beta-cell function and anti-diabetic pharmacotherapy

Type III Secretion System in Intestinal Pathogens and Metabolic Diseases

Modern lifestyle changes, especially the consumption of a diet high in salt, sugar, and fat, have contributed to the increasing incidence and prevalence of chronic metabolic diseases such as diabetes, obesity, and gout. Changing lifestyles continuously shape the gut microbiota which is closely related to the occurrence and development of metabolic diseases due to its specificity of composition and structural diversity. A large number of pathogenic bacteria such as Yersinia, Salmonella, Shigella, and pathogenic E. coli in the gut utilize the type III secretion system (T3SS) to help them resist host defenses and cause disease. Although the T3SS is critical for the virulence of many important human pathogens, its relationship with metabolic diseases remains unknown. This article reviews the structure and function of the T3SS, the disruption of intestinal barrier integrity by the T3SS, the changes in intestinal flora containing the T3SS in metabolic diseases, the possible mechanisms of the T3SS affecting metabolic diseases, and the application of the T3SS in the treatment of metabolic diseases. The aim is to provide insights into metabolic diseases targeting the T3SS, thereby serving as a valuable reference for future research on disease diagnosis, prevention, and treatment.

Gypenoside A attenuates dysfunction of pancreatic β cells by activating PDX1 signal transduction via the inhibition of miR-150-3p both in vivo and in vitro

Saponin gypenoside A (GP) has shown its potential to handle diabetes mellitus. MicroRNA-150-3p (miR-150-3p) is closely related to the dysfunction of pancreatic β cells by targeting PDX1. Given the function of GP is related to its regulation on different miRs, the current study assessed the role of miR-150-3p as a therapeutic target for the hypoglycemic effects of GP. Pancreatic β cell dysfunction was induced in mice using the high-fatty diet (HFD) method and then handled with GP. Changes in insulin release and resistance and the activity of the miR-150-3p/PDX1 axis were detected. The expression of miR-150-3p was induced to confirm its central in the effects of GP. The results of in vivo tests were then validated with in vitro assays. HFD administration suppressed glucose tolerance, delayed insulin release, and induced insulin resistance and pancreas apoptosis in mice, which was indicative of the dysfunction of β pancreatic cells. Changes in pancreatic β function were associated with the increased expression of miR-150-3p and suppressed expression of PDX1. After the administration of GP, the impairments of the pancreas were alleviated and the expression of miR-150-3p was inhibited, contributing to the restored level of PDX1. The injection of miR-150-3p agomir counteracted the protective effects of GP. In in vitro assays, the pretransfection of miR-150-3p mimetics also counteracted the protective effects of GP on pancreatic β cells against palmitic acid. Collectively, miR-150-3p played a key role in the protective effects of GP against pancreatic β cell dysfunction by inhibiting PDX1 expression.

A High-Content Screen for the Identification of Plant Extracts with Insulin Secretion-Modulating Activity

Bioactive plant compounds and extracts are of special interest for the development of pharmaceuticals. Here, we describe the screening of more than 1100 aqueous plant extracts and synthetic reference compounds for their ability to stimulate or inhibit insulin secretion. To quantify insulin secretion in living MIN6 β cells, an insulin–Gaussia luciferase (Ins-GLuc) biosensor was used. Positive hits included extracts from Quillaja saponaria, Anagallis arvensis, Sapindus mukorossi, Gleditsia sinensis and Albizia julibrissin, which were identified as insulin secretion stimulators, whereas extracts of Acacia catechu, Myrtus communis, Actaea spicata L., Vaccinium vitis-idaea and Calendula officinalis were found to exhibit insulin secretion inhibitory properties. Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) were used to characterize several bioactive compounds in the selected plant extracts, and these bioactives were retested for their insulin-modulating properties. Overall, we identified several plant extracts and some of their bioactive compounds that may be used to manipulate pancreatic insulin secretion.

Pancreatic β cell regeneration induced by clinical and preclinical agents

Diabetes, one of the most common chronic diseases in the modern world, has pancreatic β cell deficiency as a major part of its pathophysiological mechanism. Pancreatic regeneration is a potential therapeutic strategy for the recovery of β cell loss. However, endocrine islets have limited regenerative capacity, especially in adult humans. Almost all hypoglycemic drugs can protect β cells by inhibiting β cell apoptosis and dedifferentiation via correction of hyperglycemia and amelioration of the consequent inflammation and oxidative stress. Several agents, including glucagon-like peptide-1 and γ-aminobutyric acid, have been shown to promote β cell proliferation, which is considered the main source of the regenerated β cells in adult rodents, but with less clarity in humans. Pancreatic progenitor cells might exist and be activated under particular circumstances. Artemisinins and γ-aminobutyric acid can induce α-to-β cell conversion, although some disputes exist. Intestinal endocrine progenitors can transdeterminate into insulin-producing cells in the gut after FoxO1 deletion, and pharmacological research into FoxO1 inhibition is ongoing. Other cells, including pancreatic acinar cells, can transdifferentiate into β cells, and clinical and preclinical strategies are currently underway. In this review, we summarize the clinical and preclinical agents used in different approaches for β cell regeneration and make some suggestions regarding future perspectives for clinical application.

MiR-34a-5p and miR-452-5p: The Novel Regulators of Pancreatic Endocrine Dysfunction in Diabetic Zucker Rats?

Objective: The pancreatic endocrinal system dominates the regulation of blood glucose levels in vivo, and the dysfunction of pancreatic endocrine β-cells is a major cause of the occurrence and development of Type 2 diabetes (T2D). Although microRNA (miRNA) have been found to be key regulators of pancreatic β-cells proliferation, differentiation and apoptosis, the underlying mechanism remains enigmatic. The aim of this study was to identify several novel miRNAs which might be involved in the etiopathogenesis of diabetic β-cells dysfunction. Methods: The miRNA expression profiles in the pancreas of high-fat diet (HFD) fed Zucker diabetic fatty (ZDF) rats and Zucker lean (ZL) rats feed with normal-fat diet (NFD) were detected by using miRNA microarray chip, and individually verified the most significant factors by quantitative real-time polymerase chain reaction (qRT-PCR) assay. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were used to predict the target genes related to each of the identified miRNAs and the functions of these target genes in different metabolic signaling pathways. Results: Compared with the ZL rats, a total of 24 differentially expressed miRNAs were detected in ZDF rats. Among which miR-34a-5p and miR-452-5p were the most significantly up-regulated and down-regulated respectively. These miRNAs have not been reported in rats' pancreas before. By GO and KEGG enrichment analyses, we found that miR-34a-5p could negatively regulate pancreatic β-cell proliferation through the involvement of Wnt signaling pathway. In addition, it was also found to regulate insulin secretion through the insulin signaling pathway to modulate blood glucose levels. At the same time, miR-452-5p was found to positively regulate the activity of the key rate-limiting enzyme branched-chain α-keto acid dehydrogenase-β (BCKDHB) in the catabolism of branched chain amino acids (BCAA), leading to mitochondrial dysfunction in pancreatic β-cells. Conclusions: miR-34a-5p and miR-452-5p were identified as the novel regulators of pancreatic endocrine dysfunction. These miRNAs might have the potential to be utilized as the new predictive biomarkers for the diagnosis of the occurrence and development of T2D, as well as the therapeutic targets for T2D treatment.

