Pallidol, a resveratrol dimer from red wine, is a selective singlet oxygen quencher Shan He, Liyan Jiang, Bin Wu, Yuanjiang Pan, Cuirong Sun * Department of Chemistry, Zhejiang University, 38 Zheda Road, Hangzhou 310027, China article info Article history: Received 1 December 2008 Available online 25 December 2008 Keywords: Pallidol Red wine Singlet oxygen ROS EPR Spin-trap abstract Pallidol is a naturally occurring resveratrol dimer from red wine with antioxidant and antifungal activi- ties. In this report, with the use of the EPR spin-trapping technique, the scavenging and quenching effects of pallidol on reactive oxygen species (ROS) were investigated. The results demonstrated that pallidol showed strong quenching effects on singlet oxygen at very low concentrations, but it was ineffective to scavenge hydroxyl radicals or superoxide anions. Further kinetic study revealed that the reaction of pallidol with singlet oxygen had an extremely high rate constant (k a = 1.71  10 10 ). Therefore, pallidol is a potent and selective singlet oxygen quencher in aqueous systems. It may be used in singlet oxy- gen-mediated diseases as a pharmacological agent, which may contribute to the health beneficial effects of red wine. Ó 2008 Elsevier Inc. All rights reserved. A number of large-scale epidemiological studies have demon- strated that the moderate consumption of red wine may counter- act the effect of a high fat diet in reducing the incidence of coronary heart disease and was referred to as the ‘‘French Paradox” [1,2]. The phenolic components, which exerted potent antioxidant activity in inhibiting the oxidation of human low-density lipopro- teins, were believed to be responsible for the beneficial effects of red wine [3–5]. As an important class of red wine polyphenols, stilbenes, especially resveratrol, have been reported to exhibit di- verse bioactivities [6,7]. Since pallidol (Fig. 1) was first isolated from Cissus pallida in 1986 [8], this naturally occurring resveratrol dimer has been widely found in plants belonging to Vitaceae [9–13] and Legumi- nosae [14,15]. In 2001, it was identified in red wine by Vitrac and coworkers for the first time [16]. Then the levels of pallidol in 19 French red wines were determined to range from 0.5 to 4.8 mg/L, which were comparable with that of resveratrol [17]. Reactive oxygen species (ROS, including superoxide anion O 2 Å , hydroxyl radical Å OH and singlet oxygen 1 O 2 ) have been implicated as being important causative agents of aging and var- ious human diseases, such as cancer, heart diseases, multiple sclerosis, Parkinson’s disease, autoimmune disease, and stroke [18,19]. Recently, pallidol have been reported to possess antiox- idant activities stronger than that of resveratrol [20]. These re- sults motivated us to investigate its scavenging and quenching effects on ROS using EPR spin-trapping technique. EPR spin-trap- ping is a reliable technique to detect activated species of oxygen in aqueous solutions, which provides an advantage over the con- ventional methods by avoiding the drawbacks such as low deli- cacy, reliability and precision [21]. In this report we demonstrate that pallidol is a potent and selective 1 O 2 quencher, but not an effective O 2 Å or Å OH scavenger. Its specific antioxidant activity revealed its potential pharmacological applications in 1 O 2 medi- ated diseases, which may be partially responsible for the health beneficial effects of red wine. Materials and methods Chemicals and reagents. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO), 2,2,6,6-tetramethylpiperidine (TEMP), rose bengal (RB), riboflavin, mannitol, and epigallocatechin gallate (EGCG) were purchased from Sigma, St. Louis, MO. All the other chemicals made in China, including ethylene diamine tetraacetic acid (EDTA), hydrogen peroxide (H 2 O 2 ), ferrous sulfate (FeSO 4 ), ace- tone, and water, were obtained at the highest available purity. DMPO was purified with active charcoal before use. Pallidol was isolated and purified from an extract of grape seeds (Vitis vinifera) as described previously [9], and its identity was con- firmed by comparison of its NMR and MS data with those in the literature [8]. Hydroxyl radical assay. Hydroxyl radicals were generated in a Fenton type reaction (Fe 2+ +H 2 O 2 ? Fe 3+ + Å OH + OH  ), and were detected as DMPO-OH adduct [22]. The reaction mixture contained the following reagents at the final concentration: 25 mM H 2 O 2 , 0006-291X/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2008.12.039 * Corresponding author. Fax: +86 571 87951629. E-mail address: hplcms@zju.edu.cn (C. Sun). Biochemical and Biophysical Research Communications 379 (2009) 283–287 Contents lists available at ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc