Poly(ADP-ribose) mediates bioenergetic defects and redox imbalance in neurons following oxygen and glucose deprivation

PARP-1 over-activation results in cell death via excessive PAR generation in different cell types, including neurons following brain ischemia. Glycolysis, mitochondrial function, and redox balance are key cellular processes altered in brain ischemia. Studies show that PAR generated after PARP-1 over-activation can bind hexokinase-1 (HK-1) and result in glycolytic defects and subsequent mitochondrial dysfunction. HK-1 is the neuronal hexokinase and catalyzes the first reaction of glycolysis, converting glucose to glucose-6-phosphate (G6P), a common substrate for glycolysis, and the pentose phosphate pathway (PPP). PPP is critical in maintaining NADPH and GSH levels via G6P dehydrogenase activity. Therefore, defects in HK-1 will not only decrease cellular bioenergetics but will also cause redox imbalance due to the depletion of GSH. In brain ischemia, whether PAR-mediated inhibition of HK-1 results in bioenergetics defects and redox imbalance is not known. We used oxygen-glucose deprivation (OGD) in mouse cortical neurons to mimic brain ischemia in neuronal cultures and observed that PARP-1 activation via PAR formation alters glycolysis, mitochondrial function, and redox homeostasis in neurons. We used pharmacological inhibition of PARP-1 and adenoviral-mediated overexpression of wild-type HK-1 (wtHK-1) and PAR-binding mutant HK-1 (pbmHK-1). Our data show that PAR inhibition or overexpression of HK-1 significantly improves glycolysis, mitochondrial function, redox homeostasis, and cell survival in mouse cortical neurons exposed to OGD. These results suggest that PAR binding and inhibition of HK-1 during OGD drive bioenergetic defects in neurons due to inhibition of glycolysis and impairment of mitochondrial function.

Resveratrol Preconditioning Downregulates PARP1 Protein to Alleviate PARP1-Mediated Cell Death Following Cerebral Ischemia

Stroke remains a leading cause of mortality; however, available therapeutics are limited. The study of ischemic tolerance, in paradigms such as resveratrol preconditioning (RPC), provides promise for the development of novel prophylactic therapies. The heavily oxidative environment following stroke promotes poly-ADP-ribose polymerase 1 (PARP1)-overactivation and parthanatos, both of which are major contributors to neuronal injury. In this study, we tested the hypothesis that RPC instills ischemic tolerance through decreasing PARP1 overexpression and parthanatos following in vitro and in vivo cerebral ischemia. To test this hypothesis, we utilized rat primary neuronal cultures (PNCs) and middle cerebral artery occlusion (MCAO) in the rat as in vitro and in vivo models, respectively. RPC was administered 2 days preceding ischemic insults. RPC protected PNCs against oxygen and glucose deprivation (OGD)-induced neuronal loss, as well as increases in total PARP1 protein, implying protection against PARP1-overactivation. Twelve hours following OGD, we observed reductions in NAD+/NADH as well as an increase in AIF nuclear translocation, but RPC ameliorated NAD+/NADH loss and blocked AIF nuclear translocation. MCAO in the rat induced AIF nuclear translocation in the ischemic penumbra after 24 h, which was ameliorated with RPC. We tested the hypothesis that RPC's neuroprotection was instilled through long-term downregulation of nuclear PARP1 protein. RPC downregulated nuclear PARP1 protein for at least 6 days in PNCs, likely contributing to RPC's ischemic tolerance. This study describes a novel mechanism by which RPC instills prophylaxis against ischemia-induced PARP1 overexpression and parthanatos, through a long-term reduction of nuclear PARP1 protein.

