Regulation of lipid and lipoprotein metabolism by PPAR activators

Ascochlorin derivatives as ligands for nuclear hormone receptors

Nuclear receptor family proteins are structurally related transcription factors activated by specific lipophilic compounds. Because they are activated by a variety of hormonal molecules, including retinoic acid, vitamin D, and steroid hormones, they are assumed to be promising targets for clinical drugs. We previously found that one ascochlorin (1) derivative, 4-O-carboxymethyl-ascochlorin (2), is a potent agonist of peroxisome proliferator activated receptor gamma (PPARgamma). Here, we synthesized derivatives of 1, designated as a lead compound, to create new modulators of nuclear hormone receptors. Two derivatives, 4-O-carboxymethyl-2-O-methylascochlorin (9) and 4-O-isonicotinoyl-2-O-methylascochlorin (10), showed improved agonistic activity for PPARgamma and induced differentiation of a progenitor cell line, C3H10T1/2. We also found that 1, dehydroascofuranon (29), and a 2,4-O-diacetyl-1-carboxylic acid derivative of 1 (5) specifically activated estrogen receptors, PPARalpha, and an androgen receptor. All of the derivatives (1-29) activated the pregnane X receptor. These results suggest that the chemical structure of 1 is useful in designing novel modulators of nuclear receptors.

Achievement of low-density lipoprotein cholesterol goals: new strategies to address new guidelines

Evidence that CHD morbidity and mortality can be reduced with reduction of LDL-C to less than 100 mg/dL (2.6 mmol/L) is rapidly accumulating. NCEP-ATP III guidelines should be considered minimal goals of therapy. Regarding the prevention and treatment of CHD, health care providers need to recognize the wide therapeutic gap between evidence-based medicine and customary clinical practice. Aggressive pharmacologic therapy is probably required to achieve optimal LDL-C levels in many hyperlipidemic patients. Novel agents, including selective cholesterol absorption inhibitors, will provide clinicians with a tool to safely and effectively target the exogenous pathway of cholesterol metabolism. Combination therapy with cholesterol-lowering agents that have complementary mechanisms of action and can be safely co-administered may be a new option to achieve broader lipid control.

Different short- and long-term effects of resveratrol on nuclear factor-kappaB phosphorylation and nuclear appearance in human endothelial cells

BACKGROUND

Resveratrol (a naturally occurring phytoalexin found in grapes and wine) has cardiovascular protective effects that suggest the antiatherogenic (ie, antiinflammatory) activities of the compound on endothelial cells.

OBJECTIVE

The antiinflammatory activity of resveratrol could be mediated by its interference with nuclear factor-kappaB (NF-kappaB)-dependent transcription. Thus, we studied the in vitro influence of physiologic concentrations of resveratrol (<or= 1 micromol/L) on the NF-kappaB signaling pathway after tumor necrosis factor alpha (TNF-alpha) stimulation of endothelial cells.

DESIGN

The effects of a 30-min (acute) and an overnight incubation of resveratrol on the nuclear appearance of p50-NF-kappaB and p65-NF-kappaB on serine and tyrosine phosphorylation of the inhibitory subunit kappaB alpha (IkappaBalpha), cytoplasmic concentrations of IkappaBalpha, NF-kappaB phosphorylation or nitrosylation, the reduction of the mitotic inhibitor p21, and the activation of peroxisome proliferator-activated receptor alpha were evaluated.

RESULTS

The nuclear appearance of p50-NFkappaB and p65-NFkappaB acutely induced by TNF-alpha was not modified by resveratrol but was increased after overnight incubation with resveratrol alone or in combination with TNF-alpha. Acute treatment with resveratrol did not modify TNF-alpha-induced cytoplasmic IkappaBalpha serine phosphorylation but did increase IkappaBalpha tyrosine phyophorylation. Resveratrol increased the tyrosine phosphorylation (but not nitrosylation) of immunoprecipitated NF-kappaB, did not decrease cellular p21, and did not increase peroxisome proliferator-activated receptor alpha activity.

CONCLUSIONS

Acute resveratrol treatment does not inhibit the nuclear appearance of NF-kappaB in human umbilical vein endothelial cells, but overnight treatment does. The increase in tyrosine phosphorylation of IkappaBalpha, p50-NF-kappaB, and p65-NF-kappaB suggests the involvement of such alterations in the modulation of NF-kappaB transcription activity.

Diacylglycerol on lipid metabolism

PURPOSE OF REVIEW

Diacylglycerol is an intermediate product of triacylglycerol hydrolysis and comprises up to 10% of glycerides in plant-derived edible fats and oils. Recent developments in oil chemistry have led to the availability of a novel diacylglycerol oil for clinical studies. Recent research has shown that the oil containing 70% of unusual 1,3- species has metabolic characteristics distinct from those of triacylglycerol of similar fatty acid composition. This review summarizes recent research in humans and experimental animals into the metabolic effects and possible mechanisms of action of this oil.

RECENT FINDINGS

Consumption of the oil affects lipid metabolism including lowering of plasma triacylglcerol, decreases postprandial lipemia and reduces body fat mass, compared with triacylglcerol. As the fatty acids of the two oils are similar, the metabolic differences reside in their structural differences.

