Effects of a chargrilled meat diet on expression of CYP3A, CYP1A, and P-glycoprotein levels in healthy volunteers

Long-Term Exposure to Phenanthrene Induced Gene Expressions and Enzyme Activities of Cyprinus carpio below the Safe Concentration

Phenanthrene (PHE) is a typical compound biomagnified in the food chain which endangers human health and generally accumulates from marine life. It has been listed as one of the 16 priority PAHs evaluated in toxicology. In order to evaluate the changes of CYP1A GST mRNA expression and EROD GST enzyme activity in carp exposed to lower than safe concentrations of PHE. Long-term exposure of carp to PHE at lower than safe concentrations for up to 25 days. The mRNA expression level and cytochrome P450 (CYP1A/EROD (7-Ethoxylesorufin O-deethylase)) and glutathione S-transferase (GST) activity were measured in carp liver and brain tissue. The results showed that PHE stress induced low-concentration induction and high-concentration inhibition of CYP1A expression and EROD enzyme activity in the liver and brain of carp. In both two organs, GST enzyme activity was also induced. However, the expression of GST mRNA was first induced and then inhibited, after the 15th day. These results indicate that long-term exposure to PHE at lower than safe concentrations still poses a potential threat to carp’s oxidase system and gene expression.

Gutsy science: In vitro systems of the human intestine to model oral drug disposition

The intestine has important gate-keeping functions that can profoundly affect the systemic blood exposure of orally administered drugs. Thus, characterizing a new molecular entity's (NME) disposition within the intestine is of utmost importance in drug development. While currently used in vitro systems, such as Ussing chamber, precision-cut intestinal slices, immortalized cell lines, and primary enterocytes provide substantial knowledge about drug absorption and the intestinal first-pass effect, they remain sub-optimal for quantitatively predicting this process and the oral bioavailability of many drugs. Use of novel in vitro systems such as intestinal organoids and intestinal microphysiological systems have provided substantial advances over the past decade, expanding our understanding of intestinal physiology, pathology, and development. However, application of these emerging in vitro systems in the pharmaceutical science is in its infancy. Preliminary work has demonstrated that these systems more accurately recapitulate the physiology and biochemistry of the intact intestine, as it relates to oral drug disposition, and thus they hold considerable promise as preclinical testing platforms of the future. Here we review currently used and emerging in vitro models of the human intestine employed in pharmaceutical science research. We also highlight aspects of these emerging tools that require further study.

Descriptors of Cytochrome Inhibitors and Useful Machine Learning Based Methods for the Design of Safer Drugs

Roughly 2.8% of annual hospitalizations are a result of adverse drug interactions in the United States, representing more than 245,000 hospitalizations. Drug-drug interactions commonly arise from major cytochrome P450 (CYP) inhibition. Various approaches are routinely employed in order to reduce the incidence of adverse interactions, such as altering drug dosing schemes and/or minimizing the number of drugs prescribed; however, often, a reduction in the number of medications cannot be achieved without impacting therapeutic outcomes. Nearly 80% of drugs fail in development due to pharmacokinetic issues, outlining the importance of examining cytochrome interactions during preclinical drug design. In this review, we examined the physiochemical and structural properties of small molecule inhibitors of CYPs 3A4, 2D6, 2C19, 2C9, and 1A2. Although CYP inhibitors tend to have distinct physiochemical properties and structural features, these descriptors alone are insufficient to predict major cytochrome inhibition probability and affinity. Machine learning based in silico approaches may be employed as a more robust and accurate way of predicting CYP inhibition. These various approaches are highlighted in the review.

Metabolism and Mechanism of Human Cytochrome P450 Enzyme 1A2

Human cytochrome P450 enzyme 1A2 (CYP1A2) is one of the most important cytochrome P450 (CYP) enzymes in the liver, accounting for 13% to 15% of hepatic CYP enzymes. CYP1A2 metabolises many clinical drugs, such as phenacetin, caffeine, clozapine, tacrine, propranolol, and mexiletine. CYP1A2 also metabolises certain precarcinogens such as aflatoxins, mycotoxins, nitrosamines, and endogenous substances such as steroids. The regulation of CYP1A2 is influenced by many factors. The transcription of CYP1A2 involves not only the aromatic hydrocarbon receptor pathway but also many additional transcription factors, and CYP1A2 expression may be affected by transcription coactivators and compression factors. Degradation of CYP1A2 mRNA and protein, alternative splicing, RNA stability, regulatory microRNAs, and DNA methylation are also known to affect the regulation of CYP1A2. Many factors can lead to changes in the activity of CYP1A2. Smoking, polycyclic aromatic hydrocarbon ingestion, and certain drugs (e.g., omeprazole) increase its activity, while many clinical drugs such as theophylline, fluvoxamine, quinolone antibiotics, verapamil, cimetidine, and oral contraceptives can inhibit CYP1A2 activity. Here, we review the drugs metabolised by CYP1A2, the metabolic mechanism of CYP1A2, and various factors that influence CYP1A2 metabolism. The metabolic mechanism of CYP1A2 is of great significance in the development of personalised medicine and CYP1A2 target-based drugs.

