过氧化物酶体增生物激活受体γ激动剂致水肿机制及预防的研究进展

过氧化物酶体增生物激活受体γ（peroxisome proliferator-activated receptor gamma,PPAR-γ）激动剂主要包括噻唑烷二酮类（thiazolidinediones,TZDs）和非噻唑烷二酮类新型PPAR-γ激动剂。噻唑烷二酮类药物常用的有曲格列酮、吡咯列酮及罗格列酮。PPAR-γ激动剂的常见不良反应之一为水肿,并可加重或引致充血性心力衰竭。水肿发生率为3%～28.9%;PPAR-γ激动剂和其他口服降血糖药或胰岛素合用可增加水肿发生率。PPAR-γ引起水肿的机制涉及水钠潴留、血管扩张以及血管通透性增加等因素,特别是分布于远端肾小管和集合管的水、钠转运蛋白调节异常对水钠潴留的发生起重要作用。PPAR-γ激动剂引起的水肿一般较轻,停药后可消退。糖尿病合并中、重度充血性心力衰竭患者[NYHA（New York Heart Association）Ⅲ或Ⅳ级]避免用PPAR-γ激动剂,合并轻度充血性心力衰竭患者（NYHAI至Ⅱ级）应慎用,尽可能用最小剂量,必需时,剂量应逐渐增加,可联合应用利尿剂,并应严密监测患者体重和水肿的发生情况。预防治疗水肿的方法包括应用新的选择性PPAR-γ调节剂、蛋白激酶C-β或上皮细胞钠通道的特异性抑制剂及PPAR-γ拮抗剂。     

Pharmacokinetics, efficacy and safety of aleglitazar for the treatment of type 2 diabetes with high cardiovascular risk

INTRODUCTION: In preliminary clinical studies, aleglitazar, a new dual PPAR-α-γ agonist, has been demonstrated to improve hyperglycemia and dyslipidemia in patients with type 2 diabetes mellitus. This review will provide up-to-date information on the clinical safety and efficacy of aleglitazar, which is currently under Phase III clinical investigation for reduction of cardiovascular events in patients with type 2 diabetes and recent acute coronary syndrome. AREAS COVERED: A PubMed literature search (January 1950 to February 2011) was conducted using the following search terms: aleglitazar, PPAR, PPAR α agonist, PPAR γ agonist and PPAR α/γ agonist. Additional articles were gathered using reference lists from sources obtained from the original literature search. This review summarizes available information pertaining to pharmacodynamics, pharmacokinetics, clinical studies and safety/tolerability of aleglitazar. The effects of this new drug are compared and contrasted with those of fibrates (PPAR-α agonists), thiazolidinediones (PPAR-γ agonists) and other dual PPAR-α-γ agonists. EXPERT OPINION: Preliminary evidence from clinical studies with aleglitazar is promising, with reported improvements in glycemia, high-density lipoprotein-cholesterol, low-density lipoprotein-cholesterol, triglycerides, apolipoprotein B and blood pressure. However, PPAR-α- and -γ-associated side effects have been observed and additional large-scale, long-term clinical studies are necessary to better understand the clinical implications of these effects.     

Reversal of the deleterious effects of chronic dietary HFCS-55 intake by PPAR-δ agonism correlates with impaired NLRP3 inflammasome activation

Although high-fructose corn syrup (HFCS-55) is the major sweetener in foods and soft-drinks, its potential role in the pathophysiology of diabetes and obesity (“diabesity”) remains unclear. Peroxisome-proliferator activated receptor (PPAR)-δ agonists have never been tested in models of sugar-induced metabolic abnormalities. This study was designed to evaluate (i) the metabolic and renal consequences of HFCS-55 administration (15% wt/vol in drinking water) for 30 weeks on male C57Bl6/J mice and (ii) the effects of the selective PPAR-δ agonist GW0742 (1 mg/kg/day for 16 weeks) in this condition. HFCS-55 caused (i) hyperlipidemia, (ii) insulin resistance, and (iii) renal injury/inflammation. In the liver, HFCS-55 enhanced the expression of fructokinase resulting in hyperuricemia and caused abnormalities in known insulin-driven signaling events. In the kidney, HFCS-55 enhanced the expression of the NLRP3 (nucleotide-binding domain and leucine-rich-repeat-protein 3) inflammasome complex, resulting in caspase-1 activation and interleukin-1β production. All of the above effects of HFCS-55 were attenuated by the specific PPAR-δ agonist GW0742. Thus, we demonstrate for the first time that the specific PPAR-δ agonist GW0742 attenuates the metabolic abnormalities and the renal dysfunction/inflammation caused by chronic HFCS-55 exposure by preventing upregulation of fructokinase (liver) and activation of the NLRP3 inflammasome (kidney).     

