Inhibition of human vascular smooth muscle cell proliferation by lovastatin: the role of isoprenoid intermediates of cholesterol synthesis

Polypill Therapy in Cardiovascular Disease: A Meta-analysis of Randomized Controlled Trials

BACKGROUND

The effectiveness of polypill therapy in the prevention and treatment of cardiovascular disorders is still unclear. This meta-analysis aimed to assess the efficacy of polypill therapy in reducing cardiovascular risk factors.

METHODS

We conducted a systematic search of PubMed, Cochrane CENTRAL, SCOPUS, and Google Scholar for randomized controlled trials (RCTs) that evaluated polypill therapy for cardiovascular diseases, hypertension, or dyslipidemia. We included 18 RCTs with a total of 20,463 participants in our analysis. Pooled effect estimates were reported as Odds ratios (ORs) with a 95% confidence interval (CI) using a random-effects model.

RESULTS

Polypill therapy was associated with a statistically significant reduction in systolic blood pressure (SBP) [OR: -0.33, 95% CI (-0.64, -0.03); P-value= 0.03], diastolic blood pressure (DBP) [OR: -0.70, 95% CI (-1.20, -0.21); P-value= 0.005], and total cholesterol level [OR: -1.25, 95% CI (-1.82, -0.68); P-value < 0.0001]. Polypill therapy also showed improved adherence [OR 2.18, 95% CI (1.47, 3.24); P-value= 0.0001]. However, there was no statistically significant benefit in the reduction of all-cause mortality, major cardiovascular events, and LDL-c levels.

CONCLUSIONS

The use of polypill therapy is associated with a statistically significant reduction in SBP, DBP, and total cholesterol levels, as well as improved adherence. Further research is needed to determine its impact on hard clinical outcomes such as mortality and major cardiovascular events.

The Rationale, Indications, Safety, and Use of Statins in the Pediatric Population

Together with heart-healthy lifestyle habits, statins serve as the cornerstone of primary and secondary prevention of atherosclerotic cardiovascular disease in adults. Several conditions, most notably familial hypercholesterolemia (FH), cause early dyslipidemia and vascular disease, contributing to the development and progression of atherosclerosis from childhood and increased cardiovascular risk. In recent decades, studies increasingly have evaluated the safety and efficacy of statins in such high-risk youth. The strongest evidence for pediatric statin use is for the heterozygous FH population, whereby statin use has been shown to lower low-density lipoprotein cholesterol effectively, slow the progression of atherosclerosis and vascular dysfunction, and significantly reduce cardiovascular risk in early adulthood. Numerous meta-analyses and Cochrane reviews have demonstrated that attributed adverse effects, including liver toxicity, myositis, and rhabdomyolysis, occur no more frequently in youth receiving statins than placebos, with no impact on growth or development. However, further studies evaluating the long-term safety of pediatric statin use are required. In the current review, we summarize the pediatric experience of statin use to date, focusing on its utility for FH, Kawasaki disease, post-heart transplantation, and other at-risk populations. Current guidelines and indications for use are summarized, and the short- and medium-term safety experience is reviewed. Finally, a clinical approach to the indications, initiation, and monitoring of statins in youth is provided.

Cardiovascular Risk Reduction in High-Risk Pediatric Patients: A Scientific Statement From the American Heart Association

This scientific statement presents considerations for clinical management regarding the assessment and risk reduction of select pediatric populations at high risk for premature cardiovascular disease, including acquired arteriosclerosis or atherosclerosis. For each topic, the evidence for accelerated acquired coronary artery disease and stroke in childhood and adolescence and the evidence for benefit of interventions in youth will be reviewed. Children and adolescents may be at higher risk for cardiovascular disease because of significant atherosclerotic or arteriosclerotic risk factors, high-risk conditions that promote atherosclerosis, or coronary artery or other cardiac or vascular abnormalities that make the individual more vulnerable to the adverse effects of traditional cardiovascular risk factors. Existing scientific statements and guidelines will be referenced when applicable, and suggestions for risk identification and reduction specific to each setting will be described. This statement is directed toward pediatric cardiologists, primary care providers, and subspecialists who provide clinical care for these young patients. The focus will be on management and justification for management, minimizing information on pathophysiology and epidemiology.

Influence of fixed-dose combination perindopril/amlodipine on target organ damage in patients with arterial hypertension with and without ischemic heart disease (results of EPHES trial)

Background

The EPHES trial (Evaluation of influence of fixed dose combination Perindo-pril/amlodipine on target organ damage in patients with arterial HypErtension with or without iSchemic heart disease) compared the dynamics of target organ damage (TOD) in hypertensive patients with and without ischemic heart disease (IHD) treated with the fixed-dose combination (FDC) perindopril + amlodipine.

Methods

The analysis included 60 hypertensive patients (aged >30 years): 30 without IHD and 30 with IHD. At randomization, FDC was administered at a daily baseline dose of 5/5 mg with uptitration to 10/10 mg every two weeks. If target blood pressure (BP<140/90 mmHg) was not achieved after six weeks, indapamide 1.5 mg was added to the regimen. All patients underwent body mass index measurements, office and ambulatory BP measurements, pulse wave velocity (PWVe) and central systolic BP evaluation, augmentation index adjusted to heart rate 75 (Aix@75) evaluation, biochemical analysis, ECG, echocardiography with Doppler, ankle-brachial index measurement, and intima-media thickness measurement. The follow-up period was 12 months.

Results

Therapy based on FDC perindopril/amlodipine was effective in lowering BP (office, ambulatory, central) in both groups. We noted significant decrease in Aix@75 with the therapy in both groups, but ΔAix@75 was lesser in the group with IHD than the group without IHD. FDC provided significant improvement in PWVe and left ventricular diastolic function, and decrease in albuminuria, left ventricular hypertrophy (LVH), and left atrium size. ΔPWVe was significantly (P<0.005) less in patients without IHD than those with IHD (2.5±0.2 vs 4.4±0.5 m/s, respectively). In spite of almost equal LVH regression, the positive dynamics of ΔE/A and ΔE/E´ were more in patients with IHD than those without IHD (64.4% and 54.1% vs 39.8 and 23.2%, respectively; P<0.05 for both comparisons). Adverse reactions were in 2 (6.5%) patients without IHD and 3 (10%) with IHD (P=NS). In the group with IHD, we noted significant decrease in angina episode rate – from 2.5±0.4 to 1.2±0.2 (P<0.01) per week.

Conclusion

Thus, treatment based on FDC was effective in decreasing BP and TOD regression in both patients with and without IHD. However, the dynamics of changes in TOD were different between the two groups, which should be taken into consideration during management of patients with and without IHD.

Synergistic effects of blood pressure-lowering drugs and statins: systematic review and meta-analysis

BACKGROUND

Synergistic effects of blood pressure-lowering drugs and statins are unknown, but are key to risk-based treatment decision strategies and fixed-combination polypills.

OBJECTIVE

We conducted a systematic literature review and meta-analysis to test the hypothesis that the combined relative effects of blood pressure-lowering drugs and statins on cardiovascular outcomes are multiplicative.

STUDY SELECTION

Two persons independently searched five data sources and hand-searched reference lists from earliest available to December 2017. We included factorial trials with at least two randomised interventions including one statin versus placebo factor and one blood pressure-lowering drug/more intense blood pressure-lowering regimen versus placebo/less intense regimen factor, and reported cardiovascular events or mortality as outcomes. We tested interactions as departures from additivity or multiplicativity using mixed-effects logistic regression models.

FINDINGS

Seven out of 1017 screened studies fulfilled the selection criteria, contributing a total of 27 020 patients with 857 major cardiovascular events and 725 deaths. The relative risk reduction of major cardiovascular events with active/more intense blood pressure-lowering regimen was not materially different in subgroups randomised to statins (risk ratio 0.81, 95% CI 0.66 to 1.00) or placebo (0.94, 0.79 to 1.11). Likewise, statin effects were not substantially different in subgroups randomised to active/more intense blood pressure-lowering regimen (0.69, 0.57 to 0.85) or placebo/less intense regimen (0.80, 0.67 to 0.96). No departures from either additivity or multiplicativity were observed. Heterogeneity was low.

CONCLUSIONS

The combined relative effects of blood pressure-lowering drugs and statins on cardiovascular events were multiplicative. This supports risk-based treatment decision strategies and fixed-combination polypills.

Perindopril and barnidipine alone or combined with simvastatin on hepatic steatosis and inflammatory parameters in hypertensive patients

The aim of this study was to evaluate the effects of perindopril or barnidipine alone or combined with simvastatin on metabolic parameters and hepatic steatosis degree. One hundred and forty nine mild to moderate hypertensive, normocholesterolemic, overweight or obese outpatients with hepatic steatosis were enrolled. They were treated with perindopril 5mg/day, or barnidipine, 20mg/day, for 6 months; subsequently simvastatin, 20mg/day was added to both treatments for further 6 months. Blood pressure variation was recorded. Patients also underwent an ultrasound examination, at baseline and after 6, and 12 months. We also assessed: fasting plasma glucose (FPG), fasting plasma insulin (FPI), lipid profile, adiponectin (ADN), tumor necrosis factor-α (ΤΝF-α), interleukin-6 (IL-6), high-sensitivity C reactive protein (Hs-CRP). Both perindopril and barnidipine reduced blood pressure, with barnidipine being more effective. Barnidipine, but not perindopril, slightly decreased total cholesterol and triglycerides after 6 months compared to baseline; lipid profile improved in both groups when simvastatin was added. Regarding inflammatory parameters, barnidipine reduced TNF-a, IL-6, and Hs-CRP, both in monotherapy, and after simvastatin addition. Hepatic steatosis parameters improved only when simvastatin was added. We can conclude that barnidipine better reduced blood pressure compared to perindopril and inflammatory parameters. Regarding hepatic steatosis parameters, only the addition of simvastatin improved them.

