Pharmacokinetics of exogenous GIP(1-42) in C57Bl/6 mice; Extremely rapid degradation but marked variation between available assays

Like other peptide hormones, glucose-dependent insulinotropic polypeptide (GIP) is rapidly cleared from the circulation. Dipeptidyl peptidase-4 (DPP-4) is known to be involved. Information on the overall pharmacokinetics of GIP in rodents is, however, lacking. We investigated the pharmacokinetics of exogenous GIP after intravenous, subcutaneous and intraperitoneal injection with and without DPP-4 inhibition in conscious female C57Bl/6 mice. Secondly, we compared total and intact GIP levels measured by an in-house RIA and commercially available ELISA kits to determine the suitability of these methods for in vivo and in vitro measurements. GIP half-life following intravenous injection amounted to 93 ± 2 s, which was extended to 5 ± 0.6 min by inhibition of DPP-4. Intact GIP levels following subcutaneous and intraperitoneal GIP administration were approximately 15 % of total GIP. The area under the curve of intact GIP (GIP exposure) following GIP injection was significantly increased by DPP-4 inhibition, whereas total GIP levels remained unchanged. We found significant variation between measurements of total, but not intact GIP performed with our in-house RIA and ELISAs in samples obtained after in vivo administration of GIP. Different preanalytical sample preparation (EDTA plasma, heparin plasma, assay buffer and PBS) significantly influenced results for all ELISA kits used. Thus, in experiments involving exogenous GIP(1-42) administration in mice, it is important to consider that this will result in a very low ratio of intact:total peptide but co-administration of a DPP-4 inhibitor greatly elevates this ratio. Furthermore, for comparison of GIP levels, it is essential to maintain uniformity concerning assay methodology and sample preparation.

Albumin-binding domain extends half-life of glucagon-like peptide-1

Glucagon-like peptide-1 (GLP-1) is considered to be a promising peptide for the treatment of type 2 diabetes mellitus (T2DM). However, the extremely short half-life of GLP-1 limits its clinical application. Albumin-binding domain (ABD) with high affinity for human serum albumin (HSA) has been used widely for half-life extension of therapeutic peptides and proteins. In the present study, novel GLP-1 receptor agonists were designed by genetic fusion of GLP-1 to three kinds of ABDs with different affinities for HSA: GA3, ABD035 and ABDCon. The bioactivities and half-lives of ABD-fusion GLP-1 proteins with different types and lengths of linkers were investigated in vitro and in vivo. The results demonstrated that ABD-fusion GLP-1 proteins could bind to HSA with high affinity. The blood glucose-lowering effect of GLP-1 was significantly improved and sustained by fusion to ABD. Meanwhile, the fusion proteins significantly inhibited food intake, which was beneficial for T2DM and obesity treatment. The half-life of GLP-1 was substantially extended by virtue of ABD. The in vivo results also showed that a longer linker inserted between GLP-1 and ABD resulted in a higher blood glucose-lowering effect. The fusion proteins generated by fusion of GLP-1 to GA3, ABD035 and ABDCon exhibited similar bioactivities and pharmacokinetics in vivo. These findings demonstrate that ABD-fusion GLP-1 proteins retain the bioactivities of natural GLP-1 and can be further developed for T2DM treatment and weight loss. It also indicates that the ABD-fusion strategy can be generally applicable to any peptide or protein, to improve pharmacodynamic and pharmacokinetic properties.

Is glucagon-like peptide-1 fully protected by the dipeptidyl peptidase 4 inhibitor sitagliptin when administered to patients with type 2 diabetes?

AIM

To evaluate the relationship between plasma dipeptidyl-peptidase 4 (DPP-4) activity and its protection of glucagon-like peptide-1 (GLP-1) using the DPP-4 inhibitor sitagliptin.

METHODS

On four separate days, patients with type 2 diabetes (T2D) (n = 8; age: 59.9 ±10.8 [mean ±SD] years; body mass index [BMI]: 28.8 ±4.6 kg/m² ; glycated haemoglobin A1c [HbA1c]: 43.1 ±0.5 mmol/mol [6.6% ±1.7%]) received a 380-minute continuous intravenous infusion of GLP-1 (1.0 pmol × kg bodyweight^-1  × minutes^-1 ) and a double-blind, single-dose oral administration of sitagliptin in doses of 0 (placebo), 25, 100 and 200 mg.

RESULTS

Plasma DPP-4 activity decreased compared to baseline (placebo) with increasing doses of sitagliptin (P < .01), reaching a maximal inhibition with the 100 mg dose. Levels of intact GLP-1 increased with increasing doses of sitagliptin from placebo to 100 mg (area under curve [AUC] 7.2 [95%, CI; 12.1, 16.4] [placebo], 10.7 [16.1, 21.4] [25 mg], 11.7 [17.8, 23.6] [100 mg] nmol/L × 360 minutes [P < .01]), but no further increase in intact GLP-1 levels was observed with 200 mg of sitagliptin (11.5 [17.6, 23.4] nmol/L × 360 minutes) (P = .80).

CONCLUSION

Our findings suggest that the sitagliptin dose of 100 mg is sufficient to inhibit both plasma and membrane-bound DPP-4 activity, presumably also leading to complete protection of endogenous GLP-1 in patients with T2D.

The Pharmacokinetic Properties of Glucagon-like Peptide-1 Receptor Agonists and Their Mode and Mechanism of Action in Patients with Type 2 Diabetes

Once-weekly (OW) glucagon-like peptide-1 receptor agonists (GLP-1 RAs) have demonstrated improved glycemic control in patients with type 2 diabetes (T2D), and some have a number of other benefits, including weight loss, improvements in blood pressure and lipid profiles, and cardiovascular protection. They also provide a therapy option with a low risk of hypoglycemia, an attractive choice for many patients. Molecular structure and pharmacokinetic properties vary among GLP-1 RAs, with some more closely related than others to native glucagon-like peptide-1 (GLP-1). OW GLP-1 RAs have various modifications to their molecular structure that make the molecules resistant to degradation by dipeptidyl peptidase-4 (DPP-4), increasing the half-life of these drugs and making them suitable for OW administration. These differences in the molecular structures and pharmacokinetic properties between the various OW GLP-1 RAs help to explain the differences in efficacy, mechanisms, and safety profiles among the drugs, and these considerations can help primary care physicians to optimize prescribing practices.

