Controlled Release Of Insulin Research Articles

Preparation, characterization, and in vivo evaluation of insulin-loaded PLA–PEG microspheres for controlled parenteral drug delivery

Aim: The aim of this study was to prepare insulin-loaded poly(lactic acid)–polyethylene glycol microspheres that could control insulin release at least for 1 week and evaluate their in vivo performance in a streptozotocin-induced diabetic rat model. Methods: The microspheres were prepared using a water-in-oil-in-water double emulsion solvent evaporation technique. Different formulation variables influencing the yield, particle size, entrapment efficiency, and in vitro release profiles were investigated. The pharmacokinetic study of optimized formulation was performed with single dose in comparison with multiple dose of Humulin® 30/70 as a reference product in streptozotocin-induced diabetic rats. Results: The optimized formulation of insulin microspheres was nonporous, smooth-surfaced, and spherical in structure under scanning electron microscope with a mean particle size of 3.07 ×μm and entrapment efficiency of 42.74% of the theoretical amount incorporated. The in vitro insulin release profiles was characterized by a bimodal behavior with an initial burst release because of the insulin adsorbed on the microsphere surface, followed by slower and continuous release corresponding to the insulin entrapped in polymer matrix. Conclusions: The optimized formulation and reference were comparable in the extent of absorption. Consequently, these microspheres can be proposed as new controlled parenteral delivery system.

L’invalidation sélective de la lipase hormonosensible (HSL) dans la cellule bêtapancréatique chez la souris conduit à une hyperglycémie et à un blocage de l’exocytose

Aims/hypothesis The enzyme hormone-sensitive lipase (HSL) is produced and is active in pancreatic beta cells. Because lipids are known to play a crucial role in normal control of insulin release and in the deterioration of beta cell function, as observed in type 2 diabetes, actions of HSL in beta cells may be critical. This notion has been addressed in different lines of HSL knockout mice with contradictory results.

Mesoporous Silica Nanoparticle-Based Double Drug Delivery System for Glucose-Responsive Controlled Release of Insulin and Cyclic AMP

A boronic acid-functionalized mesoporous silica nanoparticle-based drug delivery system (BA-MSN) for glucose-responsive controlled release of both insulin and cyclic adenosine monophosphate (cAMP) was synthesized. Fluorescein isothiocyanate-labeled, gluconic acid-modified insulin (FITC-G-Ins) proteins were immobilized on the exterior surface of BA-MSN and also served as caps to encapsulate cAMP molecules inside the mesopores of BA-MSN. The release of both G-Ins and cAMP was triggered by the introduction of saccharides. The selectivity of FITC-G-Ins release toward a series of carbohydrate triggers was determined to be fructose > glucose > other saccharides. The unique feature of this double-release system is that the decrease of FITC-G-Ins release with cycles can be balanced by the release of cAMP from mesopores of MSN, which is regulated by the gatekeeper effect of FITC-G-Ins. In vitro controlled release of cAMP was studied at two pH conditions (pH 7.4 and 8.5). Furthermore, the cytotoxicity of cAMP-loaded G-Ins-MSN with four different cell lines was investigated by cell viability and proliferation studies. The cellular uptake properties of cAMP-loaded FITC-BA-MSN with and without G-Ins capping were investigated by flow cytometry and fluorescence confocal microscopy. We envision that this glucose-responsive MSN-based double-release system could lead to a new generation of self-regulated insulin-releasing devices.

Novel iron–polysaccharide multilayered microcapsules for controlled insulin release

Iron–polysaccharide complexes have been extensively used for the treatment of iron-deficiency anemia without side-effects. In this study, insulin-loaded microcapsules were prepared via layer-by-layer deposition of oppositely charged Fe 3+ and dextran sulfate (DS) onto the surface of insulin microparticles. Fe 3+ was combined with DS via both electrostatic interaction and chemical complexation process, leading to the formation of a stable complex of Fe 3+/DS. Subsequently, protamine was used as the outermost layer of the insulin-loaded microcapsules to facilitate nuclear delivery. The sufficient charge reversal with successive deposition cycles and successful fabrication of hollow microcapsules provided strong evidence for the growth of (Fe 3+/DS) n multilayer on the surface of microparticles. The experiments showed that the microcapsules successfully entrapped insulin with encapsulation efficiency of 70.56 ± 0.97% and drug loading content of 46.15 ± 0.97%. It was found that the release time and hypoglycemic effect increased as the number of deposited bilayers increased. The insulin-loaded microcapsules significantly improved glucose tolerance from 2 h (free insulin) to even 12 h (insulin-loaded microcapsules with 10 bilayers). Moreover, the microcapsules with protamine as the outermost layer displayed a prolonged and stable glucose-lowering profile over a period of over 6 h compared with Fe 3+ as the outermost layer. These findings indicate that such microcapsules can be a promising approach for the construction of an effective controlled release delivery system of insulin as well as other proteins with short half-life time.

