Evolution of Peroxisome Proliferator-Activated Receptor Agonists

Chios Mastic Gum: A Promising Phytotherapeutic for Cardiometabolic Health

Chios mastic gum (CMG) is a resin obtained from the Pistacia lentiscus var. Chia tree that grows in the Mediterranean. For millennia, it has been renowned for its medicinal properties, but recently, CMG has gained attention due to its pronounced anti-inflammatory and antioxidative properties and its use in oral health, inflammatory bowel disease, cancer, and risk factors related to cardiovascular and metabolic diseases. This narrative review seeks to briefly overview its bioactive constituents and examine and describe its potential as a cardiometabolic disease (CMD) phytotherapeutic. The results of clinical trials and in vivo, in vitro, and in silico studies provide accumulating evidence of the mechanisms underlying CMG's impacts on lipid and glucose metabolism, cardiovascular and hepatic health, inflammation, oxidative stress, body composition, and microbiota. Despite the relatively limited studies with mixed results, they have provided the foundation to understand the strengths, weaknesses, and opportunities moving forward that may help to establish CMG and its bioactives as viable therapeutics for CMD.

Chiglitazar monotherapy with sitagliptin as an active comparator in patients with type 2 diabetes: a randomized, double-blind, phase 3 trial (CMAS)

Chiglitazar (Carfloglitazar) is a novel peroxisome proliferator-activated receptor (PPAR) pan-agonist that has shown promising effects on glycemic control and lipid regulation in patients with type 2 diabetes. In this randomized phase 3 trial, we compared the efficacy and safety of chiglitazar with sitagliptin in patients with type 2 diabetes who had insufficient glycemic control despite a strict diet and exercise regimen. Eligible patients were randomized (1:1:1) to receive chiglitazar 32 mg (n = 245), chiglitazar 48 mg (n = 246), or sitagliptin 100 mg (n = 248) once daily for 24 weeks. The primary endpoint was the change in glycosylated hemoglobin A1C (HbA1c) from baseline at week 24 with the non-inferiority of chiglitazar over sitagliptin. Both chiglitazar and sitagliptin significantly reduced HbA1c at week 24 with values of -1.40%, -1.47%, and -1.39% for chiglitazar 32 mg, chiglitazar 48 mg, and sitagliptin 100 mg, respectively. Chiglitazar 32 and 48 mg were both non-inferior to sitagliptin 100 mg, with mean differences of -0.04% (95% confidential interval (CI) -0.22 to 0.15) and -0.08% (95% CI -0.27 to 0.10), respectively. Compared with sitagliptin, greater reduction in fasting and 2-h postprandial plasma glucose and fasting insulin was observed with chiglitazar. Overall adverse event rates were similar between the groups. A small increase in mild edema in the chiglitazar 48 mg group and slight weight gain in both chiglitazar groups were reported. The overall results demonstrated that chiglitazar possesses good efficacy and safety profile in patients with type 2 diabetes inadequately controlled with lifestyle interventions, thereby providing adequate supporting evidence for using this PPAR pan-agonist as a treatment option for type 2 diabetes.

Further evidence for the involvement of the PPARγ system on alcohol intake and sensitivity in rodents

RATIONALE

Peroxisome Proliferator Activator receptors (PPARs) are intracellular receptors that function as transcription factors, which regulate specific metabolic and inflammatory processes. PPARs are broadly distributed in the body and are also expressed in the central nervous system, especially in areas involved in addiction-related behavioral responses. Recent studies support a role of PPARs in alcoholism and pioglitazone: a PPARγ agonist used for treatment of type 2 diabetes showed efficacy in reducing alcohol drinking, stress-induced relapse, and alcohol withdrawal syndrome in rats.

OBJECTIVES AND METHODS

In the current work, we tested the pharmacological effects of pioglitazone on binge-like alcohol consumption using an intermittent two-bottle choice paradigm in Wistar rats and on the "drinking in the dark" (DID) model in mice with selective deletion of PPARγ in neurons.

RESULTS

Our data show that repeated administration of pioglitazone (10, 30 mg/kg) reduces high voluntary alcohol consumption in Wistar rats. Pre-treatment with the selective PPARγ antagonist GW9662 (5 mg/kg) completely prevented the effect of pioglitazone, demonstrating that its action is specifically mediated by activation of PPARγ. In line with this result, repeated administration of pioglitazone (30 mg/kg) attenuated binge alcohol consumption in PPARγ^(+/+) mice. Whereas in PPARγ^(-/-) mice, which exhibit reduced alcohol consumption, pioglitazone had no effect. Of note, PPARγ^(-/-) mice exhibited lower patterns of alcohol drinking without showing difference in sucrose (control) intake. Interestingly, PPARγ^(-/-) mice displayed a higher sensitivity to the sedative and ataxic effect of alcohol compared with their wild-type counterpart.

CONCLUSIONS

Collectively, these data suggest that PPARγ agonists, and specifically pioglitazone, could be potential therapeutics for the treatment of binge alcohol drinking.

Role of peroxisome proliferator-activated receptors in stroke prevention and therapy-The best is yet to come?

Role of peroxisome proliferator-activated receptors (PPARs) in the pathophysiology of stroke and protective effects of PPAR ligands have been widely investigated in the last 20 years. Activation of all three PPAR isoforms, but especially PPAR-γ, was documented to limit postischemic injury in the numerous in vivo, as well as in in vitro studies. PPARs have been demonstrated to act on multiple mechanisms and were shown to activate multiple protective pathways related to inflammation, apoptosis, BBB protection, neurogenesis, and oxidative stress. The aim of this review was to summarize two decades of PPAR research in stroke with emphasis on in vivo animal studies. We focus on each PPAR receptor separately and detail their implication in stroke. This review also discusses recent clinical efforts in the field and the epidemiological data with regard to role of PPAR polymorphisms in susceptibility to stroke, and tries to draw conclusions and describe future perspectives.

PPARγ activation by pioglitazone does not suppress cravings for alcohol, and is associated with a risk of myopathy in treatment seeking alcohol dependent patients: a randomized controlled proof of principle study

RATIONALE

Proinflammatory processes have been implicated in alcohol addiction, craving, and relapse, while studies in experimental animals have suggested that activation of peroxisome proliferator-activated receptor gamma (PPARγ) inhibits proinflammatory signaling. Accordingly, it is hypothesized that medications with PPARγ activity may have therapeutic potential in alcohol dependence.

OBJECTIVES

We conducted a double-blind, placebo-controlled mechanistic proof of principle study in alcohol-dependent inpatients to investigate the effect of pioglitazone on alcohol craving.

METHODS

Participants were treated for withdrawal, if needed, and then randomized to pioglitazone (target dose 45 mg/day) or placebo. Once at target dose, they completed two experimental manipulations: guided imagery, which used personalized auditory scripts to induce alcohol cravings, and a low-dose challenge with i.v. lipopolysaccharide (LPS; 0.8 ng/kg) or placebo, on two separate sessions, in counterbalanced order. Behavioral and endocrine responses as well as CSF levels of proinflammatory cytokines were evaluated.

RESULTS

The study was prematurely terminated after randomization of 16 subjects, following an independent review that established a high risk of myopathy in the active treatment group. Analysis of those who completed the study indicated that pioglitazone was associated with elevated, rather than suppressed alcohol cravings in response to alcohol-associated stimuli. LPS did not induce cravings for alcohol and thus did not lend itself to evaluating pioglitazone effects; however, pioglitazone increased the neuroendocrine stress response to LPS. CSF levels of IL-6, TNF-α, or MCP-1 were unaffected by pioglitazone treatment.

