Novel aspirin-triggered neuroprotectin D1 attenuates cerebral ischemic injury after experimental stroke

https://doi.org/10.1016/j.expneurol.2012.04.007Get rights and content

Abstract

Acute ischemic stroke triggers complex neurovascular, neuroinflammatory and synaptic alterations. Aspirin and docosahexaenoic acid (DHA), an omega-3 essential fatty acid family member, have beneficial effects on cerebrovascular diseases. DHA is the precursor of neuroprotectin D1 (NPD1), which downregulates apoptosis and, in turn, promotes cell survival. Here we have tested the effect of aspirin plus DHA administration and discovered the synthesis of aspirin-triggered NPD1 (AT-NPD1) in the brain. Then we performed the total chemical synthesis of this molecule and tested in the setting of 2 h middle cerebral artery occlusion (MCAo) in Sprague–Dawley rats. Neurological status was evaluated at 24 h, 48 h, 72 h, and 7 days. At 3 h post-stroke onset, an intravenous administration of 333 μg/kg of AT-NPD1 sodium salt (AT-NPD1-SS) or methyl-ester (AT-NPD1-ME) or vehicle (saline) as treatment was given. On day 7, ex vivo magnetic resonance imaging (MRI) of the brains was conducted on 11.7 T MRI. T2WI, 3D volumes, and apparent diffusion coefficient (ADC) maps were generated. In addition, infarct volumes and number of GFAP (reactive astrocytes), ED-1 (activated microglia/macrophages) and SMI-71-positive vessels were counted in the cortex and striatum at the level of the central lesion. All animals showed similar values for rectal and cranial temperatures, arterial blood gases, and plasma glucose during and after MCAo. Treatment with both AT-NPD1-SS and AT-NPD1-ME significantly improved neurological scores compared to saline treatment at 24 h, 48 h, 72 h and 7 days. Total lesion volumes computed from T2WI images were significantly reduced by both AT-NPD1-SS and AT-NPD1-ME treatment in the cortex (by 44% and 81%), striatum (by 61% and 77%) and total infarct (by 48% and 78%, respectively). Brain edema, computed from T2WI in the cortex (penumbra) and striatum (core), was elevated in the saline group. In contrast, both AT-NPD1 decreased water content in the striatum on day 7. 3D volumes, computed from T2WI, were dramatically reduced with both AT-NPD1 and the lesion was mostly localized in the subcortical areas. Treatment with both AT-NPD1-SS and AT-NPD1-ME significantly reduced cortical (by 76% and 96%), subcortical (by 61% and 70%) and total (69% and 84%, respectively) infarct volumes as defined by histopathology. In conclusion, a novel biosynthetic pathway that leads to the formation of AT-NPD1 mediator in the brain was discovered. In addition, administration of synthetic AT-NPD1, in either its sodium salt or as the methyl ester, was able to attenuate cerebral ischemic injury which leads to a novel approach for pharmaceutical intervention and clinical translation.

Highlights

Aspirin plus DHA treatment induces endogenous brain biosynthesis of AT-NPD1. ► We examine the effects of AT-NPD1 treatment on experimental stroke model in rats. ► AT-NPD1 improves behavior and reduces brain infarction at 7 days after stroke. ► AT-NPD1 attenuates brain edema and protects white matter. ► Treatment with AT-NPD1 may be beneficial for stroke patients.

Introduction

Stroke is a major cause of death and disability worldwide (Donnan et al., 2008) and remains a challenging condition without effective therapy (Iadecola and Anrather, 2011, Moskowitz et al., 2010, Ratan, 2010). Tissue plasminogen activator is the only therapeutic option available for stroke treatment, but its use is restricted by a narrow therapeutic window and only 3–5% of patients qualify for this therapy. Acute ischemic stroke lesions encompass the penumbra, an area of hypoperfusion surrounding the core with a limited lifespan of a few hours unless reperfusion is initiated. Despite this short window, the penumbra is potentially salvageable and is a target for neuroprotection (Lo, 2008).

Antithrombotic therapy, mainly with aspirin, reduces vascular events (myocardial infarction, ischemic stroke) in subjects with increased risk of ischemic stroke (Yip and Benavente, 2011). Unlike current anti-inflammatory agents, which delay resolution and can be harmful (Schwab et al., 2007), aspirin accelerates resolution mainly due to cyclooxygenase (COX)-1 acetylation at its catalytic site, thus blocking formation of endoperoxide prostaglandin G2 and biosynthesis of thromboxanes and prostaglandins.

