Differential regulation of activator protein-1 and heat shock factor-1 in myocardial ischemia and reperfusion injury: role of poly(ADP-ribose) polymerase-1

ADP-ribosylation, a multifaceted modification: Functions and mechanisms in aging and aging-related diseases

Aging, a complex biological process, plays key roles the development of multiple disorders referred as aging-related diseases involving cardiovascular diseases, stroke, neurodegenerative diseases, cancers, lipid metabolism-related diseases. ADP-ribosylation is a reversible modification onto proteins and nucleic acids to alter their structures and/or functions. Growing evidence support the importance of ADP-ribosylation and ADP-ribosylation-associated enzymes in aging and age-related diseases. In this review, we summarized ADP-ribosylation-associated proteins including ADP-ribosyl transferases, the ADP-ribosyl hydrolyses and ADP-ribose binding domains. Furthermore, we outlined the latest knowledge about regulation of ADP-ribosylation in the pathogenesis and progression of main aging-related diseases, organism aging and cellular senescence, and we also speculated the underlying mechanisms to better disclose this novel molecular network. Moreover, we discussed current issues and provided an outlook for future research, aiming to revealing the unknown bio-properties of ADP-ribosylation, and establishing a novel therapeutic perspective in aging-related diseases and health aging via targeting ADP-ribosylation.

CB2 Cannabinoid Receptor as a Potential Target in Myocardial Infarction: Exploration of Molecular Pathogenesis and Therapeutic Strategies

The lipid endocannabinoid system has recently emerged as a novel therapeutic target for several inflammatory and tissue-damaging diseases, including those affecting the cardiovascular system. The primary targets of cannabinoids are cannabinoid type 1 (CB1) and 2 (CB2) receptors. The CB2 receptor is expressed in the cardiomyocytes. While the pathological changes in the myocardium upregulate the CB2 receptor, genetic deletion of the receptor aggravates the changes. The CB2 receptor plays a crucial role in attenuating the advancement of myocardial infarction (MI)-associated pathological changes in the myocardium. Activation of CB2 receptors exerts cardioprotection in MI via numerous molecular pathways. For instance, delta-9-tetrahydrocannabinol attenuated the progression of MI via modulation of the CB2 receptor-dependent anti-inflammatory mechanisms, including suppression of pro-inflammatory cytokines like IL-6, TNF-α, and IL-1β. Through similar mechanisms, natural and synthetic CB2 receptor ligands repair myocardial tissue damage. This review aims to offer an in-depth discussion on the ameliorative potential of CB2 receptors in myocardial injuries induced by a variety of pathogenic mechanisms. Further, the modulation of autophagy, TGF-β/Smad3 signaling, MPTP opening, and ROS production are discussed. The molecular correlation of CB2 receptors with cardiac injury markers, such as troponin I, LDH1, and CK-MB, is explored. Special attention has been paid to novel insights into the potential therapeutic implications of CB2 receptor activation in MI.

The potential of activator protein 1 (AP-1) in cancer targeted therapy

Activator protein-1 (AP-1) is a transcription factor that consists of a diverse group of members including Jun, Fos, Maf, and ATF. AP-1 involves a number of processes such as proliferation, migration, and invasion in cells. Dysfunctional AP-1 activity is associated with cancer initiation, development, invasion, migration and drug resistance. Therefore, AP-1 is a potential target for cancer targeted therapy. Currently, some small molecule inhibitors targeting AP-1 have been developed and tested, showing some anticancer effects. However, AP-1 is complex and diverse in its structure and function, and different dimers may play different roles in different type of cancers. Therefore, more research is needed to reveal the specific mechanisms of AP-1 in cancer, and how to select appropriate inhibitors and treatment strategies. Ultimately, this review summarizes the potential of combination therapy for cancer.

Endothelial SIRT6 deficiency promotes arterial thrombosis in mice

OBJECTIVE

Arterial thrombosis may be initiated by endothelial inflammation or denudation, activation of blood-borne elements or the coagulation system. Tissue factor (TF), a central trigger of the coagulation cascade, is regulated by the pro-inflammatory NF-κB-dependent pathways. Sirtuin 6 (SIRT6) is a nuclear member of the sirtuin family of NAD⁺-dependent deacetylases and is known to inhibit NF-κB signaling. Its constitutive deletion in mice shows early lethality with hypoglycemia and accelerated aging. Of note, the role of SIRT6 in arterial thrombosis remains unknown. Thus, we hypothesized that endothelial SIRT6 protects from arterial thrombosis by modulating inhibition of NF-κB-associated pathways.

APPROACH AND RESULTS

Using a laser-induced carotid thrombosis model, in vivo arterial occlusion occurred 45% faster in 12-week-old male endothelial-specific Sirt6^-/- mice as compared to Sirt6^fl/fl controls (n ≥ 9 per group; p = 0.0012). Levels of procoagulant TF were increased in animals lacking endothelial SIRT6 as compared to control littermates. Similarly, in cultured human aortic endothelial cells, SIRT6 knockdown increased TF mRNA, protein and activity. Moreover, SIRT6 knockdown increased mRNA levels of NF-κB-associated genes tumor necrosis factor alpha (TNF-α), poly [ADP-ribose] polymerase 1 (PARP-1), vascular cell adhesion molecule 1 (VCAM-1), and cyclooxygenase-2 (COX-2); at the protein level, COX-2, VCAM-1, TNF-α, and cleaved PARP-1 remained increased after Sirt6 knockdown.

CONCLUSIONS

Endothelium-specific Sirt6 deletion promotes arterial thrombosis in mice. In cultured human aortic endothelial cells, SIRT6 silencing enhances TF expression and activates pro-inflammatory pathways including TNF-α, cleaved PARP-1, VCAM-1 and COX-2. Hence, endogenous endothelial SIRT6 exerts a protective role in experimental arterial thrombosis.

Detecting and Quantifying pADPr In Vivo

Poly(ADP-ribose) polymerases (PARP) participate in diverse biological processes contributing to cellular homeostasis or exacerbating injury. PARP catalyzes the addition of ADP-ribose molecules (pADPr) to the target proteins, a process termed poly-ADP-ribosylation. Overactivation of PARP - reflected by increased poly-ADP-ribosylation and accumulation of pADPr-modified proteins or free pADPr - contributes to depletion of NAD⁺ and mitochondrial dysfunction, potentially leading to cell death. Thus, PARP overactivation and increases in free pADPr have been identified as key contributors to the pathobiology of many diseases. In stark contrast, PARP inhibitors are in clinical use in cancer patients where they potentiate cell death induced by chemotherapeutic agents. Accordingly, monitoring PARP-1 activation - responsible for up to 80-90% of cellular pADPr synthesis - by detecting and quantifying pADPr may provide valuable mechanistic insights as well as facilitating therapeutic drug monitoring for PARP inhibitors.Several non-isotopic immunodetection methods for quantifying pADPr are discussed: Western blotting of poly-ADP-ribosylated proteins, cellular localization of pADPr by immunohistochemistry, quantification of pADPr by enzyme-linked immunoassay, and small-scale two-dimensional gel electrophoresis.

The PARP Enzyme Family and the Hallmarks of Cancer Part 2: Hallmarks Related to Cancer Host Interactions

Poly (ADP-ribose) polymerases (PARPs) modify target proteins with a single ADP-ribose unit or with a poly (ADP-ribose) (PAR) polymer. PARP inhibitors (PARPis) recently became clinically available for the treatment of BRCA1/2 deficient tumors via the synthetic lethality paradigm. This personalized treatment primarily targets DNA damage-responsive PARPs (PARP1-3). However, the biological roles of PARP family member enzymes are broad; therefore, the effects of PARPis should be viewed in a much wider context, which includes complex effects on all known hallmarks of cancer. In the companion paper (part 1) to this review, we presented the fundamental roles of PARPs in intrinsic cancer cell hallmarks, such as uncontrolled proliferation, evasion of growth suppressors, cell death resistance, genome instability, replicative immortality, and reprogrammed metabolism. In the second part of this review, we present evidence linking PARPs to cancer-associated inflammation, anti-cancer immune response, invasion, and metastasis. A comprehensive overview of the roles of PARPs can facilitate the identification of novel cancer treatment opportunities and barriers limiting the efficacy of PARPi compounds.

