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Photodynamic Therapy Opens Blood-Brain Barrier

Treatment results in increasing contrast flow rate and increased contrast volume in rats

FRIDAY, Sept. 26 (HealthDay News) -- Photodynamic therapy using 5-aminolevulinic acid is highly effective in disrupting the blood-brain barrier, according to the results of a study in rats, published in the October issue of Lasers in Surgery and Medicine.

Henry Hirschberg, M.D., Ph.D., of the University of California-Irvine, and colleagues evaluated the effect of 5-aminolevulinic acid-photodynamic therapy (ALA-PDT) on non-tumor-bearing inbred Fischer rats at increasing fluence levels, using MRI scans to monitor the degree of blood-brain barrier disruption. Four to five hours after 5-aminolevulinic acid infusion, photodynamic therapy was performed to a fluence level of 9, 17 or 26 Joules.

ALA-PDT treatment at increasing fluence levels from 9 to 26 Joules resulted in both an increasing contrast flow rate and increased contrast volume, the researchers report. The blood-brain barrier was disrupted two hours post photodynamic therapy and returned to 80 to 100 percent of normal within 72 hours at the lowest fluence level, the investigators found. There was no effect on the blood-brain barrier if 26 Joules of light was given in the absence of 5-aminolevulinic acid, the report indicates.

"Photodynamic therapy at increasing fluence levels between 9 and 26 Joules demonstrated an increasing contrast flow rate. This suggests the possibility of adjusting the drug penetration into the tissue. This has to be balanced with the observation that fluences over 9 Joules resulted in a certain amount of local tissue damage, which suggests an upper limit to the maximum fluence that can be employed," the authors write.

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