A reappraisal of the blood glucose homeostat which comprehensively explains the type 2 diabetes mellitus-syndrome X complex

The Modulation of Euglycemic Endocrine and Exocrine Pancreatic Secretions in Iron Deficiency

OBJECTIVES

The contribution of pancreatic secretions in iron metabolism has been elucidated, but the clinical outcomes of iron deficiency on pancreatic function are debatable. This study aimed to investigate the modulation of euglycemic endocrine and exocrine pancreatic excretions in response to variations in iron availability.

SUBJECTS AND METHODS

Serum levels of insulin, glucagon, insulin-to-glucagon ratio (IGR), and amylase were determined in 170 adult subjects with variable levels of serum iron.

RESULTS

Control (n = 46) and iron-deficient (n = 124) subjects had significant differences (p < 0.001) in their average levels of insulin (68.7 ± 0.5 vs. 100.0 ± 2.0 pmol/dL), glucagon (17.9 ± 0.6 vs. 10.8 ± 0.8 pmol/dL), IGR (4.0 ± 0.1 vs. 19.5 ± 2.1), and amylase (29.7 ± 0.9 vs. 17.5 ± 0.2). The upregulation of serum insulin levels increases proportionally and gradually to the extent of iron deficiency as compared to an abrupt downregulation of serum levels of glucagon and amylase. A significant association was observed between serum iron and IGR (r = -0.645, p < 0.001) and amylase levels (r = 0.653, p < 0.001). The receiver operating characteristic curve analysis defines an excellent predictivity of the reduced serum iron level to discriminate subjects with upregulated IGR and amylase levels with area under curves of 0.938 and 0.905, respectively.

CONCLUSION

Iron deficiency is associated with an adaptive modulation of euglycemic endocrine and exocrine secretions that is consistent with a status of insulin resistance.

Mathematical modeling clarifies the paracrine roles of insulin and glucagon on the glucose-stimulated hormonal secretion of pancreatic alpha- and beta-cells

Introduction

Blood sugar homeostasis relies largely on the action of pancreatic islet hormones, particularly insulin and glucagon. In a prototypical fashion, glucagon is released upon hypoglycemia to elevate glucose by acting on the liver while elevated glucose induces the secretion of insulin which leads to sugar uptake by peripheral tissues. This simplified view of glucagon and insulin does not consider the paracrine roles of the two hormones modulating the response to glucose of α- and β-cells. In particular, glucose-stimulated glucagon secretion by isolated α-cells exhibits a Hill-function pattern, while experiments with intact pancreatic islets suggest a 'U'-shaped response.

Methods

To this end, a framework was developed based on first principles and coupled to experimental studies capturing the glucose-induced response of pancreatic α- and β-cells influenced by the two hormones. The model predicts both the transient and steady-state profiles of secreted insulin and glucagon, including the typical biphasic response of normal β-cells to hyperglycemia.

Results and discussion

The results underscore insulin activity as a differentiating factor of the glucagon secretion from whole islets vs. isolated α-cells, and highlight the importance of experimental conditions in interpreting the behavior of islet cells in vitro. The model also reproduces the hyperglucagonemia, which is experienced by diabetes patients, and it is linked to a failure of insulin to inhibit α-cell activity. The framework described here is amenable to the inclusion of additional islet cell types and extrapancreatic tissue cells simulating multi-organ systems. The study expands our understanding of the interplay of insulin and glucagon for pancreas function in normal and pathological conditions.

