Modulation of vascular inflammation in vitro and in vivo by peroxisome proliferator-activated receptor-gamma activators

Downregulation of PPARγ expression in peripheral blood monocytes correlated with adhesion molecules in acute coronary syndrome

BACKGROUND

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a nuclear hormone receptor and may regulate the metabolism of lipids, inhibit monocytes/macrophages function and reduce the production of cell adhesion molecules and some inflammatory factors. Thus, it may affect the occurrence and progression of atherosclerosis.

METHODS

Forty-three patients with acute coronary syndrome and 34 control subjects were studied for PPARgamma expression in peripheral blood monocytes by reverse transcription-polymerase chain reaction (RT-PCR), and adhesion molecules were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Expression of PPARgamma in peripheral blood monocytes was significantly reduced in acute coronary syndrome, which was inversely associated with intercellular adhesion molecule 1 (r=-0.339, P<0.05), vascular cell adhesion molecule 1 (r=-0.331, P<0.05) and body mass index (r=-0.334, P<0.05), respectively, and positively correlated with apoA1 (r=0.289, P<0.05).

CONCLUSIONS

The reduced expression of PPARgamma in peripheral blood monocytes of patients with acute coronary syndrome is inversely associated with plasma soluble adhesion molecules, suggesting that PPARgamma may be involved in acute coronary syndrome.

Atorvastatin reduces interleukin-6 plasma concentration and adipocyte secretion of hypercholesterolemic rabbits

BACKGROUND

Interleukin-6 (IL-6) is secreted by adipocytes and may be involved in atherosclerosis. Few studies have assessed the influence of statins on IL-6 secretion in adipocytes.

METHODS

Rabbits on high-cholesterol diets were randomly given either atorvastatin 1.5 mg/kg day(-1) (n=5) or starch (n=5) for 2 weeks. Subcutaneous adipose was collected for adipocytes culture. IL-6 concentrations in plasma and adipocytes culture supernatant were measured by ELISA. RT-PCR was used to evaluate peroxisome proliferator-activated receptor (PPAR) gamma mRNA expression. The in vitro effect of atorvastatin on IL-6 production in adipocytes was observed.

RESULTS

Two weeks atorvastatin treatment resulted in significant reduction of circulating IL-6 concentrations, which was associated with IL-6 secretion in adipocytes (r=0.849, P<0.01). Meanwhile mRNA expression of PPARgamma in adipocytes was intimately related to the IL-6 secretion in adipocytes (r=-0.900, P<0.01). Atorvastatin induced the decreased IL-6 secretion in dose-dependent manner.

CONCLUSIONS

Atorvastatin can inhibit IL-6 secretion in adipocytes possibly through upregulating PPARgamma, which may help to explain the anti-inflammatory effects of statins use.

Antiatherogenic effect of pioglitazone in type 2 diabetic patients irrespective of the responsiveness to its antidiabetic effect

OBJECTIVE

Thiazolidinediones (TZDs), a class of insulin-sensitizing agents used clinically to treat type 2 diabetes, are also antiatherogenic. This study was designed to elucidate the relationship between the antiatherogenic and antidiabetic effects of pioglitazone, a TZD, in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

A total of 136 Japanese type 2 diabetic patients were included and divided into two groups: the pioglitazone-treated group (30 mg daily for 3 months) (n = 70) and the untreated control group (n = 66). The changes in glycolipid metabolism as well as plasma high-sensitivity C-reactive protein (CRP), leptin, adiponectin, and pulse wave velocity (PWV) were monitored to analyze the relationship between the antiatherogenic and antidiabetic effects of pioglitazone.

RESULTS

The pioglitazone treatment significantly reduced hyperglycemia, hyperinsulinemia, and HbA(1c) levels and increased plasma adiponectin concentrations relative to the control group (P < 0.01). It also significantly decreased CRP and PWV (P < 0.01). The antiatherogenic effect was observed in both the nonresponders showing <1% of reduction in HbA(1c) (n = 30) and responders showing >1% of reduction (n = 40). ANCOVA revealed that treatment with pioglitazone was associated with a low CRP and PWV, independent of the changes in parameters related to glucose metabolism.

CONCLUSIONS

This study represents the first demonstration of the antiatherogenic effect of pioglitazone in both nonresponders and responders with respect to its antidiabetic effect and suggests that pioglitazone can exert its antiatherogenic effect independently of its antidiabetic effect.

Effects of a PPARgamma agonist, GI262570, on renal filtration fraction and nitric oxide level in conscious rats

PPARgamma agonists ameliorate insulin resistance and lower blood pressure. Volume expansion/edema has been observed in susceptible patients treated with these agents. Alterations of renal hemodynamics affect renal tubular reabsorption, and thus may contribute to volume expansion. This study seeks to determine whether volume expansion caused by a PPARgamma agonist, GI262570, is related to changes in glomerular filtration rate, effective renal plasma flow, or renal filtration fraction. Chronically catheter-implanted conscious rats were studied to determine the effects on glomerular filtration rate, effective renal plasma flow, and renal filtration fraction after 1, 4, and 10 days of GI262570 treatment (8 mg/kg, p.o., B.I.D.). Elevated adipose mRNA of PPARgamma target genes confirmed PPARgamma activation in GI262570-treated rats. GI262570 treatment for 10 days decreased hematocrit, hemoglobin, and serum albumin (all P < 0.05), indicating volume expansion, but did not alter glomerular filtration rate, effective renal plasma flow, or renal filtration fraction. However, nitrate + nitrite was significantly higher in plasma and hind limb muscle of GI262570-treated rats (both P < 0.05). This study demonstrated that treatment with PPARgamma agonist GI262570 resulted in volume expansion and increased nitric oxide, but did not affect glomerular filtration rate, effective renal plasma flow, or renal filtration fraction, indicating PPARgamma agonist-induced volume expansion is not related to changes in renal filtration fraction, and increased nitric oxide may contribute to the PPARgamma agonist-induced blood-pressure lowering.

Microarray analysis of peroxisome proliferator-activated receptor-gamma induced changes in gene expression in macrophages

We used a combination of expression microarray and Northern blot analyses to identify target genes for peroxisome proliferator-activated receptor (PPAR) gamma in RAW264.7 macrophages. PPARgamma natural ligand 15-deoxy-Delta(12,14) prostaglandin and synthetic ligands ciglitazone and rosiglitazone increased the expression of scavenger receptor CD36 and ATP-binding cassette transporter A1, as well as adipophilin (a lipid droplet coating protein involved in intracellular lipid storage and transport), calpain (a protease implicated in ABCA1 protein degradation), and ADAM8 (a disintegrin and metalloprotease protein involved in cell adhesion). These findings are relevant to understanding the effect of PPARgamma activation on gene expression and cognate pathways in macrophages.

Pioglitazone, a PPAR-gamma ligand, provides protection from dextran sulfate sodium-induced colitis in mice in association with inhibition of the NF-kappaB-cytokine cascade

Nuclear factor-kappaB-dependent up-regulation of inflammatory cytokines occurs in inflammatory bowel disease. We investigated the effect of pioglitazone, a peroxisome proliferator-activated receptor-gamma ligand, on dextran sulfate sodium-induced colonic mucosal injury and inflammation in mice. Acute colitis was induced in female mice receiving 0, 1, 3, and 10 mg/kg i.p. of pioglitazone daily. Colonic mucosal inflammation was evaluated chemically and histologically. Thiobarbituric acid-reactive substances and tissue-associated myeloperoxidase activity were measured in intestinal mucosa as indices of lipid peroxidation and neutrophil infiltration, respectively. Colonic mRNA expression of pro-inflammatory cytokines and inducible nitric oxide synthase was measured by reverse transcription-PCR and nuclear factor-kappaB activation was evaluated by electrophoretic mobility shift assay. Dextran sulfate sodium administration resulted in decreases in body weight and colon length and increases in lipid peroxide and neutrophil accumulation of the intestine. In contrast, co-administration with pioglitazone prevented these changes. Transcripts coding for pro-inflammatory cytokines and inducible nitric oxide were expressed in high levels after the development of colitis, and pioglitazone markedly reduced mRNA expression of these genes. DNA binding activity of nuclear factor-kappaB was markedly increased, whereas in pioglitazone co-treated intestines the effect was significantly reduced. These data suggest that peroxisome proliferator-activated receptor-gamma may be a novel therapeutic target for the therapy of inflammatory bowel disease.

