The ligands/activators for peroxisome proliferator-activated receptor alpha (PPARalpha) and PPARgamma increase Cu2+,Zn2+-superoxide dismutase and decrease p22phox message expressions in primary endothelial cells

Pioglitazone ameliorates endothelial dysfunction in obese rats with nephropathy

Endothelial dysfunction is a key event in the development of renovascular complications in the metabolic syndrome. The aim of this study was to elucidate the pathogenetic mechanisms involved in renovascular injuries in the Zucker obese rat, a model of the metabolic syndrome, and to examine the therapeutic effects of pioglitazone, a thiazolidinedione. Obese rats fed high-protein diet (OHP) for 12 weeks exhibited nephropathy and endothelial dysfunction, which were improved by pioglitazone. Accumulation of nitrotyrosine, a tracer of nitrative stress, was increased in aorta of the OHP group. The mRNA expressions of NADPH oxidase components and inducible nitric oxide synthase in the aorta were enhanced in the OHP group. Pioglitazone reduced nitrotyrosine in the aorta of the OHP group, inhibiting the augmented expression levels of both. These results suggest that nitrative stress could cause endothelial dysfunction in the rat model of metabolic syndrome with nephropathy, and that pioglitazone ameliorates these injuries, presumably by reducing nitrative stress.

Reversal of systemic hypertension-associated cardiac remodeling in chronic pressure overload myocardium by ciglitazone

Elevated oxidative stress has been characterized in numerous disorders including systemic hypertension, arterial stiffness, left ventricular hypertrophy (LVH) and heart failure. The peroxisome proliferator activated receptor gamma (PPARγ) ameliorates oxidative stress and LVH. To test the hypothesis that PPARγ decreased LVH and cardiac fibrosis in chronic pressure overload, in part, by increasing SOD, eNOS and elastin and decreasing NOX4, MMP and collagen synthesis and degradation, chronic pressure overload analogous to systemic hypertension was created in C57BL/6J mice by occluding the abdominal aorta above the kidneys (aortic stenosis-AS). The sham surgery was used as controls. Ciglitazone (CZ, a PPARγ agonist, 4 µg/ml) was administered in drinking water. LV function was measured by M-Mode Echocardiography. We found that PPARγ protein levels were increased by CZ. NOX-4 expression was increased by pressure-overload and such an increase was attenuated by CZ. SOD expression was not affected by CZ. Expression of iNOS was induced by pressure-overload, and such an increase was inhibited by CZ. Protein levels for MMP2, MMP-9, MMP-13 were induced and TIMP levels were decreased by pressure-overload. The CZ mitigated these levels. Collagen synthesis was increased and elastin levels were decreased by pressure-overload and CZ ameliorated these changes. Histochemistry showed that CZ inhibited interstitial and perivascular fibrosis. Echocardiography showed that CZ attenuated the systolic and diastolic LV dysfunction induced by pressure-overload. These observations suggested that CZ inhibited pressure-overlaod-induced cardiac remodeling, and inhibition of an induction of NOX4, iNOS, MMP-2/MMP-13 expression and collagen synthesis/degradation may play a role in pressure-overload induced cardiac remodeling.

Neurological Recovery-Promoting, Anti-Inflammatory, and Anti-Oxidative Effects Afforded by Fenofibrate, a PPAR Alpha Agonist, in Traumatic Brain Injury

We previously demonstrated that fenofibrate, a peroxisome proliferator-activated receptor alpha (PPARalpha) agonist, reduced the neurological deficit, the edema and the cerebral lesion induced by traumatic brain injury (TBI). In order to elucidate these beneficial effects, in the present study, we investigated, in the same TBI model, fenofibrate's effects on the inflammation and oxidative stress. Male Sprague Dawley rats were randomized in four groups: non-operated, sham-operated, TBI + vehicle, TBI + fenofibrate. TBI was induced by lateral fluid percussion of the temporoparietal cortex. Rats were given fenofibrate (50 mg/kg) or its vehicle (water containing 0.2% methylcellulose), p.o. 1 and 6 h after brain injury. A neurological assessment was done 24 h after TBI, then rats were killed and the brain COX2, MMP9 expression, GSx, GSSG levels were determined. The same schedule of treatment was used to evaluate the effect of fenofibrate on immunohistochemistry of 3NT, 4HNE and iNOS at 24 h post-injury. Our results showed that fenofibrate promotes neurological recovery by exerting anti-inflammatory effect evidenced by a decrease in iNOS, COX2 and MMP9 expression. In addition, fenofibrate showed anti-oxidant effect demonstrated by a reduction of markers of oxidative stress: loss of glutathione, glutathione oxidation ratio, 3NT and 4HNE staining. Our data suggest that PPARalpha activation could mediate pleiotropic effects and strengthen that it could be a promising therapeutic strategy for TBI.

Vascular effects of PPARgamma activators - from bench to bedside

Activation of the nuclear transcription factor peroxisome proliferator-activated receptor-gamma (PPARgamma) plays an important role in adipogenesis, insulin resistance, and glucose homeostasis. Activators of PPARgamma include the anti-diabetic thiazolidinediones (TZDs), drugs that are in clinical use to treat patients with type 2 diabetes mellitus. Experimental as well as clinical data gathered over the last decade suggest that PPARgamma activators may exert direct modulatory function in the vasculature in addition to their metabolic effects. PPARgamma is expressed in all vascular cells, where its activators exhibit anti-inflammatory and anti-atherogenic properties, suggesting that PPARgamma ligands could influence important processes in all phases of atherogenesis. Results from clinical trials demonstrated that TZDs reduce blood levels of inflammatory biomarkers of arteriosclerosis, improve endothelial function, and directly influence lesion morphology and plaque stability, underscoring that PPAR activators may have direct effects in the vasculature in humans. This review will focus on the vascular effects of PPARgamma activators and summarize the current knowledge of their modulatory function on atherogenesis and vascular disease.

The integration of lipid-sensing and anti-inflammatory effects: how the PPARs play a role in metabolic balance

The peroxisomal proliferating-activated receptors (PPARs) are lipid-sensing transcription factors that have a role in embryonic development, but are primarily known for modulating energy metabolism, lipid storage, and transport, as well as inflammation and wound healing. Currently, there is no consensus as to the overall combined function of PPARs and why they evolved. We hypothesize that the PPARs had to evolve to integrate lipid storage and burning with the ability to reduce oxidative stress, as energy storage is essential for survival and resistance to injury/infection, but the latter increases oxidative stress and may reduce median survival (functional longevity). In a sense, PPARs may be an evolutionary solution to something we call the 'hypoxia-lipid' conundrum, where the ability to store and burn fat is essential for survival, but is a 'double-edged sword', as fats are potentially highly toxic. Ways in which PPARs may reduce oxidative stress involve modulation of mitochondrial uncoupling protein (UCP) expression (thus reducing reactive oxygen species, ROS), optimising forkhead box class O factor (FOXO) activity (by improving whole body insulin sensitivity) and suppressing NFkB (at the transcriptional level). In light of this, we therefore postulate that inflammation-induced PPAR downregulation engenders many of the signs and symptoms of the metabolic syndrome, which shares many features with the acute phase response (APR) and is the opposite of the phenotype associated with calorie restriction and high FOXO activity. In genetically susceptible individuals (displaying the naturally mildly insulin resistant 'thrifty genotype'), suboptimal PPAR activity may follow an exaggerated but natural adipose tissue-related inflammatory signal induced by excessive calories and reduced physical activity, which normally couples energy storage with the ability to mount an immune response. This is further worsened when pancreatic decompensation occurs, resulting in gluco-oxidative stress and lipotoxicity, increased inflammatory insulin resistance and oxidative stress. Reactivating PPARs may restore a metabolic balance and help to adapt the phenotype to a modern lifestyle.

PPARalpha in atherosclerosis and inflammation

Peroxisome proliferator-activated receptor (PPAR)alpha is a nuclear receptor activated by natural ligands such as fatty acids as well as by synthetic ligands such as fibrates currently used to treat dyslipidemia. PPARalpha regulates the expression of genes encoding proteins that are involved in lipid metabolism, fatty acid oxidation, and glucose homeostasis, thereby improving markers for atherosclerosis and insulin resistance. In addition, PPARalpha exerts anti-inflammatory effects both in the vascular wall and the liver. Here we provide an overview of the mechanisms through which PPARalpha affects the initiation and progression of atherosclerosis, with emphasis on the modulation of atherosclerosis-associated inflammatory responses. PPARalpha activation interferes with early steps in atherosclerosis by reducing leukocyte adhesion to activated endothelial cells of the arterial vessel wall and inhibiting subsequent transendothelial leukocyte migration. In later stages of atherosclerosis, evidence suggests activation of PPARalpha inhibits the formation of macrophage foam cells by regulating expression of genes involved in reverse cholesterol transport, formation of reactive oxygen species (ROS), and associated lipoprotein oxidative modification among others. Furthermore, PPARalpha may increase the stability of atherosclerotic plaques and limit plaque thrombogenicity. These various effects may be linked to the generation of PPARalpha ligands by endogenous mechanisms of lipoprotein metabolism. In spite of this dataset, other reports implicate PPARalpha in responses such as hypertension and diabetic cardiomyopathy. Although some clinical trials data with fibrates suggest that fibrates may decrease cardiovascular events, other studies have been less clear, in terms of benefit. Independent of the clinical effects of currently used drugs purported to achieve PPARalpha, extensive data establish the importance of PPARalpha in the transcriptional regulation of lipid metabolism, atherosclerosis, and inflammation.