NAD+ Metabolism as an Emerging Therapeutic Target for Cardiovascular Diseases Associated With Sudden Cardiac Death

In addition to its central role in mediating oxidation reduction in fuel metabolism and bioenergetics, nicotinamide adenine dinucleotide (NAD⁺) has emerged as a vital co-substrate for a number of proteins involved in diverse cellular processes, including sirtuins, poly(ADP-ribose) polymerases and cyclic ADP-ribose synthetases. The connection with aging and age-associated diseases has led to a new wave of research in the cardiovascular field. Here, we review the basics of NAD⁺ homeostasis, the molecular physiology and new advances in ischemic-reperfusion injury, heart failure, and arrhythmias, all of which are associated with increased risks for sudden cardiac death. Finally, we summarize the progress of NAD⁺-boosting therapy in human cardiovascular diseases and the challenges for future studies.

Selective targeting of ubiquitination and degradation of PARP1 by E3 ubiquitin ligase WWP2 regulates isoproterenol-induced cardiac remodeling

The elevated expression of poly(ADP-ribose) polymerase-1 (PARP1) and increased PARP1 activity, namely, poly(ADP-ribosyl)ation (PARylation), have been observed in cardiac remodeling, leading to extreme energy consumption and myocardial damage. However, the mechanisms underlying the regulation of PARP1 require further study. WWP2, a HECT-type E3 ubiquitin ligase, is highly expressed in the heart, but its function there is largely unknown. Here, we clarified the role of WWP2 in the regulation of PARP1 and the impact of this regulatory process on cardiac remodeling. We determined that the knockout of WWP2 specifically in myocardium decreased the level of PARP1 ubiquitination and increased the effects of isoproterenol (ISO)-induced PARP1 and PARylation, in turn aggravating ISO-induced myocardial hypertrophy, heart failure, and myocardial fibrosis. Similar findings were obtained in a model of ISO-induced H9c2 cells with WWP2 knockdown, while the reexpression of WWP2 significantly increased PARP1 ubiquitination and decreased PAPR1 and PARylation levels. Mechanistically, coimmunoprecipitation results identified that WWP2 is a novel interacting protein of PARP1 and mainly interacts with its BRCT domain, thus mediating the degradation of PARP1 through the ubiquitin-proteasome system. In addition, lysine 418 (K418) and lysine 249 (K249) were shown to be of critical importance in regulating PARP1 ubiquitination and degradation by WWP2. These findings reveal a novel WWP2-PARP1 signal transduction pathway involved in controlling cardiac remodeling and may provide a basis for exploring new strategies for treating heart disorders related to cardiac remodeling.

DNA damage-induced PARP1 activation confers cardiomyocyte dysfunction through NAD+ depletion in experimental atrial fibrillation

Atrial fibrillation (AF) is the most common clinical tachyarrhythmia with a strong tendency to progress in time. AF progression is driven by derailment of protein homeostasis, which ultimately causes contractile dysfunction of the atria. Here we report that tachypacing-induced functional loss of atrial cardiomyocytes is precipitated by excessive poly(ADP)-ribose polymerase 1 (PARP1) activation in response to oxidative DNA damage. PARP1-mediated synthesis of ADP-ribose chains in turn depletes nicotinamide adenine dinucleotide (NAD⁺), induces further DNA damage and contractile dysfunction. Accordingly, NAD⁺ replenishment or PARP1 depletion precludes functional loss. Moreover, inhibition of PARP1 protects against tachypacing-induced NAD⁺ depletion, oxidative stress, DNA damage and contractile dysfunction in atrial cardiomyocytes and Drosophila. Consistently, cardiomyocytes of persistent AF patients show significant DNA damage, which correlates with PARP1 activity. The findings uncover a mechanism by which tachypacing impairs cardiomyocyte function and implicates PARP1 as a possible therapeutic target that may preserve cardiomyocyte function in clinical AF.

Poly(ADP-ribose) Polymerase (PARP) and PARP Inhibitors: Mechanisms of Action and Role in Cardiovascular Disorders

Poly(ADP-ribosyl)ation is an immediate cellular repair response to DNA damage and is catalyzed primarily by poly(ADP-ribose)polymerase-1 (PARP1), which is the most abundant of the 18 different PARP isoforms and accounts for more than 90% of the catalytic activity of PARP in the cell nucleus. Upon detection of a DNA strand break, PARP1 binds to the DNA, cleaves nicotinamide adenine dinucleotide between nicotinamide and ribose and then modifies the DNA nuclear acceptor proteins by formation of a bond between the protein and the ADP-ribose residue. This generates ribosyl-ribosyl linkages that act as a signal for other DNA-repairing enzymes and DNA base repair. Extensive DNA breakage in cells results in excessive activation of PARP with resultant depletion of the cellular stores of nicotinamide adenine dinucleotide (NAD+) which slows the rate of glycolysis, mitochondrial electron transport, and ultimately ATP formation in these cells. This paper focuses on PARP in DNA repair in atherosclerosis, acute myocardial infarction/reperfusion injury, and congestive heart failure and the role of PARP inhibitors in combating the effects of excessive PARP activation in these diseases. Free oxygen radicals and nitrogen radicals in arteries contribute to disruption of the vascular endothelial glycocalyx, which increase the permeability of the endothelium to inflammatory cells and also low-density lipoproteins and the accumulation of lipid in the vascular intima. Mild inflammation and DNA damage within vascular cells promote PARP1 activation and DNA repair. Moderate DNA damage induces caspase-dependent PARP cleavage and vascular cell apoptosis. Severe DNA damage due to vascular inflammation causes excessive activation of PARP1. This causes endothelial cell depletion of NAD+ and ATP, downregulation of atheroprotective SIRT1, necrotic cell death, and ultimately atherosclerotic plaque disruption. Inhibition of PARP decreases vascular endothelial cell adhesion P-selectin and ICAM-1 molecules, inflammatory cells, pro-death caspase-3, and c-Jun N-terminal kinase (JNK) activation and upregulates prosurvival extracellular signal-regulated kinases and AKT, which decrease vascular cell apoptosis and necrosis and limit atherosclerosis and plaque disruption. In myocardial infarction with coronary occlusion then reperfusion, which occurs with coronary angioplasty or thrombolytic therapy, reperfusion injury occurs in as many as 31% of patients and is caused by inflammatory cells, free oxygen and nitrogen radicals, the rapid transcriptional activation of inflammatory cytokines, and the activation of PARP1. Inhibition of PARP attenuates neutrophil infiltration and inflammatory cytokine expression in the reperfused myocardium and preserves myocardial NAD+ and ATP. In addition, PARP inhibition increases the activation of myocyte survival enzymes protein kinase B (Akt) and protein kinase C epsilon (PKCε), and decreases the activity of myocardial ventricular remodeling enzymes PKCα/β, PKCζ/λ, and PKCδ. As a consequence, cardiomyocyte and vascular endothelial cell necrosis is decreased and myocardial contractility is preserved. In heart failure and circulatory shock in animal models, PARP inhibition significantly attenuates decreases in left ventricular systolic pressure, ventricular contractility and relaxation, stroke volume, and increases survival by limiting or preventing upregulation of adhesion molecules, proinflammatory cytokines, myocardial mononuclear cell infiltration, and PKCα/β and PKC λ/ζ. In this manner, PARP inhibition partially restores the myocardial concentrations of NAD+, limits ventricular remodeling and fibrosis, and prevents significant decreases in myocardial contractility. Based primarily on investigations in preclinical models of atherosclerosis, myocardial infarction, and heart failure, PARP inhibition appears to be beneficial in limiting or inhibiting cardiovascular dysfunction. These studies indicate that investigations of acute and chronic PARP inhibition are warranted in patients with atherosclerotic coronary artery disease.

