Redox effects on neutrophils in wound healing conducted by wound dressings and hyperbaric oxygen

Abstract

The increased influx of neutrophils into chronic wounds results in increased production of reactive oxygen species (ROS), nitric oxide (NO) and lipid peroxidation products (LPP), as well as a ROS-induced increase in protease levels. The NO and LPP impair the respiratory burst response of the neutrophils and reduce their capacity to kill bacteria and digest debris. By adding ROS scavengers to the wound the pathophysiological effects of ROS, NO and LPP can be reversed and healthy granulation tissue may be formed. The aim of this thesis was to develop a wound dressing that has beneficial effects on chronic wound healing according to our hypothesis on neutrophil involvement in the pathophysiology of chronic wounds. In order to reach this aim, basic knowledge of neutrophil functions and interaction with wound dressings, hyperbaric oxygen and radical scavengers had to be gathered.Neutrophils were studied by using different in vitro models e.g. effects of neutrophil interaction with wound dressing materials on the respiratory burst response, effects of hyperbaric oxygen on the respiratory burst response, and neutrophil bacterial killing ability.Gel wound dressings were found to affect the respiratory burst of neutrophils in a way that impairs the ability of the cells to exert their biological function. This effect may be correlated to the content of preservatives in the gels. Hyperbaric oxygen affects the neutrophils in a way that impairs cell adhesion, the ability of the cells to phagocytize zymosan, and the zymosan-induced respiratory burst. This effect is not reversible. Hyperbaric oxygen also impairs the respiratory burst of neutrophils, induced by f-MLP and PMA. This effect is reversible within 30 minutes. Neutrophils fail to kill Staphylococcus aureus in vitro in the abscence of radical scavengers like N-acetylcysteine and glutathione. The mechanisms of this protection is probably related to the effect of NO on the neutrophils.