Excised Rat Intestine Research Articles

Impact of Peels Extracts from an Italian Ancient Tomato Variety Grown under Drought Stress Conditions on Vascular Related Dysfunction.

Background: Tomato by-products contain a great variety of biologically active substances and represent a significant source of natural antioxidant supplements of the human diet. The aim of the work was to compare the antioxidant properties of a by-product from an ancient Tuscan tomato variety, Rosso di Pitigliano (RED), obtained by growing plants in normal conditions (-Ctr) or in drought stress conditions (-Ds) for their beneficial effects on vascular related dysfunction. Methods: The antioxidant activity and total polyphenol content (TPC) were measured. The identification of bioactive compounds of tomato peel was performed by HPLC. HUVEC were pre-treated with different TPC of RED-Ctr or RED-Ds, then stressed with H2O2. Cell viability, ROS production and CAT, SOD and GPx activities were evaluated. Permeation of antioxidant molecules contained in RED across excised rat intestine was also studied. Results: RED-Ds tomato peel extract possessed higher TPC than compared to RED-Ctr (361.32 ± 7.204 mg vs. 152.46 ± 1.568 mg GAE/100 g fresh weight). All extracts were non-cytotoxic. Two hour pre-treatment with 5 µg GAE/mL from RED-Ctr or RED-Ds showed protection from H2O2-induced oxidative stress and significantly reduced ROS production raising SOD and CAT activity (* p < 0.05 and ** p < 0.005 vs. H2O2, respectively). The permeation of antioxidant molecules contained in RED-Ctr or RED-Ds across excised rat intestine was high with non-significant difference between the two RED types (41.9 ± 9.6% vs. 26.6 ± 7.8%). Conclusions: RED-Ds tomato peel extract represents a good source of bioactive molecules, which protects HUVECs from oxidative stress at low concentration.

Antioxidant Effect of Cocoa By-Product and Cherry Polyphenol Extracts: A Comparative Study.

Background: Recent studies have highlighted the importance of cherry and cocoa extracts consumption to protect cells from oxidative stress, paying particular attention to cocoa by-products. This study aims to investigate the protective effect of cocoa husk extract (CHE) and cherry extracts (CE) against ROS-induced oxidative stress in Human Umbilical Vein Endothelial Cells (HUVECs). Methods: CE and CHE had antioxidant activity characterized by total polyphenols content (TPC). HUVECs were treated for 2 h and 24 h with increasing TPC concentrations of CE and CHE (5-10-25-50-100 µg Gallic Acid Equivalent (GAE)/mL) and then with H2O2 for 1 h. Cell viability and ROS production were evaluated. CE and CHE polyphenols permeability on excised rat intestine were also studied. Results: CE and CHE showed a similar antioxidant activity (2.5 ± 0.01 mmol Fe2+/100 g FW (fresh weight) and 2.19 ± 0.09 mmol Fe2+/100 g FW, respectively, p > 0.05) whereas CHE had a higher TPC (7105.0 ± 96.9 mg GAE/100 g FW) than CE (402.5 ± 8.4 mg GAE/100 g), p < 0.05. The in vitro viability assay showed that both extracts were non-cytotoxic. CHE resulted in protection against ROS at lower concentrations than CE. CHE showed a 2-fold higher apparent permeability compared to CE. Conclusions: CHE represents a high-value antioxidant source, which is interesting for the food and pharmaceutical industries.

Oral self-emulsifying delivery systems for systemic administration of therapeutic proteins: science fiction?

