Response to Upregulation of Nitric Oxide, Inhibition of Oxidative Stress, and Antihypertensive Effects of Statins
We thank Zhou1 for his note on our meta-analysis of the effect of statin treatment on blood pressure. Zhou pointed out the potential impact of statin therapy on the imbalance between NO and reactive oxidative species production occurring in animal models of salt-sensitive hypertension.2 This ability of statins was indeed the basis for one of the explanations that we proposed for the relatively small but clinically meaningful antihypertensive effect of these drugs in humans.3 We share Zhou’s considerations and recollect the experimental evidence in support of the concept that genetic or acquired susceptibility to the blood pressure effects of excess salt intake might partly operate through an imbalance between NO bioavailability and oxygen free radical production (see Reference 4 for review). Of course, this imbalance is not unique to hypertension (nor to salt-sensitive hypertension) in as much as it also occurs in such metabolic disorders as dyslipidemia or diabetes, which, in turn, tend to cluster with high blood pressure. However, although almost all of the studies included in our meta-analysis enrolled hypercholesterolemic patients, the antihypertensive effect of statins was detected essentially in those studies in which all or most of the participating patients had high blood pressure. This finding may indicate that endothelial dysfunction and oxidative stress were particularly severe in those subjects, thus more amenable to the impact of statins. Other hypotheses about this effect of statins, for example, their influence on arterial stiffness or on the production of collagen and other components of extracellular matrix, are in keeping with the above considerations, because these processes are, in turn, affected by NO bioavailability and oxidative stress.
Also worth noting in Zhou’s letter1 was his comment about the “dual attitude” of NO as a vascular protective or damaging factor depending on the concomitant level of oxygen free radicals. There are other representations of this theory, for example, the relationship between serum uric acid and cardiovascular disease. Although in populations at relatively low risk of cardiovascular disease serum uric acid is poor predictor of future cardiovascular accidents, by contrast it is a relatively strong independent predictor among subjects at high or very high risk because of the concomitance of multiple factors. Indeed, clinical and experimental studies suggest that uric acid has intrinsic antioxidant properties; however, under conditions of local ischemia, in which it is produced in parallel with reactive oxygen species, its antioxidant activity is overcome by the pro-oxidant and proinflammatory effects of oxygen free radical accumulation.5 Therefore, Zhou’s contention that upregulation of NO and reduction of oxidative stress may cooperate into the antihypertensive effects of statins is certainly reasonable.
We wish to remark that in our meta-analysis no correlation was detected between the cholesterol and the blood pressure–lowering effects of statins3: this finding supports the hypothesis that, indeed, the antihypertensive effect of these drugs is linked to pleiotropic actions, such as the ones envisaged in Zhou’s letter.
Zhou M-S. Upregulation of nitric oxide, inhibition of oxidative stress, and antihypertensive effects of statins. Hypertension. 2007; 49: e43.
Zhou MS, Jaimes EA, Raij L. Atorvastatin prevents end-organ injury in salt-sensitive hypertension–role of eNOS and oxidant stress. Hypertension. 2004; 44: 186–190.
Strazzullo P, Kerry SM, Barbato A, Versiero M, D’Elia L, Cappuccio FP. Do statins reduce blood pressure? A meta-analysis of randomized, controlled trials. Hypertension. 2007; 49: 792–798.