Poly(adenosine diphosphate ribose) polymerase inhibition modulates spinal cord dysfunction after thoracoabdominal aortic ischemia-reperfusion

A Surgical Protocol for Establishing Spinal Cord Ischemia with Extended Lifespan and Low Complication Rates in Rats

BACKGROUND

Experimental animal models of ischemic spinal cord injury (iSCI) are essential for studying its pathogenesis and for developing new therapeutic strategies to improve functional recovery in humans. Many existing models, however, exhibit high variability or early lethality. A reliable experimental iSCI model would significantly advance novel treatment approaches for these severe neurological disorders. To this end, we have established a rat model of persistent iSCI with an extended lifespan.

METHODS

We have developed a novel iSCI model that induces localized ischemic lesions in the spinal cord of male Sprague-Dawley rats. This is achieved by cross clamping the descending aorta just rostral the azygos vein using an atraumatic bulldog clamp.

RESULTS

The experimental iSCI model consistently demonstrated symptoms specific to spinal cord ischemia at the lumbar level. The procedure takes approximately 50 min and does not require specialized surgical equipment. It has a survival rate of 84%, a recovery rate of 40%, and a complication rate of 16%.

CONCLUSIONS

We have successfully developed a rat model of persistent iSCI. This protocol proves to be highly reliable and holds promise for evaluating new therapeutic strategies aimed at promoting functional recovery in patients suffering from spinal cord ischemia.

Histological Findings After Aortic Cross-Clamping in Preclinical Animal Models

Spinal cord ischemic injury and paralysis are devastating complications after open surgical repair of thoracoabdominal aortic aneurysms. Preclinical models have been developed to simulate the clinical paradigm to better understand the neuropathophysiology and develop therapeutic treatment. Neuropathological findings in the preclinical models have not been comprehensively examined before. This systematic review studies the past 40 years of the histological findings after open surgical repair in preclinical models. Our main finding is that damage is predominantly in the grey matter of the spinal cord, although white matter damage in the spinal cord is also reported. Future research needs to examine the neuropathological findings in preclinical models after endovascular repair, a newer type of surgical repair used to treat aortic aneurysms.

Ethyl pyruvate modulates delayed paralysis following thoracic aortic ischemia reperfusion in mice

OBJECTIVE

Delayed paralysis is an unpredictable problem for patients undergoing complex repair of the thoracic/thoracoabdominal aorta. These experiments were designed to determine whether ethyl pyruvate (EP), a potent anti-inflammatory and antioxidant agent, might ameliorate delayed paralysis following thoracic aortic ischemia reperfusion (TAR).

METHODS

C57BL6 mice were subjected to 5 minutes of thoracic aortic ischemia followed by reperfusion for up to 48 hours. Mice received either 300 mg/kg EP or lactated ringers (LR) at 30 minutes before ischemia and 3 hours after reperfusion. Neurologic function was assessed using an established rodent scale. Spinal cord tissue was analyzed for markers of inflammation (keratinocyte chemoattractant [KC], interleukin-6 [IL-6]), microglial activation (ionized calcium-binding adapter molecule-1 [Iba-1]), and apoptosis (Bcl-2, Bax, and terminal deoxynucleotidyl transferase dUTP nick end labeling [TUNEL] staining) at 24 and 48 hours after TAR. Nissl body stained motor neurons were counted in the anterior horns sections from L1-L5 segments.

RESULTS

Ninety-three percent of the LR mice developed dense delayed paralysis between 40 and 48 hours after TAR, whereas only 39% of EP mice developed delayed paralysis (P < .01). Bcl-2 expression was higher (P < .05) and Iba-1 expression was lower (P < .05) in the EP group only at 24 hours reperfusion. At 48 hours, the number of motor neurons was higher (P < .01) and the number and TUNEL-positive cells was lower (P < .001) in the EP-treated mice. EP decreased the expression of KC (P < .01) and IL-6 (P < .001) at 48 hours after TAR.