Neutrophil transfer of miR-223 to lung epithelial cells dampens acute lung injury in mice

Intercellular transfer of microRNAs can mediate communication between critical effector cells. We hypothesized that transfer of neutrophil-derived microRNAs to pulmonary epithelial cells could alter mucosal gene expression during acute lung injury. Pulmonary-epithelial microRNA profiling during coculture of alveolar epithelial cells with polymorphonuclear neutrophils (PMNs) revealed a selective increase in lung epithelial cell expression of microRNA-223 (miR-223). Analysis of PMN-derived supernatants showed activation-dependent release of miR-223 and subsequent transfer to alveolar epithelial cells during coculture in vitro or after ventilator-induced acute lung injury in mice. Genetic studies indicated that miR-223 deficiency was associated with severe lung inflammation, whereas pulmonary overexpression of miR-223 in mice resulted in protection during acute lung injury induced by mechanical ventilation or by infection with Staphylococcus aureus Studies of putative miR-223 gene targets implicated repression of poly(adenosine diphosphate-ribose) polymerase-1 (PARP-1) in the miR-223-dependent attenuation of lung inflammation. Together, these findings suggest that intercellular transfer of miR-223 from neutrophils to pulmonary epithelial cells may dampen acute lung injury through repression of PARP-1.

Olaparib protects cardiomyocytes against oxidative stress and improves graft contractility during the early phase after heart transplantation in rats

BACKGROUND AND PURPOSE

Olaparib, rucaparib and niraparib, potent inhibitors of poly(ADP-ribose) polymerase (PARP) are approved as anti-cancer drugs in humans. Considering the previously demonstrated role of PARP in various forms of acute and chronic myocardial injury, we tested the effects of olaparib in in-vitro models of oxidative stress in cardiomyocytes, and in an in vivo model of cardiac transplantation.

EXPERIMENTAL APPROACH

H9c2-embryonic rat heart-derived myoblasts pretreated with vehicle or olaparib (10μM) were challenged with either hydrogen peroxide (H₂ O₂ ) or with glucose oxidase (GOx, which generates H₂ O₂ in the tissue culture medium). Cell viability assays (MTT, lactate dehydrogenase) and Western blotting for PARP and its product, PAR was performed. Heterotopic heart transplantation was performed in Lewis rats; recipients were treated either with vehicle or olaparib (10 mg kg^-1 ). Left ventricular function of transplanted hearts was monitored via a Millar catheter. Multiple gene expression in the graft was measured by qPCR.

KEY RESULTS

Olaparib blocked autoPARylation of PARP1 and attenuated the rapid onset of death in H9c2 cells, induced by H₂ O₂ , but did not affect cell death following chronic, prolonged oxidative stress induced by GOx. In rats, after transplantation, left ventricular systolic and diastolic function were improved by olaparib. In the transplanted hearts, olaparib also reduced gene expression for c-jun, caspase-12, catalase, and NADPH oxidase-2.

CONCLUSIONS AND IMPLICATIONS

Olaparib protected cardiomyocytes against oxidative stress and improved graft contractility in a rat model of heart transplantation. These findings raise the possibility of repurposing this clinically approved oncology drug, to be used in heart transplantation.

LINKED ARTICLES

This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Poly(ADP-Ribose)Polymerase-1 in Lung Inflammatory Disorders: A Review

Asthma, acute lung injury (ALI), and chronic obstructive pulmonary disease (COPD) are lung inflammatory disorders with a common outcome, that is, difficulty in breathing. Corticosteroids, a class of potent anti-inflammatory drugs, have shown less success in the treatment/management of these disorders, particularly ALI and COPD; thus, alternative therapies are needed. Poly(ADP-ribose)polymerases (PARPs) are the post-translational modifying enzymes with a primary role in DNA repair. During the last two decades, several studies have reported the critical role played by PARPs in a good of inflammatory disorders. In the current review, the studies that address the role of PARPs in asthma, ALI, and COPD have been discussed. Among the different members of the family, PARP-1 emerges as a key player in the orchestration of lung inflammation in asthma and ALI. In addition, PARP activation seems to be associated with the progression of COPD. Furthermore, PARP-14 seems to play a crucial role in asthma. STAT-6 and GATA-3 are reported to be central players in PARP-1-mediated eosinophilic inflammation in asthma. Interestingly, oxidative stress-PARP-1-NF-κB axis appears to be tightly linked with inflammatory response in all three-lung diseases despite their distinct pathophysiologies. The present review sheds light on PARP-1-regulated factors, which may be common or differential players in asthma/ALI/COPD and put forward our prospective for future studies.

Proteostasis in cardiac health and disease

The incidence and prevalence of cardiac diseases, which are the main cause of death worldwide, are likely to increase because of population ageing. Prevailing theories about the mechanisms of ageing feature the gradual derailment of cellular protein homeostasis (proteostasis) and loss of protein quality control as central factors. In the heart, loss of protein patency, owing to flaws in genetically-determined design or because of environmentally-induced 'wear and tear', can overwhelm protein quality control, thereby triggering derailment of proteostasis and contributing to cardiac ageing. Failure of protein quality control involves impairment of chaperones, ubiquitin-proteosomal systems, autophagy, and loss of sarcomeric and cytoskeletal proteins, all of which relate to induction of cardiomyocyte senescence. Targeting protein quality control to maintain cardiac proteostasis offers a novel therapeutic strategy to promote cardiac health and combat cardiac disease. Currently marketed drugs are available to explore this concept in the clinical setting.

Regulation of the mammalian heat shock factor 1

Living organisms are endowed with the capability to tackle various forms of cellular stress due to the presence of molecular chaperone machinery complexes that are ubiquitous throughout the cell. During conditions of proteotoxic stress, the transcription factor heat shock factor 1 (HSF1) mediates the elevation of heat shock proteins, which are crucial components of the chaperone complex machinery and function to ameliorate protein misfolding and aggregation and restore protein homeostasis. In addition, HSF1 orchestrates a versatile transcriptional programme that includes genes involved in repair and clearance of damaged macromolecules and maintenance of cell structure and metabolism, and provides protection against a broad range of cellular stress mediators, beyond heat shock. Here, we discuss the structure and function of the mammalian HSF1 and its regulation by post-translational modifications (phosphorylation, sumoylation and acetylation), proteasomal degradation, and small-molecule activators and inhibitors.

Detecting and Quantifying pADPr In Vivo

Poly(ADP-ribose) polymerases (PARP) participate in diverse biological processes contributing to cellular homeostasis or exacerbating injury. PARP catalyzes the addition of ADP-ribose molecules (pADPr) to the target proteins, a process termed poly-ADP-ribosylation. Overactivation of PARP, as reflected by increased poly-ADP-ribosylation, accumulation of pADPr-modified proteins or free pADPr, contributes to depletion of NAD⁺ and mitochondrial dysfunction, potentially leading to cell death. Since PARP overactivation and increases in free pADPr have been identified as key contributors to the pathobiology of many diseases, monitoring PARP-1 activation by detecting and quantifying pADPr may provide valuable mechanistic insights as well as facilitating therapeutic drug monitoring for PARP inhibitors.Several non-isotopic immunodetection methods for quantifying pADPr are discussed: western blotting of poly-ADP-ribosylated proteins, cellular localization of pADPr by immunohistochemistry, quantification of pADPr by enzyme-linked immunoassay and small scale two-dimensional gel electrophoresis.

The Role of Oxidative Stress in Myocardial Ischemia and Reperfusion Injury and Remodeling: Revisited

Oxidative and reductive stress are dual dynamic phases experienced by the cells undergoing adaptation towards endogenous or exogenous noxious stimulus. The former arises due to the imbalance between the reactive oxygen species production and antioxidant defenses, while the latter is due to the aberrant increase in the reducing equivalents. Mitochondrial malfunction is the common denominator arising from the aberrant functioning of the rheostat that maintains the homeostasis between oxidative and reductive stress. Recent experimental evidences suggest that the maladaptation during oxidative stress could play a pivotal role in the pathophysiology of major cardiovascular diseases such as myocardial infraction, atherosclerosis, and diabetic cardiovascular complications. In this review we have discussed the role of oxidative and reductive stress pathways in the pathogenesis of myocardial ischemia/reperfusion injury and diabetic cardiomyopathy (DCM). Furthermore, we have provided impetus for the development of subcellular organelle targeted antioxidant drug therapy for thwarting the deterioration of the failing myocardium in the aforementioned cardiovascular conditions.

