Assessment of cytochrome P4502E1 induction in alcoholic patients by chlorzoxazone pharmacokinetics

The Safe Use of Analgesics in Patients with Cirrhosis: A Narrative Review

Pain is prevalent in patients with cirrhosis. Due to potential alterations in drug metabolism, risk for adverse effects, and complications from cirrhosis, physicians are often faced with difficult choices when choosing appropriate analgesics in these patients. Overall, acetaminophen remains the preferred analgesic. Despite its potential for intrinsic liver toxicity, acetaminophen is safe when used at 2 g/d. In contrast, non-selective nonsteroidals should be avoided due to their multiple side effects, including worsening renal function, blunting diuretic response, and increasing risk of portal hypertensive and peptic ulcer bleeding. Celecoxib can be administered for short term (≤5 days) in patients with Child's A and Child's B cirrhosis (50% dose reduction). Opioids carry the risk of precipitating hepatic encephalopathy and should generally be avoided, when possible. If clinical situation demands their use, opioid use should be limited to short-acting agents for short duration. Gabapentin and pregabalin are generally safe. Duloxetine should be avoided in hepatic impairment. Topical diclofenac and lidocaine seem to be safe in patients with cirrhosis.

Effect of Clomethiazole Vs. Clorazepate on Hepatic Fat and Serum Transaminase Activities in Alcohol-Associated Liver Disease: Results from a Randomized, Controlled Phase II Clinical Trial

AIMS

Alcohol-associated liver disease (ALD) is a global health problem caused, among other factors, by oxidative stress from the formation of reactive oxygen species (ROS). One important source of ROS is microsomal ethanol metabolism catalyzed by cytochrome P450 2E1 (CYP2E1), which is induced by chronic ethanol consumption. Inhibition of CYP2E1 by clomethiazole (CMZ) decreases oxidative stress in cell cultures and improves ALD in animal studies. Our study aimed to assess the benefits of a CYP2E1 inhibitor (clomethiazole) in detoxification of patients with ALD.

METHODS

Open label, randomized controlled clinical trial to study whether CYP2E1 inhibition improves ALD in the patients with alcohol use disorders admitted for alcohol detoxification therapy (ADT). Patients had to have a serum aspartate aminotransferase (AST) activity exceeding twice the upper normal limit at time of admission and be non-cirrhotic defined by fibroscan value <12 kPa. Sixty patients were randomly assigned to ADT with either CMZ or clorazepate (CZP) for 7-10 days in a 1:1 ratio. The chlorzoxazone test of CYP2E1 activity was performed at enrolment and at 2 points during the study.

RESULTS

ADT improved hepatic steatosis (controlled attenuation parameter) in both groups significantly. A trend towards a greater improvement in hepatic fat content during ADT (-21.5%) was observed in the CMZ group (252 ± 48 dB/m vs. 321 ± 38 dB/m; P < 0.0001) compared with the CZP group (-13.9%; 273 ± 38 dB/m vs. 317 ± 39 dB/m; P < 0.0001). As already reported, serum AST (P < 0.004) and alanine aminotransferase (ALT) activities (P < 0.0006) significantly decreased in CMZ patients as compared with patients on CZP by the end of hospitalization. A significant correlation was found between AST (P = 0.023), ALT (P = 0.009), GGT (P = 0.039) and CAP.

CONCLUSION

This study demonstrates that CMZ improves clinical biomarkers for ALD in humans most likely due to its inhibitory effect on CYP2E1. Because of its addictive potential, CMZ can only be given for a short period of time and therefore other CYP2E1 inhibitors to treat ALD are needed.

How Can Drug Metabolism and Transporter Genetics Inform Psychotropic Prescribing?

Many genetic variants in drug metabolizing enzymes and transporters have been shown to be relevant for treating psychiatric disorders. Associations are strong enough to feature on drug labels and for prescribing guidelines based on such data. A range of commercial tests are available; however, there is variability in included genetic variants, methodology, and interpretation. We herein provide relevant background for understanding clinical associations with specific variants, other factors that are relevant to consider when interpreting such data (such as age, gender, drug-drug interactions), and summarize the data relevant to clinical utility of pharmacogenetic testing in psychiatry and the available prescribing guidelines. We also highlight areas for future research focus in this field.

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.

Herb-Drug Interactions and Hepatotoxicity

BACKGROUND

In recent times, herbals or phytomedicines have become very popular due to their global acceptance as a complementary and alternative remedy. While modern drugs are commercially available only after laboratory validations, clinical trials, as well as approval from drug regulatory authorities, majority of the marketed herbal products lack such scientific evidence of efficacy and safety. This results in herb or herb-drug interaction induced unfavorable clinical outcomes without crucial documentation on their temporal relations and concomitant use.

METHODS

An online literature search for peer-reviewed articles was conducted on the PubMed, Europe PMC, Medline and Google Scholar portals, using the phrases: complementary & alternative medicine, traditional Chinese medicine, herb-drug interaction, mechanisms of herb-drug interaction, herb-induced toxicity, herbal hepatotoxicity and causality, traditional medicine, viral hepatitis, etc.

Results

The retrieved data showed that globally, patients are attracted to herbal remedies with the misconception that these are completely safe and therefore, use them simultaneously with prescription drugs. Notably, there exists a potential risk of herb-drug interactions leading to some adverse side effects, including hepatotoxicity. The toxicological effect of a drug or herb is due to the inhibition of drug metabolizing enzymes (e.g., cytochrome P450), including interactions with certain prescription drugs through various mechanisms. Several cases of hepatotoxicity due to use of herbals in viral hepatitis-related liver diseases have been recently reported. However, limited experimental data and clinical evidence on herbal pharmacokinetics hamper the evaluation and reporting of adverse reactions and the underlying mechanisms.

CONCLUSION

Herb-drug interaction related morbidity is thus an emerging serious public health issue with broad implications for clinicians, pharmaceutical industries and health authorities. Nonetheless, despite increasing recognition of herb-drug interaction, a standard system for interaction prediction and evaluation is still nonexistent. This review article discusses the herb-drug interactions related hepatotoxicity and underlying mechanisms, including drug metabolizing enzymes and their regulation.

