Peroxisome Proliferator-activated Receptor γ-independent Activation of p38 MAPK by Thiazolidinediones Involves Calcium/Calmodulin-dependent Protein Kinase II and Protein Kinase R

Pioglitazone ameliorates sepsis-associated encephalopathy through SIRT1 signaling pathway

Sepsis is a severe immune response to an infection. It is associated with multiple organ dysfunction syndrome (MODs) along with systemic and neuronal inflammatory response. This study focused on the acute neurologic dysfunction associated with sepsis by exploring the role of PPARγ/SIRT1 pathway against sepsis. We studied the role of this axis in ameliorating sepsis-associated encephalopathy (SAE) and its linked neurobehavioral disorders by using pioglitazone (PIO). This PPARγ agonist showed neuroprotective actions in neuroinflammatory disorders. Sepsis was induced in mice by LPS (10 mg/kg). Survival rate and MODs were assessed. Furthermore, behavioral deficits, cerebral oxidative, inflammatory, and apoptotic markers, and the cerebral expression level of SIRT1 were determined. In this study, we observed that PIO attenuated sepsis-induced cerebral injury. PIO significantly enhanced survival rate, attenuated MODs, and systemic inflammatory response in septic mice. PIO also promoted cerebral SIRT1 expression and reduced cerebral activation of microglia, oxidative stress, HMGB, iNOS, NLRP3 and caspase-3 along with an obvious improvement in behavioral deficits and cerebral pathological damage induced by LPS. Most of the neuroprotective effects of PIO were abolished by EX-527, a SIRT1 inhibitor. These results highlight that the neuroprotective effect of PIO in SAE is mainly SIRT1-dependent.

Role of 4-Thiazolidinone-Pyrazoline/Indoline Hybrids Les-4369 and Les-3467 in BJ and A549 Cell Lines

Cancer is one of the most important problems of modern societies. Recently, studies have reported the anticancer properties of rosiglitazone related to its ability to bind peroxisome proliferator receptor γ (PPARγ), which has various effects on cancer and can inhibit cell proliferation. In this study, we investigated the effect of new 4-thiazolidinone (4-TZD) hybrids Les-4369 and Les-3467 and their effect on reactive oxygen species (ROS) production, metabolic activity, lactate dehydrogenase (LDH) release, caspase-3 activity, and gene and protein expression in human foreskin fibroblast (BJ) cells and lung adenocarcinoma (A549) cells. The ROS production and caspase-3 activity were mainly increased in the micromolar concentrations of the studied compounds in both cell lines. Les-3467 and Les-4369 increased the mRNA expression of PPARG, P53 (tumor protein P53), and ATM (ATM serine/threonine kinase) in the BJ cells, while the mRNA expression of these genes (except PPARG) was mainly decreased in the A549 cells treated with both of the tested compounds. Our results indicate a decrease in the protein expression of AhR, PPARγ, and PARP-1 in the BJ cells exposed to 1 µM Les-3467 and Les-4369. In the A549 cells, the protein expression of AhR, PPARγ, and PARP-1 increased in the treatment with 1 µM Les-3467 and Les-4369. We have also shown the PPARγ modulatory properties of Les-3467 and Les-4369. However, both compounds prove weak anticancer properties evidenced by their action at high concentrations and non-selective effects against BJ and A549 cells.

Ca2+ homeostasis imbalance induced by Pparg: A key factor in di (2-ethylhexyl) phthalate (DEHP)-induced cardiac dysfunction in zebrafish larvae

Widespread application of the typical phthalate plasticizers, di (2-ethylhexyl) phthalate (DEHP), poses a serious potential threat to the health of animals and even humans. Previous studies have confirmed the mechanism of DEHP-induced cardiac developmental defects in zebrafish larvae. However, the mechanism of cardiac dysfunction is still unclear. Thus, this work aimed to comprehensively investigate the mechanisms involved in DEHP-induced cardiac dysfunction through computational simulations, in vivo assays in zebrafish, and in vitro assays in cardiomyocytes. Firstly, molecular docking and western blot initially investigated the activating effect of DEHP on Pparg in zebrafish. Although GW9662 (PPARG antagonist) effectively alleviated DEHP-induced cardiac dysfunction and lipid metabolism disorders, it did not restore significant decreases in mitochondrial membrane potential and ATP levels. In vitro assays in cardiomyocytes, DEHP caused overexpression of PPARG and proteins involved in the regulation of Ca2+ homeostasis, and the above abnormalities were effectively alleviated by GW9662, suggesting that the Ca2+ homeostatic imbalance caused by activation of PPARG by DEHP seems to be the main cause of DEHP-induced cardiac dysfunction. To sum up, this work not only refines the mechanism of toxic effects of cardiotoxicity induced by DEHP, but provides an important theoretical basis for enriching the toxicological effects of DEHP.

Peroxisome proliferator-activated receptor gamma as a therapeutic target for hepatocellular carcinoma: Experimental and clinical scenarios

Hepatocellular carcinoma (HCC) is the most common type of liver cancer worldwide. Viral hepatitis is a significant risk factor for HCC, although metabolic syndrome and diabetes are more frequently associated with the HCC. With increasing prevalence, there is expected to be > 1 million cases annually by 2025. Therefore, there is an urgent need to establish potential therapeutic targets to cure this disease. Peroxisome-proliferator-activated receptor gamma (PPARγ) is a ligand-activated transcription factor that plays a crucial role in the patho-physiology of HCC. Many synthetic agonists of PPARγ suppress HCC in experimental studies and clinical trials. These synthetic agonists have shown promising results by inducing cell cycle arrest and apoptosis in HCC cells and preventing the invasion and metastasis of HCC. However, some synthetic agonists also pose severe side effects in addition to their therapeutic efficacy. Thus natural PPARγ agonists can be an alternative to exploit this potential target for HCC treatment. In this review, the regulatory role of PPARγ in the pathogenesis of HCC is elucidated. Furthermore, the experimental and clinical scenario of both synthetic and natural PPARγ agonists against HCC is discussed. Most of the available literature advocates PPARγ as a potential therapeutic target for the treatment of HCC.

Activation of dsRNA-Dependent Protein Kinase R by miR-378 Sustains Metabolic Inflammation in Hepatic Insulin Resistance

MicroRNAs (miRNAs) are noncoding small RNAs that regulate various pathophysiological cellular processes. Here, we report that expression of the miR-378 family was significantly induced by metabolic inflammatory inducers, a high-fructose diet, and inflammatory cytokine tumor necrosis factor-α. Hepatic miRNA profiling revealed that expression of miR-378a was highly upregulated, which, in turn, targeted the 3'-untranslated region of PPARα mRNA, impaired mitochondrial fatty acid β-oxidation, and induced mitochondrial and endoplasmic reticulum stress. More importantly, the upregulated miR-378a can directly bind to and activate the double-strand RNA (dsRNA)-dependent protein kinase R (PKR) to sustain the metabolic stress. In vivo, genetic depletion of miR-378a prevented PKR activation and ameliorated inflammatory stress and insulin resistance. Counterbalancing the upregulated miR-378a using nanoparticles encapsulated with an anti-miR-378a oligonucleotide restored PPARα activity, inhibited PKR activation and ER stress, and improved insulin sensitivity in fructose-fed mice. Our study delineated a novel mechanism of miR-378a in the pathogenesis of metabolic inflammation and insulin resistance through targeting metabolic signaling at both mRNA (e.g., PPARα) and protein (e.g., PKR) molecules. This novel finding of functional interaction between miRNAs (e.g., miR-378a) and cellular RNA binding proteins (e.g., PKR) is biologically significant because it greatly broadens the potential targets of miRNAs in cellular pathophysiological processes.

