Characterization of jejunal absorption and apical efflux of ropivacaine, lidocaine and bupivacaine in the rat using in situ and in vitro absorption models

Nicotine transport across calu-3 cell monolayer: effect of nicotine salts and flavored e-liquids

OBJECTIVE

This study aimed to investigate the transport capability of nicotine across Calu-3 cell monolayer in various nicotine forms, including nicotine freebase, nicotine salts, and flavored e-liquids with nicotine benzoate.

SIGNIFICANCE

Nicotine is rapidly absorbed from the respiratory system into systemic circulation during e-cigarettes use. However, the mechanism of nicotine transport in the lung has not been well understood yet. This study may offer critical biological evidence and have implications for the use and regulation of e-cigarettes.

METHODS

The viability of Calu-3 cells after administration of nicotine freebase, nicotine salts and representative e-liquid were evaluated using the MTT assay, and the integrity of the Calu-3 cell monolayer was evaluated by transepithelial electrical resistance measurement and morphological analysis. Further, the nicotine transport capacity across the Calu-3 cell monolayer in various formulations of nicotine was investigated by analysis of nicotine transport amount.

RESULTS

The findings indicated that nicotine transport occurred passively and was time-dependent across the Calu-3cell monolayer. In addition, the nicotine transport was influenced by the type of nicotine salts and their respective pH value. The nicotine benzoate exhibited the highest apparent permeability coefficient (Papp), and higher nicotine-to-benzoic acid ratios led to higher Papp values. The addition of flavors to e-liquid resulted in increased Papp values, with the most significant increment being observed in tobacco-flavored e-liquid.

CONCLUSIONS

In summary, the transport capability of nicotine across the Calu-3 cell monolayer was influenced by the pH values of nicotine salts and flavor additives in e-liquids.

Physiologically-Based Pharmacokinetic Modeling of PAXLOVID™ with First-Order Absorption Kinetics

PURPOSE

PAXLOVID™ is nirmatrelvir tablets co-packaged with ritonavir tablets. Ritonavir is used as a pharmacokinetics (PK) enhancer to reduce metabolism and increase exposure of nirmatrelvir. This is the first disclosure of Paxlovid physiologically-based pharmacokinetic (PBPK) model.

METHODS

Nirmatrelvir PBPK model with first-order absorption kinetics was developed using in vitro, preclinical, and clinical data of nirmatrelvir in the presence and absence of ritonavir. Clearance and volume of distribution were derived from nirmatrelvir PK obtained using a spray-dried dispersion (SDD) formulation where it is considered to be dosed as an oral solution, and absorption is near complete. The fraction of nirmatrelvir metabolized by CYP3A was estimated based on in vitro and clinical ritonavir drug-drug interaction (DDI) data. First-order absorption parameters were established for both SDD and tablet formulation using clinical data. Nirmatrelvir PBPK model was verified with both single and multiple dose human PK data, as well as DDI studies. Simcyp® first-order ritonavir compound file was also verified with additional clinical data.

RESULTS

The nirmatrelvir PBPK model described the observed PK profiles of nirmatrelvir well with predicted AUC and Cmax values within ± 20% of the observed. The ritonavir model performed well resulting in predicted values within twofold of observed.

CONCLUSIONS

Paxlovid PBPK model developed in this study can be applied to predict PK changes in special populations, as well as model the effect of victim and perpetrator DDI. PBPK modeling continues to play a critical role in accelerating drug discovery and development of potential treatments for devastating diseases such as COVID-19. NCT05263895, NCT05129475, NCT05032950 and NCT05064800.

Computational prediction of Calu-3-based in vitro pulmonary permeability of chemicals

Pulmonary is a potential route for drug delivery and exposure to toxic chemicals. The human bronchial epithelial cell line Calu-3 is generally considered to be a useful in vitro model of pulmonary permeability by calculating the apparent permeability coefficient (Papp) values. Since in vitro experiments are time-consuming and labor-intensive, computational models for pulmonary permeability are desirable for accelerating drug design and toxic chemical assessment. This study presents the first attempt for developing quantitative structure-activity relationship (QSAR) models for addressing this goal. A total of 57 chemicals with Papp values based on Calu-3 experiments was first curated from literature for model development and testing. Subsequently, eleven descriptors were identified by a sequential forward feature selection algorithm to maximize the cross-validation performance of a voting regression model integrating linear regression and nonlinear random forest algorithms. With applicability domain adjustment, the developed model achieved high performance with correlation coefficient values of 0.935 and 0.824 for cross-validation and independent test, respectively. The preliminary results showed that computational models could be helpful for predicting Calu-3-based in vitro Pulmonary Permeability of Chemicals. Future works include the collection of more data for further validating and improving the model.

