PPAR tissue distribution and interactions with other hormone-signaling pathways

Peroxisome Proliferator-Activated Receptors as Superior Targets for Treating Diabetic Disease, Design Strategies - Review Article

Thiazolidinedione (TZD), a class of drugs that are mainly used to control type 2 diabetes mellitus (T2DM), acts fundamentally as a ligand of peroxisome proliferator-activated receptors (PPARs). Besides activating pathways responsible for glycemic control by enhancing insulin sensitivity and lipid homeostasis, activating PPARs leads to exciting other pathways related to bone formation, inflammation, and cell proliferation. Unfortunately, this diverse effect of activating several pathways may show in some studies adverse health outcomes as osteological, hepatic, cardiovascular, and carcinogenic effects. Thus, a silver demand is present to find and develop new active and potent antiglycemic drugs for treating T2DM. To achieve this goal, the structure of TZD for research is considered a leading structure domain. This review will guide future research in the design of novel TZD derivatives by highlighting the general modifications conducted on the structure component of TZD scaffold affecting their potency, binding efficacy, and selectivity for the control of T2DM.

Parental uveitis causes elevated hair loss in offspring of C57BL/6J mice

Our previous study demonstrated that parental uveitis in a susceptible population can cause hair loss and increase the susceptibility to experimental autoimmune uveitis (EAU) in offspring. However, it is unclear whether parental uveitis affects the development of offspring in an EAU-moderate-susceptible population. Herein, moderate-susceptible C57BL/6J mice were immunized with inter-photoreceptor retinoid binding protein (IRBP) 651-670 to develop EAU and were kept together for mating. Gross examination and histopathological changes of the offspring gestated with parental uveitis were observed to evaluate the impact of parental uveitis on the development of the offspring. Differentially expressed genes (DEGs) were screened by RNA sequencing in the affected skin and eyeball of the offspring on postnatal day 27. Adult offspring were injected 75 μg IRBP_651-670 to evaluate their susceptibility to EAU. Gross examination in the offspring revealed hair loss on postnatal days 11-31. Histopathological observation showed increased melanin granules and hair follicles of skin in the affected offspring with hair loss. Gene Ontology (GO) analysis in the skin revealed differential expression of genes involved in the mitotic cell cycle, response to endogenous stimulus, hair follicle development, and hair cycle. The DEGs in the skin were predominately associated with the cell cycle and peroxisome proliferator-activated receptor (PPAR) signaling pathway. The GO enrichment analysis in the eyeball showed differential expression of genes involved in the nervous system development, camera-type eye photoreceptor cell differentiation, neuron projection morphogenesis, axon development, and calcium-induced calcium release activity; enriched pathways included the circadian entrainment and glutamatergic synapses. No increased susceptibility to EAU in offspring gestated from parental remitting EAU was observed at a low-dose 75 μg IRBP induction. These results suggested that parental uveitis in a moderate-susceptible population could affect the skin development and DEG profiles of skin and eyeball related to the response to endogenous stimulus, the PPAR signaling pathway, and glutamatergic synapse, which provides the molecular evidence to explain the influence of parental uveitis on offspring development.

Activation of PPARγ in bladder cancer via introduction of the long arm of human chromosome 9

Bladder cancer is divided into two molecular subtypes, luminal and basal, which form papillary and nodular tumors, respectively, and are identifiable by gene expression profiling. Although loss of heterozygosity (LOH) of the long arm of human chromosome 9 (9q) has been observed in the early development of both types of bladder cancer, the functional significance of LOH remains to be clarified. The present study introduced human chromosome 9q into basal bladder cancer cell line, SCaBER, using microcell-mediated chromosome transfer to investigate the effect of LOH of 9q on molecular bladder cancer subtypes. These cells demonstrated decreased proliferation and migration capacity compared with parental and control cells. Conversely, transfer of human chromosome 4 did not change the cell phenotype. Expression level of peroxisome proliferator-activated receptor (PPAR)γ, a marker of luminal type, increased 3.0-4.4 fold in SCaBER cells altered with 9q compared with parental SCaBER cells. Furthermore, the expression levels of tumor suppressor PTEN, which regulates PPARγ, also increased in 9q-altered cells. These results suggested that human chromosome 9q may carry regulatory genes for PPARγ that are involved in the progression of neoplastic transformation of bladder cancer.

Swim therapy-induced tissue specific metabolic responses in male rats

Swim therapy in the form of moderate physical activity has general health benefits. Regular exercise prevents the progression of chronic diseases affecting the different bodily systems. The metabolic alterations associated with following such lifestyle remain not fully understood. The aim of the present study was to elucidate the metabolic changes following prolonged swim therapy. Twenty-four Sprague Dawley rats were divided into sedentary and exercise groups. Our results revealed that regular exercise significantly increased the serum levels of growth hormone (GH), glucagon and corticosterone. A reduction in the circulating levels of irisin and insulin hormones, and glucose were noticed alongside with an upregulation in the mRNA expression levels of FNDC5, PGC-1α, GLUT-4 and preptin receptors with downregulation in the expression of Enho gene in the heart of exercised rats. Liver of the exercised rats showed elevation in the transcriptional levels of Enho gene, PPARα, and preptin with reduction in the transcriptional levels of preptin receptors. Exercise induced an increase in the pancreatic mRNA of Enho gene, preptin and preptin receptors, and a reduction in FNDC5, PPARα and PGC-1α. An elevation in the gastrocnemius muscle PGC-1α mRNA expression and a decline in the soleus muscle Enho mRNA were found. Exercise diminishes the activities of SOD, CAT and GPx in the gastrocnemius muscle, liver and pancreas. Myogenin expression increased in all examined skeletal muscles. This study takes into account the complex crosstalk between different signaling pathways in skeletal muscles, heart, liver and pancreas as well as the metabolic alterations in response to regular exercise.