[Metformin is a possible glucagon-like peptide 1 stimulator]

Metformin is an oral anti-hyperglycaemic drug used as first-line treatment of Type 2 diabetes. It is more effective when administered orally than when administered intravenously, and metformin formulations, which prolong the time residing in the gut are the most potent. This indicates that the intestine plays an essential role in metformin's mode of action. Metformin also increases plasma concentrations of the glucose-lowering gut incretin hormone glucagon-like peptide-1 (GLP-1). This metformin-induced GLP-1 increment may constitute an important link between the gut and the glucose-lowering effect of metformin.

Expression and Characterization of a Potent Long-Acting GLP-1 Receptor Agonist, GLP-1-IgG2σ-Fc

Human GLP-1 (glucagon-like peptide-1) can produce a remarkable improvement in glycemic control in patients with type 2 diabetes. However, its clinical benefits are limited by its short half-life, which is less than 2 min because of its small size and rapid enzymatic inactivation by dipeptidyl peptidase IV. We engineered GLP-1-IgG2σ-Fc, a 68-kDa fusion protein linking a variant human GLP-1 (A8G/G26E/R36G) to a human IgG2σ constant heavy-chain. A stably transfected Chinese hamster ovary cell line was obtained using electroporation. Western blotting showed that the expressed protein was immunoreactive to both GLP-1 and IgG antibodies. GLP-1-IgG2σ-Fc stimulated insulin secretion from INS-1 cells in a dose- and glucose-dependent manner and increased insulin mRNA expression. The half-life of GLP-1-IgG2σ-Fc in cynomolgus monkeys was approximately 57.1 ± 4.5 h. In the KKAy mouse model of diabetes, one intraperitoneal injection of GLP-1-IgG2σ-Fc (1 mg/kg) reduced blood glucose levels for 5 days. A 4-week repeat-administration study identified sustained effects on blood glucose levels. Oral glucose tolerance tests conducted at the beginning and end of this 4-week period showed that GLP-1-IgG2σ-Fc produced a stable glucose lowering effect. In addition, KKAy mice treated with GLP-1-IgG2σ-Fc showed statistically significant weight loss from day 23. In conclusion, these properties of GLP-1-IgG2σ-Fc demonstrated that it represented a potential long-acting GLP-1 receptor agonist for the treatment of type 2 diabetes.

[Albiglutide (Eperzan): a new once-weekly agonist of glucagon-like peptide-1 receptors]

Albiglutide (Eperzan) is a new once-weekly agonist of Glucagon-Like Peptide-1 (GLP-1) receptors that is indicated in the treatment of type 2 diabetes. Two doses are available, 30 mg and 50 mg, to be injected subcutaneously once a week. It has been extensively evaluated in the HARMONY programme of eight large randomised controlled trials that were performed at different stages of type 2 diabetes, in comparison with placebo or an active comparator. The endocrine and metabolic effects of albiglutide are similar to those of other GLP-1 receptor agonists: stimulation of insulin secretion (incretin effect) and inhibition of glucagon secretion, both in a glucose-dependent manner, retardation of gastric emptying and increase of satiety. These effects lead to a reduction in glycated haemoglobin (HbA(1c)) levels, combined with a weight reduction. The overall tolerance profile is good. Albiglutide is currently reimbursed in Belgium after failure (HbA(1c) > 7.5%) of and in combination with a dual therapy with metformin and a sulfonylurea as well as in combination with a basal insulin (with or without oral antidiabetic drugs). To avoid hypoglycaemia, a reduction in the dose of sulfonylurea or insulin may be recommended. A once-weekly administration should increase patient's acceptance of injectable therapy and improve compliance.

Liraglutide's safety, tolerability, pharmacokinetics, and pharmacodynamics in pediatric type 2 diabetes: a randomized, double-blind, placebo-controlled trial

BACKGROUND

The prevalence of type 2 diabetes (T2D) in youth is increasing. Treatment options beyond metformin and insulin are needed. The safety, tolerability, pharmacokinetics, and pharmacodynamics of liraglutide once daily in youth (10-17 years old) with T2D were investigated in a randomized, double-blind, placebo-controlled trial.

SUBJECTS AND METHODS

Youth treated with diet/exercise alone or with metformin and having a hemoglobin A1c (HbA1c) level of 6.5-11% were randomized to liraglutide (n=14) or placebo (n=7). Starting at 0.3 mg/day, doses were escalated weekly to 0.6, 0.9, 1.2, and 1.8 mg/day (or placebo equivalent) for 5 weeks.

RESULTS

Nineteen participants completed the trial. Baseline characteristics were similar between groups, with mean (SD) values for age of 14.8 (2.2) years, weight of 113.2 (35.6) kg (range, 57-214 kg), diabetes duration of 1.7 (1.4) years, and HbA1c level of 8.1% (1.2%). No serious adverse events (AEs), including severe hypoglycemia, occurred. Transient gastrointestinal AEs were most common at lower liraglutide doses during dose escalation. No significant changes in safety and tolerability parameters occurred. There was no evidence of pancreatitis or lipase elevations above three times the upper normal limit; calcitonin levels remained within the normal range. For liraglutide 1.8 mg, mean half-life was 12 h, and clearance was 1.7 L/h. After 5 weeks, the decline in HbA1c level was greater with liraglutide versus placebo (-0.86 vs. 0.04%, P=0.0007), whereas mean body weight remained stable (-0.50 vs. -0.54 kg, P=0.9703).

CONCLUSIONS

Liraglutide was well tolerated in youth with T2D, with safety, tolerability, and pharmacokinetic profiles similar to profiles in adults.

