Inhibition of chlorzoxazone metabolism, a clinical probe for CYP2E1, by a single ingestion of watercress

Hepatic, Extrahepatic and Extracellular Vesicle Cytochrome P450 2E1 in Alcohol and Acetaminophen-Mediated Adverse Interactions and Potential Treatment Options

Alcohol and several therapeutic drugs, including acetaminophen, are metabolized by cytochrome P450 2E1 (CYP2E1) into toxic compounds. At low levels, these compounds are not detrimental, but higher sustained levels of these compounds can lead to life-long problems such as cytotoxicity, organ damage, and cancer. Furthermore, CYP2E1 can facilitate or enhance the effects of alcohol-drug and drug-drug interactions. In this review, we discuss the role of CYP2E1 in the metabolism of alcohol and drugs (with emphasis on acetaminophen), mediating injury/toxicities, and drug-drug/alcohol-drug interactions. Next, we discuss various compounds and various nutraceuticals that can reduce or prevent alcohol/drug-induced toxicity. Additionally, we highlight experimental outcomes of alcohol/drug-induced toxicity and potential treatment strategies. Finally, we cover the role and implications of extracellular vesicles (EVs) containing CYP2E1 in hepatic and extrahepatic cells and provide perspectives on the clinical relevance of EVs containing CYP2E1 in intracellular and intercellular communications leading to drug-drug and alcohol-drug interactions. Furthermore, we provide our perspectives on CYP2E1 as a druggable target using nutraceuticals and the use of EVs for targeted drug delivery in extrahepatic and hepatic cells, especially to treat cellular toxicity.

A Literature Review of Liver Function Test Elevations in Rifampin Drug-Drug Interaction Studies

Although rifampin drug–drug interaction (DDI) studies are routinely conducted, there have been instances of liver function test (LFT) elevations, warranting further evaluation. A literature review was conducted to identify studies in which combination with rifampin resulted in hepatic events and evaluate any similarities. Over 600 abstracts and manuscripts describing rifampin DDI studies were first evaluated, of which 30 clinical studies reported LFT elevations. Out of these, 11 studies included ritonavir in combination with other drug(s) in the rifampin DDI study. The number of subjects that were discontinued from treatment on these studies ranged from 0 to 71 (0–100% of subjects in each study). The number of subjects hospitalized for adverse events in these studies ranged from 0 to 41 (0–83.67% of subjects in each study). LFT elevations in greater than 50% of subjects were noted during the concomitant administration of rifampin with ritonavir‐boosted protease inhibitors and with lorlatinib; with labeled contraindication due to observed hepatotoxicity related safety findings only for saquinavir/ritonavir and lorlatinib. In the lorlatinib and ritonavir DDI studies, considerable LFT elevations were observed rapidly, typically within 24–72 h following co‐administration. A possible sequence effect has been speculated, where rifampin induction prior to administration of the combination may be associated with increased severity of the LFT elevations. The potential role of rifampin in the metabolic activation of certain drugs into metabolites with hepatic effects needs to be taken into consideration when conducting rifampin DDI studies, particularly those for which the metabolic profiles are not fully elucidated.

Mechanisms Underlying Biological Effects of Cruciferous Glucosinolate-Derived Isothiocyanates/Indoles: A Focus on Metabolic Syndrome

An inverse correlation between vegetable consumption and the incidence of cancer has long been described. This protective effect is stronger when cruciferous vegetables are specifically consumed. The beneficial properties of vegetables are attributed to their bioactive components like fiber, antioxidants vitamins, antioxidants, minerals, and phenolic compounds. Cruciferous vegetables contain all these molecules; however, what makes them different are their sulfurous components, called glucosinolates, responsible for their special smell and taste. Glucosinolates are inactive biologically in the organism but are hydrolyzed by the enzyme myrosinase released as a result of chewing, leading to the formation of active derivatives such as isothiocyanates and indoles. A considerable number of in vitro and in vivo studies have reported that isothiocyanates and indoles elicit chemopreventive potency through multiple mechanisms that include modulation of phases I and II detoxification pathway enzymes, regulation of cell cycle arrest, and control of cell growth, induction of apoptosis, antioxidant activity, anti-angiogenic effects, and epigenetic regulation. Nuclear erythroid 2-related factor 2 (Nrf2) and Nuclear factor-κB (NF-κB) are key and central regulators in all these processes with a main role in oxidative stress and inflammation control. It has been described that isothiocyanates and indoles regulate their activity directly and indirectly. Today, the metabolic syndrome (central obesity, insulin resistance, hyperlipidemia, and hypertension) is responsible for a majority of deaths worldwide. All components of metabolic syndrome are characterized by chronic inflammation with deregulation of the PI3K/AKT/mTOR, MAPK/EKR/JNK, Nrf2, and NF-κB signaling pathways. The effects of GLSs derivatives controlling these pathways have been widely described in relation to cancer. Changes in food consumption patterns observed in the last decades to higher consumption of ultra-processed foods, with elevation in simple sugar and saturated fat contents and lower consumption of vegetables and fruits have been directly correlated with metabolic syndrome prevalence. In this review, it is summarized the knowledge regarding the mechanisms by which cruciferous glucosinolate derivatives (isothiocyanates and indoles) directly and indirectly regulate these pathways. However, the review places a special focus on the knowledge of the effects of glucosinolates derivatives in metabolic syndrome, since this has not been reviewed before.

