Peroxisome proliferator-activated receptors: from transcriptional control to clinical practice

Lipoprotein lipase: from gene to obesity

Lipoprotein lipase (LPL) is a multifunctional enzyme produced by many tissues, including adipose tissue, cardiac and skeletal muscle, islets, and macrophages. LPL is the rate-limiting enzyme for the hydrolysis of the triglyceride (TG) core of circulating TG-rich lipoproteins, chylomicrons, and very low-density lipoproteins (VLDL). LPL-catalyzed reaction products, fatty acids, and monoacylglycerol are in part taken up by the tissues locally and processed differentially; e.g., they are stored as neutral lipids in adipose tissue, oxidized, or stored in skeletal and cardiac muscle or as cholesteryl ester and TG in macrophages. LPL is regulated at transcriptional, posttranscriptional, and posttranslational levels in a tissue-specific manner. Nutrient states and hormonal levels all have divergent effects on the regulation of LPL, and a variety of proteins that interact with LPL to regulate its tissue-specific activity have also been identified. To examine this divergent regulation further, transgenic and knockout murine models of tissue-specific LPL expression have been developed. Mice with overexpression of LPL in skeletal muscle accumulate TG in muscle, develop insulin resistance, are protected from excessive weight gain, and increase their metabolic rate in the cold. Mice with LPL deletion in skeletal muscle have reduced TG accumulation and increased insulin action on glucose transport in muscle. Ultimately, this leads to increased lipid partitioning to other tissues, insulin resistance, and obesity. Mice with LPL deletion in the heart develop hypertriglyceridemia and cardiac dysfunction. The fact that the heart depends increasingly on glucose implies that free fatty acids are not a sufficient fuel for optimal cardiac function. Overall, LPL is a fascinating enzyme that contributes in a pronounced way to normal lipoprotein metabolism, tissue-specific substrate delivery and utilization, and the many aspects of obesity and other metabolic disorders that relate to energy balance, insulin action, and body weight regulation.

Pomegranate flower ameliorates fatty liver in an animal model of type 2 diabetes and obesity

AIMS OF THE STUDY

Fatty liver is the most common cause of abnormal liver function tests. We investigated the effect and its underlying mechanism of pomegranate flower (PGF), a traditional antidiabetic medicine, on fatty liver.

MATERIALS AND METHODS

At the endpoint of treatment of male Zucker diabetic fatty (ZDF) rats with PGF extract (500 mg/kg, p.o. x 6 weeks), liver weight index, hepatic lipid contents (enzymatic colorimetric methods) and droplet accumulation (Oil Red O staining) were determined. Gene profiles (RT-PCR) were analyzed in the liver of ZDF rats and in human liver-derived HepG2 cell line.

RESULTS

PGF-treated ZDF rats showed reduced ratio of liver weight to tibia length, hepatic triglyceride contents and lipid droplets. These effects were accompanied by enhanced hepatic gene expression of peroxisome proliferator-activated receptor (PPAR)-alpha, carnitine palmitoyltransferase-1 and acyl-CoA oxidase (ACO), and reduced stearoyl-CoA desaturase-1. In contrast, PGF showed minimal effects on expression of genes responsible for synthesis, hydrolysis or uptake of fatty acid and triglycerides. PGF treatment also increased PPAR-alpha and ACO mRNA levels in HepG2 cells.

CONCLUSION

Our findings suggest that this Unani medicine ameliorates diabetes and obesity-associated fatty liver, at least in part, by activating hepatic expression of genes responsible for fatty acid oxidation.

Modulating effects of chlorogenic acid on lipids and glucose metabolism and expression of hepatic peroxisome proliferator-activated receptor-alpha in golden hamsters fed on high fat diet

OBJECTIVE

To examine the effects of chlorogenic acid (CGA) on lipid and glucose metabolism under a high dietary fat burden and to explore the possible role of peroxisome proliferator-activated receptor-alpha (PPAR-alpha) in these effects.

METHODS

Twenty male golden hamsters were randomly divided into CGA treatment group (n=10, given peritoneal injection of CGA solution prepared with PBS, 80 mg CGA/kg body weight daily), and control group (n=10, given PBS i.p. at the average volume of the treatment group). Animals in both groups were given 15% high fat diet. Eight weeks after treatment with CGA, the level of biochemical parameters in fasting serum and tissues and the expression of hepatic mRNA and protein PPAR-alpha were determined.

RESULTS

Eight weeks after treatment with CGA, the levels of fasting serum triglyceride (TG), free fatty acid (FFA), total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), glucose (FSG), and insulin (FSI) were significantly lower in the GGA treatment group than in the control group. CGA also led to higher activity of hepatic lipase (HL), lower contents of TG and FFA in liver, and lower activity of lipoprotein lipase (LPL) in skeletal muscle. Furthermore, CGA significantly elevated significantly elevated the expression level of mRNA and protein expression in hepatic PPAR-alpha.

CONCLUSION

CGA can modify lipids and glucose metabolism, which may be attributed to PPAR-alpha facilitated lipid clearance in liver and improved insulin sensitivity.

Cholesterol reduction and atherosclerosis inhibition by bezafibrate in low-density lipoprotein receptor knockout mice

Fibrates, peroxisome proliferator-activated receptor a agonists, are widely used as lipid-lowering agents with anti-atherogenic activity. However, conflicting results have been reported with regard to their pharmacological effects on plasma lipoprotein profiles as well as on atherosclerosis in animal models. Furthermore, the anti-atherogenic effects of bezafibrate, one of the most commonly used fibrates, in animal models have not been reported. In the present study, we investigated the effects of bezafibrate on lipoprotein profiles as well as on atherosclerosis in low-density lipoprotein receptor knockout (LDLR-/-) mice fed an atherogenic diet for 8 weeks. Bezafibrate decreased plasma levels of both cholesterol and triglycerides (TG), while increasing plasma levels of high-density lipoprotein-cholesterol (HDL-C). Since hepatic TG production was significantly reduced in the bezafibrate-treated mice lacking LDLR, the plasma lipid-lowering effects of bezafibrate might be primarily mediated by the suppression of hepatic production of apolipoprotein-B-containing lipoproteins. In parallel with the reduced ratio of non-HDL-C to HDL-C, bezafibrate suppressed fatty streak lesions in the aortic sinus by 51%. To determine whether or not bezafibrate directly alters the expression of genes relevant to atherosclerosis, we measured mRNA expression levels of three genes in the aorta by real-time PCR: ATP-binding cassette transporter A1, lipoprotein lipase, and monocyte chemoattractant protein-1. The results showed that there were no differences in the expression of these genes between mice treated with bezafibrate and those not. In conclusion, bezafibrate inhibits atherosclerosis in LDLR-/- mice primarily by decreasing the ratio of non-HDL-C to HDL-C.

An ABC of apolipoprotein C-III: a clinically useful new cardiovascular risk factor?

BACKGROUND

Hypertriglyceridaemia, commonly found in subjects with obesity and type 2 diabetes mellitus, is associated with increased risk of coronary heart disease (CHD). Apolipoprotein C-III (apoC-III) plays an important role in regulating the metabolism of triglyceride-rich lipoproteins (TRLs) and may provide a new approach to assessing hypertriglyceridaemia.

AIMS

We review the role of apoC-III in regulating TRL metabolism and address the potential importance of apoC-III in clinical practice.

DISCUSSION

Hypertriglyceridaemia is chiefly a consequence of alterations in the kinetics of TRLs, including overproduction and delayed clearance of very-low density lipoprotein (VLDL). ApoC-III is an inhibitor of lipoprotein lipase and of TRLs remnant uptake by hepatic lipoprotein receptors. Elevated apoC-III, usually resulting from hepatic overproduction of VLDL apoC-III, may cause accumulation of plasma TRLs leading to hypertriglyceridaemia. The results from recent observational studies demonstrate that apoC-III is a strong predictor of risk for CHD, but this chiefly relates to apoC-III in apoB-containing lipoproteins. Lifestyle and pharmacological intervention can correct hypertriglyceridaemia by a mechanism of action that regulates apoC-III transport.