CONCLUSIONS

Both safety and efficacy biomarker data suggest that pioglitazone lacks potential as a medication for the treatment of alcohol dependence.

CLINICAL TRIAL REGISTRATION

NCT01631630.

Current and Future Treatments in the Fight Against Non-Alcoholic Fatty Liver Disease

Obesity is recognised as a risk factor for many types of cancers, in particular hepatocellular carcinoma (HCC). A critical factor in the development of HCC from non-alcoholic fatty liver disease (NAFLD) is the presence of non-alcoholic steatohepatitis (NASH). Therapies aimed at NASH to reduce the risk of HCC are sparse and largely unsuccessful. Lifestyle modifications such as diet and regular exercise have poor adherence. Moreover, current pharmacological treatments such as pioglitazone and vitamin E have limited effects on fibrosis, a key risk factor in HCC progression. As NAFLD is becoming more prevalent in developed countries due to rising rates of obesity, a need for directed treatment is imperative. Numerous novel therapies including PPAR agonists, anti-fibrotic therapies and agents targeting inflammation, oxidative stress and the gut-liver axis are currently in development, with the aim of targeting key processes in the progression of NASH and HCC. Here, we critically evaluate literature on the aetiology of NAFLD-related HCC, and explore the potential treatment options for NASH and HCC.

In search for potential antidiabetic compounds from natural sources: docking, synthesis and biological screening of small molecules from Lycium spp. (Goji)

Current clinical antidiabetic drugs, like rosiglitazone 1, have been implicated in some serious side effects like edema, weight gain, and heart failure, making it necessary to find alternative agents. Partial agonists of peroxisome-proliferator activated receptor-gamma (PPARγ) were determined to possess improved insulin sensitivity without undeseirable side-effects when compared to full agonists of PPARγ, like rosiglitazone 1. The traditional Chinese medicine (TCM) plants, Goji (Lycium barbarum and Lycium chinense) are widely used for treating symptoms related to various diseases including diabetes and hypertension. Twenty-seven reported compounds from Goji were docked into both partial- and full-agonist binding sites of PPARγ. Amongst the docked compounds, phenylethylamide-based phytochemicals (5–9) (termed as tyramine-derivatives, TDs) were found to possess good docking scores and binding poses with favorable interactions. Synthesis of 24 TDs, including three naturally occuring amides (6, 8, 9) were synthesized and tested for PPARγ gene induction with cell-based assay. Three compounds showed similar or higher fold induction than the positive control, rosiglitazone. Among these three active TDs, trans-N-feruloyloctopamine (9) and tyramine derivatives-enriched extract (TEE) (21%) of the root bark of L. chinense were further studied in vivo using db/db mice. However, both TEE as well as 9 did not show significant antidiabetic properties in db/db mice. In vivo results suggest that the proposed antidiabetic property of Lycium species may not be due to tyramine derivatives alone. Further studies of tyramine derivatives or enriched extract(s) for other bioactivities like hypocholesterolemic activities, and studies of novel isolated compounds from Goji will enable a more complete understanding of their bioactivities.

Saroglitazar Deactivates the Hepatic LPS/TLR4 Signaling Pathway and Ameliorates Adipocyte Dysfunction in Rats with High-Fat Emulsion/LPS Model-Induced Non-alcoholic Steatohepatitis

The most epidemic liver disorder non-alcoholic steatohepatitis (NASH) is characterized by hepatic steatosis and inflammation with hepatocellular damage. Recently, it is predictable to be the extensive cause for liver transplantation. The absence of an approved therapeutic agent for NASH is the reason for investigating saroglitazar (SAR) which showed promising effects as a dual PPAR-α/γ agonist in recent studies on NASH. Here, we aimed to investigate the effect of SAR on NASH induced in rats by the administration of high-fat emulsion (HFE) and small doses of lipopolysaccharides (LPS) for 5 weeks. Rats were divided into three groups: negative control group (saline and standard rodent chow), model group (HFE(10 ml/kg/day, oral gavage) + LPS(0.5 mg/kg/week, i.p)), and SAR-treated group (HFE(10 ml/kg/day, oral gavage) + LPS(0.5 mg/kg/week, i.p.) + SAR(4 mg/kg/day, oral gavage) starting at week 3.Treatment with SAR successfully ameliorated the damaging effects of HFE with LPS, by counteracting body weight gain and biochemically by normalization of liver function parameters activity, glucose, insulin, homeostasis model of assessment (HOMA-IR) score, lipid profile levels, and histopathological examination. Significant changes in adipokine levels were perceived, resulting in a significant decline in serum leptin and tumor necrosis factor-α (TNF-α) level concurrent with adiponectin normalization. The positive effects observed for SAR on NASH are due to the downregulation of the LPS/TLR4 pathway, as indicated by the suppression of hepatic Toll-like receptor 4 (TLR4), NF-κB, TNF-α, and transforming growth factor-β1 (TGF-β1) expression. In conclusion, this work verified that SAR ameliorates NASH through deactivation of the hepatic LPS/TLR4 pathway and inhibition of adipocyte dysfunction.

Icariin Attenuates M1 Activation of Microglia and Aβ Plaque Accumulation in the Hippocampus and Prefrontal Cortex by Up-Regulating PPARγ in Restraint/Isolation-Stressed APP/PS1 Mice

Background

Studies have shown that psychosocial stress is involved in Alzheimer's disease (AD) pathogenesis; it induces M1 microglia polarization and production of pro-inflammatory cytokines, leading to neurotoxic outcomes and decreased β-amyloid (Aβ) clearance. Icariin has been proven to be an effective anti-inflammatory agent and to activate peroxisome proliferator-activated receptors gamma (PPARγ) which induces the M2 phenotype in the microglia. However, whether restraint/isolation stress reduces the clearance ability of microglia by priming and polarizing microglia to the M1 phenotype, and the effects of icariin in attenuating the inflammatory response and relieving the pathological changes of AD are still unclear.

Methods

APP/PS1 mice (male, aged 3 months) were randomly divided into a control group, a restraint/isolation stress group, and a restraint/isolation stress + icariin group. The restraint/isolation stress group was subjected to a paradigm to build a depressive animal model. Sucrose preference, open field, elevated plus maze, and Y maze test were used to assess the stress paradigm. The Morris water maze test was performed to evaluate spatial reference learning and memory. Enzyme-linked immunosorbent assay and immunohistochemistry were used to identify the microglia phenotype and Aβ accumulation. Western blotting was used to detect the expression of PPARγ in the hippocampus and prefrontal cortex (PFC).

Results

Restraint/isolation stress induced significant depressive-like behaviors in APP/PS1 mice at 4 months of age and memory impairment at 10 months of age, while 6 months of icariin administration relieved the memory damage. Restraint/isolation stressed mice had elevated pro-inflammatory cytokines, decreased anti-inflammatory cytokines, increased Aβ plaque accumulation and more M1 phenotype microglia in the hippocampus and PFC at 10 months of age, while 6 months of icariin administration relieved these changes. Moreover, restraint/isolation stressed mice had down-regulated PPARγ expression in the hippocampus and PFC at 10 months of age, while 6 months of icariin administration reversed the alteration, especially in the hippocampus.

