In Vivo Photoacoustic Monitoring of Photosensitizer Distribution in Burned Skin for Antibacterial Photodynamic Therapy

Abstract

For efficient antibacterial photodynamic therapy for wounds, information on the distribution of a photosensitizer in tissue is important, but conventional fluorescence measurement does not provide depth-resolved information. We previously proposed in vivo photoacoustic (PA) depth profiling of a photosensitizer, but the contrast of PA signals was not sufficiently high, mainly due to light absorption by blood in tissue. In this study, we performed dual-wavelength PA measurement; green light and red light were used to excite blood and photosensitzer, respectively, and the former signal was subtracted from the latter signal to compensate a blood-associated component. Methylene blue or porfimer sodium solution was injected into subcutaneous tissue in rats with deep dermal burn and two-dimensional PA measurement was performed. The signal subtraction diminished not only the signal originating from blood but also the signal originating from the stratum corneum and acoustic reflection noise, creating a high-contrast PA image. The distribution of PA signals was confirmed to coincide well with the distribution of photosensitizer-originating fluorescence measured for tissue biopsied after the PA measurement, demonstrating the validity of this method for in vivo photosensitizer dosimetry. On the basis of this method, temporal behaviors of two photosensitizers were compared.

Optimal Photosensitizers for Photodynamic Therapy of Infections Should Kill Bacteria but Spare Neutrophils

“…While TB, MB are hydrophilic with a negative log (P) value (19,20), CV, ET, NPe6, NMB, RB and PHP are amphiphilic with progressively higher positive log (P) values (20)(21)(22)(23)(24)(25)(26). The cell membrane of a mammalian cell is composed of doublelayered phospholipids, and hydrophilic molecules therefore cannot permeate the cell membrane, while amphiphilic and hydrophobic molecules can easily permeate the cell membrane and be promptly transported into the cell (27).…”

Photodynamic therapy induces an immune response against a bacterial pathogen

“…The results suggested that PDT using TB or MB could preserve host neutrophils (>80% viability) while killing substantial amounts of MRSA (5–6 logs of killing). While TB and MB are hydrophilic with a negative easured (P) value [133,134], crystal violet, erythrosine B, NPe6, new MB, rose bengal and PHP are amphiphilic with progressively higher positive log (P) values [129]. Both mammalian cell and bacteria membrane are composed of double layered phospholipids, but the bacterial cell membrane is encased in a cell wall [135].…”

Photosensitization Reactions In Vitro and In Vivo

“…Photosensitizer dosimetry was assessed by photoacoustic signals from the photosensitizer in tissue in a study aimed at combating antibiotic-resistant bacteria. In vivo photoacoustic signals were resolved from MB or Photofrin that was injected into burned skin of rats for profiling of the sensitizer up to 3 mm in depth (31). Other themes in photodynamic action were also represented.…”