二肽基肽酶Ⅳ抑制剂辅助胰岛素治疗1型糖尿病的研究进展

二肽基肽酶Ⅳ（DPP-4）抑制剂为一类在2型糖尿病中应用广泛的口服降糖药,其疗效确切、给药方便、总体耐受性好,但目前尚未被批准用于1型糖尿病。国内外相关文献表明在1型糖尿病患者体内DPP-4抑制剂可以辅助胰岛素改善血糖、保护胰岛β细胞功能、降低谷氨酸脱羧酶抗体（GADA）滴度、减少胰岛素剂量,且不增加低血糖风险和体质量。因此,DPP-4抑制剂可能可作为1型糖尿病患者胰岛素的辅助治疗,作用机制可能源于其抑制胰岛α细胞分泌胰高血糖素,通过免疫机制使胰岛β细胞免受摧毁。     

Inhibition of insulin secretion as a new drug target in the treatment of metabolic disorders

The pattern of insulin release is crucial for regulation of glucose and lipid haemostasis. Deficient insulin release causes hyperglycemia and diabetes, whereas excessive insulin release can give rise to serious metabolic disorders, such as nesidioblastosis (Persistent Hyperinsulinemic Hypoglycemia of Infancy, PHHI) and might also be closely associated with development of type 2 diabetes and obesity. Type 2 diabetes is characterized by fasting hyperinsulinemia, insulin resistance and impaired insulin release, i.e. reduced first phase insulin release and decreased insulin pulse mass. The beta cell function of patients with type 2 diabetes slowly declines and will ultimately result in beta cell failure and increasing degrees of hyperglycemia. Type 2 diabetes, in combination with obesity and cardiovascular disorders, forms the metabolic syndrome. It has been possible to improve beta cell function and viability in preclinical models of type 1 and type 2 diabetes by reducing insulin secretion to induce beta cell rest. Clinical studies have furthermore indicated that inhibitors of insulin release will be of benefit in treatment or prevention of diabetes and obesity. Pancreatic beta cells secrete insulin in response to increased metabolism and by stimulation of different receptors. The energy status of the beta cell controls insulin release via regulation of open probability of the ATP sensitive potassium (K(ATP)) channels to affect membrane potential and the intracellular calcium concentration [Ca(2+)](i). Other membrane bound receptors and ion channels and intracellular targets that modulate [Ca(2+)](i)will affect insulin release. Thus, insulin release is regulated by e.g. somatostatin receptors, GLP-1 receptors, muscarinic receptors, cholecystokinin receptors and adrenergic receptors. Although the relationship between hyperinsulinemia and certain metabolic diseases has been known for decades, only a few inhibitors of insulin release have been characterized in vitro and in vivo. These include the K(ATP) channel openers diazoxide and NN414 and the somatostatin receptor agonist octreotide.     

Desensitization of insulin secretion

Desensitization of insulin secretion describes a reversible state of decreased secretory responsiveness of the pancreatic beta-cell, induced by a prolonged exposure to a multitude of stimuli. These include the main physiological stimulator, glucose, but also other nutrients like free fatty acids and practically all pharmacological stimulators acting by depolarization and Ca2+ influx into the beta-cell. Desensitization of insulin secretion appears to be an important step in the manifestation of type 2 diabetes and in the secondary failure of oral antidiabetic treatment. In this commentary, the basic concepts and the controversial issues in the field will be outlined. With regard to glucose-induced desensitization, two fundamentally opposing concepts have emerged. The first is that desensitization is the consequence of functional changes in the beta-cell that impair glucose-recognition. The second is that long-term increased secretory activity leads to a depletion of releasable insulin, often in spite of increased insulin synthesis. The latter concept is more appropriately termed beta-cell exhaustion. The same dichotomy applies to the desensitization evoked by pharmacological stimuli: again the relative contributions of a decreased insulin content versus alterations in signal transduction are in dispute. The action of tolbutamide on beta-cells may be an example of desensitization caused by a lack of releasable insulin since the signaling mechanisms are nearly unchanged, whereas the action of phentolamine, an imidazoline, induces a strong desensitization without reducing insulin content or secretory granules, apparently by abolishing Ca2+ influx. With pharmacological agents it seems that both, alterations in signal transduction and decreased availability of releasable insulin, can contribute to the desensitized state of the beta-cell, the relative contribution being variable depending upon the exact nature of the secretory stimulus.     

