Restoration of the endothelial function in the aortic rings of apolipoprotein E deficient mice by pharmacological inhibition of the nuclear enzyme poly(ADP-ribose) polymerase

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.

Poly (ADP-ribose) Polymerase-1 modulations in the genesis of thrombosis

Thrombosis, a coagulation disorder, occurs due to altered levels of coagulation, fibrinolytic and immune factors, which are otherwise known to maintain hemostasis in normal physiological conditions. Here, we review the direct and indirect participation of a multifunctional nuclear enzyme poly (ADP-ribose) polymerase-1 (PARP1) in the expression of key genes and cellular processes involved in thrombotic pathogenesis. PARP1 biological activities range from maintenance of genomic integrity, chromatin remodeling, base excision DNA repair, stress responses to cell death, angiogenesis and cell cycle pathways. However, under homeostatic imbalances, PARP1 activities are linked with the pathogenesis of diseases, including cancer, aging, neurological disorders, and cardiovascular diseases. Disease-associated distressed cells employ a variety of PARP-1 functions such as oxidative damage exacerbations, cellular energetics and apoptosis pathways, regulation of inflammatory mediators, promotion of endothelial dysfunction, and ERK-mediated signaling in pathogenesis. Thrombosis is one such pathogenesis that comprises exacerbation of coagulation cascade due to biochemical alterations in endothelial cells, platelet activation, overexpression of adhesion molecules, cytokines release, and leukocyte adherence. Thus, the activation of endothelial and inflammatory cells in thrombosis implicates a potential role of PARP1 activation in thrombogenesis. This review article explores the direct impact of PARP1 activation in the etiology of thrombosis and discusses PARP1-mediated endothelial dysfunction, inflammation, and epigenetic regulations in the disease manifestation. Understanding PARP1 functions associated with thrombosis may elucidate novel pathogenetic mechanisms and help in better disease management through newer therapeutic interventions targeting PARP1 activity.

DNA damage response, a double-edged sword for vascular aging

Vascular aging is a major risk factor for age-related cardiovascular diseases, which have high rates of morbidity and mortality. It is characterized by changes in the blood vessels, such as macroscopically increased vascular diameter and intima-medial thickness, chronic inflammation, vascular calcification, arterial stiffening, and atherosclerosis. DNA damage and the subsequent various DNA damage response (DDR) pathways are important causative factors of vascular aging. Deficient DDR, which may result in the accumulation of unrepaired damaged DNA or mutations, can lead to vascular aging. On the other hand, over-activation of some DDR proteins, such as poly (ADP ribose) polymerase (PARP) and ataxia telangiectasia mutated (ATM), also can enhance the process of vascular aging, suggesting that DDR can have both positive and negative effects on vascular aging. Despite the evidence reviewed in this paper, the role of DDR in vascular aging and potential therapeutic targets remain poorly understood and require further investigation.

Targeting regulated cell death in aortic aneurysm and dissection therapy

Regulated cell death (RCD) is a basic biological phenomenon associated with cell and tissue homeostasis. Recent studies have enriched our understanding of RCD, and many novel cell death types, such as ferroptosis and pyroptosis, have been discovered and defined. Aortic aneurysm and dissection (AAD) is a life-threatening condition, but the pathogenesis remains largely unclear. A series of studies have indicated that the death of smooth muscle cells, endothelial cells and inflammatory cells participates in the development of AAD and that corresponding interventions could alleviate disease progression. Many treatments against cell death have been used to impede the process of AAD in vitro and in vivo, which provides strategies to protect against this condition. In this review, we focus on various types of regulated cell death and provide a framework of their roles in AAD, and the information contributes to further exploration of the molecular mechanisms of AAD.

PARPs in lipid metabolism and related diseases

PARPs and tankyrases (TNKS) represent a family of 17 proteins. PARPs and tankyrases were originally identified as DNA repair factors, nevertheless, recent advances have shed light on their role in lipid metabolism. To date, PARP1, PARP2, PARP3, tankyrases, PARP9, PARP10, PARP14 were reported to have multi-pronged connections to lipid metabolism. The activity of PARP enzymes is fine-tuned by a set of cholesterol-based compounds as oxidized cholesterol derivatives, steroid hormones or bile acids. In turn, PARPs modulate several key processes of lipid homeostasis (lipotoxicity, fatty acid and steroid biosynthesis, lipoprotein homeostasis, fatty acid oxidation, etc.). PARPs are also cofactors of lipid-responsive nuclear receptors and transcription factors through which PARPs regulate lipid metabolism and lipid homeostasis. PARP activation often represents a disruptive signal to (lipid) metabolism, and PARP-dependent changes to lipid metabolism have pathophysiological role in the development of hyperlipidemia, obesity, alcoholic and non-alcoholic fatty liver disease, type II diabetes and its complications, atherosclerosis, cardiovascular aging and skin pathologies, just to name a few. In this synopsis we will review the evidence supporting the beneficial effects of pharmacological PARP inhibitors in these diseases/pathologies and propose repurposing PARP inhibitors already available for the treatment of various malignancies.

