Decreased sensitivity of the pancreatic beta cells to glucose in prediabetic and diabetic subjects. A glucose dose-response study

Biomolecular Mechanisms of Cardiorenal Protection with Sodium-Glucose Co-Transporter 2 Inhibitors

Diabetes mellitus (DM) is a metabolic disorder characterized by chronic hyperglycemia and associated with an increased risk of morbidity and mortality, primarily from cardiovascular and renal diseases. Sodium-glucose cotransporter 2 inhibitors (SGLT2-Is) are novel drugs for the treatment of type 2 DM and heart failure (HF). SGLT2-Is mediate protective effects on both the renal and cardiovascular systems. This review addresses the current knowledge on the biomolecular mechanisms of the cardiorenal protective effects of SGLT2-Is, which appear to act mainly through non-glucose-mediated pathways. Cardiorenal protection mechanisms lead to reduced chronic renal disease progression and improved myocardial and coronary endothelial function. Concomitantly, it is possible to observe reflected changes in biomarkers linked with diabetic kidney disease and HF.

The changing view of insulin granule mobility: From conveyor belt to signaling hub

Before the advent of TIRF microscopy the fate of the insulin granule prior to secretion was deduced from biochemical investigations, electron microscopy and electrophysiological measurements. Since Calcium-triggered granule fusion is indisputably necessary to release insulin into the extracellular space, much effort was directed to the measure this event at the single granule level. This has also been the major application of the TIRF microscopy of the pancreatic beta cell when it became available about 20 years ago. To better understand the metabolic modulation of secretion, we were interested to characterize the entirety of the insulin granules which are localized in the vicinity of the plasma membrane to identify the characteristics which predispose to fusion. In this review we concentrate on how the description of granule mobility in the submembrane space has evolved as a result of progress in methodology. The granules are in a state of constant turnover with widely different periods of residence in this space. While granule fusion is associated +with prolonged residence and decreased lateral mobility, these characteristics may not only result from binding to the plasma membrane but also from binding to the cortical actin web, which is present in the immediate submembrane space. While granule age as such affects granule mobility and fusion probability, the preceding functional states of the beta cell leave their mark on these parameters, too. In summary, the submembrane granules form a highly dynamic heterogeneous population and contribute to the metabolic memory of the beta cells.

The β Cell in Diabetes: Integrating Biomarkers With Functional Measures

The pathogenesis of hyperglycemia observed in most forms of diabetes is intimately tied to the islet β cell. Impairments in propeptide processing and secretory function, along with the loss of these vital cells, is demonstrable not only in those in whom the diagnosis is established but typically also in individuals who are at increased risk of developing the disease. Biomarkers are used to inform on the state of a biological process, pathological condition, or response to an intervention and are increasingly being used for predicting, diagnosing, and prognosticating disease. They are also proving to be of use in the different forms of diabetes in both research and clinical settings. This review focuses on the β cell, addressing the potential utility of genetic markers, circulating molecules, immune cell phenotyping, and imaging approaches as biomarkers of cellular function and loss of this critical cell. Further, we consider how these biomarkers complement the more long-established, dynamic, and often complex measurements of β-cell secretory function that themselves could be considered biomarkers.

Insulin secretion is a strong predictor for need of insulin therapy in patients with new-onset diabetes and HbA1c of more than 10%: A post hoc analysis of the EDICT study

AIM

To identify predictors of response to glucose-lowering therapy in patients with new-onset diabetes and very high HbA1c (>10%).

METHODS

The study included EDICT participants with an initial HbA1c of more than 10% (N = 104). All subjects received a 75-g oral glucose tolerance test (OGTT) before initiation of therapy, and then were randomized to receive: (a) initial triple therapy with metformin, pioglitazone and exenatide versus (b) stepwise conventional therapy with metformin followed by glipizide and then glargine insulin to reduce HbA1c to less than 6.5%. Insulin secretion and insulin resistance were calculated with OGTT-derived indices.

RESULTS

Sixty-one per cent of participants in the conventional therapy group achieved HbA1c of less than 6.5% at 6 months without need of insulin therapy compared with 78% in the triple therapy group (P = NS). Insulin secretion at baseline was the strongest predictor of subjects who did not require insulin therapy; a cut point of CPEP₁₂₀ /CPEP₀ -the ratio between plasma C-peptide concentration at 120 minutes during the OGTT and fasting plasma C-peptide concentration-of more than 1.7 predicted subjects who achieved the treatment target without insulin, irrespective of the fasting plasma glucose (FPG) concentration and whether or not they were started on conventional or triple therapy. Subjects with a CPEP₁₂₀ /CPEP₀ of less than 1.7 plus FPG of 269 mg/dL or less (≤14.9 mmoL/L) also achieved the treatment goal with triple therapy.

CONCLUSION

Insulin secretion in response to a 75-g OGTT predicts the need for insulin therapy at the time of type 2 diabetes (T2D) diagnosis. A cut point of 1.7 of CPEP₁₂₀ /CPEP₀ provides a useful clinical tool to individualize glucose-lowering therapy in patients with new-onset T2D and HbA1c of more than 10%.

Reduced glucose-induced first-phase insulin release is a danger signal that predicts diabetes

During progression to both types 1 and 2 diabetes (T1D, T2D), there is a striking loss of glucose-induced first-phase insulin release (FPIR), which is known to predict the onset of T1D. The contribution of reduced β cell mass to the onset of hyperglycemia remains unclear. In this issue of the JCI, Mezza et al. report on their study of patients with pancreatic neoplasms before and after partial pancreatectomy to evaluate the impact of reduced β cell mass on the development of diabetes. The authors found that reduced FPIR predicted diabetes when 50% of the pancreas was removed. These findings suggest that low or absent FPIR indicates that β cell mass can no longer compensate for increased insulin needs. Notably, clinicians may use reduction of FPIR as a warning that progression to T2D is underway.

Glucose-induced insulin secretion in isolated human islets: Does it truly reflect β-cell function in vivo?

BACKGROUND

Diabetes always involves variable degrees of β-cell demise and malfunction leading to insufficient insulin secretion. Besides clinical investigations, many research projects used rodent islets to study various facets of β-cell pathophysiology. Their important contributions laid the foundations of steadily increasing numbers of experimental studies resorting to isolated human islets.

SCOPE OF REVIEW

This review, based on an analysis of data published over 60 years of clinical investigations and results of more recent studies in isolated islets, addresses a question of translational nature. Does the information obtained in vitro with human islets fit with our knowledge of insulin secretion in man? The aims are not to discuss specificities of pathways controlling secretion but to compare qualitative and quantitative features of glucose-induced insulin secretion in isolated human islets and in living human subjects.

MAJOR CONCLUSIONS

Much of the information gathered in vitro can reliably be translated to the in vivo situation. There is a fairly good, though not complete, qualitative and quantitative coherence between insulin secretion rates measured in vivo and in vitro during stimulation with physiological glucose concentrations, but the concordance fades out under extreme conditions. Perplexing discrepancies also exist between insulin secretion in subjects with Type 2 diabetes and their islets studied in vitro, in particular concerning the kinetics. Future projects should ascertain that the experimental conditions are close to physiological and do not alter the function of normal and diabetic islets.

Fresh and cultured mouse islets differ in their response to nutrient stimulation

Observing different kinetics of nutrient-induced insulin secretion in fresh and cultured islets under the same condition we compared parameters of stimulus secretion coupling in freshly isolated and 22-h-cultured NMRI mouse islets. Stimulation of fresh islets with 30 mM glucose after perifusion without nutrient gave a continuously ascending secretion rate. In 22-h-cultured islets the same protocol produced a brisk first phase followed by a moderately elevated plateau, a pattern regarded to be typical for mouse islets. This was also the response of cultured islets to the nutrient secretagogue alpha-ketoisocaproic acid, whereas the secretion of fresh islets increased similarly fast but remained strongly elevated. The responses of fresh and cultured islets to purely depolarizing stimuli (tolbutamide or KCl), however, were closely similar. Signs of apoptosis and necrosis were rare in both preparations. In cultured islets, the glucose-induced rise of the cytosolic Ca2+ concentration started from a lower value and was larger as was the increase of the ATP/ADP ratio. The prestimulatory level of mitochondrial reducing equivalents, expressed as the NAD(P)H/FAD fluorescence ratio, was lower in cultured islets, but increased more strongly than in fresh islets. When culture conditions were modified by replacing RPMI with Krebs-Ringer medium and FCS with BSA, the amount of released insulin varied widely, but the kinetics always showed a predominant first phase. In conclusion, the secretion kinetics of fresh mouse islets is more responsive to variations of nutrient stimulation than cultured islets. The more uniform kinetics of the latter may be caused by a different use of endogenous metabolites.