A specific peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligand, pioglitazone, ameliorates gastric mucosal damage induced by ischemia and reperfusion in rats

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a member of the nuclear hormone receptor superfamily, has recently been implicated as a regulator of cellular proliferation and inflammatory responses. The aim of the present study was to investigate the effects of pioglitazone on ischemia-reperfusion (I/R)-induced gastric mucosal injury in rats. Gastric ischemia was induced for 30 min by applying a small vascular clamp to the celiac artery and reperfusion was produced by removal of the clamp in male Sprague-Dawley rats treated with and without pioglitazone. Pioglitazone was given to the rats intraperitoneally 2 h before the vascular clamping. The area of gastric mucosal erosion (erosion index) significantly increased from mean basal levels after 60 min of reperfusion. This erosion index was significantly inhibited by pretreatment with pioglitazone in a dose-dependent manner. The concentration of thiobarbituric acid reactive substances (TBARS) and myeloperoxidase (MPO) activity in the gastric mucosa were both significantly increased after I/R, and pretreatment with pioglitazone significantly reduced these increases. The contents of both mucosal TNF-alpha and CINC-2beta in the I/R group were significantly increased compared with the levels in the sham-operated group. These increases in TNF-alpha and CINC-2beta were significantly inhibited by pretreatment with pioglitazone at a dose of 10 mg/kg. The results of the present study indicate that pioglitazone inhibited lipid peroxidation and reduced development of the gastric mucosal inflammation induced by I/R in rats. This investigation suggests that pioglitazone has potential as a new therapeutic agent for reperfusion injury.

Suppression of intestinal ischemia-reperfusion injury by a specific peroxisome proliferator-activated receptor-gamma ligand, pioglitazone, in rats

Neutrophil activation and tumor necrosis factor-alpha (TNF-alpha) induction play a critical role in ischemia-reperfusion-induced intestinal inflammation. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a member of the nuclear hormone receptor superfamily, has recently been implicated as a regulator of inflammatory responses. The aim of the present study was to determine whether pioglitazone, a specific PPAR-gamma ligand, can ameliorate reperfusion-induced intestinal injury in rats, and whether the agent can inhibit the increase in neutrophil accumulation associated with TNF-alpha expression. Intestinal damage was induced in male Sprague-Dawley rats by clamping the superior mesenteric artery for 30 min followed by reperfusion. Reperfusion after 30 min ischemia resulted in an increase in luminal protein concentrations with levels reaching a maximum after 60 min of reperfusion. In contrast, pretreatment with pioglitazone 2 h before ischemia inhibited the increase in luminal protein concentrations after 60 min reperfusion in a dose-dependent manner (1-30 mg/kg). The increase in tissue-associated myeloperoxidase activity, an index of neutrophil infiltration, after reperfusion was significantly inhibited by pretreatment with pioglitazone. Pioglitazone also inhibited increases in intestinal TNF-alpha protein and mRNA expression determined by ELISA and RT-PCR, respectively. In conclusion, activation of PPAR-gamma may represent a novel approach to the treatment of intestinal inflammation induced by ischemia-reperfusion.

The potential role of peroxisome proliferator-activated receptors on inflammation in type 2 diabetes mellitus and atherosclerosis

Increasing attention has focused on the role of inflammation in various chronic diseases, including atherosclerosis. Recent compelling data have begun to unite work from various arenas, such as epidemiology and vascular biology, and even clinical trials to provide evidence for inflammation as a mechanism underlying cardiovascular disease. Inflammation has been implicated in the pathogenesis, progression, and complications of both atherosclerosis and diabetes mellitus-2 complex disorders often found intertwined in patients. Although this story continues to evolve, peroxisome proliferator-activated receptors (PPARs) have been implicated as a molecular pathway involved in both these disease processes. In vitro data, animal work, and some human studies suggest that synthetic PPAR agonists in clinical use, such as thiazolidinediones, may not only regulate metabolic processes but may also limit inflammatory responses, including some involved in atherosclerosis.

Peroxisome proliferator-activated receptors and the cardiovascular system

Insulin resistance syndrome (also called syndrome X) includes obesity, diabetes, hypertension, and dyslipidemia and is a complex phenotype of metabolic abnormalities. The disorder poses a major public health problem by predisposing individuals to coronary heart disease and stroke, the leading causes of mortality in Western countries. Given that hypertension, diabetes, dyslipidemia, and obesity exhibit a substantial heritable component, it is postulated that certain genes may predispose some individuals to this cluster of cardiovascular risk factors. Emerging data suggest that peroxisome proliferator-activated receptors (PPARs), including alpha, gamma, and delta, are important determinants that may provide a functional link between obesity, hypertension, and diabetes. It has been well documented that hypolipidemic fibrates and antidiabetic thiazolidinediones are synthetic ligands for PPAR alpha and PPAR gamma, respectively. In addition, PPAR natural ligands, such as leukotriene B4 for PPAR alpha, 15-deoxy-delta 12,14-prostaglandin J2 for PPAR gamma, and prostacyclin for PPAR delta, are known to be eicosanoids and fatty acids. Studies have documented that PPARs are present in all critical vascular cells: endothelial cells, vascular smooth muscle cells, and monocyte-macrophages. These observations suggest that PPARs not only control lipid metabolism but also regulate vascular diseases such as atherosclerosis and hypertension. In this review, we present structure and tissue distribution of PPAR nuclear receptors, discuss the mechanisms of action and regulation, and summarize the rapid progress made in this area of study and its impact on the cardiovascular system.

Peroxisome proliferator-activated receptors: are they involved in atherosclerosis progression?

Peroxisome proliferator-activated receptors (PPAR) are nuclear receptors present in several organs and cell types. They are subdivided into PPAR alpha, PPAR gamma and PPAR delta (or beta). PPAR alpha and gamma are the two main categories of these receptors, which are both characterized by their ability to influence lipid metabolism, glucose homeostasis, cell proliferation, differentiation and apoptosis, as well as the inflammatory response, by transcriptional activation of target genes. PPAR alpha are activated by fatty acids, eicosanoids and fibrates, while PPAR gamma activators include arachidonic acid metabolites, oxidized low density lipoprotein and thiazolidinediones. Atherosclerosis is now considered a chronic inflammatory condition. Thus, PPAR activation appears a promising approach to favorably affect atherosclerosis development through both metabolic and anti-inflammatory effects. However, the clinical data in favor of an anti-atherosclerotic action of PPAR agonists are still scanty, and some experimental data would even indicate possible pro-atherogenic effects, or a lack of effect in the female sex. New controlled clinical studies will provide the information necessary to understand the true significance and usefulness of PPAR alpha, gamma and delta activators in the control of atherosclerotic disease.

