Profile of P‐glycoprotein Distribution in the Rat and Its Possible Influence on the Salbutamol Intestinal Absorption Irocess

A Cyclodextrin-Stabilized Spermine-Tagged Drug Triplex that Targets Theophylline to the Lungs Selectively in Respiratory Emergency

Ion‐pairing a lifesaving drug such as theophylline with a targeting moiety could have a significant impact on medical emergencies such as status asthmaticus or COVID‐19 induced pneumomediastinum. However, to achieve rapid drug targeting in vivo the ion‐pair must be protected against breakdown before the entry into the target tissue. This study aims to investigate if inserting theophylline, when ion‐paired to the polyamine transporter substrate spermine, into a cyclodextrin (CD), to form a triplex, could direct the bronchodilator to the lungs selectively after intravenous administration. NMR demonstrates that upon the formation of the triplex spermine protruded from the CD cavity and this results in energy‐dependent uptake in A549 cells (1.8‐fold enhancement), which persists for more than 20 min. In vivo, the triplex produces a 2.4‐fold and 2.2‐fold increase in theophylline in the lungs 20 min after injection in rats and mice, respectively (p < 0.05). The lung targeting is selective with no increase in uptake into the brain or the heart where the side‐effects of theophylline are treatment‐limiting. Selectively doubling the concentration of theophylline in the lungs could improve the benefit‐risk ratio of this narrow therapeutic index medicine, which continues to be important in critical care.

LPS-induced inflammation delays the transportation of ASP+ due to down-regulation of OCTN1/2 in alveolar epithelial cells

Organic cation transporters (OCTNs) can significantly affect drug disposition in alveolar epithelial cells (A549), but this process is not well understood. We investigated the expression and function of OCTN1/2 in A549 cells under different inflammatory status to examine pulmonary drug distribution. This experiment used lipopolysaccharide (LPS)-treated A549 cells to mimic inflammation in alveolar epithelial cells, and the expression of OCTN1/2, interleukin-6 (IL6), IL18, IL1β and tumour necrosis factor-alpha (TNF-α) was investigated by western blot and quantitative real-time PCR (qRT-PCR). The fluorescent compound 4-(4-(dimethylamino)styryl)-N-methylpyridinium iodide (ASP⁺) was chosen as a probe to study the activity of OCTN1/2. OCTN1/2 down-regulation induced by LPS was more pronounced than that in normal control (NC) groups. Experiments further detected the release of inflammatory factors that revealed a negative correlation between OCTN1/2 expression and inflammation secretion in human alveolar epithelial cells exposed to different concentrations of LPS. The Michaelis constant (K_m) and apparent permeability coefficient (P_app) of ASP⁺ were also decreased significantly. Our results thus show that LPS-induced inflammation could inhibit the expression and activity of OCTN1/2 in vitro and reduce the distribution of inhaled medicine in pulmonary diseases.

Levofloxacin effect on erlotinib absorption. Evaluation of the interaction in undernutrition situations through population pharmacokinetic analysis in rats

The main objective of this study was to develop a pharmacokinetic model in order to describe the intestinal absorption of erlotinib in rat and to quantify the interaction of levofloxacin on this process in well- and under-nourished rats. Absorption studies were performed in male Wistar rats. Concentration-time profiles in proximal and distal intestine were analysed through non-linear mixed effect modelling using the NONMEM software version 7.3. Simulations were performed in order to explore the influence of covariates on the apparent absorption rate constant. A passive absorption and an active secretion process best-described erlotinib absorption from lumen to enterocyte. The developed model indicates that levofloxacin exerts an inhibition on erlotinib efflux transporters of the gut epithelium. Undernourishment proved to significantly decrease the maximum capacity of the secretion process. Simulations evidenced that erlotinib absorption only takes place at high enough drug concentrations to overcome the effect of efflux transporters. On the other hand, when levofloxacin is present in the intestinal lumen of undernourished rats, erlotinib drug absorption takes place even at low erlotinib concentrations. In the clinical setting, this interaction may result in increased exposure to erlotinib, especially in undernourished cancer patients. Copyright © 2017 John Wiley & Sons, Ltd.