CB13, a novel PPARγ ligand, overcomes radio-resistance via ROS generation and ER stress in human non-small cell lung cancer

Peroxisome proliferator-activated receptor gamma (PPARγ) is a well-known therapeutic target for type 2 diabetes as well as is a potential target for effective anti-cancer drug, since PPARγ ligands such as ciglitazone (Cig) frequently cause cell death in many types of cancer cells and suppress tumor growth. However, many cancer patients acquire chemo-resistance or radio-resistance after chemo or radiotherapy, and it is still unclear. In the difficulty of well-known anti-cancer drugs, we developed a novel PPARγ agonist CB13 (1-benzyl-5-(4-methylphenyl) pyrido [2,3-d]pyrimidine-2,4(1H,3H)-dione) and investigated the anti-cancer effect and cell death mechanism on human non-small cell lung cancer (NSCLC) cells. With anti-cancer effect of Cig, CB13 also causes inhibition of cell growth by decreasing cell viability, increasing the release of LDH, and increasing caspase-3, and caspase-9 activities. CB13 generates reactive oxygen species (ROS) and causes cell death via ER stress in NSCLC and radio-resistant NSCLC cells (A549R and H460R), and a combination of CB13 and radiation induces greater ER stress and cell death when compared to CB13 alone. Taken together, our results suggest that a combination of CB13 and radiation may overcome radio-resistance caused by radiotherapy.

PPARγ-Independent Side Effects of Thiazolidinediones on Mitochondrial Redox State in Rat Isolated Hearts

The effect of anti-diabetic thiazolidinediones (TZDs) on contributing to heart failure and cardiac ischemia/reperfusion (IR) injury is controversial. In this study we investigated the effect of select TZDs on myocardial and mitochondrial function in Brown Norway rat isolated hearts. In a first set of experiments, the TZD rosiglitazone was given acutely before global myocardial IR, and pre- and post-IR function and infarct size were assessed. In a second set of experiments, different concentrations of rosiglitazone and pioglitazone were administered in the presence or absence of the specific PPARγ antagonist GW9662, and their effects on the mitochondrial redox state were measured by online NADH and FAD autofluorescence. The administration of rosiglitazone did not significantly affect myocardial function except for transiently increasing coronary flow, but it increased IR injury compared to the control hearts. Both TZDs resulted in dose-dependent, reversible increases in mitochondrial oxidation which was not attenuated by GW9662. Taken together, these data suggest that TZDs cause excessive mitochondrial uncoupling by a PPARγ-independent mechanism. Acute rosiglitazone administration before IR was associated with enhanced cardiac injury. If translated clinically, susceptible patients on PPARγ agonists may experience enhanced myocardial IR injury by mitochondrial dysfunction.

Toxicant-mediated redox control of proteostasis in neurodegeneration

Disruption in redox signaling and control of cellular processes has emerged as a key player in many pathologies including neurodegeneration. As protein aggregations are a common hallmark of several neuronal pathologies, a firm understanding of the interplay between redox signaling, oxidative and free radical stress, and proteinopathies is required to sort out the complex mechanisms in these diseases. Fortunately, models of toxicant-induced neurodegeneration can be utilized to evaluate and report mechanistic alterations in the proteostasis network (PN). The epidemiological links between environmental toxicants and neurological disease gives further credence into characterizing the toxicant-mediated PN disruptions observed in these conditions. Reviewed here are examples of mechanistic interaction between oxidative or free radical stress and PN alterations. Additionally, investigations into toxicant-mediated PN disruptions, specifically focusing on environmental metals and pesticides, are discussed. Finally, we emphasize the need to distinguish whether the presence of protein aggregations are contributory to phenotypes related to neurodegeneration, or if they are a byproduct of PN deficiencies.

Crosstalk between PPARγ Ligands and Inflammatory-Related Pathways in Natural T-Regulatory Cells from Type 1 Diabetes Mouse Model

Immunomodulation, as a means of immunotherapy, has been studied in major research and clinical laboratories for many years. T-Regulatory (Treg) cell therapy is one of the modulators used in immunotherapy approaches. Similarly, nuclear receptor peroxisome proliferator activated receptor gamma (PPARγ) has extensively been shown to play a role as an immuno-modulator during inflammation. Given their mutual roles in downregulating the immune response, current study examined the influence of PPARγ ligands i.e., thiazolidinedione (TZD) class of drugs on Forkhead Box P3 (Foxp3) expression and possible crosstalk between PPARγ and nTreg cells of Non-Obese Diabetes (NOD) and Non-Obese Diabetes Resistant (NOR) mice. Results showed that TZD drug, ciglitazone and natural ligand of PPARγ 15d-prostaglandin downregulated Foxp3 expression in activated nTreg cells from both NOD and NOR mice. Interestingly, addition of the PPARγ inhibitor, GW9662 further downregulated Foxp3 expression in these cells from both mice. We also found that PPARγ ligands negatively regulate Foxp3 expression in activated nTreg cells via PPARγ-independent mechanism(s). These results demonstrate that both natural and synthetic PPARγ ligands capable of suppressing Foxp3 expression in activated nTreg cells of NOD and NOR mice. This may suggest that the effect of PPARγ ligands in modulating Foxp3 expression in activated nTreg cells is different from their reported effects on effector T cells. Given the capability to suppress Foxp3 gene, it is possible to be tested as immunomodulators in cancer-related studies. The co-lateral use of PPARγ ligands in nTreg cells in inducing tolerance towards pseudo-self antigens as in tumor microenvironment may uphold beneficial outcomes.

The utility of HepaRG cells for bioenergetic investigation and detection of drug-induced mitochondrial toxicity

The importance of mitochondrial toxicity in drug-induced liver injury is well established. The bioenergetic phenotype of the HepaRG cell line was defined in order to assess their suitability as a model of mitochondrial hepatotoxicity. Bioenergetic phenotyping categorised the HepaRG cells as less metabolically active when measured beside the more energetic HepG2 cells. However, inhibition of mitochondrial ATP synthase induced an increase in glycolytic activity of both HepaRG and HepG2 cells suggesting an active Crabtree Effect in both cell lines. The suitability of HepaRG cells for the acute metabolic modification assay as a screen for mitotoxicity was confirmed using a panel of compounds, including both positive and negative mitotoxic compounds. Seahorse respirometry studies demonstrated that a statistically significant decrease in spare respiratory capacity is the first indication of mitochondrial dysfunction. Furthermore, based upon comparing changes in respiratory parameters to those of the positive controls, rotenone and carbonyl cyanide m-chlorophenyl hydrazone, compounds were categorised into two mechanistic groups; inhibitors or uncouplers of the electron transport chain. Overall, the findings from this study have demonstrated that HepaRG cells, despite having different resting bioenergetic phenotype to HepG2 cells are a suitable model to detect drug-induced mitochondrial toxicity with similar detection rates to HepG2 cells.

Reappraisal of metallothionein: Clinical implications for patients with diabetes mellitus

Reactive oxygen and nitrogen species (ROS and RNS, respectively) are byproducts of cellular physiological processes of the metabolism of intermediary nutrients. Although physiological defense mechanisms readily convert these species into water or urea, an improper balance between their production and removal leads to oxidative stress (OS), which is harmful to cellular components. This OS may result in uncontrolled growth or, ultimately, cell death. In addition, ROS and RNS are closely related to the development of diabetes and its complications. Therefore, numerous researchers have proposed the development of strategies for the removal of ROS/RNS to prevent or treat diabetes and its complications. Some molecules that are synthesized in the body or obtained from food participate in the removal and neutralization of ROS and RNS. Metallothionein, a cysteine-rich protein, is a metal-binding protein that has a wide range of functions in cellular homeostasis and immunity. Metallothionein can be induced by a variety of conditions, including zinc supplementation, and plays a crucial role in mediating anti-OS, anti-apoptotic, detoxification, and anti-inflammatory effects. Metallothionein can modulate various stress-induced signaling pathways (mitogen-activated protein kinase, Wnt, nuclear factor-κB, phosphatidylinositol 3-kinase, sirtuin 1/AMP-activated protein kinase and fibroblast growth factor 21) to alleviate diabetes and diabetic complications. However, a deeper understanding of the functional, biochemical, and molecular characteristics of metallothionein is needed to bring about new opportunities for OS therapy. This review focuses on newly proposed functions of a metallothionein and their implications relevant to diabetes and its complications.