Evolution and Function of the ADP Ribosyl Cyclase/CD38 Gene Family in Physiology and Pathology

The membrane proteins CD38 and CD157 belong to an evolutionarily conserved family of enzymes that play crucial roles in human physiology. Expressed in distinct patterns in most tissues, CD38 (and CD157) cleaves NAD(+) and NADP(+), generating cyclic ADP ribose (cADPR), NAADP, and ADPR. These reaction products are essential for the regulation of intracellular Ca(2+), the most ancient and universal cell signaling system. The entire family of enzymes controls complex processes, including egg fertilization, cell activation and proliferation, muscle contraction, hormone secretion, and immune responses. Over the course of evolution, the molecules have developed the ability to interact laterally and frontally with other surface proteins and have acquired receptor-like features. As detailed in this review, the loss of CD38 function is associated with impaired immune responses, metabolic disturbances, and behavioral modifications in mice. CD38 is a powerful disease marker for human leukemias and myelomas, is directly involved in the pathogenesis and outcome of human immunodeficiency virus infection and chronic lymphocytic leukemia, and controls insulin release and the development of diabetes. Here, the data concerning diseases are examined in view of potential clinical applications in diagnosis, prognosis, and therapy. The concluding remarks try to frame all of the currently available information within a unified working model that takes into account both the enzymatic and receptorial functions of the molecules.

Chitosan-Polycarbophil Interpolyelectrolyte Complex as an Excipient for Bioadhesive Matrix Systems to Control Macromolecular Drug Delivery

The in vitro performance of monolithic matrix systems containing the interpolyelectrolyte complex between chitosan and polycarbophil as excipient was evaluated in terms of their swelling, bioadhesive, and drug release properties. The different matrix systems showed excellent swelling properties without erosion, except for the formulation containing the highest quantity chitosan-polycarbophil complex that exhibited surface erosion in addition to swelling. All the different matrix systems exhibited significantly higher bioadhesive properties than the control group. Furthermore, they showed controlled insulin release without an initial burst release effect. However, only the matrix system that exhibited surface erosion in combination with swelling approached zero-order release.

Effective insulin delivery using starch nanoparticles as a potential trans-nasal mucoadhesive carrier

Mucoadhesive nanoparticles (NPs) could be an exciting prospect for trans-nasal insulin delivery as they have higher surface area to cover highly vascularised nasal absorptive area providing a greater concentration gradient; hence the present study makes an attempt in this regard. Starch NPs were prepared by different crosslinkers using various methodologies and were loaded with insulin. Emulsion crosslinked particles were smaller in size compared to gel method (351 vs 997 nm), and size is further reduced when epichlorohydrin is used as crosslinking agent compared to POCl 3 (194 vs 810 nm). NPs of epichlorohydrin emulsion were further optimized with variable crosslinking to evaluate the effect of degree of crosslinking on in vivo performance. In vitro, a size dependent first order diffusion controlled insulin release with an initial burst effect was found, which is higher with NPs of small size and least crosslinking. Formulation of EE–NPs with Na glycocholate showed a superior hypoglycemic action compared to other NPs formulations containing the former and lysophosphatidylcholine as permeation enhancers. The hypoglycemic effects were more pronounced with medium crosslinked NPs (EE–L2–NPs), which showed a nadir of 70% reduction of plasma glucose and significant effects untill 6 h. The peak plasma insulin level ( C max) of medium crosslinked EE–L2–NPs (258 μIU/ml at 1 h) vindicates the pharmacodynamic effect, which was found to be superior compared to all other formulations. The release rate and higher associated surface area might work in tandem, and could be greatly amplified when combined with permeation enhancers to make starch NPs an efficient trans-nasal mucoadhesive carrier of insulin.

