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Human insulin (INS) gene diverged from the ancestral genes of invertebrate and mammalian species millions of years ago. We previously found that mouse insulin gene (Ins2) isoforms are expressed in brain choroid plexus (ChP) epithelium cells, where insulin secretion is regulated by serotonin and not by glucose. We further compared human INS isoform expression in postmortem ChP and islets of Langerhans. We uncovered novel INS upstream open reading frame isoforms and their protein products. In addition, we found a novel alternatively spliced isoform that translates to a 74-amino acid (AA) proinsulin containing a shorter 19-AA C-peptide sequence, herein designated Cα-peptide. The middle portion of the conventional C-peptide contains β-sheet (GQVEL) and hairpin (GGGPG) motifs that are not present in Cα-peptide. Islet amyloid polypeptide (IAPP) is not expressed in ChP, and its amyloid formation was inhibited in vitro more efficiently by Cα-peptide than by C-peptide. Of clinical relevance, the ratio of the 74-AA proinsulin to proconvertase-processed Cα-peptide was significantly increased in islets from type 2 diabetes mellitus autopsy donors. Intriguingly, 100 years after the discovery of insulin, we found that INS isoforms are present in ChP from insulin-deficient autopsy donors. [ABSTRACT FROM AUTHOR]

Whether individuals with insulin resistance (IR) but without criteria for diabetes exhibit reduced mitochondrial oxidative capacity is unclear; addressing this question could guide research for new therapeutics. We investigated 248 participants without diabetes from the Baltimore Longitudinal Study of Aging (BLSA) to determine whether impaired mitochondrial capacity is associated with prediabetes, IR, and duration and severity of hyperglycemia exposure. Mitochondrial capacity was assessed as the postexercise phosphocreatine recovery time constant (τPCr) by 31P-magnetic resonance spectroscopy, with higher τPCr values reflecting reduced capacity. Prediabetes was defined using the American Diabetes Association criteria from fasting and 2-h glucose measurements. IR and sensitivity were calculated using HOMA-IR and Matsuda indices. The duration and severity of hyperglycemia exposure were estimated as the number of years from prediabetes onset and the average oral glucose tolerance test (OGTT) 2-h glucose measurement over previous BLSA visits. Covariates included age, sex, body composition, physical activity, and other confounders. Higher likelihood of prediabetes, higher HOMA-IR, and lower Matsuda index were associated with longer τPCr. Among 205 participants with previous OGTT data, greater severity and longer duration of hyperglycemia were independently associated with longer τPC In conclusion, in individuals without diabetes a more impaired mitochondrial capacity is associated with greater IR and a higher likelihood of prediabetes. [ABSTRACT FROM AUTHOR]

The authors reflect on the U.S. Food and Drug Administration's (FDA) approval of glucagon-like peptide 1 (GLP-1) receptor agonists (exenatide) and dipeptidyl peptidase-4 (DPP4) inhibitors (sitagliptin) in 2005 and 2006, respectively. They discuss the relationship between incretin treatment and pancreatitis, and the drugs' link to pancreatitis and pancreatic cancer. They also mention a 2013 study which assessed pancreata from patients on incretin, patients on insulin, and nondiabetic patients.

Eating a "Westernized" diet high in fat and sugar leads to weight gain and numerous health problems, including the development of type 2 diabetes mellitus (T2DM). Rodent studies have shown that resveratrol supplementation reduces blood glucose levels, preserves β-cells in islets of Langerhans, and improves insulin action. Although rodent models are helpful for understanding β-cell biology and certain aspects of T2DM pathology, they fail to reproduce the complexity of the human disease as well as that of nonhuman primates. Rhesus monkeys were fed a standard diet (SD), or a high-fat/high-sugar diet in combination with either placebo (HFS) or resveratrol (HFS+Resv) for 24 months, and pancreata were examined before overt dysglycemia occurred. Increased glucose-stimulated insulin secretion and insulin resistance occurred in both HFS and HFS+Resv diets compared with SD. Although islet size was unaffected, there was a significant decrease in β-cell and an increase in α-cells containing glucagon and glucagon-like peptide 1 with HFS diets. Islets from HFS+Resv monkeys were morphologically similar to SD. HFS diets also resulted in decreased expression of essential β-cell transcription factors forkhead box O1 (FOXO1), NKX6-1, NKX2-2, and PDX1, which did not occur with resveratrol supplementation. Similar changes were observed in human islets where the effects of resveratrol were mediated through Sirtuin 1. These findings have implications for the management of humans with insulin resistance, prediabetes, and diabetes. [ABSTRACT FROM AUTHOR]

OBJECTIVE--Optimal glucose homeostasis requires exquisitely precise adaptation of the number of insulin-secreting β-cells in the islets of Langerhans. Insulin itself positively regulates β-cell proliferation in an autocrine manner through the insulin receptor (IR) signaling pathway. It is now coming to light that cannabinoid 1 receptor (CBIR) agonism/antagonism influences insulin action in insulin-sensitive tissues. However, the cells on which the CBIRs are expressed and their function in islets have not been firmly established. We undertook the current study to investigate if intraislet endogenous cannabinoids (ECs) regulate β-cell proliferation and if they influence insulin action. RESEARCH DESIGN AND METHODS--We measured EC production in isolated human and mouse islets and β-cell line in response to glucose and KC1. We evaluated human and mouse islets, several β-cell lines, and CB1R-null (CB1R-/-) mice for the presence of a fully functioning EC system. We investigated if ECs influence β-cell physiology through regulating insulin action and demonstrated the therapeutic potential of manipulation of the EC system in diabetic (db/db) mice. RESULTS--ECs are generated within β-cells, which also express CBIRs that are fully functioning when activated by ligands. Genetic and pharmacologic blockade of CBIR results in enhanced IR signaling through the insulin receptor substrate 2-AKT pathway in β-cells and leads to increased β-cell proliferation and mass. CBIR antagonism in db/db mice results in reduced blood glucose and increased β-cell proliferation and mass, coupled with enhanced IR signaling in β-cells. Furthermore, CBIR activation impedes insulin-stimulated IR autophosphorylation on β-cells in a Gαi-dependent manner. CONCLUSIONS--These findings provide direct evidence for a functional interaction between CB1R and IR signaling involved in the regulation of β-cell proliferation and will serve as a basis for developing new therapeutic interventions to enhance β-cell function and proliferation in diabetes. [ABSTRACT FROM AUTHOR]

