Dipeptidyl Peptidase-4 Inhibitors Administered in Combination With Metformin Result in an Additive Increase in the Plasma Concentration of Active GLP-1

Practical combination therapy based on pathophysiology of type 2 diabetes

Type 2 diabetes is a complex, chronic, and progressive condition that often necessitates the use of multiple medications to achieve glycemic goals. Clinical guidelines generally recommend intensifying pharmacotherapy if glycemic goals are not achieved after 3 months of treatment. However, for many patients with type 2 diabetes, treatment intensification is delayed or does not occur. Initiating combination therapy early in the disease course has the potential to delay disease progression and improve patient outcomes. Guidelines generally provide a list of agents that may be used in combination regimens and emphasize individualization of treatment. The purpose of this review is to discuss the rationale for combination therapy, considering treatment effects on pathophysiologic aspects of type 2 diabetes and individual drug profiles. The combination of newer antidiabetes therapies with complementary mechanisms of action provides the opportunity to target multiple sites of tissue, organ, and cellular dysfunction.

Involvement of glucagon-like peptide-1 in the glucose-lowering effect of metformin

Metformin is an oral antihyperglycaemic drug used in the first-line treatment of type 2 diabetes. Metformin's classic and most well-known blood glucose-lowering mechanisms include reduction of hepatic gluconeogenesis and increased peripheral insulin sensitivity. Interestingly, intravenously administered metformin is ineffective and recently, metformin was shown to increase plasma concentrations of the glucose-lowering gut incretin hormone glucagon-like peptide-1 (GLP-1), which may contribute to metformin's glucose-lowering effect in patients with type 2 diabetes. The mechanisms behind metformin-induced increments in GLP-1 levels remain unknown, but it has been hypothesized that metformin stimulates GLP-1 secretion directly and/or indirectly and that metformin prolongs the half-life of GLP-1. Also, it has been suggested that metformin may potentiate the glucose-lowering effects of GLP-1 by increasing target tissue sensitivity to GLP-1. The present article critically reviews the possible mechanisms by which metformin may affect GLP-1 levels and sensitivity and discusses whether such alterations may constitute important and clinically relevant glucose-lowering actions of metformin.

Prescription of oral hypoglycemic agents for patients with type 2 diabetes mellitus: A retrospective cohort study using a Japanese hospital database

Aims/Introduction

In treatment algorithms of type 2 diabetes mellitus in Western countries, biguanides are recommended as first‐line agents. In Japan, various oral hypoglycemic agents (OHAs) are available, but prescription patterns are unclear.

Materials and Methods

Data of 7,108 and 2,655 type 2 diabetes mellitus patients in study 1 and study 2, respectively, were extracted from the Medical Data Vision database (2008–2013). Cardiovascular disease history was not considered in study 1, but was in study 2. Initial choice of OHA, adherence to its use, effect on glycated hemoglobin levels for 2 years and the second choice of OHA were investigated.

Results

In study 1, α‐glucosidase inhibitor, glinide and thiazolidinedione were preferentially medicated in relatively lower glycated hemoglobin cases compared with other OHAs. The two most prevalent first prescriptions of OHAs were biguanides and dipeptidyl peptidase‐4 inhibitors, and the greatest adherence was for α‐glucosidase inhibitors. In patients treated continuously with a single OHA for 2 years, improvement in glycated hemoglobin levels was greatest for dipeptidyl peptidase‐4 inhibitors. As a second OHA added to the first OHA during the first 2 years, dipeptidyl peptidase‐4 inhibitors were chosen most often, especially if a biguanide was the first OHA. In study 2, targeting patients with a cardiovascular disease history, a similar tendency to study 1 was observed in the first choice of OHA, adherence and the second choice of OHA.

Conclusions

Even in Japanese type 2 diabetes mellitus patients, a Western algorithm seems to be respected to some degree. The OHA choice does not seem to be affected by a cardiovascular disease history.

A randomized clinical trial evaluating the safety and efficacy of sitagliptin added to the combination of sulfonylurea and metformin in patients with type 2 diabetes mellitus and inadequate glycemic control

BACKGROUND

Type 2 diabetes mellitus (T2DM) treatment generally requires multiple antihyperglycemic agents. When diet, exercise, and treatment with sulfonylurea and metformin do not achieve glycemic goals, several options are available. The present study evaluated the efficacy and tolerability of sitagliptin 100 mg/day added to therapy with sulfonylurea and metformin.

METHODS

Patients with HbA1c ≥7.5% and ≤10.5% while on a sulfonylurea and metformin were randomized 1: 1 to sitagliptin 100 mg/day or placebo for 24 weeks. At Week 24, patients in the placebo group switched to pioglitazone 30 mg/day and both groups continued treatment for another 30 weeks.

RESULTS

Of 427 patients randomized, 339 (79.4%) completed the study. At Week 24, significantly greater (P < 0.001) mean reductions from baseline were seen in the sitagliptin versus placebo group for HbA1c (-0.84% vs -0.16%, respectively), 2-h post-meal glucose (-2.0 vs -0.2 mmol/L, respectively) and fasting plasma glucose (-0.7 vs 0.3 mmol/L, respectively). At Week 54, improvements in glycemic control continued. At Week 24, the incidence of adverse events (AEs) was numerically greater with sitagliptin than placebo, primarily because of a higher incidence of hypoglycemia. At Week 54, the incidence of AEs was similar in both groups, primarily because of a higher incidence of hypoglycemia and edema in the placebo/pioglitazone group after Week 24. The only meaningful change in body weight was an increase in the placebo/pioglitazone group at Week 54.

CONCLUSIONS

In this study, sitagliptin 100 mg/day was generally well tolerated and provided improvement in glycemic control when added to the combination of sulfonylurea and metformin in patients with T2DM.

Pharmacokinetic and pharmacodynamic interactions between metformin and a novel dipeptidyl peptidase-4 inhibitor, evogliptin, in healthy subjects

Evogliptin is a newly developed dipeptidyl peptidase-4 (DPP-4) inhibitor, which is expected to be combined with metformin for treating type 2 diabetes mellitus. We investigated the potential pharmacokinetic and pharmacodynamic interactions between evogliptin and metformin. A randomized, open-label, multiple-dose, six-sequence, three-period crossover study was conducted in 36 healthy male subjects. All subjects received three treatments, separated by 7-day washout intervals: evogliptin, 5 mg od for 7 days (EVO); metformin IR, 1,000 mg bid for 7 days (MET); and the combination of EVO and MET (EVO + MET). After the last dose in a period, serial blood samples were collected for 24 hours for pharmacokinetic assessments. During steady state, serial blood samples were collected for 2 hours after an oral glucose tolerance test, and DPP-4, active glucagon-like peptide-1, glucose, glucagon, insulin, and C-peptide were measured to assess pharmacodynamic properties. EVO + MET and EVO showed similar steady state maximum concentration and area under the concentration-time curve at steady state values for evogliptin; the geometric mean ratios (90% confidence interval) were 1.06 (1.01-1.12) and 1.02 (0.99-1.06), respectively. EVO + MET slightly reduced steady state maximum concentration and area under the concentration-time curve at steady state values for metformin compared to MET, with geometric mean ratios (90% confidence interval) of 0.84 (0.79-0.89) and 0.94 (0.89-0.98), respectively. EVO + MET and EVO had similar DPP-4 inhibition efficacy, but EVO + MET increased active glucagon-like peptide-1 and reduced glucose to larger extents than either EVO or MET alone. Our results suggested that EVO+MET could provide therapeutic benefits without clinically significant pharmacokinetic interactions. Thus, the EVO + MET combination is a promising option for treating type 2 diabetes mellitus.

Once-daily delayed-release metformin lowers plasma glucose and enhances fasting and postprandial GLP-1 and PYY: results from two randomised trials

AIMS/HYPOTHESIS

Delayed-release metformin (Metformin DR) was developed to maximise gut-based mechanisms of metformin action by targeting the drug to the ileum. Metformin DR was evaluated in two studies. Study 1 compared the bioavailability and effects on circulating glucose and gut hormones (glucagon-like peptide-1, peptide YY) of Metformin DR dosed twice-daily to twice-daily immediate-release metformin (Metformin IR). Study 2 compared the bioavailability and glycaemic effects of Metformin DR dosages of 1,000 mg once-daily in the morning, 1,000 mg once-daily in the evening, and 500 mg twice-daily.

METHODS

Study 1 was a blinded, randomised, crossover study (three × 5 day treatment periods) of twice-daily 500 mg or 1,000 mg Metformin DR vs twice-daily 1,000 mg Metformin IR in 24 participants with type 2 diabetes conducted at two study sites (Celerion Inc.; Tempe, AZ, and Lincoln, NE, USA). Plasma glucose and gut hormones were assessed over 10.25 h at the start and end of each treatment period; plasma metformin was measured over 11 h at the end of each treatment period. Study 2 was a non-blinded, randomised, crossover study (three × 7 day treatment periods) of 1,000 mg Metformin DR once-daily in the morning, 1,000 mg Metformin DR once-daily in the evening, or 500 mg Metformin DR twice-daily in 26 participants with type 2 diabetes performed at a single study site (Celerion, Tempe, AZ). Plasma glucose was assessed over 24 h at the start and end of each treatment period, and plasma metformin was measured over 30 h at the end of each treatment period. Both studies implemented centrally generated computer-based randomisation using a 1:1:1 allocation ratio.

