肠促胰素的胰腺外作用研究进展

肠促胰素是经食物刺激后由肠道细胞分泌入血、能够刺激胰岛素分泌的一类激素.人体中,胰升糖素样肽1(GLP-1)和糖依赖性胰岛素释放肽((GIP)发挥肠促胰素效应.本文简要介绍肠促胰素的胰腺作用,重点回顾其胰腺外生理作用,以全面评价肠促胰素类药物的临床应用前景.

Abstract：

Incretin is defined as an intestinal hormone released in response to nutrient ingestion, which potentiates the glucose-induced insulin response. In human body, the incretin's effect is mainly induced by two peptide hormones, glucagon-like peptide-I (GLP-I)and glucose-dependent insulinotropic polypeptide (GIP). In order to fully evaluate the clinical advantages of novel agents based on incretin, this review introduces the islet actions of incretin in brief, and mainly focuses on the extra-islet effect of incretin.     

葡萄糖依赖性促胰岛素多肽：从基础研究到临床研究

肠促胰素是连接肠道与大脑和胰腺的重要激素, 对机体能量代谢发挥调节作用。葡萄糖依赖性促胰岛素多肽(GIP)是肠促胰素重要的组成部分, 与肠促胰素另一成员胰高糖素样肽-1(GLP-1)协同互补实现对能量代谢的调控。近年来, 对GIP及其受体的作用机制研究取得了重要的突破, 使得GIP成为改善葡萄糖及能量代谢的重要靶点。最新开发的GIP和GLP-1受体激动剂显示了对2型糖尿病患者血糖和体重的显著改善, 成为潜在的有吸引力的药物选择。该文就GIP在基础和临床方面的重要研究进展进行综述, 以期帮助临床深入理解肠促胰素对人体能量代谢的调控机制, 以及更好地认识基于这一靶点开发的药物。     

人胰高血糖素样肽-1受体激动剂的作用机制

<正>1987年Nauck等〔1,2〕人证实了肠促胰素效应的存在,且发现2型糖尿病(T2DM)患者餐后胰高血糖素样肽(GLP)-1水平较正常人明显降低,这提示肠促胰素异常可能是T2DM的发病机制之一。此后,两种重要的肠促胰素,葡萄糖依赖性促胰岛素多肽(GIP)与GLP-1被相继发现。但由于GIP在T2DM患者中的分泌接近正常或仅轻微下降,促胰岛素分泌作用相对较     

艾塞那肽临床研究新进展

肠促胰素是肠道在进餐后分泌的激素,能促进胰岛素的分泌.胰高糖素样肽1(GLP-1)是主要的肠促胰素,通过葡萄糖依赖的方式促进胰岛素分泌、抑制胰高糖素分泌以及延缓胃排空、增加饱腹感等作用维持体内血糖的稳定.另外,在2型糖尿病患者中,它还可改善β细胞功能.但是天然的GLP-1半寿期很短,无法用于临床治疗.艾塞那肽是从希拉巨蜥唾液中分离得到的一种多肽,它可与GLP-1受体结合,产生与GLP-1相似的生理效应,但它的半寿期远比GLP-1长,因此每天两次皮下注射即可产生满意的疗效.临床研究显示艾塞那肽可显著降低2型糖尿病患者HbA_(1C)、空腹血糖及餐后血糖,并降低体重.动物研究表明艾塞那肽还可改善β细胞功能、增加β细胞量.由于GLP-1受体激动剂的独特疗效,新近的糖尿病治疗指南已将其列入2型糖尿病的治疗药物.     