REGISTRATION NUMBER

NCT02064218, ClinicalTrials.gov.

Simvastatin Inhibits Toll-like Receptor 8 (TLR8) Signaling in Primary Human Monocytes and Spontaneous Tumor Necrosis Factor Production from Rheumatoid Synovial Membrane Cultures

Simvastatin has been shown to have antiinflammatory effects that are independent of its serum cholesterol lowering action, but the mechanisms by which these antiinflammatory effects are mediated have not been elucidated. To explore the mechanism involved, the effect of simvastatin on toll-like receptor (TLR) signaling in primary human monocytes was investigated. A short pretreatment with simvastatin dose-dependently inhibited the production of tumor necrosis factor (TNF)-α in response to TLR8 activation (but not TLR2, -4 or -5). Statins are known inhibitors of the cholesterol biosynthetic pathway, but, intriguingly, TLR8 inhibition could not be reversed by addition of mevalonate or geranylgeranyl pyrophosphate, downstream products of cholesterol biosynthesis. TLR8 signaling was examined in HEK 293 cells stably expressing TLR8, where simvastatin inhibited I kappa B kinase (IKK)α/β phosphorylation and subsequent nuclear factor (NF)-κB activation without affecting the pathway to activating protein-1 (AP-1). Because simvastatin has been reported to have antiinflammatory effects in RA patients and TLR8 signaling contributes to TNF production in human RA synovial tissue in culture, simvastatin was tested in these cultures. Simvastatin significantly inhibited the spontaneous release of TNF in this model, which was not reversed by mevalonate. Together, these results demonstrate a hitherto unrecognized mechanism of simvastatin inhibition of TLR8 signaling that may in part explain its beneficial antiinflammatory effects.

Increased Expression of RhoA in Epithelium and Smooth Muscle of Obese Mouse Models: Implications for Isoprenoid Control of Airway Smooth Muscle and Fibroblasts

The simultaneous rise in the prevalence of asthma and obesity has prompted epidemiologic studies that establish obesity as a risk factor for asthma. The alterations in cell signaling that explain this link are not well understood and warrant investigation so that therapies that target this asthma phenotype can be developed. We identified a significant increase in expression of the small GTPase RhoA in nasal epithelial cells and tracheal smooth muscle cells from leptin-deficient (ob/ob) mice compared to their wild-type counterparts. Since RhoA function is dependent on isoprenoid modification, we sought to determine the role of isoprenoid-mediated signaling in regulating the viability and proliferation of human airway smooth muscle cells (ASM) and normal human lung fibroblasts (NHLF). Inhibiting isoprenoid signaling with mevastatin significantly decreased the viability of ASM and NHLF. This inhibition was reversed by geranylgeranyl pyrophosphate (GGPP), but not farnesyl pyrophosphate (FPP), suggesting specificity to the Rho GTPases. Conversely, increasing isoprenoid synthesis significantly increased ASM proliferation and RhoA protein expression. RhoA expression is inherently increased in airway tissue from ob/ob mice, and obesity-entrained alterations in this pathway may make it a novel therapeutic target for treating airway disease in the obese population.

Calcium channel regulation in vascular smooth muscle cells: synergistic effects of statins and calcium channel blockers

In the Anglo-Scandinavian Cardiac Outcomes Trial-Lipid Lowering Arm (ASCOT-LLA) we have reported a positive interaction between atorvastatin and amlodipine-based antihypertensive strategy in terms of the prevention of coronary events. In cellular and molecular studies on human vascular smooth muscle cells (VSMC) we have reported that transformation from a differentiated to a synthetic or dedifferentiated phenotype is associated with loss of function of L-type calcium channels and hence loss of potential responsiveness to calcium channel blockers (CCB). Statins directly inhibit cell cycle progression and dedifferentiation of VSMC due to their ability to inhibit the synthesis of isoprenoid cholesterol intermediates. We hypothesize that statins promote a more differentiated VSMC phenotype that results in upregulation of L-type calcium channels and restoration of a CCB-sensitive calcium influx pathway in VSMC, favourably affecting the balance that exists between VSMC proliferation, apoptosis and matrix metalloproteinase production with an associated increase in stability of atheromatous plaques.

The SLC16 monocaboxylate transporter family

1. The monocarboxylate transporter (MCT, SLC16) family comprises 14 members, of which to date only MCT1-4 have been shown to carry monocarboxylates, transporting important metabolic compounds such as lactate, pyruvate and ketone bodies in a proton-coupled manner. The transport of such compounds is fundamental for metabolism, and the tissue locations, properties and regulation of these isoforms is discussed. 2. Of the other members of the MCT family, MCT8 (a thyroid hormone transporter) and TAT1 (an aromatic amino acid transporter) have been characterized more recently, and their physiological roles are reviewed herein. The endogenous substrates and functions of the remaining members of the MCT family await elucidation. 3. The MCT proteins have the typical twelve transmembrane-spanning domain (TMD) topology of membrane transporter proteins, and their structure-function relationship is discussed, especially in relation to the future impact of the single nucleotide polymorphism (SNP) databases and, given their ability to transport pharmacologically relevant compounds, the potential impact for pharmacogenomics.

Statins in nephrotic syndrome: a new weapon against tissue injury

The nephrotic syndrome is characterized by metabolic disorders leading to an increase in circulating lipoproteins levels. Hypertriglyceridemia and hypercholesterolemia in this case may depend on a reduction in triglyceride-rich lipoproteins catabolism and on an increase in hepatic synthesis of Apo B-containing lipoproteins. These alterations are the starting point of a self-maintaining mechanism, which can accelerate the progression of chronic renal failure. Indeed, hyperlipidemia can affect renal function, increase proteinuria and speed glomerulosclerosis, thus determining a higher risk of progression to dialysis. 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is the rate-limiting enzyme in cholesterol synthesis from mevalonate and its inhibitors, or statins, can therefore interfere with the above-mentioned consequences of hyperlipidemia. Statins are already well known for their effectiveness on primary cardiovascular prevention, which cannot be explained only through their hypolipemic effect. As far as kidney diseases are concerned, statin therapy has been shown to prevent creatinine clearance decline and to slow renal function loss, particularly in case of proteinuria, and its favorable effect may depend only partially on the attenuation of hyperlipidemia. Statins may therefore confer tissue protection through lipid-independent mechanisms, which can be triggered by other mediators, such as angiotensin receptor blockers. Possible pathways for the protective action of statins, other than any hypocholesterolemic effect, are: cellular apoptosis/proliferation balance, inflammatory cytokines production, and signal transduction regulation. Statins also play a role in the regulation of the inflammatory and immune response, coagulation process, bone turnover, neovascularization, vascular tone, and arterial pressure. In this study, we would like to provide scientific evidences for the pleiotropic effects of statins, which could be the starting point for the development of new therapeutical strategies in different clinical areas.

Statins and bone metabolism

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) are potent inhibitors of cholesterol biosynthesis. Cholesterol-lowering therapy using statins significantly reduces the risk of coronary heart disease. However, extensive use of statins leads to increases of other undesirable as well as beneficial effects, so-called pleiotropic effects. With respect to these effects, statins augment the expression of bone morphogenetic protein-2, a potent simulator of osteoblast differentiation and its activity, and promote mineralization by cultured osteoblasts, indicating that statins have an anabolic effect on bone. Chronic administration of statins in ovariectomized (OVX) rats modestly increases bone mineral density (BMD) of cancellous bone but not of compact bone. In clinical studies, there are conflicting results regarding the clinical benefits of this therapy for the treatment of osteoporosis. Observational studies suggest an association between statin use and reduction in fracture risk. Clinical trials reported no effect of statin treatment on BMD in hip and spine, and on bone turnover. Statins also may influence oral osseous tissues. Administration of statins in combination with osteoporosis therapy appears to improve alveolar bone architecture in the mandibles of OVX rats with maxillary molar extraction. Statins continue to be considered as potential therapeutic agents for patients with osteoporosis and possibly with periodontal disease. Development of new statins that are more specific and potent for bone metabolism will greatly increase the usefulness of these drugs for the treatment of bone diseases.

The Effect of HMG-CoA Reductase Inhibitors on Coenzyme Q10

The HMG-CoA reductase inhibitors, also known as statins, have an enviable safety profile; however, myotoxicity and to a lesser extent hepatotoxicity have been noted in some patients following treatment. Statins target several tissues, depending upon their lipophilicity, where they competitively inhibit HMG-CoA reductase, the rate-limiting enzyme for mevalonic acid synthesis and subsequently cholesterol biosynthesis. HMG-CoA reductase is also the first committed rate-limiting step for the synthesis of a range of other compounds including steroid hormones and ubidecarenone (ubiquinone), otherwise known as coenzyme Q(10) (CoQ(10)). Recent interest has focused on the possible role CoQ(10) deficiency may have in the pathophysiology of the rare adverse effects of statin treatment. Currently, there is insufficient evidence from human studies to link statin therapy unequivocally to pathologically significantly decreased tissue CoQ(10) levels. Although statin treatment has been reported to lower plasma/serum CoQ(10) status, few human studies have assessed tissue CoQ(10) status. The plasma/serum CoQ(10) level is influenced by a number of physiological factors and, therefore, has limited value as a means of assessing intracellular CoQ(10) status. In those limited studies that have assessed the effect of statin treatment upon tissue CoQ(10) levels, none have shown evidence of a fall in CoQ(10) levels. This may reflect the doses of statins used, since many appear to have been used at doses below those recommended for their maximum therapeutic effects. Moreover, the poor bioavailability in those peripheral tissues tested may not reflect the effects the agents are having in liver and muscle, the tissues commonly affected in those patients who do not tolerate statins. This article reviews the biochemistry of CoQ(10), its role in cellular metabolism and the available evidence linking possible CoQ(10) deficiency to statin therapy.