Objective: The aim of this study was to develop self-emulsifying drug delivery systems (SEDDS) for oral delivery of therapeutic proteins through hydrophobic ion pairing.Method: Horseradish peroxidase (HRP), a model protein, was ion paired with sodium docusate to increase its hydrophobicity. The formed enzyme - surfactant complex was incorporated into SEDDS, followed by permeation studies across Caco-2 cell monolayer and freshly excised rat intestine.Results: Hydrophobic ion pairs (HIP) were formed between HRP and sodium docusate with the efficiency of 87.49 ± 1.35%. The formed complex maintained 60.97 ± 1.48% of the original enzyme activity. The ion pair was subsequently loaded into SEDDS with a payload of 0.1% (mass per cent, m/m). The obtained emulsion formed by SEDDS had a droplet size in the range from 20 to 200 nm with negative zeta potential. Permeation mechanism of the enzyme was energy-dependent and the encapsulation of the HIP complex in SEDDS enhanced the permeation of the enzyme through the Caco-2 cell monolayer and freshly excised rat intestine by 4 times and 2.5 times compared to the free enzyme, respectively.Conclusion: According to these findings, hydrophobic ion pairing followed by incorporation to SEDDS might be considered as a potential strategy for oral delivery of therapeutic proteins.

Ex Vivo and in Vivo Study of Sucrosomial® Iron Intestinal Absorption and Bioavailability.

The present study aimed to demonstrate that Sideral® RM (SRM, Sucrosomial® Raw Material Iron) is transported across the excised intestine via a biological mechanism, and to investigate the effect that this transport route may produce on oral iron absorption, which is expected to reduce the gastrointestinal (GI) side effects caused by the bioavailability of non-absorbed iron. Excised rat intestine was exposed to fluorescein isothiocyanate (FITC)-labeled SRM in Ussing chambers followed by confocal laser scanning microscopy to look for the presence of fluorescein-tagged vesicles of the FITC-labeled SRM. To identify FITC-labeled SRM internalizing cells, an immunofluorescence analysis for macrophages and M cells was performed using specific antibodies. Microscopy analysis revealed the presence of fluorescein positive particulate structures in tissues treated with FITC-labeled SRM. These structures do not disintegrate during transit, and concentrate in macrophage cells. Iron bioavailability was assessed by determining the time-course of Fe3+ plasma levels. As references, iron contents in liver, spleen, and bone marrow were determined in healthy rats treated by gavage with SRM or ferric pyrophosphate salt (FP). SRM significantly increased both area under the curve (AUC) and clearance maxima (Cmax) compared to FP, thus increasing iron bioavailability (AUCrel = 1.8). This led to increased iron availability in the bone marrow at 5 h after single dose gavage.

Impact of mucoadhesive polymeric nanoparticulate systems on oral bioavailability of a macromolecular model drug

Nanoparticles (NP) only different in mucoadhesivity are compared for impact on drug oral bioavailability. Two polymeric NP types based on quaternary ammonium-chitosan (NP QA-Ch) and S-protected thiolated derivative thereof (NP QA-Ch-S-pro), respectively, containing the macromolecular drug model, FD4, were prepared by crosslinking each polymer with reduced MW hyaluronic acid. The structure of basic polymers was determined by H1NMR analysis. NP were similar in size (371 ± 38 vs. 376 ± 82 nm); polydispersity index (0.39 ± 0.08 vs. 0.41 ± 0.10); zeta potential (13.4 ± 0.9 vs. 11.9 ± 1.2 mV); reversible interactions with drug (bound drug, 67 vs. 66%); encapsulation efficiency (23 ± 5 vs. 23 ± 8%); release properties (15% released in 15 h in both cases); and apparent permeation across excised rat intestine (Papp, 8.8 ± 0.8 vs. 10 ± 1 cm/s). Then the differences in NP transport ratio through mucus (TR, 0.75 vs. 0.37) and adhesion to excised rat intestinal mucosa (adsorbed fraction, 23 ± 3 vs. 45 ± 2%) were ascribed to higher mucoadhesivity of NP QA-Ch-S-pro compared to NP QA-Ch. This directly influenced drug oral bioavailability in rats (Tmax, 1 vs. 2 h; AUC, 1.7 ± 0.3 vs. 2.9 ± 0.4 μg/mL min, for NP QA-Ch and NP QA-Ch-S-pro, respectively). Mucoadhesivity increases drug bioavailability by retaining NP at its absorption site and opposing its transit down the GI tract. Data on drug accumulation in rat liver allows the assertion that NP is absorbed by transcytosis across intestinal epithelium and transported from blood into liver by Kuppfer cells.

