Grapefruit juice enhances the bioavailability of the HIV protease inhibitor saquinavir in man

Food effects on gastrointestinal physiology and drug absorption

Food ingestion affects the oral absorption of many drugs in humans. In this review article, we summarize the physiological factors in the gastrointestinal (GI) tract that affect the in vivo performance of orally administered solid dosage forms in fasted and fed states in humans. In particular, we discuss the effects of food ingestion on fluid characteristics (pH, bile concentration, and volume) in the stomach and small intestine, GI transit of water and dosage forms, and microbiota. Additionally, case examples of food effects on GI physiology and subsequent changes in oral drug absorption are provided. Furthermore, the effects of food, especially fruit juices (e.g., grapefruit, orange, apple) and green tea, on transporter-mediated permeation and enzyme-catalyzed metabolism of drugs in intestinal epithelial cells are also summarized comprehensively.

Interactions of Antiretroviral Drugs with Food, Beverages, Dietary Supplements, and Alcohol: A Systematic Review and Meta-analyses

Multiple factors may affect combined antiretroviral therapy (cART). We investigated the impact of food, beverages, dietary supplements, and alcohol on the pharmacokinetic and pharmacodynamic parameters of 33 antiretroviral drugs. Systematic review in adherence to PRISMA guidelines was performed, with 109 reports of 120 studies included. For each drug, meta-analyses or qualitative analyses were conducted. We have found clinically significant interactions with food for more than half of antiretroviral agents. The following drugs should be taken with or immediately after the meal: tenofovir disoproxil, etravirine, rilpivirine, dolutegravir, elvitegravir, atazanavir, darunavir, lopinavir, nelfinavir, ritonavir, saquinavir. Didanosine, zalcitabine, zidovudine, efavirenz, amprenavir, fosamprenavir, and indinavir should be taken on an empty stomach for maximum patient benefit. Antiretroviral agents not mentioned above can be administered regardless of food. There is insufficient evidence available to make recommendations about consuming juice or alcohol with antiretroviral drugs. Resolving drug-food interactions may contribute to maximized cART effectiveness and safety.

Pharmacokinetic Outcomes of the Interactions of Antiretroviral Agents with Food and Supplements: A Systematic Review and Meta-Analysis

Because pharmacokinetic changes in antiretroviral drugs (ARV), due to their concurrent administration with food or nutritional products, have become a clinical challenge, it is necessary to monitor the therapeutic efficacy of ARV in people living with the human immunodeficiency virus (PLWH). A systematic review and meta-analysis were conducted to clarify the pharmacokinetic outcomes of the interaction between supplements such as food, dietary supplements, and nutrients, and ARV. Twenty-four articles in both healthy subjects and PLWH were included in the qualitative analysis, of which five studies were included in the meta-analysis. Food−drug coadministration significantly increased the time to reach maximum concentration (tmax) (p < 0.00001) of ARV including abacavir, amprenavir, darunavir, emtricitabine, lamivudine, zidovudine, ritonavir, and tenofovir alafenamide. In addition, the increased maximum plasma concentration (Cmax) of ARV, such as darunavir, under fed conditions was observed. Area under the curve and terminal half-life were not significantly affected. Evaluating the pharmacokinetic aspects, it is vital to clinically investigate ARV and particular supplement interaction in PLWH. Educating patients about any potential interactions would be one of the effective recommendations during this HIV epidemic.

Pharmacophore screening to identify natural origin compounds to target RNA-dependent RNA polymerase (RdRp) of SARS-CoV2

Several existing drugs have gained initial consideration due to their therapeutic characteristics against COVID-19 (Corona Virus Disease 2019). Hydroxychloroquine (HCQ) was proposed as possible therapy for shortening the duration of COVID-19, but soon after this, it was discarded. Similarly, known antiviral compounds were also proposed and investigated to treat COVID-19. We report a pharmacophore screening using essential chemical groups derived from HCQ and known antivirals to search a natural compound chemical space. Molecular docking of HCQ under physiological condition with spike protein, 3C-like protease (3CLpro), and RNA-dependent RNA polymerase (RdRp) of SARS-CoV2 showed - 8.52 kcal/mole binding score with RdRp, while the other two proteins showed relatively weaker binding affinity. Docked complex of RdRp-HCQ is further examined using 100 ns molecular dynamic simulation. Docking and simulation study confirmed active chemical moieties of HCQ, treated as 6-point pharmacophore to screen ZINC natural compound database. Pharmacophore screening resulted in the identification of potent hit molecule [(3S,3aR,6R,6aS)-3-(5-phenylsulfanyltetrazol-1-yl)-2,3,3a,5,6,6a-hexahydrofuro[3,2-b]furan-6-yl]N-naphthalen-ylcarbamate from natural compound library. Additionally, a set of antiviral compounds with similar chemical scaffolds are also used to design a separate ligand-based pharmacophore screening. Antiviral pharmacophore screening produced a potent hit 4-[(1,5-dimethyl-3-oxo-2-phenylpyrazol-4-yl)-(2-hydroxyphenyl)methyl]-1,5-dimethyl-2-phenylpyrazol-3-one containing essential moieties that showed affinity towards RdRp. Further, both these screened compounds are docked (- 8.69 and - 8.86 kcal/mol) and simulated with RdRp protein for 100 ns in explicit solvent medium. They bind at the active site of RdRp and form direct/indirect interaction with ASP618, ASP760, and ASP761 catalytic residues of the protein. Successively, their molecular mechanics Poisson Boltzmann surface area (MMPBSA) binding energies are calculated over the simulation trajectory to determine the dynamic atomistic interaction details. Overall, this study proposes two key natural chemical moieties: (a) tetrazol and (b) phenylpyrazol that can be investigated as a potential chemical group to design inhibitors against SARS-CoV2 RdRp.