3D Lung-on-Chip Model Based on Biomimetically Microcurved Culture Membranes

A comparatively straightforward approach to accomplish more physiological realism in organ-on-a-chip (OoC) models is through substrate geometry. There is increasing evidence that the strongly, microscale curved surfaces that epithelial or endothelial cells experience when lining small body lumens, such as the alveoli or blood vessels, impact their behavior. However, the most commonly used cell culture substrates for modeling of these human tissue barriers in OoCs, ion track-etched porous membranes, provide only flat surfaces. Here, we propose a more realistic culture environment for alveolar cells based on biomimetically microcurved track-etched membranes. They recreate the mainly spherical geometry of the cells’ native microenvironment. In this feasibility study, the membranes were given the shape of hexagonally arrayed hemispherical microwells by an innovative combination of three-dimensional (3D) microfilm (thermo)forming and ion track technology. Integrated in microfluidic chips, they separated a top from a bottom cell culture chamber. The microcurved membranes were seeded by infusion with primary human alveolar epithelial cells. Despite the pronounced topology, the cells fully lined the alveoli-like microwell structures on the membranes’ top side. The confluent curved epithelial cell monolayers could be cultured successfully at the air−liquid interface for 14 days. Similarly, the top and bottom sides of the microcurved membranes were seeded with cells from the Calu-3 lung epithelial cell line and human lung microvascular endothelial cells, respectively. Thereby, the latter lined the interalveolar septum-like interspace between the microwells in a network-type fashion, as in the natural counterpart. The coculture was maintained for 11 days. The presented 3D lung-on-a-chip model might set the stage for other (micro)anatomically inspired membrane-based OoCs in the future.

Enhanced dissolution and bioavailability of revaprazan using self-nanoemulsifying drug delivery system

A self-nanoemulsifying drug delivery system (SNEDDS) was developed to enhance the dissolution and oral bioavailability (BA) of revaprazan (RVP). Various SNEDDSs containing 200 mg of RVP were formulated using Capmul MCM, Tween 80, and Brij L4, and they were characterized according to their size, polydispersity index, and dissolution behavior. Dissolution rates of all SNEDDS formulations significantly (p <0.05) improved with the formation of nanoemulsion with monodispersity. Formulation D resulted in RVP dissolution exceeding 70% at 2 h. Compared to raw RVP, SNEDDS exhibited a 4.8- to 7.4-fold improved effective permeability coefficient (P_eff) throughout the intestine in the in situ single pass intestinal permeability study and a 5.1-fold increased oral BA in the in vivo oral absorption assessment in rats. To evaluate the degree of lymphatic uptake, cycloheximide (CYC), a chylomicron flowing blocker, was pretreated prior to the experiment. This pretreatment barely affected the absorption of raw RVP; however, it greatly influenced the absorption of SNEDDS, resulting in an approximately 40% reduction in both the P_eff value and oral BA representing lymphatic transport. Thus, we suggest that the SNEDDS formulation is a good candidate for improving oral absorption of RVP through enhanced lymphatic uptake.

A Novel In Vitro Membrane Permeability Methodology Using Three-dimensional Caco-2 Tubules in a Microphysiological System Which Better Mimics In Vivo Physiological Conditions

The aim of this study was to develop an in vitro drug permeability methodology which mimics the gastrointestinal environment more accurately than conventional 2D methodologies through a three-dimensional (3D) Caco-2 tubules using a microphysiological system. Such a system offers significant advantages, including accelerated cellular polarization and more accurate mimicry of the in vivo environment. This methodology was confirmed by measuring the permeability of propranolol as a model compound, and subsequently applied to those of solifenacin and bile acids for a comprehensive understanding of permeability for the drug product in the human gastrointestinal tract. To protect the Caco-2 tubules from bile acid toxicity, a mucus layer was applied on the surface of Caco-2 tubules and it enables to use simulated intestinal fluid. The assessment using propranolol reproduced results equivalent to those obtained from conventional methodology, while that using solifenacin indicated fluctuations in the permeability of solifenacin due to various factors, including interaction with bile acids. We therefore suggest that this model will serve as an alternative testing system for measuring drug absorption in an environment closely resembling that of the human gastrointestinal tract.

