Physiological and therapeutic roles of peroxisome proliferator-activated receptors

Peroxisome proliferator-activated receptor gamma agonist action of 3-methyl-1,2-cyclopentanedione

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily that plays a pivotal role in regulating inflammatory gene expression. The purpose of this study was to investigate the effects of coffee extract, 3-methyl-1,2-cyclopentanedione (3-MCP) on PPARs in vitro. Western blotting and luciferase assays using the PPAR response element (PPRE) construct revealed that 3-MCP induced PPARgamma-selective activation in YPEN-1 cells and that treatment with the PPARgamma selective antagonist, GW9662, was associated with a decrease in 3-MCP-induced PPARgamma activity. The 3-MCP also was shown to suppress reactive species generation and pro-inflammatory transcription factor NF-kappaB activity through PPARgamma activation. Theses results indicate that 3-MCP is a novel PPARgamma agonist and suggests that this agent may have a potential to minimize inflammation.

Metabolic action of peroxisome proliferator-activated receptor γ agonism in rats with exogenous hypercorticosteronemia

OBJECTIVE

The beneficial metabolic actions of peroxisome proliferator-activated receptor gamma (PPARgamma) agonism are associated with modifications in adipose tissue metabolism that include a reduction in local glucocorticoid (GC) production by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). This study aimed to assess the contribution of GC attenuation to PPARgamma agonism action on gene expression in visceral adipose tissue and global metabolic profile.

DESIGN

Rats were treated (2 weeks) with the PPARgamma agonist rosiglitazone (RSG, 10 mg/kg/day) with concomitant infusion of vehicle (cholesterol implant) or corticosterone (HiCORT, 75 mg/implant/week) to defeat PPARgamma-mediated GC attenuation.

MEASUREMENTS

mRNA levels of enzymes involved in lipid uptake (and lipoprotein lipase activity), storage, lipolysis, recycling, and oxidation in retroperitoneal white adipose tissue (RWAT). Serum glucose, insulin and lipids, and lipid content of oxidative tissues.

RESULTS

Whereas HiCORT did not alter RWAT mass, RSG increased the latter (+33%) independently of the corticosterone status. Both HiCORT and RSG increased lipoprotein lipase activity, the mRNA levels of the de novo lipogenesis enzyme fatty acid synthase, and that of the fatty acid retention-promoting enzyme acyl-CoA synthase 1, albeit in a nonadditive fashion. Expression level of the lipolysis enzyme adipose triglyceride lipase was increased additively by HiCORT and RSG. PPARgamma agonism increased mRNA of the fatty acid recycling enzymes glycerol kinase and cytosolic phosphoenolpyruvate carboxykinase and those of the fatty acid oxidation enzymes muscle-type carnitine palmitoyltransferase 1 and acyl-CoA oxidase, whereas HiCORT remained without effect. HiCORT resulted in liver steatosis and hyperinsulinemia, which were abrogated by RSG, whereas the HiCORT-induced elevation in serum nonesterified fatty acid levels was only partially prevented. The hypotriglyceridemic action of RSG was maintained in HiCORT rats.

CONCLUSION

The GC and PPARgamma pathways exert both congruent and opposite actions on specific aspects of adipose tissue metabolism. Both the modulation of adipose gene expression and the beneficial global metabolic actions of PPARgamma agonism are retained under imposed high ambient GC, and are therefore independent from PPARgamma effects on 11beta-HSD1-mediated GC production.

PPARdelta agonism induces a change in fuel metabolism and activation of an atrophy programme, but does not impair mitochondrial function in rat skeletal muscle