Quantitative prediction of pharmacokinetic properties of drugs in humans: Recent advance in in vitro models to predict the impact of efflux transporters in the small intestine and blood-brain barrier

Efflux transport systems are essential to suppress the absorption of xenobiotics from the intestinal lumen and protect the critical tissues at the blood-tissue barriers, such as the blood-brain barrier. The function of drug efflux transport is dominated by various transporters. Accumulated clinical evidences have revealed that genetic variations of the transporters, together with coadministered drugs, affect the expression and/or function of transporters and subsequently the pharmacokinetics of substrate drugs. Thus, in the preclinical stage of drug development, quantitative prediction of the impact of efflux transporters as well as that of uptake transporters and metabolic enzymes on the pharmacokinetics of drugs in humans has been performed using various in vitro experimental tools. Various kinds of human-derived cell systems can be applied to the precise prediction of drug transport in humans. Mathematical modeling consisting of each intrinsic metabolic or transport process enables us to understand the disposition of drugs both at the organ level and at the level of the whole body by integrating a variety of experimental results into model parameters. This review focuses on the role of efflux transporters in the intestinal absorption and brain distribution of drugs, in addition to recent advances in predictive tools and methodologies.

Multi-material 3D printing of programmable and stretchable oromucosal patches for delivery of saquinavir

Oromucosal patches for drug delivery allow fast onset of action and ability to circumvent hepatic first pass metabolism of drugs. While conventional fabrication methods such as solvent casting or hot melt extrusion are ideal for scalable production of low-cost delivery patches, these methods chiefly allow for simple, homogenous patch designs. As alternative, a multi-material direct-ink-write 3D printing for rapid fabrication of complex oromucosal patches with unique design features was demonstrated in the present study. Specifically, three print-materials: an acidic saquinavir-loaded hydroxypropyl methylcellulose ink, an alkaline effervescent sodium carbonate-loaded ink, and a methyl cellulose backing material were combined in various designs. The CO₂ content and pH of the microenvironment were controlled by adjusting the number of alkaline layers in the patch. Additionally, the rigid and brittle patches were converted to compliant and stretchable patches by implementing mesh-like designs. Our results illustrate how 3D printing can be used for rapid design and fabrication of multifunctional or customized oromucosal patches with tailored dosages and changed drug permeation.

Interactions between antiretroviral therapy and complementary and alternative medicine: a narrative review

BACKGROUND

The use of complementary and alternative medicine including herbal medicine (phytotherapy), vitamins, minerals and food supplements is frequent among people living with HIV/AIDS (PLWHAs) who take antiretroviral (ARV) drugs, but is often not known by their prescribing physicians. Some drug-supplement combinations may result in clinically meaningful interactions.

AIMS

In this literature review, we aimed to investigate the evidence for complementary and alternative medicine interactions with ARVs.

SOURCES

A bibliographic search of all in vitro, human studies and case reports of the PubMed database was performed to assess the risk of interactions between complementary and alternative self-medication products and ARVs. The 'HIV drug interaction' (https://www.hiv-druginteractions.org) and 'Natural medicines comprehensive database' (https://naturalmedicines.therapeuticresearch.com) interaction checkers were also analysed.

CONTENT

St John's wort, some forms of garlic, grapefruit and red rice yeast are known to have significant interaction and thus should not be co-administered, or should be used with caution with certain ARV classes. Data on other plant-based supplements come from in vitro studies or very small size in vivo studies and are thus insufficient to conclude the real in vivo impact in case of concomitant administration with ARVs. Some polyvalent minerals such as calcium, magnesium, and iron salts can reduce the absorption of integrase inhibitors by chelation. Potential interactions with vitamin C and quercetin with some ARVs should be noted and efficacy and tolerance of the treatment should be monitored.

IMPLICATIONS

This review shows the importance of screening all PLWHAs for complementary and alternative medicine use to prevent treatment failure or adverse effects related to an interaction with ARVs. Further human studies are warranted to describe the clinical significance of in vitro interactions between numerous complementary and alternative medicine and ARVs.