A Cellular Automaton Model as a First Model-Based Assessment of Interacting Mechanisms for Insulin Granule Transport in Beta Cells

In this paper a first model is derived and applied which describes the transport of insulin granules through the cell interior and at the membrane of a beta cell. A special role is assigned to the actin network, which significantly influences the transport. For this purpose, microscopically measured actin networks are characterized and then further ones are artificially generated. In a Cellular Automaton model, phenomenological laws for granule movement are formulated and implemented. Simulation results are compared with experiments, primarily using TIRF images and secretion rates. In this respect, good similarities are already apparent. The model is a first useful approach to describe complex granule transport processes in beta cells, and offers great potential for future extensions. Furthermore, the model can be used as a tool to validate hypotheses and associated mechanisms regarding their effect on exocytosis or other processes. For this purpose, the source code for the model is provided online.

Enhanced expression of β cell CaV3.1 channels impairs insulin release and glucose homeostasis

We reveal that increased expression of Ca_V3.1 channels in rat islets selectively impairs first-phase glucose-stimulated insulin secretion. This deterioration is recapitulated in human islets. Its causal role in diabetes development is clearly manifested in an in vivo diabetic model. Mechanistically, this is due to reduction of phosphorylated FoxO1 in the cytoplasm, elevated FoxO1 nuclear retention, and decreased syntaxin 1A, SNAP-25, and synaptotagmin III in a Ca_V3.1 channel- and calcineurin-dependent manner. Our findings suggest that elevated expression of Ca_V3.1 channels in pancreatic islets drives FoxO1-mediated down-regulation of exocytotic proteins resulting in the diabetic phenotypes of impaired insulin secretion and aberrant glucose homeostasis. This causal connection pinpoints β cell Ca_V3.1 channels as a potential druggable target for antidiabetes therapy.

Voltage-gated calcium 3.1 (Ca_V3.1) channels are absent in healthy mouse β cells and mediate minor T-type Ca²⁺ currents in healthy rat and human β cells but become evident under diabetic conditions. Whether more active Ca_V3.1 channels affect insulin secretion and glucose homeostasis remains enigmatic. We addressed this question by enhancing de novo expression of β cell Ca_V3.1 channels and exploring the consequent impacts on dynamic insulin secretion and glucose homeostasis as well as underlying molecular mechanisms with a series of in vitro and in vivo approaches. We now demonstrate that a recombinant adenovirus encoding enhanced green fluorescent protein–Ca_V3.1 subunit (Ad-EGFP-Ca_V3.1) efficiently transduced rat and human islets as well as dispersed islet cells. The resulting Ca_V3.1 channels conducted typical T-type Ca²⁺ currents, leading to an enhanced basal cytosolic-free Ca²⁺ concentration ([Ca²⁺]_i). Ad-EGFP-Ca_V3.1-transduced islets released significantly less insulin under both the basal and first phases following glucose stimulation and could no longer normalize hyperglycemia in recipient rats rendered diabetic by streptozotocin treatment. Furthermore, Ad-EGFP-Ca_V3.1 transduction reduced phosphorylated FoxO1 in the cytoplasm of INS-1E cells, elevated FoxO1 nuclear retention, and decreased syntaxin 1A, SNAP-25, and synaptotagmin III. These effects were prevented by inhibiting Ca_V3.1 channels or the Ca²⁺-dependent phosphatase calcineurin. Enhanced expression of β cell Ca_V3.1 channels therefore impairs insulin release and glucose homeostasis by means of initial excessive Ca²⁺ influx, subsequent activation of calcineurin, consequent dephosphorylation and nuclear retention of FoxO1, and eventual FoxO1-mediated down-regulation of β cell exocytotic proteins. The present work thus suggests an elevated expression of Ca_V3.1 channels plays a significant role in diabetes pathogenesis.

From Pre-Diabetes to Diabetes: Diagnosis, Treatments and Translational Research

Diabetes, a silent killer, is one of the most widely prevalent conditions of the present time. According to the 2017 International Diabetes Federation (IDF) statistics, the global prevalence of diabetes among the age group of 20-79 years is 8.8%. In addition, 1 in every 2 persons is unaware of the condition. This unawareness and ignorance lead to further complications. Pre-diabetes is the preceding condition of diabetes, and in most of the cases, this ultimately leads to the development of diabetes. Diabetes can be classified into three types, namely type 1 diabetes, type 2 diabetes mellitus (T2DM) and gestational diabetes. The diagnosis of both pre-diabetes and diabetes is based on glucose criteria; the common modalities used are fasting plasma glucose (FPG) test and oral glucose tolerance test (OGTT). A glucometer is commonly used by diabetic patients to measure blood glucose levels with fast and rather accurate measurements. A few of the more advanced and minimally invasive modalities include the glucose-sensing patch, SwEatch, eyeglass biosensor, breath analysis, etc. Despite a considerable amount of data being collected and analyzed regarding diabetes, the actual molecular mechanism of developing type 2 diabetes mellitus (T2DM) is still unknown. Both genetic and epigenetic factors are associated with T2DM. The complications of diabetes can predominantly be classified into two categories: microvascular and macrovascular. Retinopathy, nephropathy, and neuropathy are grouped under microvascular complications, whereas stroke, cardiovascular disease, and peripheral artery disease (PAD) belong to macrovascular complications. Unfortunately, until now, no complete cure for diabetes has been found. However, the treatment of pre-diabetes has shown significant success in preventing the further progression of diabetes. To prevent pre-diabetes from developing into T2DM, lifestyle intervention has been found to be very promising. Various aspects of diabetes, including the aforementioned topics, have been reviewed in this paper.

Outcomes Associated With the Adjunctive Use of Dipeptidyl Peptidase-4 Inhibitors With Insulin Versus Other Antihyperglycemic Medications in Patients With Prediabetes or Diabetes After Cardiac Surgery

BACKGROUND

Dipeptidyl peptidase-4 inhibitors (DPP-4i) plus basal insulin is noninferior to insulin monotherapy for glycemic control in medical-surgical patients, but data in postoperative cardiac surgery patients are sparse.

OBJECTIVE

To compare glucose control in postoperative cardiac surgery patients with prediabetes or diabetes receiving a DPP-4i plus insulin versus other antihyperglycemic regimens.

METHODS

We retrospectively identified patients with prediabetes or diabetes who underwent cardiac surgery at our hospital between May 2016 and June 2017. Included patients were stratified into cohorts: (1) DPP-4i plus insulin and (2) other antihyperglycemic regimens. Blood glucose levels were collected on postoperative days 2 to 7. Uncontrolled glucose (≥2 measurements <80 or >180 mg/dL in 1 day), hyperglycemia (>2 measurements ≥180 mg/dL in 1 day), and hypoglycemia (any measurement <70 mg/dL) were compared between cohorts using logistic regression adjusted for home antihyperglycemics.

RESULTS

We included 135 cardiac surgery patients, of which 65 received DPP-4i plus insulin. Eighty-two patients received antihyperglycemics at home. Uncontrolled glucose occurred in 61 (45.2%) patients; while hyperglycemia and hypoglycemia occurred in 50 (37.0%) and 24 (17.8%) patients, respectively. There was no difference in the adjusted odds of uncontrolled glucose (odds ratio [OR] = 1.43; 95% confidence interval [CI] = 0.65-3.11), hyperglycemia (OR = 1.20; 95% CI = 0.52-2.78), or hypoglycemia (OR = 0.69; 95% CI = 0.27-1.75) for those receiving DPP-4i plus insulin versus other regimens.

CONCLUSION

Glucose control was no different among postoperative cardiac surgery patients receiving a DPP-4i plus insulin versus other regimens. DPP-4i use was not associated with hypoglycemia.