Conclusion

Restraint/isolation stress induced depressive-like behaviors and spatial memory damage, over-expression of M1 microglia markers and more severe Aβ accumulation by suppressing PPARγ in APP/PS1 mice. Icariin can be considered a new treatment option as it induces the switch of the microglia phenotype by activating PPARγ.

shRNA-mediated PPARα knockdown in human glioma stem cells reduces in vitro proliferation and inhibits orthotopic xenograft tumour growth

The overall survival for patients with primary glioblastoma is very poor. Glioblastoma contains a subpopulation of glioma stem cells (GSC) that are responsible for tumour initiation, treatment resistance and recurrence. PPARα is a transcription factor involved in the control of lipid, carbohydrate and amino acid metabolism. We have recently shown that PPARα gene and protein expression is increased in glioblastoma and has independent clinical prognostic significance in multivariate analyses. In this work, we report that PPARα is overexpressed in GSC compared to foetal neural stem cells. To investigate the role of PPARα in GSC, we knocked down its expression using lentiviral transduction with short hairpin RNA (shRNA). Transduced GSC were tagged with luciferase and stereotactically xenografted into the striatum of NOD-SCID mice. Bioluminescent and magnetic resonance imaging showed that knockdown (KD) of PPARα reduced the tumourigenicity of GSC in vivo. PPARα-expressing control GSC xenografts formed invasive histological phenocopies of human glioblastoma, whereas PPARα KD GSC xenografts failed to establish viable intracranial tumours. PPARα KD GSC showed significantly reduced proliferative capacity and clonogenic potential in vitro with an increase in cellular senescence. In addition, PPARα KD resulted in significant downregulation of the stem cell factors c-Myc, nestin and SOX2. This was accompanied by downregulation of the PPARα-target genes and key regulators of fatty acid oxygenation ACOX1 and CPT1A, with no compensatory increase in glycolytic flux. These data establish the aberrant overexpression of PPARα in GSC and demonstrate that this expression functions as an important regulator of tumourigenesis, linking self-renewal and the malignant phenotype in this aggressive cancer stem cell subpopulation. We conclude that targeting GSC PPARα expression may be a therapeutically beneficial strategy with translational potential as an adjuvant treatment. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Thiazolidinedione drugs in the treatment of type 2 diabetes mellitus: past, present and future

Thiazolidinedione (TZD) drugs used in the treatment of type 2 diabetes mellitus (T2DM) have proven effective in improving insulin sensitivity, hyperglycemia, and lipid metabolism. Though well tolerated by some patients, their mechanism of action as ligands of peroxisome proliferator-activated receptors (PPARs) results in the activation of several pathways in addition to those responsible for glycemic control and lipid homeostasis. These pathways, which include those related to inflammation, bone formation, and cell proliferation, may lead to adverse health outcomes. As treatment with TZDs has been associated with adverse hepatic, cardiovascular, osteological, and carcinogenic events in some studies, the role of TZDs in the treatment of T2DM continues to be debated. At the same time, new therapeutic roles for TZDs are being investigated, with new forms and isoforms currently in the pre-clinical phase for use in the prevention and treatment of some cancers, inflammatory diseases, and other conditions. The aims of this review are to provide an overview of the mechanism(s) of action of TZDs, a review of their safety for use in the treatment of T2DM, and a perspective on their current and future therapeutic roles.

Peroxisome Proliferator-Activated Receptor α Facilitates Osteogenic Differentiation in MC3T3-E1 Cells via the Sirtuin 1-Dependent Signaling Pathway

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease characterized by lack of insulin and high glucose levels. T2DM can cause bone loss and fracture, thus leading to diabetic osteoporosis. Promoting osteogenic differentiation of osteoblasts may effectively treat diabetic osteoporosis. We previously reported that Sirtuin 1 (Sirt1), a NAD+-dependent deacetylase, promotes osteogenic differentiation through downregulation of peroxisome proliferator-activated receptor (PPAR) γ. We also found that miR-132 regulates osteogenic differentiation by downregulating Sirt1 in a PPARβ/δ-dependent manner. The ligand-activated transcription factor, PPARα, is another isotype of the peroxisome proliferator-activated receptor family that helps maintain bone homeostasis and promot bone formation. Whether the regulatory role of PPARα in osteogenic differentiation is mediated via Sirt1 remains unclear. In the present study, we aimed to determine this role and the underlying mechanism by using high glucose (HG) and free fatty acids (FFA) to mimic T2DM in MC3T3-E1 cells. The results showed that HG-FFA significantly inhibited expression of PPARα, Sirt1 and osteogenic differentiation, but these effects were markedly reversed by PPARα overexpression. Moreover, siSirt1 attenuated the positive effects of PPARα on osteogenic differentiation, suggesting that PPARα promotes osteogenic differentiation in a Sirt1-dependent manner. Luciferase activity assay confirmed interactions between PPARα and Sirt1. These findings indicate that PPARα promotes osteogenic differentiation via the Sirt1-dependent signaling pathway.

Regulatory landscape of AGE-RAGE-oxidative stress axis and its modulation by PPARγ activation in high fructose diet-induced metabolic syndrome

Background

The AGE-RAGE-oxidative stress (AROS) axis is involved in the onset and progression of metabolic syndrome induced by a high-fructose diet (HFD). PPARγ activation is known to modulate metabolic syndrome; however a systems-level investigation looking at the protective effects of PPARγ activation as related to the AROS axis has not been performed.

The aim of this work is to simultaneously characterize multiple molecular parameters within the AROS axis, using samples taken from different body fluids and tissues of a rat model of HFD-induced metabolic syndrome, in the presence or absence of a PPARγ agonist, Rosiglitazone (RGZ).

Methods

Rats were fed with 60% HFD for the first half of the treatment duration (21 days) then continued with either HFD alone or HFD plus RGZ for the second half.

Results

Rats receiving HFD alone showed metabolic syndrome manifestations including hypertension, dyslipidemia, increased glucose levels and insulin resistance, as well as abnormal kidney and inflammatory parameters. Systolic blood pressure, plasma triglyceride and glucose levels, plasma creatinine, and albuminuria were significantly improved in the presence of RGZ. The following molecular parameters of the AROS axis were significantly upregulated in our rat model: carboxymethyl lysine (CML) in urine and liver; carboxyethyl lysine (CEL) in urine; advanced glycation end products (AGEs) in plasma; receptor for advanced glycation end products (RAGE) in liver and kidney; advanced oxidation protein products (AOPP) in plasma; and 4-hydroxynonenal (HNE) in plasma, liver, and kidney. Conversely, with RGZ administration, the upregulation of AOPP and AGEs in plasma, CML and CEL in urine, RAGE in liver as well as HNE in plasma and liver was significantly counteracted/prevented.

Conclusions

Our data demonstrate (i) the systems-level regulatory landscape of HFD-induced metabolic syndrome involving multiple molecular parameters, including HNE, AGEs and their receptor RAGE, and (ii) attenuation of metabolic syndrome by PPARγ modulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0149-z) contains supplementary material, which is available to authorized users.

