Photodynamic therapy of arteries

When patients undergo therapeutic intervention of arteriosclerotic obstructions in their arteries, the major early procedural downfall whether it is an artery bypass, balloon angioplasty or removal of the plaque relates to the restenosis or internal scarring within the artery. Photodynamic therapy has been investigated as a method for the inhibition of this clinically difficult problem. Photodynamic therapy (PDT) is the use of an otherwise nontoxic photosensitizer dye which, when activated by the absorption of light, provides preradical moieties that are cytotoxic to cells. The target cells of photodynamic therapy, are also cells responsible for maintaining tone and general cellular maintenance of the vessel wall. The concern is that the removal of these cells could cause weakening of the artery wall thereby causing dilatation or aneurysm formation. Compliance is the elastic property of the arteries as expressed as a percentage change in the diameter per unit pressure change. Therefore, long-term studies were carried out to investigate the inhibition of intimal hyperplasia and effect on compliance of the artery wall to determine whether or not the inherent strength of the artery is significantly diminished. It is found that smooth muscle cell depletion (up to 16 weeks) in PDT treated arteries does not cause aneurysmal degeneration. The fact that there is no inflammation and that intimal hyperplasia can be inhibited is intriguing. These data confirm that experimental PDT treatment is feasible and safe, however, further optimization needs to be undertaken to understand the mechanism and to determine the optimal parameters for its use in a clinical situation