Type 2 diabetes is characterized by impaired insulin secretion. Some but not all studies suggest that a decrease in beta-cell mass contributes to this. We examined pancreatic tissue from 124 autopsies: 91 obese cases (BMI >27 kg/m(2); 41 with type 2 diabetes, 15 with impaired fasting glucose [IFG], and 35 nondiabetic subjects) and 33 lean cases (BMI <25 kg/m(2); 16 type 2 diabetic and 17 nondiabetic subjects). We measured relative beta-cell volume, frequency of beta-cell apoptosis and replication, and new islet formation from exocrine ducts (neogenesis). Relative beta-cell volume was increased in obese versus lean nondiabetic cases (P = 0.05) through the mechanism of increased neogenesis (P < 0.05). Obese humans with IFG and type 2 diabetes had a 40% (P < 0.05) and 63% (P < 0.01) deficit and lean cases of type 2 diabetes had a 41% deficit (P < 0.05) in relative beta-cell volume compared with nondiabetic obese and lean cases, respectively. The frequency of beta-cell replication was very low in all cases and no different among groups. Neogenesis, while increased with obesity, was comparable in obese type 2 diabetic, IFG, or nondiabetic subjects and in lean type 2 diabetic or nondiabetic subjects. However, the frequency of beta-cell apoptosis was increased 10-fold in lean and 3-fold in obese cases of type 2 diabetes compared with their respective nondiabetic control group (P < 0.05). We conclude that beta-cell mass is decreased in type 2 diabetes and that the mechanism underlying this is increased beta-cell apoptosis. Since the major defect leading to a decrease in beta-cell mass in type 2 diabetes is increased apoptosis, while new islet formation and beta-cell replication are normal, therapeutic approaches designed to arrest apoptosis could be a significant new development in the management of type 2 diabetes, because this approach might actually reverse the disease to a degree rather than just palliate glycemia.

https://diabetes.diabetesjournals.org/content/diabetes/52/1/102.full.pdf

β-Cell Deficit and Increased β-Cell Apoptosis in Humans With Type 2 Diabetes

The inflammasomes are innate immune system receptors and sensors that regulate the activation of caspase-1 and induce inflammation in response to infectious microbes and molecules derived from host proteins. They have been implicated in a host of inflammatory disorders. Recent developments have greatly enhanced our understanding of the molecular mechanisms by which different inflammasomes are activated. Additionally, increasing evidence in mouse models, supported by human data, strongly implicates an involvement of the inflammasome in the initiation or progression of diseases with a high impact on public health, such as metabolic disorders and neurodegenerative diseases. Finally, recent developments pointing toward promising therapeutics that target inflammasome activity in inflammatory diseases have been reported. This review will focus on these three areas of inflammasome research.

Inflammasomes: mechanism of action, role in disease, and therapeutics

Non-insulin-dependent diabetes mellitus (NIDDM) results from an imbalance between insulin sensitivity and insulin secretion. Both longitudinal and cross-sectional studies have demonstrated that the earliest detectable abnormality in NIDDM is an impairment in the body's ability to respond to insulin. Because the pancreas is able to appropriately augment its secretion of insulin to offset the insulin resistance, glucose tolerance remains normal. With time, however, the beta-cell fails to maintain its high rate of insulin secretion and the relative insulinopenia (i.e., relative to the degree of insulin resistance) leads to the development of impaired glucose tolerance and eventually overt diabetes mellitus. The cause of pancreatic "exhaustion" remains unknown but may be related to the effect of glucose toxicity in a genetically predisposed beta-cell. Information concerning the loss of first-phase insulin secretion, altered pulsatility of insulin release, and enhanced proinsulin-insulin secretory ratio is discussed as it pertains to altered beta-cell function in NIDDM. Insulin resistance in NIDDM involves both hepatic and peripheral, muscle, tissues. In the postabsorptive state hepatic glucose output is normal or increased, despite the presence of fasting hyperinsulinemia, whereas the efficiency of tissue glucose uptake is reduced. In response to both endogenously secreted or exogenously administered insulin, hepatic glucose production fails to suppress normally and muscle glucose uptake is diminished. The accelerated rate of hepatic glucose output is due entirely to augmented gluconeogenesis. In muscle many cellular defects in insulin action have been described including impaired insulin-receptor tyrosine kinase activity, diminished glucose transport, and reduced glycogen synthase and pyruvate dehydrogenase. The abnormalities account for disturbances in the two major intracellular pathways of glucose disposal, glycogen synthesis, and glucose oxidation. In the earliest stages of NIDDM, the major defect involves the inability of insulin to promote glucose uptake and storage as glycogen. Other potential mechanisms that have been put forward to explain the insulin resistance, include increased lipid oxidation, altered skeletal muscle capillary density/fiber type/blood flow, impaired insulin transport across the vascular endothelium, increased amylin, calcitonin gene-related peptide levels, and glucose toxicity.

