A recombinant human glucagon-like peptide (GLP)-1-albumin protein (albugon) mimics peptidergic activation of GLP-1 receptor-dependent pathways coupled with satiety, gastrointestinal motility, and glucose homeostasis

A recombinant polypeptide extends the in vivo half-life of peptides and proteins in a tunable manner

Increasing the in vivo residence times of protein therapeutics could decrease their dosing frequencies. We show that genetic fusion of an unstructured recombinant polypeptide of 864 amino acids, called XTEN, to a peptide or protein provides an apparently generic approach to extend plasma half-life. Allometric scaling suggests that a fusion of XTEN to the exenatide peptide should increase exenatide half-life in humans from 2.4 h to a projected time of 139 h. We confirmed the biological activity of the exenatide-XTEN fusion in mice. As extended stability might exacerbate undesirable side effects in some cases, we show that truncating the XTEN sequence can regulate plasma half-life. XTEN lacks hydrophobic amino acid residues that often contribute to immunogenicity and complicate manufacture. Based on data on XTEN fusions to exenatide, glucagon, GFP and human growth hormone, we expect that XTEN will enable dosing of otherwise rapidly cleared protein drugs at up to monthly intervals in humans.

Glucagon-like peptide 1 receptor stimulation as a means of neuroprotection

Glucagon-like peptide 1 (GLP-1) is a relatively recently discovered molecule originating in the so-called L-cells of the intestine. The peptide has insulinotrophic properties and it is this characteristic that has predominantly been investigated. This has led to the use of the GLP-1-like peptide exendin-4 (EX-4), which has a much longer plasma half-life than GLP-1 itself, being used in the treatment of type II diabetes. The mode of action of this effect appears to be a reduction in pancreatic apoptosis, an increase in beta cell proliferation or both. Thus, the effects of GLP-1 receptor stimulation are not based upon insulin replacement but an apparent repair of the pancreas. Similar data suggest that the same effects may occur in other peripheral tissues. More recently, the roles of GLP-1 and EX-4 have been studied in nervous tissue. As in the periphery, both peptides appear to promote cellular growth and reduce apoptosis. In models of Alzheimer's disease, Parkinson's disease and peripheral neuropathy, stimulation of the GLP-1 receptor has proved to be highly beneficial. In the case of Parkinson's disease this effect is evident after the neurotoxic lesion is established, suggesting real potential for therapeutic use. In the present review we examine the current status of the GLP-1 receptor and its potential as a therapeutic target.

Lesions of area postrema and subfornical organ alter exendin-4-induced brain activation without preventing the hypophagic effect of the GLP-1 receptor agonist

The mechanism and route whereby glucagon-like peptide 1 (GLP-1) receptor agonists, such as GLP-1 and exendin-4 (Ex-4), access the central nervous system (CNS) to exert their metabolic effects have yet to be clarified. The primary objective of the present study was to investigate the potential role of two circumventricular organs (CVOs), the area postrema (AP) and the subfornical organ (SFO), in mediating the metabolic and CNS-stimulating effects of Ex-4. We demonstrated that electrolytic ablation of the AP, SFO, or AP + SFO does not acutely prevent the anorectic effects of Ex-4. AP + SFO lesion chronically decreased food intake and body weight and also modulated the effect of Ex-4 on the neuronal activation of brain structures involved in the hypothalamic-pituitary-adrenal axis and glucose metabolism. The results of the study also showed that CVO lesions blunted Ex-4-induced expression of c-fos mRNA (a widely used neuronal activity marker) in 1) limbic structures (bed nucleus of the stria terminalis and central amygdala), 2) hypothalamus (paraventricular hypothalamic nucleus, supraoptic nucleus, and arcuate nucleus), and 3) hindbrain (lateral and lateral-external parabrachial nucleus, medial nucleus of the solitary tract, and ventrolateral medulla). In conclusion, although the present results do not support a role for the CVOs in the anorectic effect induced by a single injection of Ex-4, they suggest that the CVOs play important roles in mediating the actions of Ex-4 in the activation of CNS structures involved in homeostatic control.

Pleiotropic actions of the incretin hormones

The insulin secretory response to a meal results largely from glucose stimulation of the pancreatic islets and both direct and indirect (autonomic) glucose-dependent stimulation by incretin hormones released from the gastrointestinal tract. Two incretins, Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), have so far been identified. Localization of the cognate G protein-coupled receptors for GIP and GLP-1 revealed that they are present in numerous tissues in addition to the endocrine pancreas, including the gastrointestinal, cardiovascular, central nervous and autonomic nervous systems (ANSs), adipose tissue, and bone. At these sites, the incretin hormones exert a range of pleiotropic effects, many of which contribute to the integration of processes involved in the regulation of food intake, and nutrient and mineral processing and storage. From detailed studies at the cellular and molecular level, it is also evident that both incretin hormones act via multiple signal transduction pathways that regulate both acute and long-term cell function. Here, we provide an overview of current knowledge relating to the physiological roles of GIP and GLP-1, with specific emphasis on their modes of action on islet hormone secretion, β-cell proliferation and survival, central and autonomic neuronal function, gastrointestinal motility, and glucose and lipid metabolism. However, it is emphasized that despite intensive research on the various body systems, in many cases there is uncertainty as to the pathways by which the incretins mediate their pleiotropic effects and only a rudimentary understanding of the underlying cellular mechanisms involved, and these are challenges for the future.

Strategies to prolong the plasma residence time of peptidedrugs

Well established as well as recently developed strategies to prevent the fast clearance of peptide drugs from the circulation are reviewed.

Differences in the central anorectic effects of glucagon-like peptide-1 and exendin-4 in rats

OBJECTIVE

Glucagon-like peptide (GLP)-1 is a regulatory peptide synthesized in the gut and the brain that plays an important role in the regulation of food intake. Both GLP-1 and exendin (Ex)-4, a long-acting GLP-1 receptor (GLP-1r) agonist, reduce food intake when administered intracerebroventricularly, whereas Ex4 is much more potent at suppressing food intake when given peripherally. It has generally been hypothesized that this difference is due to the relative pharmacokinetic profiles of GLP-1 and Ex4, but it is possible that the two peptides control feeding via distinct mechanisms.

RESEARCH DESIGN AND METHODS

In this study, the anorectic effects of intracerebroventricular GLP-1 and Ex4, and the sensitivity of these effects to GLP-1r antagonism, were compared in rats. In addition, the GLP-1r dependence of the anorectic effect of intracerebroventricular Ex4 was assessed in GLP-1r(-/-) mice.

RESULTS

Intracerebroventricular Ex4 was 100-fold more potent than GLP-1 at reducing food intake, and this effect was insensitive to GLP-1r antagonism. However, GLP-1r antagonists completely blocked the anorectic effect of intraperitoneal Ex4. Despite the insensitivity of intracerebroventricular Ex4 to GLP-1r antagonism, intracerebroventricular Ex4 failed to reduce food intake in GLP-1r(-/-) mice.

CONCLUSIONS

These data suggest that although GLP-1rs are required for the actions of Ex4, there appear to be key differences in how GLP-1 and Ex4 interact with central nervous system GLP-1r and in how Ex4 interacts with GLP-1r in the brain versus the periphery. A better understanding of these unique differences may lead to expansion and/or improvement of GLP-1-based therapies for type 2 diabetes and obesity.

Safety, tolerability, pharmacokinetics and pharmacodynamics of albiglutide, a long-acting GLP-1-receptor agonist, in Japanese subjects with type 2 diabetes mellitus

OBJECTIVE

To investigate safety, pharmacokinetics and pharmacodynamics of albiglutide in Japanese subjects with type 2 diabetes mellitus.

