Photosensitization of DNA by b-carbolines: Kinetic analysis and photoproduct characterization

M. MICAELA GONZALEZ; MARIANA VIGNONI; MATIAS ALES-GANDOLFO; MAGALI PELLON-MAISON; M. DEL ROSARIO GONZALEZ-BARO; ROSA ERRA-BALSELLS; BERND EPE; FRANCO M. CABRERIZO

Mendoza

Conferencia; XXI Inter American Photochemical Society (I-APS) Conference; 2011

Inter-American Photochemical Society

Beta-carbolines (bCs) are alkaloids belonging to a family of heterocyclic compounds showing in its structure the 9H-pyrido[3,4-b]indole moiety. The structures of three bC alkaloids and two of its derivatives are shown in Scheme 1. bC alkaloids are present in a wide range of biological systems and play a variety of significant photo-dependent roles. bCs have demonstrated that can act as very good photosensitizers. Under UV-A irradiation, norharmane and harmane are able to induce chromosome damage in mammalian cells, and to inactivate bacteria and viruses . In addition, it has been proposed that the biological role of some bCs in plants could be related with the defense response (i.e., photo-toxic effects) against insects, webworms, etc. In a very recent work, we have demonstrated that photosensitized DNA relaxation by norharmane (upon UV-A excitation) takes place. The later process involves, mainly, electron transfer reactions (i.e., Type I mechanism). Despite their acknowledged importance, the main biological role of these alkaloids and the mechanisms involved in those processes are, to date, nevertheless still poorly understood. In the present work, we set out to systematically examine the capability of three important bCs [norharmane (nHo), harmane (Ho) and harmine (Ha)] and two bC derivatives [N-methyl-norharmane (N-Me-nHo) and N-methyl-harmane (N-Me-Ho)] to photo-induce DNA damage, in aqueous solution phase, upon UV-A excitation. In particular, a comparative kinetic analysis was performed to evaluate the extent of the DNA relaxation made by each bC and also to find out the mechanisms involved in each case. In addition, to identify the chemical nature of the DNA-photoproducts formed upon photosensitization several experiments, using specific DNA endonucleases were carried out. In all cases, the presence of 8-oxoguanine and apurinic/apyrimidinic sites was observed; whereas, only in the case that harmine was used as photosensitizer thymidine dimer formation could be detected.