Pathogenesis of NIDDM: A balanced overview

The relative contributions of insulin resistance and beta-cell dysfunction to the pathophysiology of Type 2 diabetes have been debated extensively. The concept that a feedback loop governs the interaction of the insulin-sensitive tissues and the beta cell as well as the elucidation of the hyperbolic relationship between insulin sensitivity and insulin secretion explains why insulin-resistant subjects exhibit markedly increased insulin responses while those who are insulin-sensitive have low responses. Consideration of this hyperbolic relationship has helped identify the critical role of beta-cell dysfunction in the development of Type 2 diabetes and the demonstration of reduced beta-cell function in high risk subjects. Furthermore, assessments in a number of ethnic groups emphasise that beta-cell function is a major determinant of oral glucose tolerance in subjects with normal and reduced glucose tolerance and that in all populations the progression from normal to impaired glucose tolerance and subsequently to Type 2 diabetes is associated with declining insulin sensitivity and beta-cell function. The genetic and molecular basis for these reductions in insulin sensitivity and beta-cell function are not fully understood but it does seem that body-fat distribution and especially intra-abdominal fat are major determinants of insulin resistance while reductions in beta-cell mass contribute to beta-cell dysfunction. Based on our greater understanding of the relative roles of insulin resistance and beta-cell dysfunction in Type 2 diabetes, we can anticipate advances in the identification of genes contributing to the development of the disease as well as approaches to the treatment and prevention of Type 2 diabetes.

/pdf/the-relative-contributions-of-insulin-resistance-and-beta-m1kdsk3xbt.pdf

The relative contributions of insulin resistance and beta-cell dysfunction to the pathophysiology of Type 2 diabetes.

By combining genome-wide association data from 8,130 individuals with type 2 diabetes (T2D) and 38,987 controls of European descent and following up previously unidentified meta-analysis signals in a further 34,412 cases and 59,925 controls, we identified 12 new T2D association signals with combined P<5x10(-8). These include a second independent signal at the KCNQ1 locus; the first report, to our knowledge, of an X-chromosomal association (near DUSP9); and a further instance of overlap between loci implicated in monogenic and multifactorial forms of diabetes (at HNF1A). The identified loci affect both beta-cell function and insulin action, and, overall, T2D association signals show evidence of enrichment for genes involved in cell cycle regulation. We also show that a high proportion of T2D susceptibility loci harbor independent association signals influencing apparently unrelated complex traits.

/pdf/twelve-type-2-diabetes-susceptibility-loci-identified-48vtfczwpg.pdf

Twelve type 2 diabetes susceptibility loci identified through large-scale association analysis

Deposition of amyloid in pancreatic islets is a common feature in human type 2 diabetic subjects but because of its insolubility and low tissue concentrations, the structure of its monomer has not been determined. We describe a peptide, of calculated molecular mass 3905 Da, that was a major protein component of amyloid-rich pancreatic extracts of three type 2 diabetic patients. After collagenase treatment, an extract containing 20-50% amyloid was solubilized by sonication into 70% formic acid and the peptide was purified by gel filtration followed by reverse-phase high-performance liquid chromatography. We term this peptide diabetes-associated peptide, as it was not detected in extracts of pancreas from any of six normal subjects. Diabetes-associated peptide contains 37 amino acids and is 46% identical to the sequences of rat and human calcitonin gene-related peptide, indicating that these peptides are related in evolution. Sequence identities with conserved residues of the insulin A chain were also seen in a 16-residue segment. On extraction, the islet amyloid is particulate and insoluble like the core particles of Alzheimer disease. Their monomers have similar molecular masses, each having a hydropathic region that can probably form beta-pleated sheets. The accumulation of amyloid, including diabetes-associated peptide, in islets may impair islet function in type 2 diabetes mellitus.

https://www.pnas.org/content/pnas/84/23/8628.full.pdf

Purification and characterization of a peptide from amyloid-rich pancreases of type 2 diabetic patients

