Hydroxytyrosol protects against oxidative damage by simultaneous activation of mitochondrial biogenesis and phase II detoxifying enzyme systems in retinal pigment epithelial cells☆ Lu Zhu a,b , Zhongbo Liu a,b , Zhihui Feng a,b , Jiejie Hao a,b , Weili Shen a , Xuesen Li a,b , Lijuan Sun c , Edward Sharman d , Ying Wang e , Karin Wertz e , Peter Weber e , Xianglin Shi f , Jiankang Liu f,g, ⁎ a Institute for Nutritional Science, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China b Graduate School of the Chinese Academy of Sciences, Beijing, China c College of Physical Education and Health, East China Normal University, Shanghai, China d Department of Neurology, University of California, Irvine, CA 92697, USA e DSM Nutritional Products, R and D Human Nutrition and Health, CH-4303 Kaiseraugst, Basel, Switzerland f Graduate Center for Toxicology, University of Kentucky College of Medicine, Lexington, KY 40536, USA g Institute of Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, Xi'an Jiaotong University School of Life Science and Technology, Xi'an 710049, China Received 18 March 2009; received in revised form 4 September 2009; accepted 14 September 2009 Abstract Studies in this laboratory have previously shown that hydroxytyrosol, the major antioxidant polyphenol in olives, protects ARPE-19 human retinal pigment epithelial cells from oxidative damage induced by acrolein, an environmental toxin and endogenous end product of lipid oxidation, that occurs at increased levels in age-related macular degeneration lesions. A proposed mechanism for this is that protection by hydroxytyrosol against oxidative stress is conferred by the simultaneous activation of two critically important pathways, viz., induction of phase II detoxifying enzymes and stimulation of mitochondrial biogenesis. Cultured ARPE-19 cells were pretreated with hydroxytyrosol and challenged with acrolein. The protective effects of hydroxytyrosol on key factors of mitochondrial biogenesis and phase II detoxifying enzyme systems were examined. Hydroxytyrosol treatment simultaneously protected against acrolein- induced inhibition of nuclear factor-E2-related factor 2 (Nrf2) and peroxisome proliferator-activated receptor coactivator 1 alpha (PPARGC1α) in ARPE-19 cells. The activation of Nrf2 led to activation of phase II detoxifying enzymes, including γ-glutamyl-cysteinyl-ligase, NADPH (nicotinamide adenine dinucleotide phosphate)-quinone-oxidoreductase 1, heme-oxygenase-1, superoxide dismutase, peroxiredoxin and thioredoxin as well as other antioxidant enzymes, while the activation of PPARGC1α led to increased protein expression of mitochondrial transcription factor A, uncoupling protein 2 and mitochondrial complexes. These results suggest that hydroxytyrosol is a potent inducer of phase II detoxifying enzymes and an enhancer of mitochondrial biogenesis. Dietary supplementation of hydroxytyrosol may contribute to eye health by preventing the degeneration of retinal pigment epithelial cells induced by oxidative stress. © 2010 Elsevier Inc. All rights reserved. Keywords: Hydroxytyrosol; RPE cells; Acrolein; AMD; Mitochondrial biogenesis; Phase II enzymes 1. Introduction Age-related macular degeneration (AMD) is the leading cause of vision loss in the Western world among people over 65 y of age [1], and worldwide, it is the third most common cause of blindness [2]. AMD is characterized by an age-related degeneration of retinal pigment epithelium (RPE) and the photoreceptors in the macular area of the retina. The underlying cause of the disease is unknown, but oxidative stress is involved [3], suggesting that consumption of diets rich in antioxidants may be of benefit. The Mediterranean diet has been associated with a lower incidence of not only certain cancers, but also cardiovascular disease, which is the most common and serious complication of diabetes [4–6], all conditions associated with oxidative stress. Olives and olive oil are considered an important part of the Mediterranean diet. Evidence has accumulated recently that in addition to olive lipids, which are rich in monounsaturated fatty acids, antioxidant polyphenols such as hydroxytyrosol also contribute to the health effects of olives [7–10]. Work in our laboratory has led to the proposal that oxidative damage to mitochondria in RPE cells may contribute to the retinal Available online at www.sciencedirect.com Journal of Nutritional Biochemistry xx (2010) xxx – xxx ☆ Supported by National Eye Institute, NIH grant EY0160101, 5R01 CA119028-05, R01 CA116697, R01 ES015518, R01 ES015375, a UC Davis Center for Human and Nutrition Pilot Award (CHNR08-318), and DSM Nutritional Products. ⁎ Corresponding author. Institute of Mitochondrial Biology and Medicine, Xi'an Jiaotong University School of Life Science and Technology, Xi'an, 710049, China. Tel.: +86 29 8266 4232. E-mail address: j.liu@mail.xjtu.edu.cn (J. Liu). 0955-2863/$ - see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jnutbio.2009.09.006 ARTICLE IN PRESS