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

Novel non-invasive methods of insulin delivery

INTRODUCTION

Insulin has usually been administered subcutaneously in the treatment of diabetes mellitus. Alternative delivery routes of insulin are expected to overcome some limitations, mainly concerned with the possibility of hypoglycemia episodes, weight gain and inadequate post-meal glucose control, in order to lead a better patient compliance.

AREAS COVERED

This review article covers all the most relevant non-invasive insulin delivery methods under development, respective technology and clinical data available according to their status of development. Special focus is given to the systems with late clinical trial evidences, their achievements and pitfalls. Pulmonary and oral appear to be the most advantageous routes, with regard to the long list of potentially marketed products.

EXPERT OPINION

Alternative insulin delivery to the subcutaneous administration is more and more close to the success, being fundamental that any optimized technology could overcome the overall low mucosal bioavailability of insulin, mostly due to its early degradation before absorption, inactivation and digestion by proteolytic enzymes and poor permeability across mucosal epithelium because of its high molecular weight and lack of lipophilicity.

Folate-decorated PLGA nanoparticles as a rationally designed vehicle for the oral delivery of insulin

Aims: The present study reports a novel approach for enhancing the oral absorption and hypoglycemic activity of insulin via encapsulation in folate-(FA) coupled polyethylene glycol (PEG)ylated polylactide-co-glycolide (PLGA) nanoparticles (NPs; FA-PEG-PLGA NPs). Materials & methods: Insulin-loaded FA-PEG-PLGA NPs (size ∼260 nm; insulin loading ∼6.5% [w/w]; encapsulation efficiency: 87.0 ± 1.92%) were prepared by double-emulsion solvent evaporation method. The bioavailability and hypoglycemic activity of orally administered FA–insulin NPs were studied in diabetic rats. Results & conclusion: FA-PEG-PLGA NPs (50 U/kg) exhibited a twofold increase in the oral bioavailability (double hypoglycemia) without any hypoglycemic shock as compared to subcutaneously administered standard insulin solution. Insulin NPs maintained a continual blood glucose level for 24 h, which, however, was transient (<8 h) in the case of subcutaneous insulin and associated with severe hypoglycemic shock. Overall, we have developed a patient-compliant, oral nanoformulation of insulin, once-daily administration of which would be sufficient to control diabetes for at least 24 h.

Original submitted 16 November 2011; Revised submitted 2 February 2012; Published online 14 May 2012

Insulin-loaded pH-sensitive hyaluronic acid nanoparticles enhance transcellular delivery

In the present study, we developed novel insulin-loaded hyaluronic acid (HA) nanoparticles for insulin delivery. The insulin-loaded HA nanoparticles were prepared by reverse-emulsion-freeze-drying method. This method led to a homogenous population of small HA nanoparticles with average size of 182.2 nm and achieved high insulin entrapment efficiencies (approximately 95%). The pH-sensitive HA nanoparticles as an oral delivery carrier showed advantages in protecting insulin against the strongly acidic environment of the stomach, and not destroying the junction integrity of epithelial cells which promise long-term safety for chronic insulin treatment. The results of transport experiments suggested that insulin-loaded HA nanoparticles were transported across Caco-2 cell monolayers mainly via transcellular pathway and their apparent permeability coefficient from apical to basolateral had more than twofold increase compared with insulin solution. The efflux ratio of P (app) (B to A) to P (app) (A to B) less than 1 demonstrated that HA nanoparticle-mediated transport of insulin across Caco-2 cell monolayers underwent active transport. The results of permeability through the rat small intestine confirmed that HA nanoparticles significantly enhanced insulin transport through the duodenum and ileum. Diabetic rats treated with oral insulin-loaded HA nanoparticles also showed stronger hypoglycemic effects than insulin solution. Therefore, these HA nanoparticles could be a promising candidate for oral insulin delivery.

The preparation of a complex of insulin-phospholipids and their interaction mechanism

Subcutaneous injections of insulin remain the standard treatment for insulin-dependent diabetic patients, and noninvasive routes are studied but with little success. One of the reasons is that insulin is a hydrophilic compounds and is difficult to cross the mucosa barrier. In this paper, we developed a novel technique to fabricate the insulin-phospholipids complex by a solvent evaporation method with the aim of improving the lipophilicity of insulin. A systematic study on the preparation conditions of the insulin-phospholipids complex is reported in the present work. The formation mechanism and the physicochemical properties of the complex are studied. The associated efficiency of the phospholipids and insulin can be up to 100% when their mass ratio is 7.5 : 1 or more, and the solubility of the complex is improved more than 40 000 times compared with that of insulin alone in the n-octyl alcohol. The results of the insulin content in the complex and hypoglycemic effects in diabetic mice indicated that insulin was able to withstand the preparation procedure. The stability results showed that the complex was stable for 1 year at -20 °C. The interaction mechanism of this formation is that the peptide bonds of insulin interact with the water-soluble head of phospholipids, forming a reverse micelle-like structure. This novel complex will be of great importance in the drug delivery system for insulin via noninvasive routes. This method is cost effective, scalable, and can be used in many other peptide drugs.