Induction via Functional Protein Stabilization of Hepatic Cytochromes P450 upon gp78/Autocrine Motility Factor Receptor (AMFR) Ubiquitin E3-Ligase Genetic Ablation in Mice: Therapeutic and Toxicological Relevance

The hepatic endoplasmic reticulum (ER)-anchored monotopic proteins, cytochromes P450 (P450s), are enzymes that metabolize endobiotics (physiologically active steroids and fatty acids), as well as xenobiotics including therapeutic/chemotherapeutic drugs, nutrients, carcinogens, and toxins. Alterations of hepatic P450 content through synthesis, inactivation, or proteolytic turnover influence their metabolic function. P450 proteolytic turnover occurs via ER-associated degradation (ERAD) involving ubiquitin (Ub)-dependent proteasomal degradation (UPD) as a major pathway. UPD critically involves P450 protein ubiquitination by E2/E3 Ub-ligase complexes. We have previously identified the ER-polytopic gp78/AMFR (autocrine motility factor receptor) as a relevant E3 in CYP3A4, CYP3A23, and CYP2E1 UPD. We now document that liver-conditional genetic ablation of gp78/AMFR in male mice disrupts P450 ERAD, resulting in statistically significant stabilization of Cyp2a5 and Cyp2c, in addition to that of Cyp3a and Cyp2e1. More importantly, we establish that such stabilization is of the functionally active P450 proteins, leading to corresponding statistically significant enhancement of their drug-metabolizing capacities. Our findings, with clinically relevant therapeutic drugs (nicotine, coumarin, chlorzoxazone, and acetaminophen) and the prodrug (tamoxifen) as P450 substrates, reveal that P450 ERAD disruption could influence therapeutic drug response and/or toxicity, warranting serious consideration as a potential source of clinically relevant drug-drug interactions (DDIs). Because gp78/AMFR is not only an E3 Ub-ligase, but also a cell-surface prometastatic oncogene that is upregulated in various malignant cancers, our finding that hepatic gp78/AMFR knockout can enhance P450-dependent bioactivation of relevant cancer chemotherapeutic prodrugs is of therapeutic relevance and noteworthy in prospective drug design and development. SIGNIFICANCE STATEMENT: The cell-surface and ER transmembrane protein gp78/AMFR, a receptor for the prometastatic autocrine motility factor (AMF), as well as an E3 ubiquitin-ligase involved in the ER-associated degradation (ERAD) of not only the tumor metastatic suppressor KAI1 but also of hepatic cytochromes P450, is upregulated in various human cancers, enhancing their invasiveness, metastatic potential, and poor prognosis. Liver-specific gp78/AMFR genetic ablation results in functional protein stabilization of several hepatic P450s and consequently enhanced drug and prodrug metabolism, a feature that could be therapeutically exploited in the bioactivation of chemotherapeutic prodrugs through design and development of novel short-term gp78/AMFR chemical inhibitors.

Significant change of cytochrome P450s activities in patients with hepatocellular carcinoma

The lack of information concerning individual variation in drug-metabolizing enzymes is one of the most important obstacles for designing personalized medicine approaches for hepatocellular carcinoma (HCC) patients. To assess cytochrome P450 (CYP) in the metabolism of endogenous and exogenous molecules in an HCC setting, the activity changes of 10 major CYPs in microsomes from 105 normal and 102 HCC liver tissue samples were investigated. We found that CYP activity values expressed as intrinsic clearance (CL_int) differed between HCC patients and control subjects. HCC patient samples showed increased CL_int for CYP2C9, CYP2D6, and CYP2E1 compared to controls. Meanwhile, CYP1A2, CYP2C8, and CYP2C19 CL_int values decreased and CYP2A6, CYP2B6, and CYP3A4/5 activity was unchanged relative to controls. For patients with HCC accompanied by fibrosis or cirrhosis, the same activity changes were seen for the CYP isoforms, except for CYP2D6 which had higher values in HCC patients with cirrhosis. Moreover, CYP2D6*10 (100C>T), CYP2C9*3 (42614 A>C), and CYP3A5*3 (6986A>G) polymorphisms had definite effects on enzyme activities. In the HCC group, the CL_int of CYP2D6*10 mutant homozygote was decreased by 95% compared to wild-type samples, and the frequency of this homozygote was 2.8-fold lower than the controls.

In conclusion, the activities of CYP isoforms were differentially affected in HCC patients. Genetic polymorphisms of some CYP enzymes, especially CYP2D6*10, could affect enzyme activity. CYP2D6*10 allelic frequency was significantly different between HCC patients and control subjects. These findings may be useful for personalizing the clinical treatment of HCC patients as well as predicting the risk of hepatocarcinogenesis.

Metabolic Pathway Involved in 6-Chloro-2-Benzoxazolinone Degradation by Pigmentiphaga sp. Strain DL-8 and Identification of the Novel Metal-Dependent Hydrolase CbaA

6-Chloro-2-benzoxazolinone (CDHB) is a precursor of herbicide, insecticide, and fungicide synthesis and has a broad spectrum of biological activity. Pigmentiphaga sp. strain DL-8 can transform CDHB into 2-amino-5-chlorophenol (2A5CP), which it then utilizes as a carbon source for growth. The CDHB hydrolase (CbaA) was purified from strain DL-8, which can also hydrolyze 2-benzoxazolinone (BOA), 5-chloro-2-BOA, and benzamide. The specific activity of purified CbaA was 5,900 U · mg protein(-1) for CDHB, with Km and kcat values of 0.29 mM and 8,500 s(-1), respectively. The optimal pH for purified CbaA was 9.0, the highest activity was observed at 55°C, and the inactive metal-free enzyme could be reactivated by Mg(2+), Ni(2+), Ca(2+), or Zn(2+) Based on the results obtained for the CbaA peptide mass fingerprinting and draft genome sequence of strain DL-8, cbaA (encoding 339 amino acids) was cloned and expressed in Escherichia coli BL21(DE3). CbaA shared 18 to 21% identity with some metal-dependent hydrolases of the PF01499 family and contained the signature metal-binding motif Q127XXXQ131XD133XXXH137 The conserved amino acid residues His288 and Glu301 served as the proton donor and acceptor. E. coli BL21(DE3-pET-cbaA) resting cells could transform 0.2 mM CDHB into 2A5CP. The mutant strain DL-8ΔcbaA lost the ability to degrade CDHB but retained the ability to degrade 2A5CP, consistent with strain DL-8. These results indicated that cbaA was the key gene responsible for CDHB degradation by strain DL-8.

IMPORTANCE

2-Benzoxazolinone (BOA) derivatives are widely used as synthetic intermediates and are also an important group of allelochemicals acting in response to tissue damage or pathogen attack in gramineous plants. However, the degradation mechanism of BOA derivatives by microorganisms is not clear. In the present study, we reported the identification of CbaA and metabolic pathway responsible for the degradation of CDHB in Pigmentiphaga sp. DL-8. This will provide microorganism and gene resources for the bioremediation of the environmental pollution caused by BOA derivatives.