Mutual amplification of apoptosis by statin-induced mitochondrial stress and doxorubicin toxicity in human rhabdomyosarcoma cells

Besides their cholesterol-lowering effect, 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors (statins) show antiproliferative behaviour, which has been suggested as a promising anticancer strategy. However, the signalling cascades leading to statin-induced death of cancer cells are poorly characterized. Here we show that statins activate the mitochondrial pathway of apoptosis in rhabdomyosarcoma RD cells via translocation of Bax from the cytosol to mitochondria. The prototypical representative of statins, simvastatin, induced consecutive activation of caspase 9 and 3 in a concentration-dependent manner. The permeability transition pore inhibitor bongkrekic acid was capable of completely preventing simvastatin-induced caspase 9 and 3 activity, corroborating the mitochondrial pathway of apoptosis as the sole mechanism of statin action. Alternative pathways via death receptors, that is, caspase 8 or calpain activation, were not triggered by simvastatin. Simvastatin-treated RD cells could be completely rescued from apoptosis by the co-application of mevalonic acid, indicating that deprivation of cholesterol precursors is essential for statin-induced apoptosis. However, pretreatment with subthreshold concentrations of simvastatin was sufficient to augment doxorubicin toxicity via the mitochondrial apoptotic machinery. Moreover, the presence of doxorubicin increased the potency of simvastatin to trigger caspase activation. Taken together, these data highlight the therapeutic anticancer potential of statins and their additivity and mutual sensitization, in combination with doxorubicin in human rhabdomyosarcoma cells.

Inflammation, immunity, and HMG-CoA reductase inhibitors: statins as antiinflammatory agents?

According to traditional thinking, atherosclerosis results from passive lipid deposition in the vascular wall. Thus, therapies predominantly targeted lipid metabolism. The contemporary view of atherosclerosis, however, has broadened to include an active and complex role for inflammation, orchestrated in part by mediators of the immune system. This recognition prompted the question of whether antiinflammatory interventions might provide a novel avenue for the treatment of atherosclerosis. Uncertainties about the type of antiinflammatory regimen and appropriate patient selection currently hamper clinical investigation. Yet cardiovascular scientists have begun to address these questions at the bench, in experimental models, and indirectly in humans. Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A HMG-CoA reductase (statins) have emerged as promising tools with dual functions. Originally designed to target elevated lipids, the "traditional" cause of atherosclerosis, statins might also confer cardiovascular benefit by directly or indirectly modulating the inflammatory component of this prevalent disease. Yet controversy persists regarding the (clinical) relevance of these potential non-LDL-lowering "pleiotropic" functions of statins. This overview addresses the controversy by reviewing in vitro and in vivo evidence regarding statins as antiinflammatory agents.

Comparing myotoxic effects of squalene synthase inhibitor, T-91485, and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors in human myocytes

TAK-475 is a squalene synthase inhibitor, rapidly metabolized to T-91485 in vivo. We investigated the myotoxicities of T-91485 and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors in a human rhabdomyosarcoma cell line, RD, and in human skeletal myocytes. In differentiated RD cells, T-91485, atorvastatin (ATV) and simvastatin acid (SIM) inhibited cholesterol biosynthesis, with IC(50) values of 36, 2.8 and 3.8 nM, respectively. ATV and SIM decreased the intracellular ATP content, with IC(25) values (concentrations giving a 25% decrease in intracellular ATP content) of 0.61 and 0.44 microM, respectively. Although T-91485 potently inhibited cholesterol synthesis in RD cells, the IC(25) value exceeded 100 microM. In human skeletal myocytes, T-91485, ATV and SIM concentration-dependently inhibited cholesterol biosynthesis, with IC(50) values of 45, 8.6 and 8.4 nM, respectively. ATV and SIM decreased intracellular ATP content, with IC(25) values of 2.1 and 0.72 microM, respectively. Although T-91485 potently inhibited cholesterol synthesis, the IC(25) value exceeded 100 microM. Myotoxicity induced by ATV was prevented by mevalonate or geranylgeranyl-PP, but not by squalene in skeletal cells. Furthermore, T-91485 attenuated the myotoxicity of ATV. These findings suggest that TAK-475 and T-91485 may not only be far from myotoxic, they may also decrease statin-induced myotoxicity in lipid-lowering therapy.

Statin-exposed vascular smooth muscle cells secrete proteoglycans with decreased binding affinity for LDL

Retention of LDL in the artery intima is mediated by extracellular matrix proteoglycans and plays an important role in the initiation of atherosclerosis. Compared with quiescent cells, proliferating smooth muscle cells secrete proteoglycans with elongated glycosaminoglycan side chains, which have an increased binding affinity to LDL. Because 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors (statins) decrease smooth muscle cell proliferation, we hypothesized that statin exposure would decrease both the size and LDL binding affinity of vascular proteoglycans. Monkey aortic smooth muscle cells grown in culture were exposed to simvastatin (10 and 100 microM) and cerivastatin (0.1 and 1 microM), and newly secreted proteoglycans were quantified and characterized. Both simvastatin and cerivastatin caused a concentration-dependent reduction in cell growth and reduced 35SO4 incorporation into secreted proteoglycans, on both an absolute and a per cell basis. Interestingly, statin exposure increased the apparent molecular weight and hydrodynamic size of secreted proteoglycans. However, proteoglycans secreted from statin-exposed cells demonstrated a reduction in binding affinity to LDL. Thus, statins may induce atheroprotective changes in vascular proteoglycans and lower LDL retention in the vessel wall. These findings suggest a mechanism whereby statins may benefit atherosclerosis in a manner unrelated to serum LDL lowering.

Inhibition of hydroxymethylglutaryl-coenzyme a reductase reduces Th1 development and promotes Th2 development

Several prospective clinical studies have indicated that hydroxymethylglutaryl-coenzyme A reductase inhibitors, statins, prevent cardiovascular events in part through their antiinflammatory properties. Because inflammation is positively and negatively regulated by T helper (Th) 1 cells and Th2 cells, respectively, we examined the effects of statins on the Th polarization in vitro and in vivo. Here we demonstrated that the statins tested, ie, cerivastatin, simvastatin, lovastatin, and atorvastatin, promoted Th2 polarization through both inhibition of Th1 development and augmentation of Th2 development of CD4+ T cells primed in vitro with anti-CD3 antibody and splenic antigen-presenting cells. Cerivastatin exerted most potent effect on modulation of Th1/Th2 development, and the effect was completely abrogated by an addition of mevalonate. Consistent with in vitro experiments, cerivastatin treatment decreased IFN-gamma production of lymph node cells from mice immunized with ovalbumin emulsified in complete Freund's adjuvant, indicating that Th1 development is also suppressed in an in vivo proinflammatory environment. In this murine model, cerivastatin significantly reduced mesangial matrix expansion of glomeruli in the kidney and attenuated proteinuria. The decrease of glomerular sclerosis by cerivastatin treatment was positively related to the suppression of interferon (IFN)-gamma-producing Th1 response in draining lymph node cells. Hence, these findings strongly suggest that statins' inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase regulates Th1/Th2 polarization in vivo and such a mechanism possibly plays a pathophysiological role in immune-related glomerular injury.

C-reactive protein, inflammation, and coronary risk

Advancements in understanding of the pathobiology of atherothrombosis have implicated inflammation as a central contributor to the progression of atherosclerotic vascular disease. Epidemiologic data demonstrate an association between the inflammatory marker hs-CRP and risk for future cardiovascular morbidity and mortality among those at high risk or with documented vascular disease. Moreover, a series of prospective studies provides consistent data documenting that mild elevation of baseline levels of hs-CRP among apparently healthy individuals is associated with higher long-term risk for future cardiovascular events. Among men and women, this predictive capacity of hs-CRP is independent of traditional cardiovascular risk factors and offers a prognostic advantage over measurement of lipids alone. Further, observations from the PHS and CARE trial suggest that the increased risk associated with systemic inflammation may be modified with certain preventive therapies and that inflammatory markers such as hs-CRP may help to identify those who would benefit most from these pharmacologic interventions. Given that high-throughput assays for inflammatory markers, including hs-CRP, are likely to become available for clinical use, carefully designed studies are needed to evaluate the clinical efficacy of hs-CRP as a new marker to stratify cardiovascular risk. Further, prospective, randomized trials are important to test directly the value of inflammatory markers in targeting specific preventive therapies. Finally, it is still undetermined as to whether elevation of these inflammatory markers reflects the degree of underlying atherosclerosis or plaque vulnerability or rather results from some other environmental or infectious stimulus or even has direct effects on platelet aggregation or coagulation [1]. Ongoing and future investigation will clarify the specific pathophysiologic relationships through which these markers correlate with adverse prognosis.