RESULTS

A total of 24 randomised participants were included in study 1; of these, 19 completed the study and were included in the evaluable population. In the evaluable population, all treatments produced similar significant reductions in fasting glucose (median reduction range, -0.67 to -0.81 mmol/l across treatments) and postprandial glucose (Day 5 to baseline AUC0-t ratio = 0.9 for all three treatments) and increases in gut hormones (Day 5 to baseline AUC0-t ratio range: 1.6-1.9 for GLP-1 and 1.4-1.5 for PYY) despite an almost 60% reduction in systemic metformin exposure for 500 mg Metformin DR compared with Metformin IR. A total of 26 randomised participants were included in study 2: 24 had at least one dose of study medication and at least one post-dose pharmacokinetic/pharmacodynamic assessment and were included in the pharmacokinetic/pharmacodynamic intent-to-treat analysis; and 12 completed all treatment periods and were included in the evaluable population. In the evaluable population, Metformin DR administered once-daily in the morning had 28% (90% CI -16%, -39%) lower bioavailability (least squares mean ratio of metformin AUC0-24) compared with either once-daily in the evening or twice-daily, although the glucose-lowering effects were maintained. In both studies, adverse events were primarily gastrointestinal in nature, and indicated similar or improved tolerability for Metformin DR vs Metformin IR; there were no clinically meaningful differences in vital signs, physical examinations or laboratory values.

CONCLUSIONS/INTERPRETATION

Dissociation of gut hormone release and glucose lowering from plasma metformin exposure provides strong supportive evidence for a distal small intestine-mediated mechanism of action. Directly targeting the ileum with Metformin DR once-daily in the morning may provide maximal metformin efficacy with lower doses and substantially reduce plasma exposure. Metformin DR may minimise the risk of lactic acidosis in those at increased risk from metformin therapy, such as individuals with renal impairment.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01677299, NCT01804842 FUNDING: : This study was funded by Elcelyx Therapeutics Inc.

Comparison of Vildagliptin and Pioglitazone in Korean Patients with Type 2 Diabetes Inadequately Controlled with Metformin

BACKGROUND

We compared the efficacies of vildagliptin (50 mg twice daily) relative to pioglitazone (15 mg once daily) as an add-on treatment to metformin for reducing glycosylated hemoglobin (HbA1c) levels in Korean patients with type 2 diabetes.

METHODS

The present study was a multicenter, randomized, active-controlled investigation comparing the effects of vildagliptin and pioglitazone in Korean patients receiving a stable dose of metformin but exhibiting inadequate glycemic control. Each patient underwent a 16-week treatment period with either vildagliptin or pioglitazone as an add-on treatment to metformin.

RESULTS

The mean changes in HbA1c levels from baseline were -0.94% in the vildagliptin group and -0.6% in the pioglitazone group and the difference between the treatments was below the non-inferiority margin of 0.3%. The mean changes in postprandial plasma glucose (PPG) levels were -60.2 mg/dL in the vildagliptin group and -38.2 mg/dL in the pioglitazone group and these values significantly differed (P=0.040). There were significant decreases in the levels of total, low density lipoprotein, high density lipoprotein (HDL), and non-HDL cholesterol in the vildagliptin group but increases in the pioglitazone group. The mean change in body weight was -0.07 kg in the vildagliptin group and 0.69 kg in the pioglitazone group, which were also significantly different (P=0.002).

CONCLUSION

As an add-on to metformin, the efficacy of vildagliptin for the improvement of glycemic control is not inferior to that of pioglitazone in Korean patients with type 2 diabetes. In addition, add-on treatment with vildagliptin had beneficial effects on PPG levels, lipid profiles, and body weight compared to pioglitazone.

Metformin and the gastrointestinal tract

Metformin is an effective agent with a good safety profile that is widely used as a first-line treatment for type 2 diabetes, yet its mechanisms of action and variability in terms of efficacy and side effects remain poorly understood. Although the liver is recognised as a major site of metformin pharmacodynamics, recent evidence also implicates the gut as an important site of action. Metformin has a number of actions within the gut. It increases intestinal glucose uptake and lactate production, increases GLP-1 concentrations and the bile acid pool within the intestine, and alters the microbiome. A novel delayed-release preparation of metformin has recently been shown to improve glycaemic control to a similar extent to immediate-release metformin, but with less systemic exposure. We believe that metformin response and tolerance is intrinsically linked with the gut. This review examines the passage of metformin through the gut, and how this can affect the efficacy of metformin treatment in the individual, and contribute to the side effects associated with metformin intolerance.

Pharmacokinetic and Pharmacodynamic Effects of Multiple-dose Administration of Omarigliptin, a Once-weekly Dipeptidyl Peptidase-4 Inhibitor, in Obese Participants With and Without Type 2 Diabetes Mellitus

PURPOSE

Omarigliptin (MK-3102) is a potent, oral, long-acting dipeptidyl peptidase (DPP)-4 inhibitor approved in Japan and in global development as a once-weekly treatment for type 2 diabetes mellitus (T2DM). The aim of this study was to investigate the pharmacokinetic (PK) and pharmacodynamic (PD) effects of omarigliptin in obese participants with and without T2DM.

METHODS

This was a Phase I, randomized, double-blind, placebo-controlled, multiple-dose study of 50-mg omarigliptin administered once weekly for 4 weeks. Participants included 24 obese but otherwise healthy subjects (panel A; omarigliptin, n = 18; placebo, n = 6) and 8 obese patients with T2DM (treatment naive, hemoglobin A1c ≥ 6.5% and ≤ 10.0% [panel B]; omarigliptin, n = 6; placebo, n = 2). Participants were 45 to 65 years of age with a body mass index of ≥ 30 and ≤ 40 kg/m(2). Blood sampling occurred at select time points, depending on the study panel, to evaluate the PK properties of omarigliptin, DPP-4 activity, active glucagon-like peptide 1 levels, and plasma glucose concentrations. Body weight was an exploratory end point. Due to sparse sampling in panel A, a thorough PK analysis was performed in obese patients with T2DM (panel B) only. PD analyses were performed in the overall study population (pooled panels A and B).

FINDINGS

PK profiles in obese participants with and without T2DM were similar to those observed in nonobese reference subjects (historical data). Steady state was achieved after 1 or 2 weekly doses in obese participants with and without T2DM. In obese patients with T2DM, omarigliptin was rapidly absorbed, with a median Tmax of 1 to 2.5 hours (days 1 and 22). Compared with those in reference subjects, the geometric mean ratios (95% CI) (Obese T2DM/reference) for steady-state plasma AUC0-168h, Cmax, and C168h were 0.80 (0.65-0.98), 0.86 (0.53-1.41), and 1.08 (0.88-1.33), respectively. Trough DPP-4 activity was inhibited by ~90%; postprandial (PP) 4-hour weighted mean active GLP-1 concentrations were increased ~2-fold; and PP glucose was significantly reduced with omarigliptin versus placebo in the pooled population. Omarigliptin was generally well-tolerated in the pooled population, and there were no hypoglycemic events. Consistent with other DPP-4 inhibitors, omarigliptin had no effect on body weight in this short-duration study.

IMPLICATIONS

The administration of omarigliptin was generally well-tolerated in obese participants with and without T2DM, and the favorable PK and PD profiles support once-weekly dosing. Omarigliptin may provide an important once-weekly treatment option for patients with T2DM. ClinicalTrials.gov identifier: NCT01088711.

The Primary Glucose-Lowering Effect of Metformin Resides in the Gut, Not the Circulation: Results From Short-term Pharmacokinetic and 12-Week Dose-Ranging Studies

OBJECTIVE

Delayed-release metformin (Met DR) is formulated to deliver the drug to the lower bowel to leverage the gut-based mechanisms of metformin action with lower plasma exposure. Met DR was assessed in two studies. Study 1 compared the bioavailability of single daily doses of Met DR to currently available immediate-release metformin (Met IR) and extended-release metformin (Met XR) in otherwise healthy volunteers. Study 2 assessed glycemic control in subjects with type 2 diabetes (T2DM) over 12 weeks.

RESEARCH DESIGN AND METHODS

Study 1 was a phase 1, randomized, four-period crossover study in 20 subjects. Study 2 was a 12-week, phase 2, multicenter, placebo-controlled, dose-ranging study in 240 subjects with T2DM randomized to receive Met DR 600, 800, or 1,000 mg administered once daily; blinded placebo; or unblinded Met XR 1,000 or 2,000 mg (reference).

RESULTS

The bioavailability of 1,000 mg Met DR b.i.d. was ∼50% that of Met IR and Met XR (study 1). In study 2, 600, 800, and 1,000 mg Met DR q.d. produced statistically significant, clinically relevant, and sustained reductions in fasting plasma glucose (FPG) levels over 12 weeks compared with placebo, with an ∼40% increase in potency compared with Met XR. The placebo-subtracted changes from baseline in HbA1c level at 12 weeks were consistent with changes in FPG levels. All treatments were generally well tolerated, and adverse events were consistent with Glucophage/Glucophage XR prescribing information.

CONCLUSIONS

Dissociation of the glycemic effect from plasma exposure with gut-restricted Met DR provides strong evidence for a predominantly lower bowel-mediated mechanism of metformin action.