PPAR-γ agonist pioglitazone regulates dendritic cells immunogenicity mediated by DC-SIGN via the MAPK and NF-κB pathways

Dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN) is a dendritic cell-specific lectin which participates in dendritic cell (DC) trafficking, antigen uptake and DC–T cell interactions at the initiation of immune responses. This study investigated whether peroxisome proliferator-activated receptor-gamma (PPAR-γ) activation in human DCs regulates the immunogenicity of DCs mediated by DC-SIGN and exploited the possible molecular mechanisms, especially focused on the signaling pathways of mitogen-activated protein kinases (MAPK) and nuclear factor-κB (NF-κB). Here, we show that the PPAR-γ agonist pioglitazone decreased DC adhesion and transmigration, and DC stimulation of T cell proliferation mediated by DC-SIGN dependent on activation of PPAR-γ, although it increased DC endocytosis independent of PPAR-γ activation. Furthermore, PPAR-γ activation by pioglitazone in DCs down-regulated the expression of DC-SIGN, which was mediated by modulating the balance of the signaling pathways of extracellular signal-regulated kinase, c-Jun N-terminal kinase and NF-κB, but not p38 MAPK. Therefore, we conclude that PPAR-γ activation in human DCs regulates the immunogenicity of DCs mediated by DC-SIGN via the pathways of MAPK and NF-κB. These findings may support the important role of these mediators in the regulation of DC-mediated inflammatory and immunologic processes.     

Early investigational drugs targeting PPAR-α for the treatment of metabolic disease

Introduction: The fibrates have been used for many years to treat dyslipidemias and have also recently been shown to have anti-inflammatory effects. They are relatively weak PPAR-α agonists and do have some adverse effects. Novel compounds are in development, which are selective PPAR modulators (SPPARMs) and have more potent PPAR-α agonist activity. These may prove to have advantages in the treatment of dyslipidemia, insulin resistance and non-alcoholic fatty liver disease (NAFLD).

Areas covered: This review focuses on PPAR-α agonists or SPPARMs in development describing the preclinical and early clinical studies. The information was obtained by searching the published literature and abstracts from recent meetings. Ongoing clinical trials were identified using the Clinicaltrial.gov database.

Expert opinion: There is still a need for new drugs to treat atherogenic dyslipidemia. The highly potent and selective PPAR-α agonist K-877 has shown beneficial effects on atherogenic dyslipidemia and absence of some adverse effects seen with fibrates. The dual PPAR-α/PPAR-δ agonist GFT-505 has shown favorable results in improving atherogenic dyslipidemia and insulin resistance and appears to be a potential candidate for the treatment of NAFLD. Long-term trials are needed to assess the safety and efficacy of these new agents for cardiovascular and liver outcomes.     

Saroglitazar for the treatment of dyslipidemia in diabetic patients

Introduction: Diabetes and dyslipidemia are commonly associated modifiable risk factors for cardiovascular diseases. Majority of patients with diabetes also suffer from dyslipidemia (diabetic dyslipidemia). Diabetic dyslipidemia is more atherogenic as it is commonly associated with high triglyceride (TG) levels, high proportion of small dense low-density lipoprotein cholesterol and low high-density lipoprotein cholesterol (HDL-C) level (atherogenic dyslipidemia). Currently used pharmacotherapies for the management of diabetes and dyslipidemia like thiazolidinediones (PPAR-γ agonist; for insulin resistance) and fibrates (PPAR-α agonist; for hypertriglyceridemia) have many limitations and side effects. Saroglitazar, a dual PPAR-α/γ agonists, is an emerging therapeutic option with its dual benefit on glycemic and lipid parameters.

