Effect of poly(ADP-ribose) polymerase inhibitors on oxidative stress evoked hydroxyl radical level and macromolecules oxidation in cell free system of rat brain cortex

Antileukemic potential of methylated indolequinone MAC681 through immunogenic necroptosis and PARP1 degradation

BACKGROUND

Despite advancements in chronic myeloid leukemia (CML) therapy with tyrosine kinase inhibitors (TKIs), resistance and intolerance remain significant challenges. Leukemia stem cells (LSCs) and TKI-resistant cells rely on altered mitochondrial metabolism and oxidative phosphorylation. Targeting rewired energy metabolism and inducing non-apoptotic cell death, along with the release of damage-associated molecular patterns (DAMPs), can enhance therapeutic strategies and immunogenic therapies against CML and prevent the emergence of TKI-resistant cells and LSC persistence.

METHODS

Transcriptomic analysis was conducted using datasets of CML patients' stem cells and healthy cells. DNA damage was evaluated by fluorescent microscopy and flow cytometry. Cell death was assessed by trypan blue exclusion test, fluorescent microscopy, flow cytometry, colony formation assay, and in vivo Zebrafish xenografts. Energy metabolism was determined by measuring NAD+ and NADH levels, ATP production rate by Seahorse analyzer, and intracellular ATP content. Mitochondrial fitness was estimated by measurements of mitochondrial membrane potential, ROS, and calcium accumulation by flow cytometry, and morphology was visualized by TEM. Bioinformatic analysis, real-time qPCR, western blotting, chemical reaction prediction, and molecular docking were utilized to identify the drug target. The immunogenic potential was assessed by high mobility group box (HMGB)1 ELISA assay, luciferase-based extracellular ATP assay, ectopic calreticulin expression by flow cytometry, and validated by phagocytosis assay, and in vivo vaccination assay using syngeneic C57BL/6 mice.

RESULTS

Transcriptomic analysis identified metabolic alterations and DNA repair deficiency signatures in CML patients. CML patients exhibited enrichment in immune system, DNA repair, and metabolic pathways. The gene signature associated with BRCA mutated tumors was enriched in CML datasets, suggesting a deficiency in double-strand break repair pathways. Additionally, poly(ADP-ribose) polymerase (PARP)1 was significantly upregulated in CML patients' stem cells compared to healthy counterparts. Consistent with the CML patient DNA repair signature, treatment with the methylated indolequinone MAC681 induced DNA damage, mitochondrial dysfunction, calcium homeostasis disruption, metabolic catastrophe, and necroptotic-like cell death. In parallel, MAC681 led to PARP1 degradation that was prevented by 3-aminobenzamide. MAC681-treated myeloid leukemia cells released DAMPs and demonstrated the potential to generate an immunogenic vaccine in C57BL/6 mice. MAC681 and asciminib exhibited synergistic effects in killing both imatinib-sensitive and -resistant CML, opening new therapeutic opportunities.

CONCLUSIONS

Overall, increasing the tumor mutational burden by PARP1 degradation and mitochondrial deregulation makes CML suitable for immunotherapy.

3-Aminobenzamide Prevents Concanavalin A-Induced Acute Hepatitis by an Anti-inflammatory and Anti-oxidative Mechanism

BACKGROUND AND AIMS

Concanavalin A is known to activate T cells and to cause liver injury and hepatitis, mediated in part by secretion of TNFα from macrophages. Poly(ADP-ribose) polymerase-1 (PARP-1) inhibitors have been shown to prevent tissue damage in various animal models of inflammation. The objectives of this study were to evaluate the efficacy and mechanism of the PARP-1 inhibitor 3-aminobenzamide (3-AB) in preventing concanavalin A-induced liver damage.

METHODS

We tested the in vivo effects of 3-AB on concanavalin A-treated mice, its effects on lipopolysaccharide (LPS)-stimulated macrophages in culture, and its ability to act as a scavenger in in vitro assays.

RESULTS

3-AB markedly reduced inflammation, oxidative stress, and liver tissue damage in concanavalin A-treated mice. In LPS-stimulated RAW264.7 macrophages, 3-AB inhibited NFκB transcriptional activity and subsequent expression of TNFα and iNOS and blocked NO production. In vitro, 3-AB acted as a hydrogen peroxide scavenger. The ROS scavenger N-acetylcysteine (NAC) and the ROS formation inhibitor diphenyleneiodonium (DPI) also inhibited TNFα expression in stimulated macrophages, but unlike 3-AB, NAC and DPI were unable to abolish NFκB activity. PARP-1 knockout failed to affect NFκB and TNFα suppression by 3-AB in stimulated macrophages.

CONCLUSIONS

Our results suggest that 3-AB has a therapeutic effect on concanavalin A-induced liver injury by inhibiting expression of the key pro-inflammatory cytokine TNFα, via PARP-1-independent NFκB suppression and via an NFκB-independent anti-oxidative mechanism.

Influence of PARP-1 inhibition in the cardiotoxicity of the topoisomerase 2 inhibitors doxorubicin and mitoxantrone

Doxorubicin (DOX) and Mitoxantrone (MTX) are very effective drugs for a range of tumors despite being highly cardiotoxic. DNA topoisomerase 2 beta (Top2ß) was revealed as key mediator of DOX-induced cardiotoxicity, although ROS generation is also an important mechanism. Oxidative stress is also an important issue in MTX-induced cardiotoxicity that is manifested by mitochondrial dysfunction. Studies have demonstrated the relationship between PARP-1 overactivation and cell viability in DOX-treated cardiomyocytes. In reference of MTX, data regarding PARP-1 overactivation as the mechanism responsible for cardiotoxicity is difficult to find. The aim of this study was to evaluate the influence of PARP-1 inhibitor DPQ on DOX- and MTX-mediated cardiotoxicity. Cells were exposed for 24 h to DOX or MTX in the presence or absence of DPQ. Viability, apoptosis, and genotoxicity assays were carried out. Immunofluorescence of phosphorylated histone H2AX was analyzed in H9c2 cells and cardiomyocytes from neonatal rats. Results demonstrated that DPQ co-treatment increases DOX-induced apoptosis in H9c2 cells. DPQ also prevents DOX and MTX-ROS generation in part by increasing SOD and CAT activities. Furthermore, DPQ co-treatment increased the generation of DNA strand breaks by DOX and MTX whilst also inducing phosphorylation of H2AX, MRE11, and ATM in H9c2 cells. Our results demonstrated that as well as increasing DNA damage and inducing apoptotic cell death, DPQ enhances DOX- and MTX-mediated cytotoxicity in H9c2.

