Concentration-Dependent Effect of Naringin on Intestinal Absorption of β1-Adrenoceptor Antagonist Talinolol Mediated by P-Glycoprotein and Organic Anion Transporting Polypeptide (Oatp)

Contributions of multiple transport mechanisms to intestinal uptake of serotonin

This study aimed to analyze the contributions of multiple transport mechanisms to the intestinal uptake of serotonin (5-HT) by employing a variety of in vitro experimental techniques, focusing on organic cation transporters expressed in the gastrointestinal (GI) tract, such as SERT, PMAT, THTR2, OCT3, and OCTN2. Analysis of the concentration dependence of 5-HT uptake by Caco-2 cells revealed multi-affinity kinetics with high-affinity and low-affinity components, suggesting that multiple transporters are involved in the intestinal 5-HT uptake. Comparative analysis of transporters using Km values obtained in Xenopus oocyte expression systems suggested that SERT is responsible for the high-affinity transport, while PMAT, THTR2, and OCT3 contribute to the low-affinity transport. Further analysis indicated that the relative contributions of SERT and PMAT to the intestinal 5-HT uptake (0.01 µM) are approximately 94.9% and 1.1%, respectively. Interestingly, at the concentration of 10 µM, the reported steady-state concentration of 5-HT in the human colon, the contributions of SERT, PMAT, THTR2, and OCT3 were estimated to be approximately 37.0%, 1.0%, 18.2%, and 20.5%, respectively. In conclusion, the present study indicated that the contributions of multiple transporters to 5-HT uptake in the GI tract are dependent upon the colon luminal concentration of 5-HT.

Endoplasmic reticulum stress in pancreatic β-cell dysfunction: The potential therapeutic role of dietary flavonoids

Diabetes mellitus (DM) is a global health burden that is characterized by the loss or dysfunction of pancreatic β-cells. In pancreatic β-cells, endoplasmic reticulum (ER) stress is a fact of life that contributes to β-cell loss or dysfunction. Despite recent advances in research, the existing treatment approaches such as lifestyle modification and use of conventional therapeutics could not prevent the loss or dysfunction of pancreatic β-cells to abrogate the disease progression. Therefore, targeting ER stress and the consequent unfolded protein response (UPR) in pancreatic β-cells may be a potential therapeutic strategy for diabetes treatment. Dietary phytochemicals have therapeutic applications in human health owing to their broad spectrum of biochemical and pharmacological activities. Flavonoids, which are commonly obtained from fruits and vegetables worldwide, have shown promising prospects in alleviating ER stress. Dietary flavonoids including quercetin, kaempferol, myricetin, isorhamnetin, fisetin, icariin, apigenin, apigetrin, vitexin, baicalein, baicalin, nobiletin hesperidin, naringenin, epigallocatechin 3-O-gallate hesperidin (EGCG), tectorigenin, liquiritigenin, and acacetin have shown inhibitory effects on ER stress in pancreatic β-cells. Dietary flavonoids modulate ER stress signaling components, chaperone proteins, transcription factors, oxidative stress, autophagy, apoptosis, and inflammatory responses to exert their pharmacological effects on pancreatic β-cells ER stress. This review focuses on the role of dietary flavonoids as potential therapeutic adjuvants in preserving pancreatic β-cells from ER stress. Highlights of the underlying mechanisms of action are also presented as well as possible strategies for clinical translation in the management of DM.

Conversion of Olmesartan to Olmesartan Medoxomil, A Prodrug that Improves Intestinal Absorption, Confers Substrate Recognition by OATP2B1

PURPOSE

Olmesartan medoxomil (olmesartan-MX), an ester-type prodrug of the angiotensin II receptor blocker (ARB) olmesartan, is predominantly anionic at intestinal pH. Human organic anion transporting polypeptide 2B1 (OATP2B1) is expressed in the small intestine and is involved in the absorption of various acidic drugs. This study was designed to test the hypothesis that OATP2B1-mediated uptake contributes to the enhanced intestinal absorption of olmesartan-MX, even though olmesartan itself is not a substrate of OATP2B1.

METHODS

Tetracycline-inducible human OATP2B1- and rat Oatp2b1-overexpressing HEK 293 cell lines (hOATP2B1/T-REx-293 and rOatp2b1/T-REx-293, respectively) were established to characterize OATP2B1-mediated uptake. Rat jejunal permeability was measured using Ussing chambers. ARBs were quantified by liquid chromatography-tandem mass spectrometry.