Genetic Deletion of Neuronal PPARγ Enhances the Emotional Response to Acute Stress and Exacerbates Anxiety: An Effect Reversed by Rescue of Amygdala PPARγ Function

PPARγ is one of the three isoforms of the Peroxisome Proliferator-Activated Receptors (PPARs). PPARγ is activated by thiazolidinediones such as pioglitazone and is targeted to treat insulin resistance. PPARγ is densely expressed in brain areas involved in regulation of motivational and emotional processes. Here, we investigated the role of PPARγ in the brain and explored its role in anxiety and stress responses in mice. The results show that stimulation of PPARγ by pioglitazone did not affect basal anxiety, but fully prevented the anxiogenic effect of acute stress. Using mice with genetic ablation of neuronal PPARγ (PPARγ^NestinCre), we demonstrated that a lack of receptors, specifically in neurons, exacerbated basal anxiety and enhanced stress sensitivity. The administration of GW9662, a selective PPARγ antagonist, elicited a marked anxiogenic response in PPARγ wild-type (WT), but not in PPARγ^NestinCre knock-out (KO) mice. Using c-Fos immunohistochemistry, we observed that acute stress exposure resulted in a different pattern of neuronal activation in the amygdala (AMY) and the hippocampus (HIPP) of PPARγ^NestinCre KO mice compared with WT mice. No differences were found between WT and KO mice in hypothalamic regions responsible for hormonal response to stress or in blood corticosterone levels. Microinjection of pioglitazone into the AMY, but not into the HIPP, abolished the anxiogenic response elicited by acute stress. Results also showed that, in both regions, PPARγ colocalizes with GABAergic cells. These findings demonstrate that neuronal PPARγ is involved the regulation of the stress response and that the AMY is a key substrate for the anxiolytic effect of PPARγ.

SIGNIFICANCE STATEMENT

Peroxisome Proliferator-Activated Receptor Gamma (PPARγ) is a classical target for antidiabetic therapies with thiazolidinedione compounds. PPARγ agonists such as rosiglitazone and pioglitazone are in clinical use for the treatment of insulin resistance. PPARγ has recently attracted attention for its involvement in the regulation of CNS immune response and functions. Here, we demonstrate that neuronal PPARγ activation prevented the negative emotional effects of stress and exerted anxiolytic actions without influencing hypothalamic-pituitary-adrenal axis function. Conversely, pharmacological blockade or genetic deletion of PPARγ enhanced anxiogenic responses and increased vulnerability to stress. These effects appear to be controlled by PPARγ neuronal-mediated mechanisms in the amygdala.

Bavachinin, as a novel natural pan-PPAR agonist, exhibits unique synergistic effects with synthetic PPAR-γ and PPAR-α agonists on carbohydrate and lipid metabolism in db/db and diet-induced obese mice

AIMS/HYPOTHESIS

Pan-peroxisome proliferator-activated receptor (PPAR) agonists have long been sought as therapeutics against the metabolic syndrome, but current PPAR agonists show limited efficacy and adverse effects. Natural herbs provide a structurally untapped resource to prevent and treat complicated metabolic syndrome.

METHODS

Natural PPAR agonists were screened using reporter gene, competitive binding and 3T3-L1 pre-adipocyte differentiation assays in vitro. The effects on metabolic phenotypes were verified in db/db and diet-induced obese mice. In addition, potentially synergistic actions of bavachinin (BVC, a novel natural pan-PPAR agonist from the fruit of the traditional Chinese glucose-lowering herb malaytea scurfpea) and synthetic PPAR agonists were studied through nuclear magnetic resonance, molecular docking, reporter gene assays and mouse studies.

RESULTS

BVC exhibited glucose-lowering properties without inducing weight gain and hepatotoxicity. Importantly, BVC synergised with thiazolidinediones, which are synthetic PPAR-γ agonists, and fibrates, which are PPAR-α agonists, to induce PPAR transcriptional activity, as well as to lower glucose and triacylglycerol levels in db/db mice. We further found that BVC occupies a novel alternative binding site in addition to the canonical site of synthetic agonists of PPAR, and that the synthetic PPAR-γ agonist rosiglitazone can block BVC binding to this canonical site but not to the alternative site.

CONCLUSIONS/INTERPRETATION

This is the first report of a synergistic glucose- and lipid-lowering effect of BVC and synthetic agonists induced by unique binding with PPAR-γ or -α. This combination may improve the efficacy and decrease the toxicity of marketed drugs for use as adjunctive therapy to treat the metabolic syndrome.

The effects of pioglitazone, a PPARγ receptor agonist, on the abuse liability of oxycodone among nondependent opioid users

AIMS

Activation of PPARγ by pioglitazone (PIO) has shown some efficacy in attenuating addictive-like responses in laboratory animals. The ability of PIO to alter the effects of opioids in humans has not been characterized in a controlled laboratory setting. The proposed investigation sought to examine the effects of PIO on the subjective, analgesic, physiological and cognitive effects of oxycodone (OXY).

METHODS

During this investigation, nondependent prescription opioid abusers (N=17 completers) were maintained for 2-3weeks on ascending daily doses of PIO (0mg, 15mg, 45mg) prior to completing a laboratory session assessing the aforementioned effects of OXY [using a within-session cumulative dosing procedure (0, 10, and 20mg, cumulative dose=30mg)].

RESULTS

OXY produced typical mu opioid agonist effects: miosis, decreased pain perception, and decreased respiratory rate. OXY also produced dose-dependent increases in positive subjective responses. Yet, ratings such as: drug "liking," "high," and "good drug effect," were not significantly altered as a function of PIO maintenance dose.

DISCUSSION

These data suggest that PIO may not be useful for reducing the abuse liability of OXY. These data were obtained with a sample of nondependent opioid users and therefore may not be applicable to dependent populations or to other opioids. Although PIO failed to alter the abuse liability of OXY, the interaction between glia and opioid receptors is not well understood so the possibility remains that medications that interact with glia in other ways may show more promise.

Design, Synthesis, and Biological Evaluation of Indole Biphenylcarboxylic Acids as PPARγ Antagonists

The thiazolidinediones (TZD) typified by rosiglitazone are the only approved therapeutics targeting PPARγ for the treatment of type-2 diabetes (T2DM). Unfortunately, despite robust insulin sensitizing properties, they are accompanied by a number of severe side effects including congestive heart failure, edema, weight gain, and osteoporosis. We recently identified PPARγ antagonists that bind reversibly with high affinity but do not induce transactivation of the receptor, yet they act as insulin sensitizers in mouse models of diabetes (SR1664).1 This Letter details our synthetic exploration around this novel series of PPARγ antagonists based on an N-biphenylmethylindole scaffold. Structure-activity relationship studies led to the identification of compound 46 as a high affinity PPARγ antagonist that exhibits antidiabetic properties following oral administration in diet-induced obese mice.

Early Clinical Detection of Pharmacologic Response in Insulin Action in a Nondiabetic Insulin-Resistant Population

Background

Insulin resistance heightens the risk for type 2 diabetes mellitus and cardiovascular disease. Amelioration of insulin resistance may reduce this risk. The thiazolidinedone class of insulin sensitizers improves insulin action in individuals with insulin-resistant diabetes and nondiabetic individuals. However, there are few reports on the time of onset of such effects independent of reversal of glucotoxicity.

Objective

The goal of our study was to test whether the thiazolidinedione pioglitazone has prominent early metabolic effects that can be detected in an obese, nondiabetic, insulin-resistant population.

Methods

We conducted a randomized, double-blind, placebo-controlled, parallel-group trial in men with nondiabetic insulin resistance using a hyperinsulinemic euglycemic clamp technique (at low and high doses of insulin at 10 and 40 mU/m²/min, respectively). The patients were given 30 mg daily oral pioglitazone or placebo for 28 days. Patients underwent a baseline clamp before initiation of treatment, and again at 14 and 28 days of treatment.