Elimination and degradation of glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide in patients with end-stage renal disease

CONTEXT

The affect of the kidneys in elimination and degradation of intact incretin hormones and their truncated metabolites is unclear.

OBJECTIVE

To evaluate elimination and degradation of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) in patients with dialysis-dependent kidney failure.

SETTING AND DESIGN

Twelve non-diabetic patients treated with chronic hemodialysis and 12 control subjects were examined in a double-blind, randomized, matched observational study at the Department of Nephrology, Rigshospitalet, University of Copenhagen, Denmark. Over 4 separate study days, synthetic human GIP or GLP-1 was infused with or without concurrent inhibition of dipeptidyl peptidase 4 using sitagliptin or placebo. Plasma concentrations of glucose, insulin, glucagon, and intact and total forms of GLP-1 or GIP were measured repeatedly. Plasma half-life (T1/2), metabolic clearance rate (MCR), area under curve, and volume of distribution for intact and metabolite levels of GLP-1 and GIP were calculated.

RESULTS

Fasting concentrations of intact GLP-1 and GIP were increased in dialysis patients (P < .001) whereas fasting levels of GLP-1 and GIP metabolites did not differ between groups (P > .738). MCRs of intact GLP-1 and GIP, and the GLP-1 metabolite were reduced in dialysis patients on the placebo day (P < .009), and T1/2 of intact and metabolite forms of GLP-1 and GIP were comparable between groups (P > .121).

CONCLUSIONS

Unexpectedly, degradation and elimination of the intact and metabolite forms of GLP-1 and GIP seemed preserved, although reduced, in patients with dialysis-dependent kidney failure.

Liraglutide suppresses postprandial triglyceride and apolipoprotein B48 elevations after a fat-rich meal in patients with type 2 diabetes: a randomized, double-blind, placebo-controlled, cross-over trial

AIMS

Postprandial triglyceridaemia is a risk factor for cardiovascular disease (CVD). This study investigated the effects of steady-state liraglutide 1.8 mg versus placebo on postprandial plasma lipid concentrations after 3 weeks of treatment in patients with type 2 diabetes mellitus (T2DM).

METHODS

In a cross-over trial, patients with T2DM (n = 20, 18-75 years, BMI 18.5-40 kg/m²) were randomized to once-daily subcutaneous liraglutide (weekly dose escalation from 0.6 to 1.8 mg) and placebo. After each 3-week period, a standardized fat-rich meal was provided, and the effects of liraglutide on triglyceride (primary endpoint AUC(0-8h)), apolipoprotein B48, non-esterified fatty acids, glycaemic responses and gastric emptying were assessed. ClinicalTrials.gov ID: NCT00993304.

FUNDING

Novo Nordisk A/S.

RESULTS

After 3 weeks, mean postprandial triglyceride (AUC(0-8h) liraglutide/placebo treatment-ratio 0.72, 95% CI [0.62-0.83], p = 0.0004) and apolipoprotein B48 (AUC(0-8h) ratio 0.65 [0.58-0.73], p < 0.0001) significantly decreased with liraglutide 1.8 mg versus placebo, as did iAUC(0-8h) and C(max) (p < 0.001). No significant treatment differences were observed for non-esterified fatty acids. Mean postprandial glucose and glucagon AUC(0-8h) and C(max) were significantly reduced with liraglutide versus placebo. Postprandial gastric emptying rate [assessed by paracetamol absorption (liquid phase) and the ¹³C-octanoate breath test (solid phase)] displayed no treatment differences. Mean low-density lipoprotein and total cholesterol decreased significantly with liraglutide versus placebo.

CONCLUSIONS

Liraglutide treatment in patients with T2DM significantly reduced postprandial excursions of triglyceride and apolipoprotein B48 after a fat-rich meal, independently of gastric emptying. Results indicate liraglutide's potential to reduce CVD risk via improvement of postprandial lipaemia.

An Open-Label, Parallel Group Study Investigating the Effects of Age and Gender on the Pharmacokinetics of the Once-Daily Glucagon-Like Peptide-1 Analogue Liraglutide

Liraglutide is a once-daily glucagon-like peptide-1 analogue being developed for the treatment of type 2 diabetes. The aim of this study was to investigate the effect of age and gender on the pharmacokinetics of liraglutide. Eight male and 8 female subjects were recruited from an 18- to 45-year-old group and an over-65-year-old group, respectively. All subjects received a single subcutaneous dose of 1.0 mg liraglutide. The area under the liraglutide plasma concentration curve from time 0 to last quantifiable concentration adjusted for body weight (significant covariate; P = .001) was found to be equivalent in young and elderly subjects (primary end point), with an estimated ratio of 0.94 (90% confidence interval, 0.84-1.06; P = .39). No significant impact of gender was observed (P = .38; estimated ratio, 1.08; 90% confidence interval, 0.93-1.26). Adverse events were of mild or moderate severity. The most frequently reported events were headache, vomiting, and nausea. When adjusted for body weight, no effect of gender or age was found on the pharmacokinetics of liraglutide.

Attempted suicide with liraglutide overdose did not induce hypoglycemia

We document the first reported case of attempted suicide with the GLP-1 receptor agonist, liraglutide: a 33-year-old Japanese woman with type 2 diabetes reported subcutaneously injected 72 mg of liraglutide. She experienced gastrointestinal symptoms but no hypoglycemia.

An overview of the pharmacokinetics, efficacy and safety of liraglutide

OBJECTIVE

Incretin-based therapies, including glucagon-like peptide 1 (GLP-1) receptor agonists, are the latest addition to the range of available medications for the management of patients with type 2 diabetes. The GLP-1 analog liraglutide has been approved for use in Europe and the US for over a year and has undergone evaluation in several pharmacokinetic/pharmacodynamics studies and in an extensive phase 3 clinical program. The aim of this review is to assess the pharmacokinetics, efficacy and safety of the phase 3 data.

METHODS

Data are presented from the pharmacokinetics/pharmacodynamics studies of liraglutide and from nine published phase 3 studies, including the six Liraglutide Effect and Action in Diabetes (LEAD) studies.

