Decreased Β-cell Mass Research Articles

Screening for Insulitis in Adult Autoantibody-Positive Organ Donors

Antibodies against islet cell antigens are used as predictive markers of type 1 diabetes, but it is unknown whether they reflect an ongoing autoimmune process in islet tissue. We investigated whether organs from adult donors that are positive for autoantibodies (aAbs) against islet cell antigens exhibit insulitis and/or a reduced beta-cell mass. Serum from 1,507 organ donors (age 25-60 years) was analyzed for islet cell antibodies (ICAs), glutamate decarboxylase aAbs (GADAs), insulinoma-associated protein 2 aAbs (IA-2As), and insulin aAbs. Tissue from the 62 aAb+ donors (4.1%) and from matched controls was examined for the presence of insulitis and for the relative area of insulin+ cells. Insulitis was detected in two cases; it was found in 3 and 9% of the islets and consisted of CD3+/CD8+ T-cells and CD68+ macrophages; in one case, it was associated with insulin+ cells that expressed the proliferation marker Ki67. Both subjects belonged to the subgroup of three donors with positivity for ICA, GADA, and IA-2-Ab and for the susceptible HLA-DQ genotype. Comparison of relative beta-cell area in aAb+ and aAb- donors did not show a significant difference. Insulitis was found in two of the three cases that presented at least three aAbs but in none of the other 59 antibody+ subjects or 62 matched controls. It was only detected in <10% of the islets, some of which presented signs of beta-cell proliferation. No decrease in beta-cell mass was detected in cases with insulitis or in the group of antibody+ subjects.

β-Cell Failure in Diabetes and Preservation by Clinical Treatment

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 diabetes and in cultured beta-cells. Exenatide and liraglutide enhanced postprandial beta-cell function. The inhibition of the activity of the DPP-IV enzyme enhances endogenous GLP-1 action in vivo, mediated not only by GLP-1 but also by other mediators. In preclinical studies, oral active DPP-IV inhibitors (sitagliptin and vildagliptin) also promoted beta-cell proliferation, neogenesis, and inhibition of apoptosis in rodents. Meal tolerance tests showed improvement in postprandial beta-cell function. Obviously, it is difficult to estimate the protective effects of incretin mimetics and enhancers on beta-cells in humans, and there is no clinical evidence that these drugs really have protective effects on beta-cells.

Analysis of compensatory β-cell response in mice with combined mutations of Insr and Irs2

Type 2 diabetes results from impaired insulin action and β-cell dysfunction. There are at least two components to β-cell dysfunction: impaired insulin secretion and decreased β-cell mass. To analyze how these two variables contribute to the progressive deterioration of metabolic control seen in diabetes, we asked whether mice with impaired β-cell growth due to Irs2 ablation would be able to mount a compensatory response in the background of insulin resistance caused by Insr haploinsufficiency. As previously reported, ∼70% of mice with combined Insr and Irs2 mutations developed diabetes as a consequence of markedly decreased β-cell mass. In the initial phases of the disease, we observed a robust increase in circulating insulin levels, even as β-cell mass gradually declined, indicating that replication-defective β-cells compensate for insulin resistance by increasing insulin secretion. These data provide further evidence for a heterogeneous β-cell response to insulin resistance, in which compensation can be temporarily achieved by increasing function when mass is limited. The eventual failure of compensatory insulin secretion suggests that a comprehensive treatment of β-cell dysfunction in type 2 diabetes should positively affect both aspects of β-cell physiology.

Hepatocyte growth factor protects rat RINm5F cell line against free fatty acid-induced apoptosis by counteracting oxidative stress

