二肽基肽酶-4在慢性肝病发病中的作用研究进展

二肽基肽酶-4（DPP-4）是膜相关酶,又称T细胞表面抗原CD26,在体内广泛分布,作用广泛。最有代表的作用靶肽是胰高血糖素样肽（GLP）-1,而GLP-1的失活导致糖耐量减低和糖尿病。除了其肽酶作用之外,DPP-4与免疫激活密切相关,结合并降解细胞外基质,对抗抗癌剂以及脂质积累。最近的研究表明,肝脏表达高水平的DPP-4,DPP-4在各种慢性肝病（如丙型肝炎病毒感染、非酒精性脂肪性肝病和肝细胞癌）的发病中有一定的作用。此外,在肝脏,干细胞也表达DPP-4,提示其在肝移植中有重要作用。本文介绍了DPP-4的分布及生物活性,重点讨论了DPP-4在慢性肝病发病中的作用以及DPP-4抑制剂的临床应用前景。     

肠促胰素类降糖药物对体重的作用

胰高血糖素样肽-1(GLP-1)受体激动剂和二肽基肽酶-4(DPP-4)抑制剂是新型的2型糖尿病治疗药物.普遍认为,GLP-1受体激动剂可显著减轻患者体重,DPP-4抑制剂对体重的作用为中性.然而,这两类药物与不同药物联用,患者体重可不同程度增加,尤其是与磺脲类或噻唑烷二酮类药物联用时.临床医师应了解GLP-1受体激动剂和DPP-4抑制剂对体重的影响,为2型糖尿病患者制定更合理、安全和有效的治疗方案.     

Incretin based therapies: A novel treatment approach for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease is considered a hepatic manifestation of metabolic syndrome (MS). The current treatment of non-alcoholic fatty liver disease (NAFLD) principally includes amelioration of MS components by lifestyle modifications but the lack of success in their implementation and sustainment arises the need for effective pharmacological agent in fatty liver treatment. Incretins are gut derived hormones secreted into the circulation in response to nutrient ingestion that enhances glucose-stimulated insulin secretion. Glucagon-like peptide-1 (GLP-1) is the most important incretin. Its receptor agonist and inhibitors of dipeptidyl peptidase-4 (DPP-4) are used in treatment of type 2 diabetes mellitus. DPP-4 serum activity and hepatic expression are shown to be elevated in several hepatic diseases. There are several experimental and clinical trials exploring the efficacy of incretin based therapies in NAFLD treatment. They suggest that GLP-1 analogues might have beneficial effect on hepatic steatosis acting as insulin sensitizers and directly by stimulating GLP-1 receptors expressed on hepatocytes. The use of DPP-4 inhibitors also results in hepatic fat reduction but the mechanism of action remains unclear. There is growing evidence that incretin based therapies have beneficial effects on hepatocytes, however further study analysis are needed to assess the long term effect of incretin based therapies on NAFLD.     

Effects of PKF275-055, a dipeptidyl peptidase-4 inhibitor, on the development of atherosclerotic lesions in apolipoprotein E-null mice

We recently discovered that glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide can both prevent the development of atherosclerosis in apolipoprotein E-null (Apoe(-/-)) mice. In the present study, we attempted to extend these findings to orally administered dipeptidyl peptidase (DPP)-4 inhibitor. Seventeen-week-old Apoe(-/-) mice fed an atherogenic diet were administered a DPP-4 inhibitor, vildagliptin analogue (PKF275-055 [PKF], 100 μm/[kg d]), in drinking water over a period of 4 weeks. Aortic atherosclerosis and oxidized low-density lipoprotein-induced foam cell formation were determined. Orally administered PKF increased plasma levels of active glucagon-like peptide-1 by 3.5-fold, increased total glucose-dependent insulinotropic polypeptide levels by 2-fold, reduced body weight by 13%, and reduced plasma cholesterol levels by 30%. Compared with drinking water controls, PKF significantly suppressed total aortic atherosclerotic lesions, atheromatous plaque in the aortic root, and macrophage accumulation in the aortic wall by 30% to 40% (P < .001). None of these changes were associated with the PKF-induced reductions in body weight and plasma cholesterol levels. Foam cell formation was suppressed by 40% in the exudate peritoneal macrophages obtained from the PKF-treated mice. The DPP-4 inhibitor prevents the development of atherosclerotic lesions by suppressing macrophage foam cell formation.     

