Review of the expression of peroxisome proliferator-activated receptors alpha (PPARα), beta (PPARβ), and gamma (PPARγ) in rodent and human development

The peroxisome proliferator-activated receptors (PPAR) belong to the nuclear hormone receptor superfamily and there are three primary subtypes, PPARα, β, and γ. These receptors regulate important physiological processes that impact lipid homeostasis, inflammation, adipogenesis, reproduction, wound healing, and carcinogenesis. These nuclear receptors have important roles in reproduction and development and their expression may influence the responses of an embryo exposed to PPAR agonists. PPARs are relevant to the study of the biological effects of the perfluorinated alkyl acids as these compounds, including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), activate PPARα. Exposure of the rodent to PFOA or PFOS during gestation results in neonatal deaths, developmental delay and growth deficits. Studies in PPARα knockout mice demonstrate that the developmental effects of PFOA, but not PFOS, depend on expression of PPARα. This review provides an overview of PPARα, β, and γ protein and mRNA expression during mouse, rat, and human development. The review presents the results from many published studies and the information is organized by organ system and collated to show patterns of expression at comparable developmental stages for human, mouse, and rat. The features of the PPAR nuclear receptor family are introduced and what is known or inferred about their roles in development is discussed relative to insights from genetically modified mice and studies in the adult.     

Stevioside protects against rhabdomyolysis‐induced acute kidney injury through PPAR‐γ agonism in rats

We explored the potential role of peroxisome proliferator activated receptor‐γ (PPAR‐γ) in stevioside‐mediated renoprotection using rhabdomyolysis‐induced acute kidney injury (AKI) model in rats. Rhabdomyolysis refers to intense skeletal muscle damage, which further causes AKI. Glycerol (50% w/v, 8 ml/kg) was injected intramuscularly in rats to induce rhabdomyolysis. After 24 hr, AKI was demonstrated by quantifying serum creatinine, urea, creatinine clearance, microproteinuria, and electrolytes in rats. Further, oxidative stress was measured by assaying thiobarbituric acid reactive substances, generation of superoxide anion, and reduced glutathione levels. Additionally, serum creatine kinase (CK) level was assayed to determine glycerol‐induced muscle damage in rats. Pathological changes in rat kidneys were studied using hematoxylin–eosin and periodic acid Schiff staining. Moreover, the expression of apoptotic markers (Bcl‐2, Bax) in rat kidneys was demonstrated by immunohistochemistry. Stevioside (10, 25, and 50 mg/kg) was administered to rats, prior to the induction of AKI. In a separate group, bisphenol A diglycidyl ether (BADGE, 30 mg/kg), a PPAR‐γ receptor antagonist was given prior to stevioside administration, which was followed by rhabdomyolysis‐induced AKI in rats. The significant alteration in biochemical and histological parameters in rats indicated AKI, which was attenuated by stevioside treatment. Pretreatment with BADGE abrogated stevioside‐mediated renoprotection, which is suggestive of the involvement of PPAR‐γ in its renoprotective effect. In conclusion, stevioside protects against rhabdomyolysis‐induced AKI, which may be attributed to modulation of PPAR‐γ expression.     

Synthesis of tritium and carbon‐14 labelled NNC 61‐4655: a potent dual‐acting PPARα and PPARγ agonist

The synthesis of the potent dual‐acting PPARα and PPARγ agonist NNC 61‐4655 labelled with tritium and carbon‐14 is reported. Tritium labelled NNC 61‐4655 was obtained in three steps with introduction of tritium through catalytic tritium‐halogen exchange of an aryl bromide precursor. This provided [³H]NNC 61‐4655 in 39% overall radiochemical yield with a specific activity of 49 Ci/mmol. Carbon‐14 labelled NNC 61‐4655 was obtained in five steps starting from bromo[1‐¹⁴C]acetic acid. The synthetic sequence, which included a Horner–Wadsworth–Emmons olefination and a Mitsunobu alkylation, provided [¹⁴C]NNC 61‐4655 in 33% overall radiochemical yield with a specific activity of 57.4 mCi/mmol. Copyright © 2003 John Wiley & Sons, Ltd.     

