Potent Inhibition of Human Cytochrome P450 3A4, 2D6, and 2C9 Isoenzymes by Grapefruit Juice and Its Furocoumarins

Abemaciclib pharmacology and interactions in the treatment of HR+/HER2- breast cancer: a critical review

Abemaciclib (ABE) in combination with endocrine therapy represents the mainstay treatment for either endocrine-resistant metastatic or high-risk early-stage HR+/HER2- breast cancer patients. Hence, an adequate knowledge of this agent pharmacodynamic, pharmacokinetic, and of its drug-drug interactions (DDIs) is crucial for an optimal patients management. Additionally, ABE interference with food and complementary/alternative medicines should be taken into account in the clinical practice. Several online tools allow to freely check DDIs and can be easily consulted before prescribing ABE. According to one of this instruments, ABE display the lowest number of interactions among the available cyclin-dependent kinase 4/6 inhibitors. Still, clinicians should be aware that online tools cannot replace the technical datasheet of the drug as well as a comprehensive clinical assessment for each patient. Here we critically review the main pharmacological features of ABE, then focusing on its potential interactions with drugs, food, and alternative medicine, in order to provide a guide for its optimal use in the treatment of HR+/HER2- breast cancer patients.

Bergaptol, a Major Furocoumarin in Citrus: Pharmacological Properties and Toxicity

Bergaptol (5-hydroxypsoralen or 5-hydroxyfuranocoumarin) is a naturally occurring furanocoumarin widely found in citrus fruits, which has multiple health benefits. Nonetheless, no specific review articles on bergaptol have been published. Compiling updated information on bergaptol is crucial in guiding future research direction and application. The present review focuses on the research evidence related to the pharmacological properties and toxicity of bergaptol. Bergaptol has anti-inflammatory, antioxidant, anti-cancer, anti-osteoporosis, anti-microbial, and anti-lipidemic effects. It can inhibit the activities of cytochrome P450s (CYP), especially CYP2C9 and CYP3A4, thereby affecting the metabolism and concentrations of some drugs and toxins. Compared with other coumarins, bergaptol has the least potency to inhibit CYP3A4 in cancer cells. Instead, it can suppress drug efflux transporters, such as P-glycoprotein, thereby overcoming chemotherapeutic drug resistance. Furthermore, bergaptol has antimicrobial effects with a high potential for inhibition of quorum sensing. In vivo, bergaptol can be retained in plasma for longer than other coumarins. Nevertheless, its toxicity has not been clearly reported. In vitro study suggests that, unlike most furocoumarins, bergaptol is not phototoxic or photomutagenic. Existing research on bergaptol has mostly been conducted in vitro. Further in vivo and clinical studies are warranted to identify the safe and effective doses of bergaptol for its multimodal application.

Basic concepts of mixture toxicity and relevance for risk evaluation and regulation

Exposure to multiple substances is a challenge for risk evaluation. Currently, there is an ongoing debate if generic "mixture assessment/allocation factors" (MAF) should be introduced to increase public health protection. Here, we explore concepts of mixture toxicity and the potential influence of mixture regulation concepts for human health protection. Based on this analysis, we provide recommendations for research and risk assessment. One of the concepts of mixture toxicity is additivity. Substances may act additively by affecting the same molecular mechanism within a common target cell, for example, dioxin-like substances. In a second concept, an "enhancer substance" may act by increasing the target site concentration and aggravating the adverse effect of a "driver substance". For both concepts, adequate risk management of individual substances can reliably prevent adverse effects to humans. Furthermore, we discuss the hypothesis that the large number of substances to which humans are exposed at very low and individually safe doses may interact to cause adverse effects. This commentary identifies knowledge gaps, such as the lack of a comprehensive overview of substances regulated under different silos, including food, environmentally and occupationally relevant substances, the absence of reliable human exposure data and the missing accessibility of ratios of current human exposure to threshold values, which are considered safe for individual substances. Moreover, a comprehensive overview of the molecular mechanisms and most susceptible target cells is required. We conclude that, currently, there is no scientific evidence supporting the need for a generic MAF. Rather, we recommend taking more specific measures, which focus on compounds with relatively small ratios between human exposure and doses, at which adverse effects can be expected.

Caffeinated drinks, fruit juices, and epilepsy: A systematic review

The aim of this systematic review was to provide the required information regarding different aspects of the relationship between epilepsy/antiseizure medications and non-alcoholic drinks. The recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement were followed. MEDLINE and Scopus from the inception until 7 August 2021 were systematically searched. These key words were used: "epilepsy" OR "seizure" OR "antiepileptic" OR "antiseizure" OR "anticonvulsant" AND "coffee" OR "tea" OR "soda" OR "juice" OR "drink" OR "cola" OR "diet" (35 key word combinations). The primary search yielded 21 458 publications (PubMed, n = 4778; Scopus, n = 16 680). Only 50 studies met all the inclusion criteria and were included in the current systematic review. In total, 17 articles investigated various non-alcoholic drinks in human studies, 11 studies were case reports/series, and 22 articles were animal/in vitro studies. None of the studies provided a class 1 of evidence. There is limited evidence suggesting that certain drinks (eg, caffeinated energy drinks) might trigger seizures. Patients with epilepsy should avoid excessive consumption of certain fruit juices (eg, grapefruit, lime, pomegranate, kinnow, and star fruit) and caffeinated drinks. However, daily coffee and tea intake can be part of a healthy balanced diet, and their consumption does not need to be stopped in patients with epilepsy. Coffee/tea consumption is not harmful if consumed at levels of 200 mg (caffeine) in one sitting (about 2½ cups of coffee) or 400 mg daily (about five cups of coffee).