Thiomers and thiomer-based nanoparticles in protein and DNA drug delivery

INTRODUCTION

Thanks to advances in biotechnology, more and more highly efficient protein- and DNA-based drugs have been developed. Unfortunately, these kinds of drugs underlie poor non-parental bioavailability. To overcome hindrances like low mucosal permeability and enzymatic degradation polymeric excipients are utilized as drug carrier whereat thiolated excipients showed several promising qualities in comparison to the analogical unmodified polymer.

AREAS COVERED

The article deals with the comparatively easy modification of well-established polymers like chitosan or poly(acrylates) to synthesize thiomers. Further, the recently developed "next generation" thiomers e.g. preactivated or S-protected thiomers are introduced. Designative properties like mucoadhesion, uptake and permeation enhancement, efflux pump inhibition and protection against enzymatic degradation will be discussed and differences between first and next generation thiomers will be pointed out. Additionally, nanoparticles prepared with thiomers will be dealt with regarding to protein and DNA drug delivery as thiomers seem to be a promising approach to avoid parenteral application.

EXPERT OPINION

Properties of thiomers per se and results of in vivo studies carried out so far for peptide and DNA drugs demonstrate their potential as multifunctional excipients. However, further investigations and optimizations have to be done before establishing a carrier system ready for clinical approval.

Novel preparation of PLGA/HP55 nanoparticles for oral insulin delivery

The aim of the present study was to develop the PLGA/HP55 nanoparticles with improved hypoglycemic effect for oral insulin delivery. The insulin-loaded PLGA/HP55 nanoparticles were produced by a modified multiple emulsion solvent evaporation method. The physicochemical characteristics, in vitro release of insulin, and in vivo efficacy in diabetic rats of the nanoparticles were evaluated. The insulin encapsulation efficiency was up to 94%, and insulin was released in a pH-dependent manner under simulated gastrointestinal conditions. When administered orally (50 IU/kg) to diabetic rats, the nanoparticles can decrease rapidly the blood glucose level with a maximal effect between 1 and 8 h. The relative bioavailability compared with subcutaneous injection (5 IU/kg) in diabetic rats was 11.3% ± 1.05%. This effect may be explained by the fast release of insulin in the upper intestine, where it is better absorbed by the high gradient concentration of insulin than other regions. These results show that the PLGA/HP55 nanoparticles developed in the study might be employed as a potential method for oral insulin delivery.

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.

Nanomedicine for treatment of diabetes in an aging population: state-of-the-art and future developments

Nowadays diabetes, especially type 2 diabetes (which is strongly related to the Western diet and life-style), has developed worldwide into an epidemic disease. Nanomedicine aims to provide novel tools for diagnosis, therapy and point-of-care management of patients. Several nanotechnological approaches were developed to improve life quality for patients with insulin-dependent diabetes. They facilitate blood glucose management by non-invasive glucose measurement as well as insulin administration mainly by delivering the fragile protein as protected and targeted formulation via nasal or oral route. In the present review the oral or nasal insulin delivery by polymeric nanoparticles is discussed with focus on physiological change either related to the disease, diabetes or age-related metabolic variations influencing insulin release and bioavailability. One critical point is that new generations of targeted nanoparticle based drugs are developed and optimized for certain metabolic conditions. These conditions may change with age or disease. The influence of age-related factors such as immaturity in very young age, metabolic and physiologic changes in old age or insufficient animal models are still under-investigated not only in nanomedicine but also generally in pharmacology. Summarizing it can be noted that the bioavailability of insulin administered via routes others than subcutaneously is comparably low (max. 60%). Moreover factors like changed gut permeability as described for diabetes type 1 or other metabolic peculiarities such as insulin resistance in case of type 2 diabetes also play a role in affecting the development of novel nanoparticulated drug preparations and can be responsible for unsuccessful translation of promising animal results into human therapy. In future insulin nanoparticle development for diabetes must consider not only requirements imposed by the drug but also metabolic changes inflicted by disease or by age. Moreover new approaches are required for prevention of the disease.

Oral colon delivery of insulin with the aid of functional adjuvants

Oral colon delivery is currently considered of importance not only for the treatment of local pathologies, such as primarily inflammatory bowel disease (IBD), but also as a means of accomplishing systemic therapeutic goals. Although the large bowel fails to be ideally suited for absorption processes, it may indeed offer a number of advantages over the small intestine, including a long transit time, lower levels of peptidases and higher responsiveness to permeation enhancers. Accordingly, it has been under extensive investigation as a possible strategy to improve the oral bioavailability of peptide and protein drugs. Because of a strong underlying rationale, most of these studies have focused on insulin. In the present review, the impact of key anatomical and physiological characteristics of the colon on its viability as a protein release site is discussed. Moreover, the main formulation approaches to oral colon targeting are outlined along with the design features and performance of insulin-based devices.

