Evidence Against the Production of Superoxide by Photoirradiation of Hematoporphyrin Derivative

Experiments were performed to ascertain whether superoxide anion (O2−) was produced by the photodynamic activation of hematoporphyrin derivative (HPD). Three different systems were utilized to detect formation of O2−, oxidation of epinephrine to adrenochrome, reduction of cytochrome c and reduction of nitro blue tetrazolium (NBT). The effects on these detectors under identical conditions for HPD + hν were compared to those obtained with two O2− generating systems, riboflavin + by and xanthine‐xanthine oxidase, and to a singlet oxygen generating system, photoradiation of methylene blue. The results indicated that HPD + hv differed from the two O2− generating systems in failing to reduce cytochrome c or NET, and that HPD + hν was similar to the behavior of methylene blue + hν. In addition, HPD + hν but not the O2− generating systems could inhibit mitochondrial cytochrome c oxidase activity. We conclude that the photodynamic activation of HPD does not produce O2− as a major oxygen radical and that the effects of HPD + hν on mitochondrial cytochrome c oxidase are not caused by O2−.