Analysis of inhibition kinetics of three beverage ingredients, bergamottin, dihydroxybergamottin and resveratrol, on CYP2C9 activity

Some grapefruit juice (GFJ) ingredients and resveratrol, a fruit-derived phytoalexin, are known to inhibit cytochrome P450 (CYP) 2C9. However, their inhibition modes and detailed inhibition kinetics remain undetermined. This study aimed to investigate the inhibitory effects of two GFJ ingredients, bergamottin (BG) and dihydroxybergamottin (DHB), and resveratrol on CYP2C9 activity in vitro. DHB inhibited CYP2C9 activity, as assessed by warfarin 7-hydroxylation, in a preincubation time-dependent manner (i.e., mechanism-based inhibition; MBI), in the same manner as CYP2C19 and CYP3A4. The maximal inactivation rate (k_inact,max) was 0.0638 min^-1 and 0.12- and 0.26-fold of that for CYP2C19 and CYP3A4, respectively. BG showed both MBI and time-independent competitive inhibition. Resveratrol showed non-competitive inhibition with an inhibition constant (K_i) of 3.64 μM. Unlike the inhibition of CYP2C19 and CYP3A4, resveratrol did not induce MBI. These findings are important for estimating the risk of drug interactions between CYP2C9 substrates and some beverages. (146 words).

Mechanistic study of bergamottin-induced inactivation of CYP2C9

Bergamottin (BGM) is a major furanocoumarin constituent of grapefruit and is reported to have inhibitory effects on cytochrome P450 enzymes. This study investigated the chemical interactions between BGM and the enzyme CYP2C9. BGM exhibited time-, concentration-, and NADPH-dependent inhibition of CYP2C9. Co-incubation with diclofenac, a reversible inhibitor of CYP2C9, attenuated the time-dependent enzyme inhibition. Exhaustive dialysis did not restore enzyme activity post-inhibition. Glutathione (GSH) and catalase/superoxide dismutase failed to reverse BGM-induced CYP2C9 inactivation. A GSH trapping study suggested that BGM was metabolized to an epoxide and/or γ-ketoenal that may have been responsible for the enzyme inactivation. In conclusion, BGM can be characterized as a mechanism-based inactivator of CYP2C9 acting via the formation of an epoxide and/or γ-ketoenal.

Mechanism-based inactivation of cytochrome P450 enzymes by natural products based on metabolic activation

Cytochrome P450 enzymes (P450 enzymes) are the most common and important phase I metabolic enzymes and are responsible for the majority of the metabolism of clinical drugs and other xenobiotics. Drug-drug interactions (DDIs) can occur when the activities of P450 enzymes are inhibited. In particular, irreversible inhibition of P450 enzymes may lead to severe adverse interactions, compared to reversible inhibition. Many natural products have been shown to be irreversible inhibitors of P450 enzymes. The risks for intake of naturally occurring irreversible P450 enzyme inhibitors have been rising due to the rapid growth of the global consumption of natural products. Irreversible inhibition is usually called mechanism-based inactivation, which is time-, concentration- and NADPH- dependent. Generally, the formation of electrophilic intermediates is fundamental for the inactivation of P450 enzymes. This review comprehensively classifies natural P450 enzyme inactivators, including terpenoids, phenylpropanoids, flavonoids, alkaloids, and quinones obtained from herbs or foods. Moreover, the structure - activity correlations according to the IC₅₀ (or K_i) values reported in the literature as well as the underlying mechanisms based on metabolic activation are highlighted in depth.

Curcumin ameliorates duodenal toxicity of AFB1 in chicken through inducing P-glycoprotein and downregulating cytochrome P450 enzymes

It has been reported that oral intake of aflatoxin B1 (AFB1)-contaminated feed could cause acute, sub-chronic, or chronic toxicity in livestock and poultry. However, the harmful effect of AFB1 on the small intestine is still controversial. Therefore, blocking the entry of AFB1 into the body through the digestive tract is one of the important methods to prevent its toxicity. In the present study, 1-day-old Arbor Acres broilers were randomly divided into 6 groups including control group, curcumin control group (450 mg curcumin/kg feed), curcumin low-, medium-, and high-dose group (150, 300, and 450 mg curcumin/kg feed + 5 mg AFB1/kg feed), and AFB1 group (5 mg AFB1/kg feed). After 28 d, the samples of chickens' duodenums were collected for further analyses. AFB1 caused abnormal functional and morphological changes in the duodenum, including histological lesions, increased the length of the duodenum and depth of crypt, decreased the unit weight of the duodenum, height of villus, and the value of villus height/crypt depth. Meanwhile, AFB1 administration enhanced malonaldehyde activity, 8-HOdG level, and the mRNA expression of cytochrome P450 (CYP450) enzymes, and reduced superoxide dismutase, catalase, adenosine triphosphatase (ATPase) activity and the mRNA expression of Abcb1. Importantly, curcumin supplementation partially ameliorated AFB1-induced abnormal functional and morphological signs of the duodenum, alleviated AFB1-induced oxidative stress, and decreased the mRNA expression of CYP450 enzymes. Furthermore, curcumin ameliorated AFB1-induced decrease in the Abcb1 mRNA expression, P-glycoprotein (P-gp) level, and ATPase activities. It has been suggested from these results that curcumin supplementation in the feed could ameliorate AFB1-induced duodenal toxicity and damage through downregulating CYP450 enzymes, promoting ATPase activities, and inducing P-gp in chickens.

