A closed-loop artificial pancreas based on model predictive control: Human-friendly identification and automatic meal disturbance rejection

Type 1 diabetes is characterized by a lack of insulin production by the pancreas, causing high blood glucose concentrations and requiring external insulin infusion to regulate blood glucose. Continuous glucose sensors can be coupled with continuous insulin infusion pumps to create a closed-loop artificial pancreas. A novel procedure of “human-friendly” identification testing using multisine inputs is developed to estimate suitable models for use in an artificial pancreas. A constrained model predictive control (MPC) strategy is developed to reduce risks of hypo- and hyperglycemia (low and high blood glucose concentration). Meal detection and meal size estimation algorithms are developed to improve meal glucose disturbance rejection when incoming meals are not announced. Closed-loop performance is evaluated through simulation studies of a type 1 diabetic individual, illustrating the ability of the MPC-based artificial pancreas control strategy to handle announced and unannounced meal disturbances.     

Beta- and alpha-cell dysfunction in type 2 diabetes.

Insulin resistance is a common pathogenetic feature of type 2 diabetes. However, hyperglycemia would not develop if a concomitant defect in insulin secretion were not present. Impaired insulin secretion results from functional and survival defects of the beta-cell. The functional defects can be demonstrated early in the natural history of diabetes and they are hallmarked by abnormal pulsatility of basal insulin secretion and loss of first-phase insulin release in response to a glucose challenge. Moreover, a significant reduction of the beta-cell mass is apparent at the time of the diagnosis of diabetes. The progressive increase in glucose levels, that seems to characterize the natural history of type 2 diabetes, has been claimed to be largely due to progressive reduction of function and mass of beta-cells. Although a genetic predisposition is likely to account for impaired insulin secretion, chronic exposure to hyperglycemia and high circulating FFA is likely to contribute to both functional and survival defects. The disturbance in the endocrine activity of the pancreas is not limited to insulin, since a concomitant increase in fasting plasma glucagon and impaired suppression after the ingestion of an oral glucose load are often observed. This alteration becomes prominent after the ingestion of a mixed meal, when plasma glucagon remains much higher in the diabetic patient as compared to normal individuals. The disproportionate changes in the plasma concentration of the two pancreatic hormones is clearly evident when the insulin:glucagon molar ratio is considered. It is the latter that mainly affects hepatic glucose production. Because of the reduction of the insulin:glucagon molar ratio basal endogenous glucose concentration will be higher causing fasting hyperglycemia, while the hepatic glucose output will not be efficiently suppressed after the ingestion of a meal, contributing to excessive post-prandial glucose rise. Correcting beta- and alpha-cell dysfunction becomes, therefore, an attractive and rational therapeutic approach, particularly in the light of new treatments that may directly act on these pathogenetic mechanisms of type 2 diabetes.     

Induction of insulin secretion in engineered liver cells by nitric oxide

Background  

Type 1 Diabetes Mellitus results from an autoimmune destruction of the pancreatic beta cells, which produce insulin. The lack of insulin leads to chronic hyperglycemia and secondary complications, such as cardiovascular disease. The currently approved clinical treatments for diabetes mellitus often fail to achieve sustained and optimal glycemic control. Therefore, there is a great interest in the development of surrogate beta cells as a treatment for type 1 diabetes. Normally, pancreatic beta cells produce and secrete insulin only in response to increased blood glucose levels. However in many cases, insulin secretion from non-beta cells engineered to produce insulin occurs in a glucose-independent manner. In the present study we engineered liver cells to produce and secrete insulin and insulin secretion can be stimulated via the nitric oxide pathway.     

Insulin as a physiological modulator of glucagon secretion

Glucose homeostasis is regulated primarily by the opposing actions of insulin and glucagon, hormones that are secreted by pancreatic islets from beta-cells and alpha-cells, respectively. Insulin secretion is increased in response to elevated blood glucose to maintain normoglycemia by stimulating glucose transport in muscle and adipocytes and reducing glucose production by inhibiting gluconeogenesis in the liver. Whereas glucagon secretion is suppressed by hyperglycemia, it is stimulated during hypoglycemia, promoting hepatic glucose production and ultimately raising blood glucose levels. Diabetic hyperglycemia occurs as the result of insufficient insulin secretion from the beta-cells and/or lack of insulin action due to peripheral insulin resistance. Remarkably, excessive secretion of glucagon from the alpha-cells is also a major contributor to the development of diabetic hyperglycemia. Insulin is a physiological suppressor of glucagon secretion; however, at the cellular and molecular levels, how intraislet insulin exerts its suppressive effect on the alpha-cells is not very clear. Although the inhibitory effect of insulin on glucagon gene expression is an important means to regulate glucagon secretion, recent studies suggest that the underlying mechanisms of the intraislet insulin on suppression of glucagon secretion involve the modulation of K(ATP) channel activity and the activation of the GABA-GABA(A) receptor system. Nevertheless, regulation of glucagon secretion is multifactorial and yet to be fully understood.     

