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  • Dynamic modulation of prohormone convertase 2 (PC2)-mediated precursor processing by 7B2 protein: preferential effect on glucagon synthesis. 22013069

    The small neuroendocrine protein 7B2 is required for the production of active prohormone convertase 2 (PC2), an enzyme involved in the synthesis of peptide hormones, such as glucagon and proopiomelanocortin-derived ?-melanocyte-stimulating hormone. However, whether 7B2 can dynamically modulate peptide production through regulation of PC2 activity remains unclear. Infection of the pancreatic alpha cell line ?-TC6 with 7B2-encoding adenovirus efficiently increased production of glucagon, whereas siRNA-mediated knockdown of 7B2 significantly decreased stored glucagon. Furthermore, rescue of 7B2 expression in primary pituitary cultures prepared from 7B2 null mice restored melanocyte-stimulating hormone production, substantiating the role of 7B2 as a regulatory factor in peptide biosynthesis. In anterior pituitary and pancreatic beta cell lines, however, overexpression of 7B2 affected neither production nor secretion of peptides despite increased release of active PC2. In direct contrast, 7B2 overexpression decreased the secretion and increased the activity of PC2 within ?-TC6 cells; the increased intracellular concentration of active PC2 within these cells may therefore account for the enhanced production of glucagon. In line with these findings, we found elevated circulating glucagon levels in 7B2-overexpressing cast/cast mice in vivo. Surprisingly, when proopiomelanocortin and proglucagon were co-expressed in either pituitary or pancreatic alpha cell lines, proglucagon processing was preferentially decreased when 7B2 was knocked down. Taken together, these results suggest that proglucagon cleavage has a greater dependence on PC2 activity than other precursors and moreover that 7B2-dependent routing of PC2 to secretory granules is cell line-specific. The manipulation of 7B2 could therefore represent an effective way to selectively regulate synthesis of certain PC2-dependent peptides.
    Document Type:
    Reference
    Product Catalog Number:
    GL-32K
    Product Catalog Name:
    Glucagon RIA

  • Elevated glucagon-like peptide-1-(7-36)-amide, but not glucose, associated with hyperinsulinemic compensation for fat feeding. 12414891

    We previously developed a canine model of central obesity and insulin resistance by supplementing the normal chow diet with 2 g cooked bacon grease/kg body weight. Dogs fed this fatty diet maintained glucose tolerance with compensatory hyperinsulinemia. The signal(s) responsible for this up-regulation of plasma insulin is unknown. We hypothesized that meal-derived factors such as glucose, fatty acids, or incretin hormones may signal beta-cell compensation in the fat-fed dog. We fed the same fat-supplemented diet for 12 wk to six dogs and compared metabolic responses with seven control dogs fed a normal diet. Fasting and stimulated fatty acid and glucose-dependent insulinotropic peptide concentrations were not increased by fat feeding, whereas glucose was paradoxically decreased, ruling out those three factors as signals for compensatory hyperinsulinemia. Fasting plasma glucagon-like peptide-1 (GLP-1) concentration was 2.5-fold higher in the fat-fed animals, compared with controls, and 3.4-fold higher after a mixed meal. Additionally, expression of the GLP-1 receptor in whole pancreas was increased 2.3-fold in the fat-fed dogs. The increase in both circulating GLP-1 and its target receptor may have increased beta-cell responsiveness to lower glucose. Glucose is not the primary cause of hyperinsulinemia in the fat-fed dog. Corequisite meal-related signals may be permissive for development of hyperinsulinemia.
    Document Type:
    Reference
    Product Catalog Number:
    Multiple
    Product Catalog Name:
    Multiple

  • Islet autoimmunity status in Asians with young-onset diabetes (12-40 years): association with clinical characteristics, beta cell function and cardio-metabolic risk facto ... 18207602

    In this paper, the islet autoimmunity status and relation to clinical characteristics, beta cell function and cardio-metabolic risk factors in young-onset Asian diabetic patients are evaluated at baseline. The study population consisted of 912 patients (from China, India, Malaysia and Singapore) with age 12-40 years and diabetes duration <12 months. Autoantibodies to glutamic acid decarboxylase (GADA) and tyrosine phosphatase (IA-2A), beta cell function and cardio-metabolic risk parameters were assessed. Among our young patient cohort, 105 (11.5%) patients were GADA and/or IA-2A positives (Ab +ve). Ab +ve patients were younger, leaner, had more severe hyperglycaemia and lower beta cell function. The frequency of metabolic syndrome was significantly lower in Ab +ve patients (27%) compared to Ab -ve patients (54%). However, a substantial proportion of patients in both groups of patients had atherogenic dyslipidaemia, hypertension and albuminuria (micro or macro). In our study cohort, only one in 10 Asian youth with new-onset diabetes had evidence of islet autoimmunity. At least 60% of Ab +ve and 50% of Ab -ve patients demonstrated classical features of type 1 and type 2 diabetes respectively. Regardless of autoimmunity status, the cardio-metabolic risk factors, in particular atherogenic dyslipidaemia, hypertension and albuminuria were common in our patients with young-onset diabetes.
    Document Type:
    Reference
    Product Catalog Number:
    HCP-20K
    Product Catalog Name:
    Human C-Peptide RIA