Inhibitory effects of polyphenols and their colonic metabolites on CYP2D6 enzyme using two different substrates

Polyphenolic compounds (including flavonoids, chalcones, phenolic acids, and furanocoumarins) represent a common part of our diet, but are also the active ingredients of several dietary supplements and/or medications. These compounds undergo extensive metabolism by human biotransformation enzymes and the microbial flora of the colon. CYP2D6 enzyme metabolizes approximately 25% of the drugs, some of which has narrow therapeutic window. Therefore, its inhibition can lead to the development of pharmacokinetic interactions and the disruption of drug therapy. In this study, the inhibitory effects of 17 plant-derived compounds and 19 colonic flavonoid metabolites on CYP2D6 were examined, employing two assays with different test substrates. The O-demethylation of dextromethorphan was tested employing CypExpress 2D6 kit coupled to HPLC analysis; while the O-demethylation of another CYP2D6 specific substrate (AMMC) was investigated in a plate reader assay with BioVision Fluorometric CYP2D6 kit. Interestingly, some compounds (e.g., bergamottin) inhibited both dextromethorphan and AMMC demethylation; however, certain substances proved to be inhibitors only in one of the assays applied. Our results demonstrate that some polyphenols and colonic metabolites are inhibitors of CYP2D6-catalyzed reactions. Nevertheless, the inhibitory effects showed strong substrate dependence.

Chimeric cytochrome P450 3A4 used for in vitro prediction of food-drug interactions

Inhibition of cytochrome P450 (CYP)-mediated drug metabolism by dietary substances is the main cause of drug-food interactions in humans. The present study reports on the in vitro inhibition assays of human CYP3A4 genetically linked to the reductase domain of bacterial BM3 of Bacillus megaterium (BMR) resulting in the chimeric protein CYP3A4-BMR. The activity of this chimeric enzyme was initially measured colorimetrically with erythromycin as the substrate where K_M values similar to published data were determined. Subsequently, the inhibition assays with three different dietary products, grapefruit juice, curcumin, and resveratrol, were carried out with the chimeric enzyme both in solution and immobilized on electrode surfaces. For the solution studies, nicotinamide adenine dinucleotide phosphate was added as the electron donor, whereas the need for this cofactor was obviated in the immobilized enzyme as it was supplied by the electrode. Inhibition of the N-demethylation of erythromycin by CYP3A4-BMR chimera was measured at increasing concentrations of the different dietary compounds with calculated IC₅₀ values of 0.5%, 31 μM, and 250 μM for grapefruit juice, curcumin, and resveratrol measured in solution compared with 0.7%, 24 μM, and 208 μM measured electrochemically, respectively. These data demonstrate the feasibility of the use of both CYP3A4-BMR chimera as well as bioelectrochemistry for in vitro studies of not only drug-food interactions but also prediction of adverse drug reactions in this important P450 enzyme.

Angelicin-A Furocoumarin Compound With Vast Biological Potential

Angelicin, a member of the furocoumarin group, is related to psoralen which is well known for its effectiveness in phototherapy. The furocoumarins as a group have been studied since the 1950s but only recently has angelicin begun to come into its own as the subject of several biological studies. Angelicin has demonstrated anti-cancer properties against multiple cell lines, exerting effects via both the intrinsic and extrinsic apoptotic pathways, and also demonstrated an ability to inhibit tubulin polymerization to a higher degree than psoralen. Besides that, angelicin too demonstrated anti-inflammatory activity in inflammatory-related respiratory and neurodegenerative ailments via the activation of NF-κB pathway. Angelicin also showed pro-osteogenesis and pro-chondrogenic effects on osteoblasts and pre-chondrocytes respectively. The elevated expression of pro-osteogenic and chondrogenic markers and activation of TGF-β/BMP, Wnt/β-catenin pathway confirms the positive effect of angelicin bone remodeling. Angelicin also increased the expression of estrogen receptor alpha (ERα) in osteogenesis. Other bioactivities, such as anti-viral and erythroid differentiating properties of angelicin, were also reported by several researchers with the latter even displaying an even greater aptitude as compared to the commonly prescribed drug, hydroxyurea, which is currently on the market. Apart from that, recently, a new application for angelicin against periodontitis had been studied, where reduction of bone loss was indirectly caused by its anti-microbial properties. All in all, angelicin appears to be a promising compound for further studies especially on its mechanism and application in therapies for a multitude of common and debilitating ailments such as sickle cell anaemia, osteoporosis, cancer, and neurodegeneration. Future research on the drug delivery of angelicin in cancer, inflammation and erythroid differentiation models would aid in improving the bioproperties of angelicin and efficacy of delivery to the targeted site. More in-depth studies of angelicin on bone remodeling, the pro-osteogenic effect of angelicin in various bone disease models and the anti-viral implications of angelicin in periodontitis should be researched. Finally, studies on the binding of angelicin toward regulatory genes, transcription factors, and receptors can be done through experimental research supplemented with molecular docking and molecular dynamics simulation.