Zinc Supplementation Does Not Affect Glucagon Response to Intravenous Glucose and Insulin Infusion in Patients with Well-Controlled Type 2 Diabetes

Glucagon dysregulation is an essential component in the pathophysiology of type 2 diabetes. Studies in vitro and in animal models have shown that zinc co-secreted with insulin suppresses glucagon secretion. Zinc supplementation improves blood glucose control in patients with type 2 diabetes, although there is little information about how zinc supplementation may affect glucagon secretion. The objective of this study was to evaluate the effect of 1-year zinc supplementation on fasting plasma glucagon concentration and in response to intravenous glucose and insulin infusion in patients with type 2 diabetes. A cross-sectional study was performed after 1-year of intervention with 30 mg/day zinc supplementation or a placebo on 28 patients with type 2 diabetes. Demographic, anthropometric, and biochemical parameters were determined. Fasting plasma glucagon and in response to intravenous glucose and insulin infusion were evaluated. Patients of both placebo and supplemented groups presented a well control of diabetes, with mean values of fasting blood glucose and glycated hemoglobin within the therapeutic goals established by ADA. No significant differences were observed in plasma glucagon concentration, glucagon/glucose ratio or glucagon/insulin ratio fasting, after glucose or after insulin infusions between placebo and supplemented groups. No significant effects of glucose or insulin infusions were observed on plasma glucagon concentration. One-year zinc supplementation did not affect fasting plasma glucagon nor response to intravenous glucose or insulin infusion in well-controlled type 2 diabetes patients with an adequate zinc status.     

Glucagon-like peptide 1 agonists and the development and growth of pancreatic beta-cells

Glucagon-like peptide 1 (GLP-1) is an intestine-derived insulinotropic hormone that stimulates glucose-dependent insulin production and secretion from pancreatic beta-cells. Other recognized actions of GLP-1 are to suppress glucagon secretion and hepatic glucose output, delay gastric emptying, reduce food intake, and promote glucose disposal in peripheral tissues. All of these actions are potentially beneficial for the treatment of type 2 diabetes mellitus. Several GLP-1 agonists are in clinical trials for the treatment of diabetes. More recently, GLP-1 agonists have been shown to stimulate the growth and differentiation of pancreatic beta-cells, as well as to exert cytoprotective, antiapoptotic effects on beta-cells. Recent evidence indicates that GLP-1 agonists act on receptors on pancreas-derived stem/progenitor cells to prompt their differentiation into beta-cells. These new findings suggest an approach to create beta-cells in vitro by expanding stem/progenitor cells and then to convert them into beta-cells by treatment with GLP-1. Thus GLP-1 may be a means by which to create beta-cells ex vivo for transplantation into patients with insulinopenic type 1 diabetes and severe forms of type 2 diabetes.     

A Mixed Mirror-image DNA/RNA Aptamer Inhibits Glucagon and Acutely Improves Glucose Tolerance in Models of Type 1 and Type 2 Diabetes

Excessive secretion of glucagon, a functional insulin antagonist, significantly contributes to hyperglycemia in type 1 and type 2 diabetes. Accordingly, immunoneutralization of glucagon or genetic deletion of the glucagon receptor improved glucose homeostasis in animal models of diabetes. Despite this strong evidence, agents that selectively interfere with endogenous glucagon have not been implemented in clinical practice yet. We report the discovery of mirror-image DNA-aptamers (Spiegelmer®) that bind and inhibit glucagon. The affinity of the best binding DNA oligonucleotide was remarkably increased (>25-fold) by the introduction of oxygen atoms at selected 2′-positions through deoxyribo- to ribonucleotide exchanges resulting in a mixed DNA/RNA-Spiegelmer (NOX-G15) that binds glucagon with a K_d of 3 nm. NOX-G15 shows no cross-reactivity with related peptides such as glucagon-like peptide-1, glucagon-like peptide-2, gastric-inhibitory peptide, and prepro-vasoactive intestinal peptide. In vitro, NOX-G15 inhibits glucagon-stimulated cAMP production in CHO cells overexpressing the human glucagon receptor with an IC₅₀ of 3.4 nm. A single injection of NOX-G15 ameliorated glucose excursions in intraperitoneal glucose tolerance tests in mice with streptozotocin-induced (type 1) diabetes and in a non-genetic mouse model of type 2 diabetes. In conclusion, the data suggest NOX-G15 as a therapeutic candidate with the potential to acutely attenuate hyperglycemia in type 1 and type 2 diabetes.     

Insulin secretion and islet endocrine cell content at onset and during the early stages of diabetes in the BB rat: effect of the level of glycemic control.

