The lipophilic multifunctional antioxidant edaravone (radicut) improves behavior following embolic strokes in rabbits: A combination therapy study with tissue plasminogen activator
Introduction
Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one, Radicut, MCI-186) is a low molecular weight free radical scavenger that readily crosses the blood brain barrier (BBB) (Watanabe et al., 2008, Yoshida et al., 2006). Based upon Japanese clinical trials in stroke patients Mitsubishi-Tokyo Pharmaceutical Inc (Tokyo, Japan) has obtained approval from the regulatory agency in Japan for the treatment of acute ischemic stroke (AIS) patients with edaravone if the drug was administered within 72 h of the ischemic event (Edaravone Study Group, 2003, Inatomi et al., 2006, Mishina et al., 2005, Toyoda et al., 2004, Watanabe et al., 2008, Yoshida et al., 2006). Suda et al. (2007) have recently claimed that edaravone can salvage the boundary zone of the infarct in patients (i.e. ischemic penumbra) and reduce the extent of edema, presumably resulting in clinical improvement. Recently, Yoshifumi (2007) reported preliminary findings of a clinical trial showing that patients treated with edaravone prior to administration of intravenous tPA had a reduced incidence of hemorrhage compared to tPA-treated patients. Thus, the Japanese experience with edaravone suggests that edaravone is superior, in many ways, to the failed Astra-Zeneca spin trap agent NXY-059 (Diener et al., 2008, Shuaib et al., 2007), but outside of Japan there has been little to no clinical development for the treatment of AIS. Although edaravone is purported to have significant benefit in stroke patients, there is an increased risk of renal toxicity associated with its administration (Hishida, 2007). It has been reported that approximately 45% of patients with edaravone-induced renal toxicity recover renal function after edaravone treatment is stopped (Hishida, 2007).
The preclinical experience with edaravone is quite extensive since it has been under development by Mitsubishi-Tokyo Pharmaceutical Inc. of Tokyo, Japan for over a decade (Watanabe et al., 2008, Yoshida et al., 2006). The main focus of edaravone has been its potential to scavenge free radicals. Edaravone is a potent lipid-soluble hyrdoxyl and peroxyl radical scavenger that can inhibit lipid peroxidation and prevent vascular endothelial cell injury (Watanabe et al., 2008, Yoshida et al., 2006). In rat ischemia models, edaravone lowered hydroxyl radical production, ischemic infarction and suppressed delayed neuronal death (Araki et al., 2003, Nakashima et al., 1999, Nito et al., 2003, Wu et al., 2000, Yoshida et al., 2005). Free radicals have been proposed to cause a vast array of injuries mediated by many different pathways following a stroke (Cherubini et al., 2005, Facchinetti et al., 1998, Floyd, 1999, Lapchak and Araujo, 2003, Nakashima et al., 1999, Siesjo et al., 1995, Siesjo and Siesjo, 1996). The oxidative stress that occurs after an ischemic stroke produces reactive oxygen species (ROS) like hydrogen peroxide (H2O2), hydroxyl radical (HO) and superoxide anion radical (O2−) that bring about membrane lipid peroxidation. Damage to membranes then disrupts tissue integrity leading to neuronal damage and consequent behavioral deficits (Siesjo et al., 1995, Siesjo and Siesjo, 1996). It is also possible that the free radical scavenging activities of edaravone are its ability to inhibit lipoxygenase (LOX), reduce apoptosis and prevent vascular damage (Higashi et al., 2006).
