Oral Insulin Delivery System Research Articles

Potential of single cationic amino acid molecule “Arginine” for stimulating oral absorption of insulin

We have reported that cell-penetrating peptides, such as oligoarginine, act as powerful absorption enhancers for the development of oral insulin delivery systems. However, the minimal essential sequence of oligoarginine that stimulates intestinal insulin absorption remains unclear. Therefore, the present study was conducted to clarify this minimum sequence of oligoarginine and to examine the effect of single cationic amino acid arginine on the intestinal and oral absorption of insulin. The results demonstrated that a remarkable enhancement of intestinal insulin absorption was observed after coadministration of insulin with l-arginine. The efficacy of d-forms of oligoarginine/arginine tended to decrease with a decreasing number of amino acid residues, whereas the effect of l-arginine was the strongest of any of the l-forms of oligoarginine/arginine. Interestingly, the effect of l-arginine was stronger than that of d-arginine at various concentrations, and the effect of other cationic amino acids such as lysine and histidine was relatively lower than that of arginine. In addition, no leakage of lactate dehydrogenase from the intestinal epithelium and no change in the transepithelial electrical resistance of a Caco-2 cell monolayer were detected after administration of l-arginine as the single amino acid, which suggests that there were no undesirable effects of arginine on the integrity of cell membranes and paracellular tight junctions. Oral administration study in mice demonstrated that the stronger hypoglycemic effects were observed after coadministration of insulin with l-arginine. In this study, we found that arginine is a key cationic amino acid for delivering insulin across intestinal epithelial barriers and hopefully accelerating the clinical development of oral insulin delivery systems.

Polypeptide-based polyelectrolyte complexes overcoming the biological barriers of oral insulin delivery

Abstract In this study, a novel oral insulin delivery system was prepared by combining two different artificial polypeptides with insulin. Negatively charged poly( l -glutamate- co - N -3- l -glutamylsulfanilic acid) (PLGS), cationic alpha helical peptide poly- l -lysine (PLL), and insulin formed polyelectrolyte complexes (PCs) were characterized. The property of the PCs was examined by an in vitro study. A significantly higher amount of the loaded FITC insulin was released in the intestinal condition, suggesting the controlled release of the PCs to protect insulin in the acidic stomach condition while releasing it in the small intestine. The in vitro cellular uptake study with Caco-2 cells also revealed the improved penetration of the loaded FITC labeled insulin. By virtue of the cell penetration enhancing ability of PLL, the permeation of insulin in the small intestine was notably augmented. Furthermore, the feasibility of the PCs was confirmed through an in vivo hypoglycemic effect study. The PCs showed an improved hypoglycemic effect suggesting the success of the delivery and penetration of the loaded insulin. The blood glucose level was lowered to 80% of its initial value after the oral administration of the PCs, and the hypoglycemia lasted for more than 14 h. The long lasting hypoglycemic effect of the PCs can reduce the number of administrations, and it will contribute to improving the quality of patients’ lives. The PCs provided reasonable results as a competitive candidate for oral insulin delivery. The introduction of the PCs will promote the oral delivery of charged proteins or drugs.

Preparation and evaluation of insulin-loaded nanoparticles based on hydroxypropyl-β-cyclodextrin modified carboxymethyl chitosan for oral delivery

Novel insulin-loaded nanoparticles based on hydroxypropyl-β-cyclodextrin modified carboxymethyl chitosan (CMC-HP-β-CD) were prepared to improve the oral bioavailability of insulin. The CMC-HP-β-CD was characterized by FT-IR spectroscopy and 1H-NMR spectra. The insulin-loaded nanoparticles were prepared through crosslinking with calcium ions, and the morphology and size of the prepared nanoparticles were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Cumulative release in vitro study was performed respectively in simulated gastric medium fluid (SGF, pH=1.2), simulated intestinal fluid (SIF, pH=6.8) and simulated colonic fluid (SCF, pH=7.4). The encapsulation efficiency of insulin was up to 87.14 ± 4.32% through high-performance liquid chromatography (HPLC). Statistics indicated that only 15% of the encapsulated insulin was released from the CMC-HP-β-CD nanoparticles in 36 h in SGF, and about 50% of the insulin could be released from the nanoparticles in SIF, whereas more than 80% was released in SCF. In addition, the solution containing insulin nanoparticles could effectively reduce the blood glucose level of diabetic mice. The cytotoxicity test showed that the samples had no cytotoxicity. CMC-HP-β-CD nanoparticles are promising candidates as potential carriers in oral insulin delivery systems.

