Potential roles of the peroxisome proliferator-activated receptor-gamma in macrophage biology and atherosclerosis

Management of Obesity-Related Inflammatory and Cardiovascular Diseases by Medicinal Plants: From Traditional Uses to Therapeutic Targets

Inflammation is a crucial factor in the development and progression of cardiovascular diseases (CVD). Cardiac remodeling in the presence of persistent inflammation leads to myocardial fibrosis and extracellular matrix changes, which reduce cardiac function, induce arrhythmias, and finally, cause heart failure. The majority of current CVD treatment plans concentrate on reducing risk factors such as hyperlipidemia, type 2 diabetes, and hypertension. One such strategy could be inflammation reduction. Numerous in vitro, animal, and clinical studies indicate that obesity is associated with low-grade inflammation. Recent studies have demonstrated the potential of medicinal plants and phytochemicals to cure and prevent obesity and inflammation. In comparison to conventional therapies, the synergistic effects of several phytochemicals boost their bioavailability and impact numerous cellular and molecular targets. Focusing on appetite, pancreatic lipase activity, thermogenesis, lipid metabolism, lipolysis and adipogenesis, apoptosis in adipocytes, and adipocyte life cycle by medicinal plants and phytochemicals represent an important goal in the development of new anti-obesity drugs. We conducted an extensive review of the literature and electronic databases, including Google Scholar, PubMed, Science Direct, and MedlinePlus, for collecting data on the therapeutic effects of medicinal plants/phytochemicals in curing obesity and its related inflammation and CVD diseases, including cellular and molecular mechanisms, cytokines, signal transduction cascades, and clinical trials.

Prevention and Treatment of Obesity-Related Inflammatory Diseases by Edible and Medicinal Plants and Their Active Compounds

Obesity, defined by excessive fat mass and its associated low-grade chronic inflammation, leads to insulin resistance, diabetes, and metabolic dysfunctions. The immunomodulatory properties of natural agents have gained much interest in recent decades. Some of the plant-derived agents are known to be immunomodulators that can affect both innate and adaptive immunity, e.g., thymoquinone, curcumin, punicalagin, resveratrol, quercetin, and genistein. Natural immunomodulators may contribute to the treatment of a number of inflammatory diseases, as they have significant efficacy and safety profiles. The immunomodulatory effects of traditional Greco-Arab and Islamic diets and medicinal plants are well acknowledged in abundant in vitro studies as well as in animal studies and clinical trials. This review highlights the role of Greco-Arab and Islamic diets and medicinal plants in the management of inflammation associated with obesity. Although previously published review articles address the effects of medicinal plants and phytochemicals on obesity-related inflammation, there is no systematic review that emphasizes clinical trials of the clinical significance of these plants and phytochemicals. Given this limitation, the objective of this comprehensive review is to critically evaluate the potential of the most used herbs in the management of obesity-related inflammation based on clinical trials.

Monocyte chemoattractant protein-1 gene (MCP-1) polymorphisms are associated with risk of premature coronary artery disease in Mexican patients from the Genetics of Atherosclerotic Disease (GEA) study

The CC chemokine monocyte chemoattractant protein (MCP)-1/CCL2 is involved in the formation, progression, and destabilization of atheromatous plaques and plays an essential role in postinfarction remodeling. The aim of the present study was to evaluate the role of MCP-1 gene polymorphisms as susceptibility markers for premature coronary artery disease (CAD) and cardiovascular risk factors in the Mexican population. Four MCP-1 gene polymorphisms (rs1024611, rs2857654, rs3760396, and rs1024610) were genotyped by 5' exonuclease TaqMan assays in a group of 1072 patients with premature CAD, and 1082 healthy unrelated controls (with negative calcium score by computed tomography) seeking for associations with premature CAD and other metabolic and cardiovascular risk factors using logistic regression analyses. MCP-1 polymorphism frequencies were similar in premature CAD patients and healthy controls. When the analysis included only those premature CAD patients without type 2 diabetes mellitus (T2DM), the rs1024610 polymorphism was associated with increased risk of developing premature CAD under dominant and additive models adjusted by age and gender (OR=1.33, Pdom=0.040 and OR=1.34, Padd=0.027). The effect of the MCP-1 polymorphisms on various metabolic cardiovascular risk factors and metabolic parameters was explored separately in controls, and premature CAD. In this analysis adjusted by age and gender, the rs3760396 CC genotype was associated with low levels of gamma-glutamyl transpeptidase (P=0.002), whereas, the rs1024610 TT genotype was associated with decreased risk of T2DM (P=0.035) in premature CAD patients. One haplotype (CATG) was associated with increased risk of developing premature CAD (OR=1.44, P=0.0019). In summary, in our study, the rs1024610 polymorphism was associated with increased risk of developing premature CAD only in those patients without T2DM. The four MCP-1 polymorphisms were in high linkage disequilibrium and one haplotype was significantly associated with risk of developing premature CAD.