Fibroblast Activation Protein Cleaves and Inactivates Fibroblast Growth Factor 21

FGF21 is a stress-induced hormone with potent anti-obesity, insulin-sensitizing, and hepatoprotective properties. Although proteolytic cleavage of recombinant human FGF21 in preclinical species has been observed previously, the regulation of endogenously produced FGF21 is not well understood. Here we identify fibroblast activation protein (FAP) as the enzyme that cleaves and inactivates human FGF21. A selective chemical inhibitor, immunodepletion, or genetic deletion of Fap stabilized recombinant human FGF21 in serum. In addition, administration of a selective FAP inhibitor acutely increased circulating intact FGF21 levels in cynomolgus monkeys. On the basis of our findings, we propose selective FAP inhibition as a potential therapeutic approach to increase endogenous FGF21 activity for the treatment of obesity, type 2 diabetes, non-alcoholic steatohepatitis, and related metabolic disorders.

Specific inhibition of bile acid transport alters plasma lipids and GLP-1

BACKGROUND

Elobixibat is a minimally absorbed ileal bile acid (BA) transporter (IBAT) inhibitor in development against chronic constipation (CC) and constipation-predominant Irritable Bowel Syndrome (IBS-C). CC is associated with an increased risk for cardiovascular disease and type2 diabetes mellitus. The objectives of this study were to evaluate metabolic effects of elobixibat. Effects on plasma lipids and BA synthesis were evaluated utilizing a 4-week, placebo-controlled study in patients with dyslipidemia while changes of glucagon-like peptide-1 (GLP-1) by elobixibat was assayed in samples from a 14 day high-dose elobixibat study in patients with CC.

METHODS

Thirty-six dyslipidemic patients, 21 females, mean age 63 years, were randomized to 2.5 mg or 5 mg elobixibat or placebo once daily for four weeks. The primary endpoint was the change in low density lipoprotein (LDL) cholesterol. Secondary endpoints included other lipid parameters and serum 7α-hydroxy-4-cholesten-3-one (C4), a marker of BA (bile acid) synthesis. Another study, in 36 patients with CC treated with high dose elobixibat; 15 mg or 20 mg/day or placebo for 14 days, was evaluated for changes in GLP-1.

RESULTS

In the dyslipidemia study LDL cholesterol was reduced by 7.4 % (p = 0.044), and the LDL/HDL ratio was decreased by 18 % (p = 0.004). Serum C4 increased, indicating that BA synthesis was induced. No serious adverse events were recorded. In the CC study, GLP-1 increased significantly in both the 15 mg (20.7 ± 2.4 pmol/L; p = 0.03) and the 20 mg group (25.6 ± 4.9 pmol/L; p = 0.02).

CONCLUSIONS

Elobixibat reduces LDL cholesterol and LDL/HDL ratio and increase circulating peak GLP-1 levels, the latter in line with increased intestinal BA mediated responses in humans.

TRIAL REGISTRATIONS

ClinicalTrial.gov: NCT01069783 and NCT01038687 .

Effects of aerobic exercise with or without metformin on plasma incretins in type 2 diabetes

OBJECTIVE

Despite positive effects of incretins on insulin secretion, little is known about the effect of exercise on these hormones. Metformin can affect incretin concentrations and is prescribed to a large proportion of people with diabetes. We, therefore, examined the effects of aerobic exercise and/or metformin on incretin hormones.

METHODS

Ten participants with type 2 diabetes were recruited for this randomized crossover study. Metformin or placebo was given for 28 days, followed by the alternate treatment for 28 days. On the last 2 days of each condition, participants were assessed during a non-exercise day and a subsequent exercise day. Aerobic exercise took place in the morning and blood samples were taken in the subsequent hours (before and after lunch).

RESULTS

Aerobic exercise did not increase total plasma glucagon-like peptide-1 (GLP-1) or glucose-dependent insulinotropic polypeptide (GIP) in the pre- or post-lunch periods (all p>0.1). GLP-1 was higher in the pre-lunch (p=0.016) and post-lunch (p=0.018) periods of the metformin conditions compared with the placebo. Total plasma GIP was higher in the pre-lunch period (p=0.05), but not in the post-lunch period (p=0.95), with metformin compared with placebo.

CONCLUSIONS

In contrast to our hypothesis, aerobic exercise did not acutely increase total GLP-1 and GIP levels in patients with type 2 diabetes. Metformin, independent of exercise, significantly increased total plasma GLP-1 and GIP concentrations in these patients.

Complementary glucagonostatic and insulinotropic effects of DPP-4 inhibitors in the glucose-lowering action in Japanese patients with type 2 diabetes

The dipeptidyl peptidase-4 (DPP-4) inhibitors have a low risk of causing hypoglycemia as monotherapy. However, insulin administration is frequently required, particularly in patients with type 2 diabetes and with reduced insulin secretory capacity. The effects of adding DPP-4 inhibitors were evaluated using continuous glucose monitoring (CGM) in Japanese patients with type 2 diabetes who were insufficiently controlled by basal insulin with biguanide. The effects of adding DPP-4 inhibitors on blood glucose and plasma insulin and glucagon levels were evaluated. Δ glucagon showed a significant association with post-prandial glucose increase in the group with diminished insulin secretory capacity, C-peptide index (CPI) <0.8 (p = 0.016), while Δ C-peptide reached significant association in the group with relatively intact insulin secretory capacity, CPI ≥0.8 (p = 0.017). The mean plasma glucose levels and M values were similarly improved in patients treated with the three DPP-4 inhibitors. Hypoglycemia did not occur in any of the DPP-4 inhibitor groups. In conclusion, complementary glucagonostatic and insulinotropic effects of adding DPP-4 inhibitors are involved in the glucose-lowering action of Japanese patients with type 2 diabetes according to their insulin secretory capacity. Such combination therapy may well be a superior therapeutic option for the treatment of diabetes in Japanese patients who often exhibit reduced insulin secretory capacity.

Comparison of vildagliptin as an add-on therapy and sulfonylurea dose-increasing therapy in patients with inadequately controlled type 2 diabetes using metformin and sulfonylurea (VISUAL study): A randomized trial

The aim of present study is to compare the efficacy and safety of adding vildagliptin with sulfonylurea dose-increasing as an active comparator in patients who had inadequately controlled type 2 diabetes mellitus (T2DM) using metformin plus sulfonylurea in real clinical practice. Patients using metformin plus sulfonylurea were assigned to either vildagliptin add-on (50 mg twice a day, n=172) or sulfonylurea dose-increasing by 50% (n=172) treatment groups. The primary endpoint was a change in HbA(1c) after 24 weeks. The secondary endpoints were patients achieving HbA(1c)≤7.0% (53 mmol/mol) and changes in the fasting plasma glucose (FPG), 2-h postprandial glucose (2pp), lipid profiles, and urine albumin-to-creatinine ratio. Body weight and hypoglycemia were also investigated. The mean HbA(1c) at baseline was 8.6% (70 mmol/mol) in both groups. At week 24, the adjusted mean HbA(1c) levels decreased by -1.19% (-13.09 mmol/mol) with vildagliptin add-on and -0.46% (-5.06 mmol/mol) with sulfonylurea (P<0.001). Significantly more vildagliptin add-on patients achieved HbA(1c)≤7.0% (53 mmol/mol) than did sulfonylurea patients (40.1% vs. 7.9%; P<0.001). Greater reductions in FPG and 2pp were observed with vildagliptin add-on than with sulfonylurea (P<0.001). The vildagliptin add-on group exhibited no clinically relevant weight gain and had a lower incidence of hypoglycemia compared with the sulfonylurea group. Vildagliptin add-on therapy might be a suitable option for patients with T2DM that is controlled inadequately by metformin and sulfonylurea, based on its greater glucose control and better safety profile (ClinicalTrial.gov: NCT01099137).

GLP-1 Response to Oral Glucose Is Reduced in Prediabetes, Screen-Detected Type 2 Diabetes, and Obesity and Influenced by Sex: The ADDITION-PRO Study

The role of glucose-stimulated release of GLP-1 in the development of obesity and type 2 diabetes is unclear. We assessed GLP-1 response to oral glucose in a large study population of lean and obese men and women with normal and impaired glucose regulation. Circulating concentrations of glucose, insulin, and GLP-1 during an oral glucose tolerance test (OGTT) were analyzed in individuals with normal glucose tolerance (NGT) (n = 774), prediabetes (n = 525), or screen-detected type 2 diabetes (n = 163) who attended the Danish ADDITION-PRO study (n = 1,462). Compared with individuals with NGT, women with prediabetes or type 2 diabetes had 25% lower GLP-1 response to an OGTT, and both men and women with prediabetes or type 2 diabetes had 16-21% lower 120-min GLP-1 concentrations independent of age and obesity. Obese and overweight individuals had up to 20% reduced GLP-1 response to oral glucose compared with normal weight individuals independent of glucose tolerance status. Higher GLP-1 responses were associated with better insulin sensitivity and β-cell function, older age, and lesser degree of obesity. Our findings indicate that a reduction in GLP-1 response to oral glucose occurs prior to the development of type 2 diabetes and obesity, which can have consequences for early prevention strategies for diabetes.

Effects of Miglitol, Acarbose, and Sitagliptin on Plasma Insulin and Gut Peptides in Type 2 Diabetes Mellitus: A Crossover Study

INTRODUCTION

Both dipeptidyl peptidase-4 inhibitors and α-glucosidase inhibitors (α-GI) have been reported to change the incretin and insulin secretion. To examine the effects of acarbose, miglitol, and sitagliptin on glucose metabolism and secretion of gut peptides, we conducted a crossover study in patients with type 2 diabetes mellitus (T2DM).

