Neuroprotective effects of Eleutherococcus senticosus bark on transient global cerebral ischemia in rats

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Abstract

Ethnopharmacological relevance

Eleutherococcus senticosus Maxim., classified into the family of Araliaceae, is used in a variety of diseases in traditional Korean medicine including ischemic heart disease.

Aim of the study

To determine the neuroprotective effects of Eleutherococcus senticosus on global cerebral ischemia.

Materials and methods

A four-vessel occlusion (4-VO) rat model was used to evaluate the potential protective effects against transient global cerebral ischemia ethanol extracts of Eleutherococcus senticosus was orally administered at doses of 3, 30, and 300 mg/kg twice at times of 0 and 90 min after reperfusion. The effects on memory deficit were investigated by using a Y-maze neurobehavioral test after brain ischemia, and the effects on hippocampal neuronal damage were measured 7 days after ischemia. The expressions of glial fibrillary acid protein (GFAP), CD11b antibody (OX-42), and cyclooxygenase-2 (COX-2) were investigated by immunohistochemistry.

Results

Oral administration of Eleutherococcus seticosus at 30, 100 and 300 mg/kg significantly reduced hippocampal CA1 neuronal death by 3.5%, 25.9% and 53.1%, respectively, compared with a vehicle-treated group. Oral administration of Eleutherococcus senticosus at 300 mg/kg inhibited 81.9% of the decrease in spontaneous alternation induced by 4-VOin the Y-maze test, and also attenuated ischemia-induced activation of COX-2, GFAP and OX-42 in the hippocampal CA1 region.

Conclusion

Eleutherococcus senticosus protects delayed neuronal death in the CA1 region of the hippocampus against global cerebral ischemia in rats with the recovery of spatial memory, which can be considered as the normal functioning of the hippocampus. Regarding the immunohistochemical study, the effect of Eleutherococcus senticosus may be attributable to its anti-inflammatory properties through the inhibition of COX-2 expression, microglia and astrocyte expression.

Graphical abstract

Oral administration of Eleutherococcus senticosus significantly reduced hippocampal CA1 neuronal death and decrease in spontaneous alternation against global cerebral ischemia in rats. Eleutherococcus senticosus also attenuated ischemia-induced activation of COX-2, astrocyte and microglial in the hippocampal CA1 region.

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Introduction

Transient global cerebral ischemia, arising in humans, can be a consequence of cardiac arrest or severe systemic hypotension. It leads to major neuropsychological dysfunctions, including learning and memory disabilities (Peskine et al., 2004). Although cardiac arrest and cerebral ischemia remain as leading causes of adult disability in industrialised countries, little progress has been achieved in translation of promising experimental therapies into clinical practice (O’Collins et al., 2006, Rosamond et al., 2008). The main focus of drug development to protect ischemia-induced injury has been the investigation of neuroprotective sources capable of protecting salvageable neurons from ischemic cell death. Natural products, especially medicinal plants, could be an ideal source to develop safe and effective agents for neuroprotection of ischemia-induced injury (Kim, 2005).

Eleutherococcus senticosus Maxim., known as Siberian Ginseng, is a medicinal herb with a long history of use including ischemic heart disease due to its traditional Korean medical effects such as tonify qi, strengthen muscle and bone, and tranquilize (Yi et al., 2001, Wang et al., 2010). Eleutherococcus senticosus has also been reported to possess anti-stress, anti-tumor, hypoglycemic, and anti-arrhythmic effects (Hibasami et al., 2000, Kimura and Sumiyoshi, 2004, Park et al., 2006, Maslov and Guzarova, 2007). The major active components of Eleutherococcus senticosus are eleutherosides, chiisanoside, acanthosides, daucosterin, β-sitosterol, sesamin, and they are responsible for its diverse biological activities (Davydov and Krikorian, 2000). It has been reported that eleutheroside E, liriodendrin, isofraxidin, chiisanoside and β-sitosterol have been reported to have anti-inflammatory effects (Tokiwa et al., 2006, Jung et al., 2003, Yamazaki et al., 2007). Especially, Eleutherococcus senticosus has been reported to protect against neuronal death induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and amyloid beta (Fujikawa et al., 2005, Tohda et al., 2008).

Recently, our group found that Eleutherococcus senticosus reduces the infarct volume in transient focal cerebral ischemia (Bu et al., 2005). However focal ischemia is a far more complex insult than global ischemia with several unresolved issues such as extracellular edema, vascular damage while global ischemia involves a short very intense insult in which ATP is severely lowered and is quite uniform as a delayed neuronal death (Lipton, 1999). Global ischemia is characterized by a slow development of cell death during reperfusion, which shows great selectivity. There is no intimation of involvement of the vasculature, although there is a real possibility that microglia/macrophages play a role in the process (Swan et al., 1988).

The aim of the present study was to determine the neuroprotective effects of Eleutherococcus senticosus in global cerebral ischemia in rats. We used a four-vessel occlusion (4-VO) rat model to evaluate the potential protective effects against transient global cerebral ischemia (Katsuta et al., 2003). Y-maze test was used to investigate spatial memory impairment. We observed the expression of glial fibrillary acid protein (GFAP), CD11b antibody (OX-42), and COX-2 by immunohistochemistry to find out the inhibitory effects on microglia activation, astrocyte activation and COX-2 upregulation which are related in inflammation.

Section snippets

Plant material

The dried stem bark of Eleutherococcus senticosus was purchased from Yaksudang Co. (Seoul, Korea). It was identified by Dr. Ho-Young Choi, Department of Herbal Pharmacology, College of Oriental Medicine, Kyung Hee University where the voucher specimen (#HP060) is deposited.

Sample preparation

Eleutherococcus senticosus (150 g) was extracted with 70% ethanol (3000 ml) for 3 h at 80 °C in a reflux apparatus. The extract was filtrated and concentrated under reduced pressure, then, lyophilized to yield a dark brown

Effects on neuronal cell density in the CA1 region

Typical images of hippocampal slices stained with CV from rats of Sham operated, and of 7 days after 4-VO for 10 min with distilled water and Eleutherococcus senticosus at dosages of 3, 30 and 300 mg/kg are shown in Fig. 2. The extent of the neuronal damage was quantified by counting the number of surviving pyramidal neurons in the CA1 region, which was expressed as a neuronal cell density (Fig. 3). A marked reduction in the cell densities in the CA1 region was observed in vehicle-treated group

Discussion

Our findings demonstrated that Eleutherococcus senticosus reduced neuronal cell death in the CA1 region of hippocampus and spatial memory loss on Y-maze at 7 days after 4-VO in rats. Eleutherococcus senticosus attenuated ischemia-induced COX-2 upregulation at 2 days after 4-VO and overactivation of GFAP and OX-42 at 7 days after 4-VO in hippocampal CA1 region.

Global ischemia leads to selective cell death of hippocampal CA1 pyramidal neurons while other neurons are much less vulnerable in humans

Acknowledgements

This work was supported by 2nd Stage of Brain Korea 21 Project (Ministry of Education, Korea) and a grant from the Kyung Hee University in 2008 (KHU-20080601).

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