Thiomer-coated liposomes harbor permeation enhancing and efflux pump inhibitory properties

A Window for Enhanced Oral Delivery of Therapeutics via Lipid Nanoparticles

Oral administration of dosage forms is convenient and beneficial in several respects. Lipid nanoparticulate dosage forms have emerged as a useful carrier system in deploying low solubility drugs systemically, particularly class II, III, and IV drugs of the Biopharmaceutics Classification System. Like other nanoparticulate delivery systems, their low size-to-volume ratio facilitates uptake by phagocytosis. Lipid nanoparticles also provide scope for high drug loading and extended-release capability, ensuring diminished systemic side effects and improved pharmacokinetics. However, rapid gastrointestinal (GI) clearance of particulate delivery systems impedes efficient uptake across the mucosa. Mucoadhesion of dosage forms to the GI mucosa results in longer transit times due to interactions between the former and mucus. Delayed transit times facilitate transfer of the dosage form across the mucosa. In this regard, a balance between mucoadhesion and mucopenetration guarantees optimal systemic transfer. Furthermore, the interplay between GI anatomy and physiology is key to ensuring efficient systemic uptake. This review captures salient anatomical and physiological features of the GI tract and how these can be exploited for maximal systemic delivery of lipid nanoparticles. Materials used to impart mucoadhesion and examples of successful mucoadhesive lipid nanoformulations are highlighted in this review.

SN38-loaded nanomedicine mediates chemo-radiotherapy against CD44-expressing cancer growth

Background

Chemo-radiotherapy is the combined chemotherapy and radiotherapy on tumor treatment to obtain the local radiosensitization and local cytotoxicity of the tumor and to control the microscopic metastatic disease.

Methods

In this study, 7-ethyl-10-hydroxycamptothecin (SN38) molecules could be successfully loaded into human serum albumin (HSA)–hyaluronic acid (HA) nanoparticles (SH/HA NPs) by the hydrophobic side groups of amino acid in HSA.

Results

HSA could be used to increase the biocompatibility and residence time of the nanoparticles in the blood, whereas HA could improve the benefits and overall treatment effect on CD44-expressing colorectal cancer (CRC), and reduce drug side effects. In addition to its role as a chemotherapeutic agent, SN38 could be used as a radiosensitizer, able to arrest the cell cycle, and allowing cells to stay in the G2/M stage, to improve the sensitivity of tumor cells to radiation. In vivo results demonstrated that SH/HA NPs could accumulate in the tumor and produce significant tumor suppression, with no adverse effects observed when combined with γ-ray irradiation. This SH/HA NPs-medicated chemo-radiotherapy could induce an anti-tumor immune response to inhibit the growth of distal tumors, and produce an abscopal effect.

Conclusions

Therefore, this SN38-loaded and HA-incorporated nanoparticle combined with radiotherapy may be a promising therapeutic artifice for CRC in the future.

Thiolated Cellulose: A Dual-Acting Mucoadhesive and Permeation-Enhancing Polymer

This study aims to design an anionic, thiolated cellulose derivative and to evaluate its mucoadhesive and permeation-enhancing properties utilizing enoxaparin as a model drug. 2-Mercaptosuccinic acid-modified cellulose (cellulose-mercaptosuccinate) was synthesized by the reaction of cellulose with S-acetylmercaptosuccinic anhydride. The chemical structure of the target compound was confirmed by FTIR and 1H NMR spectroscopy. The thiol content was determined by Ellman's test. The conjugate exhibited 215.5 ± 25 μmol/g of thiol groups and 84 ± 16 μmol/g of disulfide bonds. Because of thiolation, mucoadhesion on porcine intestinal mucosa was 9.6-fold enhanced. The apparent permeability (Papp) of the model dye Lucifer yellow was up to 2.2-fold improved by 0.5% cellulose-mercaptosuccinate on a Caco-2 cell monolayer. Enoxaparin permeation through rat intestinal mucosa increased 2.4-fold in the presence of 0.5% cellulose-mercaptosuccinate compared with the drug in buffer only. In vivo studies in rats showed an oral bioavailability of 8.98% using cellulose-mercaptosuccinate, which was 12.5-fold higher than that of the aqueous solution of the drug. Results of this study show that the modification of cellulose with 2-mercaptosuccinic acid provides mucoadhesive and permeation-enhancing properties, making this thiolated polymer an attractive excipient for oral drug delivery.

Structure-activity relationship of a peptide permeation enhancer

The pentapeptide L-R5 has previously been shown to transiently increase the permeability of nasal epithelial cell layers in vitro, allowing paracellular transport of molecules of up to 4 kDa. Protein kinase C zeta (PKC ζ), a member of a family of serine/threonine kinases was shown to be involved in tight junction modulation induced by L-R5. We show here that the ability of L-R5 to modulate tight junctions is comparable to other permeability enhancers such as bilobalide, latrunculin A or C₁₀. Interaction of the peptide with the target protein occurs via electrostatic interaction, with the presence of positive charges being essential for its functionality. L-R5 is myristoylated to allow quick cell entry and onset of activity. While no epithelial cytotoxicity was detected, the hydrophobic myristoyl rest was shown to cause haemolysis. Taken together, these data show that a structural optimization of L-R5 may be possible, both from a toxicological and an efficacy point of view.