SUMMARY

It is still uncertain whether longer term consumption of the diacylglycerol oil will lead to persistent and consistent reductions in plasma triacylglycerol and body fat. However future studies may demonstrate a role in managing aspects of the metabolic syndrome.

Statin-fibrate combination: therapy for hyperlipidemia: a review

Statins and fibrates are well-established treatments for hyperlipidaemias and the prevention of vascular events. However, fibrate + statin therapy has been restricted following early reports of rhabdomyolysis that mainly involved gemfibrozil, originally with bovastatin, and recently, with cerivastatin. Despite this limitation, several reports describing combination therapy have been published. This review considers these studies and the relevant indications and contraindications. Statin + fibrate therapy should be considered if monotherapy or adding other drugs (e.g. cholesterol absorption inhibitors, omega-3 fatty acids ornicotinic acid) did not achieve lipid targets or is impractical. Combination therapy should be hospital-based and reserved for high-risk patients with a mixed hyperlipidaemia characterised by low density lipoprotein cholesterol (LDL) >2.6 mmol/l(100 mg/dl, high density lipoprotein cholesterol (HDL) <1.0 mmol/l (40 mg/dl) and/or triglycerides> 5.6 mmol/l (500 mg/dl. These three 'goals' are individually mentioned in guidelines. Patients should have normal renal, liver and thyroid function tests and should not be receiving therapy with cyclosporine, protease inhibitors or drugs metabolised through cytochrome P450 (especially 3A4). Combination therapy is probably best conducted using drugs with short plasma half-lives; fibrates should be prescribed in the morning and statins at night to minimise peak dose interactions. Both drug classes should be progressively titated from low doses. Regular (3-monthly) monitoring of liver function and creatine kinase is required. In conclusion, fibrate + statin therapy remains an option in high-risk patents. However, long-term studies involving safety monitoring and vascular endpoints are required to demonstrate the efficacy of this regimen.

Reduction of atherosclerosis by the peroxisome proliferator-activated receptor alpha agonist fenofibrate in mice

Several clinical and angiographic intervention trials have shown that fibrate treatment leads to a reduction of the coronary events associated to atherosclerosis. Fibrates are ligands for peroxisome proliferator-activated receptor alpha (PPARalpha) that modulate risk factors related to atherosclerosis by acting at both systemic and vascular levels. Here, we investigated the effect of treatment with the PPARalpha agonist fenofibrate (FF) on the development of atherosclerotic lesions in apolipoprotein (apo) E-deficient mice and human apoA-I transgenic apoE-deficient (hapoA-I Tg x apoE-deficient) mice fed a Western diet. In apoE-deficient mice, plasma lipid levels were increased by FF treatment with no alteration in the cholesterol distribution profile. FF treatment did not reduce atherosclerotic lesion surface area in the aortic sinus of 5-month-old apoE-deficient mice. By contrast, FF treatment decreased total cholesterol and esterified cholesterol contents in descending aortas of these mice, an effect that was more pronounced in older mice exhibiting more advanced lesions. Furthermore, FF treatment reduced MCP-1 mRNA levels in the descending aortas of apoE-deficient mice, whereas ABCA-1 expression levels were maintained despite a significant reduction of aortic cholesterol content. In apoE-deficient mice expressing a human apoA-I transgene, FF increased human apoA-I plasma and hepatic mRNA levels without affecting plasma lipid levels. This increase in human apoA-I expression was accompanied by a significant reduction in the lesion surface area in the aortic sinus. These data indicate that the PPARalpha agonist fenofibrate reduces atherosclerosis in these animal models of atherosclerosis.

Mechanisms of the triglyceride- and cholesterol-lowering effect of fenofibrate in hyperlipidemic type 2 diabetic patients

In humans, the precise mechanisms of the hypolipidemic action of fenofibrate, a peroxisome proliferator-activated receptor-alpha agonist, remain unclear. To gain insight on these mechanisms, we measured plasma lipids levels, lipids synthesis (hepatic de novo lipogenesis and cholesterol synthesis), and mRNA concentrations in circulating mononuclear cells (RT-PCR) of hydroxymethylglutaryl (HMG)-CoA reductase, LDL receptor, LDL receptor- related protein (LRP), scavenger receptor class B type I (SR-BI), ABCAI, and liver X receptor (LXR)-alpha in 10 control subjects and 9 hyperlipidemic type 2 diabetic patients. Type 2 diabetic subjects were studied before and after 4 months of fenofibrate administration. Fenofibrate decreased plasma triglycerides (P < 0.01) and total cholesterol (P < 0.05) concentrations and slightly increased HDL cholesterol (P < 0.05). Hepatic lipogenesis, largely enhanced in diabetic subjects (16.1 +/- 2.1 vs. 7.5 +/- 1.6% in control subjects, P < 0.01), was decreased by fenofibrate (9.8 +/- 1.5%, P < 0.01). Fractional cholesterol synthesis was normal in diabetic subjects (3.5 +/- 0.4 vs. 3.3 +/- 0.5% in control subjects) and was unchanged by fenofibrate (3.5 +/- 0.5%). Absolute cholesterol synthesis was, however, increased in diabetic subjects before and after fenofibrate (P < 0.05 vs. control subjects). HMG-CoA reductase, LDL receptor, LRP, and SR-BI mRNA concentrations were not different in type 2 diabetic and control subjects and were unchanged by fenofibrate. LXR-alpha mRNA levels were increased (P < 0.05) by fenofibrate. ABCAI mRNA concentrations, which were decreased in diabetic subjects (P < 0.05) before fenofibrate, were increased (P < 0.05) by fenofibrate to values comparable to those of control subjects. The plasma triglyceride-lowering effect of fenofibrate is explained in part by a decrease in hepatic lipogenesis, the moderate fall in total plasma cholesterol is not explained by a reduction of whole-body cholesterol synthesis, and the increase in LXR-alpha and ABCAI mRNA levels suggests that fenofibrate stimulated reverse cholesterol transport.

