The effect of various liposome formulations on insulin penetration across Caco-2 cell monolayer

Recent Progress in the Oral Delivery of Therapeutic Peptides and Proteins: Overview of Pharmaceutical Strategies to Overcome Absorption Hurdles

Purpose

Proteins and peptides have secured a place as excellent therapeutic moieties on account of their high selectivity and efficacy. However due to oral absorption limitations, current formulations are mostly delivered parenterally. Oral delivery of peptides and proteins (PPs) can be considered the need of the hour due to the immense benefits of this route. This review aims to critically examine and summarize the innovations and mechanisms involved in oral delivery of peptide and protein drugs.

Methods

Comprehensive literature search was undertaken, spanning the early development to the current state of the art, using online search tools (PubMed, Google Scholar, ScienceDirect and Scopus).

Results

Research in oral delivery of proteins and peptides has a rich history and the development of biologics has encouraged additional research effort in recent decades. Enzyme hydrolysis and inadequate permeation into intestinal mucosa are the major causes that result in limited oral absorption of biologics. Pharmaceutical and technological strategies including use of absorption enhancers, enzyme inhibition, chemical modification (PEGylation, pro-drug approach, peptidomimetics, glycosylation), particulate delivery (polymeric nanoparticles, liposomes, micelles, microspheres), site-specific delivery in the gastrointestinal tract (GIT), membrane transporters, novel approaches (self-nanoemulsifying drug delivery systems, Eligen technology, Peptelligence, self-assembling bubble carrier approach, luminal unfolding microneedle injector, microneedles) and lymphatic targeting, are discussed. Limitations of these strategies and possible innovations for improving oral bioavailability of protein and peptide drugs are discussed.

Conclusion

This review underlines the application of oral route for peptide and protein delivery, which can direct the formulation scientist for better exploitation of this route.

New Insights on the Uptake and Trafficking of Coenzyme Q

Coenzyme Q (CoQ) is an essential lipid with many cellular functions, such as electron transport for cellular respiration, antioxidant protection, redox homeostasis, and ferroptosis suppression. Deficiencies in CoQ due to aging, genetic disease, or medication can be ameliorated by high-dose supplementation. As such, an understanding of the uptake and transport of CoQ may inform methods of clinical use and identify how to better treat deficiency. Here, we review what is known about the cellular uptake and intracellular distribution of CoQ from yeast, mammalian cell culture, and rodent models, as well as its absorption at the organism level. We discuss the use of these model organisms to probe the mechanisms of uptake and distribution. The literature indicates that CoQ uptake and distribution are multifaceted processes likely to have redundancies in its transport, utilizing the endomembrane system and newly identified proteins that function as lipid transporters. Impairment of the trafficking of either endogenous or exogenous CoQ exerts profound effects on metabolism and stress response. This review also highlights significant gaps in our knowledge of how CoQ is distributed within the cell and suggests future directions of research to better understand this process.

Oral insulin delivery: Barriers, strategies, and formulation approaches: A comprehensive review

Diabetes Mellitus is characterized by a hyperglycemic condition which can either be caused by the destruction of the beta cells or by the resistance developed against insulin in the cells. Insulin is a peptide hormone that regulates the metabolism of carbohydrates, proteins, and fats. Type 1 Diabetes Mellitus needs the use of Insulin for efficient management. However invasive methods of administration may lead to reduced adherence by the patients. Hence there is a need for a non-invasive method of administration. Oral Insulin has several merits over the conventional method including patient compliance, and reduced cost, and it also mimics endogenous insulin and hence reaches the liver by the portal vein at a higher concentration and thereby showing improved efficiency. However oral Insulin must pass through several barriers in the gastrointestinal tract. Some strategies that could be utilized to bypass these barriers include the use of permeation enhancers, absorption enhancers, use of suitable polymers, use of suitable carriers, and other agents. Several formulation types have been explored for the oral delivery of Insulin like hydrogels, capsules, tablets, and patches which have been described briefly by the article. A lot of attempts have been made for developing oral insulin delivery however none of them have been commercialized due to numerous shortcomings. Currently, there are several formulations from the companies that are still in the clinical phase, the success or failure of some is yet to be seen in the future.