Curcumin-carboxymethyl chitosan (CNC) conjugate and CNC/LHR mixed polymeric micelles as new approaches to improve the oral absorption of P-gp substrate drugs

The low oral bioavailability of numerous drugs has been mostly attributed to the significant effect of P-gp-mediated efflux on intestinal drug transport. Herein, we developed mixed polymeric micelles (MPMs) comprised of curcumin-carboxymethyl chitosan (CNC) conjugate, as a potential inhibitor of P-gp-mediated efflux and gastrointestinal absorption enhancer, and low-molecular-weight heparin-all-trans-retinoid acid (LHR) conjugate, as loading material, with the aim to improve the oral absorption of P-gp substrate drugs. CNC conjugate was synthesized by chemical bonding of curcumin (Cur) and carboxymethyl chitosan (CMCS) taking advantage of the inhibition of intestinal P-gp-mediated secretion by Cur and the intestinal absorption enhancement by CMCS. The chemical structure of CNC conjugate was characterized by ¹H NMR with a degree of substitution of Cur of 4.52-10.20%. More importantly, CNC conjugate markedly improved the stability of Cur in physiological pH. Cyclosporine A-loaded CNC/LHR MPMs (CsA-CNC/LHR MPMs) were prepared by dialysis method, with high drug loading 25.45% and nanoscaled particle size (∼200 nm). In situ single-pass perfusion studies in rats showed that both CsA + CNC mixture and CsA-CNC/LHR MPMs achieved significantly higher K_a and P_eff than CsA suspension in the duodenum and jejunum segments (p <  0.01), which was comparable to verapamil coperfusion effect. Similarly, CsA + CNC mixture and CsA-CNC/LHR MPMs significantly increased the oral bioavailability of CsA as compared to CsA suspension. These results suggest that CNC conjugate might be considered as a promising gastrointestinal absorption enhancer, while CNC/LHR MPMs had the potential to improve the oral absorption of P-gp substrate drugs.

Trantinterol, a novel β2-adrenoceptor agonist, noncompetitively inhibits P-glycoprotein function in vitro and in vivo

P-glycoprotein (P-gp)-mediated drug-drug interactions are important factors causing adverse effects of drugs in clinical use. The aim of this study was to determine whether trantinterol (also known as SPFF), a novel β2-adrenoceptor agonist, was a P-gp inhibitor or substrate. The results showed that trantinterol was not a substrate of P-gp but increased rhodamine 123 (Rho 123) uptake by MDCK-MDR1 cells and decreased the efflux transport of both Rho 123 and cyclosporine A (CsA) in bidirectional transport studies across MDCK-MDR1 cell monolayers. This suggested that trantinterol was a P-gp inhibitor but not a P-gp substrate. The mechanism of inhibition was investigated in the P-gp-Glo assay system, where it was found that trantinterol inhibited P-gp ATPase activity in a dose-dependent manner. A subsequent study using the antibody binding assay with the conformation-sensitive P-gp-specific antibody UIC2 confirmed that trantinterol decreased UIC2 binding at 10 μM in contrast to the competitive inhibitor, verapamil. This suggested that trantinterol was a noncompetitive inhibitor of P-gp. Finally, a pharmacokinetic study in rat showed that trantinterol significantly increased the area under the plasma concentration-time curve (AUC) and maximum plasma concentration (Cmax) of digoxin and paclitaxel (PAC), and the Cmax of cyclosporine A (CsA). In summary, trantinterol is a potent noncompetitive P-gp inhibitor which may increase the bioavailability of other P-gp substrate drugs coadministered with it.

In situ perfusion in rodents to explore intestinal drug absorption: challenges and opportunities

The in situ intestinal perfusion technique in rodents is a very important absorption model, not only because of its predictive value, but it is also very suitable to unravel the mechanisms underlying intestinal drug absorption. This literature overview covers a number of specific applications for which the in situ intestinal perfusion set-up can be applied in favor of established in vitro absorption tools, such as the Caco-2 cell model. Qualities including the expression of drug transporters and metabolizing enzymes relevant for human intestinal absorption and compatibility with complex solvent systems render the in situ technique the most designated absorption model to perform transporter-metabolism studies or to evaluate the intestinal absorption from biorelevant media. Over the years, the in situ intestinal perfusion model has exhibited an exceptional ability to adapt to the latest challenges in drug absorption profiling. For instance, the introduction of the mesenteric vein cannulation allows determining the appearance of compounds in the blood and is of great use, especially when evaluating the absorption of compounds undergoing intestinal metabolism. Moreover, the use of the closed loop intestinal perfusion set-up is interesting when compounds or perfusion media are scarce. Compatibility with emerging trends in pharmaceutical profiling, such as the use of knockout or transgenic animals, generates unparalleled possibilities to gain mechanistic insight into specific absorption processes. Notwithstanding the fact that the in situ experiments are technically challenging and relatively time-consuming, the model offers great opportunities to gain insight into the processes determining intestinal drug absorption.

