n-3 fatty acids effectively improve the reference memory-related learning ability associated with increased brain docosahexaenoic acid-derived docosanoids in aged rats Michio Hashimoto a, ⁎, Masanori Katakura a , Yoko Tanabe a , Abdullah Al Mamun a , Takayuki Inoue a , Shahdat Hossain a,b , Makoto Arita c , Osamu Shido a a Department of Environmental Physiology, Shimane University Faculty of Medicine, Izumo, Shimane 693-8501, Japan b Department of Biochemistry and Molecular Biology, Jahangirnagar University, Savar, Dhaka, Bangladesh c Laboratory for Metabolomics, RIKEN Center for Integrative Medical Sciences (IMS), Yokohama-City, Kanagawa 230-0045, Japan abstract article info Article history: Received 24 April 2014 Received in revised form 20 October 2014 Accepted 22 October 2014 Available online 22 November 2014 Keywords: Brain PUFA-derived mediators Memory Aging EPA and DHA We investigated whether a highly purified eicosapentaenoic acid (EPA) and a concentrated n-3 fatty acid formulation (prescription TAK-085) containing EPA and docosahexaenoic acid (DHA) ethyl ester could improve the learning ability of aged rats and whether this specific outcome had any relation with the brain levels of EPA- derived eicosanoids and DHA-derived docosanoids. The rats were tested for reference memory errors (RMEs) and working memory errors (WMEs) in an eight-arm radial maze. Fatty acid compositions were analyzed by GC, whereas brain eicosanoid/docosanoids were measured by LC–ESI-MS–MS-based analysis. The levels of lipid peroxides (LPOs) were measured by thiobarbituric acid reactive substances. The administration of TAK- 085 at 300 mg·kg -1 day -1 for 17 weeks reduced the number of RMEs in aged rats compared with that in the control rats. Both TAK-085 and EPA administration increased plasma EPA and DHA levels in aged rats, with concurrent increases in DHA and decreases in arachidonic acid in the corticohippocampal brain tissues. TAK- 085 administration significantly increased the formation of EPA-derived 5-HETE and DHA-derived 7-, 10-, and 17-HDoHE, PD1, RvD1, and RvD2. ARA-derived PGE 2 , PGD 2 , and PGF 2α significantly decreased in TAK-085- treated rats. DHA-derived mediators demonstrated a significantly negative correlation with the number of RMEs, whereas EPA-derived mediators did not exhibit any relationship. Furthermore, compared with the control rats, the levels of LPO in the plasma, cerebral cortex, and hippocampus were significantly reduced in TAK-085- treated rats. The findings of the present study suggest that long-term EPA + DHA administration may be a possible preventative strategy against age-related cognitive decline. © 2014 Published by Elsevier B.V. 1. Introduction Docosahexaenoic acid (DHA, C22:6, n-3) and eicosapentaenoic acid (EPA, C20:5, n-3) are the primary n-3 polyunsaturated fatty acids (PUFAs) in fish oil, and epidemiological studies have revealed that fish oil intake has significant neuroprotective effects in aging [1,2]. Increased fish consumption and DHA + EPA intake are both associated with reduction in cognitive decline [3]. In addition, daily DHA and EPA sup- plementation has beneficial effects against age-related cognitive decline in otherwise health elderly Japanese individuals with very mild demen- tia [4]. These findings suggest that increased consumption of n-3 PUFAs is associated with reduced risk of age-related cognitive decline and dementia. DHA deficiency, as observed with aging and dementia [5], impairs memory and learning and promotes age-related neurodegenerative diseases [6]. Vertebrates do not have adequate metabolic capacity to biosynthesize DHA; thus, vertebrates, including humans, depend on the diet to supply this fatty acid. As expected, dietary DHA ameliorates the learning-related spatial memory of DHA-deficient rats [7–10]. Posi- tively, the administration of a DHA precursor (i.e., EPA) should be expected to cause the neurobehavioral outcome caused by DHA. Dietary EPA has been shown to increase DHA levels in brain tissues of rats, concurrently with the enhancement of spatial cognition [11] and modulation of synaptic plasticity [12]. From these results, it is apparent Biochimica et Biophysica Acta 1851 (2015) 203–209 Abbreviations: ARA, arachidonic acid; BHT, 2,6-di-t-butyl-4-methyl-phenol; DHA, docosahexaenoic acid; EPA, eicosapentaenoic acid; 5-HETE, 5S-hydroxy-6E,8Z,11Z,14Z- eicosatetraenoic acid; 12-HETE, 12-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid; 15-HETE, 15-hydroxy-5Z,8Z,11Z,13E-eicosatetraenoic acid; 5-HEPE, 5-hydroxy-6E,8Z,11Z,14Z,17Z- eicosapentaenoic acid; 12-HEPE, 12-hydroxy-5Z,8Z,10E,14Z,17Z-eicosapentaenoic acid; 15- HEPE, 15-hydroxy-5Z,8Z,11Z,13E,17Z-eicosapentaenoic acid; HDoHE, hydroxy docosahexaenoic acid; HPLC, high-performance liquid chromatography; LPO, lipid peroxide; PG, prostaglandin; PD1, protectin D1; PLA 2 , phospholipase A 2 ; PUFAs, poly- unsaturated fatty acids; RME, reference memory error; SRM, selected reaction moni- toring; WME, working memory error ⁎ Corresponding author at: Enyacho 89-1, Izumo, Shimane 693-8501, Japan. Tel.: +81 853 20 2112; fax: +81 853 20 2110. E-mail address: michio1@med.shimane-u.ac.jp (M. Hashimoto). http://dx.doi.org/10.1016/j.bbalip.2014.10.009 1388-1981/© 2014 Published by Elsevier B.V. Contents lists available at ScienceDirect Biochimica et Biophysica Acta journal homepage: www.elsevier.com/locate/bbalip