Photodynamic therapy using intra‐articular photofrin for murine MRSA arthritis: Biphasic light dose response for neutrophil‐mediated antibacterial effect

Abstract

Background and Objective Bacterial arthritis does not respond well to antibiotics and moreover multidrug resistance is spreading. We previously tested photodynamic therapy (PDT) mediated by systemic Photofrin® in a mouse model of methicillin-resistant Staphylococcus aureus (MRSA) arthritis, but found that neutrophils were killed by PDT and therefore the infection was potentiated. Study Design/Materials and Methods The present study used an intra-articular injection of Photofrin® and optimized the light dosimetry in order to maximize bacterial killing and minimize killing of host neutrophils. MRSA (5 × 107 CFU) was injected into the mouse knee followed 3 days later by 1 μg of Photofrin® and 635-nm diode laser illumination with a range of fluences within 5 minutes. Synovial fluid was sampled 6 hours or 1–3, 5, and 7 days after PDT to determine MRSA colony-forming units (CFU), neutrophil numbers, and levels of cytokines. Results A biphasic light dose response was observed with the greatest reduction of MRSA CFU seen with a fluence of 20 J cm−2, whereas lower antibacterial efficacy was observed with fluences that were either lower or higher. Consistent with these results, a significantly higher concentration of macrophage inflammatory protein-2, a CXC chemokine, and greater accumulation of neutrophils were seen in the infected knee joint after PDT with a fluence of 20 J cm−2 compared to fluences of 5 or 70 J cm−2. Conclusion PDT for murine MRSA arthritis requires appropriate light dosimetry to simultaneously maximize bacterial killing and neutrophil accumulation into the infected site, while too little light does not kill sufficient bacteria and too much light kills neutrophils and damages host tissue as well as bacteria and allows bacteria to grow unimpeded by host defense.

Strategies to optimize photosensitizers for photodynamic inactivation of bacteria

“…Photodynamic treatment with an appropriate light dose that causes both maximal bacterial killing and neutrophil cell accumulation into the infected wound area may results in a new mechanism of action. Here in this study Tanaka et al showed a correlation between accumulated neutrophils at the infections site and bactericidal effect after aPDI [86]. Such a new mechanism is of interest, because neutrophils are the key players for host defense against bacterial infections.…”

“…When bad bugs have already affected the bloodstream neither aPDI nor disinfectants helps, so you have fall back on appropriate working antibiotics again. Recently Tanaka et al demonstrated that aPDI with Photofrin Ò in MRSA arthritis in the mouse knee could treat the infection, not only by directly killing of bacteria but also by stimulating the host immune defense [86]. Photodynamic treatment with an appropriate light dose that causes both maximal bacterial killing and neutrophil cell accumulation into the infected wound area may results in a new mechanism of action.…”

Photodynamic Therapy Can Induce a Protective Innate Immune Response against Murine Bacterial Arthritis via Neutrophil Accumulation

“…The effective light dose ranged from 50 to 80 J/cm 2 , indicating that the therapeutic window of PDT using methylene blue was broader than that of PDT using Photofrin [34]. The administration of anti-GR-1 (anti-neutrophil) antibody eliminated the therapeutic effect of PDT, indicating that the therapeutic PDT using methylene blue exerted a therapeutic effect for bacterial infection via the attraction and accumulation of neutrophils into the infected region.…”

Photodynamic therapy induces an immune response against a bacterial pathogen

“…It was hypothesized that local administration of PS and immediate irradiation at the local infection site could dramatically reduce PDT-induced damage to mammalian host cells [127]. Therefore we redesigned the Photofrin PDT protocol to include direct administration in the form of intra-articular rather than systemic intravenous injection and followed that local injection with immediate photoirradiation to increase the chances that the PS would rapidly bind to bacteria, while binding to host neutrophils would be slower [128]. In this way, it was proposed to concentrate the PS at the local infection site and limit diffusion to other areas, minimizing the uptake and hence cytotoxicity of Photofrin to the host leukocytes.…”