Bile acid-based advanced drug delivery systems, bilosomes and micelles as novel carriers for therapeutics

Diabetes mellitus affects almost half a billion patients worldwide and results from either destruction of β-cells responsible for insulin secretion or increased tissue resistance to insulin stimulation and the reduction of glycemic control. Novel drug delivery systems can improve treatment efficacy in diabetic patients. The low aqueous solubility of most oral antidiabetic drugs decreases drug bioavailability; therefore, there is a demand for the use of novel methods to overcome this issue. The application of bile acids mixed micelles and bilosomes can provide an enhancement in drug efficacy. Bile acids are amphiphilic steroidal molecules that contain a saturated tetracyclic hydrocarbon cyclopentanoperhydrophenanthrene ring, and consist of three 6-membered rings and a 5-membered ring, a short aliphatic side chain, and a tough steroid nucleus. This review offers a comprehensive and informative data focusing on the great potential of bile acid, their salts, and their derivatives for the development of new antidiabetic drug delivery system.

The Caco-2 Model: Modifications and enhancements to improve efficiency and predictive performance

The Caco-2 cell model has been widely used to assess the permeability of drug candidates. It has provided a high throughput in vitro platform, functionally resembling the enterocytes. Since the oral route is the most preferred for drug administration, the Caco-2 cell model acts as a very important tool to elucidate the oral "druggability" of a molecule by providing a fairly reliable estimate of its permeability through the intestinal membrane. Despite its shortcomings (the lack of a mucus layer, long cultivation period, inter-lab variability, and differences in expression of enzymes, transporters, and tight junction complexes) it remains heavily used due to its reliability, predictive performance, and wide acceptance. Various modifications have been made: co-culturing with other intestinal cells, applying biosimilar mucus, reducing culturing time, combining Caco-2 monolayer with the dissolution apparatus, enhancing protein expression, and redesigning the sampling apparatus. These modifications are intended to overcome some of the shortcomings of the Caco-2 model in order to make its use easier, quicker, economical, and more representative of the intestine. The aim of this review is to discuss such modifications to enhance this model's utility, predictive performance, and reproducibility.

Oral delivery of therapeutic peptides and proteins: Technology landscape of lipid-based nanocarriers

The oral administration of therapeutic peptides and proteins is favoured from a patient and commercial point of view. In order to reach the systemic circulation after oral administration, these drugs have to overcome numerous barriers including the enzymatic, sulfhydryl, mucus and epithelial barrier. The development of oral formulations for therapeutic peptides and proteins is therefore necessary. Among the most promising formulation approaches are lipid-based nanocarriers such as oil-in-water nanoemulsions, self-emulsifying drug delivery systems (SEDDS), solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), liposomes and micelles. As the lipophilic character of therapeutic peptides and proteins can be tremendously increased such as by the formation of hydrophobic ion pairs (HIP) with hydrophobic counter ions, they can be incorporated in the lipophilic phase of these carriers. Since gastrointestinal (GI) peptidases as well as sulfhydryl compounds such as glutathione and dietary proteins are too hydrophilic to enter the lipophilic phase of these carriers, the incorporated therapeutic peptide or protein is protected towards enzymatic degradation as well as unintended thiol/disulfide exchange reactions. Stability of lipid-based nanocarriers towards lipases can be provided by the use to excipients that are not or just poorly degraded by these enzymes. Nanocarriers with a size <200 nm and a mucoinert surface such as PEG or zwitterionic surfaces exhibit high mucus permeating properties. Having reached the underlying absorption membrane, lipid-based nanocarriers enable paracellular and lymphatic drug uptake, induce endocytosis and transcytosis or simply fuse with the cell membrane releasing their payload into the systemic circulation. Numerous in vivo studies provide evidence for the potential of these delivery systems. Within this review we provide an overview about the different barriers for oral peptide and protein delivery, highlight the progress made on lipid-based nanocarriers in order to overcome them and discuss strengths and weaknesses of these delivery systems in comparison to other technologies.

Evaluation of Cytotoxicity of Self-Emulsifying Formulations Containing Long-Chain Lipids Using Caco-2 Cell Model: Superior Safety Profile Compared to Medium-Chain Lipids