Inflammation and insulin resistance are independently related to all-cause of death and cardiovascular events in Japanese patients with type 2 diabetes mellitus

Insulin resistance (IR)/hyperinsulinemia and low-grade inflammation (high-sensitivity C-reactive protein [hs-CRP]) can predict cardiovascular disease. However, because IR and inflammation (IF) have not been evaluated simultaneously, it is not known whether IR and IF are independently related to cardiovascular disease. Furthermore, the combined effect of IR and IF on the prediction of cardiovascular disease is presently unknown. Thus, we measured insulin sensitivity (K index of the insulin tolerance test; KITT) and hs-CRP in 350 Japanese patients with type 2 diabetes, and followed them for 1-7 years (mean, 4.5 years). During the follow-up, 33 patients died and 53 patients developed non-fatal coronary artery disease or stroke (endpoint). Age, systolic blood pressure, current smoking, past history of cardiovascular disease, KITT, and hs-CRP independently and significantly correlated with endpoint. One-S.D. difference was associated with a significant increase of relative risk in KITT (1.45; 95% CI 1.09-1.91) and hs-CRP (1.30; 1.04-1.67). When patients were subdivided to tertile, the relative risk in the highest tertile of KITT was 1.76 (95% CI 1.01-3.11) and hs-CRP was 2.00 (1.03-3.85) compared with the patients with lowest tertile. The relative risk in the highest tertile of both KITT and hs-CRP was 5.32 (1.18-24.0) compared with the lowest tertile of both values. In conclusion, low-grade IF and IR are independently related to all-cause of death and cardiovascular disease in Japanese patients with type 2 diabetes. Coexistence of low-grade IF and IR amplify this effect.

The PPARgamma ligand, 15d-PGJ2, attenuates the severity of cerulein-induced acute pancreatitis

INTRODUCTION

The prostaglandin D2 metabolite, 15d-PGJ2, a potent natural ligand for peroxisome proliferator-activated receptor gamma (PPARgamma), exerts antiinflammatory effects by inhibiting the induction of inflammatory response genes and NF-kappaB-dependent transcription. AIM To determine whether 15d-PGJ2 decreases the severity of secretagogue-induced acute pancreatitis (AP) and to assess cellular mechanisms contributing to these effects. METHODOLOGY Swiss Webster mice were injected with either saline or cerulein (50 microg/kg) hourly for 8 hours and received either 15d-PGJ2 (2 mg/kg) or vehicle 1 hour before and 4 hours after induction of AP. RESULTS Treatment with 15d-PGJ2 significantly attenuated AP, as determined by histologic assessment of edema, vacuolization, inflammation, and necrosis. This attenuation was associated with decreased cyclooxygenase-2 (COX-2) and intercellular adhesion molecule-1 (ICAM-1) expression and decreased serum and pancreatic IL-6 levels. Treatment with 15d-PGJ2 markedly inhibited NF-kappaB DNA-binding activity, and, moreover, this decreased activity was associated with a concomitant inhibition of IkappaB protein degradation. CONCLUSION Our findings demonstrate that 15d-PGJ2 attenuates the severity of AP most likely through the inhibition of COX-2 expression, IL-6 production, and NF-kappaB activation. Ligands specific for PPARgamma may represent novel and effective means of clinical therapy for AP.

Thiazolidinediones -- some recent developments

The role of thiazolidinediones (currently rosiglitazone and pioglitazone) in the treatment of Type 2 diabetes is firmly established. The mechanism of action involves binding to the peroxisome proliferator-activated receptor-gamma, a transcription factor that regulates the expression of specific genes especially in fat cells but also other cell types such as endothelial cells, macrophages and monocytes, vascular smooth muscle cells and colonic epithelium. Thiazolidinediones have been shown to interfere with expression and release of mediators of insulin resistance originating in adipose tissue (e.g., increased free fatty acids, decreased adiponectin) in a way that results in net improvement of insulin sensitivity (i.e., in muscle and liver). A direct or indirect effect on AMP-dependent protein kinase may also be involved. Prevention of lipid accumulation in tissues critical to glycaemia such as visceral adipocytes, liver, muscle and beta-cells at the expense of lipids accumulating at the less harmful subcutaneous site may be central to their net metabolic effect. The sustained beneficial effect of troglitazone on beta-cell function in women with previous gestational diabetes in addition to the insulin-sensitising properties point to an important role of this class of drugs in the prevention of Type 2 diabetes. Original safety concerns based on animal and in vitro studies (e.g., fatty bone marrow transformation, colonic cancer, adipogenic transdifferentiation of blood cells) remain theoretical issues but become less pressing practically with prolonged uneventful clinical use. Hepatotoxicity for troglitazone and fluid retention, which can aggravate pre-existing heart failure, are the most important side effects. In summary, with the thiazolidinediones, a novel concept for the treatment of insulin resistance and possibly preservation of beta-cell function is available that could become effective in the prevention of Type 2 diabetes. Moreover, their anti-inflammatory properties also make them interesting in the prevention and treatment of atherosclerosis and possibly other inflammatory conditions (e.g., inflammatory bowel disease). Long-term data will be necessary for a final risk-benefit assessment of these substances.

Elevated plasma levels of the atherogenic mediator soluble CD40 ligand in diabetic patients: a novel target of thiazolidinediones

BACKGROUND

Considerable evidence implicates the proinflammatory cytokine CD40 ligand (CD40L) in atherosclerosis and accumulating data link type 1 and 2 diabetes, conditions associated with accelerated atherosclerosis, to inflammation. This study therefore evaluated the hypothesis that diabetic patients have elevated plasma levels of soluble CD40L (sCD40L) and that treatment with the insulin-sensitizing thiazolidinediones lowers this index of inflammation.

METHODS AND RESULTS

Subjects with type 1 (n=49) or type 2 diabetes (n=48) had higher (P<0.001) sCD40L plasma levels (6.56+/-3.27 and 6.67+/-2.90 ng/mL, respectively) compared with age-matched control groups (1.40+/-2.21 and 1.32+/-2.68 ng/mL, respectively). Multiple regression analysis demonstrated a significant (P<0.001) association between plasma sCD40L and type 1 as well as type 2 diabetes, independent of total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, blood pressure, body mass index, gender, C-reactive protein, and soluble intracellular adhesion molecule-1. Furthermore, in a pilot study, administration of troglitazone (12 weeks, 600 mg/day), but not placebo, to type 2 diabetics (n=68) significantly (P<0.001) diminished sCD40L plasma levels by 29%. The thiazolidinedione lowered plasma sCD40L in type 2 diabetic patients with long-standing disease (>3 years) with or without macrovascular complications (-34% and -29%, respectively) as well as in type 2 diabetic patients with more recent (<3 years) onset of the disease (-27%; all P<0.05).

CONCLUSIONS

This study provides new evidence that individuals with type 1 or 2 diabetes have a proinflammatory state as indicated by elevated levels of plasma sCD40L. Troglitazone treatment of type 2 diabetic patients diminishes sCD40L levels, suggesting a novel antiinflammatory mechanism for limiting diabetes-associated arterial disease.

Peroxisome proliferator-activated receptors: regulation of transcriptional activities and roles in inflammation

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear receptor superfamily. Three PPARs isoforms have been characterized: PPARalpha, beta/delta and gamma. As other nuclear receptors, the PPARs are organized in distinct functional domains: A/B, C or DNA binding domain (DBD), D, E or ligand binding domain (LBD) and F. The A/B domain contains the activation function 1 (AF-1) which is transcriptionally active in absence of ligands. The DBD and the LBD of the PPARs determine the specificity of promoter DNA sequence recognition and ligand recognition, respectively. An activation function 2 (AF-2) is contained in the E domain, which mediates the ligand-dependent activation of the receptor. The transcriptional activity of the PPARs is regulated by post-translational modifications, such as phosphorylation and ubiquitination. Phosphorylation of PPARs is controlled by environmental factors activating different kinase pathways leading to the modulation of their activities. PPARs degradation by the ubiquitin-proteasome system modulates the intensity of the ligand response by controlling the level of PPAR proteins in the cells. PPARs also control the expression of genes implicated in the inflammatory response via negative interference with different inflammatory pathways, such as NFkappaB, AP-1, C/EBP beta, STAT-1 and NFAT. As such, PPARs influence inflammatory cytokine production and cell recruitment to the inflammatory sites. A better understanding of the mechanism of action of PPARs could improve the design of more specific and more efficient novel drugs. Molecules with dissociated effects could be useful for the treatment of lipid disorders or inflammation.