METHODS

Eleven Japanese patients with T2DM underwent four meal tolerance tests with single administration of acarbose, miglitol, sitagliptin, or nothing. Fasting and postprandial plasma levels of glucose, insulin, glucagon, active glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), ghrelin, and des-acyl ghrelin were measured.

RESULTS

Early-phase insulin secretion was reduced following acarbose and miglitol, and the areas under the curve (AUC) of insulin at 180 min following acarbose and miglitol were significantly lower than sitagliptin. AUC of plasma glucose at 180 min after acarbose, miglitol, and sitagliptin tended to be lower than in controls, and plasma glucose levels at 30-60 min following miglitol were significantly lower than in controls. Plasma glucagon, ghrelin, and des-acyl ghrelin levels did not differ among the four conditions. Postprandial plasma active GLP-1 levels and AUC of GLP-1 increased significantly in both the sitagliptin and miglitol groups compared to control. Postprandial plasma total GIP levels increased following sitagliptin but decreased after acarbose and miglitol. Changes in incretin levels tended to be greater with miglitol than acarbose.

CONCLUSION

These results showed that sitagliptin and α-GIs, miglitol more so than acarbose, improved hyperglycemia in patients with T2DM after single administration, and had different effects on insulin and incretin secretion.

TRIAL REGISTRATION

UMIN-CTR number, UMIN000009981.

Pharmacokinetic and pharmacodynamic interaction between gemigliptin and metformin in healthy subjects

BACKGROUND AND OBJECTIVE

Gemigliptin is a novel dipeptidyl peptidase-4 (DPP-4) inhibitor used in the treatment of type 2 diabetes mellitus. This study evaluated possible pharmacodynamic and pharmacokinetic interactions between gemigliptin and metformin and investigated their tolerability.

METHODS

A randomized, open-label, multiple-dose, three-treatment, three-period, three-sequence crossover study was conducted in healthy male subjects. Twenty-seven subjects received gemigliptin (50 mg once daily), metformin (1,000 mg twice a day), or both drugs for 7 days per dosing period. Blood samples were drawn over 24 h on the seventh day of each period for pharmacokinetic and pharmacodynamic evaluations, including plasma DPP-4 activity and total/active glucagon-like peptide-1 (GLP-1) levels. Meal tolerance tests were conducted for pharmacodynamic assessment on the eighth day. Safety and tolerability were evaluated using adverse events, vital signs, ECGs, and clinical laboratory tests.

RESULTS

Coadministration of gemigliptin and metformin had no significant effect on the pharmacokinetics of gemigliptin or metformin. The inhibition of DPP-4 by gemigliptin was not affected by coadministration with metformin. Co-therapy of gemigliptin and metformin showed additional effects by increasing plasma active GLP-1 concentrations and lowering serum glucose levels. The plasma glucagon level was lower in co-therapy than with metformin monotherapy. The coadministration of gemigliptin and metformin was well-tolerated without serious adverse events.

CONCLUSIONS

Coadministration of gemigliptin and metformin showed beneficial anti-diabetic effects without pharmacokinetic drug-drug interactions.

Addition of sitagliptin or metformin to insulin monotherapy improves blood glucose control via different effects on insulin and glucagon secretion in hyperglycemic Japanese patients with type 2 diabetes

This study aimed to explore the effects of the dipeptidyl peptidase-4 inhibitor sitagliptin and the biguanide metformin on the secretion of insulin and glucagon, as well as incretin levels, in Japanese subjects with type 2 diabetes mellitus poorly controlled with insulin monotherapy. This was a single-center, randomized, open-label, parallel group study, enrolling 25 subjects. Eleven patients (hemoglobin A1c [HbA1c] 8.40 ± 0.96%) and 10 patients (8.10 ± 0.54%) on insulin monotherapy completed 12-week treatment with sitagliptin (50 mg) and metformin (750 mg), respectively. Before and after treatment, each subject underwent a meal tolerance test. The plasma glucose, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), C-peptide, and glucagon responses to a meal challenge were measured. HbA1c reductions were similar in patients treated with sitagliptin (0.76 ± 0.18%) and metformin (0.77 ± 0.17%). In the sitagliptin group, glucose excursion during a meal tolerance test was reduced and accompanied by elevations in active GLP-1 and active GIP concentrations. C-peptide levels were unaltered despite reduced glucose responses, while glucagon responses were significantly suppressed (-7.93 ± 1.95% of baseline). In the metformin group, glucose excursion and incretin responses were unaltered. C-peptide levels were slightly increased but glucagon responses were unchanged. Our data indicate that sitagliptin and metformin exert different effects on islet hormone secretion in Japanese type 2 diabetic patients on insulin monotherapy. A glucagon suppressing effect of sitagliptin could be one of the factors improving blood glucose control in patients inadequately controlled with insulin therapy.

Restoration of the insulinotropic effect of glucose-dependent insulinotropic polypeptide contributes to the antidiabetic effect of dipeptidyl peptidase-4 inhibitors

AIMS

To examine whether 12 weeks of treatment with a dipeptidyl peptidase-4 (DPP-4) inhibitor, sitagliptin, influences the insulin secretion induced by glucose, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) during a hyperglycaemic clamp in patients with type 2 diabetes (T2DM).

METHODS

A randomized, double-blind, placebo-controlled study was conducted over 12 weeks, during which 25 patients with T2DM completed treatment with either sitagliptin (100 mg once daily) or placebo as add-on therapy to metformin [sitagliptin group (n = 12): mean ± standard error of the mean (s.e.m.) age 54 ± 2.5 years, mean ± s.e.m. HbA1c 7.8 ± 0.2%; placebo group (n = 13): mean ± s.e.m. age: 57 ± 3.0 years, mean ± s.e.m. HbA1c 7.9 ± 0.2 %]. In weeks 1 and 12, the patients underwent three 2-h 15-mM hyperglycaemic clamp experiments with infusion of either saline, GLP-1 or GIP. β-cell function was evaluated according to first-phase, second-phase, incremental and total insulin and C-peptide responses.

RESULTS

In the sitagliptin group, the mean HbA1c concentration was significantly reduced by 0.9% (p = 0.01). The total β-cell response during GIP infusion improved significantly from week 1 to week 12, both within the sitagliptin group (p = 0.004) and when compared with the placebo group (p = 0.04). The total β-cell response during GLP-1 infusion was significantly higher (p = 0.001) when compared with saline and GIP infusion, but with no improvement from week 1 to week 12. No significant changes in β-cell function occurred in the placebo group.

CONCLUSIONS

Treatment with the DPP-4 inhibitor sitagliptin over 12 weeks in patients with T2DM partially restored the lost insulinotropic effect of GIP, whereas the preserved insulinotropic effect of GLP-1 was not further improved. A gradual enhancement of the insulinotropic effect of GIP, therefore, possibly contributes to the antidiabetic actions of DPP-4 inhibitors.

Dipeptidyl peptidase-4 inhibitors in triple oral therapy regimens in patients with type 2 diabetes mellitus

OBJECTIVE

There is no clear consensus regarding treatment of patients with type 2 diabetes mellitus (T2DM) that is inadequately controlled using dual combination therapy. Recommended agents for triple combination therapy should have complementary mechanisms of action with minimal risk of added side effects such as weight gain and hypoglycemia. We discuss considerations in selecting triple oral therapy regimens in patients with T2DM, and review clinical trial data regarding triple oral therapy using dipeptidyl peptidase-4 (DPP-4) inhibitors.

METHODS

A search of the PubMed database was conducted to identify clinical trials of triple oral therapy incorporating a DPP-4 inhibitor (November 2013 to January 2015), using the following search terms: 'type 2 diabetes' AND 'alogliptin OR linagliptin OR saxagliptin OR sitagliptin OR vildagliptin' AND 'metformin'. Trials had to include adult patients with T2DM who received triple oral therapy with a DPP-4 inhibitor for ≥18 weeks. The bibliographies of retrieved articles were also searched to identify any other relevant trials.

RESULTS

A total of 17 clinical trials evaluating metformin and a DPP-4 inhibitor combined with a sulfonylurea (SU), thiazolidinedione (TZD), or sodium-glucose cotransporter 2 (SGLT2) inhibitor were identified and included in this review. Consistently, the addition of a DPP-4 inhibitor to metformin and SU, TZD, or SGLT2 inhibitor therapy improved glycemic measures, and these combinations were generally well tolerated. An increased incidence of hypoglycemia was reported for combinations that included an SU.

CONCLUSIONS

Triple oral therapy that includes a DPP-4 inhibitor is a valid option for patients with T2DM not adequately controlled with dual combination therapy, and offers an alternative to insulin therapy. Triple oral therapy with a DPP-4 inhibitor, metformin, and a TZD or SGLT2 inhibitor should be considered when avoidance of hypoglycemia is a primary goal.

Vildagliptin , a DPP-4 inhibitor for the twice-daily treatment of type 2 diabetes mellitus with or without metformin

INTRODUCTION

Dipeptidyl peptidase-4 inhibitors increase circulating levels of glucagon-like peptide 1 (GLP-1) and glucose dependent insulinotropic polypeptide regulating glucose-dependent insulin secretion. In addition, GLP-1 suppresses glucagon secretion, delays gastric emptying and increases satiety. The combination of vildagliptin with the biguanide metformin is of particular interest because of its complementary mode of action, addressing insulin resistance, alpha- and beta cell function in the islet of the pancreas.

AREAS COVERED

Because of the abundance of data supporting the use of vildagliptin alone and in combination with metformin, the present paper aims at giving an overview on the current evidence for its use in patients with type 2 diabetes mellitus.

