Acute insulin response (AIR): review of protocols and clinical interest in islet transplantation

Surrogate measures of first-phase insulin secretion versus reference methods intravenous glucose tolerance test and hyperglycemic clamp: a systematic review and meta-analyses

INTRODUCTION

In this systematic review, we investigated the diagnostic accuracy of surrogate measures of insulin secretion based on fasting samples and the oral glucose tolerance test (OGTT). The first phase of insulin secretion was calculated using two gold standard methods; the hyperglycemic clamp (HGC) test and intravenous glucose tolerance test (IVGTT).

RESEARCH DESIGN AND METHODS

We conducted searches in the PubMed, Cochrane Central, and Web of Science databases, the last of which was conducted at the end of June 2021. Studies were included that measured first-phase insulin secretion in adults using both a gold-standard reference method (either HGC or IVGTT) and one or more surrogate measures from either fasting samples, OGTT or a meal-tolerance test. QUADAS-2, a revised tool for the quality assessment of diagnostic accuracy studies, was used for quality assessment. Random-effects meta-analyses were performed to examine the correlation between first-phase measured with gold standard and surrogate methods.

RESULTS

A total of 33 articles, encompassing 5362 individuals with normal glucose tolerance, pre-diabetes or type 2 diabetes, were included in our systematic review. Homeostatic model assessment (HOMA)-beta and Insulinogenic Index 30 (IGI(30)) were the surrogate measures validated in the largest number of studies (17 and 13, respectively). HOMA-beta's pooled correlation to the reference methods was 0.48 (95% CI 0.40 to 0.56) The pooled correlation of IGI to the reference methods was 0.61 (95% CI 0.54 to 0.68). The surrogate measures with the highest correlation to the reference methods were Kadowaki (0.67 (95% CI 0.61 to 0.73)) and Stumvoll's first-phase secretion (0.65 (95% CI 0.58 to 0.71)), both calculated from an OGTT.

CONCLUSIONS

Surrogate measures from the first 30 min of an OGTT capture the first phase of insulin secretion and are a good choice for epidemiological studies. HOMA-beta has a moderate correlation to the reference methods but is not a measure of the first phase specifically.

PROSPERO REGISTRATION NUMBER

The meta-analysis was registered at PROSPERO (Id: CRD42020169064) before inclusion started.

Beta-cell function and glucose metabolism in patients with chronic pancreatitis

AIMS

Chronic pancreatitis (CP) is - along with acute pancreatitis - the most frequent cause of diabetes of the exocrine pancreas (DEP). Although insulin deficiency is widely accepted as the major feature of DEP, it is still unclear whether diabetes associated with CP is characterized by additional or different functional defects of the insulin secretory machinery. To identify possible functional defects specifically induced by CP, we performed a cross-sectional study in individuals with normal glucose tolerance (NGT), impaired glucose tolerance (IGT) and diabetes mellitus (DM) comparing patients with and without CP (CP vs. NCP).

METHODS

We administered an oral glucose tolerance test (OGTT) to all participants and, according to their glucose tolerance, classified them as NGT, IGT and DM. Insulin sensitivity and beta-cell functional parameters were derived from OGTT, hyperglycemic clamp and hyperinsulinemic euglycemic clamp.

RESULTS

Studying 146 subjects, we found that beta-cell function and insulin secretion were significantly lower in CP compared to NCP patients. However, when we classified the subjects according to OGTT-derived glucose tolerance, we found no differences in beta-cell function or in insulin sensitivity between CP and NCP with the same glucose tolerance status. Of note, we found that arginine-stimulated insulin secretion is reduced only in subjects with CP and DM compared to NCP subjects with DM.

CONCLUSIONS

Patients with CP had no specific alterations in insulin secretion and beta-cell function. However, in patients diagnosed with diabetes, we found a lower arginine-stimulated insulin secretion, a marker of reduced functional mass.

Effects of subtotal pancreatectomy and long-term glucose and lipid overload on insulin secretion and glucose homeostasis in minipigs

INTRODUCTION

Nowadays, there are no strong diabetic pig models, yet they are required for various types of diabetes research. Using cutting-edge techniques, we attempted to develop a type 2 diabetic minipig model in this study by combining a partial pancreatectomy (Px) with an energetic overload administered either orally or parenterally.

