In Vitro Hepatic Models to Assess Herb-Drug Interactions: Approaches and Challenges

A newfound appreciation for the benefits of herbal treatments has emerged in recent decades. However, herbal medication production still needs to establish standardized protocols that adhere to strict guidelines for quality assurance and risk minimization. Although the therapeutic effects of herbal medicines are extensive, the risk of herb-drug interactions remains a serious concern, limiting their use. Therefore, a robust, well-established liver model that can fully represent the liver tissue is required to study potential herb-drug interactions to ensure herbal medicines' safe and effective use. In light of this, this mini review investigates the existing in vitro liver models applicable to detecting herbal medicines' toxicity and other pharmacological targets. This article analyzes the benefits and drawbacks of existing in vitro liver cell models. To maintain relevance and effectively express the offered research, a systematic strategy was employed to search for and include all discussed studies. In brief, from 1985 to December 2022, the phrases "liver models", "herb-drug interaction", "herbal medicine", "cytochrome P450", "drug transporters pharmacokinetics", and "pharmacodynamics" were combined to search the electronic databases PubMed, ScienceDirect, and the Cochrane Library.

Multispecies Machine Learning Predictions of In Vitro Intrinsic Clearance with Uncertainty Quantification Analyses

In pharmaceutical research, compounds are optimized for metabolic stability to avoid a too fast elimination of the drug. Intrinsic clearance (CL_int) measured in liver microsomes or hepatocytes is an important parameter during lead optimization. In this work, machine learning models were developed to relate the compound structure to microsomal metabolic stability and predict CL_int for new compounds. A multitask (MT) learning architecture was introduced to model the CL_int of six species simultaneously, giving as a result a multispecies machine learning model. MT graph neural network (MT-GNN) regression was identified as the top-performing method, and an ensemble of 10 MT-GNN models was evaluated prospectively. Geometric mean fold errors were consistently smaller than 2-fold. Moreover, high precision values were obtained in the prediction of "high" (>300 μL/min/mg) and "low" (<100 μL/min/mg) CL_int compounds. Precision values ranged from 80 to 94% for low CL_int predictions and from 75 to 97% for high CL_int predictions, depending on the species. Uncertainty on experimental values and model predictions was systematically quantified. Experimental variability (aleatoric uncertainty) of all historical Novartis in vitro clearance experiments was analyzed. Interestingly, MT-GNN models' performance approached assays' experimental variability. Moreover, uncertainty estimation in predictions (epistemic uncertainty) enabled identifying predictions associated with lower and higher error. Taken together, our manuscript combines a multispecies deep learning model and large-scale uncertainty analyses to improve CL_int predictions and facilitate early informed decisions for compound prioritization.

The Combination of Electrochemistry and Microfluidic Technology in Drug Metabolism Studies

Drugs are metabolized within the liver (pH 7.4) by phase I and phase II metabolism. During the process, reactive metabolites can be formed that react covalently with biomolecules and induce toxicity. Identifying and detecting reactive metabolites is an important part of drug development. Preclinical and clinical investigations are conducted to assess the toxicity and safety of a new drug candidate. Electrochemistry coupled to mass spectrometry is an ideal complementary technique to the current preclinical studies, a pure instrumental approach without any purification steps and tedious protocols. The combination of microfluidics with electrochemistry towards the mimicry of drug metabolism offers portability, low volume of reagents and faster reaction times. This review explores the development of microfluidic electrochemical cells for mimicking drug metabolism.

Mechanistic study on the species differences in excretion pathway of HR011303 in human and rats

Excretion of [¹⁴C]HR011303-derived radioactivity showed significant species difference. Urine (81.50% of dose) was the main excretion route in healthy male subjects, whereas feces (87.16% of dose) was the main excretion route in rats. To further elucidate the underlying cause for excretion species differences of HR011303, studies were conducted to uncover its metabolism and excretion mechanism. M5, a glucuronide metabolite of HR011303, is the main metabolite in humans and rats. Results of rat microsomes incubation study suggested that HR011303 was metabolized to M5 in the rat liver. According to previous studies, M5 is produced in both human liver and kidney microsomes. We found M5 in human liver can be transported to the blood by multidrug resistance-associated protein (MRP) 3 and then the majority of M5 can be hydrolyzed to HR011303. HR011303 enters the human kidney or liver through passive diffusion, whereas M5 is taken up through organic anion transporter (OAT) 3, organic anion-transporting polypeptide (OATP) 1B1, and OATP1B3. When HR011303 alone was present, it can be metabolized to M5 in both sandwich-cultured rat hepatocytes (SCRH) and sandwich-cultured human hepatocytes (SCHH) and excreted into bile as M5 in SCRH. Using transporter inhibitors in sandwich-cultured model and membrane vesicles that expressing MRP2 or Mrp2, we found M5 was substance of MRP2/Mrp2 and the bile efflux of M5 mainly mediated by MRP2/Mrp2. Considering the significant role of MRP3/Mrp3 and MRP2/Mrp2 in the excretion of glucuronides, the competition between them for M5 was possibly the determinant for the different excretion routes in humans and rats. Significance Statement Animal experiments are necessary to predict dosage and safety of candidate drugs prior to clinical trials. However, extrapolation results often differ from actual situation. For HR011303, excretory pathways exhibited a complete reversal, through urine in humans and feces in rats. Such phenomena have been observed in several drugs, but no in-depth studies have been conducted to date. In the present study, the excretion species differences of HR011303 can be explained by the competition for M5 between MRP2/Mrp2 and MRP3/Mrp3.

Cytochrome P450 enzymes: a review on drug metabolizing enzyme inhibition studies in drug discovery and development

Assessment of drug candidate's potential to inhibit cytochrome P450 (CYP) enzymes remains crucial in pharmaceutical drug discovery and development. Both direct and time-dependent inhibition of drug metabolizing CYP enzymes by the concomitant administered drug is the leading cause of drug-drug interactions (DDIs), resulting in the increased toxicity of the victim drug. In this context, pharmaceutical companies have grown increasingly diligent in limiting CYP inhibition liabilities of drug candidates in the early stages and examining risk assessments throughout the drug development process. This review discusses different strategies and decision-making processes for assessing the drug-drug interaction risks by enzyme inhibition and lays particular emphasis on in vitro study designs and interpretation of CYP inhibition data in a stage-appropriate context.

