Cadmium and arsenic override NF-κB developmental regulation of the intestinal UGT1A1 gene and control of hyperbilirubinemia

Developing and evaluating a predictive model for neonatal hyperbilirubinemia based on UGT1A1 gene polymorphism and clinical risk factors

Background

Neonatal hyperbilirubinemia (NHB) is one of the most common diseases in the neonatal period. Without timely diagnosis and treatment, it can lead to long-term complications. In severe cases, it may even result in fatality. The UGT1A1 gene and clinical risk factors play important roles in the development and progression of NHB.

Methods

In this study, we conducted a cohort study and analyzed 3258 newborns from the Jilin Women And Children Health Hospital in northern China, including 372 children with hyperbilirubinemia. We established a predictive model using a logistic regression model based on clinical risk factors and the polymorphism of the G211A locus in the UGT1A1 gene of newborns. Furthermore, the performance of the prediction model was evaluated using the ROC curve.

Results

The logistic regression model indicates that the following factors are associated with an increased risk of NHB: the time when stool turns yellow [P ≤ 0.001, OR 1.266 (95% CI: 1.125-1.425)]; neonatal cephalohematoma [P ≤ 0.001, OR 33.642 (95% CI: 21.823-51.861)]; hemolytic disease of newborn [P ≤ 0.001, OR 33.849 (95% CI: 18.589-61.636)]; neonatal weight loss [P ≤ 0.001, OR 11.275 (95% CI: 7.842-16.209)]; neonatal premature rupture of membranes (PROM) history [P = 0.021, OR 1.422 (95% CI: 1.056-1.917)]; genetic polymorphism at the UGT1A1 gene G211A locus. Gestational age is a protective factor [P ≤ 0.001, OR 0.766 (95% CI: 0.686-0.855)]. Compared to natural labor, cesarean section is a protective factor [P = 0.011, OR 0.711 (95% CI: 0.546-0.926)], while assisted delivery is a risk factor [P = 0.022, OR 2.207 (95% CI: 1.121-4.346)]. The area under the curve (AUC) of this prediction model is 0.804 (95% CI: 0.777-0.831), indicating good discrimination ability and value for predicting the risk of NHB after birth.

Conclusion

We have developed and evaluated a predictive model that combines UGT1A1 gene polymorphism and clinical risk factors for the first time. By using this nomogram and taking into account the results of serum total bilirubin measurement or transcutaneous bilirubin measurement, early prediction of the risk of neonatal hyperbilirubinemia can be achieved.

Regulation of Intestinal UDP-Glucuronosyltransferase 1A1 by the Farnesoid X Receptor Agonist Obeticholic Acid Is Controlled by Constitutive Androstane Receptor through Intestinal Maturation

UDP-glucuronosyltransferase (UGT) 1A1 is the only transferase capable of conjugating serum bilirubin. However, temporal delay in the development of the UGT1A1 gene leads to an accumulation of serum bilirubin in newborn children. Neonatal humanized UGT1 (hUGT1) mice, which accumulate severe levels of total serum bilirubin (TSB), were treated by oral gavage with obeticholic acid (OCA), a potent FXR agonist. OCA treatment led to dramatic reduction in TSB levels. Analysis of UGT1A1 expression confirmed that OCA induced intestinal and not hepatic UGT1A1. Interestingly, Cyp2b10, a target gene of the nuclear receptor CAR, was also induced by OCA in intestinal tissue. In neonatal hUGT1/Car ^-/- mice, OCA was unable to induce CYP2B10 and UGT1A1, confirming that CAR and not FXR is involved in the induction of intestinal UGT1A1. However, OCA did induce FXR target genes, such as Shp, in both intestines and liver with induction of Fgf15 in intestinal tissue. Circulating FGF15 activates hepatic FXR and, together with hepatic Shp, blocks Cyp7a1 and Cyp7b1 gene expression, key enzymes in bile acid metabolism. Importantly, the administration of OCA in neonatal hUGT1 mice accelerates intestinal epithelial cell maturation, which directly impacts on induction of the UGT1A1 gene and the reduction in TSB levels. Accelerated intestinal maturation is directly controlled by CAR, since induction of enterocyte marker genes sucrase-isomaltase, alkaline phosphatase 3, and keratin 20 by OCA does not occur in hUGT1/Car ^-/- mice. Thus, new findings link an important role for CAR in intestinal UGT1A1 induction and its role in the intestinal maturation pathway. SIGNIFICANCE STATEMENT: Obeticholic acid (OCA) activates FXR target genes in both liver and intestinal tissues while inducing intestinal UGT1A1, which leads to the elimination of serum bilirubin in humanized UGT1 mice. However, the induction of intestinal UGT1A1 and the elimination of bilirubin by OCA is driven entirely by activation of intestinal CAR and not FXR. The elimination of serum bilirubin is based on a CAR-dependent mechanism that facilitates the acceleration of intestinal epithelium cell differentiation, an event that underlies the induction of intestinal UGT1A1.