Effects of cerivastatin on human arterial smooth muscle cell growth and extracellular matrix expression at varying glucose and low-density lipoprotein levels

Statins exert pleiotropic effects on several other cellular functions besides lipid-lowering. Previously, it was found that cerivastatin is a very potent inhibitor of human arterial smooth muscle cell (haSMC) growth. However, because increased extracellular matrix (ECM) synthesis also accounts mainly for intimal plaque formation, the effects of cerivastatin on ECM expression was examined in this study. Furthermore, the influence of varying glucose and low-density lipoprotein (LDL) levels on cerivastatin-treated haSMCs was analyzed to mimic the conditions in patients with diabetes or hypercholesterolemia. The haSMCs were treated with 0.001-5.0 microM cerivastatin in the presence of 5.5-18.9 m glucose and 10-1000 microg/ml LDL. After 3 days, the messenger RNA (mRNA) expression of eight ECM proteins was analyzed and, after 7 days, mitotic and mitochondrial activities and thrombospondin (TSP)-1 protein expression were analyzed. TSP-1 and TSP-2 mRNA expression was inhibited highly significantly at cerivastatin doses >or=0.01 microM with maximums of 72% and 35%, respectively, at high glucose levels. The mRNA signals of the third glycoprotein fibronectin were not influenced. Furthermore, collagen-1 mRNA was inhibited highly significantly up to 71% and biglycan mRNA was similarly inhibited up to 45%. The mRNA expression of the matrix-stimulating transforming growth factor (TGF)-beta1 and matrix metalloproteinase (MMP)-2 was not altered significantly, whereas mRNA expression of the tissue inhibitor of metalloproteinase (TIMP)-2 was stimulated clearly up to 150%. Mevalonate, but not LDL replacement, reversed the effects. Immunofluorescence staining showed an unaltered TSP-1 pattern with cerivastatin doses up to 0.1 microM whereas higher doses impaired TSP-1 excretion. The effects of cerivastatin on haSMC growth and mRNA expression of the eight ECM components were not diminished by the increase in LDL and glucose levels. Since accelerated SMC growth and ECM formation contribute mainly to intimal thickening, cerivastatin may be protective against the development of atherosclerotic and restenotic lesions by its direct cellular effects. Increased LDL and glucose levels, as in diabetes, do not mitigate the beneficial effects of cerivastatin on cell growth and ECM formation in vitro.

Statins and progressive renal disease

Thanks to the administration of hypocholesterolemic drugs, important advances have been made in the treatment of patients with progressive renal disease. In vitro and in vivo findings demonstrate that statins, the inhibitors of HMG-CoA reductase, can provide protection against kidney diseases characterized by inflammation and/or enhanced proliferation of epithelial cells occurring in rapidly progressive glomerulonephritis, or by increased proliferation of mesangial cells occurring in IgA nephropathy. Many of the beneficial effects obtained occur independent of reduced cholesterol levels because statins can directly inhibit the proliferation of different cell types (e.g., mesangial, renal tubular, and vascular smooth muscle cells), and can also modulate the inflammatory response, thus inhibiting macrophage recruitment and activation, as well as fibrosis. The mechanisms underlying the action of statins are not yet well understood, although recent data in the literature indicate that they can directly affect the proliferation/apoptosis balance, the down-regulation of inflammatory chemokines, and the cytogenic messages mediated by the GTPases Ras superfamily. Therefore, as well as reducing serum lipids, statins and other lipid-lowering agents may directly influence intracellular signaling pathways involved in the prenylation of low molecular weight proteins that play a crucial role in cell signal transduction and cell activation. Statins appear to have important potential in the treatment of progressive renal disease, although further studies are required to confirm this in humans.

Diverse effects of inhibition of 3-hydroxy-3-methylglutaryl-CoA reductase on the expression of VCAM-1 and E-selectin in endothelial cells

The expression of monocyte adhesion molecules, such as VCAM-1 (vascular cell adhesion molecule-1) and E-selectin, on the surface of the endothelium is an important step in the initiation and progression of atherosclerotic lesions. We hypothesized that the inhibition of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase in endothelial cells could influence the expression of VCAM-1 and E-selectin. Using cultured human umbilical vein endothelial cells, we found that mevastatin (0.1-1 microM) significantly reduced the expression of VCAM-1 protein in cells activated by tumour necrosis factor-alpha (TNF-alpha) for 7 h. In contrast, TNF-alpha-induced E-selectin protein expression was augmented after mevastatin treatment. Mevastatin inhibited the mRNA expression of both VCAM-1 and E-selectin in TNF-alpha-stimulated endothelial cells. The activity of the transcription factor nuclear factor-kappa B, which is known to regulate the transcription of VCAM-1 and E-selectin, was significantly reduced after incubation with mevastatin. Analysis of the time-dependent variation in the TNF-alpha-induced expression of E-selectin, and estimation of the rate of surface disappearance of E-selectin together with measurement of the amounts of E-selectin molecules secreted, indicated that mevastatin inhibited the surface removal of E-selectin. This is compatible with the observed increase in E-selectin expression after statin treatment. All observed effects of mevastatin were reversed by mevalonate, the product of the HMG-CoA reductase reaction. In conclusion, inhibition of HMG-CoA reductase in endothelial cells attenuates VCAM-1 expression, but increases E-selectin expression, after cytokine induction. These diverse effects are associated with changes in the transcriptional regulation of the two adhesion molecule genes and modulation of the surface removal of E-selectin.

Pravastatin suppresses the interleukin-8 production induced by thrombin in human aortic endothelial cells cultured with high glucose by inhibiting the p44/42 mitogen activated protein kinase

1. 3-Hydroxy-3-methylglutaryl co-enzyme A reductase inhibitors (statins) prevent the progression of atherosclerosis by lowering cholesterol. However, the effect of statins on the synthesis of pro-inflammatory cytokines from endothelial cells has not yet been fully investigated. Here, we examined the effect of pravastatin, one of the statins, on IL-8 synthesis induced by thrombin in human aortic endothelial cells (AoEC) cultured with high glucose concentrations. 2. Pravastatin significantly decreased the IL-8 synthesis induced by thrombin. 3. Pravastatin inhibited the p44/42 MAP kinase activity induced by thrombin, but did not inhibit the p38 MAP kinase activity. 4. Translocation of ras protein from the cytosol to plasma membrane was inhibited by pravastatin. 5. Pravastatin inhibit the activator protein-1 activity, but did not inhibit the activation of IkappaB-alpha. 6. Dominant negative ras inhibited the p44/42 MAP kinase activity induced by PMA. 7. Our results suggest that pravastatin inhibits IL-8 synthesis by blocking the ras-MAP (p44/42) kinase pathway rather than nuclear factor-kappaB. Pravastatin may prevent atherosclerosis not only by lowering cholesterol levels, but also by suppressing IL-8 synthesis in AoEC through the inhibition of p44/42 MAP kinase, and this may be more beneficial in diabetic patients than in non-diabetics.

Action of an HMG CoA reductase inhibitor, lovastatin, on apoptosis of untransformed and ts-SV40 transformed human smooth muscle cells derived from saphenous vein

The effect of lovastatin, an inhibitor of 3-hydroxymethyl-3-glutaryl coenzyme A (HMG CoA) reductase, was examined on human vascular smooth muscle cells (HVSMC). Untransformed HVSMC were obtained from saphenous vein and in addition an SV-40 transformed immortalized cell line (HVTs-SM1) derived from saphenous vein smooth muscle was also used. HVTs-SM1 cell proliferation and DNA synthesis were measured, and cell cycle analysis was performed by flow cytometry. Apoptosis in both cell types was assessed by a combination of flow cytometry, terminal deoxynucleotidyl transferase (TUNEL) reagent-based immunocytochemistry, DAPI staining, and DNA agarose gel electrophoresis. Lovastatin had no effect on apoptosis of HVSMC over 96 h in serum-free conditions or after stimulation with platelet-derived growth factor (PDGF-BB), although PDGF-BB increased apoptosis in HVSMC, and this was prevented by lovastatin. In HVTs-SM1 cells lovastatin inhibited cell proliferation and DNA synthesis and induced apoptosis in a time- and concentration-dependent manner. The effects of lovastatin on cell proliferation, DNA synthesis, and apoptosis were prevented by coincubation with mevalonate and geranylgeranyl pyrophosphate, but not by farnesyl pyrophosphate. Lovastatin does not induce apoptosis in saphenous vein HVSMC in culture and inhibits PDGF-BB-induced DNA synthesis and apoptosis. In contrast, in SV40 transformed immortalized HVTs-SM1 cells, lovastatin induces apoptosis and inhibits cell proliferation and DNA synthesis. The pro-apoptotic effects of lovastatin in SV40 transformed HVTs-SM1 cells may be related to the enhanced rate of proliferation or deregulation of the cell cycle in this cell line.

Apoptosis in atherosclerosis: pathological and pharmacological implications

Normal embryonic development, tissue differentiation and repair in the eukaryote requires a tightly regulated apoptosis, or programmed cell death. Apoptosis also plays an essential role in different pathological processes including atherosclerosis, in which it affects all cell types in the atherosclerotic lesion, including endothelial cells, vascular smooth muscle cells, and macrophages. During atherosclerosis progression, pro- and anti-apoptotic signals abound in the evolving lesion. Apoptosis limits the number of a particular cell type that accumulates in the lesion and slows down the overall progression of the lesion. On the other hand, it contributes to the production of unstable plaques. Many pharmacological agents used to treat cardiovascular and lipid disorders have pro- or/and anti-apoptotic effects. Pharmaceuticals that modulate apoptosis in specific types of cell can potentially serve as anti-atherogenic agents. However, to develop agents for clinical use requires a thorough knowledge of the pathophysiology of apoptosis in atheromatous lesions, a highly cell-specific process. Here we review our current understanding of the process to provide a background for future pharmacological research in the area.

