Upregulation of endothelial nitric oxide synthase by HMG CoA reductase inhibitors

BACKGROUND

Oxidized low-density lipoprotein (ox-LDL) causes endothelial dysfunction in part by decreasing the availability of endothelial nitric oxide (NO). Although HMG CoA reductase inhibitors restore endothelial function by reducing serum cholesterol levels, it is not known whether they can also directly upregulate endothelial NO synthase (ecNOS) activity.

METHODS AND RESULTS

Human saphenous vein endothelial cells were treated with ox-LDL (50 microg/mL thiobarbituric acid reactive substances 12 to 16 nmol/mg) in the presence of HMG CoA reductase inhibitors simvastatin and lovastatin. In a time-dependent manner, ox-LDL decreased ecNOS mRNA and protein levels (91+/-4% and 67+/-8% reduction after 72 hours, respectively). Both simvastatin (1 micromol/L) and lovastatin (10 micromol/L) upregulated ecNOS expression by 3.8-fold and 3.6-fold, respectively, and completely prevented its downregulation by ox-LDL. These effects of simvastatin on ecNOS expression correlated with changes in ecNOS activity. Although L-mevalonate alone did not affect ecNOS expression, cotreatment with L-mevalonate completely reversed ecNOS upregulation by simvastatin. Actinomycin D studies revealed that simvastatin stabilized ecNOS mRNA (tau1/2, 43 versus 35 hours). Nuclear run-on assays and transient transfection studies with a -1.6 kb ecNOS promoter construct showed that simvastatin did not affect ecNOS gene transcription.

CONCLUSIONS

Inhibition of endothelial HMG CoA reductase upregulates ecNOS expression predominantly by posttranscriptional mechanisms. These findings suggest that HMG CoA reductase inhibitors may have beneficial effects in atherosclerosis beyond that attributed to the lowering of serum cholesterol by increasing ecNOS activity.

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

The mechanism by which 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors increase endothelial nitric oxide synthase (eNOS) expression is unknown. To determine whether changes in isoprenoid synthesis affects eNOS expression, human endothelial cells were treated with the HMG-CoA reductase inhibitor, mevastatin (1-10 microM), in the presence of L-mevalonate (200 microM), geranylgeranylpyrophosphate (GGPP, 1-10 microM), farnesylpyrophosphate (FPP, 5-10 microM), or low density lipoprotein (LDL, 1 mg/ml). Mevastatin increased eNOS mRNA and protein levels by 305 +/- 15% and 180 +/- 11%, respectively. Co-treatment with L-mevalonate or GGPP, but not FPP or LDL, reversed mevastatin's effects. Because Rho GTPases undergo geranylgeranyl modification, we investigated whether Rho regulates eNOS expression. Immunoblot analyses and [35S]GTPgammaS-binding assays revealed that mevastatin inhibited Rho membrane translocation and GTP binding activity by 60 +/- 5% and 78 +/- 6%, both of which were reversed by co-treatment with GGPP but not FPP. Furthermore, inhibition of Rho by Clostridium botulinum C3 transferase (50 microg/ml) or by overexpression of a dominant-negative N19RhoA mutant increased eNOS expression. In contrast, activation of Rho by Escherichia coli cytotoxic necrotizing factor-1 (200 ng/ml) decreased eNOS expression. These findings indicate that Rho negatively regulates eNOS expression and that HMG-CoA reductase inhibitors up-regulate eNOS expression by blocking Rho geranylgeranylation, which is necessary for its membrane-associated activity.

Stroke protection by 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors mediated by endothelial nitric oxide synthase

The treatment of ischemic strokes is limited to prophylactic agents that block the coagulation cascade. Here, we show that cholesterol-lowering agents, 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors, protect against cerebral injury by a previously unidentified mechanism involving the selective up-regulation of endothelial NO synthase (eNOS). Prophylactic treatment with HMG-CoA reductase inhibitors augments cerebral blood flow, reduces cerebral infarct size, and improves neurological function in normocholesterolemic mice. The up-regulation of eNOS by HMG-CoA reductase inhibitors is not associated with changes in serum cholesterol levels, but is reversed by cotreatment with L-mevalonate and by the downstream isoprenoid, geranylgeranyl pyrophosphate and not by farnesyl pyrophosphate. The blood flow and neuroprotective effects of HMG-CoA reductase inhibitors are completely absent in eNOS-deficient mice, indicating that enhanced eNOS activity by HMG-CoA reductase inhibitors is the predominant if not the only mechanism by which these agents protect against cerebral injury. Our results suggest that HMG-CoA reductase inhibitors provide a prophylactic treatment strategy for increasing blood flow and reducing brain injury during cerebral ischemia.

