The influence of photodynamic therapy on the ultrastructure of the normal rat bladder

In vivo detection of metastatic ovarian cancer by means of 5-aminolevulinic acid-induced fluorescence in a rat model

STUDY OBJECTIVES

To determine the feasibility of macroscopic visualization of small ovarian cancer metastases in vivo by fluorescence after intravenous administration of 5-aminolevulinic acid (ALA); to assess the time after drug injection when fluorescence of small metastases is maximum; and to correlate macroscopic in vivo fluorescence with both microscopic ex vivo fluorescence and histologic findings.

DESIGN

Controlled animal study (Canadian Task Force classification I).

SETTING

University-based facility.

SUBJECTS

Twenty-four healthy, female Fischer rats.

INTERVENTION

Diffuse peritoneal metastatic cancer was induced in Fischer 344 rats by intraperitoneal injection of 1 million syngeneic ovarian cancer cells (NuTu-19). Four weeks after induction ALA100 mg/kg was injected intravenously, and diagnostic laparotomy was performed 1, 3, 6, or 9 hours thereafter.

MEASUREMENTS AND MAIN RESULTS

The peritoneal cavity was illuminated with the Wood's lamp (ultraviolet light). Fluorescence was determined by direct visualization and compared with a calibrated fluorescent disk. Tissues were collected, sectioned, and examined by fluorescence and conventional light microscopy. Within 1 to 3 hours after intravenous injection of ALA, in vivo fluorescence of tumor nodules (diameter 0.4-5.0 mm) was macroscopically visible. Tumor-free peritoneum did not show fluorescence and was significantly distinguishable from cancer nodules. Fluorescence from intestinal tissues was comparable with tumor nodules. Microscopic fluorescence analysis showed similar values for tumor nodules and peritoneum. Stained histologic specimens of peritoneal surface revealed a superficial layer of cancer cells responsible for fluorescence. The time course of the fluorescence curve in the intestine peaked twice, at 1 and 6 hours after ALA injection. Macroscopically fluorescing nodules were histology confirmed as malignant.

CONCLUSIONS

Fluorescence detection of small cancer nodules after intravenous injection of ALA is feasible for nodules smaller than 0.5 mm on the peritoneum. One to 3 hours after drug injection is optimal for diagnosis of metastases.

The effect of aminolaevulinic acid-induced, protoporphyrin IX-mediated photodynamic therapy on the cremaster muscle microcirculation in vivo

The effect of photodynamic therapy on normal striated muscle was investigated using 30 adult male rats. Animals were divided into six groups. Three control groups received phosphate-buffered saline by gavage and violet light at 105, 178 and 300 mW cm-2 respectively. Three experimental groups received aminolaevulinic acid (ALA; 200 mg kg-1) and violet light at 105, 178 and 300 mW cm-2 respectively. After exposure of the cremaster muscle animals were allowed to equilibrate and vessel diameters and bloodflow assessed. Following photoactivation measurements were taken every 10 min over a 2 h period. Photoactivation of experimental groups at the two higher power densities resulted in an initial decrease in both arteriolar and venular diameters, and a concomitant decrease in blood flow. The magnitude of these changes and the degree of recovery by the end of the observation period was related to power density. No effects were observed in the control groups. These results suggest that microcirculatory damage may contribute to the mechanism of action of photodynamic therapy with ALA.

Effects of photodynamic treatment of platelets or endothelial cells in vitro on platelet aggregation

The purpose of this work was to gain insight into the role played by platelets and endothelial cells in the development of thrombogenic vascular events, observed after in vivo photodynamic therapy (PDT), by studying the in vitro effects of PDT on isolated human platelets and cultured human and bovine endothelial cells. Exposure to Photofrin II (PII) and light caused platelets to rapidly lose their ability to aggregate. Photofrin II alone at high concentrations also exerted inhibitory effects on aggregation. Endothelial cells exposed to PII- and phthalocyanine (GaCl-PcS2,3 or Zn-PCS1,2)-mediated PDT released potent platelet anti- and disaggregating activity which could be identified as prostacyclin by the following criteria: a close correlation between the time and dose dependent anti-aggregating effects and released 6-keto-PGF1 alpha (the spontaneous hydrolysis product of PGI2, determined by radioimmunoassay), the inhibition of these effects by indomethacin, accumulation of 6-keto-PGF1 alpha metabolite in the media of cells treated with PDT (as determined by HPLC analysis), and the absence of evidence for significant nitric oxide production. This prostacyclin release occurred following plasma membrane damage. Although no pro-aggregating activity was observed, endothelial cells were found to release considerable amounts of arachidonic acid and prostaglandin F2 alpha in response to PDT. These data, which indicate powerful anti-thrombogenic effects in vitro, are in sharp contrast to the vascular effects of PDT in vivo which are characterized by severe platelet aggregation, and imply that the in vivo effects involve additional components of the vascular system.