Medium-chain (MC) and long-chain (LC) lipids are used for development of self-emulsifying drug delivery systems (SEDDS). MC lipids are often preferred because of their ability to form stable microemulsions with relatively high drug solubilization capacity. On the other hand, LC lipids could be more biocompatible as most endogenous and dietary lipids are LC glycerides. They also maintain high drug solubilization capacity after digestion. The present study was undertaken to determine the cytotoxicity of LC lipids and their formulations on Caco-2 cells of 1-day, 5-day, and 21-day maturity. The results were compared with the cytotoxicity profiles of MC lipids reported previously from our laboratory. The cell viability and cell membrane integrity were, respectively, determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and the lactate dehydrogenase assay. The cytotoxicity was partially due to lipid surfactant-induced membrane rupture, and it was influenced by cell maturity and formulation composition. The lipid-surfactant combinations showed greater tolerance than surfactants alone, and LC-SEDDS were well-tolerated at almost 10-fold higher concentration than corresponding MC-SEDDS. Furthermore, the cytotoxicity of digestion end products of both LC and MC triglycerides in the presence of 3 mM sodium taurocholate was compared on 21-day Caco-2 cultures by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The LC lipid formulations showed better tolerance than MC lipid formulations after digestion. Thus, although MC and LC lipids are well-tolerated at doses normally administered to humans, LC lipids show much better safety than MC lipids in a cell-culture model.

Catanionic nanocarriers as a potential vehicle for insulin delivery

Diabetes is a disease that affects millions of people in the World, constituting a global problem. Patients are administered insulin subcutaneous injections, resulting in high costs and frequent infections in the injection site. A possible solution to this problem may be the use of nanotechnology. Nanotransporters can act as specific release systems able to overcome the current limitations to drug delivery. Liposomes and vesicles can deliver drugs directly and efficiently to the site of action, decreasing toxicity and adverse effects. In previous studies, we demonstrated the biocompatibility and safety of catanionic benzyl n-hexadecyldimethylammonium 1,4 -bis-2-ethylhexylsulfosuccinate (BHD-AOT) vesicles using both in vitro and in vivo tests. Thus, the aims of this work were to evaluate the ability of the BHD-AOT vesicles to encapsulate insulin; to analyze the structural properties and stability of the system, vesicle-Insulin (VIn), at different pH conditions; and to study the ability of VIn to decrease the glycemia in miceby different administration routes. Our results showed that 2 and 5 mg mL^-1 of vesicles were able to encapsulate about 55 % and 73 % of insulin, respectively. The system VIn showed a significant increase in size from 120 to 350 nm, changes in the surface zeta potential value, and high stability to different pH conditions. A significant decrease of the glycemia after VIn administration was demonstrated in in vivo assays, including the oral route. Our results reveal that BHD-AOT vesicles may be an appropriate system to encapsulate and protect insulin, and may be a potential system to be administrated in different ways as an alternative strategy to conventional therapy.

In Vitro and In Vivo Profiles and Characterization of Insulin Nanocarriers Based in Flexible Liposomes Designed for Oral Administration

Background:

Alternatives routes of delivery for Insulin have been evaluated to improve treatment for Diabetes Mellitus. The oral route is the most convenient physiologically; it releases in a similar way to endogenous secretion. Flexible liposomes have deformable abilities to pass through membranes with adequate therapeutic effects, but they have been tested only dermally.

Objective:

Our aim was to develop an oral nanocarrier based on flexible liposomes for insulin with polymer addition to reduce gastrointestinal degradation.

Methods:

Different percentages of polyethylene glycol were added to a conventional formulation of flexible liposomes. The manufacturing procedure was the heating method. Z potential, size particle, polydispersity index and encapsulation percentage were evaluated. A release profile was performed in the stomach and intestinal pH mediums by two-stage reverse dialysis method. The in-vivo test was performed in experimental diabetic rats by oral, transdermal and subcutaneous routes.

Results:

All the formulations showed polydispersity but adequate Z potential. The 10% PEG formulation obtained the best insulin enclosure with 81.9%. The insulin integrity after preparation was confirmed by polyacrylamide gel electrophoresis. PEG and non-PEG formulations showed similar behavior in acid release profile but the release and stability of lipid structures were better and longer in intestinal pH conditions. In vivo tests showed a reduction to normal glucose levels only in subcutaneous route.

Conclusion:

The polymer inclusion in flexible liposomes generates an adequate nanocarrier for proteins in terms of stability and composition; although its in-vivo use reduces glucose levels in subcutaneous route, the effect was not adequate in oral route.

Adapting liposomes for oral drug delivery

Liposomes mimic natural cell membranes and have long been investigated as drug carriers due to excellent entrapment capacity, biocompatibility and safety. Despite the success of parenteral liposomes, oral delivery of liposomes is impeded by various barriers such as instability in the gastrointestinal tract, difficulties in crossing biomembranes, and mass production problems. By modulating the compositions of the lipid bilayers and adding polymers or ligands, both the stability and permeability of liposomes can be greatly improved for oral drug delivery. This review provides an overview of the challenges and current approaches toward the oral delivery of liposomes.