Cell death and restoration of TRAIL-sensitivity by ciglitazone in resistant cervical cancer cells

Known activators of the Peroxisome Proliferator-Activated Receptor γ (PPARγ), thiazolidinediones (TZD) induce apoptosis in a variety of cancer cells through dependent and/or independent mechanisms of the receptor. We tested a panel of TZD (Rosiglitazone, Pioglitazone, Ciglitazone) to shed light on their potential therapeutic effects on three cervical cancer cell lines (HeLa, Ca Ski, C-33 A). In these cells, only ciglitazone triggered apoptosis through PPARγ-independent mechanisms and in particular via both extrinsic and intrinsic pathways in Ca Ski cells containing Human PapillomaVirus (HPV) type 16. It also inhibits cervical cancer xenograft development in nude mice. Ciglitazone kills cervical cancer cells by activating death receptor signalling pathway, caspase cascade and BH3 interacting-domain death agonist (Bid) cleavage through the up-regulation of Death Receptor 4 (DR4)/DR5 and soluble and membrane-bound TNF related apoptosis inducing ligand (TRAIL). Importantly, the drug let TRAIL-resistant Ca Ski cells to respond to TRAIL through the downregulation of cellular FLICE-Like Inhibitory Protein (c-FLIP) level. For the first time, we revealed that ciglitazone is able to decrease E6 viral oncoprotein expression known to block TRAIL pathway and this was associated with cell death. Our results highlight the capacity of ciglitazone to restore TRAIL sensitivity and to prevent E6 blocking action to induce apoptosis in cervical cancer cells.

Mammalian Metallothionein-2A and Oxidative Stress

Mammalian metallothionein-2A (MT2A) has received considerable attention in recent years due to its crucial pathophysiological role in anti-oxidant, anti-apoptosis, detoxification and anti-inflammation. For many years, most studies evaluating the effects of MT2A have focused on reactive oxygen species (ROS), as second messengers that lead to oxidative stress injury of cells and tissues. Recent studies have highlighted that oxidative stress could activate mitogen-activated protein kinases (MAPKs), and MT2A, as a mediator of MAPKs, to regulate the pathogenesis of various diseases. However, the molecule mechanism of MT2A remains elusive. A deeper understanding of the functional, biochemical and molecular characteristics of MT2A would be identified, in order to bring new opportunities for oxidative stress therapy.

Expression of calmodulin-related genes in lead-exposed mice

The toxic metal lead is a widespread environmental polutant that can adversely affect human health. However, the underlying mechanisms of lead-induced toxicity are still largely unknown. The mechanism of lead toxicity was presumed to involve cross reaction between Pb²⁺ and Ca²⁺ with calmodulin dependent systems. The aim of the present study was thus to identify differential expression of calmodulin-related genes in the spleen of lead-exposed mice. We performed microarray analysis to identify differentially expressed genes. RNAs from spleen tissue of lead exposed animals (n=6) and controls (n=6) were converted to labeled cRNA and hybridized to Illumina mouse WG-6_v2_Bead Chip. Expression profiles were analyzed using Illumina BeadStudio Application. Real-time RT-PCR was conducted to validate the microarray data. By microarray analysis 5 calmodulin-related genes (MAP2K6, CAMKK2, CXCR4, PHKA2, MYLK) were found to be differently expressed in lead exposed compared with control mice (p<0.05). The results of Real-time RT-PCR showed that MAP2K6 and CAMKK2 were up-regulated and CXCR4 was down-regulated in lead exposure, but there were no significant differences in PHKA2 and MYLK expression between the lead exposed and control group. These results show that lead exposure produced significant changes in expression of a variety of genes in the spleen and can affect calmodulin-related gene expression.

PPARγ signaling and emerging opportunities for improved therapeutics

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated nuclear receptor that regulates glucose and lipid metabolism, endothelial function and inflammation. Rosiglitazone (RGZ) and other thiazolidinedione (TZD) synthetic ligands of PPARγ are insulin sensitizers that have been used for the treatment of type 2 diabetes. However, undesirable side effects including weight gain, fluid retention, bone loss, congestive heart failure, and a possible increased risk of myocardial infarction and bladder cancer, have limited the use of TZDs. Therefore, there is a need to better understand PPARγ signaling and to develop safer and more effective PPARγ-directed therapeutics. In addition to PPARγ itself, many PPARγ ligands including TZDs bind to and activate G protein-coupled receptor 40 (GPR40), also known as free fatty acid receptor 1. GPR40 signaling activates stress kinase pathways that ultimately regulate downstream PPARγ responses. Recent studies in human endothelial cells have demonstrated that RGZ activation of GPR40 is essential to the optimal propagation of PPARγ genomic signaling. RGZ/GPR40/p38 MAPK signaling induces and activates PPARγ co-activator-1α, and recruits E1A binding protein p300 to the promoters of target genes, markedly enhancing PPARγ-dependent transcription. Therefore in endothelium, GPR40 and PPARγ function as an integrated signaling pathway. However, GPR40 can also activate ERK1/2, a proinflammatory kinase that directly phosphorylates and inactivates PPARγ. Thus the role of GPR40 in PPARγ signaling may have important implications for drug development. Ligands that strongly activate PPARγ, but do not bind to or activate GPR40 may be safer than currently approved PPARγ agonists. Alternatively, biased GPR40 agonists might be sought that activate both p38 MAPK and PPARγ, but not ERK1/2, avoiding its harmful effects on PPARγ signaling, insulin resistance and inflammation. Such next generation drugs might be useful in treating not only type 2 diabetes, but also diverse chronic and acute forms of vascular inflammation such as atherosclerosis and septic shock.

G Protein-coupled Receptor 40 (GPR40) and Peroxisome Proliferator-activated Receptor γ (PPARγ): AN INTEGRATED TWO-RECEPTOR SIGNALING PATHWAY

Peroxisome proliferator-activated receptor γ (PPARγ) ligands have been widely used to treat type 2 diabetes mellitus. However, knowledge of PPARγ signaling remains incomplete. In addition to PPARγ, these drugs also activate G protein-coupled receptor 40 (GPR40), a Gαq-coupled free fatty acid receptor linked to MAPK networks and glucose homeostasis. Notably, p38 MAPK activation has been implicated in PPARγ signaling. Here, rosiglitazone (RGZ) activation of GPR40 and p38 MAPK was found to boost PPARγ-induced gene transcription in human endothelium. Inhibition or knockdown of p38 MAPK or expression of a dominant negative (DN) p38 MAPK mutant blunted RGZ-induced PPARγ DNA binding and reporter activity in EA.hy926 human endothelial cells. GPR40 inhibition or knockdown, or expression of a DN-Gαq mutant likewise blocked activation of both p38 MAPK and PPARγ reporters. Importantly, RGZ induction of PPARγ target genes in primary human pulmonary artery endothelial cells (PAECs) was suppressed by knockdown of either p38 MAPK or GPR40. GPR40/PPARγ signal transduction was dependent on p38 MAPK activation and induction of PPARγ co-activator-1 (PGC1α). Silencing of p38 MAPK or GPR40 abolished the ability of RGZ to induce phosphorylation and expression of PGC1α in PAECs. Knockdown of PGC1α, its essential activator SIRT1, or its binding partner/co-activator EP300 inhibited RGZ induction of PPARγ-regulated genes in PAECs. RGZ/GPR40/p38 MAPK signaling also led to EP300 phosphorylation, an event that enhances PPARγ target gene transcription. Thus, GPR40 and PPARγ can function as an integrated two-receptor signal transduction pathway, a finding with implications for rational drug development.

