Role of transport proteins in drug absorption, distribution and excretion

Assessment of In Vivo Clinical Product Performance of a Weak Basic Drug by Integration of In Vitro Dissolution Tests and Physiologically Based Absorption Modeling

Effective integration of in vitro tests and absorption modeling can greatly improve our capability in understanding, comparing, and predicting in vivo performances of clinical drug products. In this case, we used a proprietary drug candidate galunisertib to describe the procedures of designing key in vitro tests, analyzing relevant experimental and trial data, and integrating them into physiologically based absorption models to evaluate the performances of its clinical products. By simulating the preclinical study result, we estimated high in vivo permeability for the drug. Given the high sensitivity of its solubility to pH, supersaturation may play an important role in the absorption of galunisertib. Using the dynamic dissolution test, i.e., artificial stomach-duodenum (ASD) model and simulation, we concluded galunisertib in solution or tablet products could maintain supersaturation during the transit in the gastrointestinal tract (GIT). A physiologically based absorption model was established by incorporating these key inputs in the simulation of Trial 1 results of galunisertib solution. To predict the performance of three tablet products, we developed z-factor dissolution models from the multi-pH USP dissolution results and integrate them into the absorption model. The resultant biopharmaceutical models provided good prediction of the extent of absorption of all three products, but underestimated the rate of absorption of one tablet product. Leveraging the ASD result and optimization with the dissolution model, we identified the limitation of the model due to complexity of estimating the dissolution parameter z and its in vitro-in vivo correlation.

Intravital multiphoton imaging of the selective uptake of water-dispersible quantum dots into sinusoidal liver cells

Although many studies reporting the organ-level biodistribution of nanoparticles (NPs) in animals, very few have addressed the fate of NPs in organs at the cellular level. The liver appears to be the main organ for accumulation of NPs after intravenous injection. In this study, for the first time, the in vivo spatiotemporal disposition of recently developed mercaptosuccinic acid (MSA)-capped cadmium telluride/cadmium sulfide (CdTe/CdS) quantum dots (QDs) is explored in rat liver using multiphoton microscopy (MPM) coupled with fluorescence lifetime imaging (FLIM), with subcellular resolution (∼1 μm). With high fluorescence efficiency and largely improved stability in the biological environment, these QDs show a distinct distribution pattern in the liver compared to organic dyes, rhodamine 123 and fluorescein. After intravenous injection, fluorescent molecules are taken up by hepatocytes and excreted into the bile, while negatively charged QDs are retained in the sinusoids and selectively taken up by sinusoidal cells (Kupffer cells and liver sinusoidal endothelial cells), but not by hepatocytes within 3 h. The results could help design NPs targeting the specific types of liver cells and choose the fluorescent markers for appropriate cellular imaging.

Targeting core (mutated) pathways of high-grade gliomas: challenges of intrinsic resistance and drug efflux

High-grade gliomas are the most common type of primary brain tumor and are among the most lethal types of human cancer. Most patients with a high-grade glioma have glioblastoma multiforme (GBM), the most malignant glioma subtype that is associated with a very aggressive disease course and short overall survival. Standard treatment of newly diagnosed GBM involves surgery followed by chemoradiation with temozolomide. However, despite this extensive treatment the mean overall survival is still only 14.6 months and more effective treatments are urgently needed. Although different types of GBMs are indistinguishable by histopathology, novel molecular pathological techniques allow discrimination between the four main GBM subtypes. Targeting the aberrations in the molecular pathways underlying these subtypes is a promising strategy to improve therapy. In this article, we will discuss the potential avenues and pitfalls of molecularly targeted therapies for the treatment of GBM.

P-glycoprotein interactions of novel psychoactive substances - stimulation of ATP consumption and transport across Caco-2 monolayers

In contrast to drugs for therapeutic use, there are only few data available concerning interactions between P-glycoprotein (P-gp) and drugs of abuse (DOA). In this work, interactions between structurally diverse DOA and P-gp were investigated using different strategies. First, the effect on the P-gp ATPase activity was studied by monitoring of ATP consumption after addition to recombinant, human P-gp. Second, DOA showing an increased ATP consumption were further characterized regarding their transport across filter grown Caco-2- monolayers. Analyses were performed by luminescence and liquid chromatography-mass spectrometry, respectively. Among the nine DOA initially screened, benzedrone, diclofensine, glaucine, JWH-200, MDBC, WIN-55,212-2 showed an increase of ATP consumption in the ATPase stimulation assay. In Caco-2 transport studies, Glaucine, JWH-200, mitragynine, WIN-55,212-2 could moreover be identified as non-transported substrates, but inhibitors of P-gp activity. Thus, drug-drug or drug-food interactions should be very likely for these compounds.