RESULTS

Liraglutide is effective at improving indices of glycemic control, and has a good tolerability and safety profile. Beneficial effects on weight (mean reduction of 1-3.4 kg) and blood pressure (systolic blood pressure decreased by 2.1-6.7 mmHg) are also observed.

CONCLUSION

Liraglutide is an effective and well tolerated option for the treatment of type 2 diabetes.

Liraglutide: short-lived effect on gastric emptying -- long lasting effects on body weight

AIM

Previous studies with the novel once daily glucagon-like peptide-1 (GLP-1) analogue liraglutide and the GLP-1 receptor agonist exenatide have revealed profound insulinotrophic and antidiabetic effects, but also potent effects on gastric emptying (GE) and long-term and lasting reductions in body weight. In this study, we examined the acute and chronic effects of two different GLP-1 analogues with different pharmacokinetic profiles on GE, food intake and body weight.

METHODS

On the basis of a series of dose-finding studies, the doses of exenatide and liraglutide with similar acute anorectic effects were identified. GE was assessed using a standard acetaminophen release assay. After the acute test, rats were dosed bi-daily for 14 days in which period food intake and body weight was monitored. On day 14, the GE rate was reassessed.

RESULTS

While both compounds exerted robust acute reductions in GE, the effect was markedly diminished following 14 days of dosing with liraglutide. In contrast, exenatide-treated rats still displayed a profound reduction in GE at the 14-day time-point. Both compounds exerted similar effects on body weight.

CONCLUSION

The data suggest that the 'gastric inhibitory' GLP-1 receptors in rats are subject to desensitization/tachyphylaxis but that this effect is dependent on full 24-h exposure as obtained by liraglutide. The body weight-lowering effects of GLP-1 receptor stimulation are not subject to desensitization. These data indicate that regulation of appetite signals in the brain, and not GE, is the main mechanism for liraglutide-induced weight loss.

Liraglutide in type 2 diabetes mellitus

Liraglutide (victoza, Novo Nordisk A/S) is human GLP-1 analogue developed by recombinant DNA technology. It is indicated along with diet and exercise in management of type 2 diabetes (T2DM) in adults. Liraglutide has been made available in India recently. Present review evaluates the efficacy and safety of liraglutide in T2DM and its comparison with other incretin based therapies. Liraglutide has been evaluated as monotherapy, in combination with one, two and three oral antidiabetic drugs similarly to routine clinical practice. These studies reported greater improvement in glycaemic control with liraglutide compared with comparators. Evaluation up to 2 years revealed sustained improvement in glycaemic control with liraglutide use. Liraglutide was well tolerated except for mild to moderate gastro-intestinal adverse events, which declined after continuation of therapy. Low risk of hypoglycaemia was reported with liraglutide therapy. Greater efficacy than other incretin based therapies was noted with liraglutide. Liraglutide has an important place in the management of T2DM. Apart from glycaemic control it also provides some important non-glycaemic benefits in terms of improving beta-cell function, weight reduction, and reduction in systolic blood pressure thereby overcoming the present therapeutic gap.

Disulfide bond prolongs the half-life of therapeutic peptide-GLP-1

The multiple physiological characterization of glucagon-like peptide-1 (GLP-1) makes it a promising drug candidate for the therapy of type 2 diabetes. However, the half-life of GLP-1 is short in vivo due to rapid degradation by dipeptidyl peptidase-IV (DPP-IV) and renal clearance. This indicates that the stabilization of GLP-1 is critical for its utility in drug development. In this study, we developed a cluster of GLP-1 homodimeric analogs, which fused the mutated GLP-1 monomer by an intra-disulfide bridge. The stabilities of the GLP-1 homodimeric analogs were investigated and the physiological functions of the analogs were compared with those of wild-type GLP-1 in rats and human serum. Single dose glucose tolerance test was performed to investigate the administration frequency which satisfied the efficient glucose regulatory in rats. Multiple dose glucose tolerance tests were employed also to study the long-acting anti-diabetic activity of GLP-1 homodimeric analog. The results indicated that the GLP-1 homodimeric analog (hdGLP1G10C) remarkably raised the biological half-life of GLP-1; also HDGLP1G10C showed better glucose tolerance and higher HbA(1c) reduction than GLP-1 in rodents. Based upon the results in this study, it was suggested that hdGLP1G10C prolonged the stability of GLP-1 and retained the biological activity of GLP-1. The improved physiological characterization of hdGLP1G10C makes it as possible potent anti-diabetic drug in the treatment of type 2 diabetes mellitus.

A novel GLP-1 analog exhibits potent utility in the treatment of type 2 diabetes with an extended half-life and efficient glucose clearance in vivo

The multiple physiological characterizations of glucagon-like peptide-1 (GLP-1) make it a promising drug candidate for the therapy of type 2 diabetes. However, the half-life of GLP-1 is short in vivo due to degradation by dipeptidyl peptidase-IV (DPP-IV) and renal clearance. Therefore, the stabilization of GLP-1 is critical for its utility in drug development. Based on our previous research, a GLP-1 analog that contained an intra-disulfide bond exhibited a prolonged biological half-life. In this study, we improved upon previous analogs with a novel GLP-1 analog that contained a tryptophan cage-like sequence for an improved binding affinity to the GLP-1 receptor. The binding capacities and the stabilities of GLP715a were investigated, and the physiological functions of the GLP715a were compared to those of the wild-type GLP-1 in animals. The results demonstrated that the new GLP-1 analog (GLP715a) increased its biological half-life to approximately 48h in vivo; GLP715a also exhibited a higher binding affinity to the GLP-1 receptor than the wild-type GLP-1. The increased binding capacity of GLP715a to its receptor resulted in a quick response to glucose administration. The long-acting anti-diabetic property of GLP715a was revealed by its increased glucose tolerance, higher HbA(1c) reduction, more efficient glucose clearance and quicker insulin stimulation upon glucose administration compared to the wild-type GLP-1 in rodents. The improved physiological characterizations of GLP715a make it a possible potent anti-diabetic drug in the treatment of type 2 diabetes mellitus.

