Glucagon-like peptide-1 (7-37) augments insulin release in elderly patients with diabetes

Type 2 diabetes management in people aged over seventy-five years: targets and treatment strategies

Older people (those aged 65 years or more) with diabetes comprise a heterogenous group of patients with special needs and features; this is particularly true for those aged 75 years or more. It is important that individualized glycemic targets be adopted in this population, after considering life expectancy, presence of diabetic complications and other comorbidities. In general, less rigorous targets and avoidance of overtreatment seems to be a reasonable strategy in daily clinical settings. There is a paucity of data regarding the efficacy and safety of various hypoglycemic agents, especially for those aged over 75. The evidence suggests that sulfonylureas and insulin regimens should be used with caution due to a high risk of hypoglycemia. Dipeptidyl peptidase-4 inhibitors are a good choice for the management of diabetes in older age groups, although a warning against the use of specific agents in people with heart failure is valid. There are insufficient data to decide whether the cardiorenal protective properties of sodium-glucose co-transporter 2 inhibitors outweigh the risks associated with these drugs. The use of glucagon-like peptide-1 receptor agonists by older patients is supported not only by their good safety and efficacy profiles, but also by their potential to improve glucose-independent outcomes, through their pleiotropic actions. The aim of this narrative review is to summarize the evidence on glycemic targets and optimal therapeutic approaches for older patients with type 2 diabetes and discuss the risk-benefit balance of various therapeutic approaches in this group.

Age-Related Changes in Glucose Metabolism, Hyperglycemia, and Cardiovascular Risk

Aging and diabetes mellitus are 2 well-known risk factors for cardiovascular disease (CVD). During the past 50 years, there has been an dramatic increase in life expectancy with a simultaneous increase in the prevalence of diabetes mellitus in the older population. This large number of older individuals with diabetes mellitus is problematic given that CVD risk associated with aging and diabetes mellitus. In this review, we summarize epidemiological data relating to diabetes mellitus and CVD, with an emphasis on the aging population. We then present data on hyperglycemia as a risk factor for CVD and review the current knowledge of age-related changes in glucose metabolism. Next, we review the role of obesity in the pathogenesis of age-related glucose dysregulation, followed by a summary of the results from major randomized controlled trials that focus on cardiovascular risk reduction through glycemic control, with a special emphasis on older adults. We then conclude with our proposed model of aging that body composition changes and insulin resistance link possible dysregulation of physiological pathways leading to obesity and diabetes mellitus-both forms of accelerated aging-and risks for CVD.

New approaches to treating type 2 diabetes mellitus in the elderly: role of incretin therapies

The increasing proportion of elderly persons in the global population, and the implications of this trend in terms of increasing rates of chronic diseases such as type 2 diabetes mellitus, continue to be a cause for concern for clinicians and healthcare policy makers. The diagnosis and treatment of type 2 diabetes in the elderly is challenging, as age-related changes alter the clinical presentation of diabetic symptoms. Once type 2 diabetes is diagnosed, the principles of its management are similar to those in younger patients, but with special considerations linked to the increased prevalence of co-morbidities and relative inability to tolerate the adverse effects of medication and hypoglycaemia. In addition, there are many underappreciated factors complicating diabetes care in the elderly, including cognitive disorders, physical disability and geriatric syndromes, such as frailty, urinary incontinence and pain. Available oral antihyperglycaemic drugs include insulin secretagogues (meglitinides and sulfonylureas), biguanides (metformin), alpha-glucosidase inhibitors and thiazolidinediones. Unfortunately, as type 2 diabetes progresses in older persons, polypharmacy intensification is required to achieve adequate glycaemic control with the attendant increased risk of adverse effects as a result of age-related changes in drug metabolism. The recent introduction of the incretins, a group of intestinal peptides that enhance insulin secretion after ingestion of food, as novel oral antihyperglycaemic treatments may prove significant in older persons. The two main categories of incretin therapy currently available are: glucagon-like peptide-1 (GLP-1) analogues and inhibitors of GLP-1 degrading enzyme dipeptidyl peptidase-4 (DPP-4). The present review discusses the effect of aging on metabolic control in elderly patients with type 2 diabetes, the current treatments used to treat this population and some of the more recent advances in the field of geriatric type 2 diabetes. In particular, we highlight the efficacy and safety of GLP-1 and DPP-4 inhibitors, administered as monotherapy or in combination with other oral antihyperglycaemic agents, especially when the relevant clinical trials included older persons. There is strong evidence that use of incretin therapy, in particular, the DPP-4 inhibitors, could offer significant advantages in older persons. Clinical evidence suggests that the DPP-4 inhibitors vildagliptin and sitagliptin are particularly suitable for frail and debilitated elderly patients because of their excellent tolerability profiles. Importantly, these agents lack the gastrointestinal effects seen with metformin and alpha-glucosidase inhibitors taken alone, and have a low risk of the hypoglycaemic events commonly seen with agents that directly lower blood glucose levels.

Gastric emptying, diabetes, and aging

Gastric emptying is mildly slowed in healthy aging, although generally remains within the normal range for young people. The significance of this is unclear, but may potentially influence the absorption of certain drugs, especially when a rapid effect is desired. Type 2 diabetes is common in the elderly, but there is little data regarding its natural history, prognosis, and management. This article focuses on the interactions between gastric emptying and diabetes, how each is influenced by the process of aging, and the implications for patient management.