OBJECTIVE--It is becoming apparent that there is a strong link between taste perception and energy homeostasis. Recent evidence implicates gut-related hormones in taste perception, including glucagon-like peptide 1 and vasoactive intestinal peptide (VIP). We used VIP knockout mice to investigate VIP's specific role in taste perception 'and connection to energy regulation. RESEARCH DESIGN AND METHODS--Body weight, food intake, and plasma levels of multiple energy-regulating hormones were measured and pancreatic morphology was determined. In addition, the immunocytochemical profile of taste cells and gustatory behavior were examined in wild-type and VIP knockout mice. RESULTS--VIP knockout mice demonstrate elevated plasma glucose, insulin, and leptin levels, with no islet β-cell number/ topography alteration. VIP and its receptors (VPAC1, VPAC2) were identified in type II taste cells of the taste bud, and VIP knockout mice exhibit enhanced taste preference to sweet tastants. VIP knockout mouse taste cells show a significant decrease in leptin receptor expression and elevated expression of glucagon-like peptide 1, which may explain sweet taste preference of VIP knockout mice. CONCLUSIONS--This study suggests that the tongue can play a direct role in modulating energy intake to correct peripheral glycemic imbalances. In this way, we could view the tongue as a sensory mechanism that is bidirectionally regulated and thus forms a bridge between available foodstuffs and the intricate hormonal balance in the animal itself. [ABSTRACT FROM AUTHOR]

Objective: Glucose-dependent insulinotropic polypeptide (GIP), unlike glucagon-like peptide (GLP)-1, lacks glucose-lowering properties in patients with type 2 diabetes. We designed this study to elucidate the underlying pathophysiology.Research Design and Methods: Twenty-two insulin-naïve subjects with type 2 diabetes were given either synthetic human GIP (20 ng x kg(-1) x min(-1)) or placebo (normal saline) over 180 min, starting with the first bite of a mixed meal (plus 1 g of acetaminophen) on two separate occasions. Frequent blood samples were obtained over 6 h to determine plasma GIP, GLP-1, glucose, insulin, glucagon, resistin, and acetaminophen levels.Results: Compared with placebo, GIP induced an early postprandial increase in insulin levels. Intriguingly, GIP also induced an early postprandial augmentation in glucagon, a significant elevation in late postprandial glucose, and a decrease in late postprandial GLP-1 levels. Resistin and acetaminophen levels were comparable in both interventions. By immunocytochemistry, GIP receptors were present on human and mouse alpha-cells. In alphaTC1 cell line, GIP induced an increase in intracellular cAMP and glucagon secretion. CONCLUSIONS; GIP, given to achieve supraphysiological plasma levels, still had an early, short-lived insulinotropic effect in type 2 diabetes. However, with a concomitant increase in glucagon, the glucose-lowering effect was lost. GIP infusion further worsened hyperglycemia postprandially, most likely through its suppressive effect on GLP-1. These findings make it unlikely that GIP or GIP receptor agonists will be useful in treating the hyperglycemia of patients with type 2 diabetes. [ABSTRACT FROM AUTHOR]

OBJECTIVE--Glucose-dependent insulinotropic polypeptide (GIP), unlike glucagon-like peptide (GLP)-1, lacks glucose-lowering properties in patients with type 2 diabetes. We designed this study to elucidate the underlying pathophysiology. RESEARCH DESIGN AND METHODS--Twenty-two insulin-naïve subjects with type 2 diabetes were given either synthetic human GIP (20 ng ⋅ kg-1 ⋅ min-1) or placebo (normal saline) over 180 min, starting with the first bite of a mixed meal (plus 1 g of acetaminophen) on two separate occasions. Frequent blood samples were obtained over 6 h to determine plasma GIP, GLP-1, glucose, insulin, glucagon, resistin, and acetaminophen levels. RESULTS--Compared with placebo, GIP induced an early postprandial increase in insulin levels. Intriguingly, GIP also induced an early postprandial augmentation in glucagon, a significant elevation in late postprandial glucose, and a decrease in late postprandial GLP-1 levels. Resistin and acetaminophen levels were comparable in both interventions. By immunocytochemistry, GIP receptors were present on human and mouse α-cells. In αTC1 cell line, GIP induced an increase in intracellular cAMP and glucagon secretion. CONCLUSIONS--GIP, given to achieve supraphysiological plasma levels, still had an early, short-lived insulinotropic effect in type 2 diabetes. However, with a concomitant increase in glucagon, the glucose-lowering effect was lost. GIP infusion further worsened hyperglycemia postprandially, most likely through its suppressive effect on GLP-1. These findings make it unlikely that GIP or GIP receptor agonists will be useful in treating the hyperglycemia of patients with type 2 diabetes. Diabetes 58:1342-1349, 2009 [ABSTRACT FROM AUTHOR]

