Obesity is a multifactorial disease with both genetic and environmental components. The prevailin... more Obesity is a multifactorial disease with both genetic and environmental components. The prevailing view is that obesity results from an imbalance between energy intake and expenditure caused by overeating and insufficient exercise. We describe another environmental element that can alter the balance between energy intake and energy expenditure: obesogens. Obesogens are a subset of environmental chemicals that act as endocrine disruptors affecting metabolic endpoints. The obesogen hypothesis posits that exposure to endocrine disruptors and other chemicals can alter the development and function of the adipose tissue, liver, pancreas, gastrointestinal tract, and brain, thus changing the set point for control of metabolism. Obesogens can determine how much food is needed to maintain homeostasis and thereby increase the susceptibility to obesity. The most sensitive time for obesogen action is in utero and early childhood, in part via epigenetic programming that can be transmitted to future generations. This review explores the evidence supporting the obesogen hypothesis and highlights knowledge gaps that have prevented widespread acceptance as a contributor to the obesity pandemic. Critically, the obesogen hypothesis changes the narrative from curing obesity to preventing obesity. 1.2. Endocrine disrupting chemicals (EDCs) Many thousands of chemicals are used in commerce today, yet most health hazards have not been characterized. Chemical toxicants have several modes of action. These include specific or non-specific lethality, organ toxicity, genotoxicity, and mutagenicity through DNA sequence and structural alterations. They can also disrupt hormone levels or action, as with EDCs [5]. EDCs have an array of key characteristics,
The nuclear receptor (NR) subclass, retinoid X receptors (RXRs), exert immunomodulatory functions... more The nuclear receptor (NR) subclass, retinoid X receptors (RXRs), exert immunomodulatory functions that control inflammation and metabolism via homodimers and heterodimers, with several other NRs, including retinoic acid receptors. IRX4204 is a novel, highly specific RXR agonist in clinical trials that potently and selectively activates RXR homodimers, but not heterodimers. In this study, in vivo IRX4204 compared favorably with FK506 in abrogating acute graft-versus-host disease (GVHD), which was associated with inhibiting allogeneic donor T-cell proliferation, reducing T-helper 1 differentiation, and promoting regulatory T-cell (Treg) generation. Recipient IRX4204 treatment reduced intestinal injury and decreased IFN-γ and TNF-α serum levels. Transcriptional analysis of donor T cells isolated from intestines of GVHD mice treated with IRX4204 revealed significant decreases in transcripts regulating proinflammatory pathways. In vitro, inducible Treg differentiation from naive CD4+ T c...
This article was originally published in Comprehensive Toxicology, 3e, published by Elsevier, and... more This article was originally published in Comprehensive Toxicology, 3e, published by Elsevier, and the attached copy is provided by Elsevier for the author's benefit and for the benefit of the author's institution, for non-commercial research and educational use including without limitation use in instruction at your institution, sending it to specific colleagues who you know, and providing a copy to your institution's administrator.
We report here the complete nucleotide and amino acid sequences for the al-chain of mouse collage... more We report here the complete nucleotide and amino acid sequences for the al-chain of mouse collagen IV which is 1669 amino acids in length, including a putative 27-residue signal peptide. In comparison with the amino acid sequence for the a2-chain (Saus, J.,
Tetrabromobisphenol A (TBBPA) is the most common flame retardant used in electrical housings, cir... more Tetrabromobisphenol A (TBBPA) is the most common flame retardant used in electrical housings, circuit boards, and automobiles. High-throughput screening and binding assays have identified TBBPA as an agonist for human peroxisome proliferator-activated receptor gamma (PPARc), the master regulator of adipogenesis. TBBPA has been suggested to be an obesogen based on in vitro cellular assays and zebrafish data. We hypothesized that exposing preadipocytes to TBBPA could influence adipogenesis via genes other than those in the PPARc pathway due to its structural similarity to bisphenol A, which demonstrates varied endocrine disrupting activities. Mouse-derived 3T3-L1 preadipocytes were induced to differentiate and continually treated with TBBPA for 8 days. High-content imaging of adipocytes displayed increased adipocyte number and lipid accumulation when treated with TBBPA. TBBPA exhibited weak induction of mPPARc, with an AC 50 of 397 mM. Quantitative PCR revealed that TBBPA exposure increased early expression of genes involved in glucocorticoid receptor (GR) signaling and PPARc transcriptional activation, as well as upregulating downstream genes needed for adipocyte maintenance and nontraditional ER signaling, such as Gpr30. Additionally, Pref1 and Thy1, inhibitors of differentiation, were downregulated by some concentrations of TBBPA. Furthermore, proliferating preadipocytes treated with TBBPA, only prior to differentiation, exhibited increased adipocyte number and lipid accumulation after 8 days in normal culture conditions. In conclusion, TBBPA influenced gene expression changes in GR, nontraditional ER, and known adipogenic regulatory genes, prior to PPARc expression; effects suggesting early programming of adipogenic pathways.
