Hirakawa Kazutaka, Kawanishi Shosuke, Hirano Toru, Segawa Hiroshi
Department of Basic Engineering (Chemistry), Faculty of Engineering, Shizuoka University, Johoku 3-5-1, Naka-ku, Hamamatsu-shi, Shizuoka 432-8561, Japan.
J Photochem Photobiol B. 2007 Jun 26;87(3):209-17. doi: 10.1016/j.jphotobiol.2007.04.001. Epub 2007 Apr 24.
The photosensitized DNA damage caused by dihydroxoP(V)tetraphenylporphyrin (P(V)TPP), a cationic water-soluble porphyrin, was examined. The study of near-infrared emission measurements demonstrated the photosensitized singlet oxygen ((1)O(2)) generation by P(V)TPP (quantum yield: 0.28 in ethanol). The fluorescence quenching of P(V)TPP by DNA showed the electron transfer (ET) from nucleobases to photoexcited P(V)TPP. These results have shown that P(V)TPP has ability to damage DNA through dual mechanisms, (1)O(2) generation and ET. Under aerobic conditions, P(V)TPP photosensitized damage was more severe for single-stranded DNA compared to its double-stranded counterpart. Photoexcited P(V)TPP damaged every guanine residue in single-stranded DNA. HPLC measurements confirmed the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), an oxidized product of 2'-deoxyguanosine, and showed that the yield of 8-oxodGuo in single-stranded DNA is larger than that in double-stranded DNA. The guanine-specific DNA damage and the enhancement in single-stranded DNA suggest that the (1)O(2) generation mainly contributes to the mechanism of DNA photodamage by P(V)TPP. Absorption spectrum measurements suggested the interaction between P(V)TPP and DNA. This interaction is expected to enhance the (1)O(2)-mediated DNA damage since the lifetime of (1)O(2) is very short. On the other hand, for double-stranded DNA, photosensitized damage at consecutive guanines was much less pronounced. Because the consecutive guanines act as a hole trap, this DNA-damaging pattern suggests the partial involvement of photoinduced ET. However, DNA damage by ET was not a main mechanism, possibly due to the reverse ET. In conclusion, P(V)TPP induces guanine specific photooxidation mainly via (1)O(2) generation. The interaction with DNA and the energy level of the photoexcited porphyrin may be advantageous for (1)O(2)-mediated DNA damage rather than ET mechanism.
对阳离子水溶性卟啉二羟基磷（V）四苯基卟啉（P（V）TPP）引起的光敏DNA损伤进行了研究。近红外发射测量研究表明，P（V）TPP能产生光敏单线态氧（（1）O（2））（量子产率：在乙醇中为0.28）。DNA对P（V）TPP的荧光猝灭表明存在从核碱基到光激发P（V）TPP的电子转移（ET）。这些结果表明，P（V）TPP能够通过（1）O（2）生成和ET这两种机制损伤DNA。在有氧条件下，与双链DNA相比，P（V）TPP对单链DNA的光敏损伤更严重。光激发的P（V）TPP会损伤单链DNA中的每个鸟嘌呤残基。高效液相色谱测量证实了2'-脱氧鸟苷的氧化产物8-氧代-7,8-二氢-2'-脱氧鸟苷（8-氧代dGuo）的形成，并表明单链DNA中8-氧代dGuo的产量高于双链DNA。鸟嘌呤特异性DNA损伤以及单链DNA中的增强表明，（1）O（2）生成主要促成了P（V）TPP对DNA的光损伤机制。吸收光谱测量表明P（V）TPP与DNA之间存在相互作用。由于（1）O（2）的寿命非常短，这种相互作用有望增强（1）O（2）介导的DNA损伤。另一方面，对于双链DNA，连续鸟嘌呤处的光敏损伤不太明显。因为连续的鸟嘌呤充当空穴陷阱，这种DNA损伤模式表明光诱导ET部分参与其中。然而，ET引起的DNA损伤不是主要机制，可能是由于反向ET。总之，P（V）TPP主要通过（1）O（2）生成诱导鸟嘌呤特异性光氧化。与DNA的相互作用以及光激发卟啉的能级可能有利于（1）O（2）介导的DNA损伤而非ET机制。