A Glimpse into Milestones of Insulin Resistance and an Updated Review of Its Management

Insulin is the main metabolic regulator of fuel molecules in the diet, such as carbohydrates, lipids, and proteins. It does so by facilitating glucose influx from the circulation into the liver, adipose tissue, and skeletal myocytes. The outcome of which is subjected to glycogenesis in skeletal muscle and lipogenesis in adipose tissue, as well as in the liver. Therefore, insulin has an anabolic action while, on the contrary, hypoinsulinemia promotes the reverse process. Protein breakdown in myocytes is also encountered during the late stages of diabetes mellitus. The balance of the blood glucose level in physiological conditions is maintained by virtue of the interactive functions of insulin and glucagon. In insulin resistance (IR), the balance is disturbed because glucose transporters (GLUTs) of cell membranes fail to respond to this peptide hormone, meaning that glucose molecules cannot be internalized into the cells, the consequence of which is hyperglycemia. To develop the full state of diabetes mellitus, IR should be associated with the impairment of insulin release from beta-cells of the pancreas. Periodic screening of individuals of high risk, such as those with obesity, hypercholesterolemia, and pregnant nulliparous women in antenatal control, is vital, as these are important checkpoints to detect cases of insulin resistance. This is pivotal as IR can be reversed, provided it is detected in its early stages, through healthy dietary habits, regular exercise, and the use of hypoglycemic agents. In this review, we discuss the pathophysiology, etiology, diagnosis, preventive methods, and management of IR in brief.

Glucose-responsive microneedle patch for closed-loop dual-hormone delivery in mice and pigs

Insulin and glucagon secreted from the pancreas with dynamic balance play a vital role in regulating blood glucose levels. Although distinct glucose-responsive insulin delivery systems have been developed, the lack of a self-regulated glucagon release module limits their clinical applications due to the potential risk of hypoglycemia. Here, we describe a transdermal polymeric microneedle patch for glucose-responsive closed-loop insulin and glucagon delivery to achieve glycemic regulation with minimized risk of hypoglycemia. The glucose-responsive phenylboronic acid units can bind to glucose to reversibly shift the net charge (from positive to negative) of the entire polymeric matrix within microneedles. Therefore, the release ratio of the negatively charged insulin and the positively charged glucagon analog from the patch can be dynamically tuned upon the fluctuation of blood glucose levels to realize glycemic homeostasis. In both chemically induced type 1 diabetic mouse and minipig models, this glucose-responsive dual-hormone microneedle patch demonstrated tight long-term regulation in blood glucose levels (>24 hours in minipigs).

Smart erythrocyte-hitchhiking insulin delivery system for prolonged automatic blood glucose control

Long and automatic control of blood glucose levels in diabetic patients could solve the problems caused by frequent insulin injections. Herein, we exploited the protection potential of erythrocytes by a "hitchhiking" strategy to significantly prolong the blood circulation time of a specifically-designed smart hitchhiking insulin delivery system (SHIDS). In the SHIDS, insulin, glucose oxidase, and catalase were co-loaded into nanoparticles formed by modified chitosan. The free glucosamines in chitosan anchor glucose transporters on the surface of erythrocytes, allowing erythrocyte-hitchhiking in the blood flow. A high glucose level triggers quick insulin release from the SHIDS to reduce the glucose level, which then slows the insulin release. This closed-loop glucose regulation by the SHIDS effectively controlled blood glucose within the normal range for at least 24 h and under 250 mg dL^-1 for ∼48 h with one injection. This injectable erythrocyte-hitchhiking nanoplatform, which achieves long-term and automatic blood glucose control, thus has potential for further development. As the carrier could be used for delivering other drugs/agents or interacting with other substances, the hitchhiking strategy is versatile and may be applied in other medical applications too.

Crosstalk Communications Between Islets Cells and Insulin Target Tissue: The Hidden Face of Iceberg

The regulation of insulin secretion is under control of a complex inter-organ/cells crosstalk involving various metabolites and/or physical connections. In this review, we try to illustrate with current knowledge how β-cells communicate with other cell types and organs in physiological and pathological contexts. Moreover, this review will provide a better understanding of the microenvironment and of the context in which β-cells exist and how this can influence their survival and function. Recent studies showed that β-cell insulin secretion is regulated also by a direct and indirect inter-organ/inter-cellular communication involving various factors, illustrating the idea of "the hidden face of the iceberg". Moreover, any disruption on the physiological communication between β-cells and other cells or organs can participate on diabetes onset. Therefore, for new anti-diabetic treatments' development, it is necessary to consider the entire network of cells and organs involved in the regulation of β-cellular function and no longer just β-cell or pancreatic islet alone. In this context, we discuss here the intra-islet communication, the β-cell/skeletal muscle, β-cell/adipose tissue and β-cell/liver cross talk.