Chitosan/lecithin liposomal nanovesicles as an oral insulin delivery system

In the present work, insulin–chitosan polyelectrolyte complexes associated to lecithin liposomes were investigated as a new carrier for oral delivery of insulin. The preparation was characterized in terms of particle size, zeta potential and encapsulation efficiency. Surface tension measurements revealed that insulin–chitosan polyelectrolyte complexes have some degree of hydrophobicity and should be added to lecithin liposomal dispersion and not the vice versa to prevent their adsorption on the surface. Stability of insulin was enhanced when it was associated to liposomes. Significant reduction of blood glucose levels was noticed after oral administration of liposomal preparation to streptozotocin diabetic rats compared to control. The hypoglycemic activity was more prolonged compared to subcutaneously administered insulin.

Enhancing insulin oral absorption by using mucoadhesive nanoparticles loaded with LMWP-linked insulin conjugates

Although significant progress has been achieved, effective oral delivery of protein drugs such as insulin by nanoparticle-based carrier systems still faces certain formidable challenges. Considerable amount of protein drug is released from the nanoparticles (NPs) in the gastrointestinal (GI) tract. Because of their low permeability through the intestinal mucosa, the released protein would be soon degraded by the large amount of proteases in the GI tract. Herein, we report an oral insulin delivery system that can overcome the above-mentioned problems by mucoadhesive NPs (MNPs) loaded with cell penetrating peptide-linked insulin conjugates. On one hand, after conjugation with low molecular weight protamine (LMWP), a cell penetrating peptide (CPP), insulin showed greatly improved permeability through intestinal mucus layer and epithelia. On the other hand, the mucoadhesive N-trimethyl chitosan chloride-coated PLGA nanoparticles (MNPs) that were loaded with conjugates enhanced the retention in the intestinal mucus layer. By adopting this delivery strategy, the LMWP-insulin conjugates released from the MNPs could be deprived from enzymatic degradation, due to the short distance in reaching the epithelia and the high permeation of the conjugates through epithelia. The oral delivery system of insulin designed by us showed a long-lasting hypoglycemia effect with a faster onset in diabetic rats. The pharmacological availability of orally delivered conjugates-loaded MNPs was 17.98±5.61% relative to subcutaneously injected insulin solution, with a 2-fold higher improvement over that by MNPs loaded with native insulin. Our results suggested that conjugation with CPP followed by encapsulation in MNPs provides an effective strategy for oral delivery of macromolecular therapeutics.

Salicylic acid-based pH-sensitive hydrogels as potential oral insulin delivery systems

Salicylic acid (SA)-based physically crosslinked pH-sensitive hydrogels were developed for oral insulin delivery using various ratios of salicylate-based poly(anhydride-ester) and poly(acrylic acid) (PAA). Pore size, swelling behavior, insulin loading, insulin and SA release rates of the gels were varied by changing PAA concentration. About 50% of insulin was incorporated within all of the hydrogels, with about 4–8% of insulin released in acidic conditions (pH 1.2) over 2 h. In pH simulating the intestine (pH 6.8), 90% of the insulin and 70% of SA were released within 24 h from the hydrogel system. These results suggest that hydrogels enable pH-dependent protein delivery and can be used for oral insulin and SA delivery to benefit diabetes patients.

Region-Dependent Role of Cell-Penetrating Peptides in Insulin Absorption Across the Rat Small Intestinal Membrane.

We have reported that the cell-penetrating peptide (CPP) penetratin acts as a potential absorption enhancer in oral insulin delivery systems and that this action occurs through noncovalent intermolecular interactions. However, the region-dependent role of CPPs in intestinal insulin absorption has not been clarified. To identify the intestinal region where CPPs have the most effect in increasing insulin absorption, the region-dependent action of penetratin was investigated using in situ closed intestinal loops in rats. The order of the insulin area under the insulin concentration-time curve (AUC) increase effect by L-penetratin was ileum > jejunum > duodenum > colon. By contrast, the AUC order after coadministration of insulin with D-penetratin was colon > duodenum ≥ jejunum and ileum. We also compared the effects of the L- and D-forms of penetratin, R8, and PenetraMax on ileal insulin absorption. Along with the CPPs used in this study, L- and D-PenetraMax produced the largest insulin AUCs. An absorption study using ilea pretreated with CPPs showed that PenetraMax had no irreversible effect on the intestinal epithelial membrane. The degradation of insulin in the presence of CPPs was assessed in rat intestinal enzymatic fluid. The half-life (t 1/2) of insulin increased from 14.5 to 23.7 and 184.7 min in the presence of L- and D-PenetraMax, respectively. These enzymatic degradation-resistant effects might contribute partly to the increased ileal absorption of insulin induced by D-PenetraMax. In conclusion, this study demonstrated that the ability of the L- and D-forms of penetratin to increase intestinal insulin absorption was maximal in the ileum and the colon, respectively, and that D-PenetraMax is a powerful but transient enhancer of oral insulin absorption.