3-Aminobenzamide Blocks MAMP-Induced Callose Deposition Independently of Its Poly(ADPribosyl)ation Inhibiting Activity

Cell wall reinforcement with callose is a frequent plant response to infection. Poly(ADP-ribosyl)ation is a protein post-translational modification mediated by poly(ADP-ribose) polymerases (PARPs). Poly(ADP-ribosyl)ation has well-known roles in DNA damage repair and has more recently been shown to contribute to plant immune responses. 3-aminobenzamide (3AB) is an established PARP inhibitor and it blocks the callose deposition elicited by flg22 or elf18, two microbe-associated molecular patterns (MAMPs). However, we report that an Arabidopsis parp1parp2parp3 triple mutant does not exhibit loss of flg22-induced callose deposition. Additionally, the more specific PARP inhibitors PJ-34 and INH₂BP inhibit PARP activity in Arabidopsis but do not block MAMP-induced callose deposition. These data demonstrate off-target activity of 3AB and indicate that 3AB inhibits callose deposition through a mechanism other than poly(ADP-ribosyl)ation. POWDERY MILDEW RESISTANT 4 (PMR4) is the callose synthase responsible for the majority of MAMP- and wound-induced callose deposition in Arabidopsis. 3AB does not block wound-induced callose deposition, and 3AB does not reduce the PMR4 mRNA abundance increase in response to flg22. Levels of PMR4-HA protein increase in response to flg22, and increase even more in flg22 + 3AB despite no callose being produced. The callose synthase inhibitor 2-deoxy-D-glucose does not cause similar impacts on PMR4-HA protein levels. Beyond MAMPs, we find that 3AB also reduces callose deposition induced by powdery mildew (Golovinomyces cichoracearum) and impairs the penetration resistance of a PMR4 overexpression line. 3AB thus reveals pathogenesis-associated pathways that activate callose synthase enzymatic activity distinct from those that elevate PMR4 mRNA and protein abundance.

Poly(ADP-ribose) polymerase inhibition suppresses inflammation and promotes recovery from adrenal injury in a rat model of acute necrotizing pancreatitis

Background

Poly(ADP-ribose) polymerase (PARP) participates in multi-organ failure in various inflammatory diseases including acute necrotizing pancreatitis (ANP). Since pancreatitis-associated adrenal insufficiency is partly caused by inflammatory damage to the adrenal cortex, we examined whether PARP antagonism could alleviate adrenal insufficiency in a rat model of ANP.

Methods

ANP was induced by retrograde infusion of sodium taurocholate into the bile-pancreatic duct. At 30 min prior to taurocholate infusion, rats were pretreated with the PARP inhibitor 3-Aminobenzamide (3-AB, 20 mg/kg) or vehicle. Pancreatic pathological injury, adrenal histology, neutrophil infiltration, cell apoptosis, and serum corticosterone level were assessed at various times points. Activities of poly(ADP-ribosyl)ated protein (PAR), nuclear factor-kappaB (NF-kB), tumor necrosis factor-α (TNF-α), intercellular adhesion molecule-1 (ICAM-1) and inducible nitric oxide synthase (iNOS) in the adrenal were also examined.

Results

PARP overactivation in ANP rats is associated with reduced serum corticosterone level and marked cellular alterations in adrenocortical tissue. Inflammatory stress caused by ANP reduced adrenal corticosterone release. 3-AB reduced the activation of PARP and inflammatory markers, decreased myeloperoxidase activity, attenuated adrenal morphologic lesions and cells apoptosis, simultaneously improved the impaired adrenal function.

Conclusions

Our data demonstrate the involvement of PARP overactivation in the pathogenesis of adrenal dysfunction after ANP. PARP inhibition may suppress inflammation and promote functional recovery from adrenal injury.

3-aminobenzamide, a poly (ADP ribose) polymerase inhibitor, enhances wound healing in whole body gamma irradiated model

The custom use of radiotherapy was found to participate in the development of chronic unhealed wounds. In general, exposure to gamma radiation stimulates the production of reactive oxygen species (ROS) that eventually leads to damaging effect. Conversely, overexpression of a nuclear poly (ADP-ribose) polymerase enzyme (PARP) after oxidative insult extremely brings about cellular injury due to excessive consumption of NAD and ATP. Here, we dedicated our study to investigate the role of 3-aminobenzamide (3-AB), a PARP inhibitor, on pregamma irradiated wounds. Two full-thickness (6 mm diameter) wounds were created on the dorsum of Swiss albino mouse. The progression of wound contraction was monitored by capturing daily photo images. Exposure to gamma radiation (6Gy) exacerbated the normal healing of excisional wounds. Remarkably, topical application of 3-AB cream (50 µM) revealed a marked acceleration in the rate of wound contraction. Likewise, PARP inhibition ameliorated the unbalanced oxidative/nitrosative status of granulated skin tissues. Such effect was significantly revealed by the correction of the reduced antioxidant capacity and the enhanced lipid peroxidation, hydrogen peroxide, and myeloperoxidase contents. Moreover, application of 3-AB modified the cutaneous nitrite content throughout healing process. Conversely, the expressions of pro-inflammatory cytokines were down-regulated by PARP inhibition. The mitochondrial ATP content showed a lower consumption rate on 3-AB-treated wound bed as well. In parallel, the mRNA expressions of Sirt-1 and acyl-COA oxidase-2 (ACOX-2) were up-regulated; whom functions control the mitochondrial ATP synthesis and lipid metabolism. The current data suggested that inhibition of PARP-1 enzyme may accelerate the delayed wound healing in whole body gamma irradiated mice by early modifying the oxidative stress as well as the inflammatory response.