Inflammatory PAF Receptor Signaling Initiates Hedgehog Signaling and Kidney Fibrogenesis During Ethanol Consumption

Acute inflammation either resolves or proceeds to fibrotic repair that replaces functional tissue. Pro-fibrotic hedgehog signaling and induction of its Gli transcription factor in pericytes induces fibrosis in kidney, but molecular instructions connecting inflammation to fibrosis are opaque. We show acute kidney inflammation resulting from chronic ingestion of the common xenobiotic ethanol initiates Gli1 transcription and hedgehog synthesis in kidney pericytes, and promotes renal fibrosis. Ethanol ingestion stimulated transcription of TGF-ß, collagens I and IV, and alpha-smooth muscle actin with accumulation of these proteins. This was accompanied by deposition of extracellular fibrils. Ethanol catabolism by CYP2E1 in kidney generates local reactive oxygen species that oxidize cellular phospholipids to phospholipid products that activate the Platelet-activating Factor receptor (PTAFR) for inflammatory phospholipids. Genetically deleting this ptafr locus abolished accumulation of mRNA for TGF-ß, collagen IV, and α-smooth muscle actin. Loss of PTAFR also abolished ethanol-stimulated Sonic (Shh) and Indian hedgehog (Ihh) expression, and abolished transcription and accumulation of Gli1. Shh induced in pericytes and Ihh in tubules escaped to urine of ethanol-fed mice. Neutrophil myeloperoxidase (MPO) is required for ethanol-induced kidney inflammation, and Shh was not present in kidney or urine of mpo^-/- mice. Shh also was present in urine of patients with acute kidney injury, but not in normal individuals or those with fibrotic liver cirrhosis We conclude neither endogenous PTAFR signaling nor CYP2E1-generated radicals alone are sufficient to initiate hedgehog signaling, but instead PTAFR-dependent neutrophil infiltration with myeloperoxidase activation is necessary to initiate ethanol-induced fibrosis in kidney. We also show fibrogenic mediators escape to urine, defining a new class of urinary mechanistic biomarkers of fibrogenesis for an organ not commonly biopsied.

Methodology to assay CYP2E1 mixed function oxidase catalytic activity and its induction

The cytochrome P450 mixed function oxidase enzymes are the major catalysts involved in drug metabolism. There are many forms of P450. CYP2E1 metabolizes many toxicologically important compounds including ethanol and is active in generating reactive oxygen species. Since several of the contributions in the common theme series “Role of CYP2E1 and Oxidative/Nitrosative Stress in the Hepatotoxic Actions of Alcohol” discuss CYP2E1, this methodology review describes assays on how CYP2E1 catalytic activity and its induction by ethanol and other inducers can be measured using substrate probes such as the oxidation of para-nitrophenol to para-nitrocatechol and the oxidation of ethanol to acetaldehyde. Approaches to validate that a particular reaction e.g. oxidation of a drug or toxin is catalyzed by CYP2E1 or that induction of that reaction is due to induction of CYP2E1 are important and specific examples using inhibitors of CYP2E1, anti-CYP2E1 IgG or CYP2E1 knockout and knockin mice will be discussed.

Cytochrome P4502E1(CYP2E1) oxidizes ethanol and activates hepatoxins and procarcinogens.

CYP2E1 produces reactive oxygen species during its catalytic cycle.

Methodology to assay CYP2E1 via oxidation of ethanol and p-nitrophenol is reviewed.

Oxidation of these substrates is enhanced after induction of CYP2E1 by ethanol.

Oxidation of these substrates is lowered by CYP2E1 inhibitors, anti-CYP2E1 IgG and in CYP2E1 knockout mice.

Nrf2 and Nrf2 activators in hepatic diseases

Oxidative stress is evidently related to hepatic diseases. Nuclear erythroid-2 related factor 2 (Nrf2) is one of the most important regulators of cells' protection against oxidative stress. Nrf2 induces the transcription of a wide array of genes encoding antioxidant enzymes and detoxification enzymes, cleans reactive oxygen species and relieves apoptosis. This review aims to illustrate the Nrf2/Keap1-ARE antioxidant pathway, investigate its relation with hepatic diseases and discuss the potential therapeutic effect of Nrf2 activators.

Eat more carrots? Dampening cell death in ethanol-induced liver fibrosis by β-carotene

Alcoholic liver disease (ALD) represents one of the principal causes of liver damage in humans. Long-term ethanol abuse leads to progressive liver injury and tissue remodeling, including steatosis, inflammation, fibrosis, cirrhosis and increased risk for hepatocellular carcinoma (HCC) development. Oxidative stress and subsequent liver cell death has long been identified as one of the key mechanisms during ALD progression, therefore antioxidants may display promising treatment options. In this issue of Hepatobiliary Surgery and Nutrition (HBSN), Peng et al. demonstrate that oral supplementation with β-carotene during chronic ethanol feeding in rats reduces oxidative stress, apoptotic cell death and inflammation. Reducing hepatocyte apoptosis, a major trigger for fibrogenesis and tumorigenesis, would make β-carotene a prospective target for treatment. However, before translating the promising findings of Peng and colleagues into clinical scenarios, it needs to be determined which cell death pathways, including necrosis and necroptosis, are affected by β-carotene, which liver cell populations are targeted by this vitamin A precursor, how specific the effects are for ALD in comparison to non-alcoholic steatohepatitis (NASH) or other chronic liver diseases, and whether reduced hepatic oxidative stress and apoptosis upon β-carotene supplementation truly relate to beneficial long-term consequences with respect to fibrosis, cirrhosis or HCC development.

In-vitro evaluation of chronic alcohol effects on expression of drug-metabolizing and drug-transporting proteins

Objectives

In alcoholics without alcoholic liver disease, boosted drug elimination has been reported. However, mechanistic explanations for this phenomenon remain uncertain. In particular, data on the potential role of drug transporters are sparse.

Methods

Using a well-established in-vitro model for induction of human drug-metabolizing and drug-transporting proteins, we evaluated the potency of ethanol and the major fermentation side-product isopentanol to alter expression and function of these proteins by quantitative real-time polymerase chain reaction, Western blotting and flow cytometry. P-glycoprotein (Pgp)-inhibiting properties of ethanol and isopentanol were investigated via calcein extrusion assay.

Key findings

Ethanol and isopentanol significantly changed expression levels of drug-metabolizing and drug-transporting proteins that normalized within 2 weeks upon withdrawal. Cytochrome P-450 2C19 and Pgp were most strongly induced. Ethanol-induced Pgp at the messenger RNA (mRNA) (twofold to eightfold) and protein level (twofold), but not at the functional level. Both compounds did not inhibit Pgp.

Conclusions

Ethanol is demonstrated to increase mRNA and protein expression of human drug transporters such as Pgp in vitro. Withdrawal of ethanol exposure causes return to non-induced conditions within weeks. Functional consequences of increased Pgp expression in alcoholics need to be evaluated by clinical trials applying selective Pgp substrates such as digoxin.

