UDP-glucuronosyltransferases (UGTs): from purification of Ah-receptor–inducible UGT1A6 to coordinate regulation of subsets of CYPs, UGTs, and ABC transporters by nuclear receptors

Co-exposure health risk of benzo[a]pyrene with aromatic VOCs: Monoaromatic hydrocarbons inhibit the glucuronidation of benzo[a]pyrene

Occupational workers and residents near petrochemical industry facilities are exposed to multiple contaminants on a daily basis. However, little is known about the co-exposure effects of different pollutants based on biotransformation. The study examined benzo[a]pyrene (BaP), a representative polycyclic aromatic hydrocarbon related to the petrochemical industry, to investigate changes in toxicity and co-exposure mechanism associated with different monoaromatic hydrocarbons (MAHs). A central composite design method was used to simulate site co-exposure scenarios to reveal biotransformation of BaP when co-exposed with benzene, toluene, chlorobenzene, or nitrobenzene in microsome systems. BaP metabolism depended on MAH concentration, and association of MAH with microsome concentration/incubation time. Particularly, MAH co-exposure negatively affected BaP glucuronidation, an important phase Ⅱ detoxification process. BaP metabolite intensities decreased to 43%-80% for OH-BaP-G, and 32%-71% for diOH-BaP-G in co-exposure system with MAHs, compared with control group. Furthermore, glucuronidation was affected by competitive and time-dependent inhibition. Co-exposure significantly decreased gene expression of UGT 1A10 and BCRP/ABCG2 in HepG2 cells, which are involved in BaP detoxification through metabolism and transmembrane transportation. Therefore, human co-exposure to multiple contaminants may deteriorate toxic effects of these chemicals by disturbing metabolic pathways. This study provides a reference for assessing toxic effects and co-exposure risks of pollutants.

The Uridine diphosphate (UDP)-glycosyltransferases (UGTs) superfamily: the role in tumor cell metabolism

UDP-glycosyltransferases (UGTs), important enzymes in biotransformation, control the levels and distribution of numerous endogenous signaling molecules and the metabolism of a wide range of endogenous and exogenous chemicals. The UGT superfamily in mammals consists of the UGT1, UGT2, UGT3, and UGT8 families. UGTs are rate-limiting enzymes in the glucuronate pathway, and in tumors, they are either overexpressed or underexpressed. Alterations in their metabolism can affect gluconeogenesis and lipid metabolism pathways, leading to alterations in tumor cell metabolism, which affect cancer development and prognosis. Glucuronidation is the most common mammalian conjugation pathway. Most of its reactions are mainly catalyzed by UGT1A, UGT2A and UGT2B. The body excretes UGT-bound small lipophilic molecules through the bile, urine, or feces. UGTs conjugate a variety of tiny lipophilic molecules to sugars, such as galactose, xylose, acetylglucosamine, glucuronic acid, and glucose, thereby inactivating and making water-soluble substrates, such as carcinogens, medicines, steroids, lipids, fatty acids, and bile acids. This review summarizes the roles of members of the four UGT enzyme families in tumor function, metabolism, and multiple regulatory mechanisms, and its Inhibitors and inducers. The function of UGTs in lipid metabolism, drug metabolism, and hormone metabolism in tumor cells are among the most important topics covered.

Changes in uridine 5'-diphospho-glucuronosyltransferase 1A6 expression by histone deacetylase inhibitor valproic acid

Valproic acid (VPA) is well-known as a histone deacetylase (HDAC) inhibitor. It has been reported that HDAC inhibitors enhance basal and aryl hydrocarbon receptor (AhR) ligand-induced aryl hydrocarbon receptor-responsive gene expression. Other studies suggested that HDAC inhibition might significantly activate the NF-E2-related factor-2 (Nrf2). Moreover, VPA activates mitogen-activated protein kinases (MAPKs). MAPK pathways regulate Nrf2 transactivation domain activity. Uridine 5'-diphospho-glucuronosyltransferase (UGT) 1A6 is one of the important isoforms to affect drug pharmacokinetics. UGT1A6 gene is regulated transcriptionally by AhR and Nrf2. The present study aimed to investigate whether UGT1A6 expression was changed by VPA and to elucidate the mechanism of the alteration. Following VPA treatment for 72 h in Caco-2 cells, UGT1A6 mRNA was increased by 7.9-fold. Moreover, UGT1A6 mRNA was increased by other HDAC inhibitors, suggesting that HDAC inhibition caused the UGT1A6 mRNA induction. AhR and Nrf2 proteins in the nucleus of Caco-2 cells were increased by 1.5- and 1.7-fold, respectively, following the VPA treatment. However, VPA treatment did not activate the extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) pathways in Caco-2 cells. In conclusion, we observed that VPA induced UGT1A6 mRNA expression via AhR and Nrf2 pathways, but not via the ERK or JNK pathways.