PARP-1 (Poly[ADP-Ribose] Polymerase 1) Inhibition Protects From Ang II (Angiotensin II)-Induced Abdominal Aortic Aneurysm in Mice

Abdominal aortic aneurysm (AAA) is a common vascular degenerative disease. PARP-1 (poly[ADP-ribose] polymerase 1) is a nuclear enzyme, which plays a critical role in vascular diseases. We hypothesized that PARP-1 inhibition might have protective effects on AAA. In vivo, Ang II (angiotensin II) was continuously infused by a micropump for 28 days to induce AAA in mice. In vitro, aortic endothelial cells and smooth muscle cells were stimulated by Ang II for 24 hours. Ang II infusion increased PARP-1 expression and activity and successfully induced AAA formation partly with a hemorrhage in ApoE^-/- mice. Genetic deletion of PARP-1 markedly reduced the AAA incidence, abdominal aortic diameter, macrophage infiltration, ICAM-1 (intercellular adhesion molecule 1) and VCAM-1 (vascular adhesion molecule 1) expression, and MMP (matrix metalloproteinase) expression, as well as MMP activity; but increased smooth muscle cells content and collagens expression in AAA. PARP-1 inhibition by PJ-34 also exerted a protective effect on AAA in mice. In aortic endothelial cells, Ang II-induced oxidative stress and DNA damage, resulting in increased PARP-1 expression and activity. Compared with the control, Ang II increased TNF-α (tumor necrosis factor α) and IL-6 (interleukin-6) secretions, ICAM-1 expression and THP-1 (human acute monocytic leukemia cell line) cells adhesion, while PARP-1 inhibition by siRNA reduced the inflammatory response probably through inhibition of the phosphorylation of ERK (extracellular signal-regulated kinase), NF-κB (nuclear factor-κB), and Akt signaling pathways. In smooth muscle cells, Ang II promoted cell migration, proliferation, and apoptosis, reduced collagens expression, but increased MMPs expression, while PARP-1 deletion alleviated these effects partly by reducing NF-κB-targeted MMP-9 expression. PARP-1 inhibition might be a feasible strategy for the treatment of AAA.

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.

Poly(ADP-ribose) polymerase 1 deficiency increases nitric oxide production and attenuates aortic atherogenesis through downregulation of arginase II

Poly (ADP-ribose) polymerase (PARP) plays an important role in endothelial dysfunction, leading to atherogenesis and vascular-related diseases. However, whether PARP regulates nitric oxide (NO), a key regulator of endothelial function, is unclear so far. We investigated whether inhibition of PARP-1, the most abundant PARP isoform, prevents atherogenesis by regulating NO production and tried to elucidate the possible mechanisms involved in this phenomenon. In apolipoprotein E-deficient (apoE^-/- ) mice fed a high-cholesterol diet for 12 weeks, PARP-1 inhibition via treatment with 3,4-dihydro-54-(1-piperindinyl) butoxy-1(2H)-isoquinoline (DPQ) or PARP-1 gene knockout reduced aortic atherosclerotic plaque areas (49% and 46%, respectively). Both the groups showed restored NO production in mouse aortas with reduced arginase II (Arg II) expression compared to that in the controls. In mouse peritoneal macrophages and aortic endothelial cells (MAECs), PARP-1 knockout resulted in lowered Arg II expression. Moreover, phosphorylation of endothelial NO synthase (eNOS) was preserved in the aortas and MAECs when PARP-1 was inhibited. Reduced NO production in vitro due to PARP-1 deficiency could be restored by treating the MAECs with oxidized low-density lipoprotein treatment, but this effect could not be achieved with peritoneal macrophages, which was likely due to a reduction in the expression of induced NOS expression. Our findings indicate that PARP-1 inhibition may attenuate atherogenesis by restoring NO production in endothelial cells and thus by reducing Arg II expression and consequently arginase the activity.

