Post-transcriptional regulation of endothelial nitric oxide synthase mRNA stability by Rho GTPase

HMG-CoA reductase inhibitors reduce senescence and increase proliferation of endothelial progenitor cells via regulation of cell cycle regulatory genes

Endothelial progenitor cells (EPCs) play an important role in postnatal neovascularization of ischemic tissue. Ex vivo expansion of EPCs might be useful for potential clinical cell therapy of myocardial ischemia. However, cultivation of primary cells leads to cellular aging (senescence), thereby severely limiting the proliferative capacity. Therefore, we investigated whether statins might be able to prevent senescence of EPCs. EPCs were isolated from peripheral blood and characterized. After ex vivo cultivation, EPCs became senescent as determined by acidic beta-galactosidase staining. Atorvastatin or mevastatin dose-dependently inhibited the onset of EPC senescence in culture. Moreover, atorvastatin increased proliferation of EPCs as assessed by BrdU incorporation and colony-forming capacity. Whereas geranylgeranylpyrophosphate or farnesylpyrophosphate reduced the senescence inhibitory effect of atorvastatin, NO synthase inhibition, antioxidants, or Rho kinase inhibitors had no effect. To get further insights into the underlying downstream effects of statins, we measured telomerase activity and determined the expression of various cell cycle regulatory genes by using a microarray assay. Whereas telomerase activity did not change, atorvastatin modulated expression of cell cycle genes including upregulation of cyclins and downregulation of the cell cycle inhibitor p27Kip1. Taken together, statins inhibited senescence of EPCs independent of NO, reactive oxygen species, and Rho kinase, but dependent on geranylgeranylpyrophosphate. Atorvastatin-mediated prevention of EPC senescence appears to be mediated by the regulation of various cell cycle proteins. The inhibition of EPC senescence and induction of EPC proliferation by statins in vitro may importantly improve the functional activity of EPCs for potential cell therapy.

Reduction of serum C-reactive protein by statin therapy may reflect decreased isoprenylation of Rac-1, a mediator of the IL-6 signal transduction pathway

Recent studies demonstrate that statin therapy decreases plasma levels of C-reactive protein (CRP), a potent risk factor for thrombotic vascular events. CRP is an acute phase reactant, and most circulating CRP is synthesized by hepatocytes in response to IL-6. Since statins do not appear to have a consistent impact on serum levels of IL-6, their impact on plasma CRP very likely reflects down-regulation of hepatocyte responsiveness to this cytokine. The ability of IL-6 to promote transcription of CRP is mediated, in large part, by activation of the transcription factor STAT3; this activation requires both a tyrosine phosphorylation (mediated by the IL-6 receptor complex) and a serine phosphorylation (Ser-727), the origin of which has been more obscure. There is new evidence that, when hepatocytes are exposed to IL-6, the consequent serine phosphorylation of STATS is mediated by a signal transduction pathway in which the G-protein Rac-1 plays an obligate role. Inasmuch as the proper function of Rac-1 is contingent on isoprenylation that anchors it to the plasma membrane, it is reasonable to hypothesize that statin therapy interferes with IL-6 signaling in hepatocytes by suppressing the isoprenylation of Rac-1; a decrease in the transcription of CRP would be a likely consequence of this effect. Whether or not a reduction in elevated CRP is directly beneficial to vascular health, statins can exert direct effects on vascular endothelial function that should help prevent vascular inflammation and thrombosis, and thus should be of particular benefit to subjects - such as those with high CRP levels - who are at high risk for vascular events.

Endothelium-dependent effects of statins

The vascular endothelium is a dynamic endocrine organ that regulates contractile, secretory, and mitogenic activities in the vessel wall and hemostatic processes within the vascular lumen. Risk factors for cardiovascular disease, such as cigarette smoking, hypertension, and elevated serum lipid levels, impair endothelial function and lead to the development of atherosclerotic vessels. Recent studies suggest that statins reduce cardiovascular events in part by improving endothelial function. Statins reduce plasma cholesterol levels, thereby decreasing the uptake of modified lipoproteins by vascular wall cells. There is increasing evidence, however, that statins may also exert effects beyond cholesterol lowering. Indeed, many of these cholesterol-independent or "pleiotropic" vascular effects of statins appear to involve restoring or improving endothelial function through increasing the bioavailability of nitric oxide, promoting re-endothelialization, reducing oxidative stress, and inhibiting inflammatory responses. Thus, the endothelium-dependent effects of statins are thought to contribute to many of the beneficial effects of statin therapy in cardiovascular disease.

Effect of HMG-CoA reductase inhibitors on proliferation and protein synthesis by rat hepatic stellate cells

BACKGROUND/AIMS

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors called statins, have besides their cholesterol-lowering function, therapeutic value in conditions such as neo-angiogenesis and atherosclerosis. We investigated the effect of two statins on the proliferation rate and protein steady state levels of hepatic stellate cells (HSC).

METHODS

Cellular DNA synthesis under the influence of statins and/or platelet derived growth factor (PDGF) and mevalonate was evaluated by measuring BrdU incorporation. Synthesis of collagens type I, III, IV and fibronectin was quantified by ELISA. Additionally, we examined the influence of simvastatin on isoprenylation of Ras and RhoA proteins.

RESULTS

Lovastatin and simvastatin induced a dose-dependent inhibition of the proliferation rate of HSC. Subsequent addition of PDGF and/or mevalonate, after long-term exposure of simvastatin to HSC, did not reverse simvastatins' antiproliferative effect. Lovastatin and simvastatin reduced the protein steady state level of collagens type I (-40%), III (-45%) and IV (-27%). Membrane bound Ras steady state levels decreased under the influence of simvastatin. Membrane bound RhoA remained unaltered, whereas, cytosolic RhoA protein level was strongly reduced.

CONCLUSIONS

Our data showed that lovastatin and simvastatin inhibited HSC proliferation and collagen steady state levels by mechanisms independent of their lipid reducing activities.

The pleiotropic effects of HMG-CoA reductase inhibitors: their role in osteoporosis and dementia

HMG-CoA reductase is the rate-limiting enzyme for cholesterol synthesis and its inhibition exerts profound effects on cellular metabolism. Inhibitors of this enzyme are used in clinical practice to lower plasma cholesterol levels and are commonly collectively referred to as 'statins'. A number of in vitro, in vivo animal, and clinical studies suggest that properties of statins other than cholesterol lowering may be of biological importance. These diverse properties are often referred to as 'pleiotropic' and suggest that statins may affect a number of diseases of ageing. In this article we review the biological plausibility and clinical evidence of a role for statins in modulating two diseases of ageing: osteoporosis and dementia (including Alzheimer's disease). In both diseases, there is a sound cellular and laboratory basis for a plausible therapeutic effect of statins. In the case of osteoporosis, there are conflicting data regarding clinical benefit, with both negative and positive results reported. In particular, secondary analyses of randomised, controlled studies have shown no reduction of fracture risk by statins. In the case of dementia there are fewer clinical studies but there is clear anticipated benefit in macrovascular dementias attributable to statin-mediated reduction of the risk of stroke. Overall, there are a lack of prospective, placebo-controlled, randomised data testing statins and modulation of the risk of osteoporosis-related fracture or of clinical dementia, where these are primary outcomes. Until such data are available, the use of statins appears promising but cannot be recommended as a primary therapeutic modality for either condition.

Pitavastatin-induced thrombomodulin expression by endothelial cells acts via inhibition of small G proteins of the Rho family

OBJECTIVE

3-hydroxyl-3-methyl coenzyme A reductase inhibitors (statins) can function to protect the vasculature in a manner that is independent of their lipid-lowering activity. The main feature of the antithrombotic properties of endothelial cells is an increase in the expression of thrombomodulin (TM) without induction of tissue factor (TF) expression. We investigated the effect of statins on the expression of TM and TF by endothelial cells.

