Fluorescence and photosensitization of experimental endometriosis in the rat after systemic 5-aminolevulinic acid administration: a potential new approach to the diagnosis and treatment of endometriosis

OBJECTIVE: Our purpose was to evaluate and compare the conversion of 5-aminolevulinic acid into the endogenous photosensitizer protoporphyrin IX in experimentally induced endometriosis and in other normal tissues in a rat model. STUDY DESIGN: Fluorescence of experimental endometriotic lesions, uterus, peritoneum, bowel mesentery, bladder, eye, skin, and skeletal muscle was assessed 3 hours after either intravenous, oral, or intrauterine administration of 5-aminolevulinic acid with use of spectrophotofluorometry. In another experiment the fluorescence of surgically induced endometriosis and adjacent normal peritoneum was evaluated every 15 minutes after 5-aminolevulinic acid administration to assess the time course of protoporphyrin IX production. RESULTS: In the rat endometriosis model intralesional and systemic 5-aminolevulinic acid produced fluorescence within implants showing viable endometrial cells. Treatment with 5-aminolevulinic acid produced low-intensity fluorescence in peritoneum, bowel mesentery, and eye. Relatively intense fluorescence was seen in skin, bladder, and uterus. No fluorescence was observed in skeletal muscle. The intensity of fluorescence varied with the dosage and route of administration of 5-aminolevulinic acid. Fluorescence intensity of protoporphyrin IX was significantly greater in implants than in adjacent normal peritoneum between 2 and 4 hours after treatment. CONCLUSIONS: Protoporphyrin IX fluorescence in experimentally induced endometriosis lesions after intravenous and oral delivery of 5-aminolevulinic acid was significantly greater than the fluorescence detected in adjacent normal peritoneum.