RESULTS

Significant olmesartan-MX uptake was observed in hOATP2B1/T-REx-293 and rOatp2b1/T-REx-293 cells, whereas olmesartan uptake was undetectable or much lower than olmesartan-MX uptake, respectively. Furthermore, olmesartan-MX exhibited several-fold higher uptake in Caco-2 cells and greater permeability in rat jejunum compared to olmesartan. Olmesartan-MX uptake in hOATP2B1/T-REx-293 cells and in Caco-2 cells was significantly decreased by OATP2B1 substrates/inhibitors such as 1 mM estrone-3-sulfate, 100 µM rifamycin SV, and 100 µM fluvastatin. Rat Oatp2b1-mediated uptake and rat jejunal permeability of olmesartan-MX were significantly decreased by 50 µM naringin, an OATP2B1 inhibitor. Oral administration of olmesartan-MX with 50 µM naringin to rats significantly reduced the area under the plasma concentration-time curve of olmesartan to 76.9%.

CONCLUSION

Olmesartan-MX is a substrate for OATP2B1, and the naringin-sensitive transport system contributes to the improved intestinal absorption of olmesartan-MX compared with its parent drug, olmesartan.

Monophasic coamorphous sulpiride: a leap in physicochemical attributes and dual inhibition of GlyT1 and P-glycoprotein, supported by experimental and computational insights

Study aimed to design and development of a supramolecular formulation of sulpiride (SUL) to enhance its solubility, dissolution and permeability by targeting a novel GlyT1 inhibition mechanism. SUL is commonly used to treat gastric and duodenal ulcers, migraine, anti-emetic, anti-depressive and anti-dyspeptic conditions. Additionally, Naringin (NARI) was incorporated as a co-former to enhance the drug's intestinal permeability by targeting P-glycoprotein (P-gp) efflux inhibition. NARI, a flavonoid has diverse biological activities, including anti-apoptotic, anti-oxidant, and anti-inflammatory properties. This study aims to design and develop a supramolecular formulation of SUL with NARI to enhance its solubility, dissolution, and permeability by targeting a novel GlyT1 inhibition mechanism, extensive experimental characterization was performed using solid-state experimental techniques in conjunction with a computational approach. This approach included quantum mechanics-based molecular dynamics (MD) simulation and density functional theory (DFT) studies to investigate intermolecular interactions, phase transformation and various electronic structure-based properties. The findings of the miscibility study, radial distribution function (RDF) analysis, quantitative simulations of hydrogen/π-π bond interactions and geometry optimization aided in comprehending the coamorphization aspects of SUL-NARI Supramolecular systems. Molecular docking and MD simulation were performed for detailed binding affinity assessment and target validation. The solubility, dissolution and ex-vivo permeability studies demonstrated significant improvements with 31.88-fold, 9.13-fold and 1.83-fold increments, respectively. Furthermore, biological assessments revealed superior neuroprotective effects in the SUL-NARI coamorphous system compared to pure SUL. In conclusion, this study highlights the advantages of a drug-nutraceutical supramolecular formulation for improving the solubility and permeability of SUL, targeting novel schizophrenia treatment approaches through combined computational and experimental analyses.Communicated by Ramaswamy H. Sarma.

The Use of an Antioxidant Enables Accurate Evaluation of the Interaction of Curcumin on Organic Anion-Transporting Polypeptides 4C1 by Preventing Auto-Oxidation

Flavonoids have garnered attention because of their beneficial bioactivities. However, some flavonoids reportedly interact with drugs via transporters and may induce adverse drug reactions. This study investigated the effects of food ingredients on organic anion-transporting polypeptide (OATP) 4C1, which handles uremic toxins and some drugs, to understand the safety profile of food ingredients in renal drug excretion. Twenty-eight food ingredients, including flavonoids, were screened. We used ascorbic acid (AA) to prevent curcumin oxidative degradation in our method. Twelve compounds, including apigenin, daidzein, fisetin, genistein, isorhamnetin, kaempferol, luteolin, morin, quercetin, curcumin, resveratrol, and ellagic acid, altered OATP4C1-mediated transport. Kaempferol and curcumin strongly inhibited OATP4C1, and the Ki values of kaempferol (AA(-)), curcumin (AA(-)), and curcumin (AA(+)) were 25.1, 52.2, and 23.5 µM, respectively. The kinetic analysis revealed that these compounds affected OATP4C1 transport in a competitive manner. Antioxidant supplementation was determined to benefit transporter interaction studies investigating the effects of curcumin because the concentration-dependent curve evidently shifted in the presence of AA. In this study, we elucidated the food-drug interaction via OATP4C1 and indicated the utility of antioxidant usage. Our findings will provide essential information regarding food-drug interactions for both clinical practice and the commercial development of supplements.