Human serum albumin-based nanoparticles alter raloxifene administration and improve bioavailability

Osteoporosis is a disease that reduces bone mass and microarchitecture, which makes bones fragile. Postmenopausal osteoporosis occurs due to estrogen deficiency. Raloxifene is a selective estrogen receptor modulator used to treat postmenopausal osteoporosis. However, it has a low bioavailability, which requires long-term, high-dose raloxifene administration to be effective and causes several side effects. Herein, raloxifene was encapsulated in human serum albumin (HSA)-based nanoparticles (Ral/HSA/PSS NPs) as an intravenous-injection pharmaceutical formulation to increase its bioavailability and reduce the treatment dosage and time. In vitro results indicated that raloxifene molecules were well distributed in HSA-based nanoparticles as an amorphous state, and the resulting raloxifene formulation was stabile during long-term storage duration. The Ral/HSA/PSS NPs were both biocompatible and hemocompatible with a decreased cytotoxicity of high-dose raloxifene. Moreover, the intravenous administration of the prepared Ral/HSA/PSS NPs to rats improved raloxifene bioavailability and improved its half-life in plasma. These raloxifene-loaded nanoparticles may be a potential nanomedicine candidate for treating postmenopausal osteoporosis with lower raloxifene dosages.

Tailoring the properties of chitosan by grafting with 2-mercaptobenzoic acid to improve mucoadhesion: in silico studies, synthesis and characterization

Mucoadhesive polymers improve oral bioavailability of drugs by prolonging the duration of adhesion of drugs with mucosa. Various methods could be employed to address the problems of mucoadhesive polymers like weak adhesion forces. Chemical modification of polymers, such as the addition of a thiol group or thiolation, is another way for improving the polymers' mucoadhesive properties that is studied in present research work. A novel thiomer of chitosan was prepared by attaching 2-mercaptobenzoic acid, a hydrophobic ligand onto it. The docking of thiomer and chitosan with mucin structure showed higher binding energy for former. The prepared thiomer was subjected to X-ray diffraction and DSC which established reduction in crystallinity and formation of a new compound through changes in glass transition, melting point and change in diffraction pattern. The NMR studies established conjugation of 2-mercapto benzoic acid to chitosan. The increased mucoadhesion in thiomer behaviour (2-3 fold) was confirmed through mucus glycoprotein assay as well as through texture analysis. The permeation enhancing the property of thiomer was established by demonstrating the permeation of phenol red across thiomer treated intestinal membrane. An in vitro cell toxicity assay was done to establish toxicity of chitosan and thiolated chitosan. Finally, the reduced water uptake of thiomer over chitosan proved that the increase in mucoadhesion is not contributed by swelling. Thus, a thiomer with improved mucoadhesion and enhanced permeation properties was prepared and characterized. Hence, all these properties render the newly synthesized polymer a better alternative to chitosan as an excipient for mucoadhesive drug delivery systems.

Recent Advances in Oral Peptide or Protein-Based Drug Liposomes

The high physiology and low toxicity of therapeutic peptides and proteins have made them a hot spot for drug development in recent years. However, their poor oral bioavailability and unstable metabolism make their clinical application difficult. The bilayer membrane of liposomes provides protection for the drug within the compartment, and their high biocompatibility makes the drug more easily absorbed by the body. However, phospholipids—which form the membranes—are subjected to various digestive enzymes and mucosal adhesion in the digestive tract and disintegrate before absorption. Improvements in the composition of liposomes or modifying their surface can enhance the stability of the liposomes in the gastrointestinal tract. This article reviews the basic strategies for liposome preparation and surface modification that promote the oral administration of therapeutic polypeptides.

Thiolated Chitosan Conjugated Liposomes for Oral Delivery of Selenium Nanoparticles

This study aimed to design a hybrid oral liposomal delivery system for selenium nanoparticles (Lip-SeNPs) to improve the bioavailability of selenium. Thiolated chitosan, a multifunctional polymer with mucoadhesive properties, was used for surface functionalization of Lip-SeNPs. Selenium nanoparticle (SeNP)-loaded liposomes were manufactured by a single step microfluidics-assisted chemical reduction and assembling process. Subsequently, chitosan-N-acetylcysteine was covalently conjugated to the preformed Lip-SeNPs. The Lip-SeNPs were characterized in terms of composition, morphology, size, zeta potential, lipid organization, loading efficiency and radical scavenging activity. A co-culture system (Caco-2:HT29-MTX) that integrates mucus secreting and enterocyte-like cell types was used as a model of the human intestinal epithelium to determine adsorption, mucus penetration, release and transport properties of Lip-SeNPs in vitro. Thiolated Lip-SeNPs were positively charged with an average size of about 250 nm. Thiolated Lip-SeNPs tightly adhered to the mucus layer without penetrating the enterocytes. This finding was consistent with ex vivo adsorption studies using freshly excised porcine small intestinal tissues. Due to the improved mucoadhesion and retention in a simulated microenvironment of the small intestine, thiolated Lip-SeNPs might be a promising tool for oral selenium delivery.