Evaluation of Tissue Stem Cell-Derived Human Intestinal Organoids, a Physiologically Relevant Model to Evaluate Cytochrome P450 Induction in Gut

Induction of cytochrome P450 can cause drug-drug interactions and efficacy failure. Induction risk in liver and gut is typically inferred from experiments with plated hepatocytes. Organoids are physiologically relevant, multicellular structures originating from stem cells. Intestinal stem cell-derived organoids retain traits of normal gut physiology, such as an epithelial barrier and cellular diversity. Matched human enteroid and colonoid lines, generated from ileal and colon biopsies from two donors, were cultured in extracellular matrix for 3 days, followed by a single 48-hour treatment with rifampin, omeprazole, CITCO, and phenytoin at concentrations that induce target genes in hepatocytes. After treatment, mRNA was analyzed for induction of target genes. Rifampin induced CYP3A4; estimated EC₅₀ and maximal fold induction were 3.75 µM and 8.96-fold, respectively, for ileal organoids and 1.40 µM and 11.3-fold, respectively, for colon organoids. Ileal, but not colon, organoids exhibited nifedipine oxidase activity, which was induced by rifampin up to 14-fold. The test compounds did not increase mRNA expression of CYP1A2, CYP2B6, multidrug resistance transporter 1 (P-glycoprotein), breast cancer resistance protein, and UDP-glucuronosyltransferase 1A1 in ileal organoids. Whereas omeprazole induced CYP3A4 (up to 5.3-fold, geometric mean, n = 4 experiments), constitutive androstane receptor activators phenytoin and CITCO did not. Omeprazole failed to induce CYP1A2 mRNA but did induce CYP1A1 mRNA (up to 7.7-fold and 15-fold in ileal and colon organoids, respectively, n = 4 experiments). Despite relatively high intra- and interexperimental variability, data suggest that the model yields induction responses that are distinct from hepatocytes and holds promise to enable evaluation of CYP1A1 and CYP3A4 induction in gut. SIGNIFICANCE STATEMENT: An adult intestinal stem cell-derived organoid model to test P450 induction in gut was evaluated. Testing several prototypical inducers for mRNA induction of P450 isoforms, UDP-glucuronosyltransferase 1A1, P-glycoprotein, and breast cancer resistance protein with both human colon and ileal organoids resulted in a range of responses, often distinct from those found in hepatocytes, indicating the potential for further development of this model as a physiologically relevant gut induction test system.

Drug-Drug Interactions Involving Intestinal and Hepatic CYP1A Enzymes

Cytochrome P450 (CYP) 1A enzymes are considerably expressed in the human intestine and liver and involved in the biotransformation of about 10% of marketed drugs. Despite this doubtless clinical relevance, CYP1A1 and CYP1A2 are still somewhat underestimated in terms of unwanted side effects and drug–drug interactions of their respective substrates. In contrast to this, many frequently prescribed drugs that are subjected to extensive CYP1A-mediated metabolism show a narrow therapeutic index and serious adverse drug reactions. Consequently, those drugs are vulnerable to any kind of inhibition or induction in the expression and function of CYP1A. However, available in vitro data are not necessarily predictive for the occurrence of clinically relevant drug–drug interactions. Thus, this review aims to provide an up-to-date summary on the expression, regulation, function, and drug–drug interactions of CYP1A enzymes in humans.

Inhibition and induction of CYP enzymes in humans: an update

The cytochrome P450 (CYP) enzyme family is the most important enzyme system catalyzing the phase 1 metabolism of pharmaceuticals and other xenobiotics such as herbal remedies and toxic compounds in the environment. The inhibition and induction of CYPs are major mechanisms causing pharmacokinetic drug–drug interactions. This review presents a comprehensive update on the inhibitors and inducers of the specific CYP enzymes in humans. The focus is on the more recent human in vitro and in vivo findings since the publication of our previous review on this topic in 2008. In addition to the general presentation of inhibitory drugs and inducers of human CYP enzymes by drugs, herbal remedies, and toxic compounds, an in-depth view on tyrosine-kinase inhibitors and antiretroviral HIV medications as victims and perpetrators of drug–drug interactions is provided as examples of the current trends in the field. Also, a concise overview of the mechanisms of CYP induction is presented to aid the understanding of the induction phenomena.

Aryl Hydrocarbon Receptor-Dependent inductions of omega-3 and omega-6 polyunsaturated fatty acid metabolism act inversely on tumor progression

The Western diet contains a high ratio of omega-6 (ω6) to omega-3 (ω3) polyunsaturated fatty acids (PUFA). The prototypical aryl hydrocarbon receptor (AHR) ligand, 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), induces CYP1 family enzymes, which can metabolize PUFA to epoxides. Mice fed ω3-rich or ω6-rich diets were treated with TCDD and injected subcutaneously with AHR-competent Hepa1-GFP hepatoma cells or AHR-deficient LLC lung cancer cells. TCDD reduced the growth rates of the resulting tumors in ω3-fed mice and inhibited their metastasis to the liver and/or lung, but had the opposite effects in mice fed ω6 PUFA. These responses were likely attributable to the corresponding PUFA epoxides generated in tumor cells and/or host, since many depended upon co-administration of a soluble epoxide hydrolase (EPHX2) inhibitor in males, and/or were associated with increases in epoxide levels in tumors and sites of metastasis. Equivalent effects occurred in females in the absence of EPHX2 inhibition, probably because this sex expressed reduced levels of EPHX2. The responses elicited by TCDD were associated with effects on tumor vascularity, tumor cell proliferation and/or apoptosis. Thus environmental AHR agonists, and potentially also endogenous, nutritional, and microbiome-derived agonists, may reduce or enhance cancer progression depending on the composition of dietary PUFA, particularly in females.

Food Bioactive Compounds and Their Interference in Drug Pharmacokinetic/Pharmacodynamic Profiles

Preclinical and clinical studies suggest that many food molecules could interact with drug transporters and metabolizing enzymes through different mechanisms, which are predictive of what would be observed clinically. Given the recent incorporation of dietary modifications or supplements in traditional medicine, an increase in potential food-drug interactions has also appeared. The objective of this article is to review data regarding the influence of food on drug efficacy. Data from Google Scholar, PubMed, and Scopus databases was reviewed for publications on pharmaceutical, pharmacokinetic, and pharmacodynamic mechanisms. The following online resources were used to integrate functional and bioinformatic results: FooDB, Phenol-Explorer, Dr. Duke's Phytochemical and Ethnobotanical Databases, DrugBank, UniProt, and IUPHAR/BPS Guide to Pharmacology. A wide range of food compounds were shown to interact with proteins involved in drug pharmacokinetic/pharmacodynamic profiles, starting from drug oral bioavailability to enteric/hepatic transport and metabolism, blood transport, and systemic transport/metabolism. Knowledge of any food components that may interfere with drug efficacy is essential, and would provide a link for obtaining a holistic view for cancer, cardiovascular, musculoskeletal, or neurological therapies. However, preclinical interaction may be irrelevant to clinical interaction, and health professionals should be aware of the limitations if they intend to optimize the therapeutic effects of drugs.