High-density lipoprotein cholesterol and triglycerides as therapeutic targets for preventing and treating coronary artery disease

Epidemiologic and clinical trials show that elevated triglycerides and low levels of high-density lipoprotein cholesterol (HDL-C) are independent risk factors for coronary heart disease (CHD). However, adjustment for covariates frequently weakens or abolishes the predictive significance of triglycerides, whereas the evidence for HDL-C is more consistently strong. Data indicate that there is a 2% to 3% decrease in coronary risk for each 1 mg/dL increase in HDL-C, whereas the benefit of triglyceride lowering appears to occur largely in patients with the highest baseline levels. The 2001 National Cholesterol Education Program Adult Treatment Panel III (ATP III) guidelines for detecting and treating high blood cholesterol reflect our improved understanding of triglycerides and HDL as CHD risk factors. However, the guidelines place more emphasis on lowering triglycerides than on raising HDL-C by identifying non-HDL-C (ie, low-density lipoprotein cholesterol [LDL-C] + very-low-density lipoprotein cholesterol [VLDL-C]) as a secondary target of therapy. In clinical practice, VLDL-C is the most readily available measure of atherogenic triglyceride-rich remnant lipoproteins. On the basis of the available epidemiologic and clinical evidence, refinement of the NCEP guidelines to include more emphasis on raising HDL-C levels should be considered. Novel drugs are being developed that have the potential to increase HDL-C concentrations and/or improve the functionality of HDL.

Existing and investigational combination drug therapy for high-density lipoprotein cholesterol

For the past 3 to 4 decades, clinical outcomes trials have shown that drugs that favorably alter serum lipid levels reduce the risk of coronary artery disease (CAD) events. However, despite these successes, the reduction in serum low-density lipoprotein (LDL) cholesterol levels with monotherapy lipid-altering drugs does not "cure" CAD to the same degree that antibiotics "cure" many infections, nor do they "prevent" CAD in the same way that childhood immunizations "prevent" the onset of such conditions as measles, mumps, and rubella. Clinical outcome trials of monotherapy lipid-altering drugs have demonstrated a reduction in the relative risk of CAD in only a minority of patients. Thus, although safe and very effective in lowering serum LDL cholesterol levels, drugs that predominantly lower cholesterol do not "cure" atherosclerotic disease, nor have they been shown to "prevent" most CAD events in numerous clinical outcome trials. The reason for the suboptimal CAD outcomes benefits of monotherapy lipid-altering drugs is likely because atherosclerosis is a complex pathologic process with many important risk factors involved in the initiation and progression of atherosclerotic lesions and involved in the onset of the CAD event itself. An elevated serum LDL cholesterol level is an important CAD risk factor, but it is not the only lipid risk factor. A decreased serum high-density lipoprotein (HDL) cholesterol level is another important risk factor for CAD. Combination therapy through existing drugs (or possibly, in the future, through investigational lipid-altering drugs) may not only improve LDL cholesterol but also improve serum HDL cholesterol levels. This more global, multidimensional approach to lipid-altering drug treatment may provide the best chance to prevent CAD.

Combination therapy for combined dyslipidemia

Patients with combined dyslipidemia are at high risk for coronary artery disease and often require combination drug therapy to achieve lipid levels recommended by the US National Cholesterol Education Program's third Adult Treatment Panel (ATP III). In addition to recommendations for low-density lipoprotein (LDL) cholesterol and triglyceride levels, ATP III established non-high-density lipoprotein (HDL) cholesterol goals for individuals with triglycerides >or=2.26 mmol/L (>or=200 mg/dL). It also introduced certain criteria for the diagnosis of the metabolic syndrome, a clustering of risk factors (abdominal obesity, elevated triglycerides, low HDL cholesterol, elevated blood pressure, impaired fasting glucose) that increases cardiovascular risk and is common in patients with combined dyslipidemia. Statin monotherapy has been shown to benefit these patients, and additional benefit may be obtained by combination therapy that provides greater reductions in both LDL cholesterol and triglycerides as well as greater increases in HDL cholesterol. However, combining a statin with either niacin or a fibrate may increase the risk for myopathy and therefore requires careful monitoring and evaluation of the risk-benefit ratio for each patient. Moreover, combination therapy may be associated with increased drug costs and decreased patient compliance. Recently developed agents that may improve the effectiveness of combination therapy include ezetimibe-a cholesterol absorption inhibitor-and a formulation that combines extended-release niacin and lovastatin in a single pill. Clinical trials are needed to determine the optimal treatment in patients with combined dyslipidemia.