PPARgamma1 attenuates cytosol to membrane translocation of PKCalpha to desensitize monocytes/macrophages

Recently, we provided evidence that PKCα depletion in monocytes/macrophages contributes to cellular desensitization during sepsis. We demonstrate that peroxisome proliferator–activated receptor γ (PPARγ) agonists dose dependently block PKCα depletion in response to the diacylglycerol homologue PMA in RAW 264.7 and human monocyte–derived macrophages. In these cells, we observed PPARγ-dependent inhibition of nuclear factor-κB (NF-κB) activation and TNF-α expression in response to PMA. Elucidating the underlying mechanism, we found PPARγ1 expression not only in the nucleus but also in the cytoplasm. Activation of PPARγ1 wild type, but not an agonist-binding mutant of PPARγ1, attenuated PMA-mediated PKCα cytosol to membrane translocation. Coimmunoprecipitation assays pointed to a protein–protein interaction of PKCα and PPARγ1, which was further substantiated using a mammalian two-hybrid system. Applying PPARγ1 mutation and deletion constructs, we identified the hinge helix 1 domain of PPARγ1 that is responsible for PKCα binding. Therefore, we conclude that PPARγ1-dependent inhibition of PKCα translocation implies a new model of macrophage desensitization.

Activation of peroxisome proliferator-activated receptor gamma contributes to the survival of T lymphoma cells by affecting cellular metabolism

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a metabolic regulator involved in maintaining glucose and fatty acid homeostasis. Besides its metabolic functions, the receptor has also been implicated in tumorigenesis. Ligands of PPARgamma induce apoptosis in several types of tumor cells, leading to the proposal that these ligands may be used as antineoplastic agents. However, apoptosis induction requires high doses of ligands, suggesting the effect may not be receptor-dependent. In this report, we show that PPARgamma is expressed in human primary T-cell lymphoma tissues and activation of PPARgamma with low doses of ligands protects lymphoma cells from serum starvation-induced apoptosis. The prosurvival effect of PPARgamma was linked to its actions on cellular metabolic activities. In serum-deprived cells, PPARgamma attenuated the decline in ATP, reduced mitochondrial hyperpolarization, and limited the amount of reactive oxygen species (ROS) in favor of cell survival. Moreover, PPARgamma regulated ROS through coordinated transcriptional control of a set of proteins and enzymes involved in ROS metabolism. Our study identified cell survival promotion as a novel activity of PPARgamma. These findings highlight the need for further investigation into the role of PPARgamma in cancer before widespread use of its agonists as anticancer therapeutics.

Peroxisome proliferator-activated receptors as transcriptional nodal points and therapeutic targets

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors involved in the transcriptional regulation of key metabolic pathways such as lipid metabolism, adipogenesis, and insulin sensitivity. More recent work implicates all 3 PPAR isotypes (alpha, gamma, and delta, also known as beta or beta/delta) in inflammatory and atherosclerotic pathways. Because these nuclear receptors are activated by extracellular signals and control multiple gene targets, PPARs can be seen as nodes that control multiple inputs and outputs involved in energy balance, providing insight into how metabolism and the vasculature may be integrated. The ongoing clinical use of fibrates, which activate PPARalpha, and thiazolidinediones, which activate PPARgamma, establishes these receptors as viable drug targets, whereas considerable in vitro animal model and human surrogate marker studies suggest that PPAR activation may limit inflammation and atherosclerosis. Together, these various observations have stimulated intense interest in PPARs as therapeutic targets and led to large-scale cardiovascular end-point trials with PPAR agonists. The first of these studies has generated mixed results that require careful review, especially in anticipation of additional clinical trial data and ongoing attempts to develop novel PPAR modulators. Such analysis of the existing PPAR data, the appropriate use of currently approved PPAR agonists, and continued progress in PPAR therapeutics will be predicated on a better understanding of PPAR biology.

Regulation of inflammation by PPARs: a future approach to treat lung inflammatory diseases?

Lung inflammatory diseases, such as acute lung injury (ALI), asthma, chronic obstructive pulmonary disease (COPD) and lung fibrosis, represent a major health problem worldwide. Although glucocorticoids are the most potent anti-inflammatory drug in asthma, they exhibit major side effects and have poor activity in lung inflammatory disorders such as ALI or COPD. Therefore, there is growing need for the development of alternative or new therapies to treat inflammation in the lung. Peroxisome proliferator-activated receptors (PPARs), including the three isotypes PPARalpha, PPARbeta (or PPARdelta) and PPARgamma, are transcription factors belonging to the nuclear hormone receptor superfamily. PPARs, and in particular PPARalpha and PPARgamma, are well known for their critical role in the regulation of energy homeostasis by controlling expression of a variety of genes involved in lipid and carbohydrate metabolism. Synthetic ligands of the two receptor isotypes, the fibrates and the thiazolidinediones, are clinically used to treat dyslipidaemia and type 2 diabetes, respectively. Recently however, PPARalpha and PPARgamma have been shown to exert a potent anti-inflammatory activity, mainly through their ability to downregulate pro-inflammatory gene expression and inflammatory cell functions. The present article reviews the current knowledge of the role of PPARalpha and PPARgamma in controlling inflammation, and presents different findings suggesting that PPARalpha and PPARgamma activators may be helpful in the treatment of lung inflammatory diseases.

Targeted disruption of AdipoR1 and AdipoR2 causes abrogation of adiponectin binding and metabolic actions

Adiponectin plays a central role as an antidiabetic and antiatherogenic adipokine. AdipoR1 and AdipoR2 serve as receptors for adiponectin in vitro, and their reduction in obesity seems to be correlated with reduced adiponectin sensitivity. Here we show that adenovirus-mediated expression of AdipoR1 and R2 in the liver of Lepr(-/-) mice increased AMP-activated protein kinase (AMPK) activation and peroxisome proliferator-activated receptor (PPAR)-alpha signaling pathways, respectively. Activation of AMPK reduced gluconeogenesis, whereas expression of the receptors in both cases increased fatty acid oxidation and lead to an amelioration of diabetes. Alternatively, targeted disruption of AdipoR1 resulted in the abrogation of adiponectin-induced AMPK activation, whereas that of AdipoR2 resulted in decreased activity of PPAR-alpha signaling pathways. Simultaneous disruption of both AdipoR1 and R2 abolished adiponectin binding and actions, resulting in increased tissue triglyceride content, inflammation and oxidative stress, and thus leading to insulin resistance and marked glucose intolerance. Therefore, AdipoR1 and R2 serve as the predominant receptors for adiponectin in vivo and play important roles in the regulation of glucose and lipid metabolism, inflammation and oxidative stress in vivo.

Lipid-lowering drugs in the MPTP mouse model of Parkinson's disease: fenofibrate has a neuroprotective effect, whereas bezafibrate and HMG-CoA reductase inhibitors do not

We tested the ability of simvastatin, atorvastatin, fenofibrate and bezafibrate (two synthetic peroxisome proliferator-activated receptor-alpha (PPAR-alpha) agonists) to prevent dopaminergic cell death in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease. Tyrosine hydroxylase (TH) immunochemistry was performed 8 days after acute MPTP intoxication. When orally administered for the week prior to intoxication and a week thereafter, fenofibrate prevented the MPTP-induced dopaminergic cell loss in the substantia nigra pars compacta (SNpc) and attenuated the loss of tyrosine hydroxylase immunoreactivity in the striatum. The dosage of 1-methyl-4-phenyl pyridinium (MPP+) in the striatum by high-performance liquid chromatography indicated that fenofibrate did not affect MPTP metabolism. Bezafibrate had no effect and, strikingly, simvastatin and atorvastatin had a negative effect. We also demonstrated the presence of PPAR-alpha in the dopaminergic neurons of the murine substantia nigra. Our data suggest that PPAR-alpha activation by fenofibrate could have a neuroprotective effect in PD through inhibition of inflammation, oxidative stress and/or apoptosis.

Nitric oxide activation of peroxisome proliferator-activated receptor gamma through a p38 MAPK signaling pathway

Both nitric oxide (NO*) and peroxisome proliferator-activated receptors (PPARs) protect the endothelium and regulate its function. Here, we tested for crosstalk between these signaling pathways. Human umbilical vein and hybrid EA.hy926 endothelial cells were exposed to S-nitrosoglutathione (GSNO) or diethylenetriamine NONOate (DETA NONOate). Electrophoretic mobility shift assays using PPAR-response element (PPRE) probe showed that NO* caused a rapid dose-dependent increase in PPARgamma binding, an effect that was confirmed in vivo by chromatin immunoprecipitation. Conversely, N(G)-monomethyl-L-arginine, a NOS inhibitor, decreased PPARgamma binding. NO*-mediated PPARgamma binding and NO* induction of cyclooxygenase-2 (COX-2), diacylglycerol (DAG) kinase alpha (DGKalpha), and heme oxygenase-1 (HO-1), genes with well-characterized PPRE motifs, were cGMP independent. NO* dose dependently activated p38 MAPK, and p38 MAPK inhibition with SB202190 or knockdown with siRNA was shown to block NO* activation of PPARgamma. Likewise, p38 MAPK and PPARgamma inhibitors or knockdown of either transcript all significantly blocked NO* induction of PPRE-regulated genes. PPARgamma activation by p38 MAPK may contribute to the anti-inflammatory and cytoprotective effects of NO* in the vasculature. This crosstalk mechanism suggests new strategies for preventing and treating vascular dysfunction.