Synthesis of Spin-Labelled Bergamottin: A Potent CYP3A4 Inhibitor with Antiproliferative Activity

Bergamottin (BM, 1), a component of grapefruit juice, acts as an inhibitor of some isoforms of the cytochrome P450 (CYP) enzyme, particularly CYP3A4. Herein, a new bergamottin containing a nitroxide moiety (SL-bergamottin, SL-BM, 10) was synthesized; chemically characterized, evaluated as a potential inhibitor of the CYP2C19, CYP3A4, and CYP2C9 enzymes; and compared to BM and known inhibitors such as ketoconazole (KET) (3A4), warfarin (WAR) (2C9), and ticlopidine (TIC) (2C19). The antitumor activity of the new SL-bergamottin was also investigated. Among the compounds studied, BM showed the strongest inhibition of the CYP2C9 and 2C19 enzymes. SL-BM is a more potent inhibitor of CYP3A4 than the parent compound; this finding was also supported by docking studies, suggesting that the binding positions of BM and SL-BM to the active site of CYP3A4 are very similar, but that SL-BM had a better ∆G_bind value than that of BM. The nitroxide moiety markedly increased the antitumor activity of BM toward HeLa cells and marginally increased its toxicity toward a normal cell line. In conclusion, modification of the geranyl sidechain of BM can result in new CYP3A4 enzyme inhibitors with strong antitumor effects.

Effects of dibutyl phthalate and di(2-ethylhexyl) phthalate with their metabolites on CYP2C9*1 and CYP2C19*1 activities in vitro

The aim of this article is to assess the effect of phthalates on the activities of CYP2C9 and CYP2C19 in vitro. In this study, recombinant CYP2C9*1 and CYP2C19*1 microsomes were used to investigate the effects of phthalates and their metabolites on corresponding enzyme activities in vitro. 2-100 μM substrate of enzyme was incubated with series concentration of phthalates for 30 min at 37 °C. The metabolic products were detected using ultra-high performance liquid chromatography (UHPLC) and ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS/MS) methods. The results showed dibutyl phthalate (DBP) significantly inhibited CYP2C9*1 with an activity inhibition rate of 67.3% and half-maximal inhibitory concentration (IC50) of 29.63 μmol L^-1, but its metabolite monobutyl phthalate (MBP) had no significant effect. On the other hand, di(2-ethylhexyl)phthalate (DEHP) had no effect on CYP2C9*1, but its metabolite monoethylhexyl phthalate (MEHP) significantly inhibited the enzyme activity with an activity inhibition rate of 90.6% and IC50 of 6.37 μmol L^-1. With regards to CYP2C19*1, DBP completely inhibited the enzyme activity with an activity inhibition rate of 100% and IC50 of 2.63 μmol L^-1, but its metabolite MBP had no effect on it. DEHP and MEHP also inhibited the activity of CYP2C19*1. Further investigation showed MEHP was a competitive inhibitor of CYP2C9*1 (Ki = 7.063 μmol L^-1), and DBP was a competitive inhibitor of CYP2C19*1 (Ki = 7.013 μmol L^-1) against their substrates, both phthalates were non-competitive inhibitors of the cofactor NADPH. Our results suggested that DBP, DEHP, and their metabolites exhibited significant inhibitory effects toward either CYP2C9*1 or CYP2C19*1. These findings provided valuable information for a potentially toxic mechanism of DEHP and DBP on endocrine disruption and a useful guidance for safe and effective usage of drugs in patients with long-term DEHP and DBP exposure.

Protective effects of curcumin against aflatoxicosis: A comprehensive review

Aflatoxicosis is a deleterious medical condition that results from aflatoxins (AFs) or ochratoxins (OTs). Contamination with these toxins exerts detrimental effects on the liver, kidneys, reproductive organs, and also on immunological and cardiovascular systems. Aflatoxicosis is closely associated with overproduction of reactive oxygen species (ROS) as key contributors to oxidative and nitrosative stress responses, and subsequent damages to lipids, proteins, RNA, and DNA. The main target organ for AF toxicity is the liver, where DNA adducts, degranulation of endoplasmic reticulum, increased hepatic lipid peroxide, GSH depletion, mitochondrial dysfunction, and reduction of enzymatic and non-enzymatic antioxidants are manifestations of aflatoxicosis. Curcuma longa L. (turmeric) is a medicinal plant widely utilized all over the world for culinary and phytomedical purposes. Considering the antioxidant characteristic of curcumin, the main active component of turmeric, this review is intended to critically summarize the available evidence supporting possible effectiveness of curcumin against aflatoxicosis. Curcumin can serve as a promising candidate for attenuation of the adverse consequences of aflatoxicosis, acting mainly through intrinsic antioxidant effects aroused from its structure, modulation of the immune system as reflected by interleukin-1β and transforming growth factor-β, and interfering with AF's biotransformation by cytochrome P450 isoenzymes CYP1A, CYP3A, CYP2A, CYP2B, and CYP2C.

Simvastatin in combination with bergamottin potentiates TNF-induced apoptosis through modulation of NF-κB signalling pathway in human chronic myelogenous leukaemia

Context Simvastatin (SV) and bergamottin (BGM) are known to exhibit diverse anti-cancer and anti-inflammatory activities. Objective Very little is known about the potential efficacy of combination of these two agents to potentiate TNF-induced apoptosis in human chronic myelogenous leukaemia (CML). Materials and methods In the present study, we investigated whether SV combined with BGM mediates its effect through suppression of NF-κB-signalling pathway. Results We found that the combination treatment enhanced cytotoxicity and potentiated the apoptosis induced by TNF as indicated by intracellular esterase activity, Annexin V staining and caspase activation. This effect of co-treatment correlated with down-regulation of various gene products that mediate cell proliferation (cyclin D1), cell survival (cIAP-1, Bcl-2, Bcl-xL and Survivin), invasion (MMP-9) and angiogenesis (VEGF); all known to be regulated by NF-κB. SV combined with BGM also produced TNF-induced cell-cycle arrest in S-phase and this arrest correlated with a concomitant increase in the levels of cyclin-dependent inhibitor p21 and p27. The combination therapy inhibited TNF-induced NF-κB activation, IκBα degradation and p65 translocation to the nucleus as compared with the treatment with individual agents alone. Besides, SV combined with BGM did not significantly potentiate apoptotic effect induced by TNF in p65(-)(/)(-) cells, as compared with wild-type fibroblasts. Discussion and conclusion Our results provide novel insight into the role of SV and BGM in potentially preventing and treating cancer through modulation of NF-κB signalling pathway and its regulated gene products.