Omega-3 essential fatty acids (found in fish oils) are of increasing interest for managing cerebrovascular disease (Bazan, 2007, Kakar et al., 2008). Docosahexaenoic acid (DHA), an omega-3 fatty acid, is involved in memory, synaptic membrane biogenesis and function, and neuroprotection (Bazan, 2006). DHA is the precursor of novel mediators, including resolvins and protectins, in resolving inflammatory exudates (Serhan et al., 2002). One of the protectins, 10,17-docosatriene, is produced in murine ischemic stroke and is a potent regulator of polymorphonuclear neutrophil (PMN) infiltration, reducing stroke-mediated tissue damage (Marcheselli et al., 2003, Serhan et al., 2002). Given its potent protective actions in the retina and brain, we initially termed this DHA-derived mediator neuroprotectin D1 (NPD1) (Bazan et al., 2010, Mukherjee et al., 2004, Stark and Bazan, 2011a). Recently, we reported discovery of novel aspirin-triggered DHA metabolome, a potent anti-inflammatory proresolving molecule, namely aspirin-triggered Neuroprotectin D1 (AT-NPD1, 10R, 17R–dihydroxy-docosa-4Z,7Z,11E,13E,15Z,19Z-hexaenoic acid) (Serhan et al., 2011). We demonstrated that AT-NPD1 treatment reduced PMN recruitment in murine peritonitis, decreased transendothelial PMN migration as well as enhanced efferocytosis of apoptotic human PMN by macrophages (Serhan et al., 2011). Since DHA is released from membrane phospholipids, we asked if novel COX-2-derived DHA bioactive derivatives are formed during brain ischemic reperfusion in the presence of DHA plus aspirin.

The present study was designed to identify a novel biosynthetic pathway that leads to the formation of AT-NPD1, when DHA plus aspirin is administered after stroke. In addition, we investigated whether administration of synthetic AT-NPD1 in either its sodium salt or as the methyl ester is able to salvage ischemic penumbra. We used magnetic resonance imaging (MRI) and lipidomic analysis in conjunction with behavioral, histological, and immunostaining methods to understand this novel therapeutic approach.

Section snippets

Animal preparation

All studies were approved by the Institutional Animal Care and Use Committee of the Louisiana State University Health Sciences Center. Male Sprague–Dawley rats, weighing 279–340 g (Charles River Lab., Wilmington, MA), were used in all studies. Atropine sulfate (0.5 mg/kg, i.p.) was injected 10 min before anesthesia. Anesthesia was induced with 3% isoflurane in a mixture of 70% nitrous oxide and 30% oxygen. All rats were orally intubated and mechanically ventilated. During ventilation, the animals

Physiological variables

Rectal and cranial (temporalis muscle) temperatures, arterial blood gases, and plasma glucose showed no significant differences between animals (Table 1). There were no adverse behavioral side effects observed after aspirin, DHA, or AT-NPD1 administration to rats in all groups. No animals died during this study.

Aspirin plus DHA treatment induces endogenous brain biosynthesis of AT-NPD1

Liquid chromatography–photodiode array detection–electrospray ionization–tandem mass spectrometry (LC-PDA-ESI-MS/MS)-based mediator lipidomic analysis of contralateral and ipsilateral

Discussion

The present study had two main goals: 1) to identify a novel biosynthetic pathway that leads to the formation of AT-NPD1 mediator, and 2) to evaluate whether administration of synthetic AT-NPD1 in either its sodium salt or as the methyl ester is able to salvage the ischemic penumbra.

We identified a novel biosynthetic pathway that leads to the formation of AT-NPD1 mediator, when aspirin plus DHA are administered after stroke. AT-NPD1 displays a 17R-stereochemistry (Marcheselli et al., 2003,

Acknowledgments

This work was supported in part by National Institutes of Health (NIH, Bethesda, MD), National Center for Complementary and Alternative Medicine grant RC2 AT005909 (N.G.B., C.N.S., N.A.P.). We thank Sonny Kim and Kamalakar Ambadipudi for MRI acquisition and analysis assistance, and Neuroscience Associates, Inc. for histology service.

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