Dietary chromium modulates glucose homeostasis and induces oxidative stress in Pacific white shrimp (Litopenaeus vannamei)

While chromium (Cr) has been recognized as an essential nutrient for all animals, and dietary supplementation can be beneficial, it can also be toxic. The present study aimed to investigate the contrasting effects of dietary chromium in Pacific white shrimp Litopenaeus vannamei. Five experimental diets were formulated to contain Cr at levels of 0.82 (Cr0.82, unsupplemented diet), 1.01 (Cr1.01), 1.22 (Cu1.22), 1.43 (Cr1.43) and 1.63 (Cr1.63) mg/kg and were fed to shrimp for 8 weeks. Highest weight gain was recorded in shrimp fed the diet containing 1.22 mg/kg Cr. Shrimp fed the diet containing the highest level of Cr (1.63 mg/kg) showed the lowest weight gain and clear signs of oxidative stress and apoptosis as evidenced by higher levels of H₂O₂, malondialdehyde and 8-hydroxydeoxyguanosine, and expression of caspase 2, 3, 5, and lower contents of total and oxidized glutathione, and expression of Cu/Zn sod, cat, gpx, mt, bcl2. Chromium supplementation promoted glycolysis and inhibited gluconeogenesis as shown by increased activities of hexokinase, phosphofructokinase and pyruvate kinase, and reduced activity of phosphoenolpyruvate carboxykinase in shrimp fed the diet containing 1.43 mg/kg Cr. Shrimp fed the diet with 1.63 mg/kg Cr had lowest contents of crustacean hyperglycemic hormone and insulin like peptide in hemolymph. Expression of genes involved in insulin signaling pathway and glycose metabolism including insr, irs1, pik3ca, pdpk1, akt, acc1, gys, glut1, pk, hk were up-regulated, and foxO1, gsk-3β, g6pc, pepck were down-regulated in shrimp fed the diets supplemented with Cr. This study demonstrated that optimum dietary supplementation of Cr had beneficial effects on glucose homeostasis and growth, whereas excess caused oxidative damage and impaired growth. The results contribute to our understanding of the biological functions of chromium in shrimp.

Alpha cell regulation of beta cell function

The islet of Langerhans is a complex endocrine micro-organ consisting of a multitude of endocrine and non-endocrine cell types. The two most abundant and prominent endocrine cell types, the beta and the alpha cells, are essential for the maintenance of blood glucose homeostasis. While the beta cell produces insulin, the only blood glucose-lowering hormone of the body, the alpha cell releases glucagon, which elevates blood glucose. Under physiological conditions, these two cell types affect each other in a paracrine manner. While the release products of the beta cell inhibit alpha cell function, the alpha cell releases factors that are stimulatory for beta cell function and increase glucose-stimulated insulin secretion. The aim of this review is to provide a comprehensive overview of recent research into the regulation of beta cell function by alpha cells, focusing on the effect of alpha cell-secreted factors, such as glucagon and acetylcholine. The consequences of differences in islet architecture between species on the interplay between alpha and beta cells is also discussed. Finally, we give a perspective on the possibility of using an in vivo imaging approach to study the interactions between human alpha and beta cells under in vivo conditions. Graphical abstract.

Relationship between serum insulin and point-of-admission blood glucose of ill neonates at a tertiary health facility in Nigeria

Introduction

Optimal glucose metabolism is important in neonatal survival especially in the first days of life. Insulin play a significant role in maintaining blood glucose homeostasis. This study set out to determine the serum insulin levels of ill neonates as related to their point-of-admission blood glucose estimation at the Wesley Guild Hospital, Ilesa, Nigeria.