OBJECTIVE--The aim of this study was to find an effective treatment for the genetic form of diabetes that is present in some Huntington's disease patients and in Huntington's disease mouse models. Huntington's disease is a neurodegenerative disorder caused by a polyglutamine expansion within the huntingtin protein. Huntington's disease patients exhibit neuronal dysfunction/degeneration, chorea, and progressive weight loss. Additionally, they suffer from abnormalities in energy metabolism affecting both the brain and periphery. Similarly to Huntington's disease patients, mice expressing the mutated human huntingtin protein also exhibit neurodegenerative changes, motor dysfunction, perturbed energy metabolism, and elevated blood glucose levels. RESEARCH DESIGN AND METHODS--Huntington's disease mice were treated with an FDA-approved antidiabetic glucagonlike peptide 1 receptor agonist, exendin-4 (Ex-4), to test whether euglycemia could be achieved, whether pancreatic dysfunction could be alleviated, and whether the mice showed any neurological benefit. Blood glucose and insulin levels and various appetite hormone concentrations were measured during the study. Additionally, motor performance and life span were quantified and mutant huntingtin (mhtt) aggregates were measured in both the pancreas and brain. RESULTS--Ex-4 treatment ameliorated abnormalities in peripheral glucose regulation and suppressed cellular pathology in both brain and pancreas in a mouse model of Huntington's disease. The treatment also improved motor function and extended the survival time of the Huntington's disease mice. These clinical improvements were correlated with reduced accumulation of mhtt protein aggregates in both islet and brain cells. CONCLUSIONS--Targeting both peripheral and neuronal deficits, Ex-4 is an attractive agent for therapeutic intervention in Huntington's disease patients suffering from diabetes. Diabetes 58:318-328, 2009 [ABSTRACT FROM AUTHOR]

OBJECTIVE -- To verify what information from oral glucose tolerance tests (OGTTs) independently predicts mortality. RESEARCH DESIGN AND METHODS -- A total of 1,401 initially nondiabetic participants from the Baltimore Longitudinal Study of Aging aged 17-95 years underwent one or more OGTTs (median 2, range 1-8), with insulin and glucose measurements taken every 20 min over the course of 2 h included in this study. Proportional hazards using the longitudinally collected data and Bayesian model averaging were used to examine the association of OGTT measurements individually and grouped with mortality, adjusting for covariates. RESULTS -- Participants were followed for a median 20.3 years (range 0.5-40). The first-hour OGTT glucose and insulin levels increased only modestly with age, whereas levels during the second hour increased 4% per decade. Individually, 100- and 120-min glucose measures and fasting and 100-min insulin levels were all independent predictors of mortality. When all measures were considered together, only higher 120-min glucose was a significant independent risk factor for mortality. CONCLUSION -- The steeper rise with age of the OGTT 2-h glucose values and the prognostic primacy of the 120-min glucose value for mortality is consistent with previous reports and suggests the value of using the OGTT in clinical practice. [ABSTRACT FROM AUTHOR]

Objective: The role of gut-derived incretin, glucose-dependent insulinotropic polypeptide (also known as gastric inhibitory peptide [GIP]), in compensatory beta-cell hypersecretion during insulin-resistant states and in transition to beta-cell failure in type 2 diabetes is unknown.Research Design and Methods: We carried out oral glucose tolerance testing followed by blood sampling 10 times for 2 h on 68 age- and BMI-matched participants of the Baltimore Longitudinal Study on Aging (BLSA) with normal glucose tolerance (34 subjects), impaired glucose tolerance (IGT) (18 subjects with both impaired fasting and 2-h plasma glucose levels), and type 2 diabetes (16 subjects with both diabetic fasting and 2-h plasma glucose levels). We assayed plasma glucose, insulin, C-peptide, glucagon, and intact and total GIP levels and quantitated glucose and hormone responses to the oral glucose tolerance test. We also compared GIP and insulin release and sensitivity indexes between groups.Results: After glucose ingestion, subjects with IGT had both hyperinsulinemia and hyperemia, while subjects with type 2 diabetes had both beta- and GIP-cell deficiency. In the former group, there was also a significant positive correlation between the augmented plasma intact and total GIP levels and both fasting and post-oral glucose load plasma insulin levels.Conclusions: Elevated plasma GIP levels are correlated with hyperinsulinemia in the impaired glucose-tolerant state, whereas type 2 diabetes is associated with a failure to secrete adequate amounts of both GIP and insulin, indicating a common pathway of resistance to and eventually failure of glucose responsiveness in beta- and GIP-cells. [ABSTRACT FROM AUTHOR]