DNA damage-dependent mechanisms of ageing and disease in the macro- and microvasculature

A decline in the function of the macro- and micro-vasculature occurs with ageing. DNA damage also accumulates with ageing, and thus DNA damage and repair have important roles in physiological ageing. Considerable evidence also supports a crucial role for DNA damage in the development and progression of macrovascular disease such as atherosclerosis. These findings support the concept that prolonged exposure to risk factors is a major stimulus for DNA damage within the vasculature, in part via the generation of reactive oxygen species. Genomic instability can directly affect vascular cellular function, leading to cell cycle arrest, apoptosis and premature vascular cell senescence. In contrast, the study of age-related impaired function and DNA damage mechanisms in the microvasculature is limited, although ageing is associated with microvessel endothelial dysfunction. This review examines current knowledge on the role of DNA damage and DNA repair systems in macrovascular disease such as atherosclerosis and microvascular disease. We also discuss the cellular responses to DNA damage to identify possible strategies for prevention and treatment.

Deletion of PARP-2 induces hepatic cholesterol accumulation and decrease in HDL levels

Poly(ADP-ribose) polymerase-2 (PARP-2) is acknowledged as a DNA repair enzyme. However, recent investigations have attributed unique roles to PARP-2 in metabolic regulation in the liver. We assessed changes in hepatic lipid homeostasis upon the deletion of PARP-2 and found that cholesterol levels were higher in PARP-2(-/-) mice as compared to wild-type littermates. To uncover the molecular background, we analyzed changes in steady-state mRNA levels upon the knockdown of PARP-2 in HepG2 cells and in murine liver that revealed higher expression of sterol-regulatory element binding protein (SREBP)-1 dependent genes. We demonstrated that PARP-2 is a suppressor of the SREBP1 promoter, and the suppression of the SREBP1 gene depends on the enzymatic activation of PARP-2. Consequently, the knockdown of PARP-2 enhances SREBP1 expression that in turn induces the genes driven by SREBP1 culminating in higher hepatic cholesterol content. We did not detect hypercholesterolemia, higher fecal cholesterol content or increase in serum LDL, although serum HDL levels decreased in the PARP-2(-/-) mice. In cells and mice where PARP-2 was deleted we observed decreased ABCA1 mRNA and protein expression that is probably linked to lower HDL levels. In our current study we show that PARP-2 impacts on hepatic and systemic cholesterol homeostasis. Furthermore, the depletion of PARP-2 leads to lower HDL levels which represent a risk factor to cardiovascular diseases.

Therapeutic applications of PARP inhibitors: anticancer therapy and beyond

The aim of this article is to describe the current and potential clinical translation of pharmacological inhibitors of poly(ADP-ribose) polymerase (PARP) for the therapy of various diseases. The first section of the present review summarizes the available preclinical and clinical data with PARP inhibitors in various forms of cancer. In this context, the role of PARP in single-strand DNA break repair is relevant, leading to replication-associated lesions that cannot be repaired if homologous recombination repair (HRR) is defective, and the synthetic lethality of PARP inhibitors in HRR-defective cancer. HRR defects are classically associated with BRCA1 and 2 mutations associated with familial breast and ovarian cancer, but there may be many other causes of HRR defects. Thus, PARP inhibitors may be the drugs of choice for BRCA mutant breast and ovarian cancers, and extend beyond these tumors if appropriate biomarkers can be developed to identify HRR defects. Multiple lines of preclinical data demonstrate that PARP inhibition increases cytotoxicity and tumor growth delay in combination with temozolomide, topoisomerase inhibitors and ionizing radiation. Both single agent and combination clinical trials are underway. The final part of the first section of the present review summarizes the current status of the various PARP inhibitors that are in various stages of clinical development. The second section of the present review summarizes the role of PARP in selected non-oncologic indications. In a number of severe, acute diseases (such as stroke, neurotrauma, circulatory shock and acute myocardial infarction) the clinical translatability of PARP inhibition is supported by multiple lines of preclinical data, as well as observational data demonstrating PARP activation in human tissue samples. In these disease indications, PARP overactivation due to oxidative and nitrative stress drives cell necrosis and pro-inflammatory gene expression, which contributes to disease pathology. Accordingly, multiple lines of preclinical data indicate the efficacy of PARP inhibitors to preserve viable tissue and to down-regulate inflammatory responses. As the clinical trials with PARP inhibitors in various forms of cancer progress, it is hoped that a second line of clinical investigations, aimed at testing of PARP inhibitors for various non-oncologic indications, will be initiated, as well.

