Temperature- and rigidity-mediated rapid transport of lipid nanovesicles in hydrogels.

Lipid nanovesicles are widely present as transport vehicles in living organisms and can serve as efficient drug delivery vectors. It is known that the size and surface charge of nanovesicles can affect their diffusion behaviors in biological hydrogels such as mucus. However, how temperature effects, including those of both ambient temperature and phase transition temperature (Tm), influence vehicle transport across various biological barriers outside and inside the cell remains unclear. Here, we utilize a series of liposomes with different Tm as typical models of nanovesicles to examine their diffusion behavior in vitro in biological hydrogels. We observe that the liposomes gain optimal diffusivity when their Tm is around the ambient temperature, which signals a drastic change in the nanovesicle rigidity, and that liposomes with Tm around body temperature (i.e., ∼37 °C) exhibit enhanced cellular uptake in mucus-secreting epithelium and show significant improvement in oral insulin delivery efficacy in diabetic rats compared with those with higher or lower Tm Molecular-dynamics (MD) simulations and superresolution microscopy reveal a temperature- and rigidity-mediated rapid transport mechanism in which the liposomes frequently deform into an ellipsoidal shape near the phase transition temperature during diffusion in biological hydrogels. These findings enhance our understanding of the effect of temperature and rigidity on extracellular and intracellular functions of nanovesicles such as endosomes, exosomes, and argosomes, and suggest that matching Tm to ambient temperature could be a feasible way to design highly efficient nanovesicle-based drug delivery vectors.

Protein Corona Liposomes Achieve Efficient Oral Insulin Delivery by Overcoming Mucus and Epithelial Barriers.

Oral delivery of peptide/protein drugs has attracted worldwide attention due to its good patient compliance and convenience of administration. Orally administered nanocarriers always encounter the rigorous defenses of the gastrointestinal tract, which mainly consist of mucus and epithelium barriers. However, diametrically opposite surface properties of nanocarriers are required for good mucus penetration and high epithelial uptake. Here, bovine serum albumin (BSA) is adsorbed to cationic liposomes (CLs) to form protein corona liposomes (PcCLs). The aim of using PcCLs is to conquer the mucus and epithelium barriers, eventually improving the oral bioavailability of insulin. Investigations using in vitro and in vivo experiments show that the uptake amounts and transepithelial permeability of PcCLs are 3.24- and 7.91-fold higher than that of free insulin, respectively. Further study of the behavior of PcCLs implies that BSA corona can be shed from PcCLs as they cross the mucus layer, which results in the exposure of CLs to improve the transepithelial transport. Intrajejunal administration of PcCLs in type I diabetic rats produces a remarkable hypoglycemic effect and increases the oral bioavailability up to 11.9%. All of these results imply that PcCLs may provide a new insight into the method for oral insulin delivery by overcoming the multiple barriers.

Enhanced digestion inhibition and mucus penetration of F127-modified self-nanoemulsions for improved oral delivery.

Self-nanoemulsifying systems (SNEs) have excellent ability to improve the solubility of poorly water-soluble drugs (PWSD). However, SNEs are likely to be degraded in gastrointestinal (GIT) when their surface is recognized by lipase/co-lipase enzyme complex, resulting in rapid release and precipitation of encapsulated drugs. The precipitates are then captured and removed by intestinal mucus, reducing the delivery efficacy of SNEs. Herein, the amphiphilic polymer Pluronic® F127 was incorporated into long and short-chain triglycerides (LCT, SCT) based SNEs to diminish the recognition and therefore minimized their degradation by enzymes and clearance by mucus. The SNEs were characterized in terms of particle size, zeta potential and stability. Ex vivo multiple particles tracking studies were performed by adding particle solution into fresh rat mucus. Cellular uptake of SNEs were conducted by using E12 cells, the absorption and distribution in small intestine were also studied after oral administration in male Sprague-Dawley (SD) rats. The in vitro digestion rate of SNEs were found to be in following order SCT-SNE > SCT-F127-SNE > LCT-SNE > LCT-F127-SNE. Moreover, the LCT-F127-SNE was found to be most effective in enhancing cellular uptake, resulting in 3.5-fold, 2.1-fold and 1.7-fold higher than that of SCT-SNE, LCT-SNE and SCT-F127-SNE, respectively. After incubating the SNE with E12 cells, the LCT-F127-SNE exhibited the highest amount regarding both mucus penetration and cellular uptake, with an uptake amount number (via bicinchoninic acid (BCA) analysis) of 3.5-fold, 2.1-fold and 1.7-fold higher than that of SCT-SNE, LCT-SNE and SCT-F127-SNE, respectively. The in vivo results revealed that orally administered LCT-F127-SNE could significantly increase the bioavailability of Cyclosporine A (CsA), which was approximately 2.43-fold, 1.33-fold and 1.80-fold higher than that of SCT-SNE, SCT-F127-SNE and LCT-SNE, respectively. We address in this work that F127-modified SNEs have potentials to improve oral drug absorption by significantly reducing gastrointestinal enzymatic degradation and simultaneously enhancing mucus penetration.

