Photodynamic effects on rabbit auricular veins after photosensitization with porfimer sodium: Implications of the results with respect to the treatment of esophageal varices with photodynamic therapy

Vascular targeted photodynamic therapy for bleeding gastrointestinal mucosal vascular lesions: a preliminary study

BACKGROUND

Vascular-targeted photodynamic therapy (V-PDT) has shown good selectivity and efficacy in the treatment of certain types of vascular disease, including port wine stains, age-related macular degeneration, and esophageal varices. This study was conducted to test the efficacy and safety of V-PDT in the treatment of gastrointestinal (GI) bleeding caused by the abnormal dilatation of capillaries.

METHODS

Patients with bleeding GI mucosal vascular lesions treated with V-PDT were included in this retrospective study. The efficiency of V-PDT was analyzed by comparing the documented endoscopy results, hemoglobin levels, and transfusion requirements before and at 6 months after the last V-PDT. Side effects during and after V-PDT and follow-up results were also analyzed.

RESULTS

Seven patients with bleeding GI mucosal vascular lesions were treated with V-PDT. After 1-4 V-PDT sessions, all patients no longer needed transfusions to maintain a stable hemoglobin level during the follow-up period of 6 months. The mean hemoglobin level of the seven patients improved from 6.21±1.48 g/dl to 11.66±1.21 g/dl (p<0.001), and the GI bleeding and melena of all the patients disappeared. No perforations, strictures, scars, or episodes of photosensitization occurred in the seven patients, and there were no recurrences of GI bleeding during the 1-21 months of further follow-up.

CONCLUSIONS

This preliminary study indicated that V-PDT is a highly selective, safe, well-tolerated, and effective treatment modality for bleeding GI mucosal vascular lesions. However, prospective studies with larger sample sizes are needed to confirm this finding.

Microvascular hyperpermeability and thrombosis induced by light/dye treatment

To investigate microvascular hyperpermeability and thrombosis induced by photodynamic therapy or light/dye treatment, we quantified the initiation time for thrombus formation, thrombus growth rate, and the time for the microvessel occlusion in post-capillary venules of rat mesenteries. Under similar light/dye treatments, we also measured the microvessel hydraulic conductivity (Lp) and solute permeability (P) to TRITC-BSA (bovine serum albumin), respectively, in the same type of microvessels as for thrombosis. Under an irradiation power of 0.37 mW/mm(2), thrombus was initiated in 3.8 ± 0.4 min, its growth rate was 3.9 ± 0.3% of the vessel mid-plane area/min, and the microvessels were completely occluded in 29.3 ± 2.2 min (SE, n = 8). Under the same irradiation power, Lp and P increased gradually, reaching a plateau in 3-5 min. At the plateau, Lp had increased to 2.2 ± 0.2 times (n = 11), while P had increased to 4.1 ± 0.7 (n = 7) times their baseline values, respectively. Neither Lp nor P increased further after longer time exposure (up to 30 min). Comparison of the measured Lp and P data with predictions from a mathematical model for the inter-endothelial cleft suggests that an almost complete depletion of the glycocalyx layer at the luminal surface of the endothelium might be one of the structural mechanisms by which the light/dye increases microvascular permeability and induces thrombosis.