The Effects of Cruciferous Vegetable-Enriched Diets on Drug Metabolism: A Systematic Review and Meta-Analysis of Dietary Intervention Trials in Humans

Relatively few studies exist in the literature that discuss the effects of diet on drug metabolism and how this can affect interindividual differences in systemic drug exposure. Several studies have investigated the effects of cruciferous vegetables (Cruciferae) or their constituents on drug-metabolizing activity, as these vegetables form an important part of many peoples' diets. In general, the ingestion of cruciferous vegetables is associated with induction of cytochrome P450 (CYP) 1A2 activity in vivo; however, there is contention between reports, and the clinical significance of potential diet-drug interactions remains unclear. This study reports a systematic review, critical appraisal, and meta-analysis of the published literature in this area, and discusses the clinical significance of Cruciferae-enriched diets in the context of diet-drug interactions. Twenty-three dietary intervention trials with drug metabolism end points were identified across Embase, Medline, and the Cochrane Controlled Register of Trials (CENTRAL). Cruciferous vegetables represented in the literature included broccoli, Brussels sprout, cabbage, cauliflower, radish, and watercress. A range of phase I and II drug-metabolizing enzymes and phenotyping metrics were represented in the literature. The meta-analyses performed demonstrated a significant effect on CYP1A2 and glutathione S-transferase-alpha (GST-α), with consumption of Cruciferae increasing the activities of these enzymes by 20-40% and 15-35%, respectively. The results herein suggest that patients undergoing pharmacotherapy with CYP1A2 or GST-α substrates could have altered drug exposure profiles if they regularly eat large or variable amounts of cruciferous vegetables. Recommendations regarding the design of future randomized, controlled trials to test hypotheses in this area are included.

Effects of phytochemicals on cellular signaling: reviewing their recent usage approaches

Most of the previous studies in last three decades report evidence of interactions between the different phytochemicals and the proteins involved in signal transduction pathways using in silico, in vitro, ex vivo, and in vivo analyses. However, extrapolation of these findings for clinical purposes has not been that fruitful. The efficacy of the phytochemicals in vivo studies is limited by parameters such as solubility, metabolic degradation, excretion, etc. Various approaches have now been devised to circumvent these limitations. Recently, chemical modification of the phytochemicals are demonstrated to reduce some of the limitations and improve their efficacy. Similar to traditional medicines several combinatorial phytochemical formulations have shown to be more efficient. Further, phytochemicals have been reported to be even more efficient in the form of nanoparticles. However, systematic evaluation of their efficacy, mode of action in pathway modulation, usage and associated challenges is required to be done. The present review begins with basic understanding of how signaling cascades regulate cellular response and the consequences of their dysregulation further summarizing the developments and problems associated with the dietary phytochemicals and also discuss recent approaches in strengthening these compounds in pharmacological applications. Only context relevant studies have been reviewed. Considering the limitations and scope of the article, authors do not claim inclusion of all the early and recent studies.

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.

Dietary Cold Pressed Watercress and Coconut Oil Mixture Enhances Growth Performance, Intestinal Microbiota, Antioxidant Status, and Immunity of Growing Rabbits

The present study assessed the effect of dietary supplementation with coconut oil (CNO), watercress oil (WCO), and their mixture as promoters of growth, antioxidant status, immunity, and intestinal microbiota in growing rabbits. A total of 120 rabbits were distributed into six groups (20 rabbits/group) receiving a basal diet without supplementation (G1) or diet supplemented with 2 g CNO (G2), 2 g WCO (G3), 0.5 g CNO plus 1.5 g WCO (G4), 1 g CNO plus 1 g WCO (G5), or 1.5 g CNO plus 0.5 g WCO/kg (G6). Live body weight and feed conversion ratio were significantly higher in the G4 and G5 groups than in the other groups. Superoxide dismutase activity and reduced glutathione concentration were significantly improved in the CNO or WCO diets. Supplemental CNO plus WCO at all tested levels produced the best lysozyme and complement 3 activities. Cecal lactobacilli, coliform, Enterobacteriaceae, and Clostridium spp. populations were lower in the group who received the 1 g CNO + 1 g WCO/kg diet than that in the control group. Dietary supplementation of 1 g CNO + 1 g WCO or 0.5 g CNO + 1.5 g WCO/kg had the potential to improve growth, feed utilization, antioxidant status, and immunity, and reduce cecal pathogenic bacteria in rabbits.

Clinical Corner: Herb-Drug Interactions in Cancer Chemotherapy: Theoretical Concerns Regarding Drug Metabolizing Enzymes

Interactions between herbal medicines and conventional drugs have recently been reported; the most significant herb with such drug interactions is Saint John's wort, an inducer of cytochrome P450 3A3/4, an enzyme responsible for clearance of many clinically important drugs from the body. Foods (especially grapefruit) and habits or lifestyle factors such as smoking or alcohol consumption may also alter the metabolism of drugs through effects on the cytochrome P450 system. The authors review here the functioning of the drug-metabolizing enzymes and discuss their particular sig nificance in cancer chemotherapy treatment. They then present the herbal medicines, foods, and lifestyle factors that induce or inhibit drug-metabolizing enzymes that are important for both cancer chemotherapy drugs and drugs used adjunctively in cancer treatment. It is notable that no actual herb-drug interactions have been reported clinically in cancer treatment, and their potential for interaction still must be regarded as theoretical. Although some chemotherapy patients may be interested in taking herbal medicines that could potentially interact with cancer chemotherapy agents, it may be wise to counsel them to use other means of addressing the problems for which they use specific herbs during the time they receive chemotherapy.