The Segregated Intestinal Flow Model (SFM) for Drug Absorption and Drug Metabolism: Implications on Intestinal and Liver Metabolism and Drug-Drug Interactions

The properties of the segregated flow model (SFM), which considers split intestinal flow patterns perfusing an active enterocyte region that houses enzymes and transporters (<20% of the total intestinal blood flow) and an inactive serosal region (>80%), were compared to those of the traditional model (TM), wherein 100% of the flow perfuses the non-segregated intestine tissue. The appropriateness of the SFM model is important in terms of drug absorption and intestinal and liver drug metabolism. Model behaviors were examined with respect to intestinally (M1) versus hepatically (M2) formed metabolites and the availabilities in the intestine (F_I) and liver (F_H) and the route of drug administration. The %contribution of the intestine to total first-pass metabolism bears a reciprocal relation to that for the liver, since the intestine, a gateway tissue, regulates the flow of substrate to the liver. The SFM predicts the highest and lowest M1 formed with oral (po) and intravenous (iv) dosing, respectively, whereas the extent of M1 formation is similar for the drug administered po or iv according to the TM, and these values sit intermediate those of the SFM. The SFM is significant, as this drug metabolism model explains route-dependent intestinal metabolism, describing a higher extent of intestinal metabolism with po versus the much reduced or absence of intestinal metabolism with iv dosing. A similar pattern exists for drug–drug interactions (DDIs). The inhibitor or inducer exerts its greatest effect on victim drugs when both inhibitor/inducer and drug are given po. With po dosing, more drug or inhibitor/inducer is brought into the intestine for DDIs. The bypass of flow and drug to the enterocyte region of the intestine after intravenous administration adds complications to in vitro–in vivo extrapolations (IVIVE).

Review on Preclinical and Clinical Evidence of Food (Beverages, Fruits and Vegetables) and Drug Interactions: Mechanism and Safety

Background:

The therapeutic potency and efficacy of drugs can be affected by a patient’s dietary habit. The food composition and their nutritional value interact with drugs that lead to alteration of the therapeutic response of drugs in patients.

Objective:

This present review is an attempt to illustrate clinical reports of food-drug interaction. Further, it also highlights specific interaction mechanism(s) and the safety thereof.

Methods:

Through the search engine “Scopus”; literature on recent advances in food and drug interactions includes almost all therapeutic categories such as antimicrobials, antiviral, antifungal, antihistamines, anticoagulants, non-steroidal anti-inflammatory drugs, and drugs acting on the central nervous system and cardiovascular system.

Results:

Preclinical and clinical studies that have been conducted by various researchers affirm significant drug-food interactions across the various therapeutic categories of drugs. Preclinical studies have documented the effects of food, milk products, alcohols, fruit and vegetables on the drug absorption, metabolizing enzymes and drug transporters. The clinical studies on fruits/vegetables and drugs interactions report significant alteration in therapeutic response.

Conclusion:

Based on the preclinical and clinical reports, it can be concluded that the interaction of food with drug(s) significantly alters their therapeutic potential. The inputs from clinical practitioners to elucidate potential risk of food-drug interaction need to be intensified in order to prevent adverse clinical consequences.

Pharmacokinetic parameters of ifosfamide in mouse pre-administered with grapefruit juice or naringin

Grapefruit juice (GFJ) and naringin when consumed previously or together with medications may alter their bioavailavility and consequently the clinical effect. Ifosfamide (IF) is an antitumoral agent prescribed against various types of cancer. Nevertheless, there is no information regarding its interaction with the ingestion of GFJ or naringin. The aims of the present report were validating a method for the quantitation of IF in the plasma of mouse, and determine if mice pretreated with GFJ or naringin may modify the IF pharmacokinetics. Our HPLC results to quantify IF showed adequate intra and inter-day precision (RSD < 15%) and accuracy (RE < 15%) indicating reliability. Also, the administration of GFJ or naringin increased C_max of IF 22.9% and 17.8%, respectively, and decreased T_max of IF 19.2 and 53.8%, respectively. The concentration of IF was higher when GFJ (71.35 ± 3.5 µg/mL) was administered with respect to that obtained in the combination naringin with IF (64.12 ± µg/mL); however, the time required to reach such concentration was significantly lower when naringin was administered (p < 0.5). We concluded that pre-administering GFJ and naringin to mice increased the T_max and decreased the C_max of IF.