Liraglutide - overview of the preclinical and clinical data and its role in the treatment of type 2 diabetes

Type 2 diabetes is characterized by a progressive decline in glycaemic control. Many standard diabetes treatments, however, fail to achieve or maintain glycaemic control, and are often associated with an increased risk of hypoglycaemia and weight gain. Recently developed incretin-based therapies are a promising addition to the current armamentarium of diabetes treatments. Two types of incretin-based therapies are currently available: glucagon-like peptide (GLP)-1 receptor agonists (liraglutide and exenatide) and dipeptidyl peptidase-4 inhibitors (sitaglipin, vildagliptin and saxagliptin). This review aims to summarize the key efficacy and safety data of liraglutide, a once-daily human GLP-1 analogue. Extensive phase III clinical trials have shown liraglutide to improve glycaemic control with additional benefits on body weight, blood pressure and β-cell function. Liraglutide is also generally well tolerated with a low risk of hypoglycaemia. Liraglutide has recently been approved for marketing in Europe, Japan and the USA.

Co-administration of liraglutide with insulin detemir demonstrates additive pharmacodynamic effects with no pharmacokinetic interaction

AIM

To compare the pharmacokinetic (PK) [area under the curve (AUC₀(-)₂₄ (h), C(max))] and pharmacodynamic (PD) (AUC(GIR) ₀(-)₂₄ (h), GIR(max)) properties of single-dose insulin detemir in the presence or absence of steady-state liraglutide (1.8 mg dose) in subjects with type 2 diabetes to determine whether co-administration affected the PK and PD profiles of either therapeutic agent.

METHODS

Following a 3-week washout of oral antidiabetic agents (OADs) other than metformin, PK and PD assessments during three euglycaemia clamps were conducted: day 1 following a single dose of insulin detemir alone (0.5 U/kg), day 22 after 3 weeks of once-daily liraglutide with weekly dose escalation to 1.8 mg daily, and day 36 after 2 weeks of steady-state liraglutide maintenance at the 1.8 mg dose following co-administration with a single dose of insulin detemir (0.5 U/kg).

RESULTS

The study population (N = 33; age 49.6 (±8.5) years) had diabetes for an average of 6.5 (±4.1) years, BMI 33 (±6.4) kg/m², FPG 9.7 (±1.6) mmol/l and HbA1c 8.3% (±0.9). PK: The PK profiles of insulin detemir were similar with and without steady-state liraglutide. Liraglutide did not affect AUC or C(max) of insulin detemir and vice versa. The 90% confidence intervals (CIs) for ratios of insulin detemir AUC [1.03; CI (0.97, 1.09)] and C(max) [1.05; CI (0.98, 1.13)] and liraglutide AUC [0.97; CI (0.87, 1.08)] and C(max) [1.03, CI (0.93, 1.13)] were all within the no-effect boundary (0.80, 1.25) (bioequivalence criterion). A stable mean insulin detemir concentration with and without liraglutide was maintained at the end of the 24-h PK sampling period. PD: The sum of AUC(GIR) for liraglutide (1982 mg/kg) and insulin detemir (1058 mg/kg) when given alone was similar to that obtained when the two were co-administered (2947 mg/kg). No serious adverse events were reported and no adverse events led to study withdrawal.

CONCLUSION

Co-administration of liraglutide 1.8 mg at steady state and insulin detemir produces an additive glucose-lowering effect without affecting the PK profile of either therapeutic agent suggesting that the addition of insulin detemir to patients treated with liraglutide will not require titration algorithms different from when insulin is added to OADs. The co-administration of insulin detemir and liraglutide was well tolerated.

Dynamics of plasma active GLP-1 versus insulin and glucose concentrations during GLP-1 infusion in rat model of postprandial hyperglycemia

In vitro studies in isolated pancreas and islets have shown that glucagon-like peptide-1 (GLP-1) promotes insulin release in a typical concentration-dependent manner. In contrast, the relationship between plasma GLP-1 and insulin concentrations in vivo is complicated, because GLP-1-promoted insulin release lowers blood glucose, which influences glucose-dependent insulinotropic ability of GLP-1. GLP-1 also stimulates insulin release via hepatoportal neuronal mechanism. Hence, the dynamic relationship between plasma active GLP-1 vs. insulin and glucose concentrations is obscure. In this study, we aimed to determine in vivo relationships between these parameters in rats. To mimic postprandial state, intraduodenal glucose challenge in anesthetized rats was performed, which can minimize the release of endogenous GLP-1. The glucose challenge induced the 1st phase and 2nd phase insulin release. GLP-1 infusion from jugular vein significantly and concentration-dependently enhanced area under the curve (AUC) of the 1st phase insulin, in which the minimum effective active GLP-1 concentration was 6.6 pmol/l. In contrast, bell-shaped dose responses were observed for both the 2nd phase and total insulin AUCs, in which a significant increase was obtained only with 11 pmol/l of active GLP-1 for total insulin AUC. A statistically significant reduction in the plasma glucose AUC was observed when active GLP-1 concentration was 11 pmol/l and 21 pmol/l. These results indicate that GLP-1 markedly enhances the 1st phase insulin release while less potently the 2nd phase insulin release, possibly due to a negative feedback regulation of β-cells via reduced plasma glucose levels by the enhanced 1st phase insulin release.

Novel glucagon-like peptide-1 analog delivered orally reduces postprandial glucose excursions in porcine and canine models

BACKGROUND

Glucagon-like peptide-1 (GLP-1) and its analogs are associated with a gamut of physiological processes, including induction of insulin release, support of normoglycemia, β-cell function preservation, improved lipid profiles, and increased insulin sensitivity. Thus, GLP-1 harbors significant therapeutic potential for regulating type 2 diabetes mellitus, where its physiological impact is markedly impaired. To date, GLP-1 analogs are only available as injectable dosage forms, and its oral delivery is expected to provide physiological portal/peripheral concentration ratios while fostering patient compliance and adherence.