The effects of ertugliflozin on β-cell function: Pooled analysis from four phase 3 randomized controlled studies

AIM

To identify potential predictors and mediators of changes in β-cell function in response to ertugliflozin treatment in people with type 2 diabetes mellitus (T2DM).

PARTICIPANTS AND METHODS

Data from patients with T2DM randomized to ertugliflozin (5 or 15 mg; observations from both doses were pooled) or placebo in four phase 3 clinical studies (clinicaltrials.gov: NCT01958671, NCT02226003, NCT02036515, NCT02099110) were pooled and analysed. Change from baseline in β-cell function at week 26 was assessed, and its potential predictors and mediators were analysed using linear and multiple regression analyses.

RESULTS

Compared with placebo, ertugliflozin improved β-cell function when assessed by mean percent change from baseline in homeostatic model assessment of β-cell function (HOMA-%β; ertugliflozin: 14.7%, 95% confidence interval [CI] 12.3, 17.1; placebo: -0.4%, 95% CI -3.4, 2.5], but not when assessed by change in C-peptide index following a mixed meal tolerance test. Change in HOMA-%β correlated with change from baseline in glycated haemoglobin (HbA1c) and treatment with ertugliflozin, and weakly with change from baseline in body weight. In the ertugliflozin group, change in HOMA-%β correlated with baseline fasting plasma glucose (FPG; r = 0.235, P < 0.001), baseline HbA1c (r = 0.138, P < 0.001), baseline homeostatic model assessment of insulin resistance (HOMA-IR; r = 0.162, P < 0.01), and baseline HOMA-%β (r = -0.321, P < 0.001) in linear regression analyses. Multiple regression analyses yielded similar results.

DISCUSSION

In people with T2DM, ertugliflozin treatment improved fasting β-cell function, but no effect on postprandial β-cell function was observed in this analysis. Improvement in HOMA-%β was predicted by high baseline FPG, HbA1c, HOMA-IR, and low baseline HOMA-%β, and mediated by ertugliflozin treatment, and improved HbA1c and body weight.

New combination therapy of gliclazide and quercetin for protection against STZ-induced diabetic rats

AIMS

The use of natural agents with anti-diabetic effect in combination therapy adds further positive clinical implications in the management of diabetes mellitus. Interestingly, quercetin is one of the most potent naturally occurring antioxidant which possesses various pharmacological actions including anti-diabetic effect. Thus, this research was conducted to assess the efficiency of a new combination from gliclazide and quercetin on glycemic control as well as pancreatic islets and beta cells in STZ-experimental model of diabetes.

MAIN METHODS

Diabetes has been induced by a single intraperitoneal injection of streptozotocin (STZ; 45 mg/kg) in adult male Wistar rats. For 3 consecutive weeks, diabetic rats were given orally either gliclazide (10 mg/kg), quercetin (50 mg/kg), or their combination. At the end of the experiment, histological, immunohistochemical and morphometrical examination of pancreatic tissues was performed. Furthermore, the changes in glucose metabolism, lipid profile, oxidative and inflammatory status were evaluated.

KEY FINDINGS

Treatment with gliclazide alone decreased serum glucose, total cholesterol, triglycerides, malondialdehyde, tumor necrosis factor-alpha and nuclear factor kappa-Beta while increased serum C-peptide, superoxide dismutase, reduced glutathione and adiponectin levels. Combined administration of quercetin with gliclazide markedly augmented serum superoxide dismutase and reduced glutathione more than gliclazide alone and normalized all the above-mentioned parameters. Besides, this combination therapy restored immunostaining intensity, number of pancreatic islets and beta cells along with its area and perimeter.

SIGNIFICANCE

Based on the aforementioned results, this combination could be considered a promising one in diabetes mellitus management.

Antioxidative and antidiabetic effects of germinated rough rice extract in 3T3-L1 adipocytes and C57BLKS/J-db/db mice

Background

To overcome disadvantages of germinated brown rice, we germinated rough rice and tested effects of its useful ingredients on prevention of diabetes.

Objective

This study investigated the in vitro antioxidant and in vivo antidiabetic effects of rough rice (Oryza sativa L.) with hulls, before and after germination. Rough rice was germinated for 4 days and extracted with water at 120°C.

Design

This study measured antioxidants and antioxidative effects and inhibitory activities against α-amylase and α-glucosidase of rough rice before and after germination and investigated antidiabetic effects of rough rice through animal experiments.

Results

All these factors increased after germination. Also, α-amylase and α-glucosidase inhibition and glucose uptake by 3T3-L1 adipocytes were significantly increased after germination. Oral administration of the germinated rough rice extract for 8 weeks significantly increased insulin levels and decreased blood glucose levels in a C57BLKS/J-db/db mice model. Immunohistochemical analysis showed that germinated rough rice effectively protected against liver, kidney, and pancreatic tissue damage.

Discussion

Useful ingredients in germinated rough rice could be used to prevent diabetes.

Conclusions

These results suggest that germinated rough rice extract had a beneficial effect on diabetes by increasing the antioxidant activity and further purification studies are necessary to elucidate the mechanism of the extract’s antidiabetic activity.

G-protein coupled receptor 55 agonists increase insulin secretion through inositol trisphosphate-mediated calcium release in pancreatic β-cells

G-protein coupled receptor 55 (GPR55) is an orphan G-protein coupled receptor, which is activated by endocannabinoids and lipid transmitters. Recently, GPR55 was shown to play a role in glucose and energy homeostasis, and insulin secretion is essential to maintain glucose homeostasis in the body. In Type 2 Diabetes Mellitus (T2DM), chronic insulin resistance and a progressive decline in β-cell function result in β-cell dysfunction, this leads to defect in insulin secretion, which is the key process in the development and progression of T2DM. GPR55 agonists were shown to increase insulin secretion, however the underlying mechanisms were not fully understood. Therefore the aim of the present study was to examine the effects of potent GPR55 agonists, O-1602 and abnormal cannabidiol (Abn-CBD), on glucose-induced insulin secretion in a mouse pancreatic β-cell line, MIN6, and the underlying mechanisms with a focus on intracellular calcium (Ca²⁺). Our results demonstrated that O-1602 and Abn-CBD increased glucose-induced insulin secretion in MIN6 cells, which was abolished by a PLC inhibitor, U73122. Glucose-induced Ca²⁺ transients were enhanced by O-1602 and Abn-CBD, and this was significantly reduced by U73122 and inositol trisphosphate (IP₃) receptor inhibitors, 2-aminoethoxydiphenyl borate (2-APB) and xestospongin C, as well as by Y-27632, a Rho-associated protein kinase (ROCK) inhibitor. Interestingly, O-1602 and Abn-CBD could directly induce intracellular Ca²⁺ transients through IP₃-mediated Ca²⁺ release. In conclusion, GPR55 agonists increased insulin secretion through calcium mobilisation from IP₃-sensitive ER stores in β-cells.