Changes in PPARδ expression in a rat model of stress‐induced depression

Depression is a common mental disorder that has been linked to a decrease in the expression of serotonin and/or the serotonin transporter in the brain. Antidepressants that target the monoaminergic system are widely used in the clinical setting. Peroxisome proliferator‐activated receptor δ (PPAR δ) overexpression or activation is thought to improve depression‐like behaviours in rodents. The present study was designed to characterize the changes in PPARδ expression in the hippocampus in rats with stress‐induced depression. We used an unpredictable chronic mild stress (CMS) model in rats to study the role of PPARδ in the hippocampus. Behaviour was evaluated via a forced swim test (FST), a tail suspension test (TST), and a sucrose preference test (SPT). Then, the changes in PPARδ expression and other signals were determined using Western blots. We found that PPARδ expression in the hippocampus was markedly reduced in rats with depression. Moreover, the expression of the serotonin transporter was also significantly decreased. Treatment with a PPARδ agonist enhanced the expression of PPARδ and the serotonin transporter in the hippocampus of rats with stress‐induced depression. Additionally, treatment with a PPARδ agonist increased the expression of the serotonin transporter in cultured hippocampal (H19‐7) cells, and this action was ablated in the absence of PPARδ, which was attenuated with shRNA. Taken together, we found that PPARδ plays an important role in the regulation of serotonin transporter expression and that chronic stress may lower PPARδ expression in the brain via apoptosis and may attenuate serotonin transporter expression, thus inducing depression in rats.     

[14C] and [3H]‐labelling of Ragaglitazar: A dual acting PPARα and PPARγ agonist with hypolipidemic and anti‐diabetic activity

Currently, Ragaglitazar is being developed as a drug for the treatment of hyperglycaemia and hyperlipidemia in patients with type 2 diabetes. Here, we report the labelling of Ragaglitazar with carbon‐14 and tritium for in vivo and in vitro investigations. Two different carbon‐14 labelled as well as two different tritium labelled tracers of Ragaglitazar were synthesised. The carbon‐14 label was introduced from either ethyl bromo[2‐¹⁴C]acetate (5 steps/33% overall yield) or [U‐¹⁴C]phenoxazine (4 steps/48% overall yield). Tritium was incorporated either by catalytic tritiation of an alkene precursor followed by chiral HPLC separation (2 steps/17% overall yield) or by catalytic tritium–halogen exchange of an aryl bromide precursor (2 steps/68% overall yield). Copyright © 2003 John Wiley & Sons, Ltd.     

Arctigenin promotes bone formation involving PI3K/Akt/PPARγ signaling pathway

This study investigated the mechanisms through which arctigenin promotes osteogenesis. Bone marrow mesenchymal stem cells (BMSCs) from ovariectomized (OVX) rats were differentiated into osteoblasts, and osteogenesis was evaluated via Alizarin Red S (ARS) staining and alkaline phosphatase (ALP) measurements in cultured BMSCs. The levels of phosphorylated AKT serine/threonine kinase 1 (p‐Akt), and peroxisome proliferator‐activated receptor gamma (PPARγ) expression were quantified by Western blot analysis. The levels of urine calcium (U‐Ca), urine phosphorus (U‐P), serum ALP, and bone mineral density (BMD) of OVX rats were assessed in vivo. The results showed that treatment with arctigenin in rat BMSCs enhanced mineralization, increased ALP activity, increased the expression of Akt and p‐Akt, and decreased PPARγ expression, consistent with its ability to promote osteoblast differentiation. Furthermore, arctigenin prevented OVX‐induced osteoporosis in rats by increasing BMD and ALP activity and inhibiting the loss of Ca and P. In contrast, treatment with LY294002, a selective inhibitor of the phosphatidylinositol 3‐kinase (PI3K), produced the opposite phenotype. These data suggest that the protective effects of arctigenin on BMSCs and OVX rat models result from the induction of osteogenesis involving the PI3K/Akt/PPARγ axis.     