CONCLUSIONS

Targeting apoC-III metabolism may therefore be an important, new therapeutic approach to managing dyslipidaemia and CHD risk in obesity, insulin resistance and type 2 diabetes mellitus. However, further work is required to establish the practical aspects of measuring apoC-III in routine laboratory service and the precise therapeutic targets for serum total apoC-III and/or apoC-III in apoB-containing lipoproteins. While showing much promise as a potentially useful cardiovascular risk factor, apoC-III is not yet ready for prime time use in clinical practice.

Pomegranate flower: a unique traditional antidiabetic medicine with dual PPAR-alpha/-gamma activator properties

PPARs are transcription factors belonging to the superfamily of nuclear receptors. PPAR-alpha is involved in the regulation of fatty acid (FA) uptake and oxidation, inflammation and vascular function, while PPAR-gamma participates in FA uptake and storage, glucose homeostasis and inflammation. The PPARs are thus major regulators of lipid and glucose metabolism. Synthetic PPAR-alpha or PPAR-gamma agonists have been widely used in the treatment of dyslipidaemia, hyperglycaemia and their complications. However, they are associated with an incidence of adverse events. Given the favourable metabolic effects of both PPAR-alpha and PPAR-gamma activators, as well as their potential to modulate vascular disease, combined PPAR-alpha/-gamma activation has recently emerged as a promising concept, leading to the development of mixed PPAR-alpha/-gamma activators. However, some major side effects associated with the synthetic dual activators have been reported. It is unclear whether this is a specific effect of the particular synthetic compounds or a class effect. To date, a medication that may combine the beneficial metabolic effects of PPAR-alpha and PPAR-gamma activation with fewer undesirable side effects has not been successfully developed. Pomegranate plant parts are used traditionally for the treatment of various disorders. However, only pomegranate flower has been prescribed in Unani and Ayurvedic medicines for the treatment of diabetes. This review provides a new understanding of the dual PPAR-alpha/-gamma activator properties of pomegranate flower in the potential treatment of diabetes and its associated complications.

The PPARgamma agonist FMOC-L-leucine protects both mature and immature brain

(N-[9-fluorenylmethoxycarbonyl]-)-L-leucine (FMOC-L-leucine) and rosiglitazone, two ligands of peroxisome proliferator-activated receptor gamma (PPARgamma), were evaluated in mature (adult mice) and immature (pups) brain injury models. In adult magnesium-deficient mice, a model responsive to both neuroprotective and anti-seizure compounds, FMOC-L-leucine, but not rosiglitazone, protected against audiogenic seizures. The protection afforded by FMOC-L-leucine was alleviated by the PPARgamma antagonist GW9662 (1-2 mg/kg) and was induced in 50% animals by 4.8+/-1.2 mg/kg. At this dose, FMOC-L-leucine modified audiogenic seizure phase durations in convulsing mice differently than prototype antiepileptic drugs did. FMOC-L-leucine (up to 100 mg/kg) was inactive in the 6 Hz seizure test, an adult animal model largely responsive to anti-seizure drugs. In a model of neonatal brain injury, FMOC-L-leucine (4 microg/kg) was neuroprotective against cerebral ibotenate toxicity. It reduced significantly the size of lesions in grey but not in white matter, while rosiglitazone (10 microg/kg) was inactive. Taken as a whole, the present data support neuroprotective potentialities of FMOC-L-leucine towards both mature and immature brain. The PPAR-based protection of immature brain is more important as it is known that classic adult brain protectants (GABA(A) activators, N-methyl-D-aspartate and sodium channel blockers) may be toxic for immature brain. The PPARgamma agonist FMOC-L-leucine is likely to be devoid of these classic protective mechanisms because of its inactivity in the 6 Hz seizure test, its activity in the audiogenic test being explained by neuroprotective rather than intrinsic anti-seizure mechanisms. Targeting PPARs might be thus a promising way to protect immature brain.

Fenofibrate modulates cardiac and hepatic metabolism and increases ischemic tolerance in diet-induced obese mice

Peroxisome proliferator-activated receptors (PPARs) play an important role in the transcriptional regulation of lipid utilization and storage in several organs, including liver and heart. Our working hypothesis is that treatment of obesity/hyperlipedemia with the PPARalpha ligand fenofibrate leads to drainage of plasma lipids by the liver, resulting in reduced myocardial lipid supply, reduced myocardial fatty acid oxidation and improved myocardial tolerance to ischemic stress. Thus, we investigated changes in substrate utilization in heart and liver, as well as post-ischemic functional recovery in hearts from diet-induced obese (DIO) mice following long-term (11-12 weeks) treatment with fenofibrate. The present study shows that DIO mice express increased plasma lipids and glucose, as well as increased myocardial fatty acid oxidation and a concomitant decrease in glucose oxidation. The lipid-lowering effect of fenofibrate was associated with increased hepatic mitochondrial and peroxisomal fatty acid oxidation, as indicated by a more than 30% increase in hepatic palmiotyl-CoA oxidation and more than a 10-fold increase in acyl-CoA oxidase (ACO) activity. In line with an adaptation to the reduced myocardial lipid supply, isolated hearts from fenofibrate-treated DIO mice showed increased glucose oxidation and decreased fatty acid oxidation, as well as reduced ACO activity. Fenofibrate treatment also prevented the diet-induced decrease in cardiac function and improved post-ischemic functional recovery. We also found that, while fenofibrate treatment markedly increased the expression of PPARalpha target genes in the liver, there were no such changes in the heart. These data demonstrate that fenofibrate results in a direct activation of PPARalpha in the liver with increased hepatic drainage of plasma lipids, while the cardiac effect of the compound most likely is secondary to its lipid-lowering effect.

The different mechanisms of insulin sensitizers to prevent type 2 diabetes in OLETF rats

OBJECTIVE

To investigate the effects of pioglitazone and metformin treatment during pre-diabetic period for the prevention of diabetes in a rat model.

METHODS

OLETF rats aged 18-weeks, were treated with pioglitazone (10 mg/kg/day) and metformin (300 mg/kg/day) for 10 weeks from their pre-diabetic period. We measured weight, lipid profiles, fat distribution, glucose tolerance, and pancreatic insulin content.

RESULTS

Prominent weight gain (mostly subcutaneous fat area) was observed in the pioglitazone-treated OLETF (O-P) rats versus significant weight loss was observed in the metformin-treated OLETF (O-M) rats. Pioglitazone reversed the serum triglyceride (TG) and FFAs levels to normal (TG 0.46 +/- 0.04 vs 0.88 +/- 0.05 mmol/l in LETO). At the age of 28 weeks, the O-P rats showed completely normal glucose tolerance, and the glucose disposal rate (GDR) was markedly improved (25.6 +/- 0.4 vs 20.6 +/- 0.5 mg/min/kg in O-C, p < 0.05). The O-M rats also showed an improved fasting glucose and GDR level, but not as much as those with O-P rats. The pancreas insulin contents were much improved in the O-P rats (22.9 +/- 1.2 vs 18.8 +/- 1.3 nmol/pancreas in O-M rats, p < 0.05) with histological improvement.

CONCLUSION

The pre-diabetic treatment with pioglitazone, despite significant weight gain, completely prevents to develop diabetes and enhances beta cell function with preservation of islet cell changes. Metformin treatment was also effective, but mainly by ameliorating the insulin resistance with marked reduction in body weight. The reversal of dyslipidaemia and the fat redistribution might contribute to the greater improvement of pioglitazone treatment compared to metformin in OLETF rats.

13-Oxo-ODE is an endogenous ligand for PPARgamma in human colonic epithelial cells

BACKGROUND

The ligand activated nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPARgamma) induces transcriptional repression of pro-inflammatory factors. Activation of PPARgamma is followed by amelioration of colitis in animal models of inflammatory bowel disease (IBD). A reduced expression of PPARgamma was found in epithelial cells of patients with ulcerative colitis. The eicosanoids 13-HODE and 15-HETE are products of 12/15-lipoxygenase (LOX) and endogenous ligands for PPARgamma. Dehydrogenation of 13-HODE by 13-HODE dehydrogenase results in formation of the 13-Oxo-ODE. Highest activity of 13-HODE dehydrogenase is found in colonic epithelial cells (CECs). We therefore investigated whether 13-Oxo-ODE is a new endogenous ligand of PPARgamma in CECs.