NRF2-Independent Regulation of Intestinal Constitutive Androstane Receptor by the Pro-Oxidants Cadmium and Isothiocyanate in hUGT1 Mice

Environmental toxicants such as heavy metals from contaminated water or soil and isothiocyanates (ITC) from dietary sources act as pro-oxidants by directly generating reactive oxygen species (ROS) or through depleting cellular antioxidants such as glutathione. Toxicants can alter drug metabolism, and it was reported that CYP2B10 and UGT1A1 are induced by phenethyl isothiocyanate (PEITC) through the constitutive androstane receptor (CAR). The possibility that nuclear factor erythroid 2-related factor 2 (NRF2), the master regulator of the antioxidant response, could coactivate CAR was investigated in neonatal hUGT1/Nrf2 ^-/- mice. Neonatal mice were treated with PEITC or cadmium (Cd²⁺) by oral gavage for 2 days. Both PEITC and Cd²⁺ induced UGT1A1 RNA and protein in intestinal tissues in both hUGT1/Nrf2 ^+/- and hUGT1/Nrf2 ^-/- neonates, indicating NRF2-independent regulation of UGT1A1. Increases in CYP2B10 RNA in intestinal tissues were observed following PEITC or Cd²⁺ exposure. Activation of intestinal CAR by Cd²⁺ exposure was directly assessed by nuclear fractionation and Western blot analyses at 0.5, 1, 2, and 4 hours after treatment in hUGT1 neonates and after 48 hours in hUGT1/Nrf2 ^+/- and hUGT1/Nrf2 ^-/- neonates. CAR localized to the nucleus independently of NRF2 48 hours after exposure. Substantial CAR localization to the nucleus occurred at the 2- and 4-hour time points, coinciding with a decrease in phosphorylation of cytoplasmic extracellular signal-regulated kinases 1 and 2 and a nuclear increase in P38/p-P38 content. This suggests that a novel oxidative stress-MAPK-CAR axis exists with phenotypic consequences. SIGNIFICANCE STATEMENT: Pro-oxidant toxicants can alter drug metabolism through activation of CAR, independent of the NRF2-KEAP1 signaling pathway. Changes in proteins associated with drug metabolism and linked to increases in intestinal maturation are mediated through an oxidative stress-MAPK-CAR axis.

Age- and Genotype-Dependent Variability in the Protein Abundance and Activity of Six Major Uridine Diphosphate-Glucuronosyltransferases in Human Liver

The ontogeny of hepatic uridine diphosphate-glucuronosyltransferases (UGTs) was investigated by determining their protein abundance in human liver microsomes isolated from 136 pediatric (0-18 years) and 35 adult (age >18 years) donors using liquid chromatography / tandem mass spectrometry (LC-MS/MS) proteomics. Microsomal protein abundances of UGT1A1, UGT1A4, UGT1A6, UGT1A9, UGT2B7, and UGT2B15 increased by ∼8, 55, 35, 33, 8, and 3-fold from neonates to adults, respectively. The estimated age at which 50% of the adult protein abundance is observed for these UGT isoforms was between 2.6-10.3 years. Measured in vitro activity was generally consistent with the protein data. UGT1A1 protein abundance was associated with multiple single nucleotide polymorphisms exhibiting noticeable ontogeny-genotype interplay. UGT2B15 rs1902023 (*2) was associated with decreased protein activity without any change in protein abundance. Taken together, these data are invaluable to facilitate the prediction of drug disposition in children using physiologically based pharmacokinetic modeling as demonstrated here for zidovudine and morphine.

Humanized UGT1 Mice, Regulation of UGT1A1, and the Role of the Intestinal Tract in Neonatal Hyperbilirubinemia and Breast Milk-Induced Jaundice

Neonatal hyperbilirubinemia and the onset of bilirubin encephalopathy and kernicterus result in part from delayed expression of UDP-glucuronosyltransferase 1A1 (UGT1A1) and the ability to metabolize bilirubin. It is generally believed that acute neonatal forms of hyperbilirubinemia develop due to an inability of hepatic UGT1A1 to metabolize efficiently bilirubin for clearance through the hepatobiliary tract. Newly developed mouse models designed to study bilirubin metabolism have led to new insight into the role of the intestinal tract in controlling neonatal hyperbilirubinemia. Humanization of mice with the UGT1 locus (hUGT1 mice) and the UGT1A1 gene provide a unique tool to study the onset of hyperbilirubinemia since the human UGT1A1 gene is developmentally regulated during the neonatal period in hUGT1 mice. A new mechanism outlying developmental expression of intestinal UGT1A1 is presented and its implications in the control of neonatal hyperbilirubinemia discussed. New findings linking breast milk protection against necrotizing enterocolitis and intestinal control of UGT1A1 may help explain the contribution of breast milk toward the development of neonatal hyperbilirubinemia. Our findings outline a new model that includes an active intestinal ROS /IκB kinase/nuclear receptor corepressor 1 loop that can be applied to an understanding of breast milk-induced jaundice.

