Circulating Microparticles Carry a Functional Endothelial Nitric Oxide Synthase That Is Decreased in Patients With Endothelial Dysfunction

Background Microparticles ( MP s) are circulating membrane particles of less than a micrometer in diameter shed from endothelial and blood cells. Recent literature suggests that MP s are not just functionally inert cell debris but may possess biological functions and mediate the communication between vascular cells. As a significant proportion of MP s originate from platelets and endothelial cells, we hypothesized that MP s may harbor functional enzymes including an endothelial NO synthase ( eNOS ). Methods and Results Using immunoprecipitation and W estern blot analysis, we found that human circulating MP s carry an eNOS . Ca 2+ and l ‐arginine‐dependent NOS activity of crude enzyme extract from MP s was determined by measuring the conversion of [ 3 H]‐L‐arginine to [ 3 H]‐citrulline and NOS ‐dependent nitrite production. NOS ‐dependent NO production in intact MP s was assessed by the NO ‐specific fluorescent probe MNIP ‐Cu. In patients with cardiovascular disease, endothelial dysfunction was associated with an increase in the total number of circulating MP s as well as a significant decrease in the expression and activity of eNOS in MP s. No difference in reactive oxygen species was noted in MP s isolated from either group. Conclusions Our data further support the concept that circulating MP s may not only retain phenotypic markers but also preserve the functionality of enzymes of the cells they originate from, including eNOS .