Research ReportTherapeutic impact of eicosapentaenoic acid on ischemic brain damage following transient focal cerebral ischemia in rats
Introduction
Long-chain n-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are derived from marine products, have attracted considerable attention. Early epidemiological studies in Greenland discovered that the Inuit people showed a lower incidence of myocardial infarction than Danish people (Bang et al., 1971), and EPA from a fish-rich diet was considered to be responsible for preventing thrombosis and atherosclerosis in the Inuit (Dyerberg et al., 1978). Furthermore, a recent meta-analysis of cohort studies disclosed an inverse relationship between fish consumption and stroke risk (He et al., 2004). A large amount of highly purified EPA can be prepared in an ethyl-ester form (EPA-E) with an approximately 90% purity (Mizuguchi et al., 1993), and EPA-E has been clinically used as a lipid-lowering medication in Japan. In addition, a recent clinical controlled trial of the Japan EPA lipid intervention study (JELIS) has shown that EPA-E reduces stroke recurrence in Japanese hypercholesterolemic patients (Tanaka et al., 2008).
We have previously shown that long-term administration of EPA-E (100 mg/kg/day) ameliorated the age-related decline of cerebral blood flow (CBF) in stroke-prone spontaneously hypertensive rats (Katayama et al., 1997). Furthermore, we have also reported that post-ischemic delayed administration of EPA-E (100 mg/kg/day) for 4 weeks increased local CBF within the peri-infarct areas in a rat chronic cerebral infarction model (Katsumata et al., 1999). In addition, several investigations have described the neuroprotective effects of EPA on forebrain ischemia (Okabe et al., 2011, Bas et al., 2007, Ozen et al., 2008, Ajami et al., 2011). However, the protective effects of EPA on acute focal cerebral ischemia remain unclear.
Cerebral ischemia consists of complex pathological processes, and various factors can exacerbate ischemic brain damage. Oxidative stress is known to be involved in ischemia-reperfusion injury owing to an increase in reactive oxygen species (ROS), which result in DNA damage and lipid peroxidation (Floyd and Carney, 1992, Halliwell, 1992). In addition, Rho-kinase activity is associated with various cerebral vascular diseases, including ischemic brain injury (Chrissobolis and Sobey, 2006). A recent investigation revealed that endothelial Rho-kinase activation following cerebral ischemia played an important role for infarct expansion (Yagita et al., 2007). Furthermore, ROS-induced brain endothelial dysfunction involves the Rho-kinase signaling pathway (Kahles et al., 2007). Therefore oxidative stress and subsequent endothelial Rho-kinase activation may be implicated in ischemic brain injury.
The present study aimed to examine the effects of pre-ischemic and post-ischemic treatments of EPA-E on ischemic brain damage using a rat transient focal cerebral ischemia model. Furthermore we sought to determine whether EPA-E could suppress oxidative DNA damage, lipid peroxidation and endothelial Rho-kinase activation following focal cerebral ischemia.
Section snippets
Plasma fatty acids
Plasma EPA levels were significantly elevated after 7-day pretreatment with EPA-E compared with vehicle treatment (p=0.0019), although plasma arachidonic acid (AA) levels were not different between the groups (p=0.9701) (Table 1). In experiment 2, plasma EPA concentrations were significantly higher even with withdrawal of EPA-E administration for 3 days compared with vehicle administration (p=0.0022); however, EPA-E withdrawal for more than 5 days showed no differences in plasma EPA levels
Discussion
Several investigators have studied the effects of n-3 PUFAs on cerebral ischemia (Okabe et al., 2011, Bas et al., 2007, Ozen et al., 2008, Ajami et al., 2011, Cao et al., 2004, Pan et al., 2009). The examined n-3 PUFAs in each study were EPA, DHA or a mixture of EPA/DHA. Okabe and colleagues reported that EPA inhibited inflammatory responses and oxidative damage following transient forebrain ischemia in gerbils (Okabe et al., 2011), and Bas and colleagues studied the effects of fish oil
Experimental procedure
All experimental protocols were carried out in accordance with the institutional guidelines of Nippon Medical School for animal care and use.
Contributors
MU and YK conceived of the experiments. MU, TI, CN and NK performed the experiments, and analyzed the data with YK. MU wrote the paper. All authors discussed the results and commented on the manuscript.
Acknowledgment
EPA-E was a generous gift from Mochida Pharmaceutical Co., Ltd. (Tokyo, Japan).
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