Effects of poly (ADP-ribose) polymerase inhibitor treatment on the repair process of ischemic acute kidney injury

Excessive activation of poly (ADP-ribose) polymerase (PARP) contributes to ischemic acute kidney injury (AKI). PARP inhibition has been shown to be beneficial in renal ischemia-reperfusion injury (IRI) in the early phase, but its role in the repair process remains unclear. The effects of JPI-289, a novel PARP inhibitor, during the healing phase after renal IRI were investigated. IRI was performed on 9-week-old male C57BL/6 mice. Saline or JPI-289 100 mg/kg was intraperitoneally administered once at 24 h or additionally at 48 h after IRI. Hypoxic HK-2 cells were treated with JPI-289. Renal function and fibrosis extent were comparable between groups. JPI-289 treatment caused more prominent tubular atrophy and proinflammatory intrarenal leukocyte phenotypes and cytokines/chemokines changes at 12 weeks after unilateral IRI. JPI-289 treatment enhanced gene expressions associated with collagen formation, toll-like receptors, and the immune system in proximal tubules and endothelial cells after IRI. JPI-289 treatment at 3 or 6 h after hypoxia facilitated proliferation of hypoxic HK-2 cells, whereas further treatment after 24 h suppressed proliferation. Delayed inhibition of PARP after renal IRI did not facilitate the repair process during the early healing phase but rather may aggravate renal tubular atrophy during the late healing phase in ischemic AKI.

Poly (ADP-Ribose) polymerase 1 and parthanatos in neurological diseases: From pathogenesis to therapeutic opportunities

Poly (ADP-ribose) polymerase-1 (PARP-1) is the most extensively studied member of the PARP superfamily, with its primary function being the facilitation of DNA damage repair processes. Parthanatos is a type of regulated cell death cascade initiated by PARP-1 hyperactivation, which involves multiple subroutines, including the accumulation of ADP-ribose polymers (PAR), binding of PAR and apoptosis-inducing factor (AIF), release of AIF from the mitochondria, the translocation of the AIF/macrophage migration inhibitory factor (MIF) complex, and massive MIF-mediated DNA fragmentation. Over the past few decades, the role of PARP-1 in central nervous system health and disease has received increasing attention. In this review, we discuss the biological functions of PARP-1 in neural cell proliferation and differentiation, memory formation, brain ageing, and epigenetic regulation. We then elaborate on the involvement of PARP-1 and PARP-1-dependant parthanatos in various neuropathological processes, such as oxidative stress, neuroinflammation, mitochondrial dysfunction, excitotoxicity, autophagy damage, and endoplasmic reticulum (ER) stress. Additional highlight contains PARP-1's implications in the initiation, progression, and therapeutic opportunities for different neurological illnesses, including neurodegenerative diseases, stroke, autism spectrum disorder (ASD), multiple sclerosis (MS), epilepsy, and neuropathic pain (NP). Finally, emerging insights into the repurposing of PARP inhibitors for the management of neurological diseases are provided. This review aims to summarize the exciting advancements in the critical role of PARP-1 in neurological disorders, which may open new avenues for therapeutic options targeting PARP-1 or parthanatos.

Radiotherapy-Poly(ADP-ribose) Polymerase Inhibitor Combinations: Progress to Date

Radiation resistance remains a huge clinical problem for cancer patients and oncologists in the 21st century. In recent years, the mammalian DNA damage response (DDR) has been extensively characterized and shown to play a key role in determining cellular survival following ionizing radiation exposure. Genomic instability due to altered DDR is a hallmark of cancer, with many tumors exhibiting abnormal DNA repair or lack of redundancy in DDR. Targeting the abnormal DDR phenotype of tumor cells could lead to substantial gains in radiotherapy efficacy, improving local control and survival for patients with cancers that are refractory to current therapies. Poly(ADP-ribose) polymerase inhibitors (PARPi) are the most clinically advanced DDR inhibitors under investigation as radiosensitisers. Preclinical evidence suggests that PARPi may provide tumor specific radiosensitisation in certain contexts. In addition to inhibition of DNA single strand break repair, PARPi may offer other benefits in combination treatment including radiosensitisation of hypoxic cells and targeting of alternative repair pathways such as microhomology mediated end joining which are increasingly recognized to be upregulated in cancer. Several early phase clinical trials of PARPi with radiation have completed or are in progress. Early reports have highlighted tumor specific challenges, with tolerability dependent upon anatomical location and use of concomitant systemic therapies; these challenges were largely predicted by preclinical data. This review discusses the role of PARP in the cellular response to ionizing radiation, summarizes preclinical studies of PARPi in combination with radiotherapy and explores current early phase clinical trials that are evaluating these combinations.