Microgram-order ammonium perfluorooctanoate may activate mouse peroxisome proliferator-activated receptor α, but not human PPARα

Perfluorooctanoic acid (PFOA) is a ligand for peroxisome proliferator-activated receptor (PPAR) α, which exhibits marked species differences in expression and function, especially between rodents and humans. We investigated the functional difference in PFOA response between mice and humans, using a humanized PPARα transgenic mouse line. Three genotyped mice, 129/Sv wild-type (mPPARα), Pparα-null mice and humanized PPARα (hPPARα) mice (8-week-old males) were divided into three groups: the first was treated with water daily for 2 weeks by gavage (control group), and the remaining two groups were treated with 0.1 and 0.3 mg/kg ammonium perflurooctanate (APFO), respectively, for 2 weeks by gavage. The APFO dosages used did not influence the plasma triglyceride or total cholesterol levels in any mouse line, but the high dose increased both hepatic lipid levels only in mPPARα mice. APFO increased mRNA and/or protein levels of PPARα target genes cytochrome P450 Cyp4a10, peroxisomal thiolase and bifunctional protein only in the liver of mPPARα mice, but not in Pparα-null or hPPARα mice. This chemical also increased expression of mitochondrial very long chain acyl-CoA dehydrogenase only in the liver of mPPARα mice. Taken together, human PPARα may be less responsive to PFOA than that of mice when a relatively low dose is applied. This information may be very valuable in considering whether PFOA influences the lipid metabolism in humans.     

Synthesis of tritium labelled L783483 ‐ a PPARδ ligand

The potent peroxisome proliferator‐activated receptor (PPAR) δ ligand L783483 (3‐chloro‐4‐(3‐(7‐propyl‐3‐trifluoromethyl‐benzisoxazol‐6‐oxy)propylsulfanyl)phenylacetic acid) has been labelled with tritium via selective tritium/bromine exchange of 5‐bromo‐6‐(3‐bromopropyloxy)‐7‐propyl‐3‐trifluoromethyl‐benzisoxazole. [³H]‐L783483 had a specific activity of 529 GBq/mmol (14.3 Ci/mmol) and a radiochemical purity of 98%. Copyright © 2003 John Wiley & Sons, Ltd.     

Peroxisome proliferator-activated receptor δ (PPARδ), a novel target site for drug discovery in metabolic syndrome

The development of new treatments for metabolic syndrome is urgent project for decreasing the prevalence of coronary heart disease and diabetes mellitus in the advanced countries. Peroxisome proliferator-activated receptor (PPAR)α and γ agonists have shed light on the treatment of hypertriglyceridemia and type 2 diabetes mellitus, respectively. Among PPARs, analysis of the PPARδ functions is lagging behind because specific PPARδ agonists have not been developed. The appearance of new PPARδ agonists is brightening the prospects for elucidating the physiological role of PPARδ. PPARδ is a new target for the treatment of metabolic syndrome. In particular, the fact that fatty acid oxidation and energy dissipation in skeletal muscle and adipose tissue by PPARδ agonists lead to improved lipid profile, reduced adiposity and insulin sensitivity is a breakthrough. It seems that treatment of PPARδ agonists operate similarly to the caloric restriction and prolonged exercise. We suggest that the physiological role of PPARδ may be an indicator for switching from glucose metabolism to fatty acid metabolism. To receive new benefits of PPARδ agonists against metabolic syndrome by increasing fatty acid consumption in skeletal muscle and adipose tissue, we need to unveil more details on the functions of PPARδ itself and its agonists in the future.     