Dipeptidyl peptidase-4 inhibitors as add-on therapy to insulin in patients with type 2 diabetes mellitus: a meta-analysis of randomized controlled trials

PURPOSE

Addition of the dipeptidyl peptidase-4 (DPP4) inhibitors to insulin in patients with type 2 diabetes mellitus (T2DM) may achieve better glycemic control. However, results of pilot randomized controlled trials (RCTs) are inconsistent. We aimed to perform a meta-analysis of RCTs to evaluate efficacy and safety of DPP4 inhibitors compared with placebo/no treatment as add-on therapy to insulin in T2DM patients.

MATERIALS AND METHODS

Relevant studies were identified via a search of PubMed, Cochrane Library, and Embase databases. A fixed or random effect model was applied according to the heterogeneity.

RESULTS

Overall, 22 RCTs with 6,957 T2DM patients were included. Addition of DPP4 inhibitors to insulin was associated with significantly reduced HbA1c as compared with controls (weighed mean difference [WMD]: -0.54%, p<0.001). The benefits of DPP4 inhibitors as add-on therapy on HbA1c were independent of study design, follow-up duration, categories of DPP4 inhibitors used, and using of fixed/adjustable insulin doses as indicated by predefined subgroup analyses. Moreover, addition of DPP4 inhibitors to insulin was associated with significantly reduced fasting blood glucose (WMD: -0.47mmol/L, p<0.001), postprandial glucose at 2 hrs (WMD: -2.03 mmol/L, p<0.001), and daily dose of insulin (WMD: -2.73U/d, p<0.001), while body weight (WMD: 0.02 g, p=0.81) or risk of symptomatic hypoglycemia (risk ratio: 0.92, p=0.37) were not affected.

CONCLUSIONS

Addition of DPP4 inhibitors to insulin significantly improved the glycemic control in T2DM patients without further increasing the risk of weight gain and hypoglycemia.

High-fat-diet-induced remission of diabetes in a subset of KATP -GOF insulin-secretory-deficient mice

AIMS

To examine the effects of a high-fat-diet (HFD) on monogenic neonatal diabetes, without the confounding effects of compensatory hyperinsulinaemia.

METHODS

Mice expressing KATP channel gain-of-function (KATP -GOF) mutations, which models human neonatal diabetes, were fed an HFD.

RESULTS

Surprisingly, KATP -GOF mice exhibited resistance to HFD-induced obesity, accompanied by markedly divergent blood glucose control, with some KATP -GOF mice showing persistent diabetes (KATP -GOF-non-remitter [NR] mice) and others showing remission of diabetes (KATP -GOF-remitter [R] mice). Compared with the severely diabetic and insulin-resistant KATP -GOF-NR mice, HFD-fed KATP -GOF-R mice had lower blood glucose, improved insulin sensitivity, and increased circulating plasma insulin and glucagon-like peptide-1 concentrations. Strikingly, while HFD-fed KATP -GOF-NR mice showed increased food intake and decreased physical activity, reduced whole body fat mass and increased plasma lipids, KATP -GOF-R mice showed similar features to those of control littermates. Importantly, KATP -GOF-R mice had restored insulin content and β-cell mass compared with the marked loss observed in both HFD-fed KATP -GOF-NR and chow-fed KATP -GOF mice.

CONCLUSION

Together, our results suggest that restriction of dietary carbohydrates and caloric replacement by fat can induce metabolic changes that are beneficial in reducing glucotoxicity and secondary consequences of diabetes in a mouse model of insulin-secretory deficiency.

Protective effect of triterpenes against diabetes-induced β-cell damage: An overview of in vitro and in vivo studies

Accumulative evidence shows that chronic hyperglycaemia is a major factor implicated in the development of pancreatic β-cell dysfunction in diabetic patients. Furthermore, most of these patients display impaired insulin signalling that is responsible for accelerated pancreatic β-cell damage. Indeed, prominent pathways involved in glucose metabolism such as phosphatidylinositol 3-kinase/ protein kinase B (PI3-K/AKT) and 5' AMP-activated protein kinase (AMPK) are impaired in an insulin resistant state. The impairment of this pathway is associated with over production of reactive oxygen species and pro-inflammatory factors that supersede pancreatic β-cell damage. Although several antidiabetic drugs can improve β-cell function by modulating key regulators such as PI3-K/AKT and AMPK, evidence of their β-cell regenerative and protective effect is scanty. As a result, there has been continued exploration of novel antidiabetic therapeutics with abundant antioxidant and antiinflammatory properties that are essential in protecting against β-cell damage. Such therapies include triterpenes, which have displayed robust effects to improve glycaemic tolerance, insulin secretion, and pancreatic β-cell function. This review summarises most relevant effects of various triterpenes on improving pancreatic β-cell function in both in vitro and in vivo experimental models. A special focus falls on studies reporting on the ameliorative properties of these compounds against insulin resistance, oxidative stress and inflammation, the well-known factors involved in hyperglycaemia associated tissue damage.

Temporal Transcriptomic and Proteomic Landscapes of Deteriorating Pancreatic Islets in Type 2 Diabetic Rats

Progressive reduction in β-cell mass and function comprise the core of the pathogenesis mechanism of type 2 diabetes. The process of deteriorating pancreatic islets, in which a complex network of molecular events is involved, is not yet fully characterized. We used RNA sequencing and tandem mass tag-based quantitative proteomics technology to measure the temporal mRNA and protein expression changes of pancreatic islets in Goto-Kakizaki (GK) rats from 4 to 24 weeks of age. Our omics data set outlines the dynamics of the molecular network during the deterioration of GK islets as two stages: The early stage (4-6 weeks) is characterized by anaerobic glycolysis, inflammation priming, and compensation for insulin synthesis, and the late stage (8-24 weeks) is characterized by inflammation amplification and compensation failure. Further time course analysis allowed us to reveal 5,551 differentially expressed genes, a large portion of which have not been reported before. Our comprehensive and temporal transcriptome and proteome data offer a valuable resource for the diabetes research community and for quantitative biology.

Interactions between antidiabetic drugs and herbs: an overview of mechanisms of action and clinical implications

Diabetes is a complex condition with a variety of causes and pathophysiologies. The current single target approach has not provided ideal clinical outcomes for the treatment of the disease and its complications. Herbal medicine has been used for the management of various diseases such as diabetes over centuries. Many diabetic patients are known to use herbal medicines with antidiabetic properties in addition to their mainstream treatments, which may present both a benefit as well as potential risk to effective management of their disease. In this review we evaluate the clinical and experimental literature on herb-drug interactions in the treatment of diabetes. Pharmacokinetic and pharmacodynamic interactions between drugs and herbs are discussed, and some commonly used herbs which can interact with antidiabetic drugs summarised. Herb-drug interactions can be a double-edged sword presenting both risks (adverse drug events) and benefits (through enhancement). There is a general lack of data on herb-drug interactions. As such, more rigorous scientific research is urgently needed to guide clinical practice as well as to safeguard the wellbeing of diabetes patients.