Poly (ADP-ribose) polymerase-1: an emerging target in right ventricle dysfunction associated with pulmonary hypertension

Recently, inhibition of poly (ADP-ribose) polymerase-1 (PARP1) was shown to be protective in experimental pulmonary hypertension (PH) and prevented right ventricular hypertrophy (RVH) associated with it. However, molecular mechanism behind cardioprotection by PARP1 inhibition in PH still needs detailed exploration. Therefore, effect of inhibition of PARP1 on the right ventricle (RV) dysfunction was studied in monocrotaline (MCT) induced PH model. Following a single dose administration of MCT (60 mg/kg, s.c.), male Sprague-Dawley rats were treated with PARP1 inhibitor 1,5-Isoquinolinediol (ISO, 3 mg/kg, i.p.) for 35 days for preventive study and from day 21-35 for curative study. RV pressure (RVP) and RVH were measured after 35 days. Histophathological studies, PARP1 activity, mRNA and protein expression were studied in isolated RV. Oxidative and nitosative stress, inflammation and Matrix metalloproteinases (MMPs)/Tissue inhibitor of metalloproteinase 2 (TIMP2) were also assessed. Mitochondrial dysfunction was studied by mitochondrial membrane permeability and estimation of Nicotinamide adenine dinucleotide (NAD) and Adenosine triphosphate (ATP). Apoptosis in RV was assessed by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), caspase 3 activity and cleaved PARP1 expression. PARP1 inhibition significantly reversed the increase in RVP and RVH in both preventive and curative treatment in the MCT-injected rats. ISO lowered oxidative and nitrosative stress and inflammation and restored the balance of MMPs/TIMP2 expression. PARP1 inhibition prevented mitochondrial dysfunction and the release of cell death factors from mitochondria. ISO also decreased apoptosis by decreasing number of TUNEL positive cells, caspase 3 activity and PARP1 cleavage in RV. Thus, PARP1 inhibition ameliorated PH induced RV hypertrophy and may emerge as a new therapeutic target for PH.

Continuous inhibition of poly(ADP-ribose) polymerase does not reduce reperfusion injury in isolated rat heart

Poly(ADP-ribose) polymerase (PARP), an enzyme that is important to the regulation of nuclear function, is activated by DNA strand breakage. In massive DNA damage, PARP is overactivated, exhausting nicotinamide adenine dinucleotide and leading to cell death. Recent studies have succeeded in reducing cellular damage in ischemia/reperfusion by inhibiting PARP. However, PARP plays an important part in the DNA repair system, and its inhibition may be hazardous in certain situations. We compared the short-time inhibition of PARP against continuous inhibition during ischemia/reperfusion using isolated rat hearts. The hearts were reperfused after 21 minutes of ischemia with a bolus injection of 3-aminobenzamide (3-AB) (10 mg/kg) followed by continuous 3-AB infusion (50 μM) for the whole reperfusion period or for the first 6 minutes or without 3-AB. At the end of reperfusion, contractile function, high-energy phosphate content, nicotinamide adenine dinucleotide content, and infarcted area were significantly preserved in the 3-AB 6-minute group. In the 3-AB continuous group, these advantages were not apparent. At the end of reperfusion, PARP cleavage had significantly proceeded in the 3-AB continuous group, indicating initiation of the apoptotic cascade. Thus, continuous PARP inhibition by 3-AB does not reduce reperfusion injury in the isolated rat heart, which may be because of acceleration of apoptosis.

Evaluation of the antioxidative properties of lipoxygenase inhibitors

BACKGROUND

Oxidative stress is a component of many pathological conditions including neurodegenerative diseases and inflammation. An important source of reactive oxygen species (ROS) are lipoxygenases (LOX) - enzymes responsible for the metabolism of arachidonic acid and other polyunsaturated fatty acids. LOX inhibitors have a protective effect in inflammatory diseases and in neurodegenerative disorders because of their anti-inflammatory activity. However, the molecular mechanism of the protective action of LOX inhibitors has not yet been fully elucidated.

METHODS

The aim of this study was to compare the antioxidative potential of widely used LOX inhibitors: BWB70C, AA-861, zileuton, baicalein and NDGA. The antioxidative properties were evaluated in cell-free systems. We measured the effect of the tested compounds on iron/ascorbate-induced lipid peroxidation and on carbonyl group formation in the rat brain homogenate. Direct free radical scavenging was analyzed by using DPPH assay.

RESULTS

Our data showed that the inhibitor of all LOXs, i.e., NDGA, 5-LOX inhibitor BWB70C and the inhibitor of 12/15-LOX, baicalein, significantly decreased the level of lipid and protein oxidation. The free radical scavenging activity of these inhibitors was comparable to known ROS scavengers, i.e., resveratrol and trolox. Zileuton (the inhibitor of 5-LOX) slightly prevented lipid and protein oxidation, it also scavenged the DPPH radical. AA-861 (the inhibitor of 5 and 12/15-LOX) slightly protected lipids against Fe/asc-evoked lipid peroxidation at high concentrations, but had no effect on carbonyl group formation and DPPH scavenging.

CONCLUSIONS

Our results indicate that some LOX inhibitors demonstrate potent anti-oxidative, free radical scavenging properties. AA-861, whose antioxidative potential is very weak, may be a specific tool to be used in experimental and perhaps even clinical applications.