Poly(ADP-ribose) polymerase 1-sirtuin 1 functional interplay regulates LPS-mediated high mobility group box 1 secretion

Pathophysiological conditions that lead to the release of the prototypic damage-associated molecular pattern molecule high mobility group box 1 (HMGB1) also result in activation of poly(ADP-ribose) polymerase 1 (PARP1; now known as ADP-ribosyl transferase 1 [ARTD1]). Persistent activation of PARP1 promotes energy failure and cell death. The role of poly(ADP-ribosyl)ation in HMGB1 release has been explored previously; however, PARP1 is a versatile enzyme and performs several other functions including cross-talk with another nicotinamide adenine dinucleotide- (NAD(+)) dependent member of the Class III histone deacetylases (HDACs), sirtuin-1 (SIRT1). Previously, it has been shown that the hyperacetylation of HMGB1 is a seminal event prior to its secretion, a process that also is dependent on HDACs. Therefore, in this study, we seek to determine if PARP1 inhibition alters LPS-mediated HMGB1 hyperacetylation and subsequent secretion due to its effect on SIRT1. We demonstrate in an in vitro model that LPS treatment leads to hyperacetylated HMGB1 with concomitant reduction in nuclear HDAC activity. Treatment with PARP1 inhibitors mitigates the LPS-mediated reduction in nuclear HDAC activity and decreases HMGB1 acetylation. By utilizing an NAD(+)-based mechanism, PARP1 inhibition increases the activity of SIRT1. Consequently, there is an increased nuclear retention and decreased extracellular secretion of HMGB1. We also demonstrate that PARP1 physically interacts with SIRT1. Further confirmation of this data was obtained in a murine model of sepsis, that is, administration of PJ-34, a specific PARP1 inhibitor, led to decreased serum HMGB1 concentrations in mice subjected to cecal ligation and puncture (CLP) as compared with untreated mice. In conclusion, our study provides new insights in understanding the molecular mechanisms of HMGB1 secretion in sepsis.

Modeling the intra- and extracellular cytokine signaling pathway under heat stroke in the liver

Heat stroke (HS) is a life-threatening illness induced by prolonged exposure to a hot environment that causes central nervous system abnormalities and severe hyperthermia. Current data suggest that the pathophysiological responses to heat stroke may not only be due to the immediate effects of heat exposure per se but also the result of a systemic inflammatory response syndrome (SIRS). The observation that pro- (e.g., IL-1) and anti-inflammatory (e.g., IL-10) cytokines are elevated concomitantly during recovery suggests a complex network of interactions involved in the manifestation of heat-induced SIRS. In this study, we measured a set of circulating cytokine/soluble cytokine receptor proteins and liver cytokine and receptor mRNA accumulation in wild-type and tumor necrosis factor (TNF) receptor knockout mice to assess the effect of neutralization of TNF signaling on the SIRS following HS. Using a systems approach, we developed a computational model describing dynamic changes (intra- and extracellular events) in the cytokine signaling pathways in response to HS that was fitted to novel genomic (liver mRNA accumulation) and proteomic (circulating cytokines and receptors) data using global optimization. The model allows integration of relevant biological knowledge and formulation of new hypotheses regarding the molecular mechanisms behind the complex etiology of HS that may serve as future therapeutic targets. Moreover, using our unique modeling framework, we explored cytokine signaling pathways with three in silico experiments (e.g. by simulating different heat insult scenarios and responses in cytokine knockout strains in silico).

Increased PARP-1 levels in nuclear matrix isolated from heat shock treated rat liver

Poly(ADP-ribose) polymerase-1 (PARP-1), a chromatin-associated enzyme that catalyzes the NAD+-dependent addition of ADP-ribose polymers onto a variety of nuclear proteins, has been shown to be associated with the nuclear matrix. PARP-1 levels in the nuclear matrix vary depending on the matrix isolation method used. The nuclear matrix appears to be the most thermosensitive nuclear structure during heat shock. Here we provide evidence for the extensive translocation of PARP-1 from chromatin to the nuclear matrix during heat shock. This translocation is accompanied by inhibition of PARP activity in the nucleus and elevation of PARP activity in the nuclear matrix. Our data suggest that thermal destabilization of the nuclear matrix is less likely to contribute to the translocation of PARP-1 to the nuclear matrix.

Antioxidant N-acetyl cysteine reverses cigarette smoke-induced myocardial infarction by inhibiting inflammation and oxidative stress in a rat model

The contribution of chronic tobacco exposure in determining post-myocardial infarction (MI) left ventricular (LV) remodeling and possible therapeutic strategies has not been investigated systematically. In this small animal investigation, we demonstrate that chronic tobacco smoke exposure leading up to acute MI in rats is associated with greater histological extent of myocardial necrosis and consequent worse LV function. These findings are associated with increased transcriptomic expression of pro-inflammatory cytokines, tissue repair molecules and markers of oxidative stress in the myocardium. The results demonstrate that an N-acetyl cysteine (NAC) treatment significantly reduced tobacco-exposed induced infarct size and percent fractional shortening. A significantly increased LV end-systolic diameter was observed in tobacco-exposed sham compared to tobacco-naïve sham (4.92±0.41 vs 3.45±0.33; P<0.05), and tobacco-exposed MI compared to tobacco-naïve MI (8.24±0.3 vs 6.1±0.49; P<0.01) rats. Decreased intracardiac mRNA expression of the markers of inflammation, tissue repair and oxidative stress and circulating levels of pro-inflammatory cytokines accompanied these positive effects of NAC. The treatment of tobacco-exposed MI rats with NAC resulted in significantly increased levels of intracardiac mRNA expression of antioxidants, including superoxide dismutase, thioredoxin and nuclear factor-E2-related factor 2, as well as circulating levels of glutathione (7±0.12 vs 10±0.18; P≤0.001), where the levels were almost identical to the tobacco-naïve sham rats. These findings identify a novel post-infarction therapy for amelioration of the adverse effects of tobacco exposure on the infracted myocardium and advocate the use of dietary supplement antioxidants for habitual smokers to prevent and reverse cardiovascular adverse effects in the absence of successful achievement of cessation of smoking.

Small interfering RNA mediated Poly (ADP-ribose) Polymerase-1 inhibition upregulates the heat shock response in a murine fibroblast cell line

Poly (ADP-ribose) polymerase-1 (PARP-1) is a highly conserved multifunctional enzyme, and its catalytic activity is stimulated by DNA breaks. The activation of PARP-1 and subsequent depletion of nicotinamide adenine dinucleotide (NAD⁺) and adenosine triphosphate (ATP) contributes to significant cytotoxicity in inflammation of various etiologies. On the contrary, induction of heat shock response and production of heat shock protein 70 (HSP-70) is a cytoprotective defense mechanism in inflammation. Recent data suggests that PARP-1 modulates the expression of a number of cellular proteins at the transcriptional level. In this study, small interfering RNA (siRNA) mediated PARP-1 knockdown in murine wild-type fibroblasts augmented heat shock response as compared to untreated cells (as evaluated by quantitative analysis of HSP-70 mRNA and HSP-70 protein expression). These events were associated with increased DNA binding of the heat shock factor-1 (HSF-1), the major transcription factor of the heat shock response. Co-immunoprecipitation experiments in nuclear extracts of the wild type cells demonstrated that PARP-1directly interacted with HSF-1. These data demonstrate that, in wild type fibroblasts, PARP-1 plays a pivotal role in modulating the heat shock response both through direct interaction with HSF-1 and poly (ADP-ribosylation).