METHODS

Different groups of minipigs, including Göttingen-like (GL, n = 17) and Ossabaw (O, n = 4), were developed. Prior to and following each intervention, metabolic assessments were conducted. First, the metabolic responses of the Göttingen-like (n = 3) and Ossabaw (n = 4) strains to a 2-month High-Fat, High-Sucrose diet (HFHSD) were compared. Then, other groups of GL minipigs were established: with a single Px (n = 10), a Px combined with a 2-month HFHSD (n = 6), and long-term intraportal glucose and lipid infusions that were either preceded by a Px (n = 4) or not (n = 4).

RESULTS

After the 2-month HFHSD, there was no discernible change between the GL and O minipigs. The pancreatectomized group in GL minipigs showed a significantly lower Acute Insulin Response (AIR) (18.3 ± 10.0 IU/mL after Px vs. 34.9 ± 13.7 IU/mL before, p < .0005). In both long-term intraportal infusion groups, an increase in the Insulinogenic (IGI) and Hepatic Insulin Resistance Indexes (HIRI) was found with a decrease in the AIR, especially in the pancreatectomized group (IGI: 4.2 ± 1.9 after vs. 1.5 ± 0.8 before, p < .05; HIRI (×10^-5 ): 12.6 ± 7.9 after vs. 3.8 ± 4.3 before, p < .05; AIR: 24.4 ± 13.7 µIU/mL after vs. 43.9 ± 14.5 µIU/mL before, p < .005). Regardless of the group, there was no fasting hyperglycemia.

CONCLUSIONS

In this study, we used pancreatectomy followed by long-term intraportal glucose and lipid infusions to develop an original minipig model with metabolic syndrome and early signs of glucose intolerance. We reaffirm the pig's usefulness as a preclinical model for the metabolic syndrome but without the fasting hyperglycemia that characterizes diabetes mellitus.

Insulin regulates arginine-stimulated insulin secretion in humans

AIMS

Insulin potentiates glucose-stimulated insulin secretion. These effects are attenuated in beta cell-specific insulin receptor knockout mice and insulin resistant humans. This investigation examines whether short duration insulin exposure regulates beta cell responsiveness to arginine, a non-glucose secretagogue, in healthy humans.

MATERIALS AND METHODS

Arginine-stimulated insulin secretion was studied in 10 healthy humans. In each subject arginine was administered as a bolus followed by continuous infusion on two occasions one month apart, after sham/saline or hyperinsulinemic-isoglycemic clamp, respectively providing low and high insulin pre-exposure conditions. Arginine-stimulated insulin secretion was measured by C-peptide deconvolution, and by a selective immunogenic (DAKO) assay for direct measurement of endogenous but not exogenous insulin.

RESULTS

Pre-exposure to exogenous insulin augmented arginine-stimulated insulin secretion. The effect was seen acutely following arginine bolus (endogenous DAKO insulin incremental AUC_240-255min 311.6 ± 208.1 (post-insulin exposure) versus 120.6 ± 42.2 μU/ml•min (sham/saline) (t-test P = 0.021)), as well as in response to continuous arginine infusion (DAKO insulin incremental AUC_260-290min 1095.3 ± 592.1 (sham/saline) versus 564.8 ± 207.1 μU/ml•min (high insulin)(P = 0.009)). Findings were similar when beta cell response was assessed using C-peptide, insulin secretion rates by deconvolution, and the C-peptide to glucose ratio.

CONCLUSIONS

We demonstrate a physiologic role of insulin in regulation of the beta cell secretory response to arginine.

Profile of Daughters and Sisters of Women With Polycystic Ovary Syndrome: The Role of Proband's Glucose Tolerance

CONTEXT

First-degree relatives of women with polycystic ovary syndrome (PCOS) present hormonal and metabolic alterations compared to girls unrelated to PCOS. It is unknown whether glucose intolerance in the PCOS proband confers a more severe metabolic predisposition on their first-degree relatives.

OBJECTIVE

To determine whether glucose tolerance status in women with PCOS is associated with worsened glucose metabolism and sex hormone levels in their peripubertal daughters or sisters.

DESIGN

Cross-sectional study.

SETTING

Seven academic centers in North America, South America, and Europe.