The increasing incidence of obesity is a serious global public health challenge. Although the obe... more The increasing incidence of obesity is a serious global public health challenge. Although the obesity epidemic is largely fueled by poor nutrition and lack of exercise, certain chemicals have been shown to potentially have a role in its aetiology. A substantial body of evidence suggests that a subclass of endocrine-disrupting chemicals (EDCs), which interfere with endocrine signalling, can disrupt hormonally regulated metabolic processes, especially if exposure occurs during early development. These chemicals, so-called 'obesogens' might predispose some individuals to gain weight despite their efforts to limit caloric intake and increase levels of physical activity. This Review discusses the role of EDCs in the obesity epidemic, the latest research on the obesogen concept, epidemiological and experimental findings on obesogens, and their modes of action. The research reviewed here provides knowledge that health scientists can use to inform their research and decision-making ...
The rate of biosynthesis of procollagen IV, the principal collagen of basement membranes, and the... more The rate of biosynthesis of procollagen IV, the principal collagen of basement membranes, and the concentration of specific RNAs coding for procollagen IV were measured in neonatal rat lungs. Both decreased sharply at birth and then recovered again a few days later. The supramolecular assembly of procollagen IV was followed in neonatal rat, mouse, and chick lungs, which actively elaborate endothelial and alveolar basement membranes, and in chick embryo gizzard which is rich in smooth muscle. The tetramer of four procollagen IV molecules linked covalently through their amino ends was isolated as an assembly intermediate from all these tissues. While noncovalent association of the carboxyl ends of two procollagen IV molecules occurred readily, the subsequent establishment of covalent cross-links was substantially slower in the junctional complexes of the carboxyl ends than of the amino ends. Both disulfide bonds and other, unidentified covalent links formed. The six component carboxyl...
Burgeoning evidence demonstrates that responses to environmental exposures can be transmitted to ... more Burgeoning evidence demonstrates that responses to environmental exposures can be transmitted to subsequent generations through the germline without DNA mutations1,2. This is controversial because underlying mechanisms remain to be identified. Therefore, understanding how effects of environmental exposures are transmitted to unexposed generations without DNA mutations is a fundamental unanswered question in biology. Here, we used an established murine model of transgenerational obesity to show that direct or ancestral exposure to the obesogen tributyltin (TBT) elicited persistent changes in topologically associating domains (TADs) in primordial germ cells (PGCs) isolated from embryos of exposed and subsequent unexposed generations. New TAD boundaries were formed within theIdegene encoding insulin degrading enzyme in the exposed PGCs, then stably maintained in PGCs of the subsequent (unexposed) two generations. Concomitantly,IdemRNA expression was decreased in livers of male descenda...
2,4-Di-tert-butylphenol (2,4-DTBP) is an important commercial antioxidant and a toxic natural sec... more 2,4-Di-tert-butylphenol (2,4-DTBP) is an important commercial antioxidant and a toxic natural secondary metabolite that has been detected in humans. However, there is scant information regarding its toxicological effects. We asked whether 2,4-DTBP is a potential obesogen. Using a human mesenchymal stem cell adipogenesis assay, we found that exposure to 2,4-DTBP led to increased lipid accumulation and expression of adipogenic marker genes. Antagonist assays revealed that 2,4-DTBP increased lipid accumulation by activating the peroxisome proliferator-activated receptor (PPAR) γ-retinoid X receptor (RXR) heterodimer. 2,4-DTBP likely activated the PPARγ/RXRα heterodimer by activating RXRα but not directly binding to PPARγ. We confirmed that 2,4-DTBP directly bound to RXRα by solving the crystal structure of this complex, then predicted and demonstrated that related compounds could also activate RXRα. Our study demonstrated that 2,4-DTBP and related chemicals could act as obesogens and e...