Analgesics in patients with hepatic impairment: pharmacology and clinical implications

The physiological changes that accompany hepatic impairment alter drug disposition. Porto-systemic shunting might decrease the first-pass metabolism of a drug and lead to increased oral bioavailability of highly extracted drugs. Distribution can also be altered as a result of impaired production of drug-binding proteins or changes in body composition. Furthermore, the activity and capacity of hepatic drug metabolizing enzymes might be affected to various degrees in patients with chronic liver disease. These changes would result in increased concentrations and reduced plasma clearance of drugs, which is often difficult to predict. The pharmacology of analgesics is also altered in liver disease. Pain management in hepatically impaired patients is challenging owing to a lack of evidence-based guidelines for the use of analgesics in this population. Complications such as bleeding due to antiplatelet activity, gastrointestinal irritation, and renal failure are more likely to occur with nonsteroidal anti-inflammatory drugs in patients with severe hepatic impairment. Thus, this analgesic class should be avoided in this population. The pharmacokinetic parameters of paracetamol (acetaminophen) are altered in patients with severe liver disease, but the short-term use of this drug at reduced doses (2 grams daily) appears to be safe in patients with non-alcoholic liver disease. The disposition of a large number of opioid drugs is affected in the presence of hepatic impairment. Certain opioids such as codeine or tramadol, for instance, rely on hepatic biotransformation to active metabolites. A possible reduction of their analgesic effect would be the expected pharmacodynamic consequence of hepatic impairment. Some opioids, such as pethidine (meperidine), have toxic metabolites. The slower elimination of these metabolites can result in an increased risk of toxicity in patients with liver disease, and these drugs should be avoided in this population. The drug clearance of a number of opioids, such as morphine, oxycodone, tramadol and alfentanil, might be decreased in moderate or severe hepatic impairment. For the highly excreted morphine, hydromorphone and oxycodone, an important increase in bioavailability occurs after oral administration in patients with hepatic impairment. Lower doses and/or longer administration intervals should be used when these opioids are administered to patients with liver disease to avoid the risk of accumulation and the potential increase of adverse effects. Finally, the pharmacokinetics of phenylpiperidine opioids such as fentanyl, sufentanil and remifentanil appear to be unaffected in hepatic disease. All opioid drugs can precipitate or aggravate hepatic encephalopathy in patients with severe liver disease, thus requiring cautious use and careful monitoring.

Nrf2: a potential target for new therapeutics in liver disease

Nuclear erythroid 2-related factor 2 (Nrf2) is an oxidative stress-mediated transcription factor with a variety of downstream targets aimed at cytoprotection. Nrf2 has recently been implicated as a new therapeutic target for the treatment of liver disease. Here, we focus on the most common liver diseases-nonalcoholic fatty liver disease/steatohepatitis, alcoholic liver disease, and drug-induced liver injury-and highlight areas in the development of these conditions where activation of Nrf2 may alleviate disease progression.

Association of liver stiffness with hepatic expression of pharmacokinetically important genes in alcoholic liver disease

BACKGROUND

Enhanced drug elimination in alcoholics remains largely indefinable. In contrast, the reduced elimination of drugs in patients with advanced alcoholic liver disease (ALD) is normally owing to hepatic end-stage disease such as cirrhosis. We here study the mRNA expression of various hepatic drug metabolizing enzymes and transporters in association with liver stiffness (LS) being a novel noninvasive parameter for the assessment of cirrhosis to unravel the dynamic relationship between ALD and determinants of pharmacokinetics such as drug metabolizing enzymes and transporters.

METHODS

We quantified mRNA expression levels of various cytochrome P-450 isoenzymes (CYPs) and drug transporters in 26 liver specimens of chronic alcoholics and 5 controls by quantitative polymerase chain reaction. In addition, liver histology, clinical data, and LS evaluated by transient elastography (Fibroscan) were obtained.

RESULTS

Eighteen patients had a normal or moderate LS < 8 kPa (69.2%), while in the remaining 8 patients (30.7%) advanced F3 or F4 fibrosis could be established with an LS > 8 kPa. Overall, CYP3A4, CYP2E1, and solute carrier organic anion transporter 1B1 (SLCO1B1) were negatively correlated with increasing LS. CYPs and drug transporters tended to be up-regulated in alcoholics without advanced fibrosis (LS < 8.0 kPa) compared to healthy controls supporting data of boosted drug elimination in alcoholics without advanced ALD. However, in alcoholics with severely increased LS (>8 kPa), expression levels of CYP2E1, SLC22A2, and SLCO1B1 were significantly lower.

CONCLUSIONS

In conclusion, CYPs and drug transporters seem to be induced in chronic alcoholics without irreversible liver damage but decline in case of manifest cirrhosis. Our study also suggests that noninvasive measurements of LS could be useful for pharmacokinetic predictions and individualized pharmacotherapy.

Effect of buagafuran on liver microsomal cytochrome P450 in rats

Buagafuran (BF), derived from alpha-agarofuran, is a promising anti-anxiety drug in phase I clinical trials. The present study was undertaken to examine the regulation of BF on liver cytochrome P450 (CYP) isoforms in rats. After being administered (4, 16, and 64 mg/kg) by gavage for 7 continuous days, the activities of CYP isoforms were measured by the qualification of six metabolites from CYP probe substrates using LC-MS/MS analysis. The mRNA and protein levels of CYPs were detected by reverse transcription polymerase chain reaction and Western blotting assay, respectively. Using phenacetin and chlorzoxazone as probe drugs, the activities of CYP1A2 and CYP2E1 were monitored in vivo. The result indicated that BF significantly increased the activity and protein levels of CYP1A2 and CYP2E1, while the mRNA levels were elevated to a certain extent. CYP2C6 and CYP2C11 were also slightly induced by BF, but no effect on liver CYP3A was detected in rats. Treatment of BF orally resulted in the decreasing of AUC, MRT and increasing of CL/F of phenacetin as well as production of acetaminophen in rats. The similar pharmacokinetic changes were also observed when using chlorzoxazone as a probe drug. Collectively, BF has inducing potential of liver CYP1A2 and CYP2E1 and may influence the corresponding pharmacokinetics of other drugs.