Novel strategies in the oral delivery of antidiabetic peptide drugs - Insulin, GLP 1 and its analogs

As diabetes is a complex disorder being a major cause of mortality and morbidity in epidemic rates, continuous research has been done on new drug types and administration routes. Up to now, a large number of therapeutic peptides have been produced to treat diabetes including insulin, glucagon-like peptide-1 (GLP-1) and its analogs. The most common route of administration of these antidiabetic peptides is parenteral. Due to several drawbacks associated with this invasive route, delivery of these antidiabetic peptides by the oral route has been a goal of pharmaceutical technology for many decades. Dosage form development should focus on overcoming the limitations facing oral peptides delivery as degradation by proteolytic enzymes and poor absorption in the gastrointestinal tract (GIT). This review focuses on currently developed strategies to improve oral bioavailability of these peptide based drugs; evaluating their advantages and limitations in addition to discussing future perspectives on oral peptides delivery. Depending on the previous reports and papers, the area of nanocarriers systems including polymeric nanoparticles, solid lipid nanoparticles, liposomes and micelles seem to be the most promising strategy that could be applied for successful oral peptides delivery; but still further potential attempts are required to be able to achieve the FDA approved oral antidiabetic peptide delivery system.

In-vitro evaluation of enteric coated insulin tablets containing absorption enhancer and enzyme inhibitor

Objectives

The aim of this study was to develop an enteric coated insulin tablet formulation using polymers, absorption enhancer and enzyme inhibitor, which protect the tablets in acidic pH and enhance systemic bioavailability.

Methods

In this study, the influence of coating by cellulose acetate hydrogen phthalate solution and chosen excipients on Glut-4 transporter translocation in C2C12 skeletal muscle cells was examined. Following the determination of optimum number of coating layers, two dissolution buffers such as 0.01 m hydrochloric acid, pH 2, and 50 mm phosphate, pH 7.4, were employed to determine the in-vitro release of insulin.

Key findings

Insulin was protected by the coating during the dissolution process. Five (5-CL) coating layers and eight (8-CL) coating layers had minimal insulin release in hydrochloric acid, but not three (3-CL) coating layers. Glut-4 translocation in C2C12 cells was promoted by the chosen excipients. No detrimental metabolic effects were observed in these cells.

Conclusion

To date, limited studies combine the overall effectiveness of multiple excipients. Our study showed that the coated tablets have an immediate release effect in phosphate buffer. In Glut-4 translocation assay, insulin was still functional after releasing from the tablet. Such tablet formulation can be potentially beneficial to type 1 diabetes patients.

A review on the strategies for oral delivery of proteins and peptides and their clinical perspectives

In the modern world, a number of therapeutic proteins such as vaccines, antigens, and hormones are being developed utilizing different sophisticated biotechnological techniques like recombinant DNA technology and protein purification. However, the major glitches in the optimal utilization of therapeutic proteins and peptides by the oral route are their extensive hepatic first-pass metabolism, degradation in the gastrointestinal tract (presence of enzymes and pH-dependent factors), large molecular size and poor permeation. These problems can be overcome by adopting techniques such as chemical transformation of protein structures, enzyme inhibitors, mucoadhesive polymers and permeation enhancers. Being invasive, parenteral route is inconvenient for the administration of protein and peptides, several research endeavors have been undertaken to formulate a better delivery system for proteins and peptides with major emphasis on non-invasive routes such as oral, transdermal, vaginal, rectal, pulmonary and intrauterine. This review article emphasizes on the recent advancements made in the delivery of protein and peptides by a non-invasive (peroral) route into the body.

Lipid-based nanovesicles for nanomedicine

Multifunctional lipid-based nanovesicles (L-NVs) prepared by molecular self-assembly of membrane components together with (bio)-active molecules, by means of compressed CO₂-media or other non-conventional methods lead to highly homogeneous, tailor-made nanovesicles that are used for advanced nanomedicine. Confocal microscopy image of siRNA transfection using L-NVs, reprinted with permission from de Jonge,et al.,Gene Therapy, 2006,13, 400–411.