Grapefruit and its biomedical, antigenotoxic and chemopreventive properties

Grapefruit (Citrus paradisi Mcfad) is a perenifolium tree 5-6 m high with a fruit of about 15 cm in diameter, protected by the peel we can find about 11-14 segments (carpels), each of which is surrounded by a membrane and each containing the juice sacs, as well as the seeds. The fruit is made up of numerous compounds, and is known to have nutritive value because of the presence of various vitamins and minerals, among other chemicals. The fruit is also used in the field of gastronomy. Information has been accumulated regarding the participation of the fruit structures in a variety of biomedical, antigenotoxic and chemopreventive effects, surely related with the presence of the numerous chemicals that have been determined to constitute the fruit. Such studies have been carried out in different in vitro and in vivo experimental models, and in a few human assays. The information published so far has shown interesting results, therefore, the aims of the present review are to initially examine the main characteristics of the fruit, followed by systematization of the acquired knowledge concerning the biomedical, antigenotoxic and chemopreventive effects produced by the three main structures of the fruit: peel, seed, and pulp.

Phytotherapeutics: The Emerging Role of Intestinal and Hepatocellular Transporters in Drug Interactions with Botanical Supplements

In herbalism, botanical supplements are commonly believed to be safe remedies, however, botanical supplements and dietary ingredients interact with transport and metabolic processes, affecting drug disposition. Although a large number of studies have described that botanical supplements interfere with drug metabolism, the mode of their interaction with drug transport processes is not well described. Such interactions may result in serious undesired effects and changed drug efficacy, therefore, some studies on interaction between botanical supplement ingredients and drug transporters such as P-gp and OATPs are described here, suggesting that the interaction between botanical supplements and the drug transporters is clinically significant.

Quercetin nanoparticles alter pharmacokinetics of bromocriptine, reflecting its enhanced inhibitory action on liver and intestinal CYP 3A enzymes in rats

1. Quercetin is a dietary flavonoid has extremely low water solubility and found to possess CYP3A inhibitory activity. The purpose of the present study was to evaluate the effect of quercetin and quercetin nanoparticles (NQC) on the pharmacokinetics of bromocriptine (BRO) in rats. 2. NQC prepared by antisolvent precipitation method and characterized by SEM and dissolution test. The following methods were used in this study i.e. in vitro liver and intestinal CYP3A microsomal activity and in vitro non-everted sac method. To confirm these findings, an in vivo pharmacokinetic study was also performed. 3. The results indicate that quercetin significantly (p < 0.05) inhibited the CYP3A activity in liver and intestinal microsomes. In non-everted sac study, the intestinal transport and P_app of BRO were significantly increased in NQC and quercetin groups. Furthermore, in vivo study revealed that the increased levels of C_max and AUC were comparatively high in NQC pretreated group than quercetin group. In addition, pretreatment with quercetin and NQC significantly (p < 0.05) decreased the mean CL/F and Vd/F of BRO. 4. NQC pretreatment might be result in higher plasma levels of quercetin that could inhibit the CYP3A enzyme and enhanced the bioavailability of BRO.

Unequivocal evidence supporting the segregated flow intestinal model that discriminates intestine versus liver first-pass removal with PBPK modeling

Merits of the segregated flow model (SFM), highlighting the intestine as inert serosa and active enterocyte regions, with a smaller fractional (f_Q < 0.3) intestinal flow (Q_I ) perfusing the enterocyte region, are described. Less drug in the circulation reaches the enterocytes due to the lower flow (f_Q Q_I ) in comparison with drug administered into the gut lumen, fostering the idea of route-dependent intestinal removal. The SFM has been found superior to the traditional model (TM), which views the serosa and enterocytes totally as a well-mixed tissue perfused by 100% of the intestinal flow, Q_I . The SFM model is able to explain the lower extents of intestinal metabolism of enalapril, morphine and midazolam with i.v. vs. p.o. dosing. For morphine, the urine/bile ratio of the metabolite, morphine glucuronide MGurineMGbile for p.o. was 2.6× that of i.v. This was due to the higher proportion of intestinally formed morphine glucuronide, appearing more in urine than in bile due to its low permeability and greater extent of intestinal formation with p.o. administration. By contrast, the TM predicted the same MGurineMGbile for p.o. vs. i.v. The TM predicted that the contributions of the intestine:liver to first-pass removal were 46%:54% for both p.o. and i.v. The SFM predicted same 46%:54% (intestine:liver) for p.o., but 9%:91% for i.v. By contrast, the kinetics of codeine, the precursor of morphine, was described equally well by the SFM- and TM-PBPK models, a trend suggesting that intestinal metabolism of codeine is negligible. Fits to these PBPK models further provide insightful information towards metabolite formation: available fractions and the fractions of hepatic and total clearances that form the metabolite in question. The SFM-PBPK model is useful to identify not only the presence of intestinal metabolism but the contributions of the intestine and liver for metabolite formation. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of resveratrol on P-glycoprotein and cytochrome P450 3A in vitro and on pharmacokinetics of oral saquinavir in rats

Background

The intestinal cytochrome P450 3A (CYP 3A) and P-glycoprotein (P-gp) present a barrier to the oral absorption of saquinavir (SQV). Resveratrol (RESV) has been indicated to have modulatory effects on P-gp and CYP 3A. Therefore, this study was to investigate the effects of RESV on P-gp and CYP 3A activities in vitro and in vivo on oral SQV pharmacokinetics in rats.

