Transport Kinetics of Iron Chelators and Their Chelates in Caco-2 Cells

Purpose Caco-2 monolayers were used to contrast the bidirectional transport of iron chelators and their chelates and to estimate fundamental kinetics associated with their intestinal absorption. Methods Bidirectional transport was studied at 37°C and pH 7.4 using 500-μM concentrations. Monolayer integrity was tested via transepithelial electrical resistance and sodium fluorescein permeability. Apical and basolateral analysis provided mass balance evidence. Apparent permeability coefficient (P_app) served to rank and compare molecules and estimate in vivo bioavailability. Model-dependent rate constants defined cellular influx and efflux. Results 1) P_app ranked in decreasing order for chelators from directional transport studies were CP363 > deferiprone> ICL670 > CP502 > deferoxamine (DFO). 2) Fe(CP502)₃, Fe(ICL670)₂, and FeDFO were not measurable in receiving chambers, whereas Fe(deferiprone)₃ and Fe(CP363)₃ were detected in both directions. 3) CP363 was transported significantly faster from the basolateral to the apical direction than the converse. 4) Mass balance of donor and receiver chambers gave approximately 100% recovery in all cases. 5) Kinetic analysis supports the view that the Caco-2 chelator efflux constants are generally greater than their influx constants. Conclusions Caco-2 cells are useful in screening iron chelators and chelates and estimating bioavailabilities. Structure and distribution coefficients partially predict passive transport through Caco-2 monolayers.     

Absorption mechanism of oxymatrine in cultured Madin–Darby canine kidney cell monolayers

Context Oxymatrine (OMT) is beneficial to human health by exerting various biological effects. Objective To investigate the absorption mechanism of OMT and discover absorption enhancers using Madin–Darby canine kidney (MDCK) cell monolayers.

Materials and methods Concentration effects on the transport of OMT were measured in the range of 1.0?×?10^?5–1.0?×?10^?3 M in 2?h. Then, the effect of time, direction, temperature and pH on the transport of OMT at 10^?4 M was studied. Moreover, P_app of OMT was determined in the absence/presence of cyclosporine and surfactants at 100?μM to further confirm the relative transport mechanism.

Results The P_{app AP→BL} ranged from (3.040?±?0.23)?×?10^?6 to (3.697?±?0.19)?×?10^?6?cm/s as the concentration varied from 10^?5 to 10^?3 M. OMT showed similar P_app at 4 and 37?°C (p?>?0.05). Increasing the apical pH 7.4 and 8.0 resulted in P_app versus pH 5.0 (p?<?0.01). Furthermore, in the presence of cyclosporine and surfactants including sodium citrate, sodium dodecyl sulphate (SDS) and deoxysodium cholate, P_app was (0.318?±?0.033)?×?10^?5, (0.464?±?0.048)?×?10^?5, (0.897?±?0.115)?×?10^?5 and (1.341?±?0.122)?×?10^?5?cm/s, respectively. In the presence of surfactants, P_app significantly increased up to 1.5–4.3-fold (p?<?0.05).

Discussion and conclusion OMT transport across MDCK cell monolayers was by passive diffusion. Sodium citrate, SDS and deoxysodium cholate serve as excellent absorption enhancers which are useful for the related research improving the oral bioavailability of OMT.     

Bioavailability of caffeic acid in rats and its absorption properties in the Caco-2 cell model

Context: Caffeic acid (CA) is widely distributed in edible plants, and it is beneficial to human health by exerting various biological effects. The potential pharmacological activities of CA are dependent on its absorption in the gastrointestinal tract.

Objective: To investigate the bioavailability of CA in rats and its absorption properties in the Caco-2 cell model.