Liposomes containing cholesterol analogues of botanical origin as drug delivery systems to enhance the oral absorption of insulin

In fear of animal-associated diseases, there is a trend in searching for non-animal derived substitutes for existing excipients in the pharmaceutical industries. This paper aimed to screen cholesterol analogues as membrane stabilizers of liposomes from botanical sterols, including β-sitosterol, stigmasterol, ergosterol and lanosterol. Liposomes containing four kinds of sterols were prepared and evaluated in vitro and in vivo as oral delivery system of insulin. Liposomes containing β-sitosterol (Si-Lip), stigmasterol (St-Lip) and lanosterol (La-Lip) was found not to protect insulin against degradation. Only 10% of the initial insulin in liposomes was preserved after a 30min exposure to simulated gastric fluids. However, the protective ability of liposomes containing ergosterol (Er-Lip) was similar to that of liposomes containing sodium glycocholate (Sgc-Lip) and superior to that of liposomes containing cholesterol (Ch-Lip). In addition, the blood glucose level can decrease to about 50% of initial level after oral Er-Lip which was significantly superior to the in vivo performance of Si-Lip and Ch-Lip and similar to Sgc-Lip. Er-Lips of ergosterol/phospholipids ratios of 1:4 or 1:6 exerts more pronounced protective ability of insulin in simulated gastrointestinal fluids and hypoglycemic effects in rats than other formulations. Furthermore, Er-Lips exerted low toxicity to Caco-2 cells through a cell viability study. Meahwhile, insulin permeability was significantly increased across Caco-2 monolayers by encapsulating in Er-Lip. It was concluded that ergosterol could be used as a substitute for cholesterol and bile salt derivatives in liposomes to enhance oral bioavailability of insulin.

Chitosan-Modified Cationic Amino Acid Nanoparticles as a Novel Oral Delivery System for Insulin.

In this study, chitosan-modified basic amino acid derivatives were explored as novel absorption enhancers and nanocarriers for oral insulin delivery. N-Arginine-chitosan (ACS) and N-histidine-chitosan (HCS) were successfully synthesized, and their polyelectrolyte complexes (PECs) with insulin were formed by the ordinary self-assembly method. The obtained PECs exhibited a spherical morphology with a narrow size of 205-303 nm, positive surface charge (ζ potential + 14- + 27 mV) and encapsulation efficiency of approximately 80%. The electrostatic interactions between chitosan derivatives and insulin were confirmed by molecular modeling simulation. In vitro studies demonstrated that PECs could partially protect insulin from proteolysis and degradation at 50 degrees C for at least 6 h. Compared with the insulin solution, internalization of PECs into Caco-2 cells was increased by up to 20.7-fold. Moreover, permeability was enhanced as the degrees of substitution of arginine and histidine increased. The PECs had in vivo pharmacological activities of 2.29%-5.39%, with a significant reduction of blood glucose levels in diabetic rats. These results suggested that ACS and HCS PECs hold promising potential for the oral delivery of insulin, peptides and proteins.

Recent advances in the oral delivery of insulin.

Insulin was discovered over 90 years ago. However oral insulin still remains a challenging and elusive goal. Extensive efforts are being made worldwide for developing noninvasive drug delivery systems, mainly via oral route as it is the most widely accepted means of administration. The main barriers faced in oral protein delivery are the enzymatic degradation and poor permeability across the intestinal wall. The approaches for developing an oral insulin delivery system mainly focus on overcoming these barriers. To overcome the gastro-intestinal barriers various types of formulations such as insulin conjugates, permeation enhancers, micro/nanoparticles, liposomes etc. are investigated. In the recent years a number of advances have taken place in understanding the needs and workable mechanisms of improved oral peptide delivery systems. In this review the recent patents on oral insulin is focused. Emphasis is on the technologies based on permeation enhancers and nanoparticle based carrier systems.