Acute dipeptidyl peptidase-4 inhibition rapidly enhances insulin-mediated suppression of endogenous glucose production in mice

Pharmacological approaches that enhance incretin action for the treatment of type 2 diabetes mellitus have recently been developed, i.e. injectable glucagon-like peptide-1 receptor (GLP-1R) agonists with prolonged plasma half-lives and orally available inhibitors of dipeptidyl peptidase (DPP)-4, the main enzyme responsible for the rapid degradation of circulating glucagon-like peptide-1 and glucose-dependent insulinotropic peptide. The mechanism(s) underlying the glucose-lowering effect of these two pharmacotherapies differs and is not yet fully understood. Here we investigated whether acute GLP-1R activation (exendin-4) or DPP-4 inhibition (des-F-sitagliptin) modulates insulin action in mice using a hyperinsulinemic euglycemic clamp. A single iv bolus of des-F-sitagliptin (11 mg/kg) was administered to mice 15 min after the start of the clamp, and its effect was compared with a 50-ng bolus of exendin-4 or the same volume of saline. Despite matched levels of plasma glucose and insulin, within 15 min the glucose infusion rate required to maintain euglycemia was significantly greater after des-F-sitagliptin compared with saline or exendin-4. This difference was entirely due to enhancement of insulin-mediated suppression of endogenous glucose production by des-F-sitagliptin, with no difference in glucose disposal rate. These findings illustrate that DPP-4 inhibition modulates glucose homeostasis through pathways distinct from those used by GLP-1R agonists in mice.     

Multifactorial intervention in Type 2 diabetes: the promise of incretin-based therapies

Type 2 diabetes mellitus is increasing in prevalence at alarming rates. Concurrent with its expanding prevalence is the increase in the related risk of morbidity and mortality. Because diabetic patients are prone to cardiovascular disease, treatment strategies should address the cardiovascular risk factors, including blood pressure, lipids, and body weight, in addition to the glycemic aspects of the disease. Newer agents, such as glucagon-like peptide-1 (GLP-1) analogs and dipeptidyl peptidase-4 (DPP-4) inhibitors, have varying degrees of evidence to support their effects on body weight, blood pressure, and lipid levels, beyond glycated hemoglobin reduction. While GLP-1 agonists produce a weight loss, the DPP-4 inhibitors, conversely, appear to have a weight-neutral effect. Substantial evidence demonstrates that both medications produce modest reductions in systolic blood pressure and, in some cases, diastolic blood pressure, and reduce several markers of cardiovascular risk, including C-reactive protein. Moreover, GLP-1 influences endothelial function. The effect of the incretin hormones on serum lipids are either neutral or beneficial, with small, non-significant decreases in LDL cholesterol, increases in HDL cholesterol, and occasionally significant decreases in fasting triglyceride levels. Also, they have positive effects on hepatic steatosis. Although GLP-1 agonists and DPP-4 inhibitors are at present not appropriate for primary treatment of cardiovascular risks factors, the reduction of these parameters is evidently beneficial.     

Targeting Left Ventricular Lead Placement to Improve Cardiac Resynchronization Therapy Outcomes

It is well known that patients with type 2 diabetes mellitus (T2DM) are at increased risk of cardiovascular (CV) disease. Elevated plasma glucose levels that independently lead to increased cardiovascular risk, combined with associated co-morbidities such as obesity, hypertension, and dyslipidemia, further contribute to the development of CV complications. Dipeptidyl peptidase 4 inhibitors (DPP-4 inhibitors) are a relatively new class of drugs used for the treatment of diabetes and recently have been widely used in clinical practice. They exert their actions through degradation inhibition of endogenous glucagon-like peptides (GLP-1) and glucose-dependent insulinotropic peptides (GIP), with a resulting increase in glucose mediated insulin secretion and a suppression of glucagon secretion. Since GLP-1 is known to have an impact not only on plasma glucose levels but also to have cardiovascular protective effects there is increased speculation of whether DPP-4 inhibitors will have similar effects. Though many short-term studies have been encouraging, ongoing long-term clinical trials on humans are needed to provide further clarity to the complete safety profiles of these agents in terms of cardiovascular risk, and whether they may exert potential cardiovascular benefit. This review includes available data on the cardiovascular effects of DPP-4 inhibitors as well as their overall safety profile.     

