Objective-Endothelial nitric oxide synthase (eNOS) activity is supported by tetrahydrobiopterin (BH4), which appears to be important for generating protective NO but decreases uncoupling formation of superoxide. We investigated the effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, in terms of BH4 metabolism in human umbilical vein endothelial cells (HUVECs). Methods and Results-We measured the mRNA levels of GTP cyclohydrolase I (GTPCH), the rate-limiting enzyme in the first step of de novo BH4 synthesis, by real-time polymerase chain reaction. The mRNA of GTPCH, as well as of eNOS, was upregulated in HUVECs treated with cerivastatin. This increase was time and dose dependent. Fluvastatin was also observed to enhance GTPCH and eNOS mRNA levels. In parallel with this observation, cerivastatin increased intracellular BH4. Incubating HUVECs with tumor necrosis factor (TNF-␣) was observed to increase GTPCH mRNA while decreasing eNOS mRNA. In the presence of cerivastatin, the TNF-␣-mediated increase in GTPCH mRNA was enhanced, and the TNF-␣-mediated decrease in eNOS mRNA was attenuated. Cerivastatin increased the stability of eNOS mRNA. However, it did not alter the stability of GTPCH mRNA but increased GTPCH gene transcription, as shown by nuclear run-on assays. Preteatment of HUVECs with the selective GTPCH inhibitor, 2,4-diamino-6-hydroxypyrimidine, caused a decrease in intracellular BH4 and decreased citrulline formation after stimulation with ionomycin. Furthermore, the potentiating effect of cerivastatin was decreased by limiting the cellular availability of BH4. Conclusions-Our data demonstrate that statins elevate GTPCH mRNA, thereby increasing BH4 levels in vascular endothelial cells. In addition to augmenting eNOS expression, statins potentiate GTPCH gene expression and BH4 synthesis, thereby increasing NO production and preventing relative shortages of BH4. Key Words: statins Ⅲ cytokines Ⅲ nitric oxide Ⅲ tetrahydrobiopterin Ⅲ endothelial cells T he effectiveness and speed with which 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statin medications) can favorably influence vascular biology by mechanisms other than causing a reduction in plasma cholesterol have been demonstrated in a number of reports. [1][2][3][4][5][6] During the past several years, numerous additional effects of statins on vascular cells have been identified, which appear to modulate atherogenesis, plaque rupture, or thrombosis. Some of these appear to operate independently of the cholesterol-lowering mechanism. 4,5 For example, statins may upregulate nitric oxide (NO) expression by interfering with posttranscriptional regulation of endothelial NO synthase (eNOS). 7,8 Evidence regarding the importance of this mechanism in vivo was provided by the observation that statins inhibit ischemic cerebral stroke induced by occlusion of the middle cerebral artery in normal but not e-NOS-deficient mice. 9Tetrahydrobiopterin (BH4) is 1 of the most potent, naturally occurring reducing agents and ...

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Our findings suggest that the beneficial effects of cilostazol on endothelial function may be due to AMPK activation. Restoration of endothelial dysfunction in diabetic rats by cilostazol is at least partly attributed to amelioration of biopterin metabolism in the aorta.