Food effects on gastrointestinal physiology and drug absorption

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

Selection of bionic Co-former improves the dissolution of Neohesperidin via Co-amorphous solid dispersion with Naringin

The co-amorphous solid dispersion (c-ASD) is a useful method to enhance water solubility of poorly soluble drugs. The objective of this study was to improve the dissolution of Neohesperidin (NE) via binary c-ASD which, to the best of our knowledge, has not yet been reported. Since NE and Naringin (NA) co-exist abundantly in Chinese herbal medicine Fructus Aurantii Immaturus, it was hypothesised that NA served as a co-former of NE-NA c-ASD to improve the dissolution profile of NE. Hence, NA was selected to prepare c-ASD with NE at a weight ratio of 4:10, 10:10, 10:4 by lyophilisation. They were characterised according to thermal properties, molecular interactions, dissolution properties and physical stability. We found that the 10:10 ratio was the most potent in enhancing the dissolution behaviour of NE; whereby NE and NA are highly synchronous in pair-wise solvation process. A molecular mixture was achieved through the intermolecular H-bond and pi-pi stacking force formed between NE and NA and was stable for 7 -months. We concluded that the NE-NA co-amorphous binary system is a promising strategy to improve the dissolution behaviour and stabilise the amorphous state of NE. Bionic co-former selection may be an innovative and effective way to accurately determine the appropriate co-former of poorly water soluble substances.

P-glycoprotein: new insights into structure, physiological function, regulation and alterations in disease

The multidrug resistance phenomenon presents a major threat to the pharmaceutical industry. This resistance is a common occurrence in several diseases and is mediated by multidrug transporters that actively pump substances out of the cell and away from their target regions. The most well-known multidrug transporter is the P-glycoprotein transporter. The binding sites within P-glycoprotein can accommodate a variety of compounds with diverse structures. Hence, numerous drugs are P-glycoprotein substrates, with new ones being identified every day. For many years, the mechanisms of action of P-glycoprotein have been shrouded in mystery, and scientists have only recently been able to elucidate certain structural and functional aspects of this protein. Although P-glycoprotein is highly implicated in multidrug resistant diseases, this transporter also performs various physiological roles in the human body and is expressed in several tissues, including the brain, kidneys, liver, gastrointestinal tract, testis, and placenta. The expression levels of P-glycoprotein are regulated by different enzymes, inflammatory mediators and transcription factors; alterations in which can result in the generation of a disease phenotype. This review details the discovery, the recently proposed structure and the regulatory functions of P-glycoprotein, as well as the crucial role it plays in health and disease.

Effect of Ingested Fluid Volume and Solution Osmolality on Intestinal Drug Absorption: Impact on Drug Interaction with Beverages

It was recently shown that osmolality-dependent fluid movement is a significant factor causing the clinically observed apple juice (AJ)-atenolol interaction. Here we examined whether osmolality-dependent fluid movement may also explain the AJ volume dependence of the AJ-atenolol interaction. In Wistar rats, the luminal fluid volume after administration of different volumes of purified water (0.5 and 1.0 mL) gradually reduced to a similar steady-state level, while that after administration of different volumes of AJ (0.5 and 1.0 mL) increased and attained different apparent steady-state levels. It was hypothesized that osmolality-dependent fluid secretion would account for the volume dependence of the apparent steady-state. Indeed, the luminal concentration of FD-4, a non-permeable compound, after administration in AJ was attenuated depending upon the ingested volume, whereas that after administration in purified water was independent of the ingested fluid volume. An in vivo pharmacokinetic study in rats showed that co-administration of AJ and hyperosmotic solution (adjusted to the osmolality of AJ) with atenolol volume-dependently reduced the AUC and C_max of atenolol significantly. These results show that osmolality-dependent variations in luminal fluid volume may indirectly influence the absorption characteristics of drugs, and can account for the observed volume dependence of beverage-drug interactions.

Determination of effective concentrations of drug absorption enhancers using in vitro and ex vivo models

BACKGROUND

Achievement of an effective concentration of the pharmaceutically active ingredient in the blood and/or at the target site is an important aspect in the formulation of drugs and therefore needs to be quantified. Any concentration above therapeutic levels can cause toxic effects whereas low concentrations can be sub-therapeutic. This paper investigated different concentrations of selected commercially sourced analytical-grade pure chemicals as potential drug absorption enhancers in vitro and ex vivo to determine the lowest effective concentrations for optimizing drug absorption in oral dosage forms.

METHODS

Recombinant cytochrome (CYP) 3A4 enzyme and recombinant p-glycoprotein membrane models were utilized for the investigation of in vitro inhibitory effects of drug absorption enhancers. Promega (2015) protocols were adopted for both assays. The everted porcine intestinal ex vivo model was employed for assessing effects of the drug absorption enhancers on the absorption of propranolol.