A review of biodegradable polymeric systems for oral insulin delivery

Currently, repeated routine subcutaneous injections of insulin are the standard treatment for insulin-dependent diabetic patients. However, patients' poor compliance for injections often fails to achieve the stable concentration of blood glucose. As a protein drug, the oral bioavailability of insulin is low due to many physiological reasons. Several carriers, such as macromolecules and liposomes have been used to deliver drugs in vivo. In this review article, the gastrointestinal barriers of oral insulin administration are described. Strategies for increasing the bioavailability of oral insulin, such absorption enhancers, enzyme inhibitors, enteric coatings are also introduced. The potential absorption mechanisms of insulin-loaded nanoparticles across the intestinal epithelium, including intestinal lymphatic route, transcellular route and paracellular route are discussed in this review. Natural polymers, such as chitosan and its derivates, alginate derivatives, γ-PGA-based materials and starch-based nanoparticles have been exploited for oral insulin delivery; synthetic polymers, such as PLGA, PLA, PCL and PEA have also been developed for oral administration of insulin. This review focuses on recent advances in using biodegradable natural and synthetic polymers for oral insulin delivery along with their future prospects.

Noninvasive insulin delivery: the great potential of cell-penetrating peptides

Insulin, a potent therapeutic peptide used in the treatment of diabetes, is administered to patients via subcutaneous injections because of the poor pharmacokinetics associated with alternative routes of administration such as oral, nasal and pulmonary delivery. Noninvasive nasal and oral formulations are appealing to patients who need consecutive daily treatments of insulin. However, to achieve mucosal absorption of insulin via oral or nasal administration, two barriers must be overcome: the impermeability of insulin through the epithelial membranes and local digestion and enzymatic degradation. Cell-penetrating peptides (CPPs), which efficiently bring exogenous proteins and nucleic acids into cells, have great potential to facilitate insulin permeation from the intestinal lumen or nasal cavity into systemic circulation via efficient uptake by epithelial cells. In fact, the coadministration of insulin with the peptide penetratin, a typical CPP, increased intestinal and nasal insulin bioavailability to 35 and 50%, respectively. In this review, the authors describe recent findings using this novel CPP-based formulation for noninvasive delivery of insulin.

Liposomal delivery of proteins and peptides

INTRODUCTION

A number of delivery issues exist for biotech molecules including peptides, proteins and gene-based medicines that now make up over 60% of the drug pipeline. The problems comprise pharmaceutical ad biopharmaceutical issues. One of the common approaches to overcome these issues is the use of a carrier and liposomes as carriers have been investigated extensively over the last decade.

AREAS COVERED

The review has been discussed in terms of formulation and preclinical development studies and in vivo studies encompassing different delivery routes including parenteral, oral, buccal, pulmonary, intranasal, ocular and transdermal involving liposomes as carriers. Important research findings have been tabulated under each side heading and an expert opinion has been summarised for each delivery route.

EXPERT OPINION

The conclusion and expert opinion - conclusion sections discuss in detail troubleshooting aspects related to the use of liposomes as carriers for delivery of biopharmaceutical moieties and scrutinises the aspects behind the absence of a protein/peptide-containing liposome in market.

Strategies for non-invasive delivery of biologics

Macromolecular therapeutics, in particular, many biologics, is the most advancing category of drugs over conventional chemical drugs. The potency and specificity of the biologics for curing certain disease made them to be a leading compound in the pharmaceutical industry. However, due to their intrinsic nature, including high molecular weight, hydrophilicity and instability, they are difficult to be administered via non-invasive route. This is a major quest especially in biologics, as they are frequently used clinically for chronic disorders, which requires long-term administration. Therefore, many efforts have been made to develop formulation for non-invasive administration, in attempt to improve patient compliance and convenience. In this review, strategies for non-invasive delivery, in particular, oral, pulmonary and nasal delivery, that are recently adopted for delivery of biologics are discussed. Insulin, calcitonin and heparin were mainly focused for the discussion as they could represent protein, polypeptide and polysaccharide drugs, respectively. Many recent attempts for non-invasive delivery of biologics are compared to provide an insight of developing successful delivery system.

Liposomes containing glycocholate as potential oral insulin delivery systems: preparation, in vitro characterization, and improved protection against enzymatic degradation

Background:

Oral delivery of insulin is challenging and must overcome the barriers of gastric and enzymatic degradation as well as low permeation across the intestinal epithelium. The present study aimed to develop a liposomal delivery system containing glycocholate as an enzyme inhibitor and permeation enhancer for oral insulin delivery.

Methods:

Liposomes containing sodium glycocholate were prepared by a reversed-phase evaporation method followed by homogenization. The particle size and entrapment efficiency of recombinant human insulin (rhINS)-loaded sodium glycocholate liposomes can be easily adjusted by tuning the homogenization parameters, phospholipid:sodium glycocholate ratio, insulin:phospholipid ratio, water:ether volume ratio, interior water phase pH, and the hydration buffer pH.

