β-Cell Failure in Diabetes and Preservation by Clinical Treatment

Abstract

There is a progressive deterioration in beta-cell function and mass in type 2 diabetics. It was found that islet function was about 50% of normal at the time of diagnosis, and a reduction in beta-cell mass of about 60% was shown at necropsy. The reduction of beta-cell mass is attributable to accelerated apoptosis. The major factors for progressive loss of beta-cell function and mass are glucotoxicity, lipotoxicity, proinflammatory cytokines, leptin, and islet cell amyloid. Impaired beta-cell function and possibly beta-cell mass appear to be reversible, particularly at early stages of the disease where the limiting threshold for reversibility of decreased beta-cell mass has probably not been passed. Among the interventions to preserve or "rejuvenate" beta-cells, short-term intensive insulin therapy of newly diagnosed type 2 diabetes will improve beta-cell function, usually leading to a temporary remission time. Another intervention is the induction of beta-cell "rest" by selective activation of ATP-sensitive K+ (K(ATP)) channels, using drugs such as diazoxide. A third type of intervention is the use of antiapoptotic drugs, such as the thiazolidinediones (TZDs), and incretin mimetics and enhancers, which have demonstrated significant clinical evidence of effects on human beta-cell function. The TZDs improve insulin secretory capacity, decrease beta-cell apoptosis, and reduce islet cell amyloid with maintenance of neogenesis. The TZDs have indirect effects on beta-cells by being insulin sensitizers. The direct effects are via peroxisome proliferator-activated receptor gamma activation in pancreatic islets, with TZDs consistently improving basal beta-cell function. These beneficial effects are sustained in some individuals with time. There are several trials on prevention of diabetes with TZDs. Incretin hormones, which are released from the gastrointestinal tract in response to nutrient ingestion to enhance glucose-dependent insulin secretion from the pancreas, aid the overall maintenance of glucose homeostasis through slowing of gastric emptying, inhibition of glucagon secretion, and control of body weight. From the two major incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), only the first one or its mimetics or enhancers can be used for treatment because the diabetic beta-cell is resistant to GIP action. Because of the rapid inactivation of GLP-1 by dipeptidyl peptidase (DPP)-IV, several incretin analogs were developed: GLP-1 receptor agonists (incretin mimetics) exenatide (synthetic exendin-4) and liraglutide, by conjugation of GLP-1 to circulating albumin. The acute effect of GLP-1 and GLP-1 receptor agonists on beta-cells is stimulation of glucose-dependent insulin release, followed by enhancement of insulin biosynthesis and stimulation of insulin gene transcription. The chronic action is stimulating beta-cell proliferation, induction of islet neogenesis, and inhibition of beta-cell apoptosis, thus promoting expansion of beta-cell mass, as observed in rodent diabe...

G-protein-coupled receptors and islet function—Implications for treatment of type 2 diabetes

“…In fact, islet dysfunction is a key event underlying development of type 2 diabetes, as manifested by impaired insulin secretion and increased secretion of glucagon (Dunning et al, 2005;Wajchenberg 2007). Recently, it has also been proposed that reduced β cell mass is associated with type 2 diabetes (Butler et al, 2003;Wajchenberg 2007). Since glycemic control of type 2 diabetes often deteriorates in spite of aggressive treatment (Turner 1998), there is today an active search for novel therapy.…”

Noninvasive in vivo imaging of pancreatic islet cell biology

“…Adequate release of insulin by pancreatic beta cells in response to changing blood glucose levels is a vital requirement for maintaining glucose homeostasis. Failure to do so is one of the major causes of type 2 diabetes mellitus, the most common metabolic disorder in humans 1 . Under physiological conditions, insulin release is regulated by the complex interplay between glucose and a plethora of additional factors-for example, nutrients, autocrine-paracrine signaling and the continuous input from hormones and neurotransmitters 2 .…”

Seven Transmembrane-spanning Receptors for Free Fatty Acids as Therapeutic Targets for Diabetes Mellitus: Pharmacological, Phylogenetic, and Drug Discovery Aspects

“…Islet dysfunction is a pivotal cause of type 2 diabetes mellitus, which is manifest by impaired insulin secretion and increased secretion of glucagon (26). An important pharmacological strategy for treatment of this disease is to stimulate insulin secretion and to reduce glucagon secretion.…”