Expression and inducibility of CYP1A1, 1A2, 1B1 by beta-naphthoflavone and CYP2B22, 3A22, 3A29, 3A46 by rifampicin in the respiratory and olfactory mucosa of pig

Indole compounds from fermented soybean products activate the aryl hydrocarbon receptor to reduce liver injury

The consumption of stinky tofu, a traditional fermented soybean product from China, elevates the concentrations of indole and trimethylindole in murine feces and increases the levels of indole in serum, as well as indole in the liver. These hepatic compounds act as ligands for the Aryl Hydrocarbon Receptor (AHR), triggering activation of this receptor, which subsequently enhances the expression of the enzyme cytochrome P450 (CYP) 1A1. This upregulation diminishes the levels of pro-inflammatory cytokines, thereby attenuating alcohol-induced liver injury. This study underscores the potential of dietary indole from stinky tofu to mitigate Alcoholic liver disease (ALD), laying a foundation for the development of functional foods and novel treatment strategies for ALD.

A variety of cytochrome P450 enzymes and flavin-containing monooxygenases in dogs and pigs commonly used as preclinical animal models

Drug oxygenation is mainly mediated by cytochromes P450 (P450s, CYPs) and flavin-containing monooxygenases (FMOs). Polymorphic variants of P450s and FMOs are known to influence drug metabolism.　Species differences exist in terms of drug metabolism and can be important when determining the contributions of individual enzymes. The success of research into drug-metabolizing enzymes and their impacts on drug discovery and development has been remarkable. Dogs and pigs are often used as preclinical animal models. This research update provides information on P450 and FMO enzymes in dogs and pigs and makes comparisons with their human enzymes. Newly identified dog CYP3A98, a testosterone 6β- and estradiol 16α-hydroxylase, is abundantly expressed in small intestine and is likely the major CYP3A enzyme in small intestine, whereas dog CYP3A12 is the major CYP3A enzyme in liver. The roles of recently identified dog CYP2J2 and pig CYP2J33/34/35 were investigated. FMOs have been characterized in humans and several other species including dogs and pigs. P450 and FMO family members have been characterized also in cynomolgus macaques and common marmosets. P450s have industrial applications and have been the focus of attention of many pharmaceutical companies. The techniques used to investigate the roles of P450/FMO enzymes in drug oxidation and clinical treatments have not yet reached maturity and require further development. The findings summarized here provide a foundation for understanding individual pharmacokinetic and toxicological results in dogs and pigs as preclinical models and will help to further support understanding of the molecular mechanisms of human P450/FMO functionality.

Cytochrome P450 enzymes mediated by DNA methylation is involved in deoxynivalenol-induced hepatoxicity in piglets

Deoxynivalenol (DON) is an inevitable contaminant in animal feed and can lead to liver damage, then decreasing appetite and causing growth retardation in piglets. Although many molecular mechanisms are related to hepatoxicity caused by DON, few studies have been done on cytochrome P450 (CYP450) enzymes and DNA methylation. To explore the role of CYP450 enzymes and DNA methylation in DON-induced liver injury, male piglets were fed a control diet, or diet containing 1.0 or 3.0 mg/kg DON for 4 weeks. DON significantly raised the activity of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and glutamyl transpeptidase (GGT) (P < 0.01), leading to liver injury. In vivo study found that DON exposure increased the expression of CYP450 enzymes (such as CYP1A1, CYP2E1, CYP3A29) (P < 0.05), and disturbed the expression of nicotinamide N-methyltransferase (NNMT), galanin-like peptide (GALP) and insulin-like growth factor 1 (IGF-1) (P < 0.05), in which DNA methylation affected the expression of these genes. In vitro study (human normal hepatocytes L02) further proved that DON elevated the expression of CYP1A1, CYP2E1 and CYP3A4 (P < 0.05), and inhibited cell growth in a dose-dependent manner, resulting in cell necrosis. More importantly, knockdown of CYP1A1 or CYP2E1 could alleviate DON-induced growth inhibition by promoting IGF-1 expression. Taken together, increased CYP450 enzymes expression was one of the mechanisms of hepatoxicity and growth inhibition induced by DON, suggesting that the decrease of CYP450 enzymes can antagonize the hepatoxicity in animals, which provides some value for animal feed safety.