RESEARCH DESIGN AND METHODS

This randomized, single-blind, placebo-controlled study examined four doses/dose schedules of subcutaneously (sc) administered albiglutide: 15 mg weekly, 30 mg weekly, 50 mg biweekly, and 100 mg monthly (cohorts A-D, respectively) in 40 subjects (mean age 54.5 years, mean range of glycosylated hemoglobin [HbA(1c)] 7.1-8.3%), over a 4-week treatment period.

MAIN OUTCOME MEASURES

Safety parameters, including adverse events, clinical laboratory tests, vital signs, and 12-lead electrocardiogram; plasma concentrations of albiglutide; and pharmacodynamic parameters, including change from baseline and weighted mean AUC(0-4) in plasma glucose, glucagon, insulin, and C-peptide levels.

CLINICAL TRIAL REGISTRATION

NCT00530309.

RESULTS

At day 29, mean changes from baseline (vs. placebo) in fasting plasma glucose (FPG) were: cohort A, -1.92 mmol/L; B, -1.98 mmol/L; C, -1.74 mmol/L; D, -0.73 mmol/L; changes in weighted mean glucose AUC(0-4) were: cohort A, -2.86 mmol/L; B, -3.58 mmol/L; C, -2.51 mmol/L; D, -1.44 mmol/L (for FPG and AUC(0-4), all p < or = 0.002 except 100 mg sc monthly, p = NS); changes from baseline HbA(1c) were: cohort A, -0.58%; B, -0.57%; C, -0.63%; and D, -0.51% (all p < 0.03). Albiglutide sc had a median half-life of 5.3 days, plasma apparent systemic clearance of 68.7 mL/h, and apparent volume of distribution of 12.6 L. Incidence of adverse events was low and comparable to sc placebo in all albiglutide treatment arms except 100 mg sc monthly, where gastrointestinal (GI) adverse events were most common. Limitations of this study include the small sample size, short treatment duration, and enrollment of predominantly male subjects.

CONCLUSIONS

Weekly and biweekly albiglutide improved glycemic control and were well-tolerated in Japanese subjects with type 2 diabetes mellitus.

Biological activity of EXf, a peptide analogue of exendin-4

Exendin-4 is an incretin mimetic that has been developed for the treatment of patients with type 2 diabetes. EXf is an available carboxy-terminal truncated fragment of exendin-4 with two amino acid substitutions. The purpose of these studies was to evaluate the biological activity of EXf. After a single subcutaneous injection, EXf significantly decreased plasma glucose concentration and glucose excursion following the administration of an oral glucose challenge both in non-diabetic (ICR), monosodium l-glutamate induced insulin resistance (MSG-IR) and diabetic KK-ay mice. Meanwhile, EXf resulted in an increase of first-phase insulin secretion in normal mice and KK-ay mice following the glucose challenge. EXf was also shown to inhibit small intestinal transit in rodent models. EXf activated the cAMP response element (CRE) of the rat insulin I gene promoter (RIP1) GFP-construct in a dose-dependent manner in the cultured mouse insulinoma cell line, termed NIT-1, and this agonist activity was blocked by the glucagon-like peptide 1 (GLP-1) receptor antagonist exendin(9-39). In summary, EXf, an analogue of exendin-4, has agonist activity to GLP-1 receptor in vitro and glucoregulatory activities in vivo, thus it can be considered as a new candidate for the treatment of type 2 diabetes.

Poly-GLP-1, a novel long-lasting glucagon-like peptide-1 polymer, ameliorates hyperglycaemia by improving insulin sensitivity and increasing pancreatic beta-cell proliferation

AIM

The clinical value of glucagon-like peptide-1 (GLP-1) is restricted because of its short half-life. To overcome this limitation, a new polymer of GLP-1 was developed by prodrug strategy, termed Poly-GLP-1, and its pharmacological properties were investigated.

METHODS

The in vitro release kinetics of GLP-1 from Poly-GLP-1 was analysed by Western blot. Plasma GLP-1 levels following a single administration of Poly-GLP-1 were determined by enzyme-linked immunosorbent assay. The in vitro effects of Poly-GLP-1 were evaluated using isolated pancreatic islets. The acute effects on glycaemic control and food intake were investigated in C57BL/6J mice s.c. administered with Poly-GLP-1. The chronic effects of Poly-GLP-1 on glycaemic control were further assessed in C57BL/6J and db/db mice treated twice daily for 6 weeks.

RESULTS

Pro-GLP-1 dose dependently increased insulin secretion and decreased glucose, but did not exhibit the insulinotropic action in isolated pancreatic islets without plasma. The glucose-lowering actions of Poly-GLP-1 (3 nmol/kg) remained no less than 12 h after a single injection. Poly-GLP-1 caused a durable restoration of glycaemic control, food intake and body weight gain in db/db mice following 6-week administration. The chronic treatment with Poly-GLP-1 improved glucose tolerance and insulin sensitivity and increased beta-cell mass and proliferation in db/db mice. There was little effect on normal mice treated in the same manner.

CONCLUSIONS

Our results indicated that Poly-GLP-1, a novel GLP-1 polymer, has long-lasting and potent effects on glycaemic control in vivo, and these beneficial effects may be because of improvement of insulin sensitivity and promotion of islet growth and function.

Potential of albiglutide, a long-acting GLP-1 receptor agonist, in type 2 diabetes: a randomized controlled trial exploring weekly, biweekly, and monthly dosing

OBJECTIVE

To evaluate the efficacy, safety, and tolerability of incremental doses of albiglutide, a long-acting glucagon-like peptide-1 receptor agonist, administered with three dosing schedules in patients with type 2 diabetes inadequately controlled with diet and exercise or metformin monotherapy.

RESEARCH DESIGN AND METHODS

In this randomized multicenter double-blind parallel-group study, 356 type 2 diabetic subjects with similar mean baseline characteristics (age 54 years, diabetes duration 4.9 years, BMI 32.1 kg/m(2), A1C 8.0%) received subcutaneous placebo or albiglutide (weekly [4, 15, or 30 mg], biweekly [15, 30, or 50 mg], or monthly [50 or 100 mg]) or exenatide twice daily as an open-label active reference (per labeling in metformin subjects only) over 16 weeks followed by an 11-week washout period. The main outcome measure was change from baseline A1C of albiglutide groups versus placebo at week 16.

RESULTS

Dose-dependent reductions in A1C were observed within all albiglutide schedules. Mean A1C was similarly reduced from baseline by albiglutide 30 mg weekly, 50 mg biweekly (every 2 weeks), and 100 mg monthly (-0.87, -0.79, and -0.87%, respectively) versus placebo (-0.17%, P < 0.004) and exenatide (-0.54%). Weight loss (-1.1 to -1.7 kg) was observed with these three albiglutide doses with no significant between-group effects. The incidence of gastrointestinal adverse events in subjects receiving albiglutide 30 mg weekly was less than that observed for the highest biweekly and monthly doses of albiglutide or exenatide.

CONCLUSIONS

Weekly albiglutide administration significantly improved glycemic control and elicited weight loss in type 2 diabetic patients, with a favorable safety and tolerability profile.