A principal mechanism for the cancer chemopreventive activity of phenethyl isothiocyanate is modulation of carcinogen metabolism

Isothiocyanates are small molecules characterized by high chemical reactivity that allows them to interact readily with cellular constituents eliciting a plethora of biological activities. They are present exclusively in cruciferous vegetables, as glucosinolates, the intake of which has been associated with cancer chemoprevention. When the physical structure of these vegetables is disturbed, e.g. during mastication, the enzyme myrosinase is released and converts the glucosinolates to isothiocyanates (R-N=C=S), where R can be aliphatic or aromatic. Although sulforaphane, an aliphatic isothiocyanate, has received most attention worldwide, the most extensively studied aromatic isothiocyanate is phenethyl isothiocyanate (PEITC), and there are substantial differences in biological activity between the two sub-classes. In animal cancer models, PEITC effectively antagonized the carcinogenicity of chemicals, especially nitrosocompounds. A principal mechanism of their action is to protect the integrity of DNA by decreasing the levels of the genotoxic metabolites of chemical carcinogens. Extensive studies established that PEITC modulates the metabolism of the tobacco-specific carcinogenic nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by inhibiting its cytochrome P450-mediated bioactivation. Moreover, PEITC is a potent inducer of detoxification enzymes such as quinone reductase, glutathione S-transferase and glucuronosyl transferase. PEITC is rapidly absorbed and is characterized by a large bioavailability; Cmax concentrations achieved in plasma after dietary intake are sufficient to modulate carcinogen metabolism. PEITC is primarily metabolized by glutathione conjugation and is excreted in the urine and bile as the mercapturate. The ability of PEITC to perturb carcinogen metabolism through modulation of cytochrome P450 and phase II detoxification enzymes is comprehensively and critically reviewed.

Modulation of Metabolic Detoxification Pathways Using Foods and Food-Derived Components: A Scientific Review with Clinical Application

Research into human biotransformation and elimination systems continues to evolve. Various clinical and in vivo studies have been undertaken to evaluate the effects of foods and food-derived components on the activity of detoxification pathways, including phase I cytochrome P450 enzymes, phase II conjugation enzymes, Nrf2 signaling, and metallothionein. This review summarizes the research in this area to date, highlighting the potential for foods and nutrients to support and/or modulate detoxification functions. Clinical applications to alter detoxification pathway activity and improve patient outcomes are considered, drawing on the growing understanding of the relationship between detoxification functions and different disease states, genetic polymorphisms, and drug-nutrient interactions. Some caution is recommended, however, due to the limitations of current research as well as indications that many nutrients exert biphasic, dose-dependent effects and that genetic polymorphisms may alter outcomes. A whole-foods approach may, therefore, be prudent.

The inactivation of human CYP2E1 by phenethyl isothiocyanate, a naturally occurring chemopreventive agent, and its oxidative bioactivation

Phenethylisothiocyanate (PEITC), a naturally occurring isothiocyanate and potent cancer chemopreventive agent, works by multiple mechanisms, including the inhibition of cytochrome P450 (P450) enzymes, such as CYP2E1, that are involved in the bioactivation of carcinogens. PEITC has been reported to be a mechanism-based inactivator of some P450s. We describe here the possible mechanism for the inactivation of human CYP2E1 by PEITC, as well as the putative intermediate that might be involved in the bioactivation of PEITC. PEITC inactivated recombinant CYP2E1 with a partition ratio of 12, and the inactivation was not inhibited in the presence of glutathione (GSH) and not fully recovered by dialysis. The inactivation of CYP2E1 by PEITC is due to both heme destruction and protein modification, with the latter being the major pathway for inactivation. GSH-adducts of phenethyl isocyanate (PIC) and phenethylamine were detected during the metabolism by CYP2E1, indicating formation of PIC as a reactive intermediate following P450-catalyzed desulfurization of PEITC. Surprisingly, PIC bound covalently to CYP2E1 to form protein adducts but did not inactivate the enzyme. Liquid chromatography mass spectroscopy analysis of the inactivated CYP2E1 apo-protein suggests that a reactive sulfur atom generated during desulfurization of PEITC is involved in the inactivation of CYP2E1. Our data suggest that the metabolism of PEITC by CYP2E1 that results in the inactivation of CYP2E1 may occur by a mechanism similar to that observed with other sulfur-containing compounds, such as parathion. Digestion of the inactivated enzyme and analysis by SEQUEST showed that Cys 268 may be the residue modified by PIC.

Potential risks resulting from fruit/vegetable-drug interactions: effects on drug-metabolizing enzymes and drug transporters

It has been well established that complex mixtures of phytochemicals in fruits and vegetables can be beneficial for human health. Moreover, it is becoming increasingly apparent that phytochemicals can influence the pharmacological activity of drugs by modifying their absorption characteristics through interactions with drug transporters as well as drug-metabolizing enzyme systems. Such effects are more likely to occur in the intestine and liver, where high concentrations of phytochemicals may occur. Alterations in cytochrome P450 and other enzyme activities may influence the fate of drugs subject to extensive first-pass metabolism. Although numerous studies of nutrient-drug interactions have been published and systematic reviews and meta-analyses of these studies are available, no generalizations on the effect of nutrient-drug interactions on drug bioavailability are currently available. Several publications have highlighted the unintended consequences of the combined use of nutrients and drugs. Many phytochemicals have been shown to have pharmacokinetic interactions with drugs. The present review is limited to commonly consumed fruits and vegetables with significant beneficial effects as nutrients and components in folk medicine. Here, we discuss the phytochemistry and pharmacokinetic interactions of the following fruit and vegetables: grapefruit, orange, tangerine, grapes, cranberry, pomegranate, mango, guava, black raspberry, black mulberry, apple, broccoli, cauliflower, watercress, spinach, tomato, carrot, and avocado. We conclude that our knowledge of the potential risk of nutrient-drug interactions is still limited. Therefore, efforts to elucidate potential risks resulting from food-drug interactions should be intensified in order to prevent undesired and harmful clinical consequences.