Nitazoxanide, an antiviral thiazolide, depletes ATP-sensitive intracellular Ca(2+) stores

Nitazoxanide (NTZ) inhibits influenza, Japanese encephalitis, hepatitis B and hepatitis C virus replication but effects on the replication of other members of the Flaviviridae family has yet to be defined. The pestivirus bovine viral diarrhoea virus (BVDV) is a surrogate model for HCV infection and NTZ induced PKR and eIF2α phosphorylation in both uninfected and BVDV-infected cells. This led to the observation that NTZ depletes ATP-sensitive intracellular Ca(2+) stores. In addition to PKR and eIF2α phosphorylation, consequences of NTZ-mediated Ca(2+) mobilisation included induction of chronic sub-lethal ER stress as well as perturbation of viral protein N-linked glycosylation and trafficking. To adapt to NTZ-mediated ER stress, NTZ treated cells upregulated translation of Ca(2+)-binding proteins, including the ER chaperone Bip and the cytosolic pro-survival and anti-viral protein TCTP. Depletion of intracellular Ca(2+) stores is the primary consequence of NTZ treatment and is likely to underpin all antiviral mechanisms attributed to the thiazolide.

Selected terpenoids from medicinal plants modulate endoplasmic reticulum stress in metabolic disorders

Objectives

The majority of research performed on cellular stress and apoptosis focuses on mitochondrial dysfunction; however, the importance of the endoplasmic reticulum dysfunction and the link to metabolic diseases has gained a substantial interest. This review focuses on the potential of terpenoids to influence endoplasmic reticulum stress and the possible role terpenoids play as the treatment of metabolic diseases.

Key findings

Metabolic diseases develop as a result of a cascade of cellular pathways. In most cases, cells are able to compensate for the disruption of the cellular homeostasis although the initiation of response pathways; however, chronic stress initiates apoptotic pathways. This reviewed (1) showed the importance of phytoterpenoids to influence endoplasmic reticulum (ER) stress and homeostasis, (2) showed how regulating ER stress affect the cell survival and death, and (3) highlighted some examples of how the progression of metabolic diseases can be influenced by ER.

Summary

Due to the substantial number of terpenoids that have been identified in literature, this review gave examples of 21 terpenoids that have been documented to have an effect on the different proteins associated with ER stress, how these plant terpenoids influence ER dysfunction and metabolic diseases such as diabetes, cancer, liver, and neurological diseases and parasitic infections.

Rosiglitazone causes cardiotoxicity via peroxisome proliferator-activated receptor γ-independent mitochondrial oxidative stress in mouse hearts

This study aims to test the hypothesis that thiazolidinedione rosiglitazone (RSG), a selective peroxisome proliferator-activated receptor γ (PPARγ) agonist, causes cardiotoxicity independently of PPARγ. Energy metabolism and mitochondrial function were measured in perfused hearts isolated from C57BL/6, cardiomyocyte-specific PPARγ-deficient mice, and their littermates. Cardiac function and mitochondrial oxidative stress were measured in both in vitro and in vivo settings. Treatment of isolated hearts with RSG at the supratherapeutic concentrations of 10 and 30 μM caused myocardial energy deficiency as evidenced by the decreases in [PCr], [ATP], ATP/ADP ratio, energy charge with a concomitant cardiac dysfunction as indicated by the decreases in left ventricular systolic pressure, rates of tension development and relaxation, and by an increase in end-diastolic pressure. When incubated with tissue homogenate or isolated mitochondria at these same concentrations, RSG caused mitochondrial dysfunction as evidenced by the decreases in respiration rate, substrate oxidation rates, and activities of complexes I and IV. RSG also increased complexes I- and III-dependent O₂⁻ production, decreased glutathione content, inhibited superoxide dismutase, and increased the levels of malondialdehyde, protein carbonyl, and 8-hydroxy-2-deoxyguanosine in mitochondria, consistent with oxidative stress. N-acetyl-L-cysteine (NAC) 20 mM prevented RSG-induced above toxicity at those in vitro settings. Cardiomyocyte-specific PPARγ deletion and PPARγ antagonist GW9662 did not prevent the observed cardiotoxicity. Intravenous injection of 10 mg/kg RSG also caused cardiac dysfunction and oxidative stress, 600 mg/kg NAC antagonized these adverse effects. In conclusion, this study demonstrates that RSG at supratherapeutic concentrations causes cardiotoxicity via a PPARγ-independent mechanism involving oxidative stress-induced mitochondrial dysfunction in mouse hearts.

Endoplasmic reticulum stress in drug- and environmental toxicant-induced liver toxicity

Liver injury resulting from exposure to drugs and environmental chemicals is a major health problem. Endoplasmic reticulum stress (ER stress) is considered to be an important factor in a wide range of diseases, such as cancer, neurological and cardiovascular disease, diabetes, and inflammatory diseases. The role of ER stress in drug-induced and environmental toxicant-induced liver toxicity has been underestimated in the past; emerging evidence indicates that ER stress makes a substantial contribution to the pathogenesis of drug-induced liver toxicity. In this review, we summarize current knowledge on drugs and environmental toxicants that trigger ER stress in liver and on the underlying molecular mechanisms. We also discuss experimental approaches for ER stress studies.

PPARγ-inactive Δ2-troglitazone independently triggers ER stress and apoptosis in breast cancer cells

Our aim was to better understand peroxisome proliferator-activated receptor gamma (PPARγ)-independent pathways involved in anti-cancer effects of thiazolidinediones (TZDs). We focused on Δ2-troglitazone (Δ2-TGZ), a PPARγ inactive TZD that affects breast cancer cell viability. Appearance of TUNEL positive cells, changes in mitochondrial membrane potential, cleavage of poly(ADP-ribose) polymerase (PARP)-1 and caspase-7 revealed that apoptosis occurred in both hormone-dependent MCF7 and hormone-independent MDA-MB-231 breast cancer cells after 24 and 48 h of treatment. A microarray study identified endoplasmic reticulum (ER) stress as an essential cellular function since many genes involved in ER stress were upregulated in MCF7 cells following Δ2-TGZ treatment. Δ2-TGZ-induced ER stress was further confirmed in MCF7 cells by phosphorylation of pancreatic endoplasmic reticulum kinase-like endoplasmic reticulum kinase (PERK) and its target eIF2α after 1.5 h, rapid increase in activating transcription factor (ATF) 3 mRNA levels, splicing of X-box binding protein 1 (XBP1) after 3 h, accumulation of binding immunogloblulin protein (BiP) and CCAAT-enhancer-binding protein homologous protein (CHOP) after 6 h. Immunofluorescence microscopy indicated that CHOP was relocalized to the nucleus of treated cells. Similarly, in MDA-MB-231 cells, overexpression of ATF3, splicing of XBP1, and accumulation of BiP and CHOP were observed following Δ2-TGZ treatment. In MCF7 cells, knock-down of CHOP or the inhibition of c-Jun N-terminal kinase (JNK) did not impair cleavage of PARP-1 and caspase-7. Altogether, our results show that ER stress is an early response of major types of breast cancer cells to Δ2-TGZ, prior to, but not causative of apoptosis.

Regulation of mitochondrial biogenesis and GLUT4 expression by exercise

Endurance exercise training can induce large increases mitochondria and the GLUT4 isoform of the glucose transporter in skeletal muscle. For a long time after the discovery in the 1960s that exercise results in an increase in muscle mitochondria, there was no progress in elucidation of the mechanisms involved. The reason for this lack of progress was that nothing was known regarding how expression of the genes-encoding mitochondrial proteins is coordinately regulated. This situation changed rapidly after discovery of transcription factors that control transcription of genes-encoding mitochondrial proteins and, most importantly, the discovery of peroxisome proliferator-gamma coactivator-1α (PGC-1α). This transcription coactivator binds to and activates transcription factors that regulate transcription of genes-encoding mitochondrial proteins. Thus, PGC-1α activates and coordinates mitochondrial biogenesis. It is now known that exercise rapidly activates and induces increased expression of PGC-1α. The exercise-generated signals that lead to PGC-1α activation and increased expression are the increases in cytosolic Ca(2+) and decreases in ATP and creatine phosphate (∼P). Ca(2+) mediates its effect by activating CAMKII, while the decrease in ∼P mediates its effect via activation of AMPK. Expression of the GLUT4 isoform of the glucose transporter is regulated in parallel with mitochondrial biogenesis via the same signaling pathways. This review describes what is known regarding the regulation of mitochondrial biogenesis and GLUT4 expression by exercise. A major component of this review deals with the physiological and metabolic consequences of the exercise-induced increase in mitochondria and GLUT4.

