Pancreatic beta-cell mass in European subjects with type 2 diabetes

Decreases in both beta-cell function and number can contribute to insulin deficiency in type 2 diabetes. Here, we quantified the beta-cell mass in pancreas obtained at autopsy of 57 type 2 diabetic (T2D) and 52 non-diabetic subjects of European origin. Sections from the body and tail were immunostained for insulin. The beta-cell mass was calculated from the volume density of beta-cells (measured by point-counting methods) and the weight of the pancreas. The pancreatic insulin concentration was measured in some of the subjects. beta-cell mass increased only slightly with body mass index (BMI). After matching for BMI, the beta-cell mass was 41% (BMI < 25) and 38% (BMI 26-40) lower in T2D compared with non-diabetic subjects, and neither gender nor type of treatment influenced these differences. beta-cell mass did not correlate with age at diagnosis but decreased with duration of clinical diabetes (24 and 54% lower than controls in subjects with <5 and >15 years of overt diabetes respectively). Pancreatic insulin concentration was 30% lower in patients. In conclusion, the average beta-cell mass is about 39% lower in T2D subjects compared with matched controls. Its decrease with duration of the disease could be a consequence of diabetes that, with further impairment of insulin secretion, contributes to the progressive deterioration of glucose homeostasis. We do not believe that the small difference in beta-cell mass observed within 5 years of onset could cause diabetes in the absence of beta-cell dysfunction.     

Molecular control of cell cycle progression in the pancreatic beta-cell

Type 1 and type 2 diabetes both result from inadequate production of insulin by the beta-cells of the pancreatic islet. Accordingly, strategies that lead to increased pancreatic beta-cell mass, as well as retained or enhanced function of islets, would be desirable for the treatment of diabetes. Although pancreatic beta-cells have long been viewed as terminally differentiated and irreversibly arrested, evidence now indicates that beta-cells can and do replicate, that this replication can be enhanced by a variety of maneuvers, and that beta-cell replication plays a quantitatively significant role in maintaining pancreatic beta-cell mass and function. Because beta-cells have been viewed as being unable to proliferate, the science of beta-cell replication is undeveloped. In the past several years, however, this has begun to change at a rapid pace, and many laboratories are now focused on elucidating the molecular details of the control of cell cycle in the beta-cell. In this review, we review the molecular details of cell cycle control as they relate to the pancreatic beta-cell. Our hope is that this review can serve as a common basis and also a roadmap for those interested in developing novel strategies for enhancing beta-cell replication and improving insulin production in animal models as well as in human pancreatic beta-cells.     

��-Zell-Erhalt durch inkretinbasierte Therapien

Preservation of pancreatic beta-cells in patients with type 2 diabetes would be a substantial therapeutic improvement as the disease is associated with a progressive loss of insulin-producing beta-cells. In various preclinical studies glucagon-like peptide 1 (GLP-1) led to preservation of beta-cell mass by inducing beta-cell proliferation and neogenesis as well as inhibiting apoptosis. These results cannot readily be translated to the situation in humans and further clinical evidence is needed.     

Cell therapy for type 2 diabetes: is it desirable and can we get it?

The functional mass of beta-cells is decreased in type 2 diabetes. Replacing missing beta-cells or triggering their regeneration may thus allow for improved treatment of type 2 diabetes, to the extent that this is combined with therapy for improved insulin sensitivity. Although progress has been made in deriving beta-cell-like cells from stem or precursor cells in vitro, these cannot yet be obtained in sufficient quantities or well enough differentiated to envisage their therapeutic use in beta-cell replacement therapy. Likewise, our very limited understanding of beta-cell regeneration in adult man does not yet allow for development of a valid strategy for kick-starting such a process in individuals with type 2 diabetes, whether by bona fide neogenesis or self-replication of existing beta-cells. Regardless of how beta-cell mass is restored in type 2 diabetes, it will be important to prevent any renewed decrease thereafter. Current understanding suggests that islet inflammation as well as signals from (insulin-resistant/inflamed) adipose tissue and skeletal muscle contribute towards decreased beta-cell mass in type 2 diabetes. It will likely be important to protect newly formed or implanted beta-cells from these negative influences to ensure their long-term survival.     