METHODS AND RESULTS

The incubation of endothelial cells with pitavastatin led to a concentration- and time-dependent increase in cellular TM antigen and mRNA levels. In contrast, the expression of TF mRNA was not induced under the same conditions. A nuclear run-on study revealed that pitavastatin accelerates TM transcription rate. The stimulation of TM expression by pitavastatin was prevented by either mevalonate or geranylgeranylpyrophosphate. Specific inhibition of geranylgeranyltransferase-I and Rac/Cdc42 by GGTI-286 and Clostridium sordellii lethal toxin, respectively, enhanced TM expression, whereas inactivation of Rho by Clostridium botulinum C3 exoenzyme was ineffective.

CONCLUSIONS

Statins regulate TM expression via inhibition of small G proteins of the Rho family; Rac/Cdc42. A statin-mediated increase in TM expression by endothelial cells may contribute to the beneficial effects of statins on endothelial function.

Acute reduction of myocardial infarct size by a hydroxymethyl glutaryl coenzyme A reductase inhibitor is mediated by endothelial nitric oxide synthase

In addition to their lipid-lowering properties, statins improve endothelial function by increasing the activity of endothelial nitric oxide synthase (eNOS). It was hypothesized that, by this mechanism, statins protect the myocardium from ischemia/reperfusion injury in normocholesterolemic animals. Rats were pretreated for 1 week with either cerivastatin (0.3 mg/kg/d) or placebo. Anesthetized animals underwent 30 minutes of coronary artery occlusion (CAO) followed by 180 minutes of reperfusion. In a separate set of experiments, the NOS inhibitor l-NAME (15 mg/kg; N -nitro-l-arginine methyl ester) was administered 15 minutes before CAO. Cerivastatin decreased infarct size by 49% (P < 0.05) without reducing plasma cholesterol levels. Cerivastatin increased myocardial eNOS mRNA and NOS activity and by 52% and 58% (P < 0.05), respectively. Cardioprotection and upregulation of eNOS activity evoked by cerivastatin were not observed in rats cotreated with l-NAME. These results show that statins reduce the extent of myocardial necrosis in normocholesterolemic rats after acute ischemia/reperfusion injury by increasing myocardial eNOS activity. Therefore, statins may protect the heart not only by reducing the incidence of ischemic events, but also by limiting cell damage during acute myocardial infarction.

Beyond lipid-lowering: effects of statins on endothelial nitric oxide

Endothelial dysfunction is now recognised as an important process in the pathogenesis of atherosclerosis. Nitric oxide (NO) release by the endothelium regulates blood flow, inflammation and platelet aggregation, and consequently its disruption during endothelial dysfunction can decrease plaque stability and encourage the formation of atherosclerotic lesions and thrombi. Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (statins) are often utilised in the prevention of coronary heart disease due to their efficacy at lowering lipid levels. However, statins may also prevent atherosclerotic disease by non-lipid or pleiotropic effects, for example, improving endothelial function by promoting the production of NO. There are various mechanisms whereby statins may alter NO release, such as inhibiting the production of mevalonate and important isoprenoid intermediates, thereby preventing the isoprenylation of the small GTPase Rho, which negatively regulates the expression of endothelial nitric oxide synthase (eNOS). Furthermore, statins may also increase eNOS activity via post-translational activation of the phosphatidylinositol 3-kinase/protein kinase Akt (PI3 K/Akt) pathway and/or through an interaction with the molecular chaperone heat-shock protein 90 (HSP90). Data suggest that statins may vary in their efficacy for enhancing the release of NO, and the mechanisms dictating these differences are not yet clear. By increasing NO production, statins may interfere with atherosclerotic lesion development, stabilise plaque, inhibit platelet aggregation, improve blood flow and protect against ischaemia. Therefore, the ability of statins to improve endothelial function through the release of NO may partially account for their beneficial effects at reducing the incidence of cardiovascular events.

Down-regulation of Rac-1 GTPase by Estrogen

Rac1 GTPase is essential for the activation of the NAD(P)H oxidase complex and, thereby, regulates the release of reactive oxygen species (ROS) in the vessel wall. 17 beta-estradiol (E2) inhibits vascular ROS production. To elucidate the underlying molecular mechanisms we investigated the potential regulation of Rac1 by E2 in vascular smooth muscle cells. Treatment of vascular smooth muscle cells with angiotensin II as well as overexpression of the constitutively active mutant RacL61 increased ROS release as assessed by dichlorofluorescein fluorescence, whereas inhibition of Rac1 by Clostridium sordellii lethal toxin or overexpression of dominant-negative RacN17 inhibited ROS production. Treatment with E2 (100 nm) completely prevented angiotensin II-induced NAD(P)H oxidase activity and ROS production. E2 time and concentration dependently decreased angiotensin II-induced and basal Rac1 mRNA and protein expression as well as Rac1 activity. Down-regulation of Rac1 expression by E2 was mediated by inhibition of gene transcription (nuclear run-on assays), but E2 had no effect on Rac1 mRNA stability. Regulation of Rac1 was mediated by estrogen receptors since co-incubation with ICI 182.780 prevented down-regulation of Rac1. To test these observations in vivo, ovariectomized spontaneously hypertensive rats were treated with E2 or vehicle. Real-time PCR and Western blotting showed reduction of aortic Rac1 mRNA and protein by 32 and 58%, respectively. Furthermore, down-regulation of Rac1 by E2 was observed in human mononuclear cells of women with elevated E2 levels after controlled ovarian hyperstimulation. Rac1 GTPase gene-transcription and activity is regulated by 17 beta-estradiol, which may be an important molecular mechanism contributing to the cardiovascular effects of estrogens.

Regulation of isoprenoid/cholesterol biosynthesis in cells from mevalonate kinase-deficient patients

Mevalonic aciduria (MA) and hyper-IgD and periodic fever syndrome (HIDS) are two inherited disorders both caused by depressed mevalonate kinase (MK) activity. MK is the first enzyme to follow the highly regulated 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase (HMGR), which catalyzes the rate-limiting step in the isoprenoid/cholesterol biosynthesis pathway. In fibroblasts of MA patients, but not of HIDS patients, HMGR activity is elevated under normal growth conditions. This activity is down-regulated when cells are supplemented with the isoprenoid precursors geraniol, farnesol, and geranylgeraniol, and a mixture of 25-hydroxycholesterol and cholesterol. This indicates that the regulation of the pathway in these cells is not disturbed. The elevated HMGR activity is probably due to a shortage of non-sterol isoprenoid end products, as indicated by normal HMGR mRNA levels in MA fibroblasts. Furthermore, the HMGR activity in MA cells was more sensitive to geranylgeraniol suppression and less sensitive to sterol suppression than the HMGR activity in low density lipoprotein receptor-deficient cells. HMGR activity in MA cells was down-regulated also by addition of its product mevalonate to the culture medium. Thus, it appears that the elevation of mevalonate levels, which are high in MA patients and moderate in HIDS patients, allows the cells to compensate for the depressed MK activity. Indeed, the isoprenylation of Ras and RhoA protein appeared normal in HIDS and MA fibroblasts under normal conditions but showed increased sensitivity toward inhibition of HMGR by simvastatin. Our results indicate that MK-deficient cells maintain the flux through the isoprenoid/cholesterol biosynthesis pathway by elevating intracellular mevalonate levels.

Effects of statins on the vasculature: Implications for aggressive lipid management in the cardiovascular metabolic syndrome

The cardiovascular metabolic syndrome is a family of risk factors that predispose patients to develop diabetes and cardiovascular disease. Indeed, macrovascular, not microvascular, disease is the leading cause of death in these patients. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) exert both direct and indirect (cholesterol-lowering) effects on the vasculature. Clinical trials have shown that these agents reduce cardiovascular disease and cerebrovascular disease in persons with diabetes. However, their beneficial effects on diabetic dyslipidemia do not account for all of the observed risk reduction. Positive effects on nitric oxide metabolism, inflammation, coagulability, and adhesion of cells to the vascular endothelium likely contribute to the mechanism of action of these agents. These pleiotropic effects of statins on the vasculature will be discussed in this review.