METHODS

LOX activity and 13-HODE dehydrogenase in CECs were investigated after stimulation with arachidonic or linoleic acid. LOX metabolites were identified by RP-18 reversed-phase HPLC. Binding of (14)C-labelled 13-Oxo-ODE was demonstrated using a His-tagged PPARgamma.

RESULTS

Stimulation of HT-29 and primary CECs homogenates with and without Ca-ionophor was followed by the formation of high amounts of the linoleic acid metabolite 13-Oxo-ODE (155 and 85 ng/ml). The decrease of IL-8 secretion from IEC was more pronounced after pre-incubation with 13-Oxo-ODE compared to the PPARgamma agonist troglitazone and higher as with the known PPARgamma ligands 13-HODE and 15-HETE. Binding assays with (14)C-labelled 13-Oxo-ODE clearly demonstrated a direct interaction.

CONCLUSION

High amounts of 13-Oxo-ODE can be induced in CECs by stimulation of linoleic acid metabolism. 13-Oxo-ODE binds to PPARgamma and has anti-inflammatory effects. 13-HODE dehydrogenase might be a therapeutic target in IBD.

Understanding diet-gene interactions: lessons from studying nutrigenomics and cardiovascular disease

Socioeconomic development has resulted in an epidemiologic transition which has involved an increase in mortality and morbidity from chronic non-communicable diseases. Cardiovascular disease is one such disease. The rapidity with which this transition has occurred suggests that genetic factors are unlikely to be responsible. However, studies in twins suggest significant heritability for cardiovascular disease and its associated risk factors. We present data showing diet-gene interactions involving polymorphisms at the PPARA and PLIN loci. These data support the hypothesis that chronic diseases such as cardiovascular disease are a consequence of a complex interplay of genetic and environmental factors, of which diet plays an important role. They suggest that the effects of diet on chronic disease may be masked by heterogeneity of effect related to genetic variability between individuals and that consideration of diet-gene interactions may contribute to our understanding of the pathogenesis of cardiovascular disease. The identification of diet-gene interactions offers us an opportunity to develop dietary interventions that will obviate the effects of genetic factors on the risk of disease. In this way, we may be able to develop personalized dietary recommendations that optimize the outcome for the individual concerned. Nevertheless, while existing data points to the value of these studies, significant challenges need to be met to ensure that our conclusions are scientifically valid.

Mutation screen and association studies in the diacylglycerol O-acyltransferase homolog 2 gene (DGAT2), a positional candidate gene for early onset obesity on chromosome 11q13

Background

DGAT2 is a promising candidate gene for obesity because of its function as a key enzyme in fat metabolism and because of its localization on chromosome 11q13, a linkage region for extreme early onset obesity detected in our sample.

We performed a mutation screen in 93 extremely obese children and adolescents and 94 healthy underweight controls. Association studies were performed in samples of up to 361 extremely obese children and adolescents and 445 healthy underweight and normal weight controls. Additionally, we tested for linkage and performed family based association studies at four common variants in the 165 families of our initial genome scan.

Results

The mutation screen revealed 15 DNA variants, four of which were coding non-synonymous exchanges: p.Val82Ala, p.Arg297Gln, p.Gly318Ser and p.Leu385Val. Ten variants were synonymous: c.-9447A > G, c.-584C > G, c.-140C > T, c.-30C > T, IVS2-3C > G, c.812A > G, c.920T > C, IVS7+23C > T, IVS7+73C > T and *22C > T. Additionally, the small biallelic trinucleotide repeat rs3841596 was identified. None of the case control and family based association studies showed an association of investigated variants or haplotypes in the genomic region of DGAT2.

Conclusion

In conclusion, our results do not support the hypothesis of an important role of common genetic variation in DGAT2 for the development of obesity in our sample. Anyhow, if there is an influence of genetic variation in DGAT2 on body weight regulation, it might either be conferred by the less common variants (MAF < 0.1) or the detected, rare non-synonymous variants.

Ligands of peroxisome proliferator-activated receptor inhibit homocysteine-induced DNA methylation of inducible nitric oxide synthase gene

Homocysteine (Hcy) is a risk factor for atherosclerosis. It is generally accepted that inducible nitric oxide synthase (iNOS) is a key enzyme in the regulation of vascular disease. The aim of the present study is to investigate the effects of peroxisome proliferator-activated receptor ligands on iNOS in the presence of Hcy in human monocytes. Foam cells, induced by oxidize low density lipoprotein (ox-LDL) and phorbol myristate acetate (PMA) in the presence of different concentrations of Hcy, clofibrate and pioglitazone in human monocytes for 4 d, were examined by oil red O staining. The activity of iNOS was detected by real-time quantitative reverse transcription-polymerase chain reaction and Western blot analysis. The capability of DNA methylation was measured by assaying endogenous C5 DNA methyltransferase (C5MTase) activity, and the iNOS promoter methylation level was determined by quantitative MethyLight assays. The results indicated that Hcy increased the activity of C5MTase and the level of iNOS gene DNA methylation, resulting in a decrease of iNOS expression. Clofibrate and pioglitazone could antagonize the hcy effect on iNOS expression through DNA methylation, resulting in attenuation of iNOS transcription. These findings suggested that Hcy decreased the expression of iNOS by elevating iNOS DNA methylation levels, which can repress the transcription of some genes. Peroxisome proliferator-activated receptor alpha/gamma ligands can down-regulate iNOS DNA methylation, and could be useful for preventing Hcy-induced atherosclerosis by repressing iNOS expression.

Discovery of tertiary aminoacids as dual PPARα/γ agonists-I

A novel series of potent dual agonists of PPARalpha and PPARgamma, the alkoxybenzylglycines, was identified and explored using a solution-phase library approach. The synthesis and structure-activity relationships of this series of dual PPARalpha/gamma agonists are described.

Transcriptional regulation of macrophage cholesterol trafficking by PPARalpha and LXR

PPARs (peroxisome-proliferator-activated receptors) and LXRs (liver X receptors) are ligand-activated transcription factors that control lipid and glucose metabolism, as well as the inflammatory response. Since the macrophage plays an important role in host defence and immuno-inflammatory pathologies, particular attention has been paid to the role of PPARs and LXRs in the control of macrophage gene expression and function. Altered macrophage functions contribute to the pathogenesis of many infectious, immunological and inflammatory disease processes, including atherosclerosis. Research over the last few years has revealed important roles for PPARs and LXRs in macrophage inflammation and cholesterol homoeostasis with consequences in atherosclerosis development. This review will discuss the role of these transcription factors in the control of cholesterol trafficking in macrophages.

Peroxisome proliferator-activated receptor-gamma agonists for management and prevention of vascular disease in patients with and without diabetes mellitus

Inflammation is known to have a pathogenic role in atherosclerosis and the genesis of acute coronary syndromes. The peroxisome proliferator-activated receptor (PPAR)-gamma, which is expressed in many constituent cells of atheromatous plaques, inhibits the activation of several proinflammatory genes responsible for atheromatous plaque development and maturation. Agonists of this receptor, such as rosiglitazone and pioglitazone, are currently available for the treatment of type 2 diabetes mellitus, and several lines of evidence have shown that these drugs have antiatherogenic effects. Insulin resistance is associated with inflammation and has a key role in atherogenesis. The antiatherogenic and insulin sensitizing effects of the thiazolidinediones in patients with type 2 diabetes mellitus may be associated with this action. However, in recent years there has been growing evidence that the antiatherogenic effects of PPAR-gamma agonists are not confined to patients with diabetes mellitus. PPAR-gamma agonists have been shown to downregulate the expression of endothelial activation markers, reduce circulating platelet activity, improve flow-mediated dilatation and attenuate atheromatous plaque progression in patients without diabetes mellitus. These effects of PPAR-gamma agonists appear to result from both insulin sensitization and a direct modulation of transcriptional activity in the vessel wall. This review summarizes the current understanding of the role of PPAR-gamma agonists in atherogenesis and discusses their potential role in the treatment of coronary artery disease in patients with type 2 diabetes mellitus and in nondiabetic patients.