Poly(ADP-ribose) polymerase 1 (PARP1) in atherosclerosis: from molecular mechanisms to therapeutic implications

Poly(ADP-ribosyl)ation reactions, carried out by poly(ADP-ribose) polymerases (PARPs/ARTDs), are reversible posttranslational modifications impacting on numerous cellular processes (e.g., DNA repair, transcription, metabolism, or immune functions). PARP1 (EC 2.4.2.30), the founding member of PARPs, is particularly important for drug development for its role in DNA repair, cell death, and transcription of proinflammatory genes. Recent studies have established a novel concept that PARP1 is critically involved in the formation and destabilization of atherosclerotic plaques in experimental animal models and in humans. Reduction of PARP1 activity by pharmacological or molecular approaches attenuates atherosclerotic plaque development and enhances plaque stability as well as promotes the regression of pre-established atherosclerotic plaques. Mechanistically, PARP1 inhibition significantly reduces monocyte differentiation, macrophage recruitment, Sirtuin 1 (SIRT1) inactivation, endothelial dysfunction, neointima formation, foam cell death, and inflammatory responses within plaques, all of which are central to the pathogenesis of atherosclerosis. This article presents an overview of the multiple roles and underlying mechanisms of PARP1 activation (poly(ADP-ribose) accumulation) in atherosclerosis and emphasizes the therapeutic potential of PARP1 inhibition in preventing or reversing atherosclerosis and its cardiovascular clinical sequalae.

PARP-1: Friend or Foe of DNA Damage and Repair in Tumorigenesis?

Oxidative stress induced by reactive oxygen species can result in DNA damage within cells and subsequently increase risk for carcinogenesis. This may be averted by repair of DNA damage through the base or nucleotide excision repair (BER/NER) pathways. PARP, a BER protein, is known for its role in DNA-repair. However, multiple lesions can occur within a small range of DNA, known as oxidative clustered DNA lesions (OCDLs), which are difficult to repair and may lead to the more severe DNA double-strand break (DSB). Inefficient DSB repair can then result in increased mutagenesis and neoplastic transformation. OCDLs occur more frequently within a variety of tumor tissues. Interestingly, PARP is highly expressed in several human cancers. Additionally, chronic inflammation may contribute to tumorigenesis through ROS-induced DNA damage. Furthermore, PARP can modulate inflammation through interaction with NFκB and regulating the expression of inflammatory signaling molecules. Thus, the upregulation of PARP may present a double-edged sword. PARP is needed to repair ROS-induced DNA lesions, but PARP expression may lead to increased inflammation via upregulation of NFκB signaling. Here, we discuss the role of PARP in the repair of oxidative damage versus the formation of OCDLs and speculate on the feasibility of PARP inhibition for the treatment and prevention of cancers by exploiting its role in inflammation.

Induction of thoracic aortic remodeling by endothelial-specific deletion of microRNA-21 in mice

MicroRNAs (miRs) are known to have an important role in modulating vascular biology. MiR21 was found to be involved in the pathogenesis of proliferative vascular disease. The role of miR21 in endothelial cells (ECs) has well studied in vitro, but the study in vivo remains to be elucidated. In this study, miR21 endothelial-specific knockout mice were generated by Cre/LoxP system. Compared with wild-type mice, the miR21 deletion in ECs resulted in structural and functional remodeling of aorta significantly, such as diastolic pressure dropping, maximal tension depression, endothelium-dependent relaxation impairment, an increase of opening angles and wall-thickness/inner diameter ratio, and compliance decrease, in the miR21 endothelial-specific knockout mice. Furthermore, the miR21 deletion in ECs induced down-regulation of collagen I, collagen III and elastin mRNA and proteins, as well as up-regulation of Smad7 and down-regulation of Smad2/5 in the aorta of miR21 endothelial-specific knockout mice. CTGF and downstream MMP/TIMP changes were also identified to mediate vascular remodeling. The results showed that miR21 is identified as a critical molecule to modulate vascular remodeling, which will help to understand the role of miR21 in vascular biology and the pathogenesis of vascular diseases.

DNA damage and repair in atherosclerosis: current insights and future perspectives

Atherosclerosis is the leading cause of morbidity and mortality among Western populations. Over the past two decades, considerable evidence has supported a crucial role for DNA damage in the development and progression of atherosclerosis. These findings support the concept that the prolonged exposure to risk factors (e.g., dyslipidemia, smoking and diabetes mellitus) leading to reactive oxygen species are major stimuli for DNA damage within the plaque. Genomic instability at the cellular level can directly affect vascular function, leading to cell cycle arrest, apoptosis and premature vascular senescence. The purpose of this paper is to review current knowledge on the role of DNA damage and DNA repair systems in atherosclerosis, as well as to discuss the cellular response to DNA damage in order to shed light on possible strategies for prevention and treatment.