Type 2 diabetes is characterized by peripheral insulin resistance, pancreatic beta-cells dysfunction, and decreased beta-cell mass with increased rate of apoptosis. Chronic exposure to high levels of free fatty acids (FFAs) has detrimental effects on beta-cell function and survival. FFAs have adverse effects on mitochondrial function, with a consequent increase in the production of reactive oxygen species. Hepatocyte growth factor (HGF) plays a critical role in promoting beta-cell survival. In the present study, we investigated whether HGF was capable of protecting beta-cells from death induced by prolonged exposure to FFAs. RINm5F cell line was cultured in the presence of FFAs (oleate:palmitate 2:1) for 72 h in order to induce apoptosis. Simultaneous administration of HGF and FFAs significantly suppressed the impaired insulin secretion and FFA-induced apoptosis. Specifically, HGF exerted its protective effect by counteracting: (i) the overproduction of either hydrogen peroxide and superoxide anion, (ii) the reduction of intracellular gamma-glutamylcysteinylglycine level, and (iii) the depolarization of mitochondrial membrane, induced by prolonged FFAs exposure. These effects appear to be mediated by bcl-2 and phosphatidylinositol 3 kinase (PI3K)/Akt pathways. Indeed, HGF increased mRNA and protein expression of bcl-2 downregulated by FFAs-treatment; moreover, pre-treatment with the specific PI3-kinase inhibitor LY294002, significantly abolished the protective effect of HGF. In conclusion, in rat insulin-producing RINm5F cells, HGF exerts its prosurvival effect by counteracting the increased intracellular oxidative stress and, consequently, by inhibiting apoptosis induced by chronic exposure to FFAs.

Metabolic Diapause in Pancreatic β-Cells Expressing a Gain-of-function Mutant of the Forkhead Protein Foxo1

Diabetes is associated with decreased pancreatic beta-cell function and mass. It is unclear whether diabetes treatment should aim at restoring beta-cell performance/mass or at inducing "beta-cell rest" to prevent further deterioration. The transcription factor Foxo1 protects beta-cells against oxidative stress induced by hyperglycemia and prevents beta-cell replication in insulin-resistant states. Here we show that these combined effects are associated with a concerted repression of genes involved in glycolysis, nitric-oxide synthesis, G protein-coupled receptor signaling, and ion transport. Conversely, Foxo1 increases expression of several neurotransmitter receptors and fails to regulate target genes predicted from Caenorhabditis elegans and Drosophila studies. Functional analyses show decreased glucose utilization and insulin secretion in beta-cells overexpressing Foxo1. We propose the definition of "metabolic diapause" for the changes induced by Foxo1 to protect beta-cells against oxidative stress. The data provide genetic underpinning for the concept of beta-cell rest as a treatment goal in diabetes.

Effects of Autoimmunity and Immune Therapy on β-Cell Turnover in Type 1 Diabetes

beta-Cell mass can expand in response to demand: during pregnancy, in the setting of insulin resistance, or after pancreatectomy. It is not known whether similar beta-cell hyperplasia occurs following immune therapy of autoimmune diabetes, but the clinical remission soon after diagnosis and the results of recent immune therapy studies suggest that beta-cell recovery is possible. We studied changes in beta-cell replication, mass, and apoptosis in NOD mice during progression to overt diabetes and following immune therapy with anti-CD3 monoclonal antibodies (mAbs) or immune regulatory T-cells (Tregs). beta-Cell replication increases in pre-diabetic mice, after adoptive transfer of diabetes with increasing islet inflammation but before an increase in blood glucose concentration or a significant decrease in beta-cell mass. The pathogenic cells are responsible for increasing beta-cell replication because replication was reduced during diabetes remission induced by anti-CD3 mAb or Tregs. beta-Cell replication stimulated by the initial inflammatory infiltrate results in increased production of new beta-cells after immune therapy and increased beta-cell area, but the majority of this increased beta-cell area represents regranulated beta-cells rather than newly produced cells. We conclude that beta-cell replication is closely linked to the islet inflammatory process. A significant proportion of degranulated beta-cells remain, at the time of diagnosis of diabetes, that can recover after metabolic correction of hyperglycemia. Correction of the beta-cell loss in type 1 diabetes will, therefore, require strategies that target both the immunologic and cellular mechanisms that destroy and maintain beta-cell mass.

Transcription Factor 7-like 2 (TCFL2) - A Novel Factor Involved in Pathogenesis of Type 2 Diabetes

Type 2 diabetes is a heterogeneous disease characterized by hyperglycemia. This disease results from impaired secretion of insulin from pancreatic β-cells, decreased β-cell mass, insulin resistance in peripheral tissues and hepatic overproduction of glucose. The development of type 2 diabetes is a complex result of lifestyle and genetic components and their interaction.