cep-1 mediated the mitohormesis effect of Shengmai formula in regulating Caenorhabditis elegans lifespan

Ageing is one of the major causes of many diseases such as cardiovascular diseases, diabetes, neurodegenerative disorders, and cancer. It has been found that mitochondrion acts as a crucial regulator of healthy lifespan. In this work, traditional Chinese medicine Shengmai formula (SMH) was used to treat mitochondrial mutants of Caenorhabditis elegans. The results showed that SMH shortened the lifespan of short-lived mev-1 mutant, but lengthened the lifespan of long-lived isp-1 mutant. Acute SMH treatment has benefit effect by increasing resistance capacity and motion activity in both ETC mutants and wild type N2. Compared with N2, the genome-wide transcriptome profile of ETC mutants showed on a similar pattern after SMH treatment. GO and KEGG enrichment analysis addressed that SMH-induced genes mainly enriched in metabolic process and oxidation-reduction process. The ROS levels in ETC mutants and N2 firstly rose then fell after SMH treatment, in company with the elevation of SOD-1, SOD-3 and GST-4, the increment of HSP-16.2 combined with heat shock. SMH increased oxygen consumption and ATP content, improved the restoration of mitochondrial homeostasis. SMH-induced opposed lifespan outcomes were markedly counteracted by cep-1 RNAi, together with the mitochondrial dynamics. Western blot assay also demonstrated a SMH-induced CEP-1 expression. Collectively, SMH acts as a prooxidant to regulate mitochondrial homeostasis and causes mitohormesis to exert therapeutic effect based on the redox background of the recipients, and cep-1 was required for the mitochondrial hormetic responses. The results shed a light on the rational clinical anti-ageing applications of SMH in the future.

Induction by Phenobarbital of Phase I and II Xenobiotic-Metabolizing Enzymes in Bovine Liver: An Overall Catalytic and Immunochemical Characterization

In cattle, phenobarbital (PB) upregulates target drug-metabolizing enzyme (DME) mRNA levels. However, few data about PB's post-transcriptional effects are actually available. This work provides the first, and an almost complete, characterization of PB-dependent changes in DME catalytic activities in bovine liver using common probe substrates and confirmatory immunoblotting investigations. As expected, PB increased the total cytochrome P450 (CYP) content and the extent of metyrapone binding; moreover, an augmentation of protein amounts and related enzyme activities was observed for known PB targets such as CYP2B, 2C, and 3A, but also CYP2E1. However, contradictory results were obtained for CYP1A, while a decreased catalytic activity was observed for flavin-containing monooxygenases 1 and 3. The barbiturate had no effect on the chosen hydrolytic and conjugative DMEs. For the first time, we also measured the 26S proteasome activity, and the increase observed in PB-treated cattle would suggest this post-translational event might contribute to cattle DME regulation. Overall, this study increased the knowledge of cattle hepatic drug metabolism, and further confirmed the presence of species differences in DME expression and activity between cattle, humans, and rodents. This reinforced the need for an extensive characterization and understanding of comparative molecular mechanisms involved in expression, regulation, and function of DMEs.

Aryl Hydrocarbon Receptor Mechanisms Affecting Chronic Kidney Disease

The aryl hydrocarbon receptor (AHR) is a basic helix-loop-helix transcription factor that binds diverse endogenous and xenobiotic ligands, which regulate AHR stability, transcriptional activity, and cell signaling. AHR activity is strongly implicated throughout the course of chronic kidney disease (CKD). Many diverse organic molecules bind and activate AHR and these ligands are reported to either promote glomerular and tubular damage or protect against kidney injury. AHR crosstalk with estrogen, peroxisome proliferator-activated receptor-γ, and NF-κB pathways may contribute to the diversity of AHR responses during the various forms and stages of CKD. The roles of AHR in kidney fibrosis, metabolism and the renin angiotensin system are described to offer insight into CKD pathogenesis and therapies.

