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We sought to establish whether an increase in chromogranin A-positive, hormone-negative (CPHN) endocrine cells occurs in the pancreas of patients with cystic fibrosis (CF), as potential evidence of neogenesis. Pancreata were obtained at autopsy from nondiabetic patients with CF (n = 12) and age-matched nondiabetic control subject (CS) individuals without CF (n = 12). In addition, pancreas from three diabetic patients with CF was obtained. Pancreas sections were stained for chromogranin A, insulin, and a cocktail of glucagon, somatostatin, pancreatic polypeptide, and ghrelin and evaluated for the frequency of CPHN cells. There was a higher frequency of CPHN cells in islets of the patients with CF compared with the CS group. Moreover, CPHN cells occurring as single cells or clusters scattered in the exocrine pancreas were also more frequent in patients with CF. The increased frequency of CPHN cells in pancreas of patients with CF may indicate an attempt at endocrine cell regeneration.

We sought to establish whether an increase in chromogranin A-positive, hormone-negative (CPHN) endocrine cells occurs in the pancreas of patients with cystic fibrosis (CF), as potential evidence of neogenesis. Pancreata were obtained at autopsy from nondiabetic patients with CF (n = 12) and age-matched nondiabetic control subject (CS) individuals without CF (n = 12). In addition, pancreas from three diabetic patients with CF was obtained. Pancreas sections were stained for chromogranin A, insulin, and a cocktail of glucagon, somatostatin, pancreatic polypeptide, and ghrelin and evaluated for the frequency of CPHN cells. There was a higher frequency of CPHN cells in islets of the patients with CF compared with the CS group. Moreover, CPHN cells occurring as single cells or clusters scattered in the exocrine pancreas were also more frequent in patients with CF. The increased frequency of CPHN cells in pancreas of patients with CF may indicate an attempt at endocrine cell regeneration.

ContextChronic pancreatitis (CP) is characterized by inflammation, fibrosis, and a loss of pancreatic acinar cells, which can result in exocrine and eventually endocrine deficiency. Pancreatitis has been reported to induce formation of new endocrine cells (neogenesis) in mice. Our recent data have implicated chromogranin A-positive hormone-negative (CPHN) cells as potential evidence of neogenesis in humans.ObjectiveWe sought to establish if CPHN cells were more abundant in CP in humans.Design, setting, and participantsWe investigated the frequency and distribution of CPHN cells and the expression of the chemokine C-X-C motif ligand 10 (CXCL10) and its receptor chemokine C-X-C motif receptor 3 in pancreas of nondiabetic subjects with CP.ResultsCPHN cell frequency in islets was increased sevenfold in CP [2.1% ± 0.67% vs 0.35% ± 0.09% CPHN cells in islets, CP vs nonpancreatitis (NP), P < 0.01], as were the CPHN cells found as scattered cells in the exocrine areas (17.4 ± 2.9 vs 4.2 ± 0.6, CP vs NP, P < 0.001). Polyhormonal endocrine cells were also increased in CP (2.7 ± 1.2 vs 0.1 ± 0.04, CP vs NP, % of polyhormonal cells of total endocrine cells, P < 0.01), as was expression of CXCL10 in α and β cells.ConclusionThere is increased islet endogenous expression of the inflammation marker CXCL10 in islets in the setting of nondiabetic CP and an increase in polyhormonal (insulin-glucagon expressing) cells. The increase in CPHN cells in CP, often in a lobular distribution, may indicate foci of attempted endocrine cell regeneration.

Aims/hypothesisWe sought to establish whether the increased incidence of diabetes associated with Down syndrome was due to a congenital deficit in β cells.MethodsThe pancreas was obtained at autopsy from nondiabetic subjects with Down syndrome (n = 29) and age-matched nondiabetic control subjects without Down syndrome (n = 28). The pancreas sections were evaluated for the fractional β-cell area.ResultsNo difference was found in the fractional β-cell area between the subjects with Down syndrome and the control subjects.Conclusions/interpretationsThe increased incidence and prevalence of diabetes in individuals with Down syndrome is not due to an underlying congenital deficiency of β cells.