PPARalpha agonism impairs mitochondrial function, but the effect of PPARdelta agonism on mitochondrial function is equivocal. Furthermore, PPARalpha and delta agonism increases muscle fatty acid oxidation, potentially via activation of FOXO1 signalling and PDK4 transcription. Since FOXO1 activation has also been suggested to increase transcription of MAFbx and MuRF-1, and thereby the activation of ubiquitin-proteasome mediated muscle proteolysis, this raises the possibility that muscle fuel selection and the induction of a muscle atrophy programme could be regulated by a single common signalling pathway. We therefore investigated the effect of PPARdelta (delta) agonist, GW610742, administration on muscle mitochondrial function, fuel regulation, and atrophy and growth related signalling pathways in vivo. Twenty-four male Wistar rats received vehicle or GW610742 (5 and 100 mg per kg body mass (bm)) orally for 6 days. Soleus muscle was used to determine maximal rates of ATP production (MRATP) in isolated mitochondria, gene and protein expression, and enzyme activities. MRATP were unchanged by GW610742. Muscle PDK2 and PDK4 mRNA expression increased with GW610742 (100 mg (kg bm)(-1)) compared to vehicle (P<0.05), and was paralleled by a twofold increase in PDK4 protein expression (P<0.05). The activity of beta-hydroxyacyl-CoA dehydrogenase increased with GW610742 (P<0.05). Muscle MuRF1 and MAFbx mRNA expression was increased by GW610742 (100 mg (kg bm)(-1)) compared to vehicle (P<0.05), and was matched by increased protein expression (P<0.001), whilst Akt1 protein declined (P<0.05). There was no effect of GW610742 on 20S proteasome activity and mRNA expression, or the muscle DNA: protein ratio. GW610742 switched muscle fuel metabolism towards decreased carbohydrate use and enhanced lipid utilization, but did not induce mitochondrial dysfunction. Furthermore, GW610742 initiated a muscle atrophy programme, possibly via changes in the Akt1/FOXO/MAFbx and MuRF1 signalling pathway.

Evaluation of proinflammatory cytokines and inflammation markers as biomarkers for the action of thiazolidinediones in Type 2 diabetes mellitus patients and healthy volunteers

AIMS

Thiazolidinediones (TZDs) not only enhance cellular glucose transport but are reported to have potent anti-inflammatory effects. These effects may play an important role in the insulin sensitizing mechanism, and possibly precede the effects on parameters of glucoregulation. We sought to investigate whether these anti-inflammatory effects could yield early responding biomarkers for TZD action in Type 2 diabetes mellitus (T2DM) patients and healthy volunteers (HV) to expedite early clinical development of novel compounds.

METHODS

We investigated the timing of treatment effects on several proinflammatory cytokines and markers of inflammation in comparison with effects on typical measures of glucoregulation in T2DM patients and HV receiving rosiglitazone 4 mg or placebo twice daily for 6 weeks.

RESULTS

We found a significant reduction in interleukin (IL)-6 [-39.4%, confidence interval (CI) - 60.0, - 8.2] and white blood cell count (-18.4%, CI - 30.2, - 4.5) after 4 weeks of treatment in the T2DM group. These anti-inflammatory effects did not precede the effects on typical parameters of glucoregulation in the T2DM group and there was no significant anti-inflammatory response in the HV group.

CONCLUSION

We could not identify biomarkers that precede the effects of rosiglitazone on parameters of glucoregulation in T2DM or that have a significant response in HV. However, the IL-6 response observed in this study indicates a potential role for this cytokine as complementary biomarker in clinical 'proof of concept' studies with novel TZDs.

Thiazolidinediones and risk of repeat target vessel revascularization following percutaneous coronary intervention: a meta-analysis

OBJECTIVE

Thiazolidinediones (TZDs) (rosiglitazone and pioglitazone) are a class of antidiabetes agents that have a high affinity for peroxisome proliferator-activated receptor-gamma. TZDs initiate a multitude of physiologic processes that may elicit benefits as systemic agents for the prevention of restenosis requiring revascularization following percutaneous coronary intervention (PCI). Numerous trials have evaluated the impact of TZDs on repeat target vessel revascularization (TVR) in patients following PCI; however, several limitations (small sample size, inconclusive results, and risk factor stratification) complicate definitive conclusions. A meta-analysis was performed to evaluate the impact of TZDs on repeat TVR following PCI.

RESEARCH DESIGN AND METHODS

Included trials met the following criteria: 1) prospective, randomized controlled trials evaluating available TZDs versus standards of care; 2) well-described protocol; 3) minimum of 6 months of follow-up; and 4) data provided on repeat TVR. Data are presented as relative risks (RRs) with 95% CIs.