The Effectiveness of Dietary Byproduct Antioxidants on Induced CYP Genes Expression and Histological Alteration in Piglets Liver and Kidney Fed with Aflatoxin B1 and Ochratoxin A

The purpose of this study was to investigate the potential of a byproduct mixture derived from grapeseed and sea buckthorn oil industry to mitigate the harmful damage produced by ochratoxin A and aflatoxin B1 at hepatic and renal level in piglets after weaning. Forty cross-bred TOPIGS-40 hybrid piglets after weaning were assigned to three experimental groups (E1, E2, E3) and one control group (C), and fed with experimental diets for 30 days. The basal diet was served as a control and contained normal compound feed for starter piglets without mycotoxins. The experimental groups were fed as follows: E1-basal diet plus a mixture (1:1) of two byproducts (grapeseed and sea buckthorn meal); E2-the basal diet experimentally contaminated with mycotoxins (479 ppb OTA and 62ppb AFB1); and E3-basal diet containing 5% of the mixture (1:1) of grapeseed and sea buckthorn meal and contaminated with the mix of OTA and AFB1. After 4 weeks, the animals were slaughtered, and tissue samples were taken from liver and kidney in order to perform gene expression and histological analysis. The gene expression analysis showed that when weaned piglets were fed with contaminated diet, the expression of most analyzed genes was downregulated. Among the CYP450 family, CYP1A2 was the gene with the highest downregulation. According to these results, in liver, we found that mycotoxins induced histomorphological alterations in liver and kidney and had an effect on the expression level of CYP1A2, CYP2A19, CYP2E1, and CYP3A29, but we did not detect important changes in the expression level of CY4A24, MRP2 and GSTA1 genes.

The constitutive androstane receptor and pregnane X receptor in the brain

Since their discovery, the orphan nuclear receptors constitutive androstane receptor (CAR;NR1I3) and pregnane X receptor (PXR;NR1I2) have been regarded as master regulators of drug disposition and detoxification mechanisms. They regulate the metabolism and transport of endogenous mediators and xenobiotics in organs including the liver, intestine and brain. However, with proposals of new physiological functions for NR1I3 and NR1I2, there is increasing interest in the role of these receptors in influencing brain function. This review will summarise key findings regarding the expression and function of NR1I3 and NR1I2 in the brain, hereby highlighting the need for further research in this field.

Porcine cytochrome P450 3A: current status on expression and regulation

The cytochrome P450s (CYPs) constitute a family of enzymes maintaining vital functions in the body and are mostly recognized for their significant role in detoxification. Of the CYP subfamilies, CYP3A, is one of the most active in the clearance of drugs and other xenobiotics. During the last decades, much focus has been on exploring different models for human CYP3A regulation, expression and activity. In that respect, the growing knowledge of the porcine CYP3As is of great interest. Although many aspects of porcine CYP3A regulation and activity are still unknown, the current literature provides a basic understanding of the porcine CYP3As that can be used e.g., when translating results from studies done in the porcine model into human settings. In this review, the current knowledge about porcine CYP3A expression, regulation, activity and metabolic significance are highlighted. Future research needs are also identified.

Xenobiotica-metabolizing enzymes in the lung of experimental animals, man and in human lung models

The xenobiotic metabolism in the lung, an organ of first entry of xenobiotics into the organism, is crucial for inhaled compounds entering this organ intentionally (e.g. drugs) and unintentionally (e.g. work place and environmental compounds). Additionally, local metabolism by enzymes preferentially or exclusively occurring in the lung is important for favorable or toxic effects of xenobiotics entering the organism also by routes other than by inhalation. The data collected in this review show that generally activities of cytochromes P450 are low in the lung of all investigated species and in vitro models. Other oxidoreductases may turn out to be more important, but are largely not investigated. Phase II enzymes are generally much higher with the exception of UGT glucuronosyltransferases which are generally very low. Insofar as data are available the xenobiotic metabolism in the lung of monkeys comes closed to that in the human lung; however, very few data are available for this comparison. Second best rate the mouse and rat lung, followed by the rabbit. Of the human in vitro model primary cells in culture, such as alveolar macrophages and alveolar type II cells as well as the A549 cell line appear quite acceptable. However, (1) this generalization represents a temporary oversimplification born from the lack of more comparable data; (2) the relative suitability of individual species/models is different for different enzymes; (3) when more data become available, the conclusions derived from these comparisons quite possibly may change.