Lovastatin blocks basic fibroblast growth factor-induced mitogen-activated protein kinase signaling in coronary smooth muscle cells via phosphatase inhibition

We have recently reported that the activation of mitogen-activated protein kinase (MAPK) through specific protein kinase C (PKC) isoforms is required for basic fibroblast growth factor (bFGF)-induced proliferation of coronary smooth muscle cells (cSMC). In this study, we investigated the effects of the 3hydroxy-3-methyl glutaryl coenzyme A (HMG CoA) reductase inhibitor lovastatin on bFGF-induced signal transduction in cSMC. The present study shows that lovastatin inhibits bFGF-stimulated DNA synthesis in cSMC, and that this inhibition is reversed by mevalonate (50 micromol/l) and by geranylgeranyl-pyrophosphate (1-5 micromol/l). Although lovastatin prevented Ras farnesylation the amount of bFGF-stimulated MAPK phosphorylation decreased only partially after lovastatin treatment. In addition, lovastatin pretreatment resulted in a sustained phosphorylation of MAPK. We observed a dose-dependent lovastatin-dependent increase in PKC activity, which could be prevented by mevalonate. This increase was comparable to the one induced by calyculin A (2 nmol/l), an inhibitor of protein phosphatase PP-1 and PP-2A. Lovastatin inhibited the expression of the PP-1 protein, which is involved in bFGF-induced DNA synthesis in cSMC. Thus, our data suggest that, lovastatin possibly affects the dephosphorylation processes of PKC and MAPK by inhibition of PP-1/PP-2A protein phosphatases which are involved in the bFGF-induced mitogenesis in cSMC.

Lovastatin induces apoptosis in a primitive neuroectodermal tumor cell line in association with RB down-regulation and loss of the G1 checkpoint

To develop a new approach to the treatment of primitive neuroectodermal tumors we evaluated the effect of the HMG-CoA reductase inhibitor lovastatin on the Ewing's sarcoma cell line CHP-100. Lovastatin induced neural morphology and markers including neuron-specific enolase and neurofilament protein. The acquisition of neural morphology required new mRNA synthesis, and cDNA microarray analysis confirmed that lovastatin altered the program of gene expression. After morphologic differentiation the cells underwent rapidly progressive apoptosis. In normal development of neuronal progenitors, differentiation signals trigger p21WAF1 accumulation, RB hypophosphorylation, enhanced RB-E2F-1 association, and G1 arrest, and these events have been shown to protect from apoptosis. In contrast, in the Ewing's sarcoma cells lovastatin triggered differentiation without causing cell cycle arrest: p21WAF1 was not induced, RB remained hyperphosphorylated, and RB protein expression and RB-E2F-1 association were markedly downregulated, suggesting that loss of an RB-regulated G1 checkpoint promoted apoptosis. Consistent with this hypothesis, adenoviral p21WAF1 decreased DNA synthesis and partially protected from lovastatin-induced cytotoxicity. The data demonstrate a new model for examining the genetic regulation of cell fate in a neural progenitor tumor and suggest a new approach to the treatment of this neoplasm.

PPAR agonists as direct modulators of the vessel wall in cardiovascular disease

Successful management of cardiovascular (CV) disease and associated metabolic syndromes, such as diabetes, is a major challenge to the clinician. Reducing CV risk factors, such as abnormal lipid profiles, insulin resistance or hypertension is the foundation of such therapy. A relatively new class of therapeutic agent, activators of peroxisome proliferator-activated receptors (PPAR), is poised to make a major impact with regard to several areas of risk factor management. However, there is growing evidence that PPAR agonists may also influence the CV system directly by modulating vessel wall function. These observations suggest that additional benefit, in the treatment of CV disease, may derive not only from the ability of agents to modify risk factors but also to influence directly the cellular mechanisms of disease within the vessel wall. A precedent for this dual action comes from examination of the effects of inhibitors of HMG CoA reductase (statins), where risk factor modulation is accompanied by direct actions on the vessel wall. In this review, we summarize the evidence suggesting that PPAR agonists may directly modulate vessel wall function, and that these may parallel those effects reported recently for the statins.

L-arginine supplementation in hypercholesterolemic rabbits normalizes leukocyte adhesion to non-endothelial matrix

L-arginine slows the development of atheromatous lesions, improves endothelium-dependent relaxation, and reduces the vascular superoxide anion production in hypercholesterolemic rabbits. These beneficial effects have been attributed to L-arginine-dependent formation of nitric oxide within the endothelial layer; a direct effect of L-arginine on other cells, however, has not been investigated. We hypothesised that in hypercholesterolemia L-arginine also specifically acts via a direct inhibitory effect on leukocytes, without affecting endothelial cells. The action of L-arginine was compared to vitamin E and the HMG CoA reductase inhibitor lovastatin which are known to attenuate progression of atherosclerosis. Rabbits were fed cholesterol enriched diet and from week five on lovastatin (10 mg/day), vitamin E (300 mg/d) or L-arginine (2% in drinking water) were given. After 16 weeks, blood cholesterol concentration was determined and leukocyte adhesion to cotton wool was measured. In order to exclude any endothelium-mediated effects an adhesion assay to endothelial cells was avoided. Cholesterol-enriched diet increased plasma cholesterol concentration (19+/-3 vs. 1427+/-117 mg/dl). Cholesterol levels were not affected by L-arginine (1344+/-163 mg/dl) or vitamine E (1312+/-243 mg/dl). Lovastatin treatment reduced cholesterol concentration by 35% as compared to the cholesterol group (899+/-51, p<0.05 vs. cholesterol). Cholesterol diet significantly increased leukocyte adhesion to cotton wool (16+/-3% vs 27+/-4%, p<0.05). Lovastatin or vitamine E had no effect on leukocyte adhesion (31+/-4%, 39+/-5), whereas L-arginine completely normalized adhesion (8.8+/-3%).

CONCLUSION

Rabbits fed high cholesterol diet have increased leukocyte adhesion, which is not affected by lovastatin or vitamine E treatment, but prevented by L-arginine supplementation. A direct inhibitory effect of L-arginine on leukocyte adhesion may contribute to the beneficial effects observed with this substance.

Simvastatin attenuates vascular hypercoagulability in cardiac transplant recipients

BACKGROUND

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors have been shown to reduce cardiac allograft failure and to lower the incidence of transplant coronary artery disease. These effects result from as yet unknown mechanisms not clearly attributable to lipid lowering. We here report that low-dose simvastatin treatment inhibits excessive expression of monocyte tissue factor (TF) and reduces the persistent hypercoagulability state seen in cardiac transplant recipients.

METHODS

Fifteen consecutive heart transplant recipients receiving standard oral immunosuppression were newly assigned to a 10 mg daily simvastatin therapy. Levels of TF activity in both unstimulated and lipopolysaccharide-stimulated peripheral blood mononuclear cells drawn from transplant recipients before and under simvastatin therapy were evaluated by one-stage clotting assay.

RESULTS

Monocyte TF activity was found to be significantly increased in cardiac transplant recipients when compared with healthy controls. Excessive monocyte procoagulant activity was reduced in cardiac transplant recipients during simvastatin treatment. This effect occurred independently of the reduction of serum low-density lipoprotein cholesterol. As demonstrated by reverse transcriptase-polymerase chain reaction, monocyte TF reduction by simvastatin, observed in 13 of the 15 transplant recipients investigated, could be ascribed to an inhibition of monocyte TF gene transcription. The reduction of monocyte TF activity during treatment with simvastatin paralleled with the normalization of elevated levels of thrombin-antithrombin complex, prothrombin fragment F1+2, and D-dimer, which are markers of thrombin and fibrin formation indicating coagulation activation after cardiac transplantation.

CONCLUSION

Inhibition of monocyte TF expression and attenuation of the persistent hypercoagulable state observed in cardiac transplant recipients during treatment with simvastatin may represent an important mechanism by which HMG-CoA reductase inhibitors protect against the development of transplant coronary artery disease.

Effect of lovastatin on cerebral circulation in spontaneously hypertensive rats

Statins, which are often given to hypertensive patients, reduce the incidence of stroke. However, their effects on the cerebral circulation have been scarcely studied, although lovastatin has been reported to reduce hypertension-induced renal arteriolar hypertrophy. We examined the structure and mechanics of cerebral arterioles and the lower limit of cerebral blood flow (CBF) autoregulation in spontaneously hypertensive rats (SHR) that were untreated (n=9) or treated for 1 month with lovastatin (n=12; 20 mg x kg(-1) x d(-1)) and in untreated Wistar-Kyoto rats (WKY; n=8). We studied the lower limit of CBF autoregulation by repeated measurement of CBF (arbitrary units; laser Doppler) and internal arteriolar diameter (microm; cranial window) at baseline and during stepwise hypotension. Stress-strain relationships were calculated from repeated measurement of internal arteriolar diameter during stepwise hypotension and cross-sectional area (CSA) of the vessel wall in maximally dilated cerebral arterioles (EDTA, 67 mmol/L). Lovastatin slightly reduced mean arterial pressure (treated, 153+/-3 versus untreated, 171+/-5 mm Hg, P<0.05; WKY, 106+/-3 mm Hg) and normalized CSA (treated, 826+/-52 versus untreated, 1099+/-16 microm(2), P<0. 05; WKY, 774+/-28 microm(2)). Stress-strain curves show that lovastatin also attenuated the increase in passive distensibility. Lovastatin had no effect on the external diameter of cerebral arterioles or the lower limit of CBF autoregulation. Our results show that although lovastatin has substantial effects on arteriolar mechanics and wall CSA, it has little effect on internal diameter. This phenomenon may explain its lack of effect on CBF autoregulation.