Astragaloside IV- and nesfatin-1-encapsulated phosphatidylserine liposomes conjugated with wheat germ agglutinin and leptin to activate anti-apoptotic pathway and block phosphorylated tau protein expression for Parkinson's disease treatment

Heap-up of α-synuclein (α-Syn) and its association with tau protein are esteemed to trigger the onset of Parkinson's disease (PD). The purpose of this study was to develop multi-functional liposomes incorporated with 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), cholesterol, 1,2-dimyristoyl-sn-glycero-3-phosphocholine and phosphatidylserine (PS) to load astragaloside IV (AS-IV) and nestifin-1 (NF-1), followed by grafting with wheat germ agglutinin (WGA) and leptin (Lep) (WGA-Lep-AS-IV-NF-1-PS-liposomes) to protect dopaminergic neurons from apoptosis. Experimental results showed that increasing the mole percentage of DSPC and PS enhanced the particle size, particle stability and entrapment efficiency of AS-IV and NF-1, and reduced the drug releasing rate. Strong affinity of NF-1 to PS was evidenced by nuclear magnetic resonance spectroscopy. WGA-Lep-AS-IV-NF-1-PS-liposomes diminished transendothelial electrical resistance and improved the capacity of propidium iodide, AS-IV and NF-1 to penetrate the blood-brain barrier (BBB). Immunocytochemical staining exhibited the ability of functionalized liposomes to target Lep receptor and α-Syn in MPP⁺-insulted SH-SY5Y cells. Western blots revealed a substantial reduction of α-Syn and phosphorylated tau protein in the anti-oxidative pathway through interaction with PS. During the course of treatment with WGA-Lep-AS-IV-NF-1-PS-liposomes, the combined activity of AS-IV and NF-1 and recognition capability simultaneously decreased the expression of Bax, and increased the expressions of Bcl-2, tyrosine hydroxylase and dopamine transporter. The liposomes carrying AS-IV and NF-1 can rescue degenerated neurons and are a promising formulation to achieve better PD management.

In Vitro Investigation of Thiolated Chitosan Derivatives as Mucoadhesive Coating Materials for Solid Lipid Nanoparticles

In the present study, chitosan (CS) was thiolated by introducing l-cysteine via amide bond formation. Free thiol groups were protected with highly reactive 6-mercaptonicotinic acid (6-MNA) and less-reactive l-cysteine, respectively, via thiol/disulfide-exchange reactions. Unmodified CS, l-cysteine-modified thiolated CS (CS-Cys), 6-MNA-S-protected thiolated CS (CS-Cys-MNA), and l-cysteine-S-protected thiolated CS (CS-Cys-Cys) were applied as coating materials to solid lipid nanoparticles (SLN). The strength of mucus interaction followed the rank order plain < CS < CS-Cys-Cys < CS-Cys < CS-Cys-MNA, whereas mucus diffusion followed the rank order CS-Cys < CS-Cys-Cys < CS < CS-Cys-MNA < plain. In accordance with lower reactivity, CS-Cys-Cys-coated SLN were immobilized to a lower extent than CS-Cys-coated SLN, while CS-Cys-MNA-coated SLN dissociated from their coating material resulting in a similar diffusion behavior as plain SLN. Consequently, CS-Cys-Cys-coated SLN and CS-Cys-MNA-coated SLN showed the highest retention on porcine intestinal mucosa by enabling a synergism of efficient mucus diffusion and strong mucoadhesion.

Recent Biomedical Approaches for Chitosan Based Materials as Drug Delivery Nanocarriers

In recent decades, drug delivery systems (DDSs) based on nanotechnology have been attracting substantial interest in the pharmaceutical field, especially those developed based on natural polymers such as chitosan, cellulose, starch, collagen, gelatin, alginate and elastin. Nanomaterials based on chitosan (CS) or chitosan derivatives are broadly investigated as promising nanocarriers due to their biodegradability, good biocompatibility, non-toxicity, low immunogenicity, great versatility and beneficial biological effects. CS, either alone or as composites, are suitable substrates in the fabrication of different types of products like hydrogels, membranes, beads, porous foams, nanoparticles, in-situ gel, microparticles, sponges and nanofibers/scaffolds. Currently, the CS based nanocarriers are intensely studied as controlled and targeted drug release systems for different drugs (anti-inflammatory, antibiotic, anticancer etc.) as well as for proteins/peptides, growth factors, vaccines, small DNA (DNAs) and short interfering RNA (siRNA). This review targets the latest biomedical approaches for CS based nanocarriers such as nanoparticles (NPs) nanofibers (NFs), nanogels (NGs) and chitosan coated liposomes (LPs) and their potential applications for medical and pharmaceutical fields. The advantages and challenges of reviewed CS based nanocarriers for different routes of administration (oral, transmucosal, pulmonary and transdermal) with reference to classical formulations are also emphasized.

Per-6-Thiolated Cyclodextrins: A Novel Type of Permeation Enhancing Excipients for BCS Class IV Drugs

The purpose of the study was to develop a per-6-thiolated α-cyclodextrin (α-CD) by substituting all primary hydroxyl groups of α-CD with thiol groups and to assess its solubility-improving and permeation-enhancing properties for a BCS Class IV drug in vitro as well as in vivo. The primary hydroxyl groups of α-CD were replaced by iodine, followed by substitution with -SH groups. The structure of per-6-thiolated α-CD was approved by FT-IR and ¹H NMR spectroscopy. The per-6-thiolated was characterized for thiol content, -SH stability, cytotoxicity, and solubility-improving properties by using the model BCS Class IV drug furosemide (FUR). The mucoadhesive properties of the thiolated oligomer were investigated via viscoelastic measurements with porcine mucus, whereas permeation-enhancing features were evaluated on the Caco-2 cell monolayer and rat gut mucosa. Furthermore, oral bioavailability studies were performed in rats. The per-6-thiolated α-CD oligomer displayed 4244 ± 402 μmol/g thiol groups. These -SH groups were stable at pH ≤ 4, exhibiting a pK_a value of 8.1, but subject to oxidation at higher pH. Per-6-thiolated α-CD was not cytotoxic to Caco-2 cells in 0.5% (m/v) concentration within 24 h. It improved the solubility of FUR in the same manner as unmodified α-CD. The addition of per-6-thiolated α-CD (0.5% m/v) increased the mucus viscosity up to 5.8-fold at 37 °C within 4 h. Because of the incorporation in per-6-thiolated α-CD, the apparent permeability coefficient (P_app) of FUR was 6.87-fold improved on the Caco-2 cell monolayer and 6.55-fold on the intestinal mucosa. Moreover, in vivo studies showed a 4.9-fold improved oral bioavailability of FUR due to the incorporation in per-6-thiolated α-CD. These results indicate that per-6-thiolated α-CD would be a promising auxiliary agent for the mucosal delivery of, in particular, BCS Class IV drugs.