Individualized Hydrocodone Therapy Based on Phenotype, Pharmacogenetics, and Pharmacokinetic Dosing

OBJECTIVES

(1) To quantify hydrocodone (HC) and hydromorphone (HM) metabolite pharmacokinetics with pharmacogenetics in CYP2D6 ultra-rapid metabolizer (UM), extensive metabolizer (EM), and poor metabolizer (PM) metabolizer phenotypes. (2) To develop an HC phenotype-specific dosing strategy for HC that accounts for HM production using clinical pharmacokinetics integrated with pharmacogenetics for patient safety.

SETTING

In silico clinical trial simulation.

PARTICIPANTS

Healthy white men and women without comorbidities or history of opioid, or any other drug or nutraceutical use, age 26.3±5.7 years (mean±SD; range, 19 to 36 y) and weight 71.9±16.8 kg (range, 50 to 108 kg).

MAIN OUTCOME MEASURES

CYP2D6 phenotype-specific HC clinical pharmacokinetic parameter estimates and phenotype-specific percentages of HM formed from HC.

RESULTS

PMs had lower indices of HC disposition compared with UMs and EMs. Clearance was reduced by nearly 60% and the t1/2 was increased by about 68% compared with EMs. The canonical order for HC clearance was UM>EM>PM. HC elimination mainly by the liver, represented by ke, was reduced about 70% in PM. However, HC's apparent Vd was not significantly different among UMs, EMs, and PM. The canonical order of predicted plasma HM concentrations was UM>EM>PM. For each of the CYP2D6 phenotypes, the mean predicted HM levels were within HM's therapeutic range, which indicates HC has significant phenotype-dependent pro-drug effects.

CONCLUSIONS

Our results demonstrate that pharmacogenetics afford clinicians an opportunity to individualize HC dosing, while adding enhanced opportunity to account for its conversion to HM in the body.

Modulation of Hepatic Cytochrome P450 Enzymes by Curcumin and its Pharmacokinetic Consequences in Sprague-dawley Rats

Background:

Curcumin (CUR) is a polyphenolic component derived from an herbal remedy and dietary spice turmeric (Curcuma longa).

Objective:

The aim of this study was to investigate inhibitory effects of CUR on in vitro cytochrome P450 (CYP) activity and in vivo pharmacokinetic consequences of single CUR dose in rats.

Materials and Methods:

An in vitro CYP inhibition study in rat liver microsomes (RLM) was conducted using probe substrates for CYPs. Then, an in vivo pharmacokinetics of intravenous buspirone (BUS), a probe substrate for CYP3A, was studied with the concurrent administration of oral CUR in rats.

Results:

In the in vitro CYP inhibition study, CUR inhibited the CYP3A-mediated metabolism of testosterone (TES) with a half maximal inhibitory concentration of 11.0 ± 3.3 μM. However, the impact of a single oral CUR dose on the pharmacokinetics of BUS in rats is limited, showing that CUR cannot function as an inhibitor for CYP3A-mediated drug metabolism in vivo.

Conclusion:

To the best of our knowledge, our results are the first reported data regarding the inhibition of in vitro CYP3A-mediated metabolism of TES and the in vivo impact of a single CUR dose on the pharmacokinetics of BUS in rats. Further study is required to draw a confirmative conclusion on whether CUR can be a clinically relevant CYP3A4 inhibitor.

SUMMARY

CUR can inhibit the in vitro CYP3A-mediated metabolism of TES in RLM. However, the impact of a single oral CUR dose on the pharmacokinetics of BUS in rats is limited, showing that CUR cannot function as an inhibitor for CYP3A-mediated drug metabolism in vivo.

Modulation of Cytochrome P450 Activity by 18β-Glycyrrhetic Acid and its Consequence on Buspirone Pharmacokinetics in Rats

The aim of this study was to elucidate the inhibition mechanism of 18β-glycyrrhetic acid (GLY) on cytochrome P450 (CYP) activity and in vivo pharmacokinetic consequences of single GLY dose in rats. An in vitro CYP inhibition study in rat liver microsomes (RLM) was conducted using probe substrates for CYPs. Then, an in vivo pharmacokinetics of intravenous and oral buspirone (BUS), a probe substrate for CYP3A, was studied with the concurrent administration of oral GLY in rats. In the in vitro CYP inhibition study, CYP3A was involved in the metabolism of GLY. Moreover, GLY inhibited CYP3A activity with an IC50 of 20.1 ± 10.7 μM via a mixed inhibition mechanism. In the in vivo rat pharmacokinetic study, single oral GLY dose enhanced the area under plasma concentration-time curve (AUC) of intravenous and oral BUS, but the extent of increase in AUC was only minimal (1.12-1.45 fold). These results indicate that GLY can inhibit the in vitro CYP3A-mediated drug metabolism in RLM via a mixed inhibition mechanism. However, the impact of single oral GLY dose on the pharmacokinetics of BUS in rats was limited, showing that GLY could function as merely a weak inhibitor for CYP3A-mediated drug metabolism in vivo. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of lyophilized grapefruit juice on P-glycoprotein-mediated drug transport in-vitro and in-vivo

