Development of glucose-triggered pH-sensitive liposomes for a potential insulin delivery

NANO-BIOTECHNOLOGY AND ITS INNOVATIVE PERSPECTIVE IN DIABETES MANAGEMENT

Diabetes occurs due to the imbalance of glucose in the body known as glucose homeostasis, thus leading to metabolic changes in the body. The two stages hypoglycemia or hyperglycemia classify diabetes into various categories. Various bio-nanotechnological approaches are coupled up with nano particulates, polymers, liposome, various gold plated and solid lipid particulates, regulating transcellular transport, non specific cellular uptake, and paracellular transport, leading to oral, trans-dermal , pulmonary, buccal , nasal , specific gene oriented administration to avoid the patient's non compliance with the parental routes of administration. Phytochemicals are emerging strategies for the future prospects of diabetes management.

Glucose-Responsive Insulin and Delivery Systems: Innovation and Translation

Type 1 and advanced type 2 diabetes treatment involves daily injections or continuous infusion of exogenous insulin aimed at regulating blood glucose levels in the normoglycemic range. However, current options for insulin therapy are limited by the risk of hypoglycemia and are associated with suboptimal glycemic control outcomes. Therefore, a range of glucose-responsive components that can undergo changes in conformation or show alterations in intermolecular binding capability in response to glucose stimulation has been studied for ultimate integration into closed-loop insulin delivery or "smart insulin" systems. Here, an overview of the evolution and recent progress in the development of molecular approaches for glucose-responsive insulin delivery systems, a rapidly growing subfield of precision medicine, is presented. Three central glucose-responsive moieties, including glucose oxidase, phenylboronic acid, and glucose-binding molecules are examined in detail. Future opportunities and challenges regarding translation are also discussed.

Glucose-responsive insulin release: Analysis of mechanisms, formulations, and evaluation criteria

Diabetes mellitus has become one of the biggest medical challenges affecting millions of people globally. Alternative treatments for diabetes are currently being intensively investigated to improve the treatment efficacy and life qualities for diabetic patients. Glucose-responsive insulin release (GRIR) systems have exhibited tremendous potential to improve the normal glycemic control and to reduce the incidence of hyperglycemia and hypoglycemia, which further reduces potential complications in diabetic patients. In a given GRIR drug formulation, accuracy, response time, and reversibility of the GRIR functions are three key features enabling potential seamless control of blood glucose level. Nevertheless, there is significant challenge preventing current GRIR formulations from achieving them. This review article analyzes the most updated literature and provides insights on the impact of GRIR mechanisms, and formulations on these key features, and the relevant in vitro and in vivo evaluation methods to test these functions.

Alizarin Complexone Functionalized Mesoporous Silica Nanoparticles: A Smart System Integrating Glucose-Responsive Double-Drugs Release and Real-Time Monitoring Capabilities

The outstanding progress of nanoparticles-based delivery systems capable of releasing hypoglycemic drugs in response to glucose has dramatically changed the outlook of diabetes management. However, the developed glucose-responsive systems have not offered real-time monitoring capabilities for accurate quantifying hypoglycemic drugs released. In this study, we present a multifunctional delivery system that integrates both delivery and monitoring issues using glucose-triggered competitive binding scheme on alizarin complexone (ALC) functionalized mesoporous silica nanoparticles (MSN). In this system, ALC is modified on the surface of MSN as the signal reporter. Gluconated insulin (G-Ins) is then introduced onto MSN-ALC via benzene-1,4-diboronic acid (BA) mediated esterification reaction, where G-Ins not only blocks drugs inside the mesopores but also works as a hypoglycemic drug. In the absence of glucose, the sandwich-type boronate ester structure formed by BA binding to the diols of ALC and G-Ins remains intact, resulting in an fluorescence emission peak at 570 nm and blockage of pores. Following a competitive binding, the presence of glucose cause the dissociation of boronate ester between ALC and BA, which lead to the pores opening and disappearance of fluorescence. As proof of concept, rosiglitazone maleate (RSM), an insulin-sensitizing agent, was doped into the MSN to form a multifunctional MSN (RSM@MSN-ALC-BA-Ins), integrating with double-drugs loading, glucose-responsive performance, and real-time monitoring capability. It has been demonstrated that the glucose-responsive release behaviors of insulin and RSM in buffer or in human serum can be quantified in real-time through evaluating the changes of fluorescence signal. We believe that this developed multifunctional system can shed light on the invention of a new generation of smart nanoformulations for optical diagnosis, individualized treatment, and noninvasive monitoring of diabetes management.