Nrf2 and antioxidant defense against CYP2E1 toxicity

The transcription factor Nrf2 regulates the expression of important cytoprotective enzymes. Induction of CYP2E1 is one of the central pathways by which ethanol generates oxidative stress. CYP2E1 can be induced by ethanol and several low molecular mass chemicals such as pyrazole. This review discusses biochemical and toxicological effects of CYP2E1 and the effects of Nrf2 in modulating these actions of CYP2E1. Besides ethanol, CYP2E1 metabolizes and activates many other toxicologic important compounds. One approach to try to understand the basic effects and actions of CYP2E1 was to establish HepG2 cell lines that constitutively express human CYP2E1. Ethanol, polyunsaturated fatty acids and iron were toxic to the HepG2 cells, which express CYP2E1 (E47 cells) but not control C34HepG2 cells, which do not express CYP2E1. Toxicity was associated with enhanced oxidant stress and could be prevented by antioxidants and potentiated if glutathione was removed. The E47 cells had higher glutathione levels and a twofold increase in catalase, cytosolic and microsomal glutathione transferase, and heme oxygenase-1 than control HepG2 cells due to activation of their respective genes. These activations were prevented by antioxidants, suggesting that reactive oxygen species generated by CYP2E1 were responsible for the upregulation of these antioxidant genes. This upregulation may reflect an adaptive mechanism to remove CYP2E1-derived oxidants. Increases in Nrf2 protein and mRNA were observed in livers of chronic alcohol-fed mice or rats and of pyrzole-treated rats or mice, conditions known to elevate CYP2E1. E47 cells showed increased Nrf2 mRNA and protein expression compared with control HepG2 C34 cells. Upregulation of antioxidant genes in E47 cells is dependent on Nrf2 and is prevented by siRNA-Nrf2. Blocking Nrf2 by siRNA-Nrf2 decreases glutathione and increases reactive oxygen species and lipid peroxidation, resulting in decreased mitochondrial membrane potential and loss of cell viability of E47 cells, but not C34 cells. Nrf2 is activated and levels of Nrf2 protein and mRNA are increased when CYP2E1 is elevated. These results suggest that Nrf2 plays a key role in the adaptive response against increased oxidative stress caused by CYP2E1 in the HepG2 cells. However, it is not clear whether Nrf2 is protective against CYP2E1 toxicity in vivo as pyrazole which elevates CYP2E1 in wild-type mice did not elevate CYP2E1 in Nrf2 knockout mice, although pyrazole produced toxicity in the Nrf2 knockout mice.

CYP2E1 potentiation of LPS and TNFα-induced hepatotoxicity by mechanisms involving enhanced oxidative and nitrosative stress, activation of MAP kinases, and mitochondrial dysfunction

The mechanisms by which alcohol causes cell injury are not clear. A major mechanism that is the focus of considerable research is the role of lipid peroxidation and oxidative stress in alcohol toxicity. Many pathways have been suggested to play a role in how alcohol induces oxidative stress. Considerable attention has been given to alcohol-elevated production of lipopolysaccharide (LPS) and TNFα and to alcohol induction of CYP2E1. These two pathways are not exclusive of each other, however, associations and interactions between them, especially in vivo, have not been extensively evaluated. We have shown that increased oxidative stress from induction of CYP2E1 in vivo sensitizes hepatocytes to LPS and TNF toxicity and that oxidants, such as peroxynitrite, activation of p38 and JNK MAP kinases, inactivation of NF-kB protective pathways and mitochondrial dysfunction are downstream mediators of this CYP2E1-LPS/TNF potentiated hepatotoxicity. This review will summarize studies showing potentiated interactions between these two risk factors in promoting liver injury and the mechanisms involved.

Hepatocyte growth factor protects hepatocytes against oxidative injury induced by ethanol metabolism

Hepatocyte growth factor (HGF) is involved in many cellular responses, such as mitogenesis and apoptosis protection; however, its effect against oxidative injury induced by ethanol metabolism is not well understood. The aim of this work was to address the mechanism of HGF-induced protection against ethanol-generated oxidative stress damage in the human cell line VL-17A (cytochrome P450 2E1/alcohol dehydrogenase-transfected HepG2 cells). Cells were pretreated with 50 ng/ml HGF for 12 h and then treated with 100 mM ethanol for 0-48 h. Some parameters of oxidative damage were evaluated. We found that ethanol induced peroxide formation (3.3-fold) and oxidative damage as judged by lipid peroxidation (5.4-fold). Damage was prevented by HGF. To address the mechanisms of HGF-induced protection we investigated the cellular antioxidant system. We found that HGF increased the GSH/GSSG ratio, as well as SOD1, catalase, and gamma-glutamylcysteine synthetase expression. To explore the signaling pathways involved in this process, VL-17A cells were pretreated with inhibitors against PI3K, Akt, and NF-kappaB. We found that all treatments decreased the expression of the antioxidant enzymes, thus abrogating the HGF-induced protection against oxidative stress. Our results demonstrate that HGF protects cells from the oxidative damage induced by ethanol metabolism by a mechanism driven by NF-kappaB and PI3K/Akt signaling.

Role of oxidative stress in alcohol-induced liver injury

Reactive oxygen species (ROS) are highly reactive molecules that are naturally generated in small amounts during the body's metabolic reactions and can react with and damage complex cellular molecules such as lipids, proteins, or DNA. Acute and chronic ethanol treatments increase the production of ROS, lower cellular antioxidant levels, and enhance oxidative stress in many tissues, especially the liver. Ethanol-induced oxidative stress plays a major role in the mechanisms by which ethanol produces liver injury. Many pathways play a key role in how ethanol induces oxidative stress. This review summarizes some of the leading pathways and discusses the evidence for their contribution to alcohol-induced liver injury. Special emphasis is placed on CYP2E1, which is induced by alcohol and is reactive in metabolizing and activating many hepatotoxins, including ethanol, to reactive products, and in generating ROS.

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.

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.

CYP2E1 and oxidative liver injury by alcohol

Ethanol-induced oxidative stress seems to play a major role in mechanisms by which ethanol causes liver injury. Many pathways have been suggested to contribute to the ability of ethanol to induce a state of oxidative stress. One central pathway seems to be the induction of cytochrome P450 2E1 (CYP2E1) by ethanol. CYP2E1 metabolizes and activates many toxicological substrates, including ethanol, to more reactive, toxic products. Levels of CYP2E1 are elevated under a variety of physiological and pathophysiological conditions and after acute and chronic alcohol treatment. CYP2E1 is also an effective generator of reactive oxygen species such as the superoxide anion radical and hydrogen peroxide and, in the presence of iron catalysts, produces powerful oxidants such as the hydroxyl radical. This review article summarizes some of the biochemical and toxicological properties of CYP2E1 and briefly describes the use of cell lines developed to constitutively express CYP2E1 and CYP2E1 knockout mice in assessing the actions of CYP2E1. Possible therapeutic implications for treatment of alcoholic liver injury by inhibition of CYP2E1 or CYP2E1-dependent oxidative stress will be discussed, followed by some future directions which may help us to understand the actions of CYP2E1 and its role in alcoholic liver injury.