Extracellular Vesicles Attenuate Nitrofen-Mediated Human Pulmonary Artery Endothelial Dysfunction: Implications for Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) leads to pathophysiologic pulmonary vasoreactivity. Previous studies show that mesenchymal stromal cell-derived extracellular vesicles (MSCEv) inhibit lung inflammation and vascular remodeling. We characterize MSCEv and human pulmonary artery endothelial cell (HPAEC) interaction, as well as the pulmonary artery (PA) response to MSCEv treatment. HPAECs were cultured with and without exposure to nitrofen (2,4-dichloro-phenyl-p-nitrophenylether) and treated with MSCEv. HPAEC viability, architecture, production of reactive oxygen species (ROS), endothelial dysfunction-associated protein levels (PPARγ, LOX-1, LOX-2, nuclear factor-κB [NF-κB], endothelial NO synthase [eNOS], ET-1 [endothelin 1]), and the nature of MSCEv-cellular interaction were assessed. Newborn rodents with and without CDH (nitrofen model and Sprague-Dawley) were treated with intravascular MSCEv or vehicle control, and their PAs were isolated. Contractility was assessed by wire myography. The contractile (KCL and ET-1) and relaxation (fasudil) responses were evaluated. HPAEC viability correlated inversely with nitrofen dose, while architectural compromise was directly proportional. There was a 2.1 × increase in ROS levels in nitrofen HPAECs (P < 0.001), and MSCEv treatment attenuated ROS levels by 1.5 × versus nitrofen HPAECs (P < 0.01). Nitrofen-induced alterations in endothelial dysfunction-associated proteins are shown, and exposure to MSCEv restored more physiologic expression. Nitrofen HPAEC displayed greater MSCEv uptake (80% increase, P < 0.05). Adenosine, a clathrin-mediated endocytosis inhibitor, decreased uptake by 46% (P < 0.05). CDH PA contraction was impaired with KCL (108.6% ± 1.4% vs. 112.0% ± 1.4%, P = 0.092) and ET-1 (121.7% ± 3.0% vs. 131.2% ± 1.8%, P < 0.01). CDH PA relaxation was impaired with fasudil (32.2% ± 1.9% vs. 42.1% ± 2.2%, P < 0.001). After MSCEv treatment, CDH PA contraction improved (125.9% ± 3.4% vs. 116.4 ± 3.5, P = 0.06), and relaxation was unchanged (32.5% ± 3.2% vs. 29.4% ± 3.1%, P = 0.496). HPAEC exposure to nitrofen led to changes consistent with vasculopathy in CDH, and MSCEv treatment led to a more physiologic cellular response. MSCEv were preferentially taken up by nitrofen-treated cells by clathrin-dependent endocytosis. In vivo, MSCEv exposure improved PA contractile response. These data reveal mechanisms of cellular and signaling alterations that characterize MSCEv-mediated attenuation of pulmonary vascular dysfunction in CDH-associated pulmonary hypertension.

Bromocriptine mesylate improves glucose tolerance and disposal in a high-fat-fed canine model

Bromocriptine mesylate treatment was examined in dogs fed a high fat diet (HFD) for 8 wk. After 4 wk on HFD, daily bromocriptine (Bromo; n = 6) or vehicle (CTR; n = 5) injections were administered. Oral glucose tolerance tests were performed before beginning HFD (OGTT1), 4 wk after HFD began (Bromo only), and after 7.5 wk on HFD (OGTT3). After 8 wk on HFD, clamp studies were performed, with infusion of somatostatin and intraportal replacement of insulin (4× basal) and glucagon (basal). From 0 to 90 min (P1), glucose was infused via peripheral vein to double the hepatic glucose load; and from 90 to 180 min (P2), glucose was infused via the hepatic portal vein at 4 mg·kg^-1·min^-1, with the HGL maintained at 2× basal. Bromo decreased the OGTT glucose ΔAUC_0-30 and ΔAUC_0-120 by 62 and 27%, respectively, P < 0.05 for both) without significantly altering the insulin response. Bromo dogs exhibited enhanced net hepatic glucose uptake (NHGU) compared with CTR (~33 and 21% greater, P1 and P2, respectively, P < 0.05). Nonhepatic glucose uptake (non-HGU) was increased ~38% in Bromo in P2 (P < 0.05). Bromo vs. CTR had higher (P < 0.05) rates of glucose infusion (36 and 30%) and non-HGU (~40 and 27%) than CTR during P1 and P2, respectively. In Bromo vs. CTR, hepatic 18:0/16:0 and 16:1/16:0 ratios tended to be elevated in triglycerides and were higher (P < 0.05) in phospholipids, consistent with a beneficial effect of bromocriptine on liver fat accumulation. Thus, bromocriptine treatment improved glucose disposal in a glucose-intolerant model, enhancing both NHGU and non-HGU.

The role and function of PPARγ in bladder cancer

Peroxisome proliferator-activated receptor gamma (PPARγ), a member of the nuclear receptor superfamily, participates in multiple physiological and pathological processes. Extensive studies have revealed the relationship between PPARγ and various tumors. However, the expression and function of PPARγ in bladder cancer seem to be controversial. It has been demonstrated that PPARγ affects the occurrence and progression of bladder cancer by regulating proliferation, apoptosis, metastasis, and reactive oxygen species (ROS) and lipid metabolism, probably through PPARγ-SIRT1 feedback loops, the PI3K-Akt signaling pathway, and the WNT/β-catenin signaling pathway. Considering the frequent relapses after chemotherapy, some researchers have focused on the relationship between PPARγ and chemotherapy sensitivity in bladder cancer. Moreover, the feasibility of PPARγ ligands as potential therapeutic targets for bladder cancer has been uncovered. Taken together, this review summarizes the relevant literature and our findings to explore the complicated role and function of PPARγ in bladder cancer.

Hippocampal Genetic Knockdown of PPARδ Causes Depression-Like Behaviors and Neurogenesis Suppression

BACKGROUND

Although depression is the leading cause of disability worldwide, its pathophysiology is poorly understood. Our previous study showed that hippocampal peroxisome proliferator-activated receptor δ (PPARδ) overexpression displays antidepressive effect and enhances hippocampal neurogenesis during chronic stress. Herein, we further extended our curiosity to investigate whether downregulating PPARδ could cause depressive-like behaviors through downregulation of neurogenesis.

METHODS

Stereotaxic injection of lentiviral vector, expressing short hairpin RNA complementary to the coding exon of PPARδ, was done into the bilateral dentate gyri of the hippocampus, and the depression-like behaviors were observed in mice. Additionally, hippocampal neurogenesis, brain-derived neurotrophic factor and cAMP response element-binding protein were measured both in vivo and in vitro.

RESULTS

Hippocampal PPARδ knockdown caused depressive-like behaviors and significantly decreased neurogenesis, neuronal differentiation, levels of mature brain-derived neurotrophic factor and phosphorylated cAMP response element-binding protein in the hippocampus. In vitro study further confirmed that PPARδ knockdown could inhibit proliferation and differentiation of neural stem cells. Furthermore, these effects were mimicked by repeated systemic administration of a PPARδ antagonist, GSK0660 (1 or 3 mg/kg i.p. for 21 d).

CONCLUSIONS

These findings suggest that downregulation of hippocampal PPARδ is associated with depressive behaviors in mice through an inhibitory effect on cAMP response element-binding protein/brain-derived neurotrophic factor-mediated adult neurogenesis in the hippocampus, providing new insights into the pathogenesis of depression.

The Impact of Di(2-ethylhexyl)phthalate on Cancer Progression

Di(2-ethylhexyl)phthalate (DEHP), a widely used plasticizer, mainly serves as an additive to render polyvinyl chloride (PVC) soft and flexible. PVC plastics have become ubiquitous in our modern society. Yet, the leaching of DEHP from PVC-based consumables ultimately results in the deposition in certain tissues via inadvertent applications. Health risks for human populations exposed to DEHP has been assumed by studies on rodents and other species, including the DEHP-induced developmental dysregulation, reproductive impairments, tumorigenesis, and diseases in a transgenerational manner. In this review, we comprehensively summarize the accumulated literature regarding the multifaceted roles of DEHP in the activation of the nuclear receptors, the alteration of the redox homeostasis, epigenetic modifications and the acquisition of chemoresistance.