ContextIt has been suggested that beta cell loss in type 2 diabetes (T2D) may be due to beta cell degranulation and/or altered cell identity. While shown to have a minor role in obese T2D, this has not been evaluated in lean T2D.ObjectiveTo establish the contribution of altered beta cell identity in lean T2D and, using a rodent model of lean T2D, whether changes in beta cell identity precede hyperglycemia.Design, setting, and participantsWe investigated the frequency of chromogranin A positive hormone negative (CPHN) and polyhormonal endocrine cells in pancreas from 10 lean nondiabetic and 10 lean T2D subjects and in pancreas from wild-type and human IAPP transgenic rats at the prediabetic and diabetic stages.ResultsCPHN cells and polyhormonal-expressing cells were comparably increased in lean T2D and human IAPP transgenic rats, in the latter both before and at onset of diabetes. However, the extent of these cells could only account for approximately 2% of beta cell loss.ConclusionDegranulation and altered identity play at most a minor role in the beta cell deficit in lean T2D. Because the increase in CPHN and polyhormonal cells precede diabetes onset, these changes are likely a response to stress rather than hyperglycemia, and may reflect attempted regeneration.

ContextType 2 diabetes is characterized by a β-cell deficit and a progressive defect in β-cell function. It has been proposed that the deficit in β-cells may be due to β-cell degranulation and transdifferentiation to other endocrine cell types.ObjectiveThe objective of the study was to establish the potential impact of β-cell dedifferentiation and transdifferentiation on β-cell deficit in type 2 diabetes and to consider the alternative that cells with an incomplete identity may be newly forming rather than dedifferentiated.Design, setting, and participantsPancreata obtained at autopsy were evaluated from 14 nondiabetic and 13 type 2 diabetic individuals, from four fetal cases, and from 10 neonatal cases.ResultsWhereas there was a slight increase in islet endocrine cells expressing no hormone in type 2 diabetes (0.11 ± 0.03 cells/islet vs 0.03 ± 0.01 cells/islet, P < .01), the impact on the β-cell deficit would be minimal. Furthermore, we established that the deficit in β-cells per islet cannot be accounted for by an increase in other endocrine cell types. The distribution of hormone negative endocrine cells in type 2 diabetes (most abundant in cells scattered in the exocrine pancreas) mirrors that in developing (embryo and neonatal) pancreas, implying that these may represent newly forming cells.ConclusionsTherefore, although we concur that in type 2 diabetes there are endocrine cells with altered cell identity, this process does not account for the deficit in β-cells in type 2 diabetes but may reflect, in part, attempted β-cell regeneration.

ObjectiveWe sought to establish β-cell mass, β-cell apoptosis, and β-cell replication in humans in response to obesity and advanced age.Research design and methodsWe examined human autopsy pancreas from 167 nondiabetic individuals 20-102 years of age. The effect of obesity on β-cell mass was examined in 53 lean and 61 obese subjects, and the effect of aging was examined in 106 lean subjects.Resultsβ-Cell mass is increased by ~50% with obesity (from 0.8 to 1.2 g). With advanced aging, the exocrine pancreas undergoes atrophy but β-cell mass is remarkably preserved. There is minimal β-cell replication or apoptosis in lean humans throughout life with no detectable changes with obesity or advanced age.Conclusionsβ-Cell mass in human obesity increases by ~50% by an increase in β-cell number, the source of which is unknown. β-Cell mass is well preserved in humans with advanced aging.

ObjectiveThe islet in type 2 diabetes is characterized by β-cell apoptosis, β-cell endoplasmic reticulum stress, and islet amyloid deposits derived from islet amyloid polypeptide (IAPP). Toxic oligomers of IAPP form intracellularly in β-cells in humans with type 2 diabetes, suggesting impaired clearance of misfolded proteins. In this study, we investigated whether human-IAPP (h-IAPP) disrupts the endoplasmic reticulum-associated degradation/ubiquitin/proteasome system.Research design and methodsWe used pancreatic tissue from humans with and without type 2 diabetes, isolated islets from h-IAPP transgenic rats, isolated human islets, and INS 832/13 cells transduced with adenoviruses expressing either h-IAPP or a comparable expression of rodent-IAPP. Immunofluorescence and Western blotting were used to detect polyubiquitinated proteins and ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) protein levels. Proteasome activity was measured in isolated rat and human islets. UCH-L1 was knocked down by small-interfering RNA in INS 832/13 cells and apoptosis was evaluated.ResultsWe report accumulation of polyubiquinated proteins and UCH-L1 deficiency in β-cells of humans with type 2 diabetes. These findings were reproduced by expression of oligomeric h-IAPP but not soluble rat-IAPP. Downregulation of UCH-L1 expression and activity to reproduce that caused by h-IAPP in β-cells induced endoplasmic reticulum stress leading to apoptosis.ConclusionsOur results indicate that defective protein degradation in β-cells in type 2 diabetes can, at least in part, be attributed to misfolded h-IAPP leading to UCH-L1 deficiency, which in turn further compromises β-cell viability.