  • Phentolamine inhibits exocytosis of glucagon by Gi2 protein-dependent activation of calcineurin in rat pancreatic alpha -cells. 10995774

    Capacitance measurements were used to investigate the molecular mechanisms by which imidazoline compounds inhibit glucagon release in rat pancreatic alpha-cells. The imidazoline compound phentolamine reversibly decreased depolarization-evoked exocytosis >80% without affecting the whole-cell Ca(2+) current. During intracellular application through the recording pipette, phentolamine produced a concentration-dependent decrease in the rate of exocytosis (IC(50) = 9.7 microm). Another imidazoline compound, RX871024, exhibited similar effects on exocytosis (IC(50) = 13 microm). These actions were dependent on activation of pertussis toxin-sensitive G(i2) proteins but were not associated with stimulation of ATP-sensitive K(+) channels or adenylate cyclase activity. The inhibitory effect of phentolamine on exocytosis resulted from activation of the protein phosphatase calcineurin and was abolished by cyclosporin A and deltamethrin. Exocytosis was not affected by intracellular application of specific alpha(2), I(1), and I(2) ligands. Phentolamine reduced glucagon release (IC(50) = 1.2 microm) from intact islets by 40%, an effect abolished by pertussis toxin, cyclosporin A, and deltamethrin. These data suggest that imidazoline compounds inhibit glucagon secretion via G(i2)-dependent activation of calcineurin in the pancreatic alpha-cell. The imidazoline binding site is likely to be localized intracellularly and probably closely associated with the secretory granules.
    Document Type:
    Reference
    Product Catalog Number:
    GL-32K
    Product Catalog Name:
    Glucagon RIA

  • Compensation for obesity-induced insulin resistance in dogs: assessment of the effects of leptin, adiponectin, and glucagon-like peptide-1 using path analysis. 21474268

    The hormonal mediators of obesity-induced insulin resistance and compensatory hyperinsulinemia in dogs have not been identified. Plasma samples were obtained after a 24-h fast from 104 client-owned lean, overweight, and obese dogs. Plasma glucose and insulin concentrations were used to calculate insulin sensitivity and β-cell function with the use of the homeostasis model assessment (HOMA(insulin sensitivity) and HOMA(β-cell function), respectively). Path analysis with multivariable linear regression was used to identify whether fasting plasma leptin, adiponectin, or glucagon-like peptide-1 concentrations were associated with adiposity, insulin sensitivity, and basal insulin secretion. None of the dogs were hyperglycemic. In the final path model, adiposity was positively associated with leptin (P < 0.01) and glucagon-like peptide-1 (P = 0.04) concentrations. No significant total effect of adiposity on adiponectin in dogs (P = 0.24) was observed. If there is a direct effect of leptin on adiponectin, then our results indicate that this is a positive relationship, which at least partly counters a negative direct relationship between adiposity and adiponectin. Fasting plasma leptin concentration was directly negatively associated with fasting insulin sensitivity (P = 0.01) and positively associated with β-cell function (P < 0.01), but no direct association was observed between adiponectin concentration and either insulin sensitivity or β-cell function (P = 0.42 and 0.11, respectively). We conclude that dogs compensate effectively for obesity-induced insulin resistance. Fasting plasma leptin concentrations appear to be associated with obesity-associated changes in insulin sensitivity and compensatory hyperinsulinemia in naturally occurring obese dogs. Adiponectin does not appear to be involved in the pathophysiology of obesity-associated changes in insulin sensitivity.Copyright © 2011 Elsevier Inc. All rights reserved.
    Document Type:
    Reference
    Product Catalog Number:
    EGLP-35K
    Product Catalog Name:
    Glucagon Like Peptide-1 (Active) ELISA

  • Engineering physiologically regulated insulin secretion in non-beta cells by expressing glucagon-like peptide 1 receptor. 12923570

    Glucagon-like peptide 1 (GLP-1) is released from neuroendocrine cells in the intestine in the postprandial state and augments glucose-stimulated insulin secretion from pancreatic beta cells. To develop non-beta cells that exhibit physiologically regulated insulin secretion, we coexpressed the GLP-1 receptor and human insulin in primary rat pituitary cells using adenovirus-mediated gene transfer. The transduced cells were analyzed in a perifusion system and after transplantation into mice. Normal pituitary cells do not express the GLP-1 receptor as shown by the absence of GLP-1 receptor mRNA and the inability of GLP-1 to stimulate pituitary hormone secretion. Following transduction with an adenovirus carrying the GLP-1 receptor cDNA, the pituitary cells expressed functional GLP-1 receptors as reflected by the ability of GLP-1 to stimulate secretion of pituitary hormones. When both the GLP-1 receptor and human insulin were introduced, GLP-1 stimulated cosecretion of human insulin and endogenous pituitary hormones. GLP-1 was similar in potency to the hypothalamic-releasing hormones and stimulated hormone secretion in a dose-dependent fashion. In contrast to pancreatic beta cells, the hormone-releasing effect of GLP-1 on transduced pituitary cells was not dependent on the concentration of extracellular glucose. After transplantation of pituitary cells coexpressing human insulin and GLP-1 receptor into mice, enteral glucose stimulated insulin secretion. These results demonstrate a new approach to engineer physiologically regulated insulin secretion by non-beta cells.
    Document Type:
    Reference
    Product Catalog Number:
    HI-14K
    Product Catalog Name:
    Human Insulin-Specific RIA

