Characterization of the cell death modes and the associated changes in cellular energy supply in response to AlPcS4-PDT

Abstract

Photodynamic therapy (PDT) can result in both types of cell death, apoptosis or necrosis. Several steps in the induction and execution of apoptosis depend on ATP and the intracellular ATP level has been shown to be one determinant in whether apoptosis or necrosis occurs. Therefore, photochemical damage of cellular targets involved in energy supply might play a crucial role in the mode of cell death being executed. The present study is aimed at the characterization of changes in cellular energy supply and the associated cell death modes in response to PDT. Using the human epidermoid carcinoma cell line A431 and aluminium(III) phthalocyanine tetrasulfonate chloride (2.5 microM) as a photosensitizer, we studied the changes in mitochondrial function and intracellular ATP level after irradiation with different light doses. Employing assays for caspase-3 activation and nuclear fragmentation, 50% of the cells were found to undergo apoptosis after irradiation between 2.5 to 3.5 J cm(-2) while the remainder died by necrosis. At higher light doses (> 6 J cm(-2)), neither caspase-3 activation nor nuclear fragmentation was observed and this suggests that these cells died exclusively by necrosis. Necrotic cell death was also associated with a rapid decline in mitochondrial activity and intracellular ATP. By contrast, with apoptosis the loss of mitochondrial function was delayed and the ATP level was maintained at near control levels for up to eight hours which was far beyond the onset of morphological changes. These data suggest that, depending on the light dose applied, both, necrosis as well as apoptosis can be induced with AlPcS4 mediated PDT and that photodamage in energy supplying cellular targets may influence the mode of cell death. Further, it is speculated that cells undergoing apoptosis in response to PDT might maintain a high ATP level long enough to complete the apoptotic program.

Porphyrin-based cationic amphiphilic photosensitisers as potential anticancer, antimicrobial and immunosuppressive agents

“…Finally, a mode of cell death depends not only on a PDT dose (Plaetzer et al 2002) but also on cell type (Wyld et al 2001. Therefore, dosimetry investigations in different cell types may provide evidence to facilitate the choice of the appropriate application for a certain PS.…”

ROS: Reactive Oxygen Species

“…Plaetzer proposes that the mode of cell death is related directly to the changes in the ATP pool. Assays of procaspace-3 activation and nuclear fragmentation on human epidermoid carcinoma cell line A431 have shown that while impairment of mitochondrial functions and rapid decrease of ATP are symptomatic of necrotic cell death, the preservation of high ATP levels allows the execution of the apoptotic program (Plaetzer et al 2002). The photosensitized damages on lysosomes are generally less lethal than that sustained by mitochondria (Berg and Moan 1994).…”

“…EVects on the bioenergetics, (Atlante et al 1989;Moreno 1981, 1990) primarily on the mitochondrial permeability transition pore (Salet et al 1997) have been investigated in detail (Dummin et al 1997;Morgan and OseroV 2001;Plaetzer et al 2002). PDT may induce permeabilization of both mitochondrial membranes, dissipation of the transmembrane potential, and a release of apoptosis-related proteins (such as cytochrome c, apoptosis inducing factor, second mitochondria derived activator of caspases and certain procaspases) into the intermembrane space (Almeida et al 2004;Oleinick et al 2002).…”

Biological Function of Low Reactive Level Laser Therapy (LLLT)

“…In this technique, patients are administered PPIX or its precursor, 5-aminolevulinic acid (ALA), and reactive oxygen species are generated with local laser irradiation to kill malignant cells or epithelial cells of vascular neoplasms. In addition to the tumoricidal effects of reactive oxygen species, photodynamic therapy also induces energy-demanding apoptotic process by maintaining intracellular ATP levels [66].…”