Detecting and quantifying pADPr in vivo

Poly(ADP-ribose) polymerases (PARP) participate in diverse biological processes contributing to cellular homeostasis or exacerbating injury. PARP catalyzes the addition of ADP-ribose molecules (pADPr) to the target proteins, a process termed poly-ADP-ribosylation. Overactivation of PARP, as reflected by increased poly-ADP-ribosylation, accumulation of pADPr-modified proteins or free pADPr, contributes to the depletion of NAD(+) and mitochondrial dysfunction, potentially leading to cell death via apoptosis or necrosis. Since PARP over-activation has been identified as a key contributor to the pathobiology of many diseases, monitoring PARP 1 activation by detecting and quantifying pADPr may provide valuable mechanistic insights as well as facilitating therapeutic drug monitoring for PARP inhibitors.Several non-isotopic immunodetection methods for quantifying pADPr are discussed: western blotting of poly-ADP-ribosylated proteins, cellular localization of pADPr by immunohistochemistry, quantification of pADPr by enzyme-linked immunoassay and small-scale two-dimensional gel electrophoresis.

Inhibition of acute pulmonary and systemic inflammation by 1,7-dimethylxanthine

The nuclear enzyme poly(ADP-ribose) polymerse-1 (PARP-1) has previously been reported to play an important role in lipopolysaccharide (LPS)-induced pulmonary inflammation and is highly activated in COPD patients. In the present study, the anti-inflammatory efficacy of a previously identified poly(ADP-ribose) polymerase-1 (PARP-1) inhibiting caffeine metabolite, 1,7-dimethylxanthine, was both in vivo as well as ex vivo evaluated. Orally administered 1,7-dimethylxanthine significantly attenuated lung myeloperoxidase-levels, transcription of IL-6, TNF-alpha, MIP1alpha and MIP2 genes as well as PAR-polymer formation in a mouse model of intratracheally LPS-induced acute pulmonary inflammation. Serum amyloid P component and plasma IL-6 were also lowered in 1,7-dimethylxanthine treated mice, indicating a reduced systemic inflammatory response. In addition, at 24h after LPS administration anti-inflammatory effects of 1,7-dimethylxanthine appeared more pronounced than those of the orally administered PARP-1 inhibitor 3-aminobenzamide. In the second model, in blood of COPD-patients and healthy controls ex vivo pre-incubated with a physiological concentration of 1,7-dimethylxanthine (10microM), LPS-induced production of the cytokines IL-6 and TNF-alpha was significantly suppressed. 1,7-Dimethylxanthine exerts anti-inflammatory effects, both in vivo mouse as well as ex vivo human. These results suggest that the PARP-1 inhibiting caffeine metabolite 1,7-dimethylxanthine may have therapeutic potential in pulmonary inflammatory diseases such as COPD.

Angiotensin II promotes poly(ADP-ribosyl)ation of c-Jun/c-Fos in cardiac fibroblasts

Although c-Jun/c-Fos (activator protein 1, AP1) contributes importantly to Ang II-induced cardiac fibrosis through induction of extracellular matrix protein over-expression in cardiac fibroblasts, the mechanism by which Ang II promotes c-Jun/c-Fos transactivation remains unclear. In this study, we demonstrated that c-Fos and c-Jun were poly(ADP-ribosyl)ated in cultured cardiac fibroblasts. Southwestern blot and EMSA assays showed that incubation of nuclear extracts with NAD(+) and active DNA increased the basal DNA binding activities of c-Jun (31.0+/-1.0%, P<0.01) and AP1 (14.2+/-3.1%, P<0.01); incubation of recombinant c-Fos or/and c-Jun with PARP-1, NAD(+) and active DNA increased the basal DNA binding activities of c-Jun (48.3+/-4.2%, P<0.01) and AP1 (21.2+/-1.5%, P<0.01). Treatment with Ang II promoted PARP-1 activation and enhanced poly(ADP-ribosyl)ation of c-Fos (14.1+1.1%, P<0.01) and c-Jun (15.5+/-5.6%, P<0.01). Ang II also increased the basal DNA binding activities of c-Jun (13.5+/-2.4%, P<0.01) and AP1 (18.7+/-3.5%, P<0.01) in cultured cells. Inhibition of PARP-1 by PJ34 or siRNA effectively prevented Ang II-induced increases in the DNA binding of c-Jun and AP1, and decreased AP1-driven transcription (including collagen Ialpha1 and IIIalpha1, MMP-9 and TIMP-1). This study illustrated that c-Jun and c-Fos were poly(ADP-ribosyl)ated by PARP-1, and poly(ADP-ribosyl)ation enhanced the DNA binding of AP1. Ang II promoted poly(ADP-ribosyl)ation of c-Jun and c-Fos through activation of PARP-1 and, subsequently, enhanced AP1-driven transcription in cardiac fibroblasts.

Poly(ADP-ribose) polymerase-1 inhibition increases expression of heat shock proteins and attenuates heat stroke-induced liver injury

OBJECTIVE

Heat stroke is a life-threatening illness characterized by an increased core body temperature as a result of exposure to high ambient temperature. Despite advances in supportive care, heat stroke is often fatal, and no specific and effective therapies exist. The pathophysiological responses to heat stroke involve a systemic inflammatory response and a disseminated intravascular coagulation in the host, which lead to a multiorgan dysfunction syndrome. Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear DNA-binding protein that has been shown to play a relevant role in cell necrosis and organ failure in various diseases associated with inflammation. Therefore, we set out to investigate whether inhibition of PARP activity might affect the heat stroke-induced injury.

DESIGN

Controlled animal study.

SETTING

Research laboratory of an academic institution.

SUBJECTS

PARP-1-deficient mice (Parp-1(-/-)) and wild-type mice (C57BL/6J).

INTERVENTIONS

Wild-type mice untreated or treated with either PJ34 or 3-AB, two generic PARP inhibitors, and Parp-1(-/-) mice were subjected to heat exposure as a model to study heat stroke.

MEASUREMENTS AND MAIN RESULTS

We measured rectal temperature, serum interleukin-1beta and interleukin-6, liver histology, and heat shock proteins expression. We found that the heat stroke-induced injury was attenuated in mice lacking PARP-1 and was markedly reduced in wild-type mice treated with PARP inhibitors. Interestingly, heat-induced expression of heat shock proteins 27 and 70 was boosted after PARP inhibition. Indeed, PARP inhibition increased expression of heat shock proteins 27 and 70 even in the absence of heat exposure. Accordingly, PARP inhibition increased thermal tolerance that may contribute to attenuate the clinical effects of heat stroke, resulting in increased survival.

CONCLUSIONS

Our results find a new protective function of PARP inhibitors and support their potential therapeutic application in the treatment of heat stroke.

PARP1 is required for adhesion molecule expression in atherogenesis

AIMS

Atherosclerosis is the leading cause of death in Western societies and a chronic inflammatory disease. However, the key mediators linking recruitment of inflammatory cells to atherogenesis remain poorly defined. Poly(ADP-ribose) polymerase 1 (PARP1) is a nuclear enzyme, which plays a role in acute inflammatory diseases.

METHODS AND RESULTS

In order to test the role of PARP in atherogenesis, we applied chronic pharmacological PARP inhibition or genetic PARP1 deletion in atherosclerosis-prone apolipoprotein E-deficient mice and measured plaque formation, adhesion molecules, and features of plaque vulnerability. After 12 weeks of high-cholesterol diet, plaque formation in male apolipoprotein E-deficient mice was decreased by chronic inhibition of enzymatic PARP activity or genetic deletion of PARP1 by 46 or 51%, respectively (P < 0.05, n >or= 9). PARP inhibition or PARP1 deletion reduced PARP activity and diminished expression of inducible nitric oxide synthase, vascular cell adhesion molecule-1, and P- and E-selectin. Furthermore, chronic PARP inhibition reduced plaque macrophage (CD68) and T-cell infiltration (CD3), increased fibrous cap thickness, and decreased necrotic core size and cell death (P < 0.05, n >or= 6).

CONCLUSION

Our data provide pharmacological and genetic evidence that endogenous PARP1 is required for atherogenesis in vivo by increasing adhesion molecules with endothelial activation, enhancing inflammation, and inducing features of plaque vulnerability. Thus, inhibition of PARP1 may represent a promising therapeutic target in atherosclerosis.