PATIENTS

Sixty-four pairs of women with PCOS and their daughters or younger sisters aged between 8 and 14 years were recruited. Twenty-five mothers or older sisters with PCOS were glucose intolerant (GI) and 39 were normal glucose tolerant (NGT).

MAIN OUTCOME MEASURES

Beta-cell function estimated by the insulin secretion-sensitivity index-2 (ISSI-2) during an oral glucose tolerance test and by the disposition index during a frequently sampled IV glucose tolerance test. Free testosterone and 17-hydroxyprogesterone (17-OHP) levels.

RESULTS

Being related to a GI PCOS proband was associated with a lower ISSI-2 (P-value = 0.032) after adjusting for ethnicity, body mass index z-score, and pubertal stage. They also had higher free testosterone (P-value = 0.011) and 17-OHP levels compared to girls with an NGT proband, the latter becoming significant after adjusting for confounders (P-value = 0.040).

CONCLUSIONS

Compared to first-degree female relatives of women with PCOS and NGT, first-degree relatives of women with PCOS and GI display lower beta-cell function and hyperandrogenemia, putting them at higher risk of GI and PCOS development.

PPARGC1A Gene Promoter Methylation as a Biomarker of Insulin Secretion and Sensitivity in Response to Glucose Challenges

Methylation in CpG sites of the PPARGC1A gene (encoding PGC1-α) has been associated with adiposity, insulin secretion/sensitivity indexes and type 2 diabetes. We assessed the association between the methylation profile of the PPARGC1A gene promoter gene in leukocytes with insulin secretion/sensitivity indexes in normoglycemic women. A standard oral glucose tolerance test (OGTT) and an abbreviated version of the intravenous glucose tolerance test (IVGTT) were carried out in n = 57 Chilean nondiabetic women with measurements of plasma glucose, insulin, and C-peptide. Bisulfite-treated DNA from leukocytes was evaluated for methylation levels in six CpG sites of the proximal promoter of the PPARGC1A gene by pyrosequencing (positions -816, -783, -652, -617, -521 and -515). A strong correlation between the DNA methylation percentage of different CpG sites of the PPARGC1A promoter in leukocytes was found, suggesting an integrated epigenetic control of this region. We found a positive association between the methylation levels of the CpG site -783 with the insulin sensitivity Matsuda composite index (rho = 0.31; p = 0.02) derived from the OGTT. The CpG hypomethylation in the promoter position -783 of the PPARGC1A gene in leukocytes may represent a biomarker of reduced insulin sensitivity after the ingestion of glucose.

GIP and GLP-1 Potentiate Sulfonylurea-Induced Insulin Secretion in Hepatocyte Nuclear Factor 1α Mutation Carriers

Sulfonylureas (SUs) provide an efficacious first-line treatment in patients with hepatocyte nuclear factor 1α (HNF1A) diabetes, but SUs have limitations due to risk of hypoglycemia. Treatment based on the incretin hormones glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide 1 (GLP-1) is characterized by their glucose-dependent insulinotropic actions without risk of hypoglycemia. The effect of SUs together with GIP or GLP-1, respectively, on insulin and glucagon secretion in patients with HNF1A diabetes is currently unknown. To investigate this, 10 HNF1A mutation carriers and 10 control subjects without diabetes were recruited for a double-blinded, placebo-controlled, crossover study including 6 experimental days in a randomized order involving 2-h euglycemic-hyperglycemic clamps with coadministration of: 1) SU (glimepiride 1 mg) or placebo, combined with 2) infusions of GIP (1.5 pmol/kg/min), GLP-1 (0.5 pmol/kg/min), or saline (NaCl). In HNF1A mutation carriers, we observed: 1) hypoinsulinemia, 2) insulinotropic effects of both GIP and GLP-1, 3) additive to supra-additive effects on insulin secretion when combining SU+GIP and SU+GLP-1, respectively, and 4) increased fasting and arginine-induced glucagon levels compared with control subjects without diabetes. Our study suggests that a combination of SU and incretin-based treatment may be efficacious in patients with HNF1A diabetes via potentiation of glucose-stimulated insulin secretion.