3D alveolar in vitro model based on epithelialized biomimetically curved culture membranes

There is increasing evidence that surface curvature at a near-cell-scale influences cell behaviour. Epithelial or endothelial cells lining small acinar or tubular body lumens, as those of the alveoli or blood vessels, experience such highly curved surfaces. In contrast, the most commonly used culture substrates for in vitro modelling of these human tissue barriers, ion track-etched membranes, offer only flat surfaces. Here, we propose a more realistic culture environment for alveolar cells based on biomimetically curved track-etched membranes, preserving the mainly spherical geometry of the cells' native microenvironment. The curved membranes were created by a combination of three-dimensional (3D) micro film (thermo)forming and ion track technology. We could successfully demonstrate the formation, the growth and a first characterization of confluent layers of lung epithelial cell lines and primary alveolar epithelial cells on membranes shaped into an array of hemispherical microwells. Besides their application in submerged culture, we could also demonstrate the compatibility of the bioinspired membranes for air-exposed culture. We observed a distinct cellular response to membrane curvature. Cells (or cell layers) on the curved membranes reveal significant differences compared to cells on flat membranes concerning membrane epithelialization, areal cell density of the formed epithelial layers, their cross-sectional morphology, and proliferation and apoptosis rates, and the same tight barrier function as on the flat membranes. The presented 3D membrane technology might pave the way for more predictive barrier in vitro models in future.

The assembly of integrated rat intestinal-hepatocyte cultures

The jejunum is the segment of the small intestine responsible for several metabolism and biotransformation functions. In this report, we have cultured rat jejunum explants in vitro and integrated them with hepatocyte cultures. We have also investigated the changes in jejunum function at different locations since spatial variations in intestinal functions have been reported previously. We divided the length of the rat jejunum into three distinct regions of approximately 9 cm each. We defined the regions as proximal (adjacent to the duodenum), medial, and distal (adjacent to the ileum). Spatiotemporal variations in functions were observed between these regions within the jejunum. Alkaline phosphatase activity (a marker of enterocyte function), decreased twofold between the proximal and distal regions at 4 hr. Lysozyme activity (a marker of Paneth cell function) increased from the proximal to the distal jejunum by 40% at 24 hr. Mucin-covered areas, a marker of goblet cell function, increased by twofold between the proximal and distal segments of the jejunum at 24 hr. When hepatocytes were integrated with proximal jejunum explants, statistically higher urea (~2.4-fold) and mucin (57%) production were observed in the jejunum explants. The integrated intestine-liver cultures can be used as a platform for future investigations.

Enhanced oral bioavailability of valsartan in rats using a supersaturable self-microemulsifying drug delivery system with P-glycoprotein inhibitors

Valsartan (VST) is a poorly water-soluble drug and a P-glycoprotein (P-gp) substrate. To enhance the dissolution and oral absorption of VST, a novel supersaturable self-microemulsifying drug delivery system (Su-SMEDDS) was formulated. Based on the previously reported Su-SMEDDS composed of Capmul^® MCM (oil), Tween^® 20 (T20; surfactant), Transcutol^® P (cosurfactant), and Poloxamer 407 (supersaturating agent), P-gp inhibitory surfactants including Tween^® 80 (T80) and Cremophor^® EL (CR) were newly introduced to replace T20. All Su-SMEDDS formulations had a droplet size of <200 nm and showed rapid (>90% within 5 min) and pH-independent dissolution characteristics. The effective permeability coefficient (P_eff) in rat jejunum was obtained using an in situ single-pass intestinal perfusion study: P_eff values of Su-SMEDDS-T20, Su-SMEDDS-T80, and Su-SMEDDS-CR were 2.3, 4.1, and 3.4 times greater, respectively, than that of the VST solution. After oral administration of various formulations to rats (equivalent dose of VST 10 mg/kg), plasma drug levels were measured by liquid chromatography-tandem mass spectrometry. The relative bioavailabilities of Su-SMEDDS-T20, Su-SMEDDS-T80, and Su-SMEDDS-CR were 262%, 470%, and 458%, respectively, compared with the VST suspension. Thus, we propose that the Su-SMEDDS-T80 formulation is a good candidate for improving the oral absorption of poorly water-soluble and P-gp substrate drugs such as VST.

Regional Intestinal Permeability in Rats: A Comparison of Methods

Currently, the screening of new drug candidates for intestinal permeation is typically based on in vitro models which give no information regarding regional differences along the gut. When evaluation of intestinal permeability by region is undertaken, two preclinical rat models are commonly used, the Ussing chamber method and single-pass intestinal perfusion (SPIP). To investigate the robustness of in vivo predictions of human intestinal permeability, a set of four model compounds was systematically investigated in both these models, using tissue specimens and segments from the jejunum, ileum, and colon of rats from the same genetic strain. The influence of luminal pH was also determined at two pH levels. Ketoprofen had high and enalaprilat had low effective (P_eff) and apparent (P_app) permeability in all three regions and at both pH levels. Metoprolol had high P_eff in all regions and at both pHs and high P_app at both pHs and in all regions except the jejunum, where P_app was low. Atenolol had low P_eff in all regions and at both pHs, but had high P_app at pH 6.5 and low P_app at pH 7.4. There were good correlations between these rat in situ P_eff (SPIP) and human in vivo P_eff determined previously for the same compounds by both intestinal perfusion of the jejunum and regional intestinal dosing. The results of this study indicate that both investigated models are suitable for determining the regional permeability of the intestine; however, the SPIP model seems to be the more robust and accurate regional permeability model.

