CHAPTER 31: Photodynamic Reactions As a Marker of Cerebral Vascular Diseases

Photo-produced singlet oxygen may be deactivated through the production of secondary reactive oxygen species (ROS). The lifespan, nature and the effects of these ROS depend on the local biochemical conditions such as tissue resistance to ROS. Using an in vitro assay involving Rose Bengal as a photosensitizer (¹O₂ quantum yield of 0.75), we noted that patients showed decreased systemic resistance to ¹O₂ during ischemic strokes (¹O₂ quantum yield of 1.83) or silent aneurysms (¹O₂ quantum yield of 1.15) and increased systemic resistance after subarachnoid hemorrhages (¹O₂ quantum yield of 0.65) (n = 20 for each) as compared to controls (¹O₂ quantum yield of 0.9 ± 10%). An inverse correlation (R² = 0.98) was found with the vitamin D content of serum. This suggests that systemic oxidative changes are induced early during cerebral suffering, but differently according to the cause of brain tissue necrosis.