OBJECTIVE — Glucagon-like peptide 1 (GLP-1) is an insulinotropic gut hormone that, when given exogenously, may be a useful agent in the treatment of type 2 diabetes. We conducted a 3-month trial to determine the efficacy and safety of GLP-1 in elderly diabetic patients. RESEARCH DESIGN AND METHODS — A total of 16 patients with type 2 diabetes who were being treated with oral hypoglycemic agents were enrolled. Eight patients (aged 75 ± 2 years, BM127 ± 1 kg/m²) remained on usual glucose-lowering therapy and eight patients (aged 73 ± 1 years, BMI 27 ± 1 kg/m²), after discontinuing hypoglycemic medications, received GLP-1 delivered by continuous subcutaneous infusion for 12 weeks. The maximum dose was 120 pmol · kg[sup -1] · h[sup -1]. Patients recorded their capillary blood glucose (CBG) levels (four times per day, 3 days per week) and whenever they perceived hypoglycemic symptoms. The primary end points were HbA[sub 1c] and CBG determinations. Additionally, changes in β-cell sensitivity to glucose, peripheral tissue sensitivity to insulin, and changes in plasma ghrelin levels were examined. RESULTS — HbA[sub 1c] levels (7.1%) and body weight were equally maintained in both groups. The usual treatment group had a total of 87 CBG measurements of ≤3.6 mmol/l during the study, and only 1 such measurement (3.5 mmol/l) was recorded in the GLP-1 group. Infusion of GLP-1 enhanced glucose-induced insulin secretion (pre: 119 ± 21; post: 202 ± 51 pmol/l; P < 0.05) and insulin-mediated glucose disposal (pre: 29.8 ± 3.3; post: 35.9 ± 2.3 µmol · kg[sup -1] · min[sup -1]; P < 0.01). No effect of GLP-1 treatment was seen on the fasting plasma ghrelin levels. Although plasma ghrelin levels decreased during both portions of the clamp, a drug effect was not present. CONCLUSIONS — A GLP-1 compound is a promising therapeutic option for elderly diabetic patients. [ABSTRACT FROM AUTHOR]

Objective: The purpose of this study was to determine the relationships between plasma adiponectin and leptin levels, total and central obesity, and glucose utilization across the adult age span.Research Design and Methods: We studied 148 women aged 18-81 years with a BMI range of 17.2-44.3 kg/m(2). Total percent body fat was determined by dual-energy X-ray absorptiometry and abdominal fat by computed tomography. Glucose tolerance in non-type 2 diabetic volunteers was determined with an oral glucose tolerance test. Glucose utilization (M) was measured during the last 60 min of hyperinsulinemic-euglycemic clamps (240 pmol x m(-2) x min(-1)). Plasma adiponectin levels were measured by radioimmunoassay. The women were separated into three age-groups: young, middle, and old (<40, 40-59, and >or=60 years, respectively), as well as by glucose tolerance status.Results: Adiponectin concentrations did not differ by age-groups. There were significant age effects for BMI, percent body fat, visceral fat, subcutaneous abdominal fat, VO(2max), and M. Adiponectin levels were lower in the prediabetic women (n = 18) than in the normal glucose-tolerant women (n = 108) and the women with type 2 diabetes (n = 22) (both P < 0.05). Univariate correlations revealed significant negative relationships between plasma adiponectin levels and BMI, percent body fat, visceral fat, subcutaneous abdominal fat, fasting leptin, and fasting insulin and positive relationship with M (all P < 0.05). In a multiple stepwise regression model to predict adiponectin, only M remained in the model at P < 0.001. Multivariate analyses revealed a significant relation for M as a function of adiponectin, insulin, and VO(2max).Conclusions: The data suggest that plasma adiponectin does not change with age but levels are negatively associated with percent body fat, visceral fat, subcutaneous abdominal fat, insulin, and leptin levels in women. Adiponectin is positively associated with M across the age span in women. [ABSTRACT FROM AUTHOR]

Objective: To examine the insulinomimetic insulin-independent effects of glucagon-like peptide (GLP)-1 on glucose uptake in type 1 diabetic patients.Research Design and Methods: We used the hyperinsulinemic-euglycemic clamp (480 pmol. m(-2) x min(-1)) in paired randomized studies of six women and five men with type 1 diabetes. In the course of one of the paired studies, the subjects also received GLP-1 at a dose of 1.5 pmol. kg(-1) x min(-1). The patients were 41 +/- 3 years old with a BMI of 25 +/- 1 kg/m(2). The mean duration of diabetes was 23 +/- 3 years.Results: Plasma glucose was allowed to fall from a fasting level of approximately 11 mmol/l to 5.3 mmol/l in each study and thereafter was held stable at that level. Plasma insulin levels during both studies were approximately 900 pmol/l. Plasma C-peptide levels did not change during the studies. In the GLP-1 study, plasma total GLP-1 levels were elevated from the fasting level of 31 +/- 3 to 150 +/- 17 pmol/l. Plasma glucagon levels fell from the fasting levels of approximately 14 pmol/l to 9 pmol/l during both paired studies. Hepatic glucose production was suppressed during the glucose clamps in all studies. Glucose uptake was not different between the two studies ( approximately 40 micromol. kg(-1) x min(-1)).Conclusions: GLP-1 does not augment insulin-mediated glucose uptake in lean type 1 diabetic patients. [ABSTRACT FROM AUTHOR]

An important cause of elevated glucose levels in elderly patients with diabetes is an alteration in non-insulin-mediated glucose uptake (NIMGU). Glucagon-like peptide 1 (GLP-1) is an intestinal insulinotropic hormone. It has been proposed that this hormone also lowers glucose levels by enhancing NIMGU. This study was conducted to determine whether GLP-1 augments NIMGU in elderly patients with diabetes, a group in which NIMGU is known to be impaired. Studies were conducted on 10 elderly patients with type 2 diabetes (aged 75 +/- 2 years, BMI 27 +/- 1 kg/m(2)) who underwent paired 240-min glucose clamp studies. In each study, octreotide was infused to suppress endogenous insulin release, and tritiated glucose methodology was used to measure glucose production and disposal rates. For the first 180 min, no glucose was infused. From 180 to 240 min, glucose was increased to 11 mmol/l using the glucose clamp protocol. In the GLP-1 study, GLP-1 was infused from 30 to 240 min. In a subsequent control study, insulin was infused using the glucose clamp protocol from 30 to 240 min to match the insulin levels that occurred during the GLP-1 infusion study. During hyperglycemia, GLP-1 enhanced glucose disposal (control study: 2.52 +/- 0.19 mg x kg(-1) x min(-1); GLP-1 study: 2.90 +/- 0.17 mg x kg(-1) x min(-1); P < 0.0001). Hepatic glucose output was not different between studies. We conclude that GLP-1 may partially reverse the defect in NIMGU that occurs in elderly patients with diabetes. [ABSTRACT FROM AUTHOR]