Role of poly(ADP-ribose) polymerases in the regulation of inflammatory processes

PARP enzymes influence the immune system at several key points and thus modulate inflammatory diseases. PARP enzymes affect immune cell maturation and differentiation and regulate the expression of inflammatory mediators such as cytokines, chemokines, inducible nitric oxide synthase and adhesion molecules. Moreover, PARP enzymes are key regulators of cell death during inflammation-related oxidative and nitrosative stress. Here we provide an overview of the different inflammatory diseases regulated by PARP enzymes.

Thioredoxin-interacting protein mediates nuclear-to-plasma membrane communication: role in vascular endothelial growth factor 2 signaling

OBJECTIVE

Thioredoxin-interacting protein (TXNIP) and poly-ADP-ribose polymerase 1 (PARP1) are both regulated by changes in cellular reduction-oxidation (redox) state and localize to the nucleus basally in human umbilical vein endothelial cells (HUVEC). Previously we showed a novel mechanism for PARP1 inhibition-mediated HUVEC survival through activation of vascular endothelial growth factor receptor 2 (VEGFR2) signaling in response to stress-induced apoptosis. In addition, we showed TXNIP translocation to the plasma membrane (PM) and activation of VEGFR2 in response to physiological stimuli. Because TXNIP is an α-arrestin that regulates VEGFR2 signaling, we hypothesized that PARP1 regulates TXNIP localization and function that might affect HUVEC stress-induced apoptosis.

METHODS AND RESULTS

HUVEC treated with 10 μmol/L PARP1 inhibitor (PJ34) were protected from TNF (10 ng/mL) or H(2)O(2) (300 μmol/L) mediated cell death. HUVEC transfected with TXNIP siRNA lost the protective effect of PARP1 inhibition, suggesting a protective role for TXNIP. Using immunofluorescence, cell fractionation analysis, and plasma membrane sheet assay, TXNIP was shown to translocate to the plasma membrane after PARP1 inhibition. TXNIP translocation was associated with activation of VEGFR2 signaling. Functionally, TXNIP-PARP1 interaction was decreased on PJ34 treatment, suggesting PARP1 as a novel regulator of TXNIP localization and function.

CONCLUSIONS

These findings demonstrate a novel regulatory mechanism of TXNIP by PARP1 to mediate activation of plasma membrane signaling and cell survival.

Cardiac and vascular phenotypes in the apolipoprotein E-deficient mouse

Cardiovascular death is frequently associated with atherosclerosis, a chronic multifactorial disease and a leading cause of death worldwide. Genetically engineered mouse models have proven useful for the study of the mechanisms underlying cardiovascular diseases. The apolipoprotein E-deficient mouse has been the most widely used animal model of atherosclerosis because it rapidly develops severe hypercholesterolemia and spontaneous atherosclerotic lesions similar to those observed in humans. In this review, we provide an overview of the cardiac and vascular phenotypes and discuss the interplay among nitric oxide, reactive oxygen species, aging and diet in the impairment of cardiovascular function in this mouse model.

Endothelial dysfunction in the apolipoprotein E-deficient mouse: insights into the influence of diet, gender and aging

Since the early 1990s, several strains of genetically modified mice have been developed as models for experimental atherosclerosis. Among the available models, the apolipoprotein E-deficient (apoE⁻/⁻) mouse is of particular relevance because of its propensity to spontaneously develop hypercholesterolemia and atherosclerotic lesions that are similar to those found in humans, even when the mice are fed a chow diet. The main purpose of this review is to highlight the key achievements that have contributed to elucidating the mechanisms pertaining to vascular dysfunction in the apoE⁻/⁻ mouse. First, we summarize lipoproteins and atherosclerosis phenotypes in the apoE⁻/⁻ mouse, and then we briefly discuss controversial evidence relative to the influence of gender on the development of atherosclerosis in this murine model. Second, we discuss the main mechanisms underlying the endothelial dysfunction of conducting vessels and resistance vessels and examine how this vascular defect can be influenced by diet, aging and gender in the apoE⁻/⁻ mouse.

Human internal thoracic artery grafts exhibit severe morphological and functional damage and spasmic vasomotion due to oxidative stress

Background

The internal thoracic artery (ITA) is the first choice for myocardial revascularization, but atherosclerotic lesions and perioperative vasospasm may still limit its functionality. Oxidative stress via the peroxynitrite – poly-(ADP-ribose) polymerase (PARP) cascade plays an important role in the pathogenesis of impaired vascular tone via endothelial injury. We aimed to investigate and describe the histology, PARP activation and functionality of ITA grafts and to assess the possible beneficial effect of PARP-inhibition.

