molecules Article
Neuroprotection by Combined Administration with Maslinic Acid, a Natural Product from Olea europaea, and MK-801 in the Cerebral Ischemia Model Yisong Qian 1, *, Xuzhen Tang 2 , Teng Guan 3 , Yunman Li 2, * and Hongbin Sun 4 1 2 3 4
*
Institute of Translational Medicine, Nanchang University, 1299 Xuefu Avenue, Nanchang 330001, China Department of Physiology, China Pharmaceutical University, 24 Tongjiaxiang Street, Nanjing 210009, China;
[email protected] Department of Human Anatomy and Cell Science, University of Manitoba, 745 Bannatyne Avenue, Winnipeg, MB R3E 0J9, Canada;
[email protected] Center for Drug Discovery, China Pharmaceutical University, 24 Tongjiaxiang Street, Nanjing 210009, China;
[email protected] Correspondence:
[email protected] (Y.Q.);
[email protected] (Y.L.); Tel.: +86-25-8327-1173 (Y.L.)
Academic Editor: Peter Koulen Received: 19 June 2016; Accepted: 17 August 2016; Published: 19 August 2016
Abstract: Glutamate-mediated excitotoxicity is a major cause of ischemic brain damage. MK-801 confers neuroprotection by attenuating the activation of the N-methyl-D-aspartate (NMDA) receptor, but it failed in clinical use due to the short therapeutic window. Here we aim to investigate the effects of maslinic acid, a natural product from Olea europaea, on the therapeutic time window and dose range for the neuroprotection of MK-801. Rats were administered with maslinic acid intracerebroventricularly and cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) followed by reperfusion. MK-801 was administered at 1 h, 2 h, 3 h and 4 h after ischemia, respectively. The cerebral infarct volume was determined by 2,3,5-Triphenyltetrazolium chloride (TTC) staining, neuronal damage was assessed by Haematoxylin Eosin (H&E) staining, and the expression of glial glutamate transporters and glial fibrillary acidic protein (GFAP) was evaluated by immunohistochemistry and Western blot post-ischemia. Results showed that the presence of maslinic acid extended the therapeutic time window for MK-801 from 1 h to 3 h. Co-treatment of maslinic acid and MK-801 at a subthreshold dosage obviously induced neuroprotection after ischemia. The combination of these two compounds improved the outcome in ischemic rats. Moreover, maslinic acid treatment promoted the expression of GLT-1 and GFAP post-ischemia. These data suggest that the synergistic effect of maslinic acid on neurological protection might be associated with the improvement of glial function, especially with the increased expression of GLT-1. The combination therapy of maslinic acid and MK-801 may prove to be a potential strategy for treating acute ischemic stroke. Keywords: cerebral ischemia; maslinic acid; MK-801; GLT-1
1. Introduction Stroke represents the leading cause of death and permanent disability for old people. Up to now, no single pharmacological agents have shown any neurological improvement for patients with acute ischemic stroke except thrombolytic drugs, despite promising preclinical data [1,2]. Several key factors have been implicated in ischemic cell death, including excitotoxicity, oxidative and nitrosative stress, and inflammation [3]. Excessive release of glutamate and N-methyl-D-aspartate (NMDA) receptor-related excitotoxicity has been regarded as major causes of brain tissue damage [1]. One approach to addressing these problems is to lower the concentration of extracellular glutamate Molecules 2016, 21, 1093; doi:10.3390/molecules21081093
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increasing Another the wayintake is to [4,5]. attenuate the activation of the NMDA receptorofwith via blockingthe itsintake release[4,5]. or increasing Another way is to attenuate the activation the antagonists. NMDA receptor with NMDA receptor antagonists. receptor antagonist, antagonist, affords reliable protection against ischemic injury in MK-801, an NMDA receptor experimental focal stroke [6]. However, clinical trials using MK-801 as a protective agent against acute ischemic stroke have failed due to its short therapeutic window. MK-801 reduced the cortical infarct butbut had no no neuroprotective activity when given 30 min volume when when given givenjust justprior priortotoischemia, ischemia, had neuroprotective activity when given 30 after min the onset of ischemia [7], suggesting that MK-801 plays plays only aonly transient role in reversible focal after the onset of ischemia [7], suggesting that MK-801 a transient role in reversible ischemia. Moreover, a high adosage of MK-801 may cause effects behavioral toxicity focal ischemia. Moreover, high dosage of MK-801 mayside cause side including effects including behavioral and psychotomimetic effects [8], which[8], also restrict clinicalitsuse. There is accumulating evidence toxicity and psychotomimetic effects which alsoitsrestrict clinical use. There is accumulating that a combination treatmenttreatment with MK-801 otherand agents reduced reduced infarct volume