Potentiation of antimicrobial photodynamic inactivation mediated by a cationic fullerene by added iodide: in vitro and in vivo studies

Abstract

Background: Antimicrobial photodynamic inactivation with fullerenes bearing cationic charges may overcome resistant microbes.

Methods & results: We synthesized C60-fullerene (LC16) bearing decaquaternary chain and deca-tertiary-amino groups that facilitates electron-transfer reactions via the photoexcited fullerene. Addition of the harmless salt, potassium iodide (10 mM) potentiated the ultraviolet A (UVA) or white light-mediated killing of Gram-negative bacteria Acinetobacter baumannii, Gram-positive methicillin-resistant Staphylococcus aureus and fungal yeast Candida albicans by 1-2+ logs. Mouse model infected with bioluminescent Acinetobacter baumannii gave increased loss of bioluminescence when iodide (10 mM) was combined with LC16 and UVA/white light.

Conclusion: The mechanism may involve photoinduced electron reduction of (1)(C60>)* or (3)(C60>)* by iodide producing I· or I2 followed by subsequent intermolecular electron-transfer events of (C60>)-· to produce reactive radicals.

Keywords: antimicrobial photodynamic therapy; bioluminescent bacteria; decacationic fullerene; decatertiary-amine chain; in vivo infection model; iodide potentiation.

Figure 1. Structure and synthesis of C₆₀-fullerene

LC16: C₆₀-fullerene.

Figure 2. Light dose response for photodynamic inactivation of Gram-negative Acinetobacter baumannii mediated by C₆₀-fullerene (20 μM) with and without the addition of KI (10 mM)

(A) UVA light; (B) white light. Points are averages of five separate experiments and bars are standard deviations. LC16: C₆₀-fullerene; UVA: Ultraviolet A.

Figure 3. Light dose response for photodynamic inactivation of Gram-positive methicillin-resistant Staphyloccus aureus (MRSA) mediated by C₆₀-fullerene (20 μM) with and without the addition of KI (10 mM)

(A) UVA light; (B) white light. Points are averages of five separate experiments and bars are standard deviations. LC16: C₆₀-fullerene; MRSA: Methicillin-resistant Staphyloccus aureus; UVA: Ultraviolet A.

Figure 4. Light dose response for photodynamic inactivation of fungal yeast Candida albicans mediated by C₆₀-fullerene (20 μM) with and without the addition of KI (10 mM)

(A) UVA light; (B) white light. Points are averages of 5 separate experiments and bars are standard deviations. LC16: C₆₀-fullerene; UVA: Ultraviolet A.

Figure 5. Panel of successive bioluminescence images of representative mice with abrasion wounds infected with bioluminescent Acinetobacter baumannii (left for 30 min) and treated by topical application of 200 μM C₆₀-fullerene with or without addition of 10 mM KI solution (left for 10 min)

Mice wounds were exposed to increasing fluences of ultraviolet A (5, 10, 15 and 20 J/cm²) with imaging taking place after each exposure. DC: Dark control; LC: Light control; LC16: C₆₀-fullerene; PS: Photosensitizer.

Figure 6. Panel of successive bioluminescence images of representative mice with abrasion wounds infected with bioluminescent Acinetobacter baumannii (left for 30 min) and treated by topical application of 200 μM C₆₀-fullerene with or without addition of 10 mM KI solution (left for 10 min)

Mice wounds were exposed to increasing fluences of white light (30, 60, 90 and 120 J/cm²) with imaging taking place after each exposure. DC: Dark control; LC: Light control; LC16: C₆₀-fullerene; PS: Photosensitizer.

Figure 7. Quantification of relative light units from bioluminescence images captured from groups of mice (n = 6) with Acinetobacter baumannii infected wounds treated with C60-fullerene +/− KI and light

(A) UVA light-treated mice shown in Figure 5; (B) White light-treated mice shown in Figure 6. LC16: C₆₀-fullerene; PDT: Photodynamic therapy; RLU: Relative light units; UVA: Ultraviolet A.