Results:

The optimal formulation showed an insulin entrapment efficiency of 30% ± 2% and a particle size of 154 ± 18 nm. A conformational study by circular dichroism spectroscopy and a bioactivity study confirmed the preserved integrity of rhINS against preparative stress. Transmission electron micrographs revealed a nearly spherical and deformed structure with discernable lamella for sodium glycocholate liposomes. Sodium glycocholate liposomes showed better protection of insulin against enzymatic degradation by pepsin, trypsin, and α-chymotrypsin than liposomes containing the bile salt counterparts of sodium taurocholate and sodium deoxycholate.

Conclusion:

Sodium glycocholate liposomes showed promising in vitro characteristics and have the potential to be able to deliver insulin orally.

New perspective for the treatment of Alzheimer diseases: liposomal rivastigmine formulations

The aim of this study was to determine the transportations of rivastigmine containing from various liposome formulations through Madin Darby Canine Kidney (MDCK) cells monolayer and to compare the in vitro test results with in vivo. There is no other liposome formulation of rivastigmine and the transportations of rivastigmine through MDCK cell monolayers or related study available in the literature. Cytotoxicity (MTT) test was used to determine cell viabilities. The effect of sodium-taurocholate or dimethyl-beta-cyclodextrine as penetration enhancer was also investigated. Characterization and stability studies for liposome formulations were performed. Permeation experiments of rivastigmine were performed through MDCK cells and dialysis membrane. The kinetic of release from liposomes was also investigated. The highest apparent permeability coefficient (log. values) was obtained with sodium-taurocholate liposomes for -1.15 ± 0.16 for MDCK cell. Rivastigmine liposomes and solutions were also administered to mice orally and intraperitonally. Acetylcholinesterase (AChE) activity was determined by Ellman method. AChE% inhibition values were calculated for both blood and brain after administration of rivastigmine solution and liposomes. The highest AChE inhibition was observed for rivastigmine-sodium-taurocholate liposomes. Histological observations of the mice' brains were performed under transmission electron microscope (TEM). The histological results were also indicated and supported all these findings.

Effects of oridonin nanosuspension on cell proliferation and apoptosis of human prostatic carcinoma PC-3 cell line

This study aims to investigate the inhibitory effects of oridonin nanosuspension on human prostatic carcinoma PC-3 cell line in vitro. The PC-3 cells were incubated with increasing concentrations of oridonin solution and nanosuspensions for 12 hours, 24 hours, and 36 hours. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay was performed to measure cellular viability and investigate the effect of oridonin on cell growth of PC-3. Annexin V-FITC/PI staining method was used to determine the effect of oridonin by fluorescence microscope and flow cytometry, respectively. Nanosuspension on early apoptosis of PC-3 cells was also evaluated. Oridonin significantly inhibited the growth of PC-3 cells after 12 hours, 24 hours, and 36 hours of treatment in a dose-dependent manner (P < 0.05). Compared with the same concentration of oridonin solution, oridonin nanosuspension enhanced the inhibition ratio of proliferation. The observation of propidium iodide fluorescence staining confirmed the MTT assay results. The cell proportion of PC-3 at the G2/M phase in the nanosuspension treatment group was upregulated compared with that of the control and oridonin solution groups. Both oridonin solution and nanosuspension promoted the early apoptosis of PC-3 cells. Furthermore, while improving the ratio of early apoptosis, oridonin nanosuspensions also enhanced growth suppression, and induced apoptosis of PC-3 cells. This shows great potential in the treatment of androgen-independent carcinoma of prostate by oridonin nanosuspensions.

In vitro and in vivo evaluation of silybin nanosuspensions for oral and intravenous delivery

In this study, we evaluate the effect of particle sizes on the physicochemical properties of silybin and identify the influence of silybin nanosuspensions on its permeation across the Caco-2 cell monolayer. In vivo pharmacokinetic evaluation of silybin nanosuspensions was also carried out in beagle dogs. TEM, AFM and SEM analyses revealed the effect of homogenization pressure on particle size and morphology, and confirmed the existence of a surfactant-stabilizer film on the surface of nanoparticles. DSC and XRPD experiments manifested that the crystalline state was maintained as particle size was reduced and the enhanced dissolution property was due to the increased surface area. Nanosuspensions had a significant influence on drug transport across the Caco-2 cell monolayer and the enhanced dissolution velocity was responsible for the increased permeability. A pharmacokinetics study in beagle dogs further confirmed the in vitro results and demonstrated that oral administration of silybin nanosuspensions significantly increase its bioavailability compared to the coarse powder. Nanosuspensions of silybin with smaller particle size reveal a higher potential to increase their oral bioavailability; while for intravenous infusion the lower pressure produced silybin nanosuspensions appeared to maintain a more sustained drug release profile.

