Induction of apoptosis in Jurkat cells by photoexcited psoralen derivatives: Implication of mitochondrial dysfunctions and caspases activation G. Viola a, * , E. Fortunato b , L. Cecconet b , S. Disaro ` b , G. Basso b a Department of Pharmaceutical Sciences, University of Padova, via Marzolo 5, Padova, Italy b Department of Pediatrics, University of Padova, via Giustiniani 3, 35131 Padova, Italy Received 31 March 2006; revised 24 August 2006; accepted 14 September 2006 Available online 30 September 2006 Abstract The prevailing form of cell death in lymphocytes exposed to psoralen plus UVA light (PUVA), was investigated. We studied the well known drug 8-methoxypsoralen (8-MOP) and an angular derivatives: angelicin (ANG). We evaluated the induction of apoptosis in a human tumor T-cell line (Jurkat). Both compounds provoke a significant induction of apoptosis at 24 h from irradiation as demonstrated by a remarkable percentage of cells Annexin-V positive. We investigated the effects of the psoralen derivatives upon UVA irradiation on the cell cycle. The flow cytometric analysis of propidium labeled cells indicates that treatment induces, in a dose dependent manner, a massive accumulation of cells, for both compounds, in G2–S phase after 24 h from the irradiation. We have focused our attention on the mitochondrial functionality after irradiation in the presence of psoralen derivatives. We evaluated, by flow cytometry, (i) the mitochon- drial potential (Dw mt ), (ii) the production of reactive oxygen species (ROS) and (iii) the oxidation of cardiolipin, a phospholipid restricted to the inner mitochondrial membrane. Furthermore the activation of caspases -3, -8 and -9 was also investigated. The obtained data indicated that, upon UVA irradiation, the two compounds induce a strong decrease in mitochondrial functions and activate caspase- 3, -8 and -9. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Psoralen; Apoptosis; Cell cycle; UVA irradiation; Mitochondrial potential; Caspases 1. Introduction Psoralens also known as furocoumarins are naturally occurring or synthetic tricyclic aromatic compounds deriv- ing from the condensation of a coumarine nucleus with a furan ring. Their planar structure helps them to intercalate between nucleic acid base pairs. UVA irradiation activates the intercalated complex, resulting in the formation of pho- toadducts with pyrimidines in cellular DNA (Dall’Acqua et al., 2004). The psoralen monoadducts formed in the DNA can further react photochemically with a pyrimidine base on the complementary strand of the DNA thus lead- ing to interstrand cross link (ICL) that are believed to be the primary cause of photoinduced cell killing. New psora- len derivatives have been synthesized such as angelicin that is an angular psoralen. It allows only monofunctional photobinding thus reducing undesirable side effects, espe- cially long term ones such as genotoxicity and risk of skin cancer (Bordin et al., 1991). Nowadays, many human skin diseases such as psoriasis, T-cell lymphoma (Cutaneous T-cell lymphoma, CTCL), and vitiligo are commonly 0887-2333/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.tiv.2006.09.016 Abbreviations: ANG, angelicin; 8-MOP, 8-methoxypsoralen; Dw mt , mitochondrial potential; HBSS, Hank’s balanced salt solution; NAO, 10N-nonyl-acridine orange; PI, propidium iodide; ROS, reactive oxygen species. * Corresponding author. Tel.: +39 49 8275363; fax: +39 49 8275366. E-mail address: giampietro.viola.1@unipd.it (G. Viola). www.elsevier.com/locate/toxinvit Toxicology in Vitro 21 (2007) 211–216