Comparison of the permeability of metoprolol and labetalol in rat, mouse, and Caco-2 cells: use as a reference standard for BCS classification

The purpose of this study was to investigate labetalol as a potential high permeability reference standard for the application of Biopharmaceutics Classification Systems (BCS). Permeabilities of labetalol and metoprolol were investigated in animal intestinal perfusion models and Caco-2 cell monolayers. After isolating specific intestinal segments, in situ single-pass intestinal perfusions (SPIP) were performed in rats and mice. The effective permeabilities (Peff) of labetalol and metoprolol, an FDA standard for the low/high Peff class boundary, were investigated in two different segments of rat intestine (proximal jejunum and distal ileum) and in the proximal jejunum of mouse. No significant difference was found between Peff of metoprolol and labetalol in the jejunum and ileum of rat (0.33 ± 0.11 × 10(-4) vs 0.38 ± 0.06 × 10(-4) and 0.57 ± 0.17 × 10(-4) vs 0.64 ± 0.30 × 10(-4) cm/s, respectively) and in the jejunum of mouse (0.55 ± 0.05 × 10(-4) vs 0.59 ± 0.13 × 10(-4) cm/s). However, Peff of metoprolol and labetalol were 1.7 and 1.6 times higher in the jejunum of mouse, compared to the jejunum of rat, respectively. Metoprolol and labetalol showed segmental-dependent permeability through the rat intestine, with increased Peff in the distal ileum in comparison to the proximal jejunum. Most significantly, Peff of labetalol was found to be concentration-dependent. Decreasing concentrations of labetalol in the perfusate resulted in decreased Peff compared to Peff of metoprolol. The intestinal epithelial permeability of labetalol was lower than that of metoprolol in Caco-2 cells at both apical pH 6.5 and 7.5 (5.96 ± 1.96 × 10(-6) vs 9.44 ± 3.44 × 10(-6) and 15.9 ± 2.2 × 10(-6) vs 23.2 ± 7.1 × 10(-6) cm/s, respectively). Labetalol exhibited higher permeability in basolateral to apical (BL-AP) compared to AP-BL direction in Caco-2 cells at 0.1 times the highest dose strength (HDS) (46.7 ± 6.5 × 10(-6) vs 14.2 ± 1.5 × 10(-6) cm/s). The P-gp inhibitor, verapamil, significantly increased AP-BL and decreased BL-AP direction transport of labetalol. Overall, labetalol showed high Peff in rat and mouse intestinal perfusion models similar to metoprolol at a concentration based on HDS. However, the concentration-dependent permeability of labetalol in mice due to P-gp and the inhibition study with verapamil in Caco-2 cells indicated that labetalol is not an ideal reference standard for BCS classification.

Multidrug resistance protein gene expression in Trichoplusia ni caterpillars

Many insect species exhibit pesticide-resistant phenotypes. One of the mechanisms capable of contributing to resistance is the overexpression of multidrug resistance (MDR) transporter proteins. Here we describe the cloning of three genes encoding MDR proteins from Trichoplusia ni: trnMDR1, trnMDR2 and trnMDR3. Real-time quantitative PCR (qPCR) detected trnMDR mRNA in the whole nervous system, midgut and Malpighian tubules of final instar T. ni caterpillars. To test whether these genes are upregulated in response to chemical challenge in this insect, qPCR was used to compare trnMDR mRNA levels in unchallenged insects with those of insects fed the synthetic pyrethroid, deltamethrin. Only limited increases were detected in a single gene, trnMDR2, which is the most weakly expressed of the three MDR genes, suggesting that increased multidrug resistance of this type is not a significant part of the response to deltamethrin exposure.

Enhanced oral bioavailability of paclitaxel in pluronic/LHR mixed polymeric micelles: preparation, in vitro and in vivo evaluation