Suppression of endothelial adhesion molecule up-regulation with cyclopentenone prostaglandins is dissociated from IkappaB-alpha kinase inhibition and cell death induction

The cyclopentenone prostaglandins (cPG) 15-deoxy-Delta12,14-prostaglandin J2 (dPGJ2) and PGA1 can inhibit multiple steps in nuclear factor (NF)-kappaB signaling and can induce cell death. Here we characterized the effects of dPGJ2 and PGA1 on the inflammatory induction of endothelial cell adhesion molecules (CAM). Pretreatment of endothelial cells with dPGJ2 or PGA1 at low concentrations dose dependently inhibited the up-regulation of CAM expression and monocyte arrest by tumor necrosis factor (TNF)-alpha but not expression of inhibitor of apoptosis proteins. Only at high concentrations, cPG enhanced TNF-alpha-induced cell death and inhibited TNF-alpha-induced IkappaB-alpha kinase (IKK) activation, IkappaB-alpha degradation, and NF-kappaB/p65 translocation, while promoting AP-1/c-jun phosphorylation. Expression of an IKK-beta mutant (C179A) resistant to interaction with cPG impaired cell death induction but not inhibition of CAM up-regulation by cPG. Gel shift and reporter gene analysis revealed that cPG at low concentrations directly impaired DNA binding of NF-kappaB and NF-kappaB-dependent transactivation. The synthetic analogs dPGA1 or dPGA2 were ineffective, indicating structural specificity of cPG. Thus, the suppression of endothelial CAM up-regulation with cPG is dissociated from cell death sensitization and IKK inhibition above threshold concentrations and related to interference with NF-kappaB binding. Our findings define distinct mechanisms for anti-inflammatory and proapoptotic effects of cPG in endothelial cells.

Prevention of autoimmune diabetes in NOD mice by troglitazone is associated with modulation of ICAM-1 expression on pancreatic islet cells and IFN-gamma expression in splenic T cells

Thiazolidinediones acting as PPAR-gamma agonists are a new generation of oral antidiabetics addressing insulin resistance as a main feature of type-2 diabetes. In accordance to our results, pre-clinical studies have demonstrated that the thiazolinedione troglitazone prevents the development of insulin-dependent autoimmune type-1 diabetes. To investigate whether TGZ acts by affecting the ICAM-1/LFA-1 pathway and/or the Th1/Th2 cytokine balance in NOD mice, we analysed the IL-1beta-induced ICAM-1 expression on islet-cells and the LFA-1, CD25, IL-2, IFN-gamma, IL-4, and IL-10 expression on splenocytes. After 200 days of oral TGZ administration, islet cells from TGZ-treated NOD mice showed a reduced ICAM-1 expression in response to the pro-inflammatory cytokine IL-1beta. The expression of the ligand LFA-1 on CD4(+) and CD8(+) T-cells was comparable to that of placebo- and untreated controls. Also, the expression of Th1/Th2 cytokines was comparable in groups receiving TGZ or Placebo. Nevertheless, the investigated NOD mice segregated into IFN-gamma low- and IFN-gamma high producers as revealed by cluster analysis. Interestingly, the majority of TGZ-treated mice belonged to the cluster of IFN-gamma low producers. Thus, the prevention of autoimmune diabetes in NOD mice by TGZ seems to be associated with suppression of IL-1beta-induced ICAM-1 expression leading to a reduced vulnerability of pancreatic beta-cells during the effector stage of beta-cell destruction. In addition, IFN-gamma production was modulated, implicating that alteration of the Th1/Th2 cytokine balance might have contributed to diabetes prevention. The findings of this study suggest that TGZ exerts its effects by influencing both the beta-cells as the target of autoimmune beta-cell destruction and the T-cells as major effectors of the autoimmune process.

Alanine for proline substitution in the peroxisome proliferator-activated receptor gamma-2 (PPARG2) gene and the risk of incident myocardial infarction

OBJECTIVE

Recent studies have implicated the potential importance of peroxisome proliferator-activated receptors as a molecular mechanism involved in atherothrombosis. A common alanine (A) for proline (P) substitution at codon 12 in the peroxisome proliferator activated receptor gamma-2 gene (PPARG2) has been associated with reduced risk of developing type 2 diabetes mellitus. Because diabetes and atherothrombosis share common antecedents, we sought evidence that this polymorphism might also be associated with reduced risk of myocardial infarction.

METHODS AND RESULTS

Using DNA samples collected at baseline in a prospective cohort of 14 916 initially healthy American men, we evaluated a P12A polymorphism in the PPARG2 among 523 individuals who subsequently developed myocardial infarction and among 2092 individuals who remained free of reported cardiovascular disease over a mean follow-up period of 13.2 years. As hypothesized, presence of the A12 allele was associated with significantly reduced risk of myocardial infarction (odds ratio in an age- and smoking-adjusted dominant model of inheritance, 0.77; 95% CI, 0.60 to 0.98; P=0.034). This protective effect remained statistically significant in analyses controlling for traditional cardiovascular risk factors, was present among nondiabetic study participants, was observed to be of similar magnitude in analyses assuming codominant or dominant modes of inheritance, and was seen in fully adjusted post hoc analyses in which we limited our control group to those individuals specifically matched to myocardial infarction cases (OR, 0.71; 95% CI, 0.53 to 0.96; P=0.024).

CONCLUSIONS

In this cohort, a common A for P substitution at codon 12 in the PPARG2 was associated with reduced incidence of myocardial infarction. If confirmed in other cohorts, these data would have implications for novel treatments of cardiovascular disease, including development of PPARG-targeted therapy.

Atherothrombosis, inflammation, and diabetes

Diabetes represents a major cause of cardiovascular morbidity and mortality in developed countries, and atherothrombosis accounts for most deaths among diabetics. Recent evidence has reliably shown the relevant etiopathogenetic role of inflammation in atherothrombotic disease. This review summarizes and discusses the possible synergistic effects of diabetes and inflammation in promoting atherothrombosis and its complications, as well as potential avenues for diagnostic, preventive, and therapeutic benefits in the modulation of inflammatory mechanisms in diabetic atherothrombotic disease.

Early stimulation and late inhibition of peroxisome proliferator-activated receptor gamma (PPAR gamma) gene expression by transforming growth factor beta in human aortic smooth muscle cells: role of early growth-response factor-1 (Egr-1), activator protein 1 (AP1) and Smads

Transforming growth factor beta (TGF beta) and peroxisome proliferator-activated receptor gamma (PPAR gamma) play major roles in the development of vascular diseases. It has been documented that PPAR gamma activation inhibits the TGF beta signal pathway in vascular smooth muscle cells (VSMC). Here we examined whether TGF beta can regulate PPAR gamma expression. Northern blot analyses revealed that both TGF beta 1 and 2 exert a biphasic effect (early stimulation and late repression) on PPAR gamma gene expression in VSMC. TGF beta rapidly and transiently induced early growth-response factor-1 (Egr-1) expression through the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1 (MEK1)/ERK-mediated pathway. Inhibition of MEK1/ERK by PD98059 not only abrogated the induction of Egr-1 but also abolished the rapid and transient induction of PPAR gamma by TGF beta. Furthermore, overexpression of NAB2, a repressor of Egr-1 activation, also blocked the induction of PPAR gamma by TGF beta in VSMC, suggesting that Egr-1 mediates the rapid and transient induction of PPAR gamma by TGF beta. With regard to the TGF beta repression of PPAR gamma expression, activator protein 1 (AP1) and Smad3/4 dramatically inhibited the PPAR gamma promoter activity in transient-transfection studies. In contrast, adenovirus-mediated overexpression of a dominant-negative form of c-Jun partially rescued the TGF beta-induced PPAR gamma repression in VSMC. Taken together, our data demonstrate that Egr-1, AP1 and Smad are part components of the TGF beta signal transduction pathway that regulates PPAR gamma expression.