Peroxisome Proliferator-Activated Receptor γ Ligand Pioglitazone Alters Neointimal Composition in a Balloon-Denuded and Radiated Hypercholesterolemic Rabbit

Peroxisome proliferator-activated receptor (PPAR)-gamma activation suppresses inflammatory response, monocyte recruitment, and vascular cell proliferation. Because inflammation, deregulated growth, and migration of monocytes and vascular smooth muscle cells (VSMC) play important roles in the development of neointima, we tested the effect of pioglitazone, a high-affinity ligand, for PPAR-gamma on neointima formation in the iliac arteries of a balloon-denuded and radiated hypercholesterolemic rabbit. Rabbits were fed a 1.0% cholesterol diet for 7 days followed by denudation of endothelial layer and continued on a 0.15% cholesterol diet. On day 32, animals were divided into 2 groups. One group received a 0.15% cholesterol diet (n = 7) and the other group received a 0.15% cholesterol diet supplemented with 400 mg of pioglitazone per kilogram. On day 35, the balloon-denuded area was radiated. Four weeks after radiation, animals were sacrificed and arterial segments were processed for morphometry and immunohistochemistry. Data analysis showed that the pioglitazone group had smaller neointima (0.85 +/- 0.36 vs. 1.41 +/- 0.56, P < 0.05), with more cells positive for VSMC (23.07 +/- 6.16 vs. 18.33 +/- 5.19, P = 0.04), less for monocytes (16.01 +/- 5.33 vs. 21.29 +/- 4.33, P < 0.05), and fewer cells expressing metalloproteinase (MMP)-1 and MMP-9 (3.69 +/- 0.47 vs. 4.82 +/- 0.93, P < 0.05 and 3.24 +/- 0.71 vs. 4.29 +/- 0.74, P < 0.05, respectively). Pioglitazone reduced neointimal area and modified its composition in a balloon-denuded and radiated hypercholesterolemic rabbit model.

The direct antioxidative and anti-inflammatory effects of peroxisome proliferator-activated receptors ligands are associated with the inhibition of angiotensin converting enzyme expression in streptozotocin-induced diabetic rat aorta

Peroxisome proliferator-activated receptors (PPARs) are expressed on vascular tissue. To investigate the direct vasoprotective effects of PPARgamma and PPARalpha ligands, pioglitazone (3 mg/kg/day) and bezafibrate (10 mg/kg/day) were given by gavage to streptozotocin-induced diabetic rats for 4 weeks. Streptozotocin (65 mg/kg, i.p.) significantly increased NADPH oxidase, vascular call adhesion molecule-1 (VCAM-1), and osteopontin mRNA levels in the aorta, as determined by reverse transcription (RT)-polymerase chain reaction (PCR). Immunohistochemical analysis revealed that the expression of osteopontin protein was also enhanced in the streptozotocin-injected rat aorta. Pioglitazone or bezafibrate attenuated the streptozotocin-induced increase in the expression of NADPH oxidase and VCAM-1 mRNA. The enhanced expression of osteopontin gene and protein induced by streptozotocin was suppressed by pioglitazone, whereas treatment with bezafibrate had no effect on the expression of osteopontin. We also demonstrated that pioglitazone or bezafibrate prevented the streptozotocin-induced increase in angiotensin converting enzyme (ACE) gene and protein content, by the means of RT-PCR and Western blotting. On the other hand, the treatment of pioglitazone or bezafibrate in the present study did not affect glucose tolerance, serum insulin or lipid level in streptozotocin-induced diabetic rats. These results suggest that the direct anti-oxidant and anti-inflammatory effects of PPARs ligands in the aorta of streptozotocin-induced diabetic rats were not likely to have been mediated by the normalization of glucose or lipid metabolism, but instead these salutary effects appear to have been associated with the inhibition of the expression of ACE. In addition, pioglitazone appeared to be more effective on the suppression of osteopontin expression compared with bezafibrate.

Peroxisome proliferator-activated receptor gamma promotes lymphocyte survival through its actions on cellular metabolic activities

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a metabolic regulator that plays an important role in sensitizing tissues to the action of insulin and in normalizing serum glucose and free fatty acids in type 2 diabetic patients. The receptor has also been implicated in the modulation of inflammatory responses, and ligands of PPARgamma have been found to induce apoptosis in lymphocytes. However, apoptosis induction may not depend on the receptor, because high doses of PPARgamma agonists are required for this process. Using cells containing or lacking PPARgamma, we reported previously that PPARgamma attenuates apoptosis induced by cytokine withdrawal in a murine lymphocytic cell line via a receptor-dependent mechanism. PPARgamma exerts this effect by enhancing the ability of cells to maintain their mitochondrial membrane potential during cytokine deprivation. In this report, we demonstrate that activation of PPARgamma also protects cells from serum starvation-induced apoptosis in human T lymphoma cell lines. Furthermore, we show that the survival effect of PPARgamma is mediated through its actions on cellular metabolic activities. In cytokine-deprived cells, PPARgamma attenuates the decline in ATP level and suppresses accumulation of reactive oxygen species (ROS). Moreover, PPARgamma regulates ROS through its coordinated transcriptional control of proteins and enzymes involved in ROS scavenging, including uncoupling protein 2, catalase, and copper zinc superoxide dismutase. Our studies identify cell survival promotion as a novel activity of PPARgamma and suggest that PPARgamma may modulate cytokine withdrawal-induced activated T cell death.

Regulation of antioxidant and oxidant enzymes in vascular cells and implications for vascular disease

Data from numerous studies demonstrate that oxidative stress plays an important role in the pathogenesis of vascular disease. Oxidative stress leads to many pathologic events, such as inactivation of nitric oxide, lipid oxidation, enhanced mitogenicity and apoptosis of vascular cells, and increased expression and activation of redox-sensitive genes, which contribute to atherogenesis at all stages of the disease. Multiple enzymes are expressed in vascular cells that are involved in the elimination and production of reactive oxygen species, including the superoxide dismutases, catalase, thioredoxin reductase, glutathione peroxidase, NAD(P)H oxidase, xanthine oxidase, myeloperoxidase, and endothelial nitric oxide synthase. Several agonists and pathologic conditions that predispose to vascular disease induce changes in the expression and activity levels of these antioxidant and oxidant enzyme systems, leading to modulation of vascular oxygen radical load. Identification of key enzymes and mechanisms of vascular oxidative stress is important for the development of novel, specific pharmacologic interventions.

Preventing oxidative stress in rats with aldosteronism by calcitriol and dietary calcium and magnesium supplements

BACKGROUND

Prominent features of the clinical syndrome of congestive heart failure (CHF) include aldosteronism and the presence of oxidative stress. Secondary hyperparathyroidism (SHPT) accompanies aldosteronism due to increased urinary and fecal excretion of Ca. SHPT accounts for intracellular Ca overloading of diverse cells, including peripheral blood mononuclear cells (PBMC), and the appearance of oxidative stress. Parathyroidectomy or a Ca channel blocker each prevent these responses. Herein, we hypothesized calcitriol, or 1,25(OH)2D3, plus a diet supplemented with Ca and Mg (CMD) would prevent SHPT and Ca overloading of PBMC and thereby oxidative stress in these cells in rats receiving aldosterone/salt treatment (ALDOST).

METHODS AND RESULTS

In rats with ALDOST for 4 weeks, without or with CMD, we monitored plasma-ionized [Ca]o and parathyroid hormone (PTH), and PBMC cytosolic-free [Ca]i and H2O2 production. Untreated, age- and gender-matched rats served as controls. Compared to controls, ALDOST led to an expected fall in plasma [Ca]o level with accompanying rise in plasma PTH level and intracellular Ca overloading of PBMC and their increased production of H2O2. CMD prevented SHPT and abrogated intracellular Ca overloading of PBMC and their increased H2O2 production.

CONCLUSIONS

The appearance of SHPT in aldosteronism, induced by fallen plasma [Ca]o, leads to PTH-mediated Ca overloading of PBMC and their increased production of H2O2. SHPT in rats with aldosteronism can be prevented by calcitriol and a diet supplemented with Ca and Mg. These findings raise the prospect that the SHPT found in CHF could be managed with macro- and micronutrients.