RESULTS

Seven clinical trials (n = 608) met the inclusion criteria. Upon meta-analysis, the risk of repeat TVR was significantly reduced in patients who received TZD therapy compared with standards of care (RR 0.35 [95% CI 0.22-0.57]). In studies using rosiglitazone (0.45 [0.25-0.83]) and pioglitazone (0.24 [0.11-0.51]), risk of repeat TVR was significantly reduced. Risk of repeat TVR was also significantly reduced among patients with (0.34 [0.19-0.63]) and without (0.37 [0.18-0.77]) diabetes.

CONCLUSIONS

Results from this meta-analysis suggest that TZDs effectively reduce the risk of repeat TVR following PCI.

Effect of pioglitazone treatment on behavioral symptoms in autistic children

Introduction

Autism is complex neuro-developmental disorder which has a symptomatic diagnosis in patients characterized by disorders in language/communication, behavior, and social interactions. The exact causes for autism are largely unknown, but is has been speculated that immune and inflammatory responses, particularly those of Th2 type, may be involved. Thiazolidinediones (TZDs) are agonists of the peroxisome proliferator activated receptor gamma (PPARγ), a nuclear hormone receptor which modulates insulin sensitivity, and have been shown to induce apoptosis in activated T-lymphocytes and exert anti-inflammatory effects in glial cells. The TZD pioglitazone (Actos) is an FDA-approved PPARγ agonist used to treat type 2 diabetes, with a good safety profile, currently being tested in clinical trials of other neurological diseases including AD and MS. We therefore tested the safety and therapeutic potential of oral pioglitazone in a small cohort of children with diagnosed autism.

Case description

The rationale and risks of taking pioglitazone were explained to the parents, consent was obtained, and treatment was initiated at either 30 or 60 mg per day p.o. A total of 25 children (average age 7.9 ± 0.7 year old) were enrolled. Safety was assessed by measurements of metabolic profiles and blood pressure; effects on behavioral symptoms were assessed by the Aberrant Behavior Checklist (ABC), which measures hyperactivity, inappropriate speech, irritability, lethargy, and stereotypy, done at baseline and after 3–4 months of treatment.

Discussion and evaluation

In a small cohort of autistic children, daily treatment with 30 or 60 mg p.o. pioglitazone for 3–4 months induced apparent clinical improvement without adverse events. There were no adverse effects noted and behavioral measurements revealed a significant decrease in 4 out of 5 subcategories (irritability, lethargy, stereotypy, and hyperactivity). Improved behaviors were inversely correlated with patient age, indicating stronger effects on the younger patients.

Conclusion

Pioglitazone should be considered for further testing of therapeutic potential in autistic patients.

Key issues in the role of peroxisome proliferator-activated receptor agonism and cell signaling in trichloroethylene toxicity

Peroxisome proliferator-activated receptor alpha (PPARalpha) is thought to be involved in several different diseases, toxic responses, and receptor pathways. The U.S. Environmental Protection Agency 2001 draft trichloroethylene (TCE) risk assessment concluded that although PPAR may play a role in liver tumor induction, the role of its activation and the sequence of subsequent events important to tumorigenesis are not well defined, particularly because of uncertainties concerning the extraperoxisomal effects. In this article, which is part of a mini-monograph on key issues in the health risk assessment of TCE, we summarize some of the scientific literature published since that time on the effects and actions of PPARalpha that help inform and illustrate the key scientific questions relevant to TCE risk assessment. Recent analyses of the role of PPARalpha in gene expression changes caused by TCE and its metabolites provide only limited data for comparison with other PPARalpha agonists, particularly given the difficulties in interpreting results involving PPARalpha knockout mice. Moreover, the increase in data over the last 5 years from the broader literature on PPARalpha agonists presents a more complex array of extraperoxisomal effects and actions, suggesting the possibility that PPARalpha may be involved in modes of action (MOAs) not only for liver tumors but also for other effects of TCE and its metabolites. In summary, recent studies support the conclusion that determinations of the human relevance and susceptibility to PPARalpha-related MOA(s) of TCE-induced effects cannot rely on inferences regarding peroxisome proliferation per se and require a better understanding of the interplay of extraperoxisomal events after PPARalpha agonism.

