Histological Changes in Photorejuvenation Induced by 5-Aminolevulinic Acid Photodynamic Therapy in a Photoaged Mouse Model

Abstract

Background: Photoaging is defined as the premature skin aging induced by ultraviolet (UV) irradiation, which is histologivally characterized by degradation of collagen fiber and accumulation of abnormal elastotic material in the dermis. Photodynamic therapy (PDT) is a noninvasive technique used in the treatment of various skin disorders, and recently it has been shown to be effective for photoaged skins. However, the histological studies of PDT in animal model have rarely been reported.

Objectives: I observed the histological changes in photoaged mouse skin specimens and in the specimens after photorejuvenation induced by 5-aminolevulinic acid (ALA)-PDT. Furthermore, I investigated transmission electron microscopic (TEM) studies to observe the differences among normal, photoaged, and post-ALA-PDT biopsy specimens.

Materials and Methods: Total 32 of 6-week-old female albino hairless mice (Skh:hr-1) were divided into six groups: control group (group A), photoaging group (group B), ALA only group (group C), light-emitting diode (LED) only group (group D), 5-ALA PDT group with 20J/cm2 of light dose (group E), and 5-ALA PDT group with 40J/cm2 of light dose (group F). For group E, it was divided to 3 identical groups; which were performed from 1 session to 3 sessions of ALA-PDT to investigate the differences among the number of total sessions of PDT. Serial skin biopsies were performed from each mouse at day 2, day 7, day 14, and day 21 from each intervention. For group E, the additional skin biopsies were performed at day 28 from each session. Hematoxylin & Eosin staining, Masson-trichrome staining, and Verhoeff’s elastic staining were performed with additional immunohistochemical staining. Furthermore, TEM studies performed.

Results: During photoaging, both epidermal thickness and dermal thickness were increased, the amount of dermal collagen fiber was decreased, and the elastotic materials were increased. After ALA-PDT application, both epidermal thickness and dermal thickness were decreased, as the range of the control group. The amount of collagen fiber was increased through day 2 to day 21, and the increased elastotic materials during photoaging period were reversed by 5-ALA PDT. With TEM, the collagen fibers were much decreased during photoaging compared with control group. However, during PDT application, the decreased collagen fibers were remarkably increased. During photoaging, much distended dermal fibroblast with much distended endoplasmic reticulum was noted; however, after PDT application, healthy fibroblast with normalized endoplasmic reticulum was observed. There was minimal difference between PDT with light dose of 20J/cm2 and 40J/cm2 or among the number of sessions of PDT from one to three.

Conclusion: In conclusion, this study provided the histologic evidence of the beneficial effects of ALA-PDT chronologically for photodamaged skin in mice model. ALA-PDT induces deposition of collagen in the dermis, normalizes the elastotic materials by photoaging, and normalizes the function of fibroblasts itself. Further studies will be necessary to fully determine the adequate parameters for photorejuvenation.