Nutrient-deprivation autophagy factor-1 (NAF-1): biochemical properties of a novel cellular target for anti-diabetic drugs

Nutrient-deprivation autophagy factor-1 (NAF-1) (synonyms: Cisd2, Eris, Miner1, and Noxp70) is a [2Fe-2S] cluster protein immune-detected both in endoplasmic reticulum (ER) and mitochondrial outer membrane. It was implicated in human pathology (Wolfram Syndrome 2) and in BCL-2 mediated antagonization of Beclin 1-dependent autophagy and depression of ER calcium stores. To gain insights about NAF-1 functions, we investigated the biochemical properties of its 2Fe-2S cluster and sensitivity of those properties to small molecules. The structure of the soluble domain of NAF-1 shows that it forms a homodimer with each protomer containing a [2Fe-2S] cluster bound by 3 Cys and one His. NAF-1 has shown the unusual abilities to transfer its 2Fe-2S cluster to an apo-acceptor protein (followed in vitro by spectrophotometry and by native PAGE electrophoresis) and to transfer iron to intact mitochondria in cell models (monitored by fluorescence imaging with iron fluorescent sensors targeted to mitochondria). Importantly, the drug pioglitazone abrogates NAF-1's ability to transfer the cluster to acceptor proteins and iron to mitochondria. Similar effects were found for the anti-diabetes and longevity-promoting antioxidant resveratrol. These results reveal NAF-1 as a previously unidentified cell target of anti-diabetes thiazolidinedione drugs like pioglitazone and of the natural product resveratrol, both of which interact with the protein and stabilize its labile [2Fe-2S] cluster.

Thiazolidinediones protect mouse pancreatic β-cells directly from cytokine-induced cytotoxicity through PPARγ-dependent mechanisms

Since most of the current studies of thiazolidinediones (TZDs) are only focused on improving glycemic control, increasing insulin sensitivity, and regulating inflammatory states in Type 2 Diabetes, it is still controversial whether TZDs have direct, protective effects on pancreatic β-cells in autoimmune diabetes. Here, we show the protective effects of TZDs on mouse pancreatic β-cell line cells (NIT-1) impaired by exposure to inflammatory cytokines (IL-1β and IFN-γ) and explore the potential mechanisms for this. The apoptosis rate and caspase-3 activity were remarkably increased, and insulin secretion response to glucose was impaired severely by exposure to IL-1β/IFN-γ for 48 h compared to control cells, whereas apoptosis rate and caspase-3 activity were significantly decreased in cells with treatment of rosiglitazone (RGZ) or pioglitazone (PIG), and the capacity for insulin secretion response to glucose was recovered. TZDs protect pancreatic β-cells from cytokine-induced cytotoxicity through PPARγ activation. The protective effects of the TZDs on NIT-1 cells disappeared when PPARγ was blocked with PPARγ-siRNA interference or treatment with GW9662, the PPARγ antagonist. Additionally, the enhancement of PPARγ expression by treatment with TZDs inhibited the expression of caspase 3 in IL-1β/IFN-γ-induced NIT-cells. Also, the inhibition of caspase 3 expression by TZDs was blocked by co-treatment with GW9662 or infection with PPARγ-siRNA. Taken together, our data suggest that TZDs might serve to protect pancreatic β-cells directly from cytokine-induced cytotoxicity through a PPARγ-dependent pathway, and caspase-3 may play an important role in the mechanisms involved.

Functional role of peroxisome-proliferator-activated receptor γ in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide. Major risk factors of HCC include infection with hepatitis B or C viruses, alcohol and non-alcoholic fatty liver disease. HCC is difficult to diagnose at early stage, and has a very poor survival rate when diagnosed at a late stage. The majority of HCC-related deaths result from local invasion (to cause liver failure) or distant metastases. There is an urgent need to identify effective molecular targets for the treatment of the disease. As the target of an established class of therapeutic agent thiazolidinediones (TZDs), peroxisome-proliferator-activated receptor γ (PPARγ) has been widely studied for its role in the development of HCC. A substantial body of evidence based on in vitro and in vivo models indicates that the activation of PPARγ is able to inhibit HCC cell proliferation and tumor growth through inducing cell cycle arrest and apoptosis via the regulation of a panel of downstream effector molecules. PPARγ activation also induces an inhibitory effect on HCC metastasis. Meanwhile, there is new evidence suggesting that PPARγ inhibition could also be anti-tumorigenic. In the present review, we summarize the available information on the role of PPARγ in HCC development and spread, and discuss whether PPARγ activation by TZDs could play a role in the treatment of HCC, summarizing both in vitro and in vivo. Considering the available data, PPARγ seems to exert beneficial effects against HCC and may therefore represent as a therapeutic target.

Activation of Peroxisome Proliferator-Activated Receptor γ Prolongs Islet Allograft Survival

Exposing donor mice to carbon monoxide (CO) protects transplanted islet allografts from immune rejection after transplantation (referred as the “donor” effect). In an attempt to understand the mechanisms of the donor effect of CO, we found that donor treatment with CO upregulates expression of peroxisome proliferatoractivated receptor γ (PPARγ), a transcriptional regulator, in isolated islets. In this study, we evaluated whether PPARγ contributes to the survival and function of transplanted islets and whether PPARγ mediates the protective effect of CO in a major mismatch islet allogeneic transplantation model. BALB/c (H-2d) islets in which PPARγ activity was induced by its agonists, 15-deoxy-Δ12–14-prostaglandin J2 (15d-PGJ2) or troglitazone were transplanted into C57BL/6 (H-2b) recipients that had been rendered diabetic by streptozotocin (STZ). Blood glucose levels of recipients were monitored to determine the function of transplanted islets. Our data indicated that PPARγ activation in islets led to a high percentage of BALB/c islets survived long-term in C57BL/6 recipients. Activation of PPARγ in the donor suppresses expressions of proinflammatory cytokines including tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) in transplanted islets. Blocking PPARγ activity by its antagonist, GW9662, abrogated the donor effect of CO in vivo and in vitro. Our data demonstrate that PPARγ plays a critical role in the survival and function of transplanted islets after transplantation in the recipient. The protective effects of CO are at least in part mediated by PPARγ.

Peroxisome proliferating activating receptor gamma-independent attenuation of interleukin 6 and interleukin 8 secretion from primary endometrial stromal cells by thiazolidinediones

OBJECTIVE

To assess the effect of thiazolidinediones on the regulation of inflammatory cytokines related to endometriosis in endometrial tissue and determine whether these effects occur via activation of the peroxisome proliferating activating receptor gamma (PPAR)-γ.

DESIGN

In vitro study using eutopic endometrial tissue.

SETTING

University hospital.

PATIENT(S)

Premenopausal women undergoing laparoscopy for infertility or abdominal pain.

INTERVENTION(S)

Isolation of endometrial stromal cells and the culture of these cells in the presence of thiazolidinediones, ciglitazone and pioglitazone, both with and without a pretreatment of the specific, irreversible PPAR-γ antagonist GW9662.

MAIN OUTCOME MEASURE(S)

Quantitation of interleukin (IL)-6 and IL-8 released into the cell culture medium by ELISA. Real-time polymerase chain reaction to quantitate PPAR-γ gene expression in the primary cell preparations and the expression of IL-6 and IL-8 after thiazolidinedione treatment.