Results

Compared with placebo, under high-dose hyperinsulinemia, pioglitazone led to significant increases in glucose disposal rates (GDR) of 1.29 mg/kg/min (90% CI, 0.43–2.15; 39%; P=0.008) that were detectable at 2 weeks of treatment and persisted at 4 weeks of treatment. Under low-dose hyperinsulinemia, significant increases in GDR of 0.40 mg/kg/min (90% CI, 0.17–0.62; 95%; P=0.003) were observed at 4 weeks of treatment. These responses were accompanied by robust suppression of free fatty acids under hyperinsulinemic conditions, and by significant increases in circulating basal total adiponectin at 2 and 4 weeks of treatment.

Conclusions

Significant changes in insulin action across multiple insulin-sensitive tissues can be detected within 2 weeks of initiation of insulin-sensitizing therapy with pioglitazone in obese patients with nondiabetic insulin resistance. ClinicalTrials.gov identifier: NCT01115712.

Chronic Ethanol-Induced Impairment of Wnt/β-Catenin Signaling is Attenuated by PPAR-δ Agonist

BACKGROUND

The Wnt/β-catenin pathway regulates liver growth, repair, and regeneration. Chronic ethanol (EtOH) exposure blunts normal liver regenerative responses, in part by inhibiting insulin/IGF signaling, and correspondingly, previous studies showed that EtOH-impaired liver regeneration could be restored by insulin sensitizer (proliferator-activated receptor [PPAR]-δ agonist) treatment. As Wnt/β-catenin functions overlap and cross talk with insulin/IGF pathways, we investigated the effects of EtOH exposure and PPAR-δ agonist treatment on Wnt pathway gene expression in relation to liver regeneration.

METHODS

Adult male Long Evans rats were fed with isocaloric liquid diets containing 0 or 37% EtOH for 8 weeks and also treated with vehicle or a PPAR-δ agonist during the last 3 weeks of the feeding regimen. The rats were then subjected to 70% partial hepatectomy (PH) and livers harvested at various post-PH time points were used to quantitate expression of 19 Wnt pathway genes using Quantigene 2.0 Multiplex Assay.

RESULTS

EtOH broadly inhibited expression of Wnt/β-catenin signaling-related genes, including down-regulation of Wnt1, Fzd3, Lef1, and Bcl9 throughout the post-PH time course (0 to 72 hours), and suppression of Wnt7a, Ccnd1, Fgf4, Wif1, Sfrp2, and Sfrp5 at 18- and 24-hour post-PH time points. PPAR-δ agonist treatments rescued the EtOH-induced suppression of Wnt1, Wnt7a, Fzd3, Lef1, Bcl9, Ccnd1, and Sfrp2 gene expression in liver, corresponding with the improvements in DNA synthesis and restoration of hepatic architecture.

CONCLUSIONS

Chronic high-dose EtOH exposures inhibit Wnt signaling, which likely contributes to the impairments in liver regeneration. Therapeutic effects of PPAR-δ agonists extend beyond restoration of insulin/IGF signaling mechanisms and are mediated in part by enhancement of Wnt pathway signaling. Future studies will determine the degree to which targeted restoration of Wnt signaling is sufficient to improve liver regeneration and remodeling in the context of chronic EtOH exposure.

Thiazolidinedione-induced lipid droplet formation during osteogenic differentiation

Chronic administration of the insulin-sensitising drugs, thiazolidinediones (TZDs), results in low bone mineral density and 'fatty bones'. This is thought to be due, at least in part, to aberrant differentiation of progenitor mesenchymal stem cells (MSCs) away from osteogenesis towards adipogenesis. This study directly compared the effects of rosiglitazone, pioglitazone, and netoglitazone treatment on osteogenesis and adipogenesis in MSCs derived from subcutaneous (SC) or visceral (PV) white adipose tissue. MSCs were isolated from adipose tissue depots of male Wistar rats and characterised using flow cytometry. The effects of TZD treatment on osteogenic and adipogenic differentiation were assessed histologically (day 14) and by quantitative PCR analysis (Pparγ2 (Pparg2), Ap2 (Fabp4), Adipsin (Adps), Msx2, Collagen I (Col1a1), and Alp) on days 0, 7, and 10. Uniquely, lipid droplet formation and mineralisation were found to occur concurrently in response to TZD treatment during osteogenesis. Compared with SC MSCs, PV MSCs were more prone to lipid accumulation under controlled osteogenic and adipogenic differentiation conditions. This study demonstrated that the extent of lipid accumulation is dependent on the nature of the Ppar ligand and that SC and PV MSCs respond differently to in vitro TZD treatment, suggesting that metabolic status can contribute to the adverse effects associated with TZD treatment.

Clofibric acid induces hepatic CYP 2B1/2 via constitutive androstane receptor not via peroxisome proliferator activated receptor alpha in rat

Peroxisome proliferator activated receptor α (PPARα) ligands, fibrates used to control hyperlipidemia. We demonstrated CYP2B induction by clofibric acid (CFA) however, the mechanism was not clear. In this study, HepG2 cells transfected with expression plasmid of mouse constitutive androstane receptor (CAR) or PPARα were treated with CFA, phenobarbital (PB) or TCPOBOP. Luciferase assays showed that CFA increased CYP2B1 transcription to the same level as PB, or TCPOBOP in HepG2 transfected with mouse CAR But failed to induce it in PPARα transfected cells. CYP2B expressions were increased with PB or CFA in Wistar female rats (having normal levels of CAR) but not in Wistar Kyoto female rats (having low levels of CAR). The induction of CYP2B by PB or CFA was comparable to nuclear CAR levels. CAR nuclear translocation was induced by CFA in both rat strains. This indicates that fibrates can activate CAR and that fibrates-insulin sensitization effect may occur through CAR, while hypolipidemic effect may operate through PPARα.

Canola oil influence on azoxymethane-induced colon carcinogenesis, hypertriglyceridemia and hyperglycemia in Kunming mice

Azoxymethane (AOM) is a potent genotoxic carcinogen which specifically induces colon cancer. Hyperlipidemia and diabetes have several influences on colon cancer development, with genetic and environmental exposure aspects. Here, we investigated plasma lipid and glucose concentrations in Kunming mice randomized into four groups; control (no AOM or oil exposure), AOM control, AOM + pork oil, and AOM + canola oil. Aberrant crypt foci (ACF), plasma cholesterol, plasma triglyceride, plasma glucose and organ weight were examined 32 weeks after AOM injection. Results revealed that AOM exposure significantly increased ACF number, plasma triglyceride and glucose level. Further, male mice displayed a much higher plasma triglyceride level than female mice in the AOM control group. Dietary fat significantly inhibited AOM-induced hypertriglyceridemia, and canola oil had stronger inhibitory effect than pork oil. AOM-induced hyperglycemia had no sex-difference and was not significantly modified by dietary fat. However, AOM itself not change plasma cholesterol level. AOM significantly increased liver and spleen weight in male mice, but decreased kidney weight in female mice. On the other hand, mice testis weight decreased when fed canola oil. AOM could induce colorectal carcinogenesis, hypertriglyceridemia and hyperglycemia in Kunming mice at the same time, with subsequent studies required to investigate their genome association.