Obesogens such as tributyltin (TBT) are xenobiotic compounds that promote obesity, in part by dis... more Obesogens such as tributyltin (TBT) are xenobiotic compounds that promote obesity, in part by distorting the normal balance of lipid metabolism. The obesogenic effects of TBT can be observed in directly exposed (F1 and F2 generations) and also subsequent generations (F3 and beyond) that were never exposed. To address the effects of TBT exposure on germ cells, we exposed pregnant transgenic OG2 mouse dams (F0), which specifically express EGFP in germline cells, to an environmentally relevant dose of TBT or DMSO throughout gestation through drinking water. When fed with a high-fat diet, F3 male offspring of TBT-exposed F0 dams (TBT-F3) accumulated much more body fat than did DMSO-F3 males. TBT-F3 males also lost more body fluid and lean compositions than did DMSO-F3 males. Expression of genes involved in transcriptional regulation or mesenchymal differentiation was up-regulated in somatic cells of TBT-F1 (but not TBT-F3) E18.5 fetal testes, and promoter-associated CpG islands were hyp...
Exposure of pregnant F0 mouse dams to the obesogen tributyltin (TBT) predisposes unexposed male d... more Exposure of pregnant F0 mouse dams to the obesogen tributyltin (TBT) predisposes unexposed male descendants to obesity and diverts mesenchymal stem cells (MSCs) toward the adipocytic lineage. TBT promotes adipogenic commitment and differentiation of MSCs in vitro. To identify TBT-induced factors predisposing MSCs toward the adipocytic fate, we exposed mouse MSCs to TBT, the peroxisome proliferator activated receptor gamma (PPARγ)-selective agonist rosiglitazone, or the retinoid X receptor (RXR)-selective agonist LG-100268. Then we determined their transcriptomal profiles to determine candidate microRNAs (miR) regulating adipogenic commitment and differentiation. Of the top 10 candidate microRNAs predicted by Ingenuity Pathway Analysis, miR-21, miR-33, and miR-223 were expressed consistent with an ability to differentially regulate target genes during adipogenesis. We found that 24-hour exposure to 50nM TBT caused miR-223 levels in MSCs to increase; expression of its target genes ZEB...
BACKGROUND: Polychlorinated biphenyls (PCBs) are environmental toxicants; PCB exposure has been a... more BACKGROUND: Polychlorinated biphenyls (PCBs) are environmental toxicants; PCB exposure has been associated with adverse effects on wildlife and humans. However, the mechanisms underlying these adverse effects are not fully understood. The steroid and xenobiotic receptor [SXR; also known as the pregnane X receptor (PXR) and formally known as NR1I2] is a nuclear hormone receptor that regulates inducible metabolism of drugs and xenobiotics and is activated or inhibited by various PCB congeners. OBJECTIVES: The aim of this study was to investigate the effects of exposure to PCB-153, the most prevalent PCB congener in human tissues, on SXR knockout mice (SXRKO) and to elucidate the role of SXR in PCB-153 metabolism and promotion of its harmful effects. METHODS: Wild-type (WT) and SXRKO mice were chronically or perinatally exposed to a low dose (54 lg=kg=d) of PCB-153. Blood, livers, and spleens were analyzed using transcriptome sequencing (RNA-seq) and molecular techniques to investigate the impacts of exposure on metabolism, oxidative stress, and hematological parameters. RESULTS: SXRKO mice perinatally exposed to PCB-153 displayed elevated oxidative stress, symptoms of hemolytic anemia, and premature death. Transcriptomal analysis revealed that expression of genes involved in metabolic processes was altered in SXRKO mice. Elevated levels of the PCB-153 metabolite, 3-OH-PCB-153, were found in exposed SXRKO mice compared to exposed WT mice. Blood hemoglobin (HGB) levels were lower throughout the lifespan, and the occurrence of intestinal tumors was larger in SXRKO mice chronically exposed to PCB-153 compared to vehicle and WT controls. DISCUSSION: Our results suggest that altered metabolism induced by SXR loss of function resulted in the accumulation of hydroxylated metabolites upon exposure to PCB-153, leading to oxidative stress, hemolytic anemia, and tumor development in a mouse model. These results support a major role for SXR/PXR in protection against xenobiotic-induced oxidative stress by maintaining proper metabolism in response to PCB-153 exposure. This role of SXR could be generally applicable to other environmental toxicants as well as pharmaceutical drugs.