The pharmacology of novel oral anticoagulants

Anticoagulation for the prevention of stroke is an important aspect of the management of atrial fibrillation. Novel anticoagulants including oral factor Xa inhibitors rivaroxaban and apixaban and the direct thrombin inhibitor dabigatran have emerged as important therapeutic treatment options for prevention of stroke in non-valvular atrial fibrillation. These agents offer practical advantages over traditional vitamin K antagonists, however an understanding of their individual pharmacokinetic and other agent-specific differences is essential for identifying appropriate candidates for therapy, and for selecting the appropriate agent that will be effective and safe. Here, we review the pharmacokinetic process of oral medication use, summarize the newer anticoagulants, their pharmacology, individual pharmacokinetic features, and explore possible explanations for the differences in bleeding outcomes observed in the clinical trials.

Interference of flavonoids with fluorescent intracellular probes: methodological implications in the evaluation of the oxidative burst by flow cytometry

The evaluation of oxidative burst is particularly relevant in many pathological and subclinical conditions. Flow cytometry provides quick and accurate measures of the reactive oxygen species production by leukocytes in most situations. However, spurious results, related to probes' efflux may be observed in several instances. Many factors affect the evaluation of the oxidative burst with fluorescent probes that require intracellular deacetylation and could be substrate of the multidrug resistance proteins (MDR). After discussing the implications of the efflux of fluorophores in the normalization strategies in flow cytometry assays, we have pointed out the possible interference of flavonoids with fluorescet probes' staining and signal. We have also reviewed the results from human intervention studies regarding the evaluation of oxidative burst with these probes. In vitro, at concentrations close to post-ingestion circulating levels, some flavonoids and their metabolites could interfere with probes' staining and fluorescence signal through different mechanisms, such as the inhibition of esterases, the modulation of the MDR-mediate efflux of probe and the inhibition of the oxidation of probe. These effects may explain the contrasting results obtained by human intervention studies. Finally, also inflammatory state or the use of drugs substrate of MDR proteins could affect the evaluation of the oxidative burst with intracellular probes.

Impact of endogenous esterase activity on in vitro p-glycoprotein profiling of dabigatran etexilate in Caco-2 monolayers

Dabigatran etexilate, a double prodrug of dabigatran, is a reversible, competitive, direct thrombin inhibitor that has been approved for use in many countries. A recent guideline from the European Medicines Agency on drug-drug interactions proposed dabigatran etexilate as a sensitive in vivo and in vitro probe substrate for intestinal P-glycoprotein (P-gp) inhibition. We therefore performed a series of in vitro studies to determine the best experimental conditions for evaluation of P-gp involvement on the transport process of dabigatran etexilate across colorectal adenocarcinoma Caco-2 cell monolayers. Experiments using expressed carboxylesterase 1 (CES1) and CES2 bactosomes revealed that dabigatran etexilate was hydrolyzed into BIBR 1087 by CES1 expressed in our Caco-2 cells. The impact of CES1-mediated BIBR 1087 formation during transcellular transport experiments was assessed by comparing several combinations of three experimental approaches: radioactivity detection using [(14)C]dabigatran etexilate as substrate, liquid chromatography-tandem mass spectrometry (LC-MS/MS) quantification of dabigatran etexilate, and in the presence and absence of a CES inhibitor bis(p-nitrophenyl) phosphate (BNPP). The experimental approach that was based on the use of nonlabeled dabigatran etexilate together with LC-MS/MS quantification and the addition of BNPP was selected as the most favorable condition in which to correctly evaluate the permeability coefficient (Papp) of dabigatran etexilate and its transcellular transport by P-gp. The in vitro Caco-2 study at the selected condition revealed that dabigatran etexilate is a P-gp substrate with an efflux ratio of 13.8 and an intrinsic Papp, which is the Papp under the condition of complete blockage of P-gp by P-gp inhibitor, of 29 × 10(-6) cm/s.

The effect of piperine on midazolam plasma concentration in healthy volunteers, a research on the CYP3A-involving metabolism

Some studies showed that piperine (the alkaloid of piper nigrum) can change the activities of microsomal enzymes. Midazolam concentration is applied as a probe to determine the CYP3A enzyme activity. This study was done to determine piperine pretreatment role on midazolam plasma concentration.Twenty healthy volunteers (14 men and 6 women) received oral dose of piperine (15 mg) or placebo for three days as pretreatment and midazolam (10 mg) on fourth day of study and the blood samples were taken at 0.5, 2.5 and 5 h after midazolam administration. The midazolam plasma levels were assayed using HPLC method (C18 analytical column, 75:25 methanol:water as mobile phase, UV detector at 242 nm wavelength and diazepam as internal standard). Data were fit in a "one-compartment PK model" using P-Pharm 1.5 software and analyzed under statistical tests.The mean ±SD of the age and body mass index were 24.3 ± 1.83 years (range: 21-28 years) and 23.46± 2.85, respectively. The duration of sedation in piperine receiving group was greater that the placebo group (188±59 vs. 102±43 min, p<0.0001). Half-life and clearance of midazolam were higher in piperine pretreatment group compared to placebo [1.88±0.03 vs. 1.71± 0.04 h (p<0.0001) and 33.62 ± 0.4 vs. 37.09 ± 1.07 ml/min (p<0.0001), respectively].According to the results, piperine can significantly increases half-life and decreases clearance of midazolam compared to placebo. It is suggested that piperine can demonstrate those effects by inhibition CYP3A4 enzyme activity in liver microsomal system.