ERK5 activation inhibits inflammatory responses via peroxisome proliferator-activated receptor delta (PPARdelta) stimulation

Peroxisome proliferator-activated receptors (PPAR) decrease the production of cytokine and inducible nitric-oxide synthase (iNOS) expression, which are associated with aging-related inflammation and insulin resistance. Recently, the involvement of the induction of heme oxygenase-1 (HO-1) in regulating inflammation has been suggested, but the exact mechanisms for reducing inflammation by HO-1 remains unclear. We found that overexpression of HO-1 and [Ru(CO)(3)Cl(2)](2), a carbon monoxide (CO)-releasing compound, increased not only ERK5 kinase activity, but also its transcriptional activity measured by luciferase assay with the transfection of the Gal4-ERK5 reporter gene. This transcriptional activity is required for coactivation of PPARdelta by ERK5 in C2C12 cells. [Ru(CO)(3)Cl(2)](2) activated PPARdelta transcriptional activity via the MEK5/ERK5 signaling pathway. The inhibition of NF-kappaB activity by ERK5 activation was reversed by a dominant negative form of PPARdelta suggesting that ERK5/PPARdelta activation is required for the anti-inflammatory effects of CO and HO-1. Based on these data, we propose a new mechanism by which CO and HO-1 mediate anti-inflammatory effects via activating ERK5/PPARdelta, and ERK5 mediates CO and HO-1-induced PPARdelta activation via its interaction with PPARdelta.

Conjugated linoleic acid reduced metastasized LL2 tumors in mouse peritoneum

The effect of conjugated linoleic acid (CLA) on pre-existent peritoneal metastasis was examined by mouse peritoneal metastasis models. The cell growth of LL2 mouse cancer cells was suppressed by CLA in a dose-dependent manner. CLA-induced growth inhibition was recovered by the exposure to antisense S-oligodeoxynucleotide for peroxisome proliferator-activated receptor (PPAR)-gamma. C57B6 mice were inoculated with LL2 cells into their peritoneal cavity. Two weeks after inoculation, colonized peritoneal cancer foci (2.2+/-0.4 mm in diameter) were treated with CLA administrated intraperitoneally (200 or 600 pmol/mouse, twice a week). CLA treatment decreased the number of peritoneal tumors: 8.7+/-0.6, 5.7+/-0.6, and 2.3+/-0.6 in untreated, 200 pmol/mouse CLA, and 600 pmol/mouse CLA groups, respectively (P<0.0001). CLA treatment decreased the size of peritoneal tumors: 3.7+/-1.5, 1.3+/-0.5, and 1.0+/-0.4 mm in untreated, 200 pmol/mouse CLA, and 600 pmol/mouse CLA groups, respectively (P<0.0001). In CLA-treated tumors, proliferating cells were decreased (P<0.0001), whereas apoptotic cells were increased (P=0.0010). CLA-treated LL2 tumors showed decrease of PPARgamma and EGFR proteins and increase of BAX protein in comparison with untreated tumors. These findings suggest that CLA possesses anti-tumor capability to peritoneal metastasis.

The complex role of PPARgamma in renal dysfunction in obesity: managing a Janus-faced receptor

Obesity is frequently accompanied by insulin resistance, type II diabetes, hypertension and atherosclerosis, a cluster of pathologies that are the major components of the metabolic syndrome. Obesity is a known cause for renal dysfunction that leads to two major renal pathologies: hypertension and glomerular and tubulointerstitial injury. Peroxizome proliferator activated receptors (PPARs) are transcription factors belonging to the nuclear hormone receptor superfamily with important functions in the regulation of metabolism. The role of PPARgamma isoforms in adipogenesis and vascular inflammation associated to obesity has been vastly studied and is well recognized, albeit not completely mechanistically understood. Also, the effect of various PPARgamma agonists on blood pressure reduction in different forms of hypertension, including obesity related hypertension has been reported, but the mechanisms involved are only beginning to be studied. Even less clear is the concurrent beneficial effect of PPARgamma agonists thiazolinendiones (TZD) on blood pressure reduction in different forms of hypertension and, at the same time, in some cases, the significant water retention leading to edema and heart failure. The occurrence of both these apparently opposite effects on the renal water and sodium handling suggests a complex role of PPARgamma in the kidney that is likely related to the metabolic state. Also, PPARgamma activation leads to a reduction in mesangial cell proliferation while stimulating apoptosis. TZD treatment reduces albuminuria in obese and diabetic humans and rodent models suggesting protective effects against renal tubuloglomerular injury. The focus of this review is to present and critically discuss the recent findings on the roles of PPARgamma in the kidney in direct relation to renal function and renal injury in obesity and obesity-initiated diabetes.