Vesicular monoamine transporter 2 (VMAT2) is expressed in pancreatic beta cells and has recently been proposed as a target for measurement of beta cell mass in vivo. We questioned, (1) What proportion of beta cells express VMAT2? (2) Is VMAT2 expressed by other pancreatic endocrine or non-endocrine cells? (3) Is the relationship between VMAT2 and insulin expression disturbed in type 1 (T1DM) or type 2 diabetes (T2DM)? Human pancreas (7 non-diabetics, 5 T2DM, 10 T1DM) was immunostained for insulin, VMAT2 and other pancreatic hormones. Most beta cells expressed VMAT2. VMAT2 expression was not changed by the presence of diabetes. In tail of pancreas VMAT2 immunostaining closely correlated with insulin staining. However, VMAT2 was also expressed in some pancreatic polypeptide (PP) cells. Although VMAT2 was not excluded as a target for beta cell mass measurement, expression of VMAT2 in PP cells predicts residual VMAT2 expression in human pancreas even in the absence of beta cells.

Glucagon-like peptide-1 (GLP-1)-based therapies for diabetes have aroused interest because of their effects on insulin secretion and glycemic control. However, a mechanistic model enabling quantitation of pancreatic response to GLP-1 has never been developed. To develop such a model we studied 88 healthy individuals (age 26.3 [+ or -] 0.6 yr, BMI 24.9 [+ or -] 0.4 kg/[m.sup.2]) by use of a hyperglycemic clamp. A variable infusion maintained glucose concentrations at 150 mg/dl for 240 min. At 120 min, an intravenous infusion of GLP-1 was started (0.75 pmol x [kg.sup.-1] x [min.sup.-1] from 120-180 min, 1.5 pmol x [kg.sup.-1] x [min.sup.-1] from 181-240 min). Consequently, plasma C-peptide concentration rose from 1,852.0 [+ or -] 62.8 pmol/1 at 120 min to 4,272.2 [+ or -] 176.4 pmol/l at 180 min and to 6,995.8 [+ or -] 323.5 pmol/l at 240 min. Four models of GLP-1 action on insulin secretion were considered. All models share the common assumption that insulin secretion is made up of two components, one proportional to glucose rate of change through dynamic responsivity, [[PHI].sub.d], and one proportional to glucose through static responsivity, [[PHI].sub.s], but differing by modality of GLP-1 control. The model that best fit C-peptide data assumes that above-basal insulin secretion depends linearly on GLP-1 concentration and its rate of change. An index ([PI]) measuring the percentage increase of secretion due to GLP-1 is derived. Before GLP-1 infusion, [[PI].sub.d] = 245.7 [+ or -] 15.6 [10.sup.-9] and [[PI].sub.s] = 25.2 [+ or -] 1.4 [10.sup.-9] [min.sup.-1]. Under GLP-1 stimulus, [PI] = 12.6 [+ or -] 0.71% per pmol/l, meaning that an increase of 5 pmol/l in peripheral GLP-1 concentrations induces an ~60% increase in over-basal insulin secretion. glucagon-like peptide-1; incretins; C-peptide; hyperglycemic clamp; [beta]-cell responsivity; parameter estimation doi: 10.1152/ajpendo.00705.2009.

