Interaction of safranal and picrocrocin with ctDNA and their preferential mechanisms of binding to GC- and AT-rich oligonucleotides.

Saffron (Crocus sativus L.) shows different biological properties, some of which relate to its special components including safranal (deglycosylated picrocrocin). In our previous study on the mechanism of saffron functions, interaction of saffron carotenoids with DNA and oligonucleotides was reported. The present study aimed to investigate the interaction of safranal with calf thymus DNA (ctDNA), oligo(GC)15, and oligo(AT)15 in comparison with picrocrocin. Circular dichroism (CD) and fluorometric results show the nonintercalative/minor groove binding of the mentioned ligands to ctDNA. The CD plots indicate that picrocrocin interacts with DNA and oligonucleotides at lower concentrations than safranal does, which is accompanied by B- to C-DNA transition. At higher concentrations, it induces more conformational changes, that is, unstacking of DNA and oligonucleotides bases, the same as saffron carotenoids. However, similar results are obtained for safranal interaction with ctDNA (56% AT) and oligo(AT)15, but after adding safranal (with a free aldehyde group) to oligo(GC)15, the CD spectra show some changes (two positive and a displaced negative peaks) that are characteristics of triple-helix DNA. Thus, the mechanism for B- to H-DNA transition, due to the interaction of safranal with GC-rich sequences, is presented here.