Minireview: finding the sweet spot: peripheral versus central glucagon-like peptide 1 action in feeding and glucose homeostasis

Glucagon-like peptide 1 (GLP-1) is both a gut-derived hormone and a neurotransmitter synthesized in the brain. Early reports suggested that GLP-1 acts in the periphery to promote insulin secretion and affect glucose homeostasis, whereas central GLP-1 reduces food intake and body weight. However, current research indicates that in fact, GLP-1 in each location plays a role in these functions. This review summarizes the evidence for involvement of peripheral and brain GLP-1 in food intake regulation and glucose homeostasis and proposes a model for the coordinated actions of GLP-1 at multiple sites.

Chemoenzymatic synthesis of glycosylated glucagon-like peptide 1: effect of glycosylation on proteolytic resistance and in vivo blood glucose-lowering activity

Glucagon-like peptide 1 (7-36) amide (GLP-1) has been attracting considerable attention as a therapeutic agent for the treatment of type 2 diabetes. In this study, we applied a glycoengineering strategy to GLP-1 to improve its proteolytic stability and in vivo blood glucose-lowering activity. Glycosylated analogues with N-acetylglucosamine (GlcNAc), N-acetyllactosamine (LacNAc), and alpha2,6-sialyl N-acetyllactosamine (sialyl LacNAc) were prepared by chemoenzymatic approaches. We assessed the receptor binding affinity and cAMP production activity in vitro, the proteolytic resistance against dipeptidyl peptidase-IV (DPP-IV) and neutral endopeptidase (NEP) 24.11, and the blood glucose-lowering activity in diabetic db/db mice. Addition of sialyl LacNAc to GLP-1 greatly improved stability against DPP-IV and NEP 24.11 as compared to the native type. Also, the sialyl LacNAc moiety extended the blood glucose-lowering activity in vivo. Kinetic analysis of the degradation reactions suggested that the sialic acid component played an important role in decreasing the affinity of peptide to DPP-IV. In addition, the stability of GLP-1 against both DPP-IV and NEP24.11 incrementally improved with an increase in the content of sialyl LacNAc in the peptide. The di- and triglycosylated analogues with sialyl LacNAc showed greatly prolonged blood glucose-lowering activity of up to 5 h after administration (100 nmol/kg), although native GLP-1 showed only a brief duration. This study is the first attempt to thoroughly examine the effect of glycosylation on proteolytic resistance by using synthetic glycopeptides having homogeneous glycoforms. This information should be useful for the design of glycosylated analogues of other bioactive peptides as desirable pharmaceuticals.

Clinical review: The extrapancreatic effects of glucagon-like peptide-1 and related peptides

CONTEXT

Glucagon-like peptide-1 (GLP-1) 7-36 amide, an insulinotropic hormone released from the intestinal L cells in response to nutrient ingestion, has been extensively reviewed with respect to beta-cell function. However GLP-1 receptors are abundant in many other tissues. Thus, the function of GLP-1 is not limited to the islet cells, and it has regulatory actions on many other organs.

EVIDENCE ACQUISITION

A review of published, peer-reviewed medical literature (1987 to September 2008) on the extrapancreatic actions of GLP-1 was performed.

EVIDENCE SYNTHESIS

The extrapancreatic actions of GLP-1 include inhibition of gastric emptying and gastric acid secretion, thereby fulfilling the definition of GLP-1 as an enterogastrone. Other important extrapancreatic actions of GLP-1 include a regulatory role in hepatic glucose production, the inhibition of pancreatic exocrine secretion, cardioprotective and cardiotropic effects, the regulation of appetite and satiety, and stimulation of afferent sensory nerves. The primary metabolite of GLP-1, GLP-1 (9-36) amide, or GLP-1m, is the truncated product of degradation by dipeptidyl peptidase-4. GLP-1m has insulinomimetic effects on hepatic glucose production and cardiac function. Exendin-4 present in the salivary gland of the reptile, Gila monster (Heloderma suspectum), is a high-affinity agonist for the mammalian GLP-1 receptor. It is resistant to degradation by dipeptidyl peptidase-4, and therefore has a prolonged half-life.

CONCLUSION

GLP-1 and its metabolite have important extrapancreatic effects particularly with regard to the cardiovascular system and insulinomimetic effects with respect to glucose homeostasis. These effects may be particularly important in the obese state. GLP-1, GLP-1m, and exendin-4 therefore have potential therapeutic roles because of their diffuse extrapancreatic actions.

Direct control of peripheral lipid deposition by CNS GLP-1 receptor signaling is mediated by the sympathetic nervous system and blunted in diet-induced obesity

We investigated a possible role of the central glucagon-like peptide (GLP-1) receptor system as an essential brain circuit regulating adiposity through effects on nutrient partitioning and lipid metabolism independent from feeding behavior. Both lean and diet-induced obesity mice were used for our experiments. GLP-1 (7-36) amide was infused in the brain for 2 or 7 d. The expression of key enzymes involved in lipid metabolism was measured by real-time PCR or Western blot. To test the hypothesis that the sympathetic nervous system may be responsible for informing adipocytes about changes in CNS GLP-1 tone, we have performed direct recording of sympathetic nerve activity combined with experiments in genetically manipulated mice lacking beta-adrenergic receptors. Intracerebroventricular infusion of GLP-1 in mice directly and potently decreases lipid storage in white adipose tissue. These effects are independent from nutrient intake. Such CNS control of adipocyte metabolism was found to depend partially on a functional sympathetic nervous system. Furthermore, the effects of CNS GLP-1 on adipocyte metabolism were blunted in diet-induced obese mice. The CNS GLP-1 system decreases fat storage via direct modulation of adipocyte metabolism. This CNS GLP-1 control of adipocyte lipid metabolism appears to be mediated at least in part by the sympathetic nervous system and is independent of parallel changes in food intake and body weight. Importantly, the CNS GLP-1 system loses the capacity to modulate adipocyte metabolism in obese states, suggesting an obesity-induced adipocyte resistance to CNS GLP-1.

Pax6 haploinsufficiency causes abnormal metabolic homeostasis by down-regulating glucagon-like peptide 1 in mice

Heterozygosity for the Pax6 allele is associated with impaired glucose tolerance in humans. With a Pax6 mutant mouse model, we found many of the metabolic abnormalities were consistent with the effects of down-regulating the expression of glucagon-like peptide 1 (GLP-1). In addition to impaired glucose tolerance, adult heterozygous mutant mice (Pax6(m/+)) secreted less insulin responding to glucose and arginine administration compared with control mice. Moreover, Pax6(m/+) mice showed increased food intake compared with control mice, although they were resistant to diet-induced fat accumulation. Indeed, levels of circulating GLP-1 and intestinal transcription of Gcg/Proglucagon were dramatically reduced in Pax6(m/+) mice. Mutated Pax6 also failed to activate the Gcg/Proglucagon promoter by in vitro transfection assay. Finally, administering the GLP-1 receptor agonist exendin-4 to Pax6(m/+) mice largely reversed their abnormal food intake, glycemic excursion, and insulin secretion. Our studies suggested that disruption of metabolic homeostasis mainly caused by Pax6 haploinsufficiency was mainly mediated by down-regulation of GLP-1. Administration of exendin-4 may be a useful therapy in humans with a similar mutation.

Incretin-based therapies for type 2 diabetes mellitus

Incretin-based drugs, such as glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase 4 inhibitors, are now routinely used to treat type 2 diabetes mellitus. These agents regulate glucose metabolism through multiple mechanisms, their use is associated with low rates of hypoglycemia, and they either do not affect body weight (dipeptidyl peptidase 4 inhibitors), or promote weight loss (glucagon-like peptide-1 receptor agonists). The success of exenatide and sitagliptin, the first therapies in their respective drug classes to be based on incretins, has fostered the development of multiple new agents that are currently in late stages of clinical development or awaiting approval. This Review highlights our current understanding of the mechanisms of action of incretin-based drugs, with an emphasis on the emerging clinical profile of new agents.