The administration of grapefruit juice (GFJ) has been postulated to inhibit the activity of P-glycoprotein (P-gp) transport system and thus can enhance the uptake of substrate drugs. However, for various reasons, the results obtained have been always swaying between confirmation and refutation. This study aims at re-evaluating the effect of lyophilized freshly-prepared grapefruit juice (LGFJ) prepared from the whole peeled fruit on P-gp activity using the model drug doxorubicin (DOX) in-vitro and timolol maleate (TM) in-vivo. Human uterine sarcoma MES-SA/DX5v cells, grown under nanomolar concentration of DOX and highly expressing P-gp, were used as model cells for in-vitro studies whereas white New Zealand male rabbits were used for in-vivo studies. Results showed that the accumulation of DOX in MES-SA/DX5v cells was increased by 18.3 ± 2.0% in presence of LGFJ compared to control experiments. Results from in-vivo absorption studies showed that the relative oral bioavailability of TM ingested with LGFJ was significantly higher by 70% and 43% compared to the oral bioavailability of TM ingested with saline and a commercial GFJ, respectively. This study as such confirms the inhibitory effects of LGFJ on P-gp efflux proteins and highlights the superiority of using lyophilized freshly prepared juices over the commercially available juices in research studies. Also, the results call for further studies to assess the possibility of co-administrating LGFJ with anti-cancer agents to modulate multidrug resistance in their cellular environment or incorporating LGFJ in solid dosage forms to improve oral bioavailability of drugs.

Diclofenac prolongs repolarization in ventricular muscle with impaired repolarization reserve

BACKGROUND

The aim of the present work was to characterize the electrophysiological effects of the non-steroidal anti-inflammatory drug diclofenac and to study the possible proarrhythmic potency of the drug in ventricular muscle.

METHODS

Ion currents were recorded using voltage clamp technique in canine single ventricular cells and action potentials were obtained from canine ventricular preparations using microelectrodes. The proarrhythmic potency of the drug was investigated in an anaesthetized rabbit proarrhythmia model.

RESULTS

Action potentials were slightly lengthened in ventricular muscle but were shortened in Purkinje fibers by diclofenac (20 µM). The maximum upstroke velocity was decreased in both preparations. Larger repolarization prolongation was observed when repolarization reserve was impaired by previous BaCl(2) application. Diclofenac (3 mg/kg) did not prolong while dofetilide (25 µg/kg) significantly lengthened the QT(c) interval in anaesthetized rabbits. The addition of diclofenac following reduction of repolarization reserve by dofetilide further prolonged QT(c). Diclofenac alone did not induce Torsades de Pointes ventricular tachycardia (TdP) while TdP incidence following dofetilide was 20%. However, the combination of diclofenac and dofetilide significantly increased TdP incidence (62%). In single ventricular cells diclofenac (30 µM) decreased the amplitude of rapid (I(Kr)) and slow (I(Ks)) delayed rectifier currents thereby attenuating repolarization reserve. L-type calcium current (I(Ca)) was slightly diminished, but the transient outward (I(to)) and inward rectifier (I(K1)) potassium currents were not influenced.

CONCLUSIONS

Diclofenac at therapeutic concentrations and even at high dose does not prolong repolarization markedly and does not increase the risk of arrhythmia in normal heart. However, high dose diclofenac treatment may lengthen repolarization and enhance proarrhythmic risk in hearts with reduced repolarization reserve.

Opioid therapies and cytochrome p450 interactions

Adverse drug reactions are common and associated with substantial economic and human costs. Particularly among older adult populations, preventable adverse drug reactions are often caused by drug-drug interactions. All analgesics have side effect profiles and many have known drug-drug interactions. Opioids are recognized as a necessary option for managing moderate-to-severe pain, yet many opioid side effects can be enhanced by metabolic interactions within the liver, involving other drugs, diseases, or genetics.

The clinical implications of cytochrome p450 interactions with opioids and strategies for pain management

Pharmacokinetic differences among opioids influence a patient's response to opioid treatment. An important element affecting a drug's pharmacokinetics, its metabolism, may be altered under various circumstances, thereby enhancing or mitigating a patient's response to opioids. The genetic background of the metabolic enzymes involved in opioid metabolism, comorbid medical conditions, older age, and the presence of other drugs that influence metabolism are such factors that can cause the response to opioid therapy to vary greatly from the expected response to a standard dose. As a result of the variability in individual responses to opioids, clinical management of pain with opioids must be empirical.

Effect of ciprofloxacin and grapefruit juice on oral pharmacokinetics of riluzole in Wistar rats

Objectives

The objective of this study was to explore potential drug–drug/food interactions of ciprofloxacin and grapefruit juice, known hepatic cytochrome P450 (CYP) 1A2 inhibitors, on single-dose oral pharmacokinetics of riluzole, a substrate of CYP 1A2 enzymes.

Methods

Pharmacokinetic parameters of riluzole were determined in Wistar rats after single-dose co-administration with ciprofloxacin and grapefruit juice. In-vitro metabolic inhibition studies using rat and human liver microsomes and intestinal absorption studies of riluzole in a rat everted gut-sac model were conducted to elucidate the mechanism of interaction. A validated HPLC method was employed to quantify riluzole in the samples obtained in various studies.