Materials and methods: A sensitive LC-MS/MS method was successfully applied to determine CA in rat plasma, perfusate, and Hank's balanced salt solution (HBSS). The absolute bioavailability (F_abs) of CA was obtained after i.v. (2?mg/kg) or i.g. administration (10?mg/kg) to rats. Blood samples (approximately 250?µL) were collected from the jugular vein catheter. Pharmacokinetic parameters were calculated using the 3P97 software (version 2.0 PK software; Chinese Society of Mathematical Pharmacology, Anhui, China). The intestinal absorption of CA was explored by the in situ vascularly perfused rat intestinal preparation. CA (5?mg/kg) was administered into the duodenum. Samples (250?µL) were collected from reservoir at specific times, and the same volume fresh perfusate was replaced. The Caco-2 cell model was applied to measure the permeability of CA from the apical to basolateral side (A?→?B) and from the basolateral to apical side (B?→?A).

Results: The absolute bioavailability (F_abs) of CA was 14.7%, and its intestinal absorption was 12.4%. The P_{app A→B} values of CA were ranging from (4.87?±?1.72)?×?10^?7?cm/s to (5.05?±?0.66)?×?10^?7?cm/s as the concentration varied from 5 to 15?µg/mL.

Conclusion: CA was shown to have low oral bioavailability in rats, low intestinal absorption, and poor permeability across Caco-2 cells.     

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

Abstract

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 AUC_0→t for Cur-SLNs was 12.27-folds greater than curcumin suspension and the relative bioavailability of Cur-SLNs was 942.53%. Meanwhile, T_max 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 (P_eff) 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.     

Modulation of ganciclovir intestinal absorption in presence of absorption enhancers

The purpose of this investigation was to study the influences of absorption enhancers in increasing oral bioavailability of Ganciclovir (GAN) by assessing the transepithelial permeation across cell monolayers in vitro and bioavailability in rats in vivo. The permeation of GAN across Caco-2 and MDCK cell monolayers in the absence/presence of dimethyl-beta-cyclodextrin (DMbetaCD), chitosan hydrochloride (CH), sodium lauryl sulphate (SLS), and their combinations was studied for a 2-h period. GAN was administered to rats in absence/presence of absorption enhancers and drug contents in plasma were estimated. We found that the apparent permeability coefficient (Papp) of GAN in absence of absorption enhancers (control) were 0.261 +/- 0.072 x 10(-6) and 0.486 +/- 0.063 x 10(-6) cm/s in Caco-2 and MDCK cell monolayers, respectively, whereas in the presence of DMbetaCD, CH, SLS, and their combinations, Papp of GAN increased by 5- to 25-fold and 7- to 33-fold as compared to control in Caco-2 and MDCK cell monolayers, respectively. However, in rats, the maximum enhancement in bioavailability of GAN during coadministration of these absorption enhancers was only fivefold compared to GAN control. To conclude, the absorption enhancers-DMbetaCD, CH, SLS, and their combinations demonstrated significant improvement in transepithelial permeation and bioavailability of GAN.     

Development and characterization of lutein-loaded SNEDDS for enhanced absorption in Caco-2 cells

Abstract

A self-nanoemulsifying drug delivery system (SNEDDS) has been developed for enhanced oral bioavailability of lutein. Its permeation enhancement has been evaluated using monolayers of Caco-2 cells. SNEDDS is composed of a mixture of Lexol® and Emulmetik® 900, Labrasol®, and Tween 80 as oil, surfactant and co-surfactant, respectively. Upon dilution of lutein-loaded SNEDDS with water, a nanoemulsion was obtained in <10?s with spherical droplets of 40–150?nm in diameter. The zeta potential was in the range of ?19 to ?32?mV. Increasing the ratio of surfactant to co-surfactant decreased the mean droplet size. Dissolution studies showed that lutein was released rapidly (<5?min) from SNEDDS into 0.1?N HCl and pH 6.8 phosphate buffer solution without any aggregation. In vitro studies using Caco-2 cells revealed that lutein-loaded SNEDDS showed shorter lag time and greater (2-fold) cellular accumulation compared with the lutein dispersion.     

The limited intestinal absorption via paracellular pathway is responsible for the low oral bioavailability of doxorubicin

Abstract

1. Doxorubicin exhibited dose-independent pharmacokinetics after intravenous (5–20?mg/kg) and oral (20–100?mg/kg) administration to rats. Nearly all (82.1–99.7%) of the orally administered doxorubicin remained unabsorbed, and the hepatic first-pass extraction ratio and oral bioavailability of doxorubicin were approximately 0.5% and 1%, respectively. Based on these results, it is likely that the primary factor responsible for the low oral bioavailability of doxorubicin is the limited intestinal absorption, rather than the CYP3A4-mediated first-pass metabolism.