Specific α7 nicotinic acetylcholine receptor agonist ameliorates isoproterenol‐induced cardiac remodelling in mice through TGF‐β1/Smad3 pathway

It is well‐accepted that inflammation plays an important role in the development of cardiac remodelling and that therapeutic approaches targeting inflammation can inhibit cardiac remodelling. Although a large amount of evidence indicates that activation of α7 nicotinic acetylcholine receptor (α7nAChR) causes an anti‐inflammatory effect, the role of α7nAChR in cardiac remodelling and the underlying mechanism have not been established. To investigate the effect of the specific α7nAChR agonist, PNU282987, on cardiac remodelling induced by isoproterenol (ISO 60 mg/kg per day) in mice, the cardiomyocyte cross‐sectional area (CSA) and collagen volume fraction were evaluated by hematoxylin and eosin (HE) and Masson staining, respectively. Cardiac function and ventricular wall thickness were measured by echocardiography. The protein expressions of collagen I, matrix metalloproteinase 9 (MMP‐9), transforming growth factor β1 (TGF‐β1), and Smad3 were analyzed by Western blot. ISO‐induced cardiac hypertrophy, characterized by an increase in the heart weight/body weight ratio, CSA and ventricular wall thickness. Moreover, cardiac fibrosis indices, such as collagen volume fraction, MMP‐9 and collagen I protein expression, were also increased by ISO. PNU282987 not only attenuated cardiac hypertrophy but also decreased the cardiac fibrosis induced by ISO. Furthermore, PNU282987 suppressed TGF‐β1 protein expression and the phosphorylation of Smad3 induced by ISO. In conclusion, PNU282987 ameliorated the cardiac remodelling induced by ISO, which may be related to the TGF‐β1/Smad3 pathway. These data imply that the α7nAChR may represent a novel therapeutic target for cardiac remodelling in many cardiovascular diseases.     

A role of peroxisome proliferator‐activated receptor γ in non‐alcoholic fatty liver disease

Non‐alcoholic fatty liver disease is becoming a major health burden, as prevalence increases and there are no approved treatment options. Thiazolidinediones target the nuclear receptor peroxisome proliferator‐activated receptor γ (PPARγ) and have been investigated in several clinical trials for their potential in treating non‐alcoholic fatty liver disease (NAFLD) and non‐alcoholic steatohepatitis (NASH). PPARγ has specialized roles in distinct tissues and cell types, and although the primary function of PPARγ is in adipose tissue, where the highest expression levels are observed, hepatic expression levels of PPARγ are significantly increased in patients with NAFLD. Thus, NAFLD patients receiving treatment with PPARγ agonists might have a liver response apart from the one in adipose tissue. Owing to the different roles of PPARγ, new treatment strategies include development of compounds harnessing the beneficial effects of PPARγ while restricting PPARγ unwanted effects such as adipogenesis resulting in weight gain. Furthermore, dual or pan agonists targeting two or more of the PPARs have shown promising results in pre‐clinical research and some are currently proceeding to clinical trials. This MiniReview explores adipose‐ and liver‐specific actions of PPARγ, and how this knowledge may contribute in the search for new treatment modalities in NAFLD/NASH.     

Pharmacological characterization of A-131701, a novel α1-adrenoceptor antagonist selective for α1A- and α1D-compared to α1B-adrenoceptors

