Determination of aminolevulinic-acid-induced protoporphyrin IX in mice skin

The kinetics of Protoporphyrin IX (PpIX) production in mice skin was studied by photoacoustic spectroscopy. PpIX was induced in mice by intraperitoneal administration of δ-aminolevulinic acid (δ-ALA) in doses of 10, 20, and 30 mg/kg. Mice were sacrificed at specific times within an 8 h interval following δ-ALA administration, and their abdominal skin was excised for the optical measurements. The PpIX content was determined from the photoacoustic amplitude at 410 nm, where PpIX presents its Soret band. For each dose, maximum PpIX was observed at two points. The first maximum occurred at around 15–45 min, depending on the ALA dose, and the second one took place approximately 2 h after δ-ALA administration. These peaks are associated with PpIX production in blood vessels and tissue, respectively. Fluorescence measurements of the PpIX content in plasma extracted intracardiacally confirmed the previous statement. Finally, phase resolved photoacoustic spectroscopy was applied to evaluate the mean depth at which PpIX is generated within the mice skin. This evaluation confirms that the ALA-induced porphyrins in skin are rather produced in the epidermis than in the dermis.