IL-24 gene polymorphisms are associated with cardiometabolic parameters and cardiovascular risk factors but not with premature coronary artery disease: the genetics of atherosclerotic disease Mexican study

Coronary artery disease (CAD) is a multifactorial and polygenic disorder that results from an excessive inflammatory response. We analyzed whether interleukin-24 (IL-24) gene polymorphisms are associated with premature CAD in a case-control association study. Four polymorphisms (rs1150253, rs1150256, rs1150258, and rs3762344) of the IL-24 gene were analyzed by 5' exonuclease TaqMan genotyping assays in a group of 952 patients with premature CAD, 284 individuals with subclinical atherosclerosis (SA), and 912 controls. The studied polymorphisms were not associated with the risk of premature CAD or SA (P>0.05). Under dominant models adjusted for age, sex, body mass index, and medication, the polymorphisms were associated with cardiometabolic parameters and cardiovascular risk factors. Three polymorphisms (rs1150253, rs1150256, and rs3762344) were associated with hypertension and increased levels of systolic blood pressure in controls. In SA, 2 polymorphisms (rs1150256 and rs3762344) were associated with type 2 diabetes mellitus, gamma-glutamyl transpeptidase (GGT), and alkaline phosphatase, whereas rs1150253 was associated with GGT and type 2 diabetes mellitus and rs1150258 with GGT and alkaline phosphatase. In premature CAD, the 4 polymorphisms were associated with total cholesterol >200 mg/dL, low-density lipoprotein cholesterol (LDL-C), and GGT, whereas rs1150256 was associated also with ApoA. On the other hand, rs1150258 was associated with ApoA, LDL-C >100 mg/dL, and apoB/apoA ratio, and rs3762344 with ApoA, apoB/apoA ratio, LDL-C >100 mg/dL, and total cholesterol. On the basis of single-nucleotide polymorphism functional prediction software, rs1150253 and rs1150258 polymorphisms seem to be functional. The 4 studied polymorphisms were in linkage disequilibrium and had a similar haplotype distribution in patients and controls. Our study demonstrates the association of IL-24 polymorphisms with metabolic and cardiovascular risk factors in individuals with premature CAD, SA, and controls.

Modulating peroxisome proliferator-activated receptors for therapeutic benefit? Biology, clinical experience, and future prospects

Clinical trials of cardiovascular disease (CVD) prevention in patients with type 2 diabetes mellitus primarily have been directed at the modification of a single major risk factor; however, in trials that enroll patients with and without diabetes, the absolute risk in CVD events remains higher in patients with diabetes. Efforts to reduce the macrovascular and microvascular residual risk have been directed toward a multifactorial CVD risk-factor modification; nonetheless, long-term complications remain high. Dual-peroxisome proliferator-activated receptor (PPAR) α/γ agonists may offer opportunities to lower macrovascular and microvascular complications of type 2 diabetes mellitus beyond the reductions achieved with conventional risk-factor modification. The information presented elucidates the differentiation of compound-specific vs class-effect properties of PPARs as the basis for future development of a new candidate molecule. Prior experience with thiazolidinediones, an approved class of PPARγ agonists, and glitazars, investigational class of dual-PPARα/γ agonists, also provides important lessons about the risks and benefits of targeting a nuclear receptor while revealing some of the future challenges for regulatory approval.

Activation of peroxisome proliferator activated receptor-gamma results in an atheroprotective apolipoprotein profile in HepG2 cells

BACKGROUND

Insulin resistance is linked to dyslipidemia, characterized by a decrease in high density lipoproteins and an increase in low density lipoproteins. Thiazolidinediones (TZDs) are insulin-sensitizing agents used to improve glycemic control in patients with type 2 diabetes. Recently, the safety of certain TZD regimens has been questioned because of associated adverse effects on the plasma lipid profile. We examined the effect of a TZD, Ciglitazone, on apolipoprotein synthesis and secretion in human liver HepG2 cells.

METHODS AND RESULTS

The effect of Ciglitazone treatment on apolipoprotein synthesis was addressed at the level of transcription, translation and secretion. RT-PCR showed that Ciglitazone increased the transcription of apoE and apoAI but reduced the levels of apoCI and apoB mRNA. Western blot analysis showed an increase in apoAI and apoE secreted in the cell culture media, whereas the amounts of apoB100 and apoCI were reduced. To confirm that Ciglitazone regulates apolipoprotein translation, its effect on de novo protein synthesis was evaluated by metabolic labeling with [³⁵S]-methionine/cysteine, and a similar pattern of regulation was observed. The change in apolipoprotein levels was not secondary to cholesterol biosynthesis or clearance, since Ciglitazone did not regulate the transcription of HMGCoA reductase, or the LDL receptor. However, mRNA levels for both PPAR-γ and LXRα were induced, suggesting a role for either or both receptors in modulating the hepatic apolipoprotein profile. The involvement of these nuclear receptor transcription factors was confirmed since direct activation of these receptors by endogenous PPAR-γ ligand, 15d-prostaglandin J₂, or LXRα ligand, 22(R)hydroxycholesterol, similarly upregulated apoAI and apoE, but down-regulated apoB100 protein synthesis.