In vivo proof of concept of oral insulin delivery based on a co-administration strategy with the cell-penetrating peptide penetratin

Oral delivery of insulin is blocked by low intestinal absorption caused by the poor permeability of insulin across cellular membranes and the susceptibility to enzymatic degradation in the gastrointestinal tract. Cell-penetrating peptides (CPPs) have been investigated for a number of years as oral absorption enhancers for hydrophilic macromolecules. Penetratin, a cationic and amphipathic CPP, effectively enhances insulin absorption and we were able to alleviate the enzymatic barrier by using the enzymatic resistant D-form of penetratin. In this study, mice were dosed orally with a physical mixture of insulin and penetratin. Blood glucose concentrations were measured and a pharmacological availability (PA) of 18.2% was achieved in mice dosed with insulin and D-penetratin. Following the promising data, we investigated the degradation parameters of insulin and penetratin in rat intestinal fluid. As expected, L-penetratin was degraded rapidly whereas D-penetratin had a halflife of 67±7min in 10-fold diluted gastrointestinal fluid. Insulin degradation was slowed by the presence of penetratin in intestinal fluid. The half-life of insulin increased from 24.9±4.5min to 55.6±14min and 90.5±11.8min in the presence of L- and D-penetratin respectively. In conclusion, both Land D-penetratin acted as oral absorption enhancers at select CPP concentrations for insulin and the current study is the first solid evidence of pharmacological activity of oral insulin delivery systems based on non-covalent intermolecular interactions with penetratin.

Emerging Trends in Noninvasive Insulin Delivery.

This paper deals with various aspects of oral insulin delivery system. Insulin is used for the treatment of diabetes mellitus, which is characterized by the elevated glucose level (above the normal range) in the blood stream, that is, hyperglycemia. Oral route of administration of any drug is the most convenient route. Development of oral insulin is still under research. Oral insulin will cause the avoidance of pain during the injection (in subcutaneous administration), anxiety due to needle, and infections which can be developed. Different types of enzyme inhibitors, like sodium cholate, camostat, mesilate, bacitracin, leupeptin, and so forth, have been used to prevent insulin from enzymatic degradation. Subcutaneous route has been used for administration of insulin, but pain and itching at the site of administration can occur. That is why various alternative routes of insulin administration like oral route are under investigation. In this paper authors summarized advancement in insulin delivery with their formulation aspects.

Nanocarriers Based Oral Insulin Delivery

Nanocarriers Based Oral Insulin Delivery Successful oral administration of protein drugs remains an obscure challenge. In this context, oral insulin delivery has always been a significant challenge for pharmaceutical researchers and considerable efforts are being made to deliver insulin orally. Oral insulin therapy seems to have progressed with nanotechnology research, allowing for several types of encapsulations to bypass the gastric acidic environment. Nanoparticles protect insulin against degradation and facilitate the uptake of insulin (associated or not associated to the nanoparticles) through a paracellular or a transcellular pathway. In oral insulin, the mechanism involves various nanoparticle encasings bound to insulin delivery. Continuous comparisons of in vitro and in vivo studies are essential to develop oral insulin delivery systems in near future.

Application of Artificial Neural Networks for Optimization of Preparation of Insulin Nanoparticles Composed of Quaternized Aromatic Derivatives of Chitosan

The aim of this research was to develop an artificial neural network (ANN) in order to design a nanoparticulate oral drug delivery system for insulin. The pH of polymer solution (X1), concentration ratio of polymer/insulin (X2) and polymer type (X3) in 3 level including methylated N-(4-N,N- dimethyl aminobenzyl) chitosan, methylated N-(4-pyridinyl) chitosan, and methylated N-(benzyl) chitosan are considered as the input values and the particle size, zeta potential, PdI, and entrapment efficiency (EE %) as output data. ANNs are employed to generate the best model to determining the relationships between input and response values. In this research, a multi-layer percepteron with different topologies has been tested in order to define the one with the best accuracy and performance. The optimization was used by minimizing the error between the predicted and observed values. Three training algorithms (Levenberg-Marquardt (LM), Bayesian-Regularization (BR), and Gradient Descent (GD)) were employed to train ANNs with various numbers of nodes, hidden layers and transfer functions by random selection. The accuracy of prediction data were assayed by the mean squared error (MSE).The ability of all algorithms was in the order: BR>LM>GD. Thus, BR was selected as the best algorithm.