The role of dysregulated glucagon secretion in type 2 diabetes

Excessive production of glucose by the liver contributes to fasting and postprandial hyperglycaemia, hallmarks of type 2 diabetes. A central feature of this pathologic response is insufficient hepatic insulin action, due to a combination of insulin resistance and impaired β-cell function. However, a case can be made that glucagon also plays a role in dysregulated hepatic glucose production and abnormal glucose homeostasis. Plasma glucagon concentrations are inappropriately elevated in diabetic individuals, and α-cell suppression by hyperglycaemia is blunted. Experimental evidence suggests that this contributes to greater rates of hepatic glucose production in the fasting state and attenuated reduction after meals. Recent studies in animal models indicate that reduction of glucagon action can have profound effects to mitigate hyperglycaemia even in the face of severe hypoinsulinaemia. While there are no specific treatments for diabetic patients yet available that act specifically on the glucagon signalling pathway, newer agents including glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors reduce plasma glucagon and this is thought to contribute to their action to lower blood glucose. The α-cell and glucagon receptor remain tempting targets for novel diabetes treatments, but it is important to understand the magnitude of benefit new strategies would provide as preclinical models suggest that chronic interference with glucagon action could entail adverse effects as well.     

Liraglutide in oral antidiabetic drug combination therapy

The glucagon-like peptide-1 (GLP-1) receptor agonist liraglutide is indicated as an add-on to oral antidiabetic drug regimens in subjects with type 2 diabetes. Herein, the results of clinical trials assessing the efficacy, safety and tolerability of liraglutide when used in combination with either one or two oral antidiabetic therapies are summarised, then contrasted with the effects of exenatide and dipeptidyl peptidase (DPP-4) inhibitors. GLP-1 receptor agonists lead to effective glycaemic control when used as combination therapy with either one or two oral antidiabetic agents, and may confer overall benefits in weight loss and blood pressure in some subjects. These agents are well tolerated; the most commonly reported adverse effect is mild-to-moderate gastrointestinal symptoms, which are usually transient. Rates of hypoglycaemia in these trials were low, although higher rates were noted when combined with a sulphonylurea. While further study will be required, GLP-1 receptor agonists may offer important advantages over other diabetic therapies, including DPP-4 inhibitors.     

The treatment of diabetes mellitus of patients with chronic liver disease

About 80% of patients with liver cirrhosis may have glucose metabolism disorders, 30% show overt diabetes mellitus (DM). Prospective studies have demonstrated that DM is associated with an increased risk of hepatic complications and death in patients with liver cirrhosis. DM might contribute to liver damage by promoting inflammation and fibrosis through an increase in mitochondrial oxidative stress mediated by adipokines. Based on the above mentioned the effective control of hyperglycemia may have a favorable impact on the evolution of these patients. However, only few therapeutic studies have evaluated the effectiveness and safety of antidiabetic drugs and the impact of the treatment of DM on morbidity and mortality in patients with liver cirrhosis. In addition, oral hypoglycemic agents and insulin may produce hypoglycemia and lactic acidosis, as most of these agents are metabolized by the liver. This review discusses the clinical implications of DM in patients with chronic liver disease. In addition the effectiveness and safety of old, but particularly the new antidiabetic drugs will be described based on pharmacokinetic studies and chronic administration to patients. Recent reports regarding the use of the SGLT2 inhibitors as well as the new incretin-based therapies such as injectable glucagon-like peptide-1 (GLP-1) receptor agonists and oral inhibitors of dipeptidylpeptidase-4 (DPP-4) will be discussed. The establishment of clear guidelines for the management of diabetes in patients with CLD is strongly required.     

依折麦布在分子水平治疗冠心病并发糖尿病的进展

尼曼-皮克C1型类似蛋白(NPC1L)1在依折麦布降脂治疗中起到举足轻重的作用。同时依折麦布可以降低血清二肽基肽酶(DPP)-4活性和增加血清活性胰高血糖素样肽(GLP)-1水平,在糖尿病患者中对血糖可以进行一定程度的控制。临床研究表明,依折麦布具有降脂,预防冠心病,降低心血管发病率,尤其是应用在冠心病并发糖尿病患者中。近年来人们对NPC1L1、DPP-4和GLP-1在冠心病并发糖尿病患者中的作用有了更深一步的研究。     

Neue Substanzen in der oralen Medikation des Diabetes mellitus Typ 2

Two new classes of orally active compounds were developed recently. Rimonabant is the first endocannabinoid-1-receptor antagonist to be approved. It improves the parameters of lipid metabolism and HbA1c by paracrine and endocrine effects on adipose tissue, muscle, brain, and liver, and lowers body weight. Second, dipeptidyl-peptidase IV (DPP-4) inhibitors are about to be introduced. They inhibit the degradation of regulatory peptides involved in stimulating insulin secretion, mainly glucagon-like peptide-1 and gastric inhibitory polypeptide. Both hormones are secreted postprandially and contribute to 50–70% of the stimulation of insulin secretion after a meal. DPP-4 inhibitors themselves do not cause hypoglycemia and have further favorable effects in type 2 diabetes therapy, inhibiting glucagon secretion and improving beta cell function.     