Methyl-β-cyclodextrin quaternary ammonium chitosan conjugate: nanoparticles vs macromolecular soluble complex.

PurposeThe present study aimed to compare a novel cyclodextrin–polymer–drug complex in solution with a dispersed supramolecular nanosize system, made of the same complex, for ability to carry dexamethasone (DEX) across excised rat intestine.ResultsMethyl-β-cyclodextrin-quaternary ammonium chitosan conjugate (QA-Ch-MCD) was obtained by covalent grafting through a 10-atom spacer. The conjugate was characterized by 1H-NMR, resulting in 24.4% w/w of MCD content. Phase solubility profile analysis of the QA-Ch-MCD/DEX complex yielded an association constant of 14037 M−1, vs 4428 M−1 for the plain MCD/DEX complex. Nanoparticle (NP) dispersions resulted from ionotropic gelation of the QA-Ch-MCD/DEX complex by sodium tripolyphosphate, leading to 9.9%±1.4% drug loading efficiency. The mean diameter and zeta potential for NP were 299±32 nm (polydispersity index [PI] 0.049) and 11.5±1.1 mV, respectively. Those for QA-Ch-MCD/DEX were 2.7±0.4 nm (PI 0.048) and 6.7±0.6 mV. QA-Ch-MCD/DEX solutions and corresponding NP dispersions were compared in vitro for water-assisted transport through mucus, DEX permeation through excised rat intestine, and ex vivo mucoadhesivity. The complex showed higher mucoadhesion and lower transport rate through mucus; also, it provided faster drug permeation across excised rat intestine.ConclusionCarrier adhesion to mucus surface has played a most important role in favoring transepithelial permeation. Then, within the concerns of the present study, the use of NP seems not to provide any determinant advantage over using the simpler macromolecular complex.

Retrograded starch/pectin coated gellan gum-microparticles for oral administration of insulin: A technological platform for protection against enzymatic degradation and improvement of intestinal permeability

Gellan gum microparticles coated with colon-specific films based on retrograded starch and pectin was developed for enhancing the oral release of insulin (INS). The system developed promoted an impressive protection of INS (80%) after 120 min of incubation with trypsin and alpha-chymotrypsin, while only 3% of free INS remained intact after the same time, possibility due to the calcium chelating activity of the polymers in inhibiting the proteolytic activity. In vitro INS release in media simulating the gastrointestinal portions revealed a pH-dependent behavior, as well as the significance of the coating in lowering the release rates in relation to their counterparts. The permeability of INS on Caco-2 cells monolayers and excised rat intestine were significantly improved, mainly due to the influence of the anionic polymers on tight junctions opening, along with the excellent mucoadhesive properties of the gellan gum. All these features together contributed greatly to the hypoglycemic effect observed after the oral administration of the INS-loaded MP in diabetic rats, with reduction of up to 51% of blood glucose levels. The important findings of this work should contribute to the advances about the search of alternatives for oral administration of INS.

N-Deoxycholic acid-N,O-hydroxyethyl Chitosan with a Sulfhydryl Modification To Enhance the Oral Absorptive Efficiency of Paclitaxel.