Calcium signaling and secretory granule pool dynamics underlie biphasic insulin secretion and its amplification by glucose: experiments and modeling

Glucose-stimulated insulin secretion from pancreatic β-cells is controlled by a triggering pathway that culminates in calcium influx and regulated exocytosis of secretory granules, and by a less understood amplifying pathway that augments calcium-induced exocytosis. In response to an abrupt increase in glucose concentration, insulin secretion exhibits a first peak followed by a lower sustained second phase. This biphasic secretion pattern is disturbed in diabetes. It has been attributed to depletion and subsequent refilling of a readily releasable pool of granules or to the phasic cytosolic calcium dynamics induced by glucose. Here, we apply mathematical modeling to experimental data from mouse islets to investigate how calcium and granule pool dynamics interact to control dynamic insulin secretion. Experimental calcium traces are used as inputs in three increasingly complex models of pool dynamics, which are fitted to insulin secretory patterns obtained using a set of protocols of glucose and tolbutamide stimulation. New calcium and secretion data for so-called staircase protocols, in which the glucose concentration is progressively increased, are presented. These data can be reproduced without assuming any heterogeneity in the model, in contrast to previous modeling, because of nontrivial calcium dynamics. We find that amplification by glucose can be explained by increased mobilization and priming of granules. Overall, our results indicate that calcium dynamics contribute substantially to shaping insulin secretion kinetics, which implies that better insight into the events creating phasic calcium changes in human β-cells is needed to understand the cellular mechanisms that disturb biphasic insulin secretion in diabetes.

Efficacy of Exenatide Plus Pioglitazone Vs Basal/Bolus Insulin in T2DM Patients With Very High HbA1c

OBJECTIVE

To examine the efficacy and safety of combination therapy with exenatide plus pioglitazone vs basal/bolus insulin in patients with poorly controlled type 2 diabetes mellitus (T2DM) with very high hemoglobin A1c (HbA1c) (>10%) receiving sulfonylurea plus metformin and with a long duration of disease.

DESIGN AND PARTICIPANTS

Participants (n = 101) in the Qatar Study with very poor glycemic control (HbA1c >10%) and a long duration of diabetes (10.9 years) receiving maximum/near-maximum doses of sulfonylurea plus metformin were randomly assigned to receive pioglitazone plus weekly exenatide (combination therapy), or basal plus prandial insulin (insulin therapy), to maintain HbA1c <7.0%.

RESULTS

Baseline HbA1c was 11.5% ± 0.2% and 11.2% ± 0.2% (P = not significant) in combination therapy and insulin therapy groups, respectively. At 6 months, combination therapy caused a robust decrease in HbA1c to 6.7% ± 0.1% (∆ = -4.8%) compared with 7.4% ± 0.1% (∆ = -3.8%) in subjects receiving insulin therapy. Combination therapy was effective in lowering the HbA1c independent of sex, ethnicity, or body mass index. Subjects in the insulin therapy group experienced significantly greater weight gain and a 2.5-fold higher rate of hypoglycemia compared with patients receiving combination therapy.

CONCLUSION

Exenatide/pioglitazone combination therapy is an effective and safe therapeutic option in patients with poorly controlled T2DM receiving metformin plus sulfonylurea with very high HbA1c (>10%).

A stable isotope method for in vivo assessment of human insulin synthesis and secretion

AIMS

In vitro, beta cells immediately secrete stored but readily releasable insulin in response to a rise of glucose. During a prolonged insulin response, this is followed by newly synthesized insulin. Our aim was to develop an in vivo test to determine the ratio between readily available and newly synthesized insulin after a stimulus in humans by labelling newly synthesized insulin.

METHODS

A stable isotope tracer of 1.0 g ¹³C leucine with C-peptide as target peptide was administered 45 min prior to 75 g glucose load of a frequently blood sampled 210-min oral glucose tolerance test (OGTT). Our OGTT also encompassed collection of urine, which has a high content of C-peptide. Prior, the optimal conditions under which the tracer ¹³C leucine was administered for enrichment of (pre) proinsulin were established. Also, techniques to obtain urinary C-peptide under highly purified circumstances were set up. Our main outcome measure was the stable isotope enrichment of de novo C-peptide, which we related to early plasma insulin and glucose AUC. Twelve healthy Caucasian individuals (M4F8, age 41.8 ± 2.3, BMI 28.3 ± 1.7) with normal glucose tolerance underwent our OGTT.

RESULTS

We found that during a 75-g OGTT, newly synthesized insulin contributed approximately 20 % of total insulin secretion. The pattern of isotope enrichment obtained by collecting multiple urine voids was suggestive that the newly synthesized insulin contributes to the late phase of insulin secretion. De novo C-peptide correlated negatively with both early plasma insulin AUC (r = -0.629, P = 0.028) and early plasma glucose AUC (r = -0.605, P = 0.037).

CONCLUSIONS

With stable isotope technique added to OGTT, we were able to measure newly synthesized insulin in healthy individuals. This new technique holds the promise that it is feasible to develop a direct in vivo beta cell function test.

Linearity of β-cell response across the metabolic spectrum and to pharmacology: insights from a graded glucose infusion-based investigation series

The graded glucose infusion (GGI) examines insulin secretory response patterns to continuously escalating glycemia. The current study series sought to more fully appraise its performance characteristics. Key questions addressed were comparison of the GGI to the hyperglycemic clamp (HGC), comparison of insulin secretory response patterns across three volunteer populations known to differ in β-cell function (healthy nonobese, obese nondiabetic, and type 2 diabetic), and characterization of effects of known insulin secretagogues in the context of a GGI. Insulin secretory response was measured as changes in insulin, C-peptide, insulin secretion rates (ISR), and ratio of ISR to prevailing glucose (ISR/G). The GGI correlated well with the HGC (r = 0.72 for ISR/G, P < 0.01). The insulin secretory response in type 2 diabetes (T2DM) was significantly blunted (P < 0.001), whereas it was significantly increased in obese nondiabetics compared with healthy nonobese (P < 0.001). Finally, robust (P < 0.001 over placebo) pharmacological effects were observed in T2DM and healthy nonobese volunteers. Collectively, the findings of this investigational series bolster confidence that the GGI has solid attributes for assessing insulin secretory response to glucose across populations and pharmacology. Notably, the coupling of insulin secretory response to glycemic changes was distinctly and uniformly linear across populations and in the context of insulin secretagogues. (Clinical Trial Registration Nos. NCT00782418, NCT01055340, NCT01373450).

Effect of body mass index on insulin secretion or sensitivity and diabetes

BACKGROUND

Although the association between obesity and diabetes is well known, the factors predisposing to diabetes in non-obese Asians are less clearly characterized.

PURPOSE

To investigate the effects of impaired insulin secretion (IIS) and insulin resistance (IR) according to BMI on the incidence of diabetes in the Saku Study.

METHODS

This 4-year cohort study involved 3,083 participants aged 30-69 years without diabetes at baseline (2006-2007). Participants were stratified by BMI (<23.0, 23.0-24.9, and ≥25). Based on insulinogenic index and homeostasis model of IR values, participants were classified into four categories: normal; isolated IIS (i-IIS); isolated IR (i-IR); and IIS plus IR. All data were collected in 2006-2011 and analyzed in 2013-2014.

RESULTS

For participants with BMI <23.0, the risk of developing diabetes was higher in the i-IIS (adjusted hazard ratio=6.6; 95% CI=3.7, 11.6) and IIS plus IR groups (9.4; 3.1, 28.4) than in the normal group. For participants with BMI 23.0-24.9, risk was higher in the i-IIS (9.9; 4.4, 22.1); i-IR (3.4; 1.2, 9.5); and IIS plus IR (23.4; 9.3, 58.9) groups. Among participants with BMI ≥25, risk was higher in the i-IIS (16.9; 6.0, 47.7); i-IR (7.9; 2.8, 22.6); and IIS plus IR (26.9; 9.0, 80.8) groups. BMI was negatively associated with incidence of IIS but positively associated with IR incidence.

CONCLUSIONS

Individuals with normal BMI may develop diabetes mainly through IIS, whereas individuals with high BMI may develop diabetes primarily through IR.

Serum C-peptide assay of patients with hyperglycemic emergencies at the Lagos State University Teaching Hospital (LASUTH), Ikeja

INTRODUCTION

HE are common acute complications of diabetes mellitus (DM) and include diabetic ketoacidosis (DKA), normo-osmolar hyperglycemic state (NHS) and hyperosmolar hyperglycemic state (HHS). They contribute a lot to the mortality and morbidity of DM. The clinical features include dehydration, hyperglycemia, altered mental status and ketosis. The basic mechanism of HE is a reduction in the net effective action of circulating insulin, resulting in hyperglycemia and ketonemia (in DKA) causing osmotic diuresis and electrolytes loss. Infection is a common precipitating factor. Measurement of serum C-peptide provides an accurate assessment of residual β-cell function and is a marker of insulin secretion in DM patients.