miR‑433 protects pancreatic β cell growth in high‑glucose conditions

Pancreatic β cell dysfunction is a key characteristic in the pathogenesis of diabetes mellitus (DM). MicroRNAs (miRNAs) have been identified to serve a role in DM pathogenesis, but how specific miRNAs regulate glucose-stimulated β cell functions remain unclear. The present study aimed to explore the effects of miR-433 on cell growth under high-glucose culture conditions and to determine the possible mechanisms involved. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis was performed to detect the expression levels of miRNAs in Min-6 pancreatic β cells cultured in high-glucose medium, which revealed that miR-433 was significantly downregulated. Results from in vitro Cell Counting Kit-8, colony formation and flow cytometry analyses indicated that overexpression of miR-433 may enhance cell viability and proliferation by promoting cell cycle progression and suppressing apoptosis. Furthermore, bioinformatics prediction and luciferase analysis demonstrated that miR-433 was able to inhibit the expression of cyclooxygenase 2 (COX2) through targeting its 3′-UTR. Moreover, knockdown of COX2 expression alleviated the inhibition of cell growth induced by high glucose, similar to overexpression of miR-433. In conclusion, the present results suggested that miR-433 may protect pancreatic β cells cultured in high glucose, which suggests that miR-433 may have beneficial effects in preventing and treating DM.

Sex differences in vascular stiffness and relationship to the risk of renal functional decline in patients with type 2 diabetes

BACKGROUND

Recent data suggest that the higher risk of end-stage renal disease in women compared with men is associated with waist circumference. We investigated whether vascular stiffness which is linked to visceral fat accumulation is gender specific and associated with a loss in renal function.

METHODS

We studied 166 patients with type 2 diabetes at high risk of progressive renal disease. A vascular stiffness index was derived from measurement of the peripheral arterial pulse waveform using infrared finger photoplethysmography. Multiple regression analysis was used to examine the relationship between vascular stiffness and traditional clinical and biochemical renal disease risk factors.

RESULTS

Women were of similar mean (standard deviation) age [61.6 (6.8) vs 60.0 (8.3) years; p = 0.444] and duration of diabetes [9.8 (7.2) vs 10.9 (8.1) years; p = 0.885] compared to men. Waist circumference was significantly associated with vascular stiffness [regression coefficient B = 0.15 (95% confidence interval: 0.06-2.24); p = 0.001]. There was a negative slope parameter for the relationship between glomerular filtration rate and vascular stiffness [ B = -0.15 (95% confidence interval: -0.22 to -0.09); p < 0.001] in women only.

CONCLUSION

In this cohort, early renal functional decline in women is linked to increased vascular stiffness which may be associated with visceral fat accumulation as determined by waist circumference.

Pharmacology and therapeutic implications of current drugs for type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a global epidemic that poses a major challenge to health-care systems. Improving metabolic control to approach normal glycaemia (where practical) greatly benefits long-term prognoses and justifies early, effective, sustained and safety-conscious intervention. Improvements in the understanding of the complex pathogenesis of T2DM have underpinned the development of glucose-lowering therapies with complementary mechanisms of action, which have expanded treatment options and facilitated individualized management strategies. Over the past decade, several new classes of glucose-lowering agents have been licensed, including glucagon-like peptide 1 receptor (GLP-1R) agonists, dipeptidyl peptidase 4 (DPP-4) inhibitors and sodium/glucose cotransporter 2 (SGLT2) inhibitors. These agents can be used individually or in combination with well-established treatments such as biguanides, sulfonylureas and thiazolidinediones. Although novel agents have potential advantages including low risk of hypoglycaemia and help with weight control, long-term safety has yet to be established. In this Review, we assess the pharmacokinetics, pharmacodynamics and safety profiles, including cardiovascular safety, of currently available therapies for management of hyperglycaemia in patients with T2DM within the context of disease pathogenesis and natural history. In addition, we briefly describe treatment algorithms for patients with T2DM and lessons from present therapies to inform the development of future therapies.

Pancreatic β-cell identity in diabetes

Recovery of functional β-cell mass continues to be an ongoing challenge in treating diabetes. Initial work studying β-cells suggested apoptotic β-cell death as a main contributor for the loss of β-cell mass in diabetes. Restoration of β-cells either by transplant or stimulating proliferation of remaining β-cells or precursors would then logically be a viable therapeutic option for diabetes. However, recent work has highlighted the inherent β-cell plasticity and the critical role of loss of β-cell identity in diabetes, and has suggested that β-cells fail to maintain a fully differentiated glucose-responsive and drug-responsive state, particularly in diabetic individuals with poorly controlled, long-lasting periods of hyperglycaemia. Understanding the underlying mechanisms of loss of β-cell identity and conversion in other cell types, as well as how to regain their mature differentiated functional state, is critical to develop novel therapeutic strategies to prevent or reverse these processes. In this review, we discuss the role of plasticity and loss of β-cell identity in diabetes, the current understanding of mechanisms involved in altering this mature functional β-cell state and potential progresses to identify novel therapeutic targets providing better opportunities for slowing or preventing diabetes progression.

Glucagon-like peptide-1 prevents methylglyoxal-induced apoptosis of beta cells through improving mitochondrial function and suppressing prolonged AMPK activation

Accumulation of methylglyoxal (MG) contributes to glucotoxicity and mediates beta cell apoptosis. The molecular mechanism by which GLP-1 protects MG-induced beta cell apoptosis remains unclear. Metformin is a first-line drug for treating type 2 diabetes associated with AMPK activation. However, whether metformin prevents MG-induced beta cell apoptosis is controversial. Here, we explored the signaling pathway involved in the anti-apoptotic effect of GLP-1, and investigated whether metformin had an anti-apoptotic effect on beta cells. MG treatment induced apoptosis of beta cells, impaired mitochondrial function, and prolonged activation of AMP-dependent protein kinase (AMPK). The MG-induced pro-apoptotic effects were abolished by an AMPK inhibitor. Pretreatment of GLP-1 reversed MG-induced apoptosis, and mitochondrial dysfunction, and suppressed prolonged AMPK activation. Pretreatment of GLP-1 reversed AMPK activator 5-aminoimidazole-4-carboxamide riboside (AICAR)-induced apoptosis, and suppressed prolonged AMPK activation. However, metformin neither leads to beta cell apoptosis nor ameliorates MG-induced beta cell apoptosis. In parallel, GLP-1 also prevents MG-induced beta cell apoptosis through PKA and PI3K-dependent pathway. In conclusion, these data indicates GLP-1 but not metformin protects MG-induced beta cell apoptosis through improving mitochondrial function, and alleviating the prolonged AMPK activation. Whether adding GLP-1 to metformin provides better beta cell survival and delays disease progression remains to be validated.