Effects of cerivastatin on human arterial smooth muscle cell proliferation and migration in transfilter cocultures

Statins competitively inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity reducing mevalonate synthesis. In this study, antiproliferative and antimigratory effects of the new compound cerivastatin were analyzed and compared with classic statins of the first and second generation using mono- and cocultures of human arterial smooth muscle (haSMC) and endothelial (haEC) cells. Effects on the mitotic index and mitochondrial activity of haEC and haSMC monocultures were tested using BrdU enzyme-linked immunosorbent assay (ELISA) and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) tests, respectively. In lactate dehydrogenase (LDH) assays, cytotoxicity of statins was studied. Transfilter cocultures were performed for 14 days to evaluate haSMC growth under the stimulatory effect of proliferating haEC, which release growth factors [e.g., platelet-derived growth factor (PDGF)]. The hydrophobic statins simvastatin, lovastatin, and atorvastatin significantly inhibited haSMC and haEC growth in monocultures at 0.5-50 microM. However, most potent effects were exerted by cerivastatin in 10- to 30-fold lower doses without any significant cytotoxicity. More important, cerivastatin showed also significant effects on haSMC proliferation and migration in transfilter cocultures at extremely low doses (IC50, 0.04-0.06 microM), even when applied exclusively to the endothelial side and in the presence of low-density lipoprotein (LDL). Addition of mevalonate abolished the effects of cerivastatin completely. Even in the presence of growth-stimulating haEC and LDL, cerivastatin was found to be the most potent inhibitor of haSMC proliferation and migration in doses that also can be reached in human serum after oral drug administration. The results support the concept that statins seems to influence additional cellular mechanisms beyond cholesterol reduction, which might also have a relevance for the prevention of restenosis.

Improvement of nitric oxide-dependent vasodilatation by HMG-CoA reductase inhibitors through attenuation of endothelial superoxide anion formation

Three 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (HCRIs), atorvastatin, pravastatin, and cerivastatin, inhibited phorbol ester-stimulated superoxide anion (O(2)(-)) formation in endothelium-intact segments of the rat aorta in a time- and concentration-dependent manner (maximum inhibition of 70% after 18 hours at 1 to 10 micromol/L). The HMG-CoA reductase product mevalonic acid (400 micromol/L) reversed the inhibitory effect of the HCRIs, which, conversely, was mimicked by inactivation of p21 Rac with Clostridium sordellii lethal toxin but not by inactivation of p21 Rho with Clostridium botulinum exoenzyme (C3). A mevalonate-sensitive inhibition of phorbol ester-stimulated O(2)(-) formation by atorvastatin was also observed in porcine cultured endothelial cells and in a murine macrophage cell line. In the rat aorta, no effect of the HCRIs on protein kinase C, NADPH oxidase, or superoxide dismutase (SOD) activity and expression was detected, whereas that of endothelial nitric oxide (NO) synthase was enhanced approximately 2-fold. Moreover, exposure of the segments to atorvastatin resulted in a significant improvement of endothelium-dependent NO-mediated relaxation, and this effect was abolished in the presence of SOD. Taken together, these findings suggest that in addition to augmenting endothelial NO synthesis, HCRIs inhibit endothelial O(2)(-) formation by preventing the isoprenylation of p21 Rac, which is critical for the assembly of NADPH oxidase after activation of protein kinase C. The resulting shift in the balance between NO and O(2)(-) in the endothelium improves endothelial function even in healthy blood vessels and therefore may provide a reasonable explanation for the beneficial effects of HCRIs in patients with coronary heart disease in addition to or as an alternative to the reduction in serum LDL cholesterol.

C-reactive protein, inflammation, and coronary risk

Data have revealed interactions between baseline concentration of hs-CRP and the efficacy of common pharmacologic therapies in primary and secondary prevention, suggesting not only that it may be possible to modify the increased risk associated with elevated hs-CRP, but also that inflammatory markers may be useful in targeting preventive therapies. Inflammatory markers may become a valuable component of routine cardiovascular risk assessment.

HMG CoA reductase inhibitors are related to improved systemic endothelial function in coronary artery disease

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase (statins) may enhance vascular endothelial function independent of their cholesterol lowering effect. To test this hypothesis, we surveyed two groups of patients (age 55+/-7, mean+/-SD) with coronary artery disease that were matched for age, blood pressure and serum lipid levels. Group 1 comprised 23 men without lipid-lowering medication and Group 2 included 22 patients with ongoing HMG CoA reductase inhibitor medication. Flow-mediated (endothelium-dependent) arterial dilatation (FMD) and nitrate-mediated (smooth muscle dependent) dilatation (NMD) were measured in the brachial artery using high resolution ultrasound. FMD was considerably higher in group 2 (4.3+/-2.6 vs. 2.6+/-2.8%; P<0.05). In multivariate regression model, statin use was the only significant (P<0.05) predictor of FMD. In all subjects, FMD correlated with statin dose (P<0.05 for trend). NMD was non-significantly higher in group 2 (11.4+/-5.0 vs. 9.0+/-4.2%, P=0. 08). We conclude that patients with established coronary artery disease on HMG CoA reductase inhibitor therapy have better vascular endothelial function than similar patients without the medication. These data provide further support for the idea that HMG CoA reductase inhibitors enhance endothelial function independent of their lipid-lowering effects. This may suggest that these drugs could be beneficial in secondary prevention of coronary artery disease regardless of the serum cholesterol concentration.

New insights into the pharmacodynamic and pharmacokinetic properties of statins

The beneficial effects of statins are assumed to result from their ability to reduce cholesterol biosynthesis. However, because mevalonic acid is the precursor not only of cholesterol, but also of many nonsteroidal isoprenoid compounds, inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase may result in pleiotropic effects. It has been shown that several statins decrease smooth muscle cell migration and proliferation and that sera from fluvastatin-treated patients interfere with its proliferation. Cholesterol accumulation in macrophages can be inhibited by different statins, while both fluvastatin and simvastatin inhibit secretion of metalloproteinases by human monocyte-derived macrophages. The antiatherosclerotic effects of statins may be achieved by modifying hypercholesterolemia and the arterial wall environment as well. Although statins rarely have severe adverse effects, interactions with other drugs deserve attention. Simvastatin, lovastatin, cerivastatin, and atorvastatin are biotransformed in the liver primarily by cytochrome P450-3A4, and are susceptible to drug interactions when co-administered with potential inhibitors of this enzyme. Indeed, pharmacokinetic interactions (e.g., increased bioavailability), myositis, and rhabdomyolysis have been reported following concurrent use of simvastatin or lovastatin and cyclosporine A, mibefradil, or nefazodone. In contrast, fluvastatin (mainly metabolized by cytochrome P450-2C9) and pravastatin (eliminated by other metabolic routes) are less subject to this interaction. Nevertheless, a 5- to 23-fold increase in pravastatin bioavailability has been reported in the presence of cyclosporine A. In summary, statins may have direct effects on the arterial wall, which may contribute to their antiatherosclerotic actions. Furthermore, some statins may have lower adverse drug interaction potential than others, which is an important determinant of safety during long-term therapy.

Atorvastatin reduces NF-kappaB activation and chemokine expression in vascular smooth muscle cells and mononuclear cells

Cardiovascular mortality, mainly due to the rupture of unstable atherosclerotic plaques, is reduced by 3-hydroxy-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors. Inflammatory cells, attracted to the vascular lesion by chemokines, have been implicated in the process of the plaque rupture. In cultured vascular smooth muscle cells (VSMC) and U937 mononuclear cells we have studied the effect of Atorvastatin (Atv) on nuclear factor kappaB (NF-kappaB) activity, an inducer of the mRNA expression of chemokines such as interferon-inducible protein 10 (IP-10) and monocyte chemoattractant protein 1 (MCP-1). Angiotensin II (Ang II) and tumor necrosis factor alpha (TNF-alpha) increased NF-kappaB activity in VSMC (2 and 5-fold, respectively). Preincubation of cells with 10(-7) mol/l Atv diminished this activation (44 and 53%). The inhibition was reversed by mevalonate, farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP), but not by other isoprenoids. Coinciding with the NF-kappaB activation in VSMC, there was a diminution of cytoplasmic IkappaB levels that was recovered by pretreatment with Atv. Ang II and TNF-alpha induced the expression of IP-10 (1.5 and 3.4-fold) and MCP-1 (2.4 and 4-fold) in VSMC. Atv reduced this overexpression around 38 and 35% (IP-10), and 54 and 39% (MCP-1), respectively. Our results strongly suggest that Atv, through the inhibition of NF-kappaB activity and chemokine gene expression, could reduce the inflammation within the atherosclerotic lesion and play a role in the stabilization of the lesion.