CONCLUSIONS

The protection provided by EP against delayed paralysis correlated with preservation of motor neurons, higher expression of antiapoptotic molecules, decreased microglial cell activation, and decreased spinal cord inflammation. EP may be a treatment for humans at risk for delayed paralysis.

Spinal Cord Inflammation: Molecular Imaging after Thoracic Aortic Ischemia Reperfusion Injury

Purpose To evaluate whether noninvasive molecular imaging technologies targeting myeloperoxidase (MPO) can reveal early inflammation associated with spinal cord injury after thoracic aortic ischemia-reperfusion (TAR) in mice. Materials and Methods The study was approved by the institutional animal care and use committee. C57BL6 mice that were 8-10 weeks old underwent TAR (n = 55) or sham (n = 26) surgery. Magnetic resonance (MR) imaging (n = 6) or single photon emission computed tomography (SPECT)/computed tomography (CT) (n = 15) studies targeting MPO activity were performed after intravenous injection of MPO sensors (bis-5-hydroxytryptamide-tetraazacyclododecane [HT]-diethyneletriaminepentaacetic acid [DTPA]-gadolinium or indium 111-bis-5-HT-DTPA, respectively). Immunohistochemistry and flow cytometry were used to identify myeloid cells and neuronal loss. Proinflammatory cytokines, keratinocyte chemoattractant (KC), and interleukin 6 (IL-6) were measured with enzyme-linked immunosorbent assay. Statistical analyses were performed by using nonparametric tests and the Pearson correlation coefficient. P < .05 was considered to indicate a significant difference. Results Myeloid cells infiltrated into the injured cord at 6 and 24 hours after TAR. MR imaging confirmed the presence of ischemic lesions associated with mild MPO-mediated enhancement in the thoracolumbar spine at 24 hours compared with the sham procedure. SPECT/CT imaging of MPO activity showed marked MPO-sensor retention at 6 hours (P = .003) that continued to increase at 24 hours after TAR (P = .0001). The number of motor neurons decreased substantially at 24 hours after TAR (P < .01), which correlated inversely with in vivo inflammatory changes detected at molecular imaging (r = 0.64, P = .0099). MPO was primarily secreted by neutrophils, followed by lymphocyte antigen 6 complex^high monocytes and/or macrophages. There were corresponding increased levels of proinflammatory cytokines KC (P = .0001) and IL-6 (P = .0001) that mirrored changes in MPO activity. Conclusion MPO is a suitable imaging biomarker for identifying and tracking inflammatory damage in the spinal cord after TAR in a mouse model. ^© RSNA, 2016 Online supplemental material is available for this article.

Unusual increase in lumbar network excitability of the rat spinal cord evoked by the PARP-1 inhibitor PJ-34 through inhibition of glutamate uptake

Overactivity of poly(ADP-ribose) polymerase enzyme 1 (PARP-1) is suggested to be a major contributor to neuronal damage following brain or spinal cord injury, and has led to study the PARP-1 inhibitor 2-(dimethylamino)-N-(5,6-dihydro-6-oxophenanthridin-2yl)acetamide (PJ-34) as a neuroprotective agent. Unexpectedly, electrophysiological recording from the neonatal rat spinal cord in vitro showed that, under control conditions, 1-60 μM PJ-34 per se strongly increased spontaneous network discharges occurring synchronously on ventral roots, persisting for 24 h even after PJ-34 washout. The PARP-1 inhibitor PHE had no similar effect. The action by PJ-34 was reversibly suppressed by glutamate ionotropic receptor blockers and remained after applying strychnine and bicuculline. Fictive locomotion evoked by neurochemicals or by dorsal root stimulation was present 24 h after PJ-34 application. In accordance with this observation, lumbar neurons and glia were undamaged. Neurochemical experiments showed that PJ-34 produced up to 33% inhibition of synaptosomal glutamate uptake with no effect on GABA uptake. In keeping with this result, the glutamate uptake blocker TBOA (5 μM) induced long-lasting synchronous discharges without suppressing the ability to produce fictive locomotion after 24 h. The novel inhibition of glutamate uptake by PJ-34 suggested that this effect may compound tests for its neuroprotective activity which cannot be merely attributed to PARP-1 block. Furthermore, the current data indicate that the neonatal rat spinal cord could withstand a strong, long-lasting rise in network excitability without compromising locomotor pattern generation or circuit structure in contrast with the damage to brain circuits known to be readily produced by persistent seizures.