Methods

In vitro, intestinal microsomes were used to evaluate RESV effect on CYP 3A-mediated metabolism of SQV; MDR1-expressing Madin–Darby canine kidney (MDCKII-MDR1) cells were employed to assess the impact of RESV on P-gp-mediated efflux of SQV. In vivo effects were studied using 10 rats randomly assigned to receive oral SQV (30 mg/kg) with or without RESV (20 mg/kg). Serial blood samples were obtained over the following 24 h. Concentrations of SQV in samples were ascertained using high-performance liquid chromatography-tandem mass spectrometry analysis.

Results

RESV (1–100 μM) enhanced residual SQV (% of control) in a dose-dependent manner after incubation with intestinal microsomes. RESV (1–100 μM) reduced the accumulation of SQV in MDCKII-MDR1 cells in a concentration-dependent manner. A double peaking phenomenon was observed in the plasma SQV profiles in rats. The first peak of plasma SQV concentration was increased, but the second peak was reduced by coadministration with RESV. The mean AUC_0–∞ of SQV was slightly decreased, with no statistical significance probably due to the high individual variation.

Conclusion

RESV can alter the plasma SQV concentration profiles, shorten the T_max of SQV. RESV might also cause a slight decrease tendency in the SQV bioavailability in rats.

Drug interactions in HIV treatment: complementary & alternative medicines and over-the-counter products

INTRODUCTION

Use of complementary and alternative medicines (CAMs) and over-the-counter (OTC) medications are very common among HIV-infected patients. These products can cause clinically significant drug-drug interactions (DDIs) with antiretroviral (ARV) medications, thereby increasing risk for negative outcomes such as toxicity or loss of virologic control. Areas covered: This article provides an updated review of the different mechanisms by which CAM and OTC products are implicated in DDIs with ARV medications. Expert commentary: Much of the literature published to date involves studies of CAMs interacting with older ARV agents via the cytochrome P450 (CYP450) system. However, the HIV treatment and prevention arsenal is continually evolving. Furthermore, our elucidation of the role of non-CYP450 mediated DDIs with ARV medications is greatly increasing. Therefore, clinicians are well served to understand the various mechanisms and extent by which new ARV therapies may be involved in drug interactions with CAMs and OTC medications.

An update on the role of intestinal cytochrome P450 enzymes in drug disposition

Oral administration is the most commonly used route for drug treatment. Intestinal cytochrome P450 (CYP)-mediated metabolism can eliminate a large proportion of some orally administered drugs before they reach systemic circulation, while leaving the passage of other drugs unimpeded. A better understanding of the ability of intestinal P450 enzymes to metabolize various clinical drugs in both humans and preclinical animal species, including the identification of the CYP enzymes expressed, their regulation, and the relative importance of intestinal metabolism compared to hepatic metabolism, is important for improving bioavailability of current drugs and new drugs in development. Here, we briefly review the expression of drug-metabolizing P450 enzymes in the small intestine of humans and several preclinical animal species, and provide an update of the various factors or events that regulate intestinal P450 expression, including a cross talk between the liver and the intestine. We further compare various clinical and preclinical approaches for assessing the impact of intestinal drug metabolism on bioavailability, and discuss the utility of the intestinal epithelium–specific NADPH-cytochrome P450 reductase-null (IECN) mouse as a useful model for studying in vivo roles of intestinal P450 in the disposition of orally administered drugs.

Indication of nerve growth factor binding components from herbal extracts by HerboChip: a platform for drug screening on a chip

Background

HerboChip is an array of different fractions deriving from herbal extracts. This study aimed to identify effective components from Chinese medicine (CM) that interact with nerve growth factor (NGF) as a target using HerboChip.

Methods

Fifty types of CM that are traditionally used as remedies for emotion imbalance were selected and extracted with 50 % ethanol. Biotinylated-NGF was hybridized with over 300 chips coated with different HPLC-separated fractions from CM extracts and straptavidin-Cy5 was used to identify the NGF-bound fractions.

Results

Over 300 chips were screened within a week, and 17 positive hits were identified. The interaction of the identified herbal extracts with NGF was confirmed in cultured PC12 cells. Co-application of NGF and herbal extract interfered with NGF-induced expression of neurofilaments, including NF68 and NF200 in cell cultures. Western blot analysis comparing the intensity of phosphorylated cAMP response element-binding protein (CREB) over total CREB showed NGF-induced CREB phosphorylation was modulated by the identified herbal extracts. Five CM herbs showed activating activities on the NGF response and nine CM herbs showed inhibiting activities.

Conclusion

The current result supported the applicability of HerboChip for screening NGF binding components from herbal extracts.