EXPERT OPINION

The data suggest that vildagliptin offers similar glycemic control compared to sulfonylureas and thiazolidinediones, while having the benefit of being associated with fewer cases of hypoglycemia and less body weight gain. There is increasing evidence that compared with sulfonylureas, vildagliptin has favorable effects on pancreatic alpha- and beta-cell function. Vildagliptin in combination with metformin, improve glycemic control with a favorable safety and tolerability profile, making it an attractive therapeutic option in patients where metformin monotherapy alone is not sufficient.

Postprandial gallbladder emptying in patients with type 2 diabetes: potential implications for bile-induced secretion of glucagon-like peptide 1

OBJECTIVE

Recent preclinical work has suggested that postprandial flow of bile acids into the small intestine potentiates nutrient-induced glucagon-like peptide 1 (GLP1(GCG)) secretion via bile acid-induced activation of the G protein-coupled receptor TGR5 in intestinal L cells. The notion of bile-induced GLP1 secretion combined with the findings of reduced postprandial gallbladder emptying in patients with type 2 diabetes (T2DM) led us to speculate whether reduced postprandial GLP1 responses in some patients with T2DM arise as a consequence of diabetic gallbladder dysmotility.

DESIGN AND METHODS

In a randomised design, 15 patients with long-standing T2DM and 15 healthy age-, gender- and BMI-matched control subjects were studied during 75-g oral glucose tolerance test (OGTT) and three isocaloric (500 kcal) and isovolaemic (350 ml) liquid meals: i) 2.5 g fat, 107 g carbohydrate and 13 g protein; ii) 10 g fat, 93 g carbohydrate and 11 g protein; and iii) 40 g fat, 32 g carbohydrate and 3 g protein. Basal and postprandial plasma concentrations of glucose, insulin, C-peptide, glucagon, GLP1, glucose-dependent insulinotropic polypeptide (GIP), cholecystokinin and gastrin were measured. Furthermore, gallbladder emptying and gastric emptying were examined.

RESULTS

Gallbladder emptying increased with increasing meal fat content, but no intergroup differences were demonstrated. GIP and GLP1 responses were comparable among the groups with GIP levels being higher following high-fat meals, whereas GLP1 secretion was similar after both OGTT and meals.

CONCLUSIONS

In conclusion, patients with T2DM exhibited normal gallbladder emptying to meals with a wide range of fat content. Incretin responses were similar to that in controls, and an association with postprandial gallbladder contraction could not be demonstrated.

Mechanism of increase in plasma intact GLP-1 by metformin in type 2 diabetes: stimulation of GLP-1 secretion or reduction in plasma DPP-4 activity?

Metformin was reported to increase plasma intact glucagon-like peptide-1 (GLP-1) concentrations in type 2 diabetes. This is, at least partly, attributable to stimulation of GLP-1 secretion. A reduction in soluble dipeptidyl peptidase-4 activity may also make a modest contribution.

Therapies for inter-relating diabetes and obesity - GLP-1 and obesity

INTRODUCTION

The dramatic rise in the prevalence of obesity and type 2 diabetes mellitus (T2DM) is associated with increased mortality, morbidity as well as public health care expenses worldwide. The need for effective and long-lasting pharmaceutical treatment is obvious. The record of anti-obesity drugs has been poor so far and the only efficient treatment today is bariatric surgery. Research has indicated that appetite inhibiting hormones from the gut may have a therapeutic potential in obesity. The gut incretin hormone, glucagon-like peptide-1 (GLP-1), appears to be involved in both peripheral and central pathways mediating satiety. Clinical trials have shown that two GLP-1 receptor agonists exenatide and liraglutide have a weight-lowering potential in non-diabetic obese individuals. Furthermore, they may also hold a potential in preventing diabetes as compared to other weight loss agents.

AREAS COVERED

The purpose of this review is to cover the background for the GLP-1-based therapies and their potential in obesity and pre-diabetes. Up-to-date literature on incretin-based therapies will be summarized with a special mention of their weight-lowering properties. The literature updated to August 2014 from PubMed was identified using the combinations: GLP-1, GLP-1 receptor agonists, incretins, obesity and pre-diabetes.

EXPERT OPINION

The incretin impairment, which seems to exist in both obesity and diabetes, may link these two pathologies and underlines the potential of GLP-1-based therapies in the prevention and treatment of these diseases.

Efficacy and safety of the dipeptidyl peptidase-4 inhibitor sitagliptin compared with alpha-glucosidase inhibitor in Japanese patients with type 2 diabetes inadequately controlled on metformin or pioglitazone alone (Study for an Ultimate Combination Therapy to Control Diabetes with Sitagliptin-1): A multicenter, randomized, open-label, non-inferiority trial

Aims/Introduction

To assess the efficacy and safety of sitagliptin compared with α-glucosidase inhibitors in Japanese patients with type 2 diabetes inadequately controlled by metformin or pioglitazone alone.

Materials and Methods

In the present multicenter, randomized, open-label, parallel-group, active-controlled, non-inferiority trial, 119 patients aged 20–79 years with type 2 diabetes who had glycated hemoglobin 6.9–8.8% on stable metformin (500–1,500 mg/day) or pioglitazone (15–30 mg/day) alone were randomly assigned (1:1) to receive the addition of sitagliptin (50 mg/day) or an α-glucosidase inhibitor (0.6 mg/day voglibose or 150 mg/day miglitol) for 24 weeks. The primary end-point was change in glycated hemoglobin from baseline to week 12. All data were analyzed according to the intention-to-treat principle.

Results

After 12 weeks, reductions in adjusted mean glycated hemoglobin from baseline were −0.70% in sitagliptin and −0.21% in the α-glucosidase inhibitor groups respectively; between-group difference was −0.49% (95% confidence interval −0.66 to −0.32, P < 0.0001), meeting the predefined non-inferiority criterion (0.25%) and showing statistical significance. This statistical significance also continued after 24 weeks. Although sitagliptin did not affect bodyweight, α-glucosidase inhibitors decreased bodyweight significantly from baseline (−0.39 kg; P = 0.0079). Gastrointestinal disorders were significantly lower with sitagliptin than with an α-glucosidase inhibitor (6 [10.3%] patients vs 23 [39.7%]; P = 0.0003). Minor hypoglycemia occurred in two patients (3.5%) in each group.

Conclusions

Sitagliptin showed greater efficacy and better tolerability than an α-glucosidase inhibitor when added to stable doses of metformin or pioglitazone. These findings support the use of sitagliptin in Japanese patients with type 2 diabetes inadequately controlled by insulin-sensitizing agents. This trial was registered with UMIN (no. 000004675).

Evidence-based practice use of incretin-based therapy in the natural history of diabetes

The incretin class of anti-hyperglycemic agents, including glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-inhibitors, is an important addition to the therapeutic armamentarium for the management of appropriate patients with type 2 diabetes mellitus as an adjunct to diet and exercise and/or with the agents metformin, sulfonylureas, thiazolidinediones, or any combination thereof. More recently, US Food and Drug Administration (FDA)-approved indications for incretins were expanded to include use with basal insulin. This review article takes an evidence-based practice approach in discussing the importance of aggressive treatment for diabetes, the principles of incretin physiology and pathophysiology, use of glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors, and patient types and contexts where incretin therapy has been found beneficial, from metabolic syndrome to overt diabetes.

Dipeptidyl peptidase 4 (DPP-4) is expressed in mouse and human islets and its activity is decreased in human islets from individuals with type 2 diabetes

AIMS/HYPOTHESIS

Inhibition of the enzyme dipeptidyl peptidase 4 (DPP-4), which cleaves and inactivates glucagon-like peptide 1 (GLP-1), is a glucose-lowering strategy in type 2 diabetes. Since DPP-4 is a ubiquitously distributed enzyme, we examined whether it is expressed in islets and whether an islet effect to inhibit DPP-4 may result in stimulated insulin secretion.

METHODS

We investigated DPP-4 expression and activity in the islets of mouse models of obesity as well as human islets from non-diabetic and type 2 diabetic donors. We further investigated whether inhibition with DPP-4 inhibitors could promote insulin secretion via islet GLP-1 in isolated islets.

RESULTS

DPP-4 was readily detected in mouse and human islets with species-specific cellular localisation. In mice, DPP-4 was expressed predominantly in beta cells, whereas in humans it was expressed nearly exclusively in alpha cells. DPP-4 activity was significantly increased in islets from diet-induced obese mice compared with mice fed a control diet. In humans, DPP-4 activity was significantly lower in islets from type 2 diabetic donors than in non-diabetic donors. In human islets, there was a significant positive correlation between DPP-4 activity and insulin secretory response to 16.7 mmol/l glucose. Treatment of mouse islets with the DPP-4 inhibitors, NVPDPP728 and vildagliptin, resulted in a significant potentiation of insulin secretion in a GLP-1-dependent manner, as this was inhibited by the GLP-1 receptor antagonist, Exendin (9-39), and was retained in glucose-dependent insulinotropic polypeptide (GIP) receptor-deficient mice but lost in mice lacking GLP-1 receptors or both incretin receptors. Human islets treated with the DPP-4 inhibitor, vildagliptin, showed increased secretion of insulin and intact GLP-1.