evidence that a combination with and MK-801 othersynergistically agents synergistically infarct and improved neurological deficits indeficits experimental stroke. These effects may be partially to volume and improved neurological in experimental stroke. These effects mayattributed be partially other pathways non-excitotoxic processes activated by the combination strategystrategy [9,10]. These attributed to otherand pathways and non-excitotoxic processes activated by the combination [9,10]. studiesstudies suggested a possibility for the new usenew of NMDA blockers in the treatment of stroke. These suggested a possibility for the use of receptor NMDA receptor blockers in the treatment Maslinic (2-α,3-β-dihydroxyolean-12-en-28-oic acid) is an acid) oleanane-type triterpenoidtriterpenoid compound of stroke. acid Maslinic acid (2-α,3-β-dihydroxyolean-12-en-28-oic is an oleanane-type abundantly expressed in expressed the wax skin of Olea species of small tree in of thesmall family Oleaceae compound abundantly in the waxeuropaea, skin of aOlea europaea, a species tree in the (FigureOleaceae 1A) [11].(Figure It was1A) previously demonstrated as a potent as inhibitor astrocytic glycogen family [11]. It was previously demonstrated a potentofinhibitor of astrocytic phosphorylase with low with toxicity and has been pathological processes processes including glycogen phosphorylase low[12,13], toxicity [12,13], and applied has beeninapplied in pathological hypoglycemia and diabetes due[14,15] to its due glucose-lowering effects by effects interfering with abnormal including hypoglycemia and[14,15] diabetes to its glucose-lowering by interfering with glycogen metabolism. We have reported maslinic regulated extracellular glutamate abnormal glycogen metabolism. We havethat reported thatacid maslinic acid the regulated the extracellular concentration by increasing expression astrocyticofglutamate both in vivo both and in glutamate concentration by the increasing the of expression astrocytictransporters glutamate transporters invitro, vivo thus providing neuroprotection against excitotoxic injury [15,16]. In this regard, we hypothized that the and in vitro, thus providing neuroprotection against excitotoxic injury [15,16]. In this regard, we mechanism of neuroprotection byofmaslinic acid may be withmay improved glutamate metabolism. hypothized that the mechanism neuroprotection by associated maslinic acid be associated with improved The main objective of the present study is to timeiswindow for neuroprotection of the glutamate metabolism. The main objective of determine the presentthe study to determine the time window for combination treatment with MK-801 and maslinic acid in a rat model of cerebral ischemia. We also neuroprotection of the combination treatment with MK-801 and maslinic acid in a rat model of cerebral investigated the combination protocol could allow a lowered dosage MK-801 dosage to a yield ischemia. Wewhether also investigated whether the combination protocol could allow of a lowered of positive to neurologic outcome. Furthermore, since glutamatesince transporters have been shown be MK-801 a yield positive neurologic outcome. Furthermore, glutamate transporters haveto been involved in involved the mechanism of maslinic acid-mediated neuroprotection, the expression of two shown to be in the mechanism of maslinic acid-mediated neuroprotection, the expression of glutamate transporters, GLAST and and GLT-1, waswas alsoalso examined afterafter ischemic stroke. two glutamate transporters, GLAST GLT-1, examined ischemic stroke.
Figure 1. (A) Chemical showing thethe timeline of Chemical structure structureof ofmaslinic maslinicacid; acid;(B) (B)Schematic Schematicrepresentation representation showing timeline the experimental protocols. Maslinic of the experimental protocols. Maslinicacid acidwas wasadministered administeredintracerebroventricularly intracerebroventricularly(i.c.v.) (i.c.v.) 15 15 min before MCAO. MK-801 was administered at the indicated time points after the induction of ischemia through intravenous injection (i.v.). (i.v.).
2. Results Results 2.1. Physiological Variables Physiological variables,including including arterial blood pressure, blood gases temperatures, Physiological variables, arterial blood pressure, blood gases and and rectalrectal temperatures, were were not significantly of the experimental groups before, after not significantly differentdifferent between between any of theany experimental groups before, during, or afterduring, middle or cerebral middle cerebral artery occlusion (MCAO). The laser Doppler flowmetry signal showed no significant artery occlusion (MCAO). The laser Doppler flowmetry signal showed no significant differences among differences among groups before surgery. with the sham-operated group,blood regional cerebral groups before surgery. Compared with theCompared sham-operated group, regional cerebral blow (rCBF) blood blow (rCBF) to