In vitro assessment of the potential for dolutegravir to affect hepatic clearance of levonorgestrel

Objectives:

The World Health Organization recommends that all countries adopt dolutegravir-based antiretroviral therapy as the preferred regimen for all individuals living with HIV. Levonorgestrel is a commonly used hormonal contraceptive, which undergoes drug–drug interactions with some antiretrovirals, but the potential interaction between dolutegravir and levonorgestrel has not been examined. We aimed to evaluate cytochrome P450 (CYP)-mediated levonorgestrel metabolism and quantify the effects of dolutegravir on levonorgestrel apparent intrinsic clearance (CL_int.app.) and CYP gene expression.

Methods:

In vitro CYP-mediated CL_int.app. of levonorgestrel was quantified using a recombinant human CYP (rhCYP) enzyme system. A primary human hepatocyte model of drug metabolism was used to assess the effects of dolutegravir on (1) levonorgestrel CL_int.app., using liquid chromatography-tandem mass spectrometry, and (2) the expression of specific CYP enzymes, using quantitative real-time polymerase chain reaction.

Results:

Levonorgestrel clearance was mediated by multiple rhCYPs, including rhCYP3A4. Under control conditions, levonorgestrel CL_int.app. was 22.4 ± 5.0 μL/min/10⁶ hepatocytes. Incubation with 43.1 nM of unbound dolutegravir elevated levonorgestrel CL_int.app. to 31.4 ± 7.8 μL/min/10⁶ hepatocytes (P = 0.168), while 142.23 nM increased levonorgestrel CL_int.app. to 37.0 ± 2.9 μL/min/10⁶ hepatocytes (P = 0.012). Unbound dolutegravir ≥ 431 nM induced expression of CYP3A4 (≥ two-fold) in a dose-dependent manner, while 1.44 μM of unbound dolutegravir induced CYP2B6 expression 2.2 ± 0.3-fold (P = 0.0004).

Conclusions:

In summary, this in vitro study suggests that dolutegravir has the potential to increase hepatic clearance of levonorgestrel by inducing both CYP3A and non-CYP3A enzymes. The observed in vitro dolutegravir–levonorgestrel drug–drug interaction should be further examined in clinical studies.

Metabolism and Interactions of Chloroquine and Hydroxychloroquine with Human Cytochrome P450 Enzymes and Drug Transporters

BACKGROUND

In clinical practice, chloroquine and hydroxychloroquine are often co-administered with other drugs in the treatment of malaria, chronic inflammatory diseases, and COVID-19. Therefore, their metabolic properties and the effects on the activity of cytochrome P450 (P450, CYP) enzymes and drug transporters should be considered when developing the most efficient treatments for patients.

METHODS

Scientific literature on the interactions of chloroquine and hydroxychloroquine with human P450 enzymes and drug transporters, was searched using PUBMED.Gov (https://pubmed.ncbi.nlm.nih.gov/) and the ADME database (https://life-science.kyushu.fujitsu.com/admedb/).

RESULTS

Chloroquine and hydroxychloroquine are metabolized by P450 1A2, 2C8, 2C19, 2D6, and 3A4/5 in vitro and by P450s 2C8 and 3A4/5 in vivo by N-deethylation. Chloroquine effectively inhibited P450 2D6 in vitro; however, in vivo inhibition was not apparent except in individuals with limited P450 2D6 activity. Chloroquine is both an inhibitor and inducer of the transporter MRP1 and is also a substrate of the Mate and MRP1 transport systems. Hydroxychloroquine also inhibited P450 2D6 and the transporter OATP1A2.

CONCLUSIONS

Chloroquine caused a statistically significant decrease in P450 2D6 activity in vitro and in vivo, also inhibiting its own metabolism by the enzyme. The inhibition indicates a potential for clinical drug-drug interactions when taken with other drugs that are predominant substrates of the P450 2D6. When chloroquine and hydroxychloroquine are used clinically with other drugs, substrates of P450 2D6 enzyme, attention should be given to substrate-specific metabolism by P450 2D6 alleles present in individuals taking the drugs.

Application of In Vitro Metabolism Activation in High-Throughput Screening

In vitro methods which incorporate metabolic capability into the assays allow us to assess the activity of metabolites from their parent compounds. These methods can be applied into high-throughput screening (HTS) platforms, thereby increasing the speed to identify compounds that become active via the metabolism process. HTS was originally used in the pharmaceutical industry and now is also used in academic settings to evaluate biological activity and/or toxicity of chemicals. Although most chemicals are metabolized in our body, many HTS assays lack the capability to determine compound activity via metabolism. To overcome this problem, several in vitro metabolic methods have been applied to an HTS format. In this review, we describe in vitro metabolism methods and their application in HTS assays, as well as discuss the future perspectives of HTS with metabolic activity. Each in vitro metabolism method has advantages and disadvantages. For instance, the S9 mix has a full set of liver metabolic enzymes, but it displays high cytotoxicity in cell-based assays. In vitro metabolism requires liver fractions or the use of other metabolically capable systems, including primary hepatocytes or recombinant enzymes. Several newly developed in vitro metabolic methods, including HepaRG cells, three-dimensional (3D) cell models, and organ-on-a-chip technology, will also be discussed. These newly developed in vitro metabolism approaches offer significant progress in dissecting biological processes, developing drugs, and making toxicology studies quicker and more efficient.