Background: Endocrine disrupting chemicals (EDCs) contribute to the etiology of metabolic disorde... more Background: Endocrine disrupting chemicals (EDCs) contribute to the etiology of metabolic disorders such as obesity, insulin resistance and hepatic dysfunction. Concern is growing about the consequences of perinatal EDC exposure on disease predisposition later in life. Metabolomics are promising approaches for studying long-term consequences of early life EDC exposure. These approaches allow for the identification and characterization of biomarkers of direct or ancestral exposures that could be diagnostic for individual susceptibility to disease and help to understand mechanisms through which EDCs act. Objectives: We sought to identify metabolomic fingerprints in mice ancestrally exposed to the model obesogen tributyltin (TBT), to assess whether metabolomics could discriminate potential trans-generational susceptibility to obesity and recognize metabolic pathways modulated by ancestral TBT exposure. Methods: We used non-targeted 1 H NMR metabolomic analyses of plasma and liver samples collected from male and female mice ancestrally exposed to TBT in two independent transgenerational experiments in which F3 and F4 males became obese when challenged with increased dietary fat. Results: Metabolomics confirmed transgenerational obesogenic effects of environmentally relevant doses of TBT in F3 and F4 males, in two independent studies. Although females never became obese, their specific metabolomic fingerprint evidenced distinct transgenerational effects of TBT in female mice consistent with impaired capacity for liver biotransformation. Discussion: This study is the first application of metabolomics to unveil the transgenerational effects of EDC exposure. Very early, significant changes in the plasma metabolome were observed in animals ancestrally exposed to TBT. These changes preceded the onset of obesogenic effects elicited by increased dietary fat in the TBT groups, and which ultimately resulted in significant changes in the liver metabolome. Development of metabolomic fingerprints could facilitate the identification of individuals carrying the signature of ancestral obesogen exposure that might increase their susceptibility to other risk factor such as increased dietary fat.
The incidence of obesity has reached an all-time high and this increase is observed worldwide. Th... more The incidence of obesity has reached an all-time high and this increase is observed worldwide. There is a growing need to understand all of the factors that contribute to obesity in order to effectively treat and prevent it and associated comorbidities. The obesogen hypothesis proposes that there are chemicals in our environment termed “obesogens” that can impact individual susceptibility to obesity and thus help explain the recent large increases in obesity. This review discusses current advances in our understanding of how obesogens act to impact health and obesity susceptibility. Newly discovered obesogens, and potential obesogens are discussed, together with future directions for research that may help to reduce the impact of these pervasive chemicals.
BACKGROUND. Cytochrome P450s (CYPs) influence the biological effects of carcinogens, drugs and ho... more BACKGROUND. Cytochrome P450s (CYPs) influence the biological effects of carcinogens, drugs and hormones including testosterones. Among them, Cytochrome P450 2B6 (CYP2B6) plays a critical role in the deactivation of testosterone. In the present study, we examined CYP2B6 expression in human prostate tissues and prostate cancer. METHODS. Immunohistochemical analysis was performed in 98 benign and 106 malignant prostate tissues and patients' charts were reviewed for clinical, pathologic and survival data. We also investigated whether stable expression of CYP2B6 in LNCaP (human prostate cancer cell line) influences cellular proliferation. RESULTS. CYP2B6 was abundantly expressed in the normal epithelial cells compared to the prostate cancer cells. Significant immunostaining of CYP2B6 was found in 75 of 106 samples (71%), in the cytoplasm of cancerous tissue samples. CYP2B6 immunoreactivity was inversely correlated with high Gleason score (P < 0.001). Decreased immunoreactivity of CYP2B6 significantly correlated with poor prognosis (P < 0.0001). Univariate and multivariate hazard analyses revealed a significant correlation of decreased CYP2B6 expression with poor cancerspecific survival (P ¼ 0.0028 and 0.0142, respectively). Furthermore, overexpression of CYP2B6 in LNCaP cells significantly decreased testosterone-induced proliferation. CONCLUSIONS. These results demonstrated that decreased expression of CYP2B6 might play a role in the development of prostate cancer, and be useful as the prognostic predictor for human prostate cancer.
Since the early 1990s, a substantial number of deformed frogs have been observed in North America... more Since the early 1990s, a substantial number of deformed frogs have been observed in North America, particularly in the upper Midwest and Canada. Attempts to understand the etiology of the deformed frog problem have met with limited success to date with nearly as many proposed explanations as research groups working on the problem. Models for the mechanism underlying the development of deformed frogs include parasite/predation, ultraviolet radiation, and chemical exposure. Each model has its strengths and weaknesses. Despite contentious debate among researchers, there is an overall consensus that the increasing prevalence of deformed frogs is the result of a water-borne contaminant that has recently appeared, or reached a critical concentration. Our detailed analysis of malformed frogs collected in Minnesota ponds and lakes suggested that limb patterning was being modified by the disruption of a retinoid-sensitive developmental signaling pathway. Accordingly, we focused in the identi...