AIM AND OBJECTIVES

To assess the level of pancreatic beta cell function in HE patients, using the serum C-peptide.

METHODOLOGY

The biodata and clinical characteristics of the 99 subjects were collated using a questionnaire. All subjects had their serum C-peptide, glucose, electrolytes, urea, creatinine levels, urine ketones determined at admission. Results of statistical analysis were expressed as mean ± standard deviation (SD). A p value <0.05 was regarded statistically significant. Correlation between levels of serum C-peptide and admission blood glucose levels and the duration of DM respectively was done.

RESULTS

The mean age of the subjects was 51 (SD ± 16) years and comparable in both sexes. Mean duration of DM was 6.3 (SD ± 7.1) years, with 35% newly diagnosed at admission. The types of HE in this study are: DKA (24.7%), NHS (36.1%), and HHS (39.2%). Mean blood glucose in this study was 685 mg/dL, significantly highest in HHS and lowest in NHS. Mean serum C-peptide level was 1.6 ng/dL. It was 0.9 ng/dL in subjects with DKA and NHS while 2.7 ng/dL in HHS (p>0.05). Main precipitating factors were poor drug compliance, new-onset of DM and infection.

CONCLUSION

Most (70%) of subjects had poor pancreatic beta cell function, this may be a contributory factor to developing HE. Most subjects with high C-peptide levels had HHS.

Systems analysis and the prediction and prevention of Type 2 diabetes mellitus

Prevalence of Type 2 diabetes has increased at an alarming rate, highlighting the need to correctly predict the development of this disease in order to allow intervention and thus, slow progression of the disease and resulting metabolic derangement. There have been many recent 'advances' geared toward the detection of pre-diabetes, including genome wide association studies and metabolomics. Although these approaches generate a large amount of data with a single blood sample, studies have indicated limited success using genetic and metabolomics information alone for identification of disease risk. Clinical assessment of the disposition index (DI), based on the hyperbolic law of glucose tolerance, is a powerful predictor of Type 2 diabetes, but is not easily assessed in the clinical setting. Thus, it is evident that combining genetic or metabolomic approaches for a more simple assessment of DI may provide a useful tool to identify those at highest risk for Type 2 diabetes, allowing for intervention and prevention.

Assessment of the metabolic pathways associated with glucose-stimulated biphasic insulin secretion

Biphasic glucose-stimulated insulin secretion involves a rapid first phase followed by a prolonged second phase of insulin secretion. The biochemical pathways that control these 2 phases of insulin secretion are poorly defined. In this study, we used a gas chromatography mass spectroscopy-based metabolomics approach to perform a global analysis of cellular metabolism during biphasic insulin secretion. A time course metabolomic analysis of the clonal β-cell line 832/13 cells showed that glycolytic, tricarboxylic acid, pentose phosphate pathway, and several amino acids were strongly correlated to biphasic insulin secretion. Interestingly, first-phase insulin secretion was negatively associated with L-valine, trans-4-hydroxy-L-proline, trans-3-hydroxy-L-proline, DL-3-aminoisobutyric acid, L-glutamine, sarcosine, L-lysine, and thymine and positively with L-glutamic acid, flavin adenine dinucleotide, caprylic acid, uridine 5'-monophosphate, phosphoglycerate, myristic acid, capric acid, oleic acid, linoleic acid, and palmitoleic acid. Tricarboxylic acid cycle intermediates pyruvate, α-ketoglutarate, and succinate were positively associated with second-phase insulin secretion. Other metabolites such as myo-inositol, cholesterol, DL-3-aminobutyric acid, and L-norleucine were negatively associated metabolites with the second-phase of insulin secretion. These studies provide a detailed analysis of key metabolites that are either negatively or positively associated with biphasic insulin secretion. The insights provided by these data set create a framework for planning future studies in the assessment of the metabolic regulation of biphasic insulin secretion.

Role of PPARg2 transcription factor in thiazolidinedione-induced insulin sensitization

OBJECTIVES

Adipose tissue is the key regulator of energy balance, playing an active role in lipid storage and metabolism and may be a dynamic buffer to control fatty acid flux. Peroxisome proliferator-activated receptor gamma isoform-2 (PPARg2), an isoform of the nuclear hormone receptor superfamily, has been implicated in almost all aspects of human metabolic alterations such as obesity, insulin resistance, type-2 diabetes and dyslipidaemia. The PPARg2 isoform is highly present in adipose tissue where it functions as a thrifty phenotype, which promotes adipocyte differentiation and triglyceride storage. Thiazolidinediones, antidiabetic drugs, induce insulin sensitivity by controlling adipokines. The thiazolidinediones bind with PPARg2 in adipocytes and exert an agonist effect by enhancing adipogenesis and fatty acid uptake. Thiazolidinediones stimulate PPARg2, by which they down-regulate tumour necrosis factor-α, leptin, interleukin-6 and plasminogen and also enhance insulin sensitivity. The aim of this work is to define role of PPARg2 transcription factor in thiazolidinedione-induced insulin sensitization.

KEY FINDINGS

The PPARg2 alters the transcription of the target gene. This altered gene transcription results in the up-regulation of insulin-sensitizing factors and down-regulation of insulin-resistant factors. The variant Pro12Ala of the PPARg2 gene is an important modulator in metabolic control in the body. Thiazolidinediones stimulate PPARg2 transcription factor by which PPARg2 binds to responsive elements located in the promoter regions of many genes and modulates their transcriptive activity. There is a strong mutual relationship between receptor binding and agonism, which is evidence of the insulin-sensitizing target of thiazolidinediones in PPARg2. This evidently increases the biological potency of the glucose-lowering effect of thiazolidinediones in vivo as well as their antidiabetic activity.

CONCLUSIONS

PPARg2 transcription factor plays an important role in treatment of type-2 diabetes with thiazolidindiones. The variant Pro12Ala of the PPARg2 gene promotes the activity of thiazolidinediones in minimizing insulin resistance. Transcriptional activity of Pro12Ala variant improves the activity of insulin. Thus thiazolidinediones promote the phosphorylation of PPARg2 to induce insulin sensitivity.

Taurine supplementation restored the changes in pancreatic islet mitochondria in the fetal protein-malnourished rat

Intra-uterine growth retardation has been linked to the development of type 2 diabetes in later life. Mitochondrial changes have been suggested as a link between fetal malnutrition and adult insulin resistance. Taurine has been implicated in this process. We investigated whether protein malnutrition in early life alters mitochondria of the pancreatic islets in adulthood, and whether taurine supplementation restores these changes. Male offspring of rats fed a control diet, a low-protein diet or a low-protein diet supplemented with taurine during pregnancy and lactation were weaned onto the control diet. In each group, at 20 weeks of age, intravenous glucose tolerance tests, euglycaemic–hyperinsulinaemic clamp studies, morphometric analysis of the pancreatic islets and ultra-structural analysis of the mitochondria of the β-cells were performed. The expressions of cytochrome c oxidase (COX) I and mitochondrial respiratory chain complex II were also measured. Fetal protein-malnourished rats showed decreased pancreatic islet mass and reduced insulin-secretory responses to a glucose load. These rats also showed reduced mitochondrial DNA-encoded COX I gene expression in the islets. Electron microscopic examination showed abnormal mitochondrial shapes in the β-cells of fetal protein-malnourished rats. Taurine supplementation to the low-protein diet restored all these changes. Our findings indicate that a maternal protein-restriction diet causes long-lasting mitochondrial changes that may contribute to the development of type 2 diabetes later in life. The lack of taurine may be a key causative factor for these dysfunctional mitochondrial changes.