Comparative digestive physiology

In vertebrates and invertebrates, morphological and functional features of gastrointestinal (GI) tracts generally reflect food chemistry, such as content of carbohydrates, proteins, fats, and material(s) refractory to rapid digestion (e.g., cellulose). The expression of digestive enzymes and nutrient transporters approximately matches the dietary load of their respective substrates, with relatively modest excess capacity. Mechanisms explaining differences in hydrolase activity between populations and species include gene copy number variations and single-nucleotide polymorphisms. Transcriptional and posttranscriptional adjustments mediate phenotypic changes in the expression of hydrolases and transporters in response to dietary signals. Many species respond to higher food intake by flexibly increasing digestive compartment size. Fermentative processes by symbiotic microorganisms are important for cellulose degradation but are relatively slow, so animals that rely on those processes typically possess special enlarged compartment(s) to maintain a microbiota and other GI structures that slow digesta flow. The taxon richness of the gut microbiota, usually identified by 16S rRNA gene sequencing, is typically an order of magnitude greater in vertebrates than invertebrates, and the interspecific variation in microbial composition is strongly influenced by diet. Many of the nutrient transporters are orthologous across different animal phyla, though functional details may vary (e.g., glucose and amino acid transport with K+ rather than Na+ as a counter ion). Paracellular absorption is important in many birds. Natural toxins are ubiquitous in foods and may influence key features such as digesta transit, enzymatic breakdown, microbial fermentation, and absorption.

Role of hepatic efflux transporters in regulating systemic and hepatocyte exposure to xenobiotics

Hepatic efflux transporters include numerous well-known and emerging proteins localized to the canalicular or basolateral membrane of the hepatocyte that are responsible for the excretion of drugs into the bile or blood, respectively. Altered function of hepatic efflux transporters due to drug-drug interactions, genetic variation, and/or disease states may lead to changes in xenobiotic exposure in the hepatocyte and/or systemic circulation. This review focuses on transport proteins involved in the hepatocellular efflux of drugs and metabolites, discusses mechanisms of altered transporter function as well as the interplay between multiple transport pathways, and highlights the importance of considering intracellular unbound concentrations of transporter substrates and/or inhibitors. Methods to evaluate hepatic efflux transport and predict the effects of impaired transporter function on systemic and hepatocyte exposure are discussed, and the sandwich-cultured hepatocyte model to evaluate comprehensively the role of hepatic efflux in the hepatobiliary disposition of xenobiotics is characterized.

Modulation of biotransformation systems and ABC transporters by benznidazole in rats

The effect of antichagasic benznidazole (BZL; 100 mg/kg body weight/day, 3 consecutive days, intraperitoneally) on biotransformation systems and ABC transporters was evaluated in rats. Expression of cytochrome P-450 (CYP3A), UDP-glucuronosyltransferase (UGT1A), glutathione S-transferases (alpha glutathione S-transferase [GST-α], GST-μ, and GST-π), multidrug-resistance-associated protein 2 (Mrp2), and P glycoprotein (P-gp) in liver, small intestine, and kidney was estimated by Western blotting. Increases in hepatic CYP3A (30%) and GST-μ (40%) and in intestinal GST-α (72% in jejunum and 136% in ileum) were detected. Significant increases in Mrp2 (300%) and P-gp (500%) proteins in liver from BZL-treated rats were observed without changes in kidney. P-gp and Mrp2 were also increased by BZL in jejunum (170% and 120%, respectively). In ileum, only P-gp was increased by BZL (50%). The activities of GST, P-gp, and Mrp2 correlated well with the upregulation of proteins in liver and jejunum. Plasma decay of a test dose of BZL (5 mg/kg body weight) administered intraduodenally was faster (295%) and the area under the concentration-time curve (AUC) was lower (41%) for BZL-pretreated rats than for controls. The biliary excretion of BZL was higher (60%) in the BZL group, and urinary excretion of BZL did not show differences between groups. The amount of absorbed BZL in intestinal sacs was lower (25%) in pretreated rats than in controls. In conclusion, induction of biotransformation enzymes and/or transporters by BZL could increase the clearance and/or decrease the intestinal absorption of coadministered drugs that are substrates of these systems, including BZL itself.