DNA oxidation and superoxide dismutase in the kidney of diabetic animals: effects of pioglitazone and repaglinide

In the present study, DNA oxidative damage was elevated and superoxide dismutase (Cu,Zn-SOD) metabolism was disturbed in the kidney of alloxan-induced diabetic animals. The effects of pioglitazone and repaglinide, new oral antidiabetics, on 8-hydroxy-2′-deoxyguanosine (8-OHdG) and Cu,Zn-SOD were studied. Diabetic versus control levels (mean ± SE) of 8-OHdG were 24.9 ± 0.2 vs. 21.8 ± 0.1 and 21.5 ± 0.2 vs 20.1 ± 0.2 pmol/µg DNA after 4 and 8 weeks, respectively. At p<0.05, pioglitazone diminished this parameter in diabetic animals (22.0 ± 0.2 and 20.1 ± 0.3 pmol/µg DNA). The level was not affected in diabetic groups receiving repaglinide (24.9 ± 0.2 and 21.5 ± 0.3 pmol/µg DNA). In diabetic kidney, Cu,Zn-SOD mRNA was diminished relative to control animals and was modulated by pioglitazone and repaglinide treatments. Simultaneously, Cu,Zn-SOD activity was also diminished (1.5 ± 0.2 vs. 2.8 ± 0.3 and 1.8 ± 0.1 vs 2.9 ± 0.3 U/mg protein after 4 and 8 weeks, respectively) and partly changed after pioglitazone (2.1 ± 0.4 and 2.3 ± 0.3 U/mg protein) and repaglinide (2.0 ± 0.1 and 2.4 ± 0.2 U/mg protein). These results suggest that a reduction in oxidative stress in diabetic kidney can be achieved with the administration of pioglitazone and to some extent using repaglinide treatment.

Cardioprotection mediated by rosiglitazone, a peroxisome proliferator-activated receptor gamma ligand, in relation to nitric oxide

Activation of peroxisome proliferator-activated receptor (PPAR) gamma protects from myocardial ischemia/reperfusion injury. The aim of the study was to investigate whether the cardioprotective effect of PPARgamma is related to nitric oxide (NO).

METHODS

Wild type (WT) and endothelial NO synthase (eNOS) knockout (KO) mice received 3 mg/kg of the PPARgamma agonist rosiglitazone or vehicle (n = 6-9 in each group) i. p. 45 min before anesthesia. The hearts were isolated, perfused in a Langendorff mode and subjected to global ischemia and 30 min reperfusion. The hearts of another two groups of WT mice received the NOS inhibitor L-NNA (100 micromol/l) or vehicle in addition to pre-treatment with vehicle or rosiglitazone.

RESULTS

In the WT heart, rosiglitazone increased the recovery of left ventricular function and coronary flow following ischemia in comparison with the vehicle group.L-NNA did not affect recovery per se but significantly blunted the improvement in the recovery of left ventricular function induced by rosiglitazone. In the KO group rosiglitazone suppressed the recovery of myocardial function following ischemia. Expression of eNOS was not affected, but phosphorylated eNOS was significantly increased by rosiglitazone in the WT hearts (P < 0.05).

CONCLUSION

These results suggest that the cardioprotective effect of the PPARgamma agonist rosiglitazone is mediated via NO by phosphorylation of eNOS.

Comparative effects of pitavastatin and probucol on oxidative stress, Cu/Zn superoxide dismutase, PPAR-gamma, and aortic stiffness in hypercholesterolemia

Reactive oxygen species-scavenging enzyme Cu/Zn superoxide dismutase (SOD) regulated by peroxisome proliferator-activated receptors (PPARs) plays an important role in vascular responsiveness. However, it remains unknown whether statin restores vascular dysfunction through the activation of reactive oxygen species-scavenging enzymes in vivo. We hypothesized that pitavastatin restores vascular function by modulating oxidative stress through the activation of Cu/ZnSOD and PPAR-gamma in hypercholesterolemia. New Zealand White male rabbits were fed either normal chow or a 1% cholesterol (CHO) diet for 14 wk. After the first 7 wk, the CHO-fed rabbits were further divided into three groups: those fed with CHO feed only (HC), those additionally given pitavastatin, and those additionally given an antioxidant, probucol. The extent of atherosclerosis was assessed by examining aortic stiffness. When compared with the HC group, both the pitavastatin and probucol groups showed improved aortic stiffness by reducing aortic levels of reactive oxidative stress, nitrotyrosine, and collagen, without affecting serum cholesterol or blood pressure levels. Pitavastatin restored both Cu/ZnSOD activity (P < 0.005) and PPAR-gamma expression and activity (P < 0.01) and inhibited NAD(P)H oxidase activity (P < 0.0001) in the aorta, whereas probucol inhibited NAD(P)H oxidase activity more than did pitavastatin (P < 0.0005) without affecting Cu/ZnSOD activity or PPAR-gamma expression and activity. Importantly, Cu/ZnSOD activity was positively correlated with the PPAR-gamma activity in the aorta (P < 0.005), both of which were negatively correlated with aortic stiffness (P < 0.05). Vascular Cu/ZnSOD and PPAR-gamma may play a crucial role in the antiatherogenic effects of pitavastatin in hypercholesterolemia in vivo.

Aspirin and PPAR-α activators inhibit monocyte chemoattractant protein-1 expression induced by high glucose concentration in human endothelial cells

Activated endothelial cells express monocyte chemoattractant protein-1 (MCP-1), a chemokine which is reportedly involved in the recruitment of plasma monocytes in the early stages of atherosclerosis. Since accelerated atherosclerosis is the main complication of diabetes and both diseases encompass an inflammatory reaction, we hypothesized that the anti-inflammatory drugs, aspirin and peroxisome proliferator-activated receptor (PPAR-alpha) activators (fenofibrate and clofibrate), could have an effect on the high glucose-induced MCP-1 expression in endothelial cells. To test this assumption, as well as the possible mechanisms involved, the MCP-1 expression and secretion, the reactive oxygen species levels, nuclear factor-kB (NF-kB) and activator protein-1 (AP-1) expression were determined in human endothelial cells exposed to high glucose concentrations in the presence of aspirin, fenofibrate and clofibrate. Human endothelial cells kept in normal glucose concentration in the absence of drugs were used as control. The results showed that (i) aspirin, fenofibrate and clofibrate decrease significantly the MCP-1 expression and secretion in human endothelial cells; (ii) the high glucose up-regulated expression of MCP-1 in endothelial cells was significantly reduced by inhibitors of NF-kB and reactive oxygen species; (iii) all drugs notably decrease the level of the reactive oxygen species and activation of NF-kB and AP-1. Together, the findings indicate that in endothelial cells aspirin and PPAR-alpha activators reduce the high glucose-increased expression of MCP-1 by a mechanism that includes the inhibition of reactive oxygen species, and decrease of AP-1 and NF-kB activation.

Modulation of Hepatic Inflammatory Risk Markers of Cardiovascular Diseases by PPAR–α Activators

Atherosclerosis is a long-term chronic inflammatory disease associated with increased concentrations of inflammatory hepatic markers, such as CRP and fibrinogen, and of peripheral origin, such as tumor necrosis factor (TNF)-α and interleukin (IL)-6. Peroxisome proliferator-activated receptor (PPAR-)-α is a ligand-activated transcription factor that regulates expression of key genes involved in lipid homeostasis and modulates the inflammatory response both in the vascular wall and the liver. PPAR-α is activated by natural ligands, such as fatty acids, as well as the lipid-lowering fibrates. PPAR-α agonists impact on different steps of atherogenesis: (1) early markers of atherosclerosis, such as vascular wall reactivity, are improved, (2) however, reduced expression of adhesion molecules on the surface of endothelial cells, accompanied by decreased levels of inflammatory cytokines, such as TNF-α, IL-1, and IL-6, leads to a decreased leukocyte recruitment into the arterial wall; (3) in later stages of the atherosclerotic process, PPAR-α agonists may promote plaque stabilization and reduce cardiovascular events, via effects on metalloproteinases, such as MMP9. Moreover, PPAR-α activation by fibrates also impairs proinflammatory cytokine-signaling pathways in the liver resulting in the modulation of the acute phase response reaction via mechanisms independent of changes in lipoprotein levels. Effective coronary artery disease (CAD) prevention requires the use of agents that act beyond low-density lipoprotein cholesterol-lowering. PPAR-α agonists appear to comprehensively address some of the abnormalities of the most common clinical phenotypes of the high CAD risk patient of the 21st century such as in the metabolic syndrome and type 2 diabetes: low high-density lipoprotein cholesterol, high triglycerides, small, dense low-density lipoprotein, and a proinflammatory, procoagulant state.

Effects of 15d-PGJ(2) on VEGF-induced angiogenic activities and expression of VEGF receptors in endothelial cells

15-Deoxy-Delta(12,14)-prostaglandin-J(2) (15d-PGJ(2)) upregulates expression of vascular endothelial growth factor (VEGF), but may inhibit angiogenesis. We found that 15d-PGJ(2) (1-10muM) attenuated all VEGF-induced angiogenic activities in human umbilical vein endothelial cells (HUVEC). It blocked almost completely cell proliferation, potently reduced migration, assembly into tube-like network on matrigel, and growth of capillaries into collagen gel. 15d-PGJ(2) inhibited expression of VEGFR-1 and VEGFR-2 receptors both at mRNA and protein levels. This inhibition, however, was transient (observed after 6-12h, but not after 24h) and weak (20-30%), and could not fully explain inhibition of response to VEGF. Accordingly, proliferation was inhibited when 15d-PGJ(2) was added 24h after VEGF or in cells stimulated with basic fibroblast growth factor. Interestingly, 15d-PGJ(2) decreased activities of c-jun and c-myc in HUVEC and overexpression of c-myc attenuated its antiproliferative effects. This suggests that inhibition of this transcription factor by 15d-PGJ(2) contributes to decrease in angiogenic response.