PARP-1-Associated Pathological Processes: Inhibition by Natural Polyphenols

Poly (ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme involved in processes of cell cycle regulation, DNA repair, transcription, and replication. Hyperactivity of PARP-1 induced by changes in cell homeostasis promotes development of chronic pathological processes leading to cell death during various metabolic disorders, cardiovascular and neurodegenerative diseases. In contrast, tumor growth is accompanied by a moderate activation of PARP-1 that supports survival of tumor cells due to enhancement of DNA lesion repair and resistance to therapy by DNA damaging agents. That is why PARP inhibitors (PARPi) are promising agents for the therapy of tumor and metabolic diseases. A PARPi family is rapidly growing partly due to natural polyphenols discovered among plant secondary metabolites. This review describes mechanisms of PARP-1 participation in the development of various pathologies, analyzes multiple PARP-dependent pathways of cell degeneration and death, and discusses representative plant polyphenols, which can inhibit PARP-1 directly or suppress unwanted PARP-dependent cellular processes.

Discovery of 5-{4-[(7-Ethyl-6-oxo-5,6-dihydro-1,5-naphthyridin-3-yl)methyl]piperazin-1-yl}-N-methylpyridine-2-carboxamide (AZD5305): A PARP1-DNA Trapper with High Selectivity for PARP1 over PARP2 and Other PARPs

Poly-ADP-ribose-polymerase (PARP) inhibitors have achieved regulatory approval in oncology for homologous recombination repair deficient tumors including BRCA mutation. However, some have failed in combination with first-line chemotherapies, usually due to overlapping hematological toxicities. Currently approved PARP inhibitors lack selectivity for PARP1 over PARP2 and some other 16 PARP family members, and we hypothesized that this could contribute to toxicity. Recent literature has demonstrated that PARP1 inhibition and PARP1-DNA trapping are key for driving efficacy in a BRCA mutant background. Herein, we describe the structure- and property-based design of 25 (AZD5305), a potent and selective PARP1 inhibitor and PARP1-DNA trapper with excellent in vivo efficacy in a BRCA mutant HBCx-17 PDX model. Compound 25 is highly selective for PARP1 over other PARP family members, with good secondary pharmacology and physicochemical properties and excellent pharmacokinetics in preclinical species, with reduced effects on human bone marrow progenitor cells in vitro.

Why structure and chain length matter: on the biological significance underlying the structural heterogeneity of poly(ADP-ribose)

Poly(ADP-ribosyl)ation (PARylation) is a multifaceted post-translational modification, carried out by poly(ADP-ribosyl)transferases (poly-ARTs, PARPs), which play essential roles in (patho-) physiology, as well as cancer therapy. Using NAD+ as a substrate, acceptors, such as proteins and nucleic acids, can be modified with either single ADP-ribose units or polymers, varying considerably in length and branching. Recently, the importance of PAR structural heterogeneity with regards to chain length and branching came into focus. Here, we provide a concise overview on the current knowledge of the biochemical and physiological significance of such differently structured PAR. There is increasing evidence revealing that PAR's structural diversity influences the binding characteristics of its readers, PAR catabolism, and the dynamics of biomolecular condensates. Thereby, it shapes various cellular processes, such as DNA damage response and cell cycle regulation. Contrary to the knowledge on the consequences of PAR's structural diversity, insight into its determinants is just emerging, pointing to specific roles of different PARP members and accessory factors. In the future, it will be interesting to study the interplay with other post-translational modifications, the contribution of natural PARP variants, and the regulatory role of accessory molecules. This has the exciting potential for new therapeutic approaches, with the targeted modulation and tuning of PARPs' enzymatic functions, rather than their complete inhibition, as a central premise.

Poly (ADP-ribose) polymerase-1 as a promising drug target for neurodegenerative diseases

AIMS

Poly (ADP-ribose) polymerase- (PARP)-1 is predominantly triggered by DNA damage. Overexpression of PARP-1 is known for its association with the pathogenesis of several CNS disorders, such as Stroke, Parkinson's disease (PD), Alzheimer's disease (AD), Huntington (HD) and Amyotrophic lateral sclerosis (ALS). NAD+ depletion resulted PARP related cell death only happened when the trial used extreme high oxidization treatment. Inhibition of PARP1/2 may induce replication related cell death due to un-repaired DNA damage. This review has discussed PARP-1 modulated downstream pathways in neurodegeneration and various FDA approved PARP-1 inhibitors.