  • Performance and metabolic and endocrine changes with emphasis on glucose metabolism in high-yielding dairy cows with high and low fat content in liver after calving. 19307636

    Elevated liver fat content occurs in high-yielding dairy cows during the transition from pregnancy to lactation after fat mobilization and may affect hepatic glucose metabolism, but the degree of liver fat storage is highly variable. Therefore, we studied metabolic and endocrine changes and hepatic glucose metabolism in cows that markedly differ in liver fat content. Multiparous cows from the same herd with high (HFL; n = 10) and low (LFL; n = 10) liver fat contents (mean of d 1, 10, and 21 after calving for each cow, respectively) were studied from 60 d before expected calving to 56 d in milk. Cows were fed ad libitum and all cows received the same diets. Liver samples were taken on d 1, 10, and 21 after calving; mean fat content (+/-SEM) in liver of HFL cows was 174 +/- 9.6 mg/g, whereas mean liver fat content in LFL cows was 77 +/- 3.3 mg/g. Blood samples were taken 20 and 7 d before expected calving and 0, 7, 14, 28, and 56 d after calving to measure plasma concentrations of nonesterified fatty acids, beta-hydroxybutyrate, glucose, insulin, glucagon, insulin-like growth factor-I, and leptin. In liver, glycogen content as well as mRNA levels of phosphoenolpyruvate carboxykinase, pyruvate carboxylase, glucose-6-phosphatase, and glucose transporter were measured by quantitative real-time PCR. Back fat thickness decreased and dry matter intake increased with onset of lactation, and back fat thickness was higher but dry matter intake was lower in HFL than in LFL. Energy-corrected milk yield did not differ between groups, but milk fat content was higher and lactose content was lower in HFL than LFL at the beginning of lactation. Energy balance was more negative in HFL than in LFL. Plasma nonesterified fatty acids and beta-hydroxybutyrate concentrations increased and plasma glucose concentration tended to decrease more in HFL than LFL with onset of lactation. Glucagon to insulin ratios increased more in HFL than LFL with onset of lactation. Hepatic glycogen content was higher in LFL than HFL, whereas mRNA levels of glucose-6-phosphatase and pyruvate carboxylase were higher in HFL than in LFL, and cytosolic phosphoenolpyruvate carboxykinase mRNA level increased similarly after parturition in both groups. In conclusion, an elevated liver fat content was related to greater fat mobilization and reduced feed intake and was associated with effects on hepatic glucose metabolism. As environment and feeding management were the same, individual cow factors were responsible for differences in energy metabolism during the transition period.
    Document Type:
    Reference
    Product Catalog Number:
    Multiple
    Product Catalog Name:
    Multiple

  • Inhibition of Ca2+ signaling and glucagon secretion in mouse pancreatic alpha-cells by extracellular ATP and purinergic receptors. 18349114

    Glucagon secreted from pancreatic alpha-cells plays a critical role in glycemia, mainly by hepatic glucose mobilization. In diabetic patients, an impaired control of glucagon release can worsen glucose homeostasis. Despite its importance, the mechanisms that regulate its secretion are still poorly understood. Since alpha-cells are particularly sensitive to neural and paracrine factors, in this report we studied the role of purinergic receptors and extracellular ATP, which can be released from nerve terminals and beta-cell secretory granules. Using immunocytochemistry, we identified in alpha-cells the P2 receptor subtype P2Y1, as well as the P1 receptors A1 and A2A. In contrast, only P2Y1 and A1 receptors were localized in beta-cells. To analyze the role of purinergic receptors in alpha-cell function, we studied their participation in Ca2+ signaling. At low glucose concentrations, mouse alpha-cells exhibited the characteristic oscillatory Ca2+ signals that lead to secretion. Application of ATP (1-10 microM) abolished these oscillations or reduced their frequency in alpha-cells within intact islets and isolated in culture. ATPgammaS, a nonhydrolyzable ATP derivative, indicated that the ATP effect was mainly direct rather than through ATP-hydrolytic products. Additionally, adenosine (1-10 microM) was also found to reduce Ca2+ signals. ATP-mediated inhibition of Ca2+ signaling was accompanied by a decrease in glucagon release from intact islets in contrast to the adenosine effect. Using pharmacological agonists, we found that only P2Y1 and A2A were likely involved in the inhibitory effect on Ca2+ signaling. All these findings indicate that extracellular ATP and purinergic stimulation are effective regulators of the alpha-cell function.
    Document Type:
    Reference
    Product Catalog Number:
    GL-32K
    Product Catalog Name:
    Glucagon RIA