Treatment of insulin resistance in diabetes mellitus

Insulin resistance is a condition in which the glycemic response to insulin is less than normal. The change in insulin sensitivity leads to several sets of responses. One set effects the beta cell and leads to its accelerated destruction and the development of diabetes mellitus. The other set generates a series of nontraditional cardiovascular risk factors that result in accelerated atherosclerosis. Both of these sets of responses may have impacts on other tissues such as the nervous system. Insulin resistance is probably the result of increased visceral adiposity with increased release of free fatty acids and cytokines and a decreased release of adiponectin. Treatment of insulin resistance and its associated abnormalities can be achieved by lifestyle modification which results in weight loss, by drugs that reverse the abnormal adipocyte effects, by drugs that improve insulin sensitivity at the level of the liver and by anti-inflammatory agents that block activation of the nuclear factor kappa B cascade.     

Alterations of insulin secretion from mouse islets treated with sulphonylureas: perturbations of Ca2+ regulation prevail over changes in insulin content.

1. To determine how pretreatment with sulphonylureas alters the beta cell function, mouse islets were cultured (18 - 20 h) without (controls) or with (test) 0.01 microM glibenclamide. Acute responses to glucose were then determined in the absence of glibenclamide. 2. Test islets were insensitive to drugs (sulphonylureas and diazoxide) acting on K+-ATP channels, and their [Ca2+]i was already elevated in the absence of stimulation. 3. Insulin secretion was increased in the absence of glucose, and mainly stimulated between 0 - 10 instead of 7 - 20 mM glucose in controls. The maximum response was halved, but this difference disappeared after correction for the 45% decrease in the islet insulin content. 4. The first phase of glucose-induced insulin secretion was abrogated because of a paradoxical decrease of the high basal [Ca2+]i in beta cells. The second phase was preserved but occurred with little rise of [Ca2+]i. These abnormalities did not result from alterations of glucose metabolism (NADPH fluorescence). 5. In islets cultured with 50 microM tolbutamide, glucose induced biphasic increases in [Ca2+]i and insulin secretion. The decrease in the secretory response was matched by the decrease in insulin content (45%) except at maximal glucose concentrations. Islets pretreated with tolbutamide, however, behaved like those cultured with glibenclamide if tolbutamide was also present during the acute functional tests. 6. In conclusion, treatment with a low glibenclamide concentration causes long-lasting blockade of K+-ATP channels and rise of [Ca2+]i in beta cells. Glucose-induced insulin secretion occurs at lower concentrations, is delayed and is largely mediated by a modulation of Ca2+ action on exocytosis. It is suggested that glucose regulation of insulin secretion mainly depends on a K+-ATP channel-independent pathway during in vivo sulphonylurea treatment.     

The insulin receptor concept and its relation to the treatment of diabetes

The initial step in insulin action is binding to specific receptors. Two covalent receptor modifications possibly involved in producing pharmacodynamic effects as a result of insulin receptor binding are autophosphorylation and disulphide insulin binding. Insulin receptor numbers are 'down regulated' by insulin, but this effect may be minimised by pulsatile insulin secretion. Insulin receptor affinity is modulated rapidly by fasting, exercise and dietary composition. In non-insulin-dependent diabetes coupling of receptor binding to bioeffects is impaired. Binding is also reduced in those subjects with hyperinsulinaemia and non-insulin-dependent diabetes. Insulin-dependent diabetics have reduced insulin sensitivity, which is only partially reversed by conventional insulin therapy. 'Post-binding defects' in some diabetics could be related to defective covalent receptor modifications resulting from genetic receptor defects. High carbohydrate diets improve diabetes control through effects on the binding and coupling defects. In addition to stimulating insulin secretion, oral hypoglycaemics stimulate post-binding insulin action in vivo and in vitro. Insulin therapy in diabetes also tends to reverse post-binding defects. Pulsatile insulin delivery is more effective in lowering blood sugar than continuous administration, and produces less 'down regulation' of receptors. Combined insulin and sulphonylurea drugs reduce insulin requirements only in insulin-dependent diabetics with some endogenous insulin secretion, whereas metformin reduces insulin requirement in C-peptide negative insulin-dependent diabetes mellitus.     

