Potential Molecular Mechanisms Involved in 5-Aminolevulinic Acid-Based Photodynamic Therapy against Human Hypertrophic Scars.

BACKGROUND

Hypertrophic scars are manifestations of an abnormal process of tissue repair. Although photodynamic therapy is a promising treatment, details of the mechanisms underlying its inhibitory effects remain to be elucidated.

METHODS

Fibroblasts were isolated from human hypertrophic scar specimens and subjected to photodynamic therapy; 5-aminolevulinic acid was used as a photosensitizer. The accumulation of 5-aminolevulinic acid-derived protoporphyrin IX was detected under fluorescence microscopy. The potential cytotoxicity of 5-aminolevulinic acid alone and with photodynamic therapy was measured by 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide. Hoechst 33258 staining and flow cytometry were conducted to search for clues to apoptosis. Protein and/or mRNA expression levels of apoptosis-related pathways and other hypertrophic scar pathogenesis-associated signaling were investigated by Western blot analysis and/or real-time polymerase chain reaction.

RESULTS

Protoporphyrin IX accumulation peak was achieved at 1.0 mM 5-aminolevulinic acid. 5-Aminolevulinic acid ranging from 0 to 1.0 mM was demonstrated to be noncytotoxic but reduced cell viabilities in a dose-dependent manner with acid-based photodynamic therapy were demonstrated. Reduction of cell viability was attributed mainly to cell apoptosis and probably to mechanisms such as up-regulation of p53/p21, Bax/Bcl-2 ratio, and cleaved caspase-3. Concurrently, deregulation of transforming growth factor-β1-mediated signaling, serving as another putative mechanism underlying hypertrophic scar formation, was found to be reversely modulated in response to acid-based photodynamic therapy.

CONCLUSION

The p53-related apoptosis pathway and transforming growth factor-β1-mediated signaling may be important factors used to predict and evaluate the treatment outcomes of 5-aminolevulinic acid-based photodynamic therapy used in hypertrophic scar patients.

CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, V.