Importance of intermolecular interaction on the improvement of intestinal therapeutic peptide/protein absorption using cell-penetrating peptides

Our previous reports showed that the absorption of therapeutic peptides and proteins was significantly improved by coadministration of cell-penetrating peptides (CPPs) as the physical mixture. However, the mechanisms for this improvement are not clear. In the present study, we verified the hypothesis that the electrostatic interaction between drug and CPP is related to the enhancing effect of the CPP on the intestinal absorption of therapeutic peptides and proteins. In this study, the intermolecular binding was analyzed by surface plasmon resonance (SPR)-based binding assay, and the effect of CPPs on the intestinal absorption of peptide drugs was examined by in situ absorption study using a rat intestinal loop. Among the 16 peptide drugs possessing different isoelectric points, it was observed that only gastrin, insulin and glucagon-like peptide-1 (GLP-1) bound to D-R8 (D-form arginine octamer, a typical CPP), and subsequently their intestinal absorption increased by coadministration of D-R8. In contrast, the intestinal absorption of other peptide drugs that did not bind to D-R8 was not affected in the presence of D-R8. Thus, this study suggests that intermolecular binding between drug and CPP is an important factor governing the enhancing effect of the CPP on the intestinal absorption of therapeutic peptides and proteins.

The influence of sodium hyaluronate, L-leucine and sodium taurocholate on the nebulization of aqueous betamethasone-17-valerate suspensions

The purpose of this research was to evaluate the variables that are suggested to influence the adsorption of the hydrophilic hyaluronic acid (HA) onto the surface of the hydrophobic betamethasone-17-valerate (BV) particles in order to formulate a nebulizable suspension. The adsorption of HA from aqueous solutions (0.04% to 0.16%, w/v) to a fixed BV concentration (0.04%, w/v) under different experimental conditions, was investigated. The method of preparation of HA-BV suspensions involved suspending BV particles either in the hydrated HA solution (method 1) or in water followed by addition of solid HA (method 2). Other variables like the time required for the adsorption to complete and temperature at which adsorption is carried out were studied. The nebulization of the suspensions was tested via an air jet nebulizer connected to a twin stage impinger. In order to improve the nebulization behavior of the optimized suspension, L-leucine or sodium taurocholate was incorporated in increasing concentrations (0.01-0.04%, w/v). The optimized suspension, having a nebulization efficiency of 33.75%, was achieved following the adsorption of HA (0.1%, w/v) onto BV particles adopting method 2 of preparation and extending for three days at 4 degrees C. Incorporation of either l-leucine or sodium taurocholate significantly decreased the aggregate size of the optimized suspension and consequently caused significant increases in the nebulization efficiency to reach 46.87% and 56.25%, respectively.

In vitro stability and permeability studies of liposomal delivery systems for a novel lipophilic endomorphin 1 analogue

We have previously shown that the stability and permeability of peptides can be greatly improved by conjugation with lipoamino acids such as 2-aminododecanoic acid (C12Laa). However, the increase in lipophilicity which this conjugation provides can also cause a significant decrease in the compound's water solubility. In this study, we coupled C12Laa to the N-terminus of endomorphin1 (Endo-1, Tyr-Pro-Trp-Phe-NH(2)), and addressed its solubility issue by formulating C12Laa-Endo-1 into phosphatidylcholine liposomes. The aqueous solubility of the lipidic analogue was greatly improved, facilitating the accurate analysis of the compound in in vitro assays. The metabolic stability and in vitro endothelial permeability of the C12Laa-Endo-1 liposomal formulation was assessed using Caco-2 cells, and compared with the formulation of the parent peptide Endo-1. The liposome-encapsulated C12Laa-Endo exhibited significant increases in both stability and permeability. These results suggest that the combination of chemical modification and liposome formulation has great potentials in improving the bioavailability of neuroactive peptides.

