Activation of Nrf2 decreases bile acid concentrations in livers of female mice.

1. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master regulator of oxidative/electrophilic stress. Studies suggest a role of Nrf2 in regulating bile acid (BA) metabolism in male mice. However, whether Nrf2 is important for BA homeostasis in female mice remains undefined. In this study, we systematically investigated the effect of Nrf2 activation, either through CDDO-imidazolide (CDDO-Im) treatment or genetic modulation of Kelch-like ECH associating protein 1 (Keap1), on BA homeostasis in female mice.2. Both pharmacological and genetic Nrf2 activation increased mRNA levels of multidrug resistance-associated protein 2 and 3 (Mrp2 and Mrp3), two Nrf2 target genes, in livers and ilea of female mice. Both pharmacological and genetic activation of Nrf2 decreased BA concentrations in the liver, which did not appear to be due to increased biliary BA excretion or decreased ileal BA absorption. Importantly, both pharmacological and genetic activation of Nrf2 downregulated hepatic Cyp7a1 mRNA, which might be attributable to the upregulation of the Fxr-Fgf15 signalling in the ileum.3. To conclude, Nrf2 activation lowers BA concentrations in livers of female mice, which appears to be attributable to the decreased hepatic BA synthesis.

Effects of patent ductus venosus on bile acid homeostasis in aryl hydrocarbon receptor (AhR)-null mice.

The Aryl hydrocarbon receptor (AhR) is primarily known as one of the xenosensors and regulators of drug-metabolizing genes. Bile acids (BAs) are synthesized in the liver, and undergo several enterohepatic recirculations in which the liver removes BAs from the portal blood, minimizing the BAs that spill over into the systemic circulation. Previous studies revealed a lifelong patent ductus venosus (PDV) in AhR-null mice. Increased concentration of total BAs (Σ-BAs) in AhR-null mice is known; however, the impact of PDV on BA homeostasis in liver and bile remains unclear. This work investigated the consequences of PDV on BA homeostasis by comparing AhR-null and wild-type (WT) mice of both genders. In serum, Σ-BAs were markedly higher (64-85-fold) in AhR-null mice than in WT mice, especially due to the increase of tri-OH primary BAs (86-142-fold). Despite the extremely high concentration of serum BAs, the concentration of BAs in livers of AhR-null mice remained similar to WT mice. AhR-null livers were protected against increased BA influx by downregulation of uptake transporters and BA synthetic enzymes in the alternative pathway. Although livers of AhR-null mice are 20-25% smaller than WT mice, biliary excretion of BAs was maintained in the AhR-null mice, and even tended to increase. Surprisingly, intestinal Fgf15 expression was not increased, even though there was a marked increase in serum BA concentrations. Although PDV resulted in extremely high BA concentrations in serum of AhR-null mice, they maintained a concentration of BAs in liver and biliary excretion of BAs similar to control mice.

Effects of ablation and activation of Nrf2 on bile acid homeostasis in male mice.

The role of nuclear factor erythroid 2-related factor 2 (Nrf2) in bile acid (BA) homeostasis remains controversial. In this study, activation of Nrf2 was achieved either pharmacologically by CDDO-imidazolide (CDDO-Im) or genetically through a "gene dose-response" model consisting of Nrf2-null, wild-type (WT), Keap1-knockdown (Keap1-KD), and Keap1-hepatocyte knockout (Keap1-HKO) mice. In WT mice, CDDO-Im increased bile flow and decreased hepatic BAs, which was associated with a down-regulation of the canalicular BA efflux transporter Bsep and an increase in biliary BA excretion. In contrast, hepatic Bsep and biliary BA excretion were not altered in Keap1-KD or Keap1-HKO mice, suggesting that Nrf2 is not important for regulating Bsep or BA-dependent bile flow. In contrast, hepatic Mrp2 and Mrp3 were up-regulated by both pharmacological and genetic activations of Nrf2. Furthermore, ileal BA transporters (Asbt and Ostß) and cholesterol transporters (Abcg5 and Abcg8) were down-regulated by both pharmacological and genetic activations of Nrf2, suggesting a role of Nrf2 in intestinal absorption of BAs and cholesterol. In Nrf2-null mice, CDDO-Im down-regulated hepatic BA uptake transporters (Ntcp, Oatp1a1, and Oatp1b2), leading to a 39-fold increase of serum BAs. To conclude, the present study demonstrates that activation of Nrf2 in mice up-regulates Mrp2 and Mrp3 in the liver and down-regulates BA and cholesterol transporters in the intestine.