Oral biodrug delivery using cell-penetrating peptide

During the past few decades, the novel biotherapeutic agents such as peptides and proteins have been contributed to the treatment of several diseases. However, their oral absorption is significantly limited due to their poor delivery through the intestinal mucosa. Therefore, the feasible approaches are needed for improving the oral bioavailability of biodrugs. Recently, cell-penetrating peptides (CPPs) such as HIV-1 Tat, penetratin and oligoarginine are considered as a useful tool for the intracellular delivery of therapeutic macromolecules. Hence, it was expected that the ability of CPPs may be applicable to enhance the absorption of biodrugs through intestinal epithelial membrane. CPPs are likely to become powerful tools for overcoming the low permeability of therapeutic peptides and proteins through the intestinal membrane, the major barrier to their oral delivery. Further advantage of this promising strategy is that this successful intestinal absorption could be achieved by more convenient methodology, coadministration of CPP with drugs via intermolecular interaction among them. Hereafter, the further establishment of delivery system based on CPPs is required to realize the development of the oral forms of therapeutic peptides and proteins. The aim here is to introduce our vision focusing on oral biodrug delivery by the use of CPPs as potential peptide carrier in order to provide new information in the design and development of new oral delivery systems for novel biotherapeutics.

Oral delivery of therapeutic protein/peptide for diabetes--future perspectives

Diabetes is a metabolic disease and is a major cause of mortality and morbidity in epidemic proportions. A type I diabetic patient is dependent on daily injections of insulin, for survival and also to maintain a normal life, which is uncomfortable, painful and also has deleterious effects. Extensive efforts are being made worldwide for developing noninvasive drug delivery systems, especially via oral route. Oral route is the most widely accepted means of administration. However it is not feasible for direct delivery of peptide and protein drugs. To overcome the gastro-intestinal barriers various types of formulations such as polymeric micro/nanoparticles, liposomes, etc. are investigated. In the recent years lot of advances have taken place in developing and understanding the oral peptide delivery systems. Simultaneously, the development and usage of other peptides having anti-diabetic potentials are also considered for diabetes therapy. In this review we are focusing on the advances reported during the past decade in the field of oral insulin delivery along with the possibility of other peptidic incretin hormones such as GLP-1, exendin-4, for diabetes therapy.

Formulation, optimization and evaluation of transferosomal gel for transdermal insulin delivery

The present study deals with the development of transferosomal gel containing insulin by reverse phase evaporation method for painless insulin delivery for use in the treatment of insulin dependent diabetes mellitus. The effect of independent process variables like ratio of lipids (soya lecithin:cholesterol), ratio of lipids and surfactants, and ratio of surfactants (Tween 80:sodium deoxycholate) on the in vitro permeation flux (μg/cm(2)/h) of formulated transferosomal gels containing insulin through porcine ear skin was optimized using 2(3) factorial design. The optimal permeation flux was achieved as 13.50 ± 0.22 μg/cm(2)/h with drug entrapment efficiency of 56.55 ± 0.37% and average vesicle diameter range, 625-815 nm. The in vitro insulin permeation through porcine ear skin from these transferosomal gel followed zero-order kinetics (R (2) = 0.9232-0.9989) over a period of 24 h with case-II transport mechanism. The in vitro skin permeation of insulin from optimized transferosomal gel by iontophoretic influence (with 0.5 mA/cm(2) current supply) also provided further enhancement of permeation flux to 17.60 ± 0.03 μg/cm(2)/h. The in vivo study of optimized transferosomal gel in alloxan-induced diabetic rat has demonstrated prolonged hypoglycemic effect in diabetic rats over 24 h after transdermal administration.

HP55-coated capsule containing PLGA/RS nanoparticles for oral delivery of insulin

In this work, we designed and developed a two-stage delivery system composed of enteric capsule and cationic nanoparticles for oral delivery of insulin. The enteric capsule was coated with pH-sensitive hydroxypropyl methylcellulose phthalate (HP55), which could selectively release insulin from nanoparticles in the intestinal tract, instead of stomach. The biodegradable poly(lactic-co-glycolic acid) (PLGA) was selected as the matrix for loading insulin. Eurdragit(®) RS (RS) was also introduced to the nanoparticles for enhancing the penetration of insulin across the mucosal surface in the intestine. The nanoparticles were prepared with the multiple emulsions solvent evaporation method via ultrasonic emulsification. The optimized nanoparticles have a mean size of 285nm, a positive zeta potential of 42mV. The encapsulation efficiency was up to 73.9%. In vitro results revealed that the initial burst release of insulin from nanoparticles was markedly reduced at pH 1.2, which mimics the stomach environment. In vivo effects of the capsule containing insulin PLGA/RS nanoparticles were also investigated in diabetic rat models. The oral delivered capsules induced a prolonged reduction in blood glucose levels. The pharmacological availability was found to be approximately 9.2%. All the results indicated that the integration of HP55-coated capsule with cationic nanoparticles may be a promising platform for oral delivery of insulin with high bioavailability.