Current challenges in non-invasive insulin delivery systems: a comparative review

The quest to eliminate the needle from insulin delivery and to replace it with non- or less-invasive alternative routes has driven rigorous pharmaceutical research to replace the injectable forms of insulin. Recently, various approaches have been studied involving many strategies using various technologies that have shown success in delivering insulin, which are designed to overcome the inherent barriers for insulin uptake across the gastrointestinal tract, mucosal membranes and skin. This review examines some of the many attempts made to develop alternative, more convenient routes for insulin delivery to avoid existing long-term dependence on multiple subcutaneous injections and to improve the pharmacodynamic properties of insulin. In addition, this article concentrates on the successes in this new millennium in developing potential non-invasive technologies and devices, and on major new milestones in modern insulin delivery for the effective treatment of diabetes.

A novel approach using functional peptides for efficient intestinal absorption of insulin

The aim of this study was to evaluate whether oligoarginine, a cell-penetrating peptide (CPP), can improve intestinal absorption of insulin in rats. Peptides composed of six (R(6)), eight (R(8)) and 10 (R(10)) residues of arginine were used as the CPP. No insulin absorption was observed following administration of insulin solution alone; however, insulin absorption increased dramatically after coadministration of the D-form of R(6) (D-R(6)) and the L-form of R(6) (L-R(6)) in a dose-dependent manner. The effects on insulin absorption were more pronounced for D-R(6) than for L-R(6). Among oligoarginines composed of six, eight, or 10 arginine residues, D-R(8) showed the strongest enhancing effects on insulin intestinal absorption. In contrast, intestinal absorption of other model hydrophilic macromolecules, interferon-beta and fluorescein isothiocyanate-labeled dextran 4400, was not affected by coadministration with oligoarginine. Pretreatment by the effective dose of L-R(6) did not induce lactate dehydrogenase leakage or histological damage, suggesting that oligoarginine has no untoward effect on the intestinal mucosa. Our data demonstrate that coadministration of oligoarginine increases intestinal insulin absorption markedly without causing detectable damage in cellular integrity and that the covalent binding between insulin and oligoarginine is not necessary for this effect. We conclude that oligoarginines are likely to become powerful tools for overcoming the low permeability of insulin through the epithelial cell membrane, the major barrier to oral insulin delivery.

Chemical modification and formulation approaches to elevated drug transport across cell membranes

Drug delivery across cellular barriers, such as intestinal, nasal, buccal, alveolar, vaginal, ocular and blood-brain, is a challenging task. Multiple physiological mechanisms, such as cellular organisation, efflux, and chemical and enzymatic degradation, as well as physicochemical properties of the drug molecule itself, determine the penetration of xenobiotics across epithelial cell layers. Limited intestinal absorption of many novel and highly potent lead compounds has stimulated an intense search for strategies that can effectively enhance permeation across these biological barriers. This review discusses some of the approaches that have been, and are currently being, investigated for transepithelial drug delivery. Transdermal drug delivery requires a separate discussion on its own and is thus outside the scope of this review article.

Nanotechnology: intelligent design to treat complex disease

The purpose of this expert review is to discuss the impact of nanotechnology in the treatment of the major health threats including cancer, infections, metabolic diseases, autoimmune diseases, and inflammations. Indeed, during the past 30 years, the explosive growth of nanotechnology has burst into challenging innovations in pharmacology, the main input being the ability to perform temporal and spatial site-specific delivery. This has led to some marketed compounds through the last decade. Although the introduction of nanotechnology obviously permitted to step over numerous milestones toward the development of the "magic bullet" proposed a century ago by the immunologist Paul Ehrlich, there are, however, unresolved delivery problems to be still addressed. These scientific and technological locks are discussed along this review together with an analysis of the current situation concerning the industrial development.

Lipid vesicles in capillary electrophoretic techniques: characterization of structural properties and associated membrane-molecule interactions

This paper reviews the use of lipid vesicles as model membranes in capillary electrophoresis (CE). The history and utility of CE in the characterization of microparticles is summarized, focusing on the application of colloidal electromigration theories to lipid vesicles. For instance, CE experiments have been used to characterize the size, surface properties, enclosed volumes, and electrophoretic mobilities of lipid vesicles and of lipoprotein particles. Several techniques involving small molecules or macromolecules separated in the presence of lipid vesicles are discussed. Interactions between the analytes and the lipid vesicles - acting as a pseudostationary phase or coated stationary phase in electrokinetic chromatography (EKC) - can be used to obtain additional information on the characteristics of the vesicles and analytes, and to study the biophysical properties of membrane-molecule interactions in lipid vesicles and lipoproteins. Different methods of determining binding constants by EKC are reviewed, along with the relevant binding constant calculations and a discussion of the application and limitations of these techniques as they apply to lipid vesicle systems.