Paracrine regulation and improvement of β-cell function by thioredoxin

The failure of insulin-producing β-cells is the underlying cause of hyperglycemia in diabetes mellitus. β-cell decay has been linked to hypoxia, chronic inflammation, and oxidative stress. Thioredoxin (Trx) proteins are major actors in redox signaling and essential for signal transduction and the cellular stress response. We have analyzed the cytosolic, mitochondrial, and extracellular Trx system proteins in hypoxic and cytokine-induced stress using β-cell culture, isolated pancreatic islets, and pancreatic islet transplantation modelling low oxygen supply. Protein levels of cytosolic Trx1 and Trx reductase (TrxR) 1 significantly decreased, while mitochondrial Trx2 and TrxR2 increased upon hypoxia and reoxygenation. Interestingly, Trx1 was secreted by β-cells during hypoxia. Moreover, murine and human pancreatic islet grafts released Trx1 upon glucose stimulation. Survival of transplanted islets was substantially impaired by the TrxR inhibitor auranofin. Since a release was prominent upon hypoxia, putative paracrine effects of Trx1 on β-cells were examined. In fact, exogenously added recombinant hTrx1 mitigated apoptosis and preserved glucose sensitivity in pancreatic islets subjected to hypoxia and inflammatory stimuli, dependent on its redox activity. Human subjects were studied, demonstrating a transient increase in extracellular Trx1 in serum after glucose challenge. This increase correlated with better pancreatic islet function. Moreover, hTrx1 inhibited the migration of primary murine macrophages. In conclusion, our study offers evidence for paracrine functions of extracellular Trx1 that improve the survival and function of pancreatic β-cells.

Insulin Sensitivity Is Associated with Lipoprotein Lipase (LPL) and Catenin Delta 2 (CTNND2) DNA Methylation in Peripheral White Blood Cells in Non-Diabetic Young Women

Hyperglycaemia and type 2 diabetes (T2D) are associated with impaired insulin secretion and/or insulin action. Since few studies have addressed the relation between DNA methylation patterns with elaborated surrogates of insulin secretion/sensitivity based on the intravenous glucose tolerance test (IVGTT), the aim of this study was to evaluate the association between DNA methylation and an insulin sensitivity index based on IVGTT (calculated insulin sensitivity index (CSi)) in peripheral white blood cells from 57 non-diabetic female volunteers. The CSi and acute insulin response (AIR) indexes, as well as the disposition index (DI = CSi × AIR), were estimated from abbreviated IVGTT in 49 apparently healthy Chilean women. Methylation levels were assessed using the Illumina Infinium Human Methylation 450k BeadChip. After a statistical probe filtering, the two top CpGs whose methylation was associated with CSi were cg04615668 and cg07263235, located in the catenin delta 2 (CTNND2) and lipoprotein lipase (LPL) genes, respectively. Both CpGs conjointly predicted insulin sensitivity status with an area under the curve of 0.90. Additionally, cg04615668 correlated with homeostasis model assessment insulin-sensitivity (HOMA-S) and AIR, whereas cg07263235 was associated with plasma creatinine and DI. These results add further insights into the epigenetic regulation of insulin sensitivity and associated complications, pointing the CTNND2 and LPL genes as potential underlying epigenetic biomarkers for future risk of insulin-related diseases.

Evolution of metabolic alterations 5 Years after early puberty in a cohort of girls predisposed to polycystic ovary syndrome

BACKGROUND

We and others have observed that young girls predisposed to polycystic ovary syndrome (PCOS) display defective insulin sensitivity, beta-cell function and non-esterified fatty acids (NEFA) suppressibility during early pubertal years, compared to controls. Our objective is to assess whether these differences in glucose and NEFA metabolisms persist after 5 years in late/post-puberty.

METHODS

We conducted a prospective cohort study between 2007 and 2015 with 4-6 years of follow-up in an academic institution research center. We compared 8 daughters and sisters of PCOS women (PCOSr) to 8 age-matched girls unrelated to PCOS (±1.5 years). Girls were assessed initially at 8-14 years old and re-assessed after a median follow-up of 5.4 years, at 13-21 years old. Our main measures were a frequently sampled intravenous glucose tolerance test (FSivGTT)-derived insulin sensitivity (IS) and beta-cell function (disposition index, DI_FSivGTT); and indices of NEFA suppression during FSivGTT (log_n-linear slope of NEFA and T₅₀ of NEFA suppression).