Methods

Three hundred babies took part in the study. Blood glucose and serum insulin levels were assayed at admission using Accu-Chek Active glucometer^(R) and Accu-Ɔ-Bind ELISA Microwells^(R) respectively. Hyperglycaemia was defined as blood glucose ≥7mmol/L and hypoglycaemia as blood glucose <2.2mmol/L.

Results

The median (IQR) age of the babies was 10.0 (0.5 - 70.0) hours with male to female ratio of 1.5:1. Seventy-four (24.7%) were preterms and 35 (11.7%) were small-for-gestational age. The mean (SD) blood glucose level of the babies was 4.1(2.1) mmol/L with a range of 0.6-13.4mmol/L. Hyperglycaemia and hypoglycaemia were observed in 18(6.0%) and 40(13.3%) babies respectively. The median (IQR) serum insulin level was 9.8(3.0-35.3) μIU/ml. There was weak positive correlation between serum insulin and blood glucose levels of the babies (r = 0.197, p = 0.001). Birth asphyxia was associated with lower serum insulin, while probable sepsis with relatively higher levels.

Conclusion

Serum insulin level increases with increasing blood glucose in ill Nigerian babies at presentation to the hospital. Babies with asphyxia and sepsis particularly tend to have abnormal serum insulin at admission. Hyperinsulinaemia in ill babies may connote a compensatory mechanism to normalise abnormal blood glucose rather than playing significant role in its aetio-pathogenesis.

The Local Paracrine Actions of the Pancreatic α-Cell

Secretion of glucagon from the pancreatic α-cells is conventionally seen as the first and most important defense against hypoglycemia. Recent findings, however, show that α-cell signals stimulate insulin secretion from the neighboring β-cell. This article focuses on these seemingly counterintuitive local actions of α-cells and describes how they impact islet biology and glucose metabolism. It is mostly based on studies published in the last decade on the physiology of α-cells in human islets and incorporates results from rodents where appropriate. As this and the accompanying articles show, the emerging picture of α-cell function is one of increased complexity that needs to be considered when developing new therapies aimed at promoting islet function in the context of diabetes.

Glucose-Responsive Insulin and Delivery Systems: Innovation and Translation

Type 1 and advanced type 2 diabetes treatment involves daily injections or continuous infusion of exogenous insulin aimed at regulating blood glucose levels in the normoglycemic range. However, current options for insulin therapy are limited by the risk of hypoglycemia and are associated with suboptimal glycemic control outcomes. Therefore, a range of glucose-responsive components that can undergo changes in conformation or show alterations in intermolecular binding capability in response to glucose stimulation has been studied for ultimate integration into closed-loop insulin delivery or "smart insulin" systems. Here, an overview of the evolution and recent progress in the development of molecular approaches for glucose-responsive insulin delivery systems, a rapidly growing subfield of precision medicine, is presented. Three central glucose-responsive moieties, including glucose oxidase, phenylboronic acid, and glucose-binding molecules are examined in detail. Future opportunities and challenges regarding translation are also discussed.

Mechanism and effects of pulsatile GABA secretion from cytosolic pools in the human beta cell

Pancreatic beta cells synthesize and secrete the neurotransmitter γ-aminobutyric acid (GABA) as a paracrine and autocrine signal to help regulate hormone secretion and islet homeostasis. Islet GABA release has classically been described as a secretory vesicle-mediated event. Yet, a limitation of the hypothesized vesicular GABA release from islets is the lack of expression of a vesicular GABA transporter in beta cells. Consequentially, GABA accumulates in the cytosol. Here we provide evidence that the human beta cell effluxes GABA from a cytosolic pool in a pulsatile manner, imposing a synchronizing rhythm on pulsatile insulin secretion. The volume regulatory anion channel (VRAC), functionally encoded by LRRC8A or Swell1, is critical for pulsatile GABA secretion. GABA content in beta cells is depleted and secretion is disrupted in islets from type 1 and type 2 diabetic patients, suggesting that loss of GABA as a synchronizing signal for hormone output may correlate with diabetes pathogenesis.