Potential role of oral thiazolidinedione therapy in preserving beta-cell function in type 2 diabetes mellitus

Worsening glycaemic control in type 2 diabetes mellitus relates to a decline in beta-cell function, associated with impaired negative feedback regulation of insulin release. Insulin resistance, the 'traditional' cornerstone defect of type 2 diabetes, leads to an array of adverse effects on beta cells, including hypertrophy, apoptosis and those caused by lipotoxicity and glucotoxicity. In particular, increased levels of free fatty acids and their metabolites are thought to diminish both insulin synthesis and glucose-stimulated insulin secretion. Thiazolidinediones are synthetic peroxisome proliferator-activated receptor-gamma agonists that decrease insulin resistance but, as in vitro and in vivo studies suggest, may have direct beneficial effects on pancreatic beta cells. Troglitazone, for example, demonstrated improvements in insulin secretory capacity in isolated pancreatic islets from Wistar rats and a hamster beta-cell line. In vivo studies reveal thiazolidinediones promote beta-cell survival and regranulation as well as maintenance of beta-cell mass and reduction in amyloid deposition. Clinical evidence for thiazolidinediones is largely derived from comparative trials, mainly against sulfonylureas and metformin. Data at 2 years from a number of trials are now available and establish the positive effects of thiazolidinediones on glycaemic control. Empirical evidence showing decreases in fasting plasma insulin levels with pioglitazone and rosiglitazone indicate thiazolidinediones also improve insulin sensitivity. A possible effect of thiazolidinediones on normalising asynchronous insulin secretion, as assessed in a short-term placebo-controlled study, is less established. However, recent and ongoing clinical studies are focusing attention on verifying animal and other data, which support the notion that thiazolidinediones have beneficial effects on beta-cell function. These clinical studies have shown thiazolidinediones capable of preventing or delaying the development of type 2 diabetes in a high-risk population; restoring the first-phase insulin response; and improving secretory responses to oscillations in plasma glucose levels. Many of these effects appear to be independent of improvements in insulin sensitivity. Other research efforts are examining the potential cardiovascular protective effects of thiazolidinediones. Available data imply thiazolidinediones are associated with cardiovascular risk reduction, although results from large, clinical outcome trials, currently in progress, are still needed. Improved understanding of the role that declining beta-cell function has in the development of type 2 diabetes has drawn attention to the need for hypoglycaemic agents that can address this process. Emerging evidence suggests thiazolidinediones offer specific benefits for preventing or delaying the decline in beta-cell function and, thereby, a substrate for early intervention efforts aimed at lowering the worldwide burden of type 2 diabetes.     