Aryl hydrocarbon receptor (AhR) mediated short-term effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on bile acid homeostasis in mice.

The effects of the most potent aryl hydrocarbon receptor (AhR) agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on bile acid (BA) homeostasis was examined in male and female wild-type and AhR-null mice shortly after 4-day exposure, rather than at a later time when secondary non-AhR dependent effects are more likely to occur. TCDD had similar effects on BA homeostasis in male and female mice. TCDD decreased the concentration of total-(Σ) BAs in liver by approximately 50% (all major BA categories except for the non-6,12-OH BAs), without decreasing the expression of the rate limiting BA synthetic enzyme (Cyp7a1) or altering the major BA regulatory pathways (FXR) in liver and intestine. Even though the Σ-BAs in liver were markedly decreased, the Σ-BAs excreted into bile were not altered. TCDD decreased the relative amount of 12-OH BAs (TCA, TDCA, CA, DCA) in bile and increased the biliary excretion of TCDCA and its metabolites (TαMCA, TUDCA); this was likely due to the decreased Cyp8b1 (12α-hydroxylase) in liver. The concentration of Σ-BAs in serum was not altered by TCDD, indicating that serum BAs do not reflect BA status in liver. However, proportions of individual BAs in serum reflected the decreased expression of Cyp8b1. All these TCDD-induced changes in BA homeostasis were absent in AhR-null mice. In summary, through the AhR, TCDD markedly decreases BA concentrations in liver and reduces the 12α-hydroxylation of BAs without altering Cyp7a1 and FXR signaling. The TCDD-induced decrease in Σ-BAs in liver did not result in a decrease in biliary excretion or serum concentrations of Σ-BAs.

Activation of PPARα decreases bile acids in livers of female mice while maintaining bile flow and biliary bile acid excretion.

Fibrates are hypolipidemic drugs that act as activators of peroxisome proliferator-activated receptor α (PPARα). In both humans and rodents, females were reported to be less responsive to fibrates than males. Previous studies on fibrates and PPARα usually involved male mice, but little has been done in females. The present study aimed to provide the first comprehensive analysis of the effects of clofibrate (CLOF) and PPARα on bile acid (BA) homeostasis in female mice. Study in WT male mice showed that a 4-day CLOF treatment increased liver weight, bile flow, and biliary BA excretion, but decreased total BAs in both serum and liver. In contrast, WT female mice were less susceptible to these CLOF-mediated responses observed in males. In WT female mice, CLOF decreased total BAs in the liver, but had little effect on the mRNAs of hepatic BA-related genes. Next, a comparative analysis between WT and PPARα-null female mice showed that lack of PPARα in female mice decreased total BAs in serum, but had little effect on total BAs in liver or bile. However, lack of PPARα in female mice increased mRNAs of BA synthetic enzymes (Cyp7a1, Cyp8b1, Cyp27a1, and Cyp7b1) and transporters (Ntcp, Oatp1a1, Oatp1b2, and Mrp3). Furthermore, the increase of Cyp7a1 in PPARα-null female mice was associated with an increase in liver Fxr-Shp-Lrh-1 signaling. In conclusion, female mice are resistant to CLOF-mediated effects on BA metabolism observed in males, which could be attributed to PPARα-mediated suppression in females on genes involved in BA synthesis and transport.

Identification of a functional antioxidant response element within the eighth intron of the human ABCC3 gene.