The first and second phase of insulin secretion in naive Chinese type 2 diabetes mellitus

Impaired insulin secretion (ISEC) has been recognized as one of the most important pathophysiologies of type 2 diabetes mellitus. There are 2 phases of ISEC: the first phase (first ISEC) and second phase (second ISEC). This study aimed to evaluate the 2 phases of ISEC in newly diagnosed type 2 diabetes mellitus patients. Fifty-two drug-naive type 2 diabetes mellitus patients were given 2 tests: a modified low-dose graded glucose infusion (M-LDGGI) and frequent sample intravenous glucose tolerance test. The M-LDGGI is a simplified version of the Polonsky method. Two stages of intravenous infusion of glucose with different rates were given, starting from 2 mg/(kg min) and then followed by 6 mg/(kg min). Each stage was maintained for 80 minutes. The results were interpreted as the slope of the changes of plasma insulin against the glucose levels. The slope of these curves was regarded as the second ISEC and used as the criterion for grouping-the responders and nonresponders. The responders are older and had higher body mass index and log (homeostasis model assessment of beta-cell function) (log HOMA-beta) but lower fasting plasma glucose and hemoglobin A(1c) (HbA(1c)) than the nonresponders. Significant correlations were only noted between the second ISEC and first ISEC (r = 0.278, P = .046) and between the second ISEC and log HOMA-beta (r = 0.533, P = .000). Correlation between different parameters and HbA(1c) was also evaluated. Only second ISEC and log HOMA-beta were correlated significantly with HbA(1c) (r = -0.388, P = .015 and r = -0.357, P = .026, respectively). In type 2 diabetes mellitus, subjects with higher second ISEC are older and have higher body mass index. At the same time, second ISEC is the most important factor for determining glucose levels in naive Chinese type 2 diabetes mellitus patients. The first and second ISECs were only modestly correlated, which indicated that the deterioration of these 2 phases was not synchronized. Finally, we also recommend using the M-LDGGI for quantifying second ISEC. This practical method could be done in many centers without difficulty.

Glucose toxicity: the leading actor in the pathogenesis and clinical history of type 2 diabetes - mechanisms and potentials for treatment

AIM

Although it is now well established that the deleterious effects of chronic hyperglycaemia (i.e., glucose toxicity) play an important role in the progressive impairment of insulin secretion and sensitivity, the two major actors of the pathogenesis of type 2 diabetes mellitus, the precise biochemical and molecular mechanisms responsible for the defects induced by glucose toxicity still remain to be defined.

DATA SYNTHESIS

here we will briefly report on convincing evidence that glucose toxicity acts through oxidative stress, modifications in the exosamine pathway, protein kinase C and others. After inducing or contributing to the genesis of type 2 diabetes, these same mechanisms are considered responsible for the appearance and worsening of diabetic specific microvascular complications, while its role in increasing the risk of cardiovascular diseases is less clear. Recent intervention studies (ADVANCE, ACCORD, VADT), conducted to evaluate the effects of strict glycaemic control, apparently failed to demonstrate an effect of glucose toxicity on cardiovascular diseases, at least in secondary prevention or when diabetes is present for a prolonged time. The re-examination, 20 years later, of the population studied in the UKPDS study, however, clearly demonstrated that the earliest is the strict glycaemic control reached, the lowest is the incidence of cardiovascular diseases observed, including myocardial infarction.

CONCLUSION

The acquaintance of the role of glucose toxicity should strongly influence the usual therapeutic choices and glycaemic targets where the reduced or absent risk of hypoglycaemia, durability of action, and data on prolonged safety should be the preferred characteristics of the drug of choice in the treatment of type 2 diabetes mellitus.

Analysis of factors influencing pancreatic beta-cell function in Japanese patients with type 2 diabetes: association with body mass index and duration of diabetic exposure

AIMS

To elucidate the clinical factors affecting beta-cell function, serum C-peptide immunoreactivity (CPR) levels of patients with type 2 diabetes were analyzed.

METHODS

Seven hundred Japanese patients with type 2 diabetes were enrolled. beta-Cell function was evaluated by fasting CPR (FCPR), 6 min after intravenous injection of 1mg glucagon (CPR-6 min), and the increment of CPR (DeltaCPR). Simple regression analysis between FCPR, CPR-6 min, and DeltaCPR and measures of variables and stepwise multiple regression analysis were carried out.

RESULTS

Years from diagnosis and BMI were the major independent variables predicting beta-cell function. Years from diagnosis was negatively correlated with CPR-6 min (P<0.0001, r=-0.271), and decrease in CPR-6 min was 0.050 ng/(ml year). BMI was positively correlated with CPR-6 min (P<0.0001, r=0.369). When subjects were divided according to BMI, the decrease in CPR-6 min per year in the high-BMI group (0.068 ng/(ml year)) was greater than that in the low-BMI group (0.035 ng/(ml year)).

CONCLUSION

A linear decline in endogenous insulin secretion over more than several decades of diabetes was confirmed by this cross-sectional study. The duration of diabetes exposure and BMI are thus major factors in beta-cell function in Japanese patients with type 2 diabetes.

CS-917, a fructose 1,6-bisphosphatase inhibitor, improves postprandial hyperglycemia after meal loading in non-obese type 2 diabetic Goto-Kakizaki rats

Postprandial hyperglycemia is one of the features of type 2 diabetes. Increased hepatic gluconeogenesis is a predominant cause of postprandial hyperglycemia in type 2 diabetes. In this study, we evaluated the effect of gluconeogenesis inhibition on postprandial hyperglycemia using CS-917, a novel inhibitor of fructose 1,6-bisphphosphatase (FBPase) which is one of the rate-limiting enzymes of gluconeogenesis. The suppressive effect of CS-917 on postprandial hyperglycemia was evaluated in a meal loading test in Goto-Kakizaki (GK) rats, non-obese type 2 diabetic animal model characterized by impaired insulin secretion. In addition, we describe acute effect of CS-917 on fasting hyperglycemia in overnight-fasted GK rats and chronic effect of CS-917 in multiple dosing GK rats.CS-917 suppressed plasma glucose elevation after meal loading in a dose-dependent manner at doses ranging from 10 to 40 mg/kg. In an overnight-fasted state, CS-917 decreased the plasma glucose levels dose-dependently at doses ranging from 2.5 to 40 mg/kg. Consistent with the inhibition of FBPase, glucose-lowering was associated with an accumulation of hepatic d-fructose 1,6-bisphosphate and a reduction in hepatic d-fructose 6-phosphate. Chronic treatment of CS-917 decreased plasma glucose significantly, and no significant increase in plasma lactate and no profound elevation in plasma triglycerides were observed by both acute and chronic treatment of CS-917 in GK rats.These findings suggest that enhanced gluconeogenesis contributes to hyperglycemia in postprandial conditions as well as in fasting conditions, and that CS-917 as an FBPase inhibitor corrects postprandial hyperglycemia as well as fasting hyperglycemia.

Abnormalities in insulin secretion in type 2 diabetes mellitus

Type 2 diabetes mellitus is a multifactorial disease, due to decreased glucose peripheral uptake, and increased hepatic glucose production, due to reduced both insulin secretion and insulin sensitivity. Multiple insulin secretory defects are present, including absence of pulsatility, loss of early phase of insulin secretion after glucose, decreased basal and stimulated plasma insulin concentrations, excess in prohormone secretion, and progressive decrease in insulin secretory capacity with time. beta-cell dysfunction is genetically determined and appears early in the course of the disease. The interplay between insulin secretory defect and insulin resistance is now better understood. In subjects with normal beta-cell function, increase in insulin is compensated by an increase in insulin secretion and plasma glucose levels remain normal. In subjects genetically predisposed to type 2 diabetes, failure of beta-cell to compensate leads to a progressive elevation in plasma glucose levels, then to overt diabetes. When permanent hyperglycaemia is present, progressive severe insulin secretory failure with time ensues, due to glucotoxicity and lipotoxicity, and oxidative stress. A marked reduction in beta-cell mass at post-mortem examination of pancreas of patients with type 2 diabetes has been reported, with an increase in beta-cell apoptosis non-compensated by neogenesis.