The role of sulphonylureas in the management of type 2 diabetes mellitus

The sulphonylureas act by triggering insulin release from the pancreatic beta cell. A specific site on the adenosine triphosphate (ATP)-sensitive potassium channels is occupied by sulphonylureas leading to closure of the potassium channels and subsequent opening of calcium channels. This results in exocytosis of insulin. The meglitinides are not sulphonylureas but also occupy the sulphonylurea receptor unit coupled to the ATP-sensitive potassium channel.Glibenclamide (glyburide), gliclazide, glipizide and glimepiride are the primary sulphonylureas in current clinical use for type 2 diabetes mellitus. Glibenclamide has a higher frequency of hypoglycaemia than the other agents. With long-term use, there is a progressive decrease in the effectiveness of sulphonylureas. This loss of effect is the result of a reduction in insulin-producing capacity by the pancreatic beta cell and is also seen with other antihyperglycaemic agents.The major adverse effect of sulphonylureas is hypoglycaemia. There is a theoretical concern that sulphonylureas may affect cardiac potassium channels resulting in a diminished response to ischaemia.There are now many choices for initial therapy of type 2 diabetes in addition to sulphonylureas. Metformin and thiazolidinediones affect insulin sensitivity by independent mechanisms. Disaccharidase inhibitors reduce rapid carbohydrate absorption. No single agent appears capable of achieving target glucose levels in the majority of patients with type 2 diabetes. Combinations of agents are successful in lowering glycosylated haemoglobin levels more than with a single agent. Sulphonylureas are particularly beneficial when combined with agents such as metformin that decrease insulin resistance. Sulphonylureas can also be given with a basal insulin injection to provide enhanced endogenous insulin secretion after meals. Sulphonylureas will continue to be used both primarily and as part of combined therapy for most patients with type 2 diabetes.     

Investigational insulin secretagogues for type 2 diabetes

Introduction: Insulin secretory defects are a key feature in the pathophysiology of type 2 diabetes (T2D). Classical insulin-secreting agents such as sulfonlyureas stimulate insulin secretion independent of glucose and cause hypoglycemia. Despite the advantages offered by incretin-based therapies, there is still a medical need for developing new insulin secretagogues for treating T2D.

Area covered: This article discusses: the new advances in the field of incretin-based therapies, glucokinase (GK) activators, free fatty acid receptor (FFAR) or G protein-coupled receptor (GPR) agonists (GPR40, GPR119, GPR120), imeglimin and some other insulin secretagogues with diverse mechanisms of action still in preclinical development.

Expert opinion: New insulin secretagogues should offer major advantages over sulfonylureas and gliptins. The challenge is to avoid uncontrolled insulin secretion and minimize the risk of hypoglycemia, to protect cells from progressive loss of mass and function for a better durability of glucose control, and to offer a good safety profile. Numerous approaches are in development. However, it is too early to decide whether one new pharmacological class will emerge as a clinically useful insulin secretagogue in the near feature.     

瑞格列奈对2型糖尿病患者血糖和胰岛功能的影响

目的探讨瑞格列奈(孚来迪)对2型糖尿病血糖和胰岛素分泌的影响.方法采用口服葡萄糖耐量试验(OGTT)和胰岛素释放试验新诊断的46例2型糖尿病患者,随机分为两组,23例为A组,口服孚来迪1mg/次,3 次/日,于三餐进餐前服用.23例B组,口服格列齐特80 mg/次,2 次/日,于早晚餐进餐前服用.治疗5周后比较两组间血糖和胰岛素分泌的变化.结果口服孚来迪治疗后,血糖特别是餐后血糖得到明显控制,胰岛素早期分泌相基本恢复.与格列齐特相比对早期分泌时相的恢复效果显著.结论孚来迪是一种效果显著的2型糖尿病降糖药,副作用小,适用于早期诊断的2型糖尿病患者.     

初发2型糖尿病胰岛素或口服降糖药治疗对改善B细胞功能的研究

目的对初发2型糖尿病患者进行早期的强化治疗,并探讨改善B细胞功能的可能机制。方法选择50例患者使用胰岛素泵治疗,并与口服降糖药物治疗的50例患者做比较,观察两组患者治疗后空腹血糖、胰岛B细胞功能指数、胰岛素抵抗指数（Homa-IR）以及空腹C肽水平的变化。结果治疗后两组患者空腹血糖均值均恢复到正常范围,且差异无统计学意义（P〉0.05）,观察组Homa-β和糖化血红蛋白比值显著优于对照组（P〈0.05）,两组Homa-IR间差异无统计学意义（P〉0.05）,观察组空腹C肽水平高于对照组（P〈0.05）。结论高糖毒性的解除和胰岛细胞休息学说在2型糖尿病的发生发展中均占据重要地位。     