Gastric bypass surgery, but not caloric restriction, decreases dipeptidyl peptidase-4 activity in obese patients with type 2 diabetes

The mechanism by which incretins and their effect on insulin secretion increase markedly following gastric bypass (GBP) surgery is not fully elucidated. We hypothesized that a decrease in the activity of dipeptidyl peptidase-4 (DPP-4), the enzyme which inactivates incretins, may explain the rise in incretin levels post-GBP. Fasting plasma DPP-4 activity was measured after 10-kg equivalent weight loss by GBP (n = 16) or by caloric restriction (CR,n = 14) in obese patients with type 2 diabetes. DPP-4 activity decreased after GBP by 11.6% (p = 0.01), but not after CR. The increased peak glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) response to oral glucose after GBP did not correlate with DPP-4 activity. The decrease in fasting plasma DPP-4 activity after GBP occurred by a mechanism independent of weight loss and did not relate to change in incretin concentrations. Whether the change in DPP-4 activity contributes to improved diabetes control after GBP remains therefore to be determined.     

DPP-4抑制剂对糖尿病肾病的保护作用

高血糖是糖尿病肾病发病的重要原因之一.二肽基肽酶-4（DPP-4）抑制剂可减少胰高血糖素样肽-1（GLP-1）降解,改善机体高血糖状态,从而延缓糖尿病肾病病程的进展.此外,DPP-4抑制剂还可影响其他与糖尿病肾病相关的非GLP-1底物,如基质细胞衍生因子-1α、脑钠尿肽及金属内肽酶的表达,继而发挥GLP-1非依赖性的肾脏保护作用.研究DPP-4抑制剂对糖尿病患者肾脏的保护作用及其机制,将为其在糖尿病肾病治疗中的应用提供新的认识.     

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.     

Dipeptidyl peptidase-4 inhibitors in cardioprotection: a promising therapeutic approach

Cardiovascular diseases are major killers in all developed societies and rapidly becoming the leading cause of morbidity and mortality in the developing world. Patients with diabetes mellitus are at particular risk of developing cardiovascular diseases. The present treatment options for management of diabetes have expanded since the development of glucagon-like peptide-1 agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors. There is a growing body of evidence that these agents may have cardioprotective effects even in patients who do not have diabetes. Here, we discuss this evidence as well as pathways that DPP-4 inhibitors target in the cardiovascular system. These agents over time will find an appropriate place in the management of cardiovascular diseases.     

Neprilysin inhibition in mouse islets enhances insulin secretion in a GLP-1 receptor dependent manner

ABSTRACT

Neprilysin, a widely expressed peptidase upregulated in type 2 diabetes, is capable of cleaving and inactivating the insulinotropic glucagon-like peptide-1 (GLP-1). Like dipeptidyl peptidase-4 (DPP-4), inhibition of neprilysin activity under diabetic conditions is associated with increased active GLP-1 levels and improved glycemic control. While neprilysin expression has been demonstrated in islets, its local contribution to GLP-1-mediated insulin secretion remains unknown. We investigated in vitro whether islet neprilysin inhibition enhances insulin secretion in response to glucose and/or exogenous GLP-1, and whether these effects are mediated by GLP-1 receptor (GLP-1R). Further, we compared the effect of neprilysin versus DPP-4 inhibition on insulin secretion. Isolated islets from wild-type (Glp1r^+/+) and GLP-1 receptor knockout (Glp1r^?/?) mice were incubated with or without the neprilysin inhibitor thiorphan and/or the DPP-4 inhibitor sitagliptin for 2.5 hours. During the last hour, insulin secretion was assessed in response to 2.8 mmol/l or 20 mmol/l glucose alone or plus exogenous active GLP-1. In Glp1r^+/+ islets, neprilysin inhibition enhanced 2.8 mmol/l and 20 mmol/l glucose- and GLP-1-mediated insulin secretion to the same extent as DPP-4 inhibition. These effects were blunted in Glp1r^?/? islets. In conclusion, inhibition of islet neprilysin in vitro increases glucose-mediated insulin secretion in a GLP-1R-dependent manner and enhances the insulinotropic effect of exogenous active GLP-1. Thus, neprilysin inhibitors may have therapeutic potential in type 2 diabetes by preserving islet-derived and circulating active GLP-1 levels.     