In order to enhance paclitaxel oral bioavailability, mixed polymeric micelles that comprised of pluronic copolymers and low molecular weight heparin-all-trans-retinoid acid (LHR) conjugate were developed. PTX-loaded mixed polymeric micelles (MPMs) were prepared by dialysis method with high drug loading 26.92 ± 2.08% and 25.82 ± 1.9% for F127/LHR and P188/LHR MPMs respectively, and were found to be spherical in shape with an average size of around 140 nm and a narrow size distribution. In vitro release study showed that pluronic/LHR MPMs exhibited delayed release characteristics compared to Taxol and faster drug release profile compared to LHR plain polymeric micelles (PPMs). The cytotoxic activity of PTX-loaded pluronic/LHR MPMs was slightly higher than LHR PPMs in MCF-7 cells (p<0.01). In situ effective permeability of PTX through rat small intestine was 5- to 6-fold higher with mixed micelles than that of Taxol. Moreover, pluronic/LHR MPMs achieved significantly higher AUC and C(max) level than both of LHR PPMs and Taxol. This enhancement might be due to the inhibition of both P-glycoprotein efflux system and cytochrome P450 metabolism by pluronic copolymers. The current results encourage further development of paclitaxel mixed polymeric micelles as an oral drug delivery system.

Drug transporters in the lung--do they play a role in the biopharmaceutics of inhaled drugs?

The role of transporters in drug absorption, distribution and elimination processes as well as in drug-drug interactions is increasingly being recognised. Although the lungs express high levels of both efflux and uptake drug transporters, little is known of the implications for the biopharmaceutics of inhaled drugs. The current knowledge of the expression, localisation and functionality of drug transporters in the pulmonary tissue and the few studies that have looked at their impact on pulmonary drug absorption is extensively reviewed. The emphasis is on transporters most likely to affect the disposition of inhaled drugs: (1) the ATP-binding cassette (ABC) superfamily which includes the efflux pumps P-glycoprotein (P-gp), multidrug resistance associated proteins (MRPs), breast cancer resistance protein (BCRP) and (2) the solute-linked carrier (SLC and SLCO) superfamily to which belong the organic cation transporter (OCT) family, the peptide transporter (PEPT) family, the organic anion transporter (OAT) family and the organic anion transporting polypeptide (OATP) family. Whenever available, expression and localisation in the intact human tissue are compared with those in animal lungs and respiratory epithelial cell models in vitro. The influence of lung diseases or exogenous agents on transporter expression is also mentioned.

In vitro and in vivo evaluation of buccal bioadhesive films containing salbutamol sulphate

The aim of present study was to prepare and evaluate buccal bioadhesive films of salbutamol sulphate (SS) for the treatment of asthma. The films were designed to release the drug for a prolonged period of time so as to reduce the frequency of administration of the available conventional dosage forms of SS. The different proportions of sodium carboxymethylcellulose (SCMC) and Carbopol 940P (CP 940P) were used for the preparation of films. Carbopol was used to incorporate the desired bioadhesiveness in the films. The films were prepared by solvent casting method and evaluated for bioadhesion, in vitro drug release and anti asthmatic effect (bronchoprotection) in histamine induced bronchospasm of guinea pigs. In vitro drug release from the film was determined using a modified Franz diffusion cell while bioadhesiveness was evaluated with a modified two-arm balance using guinea pig buccal mucosa as a model tissue. Films containing SCMC : CP 940P ratio of 76 : 24 was found to be the best with moderate swelling along with favorable bioadhesion force and in vitro drug release. The drug release mechanism was found to follow non-Fickian diffusion as release mechanism. The prolonged in vivo effect (bronchoprotection) obtained from the buccal bioadhesive film of SS administered via buccal route may improve the treatment of asthmatic disorders by reducing the frequency of administration which is associated with the tolerance effect of SS. Additionally for the clinical benefit, it is also expected to reduce the major adverse effects of SS such as tachycardia and arrhythmias via buccal absorption.

Synthesis and preclinical evaluation of novel PET probes for P-glycoprotein function and expression

P-glycoprotein (P-gp) is an ATP-dependent efflux pump protecting the body against xenobiotics. A P-gp substrate (7) and an inhibitor (6) were labeled with (11)C, resulting in potential tracers of P-gp function and expression.

METHODS

6 and 7 were labeled using (11)CH(3)I. (11)C-verapamil was prepared as published previously, using (11)C-methyl triflate. MicroPET scans (with arterial sampling) and biodistribution studies were performed in rats pretreated with saline, cyclosporin A (CsA, 50 mg/kg), or cold 6 (15 mg/kg).

RESULTS

The radiochemical yields of (11)C-6 and (11)C-7 were approximately 30% with a total synthesis time of 45 min. Cerebral distribution volumes (DV) of (11)C-6 (2.35 +/- 0.11) and (11)C-7 (1.86 +/- 0.15) in saline-treated rats were higher than of (11)C-verapamil (0.64 +/- 0.12). DVs of (11)C-7 and (11)C-verapamil were significantly increased by CsA (to 5.26 +/- 0.14 and 5.85 +/- 0.32, respectively). The DV of (11)C-6 was reduced by cold 6 (to 1.65 +/- 0.03). Its uptake was also reduced (up to 67%) in several peripheral organs that express P-gp.