RESULTS

At follow-up, both PCOSr and controls had similar results: IS = 3.2 vs 3.4 (p = 0.88), DI_FSivGTT = 1926 vs 1380 (p = 0.44), log_n-linear slope = -0.032 vs -0.032 (p = 0.88) and T₅₀NEFA = 18.1 vs 20.8 min (p = 0.57). IS, DI_FSivGTT and NEFA suppressibility were stable in PCOSr after 5 years, but decreased significantly in controls (all p < 0.05).

CONCLUSIONS

Impaired metabolism observed during early puberty in girls predisposed to PCOS remains stable after 5 years whereas control girls deteriorated their metabolic parameters. Therefore, both groups become comparable in late/post-puberty. Early puberty may thus represent a window during which metabolic alterations are transiently apparent in girls at risk of PCOS.

Validation of the BETA-2 Score: An Improved Tool to Estimate Beta Cell Function After Clinical Islet Transplantation Using a Single Fasting Blood Sample

The beta score, a composite measure of beta cell function after islet transplantation, has limited sensitivity because of its categorical nature and requires a mixed-meal tolerance test (MMTT). We developed a novel score based on a single fasting blood sample. The BETA-2 score used stepwise forward linear regression incorporating glucose (in millimoles per liter), C-peptide (in nanomoles per liter), hemoglobin A1c (as a percentage) and insulin dose (U/kg per day) as continuous variables from the original beta score data set (n = 183 MMTTs). Primary and secondary analyses assessed the score's ability to detect glucose intolerance (90-min MMTT glucose ≥8 mmol/L) and insulin independence, respectively. A validation cohort of islet transplant recipients (n = 114 MMTTs) examined 12 mo after transplantation was used to compare the score's ability to detect these outcomes. The BETA-2 score was expressed as follows (range 0-42): [Formula: see text] A score <20 and ≥15 detected glucose intolerance and insulin independence, respectively, with >82% sensitivity and specificity. The BETA-2 score demonstrated greater discrimination than the beta score for these outcomes (p < 0.05). Using a fasting blood sample, the BETA-2 score estimates graft function as a continuous variable and shows greater discrimination of glucose intolerance and insulin independence after transplantation versus the beta score, allowing frequent assessments of graft function. Studies examining its utility to track long-term graft function are required.

Development and assessment of the disposition index based on the oral glucose tolerance test in subjects with different glycaemic status

Insulin secretion and insulin sensitivity indexes are related by hyperbolic functions, allowing the calculation of the disposition index (DI) as the product of the acute insulin response (AIR) and the insulin sensitivity index (Si) from intravenous glucose tolerance test (IVGTT). Our objective was to develop an oral-DI based on the oral glucose tolerance test (OGTT) and to assess its association with glucose tolerance status. This research is structured in three studies. Study 1: OGTT were performed in 833 non-diabetic Chilean women (18-60 years) without family history of diabetes mellitus. Study 2: an independent group of n = 57 non-diabetic (18-46 years) without family history of diabetes mellitus carried out an OGTT and an abbreviated IVGTT. Study 3: a sample of 1674 Chilean adults (18-60 years) with different glycaemic status performed an OGTT. An adequate statistical fit for a rectangular hyperbola was found between the area under the curve of insulin-to-glucose ratio (AUCI/G-R) and the Matsuda ISI-COMP index (study 1). The oral-DI derived as AUCI/G-R × ISI-COMP was previously termed insulin-secretion-sensitivity index-2 (ISSI-2). ISSI-2 significantly correlated with DI from IVGTT (rho = 0.34; p = 0.009) (study 2). ISSI-2 shows important differences across groups of subjects with different glycaemic status (study 3). We have confirmed that ISSI-2 replicates the mathematical properties of DI, showing significant correlations with DI from the abbreviated MM-IVGTT. These results indicate that ISSI-2 constitutes a surrogate measure of insulin secretion relative to insulin sensitivity and emphasizes the pivotal role of impaired insulin secretion in the development of glucose homeostasis dysregulation.