Effect of PJ-34 PARP-Inhibitor on Rat Liver Microcirculation and Antioxidant Status

BACKGROUND

Ischemia-reperfusion (I-R) injury during liver resection leads to the production of toxic free radicals and oxidants that influence the microcirculation. DNA single-strand breaks can be induced by these reactive species. In response to excessive DNA damage, PARP [poly(ADP-ribose) polymerase] becomes overactivated, which can lead to cellular ATP depletion and cell death. The aim of our study was to evaluate whether PARP is expressed in post-ischemic liver, and to examine the effect of the administration of PJ-34 PARP inhibitor on liver function, histopathology, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) reaction, and the oxidative state of the liver after injury.

METHODS

Male Wistar rats (weighing 250 g) underwent 60 min of normothermic, segmental liver ischemia followed by 30 min of reperfusion. The animals (n = 45) were divided into three groups: sham operated; I-R (control) treated with saline; and PJ-34 pre-treated (10 mg/kg i.v.). Hepatic microcirculation was monitored by a laser Doppler flowmeter. The reperfusion was characterized as the integral of the reperfusion area (RA) and the maximal plateau (PM). Histological alterations, TUNEL-reaction, serum, and liver tissue antioxidant levels, as well as serum ALT and AST levels were measured.

RESULTS

Upon reperfusion, the PJ-34 group had significantly (P < 0.05) higher flow rates than control groups (PM(PJ-34): 58%, PM(control): 37%; RA(PJ-34.): 48%, RA(control): 25%). At the end of the 30 min reperfusion, PJ-34 resulted in significantly (P < 0.05) lower serum ALT and AST levels and chemiluminescent intensity (free radicals) of the liver. The liver's free SH-group concentration and H-donor ability of the plasma was elevated in the PARP-inhibitor treated group. Positive staining for TUNEL, after PJ-34 pre-treatment was significantly increased (P < 0.05); in contrast, the control tissues were less positively stained for TUNEL but necrotic tissue was abundant.

CONCLUSION

PARP plays a pathogenetic role in the deterioration of the hepatic microcirculation and promotes hepatocellular necrosis in liver reperfusion injury.

Poly(ADP-ribosyl)ation regulates heat shock factor-1 activity and the heat shock response in murine fibroblasts

Poly(ADP-ribose) polymerase-1 (PARP-1)-dependent poly(ADP-ribose) formation is emerging as a key regulator of transcriptional regulation, even though the targets and underlying molecular mechanisms have not yet been clearly identified. In this study, we gathered information on the role of PARP-1 activity in the heat shock response of mouse fibroblasts. We show that DNA binding of heat shock factor (HSF)-1 was impaired by PARP-1 activity in cellular extracts, and was higher in PARP-1(-/-) than in PARP-1+/+ cells. No evidence for HSF-1 poly(ADP-ribosyl)ation or PARP-1 interaction was found, but a poly(ADP-ribose) binding motif was identified in the transcription factor amino acid sequence. Consistent with data on HSF-1, the expression of heat-shock protein (HSP)-70 and HSP-27 was facilitated in cells lacking PARP-1. Thermosensitivity, however, was higher in PARP-1(-/-) than in PARP-1+/+ cells. Accordingly, we report that heat-shocked PARP-1 null fibroblasts showed an increased activation of proapoptotic JNK and decreased transcriptional efficiency of prosurvival NF-kappaB compared with wild-type counterparts. The data indicate that poly(ADP-ribosyl)ation finely regulates HSF-1 activity, and emphasize the complex role of PARP-1 in the heat-shock response of mammalian cells.

Cardiac molecular signaling after burn trauma

Research using mammalian burn models has defined significant cardiac deficits after burn injury. The physiologic response to burn and burn complicated by sepsis, including the cardiac dysfunction associated with these insults, remains a very complex physiologic process which, despite active study, remains unclear. The well-characterized inflammatory mediators such as tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 continue to play an active role in mediating cardiac dysfunction. However, perhaps of greater interest are the late mediators, high mobility group box 1 and macrophage migration inhibitory factor, because they offer a very realistic window for therapeutic intervention for controlling the inflammatory response. In addition, several other mediators of cardiac dysfunction have been identified and include the heat shock proteins, apoptosis, and the inflammatory caspases. These new mediators provide opportunities for therapeutic intervention, but further research is needed to clarify the importance of their mechanisms of action and the complex interactions between these various signaling pathways.

Role of poly(ADP-ribose) polymerase 1 (PARP-1) in cardiovascular diseases: the therapeutic potential of PARP inhibitors

Accumulating evidence suggests that the reactive oxygen and nitrogen species are generated in cardiomyocytes and endothelial cells during myocardial ischemia/reperfusion injury, various forms of heart failure or cardiomyopathies, circulatory shock, cardiovascular aging, diabetic complications, myocardial hypertrophy, atherosclerosis, and vascular remodeling following injury. These reactive species induce oxidative DNA damage and consequent activation of the nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP-1), the most abundant isoform of the PARP enzyme family. PARP overactivation, on the one hand, depletes its substrate, NAD+, slowing the rate of glycolysis, electron transport, and ATP formation, eventually leading to the functional impairment or death of the endothelial cells and cardiomyocytes. On the other hand, PARP activation modulates important inflammatory pathways, and PARP-1 activity can also be modulated by several endogenous factors such as various kinases, purines, vitamin D, thyroid hormones, polyamines, and estrogens, just to mention a few. Recent studies have demonstrated that pharmacological inhibition of PARP provides significant benefits in animal models of cardiovascular disorders, and novel PARP inhibitors have entered clinical development for various cardiovascular indications. Because PARP inhibitors can enhance the effect of anticancer drugs and decrease angiogenesis, their therapeutic potential is also being explored for cancer treatment. This review discusses the therapeutic effects of PARP inhibitors in myocardial ischemia/reperfusion injury, various forms of heart failure, cardiomyopathies, circulatory shock, cardiovascular aging, diabetic cardiovascular complications, myocardial hypertrophy, atherosclerosis, vascular remodeling following injury, angiogenesis, and also summarizes our knowledge obtained from the use of PARP-1 knockout mice in the various preclinical models of cardiovascular diseases.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Poly(ADP-ribose) polymerase-1 hyperactivation and impairment of mitochondrial respiratory chain complex I function in reperfused mouse hearts

Poly(ADP-ribose) polymerase-1 (PARP-1), the most abundant member of the PARP family, is a nuclear enzyme that catalyzes ADP-ribose transfer from NAD+ to specific acceptor proteins in response to DNA damage. Excessive PARP-1 activation is an important cause of infarction and contractile dysfunction in heart tissue during interruptions of blood flow. The mechanisms by which PARP-1 inhibition and disruption dramatically improve metabolic recovery and reduce oxidative stress during cardiac reperfusion have not been fully explored. We developed a mouse heart experimental protocol to test the hypothesis that mitochondrial respiratory complex I is a downstream mediator of beneficial effects of PARP-1 inhibition or disruption. Pharmacological inhibition of PARP-1 activity produced no deterioration of hemodynamic function in C57BL/6 mouse hearts. Hearts from PARP-1 knockout mice also exhibited normal baseline contractility. Prolonged ischemia-reperfusion produced a selective defect in complex I function distal to the NADH dehydrogenase component. PARP-1 inhibition and PARP-1 gene disruption conferred equivalent protection against mitochondrial complex I injury and were strongly associated with improvement in myocardial energetics, contractility, and tissue viability. Interestingly, ischemic preconditioning abolished cardioprotection stimulated by PARP-1 gene disruption. Treatment with the antioxidant N-(2-mercaptopropionyl)-glycine or xanthine oxidase inhibitor allopurinol restored the function of preconditioned PARP-1 knockout hearts. This investigation establishes a strong association between PARP-1 hyperactivity and mitochondrial complex I dysfunction in cardiac myocytes. Our findings advance understanding of metabolic regulation in myocardium and identify potential therapeutic targets for prevention and treatment of ischemic heart disease.