二肽基肽酶4抑制剂治疗2型糖尿病的研究进展

肠促胰素是一类由肠道分泌的葡萄糖依赖性的促胰岛素分泌因子，主要由胰高糖素样肽-1（GLP-1）和糖依赖性胰岛素释放肽（GIP）组成，其中GLP-1在2型糖尿病的发生、发展中发挥重要作用。二肽基肽酶4（DPP-4）是灭活GLP-1的关键酶，其抑制剂是一种新型的口服降糖药，可以提高血液中内源性GLP-1和GIP水平，有效降低血糖并有良好的耐受性。本文就DPP-4抑制剂治疗2型糖尿病的进展作一综述。     

DPP-4抑制剂的作用机制及在2型糖尿病治疗中的应用

α及母细胞功能障碍在2型糖尿病的发生中发挥重要作用.二肽基肽酶4( DPP-4)抑制剂是一类基于肠促胰素的新型的口服降糖药物,通过增加内源性活性胰升糖素样肽-1( GLP-1)及葡萄糖依赖性促胰岛素分泌多肽(GIP)水平改善α及β细胞功能障碍,表现为α及β细胞对葡萄糖的敏感性增加,葡萄糖依赖性地促进胰岛素分泌并抑制胰升糖素分泌.同时还具有增加胰岛素敏感性及调节血脂代谢等胰腺外作用.并具有较少发生低血糖,对体重的影响中性,不影响胃排空等特点.临床研究证实其无论单药还是与其他药物联合使用均具有较高的有效性及良好的安全性和耐受性.     

GLP-1受体激动剂与二肽基肽酶4抑制剂治疗2型糖尿病的比较

随着对肠促胰素在维持葡萄糖稳定作用认识的日益增多,促进了针对2型糖尿病患者肠促胰素活性缺乏治疗药物的研发.根据肠促胰素治疗药物不同的作用机制,可分为以下2类:(1)胰升糖素样肽1(GLP-1)受体激动剂,包括利拉鲁肽(liraglutide)、艾塞那肽每日2次制剂和艾塞那肽每周1次制剂;(2)二肽基肽酶4(DPP-4)抑制剂,包括西格列汀(sitagliptin)、利拉利汀(linagliptin)、沙格列汀(saxagliptin)和维格列汀(vildagliptin),DPP-4抑制剂可限制内源性GLP-1的降解.这2类药物具有某些共性,如葡萄糖依赖性刺激胰岛素分泌,低血糖发生率低.然而这2类药物在疗效方面的表现却有所不同.本文综述了这2类基于肠促胰素治疗药物的药代动力学及其临床方面的疗效和安全性,阐明了此类药物在2型糖尿病治疗中的地位.     

胰高血糖素样多肽-1类似物利拉鲁肽全球Ⅲ期临床研究结果回顾

人们很早就认识到口服葡萄糖刺激胰岛素分泌的量明显大于静脉葡萄糖所引起的胰岛素释放,这种现象被称为"肠促胰素"效应[1].胰高血糖素样多肽-1(GLP-1)和葡萄糖依赖性胰岛素释放肽(GIP)均属于肠促胰素,但GIP对胰岛α细胞无作用且2型糖尿病患者的胰岛β细胞对GIP反应显著下降,因而限制了GIP的临床应用.     

葡萄糖依赖性促胰岛素释放肽-受体信号通路与肥胖症的研究进展

葡萄糖依赖性促胰岛素释放肽（GIP）是一种由小肠黏膜上皮K细胞合成并分泌的肠促胰岛素分泌肽,能够刺激胰岛素和胰高糖素的分泌。近年来研究发现,GIP-GIP受体（GIPR）信号通路在肥胖症及其相关代谢异常中起到重要作用。GIP和GIPR基因的多态性与肥胖易感性显著相关。激活GIP-GIPR通路能增加脂肪合成和储存,促进肥...     