Lipolysis of triglyceride-rich lipoproteins generates PPAR ligands: evidence for an antiinflammatory role for lipoprotein lipase

Increased levels of triglyceride-rich lipoproteins provoke lipid accumulation in the artery wall, triggering early inflammatory responses central to atherosclerosis like endothelial adhesion molecule expression. The endogenous mechanisms limiting such reactions remain poorly defined. Lipoprotein lipase (LPL) plays a central role in lipid metabolism by hydrolyzing triglyceride rich lipoproteins and releasing fatty acids. We found that LPL treatment reversed tumor necrosis factor alpha and very low-density lipoprotein (VLDL)-stimulated endothelial vascular cell adhesion molecule 1 (VCAM1) induction and VCAM1 promoter responses, thus recapitulating effects reported with synthetic peroxisome proliferator-activated receptor (PPAR) agonists. In fact, these LPL effects on VCAM1 were absent in endothelial cells isolated from PPAR alpha-deficient mice. This finding suggests a novel antiinflammatory role for LPL. Further studies reveal specificity for PPAR activation through lipolysis in regards to lipoprotein substrate (VLDL >> LDL > HDL), PPAR isoform (PPAR alpha >> PPAR delta > PPAR gamma), and among fatty acid-releasing lipases. These PPAR responses required intact LPL catalytic activity. In vivo, transgenic mice overexpressing LPL had increased peroxisome proliferation, but not in the genetic absence of PPAR alpha. Although human plasma possesses minimal PPAR alpha activation despite containing abundant free fatty acids, marked PPAR alpha activation is seen with human plasma after LPL is added in vitro or systemically released in vivo. These data suggest a previously uncharacterized pathway in which the key lipolytic enzyme LPL can act on circulating lipoproteins to generate PPAR alpha ligands, providing a potentially important link between lipoprotein metabolism and distal PPAR alpha transcriptional effects.

New understanding, diagnosis, and prognosis of atherothrombosis and the role of imaging

Despite crucial advances in our knowledge of the pathologic mechanisms and the availability of effective diagnostic and treatment modalities, coronary atherothrombosis remains the most frequent cause of ischemic heart disease. Plaque disruption with superimposed thrombosis is the main cause of unstable angina, myocardial infarction, and sudden death. New findings have recently introduced exciting concepts that could have major impact on the treatment of the atherothrombotic disease. We will discuss the mechanisms that lead to the development of atherothrombosis and those responsible for the acute coronary syndromes, as well as some of the concepts derived from in vivo observations using new imaging technologies (eg, high-resolution magnetic resonance imaging).

The effects of troglitazone, an insulin-sensitizing agent, on the endothelial function in early and late type 2 diabetes: a placebo-controlled randomized clinical trial

Activation of the peroxisome proliferator-activator receptor gamma (PPARgamma) improves insulin resistance and glycemic control in patients with diabetes. As PPARgamma is expressed in the endothelial cell, we have investigated the effect of troglitazone, a PPARgamma activator, on the endothelial function in people with type 2 diabetes in a 12-week, prospective, randomized, double-blinded clinical trial. We studied 87 type 2 diabetic patients who were divided into 3 groups. Group A consisted of 27 patients with recently diagnosed diabetes and no clinical manifestations of macrovascular disease; group B, 29 patients with long-term diabetes and no clinically evident macrovascular disease; and group C, 31 diabetic patients with documented macrovascular disease (cardiovascular, cerebrovascular, or peripheral vascular disease). High-resolution ultrasound images were used to measure the flow-mediated dilation (FMD, endothelium-dependent) and nitroglycerin-induced dilation (NID, endothelium-independent) in the brachial artery. Laser Doppler perfusion imaging was used to measure vasodilation in the forearm skin in response to iontophoresis of 1% acetylcholine (Ach, endothelium-dependent) and 1% sodium nitroprusside (NaNP, endothelium-independent). The plasma concentrations of von Willebrand factor (vWF), soluble intercellular adhesion molecule (sICAM), and soluble vascular cell adhesion molecule (sVCAM) were also measured as indicators of endothelial cell activation. The FMD improved in the troglitazone-treated patients in group A (7.72 +/- 3.4 v 5.27 +/- 2.0, P <.05 [exit visit v baseline, percent of increase in brachial artery diameter, mean +/- SD]). The fasting insulin level also improved in this group (15.6 +/- 10 v 19.7 +/- 10, P <.05) and was strongly correlated to changes in FMD (r = -.73, P <.01). No changes were found in the FMD or the fasting insulin levels in the troglitazone-treated patients in groups B or C. The NID was not changed by troglitazone treatment in any of the 3 groups. Also, no differences were found in the microcirculation reactivity measurements or in the biochemical markers of endothelial dysfunction in all 3 groups. A small, but significant, improvement of the FMD was found in placebo-treated patients in group B, probably related to the low FMD levels at baseline in the patients (5.40 +/- 3.0 v 4.36 +/- 2.4, P <.05). We concluded that troglitazone treatment for 12 weeks improved endothelial function in the macrocirculation of patients with recently diagnosed type 2 diabetes and no clinical evidence of macrovascular disease. This improvement was strongly associated with the improvement of fasting plasma insulin concentrations.

Antidiabetic PPAR gamma-activator rosiglitazone reduces MMP-9 serum levels in type 2 diabetic patients with coronary artery disease

BACKGROUND

Matrix metalloproteinases (MMPs) are critically involved in the development of unstable plaques. Although arteriosclerotic lesions in patients with diabetes mellitus are more unstable than those of nondiabetic subjects, nothing is known about serum levels of MMPs in these patients or about mechanisms to modulate MMP levels. We investigated MMP levels in diabetic and nondiabetic coronary artery disease (CAD) patients and performed a clinical trial to assess the effect of the PPARgamma-activating, antidiabetic thiazolidinedione rosiglitazone on MMP levels in diabetic CAD patients.

METHODS AND RESULTS

In CAD patients, MMP-2, -8, and -9 serum levels were significantly higher in type 2 diabetic subjects compared with age-, sex-, and body mass index-matched nondiabetics. Thirty-nine diabetic patients with CAD were randomized to receive rosiglitazone 4 mg (twice daily) or placebo for 12 weeks. Rosiglitazone treatment, but not placebo, significantly reduced MMP-9 levels already after 2 weeks by -19.6% (-38.3% to 8.6%, P<0.05), and levels remained suppressed until the end of the study. In addition, rosiglitazone significantly decreased serum amyloid A (SAA) and tumor necrosis factor-alpha levels.

CONCLUSION

MMP-9 levels are increased in type 2 diabetic patients with CAD, and treatment of these patients with the antidiabetic PPARgamma-activator rosiglitazone significantly reduces MMP-9, tumor necrosis factor-alpha, and SAA serum levels. These data support anti-inflammatory and potential antiatherogenic effects of thiazolidinediones.

[Cardiovascular syndrome X and endothelial dysfunction]

Up to 30% of patients with chest pain who undergo coronary arteriography, have completely normal coronary angiograms. The subgroup with typical angina and a positive response to stress testing is generally included under the diagnosis of cardiovascular syndrome X. Several causes and mechanisms have been investigated in the past twenty years, to explain both chest pain and ischemic angina-like ST segment depression that are commonly observed in these patients. Clinical and pathogenic heterogeneity appears to be the main features of the syndrome. Among the suggested pathophysiological mechanisms, endothelial dysfunction of the coronary microcirculation features prominently. In this review, we present the available evidence regarding endothelial dysfunction in cardiovascular syndrome X.