Fasting plasma free fatty acid concentrations and Pro12Ala polymorphism of the peroxisome proliferator-activated receptor (PPAR) gamma2 gene in healthy individuals

BACKGROUND

The Pro12Ala polymorphism of the peroxisome proliferator-activated receptor (PPAR) gamma gene has been associated in some, but not all, studies with lower body mass index (BMI) and improved insulin sensitivity; how an altered transcriptional activity of PPARgamma2 could influence insulin sensitivity is currently unclear. The free fatty acids (FFAs) released from adipose tissue triglycerides via lipolysis are key mediators of impaired insulin sensitivity; however, no study has described the relationship of the Pro12Ala mutation with circulating levels of FFAs under physiological conditions.

OBJECTIVE

To investigate in a population-based sample of Caucasians the relation of the Pro12Ala polymorphism with plasma concentrations of FFAs and other markers of lipid and glucose metabolism described as components of the insulin resistance syndrome.

SUBJECTS

Four hundred and thirty-eight nondiabetic employees of the Italian Telephone Company, aged 35-65 years, randomly selected from a total population of 3900 participants in a company-sponsored health screening.

MEASUREMENTS

The Pro12Ala polymorphism of the PPARgamma was studied together with plasma FFAs, insulin, glucose, triglycerides, high density lipoprotein (HDL) cholesterol, blood pressure and anthropometry. The Homeostatic Model Assessment (HOMA) index was calculated as a measure of insulin resistance.

RESULTS

Carriers and noncarriers of the Pro12Ala polymorphism showed very similar circulating levels of FFA (0.46 +/- 0.2 vs. 0.47 +/- 0.2, NS); plasma glucose, triglycerides, HDL cholesterol and blood pressure were also similar in the two groups with or without the polymorphism. To allow for the possible confounding effect of obesity, a separate analysis was conducted in overweight (BMI > or = 25 kg/m(2)) and normal-weight people (BMI < 25 kg/m(2)). Circulating plasma FFA concentrations, as well as triglycerides, blood pressure and HOMA, were significantly higher in overweight than normal-weight, as expected, but no significant differences were detected between carriers and noncarriers of the Pro12Ala polymorphism within each BMI group (0.49 +/- 0.2 vs. 0.48 +/- 0.2, NS, and 0.44 +/- 0.2 vs. 0.47 +/- 0.2, NS, in overweight and normal-weight, respectively). The Pro12Ala polymorphism was also analysed across increasing quartiles of FFA concentrations and no relationship was observed between the frequency of the polymorphism and FFA values (overall chi2 = 0.48, NS).

CONCLUSION

This study does not show any relationship between the Pro12Ala polymorphism of the PPARgamma gene and fasting FFAs in the general population. The possibility of a different handling of FFAs under different conditions (i.e. postprandial) cannot be excluded and remains to be explored.

The role of PPARs in atherosclerosis

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

Peroxisome proliferator-activated receptor agonists, hyperlipidaemia, and atherosclerosis

Dyslipidaemia is a major risk factor in the development of atherosclerosis, and lipid lowering is achieved clinically using fibrate drugs and statins. Fibrate drugs are ligands for the fatty acid receptor peroxisome proliferator-activated receptor (PPAR)alpha, and the lipid-lowering effects of this class of drugs are mediated by the control of lipid metabolism, as directed by PPARalpha. PPARalpha ligands also mediate potentially protective changes in the expression of several proteins that are not involved in lipid metabolism, but are implicated in the pathogenesis of heart disease. Clinical studies with bezafibrate and gemfibrozil support the hypothesis that these drugs may have a significant protective effect against cardiovascular disease. The thiazolidinedione group of insulin-sensitising drugs are PPARgamma ligands, and these have beneficial effects on serum lipids in diabetic patients and have also been shown to inhibit the progression of atherosclerosis in animal models. However, their efficacy in the prevention of cardiovascular-associated mortality has yet to be determined. Recent studies have found that PPARdelta is also a regulator of serum lipids. However, there are currently no drugs in clinical use that selectively activate this receptor. It is clear that all three forms of PPARs have mechanistically different modes of lipid lowering and that drugs currently available have not been optimised on the basis of PPAR biology. A new generation of rationally designed PPAR ligands may provide substantially improved drugs for the prevention of cardiovascular disease.

Evaluation of the role of peroxisome-proliferator-activated receptor alpha in the regulation of cardiac pyruvate dehydrogenase kinase 4 protein expression in response to starvation, high-fat feeding and hyperthyroidism