Characterization of Porcine Hepatic and Intestinal Drug Metabolizing CYP450: Comparison with Human Orthologues from A Quantitative, Activity and Selectivity Perspective

Over the past two decades, the pig has gained attention as a potential model for human drug metabolism. Cytochrome P450 enzymes (CYP450), a superfamily of biotransformation enzymes, are pivotal in drug metabolism. Porcine CYP450 has been demonstrated to convert typical substrates of human CYP450. Nevertheless, knowledge and insight into porcine CYP450 quantity and substrate selectivity is scant, especially regarding intestinal CYP450. The current study aimed to map the quantities of hepatic and intestinal CYP450 in the conventional pig by using a proteomic approach. Moreover, the selectivity of the six most common used probe substrates (phenacetin, coumarin, midazolam, tolbutamide, dextromethorphan, and chlorzoxazone) for drug metabolizing enzyme subfamilies (CYP1A, CYP2A, CYP3A, CYP2C, CYP2D and CYP2E respectively), was investigated. Hepatic relative quantities were 4% (CYP1A), 31% (CYP2A), 14% (CYP3A), 10% (CYP2C), 28% (CYP2D) and 13% (CYP2E), whereas for the intestine only duodenal CYP450 could be determined with 88% for CYP3A and 12% for CYP2C. Furthermore, the results indicate that coumarin (CYP2A), midazolam (CYP3A), tolbutamide (CYP2C), and dextromethorphan (CYP2D) are as selective for porcine as for human CYP450. However, phenacetin (CYP1A2) and chlorzoxazone (CYP2E1) are less selective for the specific enzyme, despite similarities in selectivity towards the different enzymes involved compared to humans.

Effect of white wheat bread and white wheat bread added with bioactive compounds on hypercholesterolemic and steatotic mice fed a high-fat diet

BACKGROUND

The effects of white wheat bread and white wheat bread added with a bioactive compound mixture (Cyclanthera pedata, Glycine max, Monascus-fermented red mold rice, Cynara scolymus and Medicago sativa) were examined on hypercholesterolemic and steatotic mice, divided into four groups: control diet (CTR), high-fat diet (HFD), high-fat diet with white wheat bread added with 1.5 g kg(-1) of mixture (HFD+AB) and high-fat diet with white wheat bread (HFD+B).

RESULTS

Total serum cholesterol in the HFD+AB and HFD+B groups and hepatic triglycerides in the HFD+AB group decreased compared with the HFD group. Liver histology confirmed lower lipid drop accumulation in the HFD+AB group than in the HFD and HFD+B groups. HFD+AB caused a 7.0-fold increase and a 3.5-fold reduction in CYP7A1 and SREBP-1c gene expression respectively compared with the HFD group. Moreover, the HFD+B group showed a 2.2-, 8.4- and 1.5-fold increase in HMG CoA reductase, CYP7A1 and LDLr gene expression respectively compared with the HFD group.

CONCLUSION

Both the white wheat bread and the added white wheat bread induced cholesterol reduction by increasing CYP7A1. Moreover, the added white wheat bread improved steatosis by decreasing SREBP-1c gene expression.

Determination of CYP3A4 Inducing Properties of Compounds Using a Laboratory-Developed Cell-Based Assay

A cell-based assay to measure cytochrome P450 3A4 (CYP3A4) induction was developed to screen for potential CYP3A4 inducers. This 96-well format assay utilizes HepG2 cells transfected with a gene construct of CYP3A4 proximal promoter linked to green fluorescence protein (GFP) gene, and the expression of the GFP is then measured quantitatively. Bergamottin at 5 to 25 µmol/L produced low induction relative to the positive control. Both curcumin and lycopene were not found to affect the expression of GFP, suggesting no induction properties toward CYP3A4. Interestingly, resveratrol produced significant induction from 25 µmol/L onward, which was similar to omeprazole and may warrant further studies. In conclusion, the present study demonstrated that this cell-based assay can be used as a tool to evaluate the potential CYP3A4 induction properties of compounds. However, molecular docking data have not provided satisfactory pointers to differentiate between CYP3A4 inducers from noninducers or from inhibitors, more comprehensive molecular screening may be indicated.

Effect of Natural Polyphenols on CYP Metabolism: Implications for Diseases

Cytochromes P450 (CYPs) are a large group of hemeproteins located on mitochondrial membranes or the endoplasmic reticulum. They play a crucial role in the metabolism of endogenous and exogenous molecules. The activity of CYP is associated with a number of factors including redox potential, protein conformation, the accessibility of the active site by substrates, and others. This activity may be potentially modulated by a variety of small molecules. Extensive experimental data collected over the past decade point at the active role of natural polyphenols in modulating the catalytic activity of CYP. Polyphenols are widespread micronutrients present in human diets of plant origin and in medicinal herbs. These compounds may alter the activity of CYP either via direct interactions with the enzymes or by affecting CYP gene expression. The polyphenol-CYP interactions may significantly alter the pharmacokinetics of drugs and thus influence the effectiveness of chemical therapies used in the treatment of different types of cancers, diabetes, obesity, and cardiovascular diseases (CVD). CYPs are involved in the oxidation and activation of external carcinogenic agents, in which case the inhibition of the CYP activity is beneficial for health. CYPs also support detoxification processes. In this case, it is the upregulation of CYP genes that would be favorable for the organism. A CYP enzyme aromatase catalyzes the formation of estrone and estradiol from their precursors. CYPs also catalyze multiple reactions leading to the oxidation of estrogen. Estrogen signaling and oxidative metabolism of estrogen are associated with the development of cancer. Thus, polyphenol-mediated modulation of the CYP's activity also plays a vital role in estrogen carcinogenesis. The aim of the present review is to summarize the data collected over the last five to six years on the following topics: (1) the mechanisms of the interactions of CYP with food constituents that occur via the direct binding of polyphenols to the enzymes and (2) the mechanisms of the regulation of CYP gene expression mediated by polyphenols. The structure-activity relationship relevant to the ability of polyphenols to affect the activity of CYP is analyzed. The application of polyphenol-CYP interactions to diseases is discussed.

Regulation of porcine hepatic cytochrome p450 - implication for boar taint

Cytochrome P450 (CYP450) is the major family of enzymes involved in the metabolism of several xenobiotic and endogenous compounds. Among substrates for CYP450 is the tryptophan metabolite skatole (3-methylindole), one of the major contributors to the off-odour associated with boar-tainted meat. The accumulation of skatole in pigs is highly dependent on the hepatic clearance by CYP450s. In recent years, the porcine CYP450 has attracted attention both in relation to meat quality and as a potential model for human CYP450. The molecular regulation of CYP450 mRNA expression is controlled by several nuclear receptors and transcription factors that are targets for numerous endogenously and exogenously produced agonists and antagonists. Moreover, CYP450 expression and activity are affected by factors such as age, gender and feeding. The regulation of porcine CYP450 has been suggested to have more similarities with human CYP450 than other animal models, including rodents. This article reviews the available data on porcine hepatic CYP450s and its implications for boar taint.

Regulation of cytochrome P450 mRNA expression in primary porcine hepatocytes by selected secondary plant metabolites from chicory (Cichorium intybus L.)

Chicory (Cichorium intybus) has been shown to induce enzymes of pharmacokinetic relevance (cytochrome P450; CYP). The aim of this study was to investigate the effects of selected secondary plant metabolites with a global extract of chicory root, on the expression of hepatic CYP mRNA (1A2, 2A19, 2C33, 2D25, 2E1 and 3A29), using primary porcine hepatocytes. Of the tested secondary plant metabolites, artemisinin, scoparone, lactucin and esculetin all induced increased expression of specific CYPs, while esculin showed no effect. In contrast, a global extract of chicory root decreased the expression of CYP1A2, 2C33, 2D25 and 3A29 at high concentrations. The results suggest that purified secondary metabolites from chicory affect CYP expression and thereby might affect detoxification in general, and that global extracts of plants can have effects different from individual components.

Cytochrome P450 isoforms are differently up-regulated in aflatoxin B₁-exposed human lymphocytes and monocytes

CONTEXT

Aflatoxins (AFs) are highly hazardous mycotoxins with potent carcinogenic, mutagenic and immune disregulatory properties. Cytochrome P450 (CYP) isoforms are central for enhanced AFB₁ toxicity in situ. It remains to be seen whether and how these AFB₁ activators work in human leukocytes.

OBJECTIVE

To investigate the involvement of CYP isoforms in AFB₁ toxicity of circulating mononuclear cells, we examined the impact of environmentally relevant levels of AFB1 on lymphocytes and monocytes.

MATERIALS AND METHODS

Very low and moderate doses of AFB₁ with/without CYP inducers on transcription of key CYP isoforms and toll-like receptor 4 (TLR4) were examined in human lymphocytes, monocytes and HepG2 cells; cell cycle distribution and viability were also analyzed in AFB₁-exposed lymphocytes and monocytes.

RESULTS

Only CYP1A1, CYP1B1, CYP3A4, CYP3A5 and CYP3A7 expressed in lymphocytes and monocytes. TLR4 much more expressed in monocytes than in lymphocytes, but HepG2 showed little TLR4 transcription. While CYP1A1, CYP1B1 and CYP3A4 were highly induced by AFB₁ in monocytes, in lymphocytes only CYP1A1 was induced. Among CYP1A1, CYP1B1 and CYP3A4 only CYP1A1 responded to low and moderate levels of AFB₁. Enhanced transcripts of CYPs by AFB₁ yielded little synergies on TLR4 transcription in lymphocytes and monocytes. Cell cycle arrest and necrosis were also detected in AFB₁-exposed lymphocytes and monocytes.

CONCLUSIONS

Our novel findings indicate that AFB₁ more intensively stimulates CYP genes expression in monocytes than in lymphocytes. Mechanistically, this could explain a more pronounced immunotoxicity of AFB₁ in myeloid than in lymphoid lineage cells in vitro/situ/vivo.

Modulation of cytochrome P450 enzymes in response to continuous or intermittent high-fat diet in pigs

1. To date, no information has been available on the modulation of cytochrome P450 enzymes (CYPs) following the administration of a hyperlipidemic diet in pigs. 2. We investigated the potential modulation of xenobiotic-metabolizing CYPs in liver, heart and duodenum of pigs subjected to a high-fat/high-cholesterol diet for 2 months continuously (C-HFD) or on alternate weeks (A-HFD). 3. The administration of the high-fat diet resulted in considerably increased plasma cholesterol levels although the animals were still able to manage the lipid overload efficiently, and no sign of effective tissue inflammation occurred in livers. Plasma lipid profile and liver histology indicated a better adaptive response of the A-HFD pigs compared to the C-HFD group. We showed a post-transcriptional induction of hepatic CYP2E1 activity in C-HFD pigs and a transcriptional induction of hepatic CYP3As - especially in the A-HFD group. No further CYP modulation was observed in either liver or extra-hepatic tissues. 4. In conclusion, the administration of a high-fat diet in pigs resulted in limited effects on the drug metabolism system. The better adaptive response of A-HFD pigs compared to C-HFD pigs is a very interesting observation since the intermittent administration of the diet reflects the mode of human behavior more closely.

Dried chicory root modifies the activity and expression of porcine hepatic CYP3A but not 2C--effect of in vitro and in vivo exposure

Hepatic cytochrome P450 expression and activity are dependent on many factors, including dietary ingredients. In the present study, we investigated the in vivo and in vitro effect of chicory root on hepatic CYP3A and 2C in male pigs. Chicory feeding increased the expression of CYP3A29 mRNA but not CYP2C33. Correspondingly, CYP3A activity was increased by chicory feeding, while CYP2C activity was not affected. Additionally, the in vitro effect of chicory extract on the CYP3A activity was investigated. It was shown that CYP3A activity in the microsomes from male pigs was inhibited, but this effect was eliminated by pre-incubation. In both male and female pigs the CYP3A activity was increased in the presence of chicory after pre-incubation. Furthermore, gender-related differences in mRNA expression and activity were observed. CYP3A mRNA expression was greater in female pigs; this was not reflected on activity. For CYP2C, no difference in mRNA expression was observed, while CYP2C activity was greater in female pigs. Surprisingly, the expression of the constitutive androstane receptor, pregnane X receptor and aryl hydrocarbon receptor did not differ with feed or gender. In conclusion, chicory root modifies the expression and activity of CYP3A in vivo and in vitro, while CYP2C is not affected.

Expression and inducibility of CYP1A1, 1A2, 1B1 by β-naphthoflavone and CYP2B22, CYP3As by rifampicin in heart regions and coronary arteries of pig

In this study, the constitutive and inducible expression of the CYP genes (1A1, 1A2, 1B1, 2B22, 3A22, 3A29 and 3A46), related transcriptional factors (AhR, CAR, PXR, and Nrf2) and the antioxidant enzymes SOD, catalase, GSSH-reductase and GSH-peroxidase were investigated in the liver, heart regions and coronary arteries of control pigs and pigs treated with β-naphthoflavone (βNF) or with rifampicin (RIF). Real-time PCR experiments and enzymatic or immunoblot assays showed that CYP1A1 was predominantly enhanced by βNF in a similar manner in all the heart regions, whereas antioxidant enzyme activity was not affected. The rifampicin treatment resulted in an induction of CYP2B22 and CYP3As, at the transcriptional, activity and protein level in liver but not in heart nor in the coronary arteries, despite the expression of CAR and PXR in the cardiac tissues. These results obtained in vivo suggest that pig cardiac tissues may represent a useful model for humans.

mRNA expression profiles of P450 3A enzymes in the liver and small intestine of the domestic pig

The cytochrome P450 (P450) 3A family is considered to be the most important and abundantly expressed P450 subfamily in mammals. The mRNA expression levels of four P450 3A enzymes in porcine liver and small intestine were investigated using real-time reverse transcriptase-polymerase chain reaction (RT-PCR). The expression of P450 3A mRNAs (P450 3A pool) was higher in the liver than that in the small intestine. In the small intestine, the P450 3A mRNAs were gradually decreased from the duodenum to the ileum. P450 3A29 and P450 3A22 were predominantly expressed both in liver and small intestine tissues with larger ratios in the P450 3A pool than the other P450 3A enzymes. These results demonstrate that P450 3A29 and P450 3A22 probably serve as the major P450 3A contributors for both the hepatic and intestinal P450 3A pool. This work provides a deeper comprehension of the contribution of P450 3A enzymes to xenobiotic metabolism in pigs.

Hepatic ethoxy-, methoxy- and pentoxyresorufin O-dealkylase activities in Landrace and Duroc pigs stimulated with HCG

The effect of human chorionic gonadotropin (hCG) stimulation on the activities of ethoxyresorufin O-deethylase (EROD), methoxyresorufin O-demethylase (MROD) and pentoxyresorufin O-depentylase (PROD) was studied in intact male pigs of purebred Landrace and Duroc breeds. Pigs were divided into four groups: two control groups of each breed, without hCG stimulation (n = 20 for each breed), and two experimental groups (n = 18 for each breed), with hCG stimulation (Pregnyl(®); N.V. Organon, Oss, The Netherlands, 30 IU/kg live weight). Pigs were slaughtered 3 days after hCG stimulation and enzyme activities were measured in hepatic microsomes using two approaches. First, only one substrate concentration was used for the analysis of each enzyme activity. We found that EROD activity was suppressed by hCG-stimulation in Landrace (p = 0.004), but not Duroc pigs (p > 0.05). Generally, EROD activity was higher in Duroc pigs compared with Landrace (p = 0.017). Methoxyresorufin O-demethylase and PROD activities did not differ between groups (p > 0.05). To further characterize EROD, MROD and PROD, enzyme kinetic studies were performed. V(max) values for EROD and MROD in both breeds were lower after hCG stimulation (p < 0.001 for Landrace and p < 0.05 for Duroc). Additionally, V(max) values for EROD significantly differed between Landrace and Duroc pigs being higher in Duroc pigs (p < 0.05). We concluded that both hCG stimulation and breed differences may be important in the regulation of EROD and MROD activities. This study provides the first data on the effect of hCG stimulation and thus high testicular steroids, on EROD, MROD and PROD activities. Further studies are needed to investigate individual CYP450 enzymes and their regulation in porcine tissues.