PKA Enhances the Acute Insulin Response Leading to the Restoration of Glucose Control

Diabetes arises from insufficient insulin secretion and failure of the β-cell mass to persist and expand. These deficits can be treated with ligands to Gs-coupled G-protein-coupled receptors that raise β-cell cAMP. Here we studied the therapeutic potential of β-cell cAMP-dependent protein kinase (PKA) activity in restoring glucose control using β-caPKA mice. PKA activity enhanced the acute insulin response (AIR) to glucose, which is a primary determinant of the efficacy of glucose clearance. Enhanced AIR improved peripheral insulin action, leading to more rapid muscle glucose uptake. In the setting of pre-established glucose intolerance caused by diet-induced insulin resistance or streptozotocin-mediated β-cell mass depletion, PKA activation enhanced β-cell secretory function to restore glucose control, primarily through augmentation of the AIR. Enhanced AIR and improved glucose control were maintained through 16 weeks of a high-fat diet and aging to 1 year. Importantly, improved glucose tolerance did not increase the risk for hypoglycemia, nor did it rely upon hyperinsulinemia or β-cell hyperplasia, although PKA activity was protective for β-cell mass. These data highlight that improving β-cell function through the activation of PKA has a large and underappreciated capacity to restore glucose control with minimal risk for adverse side effects.

β-Cell-specific protein kinase A activation enhances the efficiency of glucose control by increasing acute-phase insulin secretion

Acute insulin secretion determines the efficiency of glucose clearance. Moreover, impaired acute insulin release is characteristic of reduced glucose control in the prediabetic state. Incretin hormones, which increase β-cell cAMP, restore acute-phase insulin secretion and improve glucose control. To determine the physiological role of the cAMP-dependent protein kinase (PKA), a mouse model was developed to increase PKA activity specifically in the pancreatic β-cells. In response to sustained hyperglycemia, PKA activity potentiated both acute and sustained insulin release. In contrast, a glucose bolus enhanced acute-phase insulin secretion alone. Acute-phase insulin secretion was increased 3.5-fold, reducing circulating glucose to 58% of levels in controls. Exendin-4 increased acute-phase insulin release to a similar degree as PKA activation. However, incretins did not augment the effects of PKA on acute-phase insulin secretion, consistent with incretins acting primarily via PKA to potentiate acute-phase insulin secretion. Intracellular calcium signaling was unaffected by PKA activation, suggesting that the effects of PKA on acute-phase insulin secretion are mediated by the phosphorylation of proteins involved in β-cell exocytosis. Thus, β-cell PKA activity transduces the cAMP signal to dramatically increase acute-phase insulin secretion, thereby enhancing the efficiency of insulin to control circulating glucose.

Adipose tissue insulin resistance in peripubertal girls with first-degree family history of polycystic ovary syndrome

OBJECTIVE

To assess metabolic and endocrine defects in girls genetically predisposed to polycystic ovary syndrome (PCOS).

DESIGN

Controlled cross-sectional study.

SETTING

University hospital.

PATIENT(S)

Nine girls, aged 8-14 years, having a first-degree relative diagnosed with PCOS (PCOSr) and 10 age-matched girls without a family history of PCOS.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Insulin sensitivity (IS(FSIVGTT)) determined by frequently sampled IV glucose tolerance testing (GTT) and insulin-induced nonesterified fatty acid (NEFA) suppression, estimated by the log-linear slope of NEFA levels during the first 20 minutes of GTT.

RESULT(S)

In comparison to controls, PCOSr had higher body mass index (BMI) Z-score, waist circumference, and waist-to-height ratio. Levels of the androgen 17α-hydroxyprogesterone (17-OHP) were significantly increased in PCOSr, independent of adiposity, and inversely correlated with IS(FSIVGTT). The IS(FSIVGTT) was decreased and the NEFA suppression was less steep in PCOSr compared with controls, independent of BMI and 17-OHP. The NEFA suppression was more pronounced with increasing IS(FSIVGTT), independent of adiposity.

CONCLUSION(S)

Girls at high risk of developing PCOS display increased adiposity and 17-OHP levels, but are mainly characterized by global insulin resistance and resistance to insulin-induced suppression of lipolysis that were independent of adiposity and 17-OHP levels. Therefore, genetic predisposition to PCOS may be related to early insulin resistance and adipocyte dysfunction.