Poly(ADP-ribose) polymerase-1 mediates angiotensin II-induced expression of plasminogen activator inhibitor-1 and fibronectin in rat mesangial cells

OBJECTIVE

To investigate the effects of poly(ADP-ribose) polymerase-1 (PARP-1) on angiotensin II (Ang II)-induced plasminogen activator inhibitor-1 (PAI-1) and fibronectin (FN) in rat mesangial cells (RMCs).

METHODS

Followed by serum starvation for 16 h, RMCs were exposed to Ang II for an indicated time to examine the protein expression of PARP-1. The cells were treated with or without Ang II for 12-24 h in the presence or absence of an inhibitor of PARP, N-(6-oxo-5,6-dihydrophenanthridin-2-yl)-N,N-dimethylacetamide hydrochloride (PJ34) or small interfering RNA (siRNA) duplexes targeting PARP-1. The mRNA and protein expressions of PARP-1, PAI-1 and FN were determined by real-time RT-PCR and Western blot, respectively. The activity of PARP-1 was examined by colorimetric assay.

RESULTS

Ang II did not only significantly induce PARP-1 expression and activity, but also increased PAI-1 and FN expression in RMCs. All these responses induced by Ang II were significantly inhibited by both the PARP inhibitor PJ34 and downregulating PARP-1 with the siRNA technique.

CONCLUSIONS

Our data suggest that PARP-1 mediates Ang II-induced PAI-1 and FN in RMCs and may thus represent a potential therapeutic target in the treatment of glomerular disease.

Effect of the PARP-1 inhibitor PJ 34 on excitotoxic damage evoked by kainate on rat spinal cord organotypic slices

Excitotoxicity triggered by over-activation of glutamate receptors is thought to be an early mechanism of extensive neuronal death with consequent loss of function following lesion of spinal networks. One important process responsible for excitotoxic death is 'parthanatos' caused by hyperactivation of poly(ADP-ribose) polymerase (PARP) enzyme 1. Using rat organotypic spinal slices as in vitro models, the present study enquired if 2-(dimethylamino)-N-(5,6-dihydro-6-oxophenanthridin-2yl)acetamide (PJ 34), a pharmacological inhibitor of PARP-1, could counteract the excitotoxic damage evoked by transient application (1 h) of kainate, a potent analogue of glutamate. Kainate induced dose-dependent (1 μM threshold) neuronal loss (without damage to astrocytes) detected 24 h later via a PARP-1 dependent process that had peaked at 4 h after washout kainate. All spinal regions (ventral, central and dorsal) were affected, even though the largest damage was found in the dorsal area. Whereas PJ 34 did not protect against a large concentration (100 μM) of kainate, it significantly inhibited neuronal losses evoked by 10 μM kainate as long as it was co-applied with this glutamate agonist. When the application of PJ 34 was delayed to the washout time, neuroprotection was weak and regionally restricted. These data suggest that kainate-induced parthanatos developed early and was prevented by PJ 34 only when it was co-applied together with excitotoxic stimulus. Our results highlight the difficulty to arrest parthanatos as a mechanism of spinal neuron death in view of its low threshold of activation by kainate, its widespread distribution, and relatively fast development.

A mouse model of ischemic spinal cord injury with delayed paralysis caused by aortic cross-clamping

BACKGROUND

Spinal cord ischemia and paralysis are devastating perioperative complications that can accompany open or endovascular repair surgery for aortic aneurysms. Here, we report on the development of a new mouse model of spinal cord ischemia with delayed paralysis induced by cross-clamping the descending aorta.

