Antimicrobial photodynamic therapy using chlorin e6 with halogen light for acne bacteria-induced inflammation.

Aims: The present study was designed to evaluate the therapeutic potential of antimicrobial photodynamic therapy (PDT) using chlorin e6 with halogen light against acne bacteria-induced inflammation.

Main Methods: Highly purified chlorin e6 (Ce6), as a second generation photosensitizer, was synthesized from Spirulina chlorophyll. To evaluate the antimicrobial property of Ce6-mediated PDT with halogen light, the broth microdilution method and two-color fluorescence assay were used. The free radicals generated upon irradiating Ce6 with halogen light were measured using 2,7-dichlorofluorescin diacetate. Propionibacterium acnes was intradermally injected into the left ear of the ICR mice, and the anti-inflammatory effect of Ce6-mediated PDT with halogen light was measured by the histological examination. The expressions of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS) as well as pro-inflammatory cytokines were also measured by Western blotting.

Key Findings: Chlorin e6-mediated PDT with halogen light (30,000 lx) inactivated various skin bacteria, including P. acnes in a dose-dependent manner. The MIC99 value against P. acnes (KCTC3314) of Ce6 with light was >0.49 μg/ml, whereas the MIC99 for Ce6 alone was >31.25 μg/ml. Ce6-mediated PDT suppressed the expression of P. acnes-induced pro-inflammatory cytokines and iNOS, but not COX-2 in a mouse model.

Significance: This study showed a remarkable therapeutic effect of chlorin e6-mediated PDT with halogen light against P. acnes-induced inflammation. Our results suggest for the first time the potential of Ce6-mediated PDT with halogen light as a more effective and safer alternative treatment to antibiotic therapy against pathogenic infections of the skin.