Obesity is a multifactorial disease with both genetic and environmental components. The prevailin... more Obesity is a multifactorial disease with both genetic and environmental components. The prevailing view is that obesity results from an imbalance between energy intake and expenditure caused by overeating and insufficient exercise. We describe another environmental element that can alter the balance between energy intake and energy expenditure: obesogens. Obesogens are a subset of environmental chemicals that act as endocrine disruptors affecting metabolic endpoints. The obesogen hypothesis posits that exposure to endocrine disruptors and other chemicals can alter the development and function of the adipose tissue, liver, pancreas, gastrointestinal tract, and brain, thus changing the set point for control of metabolism. Obesogens can determine how much food is needed to maintain homeostasis and thereby increase the susceptibility to obesity. The most sensitive time for obesogen action is in utero and early childhood, in part via epigenetic programming that can be transmitted to future generations. This review explores the evidence supporting the obesogen hypothesis and highlights knowledge gaps that have prevented widespread acceptance as a contributor to the obesity pandemic. Critically, the obesogen hypothesis changes the narrative from curing obesity to preventing obesity. 1.2. Endocrine disrupting chemicals (EDCs) Many thousands of chemicals are used in commerce today, yet most health hazards have not been characterized. Chemical toxicants have several modes of action. These include specific or non-specific lethality, organ toxicity, genotoxicity, and mutagenicity through DNA sequence and structural alterations. They can also disrupt hormone levels or action, as with EDCs [5]. EDCs have an array of key characteristics,
The nuclear receptor (NR) subclass, retinoid X receptors (RXRs), exert immunomodulatory functions... more The nuclear receptor (NR) subclass, retinoid X receptors (RXRs), exert immunomodulatory functions that control inflammation and metabolism via homodimers and heterodimers, with several other NRs, including retinoic acid receptors. IRX4204 is a novel, highly specific RXR agonist in clinical trials that potently and selectively activates RXR homodimers, but not heterodimers. In this study, in vivo IRX4204 compared favorably with FK506 in abrogating acute graft-versus-host disease (GVHD), which was associated with inhibiting allogeneic donor T-cell proliferation, reducing T-helper 1 differentiation, and promoting regulatory T-cell (Treg) generation. Recipient IRX4204 treatment reduced intestinal injury and decreased IFN-γ and TNF-α serum levels. Transcriptional analysis of donor T cells isolated from intestines of GVHD mice treated with IRX4204 revealed significant decreases in transcripts regulating proinflammatory pathways. In vitro, inducible Treg differentiation from naive CD4+ T c...
This article was originally published in Comprehensive Toxicology, 3e, published by Elsevier, and... more This article was originally published in Comprehensive Toxicology, 3e, published by Elsevier, and the attached copy is provided by Elsevier for the author's benefit and for the benefit of the author's institution, for non-commercial research and educational use including without limitation use in instruction at your institution, sending it to specific colleagues who you know, and providing a copy to your institution's administrator.
We report here the complete nucleotide and amino acid sequences for the al-chain of mouse collage... more We report here the complete nucleotide and amino acid sequences for the al-chain of mouse collagen IV which is 1669 amino acids in length, including a putative 27-residue signal peptide. In comparison with the amino acid sequence for the a2-chain (Saus, J.,
Tetrabromobisphenol A (TBBPA) is the most common flame retardant used in electrical housings, cir... more Tetrabromobisphenol A (TBBPA) is the most common flame retardant used in electrical housings, circuit boards, and automobiles. High-throughput screening and binding assays have identified TBBPA as an agonist for human peroxisome proliferator-activated receptor gamma (PPARc), the master regulator of adipogenesis. TBBPA has been suggested to be an obesogen based on in vitro cellular assays and zebrafish data. We hypothesized that exposing preadipocytes to TBBPA could influence adipogenesis via genes other than those in the PPARc pathway due to its structural similarity to bisphenol A, which demonstrates varied endocrine disrupting activities. Mouse-derived 3T3-L1 preadipocytes were induced to differentiate and continually treated with TBBPA for 8 days. High-content imaging of adipocytes displayed increased adipocyte number and lipid accumulation when treated with TBBPA. TBBPA exhibited weak induction of mPPARc, with an AC 50 of 397 mM. Quantitative PCR revealed that TBBPA exposure increased early expression of genes involved in glucocorticoid receptor (GR) signaling and PPARc transcriptional activation, as well as upregulating downstream genes needed for adipocyte maintenance and nontraditional ER signaling, such as Gpr30. Additionally, Pref1 and Thy1, inhibitors of differentiation, were downregulated by some concentrations of TBBPA. Furthermore, proliferating preadipocytes treated with TBBPA, only prior to differentiation, exhibited increased adipocyte number and lipid accumulation after 8 days in normal culture conditions. In conclusion, TBBPA influenced gene expression changes in GR, nontraditional ER, and known adipogenic regulatory genes, prior to PPARc expression; effects suggesting early programming of adipogenic pathways.