RESULT(S)

Treatment of stromal cells with thiazolidinediones attenuated IL-6 and IL-8 release in a dose-dependent manner. This effect was not inhibited by GW9662 pretreatment. Ciglitazone induced IL-6 messenger RNA expression, an effect that was suppressed by GW9662 pretreatment.

CONCLUSION(S)

Thiazolidinediones decrease the proinflammatory cytokines IL-6 and IL-8 in endometrial stromal cells via a PPAR-γ-independent mechanism. A better understanding of the anti-inflammatory action of this class of drugs may improve their safety and efficacy for endometriosis treatment.

Peroxisome Proliferator-Activated Receptor-γ Ligands Alter Breast Cancer Cell Motility through Modulation of the Plasminogen Activator System

We investigated peroxisome proliferator-activated receptor-γ (PPAR-γ) ligands effect on cell motility and the plasminogen activator system using normal MCF-10A and malignant MCF-10CA1 cell lines. Ciglitazone reduced both wound-induced migration and chemotaxis. However, the effect was not reversed with pretreatment of cells with the PPAR-γ-specific antagonist GW9662. Immunoblot analysis of conditioned media showed ciglitazone decreased plasminogen activator inhibitor-1 (PAI-1) in both cell lines; this effect was also unaltered by PPAR-γ antagonism. Alternatively, treatment with the ω-6 fatty acid arachidonic acid (ArA), but not the ω-3 fatty acid docosahexanoic acid, increased both MCF-10A cell migration and cell surface uPA activity. Pretreatment with a PPAR-γ antagonist reversed these effects, suggesting that ArA mediates its effect on cell motility and uPA activity through PPAR-γ activation. Collectively, the data suggest PPAR-γ ligands have a differential effect on normal and malignant cell migration and the plasminogen activation system, resulting from PPAR-γ-dependent and PPAR-γ-independent effects.

EGR1 expression: a calcium and ERK1/2 mediated PPARγ-independent event involved in the antiproliferative effect of 15-deoxy-Δ12,14-prostaglandin J2 and thiazolidinediones in breast cancer cells

Our aim was to get new information about the Peroxisome Proliferator Activated Receptor gamma (PPARγ)-independent pathway involved in the antiproliferative action of PPARγ ligands in breast cancer cells. We investigated the effects of Troglitazone (TGZ), Ciglitazone (CGZ), Rosiglitazone (RGZ) and, 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ(2)) on the hormone-dependent breast cancer cell line MCF7. The early transcription factor EGR1 (Early Growth Response gene 1) mRNA and protein levels peaked after 3h of incubation with 25μM TGZ, CGZ or 15d-PGJ(2) and then gradually decreased. RGZ, the most potent activator of PPARγ, did not show this effect. The PPARγ antagonist GW 9662 did not block EGR1 mRNA induction which also still occurred in case of PPARγ silencing as well as in case of treatment with the PPARγ-inactive compound Δ2-TGZ. EGR1 mRNA induction required ERK1/2 phosphorylation which was not blocked by EGF Receptor (EGFR) inhibition. The ERK1/2 pathway was also involved in Δ2-TGZ-induced EGR1 mRNA expression in the hormone-independent breast cancer cell line MDA-MB-231. Using the fluorescent dye Fura2, we showed in MCF7 that TGZ or Δ2-TGZ induced an immediate increase in cytosolic calcium which was required for ERK1/2 phosphorylation and EGR1 mRNA induction as demonstrated by calcium chelation experiments. Furthermore, in MCF7 transfected with siRNA targeting EGR1, Δ2-TGZ inhibited less efficiently cell proliferation.

Roles of zinc and metallothionein-3 in oxidative stress-induced lysosomal dysfunction, cell death, and autophagy in neurons and astrocytes

Zinc dyshomeostasis has been recognized as an important mechanism for cell death in acute brain injury. An increase in the level of free or histochemically reactive zinc in astrocytes and neurons is considered one of the major causes of death of these cells in ischemia and trauma. Although zinc dyshomeostasis can lead to cell death via diverse routes, the major pathway appears to involve oxidative stress.

Recently, we found that a rise of zinc in autophagic vacuoles, including autolysosomes, is a prerequisite for lysosomal membrane permeabilization and cell death in cultured brain cells exposed to oxidative stress conditions. The source of zinc in this process is likely redox-sensitive zinc-binding proteins such as metallothioneins, which release zinc under oxidative conditions. Of the metallothioneins, metallothionein-3 is especially enriched in the central nervous system, but its physiologic role in this tissue is not well established. Like other metallothioneins, metallothionein-3 may function as metal detoxicant, but is also known to inhibit neurite outgrowth and, sometimes, promote neuronal death, likely by serving as a source of toxic zinc release. In addition, metallothionein-3 regulates lysosomal functions. In the absence of metallothionein-3, there are changes in lysosome-associated membrane protein-1 and -2, and reductions in certain lysosomal enzymes that result in decreased autophagic flux. This may have dual effects on cell survival. In acute oxidative injury, zinc dyshomeostasis and lysosomal membrane permeabilization are diminished in metallothionein-3 null cells, resulting in less cell death. But over the longer term, diminished lysosomal function may lead to the accumulation of abnormal proteins and cause cytotoxicity.

The roles of zinc and metallothionein-3 in autophagy and/or lysosomal function have just begun to be investigated. In light of evidence that autophagy and lysosomes may play significant roles in the pathogenesis of various neurological diseases, further insight into the contribution of zinc dynamics and metallothionein-3 function may help provide ways to effectively regulate these processes in brain cells.

The role of CaMKII in calcium-activated death pathways in bone marrow B cells

Calcium is an essential signaling molecule in developing B cells, thus altering calcium dynamics represents a potential target for toxicant effects. GW7845, a tyrosine analog and potent peroxisome proliferator-activated receptor γ agonist, induces rapid mitogen-activated protein kinase (MAPK)-dependent apoptosis in bone marrow B cells. Changes in calcium dynamics are capable of mediating rapid initiation of cell death; therefore, we investigated the contribution of calcium to GW7845-induced apoptosis. Treatment of a nontransformed murine pro/pre-B cell line (BU-11) with GW7845 (40 μM) resulted in intracellular calcium release. Multiple features of GW7845-induced cell death were suppressed by the calcium chelator BAPTA, including MAPK activation, loss of mitochondrial membrane potential, cytochrome c release, caspase-3 activation, and DNA fragmentation. A likely mechanism for the calcium-mediated effects is activation of CaMKII, a calcium-dependent MAP4K. We observed that three CaMKII isoforms (β, γ, and δ) are expressed in lymphoid tissues and bone marrow B cells. Treatment with GW7845 increased CaMKII activity. All features of GW7845-induced cell death, except loss of mitochondrial membrane potential, were suppressed by CaMKII inhibitors (KN93 and AIP-II), suggesting the activation of multiple calcium-driven pathways. To determine if CaMKII activation is a common feature of early B cell death following perturbation of Ca(2+) flux, we dissected tributyltin (TBT)-induced death signaling. High-dose TBT (1 μM) is known to activate calcium-dependent death. TBT induced rapid apoptosis that was associated with intracellular calcium release, CaMKII activation and MAPK activation, and was inhibited by AIP-II. Thus, we show that early B cells are susceptible to calcium-triggered cell death through a CaMKII/MAPK-dependent pathway.