Drug-Drug Interactions within Protein Cavities Probed by Triplet-Triplet Energy Transfer

A new direct and noninvasive methodology based on transient absorption spectroscopy has been developed to probe the feasibility of drug-drug interactions within a common protein binding site. The simultaneous presence of (R)-cinacalcet (CIN) and (S)-propranolol (PPN) within human or bovine α1-acid glycoproteins (AAGs) is revealed by detection of (3)CIN* as the only transient species after laser flash photolysis of CIN/PPN/AAG mixtures at 308 nm. This is the result of triplet-triplet energy transfer from (3)PPN* to CIN, which requires close contact between the two drugs within the same biological compartment. Similar results are obtained with nabumetone and CIN as donor/acceptor partners. This new methodology can, in principle, be extended to a variety of drug/drug/biomolecule combinations.

Functional foods and nutraceuticals as therapeutic tools for the treatment of diet-related diseases

In Western societies, the incidence of diet-related diseases is progressively increasing due to greater availability of hypercaloric food and a sedentary lifestyle. Obesity, diabetes, atherosclerosis, and neurodegeneration are major diet-related pathologies that share a common pathogenic denominator of low-grade inflammation. Functional foods and nutraceuticals may represent a novel therapeutic approach to prevent or attenuate diet-related disease in view of their ability to exert anti-inflammatory responses. In particular, activation of intestinal T regulatory cells and homeostatic regulation of the gut microbiota have the potential to reduce low-grade inflammation in diet-related diseases. In this review, clinical applications of polyphenol-rich functional foods and nutraceuticals in postprandial inflammation, obesity, and ageing will be discussed. We have placed special emphasis on polyphenols since they are broadly distributed in plants.

Odorant metabolism catalyzed by olfactory mucosal enzymes influences peripheral olfactory responses in rats

A large set of xenobiotic-metabolizing enzymes (XMEs), such as the cytochrome P450 monooxygenases (CYPs), esterases and transferases, are highly expressed in mammalian olfactory mucosa (OM). These enzymes are known to catalyze the biotransformation of exogenous compounds to facilitate elimination. However, the functions of these enzymes in the olfactory epithelium are not clearly understood. In addition to protecting against inhaled toxic compounds, these enzymes could also metabolize odorant molecules, and thus modify their stimulating properties or inactivate them. In the present study, we investigated the in vitro biotransformation of odorant molecules in the rat OM and assessed the impact of this metabolism on peripheral olfactory responses. Rat OM was found to efficiently metabolize quinoline, coumarin and isoamyl acetate. Quinoline and coumarin are metabolized by CYPs whereas isoamyl acetate is hydrolyzed by carboxylesterases. Electro-olfactogram (EOG) recordings revealed that the hydroxylated metabolites derived from these odorants elicited lower olfactory response amplitudes than the parent molecules. We also observed that glucurono-conjugated derivatives induced no olfactory signal. Furthermore, we demonstrated that the local application of a CYP inhibitor on rat olfactory epithelium increased EOG responses elicited by quinoline and coumarin. Similarly, the application of a carboxylesterase inhibitor increased the EOG response elicited by isoamyl acetate. This increase in EOG amplitude provoked by XME inhibitors is likely due to enhanced olfactory sensory neuron activation in response to odorant accumulation. Taken together, these findings strongly suggest that biotransformation of odorant molecules by enzymes localized to the olfactory mucosa may change the odorant’s stimulating properties and may facilitate the clearance of odorants to avoid receptor saturation.

Molecular insight into affinities of drugs and their metabolites to lipid bilayers

The penetration properties of drug-like molecules on human cell membranes are crucial for understanding the metabolism of xenobiotics and overall drug distribution in the human body. Here, we analyze partitioning of substrates of cytochrome P450s (caffeine, chlorzoxazone, coumarin, ibuprofen, and debrisoquine) and their metabolites (paraxanthine, 6-hydroxychlorzoxazone, 7-hydroxycoumarin, 3-hydroxyibuprofen, and 4-hydroxydebrisoquine) on two model membranes: dioleoylphosphatidylcholine (DOPC) and palmitoyloleoylphophatidylglycerol (POPG). We calculated the free energy profiles of these molecules and the distribution coefficients on the model membranes. The drugs were usually located deeper in the membrane than the corresponding metabolites and also had a higher affinity to the membranes. Moreover, the behavior of the molecules on the membranes differed, as they seemed to have a higher affinity to the DOPC membrane than to POPG, implying they have different modes of action in human (mostly PC) and bacterial (mostly PG) cells. As the xenobiotics need to pass through lipid membranes on their way through the body and the effect of some drugs might depend on their accumulation on membranes, we believe that detailed information of penetration phenomenon is important for understanding the overall metabolism of xenobiotics.