3-Aminobenzamide protects primary human keratinocytes from UV-induced cell death by a poly(ADP-ribosyl)ation independent mechanism

Poly(ADP-ribosyl)ation (PARylation) is a NAD(+)-dependent protein modification carried out by PARP [poly(ADP-ribose) polymerase] enzymes. Here we set out to investigate whether PARylation regulates UVB-induced cell death in primary human keratinocytes. We used the benchmark PARP inhibitor 3-aminobenzamide (3AB) and a more potent and specific inhibitor PJ34 and found that UVB (0.05-0.2J/cm(2)) induced a dose dependent loss of viability that was prevented by 3AB but not by PJ34. Similarly to PJ34, two other new generation PARP inhibitors also failed to protect keratinocytes from UVB-induced loss of viability. Moreover, silencing PARP-1 in HaCaT human keratinocytes sensitized cells to UVB toxicity but 3AB provided protection to both control HaCaT cells and to PARP-1 silenced cells indicating that the photoprotective effect of 3AB is independent of PARP inhibition. Lower UVB doses (0.0125-0.05J/cm(2)) caused inhibition of proliferation of keratinocytes which was prevented by 3AB but augmented by PJ34. UVB-induced keratinocyte death displayed the characteristics of both apoptosis (morphology, caspase activity, DNA fragmentation) and necrosis (morphology, LDH release) with all of these parameters being inhibited by 3AB and apoptotic parameters slightly enhanced by PJ34. UVA also caused apoptotic and necrotic cell death in keratinocytes with 3AB protecting and PJ34 sensitizing cells to UVA-induced toxicity. 3AB prevented UVB-induced mitochondrial membrane depolarization and generation of hydrogen peroxide. In summary, PARylation is a survival mechanism in UV-treated keratinocytes. Moreover, 3-aminobenzamide is photoprotective and acts by a PARP-independent mechanism at a premitochondrial step of phototoxicity.

BID is a critical factor controlling cell viability regulated by IFN-α

Clinical applications of human interferon (IFN)-α have met with varying degrees of success. Nevertheless, key molecules in cell viability regulated by IFN-α have not been clearly identified. Our previous study indicated that IFN (α, β, and ω) receptor (IFNAR) 1/2- and IFN regulatory factor 9-RNA interference (RNAi) completely restored cell viability after IFN-α treatment in human ovarian adenocarcinoma OVCAR3 cells sensitive to IFN-α. In this study, IFNAR1/2- and IFN regulatory factor 9-RNAi inhibited the gene expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), but not of Fas ligand, after IFN-α treatment. In fact, TRAIL but not Fas ligand inhibited the viability of OVCAR3 cells. IFN-α notably upregulated the levels of TRAIL protein in the supernatant and on the membrane of OVCAR3 cells. After TRAIL signaling, caspase 8 inhibitor and BH3 interacting domain death agonist (BID)-RNAi significantly restored cell viability in response to IFN-α and TRAIL in OVCAR3 cells. Furthermore, BID-RNAi prevented both IFN-α and TRAIL from collapsing the mitochondrial membrane potential (ΔΨm). Finally, we provided important evidence that BID overexpression led to significant inhibition of cell viability after IFN-α or TRAIL treatments in human lung carcinoma A549 cells resistant to IFN-α. Thus, this study suggests that BID is crucial for cell viability regulated by IFN-α which can induce mitochondria-mediated apoptosis, indicating a notable potential to be a targeted therapy for IFN-α resistant tumors.

PARP-1 regulates the expression of caspase-11

Poly(ADP-ribose) polymerase-1 (PARP-1) is a multifunctional enzyme that regulates DNA repair, cell death and transcription of inflammatory proteins. In the present study, we present evidence that PARP-1 regulates the expression of caspase-11 following lipopolysaccharide (LPS) stimulation. Knockdown of PARP-1 suppressed the LPS-induced expression of caspase-11 at both mRNA and protein levels as well as caspase-11 promoter activity. Importantly, PARP-1 was recruited to the caspase-11 promoter region containing predicted nuclear factor (NF)-κB-binding sites when examined by chromatin immunoprecipitation assay. However, knockdown of PARP-1 did not suppress the expression of caspase-11 induced by interferon-γ that activates signal transducer and activator of transcription 1 but not NF-κB. PARP-1 enzymatic activity was not required for the caspase-11 upregulation since pharmacological inhibitors of PARP-1 did not suppress the induction of caspase-11. Our results suggest that PARP-1, as a transcriptional cofactor for NF-κB, regulates the induction of caspase-11 at a transcriptional level.

Comparative study of the binding characteristics to and inhibitory potencies towards PARP and in vivo antidiabetogenic potencies of taurine, 3-aminobenzamide and nicotinamide

BACKGROUND

Poly(ADP-ribose) is a NAD+-requiring, DNA-repairing, enzyme playing a central role in pancreatic beta-cell death and in the development of endothelial dysfunction in humans and experimental animals. PARP activation is also relevant to the development of complications of diabetes. Hence, agents capable of inhibiting PARP may be useful in preventing the development of diabetes and in slowing down complications of diabetes.

METHODS

PARP inhibition was assessed with a colorimetric assay kit. Molecular docking studies on the active site of PARP were conducted using the crystalline structure of the enzyme available as Protein Data Bank Identification No. 1UK1. Type 2 diabetes was induced in male Sprague-Dawley rats with streptozotocin (STZ, 60 mg/kg, i.p.). The test compounds (3-aminobenzamide = 3-AB, nicotinamide = NIC, taurine = TAU) were given by the i.p. route 45 min before STZ at 2.4 mM/kg (all three compounds) or 1.2 and 3.6 mM/kg (only NIC and TAU). Blood samples were collected at 24 hr after STZ and processed for their plasma. The plasma samples were used to measure glucose, insulin, cholesterol, triglycerides, malondialdehyde, nitric oxide, and glutathione levels using reported methods.

RESULTS

3-AB, NIC and TAU were able to inhibit PARP, with the inhibitory potency order being 3-AB>NIC> or =TAU. Molecular docking studies at the active site of PARP showed 3-AB and NIC to interact with the binding site for the nicotinamide moiety of NAD+ and TAU to interact with the binding site for the adenine moiety of NAD+. While STZ-induced diabetes elevated all the experimental parameters examined and lowered the insulin output, a pretreatment with 3-AB, NIC or TAU reversed these trends to a significant extent. At a dose of 2.4 mm/kg, the protective effect decreased in the approximate order 3-AB>NIC> or =TAU. The attenuating actions of both NIC and TAU were dose-related except for the plasma lipids since NIC was without a significant effect at all doses tested.