Rational Design of a Multipurpose Bioadhesive Vaginal Film for Co-Delivery of Dapivirine and Levonorgestrel

Human immunodeficiency virus (HIV) infection and unintended pregnancy, which can lead to life-threatening complications, are two major burdens for female reproductive health. To address these pressing health issues, multipurpose prevention technologies (MPTs) are proposed to deliver two or more drugs simultaneously. MPTs could offer several benefits for users such as improved convenience, increased effectiveness, reduced cost, and decreased environmental burden. Here, we report the development, and in vitro and in vivo assessment of a bioadhesive vaginal film as a coitally-independent MPT dosage form for delivering dapivirine (DPV) and levonorgestrel (LNG) to prevent HIV infection and unintended pregnancy, respectively. After confirming the feasibility of bioadhesive film use for weekly drug delivery in vivo through colpophotography and MRI evaluation, the pharmacokinetics (PK) of DPV/LNG single entity and combination bioadhesive films was investigated in pigtailed macaques (n = 5). Both drugs from single entity or combination films were able to provide sustained drug release in vivo. The combination film showed lower local tissue clearance for DPV and exhibited significantly increased plasma concentration for LNG as compared to the single entity film. This proof-of-concept study demonstrates the ability of this novel bioadhesive film platform to deliver LNG and DPV simultaneously as an MPT product for the prevention of HIV infection and unintended pregnancy.

Coating of PLA-nanoparticles with cyclic, arginine-rich cell penetrating peptides enables oral delivery of liraglutide

Until today, the oral delivery of peptide drugs is hampered due to their instability in the gastrointestinal tract and low mucosal penetration. To overcome these hurdles, PLA (polylactide acid)-nanoparticles were coated with a cyclic, polyarginine-rich, cell penetrating peptide (cyclic R9-CPP). These surface-modified nanoparticles showed a size and polydispersity index comparable to standard PLA-nanoparticles. The zeta potential showed a significant increase indicating successful CPP-coupling to the surface of the nanoparticles. Cryo-EM micrographs confirmed the appropriate size and morphology of the modified nanoparticles. A high encapsulation efficiency of liraglutide could be achieved. In vitro tests using Caco-2 cells showed high viability indicating the tolerability of this novel formulation. A strongly enhanced mucosal binding and penetration was demonstrated by a Caco-2 binding and uptake assay. In Wistar rats, the novel nanoparticles showed a substantial, 4.5-fold increase in the oral bioavailability of liraglutide revealing great potential for the oral delivery of peptide drugs.

Thiolated polymers: Bioinspired polymers utilizing one of the most important bridging structures in nature

Thiolated polymers designated "thiomers" are obtained by covalent attachment of thiol functionalities on the polymeric backbone of polymers. In 1998 these polymers were first described as mucoadhesive and in situ gelling compounds forming disulfide bonds with cysteine-rich substructures of mucus glycoproteins and crosslinking through inter- and intrachain disulfide bond formation. In the following, it was shown that thiomers are able to form disulfides with keratins and membrane-associated proteins exhibiting also cysteine-rich substructures. Furthermore, permeation enhancing, enzyme inhibiting and efflux pump inhibiting properties were demonstrated. Because of these capabilities thiomers are promising tools for drug delivery guaranteeing a strongly prolonged residence time as well as sustained release on mucosal membranes. Apart from that, thiomers are used as drugs per se. In particular, for treatment of dry eye syndrome various thiolated polymers are in development and a first product has already reached the market. Within this review an overview about the thiomer-technology and its potential for different applications is provided discussing especially the outcome of studies in non-rodent animal models and that of numerous clinical trials. Moreover, an overview on product developments is given.

BSA Nanoparticles Modified with N-Acetylcysteine for Improving the Stability and Mucoadhesion of Curcumin in the Gastrointestinal Tract

A major obstacle to the clinical use of curcumin (CUR) is its reduced bioavailability because of the drug's hydrophobic nature, low intestinal absorption, and rapid metabolism. In this study, a novel oral drug delivery system was constructed for improving the stability and enhancing mucoadhesion of CUR in the gastrointestinal (GI) tract. First, CUR was encapsulated in the bovine serum albumin nanoparticles (CUR-BSA-NPs). Then, N-acetyl cysteine (NAC)-modified CUR-BSA-NPs (CUR-NBSA-NPs) were obtained. The average particle size and zeta potential of CUR-NBSA-NPs were 251.6 nm and -30.66 mV, respectively; encapsulation efficiency and drug loading were 85.79 and 10.9%, respectively. CUR-NBSA-NPs exhibited a sustained release property and prominently enhanced stability in simulated GI conditions. Additionally, enhanced mucoadhesion of CUR-NBSA-NPs was also observed. An MTT study showed that the CUR-NBSA-NPs were safe for oral administration. Overall, NAC-modified BSA-NPs may potentially serve as an oral vehicle for improving CUR stability in the GI tract and enhancing mucoadhesion.