An examination of beta-cell function measures and their potential use for estimating beta-cell mass

A characteristic and dominant feature of type 2 diabetes is a reduction in beta-cell function that is associated with a decrease in beta-cell volume. A decline in the first-phase insulin response following intravenous glucose administration can be demonstrated as the fasting glucose concentration increases. This response is completely absent before the glucose threshold that defines diabetes has been reached and at a time when beta-cells are clearly still present, implying that a functional beta-cell lesion has to exist independent of beta-cell loss. Surgical or chemical reductions of up to 65% of beta-cell volume demonstrate that functional adaptation of the normal beta-cell prevents a rise in fasting glucose or reduction in first-phase insulin response. However, the ability of glucose to potentiate the beta-cell's response to non-glucose secretagogues is reduced and is more closely associated with the reduction in beta-cell volume. The future, in terms of prevention and treatment of type 2 diabetes, lies in the ability to prevent and revert both beta-cell loss and dysfunction. However, until beta-cell volume can be quantified reliably and non-invasively, we will need to rely on the ability of glucose to potentiate insulin release as the best surrogate estimate of the number of beta-cells.     

Relationship between beta-cell mass and diabetes onset

Regulation of blood glucose concentrations requires an adequate number of beta-cells that respond appropriately to blood glucose levels. beta-Cell mass cannot yet be measured in humans in vivo, necessitating autopsy studies, although both pre- and postmorbid changes may confound this approach. Autopsy studies report deficits in beta-cell mass ranging from 0 to 65% in type 2 diabetes (T2DM), and approximately 70-100% in type 1 diabetes (T1DM), and, when evaluated, increased beta-cell apoptosis in both T1DM and T2DM. A deficit of beta-cell mass of approximately 50% in animal studies leads to impaired insulin secretion (when evaluated directly in the portal vein) and induction of insulin resistance. We postulate three phases for diabetes progression. Phase 1: selective beta-cell cytotoxicity (autoimmune in T1DM, unknown in T2DM) leading to impaired beta-cell function and gradual loss of beta-cell mass through apoptosis. Phase 2: decompensation of glucose control when the pattern of portal vein insulin secretion is sufficiently impaired to cause hepatic insulin resistance. Phase 3: adverse consequences of glucose toxicity accelerate beta-cell dysfunction and insulin resistance. The relative contribution of beta-cell loss versus beta-cell dysfunction to diabetes onset remains an area of controversy. However, because cytotoxicity sufficient to induce beta-cell apoptosis predictably disturbs beta-cell function, it is naive to attempt to distinguish the relative contributions of these linked processes to diabetes onset.     

Anatomical versus functional beta-cell mass in experimental diabetes

The ability of pancreatic beta-cell mass to vary according to insulin requirements is an important component of optimal long-term control of glucose homeostasis. It is generally assumed that alteration of this property largely contributes to the impairment of insulin secretion in type 2 diabetes. However, data in humans are scarce and it is impossible to correlate beta-cell mass and function with the various stages of the disease. Thus, the importance of animal models is obvious. In rodents, increased beta-cell mass associated with an increase in the function of individual beta-cells contributes to the adaptation of the insulin response to insulin resistance in late pregnancy and in obesity. A reduction in beta-cell mass always corresponds to an alteration in insulin secretory capacity of islet tissue (Zucker diabetic fatty and Goto-Kakisaki rats, db/db mice). During regenerative processes following experimental reduction of beta-cell mass [partial pancreatectomy, streptozocin (STZ) injection], beta-cell mass increase is not associated with a corresponding improvement of beta-cell function, thus indicating that regenerative beta-cells did not achieve functional maturity. The main lesson from experimental diabetes is therefore that beta-cell mass cannot always predict functional capacity of the beta-cell tissue and that the functional beta-cell mass rather than the anatomical beta-cell mass must be taken into account at all times.     

Insulin resistance in type 1 diabetes

Insulin resistance plays a larger role in the type 1 diabetes disease process than is commonly recognized. The onset of type 1 diabetes is often heralded by an antecedent illness and/or the onset of puberty, both conditions associated with insulin resistance. In the face of a damaged beta-cell and thus reduced insulin secretion, this change is enough to manifest hyperglycemia. During the first year of clinical disease, considerable evidence suggests that the occurrence of clinical remission or 'honeymoon period' is due to a temporary resolution of the insulin-resistant state present at diagnosis. Intensive diabetes management is associated with both improved insulin sensitivity and beta-cell function. This indicates that the historical data on the changes in insulin secretion post-diagnosis may be inappropriate when designing current studies. The known physiological relationship between beta-cell function and insulin sensitivity complicates interpretation of insulin secretion data obtained as part of prevention or intervention trials. While it is recommended that at least a subset of subjects participating in these trials undergo formal measurements of insulin sensitivity to evaluate effects of therapy on this parameter independent of effects on the beta-cell, the sample size must be sufficient to determine an effect if present. Finally, one could speculate that it is possible that subsets of people with mild manifestations of the type 1 autoimmune disease process could benefit from treatments aimed at improving the insulin-resistant state.     