RESULTS

The lowest effective CYP3A4 inhibitory concentrations were observed for curcumin (75µM and 100 µM), quercetin (75 and 100 µM) and glycyrrhizic acid (50 µM) while the most effective p-glycoprotein (P-gp) inhibition concentrations were curcumin (10, 15, 25, 50, 75 and 100 µM), sinomenine (50, 75, and 100 µM), quercetin (75 and 100 µM) and naringin (50 µM). Additive effects were observed between combinations of quercetin (75 µM) and curcumin (100 µM); quercetin (75 µM) and curcumin (75 µM); quercetin (75 µM) and curcumin (50 µM), and quercetin (75 µM) with curcumin (10 µM), which increased the basal ex vivo absorption of propranolol from 1.24 ± 0.03 µg/mL to 5.19 ± 0.12 µg/mL, 4.17 ± 0.05 µg/mL, 3.86 ± 0.10 µg/mL, and 4.07± 0.05 µg/mL respectively, after 2 hours.

CONCLUSION

Incorporation of the drug absorption enhancers (e.g., curcumin and quercetin), at specific concentrations, in dosage forms could improve the bioavailability of the BCS Class III and IV drugs that are substrates of CYP3A4 and p-glycoprotein.

Influence of osmolality on gastrointestinal fluid volume and drug absorption: potential impact on oral salt supplementation

Background

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is the most frequent cause of hyponatremia in patients with cerebrovascular disease, and is often treated with oral salt tablets. However, we have shown that osmolality-dependent variations in gastrointestinal (GI) fluid volume can alter the concentration of a poorly permeable drug in the GI tract, potentially affecting its absorption. Here, we examined the effect of ingestion of hyperosmotic solution (10% NaCl) on drug concentration and absorption in the GI tract.

Methods

The effects of osmolality on luminal fluid volume and drug absorption in rat intestine (jejunum, ileum and colon) were examined by means of an in situ closed loop method using fluorescein isothiocyanate-dextran 4000 (FD-4) and atenolol. In vivo absorption in rats was determined by measuring the plasma concentration after oral administration of the test compounds dissolved in purified water or hyperosmotic solution (10% NaCl).

Results

Administration of hyperosmotic solution directly into the GI tract significantly increased the GI fluid volume, owing to secretion of water into the lumen. After administration in hyperosmotic solution, the luminal concentration of non-permeable FD-4 was significantly lower than the initial dosing concentration, whereas after administration in purified water, the luminal concentration exceeded the initial concentration. The fraction absorbed of atenolol was markedly lower after administration in hyperosmotic solution than after administration in purified water. An in vivo pharmacokinetic study in rats was consistent with these findings.

Conclusions

Administration of hyperosmotic NaCl solution increased GI fluid volume and reduced the plasma level of orally administered atenolol. This may imply that oral salt tablets used to treat hyponatremia in SIADH patients could decrease the intestinal absorption of concomitantly administered drugs, resulting in lower plasma exposure.

Fertility and early embryonic development toxicity assessment of naringin in Sprague-Dawley rats

Naringin is a dihydroflavonoid abundantly existed in grapefruit and related citrus species. The double directional adjusting function of estrogenic and anti-estrogenic activities of naringin and its aglycone naringenin has raised concern about possible risks of unwanted interference with endocrine regulation. Herein we assessed the safety of naringin on fertility and early embryonic development toxicity in Sprague-Dawley rats. Twenty-two male and 22 female rats per group were orally given naringin at 0, 50, 250, and 1250 mg/kg/day. Male rats were administered beginning 9 weeks prior to mating and continued until necropsy. Dosing to female began 2 weeks before mating and continued until gestation day 7. There were no obvious effects of naringin on physical signs, animal behavior, and survival rate, although female and male rats from 1250 mg/kg group had lower body weight and tended to have less food consumption. Importantly, no treatment-related effects of naringin were found in relation to fertility and early embryonic development. Under these experimental conditions, it was concluded that the no-observed-adverse-effect levels (NOAEL) of naringin were at least 1250 mg/kg/day for fertility and early embryonic development in rats.

Is aspirin a substrate of MDR1/P-glycoprotein?

Aspirin (acetyl salicylic acid) is widely used co-medication in patients with cardiovascular and cerebrovascular diseases. Given the prevalence of acetyl salicylic acid's use as a co-medication and conflicting reports in the literature on it being a substrate of P-glycoprotein (P-gp). There is a potential risk for its interaction with compounds with P-gp liability, therefore, we have conducted a detailed investigation to determine substrate potential of acetyl salicylic acid towards P-gp. We observed significantly lower cellular uptake of acetyl salicylic acid in MDR1 transfected LLC-PK1 cells compared to LLC-PK1 wild-type (WT) cells, however, the in vitro efflux of acetyl salicylic acid in MDR1 transfected LLC-PK1 cells was not inhibited by known inhibitors under various conditions. Acetyl salicylic acid did not show active asymmetrical transport across MDR1 transfected LLC-PK1 cells compared to LLC-PK1-WT cells in transwell assay. Moreover, no difference in plasma and brain exposure of acetyl salicylic acid and its metabolite salicylic acid was observed between FVB-WT and Mdr1a/b knockout (KO) mice. Taken together, our findings indicate that acetyl salicylic acid is not a substrate of P-gp.

