[Oxygen consumption during photodynamic therapy in vitro]

The consumption of dissolved molecular oxygen was measured during photodynamic therapy in vitro. Aqueous solutions of hematoporphyrin derivative (HpD) containing different concentrations of serum or numbers of cells were prepared. Decrease in oxygen in the solution and cell suspensions was monitored during light-irradiation (at a wavelength of 610 to 640 nm). The rate of oxygen consumption increased with increasing concentrations of HpD, serum levels or numbers of cells. Upon repeated irradiation of the same solutions (after restitution of the initial pO2 of 100 mm Hg), the rate of oxygen consumption decreased indicating a disaggregation process of HpD. The rate of oxygen content of the solutions decreased independently of the actual oxygen partial pressure. Even at a low pO2 below 10 mm Hg, oxygen consumption was unimpeded until the solutions were free of oxygen. No O2-consumption was noted in aqueous solutions of HpD (up to 40 g/ml) without serum or cells during irradiation.