Functional nanoparticles exploit the bile acid pathway to overcome multiple barriers of the intestinal epithelium for oral insulin delivery.

Oral absorption of protein/peptide-loaded nanoparticles is often limited by multiple barriers of the intestinal epithelium. In addition to mucus translocation and apical endocytosis, highly efficient transepithelial absorption of nanoparticles requires successful intracellular trafficking, especially to avoid lysosomal degradation, and basolateral release. Here, the functional material, deoxycholic acid-conjugated chitosan, is synthesized and loaded with the model protein drug insulin into deoxycholic acid-modified nanoparticles (DNPs). The DNPs designed in this study are demonstrated to overcome multiple barriers of the intestinal epithelium by exploiting the bile acid pathway. In Caco-2 cell monolayers, DNPs are internalized via apical sodium-dependent bile acid transporter (ASBT)-mediated endocytosis. Interestingly, insulin degradation in the epithelium is significantly prevented due to endolysosomal escape of DNPs. Additionally, DNPs can interact with a cytosolic ileal bile acid-binding protein that facilitates the intracellular trafficking and basolateral release of insulin. In rats, intravital two-photon microscopy also reveals that the transport of DNPs into the intestinal villi is mediated by ASBT. Further pharmacokinetic studies disclose an oral bioavailability of 15.9% in type I diabetic rats after loading freeze-dried DNPs into enteric-coated capsules. Thus, deoxycholic acid-modified chitosan nanoparticles can overcome multiple barriers of the intestinal epithelium for oral delivery of insulin.

Intracellular transport of nanocarriers across the intestinal epithelium.

The intestinal epithelium is the main barrier restricting the oral delivery of low-permeability drugs. Over recent years, numerous nanocarriers have been designed to improve the efficiency of oral drug delivery. However, the intracellular processes determining the transport of nanocarriers across the intestinal epithelium remain elusive, and only limited enhancement of the oral bioavailability of drugs has been achieved. Here, we review the processes involved in nanocarrier trafficking across the intestinal epithelium, including apical endocytosis, intracellular transport, and basolateral exocytosis. Understanding the complex intracellular processes of nanocarrier trafficking is particularly essential for the rational design of oral drug delivery systems.

Supersaturated polymeric micelles for oral cyclosporine A delivery: The role of Soluplus-sodium dodecyl sulfate complex.

Our previous study demonstrated that the retention of drug in the hydrophobic core of Soluplus micelle greatly impeded drug absorption from gastrointestinal tract. Using supersaturated polymeric micelles can improve drug release, however, insufficient maintaining of supersaturation of drug is still unfavorable for drug absorption. Here, we report adding small amount of small molecule, sodium dodecyl sulfate (SDS), to Soluplus solution can form a Soluplus-SDS complex. This complex not only showed a higher solubilization capability for the model drug cyclosporine A (CsA), but also maintained a longer period of and higher supersaturation than was achieved with Soluplus alone. The Soluplus-SDS interactions were characterized by analyzing surface tension, small-angle X-ray scattering (SAXS), fluorescence spectra, and nuclear magnetic resonance spectroscopy. The results demonstrated that the formation of Soluplus-SDS complex via SDS adsorption on hydrophobic segments of Soluplus, which have more hydrophobic domain than that of Soluplus micelle, contributed significantly to the solubilization and stabilization of supersaturated CsA. Using this amphiphilic copolymer-small molecule surfactant system, the cellular uptake and rat in vivo absorption of CsA were more effectively achieved than pure Soluplus. The area under the plasma concentration-time curve (AUC) and the maximal plasma concentration (Cmax) achieved by CsA-loaded Soluplus-SDS complex were 1.58- and 1.8-times higher than the corresponding values for CsA-loaded pure Soluplus, respectively. This study highlighted the benefits of Soluplus-SDS complex for optimizing the solubilization and oral absorption of a drug with low aqueous solubility.

Lipid-Based Formulations for Oral Drug Delivery: Effects on Drug Absorption and Metabolism.

The application of lipid-based drug delivery systems on the industrial scale has successfully demonstrated their therapeutic and manufacturing advantages. Recently, various lipid-based formulations were successfully prepared for oral delivery of compounds that are difficult to administer. Nevertheless, an improved understanding of how these formulations affect drug absorption and metabolism is required to support the rapid and successful completion of drug development programs. In this review, we report the detailed mechanisms whereby lipids and lipid-based excipients affect drug absorption and metabolism, and summarize the capacity of lipids and lipid-based formulations to improve drug absorption by improving drug solubility, mucosa penetration, lymphatic transport, and hepatic metabolism. Finally, we discuss the progress made toward the use of novel lipid formulations to enhance oral absorption by surmounting specific absorption barriers.