Engineered Enteroendocrine Cells Secrete Insulin in Response to Glucose and Reverse Hyperglycemia in Diabetic Mice

Type 1 diabetes is a metabolic disorder caused by loss of insulin-producing pancreatic beta-cells. Expression of insulin in non-beta-cells to create beta-cell surrogates has been tried to treat type 1 diabetes. Enteroendocrine K cells have characteristics similar to pancreatic beta-cells, such as a glucose-sensing system and insulin-processing proteases. In this study, we genetically engineered an enteroendocrine cell line (STC-1) to express insulin under the control of the glucose-dependent insulinotropic polypeptide promoter. We screened clones and chose one, Gi-INS-7, based on its high production of insulin. Gi-INS-7 cells expressed glucose transporter 2 (GLUT2) and glucokinase (GK) and secreted insulin in response to elevated glucose levels in vitro. To determine whether Gi-INS-7 cells can control blood glucose levels in diabetic mice, we transplanted these cells under the kidney capsule of streptozotocin (STZ)-induced diabetic mice and found that blood glucose levels became normal within 2 weeks of transplantation. In addition, glucose tolerance tests in mice that became normoglycemic after transplantation with Gi-INS-7 cells showed that exogenous glucose was cleared appropriately. These results suggest that engineered K cells may be promising surrogate beta-cells for possible therapeutic use for the treatment of type 1 diabetes.

Palmitic acid increase levels of pancreatic duodenal homeobox-1 and p38/stress-activated protein kinase in islets from rats maintained on a low protein diet

A severe reduction in insulin release in response to glucose is consistently noticed in protein-deprived rats and is attributed partly to the chronic exposure to elevated levels of NEFA. Since the pancreatic and duodenal transcription factor homeobox 1 (PDX-1) is important for the maintenance of beta-cell physiology, and since PDX-1 expression is altered in the islets of rats fed a low protein (LP) diet and that rats show high NEFA levels, we assessed PDX-1 and insulin mRNA expression, as well as PDX-1 and p38/stress activated protein kinase 2 (SAPK2) protein expression, in islets from young rats fed low (6%) or normal (17%; control) protein diets and maintained for 48 h in culture medium containing 5.6 mmol/l glucose, with or without 0.6 mmol/l palmitic acid. We also measured glucose-induced insulin secretion and glucose metabolism. Insulin secretion by isolated islets in response to 16.7 mmol/l glucose was reduced in LP compared with control rats. In the presence of NEFA, there was an increase in insulin secretion in both groups. At 2.8 mmol/l glucose, the metabolism of this sugar was reduced in LP islets, regardless of the presence of this fatty acid. However, when challenged with 16.7 mmol/l glucose, LP and control islets showed a severe reduction in glucose oxidation in the presence of NEFA. The PDX-1 and insulin mRNA were significantly higher when NEFA was added to the culture medium in both groups of islets. The effect of palmitic acid on PDX-1 and p38/SAPK2 protein levels was similar in LP and control islets, but the increase was much more evident in LP islets. These results demonstrate the complex interrelationship between nutrients in the control of insulin release and support the view that fatty acids play an important role in glucose homeostasis by affecting molecular mechanisms and stimulus/secretion coupling pathways.

Rhes expression in pancreatic β-cells is regulated by efaroxan in a calcium-dependent process

The monomeric G-protein Rhes has been described to be present in pancreatic β-cells, and a putative role in the control of insulin release has been proposed. Here, we show that treatment of β-cells with the imidazoline insulin secretagogue efaroxan resulted in a concentration- and time-dependent increase in the expression of Rhes, which peaked after 4h of efaroxan exposure; thereafter, Rhes mRNA levels decreased. Marked stereoselectivity was displayed, with (−)-efaroxan (the selectively insulinotropic enantiomer) being much more effective than (+)-efaroxan at raising Rhes transcript levels. The mechanism by which Rhes gene expression is activated in β-cells appears to require the influx of extracellular calcium and de novo protein synthesis, and is not directly associated with the release of insulin. The present results confirm our earlier proposal that Rhes is an imidazoline-regulated transcript in pancreatic β-cells. Studies to understand the role of Rhes as a regulator of β-cell function are, thus, warranted.