The increasing incidence of obesity is a serious global public health challenge. Although the obe... more The increasing incidence of obesity is a serious global public health challenge. Although the obesity epidemic is largely fueled by poor nutrition and lack of exercise, certain chemicals have been shown to potentially have a role in its aetiology. A substantial body of evidence suggests that a subclass of endocrine-disrupting chemicals (EDCs), which interfere with endocrine signalling, can disrupt hormonally regulated metabolic processes, especially if exposure occurs during early development. These chemicals, so-called 'obesogens' might predispose some individuals to gain weight despite their efforts to limit caloric intake and increase levels of physical activity. This Review discusses the role of EDCs in the obesity epidemic, the latest research on the obesogen concept, epidemiological and experimental findings on obesogens, and their modes of action. The research reviewed here provides knowledge that health scientists can use to inform their research and decision-making ...
The rate of biosynthesis of procollagen IV, the principal collagen of basement membranes, and the... more The rate of biosynthesis of procollagen IV, the principal collagen of basement membranes, and the concentration of specific RNAs coding for procollagen IV were measured in neonatal rat lungs. Both decreased sharply at birth and then recovered again a few days later. The supramolecular assembly of procollagen IV was followed in neonatal rat, mouse, and chick lungs, which actively elaborate endothelial and alveolar basement membranes, and in chick embryo gizzard which is rich in smooth muscle. The tetramer of four procollagen IV molecules linked covalently through their amino ends was isolated as an assembly intermediate from all these tissues. While noncovalent association of the carboxyl ends of two procollagen IV molecules occurred readily, the subsequent establishment of covalent cross-links was substantially slower in the junctional complexes of the carboxyl ends than of the amino ends. Both disulfide bonds and other, unidentified covalent links formed. The six component carboxyl...
Burgeoning evidence demonstrates that responses to environmental exposures can be transmitted to ... more Burgeoning evidence demonstrates that responses to environmental exposures can be transmitted to subsequent generations through the germline without DNA mutations1,2. This is controversial because underlying mechanisms remain to be identified. Therefore, understanding how effects of environmental exposures are transmitted to unexposed generations without DNA mutations is a fundamental unanswered question in biology. Here, we used an established murine model of transgenerational obesity to show that direct or ancestral exposure to the obesogen tributyltin (TBT) elicited persistent changes in topologically associating domains (TADs) in primordial germ cells (PGCs) isolated from embryos of exposed and subsequent unexposed generations. New TAD boundaries were formed within theIdegene encoding insulin degrading enzyme in the exposed PGCs, then stably maintained in PGCs of the subsequent (unexposed) two generations. Concomitantly,IdemRNA expression was decreased in livers of male descenda...
2,4-Di-tert-butylphenol (2,4-DTBP) is an important commercial antioxidant and a toxic natural sec... more 2,4-Di-tert-butylphenol (2,4-DTBP) is an important commercial antioxidant and a toxic natural secondary metabolite that has been detected in humans. However, there is scant information regarding its toxicological effects. We asked whether 2,4-DTBP is a potential obesogen. Using a human mesenchymal stem cell adipogenesis assay, we found that exposure to 2,4-DTBP led to increased lipid accumulation and expression of adipogenic marker genes. Antagonist assays revealed that 2,4-DTBP increased lipid accumulation by activating the peroxisome proliferator-activated receptor (PPAR) γ-retinoid X receptor (RXR) heterodimer. 2,4-DTBP likely activated the PPARγ/RXRα heterodimer by activating RXRα but not directly binding to PPARγ. We confirmed that 2,4-DTBP directly bound to RXRα by solving the crystal structure of this complex, then predicted and demonstrated that related compounds could also activate RXRα. Our study demonstrated that 2,4-DTBP and related chemicals could act as obesogens and e...