Effect of tildrakizumab (MK-3222), a high affinity, selective anti-IL23p19 monoclonal antibody, on cytochrome P450 metabolism in subjects with moderate to severe psoriasis

AIMS

Tildrakizumab, an interleukin (IL)-23 inhibitor, is indicated for the treatment of moderate to severe chronic plaque psoriasis. Although tildrakizumab is not metabolized by, and does not alter, cytochrome P450 (CYP) expression in vitro, clinically significant pharmacokinetic effects through changes in systemic inflammation, which alters CYP metabolism, have been well documented. At the time of study conduct, the effect of modulation of inflammation/cytokines, including IL-23 inhibition with tildrakizumab, on CYP metabolism, and therefore the potential for disease-drug interactions, in psoriasis patients was unknown. We therefore assessed whether tildrakizumab alters CYP metabolism in subjects with moderate to severe psoriasis.

METHODS

This was an open-label, fixed-sequence, two-period trial. In Period 1 (Day 1), subjects received an oral CYP probe cocktail of up to five drugs (midazolam 2 mg [3A4], caffeine 200 mg [1A2], warfarin 10 mg [2C9], omeprazole 40 mg [2C19] and dextromethorphan 30 mg [2D6]), followed by a 7-day washout. In Period 2, subjects received tildrakizumab 200 mg subcutaneously on Days 1 and 29 and a second CYP probe cocktail on Day 57. Substrate or metabolite pharmacokinetics, safety and changes in Psoriasis Severity Area Index (PASI), interleukin-6 (IL-6) and high-sensitivity C-reactive protein (hs-CRP), were assessed.

RESULTS

Twenty subjects (13 men, 7 women) were enrolled. Tildrakizumab had no clinically relevant effect on the pharmacokinetics of any of the probe substrates tested. On Day 57 of Period 2, the median percentage decrease from baseline in PASI score following tildrakizumab was ~93%. There were no clinically relevant changes in IL-6 or hs-CRP. Treatment with tildrakizumab was generally well tolerated.

CONCLUSION

In subjects with moderate to severe psoriasis, tildrakizumab 200 mg did not have a discernible effect on CYP metabolism. The potential for clinically significant drug-drug interactions (DDIs) with tildrakizumab in patients with psoriasis is low. The difference in the occurrence of DDIs seen with anti-inflammatory agents in rheumatoid arthritis patients compared with psoriasis patients may be due to the much greater extent of systemic inflammation in rheumatoid arthritis as compared to psoriasis.

The cytochrome P450 isoenzyme and some new opportunities for the prediction of negative drug interaction in vivo

Cytochrome (CYP) 450 isoenzymes are the basic enzymes involved in Phase I biotransformation. The most important role in biotransformation belongs to CYP3A4, CYP2D6, CYP2C9, CYP2C19 and CYP1A2. Inhibition and induction of CYP isoenzymes caused by drugs are important and clinically relevant pharmacokinetic mechanisms of drug interaction. Investigation of the activity of CYP isoenzymes by using phenotyping methods (such as the determination of the concentration of specific substrates and metabolites in biological fluids) during drug administration provides the prediction of negative side effects caused by drug interaction. In clinical practice, the process of phenotyping of CYP isoenzymes and some endogenous substrates in the ratio of cortisol to 6β-hydroxycortisol in urine for the evaluation of CYP3A4 activity has been deemed to be a quite promising, safe and minimally invasive method for patients nowadays.

mRNA N6-methyladenosine methylation of postnatal liver development in pig

N6-methyladenosine (m6A) is a ubiquitous reversible epigenetic RNA modification that plays an important role in the regulation of post-transcriptional protein coding gene expression. Liver is a vital organ and plays a major role in metabolism with numerous functions. Information concerning the dynamic patterns of mRNA m6A methylation during postnatal development of liver has been long overdue and elucidation of this information will benefit for further deciphering a multitude of functional outcomes of mRNA m6A methylation. Here, we profile transcriptome-wide m6A in porcine liver at three developmental stages: newborn (0 day), suckling (21 days) and adult (2 years). About 33% of transcribed genes were modified by m6A, with 1.33 to 1.42 m6A peaks per modified gene. m6A was distributed predominantly around stop codons. The consensus motif sequence RRm6ACH was observed in 78.90% of m6A peaks. A negative correlation (average Pearson's r = -0.45, P < 10-16) was found between levels of m6A methylation and gene expression. Functional enrichment analysis of genes consistently modified by m6A methylation at all three stages showed genes relevant to important functions, including regulation of growth and development, regulation of metabolic processes and protein catabolic processes. Genes with higher m6A methylation and lower expression levels at any particular stage were associated with the biological processes required for or unique to that stage. We suggest that differential m6A methylation may be important for the regulation of nutrient metabolism in porcine liver.

Assessment of CYP1A2 enzyme activity in relation to type-2 diabetes and habitual caffeine intake

BACKGROUND

Coffee consumption is a known inducer of cytochrome P450 1A2 (CYP1A2) enzyme activity. We recently observed that a group of type-2 diabetes patients consumed more caffeine (coffee) on a daily basis than non-type-2 diabetes controls. Here, we investigated whether type-2 diabetes cases may metabolize caffeine faster than non-type-2 diabetes controls.