CONCLUSION

Our results suggest that Ciglitazone treatment results in an atheroprotective lipoprotein profile in liver cells. Thus, while the adipose and muscle tissues may be primary targets in TZD-mediated glucose homeostasis, liver PPAR-γ contributes significantly to the regulation of plasma lipoprotein profile.

PPARgamma Agonists: Potential as Therapeutics for Neovascular Retinopathies

The angiogenic, neovascular proliferative retinopathies, proliferative diabetic retinopathy (PDR), and age-dependent macular degeneration (AMD) complicated by choroidal neovascularization (CNV), also termed exudative or “wet” AMD, are common causes of blindness. The antidiabetic thiazolidinediones (TZDs), rosiglitazone, and troglitazone are PPARγ agonists with demonstrable antiproliferative, and anti-inflammatory effects, in vivo, were shown to ameliorate PDR and CNV in rodent models, implying the potential efficacy of TZDs for treating proliferative retinopathies in humans. Activation of the angiotensin II type 1 receptor (AT1-R) propagates proinflammatory and proliferative pathogenic determinants underlying PDR and CNV. The antihypertensive dual AT1-R blocker (ARB), telmisartan, recently was shown to activate PPARγ and improve glucose and lipid metabolism and to clinically improve PDR and CNV in rodent models. Therefore, the TZDs and telmisartan, clinically approved antidiabetic and antihypertensive drugs, respectively, may be efficacious for treating and attenuating PDR and CNV humans. Clinical trials are needed to test these possibilities.

Functional food targeting the regulation of obesity-induced inflammatory responses and pathologies

Obesity is associated with a low-grade systemic chronic inflammatory state, characterized by the abnormal production of pro- and anti-inflammatory adipocytokines. It has been found that immune cells such as macrophages can infiltrate adipose tissue and are responsible for the majority of inflammatory cytokine production. Obesity-induced inflammation is considered a potential mechanism linking obesity to its related pathologies, such as insulin resistance, cardiovascular diseases, type-2 diabetes, and some immune disorders. Therefore, targeting obesity-related inflammatory components may be a useful strategy to prevent or ameliorate the development of such obesity-related diseases. It has been shown that several food components can modulate inflammatory responses in adipose tissue via various mechanisms, some of which are dependent on peroxisome proliferator-activated receptor γ (PPARγ), whereas others are independent on PPARγ, by attenuating signals of nuclear factor-κB (NF-κB) and/or c-Jun amino-terminal kinase (JNK). In this review, we introduce the beneficial effects of anti-inflammatory phytochemicals that can help prevent obesity-induced inflammatory responses and pathologies.

Regulation of Translational Efficiency by Disparate 5' UTRs of PPARgamma Splice Variants

The PPAR-gamma gene encodes for at least 7 unique transcripts due to alternative splicing of five exons in the 5'-untranslated region (UTR). The translated region is encoded by exons 1-6, which are identical in all isoforms. This study investigated the role of the 5'-UTR in regulating the efficiency with which the message is translated to protein. A coupled in vitro transcription-translation assay demonstrated that PPAR-gamma1, -gamma2, and -gamma5 are efficiently translated, whereas PPAR-gamma4 and -gamma7 are poorly translated. An in vivo reporter gene assay using each 5'-UTR upstream of the firefly luciferase gene showed that the 5'-UTRs for PPAR-gamma1, -gamma2, and -gamma4 enhanced translation, whereas the 5'-UTRs for PPAR-gamma5 and -gamma7 inhibited translation. Models of RNA secondary structure, obtained by the mfold software, were used to explain the mechanism of regulation by each 5'-UTR. In general, it was found that the translational efficiency was inversely correlated with the stability of the mRNA secondary structure, the presence of base-pairing in the consensus Kozak sequence, the number of start codons in the 5'-UTR, and the length of the 5'-UTR. A better understanding of posttranscriptional regulation of translation will allow modulation of protein levels without altering transcription.