Peroxisome proliferator-activated receptors and their ligands: nutritional and clinical implications--a review

Peroxisome proliferator-activated receptors are expressed in many tissues, including adipocytes, hepatocytes, muscles and endothelial cells; however, the affinity depends on the isoform of PPAR, and different distribution and expression profiles, which ultimately lead to different clinical outcomes. Because they play an important role in lipid and glucose homeostasis, they are called lipid and insulin sensors. Their actions are limited to specific tissue types and thus, reveal a characteristic influence on target cells. PPARα mainly influences fatty acid metabolism and its activation lowers lipid levels, while PPARγ is mostly involved in the regulation of the adipogenesis, energy balance, and lipid biosynthesis. PPARβ/δ participates in fatty acid oxidation, mostly in skeletal and cardiac muscles, but it also regulates blood glucose and cholesterol levels. Many natural and synthetic ligands influence the expression of these receptors. Synthetic ligands are widely used in the treatment of dyslipidemia (e.g. fibrates--PPARα activators) or in diabetes mellitus (e.g. thiazolidinediones--PPARγ agonists). New generation drugs--PPARα/γ dual agonists--reveal hypolipemic, hypotensive, antiatherogenic, anti-inflammatory and anticoagulant action while the overexpression of PPARβ/δ prevents the development of obesity and reduces lipid accumulation in cardiac cells, even during a high-fat diet. Precise data on the expression and function of natural PPAR agonists on glucose and lipid metabolism are still missing, mostly because the same ligand influences several receptors and a number of reports have provided conflicting results. To date, we know that PPARs have the capability to accommodate and bind a variety of natural and synthetic lipophilic acids, such as essential fatty acids, eicosanoids, phytanic acid and palmitoylethanolamide. A current understanding of the effects of PPARs, their molecular mechanisms and the role of these receptors in nutrition and therapeutic treatment are delineated in this paper.

Identifying druggable targets by protein microenvironments matching: application to transcription factors

Druggability of a protein is its potential to be modulated by drug-like molecules. It is important in the target selection phase. We hypothesize that: (i) known drug-binding sites contain advantageous physicochemical properties for drug binding, or “druggable microenvironments” and (ii) given a target, the presence of multiple druggable microenvironments similar to those seen previously is associated with a high likelihood of druggability. We developed DrugFEATURE to quantify druggability by assessing the microenvironments in potential small-molecule binding sites. We benchmarked DrugFEATURE using two data sets. One data set measures druggability using NMR-based screening. DrugFEATURE correlates well with this metric. The second data set is based on historical drug discovery outcomes. Using the DrugFEATURE cutoffs derived from the first, we accurately discriminated druggable and difficult targets in the second. We further identified novel druggable transcription factors with implications for cancer therapy. DrugFEATURE provides useful insight for drug discovery, by evaluating druggability and suggesting specific regions for interacting with drug-like molecules.

Polyacetylenes from Notopterygium incisum--new selective partial agonists of peroxisome proliferator-activated receptor-gamma

Peroxisome proliferator-activated receptor gamma (PPARγ) is a key regulator of glucose and lipid metabolism and therefore an important pharmacological target to combat metabolic diseases. Since the currently used full PPARγ agonists display serious side effects, identification of novel ligands, particularly partial agonists, is highly relevant. Searching for new active compounds, we investigated extracts of the underground parts of Notopterygium incisum, a medicinal plant used in traditional Chinese medicine, and observed significant PPARγ activation using a PPARγ-driven luciferase reporter model. Activity-guided fractionation of the dichloromethane extract led to the isolation of six polyacetylenes, which displayed properties of selective partial PPARγ agonists in the luciferase reporter model. Since PPARγ activation by this class of compounds has so far not been reported, we have chosen the prototypical polyacetylene falcarindiol for further investigation. The effect of falcarindiol (10 µM) in the luciferase reporter model was blocked upon co-treatment with the PPARγ antagonist T0070907 (1 µM). Falcarindiol bound to the purified human PPARγ receptor with a K_i of 3.07 µM. In silico docking studies suggested a binding mode within the ligand binding site, where hydrogen bonds to Cys285 and Glu295 are predicted to be formed in addition to extensive hydrophobic interactions. Furthermore, falcarindiol further induced 3T3-L1 preadipocyte differentiation and enhanced the insulin-induced glucose uptake in differentiated 3T3-L1 adipocytes confirming effectiveness in cell models with endogenous PPARγ expression. In conclusion, we identified falcarindiol-type polyacetylenes as a novel class of natural partial PPARγ agonists, having potential to be further explored as pharmaceutical leads or dietary supplements.

Activation of PPARγ by pioglitazone potentiates the effects of naltrexone on alcohol drinking and relapse in msP rats

BACKGROUND

Pioglitazone is a selective peroxisome proliferator-activated receptor γ (PPARγ) agonist used for the treatment of insulin resistance and type 2 diabetes. Previous studies conducted in our laboratory showed that activation of PPARγ by pioglitazone reduces alcohol drinking, stress-induced relapse, and alcohol withdrawal syndrome in rats. Pioglitazone was not able to prevent relapse elicited by alcohol cues. Conversely, the nonselective opioid antagonist naltrexone has been shown to reduce alcohol drinking and cue- but not stress-induced relapse in rodents.

METHODS

Based on these findings, this study was sought to determine the efficacy of pioglitazone and naltrexone combination on alcohol intake and relapse behavior. Genetically selected alcohol-preferring Marchigian Sardinian (msP) rats were used for the study.

RESULTS

Pioglitazone (10 and 30 mg/kg) and naltrexone (0.25 and 1.0 mg/kg) each individually reduced alcohol drinking in msP rats. The combination of the 2 drugs resulted in a more potent alcohol drinking reduction than single agents. Confirming previous studies, pioglitazone (10 and 30 mg/kg) significantly reduced relapse induced by the pharmacological stressor yohimbine (1.25 mg/kg) but not by cues predictive of alcohol availability. Conversely, naltrexone reduced reinstatement of drug seeking elicited by alcohol cues but not by yohimbine.

CONCLUSIONS

The drug combination was effective in reducing both relapse behaviors. These findings open new vistas in the use pioglitazone in combination with naltrexone for the treatment of alcoholism.

PPAR agonists for the treatment of cardiovascular disease in patients with diabetes

Diabetes is a complex disease defined by hyperglycaemia; however, strong associations with abdominal obesity, hypertension and dyslipidaemia contribute to the high risk of cardiovascular disease. Although aggressive glycaemic control reduces microvascular complications, the evidence for macrovascular complications is less certain. The theoretical benefits of the mode of action of peroxisome proliferator-activated receptor (PPAR) agonists are clear. In clinical practice, PPAR-α agonists such as fibrates improve dyslipidaemia, while PPAR-γ agonists such as thiazolidinediones improve insulin resistance and diabetes control. However, although these agents are traditionally classed according to their target, they have different and sometimes conflicting clinical benefit and adverse event profiles. It is speculated that this is because of differing properties and specificities for the PPAR receptors (each of which targets specific genes). This is most obvious in the impact on cardiovascular outcomes--in clinical trials pioglitazone appeared to reduce cardiovascular events, whereas rosiglitazone potentially increased the risk of myocardial infarction. The development of a dual PPAR-α/γ agonist may prove beneficial in effectively managing glycaemic control and improving dyslipidaemia in patients with type 2 diabetes. Yet, development of agents such as muraglitazar and tesaglitazar has been hindered by various serious adverse events. Aleglitazar, a balanced dual PPAR-α/γ agonist, is currently the most advanced in clinical development and has shown promising results in phase II clinical trials with beneficial effects on glucose and lipid variables. A phase III study, ALECARDIO, is ongoing and will establish whether improvements in laboratory test profiles translate into an improvement in cardiovascular outcomes.