Areas covered: This paper reviews the clinical development of saroglitazar for the management of diabetic dyslipidemia. The efficacy and safety profile of saroglitazar is reviewed in context to currently available therapy like pioglitazone for diabetes and fibrates for hypertriglyceridemia. In addition, this paper also reviews the association between diabetes and dyslipidemia and the role of TG in reducing cardiovascular events.

Expert opinion: Saroglitazar, a dual PPAR-α/γ agonist, is a potential therapeutic option for the management of diabetic dyslipidemia. It has dual benefit of significant improvement in glycemic parameters (glycated hemoglobin and fasting blood glucose) and significant improvement in dyslipidemia (TGs, apolipoprotein B, non-HDL-C). The results of Phase III clinical trials indicate that saroglitazar is devoid of conventional side effects of fibrates and pioglitazone. Future clinical trials of saroglitazar will further establish its place in the management of diabetes, dyslipidemia and associated cardiovascular risk.     

Palmitoylethanolamide modulates pentobarbital-evoked hypnotic effect in mice: Involvement of allopregnanolone biosynthesis

Palmitoylethanolamde (PEA) is an endogenous lipid neuromodulator that mediates a broad spectrum of pharmacological effects by activation of peroxisome proliferator-activated receptor alpha (PPAR-α). Detectable or high levels of PEA in the CNS have been found, but the specific function of this lipid remains to be clarified. Here we report evidence that PEA, activating PPAR-α receptor and involving neurosteroids de novo synthesis, modulates pentobarbital-evoked hypnotic effect. A single i.c.v. administration of PEA (1–5 µg) increases pentobarbital induced loss of righting reflex (LORR) duration in mice. This effect is mimicked by GW7647 (3 µg), a synthetic PPAR-α agonist, and disappears in PPAR-α knockout mice.Antagonism experiments strongly support the engaging of neurosteroidogenic pathway in the increase of LORR duration induced by PEA. This effect disappeared using two inhibitors blocking the key steps of neurosteroids synthesis, aminogluthetimide and finasteride. Moreover, we demonstrated that in brainstem PEA increased the expression of steroidogenic acute regulatory protein (StAR) and cytochrome P450 side-chain cleavage (P450scc), both involved in neurosteroidogenesis. Accordingly, allopregnanolone (ALLO) levels were in turn higher in brainstem of PEA and pentobarbital treated mice vs pentobarbital alone, as revealed by quantitative analysis using gas chromatography-mass spectrometry.A Our results demonstrate that exogenous administration of PEA, through a PPAR-α-dependent mechanism, modulates neurosteroids formation increasing ALLO levels and leading to a positive modulation of GABA_A receptor. These data further strengthen our previous data on the role of PPAR-α in PEA's actions and could provide a new framework to understand its role in the CNS.     

Current status of viral gene therapy for brain tumours

There is genetic evidence that reducing the activity of peroxisome proliferation receptor-γ (PPAR-γ) may increase insulin sensitivity. SR-202 is a selective antagonist at PPAR-γ, which inhibits the adipocyte differentiation normally seen with the PPAR-γ agonist rosiglitazone. SR-202 also reduces the ability of young mice to put on weight and accumulate fat. The levels of circulating TNF-α correlates with body fat stores and/or hyperinsulinaemia. SR-202- treated wild-type mice have reduced TNF-α levels. When wild-type mice are fed a high-fat diet, the plasma levels of TNF-α are raised, and SR-202 treatment protects against this rise. Feeding mice with a high-fat diet induced insulin resistance measured as increased plasma levels of glucose, insulin and free fatty acids, and SR-202 protected against these changes. The ob/ob mouse is diabetic at 8 weeks and plasma glucose and insulin levels continue to rise over the next 3 weeks, and treatment with SR-202 prevents these increases. The development of PPAR-γ antagonists should continue as the results to date suggest that they have clinical potential for the treatment of diabetes Type 2 and obesity.     