Expression of a peroxisome proliferator-activated receptor gene (xPPARalpha) from Xenopus laevis in tobacco (Nicotiana tabacum) plants

In this work, we have genetically transformed tobacco (Nicotiana tabacum) plants with the peroxisome proliferator-activated receptor cDNA (xPPARalpha) from Xenopus laevis, which is a transcriptional factor involved in the peroxisomal proliferation and induction of fatty acid beta-oxidation in animal cells. Several transgenic lines were generated and one representative line (T) from the R2 generation was selected for further studies. Analysis of free fatty acids revealed that unsaturated fatty acids such as C16:2 and C16:3 were deficient in line T, whereas saturated fatty acids like C16:0, C18:0, and C20:0 were more abundant than in non-transformed plants. Acyl-CoA oxidase (ACOX) activity was assayed as a marker enzyme of beta-oxidation in crude leaf extracts and it was found that in line T there was a threefold increase in enzyme activity. We also found that the peroxisome population was increased and that catalase (CAT) activity was induced by clofibrate, a known activator of xPPARalpha protein, in leaves from line T. Taken together, these findings suggest that xPPARalpha is functional in plants and that its expression in tobacco leads to changes in general lipid metabolism and peroxisomal proliferation as reported in animal cells. Furthermore, it indicates that there is an endogenous ligand in tobacco cells able to activate xPPARalpha.

The platelet as a therapeutic target for treating vascular diseases and the role of eicosanoid and synthetic PPARgamma ligands

The platelet was traditionally thought only to serve as the instigator of thrombus formation, but now is emerging as a pivotal player in cardiovascular disease and diabetes by inciting and maintaining inflammation. Upon activation, platelets synthesize eicosanoids such as thromboxane A2 (TXA2) and PGE2 and release pro-inflammatory mediators including CD40 ligand (CD40L). These mediators activate not only platelets, but also stimulate vascular endothelial cells and leukocytes. These autocrine and paracrine activation processes make platelets an important target for attenuating inflammation. The growing interest and recent discoveries in platelet biology has lead to the search for therapeutic platelet targets. Recently, platelets, although anucleate, were discovered to possess the transcription factor PPARgamma. Treatment with eicosanoid and synthetic PPARgamma ligands blunts platelet release of the bioactive mediators, soluble (s) CD40L and TXA2, in thrombin-activated platelets. PPARgamma ligand treatment may prove useful for dampening unwanted platelet activation and chronic inflammatory diseases such as cardiovascular disease.

Cardiac PPARα expression in patients with dilated cardiomyopathy

BACKGROUND

The peroxisome proliferator-activated receptor alpha (PPARalpha) is a central regulator of myocardial fatty acid (FA) metabolism implicated in the pathogenesis of heart failure.

AIMS

To characterize PPARalpha regulation in human dilated cardiomyopathy (DCM), we studied the expression of cardiac PPARalpha, cardiac carnitine palmitoyl-transferase I (CPT-1), a major PPARalpha target gene, and of the cardiac glucose transporter GLUT-4 in patients with DCM.

METHODS

Left ventricular biopsies were taken from patients with DCM (n=16) and control subjects (n=15), and mRNA expression was quantitated using real-time PCR (SYBR((R))Green) and protein expression was measured by Western immunoblotting.

RESULTS

Left ventricular PPARalpha mRNA levels were significantly increased in the DCM group compared to the control group (136+/-25.4% vs. control, p<0.01). Consistently, DCM patients had a significantly higher cardiac CPT-1 mRNA expression (147+/-51% vs. control, p<0.05) compared to the control group. Cardiac GLUT-4 expression was similar in both groups.

CONCLUSION

Elevated cardiac PPARalpha levels followed by an induction of cardiac CPT-1 expression may result in increased fatty acid metabolism for cardiac energy production in DCM, suggesting a specific cardiac metabolic program in human DCM compared to other types of cardiomyopathy.

Gypenoside XLIX isolated from Gynostemma pentaphyllum inhibits nuclear factor-kappaB activation via a PPAR-alpha-dependent pathway

Nuclear factor (NF)-kappaB is important in the generation of inflammation. Besides regulating lipid metabolism, peroxisome proliferator-activated receptor (PPAR)-alpha activators also reduce NF-kappaB activation to terminate activation of inflammatory pathways. Gynostemma pentaphyllum (GP) has been used to treat various inflammatory diseases and hyperlipidemia. Here, we demonstrate that GP extract and one of its main components, Gypenoside XLIX (Gyp-XLIX) inhibited LPS-induced NF-kappaB activation in murine macrophages. Furthermore, Gyp-XLIX restored the LPS- and TNF-alpha-induced decrease in cytosolic I-kappaBalpha protein expression and inhibited the translocation of NF-kappaB(p65) to the nucleus in THP-1 monocyte and HUVEC cells. The inhibition of LPS- and TNF-alpha-induced NF-kappaB luciferase activity in macrophages was abolished by MK-886, a selective PPAR-alpha antagonist. GP extract and Gyp-XLIX (EC(50): 10.1 microM) enhanced PPAR-alpha luciferase activity in HEK293 cells transfected with the tK-PPREx3-Luc reporter plasmid and expression vectors for PPAR-alpha. Additionally, Gyp-XLIX specifically enhanced PPAR-alpha mRNA and protein expression in THP-1-derived macrophage cells. The selectivity of Gyp-XLIX for PPAR-alpha was demonstrated by the activation of only PPAR-alpha in HEK293 cells transfected with expression vectors for PPAR-alpha, PPAR-beta/delta or PPAR-gamma1 plasmids and in THP-1-derived macrophage naturally expressing all three PPAR isoforms. The present study demonstrates that Gyp-XLIX, a naturally occurring gynosaponin, inhibits NF-kappaB activation via a PPAR-alpha-dependent pathway.

Recent studies of lipoprotein kinetics in the metabolic syndrome and related disorders

PURPOSE OF REVIEW

Dyslipoproteinemia is a cardinal feature of the metabolic syndrome that accelerates atherosclerosis. Recent in-vivo kinetic studies of dyslipidemia in the metabolic syndrome are reviewed here.

RECENT FINDINGS

The dysregulation of lipoprotein metabolism may be caused by a combination of overproduction of VLDL apolipoprotein B-100, decreased catabolism of apolipoprotein B-containing particles, and increased catabolism of HDL apolipoprotein A-I particles. Nutritional modifications and increased physical exercise may favourably alter lipoprotein transport by collectively decreasing the hepatic secretion of VLDL apolipoprotein B and the catabolism of HDL apolipoprotein A-I, as well as by increasing the clearance of LDL apolipoprotein B. Conventional and new pharmacological treatments, such as statins, fibrates and cholesteryl ester transfer protein inhibitors, can also correct dyslipidemia by several mechanisms, including decreased secretion and increased catabolism of apolipoprotein B, as well as increased secretion and decreased catabolism of apolipoprotein A-I.

SUMMARY

Kinetic studies provide a mechanistic insight into the dysregulation and therapy of lipid and lipoprotein disorders. Future research mandates the development of new tracer methodologies with practicable in-vivo protocols for investigating fatty acid turnover, macrophage reverse cholesterol transport, cholesterol transport in plasma, corporeal cholesterol balance, and the turnover of several subpopulations of HDL particles.