Kinetics of metabolism of deltamethrin and cis- and trans-permethrin in vitro. Studies using rat and human liver microsomes, isolated rat hepatocytes and rat liver cytosol

The kinetics of metabolism of deltamethrin (DLM) and cis- and trans-permethrin (CPM and TPM) was studied in male Sprague-Dawley rat and human liver microsomes. DLM metabolism kinetics was also studied in isolated rat hepatocytes, liver microsomes and cytosol. Apparent intrinsic clearance (CL_int) values for the metabolism of DLM, CPM and TPM by cytochrome P450 (CYP) and carboxylesterase (CES) enzymes in rat and human liver microsomes decreased with increasing microsomal protein concentration. However, when apparent CL_int values were corrected for nonspecific binding to allow calculation of unbound (i.e., corrected) CL_int values, the unbound values did not vary greatly with microsomal protein concentration. Unbound CL_int values for metabolism of 0.05-1 μM DLM in rat liver microsomes (CYP and CES enzymes) and cytosol (CES enzymes) were not significantly different from rates of DLM metabolism in isolated rat hepatocytes. This study demonstrates that the nonspecific binding of these highly lipophilic compounds needs to be taken into account in order to obtain accurate estimates of rates of in vitro metabolism of these pyrethroids. While DLM is rapidly metabolised in vitro, the hepatocyte membrane does not appear to represent a barrier to the absorption and hence subsequent hepatic metabolism of this pyrethroid.

In vitro and in vivo studies of triacetone triperoxide (TATP) metabolism in humans

Purpose

Triacetone triperoxide (TATP) is a volatile but powerful explosive that appeals to terrorists due to its ease of synthesis from household items. For this reason, bomb squad, canine (K9) units, and scientists must work with this material to mitigate this threat. However, no information on the metabolism of TATP is available.

Methods

In vitro experiments using human liver microsomes and recombinant enzymes were performed on TATP and TATP-OH for metabolite identification and enzyme phenotyping. Enzyme kinetics for TATP hydroxylation were also investigated. Urine from laboratory personnel collected before and after working with TATP was analyzed for TATP and its metabolites.

Results

While experiments with flavin monooxygenases were inconclusive, those with recombinant cytochrome P450s (CYPs) strongly suggested that CYP2B6 was the principle enzyme responsible for TATP hydroxylation. TATP-O-glucuronide was also identified and incubations with recombinant uridine diphosphoglucuronosyltransferases (UGTs) indicated that UGT2B7 catalyzes this reaction. Michaelis–Menten kinetics were determined for TATP hydroxylation, with Km = 1.4 µM and Vmax = 8.7 nmol/min/nmol CYP2B6. TATP-O-glucuronide was present in the urine of all three volunteers after being exposed to TATP vapors showing good in vivo correlation to in vitro data. TATP and TATP-OH were not observed.

Conclusions

Since scientists working to characterize and detect TATP to prevent terrorist attacks are constantly exposed to this volatile compound, attention should be paid to its metabolism. This paper is the first to elucidate some exposure, metabolism and excretion of TATP in humans and to identify a marker of TATP exposure, TATP-O-glucuronide in urine.

Phosmet bioactivation by isoform-specific cytochrome P450s in human hepatic and gut samples and metabolic interaction with chlorpyrifos

Data on the bioactivation of Phosmet (Pho), a phthalimide-derived organophosphate pesticide (OPT), to the neurotoxic metabolite Phosmet-oxon (PhOx) in human are not available. The characterization of the reaction in single human recombinant CYPs evidenced that the ranking of the intrinsic clearances was: 2C18>2C19>2B6>2C9>1A1>1A2>2D6>3A4>2A6. Considering the average human hepatic content, CYP2C19 contributed for the great majority (60%) at relevant exposure concentrations, while CYP2C9 (33%) and CYP3A4 (31%) were relevant at high substrate concentration. The dose-dependent role of the active isoforms was confirmed in human liver microsomes by using selective CYP inhibitors. This prominent role of CYP2C in oxon formation was not shared by other OPTs. The pre-systemic Pho bioactivation measured in human intestinal microsomes was relevant accounting for ¼ of that measured in the liver showing two reaction phases catalysed by CYP2C and CYP3A4. Phosmet efficiently inhibited CPF bioactivation and detoxication, with Ki values (≈30 μM) relevant to pesticide concentrations achievable in the human liver, while the opposite is unlikely (Ki ≈ 160 μM) at the actual exposure levels, depending on the peculiar isoform-specific Pho bioactivation. Kinetic information in humans can support the development of quantitative in vitro/in vivo extrapolation and in silico models for risk assessment refinement for single and multiple pesticides.

Metabolism of triflumuron in the human liver: Contribution of cytochrome P450 isoforms and esterases

Triflumuron (TFM) is a benzoylurea insecticide commonly used in Tunisian agriculture and around the world to control crop pests and flies as a promising alternative to conventional insecticides for its arthropod specificity and low toxicity. From the evidence available in animal models, it can be expected that the metabolism of TFM is catalyzed by cytochrome P450 (CYP) and esterases. However, no data are available on human metabolism of TFM with regards to phase I metabolism and CYP isoform specificity. Hence, this manuscript describes experimental investigations to underpin in vitro phase I TFM metabolism in human samples for the first time. TFM biotransformation by recombinant human CYPs was characterized, then human liver microsomes (HLM) and chemical specific inhibitors have been used to identify the relative contribution of CYPs and esterases. Our results showed that all CYP isoforms were able to metabolize TFM with different affinity and efficiency. The relative contribution based both on the kinetic parameters and the CYP hepatic content was 3A4 > >2C9 > 2C8 > 2A6 > 1A2 > 2B6 > 2D6 > 2C19 > 2C18 > 1A1 at low TFM concentration, whilst at high TFM concentration it was 1A2 > >2C9 = 3A4 = 2A6 > 2C19 > 2B6 = 2C8 > 2D6 > 1A1 > 2C18. Experiments with HLMs confirmed the involvement of the most relevant CYPs in the presence of specific chemical inhibitors with a catalytic efficiency (Cliapp) lower by an order of magnitude compared with recombinant enzymes. Esterases were also relevant to the overall TFM kinetics and metabolism, with catalytic efficiency higher than that of CYPs. It is foreseen that such isoform-specific information in humans will further support in silico models for the refinement of the human risk assessment of single pesticides or mixtures.