Nanomedicine for treatment of diabetes in an aging population: state-of-the-art and future developments

Nowadays diabetes, especially type 2 diabetes (which is strongly related to the Western diet and life-style), has developed worldwide into an epidemic disease. Nanomedicine aims to provide novel tools for diagnosis, therapy and point-of-care management of patients. Several nanotechnological approaches were developed to improve life quality for patients with insulin-dependent diabetes. They facilitate blood glucose management by non-invasive glucose measurement as well as insulin administration mainly by delivering the fragile protein as protected and targeted formulation via nasal or oral route. In the present review the oral or nasal insulin delivery by polymeric nanoparticles is discussed with focus on physiological change either related to the disease, diabetes or age-related metabolic variations influencing insulin release and bioavailability. One critical point is that new generations of targeted nanoparticle based drugs are developed and optimized for certain metabolic conditions. These conditions may change with age or disease. The influence of age-related factors such as immaturity in very young age, metabolic and physiologic changes in old age or insufficient animal models are still under-investigated not only in nanomedicine but also generally in pharmacology. Summarizing it can be noted that the bioavailability of insulin administered via routes others than subcutaneously is comparably low (max. 60%). Moreover factors like changed gut permeability as described for diabetes type 1 or other metabolic peculiarities such as insulin resistance in case of type 2 diabetes also play a role in affecting the development of novel nanoparticulated drug preparations and can be responsible for unsuccessful translation of promising animal results into human therapy. In future insulin nanoparticle development for diabetes must consider not only requirements imposed by the drug but also metabolic changes inflicted by disease or by age. Moreover new approaches are required for prevention of the disease.

Opportunities and challenges for oral delivery of hydrophobic versus hydrophilic peptide and protein-like drugs using lipid-based technologies

Peptide and protein-like drugs are macromolecules currently produced in increasing numbers by the pharmaceutical biotechnology industry. The physicochemical properties of these molecules pose barriers to oral administration. Lipid-based drug-delivery systems have the potential to overcome these barriers and may be utilized to formulate safe, stable and efficacious oral medicines. This review outlines the design of such lipid-based technologies. The mechanisms whereby these formulations enhance the absorption of lipophilic versus hydrophilic peptide and protein-like drugs are discussed. In the case of lipophilic compounds, the advantages of lipid-based drug-delivery systems including increased solubilization, decreased intestinal efflux, decreased intracellular metabolism and possible lymphatic transport are well established as is evident from the success of Neoral® and other drug products on the market. In contrast, with respect to hydrophilic compounds, the situation is more complex and, while promising formulation approaches have been studied, issues including reproducibility of response, intersubject variability and duration of response require further optimization before commercially viable products are possible.

Oral fondaparinux: use of lipid nanocapsules as nanocarriers and in vivo pharmacokinetic study

Oral anticoagulant therapy could be advanced using lipid-based nanoparticulate systems. This study examined lipid nanocapsules for their oral absorption potential as the first step in developing oral fondaparinux (Fp) novel carriers. Using phase inversion method and cationic surfactants such as hexadecyltrimethyl ammonium bromide (CTAB) or stearylamine (SA), cationic lipid nanocapsules (cLNCs), loaded with Fp on their surface, were prepared and characterized (zeta potential, size and Fp association efficiency and content). In vivo studies were conducted after single oral increasing doses of Fp-loaded cLNCs (0.5 to 5 mg/kg of Fp) in rats and the concentration of Fp in the plasma was measured by anti-factor Xa activity assay. The monodisperse, (~50 nm), positively charged Fp-cLNCs with high drug loadings demonstrated linear pharmacokinetic profiles of the drug with an increased oral absolute bioavailability (up to ~21%) compatible with therapeutic anticoagulant effect (>0.2 μg/mL).