HMG-CoA reductase inhibitors improve endothelial dysfunction in normocholesterolemic hypertension via reduced production of reactive oxygen species

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) significantly reduce cardiovascular mortality associated with hypercholesterolemia. There is evidence that statins exert beneficial effects in part through direct effects on vascular cells independent of lowering plasma cholesterol. We characterized the effect of a 30-day treatment with atorvastatin in normocholesterolemic, spontaneously hypertensive rats (SHR). Systolic blood pressure was significantly decreased in atorvastatin-treated rats (184+/-5 versus 204+/-6 mm Hg for control). Statin therapy improved endothelial dysfunction, as assessed by carbachol-induced vasorelaxation in aortic segments, and profoundly reduced angiotensin II-induced vasoconstriction. Angiotensin type 1 (AT(1)) receptor, endothelial cell NO synthase (ecNOS), and p22phox mRNA expression were determined with quantitative reverse transcription-polymerase chain reaction. Atorvastatin treatment downregulated aortic AT(1) receptor mRNA expression to 44+/-12% of control and reduced mRNA expression of the essential NAD(P)H oxidase subunit p22phox to 63+/-7% of control. Aortic AT(1) receptor protein expression was consistently decreased. Vascular production of reactive oxygen species was reduced to 62+/-12% of control in statin-treated SHR, as measured with lucigenin chemiluminescence assays. Accordingly, treatment of SHR with the AT(1) receptor antagonist fonsartan improved endothelial dysfunction and reduced vascular free-radical release. Moreover, atorvastatin caused an upregulation of ecNOS mRNA expression (138+/-7% of control) and an enhanced ecNOS activity in the vessel wall (209+/-46% of control). Treatment of SHR with atorvastatin causes a significant reduction of systolic blood pressure and a profound improvement of endothelial dysfunction mediated by a reduction of free radical release in the vasculature. The underlying mechanism could in part be based on the statin-induced downregulation of AT(1) receptor expression and decreased expression of the NAD(P)H oxidase subunit p22phox, because AT(1) receptor activation plays a pivotal role for the induction of this redox system in the vessel wall.

3-Hydroxy-3-methylglutaryl-CoA reductase inhibitors attenuate vascular smooth muscle proliferation by preventing rho GTPase-induced down-regulation of p27(Kip1)

The mechanism by which platelet-derived growth factor (PDGF) regulates vascular smooth muscle cell (SMC) DNA synthesis is unknown, but may involve isoprenoid intermediates of the cholesterol biosynthetic pathway. Inhibition of isoprenoid synthesis with the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor, simvastatin (Sim, 1-10 microM), inhibited PDGF-induced SMC DNA synthesis by >95%, retinoblastoma gene product hyperphosphorylation by 90%, and cyclin-dependent kinases (cdk)-2, -4, and -6 activity by 80 +/- 5, 50 +/- 3, and 48 +/- 3%, respectively. This correlated with a 20-fold increase in p27(Kip1) without changes in p16, p21(Waf1), or p53 levels compared with PDGF alone. Since Ras and Rho require isoprenoid modification for membrane localization and are implicated in cell cycle regulation, we investigated the effects of Sim on Ras and Rho. Up-regulation of p27(Kip1) and inhibition of Rho but not Ras membrane translocation by Sim were reversed by geranylgeranylpyrophosphate, but not farnesylpyrophosphate. Indeed, inhibition of Rho by Clostridium botulinum C3 transferase or overexpression of dominant-negative N19RhoA mutant increased p27(Kip1) and inhibited retinoblastoma hyperphosphorylation. In contrast, activation of Rho by Escherichia coli cytotoxic necrotizing factor-1 decreased p27(Kip1) and increased SMC DNA synthesis. These findings indicate that the down-regulation of p27(Kip1) by Rho GTPase mediates PDGF-induced SMC DNA synthesis and suggest a novel direct effect of 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors on the vascular wall.

Inhibition of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase blocks hypoxia-mediated down-regulation of endothelial nitric oxide synthase

Hypoxia induces vasoconstriction, in part, by down-regulating endothelial cell nitric oxide synthase (ecNOS) expression. Previous studies indicate that 3-hydroxy-3-methylglutaryl-coenzyme A (HMG CoA) reductase inhibitors improve endothelium-dependent relaxation by increasing ecNOS activity. To determine whether HMG CoA reductase inhibitors can prevent hypoxia-mediated down-regulation of ecNOS function and expression, human endothelial cells were exposed to hypoxia (3% O2) in the presence of HMG CoA reductase inhibitors simvastatin and lovastatin for various durations (0-48 h). Hypoxia decreased ecNOS protein and mRNA levels in a time-dependent manner, resulting in a 4- and 9-fold reduction after 48 h, respectively. In a concentration-dependent manner, simvastatin, and to a lesser extent, lovastatin, prevented the down-regulation of ecNOS expression by hypoxia. Simvastatin-induced changes in ecNOS expression correlated with changes in endothelial NO production and were reversed by treatment with L-mevalonate. Actinomycin D studies revealed that under hypoxic conditions, simvastatin increased ecNOS mRNA half-life from 13 to 38 h. Nuclear run-on studies showed that simvastatin had no effect on repression of ecNOS gene transcription by hypoxia. These results indicate that HMG CoA reductase inhibitors regulate ecNOS function and expression through changes in ecNOS mRNA stability and suggest that treatment with HMG CoA reductase inhibitors may have beneficial effects in patients with hypoxia-mediated pulmonary hypertension.