在健康人中由类固醇治疗、限制体力活动及高热量饮食诱发的糖耐量减退与胰岛素抵抗可降低肠促胰素的作用

肠促胰素(incretin),包括胰升糖素样肽1(GLP-1)和葡萄糖依赖性促胰岛素多肽(GIP),是在进食后释放的肠道激素.这两种激素都有强烈的葡萄糖依赖性促胰岛素作用,从进餐开始即能增强葡萄糖诱导的胰岛素分泌.口服葡萄糖后的这种胰岛素分泌增加称为肠促胰素作用.2型糖尿病患者的肠促胰素作用显著减退.导致这一病理生理特征的原因仍然不明.我们曾报道肠促胰素作用减退也见于继发于慢性胰腺炎的糖尿病患者,提示其为糖代谢失调的结果.此外,我们近年的研究显示肠促胰素缺乏是一个可逆的过程.妊娠糖尿病患者在妊娠后期肠促胰素作用减弱,餐后GLP-1水平下降,但在分娩及糖耐量恢复正常后,两者均恢复正常.Hφjberg等人也发现,2型糖尿病患者经胰岛素强化治疗使血糖接近正常4周后,β细胞对GLP-1和GIP的反应明显改善.但目前有关糖尿病患者中肠促胰素作用下降的因果关系的研究均未涉及其根本问题:即在完全健康的个体中诱发糖代谢失衡是否会引起肠促胰素缺乏.为此,我们在没有2型糖尿病风险的完全健康的男性青年中,通过服用强的松龙、限制体力活动及高热量饮食诱发胰岛素抵抗与糖耐量减退,并在此前此后测定肠促胰素作用.     

The evolving story of incretins (GIP and GLP-1) in metabolic and cardiovascular disease: A pathophysiological update

The incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) have their main physiological role in augmenting insulin secretion after their nutrient-induced secretion from the gut. A functioning entero-insular (gut-endocrine pancreas) axis is essential for the maintenance of a normal glucose tolerance. This is exemplified by the incretin effect (greater insulin secretory response to oral as compared to “isoglycaemic” intravenous glucose administration due to the secretion and action of incretin hormones). GIP and GLP-1 have additive effects on insulin secretion. Local production of GIP and/or GLP-1 in islet α-cells (instead of enteroendocrine K and L cells) has been observed, and its significance is still unclear. GLP-1 suppresses, and GIP increases glucagon secretion, both in a glucose-dependent manner. GIP plays a greater physiological role as an incretin. In type 2-diabetic patients, the incretin effect is reduced despite more or less normal secretion of GIP and GLP-1. While insulinotropic effects of GLP-1 are only slightly impaired in type 2 diabetes, GIP has lost much of its acute insulinotropic activity in type 2 diabetes, for largely unknown reasons. Besides their role in glucose homoeostasis, the incretin hormones GIP and GLP-1 have additional biological functions: GLP-1 at pharmacological concentrations reduces appetite, food intake, and—in the long run—body weight, and a similar role is evolving for GIP, at least in animal studies. Human studies, however, do not confirm these findings. GIP, but not GLP-1 increases triglyceride storage in white adipose tissue not only through stimulating insulin secretion, but also by interacting with regional blood vessels and GIP receptors. GIP, and to a lesser degree GLP-1, play a role in bone remodelling. GLP-1, but not GIP slows gastric emptying, which reduces post-meal glycaemic increments. For both GIP and GLP-1, beneficial effects on cardiovascular complications and neurodegenerative central nervous system (CNS) disorders have been observed, pointing to therapeutic potential over and above improving diabetes complications. The recent finding that GIP/GLP-1 receptor co-agonists like tirzepatide have superior efficacy compared to selective GLP-1 receptor agonists with respect to glycaemic control as well as body weight has renewed interest in GIP, which previously was thought to be without any therapeutic potential. One focus of this research is into the long-term interaction of GIP and GLP-1 receptor signalling. A GLP-1 receptor antagonist (exendin [9-39]) and, more recently, a GIP receptor agonist (GIP [3-30] NH₂) and, hopefully, longer-acting GIP receptor agonists for human use will be helpful tools to shed light on the open questions. A detailed knowledge of incretin physiology and pathophysiology will be a prerequisite for designing more effective incretin-based diabetes drugs.     