Metabolic stability and its role in the discovery of new chemical entities

Determination of metabolic profiles of new chemical entities is a key step in the process of drug discovery, since it influences pharmacokinetic characteristics of therapeutic compounds. One of the main challenges of medicinal chemistry is not only to design compounds demonstrating beneficial activity, but also molecules exhibiting favourable pharmacokinetic parameters. Chemical compounds can be divided into those which are metabolized relatively fast and those which undergo slow biotransformation. Rapid biotransformation reduces exposure to the maternal compound and may lead to the generation of active, non-active or toxic metabolites. In contrast, high metabolic stability may promote interactions between drugs and lead to parent compound toxicity. In the present paper, issues of compound metabolic stability will be discussed, with special emphasis on its significance, in vitro metabolic stability testing, dilemmas regarding in vitro-in vivo extrapolation of the results and some aspects relating to different preclinical species used in in vitro metabolic stability assessment of compounds.

Simulating the phase II metabolism of raloxifene on a screen-printed electrode

Raloxifene (RLX) is a selective estrogen receptor modulator widely used for the treatment of osteoporosis in post-menopause women. Toxicological in vitro studies suggested the reactivity of RLX through phase I metabolism. Herein, we describe a simple and inexpensive method for monitoring the reactive metabolism and detoxification of RLX by electrochemistry (EC) and mass spectrometry (MS). The phase I metabolite was synthesized electrochemically on a screen-printed electrode (SPE) and subsequently reacted with glutathione (GSH). The resulted GSH-adducts and GSH disulfides were characterized off-line by electrospray ionization (ESI)–MS.

The functional effects of physical interactions involving cytochromes P450: putative mechanisms of action and the extent of these effects in biological membranes

Cytochromes P450 represent a family of enzymes, which are responsible for the oxidative metabolism of a wide variety of xenobiotics. Although the mammalian P450s require interactions with their redox partners in order to function, more recently, P450 system proteins have been shown to exist as multi-protein complexes that include the formation of P450•P450 complexes. Evidence has shown that the metabolism of some substrates by a given P450 can be influenced by the specific interaction of the enzyme with other forms of P450. Detailed kinetic analysis of these reactions in vitro has shown that the P450-P450 interactions can alter metabolism by changing the ability of a P450 to bind to its cognate redox partner, NADPH-cytochrome P450 reductase; by altering substrate binding to the affected P450; and/or by changing the rate of a catalytic step of the reaction cycle. This review summarizes the known examples of P450-P450 interactions that have been shown in vitro to influence metabolism and categorizes them according to the mechanism(s) causing the effects. P450-P450 interactions have the potential to cause major changes in the metabolism and elimination of drugs in vivo. This review summarizes the evidence that the P450-P450 interactions influence metabolism in biological membranes and discusses the studies, which will provide further insight into the extent of these effects in the future.

Stereoselective Metabolism of Bupropion to OH-bupropion, Threohydrobupropion, Erythrohydrobupropion, and 4'-OH-bupropion in vitro

Bupropion is a widely used antidepressant, smoking cessation aid, and weight-loss therapy. It is administered as a racemic mixture, but the pharmacokinetics and activity of bupropion are stereoselective. The activity and side effects of bupropion are attributed to bupropion and its metabolites S,S- and R,R-OH-bupropion, threohydrobupropion, and erythrohydrobupropion. Yet the stereoselective metabolism in vitro and the enzymes contributing to the stereoselective disposition of bupropion have not been characterized. In humans, the fraction of bupropion metabolized (fm) to the CYP2B6 probe metabolite OH-bupropion is 5-16%, but ticlopidine increases bupropion exposure by 61%, suggesting a 40% CYP2B6 and/or CYP2C19 fm for bupropion. Yet, the CYP2C19 contribution to bupropion clearance has not been defined, and the enzymes contributing to overall bupropion metabolite formation have not been fully characterized. The aim of this study was to characterize the stereoselective metabolism of bupropion in vitro to explain the stereoselective pharmacokinetics and the effect of drug-drug interactions (DDIs) and CYP2C19 pharmacogenetics on bupropion exposure. The data predict that threohydrobupropion accounts for 50 and 82%, OH-bupropion for 34 and 12%, erythrohydrobupropion for 8 and 4%, and 4'-OH-bupropion for 8 and 2% of overall R- and S-bupropion clearance, respectively. The fm,CYP2B6 was predicted to be 21%, and the fm,CYP2C19, 6% for racemic bupropion. Importantly, ticlopidine was found to inhibit all metabolic pathways of bupropion in vitro, including threohydrobupropion, erythrohydrobupropion, and 4'OH-bupropion formation, explaining the in vivo DDI. The stereoselective pharmacokinetics of bupropion were quantitatively explained by the in vitro metabolic clearances and in vivo interconversion between bupropion stereoisomers.

Computational Identification of the Paralogs and Orthologs of Human Cytochrome P450 Superfamily and the Implication in Drug Discovery

The human cytochrome P450 (CYP) superfamily consisting of 57 functional genes is the most important group of Phase I drug metabolizing enzymes that oxidize a large number of xenobiotics and endogenous compounds, including therapeutic drugs and environmental toxicants. The CYP superfamily has been shown to expand itself through gene duplication, and some of them become pseudogenes due to gene mutations. Orthologs and paralogs are homologous genes resulting from speciation or duplication, respectively. To explore the evolutionary and functional relationships of human CYPs, we conducted this bioinformatic study to identify their corresponding paralogs, homologs, and orthologs. The functional implications and implications in drug discovery and evolutionary biology were then discussed. GeneCards and Ensembl were used to identify the paralogs of human CYPs. We have used a panel of online databases to identify the orthologs of human CYP genes: NCBI, Ensembl Compara, GeneCards, OMA ("Orthologous MAtrix") Browser, PATHER, TreeFam, EggNOG, and Roundup. The results show that each human CYP has various numbers of paralogs and orthologs using GeneCards and Ensembl. For example, the paralogs of CYP2A6 include CYP2A7, 2A13, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 2F1, 2J2, 2R1, 2S1, 2U1, and 2W1; CYP11A1 has 6 paralogs including CYP11B1, 11B2, 24A1, 27A1, 27B1, and 27C1; CYP51A1 has only three paralogs: CYP26A1, 26B1, and 26C1; while CYP20A1 has no paralog. The majority of human CYPs are well conserved from plants, amphibians, fishes, or mammals to humans due to their important functions in physiology and xenobiotic disposition. The data from different approaches are also cross-validated and validated when experimental data are available. These findings facilitate our understanding of the evolutionary relationships and functional implications of the human CYP superfamily in drug discovery.