Changing metabolic signatures of amino acids and lipids during the prediabetic period in a pig model with impaired incretin function and reduced β-cell mass

Diabetes is generally diagnosed too late. Therefore, biomarkers indicating early stages of β-cell dysfunction and mass reduction would facilitate timely counteraction. Transgenic pigs expressing a dominant-negative glucose-dependent insulinotropic polypeptide receptor (GIPR(dn)) reveal progressive deterioration of glucose control and reduction of β-cell mass, providing a unique opportunity to study metabolic changes during the prediabetic period. Plasma samples from intravenous glucose tolerance tests of 2.5- and 5-month-old GIPR(dn) transgenic and control animals were analyzed for 163 metabolites by targeted mass spectrometry. Analysis of variance revealed that 26 of 163 parameters were influenced by the interaction Genotype × Age (P ≤ 0.0001) and thus are potential markers for progression within the prediabetic state. Among them, the concentrations of seven amino acids (Phe, Orn, Val, xLeu, His, Arg, and Tyr) were increased in 2.5-month-old but decreased in 5-month-old GIPR(dn) transgenic pigs versus controls. Furthermore, specific sphingomyelins, diacylglycerols, and ether phospholipids were decreased in plasma of 5-month-old GIPR(dn) transgenic pigs. Alterations in plasma metabolite concentrations were associated with liver transcriptome changes in relevant pathways. The concentrations of a number of plasma amino acids and lipids correlated significantly with β-cell mass of 5-month-old pigs. These metabolites represent candidate biomarkers of early phases of β-cell dysfunction and mass reduction.

Saturated fatty acid and TLR signaling link β cell dysfunction and islet inflammation

Consumption of foods high in saturated fatty acids (FAs) as well as elevated levels of circulating free FAs are known to be associated with T2D. Though previous studies showed inflammation is crucially involved in the development of insulin resistance, how inflammation contributes to β cell dysfunction has remained unclear. We report here the saturated FA palmitate induces β cell dysfunction in vivo by activating inflammatory processes within islets. Through a combination of in vivo and in vitro studies, we show β cells respond to palmitate via the TLR4/MyD88 pathway and produce chemokines that recruit CD11b(+)Ly-6C(+) M1-type proinflammatory monocytes/macrophages to the islets. Depletion of M1-type cells protected mice from palmitate-induced β cell dysfunction. Islet inflammation also plays an essential role in β cell dysfunction in T2D mouse models. Collectively, these results demonstrate a clear mechanistic link between β cell dysfunction and inflammation mediated at least in part via the FFA-TLR4/MyD88 pathway.

Pancreatic beta-cell failure in obese mice with human-like CMP-Neu5Ac hydroxylase deficiency

Type 2 diabetes is highly prevalent in human populations, particularly in obese individuals, and is characterized by progressive pancreatic β-cell dysfunction and insulin resistance. Most mammals, including Old World primates, express two major kinds of sialic acids, N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc), typically found at the distal ends of glycoconjugate chains at the cell surface. Humans are uniquely unable to produce endogenous Neu5Gc due to an inactivating mutation in the CMP-Neu5Ac hydroxylase (CMAH) gene. The CMAH enzyme catalyzes the generation of CMP-Neu5Gc by the transfer of a single oxygen atom to the acyl group of CMP-Neu5Ac. Here, we show that mice bearing a human-like deletion of the Cmah gene exhibit fasting hyperglycemia and glucose intolerance following a high-fat diet. This phenotype is caused not by worsened insulin resistance but by compromised pancreatic β-cell function associated with a 65% decrease in islet size and area and 50% decrease in islet number. Obese Cmah-null mice also show an ∼40% reduction in response to insulin secretagogues in vivo. These findings show that human evolution-like changes in sialic acid composition impair pancreatic β-cell function and exacerbate glucose intolerance in mice. This may lend insight into the pathogenesis of type 2 diabetes in obese humans.

Acute insulin response to arginine in deceased donors predicts the outcome of human islet isolation

Despite a stringent donor selection, human islet isolation remains frustratingly unpredictable. In this study, we measured acute insulin response to arginine (AIRarg), an in vivo surrogate measure of islet mass, in 29 human deceased donors before organ donation, and correlated values with the outcome of islet isolation. Thirteen isolations (45%) met the threshold for clinical islet transplantation. Among all measured donor characteristics, the only discriminating variable between successful or unsuccessful isolations was donor AIRarg (p < 0.01). Using a threshold of 55 microIU/mL (ROC curve AUC: 72%), isolation was successful in 12/19 donors with high AIRarg and in 1/10 donors with low AIRarg (p < 0.001). The negative and positive predictive values were 90 and 63%, respectively. If used to select donors in the entire cohort, AIRarg would have increased our success rate by 40% and avoided 56% of unsuccessful isolations while missing only 8% of successful preparations. Our results suggest that donor AIRarg is markedly superior to body mass index (BMI) and other criteria currently used to predict isolation outcome. If routinely performed in deceased donors, this simple test could significantly reduce the failure rate of human islet isolation.