The ATP-binding cassette (ABC) family of transporters, including ABCC3, is a large family of efflux pumps that plays a pivotal role in the elimination of xenobiotics from the body. ABCC3 has been reported to be induced during hepatic stress conditions and through the progression of some forms of cancer. Several lines of evidence have implicated the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) in this induction. However, although rodent models have been investigated, a functional antioxidant response element (ARE) in the human ABCC3 gene has not been identified. The purpose of this study was to identify and characterize the ARE(s) responsible for mediating the Nrf2-dependent induction of the human ABCC3 gene. A high-throughput chromatin immunoprecipitation-sequencing analysis performed in A549 cells revealed a specific interaction between Nrf2 and the eighth intron of the human ABCC3 gene rather than the more prototypical flanking region of the gene. Subsequent in silico analysis of the intron identified two putative ARE elements that contained the core consensus ARE sequence commonly found in several Nrf2-responsive genes. Functional characterization of these two AREs using luciferase-reporter constructs with ARE mutant constructs revealed that one of these putative AREs is functionally active. Finally, DNA pull-down assays confirmed specific binding of these intronic AREs by Nrf2 in vitro. Our findings identify a functional Nrf2 response element within the eighth intron of the ABCC3 gene, which may provide mechanistic insight into the induction of ABCC3 during antioxidant response stimuli.

Synergistic interaction between genetics and disease on pravastatin disposition.

BACKGROUND & AIMS: A genome wide association study and multiple pharmacogenetic studies have implicated the hepatic uptake transporter organic anion transporting polypeptide-1B1 (OATP1B1) in the pharmacokinetics and musculoskeletal toxicity of statin drugs. Other OATP uptake transporters can participate in the transport of pravastatin, partially compensating for the loss of OATP1B1 in patients carrying the polymorphism. Non-alcoholic steatohepatitis (NASH) in humans and in a diet-induced rodent model alter the expression of multiple OATP transporters. METHODS: To determine how genetic alteration in one Oatp transporter can interact with NASH-associated changes in Oatp expression we measured the disposition of intravenously administered pravastatin in Slco1b2 knockout (Slco1b2(-/-)) and wild-type (WT) mice fed either a control or a methionine and choline deficient (MCD) diet to induce NASH. RESULTS: Genetic loss of Oatp1b2, the rodent ortholog of human OATP1B transporters, caused a modest increase in pravastatin plasma concentrations in mice with healthy livers. Although a diet-induced model of NASH decreased the expression of multiple hepatic Oatp transporters, it did not alter the disposition of pravastatin compared to WT control mice. In contrast, the combination of NASH-associated decrease in compensatory Oatp transporters and Oatp1b2 genetic loss caused a synergistic increase in plasma area under the curve (AUC) and tissue concentrations in kidney and muscle. CONCLUSIONS: Our data show that NASH alters the expression of multiple hepatic uptake transporters which, due to overlapping substrate specificity among the OATP transporters, may combine with the pharmacogenetic loss of OATP1B1 to increase the risk of statin-induced adverse drug reactions.

Tissue distribution, ontogeny, and chemical induction of aldo-keto reductases in mice.

Aldo-keto reductases (Akrs) are a conserved group of NADPH-dependent oxido-reductase enzymes. This study provides a comprehensive examination of the tissue distribution of the 16 substrate-metabolizing Akrs in mice, their expression during development, and whether they are altered by chemicals that activate distinct transcriptional factor pathways. Akr1c6, 1c14, 1c20, and 1c22 are primarily present in liver; Akr1a4, 1c18, 1c21, and 7a5 in kidney; Akr1d1 in liver and kidney; Akr1b7 in small intestine; Akr1b3 and Akr1e1 in brain; Akr1b8 in testes; Akr1c14 in ovaries; and Akrs1c12, 1c13, and 1c19 are expressed in numerous tissues. Liver expression of Akr1d1 and Akr1c is lowest during prenatal and postnatal development. However, by 20 days of age, liver Akr1d1 increases 120-fold, and Akr1c mRNAs increase as much as 5-fold (Akr1c19) to 1000-fold (Akr1c6). Treatment of mice with chemical activators of transcription factors constitutive androgen receptor (CAR), pregnane X receptor (PXR), and the nuclear factor-erythroid-2 (Nrf2) transcription factor alters liver mRNAs of Akrs. Specifically, CAR activation by 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) increases mRNAs of Akr1b7, Akr1c6, Akr1c19, and Akr1d1, whereas PXR activation by 5-pregnenolone-16α-carbonitrile (PCN) increases the mRNA of Akr1b7 and suppresses mRNAs of Akr1c13 and Akr1c20. The Nrf2 activator 2-cyano-3,12-dioxooleana-1,9-dien-28-imidazolide (CDDO-Im) induces mRNAs of Akr1c6 and Akr1c19. Moreover, Nrf2-null and Nrf2 overexpressing mice demonstrate that this induction is Nrf2-dependent.