The cyclopentenone prostaglandin 15-deoxy-delta(12,14)- PGJ2 attenuates the development of colon injury caused by dinitrobenzene sulphonic acid in the rat

1. Inflammatory bowel disease (IBD) is characterized by oxidative and nitrosative stress, leukocyte infiltration, and increased expression of the adhesion molecules intercellular adhesion molecule 1 (ICAM-1) in the colon. Recent evidence also suggests that the cyclopentenone prostaglandin (PG) 15-deoxy-delta(12,14)-PGJ(2) (15d- PGJ(2)) functions as an early anti-inflammatory signal. 2. The aim of the present paper is to investigate the effects of 15d-PGJ(2) in rats subjected to experimental colitis. 3. Colitis was induced in rats by intra-colonic instillation of dinitrobenzene sulphonic acid (DNBS). 15d-PGJ(2) was administered daily as intraperitoneal injection (20 or 40 microg kg(-1)). On day 4, animals were sacrificed and tissues were taken for histological and biochemical analysis. 4. 15d-PGJ(2) significantly reduced the degree of haemorrhagic diarrhoea and weight loss caused by administration of DNBS. 15d-PGJ(2) also caused a substantial reduction of (i) the degree of colonic injury, (ii) the rise in myeloperoxidase (MPO) activity (mucosa), (iii) the increase in the tissue levels of malondialdehyde (MDA) and (iv) of the pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta). 5. Furthermore, 15d-PGJ(2) reduced the increase in immunohistochemical staining for (i) inducible nitric oxide synthase (iNOS), (ii) nitrotyrosine and (iii) poly (ADP-ribose) polymerase (PARP), as well as (iv) the increased expression of ICAM-1 caused by DNBS in the colon. 6. Electrophoresis mobility shift assay (EMSA) of inflamed colon revealed that 15d- PGJ(2) also caused a substantial reduction of the activation of nuclear factor-kappaB (NF-kappaB). Furthermore, 15d-PGJ(2) stimulates the activation of heat shock protein 72 (hsp72) in the inflamed colon, as assessed by Western blot analysis. 7. In conclusion, 15d-PGJ(2) reduces the development of experimental colitis.

Peroxisome proliferator-activated receptor gamma ligands increase release of nitric oxide from endothelial cells

OBJECTIVE

Peroxisome proliferator-activated receptor gamma (PPARgamma) ligands reduce lesion formation in animal models of atherosclerosis by mechanisms that have not been defined completely. We hypothesized that PPARgamma ligands stimulate endothelial-derived nitric oxide release (*NO) to protect the vascular wall.

METHODS AND RESULTS

The PPARgamma ligands, 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) or ciglitazone, stimulated a PPAR response element-luciferase reporter construct in transfected porcine pulmonary artery endothelial cells (PAECs), demonstrating that PPARgamma was transcriptionally functional. Treatment with 15d-PGJ2 or ciglitazone significantly increased release of *NO from PAECs or human aortic endothelial cells and augmented calcium ionophore-induced *NO release from human umbilical vein endothelial cells measured by chemiluminescence analysis of culture media. Increases in *NO release caused by treatment with 15d-PGJ2 occurred at 24 hours, but not after 1 to 16 hours, and were abrogated by treatment with the transcriptional inhibitor alpha-amanitin. Overexpression of PPARgamma or treatment with 9-cis retinoic acid also enhanced PAEC *NO release. Neither 15d-PGJ2 nor ciglitazone altered eNOS mRNA, whereas 15d-PGJ2, but not ciglitazone, decreased eNOS protein.

CONCLUSIONS

Taken together, these findings demonstrate that PPARgamma ligands stimulate *NO release from endothelial cells derived from multiple vascular sites, through a transcriptional mechanism unrelated to eNOS expression.

PPARgamma ligands inhibit primary tumor growth and metastasis by inhibiting angiogenesis

Several drugs approved for a variety of indications have been shown to exhibit antiangiogenic effects. Our study focuses on the PPARgamma ligand rosiglitazone, a compound widely used in the treatment of type 2 diabetes. We demonstrate, for the first time to our knowledge, that PPARgamma is highly expressed in tumor endothelium and is activated by rosiglitazone in cultured endothelial cells. Furthermore, we show that rosiglitazone suppresses primary tumor growth and metastasis by both direct and indirect antiangiogenic effects. Rosiglitazone inhibits bovine capillary endothelial cell but not tumor cell proliferation at low doses in vitro and decreases VEGF production by tumor cells. In our in vivo studies, rosiglitazone suppresses angiogenesis in the chick chorioallantoic membrane, in the avascular cornea, and in a variety of primary tumors. These results suggest that PPARgamma ligands may be useful in treating angiogenic diseases such as cancer by inhibiting angiogenesis.

Insulin resistance, diabetes, and atherosclerosis: thiazolidinediones as therapeutic interventions

The insulin resistance syndrome, a cluster of metabolic abnormalities involving dyslipidemia, hypertension, diabetes, impaired glucose tolerance, and hypercoagulability, carries an increased risk of atherosclerosis. Although interventions targeting elements of this syndrome have dramatically reduced cardiovascular risk, the impact of glucose-lowering has been more disappointing. Thiazolidinediones (TZDs) are a new class of insulin-sensitizing agents that activate the nuclear receptor peroxisome proliferator-activated receptor-g. TZDs may improve not only glucose levels but also other metabolic parameters associated with insulin resistance. The TZD data are reviewed, with a focus on their potential cardiovascular effects.

Biologic aspects of vulnerable plaque

Atherosclerosis and its thrombotic complications are the major cause of morbidity and mortality in the industrialized world. The progression of atherosclerotic plaques in coronary circulation is modulated by several risk factors. It is now clear that plaque composition is a major determinant of plaque disruption and superimposed thrombosis. Plaque vulnerability, defined as the propensity of plaques to disrupt, is further determined by intrinsic and extrinsic triggering factors. After disruption, the fatty core of the plaque and its high content of tissue factor provide a powerful substrate for the activation of the coagulation cascade. Plaque disruption can be clinically silent or cause symptoms of ischemia depending on thrombus burden and the degree of vessel occlusion. In addition, plaque disruption and subsequent healing are recognized to play key roles in the rapid plaque progression. This review looks at the mechanisms underlying the development and progression of atherosclerotic plaques, factors leading to plaque rupture and subsequent thrombosis, and their clinical consequences as potential targets for future research.

Antiinflammatory and antiarteriosclerotic effects of pioglitazone

Peroxisome proliferator-activated receptor-gamma (PPARgamma) ligands are widely used in patients with insulin resistance and diabetes. Because coronary artery disease is a major complication for such patients, it is important to determine the effects of PPARgamma activation on arteriosclerosis. Long-term inhibition of endothelial NO synthesis by administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) to rats induces coronary vascular inflammation (monocyte infiltration, monocyte chemoattractant protein-1 [MCP-1] expression) and subsequent arteriosclerosis. We examined the effects of pioglitazone (a PPARgamma ligand) in this rat model to determine whether PPARgamma activation with pioglitazone inhibits arteriosclerosis by its indirect effects on metabolic conditions or by direct effects on the cells participating to the pathogenesis of arteriosclerosis. We found that pioglitazone did not affect metabolic states, systolic blood pressure, or serum NO levels, but did prevent the L-NAME-induced coronary inflammation and arteriosclerosis. Pioglitazone did not reduce local expression of MCP-1 but markedly attenuated increased expression of the MCP-1 receptor C-C chemokine receptor 2 (CCR2) in lesional and circulating monocytes. PPARgamma activation with pioglitazone prevented coronary arteriosclerosis, possibly by its antiinflammatory effects (downregulation of CCR2 in circulating monocytes). Inhibition of the CCR2-mediated inflammation may represent novel antiinflammatory actions of pioglitazone beyond improvement of metabolic state.