Electronic supplementary material

The online version of this article (doi:10.1186/s13020-016-0107-8) contains supplementary material, which is available to authorized users.

Grapefruit-Drug Interactions: Can Interactions With Drugs Be Avoided?

Grapefruit is rich in flavonoids, which have been demonstrated to have a preventive influence on many chronic diseases, such as cancer and cardiovascular disease. However, since the early 1990s, the potential health benefits of grapefruit have been overshadowed by the possible risk of interactions between drugs and grapefruit and grapefruit juice. Several drugs interacting with grapefruit are known in different drug classes, such as HMG-CoA reductase inhibitors, calcium antagonists, and immunosuppressives. Currently known mechanisms of interaction include the inhibition of cytochrome P450 as a major mechanism, but potential interactions with P-glycoprotein and organic anion transporters have also been reported. This review is designed to provide a comprehensive summary of underlying mechanisms of interaction and human clinical trials performed in the area of grapefruit drug interactions and to point out possible replacements for drugs with a high potential for interactions.

Drug-Drug, Drug-Dietary Supplement, and Drug-Citrus Fruit and Other Food Interactions: What Have We Learned?

Serious drug-drug interactions have contributed to recent U.S. market withdrawals and also recent nonapprovals of a few new molecular entities. Many of these interactions involved the inhibition or induction of metabolizing enzymes and efflux transporters, resulting in altered systemic exposure and adverse drug reactions or loss of efficacy. In addition to drug-drug interactions, drug-dietary supplement and drug-citrus fruit interactions, among others, could also cause adverse drug reactions or loss of efficacy and are important issues to consider in the evaluation of new drug candidates. This commentary reviews (1). the current understanding of the mechanistic basis of these interactions, (2). issues to consider in the interpretation of study results, and (3). recent labeling examples to illustrate the translation of study results to information useful for patients and health care providers.

A physiologically based pharmacokinetic (PBPK) approach to evaluate pharmacokinetics in patients with cancer

Potential differences in pharmacokinetics (PK) between healthy subjects and patients with cancer were investigated using a physiologically based pharmacokinetic approach integrating demographic and physiological data from patients with cancer. Demographic data such as age, sex and body weight, and clinical laboratory measurements such as albumin, alpha-1 acid glycoprotein (AAG) and hematocrit were collected in ~2500 patients with cancer. A custom oncology population profile was built using the observed relationships among demographic variables and laboratory measurements in Simcyp® software, a population based ADME simulator. Patients with cancer were older compared with the age distribution in a built-in healthy volunteer profile in Simcyp. Hematocrit and albumin levels were lower and AAG levels were higher in patients with cancer. The custom population profile was used to investigate the disease effect on the pharmacokinetics of two probe substrates, saquinavir and midazolam. Higher saquinavir exposure was predicted in patients relative to healthy subjects, which was explained by the altered drug binding due to elevated AAG levels in patients with cancer. Consistent with historical clinical data, similar midazolam exposure was predicted in patients and healthy subjects, supporting the hypothesis that the CYP3A activity is not altered in patients with cancer. These results suggest that the custom oncology population profile is a promising tool for the prediction of PK in patients with cancer. Further evaluation and extension of this population profile with more compounds and more data will be needed.

Effect of grapefruit juice and ritonavir on pharmacokinetics of lopinavir in Wistar rats

Lopinavir (LPV), a newer HIV protease inhibitor, has poor bioavailability being a substrate of both cytochrome P450 3A enzyme system (CYP3A) and permeability-glycoprotein (P-gp). Ritonavir (RTV) is a known inhibitor of both P-gp and CYP3A and is co-administered with LPV in anti-HIV therapy. Grapefruit juice (GFJ) is known to inhibit CYP3A and has conflicting effects, ranging from activation to inhibition, on P-gp. In this research work, the effects of GFJ and RTV on the pharmacokinetics of LPV were compared in rats. A mechanistic evaluation was undertaken using various in vitro and ex vivo studies to support the in vivo pharmacokinetic data. The plasma levels of LPV were found to increase significantly upon co-administration with GFJ in single dose as well as multidose pretreatment studies. Similar, but marginally higher, results were observed upon co-administration of LPV with RTV. No significant change in t(max) was observed in the various treatment groups. The apparent permeability of LPV in the ileum increased significantly after the pre-incubation with GFJ and RTV compared with no pre-incubation. The GFJ and RTV showed a significant and similar inhibitory effect on rat intestinal microsomes in the metabolism of LPV. The GFJ was equally effective as RTV in increasing the bioavailability of LPV.

