Effect of photodynamic therapy (PDT) on a rat model of bleomycin-induced interstitial pneumonia

Even if lung cancer is detected at an early stage, surgery may be difficult in patients with severe comorbidities, like interstitial pneumonia (IP). Radiation therapy cannot be performed due to the high risk of acute IP exacerbation. Therefore, an effective alternative, such as photodynamic therapy (PDT), is required. To prove that acute exacerbation is not induced after PDT in peripheral lung cancer, we investigated the effects of PDT on IP rat models.

Bleomycin (BLM) was administered intratracheally. Seven days after administration, left thoracotomy was performed. Talaporfin sodium was injected, and diode laser irradiation (664 nm, 150mW, 100J/cm²) was performed. Seven days after PDT, the whole blood and left lungs were collected. A total of 23 rats, comprising BLM + PDT (n = 4), BLM + non-PDT (n = 10), non-BLM + PDT (n = 2), non-BLM + non-PDT (n = 5), and two rats that died immediately after PDT were observed. Serum levels of Krebs von den Lungen-6, surfactant protein-D, lactate dehydrogenase, and serum C-reactive protein were measured. Fibrosis and macrophage scorings, and the ​​collagen fibers percentage were examined by staining with hematoxylin and eosin, Elastica van Gieson, anti-α smooth muscle antibody, and anti-CD68 antibodies.

There was no remarkable difference in the values of each marker in fibrosis and macrophage scores with or without PDT. In case of death, fibrosis was mild, and PDT was not affected.

In IP rat models, PDT did not induce lung fibrosis or acute exacerbation.