Therapeutic Effects of PPARα Agonist on Ocular Neovascularization in Models Recapitulating Neovascular Age-Related Macular Degeneration

Purpose

This study was designed to evaluate effects of fenofibric acid (Feno-FA), a peroxisome proliferator–activated receptor-alpha (PPARα) agonist, on ocular neovascularization (NV) in models recapitulating neovascular age-related macular degeneration (AMD), and to explore whether the effects are PPARα dependent.

Methods

Laser-induced choroidal NV (CNV) in rats and very low-density lipoprotein receptor knockout (Vldlr^−/−) mice received daily intraperitoneal injections of Feno-FA or vehicle. Vascular leakage was examined by fundus fluorescein angiography and permeability assay using Evans blue as tracer. In CNV rats, severity of CNV was evaluated by CNV areas and CNV volume. In Vldlr^−/− mice, subretinal NV (SRNV) and intraretinal NV (IRNV) were quantified in choroid flat mount and retina flat mount, respectively. Inflammatory factors were measured using Western blotting and retinal leukostasis assay. Further, Pparα^−/− mice and age-matched wild-type (WT) mice were used for laser-induced CNV and treated with Feno-FA to explore the underlying mechanism.

Results

Feno-FA significantly reduced vascular leakage in CNV rats and Vldlr^−/− mice, reduced CNV volume in laser-induced CNV rats, and suppressed SRNV and IRNV in Vldlr^−/− mice. In addition, Feno-FA downregulated the expression of inflammatory factors, including VEGF, TNF-α, and intercellular cell adhesion molecule-1 (ICAM-1), in the eyecups of CNV rats and decreased adherent retinal leukocytes in Vldlr^−/− mice. Furthermore, Pparα^−/− mice developed more severe CNV compared with WT mice, and PPARα knockout abolished the beneficial effects of Feno-FA on CNV.

Conclusions

Feno-FA has therapeutic effects on ocular NV in models recapitulating neovascular AMD through a PPARα-dependent mechanism.

Simvastatin induces cell cycle arrest and inhibits proliferation of bladder cancer cells via PPARγ signalling pathway

Simvastatin is currently one of the most common drugs for old patients with hyperlipidemia, hypercholesterolemia and atherosclerotic diseases by reducing cholesterol level and anti-lipid properties. Importantly, simvastatin has also been reported to have anti-tumor effect, but the underlying mechanism is largely unknown. We collected several human bladder samples and performed microarray. Data analysis suggested bladder cancer (BCa) was significantly associated with fatty acid/lipid metabolism via PPAR signalling pathway. We observed simvastatin did not trigger BCa cell apoptosis, but reduced cell proliferation in a dose- and time-dependent manner, accompanied by PPARγ-activation. Moreover, flow cytometry analysis indicated that simvastatin induced cell cycle arrest at G0/G1 phase, suggested by downregulation of CDK4/6 and Cyclin D1. Furthermore, simvastatin suppressed BCa cell metastasis by inhibiting EMT and affecting AKT/GSK3β. More importantly, we found that the cell cycle arrest at G0/G1 phase and the alterations of CDK4/6 and Cyclin D1 triggered by simvastatin could be recovered by PPARγ-antagonist (GW9662), whereas the treatment of PPARα-antagonist (GW6471) shown no significant effects on the BCa cells. Taken together, our study for the first time revealed that simvastatin inhibited bladder cancer cell proliferation and induced cell cycle arrest at G1/G0 phase via PPARγ signalling pathway.

The role of PPARγ-mediated signalling in skin biology and pathology: new targets and opportunities for clinical dermatology

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that modulate the expression of multiple different genes involved in the regulation of lipid, glucose and amino acid metabolism. PPARs and cognate ligands also regulate important cellular functions, including cell proliferation and differentiation, as well as inflammatory responses. This includes a role in mediating skin and pilosebaceous unit homoeostasis: PPARs appear to be essential for maintaining skin barrier permeability, inhibit keratinocyte cell growth, promote keratinocyte terminal differentiation and regulate skin inflammation. They also may have protective effects on human hair follicle (HFs) epithelial stem cells, while defects in PPARγ-mediated signalling may promote the death of these stem cells and thus facilitate the development of cicatricial alopecia (lichen planopilaris). Overall, however, selected PPARγ modulators appear to act as hair growth inhibitors that reduce the proliferation and promote apoptosis of hair matrix keratinocytes. The fact that commonly prescribed PPARγ-modulatory drugs of the thiazolidine-2,4-dione class can exhibit a battery of adverse cutaneous effects underscores the importance of distinguishing beneficial from clinically undesired cutaneous activities of PPARγ ligands and to better understand on the molecular level how PPARγ-regulated cutaneous lipid metabolism and PPARγ-mediated signalling impact on human skin physiology and pathology. Surely, the therapeutic potential that endogenous and exogenous PPARγ modulators may possess in selected skin diseases, ranging from chronic inflammatory hyperproliferative dermatoses like psoriasis and atopic dermatitis, via scarring alopecia and acne can only be harnessed if the complexities of PPARγ signalling in human skin and its appendages are systematically dissected.

Non-classical Transcriptional Activity of Retinoic Acid

It has long been established that the transcriptional activity of retinoic acid (RA) is mediated by members of the nuclear receptor family of ligand-activated transcription factors termed RA receptors (RARs). More recent observations have established that RA also activates an additional nuclear receptor, PPARβ/δ. Partitioning RA between RARs and PPARβ/δ is governed by different intracellular lipid-binding proteins: cellular RA binding protein 2 (CRABP2) delivers RA to nuclear RARs and a fatty acid binding protein (FABP5) delivers the hormone from the cytosol to nuclear PPARβ/δ. Consequently, RA signals through RARs in CRABP2-expressing cells, but activates PPARβ/δ in cells that express a high level of FABP5. RA elicits different and sometimes opposing responses in cells that express different FABP5/CRABP2 ratios because PPARβ/δ and RARs regulate the expression of distinct sets of genes. An overview of the observations that led to the discovery of this non-classical activity of RA are presented here, along with a discussion of evidence demonstrating the involvement of the dual transcriptional activities of RA in regulating energy homeostasis, insulin responses, and adipocyte and neuron differentiation.

