Rolf-Markus Szeimies

The role of singlet oxygen and oxygen concentration in photodynamic inactivation of bacteria

New antibacterial strategies are required in view of the increasing resistance of bacteria to antibiotics. One promising technique involves the photodynamic inactivation of bacteria. Upon exposure to light, a photosensitizer in bacteria can generate singlet oxygen, which oxidizes proteins or lipids, leading to bacteria death. To elucidate the oxidative processes that occur during killing of bacteria, Staphylococcus aureus was incubated with a standard photosensitizer, and the generation and decay of singlet oxygen was detected directly by its luminescence at 1,270 nm. At low bacterial concentrations, the time-resolved luminescence of singlet oxygen showed a decay time of 6 ± 2 μs, which is an intermediate time for singlet oxygen decay in phospholipids of membranes (14 ± 2 μs) and in the surrounding water (3.5 ± 0.5 μs). Obviously, at low bacterial concentrations, singlet oxygen had sufficient access to water outside of S. aureus by diffusion. Thus, singlet oxygen seems to be generated in the outer cell wall areas or in adjacent cytoplasmic membranes of S. aureus. In addition, the detection of singlet oxygen luminescence can be used as a sensor of intracellular oxygen concentration. When singlet oxygen luminescence was measured at higher bacterial concentrations, the decay time increased significantly, up to ≈40 μs, because of oxygen depletion at these concentrations. This observation is an important indicator that oxygen supply is a crucial factor in the efficacy of photodynamic inactivation of bacteria, and will be of particular significance should this approach be used against multiresistant bacteria.

European guidelines for topical photodynamic therapy part 1: treatment delivery and current indications – actinic keratoses, Bowen’s disease, basal cell carcinoma

Topical photodynamic therapy (PDT) is a widely used non‐invasive treatment for certain non‐melanoma skin cancers, permitting treatment of large and multiple lesions with excellent cosmesis. High efficacy is demonstrated for PDT using standardized protocols in non‐hyperkeratotic actinic keratoses, Bowen’s disease, superficial basal cell carcinomas (BCC) and in certain thin nodular BCC, with superiority of cosmetic outcome over conventional therapies. Recurrence rates following PDT are typically equivalent to existing therapies, although higher than surgery for nodular BCC. PDT is not recommended for invasive squamous cell carcinoma. Treatment is generally well tolerated, but tingling discomfort or pain is common during PDT. New studies identify patients most likely to experience discomfort and permit earlier adoption of pain‐minimization strategies. Reduced discomfort has been observed with novel protocols including shorter photosensitizer application times and in daylight PDT for actinic keratoses.

Wound healing in the 21st century

Delayed wound healing is one of the major therapeutic and economic issues in medicine today. Cutaneous wound healing is an extremely well-regulated and complex process basically divided into 3 phases: inflammation, proliferation, and tissue remodeling. Unfortunately, we still do not understand this process precisely enough to give direction effectively to impaired healing processes. There have been many new developments in wound healing that provide fascinating insights and may improve our ability to manage clinical problems. Our goal is to acquaint the reader with selected major novel findings about cutaneous wound healing that have been published since the beginning of the new millennium. We discuss advances in areas such as genetics, proteases, cytokines, chemokines, and regulatory peptides, as well as therapeutic strategies, all set in the framework of the different phases of wound healing.

Daylight photodynamic therapy for actinic keratosis: an international consensus: International Society for Photodynamic Therapy in Dermatology.

Photodynamic therapy (PDT) is an attractive therapy for non‐melanoma skin cancers including actinic keratoses (AKs) because it allows treatment of large areas; it has a high response rate and results in an excellent cosmesis. However, conventional PDT for AKs is associated with inconveniently long clinic visits and discomfort during therapy. In this article, we critically review daylight‐mediated PDT, which is a simpler and more tolerable treatment procedure for PDT. We review the effective light dose, efficacy and safety, the need for prior application of sunscreen, and potential clinical scope of daylight‐PDT. Three randomized controlled studies have shown that daylight‐mediated PDT is an effective treatment of thin AKs. Daylight‐mediated PDT is nearly pain‐free and more convenient for both the clinics and patients. Daylight‐mediated PDT is especially suited for patients with large field‐cancerized areas, which can easily be exposed to daylight. Further investigations are necessary to determine at which time of the year and in which weather conditions daylight‐mediated PDT will be possible in different geographical locations.

Photodynamic therapy in dermatology: state‐of‐the‐art

Photodynamic therapy (PDT) has become an established treatment modality for dermatooncologic conditions like actinic keratosis, Bowens disease, in situ squamous cell carcinoma and superficial basal cell carcinoma. There is also great promise of PDT for many non‐neoplastic dermatological diseases like localized scleroderma, acne vulgaris, granuloma anulare and leishmaniasis. Aesthetic indications like photo‐aged skin or sebaceous gland hyperplasia complete the range of applications. Major advantages of PDT are the low level of invasiveness and the excellent cosmetic results. Here, we review the principal mechanism of action, the current developments in the field of photosensitizers and light sources, practical aspects of topical PDT and therapeutical applications in oncologic as well as non‐oncologic indications.

