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Through a multiplex promoter spanning 218 kb, the phase II UDP-glucuronosyltransferase 1A (UGT1) gene encodes at least eight differently regulated mRNAs whose protein products function as the principal means to eliminate a vast array of steroids, heme metabolites, environmental toxins, and drugs. The orphan nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) were originally identified as sensors able to respond to numerous environmentally derived foreign compounds (xenobiotics) to promote detoxification by phase I cytochrome P450 genes. In this report, we show that both receptors can induce specific UGT1A isoforms including those involved in estrogen, thyroxin, bilirubin, and carcinogen metabolism. Transgenic mice expressing a constitutively active form of human PXR show markedly increased UGT activity toward steroid, heme, and carcinogens, enhanced bilirubin clearance, as well as massively increased steroid clearance. The ability of PXR and constitutive androstane receptor and their ligands to transduce both the phase I and phase II adaptive hepatic response defines a unique transcriptional interface that bridges the ingestion and metabolism of environmental compounds to body physiology.

Triclosan (TCS), employed as an antiseptic and disinfectant, comes into direct contact with humans through a plethora of consumer products and its rising environmental release. We have demonstrated that TCS promotes liver tumorigenesis in mice, yet the biological and molecular mechanisms by which TCS exerts its toxicity, especially in early stages of liver disease, are largely unexplored. When mice were fed a high-fat diet (HFD), we found that fatty liver and dyslipidemia are prominent early signs of liver abnormality induced by TCS. The presumably protective HFDinduced hepatic expression of the metabolic regulator fibroblast growth factor 21 (FGF21) was blunted by TCS. TCS-altered Fgf21 expression aligned with aberrant expression of genes encoding metabolic enzymes manifested as profound systemic metabolic changes that disturb homeostasis of amino acids, fatty acids, and glucose. Using a type 1 diabetic animal model, TCS potentiates and accelerates the development of steatohepatitis and fibrosis, accompanied by increased levels of hepatic lipid droplets and oxidative stress. Analysis of fecal samples revealed that HFD-fed mice exhibited a reduction in fecal species richness, and that TCS further diminished microbial diversity and shifted the bacterial community toward lower Bacteriodetes and higher Firmicutes, resembling changes in microbiota composition in nonalcoholic steatohepatitis (NASH) patients. Using reverse-genetic approaches, we demonstrate that, along with HFD, TCS induces hepatic steatosis and steatohepatitis jointly regulated by the transcription factor ATF4 and the nuclear receptor PPARα, which participate in the transcriptional regulation of the Fgf21 gene. This study provides evidence linking nutritional imbalance and exposure to TCS with the progression of NASH. [ABSTRACT FROM AUTHOR]

Severe neonatal hyperbilirubinemia (SNH) and the onset of bilirubin encephalopathy and kernicterus result in part from delayed expression of UDP-glucuronosyltransferase 1A1 (UGT1A1) and the inability to metabolize bilirubin. Although there is a good understanding of the early events after birth that lead to the rapid increase in serum bilirubin, the events that control delayed expression of UGT1A1 during development remain a mystery. Humanized UGT1 (hUGT1) mice develop SNH spontaneously, which is linked to repression of both liver and intestinal UGT1A1. In this study, we report that deletion of intestinal nuclear receptor corepressor 1 (NCoR1) completely diminishes hyperbilirubinemia in hUGT1 neonates because of intestinal UGT1A1 gene derepression. Transcriptomic studies and immunohistochemistry analysis demonstrate that NCoR1 plays a major role in repressing developmental maturation of the intestines. Derepression is marked by accelerated metabolic and oxidative phosphorylation, drug metabolism, fatty acid metabolism, and intestinal maturation, events that are controlled predominantly by H3K27 acetylation. The control of NCoR1 function and derepression is linked to IKKβ function, as validated in hUGT1 mice with targeted deletion of intestinal IKKβ. Physiological events during neonatal development that target activation of an IKKβ/NCoR1 loop in intestinal epithelial cells lead to derepression of genes involved in intestinal maturation and bilirubin detoxification. These findings provide a mechanism of NCoR1 in intestinal homeostasis during development and provide a key link to those events that control developmental repression of UGT1A1 and hyperbilirubinemia. [ABSTRACT FROM AUTHOR]

