Influence of intra-articular neutrophils on the effects of photodynamic therapy for murine MRSA arthritis

Hypericin and Pheophorbide a Mediated Photodynamic Therapy Fighting MRSA Wound Infections: A Translational Study from In Vitro to In Vivo

High prevalence rates of methicillin-resistant Staphylococcus aureus (MRSA) and lack of effective antibacterial treatments urge discovery of alternative therapeutic modalities. The advent of antibacterial photodynamic therapy (aPDT) is a promising alternative, composing rapid, nonselective cell destruction without generating resistance. We used a panel of clinically relevant MRSA to evaluate hypericin (Hy) and pheophobide a (Pa)-mediated PDT with clinically approved methylene blue (MB). We translated the promising in vitro anti-MRSA activity of selected compounds to a full-thick MRSA wound infection model in mice (in vivo) and the interaction of aPDT innate immune system (cytotoxicity towards neutrophils). Hy-PDT consistently displayed lower minimum bactericidal concentration (MBC) values (0.625-10 µM) against ATCC RN4220/pUL5054 and a whole panel of community-associated (CA)-MRSA compared to Pa or MB. Interestingly, Pa-PDT and Hy-PDT topical application demonstrated encouraging in vivo anti-MRSA activity (>1 log₁₀ CFU reduction). Furthermore, histological analysis showed wound healing via re-epithelization was best in the Hy-PDT group. Importantly, the dark toxicity of Hy was significantly lower (p < 0.05) on neutrophils compared to Pa or MB. Overall, Hy-mediated PDT is a promising alternative to treat MRSA wound infections, and further rigorous mechanistic studies are warranted.

Photodynamic treatment for multidrug-resistant Gram-negative bacteria: Perspectives for the treatment of Klebsiella pneumoniae infections

The emergence of multi-drug resistance for pathogenic bacteria is one of the most pressing global threats to human health in the 21st century. Hence, the availability of new treatment becomes indispensable to prevent morbidity and mortality caused by infectious agents. This article reviews the antimicrobial properties of photodynamic therapy (PDT), which is based on the use of photosensitizers compounds (PSs). The PSs are non-toxic small molecules, which induce oxidative stress only under excitation with light. Then, the PDT has the advantage to be locally activated using phototherapy devices. We focus on PDT for the Klebsiella pneumoniae, as an example of Gram-negative bacteria, due to its relevance as an agent of health-associated infections (HAI) and a multi-drug resistant bacteria. K. pneumoniae is a fermentative bacillus, member of the Enterobacteriaceae family, which is most commonly associated with producing infection of the urinary tract (UTI) and pneumonia. K. pneumoniae infections may occur in deep organs such as bladder or lungs tissues; therefore, activating light must get access or penetrate tissues with sufficient power to produce effective PDT. Consequently, the rationale for selecting the most appropriate PSs, as well as photodynamic devices and photon fluence doses, were reviewed. Also, the mechanisms by which PDT activates the immune system and its importance to eradicate the infection successfully, are discussed.

Effect of methylene blue photodynamic therapy on human neutrophil functional responses

Photodynamic therapy (PDT) has become an emerging novel therapeutic approach for treating localized microbial infections, particularly those sustained by multidrug-resistant strains. Given the irreplaceable role played by professional phagocytes in limiting infections, such as polymorphonuclear neutrophils, any newly designed antimicrobial therapeutic approach must not interfere with their function. The present investigation presents a detailed analysis of the effect of PDT on the viability and several functional responses of human polymorphonuclear neutrophils loaded with methylene blue (MB), one of the more commonly used photosensitizers in antimicrobial PDT. Taking advantage of the use of a specifically-designed optical LED array for illuminating MB-loaded human polymorphonuclear neutrophils, a number of cell functions have been assayed under miniaturized, strictly controlled and reproducible experimental conditions. The major findings of this study are the following: (1) MB-PDT increases human neutrophils adhesion and does not modify myeloperoxidase release; (2) MB-PDT markedly enhances reactive oxygen species generation that is independent of superoxide-forming phagocytic oxidase and very likely ascribable to LED-dependent excitation of accumulated methylene blue; (3) MB-PDT almost abolishes human neutrophils candidacidal activity by hindering the engulfing machinery. This in vitro study may represent a valuable reference point for future research on PDT applications for treating localized microbial infections.