Physiology of incretins (GIP and GLP-1) and abnormalities in type 2 diabetes

Incretin hormones are defined as intestinal hormones released in response to nutrient ingestion, which potentiate the glucose-induced insulin response. In humans, the incretin effect is mainly caused by two peptide hormones, glucose-dependent insulin releasing polypeptide (GIP), and glucagon-like peptide-1 (GLP-1). GIP is secreted by K cells from the upper small intestine while GLP-1 is mainly produced in the enteroendocrine L cells located in the distal intestine. Their effect is mediated through their binding with specific receptors, though part of their biological action may also involve neural modulation. GIP and GLP-1 are both rapidly degraded into inactive metabolites by the enzyme dipeptidyl-peptidase-IV (DPP-IV). In addition to its effects on insulin secretion, GLP-1 exerts other significant actions, including stimulation of insulin biosynthesis, inhibition of glucagon secretion, inhibition of gastric emptying and acid secretion, reduction of food intake, and trophic effects on the pancreas. As the insulinotropic action of GLP-1 is preserved in type 2 diabetic patients, this peptide was likely to be developed as a therapeutic agent for this disease.     

Physiology of incretins in health and disease

The incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), are gut peptides which are secreted by endocrine cells in the intestinal mucosa. Their plasma concentrations increase quickly following food ingestion, and carbohydrate, fat, and protein have all been shown to stimulate GLP-1 and GIP secretion. Although neural and hormonal mechanisms have also been proposed to regulate incretin hormone secretion, direct stimulation of the enteroendocrine cells by the presence of nutrients in the intestinal lumen is probably the most important factor in humans. The actions of the incretin hormones are crucial for maintaining normal islet function and glucose homeostasis. Furthermore, it is also now being recognized that incretin hormones may have other actions in addition to their glucoregulatory effects. Studies have shown that GLP-1 and GIP levels and actions may be perturbed in disease states, but interpretation of the precise relationship between disease and incretins is difficult. The balance of evidence seems to suggest that alterations in secretion and/or action of incretin hormones arise secondarily to the development of insulin resistance, glucose intolerance, and/or increases in body weight rather than being causative factors. However, these impairments may contribute to the deterioration of glycemic control in diabetic patients.     

The incretin system and its role in type 2 diabetes mellitus

The incretin hormones are released during meals from gut endocrine cells. They potentiate glucose-induced insulin secretion and may be responsible for up to 70% of postprandial insulin secretion. The incretin hormones include glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), both of which may also promote proliferation/neogenesis of beta cells and prevent their decay (apoptosis). Both hormones contribute to insulin secretion from the beginning of a meal and their effects are progressively amplified as plasma glucose concentrations rise. The current interest in the incretin hormones is due to the fact that the incretin effect is severely reduced or absent in patients with type 2 diabetes mellitus (T2DM). In addition, there is hyperglucagonaemia, which is not suppressible by glucose. In such patients, the secretion of GIP is near normal, but its effect on insulin secretion, particularly the late phase, is severely impaired. The loss of GIP action is probably a consequence of diabetes, since it is also observed in patients with diabetes secondary to chronic pancreatitis, in whom the incretin effect is also lost. GLP-1 secretion, on the other hand, is also impaired, but its insulinotropic and glucagon-suppressive actions are preserved, although the potency of GLP-1 in this respect is decreased compared to healthy subjects. However, in supraphysiological doses, GLP-1 administration may completely normalize beta as well as alpha cell sensitivity to glucose. The impaired action of GLP-1 and GIP in T2DM may be at least partly restored by improved glycaemic control, as shown in studies involving 4 weeks of intensive insulin therapy. The reduced incretin effect is believed to contribute to impaired regulation of insulin and glucagon secretion in T2DM, and, in support of this, exogenous GLP-1 administration may restore blood glucose regulation to near normal levels. Thus, the pathogenesis of T2DM seems to involve a dysfunction of both incretins. Enhancement of incretin action may therefore represent a therapeutic solution. Clinical strategies therefore include the development of metabolically stable activators of the GLP-1 receptor; and inhibition of DPP-4, the enzyme that destroys native GLP-1 almost immediately. Orally active DPP-4 inhibitors and the metabolically stable activators, exenatide (Byetta), are now on the market, and numerous clinical studies have shown that both principles are associated with durable antidiabetic activity.     