Genetic interactions with diet influence the risk of cardiovascular disease

Single-nucleotide polymorphisms are an integral component of the evolutionary process that over millennia have resulted from the interaction between the environment and the human genome. Relatively recent changes in diet have upset this interaction with respect to the nutritional environment, but nutritional science is beginning to better understand the interaction between genes and diet, with the resulting potential to influence cardiovascular disease risk by dietary modification. Single-nucleotide polymorphisms in several genes have been linked to differential effects in terms of lipid metabolism; however, even a simple model of benefit and risk is difficult to interpret in terms of dietary advice to carriers of the various alleles because of conflicting interactions between different genes. The n-3 family of polyunsaturated fatty acids is underrepresented in our modern diet; much of the benefit of polyunsaturated fatty acids found in studies of various polymorphisms seems to be linked to increased n-3 polyunsaturated fatty acid intake. The nascent science of nutrigenomics faces many challenges; more and better research is needed to clarify the picture, rebut scepticism, and re-invigorate the discussion concerning genetic polymorphism and its interaction with diet.

Salacia oblonga root improves cardiac lipid metabolism in Zucker diabetic fatty rats: Modulation of cardiac PPAR-α-mediated transcription of fatty acid metabolic genes

Excess cardiac triglyceride accumulation in diabetes and obesity induces lipotoxicity, which predisposes the myocytes to death. On the other hand, increased cardiac fatty acid (FA) oxidation plays a role in the development of myocardial dysfunction in diabetes. PPAR-alpha plays an important role in maintaining homeostasis of lipid metabolism. We have previously demonstrated that the extract from Salacia oblonga root (SOE), an Ayurvedic anti-diabetic and anti-obesity medicine, improves hyperlipidemia in Zucker diabetic fatty (ZDF) rats (a genetic model of type 2 diabetes and obesity) and possesses PPAR-alpha activating properties. Here we demonstrate that chronic oral administration of SOE reduces cardiac triglyceride and FA contents and decreases the Oil red O-stained area in the myocardium of ZDF rats, which parallels the effects on plasma triglyceride and FA levels. Furthermore, the treatment suppressed cardiac overexpression of both FA transporter protein-1 mRNA and protein in ZDF rats, suggesting inhibition of increased cardiac FA uptake as the basis for decreased cardiac FA levels. Additionally, the treatment also inhibited overexpression in ZDF rat heart of PPAR-alpha mRNA and protein and carnitine palmitoyltransferase-1, acyl-CoA oxidase and 5'-AMP-activated protein kinase mRNAs and restored the downregulated acetyl-CoA carboxylase mRNA. These results suggest that SOE inhibits cardiac FA oxidation in ZDF rats. Thus, our findings suggest that improvement by SOE of excess cardiac lipid accumulation and increased cardiac FA oxidation in diabetes and obesity occurs by reduction of cardiac FA uptake, thereby modulating cardiac PPAR-alpha-mediated FA metabolic gene transcription.

GLUCURONIDATION AS A MAJOR METABOLIC CLEARANCE PATHWAY OF 14C-LABELED MURAGLITAZAR IN HUMANS: METABOLIC PROFILES IN SUBJECTS WITH OR WITHOUT BILE COLLECTION

The metabolism and disposition of 14C-labeled muraglitazar (Pargluva), a novel dual alpha/gamma peroxisome proliferator-activated receptor activator, was investigated in eight healthy male subjects with and without bile collection (groups 1 and 2) after a single 20-mg oral dose. Bile samples were collected for 3 to 8 h after dosing from group 2 subjects in addition to the urine and feces collection. In plasma, the parent compound was the major component, and circulating metabolites, including several glucuronide conjugates, were minor components at all time points. The exposure to parent drug (Cmax and area under the plasma concentration versus time curve) in subjects with bile collection was generally lower than that in subjects without bile collection. The major portion of the radioactive dose was recovered in feces (91% for group 1 and 51% for group 2). In addition, 40% of the dose was recovered in the bile from group 2 subjects. In this 3- to 8-h bile, the glucuronide of muraglitazar (M13, 15% of dose) and the glucuronides of its oxidative metabolites (M17a,b,c, M18a,b,c, and M20, together, 16% of dose) accounted for approximately 80% of the biliary radioactivity; muraglitazar and its O-demethylated metabolite (M15) each accounted for approximately 4% of the dose. In contrast, fecal samples only contained muraglitazar and its oxidative metabolites, suggesting hydrolysis of biliary glucuronides in the intestine before fecal excretion. Thus, the subjects with and without bile collection showed different metabolic profiles of muraglitazar after oral administration, and glucuronidation was not observed as a major pathway of metabolic clearance from subjects with the conventional urine and fecal collection, but was found as a major elimination pathway from subjects with bile collection.

The V227A polymorphism at the PPARA locus is associated with serum lipid concentrations and modulates the association between dietary polyunsaturated fatty acid intake and serum high density lipoprotein concentrations in Chinese women

Peroxisome proliferators activated receptor alpha (PPARalpha) regulates the transcription of several proteins involved in human lipoprotein metabolism. We screened the PPARA locus for polymorphisms in 20 unrelated subjects from each of three ethnic groups (Chinese, Malays and Asian Indians). Only the V227A polymorphism was observed. We genotyped 4248 subjects (2899 Chinese, 761 Malay and 588 Asian Indians) and found allele frequencies for the A227 allele of 0.04 in Chinese, 0.006 in Malays and 0.003 in Asian Indians. We examined the associations between this polymorphism and serum lipid concentrations in Chinese. In women, but not in men, the presence of the A227 allele was associated with lower serum concentrations of total cholesterol [5.38mmol/l (95%CI: 5.22-5.54) versus 5.21mmol/l (95%CI: 4.99-5.43), p=0.047] and triglycerides [1.19mmol/l (95%CI: 1.10-1.28) versus 1.09mmol/l (95%CI: 0.98-1.21), p=0.048]. We also found that the V227A polymorphism modulates the association between dietary polyunsaturated fatty acid intake and serum high density lipoprotein concentration (p-value for interaction=0.049). Our findings implicate PPARalpha in the lipid lowering associated with diets high in PUFA and suggests that genetic variation at the PPARA locus may determine the lipid response to changes in PUFA intake.

Obesity and colorectal cancer: epidemiology, mechanisms and candidate genes

There is increasing evidence that dysregulation of energy homeostasis is associated with colorectal carcinogenesis. Epidemiological data have consistently demonstrated a positive relation between increased body size and colorectal malignancy, whereas mechanistic studies have sought to uncover obesity-related carcinogenic pathways. The phenomenon of "insulin resistance" or the impaired ability to normalize plasma glucose levels has formed the core of these pathways, but other mechanisms have also been advanced. Obesity-induced insulin resistance leads to elevated levels of plasma insulin, glucose and fatty acids. Exposure of the colonocyte to heightened concentrations of insulin may induce a mitogenic effect within these cells, whereas exposure to glucose and fatty acids may induce metabolic perturbations, alterations in cell signaling pathways and oxidative stress. The importance of chronic inflammation in the pathogenesis of obesity has recently been highlighted and may represent an additional mechanism linking increased adiposity to colorectal carcinogenesis. This review provides an overview of the epidemiology of body size and colorectal neoplasia and outlines current knowledge of putative mechanisms advanced to explain this relation. Family based studies have shown that the propensity to become obese is heritable, but this is only manifest in conditions of excess energy intake over expenditure. Inheritance of a genetic profile that predisposes to increased body size may also be predictive of colorectal cancer. Genomewide scans, linkage studies and candidate gene investigations have highlighted more than 400 chromosomal regions that may harbor variants that predispose to increased body size. The genetics underlying the pathogenesis of obesity are likely to be complex, but variants in a range of different genes have already been associated with increased body size and insulin resistance. These include genes encoding elements of insulin signaling, adipocyte metabolism and differentiation, and regulation of energy expenditure. A number of investigators have begun to study genetic variants within these pathways in relation to colorectal neoplasia, but at present data remain limited to a handful of studies. These pathways will be discussed with particular reference to genetic polymorphisms that have been associated with obesity and insulin resistance.