Material/Methods

ITA specimens from 47 patients (26 men, mean age 66.2±1.7 years) who underwent coronary bypass surgery were processed for histological and immunohistochemical studies for oxidative stress and PARP activation, and were functionally tested with acetylcholine (ACh) and sodium nitroprusside (SNP) with or without PARP inhibition.

Results

The sections showed atherosclerotic alterations and oxidative and nitrosative stress were evidenced by positive 3-nitrotyrosine, 4-hydroxynonenal and PAR stainings. Functionally, 88.1% reacted to K-Krebs, 68.7% exhibited contraction after 1 μM phenylephrine, 29.9% exhibited relaxation to 30 μM Ach, and all precontracted segments relaxed to 30 μM SNP. High amplitude vasomotion was observed in 47.8% of the segments, which could be abolished by the application of 10 μM SNP. Incubation of the preparations with PJ34 did not improve endothelium-dependent vasodilation.

Conclusions

ITA grafts are severely damaged both morphologically and functionally in patients undergoing coronary artery bypass surgery, but PARP inhibition cannot improve their functional characteristics. The topical use of SNP to the ITA during the operation may improve vascular functions by dilating the vessels and eliminating the eventual spasmic vasomotion.

PARP inhibitors: new tools to protect from inflammation

Poly(ADP-ribosylation) consists in the conversion of β-NAD(+) into ADP-ribose, which is then bound to acceptor proteins and further used to form polymers of variable length and structure. The correct turnover of poly(ADP-ribose) is ensured by the concerted action of poly(ADP-ribose) polymerase (PARP) and poly(ADP-ribose) glycohydrolase (PARG) enzymes, which are responsible for polymer synthesis and degradation, respectively. Despite the positive role of poly(ADP-ribosylation) in sensing and repairing DNA damage, generated also by ROS, PARP over-activation could allow NAD depletion and consequent necrosis, thus leading to an inflammatory condition in many diseases. In this respect, inhibition of PARP enzymes could exert a protective role towards a number of pathological conditions; i.e. the combined treatment of tumors with PARP inhibitors/anticancer agents proved to have a beneficial effect in cancer therapy. Thus, pharmacological inactivation of poly(ADP-ribosylation) could represent a novel therapeutic strategy to limit cellular injury and to attenuate the inflammatory processes that characterize many disorders.

PCB-induced endothelial cell dysfunction: role of poly(ADP-ribose) polymerase

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants implicated in the development of pro-inflammatory events critical in the pathology of atherosclerosis and cardiovascular disease. PCB exposure of endothelial cells results in increased cellular oxidative stress, activation of stress and inflammatory pathways leading to increased expression of cytokines and adhesion molecules and ultimately cell death, all of which can lead to development of atherosclerosis. To date no studies have been performed to examine the direct effects of PCB exposure on the vasculature relaxant response which if impaired may predispose individuals to hypertension, an additional risk factor for atherosclerosis. Overactivation of the DNA repair enzyme poly(ADP-ribose) polymerase (PARP) following oxidative/nitrosative stress in endothelial cells and subsequent depletion of NADPH has been identified as a central mediator of cellular dysfunction. The aim therefore was to investigate whether 2,2',4,6,6'-pentachlorobiphenyl (PCB 104) directly causes endothelial cell dysfunction via increased oxidative stress and subsequent overactivation of PARP. Exposure of ex vivo rat aortic rings to PCB 104 impaired the acetylcholine-mediated relaxant response, an effect that was dependent on both concentration and exposure time. In vitro exposure of mouse endothelial cells to PCB 104 resulted in increased cellular oxidative stress through activation of the cytochrome p450 enzyme CYP1A1 with subsequent overactivation of PARP and NADPH depletion. Pharmacological inhibition of CYP1A1 or PARP protected against the PCB 104-mediated endothelial cell dysfunction. In conclusion, the environmental contaminants, PCBs, can activate PARP directly impairing endothelial cell function that may predispose exposed individuals to development of hypertension and cardiovascular disease.