Ocular Safety and Toxicokinetics of Bevacizumab-bvzr (Zirabev), a Bevacizumab Biosimilar, Administered to Cynomolgus Monkeys by Intravitreal Injection.

Purpose: Bevacizumab-bvzr (Zirabev®), a recombinant humanized monoclonal antibody targeting vascular endothelial growth factor and a biosimilar to bevacizumab, is approved for intravenous administration for various indications worldwide. The objectives of this study were to evaluate the ocular toxicity, systemic tolerability, and toxicokinetics (TKs) of bevacizumab-bvzr following repeat intravitreal (IVT) injection to cynomolgus monkeys. Methods: Male monkeys were administered saline, vehicle, or bevacizumab-bvzr at 1.25 mg/eye/dose once every 2 weeks (3 doses total) for 1 month by bilateral IVT injection, followed by a 4-week recovery phase to evaluate the reversibility of any findings. Local and systemic safety was assessed. Ocular safety assessments included in-life ophthalmic examinations, tonometry (intraocular pressure, IOP), electroretinograms (ERGs), and histopathology. In addition, concentrations of bevacizumab-bvzr were measured in serum and in ocular tissues (vitreous humor, retina, and choroid/retinal pigment epithelium) and ocular concentration-time profiles and serum TKs were evaluated. Results: Bevacizumab-bvzr was tolerated locally and systemically, with an ocular safety profile comparable to the saline or vehicle control group. Bevacizumab-bvzr was observed in both serum and in the evaluated ocular tissues. There were no bevacizumab-bvzr-related microscopic changes or effects on IOP or ERGs. Bevacizumab-bvzr-related trace pigment or cells in vitreous humor (in 4 of 12 animals; commonly associated with IVT injection) and transient, nonadverse, mild ocular inflammation (in 1 of 12 animals) were noted upon ophthalmic examination and fully reversed during the recovery phase. Conclusions: Bevacizumab-bvzr was well tolerated via biweekly IVT administration in healthy monkeys, with an ocular safety profile comparable to saline or its vehicle control.

Expression and characterization of functional dog flavin-containing monooxygenase 3.

Mammalian flavin-containing monooxygenase (FMO) enzymes catalyze oxidation at nucleophilic, heteroatom centers and are important for drug, xenobiotic, and endogenous substrate metabolism. In human liver, human FMO3 (hFMO3) is the most abundant FMO isoform and is known to contribute to the hepatic clearance of a variety of clinical drugs. The purpose of the current study was to express and compare the dog (beagle) FMO3 (dFMO3) to hFMO3. A full-length dFMO3 cDNA was obtained from liver by reverse transcription-polymerase chain reaction. Using a baculovirus expression system in Spodoptera frugiperda insect cells, dFMO3 was expressed to protein levels of 0.50 nmol/mg, as determined by liquid chromatography-fluorescence detection. Expressed dFMO3 displayed Michaelis-Menten kinetics, catalyzing NADPH-dependent N-oxidation of benzydamine, with K(m) and V(max) values of 18.6 microM and 0.63 nmol N-oxide formed/min/nmol of enzyme, respectively. Benzydamine N-oxidation catalyzed by hFMO3 showed values of 42.6 microM (K(m)) and 3.56 nmol/min/nmol of enzyme (V(max)). Human FMO3 was observed to catalyze the S-oxidation of sulindac sulfide, with respective K(m) and V(max) values of 69.3 microM and 35.4 nmol/min/nmol of enzyme. dFMO3 also catalyzed sulindac sulfide S-oxidation with 6.8 nmol/min/nmol of enzyme being the highest velocity observed. Finally, Western blot analysis indicated protein expression levels of dFMO3 in pooled dog liver and lung microsomes to be 27 and 9 pmol/mg, respectively. In summary, dFMO3 appears to be a functional enzyme expressed at appreciable levels in liver, but one with some kinetic properties that are substantially different from its human homolog hFMO3.