Resveratrol as an anti-inflammatory and anti-aging agent: mechanisms and clinical implications

Resveratrol is a phytoalexin polyphenolic compound found in various plants, including grapes, berries, and peanuts. Multiple lines of compelling evidence indicate its beneficial effects on neurological, hepatic, and cardiovascular systems. Also one of the most striking biological activities of resveratrol soundly investigated during the late years has been its cancer-chemopreventive potential. In fact, recently it has been demonstrated that this stilbene blocks the multistep process of carcinogenesis at various stages: tumor initiation, promotion, and progression. One of the possible mechanisms for its biological activities involves downregulation of the inflammatory response through inhibition of synthesis and release of pro-inflammatory mediators, modification of eicosanoid synthesis, inhibition of activated immune cells, or inhibiting such as inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) via its inhibitory effects on nuclear factor (kappa)B (NF-(kappa)B) or the activator protein-1 (AP-1). More recent data provide interesting insights into the effect of this compound on the lifespan of yeast and flies, implicating the potential of resveratrol as an anti-aging agent in treating age-related human diseases. It is worthy to note that the phenolic compound possesses a low bioavailability and rapid clearance from the plasma. As the positive effects of resveratrol on inflammatory response regulation may comprise relevant clinical implications, the purpose of this article is to review its strong anti-inflammatory activity and the plausible mechanisms of these effects. Also, this review is intended to provide the reader an up-date of the bioavailability and pharmacokinetics of resveratrol and its impact on lifespan.

Zinc deficiency increases plasma lipids and atherosclerotic markers in LDL-receptor-deficient mice

Low zinc concentration can be associated with an increased risk of cardiovascular diseases. In the current study, we hypothesize that zinc deficiency can increase and zinc supplementation can decrease proatherosclerotic events in LDL receptor knock-out (LDL-R-/-) mice fed a moderate-fat diet. Mice were fed either a zinc-deficient (0 micromol Zn/g), a control (0.45 micromol Zn/g), or a zinc-supplemented (1.529 micromol Zn/g) diet for 4 wk. Mice fed the zinc-deficient diet had significantly increased concentrations of cholesterol and triacylglycerides in the VLDL and HDL fractions. Zinc supplementation decreased these lipid variables compared with control mice. We detected significantly higher concentrations of glutathione reductase mRNA in the thoracic aortae of zinc-deficient mice. Furthermore, inflammatory markers, such as nuclear factor-kappaB and vascular cell adhesion molecule-1, were significantly increased in zinc-deficient mice compared with mice of the control or supplemented groups. In addition, zinc deficiency significantly reduced the DNA binding activity of peroxisome proliferator activate receptors (PPARs) in liver extracts. Interestingly, mRNA expression levels of PPARgamma were significantly increased in thoracic aortae of zinc-deficient mice, indicating an adaptation process to decreased PPAR signaling. These data provide in vivo evidence of zinc deficiency inducing proinflammatory events in an atherogenic mouse model. These data also suggest that adequate zinc may be a critical component in protective PPAR signaling during atherosclerosis.

Phosphorylation of PPARs: from molecular characterization to physiological relevance

In addition to their ligand-mediated activation, nuclear receptor activity is finely tuned by their phosphorylation status. PPARs are phosphorylated by several kinases (PKA, PKC, MAPKs, and AMPK), which affect their activity in a ligand-dependent or -independent manner according to the isoform and cellular context. Molecular consequences are multiple, including changes in ligand affinity, DNA binding, recruitment of transcriptional cofactors, proteasome degradation... Finally, the physiological relevance of PPAR phosphorylation is discussed.

Diabetes in Japan

In this article, we introduce the increasing prevalence of type 2 diabetes in the Japanese population and discuss the reasons for such an explosive increase. Diabetes has been brought into prominence in Japan by enhanced insulin resistance, through the change of lifestyle against the background of fragile beta-cell function and thrifty genotypes.

Fenofibric acid, an active form of fenofibrate, increases apolipoprotein A-I-mediated high-density lipoprotein biogenesis by enhancing transcription of ATP-binding cassette transporter A1 gene in a liver X receptor-dependent manner

OBJECTIVE

Fibrates are widely used drugs to reduce plasma triglyceride and increase high-density lipoprotein. Their active forms, fibric acids, are peroxisome proliferator-activated receptor-alpha activators, but no direct evidence has been demonstrated for their activation of ATP-binding cassette transporter A1 (ABCA1) in relation to clinically used fibrates. We investigated the reaction of fenofibric acid in this regard.

METHODS AND RESULTS

Fenofibric acid was examined for the effect of increase of ABCA1 activity. It enhanced ABCA1 gene transcription and its protein level in macrophage cell line cells and fibroblasts and increased apolipoprotein A-I-mediated cellular lipid release, all in a dose-dependent manner. Enhancement of the gene transcription was examined by using a reporter assay system for liver X receptor responsive element (LXRE) and its inactive mutant. The results demonstrated that the effect of fenofibric acid is dependent on active LXRE.

CONCLUSIONS

Fenofibric acid increased transcription of ABCA1 gene in a liver X receptor-dependent manner.

Effect of BM 17.0744, a PPARα ligand, on the metabolism of perfused hearts from control and diabetic mice

Peroxisome proliferator-activated receptor-α (PPARα) regulates the expression of fatty acid (FA) oxidation genes in liver and heart. Although PPARα ligands increased FA oxidation in cultured cardiomyocytes, the cardiac effects of chronic PPARα ligand administration in vivo have not been studied. Diabetic db/db mouse hearts exhibit characteristics of a diabetic cardiomyopathy, with altered metabolism and reduced contractile function. A testable hypothesis is that chronic administration of a PPARα agonist to db/db mice will normalize cardiac metabolism and improve contractile function. Therefore, a PPARα ligand (BM 17.0744) was administered orally to control and type 2 diabetic (db/db) mice (37.9 ± 2.5 mg/(kg·d) for 8 weeks), and effects on cardiac metabolism and contractile function were assessed. BM 17.0744 reduced plasma glucose in db/db mice, but no change was observed in control mice. FA oxidation was significantly reduced in BM 17.0744 treated db/db hearts with a corresponding increase in glycolysis and glucose oxidation; glucose and FA oxidation in control hearts was unchanged by BM 17.0744. PPARα treatment did not alter expression of PPARα target genes in either control or diabetic hearts. Therefore, metabolic alterations in hearts from PPARα-treated diabetic mice most likely reflect indirect mechanisms related to improvement in diabetic status in vivo. Despite normalization of cardiac metabolism, PPARα treatment did not improve cardiac function in diabetic hearts.Key words: PPAR, cardiac metabolism and function, diabetes.

The metabolic syndrome and the hepatic fatty acid drainage hypothesis

Much data indicates that lowering of plasma triglyceride levels by hypolipidemic agents is caused by a shift in the liver metabolism towards activation of peroxisome proliferator activated receptor (PPAR)alpha-regulated fatty acid catabolism in mitochondria. Feeding rats with lipid lowering agents leads to hypolipidemia, possibly by increased channeling of fatty acids to mitochondrial fatty acid oxidation at the expense of triglyceride synthesis. Our hypothesis is that increased hepatic fatty acid oxidation and ketogenesis drain fatty acids from blood and extrahepatic tissues and that this contributes significantly to the beneficial effects on fat mass accumulation and improved peripheral insulin sensitivity. To investigate this theory we employ modified fatty acids that change the plasma profile from atherogenic to cardioprotective. One of these novel agents, tetradecylthioacetic acid (TTA), is of particular interest due to its beneficial effects on lipid transport and utilization. These hypolipidemic effects are associated with increased fatty acid oxidation and altered energy state parameters of the liver. Experiments in PPAR alpha-null mice have demonstrated that the effects hypolipidemic of TTA cannot be explained by altered PPAR alpha regulation alone. TTA also activates the other PPARs (e.g., PPAR delta) and this might compensate for deficiency of PPAR alpha. Altogether, TTA-mediated clearance of blood triglycerides may result from a lowered level of apo C-III, with a subsequently induction of hepatic lipoprotein lipase activity and (re)uptake of fatty acids from very low density lipoprotein (VLDL). This is associated with an increased hepatic capacity for fatty acid oxidation, causing drainage of fatty acids from the blood stream. This can ultimately be linked to hypolipidemia, anti-adiposity, and improved insulin sensitivity.