Short-term pravastatin mediates growth inhibition and apoptosis, independently of Ras, via the signaling proteins p27Kip1 and P13 kinase

Growth factor-stimulated DNA synthesis in a variety of cell lines has been shown to be decreased after overnight (or longer) treatment with the 3-hydroxy-3-methylglutaryl CoA reductase inhibitors, the statins. Although this anti-mitogenic effect had been presumed to be the result of the impairment of Ras lipidation, a stable modification (T1/2 approximately 20 h), this study provides new data demonstrating that brief (approximately 1 h) pretreatment of rat vascular smooth muscle cells with 100 microM pravastatin before platelet-derived growth factor-BB (PDGF-BB) stimulation results in attenuation of DNA synthesis through a Ras-independent mechanism. PDGF-BB-stimulated PDGF-beta receptor tyrosine phosphorylation, Ras activity, and mitogen-activated protein/extracellular signal-regulated kinase activity are unaffected by from 10 min to 1 h of pravastatin incubation, while Raf activity is markedly increased after 1 h of pravastatin. Phosphatidylinositol-3 kinase activity and phosphorylation of its downstream effector Akt are decreased after 1 h pravastatin incubation. Rho is stabilized by pravastatin, and ADP-ribosylation of Rho by C3 exoenzyme decreases PDGF-stimulated phosphatidylinositol-3 kinase activity, mimicking the effect of pravastatin on this signaling protein. Levels of the cyclin-dependent kinase inhibitor p27Kip1 are increased when cells were preincubated with pravastatin for 1 h and then exposed to PDGF, and apoptosis is induced by pravastatin incubation times as short as 1 to 4 h. Thus, short-term, high-dose pravastatin inhibits vascular smooth muscle cell growth and induces apoptosis independently of Ras, likely by means of the drug's effect on p27Kip1, mediated by Rho and/or phosphatidylinositol-3 kinase. This work demonstrates for the first time that the statins may be therapeutically useful when applied for short periods of time such that potential toxicity of long-term statin use (such as chronic Ras inhibition) may be avoided, suggesting future therapeutic directions for statin research.

Differential effects of pravastatin, simvastatin, and atorvastatin on Ca2+ release and vascular reactivity

The direct effects of the cholesterol-lowering agents, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG CoA) reductase inhibitors, on vascular smooth muscle responsiveness were examined by incubation of isolated aorta from normocholesterolemic rats with simvastatin, atorvastatin, or pravastatin. The smooth muscle contractions caused by phenylephrine were progressively inhibited with increasing concentrations of simvastatin. Similarly, atorvastatin at the higher concentration caused decreased responses to phenylephrine. In contrast, incubation with pravastatin had no significant effect at all concentrations studied. In Ca2+-free buffer, the transient contraction caused by phenylephrine, which results from intracellular release of Ca2+, also was inhibited by simvastatin and atorvastatin but not by pravastatin. In cultured rat aortic smooth muscle cells loaded with fura-2, increases in intracellular free-Ca2+ concentration ([Ca2+]i) induced by angiotensin II were markedly inhibited in cells incubated with simvastatin and atorvastatin but not pravastatin. The inhibitory effects of simvastatin and atorvastatin were reversed by mevalonate. These findings demonstrate that inhibition of HMG CoA reductase by using simvastatin and atorvastatin, but not pravastatin, has effects on vascular smooth muscle cell responsiveness that involve alteration of Ca2+ homeostasis through a mevalonate-dependent pathway.

Recent advances in statins and the kidney

BACKGROUND

Experimental and clinical studies have suggested a correlation between the progression of renal disease and dyslipidemia. Indeed, apolipoprotein B-containing lipoproteins have been demonstrated to be an independent risk factor for the progression of renal disease in humans. Interventional strategies in experimental models of renal disease have clearly demonstrated a beneficial effect on renal structure and function in a variety of models of renal disease. Investigations into the mechanisms whereby reduction of lipids by lipid-lowering agents benefits renal disease have suggested that the 3-hydroxy-3-methylglutaryl coenzyme reductase inhibitors, the so-called statin class of lipid-lowering agents, may have additional effects on the biology of inflammation that are germane to the progression of renal disease.

METHODS

Both in vivo and in vitro studies that investigated secondary mechanisms of statin effects are reviewed. In addition, new studies that investigated the effects on novel cellular mechanisms are presented.

RESULTS

Lipid-lowering agents appear to have biologically important effects in modulating a variety of intracellular signaling systems involved in cell proliferation, inflammatory responses that involve macrophage adhesion, recruitment, and maturation. In addition, the effects on fibrogenesis have been recently defined. These latter effects may influence not only the development of glomerulosclerosis, but also interstitial fibrosis. These potentially major effects of lipid-lowering agents appear to be related to the effects on intracellular synthesis of nonsterol isoprenoids, which are involved in prenylation of critical small molecular weight proteins involved in cell signal transduction.

CONCLUSIONS

In addition to the beneficial effects of the reduction in serum lipids, statins and other lipid-lowering agents may influence important intracellular pathways that are involved in the inflammatory and fibrogenic responses, which are common components of many forms of progressive renal injury.

Lovastatin maintains nitric oxide--but not EDHF-mediated endothelium-dependent relaxation in the hypercholesterolemic rabbit carotid artery

The endothelium contributes to the regulation of vascular tone by producing nitric oxide (NO) and the endothelium-derived hyperpolarising factor (EDHF). In hypercholesterolemia, endothelium-dependent relaxation is impaired but can be restored by treatment with lovastatin (LOVAS). We investigated the effects of LOVAS on NO and EDHF-mediated relaxation. Rabbits were fed 1% cholesterol diet for 4 weeks and 0.5%) cholesterol for the following 12 weeks (CHOL-group). The LOVAS group additionally received 10 mg of lovastatin over the last 12-week period. Experiments were performed in carotid artery rings. Relaxant responses to acetylcholine (ACh) were recorded in the presence of indomethacin. Nitro-L-arginine (NOARG, 100 microM) and potassium chloride (KCl, 35 mM) were used to differentiate between NO- and EDHF-mediated relaxations. Cholesterol impaired ACh-induced relaxations and this effect was prevented by LOVAS (control 100+/-1%, CHOL 81+/-6%, LOVAS 98+/-1%). In the presence of NOARG, relaxations to ACh were not different between the LOVAS and CHOL groups (control 78+/-4%, CHOL 64+/-6%, LOVAS 64+/-5%). When KCl was used, ACh-induced relaxations were similar in the LOVAS and control group (control 75+/-5%, CHOL 49+/-6%, LOVAS 76+/-2%). In arteries treated with NOARG and KCl together, no relaxations were observed. Relaxations of arteries from the control group were not affected by 18 h preincubation with lovastatin (10 microM). Lovastatin selectively maintains nitric oxide-mediated endothelium-dependent relaxation in hypercholesterolemic rabbit carotid arteries.

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors increase fibrinolytic activity in rat aortic endothelial cells. Role of geranylgeranylation and Rho proteins

3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors (HRIs) have been recently shown to prevent atherosclerosis progression. Clinical benefit results from combined actions on various components of the atherosclerotic lesion. This study was designed to identify the effects of HRI on one of these components, the endothelial fibrinolytic system. Aortas isolated from rats treated for 2 days with lovastatin (4 mg/kg body wt per day) showed a 3-fold increase in tissue plasminogen activator (tPA) activity. In a rat aortic endothelial cell line (SVARECs) and in human nontransformed endothelial cells (HUVECs), HRI induced an increase in tPA activity and antigen in a time- and concentration-dependent manner. In SVARECs, the maximal response was observed when cells were incubated for 48 hours with 50 micromol/L HRI. An increase of tPA mRNA was also in evidence. In contrast, HRI inhibited plasminogen activator inhibitor-1 activity and mRNA. The effects of HRI were reversed by mevalonate and geranylgeranyl pyrophosphate, but not by LDL cholesterol and farnesyl pyrophosphate, and were not induced by alpha-hydroxyfarnesyl phosphonic acid, an inhibitor of protein farnesyl transferase. C3 exoenzyme, an inhibitor of the geranylgeranylated-activated Rho protein, reproduced the effect of lovastatin on tPA and plasminogen activator inhibitor-1 activity and blocked its reversal by geranylgeranyl pyrophosphate. The effect of HRI was associated with a disruption of cellular actin filaments without modification of microtubules. A disrupter of actin filaments, cytochalasin D, induced the same effect as lovastatin on tPA, whereas a disrupter of microtubules, nocodazole, did not. In conclusion, HRI can modify the fibrinolytic potential of endothelial cells, likely via inhibition of geranylgeranylated Rho protein and disruption of the actin filaments. The resulting increase of fibrinolytic activity of endothelial cells may contribute to the beneficial effects of HRI in the progression of atherosclerosis.

3-Hydroxy-3-methylglutaryl coenzyme a reductase and isoprenylation inhibitors induce apoptosis of vascular smooth muscle cells in culture

Recent evidence suggests that apoptosis may be involved in the control of vascular smooth muscle cell (VSMC) number in atherosclerotic lesions. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors have been reported to induce apoptosis in a variety of tumor cell lines. To evaluate whether these agents also induce apoptosis of VSMCs, cultured rat VSMCs were treated with increasing doses of atorvastatin in the presence of FBS as a survival factor. The presence of apoptosis was evaluated by morphological criteria, annexin V binding, and DNA fragmentation and quantified as the proportion of hypodiploid cells by flow cytometry. Atorvastatin induced apoptosis in a dose-dependent manner, an effect also seen with simvastatin and lovastatin, but not with the hydrophilic drug pravastatin. The proapoptotic effect of statins was seen only when the inhibition of acetate incorporation into sterols was >95% and was fully reversed by mevalonate, farnesyl pyrophosphate, and geranylgeranyl pyrophosphate but not by isopentenyl adenosine, ubiquinone, or squalene, suggesting a role for prenylated proteins in the regulation of VSMC apoptosis. To further assess the role of protein prenylation, VSMCs were exposed to the prenyl transferase inhibitors perillic acid and manumycin A. Both agents induced VSMC apoptosis as evaluated by the above-mentioned criteria. Finally, VSMC treatment with lipophilic statins was associated with decreased prenylation of p21-Rho B, further supporting the role of protein prenylation inhibition in statin-induced VSMC apoptosis. The present data suggest that interference with protein prenylation by HMG-CoA reductase inhibitors or other agents may provide new strategies for the prevention of neointimal thickening.