Dosing Recommendations for Concomitant Medications During 3D Anti-HCV Therapy

The development of direct-acting antiviral (DAA) agents has reinvigorated the treatment of hepatitis C virus infection. The availability of multiple DAA agents and drug combinations has enabled the transition to interferon-free therapy that is applicable to a broad range of patients. However, these DAA combinations are not without drug-drug interactions (DDIs). As every possible DDI permutation cannot be evaluated in a clinical study, guidance is needed for healthcare providers to avoid or minimize drug interaction risk. In this review, we evaluated the DDI potential of the novel three-DAA combination of ombitasvir, paritaprevir, ritonavir, and dasabuvir (the 3D regimen) with more than 200 drugs representing 19 therapeutic drug classes. Outcomes of these DDI studies were compared with the metabolism and elimination routes of prospective concomitant medications to develop mechanism-based and drug-specific guidance on interaction potential. This analysis revealed that the 3D regimen is compatible with many of the drugs that are commonly prescribed to patients with hepatitis C virus infection. Where interaction is possible, risk can be mitigated by paying careful attention to concomitant medications, adjusting drug dosage as needed, and monitoring patient response and/or clinical parameters.

Impact of physiological, pathological and environmental factors on the expression and activity of human cytochrome P450 2D6 and implications in precision medicine

With only 1.3-4.3% in total hepatic CYP content, human CYP2D6 can metabolize more than 160 drugs. It is a highly polymorphic enzyme and subject to marked inhibition by a number of drugs, causing a large interindividual variability in drug clearance and drug response and drug-drug interactions. The expression and activity of CYP2D6 are regulated by a number of physiological, pathological and environmental factors at transcriptional, post-transcriptional, translational and epigenetic levels. DNA hypermethylation and histone modifications can repress the expression of CYP2D6. Hepatocyte nuclear factor-4α binds to a directly repeated element in the promoter of CYP2D6 and thus regulates the expression of CYP2D6. Small heterodimer partner represses hepatocyte nuclear factor-4α-mediated transactivation of CYP2D6. GW4064, a farnesoid X receptor agonist, decreases hepatic CYP2D6 expression and activity while increasing small heterodimer partner expression and its recruitment to the CYP2D6 promoter. The genotypes are key determinants of interindividual variability in CYP2D6 expression and activity. Recent genome-wide association studies have identified a large number of genes that can regulate CYP2D6. Pregnancy induces CYP2D6 via unknown mechanisms. Renal or liver diseases, smoking and alcohol use have minor to moderate effects only on CYP2D6 activity. Unlike CYP1 and 3 and other CYP2 members, CYP2D6 is resistant to typical inducers such as rifampin, phenobarbital and dexamethasone. Post-translational modifications such as phosphorylation of CYP2D6 Ser135 have been observed, but the functional impact is unknown. Further functional and validation studies are needed to clarify the role of nuclear receptors, epigenetic factors and other factors in the regulation of CYP2D6.

How to Choose In Vitro Systems to Predict In Vivo Drug Clearance: A System Pharmacology Perspective

The use of in vitro metabolism data to predict human clearance has become more significant in the current prediction of large scale drug clearance for all the drugs. The relevant information (in vitro metabolism data and in vivo human clearance values) of thirty-five drugs that satisfied the entry criteria of probe drugs was collated from the literature. Then the performance of different in vitro systems including Escherichia coli system, yeast system, lymphoblastoid system and baculovirus system is compared after in vitro-in vivo extrapolation. Baculovirus system, which can provide most of the data, has almost equal accuracy as the other systems in predicting clearance. And in most cases, baculovirus system has the smaller CV in scaling factors. Therefore, the baculovirus system can be recognized as the suitable system for the large scale drug clearance prediction.

Unique Scopolamine Withdrawal Syndrome After Standard Transdermal Use

We report the case of a 62-year-old woman who developed a withdrawal syndrome after using a standard 1.5-mg transdermal scopolamine (TDS) patch behind the ear to prevent motion sickness during sailing. The patient, who had used TDS occasionally for years without significant adverse effects, more recently, having worn a patch continuously for 7 days, approximately 24 to 36 hours after removing the patch developed dizziness, nausea, sweating, fatigue, and drowsiness. All symptoms disappeared without therapy in about 2 days. Approximately 1 year after the first episode, though, a very similar, more severe disabling reaction developed on 2 occasions. Drowsiness and malaise were accompanied by severe asthenia, orthostatic sweating, inability to stand, and hypotension. All clinical tests (electrocardiogram; spirometry; blood cell count; plasma levels of cortisol, sodium, and potassium; and liver and kidney function tests) were negative, and symptoms disappeared slowly, after several days. Although we are certain that scopolamine was responsible for the symptoms, we are less clear as to the nature of the disorder. The effects being more severe after a more prolonged use of the TDS patch, the increase in severity each successive time, and the time lag between removing the patch and appearance of symptoms all indicated a withdrawal syndrome for which several mechanisms may be suggested.

Reaction phenotyping: advances in the experimental strategies used to characterize the contribution of drug-metabolizing enzymes

During the process of drug discovery, the pharmaceutical industry is faced with numerous challenges. One challenge is the successful prediction of the major routes of human clearance of new medications. For compounds cleared by metabolism, accurate predictions help provide an early risk assessment of their potential to exhibit significant interpatient differences in pharmacokinetics via routes of metabolism catalyzed by functionally polymorphic enzymes and/or clinically significant metabolic drug-drug interactions. This review details the most recent and emerging in vitro strategies used by drug metabolism and pharmacokinetic scientists to better determine rates and routes of metabolic clearance and how to translate these parameters to estimate the amount these routes contribute to overall clearance, commonly referred to as fraction metabolized. The enzymes covered in this review include cytochrome P450s together with other enzymatic pathways whose involvement in metabolic clearance has become increasingly important as efforts to mitigate cytochrome P450 clearance are successful. Advances in the prediction of the fraction metabolized include newly developed methods to differentiate CYP3A4 from the polymorphic enzyme CYP3A5, scaling tools for UDP-glucuronosyltranferase, and estimation of fraction metabolized for substrates of aldehyde oxidase.