Loss of Control of HIV Viremia With OTC Weight-Loss Drugs: A Call for Caution?

Improved survival achieved by HIV-infected patients has complicated their medical care, as increasing numbers of comorbidities have led to polypharmacy and a higher risk of drug-drug interactions. Here, evidence is provided that weight-loss drugs should be used with caution in HIV-infected patients treated with lipophilic antiretroviral drugs because of the risk of virologic failure. This is particularly relevant considering that these agents are available on the market as over-the-counter medications, thus escaping the control of the physician.

Effect of Multi Drug Resistance Protein 4 (MRP4) Inhibition on the Pharmacokinetics and Pharmacodynamics of Ciprofloxacin in Normal and Rats with LPS-Induced Inflammation

BACKGROUND AND OBJECTIVES

Infection and inflammation are known to cause wide variability in disposition of drugs through modulation of drug transporters. However, the effects of inhibition of multidrug resistance protein 4 (MRP4) on pharmacokinetics and pharmacodynamics are poorly understood in normal and inflamed conditions. We hypothesized that inflammation alters the pharmacokinetic parameters of ciprofloxacin; and Pharmacokinetic/Pharmacodynamic indices, such as ratio of peak plasma concentration to minimum inhibitory concentration (C _max/MIC) and ratio of area under the plasma drug concentration-time curve to minimum inhibitory concentration (AUC/MIC) of ciprofloxacin will be improved with the co-administration of a MRP4 inhibitor, dipyridamole, in inflammatory conditions.

METHODS

In this study, the role of MRP4 on the pharmacokinetic and pharmacodynamic parameters of ciprofloxacin was investigated by the co-administration of dipyridamole in rats with or without lipopolysaccharide (LPS)-induced inflammation. The pharmacokinetic parameters for ciprofloxacin were calculated by non-compartmental approach. MIC of ciprofloxacin was determined using broth microdilution technique.

RESULTS

Induction of inflammation in rats resulted in marked reduction in C _max and AUC; and an increase in the volume of distribution (V _d/F) and clearance (Cl/F) of ciprofloxacin, compared to normal rats. Co-administration of dipyridamole with ciprofloxacin in inflamed rats resulted in a threefold increase in AUC, a twofold decrease in V _d/F and a threefold decrease in Cl/F of ciprofloxacin with significantly prolonged half-life compared to inflamed rats who received ciprofloxacin alone. Co-administration of dipyridamole enhanced AUC/MIC values of ciprofloxacin in both normal and inflamed rats.

CONCLUSIONS

The results suggest that MRP4 inhibition increases the systemic exposure of ciprofloxacin in both normal and inflammatory conditions.

The effects of dietary and herbal phytochemicals on drug transporters

Membrane transporter proteins (the ABC transporters and SLC transporters) play pivotal roles in drug absorption and disposition, and thus determine their efficacy and safety. Accumulating evidence suggests that the expression and activity of these transporters may be modulated by various phytochemicals (PCs) found in diets rich in plants and herbs. PC absorption and disposition are also subject to the function of membrane transporter and drug metabolizing enzymes. PC-drug interactions may involve multiple major drug transporters (and metabolizing enzymes) in the body, leading to alterations in the pharmacokinetics of substrate drugs, and thus their efficacy and toxicity. This review summarizes the reported in vitro and in vivo interactions between common dietary PCs and the major drug transporters. The oral absorption, distribution into pharmacological sanctuaries and excretion of substrate drugs and PCs are considered, along with their possible interactions with the ABC and SLC transporters which influence these processes.

Paroxetine decreased plasma exposure of glyburide partly via inhibiting intestinal absorption in rats

Accumulating evidences have shown that diabetes is often accompanied with depression, thus it is possible that oral antidiabetic agent glyburide and antidepressive agent paroxetine are co-administered in diabetic patients. The aim of this study was to assess interactions between glyburide and paroxetine in rats. Effect of paroxetine on pharmacokinetics of orally administered glyburide was investigated. Effect of naringin (NAR), an inhibitor of rat intestinal organic anion transporting polypeptides 1a5 (Oatp1a5), on pharmacokinetics of glyburide was also studied. The results showed that co-administration of paroxetine markedly reduced plasma exposure and prolonged Tmax of glyburide, accompanied by significant increase in fecal excretion of glyburide. Co-administration of naringin also significantly decreased plasma exposure of glyburide. Data from intestinal perfusion experiments showed that both paroxetine and naringin significantly inhibited intestinal absorption of glyburide. Caco-2 cells were used to investigate whether paroxetine and naringin affected intestinal transport of glyburide and fexofenadine (a substrate of Oatp1a5). The results showed that both paroxetine and naringin greatly inhibited absorption of glyburide and fexofenadine. All results gave a conclusion that co-administration of paroxetine decreased plasma exposure of glyburide in rats via inhibiting intestinal absorption of glyburide, which may partly be attributed to the inhibition of intestinal Oatp1a5 activity.