Effects of chitosan-nanoparticle-mediated tight junction opening on the oral absorption of endotoxins

Recently, we reported a pH-responsive nanoparticle (NP) system shelled with chitosan (CS), which could effectively increase the oral absorption of insulin and produce a hypoglycemic effect, presumably due to the CS-mediated tight junction (TJ) opening. It has been often questioned whether CS can also enhance the absorption of endotoxins present in the small intestine. To address this concern, we studied the effect of CS NPs on the absorption of lipopolysaccharide (LPS), the most commonly found toxin in the gastrointestinal tract. To follow their biodistribution by the single-photon emission computed tomography/computed tomography, LPS and insulin were labeled with (99m)Tc-pertechnetate ((99m)Tc-LPS) and (123)iodine ((123)I-insulin), respectively. The (99m)Tc-LPS was ingested 1 h prior to the administration of the (123)I-insulin-loaded NPs to mimic the physiological conditions. The confocal and TEM micrographs show that the orally administered CS NPs were able to adhere and infiltrate through the mucus layer, approach the epithelial cells and mediate to open their TJs. The radioactivity associated with LPS was mainly restricted to the gastrointestinal tract, whereas (123)I-insulin started to appear in the urinary bladder at 3 h post administration. This observation indicates that the insulin-loaded in CS NPs can traverse across the intestinal epithelium and enter the systemic circulation, whereas LPS was unable to do so, probably because of the charge repulsion between the anionic LPS in the form of micelles and the negatively charged mucus layer. Our in vivo toxicity study further confirms that the enhancement of paracellular permeation by CS NPs did not promote the absorption of LPS. These results suggest that CS NPs can be used as a safe carrier for oral delivery of protein drugs.

Painless skin electroporation as a novel way for insulin delivery

BACKGROUND

Rigorous research efforts have been undertaken worldwide to develop a needle-free insulin delivery for many decades with limited success. This translational study aims to deliver insulin through skin with painless electroporation.

METHODS

A recently designed microelectrode array was used to deliver insulin in mice with diabetes under electroporation conditions that are painless and harmless on human skin.

RESULTS

Under such condition, a therapeutic amount of insulin was delivered successfully through mouse skin. Electroporation alone increased insulin transport around 100-fold compared with passive diffusion. Increased skin temperature to 40°C for 20 min augmented insulin transport to 237-fold more than the control value. Repeated electroporation showed no harm on human skin.

CONCLUSION

The results indicate the potential of painless delivery of insulin through human skin in future clinical practice.

Development and evaluation of microemulsions for transdermal delivery of insulin

Insulin-loaded microemulsions for transdermal delivery were developed using isopropyl myristate or oleic acid as the oil phase, Tween 80 as the surfactant, and isopropyl alcohol as the cosurfactant. The pseudoternary phase diagrams were constructed to determine the composition of microemulsions. The insulin permeation flux of microemulsions containing oleic acid as oil phase through excised mouse skin and goat skin was comparatively greater than that of microemulsions containing isopropyl myristate as oil phase. The insulin-loaded microemulsion containing 10% oleic acid, 38% aqueous phase, and 50% surfactant phase with 2% dimethyl sulfoxide (DMSO) as permeation enhancer showed maximum permeation flux (4.93 ± 0.12 μg/cm(2)/hour) through goat skin. The in vitro insulin permeation from these microemulsions was found to follow the Korsmeyer-Peppas model (R(2) = 0.923 to 0.973) over a period of 24 hours with non-Fickian, "anomalous" mechanism. Together these preliminary data indicate the promise of microemulsions for transdermal delivery of insulin.

Insulin chewing gum: Need of the day for diabetic patients

Chewing gum is an excellent drug delivery system for self medication as it is convenient, can be administered discreetly without water and offers the removal of 'needle fear' for the patients. As it releases insulin orally, it helps in tackling of the deprivation of insulin by digestive enzyme without adding digestive enzyme inhibitor. This can be done by binding of vitamin B12 and insulin. The vitamin B12 is protected with haptocorrin which is a salivary protein. Another chemical pathway takes over to help vitamin B12 pass into the bloodstream as haptocorrin reaches the intestines. The binding of vitamin B12 and insulin molecules makes the insulin to be protected on this supply chain. The insulin could ride all the way into the bloodstream, where it is released to do its work. By stimulating the brain, chewing gum also increases the releases of insulin. Finding simpler ways to deliver insulin into the blood stream is one important avenue for tackling the diabetes epidemic that is sweeping the developed world. The conditions in gastrointestinal tract may damage the body's protecting and absorbing mechanisms for the valuable molecules. Chewing gum would be a better delivery method in humans.

Modification of microneedles using inkjet printing

In this study, biodegradable acid anhydride copolymer microneedles containing quantum dots were fabricated by means of visible light dynamic mask micro-stereolithography-micromolding and inkjet printing. Nanoindentation was performed to obtain the hardness and the Young's modulus of the biodegradable acid anhydride copolymer. Imaging of quantum dots within porcine skin was accomplished by means of multiphoton microscopy. Our results suggest that the combination of visible light dynamic mask micro-stereolithography-micromolding and inkjet printing enables fabrication of solid biodegradable microneedles with a wide range of geometries as well as a wide range of pharmacologic agent compositions.

