An overview of structural features of DNA and RNA complexes with saffron compounds: Models and antioxidant activity

Saffron is the red dried stigmas of Crocus sativus L flowers and used both as a spice and as a drug in traditional medicine. Its numerous applications as an antioxidant and anticancer agent are due to its secondary metabolites and their derivatives (safranal, crocetin, dimethylcrocetin). In this work we are comparing the spectroscopic results and antioxidant activities of saffron components safranal, crocetin (CRT) and dimethylcrocetin (DMCRT) complexes with calf-thymus DNA (ctDNA) and transfer RNA (tRNA) in aqueous solution at physiological conditions Intercalative and external binding modes of saffron compounds to DNA and RNA were observed with overall binding constants of K-safranal= 1.24 x 10(3) M-1, K-CRT = 6.20 x 10(3) M-1 and K-DMCRT = 1.85 x 10(5) M-1, for DNA adducts and = 6.80 x 10(3) M-1, K-CRT = 1.40 x 10(4) M-1 and K-DMCRT = 3.40 x 10(4) M-1 for RNA complexes. A partial B- to A-DNA transition occurred at high ligand concentrations, while tRNA remained in A-conformation in saffron-RNA complexes. The antioxidant activity of CRT, DMCRT and safranal was also tested by the DPPH- (2,2-diphenyl-1-picrylhydrazyl) antioxidant activity assay and their IC50 values were compared to that of well known antioxidants such as Trolox and Butylated Hydroxy Toluene (BHT). The IC50 values were 95 +/- 1 mu g/ml. for safranal and 18 +/- 1 mu g/mL for crocetin. The inhibition of DMCRT reached a point of 38.8%, which corresponds to a concentration of 40 mu g/mL. (C) 2009 Elsevier B.V. All rights reserved.