Effects of one-time apple juice ingestion on the pharmacokinetics of fexofenadine enantiomers

PURPOSE

We examined the effect of a single apple juice intake on the pharmacokinetics of fexofenadine enantiomers in healthy Japanese subjects.

METHODS

In a randomized two phase, open-label crossover study, 14 subjects received 60 mg of racemic fexofenadine simultaneously with water or apple juice. For the uptake studies, oocytes expressing organic anion-transporting polypeptide 2B1 (OATP2B1) were incubated with 100 μM (R)- and (S)-fexofenadine in the presence or absence of 10 % apple juice.

RESULTS

One-time ingestion of apple juice significantly decreased the area under the plasma concentration-time curve (AUC0-24) for (R)- and (S)-fexofenadine by 49 and 59 %, respectively, and prolonged the time to reach the maximum plasma concentration (t max) of both enantiomers (P < 0.001). Although apple juice greatly reduced the amount of (R)- and (S)-fexofenadine excretion into urine (Ae0-24) by 54 and 58 %, respectively, the renal clearances of both enantiomers were unchanged between the control and apple juice phases. For in vitro uptake studies, the uptake of both fexofenadine enantiomers into OATP2B1 complementary RNA (cRNA)-injected oocytes was significantly higher than that into water-injected oocytes, and this effect was greater for (R)-fexofenadine. In addition, apple juice significantly decreased the uptake of both enantiomers into OATP2B1 cRNA-injected oocytes.

CONCLUSIONS

These results suggest that OATP2B1 plays an important role in the stereoselective pharmacokinetics of fexofenadine and that one-time apple juice ingestion probably inhibits intestinal OATP2B1-mediated transport of both enantiomers. In addition, this study demonstrates that the OATP2B1 inhibition effect does not require repeated ingestion or a large volume of apple juice.

Characterization of gastrointestinal absorption of digoxin involving influx and efflux transporter in rats: application of mdr1a knockout (-/-) rats into absorption study of multiple transporter substrate

1.  This study was aimed to characterize gastrointestinal absorption of digoxin using wild-type (WT) and multidrug resistance protein 1a [mdr1a; P-glycoprotein (P-gp)] knockout (-/-) rats. 2.  In WT rats, the area under the plasma concentration-time curve (AUC) of oral digoxin increased after oral pretreatment with quinidine at 30 mg/kg compared with non-treatment, but the increasing ratio tended to decrease at a high dose of 100 mg/kg. In mdr1a (-/-) rats, however, quinidine pretreatment caused a dose-dependent decrease in the AUC. 3.  Quinidine pretreatment did not alter the hepatic availability of digoxin, indicating that the changes in the digoxin AUC were attributable to inhibition of the absorption process by quinidine; i.e. inhibition of influx by quinidine in mdr1a (-/-) rats and inhibition of efflux and influx by quinidine in WT rats. 4.  An in situ rat intestinal closed loop study using naringin implied that organic anion transporting peptide (Oatp) 1a5 may be a responsible transporter in the absorption of digoxin. 5.  These findings imply that the rat absorption behavior of digoxin is possibly governed by Oatp1a5-mediated influx and P-gp-mediated efflux. The mdr1a (-/-) rat is therefore a useful in vivo tool to investigate drug absorption associated with multiple transporters including P-gp.

Functional involvement of RFVT3/SLC52A3 in intestinal riboflavin absorption

Riboflavin, also known as vitamin B2, is transported across the biological membrane into various organs by transport systems. Riboflavin transporter RFVT3 is expressed in the small intestine and has been suggested to localize in the apical membranes of the intestinal epithelial cells. In this study, we investigated the functional involvement of RFVT3 in riboflavin absorption using intestinal epithelial T84 cells and mouse small intestine. T84 cells expressed RFVT3 and conserved unidirectional riboflavin transport corresponding to intestinal absorption. Apical [(3)H]riboflavin uptake was pH-dependent in T84 cells. This uptake was not affected by Na(+) depletion at apical pH 6.0, although it was significantly decreased at apical pH 7.4. The [(3)H]riboflavin uptake from the apical side of T84 cells was prominently inhibited by the RFVT3 selective inhibitor methylene blue and significantly decreased by transfection of RFVT3-small-interfering RNA. In the gastrointestinal tract, RFVT3 was expressed in the jejunum and ileum. Mouse jejunal and ileal permeabilities of [(3)H]riboflavin were measured by the in situ closed-loop method and were significantly reduced by methylene blue. These results strongly suggest that RFVT3 would functionally be involved in riboflavin absorption in the apical membranes of intestinal epithelial cells.