Genes and engineered cells as drugs for type I and type II diabetes mellitus therapy and prevention

Despite the manageability of diabetes mellitus, complications associated with the disorder necessitate novel approaches to prevent immune-mediated impairment and destruction in type 1 diabetes, as well as the pancreatic insufficiency and peripheral resistance to insulin in type 2 diabetes. Islet transplantation is evolving into a clinical reality to treat type 1 diabetics and novel uses of gene engineering technology promise to result in tolerance to auto-, allo- and xenoantigens as well as microenvironment-specific immunosuppression. Through the use of a variety of gene delivery vehides, an increasing number of studies demonstrate the feasibility of shielding islet transplants and surrogate beta cells from immune rejection by the local secretion of immunosuppressive soluble molecules and anti-apoptotic factors. Although the achievements of gene and cell therapy in type 2 diabetes mellitus are less clear, seminal studies demonstrate the relevance of this approach to the treatment and perhaps prevention of the underlying causes of the disease, including obesity and insulin resistance. In this review, we attempt to illustrate pivotal studies demonstrating the suitability of genes and cells as drugs in type 1 and type 2 diabetes mellitus, and also provide some other targets that may be suitable for clinical utility.     

Identification and characterization of a novel protein histidine kinase in the islet beta cell: evidence for its regulation by mastoparan,an activator of G-proteins and insulin secretion

Using insulin-secreting cells, we previously demonstrated that specific proteins associated with the cytosolic, secretory granule, and mitochondrial fractions undergo a novel type of phosphorylation on their histidine residues. Subsequently, we identified these proteins as the nucleoside diphosphate kinase (NDPK) [Kowluru and Metz, Biochemistry 1994;33:12495-503], the beta subunit of trimeric GTP-binding proteins [Kowluru et al., Biochem J 1996;313:97-107], and the alpha subunit of succinyl-CoA synthetase [Kowluru, Diabetologia 2001;44:89-94], respectively. Since several other enzymes of intermediary metabolism (e.g. ATP-citrate lyase and glucose-6-phosphatase) also undergo histidine phosphorylation, these initial findings may have a more generalized significance to beta cells. Herein, we characterized a novel protein histidine kinase in pancreatic beta cells, and determined it to be acid- and heat-labile as well as alkali-resistant in its phosphorylation of histone 4. Such an activity was detected in normal rat islets, human islets, and clonal beta (HIT-T15 and INS-1) cells, and could utilize either ATP or GTP as a phosphoryl donor (with K(m) values in the range of 60-100 microM). On a size-exclusion column, its molecular mass was estimated to be in the range of 60-70 kDa. It was stimulated by divalent cations (Mg(2+)>Mn(2+)>control=Ca(2+)=Zn(2+)=Co(2+)), but was resistant to polyamines. It was inactivated by known in vitro inhibitors of protein histidine phosphorylation (e.g. UDP or cromoglycate). Mastoparan, a global activator of G-proteins and insulin secretion from isolated beta cells, but not mastoparan-17, its inactive analog, stimulated histidine kinase activity and histidine phosphorylation of G(beta) subunit and insulin secretion from isolated rat islets. These studies identify, for the first time, a protein kinase activity in the pancreatic beta cell that does not act on traditional -Ser, -Tyr, or -Thr residues. They also establish a possible link between histidine kinase activity and G(beta) phosphorylation in isolated beta cells.     