2. Moreover, the in vitro transport and cellular uptake studies using Caco-2 cell monolayers have revealed that doxorubicin crosses the intestinal epithelium primarily via the paracellular pathway (accounting for 85.6% of the overall absorptive transport) probably due to its physicochemical properties (hydrophilic cation; pK_a?=?9.67, log?P?=??0.5). These results suggest that P-glycoprotein (P-gp)-mediated efflux activity does not play a significant role in limiting the intestinal absorption of doxorubicin, attenuating the absorptive transport by only 5.56–13.2%.

3. Taken together, the present study demonstrated that the limited and paracellular intestinal absorption of doxorubicin was a major factor responsible for its low oral bioavailability, restricting the role of CYP3A4-mediated first-pass metabolism and P-gp-mediated efflux.     

Biopharmaceutics classification and intestinal absorption of chikusetsusaponin IVa

The objective of this study was to investigate the absorption behavior of chikusetsusaponin IVa (CHS‐IVa) in the rat intestine using single‐pass intestinal perfusion (SPIP) and to classify CHS‐IVa into the biopharmaceutics classification system (BCS). The equilibrium solubility of CHS‐IVa was determined by the shaker method. The absorption mechanism of CHS‐IVa in the intestine was studied by comparing the P_eff of different concentrations of CHS‐IVa. The intestinal site dependence of CHS‐IVa absorption was studied by comparing the P_eff of the same concentration of CHS‐IVa in different intestinal segments. The relationship between CHS‐IVa and intestinal efflux protein was studied by perfusion with an efflux protein inhibitor. The permeability of CHS‐IVa was investigated by comparing the P_eff of CHS‐IVa and the reported value. The solubility of CHS‐IVa over the pH range 1.0–7.5 was 14.4 ± 0.29 to 16.9 ± 0.34 mg/ml. The P_eff of CHS‐IVa in the duodenum was 1.76 × 10^?3 to 2.00 × 10^?3 cm/min. The P_eff of CHS‐IVa in the jejunum was 1.26 × 10^?3 to 1.39 × 10^?3 cm/min. The P_eff of CHS‐IVa in the ileum was 1.25 × 10^?3 to 1.31 × 10^?3 cm/min. The P_eff of CHS‐IVa in the colon was 1.02 × 10^?3 to 1.08 × 10^?3 cm/min. There was no statistical difference of the P_eff in the four segments at different CHS‐IVa concentrations. The P_eff of CHS‐IVa (0.07, 0.7 and 7.0 mg/ml) were all notably smaller than the reported P_eff (3.00 × 10^?3 cm/min) in the jejunum. The P_eff of CHS‐IVa was not influenced by verapamil (P‐gp inhibitor), indomethacin (MRP inhibitor) and pantoprazole (BCRP inhibitor). CHS‐IVa was classified as high solubility, low permeability and BCS III. The main absorptive tracts were the upper intestinal tracts and the rank order of intestinal permeability was duodenum > jejunum ≈ ileum > colon. The transport mechanism of CHS‐IVa in all intestinal segments might be primarily passive transport. CHS‐IVa was not a substrate of P‐gp, MRP and BCRP.     