CONCLUSIONS

(11)C-7 is a novel tracer of P-gp function with higher baseline uptake than (11)C-verapamil. Upregulation of P-gp function in response to treatment (which is hard to detect with (11)C-verapamil) may be detectable using (11)C-7 and PET. Because (11)C-6 shows specific binding in target organs, this compound is the first PET tracer allowing measurement of P-gp expression.

The H2 receptor antagonist nizatidine is a P-glycoprotein substrate: characterization of its intestinal epithelial cell efflux transport

The aim of this study was to elucidate the intestinal epithelial cell efflux transport processes that are involved in the intestinal transport of the H(2) receptor antagonist nizatidine. The intestinal epithelial efflux transport mechanisms of nizatidine were investigated and characterized across Caco-2 cell monolayers, in the concentration range 0.05-10 mM in both apical-basolateral (AP-BL) and BL-AP directions, and the transport constants of P-glycoprotein (P-gp) efflux activity were calculated. The concentration-dependent effects of various P-gp (verapamil, quinidine, erythromycin, ketoconazole, and cyclosporine A), multidrug resistant-associated protein 2 (MRP2; MK-571, probenecid, indomethacin, and p-aminohipuric acid), and breast cancer resistance protein (BCRP; Fumitremorgin C) inhibitors on nizatidine bidirectional transport were examined. Nizatidine exhibited 7.7-fold higher BL-AP than AP-BL Caco-2 permeability, indicative of net mucosal secretion. All P-gp inhibitors investigated displayed concentration-dependent inhibition on nizatidine secretion in both directions. The IC(50) of verapamil on nizatidine P-gp secretion was 1.2 x 10(-2) mM. In the absence of inhibitors, nizatidine displayed concentration-dependent secretion, with one saturable (J(max) = 5.7 x 10(-3) nmol cm(-2) s(-1) and K(m) = 2.2 mM) and one nonsaturable component (K(d) = 7 x 10(-4) microL cm(-2) s(-1)). Under complete P-gp inhibition, nizatidine exhibited linear secretory flux, with a slope similar to the nonsaturable component. V(max) and K(m) estimated for nizatidine P-gp-mediated secretion were 4 x 10(-3) nmol cm(-2) s(-1) and 1.2 mM, respectively. No effect was obtained with the MRP2 or the BCRP inhibitors. Being a drug commonly used in pediatrics, adults, and elderly, nizatidine susceptibility to efflux transport by P-gp revealed in this paper may be of significance in its absorption, distribution, and clearance, as well as possible drug-drug interactions.

Segmental dependent transport of low permeability compounds along the small intestine due to P-glycoprotein: the role of efflux transport in the oral absorption of BCS class III drugs

The purpose of this study was to investigate the role of P-gp efflux in the in vivo intestinal absorption process of BCS class III P-gp substrates, i.e. high-solubility low-permeability drugs. The in vivo permeability of two H (2)-antagonists, cimetidine and famotidine, was determined by the single-pass intestinal perfusion model in different regions of the rat small intestine, in the presence or absence of the P-gp inhibitor verapamil. The apical to basolateral (AP-BL) and the BL-AP transport of the compounds in the presence or absence of various efflux transporters inhibitors (verapamil, erythromycin, quinidine, MK-571 and fumitremorgin C) was investigated across Caco-2 cell monolayers. P-gp expression levels in the different intestinal segments were confirmed by immunoblotting. Cimetidine and famotidine exhibited segmental dependent permeability through the gut wall, with decreased P(eff) in the distal ileum in comparison to the proximal regions of the intestine. Coperfusion of verapamil with the drugs significantly increased the permeability in the ileum, while no significant change in the jejunal permeability was observed. Both drugs exhibited significantly greater BL-AP than AP-BL Caco-2 permeability, indicative of net mucosal secretion. Concentration dependent decrease of this secretion was obtained by the P-gp inhibitors verapamil, erythromycin and quinidine, while no effect was evident by the MRP2 inhibitor MK-571 and the BCRP inhibitor FTC, indicating that P-gp is the transporter mediates the intestinal efflux of cimetidine and famotidine. P-gp levels throughout the intestine were inversely related to the in vivo permeability of the drugs from the different segments. The data demonstrate that for these high-solubility low-permeability P-gp substrates, P-gp limits in vivo intestinal absorption in the distal segments of the small intestine; however P-gp plays a minimal role in the proximal intestinal segments due to significant lower P-gp expression levels in this region.

