Antibacterial photodynamic treatment of periodontopathogenic bacteria with indocyanine green and near-infrared laser light enhanced by Trolox(TM).

OBJECTIVE

It has been shown that certain vitamins can significantly enhance the effect of photodynamic anti-tumor therapy. Unfortunately, there is no sufficient information available about the impact of those antioxidants on antimicrobial Photodynamic Therapy (aPDT). The present study is aimed at investigating the antimicrobial effect of the dye indocyanine green (ICG) in the presence of Trolox(TM) , a vitamin E analogue, upon irradiation with near-infrared (NIR) laser light (808 nm) on the gramnegative periodontopathogenic bacteria Aggregatibacter actinomycetemcomitans (A.a.), Porphyromonas gingivalis (P.g.) and Fusobacterium nucleatum (F.n.).

METHODS

Bacteria solved in PBS were incubated with ICG (50-500 μg/ml) in the presence and absence of Trolox(TM) (2 mM). Irradiation was performed after 10 minutes of dark-incubation with NIR-laser-light (25-100 J/cm(2) , 810 nm). During treatment, temperature was also recorded inside the bacterial solutions. The treated suspensions were serial diluted and plated onto blood agar plates. After anaerobe cultivation for 5 days the colony-forming units (CFU/ml) were determined.

RESULTS

The antibacterial effect was ICG-concentration and exposure dependent. It was found that high ICG-concentrations and light fluence rates caused bacterial reduction due to hyperthermia. Where low ICG-concentrations (<250 μg/ml) and fluence rates only induced minor regression, additional Trolox(TM) -administration significantly enhanced the photodynamic effect. While treatment of A.a. (250 μg/ml ICG, 100 J/cm(2) ) without Trolox(TM) caused no bacterial reduction, additional administration led to total eradication. In the presence of Trolox(TM) reduction to one-fifth of the original ICG-concentration (50 μg/ml) still induced total suppression of P.g. and F.n. at identical fluence (100 J/cm(2) ). Treatment with ICG, NIR-light or Trolox(TM) alone showed no remarkable bactericidal effect. Application of high ICG-concentrations (500 μg/ml) and exposure values (100 J/cm(2) ) caused peak temperatures of 64.53°C.

CONCLUSIONS

The results clearly show that Trolox(TM) significantly enhanced the antibacterial effect of ICG upon irradiation with NIR-laser-light. Additional administration of Trolox(TM) may also increase the efficiency of other aPDT systems.