Anti-inflammatory lipid mediators and insights into the resolution of inflammation

The pro-inflammatory signalling pathways and cellular mechanisms that initiate the inflammatory response have become increasingly well characterized. However, little is known about the mediators and mechanisms that switch off inflammation. Recent data indicate that the resolution of inflammation is an active process controlled by endogenous mediators that suppress pro-inflammatory gene expression and cell trafficking, as well as induce inflammatory-cell apoptosis and phagocytosis, which are crucial determinants of successful resolution. This review focuses on this emerging area of inflammation research and describes the mediators and mechanisms that are currently stealing the headlines.

PPARgamma ligands inhibit primary tumor growth and metastasis by inhibiting angiogenesis

Several drugs approved for a variety of indications have been shown to exhibit antiangiogenic effects. Our study focuses on the PPARgamma ligand rosiglitazone, a compound widely used in the treatment of type 2 diabetes. We demonstrate, for the first time to our knowledge, that PPARgamma is highly expressed in tumor endothelium and is activated by rosiglitazone in cultured endothelial cells. Furthermore, we show that rosiglitazone suppresses primary tumor growth and metastasis by both direct and indirect antiangiogenic effects. Rosiglitazone inhibits bovine capillary endothelial cell but not tumor cell proliferation at low doses in vitro and decreases VEGF production by tumor cells. In our in vivo studies, rosiglitazone suppresses angiogenesis in the chick chorioallantoic membrane, in the avascular cornea, and in a variety of primary tumors. These results suggest that PPARgamma ligands may be useful in treating angiogenic diseases such as cancer by inhibiting angiogenesis.

Constitutive activation of peroxisome proliferator-activated receptor-gamma suppresses pro-inflammatory adhesion molecules in human vascular endothelial cells

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a ligand-activated nuclear receptor that has an essential role in adipogenesis and glucose homeostasis. PPAR-gamma is expressed in vascular tissues including endothelial cells (ECs). PPAR-gamma activity can be regulated by many pathophysiological and pharmacological agonists. However, the role of PPAR-gamma activation in ECs remains unclear. In this study, we examined the effect of the constitutive activation of PPAR-gamma on the phenotypic modulation of ECs. Adenovirus-mediated expression of a constitutively active mutant of PPAR-gamma resulted in significant ligand-independent activation of PPAR-gamma and specific induction of the PPAR-gamma target genes. However, PPAR-gamma activation significantly suppressed the expression of vascular adhesion molecules in ECs and the ensuing leukocyte recruitment. Furthermore, constitutive activation of PPAR-gamma resulted in simultaneous repression of AP-1 and NF-kappaB activity, which suggests that PPAR-gamma may reduce pro-inflammatory phenotypes via, at least in part, suppression of the AP-1 and NF-kappaB pathways. Therefore, using a gain-of-function approach, our study provides novel evidence showing that constitutive activation of PPAR-gamma is sufficient to prevent ECs from converting into a pro-inflammatory phenotype. These results also suggest that, in addition to pharmacological agonists, the genetic modification of the PPAR-gamma activity in ECs may be a potential approach for therapeutic intervention in various inflammatory disorders.

The role of PPARs in atherosclerosis

Peroxisome proliferator-activated receptors (PPARs) are lipid-activated transcription factors that regulate lipid and lipoprotein metabolism, glucose homeostasis and inflammation. The PPAR family consists of three proteins, alpha, beta/delta and gamma. Recent data suggest that PPAR alpha and gamma activation decreases atherosclerosis progression not only by correcting metabolic disorders, but also through direct effects on the vascular wall. PPARs modulate the recruitment of leukocytes to endothelial cells, control the inflammatory response and lipid homeostasis of monocytes/macrophages and regulate inflammatory cytokine production by smooth muscle cells. Experiments using animal models of atherosclerosis and clinical studies in humans strongly support an anti-atherosclerotic role for PPAR alpha and gamma in vivo. Thus, PPARs remain attractive therapeutic targets for the development of drugs used in the treatment of chronic inflammatory diseases such as atherosclerosis. Future research will aim for the development of more potent drugs with co-agonist activity on PPAR alpha, PPAR beta/delta and/or PPAR gamma as well as tissue and target gene-selective PPAR receptor modulators (SPPARMs).

Anti-tumor mechanisms of valproate: a novel role for an old drug

Valproic acid (VPA, 2-propylpentanoic acid) is an established drug in the long-term therapy of epilepsy. During the past years, it has become evident that VPA is also associated with anti-cancer activity. VPA not only suppresses tumor growth and metastasis, but also induces tumor differentiation in vitro and in vivo. Several modes of action might be relevant for the biological activity of VPA: (1) VPA increases the DNA binding of activating protein-1 (AP-1) transcription factor, and the expression of genes regulated by the extracellular-regulated kinase (ERK)-AP-1 pathway; (2) VPA downregulates protein kinase C (PKC) activity; (3) VPA inhibits glycogen synthase kinase-3beta (GSK-3beta), a negative regulator of the Wnt signaling pathway; (4) VPA activates the peroxisome proliferator-activated receptors PPARgamma and delta; (5) VPA blocks HDAC (histone deacetylase), causing hyperacetylation. The findings elucidate an important role of VPA for cancer therapy. VPA might also be useful as low toxicity agent given over long time periods for chemoprevention and/or for control of residual minimal disease.

Metabolic and additional vascular effects of thiazolidinediones

Several cardiovascular risk factors (dyslipidaemia, hypertension, glucose intolerance, hypercoagulability, obesity, hyperinsulinaemia and low-grade inflammation) cluster in the insulin resistance syndrome. Treatment of these individual risk factors reduces cardiovascular complications. However, targeting the underlying pathophysiological mechanisms of the insulin resistance syndrome is a more rational treatment strategy to further improve cardiovascular outcome. Our understanding of the so-called cardiovascular dysmetabolic syndrome has been improved by the discovery of nuclear peroxisome proliferator-activated receptors (PPARs). PPARs are ligand-activated transcription factors belonging to the nuclear receptor superfamily. As transcription factors, PPARs regulate the expression of numerous genes and affect glycaemic control, lipid metabolism, vascular tone and inflammation. Activation of the subtype PPAR-gamma improves insulin sensitivity. Expression of PPAR-gamma is present in several cell types involved in the process of atherosclerosis. Thus, modulation of PPAR-gamma activity is an interesting therapeutic approach to reduce cardiovascular events. Thiazolidinediones are PPAR-gamma agonists and constitute a new class of pharmacological agents for the treatment of type 2 (non-insulin-dependent) diabetes mellitus. Two such compounds are currently available for clinical use: rosiglitazone and pioglitazone. Thiazolidinediones improve insulin sensitivity and glycaemic control in patients with type 2 diabetes. In addition, improvement in endothelial function, a decrease in inflammatory conditions, a decrease in plasma levels of free fatty acids and lower blood pressure have been observed, which may have important beneficial effects on the vasculature. Several questions remain to be answered about PPAR-gamma agonists, particularly with respect to the role of PPAR-gamma in vascular pathophysiology. More needs to be known about the adverse effects of thiazolidinediones, such as hepatotoxicity, increased low-density lipoprotein cholesterol levels and increased oedema. The paradox of adipocyte differentiation with weight gain concurring with the insulin-sensitising effect of thiazolidinediones is not completely understood. The decrease in blood pressure induced by thiazolidinedione treatment seems incompatible with an increase in the plasma volume, and the discrepancy between the stimulation of the expression of CD36 and the antiatherogenic effects of the thiazolidinediones also needs further explanation. Long-term clinical trials of thiazolidinediones with cardiovascular endpoints are currently in progress. In conclusion, studying the effects of thiazolidinediones may shed more light on the mechanisms involved in the insulin resistance syndrome. Furthermore, thiazolidinediones could have specific, direct effects on processes involved in the development of vascular abnormalities.