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.

Fenofibrate reduces tumor necrosis factor-alpha serum concentration and adipocyte secretion of hypercholesterolemic rabbits

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) is produced by cells of the macrophage-monocyte lineage and by adipocytes. It may provide the link between inflammation and atherosclerosis. The aim of this study was to evaluate the effect of fenofibrate on serum TNF-alpha concentration and TNF-alpha secretion by adipocytes from hypercholesterolemic rabbits.

METHODS

Ten male New Zealand white rabbits were fed with high-cholesterol diet for 8 weeks, and were randomly divided into two groups: (1) high cholesterol group: maintained cholesterol diet for 4 weeks; and (2) fenofibrate treated group: the same cholesterol diet supplemented with fenofibrate (30 mg/kg/day) for 4 weeks. Control group was fed with normal diet for 12 weeks. Subcutaneous adipose was collected for adipocytes culture. TNF-alpha concentrations in serum and adipocytes culture supernatant were measured by ELISA.

RESULTS

Rabbits fed with high-cholesterol diet showed higher serum levels of total cholesterol, low density lipoprotein cholesterol than those fed with normal diet (P<0.001). Fenofibrate treatment did not change serum lipid levels during the feeding period, but decreased high cholesterol diet-induced increases in body weight by 19% and serum TNF-alpha concentration by 44.7% in fenofibrate treated group compared with high cholesterol group (P<0.05). The decreased levels of TNF-alpha correlated with the weight loss (r=0.35, P<0.05). Fenofibrate (10 to 100 micromol/l) significantly reduced release of TNF-alpha in adipocytes (P<0.05). Meanwhile serum TNF-alpha concentration were significantly correlated with TNF-alpha secretion in adipocytes (r=0.51, P<0.05).

CONCLUSIONS

Our study indicated that fenofibrate reduced tumor necrosis factor-alpha serum concentration and adipocyte secretion of hypercholesterolemic rabbits. This effect of fenofibrate might contribute to its benefits on the prevention and treatment of atherosclerosis.

Sterol-regulatory-element binding protein inhibits upstream stimulatory factor-stimulated hepatic lipase gene expression

Hepatic lipase (HL) not only plays an important role in plasma lipoprotein transport, but may also affect intracellular lipid metabolism. We hypothesize that HL expression is regulated as an integral part of intracellular lipid homeostasis. Addition of oleate (1 mM) to HepG2 cells increased HL secretion to 134+/-14% of control (p<0.02), and increased the transcriptional activity of a 698-bp HL promoter-reporter construct two-fold. Atorvastatin (10 microM) abolished the oleate stimulation. The transcriptional activity of a sterol-regulatory-element binding protein (SREBP)-sensitive HMG-CoA synthase promoter construct was reduced 50% by oleate, and increased 2-3-fold by atorvastatin. Co-transfection with an SREBP-2 expression vector reduced HL promoter activity and increased HMG-CoA synthase promoter activity. Upstream stimulatory factors (USF) are also implicated in maintenance of lipid homeostasis. Co-transfection with a USF-1 expression vector stimulated HL promoter activity 4-6-fold. The USF-stimulated HL promoter activity was not further enhanced by oleate, but almost completely prevented by atorvastatin or co-transfection with the SREBP-2 vector. Opposite regulation by USF-1 and SREBP-2 was also observed with a 318-bp HL promoter construct that lacks potential SRE-like and E-box binding motifs. We conclude that the opposite regulation of HL expression by fatty acids and statins is mediated via SREBP, possibly through interaction with USF.

Rosiglitazone treatment improves insulin regulation and dyslipidemia in type 2 diabetic cynomolgus monkeys

Impairment of peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a nuclear receptor that regulates genes involved in lipid and glucose metabolism, may contribute to the onset of metabolic disorders such as diabetes and the accompanying dyslipidemia. Fat-derived tumor necrosis factor alpha (TNF-alpha) and the acute-phase response protein, C-reactive protein (CRP), may also have a role in the development of obesity-related insulin resistance and type 2 diabetes mellitus. In this study, a group of 14 naturally occurring, insulin-requiring, type 2 diabetic cynomolgus monkeys were used to evaluate the effects of the PPAR-gamma agonist, rosiglitazone, on glycemic and lipid parameters and serum levels of TNF-alpha and CRP. The animals were randomized into 2 groups of 7. One group was treated with 0.5 mg/kg rosiglitazone orally once a day for 7 weeks. Blood was collected for evaluation at baseline, at 2 and 7 weeks during the treatment period, and at 7 and 13 weeks after treatment. Daily insulin requirements were recorded during the entire study. Results showed daily exogenous insulin requirements were significantly reduced (P <.01) in those treated with rosiglitazone, while glycemic control was maintained. Plasma triglyceride concentrations were significantly lower (P <.01) whereas plasma cholesterol levels tended to be lower and high-density lipoprotein (HDL) concentrations tended to be higher after treatment. No significant differences were noted in TNF-alpha and CRP serum levels during the treatment period. Body weights remained steady in both groups during the study. These results suggest overall improvement in insulin regulation and lipid profiles during treatment with rosiglitazone.

Lipoprotein transport in the metabolic syndrome: pathophysiological and interventional studies employing stable isotopy and modelling methods

The accompanying review in this issue of Clinical Science [Chan, Barrett and Watts (2004) Clin. Sci. 107, 221–232] presented an overview of lipoprotein physiology and the methodologies for stable isotope kinetic studies. The present review focuses on our understanding of the dysregulation and therapeutic regulation of lipoprotein transport in the metabolic syndrome based on the application of stable isotope and modelling methods. Dysregulation of lipoprotein metabolism in metabolic syndrome may be due to a combination of overproduction of VLDL [very-LDL (low-density lipoprotein)]-apo (apolipoprotein) B-100, decreased catabolism of apoB-containing particles and increased catabolism of HDL (high-density lipoprotein)-apoA-I particles. These abnormalities may be consequent on a global metabolic effect of insulin resistance, partly mediated by depressed plasma adiponectin levels, that collectively increases the flux of fatty acids from adipose tissue to the liver, the accumulation of fat in the liver and skeletal muscle, the hepatic secretion of VLDL-triacylglycerols and the remodelling of both LDL (low-density lipoprotein) and HDL particles in the circulation. These lipoprotein defects are also related to perturbations in both lipolytic enzymes and lipid transfer proteins. Our knowledge of the pathophysiology of lipoprotein metabolism in the metabolic syndrome is well complemented by extensive cell biological data. Nutritional modifications may favourably alter lipoprotein transport in the metabolic syndrome by collectively decreasing the hepatic secretion of VLDL-apoB and the catabolism of HDL-apoA-I, as well as by potentially increasing the clearance of LDL-apoB. Several pharmacological treatments, such as statins, fibrates or fish oils, can also correct the dyslipidaemia by diverse kinetic mechanisms of action, including decreased secretion and increased catabolism of apoB, as well as increased secretion and decreased catabolism of apoA-I. The complementary mechanisms of action of lifestyle and drug therapies support the use of combination regimens in treating dyslipoproteinaemia in subjects with the metabolic syndrome.

Mimetics of caloric restriction include agonists of lipid-activated nuclear receptors

The obesity epidemic in industrialized countries is associated with increases in cardiovascular disease (CVD) and certain types of cancer. In animal models, caloric restriction (CR) suppresses these diseases as well as chemical-induced tissue damage. These beneficial effects of CR overlap with those altered by agonists of nuclear receptors (NR) under control of the fasting-responsive transcriptional co-activator, peroxisome proliferator-activated co-activator 1alpha (PGC-1alpha). In a screen for compounds that mimic CR effects in the liver, we found statistically significant overlaps between the CR transcript profile in wild-type mice and the profiles altered by agonists of lipid-activated NR, including peroxisome proliferator-activated receptor alpha (PPARalpha), liver X receptor, and their obligate heterodimer partner, retinoid X receptor. The overlapping genes included those involved in CVD (lipid metabolism and inflammation) and cancer (cell fate). Based on this overlap, we hypothesized that some effects of CR are mediated by PPARalpha. As determined by transcript profiling, 19% of all gene expression changes in wild-type mice were dependent on PPARalpha, including Cyp4a10 and Cyp4a14, involved in fatty acid omega-oxidation, acute phase response genes, and epidermal growth factor receptor but not increases in PGC-1alpha. CR protected the livers of wild-type mice from damage induced by thioacetamide, a liver toxicant and hepatocarcinogen. CR protection was lost in PPARalpha-null mice due to inadequate tissue repair. These results demonstrate that PPARalpha mediates some of the effects of CR and indicate that a pharmacological approach to mimicking many of the beneficial effects of CR may be possible.