Inhibition of insulin secretion by cerulenin might be due to impaired glucose metabolism

Cerulenin, an inhibitor of protein acylation, has been used as a tool to study the potential role of protein acylation in a variety of activities in different cells, and in stimulus-secretion coupling in pancreatic islets and clonal beta-cells. In the present study we investigated its effects on stimulated insulin secretion, glucose metabolism and utilization, oxygen consumption and ATP levels. In isolated rat pancreatic islets, cerulenin pre-treatment (100 microM) inhibited insulin secretion in response to glucose, and to the non-hydrolysable analogue of leucine, aminobicyclo-[2,2,1]heptane-2-carboxylic acid (BCH). These data are in accord with the hypothesis that protein acylation could be involved in the stimulation of insulin secretion. However, we also found that cerulenin profoundly decreased glucose oxidation, glucose utilization, oxygen consumption and ATP levels. Consequently, decreased metabolism provides an alternative mechanism to inhibition of protein acylation that could explain the inhibition of insulin secretion by cerulenin. Inhibition of insulin secretion by cerulenin can no longer be taken as evidence in favour of a role for protein acylation in the control of insulin release. As protein acylation is known to be involved in the normal functioning of proteins in stimulus-secretion coupling and exocytosis, more direct approaches to understand its role(s) are required.

Neuropeptide FF receptors as therapeutic targets

Neuropeptide FF (NPFF) receptors are G-protein-coupled receptors that belong to the subfamily of RF-amide receptors. Endogenous ligands for these receptors are peptides that display a conserved Arg-Phe-NH 2 (RF-amide) sequence at their carboxyl-terminal end. Several physiological functions have been proposed to be modulated by these receptors, mainly based on in vivo effects of their endogenous peptides or related molecules. These include the modulation of pain, feeding and cardiac function, and the control of insulin release. A wide body of evidence indicates a close relationship between NPFF and opioid systems. In particular, the NPFF system has been shown to display anti-opioid properties, which has led to the hypothesis that functional blockade of NPFF receptors could be a means to avoid the development of pain hypersensitivity and tolerance associated with chronic opioid treatment. This hypothesis was recently confirmed using a potent and selective antagonist of these receptors in a model of discontinuous opioid administration in rats. These results strongly suggest that NPFF receptors might represent a novel therapeutic target for improving the efficacy of opioid treatment of chronic pain.

Defective Renal Dopamine D1 Receptor Function Contributes to Hyperinsulinemia-Mediated Hypertension

Hyperinsulinemia is reported to play a role in hypertension, as abnormalities in blood pressure regulation and sodium handling exist in diabetes mellitus. Kidney dopamine promotes sodium excretion via the activation of renal D1 receptors. Because there is a close relationship between renal D1 receptor function and sodium excretion, it is hypothesized that a defect in this mechanism may contribute to decreased sodium excretion and hypertension during hyperinsulinemia. Renal D1 receptor function was studied in insulin-induced hypertension in male Sprague Dawley rats. Insulin pellets were implanted subcutaneously for controlled insulin release for three weeks; sham rats served as a control. Compared to control rats, insulin pellets increased plasma insulin levels by eight fold and decreased blood glucose by 40%. Insulin also caused a 22 mmHg increase in mean arterial blood pressure compared to control animals. The intravenous infusion of SKF-38393, a D1 receptor agonist, increased sodium excretion in control rats, but SKF-38393 failed to produce natriuresis in hyperinsulinemic animals. Renal proximal tubules from hyperinsulinemic rats had a reduced D1 receptor number, defective receptor-G protein coupling, and blunted SKF-38393 induced Na, K-ATPase inhibition. Insulin seems to reduce D1 receptor expression and coupling to the G-protein, leading to a reduced D1 receptor-mediated Na, K-ATPase inhibition, and a diminished natriuretic response to SKF-38393. These phenomena could account for sodium retention and hypertension associated with hyperinsulinemia.