Triclosan [5-chloro-2-(2,4-dichlorophenoxy)phenol; TCS] is a synthetic, broad-spectrum antibacterial chemical used in a wide range of consumer products including soaps, cosmetics, therapeutics, and plastics. The general population is exposed to TCS because of its prevalence in a variety of daily care products as well as through waterborne contamination. TCS is linked to a multitude of health and environmental effects, ranging from endocrine disruption and impaired muscle contraction to effects on aquatic ecosystems. We discovered that TCS was capable of stimulating liver cell proliferation and fibrotic responses, accompanied by signs of oxidative stress. Through a reporter screening assay with an array of nuclear xenobiotic receptors (XenoRs), we found that TCS activates the nuclear receptor constitutive androstane receptor (CAR) and, contrary to previous reports, has no significant effect on mouse peroxisome proliferation activating receptor α (PPARα). Using the procarcinogen diethylnitrosamine (DEN) to initiate tumorigenesis in mice, we discovered that TCS substantially accelerates hepatocellular carcinoma (HCC) development, acting as a liver tumor promoter. TCS-treated mice exhibited a large increase in tumor multiplicity, size, and incidence compared with control mice. TCS-mediated liver regeneration and fibrosis preceded HCC development and may constitute the primary tumor-promoting mechanism through which TCS acts. These findings strongly suggest there are adverse health effects in mice with long-term TCS exposure, especially on enhancing liver fibrogenesis and tumorigenesis, and the relevance of TCS liver toxicity to humans should be evaluated. [ABSTRACT FROM AUTHOR]

Camptothecin (CPT)-11 (irinotecan) has been used widely for cancer treatment, particularly metastatic colorectal cancer. However, up to 40% of treated patients suffer from severe late diarrhea, which prevents CPT-11 dose intensification and efficacy. CPT-11 is a prodrug that is hydrolyzed by hepatic and intestinal carboxylesterase to form SN-38, which in turn is detoxified primarily through UDPglucuronosyltransferase 1A1 (UGT1A1)-catalyzed glucuronidation. To better understand the mechanism associated with toxicity, we generated tissue-specific Ugtl locus conditional knockout mouse models and examined the role of glucuronidation in protecting against irinotecan-induced toxicity. We targeted the deletion of the Ugtl locus and the Ugtlal gene specifically in the liver (UgtΔHep) and the intestine (UgtΔGI). Control (UgtF/F), UgtΔHep, and UgtΔGI adult male mice were treated with different concentrations of CPT-11 daily for four consecutive days. Toxicities were evaluated with regard to tissue glucuronidation potential. CPT-11treated Ugt14~~ mice showed a similar lethality rate to the CPT-11treated ugt1F/F mice. However, UgtF/F mice were highly susceptible to CPT-11-induced diarrhea, developing severe and lethal mucositis at much lower CPT-1 1 doses, a result of the proliferative cell loss and inflammation in the intestinal tract. Comparative expression levels of UGT1A1 in intestinal tumors and normal surrounding tissue are dramatically different, providing for the opportunity to improve therapy by differential gene regulation. Intestinal expression of the UGT1A proteins is critical toward the detoxification of SN-38, whereas induction of the UGT1A1 gene may serve to limit toxicity and improve the efficacy associated with CPT-1 1 treatment. [ABSTRACT FROM AUTHOR]

Investigates the control of steroid, heme and carcinogen metabolism by nuclear pregnane X receptor (PXR) and constitutive androstane receptor. Receptors' ability to induce specific UGT1A; Ability of PXR and constitutive androstane receptor.

Triclosan (TCS), employed as an antiseptic and disinfectant, comes into direct contact with humans through a plethora of consumer products and its rising environmental release. We have demonstrated that TCS promotes liver tumorigenesis in mice, yet the biological and molecular mechanisms by which TCS exerts its toxicity, especially in early stages of liver disease, are largely unexplored. When mice were fed a high-fat diet (HFD), we found that fatty liver and dyslipidemia are prominent early signs of liver abnormality induced by TCS. The presumably protective HFD-induced hepatic expression of the metabolic regulator fibroblast growth factor 21 (FGF21) was blunted by TCS. TCS-altered Fgf21 expression aligned with aberrant expression of genes encoding metabolic enzymes manifested as profound systemic metabolic changes that disturb homeostasis of amino acids, fatty acids, and glucose. Using a type 1 diabetic animal model, TCS potentiates and accelerates the development of steatohepatitis and fibrosis, accompanied by increased levels of hepatic lipid droplets and oxidative stress. Analysis of fecal samples revealed that HFD-fed mice exhibited a reduction in fecal species richness, and that TCS further diminished microbial diversity and shifted the bacterial community toward lower Bacteriodetes and higher Firmicutes, resembling changes in microbiota composition in nonalcoholic steatohepatitis (NASH) patients. Using reverse-genetic approaches, we demonstrate that, along with HFD, TCS induces hepatic steatosis and steatohepatitis jointly regulated by the transcription factor ATF4 and the nuclear receptor PPARα, which participate in the transcriptional regulation of the Fgf21 gene. This study provides evidence linking nutritional imbalance and exposure to TCS with the progression of NASH., Competing Interests: The authors declare no competing interest.