Incorporating population variability and susceptible subpopulations into dosimetry for high-throughput toxicity testing

Momentum is growing worldwide to use in vitro high-throughput screening (HTS) to evaluate human health effects of chemicals. However, the integration of dosimetry into HTS assays and incorporation of population variability will be essential before its application in a risk assessment context. Previously, we employed in vitro hepatic metabolic clearance and plasma protein binding data with in vitro in vivo extrapolation (IVIVE) modeling to estimate oral equivalent doses, or daily oral chemical doses required to achieve steady-state blood concentrations (Css) equivalent to media concentrations having a defined effect in an in vitro HTS assay. In this study, hepatic clearance rates of selected ToxCast chemicals were measured in vitro for 13 cytochrome P450 and five uridine 5'-diphospho-glucuronysyltransferase isozymes using recombinantly expressed enzymes. The isozyme-specific clearance rates were then incorporated into an IVIVE model that captures known differences in isozyme expression across several life stages and ethnic populations. Comparison of the median Css for a healthy population against the median or the upper 95th percentile for more sensitive populations revealed differences of 1.3- to 4.3-fold or 3.1- to 13.1-fold, respectively. Such values may be used to derive chemical-specific human toxicokinetic adjustment factors. The IVIVE model was also used to estimate subpopulation-specific oral equivalent doses that were directly compared with subpopulation-specific exposure estimates. This study successfully combines isozyme and physiologic differences to quantitate subpopulation pharmacokinetic variability. Incorporation of these values with dosimetry and in vitro bioactivities provides a viable approach that could be employed within a high-throughput risk assessment framework.

Nalbuphine for postoperative pain treatment in children

BACKGROUND

Several surveys over the past few years have demonstrated that postoperative pain in children is not treated appropriately. One pharmacological treatment option in a multimodal approach for postoperative pain treatment is the systemic administration of opioids. However, opioids are rarely used for postoperative pain treatment in children due to fear of adverse events. One long-standing opioid for systemic use is nalbuphine, a kappa-receptor agonist and µ-receptor antagonist. The efficacy of nalbuphine is believed to be similar to morphine. Increased dosing might result in a ceiling effect, and thus less analgesia than expected. In addition, there might be a lower risk for opioid-induced side effects (nausea, vomiting) and severe adverse events (respiratory depression) due to the antagonistic effect of the µ-receptor. Nalbuphine may be an useful opioid for postoperative use in children, but exact efficacy (e.g. compared to other commonly used opioids) has not been determined yet.

OBJECTIVES

To assess the efficacy and adverse events of nalbuphine for acute postoperative pain treatment in children undergoing surgery.

SEARCH METHODS

We systematically searched the following databases: The Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2013, Issue 7), MEDLINE via Pubmed (January 1966 to July 2013) and EMBASE via Ovid (January 1947 to July 2013). We did not impose any restrictions regarding language or publication date. We checked all reference lists of retrieved articles for additional references.

SELECTION CRITERIA

All randomised controlled trials (RCTs) investigating nalbuphine compared with placebo or other opioids were included.

DATA COLLECTION AND ANALYSIS

Two review authors independently scanned the retrieved articles and made a decision regarding inclusion or exclusion of studies for this review. The same authors also performed the data extraction and the assessment of risk of bias.

MAIN RESULTS

Ten RCTs including 658 patients were finally included in this systematic review. Five trials compared nalbuphine with placebo. Data from one out of five studies for the outcome moderate/severe pain following nalbuphine compared to placebo gave a risk ratio (RR) 1 hour postoperatively (postop) of 0.1 (95% confidence interval (CI) 0.01 to 0.71; low quality evidence) and a RR 2 hours postop of 0.14 (95% CI 0.02 to 1.06; low quality evidence). The estimated RR based on data from a single study indicated that nalbuphine reduced the requirement for analgesia two hours postop (RR 0.47; 95% CI 0.27 to 0.84; low quality evidence). Two included trials compared nalbuphine with morphine and showed a nonsignificant lower or comparable RR for moderate/severe pain at 1 hour postop (RR 0.84; 95% CI 0.12 to 5.74; low quality evidence), and 2 hours postop (RR 1.09; 95% CI 0.59 to 2.01; low quality evidence) for nalbuphine versus morphine. Four trials compared nalbuphine with tramadol for postoperative pain; data from one trial (per outcome) revealed a lower but nonsignificant RR for the need of additional rescue analgesics in children receiving nalbuphine (RR 2 hours postop 0.75; 95% CI 0.39 to 1.43; low quality evidence) (RR 12 hours postop 0.33; 95% CI 0.04 to 2.77; low quality evidence). One out of three trials comparing nalbuphine with pethidine demonstrated that the RR was not significantly lower following nalbuphine administration compared to pethidine (RR 2 hours postop 1.07; 95% CI 0.52 to 2.23; low quality evidence) (RR 24 hours postop 1.13; 95% CI 0.52 to 2.44; very low quality evidence). The most common adverse event was postoperative nausea and vomiting (PONV). Only one included trial reported that the RR for PONV in the postoperative care unit (PACU) was not significantly higher following nalbuphine compared to placebo (RR 1.00; 95% CI 0.16 to 6.42; low quality evidence) nor to morphine (RR 1.33; 95% CI 0.64 to 2.77; low quality evidence).

