Mechanism of Action
The basis of PDT is the interaction of light with photosensitive agents to produce an energy transfer and a local chemical effect. This is broadly similar to what is seen in photosynthesis, although in this case, many photosensitizers work together to harvest light energy to produce chemical reactions. Of the many photosensitizers that have been used in PDT, each has its own unique excitation properties. Usually, the photosensitizer is excited from a ground singlet state to an excited singlet state. It then undergoes intersystem crossing to a longer-lived excited triplet state.
One of the few chemical species present in tissue with a ground triplet state is molecular oxygen. When the photosensitizer and an oxygen molecule are in proximity, an energy transfer can take place that allows the photosensitizer to relax to its ground singlet state, and create an excited singlet state oxygen molecule. Singlet oxygen is a very aggressive chemical species and will very rapidly react with any nearby biomolecules. Ultimately, these destructive reactions will kill cells through apoptosis or necrosis. PDT can be considered a form of targeted singlet oxygen chemotherapy, where the targeting is achieved with the combination of the photosensitizer (functioning as a catalyst) and intense light.
A similar example is that cattle may become photosensitive if they graze on plants that contain photosensitizing toxins, such as marigold (Tagetes).
Read more about this topic: Photodynamic Therapy
Famous quotes containing the words mechanism of, mechanism and/or action:
“A mechanism of some kind stands between us and almost every act of our lives.”
—Sarah Patton Boyle, U.S. civil rights activist and author. The Desegregated Heart, part 3, ch. 2 (1962)
“A mechanism of some kind stands between us and almost every act of our lives.”
—Sarah Patton Boyle, U.S. civil rights activist and author. The Desegregated Heart, part 3, ch. 2 (1962)
“There has never been in history another such culture as the Western civilization M a culture which has practiced the belief that the physical and social environment of man is subject to rational manipulation and that history is subject to the will and action of man; whereas central to the traditional cultures of the rivals of Western civilization, those of Africa and Asia, is a belief that it is environment that dominates man.”
—Ishmael Reed (b. 1938)