Obesogens such as tributyltin (TBT) are xenobiotic compounds that promote obesity, in part by dis... more Obesogens such as tributyltin (TBT) are xenobiotic compounds that promote obesity, in part by distorting the normal balance of lipid metabolism. The obesogenic effects of TBT can be observed in directly exposed (F1 and F2 generations) and also subsequent generations (F3 and beyond) that were never exposed. To address the effects of TBT exposure on germ cells, we exposed pregnant transgenic OG2 mouse dams (F0), which specifically express EGFP in germline cells, to an environmentally relevant dose of TBT or DMSO throughout gestation through drinking water. When fed with a high-fat diet, F3 male offspring of TBT-exposed F0 dams (TBT-F3) accumulated much more body fat than did DMSO-F3 males. TBT-F3 males also lost more body fluid and lean compositions than did DMSO-F3 males. Expression of genes involved in transcriptional regulation or mesenchymal differentiation was up-regulated in somatic cells of TBT-F1 (but not TBT-F3) E18.5 fetal testes, and promoter-associated CpG islands were hyp...
Exposure of pregnant F0 mouse dams to the obesogen tributyltin (TBT) predisposes unexposed male d... more Exposure of pregnant F0 mouse dams to the obesogen tributyltin (TBT) predisposes unexposed male descendants to obesity and diverts mesenchymal stem cells (MSCs) toward the adipocytic lineage. TBT promotes adipogenic commitment and differentiation of MSCs in vitro. To identify TBT-induced factors predisposing MSCs toward the adipocytic fate, we exposed mouse MSCs to TBT, the peroxisome proliferator activated receptor gamma (PPARγ)-selective agonist rosiglitazone, or the retinoid X receptor (RXR)-selective agonist LG-100268. Then we determined their transcriptomal profiles to determine candidate microRNAs (miR) regulating adipogenic commitment and differentiation. Of the top 10 candidate microRNAs predicted by Ingenuity Pathway Analysis, miR-21, miR-33, and miR-223 were expressed consistent with an ability to differentially regulate target genes during adipogenesis. We found that 24-hour exposure to 50nM TBT caused miR-223 levels in MSCs to increase; expression of its target genes ZEB...
BACKGROUND: Polychlorinated biphenyls (PCBs) are environmental toxicants; PCB exposure has been a... more BACKGROUND: Polychlorinated biphenyls (PCBs) are environmental toxicants; PCB exposure has been associated with adverse effects on wildlife and humans. However, the mechanisms underlying these adverse effects are not fully understood. The steroid and xenobiotic receptor [SXR; also known as the pregnane X receptor (PXR) and formally known as NR1I2] is a nuclear hormone receptor that regulates inducible metabolism of drugs and xenobiotics and is activated or inhibited by various PCB congeners. OBJECTIVES: The aim of this study was to investigate the effects of exposure to PCB-153, the most prevalent PCB congener in human tissues, on SXR knockout mice (SXRKO) and to elucidate the role of SXR in PCB-153 metabolism and promotion of its harmful effects. METHODS: Wild-type (WT) and SXRKO mice were chronically or perinatally exposed to a low dose (54 lg=kg=d) of PCB-153. Blood, livers, and spleens were analyzed using transcriptome sequencing (RNA-seq) and molecular techniques to investigate the impacts of exposure on metabolism, oxidative stress, and hematological parameters. RESULTS: SXRKO mice perinatally exposed to PCB-153 displayed elevated oxidative stress, symptoms of hemolytic anemia, and premature death. Transcriptomal analysis revealed that expression of genes involved in metabolic processes was altered in SXRKO mice. Elevated levels of the PCB-153 metabolite, 3-OH-PCB-153, were found in exposed SXRKO mice compared to exposed WT mice. Blood hemoglobin (HGB) levels were lower throughout the lifespan, and the occurrence of intestinal tumors was larger in SXRKO mice chronically exposed to PCB-153 compared to vehicle and WT controls. DISCUSSION: Our results suggest that altered metabolism induced by SXR loss of function resulted in the accumulation of hydroxylated metabolites upon exposure to PCB-153, leading to oxidative stress, hemolytic anemia, and tumor development in a mouse model. These results support a major role for SXR/PXR in protection against xenobiotic-induced oxidative stress by maintaining proper metabolism in response to PCB-153 exposure. This role of SXR could be generally applicable to other environmental toxicants as well as pharmaceutical drugs.