Modeling of absorption

Absorption takes place when a compound enters an organism, which occurs as soon as the molecules enter the first cellular bilayer(s) in the tissue(s) to which is it exposed. At that point, the compound is no longer part of the environment (which includes the alimentary canal for oral exposure), but has become part of the organism. If absorption is prevented or limited, then toxicological effects are also prevented or limited. Thus, modeling absorption is the first step in simulating/predicting potential toxicological effects. Simulation software used to model absorption of compounds of various types has advanced considerably over the past 15 years. There can be strong interactions between absorption and pharmacokinetics (PK), requiring state-of-the-art simulation computer programs that combine absorption with either compartmental pharmacokinetics (PK) or physiologically based pharmacokinetics (PBPK). Pharmacodynamic (PD) models for therapeutic and adverse effects are also often linked to the absorption and PK simulations, providing PK/PD or PBPK/PD capabilities in a single package. These programs simulate the interactions among a variety of factors including the physicochemical properties of the molecule of interest, the physiologies of the organisms, and in some cases, environmental factors, to produce estimates of the time course of absorption and disposition of both toxic and nontoxic substances, as well as their pharmacodynamic effects.

Food-drug interaction of tacrolimus with pomelo, ginger, and turmeric juice in rats

Tacrolimus is a well-known potent immunosuppressant agent, which has various drug-drug or food-drug interactions. Previously, we found a renal transplant recipient who increased tacrolimus blood concentrations after ingestion of pomelo as a rare case. So, we investigated the effect of pomelo after its administration for one day or 3 consecutive days on the pharmacokinetics of tacrolimus in rats. We also confirmed the effects of grapefruit, turmeric, and ginger. The tacrolimus blood concentrations of the rats pre-treated with 100% pomelo juice were significantly higher than those pre-treated with water. On the other hand, the tacrolimus blood concentrations of the rats pre-treated with 50% pomelo juice were not significantly different from those pre-treated with water. The pomelo-tacrolimus interaction showed concentration dependency. Even low concentration of pomelo juice could enhance the blood concentrations of tacrolimus by repeated administration. The inhibitory effect of 100% pomelo juice disappeared 3 days after intake. The AUC values of tacrolimus in the rats pre-treated with grapefruit juice, ginger juice, and turmeric juice were significantly larger than those pre-treated with water. We could confirm the pomelo-tacrolimus interaction, which we discovered in a case study, quantitatively. We newly found the influence of turmeric and ginger on tacrolimus pharmacokinetics, comparable to pomelo.

Novel natural inhibitors of CYP1A2 identified by in silico and in vitro screening

Inhibition of cytochrome P450 (CYP) is a major cause of herb–drug interactions. The CYP1A2 enzyme plays a major role in the metabolism of drugs in humans. Its broad substrate specificity, as well as its inhibition by a vast array of structurally diverse herbal active ingredients, has indicated the possibility of metabolic herb–drug interactions. Therefore nowadays searching inhibitors for CYP1A2 from herbal medicines are drawing much more attention by biological, chemical and pharmological scientists. In our work, a pharmacophore model as well as the docking technology is proposed to screen inhibitors from herbal ingredients data. Firstly different pharmaphore models were constructed and then validated and modified by 202 herbal ingredients. Secondly the best pharmaphore model was chosen to virtually screen the herbal data (a curated database of 989 herbal compounds). Then the hits (147 herbal compounds) were continued to be filtered by a docking process, and were tested in vitro successively. Finally, five of eighteen candidate compounds (272, 284, 300, 616 and 817) were found to have inhibition of CYP1A2 activity. The model developed in our study is efficient for in silico screening of large herbal databases in the identification of CYP1A2 inhibitors. It will play an important role to prevent the risk of herb–drug interactions at an early stage of the drug development process.

Grapefruit-drug interactions

Grapefruit juice and grapefruit product consumption have potential health benefits; however, their intake is also associated with interactions with certain drugs, including calcium channel blockers, immunosuppressants and antihistamines. The primary mechanism through which interactions are mediated is mechanism-based intestinal cytochrome P450 3A4 inhibition by furanocoumarins resulting in increased bioavailability of administered medications that are substrates. Grapefruit products have also been associated with interactions with P-glycoprotein (P-gp) and uptake transporters (e.g. organic anion-transporting polypeptides [OATPs]). Polyphenolic compounds such as flavonoids have been proposed as the causative agents of the P-gp and OATP interactions. The mechanisms and magnitudes of the interactions can be influenced by the concentrations of furanocoumarins and flavonoids in the grapefruit product, the volume of juice consumed, and the inherent variability of specific enzymes and transporter components in humans. It is therefore challenging to predict the extent of grapefruit product-drug interactions and to compare available in vitro and in vivo data. The clinical significance of such interactions also depends on the disposition and toxicity profile of the drug being administered. The aim of this review is to outline the mechanisms of grapefruit-drug interactions and present a comprehensive summary of those agents affected and whether they are likely to be of clinical relevance.

Biological effects of Byrsocarpus coccineus in vitro

CONTEXT

Byrsocarpus coccineus Schum. and Thonn. (Connaraceae) is a scandent shrub widely employed as a medicinal remedy for various disease conditions in West Africa.