Inactive cortisone is converted to active cortisol within the liver by 11[beta]-hydroxysteroid dehydrogenase-1 (11[beta]-HSD1), and impaired regulation of this process may be related to increased hepatic glucose production (HGP) in individuals with type 2 diabetes. The primary aim of this study was to investigate the effect of acute 11[beta]-HSD1 inhibition on HGP and fat metabolism during insulin deficiency. Sixteen conscious, 42-h-fasted, lean, healthy dogs were studied. Somatostatin was infused to create insulin deficiency, and the animals were treated with a specific 11[beta]-HSD1 inhibitor (compound 531) or placebo for 5 h. 11[beta]-HSD1 inhibition completely suppressed hepatic cortisol production, and this attenuated the increase in HGP that occurred during insulin deficiency. PEPCK and glucose-6-phosphatase expression were decreased when 11[beta]-HSD1 was inhibited, but gluconeogenic flux was unchanged, implying an effect on glycogenolysis. Since inhibition of hepatic cortisol production reduces HGP during insulin deficiency, 11[beta]-HSD1 is a potential therapeutic target for the treatment of excess glucose production that occurs in diabetes. endogenous glucose production; cortisol; glucocorticoids; hepatic cortisol production doi: 10.1152/ajpendo.00740.2009.

The ability to accurately quantify indexes of the individual role of glucose (GEL) and insulin ([S.sub.L.sup.I]) in the suppression of endogenous glucose production (EGP) would improve the understanding of liver metabolism. Measuring these indexes during an IVGTT by minimal modeling of tracer labeled and unlabeled glucose data is often unreliable, possibly due to an inadequate description of EGP included in the Minimal Model. Moreover, a validation of the assumptions of the Minimal Model on EGP data has never been done. Recently, Krudys et al. (Krudys KM, Dodds MG, Nissen SM, Vicini P. Am J Physiol Enclocrinol Metab 288: E1038-E1046, 2005) have proposed a PK/PD (pharmacokinetic/pharmacodynamic) model of the EGP profile that occurs during an intravenous glucose tolerance test (IVGTT); however, this model has also not been validated. The aim of this study was thus to test the Minimal Model, the PK/PD model, and six alternative EGP descriptions on recent model-independent EGP data of 20 subjects obtained with a triple-tracer meal protocol. Model performance was compared in terms of data fit, precision of the estimated parameters, and physiological plausibility. Neither the PK/PD nor the traditional Minimal Model were able to accurately describe EGP data or provide reliable estimates of the indexes. In contrast, one of the new models performed best by showing a good fit and providing accurate and precise estimates of hepatic sensitivity indexes: GEL = 0.013 [+ or -] 0.001 dl x [kg.sup.-1] x [min.sup.-1]; [S.sub.I.sup.L] = 5.34 [+ or -] 0.47 [10.sup.-4] dl x [kg.sup.-1] x [min.sup.-1] per [micro]U/ml (42 and 34%, respectively, of total sensitivity indexes [GE.sup.TOT] and [S.sub.I.sup.TOT]). Although this model requires further validation, it has the potential to improve our understanding of the role of the liver in pathophysiological states. glucose kinetics; tracer; meal; insulin resistance

Sulfonylureas (SU) with glucagon-like peptide-1 (GLP-l)-based therapy are an emerging therapeutic combination for type 2 diabetes. Prior human studies have hinted at endothelial effects of GLP-1 and SU. To study the endothelial effects of GLP-1 per se and to evaluate the modulatory effects, if any, of SU agents on GLP-l-induced changes in endothelial function, healthy, nondiabetic, normotensive, nonsmokers, age 18-50 yr with no family history of diabetes, were studied. Subjects were randomized to either placebo (n = 10), 10 mg of glyburide (n = 11), or 4 mg of glimepiride (n = 8) orally. Euglycemic somatostatin pancreatic clamp with replacement basal insulin, glucagon, and growth hormone was performed for 240 min. Forearm blood flow (FBF) was measured by venous occlusion plethysmography with graded brachial artery infusions of acetylcholine (Ach) and nitroprusside (NTP) before and after intravenous infusion of GLP-1. GLP-1 (preinfusion 3.4 [+ or 1] 0.2, postinfusion 25.5 [+ or -] 2.8 pM) enhanced (P < 0.03) Ach-mediated vasodilatation ([DELTA] + 6.5 [+ or -] 1.1 vs. [DELTA] + 9.1 [+ or -] 1.2 ml x 100 [ml.sup.-1] x [min.sup.-1], change from baseline FBF) in those on placebo. However, in contrast, glyburide abolished GLP-1-induced Ach-mediated vasodilatation ([DELTA] + 11.7 [+ or -] 2.0 vs. [DELTA]+11.7 [+ or -] 2.5 ml x 100 [ml.sup-1] x [min.sup.-1]). On the other hand, glimepiride did not alter the ability of GLP-1 to enhance Achmediated vasodilatation ([DELTA] + 7.9 [+ or -] 0.5 vs. [DELTA] + 10.2 [+ or -] 1.3 ml x 100 [ml.sup.-1] x [min.sup.-1], P < 0.04). Neither GLP-1 nor SU altered NTP-induced vasodilatation. These data demonstrate that GLP-1 per se has direct beneficial effects on endothelium-dependent vasodilatation in humans that are differentially modulated by SU. glucagon-like peptide-1; incretin; sulfonylurea; vascular reactivity

