PHOTOPROTECTION IN ERYTHROPOIETIC PROTOPORPHYRIA - MECHANISM OF PHOTOPROTECTION BY BETA CAROTENE

[摘要] Erythropoietic protoporphyria is a genetic disease caused by the accumulation of protoporphyrin IX. This molecule absorbs 400 nm light and its presence is at times associated with severe cutaneous photosensitivity. The only effective treatment for this disease is oral administration of .beta.-carotene. Several possible mechanisms of photoprotection by .beta.-carotene were investigated using the photohemolysis of red blood cells as an in vitro model. Additional studies were done in an in vivo model which involves lethal hematoporphyrin photosensitization of white mice. The photoprotective effects of .beta.-carotene were compared with those of .alpha. tocopherol, an agent which possesses some but not all the properties that were implicated in explaining the known effectiveness of .beta.-carotene. In the photohemolysis model, both compounds demonstrated partial protection. In hematoporphyrin-photosensitized mice, tocopherol showed some protection at high doses, while .beta.-carotene showed greater protection at lower concentrations. Although these results suggest that photoprotection was due to free radical scavenging or singlet oxygen quenching, properties common to both agents, they do not rule out the possible role of 400 nm light absorption, a property of .beta.-carotene alone.