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Chronic wound infections are a worldwide occurring health care problem with massive consequences for the patient and high costs for the health care system. Due to the frequent antibiotic resistance of pathogenic bacteria the therapeutic options are limited. The Pseudomonas aeruginosa is one of the commonest and most important germs in wounds with high antibiotic resistance. Its key virulence factor, the M4-Metalloproteinase (MP) Pseudolysin (PE), takes part in the intoxication, the invasion and the distribution of the pathogen. The inhibition of virulence factors is a novel promising therapeutic approach, but most of the MP-inhibitors are unspecific and thus unsuitable for the pharmaceutical use. The Insect-Metalloproteinase-Inhibitor (IMPI), however, was proved to be an efficient and highly specific inhibitor against bacterial M4-MP, like PE.
The focuses of this thesis research were the pharmacological verification of IMPI and on the development of a suitable formulation for its application in wound infections. For the first time the therapeutic potential of IMPI against infections with P. aeruginosa was investigated on molecular, cellular and histological level. The inhibitory capacity of IMPI-GST was initially tested against pure PE and the secretome of wound isolated P. aeruginosa in proteolytic activity assays. In comparison to the reference inhibitor Phosphoramidon (PA), IMPI-GST was more efficient and showed a narrower active window.
In this thesis the P. aeruginosa secretome was studied on skin cells for the first time. A strong decrease in the cell viability was measured due to an increasing secretome concentration and treatment with 10% secretome resulted in complete cell death. This was mainly caused by the detachment of cells from the surface and thus the occurrence of Anoikis. Immunohistochemical stainings of secretome-treated cells showed retraction of F Aktin and morphological changes in the cytoskeleton. Therefore, it was hypothesized that the main reasons are the destruction of cell contacts, like Tight Junctions, Adherence Junctions and Focal Adhesions, the degradation of proteins of the extracellular matrix as well as the influence in the MAPK pathway. Although the cell based examinations suggested a multifactorial virulence of the secretome PE seems to be mainly responsible. Subsequently, the potential pharmaceutic effect of IMPI-GST was examined in vitro and ex vivo. IMPI-GST showed no cytotoxic impact and prevented the secretome-related cell detachment, which resulted in a significant increase in viability of more than 60%.
The migration of keratinocytes is an essential process in wound healing. The in vitro cell migration was strongly reduced in accordance to an increased applied secretome concentration. IMPI-GST enhanced the migration and completely prevented the secretome-induced impact on the keratinocytes. Finally, the observed in vitro results were tested in an ex vivo porcine skin wound healing model. Therein the healing diminishing, necrotic and cell destructing effects of the secretome were confirmed. Also, the positive results of the IMPI-GST treatment were proved. The tissue destruction, induced by the secretome, was prevented due to a simultaneous application of IMPI-GST and a clear improvement in wound healing was observed based on a formed wound tongue.
The second part of the thesis focused on the formulation development for the application of IMPI-GST in chronic wound infections. Therefore, a thermosensitive hydrogel with the gelling agent Poloxamer 407 was designed. The suitable Poloxamers and additives as well as their appropriate concentrations were investigated in relation to their rheological parameters, elastic and viscous modulus, in oscillatory measurements. This led to a final gel composition of 16% P407, 15% P188 and 3% Glycerin. Germ-contamination-tests approved the use of the preservative combination of 0.2% potassium sorbate with 0.1% citric acid. Final activity assays demonstrated no interference in the inhibitory activity of IMPI-GST with the formulation. In Franz cell diffusion assays IMPI-GST was continuously released out of the hydrogel over a period of 10 h. Furthermore, neither the influence of IMPI-GST on the rheological characteristic of the hydrogel nor any other interaction between the formulation and the active pharmaceutical ingredient was recognized.
In conclusion, this study confirms the presumed therapeutic activity of IMPI against infections with P. aeruginosa on molecular, cellular and histological level. The influence of the pathogenic P. aeruginosa secretome on human keratinocytes and a porcine wound model was identified for the first time. An improvement in viability, morphology and migration capacity of the secretome-treated cells as well as wound healing in all in vitro and ex vivo experiments occurred by the application of IMPI-GST. For the use of this active peptide IMPI a thermosensitive hydrogel was developed.