CONCLUSIONS

At equal molar doses, 3-AB was generally more potent than either TAU or NIC as an antidiabetogenic agent, but the differences were not as dramatic as would have been predicted from their differences in PARP inhibitory potencies. NIC and TAU demonstrated dose-related effects, which in the case of TAU were only evident at doses > or =2.4 mM/kg. The present results also suggest that in the case of NIC and TAU an increase in dose will enhance the magnitude of their attenuating actions on diabetes-related biochemical alterations to that achieved with a stronger PARP inhibitor such as 3-AB. Hence, dosing will play a critical role in clinical studies assessing the merits of NIC and TAU as diabetes-preventing agents.

Mechanical stretch enhances NF-kappaB-dependent gene expression and poly(ADP-ribose) synthesis in synovial cells

Temporomandibular joint disorders (TMD) show complex symptoms associated with inflammation, pain and degeneration of the peripheral tissues including synovium. Although it is believed that excessive mechanical stress on synovium causes development of TMD, the molecular mechanism by which mechanical stress triggers TMD has still remained unclear. In order to examine the effect of mechanical stress on synoviocytes, rabbit synovial cells were cyclically stretched in vitro. The stretch efficiently increased the gene expressions of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS) and NF-kappaB responsive reporter gene constructs. The interruption of NF-kappaB activating pathway by inhibitors resulted in the abrogation of those expressions, indicating the pivotal role of NF-kappaB in the mechanical stretch-mediated COX-2 and iNOS expressions. In parallel, the stretch remarkably increased NO production and poly(ADP-ribose) (PAR) synthesis, suggesting that excessive amounts of NO causes DNA injury and in turn activates PAR synthesis by poly(ADP-ribose) polymerase (PARP). The inhibition of PAR synthesis by a PARP inhibitor or a radical scavenger enhanced the mechanical stretch-induced gene expressions in a NF-kappaB-independent manner, implying an involvement of PARP in the gene expression. Taken together, these results demonstrate that mechanical stress on synovial cells not only induces gene expressions of COX-2 and iNOS but also affects PAR synthesis.

Poly(ADP-ribose) polymerase-1 modulation of in vivo response of brain hypoxia-inducible factor-1 to hypoxia/reoxygenation is mediated by nitric oxide and factor inhibiting HIF

Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear protein that once activated by genotoxic agents, modulates its own activity and that of several other nuclear proteins. The absence or pharmacological inhibition of this protein has been proven to be beneficial in the treatment of different diseases involving a hypoxic situation. We previously reported that PARP-1 modulates the hypoxia-inducible factor-1 (HIF-1) response in vitro, but this effect has not yet been demonstrated in vivo. The brain is especially susceptible to hypoxic injury, and the present study demonstrates that PARP-1 plays a major role in the post-hypoxic response of HIF-1alpha in the cerebral cortex. Immediate post-hypoxic HIF-1alpha accumulation was higher in the presence of PARP-1, and this differential response was mediated by nitric oxide and to a lesser extent, reactive oxygen species. PARP-1 was also found to induce a more rapid but less sustained HIF-1 transcriptional activity by up-regulating the factor inhibiting HIF. The implication of PARP-1 in these results was further demonstrated by pharmacologically inhibiting PARP in wild-type mice. In conclusion, our data suggest that PARP-1 has an important regulatory role in the in vivo response of brain HIF-1 to hypoxia/reoxygenation.

Induction of apoptosis by the inhibitors of poly(ADP-ribose)polymerase in HeLa cells

To investigate the role of poly(ADP-ribose)polymerase (PARP) in the physiological condition of cell growth, we studied the ability of PARP inhibitors to induce apoptosis. Benzamide (BA) and 4-amino-1,8-naphthalimide (NAP), two well-known inhibitors of PARP, treatment increased nuclear fragmentation and caspase-3 activity in HeLa (Human cervical cancer cell line) cells. The increase of cellular NAD(+) level was observed in HeLa cells treated with BA in comparison with untreated control cells. For unrevealing the specific PARP family member responsible for such induction of apoptosis we knocked down and over-expressed PARP-1 gene in HeLa cells. PARP-1 knock down cells were sensitive to BA induced nuclear fragmentation and caspase-3 activation while exogenous expression of PARP-1 rendered cells resistant to BA induced apoptosis. This result indicated that inhibition of PARP-1 resulted in induction of apoptosis.

Poly(ADP-ribose) polymerase 1 promotes tumor cell survival by coactivating hypoxia-inducible factor-1-dependent gene expression

Hypoxia-inducible factor 1 (HIF-1) is the key transcription factor regulating hypoxia-dependent gene expression. Lack of oxygen stabilizes HIF-1, which in turn modulates the gene expression pattern to adapt cells to the hypoxic environment. Activation of HIF-1 is also detected in most solid tumors and supports tumor growth through the expression of target genes that are involved in processes like cell proliferation, energy metabolism, and oxygen delivery. Poly(ADP-ribose) polymerase 1 (PARP1) is a chromatin-associated protein, which was shown to regulate transcription. Here we report that chronic myelogenous leukemia cells expressing small interfering RNA against PARP1, which were injected into wild-type mice expressing PARP1, showed tumor growth with increased levels of necrosis, limited vascularization, and reduced expression of GLUT-1. Of note, PARP1-deficient cells showed a reduced HIF-1 transcriptional activation that was dependent on PARP1 enzymatic activity. PARP1 neither influenced binding of HIF-1 to its hypoxic response element nor changed HIF-1alpha protein levels in hypoxic cells. However, PARP1 formed a complex with HIF-1alpha through direct protein interaction and coactivated HIF-1alpha-dependent gene expression. These findings provide convincing evidence that wild-type mice expressing PARP1 cannot compensate for the loss of PARP1 in tumor cells and strengthen the importance of the role of PARP1 as a transcriptional coactivator of HIF-1-dependent gene expression during tumor progression.

