Incretin concepts

Diabetes, Incretin Therapy and Thoracic Aortic Aneurysm - What Does the Evidence Show?

Epidemiological evidence supports a reduced prevalence of Thoracic Aortic Aneurysm (TAA) and Abdominal Aortic Aneurysm (AAA) in patients with Diabetes (DM). The mechanisms underlying this negative association are unknown. Some studies support that hyperglycemia has effects on the Extracellular Matrix (ECM), resulting in collagen cross-links and altered proteolytic activity, which ultimately counteracts aneurysm formation. However, recent experimental research indicates that incretin- based anti-diabetic therapy and Glucagon-Like Peptide-1 (GLP-1) may reduce the formation of TAA. GLP-1 is a peptide hormone, released from intestinal L-cells in response to hormonal, neural and nutrient stimuli. In addition to potentiation of meal-stimulated insulin secretion, GLP-1 signaling exerts numerous pleiotropic effects on various tissues, including protective effects on the myocardium and vascular endothelium. Recent studies also report protective effects of GLP-1 based therapy on the formation of aneurysms in animal models and direct effects of GLP-1 signaling on the molecular mechanisms suggested to influence TAA formation, including inflammation, proteolytic activity and collagen composition. In this narrative review, we present the available evidence for effects of GLP-1 on experimental aneurysm development and discuss the potential role of GLP-1 in aneurysm formation based on available data from pre-clinical and clinical studies.

Pancreatic gene variants potentially associated with dipeptidyl peptidase-4 inhibitor treatment response in Type 2 diabetes

In the adult pancreas, the expression of the genes PAX4, KCNQ1, TCF7L2, KCNJ11, ABCC8, MTNR1B and WFS1 are mainly restricted to β cells to maintain glucose homeostasis. We have identified these genes as the main regulators of incretin-mediated actions, and therefore they may potentially influence the response of DPP-4 inhibitors. This review represents the first detailed exploration of pancreatic β-cell genes and their variant mechanisms, which could potentially affect the response of DPP-4 inhibitors in Type 2 diabetes. We have focused on the signaling pathways of these genes to understand their roles in gastrointestinal incretin-mediated effects; and finally, we sought to associate gene mechanisms with their Type 2 diabetes risk variants to predict the responses of DPP-4 inhibitors for this disease.

Effects of LX4211, a dual SGLT1/SGLT2 inhibitor, plus sitagliptin on postprandial active GLP-1 and glycemic control in type 2 diabetes

BACKGROUND

Combination therapy is required to provide adequate glycemic control in many patients with type 2 diabetes mellitus (T2DM). Because sodium-dependent glucose transporter (SGLT)-1 inhibition results in an increased release of glucagon-like peptide (GLP)-1, and because dipeptidyl peptidase (DPP)-4 inhibitors prevent its inactivation, the 2 mechanisms together provide an intriguing potential combination therapy.

OBJECTIVES

This combination was explored in preclinical models and then tested in patients with T2DM to compare the effects of single-dose LX4211 400 mg and sitagliptin 100 mg, administered as monotherapy or in combination, on GLP-1, peptide tyrosine tyrosine (PYY), gastric inhibitory peptide (GIP), glucose, and insulin.

METHODS

Preclinical: Obese male C57BL6J mice were assigned to 1 of 4 treatment groups: LX4211 60 mg/kg, sitagliptin 30 mg/kg, LX4211 + sitagliptin, or inactive vehicle. Clinical: This 3-treatment, 3-crossover, randomized, open-label study was conducted at a single center. Patients on metformin monotherapy were washed out from metformin and were randomly assigned to receive sequences of single-dose LX4211, sitagliptin, or the combination. In both studies, blood was collected for the analysis of pharmacodynamic variables (GLP-1, PYY, GIP, glucose, and insulin). In the clinical study, urine was collected to assess urinary glucose excretion.

RESULTS

Preclinical: 120 mice were treated and assessed (5/time point/treatment group). With repeat daily dosing, the combination was associated with apparently synergistic increases in active GLP-1 relative to monotherapy with either agent; this finding was supported by findings from an additional 14-day repeated-dose experiment. Clinical: 18 patients were enrolled and treated (mean age, 49 years; 56% male; 89% white). The LX4211 + sitagliptin combination was associated with significantly increased active GLP-1, total GLP-1, and total PYY; with a significant reduction in total GIP; and with a significantly improved blood glucose level, with less insulin, compared with sitagliptin monotherapy. LX4211 was associated with a significant increase in total GLP-1 and PYY and a reduced total GIP, likely due to a reduction in SGLT1-mediated intestinal glucose absorption, whereas sitagliptin was associated with suppression of all 3 peptides relative to baseline. All treatments were well tolerated, with no evidence of diarrhea with LX4211 treatment.