Coimmobilization of gluconolactonase with glucose oxidase for improvement in kinetic property of enzymatically induced volume collapse in ionic gels

The object of this paper is to provide an enzymatic means to attain faster swelling or shrinking kinetics of polyelectrolyte gels that undergo volume phase transition as an immobilized enzyme reaction sets in. For this, we studied the coimmobilization of gluconolactonase (GL) with glucose oxidase (GOD). A gel used was in the shape of a small cylinder (several hundred micrometers in diameter) and composed of a lightly cross-linked copolymer of N-isopropylacrylamide and acrylic acid. GL was isolated from Aspergillus niger and purified about 100-fold. It was found that in a substrate solution containing glucose, the gel with the coimmobilized GL and GOD shrinks very rapidly. The shrinking rate was identical to that of the enzyme-free gel that undergoes a shrinking transition in response to a sudden pH change of the outer medium from 7 to 5. This indicates the rate-limiting step in the shrinking process to be diffusion of the networks, but not the enzyme reaction. In the gel with singly immobilized GOD, a very slow shrinking was observed because the process is governed by the enzyme reaction. These results were discussed in full in connection with an enzymatically induced decrease in pH within and in the vicinity of the gel phase. As a result, it has become apparent that the faster shrinking kinetics in the coimmobilized enzyme system is attained by the GL-catalyzed hydrolysis of D-glucono-delta-lactone resulting from the oxidation of glucose with GOD.

pH-sensitive, serum-stable and long-circulating liposomes as a new drug delivery system

The lack of stability in blood and the short blood circulation time of pH-sensitive liposomes are major drawbacks for their application in-vivo. To develop pH-sensitive, serum-stable and long-circulating liposomes as drug delivery systems, the impact of polyethylene glycol-derived phosphatidylethanolamine (DSPE-PEG) on the properties of pH-sensitive liposomes was investigated. pH-sensitive liposomes were prepared with dioleoylphosphatidylethanolamine (DOPE) and oleic acid (DOPE/oleic acid liposome) or DOPE and 1,2-dipalmitoylsuccinylglycerol (DOPE/DPSG liposome). The inclusion of DSPE-PEG enhanced the serum stability of both DOPE/oleic acid and DOPE/DPSG liposomes, but also shifted the pH-response curve of pH-sensitive liposomes to more acidic regions and reduced the maximum leakage percentage. The impact of DSPE-PEG, however, was much lower in the DOPE/DPSG liposomes than in the DOPE/oleic acid liposomes. In tumour tissue homogenates, where the pH is lower than normal healthy tissues, the pH-sensitive DOPE/DPSG liposomes released the entrapped markers rapidly, in comparison with pH-insensitive dipalmitoylphosphatidylcholine/cholesterol/DSPE-PEG liposomes. Moreover, the release rate was not affected by the content of DSPE-PEG. The blood circulation time of methotrexate incorporated in DOPE/UDPSG liposomes was significantly prolonged with increasing content of DSPE-PEG. Taken together, the liposomes composed of DOPE, DPSG and DSPE-PEG (up to 5%) were pH sensitive, plasma stable and had a long circulation time in the blood. The complete destabilization of the liposomes at tumour tissues suggests that the liposomes might be useful for the targeted delivery of drugs such as anticancer agents.

Enzymes inside lipid vesicles: preparation, reactivity and applications

There are a number of methods that can be used for the preparation of enzyme-containing lipid vesicles (liposomes) which are lipid dispersions that contain water-soluble enzymes in the trapped aqueous space. This has been shown by many investigations carried out with a variety of enzymes. A review of these studies is given and some of the main results are summarized. With respect to the vesicle-forming amphiphiles used, most preparations are based on phosphatidylcholine, either the natural mixtures obtained from soybean or egg yolk, or chemically defined compounds, such as DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) or POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine). Charged enzyme-containing lipid vesicles are often prepared by adding a certain amount of a negatively charged amphiphile (typically dicetylphosphate) or a positively charged lipid (usually stearylamine). The presence of charges in the vesicle membrane may lead to an adsorption of the enzyme onto the interior or exterior site of the vesicle bilayers. If (i) the high enzyme encapsulation efficiencies; (ii) avoidance of the use of organic solvents during the entrapment procedure; (iii) relatively monodisperse spherical vesicles of about 100 nm diameter; and (iv) a high degree of unilamellarity are required, then the use of the so-called 'dehydration-rehydration method', followed by the 'extrusion technique' has shown to be superior over other procedures. In addition to many investigations in the field of cheese production--there are several studies on the (potential) medical and biomedical applications of enzyme-containing lipid vesicles (e.g. in the enzyme-replacement therapy or for immunoassays)--including a few in vivo studies. In many cases, the enzyme molecules are expected to be released from the vesicles at the target site, and the vesicles in these cases serve as the carrier system. For (potential) medical applications as enzyme carriers in the blood circulation, the preparation of sterically stabilized lipid vesicles has proven to be advantageous. Regarding the use of enzyme-containing vesicles as submicrometer-sized nanoreactors, substrates are added to the bulk phase. Upon permeation across the vesicle bilayer(s), the trapped enzymes inside the vesicles catalyze the conversion of the substrate molecules into products. Using physical (e.g. microwave irradiation) or chemical methods (e.g. addition of micelle-forming amphiphiles at sublytic concentration), the bilayer permeability can be controlled to a certain extent. A detailed molecular understanding of these (usually) submicrometer-sized bioreactor systems is still not there. There are only a few approaches towards a deeper understanding and modeling of the catalytic activity of the entrapped enzyme molecules upon externally added substrates. Using micrometer-sized vesicles (so-called 'giant vesicles') as simple models for the lipidic matrix of biological cells, enzyme molecules can be microinjected inside individual target vesicles, and the corresponding enzymatic reaction can be monitored by fluorescence microscopy using appropriate fluorogenic substrate molecules.