Crucial role of insulin receptor substrate-2 in compensatory beta-cell hyperplasia in response to high fat diet-induced insulin resistance

In type 2 diabetes, there is a defect in the regulation of functional beta-cell mass to overcome high-fat (HF) diet-induced insulin resistance. Many signals and pathways have been implicated in beta-cell function, proliferation and apoptosis. The co-ordinated regulation of functional beta-cell mass by insulin signalling and glucose metabolism under HF diet-induced insulin-resistant conditions is discussed in this article. Insulin receptor substrate (IRS)-2 is one of the two major substrates for the insulin signalling. Interestingly, IRS-2 is involved in the regulation of beta-cell proliferation, as has been demonstrated using knockout mice models. On the other hand, in an animal model for human type 2 diabetes with impaired insulin secretion because of insufficiency of glucose metabolism, decreased beta-cell proliferation was observed in mice with beta-cell-specific glucokinase haploinsufficiency (Gck(+/) (-)) fed a HF diet without upregulation of IRS-2 in beta-cells, which was reversed by overexpression of IRS-2 in beta-cells. As to the mechanism underlying the upregulation of IRS-2 in beta-cells, glucose metabolism plays an important role independently of insulin, and phosphorylation of cAMP response element-binding protein triggered by calcium-dependent signalling is the critical pathway. Downstream from insulin signalling via IRS-2 in beta-cells, a reduction in FoxO1 nuclear exclusion contributes to the insufficient proliferative response of beta-cells to insulin resistance. These findings suggest that IRS-2 is critical for beta-cell hyperplasia in response to HF diet-induced insulin resistance.     

Beta-cell preservation with thiazolidinediones

Progressive beta-cell dysfunction and beta-cell failure are fundamental pathogenic features of type 2 diabetes. Ultimately, the development and continued progression of diabetes is a consequence of the failure of the beta-cell to overcome insulin resistance. Strategies that aim to prevent diabetes must, therefore, ultimately aim to stabilize the progressive decline of the beta-cell. Clinical study evidence from several sources now suggests that thiazolidinediones (TZDs) have profound effects on the beta-cell, such as improving insulin secretory capacity, preserving beta-cell mass and islet structure and protecting beta-cells from oxidative stress, as well as improving measures of beta-cell function, such as insulinogenic index and homeostasis model assessment of beta-cell function (HOMA-%B). Furthermore, intervention studies suggest that TZDs have the potential to delay, stabilize and possibly even prevent the onset on diabetes in high-risk individuals, and these effects appear to accompany improvements in beta-cell function. Here, we review the evidence, from in vitro studies to large intervention trials, for the effects of TZDs on beta-cell function and the consequences for glucose-lowering therapy.     

Targeting beta-cell mass in type 2 diabetes: promise and limitations of new drugs based on incretins

Progressive insulin secretory defects, due to either functional abnormalities of the pancreatic beta-cells or a reduction in beta-cell mass, are the cornerstone of type 2 diabetes. Incretin-based drugs hold the potential to improve glucose tolerance by immediate favorable effect on beta-cell physiology as well as by expanding or at least maintaining beta-cell mass, which may delay the progression of the disease. Long-term studies in humans are needed to elaborate on these effects.     

SLC30A8 (ZnT8) Polymorphism is Associated with Young Age at Type 1 Diabetes Onset

It was recently shown that the major allele of the SLC30A8 (zinc transporter 8, ZnT8) single nucleotide polymorphism (SNP) rs13266634 was associated with type 2 diabetes and with reduced insulin secretion in non-diabetic relatives. Because of its role in beta-cell function, we hypothesized that this candidate SNP may confer increased susceptibility for beta-cell destruction in type 1 diabetes. We analyzed SLC30A8 genotypes in 874 patients with type 1 diabetes and 1021 control subjects. No difference in allele and genotype frequencies of the SLC30A8 SNP rs13266634 was found between patients and controls. Analysis with respect to age at type 1 diabetes onset, however, showed that patients with a diabetes onset before age 5 years had an increased prevalence of the cytosine (C) allele (risk allele, 82%) and the homozygous CC genotype (65%) compared to patients who developed type 1 diabetes after age 5 years (67% and 49%; p < 0.01) and compared to controls (69% and 48%; p < 0.03). These data suggest that genetic susceptibility for beta-cell dysfunction in the presence of autoimmunity may lead to accelerated progression and early manifestation of the disease.     

胰岛β细胞凋亡的分子机制

胰岛β细胞凋亡在糖尿病的发病中扮演重要角色,1、2型糖尿病β细胞凋亡的分子机制有所不同。在1型糖尿病中,胰岛β细胞主要通过死亡受体介导的信号转导途径及颗粒酶B途径发生凋亡,而在2型糖尿病中,线粒体途径是胰岛β细胞凋亡的主要信号转导途径。多种细胞因子通过激活核转录因子调节相应基因表达,进而调控胰岛β细胞的凋亡。     

Probucol preserves pancreatic beta-cell function through reduction of oxidative stress in type 2 diabetes

Oxidative stress is induced under diabetic conditions and causes various forms of tissue damage in patients with diabetes. Recently, pancreatic beta-cells have emerged as a putative target of oxidative stress-induced tissue damage and this seems to explain in part the progressive deterioration of beta-cell function in type 2 diabetes. As a step toward clinical trial of antioxidant for type 2 diabetes, we investigated the possible anti-diabetic effects of probucol, an antioxidant widely used as an anti-hyperlipidemic agent, on preservation of beta-cell function in diabetic C57BL/KsJ-db/db mice. Probucol-containing diet was given to mice from 6 to 16 weeks of age. Immunostaining for oxidative stress markers such as 4-hydroxy-2-nonenal (HNE)-modified proteins and heme oxygenase-1 revealed that probucol treatment decreased reactive oxygen species (ROS) in pancreatic islets of diabetic animals. Oxidative stress is known to enhance apoptosis of beta-cells and to suppress insulin biosynthesis, but probucol treatment led to preservation of beta-cell mass and the insulin content. According to intraperitoneal glucose tolerance tests, the probucol treatment preserved glucose-stimulated insulin secretion and improved glucose tolerance at 10 and 16 weeks: insulin, 280+/-82 vs. 914+/-238 pmol/l (120 min, at 16 weeks; P<0.05); glucose, 44.6+/-2.4 vs. 35.2+/-2.6 mmol/l (120 min, at 16 weeks; P<0.05). Thus, our present observations demonstrate the potential usefulness of probucol for treatment of type 2 diabetes.     

Review: pancreatic beta-cell neogenesis revisited

Beta-cell neogenesis triggers the generation of new beta-cells from precursor cells. Neogenesis from duct epithelium is the most currently described and the best documented process of differentiation of precursor cells into beta-cells. It is contributes not only to beta-cell mass expansion during fetal and nonatal life but it is also involved in the maintenance of the beta-cell mass in adults. It is also required for the increase in beta-cell mass in situations of increase insulin demand (obesity, pregnancy). A large number of factors controlling the differentiation of beta-cells has been identified. They are classified into the following main categories: growth factors, cytokine and inflammatory factors, and hormones such as PTHrP and GLP-1. The fact that intestinal incretin hormone GLP-1 exerts a major trophic role on pancreatic beta-cells provides insights into the possibility to pharmacologically stimulate beta-cell neogenesis. This could have important implications for the of treatment of type 1 and type 2 diabetes. Transdifferentiation, that is, the differentiation of already differentiated cells into beta-cells, remains controversial. However, more and more studies support this concept. The cells, which can potentially "transdifferentiate" into beta-cells, can belong to the pancreas (acinar cells) and even islets, or originate from extra-pancreatic tissues such as the liver. Neogenesis from intra-islet precursors also have been proposed and subpopulations of cell precursors inside islets have been described by some authors. Nestin positive cells, which have been considered as the main candidates, appear rather as progenitors of endothelial cells rather than beta-cells and contribute to angiogenesis rather than neogenesis. To take advantage of the different differentiation processes may be a direction for future cellular therapies. Ultimately, a better understanding of the molecular mechanisms involved in beta-cell neogenesis will allow us to use any type of differentiated and/or undifferentiated cells as a source of potential cell precursors.     