Mechanisms of β-Cell Death in Type 2 Diabetes

A decrease in the number of functional insulin-producing beta-cells contributes to the pathophysiology of type 2 diabetes. Opinions diverge regarding the relative contribution of a decrease in beta-cell mass versus an intrinsic defect in the secretory machinery. Here we review the evidence that glucose, dyslipidemia, cytokines, leptin, autoimmunity, and some sulfonylureas may contribute to the maladaptation of beta-cells. With respect to these causal factors, we focus on Fas, the ATP-sensitive K+ channel, insulin receptor substrate 2, oxidative stress, nuclear factor-kappaB, endoplasmic reticulum stress, and mitochondrial dysfunction as their respective mechanisms of action. Interestingly, most of these factors are involved in inflammatory processes in addition to playing a role in both the regulation of beta-cell secretory function and cell turnover. Thus, the mechanisms regulating beta-cell proliferation, apoptosis, and function are inseparable processes.

Psammomys Obesus, a Model for Environment-Gene Interactions in Type 2 Diabetes

Type 2 diabetes is characterized by insulin resistance and progressive beta-cell failure. Deficient insulin secretion, with increased proportions of insulin precursor molecules, is a common feature of type 2 diabetes; this could result from inappropriate beta-cell function and/or reduced beta-cell mass. Most studies using tissues from diabetic patients are retrospective, providing only limited information on the relative contribution of beta-cell dysfunction versus decreased beta-cell mass to the "beta-cell failure" of type 2 diabetes. The gerbil Psammomys obesus is a good model to address questions related to the role of insulin resistance and beta-cell failure in nutritionally induced diabetes. Upon a change from its natural low-calorie diet to the calorie-rich laboratory food, P. obesus develops moderate obesity associated with postprandial hyperglycemia. Continued dietary load, superimposed on its innate insulin resistance, results in depletion of pancreatic insulin stores, with increased proportions of insulin precursor molecules in the pancreas and the blood. Inadequate response of the preproinsulin gene to the increased insulin needs is an important cause of diabetes progression. Changes in beta-cell mass do not correlate with pancreatic insulin stores and are unlikely to play a role in disease initiation and progression. The major culprit is the inappropriate insulin production with depletion of insulin stores as a consequence. Similar mechanisms could operate during the evolution of type 2 diabetes in humans.

Effects of Short-Term Experimental Insulin Resistance and Family History of Diabetes on Pancreatic β-Cell Function in Nondiabetic Individuals

Normal glucose homeostasis is maintained despite reductions in insulin sensitivity by increasing insulin secretion. This ability to compensate for reduced insulin sensitivity is highly heritable, but the mechanisms for this compensation or its failure in type 2 diabetes (T2DM) are unknown. The objective of this study was to test whether individuals with a family history of T2DM have a fixed decrease in beta-cell mass or function that would be revealed as an impaired insulin secretory response to short-term insulin resistance. Glucose tolerance, insulin sensitivity (S(I)), and insulin response to i.v. glucose (AIR(G)) were compared in nondiabetic individuals with and without a family history of diabetes before and after nicotinic acid (NA) treatment. This study was performed at the Ambulatory General Clinical Research Center. Healthy, nonobese, nondiabetic individuals with or without a family history of T2DM were studied. Oral NA was given, with a final dose of 2 g/d, for at least 7 d. The main outcome measure was the disposition index (insulin sensitivity x insulin response) in response to NA. Postchallenge plasma glucose levels rose during NA therapy regardless of family history. Neither group adequately increased their AIR(G) to maintain the disposition index. Family members did not differ from controls at baseline or after NA treatment for any outcome measure, but only 28 of 52 subjects experienced a 25% or greater fall in S(I) with NA treatment. Short-term beta-cell compensation to NA-induced insulin resistance was incomplete and did not differ by genetic predisposition. A genetic defect controlling beta-cell growth in response to chronic insulin resistance better explains differences in the ability to compensate for insulin resistance than an inherited, fixed defect in beta-cell mass.