MATERIALS AND METHODS

A systematic literature review of PubMed, Medline, Bentham, Scopus and EMBASE (Elsevier) databases was carried out to understand the nature of the extensive work done on mechanistic role of Poly (ADP-ribose) polymerase and its inhibition in Neurodegenerative diseases.

KEY FINDINGS

Several researchers have put forward number of potential treatments, of which PARP-1 enzyme has been regarded as a potent target intended for the handling of neurodegenerative ailments. Targeting PARP using its chemical inhibitors in various neurodegenerative may have therapeutic outcomes by reducing neuronal death mediated by PARPi. Numerous PARP-1 inhibitors have been studied in neurodegenerative diseases but they haven't been clinically evaluated.

SIGNIFICANCE

In this review, the pathological role of PARP-1 in various neurodegenerative diseases has been discussed along with the therapeutic role of PARP-1 inhibitors in various neurodegenerative diseases.

Emerging neuroprotective strategies for the treatment of ischemic stroke: An overview of clinical and preclinical studies

Stroke is the leading cause of disability and thesecond leading cause of death worldwide. With the global population aged 65 and over growing faster than all other age groups, the incidence of stroke is also increasing. In addition, there is a shift in the overall stroke burden towards younger age groups, particularly in low and middle-income countries. Stroke in most cases is caused due to an abrupt blockage of an artery (ischemic stroke), but in some instances stroke may be caused due to bleeding into brain tissue when a blood vessel ruptures (hemorrhagic stroke). Although treatment options for stroke are still limited, with the advancement in recanalization therapy using both pharmacological and mechanical thrombolysis some progress has been made in helping patients recover from ischemic stroke. However, there is still a substantial need for the development of therapeutic agents for neuroprotection in acute ischemic stroke to protect the brain from damage prior to and during recanalization, extend the therapeutic time window for intervention and further improve functional outcome. The current review has assessed the past challenges in developing neuroprotective strategies, evaluated the recent advances in clinical trials, discussed the recent initiative by the National Institute of Neurological Disorders and Stroke in USA for the search of novel neuroprotectants (Stroke Preclinical Assessment Network, SPAN) and identified emerging neuroprotectants being currently evaluated in preclinical studies. The underlying molecular mechanism of each of the neuroprotective strategies have also been summarized, which could assist in the development of future strategies for combinational therapy in stroke treatment.

Poly (ADP-Ribose) Polymerase Inhibitor Treatment as a Novel Therapy Attenuating Renal Ischemia-Reperfusion Injury

Intrarenal robust inflammatory response following ischemia-reperfusion injury (IRI) is a major factor in the pathogenesis of renal injury in ischemic acute kidney injury (AKI). Although numerous studies have investigated various agents of immune modulation or suppression for ischemic AKI, few showed reproducible effects. We hypothesized that poly (ADP-ribose) polymerase (PARP) inhibitor may favorably change post-ischemic intrarenal immunologic micromilieu by reducing damage-associated molecular pattern (DAMP) signals and improve renal outcome in ischemic AKI. The effects of JPI-289 (a PARP inhibitor) on early renal injury in a murine IRI model and hypoxic HK-2 cell model were investigated. Bilateral IRI surgery was performed in three groups of 9-week-old male C57BL/6 mice (control, JPI-289 50 mg/kg, and JPI-289 100 mg/kg; n = 9–10 in each group). Saline or JPI-289 was intraperitoneally injected. Renal function deterioration was significantly attenuated in the JPI-289 treatment groups in a dose-dependent manner. Inflammatory cell infiltration and proinflammatory cytokine/chemokine expressions in the post-ischemic kidneys were also attenuated by JPI-289 treatment. JPI-289 treatment at 0.5 and 0.75 μg/ml facilitated the proliferation of hypoxic HK-2 cells. PARP inhibition with JPI-289 treatment showed favorable effects in ischemic AKI by attenuating intrarenal inflammatory cascade in a murine model and facilitating proliferation of hypoxic HK-2 cells.