Oxidised LDL up-regulate CD36 expression by the Nrf2 pathway in 3T3-L1 preadipocytes

The effect of oxLDL on CD36 expression has been assessed in preadipocytes induced to differentiate. Novel evidence is provided that oxLDL induce a peroxisome proliferator-activated receptor gamma-independent CD36 overexpression, by up-regulating nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2). The nuclear translocation of Nrf2 appeared to depend on PKC pathway activation. In adipocytes, the CD36 up-regulation may indicate a compensation mechanism to meet the demand of excess oxLDL and oxidised lipids in blood, reducing the risk of atherogenesis. Besides strengthening the hypothesis that oxLDL can contribute to the onset of insulin-resistance, data herein presented highlight the significance of oxLDL-induced CD36 overexpression within the cellular defence response.

Chronic exposure to schistosome eggs reduces serum cholesterol but has no effect on atherosclerotic lesion development

Previous studies have shown that people infected with schistosomiasis have lower levels of serum cholesterol than uninfected controls. To better understand the impact of this parasitic infection on serum cholesterol levels and on atherosclerotic lesion development induced by hypercholesterolemia, apolipoprotein E (ApoE)-deficient mice were chronically exposed to the eggs of Schistosoma mansoni over a period of 16 weeks. Total serum cholesterol and low-density lipoprotein (LDL) were reduced in egg-exposed ApoE-deficient mice fed a diet high in cholesterol compared to unexposed controls. However, exposure to eggs had no effect on atherosclerotic lesion size or progression in ApoE-deficient mice. Macrophages isolated from egg-exposed mice had an enhanced ability to take up LDL but not acetylated LDL (acLDL). This study suggests that schistosome eggs alone may alter serum lipid profiles through enhancing LDL uptake by macrophages, but these changes do not ultimately affect atherosclerotic lesion development.

An essential function of the SRC-3 coactivator in suppression of cytokine mRNA translation and inflammatory response

Steroid receptor coactivator-3 (SRC-3) is a transcriptional coactivator for nuclear receptors and other transcription factors. Although multiple physiological roles of SRC-3 have been revealed, its involvement in the inflammatory process remains unclear. Herein we show that SRC-3(-/-) mice are markedly hypersensitive to LPS-induced endotoxic shock. In response to LPS, SRC-3(-/-) macrophages produce significantly more proinflammatory cytokines such as TNF-alpha, IL-6, and IL-1beta than wild-type controls, although they express similar amounts of cytokine mRNAs, suggesting that SRC-3 can exert effects at translational levels. Increased heavy polysome-associated TNF-alpha and IL-1beta mRNAs in SRC-3(-/-) macrophages implicate SRC-3 as a translational repressor. SRC-3 may cooperate with other translational repressors such as TIA-1 and TIAR to regulate cytokine mRNA translation. Collectively, our studies reveal an essential function of SRC-3 as a coordinator of inflammatory mRNA translation and as a physiologic protective factor against the lethal endotoxic shock triggered by an acute inflammatory response.

Cytokine response to lipoprotein lipid loading in human monocyte-derived macrophages

Background

Macrophage foam cell formation is a prominent feature of human atherosclerotic plaques, usually considered to be correlated to uptake of and inflammatory response to oxidized low density lipoproteins (OxLDL). However, there are alternative pathways for formation of macrophage foam cells and the effect of such lipid loading on macrophage function remains to be fully characterized. In the present study we investigated basal and inducible cytokine expression in primary human macrophages either loaded with triglycerides through incubation with very low density lipoproteins (VLDL) or with cholesterol through incubation with aggregated LDL (AgLDL). We then analyzed how foam cell lipid content affected secretion of three pro-inflammatory cytokines: interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), and of one chemokine: interleukin-8 (IL-8), all of which are considered pro-inflammatory, pro-atherosclerotic, and are expressed by cells in atherosclerotic tissue.

Results

Formation of triglyceride-loaded foam cells resulted in a four-fold increase in basal IL-1β secretion, whereas cholesterol loading lacked significant effect on IL-1β secretion. In contrast, secretion of TNF-α and IL-6 decreased significantly following both cholesterol and triglyceride loading, with a similar trend for secretion of IL-8. Lipid loading did not affect cell viability or expression of caspase-3, and did not significantly affect macrophage ability to respond to stimulation with exogenous TNF-α.

Conclusion

Lipid loading of primary human macrophages resulted in altered cytokine secretion from cells, where effects were similar regardless of neutral lipid composition of cells. The exception was IL-1β, where triglyceride, but not cholesterol, lipid loading resulted in a stimulation of basal secretion of the cytokine. It is apparent that macrophage cytokine secretion is affected by lipid loading by lipoproteins other than OxLDL. As both VLDL and AgLDL have been found in the vessel wall, macrophage cytokine response to uptake of these lipoproteins may have a direct effect on atherosclerotic development in vivo. However, macrophage neutral lipid amount and composition did not affect cellular activation by exogenous TNF-α, making it likely that lipoprotein lipid loading can affect foam cell cytokine secretion during basal conditions but that the effects can be overruled by TNF-α during acute inflammation.