Safety, tolerability, pharmacodynamics and pharmacokinetics of albiglutide, a long-acting glucagon-like peptide-1 mimetic, in healthy subjects

AIMS

Albiglutide is a glucagon-like peptide-1 (GLP-1) mimetic generated by genetic fusion of a dipeptidyl peptidase-IV-resistant GLP-1 dimer to human albumin. Albiglutide was designed to retain the therapeutic effects of native GLP-1 while extending its duration of action. This study was conducted to determine the pharmacokinetics and initial safety/tolerability profile of albiglutide in non-diabetic volunteers.

METHODS

In this single-blind, randomized, placebo-controlled trial, 39 subjects (18-60 years, body mass index 19.9-35.0 kg/m(2)) received placebo (n = 10) or escalating doses of albiglutide (n = 29) on days 1 and 8 in the following sequential cohorts: cohort 1: 0.25 + 1 mg; cohort 2: 3 + 6 mg; cohort 3: 16 + 24 mg; cohort 4: 48 + 60 mg; and cohort 5: 80 + 104 mg. Dose proportionality was evaluated based on area under the plasma drug concentration versus time curve [area under the curve (AUC((0-7 days)))] and maximum plasma drug concentration (C(max)) for cohorts 2-5 during week 1.

RESULTS

Albiglutide had a terminal elimination half-life (T(1/2)) of 6-8 days and time to maximum observed plasma drug concentration (T(max)) of 3-4 days. A greater-than-dose proportional increase in albiglutide exposure was observed. Albiglutide demonstrated a dose-dependent trend in reductions of glucose weighted mean AUC and fructosamine levels in healthy subjects. The incidence and severity of adverse events (AEs) was similar between placebo and albiglutide groups. Headache was the most frequent drug-related AE, followed by constipation, flatulence and nausea.

CONCLUSIONS

Albiglutide has a half-life that favours once weekly or less frequent dosing with an acceptable safety/tolerability profile in non-diabetic subjects.

Albinterferon alfa-2b, a novel fusion protein of human albumin and human interferon alfa-2b, for chronic hepatitis C

OBJECTIVE

New treatment options for chronic hepatitis C (CHC) that offer improved efficacy, tolerability, and convenience compared with weekly interferon alfa (IFNalpha)-based regimens are needed. Longer-acting IFNalpha formulations with reduced dosing requirements and improved tolerability have been a focus of drug development efforts. The objective of this report is to review the characteristics, pharmacokinetics, pharmacodynamics, and clinical and virologic outcomes reported in studies of albinterferon alfa-2b (alb-IFN), a novel fusion protein of human albumin and human IFNalpha-2b.

METHODS

This review was based on all published data regarding alb-IFN to date. An unlimited PubMed database search was conducted using the keywords 'albuferon,' 'albinterferon,' and 'albumin AND interferon.'

RESULTS

Albinterferon alfa-2b has been developed for the treatment of CHC. This agent exhibits a prolonged half-life and duration of antiviral activity that indicate potential suitability for dosing intervals of 2-4 weeks. Phase 2 trials in prior IFN nonresponders and IFN-naïve patients with genotype 1 or 2/3 CHC have shown antiviral activity and acceptable safety/tolerability of alb-IFN 900-1500 microg every 2 weeks and 1200-1500 microg every 4 weeks. Based on the phase 2 data, alb-IFN 900 microg and 1200 microg every 2 weeks were selected for two ongoing phase 3 trials in IFN-naïve patients with genotype 1 and 2/3 CHC.

CONCLUSIONS

Albinterferon alfa-2b exhibits high antiviral activity, and appears to offer safety/tolerability comparable to the current standard of care, and health-related quality-of-life benefits in patients with CHC. Its ability to maintain drug concentrations above the 90% effective concentration over prolonged dosing intervals suggests that it may be an ideal partner for combination therapy with direct antiviral agents in CHC. The results of the phase 3 trials are eagerly anticipated as they should greatly clarify the future role of alb-IFN in the treatment of CHC.

Evidence that intestinal glucagon-like peptide-1 plays a physiological role in satiety

A physiological role in satiety is proposed for glucagon-like peptide-1 (GLP-1), secreted by the distal intestine in response to ingested nutrients. Here we report that in rats, ip injection of the GLP-1 receptor (GLP-1-R) antagonist exendin 9-39 (Ex9) elicited hyperphagia, but only at times of day when intake is otherwise low. Furthermore, ip administration of Ex9 attenuated satiety induced by either a voluntarily consumed sucrose meal (by 100%) or an intragastric glucose load (by 40%). To determine whether these effects involve blockade of GLP-1-R in brain or at a peripheral site, we injected Ex9 either centrally (into the third ventricle) or peripherally (ip) prior to GLP-1 injected either centrally or peripherally. Anorexia induced by peripheral GLP-1 was fully blocked by peripheral, but not central, pretreatment with Ex9, whereas the opposite was true for anorexic effect of central GLP-1. Thus, ip Ex9 appears to attenuate satiety via peripheral GLP-1-R blockade. Finally, anorexia induced by ip injection of exendin-4 (a GLP-1-R agonist) was due to both reduced meal size and increased duration between meals. We conclude that GLP-1 released from the intestine in response to ingested nutrients is a physiologically active satiety signal.

The glucagon-like peptide-1 receptor regulates endogenous glucose production and muscle glucose uptake independent of its incretin action

Glucagon-like peptide-1 (GLP-1) diminishes postmeal glucose excursions by enhancing insulin secretion via activation of the beta-cell GLP-1 receptor (Glp1r). GLP-1 may also control glucose levels through mechanisms that are independent of this incretin effect. The hyperinsulinemic-euglycemic clamp (insulin clamp) and exercise were used to examine the incretin-independent glucoregulatory properties of the Glp1r because both perturbations stimulate glucose flux independent of insulin secretion. Chow-fed mice with a functional disruption of the Glp1r (Glp1r(-/-)) were compared with wild-type littermates (Glp1r(+/+)). Studies were performed on 5-h-fasted mice implanted with arterial and venous catheters for sampling and infusions, respectively. During insulin clamps, [3-(3)H]glucose and 2[(14)C]deoxyglucose were used to determine whole-body glucose turnover and glucose metabolic index (R(g)), an indicator of glucose uptake. R(g) in sedentary and treadmill exercised mice was determined using 2[(3)H]deoxyglucose. Glp1r(-/-) mice exhibited increased glucose disappearance, muscle R(g), and muscle glycogen levels during insulin clamps. This was not associated with enhanced muscle insulin signaling. Glp1r(-/-) mice exhibited impaired suppression of endogenous glucose production and hepatic glycogen accumulation during insulin clamps. This was associated with impaired liver insulin signaling. Glp1r(-/-) mice became significantly hyperglycemic during exercise. Muscle R(g) was normal in exercised Glp1r(-/-) mice, suggesting that hyperglycemia resulted from an added drive to stimulate glucose production. Muscle AMP-activated protein kinase phosphorylation was higher in exercised Glp1r(-/-) mice. This was associated with increased relative exercise intensity and decreased exercise endurance. In conclusion, these results show that the endogenous Glp1r regulates hepatic and muscle glucose flux independent of its ability to enhance insulin secretion.