No evidence of QT prolongation with supratherapeutic doses of aleglitazar

Aleglitazar is a dual peroxisome proliferator-activated receptor (PPAR)-α/γ agonist in clinical development, designed to offer a balanced activation of PPAR-α and PPAR-γ. A phase 2 trial has demonstrated improvements in dyslipidemia and glycemic control and reduction of cardiovascular risk markers in patients with type 2 diabetes mellitus treated with aleglitazar. This study evaluated whether supratherapeutic doses of aleglitazar affect cardiac repolarization, as detected by changes in the QT interval.Healthy subjects were randomized to receive single oral doses of placebo, 300 μg aleglitazar, 3000 μg aleglitazar, and 400 mg moxifloxacin, in 1 of 4 sequences. Triplicate 12-lead electrocardiogram measurements were recorded predose and regularly (0.75-72 hours) after each treatment. The primary outcome was measurement of QT interval using a study-specific correction factor for heart rate.Administration of aleglitazar (300 μg and 3000 μg) did not cause any significant QT prolongation and after aleglitazar treatment any mean increases from placebo were <5 msec, at all time points. There was a trend for aleglitazar to cause a small dose-dependent decrease in QT interval using a study-specific correction factor for heart rate. The incidence of adverse events was similar with aleglitazar (18%-20%) and placebo (26%).Single supratherapeutic doses of aleglitazar are not associated with prolongation of the QT interval corrected for heart rate.

Thiazolidinedione safety

INTRODUCTION

Thiazolidinediones (TZDs) initially showed great promise as unique receptor-mediated oral therapy for type 2 diabetes, but a host of serious side effects, primarily cardiovascular, have limited their utility. It is crucial at this point to perform a risk-benefit analysis to determine what role TZDs should play in our current treatment of type 2 diabetes and where the future of this class of drugs is headed.

AREAS COVERED

This review provides a comprehensive overview of the literature from 2000 onward reporting the known side effects of rosiglitazone and pioglitazone, with commentary on the quality of the data available, putative mechanism of each side effect and clinical significance. Finally, a perspective on the future of the TZDs as a class is provided.

EXPERT OPINION

The current TZDs are first-generation, non-specific activators of peroxisome proliferator-activated receptor (PPAR) gamma, resulting in a wide array of deleterious side effects that currently limit their use. However, the development of highly targeted selective PPAR gamma modulators (SPPARγMs) and dual PPAR gamma/alpha agonists is on the horizon.

PPARs and angiogenesis

The PPAR (peroxisome-proliferator-activated receptor) family consists of three ligand-activated nuclear receptors: PPARα, PPARβ/δ and PPARγ. These PPARs have important roles in the regulation of glucose and fatty acid metabolism, cell differentiation and immune function, but were also found to be expressed in endothelial cells in the late 1990s. The early endothelial focus of PPARs was PPARγ, the molecular target for the insulin-sensitizing thiazolidinedione/glitazone class of drugs. Activation of PPARγ was shown to inhibit angiogenesis in vitro and in models of retinopathy and cancer, whereas more recent data point to a critical role in the development of the vasculature in the placenta. Similarly, PPARα, the molecular target for the fibrate class of drugs, also has anti-angiogenic properties in experimental models. In contrast, unlike PPARα or PPARγ, activation of PPARβ/δ induces angiogenesis, in vitro and in vivo, and has been suggested to be a critical component of the angiogenic switch in pancreatic cancer. Moreover, PPARβ/δ is an exercise mimetic and appears to contribute to the angiogenic remodelling of cardiac and skeletal muscle induced by exercise. This evidence and the emerging mechanisms by which PPARs act in endothelial cells are discussed in more detail.

Reduction of isoprenaline-induced myocardial TGF-β1 expression and fibrosis in osthole-treated mice

Peroxisome proliferator-activated receptor (PPAR) α and PPARγ ligands can attenuate myocardial fibrosis. Osthole, an active constituent isolated from the fruit of Cnidium monnieri (L.) Cusson, may be a dual PPARα/γ agonist, but there has been no report on its effect on myocardial fibrosis. In the present study, we investigated the inhibitory effect of osthole on myocardial fibrotic formation in mice and its possible mechanisms. A mouse model with myocardial fibrosis was induced by hypodermic injection of isoprenaline while the mice were simultaneously treated with 40 and 80 mg/kg osthole for 40 days. After the addition of osthole, the cardiac weight index and hydroxyproline content in the myocardial tissues were decreased, the degree of collagen accumulation in the heart was improved, and the downregulation of myocardial PPARα/γ mRNA expression induced by isoprenaline was reversed. Moreover, the mRNA expression of transforming growth factor (TGF)-β1 and the protein levels of nuclear factor (NF)-κB and TGF-β1 in the myocardial tissues were decreased. These findings suggest that osthole can prevent isoprenaline-induced myocardial fibrosis in mice, and its mechanisms may be related to the reduction of TGF-β1 expression via the activation of PPARα/γ and subsequent inhibition of NF-κB in myocardial tissues.

PPAR-alpha Ligands as Potential Therapeutic Agents for Wet Age-Related Macular Degeneration

The peroxisome proliferator-activated receptors (PPAR's) are members of the steroid/thyroid nuclear receptor, superfamily of transcription factors. There are currently three known PPAR subtypes, α, β, and γ. The PPARs are now recognized participants in a number of biological pathways some of which are implicated in the pathogenesis of age-related macular degeneration (AMD). These include immune modulation, lipid regulation, and oxidant/antioxidant pathways important to the onset and progression of “dry” AMD, and vascular endothelial growth factor (VEGF) mediated pathways that stimulate choroidal neovascularization (CNV), characteristic of “wet” AMD. PPAR-α is found in retina and also on vascular cells important to formation of CNV. At this time, however, relatively little is known about potential contributions of PPAR-α to the pathogenesis of dry and wet AMD. This review examines current literature for potential roles of PPAR-α in the pathogenesis and potential treatment of AMD with emphasis on prevention and treatment of wet AMD.

PPARgamma2 expression in growth plate chondrocytes is regulated by p38 and GSK-3

Although peroxisome proliferator activated receptor (PPAR)γ remains a critical regulator of preadipocyte differentiation, new roles have been discovered in inflammation, bone morphogenesis, endothelial function, cancer, longevity and atherosclerosis. Despite the demonstration of PPARγ expression in chondrocytes, its role and the pathways affecting its expression and activity in chondrocytes remain largely unknown. We investigated the effects of PPARγ activation on chondrocyte differentiation and its participation in chondrocyte lipid metabolism. PPARγ2 expression is highly regulated during chondrocyte differentiation in vivo and in vitro PPARγ activation with troglitazone resulted in increased Indian hedgehog expression and reduced collagen X expression, confirming previously described roles in the inhibition of differentiation. However, the major effect of PPARγ2 in chondrocytes appears to be on lipid metabolism. During differentiation chondrocytes increase expression of the lipid-associated metabolizing protein, Lpl, which is accompanied by increased gene expression of PPARγ. PPARγ expression is suppressed by p38 activity, but requires GSK-3 activity. Furthermore, Lpl expression is regulated by p38 and GSK-3 signalling. This is the first study demonstrating a relationship between PPARγ2 expression and chondrocyte lipid metabolism and its regulation by p38 and GSK-3 signalling.

The peroxisome proliferator-activated receptor (PPAR) alpha agonist fenofibrate maintains bone mass, while the PPAR gamma agonist pioglitazone exaggerates bone loss, in ovariectomized rats

BACKGROUND

Activation of peroxisome proliferator-activated receptor (PPAR)gamma is associated with bone loss and increased fracture risk, while PPARalpha activation seems to have positive skeletal effects. To further explore these effects we have examined the effect of the PPARalpha agonists fenofibrate and Wyeth 14643, and the PPARgamma agonist pioglitazone, on bone mineral density (BMD), bone architecture and biomechanical strength in ovariectomized rats.