How does homeostasis happen? Integrative physiological, systems biological, and evolutionary perspectives

Homeostasis is a founding principle of integrative physiology. In current systems biology, however, homeostasis seems almost invisible. Is homeostasis a key goal driving body processes, or is it an emergent mechanistic fact? In this perspective piece, I propose that the integrative physiological and systems biological viewpoints about homeostasis reflect different epistemologies, different philosophies of knowledge. Integrative physiology is concept driven. It attempts to explain biological phenomena by continuous formation of theories that experimentation or observation can test. In integrative physiology, "function" refers to goals or purposes. Systems biology is data driven. It explains biological phenomena in terms of "omics"-i.e., genomics, gene expression, epigenomics, proteomics, and metabolomics-it depicts the data in computer models of complex cascades or networks, and it makes predictions from the models. In systems biology, "function" refers more to mechanisms than to goals. The integrative physiologist emphasizes homeostasis of internal variables such as Pco₂ and blood pressure. The systems biologist views these emphases as teleological and unparsimonious in that the "regulated variable" (e.g., arterial Pco₂ and blood pressure) and the "regulator" (e.g., the "carbistat" and "barostat") are unobservable constructs. The integrative physiologist views systems biological explanations as not really explanations but descriptions that cannot account for phenomena we humans believe exist, although they cannot be observed directly, such as feelings and, ultimately, the conscious mind. This essay reviews the history of the two epistemologies, emphasizing autonomic neuroscience. I predict rapprochement of integrative physiology with systems biology. The resolution will avoid teleological purposiveness, transcend pure mechanism, and incorporate adaptiveness in evolution, i.e., "Darwinian medicine."

Paracrine Interactions within the Pancreatic Islet Determine the Glycemic Set Point

Every animal species has a signature blood glucose level or glycemic set point. These set points are different, and the normal glycemic levels (normoglycemia) of one species would be life threatening for other species. Mouse normoglycemia can be considered diabetic for humans. The biological determinants of the glycemic set point remain unclear. Here we show that the pancreatic islet imposes its glycemic set point on the organism, making it the bona fide glucostat in the body. Moreover, and in contrast to rodent islets, glucagon input from the alpha cell to the insulin-secreting beta cell is necessary to fine-tune the distinctive human set point. These findings affect transplantation and regenerative approaches to treat diabetes because restoring normoglycemia may require more than replacing only the beta cells. Furthermore, therapeutic strategies using glucagon receptor antagonists as hypoglycemic agents need to be reassessed, as they may reset the overall glucostat in the organism.

Homeostatic systems, biocybernetics, and autonomic neuroscience

In this review we describe a series of major concepts introduced during the past 150years that have contributed to our current understanding about how physiological processes required for well-being and survival are regulated. One can theorize that hierarchical networks involving input-output relationships continuously orchestrate and learn adaptive patterns of observable behaviors, cognition, memory, mood, and autonomic systems. Taken together, these networks function as "good regulators" determining levels of internal variables and act as if there were homeostatic comparators ("homeostats"). The consequences of models with vs. without homeostats remain the same in terms of allostatic load and the eventual switch from stabilizing negative feedback loops to destabilizing, pathogenic positive feedback loops. Understanding this switch seems important for comprehending senescence-related, neurodegenerative disorders that involve the autonomic nervous system. Our general proposal is that disintegration of homeostatic systems causes disorders of regulation in degenerative diseases and that medical cybernetics can inspire and rationalize new approaches to treatment and prevention.