Oxidative stress at the vascular wall. Mechanistic and pharmacological aspects

During the process of energy production in aerobic respiration, vascular cells produce reactive oxygen species (ROS). A growing body of evidence indicates that oxidative stress refers to a condition in which cells are subjected to excessive levels of ROS. Overall vascular function is dependent upon a fine balance of oxidant and antioxidant mechanisms, which determine endothelial functions. Considerable experimental and clinical data indicate that intracellular oxidant milieu is also involved in several redox-sensitive cellular signaling pathways such as ion transport systems, protein phosphorylation, and gene expression and thus also plays important roles as modulator of vascular cell functions such as cell growth, apoptosis, migration, angiogenesis and cell adhesion. Overproduction of ROS under pathophysiologic conditions is integral in the development of cardiovascular diseases. This fact has raised an intensive search of new pharmacological approaches to improve vascular hemostasis and particularly those intended to decrease oxidative stress or augment the antioxidant defense mechanisms.

NADPH oxidases in cardiovascular health and disease

Increased oxidative stress plays an important role in the pathophysiology of cardiovascular diseases such as hypertension, atherosclerosis, diabetes, cardiac hypertrophy, heart failure, and ischemia-reperfusion. Although several sources of reactive oxygen species (ROS) may be involved, a family of NADPH oxidases appears to be especially important for redox signaling and may be amenable to specific therapeutic targeting. These include the prototypic Nox2 isoform-based NADPH oxidase, which was first characterized in neutrophils, as well as other NADPH oxidases such as Nox1 and Nox4. These Nox isoforms are expressed in a cell- and tissue-specific fashion, are subject to independent activation and regulation, and may subserve distinct functions. This article reviews the potential roles of NADPH oxidases in both cardiovascular physiological processes (such as the regulation of vascular tone and oxygen sensing) and pathophysiological processes such as endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, angiogenesis, and vascular and cardiac remodeling. The complexity of regulation of NADPH oxidases in these conditions may provide the possibility of targeted therapeutic manipulation in a cell-, tissue- and/or pathway-specific manner at appropriate points in the disease process.

Sorting out the roles of PPAR alpha in energy metabolism and vascular homeostasis

PPARalpha is a nuclear receptor that regulates liver and skeletal muscle lipid metabolism as well as glucose homeostasis. Acting as a molecular sensor of endogenous fatty acids (FAs) and their derivatives, this ligand-activated transcription factor regulates the expression of genes encoding enzymes and transport proteins controlling lipid homeostasis, thereby stimulating FA oxidation and improving lipoprotein metabolism. PPARalpha also exerts pleiotropic antiinflammatory and antiproliferative effects and prevents the proatherogenic effects of cholesterol accumulation in macrophages by stimulating cholesterol efflux. Cellular and animal models of PPARalpha help explain the clinical actions of fibrates, synthetic PPARalpha agonists used to treat dyslipidemia and reduce cardiovascular disease and its complications in patients with the metabolic syndrome. Although these preclinical studies cannot predict all of the effects of PPARalpha in humans, recent findings have revealed potential adverse effects of PPARalpha action, underlining the need for further study. This Review will focus on the mechanisms of action of PPARalpha in metabolic diseases and their associated vascular pathologies.

Gemfibrozil decreases atherosclerosis in experimental diabetes in association with a reduction in oxidative stress and inflammation

AIMS/HYPOTHESIS

It is postulated that peroxisome proliferator-activated receptor alpha agonists confer cardiovascular benefits in diabetes, independently of their effects on lipid metabolism. We investigated putative mechanisms responsible for these anti-atherogenic effects in an in vivo model of diabetes-associated atherosclerosis.

MATERIALS AND METHODS

Control and streptozotocin-induced diabetic apolipoprotein-deficient mice received gemfibrozil (100 mg kg(-1) day(-1)) or no treatment for 20 weeks. Aortic plaque deposition was assessed by Sudan IV staining and subsequent en face quantification. Superoxide production was measured using lucigenin-enhanced chemiluminescence. Markers of pathways including inflammation and oxidative stress were measured using real-time RT-PCR.

RESULTS

No significant effect of gemfibrozil was observed on glycated haemoglobin, cholesterol or insulin in diabetic mice. Diabetes was associated with a three-fold increase in plaque area and a significant increase in NADPH-dependent superoxide compared with control mice. Gemfibrozil significantly attenuated plaque area and superoxide production in diabetic mice. In addition, gemfibrozil reduced the expression of the genes encoding the NADPH oxidase subunits p47phox, gp91phox and Rac-1. In addition, gemfibrozil reduced the expression of the genes encoding nuclear factor kappa B (NF-kappaB) subunit, p65, the NF-kappaB-dependent chemokine monocyte chemoattractant protein-1, and tissue factor.

CONCLUSIONS/INTERPRETATIONS

This study demonstrates that gemfibrozil exerts anti-atherogenic actions, independently of changes in cholesterol and glucose metabolism. Such findings emphasise the possible usefulness of fibrates such as gemfibrozil in a setting of atherosclerosis even in the absence of dyslipidaemia.

Synthetic peroxisome proliferator-activated receptor-gamma agonists restore impaired vasorelaxation via ATP-sensitive K+ channels by high glucose

The present study was designed to examine whether in the human artery, synthetic peroxisome proliferator-activated receptor (PPAR)-gamma agonists restore vasorelaxation as well as hyperpolarization via ATP-sensitive K+ channels impaired by the high concentration of D-glucose and whether the restoration may be mediated by the antioxidant capacity of these agents. The isometric force and membrane potential of human omental arteries without endothelium were recorded. The production rate of superoxide was evaluated using a superoxide-generating system with xanthine-xanthine oxidase in the absence of smooth muscle cells. Glibenclamide abolished vasorelaxation and hyperpolarization in response to levcromakalim. Addition of D-glucose (20 mM) but not L-glucose (20 mM) reduced this vasorelaxation and hyperpolarization. Synthetic PPAR-gamma agonists (troglitazone and rosiglitazone) and/or an inhibitor of superoxide generation (4,5-dihydroxy-1,3-benzene-disulfonic acid, Tiron), but not a PPAR-alpha agonist (fenofibrate), restored vasorelaxation and hyperpolarization in response to levcromakalim in arteries treated with D-glucose. Troglitazone and rosiglitazone, but not fenofibrate, decreased the production rate of superoxide without affecting uric acid generation. These findings suggest that synthetic PPAR-gamma agonists recover the function of ATP-sensitive K+ channels reduced by the high concentration of glucose in human vascular smooth muscle cells and that the effect of these agonists may be mediated in part by their antioxidant capacity.

Pleiotropic effects of fibrates

Fibrates are a widely used class of hypolipidemic drugs. The effects of fibrates are mediated through the activation of the transcription factor peroxisome proliferator-activated receptor a (PPARa). Fibrates act to modulate the transcription of genes that encode proteins controlling lipid transport and metabolism. Fibrates also exert pleiotropic anti-inflammatory effects by down regulating expression of genes encoding inflammatory cytokines and acute phase response proteins. These combined actions translate into clinical benefit as demonstrated by the reduction in cardiovascular morbidity and mortality in primary and secondary intervention trials.

Phagocytic NADPH oxidase overactivity underlies oxidative stress in metabolic syndrome

Oxidative stress plays a critical role in the pathogenesis of atherosclerosis in patients with metabolic syndrome. This study aimed to investigate whether a relationship exists between phagocytic NADPH oxidase activity and oxidative stress and atherosclerosis in metabolic syndrome patients. The study was performed in 56 metabolic syndrome patients (metabolic syndrome group), 99 patients with one or two cardiovascular risk factors (cardiovascular risk factor group), and 28 healthy subjects (control group). NADPH oxidase expression and activity was augmented (P < 0.05) in metabolic syndrome compared with cardiovascular risk factor and control groups. Insulin was enhanced (P < 0.05) in metabolic syndrome patients compared with cardiovascular risk factor and control groups and correlated with NADPH oxidase activity in the overall population. Insulin stimulated NADPH oxidase activity; this effect was abolished by a specific protein kinase C inhibitor. Oxidized LDL and nitrotyrosine levels and carotid intima-media thickness were increased (P < 0.05) in the metabolic syndrome group compared with cardiovascular risk factor and control groups and correlated with NADPH oxidase activity in the overall population. These findings suggest that phagocytic NADPH oxidase overactivity is involved in oxidative stress and atherosclerosis in metabolic syndrome patients. Our findings also suggest that hyperinsulinemia may contribute to oxidative stress in metabolic syndrome patients through activation of NADPH oxidase.

Fenofibrate: a novel formulation (Triglide) in the treatment of lipid disorders: a review

Cardiovascular disease is the major cause of mortality worldwide and accounts for approximately 40% of all deaths. Dyslipidemia is one of the primary causes of atherosclerosis and effective interventions to correct dyslipidemia should form an integral component of any strategy aimed at preventing cardiovascular disease. Fibrates have played a major role in the treatment of hyperlipidemia for more than two decades. Fenofibrate is one of the most commonly used fibrates worldwide. Since fenofibrate was first introduced in clinical practice, a major drawback has been its low bioavailability when taken under fasting conditions. Insoluble Drug Delivery-Microparticle fenofibrate is a new formulation that has an equivalent extent of absorption under fed or fasting conditions. In this review, we will discuss the clinical pharmacology of fenofibrate, with particular emphasis on this novel formulation, as well as its lipid-modulating and pleiotropic actions. We will also analyze the major trial that evaluated fibrates for primary and secondary prevention of cardiovascular disease, the safety and efficacy profile of fibrate-statin combination treatment, and the current recommendations regarding the use of fibrates in clinical practice.

