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

Biology of Incretins: GLP-1 and GIP

Insulin resistance in muscle and liver and β-cell failure represent the core pathophysiologic defects in type 2 diabetes. It now is recognized that the β-cell failure occurs much earlier and is more severe than previously thought. Subjects in the upper tertile of impaired glucose tolerance (IGT) are maximally/near-maximally insulin resistant and have lost over 80% of their β-cell function. In addition to the muscle, liver, and β-cell (triumvirate), the fat cell (accelerated lipolysis), gastrointestinal tract (incretin deficiency/resistance), α-cell (hyperglucagonemia), kidney (increased glucose reabsorption), and brain (insulin resistance) all play important roles in the development of glucose intolerance in type 2 diabetic individuals. Collectively, these eight players comprise the ominous octet and dictate that: 1 ) multiple drugs used in combination will be required to correct the multiple pathophysiological defects, 2 ) treatment should be based upon reversal of known pathogenic abnormalities and not simply on reducing the A1C, and 3 ) therapy must be started early to prevent/slow the progressive β-cell failure that already is well established in IGT subjects. A treatment paradigm shift is recommended in which combination therapy is initiated with diet/exercise, metformin (which improves insulin sensitivity and has antiatherogenic effects), a thiazolidinedione (TZD) (which improves insulin sensitivity, preserves β-cell function, and exerts antiatherogenic effects), and exenatide (which preserves β-cell function and promotes weight loss). Sulfonylureas are not recommended because, after an initial improvement in glycemic control, they are associated with a progressive rise in A1C and progressive loss of β-cell function.

The natural history of type 2 diabetes has been well described in multiple populations (1–16) (rev. in (17,18). Individuals destined to develop type 2 diabetes inherit a set of genes from their parents that make their tissues resistant to insulin (1,16,19–24). In liver, the insulin resistance is manifested by …

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From the Triumvirate to the Ominous Octet: A New Paradigm for the Treatment of Type 2 Diabetes Mellitus

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(09)60659-0.pdf

Liraglutide once a day versus exenatide twice a day for type 2 diabetes: a 26-week randomised, parallel-group, multinational, open-label trial (LEAD-6).

ContextPharmacotherapies that augment the incretin pathway have recently become available, but their role in the management of type 2 diabetes is not well defined.ObjectiveTo assess the efficacy and safety of incretin-based therapy in adults with type 2 diabetes based on randomized controlled trials published in peer-reviewed journals or as abstracts.Data SourcesWe searched MEDLINE (1966–May 20, 2007) and the Cochrane Central Register of Controlled Trials (second quarter, 2007) for English-language randomized controlled trials involving an incretin mimetic (glucagonlike peptide 1 [GLP-1] analogue) or enhancer (dipeptidyl peptidase 4 [DPP4] inhibitor). We also searched prescribing information, relevant Web sites, reference lists and citation sections of recovered articles, and abstracts presented at recent conferences.Study SelectionRandomized controlled trials were selected if they were at least 12 weeks in duration, compared incretin therapy with placebo or other diabetes medication, and reported hemoglobin A1c data in nonpregnant adults with type 2 diabetes.Data ExtractionTwo reviewers independently assessed trials for inclusion and extracted data. Differences were resolved by consensus. Meta-analyses were conducted for several efficacy and safety outcomes.ResultsOf 355 potentially relevant articles identified, 51 were retrieved for detailed evaluation and 29 met the inclusion criteria. Incretins lowered hemoglobin A1c compared with placebo (weighted mean difference, −0.97% [95% confidence interval {CI}, −1.13% to −0.81%] for GLP-1 analogues and −0.74% [95% CI, −0.85% to −0.62%] for DPP4 inhibitors) and were noninferior to other hypoglycemic agents. Glucagonlike peptide 1 analogues resulted in weight loss (1.4 kg and 4.8 kg vs placebo and insulin, respectively) while DPP4 inhibitors were weight neutral. Glucagonlike peptide 1 analogues had more gastrointestinal side effects (risk ratio, 2.9 [95% CI, 2.0-4.2] for nausea and 3.2 [95% CI, 2.5-4.4] for vomiting). Dipeptidyl peptidase 4 inhibitors had an increased risk of infection (risk ratio, 1.2 [95% CI, 1.0-1.4] for nasopharyngitis and 1.5 [95% CI, 1.0-2.2] for urinary tract infection) and headache (risk ratio, 1.4 [95% CI, 1.1-1.7]). All but 3 trials had a 30-week or shorter duration; thus, long-term efficacy and safety could not be evaluated.ConclusionsIncretin therapy offers an alternative option to currently available hypoglycemic agents for nonpregnant adults with type 2 diabetes, with modest efficacy and a favorable weight-change profile. Careful postmarketing surveillance for adverse effects, especially among the DPP4 inhibitors, and continued evaluation in longer-term studies and in clinical practice are required to determine the role of this new class among current pharmacotherapies for type 2 diabetes.

https://friedmanfellows.com/assets/pdfs/elibrary/37.%202007_Amori_JAMA_Incretin_Meta-Analysis.pdf

Efficacy and safety of incretin therapy in type 2 diabetes: systematic review and meta-analysis.