A Comprehensive Survey of the Roles of Highly Disordered Proteins in Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is a chronic and progressive disease that is strongly associated with hyperglycemia (high blood sugar) related to either insulin resistance or insufficient insulin production. Among the various molecular events and players implicated in the manifestation and development of diabetes mellitus, proteins play several important roles. The Kyoto Encyclopedia of Genes and Genomes (KEGG) database has information on 34 human proteins experimentally shown to be related to the T2DM pathogenesis. It is known that many proteins associated with different human maladies are intrinsically disordered as a whole, or contain intrinsically disordered regions. The presented study shows that T2DM is not an exception to this rule, and many proteins known to be associated with pathogenesis of this malady are intrinsically disordered. The multiparametric bioinformatics analysis utilizing several computational tools for the intrinsic disorder characterization revealed that IRS1, IRS2, IRS4, MAFA, PDX1, ADIPO, PIK3R2, PIK3R5, SoCS1, and SoCS3 are expected to be highly disordered, whereas VDCC, SoCS2, SoCS4, JNK9, PRKCZ, PRKCE, insulin, GCK, JNK8, JNK10, PYK, INSR, TNF-α, MAPK3, and Kir6.2 are classified as moderately disordered proteins, and GLUT2, GLUT4, mTOR, SUR1, MAPK1, IKKA, PRKCD, PIK3CB, and PIK3CA are predicted as mostly ordered. More focused computational analyses and intensive literature mining were conducted for a set of highly disordered proteins related to T2DM. The resulting work represents a comprehensive survey describing the major biological functions of these proteins and functional roles of their intrinsically disordered regions, which are frequently engaged in protein–protein interactions, and contain sites of various posttranslational modifications (PTMs). It is also shown that intrinsic disorder-associated PTMs may play important roles in controlling the functions of these proteins. Consideration of the T2DM proteins from the perspective of intrinsic disorder provides useful information that can potentially lead to future experimental studies that may uncover latent and novel pathways associated with the disease.

TFPI2AS1, a novel lncRNA that inhibits cell proliferation and migration in lung cancer

Accumulating evidence demonstrates that a series of differentially expressed lncRNAs is important in tumorigenesis. However, the function of many of the lncRNAs in lung cancer remains elusive. In the present study, we used microarray analysis to identify lncRNAs that are dysregulated in non-small-cell lung cancer (NSCLC) as compared with normal tissues. Among the dysregulated lncRNAs, we identified TFPI2AS1, an antisense transcript of the tumor suppressor TFPI2 (tissue factor pathway inhibitor 2). TFPI2AS1 was shown to be markedly upregulated in NSCLC patient tumors as compared to paired non-tumor samples. TFPI2AS1 knockdown increased NSCLC cell proliferation and migration, which was associated with enhanced G1/S transition and downregulation of cyclin D1 and cyclin-dependent kinases 2 (CDK2), while TFPI2AS1 overexpression had the opposite effect. Knockdown and overexpression experiments also suggested that TFPI2AS1 regulates NSCLC cell migration and AKT activation. Moreover, TFPI2AS1 is a positive regulator of TFPI2. Our findings bring new insights for understanding the role of TFPI2AS1 in mediating the proliferation and migration of NSCLC cells by regulating TFPI2 expression.

Linking Stress, Catecholamine Autotoxicity, and Allostatic Load with Neurodegenerative Diseases: A Focused Review in Memory of Richard Kvetnansky

In this Focused Review, we provide an update about evolving concepts that may link chronic stress and catecholamine autotoxicity with neurodegenerative diseases such as Parkinson's disease. Richard Kvetnansky's contributions to the field of stress and catecholamine systems inspired some of the ideas presented here. We propose that coordination of catecholaminergic systems mediates adjustments maintaining health and that senescence-related disintegration of these systems leads to disorders of regulation and to neurodegenerative diseases such as Parkinson's disease. Chronically repeated episodes of stress-related catecholamine release and reuptake, with attendant increases in formation of the toxic dopamine metabolite 3,4-dihydroxyphenylacetaldehyde, might accelerate this process.

Exploring potential biomarkers and determining the metabolic mechanism of type 2 diabetes mellitus using liquid chromatography coupled to high-resolution mass spectrometry

Diabetes mellitus has imposed a huge burden on modern society and is a serious threat to human health globally.