Agonists of the peroxisome proliferator-activated receptor alpha induce a fiber-type-selective transcriptional response in rat skeletal muscle

In rodents, treatment with peroxisome proliferator-activated receptor alpha (PPARalpha) agonists results in peroxisome proliferation, hepatocellular hypertrophy, and hepatomegaly. Drugs in the fibrate class of PPARalpha agonists have also been reported to produce rare skeletal muscle toxicity. Although target-driven hepatic effects of PPARalpha treatment have been extensively studied, a characterization of the transcriptional effects of this nuclear receptor/transcription factor on skeletal muscle responses has not been reported. In this study we investigated the effects of PPARalpha agonists on skeletal muscle gene transcription in rats. Further, since statins have been reported to preferentially effect type II muscle fibers, we compared PPARalpha signaling effects between type I and type II muscles. By comparing the transcriptional responses of agonists that signal through different nuclear receptors and using a selection/deselection analytical strategy based on ANOVA, we identified a PPARalpha activation signature that is evident in type I (soleus), but not type II (quadriceps femoris), skeletal muscle fibers. The fiber-type-selective nature of this response is consistent with increased fatty acid uptake and beta-oxidation, which represent the major clinical benefits of the hypolipidemic compounds used in this study, but does not reveal any obvious off-target pathways that may drive adverse effects.

Conjugated linoleic acid inhibits peritoneal metastasis in human gastrointestinal cancer cells

The effect of conjugated linoleic acid (CLA) on peritoneal metastasis was examined by in vitro treatment of cancer cells and mouse peritoneal metastasis models. First, cell growth of MKN28 human gastric cancer cells and Colo320 human colon cancer cells was suppressed by CLA in a dose-dependent manner with an increment in apoptosis. CLA significantly inhibited invasion into type IV collagen-coated membrane of MKN28 and Colo320 cells (p < 0.05). CLA-induced growth inhibition was recovered by the exposure to antisense S-oligodeoxynucleotide for peroxisome proliferator-activated receptor (PPAR)-gamma in both cell lines. BALB/c nu-nu mice were inoculated with MKN28 and Colo320 cells into their peritoneal cavity, and administrated with CLA intraperitoneally (weekly, 4 times). CLA treatment did not affect food intake or weight gain of mice. CLA treatment significantly decreased metastatic foci of both cells in the peritoneal cavity (p < 0.005). Survival rate in mice inoculated with MKN28 or Colo320 cells was significantly recovered by CLA treatment (p = 0.0025 and 0.0052, respectively). Protein production in MKN28 and Colo320 cells treated with CLA showed a decrease in epidermal growth factor receptor and transforming growth factor-alpha and an increase in Bax. These findings suggest that CLA inhibits metastasis of human gastric and colon cancer cells.

Peroxisome proliferator-activated receptor delta and gamma agonists differentially alter tumor differentiation and progression during mammary carcinogenesis

Peroxisome proliferator-activated receptor (PPAR) represents a ligand-dependent nuclear receptor family that regulates multiple metabolic processes associated with fatty acid beta-oxidation, glucose utilization, and cholesterol transport. These and other receptor-mediated actions pertain to their role in hypolipidemic and antidiabetic therapies and as potential targets for cancer chemopreventive agents. The present study evaluated the chemopreventive activity of two highly potent and selective PPARgamma and PPARdelta agonists in a progestin- and carcinogen-induced mouse mammary tumorigenesis model. Animals treated with the PPARgamma agonist GW7845 exhibited a moderate delay in tumor formation. In contrast, animals treated with the PPARdelta agonist GW501516 showed accelerated tumor formation. Significantly, tumors from GW7845-treated mice were predominantly ductal adenocarcinomas, whereas tumors from GW501516-treated animals were adenosquamous and squamous cell carcinomas. Gene expression analysis of tumors arising from GW7845- and GW501516-treated mice identified expression profiles that were distinct from each other and from untreated control tumors of the same histopathology. Only tumors from mice treated with the PPARgamma agonist expressed estrogen receptor-alpha in luminal transit cells, suggesting increased ductal progenitor cell expansion. Tumors from mice treated with the PPARdelta agonist exhibited increased PPARdelta levels and activated 3-phosphoinositide-dependent protein kinase-1 (PDK1), which co-associated, suggesting a link between the known oncogenic activity of PDK1 in mammary epithelium and PPARdelta activation. These results indicate that PPARdelta and PPARgamma agonists produce diverse, yet profound effects on mammary tumorigenesis that give rise to distinctive histopathologic patterns of tumor differentiation and tumor development.