Altered Hippocampal Lipid Profile Following Acute Postnatal Exposure to Di(2-Ethylhexyl) Phthalate in Rats

Slight changes in the abundance of certain lipid species in the brain may drastically alter normal neurodevelopment via membrane stability, cell signalling, and cell survival. Previous findings have demonstrated that postnatal exposure to di (2-ethylhexyl) phthalate (DEHP) disrupts normal axonal and neural development in the hippocampus. The goal of the current study was to determine whether postnatal exposure to DEHP alters the lipid profile in the hippocampus during postnatal development. Systemic treatment with 10 mg/kg DEHP during postnatal development led to elevated levels of phosphatidylcholine and sphingomyelin in the hippocampus of female rats. There was no effect of DEHP exposure on the overall abundance of phosphatidylcholine or sphingomyelin in male rats or of lysophosphatidylcholine in male or female rats. Individual analyses of each identified lipid species revealed 10 phosphatidylcholine and six sphingomyelin lipids in DEHP-treated females and a single lysophosphatidylcholine in DEHP-treated males with a two-fold or higher increase in relative abundance. Our results are congruent with previous work that found that postnatal exposure to DEHP had a near-selective detrimental effect on hippocampal development in males but not females. Together, results suggest a neuroprotective effect of these elevated lipid species in females.

Hippocampal PPARδ Overexpression or Activation Represses Stress-Induced Depressive Behaviors and Enhances Neurogenesis

BACKGROUND

Emerging data have demonstrated that peroxisome proliferator-activated receptor δ (PPARδ) activation confers a potentially neuroprotective role in some neurodegenerative diseases. However, whether PPARδ is involved in depression is unknown.

METHODS

In this study, PPARδ was firstly investigated in the chronic mild stress (CMS) and learned helplessness (LH) models of depression. The changes in depressive behaviors and hippocampal neurogenesis were investigated after PPARδ overexpression by microinfusion of the lentiviral vector, containing the coding sequence of mouse PPARδ (LV-PPARδ), into the bilateral dentate gyri of the hippocampus or PPARδ activation by repeated systemic administration of PPARδ agonist GW0742 (5 or 10mg/kg.d, i.p., for 21 d).

RESULTS

We found that both CMS and LH resulted in a significant decrease in the PPARδ expression in the hippocampi of mice, and this change was reversed by treatment with the antidepressant fluoxetine. PPARδ overexpression and PPARδ activation each suppressed the CMS- and LH-induced depressive-like behavior and produced an antidepressive effect. In vivo or in vitro studies also showed that both overexpression and activation of PPARδ enhanced proliferation or differentiation of neural stem cells in the hippocampi of mice.

CONCLUSIONS

These results suggest that hippocampal PPARδ upregulation represses stress-induced depressive behaviors, accompanied by enhancement of neurogenesis.

Effects of Diisodecyl Phthalate on PPAR:RXR-Dependent Gene Expression Pathways in Sea Bream Hepatocytes

Evidence that endocrine-disrupting chemicals (EDCs) may target metabolic disturbances, beyond interference with the functions of the endocrine systems has recently accumulated. Among EDCs, phthalate plasticizers like the diisodecyl phthalate (DiDP) are commonly found contaminants of aquatic environments and have been suggested to function as obesogens by activating peroxisome proliferator activated receptors (PPARs), a subset of nuclear receptors (NRs) that act as metabolic sensors, playing pivotal roles in lipid homeostasis. However, little is known about the modulation of PPAR signaling pathways by DiDP in fish. In this study, we have first investigated the ligand binding efficiency of DiDP to the ligand binding domains of PPARs and retinoid-X-receptor-α (RXRα) proteins in fish using a molecular docking approach. Furthermore, in silico predictions were integrated by in vitro experiments to show possible dose-relationship effects of DiDP on PPAR:RXR-dependent gene expression pathways using sea bream hepatocytes. We observed that DiDP shows high binding efficiency with piscine PPARs demonstrating a greater preference for RXRα. Our studies also demonstrated the coordinate increased expression of PPARs and RXRα, as well as their downstream target genes in vitro. Principal component analysis (PCA) showed the strength of relationship between transcription of most genes involved in fatty acid metabolism and PPAR mRNA levels. In particular, fatty acid binding protein (FABP) was highly correlated to all PPARs. The results of this study suggest that DiDP can be considered an environmental stressor that activates PPAR:RXR signaling to promote long-term changes in lipid homeostasis leading to potential deleterious physiological consequences in teleost fish.

Peroxisome proliferator-activated receptor gamma (PPARγ) in yellow catfish Pelteobagrus fulvidraco: molecular characterization, mRNA expression and transcriptional regulation by insulin in vivo and in vitro

Peroxisome proliferator-activated receptor gamma (PPARγ) is ligand-inducible transcription factor and has important roles in lipid metabolism, cell proliferation and inflammation. In the present study, yellow catfish Pelteobagrus fulvidraco PPARγ cDNA was isolated from liver by RT-PCR and RACE, and its molecular characterization and transcriptional regulation by insulin in vivo and in vitro were determined. The generation of PPARγ1 and PPARγ2 was due to alternative promoter of PPARγ gene. PPARγ1 and PPARγ2 mRNA covered 2426 bp and 2537 bp, respectively, with an open reading frame (ORF) of 1584 bp encoding 527 amino acid residues. Yellow catfish PPARγ gene was organized in a manner similar to that of their mammalian homologs, implying a modular organization of the protein's domains. A comparison between the yellow catfish PPARγ amino acid sequence and the correspondent sequences of several other species revealed the identity of 55-76.2%. Two PPARγ transcripts (PPARγ1 and PPARγ2) mRNAs were expressed in a wide range of tissues, but the abundance of each PPARγ mRNA showed the tissue- and developmental stage-dependent expression patterns. Intraperitoneal injection of insulin in vivo significantly stimulated the mRNA expression of total PPARγ and PPARγ1, but not PPARγ2 in the liver of yellow catfish. In contrast, incubation of hepatocytes with insulin in vitro increased the mRNA levels of PPARγ1, PPARγ2 and total PPARγ. To our knowledge, for the first time, the present study provides evidence that PPARγ1 and PPARγ2 are differentially expressed with and among tissues during different developmental stages and also regulated by insulin both in vivo and in vitro, which serves to increase our understanding on PPARγ physiological function in fish.

PPARα gene variants as predicted performance-enhancing polymorphisms in professional Italian soccer players

Background

The PPARα gene encodes the peroxisome proliferator-activator receptor alpha, a central regulator of expression of other genes involved in fatty acid metabolism. The purpose of this study was to determine the prevalence of G allele of the PPARα intron 7 G/C polymorphism (rs4253778) in professional Italian soccer players.

Methods

Sixty professional soccer players and 30 sedentary volunteers were enrolled in the study. Samples of venous blood were obtained at rest, in the morning, by conventional clinical procedures; blood serum was collected and total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides were measured. An aliquot of anticoagulant-treated blood was used to prepare genomic DNA from whole blood. The G/C polymorphic site in PPARα intron 7 was scanned by using the PCR-RFLP (polymerase chain reaction restriction fragment length polymorphism) protocol with TaqI enzyme.