Antrodia camphorata Increases Insulin Secretion and Protects from Apoptosis in MIN6 Cells

Antrodia camphorata is a Taiwanese-specific fungus which has been used clinically to treat hypertension, immune- and liver-related diseases and cancer; however, it has never been studied in type 2 diabetes mellitus (T2DM). Hyperglycemia in T2DM causes endoplasmic reticulum (ER) stress, leading to β-cell dysfunction. During chronic ER stress, misfolded proteins accumulate and initiate β-cell apoptosis. Moreover, β-cell dysfunction leads to defect in insulin secretion, which is the key process in the development and progression of T2DM. Therefore, the aim of the present study was to examine the effects of A. camphorata on insulin secretion and ER stress-induced apoptosis in a mouse β-cell line, MIN6, and their underlying mechanisms. We demonstrated that the ethanolic extract of A. camphorata increased glucose-induced insulin secretion dose-dependently through peroxisome proliferator-activated receptor-γ (PPAR-γ) pathway, and upregulated genes that were involved in insulin secretion, including PPAR-γ, glucose transporter-2 and glucokinase. Furthermore, A. camphorata slightly increased cell proliferation, as well as protected from ER stress-induced apoptosis in MIN6 cells. In conclusion, this study provided evidences that A. camphorata might have anti-diabetic effects and could be a novel drug for T2DM.

Pancreatic β cell dedifferentiation in diabetes and redifferentiation following insulin therapy

Diabetes is characterized by "glucotoxic" loss of pancreatic β cell function and insulin content, but underlying mechanisms remain unclear. A mouse model of insulin-secretory deficiency induced by β cell inexcitability (K(ATP) gain of function) demonstrates development of diabetes and reiterates the features of human neonatal diabetes. In the diabetic state, β cells lose their mature identity and dedifferentiate to neurogenin3-positive and insulin-negative cells. Lineage-tracing experiments show that dedifferentiated cells can subsequently redifferentiate to mature neurogenin3-negative, insulin-positive β cells after lowering of blood glucose by insulin therapy. We demonstrate here that β cell dedifferentiation, rather than apoptosis, is the main mechanism of loss of insulin-positive cells, and redifferentiation accounts for restoration of insulin content and antidiabetic drug responsivity in these animals. These results may help explain gradual decrease in β cell mass in long-standing diabetes and recovery of β cell function and drug responsivity in type 2 diabetic patients following insulin therapy, and they suggest an approach to rescuing "exhausted" β cells in diabetes.

Autophagy and pancreatic β-cells

Autophagy plays a key role in maintaining pancreatic β-cell homeostasis. Deregulation of this process is associated with loss of β-cell mass and function, and it is likely to be involved in type 2 diabetes development and progression. Evidence that modulation of autophagy may be beneficial to preserve β-cell mass and function is beginning to accumulate although the complexity of this process, the intricate link between autophagy and apoptosis, and the fine balance between the protective and the disruptive role of autophagy make it very difficult to develop interventional strategies. This chapter provides an overview of the role of constitutive and adaptive autophagy in pancreatic β-cell and in the context of type 2 diabetes.

Management of diabetic complications: a chemical constituents based approach

ETHNOPHARMACOLOGICAL RELEVANCE

Long term hyperglycemia leads to development of complications associated with diabetes. Diabetic complications are now a global health problem without effective therapeutic approach. Hyperglycemia and oxidative stress are important components for the development of diabetic complications. Over the past few decades, herbal medicines have attracted much attention as potential therapeutic agents in the prevention and treatment of diabetic complications due to their multiple targets and less toxic side effects. This review aims to assess the current available knowledge of medicinal herbs for attenuation and management of diabetic complications and their underlying mechanisms.

MATERIAL AND METHODS

Bibliographic investigation was carried out by scrutinizing classical text books and peer reviewed papers, consulting worldwide accepted scientific databases (SCOPUS, PUBMED, SCIELO, NISCAIR, Google Scholar) to retrieve available published literature. The inclusion criteria for the selection of plants were based upon all medicinal herbs and their active compounds with attributed potentials in relieving diabetic complications. Moreover, plants which have potential effect in ameliorating oxidative stress in diabetic animals have been included.

RESULTS

Overall, 238 articles were reviewed for plant literature and out of the reviewed literature, 127 articles were selected for the study. Various medicinal plants/plant extracts containing flavonoids, alkaloids, phenolic compounds, terpenoids, saponins and phytosterol type chemical constituents were found to be effective in the management of diabetic complications. This effect might be attributed to amelioration of persistent hyperglycemia, oxidative stress and modulation of various metabolic pathways involved in the pathogenesis of diabetic complications.

CONCLUSION

Screening chemical candidate from herbal medicine might be a promising approach for new drug discovery to treat the diabetic complications. There is still a dire need to explore the mechanism of action of various plant extracts and their toxicity profile and to determine their role in therapy of diabetic complications. Moreover, a perfect rodent model which completely mimics human diabetic complications should be developed.

Novel sulfonylurea derivatives as H3 receptor antagonists. Preliminary SAR studies

The combination of antagonism at histamine H(3) receptor and the stimulation of insulin secretion have been proposed as an approach to new dual therapeutic agents for the treatment of type 2 diabetes mellitus associated with obesity. We have designed and synthesized a new series of non-imidazole derivatives, based on a basic amine ring connected through an alkyl spacer of variable length to a phenoxysulfonylurea moiety. These compounds were initially evaluated for histamine H(3) receptor binding affinities, suggesting that a propoxy chain linker between the amine and the core ring could be essential for optimal binding affinity. Compound 56, 1-(naphthalen-1-yl)-3-[(p-(3-pyrrolidin-1-ylpropoxy)benzene)]sulfonylurea exhibited the best H(3) antagonism affinity. However, since all these derivatives failed to block K(ATP) channels, the link of these two related moieties should not be considered a good pharmacophore for obtaining new dual H(3) antagonists with insulinotropic activity, suggesting the necessity to propose a new chemical hybrid prototype.

Functional herbal food ingredients used in type 2 diabetes mellitus

From many reports it is clear that diabetes will be one of the major diseases in the coming years. As a result there is a rapidly increasing interest in searching new medicines, or even better searching prophylactic methods. Based on a large number of chemical and pharmacological research work, numerous bioactive compounds have been found in functional herbal food ingredients for diabetes. The present paper reviews functional herbal food ingredients with regards to their anti-diabetic active principles and pharmacological test results, which are commonly used in Asian culinary system and medical system and have demonstrated clinical or/and experimental anti-diabetic effectiveness. Our idea of reviewing this article is to give more attention to these functional food ingredients as targets medicinal foods in order to prevent or slow down the development of type 2 diabetes mellitus.

The role of incretin therapy at different stages of diabetes

The pathogenetic mechanisms causing type 2 diabetes are complex, and include a significant reduction of the incretin effect. In patients with type 2 diabetes, GLP-1 secretion may be impaired, while GIP secretion seems unaffected. In contrast, the insulinotropic activity of GIP is severely altered, whereas that of GLP-1 is maintained to a great extent. Better understanding of the role of incretin hormones in glucose homeostasis has led to the development of incretin-based therapies that complement and offer important advantages over previously used agents. Incretin-based agents have significant glucose-lowering effects, promote weight loss (or are weight-neutral), inhibit glucagon secretion while maintaining counter-regulatory mechanisms, exhibit cardiovascular benefits, and protect β-cells while possessing a low risk profile. At present, incretin-based therapies are most widely used as add on to metformin to provide sufficient glycemic control after metformin failure. However, they are also recommended as monotherapy early in the disease course, and later in triple combination. These agents may also be a promising therapeutic tool in prediabetic subjects. Therefore, a therapeutic algorithm is needed for their optimal application at different stages of diabetes, as suggested in this article.