Atorvastatin upregulates type III nitric oxide synthase in thrombocytes, decreases platelet activation, and protects from cerebral ischemia in normocholesterolemic mice

BACKGROUND AND PURPOSE

Thrombosis superimposed on atherosclerosis causes approximately two thirds of all brain infarctions. We previously demonstrated that statins protect from cerebral ischemia by upregulation of endothelial type III nitric oxide synthase (eNOS), but the downstream mechanisms have not been determined. Therefore, we investigated whether antithrombotic effects contribute to stroke protection by statins.

METHODS

129/SV wild-type and eNOS knockout mice were treated with atorvastatin for 14 days (0.5, 1, and 10 mg/kg). eNOS mRNA from aortas and platelets was measured by reverse-transcriptase polymerase chain reaction. Platelet factor 4 (PF 4) and beta-thromboglobulin (beta-TG) in the plasma were quantified by ELISA. Transient cerebral ischemia was induced by filamentous occlusion of the middle cerebral artery followed by reperfusion.

RESULTS

Stroke volume after 1-hour middle cerebral artery occlusion/23-hour reperfusion was significantly reduced by 38% in atorvastatin-treated animals (10 mg/kg) compared with controls. Serum cholesterol levels were not affected by the treatment. eNOS mRNA was significantly upregulated in a dose-dependent manner in aortas and in thrombocytes of statin-treated mice compared with controls. Moreover, indices of platelet activation in vivo, ie, plasma levels of PF 4 and beta-TG, were dose-dependently downregulated in the treatment group. Surprisingly, atorvastatin-treatment did not influence PF 4 and beta-TG levels in eNOS knockout mice.

CONCLUSIONS

The synthetic 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor atorvastatin upregulates eNOS in thrombocytes, decreases platelet activation in vivo, and protects from cerebral ischemia in normocholesterolemic mice. Antithrombotic and stroke-protective effects of statins are mediated in part by eNOS upregulation. Our results suggest that statins may provide a novel prophylactic treatment strategy independent of serum cholesterol levels.

Inhibition of geranylgeranylation reduces angiotensin II-mediated free radical production in vascular smooth muscle cells: involvement of angiotensin AT1 receptor expression and Rac1 GTPase

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) may exert pleiotropic effects on vascular cells independent of lowering plasma cholesterol. To elucidate the molecular mechanisms involved in these effects, we investigated the impact of statins on production of reactive oxygen species (ROS) in rat aortic vascular smooth muscle cells (VSMC). Exposure of VSMC to angiotensin II caused production of ROS via angiotensin AT1 receptor activation. Pretreatment with atorvastatin inhibited angiotensin II-induced ROS production. Atorvastatin decreased AT1 receptor mRNA levels in a time- and concentration-dependent manner and consistently reduced AT1 receptor density. L-Mevalonate but not hydroxy-cholesterol reversed the inhibitory effect of atorvastatin on AT1 receptor transcript levels. Inhibition of geranylgeranyl-transferase but not of farnesyl-transferase mimicked the effect of atorvastatin on AT1 receptor gene expression. Atorvastatin did not decrease AT1 receptor gene transcription but did reduce the half-life of the AT1 receptor mRNA. AT1 receptor activation by angiotensin II increased the expression of the GTPase rac1, enhanced rac1 GTP-binding activity, and increased the geranylgeranyl-dependent translocation of rac1 to the cell membrane. In contrast, statins inhibited rac1 activity and membrane translocation. Consequently, specific inhibition of rac1 with Clostridium sordellii lethal toxin blocked angiotensin II-induced production of free radicals. Finally, treatment of rats with atorvastatin caused down-regulation of aortic AT1 receptor mRNA expression and reduced aortic superoxide production in vivo. Cholesterol-independent down-regulation of AT1 receptor gene expression and inhibition of rac1, leading to decreased ROS production, demonstrates a novel regulatory mechanism of statins that may contribute to the beneficial effects of these drugs beyond lowering of plasma cholesterol.