Results

We found variations in genotype distribution of PPARα polymorphism between professional soccer players and sedentary volunteers. Particularly, G alleles and the GG genotype were significantly more frequent in soccer players compared with healthy controls (64% versus 48%). No significant correlations were found between lipid profile and genotype background.

Conclusion

Previous results demonstrated an association of intron 7 G allele as well as the GG genotype in endurance athletes. Our result suggests that this is the case also in professional soccer players.

Impact of nutrients on circadian rhythmicity

The suprachiasmatic nucleus (SCN) in the mammalian hypothalamus functions as an endogenous pacemaker that generates and maintains circadian rhythms throughout the body. Next to this central clock, peripheral oscillators exist in almost all mammalian tissues. Whereas the SCN is mainly entrained to the environment by light, peripheral clocks are entrained by various factors, of which feeding/fasting is the most important. Desynchronization between the central and peripheral clocks by, for instance, altered timing of food intake can lead to uncoupling of peripheral clocks from the central pacemaker and is, in humans, related to the development of metabolic disorders, including obesity and Type 2 diabetes. Diets high in fat or sugar have been shown to alter circadian clock function. This review discusses the recent findings concerning the influence of nutrients, in particular fatty acids and glucose, on behavioral and molecular circadian rhythms and will summarize critical studies describing putative mechanisms by which these nutrients are able to alter normal circadian rhythmicity, in the SCN, in non-SCN brain areas, as well as in peripheral organs. As the effects of fat and sugar on the clock could be through alterations in energy status, the role of specific nutrient sensors will be outlined, as well as the molecular studies linking these components to metabolism. Understanding the impact of specific macronutrients on the circadian clock will allow for guidance toward the composition and timing of meals optimal for physiological health, as well as putative therapeutic targets to regulate the molecular clock.

Peroxisome Proliferator-Activated Receptor γ Regulates the Expression of Lipid Phosphate Phosphohydrolase 1 in Human Vascular Endothelial Cells

Lipid phosphate phosphohydrolase 1 (LPP1), a membrane ectophosphohydrolase regulating the availability of bioactive lipid phosphates, plays important roles in cellular signaling and physiological processes such as angiogenesis and endothelial migration. However, the regulated expression of LPP1 remains largely unknown. Here, we aimed to examine a role of peroxisome proliferator-activated receptor γ (PPARγ) in the transcriptional control of LPP1 gene expression. In human umbilical vein endothelial cells (HUVECs), quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) demonstrated that activation of PPARγ increased the mRNA level of LPP1. Chromatin immunoprecipitation assay showed that PPARγ binds to the putative PPAR-responsive elements (PPREs) within the 5′-flanking region of the human LPP1 gene. Genomic fragment containing 1.7-kilobase of the promoter region was cloned by using PCR. The luciferase reporter assays demonstrated that overexpression of PPARγ and rosiglitazone, a specific ligand for PPARγ, could significantly upregulate the reporter activity. However, site-directed mutagenesis of the PPRE motif abolished the induction. In conclusion, our results demonstrated that PPARγ transcriptionally activated the expression of LPP1 gene in ECs, suggesting a potential role of PPARγ in the metabolism of phospholipids.

Bezafibrate in skeletal muscle fatty acid oxidation disorders: a randomized clinical trial

OBJECTIVE

To assess whether bezafibrate increases fatty acid oxidation (FAO) and lowers heart rate (HR) during exercise in patients with carnitine palmitoyltransferase (CPT) II and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies.

METHODS

This was a 3-month, randomized, double-blind, crossover study of bezafibrate in patients with CPT II (n = 5) and VLCAD (n = 5) deficiencies. Primary outcome measures were changes in FAO, measured with stable-isotope methodology and indirect calorimetry, and changes in HR during exercise.

RESULTS

Bezafibrate lowered low-density lipoprotein, triglyceride, and free fatty acid concentrations; however, there were no changes in palmitate oxidation, FAO, or HR during exercise.

CONCLUSION

Bezafibrate does not improve clinical symptoms or FAO during exercise in patients with CPT II and VLCAD deficiencies. These findings indicate that previous in vitro studies suggesting a therapeutic potential for fibrates in disorders of FAO do not translate into clinically meaningful effects in vivo.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that bezafibrate 200 mg 3 times daily is ineffective in improving changes in FAO and HR during exercise in adults with CPT II and VLCAD deficiencies.

The role of PPARδ signaling in the cardiovascular system

Peroxisome proliferator-activated receptors (PPARα, β/δ, and γ), members of the nuclear receptor transcription factor superfamily, play important roles in the regulation of metabolism, inflammation, and cell differentiation. All three PPAR subtypes are expressed in the cardiovascular system with various expression patterns. Among the three PPAR subtypes, PPARδ is the least studied but has arisen as a potential therapeutic target for cardiovascular and many other diseases. It is known that PPARδ is ubiquitously expressed and abundantly expressed in cardiomyocytes. Accumulated evidence illustrates the role of PPARδ in regulating cardiovascular function and determining pathological progression. In this chapter, we will discuss the current knowledge in the role of PPARδ in the cardiovascular system, the mechanistic insights, and the potential therapeutic utilization for treating cardiovascular disease.

Role of PPAR, LXR, and PXR in epidermal homeostasis and inflammation

Epidermal lipid synthesis and metabolism are regulated by nuclear hormone receptors (NHR) and in turn epidermal lipid metabolites can serve as ligands to NHR. NHR form a large superfamily of receptors modulating gene transcription through DNA binding. A subgroup of these receptors is ligand-activated and heterodimerizes with the retinoid X receptor including peroxisome proliferator-activated receptor (PPAR), liver X receptor (LXR) and pregnane X receptor (PXR). Several isotypes of these receptors exist, all of which are expressed in skin. In keratinocytes, ligand activation of PPARs and LXRs stimulates differentiation, induces lipid accumulation, and accelerates epidermal barrier regeneration. In the cutaneous immune system, ligand activation of all three receptors, PPAR, LXR, and PXR, has inhibitory properties, partially mediated by downregulation of the NF-kappaB pathway. PXR also has antifibrotic effects in the skin correlating with TGF-beta inhibition. In summary, ligands of PPAR, LXR and PXR exert beneficial therapeutic effects in skin disease and represent promising targets for future therapeutic approaches in dermatology. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Interactions between Human Liver Fatty Acid Binding Protein and Peroxisome Proliferator Activated Receptor Selective Drugs

Fatty acid binding proteins (FABPs) act as intracellular shuttles for fatty acids as well as lipophilic xenobiotics to the nucleus, where these ligands are released to a group of nuclear receptors called the peroxisome proliferator activated receptors (PPARs). PPAR mediated gene activation is ultimately involved in maintenance of cellular homeostasis through the transcriptional regulation of metabolic enzymes and transporters that target the activating ligand. Here we show that liver- (L-) FABP displays a high binding affinity for PPAR subtype selective drugs. NMR chemical shift perturbation mapping and proteolytic protection experiments show that the binding of the PPAR subtype selective drugs produces conformational changes that stabilize the portal region of L-FABP. NMR chemical shift perturbation studies also revealed that L-FABP can form a complex with the PPAR ligand binding domain (LBD) of PPARα. This protein-protein interaction may represent a mechanism for facilitating the activation of PPAR transcriptional activity via the direct channeling of ligands between the binding pocket of L-FABP and the PPARαLBD. The role of L-FABP in the delivery of ligands directly to PPARα via this channeling mechanism has important implications for regulatory pathways that mediate xenobiotic responses and host protection in tissues such as the small intestine and the liver where L-FABP is highly expressed.