Pulmonary delivery of peptide YY for food intake suppression and reduced body weight gain in rats

AIMS

Peptide YY (PYY) is an endogenous anorectic gut-secreted peptide that has been shown to suppress appetite in animals and humans, when given by injection. This study tested if needle-free pulmonary delivery of PYY enables food intake suppression and reduced body weight gain in rats. The PYY pharmacokinetics and effects on brain neuropeptide levels were also examined.

METHODS

Rats received single or once-daily 7-day pulmonary administration of saline or PYYs. Food intake and body weight gain were monitored to study the effects of different doses (0.08-0.90 mg/kg) of PYY3-36, PYY1-36 and PYY13-36. Plasma PYY pharmacokinetics were determined via enzyme-linked immunosorbent assay. Changes in orexigenic neuropeptide Y (NPY) and c-Fos protein levels in the hypothalamus arcuate nucleus (ARC) were measured by immunofluorescence microscopy.

RESULTS

PYY3-36 caused dose-dependent and 4- to 6-h food intake suppression following pulmonary delivery. At 0.80 mg/kg, the effect was significant with 35.1 ± 5.7 and 19.7 ± 4.2% suppression at 4 and 6 h, respectively. Repeated administration for 7 days reduced cumulative body weight gain by 39.4 ± 11.0%. PYY1-36, but not PYY13-36, was equipotent to PYY3-36 in food intake suppression. The plasma PYY concentration reached its peak at 10 min following pulmonary delivery with 12-14% of bioavailability. Increased c-Fos and reduced NPY expressions were observed in the hypothalamus ARC, consistent with the magnitude of food intake suppression by each of the PYYs.

CONCLUSIONS

Pulmonary delivery of PYY enabled significant 4- to 6-h food intake suppression via 12-14% of lung absorption and hypothalamic ARC interaction, leading to reduced body weight gain in rats.

Enhanced mucoadhesive capacity of novel co-polymers for oral protein delivery

Graft co-polymer networks have shown promise as devices for oral delivery of proteins. By increasing adhesion of these networks at the delivery site of the upper small intestine by utilizing small covalent chemical linkages caused by the addition of an aldehyde functional group we can make them more viable. These aldehydes bind covalently by way of a condensation reaction with the amines of the amino acids found in the glycoprotein network of the mucus layer of the small intestine to form imines. To investigate the effectiveness of this linkage the co-polymers are prepared in three different percentages of poly(ethylene glycol) (PEG) and aldehyde-modified PEG, and characterized through swelling, release and adhesion testing. The percentages of aldehyde-modified PEG used are 0.06, 0.6 and 3.3%. The swelling results indicate that the formulations with the aldehyde-modified PEG maintained the same pH sensitivity and transition around a pH of 5.8 as those formulations without the aldehyde moiety. Release results indicate that the release of insulin of the most promising 3.3% aldehyde formulation was successful with a release of about 80% after 3 h, which compares favorably with the similar release of the controls done in previous work. Adhesion testing was carried out through the use of a mechanical testing apparatus. Data have been gathered and plotted to give a detachment force (N) versus displacement (m) curve, of which the work of adhesion (μJ) was found by taking the area underneath the curve. Adhesion results indicate an increase to the already present adhesion of the co-polymers due to increased percentages of the aldehyde-modified PEG tethers where the 3.3% formulation showed an increase of 10-30 μJ over both control formulations.

Insulin nanoparticles for transdermal delivery: preparation and physicochemical characterization and in vitro evaluation

AIM

This work is aimed to study the feasibility of insulin nanoparticles for transdermal drug delivery (TDD) using supercritical antisolvent (SAS) micronization process.

METHODS

The influences of various experimental factors on the mean particle size (MPS) of insulin nanoparticles were investigated. Moreover, the insulin nanoparticles obtained were characterized by scanning electron microscopy (SEM), dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric (TG) analyses.

RESULTS

Under optimum conditions, uniform spherical insulin nanoparticles with a MPS of 68.2 +/- 10.8 nm were obtained. The Physicochemical characterization results showed that SAS process has not induced degradation of insulin. Evaluation in vitro showed that insulin nanoparticles were accorded with the Fick's first diffusion law and had a high permeation rate.

CONCLUSION

These results suggest that insulin nanoparticles can have a great potential in TDD systems of diabetes chemotherapy.