Skin biological responses to urban pollution in an ex vivo model

The skin epidermis is continuously exposed to external aggressions, including environmental pollution. The cosmetic industry must be able to offer dedicated products to fight the effects of pollutants on the skin. We set up an experimental model that exposed skin explants maintained in culture to a pollutant mixture. This mixture P representing urban pollution was designed on the basis of the French organization 'Air Parif' database. A chamber, called Pollubox®, was built to allow a controlled nebulization of P on the cultured human skin explants. We investigated ultrastructural morphology by transmission electron microscopy of high pressure frozen skin explants. A global transcriptomic analysis indicated that the pollutant mixture was able to induce relevant xenobiotic and antioxidant responses. Modulated detoxifying genes were further investigated by laser micro-dissection coupled to qPCR, and immunochemistry. Both approaches showed that P exposure correlated with overexpression of detoxifying genes and provoked skin physiological alterations down to the stratum basale. The model developed herein might be an efficient tool to study the effects of pollutants on skin as well as a powerful testing method to evaluate the efficacy of cosmetic products against pollution.

Aryl hydrocarbon receptor (AHR), integrating energy metabolism and microbial or obesity-mediated inflammation

Aryl hydrocarbon receptor (AHR) has been characterized as multifunctional sensor, integrator and ligand-activated transcription factor of the bHLH/PAS family. Regulation of inflammatory diseases and energy metabolism are among the putative functions of AHR. Challenges in AHR research include marked species differences, and cell, tissue and context dependence of AHR functions. The commentary is focused on AHR's role in the integration between energy expenditure and microbial and non-infectious inflammation, the latter exemplified by obesity-mediated nonalcoholic fatty liver disease. One of the mechanisms controlling energy-consuming inflammation is represented by a signalsome that is involved in retinoic acid-triggered neutrophil differentiation and regulation of the NADPH oxidase complex (NOX). Established signalsome components are AHR, CD38, multiple protein kinases and adaptors. To prevent chronic inflammatory diseases, the complex interplay between a range of inflammatory responses and energy expenditure must be precisely regulated. Surviving an infection requires both pathogen clearance and tissue protection from inflammatory damage. Defenses are energy-consuming anabolic programs. Therefore, anti-inflammatory, catabolic tolerance programs by metabolic reprogramming of macrophages have evolved. Therapeutic options of AHR agonists to reduce chronic inflammatory diseases are discussed.

Aryl hydrocarbon receptor (AHR) functions: Balancing opposing processes including inflammatory reactions

Aryl hydrocarbon receptor (AHR) research has shifted from exploring dioxin toxicity to elucidation of physiologic AHR functions. Control of AHR functions is challenged by the fact that AHR is often involved in balancing opposing processes. Two AHR functions are discussed. (i) Microbial defense: intestinal microbiota commensals secrete AHR ligands that are important for maintaining epithelial integrity and generation of anti-inflammatory IL-22 by multiple immune cells. On the other hand, in case of microbial defense, AHR-regulated neutrophils and Th17 cells are involved in generation of bactericidal reactive oxygen species and pro-inflammatory stimuli. However, during the process of infection resolution, 'disease tolerance' is achieved. (ii) Energy, NAD⁺ and lipid metabolism: In obese individuals AHR is involved in either generation or inhibition of fatty liver and associated hepatitis. Inhibition of hepatitis is mainly achieved by regulating NAD⁺-controlled SIRT1, 3 and 6 activity. Interestingly, these enzymes are synergistically modulated by CD38, an NAD-consuming NAD-glycohydrolase. It is proposed that inflammatory responses may be beneficially modulated by AHR agonistic and CD38 inhibiting phytochemicals. Caveats in presence of carcinogenicity have to be taken into account. AHR research is an exciting field but therapeutic options remain challenging.

Xenobiotica-metabolizing enzyme induction potential of chemicals in animal studies: NanoString nCounter gene expression and peptide group-specific immunoaffinity as accelerated and economical substitutions for enzyme activity determinations?