PPAR-γ signaling pathway in placental development and function: A potential therapeutic target in the treatment of gestational diseases

Background: PPAR-γ is a target for the treatment of metabolic disorders, as Pioglitazone and Rosiglitazone are already used against type 2 diabetes. Pleiotropic functions, such as antiproliferative and anti-inflammatory effects against several pathological states, including cardiovascular disease and cancer, are currently being explored in clinical studies. Objective: Evidence indicates that PPAR-γ is expressed in the placenta, playing a crucial role in placental development and function, while PPAR-γ ligands appear to modulate fetal membrane signals. Thus, in the last few years, the pivotal role of PPAR-γ in placental biology has been the focus of extensive research, as diabetes appears to be the most common metabolic dysfunction in pregnancy. Methods: We aim to present data concerning the expression of PPAR-γ in animal and human placenta, underlining its significance in normal placental development and several gestational diseases. The effects of PPAR-γ ligands as modulators of placental biology in normal and certain pathological conditions are also discussed. Results/conclusion: Current research provides substantial evidence that PPAR-γ plays a pivotal role in placental biology and may reveal new perspectives in the treatment of gestational diseases.     

Arsenic inhibits the adipogenic differentiation of mesenchymal stem cells by down-regulating peroxisome proliferator-activated receptor gamma and CCAAT enhancer-binding proteins

Arsenic remains a top environmental concern in the United States as well as worldwide because of its global existence and serious health impacts. Apoptotic effect of arsenic in human mesenchymal stem cells (hMSCs) has been identified in our previous study; the effects of arsenic on hMSCs remain largely unknown. Here, we report that arsenic inhibits the adipogenic differentiation of human mesenchymal stem cells (hMSCs). Arsenic reduced the formation of lipid droplets and the expression of adipogenesis-related proteins, such as CCAAT enhancer binding protein-(C/EBPs), peroxisome proliferator-activated receptor-gamma (PPAR-γ), and adipocyte fatty acid–binding protein aP2 (aP2). Arsenic mediates this process by sustaining PPAR-γ activity. In addition, inhibition of PPAR-γ activity with T0070907 and up-regulation with its agonist troglitazone, showed the direct association of PPAR-γ and arsenic-mediated inhibition of differentiating hMSCs. Taken together, these results indicate that arsenic inhibits adipogenic differentiation through PPAR-γ pathway and suggest a novel inhibitory effect of arsenic on adipogenic differentiation in hMSCs.     

Peroxisome proliferator-activated receptor-γ ligands as investigational modulators of angiogenesis

PPAR-γ ligands constitute important insulin sensitizers that have already been approved for the treatment of human metabolic disorders. They also exert pleiotropic effects on cell proliferation and cancer and are now being explored in preclinical studies. Angiogenesis constitutes a multifaceted process that is implicated in tumor development and other benign disease states that are associated with diabetes. Recent data have further extended the crucial role of PPAR-γ ligands as potential angiogenesis modulators, in vitro and in vivo. This review summarizes the latest knowledge of the role of PPAR-γ ligands in angiogenesis that are related to both malignant and non-malignant disease states. Taking into careful consideration the data so far, PPAR-γ could be considered as a therapeutic target for diverse disease states in which excessive angiogenesis is implicated, including cancer and diabetes complications.     

