NADPH oxidases in the vasculature: Molecular features, roles in disease and pharmacological inhibition

Until the 1970s, reactive oxygen species (ROS) were considered merely harmful by-products of aerobic respiration and the driving force behind the evolution of an array of cellular antioxidant enzymes with the purpose of rapidly metabolising ROS to minimise their oxidising effects. However, the perception that ROS are only harmful to cells has since been questioned by a burgeoning body of evidence pointing to the existence of enzymes with the dedicated function of generating ROS. NADPH oxidases represent the only known family of enzymes whose sole purpose is to generate ROS. Members of this enzyme family are expressed across mammalian and non-mammalian cells, and influence a multitude of biological functions including host defence and redox signalling. However, although ROS are deliberately generated by NADPH oxidases during normal cell physiology, the observations that their expression and activity is markedly upregulated in the blood vessel wall in a number of cardiovascular ‘high-risk’ states (e.g. hypertension, hypercholesterolemia) implicates them in the oxidative stress that gives rise to artery disease and ultimately heart attacks and strokes. These observations highlight the fact that NADPH oxidases are important therapeutic targets in cardiovascular disease and that, hence, there is clearly a need for the development of selective inhibitors of these enzymes. Here we highlight the structural and biochemical characteristics of the NADPH oxidase family and then comprehensively review the literature on the currently available pharmacological inhibitors of these enzymes with a particular emphasis on their mechanisms of action, isoform selectivity and therapeutic potential in cardiovascular disease.