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.

The effects of flavonoids on the ABC transporters: consequences for the pharmacokinetics of substrate drugs

INTRODUCTION

The flavonoids are a large group of dietary plant compounds with suggested health benefits. There is accumulating evidence that many of these flavonoids can interact with the major drug transporters (and metabolizing enzymes) in the body, leading to alterations in the pharmacokinetics of substrate drugs, and thus their efficacy and toxicity.

AREAS COVERED

This review summarizes and updates the reported in vitro and in vivo interactions between common dietary flavonoids and the major drug-effluxing ABC transporters; these include P-glycoprotein, breast cancer resistance protein and multidrug resistance proteins 1 and 2. In contrast to previous reviews, the ADME of flavonoids are considered, along with their glycosides and Phase II conjugates. The authors also consider their possible interactions with the ABC transporters in the oral absorption, distribution into pharmacological sanctuaries and excretion of substrate drugs. Electronic databases, including PubMed, Scopus and Google Scholar were searched to identify appropriate in vitro and in vivo ABC transporter-flavonoid interactions, particularly within the last 10 years.

EXPERT OPINION

Caution is advised when taking flavonoid-containing supplements or herbal remedies concurrently with drugs. Further clinical studies are warranted to explore the impact of flavonoids and their metabolites on the pharmacokinetics, efficacy and toxicity of drugs.

Long-lasting inhibitory effect of apple and orange juices, but not grapefruit juice, on OATP2B1-mediated drug absorption

Enzyme-based grapefruit juice (GFJ)-drug interactions are mainly due to mechanism-based irreversible inhibition of metabolizing enzyme CYP3A4 by GFJ components, but the transporter organic anion transporting polypeptide (OATP)2B1 is also a putative site of interaction between drugs and fruit juices (FJ) in the absorption process. Here we aimed to investigate the effect of preincubation with FJ on OATP2B1-mediated transport of drugs in vitro. When OATP2B1-expressing Xenopus oocytes were preincubated with GFJ, orange juice (OJ), or apple juice (AJ), AJ induced a remarkable decrease in OATP2B1-mediated estrone-3-sulfate uptake in a concentration-dependent manner (IC(50) = 1.5%). A similar but less potent effect was observed with OJ (IC(50) = 21%), whereas GFJ had no effect. Similar results were obtained in preincubation studies using fexofenadine. Preincubation with OJ and AJ resulted in time-dependent inhibition of OATP2B1. Again, AJ had the more potent effect; its action lasted for at least 240 minutes, suggesting that AJ irreversibly inhibits OATP2B1-mediated drug uptake. Kinetic analysis revealed that coincubation and preincubation with AJ reduced OATP2B1-mediated estrone-3-sulfate uptake via competitive and noncompetitive mechanisms, respectively. Thus, OATP2B1 is functionally impaired through both competitive and long-lasting inhibition mechanisms by AJ and OJ, but not GFJ. Interestingly, although GFJ but not AJ is able to irreversibly inhibit CYP3A4, in the case of OATP2B1, AJ but not GFJ has a long-lasting inhibitory effect. Accordingly, complex FJ-drug interactions may occur in vivo, and their clinical significance should be examined.

Oral drug delivery utilizing intestinal OATP transporters

Transporters play important roles in tissue distribution and urinary- and biliary-excretion of drugs and transporter molecules involved in those processes have been elucidated well. Furthermore, an involvement of efflux transporters such as P-glycoproteins, multidrug resistance associated protein 2, and breast cancer resistance protein as the intestinal absorption barrier and/or intestinal luminal secretion mechanisms has been demonstrated. However, although there are many suggestions for the contribution of uptake/influx transporters in intestinal absorption of drugs, information on the transporter molecules responsible for the intestinal absorptive process is limited. Among them, most studied absorptive drug transporter is peptide transporter PEPT1. However, utilization of PEPT1 for oral delivery of drugs may not be high due to the chemical structural requirement of PEPT1 limited to peptide-mimetics. Recently, organic anion transporting polypeptide (OATP) family such as OATP1A2 and OATP2B1 has been suggested to mediate intestinal absorption of several drugs. Since OATPs exhibit species difference in expressed tissues and functional properties between human and animals, human studies are essential to clarify the intestinal absorption mechanisms of drugs via OATPs. Recent pharmacogenomic studies demonstrated that OATP2B1 is involved in the drug absorption in human. In addition, information of drug-juice interaction in the intestine also uncovered the contribution of OATP1A2 and OATP2B1 in drug absorption. Since OATP1A2 and OATP2B1 exhibit broader substrate selectivity compared with PEPT1, their potential to be applied for oral delivery should be high. In this review, current understanding of characteristics and contribution as the absorptive transporters of OATPs in small intestine in human is described. Now, it is getting clearer that OATPs have significant roles in intestinal absorption of drugs, therefore, there are higher possibility to utilize OATPs as the tools for oral delivery.