OBJECTIVE

This study evaluated fractions of B. coccineus for modulation of cytochrome P450 (CYP) enzyme activity, cytokine production, and proliferation.

MATERIALS AND METHODS

The BROD (benzyloxyresorufin O-debenzylase) and BFCOD (benzyloxy-4-[trifluoromethyl]-coumarin O-debenzyloxylase) assays were used to evaluate effect on CYP2B1/2 and CYP3A4 enzyme activity. Effects on cytokine production and proliferation of HT29 cells were investigated using interferon expression assay and MTT (3-3[4,5-dimethyl-2-thiazolyl]-2-5-diphenyl-2H-tetrazolium bromide) assay, respectively.

RESULTS

Fractions derived from the organic solvent extraction of B. coccineus produced significant (p<0.05) stimulation of human hepatic CYP2B1/2 activity in the BROD assay. The greatest effects were elicited at 1 ng/mL corresponding to ∼ 3-fold stimulation of enzyme activity. Enhancement of CYP3A4 enzyme activity was also observed in the BFCOD assay. Other fractions from the organic extract showed significant antiproliferative effects on HT29 cells at 100 μg/mL. Fractions obtained from the aqueous extract of B. coccineus (1 µg/µL) significantly stimulated the expression of IFNα2a and IFNβ in peripheral blood mononuclear cells (PBMC), causing a maximum 26-fold increase of IFNα2a-transcript.

DISCUSSION AND CONCLUSION

The effect on CYP suggests that B. coccineus may reduce the therapeutic efficacy of co-administered drugs. This justifies the need for proper education of patients by healthcare practitioners on the outcomes of drug-herb interactions. This study identifies several in vitro activities that could underlie the attributed uses of this plant in traditional African medicine (TAM).

The effect of grapefruit juice on drug disposition

INTRODUCTION

Since their initial discovery in 1989, grapefruit juice (GFJ)-drug interactions have received extensive interest from the scientific, medical, regulatory and lay communities. Although knowledge regarding the effects of GFJ on drug disposition continues to expand, the list of drugs studied in the clinical setting remains relatively limited.

AREAS COVERED

This article reviews the in vitro effects of GFJ and its constituents on the activity of CYP enzymes, organic anion-transporting polypeptides (OATPs), P-glycoprotein, esterases and sulfotransferases. The translational applicability of the in vitro findings to the clinical setting is discussed for each drug metabolizing enzyme and transporter. Reported AUC ratios for available GFJ-drug interaction studies are also provided. Relevant investigations were identified by searching the PubMed electronic database from 1989 to 2010.

EXPERT OPINION

GFJ increases the bioavailability of some orally administered drugs that are metabolized by CYP3A and normally undergo extensive presystemic extraction. In addition, GFJ can decrease the oral absorption of a few drugs that rely on OATPs in the gastrointestinal tract for their uptake. The number of drugs shown to interact with GFJ in vitro is far greater than the number of clinically relevant GFJ-drug interactions. For the majority of patients, complete avoidance of GFJ is unwarranted.

Inhibition of in-vitro simvastatin metabolism in rat liver microsomes by bergamottin, a component of grapefruit juice

Grapefruit juice can modify the pharmacokinetic parameters of many drugs, in particular simvastatin, an orally active cholesterol-lowering agent. The exact components in grapefruit juice responsible for drug interactions are not perfectly known. However, it seems that bergamottin, a furocoumarin derivative, is one of the main active components within grapefruit juice. The objective of this paper was to quantify and to characterize in-vitro the inhibitory effect of bergamottin on simvastatin metabolism by using rat and human liver microsomes. In rat liver microsomes, the incubation conditions (± NADPH) of bergamottin were found to influence its inhibiting capacity. In co-incubation with simvastatin, the Ki value (the equilibrium dissociation constant for the enzyme-inhibitor complex) was higher (Ki = 174±36 μm) than in pre-incubation (Ki =45±6 μm and 4±2μm, without and with NADPH, respectively). It thus seems that the pre-incubation of bergamottin (in particular with NADPH) increases its inhibiting capacity on simvastatin metabolism. Bergamottin metabolism study in rat liver microsomes showed the formation of two metabolites that were CYP-450 dependent. In contrast, in human liver microsomes, the incubation conditions of bergamottin did not influence its inhibiting capacity of simvastatin metabolism (Ki = 34±5 μm, Ki = 22±5 μm, Ki = 27±11 μm in co-incubation and pre-incubation without and with NADPH, respectively). In rat and man, bergamottin was found to be a mixed-type inhibitor of simvastatin hepatic metabolism. However, in rat, bergamottin was partially a mechanism-based inhibitor by involvement of either bergamottin alone or one of its metabolites. The results highlight the importance of validating in-vitro models to help verify the suitability of the in-vitro model for predicting the nature and degree of metabolic drug interactions.

Cytochrome P450-mediated metabolism in the human gut wall

Objective

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

Key findings

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

Summary

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