Involvement of RhoA/Rho kinase signaling in VEGF-induced endothelial cell migration and angiogenesis in vitro

OBJECTIVE

Growth factor-induced angiogenesis involves migration of endothelial cells (ECs) into perivascular areas and requires active remodeling of the endothelial F-actin cytoskeleton. The small GTPase RhoA previously has been implicated in vascular endothelial growth factor (VEGF)-induced signaling pathways, but its role has not been clarified.

METHODS AND RESULTS

VEGF induced the activation of RhoA and recruited RhoA to the cell membrane of human ECs. This increase in RhoA activity is necessary for the VEGF-induced reorganization of the F-actin cytoskeleton, as demonstrated by adenoviral transfection of dominant-negative RhoA. Rho kinase mediated this effect of RhoA, as was demonstrated by the use of Y-27632, a specific inhibitor of Rho kinase. Inhibition of Rho kinase prevented the VEGF-enhanced EC migration in response to mechanical wounding but had no effect on basal EC migration. Furthermore, in an in vitro model for angiogenesis, inhibition of either RhoA or Rho kinase attenuated the VEGF-mediated ingrowth of ECs in a 3-dimensional fibrin matrix.

CONCLUSIONS

VEGF-induced cytoskeletal changes in ECs require RhoA and Rho kinase, and activation of RhoA/Rho kinase signaling is involved in the VEGF-induced in vitro EC migration and angiogenesis.

Withdrawal of statin treatment abrogates stroke protection in mice

BACKGROUND AND PURPOSE

Statins (3-hydroxy-3-methylglutaryl-coenzyme A [HMG-CoA] reductase inhibitors) reduce stroke damage independent of lipid lowering by upregulation of endothelial nitric oxide synthase (eNOS). Acute withdrawal of statin treatment may suppress endothelial NO production and impair vascular function.

METHODS

To test this hypothesis, we treated 129/SV mice with atorvastatin (10 mg/kg) for 14 days and then withdrew treatment.

RESULTS

Treatment with atorvastatin conferred stroke protection by 40% after filamentous occlusion of the middle cerebral artery followed by reperfusion. Withdrawal of statin treatment, however, resulted in the loss of stroke protection after 2 and 4 days. In mouse aortas and brain vasculature, statins upregulated eNOS message 2.3- and 1.7-fold, respectively, as measured by reverse transcription-polymerase chain reaction. Withdrawal of statins resulted in 5- and 2.7-fold downregulation of eNOS in aorta and brain, respectively, after 2 days. Statin treatment decreased RhoA GTPase membrane expression to 48%, while withdrawal of statins resulted in 4-fold increase of RhoA in the membrane. Moreover, platelet factor 4 and beta-thromboglobulin in plasma were significantly downregulated by statin treatment, but withdrawal of statins resulted in a 2.9- and 3.1-fold upregulation after 2 days, respectively. Thrombus formation induced by ligature of the inferior vena cava was significantly reduced by statin treatment. When statin treatment was withdrawn, however, protection was lost between 2 and 4 days.

CONCLUSIONS

Acute termination of statin treatment results in a rapid loss of protection in mouse models of cerebral ischemia and thrombus formation independent of lipid lowering. In patients with acute or impending stroke, withdrawal of statins may impair outcome.

A novel pleiotropic effect of statins: prevention of cardiac hypertrophy by cholesterol-independent mechanisms

Cardiac hypertrophy is an initial physiological adaptive response by the heart to pressure overload. However, if pressure overload persists, frequently, the heart decompensates and develops 'pathophysiological' hypertrophy. This leads to increased mortality and morbidity and is an independent risk factor for heart failure. Because cardiac myocytes convert this pressure overload into intracellular biochemical signals, blocking this critical signaling pathway may be an important therapeutic target to prevent cardiac hypertrophy. Small GTP-binding proteins, in particular Rac1, have been suggested to play a key role in the development of cardiac hypertrophy. Recently, 3-hydroxyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, also called statins, have been shown to inhibit cardiac hypertrophy independent of their cholesterol lowering property. Statins block the isoprenylation and activation of members of the Rho family, such as RhoA and Rac1. Rac1 also regulates NADPH oxidase, which is a major source of reactive oxygen species (ROS) in cardiovascular cells. Growing evidence suggests that ROS may be involved in the process of cardiac hypertrophy and recent research has shown that statins attenuate oxidative stress through inhibition of Rac1. Overall, these pleiotropic effects of statins will give new insights into the process of cardiac hypertrophy.

Protective role of endothelial nitric oxide synthase

Nitric oxide is a versatile molecule, with its actions ranging from haemodynamic regulation to anti-proliferative effects on vascular smooth muscle cells. Nitric oxide is produced by the nitric oxide synthases, endothelial NOS (eNOS), neural NOS (nNOS), and inducible NOS (iNOS). Constitutively expressed eNOS produces low concentrations of NO, which is necessary for a good endothelial function and integrity. Endothelial derived NO is often seen as a protective agent in a variety of diseases. This review will focus on the potential protective role of eNOS. We will discuss recent data derived from studies in eNOS knockout mice and other experimental models. Furthermore, the role of eNOS in human diseases is described and possible therapeutic intervention strategies will be discussed.

Vascular pleiotropy of statins: clinical evidence and biochemical mechanisms

The ability of statins to lower serum cholesterol and reduce coronary heart disease endpoints has confirmed portions of the lipid hypothesis. However, the time to benefit and increased benefit in overlapping populations have suggested that nonlipid or pleiotropic effects of statins may be present. The apparent benefit of statins in cerebrovascular disease may imply a similar final common pathway among the diverse mechanisms of vascular diseases. Statins' inhibition of isoprenoid intermediates may modify GTP binding proteins such as Rho. The augmentation of collateral blood flow downstream of activated plaque through endothelial cell nitric oxide synthase may be the biochemical basis of statins' vascular pleiotropy. Eventual clinical paradigms of statin use may include higher doses to enhance pleiotropic effects and treatment, even when lipid markers are within guidelines.

[Antilipemics: from prevention to protection]

Statins and fibrates have been demonstrated to prevent both cardiovascular events and stroke. While this preventive effect was initially thought to be related to their lipid-lowering effects, in particular hypocholesterolaemic effect, analysis of primary and secondary prevention trials suggest that these preventive effects could be partly independent of their effects on lipid disorders. The pleiotropic effects, such as vascular, anti-inflammatory or anti-oxidants effects, were described for both the statins and fibrates. In addition to the preventive effects, these pleiotropic effects could partially explain the decrease in myocardial or cerebral ischemia consequences in experimental models. These cellular protective effects may have a therapeutic interest to decrease severity of stroke or coronary acute syndrome. They could also explain the drugs' lipid-lowering preventive effects independent of the treatment of lipid disorders. Beyond vascular pathologies, the pleiotropic effects of lipid-lowering drugs could explain their potentially beneficial effect in different diseases, such as dementia or cancer.

Beyond lipid lowering: the role of statins in vascular protection

The introduction of the hydroxy methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) in 1987 was a major advance in the prevention and treatment of cardiovascular disease. Several landmark clinical trials have demonstrated the benefit of lipid lowering with statins for the primary and secondary prevention of coronary heart disease (CHD), namely The Scandinavian Simvastatin Survival Study (4S), Cholesterol And Recurrent Events (CARE), Long-term Intervention with Pravastatin in Ischemic Disease (LIPID), West of Scotland Coronary Prevention Study (WOSCOPS) and Air Force/Texas Coronary Atherosclerosis Prevention Study (AFCAPS/TexCAPS). Although it is widely accepted that the majority of clinical benefit obtained with statins is a direct result of their lipid-lowering properties, these agents appear to display additional cholesterol-independent or pleiotropic effects on various aspects of cardiovascular disease, including improving endothelial function, decreasing vascular inflammation and enhancing plaque stability. Although the full impact of statin therapy on each of these processes is not fully understood, ongoing studies with current and new statins are likely to shed further light on the potential cholesterol-independent benefits of these agents.