METHODS

Healthy, fasting, enterically cannulated pigs and beagle canines were administered a single dose of the exenatide-based ORMD-0901 formulation 30 min before oral glucose challenges. Blood samples were collected every 15 min for evaluation of ORMD-0901 safety and efficacy in regulating postchallenge glucose excursions.

RESULTS

Enterically delivered ORMD-0901 was well tolerated by all animals. ORMD-0901 formulations RG3 and AG2 led to reduced glucose excursions in pigs when delivered prior to a 5 g/kg glucose challenge, where area under the curve (AUC)0-120 values were up to 43% lower than in control sessions. All canines challenged with a glucose load with no prior exposure to exenatide, demonstrated higher AUC0-150 values than in their exenatide-treated sessions. Subcutaneous exenatide delivery amounted to a 51% reduction in mean glucose AUC0-150, while formulations AG4 and AG3 prompted 43% and 29% reductions, respectively.

CONCLUSIONS

When delivered enterically, GLP-1 (ORMD-0901) is absorbed from the canine and porcine gastrointestinal tracts and retains its biological activity. Further development of this drug class in an oral dosage form is expected to enhance diabetes control and patient compliance.

Effect of renal impairment on the pharmacokinetics of the GLP-1 analogue liraglutide

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

* Patients with Type 2 diabetes are likely to have or to develop renal impairment, which affects the pharmacokinetics of some antidiabetic treatments. * Whether dosing of the once-daily human glucagon-like peptide-1 analogue liraglutide should be modified in patients with renal impairment has not previously been studied.

WHAT THIS STUDY ADDS

* Renal dysfunction was not found to increase the exposure of liraglutide. * Hence, no dose adjustment is expected to be required in patients with Type 2 diabetes and renal impairment treated with liraglutide.

AIMS

To investigate whether dose adjustment of the once-daily human glucagon-like peptide-1 analogue liraglutide is required in patients with varying stages of renal impairment.

METHODS

A cohort of 30 subjects, of whom 24 had varying degrees of renal impairment and six had normal renal function, were given a single dose of liraglutide, 0.75 mg subcutaneously, and completed serial blood sampling for plasma liraglutide measurements for pharmacokinetic estimation.

RESULTS

No clear trend for change in pharmacokinetics was evident across groups with increasing renal dysfunction. While the between-group comparisons of the area under the liraglutide concentration-curve (AUC) did not demonstrate equivalence [estimated ratio AUC(severe)/AUC(healthy) 0.73, 90% confidence interval (CI) 0.57, 0.94; and AUC (continuous ambulatory peritoneal dialysis)(CAPD)/AUC(healthy) 0.74, 90% CI 0.56, 0.97], the regression analysis of log(AUC) for subjects with normal renal function and mild-to-severe renal impairment showed no significant effect of decreasing creatinine clearance on the pharmacokinetics of liraglutide. The expected AUC ratio between the two subjects with the lowest and highest creatinine clearance in the study was estimated to be 0.88 (95% CI 0.58, 1.34) (NS). Degree of renal impairment did not appear to be associated with an increased risk of adverse events.

CONCLUSIONS

This study indicated no safety concerns regarding use of liraglutide in patients with renal impairment. Renal dysfunction was not found to increase exposure of liraglutide, and patients with Type 2 diabetes and renal impairment should use standard treatment regimens of liraglutide. There is, however, currently limited experience with liraglutide in patients beyond mild-stage renal disease.

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.

Evaluation of novel particles as an inhalation system for GLP-1

AIM

The feasibility of administering native glucagon-like peptide 1 (GLP-1) as GLP-1 Technosphere Inhalation Powder for diabetes therapy has been demonstrated in a rat model.

METHODS

GLP-1 Technosphere Inhalation Powders containing 5, 10 and 15% GLP-1 were prepared and administered to healthy female Sprague-Dawley rats and to male Zucker diabetic obese rats. Rats received a single dose of GLP-1 Technosphere Powder by pulmonary insufflation. GLP-1 pharmacokinetic and pharmacodynamic responses were measured.

RESULTS

Maximum circulating GLP-1 concentrations were achieved at approximately 10 min after dosing with detectable levels at 40 min. In a food consumption study, Sprague-Dawley rats receiving GLP-1 Technosphere Powder once-daily consumed less food than control rats for up to 24 h after dosing. Cumulative food consumption was decreased approximately 10% after 78 h. In an intraperitoneal glucose tolerance test, Zucker diabetic fatty rats receiving 2 mg GLP-1 Technosphere Powder (0.3 mg GLP-1) by pulmonary insufflation exhibited lower glucose concentrations and higher insulin concentrations than control rats. Pancreatic evaluations showed no differences in apoptotic index or cell proliferation of beta-cells. In addition, a dose-related increase in insulin expression within the pancreas was observed.

CONCLUSIONS

These data demonstrate the feasibility of administering native GLP-1 as GLP-1 Technosphere Inhalation Powder for diabetes therapy.

Pharmacokinetic and pharmacodynamic properties of taspoglutide, a once-weekly, human GLP-1 analogue, after single-dose administration in patients with Type 2 diabetes

AIMS

The study objectives were to evaluate the pharmacokinetic and pharmacodynamic properties, as well as safety and tolerability, of single doses of taspoglutide, a human glucagon-like peptide-1 (GLP-1) analogue.

METHODS

In a double-blind, placebo-controlled study, 48 patients with Type 2 diabetes [mean age 56 +/- 7 years; mean body mass index (BMI) 30.4 +/- 3.0 kg/m(2)] inadequately controlled with metformin (< or = 2 g/day) were enrolled in three sequential cohorts; 12 patients in each cohort were randomized to a single subcutaneous injection of taspoglutide (1, 8 or 30 mg) and four received placebo.