Molecular Implications of the PPARs in the Diabetic Eye

Diabetic retinopathy (DR) remains as the leading cause of blindness among working age individuals in developed countries. Current treatments for DR (laser photocoagulation, intravitreal corticosteroids, intravitreal anti-VEGF agents, and vitreoretinal surgery) are applicable only at advanced stages of the disease and are associated with significant adverse effects. Therefore, new pharmacological treatments for the early stages of the disease are needed. Emerging evidence indicates that peroxisome proliferator-activator receptors (PPARs) agonists (in particular PPARα) are useful for the treatment of DR. However, the underlying molecular mechanisms are far from being elucidated. This paper mainly focuses on PPARs expression in the diabetic eye, its molecular implications, and the effect of PPAR agonists as a new approach for the treatment of DR. The availability of this new strategy will not only be beneficial in treating DR but may also result in a shift towards treating earlier stages of diabetic retinopathy, thus easing the burden of this devastating disease (Cheung et al. (2010)).

Simultaneous inhibition of COX-2 and activation of PPAR-γ resulted in the same level and pattern of neuroprotection as they were targeted separately

The inflammatory response is an immune response of the body when exposed to internal and external stimuli. Cyclooxygenases (COX) are major inflammatory mediators implicated in inflammation. COX-2 is reported to be involved in neuroinflammation. Moreover, 15-Deoxy-D (12,14)-prostaglandin J2 (15d-PGJ2), an endogenous ligand of peroxisome proliferator-activated receptor gamma (PPAR-γ), has been demonstrated to have anti-inflammatory actions. In this study, we investigated whether co-therapy of a selective COX-2 inhibitor NS-398 and 15d-PGJ2 as a PPAR-γ ligand could exert additional neuroprotective effects in rat pheochromocytoma (PC12) cells. Our findings showed that 15d-PGJ2 and NS-398 suppress the apoptotic pathway in PC12 cells exposed to H(2)O(2) by attenuation of the Bax/Bcl-2 ratio. This effect was mediated through PPAR-γ, as it was reversed by GW9662 (a PPAR-γ inhibitor). Also, 15d-PGJ2 and NS-398 induced the Nrf2 signaling pathway and decreased NF-κB level in a PPAR-γ-dependent manner. We found that coadministration of a selective COX-2 inhibitor and a PPAR-γ ligand in PC12 cells has equal neuroprotective effect compared to their effects when used separately. Considering the higher affinity of 15d-PGJ2 for PPAR-γ than NS-398, it seems that the observed neuroprotection of this combination therapy was from 15d-PGJ2.

The peroxisome proliferator-activated receptor: A family of nuclear receptors role in various diseases

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors of nuclear hormone receptor superfamily comprising of the following three subtypes: PPARα, PPARγ, and PPARβ/δ. Activation of PPAR-α reduces triglyceride level and is involved in regulation of energy homeostasis. Activation of PPAR-γ causes insulin sensitization and enhances glucose metabolism, whereas activation of PPAR-β/δ enhances fatty acids metabolism. Thus, PPAR family of nuclear receptors plays a major regulatory role in energy homeostasis and metabolic function. The present review critically analyzes the protective and detrimental effect of PPAR agonists in dyslipidemia, diabetes, adipocyte differentiation, inflammation, cancer, lung diseases, neurodegenerative disorders, fertility or reproduction, pain, and obesity.

Angiopoietin-like protein 4: health effects, modulating agents and structure-function relationships

Angiopoietin-like protein 4 (ANGPTL4) has been identified as a multifunctional signal protein. It is produced by a variety of tissues, and is secreted into the bloodstream in glycosylated, oligomerized, native and cleaved isoforms to modulate physiological events such as angiogenesis, cell differentiation and the crosstalk between liver, brain, adipose and muscle tissue in lipid and glucose metabolism. In addition, the expression and isoform appearance of ANGPTL4 are modified by the intestinal microbiota. With an eye on an effective strategy to improve health using ANGPTL4, we will focus on: health issues associated with ANGPTL4 expression, including obesity, Type 2 diabetes, cardiovascular diseases and cancer; several modulators of ANGPTL4 of chemical, microbiological, food and host origin; and the correlation of the specific ANGPTL4 isoforms with these modulators and their health effects.

PPARγ as a therapeutic target in cystic fibrosis

Cystic fibrosis (CF) is characterized by a proinflammatory pulmonary condition that may result from increased infections and altered intracellular metabolism in CFTR-deficient cells. The lipid-activated transcription factor peroxisome proliferator-activated receptor-γ (PPARγ) has well-established roles in immune cell function and inflammatory modulation and has been demonstrated to play an important role in the heightened inflammatory response in CF cells. Here, we summarize current literature describing PPARγ-dependent alterations of CF cells and discuss the potential of PPARγ ligands for treating CF.

Orally administered oleoylethanolamide protects mice from focal cerebral ischemic injury by activating peroxisome proliferator-activated receptor α

Oleoylethanolamide (OEA) is a high-affinity agonist of peroxisome proliferator-activated receptor α (PPARα) which may act as an endogenous neuroprotective factor. However, it is not clear whether orally administered OEA is effective against ischemic brain injury. In our study, transient focal cerebral ischemia was induced by middle cerebral artery occlusion for 90 min followed by reperfusion. To evaluate its preventive effects, OEA (10, 20 or 40 mg/kg, ig) was administered for 3 days before ischemia. To evaluate its therapeutic effects, OEA (40 mg/kg, ig) was administered at 0.5 or 1h before reperfusion or at 0 or 1h after reperfusion. In some experiments, the PPARα antagonist MK886 (10mg/kg, ig) was administered 0.5h before OEA. Neurological deficit score, infarct volume and brain edema degree were determined at 24h after reperfusion. Blood-brain barrier (BBB) disruption was evaluated by Evans blue (EB) leakage at 6h after reperfusion. Real-time RT-PCR and western blot were performed to detect PPARα mRNA and protein expression. Oral OEA pretreatment improved neurological dysfunction reduced infarct volume and alleviated brain edema in a dose-dependent manner; the most effective dose was 40 mg/kg. The therapeutic time is within 1h after reperfusion. OEA also increased PPARα mRNA and protein expression in the ischemic brain. The PPARα antagonist MK886 abolished the protective effects of OEA. In conclusion, our results indicate that orally administered OEA protects against acute cerebral ischemic injury in mice, at least in part by activating PPARα.