Dual-controlled oral colon-targeted delivery of bovine insulin based on mesoporous phosphonate

The time- and pH-controlled oral colon-targeted delivery system for bovine insulin was developed by dip-coating lag-time films on tablet comprising bovine insulin-loaded pH-sensitive mesoporous phosphonate (ZrBPMP-3) as tablet core and absorption enhancer of insulin, sodium glycocholate, in outer layer, in which the lag time can be controlled via adjusting coating times of lag-time films and the release of bovine insulin in the colon can be triggered by pH-sensitive ZrBPMP-3. The pH transition release experiments show that the tablet with four times lag-time films coating can carry bovine insulin passing through the stomach and small intestine with a minimum release and trigger off the release of loaded bovine insulin in the colon under dual control, time control and pH value control. Furthermore, the released bovine insulin can still retain its native conformation, as evidenced by circular dichroism spectroscopy, indicating that bovine insulin cannot denature and lose its bioactive conformation during the loading, lag-time films coating, delivery and release. In addition, it is worth mentioning that ZrBPMP-3 almost exhibits non-cytotoxicity at low concentration in MTT assays. Thus, ZrBPMP-3 as a new kind of carrier and based on which developing controllable colon-targeted delivery system have potential application in oral delivery of insulin and even other therapeutic peptides and proteins.

Noninvasive imaging oral absorption of insulin delivered by nanoparticles and its stimulated glucose utilization in controlling postprandial hyperglycemia during OGTT in diabetic rats

This work examined the feasibility of preparing a pH-responsive nanoparticle (NP) system composed of chitosan and poly(γ-glutamic acid) conjugated with ethylene glycol tetraacetic acid (γPGA–EGTA) for oral insulin delivery in diabetic rats during an oral glucose tolerance test (OGTT). OGTT has been used largely as a model to mimic the period that comprises and follows a meal, which is often associated with postprandial hyperglycemia. Based on Förster resonance energy transfer (FRET), this work also demonstrated the ability of γPGA–EGTA to protect insulin from an intestinal proteolytic attack in living rats, owing to its ability to deprive the environmental calcium. Additionally, EGTA-conjugated NPs were effective in disrupting the epithelial tight junctions, consequently facilitating the paracellular permeation of insulin throughout the entire small intestine. Moreover, results of positron emission tomography and computer tomography demonstrated the effective absorption of the permeated insulin into the systemic circulation as well as promotion of the glucose utilization in the myocardium, and skeletal muscles of the chest wall, forelimbs and hindlimbs, resulting in a significant glucose-lowering effect. Above results indicate that as-prepared EGTA-conjugated NPs are a promising oral insulin delivery system to control postprandial hyperglycemia and thus may potentially prevent the related diabetic complications.

Potent and Prolonged Hypoglycemic Activity of an Oral Insulin - Tat Mixture in Diabetic Mice

Trans-activator of transcription (Tat) is a cell penetrating peptide which can translocate and carry macromolecular cargoes through cell membranes. This study investigated the hypoglycemic activity of orally delivered insulin - Tat mixture in alloxan-induced diabetic mice. The mixtures of insulin and Tat at 1:1, 1:3 and 1:6 molar ratios were given orally at the insulin doses ranging from 1-200 IU/kg. The fasting blood glucose (FBG) levels were measured at initial, 1, 2, 4, 6, and 12 h after administration. At 1:3 molar ratio of the mixture and after 12 h of administration, insulin at 200 IU/kg showed the highest with prolonged hypoglycemic activity of 74.0±10.3% FBG reduction (2.18 folds of subcutaneously injected (SC) insulin). Free insulin administered orally did not show any hypoglycemic activity. The mixtures at the insulin doses of 100 and 50 IU/kg also showed potent FBG reduction of 73.8±8.2 and 71.3±16.9% at 12 h after administration (2.18 and 2.10 folds of SC insulin, respectively). After incubation with Mono-Mac-6 cells, only the -mixtures but not the free insulin showed intra-cellular insulin uptake, indicating the insulin penetration through the cell membranes via Tat. In simulated gastric fluid, the insulin content in the mixture was not found, demonstrating the degradation of insulin in the gastric environments. Insulin may be absorbed at upper gastrointestinal tract facilitated by Tat. The potent and prolonged hypoglycemic activity of insulin co-administered orally with Tat can be further developed as an effective oral insulin delivery system.