Neonatal Nutrition and Consequences on Adult Health

After completing this article, readers should be able to: 1. Describe aberrations in adult health that can result from nutrition in the fetal period and in neonatal life. 2. Review the results of studies from human neonates regarding early nutritional interventions designed for “catch-up” growth. 3. Review results from animal studies regarding early nutrition and “programming” for adult metabolic syndrome. 4. Describe some of the potential epigenetic mechanisms that may be responsible for “programming.” 5. Examine methods for preventing growth delays, the consequences of undernutrition, and the metabolic syndrome related to adverse “programming.” One of the traditional goals of neonatal nutrition is to maintain growth within standardized limits. In the preterm infant, growth between the 10th and 90th percentiles of intrauterine rate has been an ideal goal. More recently, maintenance of lean body mass and bone density; prevention of complications such as chronic lung disease, necrotizing enterocolitis, and infection; and optimization of neurodevelopment and adult health through early nutritional programming have become recognized as more meaningful goals than mere somatic growth. To meet these goals, current nutritional practices require thorough scrutiny in terms of quantity and quality (composition) and how they are customized, if not for the individual patient (which would be ideal), at least for subgroups such as those who are small or appropriate for gestational age, sick or healthy, preterm or term, or male or female. Fetal nutrition and development frequently are used as a template for the low-birthweight infant. A large body of literature on the consequences of fetal undernutrition shows that infants born small for gestational age (SGA) not only have short-term morbidity, but long-term morbidity manifested in what has been termed the “metabolic syndrome.” This syndrome includes abdominal obesity, arterial hypertension, and insulin resistance. Other clinical manifestations can be observed, including thyroid dysfunction, hirsutism, ovarian hyperandrogenism and infertility, dyslipidemia (increased …

Inhibition of insulin secretion as a new drug target in the treatment of metabolic disorders.

The pattern of insulin release is crucial for regulation of glucose and lipid haemostasis. Deficient insulin release causes hyperglycemia and diabetes, whereas excessive insulin release can give rise to serious metabolic disorders, such as nesidioblastosis (Persistent Hyperinsulinemic Hypoglycemia of Infancy, PHHI) and might also be closely associated with development of type 2 diabetes and obesity. Type 2 diabetes is characterized by fasting hyperinsulinemia, insulin resistance and impaired insulin release, i.e. reduced first phase insulin release and decreased insulin pulse mass. The beta cell function of patients with type 2 diabetes slowly declines and will ultimately result in beta cell failure and increasing degrees of hyperglycemia. Type 2 diabetes, in combination with obesity and cardiovascular disorders, forms the metabolic syndrome. It has been possible to improve beta cell function and viability in preclinical models of type 1 and type 2 diabetes by reducing insulin secretion to induce beta cell rest. Clinical studies have furthermore indicated that inhibitors of insulin release will be of benefit in treatment or prevention of diabetes and obesity. Pancreatic beta cells secrete insulin in response to increased metabolism and by stimulation of different receptors. The energy status of the beta cell controls insulin release via regulation of open probability of the ATP sensitive potassium (K(ATP)) channels to affect membrane potential and the intracellular calcium concentration [Ca(2+)](i). Other membrane bound receptors and ion channels and intracellular targets that modulate [Ca(2+)](i)will affect insulin release. Thus, insulin release is regulated by e.g. somatostatin receptors, GLP-1 receptors, muscarinic receptors, cholecystokinin receptors and adrenergic receptors. Although the relationship between hyperinsulinemia and certain metabolic diseases has been known for decades, only a few inhibitors of insulin release have been characterized in vitro and in vivo. These include the K(ATP) channel openers diazoxide and NN414 and the somatostatin receptor agonist octreotide.

Evolving potassium channels by means of yeast selection reveals structural elements important for selectivity.

Potassium channels are widely distributed. To serve their physiological functions, such as neuronal signaling, control of insulin release, and regulation of heart rate and blood flow, it is essential that K+ channels allow K+ but not the smaller and more abundant Na+ ions to go through. The narrowest part of the channel pore, the selectivity filter formed by backbone carbonyls of the GYG-containing K+ channel signature sequence, approximates the hydration shell of K+ ions. However, the K+ channel signature sequence is not sufficient for K+ selectivity. To identify structural elements important for K+ selectivity, we randomly mutagenized the G protein-coupled inwardly rectifying potassium channel 3.2 (GIRK2) bearing the S177W mutation on the second transmembrane segment. This mutation confers constitutive channel activity but abolishes K+ selectivity and hence the channel's ability to complement the K+ transport deficiency of Deltatrk1Deltatrk2 mutant yeast. S177W-containing GIRK2 mutants that support yeast growth in low-K+ medium contain multiple suppressors, each partially restoring K+ selectivity to S177W-containing double mutants. These suppressors include mutations in the first transmembrane segment and the pore helix, likely exerting long-range actions to restore K+ selectivity, as well as a mutation of a second transmembrane segment residue facing the cytoplasmic half of the pore, below the selectivity filter. Some of these suppressors also affected channel gating (channel open time and opening frequency determined in single-channel analyses), revealing intriguing interplay between ion permeation and channel gating.