Currently, the most prominent barrier to the success of orally delivered paclitaxel (PTX) is the extremely limited bioavailability of delivered therapeutic. In light of this issue, an amphiphilic sulfhydrylated N-deoxycholic acid-N,O-hydroxyethyl chitosan (TGA-DHC) was synthesized to improve the oral bioavailability of PTX. First, TGA-DHC demonstrated substantial loading of PTX into the inner hydrophobic core. A desirable enhancement in the bioavailability of PTX by TGA-DHC was verified by pharmacokinetic studies on rats against Taxol and non-sulfhydrylated DHC micelles. Moreover, cellular uptake studies revealed significant accumulation of TGA-DHC micelles encapsulating PTX or rhodamine-123 into Caco-2 cells via clathrin/caveolae-mediated endocytosis and inhibition of P-gp efflux of substrates. The results of the Caco-2 transport study further confirmed the mechanistic basis of TGA-DHC efficacy; which was attributed to permeabilized tight junctions, clathrin-mediated transcytosis across the endothelium, and inhibition of P-gp. Finally, in vitro mucoadhesion investigations on freshly excised rat intestine intuitively confirmed increased intestinal retention of drug-loaded TGA-DHC through thiol-mediated mucoadhesion. TGA-DHC has demonstrated the capability to overcome what is perhaps the most prominent barrier to oral PTX efficacy, low bioavailability, and serves as a prominent platform for oral delivery of P-gp substrates.

N-mercapto acetyl-N′-octyl-O, N″-glycol chitosan as an efficiency oral delivery system of paclitaxel

Herein, thioglycolic acid modified N-octyl-O, N′-glycol chitosan (N-mercapto acetyl-N′-octyl-O, N″-glycol chitosan, abbreviated as SH-OGC) was synthesized to improve the oral bioavailability of paclitaxel (PTX). PTX was readily solubilized into the hydrophobic inner core of SH-OGC. Pharmacokinetic studies demonstrated that the bioavailability of PTX was greatly enhanced when delivered by SH-OGC compared to Taxol® or non-sulfhydrylated OGC micelles. Caco-2 cell experiments confirmed PTX or rhodamine-123-loaded SH-OGC demonstrated effective cellular accumulation via caveola-mediated endocytosis along with the inhibition of P-gp efflux. Furthermore, Caco-2 transport studies demonstrated that the mechanistic basis of SH-OGC efficacy was attributed to P-gp inhibition, enhanced permeability of tight junctions and clathrin-mediated transcytosis across the endothelium. In addition, SH-OGC exhibited increased intestinal retention through thiol-mediated mucoadhesion compared with OGC according to results of mucoadhesion evaluation on freshly excised rat intestine. In summary, SH-OGC micelles may present as a promising delivery vehicle for enhancing the oral bioavailability of P-gp substrates.

Sucrosomial® iron absorption studied by in vitro and ex-vivo models

This paper presents a comparative evaluation of different oral ferric iron formulations for ability to retain Fe3+ in simulated gastric fluid (SGF), be internalized by cells lining intestinal epithelium, and cross it to reach the bloodstream. In all formulations iron was ferric pyrophosphate, the excipients were different types and fractions of lecithin plus sucrose esters of fatty acids matrix (Sideral® RM; PRT1; PRT2) or lecithin without sucrester (SUN). Dissolution kinetics of formulations in SGF was studied by USP method. The ability of the formulations to promote iron intestinal absorption was evaluated by the Caco-2 cell model, measuring cellular ferritin content, and by the excised rat intestine model, yielding apparent permeability parameters (Papp). All formulations limited iron release in SGF to ≤10%. Sideral® RM was by far the most absorbed by Caco-2, as ferritin content was in the order: Sideral® RM≫PRT2>PRT1>SUN>control. The Fe3+ crossing the intestinal barrier was in part reduced to Fe2+ by epithelial enzymes, in part it was carried by formulation rearrangement into nano-structures able to protect it from reduction and apt for internalization by epithelium cells. Papp parameters were in the order: Sideral® RM≫PRT1>PRT2>SUN=control. Relevance of transepithelial Fe2+carrier, DMT-1, to Fe3+ transport was ruled out using a DMT-1 inhibitor. In conclusion, Sideral® RM retains iron in SGF, and is the most suitable for Fe3+ internalization by Caco-2 cells, Fe3+ protection from enzymatic reduction and promotion of Fe3+ absorption across intestinal epithelium, non-mediated by DMT-1.