PPARgamma agonists exert antifibrotic effects in renal tubular cells exposed to high glucose

Peroxisome proliferator-activated receptor-gamma (PPARgamma) are ligand-activated transcription factors that regulate cell growth, inflammation, lipid metabolism, and insulin sensitivity. We recently demonstrated that PPARgamma agonists limit high glucose-induced inflammation in a model of proximal tubular cells (PTC; Panchapakesan U, Pollock CA, and Chen XM. Am J Physiol Renal Physiol 287: F528-F534, 2004). However, the role of PPARgamma in the excess extracellular matrix production is largely unknown. We evaluated the effect of 24- to 48-h 8 microM l-805645 or 10 microM pioglitazone on 25 mM D-glucose-induced markers of fibrosis in HK-2 cells. High D-glucose induced nuclear binding of activator protein-1 (AP-1) to 140.8 +/- 10.9% (P < 0.05), which was attenuated with L-805645 and pioglitazone to 82.3 +/- 14.4 (P < 0.01 vs. high D-glucose) and 99.3 +/- 12.2% (P < 0.05 vs. high D-glucose), respectively. High D-glucose increased total production of transforming growth factor (TGF)-beta(1) 139.6 +/- 6.5% (P < 0.05), which was reversed with L-805645 and pioglitazone to 68.73 +/- 5.7 (P < 0.01 vs. high D-glucose) and 112 +/- 13.6% (P < 0.05 vs. high D-glucose). L-805645 and pioglitazone reduced high d-glucose-induced fibronectin from 156.0 +/- 24.9 (P < 0.05) to 81.9 +/- 16.0 and 57.4 +/- 12.7%, respectively (both P < 0.01 vs. high D-glucose). Collagen IV was not induced by high d-glucose. L-805645 and pioglitazone suppressed collagen IV to 68.0 +/- 14.5 (P < 0.05) and 46.5 +/- 11.6% (P < 0.01) vs. high D-glucose, respectively. High D-glucose increased the nuclear binding of NF-kappaB to 167 +/- 22.4% (P < 0.05), which was not modified with PPARgamma agonists. In conclusion, PPARgamma agonists exert antifibrotic effects in human PTC in high glucose by attenuating the increase in AP-1, TGF-beta(1), and the downstream production of the extracellular matrix protein fibronectin.

Selective PPARγ modulators with improved pharmacological profiles

A series of metabolically robust N-benzyl-indole selective PPARgamma modulators with either a 3-benzoyl or 3-benzisoxazoyl moiety have been identified. In vitro, these compounds are partial agonists and exhibit reduced adipogenesis in human adipocytes. In vivo, these SPPARgammaMs result in potent glucose lowering in db/db mice and attenuate increases in heart weight and brown adipose tissue that is typically observed in rats upon treatment with PPARgamma full agonists.

Method Validation and Measurement of Biomarkers in Nonclinical and Clinical Samples in Drug Development: A Conference Report