Identification, organ expression and ligand-dependent expression levels of peroxisome proliferator activated receptors in grass carp (Ctenopharyngodon idella)

The peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors belonging to the nuclear receptor family, and can regulate various genes involved in lipid metabolism. The aim of the present study was to investigate the tissue distribution patterns of PPARs and their ligand specificities in grass carp. We cloned three PPAR isotypes of the species and evaluated their organ distribution patterns using real-time PCR. Through analyzing the deduced amino acid sequences identities between the products cloned in grass carp and those described in other species, we concluded that the same type of PPAR amino acid sequences in different species were with high homology, and different subtypes of PPAR in the same species were with low homology. The mRNA constitutive expression level of PPARα predominated in the liver, but was weak in other tested tissues. PPARβ was present in all tested organs, and particularly abundant in heart, liver and muscle. PPARγ was only detected in the liver, and to a lesser extent in brain, muscle and visceral adipose tissue. Grass carp were intraperitoneally injected with 50 mg kg(-1) body mass (bw) dose of clofibrate, 42 mg kg(-1) bw dose of 2-bromo palmitate and 1 mg kg(-1) bw dose of 15-deoxy-Δ(12,14) prostaglandin J2 (15d-PGJ2), respectively, and the relative changes of the mRNA abundance of PPARs in liver were analyzed by real-time PCR. Clofibrate was able to increase the expressions of both PPARα and β, but was not able to for PPARγ. 2-bromo palmitate could affect the expressions of both PPARβ and γ, but was not able to for PPARα. 15d-PGJ2 was able to induce PPARβ expression, but PPARα and γ were not enhanced. Consequently, these results indicate that clofibrate, 2-bromo palmitate and 15d-PGJ2 could be applied as the activators of grass carp PPARs.

5, 8, 11, 14-eicosatetraynoic acid suppresses CCL2/MCP-1 expression in IFN-γ-stimulated astrocytes by increasing MAPK phosphatase-1 mRNA stability

Background

The peroxisome proliferator-activated receptor (PPAR)-α activator, 5,8,11,14-eicosatetraynoic acid (ETYA), is an arachidonic acid analog. It is reported to inhibit up-regulation of pro-inflammatory genes; however, its underlying mechanism of action is largely unknown. In the present study, we focused on the inhibitory action of ETYA on the expression of the chemokine, CCL2/MCP-1, which plays a key role in the initiation and progression of inflammation.

Methods

To determine the effect of ETYA, primary cultured rat astrocytes and microglia were stimulated with IFN-γ in the presence of ETYA and then, expression of CCL2/MCP-1 and MAPK phosphatase (MKP-1) were determined using RT-PCR and ELISA. MKP-1 mRNA stability was evaluated by treating actinomycin D. The effect of MKP-1 and human antigen R (HuR) was analyzed by using specific siRNA transfection system. The localization of HuR was analyzed by immunocytochemistry and subcellular fractionation experiment.

Results

We found that ETYA suppressed CCL2/MCP-1 transcription and secretion of CCL2/MCP-1 protein through up-regulation of MKP-1mRNA levels, resulting in suppression of c-Jun N-terminal kinase (JNK) phosphorylation and activator protein 1 (AP1) activity in IFN-γ-stimulated brain glial cells. Moreover, these effects of ETYA were independent of PPAR-α. Experiments using actinomycin D revealed that the ETYA-induced increase in MKP-1 mRNA levels reflected an increase in transcript stability. Knockdown experiments using small interfering RNA demonstrated that this increase in MKP-1 mRNA stability depended on HuR, an RNA-binding protein known to promote enhanced mRNA stability. Furthermore, ETYA-induced, HuR-mediated mRNA stabilization resulted from HuR-MKP-1 nucleocytoplasmic translocation, which served to protect MKP-1 mRNA from the mRNA degradation machinery.

Conclusion

ETYA induces MKP-1 through HuR at the post-transcriptional level in a receptor-independent manner. The mechanism revealed here suggests eicosanoids as potential therapeutic modulators of inflammation that act through a novel target.

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.

Cryptochrome and Period Proteins Are Regulated by the CLOCK/BMAL1 Gene: Crosstalk between the PPARs/RXRalpha-Regulated and CLOCK/BMAL1-Regulated Systems

Feeding and the circadian system regulate lipid absorption and metabolism, and the expression of enzymes involved in lipid metabolism is believed to be directly controlled by the clock system. To investigate the interaction between the lipid metabolism system and the circadian system, we analyzed the effect of a CLOCK/BMAL1 heterodimer on the transcriptional regulation of PPAR-controlled genes through PPAR response elements (PPREs). Transcription of acyl-CoA oxidase, cellular retinol binding protein II (CRBPII), and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase was altered by CLOCK/BMAL1, and transcriptional activity via PPRE by PPARs/RXRα was enhanced by CLOCK/BMAL1 and/or by PPARs ligand/activators. We also found that CLOCK/BMAL1-mediated transcription of period (PER) and cryptochrome (CRY) was modulated by PPARα/RXRα. These results suggest that there may be crosstalk between the PPARs/RXRα-regulated system and the CLOCK/BMAL1-regulated system.

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.

Nuclear receptors as new perspective for the management of liver diseases

Nuclear receptors (NRs) are ligand-activated transcription factors that act as sensors for a broad range of natural and synthetic ligands and regulate several key hepatic functions including bile acid homeostasis, bile secretion, lipid and glucose metabolism, as well as drug deposition. Moreover, NRs control hepatic inflammation, regeneration, fibrosis, and tumor formation. Therefore, NRs are key for understanding the pathogenesis and pathophysiology of a wide range of hepatic disorders. Finally, targeting NRs and their alterations offers exciting new perspectives for the treatment of liver diseases.