Dissolution/permeation: The importance of the experimental setup for the prediction of formulation effects on fenofibrate in vivo performance.

The evaluation of formulation strategies in early drug development requires in vitro methods that correctly predict oral drug absorption. The present study aimed to define key parameters for the predictability of dissolution/permeation experiments. Dissolution/permeation experiments were performed in various setups. The IDAS1 chamber, Ussing chamber, and transwells were used as Caco-2 cell based dissolution/permeation models to study the impact of chamber volumes and vertical or horizontal membrane orientation. Dissolution/permeation experiments in Ussing chambers with excised rat intestine were performed to depict the impact of the permeation membrane. Fenofibrate served as model compound in formulations of different particle size. Caco-2 cell based dissolution/permeation experiments with a vertical membrane orientation correctly depicted the formulation effect seen in vivo. The chamber volumes did not affect the outcome. A horizontal membrane orientation achieved no distinction. Experiments using excised rat intestinal sheets did not distinguish between the formulations, and the permeation was much lower than across Caco-2 cells. Mucus might present an artificially enhanced barrier for fenofibrate. Factors that greatly affected the predictivity of the dissolution/permeation experiments were thus the type and orientation of the permeation membrane, whereas chamber volumes only had a minor influence. Vertically mounted Caco-2 cells resulted in the best formulation distinction.

An in-vitro exploration of permeation enhancement by novel polysulfonate thiomers

The study was aimed to synthesize preactivated polysulfonate thiomers using poly(4-styrenesulfonic acid-co-maleic acid) (PSSA-MA) and to evaluate their permeation enhancing properties. PSSA-MA-cysteamine (PC) conjugates with 2-mercaptonicotinic acid (2MNA) having different degree of preactivation (PC1608-2MNA, PC2300-2MNA, PC3100-2MNA) were synthesized from the subsequent PSSA-MA-cysteamine thiomers (PC1608, PC2300 and PC3100). The permeation-enhancing features were evaluated by in-vitro models using low-molecular size marker sodium fluorescein (Na-Flu) and with high-molecular size marker fluorescein isothiocyanate-dextran (FD4). Associating the influence of degree of preactivation on permeation enhancement, following rank order PC3100-2MNA>PC3100>PC2300-2MNA>PC2300>PC1608-2MNA>PC1608>PSSA-MA>control was observed on Caco-2 cell monolayers and with little change in sequence on freshly excised rat intestine. The apparent permeability (Papp) was improved 3.16-fold for Na-Flu and 3.51-fold for FD4 on Caco-2 cell monolayers. Similarly, 4.17- and 3.60-fold improved Papp values were observed on freshly excised rat intestine for Na-Flu and FD4, respectively. More pronounced permeation effects on rat intestine compared to Caco-2 cell monolayer by the thiomer/preactivated conjugates indicated their mucus-interpenetration capability in addition to mucoadhesion. Thus relatively low molecular weight (LMW) preactivated polysulfonate thiomers could to a higher extent enhance permeation on membranes covered by mucus layer compared to high molecular weight thiomers/preactivated conjugates that usually exhibit higher permeation enhancing effects on Caco-2 cell monolayer.

Superiority of the S,S conformation in diverse pharmacological processes: Intestinal transport and entry inhibition activity of novel anti-HIV drug lead