Peripheral signalling involved in energy homeostasis control

The alarming prevalence of obesity has led to a better understanding of the molecular mechanisms controlling energy homeostasis. Regulation of energy intake and expenditure is more complex than previously thought, being influenced by signals from many peripheral tissues. In this sense, a wide variety of peripheral signals derived from different organs contributes to the regulation of body weight and energy expenditure. Besides the well-known role of insulin and adipokines, such as leptin and adiponectin, in the regulation of energy homeostasis, signals from other tissues not previously thought to play a role in body weight regulation have emerged in recent years. The role of fibroblast growth factor 21 (FGF21), insulin-like growth factor 1 (IGF-I), and sex hormone-binding globulin (SHBG) produced by the liver in the regulation of body weight and insulin sensitivity has been recently described. Moreover, molecules expressed by skeletal muscle such as myostatin have also been involved in adipose tissue regulation. Better known is the involvement of ghrelin, cholecystokinin, glucagon-like peptide 1 (GLP-1) and PYY(3-36), produced by the gut, in energy homeostasis. Even the kidney, through the production of renin, appears to regulate body weight, with mice lacking this hormone exhibiting resistance to diet-induced obesity. In addition, the skeleton has recently emerged as an endocrine organ, with effects on body weight control and glucose homeostasis through the actions of bone-derived factors such as osteocalcin and osteopontin. The comprehension of these signals will help in a better understanding of the aetiopathology of obesity, contributing to the potential development of new therapeutic targets aimed at tackling excess body fat accumulation.

Logistic model of glucose-regulated C-peptide secretion: hysteresis pathway disruption in impaired fasting glycemia

The present analysis tests the hypothesis that quantifiable disruption of the glucose-stimulated insulin-secretion dose-response pathway mediates impaired fasting glycemia (IFG) and type 2 diabetes mellitus (DM). To this end, adults with normal and impaired fasting glycemia (NFG, n = 30), IFG (n = 32), and DM (n = 14) were given a mixed meal containing 75 g glucose. C-peptide and glucose were measured over 4 h, 13 times in NFG and IFG and 16 times in DM (age range 50-57 yr, body mass index 28-32 kg/m(2)). Wavelet-based deconvolution analysis was used to estimate time-varying C-peptide secretion rates. Logistic dose-response functions were constructed analytically of the sensitivity, potency, and efficacy (in the pharmacological sense of slope, one-half maximal stimulation, and maximal effect) of glucose's stimulation of prehepatic insulin (C-peptide) secretion. A hysteresis changepoint time, demarcating unequal glucose potencies for onset and recovery pathways, was estimated simultaneously. According to this methodology, NFG subjects exhibited distinct onset and recovery potencies of glucose in stimulating C-peptide secretion (6.5 and 8.5 mM), thereby defining in vivo hysteresis (potency shift -2.0 mM). IFG patients manifested reduced glucose onset potency (8.6 mM), and diminished C-peptide hysteretic shift (-0.80 mM). DM patients had markedly decreased glucose potency (18.8 mM), reversal of C-peptide's hysteretic shift (+4.5 mM), and 30% lower C-peptide sensitivity to glucose stimulation. From these data, we conclude that a dynamic dose-response model of glucose-dependent control of C-peptide secretion can identify disruption of in vivo hysteresis in patients with IFG and DM. Pathway-defined analytic models of this kind may aid in the search for prediabetes biomarkers.

Identification of Apolipoprotein A-I as a “STOP” Signal for Myopia

Good visual acuity requires that the axial length of the ocular globe is matched to the refractive power of the cornea and lens to focus the images of distant objects onto the retina. During the growth of the juvenile eye, this is achieved through the emmetropization process that adjusts the ocular axial length to compensate for the refractive changes that occur in the anterior segment. A failure of the emmetropization process can result in either excessive or insufficient axial growth, leading to myopia or hyperopia, respectively. Emmetropization is mainly regulated by the retina, which generates two opposite signals: "GO/GROW" signals to increase axial growth and "STOP" signals to block it. The presence of GO/GROW and STOP signals was investigated by a proteomics analysis of the retinas from chicken with experimental myopia and hyperopia. Of 18 differentially expressed proteins that were identified, five displayed an expression profile corresponding to GO/GROW signals, and two corresponded to STOP signals. Western blotting confirmed that apolipoprotein A-I (apoA-I) has the characteristics of a STOP signal both in the retina as well as in the fibrous sclera. In accordance with this, intraocular application of the peroxisome proliferator-activated receptor alpha agonist GW7647 resulted in up-regulation of apoA-I levels and in a significant reduction of experimental myopia. In conclusion, using a comprehensive functional proteomics analysis of chicken ocular growth models we identified targets for ocular growth control. The correlation of elevated apoA-I levels with reduced ocular axial growth points toward a functional relationship with the observed morphological changes of the eye.