A haplotype analysis of CYP2E1 polymorphisms in relation to alcoholic phenotypes in Mexican Americans

BACKGROUND

Studies regarding the association between the 4 polymorphisms of CYP2E1 (CYP2E1*1D, *5B, *6, and *1B) and alcoholism are inconsistent and inconclusive. The purpose of the present study was to clarify previously discordant studies by haplotype analysis in the Mexican American population.

METHODS

The 4 polymorphisms of CYP2E1 were studied in 334 alcoholics and 365 controls. Genotype, allele, and haplotype frequency comparisons between alcoholics and controls were assessed. Patterns of linkage disequilibrium (LD) at CYP2E1 were determined. Reconstructed haplotypes were tested for associations with clinical phenotypes (age onset of drinking, Maxdrinks, and smoking status).

RESULTS

No significant associations between the 4 polymorphisms of CYP2E1 and alcoholism were revealed by single allele tests. High LD was found between the CYP2E1 c2 and C alleles in Mexican Americans. Eleven haplotypes were present in the 699 participants. The 6 main haplotypes with frequencies higher than 1% made up 97% of the total halpotypes. The frequency of subjects carrying H6 (1C-c2-C-A2) was significantly higher in alcoholics than in controls (p = 0.0001). In contrast, the frequencies of H7 (1C-c2-C-A1) and H10 (1C-c2-D-A1) were significantly lower in alcoholics than in controls (p = 0.0072 for H7 and p = 0.0407 for H10). The frequency of H6 was significantly higher in alcoholics who had late onset of drinking than in nonalcoholic controls. Furthermore, the frequencies of H6 haplotype were also consistently higher in groups who had high number of maximum drinks (9 to 32 drinks) than in controls. When smokers are excluded, the frequencies of H6, H7, and H9 (1C-c2-D-A2) showed statistically significant differences between alcoholics and controls (p < 0.05). Moreover, the association between H6 and alcoholism become more robust when smokers are excluded. Furthermore, the frequency of H1 (1C-c1-D-A2) in alcoholic-smokers was much higher than in alcoholic-nonsmokers (p = 0.0028). In contrast, alcoholic-smokers carried less H2 (1C-c1-D-A1) in comparison with alcoholic-nonsmokers (p = 0.0417). The H3 (1D-c2-C-A2) frequency in alcoholic-smokers was much lower than in alcoholic-nonsmokers (p = 0.0042) and control-smokers (p = 0.0363).

CONCLUSIONS

Our data demonstrate that carrying haplotype H6 might enhance susceptibility to developing alcoholism, but possessing the H7 or H10 haplotype appears to decrease this susceptibility. The H6, H7, and H9 haplotypes may play certain roles in different clinical phenotypes in Mexican American alcoholics. In addition, our data suggest that the H1, H2, and H3 haplotypes are associated with alcohol drinking and smoking. These results support that haplotype analysis is much more informative than single allele analysis. Our findings clearly indicate the importance of H6 haplotype in alcohol drinking in Mexican Americans.

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.

Ultra-rapid rate of ethanol elimination from blood in drunken drivers with extremely high blood-alcohol concentrations

The rate of alcohol elimination from blood was determined in drunken drivers by taking two blood samples about 1 h apart. These cases were selected because the individuals concerned had reached an extremely high blood-alcohol concentration (BAC) when they were apprehended. This suggests a period of continuous heavy drinking leading to the development of metabolic tolerance. Use of double blood samples to calculate the elimination rate of alcohol from blood is valid provided that drunken drivers are in the post-absorptive phase of the BAC curve, the time between sampling is not too short, and that zero-order elimination kinetics operates. Evidence in support of this came from other drunken drivers in which three consecutive blood samples were obtained at hourly intervals. The mean BAC (N = 21) was 4.05 g/l (range, 2.71-5.18 g/l), and the average rate of alcohol elimination from blood was 0.33 g l(-1) h(-1) with a range of 0.20-0.62 g l(-1) h(-1). The possibility of ultra-rapid rates of ethanol elimination from blood in drunken drivers having extremely high BAC deserves to be considered in forensic casework, e.g., when retrograde extrapolations and other blood-alcohol calculations are made. The mechanism accounting for more rapid metabolism is probably related to induction of the microsomal enzyme (CYP2E1) pathway for ethanol oxidation, as one consequence of continuous heavy drinking. However, the dose of alcohol and the duration of drinking necessary to boost the activity of CYP2E1 enzymes in humans have not been established.

Alcohol, oxidative stress and free radical damage

The involvement of free radical mechanisms in the pathogenesis of alcoholic liver disease (ALD) is demonstrated by the detection of lipid peroxidation markers in the liver and the serum of patients with alcoholism, as well as by experiments in alcohol-feed rodents that show a relationship between alcohol-induced oxidative stress and the development of liver pathology. Ethanol-induced oxidative stress is the result of the combined impairment of antioxidant defences and the production of reactive oxygen species by the mitochondrial electron transport chain, the alcohol-inducible cytochrome P450 (CYP) 2E1 and activated phagocytes. Furthermore, hydroxyethyl free radicals (HER) are also generated during ethanol metabolism by CYP2E1. The mechanisms by which oxidative stress contributes to alcohol toxicity are still not completely understood. The available evidence indicates that, by favouring mitochondrial permeability transition, oxidative stress promotes hepatocyte necrosis and/or apoptosis and is implicated in the alcohol-induced sensitization of hepatocytes to the pro-apoptotic action of TNF-alpha. Moreover, oxidative mechanisms can contribute to liver fibrosis, by triggering the release of pro-fibrotic cytokines and collagen gene expression in hepatic stellate cells. Finally, the reactions of HER and lipid peroxidation products with hepatic proteins stimulate both humoral and cellular immune reactions and favour the breaking of self-tolerance during ALD. Thus, immune responses might represent the mechanism by which alcohol-induced oxidative stress contributes to the perpetuation of chronic hepatic inflammation. Together these observations provide a rationale for the possible clinical application of antioxidants in the therapy for ALD.

Effect of high-dose aspirin on CYP2E1 activity in healthy subjects measured using chlorzoxazone as a probe

The authors evaluated the effect of high-dose aspirin at a therapeutic dose, using chlorzoxazone as a probe for CYP2E1 enzyme activity. In a randomized, open-label, 2-way crossover study, 10 healthy men were treated 3 times daily for 6 days with 1 g aspirin or placebo. On day 7, 1 dose of 400 mg chlorzoxazone was administered orally. Plasma concentrations of chlorzoxazone and its metabolite, 6-hydroxychlorzoxazone, were measured. During the aspirin phase, the area under the time-concentration curve (AUC) and peak plasma concentration of chlorzoxazone were 95% (90% confidence interval [CI], 87%-103%) and 90% (90% CI, 80%-101%) of the values during the placebo phase, respectively. High-dose aspirin did not affect the oral clearance of chlorzoxazone significantly (90% CI, 98%-120%; P = .24). The AUC ratio and plasma concentration ratios of 6-hydroxychlorzoxazone/chlorzoxazone were not changed significantly by high-dose aspirin. High-dose aspirin at a therapeutic dose does not affect CYP2E1 activity in humans.