Diabetes resulting from heterozygosity for an inactivating mutation of the homeodomain transcription factor insulin promoter factor 1 (IPF-1) is due to a genetic defect of beta-cell function referred to as maturity-onset diabetes of the young 4. IPF-1 is required for the development of the pancreas and mediates glucose-responsive stimulation of insulin gene transcription. To quantitate islet cell responses in a family harboring a Pro63fsdelC mutation in IPF-1, we performed a five-step (1-h intervals) hyperglycemic clamp on seven heterozygous members (NM) and eight normal genotype members (NN). During the last 30 min of the fifth glucose step, glucagon-like peptide 1 (GLP-1) was also infused (1.5 pmol x kg(-1) x min(-1)). Fasting plasma glucose levels were greater in the NM group than in the NN group (9.2 vs. 5.9 mmol/l, respectively; P < 0.05). Fasting insulin levels were similar in both groups (72 vs. 105 pmol/l for NN vs. NM, respectively). First-phase insulin and C-peptide responses were absent in individuals in the NM group, who had markedly attenuated insulin responses to glucose alone compared with the NN group. At a glucose level of 16.8 mmol/l above fasting level, GLP-1 augmented insulin secretion equivalently (fold increase) in both groups, but the insulin and C-peptide responses to GLP-1 were sevenfold less in the NM subjects than in the NN subjects. In both groups, glucagon levels fell during each glycemic plateau, and a further reduction occurred during the GLP-1 infusion. Sigmoidal dose-response curves of glucose clearance versus insulin levels during the hyperglycemic clamp in the two small groups showed both a left shift and a lower maximal response in the NM group compared with the NN group, which is consistent with an increased insulin sensitivity in the NM subjects. A sharp decline occurred in the dose-response curve for suppression of nonesterified fatty acids versus insulin levels in the NM group. We conclude that the Pro63fsdelC IPF-1 mutation is associated with a severe impairment of beta-cell sensitivity to glucose and an apparent increase in peripheral tissue sensitivity to insulin and is a genetically determined cause of beta-cell dysfunction. [ABSTRACT FROM AUTHOR]

Diabetes is caused by a failure of the pancreas to produce insulin in amounts sufficient to meet the body's needs. A hallmark of diabetes is an absolute (type 1) or relative (type 2) reduction in the mass of pancreatic beta-cells that produce insulin. Mature beta-cells have a lifespan of approximately 48-56 days (rat) and are replaced by the replication of preexisting beta-cells and by the differentiation and proliferation of new beta-cells (neogenesis) derived from the pancreatic ducts. Here, we show that the insulinotropic hormone glucagon-like peptide (GLP)-1, which is produced by the intestine, enhances the pancreatic expression of the homeodomain transcription factor IDX-1 that is critical for pancreas development and the transcriptional regulation of the insulin gene. Concomitantly, GLP-1 administered to diabetic mice stimulates insulin secretion and effectively lowers their blood sugar levels. GLP-1 also enhances beta-cell neogenesis and islet size. Thus, in addition to stimulating insulin secretion, GLP-1 stimulates the expression of the transcription factor IDX-1 while stimulating beta-cell neogenesis and may thereby be an effective treatment for diabetes. [ABSTRACT FROM AUTHOR]

The choroid plexus (CP) produces cerebrospinal fluid (CSF) and forms a blood-CSF barrier. We already reported that mouse CP epithelial (CPE) cells synthesize and secrete insulin in response to serotonin but not glucose. We now report that insulin expression is present in human postmortem CP samples of humans - nondiabetic, T2DM, and T1DM - by RT-qPCR, in situ hybridization and LC-MS/MS based Selected Reaction Monitoring assay. Human CPE contains all the INS splicing machinery and the major INS splicing variants that are present in islets. Known β-cell specific transcription factors are also expressed in CPE, except for PDX1 and PAX4, which are absent. The SRM assay detected INS A-chain, B-chain, and C-peptide at similar levels in nondiabetic, T2DM, and T1DM islets and CP postmortem samples. Islet amyloid polypeptide (IAPP) expression was not detected in CPE in contrast to human islets where INS and IAPP mRNA, as expected, colocalize in β-cells. Furthermore, INS colocalizes with transthyretin (TTR) mRNA in CPE cells but in islets, TTR is expressed in α-cells and not β-cells. We found less or no expression of T1DM autoantigens in CPE compared to β-cells, with the exception of ICA1 (islet cell autoantigen1), which has similar expression in both tissues. In conclusion, human CPE expresses and synthesizes insulin, it is protected from autoimmune destruction and from IAPP amyloidogenic fibril formation. Disclosure: Q. Liu: None. M. Zhu: None. C. Mazucanti: None. S. Marenco: None. J. M. Egan: None. Funding: National Institute on Aging [ABSTRACT FROM AUTHOR]

Investigates whether glucagon-like peptide 1 (GLP-1) and exendin-4 convert pancreatic AR42J cells into glucagon- and insulin-producing cells. Effects of GLP-1 and exendin-4 on islet hormone expression; Change in amylase concentration upon incubation of AR42J cells with dexamethasone; Influence of GLP-1 on amylase release from dexamethasone-treated cells.