Plastics and carcinogenesis: The example of vinyl chloride

The manufacture, use and disposal of various plastics can pose numerous health risks, including the risk of cancer. A model example of carcinogenic risk from plastics is provided by polyvinyl chloride, since it is composed of the known human carcinogen vinyl chloride (VC). In recent years, much has been learned about the molecular biological pathways of VC carcinogenesis. This has led to molecular epidemiologic studies of VC carcinogenesis in exposed human populations which have identified useful biomarkers of exposure, effect and susceptibility for VC. These studies have in turn provided the basis for new molecular approaches for the prevention and treatment of VC cancers. This model could have much wider applicability for many other carcinogenic exposures and many other human cancers.

Dietary regulation of P-gp function and expression

Food-drug interactions have been associated with clinically important pharmacokinetic and pharmacodynamic changes of a drug. The aim of this paper is to review the regulation of P-glycoprotein (P-gp) by dietary components and to correlate the changes in cellular P-gp function and expression with drug bioavailability. In summary, the published literature has provided extensive data supporting the modulation of drug bioavailability through P-gp regulation by components in food groups such as fruit juices, spices, herbs, cruciferous vegetables and green tea. Most of these data were, however, derived from in vitro cell models and, except for the St John's wort, the clinical significance of most reported interactions remains to be clarified. Studies on piperine and capsaicin have underscored an often poor correlation between in vivo and in vitro data, whereas experiments involving curcumin highlighted differences between acute and chronic consumption of a dietary component on P-gp function and expression in vivo. A better understanding of the pharmacokinetic and pharmacodynamic profiles of the dietary components will aid in addressing these knowledge gaps.

Effect of simultaneous induction and inhibition of CYP3A by St John's Wort and ritonavir on CYP3A activity

We aimed to assess the effect of coadministration and withdrawal of a potent cytochrome P450 3A (CYP3A) inhibitor (ritonavir) and a potent CYP3A inducer (St John's wort) on CYP3A enzyme activity in an open, fixed-sequence study design. We investigated the pharmacokinetics of midazolam: (i) at baseline, (ii) after a single dose of either St John's wort or ritonavir (each n = 6), (iii) after 14 days of coadministration of ritonavir (300 mg b.i.d.) and St John's wort (300 mg t.i.d.), and (iv) at 2 days after cessation of both St John's wort and ritonavir. Combined administration of inducer and inhibitor resulted in a predominance of enzyme inhibition: coadministration of St John's wort and ritonavir with intravenous administration of midazolam resulted in an increase in the area under the plasma concentration-time curve (AUC)(0-8 h) of midazolam to 180% of baseline value, whereas with orally administered midazolam, the AUC(0-6 h) increased to 412% of baseline value (P < 0.05 for each). After cessation of the coadministered drugs, the AUC(0-6 h) of orally administered midazolam decreased to 6% of the level observed during combined administration, and the AUC(0-8 h) of intravenously administered midazolam decreased to 33% of the values observed during combined administration (P < 0.001 for each). Induction may be unmasked after the withdrawal of a combination of a potent CYP3A inhibitor and a potent CYP3A inducer, leading to substantial drops in drug exposure of CYP3A substrates. This may require substantial dose adjustments, particularly of orally administered drugs.

Genetic polymorphism in CYP2E1: Population distribution of CYP2E1 activity

Cytochrome P-450 2E1 (CYP2E1) is a key enzyme in the metabolic activation of a variety of toxicants including nitrosamines, benzene, vinyl chloride, and halogenated solvents such as trichloroethylene. CYP2E1 is also one of the enzymes that metabolizes ethanol to acetaldehyde, and is induced by recent ethanol ingestion. There is evidence that interindividual variability in the expression and functional activity of this cytochrome (CYP) may be considerable. Genetic polymorphisms in CYP2E1 were identified and linked to altered susceptibility to hepatic cirrhosis induced by ethanol and esophageal and other cancers in some epidemiological studies. Therefore, it is important to evaluate how such polymorphisms affect CYP2E1 function and whether it is possible to construct a population distribution of CYP2E1 activity based upon the known effects of these polymorphisms and their frequency in the population. This analysis is part of the genetic polymorphism database project described in the lead article in this series and followed the approach described in that article (Ginsberg et al., 2009, this issue). Review of the literature found that there are a variety of CYP2E1 variant alleles but the functional significance of these variants is still unclear. Some, but not all, studies suggest that several upstream 5' flanking mutations affect gene expression and response to inducers such as ethanol or obesity. None of the coding-region variants consistently affects enzyme function. Part of the reason for conflicting evidence regarding genotype effect on phenotype may be due to the wide variety of exposures such as ethanol or dietary factors and physiological factors including body weight or diabetes that modulate CYP2E1 expression. In conclusion, evidence is too limited to support the development of a population distribution of CYP2E1 enzyme activity based upon genotypes. Health risk assessments may best rely upon data reporting interindividual variability in CYP2E1 function for input into physiologically based pharmacokinetic (PBPK) models involving CYP2E1 substrates.