In Vivo and in Vitro Characterization of Chlorzoxazone Metabolism and Hepatic CYP2E1 Levels in African Green Monkeys: Induction by Chronic Nicotine Treatment

CYP2E1 metabolizes compounds, including clinical drugs, organic solvents, and tobacco-specific carcinogens. Chlorzoxazone (CZN) is a probe drug used to phenotype for CYP2E1 activity. Smokers have increased CZN clearance during smoking compared with nonsmoking periods; however, it is unclear which cigarette smoke component is causing the increased activity. The relationships between in vivo CZN disposition, in vitro CZN metabolism, and hepatic CYP2E1 have not been investigated in a within-animal design. In control-treated monkeys (Cercopithecus aethiops), the in vivo CZN area under the curve extrapolated to infinity (AUC(inf)) was 19.7 +/- 4.5 microg x h/ml, t1/2 was 0.57 +/- 0.07 h, and terminal disposition rate constant calculated from last three to four points on the log-linear end of the concentration versus time curve was 1.2 +/- 0.2 /h. In vitro, the apparent Vmax was 3.48 +/- 0.02 pmol/min/mug microsomal protein, and the Km was 95.4 +/- 1.8 microM. Chronic nicotine treatment increased in vivo CZN disposition, as indicated by a 52% decrease in AUC(inf) (p < 0.01) and 52% decrease in Tmax (p < 0.05) compared with control-treated monkeys. The log metabolic ratios at 0.5, 1, 2, and 4 h significantly negatively correlated with CZN AUC(inf) (p = 0.01-0.0001). Monkey hepatic CYP2E1 levels significantly correlated with both in vivo AUC(inf) (p = 0.03) and in vitro (p = 0.004) CZN metabolism. Together, the data indicated that nicotine induction of in vivo CZN disposition is related to the rates of in vitro CZN metabolism and hepatic microsomal CYP2E1 protein levels. Nicotine is one component in cigarette smoke that can increase in vivo CZN metabolism via induction of hepatic CYP2E1 levels. Thus, nicotine exposure may affect the metabolism of CYP2E1 substrates such as acetaminophen, ethanol, and benzene.

CYP2E1-dependent oxidative stress and toxicity: role in ethanol-induced liver injury

Ethanol-induced oxidative stress plays a major role in the mechanisms by which ethanol causes liver injury. Many pathways contribute to how ethanol induces a state of oxidative stress. One central pathway appears to be the induction, by ethanol, of the CYP2E1 form of cytochrome P450 enzymes. CYP2E1 is of interest because it metabolises and activates many toxicological substrates, including ethanol, to more reactive products. Levels of CYP2E1 are elevated under a variety of physiological and pathophysiological conditions. CYP2E1 is an effective generator of reactive oxygen species. This review summarises some of the biochemical and toxicological properties of CYP2E1, and briefly describes the use of HepG2 cell lines in assessing the actions of CYP2E1. Future directions, which may help to better understand the actions of CYP2E1 and its role in alcoholic liver injury, are suggested.

The Therapeutic Use of Acetaminophen in Patients with Liver Disease

Acetaminophen has been used safely and effectively for many years to manage pain and/or fever in patients of all ages. It is commonly recommended as first-line therapy for a variety of patients and conditions, including the elderly, children with viral illnesses, and patients with osteoarthritis, gastrointestinal conditions, bleeding disorders, cardiovascular disease, or renal disease. However, its use is often avoided in patients with chronic liver disease. The perception that acetaminophen should be avoided in such patients arose from awareness of the association between massive acetaminophen overdose and hepatotoxicity, combined with a lack of understanding of the metabolism of acetaminophen in patients with liver disease. There are various theoretical mechanisms of acetaminophen hepatotoxicity in chronic liver disease including: altered metabolism and depleted glutathione stores that would be expected to increase accumulation of the hepatotoxic intermediate, N-acetyl-p-benzoquinone imine (NAPQI). Available studies in patients with chronic liver disease, however, have shown that although the half-life of acetaminophen may be prolonged, cytochrome P-450 activity is not increased and glutathione stores are not depleted to critical levels in those taking recommended doses. Furthermore, acetaminophen has been studied in a variety of liver diseases without evidence of increased risk of hepatotoxicity at currently recommended doses. Therefore, acetaminophen can be used safely in patients with liver disease and is a preferred analgesic/antipyretic because of the absence of the platelet impairment, gastrointestinal toxicity, and nephrotoxicity associated with nonsteroidal antiinflammatory drugs.

Comparison of cytochrome P4502E1 (CYP2E1) activity and hepatic and lymphocyte mRNA expression in patients with chronic hepatitis C

The induction of cytochrome P4502E1 (CYP2E1) is believed to play a role in the development of fibrosis in hepatitis C patients. However, information about CYP2E1 activity in chronic hepatitis C patients is fragmentary and the relationship between CYP2E1 activity and mRNA expression is unknown in this disease. The purpose of this study was (a) to characterise CYP2E1 activity in those patients and (b) to analyse its relationship with CYP2E1 mRNA expression in the liver and in peripheral blood lymphocytes (PBLs), previously proposed as a surrogate to assess changes in CYP2E1 activity. Fourteen chronic hepatitis C patients were submitted to a routine transcutaneous liver biopsy. CYP2E1 activity was assessed by using chlorzoxazone (CZX) pharmacokinetic parameters and hepatic and PBLs CYP2E1 mRNA expression was measured by real-time RT-PCR. The mean oral clearance of CZX (CLT: 21.5+/-10.1L/h) was within the normal range and the chlorzoxazone metabolic ratio (CMR) at t = 2 h was closely related to other CZX pharmacokinetic parameters. None of the pharmacokinetic parameters did significantly correlate with CYP2E1 mRNA, neither in the liver nor in PBLs. Furthermore, there was no significant relationship between CYP2E1 mRNA levels in paired liver and PBL samples. Our data indicate that early stages of chronic hepatitis C are not associated with CYP2E1 induction. In this disease, the determination of the CMR at t = 2 h represents a reliable index to assess CYP2E1 activity. The measurement of CYP2E1 expression, at the mRNA level, in PBLs or in liver is not useful for that purpose.