Chirality is an important aspect in many pharmacological processes including drug transport and metabolism. The current investigation examined the stereospecific transport and entry inhibitory activity of four diastereomers derived from a small (macrocyclic) molecule that has two chiral centers. These molecules were designed to mimic the interaction between CD4 and gp120 site of HIV-1 and thereby to function as entry inhibitor(s).Intestinal permeability was assessed by ex-vivo model using excised rat intestine mounted in side-by-side diffusion chambers. The entry inhibitory activity was monitored using indicator HeLa-CD4-LTR-beta-gal cells (MAGI assay).The (S/S) diastereomer, named CG-1, exhibited superiority in both unrelated tested biological processes: (I) high transport through the intestine and (II) entry inhibition activity (in the low μM range). The permeability screening revealed a unique transporter-mediated absorption pathway of CG-1, suggesting a significant role of the molecule's conformation on the mechanism of intestinal absorption.Here we highlight that only the S,S enantiomer (CG-1) has both (I) promising anti HIV-1 entry inhibitory properties and (II) high transporter mediated intestinal permeability. Hence we suggest preference in pharmacological processes to the S,S conformation. This report augments the knowledge regarding stereoselectivity in receptor mediated and protein–protein interaction processes.

Nanoparticles based on quaternary ammonium–chitosan conjugate: A vehicle for oral administration of antioxidants contained in red grapes

The purpose of this study was to demonstrate that nanoparticles (NP), obtained by ionotropic crosslinking of reduced-MW chitosan (rCh) derivatives with reduced-MW hyaluronan (rHA), could be profitable vehicles for oral administration of beneficial doses of antioxidant constituents of red grape seeds extracts (GSE). NP have previously shown aptitude for internalisation by endothelial progenitor cells. Here they were seen by a fluorescence microscope migrating across excised rat intestine from mucosal to serosal side and permeating from the donor to the acceptor compartment of an Ussing chamber while carrying significant (15–20%) steadily associated fractions of initial antioxidant load. Freshly prepared NP dispersions were stabilised by lyophilisation. The NP dispersions were regenerated from the lyophilised products by adding water under gentle stirring. Lyophilisation-regeneration caused a significant NP size increase yet particles did not grow beyond the upper size limit of particles able to cross the intestinal barrier (500 nm).

S-Protected Thiolated Chitosan for Oral Delivery of Hydrophilic Macromolecules: Evaluation of Permeation Enhancing and Efflux Pump Inhibitory Properties

The objective of this study was the investigation of permeation enhancing and P-glycoprotein (P-gp) inhibition effects of a novel thiolated chitosan, the so-named S-protected thiolated chitosan. Mediated by a carbodiimide, increasing amounts of thioglycolic acid (TGA) were covalently bound to chitosan (CS) in the first step of modification. In the second step, these thiol groups of thiolated chitosan were protected by disulfide bond formation with the thiolated aromatic residue 6-mercaptonicotinamide (6-MNA). Mucoadhesive properties of all conjugates were evaluated in vitro on porcine intestinal mucosa based on tensile strength investigations. Permeation enhancing effects were evaluated ex vivo using rat intestinal mucosa and in vitro via Caco-2 cells using the hydrophilic macromolecule FD(4) as the model drug. Caco-2 cells were further used to show P-gp inhibition effects by using Rho-123 as P-gp substrate. Apparent permeability coefficients (P(app)) were calculated and compared to values obtained from each buffer control. Three different thiolated chitosans were generated in the first step of modification, which displayed increasing amounts of covalently attached free thiol groups on the polymer backbone. In the second modification step, more than 50% of these free thiol groups were covalently linked with 6-MNA. Within 3 h of permeation studies on excised rat intestine, P(app) values of all S-protected chitosans were at least 1.3-fold higher compared to those of corresponding thiomers and more than twice as high as that of unmodified chitosan. Additional permeation studies on Caco-2 cells confirmed these results. Because of the chemical modification and higher amount of reactive thiol groups, all S-protected thiolated chitosans exhibit at least 1.4-fold pronounced P-gp inhibition effects in contrast to their corresponding thiomers. These features approve S-protected thiolated chitosan as a promising excipient for various drug delivery systems providing improved permeation enhancing and efflux inhibition effects.