CONCLUSIONS/INTERPRETATION

We conclude that DPP-4 is present and active in mouse and human islets, is regulated by the disease state, and that inhibition of islet DPP-4 activity can have direct effects on islet function. Inhibiting islet DPP-4 activity may therefore contribute to the insulin-secretory and glucose-lowering action of DPP-4 inhibition.

The impact of dipeptidyl peptidase 4 inhibition on incretin effect, glucose tolerance, and gastrointestinal-mediated glucose disposal in healthy subjects

OBJECTIVE

Inhibition of dipeptidyl peptidase 4 (DPP4) is thought to intensify the physiological effects of the incretin hormones. We investigated the effects of DPP4 inhibition on plasma levels of glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP1), incretin effect, glucose tolerance, gastrointestinal-mediated glucose disposal (GIGD) and gastric emptying in healthy subjects.

DESIGN

A randomised, controlled and open-labelled study.

METHODS

Ten healthy subjects (six women; age, 40±5 years (mean±s.e.m.); BMI, 24±3 kg/m(2); fasting plasma glucose, 5.1±0.2 mmol/l and HbA1c, 34±1 mmol/mol (5.3±0.1%)) were randomised to two-paired study days comprising a 4-h 50 g oral glucose tolerance test (OGTT) with paracetamol (A) and an isoglycaemic intravenous (i.v.) glucose infusion (B), with (A1+B1) and without (A2+B2) preceding administration of the DPP4 inhibitor sitagliptin.

RESULTS

Isoglycaemia was obtained in all subjects on the paired study days. Significant increases in fasting levels and OGTT-induced responses of active GLP1 and GIP were seen after DPP4 inhibition. No significant impact of DPP4 inhibition on fasting plasma glucose (5.1±0.1 vs 4.9±0.1 mmol/l, P=0.3), glucose tolerance (area under the curve (AUC) for plasma glucose, 151±35 vs 137±26 mmol/l×min, P=0.7) or peak plasma glucose during OGTT (8.5±0.4 vs 8.1±0.3 mmol/l, P=0.3) was observed. Neither incretin effect (40±9% (without DPP4 inhibitor) vs 40±7% (with DPP4 inhibitor), P=1.0), glucagon responses (1395±165 vs 1223±195 pmol/l×min, P=0.41), GIGD (52±4 vs 56±5%, P=0.40) nor gastric emptying (Tmax for plasma paracetamol: 86±9 vs 80±12 min, P=0.60) changed following DPP4 inhibition.

CONCLUSIONS

These results suggest that acute increases in active incretin hormone levels do not affect glucose tolerance, GIGD, incretin effect, glucagon responses or gastric emptying in healthy subjects.

Effects of sitagliptin on glycemia, incretin hormones, and antropyloroduodenal motility in response to intraduodenal glucose infusion in healthy lean and obese humans and patients with type 2 diabetes treated with or without metformin

The impact of variations in gastric emptying, which influence the magnitude of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) secretion, on glucose lowering by dipeptidyl peptidase-4 (DPP-4) inhibitors is unclear. We evaluated responses to intraduodenal glucose infusion (60 g over 120 min [i.e., 2 kcal/min], a rate that predominantly stimulates GIP but not GLP-1) after sitagliptin versus control in 12 healthy lean, 12 obese, and 12 type 2 diabetic subjects taking metformin 850 mg b.i.d. versus placebo. As expected, sitagliptin augmented plasma-intact GIP substantially and intact GLP-1 modestly. Sitagliptin attenuated glycemic excursions in healthy lean and obese but not type 2 diabetic subjects, without affecting glucagon or energy intake. In contrast, metformin reduced fasting and glucose-stimulated glycemia, suppressed energy intake, and augmented total and intact GLP-1, total GIP, and glucagon in type 2 diabetic subjects, with no additional glucose lowering when combined with sitagliptin. These observations indicate that in type 2 diabetes, 1) the capacity of endogenous GIP to lower blood glucose is impaired; 2) the effect of DPP-4 inhibition on glycemia is likely to depend on adequate endogenous GLP-1 release, requiring gastric emptying >2 kcal/min; and 3) the action of metformin to lower blood glucose is not predominantly by way of the incretin axis.

Novel gut-based pharmacology of metformin in patients with type 2 diabetes mellitus

Metformin, a biguanide derivate, has pleiotropic effects beyond glucose reduction, including improvement of lipid profiles and lowering microvascular and macrovascular complications associated with type 2 diabetes mellitus (T2DM). These effects have been ascribed to adenosine monophosphate-activated protein kinase (AMPK) activation in the liver and skeletal muscle. However, metformin effects are not attenuated when AMPK is knocked out and intravenous metformin is less effective than oral medication, raising the possibility of important gut pharmacology. We hypothesized that the pharmacology of metformin includes alteration of bile acid recirculation and gut microbiota resulting in enhanced enteroendocrine hormone secretion. In this study we evaluated T2DM subjects on and off metformin monotherapy to characterize the gut-based mechanisms of metformin. Subjects were studied at 4 time points: (i) at baseline on metformin, (ii) 7 days after stopping metformin, (iii) when fasting blood glucose (FBG) had risen by 25% after stopping metformin, and (iv) when FBG returned to baseline levels after restarting the metformin. At these timepoints we profiled glucose, insulin, gut hormones (glucagon-like peptide-1 (GLP-1), peptide tyrosine-tyrosine (PYY) and glucose-dependent insulinotropic peptide (GIP) and bile acids in blood, as well as duodenal and faecal bile acids and gut microbiota. We found that metformin withdrawal was associated with a reduction of active and total GLP-1 and elevation of serum bile acids, especially cholic acid and its conjugates. These effects reversed when metformin was restarted. Effects on circulating PYY were more modest, while GIP changes were negligible. Microbiota abundance of the phylum Firmicutes was positively correlated with changes in cholic acid and conjugates, while Bacteroidetes abundance was negatively correlated. Firmicutes and Bacteroidetes representation were also correlated with levels of serum PYY. Our study suggests that metformin has complex effects due to gut-based pharmacology which might provide insights into novel therapeutic approaches to treat T2DM and associated metabolic diseases.

TRIAL REGISTRATION

www.ClinicalTrials.gov NCT01357876.

Efficacy and safety of initial combination therapy with alogliptin plus metformin versus either as monotherapy in drug-naïve patients with type 2 diabetes: a randomized, double-blind, 6-month study

AIM

To evaluate the efficacy and safety of the dipeptidyl peptidase-4 inhibitor alogliptin plus metformin (A + M) initial combination therapy versus either as monotherapy in drug-naïve T2DM patients.

METHODS

This international, randomized, double-blind, placebo-controlled, 26-week study involved T2DM patients with hyperglycaemia (HbA1c 7.5-10.0%) following diet/exercise therapy. Patients (N = 784) received placebo, alogliptin (A, 12.5 mg BID or 25 mg QD), metformin (M, 500 or 1000 mg BID) or A + M (12.5/500 or 12.5/1000 mg BID); placebo, A25 for secondary analyses only.

ENDPOINTS

week 26 changes from baseline in HbA1c (primary), fasting plasma glucose (FPG) and 2-h postprandial glucose (PPG); incidences of clinical response and hyperglycaemic rescue.

RESULTS

Week 26 mean HbA1c reductions from baseline (8.45%) were -1.22 and -1.55% with A + M 12.5/500 and 12.5/1000 versus -0.56, -0.65, and -1.11% with A12.5, M500 and M1000 (p<0.001, A + M vs. component monotherapies). FPG reductions were -1.76 and -2.55 mmol/L with 12.5/500 and 12.5/1000 versus -0.54, -0.64 and -1.78 mmol/L with A12.5, M500 and M1000 (p < 0.05, A + M vs. component monotherapies). Significantly more A + M-treated patients achieved HbA1c < 7% (47.1-59.5% vs. 20.2-34.3% with monotherapy), significantly fewer required hyperglycaemic rescue (2.6-12.3% vs. 10.8-22.9% with monotherapy). A + M caused only mild/moderate hypoglycaemia (1.9-5.3%) and weight loss (0.6-1.2 kg).

CONCLUSIONS

Alogliptin plus metformin initial combination therapy was well tolerated yet more efficacious in controlling glycaemia in drug-naïve T2DM patients than either as monotherapy.

Efficacy and Safety of Vildagliptin as Add-on to Metformin in Japanese Patients with Type 2 Diabetes Mellitus

INTRODUCTION

The objective of this study was to evaluate the efficacy and safety of vildagliptin, a potent dipeptidyl peptidase-4 inhibitor, as an add-on to metformin in Japanese patients with type 2 diabetes mellitus (T2DM).

METHODS

This multicenter, 12-week, randomized, double-blind, placebo-controlled, parallel-arm study compared vildagliptin 50 mg bid with placebo in T2DM patients who were inadequately controlled [glycosylated hemoglobin (HbA1c) 7.0-10.0%] on a stable daily dose of metformin monotherapy (250 mg bid or 500 mg bid).

RESULTS

A total of 139 patients were randomized to receive either vildagliptin (n = 69) or placebo (n = 70). Patient demographics were comparable between the groups at baseline. After 12 weeks of treatment, adjusted mean change in HbA1c was -1.1% in the vildagliptin group (baseline 8.0%) and -0.1% in the placebo group (baseline 8.0%), with a between-treatment difference of -1.0% (P < 0.001). Vildagliptin showed a similar reduction in HbA1c of -1.1% for both the subpopulations of patients receiving metformin 250 mg bid or 500 mg bid (P < 0.001 vs. baseline). Significantly more patients in the vildagliptin group achieved an HbA1c target of ≤6.5% (30.9%) and <7.0% (64.1%) compared with the placebo group (P < 0.001). The between-treatment difference in adjusted mean change in fasting plasma glucose was -1.6 mmol/L (P < 0.001) in favor of vildagliptin. Patients in the vildagliptin and placebo groups reported comparable incidences of adverse events (44.1% vs. 41.4%). No deaths or hypoglycemic events were reported in the study.