Identification and regulation of novel PPAR-gamma splice variants in human THP-1 macrophages

We have previously identified four novel isoforms of PPAR-gamma transcripts in monkey macrophages (J. Zhou, K.M. Wilson, J.D. Medh, Genetic analysis of four novel peroxisome proliferator receptor-gamma splice variants in monkey macrophages. Biochem. Biophys. Res. Commun., 293 (2002) 274-283). The purpose of this study was to ascertain that these isoforms are also present in humans. Specific primers were designed to amplify individual isoform transcripts. The presence of PPAR-gamma4, PPAR-gamma5, and PPAR-gamma7 transcripts in human THP-1 macrophages was confirmed by RT-PCR and sequencing. A transcript corresponding to PPAR-gamma6 was not detected. The presence of novel full-length transcripts and protein was also ascertained by Northern and Western blot analysis. Treatment of THP-1 cells with 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) resulted in more than 20% induction in the expression of PPAR-gamma5 and PPAR-gamma7 transcripts by both Northern blot analysis and RT-PCR. Another PPAR-gamma ligand, troglitazone, induced expression of only PPAR-gamma5. Both ligands inhibited the expression of PPAR-gamma1 and PPAR-gamma2. Additionally, 15d-PGJ2 and troglitazone increased the level of apolipoprotein E transcript by 60% but decreased lipoprotein lipase expression by 15% in THP-1 cells. The differential regulation of PPAR-gamma transcripts suggests that each transcript isoform may contribute to macrophage function.

Monosodium urate and calcium pyrophosphate dihydrate (CPPD) crystals, inflammation, and cellular signaling

Monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) crystals are responsible for acute synovial inflammation but also contribute to cartilage degradation and bone lesions within the joint. They activate multiple signal transduction pathways leading to cell activation and recruitment. Some signalling pathways are activated by both types of crystals, and other pathways may only be activated by one type depending on cell type, namely neutrophils, monocytes, macrophages, synovial fibroblasts, endothelial cells and chondrocytes. Cascades of activated proteins involve cytoplasmic membrane related proteins (FAK complex, Src family tyrosine kinases), but also MAPK and NF-kB pathways, leading to NO, prostanoid and cytokine production, and protease activation. This review will also focus on potential therapeutic targets related to cellular signalling in MSU and CPPD crystal-induced inflammation.

Differential Effects of Lipoprotein Lipase on Tumor Necrosis Factor-α and Interferon-γ-mediated Gene Expression in Human Endothelial Cells

Lipoprotein lipase (LPL) is a key enzyme in the hydrolysis of triglyceride-rich lipoproteins. In vascular diseases, such as atherosclerosis, inflammation plays an important role in the pathogenesis of the disease. We examined the role of LPL in modulating tumor necrosis factor-alpha (TNF-alpha)- and interferon-gamma (IFN-gamma)-mediated inflammatory cytokine signal transduction pathways in human aortic endothelial cells (HAECs). LPL significantly suppressed TNF-alpha-induced gene expression, and this suppression was reversed by tetrahydrolipstatin and heparinase. In contrast, LPL synergistically enhanced IFN-gamma-induced gene expression in HAECs. To elucidate the molecular mechanisms of LPL action, we investigated the role of transcription factors nuclear factor kappa B (NF-kappaB) and signal transducer and activator of transcription factor 1 (Stat1). The anti-inflammatory response of LPL in suppressing TNF-alpha-induced gene expression was a result of its inhibition of NF-kappaB activity by the abrogation of IkappaB-alpha degradation and phosphorylation of the p65 subunit. Although LPL alone had no effect on Stat1 activation, LPL enhanced IFN-gamma-induced phosphorylation of Stat1 on tyrosine 701 and serine 727, as well as Stat1-mediated transactivation. The synergistic effect of LPL on IFN-gamma-induced Stat1 activation was mediated by enhanced activation of the tyrosine kinase JAK2 and was abrogated by LY294002, a specific inhibitor of the phosphatidylinositol 3'-kinase pathway. Our studies indicate that LPL has differential effects on several inflammatory pathways known to be important in atherosclerosis.