Effects of rifampicin, dexamethasone, St. John's Wort and Thyroxine on maternal and foetal expression of Abcb1 and organ distribution of talinolol in pregnant rats

It is well accepted that ABCB1 plays a critical role in absorption, distribution and elimination of many xenobiotics and drugs. Only little is known about the regulation and function of ABCB1 during pregnancy. Thus, the aim of this study is to investigate maternal, placental and foetal Abcb1 expression and function in pregnant rats after induction with rifampicin, dexamethasone, St. John's wort (SJW) or thyroxine. Wistar rats were orally treated with rifampicin (250 mg/kg), SJW (1.0 g/kg), thyroxine (9 μg/kg), dexamethasone (1 mg/kg) or 0.5% methylcellulose suspension (control) for 9 days during late pregnancy (each N = 5). Afterwards, organ mRNA expression and protein content of Abcb1a were determined. Tissue concentrations of the ABCB1 probe drug talinolol were measured after repeated administration of the drug (100 mg/kg, 9 days) and after induction with oral rifampicin (250 mg/kg, 9 days, N = 5). Abcb1 expression was substantially lower in foetal than in maternal organs. Abcb1 was significantly induced by SJW in the maternal jejunum and placenta, by dexamethasone in foetal brain and liver and by thyroxine in the placenta and maternal and foetal brain. Rifampicin induced Abcb1 in all maternal and foetal organs. However, organ distribution of talinolol was not influenced by comedication of rifampicin. In conclusion, maternal and foetal Abcb1 organ expression in pregnant rats is inducible by nuclear receptor agonists. Although rifampicin regulates maternal and foetal Abcb1 expression, organ distribution of talinolol remains unchanged most likely caused by the known inhibitory effect of rifampicin on Abcb1 function.

Functional pleiotropy of organic anion transporting polypeptide OATP2B1 due to multiple binding sites

The purpose of this study was to examine whether the presence of multiple binding sites can explain the pleiotropy of substrate recognition by OATP2B1, using Xenopus oocytes expressing OATP2B1. OATP2B1-mediated uptake of estrone-3-sulfate apparently exhibited biphasic saturation kinetics, with Km values of 0.10 ± 0.05 and 29.9 ± 12.1 µM and Vmax values of 14.1 ± 6.4 and 995 ± 273 fmol/min/oocyte for high- and low-affinity sites, respectively. Contribution analysis revealed that transport of estrone-3-sulfate mediated by high- and low-affinity sites on OATP2B1 could be evaluated at the concentrations of 0.005 and 50 µM, respectively. pH-dependence study of OATP2B1-mediated estrone-3-sulfate uptake suggested that high- and low-affinity sites show different pH sensitivity. When the inhibitory effect of 12 compounds on estrone-3-sulfate uptake by high- and low-affinity sites on OATP2B1 was examined, 4 compounds appeared to be inhibitors of the high-affinity site on OATP2B1. Two other compounds appeared to be inhibitors for the low-affinity site and four others were inhibitory at both sites. These results indicated the presence of multiple binding sites on OATP2B1 with different affinity for drugs. Accordingly, it is likely that drug-drug and drug-beverage interactions occur only when two drugs share the same binding site on OATP2B1.

Characterization of multidrug resistance 1a/P-glycoprotein knockout rats generated by zinc finger nucleases

The development of zinc finger nuclease (ZFN) technology has enabled the genetic engineering of the rat genome. The ability to manipulate the rat genome has great promise to augment the utility of rats for biological and pharmacological studies. A Wistar Hannover rat model lacking the multidrug resistance protein Mdr1a P-glycoprotein (P-gp) was generated using a rat Mdr1a-specific ZFN. Mdr1a was completely absent in tissues, including brain and small intestine, of the knockout rat. Pharmacokinetic studies with the Mdr1a P-gp substrates loperamide, indinavir, and talinolol indicated that Mdr1a was functionally inactive in the blood-brain barrier and intestine in Mdr1a(-/-) rats. To identify possible compensatory mechanisms in Mdr1a(-/-) rats, the expression levels of drug-metabolizing enzyme and transporter-related genes were compared in brain, liver, kidney, and intestine of male and female Mdr1a(-/-) and control rats. In general, alterations in gene expression of these genes in Mdr1a(-/-) rats seemed to be modest, with more changes in female than in male rats. Taken together, our studies demonstrate that the ZFN-generated Mdr1a(-/-) rat will be a valuable tool for central nervous system drug target validation and determining the role of P-gp in drug absorption and disposition.