METHODS

To estimate CYP1A2 enzyme activity, an established marker of caffeine metabolism, we quantified the paraxanthine/caffeine concentration ratio in saliva in 57 type-2 diabetes and 146 non-type-2 diabetes participants in a case-control field study. All participants completed validated questionnaires regarding demographic status, health and habitual caffeine intake, and were genotyped for the functional -163C > A polymorphism of the CYP1A2 gene.

RESULTS

In the diabetes group, we found a larger proportion of participants with the highly inducible CYP1A2 genotype. Furthermore, the paraxanthine/caffeine ratio, time-corrected to mitigate the impact of different saliva sampling times with respect to the last caffeine intake, was higher than in the control group. Participants who reported habitually consuming more caffeine than the population average showed higher CYP1A2 activity than participants with lower than average caffeine consumption. Multiple regression analyses revealed that higher caffeine intake was potentially an important mediator of higher CYP1A2 activity.

CONCLUSIONS

Estimated CYP1A2 enzyme activity, and thus speed of caffeine metabolism, was higher in our type-2 diabetes group; this was possibly due to higher intake of caffeine, a known inducer of CYP1A2 enzyme activity. Given the fairly small sample sizes, the results need to be considered as preliminary and require validation in larger populations.

The role of AHR-inducible cytochrome P450s in metabolism of polyunsaturated fatty acids

The environmental pollutant 2,3,7,8-tetrachlorodibenzo-ρ-dioxin (TCDD) is the prototype of a large number of non-genotoxic carcinogens, dietary phytochemicals and endogenous metabolites that act via binding the aryl hydrocarbon receptor (AHR). The TCDD-liganded AHR massively upregulates CYP1A1, CYP1A2 and CYP1B1 in many mammalian organs. We demonstrated that TCDD treatment markedly increases the levels of several epoxides and diol metabolites of the epoxides of both ω-6 and ω-3 polyunsaturated fatty acids (PUFA) in the liver and lungs of mice, in an aryl hydrocarbon receptor-dependent fashion, and most likely via the activities of the CYP1 family members. ω-6 Epoxides are known to stimulate tumor growth, angiogenesis, and metastasis in mice. Interestingly, ω-3 epoxides have the opposite effect on these parameters. TCDD and other AHR agonists may, therefore, impact angiogenesis, growth and metastasis of tumors in either a positive or negative way, depending on the relative levels of ω -6 epoxides and ω-3 epoxides generated in the host and/or tumor cells. This is of potential relevance to carcinogenesis by AHR agonists in the human, since the human population is exposed to widely varying ω-6: ω-3 PUFA ratios in the diet.

Measurement of human CYP1A2 induction by inhalation exposure to benzo(a)pyrene based on in vivo isotope breath method

Cytochrome P450 1A2 (CYP1A2) is an enzyme involved in the metabolic activation of certain carcinogens, and inducible by toxic substrates. To date, few studies have investigated in vivo CYP1A2 induction in humans and its relationship to polycylic aromatic hydrocarbons (PAHs) like benzo(a)pyrene (BaP). Non-smoking healthy male coke-oven workers (n = 30) were recruited as 'exposure' group, and non-smoking healthy office workers in the same city (n = 10) were selected as 'control' group, to test whether high inhalation exposure to PAHs can induce CYP1A2 activity in human livers. Significantly higher inhalation exposure of PAHs were found among the exposure group compared to the control. Inhalation BaP exposure concentration in the exposure group was more than 30 times higher than the control group (p < 0.001). However, the exposure group did not exhale significant higher levels of (13)CO2/(12)CO2 in breath samples (p = 0.81), and no significant relationship was found between the inhaled BaP concentration and the (13)CO2/(12)CO2 ratio (p = 0.91). A significant association was found between the (13)CO2/(12)CO2 exhalation and dietary BaP intake level. Hepatic CYP1A2 activity/induction level was not effected by inhaled BaP but was altered by ingestion of BaP.

The utility of metabolic activation mixtures containing human hepatic post-mitochondrial supernatant (S9) for in vitro genetic toxicity assessment

In vitro genotoxicity assessment routinely employs an exogenous metabolic activation mixture to simulate mammalian metabolism. Activation mixtures commonly contain post-mitochondrial liver supernatant (i.e. S9) from chemically induced Sprague Dawley rats. Although Organization for Economic Cooperation and Development (OECD) test guidelines permit the use of other S9 preparations, assessments rarely employ human-derived S9. The objective of this study is to review and evaluate the use of human-derived S9 for in vitro genetic toxicity assessment. All available published genotoxicity assessments employing human S9 were compiled for analysis. To facilitate comparative analyses, additional matched Ames data using induced rat liver S9 were obtained for certain highly cited chemicals. Historical human and induced rat S9 quality control reports from Moltox were obtained and mined for enzyme activity and mutagenic potency data. Additional in vitro micronucleus data were experimentally generated using human and induced rat S9. The metabolic activity of induced rat S9 was found to be higher than human S9, and linked to high mutagenic potency results. This study revealed that human S9 often yields significantly lower Salmonella mutagenic potency values, especially for polycyclic aromatic hydrocarbons, aflatoxin B1 and heterocyclic amines (~3- to 350-fold). Conversely, assessment with human S9 activation yields higher potency for aromatic amines (~2- to 50-fold). Outliers with extremely high mutagenic potency results were observed in the human S9 data. Similar trends were observed in experimentally generated mammalian micronucleus cell assays, however human S9 elicited potent cytotoxicity L5178Y, CHO and TK6 cell lines. Due to the potential for reduced sensitivity and the absence of a link between enzyme activity levels and mutagenic potency, human liver S9 is not recommended for use alone in in vitro genotoxicity screening assays; however, human S9 may be extremely useful in follow-up tests, especially in the case of chemicals with species-specific metabolic differences, such as aromatic amines.