[Anatomical and functional plasticity of pancreatic beta-cells and type 2 diabetes]

The most common form of diabetes, type 2 diabetes (T2D) is a major Public Health issue which is receiving a great deal of attention both in industrial and public research, in order to develop new and more effective drugs. The hyperglycaemia of T2D is the result of two interdependent defects : decreased biological efficacy of insulin in target tissues (insulin resistance), and a decreased capacity for beta cells to secrete insulin in response to glucose. Furthermore, hyperglycaemia evolves with time and even with rigorous treatment there is a progressive deterioration of glucose homeostasis. Seventy five percent of DT2 patients are obese and show a perturbed lipid profile. beta-cell plasticity is a unique property of these cells to adapt their number and volume (beta-cell mass) and their function to the increased secretory demand linked to insulin resistance. This is well documented in physiological (pregnancy) as well in pathophysiological conditions (obesity, acromegaly). Although the lack of reliable techniques makes it very difficult to document it in humans, this property is likely altered in DT2, mainly as a consequence of the prolonged exposure of islet cells to high plasma levels of glucose and free fatty acids (gluco-lipotoxicity). The mechanisms by which hyperglycaemia and hyperlipidemia exert their deleterious effects on the beta-cell include the generation of Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS) and Advanced Glycosylation End Products (AGE). Altogether the prevailing clinical and experimental data urge us to consider that the pathophysiology of DT2 lies, at least in part, the inability of beta-cells to adapt their functional mass to the prevailing insulin demand. This re-evaluation of the pathophysiology of DT2 stimulates the research of new therapeutic approaches aimed at maintaining and/or restoring the functional beta-cell mass by targeting the mechanisms responsible for its decrease.

The role of voltage-gated calcium channels in pancreatic beta-cell physiology and pathophysiology

Voltage-gated calcium (CaV) channels are ubiquitously expressed in various cell types throughout the body. In principle, the molecular identity, biophysical profile, and pharmacological property of CaV channels are independent of the cell type where they reside, whereas these channels execute unique functions in different cell types, such as muscle contraction, neurotransmitter release, and hormone secretion. At least six CaValpha1 subunits, including CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1, have been identified in pancreatic beta-cells. These pore-forming subunits complex with certain auxiliary subunits to conduct L-, P/Q-, N-, R-, and T-type CaV currents, respectively. beta-Cell CaV channels take center stage in insulin secretion and play an important role in beta-cell physiology and pathophysiology. CaV3 channels become expressed in diabetes-prone mouse beta-cells. Point mutation in the human CaV1.2 gene results in excessive insulin secretion. Trinucleotide expansion in the human CaV1.3 and CaV2.1 gene is revealed in a subgroup of patients with type 2 diabetes. beta-Cell CaV channels are regulated by a wide range of mechanisms, either shared by other cell types or specific to beta-cells, to always guarantee a satisfactory concentration of Ca2+. Inappropriate regulation of beta-cell CaV channels causes beta-cell dysfunction and even death manifested in both type 1 and type 2 diabetes. This review summarizes current knowledge of CaV channels in beta-cell physiology and pathophysiology.

How Can We Implement Current Therapies and Interventions to Achieve Glycemic Control?

OBJECTIVE

To discuss the appropriate use of oral therapies to achieve and sustain glycemic targets in patients with type 2 diabetes.

METHODS

The stages in the development and progression of type 2 diabetes are reviewed, and the limitations of single-drug therapy are addressed.

RESULTS

The development of diabetes is a staged progression; affected patients show evolution through numerous stages of glucose intolerance before clinical diabetes manifests. Beta cell function continues to deteriorate until absolute failure occurs; however, other factors, such as glucose and lipid toxicities, insulin resistance in peripheral tissues, and loss of the first-phase insulin response, further impair the body's ability to regulate release of insulin in response to glucose. Traditional treatment algorithms often fail to address the progressive, multifaceted nature of type 2 diabetes, with its numerous related abnormalities. Combination therapy with orally administered agents can be used to manage glucose concentrations and other risk factors safely and effectively.

CONCLUSION

The therapeutic goal in type 2 diabetes is to achieve and maintain a physiologic profile as close to normal as possible. This outcome necessitates treatment of multiple defects with use of various combinations of orally administered agents. Clinicians should focus on effective treatment of these defects to achieve established targets.

Timing of Ca2+ response in pancreatic beta-cells is related to mitochondrial mass

The timing and magnitude of calcium response are cell-specific in individual beta-cells. This may indicate that the cells have different roles in the intact islet. It is unknown what mechanisms determine these characteristics. We previously found that the mechanisms setting cell-specific response timing are disturbed in beta-cells from hyperglycemic mice and one of the causes is likely to be an altered mitochondrial metabolism. Mitochondria play a key role in the control of nutrient-induced insulin secretion. Here, we used confocal microscopy with the fluorescent probe MitoTracker Red CMXRos and Fluo-3 to study how the amount of active mitochondria is related to the lag-time and the magnitude of calcium response to 20mM glucose in isolated beta-cells and in cells within intact lean and ob/ob mouse islets. Results show that the mitochondrial mass is inversely correlated with the lag-times for calcium response both in lean and ob/ob mouse beta-cells (r=-0.73 and r=-0.43, respectively, P<0.05). Thus, the state of mitochondria may determine the timing of calcium response.

Pancreatic beta cells from db/db mice show cell-specific [Ca2+]i and NADH responses to glucose but not to alpha-ketoisocaproic acid

OBJECTIVE

We recently showed that timing and magnitude of the glucose-induced cytoplasmic calcium [Ca2+]i response are reproducible and specific for the individual beta cell. We now wanted to identify which step(s) of stimulus-secretion coupling determine the cell specificity of the [Ca2+]i response and whether cell specificity is lost in beta-cells from diabetic animals. Besides glucose, we studied the effects of glyceraldehyde, a glycolytic intermediate, and alpha-ketoisocaproic acid (KIC), a mitochondrial substrate.

METHODS

Early [Ca2+]i changes were studied stimulations in fura-2-labeled dispersed beta cells from lean, ob/ob, and db/db mice. Lag time and peak height were compared during 2 consecutive stimulations with the same stimulator. Nicotinamide adenine dinucleotide (NADH) responses to glucose and KIC were studied as a measure of metabolic flux.

RESULTS

Both glyceraldehyde and KIC induced cell-specific temporal responses in lean mouse beta cells with a correlation between lag times for [Ca2+]i rise during the first and second stimulation. Beta cells from ob/ob and db/db mice showed cell-specific temporal [Ca2+]i responses to glucose and glyceraldehyde but not to KIC. Glucose induced cell-specific NADH responses in all 3 models, but KIC did so only in lean mouse [beta] cells.

CONCLUSIONS

A cell-specific response may be induced at several steps of beta-cell stimulus-secretion coupling. Mitochondrial metabolism generates a cell-specific response in normal beta cells but not in db/db and ob/ob mouse beta cells.

Role of early insulin secretion in postglucose-loading hyperglycaemia and postfat-loading hyperlipidaemia: comparing nateglinide and glibenclamide for acute effects on insulin secretion in OLETF rats

AIM

The aim of this study was to clarify the role of an early insulin secretion in postprandial hyperglycaemia and hyperlipidaemia; a study using spontaneously type 2 diabetic Otsuka Long-Evans Tokushima Fatty rats with visceral obesity was performed to investigate the acute effect of nateglinide (NAT) vs. glibenclamide (GB) on increases in glucose after glucose loading and on increases in triglyceride (TG) after fat loading.

METHODS

Fasting rats were given 50 mg/kg of NAT, 1 mg/kg of GB or 5% methyl cellulose (vehicle) as control and then immediately given oral glucose 1 g/kg.

RESULTS

An acute increase in insulin levels in portal blood peaked at 15 min in the NAT group, while insulin levels in the GB group continued to increase significantly after 60 min. Glucose levels in peripheral blood were significantly lower in the NAT group at 30 and 60 min and in the GB group at 120, 180 and 270 min after glucose loading, compared with those in the vehicle group. Subsequently, fasting rats were given NAT, GB or vehicle and then immediately given oral fat emulsion (soy oil 2 g/kg). An acute increase in insulin secretion was seen with NAT, peaking at 30 min, while TG, chylomicron and very low-density lipoprotein levels after fat loading were shown to be significantly lower with NAT than with vehicle. However, the continued insulin secretion observed with GB led to no significant decrease in TG levels after fat loading. In addition, lipoprotein lipase mRNA expression in adipose tissue increased significantly 120 min after NAT administration in comparison with baseline. This increase was not noted with GB administration.

CONCLUSION

Abnormalities in early insulin secretion are closely associated with the pathogenesis of various disease conditions that combine to characterize type 2 diabetes, suggesting that normalizing early insulin response in portal blood represents an important treatment not only for postprandial hyperglycaemia but also for postprandial hyperlipidaemia.