Neuroprotection mediated by changes in the endothelial actin cytoskeleton

Cerebral blood flow is regulated by endothelium-derived nitric oxide (NO), and endothelial NO synthase-deficient (eNOS-deficient; eNOS(-/-)) mice develop larger cerebral infarctions following middle cerebral artery (MCA) occlusion. We report that disruption of Rho-mediated endothelial actin cytoskeleton leads to the upregulation of eNOS expression and reduces the severity of cerebral ischemia following MCA occlusion. Mice treated with the Rho inhibitor Clostridium botulinum C3 transferase (10 microgram/d) or the actin cytoskeleton disrupter cytochalasin D (1 mg/kg) showed a two- to fourfold increase in vascular eNOS expression and activity. This increase in eNOS expression was not due to increases in eNOS gene transcription, but to prolongation of eNOS mRNA half-life from 10 +/- 3 hours to 24 +/- 4 hours. Indeed, endothelial cells overexpressing a dominant-negative Rho mutant (N19RhoA) exhibited decreased actin stress fiber formation and increased eNOS expression. Inhibition of vascular Rho guanosine-5'-triphosphate binding activity by the 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor simvastatin increased cerebral blood flow to ischemic regions of the brain, and mice treated with simvastatin, C3 transferase, or cytochalasin D showed smaller cerebral infarctions following MCA occlusion. No neuroprotection was observed with these agents in eNOS(-/-) mice. These findings suggest that therapies which target the endothelial actin cytoskeleton may have beneficial effects in ischemic stroke.

Effects of surgical and FFP2/N95 face masks on cardiopulmonary exercise capacity

Background

Due to the SARS-CoV2 pandemic, medical face masks are widely recommended for a large number of individuals and long durations. The effect of wearing a surgical and a FFP2/N95 face mask on cardiopulmonary exercise capacity has not been systematically reported.

Methods

This prospective cross-over study quantitated the effects of wearing no mask (nm), a surgical mask (sm) and a FFP2/N95 mask (ffpm) in 12 healthy males (age 38.1 ± 6.2 years, BMI 24.5 ± 2.0 kg/m²). The 36 tests were performed in randomized order. The cardiopulmonary and metabolic responses were monitored by ergo-spirometry and impedance cardiography. Ten domains of comfort/discomfort of wearing a mask were assessed by questionnaire.

Results

The pulmonary function parameters were significantly lower with mask (forced expiratory volume: 5.6 ± 1.0 vs 5.3 ± 0.8 vs 6.1 ± 1.0 l/s with sm, ffpm and nm, respectively; p = 0.001; peak expiratory flow: 8.7 ± 1.4 vs 7.5 ± 1.1 vs 9.7 ± 1.6 l/s; p < 0.001). The maximum power was 269 ± 45, 263 ± 42 and 277 ± 46 W with sm, ffpm and nm, respectively; p = 0.002; the ventilation was significantly reduced with both face masks (131 ± 28 vs 114 ± 23 vs 99 ± 19 l/m; p < 0.001). Peak blood lactate response was reduced with mask. Cardiac output was similar with and without mask. Participants reported consistent and marked discomfort wearing the masks, especially ffpm.

Conclusion

Ventilation, cardiopulmonary exercise capacity and comfort are reduced by surgical masks and highly impaired by FFP2/N95 face masks in healthy individuals. These data are important for recommendations on wearing face masks at work or during physical exercise.

Suppression of endothelial nitric oxide production after withdrawal of statin treatment is mediated by negative feedback regulation of rho GTPase gene transcription

BACKGROUND

Statins improve endothelial function by upregulating endothelial nitric oxide (NO) production that is mediated by inhibiting the isoprenylation of rho GTPase. Withdrawal of statin treatment could suppress endothelial NO production and may impair vascular function.

METHODS AND RESULTS

To test this hypothesis, mice were treated for 14 days with 10 mg/kg atorvastatin per day; this led to the upregulation of endothelial NO synthase expression and activity by 2.3- and 3-fold, respectively. Withdrawal of statins resulted in a dramatic, 90% decrease of NO production after 2 days. In mouse aortas and cultured endothelial cells, statins upregulated the expression of rho GTPase in the cytosol, but statins blocked isoprenoid-dependent rho membrane translocation and GTP-binding activity. Inhibiting the downstream targets of rho showed that rho expression is controlled by a negative feedback mechanism mediated by the actin cytoskeleton. Measuring rho mRNA half-life and nuclear run-on assays demonstrated that statins or disruption of actin stress fibers increased rho gene transcription but not rho mRNA stability. Therefore, treatment with statins leads to the accumulation of nonisoprenylated rho in the cytosol. Withdrawing statin treatment restored the availability of isoprenoids and resulted in a massive membrane translocation and activation of rho, causing downregulation of endothelial NO production.