The antiplatelet activity of magnolol is mediated by PPAR-β/γ

Activation of peroxisome proliferator-activated receptor (PPAR) isoforms (α, β/δ, and γ) is known to inhibit platelet aggregation. In the present study, we examined whether PPARs-mediated pathways contribute to the antiplatelet activity of magnolol, a compound purified from Magnolia officinalis. Magnolol (20-60μM) dose-dependently enhanced the activity and intracellular level of PPAR-β/γ in platelets. In the presence of selective PPAR-β antagonist (GSK0660) or PPAR-γ antagonist (GW9662), the inhibition of magnolol on collagen-induced platelet aggregation and intracellular Ca(2+) mobilization was significantly reversed. Moreover, magnolol-mediated up-regulation of NO/cyclic GMP/PKG pathway and Akt phosphorylation leading to increase of eNOS activity were markedly abolished by blocking PPAR-β/γ activity. Additionally, magnolol significantly inhibited collagen-induced PKCα activation through a PPAR-β/γ and PKCα interaction manner. The arachidonic acid (AA) or collagen-induced thromboxane B(2) formation and elevation of COX-1 activity caused by AA were also markedly attenuated by magnolol. However, these above effects of magnolol on platelet responses were strongly reduced by simultaneous addition of GSK0660 or GW9662, suggesting that PPAR-β/γ-mediated processes may account for magnolol-regulated antiplatelet mechanisms. Similarly, administration of PPAR-β/γ antagonists remarkably abolished the actions of magnolol in preventing platelet plug formation and prolonging bleeding time in mice. Taken together, we demonstrate for the first time that the antiplatelet and anti-thrombotic activities of magnolol are modulated by up-regulation of PPAR-β/γ-dependent pathways.     

Peroxisome proliferator-activated receptor ligands in atherosclerosis

In this review, the effect of peroxisome proliferator-activated receptor (PPAR) ligands on atherosclerosis is examined. The PPAR-gamma agonist thiazolidinediones are currently indicated for the management of Type 2 diabetes mellitus, and the PPAR-alpha agonist fibrates are used in dyslipidaemia. Here their mechanism of action and the pre-clinical and clinical evidence for the use of these medications for the prevention and treatment of atherosclerotic disease is explored. In addition, the role of PPAR-delta and the possibilities for the role of dual-binding agonists are examined.     

The peroxisome proliferator-activated receptor pan-agonist bezafibrate suppresses microvascular inflammatory responses of retinal endothelial cells and vascular endothelial growth factor production in retinal pigmented epithelial cells

A randomized clinical trial showed the beneficial effects of the selective peroxisome proliferator-activated receptor (PPAR)-α agonist, fenofibrate, in reducing the progression of diabetic retinopathy independent of serum lipid levels. All subtypes of PPAR (PPAR-α, PPAR-γ, and PPAR-β/δ) have been reported to play a key role in microvascular inflammation and angiogenesis. Therefore, the agonistic function of fenofibrate against the PPAR-α has been suggested to contribute to its medicinal effect. Furthermore, bezafibrate is a fibrate drug commonly used as a lipid-lowering agent to treat hyperlipidemia and acts as a pan-agonist of all PPARs subtypes. However, the effects of bezafibrate in diabetic retinopathy remain unclear. Therefore, the purpose of this study was to investigate the effects of bezafibrate on retinal microvascular inflammation. Bezafibrate was not cytotoxic against human retinal microvascular endothelial cells (HRMECs) and human retinal pigment epithelial cells (ARPE-19 cells) treated with < 100 and 200 μM bezafibrate, respectively. In HRMECs, the expression levels of tumor necrosis factor (TNF)-α-induced monocyte chemoattractant protein (MCP)-1, intercellular adhesion molecule (ICAM)-1, and vascular cell adhesion molecule (VCAM)-1 were significantly suppressed by bezafibrate in a dose-dependent manner. TNF-α-induced nuclear translocation of nuclear factor (NF)-κB p65 and cell migration were also significantly inhibited in bezafibrate-treated HRMECs. Furthermore, bezafibrate treatment significantly suppressed interleukin (IL)-1β-induced vascular endothelial growth factor (VEGF) production in ARPE-19 cells. These results suggest that bezafibrate has beneficial effects on retinal microvascular inflammation. Our study demonstrates the therapeutic potential of bezafibrate for managing diabetic retinopathy.     

