Effects of photosensitization and low-power helium-neon laser irradiation on liposomes and cell membranes.

Low-power He-Ne laser irradiation causes a well-defined and energy dependent cell destruction of in vitro cultured cell lines sensitized by hematoporphyrin derivative (HPD). The mechanism of this photosensitization was studied by measuring with polarization microscopic, scanning electron microscopic, and electron-spin-resonance (ESR) spectroscopic parameters. The cell damage caused by photosensitization and laser irradiation seems to be a complex process, however the biological membranes seem to be one of the primary targets. The energy of laser light causes rotation and resonance changes of macromolecules and the water molecules, resulting in an increased structural order of the submembraneous components in the living cells, detectable microscopically. During the photosensitization process, the red (630 nm) He-Ne laser light, during a one-photon energy activation, causes excitation of hematoporphyrin molecules to their triplet state. The excitation of HPD molecules results in a multi-step, free-radical generating effect, measured by ESR spectroscopy and studied by the ultrastructural changes of membrane organization and cell shape. Similar effects could be observed on in vitro lipid-water liposome membranes.