Single-Pass Intestinal Perfusion (SPIP) and prediction of fraction absorbed and permeability in humans: A study with antiretroviral drugs

In recent years, the prediction of oral drug absorption in humans has been a challenge for researchers and many techniques for permeability studies have been developed for several purposes, including biowaiver processes. The Single-Pass Intestinal Perfusion (SPIP) method performed in rats can provide permeability results closest to in vivo condition. The purpose of the present study was to evaluate the intestinal permeability of the antiretroviral drugs lamivudine, stavudine and zidovudine using the SPIP method in rats and to predict their permeability (Peff,humans) and fraction absorbed (Fa) in humans. Metoprolol and fluorescein were used as marker compounds of high and low permeability, respectively. The effective permeability (Peff) results showed that stavudine and zidovudine have high permeability characteristics while lamivudine presented the lowest result. From Peff values obtained in rats, the Peff,humans and Fa were calculated. The use of SPIP in rats and calculations for absorption prediction in humans may indicate the transport mechanisms and/or pre-systemic metabolism involved on permeation processes of drugs, since this model is the closest to in vivo conditions.

Cell-based assays using calcein acetoxymethyl ester show variation in fluorescence with treatment conditions

The use of fluorogenic compounds in cell and molecular biology has increased in both frequency and range of applications. However, such compounds may introduce artifacts in intracellular fluorescence and cell number estimations as a consequence of interaction with exogenous stimulants, necessitating the use of adequate controls for accurate measurements and valid conclusions. Using calcein acetoxymethyl ester (AM) in combination with various exogenous cellular treatments, we report that the standard practice of direct normalization of experimental values to controls is insufficient for fluorogenic measurements. Treatments applied to cells may influence intracellular conversion of the fluorogenic compound, thereby enhancing or decreasing fluorescence relative to controls. We hereby encourage caution and recommend normalization of cellular fluorescence within each treatment group before comparison to controls.

Systematic development of novel cationic self-nanoemulsifying drug delivery systems of candesartan cilexetil with enhanced biopharmaceutical performance

The current studies entail systematic development, optimization and evaluation of cationic self-nanoemulsifying drug delivery systems (C-SNEDDS) for enhancing the oral bioavailability of candesartan cilexetil.

Lecithin-linker formulations for self-emulsifying delivery of nutraceuticals

Lecithin-linker microemulsions are formulations produced with soybean lecithin in combination with a highly lipophilic (lipophilic linker) and highly hydrophilic (hydrophilic linkers) surfactant-like additives. In this work, lecithin-linker systems were formulated to produce self-emulsifying delivery systems for β-carotene and β-sitosterol. The concentration of the lipophilic linker, sorbitan monooleate, was adjusted to minimize the formation of liquid crystals. The concentration of hydrophilic linkers, decaglyceryl caprylate/caprate and PEG-6-caprylic/capric glycerides, was gradually increased (scanned) until single phase clear microemulsions were obtained. For these scans, the oil (ethyl caprate) to water ratio was set to 1. The single phase, clear microemulsions were diluted with fed-state simulated intestinal fluid (FeSSIF) and produced stable emulsions, with drop sizes close to 200 nm. Using pseudo-ternary phase diagrams to evaluate the process of dilution of microemulsion preconcentrates (mixtures of oil, lecithin and linkers with little or no water) with FeSSIF, it was determined that self-emulsifying systems are obtained when the early stages of the dilution produce single phase microemulsions. If liquid crystals or multiple phase systems are obtained during those early stages, then the emulsification yields unstable emulsions with large drop sizes. An in vitro permeability study conducted using a Flow-Thru Dialyzer revealed that stable emulsions with drop sizes of 150-300 nm produce large and irreversible permeation of β-carotene to sheep intestine. On the other hand, unstable emulsions produced without the linker combination separated in the dialyzer chamber.

Amorphous azithromycin with improved aqueous solubility and intestinal membrane permeability

Azithromycin (AZM) is a poorly soluble macrolide antibacterial agent. Its low solubility is considered as the major contributing factor to its relatively low oral bioavailability. The aim of this study was to improve the solubility of this active pharmaceutical ingredient (API) by preparing an amorphous form by quench cooling of the melt and to study the influence of the improved solubility on membrane permeability. The amorphous azithromycin (AZM-A) exhibited a significant increase in water solubility when compared to the crystalline azithromycin dihydrate (AZM-DH). The influence that the improved solubility could have on membrane permeability was also studied. The apparent permeability coefficient (Papp) values of AZM-A were statistically significantly higher (p < 0.05) than crystalline AZM-DH at pH values of 6.8 and 7.2. The results therefore indicated that the improved solubility of AZM in the amorphous form also produced improved permeability across excised intestinal tissue at physiological pH values found in the small intestine.