Red grape skin and seeds polyphenols: Evidence of their protective effects on endothelial progenitor cells and improvement of their intestinal absorption

Scope To evaluate the ability of grape skin and seeds to protect endothelial progenitor cells (EPC) from oxidative stress induced by hyperglycemia (HG) compared to red wine (RW) and prepare innovative pharmaceutical systems for the oral administration of red grape extract allowing the overcoming of its poor intestinal absorption. Methods and results Human EPC were characterized by expression of cell surface markers. Cells were incubated with different concentrations of total polyphenols from grape components or RW in the presence or absence of HG. Cell viability, migration, adhesion, and reactive oxygen species (ROS) production were assayed. Intestinal permeation of polyphenols was studied in the absence or presence of a quaternary ammonium-chitosan conjugate (N +(60)-Ch). Grape components and RW increased EPC viability, adhesion and migration, and prevented the HG effect ( P < 0.01). ROS production induced by HG was significantly reduced only by grape seed extract and RW ( P < 0.01). N +(60)-Ch acted as an effective enhancer of polyphenol permeability across the excised rat intestine. Conclusions Red grape components are a source of antioxidant compounds that ameliorate EPC viability and function, while preventing endothelial dysfunction. The use of polycationic chitosan derivatives can promote the absorption of polyphenols across intestinal epithelium, thus increasing their bioavailability and potential therapeutic value in atherosclerosis.

Design and synthesis of a novel cationic thiolated polymer

The purpose of this study was to design and characterize a novel cationic thiolated polymer. In this regard a hydroxyethylcellulose-cysteamine conjugate (HEC-cysteamine) was synthesized. Oxidative ring opening with periodate and reductive amination with cysteamine were performed in order to immobilize free thiol groups to HEC. The resulting HEC-cysteamine displayed 2035 ± 162 μmol immobilized free thiol groups and 185 ± 64 μmol disulfide bonds per gram of polymer being soluble in both acidic and basic conditions. Unlike the unmodified HEC, in case of HEC-cysteamine, a three-fold increase in the viscosity was observed when equal volumes of the polymer were mixed with mucin solution. Tablets based on HEC-cysteamine remained attached on freshly excised porcine mucosa for 80 h and displayed increased disintegration time of 2 h. Swelling behavior of HEC-cysteamine tablets in 0.1 M phosphate buffer pH 6.8 indicated swelling ratio of 19 within 8 h. In contrast, tablets comprising unmodified HEC detached from the mucosa within few seconds and immediately disintegrated. In addition, they did not exhibit swelling behavior. The transport of rhodamine 123 across freshly excised rat intestine enhanced by a value of approximately 1.6-fold ( p-value = 0.0024) in the presence of 0.5% (m/v) HEC-cysteamine as compared to buffer control. Result from cytotoxicity test of HEC-cysteamine applied to Caco-2 cells in concentration of 0.5% (m/v) revealed 82.4 ± 4.60% cell viability. According to these results, HEC-cysteamine seems to be a promising polymer for various pharmaceutical applications especially for intestinal drug delivery.

Thiolated chitosans: influence of various sulfhydryl ligands on permeation-enhancing and P-gp inhibitory properties

Purpose: The influence of various sulfhydryl ligands on permeation-enhancing and P-glycoprotein (P-gp) inhibitory properties of the six established thiolated chitosan conjugates was investigated using Rhodamine-123 (Rho-123) and fluorescein isothiocyanate-dextran 4 (FD4) as model compounds. Methods: Permeation of these compounds was tested on freshly excised rat intestine in Ussing-type chambers. Apparent permeability coefficients (Papp) were calculated and compared to values obtained from the buffer only control. Results: The lyophilized polymers had a thiol group content in the range of 230–520 μmol/g. Results of this study led to the following rank order in permeation enhancement: chitosan-6-mercaptonicotinic acid (chitosan-6MNA) > chitosan-cysteine (chitosan-Cys) > chitosan-glutathione (chitosan-GSH) > chitosan-4-thiobutylamidine (chitosan-TBA) > chitosan-thioglycolic acid (chitosan-TGA) > chitosan-N-acetyl cysteine (chitosan-NAC). In P-gp inhibition studies, 0.5% (m/v) chitosan-NAC showed the highest inhibitory effect on P-gp, where the Papp was determined to be 3.78-fold increased compared with the buffer control. Among these thiolated chitosans, chitosan-NAC and chitosan-6MNA are the most effective polymers being responsible for P-gp inhibition and permeation enhancement, respectively. Conclusion: These thiolated chitosans would therefore be advantageous tools for enhancing the noninvasive bioavailability of active pharmaceutical ingredients.