Thus, in the present study we evaluated the pharmacological effects of edaravone in a rabbit small clot embolic stroke model (RSCEM) as a basis for the further development of this type of multifunctional compound. The RSCEM (Lapchak et al., 2002, Lapchak et al., 2004a, Lapchak et al., 2007, Lapchak et al., 2004c) is produced by the injection of blood clots into the cerebral vasculature. A wide range of clots doses are injected in order to generate both normal and abnormal animals with various behavioral deficits, which can be measured quantitatively using a simple dichotomous rating scale (Lapchak et al., 2002, Lapchak et al., 2004a, Lapchak et al., 2007, Lapchak et al., 2004c). Using the RSCEM, the present study tested the hypothesis that edaravone would be useful to attenuate embolism-induced behavioral deficits. Moreover, since optimal doses of tPA do not eliminate all brain damage, even though tPA does increase cerebral reperfusion (reviewed in Lapchak, 2002a), we investigated the interaction between tPA and edaravone to determine whether there are any positive or negative interactions when the drugs are combined. To simulate the design of recent clinical trials with neuroprotective agents and thrombolytics, edaravone was administered following tPA when thrombolysis is complete.
Section snippets
Materials and methods
Male New Zealand white rabbits weighing 2 to 2.5 kg were purchased from Rabbit Source Farms, Ramona, CA. Rabbits were supplied food (alfalfa cubes) and water ad libitum while under quarantine in an enriched environment for at least 5 days prior to experimental use. Surgery was done in a sterile controlled environment with a room temperature between 22.8 and 23.2 °C. The Department of Veterans Affairs and Institutional Animal Care and Use Committee (IACUC) approved the surgical and treatment
Effect of bolus injections of edaravone on behavior following embolic strokes: defining the therapeutic window
In the first series of experiments, we administered either vehicle (DMSO) or bolus injections of edaravone SC starting 5 min following small clot embolization. Subsequently, behavioral analysis was conducted. As shown in Table 1, edaravone at 100 mg/kg significantly improved stroke-induced behavioral deficits. The P50 value measured for the edaravone-treated group was 1.80 ± 0.24 mg, compared to a P50 of 0.93 ± 0.16 mg for the control group. For this series of experiments, we used the cumulative
Discussion
Recent efforts in developing new therapeutic molecules that could be used to treat acute ischemic stroke have been extremely disappointing (O'Collins et al., 2006). Despite the failure of so many drugs in western countries, the Japanese have had what they consider to be a success, so we have decided to evaluate their claims independently. We established that edaravone has a therapeutic window of at least 3 h in the rabbit embolic stroke model. Because the primary component of the clinical score
Acknowledgment
This study was supported by a Merit Review grant from the Veterans Administration.
References (51)
- et al.
Potential markers of oxidative stress in stroke
Free Radic. Biol. Med.
(2005) 3alpha-OL-5-beta-pregnan-20-one hemisuccinate, a steroidal low-affinity NMDA receptor antagonist improves clinical rating scores in a rabbit multiple infarct ischemia model: synergism with tissue plasminogen activator
Exp. Neurol.
(2006)The phenylpropanoid micronutrient chlorogenic acid improves clinical rating scores in rabbits following multiple infarct ischemic strokes: synergism with tissue plasminogen activator
Exp. Neurol.
(2007)- et al.
Comparison of Tenecteplase with Alteplase on clinical rating scores following small clot embolic strokes in rabbits
Exp. Neurol.
(2004) - et al.
Baicalein, an antioxidant 12/15-lipoxygenase inhibitor improves clinical rating scores following multiple infarct embolic strokes
Neuroscience
(2007) - et al.
Coadministration of NXY-059 and tenecteplase six hours following embolic strokes in rabbits improves clinical rating scores
Exp. Neurol.
(2004) - et al.
Involvement of free radicals in cerebral vascular reperfusion injury evaluated in a transient focal cerebral ischemia model of rat
Free Radic. Biol. Med.
(1999) - et al.
Free radical scavenger, edaravone, in stroke with internal carotid artery occlusion
J. Neurol. Sci.
(2004) - et al.
MCI-186: further histochemical and biochemical evidence of neuroprotection
Life Sci.
(2000) - et al.
Edaravone, a novel radical scavenger, inhibits oxidative modification of low-density lipoprotein (LDL) and reverses oxidized LDL-mediated reduction in the expression of endothelial nitric oxide synthase
Atherosclerosis
(2005)