Gene medicine : a new field of molecular medicine

Gene therapy has emerged as a new concept of therapeutic strategies to treat diseases which do not respond to the conventional therapies. The principle of gene therapy is to introduce genetic materials into patient cells to produce therapeutic proteins in these cells. Gene therapy is now at the stage where a number of dinical trials have been carried out to patients with gene-deficiency disease or cancer. Genetic materials for gene therapy are generally composed of gene expression system and gene delivery system. For the dinical application of gene therapy in a way which conventional drugs are used, researches have been focused on the design of gene delivery system which can offer high transfection efficiency with minimal toxicity. Currently, viral delivery systems generally provide higher transfection efficiency compared with non-viral delivery systems while non-viral delivery systems are less toxic, less immunogenic and manufacturable in large scale compared with viral systems. Recently, novel strategies towards the design of new non-viral delivery system, combination of viral and non-viral delivery systems and targeted delivery system have been extensively studied. The continued effort in this area will lead us to develop gene medicine as 'gene as a drug' in the near future.

Pharmacodynamics of insulin in polyethylene glycol-coated liposomes

To reduce the injection frequency and toxicity of intravenously administered protein drugs, it is necessary to develop safe and sustained injectable delivery systems. In this study, to evaluate liposomes as safe and sustained injectable delivery systems of proteins, we chose insulin as a model protein drug and tested its incorporation efficiency and pharmacodynamics in various liposomes with and without polyethylene glycol (PEG)-derivatized phospholipid. The liposomes coated with PEG showed 3-fold higher efficiency of insulin incorporation than did the liposomes without PEG. Moreover, among the liposomes coated with PEG, dipalmitoylphosphocholine (DPPC) liposomes showed higher incorporation efficiency than did dimyristoylphosphocholine (DMPC) liposomes. For pharmacodynamic study, insulin (2 IU/kg) was administered in various formulations, such as insulin alone in phosphate-buffered saline and insulin in the DPPC liposomes with and without PEG, to streptozotocin-treated diabetic rats. The pharmacodynamics of insulin alone, however, could not be measured due to the immediate death of rats caused by hypoglycemic shock. In contrast, all the rats treated with liposomal insulin survived, probably by the sustained release of insulin from liposomes. Pharmacodynamics of liposomal insulin showed that PEG-coated liposomes induced the lowest level of blood glucose-the nadir-1 h later than did the liposomes without PEG. These results indicate that PEG-coated liposomes could be developed as a relatively safe and sustained injectable delivery system for insulin with improved incorporation efficiency. Moreover, it is suggested that the liposomes coated with PEG might have a potential as safe injectable delivery systems for other protein and peptide drugs.

The delivery of insulin from aqueous and non-aqueous reservoirs governed by a glucose sensitive gel membrane

A self regulating delivery device, responsive to glucose, has been shown to operate successfully in vitro. This comprises a gel membrane which determines the delivery rate of insulin from a reservoir. The gel consists of a synthetic polysucrose and the lectin, concanavalin A. The mechanism is one of displacement of the branched polysaccharide from the lectin receptors by incoming glucose. The gel loses its high viscosity as a result but reforms on removal of glucose, thus providing the switch controlling the drug diffusion rate. The drug does not require to be chemically modified and thus the device is adaptable to other anti-hyperglycaemic drugs. However, results here indicate that the molecular weight of the solute may be an important parameter. Others include path length, gel formulation and temperature. It had been hypothesised that the reversal might be improved by the use of a non-aqueous reservoir of insulin. However, with the use of insulin, the switching off was found to be superior to that found with other test solutes used in previous studies, irrespective of the reservoir solvent. The advantages in the use of the non-aqueous system include, however, more reproducibility in the magnitude of response and a reduced temperature sensitivity.