Preventing type 2 diabetes

The rapid and often relentless progression of type 2 diabetes suggests that high-risk patients should be provided with an equally aggressive strategy to protect their remaining beta-cell function and endogenous insulin secretion. Management of patients with prediabetes should incorporate both lifestyle and pharmacologic intervention. Although no specific recommendations are published for the management of prediabetes, one can assume that preservation of pancreatic beta-cell function, improvement in peripheral insulin resistance and pancreatic insulin secretion, reducing pancreatic alpha-cell secretion of glucagon, preventing long- and short-term diabetes-related complications, and assisting patients to loose weight are beneficial. Aggressive, timely, and physiologic management of prediabetes should be advocated.

The role of incretins in glucose homeostasis and diabetes treatment

Incretins are gut hormones that are secreted from enteroendocrine cells into the blood within minutes after eating. One of their many physiological roles is to regulate the amount of insulin that is secreted after eating. In this manner, as well as others to be described in this review, their final common raison d'être is to aid in disposal of the products of digestion. There are two incretins, known as glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide-1 (GLP-1), that share many common actions in the pancreas but have distinct actions outside of the pancreas. Both incretins are rapidly deactivated by an enzyme called dipeptidyl peptidase 4 (DPP4). A lack of secretion of incretins or an increase in their clearance are not pathogenic factors in diabetes. However, in type 2 diabetes (T2DM), GIP no longer modulates glucose-dependent insulin secretion, even at supraphysiological (pharmacological) plasma levels, and therefore GIP incompetence is detrimental to beta-cell function, especially after eating. GLP-1, on the other hand, is still insulinotropic in T2DM, and this has led to the development of compounds that activate the GLP-1 receptor with a view to improving insulin secretion. Since 2005, two new classes of drugs based on incretin action have been approved for lowering blood glucose levels in T2DM: an incretin mimetic (exenatide, which is a potent long-acting agonist of the GLP-1 receptor) and an incretin enhancer (sitagliptin, which is a DPP4 inhibitor). Exenatide is injected subcutaneously twice daily and its use leads to lower blood glucose and higher insulin levels, especially in the fed state. There is glucose-dependency to its insulin secretory capacity, making it unlikely to cause low blood sugars (hypoglycemia). DPP4 inhibitors are orally active and they increase endogenous blood levels of active incretins, thus leading to prolonged incretin action. The elevated levels of GLP-1 are thought to be the mechanism underlying their blood glucose-lowering effects.

Pharmacodynamics, pharmacokinetics, safety, and tolerability of albiglutide, a long-acting glucagon-like peptide-1 mimetic, in patients with type 2 diabetes

CONTEXT

Native glucagon-like peptide-1 increases insulin secretion, decreases glucagon secretion, and reduces appetite but is rapidly inactivated by dipeptidyl peptidase-4. Albiglutide is a novel dipeptidyl peptidase-4-resistant glucagon-like peptide-1 dimer fused to human albumin designed to have sustained efficacy in vivo.

OBJECTIVES

The objectives were to investigate pharmacodynamics, pharmacokinetics, safety, and tolerability of albiglutide in type 2 diabetes subjects.

METHODS

In a single-blind dose-escalation study, 54 subjects were randomized to receive placebo or 9-, 16-, or 32-mg albiglutide on d 1 and 8. In a complementary study, 46 subjects were randomized to a single dose (16 or 64 mg) of albiglutide to the arm, leg, or abdomen.

RESULTS

Significant dose-dependent reductions in 24-h mean weighted glucose [area under the curve((0-24 h))] were observed, with placebo-adjusted least squares means difference values in the 32-mg cohort of -34.8 and -56.4 mg/dl [95% confidence interval (-54.1, -15.5) and (-82.2, -30.5)] for d 2 and 9, respectively. Placebo-adjusted fasting plasma glucose decreased by -26.7 and -50.7 mg/dl [95% confidence interval (-46.3, -7.06) and (-75.4, -26.0)] on d 2 and 9, respectively. Postprandial glucose was also reduced. No hypoglycemic episodes were detected in the albiglutide cohorts. The frequency and severity of the most common adverse events, headache and nausea, were comparable with placebo controls. Albiglutide half-life ranged between 6 and 7 d. The pharmacokinetics or pharmacodynamic of albiglutide was unaffected by injection site.

CONCLUSIONS

Albiglutide improved fasting plasma glucose and postprandial glucose with a favorable safety profile in subjects with type 2 diabetes. Albiglutide's long half-life may allow for once-weekly or less frequent dosing.

GLP-1: physiological effects and potential therapeutic applications

Glucagon-like peptide 1 (GLP-1) is a gut-derived incretin hormone with the potential to change diabetes. The physiological effects of GLP-1 are multiple, and many seem to ameliorate the different conditions defining the diverse physiopathology seen in type 2 diabetes. In animal studies, GLP-1 stimulates beta-cell proliferation and neogenesis and inhibits beta-cell apoptosis. In humans, GLP-1 stimulates insulin secretion and inhibits glucagon and gastrointestinal secretions and motility. It enhances satiety and reduces food intake and has beneficial effects on cardiovascular function and endothelial dysfunction. Enhancing incretin action for therapeutic use includes GLP-1 receptor agonists resistant to degradation (incretin mimetics) and dipeptidyl peptidase (DPP)-4 inhibitors. In clinical trials with type 2 diabetic patients on various oral antidiabetic regimes, both treatment modalities efficaciously improve glycaemic control and beta-cell function. Whereas the incretin mimetics induce weight loss, the DPP-4 inhibitors are considered weight neutral. In type 1 diabetes, treatment with GLP-1 shows promising effects. However, several areas need clinical confirmation: the durability of the weight loss, the ability to preserve functional beta-cell mass and the applicability in other than type 2 diabetes. As such, long-term studies and studies with cardiovascular end-points are needed to confirm the true benefits of these new classes of antidiabetic drugs in the treatment of diabetes mellitus.

Targeting Incretins in Type 2 Diabetes: Role of GLP-1 Receptor Agonists and DPP-4 Inhibitors

Until recently, the pathogenesis of type 2 diabetes mellitus (T2DM) has been conceptualized in terms of the predominant defects in insulin secretion and insulin action. It is now recognized that abnormalities in other hormones also contribute to the development of hyperglycemia. For example, the incretin effect, mediated by glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP), is attenuated in T2DM. Intravenous administration of GLP-1 ameliorates hyperglycemia in patients with T2DM, but an extremely short half-life limits its utility as a therapeutic agent. Strategies to leverage the beneficial effects of GLP-1 include GLP-1 receptor agonists or analogs or dipeptidyl peptidase-4 (DPP-4) inhibitors-agents that act by slowing the inactivation of endogenous GLP-1 and GIP. The GLP-1 agonist exenatide has been shown to improve HbA1c and decrease body weight. However, exenatide is limited by its relatively short pharmacologic half-life, various gastrointestinal (GI) side effects, and the development of antibodies. Studies of a long-acting exenatide formulation suggest that it has improved efficacy and also promotes weight loss. Another prospect is liraglutide, a once-daily human GLP-1 analog. In phase 2 studies, liraglutide lowered HbA1c by up to 1.7% and weight by approximately 3 kg, with apparently fewer GI side effects than exenatide. DPP-4 inhibitors such as sitagliptin and vildagliptin result in clinically significant reductions in HbA1c, and are weight neutral with few GI side effects. This review will provide an overview of current and emerging agents that augment the incretin system with a focus on the role of GLP-1 receptor agonists and DPP-4 inhibitors.