The thiolated chitosan: Synthesis, gelling and antibacterial capability

Chitosan-1-(mercaptomethyl)-cyclopropane acetic acid (CS-MCA) copolymer was synthesized by amino linkage. The obtained copolymer was characterized by FTIR, ¹H NMR, XRD, TGA and SEM. Porous and reticulate morphologies were found on the CS-MCA surface. The effects of pH on the rheological properties of CS-MCA were investigated. On the one hand, the apparent viscosity of CS-MCA indicated a shear-thinning behavior. The graft of MCA enhanced the moduli and the maximum elastic properties were observed at pH = 7.00. The addition of dithiothreitol reduced the viscosity and modulus of CS-MCA hydrogel, and the gelation time, temperature and frequency were obtained in dynamic oscillatory tests. The antibacterial effect of CS-MCA against E. coli was investigated for the inhibition zone and bacterial growth curve. These results showed that CS-MCA had better antibacterial ability than chitosan without modification. Therefore, the rheological behavior and functional activities can be applied for the hydrocolloid gels in food and pharmaceutical applications.

Potential of Lipid Nanoparticles (SLNs and NLCs) in Enhancing Oral Bioavailability of Drugs with Poor Intestinal Permeability

Lipid-based drug delivery systems has become a popular choice for oral delivery of lipophilic drugs with dissolution rate limited oral absorption. Lipids are known to enhance oral bioavailability of poorly water-soluble drugs in multiple ways like facilitating dissolution as micellar solution, enhancing the lymphatic uptake and acting as inhibitors of efflux transporters. Lipid nanoparticles are matrix type lipid-based carrier systems which can effectively encapsulate both lipophilic and hydrophilic drugs. Lipid nanoparticles namely solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) are versatile drug delivery system and can be used for multiple routes of delivery like parenteral, topical, ocular, transdermal, and oral. Lipid nanoparticles are particularly attractive vehicles for peroral delivery of drugs with oral bioavailability problems as they are composed of lipid excipients which are cheap, easily available, and non-toxic; manufacturing technique is simple and readily scalable for large-scale production; the formulations provide controlled release of active components and have no stability issue. A large number of drugs have been incorporated into lipid nanoparticles with the objective of overcoming their poor oral bioavailability. This review tries to assess the potential of lipid nanoparticles for enhancing the oral bioavailability of drugs with permeability limited oral absorption such as drugs belonging to class IV of Biopharmaceutic Classification System (BCS) and protein and peptide drugs and also discusses the mechanism behind the bioavailability enhancement and safety issues related to such delivery systems.

Mutlifunctional nanoparticles prepared from arginine-modified chitosan and thiolated fucoidan for oral delivery of hydrophobic and hydrophilic drugs

Self-assembled nanoparticles (NPs) from arginine-modified chitosan (CS-N-Arg) and thiolated fucoidan (THL-fucoidan) were synthesized to enhance the transport of dextran and curcumin across intestinal epithelial cell layer. CS-N-Arg/THL-fucoidan NPs exhibited a pH-sensitive assembly-disassembly and drug release property. Evaluations of the NPs in enhancing the transport of a hydrophilic macromolecule (FITC-dextran) and a hydrophobic drug (curcumin) were investigated in Caco-2 cell monolayers. The cationic CS-N-Arg in the NPs induced disruption of intestinal epithelial tight junctions as indicated by the decrease of transepithelial electrical resistance (TEER). Permeation studies revealed that the NPs enhanced the paracellular permeation of macromolecular dextran through the monolayer barrier. In addition, the multifunctional NPs increased the permeability of rhodamine 123 because the thiomer THL-fucoidan in the NPs inhibited P-glycoprotein. Cellular uptake and permeability of curcumin encapsulated in the NPs were improved due to increasing their water solubility and stability.

PEGylation for enhancing nanoparticle diffusion in mucus

The viscoelastic mucus secretions coating exposed organs such as the lung airways and the female reproductive tract can trap and quickly eliminate not only foreign pathogens and ultrafine particles but also particle-based drug delivery systems, thus limiting sustained and targeted drug delivery at mucosal surfaces. To improve particle distribution across the mucosa and enhance delivery to the underlying epithelium, many investigators have sought to develop nanoparticles capable of readily traversing mucus. The first synthetic nanoparticles shown capable of rapidly penetrating physiological mucus secretions utilized a dense coating of polyethylene glycol (PEG) covalently grafted onto the surface of preformed polymeric nanoparticles. In the decade since, PEG has become the gold standard in engineering mucus-penetrating drug carriers for sustained and targeted drug delivery to the lungs, gastrointestinal tract, eyes, and female reproductive tract. This review summarizes the history of the development of various PEG-based mucus-penetrating particles, and highlights the key physicochemical properties of PEG coatings and PEGylation strategies to achieve muco-inert PEG coatings on nanoparticle drug carriers for improved drug and gene delivery at mucosal surfaces.

Improved Bioavailability and Antitumor Effect of Docetaxel by TPGS Modified Proniosomes: In Vitro and In Vivo Evaluations

A novel oral drug delivery system, TPGS modified docetaxel proniosomes (DTX-TPGS-PNs), was designed to enhance the oral bioavailability and antitumor efficiency of the poorly water-soluble drug docetaxel. DTX-TPGS-PN niosomes were 93 ± 6.5 nm in size, -18.53 ± 1.65 mV in zeta potential and exhibited spherical morphology, with an encapsulation efficiency of 97.31 ± 0.60%. The system showed sustained release in both simulated gastric and intestinal fluid. The results of caco-2 monolayer, everted gut sac model and improved single-pass intestinal perfusion model transport studies showed that DTX-TPGS-PN niosomes could significantly improve the absorption of DTX. The pharmacokinetics study suggested the absolute bioavailability of DTX-TPGS-PN niosomes were 7.3 times that of DTX solution. In addition, a higher antitumor efficacy than DTX solution was demonstrated in MCF-7 and MDA-MB-231 cells in vitro and in MCF-7 tumor-bearing mice model in vivo. Our results demonstrated DTX-TPGS-PN is promising in enhancing the bioavailability and efficiency of poorly water-soluble drug DTX, and the potential of proniosomes as stable precursors for oral drug delivery.