Clinical characteristics of nateglinide response as assessed by insulinogenic indices: preliminary study to determine an optimal indication for nateglinide

Insulin secretion dynamics and response to nateglinide were studied in patients with type 2 diabetes and reduced early-phase insulin secretion. On day 1, 24 patients underwent a 75-g oral glucose tolerance test without taking nateglinide. On day 2, they were given oral nateglinide 90 mg immediately before the oral glucose tolerance test. After glucose loading, insulin levels increased significantly at 30, 60, 90, and 120 minutes after the patients took nateglinide, along with insulinogenic indices, the total area under the insulin curve, the area under the 0- to 90-minute insulin curve, and the area under the 90- to 180-minute insulin curve. Both the plasma glucose level at 60, 90, 120, and 180 minutes and the total area under the glucose curve were significantly reduced following nateglinide administration. Compared with the low responders (n=13), the high responders (n=11) had a significantly shorter duration of disease, significantly higher insulinogenic indices in the absence of nateglinide administration, and a higher homeostasis model assessment-beta cell performance. Nateglinide demonstrated a rapid-onset and rapid-offset insulin secretion-stimulating effect in this study population. A single dose of nateglinide may be indicated for patients with a relatively high homeostasis model assessment-beta cell performance, a short duration of disease, and relatively high insulinogenic indices prior to nateglinide administration.

Cell-specific Ca(2+) responses in glucose-stimulated single and aggregated beta-cells

A rise in the cytoplasmic calcium concentration ([Ca(2+)](i)) is a key event for insulin exocytosis. We have recently found that the 'early [Ca(2+)](i) response' in single ob/ob mouse beta-cells is reproduced during consecutive glucose stimulations. It, therefore, appears that the response pattern is a characteristic of the individual beta-cell. We have now investigated if a cell-specific [Ca(2+)](i) response is a general phenomenon in rodent beta-cells, and if it can be observed when cells are functionally coupled. With the use of the fura-2 technique, we have studied the 'early [Ca(2+)](i) response' in single dispersed beta-cells, in beta-cell clusters of different size and in intact islets from the ob/ob mouse during repeated glucose stimulation (20mM). beta-Cells from lean mouse and rat, and intact islets from lean mouse were also investigated. Significant correlations between the first and second stimulation were found for the parameters lag-time for Ca(2+) rise (calculated as the time from start of stimulation of the cell until the first value above an extrapolated baseline), nadir of initial lowering (difference between the baseline and lowest [Ca(2+)](i) value), and peak height (difference between baseline and the highest [Ca(2+)](i) value of the first calcium peak) in single dispersed beta-cells, in 'single beta-cell within a small cluster', in clusters of medium and large size, and in single dispersed beta-cells from lean mouse and rat. The lag-times for Ca(2+) rise and peak heights were correlated within the pairs of stimulation also in intact ob/ob islets. In summary, despite a large heterogeneity of the 'early [Ca(2+)](i) response' among individual cells, the lag-time for [Ca(2+)](i) rise, the nadir of initial lowering and the height of the first peak response can be identified as cell-specific markers in beta-cells.

The impact of ethnicity on type 2 diabetes

The rapid increase of diabetes prevalence in the US population and across all westernized world has been associated with environmental changes that promote obesity. Although dietary factors, such as total caloric intake, relative excess of dietary saturated fats content and lack of fibers, together with reduced level of physical activity clearly determine the main features of the "obesogenic" environment typical of "western" societies, the impact of lifestyle factors on obesity and diabetes appears to differ in various ethnic groups. Although ethnic-related differences in lifestyle factors may account for some of the predisposition to obesity and diabetes of various ethnic groups, genetic factors may play a more determinant role. These observations pose important public health questions in regard to strategies for treatment and prevention of diabetes both within the multiethnic US population and in the population of origin of various ethnicities. The elucidation of the pathophysiologic mechanisms responsible for the heterogeneous relationship between obesity and type 2 diabetes in various ethnicities may give important contributions to better understand the complex mechanisms involved in the development of this disease. This review examines epidemiological and pathophysiological aspects of the interaction between environment and ethnic predisposition to type 2 diabetes.

Isulinotropic properties of Nigella sativa oil in Streptozotocin plus Nicotinamide diabetic hamster

The present study was designed to investigate the possible insulinotropic properties of Nigella sativa L. (N. sativa) oil in Streptozotocin plus Nicotinamide-induced diabetes mellitus in hamsters. Nicotinamide was injected intraperitoneally 15min before injection of Streptozotocin intravenously. Oral treatment with N. sativa oil began 4 weeks after induction of diabetes. Serum insulin was measured by enzymeimmunoassay. Islets insulin was stained using anti-insulin monoclonal antibody. Significant decrease in blood glucose level together with significant increase in serum insulin level were observed after treatment with N. sativa oil for 4 weeks. Big areas with positive immuno-reactivity for the presence of insulin were observed in the pancreases from N. sativa oil-treated group compared to non-treated one using immunohistochemical staining. Therefore, our data show that the hypoglycemic effect of N. sativa oil in Streptozotocin plus Nicotinamide diabetic hamsters resulted, at least partly, from a stimulatory effect on beta cell function with consequent increase in serum insulin level. These results indicate that N. sativa oil has insulinotropic properties in type 2-like model.

An etiologic model proposing that non-insulin-dependent diabetes mellitus is chronic hypoxic stress hyperglycemia

This etiologic model equates non-insulin-dependent diabetes mellitus (NIDDM) to chronic hypoxic stress hyperglycemia produced by increased stimulation of the sympathetic nervous system and hypothalamic-pituitary-adrenal axis. In the initial stages of the disease, hypoxia is believed to result from hemodilutional anemia precipitated by a reduction in vascular smooth muscle tone. The reduction increases lumen diameter necessitating an increased blood volume to maintain pressure. Increased lumen diameter may also trigger atherosclerotic changes that characterize the later stages of NIDDM. The increased diameter decreases the shear stress experienced by endothelial cells and they respond by releasing endothelin, a smooth muscle constrictor and mitogen. The constricting action is hypothesized to be relatively ineffective in NIDDM leading to long-term endothelin release and activation of its mitogenic properties. The resulting increase in the number of smooth muscle cells may explain the intimal thickening of atherosclerosis. Restoration of vascular muscle tone is proposed as a treatment strategy for mild NIDDM.

Diminution of early insulin response to glucose in subjects with normal but minimally elevated fasting plasma glucose. Evidence for early beta-cell dysfunction

AIM

Systematic analysis of beta-cell function in Japanese health examinees.

METHODS

In 938 Japanese health examinees (627 men and 311 women, mean age and body mass index, 54.0 years and 23.6 kg/m2, respectively), plasma specific insulin was measured at fasting and during a 75-g oral glucose tolerance test. The subjects were stratified into six groups based on fasting plasma glucose < or = 5.1 mmol/l, 5.2-6.0 mmol/l, 6.1-6.9 mmol/l, 7.0-7.8 mmol/l, 7.9-8.7 mmol/l, and > or = 8.8 mmol/l as the 1st, 2nd, 3rd, 4th, 5th and 6th groups, respectively.

RESULTS

Distribution of fasting insulin showed a very modest 'inverted U' shape, with the peak in the 5th group. Progressive increase from the 1st toward the 5th group was significant. In contrast, the ratio of change in insulin to change in glucose from 0 to 30 min during the glucose tolerance test was greatest in the 1st group and progressively declined in the groups with higher fasting glycaemia. Difference in the ratio was most striking and highly significant between the 1st and 2nd groups. Distribution of the insulin to glucose ratio of subjects with normal glucose tolerance significantly overlapped with that of untreated patients with diabetes.

CONCLUSIONS

In a Japanese population, (i) beta-cell starts to deteriorate during normoglycaemia with a minimal elevation of fasting plasma glucose, and (ii) there are glucose-tolerant subjects with beta-cell dysfunction.