Hydrogen sulphide protects mouse pancreatic β-cells from cell death induced by oxidative stress, but not by endoplasmic reticulum stress

BACKGROUND AND PURPOSE

Hydrogen sulphide (H₂S), a potentially toxic gas, is also involved in the neuroprotection, neuromodulation, cardioprotection, vasodilatation and the regulation of inflammatory response and insulin secretion. We have recently reported that H₂S suppresses pancreatic β-cell apoptosis induced by long-term exposure to high glucose. Here we examined the protective effects of sodium hydrosulphide (NaHS), an H₂S donor, on various types of β-cell damage.

EXPERIMENTAL APPROACH

Isolated islets from mice or the mouse insulinoma MIN6 cells were cultured with palmitate, cytokines (a mixture of tumour necrosis factor-α, interferon-γ and interleukin-1β), hydrogen peroxide, thapsigargin or tunicamycin with or without NaHS. We examined DNA fragmentation, caspase-3 and -7 activities and reactive oxygen species (ROS) production in the treated cells thereafter. Apoptotic cell death in isolated islets was also assessed by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) method.

KEY RESULTS

NaHS suppressed DNA fragmentation and the activities of caspase-3 and -7 induced by palmitate, the cytokines or hydrogen peroxide. In contrast, NaHS failed to protect islets and MIN6 cells from apoptosis induced by thapsigargin and tunicamycin, both of which cause endoplasmic reticulum stress. NaHS suppressed ROS production induced by cytokines or hydrogen peroxide but it had no effect on ROS production in thapsigargin-treated cells. NaHS increased Akt phosphorylation in MIN6 cells treated with cytokines but not in cells treated with thapsigargin. Treatment with NaHS decreased TUNEL-positive cells in cytokine-exposed islets.

CONCLUSIONS AND IMPLICATIONS

H₂S may prevent pancreatic β-cells from cell apoptosis via an anti-oxidative mechanism and the activation of Akt signalling.

Class II phosphoinositide 3-kinase regulates exocytosis of insulin granules in pancreatic beta cells

Phosphoinositide 3-kinases (PI3Ks) are critical regulators of pancreatic β cell mass and survival, whereas their involvement in insulin secretion is more controversial. Furthermore, of the different PI3Ks, the class II isoforms were detected in β cells, although their role is still not well understood. Here we show that down-regulation of the class II PI3K isoform PI3K-C2α specifically impairs insulin granule exocytosis in rat insulinoma cells without affecting insulin content, the number of insulin granules at the plasma membrane, or the expression levels of key proteins involved in insulin secretion. Proteolysis of synaptosomal-associated protein of 25 kDa, a process involved in insulin granule exocytosis, is impaired in cells lacking PI3K-C2α. Finally, our data suggest that the mRNA for PI3K-C2α may be down-regulated in islets of Langerhans from type 2 diabetic compared with non-diabetic individuals. Our results reveal a critical role for PI3K-C2α in β cells and suggest that down-regulation of PI3K-C2α may be a feature of type 2 diabetes.

α-Synuclein binds the K(ATP) channel at insulin-secretory granules and inhibits insulin secretion

α-Synuclein has been studied in numerous cell types often associated with secretory processes. In pancreatic β-cells, α-synuclein might therefore play a similar role by interacting with organelles involved in insulin secretion. We tested for α-synuclein localizing to insulin-secretory granules and characterized its role in glucose-stimulated insulin secretion. Immunohistochemistry and fluorescent sulfonylureas were used to test for α-synuclein localization to insulin granules in β-cells, immunoprecipitation with Western blot analysis for interaction between α-synuclein and K(ATP) channels, and ELISA assays for the effect of altering α-synuclein expression up or down on insulin secretion in INS1 cells or mouse islets, respectively. Differences in cellular phenotype between α-synuclein knockout and wild-type β-cells were found by using confocal microscopy to image the fluorescent insulin biosensor Ins-C-emGFP and by using transmission electron microscopy. The results show that anti-α-synuclein antibodies labeled secretory organelles within β-cells. Anti-α-synuclein antibodies colocalized with K(ATP) channel, anti-insulin, and anti-C-peptide antibodies. α-Synuclein coimmunoprecipitated in complexes with K(ATP) channels. Expression of α-synuclein downregulated insulin secretion at 2.8 mM glucose with little effect following 16.7 mM glucose stimulation. α-Synuclein knockout islets upregulated insulin secretion at 2.8 and 8.4 mM but not 16.7 mM glucose, consistent with the depleted insulin granule density at the β-cell surface membranes observed in these islets. These findings demonstrate that α-synuclein interacts with K(ATP) channels and insulin-secretory granules and functionally acts as a brake on secretion that glucose stimulation can override. α-Synuclein might play similar roles in diabetes as it does in other degenerative diseases, including Alzheimer's and Parkinson's diseases.

Failure to metformin and insulin secretagogue monotherapy: an observational cohort study

The aim of the present cohort study is the assessment of treatment failure rates in patients on monotherapy with metformin or insulin secretagogues, observed in a routine clinical setting. A cohort of patients without any pharmacological treatment was also observed. A retrospective observational cohort study was performed on a consecutive series of 2,020 type 2 diabetic patients receiving monotherapy with an oral agent (metformin or insulin secretagogue, n = 1,126) or drug-naive (n = 894). HbA1c and prescribed hypoglycemic therapy were recorded yearly. Patients were followed until death, change of residence, failure to treatment, or up to 48 months. The mean duration of follow up was 34.8 ± 18.0 months. In a Cox regression analysis, metformin was associated with a significant reduction, and insulin secretagogues with a significant increase, in the risk of failure to therapy during follow up. When duration of diabetes and baseline BMI were added to the model, insulin secretagogues, but not metformin, were still associated with increased risk of failure. In conclusion, insulin secretagogues are associated with increased failure rate in comparison with metformin. This difference could be due to detrimental effect of secretagogues, rather than to a beneficial action of metformin.

Defining and achieving treatment success in patients with type 2 diabetes mellitus

Traditionally, successful treatment of patients with type 2 diabetes mellitus (DM) has been defined strictly by achievement of targeted glycemic control, primarily using a stepped-care approach that begins with changes in lifestyle combined with oral therapy that is slowly intensified as disease progression advances and β-cell function declines. However, stepped care is often adjusted without regard to the mechanism of hyperglycemia or without long-term objectives. A more comprehensive definition of treatment success in patients with type 2 DM should include slowing or stopping disease progression and optimizing the reduction of all risk factors associated with microvascular and macrovascular disease complications. To achieve these broader goals, it is important to diagnose diabetes earlier in the disease course and to consider use of more aggressive combination therapy much earlier with agents that have the potential to slow or halt the progressive β-cell dysfunction and loss characteristic of type 2 DM. A new paradigm for managing patients with type 2 DM should address the concomitant risk factors and morbidities of obesity, hypertension, and dyslipidemia with equal or occasionally even greater aggressiveness than for hyperglycemia. The use of antidiabetes agents that may favorably address cardiovascular risk factors should be considered more strongly in treatment algorithms, although no pharmacological therapy is likely to be ultimately successful without concomitant synergistic lifestyle changes. Newer incretin-based therapies, such as glucagon-like peptide 1 receptor agonists and dipeptidyl peptidase 4 inhibitors, which appear to have a favorable cardiovascular safety profile as well as the mechanistic possibility for a favorable cardiovascular risk impact, are suitable for earlier inclusion as part of combination regimens aimed at achieving comprehensive treatment success in patients with type 2 DM.