Although it is agreed that autoimmune destruction of pancreatic islets in diabetic BB rats is rapid, reports of endocrine cell content of islets from BB diabetic rats at the time of onset of diabetes vary considerably. Because of the rapid onset of the disease (hours) and the attendant changes in islet morphology and insulin secretion, it was the aim of this study to compare islet beta-cell numbers to other islet endocrine cells as close to the time of onset of hyperglycemia as possible (within 12 h). As it has been reported that hyperglycemia renders the beta cell insensitive to glucose, the early effects of different levels of insulin therapy (well-controlled vs. poorly controlled glycemia) on islet morphology and insulin secretion were examined. When measured within 12 h of onset, insulin content of BB diabetic islets, measured by morphometric analysis or pancreatic extraction, was 60% of insulin content of control islets. Despite significant amounts of insulin remaining in the pancreas, 1-day diabetic rats exhibited fasting hyperglycemia and were glucose intolerant. The insulin response from the isolated perfused pancreas to glucose and the glucose-dependent insulinotropic hormone, gastric inhibitory polypeptide (GIP), was reduced by 95%. Islet content of other endocrine peptides, glucagon, somatostatin, and pancreatic polypeptide, was normal at onset and at 2 weeks post onset. A group of diabetic animals, maintained in a hyperglycemic state for 7 days with low doses of insulin, were compared with a group kept normoglycemic by appropriate insulin therapy. No insulin could be detected in islets of poorly controlled diabetics, while well-controlled animals had 30% of the normal islet insulin content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Contribution of free fatty acids to impairment of insulin secretion and action: mechanism of beta-cell lipotoxicity

Type 2 diabetes is characterized by two major defects: a dysregulation of pancreatic hormone secretion (quantitative and qualitative--early phase, pulsatility--decrease of insulin secretion, increase in glucagon secretion), and a decrease in insulin action on target tissues (insulin resistance). The defects in insulin action on target tissues are characterized by a decreased in muscle glucose uptake and by an increased hepatic glucose production. These abnomalities are linked to several defects in insulin signaling mechanisms and in several steps regulating glucose metabolism (transport, key enzymes of glycogen synthesis or of mitochondrial oxidation). These postreceptors defects are amplified by the presence of high circulating concentrations of free fatty acids. The mechanisms involved in the of long-chain fatty acids are reviewed in this paper. Indeed, elevated plasma free fatty acids contribute to decrease muscle glucose uptake (mainly by reducing insulin signaling) and to increase hepatic glucose production (stimulation of gluconeogenesis by providing cofactors such as acetyl-CoA, ATP and NADH). Chronic exposure to high levels of plasma free fatty acids induces accumulation of long-chain acyl-CoA into pancreatic beta-cells and to the death of 50 % of beta-cell by apoptosis (lipotoxicity).     

Diminished glucagon suppression after β-cell reduction is due to impaired α-cell function rather than an expansion of α-cell mass

Impaired suppression of glucagon levels after oral glucose or meal ingestion is a hallmark of type 2 diabetes. Whether hyperglucagonemia after a β-cell loss results from a functional upregulation of glucagon secretion or an increase in α-cell mass is yet unclear. CD-1 mice were treated with streptozotocin (STZ) or saline. Pancreatic tissue was collected after 14, 21, and 28 days and examined for α- and β-cell mass and turnover. Intraperitoneal (ip) glucose tolerance tests were performed at day 28 as well as after 12 days of subcutaneous insulin treatment, and glucose, insulin, and glucagon levels were determined. STZ treatment led to fasting and post-challenge hyperglycemia (P < 0.001 vs. controls). Insulin levels increased after glucose injection in controls (P < 0.001) but were unchanged in STZ mice (P = 0.36). Intraperitoneal glucose elicited a 63.1 ± 4.1% glucagon suppression in control mice (P < 0.001), whereas the glucagon suppression was absent in STZ mice (P = 0.47). Insulin treatment failed to normalize glucagon levels. There was a significant inverse association between insulin and glucagon levels after ip glucose ingestion (r(2) = 0.99). β-Cell mass was reduced by ～75% in STZ mice compared with controls (P < 0.001), whereas α-cell mass remained unchanged (P > 0.05). α-Cell apoptosis (TUNEL) and replication (Ki67) were rather infrequently noticed, with no significant differences between the groups. These studies underline the importance of endogenous insulin for the glucose-induced suppression of glucagon secretion and suggest that the insufficient decline in glucagon levels after glucose administration in diabetes is primarily due to a functional loss of intraislet inhibition of α-cell function rather than an expansion of α-cell mass.     