Diabetes, aging and physical activity

Diabetes mellitus (DM) is a metabolic disease affecting the regulation of insulin and glucose causing a disruption in the normal control of counterregulatory hormones and macronutrients, resulting in blood glucose accumulation. Metabolic deregulation leads to the production of noxious substances that have a particular propensity for damaging vascular and nervous structures. Physiological changes observed with aging are correlated with a concomitant increase in DM and its associated complications. Long-term complications, including peripheral and central neuropathies, micro- and macrovascular damage, retinopathy, and nephropathy are the major causes of mortality in diabetics [cardiovascular disease (CVD) being the primary complication causing death in this population]. All-cause mortality is three to four times greater in the DM population; hence, management of DM is of timely importance, particularly with a projected prevalence increase of 134% within the next 25 years among individuals over the age of 65 years. Exercise modalities, including endurance and resistance training, were employed to improve glycemic/metabolic control and to ameliorate the progression of DM-related complications. Several risk factors, including glucose levels, blood pressure, lipid/cholesterol profile, and BMI, are reportedly improved with these modes of exercise. However, not all studies demonstrate an improvement in risk factors, but consistently note improvement in complications and a reduction of DM incidence. There is convincing evidence that exercise, with or without specific improvements to traditional DM-related risk factors, is an effective therapy for the management of DM.

The granin family of uniquely acidic proteins of the diffuse neuroendocrine system: comparative and functional aspects

The chromogranins A (CgA) and B (CgB) and secretogranin II (SgII) constitute the main members of a family of uniquely acidic secretory proteins in elements of the diffuse neuroendocrine system. These genetically distinct proteins, CgA, CgB, SgII and the less well known secretogranins III-VII are collectively referred to as 'granins' and characterised by numerous pairs of basic amino acids as potential cleavage sites for processing by the co-stored prohormone converting enzymes PC 1/3 and PC2. This review is directed towards comparative and functional aspects of the granins with emphasis on their phylogenetically conserved sequences. Recent developments provide ample evidence of widely different effects and targets for the intact granins and their derived peptides, intracellularly in the directed trafficking of storage components during granule maturation and extracellularly in autocrine, paracrine and endocrine interactions. Most of the effects assigned to the granin derived peptides fit into patterns of direct or indirect inhibitory modulations of major functions. So far, peptides derived from CgA (vasostatins, chromacin, pancreastatin, WE-14, catestatin and parastatin), CgB (secretolytin) and SgII (secretoneurin) are the most likely candidates for granin-derived regulatory peptides, of postulated relevance not only for homeostatic processes, but also for tissue assembly and repair, inflammatory responses and the first line of defence against invading microorganisms.

Modeling approaches to type 2 diabetes

The incidence of type 2 diabetes is increasing rapidly, but clinical maintenance of normoglycemia remains challenging. The systemic, multifactorial character of diabetes is a key reason its treatment is so difficult. In the past 25 years, a number of mathematical and computational models have been developed to study this disease. These models offer promise in identifying the underlying disease pathophysiology in individual patients and in understanding the general pathophysiology characterizing the disease in large populations. To exploit these models most effectively, it is necessary to understand both the strengths and limitations of each model. This review outlines a selection of the models available for the study of diabetes, with a particular focus on the types of problems for which each model is well suited and the limitations that restrict how each model can be used.