Xenobiotica-metabolizing enzyme (XME) induction is a relevant biological/biochemical process vital to understanding the toxicological profile of xenobiotics. Early recognition of XME induction potential of compounds under development is therefore important, yet its determination by traditional XME activity measurements is time consuming and cost intensive. A proof-of-principle study was therefore designed due to the advent of faster and less cost-intensive methods for determination of enzyme protein and transcript levels to determine whether two such methods may substitute for traditional measurement of XME activity determinations. The results of the study show that determination of enzyme protein levels by peptide group-specific immunoaffinity enrichment/MS and/or determination of gene expression by NanoString nCounter may serve as substitutes for traditional evaluation methodology and/or as an early predictor of potential changes in liver enzymes. In this study, changes of XME activity by the known standard XME inducers phenobarbital, beta-naphthoflavone and Aroclor 1254 were demonstrated by these two methods. To investigate the applicability of these methods to demonstrate XME-inducing activity of an unknown, TS was also examined and found to be an XME inducer. More specifically, TS was found to be a phenobarbital-type inducer (likely mediated by CAR rather than PXR as nuclear receptor), but not due to Ah receptor-mediated or antioxidant response element-mediated beta-naphthoflavone-type induction. The results for TS were confirmed via enzymatic activity measurements. The results of the present study demonstrate the potential applicability of NanoString nCounter mRNA quantitation and peptide group-specific immunoaffinity enrichment/MS protein quantitation for predicting compounds under development to be inducers of liver XME activity.

Assessment of biological functions for C3A cells interacting with adverse environments of liver failure plasma

BACKGROUND

For its better differentiated hepatocyte phenotype, C3A cell line has been utilized in bioartificial liver system. However, up to now, there are only a few of studies working at the metabolic alternations of C3A cells under the culture conditions with liver failure plasma, which mainly focus on carbohydrate metabolism, total protein synthesis and ureagenesis. In this study, we investigated the effects of acute liver failure plasma on the growth and biological functions of C3A cells, especially on CYP450 enzymes.

METHODS

C3A cells were treated with fresh DMEM medium containing 10% FBS, fresh DMEM medium containing 10% normal plasma and acute liver failure plasma, respectively. After incubation, the C3A cells were assessed for cell viabilities, lactate dehydrogenase leakage, gene transcription, protein levels, albumin secretion, ammonia metabolism and CYP450 enzyme activities.

RESULTS

Cell viabilities decreased 15%, and lactate dehydrogenase leakage had 1.3-fold elevation in acute liver failure plasma group. Gene transcription exhibited up-regulation, down-regulation or stability for different hepatic genes. In contrast, protein expression levels for several CYP450 enzymes kept constant, while the CYP450 enzyme activities decreased or remained stable. Albumin secretion reduced about 48%, and ammonia accumulation increased approximately 41%.

CONCLUSIONS

C3A cells cultured with acute liver failure plasma showed mild inhibition of cell viabilities, reduction of albumin secretion, and increase of ammonia accumulation. Furthermore, CYP450 enzymes demonstrated various alterations on gene transcription, protein expression and enzyme activities.

From TCDD-mediated toxicity to searches of physiologic AHR functions

TCDD-mediated toxicity of human individuals together with animal studies led to identification of the aryl hydrocarbon receptor (AHR). It was characterized as multifunctional ligand-activated transcription factor and environmental sensor. Comparison of human toxic responses and animal models provide hints to physiologic AHR functions including chemical and microbial defense, homeostasis of stem/progenitor cells and modulation of the immune system in barrier organs such as skin and the gastrointestinal tract. Extrapolation from animals to humans is difficult due to marked species differences and dependence of AHR function on the cellular context. Nevertheless, therapeutic possibilities of AHR agonists and antagonists are in development. The AHR remains challenging and fascinating.

Mechanisms and therapeutic prospects of polyphenols as modulators of the aryl hydrocarbon receptor

Polyphenolic AhR modulators displayed concentration-, XRE-, gene-, species- and cell-specific agonistic/antagonistic activity.