Troglitazone stimulates beta-arrestin-dependent cardiomyocyte contractility via the angiotensin II type 1A receptor

Peroxisome proliferator-activated receptor gamma (PPAR gamma) agonists are commonly used to treat cardiovascular diseases, and are reported to have several effects on cardiovascular function that may be due to PPAR gamma-independent signaling events. Select angiotensin receptor blockers (ARBs) interact with and modulate PPAR gamma activity, thus we hypothesized that a PPAR gamma agonist may exert physiologic effects via the angiotensin II type 1(A) receptor (AT1(A)R). In AT1(A)R-overexpressing HEK 293 cells, both angiotensin II (Ang II) and the PPAR gamma agonist troglitazone (Trog) enhanced AT1(A)R internalization and recruitment of endogenous beta-arrestin 1/2 (beta arr1/2) to the AT1(A)R. A fluorescence assay to measure diacylglycerol (DAG) accumulation showed that although Ang II induced AT1(A)R-G(q) protein-mediated DAG accumulation, Trog had no impact on DAG generation. Trog-mediated recruitment of beta arr1/2 was selective to AT1(A)R as the response was prevented by an ARB- and Trog-mediated beta arr1/2 recruitment to beta1-adrenergic receptor (beta 1AR) was not observed. In isolated mouse cardiomyocytes, Trog increased both % and rate of cell shortening to a similar extent as Ang II, effects which were blocked with an ARB. Additionally, these effects were found to be beta arr2-dependent, as cardiomyocytes isolated from beta arr2-KO mice showed blunted contractile responses to Trog. These findings show for the first time that the PPAR gamma agonist Trog acts at the AT1(A)R to simultaneously block G(q) protein activation and induce the recruitment of beta arr1/2, which leads to an increase in cardiomyocyte contractility.

Troglitazone

Troglitazone was the first thiazolidinedione antidiabetic agent approved for clinical use in 1997, but it was withdrawn from the market in 2000 due to serious idiosyncratic hepatotoxicity. Troglitazone contains the structure of a unique chroman ring of vitamin E, and this structure has the potential to undergo metabolic biotransformation to form quinone metabolites, phenoxy radical intermediate, and epoxide species. Although troglitazone has been shown to induce apoptosis in various hepatic and nonhepatic cells, the involvement of reactive metabolites in the troglitazone cytotoxicity is controversial. Numerous toxicological tests, both in vivo and in vitro, have been used to try to predict the toxicity, but no direct mechanism has been demonstrated that can explain the hepatotoxicity that occurred in some individuals. This chapter summarizes the proposed mechanisms of troglitazone hepatotoxicity based in vivo and in vitro studies. Many factors have been proposed to contribute to the mechanism underlying this idiosyncratic toxicity.

Peroxisome proliferator-activated receptors and angiogenesis

The peroxisome proliferator-activated receptors (PPARs) are a group of three nuclear receptor isoforms, PPARalpha, PPARgamma and PPARdelta, encoded by different genes, and they form a subfamily of the nuclear receptor superfamily. The clinical interest in PPARs originates with fibrates and thiazolidinediones, which, respectively, act on PPARalpha and PPARgamma and are used to ameliorate hyperlipidaemia and hyperglycaemia in subjects with type 2 diabetes mellitus (T2DM). PPARs play a central role in these patients due to their ability to regulate the expression of numerous genes involved in glycaemic control, lipid metabolism, vascular tone and inflammation. Abnormal angiogenesis is implicated in several of the long-term complications of diabetes mellitus, characterized by vasculopathy associated with aberrant growth of new blood vessels. This pathological process plays a crucial role in diabetic retinopathy, nephropathy and neuropathy, impaired wound healing and impaired coronary collateral vessel development. In recent years, there has been increasing appreciation of the fact that PPARs might be involved in the molecular mechanisms that regulate angiogenesis through the action of growth factors and cytokines that stimulate migration, proliferation and survival of endothelial cells. During the last few years direct comparative analyses have been performed, using selective PPARs agonists, to clarify the angiogenic properties of the different members of the PPAR family. Lately, the findings provide new information to order to understand the biological, clinical and therapeutic effects of PPARs, and the role of these nuclear receptors in angiogenesis, with potentially important implications for the management of subjects affected by T2DM.

Angiotensin II-induced oxidative stress resets the Ca2+ dependence of Ca2+-calmodulin protein kinase II and promotes a death pathway conserved across different species

RATIONALE

Angiotensin (Ang) II-induced apoptosis was reported to be mediated by different signaling molecules. Whether these molecules are either interconnected in a single pathway or constitute different and alternative cascades by which Ang II exerts its apoptotic action, is not known.

OBJECTIVE

To investigate in cultured myocytes from adult cat and rat, 2 species in which Ang II has opposite inotropic effects, the signaling cascade involved in Ang II-induced apoptosis.

METHODS AND RESULTS

Ang II (1 micromol/L) reduced cat/rat myocytes viability by approximately 40%, in part, because of apoptosis (TUNEL/caspase-3 activity). In both species, apoptosis was associated with reactive oxygen species (ROS) production, Ca(2+)/calmodulin-dependent protein kinase (CaMK)II, and p38 mitogen-activated protein kinase (p38MAPK) activation and was prevented by the ROS scavenger MPG (2-mercaptopropionylglycine) or the NADPH oxidase inhibitor DPI (diphenyleneiodonium) by CaMKII inhibitors (KN-93 and AIP [autocamtide 2-related inhibitory peptide]) or in transgenic mice expressing a CaMKII inhibitory peptide and by the p38MAPK inhibitor, SB202190. Furthermore, p38MAPK overexpression exacerbated Ang II-induced cell mortality. Moreover, although KN-93 did not affect Ang II-induced ROS production, it prevented p38MAPK activation. Results further show that CaMKII can be activated by Ang II or H(2)O(2), even in the presence of the Ca(2+) chelator BAPTA-AM, in myocytes and in EGTA-Ca(2+)-free solutions in the presence of the calmodulin inhibitor W-7 in in vitro experiments.

CONCLUSIONS

(1) The Ang II-induced apoptotic cascade converges in both species, in a common pathway mediated by ROS-dependent CaMKII activation which results in p38MAPK activation and apoptosis. (2) In the presence of Ang II or ROS, CaMKII may be activated at subdiastolic Ca(2+) concentrations, suggesting a new mechanism by which ROS reset the Ca(2+) dependence of CaMKII to extremely low Ca(2+) levels.

Reduced spatial learning in mice treated with NVP-AAM077 through down-regulating neurogenesis

NR2A-containing N-methyl-D-aspartate (NMDA) receptors have important roles in influencing the long-term potentiation and spatial memory. Here using Morris water maze, we found that inhibition of NR2A-containing NMDA receptors by [(R)-[(S)-1-(4-bromophenyl)-ethylamino]-(2, 3-dioxo-1,2,3,4-tetrahydroquinoxalin-5-yl)-methyl]-phosphonic acid (NVP-AAM077) hindered the formation of spatial memory. An increasing number of reports suggest that adult hippocampal neurogenesis is involved in hippocampal-mediated learning. To explore the possible mechanisms understanding the reduced spatial memory by NVP-AAM077, we investigated the effects of NVP-AAM077 on neurogenesis. We found that NVP-AAM077 inhibited progenitor cells proliferation in the subventricular zone and dentate gyrus and reduced the survival of newborn cells in the dentate gyrus in the adult mice. In null mutant mice lacking neuronal nitric oxide synthase (nNOS) gene (nNOS(-/-)), the effects of NVP-AAM077 on neurogenesis disappeared. In addition, NVP-AAM077 increased nNOS enzymatic activity. Our findings suggest that NVP-AAM077 reduced spatial learning through down-regulating neurogenesis in the adult hippocampus.

Pioglitazone enhances collateral blood flow in ischemic hindlimb of diabetic mice through an Akt-dependent VEGF-mediated mechanism, regardless of PPARgamma stimulation

Background

Type 2 diabetes mellitus (T2DM) is commonly associated with both microvascular and macrovascular complications and a strong correlation exists between glycaemic control and the incidence and progression of vascular complications. Pioglitazone, a Peroxisome proliferator-activated receptor-γ (PPARγ) ligand indicated for therapy of type T2DM, induces vascular effects that seem to occur independently of glucose lowering.