Hepatic cytochrome P450 enzyme alterations in humans with progressive stages of nonalcoholic fatty liver disease.

Members of the cytochrome P450 (P450) enzyme families CYP1, CYP2, and CYP3 are responsible for the metabolism of approximately 75% of all clinically relevant drugs. With the increased prevalence of nonalcoholic fatty liver disease (NAFLD), it is likely that patients with this disease represent an emerging population at significant risk for alterations in these important drug-metabolizing enzymes. The purpose of this study was to determine whether three progressive stages of human NALFD alter hepatic P450 expression and activity. Microsomes isolated from human liver samples diagnosed as normal, n = 20; steatosis, n = 11; nonalcoholic steatohepatitis (NASH) (fatty liver), n = 10; and NASH (no longer fatty), n = 11 were analyzed for P450 mRNA, protein, and enzyme activity. Microsomal CYP1A2, CYP2D6, and CYP2E1 mRNA levels were decreased with NAFLD progression, whereas CYP2A6, CYP2B6, and CYP2C9 mRNA expression increased. Microsomal protein expression of CYP1A2, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 tended to decrease with NAFLD progression. Likewise, functional activity assays revealed decreasing trends in CYP1A2 (p = 0.001) and CYP2C19 (p = 0.05) enzymatic activity with increasing NAFLD severity. In contrast, activity of CYP2A6 (p = 0.001) and CYP2C9 (diclofenac, p = 0.0001; tolbutamide, p = 0.004) was significantly increased with NAFLD progression. Increased expression of proinflammatory cytokines tumor necrosis factor alpha and interleukin 1beta was observed and may be responsible for observed decreases in respective P450 activity. Furthermore, elevated CYP2C9 activity during NAFLD progression correlated with elevated hypoxia-induced factor 1alpha expression in the later stages of NAFLD. These results suggest that significant and novel changes occur in hepatic P450 activity during progressive stages of NAFLD.

Effects of Absence of Constitutive Androstane Receptor (CAR) on Bile Acid Homeostasis in Male and Female Mice.

Accumulation of bile acids (BAs) in hepatocytes has a role in liver disease and also in drug-induced liver injury. The constitutive androstane receptor (CAR) has been shown to protect against BA-induced liver injury. The polymorphism of CAR has recently been shown to modify the pharmacokinetics and pharmacodynamics of various drugs. Thus, it was hypothesized that polymorphism of CAR may also influence BA homeostasis. Using CAR-null and WT mice, this study modeled the potential consequences of CAR polymorphism on BA homeostasis. Our previous study showed that chemical activation of CAR decreases the total BA concentrations in livers of mice. Surprisingly the absence of CAR also decreased the BA concentrations in livers of mice, but to a lesser extent than in CAR-activated mice. Neither CAR activation nor elimination of CAR altered the biliary excretion of total BAs, but CAR activation increased the proportion of 6-OH BAs (TMCA), whereas the lack of CAR increased the excretion of taurocholic acid, TCDCA, and TDCA. Serum BA concentrations did not parallel the decrease in BA concentrations in the liver in either the mice after CAR activation or mice lacking CAR. Gene expression of BA synthesis, transporter and regulator genes were mainly similar in livers of CAR-null and WT mice. In summary, CAR activation decreases primarily the 12-OH BA concentrations in liver, whereas lack of CAR decreases the concentrations of 6-OH BAs in liver. In bile, CAR activation increases the biliary excretion of 6-OH BAs, whereas absence of CAR increases the biliary excretion of 12-OH BAs and TCDCA.

Tissue distribution, ontogeny and induction of the transporters Multidrug and toxin extrusion (MATE) 1 and MATE2 mRNA expression levels in mice.