Transcriptome association analysis identifies miR-375 as a major determinant of variable acetaminophen glucuronidation by human liver

Acetaminophen is the leading cause of acute liver failure (ALF) in many countries including the United States. Hepatic glucuronidation by UDP-glucuronosyltransferase (UGT) 1A subfamily enzymes is the major route of acetaminophen elimination. Reduced glucuronidation may predispose some individuals to acetaminophen-induced ALF, but mechanisms underlying reduced glucuronidation are poorly understood. We hypothesized that specific microRNAs (miRNAs) may reduce UGT1A activity by direct effects on the UGT1A 3'-UTR shared by all UGT1A enzyme transcripts, or by indirect effects on transcription factors regulating UGT1A expression. We performed an unbiased miRNA whole transcriptome association analysis using a bank of human livers with known acetaminophen glucuronidation activities. Of 754 miRNAs evaluated, 9 miRNAs were identified that were significantly overexpressed (p<0.05; >2-fold) in livers with low acetaminophen glucuronidation activities compared with those with high activities. miR-375 showed the highest difference (>10-fold), and was chosen for further mechanistic validation. We demonstrated using in silico analysis and luciferase reporter assays that miR-375 has a unique functional binding site in the 3'-UTR of the aryl hydrocarbon receptor (AhR) gene. Furthermore overexpression of miR-375 in LS180 cells demonstrated significant repression of endogenous AhR protein (by 40%) and mRNA (by 10%), as well as enzyme activity and/or mRNA of AhR regulated enzymes including UGT1A1, UGT1A6, and CYP1A2, without affecting UGT2B7, which is not regulated by AhR. Thus miR-375 is identified as a novel repressor of UGT1A-mediated hepatic acetaminophen glucuronidation through reduced AhR expression, which could predispose some individuals to increased risk for acetaminophen-induced ALF.

Establishment and use of new MDCK II cells overexpressing both UGT1A1 and MRP2 to characterize flavonoid metabolism via the glucuronidation pathway

SCOPE

The purpose of this study is to characterize how overexpression of an efflux transporter and an UDP-glucuronosyltransferase (UGT) affects the cellular kinetics of glucuronidation processes.

METHODS AND RESULTS

A new MDCK II cell line overexpressing both MRP2 and UGT1A1 (MDCKII-UGT1A1/MRP2 cells) was developed and used to determine how overexpression of an efflux transporter affects the kinetics of cellular flavonoid glucuronide production. The results showed that most model flavonoids (from a total of 13) were mainly metabolized into glucuronides in the MDCKII-UGT1A1/MRP2 cells and the glucuronides were rapidly excreted. Flavonoids with three or fewer hydroxyl group at 7, 3' or 6 hydroxyl group were also metabolized into sulfates. Mechanistic studies using 7-hydroxylflavone showed that its glucuronide was mainly (90%) effluxed by BCRP with a small (10%) but significant contribution from MRP2. Maximal velocity of glucuronide production MDCK-MRP2/UGT1A1 cells showed a fairly good correlation (R(2) >0.8) with those derived using UGT1A1 microsomes, but other kinetic parameters (e.g., Km ) did not correlate.

CONCLUSION

Overexpression of a second efficient efflux transporter did not significantly change the fact that BCRP is the dominant transporter for flavonoid glucuronide nor did it diminish the influence of the efflux transporter as the "gate keeper" of glucuronidation process.

Dietary Dihydromethysticin Increases Glucuronidation of 4-(Methylnitrosamino)-1-(3-Pyridyl)-1-Butanol in A/J Mice, Potentially Enhancing Its Detoxification

Effective chemopreventive agents are needed against lung cancer, the leading cause of cancer death. Results from our previous work showed that dietary dihydromethysticin (DHM) effectively blocked initiation of lung tumorigenesis by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in A/J mice, and it preferentially reduced 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL)-derived DNA adducts in lung. This study explored the mechanism(s) responsible for DHM's differential effects on NNK/NNAL-derived DNA damage by quantifying their metabolites in A/J mice. The results showed that dietary DHM had no effect on NNK or NNAL abundance in vivo, indicating that DHM does not affect NNAL formation from NNK. DHM had a minimal effect on cytochrome P450 2A5 (CYP2A5, which catalyzes NNK and NNAL bioactivation in A/J mouse lung), suggesting that it does not inhibit NNAL bioactivation. Dietary DHM significantly increased O-glucuronidated NNAL (NNAL-O-gluc) in A/J mice. Lung and liver microsomes from dietary DHM-treated mice showed enhanced activities for NNAL O-glucuronidation. These results overall support the notion that dietary DHM treatment increases NNAL detoxification, potentially accounting for its chemopreventive efficacy against NNK-induced lung tumorigenesis in A/J mice. The ratio of urinary NNAL-O-gluc and free NNAL may serve as a biomarker to facilitate the clinical evaluation of DHM-based lung cancer chemopreventive agents.