A simulation model of the glucose-insulin system in the postprandial state can be useful in several circumstances, including testing of glucose sensors, insulin infusion algorithms and decision support systems for diabetes. Here, we present a new simulation model in normal humans that describes the physiological events that occur after a meal, by employing the quantitative knowledge that has become available in recent years. Model parameters were set to fit the mean data of a large normal subject database that underwent a triple tracer meal protocol which provided quasi-model-independent estimates of major glucose and insulin fluxes, e.g., meal rate of appearance, endogenous glucose production, utilization of glucose, insulin secretion. By decomposing the system into subsystems, we have developed parametric models of each subsystem by using a forcing function strategy. Model results are shown in describing both a single meal and normal daily life (breakfast, lunch, dinner) in normal. The same strategy is also applied on a smaller database for extending the model to type 2 diabetes. Index Terms--Artificial pancreas, diabetes, glucose homeostasis, glucose production, glucose sensors, glucose utilization, insulin infusion system, insulin secretion, kinetics, physiological control.

Assessment of insulin secretion in humans under physiological conditions has been a challenge because of its complex interplay with insulin action and hepatic insulin extraction. The possibility of simultaneously assessing [beta]-cell function, insulin sensitivity, and hepatic insulin extraction under physiological conditions using a simple protocol is appealing, since it has the potential to provide novel insights regarding the regulation of fasting and postprandial glucose metabolism in diabetic and nondiabetic humans. In this Perspective, we review data indicating that an oral glucose tolerance test (OGTT) or a meal test is able to accomplish this goal when interpreted with the oral [beta]-cell minimal model. We begin by using the well-established intravenous minimal model to highlight how the oral minimal model was developed and how the oral assessment parallels that of an intravenous glucose tolerance test (IVGTT). We also point out the unique aspects of both approaches in relation to their ability to assess different aspects of the [beta]-cell secretory cascade. We review the ability of the oral model to concurrently measure insulin sensitivity and hepatic insulin extraction, thereby enabling it to quantitatively portray the complex relationship among [beta]-cell function, hepatic insulin extraction, and insulin action. In addition, data from 204 individuals (54 young and 159 elderly) who underwent both IVGTT and meal tolerance tests are used to illustrate how these different approaches provide complementary but differing insights regarding the regulation of [beta]-cell function in humans. glucose tolerance; disposition index; oral glucose tolerance test; meal; intravenous glucose tolerance test doi:10.1152/ajpendo.00421.2006

The aim of this study is to gain greater insight into the mechanism whereby 'incretins' (greater insulinemia after oral than intravenous glucose) enhance insulin secretion. To do so, we use a model of C-peptide secretion to reanalyze data from a previously published study in which glycemic profiles observed following glucose ingestion were matched in the same 10 subjects by means of an intravenous glucose infusion. We report that incretins increase insulin secretion by enhancing both the dynamic (to the rate of increase of glucose) and static (to given glucose concentration) response with an increase of 58% for the static ([[PHI].sub.s] = 16.4 [+ or -] 1.8 vs. 24.6 [+ or -] 2.0 [10.sup.-9] [min.sup.-1], P = 0.01) and 63% for the dynamic ([[PHI].sub.d] = 278 [+ or -] 32 vs. 463 [+ or -] 86 [10.sup.-9], P = 0.02) indexes. Since increases in the dynamic response to glucose are believed to be due to an increase in the rate of docking, and exocytosis of insulin containing granules and increases in the static response to glucose are believed to be caused by a shift in the sensitivity of the [beta]-cell to glucose, these results suggest that incretins may modulate more than one step in the [beta]-cell insulin secretory cascade. oral glucose tolertance test; insulin secretion; [beta]-cell function; minimal model