Peroxisome proliferator activated receptors alpha and gamma require zinc for their anti-inflammatory properties in porcine vascular endothelial cells

Zinc is an essential structural component of various proteins and is crucial for the integrity of the vascular endothelium. The present study focused on the effect of zinc deficiency on the anti-inflammatory properties of peroxisome proliferator activated receptor (PPAR) alpha and gamma agonists. Porcine pulmonary-arterial endothelial cells were deprived from zinc by chelator N,N,N',N'-tetrakis (2-pyridylmethyl)ethylene diamine. Cells were exposed to TNF-alpha for 2 h following pretreament with the PPARalpha agonists fenofibrate or ciprofibrate or the PPARgamma agonists thiazolidinedione or troglitazone. The inflammatory response was tested by measuring nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) binding activities as well as by measuring mRNA expression levels of inflammatory genes, such as vascular cell adhesion molecule-1 (VCAM-1) and IL-6. All PPAR agonists tested lost their potency to downregulate the TNF-alpha-induced inflammatory response in zinc-deficient cells. However, if zinc was added back, all PPAR agonists significantly downregulated the TNF-alpha-mediated induction of inflammatory transcription factors NF-kappaB and AP-1 and significantly reduced the expression of their target genes, VCAM-1 and IL-6. We therefore hypothesize that zinc is required for the PPARalpha and -gamma DNA binding activity. Indeed, zinc deficiency significantly reduced the agonist-induced binding activity of PPARalpha and -gamma to the PPAR response element. Our data demonstrate the importance of zinc in PPAR signaling and the requirement of zinc for the anti-inflammatory properties of PPARalpha and -gamma agonists.

Effects of gemfibrozil treatment on vascular reactivity of streptozotocin-diabetic rat aorta

The effects of gemfibrozil treatment on plasma lipids, lipid peroxides and vascular reactivity of aorta were investigated in diabetic rats. Rats were divided randomly into two groups: control and diabetic. Diabetes was induced by a single intraperitoneal injection of streptozotocin (45 mg kg(-1)). Twelve weeks after the induction of diabetes, some of the control and diabetic rats were started treatment with gemfibrozil (100 mg kg(-1) daily; gavage) for 2 weeks. Blood glucose, plasma triglyceride, cholesterol, low-density lipoprotein (LDL) cholesterol and thiobarbituric acid reactive substances (TBARS) levels were markedly increased and gemfibrozil treatment restored these parameters in diabetic rats. However high-density lipoprotein (HDL) cholesterol levels did not differ in all experimental groups. In diabetic rats, the endothelium-dependent relaxations to acetylcholine were decreased when compared with control rats. Gemfibrozil treatment restored the endothelium-dependent responses to acetylcholine in diabetic rats. The endothelium-independent relaxation responses to sodium nitroprusside were not altered in all groups. These findings suggest that gemfibrozil treatment has beneficial effects against cardiovascular and metabolic complications of diabetes via its hypolipidaemic and antioxidant properties.

Association between the PPARalpha L162V polymorphism, plasma lipoprotein levels, and atherosclerotic disease in patients with diabetes mellitus type 2 and in nondiabetic controls

BACKGROUND

Peroxisome proliferator activated receptor alpha (PPARalpha) regulates genes involved in lipoprotein metabolism, hemostasis, and inflammation. It thus represents a candidate gene for the risk of dyslipidemia, atherosclerosis, and coronary heart disease (CHD). Nonesterified fatty acids are PPARalpha ligands and their levels are increased in patients with diabetes mellitus type 2 (DM-2). The effects of the polymorphism of PPARalpha on plasma lipids and atherosclerosis development have been until now contradictory. The present study was performed to evaluate the association between the PPARalpha polymorphism L162V and the presence of dyslipidemia and/or atherosclerotic disease in patients with DM-2 in comparison with nondiabetic controls.

METHODS AND RESULTS

We determined this polymorphism in 404 subjects with DM-2 and in 438 age and sex-matched nondiabetic controls. The V allele was present in 9.4% of patients with DM-2 and in 11.4% of the control group (P =.34). There was no significant association between the presence of the polymorphism and body mass index. There was no association between the polymorphism and lipoprotein concentrations in either group, independent of lipid-lowering therapy. In patients with DM-2, there was a trend towards a lower prevalence of atherosclerosis in carriers versus noncarriers of the V allele (P =.0837). In the control group, the presence of the V allele was not associated with an altered prevalence of atherosclerotic disease (P =.45). Likewise, there was a trend towards lower CHD prevalence in carriers versus noncarriers of the V allele (P =.0622). The presence of the polymorphism was not associated with CHD in the control group (P =.80).

CONCLUSIONS

The data suggest that the PPARalpha polymorphism L162V might protect against the development of atherosclerosis or CHD in patients with DM-2. The absence of an association between the polymorphism and plasma lipoprotein concentrations may suggest that these protective effects are exerted directly on the arterial wall.

Obesity and post-prandial lipid metabolism. Feast or famine?

Both in Western countries and in third world countries there is an increasing incidence of obesity. Obesity per se or insulin resistance associated with obesity may increase cardiovascular risk factors including dyslipidemia, hypertension and Type 2 diabetes. Over the past decade the understanding has increased of specific mediators in the hypothalamus that are involved in regulating food intake and body weight. In obese humans fasting plasma lipids can be normal but postprandial lipid metabolism is abnormal with an accumulation of triglyceride-rich remnant lipoproteins. In viscerally obese men chylomicron remnant catabolism was markedly decreased when compared with lean individuals. The decreased clearance of chylomicron remnants in viscerally obese subjects may be explained by competition between chylomicron remnants and the increased hepatic production of VLDL for clearance by low density lipoprotein receptors. Increased food intake in rodent models of obesity was shown to be associated with a delay in the catabolism of remnant lipoprotein particles. Prevention of hyperphagia was found to correct the impairment in the metabolism of remnant lipoproteins. Under fasting and food restricted conditions the improvement of remnant metabolism was associated with an increased oxidation of remnant lipids as determined by a novel stable isotope breath test. Anti-obesity and lipid lowering drugs have been used for the treatment of obesity. Inhibitors of cholesterol synthesis inhibitors (statins) have been shown to be effective in treating dyslipidemia. Inhibition of cholesterol synthesis with Atorvastatin was shown to improve chylomicron metabolism by increasing chylomicron remnant catabolism in obese subjects as assessed by the newly developed stable isotope breath test.

Brain protection by resveratrol and fenofibrate against stroke requires peroxisome proliferator-activated receptor alpha in mice

Peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors which belong to the nuclear receptor family. We examined whether PPARalpha agonists and resveratrol, a polyphenol contained in grapes, protect the brain against ischemia. To investigate whether resveratrol activates PPARs, we performed a cell-based transfection activity assay using luciferase reporter plasmid. PPARalpha and PPARgamma were activated by resveratrol in primary cortical cultures and vascular endothelial cells. Resveratrol (20 mg/kg, 3 days) reduced infarct volume by 36% at 24 h after middle cerebral artery occlusion in wild-type mice. The PPARalpha agonists fenofibrate (30 mg/kg, 3 days) and Wy-14643 (30 mg/kg, days) exerted similar brain protection. However, resveratrol and fenofibrate failed to protect the brain in PPARalpha knockout mice. The data indicate that PPARalpha agonists protect the brain through PPARalpha.