Expression of glucagon receptors in tetracycline-inducible HEK293S GnT1- stable cell lines: an approach toward purification of receptor protein for structural studies

Glucagon is a 29-amino acid polypeptide hormone secreted by pancreatic A cells. Together with insulin, it is an important regulator of glucose metabolism. Type 2 diabetes is characterized by reduced insulin secretion from pancreatic B cells and increased glucose output by the liver which has been attributed to abnormally elevated levels of glucagon. The glucagon receptor (GR) is a member of family B G protein-coupled receptors, ligands for which are peptides composed of 30-40 amino acids. The impetus for studying how glucagon interacts with its membrane receptor is to gain insight into the mechanism of glucagon action in normal physiology as well as in diabetes mellitus. The principal approach toward this goal is to design and synthesize antagonists of glucagon that will bind with high affinity to the GR but will not activate it. Site-directed mutagenesis of the GR has provided some insight into the interactions between glucagon and GR. The rational design of potent antagonists has been hampered by the lack of structural information on receptor-bound glucagon. To obtain adequate amounts of receptor protein for structural studies, a tetracycline-inducible HEK293S GnT1(-) cell line that stably expresses human GR at high-levels was developed. The recombinant receptor protein was characterized, solubilized, and isolated by one-step affinity chromatography. This report describes a feasible approach for the preparation of human GR and other family B GPCRs in the quantities required for structural studies.     

Oxidative stress and the JNK pathway are involved in the development of type 1 and type 2 diabetes

Failure of pancreatic beta-cells is the common characteristic of type 1 and type 2 diabetes. Type 1 diabetes mellitus is induced by destruction of pancreatic beta-cells which is mediated by an autoimmune mechanism and consequent inflammatory process. Various inflammatory cytokines and oxidative stress are produced during this process, which has been proposed to play an important role in mediating beta-cell destruction. The JNK pathway is also activated by such cytokines and oxidative stress, and is involved in beta-cell destruction. Type 2 diabetes is the most prevalent and serious metabolic disease, and beta-cell dysfunction and insulin resistance are the hallmark of type 2 diabetes. Under diabetic conditions, chronic hyperglycemia gradually deteriorates beta-cell function and aggravates insulin resistance. This process is called "glucose toxicity". Under such conditions, oxidative stress is provoked and the JNK pathway is activated, which is likely involved in pancreatic beta-cells dysfunction and insulin resistance. In addition, oxidative stress and activation of the JNK pathway are also involved in the progression of atherosclerosis which is often observed under diabetic conditions. Taken together, it is likely that oxidative stress and subsequent activation of the JNK pathway are involved in the pathogenesis of type 1 and type 2 diabetes.     

A Potent Class of GPR40 Full Agonists Engages the EnteroInsular Axis to Promote Glucose Control in Rodents

Type 2 diabetes is characterized by impaired glucose homeostasis due to defects in insulin secretion, insulin resistance and the incretin response. GPR40 (FFAR1 or FFA1) is a G-protein-coupled receptor (GPCR), primarily expressed in insulin-producing pancreatic β-cells and incretin-producing enteroendocrine cells of the small intestine. Several GPR40 agonists, including AMG 837 and TAK-875, have been disclosed, but no GPR40 synthetic agonists have been reported that engage both the insulinogenic and incretinogenic axes. In this report we provide a molecular explanation and describe the discovery of a unique and potent class of GPR40 full agonists that engages the enteroinsular axis to promote dramatic improvement in glucose control in rodents. GPR40 full agonists AM-1638 and AM-6226 stimulate GLP-1 and GIP secretion from intestinal enteroendocrine cells and increase GSIS from pancreatic islets, leading to enhanced glucose control in the high fat fed, streptozotocin treated and NONcNZO10/LtJ mouse models of type 2 diabetes. The improvement in hyperglycemia by AM-1638 was reduced in the presence of the GLP-1 receptor antagonist Ex(9–39)NH₂.     

Acute pancreatic beta cell apoptosis by IL-1β is responsible for postburn hyperglycemia: Evidence from humans and mice

Background

Acute hyperglycemia is regarded as a risk factor for critically ill patients; however, insufficient understanding of its nature and underlying mechanisms hinders widespread adoption of glycemic control in critical care units.

Intra-islet insulin suppresses glucagon release via GABA-GABAA receptor system

Excessive secretion of glucagon is a major contributor to the development of diabetic hyperglycemia. Secretion of glucagon is regulated by various nutrients, with glucose being a primary determinant of the rate of alpha cell glucagon secretion. The intra-islet action of insulin is essential to exert the effect of glucose on the alpha cells since, in the absence of insulin, glucose is not able to suppress glucagon release in vivo. However, the precise mechanism by which insulin suppresses glucagon secretion from alpha cells is unknown. In this study, we show that insulin induces activation of GABAA receptors in the alpha cells by receptor translocation via an Akt kinase-dependent pathway. This leads to membrane hyperpolarization in the alpha cells and, ultimately, suppression of glucagon secretion. We propose that defects in this pathway(s) contribute to diabetic hyperglycemia.