METHODS

Fifty-five female Sprague-Dawley rats were assigned to five groups. One group was sham-operated and given vehicle (methylcellulose), the other groups were ovariectomized and given vehicle, fenofibrate, Wyeth 14643 and pioglitazone, respectively, daily for four months. Whole body and femoral BMD were measured by dual X-ray absorptiometry (DXA), and biomechanical testing of femurs, and micro-computed tomography (microCT) of the femoral shaft and head, were performed.

RESULTS

Whole body and femoral BMD were significantly higher in sham controls and ovariectomized animals given fenofibrate, compared to ovariectomized controls. Ovariectomized rats given Wyeth 14643, maintained whole body BMD at sham levels, while rats on pioglitazone had lower whole body and femoral BMD, impaired bone quality and less mechanical strength compared to sham and ovariectomized controls. In contrast, cortical volume, trabecular bone volume and thickness, and endocortical volume were maintained at sham levels in rats given fenofibrate.

CONCLUSIONS

The PPARalpha agonist fenofibrate, and to a lesser extent the PPARaplha agonist Wyeth 14643, maintained BMD and bone architecture at sham levels, while the PPARgamma agonist pioglitazone exaggerated bone loss and negatively affected bone architecture, in ovariectomized rats.

Pharmacokinetics, efficacy and safety of aleglitazar for the treatment of type 2 diabetes with high cardiovascular risk

INTRODUCTION

In preliminary clinical studies, aleglitazar, a new dual PPAR-α-γ agonist, has been demonstrated to improve hyperglycemia and dyslipidemia in patients with type 2 diabetes mellitus. This review will provide up-to-date information on the clinical safety and efficacy of aleglitazar, which is currently under Phase III clinical investigation for reduction of cardiovascular events in patients with type 2 diabetes and recent acute coronary syndrome.

AREAS COVERED

A PubMed literature search (January 1950 to February 2011) was conducted using the following search terms: aleglitazar, PPAR, PPAR α agonist, PPAR γ agonist and PPAR α/γ agonist. Additional articles were gathered using reference lists from sources obtained from the original literature search. This review summarizes available information pertaining to pharmacodynamics, pharmacokinetics, clinical studies and safety/tolerability of aleglitazar. The effects of this new drug are compared and contrasted with those of fibrates (PPAR-α agonists), thiazolidinediones (PPAR-γ agonists) and other dual PPAR-α-γ agonists.

EXPERT OPINION

Preliminary evidence from clinical studies with aleglitazar is promising, with reported improvements in glycemia, high-density lipoprotein-cholesterol, low-density lipoprotein-cholesterol, triglycerides, apolipoprotein B and blood pressure. However, PPAR-α- and -γ-associated side effects have been observed and additional large-scale, long-term clinical studies are necessary to better understand the clinical implications of these effects.

Activation of nuclear PPARγ receptors by the antidiabetic agent pioglitazone suppresses alcohol drinking and relapse to alcohol seeking

BACKGROUND

Pioglitazone and rosiglitazone belong to the class of thiazolidinediones (TZDs). They were first developed as antioxidants and then approved for the clinical treatment of insulin resistance and Type 2 diabetes. TZDs bind with high affinity and activate peroxisome proliferator-activated receptor-gamma (PPARγ) receptors, which in the brain are expressed both in neurons and in glia.

METHODS

We evaluated the effect of PPARγ activation by TZDs on alcohol drinking, relapse-like behavior, and withdrawal in the rat. We also tested the effect of TZDs on alcohol and saccharin self-administration.

RESULTS

We showed that activation of PPARγ receptors by pioglitazone (0, 10, and 30 mg/kg) and rosiglitazone (0, 10 and 30 mg/kg) given orally selectively reduced alcohol drinking. The effect was blocked by pretreatment with the selective PPARγ antagonist GW9662 (5 μg/rat) given into the lateral cerebroventricle, suggesting that this TZD's effect is mediated by PPARγ receptors in the central nervous system. Pioglitazone abolished reinstatement of alcohol seeking, a relapse-like behavior, induced by yohimbine, a pharmacologic stressor, but did not affect cue-induced relapse. In the self-administration experiments, pioglitazone reduced lever pressing for alcohol but not for saccharin. Finally, pioglitazone prevented the expression of somatic signs of alcohol withdrawal.

CONCLUSIONS

These findings provide new information about the role of brain PPARγ receptors and identify pioglitazone as candidate treatments for alcoholism and possibly other addictions.

Pharmacophore-driven identification of PPARγ agonists from natural sources

In a search for more effective and safe anti-diabetic compounds, we developed a pharmacophore model based on partial agonists of PPARγ. The model was used for the virtual screening of the Chinese Natural Product Database (CNPD), a library of plant-derived natural products primarily used in folk medicine. From the resulting hits, we selected methyl oleanonate, a compound found, among others, in Pistacia lentiscus var. Chia oleoresin (Chios mastic gum). The acid of methyl oleanonate, oleanonic acid, was identified as a PPARγ agonist through bioassay-guided chromatographic fractionations of Chios mastic gum fractions, whereas some other sub-fractions exhibited also biological activity towards PPARγ. The results from the present work are two-fold: on the one hand we demonstrate that the pharmacophore model we developed is able to select novel ligand scaffolds that act as PPARγ agonists; while at the same time it manifests that natural products are highly relevant for use in virtual screening-based drug discovery.

Therapeutic potential of aleglitazar, a new dual PPAR-α/γ agonist: implications for cardiovascular disease in patients with diabetes mellitus

Preventing morbidity and mortality from diabetes mellitus is of paramount importance as the incidence of this disease is increasing across the world. While microvascular complications of diabetes such as nephropathy, retinopathy, and neuropathy are reduced with intensive glycemic control, treatment of hyperglycemia has not been consistently shown to have effects on the macrovascular complications of diabetes such as coronary artery, cerebrovascular, and peripheral vascular disease. Preventive efforts have accordingly shifted toward the modification of other cardiovascular risk factors in diabetic patients. Agonism of the peroxisome proliferator-activated receptors (PPARs) has long been an attractive target for antidiabetic therapy due to the role of PPARs in glycemic control and lipid metabolism. PPAR-α agonists such as rosiglitazone and pioglitazone are used in clinical practice for the treatment of diabetes, and there is some evidence that pioglitazone may have positive effects on cardiovascular complications by virtue of its favorable effects on lipid profiles. However, they have not been shown to reduce macrovascular events. PPAR-α agonism is the mechanism of action in the fibrate class of medications; these agents have been shown to increase high-density lipoprotein cholesterol (HDL-C) levels, reduce triglyceride levels, and improve cardiovascular outcomes. Given the prevalence of lipid abnormalities in patients with diabetes, dual PPAR-α/γ agonists (glitazars) could potentially benefit patients with diabetes. A phase II trial examining a novel dual PPAR agonist, aleglitazar, showed that therapy with this agent reduced hyperglycemia and favorably modified levels of HDL-C and triglycerides with an acceptable safety profile. Aleglitazar is currently being studied in large-scale clinical trials to assess whether it will reduce the risk of major cardiovascular endpoints (death, myocardial infarction, or stroke) among patients with diabetes and coronary artery disease. If ongoing studies confirm the theoretical benefit and safety of dual PPAR-α/γ agonism, aleglitazar may become the first therapy demonstrated to reduce macrovascular complications in patients with diabetes.