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Michael A Nauck and Juris J Meier

GLP-1, a peptide hormone secreted from the gut stimulating insulin and suppressing glucagon secretion was identified as a parent compound for novel treatments of diabetes, but was degraded (dipeptidyl peptidase-4) eliminated (mainly kidneys) too fast (half-life 1-2 min) to be useful as a therapeutic agent. GLP-1 receptor agonist have been used to treat patients with type 2 diabetes since 2007, when exenatide (twice daily) was approved in 2007. Compounds with longer duration of action (once daily, once weekly) and with increasingly better efficacy with respect to glycaemic control and body weight reduction have been developed, and in a recent ADA/EASD consensus statement were recommended as the first injectable diabetes therapy after failure of oral glucose-lowering medications. Most GLP-1 receptor agonists (lixisenatide q.d., liraglutide q.d., exenatide q.w., albiglutide q.w., albiglutide q.w., semaglutide q.w., all for subcutaneous injection, and the first oral preparation, oral semaglutide) have been examined in cardiovascular outcomes studies. Beyond proving their safety in vulnerable patients, most of whom had pre-existing heart disease, liraglutide, semaglutide, albiglutide, and dulaglutide reduced the time to first major adverse cardiovascular events (non-fatal myocardial infarction and stroke, cardiovascular death). Liraglutide, in addition, reduced cardiovascular and all-cause mortality. It is the purpose of the present review to describe clinically important differences, regarding pharmacokinetic behaviour, glucose-lowering potency, effectiveness of reducing body weight and controlling other cardiovascular risk factors, and of the influence of GLP-1 receptor agonist treatment on cardiovascular outcomes in patients either presenting with or without pre-existing cardiovascular disease (atherosclerotic, ischemic or congestive heart failure).

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Thomas G K Breuer, Laura Borker, Daniel R Quast, Andrea Tannapfel, Wolfgang E Schmidt, Waldemar Uhl and Juris J Meier

Introduction

Gastrin has been shown to promote beta-cell proliferation in rodents, but its effects in adult humans are largely unclear. Proton pump inhibitors (PPIs) lead to endogenous hypergastrinaemia, and improved glucose control during PPI therapy has been reported in patients with diabetes. Therefore, we addressed whether PPI treatment is associated with improved glucose homoeostasis, islet cell hyperplasia or increased new beta-cell formation in humans.

Patients and methods

Pancreatic tissue specimens from 60 patients with and 33 patients without previous PPI therapy were examined. The group was subdivided into patients without diabetes (n = 27), pre-diabetic patients (n = 31) and patients with diabetes (n = 35).

Results

Fasting glucose and HbA1c levels were not different between patients with and without PPI therapy (P = 0.34 and P = 0.30 respectively). Beta-cell area was higher in patients without diabetes than in patients with pre-diabetes or diabetes (1.33 ± 0.12%, 1.05 ± 0.09% and 0.66 ± 0.07% respectively; P < 0.0001). There was no difference in beta-cell area between patients with and without PPI treatment (1.05 ± 0.08% vs 0.87 ± 0.08%, respectively; P = 0.16). Beta-cell replication was rare and not different between patients with and without PPI therapy (P = 0.20). PPI treatment was not associated with increased duct-cell replication (P = 0.18), insulin expression in ducts (P = 0.28) or beta-cell size (P = 0.63).

Conclusions

These results suggest that in adult humans, chronic PPI treatment does not enhance beta-cell mass or beta-cell function to a relevant extent.

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Juris J Meier, Christina U Köhler, Bacel Alkhatib, Consolato Sergi, Theresa Junker, Harald H Klein, Wolfgang E Schmidt and Helga Fritsch

Introduction

β-cell regeneration is an area under active investigation for the future treatment of diabetes, but little is known about the patterns and dynamics of prenatal β-cell development in humans. In particular, the quantitative changes in β-cell mass in the developing pancreas have not been elucidated in detail. We addressed the following questions in prenatal humans: i) what is the timing of β-cell occurrence and islet growth? ii) What are the dynamics of β-cell replication and apoptosis?

Methods

Pancreatic tissue was obtained from 65 human embryos and foetuses aged between 8 weeks post conception (p.c.) and birth. Sections were stained for insulin, glucagon, Ki67 (proliferation marker), TUNEL (apoptosis marker) and CD31 (blood vessel marker), and morphometric analyses were performed.

Results

β-cells were detected from gestational week 9 onward, whereas glucagon expression was detected already at week 8. The fractional β-cell area of the pancreas increased in a linear fashion until birth (r=0.60, P<0.001). The first endocrine cells were found within or adjacent to the primitive ductal epithelium. β-cell replication was readily detected in the newly forming islets already starting at week 9 p.c. (average frequency 2.8±0.4%). A small percentage of cells co-expressed insulin and glucagon during the early foetal period. There was a close relationship between the development of endocrine islets and blood vessels during all stages of prenatal pancreas development suggesting a possible interaction between both cell types. The frequency of β-cell apoptosis was relatively high throughout all ages (1.5±0.3%).

Conclusions

β-cell differentiation in humans occurs from week 9 p.c. onward. The first endocrine cells are closely associated with the ductal epithelium suggesting differentiation from precursor cells. High rates of β-cell replication suggest that this mechanism plays an important role in the prenatal expansion of β-cell mass.

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Thomas G K Breuer, Bjoern A Menge, Matthias Banasch, Waldemar Uhl, Andrea Tannapfel, Wolfgang E Schmidt, Michael A Nauck and Juris J Meier

Introduction

Hyperproinsulinaemia has been reported in patients with type 2 diabetes. It is unclear whether this is due to an intrinsic defect in β-cell function or secondary to the increased demand on the β-cells. We investigated whether hyperproinsulinaemia is also present in patients with secondary diabetes, and whether proinsulin levels are associated with impaired β-cell area or function.

Patients and methods

Thirty-three patients with and without diabetes secondary to pancreatic diseases were studied prior to pancreatic surgery. Intact and total proinsulin levels were compared with the pancreatic β-cell area and measures of insulin secretion and action.

Results

Fasting concentrations of total and intact proinsulin were similar in patients with normal, impaired (including two cases of impaired fasting glucose) and diabetic glucose tolerance (P=0.58 and P=0.98 respectively). There were no differences in the total proinsulin/insulin or intact proinsulin/insulin ratio between the groups (P=0.23 and P=0.71 respectively). There was a weak inverse association between the total proinsulin/insulin ratio and pancreatic β-cell area (r 2=0.14, P=0.032), whereas the intact proinsulin/insulin ratio and the intact and total proinsulin levels were unrelated to β-cell area. However, a strong inverse relationship between homeostasis model assessment index of β-cell function and both the total and the intact proinsulin/insulin ratio was found (r 2=0.55 and r 2=0.48 respectively). The association of insulin resistance (IR) with intact proinsulin was much weaker than the correlation with fasting insulin.

Conclusions

Hyperproinsulinaemia is associated with defects in insulin secretion rather than a reduction in β-cell area. The weak association between intact proinsulin and IR argues against the usefulness of this parameter in clinical practice.