Objective: Optimal glucose homeostasis requires exquisitely precise adaptation of the number of insulin-secreting \(\beta\)-cells in the islets of Langerhans. Insulin itself positively regulates \(\beta\)-cell proliferation in an autocrine manner through the insulin receptor (IR) signaling pathway. It is now coming to light that cannabinoid 1 receptor (CB1R) agonism/antagonism influences insulin action in insulin-sensitive tissues. However, the cells on which the CB1Rs are expressed and their function in islets have not been firmly established. We undertook the current study to investigate if intraislet endogenous cannabinoids (ECs) regulate \(\beta\)-cell proliferation and if they influence insulin action. Research Design and Methods: We measured EC production in isolated human and mouse islets and \(\beta\)-cell line in response to glucose and KCl. We evaluated human and mouse islets, several \(\beta\)-cell lines, and CB1R-null (CB1R\(^{−/−}\)) mice for the presence of a fully functioning EC system. We investigated if ECs influence \(\beta\)-cell physiology through regulating insulin action and demonstrated the therapeutic potential of manipulation of the EC system in diabetic (db/db) mice. Results: ECs are generated within \(\beta\)-cells, which also express CB1Rs that are fully functioning when activated by ligands. Genetic and pharmacologic blockade of CB1R results in enhanced IR signaling through the insulin receptor substrate 2-AKT pathway in \(\beta\)-cells and leads to increased \(\beta\)-cell proliferation and mass. CB1R antagonism in db/db mice results in reduced blood glucose and increased \(\beta\)-cell proliferation and mass, coupled with enhanced IR signaling in \(\beta\)-cells. Furthermore, CB1R activation impedes insulin-stimulated IR autophosphorylation on \(\beta\)-cells in a G\(\alpha_i\)-dependent manner. Conclusions: These findings provide direct evidence for a functional interaction between CB1R and IR signaling involved in the regulation of \(\beta\)-cell proliferation and will serve as a basis for developing new therapeutic interventions to enhance \(\beta\)-cell function and proliferation in diabetes.

Circulating insulin levels are routinely measured using Enzyme-linked Immunosorbent Assay (ELISA). However, ELISA is not sensitive enough to measure cerebrospinal fluid (CSF) insulin levels which are 10-100 times lower than those of plasma: yet ELISA results are often reported for insulin analysis in CSF where it serves as a surrogate for brain interstitial fluid insulin levels. We developed a novel LC-MS/MS based selected reaction monitoring (SRM) proteomics assay for quantitative analyses targeting predetermined peptides derived from trypsin digests of insulin; each peptide depends on specific SRM transitions. We determined insulin levels using our novel insulin SRM proteomics method in the matching plasma and CSF samples that were from individuals fasting ≥12 hours and individuals after 2 hours of steady state hyperglycemia by clamp technology (2 hr SS HG). All samples were obtained in individuals with normal fasting glucose and HbA1C levels. Statistically significant differences were observed in both plasma and CSF between fasting and 2 hr SS HG by two tailed and unpaired student t test and 2-way matched ANOVA as shown in Table below. Our results confirmed that peripheral endogenous insulin appears in CSF at least 2 hours after steady state hyperglycemia in subjects with normal glucose tolerance. Our SRM insulin tryptic peptide panel reliably quantified insulin peptide levels in human CSF samples. Disclosure: Q. Liu: None. M. Zhu: None. C.W. Chia: None. J.F. O'Connell: None. P. Zhang: None. J.M. Egan: None. Funding: National Institute on Aging [ABSTRACT FROM AUTHOR]

Approximately 1.25 million Americans have type 1 diabetes mellitus (T1DM), resulting from autoimmune β-cell destruction: there is no known way to prevent such destruction of β-cells. We have already reported that activation of cannabinoid 1 receptor (CB1R) contributes to the pathogenesis of pancreatic β-cell dysfunction during high fat feeding. To uncover if CB1R signaling might influence toxin-induced β-cell injury, we induced β-cell destruction in wild type mice (WT: n=8) and in mice in which CB1R was genetically nullified in β-cells only (β-CB1R-/-: n=8) in adulthood by five daily injections of streptozotocin (STZ; 50 mg/kg intraperitoneally [IP]), a toxin selective for β-cells. We found that β-CB1R-/- mice had random blood glucose (BG) levels in the range of 137-220 mg/dL throughout the study period (28 days following STZ) as well as preserved insulin secretion with superior glucose tolerance after a glucose challenge (2g/kg) at day 8, 15 or 27, relative to their WT littermates (random BG 500-600 mg/dL). CB1R-deficient β-cells exhibited significant increases in autophagy flux following STZ. We determined that mice or β-cells lacking CB1R had reduced mTOR activation and increased nuclear translocation of TFEB, a key prerequisite for lysosome biogenesis and autophagy. Importantly, we found that CB1R deletion protected against oxidative stress, endoplasmic reticulum stress, and prevented the induction of apoptosis by STZ. These anti-stress functions were accompanied by increased phosphorylation of AKT (ser) 473 and ERK1/2 in β-cells, which reveals a previously unrecognized route for mTOR/AKT axis to regulate autophagy that coordinately is permissive to β-cell survival. We conclude that CB1R nullification confers resistance to pancreatic β-cell dysfunction by upregulating autophagy and subsequently antagonizing the decline in lysosomal activity. Altogether, we propose that CB1R is a potential therapeutic target during the honeymoon phase of T1DM. Disclosure: K. Aseer: None. J.F. O'Connell: None. J.M. Egan: None. [ABSTRACT FROM AUTHOR]