Crypt Organoid Culture as an in Vitro Model in Drug Metabolism and Cytotoxicity Studies

The gastrointestinal tract is enriched with xenobiotic processing proteins that play important roles in xenobiotic bioactivation, metabolism, and detoxification. The application of genetically modified mouse models has been instrumental in characterizing the function of xenobiotic processing genes (XPG) and their proteins in drug metabolism. Here, we report the utilization of three-dimensional crypt organoid cultures from these animal models to study intestinal drug metabolism and toxicity. With the successful culturing of crypt organoids, we profiled the abundance of Phase I and Phase II XPG expression, drug transporter gene expression, and xenobiotic nuclear receptor (XNR) gene expression. Functions of XNRs were examined by treating crypt cells with XNR prototypical agonists. Real-time quantitative polymerase chain reaction demonstrated that the representative downstream target genes were induced. These findings were validated from cultures developed from XNR-null mice. In crypt cultures isolated from Pxr^-/- mice, pregnenolone 16α-carbonitrile failed to induce Cyp3a11 gene expression; similarly, WY14643 failed to induce Cyp4a10 in the Pparα^-/- crypts. Crypt cultures from control (Ugt1^F/F ) and intestinal epithelial cell (IEC) specific Ugt1 null mice (Ugt1^ΔIEC ) were treated with camptothecin-11, an anticancer prodrug with severe intestinal toxicity that originates from insufficient UGT1A1-dependent glucuronidation of its active metabolite SN-38. In the absence of Ugt1 gene expression, Ugt1^ΔIEC crypt cultures exhibit very limited production of SN-38 glucuronide, concordant with increased apoptosis in comparison with Ugt1^F/F crypt cultures. This study suggests crypt organoid cultures as an effective in vitro model for studying intestinal drug metabolism and toxicity.

Isothiocyanates induce UGT1A1 in humanized UGT1 mice in a CAR dependent fashion that is highly dependent upon oxidative stress

Isothiocyanates, such as phenethyl isothiocyanate (PEITC), are formed following the consumption of cruciferous vegetables and generate reactive oxygen species (ROS) that lead to the induction of cytoprotective genes such as the UDP-glucuronosyltransferases (UGTs). The induction of ROS activates the Nrf2-Keap 1 pathway leading to the induction of genes through antioxidant response elements (AREs). UGT1A1, the sole enzyme responsible for the metabolism of bilirubin, can be induced following activation of Nrf2. When neonatal humanized UGT1 (hUGT1) mice, which exhibit severe levels of total serum bilirubin (TSB) because of a developmental delay in expression of the UGT1A1 gene, were treated with PEITC, TSB levels were reduced. Liver and intestinal UGT1A1 were induced, along with murine CYP2B10, a consensus CAR target gene. In both neonatal and adult hUGT1/Car^−/− mice, PEITC was unable to induce CYP2B10. A similar result was observed following analysis of UGT1A1 expression in liver. However, TSB levels were still reduced in hUGT1/Car^−/− neonatal mice because of ROS induction of intestinal UGT1A1. When oxidative stress was blocked by exposing mice to N-acetylcysteine, induction of liver UGT1A1 and CYP2B10 by PEITC was prevented. Thus, new findings in this report link an important role in CAR activation that is dependent upon oxidative stress.

Developmental, Genetic, Dietary, and Xenobiotic Influences on Neonatal Hyperbilirubinemia

Hyperbilirubinemia, caused by the accumulation of unconjugated bilirubin, is one of the most common clinical diagnoses in both premature and term newborns. Owing to the fact that bilirubin is metabolized solely through glucuronidation by UDP-glucuronosyltransferase (UGT) 1A1, it is now known that immaturity of UGT1A1, in combination with the overproduction of bilirubin during the developmental stage, acts as a bottleneck to bilirubin elimination and predisposes the infant to high total serum bilirubin levels. Although neonatal jaundice is mostly benign, excessively high levels of serum bilirubin in a small percentage of newborns can cause bilirubin-induced neurologic dysfunction, potentially leading to permanent brain damage, a condition known as kernicterus Although a large portion of hyperbilirubinemia cases in newborns are associated with hemolytic diseases, we emphasize here the impaired ability of UGT1A1 to eliminate bilirubin that contributes to hyperbilirubinemia-induced neurotoxicity in the developmental stage. As a series of hereditary UGT1A1 mutations have been identified that are associated with UGT1A1 deficiency, new evidence has verified that delayed expression of UGT1A1 during the early stages of neonatal development is a tightly controlled event involving coordinated intrahepatic and extrahepatic regulation. This review recapitulates the progress that has been made in recent years in understanding the causes and physiopathology of severe hyperbilirubinemia, investigating molecular mechanisms underlying bilirubin-induced encephalopathy, and searching for potential therapies for treating pathologic hyperbilirubinemia. Several animal models have been developed to make it possible to examine bilirubin-induced neurotoxicity from multiple directions. Moreover, environmental factors that may alleviate or worsen the condition of hyperbilirubinemia are discussed.

Intestinal NCoR1, a regulator of epithelial cell maturation, controls neonatal hyperbilirubinemia

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.