Diabetes mellitus (DM) is an established cause of increased mortality. Most deaths linked to DM are attributable to cardiovascular disease, and hyperglycaemia alone is not sufficient to explain the increased cardiovascular risk associated with DM. It is accepted that insulin resistance, the principal underlying cause of the most common form of DM, is independently linked to CVD. Prior research demonstrates insulin resistance is associated with excessive production of reactive oxygen species (ROS), in part via the enzyme NADPH oxidase 2 (NOX2). We hypothesised that reduction of NOX2-derived ROS represents a translationally promising strategy to improve the diminished vascular repair and regeneration observed in insulin resistance. This project explores the effect of NOX2 inhibition on angiogenesis and vascular repair in murine models of whole-body and endothelial-specific insulin resistance.
Mice with haploinsufficiency of the insulin receptor (IRKO), and those expressing a kinase dead human insulin receptor transgene in the endothelium (ESMIRO), were bred with NOX2 deficient mice. NOX2 knockdown was associated with significant improvement in vascular repair following arterial injury in ESMIRO mice. Subsequent work provided two potential explanations: improved endothelial cell migration, and an increased abundance of circulating progenitor cells. Pharmacological NOX2 inhibition partly recapitulated these findings in vitro, as treatment of insulin resistant human umbilical vein endothelial cells with the NOX2 inhibitor GP91-ds tat was associated with improved cell migration.
Whilst this project yielded a number of promising findings, it also highlighted pitfalls associated with manipulation of ROS. We corroborated two existing concerns relating to NOX2 inhibition: the potential to compromise immune function, and the risk of inciting a pro-inflammatory state. Although NOX2 remains a potentially suitable target for therapeutic intervention, greater understanding of NOX2 biology is required. We hope the work carried out in this project can be built upon to facilitate that understanding, ultimately generating novel therapeutic agents