Modulation of cytokine-induced cyclooxygenase 2 expression by PPARG ligands through NFkappaB signal disruption in human WISH and amnion cells

Cyclooxygenase (COX) activity increases in the human amnion in the settings of term and idiopathic preterm labor, contributing to the generation of uterotonic prostaglandins (PGs) known to participate in mammalian parturition. Augmented COX activity is highly correlated with increased COX2 (also known as prostaglandin-endoperoxide synthase 2, PTGS2) gene expression. We and others have demonstrated an essential role for nuclear factor kappaB (NFkappaB) in cytokine-driven COX2 expression. Peroxisome proliferator-activated receptor gamma (PPARG), a member of the nuclear hormone receptor superfamily, has been shown to antagonize NFkappaB activation and inflammatory gene expression, including COX2. We hypothesized that PPARG activation might suppress COX2 expression during pregnancy. Using primary amnion and WISH cells, we evaluated the effects of pharmacological (thiazolidinediones) and putative endogenous (15-deoxy-Delta(12,14)-prostaglandin J2, 15d-PGJ2) PPARG ligands on cytokine-induced NFkappaB activation, COX2 expression, and PGE2 production. We observed that COX2 expression and PGE2 production induced by tumor necrosis factor alpha (TNF) were significantly abrogated by 15d-PGJ2. The thiazolidinediones rosiglitazone (ROSI) and troglitazone (TRO) had relatively little effect on cytokine-induced COX2 expression except at high concentrations, at which these agents tended to increase COX2 abundance relative to cells treated with TNF alone. Interestingly, treatment with ROSI, but not TRO, led to augmentation of TNF-stimulated PGE2 production. Mechanistically, we observed that 15d-PGJ2 markedly diminished cytokine-induced activity of the NFkappaB transcription factor, whereas thiazolidinediones had no discernable effect on this system. Our data suggest that pharmacological and endogenous PPARG ligands use both receptor-dependent and -independent mechanisms to influence COX2 expression.

Inhibition of corneal neovascularization by a peroxisome proliferator-activated receptor-gamma ligand

PURPOSE

To determine the efficacy of the peroxisome proliferator-activated receptor gamma agonist, pioglitazone, in inhibiting corneal neovascularization.

METHODS

Twenty-six adult male Sprague-Dawley rats were randomly divided into three groups. Each group received intrastromal polymer micropellets containing one of the following: Group 1, no active ingredient (n=10); Group 2, vascular endothelial growth factor (VEGF) (n=7); Group 3, VEGF and pioglitazone (n=9). Neovascularization was evaluated 7 days after pellet implantation. After systemic India ink injection, digital photographs of the eyes were taken. The area and density of neovascularization were measured using imaging software.

RESULTS

Mean area of neovascularization was 0.43+/-0.18 mm2 for Group 1, 2.87+/-0.48 mm2 for Group 2 and 2.10+/-0.22 mm2 for Group 3. Statistical analysis showed significant differences between Groups 1 and 2 and Groups 1 and 3. There was no significant difference between Groups 2 and 3. Mean density of neovascularization was 2.16+/-0.66 for Group 1, 27.14+/-2.93 for Group 2 and 12.02+/-2.24 for Group 3. All comparisons between groups were statistically significant (P<0.01).

CONCLUSIONS

Pioglitazone is effective in decreasing the density of angiogenesis in a VEGF-induced neovascular rat cornea model. There is possibility of even greater effect with higher doses of the drug. Pioglitazone is a promising drug for the treatment of ocular neovascularization.

Mouse Strain–Specific Differences in Vascular Wall Gene Expression and Their Relationship to Vascular Disease

Objective— Different strains of inbred mice exhibit different susceptibility to the development of atherosclerosis. The C3H/HeJ and C57Bl/6 mice have been used in several studies aimed at understanding the genetic basis of atherosclerosis. Under controlled environmental conditions, variations in susceptibility to atherosclerosis reflect differences in genetic makeup, and these differences must be reflected in gene expression patterns that are temporally related to the development of disease. In this study, we sought to identify the genetic pathways that are differentially activated in the aortas of these mice.

Methods and Results— We performed genome-wide transcriptional profiling of aortas from C3H/HeJ and C57Bl/6 mice. Differences in gene expression were identified at baseline as well as during normal aging and longitudinal exposure to high-fat diet. The significance of these genes to the development of atherosclerosis was evaluated by observing their temporal pattern of expression in the well-studied apolipoprotein E model of atherosclerosis.

Conclusion— Gene expression differences between the 2 strains suggest that aortas of C57Bl/6 mice have a higher genetic propensity to develop inflammation in response to appropriate atherogenic stimuli. This study expands the repertoire of factors in known disease-related signaling pathways and identifies novel candidate genes for future study.

Will the potential of peroxisome proliferator-activated receptor agonists be realized in the clinical setting?

Drugs targeting both peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists (the thiazolidinediones) and PPAR-alpha (the fibrates) have already been developed for clinical use. However, the thiazolidinediones, currently prescribed to treat hyperglycemia and improve peripheral insulin resistance, may also have cardiovascular benefits that have yet to be fully realized. Animal models of atherosclerosis have shown that the thiazolidinediones reduce the extent of atherosclerotic lesions and inhibit macrophage accumulation. Clinical studies have also shown that these drugs improve the lipid profile of patients at risk of developing atherosclerosis and reduce circulating levels of inflammatory markers. This combination of lower lipid concentrations and reduced inflammation may explain the cardiovascular benefits of this class of drugs. Early trials in patients with coronary stents have reported promising findings, with restenosis rates being greatly reduced with thiazolidinedione therapy. It is hoped that the results of future clinical trials will continue to be encouraging, so that the thiazolidinediones' cardiovascular benefits can be fully realized in the clinic.

