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Proceedings Paper

Fluence- and time-dependant lysosomal and mitochondrial damage induced by LS11 PDT characterized with light scattering
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Paper Abstract

Light scattering from cells originates from sub-cellular organelles. Our measurements of angularly resolved light scattering have demonstrated that at 633 nm, the dominant scattering centers within EMT6 cells are mitochondria and lysosomes. To assess their specific contributions, we have used photodynamic therapy (PDT) to induce organelle-specific perturbations within intact cells. We have developed a coated sphere scattering model for mitochondrial swelling in response to ALA- and Pc 4-PDT, and in the case of Pc 4-PDT we have used this model to map the scattering responses into clonogenic cell survival. More recently, we demonstrated the ability to measure the size, scattering contribution, and refractive index of lysosomes within cells by exploiting the localization and high extinction of the photosensitizer LS11 and an absorbing sphere scattering model. Here we report on time- and fluence-dependant scattering measurements from cells treated with LS11-PDT. LS11-PDT causes rapid lysosomal disruption, as quantified by uptake of acridine orange, and can induce downstream effects including release of mitochondrial cytochrome c preceding the loss of mitochondrial membrane potential (Reiners et al., Cell Death Differ. 9:934, 2002). Using scattering and these various methods of analysis, we observed that the induction of lysosomal morphology changes requires a fluence significantly higher than that reported for cell killing. At lower fluences, we observe that at 1 h after irradiation there is significant mitochondrial swelling, consistent with the onset of cytochrome c-induced cell death, while the morphology of lysosomes remains unchanged. We also expand on the ideas of lysosomal staining to demonstrate the sensitivity of scattering measurements at different wavelengths to different organelle populations.

Paper Details

Date Published: 16 February 2007
PDF: 11 pages
Proc. SPIE 6446, Biomedical Applications of Light Scattering, 64460F (16 February 2007); doi: 10.1117/12.697458
Show Author Affiliations
Jeremy D. Wilson, Univ. of Rochester (United States)
Thomas H. Foster, Univ. of Rochester (United States)

Published in SPIE Proceedings Vol. 6446:
Biomedical Applications of Light Scattering
Adam Wax; Vadim Backman, Editor(s)

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