New compounds selective for α_1A-adrenoceptors in the prostate may offer enhanced efficacy for benign prostatic hyperplasia (BPH), with fewer side effects than current treatment. A-131701 (3-[2-((3aR,9bR)-cis-6-methoxy-2,3,3a,4,5,9b,hexahydro-[1H]-benz[e]isoindol-2-yl)ethyl]pyrido[3′,4′:4,5]thieno [3,2-d]pyrimidine-2,4(1H,3H)-dione), from a novel class of benz[e]isolindole pyridothienopyrimidines and pyridothienopyrazines, is selective for α_1a- and α_1d-adrenoceptors in radioligand binding studies (0.22 nM at α_1a-, 0.97 nM at α_1d-) compared to α_1b-sites (2.5 nM) and in isolated tissue bioassays (pA₂ values of 8.9–9.0 for α_1A-receptors in rat vas deferens or canine prostate strips, 9.1 at α_1D-sites (rat aorta)), compared to 7.9 at α_1B-sites (rat spleen). A-131701 also potently blocked radioligand binding to α₁-adrenoceptors in canine and human prostatic membranes, but was considerably weaker at α₂-adrenoceptors. In isoflurane-anesthetized dogs, A-131701 antagonized epinephrine-induced increases in intraurethral pressure (IUP) with a pseudo-pA₂ value of 8.17. In spontaneously hypertensive rats, A-131701 caused transient decreases in mean arterial blood pressure (MABP) and transient tachycardia. The area under the curve (AUC₀→₆₀ min) for the hypotensive response was dose-related, with a log index value for A-131701 of 5.33, suggesting a selectivity of >600-fold comparing IUP to MABP effects. In pentobarbital-anesthetized dogs, A-131701 was more potent in blocking phenylephrine (PHE)-induced increases in IUP (pseudo-pA₂ = 8.0) compared to concurrently measured MABP (pseudo-pA₂ = 7.2), or sixfold selective. Doses greater than 1,000 nmol/kg i.v. of A-131701 were required to lower blood pressure by 10 mm Hg in these dogs (pED₁₀ =. 5.57), indicating a uroselectivity ratio of >250, superior to doxazosin, terazosin, or tamsulosin. Thus, A-131701 is selective for α_1A- and α_1D- vs. α_1B-adrenoceptors in vitro, and prostatic function vs. blood pressure effects in vivo, which may provide therapeutic advantages in the treatment of BPH. Drug Dev. Res. 44:140–162, 1998. © 1998 Wiley-Liss, Inc.     

Up‐regulation of Gadd45α after exposure to metal nanoparticles: The role of hypoxia inducible factor 1α

The increased development and use of nanoparticles in various fields may lead to increased exposure, directly affecting human health. Our current knowledge of the health effects of metal nanoparticles such as cobalt and titanium dioxide (Nano‐Co and Nano‐TiO₂) is limited but suggests that some metal nanoparticles may cause genotoxic effects including cell cycle arrest, DNA damage, and apoptosis. The growth arrest and DNA damage‐inducible 45α protein (Gadd45α) has been characterized as one of the key players in the cellular responses to a variety of DNA damaging agents. The aim of this study was to investigate the alteration of Gadd45α expression in mouse embryo fibroblasts (PW) exposed to metal nanoparticles and the possible mechanisms. Non‐toxic doses of Nano‐Co and Nano‐TiO₂ were selected to treat cells. Our results showed that Nano‐Co caused a dose‐ and time‐dependent increase in Gadd45α expression, but Nano‐TiO₂ did not. To investigate the potential pathways involved in Nano‐Co‐induced Gadd45α up‐regulation, we measured the expression of hypoxia inducible factor 1α (HIF‐1α) in PW cells exposed to Nano‐Co and Nano‐TiO₂. Our results showed that exposure to Nano‐Co caused HIF‐1α accumulation in the nucleus. In addition, hypoxia inducible factor 1α knock‐out cells [HIF‐1α (?/?)] and its wild‐type cells [HIF‐1α (+/+)] were used. Our results demonstrated that Nano‐Co caused a dose‐ and time‐dependent increase in Gadd45α expression in wild‐type HIF‐1α (+/+) cells, but only a slight increase in HIF‐1α (?/?) cells. Pre‐treatment of PW cells with heat shock protein 90 inhibitor, 17‐(Allylamino)?17‐demethoxygeldanamycin (17‐AAG), prior to exposure to Nano‐Co significantly abolished Nano‐Co‐induced Gadd45α expression. These results suggest that HIF‐1α accumulation may be partially involved in the increased Gadd45α expression in cells exposed to Nano‐Co. These findings may have important implications for understanding the potential health effects of metal nanoparticle exposure. © 2013 Wiley Periodicals, Inc. Environ Toxicol 30: 490–499, 2015.