Nanoencapsulation of insulin into zirconium phosphate for oral delivery applications

The encapsulation of insulin into different kinds of materials for noninvasive delivery is an important field of study because of the many drawbacks of painful needle and syringe delivery such as physiological stress, infection, and local hypertrophy, among others (Khafagy, E.-S.; et al. Adv. Drug Delivery Rev. 2007, 59 (15), 1521-1546). A stable, robust, nontoxic, and viable noninvasive carrier for insulin delivery is needed. We present a new approach for protein nanoencapsulation using layered zirconium phosphate (ZrP) nanoparticles produced without any preintercalator present. The use of ZrP without preintercalators produces a highly pure material, without any kinds of contaminants, such as the preintercalator, which can be noxious. Cytotoxicity cell viability in vitro experiments for the ZrP nanoparticles show that ZrP is not toxic, or harmful, in a biological environment, as previously reported for rats (Zhu, Z. Y.; et al. Mater. Sci. Forum 2009, 620-622, 307-310). Contrary to previous preintercalator-based methods, we show that insulin can be nanoencapsulated in ZrP if a highly hydrate phase of ZrP with an interlayer distance of 10.3 Å (10.3 Å-ZrP or θ-ZrP) is used as a precursor. The intercalation of insulin into ZrP produced a new insulin-intercalated ZrP phase with about a 27 A interlayer distance, as determined by X-ray powder diffraction, demonstrating a successful nanoencapsulation of the hormone. The in vitro release profile of the hormone after the intercalation was determined and circular dichroism was used to study the hormone stability upon intercalation and release. The insulin remains stable in the layered material, at room temperature, for a considerable amount of time, improving the shell life of the peptidic hormone. This type of material represents a strong candidate to developing a noninvasive insulin carrier for the treatment of diabetes mellitus.

Evaluation of Pistacia lentiscus fatty oil effects on glycemic index, liver functions and kidney functions of New Zealand rabbits

Pistacia lentiscus fatty oil (PLFO) is a well known natural remedy in eastern Algeria folk medicine. It is widely used in the treatment of respiratory disorders and dermal burns. The present study has been carried out to investigate effects of this oil on fasting glucose and some functional parameters of the liver and kidney in white male New Zealand rabbits (Initial mean weight 1.95 Kg). PLFO was applied to tested rabbits (PLFO group) via rectal route, once daily 5-day per week, for six consecutive weeks at the dose of 1 ml/Kg body weight. The same number of animals (n=6) was not treated and served as control (CRL group). The results showed that PLFO was tolerated by rectal route. No significant differences were observed in body weights of the two groups. Biochemical analysis showed that aspartate transaminase (AST) and alanine transaminase (ALT) were significantly decreased in blood plasma at (P< 0.05) and (P< 0.01) respectively in PLFO group (Mann-Whitney test). On the other hand, the fasting glucose level (GLU) was significantly increased (Mann-Whitney test, P< 0.05), while the rest of the tested parameters (Albumin, total proteins, creatinine, urea) was not significantly affected. However, these variations have not biologic signification toxicity. The study concludes that PLFO is tolerable via rectal route; it is safe with no adverse effect on liver functions and renal functions with possible anti-glycogenesis activity.

The use of chitosan-6-mercaptonicotinic acid nanoparticles for oral peptide drug delivery

The aim of this study was to develop a novel nanoparticulate formulation and test its potential for oral peptide drug delivery. Chitosan-6-mercaptonicotinic acid is a novel thiolated chitosan with strong mucoadhesive properties. Nanoparticles were developed by an ionic gellation method. The obtained particles were characterized in terms of mucoadhesion, stability, toxicity, and in vitro release. Human insulin (HI) was chosen as a model peptide drug, incorporated in the particles and orally administered to rats. Human insulin was quantified in the blood by means of ELISA. The size of the obtained particles was in the range of 200-300 nm and the zeta potential was determined to be +8-+23 depending on the amount of thiol groups attached on the polymer. After 3 h of incubation up to 60% of the thiolated chitosan nanoparticles remained attached to the mucosa in contrast to 20% of unmodified chitosan particles. The AUC of HI after oral administration of thiolated chitosan nanoparticles was 4-fold improved compared to unmodified chitosan nanoparticles. Due to these improvements, chitosan-6-mercaptonicotinic acid nanoparticles are promising vehicles for oral delivery of peptide drugs.

Investigation on the synergistic effect of a combination of chemical enhancers and modulated iontophoresis for transdermal delivery of insulin

PURPOSE

The main objective of this study was to assess the flux enhancement of insulin transdermally by utilizing a complex of chemical enhancers in combination with modulated iontophoresis.

METHODS

The experiments were performed on porcine epidermis model under three different circumstances, namely, (a) 1-hour modulated iontophoresis alone; (b) pretreatment with vehicle and chemical enhancer combinations and (c) combination of (a) and (b). The mechanism of action of the enhancers was studied using infra-red spectra by derivative and curve-fitting techniques and Confocal laser scanning microscopy. The efficacy of the optimized combination was tested in vivo in streptozocin-diabetic Wistar rats.

