The Role of Oxidative Metabolic Processes in Microvascular Function

In this project we hope to understand how the role of oxygen radicals as well as nitrogen radicals might affect the function of the microvasculature. Dysfunction of the microvascular circulation is determined in diabetes and in trauma where physical damage causes disruption in the normal microvascular tissue. The role inflammatory mechanisms play in regulating normal microvascular function is being investigated.

Aims of the research program

Atherosclerosis affects diabetic patients in a disproportionate manner when compared to the non-diabetic population. However, in the microcirculation, atherosclerosis is not a consistent feature of ischemic or neuropathic diabetic lesions. The difference in microvascular responses to injury compared to macrovascular injury is poorly understood. Ischemic injury follows a common pathway in different cell types and has been widely studied. However, the magnitude of the cellular response to oxidative damage depends upon the cell type examined. We hypothesize that microvascular endothelial cells differ from macrovascular endothelial cells from the same vascular bed and in turn diabetic micro- and macrovascular cells differ from the corresponding non-diabetic vascular endothelial cells. This project is designed to e to isolate and culture microvascular arteriolar and venular endothelial cells from specific microvessels from the dermal microvascular bed of the dorsum of the foot in both diabetic and non-diabetic animals. From the same vascular bed corresponding macrovascular arterial and venous endothelial cells will be isolated.

Several investigators have documented a decrease in endothelium dependent- NO· mediated vasodilation in diabetic patients. The beneficial effect of NO· released by endothelial cells include inhibition of platelet aggregation, inhibition of neutrophil adhesion to vascular endothelium (a step in the atherogenic process), and chemical reaction with superoxide anion. There is increasing evidence that, rather than a lack of NO· synthesis, an imbalance between superoxide production and the protective mechanisms of NO· is responsible for the lack of endothelium dependent vasodilation and for other contributors to diabetic ischemic lesions. It is likely, however, that microvascular endothelial cells produce increased amounts of reactive oxygen species in both stimulated and "resting" states when compared to corresponding macrovascular endothelial cells and are therefore more prone to injury.

It may also be that diabetic microvascular endothelial cells are more compromised in their response to oxidative injury than their non-diabetic equivalent. In this study we propose to determine whether an increase of oxidative damage or a decrease in nitric oxide defense mechanism is responsible for the disproportionate microvascular endothelial cell damage in diabetes. There is evidence that superoxide production, decreased NO· release and elevated glucose concentrations can all lead to an increase in programmed cell death. Lack of neovascularization and angiogenesis are a pertinent problems in diabetic wound healing. The endothelial cell plays a central role in angiogenesis. We believe that a clear understanding of the balance between oxidative injury and nitric oxide defense mechanisms and a subsequent correlation with endothelial cell proliferation and programmed cell death, may provide a more rational approach to the pharmacological interventions in (diabetic) ischemic injury in peripheral tissues, in particular the skin.

The above studies involve isolation of microvascular and macrovascular endothelial cells, development of functional assays for these cells, and expanding the studies from in vitro to in vivo using intravital microscopy.