Targeted Antimicrobial Photochemotherapy

Abstract

This study explores a new approach for antimicrobial therapy with light activation of targeted poly-l-lysine (pL)–chlorine6 (c e6 ) conjugates. The goal was to test the hypothesis that these conjugates between pL and c e6 would efficiently target photodestruction towards gram-positive (Actinomyces viscosus) and gram-negative (Porphyromonas gingivalis) oral species while sparing an oral epithelial cell line (HCPC-1). Conjugates of c e6 with pL (average molecular weight, 2,000) having a positive, neutral, or negative charge were prepared. Illumination with red light (λmax = 671 nm) from a diode array produced a dose-dependent loss of CFU from the bacteria, under conditions that did not affect the viability of the epithelial cells. For P. gingivalis, the cationic conjugate produced 99% killing, while the neutral conjugate killed 91% and the anionic conjugate killed 76% after 1 min of incubation and exposure to red light for 10 min. For A. viscosus, the cationic conjugate produced >99.99% killing while HCPC-1 cells remained intact. The importance of the positive charge was shown by the effectiveness of c e6 -monoethylenediamine monoamide (a monocationic derivative of c e6 ) in killing both bacteria. The clinically employed benzoporphyrin derivative under the same conditions killed epithelial cells while leaving P. gingivalis relatively unharmed. A mixture of c e6 with pL did not show phototoxicity comparable with that of the cationic conjugate. These results were explained by the selective uptake of the conjugates by bacteria (20- to 100-fold) compared to that by mammalian cells, while free c e6 showed much less selectivity for bacteria (5- to 20-fold). The data suggest that the cationic pL-c e6 conjugate may have an application for the photodynamic therapy of periodontal disease.

Photodestruction of human dental plaque bacteria: Enhancement of the photodynamic effect by photomechanical waves in an oral biofilm model

“…In our previous studies, we have shown that a cationic conjugate between c e6 and a pL chain of 20 amino acids was effective in photoinactivation of the Gramnegative P. gingivalis and the Gram-positive A. naeslundii genospecies 2 [22]. Hamblin et al [38] have recently shown that photoinactivation of E. coli was achieved by a 37-lysine pL-c e6 conjugate at concentrations up to 4 mM c e6 equivalent whereas the concentration of a 8-lysine conjugate needed to be raised to 100 mM c e6 equivalent to kill E. coli.…”

“…We have shown in vitro that a polycationic conjugate between poly-L-lysine (pL) and the PS chlorin e6 (c e6 ) could efficiently target photodestruction of Gram-negative (Porphyromonas gingivalis) and Gram-positive (Actinomyces naeslundii, formerly Actinomyces viscosus) oral species while sparing an oral epithelial cell line [22]. We have also shown that a single photomechanical wave (PW) generated by a Q-switched laser induced a 75% increase in the penetration depth of the cationic PS methylene blue into a population of A. naeslundii genospecies 2 43146 growing in vitro on bovine enamel surfaces [23].…”

Photodynamic therapy in dentistry: a literature review

“…Several studies have shown that oral bacteria in planktonic cultures and in plaque scrapings are susceptible to antimicrobial photodynamic therapy [77][78][79][80][81]. Moreover, recent studies have reported that photodynamic therapy induced bacterial cell killing and reduced bacterial numbers by more than tenfold in S. mutans, Streptococcus sobrinus, and Streptococcus sanguinis biofilms when toluidine blue O or erythrosine was used as the photosensitizer [82][83][84][85].…”

A possible mechanism for visible light‐induced wound healing

“…In PDT, ROS generated by an illuminated photosensitizer introduced exogenously into the bacteria induce a toxic effect [32][33][34]. This photochemical treatment has been used successfully in vitro [7].…”