Review of clinical studies of Polygonum multiflorum Thunb. and its isolated bioactive compounds

Polygonum multiflorum Thunb. (PMT), officially listed in the Chinese Pharmacopoeia, is one of the most popular perennial Chinese traditional medicines known as He shou wu in China and East Asia, and as Fo-ti in North America. Mounting pharmacological studies have stressed out its key benefice for the treatment of various diseases and medical conditions such as liver injury, cancer, diabetes, alopecia, atherosclerosis, and neurodegenerative diseases as well. International databases such as PubMed/Medline, Science citation Index and Google Scholar were searched for clinical studies recently published on P. multiflorum. Various clinical studies published articles were retrieved, providing information relevant to pharmacokinetics-pharmacodynamics analysis, sleep disorders, dyslipidemia treatment, and neurodegenerative diseases. This review is an effort to update the clinical picture of investigations ever carried on PMT and/or its isolated bio-compounds and to enlighten its therapeutic assessment.

SNP genetic polymorphisms of MDR-1, CYP1A2 and CYPB11 genes in four canine breeds upon toxicological evaluation

The fields of pharmacogenetics and pharmacogenomics have become increasingly promising regarding the clinical application of genetic data to aid in prevention of adverse reactions. Specific screening tests can predict which animals express modified proteins or genetic sequences responsible for adverse effects associated with a drug. Among the genetic variations that have been investigated in dogs, the multidrug resistance gene (MDR) is the best studied. However, other genes such as CYP1A2 and CYP2B11 control the protein syntheses involved in the metabolism of many drugs. In the present study, the MDR-1, CYP1A2 and CYP2B11 genes were examined to identify SNP polymorphisms associated with these genes in the following four canine breeds: Uruguayan Cimarron, Border Collie, Labrador Retriever and German Shepherd. The results revealed that several SNPs of the CYP1A2 and CYP2B11 genes are potential targets for drug sensitivity investigations.

Biotransformation of xenobiotics in the human colon and rectum and its association with colorectal cancer

In humans, the liver is generally considered to be the major organ contributing to drug metabolism, but studies during the last years have suggested an important role of the extra-hepatic drug metabolism. The gastrointestinal tract (GI-tract) is the major path of entry for a wide variety of compounds including food, and orally administered drugs, but also compounds - with neither nutrient nor other functional value - such as carcinogens. These compounds are metabolized by a large number of enzymes, including the cytochrome P450 (CYP), the glutathione S-transferase (GST) family, the uridine 5'-diphospho- glucuronosyltransferase (UDP-glucuronosyltransferase - UGT) superfamily, alcohol-metabolizing enzymes, sulfotransferases, etc. These enzymes can either inactivate carcinogens or, in some cases, generate reactive species with higher reactivity compared to the original compound. Most data in this field of research originate from animal or in vitro studies, wherein human studies are limited. Here, we review the human studies, in particular the studies on the phenotypic expression of these enzymes in the colon and rectum to get an impression of the actual enzyme levels in this primary organ of exposure. The aim of this review is to give a summary of currently available data on the relation between the CYP, the GST and the UGT biotransformation system and colorectal cancer obtained from clinical and epidemiological studies in humans.

Modulation of cytochrome P450 metabolism and transport across intestinal epithelial barrier by ginger biophenolics

Natural and complementary therapies in conjunction with mainstream cancer care are steadily gaining popularity. Ginger extract (GE) confers significant health-promoting benefits owing to complex additive and/or synergistic interactions between its bioactive constituents. Recently, we showed that preservation of natural "milieu" confers superior anticancer activity on GE over its constituent phytochemicals, 6-gingerol (6G), 8-gingerol (8 G), 10-gingerol (10 G) and 6-shogaol (6S), through enterohepatic recirculation. Here we further evaluate and compare the effects of GE and its major bioactive constituents on cytochrome P450 (CYP) enzyme activity in human liver microsomes by monitoring metabolites of CYP-specific substrates using LC/MS/MS detection methods. Our data demonstrate that individual gingerols are potent inhibitors of CYP isozymes, whereas GE exhibits a much higher half-maximal inhibition value, indicating no possible herb-drug interactions. However, GE's inhibition of CYP1A2 and CYP2C8 reflects additive interactions among the constituents. In addition, studies performed to evaluate transporter-mediated intestinal efflux using Caco-2 cells revealed that GE and its phenolics are not substrates of P-glycoprotein (Pgp). Intriguingly, however, 10 G and 6S were not detected in the receiver compartment, indicating possible biotransformation across the Caco-2 monolayer. These data strengthen the notion that an interplay of complex interactions among ginger phytochemicals when fed as whole extract dictates its bioactivity highlighting the importance of consuming whole foods over single agents. Our study substantiates the need for an in-depth analysis of hepatic biotransformation events and distribution profiles of GE and its active phenolics for the design of safe regimens.

Thienopyridine efficacy and cigarette smoking status

Dual antiplatelet therapy with aspirin and a P2Y12 receptor blocker is an established regimen to reduce the risk of ischemic event occurrence in patients with high-risk cardiovascular (CV) disease. Cigarette smoking is an important cardiovascular risk factor. However, several investigators have reported what may be termed a "new" "smoker's paradox", whereby clopidogrel-treated nonsmokers appear to have either less or no CV-event reduction when compared to the substantial CV-event reduction in clopidogrel-treated smokers based on several large-scale trials. This "smoker's paradox" observed in multiple clinical outcome studies is also supported by emerging "real-world" data that also suggest clopidogrel nonsmokers do not fare as well as smokers treated with clopidogrel. In support of the new "smoker's paradox", pharmacodynamic studies have also shown that smoking status influences clopidogrel responsiveness in healthy volunteers, acute coronary syndrome patients, and patients treated with percutaneous coronary intervention. Finally, there is a substantial, albeit not entirely consistent, body of pharmacodynamic and clinical outcome data supporting a reduced antiplatelet effect of clopidogrel in non-smokers as compared to smokers. The clinical relevance of this interaction has never been demonstrated in a prospective trial. The focus of this review is to critically evaluate the reported interaction between cigarette smoking status and thienopyridine efficacy.

Development and assessment of healthy properties of meat and meat products designed as functional foods

This review deals with the two major aspects to be considered in the context of meat-based functional foods and human health. One involves the different strategies used to improve (increase or reduce) the presence of bioactive (healthy and unhealthy) compounds in meat and meat products in order to develop potential meat-based functional foods; these strategies are basically concerned with animal production practices, meat processing and storage, distribution and consumption conditions. Since the link between the consumption of those foods and their potentially beneficial effects (improving health and/or reducing the risk of several chronic diseases) needs to be demonstrated scientifically, the second aspect considered is related to intervention studies to examine the functional capacity of meat-based potentially functional foods in humans, discussing how the functionality of a food can be assessed in terms of its effects on health in relation to both target body functions and risk factors.

Combined genotoxic effects of a polycyclic aromatic hydrocarbon (B(a)P) and an heterocyclic amine (PhIP) in relation to colorectal carcinogenesis

Colorectal neoplasia is the third most common cancer worldwide. Environmental factors such as diet are known to be involved in the etiology of this cancer. Several epidemiological studies have suggested that specific neo-formed mutagenic compounds related to meat consumption are an underlying factor involved in the association between diet and colorectal cancer. Heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) are known mutagens and possible human carcinogens formed at the same time in meat during cooking processes. We studied the genotoxicity of the model PAH benzo(a)pyrene (B(a)P) and HCA 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), alone or in mixture, using the mouse intestinal cell line Apc^Min/+, mimicking the early step of colorectal carcinogenesis, and control Apc^+/+ cells. The genotoxicity of B(a)P and PhIP was investigated using both cell lines, through the quantification of B(a)P and PhIP derived DNA adducts, as well as the use of a genotoxic assay based on histone H2AX phosphorylation quantification. Our results demonstrate that heterozygous Apc mutated cells are more effective to metabolize B(a)P. We also established in different experiments that PhIP and B(a)P were more genotoxic on Apc^Min/+ cells compared to Apc^+/+. Moreover when tested in mixture, we observed a combined genotoxicity of B(a)P and PhIP on the two cell lines, with an increase of PhIP derived DNA adducts in the presence of B(a)P. Because of their genotoxic effects observed on heterozygous Apc mutated cells and their possible combined genotoxic effects, both B(a)P and PhIP, taken together, could be implicated in the observed association between meat consumption and colorectal cancer.

Influence of environmental and genetic factors on CYP1A2 activity in individuals of South Asian and European ancestry

The drug-metabolizing enzyme CYP1A2 contributes to the metabolism of a number of commonly used medicines and displays wide interindividual variability. The aim of this study was to investigate CYP1A2 activity in a population of South Asian ancestry and compare it with a population of European ancestry. CYP1A2 activity was determined using the 4 h paraxanthine/caffeine saliva concentration ratio following a 100-mg oral dose of caffeine in healthy individuals of South Asian (n = 166) and European (n = 166) ancestry. Participants were surveyed for extrinsic ethnic factors and genotyped for polymorphisms in CYP1A2 and related genes. Significantly lower CYP1A2 activity was observed in South Asian participants (median: 0.42; range: 0.10-1.06) as compared with European participants (0.54; 0.12-1.64) (P < 0.01). Multiple linear regression indicated that 41% of the variability in CYP1A2 activity could be explained by the diet, lifestyle, and genetic factors studied.

TLR2 controls intestinal carcinogen detoxication by CYP1A1

Intestinal cytochrome P450 subclass 1A1 (CYP1A1) contributes to a metabolic “shield” protecting the host from ingested carcinogens such as polycyclic aromatic hydrocarbons (PAH). The expression of CYP1 (including CYP1A2 and CYP1B1) is considered to depend solely on a heterodimeric transcription factor consisting of the arylhydrocarbon receptor (AHR) and the AHR nuclear translocator (ARNT). So far, no interference has been noted between the regulation of CYP1 and the activation of Toll-like receptor 2 (TLR2), which modulates the inflammatory response to bacterial cell wall components in immune cells and enterocytes. Here we report that intestinal CYP1A1 is silenced in TLR2-deficient mice, even when under exposure to the carcinogenic PAH benzo[a]pyrene (BaP). In contrast, hepatic CYP1A1 was moderately induced in TLR2-deficient mice without restoring their ability to clear BaP from systemic circulation, as present in wild-type animals. After feeding of BaP for 21 days, only TLR2^−/− mice, but not their wild type littermates developed polyps in the colon. Gene expressions and protein concentrations of AHR and ARNT in the intestine did not differ between the genotypes. In conclusion, the presence of ligands for TLR2 of bacterial origin seems to be crucial for detoxication of luminal carcinogens by CYP1A1 in the intestine. This unprecedented finding indicates a complex interplay between the immune system of the host and intestinal bacteria with detoxication mechanisms. This highlights the relevance of intestinal microbiota when trying to unravel pathways present in mammals and opens new perspectives for research in human health.