Transporters are expressed in a wide variety of tissues where they perform the critical function of enabling anionic and cationic chemicals of exogenous and endogenous origin to cross otherwise impermeable cell membranes. The Multidrug and toxin extrusion (MATE) transporters mediate cellular efflux of a variety of organic cations, including many drugs. The purpose of the current study was to determine (1) constitutive expression levels of MATE mRNA in various tissues, (2) whether there are gender differences in the expression of MATEs, (3) the ontogenic expression pattern of MATE1 in kidney and (4) whether MATEs are pharmacologically inducible in liver via activation of known transcription factors. In both male and female mice, MATE1 mRNA levels were highest in the kidney, where male expression was higher than female. MATE2 mRNA expression levels were the highest in the testis, where high expression was localized to Sertoli cells, a critical cell type of the blood testis barrier. In female mice, MATE2 mRNA levels were expressed most highly in the colon. The ontogenic pattern of expression of MATE1 mRNA in the kidneys of both males and females was gradual, with levels increasing steadily from prenatal day -2 to 45 days of age, and a gender difference appearing at day 30. Of the transcription factor activators examined (AhR, CAR, Nrf2, PPARalpha and PXR), none were capable of altering MATE1 or MATE2. The current findings support a potential role for MATE1 and MATE2 in a wide range of tissues and, notably, a unique role for MATE2 in the blood-testis barrier.

Gender divergent expression of Nqo1 in Sprague Dawley and August Copenhagen x Irish rats.

In the mammalian liver, there is an abundance of enzymes that function to enable the safe and efficient elimination of potentially harmful xenobiotics that are encountered through environmental exposure. A variety of factors, including gender and genetic polymorphisms, contribute to the variation between an individual system's detoxification capacity and thus its ability to protect itself against oxidative stress, cellular damage, cell death, etc. NAD(P)H:quinone oxidoreducatase 1 (Nqo1) is an antioxidant enzyme that plays a major role in reducing reactive electrophiles, thereby protecting cells from free-radical damage and oxidative stress. The goal of this study was to determine the gender-specific expression and inducibility of Nqo1 in the Sprague Dawley (SD) and August Copenhagen x Irish (ACI) rat strains, two strains that are commonly used in drug metabolism and drug-induced enzyme induction, toxicity, and carcinogenesis studies. Nqo1 mRNA, protein, and activity levels were determined through 96 h in SD and ACI males and females following treatment with known Nqo1 inducers oltipraz and butylated hydroxyanisole. In the SD strain, gender dimorphic expression of Nqo1 was observed with female mRNA, protein, and activity levels being significantly higher than in males. In contrast, there were minimal differences in Nqo1 mRNA, protein, and activity levels between ACI males and females. The gender dimorphic expression of Nqo1 in the SD rats was maintained through the course of induction, with female-induced levels greater than male-induced levels indicating that SD females may have a greater capacity to protect against oxidative stress and thus a decreased susceptibility to carcinogens.

Drug metabolizing enzyme induction pathways in experimental non-alcoholic steatohepatitis.

Non-alcoholic steatohepatitis (NASH) is a disease that compromises hepatic function and the capacity to metabolize numerous drugs. Aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor alpha (PPARalpha), and nuclear factor-E2 related factor 2 (Nrf2) are xenobiotic activated transcription factors that regulate induction of a number of drug metabolizing enzymes (DMEs). The purpose of the current study was to determine whether experimental NASH alters the xenobiotic activation of these transcription factors and induction of downstream DME targets Cyp1A1, Cyp2B10, Cyp3A11, Cyp4A14 and NAD(P)H:quinone oxidoreductase 1 (Nqo1), respectively. Mice fed normal rodent chow or methionine-choline-deficient (MCD) diet for 8 weeks were then treated with microsomal enzyme inducers beta-naphoflavone (BNF), 1,4-bis-[2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP), pregnenolone-16alpha-carbonitrile (PCN), clofibrate (CFB) or oltipraz (OPZ), known activators of AhR, CAR, PXR, PPARalpha and Nrf2, respectively. Results of this study show that (1) Hepatic PXR mRNA levels were significantly increased (1.4-fold) in mice fed MCD diet, while AhR, CAR, PPARalpha and Nrf2 were not affected. (2) The MCD diet did not alter hepatic inducibility of Cyp1A1, Cyp2B10, Cyp3A11 mRNA levels by their respective microsomal inducers. (3) Constitutive levels of Cyp4A14 mRNA were significantly increased in mice fed the MCD diet, yet further induction by clofibrate was not observed. (4) Hepatic Nqo1 mRNA levels were significantly increased by the MCD diet; however, additional induction of Nqo1 was still achievable following treatment with the Nrf2 activator OPZ.