Modeling phasic insulin release: immediate and time-dependent effects of glucose

The cellular and molecular mechanisms of insulin secretion are being intensively investigated, yet most researchers are seemingly unaware of the complexity of the dynamic regulation of the secretion. In this article, we summarize studies of the physiology of insulin secretion performed over several decades. The insulin response of perifused islets of rats, perfused rat pancreas, or that of a human, to a square-wave glucose stimulus is biphasic, a transient first-phase response of 4- to 10-min duration followed by a gradual rise in secretion rates (second-phase response). Several hypotheses have been proposed to account for the phasic nature of insulin secretion; they are briefly discussed in this review. We have favored the hypothesis that nutrient stimulators such as glucose, in addition to a primary and almost immediate secretory signal, with time induce both stimulatory and inhibitory messages in the beta-cell, and those messages modulate the primary insulinogenic signal. Indeed, studies in the rat pancreas and in humans have demonstrated that short stimulations with glucose generate a state of refractoriness of the insulin secretion, which we have termed time-dependent inhibition (TDI). Nonnutrient secretagogues such as arginine induce strong TDI independent of the duration of stimulation. Once the agent is removed, TDI persists for a considerable period. In contrast, prolonged stimulations with glucose (and other nutrients) lead to the amplification of the insulin response to subsequent stimuli; this can be demonstrated in the perfused rat pancreas, in perifused islets from several rodents, and in humans. We have termed this stimulatory signal time-dependent potentiation (TDP). The generation of TDP requires higher glucose concentrations and prolonged stimulation; the effect is retained for some time after cessation of the stimulus. Of major interest is the observation that, while the acute insulin response to glucose is severely reduced in glucose-intolerant animals and humans, TDP seems to be intact. The cellular mechanisms of TDI and TDP are poorly understood, but data reviewed here suggest that they are distinct from those that lead to the acute insulin response to stimuli. A model is proposed whereby the magnitude and kinetics of the insulin response to a given stimulus reflect the balance between TDP and TDI. Researchers studying the cellular and molecular mechanisms of insulin release are urged to take into consideration these complex and opposing factors which regulate insulin secretion.

Clinical importance of insulin secretion and its interaction with insulin resistance in the treatment of type 2 diabetes mellitus and its complications

Type 2 diabetes primarily develops from pathogenic defects in the mechanisms of insulin secretion and hepatic and peripheral insulin action. The consequent disruption of normal glucose metabolism involves a number of organ systems and is ultimately manifested in fasting and daytime hyperglycemia. Chronically elevated blood glucose concentrations determine the progression of the disease by further exacerbating insulin resistance and causing beta-cell exhaustion in addition to decreasing their responsiveness to glucose. The beta-cell secretory dysfunction is characterized by the lack of the early phase of glucose-induced insulin secretion and the insufficient and delayed late phase of secretion. Glycemic levels in patients with type 2 diabetes are directly related to the risk of developing microvascular and macrovascular complications, the main cause of the morbidity and mortality associated with this disease. The goal of treatment is to decrease the risk and delay the progression of these complications by improving glycemic control. Current oral antidiabetic agents, used as monotherapy or in combination, include traditional insulin secretagogues, insulin sensitizers and inhibitors of carbohydrate absorption. A greater understanding of the pathophysiology of type 2 diabetes and recent findings on the significance of meal-related glycemia to overall glycemic control are expanding the therapeutic options for treating this disease.

IS BETA CELL DYSFUNCTION RESPONSIBLE FOR FLAT GLUCOSE TOLERANCE CURVE IN PRIMARY HYPOTHYROIDISM? (A HYPOTHESIS)

An intimate relationship between thyroid hormones and carbohydrate metabolism has long been recognised and oral glucose load produces flat glucose tolerance curve in patients with primary hypothyroidism. Although delayed glucose absorption was proposed to explain flat glucose tolerance curve exact mechanism remains to be elucidated. Hence this study was undertaken to assess glucose and insulin response to OGTT and IVGTT in 25 freshly detected cases of hypothyroidism and 25 healthy control. The cases were matched for sex, age, BMI, and waist hip ratio with controls. Cases and controls with past or family history of obesity, diabetes mellitus, or hypertension were excluded from study. The biochemical profile of the cases and controls was also comparable except for haemoglobin (11.2±0.31 vs 12.9±0.22 gm/dl)(p=0.0004). Serum cholesterol and triglyceride levels were higher in the cases but difference was not statistically significant Fasting plasma glucose level was significantly lower in hypothyroid patients (78±2.2 vs88±4.4 mg/dl, p=0.049). The oral glucose tolerance curve was flat with plasma glucose levels significantly lower at 30 minutes. The insulin levels during OGTT were found to be higher in the cases at all stages. There was loss of first phase insulin response to the glucose load during the IVGTT, which was blunted at all stages and the difference was statistically significant at 0 and 3 minutes. Loss of first phase insulin response to IV glucose suggests that there is evidence of beta-cell dysfunction. Patients with hypothyroidism were more insulin sensitive than control and insulin secretion was comparable with controls. Therefore flat glucose tolerance curve can be explained by absence of insulin priming effect leading to decreased glucose absorption followed by increased glucose disposal because of higher insulin levels following OGTT and increased glucose disposal caused by increased insulin sensitivity.

Hypoglycaemic effect of spergularia purpurea in normal and streptozotocin-induced diabetic rats

Single and repeated oral administration of the water extracts of Spergularia purpurea (SP) at a dose of 10 mg/kg were tested on hypoglycaemic activity in normal and streptozotocin-induced diabetic rats. In normal rats, the water extract of SP decreased significantly the plasma glucose levels 4 h after single oral administration (P<0.01), and one week after repeated oral administration (P<0.05). A significant decrease of plasma glucose levels was observed 6 h after a single oral administration of the water extract of S. purpurea in severe hyperglycaemic rats (n=6) from 22.78+/-0.60 to 11.21+/-0.49 mmol/l (P<0.001). On other hand, water extract of S. purpurea normalised plasma glucose levels after two weeks of repeated oral administration in diabetic rats; 24.05+/-1.16 versus 7.18+/-0.51 mmol/l (P<0.001) at the start and 2 weeks after water extract administration, respectively. We conclude that the water extract of SP induces hypoglycaemic activity when administered orally in normal and STZ diabetic rats. In order to determine the active principle (s) responsible of the hypoglycaemic effect, preliminary phytochemical analysis of the water extract has been investigated.

4-Hydroxyisoleucine: experimental evidence of its insulinotropic and antidiabetic properties

We have recently shown in vitro that 4-hydroxyisoleucine (4-OH-Ile), an amino acid extracted from fenugreek seeds, potentiates insulin secretion in a glucose-dependent manner. The present study was designed to investigate whether 4-OH-Ile could exert in vivo insulinotropic and antidiabetic properties. For this purpose, intravenous or oral glucose tolerance tests (IVGTTs and OGTTs, respectively) were performed not only in normal animals but also in a type II diabetes rat model. During IVGTT in normal rats or OGTT in normal dogs, 4-OH-Ile (18 mg/kg) improved glucose tolerance. The lactonic form of 4-OH-Ile was ineffective in normal rats. In non-insulin-dependent diabetic (NIDD) rats, a single intravenous administration of 4-OH-Ile (50 mg/kg) partially restored glucose-induced insulin response without affecting glucose tolerance; a 6-day subchronic administration of 4-OH-Ile (50 mg/kg, daily) reduced basal hyperglycemia, decreased basal insulinemia, and slightly, but significantly, improved glucose tolerance. In vitro, 4-OH-Ile (200 microM) potentiated glucose (16.7 mM)-induced insulin release from NIDD rat-isolated islets. So, the antidiabetic effects of 4-OH-Ile on NIDD rats result, at least in part, from a direct pancreatic B cell stimulation.

The natural history of insulin secretory dysfunction and insulin resistance in the pathogenesis of type 2 diabetes mellitus

The pathogenesis of type 2 diabetes involves abnormalities in insulin action, insulin secretion, and endogenous glucose output (EGO). However, the sequence with which these abnormalities develop and their relative contributions to the deterioration in glucose tolerance remain unclear in the absence of a detailed longitudinal study. We measured insulin action, insulin secretion, and EGO longitudinally in 17 Pima Indians, in whom glucose tolerance deteriorated from normal (NGT) to impaired (IGT) to diabetic over 5.1 +/- 1.4 years. Transition from NGT to IGT was associated with an increase in body weight, a decline in insulin-stimulated glucose disposal, and a decline in the acute insulin secretory response (AIR) to intravenous glucose, but no change in EGO. Progression from IGT to diabetes was accompanied by a further increase in body weight, further decreases in insulin-stimulated glucose disposal and AIR, and an increase in basal EGO. Thirty-one subjects who retained NGT over a similar period also gained weight, but their AIR increased with decreasing insulin-stimulated glucose disposal. Thus, defects in insulin secretion and insulin action occur early in the pathogenesis of diabetes. Intervention to prevent diabetes should target both abnormalities.