CONCLUSIONS

Withdrawal of statin therapy in normocholesterolemic mice results in a transient increase of rho activity, causing a suppression of endothelial NO production. The underlying molecular mechanism is a negative feedback regulation of rho gene transcription mediated by the actin cytoskeleton.

Inflammatory cytokines and oxidized low density lipoproteins increase endothelial cell expression of membrane type 1-matrix metalloproteinase

We investigated whether inflammatory cytokines or oxidized low density lipoproteins (Ox-LDL) present in human atheroma modulate extracellular matrix degradation by inducing membrane type 1-matrix metalloproteinase (MT1-MMP) expression. Cultured human endothelial cells (EC) constitutively expressed MT1-MMP mRNA and protein with enzymatic activity. Tumor necrosis factor-alpha (TNF-alpha), interleukin-1alpha, or interleukin-1beta caused a time-dependent increase in the steady-state MT1-MMP mRNA levels within 4 h of exposure, peaking about 4-fold by 6 h, and remaining elevated for 12 h. Increased MT1-MMP mRNA correlated with a 2.5-fold increase in MT1-MMP protein in EC membranes. Ox-LDL also increased MT1-MMP mRNA levels that varied with the duration of exposure and degree of LDL oxidation. The increase in MT1-MMP mRNA occurred within 6 h of exposure to Ox-LDL and peaked over 3-fold by 6 h. Ox-LDL, but not native LDL, increased MT1-MMP protein by 2-fold in EC membranes. A combination of TNF-alpha and Ox-LDL was additive in increasing MT1-MMP expression. Nuclear run-on assays showed that TNF-alpha or Ox-LDL augmented steady-state mRNA levels by increased transcription of the MT1-MMP gene. These findings indicate that activation of EC by inflammatory cytokines and/or Ox-LDL increase MT1-MMP expression. Since MT1-MMP promotes matrix degradation by activating pro-MMP-2, these results suggest a novel mechanism whereby cytokines or Ox-LDL may influence extracellular matrix remodeling.

Recommendations for the emergency management of complications associated with the new direct oral anticoagulants (DOACs), apixaban, dabigatran and rivaroxaban

Dabigatran, apixaban, and rivaroxaban have been approved for primary and secondary stroke prevention in patients with atrial fibrillation. However, questions have arisen about how to manage emergency situations, such as when thrombolysis would be required for acute ischemic stroke or for the managing intracranial or gastrointestinal bleedings. We summarize the current literature and provide recommendations for the management of these situations. Peak plasma levels of the direct oral anticoagulants (DOACs) apixaban, dabigatran, or rivaroxaban are observed about 2-4 h after intake. Elimination of dabigatran is mainly dependent on renal function. Consequently, if renal function is impaired, there is a risk of drug accumulation that is highest for dabigatran followed by rivaroxaban and then apixaban and thus dosing recommendations are different. To date, no bedside tests are available that reliably assess the anticoagulatory effect of DOACs, nor are specific antidotes available. We recommend performing the following tests if DOAC intake is unknown: dabigatran-associated bleeding risk is minimized or can be neglected if thrombin time, Hemoclot test, or Ecarin clotting time is normal. Apixaban and rivaroxaban effects can be ruled out if findings from the anti-factor Xa activity test are normal. High plasma levels of DOAC are also mostly excluded if PTT and PTZ are normal four or more hours after DOAC intake. However, normal values of global coagulation tests are not sufficient if thrombolysis is indicated for treating acute stroke. The decision for or against thrombolysis is an individual decision; in these cases, thrombolysis use is off-label. In case of bleeding, prothrombin complex concentrates seems to be the most plausible treatment. For severe gastrointestinal bleeding with life-threatening blood loss, the bleeding source needs to be identified and treated by invasive measures. Use of procoagulant drugs (antifibrinolytics) might also be considered. However, there is very limited clinical experience with these products in conjunction with DOAC.

Direct vascular effects of HMG-CoA reductase inhibitors

The 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors, or statins, are potent inhibitors of cholesterol synthesis and large clinical trials have demonstrated that these agents reduce cholesterol and the incidence of cardiovascular diseases. Recent evidence, however, suggests that the beneficial effects of statins may extend beyond their effects on serum cholesterol levels. Because statins also inhibit the synthesis of isoprenoid intermediates in the cholesterol biosynthetic pathway, they may have pleiotropic effects on vascular wall cells. In particular, the small GTP-binding protein, Rho, whose membrane localization and activity are affected by post-translational isoprenylation, may play an important role in mediating the direct vascular effects of statins.