Polymer integrity related absorption mechanism of superporous hydrogel containing interpenetrating polymer networks for oral delivery of insulin

Superporous hydrogel containing poly(acrylic acid- co-acrylamide)/ O-carboxymethyl chitosan interpenetrating polymer networks (SPH-IPN) was evaluated as the oral delivery vehicle for insulin, emphasizing on the effect of polymer integrity on insulin absorption mechanisms. The integral SPH-IPN (I-SPH-IPN) and powdered SPH-IPN (P-SPH-IPN) exhibited potent and equivalent in vitro enzymatic inhibition capacities, which were attributed to both enzyme incorporation and Ca 2+ deprivation. Nevertheless, I-SPH-IPN showed marked superiority to P-SPH-IPN in in vivo enzymatic inhibition. Through reversible opening of epithelial tight junctions, I-SPH-IPN notably enhanced paracellular permeability of insulin in Caco-2 cell monolayers and excised rat intestine by 4.9 and 4.2 folds, respectively, wherein I-SPH-IPN outperformed P-SPH-IPN by 2.5 and 2.3 folds, respectively. Besides, orally delivered I-SPH-IPN could retain in rat intestine for more than 8 h while P-SPH-IPN was quickly eliminated, suggesting better retentive properties of I-SPH-IPN. Such results were further confirmed by in vivo assessment in that oral administration of insulin-loaded I-SPH-IPN yielded notable insulin absorption and hypoglycemic effect, while P-SPH-IPN was ineffective. Finally, an oral acute and sub-acute toxicity study in mice confirmed biocompatibility of SPH-IPN. Therefore, the detailed mechanism assessment confirmed that I-SPH-IPN was an effective and safe peroral carrier for protein drugs.

Improved synthesis of quaternary ammonium-chitosan conjugates (N +-Ch) for enhanced intestinal drug permeation

The pH-induced structural modifications of the reaction product between chitosan and 2-diethylaminoethyl chloride are studied with the purpose of testing and comparing the resulting chitosan derivatives on the basis of their intestinal drug permeability-enhancing properties. The reaction reproducibly yielded conjugates comprising short pendant chains of n adjacent diethyl-dimethylene-ammonium groups substituted onto the primary amino group of the chitosan repeating unit. The more significant derivatives, N +-Ch-7 (degree of substitution, DS = 41%; n = 3) and N +-Ch-8 (DS = 59%; n = 1.7) were prepared at pH 7 and 8, respectively. The apparent permeability ( P app) of excised rat intestine was determined by means of Ussing type chambers. The hydrophilic fluorescein sodium (NaFlu) and fluorescein isothiocyanate dextran (MW 4400 Da) (FD-4), and the lipophilic rhodamine 123 (Rh-123), were applied in Ringer buffer to the apical side. Apical to basolateral transport was measured in the absence or presence of 0.5% (w/v) of the polymer under test. N +-Ch-7 and N +-Ch-8 were more effective P app enhancers than N-trimethyl-chitosan. Both N +-Ch-7 and N +-Ch-8 enhanced the P app of NaFlu (enhancement ratio, ER = 1.84 and 1.33, respectively), while N +-Ch-8 was the more effective enhancer for FD-4 (ER = 2.14). The P app of Rh-123 was significantly enhanced only by N +-Ch-7 (ER = 1.37). Permeant-polymer binding counteracted the enhancement effect of polymer on transmembrane permeant flux. Contact with the chitosan conjugates did not impair the mucosal epithelium integrity.