Severe neonatal hyperbilirubinemia (SNH) and the onset of bilirubin encephalopathy and kernicterus result in part from delayed expression of UDP-glucuronosyltransferase 1A1 (UGT1A1) and the inability to metabolize bilirubin. Although there is a good understanding of the early events after birth that lead to the rapid increase in serum bilirubin, the events that control delayed expression of UGT1A1 during development remain a mystery. Humanized UGT1 ( hUGT1 ) mice develop SNH spontaneously, which is linked to repression of both liver and intestinal UGT1A1. In this study, we report that deletion of intestinal nuclear receptor corepressor 1 (NCoR1) completely diminishes hyperbilirubinemia in hUGT1 neonates because of intestinal UGT1A1 gene derepression. Transcriptomic studies and immunohistochemistry analysis demonstrate that NCoR1 plays a major role in repressing developmental maturation of the intestines. Derepression is marked by accelerated metabolic and oxidative phosphorylation, drug metabolism, fatty acid metabolism, and intestinal maturation, events that are controlled predominantly by H3K27 acetylation. The control of NCoR1 function and derepression is linked to IKKβ function, as validated in hUGT1 mice with targeted deletion of intestinal IKKβ. Physiological events during neonatal development that target activation of an IKKβ/NCoR1 loop in intestinal epithelial cells lead to derepression of genes involved in intestinal maturation and bilirubin detoxification. These findings provide a mechanism of NCoR1 in intestinal homeostasis during development and provide a key link to those events that control developmental repression of UGT1A1 and hyperbilirubinemia.

Triclosan [5-chloro-2-(2,4-dichlorophenoxy)phenol; TCS] is a synthetic, broad-spectrum antibacterial chemical used in a wide range of consumer products including soaps, cosmetics, therapeutics, and plastics. The general population is exposed to TCS because of its prevalence in a variety of daily care products as well as through waterborne contamination. TCS is linked to a multitude of health and environmental effects, ranging from endocrine disruption and impaired muscle contraction to effects on aquatic ecosystems. We discovered that TCS was capable of stimulating liver cell proliferation and fibrotic responses, accompanied by signs of oxidative stress. Through a reporter screening assay with an array of nuclear xenobiotic receptors (XenoRs), we found that TCS activates the nuclear receptor constitutive androstane receptor (CAR) and, contrary to previous reports, has no significant effect on mouse peroxisome proliferation activating receptor α (PPARα). Using the procarcinogen diethylnitrosamine (DEN) to initiate tumorigenesis in mice, we discovered that TCS substantially accelerates hepatocellular carcinoma (HCC) development, acting as a liver tumor promoter. TCS-treated mice exhibited a large increase in tumor multiplicity, size, and incidence compared with control mice. TCS-mediated liver regeneration and fibrosis preceded HCC development and may constitute the primary tumor-promoting mechanism through which TCS acts. These findings strongly suggest there are adverse health effects in mice with long-term TCS exposure, especially on enhancing liver fibrogenesis and tumorigenesis, and the relevance of TCS liver toxicity to humans should be evaluated.

Camptothecin (CPT)-11 (irinotecan) has been used widely for cancer treatment, particularly metastatic colorectal cancer. However, up to 40% of treated patients suffer from severe late diarrhea, which prevents CPT-11 dose intensification and efficacy. CPT-11 is a prodrug that is hydrolyzed by hepatic and intestinal carboxylesterase to form SN-38, which in turn is detoxified primarily through UDP-glucuronosyltransferase 1A1 (UGT1A1)-catalyzed glucuronidation. To better understand the mechanism associated with toxicity, we generated tissue-specific Ugt1 locus conditional knockout mouse models and examined the role of glucuronidation in protecting against irinotecan-induced toxicity. We targeted the deletion of the Ugt1 locus and the Ugt1a1 gene specifically in the liver (Ugt1(ΔHep)) and the intestine (Ugt1(ΔGI)). Control (Ugt1(F/F)), Ugt1(ΔHep), and Ugt1(ΔGI) adult male mice were treated with different concentrations of CPT-11 daily for four consecutive days. Toxicities were evaluated with regard to tissue glucuronidation potential. CPT-11-treated Ugt1(ΔHep) mice showed a similar lethality rate to the CPT-11-treated Ugt1(F/F) mice. However, Ugt1(ΔGI) mice were highly susceptible to CPT-11-induced diarrhea, developing severe and lethal mucositis at much lower CPT-11 doses, a result of the proliferative cell loss and inflammation in the intestinal tract. Comparative expression levels of UGT1A1 in intestinal tumors and normal surrounding tissue are dramatically different, providing for the opportunity to improve therapy by differential gene regulation. Intestinal expression of the UGT1A proteins is critical toward the detoxification of SN-38, whereas induction of the UGT1A1 gene may serve to limit toxicity and improve the efficacy associated with CPT-11 treatment.