Endothelial nitric oxide synthase-dependent cerebral blood flow augmentation by L-arginine after chronic statin treatment

Nitric oxide, a product of nitric oxide synthase activity, relaxes vascular smooth muscle and elevates brain blood flow. We evaluated the importance of eNOS to cerebral blood flow augmentation after L-arginine infusion and increases in flow after eNOS upregulation in SV-129 mice. Blood flow was measured by laser-Doppler flowmetry before and after L-arginine infusion (450 mg/kg during a 15-minute period) or measured by 14C-iodoamphetamine indicator fractionation or 14C-iodoantipyrine tissue equilibration techniques. rCBF increased by 26% (laser Doppler flowmetry) after L-arginine infusion but did not change in mutant mice deficient in eNOS expression. After eNOS upregulation by chronic simvastatin treatment (2 mg/kg subcutaneously, daily for 14 days), L-arginine amplified and sustained the hyperemia (38%) and increased absolute brain blood flow from 86 +/- 7 to 119 +/- 10 mL/100 g per minute. Furthermore, pretreatment with simvastatin enhanced blood flow within ischemic brain tissue after middle cerebral artery occlusion. Together, these findings suggest that eNOS activity is critical for blood flow augmentation during acute L-arginine infusion, and chronic eNOS upregulation combined with L-arginine administration provides a novel strategy to elevate cerebral blood flow in the normal and ischemic brain.

Anti-inflammatory effects of atorvastatin improve left ventricular function in experimental diabetic cardiomyopathy

AIMS/HYPOTHESIS

Emerging evidence suggests that statins exert beneficial effects beyond those predicted by their cholesterol-lowering actions. We investigated whether atorvastatin influences the development of left ventricular (LV) dysfunction, independently of cholesterol-lowering, in an experimental model of type 1 diabetes mellitus cardiomyopathy.

METHODS

Streptozotocin-induced diabetic rats were treated with atorvastatin (50 mg/kg daily, orally) or with vehicle for 6 weeks. LV function was analysed using tip-catheter measurements. Cardiac stainings of TNF-alpha, IL-1beta, intercellular adhesion molecule-1, vascular cellular adhesion molecule-1, CD11a/lymphocyte-associated antigen-1, CD11b/macrophage antigen alpha, CD18/beta2-integrin, ED1/CD68, collagen I and III, and Sirius Red were assessed by digital image analysis. Ras-related C3 botulinum toxin substrate (RAC1) and ras homologue gene family, member A (RHOA) activities were determined by RAC1 glutathione-S-transferase-p21-activated kinase and rhotekin pull-down assays, respectively. Cardiac lipid peroxides were measured by a colorimetric assay. The phosphorylation state of p38 mitogen-activated protein kinase (MAPK) and endothelial nitric oxide synthase (eNOS) protein production were analysed by western blot.

RESULTS

Diabetes was associated with induced cardiac stainings of TNF-alpha, IL-1beta, cellular adhesion molecules, increased leucocyte infiltration, macrophage residence and cardiac collagen content. In contrast, atorvastatin reduced both intramyocardial inflammation and myocardial fibrosis, resulting in improved LV function. This effect was paralleled with a normalisation of diabetes-induced RAC1 and RHOA activity, in the absence of LDL-cholesterol lowering. In addition, atorvastatin decreased diabetes-induced cardiac lipid peroxide levels and p38 MAPK phosphorylation by 1.3-fold (p < 0.05) and 3.2-fold (p < 0.0005), respectively, and normalised the reduced eNOS production caused by diabetes.

CONCLUSIONS/INTERPRETATION

These data indicate that atorvastatin, independently of its LDL-cholesterol-lowering capacity, reduces intramyocardial inflammation and myocardial fibrosis, resulting in improved LV function in an experimental model of diabetic cardiomyopathy.

Effects of DPP-4 inhibition on cardiac metabolism and function in mice

Type 2 diabetes is associated with an increased risk of cardiac complications. Inhibitors of dipeptidylpeptidase 4 (DPP-4) are novel drugs for the treatment of patients with type 2 diabetes. The effect of DPP-4 inhibitors on myocardial metabolism has not been studied in detail. In wild-type C57Bl6-mice, 3weeks of treatment with sitagliptin had no effect on body weight and glucose tolerance nor on phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-CoAcarboxylase (ACC), phosphofructokinase-2 (PFK2) or tuberin-2 (TSC2) in the left ventricular myocardium. However, in 10week old db/db-/- mice, a model of diabetes and obesity, sitagliptin potently reduced plasma glucose rise in peritoneal glucose tolerance tests and reduced weight increase. The myocardium of untreated db/db-/- mice exhibited a marked increase of the phosphorylation of AMPK, ACC, TSC2, expression of p53 and fatty acid translocase (FAT/CD36) membrane expression. These changes were reduced by DPP-4 inhibition. Sitagliptin showed no effect on cardiomyocyte size but prevented myocardial fibrosis in the 10week old db/db-/- mice and reduced expression of TGF-β1, markers of oxidative stress and the accumulation of advanced glycation end products in cardiomyocytes. Working heart analyses did not show an effect of sitagliptin on parameters of systolic cardiac function. In animals with diabetes and obesity, sitagliptin improved glucose tolerance, reduced weight gain, myocardial fibrosis and oxidative stress. Furthermore the study provides evidence that treatment with sitagliptin decreases elevated myocardial fatty acid uptake and oxidation in the diabetic heart. These observations show beneficial myocardial metabolic effect of DPP-4 inhibition in this mouse model of diabetes and obesity.