Modulation of PPARalpha expression and inflammatory interleukin-6 production by chronic glucose increases monocyte/endothelial adhesion

OBJECTIVE

We have previously reported increased monocyte adhesion to human aortic endothelial cells (HAECs) cultured in 25 mmol/L glucose (HG) compared with normal glucose (NG) (5.5 mmol/L). In this study, we explored mechanisms that contribute to increased monocyte adhesion by elevated glucose.

METHODS AND RESULTS

We found that HAECs cultured in HG have increased production of the chemokine interleukin-6 (IL-6). We examined whether IL-6 directly modulated monocyte adhesion to EC. Inhibition of IL-6 using a neutralizing antibody significantly reduced glucose-mediated monocyte adhesion by 50%, and addition of IL-6 directly to human EC stimulated monocyte adhesion. PPARalpha has been reported to negatively regulate expression of IL-6 in vascular cells, so we examined PPARalpha-associated signaling in EC. A known PPARalpha agonist, Wy14,643, prevented glucose-mediated IL-6 production by EC and reduced glucose-mediated monocyte adhesion by 40%. HG-cultured HAEC had a 50% reduction in expression of PPARalpha compared with control EC. Primary aortic EC isolated from PPARalpha knockout (KO) mice showed increased monocyte adhesion compared with EC isolated from control mice. PPARalpha KO EC also had increased production of IL-6. Finally, we measured IL-6 levels in diabetic db/db mice and found significant 6-fold elevations in IL-6 levels in db/db EC.

CONCLUSIONS

These data indicate that IL-6 production is increased in diabetes and contributes to early vascular inflammatory changes. PPARalpha protects EC from glucose-mediated monocyte adhesion, in part through regulation of IL-6 production.

Role of Nrf2 in the regulation of CD36 and stress protein expression in murine macrophages: activation by oxidatively modified LDL and 4-hydroxynonenal

CD36 is an important scavenger receptor mediating uptake of oxidized low-density lipoproteins (oxLDLs) and plays a key role in foam cell formation and the pathogenesis of atherosclerosis. We report the first evidence that the transcription factor Nrf2 is expressed in vascular smooth muscle cells, and demonstrate that oxLDLs cause nuclear accumulation of Nrf2 in murine macrophages, resulting in the activation of genes encoding CD36 and the stress proteins A170, heme oxygenase-1 (HO-1), and peroxiredoxin I (Prx I). 4-Hydroxy-2-nonenal (HNE), derived from lipid peroxidation, was one of the most effective activators of Nrf2. Using Nrf2-deficient macrophages, we established that Nrf2 partially regulates CD36 expression in response to oxLDLs, HNE, or the electrophilic agent diethylmaleate. In murine aortic smooth muscle cells, expressing negligible levels of CD36, both moderately and highly oxidized LDL caused only limited Nrf2 translocation and negligible increases in A170, HO-1, and Prx I expression. However, treatment of smooth muscle cells with HNE significantly enhanced nuclear accumulation of Nrf2 and increased A170, HO-1, and Prx I protein levels. Because PPAR-gamma can be activated by oxLDLs and controls expression of CD36 in macrophages, our results implicate Nrf2 as a second important transcription factor involved in the induction of the scavenger receptor CD36 and antioxidant stress genes in atherosclerosis.

Novel actions of thiazolidinediones on vascular function and exercise capacity

The endothelium is the first line of defense for maintaining normal vascular function in the vessel wall; however, the endothelium is sensitive to metabolic stress. In patients with insulin resistance or type 2 diabetes mellitus, a set of metabolic insults--namely high plasma levels of glucose and free fatty acids, increased inflammation, dyslipidemia, and hypertension--cause endothelial dysfunction and a transition from an antiatherogenic endothelium to a proatherogenic endothelium. Disruption of endothelial function leads to activation of platelets and macrophages, increased thrombotic potential, transition of macrophages to foam cells, stimulation of cytokine secretion, and proliferation of vascular smooth muscle cells. Insulin-sensitizing agents, such as the thiazolidinediones (TZDs), improve flow-mediated vasodilation, decrease macrophage and smooth muscle cell activation, proliferation, and migration, and decrease plaque formation. The TZDs exert multifaceted effects on the vasculature by regulating the expression of transcription factors and orchestrating whole-gene programs that restore vascular physiology to the healthy state. Exercise training and increased levels of habitual physical activity have therapeutic benefit in terms of both preventing and treating insulin resistance and diabetes. However, this benefit of exercise training and increased physical activity is complicated by the fact that individuals with insulin resistance or type 2 diabetes have decreased maximal exercise capacity or maximal oxygen consumption and have slower oxygen uptake kinetics at the beginning of exercise. Both of these abnormalities contribute to the decreased levels of habitual physical activity observed in patients with diabetes. Preliminary data suggest that TZDs improve measures of cardiac function and exercise capacity, and investigators are assessing the impact of treatment with rosiglitazone on exercise capacity in an ongoing clinical trial.