Preparation and characterization of a novel exendin-4 human serum albumin fusion protein expressed in Pichia pastoris

A novel recombinant exendin-4 human serum albumin fusion protein (rEx-4/HSA) expressed in Pichia pastoris was prepared and characterized. Ex-4 is a 39-amino acid peptide isolated from the salivary gland of the lizard Heloderma suspectum and is thought to be a novel therapeutic agent for type 2 diabetes. But to gain a continued effect, the peptide has to be injected twice a day owing to its short plasma half-life (t(1/2) = 2.4 h). To extend the half-life of Ex-4 molecule in vivo, we designed a genetically engineered Ex-4/HSA fusion protein. Between Ex-4 and HSA, a peptide linker GGGGS was inserted and the fusion protein was expressed in methylotrophic yeast P. pastoris with native HSA secretion signal sequence. The recombinant protein was secreted correctly and was obtained with high purity (typically > 98%) by a three-step purification procedure. cAMP assay demonstrated that the fusion protein had a bioactivity similar to Ex-4 for interaction with GLP-1 receptors in vitro. Results from oral glucose tolerance test indicated that rEx-4/HSA could effectively improve glucose tolerance in diabetic db/db mice. Pharmacokinetics studies in cynomologus monkeys also showed that rEx-4/HSA had a much longer plasma half-life. Therefore, rEx-4/HSA fusion protein could potentially be used as a new recombinant biodrug for type 2 diabetes therapy.

Protein engineering strategies for sustained glucagon-like peptide-1 receptor-dependent control of glucose homeostasis

OBJECTIVE

We have developed a novel platform for display and delivery of bioactive peptides that links the biological properties of the peptide to the pharmacokinetic properties of an antibody. Peptides engineered in the MIMETIBODY platform have improved biochemical and biophysical properties that are quite distinct from those of Fc-fusion proteins. CNTO736 is a glucagon-like peptide 1 (GLP-1) receptor agonist engineered in our MIMETIBODY platform. It retains many activities of native GLP-1 yet has a significantly enhanced pharmacokinetic profile. Our goal was to develop a long-acting GLP-1 receptor agonist with sustained efficacy.

RESEARCH DESIGN AND METHODS

In vitro and in vivo activity of CNTO736 was evaluated using a variety of rodent cell lines and diabetic animal models.

RESULTS

Acute pharmacodynamic studies in diabetic rodents demonstrate that CNTO736 reduces fasting and postprandial glucose, decreases gastric emptying, and inhibits food intake in a GLP-1 receptor-specific manner. Reduction of food intake following CNTO736 dosing is coincident with detection of the molecule in the circumventricular organs of the brain and activation of c-fos in regions protected by the blood-brain barrier. Diabetic rodents dosed chronically with CNTO736 have lower fasting and postprandial glucose and reduced body weight.

CONCLUSIONS

Taken together, our data demonstrate that CNTO736 produces a spectrum of GLP-1 receptor-dependent actions while exhibiting significantly improved pharmacokinetics relative to the native GLP-1 peptide.

Exploiting the antidiabetic properties of incretins to treat type 2 diabetes mellitus: glucagon-like peptide 1 receptor agonists or insulin for patients with inadequate glycemic control?

Type 2 diabetes mellitus is associated with progressive decreases in pancreatic beta-cell function. Most patients thus require increasingly intensive treatment, including oral combination therapies followed by insulin. Fear of hypoglycemia is a potential barrier to treatment adherence and glycemic control, while weight gain can exacerbate hyperglycemia or insulin resistance. Administration of insulin can roughly mimic physiologic insulin secretion but does not address underlying pathophysiology. Glucagon-like peptide 1 (GLP-1) is an incretin hormone released by the gut in response to meal intake that helps to maintain glucose homeostasis through coordinated effects on islet alpha- and beta-cells, inhibiting glucagon output, and stimulating insulin secretion in a glucose-dependent manner. Biological effects of GLP-1 include slowing gastric emptying and decreasing appetite. Incretin mimetics (GLP-1 receptor agonists with more suitable pharmacokinetic properties versus GLP-1) significantly lower hemoglobin A1c, body weight, and postprandial glucose excursions in humans and significantly improve beta-cell function in vivo (animal data). These novel incretin-based therapies offer the potential to reduce body weight or prevent weight gain, although the durability of these effects and their potential long-term benefits need to be studied further. This article reviews recent clinical trials comparing therapy with the incretin mimetic exenatide to insulin in patients with oral treatment failure, identifies factors consistent with the use of each treatment, and delineates areas for future research.

CNS GLP-1 regulation of peripheral glucose homeostasis

Current models hold that peripheral and CNS GLP-1 signaling operate as distinct systems whereby CNS GLP-1 regulates food intake and circulating GLP-1 regulates glucose homeostasis. There is accumulating evidence that the arcuate nucleus, an area of the CNS that regulates energy homeostasis, responds to hormones and nutrients to regulate glucose homeostasis as well. Recent data suggest that GLP-1 may be another signal acting on the arcuate to regulate glucose homeostasis challenging the conventional model of GLP-1 physiology. This review discusses the peripheral and central GLP-1 systems and presents a model whereby these systems are integrated in regulation of glucose homeostasis.

Expression, purification, and characterization of recombinant human serum albumin fusion protein with two human glucagon-like peptide-1 mutants in Pichia pastoris

Glucagon-like peptide-1 (GLP-1) is a 30-residue peptide hormone secreted by intestinal L-cells in response to nutrient ingestion. In the present study, overlapping PCR technology was employed to construct two GLP-1 mutants (GLP-1(A2G))2 and human albumin (HSA) genes in vitro without linker. The spliced gene, (GLP-1(A2G))2-HSA, was over expressed under the control of promoter AOX1 and Mat alpha signal peptide in Pichia pastoris. SDS-PAGE and Western blotting were applied to assay the recombinant fusion protein in the culture broth. The results demonstrated that the recombinant (GLP-1(A2G))2-HSA concentration in the broth could reach a level of 245.0 mg/L and the expressed fusion protein was capable of cross-reacting with anti-human GLP-1 and anti-human albumin antibody. The recombinant (GLP-1(A2G))2-HSA protein was purified by ultrafiltration, columns of Q-sepharose fast flow and Superdex 75 size-exclusion. The recombinant (GLP-1(A2G))2-HSA protein obtained could lower in vivo glucose concentration in blood and stimulate in vitro islet cell proliferation. In mouse model, the fusion protein was detectable in plasma even 308 h after a single subcutaneous dose of 1.25 mg/kg. The result showed that the terminal biological half-time of the protein was about 54.2 h which is 650-fold longer than that of GLP-1. The pharmacokinetic analysis of the protein suggests its promising application in clinical medicine.

An albumin-exendin-4 conjugate engages central and peripheral circuits regulating murine energy and glucose homeostasis

BACKGROUND & AIMS

Glucagon-like peptide-1 (GLP-1) regulates glucose homeostasis through multiple mechanisms including direct actions on the endocrine pancreas and indirect activation of central nervous system circuits regulating gastric emptying, satiety, and body weight. Because native GLP-1 is rapidly degraded, there is considerable interest in development of more potent GLP-1 receptor (GLP-1R) agonists with sustained activity; however, the extent to which much larger GLP-1R agonists will mimic some or all of the actions of smaller peptides remains uncertain.

METHODS

We studied the actions of CJC-1134-PC, a recombinant human serum albumin-exendin-4 conjugated protein, at the GLP-1R using heterologous cells expressing the GLP-1R in vitro and both wild-type and Glp1r(-/-) mice in vivo.