Isoprenylation of RhoB is necessary for its degradation. A novel determinant in the complex regulation of RhoB expression by the mevalonate pathway

Statins improve vascular functions by mechanisms independent from their cholesterol-lowering effect. Rho GTPases are emerging as key targets for the vascular effects of statins. RhoB is a short-lived, early-response inducible protein involved in receptor endocytosis, apoptosis, and gene expression. Here we show that statins regulate RhoB expression by acting at multiple levels. Simvastatin increased RhoB protein levels by 8- to 10-fold. This effect was related to a depletion of isoprenoid intermediates, as deduced from the observation that several metabolites of the cholesterol biosynthetic pathway, namely, mevalonate and geranylgeranyl-pyrophosphate, attenuated simvastatin-induced RhoB up-regulation. Moreover, prenyltransferase inhibitors mimicked simvastatin effect. Cholesterol supplementation did not prevent simvastatin-elicited up-regulation but increased RhoB levels per se. Simvastatin moderately augmented RhoB transcript levels, but markedly impaired the degradation of RhoB protein, which accumulated in the cytosol in its non-isoprenylated form. Inhibition of RhoB isoprenylation was apparently required for simvastatin-induced up-regulation, because levels of an isoprenylation-deficient RhoB mutant were not affected by simvastatin. Moreover, this mutant was found to be markedly more stable than the wild-type protein. These results show that RhoB isoprenylation is necessary for rapid turnover of this protein and identify a novel link between the cholesterol biosynthetic pathway and the regulation of G-protein expression.

Cerivastatin, a HMG-CoA reductase inhibitor, reduces plasminogen activator inhibitor-1 (PAI-1) expression in endothelial cells by down-regulation of cellular signaling and the inhibition of PAI-1 promoter activity

Statins, which competitively inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity and reduce mevalonate synthesis, are believed to exert a plethora of pleiotropic effects. In this report, molecular mechanisms of the inhibitory effect on plasminogen activator inhibitor type 1 (PAI-1) expression produced by cerivastatin (CRV), the most active compound in this class, were studied using monocultures of human endothelial cell line (EA.hy 926). CRV similar to another statin, lovastatin (LOV), significantly inhibited PAI-1 expression and its release from endothelial cells, nonstimulated and stimulated with TNF-alpha. The inhibitory effect of CRV could be detected at the level of PAI-1 promoter in EA.hy 926 cells transfected with plasmid p800 LUC containing PAI-1 promoter fragment (+71 to -800), as well as at the level of PAI-1 mRNA. The PAI-1 promoter activity was markedly suppressed in the nonstimulated cells and almost completely inhibited in TNF-alpha-stimulated cells. In addition, CRV at low doses (IC(50) of 4 - 6 microM) significantly inhibited mitogen-activated protein kinases (MAPKs) phosphorylation. The majority of inhibitory effects occurred at significantly lower concentrations for CRV compared to LOV. The mechanism by which CRV inhibits PAI-1 expression appears to be directly associated with geranylgeranylation of some cell proteins, since the inhibitory effect on PAI-1 expression can be reversed by geranylgeranyl-pyrophosphate but not by farnesyl-pyrophosphate.

Microcirculation as a target for the anti-inflammatory properties of statins

Statins are inhibitors of the 3-hydroxy-3-methylglutaryl coenzyme A reductase, a ubiquitous enzyme critical for the biosynthesis of cholesterol. Because of their cholesterol-lowering properties, statins are extensively used in medical practice, and large clinical trials have shown that statins effectively reduce cardiovascular related morbidity and mortality. In the past 5 years, an important, new concept suggesting that the cardioprotective effects of statins are not necessarily related to cholesterol-lowering actions has emerged. Indeed, in vivo findings have clearly shown that statins exert anti-inflammatory and immunomodulatory effects and that they modulate vascular remodeling under normocholesterolemic conditions. These pleiotropic properties of statins affect important molecules in vascular biology and help preserve endothelial function in acute and chronic inflammatory states of the cardiovascular system, including coronary and cerebral artery diseases, diabetes, and atherosclerosis. Emerging evidence indicates that the microcirculation is a crucial target for the pleiotropic actions of statins because of its important role in regulating blood flow, leukocyte-endothelium interactions, and vascular remodeling. Accordingly, this review focuses on the role that the microcirculation plays in the vascular protective action of statins.

Rho GTPase/Rho kinase negatively regulates endothelial nitric oxide synthase phosphorylation through the inhibition of protein kinase B/Akt in human endothelial cells

Endothelial nitric oxide synthase (eNOS) is an important regulator of cardiovascular homeostasis by production of nitric oxide (NO) from vascular endothelial cells. It can be activated by protein kinase B (PKB)/Akt via phosphorylation at Ser-1177. We are interested in the role of Rho GTPase/Rho kinase (ROCK) pathway in regulation of eNOS expression and activation. Using adenovirus-mediated gene transfer in human umbilical vein endothelial cells (HUVECs), we show here that both active RhoA and ROCK not only downregulate eNOS gene expression as reported previously but also inhibit eNOS phosphorylation at Ser-1177 and cellular NO production with concomitant suppression of PKB activation. Moreover, coexpression of a constitutive active form of PKB restores the phosphorylation but not gene expression of eNOS in the presence of active RhoA. Furthermore, we show that thrombin inhibits eNOS phosphorylation, as well as expression via Rho/ROCK pathway. Expression of the active PKB reverses eNOS phosphorylation but has no effect on downregulation of eNOS expression induced by thrombin. Taken together, these data demonstrate that Rho/ROCK pathway negatively regulates eNOS phosphorylation through inhibition of PKB, whereas it downregulates eNOS expression independent of PKB.

Insulin resistance, a new target for nitric oxide-delivery drugs

In the Western hemisphere, the incidence of insulin resistance and its complications has been growing rapidly and is reaching epidemic proportions. Over the past decade, evidence has accumulated, indicating that nitric oxide (NO) plays a key role in the regulation of metabolic and cardiovascular homeostasis. Defective endothelial nitric oxide synthase (eNOS) driven NO synthesis causes insulin resistance, arterial hypertension and dyslipidemia in mice, and characterizes insulin-resistant humans. On the other hand, stimulation of inducible nitric oxide synthase (iNOS) and NO overproduction in mice, may also cause metabolic insulin resistance, suggesting a Yin-Yang effect of NO in the regulation of glucose homeostasis. Here, we will review the evidence for this novel concept, and thereby provide the conceptual framework for the use of NO-delivery drugs and pharmacological agents that modulate the bioavailability of endogenously produced NO for the treatment of insulin resistance.

A 3-hydroxy-3-methylglutaryl co-enzyme A reductase inhibitor reduces hypertensive nephrosclerosis in stroke-prone spontaneously hypertensive rats

BACKGROUND

Recent studies suggest that 3-hydroxy-3-methylglutaryl co-enzyme A reductase inhibitors (statins) exert their protective effects against cardiovascular diseases independently of their cholesterol-decreasing effects.

OBJECTIVE

To clarify the effect of a statin on hypertensive nephrosclerosis.

METHODS

We treated stroke-prone spontaneously hypertensive rats (spSHRs) chronically, starting at the age of 4 weeks, with cerivastatin (2 mg/kg per day by gavage) or vehicle. Physiological parameters, plasma chemistry and urine protein excretion were analysed. At 14 weeks of age, the rats had their kidneys removed for use in assays.

RESULTS

Compared with vehicle treatment, statin treatment reduced proteinuria and renal injury independently of blood pressure and cholesterol concentrations in spSHRs. Although expression of adhesion molecules and infiltration of inflammatory cells were not different whether or not cerivastatin treatment was used, renal fibrosis was significantly reduced in statin-treated spSHRs. We also found that expression of transforming growth factor-beta1 in kidneys was significantly inhibited in statin-treated spSHRs.

CONCLUSION

Cerivastatin prevents or retards hypertension-induced renal injury via inhibition of renal fibrosis and proteinuria. These results show the potential of statins as protective tools against proteinuric renal diseases, independent of their cholesterol-decreasing effects.