A 2-year, randomized, placebo-controlled, double-blind study is conducted to determine the effects of full dehydroepiandrosterone (DHEA) replacement and low-dose testosterone replacement on body composition, physical performance, bone mineral density (BMD) and glucose tolerance in elderly people with low androgen levels. The results have shown that neither DHEA nor low-dose testosterone replacement in elderly people has physiologically relevant effects on body composition, physical performance, insulin sensitivity or quality of life.

The dual-tracer method has been used conventionally for assessment of postprandial fluxes, i.e., appearance in plasma of ingested glucose ([R.sub.a meal]), endogenous glucose production (EGP), and disposal ([R.sub.d]). To quantify the magnitude of errors affecting the calculations and their dependence on model assumptions, this method was assessed and compared with the triple-tracer method, which provides model-independent estimates. For this purpose, the dual-tracer protocol was performed twice in eight normal subjects, with [1-[sup.13]C]glucose to trace ingested glucose and [6,6-[sup.2][H.sub.2]]glucose constantly infused. A third tracer, [6-[sup.3]H]glucose, was infused at variable rates to render the calculation of [R.sub.a meal] and EGP virtually model independent. The dual-tracer method analyzed with a one-compartment model performed poorly, since [R.sub.a meal] peak was significantly lower and delayed compared with triple-tracer reference, resulting in a significantly lower estimation of the amount of absorbed glucose (9,036 [+ or -] 558 vs. 11,316 [+ or -] 823 [micro]mol/kg, P = 0.0117). EGP showed a paradoxical pattern, with an initial overshoot followed by a rapid decay to negative values, resulting in a significant underestimation of EGP suppression (57 [+ or -] 3 vs. 65 [+ or -] 4%, P = 0.0117). A two-compartment model performed better but did not overcome the limitations of the dual-tracer approach, since the amount of absorbed glucose was still significantly underestimated (10,231 [+ or -] 661 vs. 12,169 [+ or -] 838 [micro]mol/kg, P = 0.0117) and EGP still showed a paradoxical behavior. [R.sub.d], estimated from [R.sub.a meal] and EGP, was significantly underestimated with the dual-tracer method, irrespective of adopted model. We conclude that three suitably infused tracers are required for accurate assessment of postprandial [R.sub.a meal], EGP, and [R.sub.d]. nonsteady state; turnover; meal; kinetics; compartmental models

The liver is the principal site of insulin degradation, and assessing its ability to extract insulin is important to understand several pathological states. Noninvasive quantification of hepatic extraction (HE) in an individual requires comparing the profiles of insulin secretion (ISR) and posthepatic insulin delivery rate (IDR). To do this, we propose here the combined use of the classical C-peptide minimal model with a new minimal model of insulin delivery and kinetics. The models were identified on insulin-modified intravenous glucose tolerance test (IM-IVGTT) data of 20 healthy subjects. C-peptide kinetics were fixed to standard population values, whereas insulin kinetics were assessed in each individual, along with IDR parameters, thanks to the presence of insulin decay data observed after exogenous insulin administration. From the two models, profiles of ISR and IDR were predicted, and ISR and IDR indexes of [beta]-cell responsivity to glucose in the basal state, as well as during first- and second-phase secretion, were estimated. HE profile, obtained by comparing ISR and IDR profiles, showed a rapid suppression immediately after the glucose administration. HE indexes, obtained by comparing ISR and IDR indexes, indicated that the liver is able to extract 70 [+ or -] 9% of insulin passing through it in the basal state and 54 [+ or -] 14% during IM-IVGTT. In conclusion, insulin secretion, kinetics, and hepatic extraction can be reliably assessed during an IM-IVGTT by using insulin and C-peptide minimal models. hepatic extraction; intravenous glucose tolerance test; parameter estimation