Antioxidant activity of isocoumarins isolated from Paepalanthus bromelioides on mitochondria Karina F. Devienne a , Anaı ´sa F. Ca ´lgaro-Helena b , Daniel J. Dorta b , Ieda M.R. Prado b , Maria Stella G. Raddi c , Wagner Vilegas a , Se ´rgio A. Uyemura d , Antonio C. Santos d , Carlos Curti b, * a Instituto de Quı ´mica de Araraquara, Universidade Estadual Paulista, Araraquara, SP, Brazil b Departamento de Fı ´sica e Quı ´mica, Faculdade de Cie ˆncias Farmace ˆuticas de Ribeira ˜o Preto, Universidade de Sa ˜o Paulo, Av. Cafe ´ s/n, 14040-903 Ribeira ˜o Preto, SP, Brazil c Faculdade de Cie ˆncias Farmace ˆuticas de Araraquara, Universidade Estadual Paulista, Araraquara, SP, Brazil d Departamento de Ana ´ lises Clı ´nicas, Toxicolo ´ gicas e Bromatolo ´ gicas, Faculdade de Cie ˆncias Farmace ˆuticas de Ribeira ˜o Preto, Universidade de Sa ˜o Paulo, Ribeira ˜o Preto, SP, Brazil Received 15 February 2006; received in revised form 5 July 2006 Available online 6 March 2007 Abstract The isocoumarins (1–50 lM) paepalantine (9,10-dihydroxy-5,7-dimethoxy-1H-naptho(2,3c)pyran-1-one), 8,8 0 -paepalantine dimer, and vioxanthin isolated from Paepalanthus bromelioides, were assessed for antioxidant activity using isolated rat liver mitochondria and non-mitochondrial systems, and compared with the flavonoid quercetin. The paepalantine and paepalantine dimers, but not vioxan- thin, were effective at scavenging both 1,1-diphenyl-2-picrylhydrazyl (DPPH  ) and superoxide (O Å 2 ) radicals in non-mitochondrial sys- tems, and protected mitochondria from tert-butylhydroperoxide-induced H 2 O 2 accumulation and Fe 2+ -citrate-mediated mitochondrial membrane lipid peroxidation, with almost the same potency as quercetin. These results point towards paepalantine, followed by paepal- antine dimer, as being a powerful agent affording protection, apparently via O Å 2 scavenging, from oxidative stress conditions imposed on mitochondria, the main intracellular source and target of those reactive oxygen species. This strong antioxidant action of paepalantine was reproduced in HepG2 cells exposed to oxidative stress condition induced by H 2 O 2 . Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Paepalanthus bromelioides; Eriocaulaceae; Isocoumarins; Paepalantine; Mitochondria; Reactive oxygen species; Oxidative stress; Membrane lipid peroxidation 1. Introduction Mitochondria are important intracellular sources of reactive oxygen species (ROS). During the oxidative phos- phorylation process, mitochondria reduce O 2 to H 2 O via the respiratory chain. However, a small fraction of the O 2 available to this system may undergo incomplete reduction giving rise in the complex I and ubisemiquinone formed at the complex III of the respiratory chain, to the superoxide radical (O Å 2 )(Brookes, 2005), which is scavenged by the antioxidant defences of the organelle. When O Å 2 is addition- ally formed or not adequately removed, H 2 O 2 accumulates (Boveris and Chance, 1973; Turrens et al., 1985; St-Pierre et al., 2002). In the presence of iron, a hydroxyl radical (  OH) is produced via the Fenton/Haber–Weiss reaction, leading to membrane lipid peroxidation (Halliwell and 0031-9422/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.phytochem.2007.01.014 Abbreviations: P. bromelioides, Paepanthus bromelioides; CM-H 2 DC- FDA, 5-(and-6)-chloromethyl-2 0 ,7 0 -dichlorodihydrofluorescein diacetate, acetyl ester; DPPH, 2,2-diphenyl-1-picrylhydrazyl; EGTA, ethylene glycol bis (-aminoethyl ether)-N,N,N 0 ,N 0 -tetraacetic acid; HEPES, N-(2-hydro- xyethyl) piperazine-N 0 -(2-ethanesulfonic acid); ROS, reactive oxygen species; TRIS, tris(hydroxymethyl)-aminomethane. * Corresponding author. Fax: +55 016 3602 4880. E-mail address: ccurti@fcfrp.usp.br (C. Curti). www.elsevier.com/locate/phytochem Phytochemistry 68 (2007) 1075–1080 PHYTOCHEMISTRY