Drug interactions involving ethanol and alcoholic beverages

Ethanol is likely among the most widely and extensively used drugs in the world. It has also been demonstrated to alter the expression or activity of some drug-metabolizing enzymes. Thus, marked ethanol-provoked drug interactions could be of notable clinical importance. To date, relatively few clinically important interactions have been reported, involving cocaine, disulfiram and tacrolimus. Limited or modest interactions with ethanol have also been reported for drugs such as abacavir, cisapride, 'ecstasy' (3,4-methylenedioxymetamfetamine), gamma-hydroxybutyrate, methylyphenidate, metronidazole and verapamil. Most of these interactions do not seem to involve CYP2E1, the enzyme initially characterized and cloned based on its ability to metabolize and be induced by ethanol. Important work has elucidated the relationship between CYP2E1-mediated formation of the hepatotoxic metabolite of acetaminophen and alcohol consumption. Lastly, drug interactions involving other components of alcoholic beverages such as flavonoid and other polyphenolic components of red wine have been reported.

CYP2E1 Rsa I polymorphism impacts on risk of colorectal cancer association with smoking and alcohol drinking

AIM: To investigate associations between the Rsa I polymorphism of CYP2E1 and risk of colorectal cancer.

METHODS: A case-control study was conducted with 315 colorectal cancer cases (105 colon, 210 rectal) and 439 population-based controls in Jiangsu Province of China. Genomic DNA samples were assayed for restriction fragment length polymorphisms in CYP2E1 by PCR amplification followed by digestion with Rsa I. Information on smoking and alcohol drinking was collected using a questionnaire. Odds ratios (ORs) were estimated with an unconditional logistic model.

RESULTS: The proportional distribution of the CYP2E1 Rsa I c1/c1, c1/c2 and c2/c2 genotypes were 61.4%, 35.6% and 3.0% in controls, 60.6%, 33.7% and 5.8% in colon cancer cases, and 58.4%, 34.0% and 7.7% in rectal cancer cases, respectively. A significant difference was noted between controls and rectal cancer cases (P = 0.029), the c2/c2 genotype being associated with elevated OR (adjusted age, sex and status of the smoking and alcohol drinking) for rectal cancer (1.64, 95% CI, 1.12-2.41, vs c1 allele carriers), but not for colon cancer. In interaction analysis between the CYP2E1 Rsa I genotype and smoking and drinking habits, we found a significant cooperative action between the c2/c2 genotype and alcohol drinking in the sex-, age-adjusted ORs for both colon (4.74, 95% CI, 1.10-20.40) and rectal (5.75, 95% CI, 1.65-20.05) cancers. Among non-smokers, the CYP2E1 Rsa I c2/c2 genotype was also associated with elevated ORs in the two sites (1.95, 95% CI, 0.99-3.86 and 2.30, 95% CI, 1.32-3.99).

CONCLUSION: The results of the present study suggest that the CYP2E1 c2/c2 genotype increases susceptibility to rectal cancer and the gene-environmental interactions between the CYP2E1 polymorphism and smoking or alcohol drinking exist for colorectal neoplasia in general.

The effect of genetic polymorphisms in the vinyl chloride metabolic pathway on mutagenic risk

Vinyl chloride (VC) is a human carcinogen known to undergo metabolism by cytochrome P450 2E1 (CYP2E1) to reactive intermediates that can cause oncogene and tumor suppressor gene mutations and that are further metabolized by acetaldehyde dehydrogenase (ALDH2) and glutathione-S-transferases (GSTs) to non-mutagenic end products. These metabolic enzymes have known polymorphisms that could lead to increased levels of the VC reactive intermediates and thus an increased risk for mutations and cancer following exposure. Using restriction fragment length polymorphism (RFLP) analysis, we have examined a cohort of 597 French VC workers for polymorphisms in CYP2E1, ALDH2, GSTM1 and GSTT1 in relation to the occurrence of mutant oncogene and tumor suppressor gene biomarkers that are attributable to VC exposure. The presence of the biomarkers for mutant ras-p21 and mutant p53 was found to be highly significantly associated with cumulative VC exposure (P for trend <0.0001). The presence of the CYP2E1 variant c2 allele was found to be significantly associated with the presence of either or both mutant biomarkers even after controlling for potential confounders including cumulative VC exposure (OR = 2.3, 95% CI = 1.2-4.1), and the effects of the c2 allele and VC exposure were approximately additive. GSTT1 null status was found to have an increased, but not significant association with the presence of either or both biomarkers after controlling for confounders (OR = 1.3, 95% CI = 0.8-2.0). These results suggest the existence of a possible gene-environment interaction between polymorphisms in the VC metabolic pathway and VC exposure that could contribute to the variable susceptibility to the mutagenic effects of VC in exposed populations.

Dietary restriction of energy and sugar results in a reduction in human cytochrome P450 2E1 activity

Dietary habits are often considered as a pathogenic factor for fatty liver. The impact of dietary intake and steatosis on drug metabolism remains poorly investigated. Our aim was to assess the effect of dietary intake on in vivo cytochrome P450 (CYP) activities in eleven patients with abnormal liver function tests potentially due to fatty liver and associated with a high-sugar diet. Liver function tests, liver volume, aminopyrine breath test (ABT) and chlorzoxazone (CZ) pharmacokinetics (area under the curve, AUC) which are known to reflect CYP2E1 activity were evaluated before and after 2 months restriction of dietary sugar intake. Features at inclusion were an increased BMI (30·3 (sd 3·2) kg/m2), high hepatic volume (1·96 (sd 0·48) litres), hyperechogenic liver parenchyma, elevated liver enzyme activities (alanine aminotransferase (EC 2.6.1.2) 58·6 (sd 17·4) IU/l with alanine aminotransferase : aspartate aminotransferase (EC 2.6.1.1) ratio > 1), together with a normal ABT value (0·68 (sd 0·21) % specific activity of administered dose of [14C]aminopyrine in breath after 1 h) and a high CYP2E1 activity (CZ AUC 20·3 (sd 7·1) μg/ml per h). A dietary sugar restriction was prescribed. On the basis of repeated interviews by the same dietitian, unaware of any clinical and biochemical data, six patients remained compliant to the diet and exhibited reductions in BMI (P < 0·001), serum alanine aminotransferase (P = 0·008), liver volume (P = 0·002) and CYP2E1 activity (P = 0·007), a significant increase in ABT (P < 0·001) together with the disappearance of liver hyperechogenicity at ultrasound. In contrast, the five non-compliant patients did not show any significant change in any of these variables. In conclusion, CYP2E1 activity is induced in patients with perturbations of liver function tests potentially due to fatty liver. In these patients, effective dietary sugar restriction is associated with a reduction in liver volume, a reduction in CYP2E1 activity and an increased aminopyrine metabolism rate.