Curcumin-loaded solid lipid nanoparticles with Brij78 and TPGS improved in vivo oral bioavailability and in situ intestinal absorption of curcumin

PURPOSE

The present study was to formulate curcumin solid lipid nanoparticles (Cur-SLNs) with P-gp modulator excipients, TPGS and Brij78, to enhance the solubility and bioavailability of curcumin.

METHODS

The formulation was optimized by Plackett-Burman screening design and Box-Behnken experiment design. Then physiochemical properties, entrapment efficiency and in vitro release of Cur-SLNs were characterized. In vivo pharmacokinetics study and in situ single-pass intestinal perfusion were performed to investigate the effects of Cur-SLNs on the bioavailability and intestinal absorption of curcumin.

RESULTS

The optimized formulations showed an average size of 135.3 ± 1.5 nm with a zeta potential value of -24.7 ± 2.1 mV and 91.09% ± 1.23% drug entrapment efficiency, meanwhile displayed a sustained release profile. In vivo pharmacokinetic study showed AUC0→t for Cur-SLNs was 12.27-folds greater than curcumin suspension and the relative bioavailability of Cur-SLNs was 942.53%. Meanwhile, Tmax and t(1/2) of curcumin for Cur-SLNs were both delayed comparing to the suspensions (p < 0.01). The in situ intestinal absorption study revealed that the effective permeability (Peff) value of curcumin for SLNs was significantly improved (p < 0.01) comparing to curcumin solution.

CONCLUSION

Cur-SLNs with TPGS and Brij78 could improve the oral bioavailability and intestinal absorption of curcumin effectively.

Study on biopharmaceutics classification and oral bioavailability of a novel multikinase inhibitor NCE for cancer therapy

Specific biopharmaceutics classification investigation and study on phamacokinetic profile of a novel drug candidate (2-methylcarbamoyl-4-{4-[3- (trifluoromethyl) benzamido] phenoxy} pyridinium 4-methylbenzenesulfonate monohydrate, NCE) were carried out. Equilibrium solubility and intrinsic dissolution rate (IDR) of NCE were estimated in different phosphate buffers. Effective intestinal permeability (P(eff)) of NCE was determined using single-pass intestinal perfusion technique in rat duodenum, jejunum and ileum at three concentrations. Theophylline (high permeability) and ranitidine (low permeability) were also applied to access the permeability of NCE as reference compounds. The bioavailability after intragastrical and intravenous administration was measured in beagle dogs. The solubility of NCE in tested phosphate buffers was quite low with the maximum solubility of 81.73 μg/mL at pH 1.0. The intrinsic dissolution ratio of NCE was 1 × 10⁻⁴ mg·min⁻¹·cm⁻². The P(eff) value of NCE in all intestinal segments was more proximate to the high-permeability reference theophylline. Therefore, NCE was classified as class II drug according to Biopharmaceutics Classification System due to its low solubility and high intestinal permeability. In addition, concentration-dependent permeability was not observed in all the segments, indicating that there might be passive transportation for NCE. The absolute oral bioavailability of NCE in beagle dogs was 26.75%. Therefore, dissolution promotion will be crucial for oral formulation development and intravenous administration route will also be suggested for further NCE formulation development. All the data would provide a reference for biopharmaceutics classification research of other novel drug candidates.

In situ intestinal permeability and in vivo oral bioavailability of celecoxib in supersaturating self-emulsifying drug delivery system

In order to characterize the in situ intestinal permeability and in vivo oral bioavailability of celecoxib (CXB), a poorly water-soluble cyclooxygenase (COX)-2 inhibitor, various formulations including the self-emulsifying drug delivery system (SEDDS) and supersaturating SEDDS (S-SEDDS) were compared. The S-SEDDS formulation was obtained by adding Soluplus as a precipitation inhibitor to SEDDS, composed of Capryol 90 as oil, Tween 20 as surfactant, and Tetraglycol as cosurfactant (1:4.5:4.5 in volume ratio). An in situ single pass intestinal perfusion study in rats was performed with CXB-dissolved solutions at a concentration of 40 μg/mL. The effective permeability (Peff) of CXB in the control solution (2.5 v/v% Tween 20-containing PBS) was 6.39 × 10(-5) cm/s. The Peff value was significantly increased (P < 0.05) by the lipid-based formulation, yielding 1.5- and 2.9-fold increases for the SEDDS and S-SEDDS solutions, respectively, compared to the control solution. After oral administration of various formulations to rats at the equivalent dose of 100 mg/kg of CXB, the plasma drug level was measured by LC-MS/MS. The relative bioavailabilities of SEDDS and S-SEDDS were 263 and 355 %, respectively, compared to the CXB suspension as a reference. In particular, S-SEDDS revealed the highest Cmax and the smallest Tmax, indicating rapid and enhanced absorption with this formulation. This study illustrates the potential use of the S-SEDDS formulation in the oral delivery of poorly water-soluble compounds.

