Phototherapy for the treatment of wound infections and the improvement of wound healing

Abstract

1-2 % of all people suffer from chronic wounds once in a lifetime. Advanced age, chronic underlying diseases (e.g. diabetes mellitus, vascular diseases) and factors such as restricted mobility and infections are the most common causes of a disrupted healing process. The rapidly increasing number of antibiotic resistances and the associated lack of effective treatment strategies further aggravate the problem.Biophysical therapeutic methods have gained popularity and trust in the past decades through numerous positive reports from preclinical and clinical studies. Enabling a combination of promoting wound healing and fighting infections, phototherapy plays a special role within this field. By irradiation with light, especially in the red and infrared range, photobiomodulation (PBM) stimulates many molecular mechanisms, which in turn stimulate processes relevant to wound healing, such as cell proliferation, cell migration and vascularization. However, by activating photoactive substances, so-called photosensitizers, light can also have a destructive effect on cells. Therefore, in addition to its use in tumor treatment, antimicrobial photodynamic therapy (aPDT) is more and more used for the fight against infections.The first part of this work deals with the effects and the underlying mechanisms of PBM on wound-relevant cell lines, challenged by hypoxia/reoxygenation (H/R) and nutrient deprivation to simulate a wound environment. It was demonstrated that 10 min of pulsed red LED (light-emitting diode) light irradiation significantly increased the proliferation of fibroblasts and myoblasts. The effects were associated with elevated oxygen flux, ATP (adenosine triphosphate) levels and ROS (reactive oxygen species) concentrations.To be able to test alternative therapeutic options for fighting infection under conditions as realistic as possible, the second part of this thesis was dedicated to the development of an infection wound model in mice that reflects the wound situation of immunocompromised patients. The precise dosing of immunosuppressant and polymicrobial, fecal suspension led to an established wound infection and wound healing was significantly impaired. The wounds were analyzed by the measurement of wound size, microbiological swabs and grading on a developed wound score scale.The third part of this work focused on the extensive testing of aPDT. In vitro, bacteria were treated in suspension culture and in more wound-relevant assays on agar surface and in fibrin matrix. In a subsequent in vivo study, the prior established infection wound9model was used to test the effect of aPDT. In vitro, a strong dependency of aPDT on the treatment environment was shown and partially caused a markedly diminished efficacy. In vivo, a two-times application of aPDT showed significantly improved and faster wound healing compared to the untreated, infected wounds, graded by both, quantitative wound size and qualitative parameters based on clinical observation of wound parameters.In summary, phototherapy and especially the use of red LED light showed a high potential in the stimulation of wound healing and in infection control. These results contribute to further knowledge important for the advancement of treatment protocols to reach the highest benefit for affected patients in the future.