Photodynamic therapy using systemic administration of 5-aminolevulinic acid and a 410-nm wavelength light-emitting diode for methicillin-resistant Staphylococcus aureus-infected ulcers in mice

Bacterial resistance to antibiotics has become a worldwide problem. One potential alternative for bacterial control is photodynamic therapy. 5-aminolevulinic acid is a natural precursor of the photosensitizer protoporphyrin IX. Relatively little is known about the antibacterial efficacy of photodynamic therapy using the systemic administration of 5-aminolevulinic acid; a few reports have shown that 5-aminolevulinic acid exerts photodynamic effects on methicillin-resistant Staphylococcus aureus (MRSA) in vitro. In this study, we evaluated the effectiveness of photodynamic therapy using 5-aminolevulinic acid and a 410-nm wavelength light-emitting diode in vitro and in vivo for the treatment of MRSA. We found that 5-aminolevulinic acid photodynamic therapy with the light-emitting diode had an in-vitro bactericidal effect on MRSA. In vivo, protoporphyrin IX successfully accumulated in MRSA on ulcer surfaces after intraperitoneal administration of 5-aminolevulinic acid to mice. Furthermore, 5-aminolevulinic acid photodynamic therapy accelerated wound healing and decreased bacterial counts on ulcer surfaces; in contrast, vancomycin treatment did not accelerate wound healing. Our findings indicate that 5-aminolevulinic acid photodynamic therapy may be a new treatment option for MRSA-infected wounds.

Antimicrobial photodynamic therapy for methicillin-resistant Staphylococcus aureus infection

Nowadays methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common multidrug resistant bacteria both in hospitals and in the community. In the last two decades, there has been growing concern about the increasing resistance to MRSA of the most potent antibiotic glycopeptides. MRSA infection poses a serious problem for physicians and their patients. Photosensitizer-mediated antimicrobial photodynamic therapy (PDT) appears to be a promising and innovative approach for treating multidrug resistant infection. In spite of encouraging reports of the use of antimicrobial PDT to inactivate MRSA in large in vitro studies, there are only few in vivo studies. Therefore, applying PDT in the clinic for MRSA infection is still a long way off.

Linezolid and vancomycin decrease the therapeutic effect of methylene blue-photodynamic therapy in a mouse model of MRSA bacterial arthritis

We previously reported that photodynamic therapy (PDT) using intra-articular methylene blue (MB) could be used to treat arthritis in mice caused by bioluminescent methicillin-resistant Staphylococcus aureus (MRSA) either in a therapeutic or in a preventative mode. PDT accumulated neutrophils into the mouse knee via activation of chemoattractants such as inflammatory cytokines or chemokines. In this study, we asked whether PDT combined with antibiotics used for MRSA could provide added benefit in controlling the infection. We compared MB-PDT alone, systemic administration of either linezolid (LZD) alone or vancomycin (VCM) alone or the combination of PDT with either LZD or VCM. Real-time noninvasive imaging was used to serially follow the progress of the infection. PDT alone was the most effective, whereas LZD alone was ineffective and VCM alone showed some benefit. Surprisingly the addition of LZD or VCM reduced the therapeutic effect of PDT alone (P < 0.05). Considering that PDT in this mouse model stimulates neutrophils to be antibacterial rather than actively killing the bacteria, we propose that LZD and VCM might inhibit the activation of inflammatory cytokines without eradicating the bacteria, and thereby reduce the therapeutic effect of PDT.

Photodynamic therapy induces an immune response against a bacterial pathogen

Photodynamic therapy (PDT) employs the triple combination of photosensitizers, visible light and ambient oxygen. When PDT is used for cancer, it has been observed that both arms of the host immune system (innate and adaptive) are activated. When PDT is used for infectious disease, however, it has been assumed that the direct antimicrobial PDT effect dominates. Murine arthritis caused by methicillin-resistant Staphylococcus aureus in the knee failed to respond to PDT with intravenously injected Photofrin(®). PDT with intra-articular Photofrin produced a biphasic dose response that killed bacteria without destroying host neutrophils. Methylene blue was the optimum photosensitizer to kill bacteria while preserving neutrophils. We used bioluminescence imaging to noninvasively monitor murine bacterial arthritis and found that PDT with intra-articular methylene blue was not only effective, but when used before infection, could protect the mice against a subsequent bacterial challenge. The data emphasize the importance of considering the host immune response in PDT for infectious disease.