CONCLUSIONS

The findings from the preclinical studies suggest that the LX4211 + sitagliptin combination produced synergistic increases in active GLP-1 after a meal challenge containing glucose. These initial clinical results also suggest that a LX4211 + DPP-4 inhibitor combination may provide an option in patients with T2DM. The potential long-term clinical benefits of such combination treatment need to be confirmed in large clinical trials. ClinicalTrials.gov identifier: NCT01441232.

Pleiotropic effects of incretins and antidiabetics with incretine mechanism

Discovery of physiological and pharmacological characteristics of incretins (glucagon-like peptide-1 and glucose-dependent insulinotrop polypeptide), and the introduction of various products of those into the clinical practice has fundamentally changed blood glucose lowering therapy in type 2 diabetes. In addition to the antidiabetic properties more attention is paid to their favourable pleiotropic effects independent from the blood glucose lowering such as cardio-, vaso- and renoprotectiv, blood pressure lowering effects, as well as beneficial changes on blood lipid values and hepatic steatosis. These preferential changes prevail in slightly different way when incretin mimetics applied and dipeptidyl peptidase-4 inhibitors, furthermore, prolonged action of peptides metabolised by this enzyme may serve additional benefits in this latter mentioned group. The article overviews the currently known most important pleiotropic effects of incretins from the point of view of cardiorenal risk accompanying type 2 diabetes. Orv. Hetil., 2013, 154, 248–255.

Glucagon-like peptide-1 preserves coronary microvascular endothelial function after cardiac arrest and resuscitation: potential antioxidant effects

Glucagon-like peptide-1 (GLP-1) has protective effects in the heart. We hypothesized that GLP-1 would mitigate coronary microvascular and left ventricular (LV) dysfunction if administered after cardiac arrest and resuscitation (CAR). Eighteen swine were subjected to ventricular fibrillation followed by resuscitation. Swine surviving to return of spontaneous circulation (ROSC) were randomized to receive an intravenous infusion of either human rGLP-1 (10 pmol·kg(-1)·min(-1); n = 8) or 0.9% saline (n = 8) for 4 h, beginning 1 min after ROSC. CAR caused a decline in coronary flow reserve (CFR) in control animals (pre-arrest, 1.86 ± 0.20; 1 h post-ROSC, 1.3 ± 0.05; 4 h post-ROSC, 1.25 ± 0.06; P < 0.05). GLP-1 preserved CFR for up to 4 h after ROSC (pre-arrest, 1.31 ± 0.17; 1 h post-ROSC, 1.5 ± 0.01; 4 h post-ROSC, 1.55 ± 0.22). Although there was a trend toward improvement in LV relaxation in the GLP-1-treated animals, overall LV function was not consistently different between groups. 8-iso-PGF(2α), a measure of reactive oxygen species load, was decreased in post-ROSC GLP-1-treated animals [placebo, control (NS): 38.1 ± 1.54 pg/ml; GLP-1: 26.59 ± 1.56 pg/ml; P < 0.05]. Infusion of GLP-1 after CAR preserved coronary microvascular and LV diastolic function. These effects may be mediated through a reduction in oxidative stress.

Adipose tissue, hormones, and treatment of type 1 diabetes

Type 1 diabetes (T1D) is a serious disease with increasing incidence worldwide, with fatal consequences if untreated. Traditional therapies require direct or indirect insulin replacement, which involves numerous limitations and complications. While insulin is the major regulator of blood glucose, recent reports demonstrate the ability of several extra-pancreatic hormones to decrease blood glucose and improve metabolic homeostasis. Such hormones mainly include adipokines originating from adipose tissue (AT), while specific factors from the gut and liver also contribute to glucose homeostasis. Correction of T1D with adipokines is progressively becoming a realistic option, with the potential to overcome many problems associated with insulin replacement. Several recent studies demonstrate insulin-independent reversal or amelioration of T1D through administration of specific adipokines. Our recent work demonstrates the ability of healthy AT to compensate for the function of endocrine pancreas in long-term correction of T1D. This review discusses the potential of AT-related therapies for T1D as viable alternatives to insulin replacement.

The physiology of incretins

The discovery of incretins − glucagon-like peptide (GLP)-1 and glucose-dependent insulinotrop peptide (GIP) −, clarification of their physiological properties as well as therapeutic application of incretin-based blood glucose lowering drugs opened new perspectives in the medical management of type 2 diabetes. New results of basic research investigations led to revaluation of the role of GIP in metabolic processes and a more established use of GLP-1 action. The article overviews the most relevant data of production and effects of incretins, as well as future possibilities of their therapeutic use. Orv. Hetil., 2011, 152, 1922–1930.