Emerging treatment options for type 2 diabetes

Type 2 diabetes mellitus (T2DM) is rapidly increasing in prevalence and is a major public health problem. It is a progressive disease which commonly requires multiple pharmacotherapy. Current options for treatment may have undesirable side effects (particularly weight gain and hypoglycaemia) and contraindications, and little effect on disease progression. Incretin based therapy is one of several newer therapies to improve glycaemia and is available in two different forms, dipeptidyl peptidase-4 (DPP-4) inhibitors and glucagon-like peptide-1 (GLP-1) agonists. Use of these agents results in a 'glucose-dependant' increase in insulin secretion and glucagon suppression resulting in improved glycaemia with low incidence of hypoglycaemia. DPP-4 inhibitors are oral drugs which are weight neutral, while GLP-1 agonists are injected subcutaneously and help promote weight loss while improving glycaemia. GLP-1 agonists have also been shown to increase beta cell mass in rat models. Bariatric surgery is another option for the obese patient with T2DM, with blood glucose normalizing in over half of the patients following surgery. Other therapies in development for the treatment of T2DM include sodium-glucose transporter 2 (SGLT-2) inhibitors, glucagon receptor antagonists, glucokinase activators and sirtuins. In this article, we will review the various existing and emerging treatment options for T2DM.

Exenatide once weekly: clinical outcomes and patient satisfaction

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a complex disorder in which interactions between environmental and genetic factors result in the development of insulin resistance (in most cases) and progressive pancreatic β-cell failure. The currently available oral anti-diabetes treatments are effective as monotherapy; however, due to the progressive decline in β-cell function, most patients will require the use of combination therapy and eventually insulin to reach glycemic targets. These therapeutic options are not without undesirable side effects such as weight gain and hypoglycemia. Furthermore, T2DM is associated with impaired quality of life (QOL) and poor compliance with treatment. Hence, there is a need for anti-diabetes agents that result in sustained improvements in glycemic control without hypoglycemia or weight gain and have a positive impact on patients QOL and thereby hopefully improve compliance. Incretin-based therapy is the latest addition to anti-diabetes treatments which addresses some of the shortcomings of older treatments.

AIMS

To review the evidence for the use of exenatide once-weekly.

METHODS

We have searched Medline using the terms "exenatide", "exenatide once-weekly", and "exenatide LA".

RESULTS

Exenatide once-weekly is an incretin mimetic that is currently undergoing phase 3 clinical trials, and has been shown to improve glycemic parameters (HbA(1c) and fasting and postprandial glucose levels), with low risk of hypoglycemia, causes weight loss, and use was associated with improvements in patient satisfaction which might have a positive impact on treatment compliance.

CONCLUSIONS

Exenatide once-weekly is effective, well tolerated in patients with T2DM and should be a useful addition to the available range of anti-diabetes treatments.

Targeting beta-cell function early in the course of therapy for type 2 diabetes mellitus

OBJECTIVE

This report examines current perspectives regarding likely mechanisms of beta-cell failure in type 2 diabetes and their clinical implications for protecting or sparing beta-cells early in the disease progression. In addition, it considers translation strategies to incorporate relevant scientific findings into educational initiatives targeting clinical practice behavior.

PARTICIPANTS

On January 10, 2009, a working group of basic researchers, clinical endocrinologists, and primary care physicians met to consider whether current knowledge regarding pancreatic beta-cell defects justifies retargeting and retiming treatment for clinical practice. Based on this meeting, a writing group comprised of four meeting participants subsequently prepared this consensus statement. The conference was convened by The Endocrine Society and funded by an unrestricted educational grant from Novo Nordisk.

EVIDENCE

Participants reviewed and discussed published literature, plus their own unpublished data.

CONSENSUS PROCESS

The summary and recommendations were supported unanimously by the writing group as representing the consensus opinions of the working group.

CONCLUSIONS

Workshop participants strongly advocated developing new systems to address common barriers to glycemic control and recommended several initial steps toward this goal. These recommendations included further studies to establish the clinical value of pharmacological therapies, continuing basic research to elucidate the nature and mechanisms of beta-cell failure in type 2 diabetes mellitus, and exploring new educational approaches to promote pathophysiology-based clinical practices. The Endocrine Society has launched a new website to continue the discussion between endocrinologists and primary care physicians on beta-cell pathophysiology in type 2 diabetes and its clinical implications. Join the conversation at http://www.betacellsindiabetes.org

A model for glucose, insulin, and beta-cell dynamics in subjects with insulin resistance and patients with type 2 diabetes

Type 2 diabetes mellitus (T2DM) is a progressive, metabolic disorder characterized by reduced insulin sensitivity and loss of beta-cell mass (BCM), resulting in hyperglycemia. Population pharmacokinetic-pharmacodynamic (PKPD) modeling is a valuable method to gain insight into disease and drug action. A semi-mechanistic PKPD model incorporating fasting plasma glucose (FPG), fasting insulin, insulin sensitivity, and BCM in patients at various disease stages was developed. Data from 3 clinical trials (phase II/III) with a peroxisome proliferator-activated receptor agonist, tesaglitazar, were used to develop the model. In this, a modeling framework proposed by Topp et al was expanded to incorporate the effects of treatment and impact of disease, as well as variability between subjects. The model accurately described FPG and fasting insulin data over time. The model included a strong relation between insulin clearance and insulin sensitivity, predicted 40% to 60% lower BCM in T2DM patients, and realistic improvements of BCM and insulin sensitivity with treatment. The treatment response on insulin sensitivity occurs within the first weeks, whereas the positive effects on BCM arise over several months. The semi-mechanistic PKPD model well described the heterogeneous populations, ranging from nondiabetic, insulin-resistant subjects to long-term treated T2DM patients. This model also allows incorporation of clinical-experimental studies and actual observations of BCM.

Combination therapy for patients with Type 2 diabetes: repaglinide in combination with metformin

In patients with Type 2 diabetes mellitus (T2DM), adequate glycemic control is a critical factor in reducing long-term micro- and macro-vascular complications. Traditionally, the approach is to initiate monotherapy first, followed by combination therapy that targets two main defects in T2DM. Repaglinide, a rapidly acting insulin secretagog, stimulates insulin secretion via closure of ATP-dependent potassium channels on the cell membrane of β-cells. Repaglinide is ideally used at mealtime to reduce postprandial glucose levels, thus lowering the 24-h blood glucose profile and improving HbA1c levels. Metformin is an insulin sensitizer that effectively acts against insulin resistance, one of the predominant metabolic defects in T2DM. A combination of repaglinide and metformin is indicated as an adjunct to diet and exercise to improve glycemic control in adults with T2DM. When monotherapy with oral antidiabetic agents fails, combination therapy with repaglinide plus metformin has been demonstrated to be safe and effective in the treatment of T2DM.