Morphometric analysis of the endocrine and exocrine pancreas was done on immunoperoxidase stained post-mortem tissue from 15 Type 2 diabetic and 10 age-matched control subjects. Thirteen of the 15 Type 2 diabetic patients had islet amyloid deposits (mean, 6.5% islet area) in the corpus (body, tail and anterior part of the head) but not in the caput (the "pancreatic polypeptide rich" part of the head) whereas none was seen in control subjects. In the corpus in diabetic subjects, the pancreatic area density of B-cells was decreased by 24% (p = 0.005) and A-cells increased by 58% (p less than 0.001) compared with control subjects. The mean A/B-cell ratio increased in the corpus from 0.27 in control subjects to 0.57 in Type 2 diabetic patients. Positive immunoreactivity for the amyloid constituent peptide, Diabetes Associated Peptide, was demonstrated in islet amyloid of diabetic subjects and in B-cells of control and diabetic subjects. The increase in A-cells may contribute to the hyperglucagonaemia and hyperglycaemia of Type 2 diabetes. The impaired insulin secretion in Type 2 diabetes may be due to a decrease in B-cells and to disruption of the islet structure by amyloid. Exocrine fat was similar in the control and diabetic subjects with both groups having more in the corpus than the caput. Diabetic subjects had increased exocrine fibrosis in the corpus region (p less than 0.001), but not in the caput. Exocrine fibrosis may be secondary to disordered islet cell function.

Islet amyloid, increased A-cells, reduced B-cells and exocrine fibrosis: quantitative changes in the pancreas in type 2 diabetes.

Islet amyloid formed from diabetes-associated peptide may be pathogenic in type-2 diabetes.

Diabetes is characterized by hyperglycaemia due to impaired insulin secretion and aberrant glucagon secretion resulting from changes in pancreatic islet cell function and/or mass. The extent to which hyperglycaemia per se underlies these alterations remains poorly understood. Here we show that β-cell-specific expression of a human activating KATP channel mutation in adult mice leads to rapid diabetes and marked alterations in islet morphology, ultrastructure and gene expression. Chronic hyperglycaemia is associated with a dramatic reduction in insulin-positive cells and an increase in glucagon-positive cells in islets, without alterations in cell turnover. Furthermore, some β-cells begin expressing glucagon, whilst retaining many β-cell characteristics. Hyperglycaemia, rather than KATP channel activation, underlies these changes, as they are prevented by insulin therapy and fully reversed by sulphonylureas. Our data suggest that many changes in islet structure and function associated with diabetes are attributable to hyperglycaemia alone and are reversed when blood glucose is normalized.

Reversible changes in pancreatic islet structure and function produced by elevated blood glucose

Diabetes mellitus in Macaca mulatta rhesus monkeys is preceded by phases of obesity and hyperinsulinaemia and is similar to Type 2 (non-insulin-dependent) diabetes mellitus in man. To relate the progression of the disease to quantitative changes in islet morphology, post-mortem pancreatic tissue from 26 monkeys was examined. Four groups of animals were studied: group I--young, lean and normal (n = 3); group II--older (> 10 years), lean and obese, normoglycaemic (n = 9); group III--normoglycaemic and hyperinsulinaemic (n = 6); group IV--diabetic (n = 8). Areas of islet amyloid, beta cells and islets were measured on stained histological sections. Islet size was larger in animals from groups III (p < 0.01) and IV (p < 0.0001) compared to groups I and II. The mean beta-cell area per islet in micron 2 was increased in group III (p < 0.05) and reduced in group IV (p < 0.001) compared to groups I and II. Mean beta-cell area per islet correlated with fasting plasma insulin (r = 0.76, p < 0.001) suggesting that hyper- and hypoinsulinaemia are related to the beta-cell population. Amyloid was absent in group I but small deposits were present in three of nine (group II) and in four of six (group III) animals, occupying between 0.03-45% of the islet space. Amyloid was present in eight of eight diabetic animals (group IV) occupying between 37-81% of the islet area. Every islet was affected in seven of eight diabetic monkeys. There was no correlation of degree of amyloidosis with age, body weight, body fat proportion or fasting insulin. Islet amyloid appears to precede the development of overt diabetes in Macaca mulatta and is likely to be a factor in the destruction of islet cells and onset of hyperglycaemia.

/pdf/diabetes-mellitus-in-macaca-mulatta-monkeys-is-characterised-2ireo6ac8n.pdf

A Clark

Papers

Purification and characterization of a peptide from amyloid-rich pancreases of type 2 diabetic patients

Islet amyloid, increased A-cells, reduced B-cells and exocrine fibrosis: quantitative changes in the pancreas in type 2 diabetes.

Islet amyloid formed from diabetes-associated peptide may be pathogenic in type-2 diabetes.

Reversible changes in pancreatic islet structure and function produced by elevated blood glucose

Diabetes mellitus in Macaca mulatta monkeys is characterised by islet amyloidosis and reduction in beta-cell population