Editor's Highlight: Clofibrate Decreases Bile Acids in Livers of Male Mice by Increasing Biliary Bile Acid Excretion in a PPARα-Dependent Manner.

Fibrates and their receptor, namely peroxisome proliferator-activated receptor α (PPARα), have been reported to regulate bile acid (BA) synthesis and transport. However, the effect of fibrate treatment and PPARα activation on BA homeostasis remains controversial. In this study, both wild-type (WT) and PPARα-null male mice were treated with clofibrate (CLOF) for 4 days to evaluate the effects of short-term PPARα activation on BA homeostasis. Although a decrease in total BAs (ΣBAs) was observed in livers of CLOF-treated WT mice, it was not observed in PPARα-null mice. CLOF-mediated decrease in ΣBAs in the liver was not likely due to the reduction in BA synthesis or BA uptake, as evidenced by an increase in the BA synthetic enzyme (Cyp7a1) and 2 BA uptake transporters (Na (+)-taurocholate cotransporting polypeptide [Ntcp] and organic anion transporting polypeptide [Oatp]1b2). Instead, the decrease in liver BAs by CLOF is largely a result of increased biliary excretion of BAs, which was associated with a significant induction of the canalicular efflux transporter (bile salt export pump [Bsep]) in the liver. The PPARα-mediated increase in Cyp7a1 in CLOF-treated WT mice was not due to farnesoid X receptor (Fxr)-small heterodimer partner (Shp) signaling in the liver, but due to suppression of Fxr- fibroblast growth factor15 signaling in the ileum. Additionally, CLOF also suppressed intestinal BA transporters (apical sodium-dependent bile acid transporter and organic solute transporterß) and cholesterol efflux transporters (Abcg5 and Abcg8) in a PPARα-dependent manner. In summary, this study provides the first comprehensive analysis on the effect of a short-term CLOF treatment on BA homeostasis, and revealed an essential role of PPARα in regulating BA synthesis, transport and signaling.

Urinary Concentrations of Topically Administered Pain Medications.

A common treatment for chronic pain is prescription of analgesics, but their long-term use entails risk of morbidity, addiction and misuse. One way to reduce the risk of abuse is prescribing of analgesics in a topical form. Physicians are urged to perform urine drug testing to ensure that patients are compliant with their medication regimens. However, there is little data on the efficiency of transdermal delivery for many analgesic drugs, and no data on expected urine drug levels. This study includes data from over 29,000 specimens tested for gabapentin, ketamine, cyclobenzaprine or amitriptyline used orally or topically. Gabapentin and amitriptyline concentrations were more likely to be below the limits of detection (25-40 ng/mL) in the urine of patients using them topically as compared with patients using them orally. Levels in gabapentin-positive topical specimens were much lower than in gabapentin-positive oral specimens (261 ng/mL vs >10,000 ng/mL). In contrast, ketamine and cyclobenzaprine were more readily detectable in the urine of topical users. Ketamine topical specimens were positive 12% more often than oral specimens, and mean topical specimen levels were 68-100% those of oral specimens. Cyclobenzaprine specimens were equally likely to be positive whether the dose was oral or topical, although mean levels after topical dosing were approximately 13-21% those after oral dosing. These findings are consistent with the reported percutaneous absorption efficiencies of gabapentin and ketamine, and are likely to be related to the absorption efficiencies of cyclobenzaprine and amitriptyline.

Activation of Constitutive Androstane Receptor (CAR) in Mice Results in Maintained Biliary Excretion of Bile Acids Despite a Marked Decrease of Bile Acids in Liver.