N-octyl-N-arginine-chitosan (OACS) micelles for gambogic acid oral delivery: preparation, characterization and its study on in situ intestinal perfusion

CONTEXT

Gambogic acid (GA) can inhibit the growth of various cancer cells. However, the low bioavailability caused by insolubility, limits its clinical application. L-arginine is always used with GA to form a complex to obtain the higher solubility. Moreover, guanidyl group from arginine, which can facilitate the cellular uptake, was identified.

OBJECTIVE

In this study, L-arginine and chitosan (CS) were used for the first time to prepare N-octyl-N-arginine CS (OACS), a novel amphiphilic carrier for GA with solubility- and absorption-enhancing functions; the characterization of the GA loaded OACS micelles (GA-OACS) and its absorption-enhancing effect were also investigated.

MATERIALS AND METHODS

GA-OACS were prepared by the dialysis method. The formed micelles were characterized and evaluated by atomic force microscope (AFM), dynamic light scattering, differential scanning calorimeter (DSC), solubility test, in vitro release and in situ intestinal perfusion.

RESULTS

The GA-OACS micelles were successfully prepared attaining a 35.3% drug loading and 82.2% entrapment efficiency. GA-OACS had a homogeneous particle size of 160.3 nm; +21.8 mv zeta potential with smooth continuous surface was observed by using AFM. DSC diagram suggested that GA was encapsulated in the micelles. Meanwhile, GA encapsulated in micelles exhibited a desirable slow release in vitro experiment. The solubility of GA in OACS micelles was increased up to 3.16 ± 0.13 mg/mL, 2320 times than that of free GA. The single pass perfusion showed that the absorption of GA-OACS micelles was enhanced 3.6-fold, 2.1-fold and 2.2-fold for jejunum, ileum and colon, respectively.

DISCUSSION AND CONCLUSION

OACS provided excellent ability of drug loading, increasing solubility and enhanced absorption for GA, which indicated that OACS micelles as an oral drug delivery carrier may have potential research and application values.

In situ intestinal permeability and in vivo absorption characteristics of olmesartan medoxomil in self-microemulsifying drug delivery system

To characterize the intestinal absorption behavior of olmesartan medoxomil (OLM) and to evaluate the absorption-improving potential of a self-microemulsifying drug delivery system (SMEDDS), we performed in situ single-pass intestinal perfusion (SPIP) and in vivo pharmacokinetic studies in rats. The SPIP study revealed that OLM is absorbed throughout whole intestinal regions, favoring proximal segments, at drug levels of 10-90 μM. The greatest value for effective permeability coefficient (P(eff)) was 11.4 × 10(-6) cm/s in the duodenum (90 μM); the lowest value was 2.9 × 10(-6) cm/s in the ileum (10 μM). A SMEDDS formulation consisting of Capryol 90, Labrasol, and Transcutol, which has a droplet size of 200 nm and self-dispersion time of 21 s, doubled upper intestinal permeability of OLM. The SMEDDS also improved oral bioavailability of OLM in vivo: a 2.7-fold increase in the area under the curve (AUC) with elevated maximum plasma concentration (C(max)) and shortened peak time (T(max)) compared to an OLM suspension. A strong correlation (r(2) = 0.955) was also found between the in situ jejunal P(eff) and the in vivo AUC values. Our study illustrates that the SMEDDS formulation holds great potential as an alternative to increased oral absorption of OLM.

Spray-dried oil-in-water emulsion to improve the intestinal absorption and oral bioavailability of ZLR-8, a nitric oxide-releasing derivative of diclofenac

Objectives

Spray-dried emulsion (SDE) was prepared and characterized to improve the intestinal absorption and oral bioavailability of ZLR-8, a nitric oxide-releasing derivative of diclofenac, currently under preclinical development.

Methods

The intestinal absorption of ZLR-8 was characterized by single pass intestinal perfusion technique to obtain its absorption and permeability parameters. SDE of ZLR-8 was prepared and characterized by particle size measurements and in-vitro release study. Accurate and precise RP-HPLC methods for the detection of ZLR-8 and its metabolite diclofenac were constructed to perform the bioavailability study.