Biomarkers are increasingly used in drug development to aid scientific and clinical decisions regarding the progress of candidate and marketed therapeutics. Biomarkers can improve the understanding of diseases as well as therapeutic and off-target effects of drugs. Early implementation of biomarker strategies thus promises to reduce costs and time-to-market as drugs proceed through increasingly costly and complex clinical development programs. The 2003 American Association of Pharmaceutical Sciences/Clinical Ligand Assay Society Biomarkers Workshop (Salt Lake City, UT, USA, October 24-25, 2003) addressed key issues in biomarker research, with an emphasis on the validation and implementation of biochemical biomarker assays, covering from preclinical discovery of efficacy and toxicity biomarkers through clinical and postmarketing implementation. This summary report of the workshop focuses on the major issues discussed during presentations and open forums and noted consensus achieved among the participants on topics from nomenclature to best practices. For example, it was agreed that because reliable and accurate data provide the basis for sound decision making, biomarker assays must be validated in a manner that enables the creation of such data. The nature of biomarker measurements often precludes direct application of regulatory guidelines established for clinical diagnostics or drug bioanalysis, and future guidance on biomarker assay validation should therefore be adaptable enough that validation criteria do not stifle creative biomarker solutions.

Pioglitazone inhibits cell growth and reduces matrix production in human kidney fibroblasts

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists are increasingly used in patients with diabetes, and small studies have suggested a beneficial effect on renal function, but their effects on extracellular matrix (ECM) turnover are unknown. The aims of this study were to investigate the effects of the PPAR-gamma agonist pioglitazone on growth and matrix production in human cortical fibroblasts (CF). Cell growth and ECM production and turnover were measured in human CF in the presence and absence of 1 and 3 muM pioglitazone. Exposure of CF to pioglitazone caused an antiproliferative (P < 0.0001) and hypertrophic (P < 0.0001) effect; reduced type IV collagen secretion (P < 0.01), fibronectin secretion (P < 0.0001), and proline incorporation (P < 0.0001); decreased MMP-9 activity (P < 0.05); and reduced tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2 secretion (P < 0.001 and P < 0.0001, respectively). These effects were independent of TGF-beta1. A reduction in ECM production was similarly observed when CF were exposed to a selective PPAR-gamma agonist (L-805645) in concentrations that caused no toxicity, confirming the antifibrotic effects of pioglitazone were mediated through a PPAR-gamma-dependent mechanism. Exposure of CF to high glucose conditions induced an increase in the expression of collagen IV (P < 0.05), which was reversed both in the presence of pioglitazone (1 and 3 muM) and by L-805645. In summary, exposure of human CF to pioglitazone causes an antiproliferative effect and reduces ECM production through mechanisms that include reducing TIMP activity, independent of TGF-beta1. These studies suggest that the PPAR-gamma agonists may have a specific role in ameliorating the course of progressive tubulointerstitial fibrosis under both normoglycemic and hyperglycemic states.

Benzoyl 2-methyl indoles as selective PPARγ modulators

Routine screening for human PPAR ligands yielded compounds 1 and 2, both of which were sub-micromolar hPPARgamma agonists. Synthetic modifications of these leads led to a series of potent substituted 3-benzyl-2-methyl indoles, a subset of which were noted to be selective PPARgamma modulators (SPPARgammaMs). SPPARgammaM 24 displayed robust anti-diabetic activity with an improved therapeutic window in comparison to a PPARgamma full agonist in a rodent efficacy model.

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.

Macrovascular complications of metabolic syndrome: an early intervention is imperative

The metabolic syndrome is a widespread clinical condition and an important cluster of atherothrombotic disease risk factors. The inclusion of this syndrome in the recently published Adult Treatment Panel III (ATP III) guidelines focused the attention of the physicians on this entity. Abdominal obesity, PPAR modulation, insulin resistance (with or without glucose intolerance), atherogenic dyslipidemia, elevated blood pressure, prothrombotic and proinflammatory states are the principal factors of this multifaceted syndrome. There are two major pathways of metabolic syndrome progress: (1) With preserved pancreatic beta cells function and insulin hypersecretion, which can recompense for insulin resistance. This pathway leads mostly to the macrovascular complications of metabolic syndrome. (2) With substantial injure of pancreatic beta cells leading to gradually reduced insulin secretion and to hyperglycemia (e.g. overt type 2 diabetes). This pathway leads to both microvascular and macrovascular complications. Because macrovascular complications of insulin resistance state precede the onset of hyperglycemia, early intervention in patients with metabolic syndrome is particularly important. Since central obesity (accompanied by insulin resistance even in the absence of hyperglycemia) is the key factor leading to development of metabolic syndrome and its future macrovascular complications, we assume that next logical step is the recognition of central obesity itself as a major risk factor for cardiovascular diseases.