Comparative beneficial effects of simvastatin and pravastatin on cardiac allograft rejection and survival

OBJECTIVES

We sought to evaluate the relative effects of low doses of pravastatin (20 mg/day) and simvastatin (10 mg/day) on indices of cardiac allograft rejection. We further examined the relative efficacy and safety of these two drugs on lipid-lowering in heart transplantation.

BACKGROUND

The immunomodulatory effects of hydroxy methyl glutaryl-coenzyme A reductase inhibitors have been increasingly recognized. Previous studies have demonstrated an ameliorative influence of pravastatin on hemodynamically compromising rejection after heart transplantation. A recent observational trial suggested that simvastatin 20 mg/day was associated with trends to lower survival and more adverse effects than pravastatin 40 mg/day.

METHODS

In a 12-month prospective, open-label study, 50 heart transplant recipients received either open-label pravastatin 20 mg daily (n = 24) or simvastatin 10 mg daily (n = 26) within four weeks of transplantation. Indices of allograft rejection including treated rejection, rejection with hemodynamic compromise, noncellular rejection, and mean one-year biopsy score were compared between the two cohorts, as well as with a statin-naive control population (n = 37). Lipid levels, safety, and post-transplant outcomes were also assessed as secondary end points.

RESULTS

We found no significant differences in any allograft rejection parameter between the two groups. However, total low-density lipoprotein (LDL), but not high-density lipoprotein cholesterol or triglycerides, were lower in the simvastatin arm (-23% vs. -11%, p = 0.02). No cases of rhabdomyolysis or myositis occurred in either group. Survival at one year was similar in both treatment groups (91% for patients on pravastatin and 92% for patients on simvastatin). Both groups had better survival compared with the statin-naive control group (80%, p = 0.04).

CONCLUSIONS

Simvastatin (10 mg/day) and pravastatin (20 mg/day) are associated with similar beneficial effects on cardiac allograft rejection and one-year survival. At these doses, simvastatin decreases LDL cholesterol more so than pravastatin with no increase in adverse effects in heart transplantation.

Smad2 mediates transforming growth factor-beta induction of endothelial nitric oxide synthase expression

Transforming growth factor-beta (TGF-beta) increases expression of endothelial nitric oxide synthase (eNOS), although the precise mechanism by which it does so is unclear. We report that Smad2, a transcription factor activated by TGF-beta, mediates TGF-beta induction of eNOS in endothelial cells. TGF-beta induces Smad2 translocation from cytoplasm to nucleus, where it directly interacts with a specific region of the eNOS promoter. Overexpression of Smad2 increases basal levels of eNOS, and further increases TGF-beta stimulation of eNOS expression. Ectopic expression of Smurf, an antagonizer of Smad2, decreases Smad2 expression and blocks TGF-beta induction of eNOS. Because Smad2 can interact with a variety of transcription factors, coactivators, and corepressors, Smad2 may thus act as an integrator of multiple signals in the regulation of eNOS expression.

Regulation of endothelial-type NO synthase expression in pathophysiology and in response to drugs

In many types of cardiovascular pathophysiology such as hypercholesterolemia and atherosclerosis, diabetes, cigarette smoking, or hypertension (with its sequelae stroke and heart failure) the expression of endothelial NO synthase (eNOS) is altered. Both up- and downregulation of eNOS have been observed, depending on the underlying disease. When eNOS is upregulated, the upregulation is often futile and goes along with a reduction in bioactive NO. This is due to an increased production of superoxide generated by NAD(P)H oxidase and by an uncoupled eNOS. A number of drugs with favorable effects on cardiovascular disease upregulate eNOS expression. The resulting increase in vascular NO production may contribute to their beneficial effects. These compounds include statins, angiotensin-converting enzyme inhibitors, AT1 receptor antagonists, calcium channel blockers, and some antioxidants. Other drugs such as glucocorticoids, whose administration is associated with cardiovascular side effects, downregulate eNOS expression. Stills others such as the immunosuppressants cyclosporine A and FK506/tacrolimus or erythropoietin have inconsistent effects on eNOS. Thus regulation of eNOS expression and activity contributes to the overall action of several classes of drugs, and the development of compounds that specifically upregulate this protective enzyme appears as a desirable target for drug development.

[Effect of HMG-CoA reductase inhibition on endothelial dysfunction-inducing protein in hypercholesterolemic rabbits]

INTRODUCTION AND OBJECTIVES

In our laboratory, we recently obtained evidence that cultured bovine endothelial cells contain cytosolic proteins that form complexes with the 3'-unstranslated region of endothelial nitric oxide synthase (eNOS) mRNA and are associated with its destabilization. The aim of this study was to determine the presence of such proteins and the level of eNOS expression in hypercholesterolemic rabbits as an in vivo model of endothelial dysfunction.

METHODS AND RESULTS

Endothelium-dependent relaxation in response to acetylcholine was reduced in aortic segments from hypercholesterolemic rabbits compared with controls. Treatment of hypercholesterolemic rabbits with simvastatin (25 mg/kg body weight/day) restored endothelium-dependent relaxation. Aortic eNOS expression was reduced in hypercholesterolemic rabbits and was accompanied by enhanced binding activity of a 60-KDa cytosolic protein and reduced stability of eNOS mRNA. Simvastatin treatment upregulated eNOS expression and reduced the interaction of cytosolic protein with the 3'-untranslated region of eNOS mRNA.

CONCLUSIONS

These results demonstrate the presence of a 60-KDa protein that binds to eNOS mRNA and reduces eNOS expression in the vascular wall.

Inhibitors of histone deacetylation downregulate the expression of endothelial nitric oxide synthase and compromise endothelial cell function in vasorelaxation and angiogenesis

The histone deacetylase (HDAC) inhibitor trichostatin A (TSA) inhibits hypoxia-stimulated angiogenesis. Endothelial nitric oxide synthase (eNOS)-derived NO is central to angiogenesis signaling in endothelial cells (ECs). We hypothesized that the HDAC-dependent regulation of angiogenesis may involve a modulatory effect on eNOS expression. The HDAC inhibitors TSA, butyric acid (BuA), and MS-275 time- and concentration-dependently suppressed eNOS protein levels to 41+/-2%, 46+/-12%, and 40+/-12% of control, respectively. In parallel, TSA and BuA also downregulated eNOS mRNA expression to 21+/-4% and 37+/-4% of control. TSA also attenuated the NO-dependent relaxation of porcine coronary arteries (P<0.0001, TSA 1 micromol/L) and prevented tube formation in a human angiogenesis assay. Although vascular endothelial growth factor substitution did not compensate for the inhibitory effect of TSA, exogenous NO reversed the inhibition of angiogenesis by TSA. To address the underlying signaling mechanism, we characterized the effect of TSA on eNOS gene transcription and mRNA half-life. Although TSA decreased both eNOS protein and mRNA levels, TSA paradoxically enhanced the activity of the eNOS promoter, and did not alter the eNOS transcription rate in nuclear run-on experiments, suggesting that TSA posttranscriptionally targets eNOS mRNA. These data indicate that HDAC-dependent mechanisms contribute to the regulation of eNOS expression in ECs.

Targets for pharmacological intervention of endothelial hyperpermeability and barrier function

Many diseases share the common feature of vascular leakage, and endothelial barrier dysfunction is often the underlying cause. The subsequent stages of endothelial barrier dysfunction contribute to endothelial hyperpermeability. Vasoactive agents induce loss of junctional integrity, a process that involves actin-myosin interaction. Subsequently, the interaction of leukocytes amplifies leakage by the leukocyte-derived mediators. The processes mainly occur at the postcapillary venules. The whole microvascular bed, including the capillaries, becomes involved in vascular leakage by the induction of angiogenesis. Plasma leakage results from gaps between endothelial cells as well as by the induction of transcellular transport pathways. Several mechanisms can improve endothelial barrier function, depending on the tissue affected and the cause of hyperpermeability. They include blockade of specific receptors and elevation of cyclic AMP (cAMP) by agents such as beta(2)-adrenergic agents. However, current therapies based on these principles often fail. Recent research has identified several new promising targets for pharmacological therapy. Endogenous compounds were also found with barrier-improving characteristics. Important insights were obtained in the different pathways involved in barrier dysfunction. Such insights regard the regulation of endothelial contraction and endothelial junction integrity: inhibitors of RhoA activation and Rho kinase represent a potentially valuable group of agents with endothelial hyperpermeability reducing properties, and strategies to target vascular endothelial growth factor (VEGF)-mediated edema are under current investigation. In clinical practice, not only tools to improve an impaired endothelial barrier function are necessary. Sometimes, a controlled, temporal, and local increase in permeability can also be desired, for example, with the aim to enhance drug delivery. Therefore, vessel leakiness is also being exploited to enable tissue access of liposomes, viral vectors, and other therapeutic agents that do not readily cross healthy endothelium. This review discusses strategies for targeting signaling molecules in therapies for diseases involving altered endothelial permeability.