Inactivation of cardiac pyruvate dehydrogenase complex (PDC) after prolonged starvation and in response to hyperthyroidism is associated with enhanced protein expression of pyruvate dehydrogenase kinase (PDK) isoform 4. The present study examined the potential role of peroxisome-proliferator-activated receptor alpha (PPARalpha) in adaptive modification of cardiac PDK4 protein expression after starvation and in hyperthyroidism. PDK4 protein expression was analysed by immunoblotting in homogenates of hearts from fed or 48 h-starved rats, rats rendered hyperthyroid by subcutaneous injection of tri-iodothyronine and a subgroup of euthyroid rats maintained on a high-fat/low-carbohydrate diet, with or without treatment with the PPARalpha agonist WY14,643. In addition, PDK4 protein expression was analysed in hearts from fed, 24 h-starved or 6 h-refed wild-type or PPARalpha-null mice. PPARalpha activation by WY14,643 in vivo over the timescale of the response to starvation failed to up-regulate cardiac PDK4 protein expression in rats maintained on standard diet (WY14,643, 1.1-fold increase; starvation, 1.8-fold increase) or influence the cardiac PDK4 response to starvation. By contrast, PPARalpha activation by WY14,643 in vivo significantly enhanced cardiac PDK4 protein expression in rats maintained on a high-fat diet, which itself increased cardiac PDK4 protein expression. PPARalpha deficiency did not abolish up-regulation of cardiac PDK4 protein expression in response to starvation (2.9-fold increases in both wild-type and PPARalpha-null mice). Starvation and hyperthyroidism exerted additive effects on cardiac PDK4 protein expression, but PPARalpha activation by WY14,643 did not influence the response of cardiac PDK4 protein expression to hyperthyroidism in either the fed or starved state. Our data support the hypothesis that cardiac PDK4 protein expression is regulated, at least in part, by a fatty acid-dependent, PPARalpha-independent mechanism and strongly implicate a fall in insulin in either initiating or facilitating the response of cardiac PDK4 protein expression to starvation.

Management of dyslipidemia

The 2 principal approaches to management of dyslipidemias are lifestyle intervention and lipid-modifying drug therapy. Recent revisions to the American Heart Association's dietary guidelines for reducing cardiovascular disease emphasize an overall healthy eating pattern and maintenance of appropriate body weight, together with achieving a desirable blood pressure and a desirable lipoprotein profile. New National Cholesterol Education Program treatment guidelines include a scoring system for calculating coronary heart disease (CHD) risk that is adapted from the Framingham Heart Study, as well as a category of CHD risk equivalents (e.g., diabetes) that will encourage more aggressive therapeutic intervention for individuals at high short-term risk for CHD, even in the absence of clinically evident coronary disease. Classes of lipid-modifying drugs include bile acid sequestrants (resins), fibrates, and statins, with each class exerting different effects on the lipid profile. Nicotinic acid (niacin) is also an approved lipid-modifying agent. The armamentarium for treating lipid disorders and atherosclerosis now includes statins that can decrease low-density lipoprotein (LDL) cholesterol levels by up to 55%, as well as a resin with improved tolerability. In patients with high levels of LDL cholesterol and triglycerides, together with low concentrations of high-density lipoprotein cholesterol, combination therapy may be effective. Moreover, researchers are currently investigating the development of drugs directed at molecular targets, including cholesterol esterification and accumulation in macrophage foam cells (e.g., inhibiting acyl-coenzyme A : cholesterol acyltransferase), degradation of atherosclerotic plaque (e.g., decreasing the expression of matrix metalloproteinases), and reverse cholesterol transport (e.g., stimulating ATP-binding cassette transporter A1).

Peroxisome-proliferator-activated receptor-alpha (PPARalpha) deficiency leads to dysregulation of hepatic lipid and carbohydrate metabolism by fatty acids and insulin

The aim of the present study was to determine whether peroxisome-proliferator-activated receptor-alpha (PPARalpha) deficiency disrupts the normal regulation of triacylglycerol (TAG) accumulation, hepatic lipogenesis and glycogenesis by fatty acids and insulin using PPARalpha-null mice. In wild-type mice, hepatic TAG concentrations increased (P<0.01) with fasting (24 h), with substantial reversal after refeeding (6 h). Hepatic TAG levels in fed PPARalpha-null mice were 2.4-fold higher than in the wild-type (P<0.05), increased with fasting, but remained elevated after refeeding. PPARalpha deficiency also impaired hepatic glycogen repletion (P<0.001), despite normal insulin and glucose levels after refeeding. Higher levels of plasma insulin were required to support similar levels of hepatic lipogenesis de novo ((3)H(2)O incorporation) in the PPARalpha-null mice compared with the wild-type. This difference was reflected by corresponding changes in the relationship between plasma insulin and the mRNA expression of the lipogenic transcription factor sterol-regulatory-element-binding protein-1c, and that of one of its known targets, fatty acid synthase. In wild-type mice, hepatic pyruvate dehydrogenase kinase (PDK) 4 protein expression (a downstream marker of altered fatty acid catabolism) increased (P<0.01) in response to fasting, with suppression (P<0.001) by refeeding. Although PDK4 up-regulation after fasting was halved by PPARalpha deficiency, PDK4 suppression after refeeding was attenuated. In summary, PPARalpha deficiency leads to accumulation of hepatic TAG and elicits dysregulation of hepatic lipid and carbohydrate metabolism, emphasizing the importance of precise control of lipid oxidation for hepatic fuel homoeostasis.

Design of a chimeric promoter induced by pro-inflammatory mediators in articular chondrocytes

We have designed a chimeric promoter that can be stimulated by various pro-inflammatory mediators and so drive the expression of therapeutic genes under inflammatory conditions. The promoter has two parts, the [-247/+20] fragment of the human type IIA secreted phospholipase A2 gene promoter, which is stimulated by the pro-inflammatory cytokine interleukin-1beta (IL-1beta), and a double peroxisome proliferator-activated receptor response element that is activated by some eicosanoids and by non-steroidal anti-inflammatory drugs (NSAIDs). Transfection experiments using rabbit articular chondrocytes in primary culture showed that this chimeric promoter produced a low basal activity and was induced by NSAIDs, WY-14643, IL-1beta, and 15-deoxy Delta12,14 prostaglandin J2. The latter two compounds stimulated the promoter synergistically.