Caffeine metabolites are inhibitors of the nuclear enzyme poly(ADP-ribose)polymerase-1 at physiological concentrations

The activity of the nuclear enzyme poly(ADP-ribose)polymerase-1 (E.C.2.4.2.30), which is highly activated by DNA strand breaks, is associated with the pathophysiology of both acute as well as chronic inflammatory diseases. PARP-1 overactivation and the subsequent extensive turnover of its substrate NAD+ put a large demand on mitochondrial ATP-production. Furthermore, due to its reported role in NF-kappaB and AP-1 mediated production of pro-inflammatory cytokines, PARP-1 is considered an interesting target in the treatment of these diseases. In this study the PARP-1 inhibiting capacity of caffeine and several metabolites as well as other (methyl)xanthines was tested using an ELISA-assay with purified human PARP-1. Caffeine itself showed only weak PARP-1 inhibiting activity, whereas the caffeine metabolites 1,7-dimethylxanthine, 3-methylxanthine and 1-methylxanthine, as well as theobromine and theophylline showed significant PARP-1 inhibiting activity. Further evaluation of these compounds in H2O2-treated A549 lung epithelial and RF24 vascular endothelial cells revealed that the decrease in NAD+-levels as well as the formation of the poly(ADP-ribose)polymer was significantly prevented by the major caffeine metabolite 1,7-dimethylxanthine. Furthermore, H2O2-induced necrosis could be prevented by a high dose of 1,7-dimethylxanthine. Finally, antioxidant effects of the methylxanthines could be ruled out with ESR and measurement of the TEAC. Concluding, caffeine metabolites are inhibitors of PARP-1 and the major caffeine metabolite 1,7-dimethylxanthine has significant PARP-1 inhibiting activity in cultured epithelial and endothelial cells at physiological concentrations. This inhibition could have important implications for nutritional treatment of acute and chronic inflammatory pathologies, like prevention of ischemia-reperfusion injury or vascular complications in diabetes.

Anti-inflammatory effects of PJ34, a poly(ADP-ribose) polymerase inhibitor, in transient focal cerebral ischemia in mice

BACKGROUND AND PURPOSE

Activation of poly(ADP-ribose) polymerase (PARP) is deleterious during cerebral ischemia. We assessed the influence of PARP activation induced by cerebral ischemia on the synthesis of proinflammatory mediators including the cytokines, tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) and the adhesion molecules, E-selectin and intercellular adhesion molecule-1 (ICAM-1).

EXPERIMENTAL APPROACH

Ischemia was induced by intravascular occlusion of the left middle cerebral artery for 1 h in male Swiss mice anaesthetized with ketamine and xylazine. The PARP inhibitor PJ34 (1.25-25 mg kg(-1)) was administered intraperitoneally 15 min before and 4 hours after, the onset of ischemia. Animals were killed 6 h or 24 h after ischemia and cerebral tissue removed for analysis.

KEY RESULTS

Ischemia increased TNF-alpha protein in cerebral tissue at 6 and 24 h after ischemia. All doses of PJ34 blocked the increase in TNF-alpha at 6 h and 25 mg kg(-1) PJ34 had a sustained effect for up to 24 h. Quantitative real time polymerase chain reaction showed that PJ34 (25 mg kg(-1)) reduced the increase in TNF-alpha mRNA by 70% at 6 h. PJ34 also prevented the increase in mRNAs encoding IL-6 (-41%), E-selectin (-81%) and ICAM-1 (-54%). PJ34 (25 mg kg(-1)) reduced the infarct volume (-26%) and improved neurological deficit, 24 h after ischemia.

CONCLUSIONS AND IMPLICATIONS

PJ34 inhibited the increase in the mRNAs of four inflammatory mediators, caused by cerebral ischemia. The contribution of this effect of PJ34 to neuroprotection remains to be clarified.

Earliest changes in the left ventricular transcriptome postmyocardial infarction

We report a genome-wide survey of early responses of the mouse heart transcriptome to acute myocardial infarction (AMI). For three regions of the left ventricle (LV), namely, ischemic/infarcted tissue (IF), the surviving LV free wall (FW), and the interventricular septum (IVS), 36,899 transcripts were assayed at six time points from 15 min to 48 h post-AMI in both AMI and sham surgery mice. For each transcript, temporal expression patterns were systematically compared between AMI and sham groups, which identified 515 AMI-responsive genes in IF tissue, 35 in the FW, 7 in the IVS, with three genes induced in all three regions. Using the literature, we assigned functional annotations to all 519 nonredundant AMI-induced genes and present two testable models for central signaling pathways induced early post-AMI. First, the early induction of 15 genes involved in assembly and activation of the activator protein-1 (AP-1) family of transcription factors implicates AP-1 as a dominant regulator of earliest post-ischemic molecular events. Second, dramatic increases in transcripts for arginase 1 (ARG1), the enzymes of polyamine biosynthesis, and protein inhibitor of nitric oxide synthase (NOS) activity indicate that NO production may be regulated, in part, by inhibition of NOS and coordinate depletion of the NOS substrate, L: -arginine. ARG1: was the single-most highly induced transcript in the database (121-fold in IF region) and its induction in heart has not been previously reported.

Poly(ADP-ribose) accumulation and enhancement of postischemic brain damage in 110-kDa poly(ADP-ribose) glycohydrolase null mice

Poly(ADP-ribose) (PAR) is a polymer synthesized by poly(ADP-ribose) polymerases (PARPs) and metabolized into free adenosine diphosphate (ADP)-ribose units by poly(ADP-ribose) glycohydrolase (PARG). Perturbations in PAR synthesis have been shown to play a key role in brain disorders including postischemic brain damage. A single parg gene but two PARG isoforms (110 and 60 kDa) have been detected in mouse cells. Complete suppression of parg gene causes early embryonic lethality, whereas mice selectively lacking the 110 kDa PARG isoform (PARG(110)(-/-)) develop normally. We used PARG(110)(-/-) mice to evaluate the importance of PAR catabolism to postischemic brain damage. Poly(ADP-ribose) contents were higher in the brain tissue of PARG(110)(-/-) than PARG(110)(+/+) mice, both under basal conditions and after PARP activation. Distal middle cerebral artery occlusion caused higher increase of brain PAR levels and larger infarct volumes in PARG(110)(-/-) mice than in wild-type counterparts. Of note, the brain of PARG(110)(-/-) mice showed reduced heat-shock protein (HSP)-70 and increased cyclooxygenase-2 expression under both control and ischemic conditions. No differences were detected in brain expression/activation of procaspase-3, PARP-1, Akt, HSP-25 and interleukin-1beta. Our findings show that PAR accumulation worsens ischemic brain injury, and highlight the therapeutic potential of strategies capable of maintaining PAR homeostasis.

Regulation of the poly(ADP-ribose) polymerase-1 gene expression by the transcription factors Sp1 and Sp3 is under the influence of cell density in primary cultured cells

PARP-1 [poly(ADP-ribose) polymerase-1) is a nuclear enzyme that is involved in several cellular functions, including DNA repair, DNA transcription, carcinogenesis and apoptosis. The activity directed by the PARP-1 gene promoter is mainly dictated through its recognition by the transcription factors Sp1 and Sp3 (where Sp is specificity protein). In the present study, we investigated whether (i) both PARP-1 expression and PARP-1 enzymatic activity are under the influence of cell density in primary cultured cells, and (ii) whether its pattern of expression is co-ordinated with that of Sp1/Sp3 at varying cell densities and upon cell passages. All types of cultured cells expressed PARP-1 in Western blot when grown to sub-confluence. However, a dramatic reduction was observed at post-confluence. Similarly, high levels of Sp1/Sp3 were observed by both Western blot and EMSAs (electrophoretic mobility-shift assays) in sub-confluent,but not post-confluent, cells. Consistent with these results, the promoter of the rPARP-1 (rat PARP-1) gene directed high levels of activity in sub-confluent, but not confluent, cells upon transfection of various CAT (chloramphenicol acetyltransferase)-rPARP-1 promoter constructs into cultured cells. The positive regulatory influence of Sp1 was not solely exerted on the rPARP-1 promoter constructs, as inhibition of endogenous Sp1 expression in HDKs(human dermal keratinocytes) through the transfection of Sp1 RNAi (RNA interference) considerably reduced endogenous hPARP-1 (human PARP-1) expression as well. The reduction in PARP-1 protein expression as cells reached confluence also translated into a corresponding reduction in PARP-1 activity. In addition, expression of both Sp1/Sp3, as well as that of PARP-1,was dramatically reduced as cells were passaged in culture and progressed towards irreversible terminal differentiation. PARP-1 gene expression therefore appears to be co-ordinated with that of Sp1 and Sp3 in primary cultured cells, suggesting that PARP-1 may play some important functions during the proliferative burst that characterizes wound healing.