Estrogen and Exercise May Enhance β-Cell Function and Mass via Insulin Receptor Substrate 2 Induction in Ovariectomized Diabetic Rats

The prevalence and progression of type 2 diabetes have increased remarkably in postmenopausal women. Although estrogen replacement and exercise have been studied for their effect in modulating insulin sensitivity in the case of insufficient estrogen states, their effects on beta-cell function and mass have not been studied. Ovariectomized (OVX) female rats with 90% pancreatectomy were given a 30% fat diet for 8 wk with a corresponding administration of 17beta-estradiol (30 microg/kg body weight) and/or regular exercise. Amelioration of insulin resistance by estrogen replacement or exercise was closely related to body weight reduction. Insulin secretion in first and second phases was lower in OVX during hyperglycemic clamp, which was improved by estrogen replacement and exercise but not by weight reduction induced by restricted diets. Both estrogen replacement and exercise overcame reduced pancreatic beta-cell mass in OVX rats via increased proliferation and decreased apoptosis of beta-cells, but they did not exhibit an additive effect. However, restricted diets did not stimulate beta-cell proliferation. Increased beta-cell proliferation was associated with the induction of insulin receptor substrate-2 and pancreatic homeodomain protein-1 via the activation of the cAMP response element binding protein. Estrogen replacement and exercise shared a common pathway, which led to the improvement of beta-cell function and mass, via cAMP response element binding protein activation, explaining the lack of an additive effect with combined treatments. In conclusion, decreased beta-cell mass leading to impaired insulin secretion triggers glucose dysregulation in estrogen insufficiency, regardless of body fat. Regular moderate exercise eliminates the risk factors of contracting diabetes in the postmenopausal state.

Long-Term Treatment With Rosiglitazone and Metformin Reduces the Extent of, but Does Not Prevent, Islet Amyloid Deposition in Mice Expressing the Gene for Human Islet Amyloid Polypeptide

Islet amyloid deposition in type 2 diabetes is associated with reduced beta-cell mass. Therefore, interventions aimed at reducing islet amyloid formation may help preserve beta-cell mass in type 2 diabetes. Rosiglitazone and metformin act by different mechanisms to improve insulin sensitivity and thereby reduce beta-cell secretory demand, resulting in decreased release of insulin and islet amyloid polypeptide (IAPP), the unique constituent of islet amyloid deposits. We hypothesized that this reduced beta-cell secretory demand would lead to reduced islet amyloid formation. Human IAPP (hIAPP) transgenic mice, a model of islet amyloid, were treated for 12 months with rosiglitazone (1.5 mg.kg(-1).day(-1), n = 19), metformin (1 g.kg(-1).day(-1), n = 18), or control (n = 17). At the end of the study, islet amyloid prevalence (percent islets containing amyloid) and severity (percent islet area occupied by amyloid), islet mass, beta-cell mass, and insulin release were determined. Islet amyloid prevalence (44 +/- 8, 13 +/- 4, and 11 +/- 3% for control, metformin-, and rosiglitazone-treated mice, respectively) and severity (9.2 +/- 3.0, 0.22 +/- 0.11, and 0.10 +/- 0.05% for control, metformin-, and rosiglitazone-treated mice, respectively) were markedly reduced with both rosiglitazone (P < 0.001 for both measures) and metformin treatment (P < 0.001 for both measures). Both treatments were associated with reduced insulin release assessed as the acute insulin response to intravenous glucose (2,189 +/- 857, 621 +/- 256, and 14 +/- 158 pmol/l for control, metformin-, and rosiglitazone-treated mice, respectively; P < 0.05 for metformin vs. control and P < 0.005 for rosiglitazone vs. control), consistent with reduced secretory demand. Similarly, islet mass (33.4 +/- 7.0, 16.6 +/- 3.6, and 12.2 +/- 2.1 mg for control, metformin-, and rosiglitazone-treated mice, respectively) was not different with metformin treatment (P = 0.06 vs. control) but was significantly lower with rosiglitazone treatment (P < 0.05 vs. control). When the decreased islet mass was accounted for, the islet amyloid-related decrease in beta-cell mass (percent beta-cell mass/islet mass) was ameliorated in both rosiglitazone- and metformin-treated animals (57.9 +/- 3.1, 64.7 +/- 1.4, and 66.1 +/- 1.6% for control, metformin-, and rosiglitazone-treated mice, respectively; P < 0.05 for metformin or rosiglitazone vs. control). In summary, rosiglitazone and metformin protect beta-cells from the deleterious effects of islet amyloid, and this effect may contribute to the ability of these treatments to alleviate the progressive loss of beta-cell mass and function in type 2 diabetes.