A poly-l-glutamic acid functionalized nanocomplex for improved oral drug absorption.

Poor permeability of the intestinal epithelium limits the oral absorption of many drugs. Here, a poly-l-glutamic acid (PGA)-based functional ternary nanocomplex (TC) is reported for enhancing the intestinal absorption of poorly permeable drug doxorubicin hydrochloride (Dox·HCl). The particle size and zeta potential of TC were 189.3 ± 13.7 nm and -29.1 ± 7.4 mV, respectively. The TC was shown to be more stable under simulated gastrointestinal changing pH or electrolyte content conditions than the binary nanocomplex Dox·HCl/PGA. Cellular uptake and the apparent permeability coefficient value (Papp) of the TC were determined to be 5.2- and 4.6-fold higher than that of Dox·HCl solutions, respectively. Mechanistic studies showed that active endocytosis caused by specific interactions between γ-glutamyl terminal groups of PGA and membrane-bound γ-glutamyl transferase contributed much to the TC-dependent Dox·HCl absorption. Studies on the rat model also demonstrated the highest efficiency for Dox·HCl absorption by the TC throughout the intestinal tract, with 2.6- and 4.2-fold higher Cmax and AUC0-24h values compared to Dox·HCl solutions. In conclusion, the TC is a promising carrier for improving Dox·HCl intestinal absorption, and the rational design of carriers with functional polymer PGA could implement the efficient active absorption of poorly permeable drugs.

Enhanced transport of nanocage stabilized pure nanodrug across intestinal epithelial barrier mimicking Listeria monocytogenes.

Ligand grafted nanoparticles have been shown to enhance drug transport across epithelium barrier and are expected to improve drug delivery. However, grafting of these ligands to the surface of pure nanodrug, i.e., nanocrystals (NCs), is a critical challenge due to the shedding of ligands along with the stabilizer upon high dilution or dissolving of the drug. Herein, a non-sheddable nanocage-like stabilizer was designed by covalent cross-linking of poly(acrylic acid)-b-poly(methyl acrylate) on drug nanocrystal surface, and a ligand, wheat germ agglutinin (WGA), was successfully anchored to the surface of itraconazole (ITZ) NCs by covalent conjugation to the nanocage (WGA-cage-NCs). The cellular study showed that large amount of WGA-cage-NCs were adhered to Caco-2 cell membrane, and invaded into cells, resulting in a higher drug uptake than that of ordinary NCs (ONCs). After oral administration to rats, WGA-cage-NC were largely accumulated on the apical side of epithelium cells, facilitating drug diffusing across epithelium barrier. Interestingly, WGA-cage-NCs were capable of invading rat intestinal villi and reaching to lamina propria by transcytosis across goblet cells, which behaved like a foodborne pathogen, Listeria monocytogenes. The WGA-cage-NCs showed an improved oral bioavailability, which was 17.5- and 2.41-folds higher than that of coarse crystals and ONCs, respectively. To our best knowledge, this may represent the first report that a functional ligand was successfully anchored to the surface of pure nanodrug by using a cage-like stabilizer, showing unique biological functions in gastrointestinal tract and having an important significance in oral drug delivery.

Comparative study of Pluronic(®) F127-modified liposomes and chitosan-modified liposomes for mucus penetration and oral absorption of cyclosporine A in rats.

Liposomes modified using cationic and hydrophilic nonionic polymers are 2 popular carriers for improving oral drug absorption. Cationic polymer-modified liposomes can adhere to the intestinal wall mucus (mucoadhesive type), while liposomes modified using hydrophilic nonionic polymers can penetrate across the mucus barrier (mucus-penetrating type). Chitosan-modified liposomes (CS-Lip, mucoadhesive type) and Pluronic(®) F127-modified liposomes (PF127-Lip, mucus-penetrating type) were engineered to investigate the differences between these mucoadhesive and mucus-penetrating systems in oral absorption of a poorly soluble drug, cyclosporine A (CyA). Stability of CS-Lip and PF127-Lip was studied in simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). The intestinal mucus adhesion or penetration of liposomes was studied by confocal laser scanning microcopy and fluorophotometry using coumarin 6 as the fluorescent probe. The oral absorption of CyA-loaded liposomes was also studied in Sprague-Dawley rats. In vitro and in vivo studies revealed that CS-Lip tended to aggregate in SIF, to be trapped by mucus, to remain mainly in the upper portion of the intestinal tract, and to show limited penetration ability. In contrast, PF127-Lip were more stable in the SIF and SGF, were found throughout the intestinal tract, and were able to penetrate the mucus layers to reach the epithelial surface. Pharmacokinetic analysis in rats showed that the Cmax and AUC0-t of PF127-Lip were 1.73- and 1.84-fold higher than those of CS-Lip, respectively (P<0.05). In conclusion, the stability and mucus-penetrating ability of PF127-Lip in the gastrointestinal tract rendered it more suitable than the mucoadhesive CS-Lip for oral delivery CyA.