RESULTS

CJC-1134-PC activated GLP-1R-dependent signaling in baby hamster kidney-GLP-1R cells and acutely lowered blood glucose in wild-type but not in Glp1r(-/-) mice. Moreover, acute administration of CJC-1134-PC rapidly activated c-Fos expression in multiple regions of the central nervous system, acutely inhibited gastric emptying, and produced sustained inhibition of food intake in a GLP-1R-dependent manner. Furthermore, chronic daily treatment of high-fat diet-fed wild-type mice with CJC-1134-PC for 4 weeks led to improved glucose tolerance, increased levels of glucose-stimulated insulin, decreased HbA1c, and weight loss associated with decreased hepatic triglyceride content.

CONCLUSIONS

These findings illustrate that a high-molecular-weight exendin-4-albumin conjugate retains the ability to mimic a full spectrum of GLP-1R-dependent actions, including activation of central nervous system circuits regulating gastric emptying, food intake, and body weight.

Albinterferon alpha-2b: a genetic fusion protein for the treatment of chronic hepatitis C

Treatment regimens based on the use of interferon-alpha (IFN-alpha) remain the cornerstone of therapy for chronic hepatitis C virus infection, which affects nearly 170 million people worldwide. Treatment options include unmodified IFN-alpha given three times weekly or pegylated IFNs given once weekly. The albumin-fusion platform takes advantage of the long half-life of human albumin to provide a new treatment approach that allows the dosing frequency of IFN-alpha to be reduced in individuals with chronic hepatitis C. Albinterferon alpha-2b (alb-IFN), a recombinant polypeptide composed of IFN-alpha2b genetically fused to human albumin, has an extended half-life and early evidence indicates that it is efficacious and well tolerated. Pharmacodynamic modeling supports treatment with alb-IFN at 2- or 4-week intervals. Phase 3 registration trials are in progress. The albumin-fusion platform is currently being applied to other important bioactive peptides with short half-lives. These fusion proteins, which are at present in different phases of clinical development, might lead to improved therapies across a broad range of diseases.

Exenatide

Exenatide is the first in a new class of compounds, which possess similar activity to the naturally-occurring hormone glucagon-like peptide-1 (GLP-1). It mirrors many of the effects of GLP-1, improving glycaemic control through a combination of mechanisms, which include glucose-dependent stimulation of insulin secretion, suppression of glucagon secretion, slowing of gastric emptying and reduced appetite. Phase III clinical trials showed exenatide therapy for 30 weeks significantly reduced glycated haemoglobin, and fasting and postprandial plasma glucose compared with baseline when added to metformin and sulfonylureas or a combination of the two, with an average weight loss of approximately 2 kg. Exenatide can also be used in combination with thiazolidinediones and may be an alternative to insulin in patients requiring additional therapy. In patients with established Type 2 diabetes, control of both glycaemia and body weight are important to minimise the risk of future diabetes complications. Open-label extensions from these pivotal trials demonstrate that patients treated with exenatide for < or = 3 years sustained the reductions in glycaemic control achieved at 30 weeks and had a progressive reduction in body weight. Exenatide is generally well tolerated; nausea is the most commonly reported side effect, but can be significantly reduced when a target dose of exenatide is achieved in patients with gradual dose titration. Hypoglycaemia has been encountered in clinical trials of exenatide, especially on initiation of therapy with sulfonylureas (not with metformin). Exenatide may enable patients with Type 2 diabetes to improve glycaemic control and reduce or eliminate the risk of hypoglycaemia and weight gain.

Incretin hormone mimetics and analogues in diabetes therapeutics

The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are physiological gut peptides with insulin-releasing and extrapancreatic glucoregulatory actions. Incretin analogues/mimetics activate GLP-1 or GIP receptors whilst avoiding physiological inactivation by dipeptidyl peptidase 4 (DPP-4), and they represent one of the newest classes of antidiabetic drug. The first clinically approved GLP-1 mimetic for the treatment of type-2 diabetes is exenatide (Byetta/exendin) which is administered subcutaneously twice daily. Clinical trials of liraglutide, a GLP-1 analogue suitable for once-daily administration, are ongoing. A number of other incretin molecules are at earlier stages of development. This review discusses the various attributes of GLP-1 and GIP for diabetes treatment and summarises current clinical data. Additionally, it explores the therapeutic possibilities offered by preclinical agents, such as non-peptide GLP-1 mimetics, GLP-1/glucagon hybrid peptides, and specific GIP receptor antagonists.

Incretin-based therapies: mimetics versus protease inhibitors

The physiological incretins, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), lower blood glucose levels through multiple mechanisms, including enhancement of glucose-stimulated insulin secretion. Although of demonstrated benefit to glycemic control in patients with type 2 diabetes, particularly for GLP-1, the half-lives of these peptides are too short for practical therapeutic utility. Here, we discuss recent approaches to incretin-based therapy, including the use of long-acting GLP-1 receptor agonists, degradation-resistant GLP-1 analogs, GLP-1 analogs conjugated to albumin, non-peptide small molecules that bind to the GLP-1 receptor, and inhibitors of dipeptidyl peptidase IV, the enzyme that degrades both GIP and GLP-1.

Peptide Drug Delivery Strategies for the Treatment of Diabetes

Drug delivery strategies for diabetes have included a wide range of scientific and engineering approaches, including molecular design, formulation and device design. Molecular engineering has resulted in modified pharmacokinetics, such as rapid-acting or slow-release analogs of insulin. Long-acting insulin formulations are designed to meet the body's basal needs, whereas rapid-acting insulin formulations are designed to cover mealtime glucose spikes. Furthermore, the discovery of new therapeutic biomolecules, which like insulin need to be injected, will drive the need for more flexible and universally applicable delivery systems. Formulation design, such as particle engineering, can be used to modify pharmacokinetic profiles. In general, suspension formulations of insulin commonly demonstrate reduced solubility and result in sustained release. Similarly, depot injections can result in precipitation of insulin at the site of injection, again resulting in lower solubility and sustained release. Particle engineering also has been applied to pulmonary formulations for delivery to the deep lung. The creation of novel drug delivery methods for the treatment of diabetes should remove barriers to insulin therapy and increase patient acceptance and compliance. Eliminating routine injections with needle-free injectors, insulin pumps, inhalation, buccal sprays, intra-nasal delivery, and transdermal patches may offer increasingly attractive alternatives.

[Incretins as new therapeutic targets of type 2 diabetes]

The epidemic characteristics of type 2 diabetes mellitus (DM) pose a formidable challenge in terms of healthcare, given the tremendous impact it has on the healthcare resources needed not only to treat it, but also to prevent and treat the associated cardiovascular complications. This makes up the number 1 cause of DM-associated morbidity-mortality in addition to its social and personal impact. We currently have a growing number of available treatment tools that make it possible to achieve the target glycemic control in most of our patients, albeit unfortunately, only temporarily in a good many of them, because of the progressive nature of the disease. Furthermore, current therapy often entails undesirable effects, such as weight gain or the emergence of hypoglycemias that limit their optimization. Recently, a new class of drugs has been incorporated into the treatment of DM - incretin mimetics. These new drugs act in very much the same way as the intestinal hormones that are naturally secreted following the intake of nutrients, called incretins (e.g., glucagon like peptide-1 [GLP-1]), with the added advantage that these molecules are resistant to enzymatic degradation by the DPP-IV enzyme. This provides them with a half-life that makes ambulatory treatment possible, unlike natural incretins whose half-life is too short to make them viable as treatment. The incretin mimetics bind to GLP-1 receptors, increasing glucose-dependent secretion of insulin and decreasing glucose-dependent posprandial secretion of glucagon, slowing gastric emptying, and reducing food intake. All these mechanisms have a significant impact on glucose homeostasis and a beneficial effect on body weight. Moreover, studies in experimental models suggest that these new molecules might have a promising effect on pancreatic beta cell function and mass. Exenatide is the first incretin mimetic available to date. Efficacy and safety data of this drug show it as a therapeutic option for the treatment of type 2 DM.