Comparison of toxicogenomics and traditional approaches to inform mode of action and points of departure in human health risk assessment of benzo[a]pyrene in drinking water

Toxicogenomics is proposed to be a useful tool in human health risk assessment. However, a systematic comparison of traditional risk assessment approaches with those applying toxicogenomics has never been done. We conducted a case study to evaluate the utility of toxicogenomics in the risk assessment of benzo[a]pyrene (BaP), a well-studied carcinogen, for drinking water exposures. Our study was intended to compare methodologies, not to evaluate drinking water safety. We compared traditional (RA1), genomics-informed (RA2) and genomics-only (RA3) approaches. RA2 and RA3 applied toxicogenomics data from human cell cultures and mice exposed to BaP to determine if these data could provide insight into BaP's mode of action (MOA) and derive tissue-specific points of departure (POD). Our global gene expression analysis supported that BaP is genotoxic in mice and allowed the development of a detailed MOA. Toxicogenomics analysis in human lymphoblastoid TK6 cells demonstrated a high degree of consistency in perturbed pathways with animal tissues. Quantitatively, the PODs for traditional and transcriptional approaches were similar (liver 1.2 vs. 1.0 mg/kg-bw/day; lungs 0.8 vs. 3.7 mg/kg-bw/day; forestomach 0.5 vs. 7.4 mg/kg-bw/day). RA3, which applied toxicogenomics in the absence of apical toxicology data, demonstrates that this approach provides useful information in data-poor situations. Overall, our study supports the use of toxicogenomics as a relatively fast and cost-effective tool for hazard identification, preliminary evaluation of potential carcinogens, and carcinogenic potency, in addition to identifying current limitations and practical questions for future work.

Baicalin Protects Mice from Aristolochic Acid I-Induced Kidney Injury by Induction of CYP1A through the Aromatic Hydrocarbon Receptor

Exposure to aristolochic acid I (AAI) can lead to aristolochic acid nephropathy (AAN), Balkan endemic nephropathy (BEN) and urothelial cancer. The induction of hepatic CYP1A, especially CYP1A2, was considered to detoxify AAI so as to reduce its nephrotoxicity. We previously found that baicalin had the strong ability to induce CYP1A2 expression; therefore in this study, we examined the effects of baicalin on AAI toxicity, metabolism and disposition, as well as investigated the underlying mechanisms. Our toxicological studies showed that baicalin reduced the levels of blood urea nitrogen (BUN) and creatinine (CRE) in AAI-treated mice and attenuated renal injury induced by AAI. Pharmacokinetic analysis demonstrated that baicalin markedly decreased AUC of AAI in plasma and the content of AAI in liver and kidney. CYP1A induction assays showed that baicalin exposure significantly increased the hepatic expression of CYP1A1/2, which was completely abolished by inhibitors of the Aromatic hydrocarbon receptor (AhR), 3ʹ,4ʹ-dimethoxyflavone and resveratrol, in vitro and in vivo, respectively. Moreover, the luciferase assays revealed that baicalin significantly increased the luciferase activity of the reporter gene incorporated with the Xenobiotic response elements recognized by AhR. In summary, baicalin significantly reduced the disposition of AAI and ameliorated AAI-induced kidney toxicity through AhR-dependent CYP1A1/2 induction in the liver.