Oxidized omega-3 fatty acids in fish oil inhibit leukocyte-endothelial interactions through activation of PPAR alpha

Omega-3 fatty acids, which are abundant in fish oil, improve the prognosis of several chronic inflammatory diseases although the mechanism for such effects remains unclear. These fatty acids, such as eicosapentaenoic acid (EPA), are highly polyunsaturated and readily undergo oxidation. We show that oxidized, but not native unoxidized, EPA significantly inhibited human neutrophil and monocyte adhesion to endothelial cells in vitro by inhibiting endothelial adhesion receptor expression. In transcriptional coactivation assays, oxidized EPA potently activated the peroxisome proliferator-activated receptor alpha (PPAR alpha), a member of the nuclear receptor family. In vivo, oxidized, but not native, EPA markedly reduced leukocyte rolling and adhesion to venular endothelium of lipopolysaccharide (LPS)-treated mice. This occurred via a PPAR alpha-dependent mechanism because oxidized EPA had no such effect in LPS-treated PPAR alpha-deficient mice. Therefore, the beneficial effects of omega-3 fatty acids may be explained by a PPAR alpha-mediated anti-inflammatory effect of oxidized EPA.

Vascular effects of GI262570X (PPAR-gamma agonist) in the brown adipose tissue of Han Wistar rats: a review of 1-month, 13-week, 27-week and 2-year oral toxicity studies

We describe and discuss microscopic findings in the brown adipose tissue (BAT) blood vessels of Han Wistar rats treated with GI262570X, a peroxisome proliferator-activated receptor-gamma agonist (PPAR-gamma agonist) by oral gavage for 28 days, 13 weeks, 27 weeks, and 2 years. Review of these studies revealed a consistent vascular change, consisting of multifocal fatty infiltration in the BAT of treated rats. A similar vascular change was not seen in other vessels or organs. Microscopically, fatty infiltration was characterized primarily by round, clear vacuoles within the tunica media and/or tunica adventitia of small and medium-sized arteries and arterioles. Occasionally, these vacuoles had peripherally located nuclei and morphologically resembled adipocytes, suggesting a well-characterized PPAR effect (ie, differentiation of stem cells or preadipocytes into mature adipocytes). However, administration of GI262570X up to 2 years failed to induce more severe or progressive lesions in the blood vessels of rat BAT and, in particular, did not result in induction of any atherosclerotic-like lesions or foam cell infiltration. At the longer exposure, there was an apparent reduction of severity and/or incidence, indicating a possible adaptive response. These results suggest that the possibility of generating atherosclerotic-like lesions through prolonged treatment of GI262570X (PPAR-gamma agonist) is highly unlikely in rats.

Roles of peroxisome proliferator-activated receptor gamma in lipid homeostasis and inflammatory responses of macrophages

Monocytes play a critical role in atherogenesis by their inflammatory signals and differentiation into macrophage foam cells through cholesterol accumulation. The seminal finding of high levels of the peroxisome proliferator-activated receptor gamma in macrophage foam cells has opened up the prospect that its ligands, most importantly the thiazolidinedione class of drugs, might directly influence the development of atheromatous lesions. The present review weighs the growing evidence on regulation of both inflammatory responses and cholesterol homeostasis in macrophages by peroxisome proliferator-activated receptor gamma ligands with regard to their overall impact as antiatherogenic agents.

PPAR activators inhibit endothelial cell migration by targeting Akt

Peroxisome proliferator-activated receptors (PPARs) regulate lipid and glucose metabolism and exert several vascular effects that may provide a dual benefit of these receptors on metabolic disorders and atherosclerotic vascular disease. Endothelial cell migration is a key event in the pathogenesis of atherosclerosis. We therefore investigated the effects of lipid-lowering PPARalpha-activators (fenofibrate, WY14643) and antidiabetic PPARgamma-activators (troglitazone, ciglitazone) on this endothelial cell function. Both PPARalpha- and PPARgamma-activators significantly inhibited VEGF-induced migration of human umbilical vein endothelial cells (EC) in a concentration-dependent manner. Chemotactic signaling in EC is known to require activation of two signaling pathways: the phosphatidylinositol-3-kinase (PI3K)-->Akt- and the ERK1/2 mitogen-activated protein kinase (ERK MAPK) pathway. Using the pharmacological PI3K-inhibitor wortmannin and the ERK MAPK-pathway inhibitor PD98059, we observed a complete inhibition of VEGF-induced EC migration. VEGF-induced Akt phosphorylation was significantly inhibited by both PPARalpha- and gamma-activators. In contrast, VEGF-stimulated ERK MAPK-activation was not affected by any of the PPAR-activators, indicating that they inhibit migration either downstream of ERK MAPK or independent from this pathway. These results provide first evidence for the antimigratory effects of PPAR-activators in EC. By inhibiting EC migration PPAR-activators may protect the vasculature from pathological alterations associated with metabolic disorders.

Systemic and local inflammation in patients with unstable atherosclerotic plaques

The response to injury in the vasculature and the heart is inflammation. Atherosclerosis is often the result of injury followed by inflammation and atherosclerosis. Vascular and myocardial infections from various pathogens, including viruses, bacteria, chlamydia, and other infections result in vascular inflammation and almost certainly play a role in the development of atherosclerosis and acute coronary heart disease syndromes in at least some patients. Current evidence favors prior exposure to multiple pathogens as most likely playing a role in initiating inflammation and contributing to atherosclerosis. Genetic predisposition is almost certainly an important factor in the development of inflammation, impaired endothelial vascular repair, vascular infection, thrombosis, and atherosclerosis. The aging process itself is most likely associated with altered vascular and myocardial defense mechanisms predisposing to inflammation. The oxidation of cholesterol and low-density lipoprotein (LDL) leads to the production of oxidized radicals that promote vascular inflammation. Interventional injury, including angioplasty and stenting, causes endothelial inflammation, thrombosis, and fibroproliferation. Systemic evidence of inflammation identifies patients at high risk of future coronary events, including those who appear to be healthy initially as well as those with stable and unstable coronary heart disease syndromes. Increases in serum C-reactive protein (CRP) identify individuals at risk for future vascular events, including unstable angina, acute myocardial infarction, acute cerebrovascular accident, and sudden death. Similarly, systemic elevations in serum troponin 1, serum amyloid-like protein, fibrinogen, and interleukins-1, 2, 6, 8, and 18 identify patients with unstable angina and non-Q-wave myocardial infarction at increased risk for future coronary events. The presence of vascular inflammation may be detected by identifying temperature heterogeneity within plaques that demonstrate inflammation. In the future, the local evaluation of atherosclerotic plaques to detect the presence of inflammation coupled to measurements of systemic markers of inflammation, such as C-reactive protein, may help identify patients at increased risk and allow both local and systemic therapies that reduce their risk and prevent the development of acute coronary syndromes in at least some patients.

The mechanisms of action of PPARs

The peroxisome proliferator-activated receptors (PPARs) are a group of three nuclear receptor isoforms, PPAR gamma, PPAR alpha, and PPAR delta, encoded by different genes. PPARs are ligand-regulated transcription factors that control gene expression by binding to specific response elements (PPREs) within promoters. PPARs bind as heterodimers with a retinoid X receptor and, upon binding agonist, interact with cofactors such that the rate of transcription initiation is increased. The PPARs play a critical physiological role as lipid sensors and regulators of lipid metabolism. Fatty acids and eicosanoids have been identified as natural ligands for the PPARs. More potent synthetic PPAR ligands, including the fibrates and thiazolidinediones, have proven effective in the treatment of dyslipidemia and diabetes. Use of such ligands has allowed researchers to unveil many potential roles for the PPARs in pathological states including atherosclerosis, inflammation, cancer, infertility, and demyelination. Here, we present the current state of knowledge regarding the molecular mechanisms of PPAR action and the involvement of the PPARs in the etiology and treatment of several chronic diseases.