CONCLUSIONS

Vildagliptin 50 mg bid added to metformin improved glycemic control without any tolerability issues and hypoglycemia in Japanese patients with T2DM inadequately controlled on metformin monotherapy.

GLP-1 and peptide YY secretory response after fat load is impaired by insulin resistance, impaired fasting glucose and type 2 diabetes in morbidly obese subjects

OBJECTIVE

Both glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) are gut hormones involved in energy homoeostasis. Obesity, insulin resistance and hyperglycaemia are significant confounders when GLP-1 and PYY secretion is assessed. Thus, we evaluated GLP-1 and PYY response after fat load in morbidly obese patients with different degrees of insulin resistance and glycemic status.

DESIGN

We studied 40 morbidly obese subjects (mean age, 40·6 ± 1·3 years; mean BMI, 53·1 ± 1·2 kg/m(2) ) divided into groups according to their glycemic status: normal fasting glucose (NFG) group, impaired fasting glucose (IFG) group and type 2 diabetes mellitus (T2D) group. NFG patients were additionally subclassified, according to the homoeostasis model assessment of insulin resistance (HOMAIR ), into a low insulin-resistance (LIR) group (HOMAIR <3·9) or a high insulin-resistance (HIR) group (HOMAIR ≥3·9).

MEASUREMENTS

Lipid emulsion was administered orally and measurements made at baseline and 180 min postprandially of levels of GLP-1, PYY, insulin, glucose, free fatty acids, triglycerides and leptin.

RESULTS

At the 180-minute postprandial reading, GLP-1 and PYY had increased in LIR-NFG subjects (41·84%, P = 0·01; 35·7%, P = 0·05; respectively), whereas no changes were observed in HIR-NFG, IFG or T2D subjects.

CONCLUSIONS

These results suggest that in morbidly obese subjects, both insulin resistance and abnormal glucose metabolism (IFG or T2D) impair the GLP-1 and PYY response to fat load. The implications of this attenuated enteroendocrine response should be elucidated by further studies.

Gut hormone pharmacology of a novel GPR119 agonist (GSK1292263), metformin, and sitagliptin in type 2 diabetes mellitus: results from two randomized studies

GPR119 receptor agonists improve glucose metabolism and alter gut hormone profiles in animal models and healthy subjects. We therefore investigated the pharmacology of GSK1292263 (GSK263), a selective GPR119 agonist, in two randomized, placebo-controlled studies that enrolled subjects with type 2 diabetes. Study 1 had drug-naive subjects or subjects who had stopped their diabetic medications, and Study 2 had subjects taking metformin. GSK263 was administered as single (25–800 mg; n = 45) or multiple doses (100–600 mg/day for 14 days; n = 96). Placebo and sitagliptin 100 mg/day were administered as comparators. In Study 1, sitagliptin was co-administered with GSK263 or placebo on Day 14 of dosing. Oral glucose and meal challenges were used to assess the effects on plasma glucose, insulin, C-peptide, glucagon, peptide tyrosine-tyrosine (PYY), glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). After 13 days of dosing, GSK263 significantly increased plasma total PYY levels by ∼five-fold compared with placebo, reaching peak concentrations of ∼50 pM after each of the three standardized meals with the 300 mg BID dose. Co-dosing of GSK263 and metformin augmented peak concentrations to ∼100 pM at lunchtime. GSK263 had no effect on active or total GLP-1 or GIP, but co-dosing with metformin increased post-prandial total GLP-1, with little effect on active GLP-1. Sitagliptin increased active GLP-1, but caused a profound suppression of total PYY, GLP-1, and GIP when dosed alone or with GSK263. This suppression of peptides was reduced when sitagliptin was co-dosed with metformin. GSK263 had no significant effect on circulating glucose, insulin, C-peptide or glucagon levels. We conclude that GSK263 did not improve glucose control in type 2 diabetics, but it had profound effects on circulating PYY. The gut hormone effects of this GPR119 agonist were modulated when co-dosed with metformin and sitagliptin. Metformin may modulate negative feedback loops controlling the secretion of enteroendocrine peptides.

Trial Registration:

Clinicaltrials.gov NCT01119846 Clinicaltrials.gov NCT01128621

Combination therapy of dipeptidyl peptidase-4 inhibitors and metformin in type 2 diabetes: rationale and evidence

The main pathogenesis of type 2 diabetes mellitus (T2DM) includes insulin resistance and pancreatic islet dysfunction. Metformin, which attenuates insulin resistance, has been recommended as the first-line antidiabetic medication. Dipeptidyl peptidase-4 (DPP-4) inhibitors are novel oral hypoglycaemic agents that protect glucagon-like peptide-1 (GLP-1) from degradation, maintain the bioactivity of endogenous GLP-1, and thus improve islet dysfunction. Results from clinical trials have shown that the combination therapy of DPP-4 inhibitors and metformin [as an add-on, an initial combination or a fixed-dose combination (FDC)] provides excellent efficacy and safety in patients with T2DM. Moreover, recent studies have suggested that metformin enhances the biological effect of GLP-1 by increasing GLP-1 secretion, suppressing activity of DPP-4 and upregulating the expression of GLP-1 receptor in pancreatic β-cells. Conversely, DPP-4 inhibitors have a favourable effect on insulin sensitivity in patients with T2DM. Therefore, the combination of DPP-4 inhibitors and metformin provides an additive or even synergistic effect on metabolic control in patients with T2DM. This article provides an overview of clinical evidence and discusses the rationale for the combination therapy of DPP-4 inhibitors and metformin.

Effects of sitagliptin and metformin treatment on incretin hormone and insulin secretory responses to oral and "isoglycemic" intravenous glucose

Dipeptidyl peptidase-4 (DPP-4) inhibitors prevent degradation of incretin hormones (glucagon-like peptide 1 [GLP-1] and glucose-dependent insulinotropic polypeptide [GIP]), whereas metformin may increase GLP-1 levels. We examined, in a four-period crossover trial, the influence of metformin (2,000 mg/day), sitagliptin (100 mg/day), or their combination, on GLP-1 responses and on the incretin effect in 20 patients with type 2 diabetes, comparing an oral glucose challenge (75 g, day 5) and an "isoglycemic" intravenous glucose infusion (day 6). Fasting total GLP-1 was significantly increased by metformin and not changed by sitagliptin. After oral glucose, metformin increased and sitagliptin significantly decreased (by 53%) total GLP-1. Fasting and postload intact GLP-1 increased with sitagliptin but not with metformin. After oral glucose, only sitagliptin, but not metformin, significantly augmented insulin secretion, in monotherapy and as an add-on to metformin. The incretin effect was not changed numerically with any of the treatments. In conclusion, sitagliptin increased intact GLP-1 and GIP through DPP-4 inhibition but reduced total GLP-1 and GIP (feedback inhibition) without affecting the numerical contribution of the incretin effect. Insulin secretion with sitagliptin treatment was similarly stimulated with oral and "isoglycemic" intravenous glucose. This points to an important contribution of small changes in incretin concentrations within the basal range or to additional insulinotropic agents besides GLP mediating the antidiabetic effects of DPP-4 inhibition.

Targeting the intestinal L-cell for obesity and type 2 diabetes treatment

Degradation-resistant glucagon-like peptide-1 (GLP-1) mimetics and GLP-1 enhancers (inhibitors of dipeptidyl peptidase-4, the enzyme which degrades and inactivates GLP-1) have been used for treatment of type 2 diabetes mellitus since 2005-2006. Cutting-edge research is now focusing on uncovering the secretory mechanisms of the GLP-1-producing cells (L-cells) with the purpose of developing agonists that enhance endogenous hormone secretion. Since GLP-1 co-localizes with other anorectic peptides, cholecystokinin, oxyntomodulin/glicentin and peptide YY, L-cell targeting might cause release of several hormones at the same time, providing additive effects on appetite and glucose regulation. In this review, we explore the role of proglucagon-derived peptides and other L-cell co-localizing hormones, in appetite regulation and the mechanism regulating their secretion.

Initial combination of linagliptin and metformin in patients with type 2 diabetes: efficacy and safety in a randomised, double-blind 1-year extension study

OBJECTIVE

To determine the efficacy and safety of linagliptin in initial combination with metformin in patients with type 2 diabetes.

METHODS

This 1-year randomised, double-blind study was an extension of a 6-month randomised controlled trial, in which adults with type 2 diabetes received one of six treatment regimens (linagliptin 2.5 mg plus metformin 500 mg bid, linagliptin 2.5 mg plus metformin mg 1000 bid, metformin 1000 mg bid, metformin 500 mg bid, linagliptin 5 mg qd or placebo). In the extension, patients in the first three treatment groups continued their regimen (non-switched group, n = 333) while the metformin 500 mg bid, linagliptin 5 mg qd and placebo groups were re-randomised to one of the three continuing regimens (switched group, n = 233).