RESULTS

A blend of 1,8 cineole, oleic acid and sodium deoxycholate in propylene glycol : ethanol (7:3) resulted in 45% enhancement, when permeation was performed in combination with iontophoresis as compared to the latter alone. In-depth analysis of infra-red spectra revealed that each of the enhancers acted differentially on lipid-protein domains of the stratum corneum thereby supporting the observed synergism. Movement of fluorescently labeled insulin depicted highlighted follicular regions and paracellular accumulation of the probe after iontophoresis and chemical enhancer treatment respectively. Presence of the fluorescent peptide in these regions 4 hour after treatment with the combination reinforced the results of the permeation studies. Finally the combination of modulated iontophoresis with chemical enhancer blend resulted in lowering of blood glucose for 8 hour in vivo.

CONCLUSIONS

The study proved the applicability of modulated iontophoresis with chemical pretreatment in delivering insulin transdermally.

Nasal and rectal delivery of insulin with chitosan and N-trimethyl chitosan chloride

The aim of this study was to evaluate the ability of TMC, with different degrees of quaternization, to increase insulin absorption in vivo following nasal and rectal administration in rats. Two batches of TMC with different degrees of quaternization (TMC-L, 12.3% quaternized and TMC-H, 61.2% quaternized) and chitosan hydrochloride were administered intranasally (0.25 and 0.5% w/v) and rectally (0.5% w/v) with insulin (4 IU/kg body weight), at a pH of 4.40 and 7.40, in rats. Blood samples were taken over a period of 2 h for measurement of blood glucose levels and plasma insulin levels. Local toxicity evaluation was done by histological examination of the nasal and rectal epithelia. At pH 4.40 all these polymers were able to increase nasal and rectal insulin absorption, compared to the control groups. However, at a pH of 7.40, only TMC-H was able to increase the nasal and rectal absorption of insulin. These results relate to the insolubility of chitosan hydrochloride at neutral pH values, while the charge density of TMC-L is still too low for any significant interaction at pH 7.40. Histological evaluation of the nasal and rectal eptihelia shows no changes in the morphology of the cells after exposure to these polymers. Only slight congestion of the nasal submucosa was observed and all these polymers led to a mild increase in mucus secretion at pH 4.40. Highly quaternized TMC proves to be a potent absorption enhancer in vivo, especially at neutral pH values where chitosan salts are ineffective.

Formulation and in vitro evaluation of highly dispersive insulin dry powder formulations for lung administration

The aim of this work was to develop highly dispersible and dry formulations of insulin for use in dry powder inhalers (DPIs) using high-pressure homogenisation (HPH) and spray-drying. Several formulations were evaluated, including formulations spray-dried without excipients and formulations coated with lipids. A physiological lipid composition based on a mixture of cholesterol and phospholipids was used to form the coating film around micronised drug particles. The production technique and excipients were chosen in order to limit the degradation of the active ingredient. The resulting powders exhibited a size and shape suitable for the deep lung deposition of drugs, and good aerodynamic features were obtained for the different formulations tested, with fine particle fractions between 46% and 63% vs. 11% for raw insulin powder. The presence of a lipid coating of up to 30% (w/w) did not significantly affect the aerodynamic behaviour, and the coated formulations also exhibited a decreased residual moisture content of between 2.3% and 3.7% vs. 4.8% for raw insulin, which should improve the long-term stability of the protein formulations. No degradation of the insulin molecule occurred during the HPH/spray-drying process, as it was shown using an HPLC method (insulin content between 98.4% and 100.5%), and the content in high molecular weight proteins, assessed using a gel filtration method, stayed below 0.4%.

Two-photon polymerization of microneedles for transdermal drug delivery

IMPORTANCE OF THE FIELD

Microneedles are small-scale devices that are finding use for transdermal delivery of protein-based pharmacologic agents and nucleic acid-based pharmacologic agents; however, microneedles prepared using conventional microelectronics-based technologies have several shortcomings, which have limited translation of these devices into widespread clinical use.

AREAS COVERED IN THIS REVIEW

Two-photon polymerization is a laser-based rapid prototyping technique that has been used recently for direct fabrication of hollow microneedles with a wide variety of geometries. In addition, an indirect rapid prototyping method that involves two-photon polymerization and polydimethyl siloxane micromolding has been used for fabrication of solid microneedles with exceptional mechanical properties.

WHAT THE READER WILL GAIN

In this review, the use of two-photon polymerization for fabricating in-plane and out-of-plane hollow microneedle arrays is described. The use of two-photon polymerization-micromolding for fabrication of solid microneedles is also reviewed. In addition, fabrication of microneedles with antimicrobial properties is discussed; antimicrobial microneedles may reduce the risk of infection associated with the formation of channels through the stratum corneum.

TAKE HOME MESSAGE

It is anticipated that the use of two-photon polymerization as well as two-photon polymerization-micromolding for fabrication of microneedles and other microstructured drug delivery devices will increase over the coming years.