Multiple molecular targets underlie the antidiabetic effect of Nigella sativa seed extract in skeletal muscle, adipocyte and liver cells

AIM

Nigella sativa (N. sativa) is a plant widely used in traditional medicine of North African countries. During the last decade, several studies have shown that extracts from the seeds of N. sativa have antidiabetic effects.

METHODS

Our group has recently demonstrated that N. sativa seed ethanol extract (NSE) induces an important insulin-like stimulation of glucose uptake in C2C12 skeletal muscle cells and 3T3-L1 adipocytes following an 18 h treatment. The purpose of the present study was to elucidate the pathways mediating this insulin-like effect and the mechanisms through which these pathways are activated.

RESULTS

Results from western immunoblot experiments indicate that in C2C12 cells as well as in H4IIE hepatocytes, but not in 3T3-L1 cells, NSE increases activity of Akt, a key mediator of the effects of insulin, and activity of AMP-activated protein kinase (AMPK), a master metabolic regulating enzyme. To test whether the activation of AMPK resulted from a disruption of mitochondrial function, the effects of NSE on oxygen consumption were assessed in isolated liver mitochondria. NSE was found to exhibit potent uncoupling activity.

CONCLUSION

Finally, to provide an explanation for the effects of NSE in adipocytes, PPARgamma stimulating activity was tested using a reporter gene assay. Results indicate that NSE behaves as an agonist of PPARgamma. The data supports the ethnobotanical use of N. sativa seed oil as a treatment for diabetes, and suggests potential uses of this product, or compounds derived thereof, against obesity and the metabolic syndrome.

DPP-4 inhibitors in clinical practice

Type 2 diabetes is a very common worldwide disorder, with major consequences for patients, society, and health care services. Good glycemic control is an important aspect of diabetes management because it has a significant impact on diabetes-related microvascular and possibly macrovascular complications. Based on our understanding of the pathogenesis of diabetes, multiple pharmacological interventions have been developed in the past 60 years. Although effective, none have had a lasting effect on glycemic control because of the progressive nature of type 2 diabetes requiring combination therapies and insulin treatment. In addition, several pharmacologic interventions have undesirable side effects, including hypoglycemia and weight gain. Drugs targeting the incretin pathway are the latest addition to the available antidiabetes agents. Incretin-based therapy is either delivered orally (dipeptidyl peptidase-4 [DPP-4]) inhibitors or injected subcutaneously (glucagon-like peptide-1 [GLP-1] mimetics and analogues). Dipeptidyl peptidase-4 inhibitors are effective either as a single or combination therapy in lowering glycated hemoglobin, fasting and postprandial glucose levels, with a low incidence of hypoglycemia and no weight gain. There are 3 DPP-4 inhibitors currently available (sitagliptin, saxagliptin, and vildagliptin), with more expected to be available in the future. In this article, we review the scientific background for incretin-based therapy and the available evidence regarding the role and efficacy of DPP-4 inhibitors in the treatment of patients with type 2 diabetes.

Hyperinsulinism and diabetes: genetic dissection of beta cell metabolism-excitation coupling in mice

The role of metabolism-excitation coupling in insulin secretion has long been apparent, but in recent years, in parallel with studies of human hyperinsulinism and diabetes, genetic manipulation of proteins involved in glucose transport, metabolism, and excitability in mice has brought the central importance of this pathway into sharp relief. We focus on these animal studies and how they provide important insights into not only metabolic and electrical regulation of insulin secretion, but also downstream consequences of alterations in this pathway and the etiology and treatment of insulin-secretion diseases in humans.

Glycaemic control in type 2 diabetes: targets and new therapies

Type 2 diabetes mellitus (T2DM) is a worldwide public health challenge. Despite the availability of many antidiabetes agents and pharmacotherapies targeting cardiovascular risk factors, the morbidity, mortality and economic consequences of T2DM are still a great burden to patients, society, health care systems and the economy. The need for new therapies for glycaemic control is compounded by the fact that existing treatments have limitations either because of their side effects (particularly weight gain and hypoglycaemia) or contraindications that limit their use. Furthermore, none of the current therapies have a significant impact on disease progression. Incretin-based therapies offer a new therapeutic approach to the management of T2DM, and there are also several even newer therapies in development. There are two groups of incretin-based therapies currently available; dipeptidyl peptidase-4 (DPP-4) inhibitors and GLP-1 analogues/mimetics. The former are given orally while the latter subcutaneously. These drugs result in glucose-dependent insulin secretion and glucose-dependent glucagon suppression, with consequent low risk of hypoglycaemia when used as mono- or combination therapy (except when used with sulphonylureas). In addition, they are either weight neutral in the case of DPP-4 inhibitors or cause weight loss in the case of incretin mimetics/analogues. Furthermore, animal studies have shown that these agents prolong beta cell survival which offers the theoretical possibility of slowing the progression to T2DM. In this article we will review the currently available antidiabetes agents with particular emphasis on incretin-based and future therapies. In addition, we will review and discuss the evidence relating to glycaemic control and cardiovascular disease.

Fate of the beta-cell in the pathophysiology of type 2 diabetes

OBJECTIVE

To describe the progression of beta-cell dysfunction, now presumed to be the primary progenitor of type 2 diabetes, which appears early in the clinical course (perhaps antedating and even contributing to the development of insulin resistance) and progressively worsens even under treatment.

DATA SOURCES

Medline search of all relevant clinical and review articles.

STUDY SELECTION

By the author.

DATA EXTRACTION

By the author.

DATA SYNTHESIS

The physiology of glucose homeostasis requires the close cooperation of a number of organ systems, humoral secretions, and neural signaling complexes; disruption of any of these processes may lead to the development of type 2 diabetes. Predisposing risk factors for type 2 diabetes include overweight and obesity, poor diet, and lack of exercise. Genetic factors, many of which as yet require elucidation, may also elevate the risk of developing type 2 diabetes. Insulin resistance (IR) has long been recognized as a primary, if not the primary, cause of type 2 diabetes. Recent research in disease pathogenesis suggests that IR is neither a necessary nor sufficient condition for development and progression of type 2 diabetes. Although IR is highly correlated with type 2 diabetes, many individuals with IR will not go on to develop the disease; and the disease may be present in individuals not markedly insulin resistant. The primary progenitor of type 2 diabetes is now presumed to be progressive beta-cell dysfunction, which appears early in the clinical course (perhaps antedating and even contributing to the development of IR) and progressively worsens even under treatment. Among the mechanisms of beta-cell dysfunction in type 2 diabetes is the reduction or abrogation of the "incretin effect."

CONCLUSION

The incretins are gut hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), which in healthy individuals potentiate glucose-dependent insulin secretion. In addition, these hormones, and particularly GLP-1, have a number of protective effects on the beta-cell, including reduction in apoptosis and promotion of beta-cell proliferation and neogenesis. As these benefits are lost in diabetes, "repairing" the incretin effect has become an important treatment target. Treatments that maintain the beta-cell could offer durable glycemic control and potentially reduce the micro- and macrovascular complications associated with type 2 diabetes.