Assessment of safety of 5-aminolevulinic acid-mediated photodynamic therapy in rat brain.

BACKGROUND: Oral 5-aminolevulinic acid (ALA) induces biosynthesis/accumulation of the natural photo-sensitizer protoporphyrin IX (PpIX) in cancer cells. ALA is used widely in photodynamic diagnosis (PDD) and therapy (PDT) during malignant glioma surgery, but few studies have examined the effects of photodynamics plus ALA on normal brain tissue in vivo. We investigated the effects of ALA-mediated PDD and PDT on normal brain tissue.

METHODS: We established a rat model in which the brain surface was irradiated through the skull by light-emitting diode (635 nm) after ALA administration. Using this model, we investigated the effects of various amounts of light irradiation with various ALA doses on brain tissue.

RESULTS: Neurological symptoms developed with administration of ALA at 240 or 120 mg/kg accompanied by irradiation at 100 or 400 J/cm2 , respectively. Dye leakage occurred due to disruption of the blood-brain barrier (BBB) at 90 mg/kg and 100 J/cm2 , respectively. Thickness of the cortex increased significantly at 240 mg/kg and 400 J/cm2 , respectively. The number of neurons appeared to decrease at 200 mg/kg plus 400 J/cm2 , respectively, and there was an increase in the number of cells that were positive for terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling (TUNEL) staining.

CONCLUSIONS: ALA-mediated PDT is safe at doses of 90 mg/kg or less followed by light irradiation of 100 J/cm2 in rat brains. At doses above this threshold, ALA-PDT led to irreversible BBB and brain damage in rats.