Approximately 1.25 million Americans have type 1 diabetes mellitus (T1DM), resulting from β-cell destruction. There is no known way to prevent it or to stop destruction of any remaining β-cells. Although the cannabinoid system, specifically cannabinoid 1 receptor (CB1R), is implicated in obesity and T2DM, its role, if any, in T1DM has not been studied. To address this, we induced β-cell destruction in wild type mice (WT: n=8) and mice in which CB1R was genetically nullified in β-cells only (β-CB1R-/-: n=8) in adulthood by five injections of streptozotocin (50 mg/kg intraperitoneally [IP]), a toxin selective for β-cells. We found that β-CB1R-/- mice had random blood glucose (BG) levels in the range of 137-289 mg/dL throughout the study period (28 days) as well as preserved insulin secretion with superior glucose tolerance after IP glucose (2g/kg) at day 8, 15 or 27, relative to their (random BG 500-600 mg/dL) WT littermates. CB1R knockout drove significant increases in pancreatic islet autophagic activity based on increased accumulation of autophagosome hallmarks (LC3B, Beclin-1, ATG5 and ATG7) and reduced p62 expression. Insulin and LC3B were colocalized in CB1R-deficient β-cells. Remarkably, the islets did not show the upregulation of ER unfolded protein response, which was present in β-cells of WT mice, while exerting the induction of protective chaperones. These anti-stress functions were accompanied by increased phosphorylation of AKT (ser) 473 and ERK in β-cells, which reveals a previously unrecognized route for PI3K-AKT pathway to activate the anti-apoptotic NFkB/p65 signaling that coordinately is permissive to β-cell survival. We conclude that CB1R nullification restores autophagy machinery as a novel signaling pathway to counteract ER stress-mediated cell death and confers resistance to β-cell destruction. We propose that CB1R is a potential therapeutic target during the honeymoon phase of T1DM. Disclosure: K. Aseer: None. J.M. Egan: None. [ABSTRACT FROM AUTHOR]

Cannabinoid 1 receptors (CB1Rs) are G protein-coupled receptors that are present in peripheral organs such as liver, pancreas, adipose tissue and skeletal muscle where they are involved in fine-tuning many metabolic functions. It was previously reported that liver-specific genetic deletion of CB1R (hCNR1-/-) mice fed high fat diets (HFD) had similar body weight to HFD-fed hCNR1+/+ mice, but they retained insulin sensitivity comparable to normal chow-fed (NCD) hCNR1+/+ mice. Therefore, this study was undertaken to uncover how hCB1Rs impact the insulin signaling pathway. Male hCNR1-/- and hCNR1+/+ mice were fed with a high fat high sugar diet (HFSD: N = 8-12) for 15 weeks. In contrast with the previous study of HFD only, HFSD-fed hCNR1-/- mice had less body weight gain than HFSD-fed hCNR1+/+ mice (25.1±2.7 vs. 19.8±1.7g), less fat accumulation in the liver, 1.3-fold increase in glucose disposal and 1.7-fold increase in insulin sensitivity compared to HFSD-fed hCNR1+/+ mice. Further study demonstrated that the lack of hepatic CB1R resulted in upregulated phosphorylation in liver of protein kinase B (AKT), causing activation of downstream target molecules, such as proline-rich AKT substrate 40 (PRAS40) in the mammalian target of rapamycin complex 1 (mTORC1). Similarly, primary hepatocytes isolated from hCNR1-/- mice had increased amounts of phosphorylated AKT and PRAS40 in comparison to hepatocytes from hCNR1+/+ mice. The co-immunoprecipitation studies clearly revealed hepatic CB1R modulates insulin signaling by the association or dissociation of the components of mTORC1. In support of these data, the deficiency of hepatic CB1R leads to upregulation of phosphoinositide 3-kinase (PI3K) class IB, p110γ, resulting in increased association between p110γ and G-protein beta. These findings indicate that genetic deletion of hepatic CB1R contributes to improved glucose homeostasis. Therefore, modulation of CB1R activity in liver may be a useful therapeutic in obese and diabetic individuals. Disclosure: Y. Kim: None. J.M. Egan: None. [ABSTRACT FROM AUTHOR]

Deals with a study which determined whether the effects of glucagon-like peptide-1 on glucose-induced insulin release are preserved in elderly patients with diabetes. Subjects; Procedures of the study; Significance.