Insulin sensitizers for the treatment of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease(NAFLD) is the leading cause of liver disease in the Western world and is closely associated with metabolic syndrome,which includes hypertension,central obesity,dyslipidemia and insulin resistance.NAFLD includes a wide spectrum of liver alterations,ranging from simple hepatic steatosis to variable degrees of fibrosis,cirrhosis and even hepatocellular carcinoma.Although the etiology and progression of the disorder remain poorly understood,insulin resistance is considered to play a pivotal role in the pathogenesis.Insulin sensitizers such as biguanides,thiazolidinediones(TZDs),glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase 4 inhibitors have been studied as therapeutic approaches for NAFLD in recent years.Metformin improves insulin sensitivity and serum alanine transaminase and aspartate transaminase(ALT/AST) levels in the majority of subjects; however,it has no significant effect on liver histology.TZDs improve insulin sensitivity,serum ALT/ AST levels and histology in some cases,but there are some concerns about the safety of long-term therapy.Selection of appropriate patients for avoiding side effects and the treatment of underlying disease are themain points.These drugs are the best choice for the treatment of NAFLD in patients with type 2 DM who are also candidates for treatment with an insulin sensitizer.The present review provides an overview of insulin sensitizers in the treatment of NAFLD.     

DPP-4 inhibitors

Inhibition of dipeptidyl peptidase 4 (DPP-4) is a novel treatment for type-2 diabetes. DPP-4 inhibition prevents the inactivation of glucagon-like peptide 1 (GLP-1), which increases levels of active GLP-1. This increases insulin secretion and reduces glucagon secretion, thereby lowering glucose levels. Several DPP-4 inhibitors are in clinical development. Most experience so far has been with sitagliptin (Merck; approved by the FDA) and vildagliptin (Novartis; filed). These are orally active compounds with a long duration, allowing once-daily administration. Both sitagliptin and vildagliptin improve metabolic control in type-2 diabetes, both in monotherapy and in combination with metformin and thiazolidinediones. A reduction in HbA(1c) of approximately 1% is seen in studies of DPP-4 inhibition of up to 52 weeks' duration. DPP-4 inhibition is safe and well tolerated, the risk of hypoglycaemia is minimal, and DPP-4 inhibition is body-weight neutral. DPP-4 inhibition is suggested to be a first-line treatment of type-2 diabetes, particularly in its early stages in combination with metformin. However, the durability and long-term safety of DPP-4 inhibition remain to be established.     

The Emerging Role of Dipeptidyl Peptidase-4 Inhibitors in Cardiovascular Protection: Current Position and Perspectives

Dipeptidyl peptidase-4 (DPP-4 or CD26) inhibitors, a new class of oral anti-hyperglycemic agents that prolong the bioavailability of the endogenously secreted incretin hormone glucagon-like peptide-1 (GLP-1) and the glucose-dependent insulinotropic polypeptide (GIP), are effective in the treatment of diabetes. Accumulating data have indicated that DPP-4 inhibitors play important protective roles in the cardiovascular system. DPP-4 inhibitors act to decrease myocardial infarct size, stabilize the cardiac electrophysiological state during myocardial ischemia, reduce ischemia/reperfusion injury, and prevent left ventricular remodeling after myocardial infarction. Moreover, DPP-4 inhibitors can mobilize stem/progenitor cells to move to sites of cardiovascular injury, thus further promoting tissue repair. In addition, DPP-4 inhibitors not only improve myocardial metabolism but also regulate cardioactive peptides. DPP-4 inhibitors can also protect the vasculature through their anti-inflammatory and anti-atherosclerotic effects and through the ability of the inhibitors to promote vascular relaxation. Finally, the potential effects of DPP-4 inhibitors on blood pressure and lipid metabolism have also been investigated. However, some reports on the cardioprotective activities of DPP-4 inhibitors are controversial. Herein, we summarize the available data on cardiovascular protection by DPP-4 inhibitors that have emerged in recent years and discuss current position and future perspectives concerning the use of DPP-4 inhibitors in cardiovascular medicine.