Abietic acid activates peroxisome proliferator-activated receptor-gamma (PPARgamma) in RAW264.7 macrophages and 3T3-L1 adipocytes to regulate gene expression involved in inflammation and lipid metabolism

Abietic acid is one of the terpenoids, which are multifunctional natural compounds. It has been reported that abietic acid suppresses effects on inflammation. However, the mechanism underlying the anti-inflammatory effects remains unclear. The present work indicates that abietic acid suppresses the protein expression of tumor necrosis factor-alpha and cyclooxygenase 2, which are involved in inflammation, in lipopolysaccharide-stimulated macrophages. Moreover, this effect resembles that of thiazolidinedione, a synthetic peroxisome proliferator-activated receptor-gamma (PPARgamma) ligand. Indeed, abietic acid activates PPARgamma in luciferase reporter assays. The activity of abietic acid induces PPARgamma target gene expression in RAW264.7 macrophages and 3T3-L1 adipocytes. These data indicate that abietic acid is a PPARgamma ligand and that its anti-inflammatory effect is partly due to the activation of PPARgamma in stimulated macrophages. The present work suggests a novel possibility that abietic acid, a naturally occurring compound, can be used not only for anti-inflammation but also for regulating lipid metabolism and atherosclerosis.

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.

The aryl hydrocarbon receptor and its xenobiotic ligands: a fundamental trigger for cardiovascular diseases

This review reconsiders a major cause of cardiovascular diseases, tobacco smoking, as the activation of the Aryl hydrocarbon Receptor (AhR), also known as the dioxin receptor, by aryl hydrocarbons from the tar fraction of tobacco in various organs of the cardiovascular domain. This concept sheds new light on well-known albeit controversial epidemiological concepts such as the Mediterranean diet and the French paradox. We also review the discovery that resveratrol, a natural AhR antagonist, may be of interest in the prevention and treatment of cardiovascular diseases.

Peroxisome proliferator-activated receptors: a critical review on endogenous pathways for ligand generation

Lipid mediators can exert their effects by interactions with well-characterised cell surface G-protein-linked receptors. Recently, a group of intracellular receptors have been identified that are activated by a large variety of lipid-derived mediators. Amongst these novel targets, the peroxisome proliferator-activated receptors (PPARs), a family of three (PPARalpha, beta/delta and gamma) nuclear receptor/transcription factors have become a major area for investigation. PPARs are found throughout the body, where they have diverse roles regulating lipid homeostasis, cellular differentiation, proliferation and the immune response. There is a great interest, therefore, in the roles of PPARs in a variety of pathological conditions, including diabetes, atherosclerosis, cancer and chronic inflammation. Although, a number of naturally occurring compounds can activate PPARs, it has been difficult, as yet, to characterise any of these mediators as truly endogenous ligands. These findings have lead to the suggestion that PPARs may act just as general lipid sensors. Acting as lipid sensors, PPARs may take changes in lipid/fatty acid balance in the diet or local metabolism and translate them to tissue-specific ligands, exerting tissue-specific effects. Using classical pharmacological criteria for endogenous mediator classification we will critically discuss the variety of pathways for putative ligand generation.

The peroxisome proliferator-activated receptor alpha (PPARalpha): role in hepatocarcinogenesis

The peroxisome proliferator-activated receptor alpha (PPARalpha) is a member of the nuclear receptor superfamily and mediates most of the known biological effects of peroxisome proliferators. The latter represents a large group of chemicals that include the fibrate hyperlipidemic drugs, the pthalate plasticizers, various solvents and degreasing agents, and endogenous hormones and fatty acids. Peroxisome proliferators are classical members of the nongenotoxic group of chemical carcinogens that do not require metabolic activation to electrophiles in order to exert their harmful effects. These chemicals are of particular concern to regulatory agencies since they can only be detected by long-term carcinogen bioassays using rodents. The mechanism of the carcinogenic action of peroxisome proliferators is beginning to emerge. PPARalpha-null mice are resistant to hepatocarcinogenesis indicating that this receptor is necessary for cancer. However, recent studies indicate that Kupffer cells, in a PPARalpha independent manor, are required for the major effects of peroxisome proliferators on cell proliferation. An interaction between PPARalpha and estrogen carcinogenesis has also been elucidated.