Ischemia/Reperfusion of the Liver Induces Heart Injury in Rats

OBJECTIVE

We evaluated the cardiovascular injury induced by ischemia and reperfusion (I/R) of the liver by measuring changes in blood levels of cardiac troponin I (cTNI), an index of cardiovascular injury, as well as levels of selected indicators of an inflammatory response.

MATERIALS AND METHODS

Ischemia was induced in the rat liver by clamping the common hepatic artery and portal vein for 40 minutes, after which flow was restored, and the liver reperfused for 90 minutes. Blood samples were collected prior to ischemia and after reperfusion. cTNI as well as levels of tumor necrosis factor alpha (TNFalpha), hydroxyl radical (.OH), nitric oxide (NO), and alanine transferase (ALT) were measured.

RESULTS

I/R of the liver induced a significant increase in ALT (P<.001). Increased cTNI levels (P<.05) were associated with inflammatory responses, such as elevated levels of TNFalpha (P<.001), . OH (P<.001), and NO (P<.001). After administration of 3-aminobenzamide, a poly(ADP-ribose) polymerase (PARP) inhibitor, liver and heart injuries were significantly attenuated (P<.05).

CONCLUSIONS

I/R-induced liver injury was associated with cardiovascular injury, perhaps resulting from inflammatory responses triggered by elevated levels of reactive radical species of nitric oxide, superoxide, and peroxynitrite, by which PARP was activated. 3-Aminobenzamide, significantly attenuated I/R-induced liver and heart injuries.

The role of poly(ADP-ribose) polymerase-1 in CNS disease

Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme that contributes to both neuronal death and survival under stress conditions. PARP-1 is the most abundant of several PARP family members, accounting for more than 85% of nuclear PARP activity, and is present in all nucleated cells of multicellular animals. When activated by DNA damage, PARP-1 consumes nicotinamide adenine dinucleotide (NAD+) to form branched polymers of ADP-ribose on target proteins. This process can have at least three important consequences in the CNS, depending on the cell type and the extent of DNA damage: 1) Poly(ADP-ribose) formation on histones and on enzymes involved in DNA repair can prevent sister chromatid exchange and facilitate base-excision repair; 2) poly(ADP-ribose) formation can influence the action of transcription factors, notably nuclear factor kappaB, and thereby promote inflammation; and 3) extensive PARP-1 activation can promote neuronal death through mechanisms involving NAD+ depletion and release of apoptosis inducing factor from the mitochondria. PARP-1 activation is thereby a key mediator of neuronal death during excitotoxicity, ischemia, and oxidative stress, and PARP-1 gene deletion or pharmacological inhibition can markedly improve neuronal survival in these settings. PARP-1 activation has also been identified in Alzheimer's disease and in experimental allergic encephalitis, but the role of PARP-1 in these disorders remains to be established.

Poly(ADP-ribose) polymerase-1 inhibition protects the brain against systemic inflammation

Poly(ADP-ribose) polymerase-1 (PARP-1) is involved in DNA repair, but its overactivation can induce cell death. Our aim was to investigate the role of PARP-1 in activation of programmed cell death processes in the brain during systemic inflammation. Our data indicated that lipopolysaccharide (1mg/kgb.w., i.p.)-evoked systemic inflammation enhanced PARP-1 activity in the mouse brain, leading to the lowering of beta-NAD(+) concentration, to translocation of apoptosis inducing factor from mitochondria to the nucleus, and to enhanced lipid peroxidation. Inhibitor of PARP-1, 3-aminobenzamide (30 mg/kgb.w., i.p.), protected the brain against prooxidative and cell death processes, suggesting involvement of PARP-1 in systemic inflammation-related processes in the brain.

The Rothmund-Thomson gene product RECQL4 localizes to the nucleolus in response to oxidative stress

Mutations in the RECQL4 helicase gene have been linked to Rothmund-Thomson syndrome (RTS), which is characterized by poikiloderma, growth deficiency, and a predisposition to cancer. Examination of RECQL4 subcellular localization in live cells demonstrated a nucleoplasmic pattern and, to a lesser degree, staining in nucleoli. Analysis of RECQL4-GFP deletion mutants revealed two nuclear localization regions in the N-terminal region of RECQL4 and a nucleolar localization signal at amino acids 376-386. RECQL4 localization did not change after treatment with the DNA-damaging agents bleomycin, etoposide, UV irradiation and gamma irradiation, in contrast to the Bloom and Werner syndrome helicases that relocate to distinct nuclear foci after damage. However, in a significant number of cells exposed to hydrogen peroxide or streptonigrin, RECQL4 accumulated in nucleoli. Using a T7 phage display screen, we determined that RECQL4 interacts with poly(ADP-ribose) polymerase-1 (PARP-1), a nuclear enzyme that promotes genomic integrity through its involvement in DNA repair and signaling pathways. The RECQL4 nucleolar localization was inhibited by pretreatment with a PARP-1 inhibitor. The C-terminal portion of RECQL4 was found to be an in vitro substrate for PARP-1. These results demonstrate changes in the intracellular localization of RECQL4 in response to oxidative stress and identify an interaction between RECQL4 and PARP-1.