Inflammation, pravastatin, and the risk of coronary events after myocardial infarction in patients with average cholesterol levels. Cholesterol and Recurrent Events (CARE) Investigators

BACKGROUND

We studied whether inflammation after myocardial infarction (MI) is a risk factor for recurrent coronary events and whether randomized treatment with pravastatin reduces that risk.

METHODS AND RESULTS

A nested case-control design was used to compare C-reactive protein (CRP) and serum amyloid A (SAA) levels in prerandomization blood samples from 391 participants in the Cholesterol and Recurrent Events (CARE) trial who subsequently developed recurrent nonfatal MI or a fatal coronary event (cases) and from an equal number of age- and sex-matched participants who remained free of these events during follow-up (control subjects). Overall, CRP and SAA were higher among cases than control subjects (for CRP P=0.05; for SAA P=0.006) such that those with levels in the highest quintile had a relative risk (RR) of recurrent events 75% higher than those with levels in the lowest quintile (for CRP RR= 1.77, P=0.02; for SAA RR= 1.74, P=0.02). The study group with the highest risk was that with consistent evidence of inflammation (elevation of both CRP and SAA) who were randomly assigned to placebo (RR=2.81, P=0.007); this risk estimate was greater than the product of the individual risks associated with inflammation or placebo assignment alone. In stratified analyses, the association between inflammation and risk was significant among those randomized to placebo (RR=2.11, P=0.048) but was attenuated and nonsignificant among those randomized to pravastatin (RR=1.29, P=0.5).

CONCLUSIONS

Evidence of inflammation after MI is associated with increased risk of recurrent coronary events. Therapy with pravastatin may decrease this risk, an observation consistent with a nonlipid effect of this agent.

Inhibitory effect of photooxidation on intimal and medial thickening of saphenous vein

BACKGROUND

The inhibitory effect of short-term photooxidation on medial and neointimal proliferation of human saphenous vein was investigated.

METHODS

Culture medium-filled surgically prepared saphenous vein segments were photooxidized in 0.01% methylene blue solution for 5 minutes. Photooxidized and nonphotooxidized saphenous veins were checked for viability of endothelial cells by culturing vein segments for 21 days followed by histologic and immunohistochemical studies.

RESULTS

Endothelial cells of saphenous vein segments remained unaffected after photooxidation. Both the intima and media of nonphotooxidized veins became highly cellular and thickened because of the proliferation and migration of smooth muscle cells. Like precultured fresh saphenous vein, intimal (0.031+/-0.017 mm; p=0.0067) and medial thicknesses (0.702+/-0.123 mm; p < 0.0001) and proliferating cell nuclear antigen-positive cell count (14+/-8/mm2; p=0.0005) of cultured photooxidized veins were significantly less than those of cultured nonphotooxidized veins (intimal thickness, 0.059+/-0.041 mm; medial thickness, 0.997+/-0.228 mm; proliferating cell nuclear antigen positive cell count, 34+/-16/mm2.

CONCLUSIONS

Methylene blue-induced short-term photooxidation is effective in inhibition of intimal and medial thickening of saphenous vein.

Alpha1-adrenoreceptor stimulation causes vascular smooth muscle cell hypertrophy: a possible role for isoprenoid intermediates

We investigated whether contraction-induced agonists such as alpha1-adrenoceptor agonists are important regulators of smooth muscle cell hypertrophy by examining the effects of one potent agonists, phenylephrine, on the hypertrophy. Under the experimental conditions used, we found that phenylephrine was potent in inducing alpha1-adrenoreceptor-dependent hypertrophy of vascular smooth muscle cells as defined by increased incorporation of [14C]leucine in a dose-dependent fashion. Further, we assessed the effect of lovastatin, an 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on hypertrophy of cultured vascular smooth muscle cells as defined by the increased incorporation of [14C]leucine caused by phenylephrine. Lovastatin (5-15 microM) caused a significant dose-dependent reduction in [14C]leucine incorporation which was completely prevented in the presence of exogenous mevalonate (100 microM). Exogenous low density lipoprotein (100 microg/ml) and cholesterol (15 microg/ml) did not prevent lovastatin inhibition of [14C]leucine incorporation. In contrast, the isoprenoid farnesol largely prevented inhibition of [14C]leucine incorporation by the lovastatin. We conclude that mevalonate metabolites are essential for phenylephrine-induced smooth muscle cell hypertrophy, possibly through the production of the isoprenoid farnesol.

Tyrosine kinase-dependent modulation of 3-hydroxy-3-methylglutaryl-CoA reductase in human breast adenocarcinoma SKBR-3 cells

3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase is the major rate-limiting enzyme in sterol and non-sterol isoprenoid synthesis. Isoprenoids are involved in the mechanisms of cell proliferation and transformation leading notably to crucial post-translational maturation of small G-proteins of the Ras superfamily. HMG-CoA reductase is among the most highly regulated enzymes. It is controlled by several feedback regulation mechanisms induced by sterol and non-sterol metabolites. The present results show that tyrosine kinase activity is also involved in the regulation of HMG-CoA reductase activity in the human breast cancer cell line SKBR-3. Incubation of SKBR-3 cells with the tyrosine kinase inhibitor, herbimycin A, induces a concentration-dependent reduction of HMG-CoA reductase activity with an IC50 of 80nM. The inhibition of HMG-CoA reductase activity by herbimycin A is also time-dependent. A similar effect of herbimycin A was obtained on the steady-state level of the HMG-CoA reductase protein. The effect of herbimycin A is probably specific as it abolished the stimulation of reductase activity by epidermal growth factor. To elucidate the molecular basis of the inhibition of HMG-CoA reductase activity and protein level by herbimycin A, we performed experiments to study the metabolic turnover of this enzyme using [35S]methionine and [35]cysteine. Herbimycin A (1 microM) did not have any significant effect on the rate of HMG-CoA reductase protein degradation but did affect its rate of synthesis and mRNA levels. The decrease in protein synthesis rate correlates with the lower reductase protein level but is more pronounced than the decrease in mRNA levels. Taken together, the results reveal a novel pathway of regulation of HMG-CoA reductase expression and activity by cellular tyrosine kinase activities.

Vascular effects of statins in stroke

BACKGROUND

Recent clinical trials and meta-analyses of beta-hydroxy-beta-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have demonstrated a reduction in ischemic stroke in patients with a history of coronary artery disease both with and without elevations of serum cholesterol. This review summarizes clinical trials of these compounds and their recent impact on stroke and explores the underlying vascular mechanisms of their actions.

SUMMARY OF REVIEW

Use of statins in patients with vascular disease has been shown to lower the incidence of stroke by approximately 30%. Statins exhibit a number of antiatherosclerotic and antithrombotic properties that likely underlie the recently observed reductions in cerebrovascular disease. Statins reduce inflammatory, proliferative, and thrombogenic processes in plaque, making it less likely to rupture. Additionally, they reverse the endothelial dysfunction and platelet activation accompanying hypercholesterolemia and may reduce the tendency to thrombosis.

CONCLUSIONS

Hypercholesterolemia has reemerged as a risk factor for ischemic stroke. Statins protect against thromboembolic stroke through multiple beneficial effects within the vascular milieu. Further data are awaited to support the growing importance of cholesterol as a risk factor for ischemic stroke and the benefits of statin therapy in patients with cerebrovascular disease.

Platelet-derived growth factor beta-receptors can both promote and inhibit chemotaxis in human vascular smooth muscle cells

The effect of the three platelet-derived growth factor (PDGF) isoforms AA, AB, and BB on migration was investigated in cultured human saphenous vein smooth muscle cells. The modified Boyden chamber technique yielded efficacies BB >> AB, AA = 0. However, the BB concentration-response relationship displayed a pronounced peak, occurring between 1 and 10 ng/mL, with no response above this range. Checkerboard analysis showed that the promotion of migration at low concentrations was chemotactic in nature but that the downturn was independent of gradient. Furthermore, at high concentrations BB was able to prevent chemotaxis induced by fetal calf serum and epidermal growth factor (EGF). Experiments using low concentrations of BB in combination with high concentrations of AA to saturate PDGF alpha-receptors in the presence and absence of a neutralizing antibody to alpha-receptors revealed that alpha-receptor activation induced partial inhibition of chemotaxis but this did not account for the inhibition of migration by high concentrations of BB. Despite possessing no significant chemotactic action itself, high concentrations of the AB isoform completely inhibited BB induced chemotaxis. Taken together these results suggest that the chemotactic signal induced by PDGF is dominated by PDGF beta-receptors and switches from positive at low concentrations to negative at higher concentrations. Stimulation of DNA synthesis by the three isoforms (as measured by [3H] thymidine incorporation) yielded saturable responses for the AB and BB isoforms, with similar efficacy and weak or no response for the AA isoform. Concentration-dependent patterns of tyrosine phosphorylation of certain proteins mirrored the form of the chemotactic response and suggest one possible underlying regulatory mechanism to account for the disparity between PDGF-induced chemotaxis and DNA synthesis.