Identification and validation of novel human pregnane X receptor activators among prescribed drugs via ligand-based virtual screening

Human pregnane X receptor (hPXR) plays a key role in regulating metabolism and clearance of endogenous and exogenous substances. Identification of novel hPXR activators among commercial drugs may aid in avoiding drug-drug interactions during coadministration. We applied ligand-based computational approaches for virtual screening of a commonly prescribed drug database (SCUT). Bayesian classification models were generated with a training set comprising 177 compounds using Fingerprints and 117 structural descriptors. A cell-based luciferase reporter assay was used for evaluation of chemical-mediated hPXR activation in HepG2 cells. All compounds were tested at 10 μM concentration with rifampicin and dimethyl sulfoxide as positive and negative controls, respectively. The Bayesian models showed specificity and overall prediction accuracy up to 0.92 and 0.69 for test set compounds. Screening the SCUT database with this model retrieved 105 hits and 17 compounds from the top 25 hits were chosen for in vitro testing. The reporter assay confirmed that nine drugs, i.e., fluticasone, nimodipine, nisoldipine, beclomethasone, finasteride, flunisolide, megestrol, secobarbital, and aminoglutethimide, were previously unidentified hPXR activators. Thus, the present study demonstrates that novel hPXR activators can be efficiently identified among U.S. Food and Drug Administration-approved and commonly prescribed drugs, which should lead to detection and prevention of potential drug-drug interactions.

Comparison of the substrate kinetics of pig CYP3A29 with pig liver microsomes and human CYP3A4

CYP (cytochrome P450) 3A29 in pigs could be an important candidate gene responsible for xenobiotic metabolism, similar to CYP3A4 in humans. Accordingly, the tissue expression of CYP3A29 mRNA in domestic pigs has been determined by a real-time PCR. The enzymatic properties of CYP3A29, CYP3A4 and PLM (pig liver microsomes) were compared by kinetic analysis of TST (testosterone) 6β-hydroxylation and NIF (nifedipine) oxidation. CYP3A29 mRNA was highly expressed in the liver and small intestines of domestic pigs. The CYP3A29 enzyme expressed in Sf9 cells had the same TST-metabolizing activity as human CYP3A4 based on their roughly equal in vitro intrinsic clearance values. The affinity of CYP3A29 for NIF was lower than that of CYP3A4 but higher than that of PLM. KET (ketoconazole) was a more potent inhibitor of TST 6β-hydroxylation and NIF oxidation activities of CYP3A29 than TAO (troleandomycin). These findings indicate that pig CYP3A29 is similar to human CYP3A4 in both extent of expression and activity. The results reported in this paper provide a basis for future in vitro toxicity and metabolism studies.

Expression and inducibility by phenobarbital of CYP2C33, CYP2C42, CYP2C49, CYP2B22, and CYP3As in porcine liver, kidney, small intestine, and nasal tissues

In this study, the expression and inducibility of CYP2C33, CYP2C42, CYP2C49, CYP2B22, CYP3A22, CYP3A29, and CYP3A46 were investigated at activity and/or transcriptional level in liver, kidney, small intestine, respiratory, and olfactory nasal mucosa of control and phenobarbital (PB)-treated pigs. PB treatment resulted in an up-regulation of mRNA levels of all analyzed CYPs in liver, of CYP2C42 and CYP2C49 in kidney, of CYP2C42, CYP2C49, CYP2B22, and CYP3As in small intestine. In liver microsomes from PB-treated pigs, these transcriptional activations were accompanied by an increase of various marker activities of human CYP2B6, CYP3As, CYP2C9, CYP2C19. Among the extrahepatic tissues, a significant induction by PB was observed only in kidney for the marker activities of CYP2C9. Taken together, our results demonstrated that the PB administration in pigs induced at least in liver, in addition to CYP2B22 and CYP3As, the expression of CYP2C33, CYP2C42, and CYP2C49 at transcriptional and activity levels. Furthermore our findings showed that the catalytic activities of porcine CYP2Cs are different amongst those observed and with respect to the human counterparts. Thus, the use of pigs as a model for humans in studies using drugs as substrates and/or inducers of CYP2Cs should be considered carefully.