Robustness of chlorzoxazone as an in vivo measure of cytochrome P450 2E1 activity

AIMS

Chlorzoxazone is metabolized by cytochrome P450 2E1 (CYP2E1) to a single oxidized metabolite, 6-hydroxychlorzoxazone. The aim of the study was to test the robustness of chlorzoxazone as an in vivo probe of CYP2E1 activity in humans, with emphasis on investigating short-term and long-term intra-individual variabilities and effects of different doses of the drug. In addition, the influences of body build, drug metabolizing enzyme genotype, blood sampling time, and moderate recent ethanol intake were investigated.

METHODS

The 6-hydroxychlorzoxazone:chlorzoxazone (metabolic) ratio in plasma was measured at 2 h in 28 male and nine female volunteers following a single oral dose of 500 mg chlorzoxazone. Similarly, the metabolic ratios at 4 h and 6 h were measured in 20 of the males. The metabolic ratio at 2 h was also determined 1.5 and 2.5 years later in 13 and seven males, respectively, and weekly for 3 weeks in seven males, after a dose of 500 mg, once at higher (750 mg) and lower (250 mg) doses, and once (500 mg) following moderate ethanol intake (0.5 g kg(-1) body weight) the preceding evening. Genotypes were determined for CYP2E1 as well as for N-acetyltransferase 2 and glutathione transferase M1.

RESULTS

Excluding an outlier (ratio = 1.6) the metabolic ratio at 2 h ranged from 0.12 to 0.61 (n = 36). A positive correlation with body weight (r = 0.61, P < 0.001) suggested dose-dependent metabolism of chlorzoxazone. The metabolic ratio decreased with increasing chlorzoxazone dose (P = 0.01), again suggesting dose-dependent metabolism. Long-term (yearly intervals) and short-term (weekly intervals) intra- and interindividual variabilities in metabolic ratio were similar (30% and 63%vs 28% and 54%, respectively). Both inter- and intra-individual variabilities tended to decrease with increasing dose of chlorzoxazone. There was no significant influence of moderate ethanol intake the preceding evening, or of CYP2E1 genotype on the metabolic ratio.

CONCLUSIONS

The relatively low intra-individual variability in the metabolism of chlorzoxazone suggests that a single-sample procedure may suffice to assess CYP2E1 activity in vivo. However, chlorzoxazone metabolism is dose-dependent at commonly used doses and it is therefore advisable to adjust the dose for body weight. Moderate intake of ethanol the preceding evening did not significantly affect the chlorzoxazone metabolic ratio.

Acetaminophen misconceptions

Examination of the pharmacokinetics of acetaminophen can decrease misconceptions involved in clinical evaluation. Enzyme patterns and acetaminophen levels must be related to time and known metabolic phenomena. A careful look at ethanol and nutrition, especially fasting demonstrates that therapeutic doses of acetaminophen do not place patients at a greater risk in either of these instances. An overdose of acetaminophen in a chronic alcohol abuser may result in more severe hepatotoxicity than in the nonalcoholic. CYP2E1 and glutathione must be evaluated simultaneously rather than in isolation. Glucuronidation capacity in humans is not a factor except in massively overdosed patients.

Serum aminotransferase activity as a predictor of clearance of drugs metabolized by CYP isoforms in rats with acute hepatic failure induced by carbon tetrachloride

The values of serum aminotransferase activity (AST) in untreated rats and rats with acute hepatic failure at 24h after an oral administration of CCl(4) (0.5 ml/kg) were 85+/-9 IU/l and 4260+/-620 IU/l (mean+/-S.D., n=6), respectively. The values of total clearance (CL(tot)) after intravenous administration of caffeine, tolbutamide, chlorzoxazone or lidocaine (as probe drugs for various CYP isoforms) to CCl(4)-treated rats were decreased to about 1/8, 1/3, 1/3 or 1/2 compared with those in untreated rats. Good correlations were observed between mRNA expression and enzyme activity of CYP2C11, CYP2E1, CYP3A2 and CYP1A2 in livers of rats given various doses of CCl(4). There was also a good negative correlation between serum AST activity and hepatic enzyme activity of each CYP. The serum AST activities corresponding to a 50% decrease of CYP2C 11, CYP2E1, CYP3A2 and CYP1A2 activities were about 710, 780, 1030 and 1300 IU/l, respectively. In conclusion, when the serum AST value in CCl(4)-treated rats reached about 4000 IU/l, the hepatic CYP activities were one-tenth or less of the control, although the degree of decrease of the CL(tot) values varied markedly. Nevertheless, the AST value appears to be a promising candidate for an indicator to predict appropriate dose modification of drugs for patients with acute hepatic failure.

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.

Pharmacokinetic and pharmacodynamic assessment of a five-probe metabolic cocktail for CYPs 1A2, 3A4, 2C9, 2D6 and 2E1

AIMS

The primary objectives of the present study were to establish whether there was a pharmacokinetic or pharmacodynamic interaction between the probe drugs caffeine (CYP1A2), tolbutamide (CYP2C9), debrisoquine (CYP2D6), chlorzoxazone (CYP2E1) and midazolam (CYP3A4), when administered in combination as a cocktail. Furthermore, the tolerability of these probe drugs, both alone and in combination as a cocktail was assessed.

METHODS

Twelve healthy volunteer subjects (age range 22-48 years) were entered into an open, fixed sequence, 6-limb, single centre study. The randomization was such that all drugs were given individually followed by the full "cocktail" as the last treatment limb. The phenotypic index used to assess the intrinsic activity of the CYP isoforms included metabolite/parent ratios in plasma and urine (CYPs 1A2, 2E1 & 2C9), parent/metabolite ratios in urine (CYP2D6) and plasma AUClast (CYP3A4). Blood pressure and blood glucose measurements were used to assess pharmacodynamic interactions. Tolerability was assessed through reporting of adverse events

RESULTS

Overall, there was little evidence that the probe drugs interacted metabolically when co-administered as the cocktail. The ratio of the geometric mean (and 90% confidence interval) of the phenotypic index, obtained after administration of the probe as part of the cocktail and when given alone were: caffeine, 0.86 (0.67-1.10), midazolam, 0.96 (0.74-1.24), tolbutamide, 0.86 (0.72-1.03), debrisoquine 1.04 (0.97-1.12) and chlorzoxazone, 0.95 (0.86-1.05). There was no difference in blood pressure and blood glucose concentrations following the cocktail and dosing of the individual probes. There was no effect on ECG recordings at any time-point. The adverse events reported for individual drug administrations were mild, transient and expected. Overall no more adverse events were reported on the cocktail study days than on the days when the drugs were administered alone.

CONCLUSIONS

The five probe drugs when coadministered, in this dosing regimen, demonstrated no evidence of either a metabolic or pharmacodynamic interaction that might confound the conclusions drawn during a cocktail study. The present cocktail methodology has the potential to become a useful tool to aid the detection of clinically important drug-drug interactions during drug development.