Biomarkers of benzene: urinary metabolites in relation to individual genotype and personal exposure

This report is part of an extensive biomarker study conducted in a Chinese occupational population with benzene exposures ranging from 0.06 to 122 ppm (median exposure of 3.2 ppm). All urinary benzene metabolites measured in this study were significantly elevated after exposure to benzene at or above 5 ppm. Among these metabolites, however, only S-phenylmercapturic acid (S-PMA) and trans,trans-muconic acid (t,t-MA) showed a significant exposure-response trend over the exposure range from 0 to 1 ppm (for S-PMA, p<0.0001 and for t,t-MA, p=0.006). For benzene exposure monitoring, both S-PMA and t,t-MA were judged to be good and sensitive markers, which detected benzene exposure at around 0.1 and 1 ppm, respectively. Polymorphisms of the metabolic genes, including CYP2E1, quinone oxidoreductase (NQO1), GSTT1, and myeloperoxidase (MPO), were identified and did not show significant effects on the formation of metabolites, except GSTT1 on S-PMA. The production rate of S-PMA from benzene in exposed workers with GSTT1 null alleles (24.72+/-32.48 microg/g creatinine/ppm benzene) was significantly lower than that in subjects with the wild type of GSTT1 (59.84+/-47.66 microg/g creatinine/ppm benzene, p<0.0001). Further regression analysis of S-PMA production rate on GSTT1 genotype with adjustment of sex, age, benzene exposure, and cotinine levels indicated that the genotype of GSTT1 plays a critical role in determining the inter-individual variations of S-PMA formation from benzene exposure. Therefore, the individual genotype of GSTT1 needs to be identified and considered while using S-PMA as a marker to estimate the personal exposure levels of benzene in future population studies.

Dietary organic isothiocyanates are cytotoxic in human breast cancer MCF-7 and mammary epithelial MCF-12A cell lines

Organic isothiocyanates (ITCs) are dietary components present in cruciferous vegetables. The purpose of this investigation was to examine the cytotoxicity of 1-naphthyl isothiocyanate (NITC), benzyl isothiocyanate (BITC), beta-phenethyl isothiocyanate (PEITC), and sulforaphane in human breast cancer MCF-7 and human mammary epithelium MCF-12A cell lines, as well as in a second human epithelial cell line, human kidney HK-2 cells. The cytotoxicity of NITC, BITC, PEITC, and sulforaphane, as well as the cytotoxicity of the chemotherapeutic agents daunomycin (DNM) and vinblastine (VBL), were examined in MCF-7/sensitive (wt), MCF-7/Adr (which overexpresses P-glycoprotein), MCF-12A, and HK-2 cells. Cell growth was determined by a sulforhodamine B assay. The IC50 values for DNM and VBL in MCF-7/Adr cells were 7.12 +/- 0.42 microM and 0.106 +/- 0.004 microM (mean +/- SE) following a 48-hr exposure; IC50 values for BITC, PEITC, NITC, and sulforaphane were 5.95 +/- 0.10, 7.32 +/- 0.25, 77.9 +/- 8.03, and 13.7 +/- 0.82 microM, respectively, with similar values obtained in MCF-7/wt cells. Corresponding values for BITC, PEITC, NITC, and sulforaphane in MCF-12A cells were 8.07 +/- 0.29, 7.71 +/- 0.07, 33.6 +/- 1.69, and 40.5 +/- 1.25 microM, respectively. BITC and PEITC can inhibit the growth of human breast cancer cells as well as human mammary epithelium cells at concentrations similar to those of the chemotherapeutic drug DNM. Sulforaphane and NITC exhibited higher IC50 values. The effect of these ITCs on cell growth may contribute to the cancer chemopreventive properties of ITCs by suppressing the growth of preclinical tumors, and may indicate a potential use of these compounds as chemotherapeutic agents in cancer treatment.