Statin-induced expression of decay-accelerating factor protects vascular endothelium against complement-mediated injury

Complement-mediated vascular injury is important in the pathophysiology of atherosclerosis and myocardial infarction. Because recent evidence shows that statins have beneficial effects on endothelial cell (EC) function independent of lipid lowering, we explored the hypothesis that statins modulate vascular EC resistance to complement through the upregulation of complement-inhibitory proteins. Human umbilical vein and aortic ECs were treated with atorvastatin or simvastatin, and decay-accelerating factor (DAF), membrane cofactor protein, and CD59 expression was measured by flow cytometry. A dose-dependent increase in DAF expression of up to 4-fold was seen 24 to 48 hours after treatment. Statin-induced upregulation of DAF required increased steady-state mRNA and de novo protein synthesis. L-Mevalonate and geranylgeranyl pyrophosphate reversed the effect, confirming the role of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibition and suggesting that constitutive DAF expression is negatively regulated by geranylgeranylation. Neither farnesyl pyrophosphate nor squalene inhibited statin-induced DAF expression, suggesting that the effect is independent of cholesterol lowering. Statin-induced DAF upregulation was mediated by the activation of protein kinase Calpha and inhibition of RhoA and was independent of phosphatidylinositol-3 kinase and NO activity. The increased DAF expression was functionally effective, resulting in significant reduction of C3 deposition and complement-mediated lysis of antibody-coated ECs. These observations provide evidence for a novel cytoprotective action of statins on vascular endothelium that is independent of the effect on lipids and results in enhanced protection against complement-mediated injury. Modulation of complement regulatory protein expression may contribute to the early beneficial effects of statins in reducing the morbidity and mortality associated with atherosclerosis.

Statins as anti-inflammatory agents

The beneficial effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) in cardiovascular disease have generally been attributed to their cholesterol-lowering property. However, an increasing number of in vitro and in vivo studies indicate that statins have direct anti-inflammatory effects that are not mediated by their hypocholesterolemic activity. In this article, the HMG-CoA-reductase-dependent and -independent mechanisms by which statins might affect leukocyte adhesion and migration to sites of inflammation are reviewed and the implications for the design of new statin-derived drugs are discussed.

Policosanol safely down-regulates HMG-CoA reductase - potential as a component of the Esselstyn regimen

Many of the wide-ranging health benefits conferred by statin therapy are mediated, not by reductions in LDL cholesterol, but rather by inhibition of isoprenylation reactions essential to the activation of Rho family GTPases; this may be the mechanism primarily responsible for the favorable impact of statins on risk for ischemic stroke, senile dementia, and fractures, as well as the anti-hypertensive and platelet-stabilizing actions of these drugs. Indeed, the extent of these benefits is such as to suggest that most adults would be wise to take statins; however, owing to the significant expense of statin therapy, as well as to the potential for dangerous side effects that mandates regular physician follow-up, this strategy appears impractical. However, policosanol, a mixture of long-chain aliphatic alcohols extractable from sugar cane wax, has shown cholesterol-lowering potency comparable to that of statins, and yet appears to be devoid of toxic risk. Recent evidence indicates that policosanol down-regulates cellular expression of HMG-CoA reductase, and thus has the potential to suppress isoprenylation reactions much like statins do. Consistent with this possibility, the results of certain clinical and animal studies demonstrate that policosanol has many effects analogous to those of statins that are not likely explained by reductions of LDL cholesterol. However, unlike statins, policosanol does not directly inhibit HMG-CoA reductase, and even in high concentrations it fails to down-regulate this enzyme by more than 50% - thus likely accounting for the safety of this nutraceutical. In light of the fact that policosanol is quite inexpensive and is becoming available as a non-prescription dietary supplement, it may represent a practical resource that could enable the general public to enjoy health benefits comparable to those conferred by statins. In a long-term clinical study enrolling patients with significant symptomatic coronary disease, Esselstyn has demonstrated that a low-fat, whole-food vegan diet, coupled with sufficient statin therapy to maintain serum cholesterol below 150 mg/dL, can stop the progression of coronary disease and virtually eliminate further risk for heart attack. A comparable regimen, in which policosanol is used in place of statins, may represent a practical strategy whereby nearly everyone willing to commit to health-protective eating can either prevent coronary disease, or prevent pre-existing coronary disease from progressing to a life-threatening event.

Physiological mechanisms regulating the expression of endothelial-type NO synthase

Although endothelial nitric oxide synthase (eNOS) is a constitutively expressed enzyme, its expression is regulated by a number of biophysical, biochemical, and hormonal stimuli, both under physiological conditions and in pathology. This review summarizes the recent findings in this field. Shear stress, growth factors (such as transforming growth factor-beta, fibroblast growth factor, vascular endothelial growth factor, and platelet-derived growth factor), hormones (such as estrogens, insulin, angiotensin II, and endothelin 1), and other compounds (such as lysophosphatidylcholine) upregulate eNOS expression. On the other hand, the cytokine tumor necrosis factor-alpha and bacterial lipopolysaccharide downregulate the expression of this enzyme. The growth status of cells, the actin cytoskeleton, and NO itself are also important regulators of eNOS expression. Both transcriptional and posttranscriptional mechanisms are involved in the expressional regulation of eNOS. Different signaling pathways are involved in the regulation of eNOS promoter activity and eNOS mRNA stability. Changes in eNOS expression and activity under pathophysiological conditions and the pharmacological modulation of eNOS expression are subject of a subsequent brief review (part 2) to be published in the next issue of this journal.

Inhibitory effect of fluvastatin on lysophosphatidylcholine-induced nonselective cation current in Guinea pig ventricular myocytes

Using the whole-cell voltage-clamp method, we investigated the effect of fluvastatin, a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor, on lysophosphatidylcholine (LPC)-induced nonselective cation current (I(NSC)) in guinea pig cardiac ventricular myocytes. External LPC (3 to approximately 50 microM) induced I(NSC) in a dose-dependent manner with a lag. With fluvastatin (5 microM) in the external solution, LPC induced I(NSC), which was significantly smaller and with a longer lag compared with that in the absence of fluvastatin. With mevalonic acid (MVA) (100 microM) in the external solution, fluvastatin did not diminish LPC-induced I(NSC). Geranylgeranylpyrophosphate, an MVA metabolite, in the pipette solution prevented fluvastatin from diminishing LPC-induced I(NSC), suggesting that isoprenylated signaling molecules, such as the small G-protein Rho, might be involved in the LPC effect. Botulinum toxin C3, Rho-kinase inhibitor (R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide, 2 HCl (Y-27632), or pertussis toxin in the pipette solution suppressed LPC-induced I(NSC). We conclude that LPC induces I(NSC) via a Gi/Go-coupled receptor and Rho-mediated pathway. The inhibitory effect of fluvastatin on LPC-induced I(NSC) provides a new insight into the signal transduction mechanism and may have important clinical implications.