Type 2 Diabetes-a Matter of ß-Cell Life and Death?

In type 2 diabetes, the beta cells of the pancreas fail to produce enough insulin to meet the body's demand, in part because of an acquired decrease in beta-cell mass. In adults, pancreatic beta-cell mass is controlled by several mechanisms, including beta-cell replication, neogenesis, hypertrophy, and survival. Here, I discuss evidence supporting the notion that increased beta-cell apoptosis is an important factor contributing to beta-cell loss and the onset of type 2 diabetes. Interestingly, a key signaling molecule that promotes beta-cell growth and survival, insulin receptor substrate 2 (IRS-2), is a member of a family of proteins whose inhibition contributes to the development of insulin resistance in the liver and other insulin-responsive tissues. Thus, the IRS-2 pathway appears to be a crucial participant in the tenuous balance between effective pancreatic beta-cell mass and insulin resistance.

Diazoxide attenuates glucose-induced defects in first-phase insulin release and pulsatile insulin secretion in human islets.

Humans with type-2 diabetes mellitus (TTDM) have hyperglycemia ( approximately 11 mM) and impaired glucose-mediated insulin secretion characterized by impaired first-phase insulin release (FPIR) and pulsatile insulin release. Culture of islets from nondiabetic humans in very high glucose concentrations ( approximately 20-30 mM) for 96 h causes impaired FPIR. We sought to determine 1). whether human islets cultured at a glucose concentration of approximately 11 mM (comparable to TTDM) recapitulates impaired insulin secretion in TTDM, specifically impaired FPIR and insulin pulse mass with an increased proinsulin/insulin (PI/I) secretion ratio; and 2). whether these changes can be attenuated by addition of diazoxide to islets cultured with 11 mM glucose. Islets cultured with 11 mM glucose for 96 h had 75% depleted insulin stores (P < 0.05), decreased FPIR and insulin pulse mass (P < 0.05), and an approximately 3-fold increase in the ratio of PI/I islet content and in secretion ratio (P < 0.05). Addition of diazoxide to islets cultured with 11 mM glucose decreased insulin secretion during static incubation, leading to relative preservation of insulin stores and enhanced insulin secretion during subsequent perifusion; FPIR increased by 162% (P < 0.05) and insulin pulse mass by 150% (P < 0.05) vs. no diazoxide. The mean islet PI/I content and islet PI/I secretion ratio were also decreased by approximately 70% (P < 0.05) by prior addition of diazoxide to islets during culture with 11 mM glucose. FPIR and insulin pulse mass were related to islet insulin stores (P < 0.001 for FPIR and P < 0.001 for pulse amplitude). In conclusion, the pattern of defects of insulin secretion present in TTDM (impaired FPIR and pulsatile insulin secretion, increased PI/I ratio) can be recapitulated in human islets cultured with 11 mM glucose for 96 h. These defects can be at least partially offset by concurrent inhibition of insulin secretion by diazoxide, which also preserves insulin stores. Defective insulin secretion in TTDM may be, at least in part, due to depletion of available insulin stores secondary to chronic increased demand (insulin resistance and hyperglycemia) in the setting of a decreased beta-cell mass.

Beta-cell deficit and increased beta-cell apoptosis in humans with type 2 diabetes.

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.

Development of beta-cell mass in fetuses of rats deprived of protein and/or energy in last trimester of pregnancy.