MafA expression and insulin promoter activity are induced by nicotinamide and related compounds in INS-1 pancreatic beta-cells

Nicotinamide has been reported to induce differentiation of precursor/stem cells toward a beta-cell phenotype, increase islet regeneration, and enhance insulin biosynthesis. Exposure of INS-1 beta-cells to elevated glucose leads to reduced insulin gene transcription, and this is associated with diminished binding of pancreatic duodenal homeobox factor 1 (PDX-1) and mammalian homologue of avian MafA/l-Maf (MafA). Nicotinamide and other low-potency poly(ADP-ribose) polymerase (PARP) inhibitors were thus tested for their ability to restore insulin promoter activity. The low-potency PARP inhibitors nicotinamide, 3-aminobenzamide, or PD128763 increased expression of a human insulin reporter gene suppressed by elevated glucose. In contrast, the potent PARP-1 inhibitors PJ34 or INO-1001 had no effect on promoter activity. Antioxidants, including N-acetylcysteine, lipoic acid, or quercetin, only minimally induced the insulin promoter. Site-directed mutations of the human insulin promoter mapped the low-potency PARP inhibitor response to the C1 element, which serves as a MafA binding site. INS-1 cells exposed to elevated glucose had markedly reduced MafA protein and mRNA levels. Low-potency PARP inhibitors restored MafA mRNA and protein levels, but they had no affect on PDX-1 protein levels or binding activity. Increased MafA expression by low-potency PARP inhibitors was independent of increased MafA protein or mRNA stability. These data suggest that low-potency PARP inhibitors increase insulin biosynthesis, in part, through a mechanism involving increased MafA gene transcription.

Effect of 3-aminobenzamide, PARP inhibitor, on matrix metalloproteinase-9 level in plasma and brain of ischemic stroke model

We investigated the effect of poly(ADP-ribose) polymerase (PARP) inhibitor on the levels of plasma and brain matrix metalloproteinase-9 (MMP-9) and the expression of nuclear factor kappa B (NF-kappaB) during experimental focal cerebral ischemia. The 3-aminobenzamide (3-AB), a PARP inhibitor, and saline were administered to 80 Sprague-Dawley rats [3-AB group; 5 rats for plasma sampling, 35 for brain sampling, and 40 for TTC staining] and to 85 rats (10, 35, and 40, respectively), respectively, 10 min before the occlusion of the left middle cerebral artery (MCAo) for 2 h. Infarct volume was measured by TTC staining, the serial levels of plasma and brain MMP-9 were measured by zymography just before and 2, 4, 8, 24, 48, and 72 h after MCAo, brain NF-kappaB activity was determined by Western blotting, and neutrophil infiltration was evaluated by assessing myeloperoxidase activity. Compared with control group, the levels of plasma and brain MMP-9, brain NF-kappaB, and MPO activities were significantly reduced in 3-AB group at each time point (p<0.05). Plasma MMP-9 increased maximally at 4h and then decreased rapidly, brain MMP-9 increased maximally at 24 h and persisted until 72 h, and NF-kappaB increased maximally at 24h and then decreased slowly in both groups. Therefore, the PARP inhibitor reduces the expression of MMP-9 and NF-kappaB and the infiltration of neutrophils in ischemic stroke.

15-Deoxy-delta12,14-prostaglandin J2, a neuroprotectant or a neurotoxicant?

15-Deoxy-delta12,14-prostaglandin J2 (15d-PGJ2) is a potent ligand for peroxisome proliferators-activated receptor gamma (PPARgamma). However, its various effects independent of PPARgamma have recently been observed. The effect of 15d-PGJ2 on neuronal cells is still controversial. We investigated its effect on neuronal cells (N18D3 cells). When N18D3 cells were treated with 15d-PGJ2, the viability was not changed up to 8 microM, but decreased at higher than 8 microM. The expressions of survival signals, such as p85a phosphatidylinositol 3-kinase, phospho-Akt, and phospho-glycogen synthase kinase-3 beta (Ser-9), slightly increased up to 8 microM, however, decreased at higher than 8 microM. The levels of free radicals and membrane lipid peroxidation and the expression of c-Jun N-terminal Kinase increased in a dose-dependent manner, especially at higher than 8 microM. However, the expressions of death signals, such as cytosolic cytochrome c, activated caspase-3, and cleaved poly(ADP-ribose) polymerase, decreased up to 8 microM, however, increased at higher than 8 microM. In the study to evaluate whether low dose of 15d-PGJ2, up to 8 microM, had protective effect on oxidative stress-injured N18D3 cells, compared to the cells treated with only 100 microM H2O2, the pretreatment with 8 microM 15d-PGJ2 increased the viability and the expressions of the survival signals, but decreased them of the death signals. These results indicate that 15d-PGJ2 could be a neuroprotectant or a neurotoxicant, depending on its concentration. Therefore, some specific optimum dose of 15d-PGJ2 may be a new potential therapeutic candidate for oxidative stress-injury model of neurodegenerative diseases.

Differential effects of diallyl disulfide on neuronal cells depend on its concentration

Diallyl disulfide (DADS) is one of the organosulfur compounds of garlic. The effects of DADS on neuronal cells have not clearly been established. We investigated its effects on the viability of neuronal cells (N18D3 cells), the levels of free radical and membrane lipid peroxidation, and the cell signals, such as phosphatidylinositol 3-kinase (PI3K)/Akt and glycogen synthase kinase-3 (GSK-3). When N18D3 cells were treated with several concentrations of DADS, the viability was not affected up to 25 microM, however, decreased at higher than 25 microM. The levels of free radicals and membrane lipid peroxidation were increased in a dose-dependent manner, especially at higher than 25 microM. The treatment of N18D3 cells with 25 microM DADS slightly increased the expressions of p85a PI3K, phosphorylated Akt and phosphorylated GSK-3, but the treatment with 100 microM significantly reduced them. To evaluate whether low concentration of DADS, up to 25 microM, had protective effect on oxidative stress-injured N18D3 cells, the viability of N18D3 cells (pretreated with DADS for 2h versus not pretreated) was evaluated 24h after their exposure to 100 microM H(2)O(2) for 30 min. Compared to the cells treated with only 100 microM H(2)O(2), the pretreatment with 25 microM DADS increased the viability, and the expressions of p85a PI3K, phosphorylated Akt and phosphorylated GSK-3. These results indicate that low concentration of DADS has protective effects on N18D3 cells, whereas high concentration is rather cytotoxic. Therefore, some specific optimum concentration of DADS may be a new potential therapeutic strategy for oxidative stress-injury in vitro model of neurodegenerative diseases.