PENETRATION POTENCY OF TOPICAL APPLIED δ-AMINOLEVULINIC ACID FOR PHOTODYNAMIC THERAPY OF BASAL CELL CARCINOMA *

Abstract Penetration potency of δ‐aminolevulinic acid (ALA) was studied by examining fluorescence of endogenous protoporphyrin IX in different histological types of basal cell carcinoma. Ten basal cell carcinomas were coated with an ointment containing 10% ALA prior to excision; five served as controls. Tumors were excised either 4 h or 12 h after application of ALA using a modified Mohs’micrographic surgical technique. Horizontal sections were cut from deep dermis to tumor surface and examined under a fluorescence microscope. After 4 h of application, only skin appendages demonstrated fluorescence typical of protoporphyrin IX. After 12 h, fluorescence was detectable in tumor cells in deep dermis. The five controls revealed no fluorescence at any site. These results may confirm the high penetration potential of topically applied ALA and its usefulness in photodynamic therapy. For tumors penetrating to deep dermis, an application time of more than 4 h seems necessary, at least when hydrophilic solvents for ALA are used.

Light-Induced Decomposition of Indocyanine Green

PURPOSE To investigate the light-induced decomposition of indocyanine green (ICG) and to test the cytotoxicity of light-induced ICG decomposition products. METHODS ICG in solution was irradiated with laser light, solar light, or surgical endolight. The light-induced decomposition of ICG was analyzed by high-performance liquid chromatography (HPLC) and mass spectrometry. Porcine retinal pigment epithelial (RPE) cells were incubated with the light-induced decomposition products of ICG, and cell viability was measured by trypan blue exclusion assay. RESULTS Independent of the light source used, singlet oxygen (photodynamic type 2 reaction) is generated by ICG leading to dioxetanes by [2+2]-cycloaddition of singlet oxygen. These dioxetanes thermally decompose into several carbonyl compounds. The decomposition products were identified by mass spectrometry. The decomposition of ICG was inhibited by adding sodium azide, a quencher of singlet oxygen. Incubation with ICG decomposition products significantly reduced the viability of RPE cells in contrast to control cells. CONCLUSIONS ICG is decomposed by light within a self-sensitized photo oxidation. The decomposition products reduce the viability of RPE cells in vitro. The toxic effects of decomposed ICG should be further investigated under in vivo conditions.

Topical photodynamic therapy for localized scleroderma.

Therapy of localized scleroderma is unsatisfactory, with numerous treatments being used that have only limited success or considerable side-effects. The aim of this trial was to determine whether topical photodynamic therapy would be effective in patients with localized scleroderma. Five patients with progressive disease, in whom conventional therapies had failed, were treated by application of a gel containing 3% 5-aminolevulinic acid followed by irradiation with an incoherent lamp (40 mW/cm2, 10 J/cm2). The treatment was performed once or twice weekly for 3-6 months. In all patients the therapy was highly effective for sclerotic plaques, as measured by a quantitative durometer score and a clinical skin score. The only side-effect was a transient hyperpigmentation of the treated lesions. These cases document the beneficial effect of topical photodynamic therapy in localized scleroderma. Controlled trials are now necessary to confirm these preliminary results.

Long-pulse dye laser for photodynamic therapy: investigations in vitro and in vivo.

Continuous wave lasers or incoherent lamps are used effectively for photodynamic therapy (PDT). As the mechanism of action of pulsed lasers in PDT is not known, we investigated the efficacy of PDT with 5‐aminolevulinic acid (ALA) using a long‐pulse (1.5 ms) tunable flashlamp‐pumped pulsed dye laser (LPDL) in vitro and in vivo.

2D luminescence imaging of pH in vivo

Luminescence imaging of biological parameters is an emerging field in biomedical sciences. Tools to study 2D pH distribution are needed to gain new insights into complex disease processes, such as wound healing and tumor metabolism. In recent years, luminescence-based methods for pH measurement have been developed. However, for in vivo applications, especially for studies on humans, biocompatibility and reliability under varying conditions have to be ensured. Here, we present a referenced luminescent sensor for 2D high-resolution imaging of pH in vivo. The ratiometric sensing scheme is based on time-domain luminescence imaging of FITC and ruthenium(II)tris-(4,7-diphenyl-1,10-phenanthroline). To create a biocompatible 2D sensor, these dyes were bound to or incorporated into microparticles (aminocellulose and polyacrylonitrile), and particles were immobilized in polyurethane hydrogel on transparent foils. We show sensor precision and validity by conducting in vitro and in vivo experiments, and we show the versatility in imaging pH during physiological and chronic cutaneous wound healing in humans. Implementation of this technique may open vistas in wound healing, tumor biology, and other biomedical fields.