Intestinal permeability and its relevance for absorption and elimination

Human jejunal permeability (P_eff) is determined in the intestinal region with the highest expression of carrier proteins and largest surface area. Intestinal P_eff are often based on multiple parallel transport processes. Site-specific jejunal P_eff cannot reflect the permeability along the intestinal tract, but they are useful for approximating the fraction oral dose absorbed. It seems like drugs with a jejunal P_eff > 1.5 x 10^–4 cm s^–1 will be completely absorbed no matter which transport mechanism(s) are utilized. Many drugs that are significantly effluxed in vitro have a rapid and complete intestinal absorption (i.e. >85%) mediated by passive transcellular diffusion. The determined jejunal P_eff for drugs transported mainly by absorptive carriers (such as peptide and amino acid transporters) will accurately predict the fraction of the dose absorbed as a consequence of the regional expression. The data also show that: (1) the human intestinal epithelium has a large resistance towards large and hydrophilic compounds; and (2) the paracellular route has a low contribution for compounds larger than approximately molecular weight 200. There is a need for more exploratory in vivo studies to clarify drug absorption and first-pass extraction along the intestine. One is encouraged to develop in vivo perfusion techniques for more distal parts of the gastrointestinal tract in humans. This would stimulate the development of more relevant and complex in vitro absorption models and form the basis for an accurate physiologically based pharmacokinetic modelling of oral drug absorption.     

Comparison of Bidirectional Cephalexin Transport Across MDCK and Caco-2 Cell Monolayers: Interactions with Peptide Transporters

Purpose. Bidirectional transport studies were conducted to determine whether Madin-Darby canine kidney (MDCK) cell monolayers could be used as an alternative to the traditional Caco-2 assay as a fast-growingin vitro model of peptide transport. Methods. Transport of cephalexin and glycylsarcosine across MDCK and Caco-2 cell monolayers was quantified using LC-LC/MS. Glycylsarcosine, p-aminohippuric acid (PAH), and tetraethylammonium chloride (TEA) were tested as inhibitors of cephalexin transport. Results. The ratio of apparent cephalexin permeabilities (apical to basolateral/basolateral to apical) obtained from MDCK monolayers was almost 5-fold greater than that obtained from Caco-2 monolayers. The opposite trend was observed for glycylsarcosine. When MDCK monolayers were used, glycylsarcosine reduced the cephalexin/apparent permeability ratio almost 90%. PAH and TEA did not inhibit cephalexin transport across MDCK or Caco-2 cell monolayers. Conclusion. MDCK cell monolayers may be a promising, fast-growing alternative to Caco-2 cells for identifying peptide transporter substrates. However, differences in the apical-to-basolateral transport of cephalexin and glycylsarcosine suggest that the basolateral transport mechanisms for these compounds are different in the two cell lines. Additionally, because the activity of the peptide transporter in MDCK cells was low, scaling factors may be required when using this cell line to predict in vivo drug absorption.     

Passive Transepithelial Absorption of Thyrotropin-Releasing Hormone (TRH) via a Paracellular Route in Cultured Intestinal and Renal Epithelial Cell Lines

Transport studies using intestinal brush-border membrane vesicles isolated from rats and rabbits have failed to demonstrate proton- or Na⁺-dependent carrier-mediated transport of thyrotropin-releasing hormone (TRH), despite a pharmacologically relevant oral bioavailability. To examine the hypothesis that reported levels of oral bioavailability reflect predominately a paracellular rather than transcellular route for transepithelial transport of TRH, we have studied TRH transport in cultured epithelial cell types of intestinal (Caco-2 and T₈₄) and renal (MDCK I, MDCK II, and LLC-PK₁ origin, whose paracellular pathways span the range of permeability values observed in natural epithelia. Transport of TRH across monolayers of intestinal Caco-2 cells was similar to the flux of mannitol (1–4% per 4 hr), and unlike other putative substrates for the di-/tripeptide carrier, apical-to-basolateral transport was not increased by the presence of an acidic pH in the apical chamber. TRH transport did not show saturation, being uneffected in the presence of 20 mM cold TRH. In each cell type studied TRH and mannitol transport were similar and positively correlated with the conductance of the cell layers, consistent with a passive mechanism of absorption. This evidence suggests that, providing that a peptide is resistant to luminal hydrolysis, small but pharmacologically significant amounts of peptide absorption may be achieved by passive absorption across a paracellular route.     

In Vitro and In Situ Evaluation of pH-Dependence of Atazanavir Intestinal Permeability and Interactions with Acid-Reducing Agents

Purpose

The objectives of this study were to evaluate the effects of intestinal lumen pH, food intake, and acid-reducing agents on the intestinal permeability of atazanavir, an HIV-1 protease inhibitor.