AUTHORS' CONCLUSIONS

Because the overall quality of available evidence was low, this systematic review could not definitively show that the analgesic efficacy of nalbuphine is superior compared to placebo. Furthermore, due to the lack of significant results the comparison with other common opioids is also unclear. The same holds true for the evidence focusing on adverse events following nalbuphine compared to placebo or other opioid administration. The evidence is limited, because studies did not report conclusively all important postoperative pain outcomes (e.g. number of patients with the need for rescue analgesia, postoperative pain scores). Thus, a quantitative analysis was not possible for many major aspects (e.g. rescue analgesia, pain scores) and heterogeneity could not be further explored.

Reaction phenotyping of vinblastine metabolism in dogs

Vinblastine is a vinca alkaloid used either as a single agent or in combination therapy for the treatment of canine mast cell tumours and lymphomas. The objective of this study was to determine which isoform of cytochrome P450 enzyme is responsible for the majority of vinblastine metabolism in dogs. A panel of eight recombinant canine cytochrome P450 enzymes (CYP1A1, CYP1A2, CYP3A12, CYP3A26, CYP2B11, CYP2C41, CYP2C21 and CYP2D15) were incubated in vitro with vinblastine. Findings were confirmed by the use of canine polyclonal antibodies of cytochrome P450 enzymes (CYP1A1, CYP3A12, CYP2B11 and CYP2C21) that were pre-incubated with individual and pooled hepatic microsomes that were purified from canine liver. Substrate depletion was observed in the presence of recombinant CYP3A12, whereas depletion did not substantially occur when microsomes were pre-incubated with polyclonal antibodies against CYP3A12. These findings confirmed that CYP3A12 is the major cytochrome P450 isoform responsible for the metabolism of vinblastine in dogs.

A perspective on the prediction of drug pharmacokinetics and disposition in drug research and development

Prediction of human pharmacokinetics of new drugs, as well as other disposition attributes, has become a routine practice in drug research and development. Prior to the 1990s, drug disposition science was used in a mostly descriptive manner in the drug development phase. With the advent of in vitro methods and availability of human-derived reagents for in vitro studies, drug-disposition scientists became engaged in the compound design phase of drug discovery to optimize and predict human disposition properties prior to nomination of candidate compounds into the drug development phase. This has reaped benefits in that the attrition rate of new drug candidates in drug development for reasons of unacceptable pharmacokinetics has greatly decreased. Attributes that are predicted include clearance, volume of distribution, half-life, absorption, and drug-drug interactions. In this article, we offer our experience-based perspectives on the tools and methods of predicting human drug disposition using in vitro and animal data.

Protein expression profiling of nuclear membrane protein reveals potential biomarker of human hepatocellular carcinoma

Background

Complex molecular events lead to development and progression of liver cirrhosis to HCC. Differentially expressed nuclear membrane associated proteins are responsible for the functional and structural alteration during the progression from cirrhosis to carcinoma. Although alterations/ post translational modifications in protein expression have been extensively quantified, complementary analysis of nuclear membrane proteome changes have been limited. Deciphering the molecular mechanism that differentiate between normal and disease state may lead to identification of biomarkers for carcinoma.

Results

Many proteins displayed differential expression when nuclear membrane proteome of hepatocellular carcinoma (HCC), fibrotic liver, and HepG2 cell line were assessed using 2-DE and ESI-Q-TOF MS/MS. From the down regulated set in HCC, we have identified for the first time a 15 KDa cytochrome b5A (CYB5A), ATP synthase subunit delta (ATPD) and Hemoglobin subunit beta (HBB) with 11, 5 and 22 peptide matches respectively. Furthermore, nitrosylation studies with S-nitrosocysteine followed by immunoblotting with anti SNO-cysteine demonstrated a novel and biologically relevant post translational modification of thiols of CYB5A in HCC specimens only. Immunofluorescence images demonstrated increased protein S-nitrosylation signals in the tumor cells and fibrotic region of HCC tissues. The two other nuclear membrane proteins which were only found to be nitrosylated in case of HCC were up regulated ATP synthase subunit beta (ATPB) and down regulated HBB. The decrease in expression of CYB5A in HCC suggests their possible role in disease progression. Further insight of the functional association of the identified proteins was obtained through KEGG/ REACTOME pathway analysis databases. String 8.3 interaction network shows strong interactions with proteins at high confidence score, which is helpful in characterization of functional abnormalities that may be a causative factor of liver pathology.

Conclusion

These findings may have broader implications for understanding the mechanism of development of carcinoma. However, large scale studies will be required for further verification of their critical role in development and progression of HCC.

Utility of drug depletion-time profiles in isolated hepatocytes for accessing hepatic uptake clearance: identifying rate-limiting steps and role of passive processes

Drug depletion-time profiles in isolated hepatocytes, as well as microsomes, have become a standard method of assessing hepatic metabolic clearance in vitro. There is a previously described adaptation of the depletion approach to allow determination of hepatic uptake by transporters in addition to metabolism (Drug Metab Dispos 35:859-865, 2007). Dual incubations are performed where one set of incubations undergo conventional methodology, whereas for the second set, cells and media are separated for determination of drug loss from the media. The utility of this dual incubation approach has been assessed using eight drugs (atorvastatin, clarithromycin, erythromycin, fexofenadine, pitavastatin, repaglinide, rosuvastatin, and saquinavir) with a range of active uptake, passive permeability, cell binding, and metabolic characteristics. Four of these compounds (fexofenadine, rosuvastatin, pitavastatin, and atorvastatin) show a biphasic time profile when assessing drug loss from media indicative of hepatic uptake before elimination within the hepatocyte, which is distinct from the time profile in a conventional incubation, and show higher clearances. The four other compounds (clarithromycin, saquinavir, erythromycin, and repaglinide) show identical depletion-time profiles (and clearances) in both sets of incubations. Whether or not the biphasic nature (and higher clearance) is evident, indicating transporter activity for a particular drug, appears to be dependent on its passive permeability. Using the parameter K(pu) to reflect the relative importance of hepatic transporters versus passive diffusion, a value of 10 was identified as a cutoff for whether the biphasic nature was evident; those compounds in excess of 10 show this characteristic clearly. There appears to be no relationship between the presence of the biphasic nature and any other parameter, including cellular binding, extent of metabolism, or the magnitude of active uptake.