Diabetes mellitus-associated atherosclerosis: mechanisms involved and potential for pharmacological invention

While diabetes mellitus is most often associated with hypertension, dyslipidemia, and obesity, these factors do not fully account for the increased burden of cardiovascular disease in patients with the disease. This strengthens the need for comprehensive studies investigating the underlying mechanisms mediating diabetic cardiovascular disease and, more specifically, diabetes-associated atherosclerosis. In addition to the recognized metabolic abnormalities associated with diabetes mellitus, upregulation of putative pathological pathways such as advanced glycation end products, the renin-angiotensin system, oxidative stress, and increased expression of growth factors and cytokines have been shown to play a causal role in atherosclerotic plaque formation and may explain the increased risk of macrovascular complications. This review discusses the methods used to assess the development of atherosclerosis in the clinic as well as addressing novel biomarkers of atherosclerosis, such as low-density lipoprotein receptor-1. Experimental models of diabetes-associated atherosclerosis are discussed, such as the streptozocin-induced diabetic apolipoprotein E knockout mouse. Results of major clinical trials with inhibitors of putative atherosclerotic pathways are presented. Other topics covered include the role of HMG-CoA reductase inhibitors and fibric acid derivatives with respect to their lipid-altering ability, as well as their emerging pleiotropic anti-atherogenic actions; the effect of inhibiting the renin-angiotensin system by either ACE inhibition or angiotensin II receptor antagonism; the effect of glycemic control and, in particular, the promising role of thiazolidinediones with respect to their direct anti-atherogenic actions; and newly emerging mediators of diabetes-associated atherosclerosis, such as advanced glycation end products, vascular endothelial growth factor and platelet-derived growth factor. Overall, this review aims to highlight the observation that various pathways, both independently and in concert, appear to contribute toward the pathology of diabetes-associated atherosclerosis. Furthermore, it reflects the need for combination therapy to combat this disease.

Altered protein expression and protein nitration pattern during d-galactosamine-induced cell death in human hepatocytes: a proteomic analysis

BACKGROUND/AIMS

Hepatic injury by d-galactosamine (d-GalN) is a suitable experimental model of hepatocellular injury. The induction of oxidative and nitrosative stress participates during d-GalN-induced cell death in cultured rat hepatocytes. This study aimed to identify protein expression changes during the induction of apoptosis and necrosis by d-GalN in cultured human hepatocytes.

METHODS

A proteomic approach was used to identify the proteins involved and those altered by tyrosine nitration. A high dose of d-GalN (40 mM) was used to induce apoptosis and necrosis in primary culture of human hepatocytes. Cellular lysates prepared at different times after addition of d-GalN were separated by two-dimensional electrophoresis. Gel spots with an altered expression and those matching nitrotyrosine-immunopositive proteins were excised and analyzed by mass spectrometry.

RESULTS

d-GalN treatment upregulated microsomal cytochrome b5, fatty acid binding protein and manganese superoxide dismutase, and enhanced annexin degradation. d-GalN increased tyrosine nitration of four cytosolic (Hsc70, Hsp70, annexin A4 and carbonyl reductase) and three mitochondrial (glycine amidinotransferase, ATP synthase beta chain, and thiosulfate sulfurtransferase) proteins in human hepatocytes.

CONCLUSIONS

The results provide evidences that oxidative stress and nitric oxide-derived reactive oxygen intermediates induce specific alterations in protein expression that may be critical for the induction of apoptosis and necrosis by d-GalN in cultured human hepatocytes.

Rosiglitazone Attenuates Atherosclerosis in a Model of Insulin Insufficiency Independent of Its Metabolic Effects

Objectives— Recent studies have demonstrated a role for thiazolidinediones in attenuating atherosclerosis. However, these studies were performed in insulin-resistant animal models in association with reductions in insulin and glucose levels. To assess the vascular effects of thiazolidinediones, independent of their metabolic effects, we observed the effect of rosiglitazone on diabetes-associated atherosclerosis in a model of insulin insufficiency.

Methods and Results— Control and diabetic apolipoprotein E–deficient mice received rosiglitazone or placebo. Diabetic mice demonstrated a 3-fold increase in plaque area, which was attenuated by rosiglitazone. There was no significant difference in glucose, insulin, or cholesterol levels between treated and untreated diabetic animals. Rosiglitazone attenuated the increase in superoxide production observed in diabetic mice. A 4-fold increase in the reverse cholesterol transport marker ABCA1 was observed in treated diabetic mice. Rosiglitazone reduced angiotensin II receptor gene expression in control and diabetic mice, and macrophage accumulation was increased in diabetic mice compared with controls and was attenuated by rosiglitazone.

Conclusions— These findings suggest peroxisome proliferator-activated receptor-γ ligands such as rosiglitazone confer vascular protection independent of their effects on metabolic control. These antiatherosclerotic effects may have important clinical ramifications not only in insulin resistance/type 2 diabetes and also in type 1 diabetes.

NAD(P)H oxidase/nitric oxide interactions in peroxisome proliferator activated receptor (PPAR)alpha-mediated cardiovascular effects

Activation of peroxisome proliferator activated receptor (PPAR)alpha and its protective role in cardiovascular function has been reported but the exact mechanism(s) involved is not clear. As we have shown that PPARalpha ligands increased nitric oxide (NO) production and cardiovascular function is controlled by a balance between NO and free radicals, we hypothesize that PPARalpha activation tilts the balance between NO and free radicals and that this mechanism defines the protective effects of PPARalpha ligands on cardiovascular system. Systolic blood pressure (SBP) was greater in PPARalpha knockout (KO) mice compared with its wild type (WT) litter mates (130+/-10 mmHg versus 107+/-4 mmHg). L-NAME (100mg/L p.o.), the inhibitor of NO production abolished the difference between PPARalpha KO and WT mice. In kidney homogenates, tissue lipid hydroperoxide generation was greater in KO mice (11.8+/-1.4 pM/mg versus 8.3+/-0.6 pM/mg protein). This was accompanied by a higher total NOS activity (46+/-6%, p<0.05) and a approximately 3 fold greater Ca2+-dependent NOS activity in kidney homogenates of untreated PPARalpha WT compared with the KO mice. Clofibrate, a PPARalpha ligand, increased NOS activity in WT but not KO mice. Bezafibrate (30 mg/kg) reduced SBP in conscious rats (19+/-4%, p<0.05), increased urinary NO excretion (4.06+/-0.53-7.07+/-1.59 microM/24 h; p<0.05) and reduced plasma 8-isoprostane level (45.8+/-15 microM versus 31.4+/-8 microM), and NADP(H) oxidase activity (16+/-5%). Implantation of DOCA pellet (20mg s.c.) in uninephrectomized mice placed on 1% NaCl drinking water increased SBP by a margin that was markedly greater in KO mice (193+/-13 mmHg versus 130+/-12 mmHg). In the rat, DOCA increased SBP and NAD(P)H oxidase activity and both effects were diminished by clofibrate. In addition, clofibrate reduced ET-1 production in DOCA/salt hypertensive rats. Thus, apart from inhibition of ET-1 production, PPARalpha activation exerts protective actions in hypertension via a mechanism that involves NO production and/or inhibition of NAD(P)H oxidase activity.

Homocysteine-dependent cardiac remodeling and endothelial-myocyte coupling in a 2 kidney, 1 clip Goldblatt hypertension mouse model

Accumulation of interstitial collagen (fibrosis) between the endothelium and myocytes is one of the hallmarks of cardiac failure in renovascular hypertension (RVH). Renal insufficiency increases plasma homocysteine (Hcy), and levels of peroxisome proliferator-activated receptor-γ (PPAR-γ) are inversely related to plasma Hcy levels. We hypothesize that in RVH, accumulation of collagen between the endothelium and myocytes leads to endothelial-myocyte disconnection and uncoupling, in part, by hyperhomocysteinemia. Furthermore, we hypothesize that Hcy increases reactive oxygen species, generates nitrotyrosine, activates latent matrix metalloproteinase, and decreases the levels of endothelial nitric oxide in response to antagonizing PPAR-γ. To create RVH in mice, the left renal artery was clipped with 0.4-mm sliver wire for the 2 kidney, 1 clip (2K1C) method. Sham surgery was used as a control. To induce PPAR-γ, 8 µg/mL ciglitazone (CZ) was administered to drinking water 2 days before surgery and continued for 4 weeks. Mice were grouped as 2K1C, sham, 2K1C+CZ, or sham+CZ (n = 6 in each group). Plasma Hcy increased 2-fold in the 2K1C-treated group (p < 0.05) as compared with the sham, and CZ had no effect on Hcy levels as compared to the 2K1C-treated group. Hcy binding in cardiac tissue homogenates decreased in the 2K1C-treated group but was substantially higher in the CZ-treated group. Cardiac reactive oxygen species levels were increased and endothelial nitric oxide were decreased in the 2K1C-treated group. Matrix metalloproteinase-2 and -9 activities were increased in the 2K1C-treated group compared with the control. Levels of cardiac inhibitor of metallopoteinase were decreased, whereas there was no change in tissue inhibitor of metalloproteinase-1 expression in the 2K1C-treated group vs. the sham-treated group. Collagen and nitrotyrosine levels were increased in the 2K1C-treated group, but mice treated with CZ showed lower levels comparatively. Cardiac transferase deoxyuridine nick-end labeling-positive cells were increased, and muscle cells were impaired in the 2K1C-treated mice vs. the sham-control mice. This was associated with decreased acetylcholine and bradykinin responses, which suggests endothelial-myocyte uncoupling in 2K1C-treated mice. Our results suggest that fibrosis between the endothelium and myocytes leads to an endothelial-myocyte disconnection and uncoupling by Hcy accumulation secondary to increased reactive oxygen species, nitrotyrosine, matrix metalloproteinase, and decreased endothelial nitric oxide in response to antagonizing PPAR-γ. Key words: ECM, collagen, elastin, cystathione β synthase, nitric oxide, arteriosclerosis, renal mechanism.

