Research paper Evaluation of the antioxidant activity of soybean extract by different in vitro methods and investigation of this activity after its incorporation in topical formulations Sandra Regina Georgetti a, * , Ru ´ bia Casagrande b , Fabiana Testa Moura-de-Carvalho Vicentini a , Waldiceu A. Verri, Jr. c , Maria Jose ´ Vieira Fonseca a a Department of Pharmaceutical Science, Faculty of Pharmaceutical Sciences of Ribeirao Preto, USP, Brazil b Department of Food and Drugs Technology, Agricultural Sciences Center, Londrina, UEL, Brazil c Department of Pharmacology, Faculty of Medicine of Ribeirao Preto, USP, Brazil Received 10 February 2006; accepted in revised form 21 April 2006 Available online 16 June 2006 Abstract Chemoprevention by natural products is an emerging therapeutic approach for free radical-mediated diseases including cancer. This is a consequence of its wide applicability and acceptance. In the present study, the antioxidant activity of the soybean extract (Isoflavin Beta Ò ) and of formulations added with this extract were evaluated using stable free radical 2,2-diphenyl-1-pycrylhydrazyl (DPPH Å ) and deoxyribose as well as the lipid peroxidation inhibition assays. For all the assays the extract showed a dose-dependent activity, and IC 50 of 21.03 lg/mL in lipid peroxidation inhibition, 161.8 lg/mL in DPPH Å , and 33.5 ng/mL in hydroxyl radical scavenging assay. The antioxidant activity of the extract added in the formulations could not be assessed using the deoxyribose assay. However, the lipid peroxidation inhibition and DPPH Å scavenging assays could be successfully applied for the antioxidant activity evaluation of the formu- lations added with soybean extract to protect the skin against free radicals, which can be generated by the ultraviolet radiation exposure. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Soybean extract; Antioxidant; Polyphenols; Topical formulation; DPPH Å ; Deoxyribose; Lipid peroxidation 1. Introduction It is well established that the inflammatory response fol- lowing acute UV light skin irradiation and the degenerative processes related to chronic UV radiation skin exposure are largely mediated by the overproduction of reactive oxy- gen species (ROS) and free radicals, and by impairment of antioxidant systems [1]. Furthermore, ROS are believed to be involved in many skin disorders such as cancer formation, cutaneous autoimmune diseases, phototoxicity, photosensitivity and skin aging. Two of the early cellular events following UV light exposure are the lipid peroxidation induction and the suppression of replicate DNA synthesis due to DNA damage [2]. Considering that solar UV radiation is the major envi- ronmental inducer factor of skin cancer, various efforts have been made to prevent skin cancer caused by sun exposure. For instance, application of sunscreens agents on the body surface is the most used [3]. However, the currently used sunscreens may be sometimes overwhelmed by excessive sun exposure or present several deleterious effects (i.e. allergy, inflammation) on the skin. Therefore, novel materials for chemoprevention of UV-induced skin cancer are needed. In this regard, one of the safest approaches is the prevention by anti-oxidative chemicals or plants materials [3]. Corroborating, soybean-germ oil 0939-6411/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ejpb.2006.04.003 * Corresponding author. Av. do Cafe ´ s/n, CEP 14040-903, Ribeirao Preto, SP, Brazil. Tel.: +55 16 3602 4726/3602 4433; fax: +55 16 3602 4879. E-mail address: sangeo@fcfrp.usp.br (S.R. Georgetti). www.elsevier.com/locate/ejpb European Journal of Pharmaceutics and Biopharmaceutics 64 (2006) 99–106