Fetal malnutrition is now proposed as a risk factor of later obesity and type II diabetes. We previously analyzed the long-term impact of reduced protein and/or energy intake strictly limited to the last week of pregnancy in Wistar rats. Three protocols of gestational malnutrition were used: 1) low-protein isocaloric diet (5 instead of 15%) with pair feeding to the mothers receiving the control diet, 2) restricted diet (50% of control diet), and 3) low protein-restricted diet (50% of low-protein diet). Only isolated protein restriction induced a long-term beta-cell mass decrease. In the present study, we used the same protocols of food restriction to analyze their short-term impact (on day 21.5 of pregnancy) on beta-cell mass development. A 50% beta-cell mass decrease was present in the three restricted groups, but low-protein diet, either associated or not to energy restriction, increased fetal beta-cell insulin content. Among all the parameters analyzed to further explain our results, we found that the fetal plasma level of taurine was lowered by low-protein diet and was the main predictor of the fetal plasma insulin level (r = 0.63, P < 0.01). In conclusion, rat fetuses exposed to protein and/or energy restriction during the third part of pregnancy have a similar dramatic decrease in beta-cell mass, and their ability to recover beta-cell mass development retardation depends on the type of malnutrition used. Moreover, our results support the hypothesis that taurine might play an important role in fetal beta-cell mass function.

Decrease in beta-cell mass leads to impaired pulsatile insulin secretion, reduced postprandial hepatic insulin clearance, and relative hyperglucagonemia in the minipig.

Most insulin is secreted in discrete pulses at an interval of approximately 6 min. Increased insulin secretion after meal ingestion is achieved through the mechanism of amplification of the burst mass. Conversely, in type 2 diabetes, insulin secretion is impaired as a consequence of decreased insulin pulse mass. beta-cell mass is reported to be deficient in type 2 diabetes. We tested the hypothesis that decreased beta-cell mass leads to decreased insulin pulse mass. Insulin secretion was examined before and after an approximately 60% decrease in beta-cell mass achieved by a single injection of alloxan in a porcine model. Alloxan injection resulted in stable diabetes (fasting plasma glucose 7.4 +/- 1.1 vs. 4.4 +/- 0.1 mmol/l; P < 0.01) with impaired insulin secretion in the fasting and fed states and during a hyperglycemic clamp (decreased by 54, 80, and 90%, respectively). Deconvolution analysis revealed a selective decrease in insulin pulse mass (by 54, 60, and 90%) with no change in pulse frequency. Rhythm analysis revealed no change in the periodicity of regular oscillations after alloxan administration in the fasting state but was unable to detect stable rhythms reliably after enteric or intravenous glucose stimulation. After alloxan administration, insulin secretion and insulin pulse mass (but not insulin pulse interval) decreased in relation to beta-cell mass. However, the decreased pulse mass (and pulse amplitude delivered to the liver) was associated with a decrease in hepatic insulin clearance, which partially offset the decreased insulin secretion. Despite hyperglycemia, postprandial glucagon concentrations were increased after alloxan administration (103.4 +/- 6.3 vs. 92.2 +/- 2.5 pg/ml; P < 0.01). We conclude that an alloxan-induced selective decrease in beta-cell mass leads to deficient insulin secretion by attenuating insulin pulse mass, and that the latter is associated with decreased hepatic insulin clearance and relative hyperglucagonemia, thereby emulating the pattern of islet dysfunction observed in type 2 diabetes.

Glucocorticoids impair fetal beta-cell development in rats.

In rats, poor fetal growth due to maternal food restriction during pregnancy is associated with decreased beta-cell mass at birth and glucose intolerance in adulthood. Overexposure to glucocorticoids in utero can induce intrauterine growth retardation in humans and animals and subsequent glucose intolerance in rodents. The aims of this study were to investigate whether glucocorticoid overexposure mediates the effect of undernutrition on beta-cell mass and to study their potential role in normally nourished rats. Undernutrition significantly increased maternal and fetal corticosterone levels. Twenty-one-day-old fetuses with undernutrition showed growth retardation and decreased pancreatic insulin content; adrenalectomy and subcutaneous corticosterone implants in their dams prevented the maternal corticosterone increase and restored fetal beta-cell mass. In fetuses with normal nutrition, fetal corticosterone levels were negatively correlated to fetal weight and insulin content; fetal beta-cell mass increased from 355 +/- 48 microg in sham to 516 +/- 160 microg after maternal adrenalectomy; inhibition of steroid production by metyrapone induced a further increase to 757 +/- 125 microg. Our data support the new concept of a negative role of glucocorticoids in fetal beta-cell development.