Key findings

Co-administration of ciprofloxacin with riluzole caused significant increase in systemic exposure of riluzole (area under the curve, maximum plasma concentration and mean residence time were found to increase). Co-administration of grapefruit juice with riluzole did not cause any significant difference in the pharmacokinetic parameters of riluzole. In-vitro metabolism studies demonstrated significant inhibition of riluzole metabolism when it was co-incubated with ciprofloxacin or grapefruit juice. No significant change was observed in apparent permeability of riluzole.

Conclusions

Co-administration of ciprofloxacin with riluzole increases the systemic levels of riluzole and thereby the oral pharmacokinetic properties of riluzole while co-administration of grapefruit juice with riluzole has no significant effect.

Role of intestinal cytochrome p450 enzymes in diclofenac-induced toxicity in the small intestine

The aim of this study was to determine the role of small intestinal (SI) cytochrome P450 (P450) enzymes in the metabolic activation of diclofenac (DCF), a widely used nonsteroidal anti-inflammatory drug, and DCF-induced intestinal toxicity. DCF induces intestinal ulcers in humans and mice, but the underlying mechanisms, including the necessity for drug bioactivation in the target tissues and the sources and identities of reactive intermediates, are not fully understood. We found that the number of DCF-induced (at 50 mg/kg p.o.) intestinal ulcers was significantly smaller in an intestinal epithelium (IE)-specific P450 reductase (CPR) knockout (IE-Cpr-null) mouse model, which has little P450 activity in the IE, than in wild-type (WT) mice, determined at 14 h after DCF administration. The involvement of intestinal P450 enzymes was confirmed by large reductions (>80-90%) in the rates of in vitro formation, in SI microsomal reactions, of hydroxylated DCF metabolites and reactive intermediates, trapped as DCF-glutathione (GSH) conjugates, in the IE-Cpr-null, compared with WT mice. The SI levels of DCF-GSH conjugates (at 4 h after dosing) and DCF-protein adducts (at 14 h after dosing) were significantly lower in IE-Cpr-null than in WT mice. In additional experiments, we found that pretreatment of mice with grapefruit juice, which is known to inhibit SI P450 activity, ameliorated DCF-induced intestinal toxicity in WT mice. Our results not only strongly support the notion that SI P450 enzymes play an important role in DCF-induced intestinal toxicity, but also illustrate the possibility of preventing DCF-induced intestinal toxicity through dietary intervention.

[Extensive mesenteric ischemia related to naratriptan overuse associated with grapefruit juice absorption]

We reported the case of a 61-year-old woman, who has been hospitalized in ICU because of an extensive mesenteric ischaemia, involving the small bowel, secondary to a naratriptan overuse. This mesenteric ischaemia was complicated by multiple organ failure and was responsible for extensive small bowel resection and left colectomy. A concomitant abundant absorption of grapefruit juice, a well-known P450 inhibitor, may have enhanced this naratriptan toxicity. This case underscore that an abdominal pain occurring in the context of headache treatment may be related to a mesenteric ischaemia.

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.

Transporter-mediated drug-drug interactions

Drug-drug interactions are a serious clinical issue. An important mechanism underlying drug-drug interactions is induction or inhibition of drug transporters that mediate the cellular uptake and efflux of xenobiotics. Especially drug transporters of the small intestine, liver and kidney are major determinants of the pharmacokinetic profile of drugs. Transporter-mediated drug-drug interactions in these three organs can considerably influence the pharmacokinetics and clinical effects of drugs. In this article, we focus on probe drugs lacking significant metabolism to highlight mechanisms of interactions of selected intestinal, hepatic and renal drug transporters (e.g., organic anion transporting polypeptide [OATP] 1A2, OATP2B1, OATP1B1, OATP1B3, P-gp, organic anion transporter [OAT] 1, OAT3, breast cancer resistance protein [BCRP], organic cation transporter [OCT] 2 and multidrug and toxin extrusion protein [MATE] 1). Genotype-dependent drug-drug interactions are also discussed.

Oral agents in cancer treatment: the context for adherence

OBJECTIVES

To review oral agents approved for cancer, discuss their mechanism of action and/or molecular targets, and outline side effects and challenges that impact adherence.

DATA SOURCES

Peer reviewed literature and on-line drug information.

CONCLUSION

Oral agents to treat cancer, although not new, are common and increasing dramatically. The context of adherence to oral agents is complicated by increased knowledge of food-drug interactions and combinations of agents with overlapping or synergistic toxicity profiles.

IMPLICATIONS FOR NURSING PRACTICE

The role of nursing in the administration and education of oral cancer treatments is critical to optimal treatment outcomes.

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).

Important drug–nutrient interactions

Drugs have the potential to interact with nutrients potentially leading to reduced therapeutic efficacy of the drug, nutritional risk or increased adverse effects of the drug. Despite significant interest in such interactions going back to over more than 40 years, the occurrence and clinical significance of many drug–nutrient interactions remains unclear. However, interactions involving drugs with a narrow therapeutic margin such as theophylline and digoxin and those that require careful blood monitoring such as warfarin are likely to be those of clinical significance. Drugs can affect nutrition as a result of changes in appetite and taste as well as having an influence on absorption or metabolism of nutrients. Moreover, foods and supplements can also interact with drugs, of which grapefruit juice and St John's wort are key examples. Significant numbers of people take both supplements and medication and are potentially at risk from interactions. Professionals, such as pharmacists, dietitians, nurses and doctors, responsible for the care of patients should therefore check whether supplements are being taken, while for researchers this is an area worthy of significant further study, particularly in the context of increasingly complex drug regimens and the plethora of new drugs.