Incretins and the development of type 2 diabetes

The incretin hormones gastric inhibitory polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) are released in response to nutrient ingestion and potentiate glucosestimulated insulin secretion from pancreatic β cells. The augmentation of postprandial insulin secretion by such gastrointestinal hormones is called the incretin effect. The incretin effect is almost completely absent in patients with type 2 diabetes. This is due to 1) an approximate 15% reduction in postprandial GLP-1 secretion and 2) a near total loss of insulinotropic activity of GIP. This review article summarizes clinical studies on abnormalities in the secretion and insulinotropic effects of GIP and GLP-1 in patients with type 2 diabetes as well as in individuals at high risk. A significant proportion of first-degree relatives are characterized by a reduced insulinotropic response to exogenous GIP. Nevertheless, this phenomenon does not predispose to a more rapid deterioration in glucose tolerance or conversion to impaired glucose tolerance or diabetes. Therefore, although there are hints of early abnormalities in incretin secretion and action in prediabetic populations, it has not been proven that such phenomena are central to the pathogenesis of type 2 diabetes.     

Incretins, insulin secretion and Type 2 diabetes mellitus

When glucose is taken orally, insulin secretion is stimulated much more than it is when glucose is infused intravenously so as to result in similar glucose concentrations. This effect, which is called the incretin effect and is estimated to be responsible for 50 to 70% of the insulin response to glucose, is caused mainly by the two intestinal insulin-stimulating hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Their contributions have been confirmed in mimicry experiments, in experiments with antagonists of their actions, and in experiments where the genes encoding their receptors have been deleted. In patients with Type 2 diabetes, the incretin effect is either greatly impaired or absent, and it is assumed that this could contribute to the inability of these patients to adjust their insulin secretion to their needs. In studies of the mechanism of the impaired incretin effect in Type 2 diabetic patients, it has been found that the secretion of GIP is generally normal, whereas the secretion of GLP-1 is reduced, presumably as a consequence of the diabetic state. It might be of even greater importance that the effect of GLP-1 is preserved whereas the effect of GIP is severely impaired. The impaired GIP effect seems to have a genetic background, but could be aggravated by the diabetic state. The preserved effect of GLP-1 has inspired attempts to treat Type 2 diabetes with GLP-1 or analogues thereof, and intravenous GLP-1 administration has been shown to be able to near-normalize both fasting and postprandial glycaemic concentrations in the patients, perhaps because the treatment compensates for both the impaired secretion of GLP-1 and the impaired action of GIP. Several GLP-1 analogues are currently in clinical development and the reported results are, so far, encouraging.Abbreviations GLP-1 Glucagon-like peptide-1 - GIP glucose-dependent insulinotropic polypeptide - FPG fasting plasma glucose     

Incretin secretion in relation to meal size and body weight in healthy subjects and people with type 1 and type 2 diabetes mellitus