The effect of high glucose and PPAR-gamma agonists on PPAR-gamma expression and function in HK-2 cells

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) are ligand-activated transcription factors that regulate cell growth, inflammation, lipid metabolism, and insulin sensitivity. PPAR-gamma in the human kidney has been described. However, the role of PPAR-gamma in proximal tubular cells with respect to cell growth and inflammation in diabetic nephropathy is largely unknown. We evaluated the effect of high (30 mM) D-glucose, thiazolidinedione pioglitazone (10 microM), and the selective PPAR-gamma agonist L-805645 (8 microM) on PPAR-gamma expression, growth, and inflammatory parameters in the proximal tubular model of HK-2 cells. PPAR-gamma was present in HK-2 cells and upregulated with 30 mM D-glucose to 177 +/- 31.2% of control (P < 0.05). PPAR-gamma activation was induced by pioglitazone to a similar level to that observed by exposure to high glucose but maximally induced by the selective agonist L-805645. However, L-805645 reduced cell viability in both 5 and 30 mM d-glucose to 73.8 +/- 3.1 and 77.6 +/- 1.4% of control (both P < 0.0001). In parallel, thymidine incorporation was reduced with L-805645 in both 5 and 30 mM D-glucose to 33.3 +/- 3.4 and 37.9 +/- 2.2%, respectively (both P < 0.0001). Flow cytometry demonstrated increased apoptosis and G(1) phase arrest in association with an increase in p21(cip1/waf1) in cells exposed to L-805645. Exposure to 30 mM D-glucose did not significantly change AP-1 promoter activity (89.0 +/- 5.5% of control); however, the addition of L-805645 significantly reduced it to 62.2 +/- 2.7% of control (P < 0.0001). Thirty nanomolar D-glucose induced transforming growth factor-beta(1) to 137.7 +/- 16.9% of control (P < 0.05), and L-805645 was able to suppress this to 68.7 +/- 5.7% of control (P < 0.01 vs. d-glucose). Exposure to 30 mM D-glucose reduced monocyte chemoattractant protein 1 levels to 78.6 +/- 7.1% (P < 0.05) of control, with the reduction more marked in the presence of either pioglitazone (P < 0.01) or L-805645 (P < 0.01). In summary, high glucose upregulates PPAR-gamma and when significantly induced demonstrates anti-proliferative and anti-inflammatory effects.

Peroxisome proliferator-activated receptor gamma thiazolidinedione agonists increase glucose metabolism in astrocytes

Activation of peroxisome proliferator-activated receptors (PPARs) can regulate brain physiology and provide protection in models of neurological disease; however, neither their exact targets nor mechanisms of action in brain are known. In many cells, PPAR gamma agonists increase glucose uptake and metabolism. Because astrocytes store glucose and provide lactate to neurons on demand, we tested effects of PPAR gamma agonists on astroglial glucose metabolism. Incubation of cortical astrocytes with the PPAR gamma thiazolidinedione (TZD) agonist pioglitazone (Pio) significantly increased glucose consumption in a time- and dose-dependent manner, with maximal increase of 36% observed after 4 h in 30 microm Pio. Pio increased 2-deoxy-glucose uptake because of increased flux through the type 1 glucose transporter. However, at this time point Pio did not increase type 1 glucose transporter expression, nor were its effects blocked by transcriptional or translational inhibitors. Pio also increased astrocyte lactate production as soon as 3 h after incubation. These effects were replicated by other TZDs; however, the order of efficacy (troglitazone > pioglitazone > rosiglitazone) suggests that effects were not mediated via PPAR gamma activation. TZDs increased astrocyte cAMP levels, and their glucose modifying effects were reduced by protein kinase A inhibitors. TZDs inhibited state III respiration in isolated brain mitochondria, whereas in astrocytes they caused mitochondrial membrane hyperpolarization. Pio protected astrocytes against hypoglycemia-induced cell death. Finally, glucose uptake was modified in brain sections prepared from Pio-fed rats. These results demonstrate that TZDs modify astrocyte metabolism and mitochondrial function, which could be beneficial in neurological conditions where glucose availability is reduced.