Effects of endotoxin on human myocardial contractility involvement of nitric oxide and peroxynitrite

OBJECTIVES

This study examined the effects of endotoxin on cardiac contractility in human myocardium.

BACKGROUND

In animal myocardium, endotoxin and cytokine treatment led to enhanced inducible nitric oxide synthase (iNOS) expression and contractile dysfunction. Effects in human myocardium are unknown.

METHODS

Left ventricular myocardial preparations from failing (n = 18) and nonfailing (n = 5) human hearts were incubated for 6 and 12 h in tyrode solution or in tyrode plus lipopolysaccharides (LPS), with LPS plus N(G)-mono-methyl-L-arginine (L-NMMA), with LPS plus hemoglobin or with LPS plus the superoxide scavenger 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron). Force of contraction in response to isoprenaline (0.001 to 3 micromol/liter) was determined in electrically stimulated muscle preparations. The iNOS mRNA expression was examined by in situ hybridization and by polymerase chain reaction. The cyclic guanosine monophosphate (cGMP) levels were determined by radioimmunoassay.

RESULTS

Isoprenaline concentration dependently increased force of contraction. Six and 12 hours of LPS treatment of failing myocardium decreased maximum inotropic response to isoprenaline by 54% (p = 0.009) and by 69% (p = 0.0023), respectively. In nonfailing myocardium, 12 h of LPS treatment decreased maximum inotropic effect of isoprenaline by 66% (p < 0.001). The LPS effects were attenuated by L-NMMA, hemoglobin and also Tiron. The iNOS mRNA was expressed in all LPS-treated preparations but also in most control myocardial preparations. In situ hybridization revealed iNOS expression within cardiac myocytes. There was no increase in myocardial cGMP content in response to endotoxin.

CONCLUSIONS

Endotoxin exposure of human myocardium leads to a depression of cardiac contractility, which is mediated by enhanced iNOS activity and release of nitric oxide (NO). Consecutive reaction of NO with superoxide and formation of peroxynitrite may contribute to the decrease in force of contraction.

Modulation of bradykinin receptor ligand binding affinity and its coupled G-proteins by nitric oxide

To determine whether nitric oxide (NO) can modulate bradykinin (BK) signaling pathways, we treated endothelial cells with an NO donor, S-nitrosoglutathione (GSNO), to determine its effect(s) on G-proteins (Gi and Gq) that are coupled to the type II kinin (BK2) receptor. Radioligand binding assays and Western analyses showed that GSNO (10-500 microM, 0-72 h) did not alter the expression of BK2 receptor, Gi, or Gq. However, GSNO caused a 6-fold increase in basal cGMP production and decreased high affinity BK bindings sites and GTPase activity by 74 and 85%, respectively. The cGMP analogue, dibutyryl-cGMP, also inhibited BK-stimulated GTPase activity by 74% suggesting that some of the effects of NO may be mediated through activation of guanylyl cyclase. The NO synthase inhibitor, Nomega-monomethyl-L-arginine, inhibited endogenous NO synthase activity and cGMP production by 91 and 76%, respectively, but increased BK-stimulated GTPase activity by 61%. To determine which G-proteins are affected by NO, we performed GTP binding assays with [35S]GTPgammaS followed by immunoprecipitation with specific G-protein antisera. Both GSNO and dibutyryl-cGMP increased basal G-protein GTP binding activities by 18-26%. However, GSNO decreased BK-stimulated Galphai2, Galphai3, and Galphaq/11 GTP binding activity by 93, 61, and 90%, respectively, whereas epinephrine-stimulated Galphas GTP binding activity was unaffected. These results suggest that NO can modulate BK signaling pathways by selectively inhibiting G-proteins of the Gi and Gq family.

Beneficial effects of statins in patients with non-ischemic heart failure

OBJECTIVE

HMG CoA reductase inhibitors (statins) may exert a wide array of cholesterol independent effects including antihypertrophic effects on the heart. Their role in the treatment of heart failure has not been studied.