Methods

By using a hindlimb ischemia murine model, in this study we have found that pioglitazone restores the blood flow recovery and capillary density in ischemic muscle of diabetic mice and that this process is associated with increased expression of Vascular Endothelial Growth Factor (VEGF). Importantly, these beneficial effects are abrogated when endogenous Akt is inhibited; furthermore, the direct activation of PPARγ, with its selective agonist GW1929, does not restore blood flow recovery and capillary density. Finally, an important collateral vessel growth is obtained with combined treatment with pioglitazone and selective PPARγ inhibitor GW9662.

Conclusion

These data demonstrate that Akt-VEGF pathway is essential for ischemia-induced angiogenic effect of pioglitazone and that pioglitazone exerts this effect via a PPARγ independent manner.

Oxidative and endoplasmic reticulum stress signaling are involved in dehydrocostuslactone-mediated apoptosis in human non-small cell lung cancer cells

This study investigates the anticancer effect of dehydrocostuslactone (DHE), a medicinal plant-derived sesquiterpene lactone, on human non-small cell lung cancer cell lines, A549, NCI-H460 and NCI-H520. Our results show that DHE inhibits the proliferation of A549, NCI-H460 and NCI-H520 cells. DHE-induced apoptosis in both A549 and NCI-H460 cells. DHE triggered endoplasmic reticulum (ER) stress, as indicated by changes in cytosol-calcium levels, PKR-like ER kinase (PERK) phosphorylation, inositol requiring protein 1 (IRE1) and CHOP/GADD153 upregulation, X-box transcription factor-1 (XBP-1) mRNA splicing, and caspase-4 activation. The release of calcium triggered the production of ROS, which further enhances calcium overloading and subsequently activates p38, JNK and ERK1/2. Both IRE1 miRNA transfection and BAPTA-AM pretreatment inhibit DHE-mediated apoptosis, supporting the hypothesis that DHE induces cell death through ER stress. Importantly, a novel anticancer agent for the treatment of non-small cell lung cancer, and is supported by animal studies which have shown a dramatic 50% reduction in tumor size after 28 days of treatment. This study demonstrates that DHE may be a novel anticancer agent for the treatment of non-small cell lung cancer.

Troglitazone inhibits cell proliferation by attenuation of epidermal growth factor receptor signaling independent of peroxisome proliferator-activated receptor gamma

Peroxisome proliferator-activated receptors (PPAR) belong to the nuclear hormone receptor superfamily of ligand-dependent transcription factors. Recent results have shown that agonists of PPARgamma, such as troglitazone (TGZ), can inhibit cell proliferation and promote cell differentiation independent of PPARgamma. In the present study, we provide evidence that TGZ may bind directly to EGFR and trigger its signaling and internalization independent of PPARgamma. Detailed studies revealed that prolonged incubation with TGZ effectively attenuated EGFR signaling by targeting the receptor to the endo-lysosomal degradation machinery. Although the extracellular signal-regulated kinase-signaling pathway was transiently activated by TGZ in EGFR overexpressing cancer cells, inhibition of EGF-induced Akt phosphorylation most likely accounted for the growth arrest of tumor cells caused by TGZ at pharmacologically achievable concentrations. Therefore, we have provided a new line of evidence indicating that TGZ inhibits cell proliferation by promoting EGFR degradation and attenuating Akt phosphorylation.

Cardiac fibroblasts: at the heart of myocardial remodeling

Cardiac fibroblasts are the most prevalent cell type in the heart and play a key role in regulating normal myocardial function and in the adverse myocardial remodeling that occurs with hypertension, myocardial infarction and heart failure. Many of the functional effects of cardiac fibroblasts are mediated through differentiation to a myofibroblast phenotype that expresses contractile proteins and exhibits increased migratory, proliferative and secretory properties. Cardiac myofibroblasts respond to proinflammatory cytokines (e.g. TNFalpha, IL-1, IL-6, TGF-beta), vasoactive peptides (e.g. angiotensin II, endothelin-1, natriuretic peptides) and hormones (e.g. noradrenaline), the levels of which are increased in the remodeling heart. Their function is also modulated by mechanical stretch and changes in oxygen availability (e.g. ischaemia-reperfusion). Myofibroblast responses to such stimuli include changes in cell proliferation, cell migration, extracellular matrix metabolism and secretion of various bioactive molecules including cytokines, vasoactive peptides and growth factors. Several classes of commonly prescribed therapeutic agents for cardiovascular disease also exert pleiotropic effects on cardiac fibroblasts that may explain some of their beneficial outcomes on the remodeling heart. These include drugs for reducing hypertension (ACE inhibitors, angiotensin receptor blockers, beta-blockers), cholesterol levels (statins, fibrates) and insulin resistance (thiazolidinediones). In this review, we provide insight into the properties of cardiac fibroblasts that underscores their importance in the remodeling heart, including their origin, electrophysiological properties, role in matrix metabolism, functional responses to environmental stimuli and ability to secrete bioactive molecules. We also review the evidence suggesting that certain cardiovascular drugs can reduce myocardial remodeling specifically via modulatory effects on cardiac fibroblasts.

Dehydrocostuslactone, a medicinal plant-derived sesquiterpene lactone, induces apoptosis coupled to endoplasmic reticulum stress in liver cancer cells

This study is the first to investigate the anticancer effect of dehydrocostuslactone [DHE (3aS,6aR,9aR,9bS)-decahydro-3,6,9-tris(methylene) azuleno[4,5-b]furan-2(3H)-one)], a medicinal plant-derived sesquiterpene lactone, on hepatocellular carcinoma. Our results showed that DHE inhibits the proliferation of HepG2 and PLC/PRF/5 cells by inducing apoptosis. DHE induces up-regulation of Bax and Bak, down-regulation of Bcl-2 and Bcl-XL, and nuclear relocation of the mitochondrial factors apoptosis-inducing factor (AIF) and endonuclease G (Endo G). DHE triggered endoplasmic reticulum (ER) stress, as indicated by changes in cytosol-calcium levels, double-stranded RNA-activated protein kinase-like endoplasmic reticulum kinase phosphorylation, inositol-requiring protein 1 (IRE1) and CHOP/GADD153 up-regulation, X-box transcription factor-1 mRNA splicing, and caspase-4 activation. Enhancement of ER stress by DHE is through p38 and extracellular signal-regulated kinase 1/2-dependent manners and subsequently causes c-Jun NH(2)-terminal kinase activation, resulting in AIF and Endo G nuclear relocation. Both of IRE1 small interfering RNA transfection and 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester pretreatment inhibit DHE-mediated apoptosis, supporting the hypothesis that DHE induces cell death through ER stress. It is noteworthy that animal studies have revealed a dramatic 50% reduction in tumor volume after 45 days of treatment. This study demonstrates that DHE may be a novel anticancer agent for the treatment of liver cancer.

Rat Urinary Bladder Carcinogenesis by Dual-Acting PPARalpha + gamma Agonists

Despite clinical promise, dual-acting activators of PPARalpha and gamma (here termed PPARalpha+gamma agonists) have experienced high attrition rates in preclinical and early clinical development, due to toxicity. In some cases, discontinuation was due to carcinogenic effect in the rat urothelium, the epithelial layer lining the urinary bladder, ureters, and kidney pelvis. Chronic pharmacological activation of PPARalpha is invariably associated with cancer in rats and mice. Chronic pharmacological activation of PPARgamma can in some cases also cause cancer in rats and mice. Urothelial cells coexpress PPARalpha as well as PPARgamma, making it plausible that the urothelial carcinogenicity of PPARalpha+gamma agonists may be caused by receptor-mediated effects (exaggerated pharmacology). Based on previously published mode of action data for the PPARalpha+gamma agonist ragaglitazar, and the available literature about the role of PPARalpha and gamma in rodent carcinogenesis, we propose a mode of action hypothesis for the carcinogenic effect of PPARalpha+gamma agonists in the rat urothelium, which combines receptor-mediated and off-target cytotoxic effects. The proposed mode of action hypothesis is being explored in our laboratories, towards understanding the human relevance of the rat cancer findings, and developing rapid in vitro or short-term in vivo screening approaches to faciliate development of new dual-acting PPAR agonist compounds.