The aim of this 52-week, open-label, non-inferiority trial was to compare the safety and efficacy of exenatide (an incretin mimetic) with that of biphasic insulin aspart. Patients on metformin and a sulfonylurea were randomised to exenatide (n = 253; 5 μg twice daily for 4 weeks, 10 μg thereafter) or biphasic insulin aspart (n = 248; twice-daily doses titrated for optimal glucose control), while continuing with metformin and sulfonylurea treatment. Glycaemic control achieved with exenatide was non-inferior to that achieved with biphasic insulin aspart (mean±SEM, HbA1c change: exenatide −1.04 ± 0.07%, biphasic insulin aspart −0.89 ± 0.06%; difference −0.15 [95% CI −0.32 to 0.01]%). Exenatide-treated patients lost weight, while patients treated with biphasic insulin aspart gained weight [between-group difference −5.4 (95% CI −5.9 to −5.0) kg]. Both treatments reduced fasting serum glucose (exenatide −1.8 ± 0.2 mmol/l, p < 0.001; biphasic insulin aspart −1.7 ± 0.2 mmol/l, p < 0.001). Greater reductions in postprandial glucose excursions following morning (p < 0.001), midday (p = 0.002) and evening meals (p < 0.001) were observed with exenatide. The withdrawal rate was 21.3% (54/253) for exenatide and 10.1% (25/248) for biphasic insulin aspart. Nausea (33% incidence, 3.5% discontinuation) was the most common adverse event observed with exenatide. Exenatide treatment resulted in HbA1c reduction similar to biphasic insulin aspart and provided better postprandial glycaemic control, making it a potential alternative for the treatment of type 2 diabetes. Treatment with biphasic insulin aspart was associated with weight gain and lower risk of adverse gastrointestinal events. Although the availability of glucose-lowering agents associated with weight reduction may be considered a therapeutic advance, the long-term implications of progressive weight reduction observed with exenatide have yet to be defined.

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A comparison of twice-daily exenatide and biphasic insulin aspart in patients with type 2 diabetes who were suboptimally controlled with sulfonylurea and metformin: a non-inferiority study.

To the Editor: In his letter to Diabetologia [1], P. D. Home highlights the difficulties of achieving optimal glycaemic control with insulins. While good glycaemic control was achievedwith insulin (endpoint HbA1c about 7.0% on average) in the several recently published trials identified by Home [1], other trials have reported less than optimal results, particularly for insulin mixtures [2, 3]. Subjects in the treat-to-target trial conducted by Janka et al. [3] achieved a mean endpoint HbA1c of 7.49% with human NPH insulin 70/30. Subjects treated with biphasic insulin aspart 30 in the study conducted by Boehm et al. [2] achieved a mean HbA1c of 8.15% at endpoint. Incidentally, this study [2] was used as a reference when designing our non-inferiority study [4]. Most of the treat-to-target trials demonstrate that it is possible to achieve substantial improvements in glycaemic control when insulin titration algorithms are strictly enforced and exceptional follow-up efforts (often weekly patient contacts) are made in a clinical trial setting. But when very similar approaches are used, some trials (even when conducted by the same sponsor) still achieve quite different results. For example, Rosenstock et al. [5] observed an endpoint HbA1c of 7.8% in a meta-analysis of glargine trials, whereas an endpoint HbA1c of 7.0% was reported in the treat-to-target trial performed by Riddle et al. [6]. How variation observed in clinical research reflects variation in clinical practice remains to be seen. The endpoint insulin dose of 24 IU/day reported in our current non-inferiority study [4] is lower than would be expected with a forced titration schedule. As outlined in the article, a forced titration schedule was not used [4]; rather, investigators were instructed to use fasting and postprandial glycaemic targets as a guide while seeking to achieve an optimal balance between glycaemic control and risk of hypoglycaemia as dictated by best clinical practice. It is not entirely clear why the physicians, who had to decide on these issues according to the perceived best interest of their patients, did not suggest higher insulin doses. Our data do not allow a more detailed analysis of potential reasons. We cannot fully exclude the possibility that study physicians interested in performing this trial were biased towards avoiding hypoglycaemia rather than achieving optimal glycaemic control (as exenatide might have been presumed to have an advantage over insulin treatment in this respect). We also cannot entirely exclude the possibility that there was Diabetologia (2007) 50:1563–1564 DOI 10.1007/s00125-007-0680-6

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Response to comment on: Nauck MA, Duran S, Kim D et al (2007) A comparison of twice-daily exenatide and biphasic insulin aspart in patients with type 2 diabetes who were suboptimally controlled with sulfonylurea and metformin: a non-inferiority study. Diabetologia 50:259–267

M. A. Nauck

Papers

A comparison of twice-daily exenatide and biphasic insulin aspart in patients with type 2 diabetes who were suboptimally controlled with sulfonylurea and metformin: a non-inferiority study.

Response to comment on: Nauck MA, Duran S, Kim D et al (2007) A comparison of twice-daily exenatide and biphasic insulin aspart in patients with type 2 diabetes who were suboptimally controlled with sulfonylurea and metformin: a non-inferiority study. Diabetologia 50:259–267