Activation of Constitutive Androstane Receptor (CAR) protects against bile acid (BA)-induced liver injury. This study was performed to determine the effect of CAR activation on bile flow, BA profile, as well as expression of BA synthesis and transport genes. Synthetic CAR ligand 1,4-bis-[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) was administered to mice for 4 days. BAs were quantified by UPLC-MS/MS (ultraperformance liquid chromatography-tandem mass spectrometry). CAR activation decreases total BAs in livers of male (49%) and female mice (26%), largely attributable to decreases of the 12α-hydroxylated BA taurocholic acid (T-CA) (males (M) 65%, females (F) 45%). Bile flow in both sexes was increased by CAR activation, and the increases were BA-independent. CAR activation did not alter biliary excretion of total BAs, but overall BA composition changed. Excretion of muricholic (6-hydroxylated) BAs was increased in males (101%), and the 12α-OH proportion of biliary BAs was decreased in both males (37%) and females (28%). The decrease of T-CA in livers of males and females correlates with the decreased mRNA of the sterol 12α-hydroxylase Cyp8b1 in males (71%) and females (54%). As a response to restore BAs to physiologic concentrations in liver, mRNA of Cyp7a1 is upregulated following TCPOBOP (males 185%, females 132%). In ilea, mRNA of the negative feedback regulator Fgf15 was unaltered by CAR activation, indicating biliary BA excretion was sufficient to maintain concentrations of total BAs in the small intestine. In summary, the effects of CAR activation on BAs in male and female mice are quite similar, with a marked decrease in the major BA T-CA in the liver.

Experimental non-alcoholic fatty liver disease results in decreased hepatic uptake transporter expression and function in rats.

Non-alcoholic fatty liver disease (NAFLD) encompasses a spectrum of diagnoses ranging from simple fatty liver (SFL), to non-alcoholic steatohepatitis (NASH). This study aimed to determine the effect of moderate and severe NAFLD on hepatic transporter expression and function in vivo. Rats were fed a high-fat diet (SFL model) or a methionine-choline-deficient diet (NASH model) for eight weeks. Hepatic uptake transporter function was determined by bromosulfophthalein (BSP) disposition. Transporter expression was determined by branched DNA signal amplification assay and western blotting; inflammation was identified by immunostaining of liver slices for interleukin 1 beta (IL-1beta). MC- rats showed significant retention of BSP in the plasma when compared to control rats. Hepatic NTCP, OATP1a1, 1a4, 1b2 and 2b1; and OAT 2 and 3 mRNA levels were significantly decreased in high-fat and MC- diet rats when compared to control. Protein expression of OATP1a1 was significantly decreased in high-fat animals, while OATP1a1 and OATP1b2 expressions were significantly lower in MC- rats when compared to control. Liver tissue from high-fat and MC- rats stained positive for IL-1beta, a pro-inflammatory cytokine known to decrease expression of NTCP, OATP and OAT transporters, suggesting a plausible mechanism for the observed transporter alterations. These data suggest that different stages of NAFLD result in altered hepatic uptake transporter expression that can lead to a functional impairment of xenobiotic uptake from the blood. Furthermore, NAFLD may alter the plasma retention time of clinically relevant drugs that are reliant on these transporters and may increase the potential drug toxicity.

Genes of the antioxidant response undergo upregulation in a rodent model of nonalcoholic steatohepatitis.

Nonalcoholic fatty liver disease encompasses a spectrum of hepatic pathologies ranging from simple fatty liver to an inflammatory state known as nonalcoholic steatohepatitis (NASH). NASH is also characterized by severe hepatic oxidative stress. The goal of this study was to determine whether genes of the antioxidant response are induced in rodent models of nonalcoholic fatty liver disease. To simulate simple fatty liver and NASH, respectively, male Sprague-Dawley rats were fed a high-fat (HF) or a methionine and choline-deficient (MCD) diet for 8 weeks. Key marker genes of the antioxidant response that are known to undergo upregulation via activation of Nuclear Factor Erythroid 2-Related Factor 2 were measured using the branched DNA signal amplification assay. Messenger RNA levels of the antioxidant response, including NAD(P)H:quinone oxidoreductase-1 (Nqo1), Glutamate cysteine ligase catalytic (Gclc), and Heme oxygenase-1 (Ho-1), were significantly induced in MCD rat liver but not in HF rat liver. Furthermore, Nqo1 protein expression and activity underwent significant upregulation in MCD rat liver but not in HF rat liver. These data strongly indicate that the pathology induced by the MCD dietary model of NASH results in upregulation of the antioxidant response in rats.