Indole-3-acetic acid: a potential new photosensitizer for photodynamic therapy of acne vulgaris.

ALA (5-aminolevulinic acid) photodynamic therapy (PDT) is a new treatment option for acne. However, it needs a relatively long incubation period and adverse effects are common. Indole-3-acetic acid (IAA) is not toxic by itself but produces free radicals with ultraviolet B. In this study we examined the potential of IAA as a photosensitizer for acne treatment. Free radical formation was measured after visible light irradiation of IAA. Antimicrobial effect was evaluated by assessing growth suppression of Propionibacterium acnes and Staphylococcus aureus after IAA PDT. To evaluate the histological changes, skin biopsies were performed on nude mice skin after IAA PDT. To evaluate the clinical efficacy of IAA PDT, 14 acne patients were treated with the following IAA PDT regimen: three times each with a 15 minutes incubation period and a 2-week interval. The number of inflammatory lesions and the amount of sebum secretion were then assessed. IAA produced free radicals with green light irradiation. Importantly, IAA lost its photosensitizing ability after exposure to certain amount of light. This implies IAA PDT would not require post-procedure photo-protection. The growth of P. acnes and S. aureus were significantly suppressed with IAA PDT. In addition, IAA PDT treated skin showed destruction of follicular ostia epithelium. Interestingly, there was no significant difference between a 4 hours and a 30 minutes incubation, which means that longer absorption time is not necessary for IAA PDT. In the clinical study, inflammatory lesions and sebum secretion were significantly reduced. The procedure was painless and no adverse effect was observed. Photo-protection was not performed and there were no further phototoxic responses. IAA PDT has therapeutic effects on acne via its antimicrobial activities, its sebum-reducing effect and through relieving follicular occlusion. It is a very simple and safe treatment option for acne. Copyright © 2011 Wiley-Liss, Inc.