PB0023 - Methylene blue- mediated photodynamic therapy reduce smooth muscle hyperplasia cells density in a model of rabbit carotid artery neointimal hyperplasia

Background: Neointimal hyperplasia is an important clinical entity in vascular surgery because it limits the long-term effectiveness of surgical and endovascular interventions. Neointimal hyperplasia is usually defined in an artery as thickening of the intimal layer after an injury such as angioplasty, stenting or surgical repair. Neointimal hyperplasia is also used to describe the thickening of venous and prosthetic bypass grafts that leads to reduced lumen diameter and flow and, ultimately, graft occlusion and thrombosis.

Aims: In this study, we aimed to investigate low- level red laser- mediated photodynamic therapy on neointimal hyperplasia reduction accompanied by methylene blue administration in a model of rabbit carotid artery neointimal hyperplasia.

Methods: The right common carotid arteries endothelial denaturation were performed by ballooning in New Zealand white rabbits. After 4 weeks, histopathology results showed the formation of neointimal hyperplasia in all of the rabbits’ arteries. Then treatment group underwent low- level red laser (650 nm, 100 mw, 130 J/cm2)- mediated photodynamic therapy accompanied by methylene blue administration.

Results: Results from histopathology, B-mode and color Doppler ultrasonography showed a significant reduction in the mean value for blood mean velocity, smooth muscle cells density in neointima layer, lumen wall mean thickness and percentage of luminal cross- sectional area of stenosis and significant increase in the mean value for blood volume flow at the stenotic region in the treatment group compared with the other groups (p < 0.05).

Conclusion(s): Anti- proliferative effect of methylene blue- induced by low- level red laser photodynamic therapy, can cause to smooth muscle hyperplasia cells density reduction (due to smooth muscle cells apoptosis in neointimal layer) and significantly dilate the luminal cross- sectional area of stenosis. This protocol may be a potential treatment to neointimal hyperplasia.