Marked impact of P-glycoprotein on the absorption of TAK-427 in rats

The role of P-glycoprotein (P-gp, ABCB1) on the absorption process was investigated by drug-drug interaction studies of TAK-427 with P-gp inhibitors (erythromycin, ketoconazole or quinidine) in rats and by transport studies using rat multidrug resistance (MDR1) stably expressing cells and rat small intestine mounted in a Ussing-type chamber. TAK-427 showed high efflux activity with low permeability in rat MDR1a and MDR1b stably expressing cells and was revealed to be a typical substrate for P-gps. Although TAK-427 was mainly absorbed from the small intestine in rats, a large part of the dosed compound remained in the gastrointestinal tract. Orally co-administered P-gp inhibitors (50 mg/kg) increased the AUC of TAK-427 after a 5 mg/kg oral dose 5.4- to 18.3-fold, whereas orally administered P-gp inhibitors had a minor effect on the increase in the AUC of TAK-427 (1.3- to 2.2-fold) after a 0.5 mg/kg intravenous dose. Thus, the bioavailability of TAK-427 after oral administration in rats (7.3%) markedly increased when co-administered with P-gp inhibitors (28.6-57.6%). Moreover, the transport of TAK-427 was predominantly secretory throughout the rat small intestine and was inhibited by P-gp inhibitors. In conclusion, P-gp can markedly reduce the absorption of a typical P-gp substrate by its efflux activity throughout the absorption site.

Closing the gaps: a full scan of the intestinal expression of p-glycoprotein, breast cancer resistance protein, and multidrug resistance-associated protein 2 in male and female rats

Intestinal ATP binding cassette (ABC) transporters may affect the bioavailability and effectiveness of orally administered drugs. Available studies on regional expression of intestinal efflux transporters were done with selected intestinal segments only and inconsistent with regard to the variability of transporter expression and the course of expression along the intestine. For an evaluation of the consistency between mRNA and protein expression, relative expression levels of P-glycoprotein (Pgp; ABCB1), breast cancer resistance protein (Bcrp; ABCG2), and multidrug resistance-associated protein (Mrp) 2 (ABCC2) were determined using quantitative real-time-polymerase chain reaction and Western blot in rat intestinal segments from duodenum, jejunum, ileum, and colon. In addition, the protein expression of Pgp, Bcrp, and Mrp2 from the entire rat intestine was studied by a complete 3-cm segmentation to evaluate the predictive power of expression analyses from selected intestinal segments. Pgp showed an increase from proximal to distal regions, Bcrp showed an arcuate pattern with highest expression toward the end of small intestine, and Mrp2 decreased along the intestinal axis from proximal to distal parts. No gender specific differences could be observed. Regarding the concordance of mRNA and protein expression, Pgp and Bcrp mRNA samples allow good estimations about the corresponding protein expression (for Pgp limited to the mdr1a isoform), but for Mrp2, pronounced deviation could be observed. All transporters showed considerable intra- and interindividual variability, especially at the protein level, making it problematic to take transporter expressions of small sections exemplary for general assumptions on intestinal abundances.

Regional Expression and Activity of Breast Cancer Resistance Protein (Bcrp/Abcg2) in Mouse Intestine: Overlapping Distribution with Sulfotransferases

Breast cancer resistance protein (Bcrp/Abcg2) is a member of the ATP-binding cassette transporter family with the ability to transport a variety of sulfate conjugates. In the present study, the regional expression and activity of Bcrp and sulfotransferases (SULTs/Sults) were investigated in mouse intestine. Western blotting analysis revealed the highest expression of Bcrp in the ileum over the duodenum, jejunum, and colon. Functional analysis of Bcrp was performed in everted intestinal sacs using 4-methylumbelliferone (4MU). The mucosal secretion clearance of 4MU sulfate formed in the enterocytes was markedly reduced in the jejunum, ileum, and colon of Bcrp (-/-) mice in comparison with wild-type mice, whereas a slight and nonsignificant reduction was observed in the duodenum. The reduction in the mucosal secretion clearance was most marked in the ileum followed by the colon and jejunum. In addition, the mucosal secretion clearance of minoxidil sulfate, an active metabolite of minoxidil, was also significantly reduced in the intestine of Bcrp (-/-) mice. The sulfation activity of 4MU was higher in the colon than in the small intestine where glucuronidation activity was somewhat higher than the sulfation activity. Real-time polymerase chain reaction analysis showed that the expression of sulfotransferases, such as Sult1a1/2, Sult1b1, and Sult1d1, was also highest in the colon. These results suggest that Bcrp activity is higher in the mid to lower intestine and that the cooperation of Bcrp and SULT provides an important detoxification pathway, particularly in the colon.