Protective effects of PARP-1 knockout on dyslipidemia-induced autonomic and vascular dysfunction in ApoE mice: effects on eNOS and oxidative stress

The aims of this study were to investigate the role of poly(ADP-ribose) polymerase (PARP)-1 in dyslipidemia-associated vascular dysfunction as well as autonomic nervous system dysregulation. Apolipoprotein (ApoE)^−/− mice fed a high-fat diet were used as a model of atherosclerosis. Vascular and autonomic functions were measured in conscious mice using telemetry. The study revealed that PARP-1 plays an important role in dyslipidemia-associated vascular and autonomic dysfunction. Inhibition of this enzyme by gene knockout partially restored baroreflex sensitivity in ApoE^−/− mice without affecting baseline heart-rate and arterial pressure, and also improved heart-rate responses following selective blockade of the autonomic nervous system. The protective effect of PARP-1 gene deletion against dyslipidemia-induced endothelial dysfunction was associated with preservation of eNOS activity. Dyslipidemia induced PARP-1 activation was accompanied by oxidative tissue damage, as evidenced by increased expression of iNOS and subsequent protein nitration. PARP-1 gene deletion reversed these effects, suggesting that PARP-1 may contribute to vascular and autonomic pathologies by promoting oxidative tissue injury. Further, inhibition of this oxidative damage may account for protective effects of PARP-1 gene deletion on vascular and autonomic functions. This study demonstrates that PARP-1 participates in dyslipidemia-mediated dysregulation of the autonomic nervous system and that PARP-1 gene deletion normalizes autonomic and vascular dysfunctions. Maintenance of eNOS activity may be associated with the protective effect of PARP-1 gene deletion against dyslipidemia-induced endothelial dysfunction.

PARP-1 inhibition prevents oxidative and nitrosative stress-induced endothelial cell death via transactivation of the VEGF receptor 2

OBJECTIVE

PARP-1, a DNA base repair enzyme, is activated by DNA breaks induced by oxidative (ROS) and nitrosative (RNS) stress. By consuming NAD(+), PARP-1 activation can lead to ATP depletion and cell death. Studies suggest that inhibiting PARP-1 activity can attenuate pathologies associated with vascular smooth muscle and endothelial dysfunction. PARP-1 inhibition can also activate the prosurvival serine/threonine kinase, Akt. Vascular endothelial growth factor (VEGF) regulates endothelial cell survival via Akt activation downstream of VEGF receptor 2 (VEGFR2) activation. Here we investigated the hypothesis that PARP-1 inhibition protects human umbilical vein endothelial cells (HUVECs) from ROS- and RNS-induced cell death by limiting NAD(+) depletion and by activating a prosurvival signaling pathway via VEGFR2 phosphorylation.

METHODS AND RESULTS

We activated PARP-1 in HUVECs by treatment with hydrogen peroxide (H(2)O(2)) and peroxynitrite (ONOO(-)). Both depleted HUVECs of NAD(+) and ATP, processes that were limited by the PARP-1 inhibitor, PJ34. ONOO(-) and H(2)O(2)-induced cell death and apoptosis were attenuated in cells treated with PJ34 or PARP-1 siRNA. PARP-1 inhibition increased Akt, BAD, and VEGFR2 phosphorylation in HUVECs and in PJ34-treated rabbit aortas. The VEGFR2-specific tyrosine kinase inhibitor SU1498 decreased PARP-1 inhibition-mediated phosphorylation of VEGFR2 and Akt, and also reversed survival effects of PJ34. Finally, PARP-1 inhibition protected cells from death induced by serum starvation, evidence for a role in cell survival independent of energy protection.

CONCLUSIONS

PARP-1 inhibition prevents ROS- and RNS-induced HUVEC death by maintaining cellular energy in the form of NAD(+) and ATP, and also by activating a survival pathway via VEGFR2, Akt, and BAD phosphorylation.

Poly(ADP-ribose) polymerase inhibition reduces atherosclerotic plaque size and promotes factors of plaque stability in apolipoprotein E-deficient mice: effects on macrophage recruitment, nuclear factor-kappaB nuclear translocation, and foam cell death

BACKGROUND

Poly(ADP-ribose) polymerase (PARP) was suggested to play a role in endothelial dysfunction that is associated with a number of cardiovascular diseases. We hypothesized that PARP may play an important role in atherogenesis and that its inhibition may attenuate atherosclerotic plaque development in an experimental model of atherosclerosis.