Background: Endocrine disrupting chemicals (EDCs) contribute to the etiology of metabolic disorde... more Background: Endocrine disrupting chemicals (EDCs) contribute to the etiology of metabolic disorders such as obesity, insulin resistance and hepatic dysfunction. Concern is growing about the consequences of perinatal EDC exposure on disease predisposition later in life. Metabolomics are promising approaches for studying long-term consequences of early life EDC exposure. These approaches allow for the identification and characterization of biomarkers of direct or ancestral exposures that could be diagnostic for individual susceptibility to disease and help to understand mechanisms through which EDCs act. Objectives: We sought to identify metabolomic fingerprints in mice ancestrally exposed to the model obesogen tributyltin (TBT), to assess whether metabolomics could discriminate potential trans-generational susceptibility to obesity and recognize metabolic pathways modulated by ancestral TBT exposure. Methods: We used non-targeted 1 H NMR metabolomic analyses of plasma and liver samples collected from male and female mice ancestrally exposed to TBT in two independent transgenerational experiments in which F3 and F4 males became obese when challenged with increased dietary fat. Results: Metabolomics confirmed transgenerational obesogenic effects of environmentally relevant doses of TBT in F3 and F4 males, in two independent studies. Although females never became obese, their specific metabolomic fingerprint evidenced distinct transgenerational effects of TBT in female mice consistent with impaired capacity for liver biotransformation. Discussion: This study is the first application of metabolomics to unveil the transgenerational effects of EDC exposure. Very early, significant changes in the plasma metabolome were observed in animals ancestrally exposed to TBT. These changes preceded the onset of obesogenic effects elicited by increased dietary fat in the TBT groups, and which ultimately resulted in significant changes in the liver metabolome. Development of metabolomic fingerprints could facilitate the identification of individuals carrying the signature of ancestral obesogen exposure that might increase their susceptibility to other risk factor such as increased dietary fat.
The incidence of obesity has reached an all-time high and this increase is observed worldwide. Th... more The incidence of obesity has reached an all-time high and this increase is observed worldwide. There is a growing need to understand all of the factors that contribute to obesity in order to effectively treat and prevent it and associated comorbidities. The obesogen hypothesis proposes that there are chemicals in our environment termed “obesogens” that can impact individual susceptibility to obesity and thus help explain the recent large increases in obesity. This review discusses current advances in our understanding of how obesogens act to impact health and obesity susceptibility. Newly discovered obesogens, and potential obesogens are discussed, together with future directions for research that may help to reduce the impact of these pervasive chemicals.
BACKGROUND. Cytochrome P450s (CYPs) influence the biological effects of carcinogens, drugs and ho... more BACKGROUND. Cytochrome P450s (CYPs) influence the biological effects of carcinogens, drugs and hormones including testosterones. Among them, Cytochrome P450 2B6 (CYP2B6) plays a critical role in the deactivation of testosterone. In the present study, we examined CYP2B6 expression in human prostate tissues and prostate cancer. METHODS. Immunohistochemical analysis was performed in 98 benign and 106 malignant prostate tissues and patients' charts were reviewed for clinical, pathologic and survival data. We also investigated whether stable expression of CYP2B6 in LNCaP (human prostate cancer cell line) influences cellular proliferation. RESULTS. CYP2B6 was abundantly expressed in the normal epithelial cells compared to the prostate cancer cells. Significant immunostaining of CYP2B6 was found in 75 of 106 samples (71%), in the cytoplasm of cancerous tissue samples. CYP2B6 immunoreactivity was inversely correlated with high Gleason score (P < 0.001). Decreased immunoreactivity of CYP2B6 significantly correlated with poor prognosis (P < 0.0001). Univariate and multivariate hazard analyses revealed a significant correlation of decreased CYP2B6 expression with poor cancerspecific survival (P ¼ 0.0028 and 0.0142, respectively). Furthermore, overexpression of CYP2B6 in LNCaP cells significantly decreased testosterone-induced proliferation. CONCLUSIONS. These results demonstrated that decreased expression of CYP2B6 might play a role in the development of prostate cancer, and be useful as the prognostic predictor for human prostate cancer.
Since the early 1990s, a substantial number of deformed frogs have been observed in North America... more Since the early 1990s, a substantial number of deformed frogs have been observed in North America, particularly in the upper Midwest and Canada. Attempts to understand the etiology of the deformed frog problem have met with limited success to date with nearly as many proposed explanations as research groups working on the problem. Models for the mechanism underlying the development of deformed frogs include parasite/predation, ultraviolet radiation, and chemical exposure. Each model has its strengths and weaknesses. Despite contentious debate among researchers, there is an overall consensus that the increasing prevalence of deformed frogs is the result of a water-borne contaminant that has recently appeared, or reached a critical concentration. Our detailed analysis of malformed frogs collected in Minnesota ponds and lakes suggested that limb patterning was being modified by the disruption of a retinoid-sensitive developmental signaling pathway. Accordingly, we focused in the identi...
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Papers by Bruce Blumberg