Methods

Atazanavir permeability across Caco-2 cell monolayers (P _app) and in situ steady-state permeability across rat jejunum and ileum (P _eff) were evaluated in buffers of varied pH (4.5–8.5), in fasted- or fed-state simulated intestinal fluid, or in presence of acid-reducing drugs (e.g., omeprazole).

Results

In vitro accumulation and apical-to-basolateral P _app of atazanavir increased with decreasing pH. This effect appeared to be associated with lower atazanavir efflux by P-glycoprotein at acidic pH (5.5) compared to neutral pH. In situ atazanavir P _eff across rat jejunum and ileum also decreased 2.7 and 2.3-fold, respectively, when pH was increased from 4.5 to 8.5. Several acid-reducing agents (e.g., omeprazole) moderately inhibited atazanavir efflux in Caco-2 monolayers; however, this effect was not observed in situ. Fed-state buffer significantly increased atazanavir apical-to-basolateral P _app (p?in situ P _eff (p?Conclusions Atazanavir permeability is sensitive to changes in intestinal lumen pH. This pH-sensitivity may contribute to atazanavir clinical interactions with acid-reducing agents and variable oral bioavailability.     

N-Trimethylated Chitosan Chloride (TMC) Improves the Intestinal Permeation of the Peptide Drug Buserelin In Vitro (Caco-2 Cells) and In Vivo (Rats)

Purpose. To evaluate N-trimethyl chitosan chloride (TMC) of highdegrees of substitution as intestinal permeation enhancers for thepeptide drug buserelin in vitro using Caco-2 cell monolayers, and toinvestigate TMCs as enhancers of the intestinal absorption of buserelinin vivo, in rats. Methods. TMCs were tested on Caco-2 cells for their efficiency toincrease the paracellular permeability of the peptide buserelin. For thein vivo studies male Wistar rats were used and buserelin wasadministered with or without the polymers intraduodenally. Both types ofexperiments were performed at pH 7.2. Results. Transport studies with Caco-2 cell monolayers confirmed thatthe increase in buserelin permeation is dependent on the degree oftrimethylation of TMC. In agreement with the in vitro results, in vivodata revealed highly increased bioavailability of buserelin followingintraduodenal co-administration with 1.0% (w/v) TMCs.Intraduodenally applied buserelin resulted in 0.8% absolute bioavailability,whereas co-administrations with TMCs resulted in mean bioavailabilityvalues between 6 and 13 %. Chitosan HCl (1.0% pH = 7.2) did notsignificantly increase the intestinal absorption of buserelin. Conclusions. Both the in vitro and in vivo results indicate that TMCsare potent mucosal permeation enhancers of the peptide drug buserelinat neutral pH values.     

The effects of verapamil on the pharmacokinetics of curculigoside in rats

Context: Clarifying the potential mechanism of the poor oral bioavailability of curculigoside would be helpful for for investigating pharmacological effects and clinical applications.

Objective: To clarify the main mechanism for poor oral bioavailability.

Materials and methods: First, the pharmacokinetics of curculigoside (20?mg/kg) in rats with and without pretreatment with verapamil (10?mg/kg) was determined using a sensitive and reliable LC-MS method. Then the effects of verapamil on the transport and metabolic stability of curculigoside were investigated using Caco-2 cell transwell model and rat liver microsome incubation systems.

Results: The results showed that verapamil could significantly increase the peak plasma concentration (from 60.17?ng/mL to 93.66?ng/mL) and AUC_0?t (from 289.57 to 764.02?ng·h/mL) of curculigoside. The Caco-2 cell experiments indicated that the efflux ratio of curculigoside was 3.92 (P_appAB 6.43?±?0.57?×?10?^?7?cm/s; P_appBA 2.52?±?0.37?×?10?^?36?cm/s), P-gp might be involved in the transport of curculigoside, and verapamil could inhibit the efflux of curculigoside and increase the absorption of curculigoside significantly in the Caco-2 cell monolayer. Additionally, the rat liver microsome incubation experiments indicated that verapamil could significantly decrease the intrinsic clearance rate of curculigoside (from 38.8 to 23.6?μL/min/mg protein).