Silymarin modulates doxorubicin-induced oxidative stress, Bcl-xL and p53 expression while preventing apoptotic and necrotic cell death in the liver

The emergence of silymarin (SMN) as a natural remedy for liver diseases, coupled with its entry into NIH clinical trial, signifies its hepatoprotective potential. SMN is noted for its ability to interfere with apoptotic signaling while acting as an antioxidant. This in vivo study was designed to explore the hepatotoxic potential of Doxorubicin (Dox), the well-known cardiotoxin, and in particular whether pre-exposures to SMN can prevent hepatotoxicity by reducing Dox-induced free radical mediated oxidative stress, by modulating expression of apoptotic signaling proteins like Bcl-xL, and by minimizing liver cell death occurring by apoptosis or necrosis. Groups of male ICR mice included Control, Dox alone, SMN alone, and Dox with SMN pre/co-treatment. Control and Dox groups received saline i.p. for 14 days. SMN was administered p.o. for 14 days at 16 mg/kg/day. An approximate LD(50) dose of Dox, 60 mg/kg, was administered i.p. on day 12 to animals receiving saline or SMN. Animals were euthanized 48 h later. Dox alone induced frank liver injury (>50-fold increase in serum ALT) and oxidative stress (>20-fold increase in malondialdehyde [MDA]), as well as direct damage to DNA (>15-fold increase in DNA fragmentation). Coincident genomic damage and oxidative stress influenced genomic stability, reflected in increased PARP activity and p53 expression. Decreases in Bcl-xL protein coupled with enhanced accumulation of cytochrome c in the cytosol accompanied elevated indexes of apoptotic and necrotic cell death. Significantly, SMN exposure reduced Dox hepatotoxicity and associated apoptotic and necrotic cell death. The effects of SMN on Dox were broad, including the ability to modulate changes in both Bcl-xL and p53 expression. In animals treated with SMN, tissue Bcl-xL expression exceeded control values after Dox treatment. Taken together, these results demonstrated that SMN (i) reduced, delayed onset, or prevented toxic effects of Dox which are typically associated with hydroxyl radical production, (ii) performed as an antioxidant limiting oxidative stress, (iii) protected the integrity of the genome, and (iv) antagonized apoptotic and necrotic cell death while increasing antiapoptotic Bcl-xL protein levels and minimizing the leakage of proapoptotic cytochrome c from liver mitochondria. These observations demonstrate the protective actions of SMN in liver, and raise the possibility that such protection may extend to other organs during Dox treatment including the heart.

[Severe overdose in vitamin K antagonist secondary to grapefruit juice absorption]

Vitamin K antagonists (VKA) are very currently used. Nevertheless, they are known to interact with numerous drugs and foods. Grapefruit juice is known to interact with some drugs metabolized by the enterocytary cytochrome P450 3A4 but its interaction with drugs as VKA that have a good biodisponibility is not clearly demonstrated. We report here the case of a woman treated with VKA in whom massive absorption of grapefruit juice entailed an excessive VKA dosage and a severe haemorrhage.

Opioid metabolism

Clinicians understand that individual patients differ in their response to specific opioid analgesics and that patients may require trials of several opioids before finding an agent that provides effective analgesia with acceptable tolerability. Reasons for this variability include factors that are not clearly understood, such as allelic variants that dictate the complement of opioid receptors and subtle differences in the receptor-binding profiles of opioids. However, altered opioid metabolism may also influence response in terms of efficacy and tolerability, and several factors contributing to this metabolic variability have been identified. For example, the risk of drug interactions with an opioid is determined largely by which enzyme systems metabolize the opioid. The rate and pathways of opioid metabolism may also be influenced by genetic factors, race, and medical conditions (most notably liver or kidney disease). This review describes the basics of opioid metabolism as well as the factors influencing it and provides recommendations for addressing metabolic issues that may compromise effective pain management. Articles cited in this review were identified via a search of MEDLINE, EMBASE, and PubMed. Articles selected for inclusion discussed general physiologic aspects of opioid metabolism, metabolic characteristics of specific opioids, patient-specific factors influencing drug metabolism, drug interactions, and adverse events.

Dose-response relationship for the pharmacokinetic interaction of grapefruit juice with dextromethorphan investigated by human urinary metabolite profiles

Grapefruit juice (GFJ) has been shown to affect the pharmacokinetics of a large number of drugs, essentially by inhibition of efflux transporters and CYP3A4 monooxygenase in the small intestine. The GFJ dose usually used in human studies was one glass single-strength (1x). Information on a respective dose-response relationship is not available. We investigated the effect of GFJ of different concentration (0.25 x, 0.5x, 1x, 2x) dosed in biweekly intervals in 19 volunteers. Components considered responsible for drug interactions, naringin, naringenin, bergamottin, and 6',7'-dihydroxybergamottin were determined by LC-tandem mass spectrometry. Immediately after ingestion of GFJ, participants took an aqueous solution of dextromethorphan (DEX) as probe drug. Urine was collected in two sampling periods, 0-2 and 2-4h, and excreted amounts of DEX and five metabolites associated with CYP3A4 and/or CYP2D6 enzyme activity were determined. Effects of GFJ were analyzed by the Wilcoxon matched-pairs signed-rank test against an average of four water control experiments. Two effects were highly significant: (i) a delay of total metabolite excretion in the first 2h and (ii) an inhibition of the CYP3A4-dependent metabolic pathways. Effect magnitude and significance levels were dose-dependent and indicated 200 ml 1x GFJ as "lowest observed effect level" LOEL.