Poly(ADP-ribose) polymerase inhibition: past, present and future

The process of poly(ADP-ribosyl)ation and the major enzyme that catalyses this reaction, poly(ADP-ribose) polymerase 1 (PARP1), were discovered more than 50 years ago. Since then, advances in our understanding of the roles of PARP1 in cellular processes such as DNA repair, gene transcription and cell death have allowed the investigation of therapeutic PARP inhibition for a variety of diseases - particularly cancers in which defects in DNA repair pathways make tumour cells highly sensitive to the inhibition of PARP activity. Efforts to identify and evaluate potent PARP inhibitors have so far led to the regulatory approval of four PARP inhibitors for the treatment of several types of cancer, and PARP inhibitors have also shown therapeutic potential in treating non-oncological diseases. This Review provides a timeline of PARP biology and medicinal chemistry, summarizes the pathophysiological processes in which PARP plays a role and highlights key opportunities and challenges in the field, such as counteracting PARP inhibitor resistance during cancer therapy and repurposing PARP inhibitors for the treatment of non-oncological diseases.

First-in-Human Evaluation of the Safety, Tolerability, and Pharmacokinetics of a Neuroprotective Poly (ADP-ribose) Polymerase-1 Inhibitor, JPI-289, in Healthy Volunteers

Background

Poly (ADP-ribose) polymerase-1 (PARP-1) inhibitor has therapeutic potential for acute ischemic stroke by suppressing microglial activation and facilitating neuroprotection. In this first-in-human study, we investigate the safety, tolerability and pharmacokinetics (PK) of JPI-289 in healthy male volunteers.

Subjects and Methods

In single ascending dose (SAD) study, 35, 75, 150, 300, 600 mg JPI-289 or placebo was infused intravenously over 30 minutes to 40 subjects. In multiple ascending dose (MAD) study, 150, 300, 450 mg JPI-289 or placebo was infused over 1 hour every 12 hours to each of 24 subjects for 3.5 days (7 times). The plasma and urine concentrations of JPI-289 and its metabolites were determined.

Results

In the SAD study, AUC_last and C_max tended to increase supra-proportionally especially at higher doses in SAD study. However, C_max showed dose-proportionality in the range of 75–600mg. JPI-289 reached a mean T_max within 0.50 hour after dosing and a mean elimination half-life (t_1/2) was 2.18 to 3.21 hours. In the MAD study, observed accumulation index ranged from 1.52 to 1.76. The effective half-life of JPI-289 was 1.88 to 3.05 hours, indicating that the plasma JPI-289 concentration rapidly reaches steady state. % recovered of JPI-289 measured in urine was 1.59–9.05%. In both studies, concentration of metabolites was less than 10% of JPI-289. Adverse events reported in the study were all mild in intensity and resolved without any sequelae.

Conclusion

The tolerable dose ranges and pharmacokinetic characteristics of JPI-289 evaluated in these studies will be useful in further clinical development of JPI-289.

Local and systemic metabolic alterations in brain, plasma, and liver of rats in response to aging and ischemic stroke, as detected by nuclear magnetic resonance (NMR) spectroscopy

Metabolic dysfunction impacts stroke incidence and outcome. However, the intricate association between altered metabolic program due to aging, and focal ischemia in brain, circulation, and peripheral organs is not completely elucidated. Here we identified locally and systemically altered metabolites in brain, liver, and plasma as a result of normal aging, ischemic-stroke, and extended time of reperfusion injury. Comprehensive quantitative metabolic profiling was carried out using nuclear magnetic resonance spectroscopy. Aging, but healthy rats showed significant metabolic alterations in the brain, but only a few metabolic changes in the liver and plasma as compared to younger rats. But, ischemic stroke altered metabolites significantly in liver and plasma of older rats during early acute phase. Major metabolic changes were also seen in the brains of younger rats following ischemic stroke during early acute phase of injury. We further report that metabolic changes occur sequentially in a tissue specific manner during extended reperfusion time of late repair phase. First metabolic alterations occurred in brain due to local injury. Next, changes in circulating metabolites in plasma occurred during acute-repair phase transition time. Lastly, the delayed systemic effect was seen in the peripheral organ, liver that exhibited significant and persistent changes in selected metabolites during later reperfusion time. The metabolic pathways involved in energy/glucose, and amino acid metabolism, inflammation, and oxidative stress were mainly altered as a result of aging and ischemia/reperfusion. Biomarker analysis revealed citrate, lysine, and tyrosine as potential age-independent blood metabolic biomarkers of ischemia/reperfusion. Overall, our study elucidates the complex network of metabolic events as a function of normal aging and acute stroke. We further provide evidence for a clear transition from local to systemic metabolic dysfunction due to ischemic injury in a time dependent manner, which may altogether greatly impact the post-stroke outcome.

Nicotinamide reverses behavioral impairments and provides neuroprotection in 3-nitropropionic acid induced animal model ofHuntington's disease: implication of oxidative stress- poly(ADP- ribose) polymerase pathway

Huntington's disease (HD) is characterized by cognitive and psychiatric impairment caused by neuronal degeneration in the brain. Several studies have supported the hypothesis that oxidative stress is the main pathogenic factor in HD. The current study aims to determine the possible neuroprotective effects of nicotinamide on 3-nitropropionic acid (3-NP) induced HD. Male Wistar albino rats were divided into six groups. Group I was the vehicle-treated control, group II received 3-NP (20 mg/kg, intraperitoneally (i.p.) for 4 days, group III received nicotinamide (500 mg/kg, i.p.). The remaining groups received a combination of 3-NP plus nicotinamide 100, 300 or 500 mg/kg, i.p. respectively for 8 days. Afterward, the motor function and hind paw activity in the limb withdrawal were tested; rats were then euthanized for biochemical and histopathological analyses. Treatment of rats with 3-NP altered the motor function, elevated oxidative stress and caused significant histopathological changes in the brain. The treatment of rats with nicotinamide (100, 300 and 500 mg/kg) improved the motor function tested by locomotor activity test, movement analysis, and limb withdrawal test, which was associated with decreased oxidative stress markers (malondialdehyde, nitrites) and increased antioxidant enzyme (glutathione) levels. In addition, nicotinamide treatment decreased lactate dehydrogenase and prevented neuronal death in the striatal region. Our study, therefore, concludes that antioxidant drugs like nicotinamide might slow progression of clinical HD and may improve the motor functions in HD patients. To the best of our knowledge, this study is the first to explore the neuroprotective effects of nicotinamide on 3-NP-induced HD.

Regulatory T cells increase after treatment with poly (ADP-ribose) polymerase-1 inhibitor in ischemic stroke patients

BACKGROUND

Regulatory T cells (Tregs) are thought to play a modulatory role in immune responses and to improve outcomes after ischemic stroke. Thus, various strategies for increasing Tregs in animal models of ischemic stroke have yielded successful results. The aim of this study was to examine the potential effect of poly (ADP-ribose) polymerase-1 (PARP-1) inhibitor on Treg proportion in stroke patients.

METHODS

Peripheral blood samples were collected from 12 ischemic stroke patients (within 72 h of stroke onset) and 5 healthy control subjects. Flow cytometry analyses and quantitative reverse transcription polymerase chain reactions (qRT-PCR) were performed on peripheral blood mononuclear cells (PBMCs) before and after treating them with PARP-1 inhibitor (3-AB; JPI-289 1 μm, JPI-289 10 μm) for 24 h.

RESULTS

Treg proportions were significantly higher in healthy controls (median 2.8%, IQR 2.6-5.0%) than ischemic stroke patients (median 1.6%, IQR 1.25-2.2%) (p < 0.001). In the latter, Treg proportions were positively correlated with age (r = 0.595, p = 0.041), but not with infarct volume (r = 0.367, p = 0.241). After PARP-1 inhibitor treatment, Treg proportions among PBMCs increased in response to high dose (10 μm) JPI-289 (median 2.3%, IQR 2.0-2.9%) as did Treg-associated transcription factors such as FoxP3 and CTLA-4 mRNA. PARP-1 inhibitor treatment also decreased pro-inflammatory cytokines (IFN-γ, TNF-α, and IL-17) and increased anti-inflammatory cytokines (IL-4, IL-10, and TGF-β1).

CONCLUSION

Treg proportions are reduced in ischemic stroke patients and increased by treatment with high-dose PARP-1 inhibitor JPI-289. The PARP-1 inhibitor also had a possible anti-inflammatory effect on cytokine levels, and may ameliorate the outcome of ischemic stroke by up-regulating Tregs.