Biology of incretins: GLP-1 and GIP

This review focuses on the mechanisms regulating the synthesis, secretion, biological actions, and therapeutic relevance of the incretin peptides glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). The published literature was reviewed, with emphasis on recent advances in our understanding of the biology of GIP and GLP-1. GIP and GLP-1 are both secreted within minutes of nutrient ingestion and facilitate the rapid disposal of ingested nutrients. Both peptides share common actions on islet beta-cells acting through structurally distinct yet related receptors. Incretin-receptor activation leads to glucose-dependent insulin secretion, induction of beta-cell proliferation, and enhanced resistance to apoptosis. GIP also promotes energy storage via direct actions on adipose tissue, and enhances bone formation via stimulation of osteoblast proliferation and inhibition of apoptosis. In contrast, GLP-1 exerts glucoregulatory actions via slowing of gastric emptying and glucose-dependent inhibition of glucagon secretion. GLP-1 also promotes satiety and sustained GLP-1-receptor activation is associated with weight loss in both preclinical and clinical studies. The rapid degradation of both GIP and GLP-1 by the enzyme dipeptidyl peptidase-4 has led to the development of degradation-resistant GLP-1-receptor agonists and dipeptidyl peptidase-4 inhibitors for the treatment of type 2 diabetes. These agents decrease hemoglobin A1c (HbA1c) safely without weight gain in subjects with type 2 diabetes. GLP-1 and GIP integrate nutrient-derived signals to control food intake, energy absorption, and assimilation. Recently approved therapeutic agents based on potentiation of incretin action provide new physiologically based approaches for the treatment of type 2 diabetes.

Unique characteristics of the geriatric diabetic population and the role for therapeutic strategies that enhance glucagon-like peptide-1 activity

PURPOSE OF REVIEW

Care for elderly diabetic patients poses a unique clinical challenge. This review highlights distinct aspects of the pathophysiology and the risks for secondary complications in the geriatric diabetic population. Based on these considerations, we discuss emerging therapeutic options based on the actions of the incretin hormone glucagon-like peptide (GLP)-1, which may be ideal for achieving glycemic control in the elderly diabetic patient.

RECENT FINDINGS

Aging is associated with diminished capacity of pancreatic beta-cells to respond to glucose. This functional decline in beta-cell insulin secretion is a major contributor to the development of diabetes in the older patient. In addition, elderly diabetics suffer from a broader range of diabetic complications than do younger diabetics, warranting aggressive glycemic control. GLP-1 is known to improve beta-cell insulin secretion, increase beta-cell mass, and suppress glucagon secretion. Recent studies investigating improved GLP-1 activity have yielded promising results, with improved glycemic control in elderly patients with type 2 diabetes and without significant risk for hypoglycemia.

SUMMARY

Elderly diabetics are a growing subset of the type 2 diabetic population with unique pathophysiologic characteristics and diabetic risk profiles. Therapeutic strategies that incorporate enhancement of GLP-1 action on beta-cells to improve beta-cell insulin secretion and glycemic control may be ideal for this distinct population and should be validated with further long-term clinical studies.

Effects of 3 months of continuous subcutaneous administration of glucagon-like peptide 1 in elderly patients with type 2 diabetes

OBJECTIVE

Glucagon-like peptide 1 (GLP-1) is an insulinotropic gut hormone that, when given exogenously, may be a useful agent in the treatment of type 2 diabetes. We conducted a 3-month trial to determine the efficacy and safety of GLP-1 in elderly diabetic patients.

RESEARCH DESIGN AND METHODS

A total of 16 patients with type 2 diabetes who were being treated with oral hypoglycemic agents were enrolled. Eight patients (aged 75 +/- 2 years, BMI 27 +/- 1 kg/m(2)) remained on usual glucose-lowering therapy and eight patients (aged 73 +/- 1 years, BMI 27 +/- 1 kg/m(2)), after discontinuing hypoglycemic medications, received GLP-1 delivered by continuous subcutaneous infusion for 12 weeks. The maximum dose was 120 pmol x kg(-1). h(-1). Patients recorded their capillary blood glucose (CBG) levels (four times per day, 3 days per week) and whenever they perceived hypoglycemic symptoms. The primary end points were HbA(1c) and CBG determinations. Additionally, changes in beta-cell sensitivity to glucose, peripheral tissue sensitivity to insulin, and changes in plasma ghrelin levels were examined.

RESULTS

HbA(1c) levels (7.1%) and body weight were equally maintained in both groups. The usual treatment group had a total of 87 CBG measurements of <or=3.6 mmol/l during the study, and only 1 such measurement (3.5 mmol/l) was recorded in the GLP-1 group. Infusion of GLP-1 enhanced glucose-induced insulin secretion (pre: 119 +/- 21; post: 202 +/- 51 pmol/l; P < 0.05) and insulin-mediated glucose disposal (pre: 29.8 +/- 3.3; post: 35.9 +/- 2.3 micromol x kg(-1 x min(-1); P < 0.01). No effect of GLP-1 treatment was seen on the fasting plasma ghrelin levels. Although plasma ghrelin levels decreased during both portions of the clamp, a drug effect was not present.

CONCLUSIONS

A GLP-1 compound is a promising therapeutic option for elderly diabetic patients.