High glucose causes apoptosis in cultured human pancreatic islets of Langerhans: a potential role for regulation of specific Bcl family genes toward an apoptotic cell death program.

Type 2 diabetes is characterized by insulin resistance and inadequate insulin secretion. In the advanced stages of the disease, beta-cell dysfunction worsens and insulin therapy may be necessary to achieve satisfactory metabolic control. Studies in autopsies found decreased beta-cell mass in pancreas of people with type 2 diabetes. Apoptosis, a constitutive program of cell death modulated by the Bcl family genes, has been implicated in loss of beta-cells in animal models of type 2 diabetes. In this study, we compared the effect of 5 days' culture in high glucose concentration (16.7 mmol/l) versus normal glucose levels (5.5 mmol/l) or hyperosmolar control (mannitol 11 mmol/l plus glucose 5 mmol/l) on the survival of human pancreatic islets. Apoptosis, analyzed by flow cytometry and electron and immunofluorescence microscopy, was increased in islets cultured in high glucose (HG5) as compared with normal glucose (NG5) or hyperosmolar control (NG5+MAN5). We also analyzed by reverse transcriptase-polymerase chain reaction and Western blotting the expression of the Bcl family genes in human islets cultured in normal glucose or high glucose. The antiapoptotic gene Bcl-2 was unaffected by glucose change, whereas Bcl-xl was reduced upon treatment with HG5. On the other hand, proapoptotic genes Bad, Bid, and Bik were overexpressed in the islets maintained in HG5. To define the pancreatic localization of Bcl proteins, we performed confocal immunofluorescence analysis on human pancreas. Bad and Bid were specifically expressed in beta-cells, and Bid was also expressed, although at low levels, in the exocrine pancreas. Bik and Bcl-xl were expressed in other endocrine islet cells as well as in the exocrine pancreas. These data suggest that in human islets, high glucose may modulate the balance of proapoptotic and antiapoptotic Bcl proteins toward apoptosis, thus favoring beta-cell death.

Age-Dependent Inability of the Endocrine Pancreas to Adapt to Pregnancy: A Long-Term Consequence of Perinatal Malnutrition in the Rat

We have recently shown that maternal food restriction during late pregnancy decreased β-cell mass in the offspring at birth. Prolonged maternal malnutrition until weaning led to irreversible decrease ofβ -cell mass in the adult male progeny. During pregnancy, the maternal endocrine pancreas demonstrates an acute and reversible increase inβ -cell mass. The aim of this work was to investigate whether perinatal malnutrition could have long-lasting effects on glucose homeostasis and the adaptation of the endocrine pancreas to a subsequent pregnancy. This study was conducted on 4- and 8-month-old female rats malnourished during their perinatal life and on age-matched control animals. Oral glucose tolerance tests (OGTT), pancreatic insulin content, and islet mass quantitation after dithizone staining were performed on the same animals. Four-month-old nonpregnant previously malnourished animals showed normal glucose tolerance but a significant decrease in insulin secretion during OGTT. These animals were, however, still able to adapt pancreatic insulin contents and doubled their islet mass in late gestation. At 8 months of age, insulin content before pregnancy was reduced to half that of controls. Moreover, it did not show the characteristic increase during gestation that could still be observed in pregnant control females. In those control animals, the islet mass increased regularly until late gestation (14.1 ± 1.8 mg at day 20.5, vs. 9.8± 1.2 mg, nonpregnant), whereas in previously malnourished animals the islet mass remained throughout pregnancy similar to the nonpregnant values (8.5 ± 1.4 mg at day 20.5 vs. 8.9 ± 3.6 mg, nonpregnant). In conclusion, early malnutrition has dramatic consequences on the capacity of the endocrine pancreas to meet the increased insulin demand during pregnancy and aging.