Streptozotocin-pancreatic damage in the rat: modulatory effect of 15-deoxy delta12,14-prostaglandin j(2) on nitridergic and prostanoid pathway

15-deoxy-delta (12,14)prostaglandin J(2) (15d-PGJ(2)) has been identified as a natural ligand of the PPARgamma subtype. PPAR activation in nonadipose tissues seems to inhibit iNOS and COX2 expression. Vasoactive compounds like nitric oxide and prostaglandins are increased in pancreatic tissue from streptozotocin-diabetic rats. We hypothesize that 15d-PGJ(2) may regulate the production of these proinflammatory compounds that lead to beta cell destruction in the diabetic pathology. In this work we evaluated Ca(2+)-dependent (cNOS) and Ca(2+)-independent (iNOS) activity, nitrate/nitrite levels, 15-dPGJ(2) and prostaglandin E(2) (PGE(2)) levels in isolated pancreatic islets, and 15d-PGJ(2) levels in plasma from control and streptozotocin-diabetic rats. Our results show that cNOS is predominant in control, while iNOS isoform is increased in the diabetic islets (P < 0.01). 15d-PGJ(2) 10(-5)M inhibits cNOS and iNOS activity both in control and diabetic islets (P < 0.05). Nitrate/nitrite and PGE(2) levels are higher in diabetic than in control islets (P < 0.05 and P < 0.01, respectively). 15d-PGJ(2) 10(-5)M decreases nitrate/nitrite and PGE(2) levels both in control and in diabetic islets. Bisphenol A diglycidyl ether (BADGE), a recently described PPARgamma antagonist, seems to act as a PPARgamma agonist, diminishing nitrate/nitrite and PGE2 levels in control and diabetic islets. 15d-PGJ(2) production is lower in islets from diabetic animals compared to control (P < 0.05). Our observations suggest that 15d-PGJ(2) is able to diminish the production of vasoactive proinflammatory agents in pancreatic islets. The diminished 15d-PGJ(2) levels in the diabetic islets are probably related to the diminished capacity to limit the inflammatory response due to experimental diabetes in the rat.

Potentiation of TNF-alpha-stimulated group IIA phospholipase A(2) expression by peroxisome proliferator-activated receptor alpha activators in rat mesangial cells

Natural activators of peroxisome proliferator-activated receptors (PPAR) are lipid metabolites, including those produced by phospholipases A(2) (PLA(2)). In glomerular mesangial cells, the secreted group IIA PLA(2) (sPLA(2)-IIA), which is thought to be a crucial factor in pathologic processes in the kidney, may provide free fatty acids and eicosanoids directly or indirectly, by activating a cytosolic PLA(2). The scope of this study was to investigate whether synthetic PPAR(alpha) activators have an effect on sPLA(2)-IIA mRNA expression in rat mesangial cells, thus constituting a feedback modulation of sPLA(2)-IIA transcription. In the presence of tumor necrosis factor-alpha (TNF-alpha), the PPAR(alpha) agonists WY14643 and LY171883 as well as the lipid-lowering compound clofibrate potentiated expression, secretion, and activity of group IIA sPLA(2) in mesangial cells. MK886, known as a noncompetitive inhibitor of PPAR(alpha), completely abolished the potentiation of sPLA(2)-IIA secretion and activity by WY14643, thus indicating that the effect of WY14643 is specifically mediated by PPAR(alpha). When cells were transfected with different constructs of the rat sPLA(2)-IIA promoter fused to a luciferase reporter gene, a stimulation with TNF-alpha in the presence of the PPAR(alpha) activators caused an enhanced promoter activity compared with that induced by TNF-alpha alone. Site-directed mutagenesis of a putative PPRE site in the sPLA(2)-IIA promoter abolished the potentiating effect of PPAR(alpha) agonists, thus strongly indicating its contribution to the enhanced promoter activity. In summary, this study shows that the rat sPLA(2)-IIA promoter is sensitive to PPAR(alpha) agonists, which act synergistically with cytokines, resulting in an enhanced expression of sPLA(2)-IIA in rat mesangial cells.

Potent suppression of the adaptive immune response in mice upon dietary exposure to the potent peroxisome proliferator, perfluorooctanoic acid

In a previous investigation, we demonstrated that severe thymus and spleen atrophy occurs in mice upon dietary exposure to several potent peroxisome proliferators (PPs). In the present investigation, the effects of the potent PP perfluorooctanoic acid (PFOA) on the adaptive immunity of mice was evaluated both in vivo and ex vivo. The in vivo immune response examined involved immunization of mice with horse red blood cells (HRBCs), displaying T-cell-dependent antigens after pre-treatment with a PFOA-containing diet for 10 days. Subsequent quantitation of the primary humoral response was performed employing both the plaque-forming cell (PFC) assay and determination of the antibody titer by ELISA. The results clearly demonstrate that oral administration of PFOA prevents both the increases in plaque formations by anti-IgM and -IgG and in serum levels of IgM and IgG normally evoked by such immunization. Ex vivo spleen cells proliferation (assayed as incorporation of 3H-thymidine) in response to both T- and B-cell activators was attenuated by dietary treatment with PFOA, although the analogous in vitro treatment of mouse spleen cells with this same compound had no such effects. Thus, the relatively metabolically inert PP PFOA may exert adaptive immunosuppression in mice by an indirect mechanism. The possible relevance of this immunosuppression to the alterations in plasma lipids caused by PPs is discussed.