Applications of human pharmacokinetic prediction in first-in-human dose estimation

Quantitative estimations of first-in-human (FIH) doses are critical for phase I clinical trials in drug development. Human pharmacokinetic (PK) prediction methods have been developed to project the human clearance (CL) and bioavailability with reasonable accuracy, which facilitates estimation of a safe yet efficacious FIH dose. However, the FIH dose estimation is still very challenging and complex. The aim of this article is to review the common approaches for FIH dose estimation with an emphasis on PK-guided estimation. We discuss 5 methods for FIH dose estimation, 17 approaches for the prediction of human CL, 6 methods for the prediction of bioavailability, and 3 tools for the prediction of PK profiles. This review may serve as a practical protocol for PK- or pharmacokinetic/pharmacodynamic-guided estimation of the FIH dose.

Are there differences in the catalytic activity per unit enzyme of recombinantly expressed and human liver microsomal cytochrome P450 2C9? A systematic investigation into inter-system extrapolation factors

The 'relative activity factor' (RAF) compares the activity per unit of microsomal protein in recombinantly expressed cytochrome P450 enzymes (rhCYP) and human liver without separating the potential sources of variation (i.e. abundance of enzyme per mg of protein or variation of activity per unit enzyme). The dimensionless 'inter-system extrapolation factor' (ISEF) dissects differences in activity from those in CYP abundance. Detailed protocols for the determination of this scalar, which is used in population in vitro-in vivo extrapolation (IVIVE), are currently lacking. The present study determined an ISEF for CYP2C9 and, for the first time, systematically evaluated the effects of probe substrate, cytochrome b5 and methods for assessing the intrinsic clearance (CL(int) ). Values of ISEF for S-warfarin, tolbutamide and diclofenac were 0.75 ± 0.18, 0.57 ± 0.07 and 0.37 ± 0.07, respectively, using CL(int) values derived from the kinetic values V(max) and K(m) of metabolite formation in rhCYP2C9 + reductase + b5 BD Supersomes™. The ISEF values obtained using rhCYP2C9 + reductase BD Supersomes™ were more variable, with values of 7.16 ± 1.25, 0.89 ± 0.52 and 0.50 ± 0.05 for S-warfarin, tolbutamide and diclofenac, respectively. Although the ISEF values obtained from rhCYP2C9 + reductase + b5 for the three probe substrates were statistically different (p < 0.001), the use of the mean value of 0.54 resulted in predicted oral clearance values for all three substrates within 1.4 fold of the observed literature values. For consistency in the relative activity across substrates, use of a b5 expressing recombinant system, with the intrinsic clearance calculated from full kinetic data is recommended for generation of the CYP2C9 ISEF. Furthermore, as ISEFs have been found to be sensitive to differences in accessory proteins, rhCYP system specific ISEFs are recommended.

Metabolite formation kinetics and intrinsic clearance of phenacetin, tolbutamide, alprazolam, and midazolam in adenoviral cytochrome P450-transfected HepG2 cells and comparison with hepatocytes and in vivo

Cryopreserved human hepatocytes and other in vitro systems often underpredict in vivo intrinsic clearance (CL(int)). The aim of this study was to explore the potential utility of HepG2 cells transduced with adenovirus vectors expressing a single cytochrome P450 enzyme (Ad-CYP1A2, Ad-CYP2C9, or Ad-CYP3A4) for metabolic clearance predictions. The kinetics of metabolite formation from phenacetin, tolbutamide, and alprazolam and midazolam, selected as substrates probes for CYP1A2, CYP2C9, and CYP3A4, respectively, were characterized in this in vitro system. The magnitude of the K(m) or S(50) values observed in Ad-P450 cells was similar to those found in the literature for other human liver-derived systems. For each substrate, CL(int) (or CL(max)), values from Ad-P450 systems were scaled to human hepatocytes in primary culture using the relative activity factor (RAF) approach. Scaled Ad-P450 CL(int) values were approximately 3- to 6-fold higher (for phenacetin O-deethylation, tolbutamide 4-hydroxylation, and alprazolam 4-hydroxyaltion) or lower (midazolam 1'-hydroxylation) than those reported for human cryopreserved hepatocytes in suspension. Comparison with the in vivo data reveals that Ad-P450 cells provide a favorable prediction of CL(int) for the substrates studied (in a range of 20-200% in vivo observed CL(int)). This is an improvement compared with the consistent underpredictions (<10-50% in in vivo observed CL(int)) found in cryopreserved hepatocyte studies with the same substrates. These results suggest that the Ad-P450 cell is a promising in vitro system for clearance predictions of P450-metabolized drugs.

Prediction of pharmacokinetic drug-drug interaction caused by changes in cytochrome P450 activity using in vivo information

The aim of the present paper was to present an overview of the current status of the methods used to predict the magnitude of pharmacokinetic drug-drug interactions (DDIs) which are caused by apparent changes in cytochrome P450 (CYP) activity with an emphasis on a method using in vivo information. In addition, more than a hundred representative CYP substrates, inhibitor and inducer drugs involved in significant pharmacokinetic DDIs were selected from the literature and are listed. Although the magnitude of DDIs has been conventionally predicted based on in vitro experiments, their predictability is restricted occasionally due to several difficulties, including a precise determination of the unbound inhibitor concentrations at the enzyme site and a reliable in vitro measurement of the inhibition constant (K(i)). Alternatively, a simple method has been recently proposed for the prediction of the magnitude of DDIs based on information fully available from in vivo clinical studies. The new in vivo-based method would be applicable to the adjustment of dose regimens in actual pharmacotherapy situations although it requires a prior clinical study for the prediction. In this review, theoretical and quantitative relationships between the in vivo- and the in vitro-based prediction methods are considered. One of the interesting outcomes of the consideration is that the K(i)-normalized dose (dose/in vitro K(i)) of larger than approximately 20L (2-200L, when variability is considered) may be a pragmatic index which predicts significant in vivo DDIs. In the last part of the article, the relevance of the inclusion of the in vivo-based method into the process of new drug development is discussed for good prediction of in vivo DDIs.