Transplant estimated function: a simple index to evaluate beta-cell secretion after islet transplantation

OBJECTIVE

The beta-score is a highly regarded approach to the assessment of transplant functionality. Our aim was to develop an index of beta-cell function that hinges on the pillars of the beta-score (daily insulin requirement and A1C), has a straightforward physiological interpretation, and does not require the execution of an insulin stimulation test.

RESEARCH DESIGN AND METHODS

The new index is denoted transplant estimated function (TEF) and is obtained from the daily insulin requirement and A1C. TEF estimates the amount of insulin secreted daily and can be normalized to the number of transplanted islets, thus permitting evaluation of the cost-effectiveness of the transplant. TEF was compared with the area under the curve of C-peptide [AUC(C-pep)] concentration over 24 h, as well as the acute insulin response to intravenous glucose (AIR(glu)) and to arginine (AIR(arg)). The association between TEF and beta-score was also investigated.

RESULTS

The correlation of TEF with 24-h AUC(C-pep) was r = 0.73 (P < 0.005), whereas that for beta-score versus 24-h AUC(C-pep) was r = 0.33 (NS). The correlation of TEF with AIR(glu) was r = 0.59 (P < 0.001) and close to that for beta-score versus AIR(glu) (r = 0.65, P < 0.001). The correlation of TEF with AIR(arg) was r = 0.33 (P < 0.005) and was similar to that for beta-score versus AIR(arg) (r = 0.34, P < 0.005). TEF and beta-score were correlated well (r = 0.69, P < 0.0001) and showed similar time profiles.

CONCLUSIONS

TEF estimates daily insulin secretion, it is simpler than the beta-score, and its performance against reference indexes of beta-cell secretion is in line with that exhibited by beta-score. TEF can be normalized to the number of transplanted islets and thereby provides a benchmarking tool to evaluate the cost-effectiveness of the transplant.

How the hindgut can cure type 2 diabetes. Ileal transposition improves glucose metabolism and beta-cell function in Goto-kakizaki rats through an enhanced Proglucagon gene expression and L-cell number

BACKGROUND

It has been hypothesized that glucagon-like peptide-1 (GLP-1), secreted by ileal L cells, plays a key-role in the resolution of type 2 diabetes after bariatric operations whose common feature is an expedite nutrient delivery to the hindgut. Ileal transposition (IT), an operation that permits L-cell stimulation by undigested food, was employed to verify this theory.

METHODS

IT was carried out in Goto-Kakizaki (GK) type 2 diabetic rats and in euglycemic Sprague-Dawley (SD) rats. Glucose tolerance, insulin resistance, food-intake, body weight, pancreas morphology, and function were evaluated to track the effects of IT on diabetes. Intact GLP-1 secretion and gene expression pattern of the transposed ileum were investigated to verify the molecular bases of the hindgut action.

RESULTS

In GK rats, IT significantly improved glucose tolerance, insulin sensitivity, and acute insulin response without affecting body weight and food intake. Immunohistochemistry revealed remodeled islets strictly resembling that of euglycemic rats and signs of beta-cell neogenesis starting with exocrine structures. GLP-1 secretion in GK transposed rats was characterized by a more sustained response to oral glucose compared with nontreated rats. Gene expression of Proglucagon, Proconvertase 1/3 (PC1/3), and Chromogranin A in the transposed ileum significantly enhanced. Effects on glucose metabolism and pancreas morphology were not observed in the euglycemic rats as a consequence of the glucose-dependent action of GLP-1.

CONCLUSIONS

This study gives strong evidences for the crucial role of the hindgut in the resolution of diabetes after Roux-en-Y gastric bypass (GBP) and biliopancreatic diversion (BPD). Moreover, these findings confirm at the preclinical level that IT is a surgical procedure of possible relevance in the therapy of type 2 diabetes in non-overweight and mildly obese patients.