Effects of aminolevulinic acid-based photodynamic therapy on chicken combs, an animal model for port wine stains

Abstract

Objective To investigate the effects of aminolevulinic acid-based photodynamic therapy (ALA-PDT) on chicken combs, an animal model for port wine stains (PWS), and to explore the feasibility of PWS treatment with ALA-PDT. Methods A total of 80 leghorns were randomly and equally divided into 10 groups: blank control group receiving no treatment, ALA group treated with ALA alone, four single laser groups irradiated with 630-nm red laser at 75, 100, 150 and 200 J/cm2 respectively, four ALA-PDT groups pretreated with ALA followed by 630-nm red laser radiation at 75, 100, 150 and 200 J/cm2 respectively. An area sized 1 cm×1 cm were marked at one side of combs in all these leghorns, and served as the experiment area to receive corresponding treatment, with that in the other side as the control area. Tissue specimens were obtained on the 14th and 28th days after treatment followed by the observation of morphological and histological changes, calculation of decrement rate in capillary number, and determination of apoptosis index in vascular endothelial cells (VECs) in chicken combs. Results In all the four ALA-PDT groups, the combs became lighter in color with apoptosis of some VECs as well as a decrease in capillary count and diameter in the dermis of the experiment areas. The decrement rate in capillary number was 33.53%±4.89%, 52.02%±2.77%, 67.48%±5.58% and 88.96%±2.47% respectively, and apoptosis index in VECs was 63.44±1.09, 88.50±6.11, 94.32±3.67 and 113.76±10.57 respectively, in the 75-, 100-, 150- and 200-J/cm2 ALA-PDT groups on the 14th day after treatment, and both the decrement rate and apoptosis index in each of these groups were significantly different from those in the blank control group, ALA group, single laser groups receiving red laser radiation at the corresponding dose, and the other ALA-PDT groups (all P<0.01) separately. The apoptosis depth of VECs, defined as the vertical distance from the basal layer to the deepest level at which VEC apoptosis occurred, was 201.19±0.33 μm, 266.15±1.02 μm, 546.09±2.45 μm and 766.37±1.08 μm respectively in the 75-, 100-, 150- and 200-J/cm2 ALA-PDT groups on the 14th day, with significant differences between these four groups (all P<0.01). Conclusions ALA-PDT can markedly damage capillaries in the animal model of port wine stains, chicken combs, with the degree and depth of capillary damage associated with red light energy density. The induction of VEC apoptosis may be an action mechanism of ALA-PDT in the treatment of PWS. Key words: Port-wine stain; Aminolevulinic acid; Photochemotherapy; Apoptosis; Models, animal; Chicken comb