Antagonism of the actions of peroxisome proliferator-activated receptor-alpha by bile acids

The peroxisome proliferator-activated receptor-alpha (PPARalpha) is a ligand-activated transcription factor that regulates the expression of a number of genes critical for fatty acid beta-oxidation. Because a number of substrates and intermediates of this metabolic pathway serve as ligand activators of this receptor, homeostatic control of fatty acid metabolism is achieved. Evidence also exists for PPARalpha-dependent regulation of genes encoding critical enzymes of bile acid biosynthesis. To determine whether the primary products of bile acid biosynthesis, cholic acid and chenodeoxycholic acid, were capable of modulating PPARalpha function, a variety of in vivo and in vitro approaches were utilized. Feeding a bile acid-enriched diet significantly reduced the degree of hepatomegaly and induction of target genes encoding enzymes of fatty acid beta-oxidation caused by treatment with the potent PPARalpha ligand Wyeth-14,643. Convergent data from mechanistic studies indicate that bile acids interfere with transactivation by PPARalpha at least in part by impairing the recruitment of transcriptional coactivators. The results of this study provide the first evidence in favor of the existence of compounds, normally found within the body, that are capable of antagonizing the physiological actions of PPARalpha. The impact of PPARalpha antagonism by endogenous bile acids is likely to be limited under normal conditions and to have only minimal effects on bile acid homeostasis. However, during certain pathophysiological states where intracellular bile acid concentrations are elevated, meaningful effects on PPARalpha-dependent target gene regulation are possible.

Regulation of mitochondrial sn-glycerol-3-phosphate acyltransferase activity: response to feeding status is unique in various rat tissues and is discordant with protein expression

Triacylglycerol plays a critical role in an organism's ability to withstand fuel deprivation, and dysregulation of triacylglycerol synthesis is important in the development of diseases such as obesity and diabetes. Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the initial and committed step of glycerolipid synthesis and is therefore a potential site for regulation of triacylglycerol synthesis. Because several studies suggest that triacylglycerol synthesis is linked to the mitochondrial isoform, we studied mitochondrial GPAT expression and the effect of feeding status on the regulation of mitochondrial GPAT in various rat tissues. Liver, adipose, and soleus muscle have high levels of GPAT mRNA, but low protein expression, whereas heart and adrenal, tissues with low GPAT mRNA abundance, have the highest GPAT protein expression. In addition, heart, which has the highest expression of mitochondrial GPAT protein, has low mitochondrial GPAT specific activity (0.02 nmol/min/mg). Liver and adipose have the highest mitochondrial GPAT specific activity (0.17 nmol/min/mg), but very low protein expression. Discrepancies between GPAT protein expression and activity suggest that mitochondrial GPAT may be regulated acutely. In response to a 48-h fast, liver and adipose mitochondrial GPAT protein expression and activity decrease 30-50%. After 24-h refeeding of either chow or high-sucrose diet, mitochondrial GPAT protein expression and activity overshoot normal levels 30-60%. In kidney, mitochondrial GPAT protein and activity increase 65 and 30%, respectively, with refeeding, whereas in the heart, mitochondrial GPAT activity increases 2.3-fold after a fast, with no change in protein expression. We also found that hepatic mitochondrial GPAT activity in the neonatal rat constitutes a lower percentage of the total GPAT activity than in the adult. We postulate that GPAT expression is modulated uniquely in each tissue according to specific needs for triacylglycerol storage.

Further evidence for the involvement of inhibition of cell proliferation and development in thymic and splenic atrophy induced by the peroxisome proliferator perfluoroctanoic acid in mice

We recently demonstrated that severe thymic and splenic atrophy occur upon dietary treatment of mice with potent peroxisome proliferators (PPs), e.g. perfluorooctanoic acid (PFOA), WY-14,643, nafenopin, and di(2-ethylhexyl)phthalate (DEHP). In the present study, we investigated this phenomenon further employing a relative inert PP, PFOA. Comparison of the dose-dependencies and time-courses indicated that the peroxisome proliferative effect occurred prior to atrophy of both the thymus and spleen. However, following withdrawal of PFOA from the diet, the weight of the thymus and spleen rapidly returned to normal within 10 and 5 days, respectively, in contrast to the more persistent peroxisome proliferation. Furthermore, the changes in thymus and spleen weight upon PFOA treatment and the following withdrawal from diet paralleled the changes in total thymocyte and splenocyte counts, respectively. It was found previously that the decreases in the thymocyte populations present in the S and G2/M phases, as well as in the number of CD4+CD8+ cells upon PFOA treatment, were the most dramatic, perhaps reflecting inhibition of thymocyte proliferation in connection with thymocyte development. Here, the recovery of thymocytes began with increases in the populations in these same phases of the cell cycle, with CD4+CD8+ cells recovering most rapidly, lending further support to our previous hypothesis. The possible relationship of these immunotoxic effects of PPs to the changes they cause in fatty acid metabolism is discussed.