Key findings

It was demonstrated that ZLR-8 was absorbed in the whole intestine, of which the duodenum segment exhibited the largest absorption ability. ZLR-8 can be classified into BCS Class 2. SDE significantly enhanced the intestinal absorption rate of ZLR-8 in duodenum and jejunum but had indistinctive effect on permeability. All concentrations of ZLR-8 in rat plasma was lower than the limit of detection. A bicompartment model gave the best fit to the plasma diclofenac concentration–time curves. Calculated on AUC0–12h, the mean relative bioavailability of SDE was 105.4-fold that of ZLR-8 suspension.

Conclusions

SDE significantly improved the intestinal absorption of ZLR-8 and resulted in a dramatic improvement in its bioavailability.

Effect of experimental temperature on the permeation of model diffusants across porcine buccal mucosa

The influence of experimental temperature on the permeability of model diffusants across porcine buccal mucosa was investigated in vitro. The permeability increased significantly as the experimental temperature was increased in increments of approximately 7°C. It was observed that the apparent permeability and temperature were related by an exponential relationship that conformed to the Arrhenius equation. Diffusants with higher lipophilicities--buspirone and bupivacaine--had lower activation energies for diffusion when compared to hydrophilic diffusants--antipyrine and caffeine. The activation energy for diffusion of the model diffusants decreased linearly with increasing distribution coefficients across porcine buccal mucosa. The results suggested that the buccal mucosa acts as a stronger barrier to the diffusion of hydrophilic diffusants than the lipophilic ones. The log-linear relationship between permeability and temperature indicates that temperature should be carefully controlled in diffusion experiments. These results also point to the possibility of developing heat-generating buccal delivery devices, especially for hydrophobic diffusants.

The effect of multiple N-methylation on intestinal permeability of cyclic hexapeptides

Recent progress in peptide synthesis simplified the synthesis of multiple N-methylation of peptides. To evaluate how multiple N-methylation affects the bioavailability of peptides, a poly alanine cyclic hexapeptide library (n = 54), varying in the number of N-methyl (N-Me) groups (1-5 groups) and their position, was synthesized. The peptides were evaluated for their intestinal permeability in vitro using the Caco-2 model. Further evaluation of the transport route of chosen analogues was performed using rat excised viable intestinal tissue, a novel colorimetric liposomal model and the parallel artificial membrane permeability assay (PAMPA). While most members were found to have poor permeability (permeability coefficient, P(app) < 1 x 10⁻⁶ cm/s, lower than mannitol, the marker for paracellular permeability), 10 analogues were found to have high Caco-2 permeability, (P(app) > 1 x 10⁻⁵ cm/s, similar to testosterone, a marker of transcellular permeability). No correlation was found between the number of N-methylated groups and the enhanced permeability. However, 9/10 permeable peptides in the Caco-2 model included an N-Me placed adjacently to the D-Ala position. While the exact transport route was not fully characterized, the data suggests a facilitated diffusion. It can be concluded that multiple N-methylation of peptides may improve intestinal permeability, and therefore can be utilized in the design of orally available peptide-based therapeutics.

Application of method suitability for drug permeability classification

Experimental models of permeability in animals, excised tissues, cell monolayers, and artificial membranes are important during drug discovery and development as permeability is one of several factors affecting the intestinal absorption of oral drug products. The utility of these models is demonstrated by their ability to predict a drug's in vivo intestinal absorption. Within the various permeability models, there are differences in the performance of the assays, along with variability in animal species, tissue sources, and cell types, resulting in a variety of experimental permeability values for the same drug among laboratories. This has led to a need for assay standardization within laboratories to ensure applicability in the drug development process. Method suitability provides a generalized approach to standardize and validate a permeability model within a laboratory. First, assay methodology is optimized and validated for its various experimental parameters along with acceptance criteria for the assay. Second, the suitability of the model is demonstrated by a rank order relationship between experimental permeability values and human extent of absorption of known model compounds. Lastly, standard compounds are employed to classify a test drug's intestinal permeability and ensure assay reproducibility and quality. This review will provide examples of the different aspects method suitability for in situ (intestinal perfusions), ex vivo (everted intestinal sacs, diffusion chambers), and in vitro (cell monolayers, artificial membranes) experimental permeability models. Through assay standardization, reference standards, and acceptance criteria, method suitability assures the dependability of experimental data to predict a drug's intestinal permeability during discovery, development, and regulatory application.