RESULTS

Plasma concentrations peaked within 24 h after injection and were sustained for > or = 14 days with all doses. In comparison with placebo, the 8- and 30-mg doses of taspoglutide significantly reduced glycaemic parameters, including 24-h blood glucose and 5-h postprandial glucose areas under the curve (AUCs), for up to 14 days with the 30-mg dose (P < 0.001). The most common adverse events, primarily gastrointestinal in nature, were dose-dependent and transient.

CONCLUSIONS

A single dose of taspoglutide significantly improved glycaemic parameters in Type 2 diabetes patients for up to 14 days. The formulation was well tolerated and appears suitable for weekly administration.

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.

[Drug therapy of type 2 diabetes and cardiovascular prevention: potentials for liraglutide]

Recently, the European Medicines Agency (EMEA) Committee for Medicinal Products for Human Use (CHMP) adopted a positive opinion, recommending to grant a marketing authorization for liraglutide for the treatment of type 2 diabetes mellitus. Liraglutide is the first human glucagon-like peptide-1 (GLP-1) analog, based on the structure of native GLP-1, with pharmacokinetic properties suitable for once-daily dosing. In the phase III Liraglutide Effect and Action in Diabetes (LEAD) program, liraglutide has been shown to lower glycated hemoglobin to the same extent or more than other antidiabetic drugs including insulin. Liraglutide determines favorable changes in the global cardiovascular risk profile because its use is associated with weight loss, blood pressure reduction, as well as improvements of several cardiovascular risk biomarkers. Liraglutide is generally well tolerated, the most frequently reported adverse effect is transient nausea, and it does not seems to have significant interactions with medications commonly used for cardiovascular prevention. This article reviews, for the practicing cardiologist, the results of the LEAD program and explores liraglutide potentials for cardiovascular prevention in type 2 diabetes mellitus.

Potential of liraglutide in the treatment of patients with type 2 diabetes

Liraglutide is a long-acting analog of GLP-1, being developed by Novo Nordisk and currently undergoing regulatory review for the treatment of type 2 diabetes. Upon injection, liraglutide binds non-covalently to albumin, giving it a pharmacokinetic profile suitable for once-daily administration. In clinical trials of up to 1 year duration, liraglutide has been demonstrated to have beneficial effects on islet cell function, leading to improvements in glycemic control. Both fasting and postprandial glucose concentrations are lowered, and are associated with lasting reductions in HbA1c levels. Liraglutide is effective as monotherapy and in combination therapy with oral antidiabetic drugs, and reduces HbA1c by up to approximately 1.5% from baseline (8.2%-8.4%). Because of the glucose-dependency of its action, there is a low incidence of hypoglycemia. Liraglutide is associated with body weight loss, and reductions in systolic blood pressure have been observed throughout the clinical trials. The most common adverse events reported with liraglutide are gastrointestinal (nausea, vomiting and diarrhea). These tend to be most pronounced during the initial period of therapy and decline with time. Further clinical experience with liraglutide will reveal its long-term durability, safety and efficacy.

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.

PEGylation improves the hypoglycaemic efficacy of intranasally administered glucagon-like peptide-1 in type 2 diabetic db/db mice

AIMS

PEGylation - covalent modification of therapeutic peptides with polyethylene glycol (PEG) - is viewed as an effective way of prolonging the short lifetime of glucagon-like peptide-1 (GLP-1). In this study, we investigated the hypoglycaemic efficacies of PEGylated GLP-1s administered intranasally in type 2 diabetic db/db mice.

METHODS

Three types of site-specific (Lys(34)) PEGylated GLP-1 analogues (PEG molecular weight: 1, 2 or 5 kDa) were synthesized. Their metabolic stabilities were evaluated in nasal mucosa enzyme pools. Oral glucose tolerance test was conducted 30, 60 and 120 min after intranasally administering these analogues in type 2 diabetic db/db mice.

RESULTS

PEGylated GLP-1 analogues were found to have significantly longer half-lives than native GLP-1 in nasal mucosa enzymes (2.4-fold to 11.0-fold, p < 0.005). Non-PEGylated GLP-1 at 100 nmol/kg was not found to have marked efficacy irrespective of nasal administration time [total hypoglycaemic degree (HD(total)) values 2.8-17.3%]. On the contrary, PEGylated GLP-1s (100 nmol/kg) showed obvious efficacies with maximum HD(total) values of >51.8 +/- 5.8% (p < 0.005 vs. GLP-1).

CONCLUSION

This study highlights the pharmacological potential of intranasally administered PEGylated GLP-1s in terms of stabilizing postprandial hyperglycaemia in type 2 diabetic patients.

BIM-51077, a dipeptidyl peptidase-IV-resistant glucagon-like peptide-1 analog

F Hoffmann-La Roche Ltd, Teijin Ltd and Chugai Pharmaceutical Co Ltd, under license from Ipsen, are developing the glucagon-like peptide 1 analog BIM-51077, for the potential treatment of type 2 diabetes. Phase II clinical trials are underway, including a phase II trial evaluating a slow release formulation.

[Long-acting injectable microspheres of glucagon-like peptide-1]

AIM

To prepare glucagon-like peptide-1 (GLP-1) loaded long-acting injectable microspheres and to evaluate their in vitro release behavior as well as its pharmacodynamics.

METHODS

GLP-1 loaded microspheres were prepared with poly (lactic-co-glycolic acid) (PLGA) as carrier materials by dowble emulsion (W/O/W) method. Physical and chemical characteristics of microspheres, such as mean diameter, morphology and drug loading were evaluated. The in vitro release behavior and its influencing factors were determined by HPLC, also the bioactivity of GLP-1 in the course of encapsulation process and in vitro release were evaluated by in vivo animal experiments. The effect of reducing plasma glucose about GLP-1 microspheres were evaluated on the diabetes mice.

RESULTS

Microspheres with good shape and dispersive quality were prepared. The drug entrapment efficiency was more than 80%. The accumulated release in one month is up to 85% and the release equation is in accord with zero-class release model. The bioactivity of GLP-1 was conserved with glutin as inner water phase, but in the course of in vitro release, the specific activity of CLP-1 in the microspheres decreased a little. GLP-1 microspheres can decrease the plasma glucose significantly and the effect can go on for one month.