Potential of an in vitro toolbox combined with exposure data as a first step for the risk assessment of dietary chemical contaminants

In vitro risk assessment of dietary contaminants has become a priority in human food safety. This paper proposes an in vitro approach associating different complementary tools in an original toolbox and aims to improve the assessment of the toxicological impact of dietary contaminants at realistic human exposure levels, with a special focus on the intestinal compartment. The system is based on the use of four complementary cellular tools, namely stress gene induction in transgenic strains of Escherichia coli, modulation of the activity of key biotransformation enzymes (cytochrome P-450 (CYP) 1A1 and 3A4) in a human intestinal cell line, and activation of aryl hydrocarbon receptor (AhR) and oestrogenic receptor (ER)-dependent genes in agonistic and antagonistic assays with luciferase reporter cells. It was applied to four chosen model molecules: ochratoxin A (OTA) and deoxynivalenol (DON), two common food-borne mycotoxins, and imazalil (IMA) and benomyl (BEN), two fungicides widely occurring in foodstuffs. All these assays were performed at or around a realistic intestinal concentration, determined through a deterministic approach based on the calculation of a theoretical maximum daily intake (TMDI). Using the four model molecules, it is clearly highlighted that induction of CYP1A1 activity and inhibition of CYP3A4 activity occurred in Caco-2 cells at a realistic intestinal concentration of IMA. Furthermore, some bacterial stress genes were induced in a range of realistic concentrations, following exposure to DON and IMA. In addition, BEN clearly provoked an ER agonistic activity in a human oestrogen sensitive reporter cell line. All these results are in accordance with the literature, suggesting that the in vitro toolbox constitutes an interesting approach in order to obtain a first 'fingerprint' of dietary contaminants at realistic human exposure for further risk assessment.

Structure, function, regulation and polymorphism and the clinical significance of human cytochrome P450 1A2

Human CYP1A2 is one of the major CYPs in human liver and metabolizes a number of clinical drugs (e.g., clozapine, tacrine, tizanidine, and theophylline; n > 110), a number of procarcinogens (e.g., benzo[a]pyrene and aromatic amines), and several important endogenous compounds (e.g., steroids). CYP1A2 is subject to reversible and/or irreversible inhibition by a number of drugs, natural substances, and other compounds. The CYP1A gene cluster has been mapped on to chromosome 15q24.1, with close link between CYP1A1 and 1A2 sharing a common 5'-flanking region. The human CYP1A2 gene spans almost 7.8 kb comprising seven exons and six introns and codes a 515-residue protein with a molecular mass of 58,294 Da. The recently resolved CYP1A2 structure has a relatively compact, planar active site cavity that is highly adapted for the size and shape of its substrates. The architecture of the active site of 1A2 is characterized by multiple residues on helices F and I that constitutes two parallel substrate binding platforms on either side of the cavity. A large interindividual variability in the expression and activity of CYP1A2 has been observed, which is largely caused by genetic, epigenetic and environmental factors (e.g., smoking). CYP1A2 is primarily regulated by the aromatic hydrocarbon receptor (AhR) and CYP1A2 is induced through AhR-mediated transactivation following ligand binding and nuclear translocation. Induction or inhibition of CYP1A2 may provide partial explanation for some clinical drug interactions. To date, more than 15 variant alleles and a series of subvariants of the CYP1A2 gene have been identified and some of them have been associated with altered drug clearance and response and disease susceptibility. Further studies are warranted to explore the clinical and toxicological significance of altered CYP1A2 expression and activity caused by genetic, epigenetic, and environmental factors.

Computational prediction of binding affinity for CYP1A2-ligand complexes using empirical free energy calculations

Predicting binding affinities for receptor-ligand complexes is still one of the challenging processes in computational structure-based ligand design. Many computational methods have been developed to achieve this goal, such as docking and scoring methods, the linear interaction energy (LIE) method, and methods based on statistical mechanics. In the present investigation, we started from an LIE model to predict the binding free energy of structurally diverse compounds of cytochrome P450 1A2 ligands, one of the important human metabolizing isoforms of the cytochrome P450 family. The data set includes both substrates and inhibitors. It appears that the electrostatic contribution to the binding free energy becomes negligible in this particular protein and a simple empirical model was derived, based on a training set of eight compounds. The root mean square error for the training set was 3.7 kJ/mol. Subsequent application of the model to an external test set gives an error of 2.1 kJ/mol, which is remarkably good, considering the simplicity of the model. The structures of the protein-ligand interactions are further analyzed, again demonstrating the large versatility and plasticity of the cytochrome P450 active site.

Effects of enzyme inducers and inhibitors on the pharmacokinetics of intravenous ipriflavone in rats

In order to find out what types of the hepatic microsomal cytochrome P450 (CYP) isozymes are involved in the metabolism of ipriflavone, ipriflavone at a dose of 20 mg kg−1 (or 15 mg kg−1) was infused in male Sprague—Dawley rats. In rats pretreated with SKF 525-A (a non-specific CYP isozyme inhibitor in rats), the total body clearance (CL) of ipriflavone was significantly slower (29.9% decrease) than that in control rats. This indicates that ipriflavone is metabolized via CYP isozymes in rats, hence various enzyme inducers and inhibitors were used in in-vitro or in-vivo studies in rats. In rats pretreated with 3-methylcholanthrene and phenobarbital (main inducers of CYP1A1/2 and 2B1/2 in rats, respectively), the CL values were significantly higher (153 and 67.2% increases, respectively). In rats pretreated with sulfaphenazole (a main inhibitor of CYP2C11 in rats), the CL was significantly slower (22.5% decrease) than that in control rats. On addition of furafylline (a main inhibitor of CYP1A2 in rats), the in-vitro intrinsic clearance for the disappearance of ipriflavone was significantly slower (50.8% decrease) than that without furafylline. However, the CL values were not significantly different in rats pretreated with orphenadrine and isoniazid (a main inducer of CYP2E1 in rats), and quinine and troleandomycin (main inhibitors of CYP2D1 and 3A23/2 in rats, respectively) compared to controls. These data suggest that ipriflavone could be metabolized mainly via CYP1A1/2, 2B1/2 and 2C11 in rats.

Cytochrome P450-mediated metabolism in the human gut wall

Objective

Although the human small intestine serves primarily as an absorptive organ for nutrients and water, it also has the ability to metabolise drugs. Interest in the small intestine as a drug-metabolising organ has been increasing since the realisation that it is probably the most important extrahepatic site of drug biotransformation.