Dietary effects on drug metabolism and transport

Metabolic food-drug interactions occur when the consumption of a particular food modulates the activity of a drug-metabolising enzyme system, resulting in an alteration of the pharmacokinetics of drugs metabolised by that system. A number of these interactions have been reported. Foods that contain complex mixtures of phytochemicals, such as fruits, vegetables, herbs, spices and teas, have the greatest potential to induce or inhibit the activity of drug-metabolising enzymes, although dietary macroconstituents (i.e. total protein, fat and carbohydrate ratios, and total energy intake) can also have effects. Particularly large interactions may result from the consumption of herbal dietary supplements. Cytochrome P450 (CYP) 3A4 appears to be especially sensitive to dietary effects, as demonstrated by reports of potentially clinically important interactions involving orally administered drugs that are substrates of this enzyme. For example, interactions of grapefruit juice with cyclosporin and felodipine, St John's wort with cyclosporin and indinavir, and red wine with cyclosporin, have the potential to require dosage adjustment to maintain drug concentrations within their therapeutic windows. The susceptibility of CYP3A4 to modulation by food constituents may be related to its high level of expression in the intestine, as well as its broad substrate specificity. Reported ethnic differences in the activity of this enzyme may be partly due to dietary factors. Food-drug interactions involving CYP1A2, CYP2E1, glucuronosyltransferases and glutathione S-transferases have also been documented, although most of these interactions are modest in magnitude and clinically relevant only for drugs that have a narrow therapeutic range. Recently, interactions involving drug transporters, including P-glycoprotein and the organic anion transporting polypeptide, have also been identified. Further research is needed to determine the scope, magnitude and clinical importance of food effects on drug metabolism and transport.

Human variability for metabolic pathways with limited data (CYP2A6, CYP2C9, CYP2E1, ADH, esterases, glycine and sulphate conjugation)

Human variability in the kinetics of a number of phase I (CYP2A6, CYP2C9, CYP2E1, alcohol dehydrogenase and hydrolysis) and phase II enzymes (glycine and sulphate conjugation) was analysed using probe substrates metabolised extensively (>60%) by these routes. Published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and available data on subgroups of the population (effects of ethnicity, age and disease) were abstracted using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration time-curve (AUC)] and acute exposure (C(max)). Interindividual differences in kinetics for all these pathways were low in healthy adults ranging from 21 to 34%. Pathway-related uncertainty factors to cover the 95th, 97.5th and 99th centiles of healthy adults were derived for each metabolic route and were all below the 3.16 kinetic default uncertainty factor in healthy adults, with the possible exception of CYP2C9*3/*3 poor metabolisers (based on a very limited number of subjects). Previous analyses of other pathways have shown that neonates represent the most susceptible subgroup and this was true also for glycine conjugation for which an uncertainty factor of 29 would be required to cover 99% of this subgroup. Neonatal data were not available for any other pathway analysed.

Induction of drug-metabolizing enzymes: a path to the discovery of multiple cytochromes P450

This article provides a personal account of the discovery of the induced synthesis of drug-metabolizing enzymes and of subsequent research that led to the discovery of multiple cytochromes P450 with different catalytic activities. The manuscript also emphasizes the role of environmental factors (in addition to genetic polymorphisms) in explaining person-to-person and day-to-day differences in rates and pathways of drug metabolism that occur in the human population.

Watercress has no Importance for the elimination of ethanol by CYP2E1 inhibition

Watercress, a cruciferous vegetable, is known to inhibit the metabolism of several CYP2E1 substrates such as paracetamol and chlorzoxazone. Since ethanol and its metabolite, acetaldehyde, are CYP2E1 substrates, the influence of watercress on ethanol and acetaldehyde was investigated in healthy human volunteers. According to a randomized cross-over design, ethanol and acetaldehyde pharmacokinetic parameters were determined in 9 persons at 3 occasions: without watercress and after watercress ingestion preceding ethanol consumption from 1 or 10.5 hr, respectively. Ethanol tmax occurred significantly later when watercress was ingested 1 hr before ethanol ingestion. Likewise, acetaldehyde Cmax was significantly higher whereas acetaldehyde AUCs were increased by watercress but not significantly. All other ethanol and acetaldehyde pharmacokinetic parameters were similar between the 3 treatments. In healthy volunteers, no major watercress effect was observed on ethanol clearance but a weak inhibiting effect on acetaldehyde metabolism is possible. Ethanol absorption is also delayed by single ingestion of watercress immediately preceding ethanol consumption.

Herb-drug, food-drug, nutrient-drug, and drug-drug interactions: mechanisms involved and their medical implications

Adverse drug reactions (ADRs) and iatrogenic diseases have been identified as significant factors responsible for patient morbidity and mortality. Significant studies on drug metabolism in humans have been published during the last few years, offering a deeper comprehension of the mechanisms underlying adverse drug reactions and interactions. More understanding of these mechanisms, and of recent advances in laboratory technology, can help to evaluate potential drug interactions when drugs are prescribed concurrently. Increasing knowledge of interindividual variation in drug breakdown capacity and recent findings concerning the influence of environment, diet, nutrients, and herbal products can be used to reduce ADRs and iatrogenic diseases. Reviewed data suggest that drug treatment should be increasingly custom tailored to suit the individual patient and that appropriately co-prescribed diet and herbal remedies, could increase drug efficacy and lessen drug toxicity. This review focuses mainly on recently published research material. The cytochrome p450 enzymes, their role in metabolism, and their mechanisms of action are reviewed, and their role in drug-drug interactions are discussed. Drug-food and drug-herb interactions have garnered attention. Interdisciplinary communication among medical herbalists, medical doctors, and dietetic experts needs to be improved and encouraged. Internet resources for obtaining current information regarding drug-drug, drug-herb, and drug-nutrient interactions are provided.

Mechanisms of carcinogenesis inhibition by isothiocyanates

Epidemiological studies have suggested that frequent consumption of cruciferous vegetables is associated with a decreased risk in various types of cancer. Cruciferous vegetables are commonly consumed foods that contain organosulfur compounds known as isothiocyanates. These compounds are potent inhibitors of chemically induced carcinogenesis in animals. Extensive work has been conducted to elucidate the mechanisms involved in the inhibition of carcinogenesis by isothiocyanates. These mechanisms include blocking the metabolic activation of the carcinogens by way of altering the enzymes involved in the process, induction of detoxification enzymes and induction of apoptosis. Since their mode of action is selective, the enzyme composition of the tissue and the inhibition or induction of the enzymes by the isothiocyanates will influence their chemopreventive activities. Isothiocyanates may potentially be beneficial in protecting against human carcinogenesis.