Discussion and conclusion: These results indicated that verapamil could significantly change the pharmacokinetic profiles of curculigoside in rats, the poor absorption due to P-gp mediated efflux in intestine and high intrinsic clearance rate in rat liver may be the main reason for the poor oral absolute bioavailability of curculigoside.     

Improved oral absorption and anti-lung cancer activity of paclitaxel-loaded mixed micelles

The aim of this study was to establish a paclitaxel (PTX)-loaded mixed micelle delivery system (PTX-TP-M) with vitamin E-TPGS (TPGS) and Plasdone®S-630 Copovidone (PVPS630) as carriers to improve the solubility, oral absorption, and anti-tumor activity of PTX against lung cancer. In this study, PTX-TP-M was prepared using the ethanol thin-film dispersion method followed by characterization of the binary mixed micelles system. The average size of the PTX-TP-M was 83.5?±?1.8?nm with a polydispersity index of 0.265?±?0.007 and the drug loading (DL%) and entrapment efficiency (EE%) were 3.09?±?0.09% and 95.67?±?2.84%, respectively, which contributed to a high solubility of PTX about 24947-fold increase in water (4.78?±?0.14?mg/mL). In addition, TEM analysis showed that the PTX-TP-M appeared spherical in structure and was well dispersed without aggregation and adhesion. In vitro release studies showed that the PTX-TP-M displayed a sustained release compared to free PTX in the dialysis bag. The efflux ratio of PTX reduced from 44.83 to 3.52 when formulated as PTX-TP-M; a 92.15% reduction, studied using the Caco-2 monolayer model. The oral bioavailability of PTX also improved by 4.35-fold, suggesting that PTX-TP-M can markedly promote the absorption in the gastrointestinal tract. Using in vitro MTT assays, it was observed that cytotoxicity was markedly increased, and IC₅₀ values of PTX-TP-M (3.14?±?0.85 and 8.28?±?1.02?μg/mL) were lower than those of PTX solution (5.21?±?0.93 and 14.53?±?1.96?μg/mL) in A549 and Lewis cell, respectively. In vivo anti-tumor studies showed that PTX-TP-M achieved higher anti-tumor efficacy compared with PTX in Lewis bared C57BL/6 mice. Furthermore, a gastrointestinal safety assay also proved the safety of PTX-TP-M. All results demonstrated that the PTX-TP-M exhibited great potential for delivering PTX with increased solubility, oral bioavailability, and anti-cancer activity and this binary mixed micelles drug delivery system has potential to be used clinically.     

Mechanism of Intestinal Absorption of Ranitidine and Ondansetron: Transport Across Caco-2 Cell Monolayers

We have investigated the transport of ranitidine and ondansetron across the Caco-2 cell monolayers. The apparent permeability coefficients (P _app) were unchanged throughout the concentration range studied, indicating a passive diffusion pathway across intestinal mucosa. No metabolism was observed for ranitidine and ondansetron during the incubation with Caco-2 cell monolayers. P _app values for ranitidine and ondansetron (bioavailability of 50 and 100% in humans, respectively) were 1.03 ± 0.17 × 10^–7 and 1.83 ± 0.055 × 10^–5 cm/sec, respectively. The P _app value for ranitidine was increased by 15- to 20-fold in a calcium-free medium or in the transport medium containing EDTA, whereas no significant change occurred with ondansetron, indicating that paracellular passive diffusion is not rate determining for ondansetron. Uptake of ondansetron by Caco-2 cell monolayers was 20- and 5-fold higher than that of ranitidine when the uptake study was carried out under sink conditions and at steady state. These results suggest that ranitidine and ondansetron are transported across Caco-2 cell monolayers predominantly via paracellular and transcellular pathways, respectively.     

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.     