Mechanisms of NOS2 regulation by Rho GTPase signaling in airway epithelial cells

The aberrant dysregulation of the inducible form of nitric oxide synthase (NOS2) is thought to play a role in many inflammatory disorders including cystic fibrosis (CF). The complex regulation of NOS2 expression is the subject of intense investigation, and one intriguing regulatory pathway known to influence NOS2 expression is the Rho GTPase cascade. We examined NOS2 regulation in response to inflammatory cytokines in a human alveolar epithelial cell line treated with inhibitors of different upstream and downstream components of the Rho GTPase pathway to better define potential signaling mechanisms. Statin-mediated 3-hydroxy-3-methylglutaryl-CoA reductase inhibition increased cytokine-dependent activation of the NOS2 promoter, reversible by the addition of geranylgeranyl pyrphosphate. However, inhibition of Rho-associated kinase (ROCK) with Y-27632 resulted in a decrease in NOS2 promoter activity, yet an increase in NOS2 mRNA and protein levels. Our results suggest that prenylation events influence NOS2 promoter activity independently of the Rho GTPase pathway and that Rho GTPase signaling mediated through ROCK suppresses NOS2 production downstream of promoter function at the message and protein level.

[Effects of statins on angiogenesis and vasculogenesis]

Statins promote the proliferation, migration, and survival of endothelial cells and bone marrow-derived endothelial progenitor cells (angioblasts) by stimulating the serine/threonine protein kinase Akt (also known as protein kinase B) pathway. Like vascular endothelial growth factor (VEGF), the statins promote angiogenesis and vasculogenesis. Therefore, Akt activation may explain some of the beneficial effects of the statins, including postnatal neovascularization.

Glucose increases endothelial-dependent superoxide formation in coronary arteries by NAD(P)H oxidase activation: attenuation by the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor atorvastatin

Increased vascular superoxide anion (O(2)(-)) formation is essentially involved in the pathophysiology of atherosclerosis. Chronic hyperglycemia induces endothelial dysfunction, probably due to increased formation of reactive oxygen intermediates. However, little is known about the localization, modulators, and molecular mechanisms of vascular O(2)(-) formation during hyperglycemia. In porcine coronary segments, high glucose significantly increased O(2)(-) formation (1,703.5 +/- 394.9 vs. 834.1 +/- 91.7 units/mg for control, n = 64, P < 0.05; measured by lucigenin-enhanced chemiluminescence). This effect was completely blocked after removal of the endothelium. Coincubation with 10 micromol/l atorvastatin, a lipophilic inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, attenuated basal and glucose-induced O(2)(-) formation (328.1 +/- 46.5 and 332.8 +/- 50.3 units/mg, P < 0.05 vs. without atorvastatin). Incubation with mevalonic acid reversed this effect. High glucose increased mRNA expression of the oxidase subunit p22(phox), which was blocked by 10 micromol/l atorvastatin, whereas expression of gp91(phox) was unchanged. In conclusion, glucose-induced increase of vascular O(2)(-) formation is endothelium dependent and is probably mediated by increased p22(phox) subunit expression. Beneficial effects of statins in diabetic patients may be explained in part by attenuation of vascular O(2)(-) formation independent of lipid lowering.

Simvastatin restores endothelial NO-mediated vasorelaxation in large arteries after myocardial infarction

Congestive heart failure (CHF) after myocardial infarction is associated with diminished endothelial nitric oxide (NO)-mediated vasorelaxation. The 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors have been shown to modulate vascular tone independent of the effects on lipid lowering. We hypothesized that simvastatin restores NO-dependent vasorelaxation with CHF. We found that incubation of the normal rat aorta with 0.1 mM simvastatin for 24 h enhanced ACh-mediated vasorelaxation (P < 0.05). Moreover, simvastatin increased (P < 0.05) endothelial NO synthase (eNOS) protein content by >200% (82.0 +/- 14.0 vs. 21.6 +/- 7.9% II/microg). In cultured endothelial cells, simvastatin (10 and 20 microM) increased eNOS levels by 114.7 +/- 39.9 and 212.0 +/- 75.0% II/microg protein, respectively (both P < 0.05; n = 8). In the rat coronary artery ligation model, oral gavage with 20 mg. kg(-1). day(-1) simvastatin for 3 wk decreased (P < 0.05) mean arterial pressure (121 +/- 20 vs. 96.5 +/- 10.8 mmHg) and left ventricular change in pressure with time (4,500 +/- 700 vs. 4,091 +/- 1,064 mmHg/s, n = 6). Simvastatin reduced (P < 0.05) basal vasoconstriction and improved ACh-mediated vasorelaxation in CHF arterial rings. Inhibition of NO generation by N(G)-nitro-L-arginine methyl ester (100 microM) abolished the ACh-induced vasorelaxation in all rats. In conclusion, chronic treatment of CHF with simvastatin restores endothelial NO-dependent dysfunction and upregulates eNOS protein content in arterial tissue.

IL-1 beta transcript stability in monocytes is linked to cytoskeletal reorganization and the availability of mRNA degradation factors

Monocyte extravasation initiates reorganization of the cytoskeleton (CSK) and adhesion-dependent cytokine gene transcription. The actin CSK is thought to be crucial for compartmentalization and translation of mRNA, many of which contain AU-rich (ARE) instability motifs in the 3' untranslated region. We investigated regulation of adhesion-induced IL-1 beta expression by the monocyte CSK. In serum-free adherent monocytes, the induced IL-1 beta mRNA was stable and did not coextract with actin filaments. In contrast, in cells adherent in autologous serum, IL-1 beta transcripts were unstable, coextracted with actin filaments and were associated with only transient activation of the mitogen-activated protein kinases (MAPK). Under both conditions of adherence, the ARE-binding protein AUF1/hnRNP D was readily extracted in the cytosolic fraction. Electro-injection with AUF1/hnRNP D modified the actin CSK and, surprisingly, stabilized IL-1 beta transcripts. These data suggest that the control of mRNA degradation is linked with changes in the CSK. Mitogen-activated protein kinase activation or alterations in the availability of mRNA degradation factors may mediate these effects.

Rho-kinase mediates hypoxia-induced downregulation of endothelial nitric oxide synthase

BACKGROUND

Hypoxia-induced pulmonary hypertension is a major cause of morbidity and mortality. Hypoxia induces pulmonary vasoconstriction, in part, by decreasing endothelial nitric oxide synthase (eNOS) expression. The mechanism by which hypoxia decreases eNOS expression is not known but may involve Rho-kinase-induced actin cytoskeletal changes in vascular endothelial cells.

METHODS AND RESULTS

To determine whether hypoxia regulates eNOS expression through Rho-kinase, we exposed human saphenous and pulmonary artery endothelial cells to hypoxia (3% O2) with and without a Rho-kinase inhibitor, hydroxyfasudil (0.1 to 100 micromol/L), for various durations (0 to 48 hours). Hypoxia increased Rho-kinase expression and activity by 50% and 74%, decreased eNOS mRNA and protein expression by 66+/-3% and 57+/-5%, and inhibited eNOS activity by 48+/-9%. All of these effects of hypoxia on eNOS were reversed by cotreatment with hydroxyfasudil. Furthermore, inhibition of Rho by Clostridium botulinum C3 transferase or Rho-kinase by overexpression of dominant-negative Rho-kinase reversed hypoxia-induced decrease in eNOS expression. Indeed, disruption of the actin cytoskeleton, the downstream target of Rho-kinase, by cytochalasin D also upregulated eNOS expression. Hypoxia reduced eNOS mRNA half-life from 22+/-2 to 13+/-2 hours, which was reversed by cotreatment with hydroxyfasudil. However, neither hypoxia nor hydroxyfasudil had any effects on eNOS gene transcription.

CONCLUSIONS

These results indicate that hypoxia-induced decrease in eNOS expression is mediated by Rho-kinase and suggest that Rho-kinase inhibitors may have therapeutic benefits in patients with hypoxia-induced pulmonary hypertension.