Clinical pharmacokinetics of the cyclooxygenase inhibiting nitric oxide donator (CINOD) AZD3582

The clinical pharmacokinetics of the COX-inhibiting nitric oxide donator (CINOD) AZD3582 and its metabolites, including naproxen, nitric oxide and nitrate, are summarized. AZD3582 has low aqueous solubility, moderate and passive intestinal permeability and is degraded by intestinal esterases. Its oral bioavailability (F) appears to be maximally a few per cent, and increases by several-fold after food intake. Ninety-four per cent or more of an AZD3582 dose is absorbed, of which at least 9–20% appears to be taken up as intact substance. AZD3582 has a predicted plasma protein binding degree of ∼ 0.1%, a half-life (t½) of 3 to 10 h and does not accumulate after repeated once- and twice-daily dosing. In patients AZD3582 does not provide a significantly better gastrointestinal (GI) side-effect profile than the highly permeable and locally irritating naproxen. Possible reasons for this include considerable GI uptake as naproxen, limited duration and extent of nitric oxide donation in the GI mucosa and the circulation, tolerance development (involving auto-inhibition of nitric oxide catalysing enzymes) and mucosal damage caused by nitric oxide. Blood pressure data suggest that nitric oxide is mainly donated within 3h. The uptake of naproxen is slightly slower and lower (≥ 94% relative GI uptake and 80–85% relative F) after AZD3582 administration compared with naproxen dosing. The naproxen t½ and trough steady-state concentrations after AZD3582 and naproxen dosing are similar. The average systemic nitrate exposure is approximately doubled after dosing of 375 to 750 mg AZD3582 twice daily.

The use of biopharmaceutic classification of drugs in drug discovery and development: current status and future extension

Bioavailability (BA) and bioequivalence (BE) play a central role in pharmaceutical product development and BE studies are presently being conducted for New Drug Applications (NDAs) of new compounds, in supplementary NDAs for new medical indications and product line extensions, in Abbreviated New Drug Applications (ANDAs) of generic products and in applications for scale-up and post-approval changes. The Biopharmaceutics Classification System (BCS) has been developed to provide a scientific approach for classifying drug compounds based on solubility as related to dose and intestinal permeability in combination with the dissolution properties of the oral immediate-release (IR) dosage form. The aim of the BCS is to provide a regulatory tool for replacing certain BE studies by accurate in-vitro dissolution tests. The aim of this review is to present the status of the BCS and discuss its future application in pharmaceutical product development. The future application of the BCS is most likely increasingly important when the present framework gains increased recognition, which will probably be the case if the BCS borders for certain class II and III drugs are extended. The future revision of the BCS guidelines by the regulatory agencies in communication with academic and industrial scientists is exciting and will hopefully result in an increased applicability in drug development. Finally, we emphasize the great use of the BCS as a simple tool in early drug development to determine the rate-limiting step in the oral absorption process, which has facilitated the information between different experts involved in the overall drug development process. This increased awareness of a proper biopharmaceutical characterization of new drugs may in the future result in drug molecules with a sufficiently high permeability, solubility and dissolution rate, and that will automatically increase the importance of the BCS as a regulatory tool over time.

Assessment and prevention of gastrointestinal toxicity of non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used for analgesic, anti-inflammatory and, in the case of aspirin, for anti-thrombotic actions. The serious gastrointestinal side-effects associated with these drugs are of concern and pose a significant obstacle to their use. This review discusses the pathogenic mechanisms by which the conventional acidic NSAIDs induce gastrointestinal toxicity, with particular emphasis on non-prostaglandin effects. Methods of assessment of NSAID-induced enteropathy are reviewed, with particular emphasis on the use of functional measurement of NSAID-induced changes in the gastrointestinal tract. The advances in our knowledge of the pathogenesis of these effects have resulted in the development of a range of novel NSAIDs. Where functional assessment of the effects of NSAIDs has been employed, it appears to be more useful as an indicator of early-stage changes rather than a predictor of the effects of long-term NSAID exposure. Successful pharmaceutical strategies now offer considerable promise for reducing the severity of NSAID damage to the gastrointestinal tract. The utility of intestinal permeability measurements for selection and assessment of these strategies is discussed.

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.

Formulation optimization and in situ absorption in rat intestinal tract of quercetin-loaded microemulsion

A new microemulsion system has been developed to increase the solubility and oral absorption of quercetin, a poorly water-soluble drug. The formulation of quercetin-loaded microemulsion was optimized by a simplex lattice experiment design. The optimized microemulsion formulation consisted of oil (7%, w/w), surfactant (48%, w/w), and cosurfactant (45%, w/w). Under this condition, the mean droplet diameter of microemulsion was 38.9 nm and solubility of quercetin in the microemulsion was 4.138 mg/ml. The in situ absorption property of quercetin-loaded microemulsion in rat intestine was studied and the results showed there was significant difference in absorption parameters such as K(a), t(1/2) and uptake percentages between microemulsion and micelle solution containing quercetin. The study on absorption percentage in different regions of rat intestine attested that the colon had the best permeability, followed by ileum, duodenum in order. It can be concluded that microemulsion can improve the solubility and oral absorption of quercetin, a poorly water-soluble drug.

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.