabolism. However, several studies have revealed the relationship among amino acids in serum, HE, and chronic liver disease; there are few studies on the contents of amino acids in brain tissues of an animal model with NAFLD. In the present research, we established a NAFLD mouse model with C57BL/6 mice and determined the contents of 13 amino acids in brain tissues of model mice by HPLC-FLD derivatization method using ortho-phthalaldehyde (OPA) to explore the relationship between the contents of amino acids in brain tissues and the progression of NAFLD. Moreover, the study showed that the changes of amino acid contents in the brain of the C57BL/6 mice were associated with the advancement of NAFLD, and this change might be related to the mechanism of HE.     

Current pharmacotherapy for treating pediatric nonalcoholic fatty liver disease

Introduction: In the past decade, nonalcoholic fatty liver disease (NAFLD) had rapidly become one of the most common liver diseases. If efficient therapeutic strategies will not reduce the prevalence of NAFLD in children soon, serious deleterious effects on the quality of life of these patients in adulthood are expected. Lifestyle modification is the current first-line therapy for pediatric NAFLD, even though it is difficult to obtain and to maintain. Therefore, lifestyle changes are usually ineffective and long-lasting improvement of the NAFLD-associated liver damage is rarely observed. As guidelines for the management of NAFLD in children are still lacking, the identification of effective treatments represents a challenge for pediatric hepatologists in the near future.

Areas covered: Here, we review the existing therapeutic approaches for treating NAFLD in children and overview all ongoing clinical trials for new promising drugs in pediatric setting.

Expert opinion: Considering the multifactorial pathogenesis and the wide spectrum of histological and clinical features of NAFLD, we believe that a drug mix, containing agents that are effective against the principal pathogenetic factors, associated with lifestyle modification, could represent the winning choice of treatment for pediatric NAFLD.     

Distribution and excretion of 2,3,7,8-tetrachlorodibenzofuran in C57BL/6J and DBA/2J mice

The distribution and excretion of the toxic pollutant, 2,3,7,8-tetrachlorodibenzofuran (TCDF), was studied in male C57BL/6J and DBA/2J mice (22–29 g). [¹⁴C]TCDF was administered iv at a dose of 0.1 μmmol/kg. The liver was the major site of TCDF accumulation, with more TCDF in the livers of C57BL/6J mice compared to DBA/2J mice. TCDF had a half-life of approximately 1.8 days in the livers of both strains. At 7 hr and 1 day, respectively, radioactivity was redistributed to adipose tissue of C57BL/6J mice and DBA/2J mice. The terminal $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of TCDF in adipose tissue of C57BL/6J mice was 1.1 days, whereas it was 6.8 days in DBA/2J mice; the sixfold longer half-life in DBA/2J mice may be related to the approximately 36% greater adipose tissue content of this strain which may sequester more TCDF. More than 80 and 55% of the dose was excreted in the feces of C57BL/6J and DBA/2J mice, respectively, within 10 days as polar metabolites. The whole body half-life of TCDF was 2 days in C57BL/6J and 4 days in DBA/2J mice. Thus, DBA/2J mice sequester more of the TCDF dose in adipose tissue, accounting for a relatively slower rate of clearance and lower concentrations of TCDF at the putative target site(s) for toxic action.