Effects of photodynamic therapy in the normal mouse tongue.

The effects of photodynamic therapy (PDT) on the normal mouse tongue were investigated. After using various doses (2.5, 10, and 20 mg/kg body wt) of the photosensitizing drug hematoporphyrin oligomers and 90 or 180 J/cm2 red light (630-nm) emitted from a pulsed neodymium:yttrium-aluminum-garnet dye laser was used to activate it 3 or 24 hours later. It was found that the 20-mg/kg dose elicited a severe response that included extensive vesicular and edema formation. A less severe response was observed with 10 mg/kg of the drug and low-power light (5 mJ/cm2/pulse) periodically delivered (1 hour interval between two 30-minute photoradiations). Such a regimen, however, produced more damage when compared with the higher power (15 mJ/cm2), continuous light delivery counterpart. Healing, except for the protocol with only a 3-hour drug-light interval, was attained by 5 days post-PDT as indicated by regeneration with histologically normal tissues and quantitatively a return to untreated, control values for cross-sectional areas and number of blood vessels. Bromodeoxyuridine immunohistochemistry disclosed an immediate increase in the labeling indices, ie, the percentage of S phase cycling cells, indicating stimulated cell proliferation secondary to repair and fast repopulation of the epithelium. Under the commonly used protocols, PDT was provided safely to the mouse tongue. The regimen of low drug dose and low power of light periodically delivered appears to be the most acceptable method. These parameter-dependent results may partly form the basis for the judicious application of PDT to the oral cavity.