Antioxidant and nitric oxide production inhibitory activities of galacturonyl hydroxamic acid Yuh-Hwa Liu a , Shyr-Yi Lin b,c , Chi-Ching Lee d , Wen-Chi Hou d, * a Division of Gastroenterology, Shin Kong Wu Ho-Su Memorial Hospital, Taipei, Taiwan b Department of Internal Medicine, School of Medicine, Taipei Medical University, Taipei, Taiwan c Department of Internal Medicine, Taipei Medical University Hospital, Taipei, Taiwan d Graduate Institute of Pharmacognosy, Taipei Medical University, No. 250, Wu-Hsing Street, Taipei 110, Taiwan Received 12 September 2007; received in revised form 13 November 2007; accepted 18 December 2007 Abstract The self-prepared pectin hydroxamic acid has been reported to have antioxidant activities [Yang, S. S., Cheng, K. D., Lin, Y. S., Liu, Y. W., & Hou, W. C. (2004). Pectin hydroxamic acids exhibit antioxidant activities in vitro. Journal of Agricultural and Food Chemistry, 52, 4270–4273]. In this study, the galacturonic acid (GalA), the monomer unit of the pectin polymer, was esterified with acidic methanol (1 N HCl) at 4 °C with gentle stirring for 5 days to get galacturonic acid methyl ester which was further reacted with alkaline hydrox- ylamine to get galacturonyl hydroxamic acid (GalA–NHOH). The GalA–NHOH was used to test the antioxidant and antiradical activ- ities in the comparison with GalA. The scavenging activities of GalA–NHOH against DPPH radicals (half-inhibition concentration, IC 50 , was 82 lM), hydroxyl radicals detected by electron spin resonance (IC 50 was 0.227 nM in the comparison with Trolox of 0.433 lM), superoxide radicals (IC 50 was 830 lM) were determined. The protection activities of GalA–NHOH against hydroxyl radi- cals-mediated calf thymus DNA damages, linoleic acid peroxidation and peroxynitrite-mediated dihydrorhodamine 123 oxidations were also investigated. It was found that the GalA–NHOH exhibited dose-dependently antioxidant activity and few or none was found in GalA. The GalA–NHOH was used to evaluate the suppressed activity of nitric oxide (NO) productions of RAW264.7 cells in the pres- ence of lipopolysaccharide (LPS, 100 ng/ml) as inducers. It was found that GalA–NHOH (0.02–0.1 mg/ml) could dose-dependently sup- press the NO productions (expressed as nitrite concentrations) in RAW264.7 cells without significant cytotoxicity. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Antioxidant activity; Electron spin resonance (ESR); Galacturonylhydroxamic acid (GalA–NHOH); Nitric oxide; RAW264.7 cells 1. Introduction Rective oxygen species and free radical-mediated reac- tions have involved in degenerative or pathological pro- cesses such as aging (Ames, Shigena, & Hegen, 1993; Harman, 1995), cancer, coronary heart disease and Alzhei- mer 0 s disease (Ames, 1983; Diaz, Frei, Vita, & Keaney, 1997; Gey, 1990; Smith et al., 1996). There were several reports concerning natural compounds in fruit and vegeta- ble for their antioxidant activities, such as anthocyanin (Espin, Soler-Rivas, Wichers, & Viguera-Garcia, 2000), water extracts of roasted Cassia tora (Yen & Chuang, 2000), and the storage proteins of sweet potato root (Hou, Han, Chen, Wen, et al., 2005), yam tuber (Hou et al., 2001), yam mucilages (Hou, Hsu, & Lee, 2002) and potato tuber (Liu, Han, Lee, Hsu, & Hou, 2003). A variety of hydroxamic acid derivatives have been reported to have biological activities toward cancer, car- diovascular diseases, Alzheimer’s disease and tuberculosis etc (Muri, Nieto, Sindelar, & Williamson, 2002). Succini- mide hydroxamic acids were proved as potent inhibitors of histone deacetylase and tumor cell proliferation (Curtin et al., 2002). Hydroxamic acid derivatives of salicylic acid were cyclooxygenase (COX)-1 and COX-2 inhibitors (Dooley et al., 2003). Oxal hydroxamic acid derivatives 0308-8146/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2007.12.055 * Corresponding author. Fax: +886 (2) 2378 0134. E-mail address: wchou@tmu.edu.tw (W.-C. Hou). www.elsevier.com/locate/foodchem Available online at www.sciencedirect.com Food Chemistry 109 (2008) 159–166 Food Chemistry