METHODS

Transient aortic occlusion was produced in mice by cross-clamping the descending aorta through a lateral thoracotomy. To establish an optimal surgical procedure with limited mortality, variable cross-clamp times and core temperatures were tested between experiments.

RESULTS

The onset of paresis or paralysis and postsurgical mortality varied as a function of cross-clamp time and core temperature that was maintained during the period of cross-clamp. Using optimal surgical parameters (7.5-min cross-clamp duration at 33°C core temperature), the onset of paralysis is delayed 24-36 h after reperfusion, and more than 95% of mice survive through 9 weeks after surgery. These mice are further stratified into two groups, 70% (n = 19/27) of mice developing severe hind limb paralysis and the remaining mice showing mild, though still permanent, behavioral deficits.

CONCLUSION

This new model should prove useful as a preclinical tool for screening neuroprotective therapeutics and for defining the basic biologic mechanisms that cause delayed paralysis and neurodegeneration after transient spinal cord ischemia.

The effects of systemic hypothermia on a murine model of thoracic aortic ischemia reperfusion

INTRODUCTION

Hypothermia is widely used to mediate ischemia-reperfusion injury associated with repair of the thoracoabdominal aorta. Experiments were designed in a murine model of thoracic aortic ischemia-reperfusion (TAR) to evaluate the effect of moderate systemic hypothermia on neurologic function, spinal cord morphology, and indices of inflammation in critical organs.

METHODS

C57BL/6 mice were subjected to TAR under hypothermic (34 degrees C) or normothermic (38 degrees C) conditions, followed by 24 or 48 hours of normothermic reperfusion. Neurologic functions were assessed during reperfusion. Spinal cords were examined at 24 and 48 hours after reperfusion, and the degree of injury qualified by counting the number of viable motor neurons within the anterior horns. Keratinocyte chemokine, interleukin-6, and myeloperoxidase levels were measured from lung, liver, and kidney at 24 and 48 hours.

RESULTS

Normothermic TAR resulted in a dense neurologic deficit in all mice throughout the reperfusion period. Mice subjected to TAR under hypothermic conditions had transient, mild neurologic deficit during the initial periods of reperfusion. Between 24 and 48 hours, delayed paralysis developed in half of these mice, whereas the other half remained neurologically intact. Spinal cord histology showed a graded degree of injury that correlated with neurologic function. There was no correlation between markers of inflammation in various organs and neurologic outcomes following TAR.

CONCLUSION

Systemic moderate hypothermia was protective against immediate paralysis after TAR in all cases and was associated with delayed paralysis in 50% of mice. This study suggests that delayed-onset paralysis may be the result of a local insult, rather than a systemic inflammatory event, precipitating spinal cord injury.

Development of a simplified spinal cord ischemia model in mice

Use of genetically manipulated mice facilitates understanding pathological mechanisms in many diseases and contributes to therapy development. However, there is no practical and clinically relevant mouse model available for spinal cord ischemia. This report introduces a simplified long-term outcome mouse model of spinal cord ischemia. Male C57Bl/6J mice were anesthetized with isoflurane and endotracheally intubated. The middle segment of the thoracic aorta was clamped for 0, 8, 10 or 12 min via left lateral thoracotomy. Rectal temperature was maintained at 37.0+/-0.5 degrees C. A laser Doppler probe was used to measure lumbar spinal cord blood flow during thoracic aorta cross-clamping. Open field locomotor function and rotarod performance were evaluated at 1h and 1, 3, 5, and 7 days post-injury. Surviving neurons in the lumbar ventral horn were counted at 7 days post-injury. Cross-clamping the middle segment of the thoracic aorta resulted in approximately 90% blood flow reduction in the lumbar spinal cord. Neurological deficit and neuronal cell death were associated with ischemia duration. Another set of mice were subjected to 10 min aortic clamping or sham surgery and neurological function was examined at 1h and 1, 3, 5, 7, 14, and 28 days. Four of 5 mice (80%) in the injured group survived 28 days and had significant neurological deficit. This study indicates that cross-clamping of the aorta via left thoracotomy is a simple and reliable method to induce spinal cord ischemia in mice allowing definition of long-term outcome.