Suppression of the pregnane X receptor during endoplasmic reticulum stress is achieved by down-regulating hepatocyte nuclear factor-4α and up-regulating liver-enriched inhibitory protein

Endoplasmic reticulum (ER) stress is recognized as a common theme in the development of metabolic syndrome and other diseases. Chronic liver diseases develop ER stress and also show decreased capacity of drug metabolism. The pregnane X receptor (PXR) is a master regulator of genes involved in drug elimination. This study was performed to determine whether ER stress condition decreases the expression of PXR and whether the decrease alters the induction of cytochrome P450 3A4 (CYP3A4). Human primary hepatocytes and HepG2 cell line (human hepatocellular carcinoma) were treated with brefeldin A and thapsigargin, 2 well-established ER stressors. Without exceptions, both stressors significantly decreased the expression of PXR. The decrease led to reduced induction of CYP3A4. Reporter dissection study, electrophoretic mobility shift assay, and chromatin immunoprecipitation located in the PXR promoter region 2 adjacent elements recognized by hepatocyte nuclear factor-4α (HNF-4α) and cytidine-cytidine-adenosine-adenosine-thymidine enhanced binding proteins (C/EBPs), respectively. Additional studies demonstrated that HNF-4α was down-regulated during ER stress but the expression of C/EBPβ varied depending on a particular form of C/EBPβ. Liver-enriched activator protein (LAP) was down-regulated but liver-enriched inhibitory protein (LIP) was highly induced. Nevertheless, over-expression of HNF-4α or LAP restored the expression of PXR. Interestingly, the very same sequence also responded to interleukin-6 (IL-6), and primary hepatocytes treated with thapsigargin significantly increased the level of IL-6 mRNA. These findings establish a functional interconnection between ER stress and signaling of proinflammatory cytokines in the regulation of PXR expression.

Tanshinone I protects mice from aristolochic acid I-induced kidney injury by induction of CYP1A

Hepatic CYP1A especially CYP1A2 plays an important role in the reduction of aristolochic acid I (AAI) nephrotoxicity. In this study, we investigated the effects of tanshinone I, a strong inducer of Cyp1a, on the nephrotoxicity induced by AAI. Histopathology and blood biochemistry assays showed that tanshinone I could reduce AAI-induced acute kidney injury. Pharmacokinetics analysis revealed that tanshinone I markedly decreased AUC of AAI in plasma and the content of AAI in both liver and kidney, indicating the enhancement of AAI metabolism. Real-time PCR and Western blot analysis confirmed that tanshinone I effectively increased the mRNA and protein levels of hepatic CYP1A1 and CYP1A2 in vivo. Luciferase assay showed that tanshinone I strongly increased the transcriptional activity of CYP1A1 and CYP1A2 in the similar extent. In summary, our data suggested that tanshinone I facilitated the metabolism of AAI and prevented AAI-induced kidney injury by induction of hepatic CYP1A 1/2 in vivo.

Revolving door action of breast cancer resistance protein (BCRP) facilitates or controls the efflux of flavone glucuronides from UGT1A9-overexpressing HeLa cells

Cellular production of flavonoid glucuronides requires the action of both UDP-glucuronosyltransferases (UGT) and efflux transporters since glucuronides are too hydrophilic to diffuse across the cellular membrane. We determined the kinetics of efflux of 13 flavonoid glucuronides using the newly developed HeLa-UGT1A9 cells and correlated them with kinetic parameters derived using expressed UGT1A9. The results indicated that, among the seven monohydroxylflavones (HFs), there was moderately good correlation (r(2) ≥ 0.65) between the fraction metabolized (fmet) derived from HeLa-UGT1A9 cells and CLint derived from the UGT1A9-mediated metabolism. However, there was weak or no correlation between these two parameters for six dihydroxylflavones (DHFs). Furthermore, there was weak or no correlation between various kinetic parameters (Km, Vmax, or CLint) for the efflux and the metabolism regardless of whether we were using seven HFs, six DHFs, or a combination thereof. Instead, the cellular excretion of many flavonoid glucuronides appears to be controlled by the efflux transporter, and the poor affinity of glucuronide to the efflux transporter resulted in major intracellular accumulation of glucuronides to a level that is above the dosing concentration of its aglycone. Hence, the efflux transporters appear to act as the "Revolving Door" to control the cellular excretion of glucuronides. In conclusion, the determination of a flavonoid's susceptibility to glucuronidation must be based on both its susceptibility to glucuronidation by the enzyme and resulting glucuronide's affinity to the relevant efflux transporters, which act as the "Revolving Door(s)" to facilitate or control its removal from the cells.