Agelaia MP-I: A peptide isolated from the venom of the social wasp, Agelaia pallipes pallipes, enhances insulin secretion in mice pancreatic islets

Peptides isolated from animal venoms have shown the ability to regulate pancreatic beta cell function. Characterization of wasp venoms is important, since some components of these venoms present large molecular variability, and potential interactions with different signal transduction pathways. For example, the well studied mastoparan peptides interact with a diversity of cell types and cellular components and stimulate insulin secretion via the inhibition of ATP dependent K⁺ (K_ATP) channels, increasing intracellular Ca²⁺ concentration. In this study, the insulin secretion of isolated pancreatic islets from adult Swiss mice was evaluated in the presence of synthetic Agelaia MP-I (AMP-I) peptide, and some mechanisms of action of this peptide on endocrine pancreatic function were characterized. AMP-I was manually synthesized using the Fmoc strategy, purified by RP-HPLC and analyzed using ESI-IT-TOF mass spectrometry. Isolated islets were incubated at increasing glucose concentrations (2.8, 11.1 and 22.2 mM) without (Control group: CTL) or with 10 μM AMP-I (AMP-I group). AMP-I increased insulin release at all tested glucose concentrations, when compared with CTL (P < 0.05). Since molecular analysis showed a potential role of the peptide interaction with ionic channels, insulin secretion was also analyzed in the presence of 250 μM diazoxide, a K_ATP channel opener and 10 μM nifedipine, a Ca²⁺ channel blocker. These drugs abolished insulin secretion in the CTL group in the presence of 2.8 and 11.1 mM glucose, whereas AMP-I also enhanced insulin secretory capacity, under these glucose conditions, when incubated with diazoxide and nifedipine. In conclusion, AMP-I increased beta cell secretion without interfering in K_ATP and L-type Ca²⁺ channel function, suggesting a different mechanism for this peptide, possibly by G protein interaction, due to the structural similarity of this peptide with Mastoparan-X, as obtained by modeling.     

Glucagon-like peptide-1: regulation of insulin secretion and therapeutic potential

Glucagon-like peptide-1 (GLP-1) is an intestinally derived insulinotropic hormone currently under investigation for use as a novel therapeutic agent in the treatment of type 2 diabetes. One of several important effects of GLP-1 is on nutrient-induced pancreatic hormone release and is mediated by binding to a specific G-protein coupled receptor resulting in the activation of adenylate cyclase and an increase in cAMP generation. In the beta-cell, cAMP binds and modulates activities of both protein kinase A and cAMP-regulated guanine nucleotide exchange factor II, thereby enhancing glucose-dependent insulin secretion. The stimulatory action of GLP-1 on insulin secretion involves interaction with a plethora of signal transduction processes including ion channel activity, intracellular Ca(2+) handling and exocytosis of the insulin-containing granules. In this review we focus principally on recent advances in our understanding on the cellular mechanisms proposed to underlie GLP-1's insulinotropic effect and attempt to incorporate this knowledge into a working model for the control of insulin secretion. Lastly, this review discusses the applicability of GLP-1 as a therapeutic agent for the treatment of type 2 diabetes.     

Pharmacological regulation of dyslipoproteinaemia in insulin resistant states

Dyslipidaemia is a common and consistent abnormality in insulin resistant subjects with obesity and type 2 diabetes mellitus associated with increased risk of cardiovascular disease. Lipoprotein metabolism is complex and abnormal plasma concentrations can result from alterations in the rates of production and/or catabolism of diverse lipoprotein particles. Our understandings of the dysregulation and therapeutic regulation of lipoprotein transport in insulin resistant states has relied on the application of advances in stable isotope and modelling methods. Dysregulation of lipoprotein metabolism in these circumstances may be caused by a combination of overproduction of VLDL apolipoprotein (apoB) B-100 and VLDL-apoC-III, decreased catabolism of apoB-containing particles, and increased catabolism of HDL apoA-I particles. These abnormalities may be consequent on a global metabolic effect of insulin resistance and accumulation of visceral fat. Several pharmacological treatments, such as statins, fibrates or fish oil can correct the dyslipidaemia by diverse kinetic mechanisms of action, including decreased secretion of apoB and apoC-III, and increased catabolism of apoB, as well as increased secretion and decreased catabolism of apoA-I. Newer agents, including insulin sensitizers, cholesterol absorption inhibitors, CETP inhibitors, peroxisome proliferator-activated receptor-delta agonists and endocannabinoid-1 receptor blockers, have also been shown to improve plasma lipid and lipoprotein abnormalities in insulin resistant states; their mechanisms of action are at present being investigated. Rimonabant is the endocannabinoid receptor blocker shown to decrease cardiometabolic risk in insulin resistant subjects. The complementary mechanisms of action of different agents support the use of combination regimens in treating dyslipoproteinaemia in subjects with central obesity and type 2 diabetes.     