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are incretin hormones secreted in response to meal ingestion, thereby enhancing postprandial insulin secretion. Therefore, an attenuated incretin response could contribute to the impaired insulin responses in patients with diabetes mellitus. The aim of the present investigation was to investigate incretin secretion, in obesity and type 1 and type 2 diabetes mellitus, and its dependence on the magnitude of the meal stimulus. Plasma concentrations of incretin hormones (total, reflecting secretion and intact, reflecting potential action) were measured during two meal tests (260 kcal and 520 kcal) in eight type 1 diabetic patients, eight lean healthy subjects, eight obese type 2 diabetic patients, and eight obese healthy subjects. Both in diabetic patients and in healthy subjects, significant increases in GLP-1 and GIP concentrations were seen after ingestion of both meals. The incretin responses were significantly higher in all groups after the large meal, compared with the small meal, with correspondingly higher C-peptide responses. Both type 1 and type 2 diabetic patients had normal GIP responses, compared with healthy subjects, whereas decreased GLP-1 responses were seen in type 2 diabetic patients, compared with matched obese healthy subjects. Incremental GLP-1 responses were normal in type 1 diabetic patients. Increased fasting concentrations of GIP and an early enhanced postprandial GIP response were seen in obese, compared with lean healthy subjects, whereas GLP-1 responses were the same in the two groups. beta-cell sensitivity to glucose, evaluated as the slope of insulin secretion rates vs. plasma glucose concentration, tended to increase in both type 2 diabetic patients (29%, P = 0.19) and obese healthy subjects (22% P = 0.04) during the large meal, compared with the small meal, perhaps reflecting the increased incretin response. We conclude: 1) that a decreased GLP-1 secretion may contribute to impaired insulin secretion in type 2 diabetes mellitus, whereas GIP and GLP-1 secretion is normal in type 1 diabetic patients; and 2) that it is possible to modulate the beta-cell sensitivity to glucose in obese healthy subjects, and possibly also in type 2 diabetic patients, by giving them a large meal, compared with a small meal.     

Incretin dysfunction in type 2 diabetes: Clinical impact and future perspectives

The incretin effect refers to the augmentation of insulin secretion after oral administration of glucose compared with intravenous glucose administration at matched glucose levels. The incretin effect is largely due to the release and action on beta-cells of the gut hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). This system has in recent years had considerable interest due to the success of incretin therapy as a glucose-lowering strategy in type 2 diabetes. In non-diabetic subjects, the incretin effect is responsible for 50–70% of insulin release during oral glucose administration. In type 2 diabetes patients, the incretin effect is impaired and contributes to only 20–35% of the insulin response to oral glucose. The reason for the defective incretin effect in type 2 diabetes has been the subject of many studies. Although the reports in the literature are mixed, most studies of GIP and GLP-1 secretory responses to oral glucose or a mixed meal have shown fairly normal results in type 2 diabetes. In contrast, the insulinotropic effects of both GIP and GLP-1 are impaired in type 2 diabetes with greater suppression of insulin secretion augmentation with GIP than with GLP-1. The suggested causes of these defects are a defective beta-cell receptor expression or post-receptor defects secondary to the diabetes milieu, defective beta-cell function in general resulting in defective incretin effect and genetic factors initiating incretin hormone resistance. Identifying the mechanisms in greater detail would be important for understanding the strengths, weaknesses and efficacy of incretin therapy in individual patients to more specifically target this glucose-lowering therapy.     

Incretin hormones

Incretin hormones are peptides that are secreted from endocrine cell of gastrointestinal tract after nutrient ingestion and stimulate insulin secretion. Glucosodependent Insulinotropic Peptide--GIP is released from K-cells of duodenum and proximal jejunum, recently GIP synthesis has been proved in pancreatic alpha cells. Besides the incretin effect causes GIP increased lipogenesis and decreased lipolysis in fat tissue, increased bone formation and decreased resorption and has protective and proliferative effect on CNS neurons. Both GIP agonists (to treat diabetes) and antagonist (to treat obesity) are being studied. Another incretin hormone is derived in intestinal I-cells by posttranslational processing of proglucagon--glucagon-like peptides 1 and 2 (GLP-1 and GLP-2). GLP-1 stimulates insuline production and inhibits glucagon secretion, exerts proliferative and antiapoptotic effect on beta-cells. Via receptors on vagal nerve and central mechanisms decreases food intake and decreases body weight. By deceleration of gastric emptying it attenuates increases in meal-associated blood glucose levels. It exerts cardioprotective effects. GLP-1 receptors have been proved in liver recently but decreased liver glucose production and increased glucose uptake by liver and muscle are mediated indirectly by altering insulin and glucagons levels. GLP-2 stimulates enterocytes proliferation, up-regulates intestinal nutrient transport, improves intestinal barrier function, and inhibits gastric and intestinal motility. GLP-2 also reduces bone resorption.