Epigallocatechin, a green tea polyphenol, attenuates myocardial ischemia reperfusion injury in rats

Epigallocatechin-3-gallate (EGCG) is the most prominent catechin in green tea. EGCG has been shown to modulate numerous molecular targets in the setting of inflammation and cancer. These molecular targets have also been demonstrated to be important participants in reperfusion injury, hence this study examines the effects of EGCG in myocardial reperfusion injury. Male Wistar rats were subjected to myocardial ischemia (30 min) and reperfusion (up to 2 h). Rats were treated with EGCG (10 mg/kg intravenously) or with vehicle at the end of the ischemia period followed by a continuous infusion (EGCG 10 mg/kg/h) during the reperfusion period. In vehicle-treated rats, extensive myocardial injury was associated with tissue neutrophil infiltration as evaluated by myeloperoxidase activity, and elevated levels of plasma creatine phosphokinase. Vehicle-treated rats also demonstrated increased plasma levels of interleukin-6. These events were associated with cytosol degradation of inhibitor kappaB-alpha, activation of IkappaB kinase, phosphorylation of c-Jun, and subsequent activation of nuclear factor-kappaB and activator protein-1 in the infarcted heart. In vivo treatment with EGCG reduced myocardial damage and myeloperoxidase activity. Plasma IL-6 and creatine phosphokinase levels were decreased after EGCG administration. This beneficial effect of EGCG was associated with reduction of nuclear factor-kB and activator protein-1 DNA binding. The results of this study suggest that EGCG is beneficial for the treatment of reperfusion-induced myocardial damage by inhibition of the NF-kappaB and AP-1 pathway.

Nicotinamide blocks N-methyl-N-nitrosourea-induced photoreceptor cell apoptosis in rats through poly (ADP-ribose) polymerase activity and Jun N-terminal kinase/activator protein-1 pathway inhibition

Nicotinamide (NAM) blocks N-methyl-N-nitrosourea (MNU)-induced photoreceptor cell apoptosis in rats, though the underlying molecular mechanisms remain unclear. Activation of the nuclear enzyme poly (ADP-ribose) polymerase (PARP) in response to DNA damage plays a pivotal role in apoptosis. Thus, the role of NAM in the regulation of PARP and Jun N-terminal kinase (JNK)/activator protein-1 (AP-1) was investigated by Western blot analyses. During 7 days after the intraperitoneal injection of MNU (60 mg/kg), rat retinas exhibited DNA fragmentation characteristic of apoptosis and activation of PARP, phosphorylation of JNK and c-Jun, induction of AP-1 (c-Jun and c-Fos) and Bax, as well as photoreceptor cell loss. However, when NAM (1000 mg/kg, subcutaneously) was given immediately after MNU, it was found that PARP activation was diminished, the phosphorylation of JNK and c-Jun was suppressed, and the induction of c-Jun, c-Fos and Bax was suppressed. This resulted in the retinal structure being protected. Therefore, NAM blocked MNU-induced photoreceptor cell apoptosis by inhibiting both PARP activity and the JNK/AP-1 signalling pathway.

Poly(ADP-ribosyl)ation and stroke

Over the past decade, poly(ADP-ribosyl)ation has emerged as a crucial event in the pathogenesis of ischemic stroke. A large body of evidence unambiguously demonstrates that activity of poly(ADP-ribose) polymerase-1 (PARP-1) significantly increases during brain ischemia, and that inhibition of this enzymatic activity affords substantial neuroprotection from ischemic brain injury. This review strictly focuses on literature on poly(ADP-ribosyl)ation and ischemic stroke, highlighting the pathogenetic role of poly(ADP-ribose) in ischemic neuronal death, and the therapeutic relevance of drugs modulating its metabolism to pharmacological treatment of cerebral ischemia.

Poly(ADP-ribosyl)ation in asthma and other lung diseases

Inhibition of poly(ADP-ribosyl)ation in oxidative stress-related pathologies has recently emerged as a very effective anti-inflammatory intervention in animal models of arthritis, colitis, diabetes and shock. Recent data from three laboratories also support the role of poly(ADP-ribose) polymerase-1 (PARP-1) activation in asthma. Similarly to other inflammatory conditions, the protective effects of PARP inhibition and the PARP-1 knock out phenotype in asthma models have been attributed to inhibition of inflammatory signal transduction (mainly via NF-kappaB) and of oxidative stress-induced cell dysfunction and tissue injury. Here I discuss the complex role of poly(ADP-ribosyl)ation in the regulation of inflammatory cell migration, chemokine and cytokine production and expression of other inflammatory mediators (inducible nitric oxide synthase, matrix metalloproteinases) in asthma. The role of PARP-1 in other oxidative stress-related lung diseases such as asbestosis, silicosis, acute respiratory distress syndrome and ischemia-reperfusion injury is also reviewed.

NF-kappaB plays a major role during the systemic and local acute inflammatory response following intestinal reperfusion injury

1 The nuclear translocation of transcription factors may be a critical factor in the intracellular pathway involved in ischaemia/reperfusion (I/R) injury. Here, we examined whether NF-kappaB and AP-1 participated in the cascade of events leading to TNF-alpha production, neutrophil recruitment, tissue injury and lethality following intestinal I/R. 2 The superior mesenteric artery (SMA) of mice was made ischaemic for 60 min followed by 30 min of reperfusion. The effects of NF-kappaB and AP-1 were studied by the administration of the thioredoxin inhibitor, MOL-294 (methyl 4-hydroxy-4-(8-methyl-1,3-dioxo-2-phenyl-2,3,5,8-tetrahydro-1H-[1,2,4]triazolo[1,2-a]pyridazin-5-yl)but-2-ynoate), and the AP-1 inhibitor, PNRI-299 (N-benzyl-2-(3-cyanophenyl)-1,3,7-trioxo-2,3,7,8-tetrahydro-1H-[1,2,4]triazolo[1,2-a]pyridazine-5-carboxamide). After I/R, there was increase of translocation of NF-kappaB, but not of AP-1, in the intestine and lungs, as assessed by a gel shift assay. 3 Treatment with MOL-294 inhibited the increase in vascular permeability, neutrophil accumulation, hemorrhage and proinflammatory cytokine levels, induced by intestinal I/R injury in the intestine. In the lungs, MOL-294 partially inhibited edema formation, TNF-alpha production, but did not alter neutrophil recruitment. 4 Treatment with MOL-294 inhibited reperfusion-associated lethality, an effect likely to be secondary to the inhibition of systemic TNF-alpha levels. PNRI-299 had no effects on the inflammatory changes or lethality induced by I/R injury. 5 Our results point to an important role for NF-kappaB in triggering endogenous proinflammatory networks during intestinal I/R injury. Inhibition of NF-kappaB prevents tissue injury and lethality, and this was associated with inhibition of TNF-alpha production and decrease in neutrophil recruitment.

Nitrosative stress and pharmacological modulation of heart failure

Dysregulation of nitric oxide (NO) and increased oxidative and nitrosative stress are implicated in the pathogenesis of heart failure. Peroxynitrite is a reactive oxidant that is produced from the reaction of nitric oxide with superoxide anion and impairs cardiovascular function through multiple mechanisms, including activation of matrix metalloproteinases (MMPs) and nuclear enzyme poly(ADP-ribose) polymerase (PARP). Recent studies suggest that the neutralization of peroxynitrite or pharmacological inhibition of MMPs and PARP are promising new approaches in the experimental therapy of various forms of myocardial injury. In this article, the role of nitrosative stress and downstream mechanisms, including activation of MMPs and PARP, in various forms of heart failure are discussed and novel emerging therapeutic strategies offered by neutralization of peroxynitrite and inhibition of MMPs and PARP in these pathophysiological conditions are reviewed.