In situ kinetic modelling of intestinal efflux in rats: functional characterization of segmental differences and correlation within vitro results

The objective was to devise and apply a novel modelling approach to combine segmental in situ rat perfusion data and in vitro cell culture data, in order to elucidate the contribution of efflux in drug absorption kinetics. The fluoroquinolone CNV97100 was used as a model P-gp substrate. In situ intestinal perfusion was performed in rat duodenum, jejunum, ileum and colon to measure the influence of P-gp expression on efflux. Inhibition studies of CNV97100 were performed in the presence of verapamil, quinidine, cyclosporin A and p-aminohippuric acid. Absorption/efflux parameters were modelled simultaneously, using data from both in situ studies as well as in vitro studies. The maximal efflux velocity was modelled as a baseline value, corrected for each segment based on the expression level. CNV97100 passive diffusional permeability (P(diff)) and its affinity for the efflux carrier (K(m)) were assumed to be the same in all segments. The results indicate the new approach to combine in situ data and in vitro data succeed in yielding a unified, quantitative model for absorption/efflux. The model incorporated a quantitative relationship between P-gp expression level and the efflux functionality, both across in situ and in vitro systems, as well across different intestinal segments in the in situ studies. Permeability values decreased from duodenum to ileum in accordance with the increasing P-gp expression levels in rat intestine. The developed model reflects a strong correlation between in vitro and in situ results, including intrinsic differences in surface area. The successful application of a model approach to combine absorption data from two different experimental systems holds promise for future efforts to predict absorption results from one system to a second system.

Labetalol absorption kinetics: Rat small intestine and colon studies

Labetalol is a widely used drug for the management of hypertension, which is preferably administered by the oral route despite its low bioavailability. The objective of this study is to ascertain the mechanisms underlying its absorption as an approach to help in predicting the influence of dosage changes, possible drug-drug and drug-fruit juice interactions. Perfusion experiments have been performed in rats in two sites of absorption: the intestine and the colon. The nonlinearity of the process has been established by means of the assay of a wide range of concentrations (2-2000 microM). Fitting of the concentration versus time data allows the estimation of passive diffusion constant in the intestine (1.42 +/- 0.05/h) and the colon (1.13 +/- 0.06/h), V(m) and K(m) of the input process (9.85 +/- 4.98 microM/h, and 10.44 +/- 26.16 microM, respectively) and K(m) of an efflux system (0.53 +/- 1.16 microM) and V(m) in both intestinal segments (2.60 +/- 11.37 microM . /h in the intestine and 0.66 +/- 1.38 microM . /h in the colon). The efflux carrier implicated is identified by means of several inhibition experiments, whose inhibition ability is mathematically estimated. Results suggest the p-glycoprotein as responsible for the efflux of labetalol.

Modelling intestinal absorption of salbutamol sulphate in rats

The objective was to develop a semiphysiological population pharmacokinetic model that describes the complex salbutamol sulphate absorption in rat small intestine. In situ techniques were used to characterize the salbutamol sulphate absorption at different concentrations (range: 0.15-18 mM). Salbutamol sulphate at concentration of 0.29 mM was administered in presence of verapamil (10 and 20 mM), grapefruit juice and sodium azide (NaN3) (0.3, 3 and 6 mM). Different pharmacokinetic models were fitted to the dataset using NONMEM. Parametric and non-parametric bootstrap analyses were employed as internal model evaluation techniques. The validated model suggested instantaneous equilibrium between salbutamol sulphate concentrations in lumen and enterocyte, and the salbutamol sulphate absorption was best described by a simultaneous passive diffusion (ka = 0.636 h(-1)) and active absorption (VMax = 0.726 mM/h, Km = 0.540 mM) processes from intestinal lumen to enterocyte, together with an active capacity-limited P-gp efflux (V'max = 0.678 mM/h, K'm = 0.357 mM) from enterocyte to intestinal lumen. The extent of salbutamol sulphate absorption in rat small intestine can be improved by NaN3, grapefruit juice and verapamil.