Alteration in endothelial function and modulation by treatment with pioglitazone in rabbit renal artery from short-term hypercholesterolemia

The present study was undertaken to investigate endothelial function and epoxyeicosatrienoic acids (EETs), which is a cytochrome P-450 monooxygenase (CYP) metabolite and one of the candidates as an endothelium-derived hyperpolarizing factor (EDHF) in the renal artery isolated from short-term hypercholesterolemic rabbits, and also to characterize the effects of pioglitazone on it. Rabbits were fed normal, 0.5% cholesterol chow, or 0.5% cholesterol chow plus 300 ppm pioglitazone for 5 weeks. The tension of isolated renal artery rings was measured isometrically. Serum lipid levels were measured and morphometric analysis was performed. EET contents in the renal artery were also determined. The cholesterol chow diet for 5 weeks increased serum lipid levels, and pioglitazone had no influence on it. In the phenylephrine precontracted renal artery, the cholesterol chow did not affect acetylcholine-induced relaxation. The N(G)-nitro-l-arginine- and indomethacin-resistant endothelium-dependent relaxation induced by acetylcholine was significantly enhanced in rabbits receiving the cholesterol chow as compared to rabbits receiving the control diet, and pioglitazone normalized it. The resistant part of acetylcholine-induced relaxation was significantly inhibited when the renal artery was treated with charybdotoxin, an inhibitor of large- and intermediate-conductance Ca(2+)-activated K(+) channels, or N,N-di-ethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF 525a), a nonselective CYP inhibitor, and it was significantly inhibited by sulfaphenazole, a selective CYP2C9 inhibitor in rabbits receiving only the cholesterol chow. In KCl-precontracted renal artery, the cholesterol chow inhibited acetylcholine-induced relaxation and pioglitazone normalized it. The cholesterol chow increased the production of EETs and reduced nitrate/nitrite contents in the renal artery, and pioglitazone strongly suppressed them. These results suggest that the EETs may be one of the EDHFs in the rabbit renal artery and beneficial effects of pioglitazone on alterations in endothelial function induced by cholesterol feeding are due, in part, to the protective action on the nitric oxide system and/or the suppression of increased production of EETs.

Cellular mechanisms and treatment of diabetes vascular complications converge on reactive oxygen species

High glucose activates a myriad of signaling and gene expression pathways in non-insulin-dependent target cells causing diabetes complications. One of the earliest responses to high glucose by vascular cells is the generation of reactive oxygen species (ROS) that act directly on intracellular proteins and DNA, or indirectly as second messengers, transforming these cells into disease phenotypes. ROS are produced by mitochondria and/or NADPH oxidase in all target cells exposed to high glucose studied to date. Reports using cell cultures and diabetic animal models indicate that inhibition of ROS generation prevents the amplification of signaling and gene expression that are implicated in vascular complications. These models convincingly demonstrate that maneuvers preventing ROS production attenuate or completely abrogate early micro- and macrovascular end-organ damage of diabetes, including nephropathy, retinopathy, and large-vessel atherosclerosis. Attention now turns to the development of more effective antioxidants that could be used in clinical trials in the prevention and treatment of diabetes complications.

CLOCK/BMAL1 is involved in lipid metabolism via transactivation of the peroxisome proliferator-activated receptor (PPAR) response element

Lipid absorption and metabolism are regulated by feeding and by the circadian system. It has been suggested that the expression of enzymes involved in lipid metabolism is directly controlled by the clock system. This study was designed to examine whether or not the CLOCK/BMAL1 heterodimer has transcriptional activity for genes via the peroxisome proliferator-activated receptor response element (PPRE). Male mice 8-12 weeks old were maintained under a 12:12 hour light-dark cycle for at least two weeks before the day of the experiment. The mRNA profiles of BMAL1 and of the PPAR target genes acyl-CoA oxidase (AOX), 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase and cellular retinol binding protein II (CRBPII) were measured in intestine. The direct effects of CLOCK/BMAL1 on the promoter activities of those three enzymes were assessed in vitro by luciferase assay. The expression of PPAR target genes changed in a cyclical manner that followed expression of BMAL1. The promoter activities of the three enzymes were increased by CLOCK/BMAL1 expression. After deletion of the PPRE from the CRBPII construct, CLOCK/BMAL1 did not affect transactivation. CLOCK/BMAL1 transactivates PPAR target genes via the PPRE.

Fibrates

Atherosclerosis of the large arteries is the main origin of cerebro- and cardiovascular diseases, the leading causes of mortality and morbidity in industrialized countries. The pathophysiology of coronary and cerebrovascular atherosclerosis is multifactorial and complex. Fibrates are hypolipidemic drugs that lower progression of atherosclerotic lesions mainly through activation of the nuclear receptor peroxisome-proliferator activated receptor-alpha. In addition, fibrates exert pleiotropic and anti-inflammatory actions. In this chapter, we will focus on the different effects of fibrates impacting on the development of atherosclerosis.

A peroxisome proliferator-activated receptor-gamma agonist reduces infarct size in transient but not in permanent ischemia

BACKGROUND AND PURPOSE

Activators of peroxisome proliferator-activated receptor-gamma (PPARgamma), a member of the PPAR family, increase levels of CuZn-superoxide dismutase (SOD) in cultured endothelium, suggesting a mechanism by which it may exert its protective effect within the brain. These properties raise the question of whether a PPARgamma agonist may be neuroprotective in models of ischemia without reperfusion, in which oxidative injury is less prevalent.

METHODS

In 2 groups of rats, 90 minutes of middle cerebral artery (MCA) occlusion was followed by 1 day of reperfusion, with 1 group receiving pioglitazone (a PPARgamma agonist) starting 72 hours before MCA occlusion (MCAO) and continuing through the day of occlusion, whereas the other group received vehicle only. In 2 comparable groups, the MCA was occluded permanently. One day after occlusion, the animals were tested neurologically and infarct volumes were calculated. In a separate group, rats were treated with pioglitazone or vehicle for 4 days. Tissue was obtained from the cortex and the striatum 2 hours into reperfusion after 90 minutes of MCAO, and the tissue was examined for CuZn-SOD by Western blot.

RESULTS

Results show a significant reduction in infarct size in the treated rats, with transient MCAO but not permanent MCAO. There was also an improvement in neurological score in the treated animals after transient MCAO. The level of CuZn-SOD was increased in the cortex in treated animals.

CONCLUSIONS

These data, which show that a PPARgamma agonist reduces infarct size in transient but not permanent MCAO, suggest that the role of PPARgamma is specific to events occurring during reperfusion. Our data point to CuZn-SOD as the mediator of this neuroprotection.

Peroxisome proliferator-activated receptor-gamma ligands regulate endothelial membrane superoxide production

Recently, we demonstrated that the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligands, either 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) or ciglitazone, increased endothelial nitric oxide (.NO) release without altering endothelial nitric oxide synthase (eNOS) expression (4). However, the precise molecular mechanisms of PPAR-gamma-stimulated endothelial.NO release remain to be defined. Superoxide anion radical (O2-.) combines with .NO to decrease.NO bioavailability. NADPH oxidase, which produces O2-., and Cu/Zn-superoxide dismutase (Cu/Zn-SOD), which degrades O2-., thereby contribute to regulation of endothelial cell.NO metabolism. Therefore, we examined the ability of PPAR-gamma ligands to modulate endothelial O2-. metabolism through alterations in the expression and activity of NADPH oxidase or Cu/Zn-SOD. Treatment with 10 microM 15d-PGJ2 or ciglitazone for 24 h decreased human umbilical vein endothelial cell (HUVEC) membrane NADPH-dependent O2-. production detected with electron spin resonance spectroscopy. Treatment with 15d-PGJ2 or ciglitazone also reduced relative mRNA levels of the NADPH oxidase subunits, nox-1, gp91phox (nox-2), and nox-4, as measured using real-time PCR analysis. Concordantly, Western blot analysis demonstrated that 15d-PGJ2 or ciglitazone decreased nox-2 and nox-4 protein expression. PPAR-gamma ligands also stimulated both activity and expression of Cu/Zn-SOD in HUVEC. These data suggest that in addition to any direct effects on endothelial.NO production, PPAR-gamma ligands enhance endothelial.NO bioavailability, in part by altering endothelial O2-. metabolism through suppression of NADPH oxidase and induction of Cu/Zn-SOD. These findings further elucidate the molecular mechanisms by which PPAR-gamma ligands directly alter vascular endothelial function.