RESULTS

All three non-switched groups maintained reductions in glycosylated haemoglobin (HbA1c; mean ± standard deviation reductions across the 1.5-year period: linagliptin 2.5 plus metformin 1000 bid, -1.63 ± 1.05%; linagliptin 2.5 plus metformin 500 bid, -1.32 ± 1.06%; metformin 1000 bid, -1.25 ± 0.91%) while the switched groups showed additional HbA1c reductions. During the extension, there were no clinically meaningful changes in body weight in any group. Adverse event rates were similar between groups, with most events being mild or moderate, and the incidence of investigator-defined hypoglycaemia was low, with no severe events.

DISCUSSION

Initial combination of linagliptin and metformin was well tolerated over the 1-year extension period, with low risk of hypoglycaemia, and improved glycaemic control vs. metformin alone.

CONCLUSION

The initial combination of linagliptin and metformin appears to provide a useful treatment option in patients whose blood glucose levels are increased to an extent that metformin monotherapy may not achieve treatment targets.

Impact of three oral antidiabetic drugs on markers of β-cell function in patients with type 2 diabetes: a meta-analysis

Background

The effect of metformin, pioglitazone and sitagliptin on β-cell function in the treatment of type 2 diabetes is controversial. Therefore, we performed a systematic review and meta-analysis to obtain a better understanding in the β-cell effects of metformin, pioglitazone and sitagliptin.

Methods

We searched Pubmed and the Cochrane Center Register of Controlled Trials to identify relevant studies. Trials investigating effects of sitagliptin, metformin or pioglitazone on β-cell function were identified. The primary outcomes were homeostasis model assessment of β-cells (HOMA-β) and proinsulin/insulin ratio (PI/IR). Secondary outcome was hemoglobin A1c level. We used version 2 of the Comprehensive Meta Analysis software for all statistical analyses.

Results

Metformin monotherapy was more effective than sitagliptin in improving HOMA-β (18.01% (95% CI 11.09% to 24.94%) vs. 11.29% (95% CI 9.21% to 13.37%), P = 0.040) and more effective (−0.137 (95% CI −0.082 to −0.192)) than both sitagliptin (−0.064 (95% CI −0.036 to −0.092), P = 0.019) and pioglitazone (−0.068 (95% CI −0.044 to −0.093), P = 0.015) in decreasing PI/IR. Metformin and sitagliptin combined (40.23% (95%CI 32.30% to 48.16%)) were more effective than sitagliptin and pioglitazone (11.82% (95% CI 6.61% to 17.04%), P = 0.000) and pioglitazone and metformin(9.81% (95% CI 1.67% to 17.95%), P = 0.022) in improving HOMA-β and decreasing PI/IR (−0.177 (95% CI −0.118 to −0.237); −0.080 (95% CI −0.045 to −0.114), P = 0.007; −0.038 (95% CI, −0.005 to 0.071), P = 0.023).

Limitations

The included RCTs were of short duration (12–54 weeks). We could not determine long term effects on β-cells.

Conclusions

Metformin improves β-cell function more effectively than pioglitazone or sitagliptin in type 2 diabetes patients. Metformin and sitagliptin improved HOMA-β and PI/IR more than other combinations.

Physiology of incretins and loss of incretin effect in type 2 diabetes and obesity

An important role in the regulation of glucose homeostasis is played by incretins, which are gut-derived hormones released in response to nutrient ingestion. In humans, the major incretin hormones are glucagon-like peptide (GLP)-1 and glucose-dependent insulinotropic polypeptide (GIP), and together they fully account for the incretin effect (that is, higher insulin release in response to an oral glucose challenge compared to an equal intravenous glucose load). Studies have shown that GLP-1 and GIP levels and actions may be perturbed in disease states, and the loss of incretin effect is likely to contribute importantly to the postprandial hyperglycaemia in type 2 diabetes. However, the specific cause-effect relationship between disease and incretins is still unclear. This review focuses on several key studies elucidating the association of defective incretin action with obesity and T2DM and the effects of metformin and other anti-diabetic agents on the incretin system.

Initial combination therapy for patients with type 2 diabetes mellitus: considerations for metformin plus linagliptin

For patients with type 2 diabetes mellitus, management of hyperglycemia is typically complex, and few patients successfully achieve and maintain recommended targets for glycated hemoglobin (HbA1c). Increasingly, combination therapy is recommended early in the disease course, or even directly at diagnosis in patients with relatively high HbA1c levels. A recent randomized, placebo-controlled, Phase III trial investigated the initial combination of linagliptin and metformin in patients with inadequate glycemic control to assess the benefits of initial combination compared with monotherapy. Linagliptin and metformin act in complementary ways, and the combination treatment showed superior efficacy compared with either monotherapy. Notably, responses were largest in patients with higher baseline HbA1c levels compared with moderate levels, suggesting this combination could be considered in these patients. This may be particularly relevant for those unwilling to start insulin because they prefer oral therapy or need to avoid body weight gain. Neither metformin nor linagliptin is associated with weight gain, and in this trial the combination was also weight neutral. As this combination therapy was well tolerated, with a low frequency of hypoglycemia, these findings suggest that initial combination of linagliptin plus metformin may have advantages for a large proportion of patients in clinical practice.

Effects of a D-xylose preload with or without sitagliptin on gastric emptying, glucagon-like peptide-1, and postprandial glycemia in type 2 diabetes

OBJECTIVE

Macronutrient "preloads" can reduce postprandial glycemia by slowing gastric emptying and stimulating glucagon-like peptide-1 (GLP-1) secretion. An ideal preload would entail minimal additional energy intake and might be optimized by concurrent inhibition of dipeptidyl peptidase-4 (DPP-4). We evaluated the effects of a low-energy D-xylose preload, with or without sitagliptin, on gastric emptying, plasma intact GLP-1 concentrations, and postprandial glycemia in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Twelve type 2 diabetic patients were studied on four occasions each. After 100 mg sitagliptin (S) or placebo (P) and an overnight fast, patients consumed a preload drink containing either 50 g D-xylose (X) or 80 mg sucralose (control [C]), followed after 40 min by a mashed potato meal labeled with (13)C-octanoate. Blood was sampled at intervals. Gastric emptying was determined.

RESULTS

Both peak blood glucose and the amplitude of glycemic excursion were lower after PX and SC than PC (P < 0.01 for each) and were lowest after SX (P < 0.05 for each), while overall blood glucose was lower after SX than PC (P < 0.05). The postprandial insulin-to-glucose ratio was attenuated (P < 0.05) and gastric emptying was slower (P < 0.01) after D-xylose, without any effect of sitagliptin. Plasma GLP-1 concentrations were higher after D-xylose than control only before the meal (P < 0.05) but were sustained postprandially when combined with sitagliptin (P < 0.05).

CONCLUSIONS

In type 2 diabetes, acute administration of a D-xylose preload reduces postprandial glycemia and enhances the effect of a DPP-4 inhibitor.

Pharmacology, physiology, and mechanisms of incretin hormone action

Incretin peptides, principally GLP-1 and GIP, regulate islet hormone secretion, glucose concentrations, lipid metabolism, gut motility, appetite and body weight, and immune function, providing a scientific basis for utilizing incretin-based therapies in the treatment of type 2 diabetes. Activation of GLP-1 and GIP receptors also leads to nonglycemic effects in multiple tissues, through direct actions on tissues expressing incretin receptors and indirect mechanisms mediated through neuronal and endocrine pathways. Here we contrast the pharmacology and physiology of incretin hormones and review recent advances in mechanisms coupling incretin receptor signaling to pleiotropic metabolic actions in preclinical studies. We discuss whether mechanisms identified in preclinical studies have potential translational relevance for the treatment of human disease and highlight controversies and uncertainties in incretin biology that require resolution in future studies.

Glucose-lowering effect of the DPP-4 inhibitor sitagliptin after glucose and non-glucose macronutrient ingestion in non-diabetic subjects

AIM

Recent studies suggest that the incretin concept is not restricted to glucose ingestion but relevant also after non-glucose macronutrient administration. We therefore hypothesized that raising incretin hormones reduces circulating glucose after both glucose and non-glucose macronutrient ingestion in healthy subjects.

METHODS

Twelve healthy subjects received the dipeptidyl peptidase-4 inhibitor sitagliptin (100 mg) or placebo before ingestion of glucose, fat (olive oil) or protein mix in equicaloric amounts (8 kcal/kg) plus paracetamol (1.5 g). The 120-min areas under curve (AUC) of intact glucagon-like peptide-1 (GLP-1), glucose, insulin, C-peptide, glucagon and paracetamol, and model-derived insulin secretion rate (ISR), insulin sensitivity, insulin clearance and glucose absorption were measured.

RESULTS

The increased plasma intact GLP-1 levels after each macronutrient was augmented by sitagliptin. This was associated with a robust lowering of glucose: glucose excursion after oral glucose was diminished, and glucose fell below baseline after oral fat and protein. In spite of lower glucose, AUCC -peptide and ISR did not differ significantly between sitagliptin and placebo after any macronutrient. AUCglucagon , insulin sensitivity and insulin clearance were also not different between sitagliptin and placebo. Glucose absorption after oral glucose was reduced by sitagliptin, whereas AUCparacetamol was not statistically different between sitagliptin and placebo.

CONCLUSIONS

Physiological elevation of intact GLP-1 levels after ingestion of glucose and non-glucose macronutrients is robustly glucose-lowering in healthy subjects. Hence, the incretin concept is not restricted to glucose ingestion in normal physiology. The glucose-lowering action of sitagliptin at these low glucose levels in healthy subjects may have complex mechanisms, involving both islet-dependent and islet-independent mechanisms.