Focused DNA microarray analysis for sex-dependent gene expression of drug metabolizing enzymes, transporters and nuclear receptors in rat livers and kidneys

Cytochrome P450(CYP)s are known to show a sexual dimorphic expression in rat livers. However, the comprehensive analysis for the sex-dependent gene expressions of drug metabolizing enzymes except for CYPs, transporters and nuclear receptors in rat livers and kidneys has not been investigated yet. The purpose of the present study was to identify the novel drug metabolizing and pharmacokinetics (DMPK)-related gene(s) which show the sex difference in the mRNA expressions in rat livers and kidneys. Total RNAs were prepared from livers and kidneys in both male and female rats (Crl:CD(SD) and Crlj:WI). A DNA microarray analysis using a "GeneSQUARE Multiple Assay DNA Microarray Drug Metabolism Gene Expression for Rat" was performed. DMPK-related genes which showed sex differences in the mRNA expression were identified in rat livers or kidneys. Especially, the female dominant expressions of UDP glucuronosyltransferase (UGT) s were seen in rat livers and kidneys. The sex difference of UGT expressions in rats might be one of the causal factors of the sex difference of the biological response to UGT substrates.

Scoparone potentiates transactivation of the bile salt export pump gene and this effect is enhanced by cytochrome P450 metabolism but abolished by a PKC inhibitor

BACKGROUND AND PURPOSE

Hyperbilirubinaemia and cholestasis are two major forms of liver abnormality. The Chinese herb Yin Chin has been used for thousands of years to treat liver dysfunctions. In mice, this herb and its principal ingredient scoparone were found to accelerate the clearance of bilirubin accompanied by the induction of uridine diphosphate-5'-glucuronosyltransferase-1A1 (UGT1A1), a bilirubin processing enzyme. The aim of this study was to determine whether scoparone induces the expression of human UGT1A1. In addition, the expression of the bile salt export pump (BSEP), a transporter of bile acids, was determined.

EXPERIMENTAL APPROACH

Primary human hepatocytes and hepatoma line Huh7 were treated with scoparone, chenodeoxycholic acid (CDCA) or both. The expression of UGT1A1 and BSEP mRNA was determined. The activation of the human BSEP promoter reporter by scoparone was determined in Huh7 cells by transient transfection and in mice by bioluminescent imaging. The metabolism of scoparone was investigated by recombinant CYP enzymes and pooled human liver microsomes.

KEY RESULTS

Scoparone did not enhance the expression of either human BSEP or, surprisingly, UGT1A1. However, scoparone significantly potentiated the expression of BSEP induced by CDCA. Consistent with this, scoparone potentiated the stimulant effect of CDCA on the human BSEP promoter. This potentiation was enhanced by co-transfection of cytochrome P4501A2 but abolished by the PKC inhibitor GF109203X.

CONCLUSIONS AND IMPLICATIONS

Scoparone and Yin Chin normalize liver function primarily by enhancing the secretion of bile acids, and this effect probably varies depending on the metabolic rate of scoparone.

Regulation of drug-metabolizing cytochrome P450 enzymes by glucocorticoids

The regulation of drug-metabolizing cytochrome P450 enzymes (CYP) is a complex process involving multiple mechanisms. Among them, transcriptional regulation through ligand-activated nuclear receptors is the crucial mechanism involved in hormone-controlled and xenobiotic-induced expression of drug-metabolizing CYPs. In this article, we focus, in detail, on the role of the glucocorticoid receptor (GR) in the transcriptional regulation of human drug-metabolizing CYP enzymes and the mechanisms of the regulation. There are at least three distinct transcriptional mechanisms by which GR controls the expression of CYPs: 1) direct binding of GR to a specific gene-promoter sequence called the glucocorticoid responsive element (GRE); 2) indirect binding of GR in the form of a multiprotein complex to gene promoters without a direct contact between GR and promoter DNA; and 3) up- or downregulation of other CYP transcriptional regulators or nuclear receptors (i.e., transcriptional regulatory cross-talk). However, due to the general effect of glucocorticoids on numerous cellular pathways and functions, the net transcriptional effect of glucocorticoids on drug-metabolizing enzymes is usually a combination of several mechanisms. Since synthetic glucocorticoids are widely prescribed in human pharmacotherapy for the treatment of many diseases, comprehensive understanding of the transcriptional regulation of drug-metabolizing CYPs via GR with respect to glucocorticoid therapy or glucocorticoid hormonal status will aid in the development of efficient individualized pharmacotherapy without drug-drug interactions.