UP-REGULATION OF ENDOTHELIAL NITRIC-OXIDE SYNTHASE BY HMG COA REDUCTASE INHIBITORS

Background - Oxidized low-density lipoprotein (ox-LDL) causes endothel ial dysfunction in part by decreasing the availability of endothelial nitric oxide (NO). Although HMG CoA reductase inhibitors restore endot helial function by reducing serum cholesterol levels, it is not known whether they can also directly upregulate endothelial NO synthase (ecN OS) activity. Methods and Results - Human saphenous vein endothelial c ells were treated with ox-LDL (50 mu g/mL thiobarbituric acid reactive substances 12 to 16 nmol/mg) in the presence of HMG CoA reductase inh ibitors simvastatin and lovastatin, In a time-dependent manner, ox-LDL decreased ecNOS mRNA and protein levels (91 +/- 4% and 67 +/- 8% redu ction after 72 hours, respectively), Both simvastatin (1 mu mol/L) and lovastatin (10 mu mol/L) upregulated ecNOS expression by 3.8-fold and 3.6-fold, respectively, and completely prevented its downregulation b y ox-LDL. These effects of simvastatin on ecNOS expression correlated with changes in ecNOS activity, Although L-mevalonate alone did not af fect ecNOS expression, cotreatment with L-mevalonate completely revers ed ecNOS upregulation by simvastatin. Actinomycin D studies revealed t hat simvastatin stabilized ecNOS mRNA (tau(1/2), 43 versus 35 hours). Nuclear run-on assays and transient transfection studies with a -1.6 k b ecNOS promoter construct showed that simvastatin did not affect ecNO S gene transcription. Conclusions - Inhibition of endothelial HMG CoA reductase upregulates ecNOS expression predominantly by posttranscript ional mechanisms. These findings suggest that HMG CoA reductase inhibi tors may have beneficial effects in atherosclerosis beyond that attrib uted to the lowering of serum cholesterol by increasing ecNOS activity .