Peroxisome proliferator-activated receptor alpha induces NADPH oxidase activity in macrophages, leading to the generation of LDL with PPAR-alpha activation properties

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors controlling lipid and glucose metabolism as well as inflammation. PPARs are expressed in macrophages, cells that also generate reactive oxygen species (ROS). In this study, we investigated whether PPARs regulate ROS production in macrophages. Different PPAR-alpha, but not PPAR-gamma agonists, increased the production of ROS (H2O2 and ) in human and murine macrophages. PPAR-alpha activation did not induce cellular toxicity, but significantly decreased intracellular glutathione levels. The increase in ROS production was not attributable to inherent prooxidant effects of the PPAR-alpha agonists tested, but was mediated by PPAR-alpha, because the effects were lost in bone marrow-derived macrophages from PPAR-alpha-/- mice. The PPAR-alpha-induced increase in ROS was attributable to the induction of NADPH oxidase, because (1) preincubation with the NADPH oxidase inhibitor diphenyleneiodinium prevented the increase in ROS production; (2) PPAR-alpha agonists increased production measured by superoxide dismutase-inhibitable cytochrome c reduction; (3) PPAR-alpha agonists induced mRNA levels of the NADPH oxidase subunits p47(phox), p67phox, and gp91phox and membrane p47phox protein levels; and (4) induction of ROS production was abolished in p47phox-/- and gp91phox-/- macrophages. Finally, induction of NADPH oxidase by PPAR-alpha agonists resulted in the formation of oxidized LDL metabolites that exert PPAR-alpha-independent proinflammatory and PPAR-alpha-dependent decrease of lipopolysaccharide-induced inducible nitric oxide synthase expression in macrophages. These data identify a novel mechanism of autogeneration of endogenous PPAR-alpha ligands via stimulation of NADPH oxidase activity.

Modulation of Oxidant and Antioxidant Enzyme Expression and Function in Vascular Cells

Pathological conditions that predispose to cardiovascular events, such as hypertension, hypercholesterolemia, and diabetes, are associated with oxidative stress. These observations and further data derived from a plethora of investigations provided accumulating evidence that oxidative stress is decisively involved in the pathogenesis of endothelial dysfunction and atherosclerosis. Several enzymes expressed in vascular tissue contribute to production and efficient degradation of reactive oxygen species, and enhanced activity of oxidant enzymes and/or reduced activity of antioxidant enzymes may cause oxidative stress. Various agonists, pathological conditions, and therapeutic interventions lead to modulated expression and function of oxidant and antioxidant enzymes, including NAD(P)H oxidase, endothelial nitric oxide synthase, xanthine oxidase, myeloperoxidase, superoxide dismutases, catalase, thioredoxin reductase, and glutathione peroxidase. Data from numerous studies underline the importance of dysregulated oxidant and antioxidant enzymes for the development and progression of atherosclerotic disease in animal models and humans. Specific pharmacological modulation of key enzymes involved in the propagation of oxidative stress rather than using direct antioxidants may be an approach to reduce oxygen radical load in the vasculature and subsequent disease progression in humans. This review focuses on the modulation of expression and activity of major antioxidant and oxidant enzymes expressed in vascular cells.

L-FABP is exclusively expressed in alveolar macrophages within the myeloid lineage

Peroxisome proliferator-activated receptors (PPARs) play a role in inflammation and, in particular, PPARgamma is involved in monocyte/macrophage differentiation. Members of the fatty acid-binding protein (FABP) family have been reported to function as transactivators for PPARs. Therefore, the expression of PPARs and FABPs in the myeloid lineage was investigated by real-time PCR and immunofluorescence analysis. We found adipocyte-, epidermal-, and heart-type FABP to be ubiquitously expressed within the myeloid lineage. In contrast, liver-type FABP was exclusively detected in murine alveolar macrophages (AM), confirmed on protein level by double fluorescence analysis. The PPAR subtypes also showed a temporally and spatially regulated expression pattern in myeloid cells: the beta-subtype was expressed in bone marrow, peritoneal, and alveolar macrophages, whereas it was not detected in dendritic cells (DCs). The gamma1-isoform was present in all cells, however, at different levels, whereas the gamma2-isoform was expressed in alveolar macrophages and dendritic cells. A low level PPARalpha mRNA could be detected in peritoneal macrophages and immature dendritic cells but not in mature dendritic cells and bone marrow macrophages. Interestingly, PPARalpha mRNA was also absent in the alveolar macrophages although liver-type FABP was expressed, indicating that gene expression of liver-type FABP was independent of PPARalpha. Since liver-type FABP is known as transactivator of PPARgamma the simultaneous expression of both proteins may have general implications for the activation of PPARgamma in alveolar macrophages.

Selenoproteins, Cholesterol-Lowering Drugs, and the Consequences Revisiting of the Mevalonate Pathway

3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) and peroxisome proliferator-activated receptor alpha activators (fibrates) are the backbone of pharmacologic hypercholesterolemia and dyslipidemia treatment. Many of their clinical effects, however, are still enigmatic. This article describes how a side road of the mevalonate pathway, characterized in recent years, can rationalize a major fraction of these unexplained observations. This side road is the enzymatic isopentenylation of selenocysteine-tRNA([Ser]Sec) (Sec-tRNA), the singular tRNA to decode the unusual amino acid selenocysteine. The functionally indispensable isopentenylation of Sec-tRNA requires a unique intermediate from the mevalonate pathway, isopentenyl pyrophosphate, which concomitantly constitutes the central building block for cholesterol biosynthesis, and whose formation is suppressed by statins and fibrates. The resultant inhibition of Sec-tRNA isopentenylation profoundly decreases selenoprotein expression. This effect might seamlessly explain the immunosuppressive, redox, endothelial, sympatholytic, and thyroidal effects of statins and fibrates as well as their common side effects and drug interactions.

Characterization of endothelium-dependent relaxation and modulation by treatment with pioglitazone in the hypercholesterolemic rabbit renal artery

The present study was undertaken to investigate vascular function in hypercholesterolemic rabbits and also to characterize the effects of pioglitazone on it. Rabbits were fed normal, 0.5% cholesterol chow, or 0.5% cholesterol chow plus 300 ppm pioglitazone for 5 or 10 weeks. The tension of isolated renal artery rings was measured isometrically, and morphometric analysis was performed. The cholesterol chow diet administered for 5 weeks did not affect acetylcholine-induced relaxation in the renal artery but that for 10 weeks decreased it. The N(G)-nitro-L-arginine (L-NOARG)- and indomethacin-resistant endothelium-dependent relaxation induced by acetylcholine in the renal artery was enhanced in rabbits receiving the cholesterol chow for 5 or 10 weeks, as compared to rabbits receiving the control diet, and the percentage of plaque area formation was increased in the renal artery by the cholesterol chow for 10 weeks. Pioglitazone normalized them without lowering serum lipid levels. The resistant parts of acetylcholine-induced relaxation was significantly inhibited when the renal artery was treated with charybdotoxin, an inhibitor of large and intermediate conductance Ca(2+)-activated K(+) channels, or N,N-diethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF 525a), a cytochrome P-450 monooxygenase inhibitor. Results indicate that hypercholesterolemia enhances endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation in the rabbit renal artery and pioglitazon normalizes it without lowering serum lipid levels, and suggest that the maintenance of endothelial function by pioglitazon is related to the mechanisms for its anti-atheromatous activity.

Gene expression profiling of potential PPARgamma target genes in mouse aorta

Diminished activity of peroxisome proliferator-activated receptor-gamma (PPARgamma) may play a role in the pathogenesis of hypertension and vascular dysfunction. To better understand what genes are regulated by PPARgamma, an experimental data set was generated by microarray analysis, in duplicate, of pooled aortic mRNA isolated from mice treated for 21 days with a PPARgamma agonist (rosiglitazone) or vehicle. Of the 12,488 probe sets present on the array (Affymetrix MG-U74Av2), 181 were differentially expressed between groups according to a statistical metric generated using Affymetrix software. A significant correlation was observed between the microarray results and real-time RT-PCR analysis of 39 of these genes. Cluster analysis revealed 3 expression patterns, 29 transcripts of moderate abundance that were decreased (-93%) to very low levels, 106 transcripts that were downregulated (-42%), and 46 transcripts that were upregulated (+70%). Functional groups that were decreased included inflammatory response (-93%, n = 6), immune response (-86%, n = 7), and cytokines (-82%, n = 7). There was an overall upregulation in the oxidoreductase activity group (+47%, n = 9). Individually, six transcripts in this group were increased (+72%), and three were decreased (-34%). Fourteen of the genes map to regions in the rat genome that have been linked to increased blood pressure, and of 142 upstream regions analyzed, sequences resembling the DNA binding site for PPARgamma were identified in 101 of the differentially expressed genes.