Peroxisome proliferator-activated receptors in endothelial cell biology

New insights into the endothelium as a dynamic, interactive organ have generated increased interest in endothelial cell transcriptional regulation. Peroxisomal proliferator-activated receptors (PPARs), as ligand-activated nuclear receptors expressed in endothelial cells, represent one important pathway that likely influences vascular responses both directly and indirectly by altering gene expression. PPAR ligands such as fibrates (PPAR-alpha) and insulin-sensitizing thiazolidinediones (PPAR-gamma) are in clinical use and may alter the process of atherosclerosis. The present review highlights the emerging evidence for PPAR-alpha and PPAR-gamma expression in the vasculature, as well as their potential roles in endothelial cell biology.

Negative regulation of human fibrinogen gene expression by peroxisome proliferator-activated receptor alpha agonists via inhibition of CCAAT box/enhancer-binding protein beta

Fibrinogen is a coagulation factor and an acute phase reactant up-regulated by inflammatory cytokines, such as interleukin 6 (IL-6). Elevated plasma fibrinogen levels are associated with coronary heart diseases. Fibrates are clinically used hypolipidemic drugs that act via the nuclear receptor peroxisome proliferator-activated receptor alpha (PPAR alpha). In addition, most fibrates also reduce plasma fibrinogen levels, but the molecular mechanism is unknown. In this study, we demonstrate that fibrates decrease basal and IL-6-stimulated expression of the human fibrinogen-beta gene in human primary hepatocytes and hepatoma HepG2 cells. Fibrates diminish basal and IL-6-induced fibrinogen-beta promoter activity, and this effect is enhanced in the presence of co-transfected PPAR alpha. Site-directed mutagenesis experiments demonstrate that PPAR alpha activators decrease human fibrinogen-beta promoter activity via the CCAAT box/enhancer-binding protein (C/EBP) response element. Co-transfection of the transcriptional intermediary factor glucocorticoid receptor-interacting protein 1/transcriptional intermediary factor 2 (GRIP1/TIF2) enhances fibrinogen-beta gene transcription and alleviates the repressive effect of PPAR alpha. Co-immunoprecipitation experiments demonstrate that PPAR alpha and GRIP1/TIF2 physically interact in vivo in human liver. These data demonstrate that PPAR alpha agonists repress human fibrinogen gene expression by interference with the C/EBP beta pathway through titration of the coactivator GRIP1/TIF2. We observed that the anti-inflammatory action of PPAR alpha is not restricted to fibrinogen but also applies to other acute phase genes containing a C/EBP response element; it also occurs under conditions in which the stimulating action of IL-6 is potentiated by dexamethasone. These findings identify a novel molecular mechanism of negative gene regulation by PPAR alpha and reveal the direct implication of PPAR alpha in the modulation of the inflammatory gene response in the liver.

Smoking diminishes the beneficial effect of statins: observations from the landmark trials

The landmark statin trials showed a significant reduction in morbidity and mortality associated with ischemic heart disease. However, it may not be widely appreciated that smoking had a marked adverse effect on outcome in these trials. In both the primary and secondary prevention setting, the effect of smoking was broadly similar. Smoking markedly increased the risk of events in the placebo and treatment groups. For example, in the primary prevention trials, this risk was 74-86% higher when smokers were compared with nonsmokers in the placebo groups. The corresponding figures for the secondary prevention trials were 23-61%. The risk of events in untreated nonsmokers was of a similar order to that seen in smokers taking statins. Although statin treatment was associated with a significant reduction in events in smokers, the best outcome was observed in nonsmokers treated with statins (primary prevention: lovastatin or pravastatin; secondary prevention: pravastatin or simvastatin). The highest risk of events in any group was in the smokers on placebo. This information may increase clinician and patient awareness as to the marked harmful effect of smoking relative to effective, evidence-based treatment (ie, the use of statins).

Lipid-lowering drugs in lupus: an unexplored therapeutic intervention

Lipid-lowering drugs have been shown to have profound actions beyond modulation of lipid profiles. Statins have been shown to reduce the levels of pro-inflammatory cytokines and markers of acute phase response including C-reactive protein and serum amyloid A. Fibrates have also shown to reduce interleukin-6 levels. Both groups of drugs seem to act through a peroxisomal proliferating activating receptor alpha mechanism to achieve these actions. In lupus, there is profound activation of cytokine production and the acute phase response and a markedly increased risk for the development of atherosclerosis. The role of lipid-lowering drugs in the management of both the acute and chronic sequelae of lupus needs to be explored.

Therapeutic modulation of transcription factor activity

Aberrant gene expression is a fundamental cause of many disease-associated pathophysiologies. The pharmacological modulation of transcription factor activity therefore represents an attractive therapeutic approach to such disorders. With the exception of nuclear receptors, which are the direct targets of pharmaceuticals, other known classes of transcription factors are largely regulated indirectly by drugs that impact upon those signal transduction cascades that alter transcription factor phosphorylation and dephosphorylation and/or nuclear import. However, recent advances in drug discovery technologies now enable high-throughput screens that can identify molecules that act directly at the level of transcription factor complexes.