Oral Insulin Delivery: How Far are We?

Oral delivery of insulin may significantly improve the quality of life of diabetes patients who routinely receive insulin by the subcutaneous route. In fact, compared with this administration route, oral delivery of insulin in diabetes treatment offers many advantages: higher patient compliance, rapid hepatic insulinization, and avoidance of peripheral hyperinsulinemia and other adverse effects such as possible hypoglycemia and weight gain. However, the oral delivery of insulin remains a challenge because its oral absorption is limited. The mainbarriers faced by insulin in the gastrointestinal tract are degradation by proteolytic enzymes and lack of transport across the intestinal epithelium. Several strategies to deliver insulin orally have been proposed, but without much clinical or commercial success. Protein encapsulation into nanoparticles is regarded as a promising alternative to administer insulin orally because they have the ability to promote insulin paracellular or transcellular transport across the intestinal mucosa. In this review, different delivery systems intended to increase the oral bioavailability of insulin will be discussed, with a special focus on nanoparticulate carrier systems, as well as the efforts that pharmaceutical companies are making to bring to the market the first oral delivery system of insulin. The toxicological and safety data of delivery systems, the clinical value and progress of oral insulin delivery, and the future prospects in this research field will be also scrutinized.

Overcoming oral insulin delivery barriers: application of cell penetrating peptide and silica-based nanoporous composites

Oral insulin delivery has received the most attention in insulin formulations due to its high patient compliance and, more importantly, to its potential to mimic the physiologic insulin secretion seen in non-diabetic individuals. However, oral insulin delivery has two major limitations: the enzymatic barrier that leads to rapid insulin degradation, and the mucosal barrier that limits insulin’s bioavailability. Several approaches have been actively pursued to circumvent the enzyme barrier, with some of them receiving promising results. Yet, thus far there has been no major success in overcoming the mucosal barrier, which is the main cause in undercutting insulin’s oral bioavailability. In this review of our group’s research, an innovative silica-based, mucoadhesive oral insulin formulation with encapsulated-insulin/cell penetrating peptide (CPP) to overcome both enzyme and mucosal barriers is discussed, and the preliminary and convincing results to confirm the plausibility of this oral insulin delivery system are reviewed. In vitro studies demonstrated that the CPPinsulin conjugates could facilitate cellular uptake of insulin while keeping insulin’s biologic functions intact. It was also confirmed that low molecular weight protamine (LMWP) behaves like a CPP peptide, with a cell translocation potency equivalent to that of the widely studied TAT. The mucoadhesive properties of the produced silica-chitosan composites could be controlled by varying both the pH and composition; the composite consisting of chitosan (25 wt-%) and silica (75 wt-%) exhibited the greatest mucoadhesion at gastric pH. Furthermore, drug release from the composite network could also be regulated by altering the chitosan content. Overall, the universal applicability of those technologies could lead to development of a generic platform for oral delivery of many other bioactive compounds, especially for peptide or protein drugs which inevitably encounter the poor bioavailability issues.

Nanoemulsions coated with alginate/chitosan as oral insulin delivery systems: preparation, characterization, and hypoglycemic effect in rats

This study aimed to prepare nanoemulsions coated with alginate/chitosan for oral insulin delivery. Uncoated nanoemulsions were prepared by homogenization of a water in oil in water (w/o/w) multiple emulsion that was composed of Labrafac® CC, phospholipid, Span™ 80 and Cremorphor® EL. Coating of the nanoemulsions was achieved based on polyelectrolyte cross-linking, with sequential addition of calcium chloride and chitosan to the bulk nanoemulsion dispersion that contained alginate. The particle size of the coated nanoemulsions was about 488 nm and the insulin entrapment ratio was 47.3%. Circular dichroism spectroscopy proved conformational stability of insulin against the preparative stress. In vitro leakage study indicated well-preserved integrity of the nanoemulsions in simulated gastric juices. Hypoglycemic effects were observed in both normal and diabetic rats. The relative pharmacological bioavailability of the coated nanoemulsion with 25 and 50 IU/kg insulin were 8.42% and 5.72% in normal rats and 8.19% and 7.84% in diabetic rats, respectively. Moreover, there were significantly prolonged hypoglycemic effects after oral administration of the coated nanoemulsions compared with subcutaneous (sc) insulin. In conclusion, the nanoemulsion coated with alginate/chitosan was a potential delivery system for oral delivery of polypeptides and proteins.