Gold nanoshell coated thermo-pH dual responsive liposomes for resveratrol delivery and chemo-photothermal synergistic cancer therapy

Stimuli-responsive drug delivery and release have a great significance in cancer therapy. Herein, a multifunctional responsive drug carrier was designed and developed by loading resveratrol (Res) in chitosan (CTS) modified liposomes, and coated by gold nanoshells (GNS@CTS@Res-lips). The resultant GNS@CTS@Res-lips possess broad near-infrared (NIR) absorbance, high capability, stability, and also high photothermal conversion ability for efficient photothermal therapy (PTT) applications. In addition, the GNS@CTS@Res-lips exhibit the on-demand pH/photothermal-sensitive drug release, and a high loading capacity of Res. Under NIR laser irradiation, the drug delivery system could significantly enhance the cellular uptake of drugs. More importantly, compared to the single chemotherapy or PTT, the carriers with NIR irradiation displayed a higher therapeutic effect for HeLa cells. Therefore, the GNS@CTS@Res-lips with a combination of chemotherapy and PTT will show great potential for application in cancer therapy.

Lipid-based nanocarriers for oral peptide delivery

This article is aimed to overview the lipid-based nanostructures designed so far for the oral administration of peptides and proteins, and to analyze the influence of their composition and physicochemical (particle size, zeta potential) and pharmaceutical (drug loading and release) properties, on their interaction with the gastro-intestinal environment, and the subsequent PK/PD profile of the associated drugs. The ultimate goal has been to highlight and comparatively analyze the key factors that may be determinant of the success of these nanocarriers for oral peptide delivery. The article ends with some prospects on the challenges to be addressed for the intended commercial success of these delivery vehicles.

Nanostructured lipid carriers: versatile oral delivery vehicle

Oral delivery is the most accepted and economical route for drug administration and leads to substantial reduction in dosing frequency. However, this route still remains a challenge for the pharmaceutical industry due to poorly soluble and permeable drugs leading to poor oral bioavailability. Incorporating bioactives into nanostructured lipid carriers (NLCs) has helped in boosting their therapeutic functionality and prolonged release from these carrier systems thus providing improved pharmacokinetic parameters. The present review provides an overview of noteworthy studies reporting impending benefits of NLCs in oral delivery and highlights recent advancements for developing engineered NLCs either by conjugating polymers over their surface or modifying their charge to overcome the mucosal barrier of GI tract for active transport across intestinal membrane.

Lay abstract: Oral administration of drugs is considered to be a convenient route; however, various drugs that are insoluble in water or unable to permeate across GI tract membrane cannot be delivered by this route. To deliver them effectively, various lipid carriers have been widely explored by researchers. Lipid carriers encapsulate drug inside them and deliver them effectively via the oral route. Also, encapsulation of drug protects them from degradation inside GI tract and safely delivers them to the site of action. This review summarizes application of lipid carriers, in other words, nanostructured lipid carriers, in eradicating these problems, with suitable examples.

Potential advantages of a novel chitosan-N-acetylcysteine surface modified nanostructured lipid carrier on the performance of ophthalmic delivery of curcumin

The transient precorneal retention time and low penetration capacity into intraocular tissues are the key obstacles that hinder the ophthalmic drug delivery of many therapeutic compounds, especially for drugs with poor solubility and permeability. To break the stalemate, N-acetyl-L-cysteine functionalized chitosan copolymer (CS-NAC), which exhibit marked bioadhesion and permeation enhancing effect, was synthesized. The curcumin encapsulated NLC (CUR-NLC) was produced and optimized followed by surface absorption of CS-NAC. After coating, changed particle size from 50.76 ± 2.21 nm to 88.64 ± 1.25 nm and reversed zeta potential from −20.38 ± 0.39 mV to 22.51 ± 0.34 mV was observed. The in vitro CUR release from NLC was slower than that of CUR-NLC and chitosan hydrochlorides (CH) coated NLC due to the inter and/or intramolecular disulfide formation of thiomers on the surface of nanocarriers. The modification also significantly enhanced transcorneal penetration compared with CH-NLC and the uncoated ones. The effect on bioadhesion and precorneal retention were evaluated by in vivo imaging technique and ocular pharmacokinetics studies revealing that the clearance of the formulations was significantly delayed in the presence of CS-NAC and the effect was positively related to the degree of thiolation. In summary, CS-NAC-NLC presented a series of notable advantages for ophthalmic drug application.

Recent advances in liposome surface modification for oral drug delivery

Oral delivery via the gastrointestinal (GI) tract is the dominant route for drug administration. Orally delivered liposomal carriers can enhance drug solubility and protect the encapsulated theraputic agents from the extreme conditions found in the GI tract. Liposomes, with their fluid lipid bilayer membrane and their nanoscale size, can significantly improve oral absorption. Unfortunately, the clinical applications of conventional liposomes have been hindered due to their poor stability and availability under the harsh conditions typically presented in the GI tract. To overcome this problem, the surface modification of liposomes has been investigated. Although liposome surface modification has been extensively studied for oral drug delivery, no review exists so far that adequately covers this topic. The purpose of this paper is to summarize and critically analyze emerging trends in liposome surface modification for oral drug delivery.