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin secreted from the enteroendocrine K-cells in response to food. Unlike the other incretin, glucagon-like peptide-1 (GLP-1), GIP is reported to have lost its insulinotropic effect and not have glucose-lowering properties in patients with type 2 diabetes mellitus (T2DM). We attempted to gain insight into the pathophysiology underlying the seeming lack of effects of GIP on glucose homeostasis in T2DM. We therefore administered synthetic human GIP (with a meal) to subjects who had T2DM, and then, for 6hr, took frequent blood samples to measure various factors known to be involved in glucose homeostasis. 22 insulin-naive subjects with T2DM (ages 52.6±9.3years; BMI 36.7±7.3kg/m²; HbA[sub 1c] 7.4±1.5%; fasting plasma glucose 155±46mg/dl; diabetes duration 4.3±4.2years; f/m ratio 13/9) that had been treated with diet alone, metformin and/or sulfonylurea were recruited. They stopped oral hypoglycemic medications for 5 days prior to testing and fasted for 8hr prior to 2 study visits, each visit separated by not less than 6 weeks. After 3 baseline blood draws, the subjects received continuous intravenous administration of either placebo (0.9%NaCl) or GIP (20ng/kg/min) for 180min starting with the first bite of a 550calorie mixed-meal, and 1g of acetaminophen to study gastric emptying. Frequent blood sampling took place over the subsequent 6hr (every 5min for the first 75min then every 15min until 180min and every 20min until 360min). Compared to placebo, GIP induced an increase in plasma insulin from 5-30min but a transient decrease in plasma glucose at the 10min time-point only (p<0.05). Intriguingly, and hitherto undescribed, GIP induced a later augmentation in glucagon secretion with a peak level at approximately 30min (p<0.05), a significant elevation in plasma glucose from 120-220min (p<0.05) and a decrease in GLP-I secretion at 135min that lasted for the remainder of the 6hr study period (p<0.05). Based on plasma acetaminophen levels, GIP did not affect gastric emptying and NEFAs were similar during both studies. In T2DM therefore, GIP, given at a pharmacological dose with a meal, still has an early, short-lived insulinotropic effect, resulting in a transient, clinically irrelevant plasma glucose drop. However, this was subsequently followed by increased plasma glucagon levels and worsening hyperglycemia. These findings make it unlikely that GIP or GIP receptor agonists will ever be useful as glucose-lowering agents. [ABSTRACT FROM AUTHOR]

Objective: Optimal glucose homeostasis requires exquisitely precise adaptation of the number of insulin-secreting β-cells in the islets of Langerhans. Insulin itself positively regulates β-cell proliferation in an autocrine manner through the insulin receptor (IR) signaling pathway. It is now coming to light that cannabinoid 1 receptor (CB1R) agonism/antagonism influences insulin action in insulin-sensitive tissues. However, the cells on which the CB1Rs are expressed and their function in islets have not been firmly established. We undertook the current study to investigate if intraislet endogenous cannabinoids (ECs) regulate β-cell proliferation and if they influence insulin action., Research Design and Methods: We measured EC production in isolated human and mouse islets and β-cell line in response to glucose and KCl. We evaluated human and mouse islets, several β-cell lines, and CB1R-null (CB1R(-/-)) mice for the presence of a fully functioning EC system. We investigated if ECs influence β-cell physiology through regulating insulin action and demonstrated the therapeutic potential of manipulation of the EC system in diabetic (db/db) mice., Results: ECs are generated within β-cells, which also express CB1Rs that are fully functioning when activated by ligands. Genetic and pharmacologic blockade of CB1R results in enhanced IR signaling through the insulin receptor substrate 2-AKT pathway in β-cells and leads to increased β-cell proliferation and mass. CB1R antagonism in db/db mice results in reduced blood glucose and increased β-cell proliferation and mass, coupled with enhanced IR signaling in β-cells. Furthermore, CB1R activation impedes insulin-stimulated IR autophosphorylation on β-cells in a Gα(i)-dependent manner., Conclusions: These findings provide direct evidence for a functional interaction between CB1R and IR signaling involved in the regulation of β-cell proliferation and will serve as a basis for developing new therapeutic interventions to enhance β-cell function and proliferation in diabetes.

Objective: Glycated hemoglobin (HbA₁(c)), used to monitor and diagnose diabetes, is influenced by average glycemia over a 2- to 3-month period. Genetic factors affecting expression, turnover, and abnormal glycation of hemoglobin could also be associated with increased levels of HbA₁(c). We aimed to identify such genetic factors and investigate the extent to which they influence diabetes classification based on HbA₁(c) levels., Research Design and Methods: We studied associations with HbA₁(c) in up to 46,368 nondiabetic adults of European descent from 23 genome-wide association studies (GWAS) and 8 cohorts with de novo genotyped single nucleotide polymorphisms (SNPs). We combined studies using inverse-variance meta-analysis and tested mediation by glycemia using conditional analyses. We estimated the global effect of HbA₁(c) loci using a multilocus risk score, and used net reclassification to estimate genetic effects on diabetes screening., Results: Ten loci reached genome-wide significant association with HbA(1c), including six new loci near FN3K (lead SNP/P value, rs1046896/P = 1.6 × 10⁻²⁶), HFE (rs1800562/P = 2.6 × 10⁻²⁰), TMPRSS6 (rs855791/P = 2.7 × 10⁻¹⁴), ANK1 (rs4737009/P = 6.1 × 10⁻¹²), SPTA1 (rs2779116/P = 2.8 × 10⁻⁹) and ATP11A/TUBGCP3 (rs7998202/P = 5.2 × 10⁻⁹), and four known HbA₁(c) loci: HK1 (rs16926246/P = 3.1 × 10⁻⁵⁴), MTNR1B (rs1387153/P = 4.0 × 10⁻¹¹), GCK (rs1799884/P = 1.5 × 10⁻²⁰) and G6PC2/ABCB11 (rs552976/P = 8.2 × 10⁻¹⁸). We show that associations with HbA₁(c) are partly a function of hyperglycemia associated with 3 of the 10 loci (GCK, G6PC2 and MTNR1B). The seven nonglycemic loci accounted for a 0.19 (% HbA₁(c)) difference between the extreme 10% tails of the risk score, and would reclassify ∼2% of a general white population screened for diabetes with HbA₁(c)., Conclusions: GWAS identified 10 genetic loci reproducibly associated with HbA₁(c). Six are novel and seven map to loci where rarer variants cause hereditary anemias and iron storage disorders. Common variants at these loci likely influence HbA₁(c) levels via erythrocyte biology, and confer a small but detectable reclassification of diabetes diagnosis by HbA₁(c).