Biology of incretins: GLP-1 and GIP

This review focuses on the mechanisms regulating the synthesis, secretion, biological actions, and therapeutic relevance of the incretin peptides glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). The published literature was reviewed, with emphasis on recent advances in our understanding of the biology of GIP and GLP-1. GIP and GLP-1 are both secreted within minutes of nutrient ingestion and facilitate the rapid disposal of ingested nutrients. Both peptides share common actions on islet beta-cells acting through structurally distinct yet related receptors. Incretin-receptor activation leads to glucose-dependent insulin secretion, induction of beta-cell proliferation, and enhanced resistance to apoptosis. GIP also promotes energy storage via direct actions on adipose tissue, and enhances bone formation via stimulation of osteoblast proliferation and inhibition of apoptosis. In contrast, GLP-1 exerts glucoregulatory actions via slowing of gastric emptying and glucose-dependent inhibition of glucagon secretion. GLP-1 also promotes satiety and sustained GLP-1-receptor activation is associated with weight loss in both preclinical and clinical studies. The rapid degradation of both GIP and GLP-1 by the enzyme dipeptidyl peptidase-4 has led to the development of degradation-resistant GLP-1-receptor agonists and dipeptidyl peptidase-4 inhibitors for the treatment of type 2 diabetes. These agents decrease hemoglobin A1c (HbA1c) safely without weight gain in subjects with type 2 diabetes. GLP-1 and GIP integrate nutrient-derived signals to control food intake, energy absorption, and assimilation. Recently approved therapeutic agents based on potentiation of incretin action provide new physiologically based approaches for the treatment of type 2 diabetes.

Endogenous cholecystokinin reduces food intake and increases Fos-like immunoreactivity in the dorsal vagal complex but not in the myenteric plexus by CCK1 receptor in the adult rat

We hypothesized that endogenous CCK reduces food intake by activating the dorsal vagal complex (DVC) and the myenteric neurons of the gut. To test this hypothesis, adult rats were given camostat mesilate; a nonnutrient releaser of endogenous CCK, by orogastric gavage, and Fos-like immunoreactivity (Fos-LI) was quantified in the DVC and the myenteric plexus. The results for endogenous CCK were compared with those for exogenous CCK-8. Exogenous CCK-8 reduced food intake and stimulated Fos-LI in the DVC and in myenteric neurons of the duodenum and jejunum. In comparison, endogenous CCK reduced food intake and increased DVC Fos-LI but did not increase Fos-LI in the myenteric plexus. Similar to CCK-8, devazepide, a specific CCK1 receptor antagonist, and not L365,260, a specific CCK2 receptor antagonist, attenuated the reduction of food intake by camostat. In addition, Fos-LI in the DVC in response to both exogenous CCK-8 and camostat administration was significantly attenuated by vagotomy, as well as by blocking CCK1 receptors. These results demonstrate for the first time that reduction of food intake in adult rats by endogenous CCK released by a nonnutrient mechanism requires CCK1 receptors, the vagus nerve, and activation of the DVC, but not the myenteric plexus.

Mechanisms of action of glucagon-like peptide 1 in the pancreas

Glucagon-like peptide 1 (GLP-1) is a hormone that is encoded in the proglucagon gene. It is mainly produced in enteroendocrine L cells of the gut and is secreted into the blood stream when food containing fat, protein hydrolysate, and/or glucose enters the duodenum. Its particular effects on insulin and glucagon secretion have generated a flurry of research activity over the past 20 years culminating in a naturally occurring GLP-1 receptor (GLP-1R) agonist, exendin 4 (Ex-4), now being used to treat type 2 diabetes mellitus (T2DM). GLP-1 engages a specific guanine nucleotide-binding protein (G-protein) coupled receptor (GPCR) that is present in tissues other than the pancreas (brain, kidney, lung, heart, and major blood vessels). The most widely studied cell activated by GLP-1 is the insulin-secreting beta cell where its defining action is augmentation of glucose-induced insulin secretion. Upon GLP-1R activation, adenylyl cyclase (AC) is activated and cAMP is generated, leading, in turn, to cAMP-dependent activation of second messenger pathways, such as the protein kinase A (PKA) and Epac pathways. As well as short-term effects of enhancing glucose-induced insulin secretion, continuous GLP-1R activation also increases insulin synthesis, beta cell proliferation, and neogenesis. Although these latter effects cannot be currently monitored in humans, there are substantial improvements in glucose tolerance and increases in both first phase and plateau phase insulin secretory responses in T2DM patients treated with Ex-4. This review will focus on the effects resulting from GLP-1R activation in the pancreas.

Beneficial effects of sub-chronic activation of glucagon-like peptide-1 (GLP-1) receptors on deterioration of glucose homeostasis and insulin secretion in aging mice

Aging is associated with an increased incidence of glucose intolerance and type 2 diabetes. Glucagon-like peptide-1 (GLP-1) is an important insulinotropic peptide secreted from the gastrointestinal tract in response to nutrient absorption. The present study was designed to assess the sub-chronic glucose regulatory effects of the potent long-acting GLP-1 receptor agonist, (Val(8))GLP-1, in aging 45-49 week old mice. Daily injection of (Val(8))GLP-1 (25 n mol/kg body weight) for 12 days had no significant effect on food intake, body weight, non-fasting plasma glucose and insulin concentrations. However, after 12 days, the glycaemic response to intraperitoneal glucose was improved (P<0.05) in (Val(8))GLP-1 treated mice. In keeping with this, glucose-mediated insulin secretion was enhanced (P<0.05) and insulin sensitivity improved (P<0.05) compared to controls. These data indicate that sub-chronic activation of the GLP-1 receptor by daily treatment with (Val(8))GLP-1 counters aspects of the age-related impairment of pancreatic beta-cell function and insulin sensitivity.

The incretin system: glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors in type 2 diabetes

Glucagon-like peptide 1 (GLP-1) is a gut-derived incretin hormone that stimulates insulin and suppresses glucagon secretion, inhibits gastric emptying, and reduces appetite and food intake. Therapeutic approaches for enhancing incretin action include degradation-resistant GLP-1 receptor agonists (incretin mimetics), and inhibitors of dipeptidyl peptidase-4 (DPP-4) activity (incretin enhancers). Clinical trials with the incretin mimetic exenatide (two injections per day or long-acting release form once weekly) and liraglutide (one injection per day) show reductions in fasting and postprandial glucose concentrations, and haemoglobin A1c (HbA1c) (1-2%), associated with weight loss (2-5 kg). The most common adverse event associated with GLP-1 receptor agonists is mild nausea, which lessens over time. Orally administered DPP-4 inhibitors, such as sitagliptin and vildagliptin, reduce HbA1c by 0.5-1.0%, with few adverse events and no weight gain. These new classes of antidiabetic agents, and incretin mimetics and enhancers, also expand beta-cell mass in preclinical studies. However, long-term clinical studies are needed to determine the benefits of targeting the incretin axis for the treatment of type 2 diabetes.