Supersaturated polymeric micelles for oral cyclosporine A delivery.

Polymeric micelles provide a promising platform for improving oral absorption of poorly soluble drugs. However, improved understanding of how drug retention within the hydrophobic micelle core can reduce drug absorption is required. We designed supersaturated polymeric micelles (Super-PMs) to increase molecularly dissolved drug concentration and gain an insight into the effect of the degree of supersaturation on oral absorption of cyclosporine A (CsA) in rats. The drug release from Super-PMs increased with an increase in initial supersaturation degrees in micelles. The cellular uptake of coumarin-6 was reduced by the retention of drug in polymer micelles. The transport flux of CsA across Caco-2 monolayer was increased with initial supersaturation degrees of 0.81-3.53 (p < 0.05). However, increase in supersaturation to 5.64 actually resulted in decreased CsA transport. The same trend was observed in a rat in vivo absorption study, in which the highest bioavailability of 134.6 ± 24.7% (relative to a commercial product, Sandimmun Neoral®, p<0.01) was achieved when the supersaturation degree was 3.53. These results demonstrated that Super-PMs were a promising drug delivery system for compounds with low aqueous solubility. This study also provided an experimental proof for the hypothesis that moderately supersaturated formulations are valuable alternative to high supersaturation formulations, resulting in optimal in vivo performance, and the degree of supersaturation should be carefully controlled to optimize drug absorption.

Intestinal mucosa permeability following oral insulin delivery using core shell corona nanolipoparticles.

Chitosan nanoparticles (NC) have excellent capacity for protein entrapment, favorable epithelial permeability, and are regarded as promising nanocarriers for oral protein delivery. Herein, we designed and evaluated a class of core shell corona nanolipoparticles (CSC) to further improve the absorption through enhanced intestinal mucus penetration. CSC contains chitosan nanoparticles as a core component and pluronic F127-lipid vesicles as a shell with hydrophilic chain and polyethylene oxide PEO as a corona. These particles were developed by hydration of a dry pluronic F127-lipid film with NC suspensions followed by extrusion. Insulin nested inside CSC was well protected from enzymatic degradation. Compared with NC, CSC exhibited significantly higher efficiency of mucosal penetration and, consequently, higher cellular internalization of insulin in mucus secreting E12 cells. The cellular level of insulin after CSC treatment was 36-fold higher compared to treatment with free insulin, and 10-fold higher compared to NC. CSC significantly facilitated the permeation of insulin across the ileum epithelia, as demonstrated in an ex vivo study and an in vivo absorption study. CSC pharmacological studies in diabetic rats showed that the hypoglycemic effects of orally administrated CSC were 2.5-fold higher compared to NC. In conclusion, CSC is a promising oral protein delivery system to enhance the stability, intestinal mucosal permeability, and oral absorption of insulin.

Pluronic F127-modified liposome-containing tacrolimus-cyclodextrin inclusion complexes: improved solubility, cellular uptake and intestinal penetration.

OBJECTIVE: The aim of this study was to investigate Pluronic F127-modified liposome-containing cyclodextrin (CD) inclusion complex (FLIC) for improving the solubility, cellular uptake and intestinal penetration of tacrolimus (FK 506) in the gastrointestinal (GI) tract. METHODS: Molecular modelling was performed to screen the optimal CD for the solubilization of FK 506. FLIC was prepared by thin-lipid film hydration with the inclusion complex solutions followed by membrane extrusion. Dilution tests were conducted in simulated gastric fluids and phosphate-buffered solution of sodium taurocholate to investigate the solubility improvement of FK506. The cellular uptake of nanocarriers was studied in Caco-2 cells, and intestinal mucous membrane penetration in the GI tract was evaluated in Sprague-Dawley rats. KEY FINDINGS: The results showed that ß-CD had the strongest binding energy with the guest molecule among the CDs. The prepared FLIC has an average diameter of 180.8 ± 8.1 nm with a spherical shape. The solubility and cellular uptake of FK 506 was greatly improved by the incorporation of CD complexes in the Pluronic F127-modified liposomes. Intestinal mucous membrane penetration was also significantly improved by the preparation of FLIC. CONCLUSION: With improved drug solubility and intestinal mucous membrane penetration, FLIC shows a promising oral delivery system for FK 506.