Effect of PJ34 on spinal cord tissue viability and gene expression in a murine model of thoracic aortic reperfusion injury

INTRODUCTION

These studies were designed to determine whether PJ34, a novel Poly-ADP Ribose Polymerase Inhibitor, modulates expression of markers of stress and inflammation in the spinal cord following ischemia/ reperfusion(TAR).

METHODS

129S1/SvImj mice were subjected to thoracic aortic occlusion and 48 hours of reperfusion (n = 38). EXPERIMENTAL GROUPS INCLUDED: Untreated Control (UC, n = 21); PJ34 (PJ34, n = 11) and sham (S, n = 6). At 48 hours, mice were euthanized for mRNA analysis and assessment of spinal cord viability.

RESULTS

PJ34 improved spinal cord tissue viability following TAR (UC:53.1 +/- 6.3, PJ34:73.5 +/- 4.1% sham, p < 0.01). mRNA analysis revealed significant expression of stress response genes in UC and PJ34 treated mice.

CONCLUSIONS

PJ34 enhanced mitochondrial activity and preserved neurologic function following TAR despite the expression of stress and pro-inflammatory markers within the spinal cord. The ongoing cord stress response in neurologically intact PJ34 treated mice may indicate the potential to develop delayed neurologic dysfunction.

Role of poly(ADP-ribose) polymerase during vascular reconstruction

Open vascular repair of ischemic myocardium and aortic aneurysms results in a systemic inflammatory response that influences the mortality and morbidity of these procedures. Recent studies in animal models of complex vascular reconstruction indicate that the activity of poly(ADP-ribose) polymerase (PARP) may influence the mortality and morbidity of these kinds of reconstructions. PARP's activity, localized to nuclei and mitochondria, is stimulated by deoxyribonucleic acid (DNA) strand breaks. Activation of PARP results in synthesis of poly(ADP-ribose) sugar moieties, whose primary role is to protect DNA from degradation during cytotoxic stress. Paradoxically, when stressful conditions similar to those experienced during vascular reconstructions result in overactivation of PARP, depletion of cellular levels of adenosine triphosphate and nicotinamide adenine dinucleotide can result in exacerbation of tissue injury. Herein we review the role of PARP in inflammation and its relevance to cardiovascular reconstructions.

Novel pharmacological approaches to the treatment of renal ischemia-reperfusion injury: a comprehensive review

Renal ischemia-reperfusion (I-R) contributes to the development of ischemic acute renal failure (ARF). Multi-factorial processes are involved in the development and progression of renal I-R injury with the generation of reactive oxygen species, nitric oxide and peroxynitrite, and the decline of antioxidant protection playing major roles, leading to dysfunction, injury, and death of the cells of the kidney. Renal inflammation, involving cytokine/adhesion molecule cascades with recruitment, activation, and diapedesis of circulating leukocytes is also implicated. Clinically, renal I-R occurs in a variety of medical and surgical settings and is responsible for the development of acute tubular necrosis (a characteristic feature of ischemic ARF), e.g., in renal transplantation where I-R of the kidney directly influences graft and patient survival. The cellular mechanisms involved in the development of renal I-R injury have been targeted by several pharmacological interventions. However, although showing promise in experimental models of renal I-R injury and ischemic ARF, they have not proved successful in the clinical setting (e.g., atrial natriuretic peptide, low-dose dopamine). This review highlights recent pharmacological developments, which have shown particular promise against experimental renal I-R injury and ischemic ARF, including novel antioxidants and antioxidant enzyme mimetics, nitric oxide and nitric oxide synthase inhibitors, erythropoietin, peroxisome-proliferator-activated receptor agonists, inhibitors of poly(ADP-ribose) polymerase, carbon monoxide-releasing molecules, statins, and adenosine. Novel approaches such as recent research involving combination therapies and the potential of non-pharmacological strategies are also considered.