Rho/Rho-kinase is involved in the synthesis of tissue factor in human monocytes

Monocytes and macrophages synthesize tissue factor (TF) which plays a role in thrombogenicity in coronary artery disease. This study was conducted to investigate the effect of Rho/Rho-kinase inhibition on the synthesis of TF in cultured human monocytes. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins), C3 exoenzyme and Rho-kinase inhibitors were added to isolated peripheral blood monocytes and the synthesis of TF was assessed by reverse transcriptase polymerase chain reaction (RT-PCR), Western blotting and immunohistochemistry. Rho activity was determined by measuring the GTP-bound form of Rho A. Cerivastatin and pravastatin reduced the levels of TF antigen and mRNA. The suppressive effect of statins on TF synthesis was reversed by geranylgeranylpyrophosphate (GGPP) and the restoring effect of GGPP was eliminated by C3 exoenzyme and Y-27632. Pravastatin decreased the activity of Rho A, suggesting that the suppression of TF synthesis by statins is mediated via inhibition of the geranylgeranylation of Rho. Moreover, inhibition of Rho and Rho-kinase downregulated the synthesis of TF. Our results suggest that Rho/Rho-kinase signaling is involved in the synthesis of TF in human monocytes and that inhibition of Rho/Rho-kinase may be useful for treating thrombogenicity in coronary artery disease.

Statins in the prevention and treatment of Alzheimer disease

Vascular risk factors such as hypertension and hypercholesterolemia during midlife increase the risk for Alzheimer's disease (AD). Treatment of hypercholesterolemia and other vascular risk factors may have great implications in the prevention of AD. Recent findings illustrate that the sterol metabolism in the brain is an active process, well controlled and regulated by 24-hydroxylase, an enzyme that is uniquely expressed in the brain. The use of statins in ischemic heart disease (IHD) has proven to be a phenomenal advance in pharmacological disease prevention and treatment. A growing body of evidence, suggest that statins exhibit additional benefits that are independent of their cholesterol-lowering actions. Statin treatment has also considerable effect in prevention of ischemic stroke. In animal models of ischemic stroke, statins have proven to reduce infarct size through up-regulation of endothelial nitric oxide synthases. Data from recent observational studies have revealed a potential role for statins in prevention of AD. The following review comments the processes leading to dementia including the involvement of cholesterol regulation, cerebral circulation and inflammation in development of dementia. The mechanisms by which statins may be beneficial in controlling these processes is discussed.

Rosuvastatin, a new HMG-CoA reductase inhibitor, upregulates endothelial nitric oxide synthase and protects from ischemic stroke in mice

HMG-CoA reductase inhibitors (statins) are cholesterol-lowering drugs and reduce the risk of myocardial infarction and stroke. In this study we investigated whether rosuvastatin, a new, potent HMG-CoA reductase inhibitor, upregulates endothelial nitric oxide (NO) expression and activity and protects from cerebral ischaemia in mice. Endothelial cells in culture and 129/SV mice were chronically treated with rosuvastatin. The expression and activity of endothelial NO synthase (eNOS) was determined by reverse-transcriptase polymerase chain reaction (RT-PCR), Western blotting and arginine-citrulline assays. Cerebral ischaemia was induced by occlusion of the middle cerebral artery (MCAo) for 2 h and infarct size was determined after 22 h of reperfusion. Treatment of endothelial cells with rosuvastatin concentration- and time-dependently upregulated eNOS mRNA and protein expression. In aortas of 129/SV wild-type mice, treatment with 0.2, 2, and 20 mg kg(-1) rosuvastatin subcutaneously (s.c.) for 10 days significantly upregulated eNOS mRNA by 50, 142, and 205%, respectively. NOS activity was significantly increased by 75, 145, and 320%, respectively. Stroke volume after 2-h MCAo was reduced by 27, 56, and 50% (for 0.2, 2 and 20 mg kg(-1), respectively). Serum cholesterol and triglygeride levels were not significantly lowered by the treatment. The novel HMG-CoA reductase inhibitor rosuvastatin dose-dependently upregulates eNOS expression and activity and protects from cerebral ischaemia in mice. The effects are independent of changes in cholesterol levels and are equivalent or even superior to the protective effects by simvastatin and atorvastatin in this animal model.

Inhibition of Rho-kinase induces alphaB-crystallin expression in lens epithelial cells

The small heat shock protein, alphaB-crystallin, has been shown to interact with actin and intermediate filament proteins. However, little is known regarding the cellular mechanisms regulating such interactions. In this study, we explored the role of the Rho/Rho-kinase pathway in alphaB-crystallin distribution and expression in porcine lens epithelial cells. alphaB-crystallin was distributed uniformly throughout the cytoplasm and did not exhibit any unique redistribution in response to actin depolymerization induced by Rho/Rho-kinase inhibitors (C3-exoenzyme or Y-27632) or by overexpression of the dominant negative mutant of Rho-kinase (DNRK) in porcine lens epithelial cells. Interestingly, alphaB-crystallin levels markedly increased in lens epithelial cells treated with the inhibitors of Rho/Rho-kinase proteins (lovastatin, Y-27632 or DNRK) while a protein kinase C inhibitor (GF109203x) was found to have no effect. Further, Y-27632 showed a dose (2-50 microM) response effect on alphaB-crystallin induction. Nocodazole, a microtubule-depolymerizing agent, elicited an increase in alphaB-crystallin levels but latrunculin, an actin depolymerizing agent, did not show any significant effect. Pretreatment with cycloheximide or genistein blocked the Rho-kinase inhibitor-induced increase in alphaB-crystallin protein levels. Rho-kinase inhibitor-induced increases in alphaB-crystallin levels were found to be associated with activation of P38 mitogen-activated protein kinase (MAPK). These results suggest that Rho/Rho-kinase negatively regulates alphaB-crystallin expression, and this response appears to be dependent on tyrosine-protein kinase and P38 MAPK function. Finally, alphaB-crystallin induction appears to be better correlated with the direct inhibition of Rho/Rho-kinase than with actin depolymerization per se.

Insulin's stimulation of endothelial superoxide generation may reflect up-regulation of isoprenyl transferase activity that promotes rac translocation

Recent research demonstrates that statin drugs exert a number of favorable effects on endothelial function, independent of lipid modulation, that appear to be mediated by a partial inhibition of prenylation reactions. Statin-induced suppression of PKC-evoked superoxide production may be attributable to an inhibition of rac prenylation and thus translocation that impedes activation of the membrane-bound NAD(P)H oxidase. Conversely, it is now known that hyperinsulinemia up-regulates prenylation reactions by boosting the activities of isoprenyl transferases. In light of new evidence that hyperinsulinemia stimulates endothelial superoxide production via NAD(P)H oxidase, it is tempting to conclude that up-regulation of rac prenylation is at least partially responsible for this phenomenon. In patients afflicted with insulin resistance syndrome, this adverse impact of hyperinsulinemia may be exacerbated by an excessive free fatty acid flux that activates endothelial PKC - another stimulant of the NAD(P)H oxidase - while impeding insulin-mediated activation of nitric oxide synthase. The resulting imbalance of endothelial nitric oxide and superoxide production may be responsible for much of the excess vascular risk associated with this syndrome.

Obesity, atherosclerosis and the vascular endothelium: mechanisms of reduced nitric oxide bioavailability in obese humans

It is now well established that obesity is an independent risk factor for the development of coronary artery atherosclerosis. The maintenance of vascular homeostasis is critically dependent on the continued integrity of vascular endothelial cell function. A key early event in the development of atherosclerosis is thought to be endothelial cell dysfunction. A primary feature of endothelial cell dysfunction is the reduced bioavailability of the signalling molecule nitric oxide (NO), which has important anti atherogenic properties. Recent studies have produced persuasive evidence showing the presence of endothelial dysfunction in obese humans NO bioavailability is dependent on the balance between its production by a family of enzymes, the nitric oxide synthases, and its reaction with reactive oxygen species. The endothelial isoform (eNOS) is responsible for a significant amount of the NO produced in the vascular wall. NO production can be modulated in both physiological and pathophysiological settings, by regulation of the activity of eNOS at a transcriptional and post-transcriptional level, by substrate and co-factor provision and through calcium dependent and independent signalling pathways. The present review discusses general mechanisms of reduced NO bioavailability including factors determining production of both NO and reactive oxygen species. We then focus on the potential factors responsible for endothelial dysfunction in obesity and possible therapeutic interventions targetted at these abnormalities.