Screening for Photoprotective Agents Using Photo-oxidized Hemolysis

Abstract

Pheophorbide a is a catabolite of chlorophyll a and often found in food such as abalones, pickles and herb tea. Upon ingestion of food contained pheophorbide a and subsequent exposure to sunlight, humans and animals will develop cutaneous photosensitivity. The molecular mechanism of this photosensitivity is that pheophorbide a, sensitized by sunlight, produces singlet oxygen (reactive oxygen) and this in turn oxidizes lipids and proteins in the cell membrane causing damage to the cells. In search for photoprotective agents, we have screened herbs and vitamin-like substances using photo-oxidized hemolysis as an in vitro model for cutaneous photosensitivity. Red blood cell suspensions from Wistar rats were exposed to visible light in the presence of pheophorbide a with or without test substances. At the end of light exposure, absorbance of the supernatants at 570 nm was measured and hemolysis ratios were calculated. Among ten herbs studied, the Indian herb Bacopa monnieri (Otomeazena) inhibited photo-oxidized hemolysis most effectively. Among vitamin-like substances, carnosine inhibited photo-oxidized hemolysis more effectively than histidine, which is a well known singlet oxygen scavenger. The photoprotective effects of these substances will be further investigated in an animal model.