Poly(ADP-ribose) polymerase-1 promotes microglial activation, proliferation, and matrix metalloproteinase-9-mediated neuron death

Activated microglia contribute to cell death in ischemic and neurodegenerative disorders of the CNS. Microglial activation is regulated in part by NF-kappaB, and the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) enhances NF-kappaB binding to DNA. In this study, the role of PARP-1 in microglia-mediated neurotoxicity was assessed using microglia from wild-type (wt) and PARP-1-/- mice. Cultured microglia were incubated with TNF-alpha, a cytokine that is up-regulated in many neurological disorders. When stimulated with TNF-alpha, wt microglia proliferated, underwent morphological changes characteristic of activation, and killed neurons placed in coculture. The effects of TNF-alpha were markedly attenuated both in PARP-1-/- microglia and in wt microglia treated with the PARP enzymatic inhibitor 3,4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2h)-isoquinolinone. These effects were also blocked by (E)-3-(4-methylphenylsulfonyl)-2-propenenenitrile, which inhibits translocation of NF-kappaB to the nucleus. TNF-alpha also up-regulated microglial release of matrix metalloproteinase-9 (MMP-9), an enzyme with potential neurotoxic properties that is transcriptionally regulated by NF-kappaB. This up-regulation was blocked in PARP-1-/- microglia and in wt microglia by the PARP inhibitor 3,4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2h)-isoquinolinone. Microglia from MMP-9-/- mice were used to evaluate the contribution of MMP-9 to microglial neurotoxicity. MMP-9-/- microglia treated with TNF-alpha showed substantially reduced neurotoxicity relative to the wt microglia. TNF-alpha-stimulated wt microglia treated with the MMP inhibitor ilomastat also showed reduced neurotoxicity. These findings suggest that PARP-1 activation is required for both TNF-alpha-induced microglial activation and the neurotoxicity resulting from TNF-alpha-induced MMP-9 release.

The effect of PARP inhibitor on ischaemic cell death, its related inflammation and survival signals

Poly(ADP-ribose) polymerase (PARP) plays an important role in ischaemic cell death, and 3-aminobenzamide (3-AB), one of the PARP inhibitors, has a protective effect on ischaemic stroke. We investigated the neuroprotective mechanisms of 3-AB in ischaemic stroke. The occlusion of middle cerebral artery (MCA) was made in 170 Sprague-Dawley rats, and reperfusion was performed 2 h after the occlusion. Another 10 Sprague-Dawley rats were used for sham operation. 3-AB was administered to 85 rats 10 min before the occlusion [3-AB group (n = 85) vs. control group without 3-AB (n = 85)]. Infarct volume and water content were measured, brain magnetic resonance imaging, terminal deoxynucleotidyltransferase (TdT)-mediated dUTP-biotin nick end-labelling (TUNEL) and Cresyl violet staining were performed, and immunoreactivities (IRs) of poly(ADP-ribose) polymer (PAR), cleaved caspase-3, CD11b, intercellular adhesion molecule-1 (ICAM-1), cyclooxygenase-2 (COX-2), phospho-Akt (pAkt) and phospho-glycogen synthase kinase-3 (pGSK-3) were compared in the peri-infarcted region of the 3-AB group and its corresponding ischaemic region of the control group at 2, 8, 24 and 72 h after the occlusion. In the 3-AB group, the infarct volume and the water content were decreased (about 45% and 3.6%, respectively, at 24 h), the number of TUNEL-positive cells was decreased (about 36% at 24 h), and the IRs of PAR, cleaved caspase-3, CD11b, ICAM-1 and COX-2 were significantly reduced, while the IRs of pAkt and pGSK-3 were increased. These results suggest that 3-AB treatment could reduce the infarct volume by reducing ischaemic cell death, its related inflammation and increasing survival signals. The inhibition of PARP could be another potential neuroprotective strategy in ischaemic stroke.

A newly synthesized poly(ADP-ribose) polymerase inhibitor, DR2313 [2-methyl-3,5,7,8-tetrahydrothiopyrano[4,3-d]-pyrimidine-4-one]: pharmacological profiles, neuroprotective effects, and therapeutic time window in cerebral ischemia in rats

We investigated the pharmacological profiles of DR2313 [2-methyl-3,5,7,8-tetrahydrothiopyrano[4,3-d]pyrimidine-4-one], a newly synthesized poly(ADP-ribose) polymerase (PARP) inhibitor, and its neuroprotective effects on ischemic injuries in vitro and in vivo. DR2313 competitively inhibited poly(ADP-ribosyl)ation in nuclear extracts of rat brain in vitro (K(i) = 0.23 microM). Among several NAD(+)-utilizing enzymes, DR2313 was specific for PARP but not selective between PARP-1 and PARP-2. DR2313 also showed excellent profiles in water solubility and rat brain penetrability. In in vitro models of cerebral ischemia, exposure to hydrogen peroxide or glutamate induced cell death with overactivation of PARP, and treatment with DR2313 reduced excessive formation of poly(ADP-ribose) and cell death. In both permanent and transient focal ischemia models in rats, pretreatment with DR2313 (10 mg/kg i.v. bolus and 10 mg/kg/h i.v. infusion for 6 h) significantly reduced the cortical infarct volume. To determine the therapeutic time window of neuroprotection by DR2313, the effect of post-treatment was examined in transient focal ischemia model and compared with that of a free radical scavenger, MCI-186 (3-methyl-1-phenyl-2-pyrazolone-5-one). Pretreatment with MCI-186 (3 mg/kg i.v. bolus and 3 mg/kg/h i.v. infusion for 6 h) significantly reduced the infarct volume, whereas the post-treatment failed to show any effects. In contrast, post-treatment with DR2313 (same regimen) delaying for 2 h after ischemia still prevented the progression of infarction. These results indicate that DR2313 exerts neuroprotective effects via its potent PARP inhibition, even when the treatment is initiated after ischemia. Thus, a PARP inhibitor like DR2313 may be more useful in treating acute stroke than a free radical scavenger.