Original Article Effects of chronic administration of arachidonic acid on lipid profiles and morphology in the skeletal muscles of aged rats $ Takayuki Inoue a,b,1,2 , Michio Hashimoto a,n , Masanori Katakura a,1 , Yoko Tanabe a,1 , Abdullah Al Mamun a,1 , Kentaro Matsuzaki a,1 , Hiroki Otani b,2 , Osamu Shido a,1 a Department of Environmental Physiology, Faculty of Medicine, Shimane University, 89-1 Enya-cho, Izumo, Shimane 693-8501, Japan b Department of Developmental Biology, Faculty of Medicine, Shimane University, 89-1 Enya-cho, Izumo, Shimane 693-8501, Japan article info Article history: Received 14 March 2014 Received in revised form 19 July 2014 Accepted 21 July 2014 Keywords: n-6 fatty acid Oxidative stress Aging Skeletal muscles Myosin heavy chain abstract Arachidonic acid (20:4n À6, ARA) is a major component of the cell membrane, whereas ARA-derived eicosanoids are formed when cells are damaged. Aging is associated with an accretion of oxidative stress in skeletal muscles. In this study, we examined the effects of chronic administration (13 weeks) of ARA (240 mg/kg/day) on fatty acid composition, antioxidative status, and morphology of slow (soleus muscles) and fast (extensor digitorum longus muscles; EDL)-twitch muscles in aged rats (21 months old). The level of reactive oxygen species was higher in the EDL of ARA-administered rats than in that of control rats. ARA administration decreased the muscle cell volumes and increased the number of slow myosin heavy chain (MHC)-positive cells in the EDL. The relative content of MHC2X was increased whereas the relative content of MHC2B was decreased in the EDL of ARA-administered rats. These results suggest that ARA deposition in the fast-twitch muscle of aged rats reduced cell volume with an increase in oxidative stress. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction The age-related loss of skeletal muscle mass and strength, i.e. sarcopenia, is becoming a growing public health problem because it contributes to decreased capacity for independent living [1,2]. Sarcopenia can be explained by several physiopathological factors, including increased oxidative stress [3]. Aging accretes oxidative stress and increases the incidence of oxidative injury in respiratory and locomotive skeletal muscles [4,5]. Furthermore, it has been reported that age-related oxidative stress causes a significant decrease in antioxidant enzymes, particularly glutathione perox- idase in rats [6]. Consequently, muscles undergoing elevated levels of oxidative stress develop sarcopenia, which causes considerable age-related decline in muscle mass [7]. On the basis of the myosin heavy chain (MHC) isoform pattern, adult mammalian limb skeletal muscles contain two and, in some species, three types of fast fibers (type 2A, 2X, and 2B) and one type of slow fiber (type 1). Fast-twitch muscles such as the extensor digitorum longus mus- cles (EDL) are composed primarily of a mixture of the fast myosin isozymes, whereas slow-twitch muscles such as the soleus muscle (SO) contain primarily the slow type 1 fibers [8,9]. The synthesis rate of the MHC protein is reportedly decreased with age in humans [10,11]. Moreover, the effects of aging on antioxidant systems in the skeletal muscle may be quite different from those on antioxidant systems in the liver, kidney, brain, and heart [12] because the lipid peroxidation (LPO) level is greater in skeletal muscle homogenate than in other tissue homogenates [6]. Arachidonic acid (20:4n À 6, ARA), a polyunsaturated fatty acid (PUFA) synthesized from linoleic acid (18:2n À 6, LA) in many tissues, is a major component of the cell membrane [13,14]. In various pathophysiological conditions, ARA is released from mem- brane phopholipids by phospholipases, particularly phospholipase A 2 (PLA 2 ). Free ARA can be converted to bioactive eicosanoids through the cyclooxygenase (COX), lipoxygenase (LOX), or P-450 epoxygenase pathways [15]. In the skeletal muscle, ARA is neces- sary for the repair and growth of muscle tissue through its conversion to active components such as prostaglandin (PG) F 2 alpha and COX-2 metabolites [16,17]. By contrast, PLA 2 activity is increased in patients with Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) [18] and PGE 2 activity is increased in isolated strips of biceps muscle from patients with Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/plefa Prostaglandins, Leukotrienes and Essential Fatty Acids http://dx.doi.org/10.1016/j.plefa.2014.07.015 0952-3278/& 2014 Elsevier Ltd. All rights reserved. ☆ Source of funding: This study was supported by a Health and Labour Sciences Research Grant of Japan (#H22-Shokuhin-Ippan-002) and a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Science, Sports and Technology of Japan (#23500955, MH). n Corresponding author. Tel.: þ81 853 20 2112; fax: þ81 853 20 110. E-mail address: michio1@med.shimane-u.ac.jp (M. Hashimoto). 1 Tel: þ81 853 20 2112, fax: þ81 853 20 2110. 2 Tel: þ81 853 20 2102, fax: þ81 853 20 2100. Please cite this article as: T. Inoue, et al., Effects of chronic administration of arachidonic acid on lipid profiles and morphology in the skeletal muscles of aged rats, Prostaglandins Leukotrienes Essent. Fatty Acids (2014), http://dx.doi.org/10.1016/j.plefa.2014.07.015i Prostaglandins, Leukotrienes and Essential Fatty Acids ∎ (∎∎∎∎) ∎∎∎–∎∎∎