Modulation of acute steroidogenesis, peroxisome proliferator-activated receptors and CYP3A/PXR in salmon interrenal tissues by tributyltin and the second messenger activator, forskolin

There are uncertainties regarding the role of sex steroids in sexual development and reproduction of gastropods, leading to the recent doubts as to whether organotin compounds do inhibit steroidogenic enzymes in these species. These doubts have led us to suspect that organotin compounds may affect other target molecules, particularly signal transduction molecules or secondary mediators of steroid hormone and lipid synthesis/metabolism. Therefore, we have studied the effects of TBT exposure through food on acute steroidogenesis, PPARs and CYP3A responses in the presence and absence of a cyclic AMP (cAMP) activator, forskolin. Two experiments were performed. Firstly, juvenile salmon were force-fed once with diet containing TBT doses (0.1, 1 and 10mg/kg fish) dissolved in ethanol and sampled after 72h. Secondly, fish exposed to solvent control and 10mg/kg TBT for 72h were transferred to new tanks and exposed to waterborne forskolin (200microg/L) for 2 and 4h. Our data show that juvenile salmon force-fed TBT showed modulations of multiple biological responses in interrenal tissues that include, steroidogenesis (cAMP/PKA activities; StAR and P450scc mRNA, and plasma cortisol), and mRNA for peroxisome proliferator-activated receptor (PPAR) isoforms (alpha, beta, gamma), acyl-CoA oxidase-1 (ACOX1) and CYP3A/PXR (pregnan X receptor). In addition, forskolin produced differential effects on these responses both singly and also in combination with TBT. Overall, combined forskolin and TBT exposure produced higher effects compared with TBT exposure alone, for most of the responses (cortisol, PPARbeta, ACOX1 and CYP3A). Interestingly, forskolin produced PPAR isoform-specific effects when given singly or in combination with TBT. Several TBT mediated toxicity in fish that includes thymus reduction, decrease in numbers of lymphocytes, inhibition of gonad development and masculinization, including the imposex phenomenon have been reported. When these effects are considered with the present findings, it suggests that studies on mechanisms of action or field studies may reveal endocrine, reproductive or other effects of TBT at lower concentrations than those reported to date from subchronic tests of fishes. Since the metabolic fate of organotin compounds may contribute to the toxicity of these chemicals, the present findings may represent some new aspects of TBT toxicity not previously reported.

Glucose deprivation, oxidative stress and peroxisome proliferator-activated receptor-alpha (PPARA) cause peroxisome proliferation in preimplantation mouse embryos

Ex vivo two-cell mouse embryos deprived of glucose in vitro can develop to blastocysts by increasing their pyruvate consumption; however, zygotes when glucose-deprived cannot adapt this metabolic profile and degenerate as morulae. Prior to their death, these glucose-deprived morulae exhibit upregulation of the H+-monocarboxylate co-transporter SLC16A7 and catalase, which partly co-localize in peroxisomes. SLC16A7 has been linked to redox shuttling for peroxisomal beta-oxidation. Peroxisomal function is unclear during preimplantation development, but as a peroxisomal transporter in embryos, SLC16A7 may be involved and influenced by peroxisome proliferators such as peroxisome proliferator-activated receptor-alpha (PPARA). PCR confirmed Ppara mRNA expression in mouse embryos. Zygotes were cultured with or without glucose and with the PPARA-selective agonist WY14643 and the developing embryos assessed for expression of PPARA and phospho-PPARA in relation to the upregulation of SLC16A7 and catalase driven by glucose deprivation, indicative of peroxisomal proliferation. Reactive oxygen species (ROS) production and relationship to PPARA expression were also analysed. In glucose-deprived zygotes, ROS was elevated within 2 h, as were PPARA expression within 8 h and catalase and SLC16A7 after 12-24 h compared with glucose-supplied embryos. Inhibition of ROS production prevented this induction of PPARA and SLC16A7. Selective PPARA agonism with WY14643 also induced SLC16A7 and catalase expression in the presence of glucose. These data suggest that glucose-deprived cleavage stage embryos, although supplied with sufficient monocarboxylate-derived energy, undergo oxidative stress and exhibit elevated ROS, which in turn upregulates PPARA, catalase and SLC16A7 in a classical peroxisomal proliferation response.

Reproductive and developmental toxicity of phthalates

The purposes of this review are to (1) evaluate human and experimental evidence for adverse effects on reproduction and development in humans, produced by exposure to phthalates, and (2) identify knowledge gaps as for future studies. The widespread use of phthalates in consumer products leads to ubiquitous and constant exposure of humans to these chemicals. Phthalates were postulated to produce endocrine-disrupting effects in rodents, where fetal exposure to these compounds was found to induce developmental and reproductive toxicity. The adverse effects observed in rodent models raised concerns as to whether exposure to phthalates represents a potential health risk to humans. At present, di(2-ethylhexyl) phthalate (DEHP), di-n-butyl phthalate (DBP), and butyl benzyl phthalate (BBP) have been demonstrated to produce reproductive and developmental toxicity; thus, this review focuses on these chemicals. For the general population, DEHP exposure is predominantly via food. The average concentrations of phthalates are highest in children and decrease with age. At present, DEHP exposures in the general population appear to be close to the tolerable daily intake (TDI), suggesting that at least some individuals exceed the TDI. In addition, specific high-risk groups exist with internal levels that are several orders of magnitude above average. Urinary metabolites used as biomarkers for the internal levels provide additional means to determine more specifically phthalate exposure levels in both general and high-risk populations. However, exposure data are not consistent and there are indications that secondary metabolites may be more accurate indicators of the internal exposure compared to primary metabolites. The present human toxicity data are not sufficient for evaluating the occurrence of reproductive effects following phthalate exposure in humans, based on existing relevant animal data. This is especially the case for data on female reproductive toxicity, which are scarce. Therefore, future research needs to focus on developmental and reproductive endpoints in humans. It should be noted that phthalates occur in mixtures but most toxicological information is based on single compounds. Thus, it is concluded that it is important to improve the knowledge of toxic interactions among the different chemicals and to develop measures for combined exposure to various groups of phthalates.

Different skeletal effects of the peroxisome proliferator activated receptor (PPAR)alpha agonist fenofibrate and the PPARgamma agonist pioglitazone

BACKGROUND

All the peroxisome proliferator activated receptors (PPARs) are found to be expressed in bone cells. The PPARgamma agonist rosiglitazone has been shown to decrease bone mass in mice and thiazolidinediones (TZDs) have recently been found to increase bone loss and fracture risk in humans treated for type 2 diabetes mellitus. The aim of the study was to examine the effect of the PPARalpha agonist fenofibrate (FENO) and the PPARgamma agonist pioglitazone (PIO) on bone in intact female rats.

METHODS

Rats were given methylcellulose (vehicle), fenofibrate or pioglitazone (35 mg/kg body weight/day) by gavage for 4 months. BMC, BMD, and body composition were measured by DXA. Histomorphometry and biomechanical testing of excised femurs were performed. Effects of the compounds on bone cells were studied.

RESULTS

The FENO group had higher femoral BMD and smaller medullary area at the distal femur; while trabecular bone volume was similar to controls. Whole body BMD, BMC, and trabecular bone volume were lower, while medullary area was increased in PIO rats compared to controls. Ultimate bending moment and energy absorption of the femoral shafts were reduced in the PIO group, while similar to controls in the FENO group. Plasma osteocalcin was higher in the FENO group than in the other groups. FENO stimulated proliferation and differentiation of, and OPG release from, the preosteoblast cell line MC3T3-E1.

CONCLUSION

We show opposite skeletal effects of PPARalpha and gamma agonists in intact female rats. FENO resulted in significantly higher femoral BMD and lower medullary area, while PIO induced bone loss and impairment of the mechanical strength. This represents a novel effect of PPARalpha activation.