原人参二醇纳米混悬剂的大鼠在体肠吸收研究

目的 考察原人参二醇纳米混悬剂的在体肠吸收特征。方法 采用溶剂蒸发法, 以白蛋白作为稳定剂制备原人参二醇纳米混悬剂。以酚红为标示物, 采用大鼠在体单向肠灌流法评价原人参二醇纳米混悬剂的大鼠在体肠吸收特性。结果 Zetasizer nano ZS仪测得原人参二醇纳米混悬剂平均粒径为(220±10)nm, Zeta电位为(-28±0.2)mV。肠吸收实验表明, 原人参二醇纳米混悬剂在整个肠段都有吸收, 且吸收速率常数(K_a)与渗透系数(P_eff)均大于原人参二醇原药(P<0.05), 原人参二醇纳米混悬剂在小肠段(十二指肠、空肠和回肠)的K_a与P_eff均大于结肠(P<0.05)。结论 原人参二醇纳米混悬剂能够有效促进原人参二醇的大鼠在体肠吸收, 其转运机制可能为主动转运或促进扩散。     

Effects of Structural Modifications on the Intestinal Permeability of Angiotensin II Receptor Antagonists and the Correlation of In Vitro,In Situ,and In Vivo Absorption

Purpose. The effects of structural modifications on the membrane permeability of angiotensin II (Ang II) receptor antagonists and the usefulness of in vitro and in situ intestinal absorption models in predicting in vivo absorption or bioavailability were investigated. Methods. Intestinal permeability was determined in vitro using Caco-2 cell monolayers and in situ using a perfused rat intestine method. Several physicochemical parameters were either measured or computed, and correlated with intestinal permeation. Results. Permeation coefficients (Pa) across Caco-2 cell monolayers correlated well with both in situ absorption rate constants (ka) and in vivo bioavailability or % absorption. For these Ang II antagonists, Pa values larger than 3 × 10^–6 cm sec^–1 and in situ ka values of 2 × 10^–4 min^–1 cm^–1 or above were associated with good in vivo absorption. Structural modifications at the R₅ position, where a COOH group was substituted with either a CHO or CH₂OH group, enhanced the permeability of the Ang II receptor antagonists up to 100-fold. There were good correlations between permeability and log P(octanol/buffer), log P_HPLCcharge, solvation/desolvation energy and assigned hydrogen bonding potential. Conclusions. The correlations obtained in this study indicate that both the Caco-2 cell model and the in situ perfused rat intestine could be used to predict intestinal absorption in vivo. Structural modifications of the Ang II antagonists had a significant impact on the intestinal permeability. Charge, solvation energy, and hydrogen bonding are predominant determinants of intestinal permeability and oral bioavailability of these compounds.     

Enhanced ocular bioavailability of fluconazole from niosomal gels and microemulsions: formulation,optimization, and in vitro–in vivo evaluation

Fungal keratitis may cause vision loss if it is not treated. Methods other than ocular delivery exhibited several limitations. No previous studies investigated and compared ocular bioavailability of fluconazole (FLZ) from niosomal gels and microemulsions. Niosomal gels of FLZ (0.3% w/w) based on Span^® 60 and cholesterol (CH) using 1% w/w carbopol^® 934 (CP) were evaluated. FLZ microemulsions (0.3% w/v) containing isopropyl myristate (IPM, as oil phase) and a 3:1 mixture of Tween^® 80 (as surfactant) and polyethylene glycol 400 (PEG 400, as cosurfactant) were characterized. Optimized formulations were compared for their ocular bioavailability in rabbit’s. Nanoscopic niosomes (63.67–117.13?nm) and microemulsions (57.05–59.93?nm) showed respective negative zeta potential ranges of ?45.37 to ?61.40 and ?20.50 to ?31.90?mV and sustained release up to 12?h. Entrapment efficiency (EE%) of niosomes ranged from 56.48% to 70.67%. Niosomal gels were more sustainable than niosomes and microemulsions. The most stable niosomal gel based on Span^® 60 and CH at a molar ratio of 5:5 and microemulsion containing 45% w/w IPM and 40% w/w of 3:1 Tween^® 80-PEG 400 mixture significantly (p?<?0.0001) enhanced FLZ ocular bioavailability compared with its solution. Niosomal gel showed higher bioavailability than microemulsion by ≈2-fold.