Secrets of insulin and IGF-1 regulation of insulin secretion revealed.

There has been ongoing controversy over the respective roles of insulin-like growth factor-1 receptors and insulin receptors in controlling insulin release from beta-cells of the pancreas. An acute knock-down experiment exploiting small interfering RNA approaches provides a resolution: both are required.

Transmitted beta-cell dysfunction as a cause for type 2-diabetes

The pathways that control insulin release and regulate pancreatic beta-cell mass are crucial on the development of type 2 diabetes mellitus. Maturity-onset diabetes of the young comprises a number of single-gene disorders affecting beta-cell development and/or function. A genetic basis for the more common forms of type 2 diabetes which affect adults in developed as well as many developing countries is less clear cut. It is also characterized by abnormal beta-cell function. Appropriate inbred rodent models are an essential tool for the identification of genes and environmental factors that increase the risk of type 2 diabetes. The informations available from studies in the Goto-Kakizaki (GK) rat are here reviewed in such a perspective. This model was obtained by selective breeding of individuals with mild glucose intolerance from a non-diabetic Wistar rat colony. Heritability of defective beta-mass and beta-cell function in GK model is proposed to reflect the complex interactions of three pathogenic players: (1) three independent loci containing genes causating impaired insulin secretion; (2) gestational metabolic (hyperglycaemic) impairment inducing a programming of endocrine pancreas (decreased beta-cell mass) which is transmitted to the next generation; (3) secondary (acquired) loss of beta-cell differentiation due to chronic exposure to hyperglycaemia (glucotoxicity). A better understanding of the mechanisms involved in the failure of beta-cell function in the GK model will lead to identification of new therapeutic targets for both the prevention and treatment of type 2 diabetes.

Sustained release of insulin from sodium hyaluronate based dry powder formulations after pulmonary delivery to beagle dogs

Hyaluronic acid (HA) and recombinant human insulin were co-spray dried to form a dry powder suitable for inhalation (Mass Median Aerodynamic Diameter, MMAD=1 to 4 μm). Insulin systemic levels and corresponding glucose levels were monitored following administration of the microparticles to the lungs of male Beagle dogs. Release kinetics were modified by addition of excess zinc ions (Zn 2+) or hydroxypropyl cellulose (HPC). HA formulations containing insulin (10%w/w) were found to extend the mean residence time (MRT) and terminal half-life ( t 1 2 ) when compared to spray dried pure insulin. Addition of Zn 2+ also improved MRT (>9 fold), AUC/dose (2.5 fold) and T max (by a factor of 3) when compared to spray dried pure insulin. Addition of HPC improved MRT (>7 fold), AUC/dose (5 fold) and T max (by a factor of 3) when compared to spray dried pure insulin. Our results demonstrate the potential of HA-based dry powder drug delivery systems in the pulmonary controlled release of insulin.

Retention and release behavior of insulin in chitosan gel beads

Chitosan (CS) gel beads were prepared in a 10% (w/v) aqueous amino acid solution (pH 9.0) as a vehicle for delivering peptide and protein drugs. CS gel beads with a weight-average molecular weight of (16-280) ×104 were employed in this study. Preparation of the CS gel beads was affected by properties such as molecular weight and degree of deacetylation. Insulin, which is commonly used to assess protein drug delivery, was retained in the CS gel beads. Drug release from the CS gel beads was governed by diffusion of drug from the gel matrix. Sustained release of insulin from the CS gel beads was observed, despite the fact that insulin is a comparatively water-soluble drug, because insulin formed a complex with CS. Modification of the CS gel matrix by chondroitin sulfate inhibited release of insulin from the gel beads. CS gel beads were implanted into air pouches prepared subcutaneously on the dorsal surface of diabetic mice in order to investigate the efficacy of insulin retained in the CS beads. Blood glucose levels were found to be reduced after implantation of CS gel beads retaining insulin. CS gel beads may possibly improve the stability and control of insulin release. These observations indicate that CS beads are a promising biocompatible and biodegradable vehicle for peptide and protein delivery.