Evaluation and prediction of potential drug-drug interactions of linagliptin using in vitro cell culture methods

Linagliptin is a highly potent dipeptidyl peptidase-4 (DPP-4) inhibitor approved for the treatment of type 2 diabetes. Unlike other DPP-4 inhibitors, linagliptin is cleared primarily via the bile and gut. We used a panel of stably and transiently transfected cell lines to elucidate the carrier-mediated transport processes that are involved in linagliptin disposition in vivo and to assess the potential for drug-drug interactions (DDIs). Our results demonstrate that linagliptin is a substrate of organic cation transporter 2 (OCT2) and P-glycoprotein (P-gp) but not of organic anion-transporting polypeptide 1B1 and 1B3; organic anion transporter 1, 3, and 4; OCT1; or organic cation/carnitine transporter 1 and 2, suggesting that OCT2 and P-gp play a role in the disposition of linagliptin in vivo. Linagliptin inhibits transcellular transport of digoxin by P-gp with an apparent IC(50) of 66.1 μM, but it did not inhibit activity of multidrug resistance-associated protein 2 and breast cancer resistance protein as represented by transport of probe substrate into membrane vesicles from respective transporter-expressing cells. In addition, the inhibitory effect of linagliptin on major solute carrier transporter isoforms was investigated. Linagliptin showed inhibitory potency against only OCT1 and OCT2 out of all major solute carrier transporter isoforms examined, and those inhibition potencies, evaluated using three different in vitro probe substrates, were substrate-specific. Considering the low therapeutic plasma concentration of linagliptin, our data clearly suggest a very low risk for transporter-mediated DDIs with comedications in clinical practice.

Inhibition of cytochrome P450 enzymes and biochemical aspects of mechanism-based inactivation (MBI)

Mechanism-based inactivation (MBI) often involves metabolic bioactivation of the xenobiotic by cytochrome P450s (CYPs) to an electrophilic reactive intermediate and results in quasi-irreversible or irreversible inactivation. Such reactive intermediate can cause quasi-irreversible inhibition through coordination to the ferrous state, Fe(II), of the P450 enzyme forming a tight noncovalent bond leading to the formation of metabolic-intermediate complex (MIC). By contrast, irreversible inactivation is one of the most common causes for the observed drug–drug interaction (DDI) and usually implies the formation of a covalent bond between the metabolite and the enzyme via alkylation of either the heme or the P450 apoprotein. Here we illustrate the important points of the current literature understanding of the mechanisms of inhibition of CYP enzymes with emphasis on general mechanistic aspects of MBI for some drugs/moieties associated with the phenomenon. Additionally, the utility of computational and in silico approaches to address bioactivation issues will be briefly discussed.

Effects of single or repeated silymarin administration on pharmacokinetics of risperidone and its major metabolite, 9-hydroxyrisperidone in rats

1. The interactions between herbal dietary supplements and therapeutic drugs have emerged as an important issue and P-glycoprotein (P-gp) has been reported as one of the significant factors of these interactions. 2. The objective of this article is to examine the effects of single and repeated administrations of silymarin on pharmacokinetics of a P-gp substrate, risperidone, and its major metabolite, 9-hydroxyrisperidone, in rats. 3. To determine the plasma levels of risperidone and 9-hydroxyrisperidone in rats, a HPLC method was developed using a liquid-liquid acid back extraction. When risperidone (6 mg/kg) was co-administered with silymarin (40 mg/kg) to rats orally, the C(max) of 9-hydroxyrisperidone was significantly increased to1.3-fold (p < 0.05), while the other pharmacokinetic parameters did not show any significant differences. Expanding the experiment where rats were repeatedly administered with silymarin for 5 days prior to giving risperidone, the C(max) of risperidone and 9-hydroxyrisperidone were significantly increased to 2.4-fold (p < 0.001) and 1.7-fold (p < 0.001), respectively, and the AUC(0-t), as well to 1.7-fold (p < 0.05) and 2.1-fold (p < 0.01), respectively. 4. The repeated exposures of silymarin, compared to single administration of silymarin, increased oral bioavailability and affected the pharmacokinetics of risperidone and 9-hydroxyrisperidone, by inhibiting P-gp.

Psychotropic drug-drug interactions involving P-glycoprotein

Multidrug resistance P-glycoprotein (P-gp; also known as MDR1 and ABCB1) is expressed in the luminal membrane of the small intestine and blood-brain barrier, and the apical membranes of excretory cells such as hepatocytes and kidney proximal tubule epithelia. P-gp regulates the absorption and elimination of a wide range of compounds, such as digoxin, paclitaxel, HIV protease inhibitors and psychotropic drugs. Its substrate specificity is as broad as that of cytochrome P450 (CYP) 3A4, which encompasses up to 50 % of the currently marketed drugs. There has been considerable interest in variations in the ABCB1 gene as predictors of the pharmacokinetics and/or treatment outcomes of several drug classes, including antidepressants and antipsychotics. Moreover, P-gp-mediated transport activity is saturable, and is subject to modulation by inhibition and induction, which can affect the pharmacokinetics, efficacy or safety of P-gp substrates. In addition, many of the P-gp substrates overlap with CYP3A4 substrates, and several psychotropic drugs that are P-gp substrates are also CYP3A4 substrates. Therefore, psychotropic drugs that are P-gp substrates may cause a drug interaction when P-gp inhibitors and inducers are coadministered, or when psychotropic drugs or other medicines that are P-gp substrates are added to a prescription. Hence, it is clinically important to accumulate data about drug interactions through studies on P-gp, in addition to CYP3A4, to assist in the selection of appropriate psychotropic medications and in avoiding inappropriate combinations of therapeutic agents. There is currently insufficient information available on the psychotropic drug interactions related to P-gp, and therefore we summarize the recent clinical data in this review.

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

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

Capacity for absorption of water-soluble secondary metabolites greater in birds than in rodents

Plant secondary metabolites (SMs) are pervasive in animal foods and potentially influence feeding behavior, interspecies interactions, and the distribution and abundance of animals. Some of the major classes of naturally occurring SMs in plants include many water-soluble compounds in the molecular size range that could cross the intestinal epithelium via the paracellular space by diffusion or solvent drag. There are differences among species in paracellular permeability. Using Middle Eastern rodent and avian consumers of fruits containing SMs, we tested the hypothesis that avian species would have significantly higher paracellular permeability than rodent species. Permeability in intact animals was assessed using standard pharmacological methodology to measure absorption of two radiolabeled, inert, neutral water-soluble probes that do not interact with intestinal nutrient transporters, L-arabinose (M_r = 150.1 Da) and lactulose (M_r = 342.3 Da). We also measured absorption of labeled 3-O-methyl-D-glucose (3OMD-glucose; M_r = 194.2 Da), which is a nonmetabolized analogue of D-glucose that is passively absorbed through the paracellular space but also transported across the enterocyte membranes. Most glucose was absorbed by all species, but arabinose fractional absorption (f) was nearly three times higher in birds (1.03±0.17, n = 15 in two species) compared to rodents (0.37±0.06, n = 10 in two species) (P<0.001). Surprisingly, the apparent rates of absorption in birds of arabinose exceeded those of 3OMD-glucose. Our findings are in agreement with previous work showing that the paracellular pathway is more prominent in birds relative to nonflying mammals, and suggests that birds may be challenged by greater absorption of water-soluble, dietary SMs. The increased expression of the paracellular pathway in birds hints at a tradeoff: the free energy birds gain by absorbing water-soluble nutrients passively may be offset by the metabolic demands placed on them to eliminate concomitantly absorbed SMs.

Identification of pharmacogenetic predictors of lipid-lowering response to atorvastatin in Chilean subjects with hypercholesterolemia

BACKGROUND

Statins are normally the first-line therapy for hypercholesterolemia (HC); however, the lipid-lowering response shows high interindividual variation. We investigated the effect of four polymorphisms in CYP3A4, CYP3A5 and ABCB1 genes on response to atorvastatin and CYP3A4 activity in Chilean subjects with HC.

METHODS

A total of 142 hypercholesterolemic individuals underwent atorvastatin therapy (10mg/day/1month). Serum lipid levels before and after treatment were measured. Genetic variants in CYP3A4 (-290A>G, rs2740574), CYP3A5 (6986A>G, rs776746) and ABCB1 (2677G>A/T, rs2032582 and 3435C>T, rs1045642) were analyzed by PCR-RFLP. CYP3A4 enzyme activity in urine samples was assessed through determination of 6β-hydroxycortisol/cortisol free ratio (6βOHC/FC).

RESULTS

After 4weeks of therapy, a significant reduction in total cholesterol (TC) and LDL-c was observed (P<0.001). The G allele for -290A>G polymorphism was related to higher percentage of variation in TC and LDL-c (P<0.001). Moreover, same allele was associated with higher HDL-c variation (P=0.017). In addition, CYP3A4 enzyme activity was lower in subjects carrying this polymorphism (P=0.009). No differences were observed for CYP3A5 and ABCB1 variants.

CONCLUSION

Our results suggest that presence of G allele for -290A>G polymorphism determines a better response to atorvastatin, being also associated with lower CYP3A4 activity in vivo, causing an increased atorvastatin activity.

The evolution of the OATP hepatic uptake transport protein family in DMPK sciences: from obscure liver transporters to key determinants of hepatobiliary clearance

Over the last two decades the impact on drug pharmacokinetics of the organic anion transporting polypeptides (OATPs: OATP-1B1, 1B3 and 2B1), expressed on the sinusoidal membrane of the hepatocyte, has been increasingly recognized. OATP-mediated uptake into the hepatocyte coupled with subsequent excretion into bile via efflux proteins, such as MRP2, is often referred to as hepatobiliary excretion. OATP transporter proteins can impact some drugs in several ways including pharmacokinetic variability, pharmacodynamic response and drug-drug interactions (DDIs). The impact of transporter mediated hepatic clearance is illustrated with case examples, from the literature and also from the Pfizer portfolio. The currently available in vitro techniques to study the hepatic transporter proteins involved in the hepatobiliary clearance of drugs are reviewed herein along with recent advances in using these in vitro data to predict the human clearance of compounds recognized by hepatic uptake transporters.

Functional analysis of nonsynonymous single nucleotide polymorphisms of multidrug resistance-associated protein 2 (ABCC2)

BACKGROUND

Multidrug resistance-associated protein 2 (MRP2; ABCC2) mediates the biliary excretion of glutathione, glucuronide, and sulfate conjugates of endobiotics and xenobiotics. Single nucleotide polymorphisms (SNPs) of MRP2 contribute to interindividual variability in drug disposition and ultimately in drug response.

OBJECTIVES

To characterize the transport function of human wild-type (WT) MRP2 and four SNP variants, S789F, A1450T, V417I, and T1477M.

METHODS

The four SNP variants were expressed in Sf9 cells using recombinant baculovirus infection. The kinetic parameters [Km, (μmol/l); V(max), (pmol/mg/min); the Hill coefficient] of ATP-dependent transport of leukotriene C(4) (LTC(4)), estradiol-3-glucuronide (E(2)3G), estradiol-17β-glucuronide (E(2)17G), and tauroursodeoxycholic acid (TUDC) were determined in Sf9-derived plasma membrane vesicles. Transport activity was normalized for expression level.

RESULTS

The V(max) for transport activity was decreased for all substrates for S789F, and for all substrates except E(2)17G for A1450T. V417I showed decreased apparent affinity for LTC(4), E(2)3G, and E(2)17G, whereas transport was similar between wild-type (WT) and T1477M, except for a modest increase in TUDC transport. Examination of substrate-stimulated MRP2-dependent ATPase activity of S789F and A1450T, SNPs located in MRP2 nucleotide-binding domains (NBDs), demonstrated significantly decreased ATPase activity and only modestly decreased affinity for ATP compared with WT.

CONCLUSION

SNPs in the NBDs (S789F in the D-loop of NBD1, or A1450T near the ABC signature motif of NBD2) variably decreased the transport of all substrates. V417I in membrane spanning domain 1 selectively decreased the apparent affinity for the glutathione and glucuronide conjugated substrates, whereas the T1477M SNP in the carboxyl terminus altered only TUDC transport.

Contribution of organic cation transporter 3 to cisplatin cytotoxicity in human cervical cancer cells

This study was conducted to investigate whether drug transporters play a role in determination of cisplatin resistance in cervical cancer cells. The transcript levels of the transporter genes previously associated with cisplatin transport and/or resistance were compared between the cisplatin-sensitive cervical adenocarcinoma KB-3-1 and its derivative cisplatin-resistant KB-CP20 cells. The expression of the efflux transporter gene multidrug resistance-associated protein 2 (MRP2) was significantly reduced in KB-CP20 cells, in support of previous studies indicating that MRP2 is unlikely responsible for cisplatin resistance in these cells. We observed that the expression of the uptake transporter organic cation transporter 3 (OCT3) was extremely downregulated in KB-CP20 compared with KB-3-1 cells. Consistently, the transport function for organic cations in the former was considerably low. OCT3 overexpression significantly increased cisplatin cellular accumulation and cytotoxicity in KB-3-1 cells, while its downregulation by short hairpin RNA or chemical inhibition increased the resistance. Interestingly, there was no effect of OCT3 overexpression on cisplatin accumulation and cytotoxicity in human embryonic kidney 293 cells. The present study indicates that OCT3 partially contributes to the sensitivity of cervical adenocarcinoma cells to cisplatin cytotoxicity. Further studies are required to determine OCT3 activity in cervical cancer tissues of different cisplatin chemoresponses and to elucidate the underlying mechanisms of different OCT3 function in different cell types.

Influence of CYP3A5 and MDR1(ABCB1) polymorphisms on the pharmacokinetics of tacrolimus in Chinese renal transplant recipients

The aims of this study were to investigate the influence of CYP3A5 and MDR1 genetic polymorphisms on tacrolimus pharmacokinetics in Chinese renal transplant recipients, so as to help rational administration in clinical practice. We calculated pharmacokinetic parameters of tacrolimus from blood concentrations in steady state at day 28. Polymerase chain reaction restriction fragment length polymorphisms were used for CYP3A5 and MDR1 analysis. The results showed that the dose-adjusted area under the concentration time curve (AUC(0-12)) and renal clearance showed a significant difference between CYP3A5*1 carriers and the CYP3A5*3/*3 genotype (P < .01). In the following study, a distinction was made between carriers of CYP3A5*1/ vs CYP3A5*3/*3 seeking to investigate the influence of the MDR13435T>C polymorphism on tacrolimus pharmacokinetics. MDR1 3435T>C polymorphism did not affect any tacrolimus pharmacokinetic parameter in either group. Renal transplant recipients who were CYP3A5*1 carriers required a higher dose of tacrolimus than CYP3A5*3/*3, indicating a significantly lower dose-adjusted AUC(0-12) of tacrolimus. In contrast, MDR1 3435T>C polymorphism was not an important factor in tacrolimus pharmacokinetics. Pharmacogenetic methods may be used prospectively to aid dose selection and individualize immunosuppressive therapy.