基于报告基因的PPAR-α激动剂筛选体系的建立

目的基于PPAR-α受体的信号传递通路和利用双萤光素酶报告基因分析方法,建立稳定的PPAR-α激动剂体外筛选体系。方法 pcDNA3.1-PPAR-α、pGL3-PPRE-luc及pRL-CMV共转染293T细胞后,设0,0.1,1,10,50μmol·L-1非诺贝特不同浓度点进行干预后,测定每浓度点重复5个样本。对转染优化试验数据,比较均值大小选取最佳结果;对不同转染组之间的差异性比较,采用t检验和方差分析。结果浓度为0.1,1,10,50μmol·L-1非诺贝特干预组相对诱导率分别为：0.82,1.29,1.72,1.94,表现有统计学差异（P〈0.05）。结论成功建立基于PPAR-信号通路及双萤光素酶报告基因分析方法的PPAR-α激动剂筛药系统。     

Therapeutic Potential of Aleglitazar,a New Dual PPAR-α/γ Agonist

Preventing morbidity and mortality from diabetes mellitus is of paramount importance as the incidence of this disease is increasing across the world. While microvascular complications of diabetes such as nephropathy, retinopathy, and neuropathy are reduced with intensive glycemic control, treatment of hyperglycemia has not been consistently shown to have effects on the macrovascular complications of diabetes such as coronary artery, cerebrovascular, and peripheral vascular disease. Preventive efforts have accordingly shifted toward the modification of other cardiovascular risk factors in diabetic patients. Agonism of the peroxisome proliferator-activated receptors (PPARs) has long been an attractive target for antidiabetic therapy due to the role of PPARs in glycemic control and lipid metabolism. PPAR-γ agonists such as rosiglitazone and pioglitazone are used in clinical practice for the treatment of diabetes, and there is some evidence that pioglitazone may have positive effects on cardiovascular complications by virtue of its favorable effects on lipid profiles. However, they have not been shown to reduce macrovascular events. PPAR-α agonism is the mechanism of action in the fibrate class of medications; these agents have been shown to increase high-density lipoprotein cholesterol (HDL-C) levels, reduce triglyceride levels, and improve cardiovascular outcomes. Given the prevalence of lipid abnormalities in patients with diabetes, dual PPAR-α/γ agonists (glitazars) could potentially benefit patients with diabetes. A phase II trial examining a novel dual PPAR agonist, aleglitazar, showed that therapy with this agent reduced hyperglycemia and favorably modified levels of HDL-C and triglycerides with an acceptable safety profile. Aleglitazar is currently being studied in large-scale clinical trials to assess whether it will reduce the risk of major cardiovascular endpoints (death, myocardial infarction, or stroke) among patients with diabetes and coronary artery disease. If ongoing studies confirm the theoretical benefit and safety of dual PPAR-α/γ agonism, aleglitazar may become the first therapy demonstrated to reduce macrovascular complications in patients with diabetes.     

The Monascus metabolite monascin against TNF-α-induced insulin resistance via suppressing PPAR-γ phosphorylation in C2C12 myotubes

Chronic inflammation in muscle tissue causes insulin resistance and type-2 diabetes. Peroxisome proliferator-activated receptor (PPAR) ligands are reported to activate the phosphatidylinositol 3-kinase (PI3K)/Akt pathway, including pioglitazone, which belong to the thiazolidinedione (TZD). Monascin (MS), a Monascus metabolite, has been reported to exert anti-inflammatory activity in our recent study. Therefore, the alleviating mechanism of MS on tumor necrosis factor-α (TNF-α; 20 ng/mL) induced insulin resistance in C2C12 cells was investigated in this study. Results showed that MS increased the uptake of 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxy-d-glucose (2-NBDG) in C2C12 myotubes. This result was associated with both PPAR-γ activity and PI3K/Akt pathway caused by MS inhibited p-JNK activity and prevented PPAR-γ phosphorylation. Moreover, we found that MS may act a PPAR-γ agonist to improve insulin sensitivity, and this issue was further confirmed by PPAR-γ antagonist (GW9662). Briefly, MS as pioglitazone, stabilized PPAR-γ structure and diminished PPAR-γ phosphorylation thereby improving insulin resistance.