Photodynamic therapy can induce a protective innate immune response against murine bacterial arthritis via neutrophil accumulation

Background

Local microbial infections induced by multiple-drug-resistant bacteria in the orthopedic field can be intractable, therefore development of new therapeutic modalities is needed. Photodynamic therapy (PDT) is a promising alternative modality to antibiotics for intractable microbial infections, and we recently reported that PDT has the potential to accumulate neutrophils into the infected site which leads to resolution of the infection. PDT for cancer has long been known to be able to stimulate the innate and adaptive arms of the immune system.

Methodology/Principal Findings

In the present study, a murine methicillin-resistant Staphylococcus aureus (MRSA) arthritis model using bioluminescent MRSA and polystyrene microparticles was established, and both the therapeutic (Th-PDT) and preventive (Pre-PDT) effects of PDT using methylene blue as photosensitizer were examined. Although Th-PDT could not demonstrate direct bacterial killing, neutrophils were accumulated into the infectious joint space after PDT and MRSA arthritis was reduced. With the preconditioning Pre-PDT regimen, neutrophils were quickly accumulated into the joint immediately after bacterial inoculation and bacterial growth was suppressed and the establishment of infection was inhibited.

Conclusions/Significance

This is the first demonstration of a protective innate immune response against a bacterial pathogen produced by PDT.

Topical photodynamic treatment with poly-L-lysine-chlorin p6 conjugate improves wound healing by reducing hyperinflammatory response in Pseudomonas aeruginosa-infected wounds of mice

We report the results of our investigations on the effect of antimicrobial photodynamic treatment (APDT) with poly-lysine-conjugated chlorin p6 (pl-cp6) on proinflammatory cytokine expression and wound healing in a murine excisional wound model infected with Pseudomonas aeruginosa. Treatment of infected wounds with pl-cp6 and light doses of 60 and 120 J/cm(2) reduced the bacterial load by ~1.5 and 2.0 log, respectively, after 24 h. The treated wounds healed ~5 days earlier as compared to untreated control and wound closure was not dependent on light dose. Interestingly, at 96 h post-treatment, drug-treated wounds irradiated at 60 J/cm(2) showed considerable reduction of proinflammatory cytokines IL-6 (approximately five times) and TNF-α (approximately four times) compared to untreated control. Further, exposure of culture supernatants to similar light dose and pl-cp6 concentration under in vitro conditions reduced the protease activity by ~50 % as compared to the untreated control, suggesting inactivation of extracellular virulent factors. Additionally, histological analysis of treated infected wounds showed complete reepithelialization, ordered collagen fibers, and considerable decrease in inflammatory cell infiltration compared to untreated wounds. These results imply that pl-cp6-mediated PDT reduces hyperinflammatory response of infected wounds, leading to acceleration of wound healing.

Optimal photosensitizers for photodynamic therapy of infections should kill bacteria but spare neutrophils

Photodynamic therapy (PDT) for localized microbial infections exerts its therapeutic effect both by direct bacterial killing and also by the bactericidal effects of host neutrophils stimulated by PDT. Therefore, PDT-induced damage to neutrophils must be minimized, while direct photoinactivation of bacteria is maintained to maximize the therapeutic efficacy of antimicrobial PDT in vivo. However, there has been no study in which the cytocidal effect of PDT on neutrophils was investigated. In this study, the cytocidal effects of PDT on neutrophils were evaluated using different antimicrobial photosensitizers to find suitable candidate photosensitizers for antimicrobial PDT. PDT on murine peripheral-blood neutrophils was performed in vitro using each photosensitizer at a concentration that exerted a maximum bactericidal effect on methicillin-resistant Staphylococcus aureus, and morphological alteration and viability of neutrophils were studied. Most neutrophils were viable (>80%) after PDT using toluidine blue-O (TB) or methylene blue (MB), while neutrophils showed morphological change and their viabilities were decreased (<70%) after PDT using other photosensitizers (erythrosine B, rose bengal, crystal violet, Photofrin, new methylene blue and Laserphyrin). These results suggest that PDT using TB or MB can preserve host neutrophils while exerting a significant therapeutic effect on in vivo localized microbial infection.

Photodynamic therapy using intra-articular Photofrin for murine MRSA arthritis: biphasic light dose response for neutrophil-mediated antibacterial effect

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 × 10(7)  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.