The selective poly(ADP)ribose-polymerase 1 inhibitor INO1001 reduces spinal cord injury during porcine aortic cross-clamping-induced ischemia/reperfusion injury

OBJECTIVE

It is well-established that poly(ADP)ribose-polymerase (PARP) assumes major importance during ischemic brain damage, and the selective PARP-1 inhibitor PJ34 reduced spinal cord damage in murine aortic occlusion-induced ischemia/reperfusion injury. We investigated the effect of the PARP-1 inhibitor INO1001 on aortic-occlusion-related porcine spinal cord injury.

DESIGN AND SETTING

Prospective, randomized, controlled experimental study in an animal laboratory.

PATIENTS AND PARTICIPANTS

Ten anesthetized, mechanically ventilated, and instrumented pigs.

INTERVENTIONS

Animals underwent 45 min of thoracic aortic cross-clamping after receiving vehicle (n=5) or intravenous INO1001 (n=5, total dose 4 mg/kg administered both before clamping and during reperfusion). During reperfusion continuous intravenous norepinephrine was incrementally adjusted to maintain blood pressure at or above 80% of the preclamping level. Plasma INO1001 levels were analyzed by HPLC. After 4[Symbol: see text]h of reperfusion spinal cord biopsy samples were analyzed for neuronal damage (hematoxyline-eosine and Nissl staining), expression of the cyclin-dependent kinase inhibitor genes p21 and p27 (immunohistochemistry), and apoptosis (terminal deoxynucleotidyl transferase mediated nick end labeling assay).

MEASUREMENTS AND RESULTS

Plasma INO1001 levels were 0.8-2.3 and 0.30-0.76 mM before and after clamping, respectively. While 3-5% of the spinal cord neurons were irreversibly damaged in the INO1001 animals, the neuronal cell injury was three times higher in the control group. Neither p21 and p27 expression nor apoptosis showed any intergroup difference.

CONCLUSIONS

The selective PARP-1 inhibitor INO1001 markedly reduced aortic occlusion-induced spinal cord injury. Given the close correlation reported in the literature between morphological damage and impaired spinal cord function, INO1001 may improve spinal cord recovery after thoracic aortic cross-clamping.

Poly adenosine diphosphate-ribose polymerase inhibitor PJ34 abolishes systemic proinflammatory responses to thoracic aortic ischemia and reperfusion

BACKGROUND

Systemic inflammatory responses contribute to mortality after thoracoabdominal aneurysm repair. Poly adenosine diphosphate (ADP) ribose polymerase (PARP) activity is known to modulate inflammation in animal models of injury. The effect of the PARP inhibitor PJ34 and genetic deletion of PARP-1(PARP -/-) on the systemic inflammatory response after thoracic aortic ischemia reperfusion (TAR) is not known.

STUDY DESIGN

In one group, all mice were subject to TAR followed by 48 hours of reperfusion. Treated mice (PJ, n=24) were given PJ34 IP; untreated mice (UN, n=41) received normal saline intraperitoneally. The number of mice in each group was selected to have a similar number of survivors by 48 hours. In a second group, sham animals were subjected to mediastinotomy alone (sham, n=10) without TAR, and were compared with mice with deletion of the PARP-1 isoform (PARP-1 -/-, n=11) subjected to TAR. Tissue extracts were assayed for keratinocyte derived chemokine and granulocyte colony stimulating factor. Serum was assayed for interleukin-6.

RESULTS

PJ34 treatment decreased mortality throughout the experimental protocol. There were no mortalities in the sham operated mice or PARP -/- mice subjected to TAR. PJ34 treatment decreased serum levels of interleukin-6 (p=0.01) and hepatic levels of interleukin-6 mRNA when compared with untreated and PARP-/- mice (p < 0.01). Only liver and kidney cytokine levels were decreased by PJ34 treatment (p < 0.05). In PARP-/- mice subjected to TAR, tissue cytokine levels were not different from those in sham mice.

CONCLUSIONS

PARP inhibition may represent a novel therapeutic approach to minimizing inflammatory sequelae after TAR.

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.