The role for endoplasmic reticulum stress in diabetes mellitus

Accumulating evidence suggests that endoplasmic reticulum (ER) stress plays a role in the pathogenesis of diabetes, contributing to pancreatic beta-cell loss and insulin resistance. Components of the unfolded protein response (UPR) play a dual role in beta-cells, acting as beneficial regulators under physiological conditions or as triggers of beta-cell dysfunction and apoptosis under situations of chronic stress. Novel findings suggest that "what makes a beta-cell a beta-cell", i.e., its enormous capacity to synthesize and secrete insulin, is also its Achilles heel, rendering it vulnerable to chronic high glucose and fatty acid exposure, agents that contribute to beta-cell failure in type 2 diabetes. In this review, we address the transition from physiology to pathology, namely how and why the physiological UPR evolves to a proapoptotic ER stress response and which defenses are triggered by beta-cells against these challenges. ER stress may also link obesity and insulin resistance in type 2 diabetes. High fat feeding and obesity induce ER stress in liver, which suppresses insulin signaling via c-Jun N-terminal kinase activation. In vitro data suggest that ER stress may also contribute to cytokine-induced beta-cell death. Thus, the cytokines IL-1beta and interferon-gamma, putative mediators of beta-cell loss in type 1 diabetes, induce severe ER stress through, respectively, NO-mediated depletion of ER calcium and inhibition of ER chaperones, thus hampering beta-cell defenses and amplifying the proapoptotic pathways. A better understanding of the pathways regulating ER stress in beta-cells may be instrumental for the design of novel therapies to prevent beta-cell loss in diabetes.     

Rosiglitazone prevents diabetes by increasing beta-cell mass in an animal model of type 2 diabetes characterized by reduced beta-cell mass at birth

Aim:  Interventions that preserve or increase beta-cell mass may also prevent type 2 diabetes. Rosiglitazone prevents diabetes in people with high glucose levels who have impaired glucose tolerance and/or impaired fasting glucose. The effect of this drug on both glucose levels and beta-cell mass was studied in a rat model of diabetes, characterized by reduced beta-cell mass at birth with normoglycaemia, and progression to dysglycaemia with age.
Methods:  Female Wistar rats were given either saline (vehicle) or nicotine during pregnancy and lactation. Offspring of saline-exposed dams were given vehicle and offspring of nicotine-exposed dams were randomized to receive either vehicle or rosiglitazone starting at weaning. Beta-cell mass, proliferation and apoptosis were determined at birth and at 4 and 26 weeks of age. Glucose homeostasis was examined following sequential oral glucose tolerance tests (OGTT).
Results:  Rosiglitazone treatment prevented the development of dysglycaemia in nicotine-exposed animals. The ability of rosiglitazone to preserve normoglycaemia appeared to be because of its ability to increase beta-cell mass through a combination of enhanced beta-cell proliferation and decreased beta-cell apoptosis.
Conclusions:  These results suggest that if rosiglitazone administration is started prior to the onset of glucometabolic abnormalities, it prevents the onset of dysglycaemia by partially restoring beta-cell mass in animals with reduced beta-cell mass at birth.     

Glucagon-like peptide-1 treatment delays the onset of diabetes in 8 week-old db/db mice

AIMS/HYPOTHESIS: Glucagon-like peptide-1 ameliorates the symptoms of diabetes through stimulation of insulin secretion and enhancement of beta-cell mass. We have therefore investigated the effects of glucagon-like peptide-1 on the development of diabetes, using db/db mice as a model of Type II diabetes. METHODS: The potent glucagon-like peptide-1 analogue Exendin-4 or vehicle (control) was administered (i.p.; 1 nmol/kg) to obese 6-week old db/db mice daily for 14 days ( n=10). RESULTS: By 8 weeks of age, control db/db mice developed hyperglycaemia (fasting: 10.4+/-0.5 mmol/l), hyperinsulinaemia and impaired glucose tolerance. However, Exendin-4 treatment prevented hyperglycaemia (fasting: 6.1+/-1.0 mmol/l, p<0.01), with reduced plasma insulin concentrations ( p<0.001) and improved glucose tolerance ( p<0.05). Peripheral insulin sensitivity was not affected. However, insulin release in vivo and in vitro from the perfused pancreas was improved by Exendin-4, as were pancreatic insulin concentrations (0.54+/-0.02 vs 0.32+/-0.01 micro g/mg protein, p<0.05). These changes occurred in conjunction with increased beta-cell mass (3.01+/-0.31 vs 2.22+/-0.22 mg, p<0.05) and proliferation (BrdU(+) beta-cells: 1.08+/-0.20 vs 0.47+/-0.11%, p<0.05), as well as decreased apoptosis (Tunel (+) beta-cells: 0.37+/-0.06 vs 1.20+/-0.21%). Western blot demonstrated increased expression of Akt1 (by fivefold, p<0.01) and p44 MAP kinase (by sixfold, p<0.01), and decreased activation of caspase-3 (by 30%, p<0.05). CONCLUSION/INTERPRETATION: Our results suggest that Ex4 treatment delays the onset of diabetes in 6-8 week old db/db mice, through a mechanism involving Akt1 and expansion of the functional beta-cell mass.