Alterations of insulin secretion following long-term manipulation of ATP-sensitive potassium channels by diazoxide and nateglinide

Previous studies have shown that prolonged exposure to drugs, which act via blocking KATP channels, can desensitize the insulinotropic effects of drugs and nutrients acting via KATP channels. In this study, effects of prolonged exposure to diazoxide, a KATP channel opener, on beta cell function were examined using clonal BRIN-BD11 cells. The findings were compared to the long-term effects of KATP channel blockers nateglinide and tolbutamide. Following 18 h exposure to 200 microM diazoxide, the amounts of insulin secreted in response to glucose, amino acids and insulinotropic drugs were increased. Secretory responsiveness to a variety of agents acting via KATP channels was retained following prolonged diazoxide exposure. In contrast, 18 h exposure to 100 microM nateglinide significantly attenuated the insulin secretory responses to tolbutamide, nateglinide and BTS 67 582. Glucose- and L-alanine-stimulated insulin release were unaffected by prolonged nateglinide exposure, however responsiveness to L-leucine and L-arginine was diminished. Prolonged exposure to nateglinide had no effect on forskolin- and PMA-stimulated insulin release, and the overall pattern of desensitization was similar to that induced by 100 microM tolbutamide. We conclude that in contrast to chronic long-term KATP channel blockade, long-term diazoxide treatment is not harmful to KATP channel mediated insulin secretion and may have beneficial protective effects on beta cell function.     

Microbial phenolic metabolites improve glucose-stimulated insulin secretion and protect pancreatic beta cells against tert-butyl hydroperoxide-induced toxicity via ERKs and PKC pathways

Oxidative stress is accepted as one of the causes of beta cell failure in type 2 diabetes. Therefore, identification of natural antioxidant agents that preserve beta cell mass and function is considered an interesting strategy to prevent or treat diabetes. Recent evidences indicated that colonic metabolites derived from flavonoids could possess beneficial effects on various tissues. The aim of this work was to establish the potential anti-diabetic properties of the microbial-derived flavonoid metabolites 3,4-dihydroxyphenylacetic acid (DHPAA), 2,3-dihydroxybenzoic acid (DHBA) and 3-hydroxyphenylpropionic acid (HPPA). To this end, we tested their ability to influence beta cell function and to protect against tert-butyl hydroperoxide-induced beta cell toxicity. DHPAA and HPPA were able to potentiate glucose-stimulated insulin secretion (GSIS) in a beta cell line INS-1E and in rat pancreatic islets. Moreover, pre-treatment of cells with both compounds protected against beta cell dysfunction and death induced by the pro-oxidant. Finally, experiments with pharmacological inhibitors indicate that these effects were mediated by the activation of protein kinase C and the extracellular regulated kinases pathways. Altogether, these findings strongly suggest that the microbial-derived flavonoid metabolites DHPAA and HPPA may have anti-diabetic potential by promoting survival and function of pancreatic beta cells.     

Ca2+ signaling and the insulin secretory cascade in the pancreatic beta-cell.

Recent progress in electrophysiological and microscopic techniques have enabled us to estimate exocytotic and pre-exocytotic events in the secretory machinery in single pancreatic beta-cells. We have been studying mechanisms involved in the regulation of insulin granule movement, which supplies release-ready granules, by direct visualization of granule traffic in living beta-cells and found the movement to be regulated by a mechanism different from that controlling exocytosis. From the obtained findings together with those from electrophysiological approaches, a new understanding of the role of the crucial second messenger Ca2+, and other second messengers, as well as resultant protein phosphorylation has been generated. The aim of this review is to describe a synergistic network for the control of insulin release by second messengers and protein kinases.