METHODS AND RESULTS

15 patients with heart failure NYHA II-III based on non-ischemic dilated cardiomyopathy were randomized in a double-blind study to 0.4 mg cerivastatin or placebo for an average treatment period of 20 weeks. Quality of life and exercise capacity increased significantly in the statin treatment but not in the placebo group (Minnesota Living with Heart Failure Questionnaire, 6 min walking test). Concomitantly, there was a trend towards increased left ventricular ejection fraction (radionuclear ventriculography) and improved endothelial function (forearm blood flow). Statins decreased plasma concentrations of troponine T, high sensitive C-reactive protein (hsCRP), plasminogen activator inhibitor-1 (PAI-1) and tumor necrosis factor alpha (TNFalpha).

CONCLUSIONS

Statins induce beneficial effects in patients with non-ischemic cardiomyopathy leading to improvement of quality of life and exercise capacity disclosing a promising novel treatment strategy for patients with heart failure.

Focal expression of intercellular adhesion molecule-1 in the human carotid bifurcation

BACKGROUND AND PURPOSE

In the carotid bifurcation, atherosclerotic plaques usually develop in the outer wall of the internal carotid artery. The aim of this study was to analyze the expression of the cell adhesion molecules intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin in the carotid bifurcation. These molecules play a role in inflammatory cell recruitment and atherosclerosis.

METHODS

We examined the expression of ICAM-1, VCAM-1, and E-selectin in 22 human carotid bifurcation specimens by means of immunohistochemistry. Double immunostaining was performed with antibodies against CD-3, CD-31, CD-68, and alpha-smooth muscle actin combined with each of the cell adhesion molecule antibodies. In situ hybridization for ICAM-1 was performed in selected specimens.

RESULTS

A profound focal expression of ICAM-1 in the outer wall of the internal carotid artery could be demonstrated (86% of all specimens). This focal expression could be shown in histologically normal appearing bifurcations of young adults. ICAM-1 was expressed by subsets of macrophages and smooth muscle cells and by endothelial cells. VCAM-1 and E-selectin showed no focal expression and were not found in normal carotids. In advanced plaques all three adhesion molecules-ICAM-1, VCAM-1, and E-selectin-were expressed.

CONCLUSIONS

We were able to demonstrate a focal expression of ICAM-1 in the outer lateral wall of the internal carotid artery, which is a high-risk region for the development of atherosclerotic lesions.

Down-regulation of aortic and cardiac AT1 receptor gene expression in transgenic (mRen-2) 27 rats

1. Transgenic(TG) (mRen-2) rats overexpressing the mouse renin gene develop fulminant hypertension and cardiac hypertrophy. Since the activation of AT1 receptor by angiotensin II is involved in blood pressure regulation, cardiac performance and myocardial growth, we investigated the biological effects of angiotensin II and the regulation of the AT1 receptor in the heart and aorta of TGR (mRen-2)27 rats in comparison to control animals. 2. Contraction studies on isolated cardiac muscle strips reveal that angiotensin II exerts no positive inotropic effect on the left ventricular myocardium of both, transgenic and control rats. In contrast, angiotensin II leads via AT1 receptor activation in the left atrium of control rats to a significant contraction (130 +/- 5% of basal contraction) which is not detectable in left atrium preparations of the transgenic animals. Furthermore, AT1 receptor activation causes a profound contraction of aortic rings isolated from control rats amounting to 1.39 +/- 0.2 mN mg-1 wet weight, whereas aortic rings from TGR (mRen-2)27 rats contract only minimally upon angiotensin II stimulation (0.2 +/- 0.02 mN mg-1 wet weight). 3. These altered physiological responses of angiotensin II in the transgenic rats are in part due to a marked down-regulation of the AT1 receptor in atrial, ventricular and aortic tissue of these transgenic animals in comparison to control Sprague-Dawley rats, as shown by radioligand binding assays and quantitative polymerase chain reaction (PCR) experiments. The AT1 receptor density Bmax in the left atrium was 1.3 +/- 0.08 fmol mg-1 protein in control rats (KD 1.1 +/- 0.18 nmol l-1) and 0.94 +/- 0.15 fmol mg-1 protein (KD 2.1 +/- 0.3 nmol l-1. In the aorta Bmax values were 15.1 +/- 0.5 fmol mg-1 protein (KD 1.9 +/- 0.27 nmol l-1) for control rats and 11.3 +/- 0.76 fmol mg-1 protein (KD 1.9 +/- 0.27 nmol l-1) for the TGR(mRen-2)27 rats AT1 receptor mRNA was reduced in the transgenic animals to 46 +/- 3% in the left atrium, 50 +/- 11% in the left ventricle and 40 +/- 3% in the aorta, respectively. 4. Together, the AT1 receptor is down-regulated in TGR (mRen-2)27 rats in comparison to wildtype Sprague Dawley rats leading to a profoundly decreased response of cardiac and aortic tissue upon stimulation with angiotensin II.