METHODS AND RESULTS

Using a mouse (apolipoprotein E [ApoE](-/-)) model of high-fat diet-induced atherosclerosis, we demonstrate an association between cell death and oxidative stress-associated DNA damage and PARP activation within atherosclerotic plaques. PARP inhibition by thieno[2,3-c]isoquinolin-5-one reduced plaque number and size and altered structural composition of plaques in these animals without affecting sera lipid contents. These results were corroborated genetically with the use of ApoE(-/-) mice that are heterozygous for PARP-1. PARP inhibition promoted an increase in collagen content, potentially through an increase in tissue inhibitor of metalloproteinase-2, and transmigration of smooth muscle cells to intima of atherosclerotic plaques as well as a decrease in monocyte chemotactic protein-1 production, all of which are markers of plaque stability. In PARP-1(-/-) macrophages, monocyte chemotactic protein-1 expression was severely inhibited because of a defective nuclear factor-kappaB nuclear translocation in response to lipopolysaccharide. Furthermore, PARP-1 gene deletion not only conferred protection to foam cells against H2O2-induced death but also switched the mode of death from necrosis to apoptosis.

CONCLUSIONS

Our results suggest that PARP inhibition interferes with plaque development and may promote plaque stability, possibly through a reduction in inflammatory factors and cellular changes related to plaque dynamics. PARP inhibition may prove beneficial for the treatment of atherosclerosis.

Single dose treatment with PARP-inhibitor INO-1001 improves aging-associated cardiac and vascular dysfunction

Overproduction of reactive oxygen species in aging tissues has been implicated in the pathogenesis of aging-associated cardiovascular dysfunction. Oxidant-induced DNA-damage activates the poly(ADP-ribose) polymerase (PARP) pathway, leading to tissue injury. In this study we investigated the acute effects of the PARP inhibitor INO-1001 on aging-associated cardiac and endothelial dysfunction. Using a pressure-volume conductance catheter, left ventricular pressure-volume analysis of young and aging rats was performed before and after a single injection of INO-1001. Endothelium-dependent and -independent vasorelaxation of isolated aortic rings were investigated by using acetylcholine and sodium nitroprusside. Aging animals showed a marked reduction of myocardial contractility and endothelium-dependent relaxant responsiveness of aortic rings. Single dose INO-1001-treatment resulted in acute improvement in their cardiac and endothelial function. Immunohistochemistry for nitrotyrosine and poly(ADP-ribose) confirmed enhanced nitro-oxidative stress and PARP-activation in aging animals. Acute treatment with INO-1001 decreased PARP-activation, but did not affect nitrotyrosine-immunoreactivity. Our results demonstrate that the aging-associated chronic cardiovascular dysfunction can be improved, at least, short term, by a single treatment course with a PARP-inhibitor, supporting the role of the nitro-oxidative stress -- PARP -- pathway in the age-related functional decline of the cardiovascular system. Pharmacological inhibition of PARP may represent a novel therapeutic utility to improve aging-associated cardiovascular dysfunction.

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.

Theophylline prevents NAD+ depletion via PARP-1 inhibition in human pulmonary epithelial cells

Oxidative DNA damage, as occurs during exacerbations in chronic obstructive pulmonary disease (COPD), highly activates the nuclear enzyme poly(ADP-ribose)polymerase-1 (PARP-1). This can lead to cellular depletion of its substrate NAD+, resulting in an energy crisis and ultimately in cell death. Inhibition of PARP-1 results in preservation of the intracellular NAD+ pool, and of NAD+-dependent cellular processes. In this study, PARP-1 activation by hydrogen peroxide decreased intracellular NAD+ levels in human pulmonary epithelial cells, which was found to be prevented in a dose-dependent manner by theophylline, a widely used compound in the treatment of COPD. This enzyme inhibition by theophylline was confirmed in an ELISA using purified human PARP-1 and was found to be competitive by nature. These findings provide new mechanistic insights into the therapeutic effect of theophylline in oxidative stress-induced lung pathologies.

Poly(ADP-ribose) polymerase and the therapeutic effects of its inhibitors

Poly(ADP-ribose) polymerases (PARPs) are involved in the regulation of many cellular functions. Three consequences of the activation of PARP1, which is the main isoform of the PARP family, are particularly important for drug development: first, its role in DNA repair; second, its capacity to deplete cellular energetic pools, which culminates in cell dysfunction and necrosis; and third, its capacity to promote the transcription of pro-inflammatory genes. Consequently, pharmacological inhibitors of PARP have the potential to enhance the cytotoxicity of certain DNA-damaging anticancer drugs, reduce parenchymal cell necrosis (for example, in stroke or myocardial infarction) and downregulate multiple simultaneous pathways of inflammation and tissue injury (for example, in circulatory shock, colitis or diabetic complications). The first ultrapotent novel PARP inhibitors have now entered human clinical trials. This article presents an overview of the principal pathophysiological pathways and mechanisms that are governed by PARP, followed by the main structures and therapeutic actions of various classes of novel PARP inhibitors.