14-Aminocamptothecins: their synthesis, preclinical activity, and potential use for cancer treatment

14-Aminocamptothecins were synthesized in good yields by treating camptothecin (1a) and 7-ethylcamptothecin (1b) with 90% fuming nitric acid either neat or in acetic anhydride and then followed by reduction of the resulting 14-nitrocamptothecins (2). 14-Aminocamptothecin (3a) and 7-ethyl-14-aminocamptothecin (3b) demonstrated excellent cytotoxic potency against human tumor cell lines in vitro, and they are not substrates for any of the major clinically relevant efflux pumps (MDR1, MRP1, and BCRP). 3a and 3b showed similar cytotoxicity against human and mouse bone marrow progenitor cells. This is in contrast to many camptothecin analogues, which are substrates for efflux pumps and are dramatically more toxic to human marrow cells relative to murine. 3a and 3b demonstrated significant brain penetration when dosed orally in mice. 3b showed significantly better efficacy relative to topotecan when dosed orally in the three ectopic xenograft models, H460, HT29, and PC-3. On the basis of its favorable in vitro and in vivo profile, 3b warrants future development.

Factors and Mechanisms for Pharmacokinetic Differences between Pediatric Population and Adults

Many physiologic differences between children and adults may result in age-related changes in pharmacokinetics and pharmacodynamics. Factors such as gastric pH and emptying time, intestinal transit time, immaturity of secretion and activity of bile and pancreatic fluid among other factors determine the oral bioavailability of pediatric and adult populations. Anatomical, physiological and biochemical characteristics in children also affect the bioavailability of other routes of administration. Key factors explaining differences in drug distribution between the pediatric population and adults are membrane permeability, plasma protein binding and total body water. As far as drug metabolism is concerned, important differences have been found in the pediatric population compared with adults both for phase I and phase II metabolic enzymes. Immaturity of glomerular filtration, renal tubular secretion and tubular reabsorption at birth and their maturation determine the different excretion of drugs in the pediatric population compared to adults.

Synthesis and in vivo evaluation of ¹⁸F-fluoroethyl GF120918 and XR9576 as positron emission tomography probes for assessing the function of drug efflux transporters

The purpose of this study was to synthesize two new positron emission tomography (PET) probes, N-(4-(2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl)phenyl)-9,10-dihydro-5-[¹⁸F]fluoroethoxy-9-oxo-4-acridine carboxamide ([¹⁸F]3) and quinoline-3-carboxylic acid [2-(4-{2-[7-(2-[¹⁸F]fluoroethoxy)-6-methoxy-3,4-dihydro-1H-isoquinolin-2-yl]ethyl}phenylcarbamoyl)-4,5-dimethoxyphenyl]amide ([¹⁸F]4), and to evaluate the potential of these PET probes for assessing the function of two major drug efflux transporters, P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP). [¹⁸F]3 and [¹⁸F]4 were synthesized by ¹⁸F-alkylation of each O-desmethyl precursor with [¹⁸F]2-fluoroethyl bromide for injection as PET probes. In vitro accumulation assay showed that treatment with P-gp/BCRP inhibitors (1 and 2) enhanced the intracellular accumulation capacity of P-gp- and BCRP-overexpressing MES-SA/Dx5 cells. In PET studies, the uptake (AUC(brain[0-)₆₀ (min])) of [¹⁸F]3 and [¹⁸F]4 in wild-type mice co-injected with 1 were approximately sevenfold higher than that in wild-type mice, and the uptake of [¹⁸F]3 and [¹⁸F]4 in P-gp/Bcrp knockout mice were eight- to ninefold higher than that in wild-type mice. The increased uptake of [¹⁸F]3 and [¹⁸F]4 was similar to that of parent compounds ([¹¹C]1 and [¹¹C]2) previously described, indicating that radioactivity levels in the brain after injection of [¹⁸F]3 and [¹⁸F]4 are related to the function of drug efflux transporters. Also, these results suggest that the structural difference between parent compounds ([¹¹C]1 and [¹¹C]2) and fluoroethyl analogs ([¹⁸F]3 and [¹⁸F]4) do not obviously affect the potency against drug efflux transporters. In metabolite analysis of mice, the unchanged form in the brain and plasma at 60 min after co-injection of [¹⁸F]4 plus 1 were higher (95% for brain; 81% for plasma) than that after co-injection of [¹⁸F]3 plus 1. [¹⁸F]4 is a promising PET probe to assess the function of drug efflux transporters.