CONCLUSION

GLP-1 can be encapsulated in injectable microspheres to yield one-month continuous release when using biodegradable polymers PLGA as carrier material, and this technique will have a favorable perspective in the near future.

Effects of intravenous glucagon-like peptide-1 on gastric emptying and intragastric distribution in healthy subjects: relationships with postprandial glycemic and insulinemic responses

CONTEXT

The inhibitory action of glucagon-like peptide-1 (GLP-1) on gastric emptying (GE) is likely to be important in mediating its effects on postprandial glycemia, appetite, and gastrointestinal symptoms.

OBJECTIVE

The objective of the study was to evaluate the effects of "low" and "high" doses of iv GLP-1 on GE, intragastric meal distribution, glycemia, insulinemia, and appetite.

DESIGN

Ten healthy males were studied on 3 d. GE of a solid (ground beef)/liquid (glucose) meal, blood glucose, plasma insulin, glucagon and glucose-dependent insulinotropic peptide, appetite perceptions, and gastrointestinal symptoms were evaluated during iv infusion of: 1) GLP-1 at 0.3 pmol x kg(-1) x min(-1) (GLP-1 0.3); 2) GLP-1 at 0.9 pmol x kg(-1) x min(-1) (GLP-1 0.9); and 3) 0.9% saline.

RESULTS

GLP-1 0.3 and 0.9 slowed GE of solid (intragastric retention at t = 100 min; saline: 28 +/- 5%; GLP-1 0.3: 53 +/- 6%; GLP-1 0.9: 58 +/- 7%; P < 0.001) and liquid (time for 50% of the liquid to empty, saline: 28 +/- 2 min; GLP-1 0.3: 42 +/- 7 min; GLP-1 0.9: 50 +/- 9 min; P < 0.001). Both doses of GLP-1 induced gastroparesis in about half the cohort and increased meal retention in the distal stomach (P < 0.05). GLP-1 attenuated the rises in glucose, insulin, and glucose-dependent insulinotropic peptide (P < 0.05). There was an inverse relationship between blood glucose at t = 15 min and the time for 50% of the liquid to empty (r = -0.70, P < 0.001).

CONCLUSIONS

In healthy subjects exogenous GLP-1 increases meal retention in the distal stomach and, even when administered in a "low" dose, frequently induces "gastroparesis," and the effects of GLP-1 on postprandial glycemia are predictable on the basis of its effect on GE, supporting the concept that GE is a major target mechanism for the clinical use of incretin mimetics.

Exendin-4, but not glucagon-like peptide-1, is cleared exclusively by glomerular filtration in anaesthetised pigs

AIMS/HYPOTHESIS

The insulinotropic hormone, glucagon-like peptide-1 (GLP-1), is rapidly degraded in vivo as a result of the combination of extensive enzymatic degradation and renal extraction. The GLP-1 receptor agonist, exendin-4, has a longer duration of action, and has recently been approved as a new agent for the treatment of type 2 diabetes mellitus. Exendin-4 is less prone to enzymatic degradation, but it is still unclear what other factors contribute to the increased metabolic stability.

MATERIALS AND METHODS

The overall metabolism of GLP-1 and exendin-4 was directly compared in anaesthetised pigs (n=9).

RESULTS

Metabolism of GLP-1 (C-terminal RIA; t (1/2) 2.0+/-0.2 min, metabolic clearance rate [MCR] 23.2+/-2.8 ml min(-1) kg(-1); N-terminal RIA; t (1/2) 1.5+/-0.2 min, MCR 88.1+/-10.6 ml min(-1) kg(-1)) was significantly faster than the metabolism of exendin-4 (t (1/2) 22.0+/-2.1 min, p<0.0001; MCR 1.7+/-0.3 ml min(-1) kg(-1), p<0.01). Differences in arteriovenous concentrations revealed organ extraction of GLP-1 by the kidneys (C-terminal 56.6+/-2.6%; N-terminal 48.3+/-5.9%), liver (N-terminal 41.4+/-3.8%), and peripheral tissues (C-terminal 42.3+/-6.0%; N-terminal 33.0+/-7.8%), whereas organ extraction of exendin-4 was limited to the kidneys (21.3+/-4.9%). While the renal extraction of exendin-4 (6.9+/-2.5 pmol/min) did not differ significantly from the amount undergoing glomerular filtration (8.4+/-2.0 pmol/min), the renal extraction of C-terminal GLP-1 (9.0+/-1.1 pmol/min), exceeded the amount which could be accounted for by glomerular filtration (4.2+/-0.5 pmol/min, p<0.0005).

CONCLUSIONS/INTERPRETATION

In addition to an increased resistance to enzymatic degradation, the increased stability of exendin-4 is the result of reduced differential organ extraction compared to GLP-1. The data suggest that in the anaesthetised pig, extraction occurs only in the kidney and can be fully accounted for by glomerular filtration.

Pharmacologic modifications of hormones to improve their therapeutic potential for diabetes management

Rapid-acting genetically engineered insulin analogues emerging in the last 10 years are now established as more effective prandial insulins than traditional short-acting human insulin. The development of analogues for use as basal insulin, however, has been much slower. Methods of pro-tracting the time-action curve of injected insulin include complexing with proteins, insulin crystal formation, shifting the iso-electric point of the amino acid sequence or attaching a fatty-acid side chain to the molecule. The latter two methods have been more successful in producing physiologic insulin profiles when compared with the former methods. The principle of acylation has also been applied to prolong the action of other hormones, such as glucagon-like peptide 1 (GLP-1), as the native peptide has a very short half-life. Preliminary results with this compound and other GLP-1 analogues show promise in treating patients with type 2 diabetes. In summary, the development of new insulin and other hormone preparations by the manipulation of native peptide structure has recently improved our antidiabetic armamentarium, and further research will continue this fruitful approach.