Novel in vitro transport method for screening the reversibility of P-glycoprotein inhibitors

The purpose of this study was to establish a novel in vitro method for screening reversibility of P-glycoprotein (P-gp) inhibitors. Caco-2 cells with 21days of cultivation were used as an in vitro model. Transport of rhodamine 123 in the presence of various inhibitors and after removing of inhibitors was determined. Transport of rhodamine 123 at 4°C and in the secretory direction assured that Caco-2 cells exhibited P-gp function at all time of experiment. The apparent permeability coefficient (Papp) of rhodamine 123 in the presence of verapamil, cyclosporin A, ritonavir, quinidine, N-ethylmaleimide, Cremophor® EL, Tween 80 and poly(acrylic acid)-cysteine-2-mercaptonicotinic acid (PAA-cys-2MNA) was 2.3-, 3.8-, 2.3-, 3.1, 7.5-, 2.1-, 2.9- and 2.5-fold higher than Papp of rhodamine 123 alone. After removing of the inhibitors, Papp decreased to the same range of control except in the case of N-ethylmaleimide which was 2.4-fold higher than the control. These results revealed a reversible inhibition of verapamil, cyclosporin A, ritonavir, quinidine, Cremophor® EL, Tween 80 and PAA-cys-2MNA and an irreversible inhibition of N-ethylmaleimide for P-gp. Thus, this novel established that in vitro method might be an effective tool for screening the reversibility of inhibition of P-gp inhibitors.

Preactivated thiomers: their role in drug delivery

INTRODUCTION

Since thiolated polymers - known as thiomers - have entered the pharmaceutical arena in the late 1990 s, more and more academic and industrial research groups have started to work with these promising polymeric excipients. Meanwhile, various thiomers are the subject of clinical trials and the first product based on thiolated chitosan will reach the market in 2015. Due to the formation of disulfide bonds with mercaptopyridine substructures, thiol groups of thiomers are on the one hand more reactive and on the other hand are protected toward oxidation. These so-called preactivated thiomers representing the second generation of thiomers are subject of this review.

AREAS COVERED

Within this review, preactivated thiomers are classified and their mode of action is described. Furthermore, different synthetic pathways, purification and chemical characterization methods of preactivated thiomers are explained. Their properties including mucoadhesive, permeation-enhancing, efflux pump inhibitory and in situ gelling properties are described. In addition, various formulations based on preactivated thiomers are introduced.

EXPERT OPINION

The first-generation thiomers have already shown great potential resulting in various product developments. Preactivated thiomers - representing the second generation of thiomers - offer the additional advantage of even comparatively more reactive sulfhydryl ligands and of stability toward oxidation. According to this, they are promising novel polymeric excipients for various applications.

Hydrogel-assisted functional reconstitution of human P-glycoprotein (ABCB1) in giant liposomes

This paper describes the formation of giant proteoliposomes containing P-glycoprotein (P-gp) from a solution of small proteoliposomes that had been deposited and partially dried on a film of agarose. This preparation method generated a significant fraction of giant proteoliposomes that were free of internalized vesicles, making it possible to determine the accessible liposome volume. Measuring the intensity of the fluorescent substrate rhodamine 123 (Rho123) inside and outside these giant proteoliposomes determined the concentration of transported substrates of P-gp. Fitting a kinetic model to the fluorescence data revealed the rate of passive diffusion as well as active transport by reconstituted P-gp in the membrane. This approach determined estimates for the membrane permeability coefficient (Ps) of passive diffusion and rate constants of active transport (kT) by P-gp as a result of different experimental conditions. The Ps value for Rho123 was larger in membranes containing P-gp under all assay conditions than in membranes without P-gp indicating increased leakiness in the presence of reconstituted transmembrane proteins. For P-gp liposomes, the kT value was significantly higher in the presence of ATP than in its absence or in the presence of ATP and the competitive inhibitor verapamil. This difference in kT values verified that P-gp was functionally active after reconstitution and quantified the rate of active transport. Lastly, patch clamp experiments on giant proteoliposomes showed ion channel activity consistent with a chloride ion channel protein that co-purified with P-gp. Together, these results demonstrate several advantages of using giant rather than small proteoliposomes to characterize transport properties of transport proteins and ion channels.

Drug delivery systems, CNS protection, and the blood brain barrier

Present review highlights various drug delivery systems used for delivery of pharmaceutical agents mainly antibiotics, antineoplastic agents, neuropeptides, and other therapeutic substances through the endothelial capillaries (BBB) for CNS therapeutics. In addition, the use of ultrasound in delivery of therapeutic agents/biomolecules such as proline rich peptides, prodrugs, radiopharmaceuticals, proteins, immunoglobulins, and chimeric peptides to the target sites in deep tissue locations inside tumor sites of brain has been explained. In addition, therapeutic applications of various types of nanoparticles such as chitosan based nanomers, dendrimers, carbon nanotubes, niosomes, beta cyclodextrin carriers, cholesterol mediated cationic solid lipid nanoparticles, colloidal drug carriers, liposomes, and micelles have been discussed with their recent advancements. Emphasis has been given on the need of physiological and therapeutic optimization of existing drug delivery methods and their carriers to deliver therapeutic amount of drug into the brain for treatment of various neurological diseases and disorders. Further, strong recommendations are being made to develop nanosized drug carriers/vehicles and noninvasive therapeutic alternatives of conventional methods for better therapeutics of CNS related diseases. Hence, there is an urgent need to design nontoxic biocompatible drugs and develop noninvasive delivery methods to check posttreatment clinical fatalities in neuropatients which occur due to existing highly toxic invasive drugs and treatment methods.

