Photobleaching kinetics of optically trapped multilamellar vesicles containing verteporfin using two-photon excitation section sign

• Published in: Photochemistry and photobiology 2006-01, Vol.82 (1), p.152-157
• Main Authors: Samkoe, Kimberley S, Fecica, Matthew S, Goyan, Rebecca L, Buchholz, Jennifer L, Campbell, Chantel, Kelly, Nicole M, Cramb, David T
• Format: Article
• Language: English
• Subjects: Humans; Kinetics; Liposomes; Oxygen; Photochemotherapy; Photons; Porphyrins - chemistry; Retinal Diseases - therapy
• ISSN: 0031-8655

Two-photon excitation photodynamic therapy (TPE-PDT) is being developed as an improved treatment for retinal diseases. TPE-PDT has advantages over one-photon PDT, including lower collateral damage to healthy tissue and more precise delivery of PDT. As with one-photon PDT, there can be local photochemical depletion of oxygen during TPE-PDT. Here, we investigate model systems and live cells to measure local photosensitizer photobleaching and through it, infer local oxygen consumption in therapeutic volumes of the order 1 microm3. Multilamellar vesicles (MLV) and African green monkey kidney (CV-1) cells were used to study the TPE photobleaching dynamics of the photosensitizer, Verteporfin. It was found that in an oxygen-rich environment, photobleaching kinetics could not be modeled using a mono-exponential function, whereas in hypoxic conditions a mono-exponential decay was adequate to represent photobleaching. A biexponential was found to adequately model the oxygen-rich conditions and it is hypothesized that the fast part of the decay is oxygen-dependent, whereas the slower rate constant is largely oxygen-independent. Photobleaching recovery studies in the CV-1 cells support this hypothesis.