Effects of typical inducers on olfactory xenobiotic-metabolizing enzyme, transporter, and transcription factor expression in rats

Several xenobiotic-metabolizing enzymes (XMEs) have been identified in the olfactory mucosa (OM) of mammals. However, the molecular mechanisms underlying the regulation of these enzymes have been little explored. In particular, information on the expression of the transcriptional factors in this tissue is quite limited. The aim of the present study was to examine the impact of five typical inducers, Aroclor 1254, 3-methylcholanthrene, dexamethasone, phenobarbital, and ethoxyquin, on the activities and mRNA expression of several XMEs in the OM and in the liver of rats. We also evaluated the effects of these treatments on the mRNA expression of transcription factors and transporters. On the whole, the intensities of the effects were lower in the OM than in the liver. Dexamethasone was found to be the most efficient treatment in the OM. Dexamethasone induced the transcription of several olfactory phase I, II, and III genes [such as cytochromes P450 2A3 and 3A9, UDP-glucuronosyltransferase (UGT) 2A1, and multidrug resistance-related protein type 1] and increased UGT activities. We observed that dexamethasone up-regulated sulfotransferase 1C1 expression in the OM but down-regulated it in the liver. Aroclor and ethoxyquin induced the gene expression of CYP1A and quinone reductase, respectively, in the OM. The transcription factors aryl hydrocarbon receptor, nuclear factor E2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor α, pregnane X receptor, and glucocorticoid receptor were detected in the OM, but no constitutive androstane receptor expression was observed. Dexamethasone and Aroclor enhanced olfactory Nrf2 expression. These results demonstrate that olfactory XME can be modulated by chemicals and that the mechanisms involved in the regulation of these enzymes are tissue-specific.

Flavonoids activate pregnane x receptor-mediated CYP3A4 gene expression by inhibiting cyclin-dependent kinases in HepG2 liver carcinoma cells

Background

The expression of the drug-metabolizing enzyme cytochrome P450 3A4 (CYP3A4) is regulated by the pregnane × receptor (PXR), which is modulated by numerous signaling pathways, including the cyclin-dependent kinase (Cdk) pathway. Flavonoids, commonly consumed by humans as dietary constituents, have been shown to modulate various signaling pathways (e.g., inhibiting Cdks). Flavonoids have also been shown to induce CYPs expression, but the underlying mechanism of action is unknown. Here, we report the mechanism responsible for flavonoid-mediated PXR activation and CYP expression.

Results

In a cell-based screen designed to identify compounds that activate PXR-mediated CYP3A4 gene expression in HepG2 human carcinoma cells, we identified several flavonoids, such as luteolin and apigenin, as PXR activators. The flavonoids did not directly bind to PXR, suggesting that an alternative mechanism may be responsible for flavonoid-mediated PXR activation. Consistent with the Cdk5-inhibitory effect of flavonoids, Cdk5 and p35 (a non-cyclin regulatory subunit required to activate Cdk5) were expressed in HepG2. The activation of Cdk5 attenuated PXR-mediated CYP3A4 expression whereas its downregulation enhanced it. The Cdk5-mediated downregulation of CYP3A4 promoter activity was restored by flavonoids, suggesting that flavonoids activate PXR by inactivating Cdk5. In vitro kinase assays showed that Cdk5 directly phosphorylates PXR. The Cdk kinase profiling assay showed that apigenin inhibits multiple Cdks, suggesting that several Cdks may be involved in activation of PXR by flavonoids.

Conclusions

Our results for the first time link the stimulatory effect of flavonoids on CYP expression to their inhibitory effect on Cdks, through a PXR-mediated mechanism. These results may have important implications on the pharmacokinetics of drugs co-administered with herbal remedy and herbal-drug interactions.