Strategies for improving mucosal drug delivery

Within this review we will provide a comprehensive understanding in order to improve existing strategies and to develop new systems to lower the barrier for improving mucosal drug delivery. Mucosal administration of drugs achieves a therapeutical effect as the permeation of significant amounts of a drug is permitted through the absorption membrane. The absorption membrane relies on the mucosal layer and the epithelial tissue. In order to overcome barriers, drug delivery systems have to exhibit various functions and features, such as mucoadhesive and protective activity, solubility improving, permeation and uptake enhancing, and drug release controlling properties. This review also aims to provide an insight of well-distinguished strategies to date, as well as provide a focus on the enhancement of membrane permeability. Furthermore, since the development and functions of drug delivery systems exert a high influence on the ability of drug permeation through membrane, these considerations will also be discussed in this review.

Reduced ABCB1 Expression and Activity in the Presence of Acrylic Copolymers

PURPOSE

P-glycoprotein (P-gp; ABCB1), an integral membrane protein in the apical surface of human intestinal epithelial cells, plays a crucial role in the intestinal transport and efflux leading to changes in the bioavailability of oral pharmaceutical compounds. This study was set to examine the potential effects of three Eudragits RL100, S100 and L100 on the intestinal epithelial membrane transport of rhodammine-123 (Rho-123), a substrate of P-gp using a monolayer of human colon cancer cell line (Caco-2).

METHODS

The least non-cytotoxic concentrations of the excipients were assessed in Caco-2 cells by the MTT assay. Then the transepithelial transport of Rho-123 across Caco-2 monolayers was determined with a fluorescence spectrophotometer. Besides, the expression of the P-gp in cells exposed to the polymers was demonstrated using Western-blotting analysis.

RESULTS

Treatment of cells with Eudragit RL100 and L100 led to a very slight change while Eudragit S100 showed 61% increase in Rho-123 accumulation (P<0.001) and also reduced transporter expression.

CONCLUSION

Our studies suggest that using proper concentrations of the Eudragit S100 in drug formulation would improve intestinal permeability and absorption of p-gp substrate drugs.

Reversal of multidrug resistance by the inhibition of ATP-binding cassette pumps employing "Generally Recognized As Safe" (GRAS) nanopharmaceuticals: A review

Pumps of the ATP-binding cassette superfamily (ABCs) regulate the access of drugs to the intracellular space. In this context, the overexpression of ABCs is a well-known mechanism of multidrug resistance (MDR) in cancer and infectious diseases (e.g., viral hepatitis and the human immunodeficiency virus) and is associated with therapeutic failure. Since their discovery, ABCs have emerged as attractive therapeutic targets and the search of compounds that inhibit their genetic expression and/or their functional activity has gained growing interest. Different generations of pharmacological ABC inhibitors have been explored over the last four decades to address resistance in cancer, though clinical results have been somehow disappointing. "Generally Recognized As Safe" (GRAS) is a U.S. Food and Drug Administration designation for substances that are accepted as safe for addition in food. Far from being "inert", some amphiphilic excipients used in the production of pharmaceutical products have been shown to inhibit the activity of ABCs in MDR tumors, emerging as a clinically translatable approach to overcome resistance. The present article initially overviews the classification, structure and function of the different ABCs, with emphasis on those pumps related to drug resistance. Then, the different attempts to capitalize on the activity of GRAS nanopharmaceuticals as ABC inhibitors are discussed.

Liposomes coated with thiolated chitosan enhance oral peptide delivery to rats

The aim of the present study was the in vivo evaluation of thiomer-coated liposomes for an oral application of peptides. For this purpose, salmon calcitonin was chosen as a model drug and encapsulated within liposomes. Subsequently, the drug loaded liposomes were coated with either chitosan-thioglycolic acid (CS-TGA) or an S-protected version of the same polymer (CS-TGA-MNA), leading to an increase in the particle size of about 500 nm and an increase in the zeta potential from approximately -40 mV to a maximum value of about +44 mV, depending on the polymer. Coated liposomes were demonstrated to effectively penetrate the intestinal mucus layer where they came in close contact with the underlying epithelium. To investigate the permeation enhancing properties of the coated liposomes ex vivo, we monitored the transport of fluoresceinisothiocyanate-labeled salmon calcitonin (FITC-sCT) through rat small intestine. Liposomes coated with CS-TGA-MNA showed the highest effect, leading to a 3.8-fold increase in the uptake of FITC-sCT versus the buffer control. In vivo evaluation of the different formulations was carried out by the oral application of 40 μg of sCT per rat, either encapsulated within uncoated liposomes, CS-TGA-coated liposomes or CS-TGA-MNA-coated liposomes, or given as a solution serving as negative control. The blood calcium level was monitored over a time period of 24h. The highest reduction in the blood calcium level, to a minimum of 65% of the initial value after 6h, was achieved for CS-TGA-MNA-coated liposomes. Comparing the areas above curves (AAC) of the blood calcium levels, CS-TGA-MNA-coated liposomes led to an 8.2-fold increase compared to the free sCT solution if applied orally in the same concentration. According to these results, liposomes coated with S-protected thiomers have demonstrated to be highly valuable carriers for enhancing the oral bioavailability of salmon calcitonin.