EFFECT OF P-GLYCOPROTEIN ON INTESTINAL ABSORPTION AND BRAIN PENETRATION OF ANTIALLERGIC AGENT BEPOTASTINE BESILATE

The antiallergic agent bepotastine besilate is a nonsedating, second-generation H1-antagonist with high oral absorption and negligible distribution into brain. To clarify the role of P-glycoprotein (P-gp) in the pharmacokinetics of bepotastine, intestinal absorption and brain penetration studies were performed. [(14)C]Bepotastine transport in P-gp-overexpressed LLC-PK1 cells indicated that bepotastine was a substrate of P-gp. The affinity of bepotastine to P-gp estimated by ATPase activity assay was low, with a K(m) value of 1.25 mM. After i.v. administration, the brain/plasma free concentration ratio in mdr1-knockout mice was 3 times higher than that in wild-type mice. The in situ intestinal absorption studies of [(14)C]bepotastine in rats showed a clear regional difference, showing highest permeability at the upper part of small intestine with a decreasing permeability in the descending part of small intestine. The apparent absorption rate constant (ka) of [(14)C]bepotastine in the small intestine was greatly increased by cyclosporin A and verapamil, especially in the distal portion, and the site-specific absorption of [(14)C]bepotastine disappeared. The concentration dependence of ka of [(14)C]bepotastine was observed with a higher ka at higher concentration (20 mM) compared with that at lower concentration (1 microM). In conclusion, bepotastine is a substrate for P-gp, and P-gp clearly limited the brain distribution of bepotastine, whereas the effect of P-gp on intestinal absorption of bepotastine was minimal, presumably because of high membrane permeability at the upper region of small intestine where P-gp is less expressed. Such intestinal absorption property of bepotastine is distinctly different from the low membrane-permeable P-gp substrate fexofenadine.

Intestinal inflammation induces adaptation of P-glycoprotein expression and activity

Recent studies suggest that P-glycoprotein (Pgp) encoded by MDR1 gene, may be an important factor in the pathogenesis of inflammatory bowel disease (IBD). In this study, we investigated intestinal Pgp expression and activity: (1) in IL10 deficient (IL10(-/-)) mice which spontaneously develop intestinal inflammation affecting the small and large intestine and (2) in DSS (dextran sodium sulfate)-induced rat colitis. In IL10(-/-) enterocolitis mice, rhodamine 123 efflux was reduced by two to three-fold along the small and large intestine. This decrease was associated with a reduction in membrane's Pgp protein levels. A similar three-fold decrease in Pgps activity and expression was observed in the proximal colon in DSS-induced colitis in rats. However, in the non-inflamed ileum in DSS-induced rat colitis, epithelial cell's Pgp activity and protein levels were unexpectedly increased. This effect was specific to local inflammation since LPS induced systemic inflammation did affect neither the intestinal rho 123 efflux transport nor the abundance of the Pgp protein. These data demonstrate for the first time, an impaired function of epithelial Pgp in IL10 deficient enterocolitis mice. They also show an increase in Pgps activity in the non-inflamed ileum in the DSS-induced rat colitis, which may represent an adaptive mechanism to compensate the impaired activity of Pgp in the colon.

Different effect of erythromycin on absorption kinetics of nimodipine in male and female rats

Effect of erythromycin (ERY) on oral absorption of nimodipine (NMD) in female and male rat was investigated in vivo and in vitro. In vivo, at 15 min following oral dose of 50 mg/kg ERY, an oral dose 20 mg/kg NMD was given to rats, plasma concentrations of NMD were determined. In vitro, everted jejunum sac and ileum sac were used, NMD transport from mucosal side to serol side was measured, in absences of ERY and cyclosprin A (CSA) or in presence of ERY and CSA. Large gender difference was found after oral dose NDM. Male rats had lower plasma concentration than female rat did. AUC180 and Cmax in male rats were less than 5-folds and 3-folds than those in female rats, respectively. Co-administrating ERY may increase plasma concentrations of NMD in rats. AUC180 in male rats and female rats were 2.2-folds and 1.9-folds of those NMD alone, respectively. Cmax was about 3-folds of that NMD alone. The NMD transport in intestine showed a regional variation and gender differences. In female rat, transport rate in the jejunum was about 1.3 higher than ileum. Both ERY and CSA significant increases transport of NMD. Contrast to female, NMD transport in jejunum was lower that that in ileum. Bothe ERY and CSA had little effect on NMD transport in intestine. These results indicated that there existed gender difference in oral absorption of NMD and effect of ERY on oral absorption kinetics of NMD in female rats was different from that in male rat.