Abstract/Summary

Chronic wounds are those that fail to proceed through an orderly and timely reparative manner, typically characterised by persistent hypoxia and infection. Since oxygen is essential in every stage of wound healing and has bactericidal activity, wound oxygenation methods including hyperbaric oxygen (HBO) and normobaric oxygen (NBO) have been proposed as therapeutic modalities in the treatment of chronic wounds. These treatments can significantly elevate the oxygen partial pressure at poorly perfused wounded tissues. However, the molecular mechanisms whereby oxygen improves wound healing remain unclear. The aims of this thesis were to explore the cellular and molecular impacts of high oxygen levels, elevated air pressure, chronic hypoxia and infection on reepithelialisation as a critical step in wound healing. It was hypothesised that increasing oxygen tension in the wounded area would improve steps in reepithelialisation process. This hypothesis was tested on human keratinocyte (HaCaT) cells where cell migration, proliferation and differentiation were examined at cellular and molecular levels using scratch assays, Western blotting, ELISA and MTT assays. Data clearly demonstrated that a chronic hypoxic state had a deleterious effect on reepithelialisation via attenuation of the rate of keratinocyte migration with increases in cellular adhesion, metabolic activities and hyperproliferation but no effects were seen on cell differentiation rates. In contrast, oxygenation of the cells via HBO and NBO resulted in a faster rate of cell migration with lower cell proliferation and metabolic activities. However, elevating air pressure alone i.e. hyperbaric air (HBA), did not have any effects on the re-epithelialisation process. Keratinocytes were stimulated with LPS and interleukins (IL-6 and IL-8) or cocultured with THP-1 monocytes to create different inflammatory models under chronic hypoxic and normoxic conditions. Data revealed that IL-6, but not IL-8, attenuated keratinocyte’s migration with a significant increase in cell adhesion and elasticity. Co-culture of monocytes with keratinocytes led to a marginal increase in cell migration under chronic hypoxic conditions. However, LPS stimulation did not lead to any significant effects on migration, proliferation and differentiation of keratinocytes. These findings show that oxygen is critical in re-epithelialisation and the results presented here provide understanding of the cellular and molecular mechanisms by which HBO and NBO improve wound healing.