Effect of organosulfur compounds from garlic and cruciferous vegetables on drug metabolism enzymes

The frequent consumption of cruciferous vegetables and garlic is associated with several health benefits. These foods contain organosulfur compounds that are known to affect the biotransformation of xenobiotics, and therefore can influence the toxicity and carcinogenicity of environmental chemicals. In this article, we review the effects of isothiocyanates and diallyl sulfide on xenobiotic metabolism and the enzymes involved in the process. Isothiocyanates and diallyl sulfide can modulate the levels of phase I and phase II drug-metabolizing enzymes by affecting the transcriptional rates of their genes, the turnover rates of specific mRNAs or enzymes, or the enzyme activity. These compounds are not general enzyme inhibitors or inducers. They elicit selectivity in their mode of action. Elucidating the mechanisms involved in the alteration of drug-metabolizing enzymes by isothiocyanates and diallyl sulfide will increase our understanding of their possible effects on the biotransformation of drugs as well as the potential beneficial or detrimental effects of these organosulfur compounds.

Inhibition of cytochrome P450 (CYP450) isoforms by isoniazid: potent inhibition of CYP2C19 and CYP3A

Isoniazid (INH) remains the most safe and cost-effective drug for the treatment and prophylaxis of tuberculosis. The use of INH has increased over the past years, largely as a result of the coepidemic of human immunodeficiency virus infection. It is frequently given chronically to critically ill patients who are coprescribed multiple medications. The ability of INH to elevate the concentrations in plasma and/or toxicity of coadministered drugs, including those of narrow therapeutic range (e.g., phenytoin), has been documented in humans, but the mechanisms involved are not well understood. Using human liver microsomes (HLMs), we tested the inhibitory effect of INH on the activity of common drug-metabolizing human cytochrome P450 (CYP450) isoforms using isoform-specific substrate probe reactions. Incubation experiments were performed at a single concentration of each substrate probe at its K(m) value with a range of INH concentrations. CYP2C19 and CYP3A were inhibited potently by INH in a concentration-dependent manner. At 50 microM INH (approximately 6.86 microg/ml), the activities of these isoforms decreased by approximately 40%. INH did not show significant inhibition (<10% at 50 microM) of other isoforms (CYP2C9, CYP1A2, and CYP2D6). To accurately estimate the inhibition constants (K(i) values) for each isoform, four concentrations of INH were incubated across a range of five concentrations of specific substrate probes. The mean K(i) values (+/- standard deviation) for the inhibition of CYP2C19 by INH in HLMs and recombinant human CYP2C19 were 25.4 +/- 6.2 and 13 +/- 2.4 microM, respectively. INH showed potent noncompetitive inhibition of CYP3A (K(i) = 51.8 +/- 2.5 to 75.9 +/- 7.8 microM, depending on the substrate used). INH was a weak noncompetitive inhibitor of CYP2E1 (K(i) = 110 +/- 33 microM) and a competitive inhibitor of CYP2D6 (K(i) = 126 +/- 23 microM), but the mean K(i) values for the inhibition of CYP2C9 and CYP1A2 were above 500 microM. Inhibition of one or both CYP2C19 and CYP3A isoforms is the likely mechanism by which INH slows the elimination of coadministered drugs, including phenytoin, carbamazepine, diazepam, triazolam, and primidone. Slow acetylators of INH may be at greater risk for adverse drug interactions, as the degree of inhibition was concentration dependent. These data provide a rational basis for understanding drug interaction with INH and predict that other drugs metabolized by these two enzymes may also interact.

Inhibition of CYP2E1 with natural agents may be a feasible strategy for minimizing the hepatotoxicity of ethanol

CYP2E1, induced in hepatocytes by heavy consumption of ethanol and certain other drugs, is a potent generator of superoxide, and is thereby thought to mediate the gravest aspects of alcoholic hepatotoxicity. Certain drugs such as the sedative chlormethiazole are effective inhibitors of CYP2E1, and may have clinical potential in the treatment of alcoholics. A number of phytochemicals can also potently inhibit CYP2E1 - most notably certain isothiocyanates found in crucifera, such as sulforaphane and phenethylisothiocyanate. Preparation of these compounds from crucifera seeds or sprouts should enable commercial production of supplements that would protect the livers of social drinkers while concurrently reducing risk for carcinogen-induced cancers.

Inhibition of carcinogenesis by isothiocyanates

Isothiocyanates occur as conjugates in a wide variety of cruciferous vegetables. Consumption of normal amounts of these vegetables results in the uptake of substantial quantities of isothiocyanates. These naturally occurring isothiocyanates as well as many synthetic analogs can be powerful inhibitors of carcinogenesis in laboratory animals. Particularly impressive results have been obtained in animal models of lung and esophageal cancer. This review summarizes available data on inhibition of carcinogenesis by isothiocyanates. The major mechanism of inhibition appears to be selective inhibition of cytochrome P450 enzymes involved in carcinogen metabolic activation. Evidence for this is reviewed. Isothiocyanates also induce Phase II enzymes and enhance apoptosis. These properties may also be involved in their chemopreventive activity. Phenethyl isothiocyanate is a particularly effective inhibitor of lung tumor induction by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and, therefore, is currently being developed as a chemopreventive agent against lung cancer.