Key findings

Among the metabolising enzymes present in the small intestinal mucosa, the cytochromes P450 (CYPs) are of particular importance, being responsible for the majority of phase I drug metabolism reactions. Many drug interactions involving induction or inhibition of CYP enzymes, in particular CYP3A, have been proposed to occur substantially at the level of the intestine rather than exclusively within the liver, as originally thought. CYP3A and CYP2C represent the major intestinal CYPs, accounting for approximately 80% and 18%, respectively, of total immunoquantified CYPs. CYP2J2 is also consistently expressed in the human gut wall. In the case of CYP1A1, large interindividual variation in the expression levels has been reported. Data for the intestinal expression of the polymorphic CYP2D6 are conflicting. Several other CYPs, including the common hepatic isoform CYP2E1, are expressed in the human small intestine to only a very low extent, if at all. The distribution of most CYP enzymes is not uniform along the human gastrointestinal tract, being generally higher in the proximal regions of the small intestine.

Summary

This article reviews the current state of knowledge of CYP enzyme expression in human small intestine, the role of the gut wall in CYP-mediated metabolism, and how this metabolism limits the bioavailability of orally administered drugs. Possible interactions between drugs and CYP activity in the small intestine are also discussed.

Update information on drug metabolism systems--2009, part II: summary of information on the effects of diseases and environmental factors on human cytochrome P450 (CYP) enzymes and transporters

The present paper is an update of the data on the effects of diseases and environmental factors on the expression and/or activity of human cytochrome P450 (CYP) enzymes and transporters. The data are presented in tabular form (Tables 1 and 2) and are a continuation of previously published summaries on the effects of drugs and other chemicals on CYP enzymes (Rendic, S.; Di Carlo, F. Drug Metab. Rev., 1997, 29(1-2), 413-580., Rendic, S. Drug Metab. Rev., 2002, 34(1-2), 83-448.). The collected information presented here is as stated by the cited author(s), and in cases when several references are cited the latest published information is included. Inconsistent results and conclusions obtained by different authors are highlighted, followed by discussion of the major findings. The searchable database is available as an Excel file, for information about file availability contact the corresponding author.

Differential induction of CYP1A1 and CYP1B1 by benzo[a]pyrene in oral squamous cell carcinoma cell lines and by tobacco smoking in oral mucosa

Polyaromatic hydrocarbons, including benzo[a]pyrene (BP), are major tobacco carcinogens. Their carcinogenic effects require metabolic activation by cytochrome p450 (CYP) enzymes. Relative CYP isoform expression is related to tissue-specific tobacco-related squamous cell carcinoma (SCC) susceptibility. There have been conflicting reports regarding relative CYP1A1 and CYP1B1 oral expression, and information regarding CYP1B1 expression in oral tissues is limited. To quantify BP- and tobacco-induced CYP1A1 and CYP1B1 expression in oral SCC cells and oral mucosa.

STUDY DESIGN

Real-time qPCR was performed to measure (1) BP-induced CYP1A1 and CYP1B1 mRNA expression in seven oral/other head and neck SCC cell lines (2) CYP1A1 and CYP1B1 mRNA expression in gingiva from 22 smokers and 24 nonsmokers. SCC lines exhibited either similar induction of both isoforms or preferential CYP1A1 induction (CYP1A1-to-CYP1B1 ratios 0.8-4.3). In contrast, gingival tissues from smokers exhibited preferential CYP1B1 induction. Marked interindividual variation in CYP1A1 and CYP1B1 expression was observed among smokers. In vitro conditions may not account for factors that modulate expression in vivo. Interindividual variation in inducible CYP1A1 and CYP1B1 expression may account in part for variation in tobacco-related oral SCC risk.

Assessing caffeine exposure in pregnant women

Studies on the effects of caffeine on health, while numerous, have produced inconsistent results. One of the most uncertain and controversial effects is on pregnancy outcome. Studies have produced conflicting results due to a number of methodological variations. The major challenge is the accurate assessment of caffeine intake. The aim of the present study was to explore different methods of assessing caffeine exposure in pregnant women. Twenty-four healthy pregnant women from the UK city of Leeds completed both a detailed questionnaire, the caffeine assessment tool (CAT) designed specifically to assess caffeine intake and a prospective 3 d food and drink diary. The women also provided nine saliva samples over two consecutive days for estimation of caffeine and a metabolite (paraxanthine). Caffeine intakes from the CAT and diary showed adequate agreement (intra-class correlation coefficient of 0·5). For saliva caffeine and paraxanthine measures, the between-sample variation (within the same woman) was greater than between-woman and between-day variation. However, there was still adequate agreement between these measures and the CAT. The CAT is a valuable tool that is now being used in a large prospective study investigating caffeine's role in pregnancy outcome.

Inhibition and induction of human cytochrome P450 enzymes: current status

Variability of drug metabolism, especially that of the most important phase I enzymes or cytochrome P450 (CYP) enzymes, is an important complicating factor in many areas of pharmacology and toxicology, in drug development, preclinical toxicity studies, clinical trials, drug therapy, environmental exposures and risk assessment. These frequently enormous consequences in mind, predictive and pre-emptying measures have been a top priority in both pharmacology and toxicology. This means the development of predictive in vitro approaches. The sound prediction is always based on the firm background of basic research on the phenomena of inhibition and induction and their underlying mechanisms; consequently the description of these aspects is the purpose of this review. We cover both inhibition and induction of CYP enzymes, always keeping in mind the basic mechanisms on which to build predictive and preventive in vitro approaches. Just because validation is an essential part of any in vitro-in vivo extrapolation scenario, we cover also necessary in vivo research and findings in order to provide a proper view to justify in vitro approaches and observations.