Michael Demosthenous

Rapid, Direct Effects of Statin Treatment on Arterial Redox State and Nitric Oxide Bioavailability in Human Atherosclerosis via Tetrahydrobiopterin-Mediated Endothelial Nitric Oxide Synthase Coupling

Background— Treatment with statins improves clinical outcome, but the exact mechanisms of pleiotropic statin effects on vascular function in human atherosclerosis remain unclear. We examined the direct effects of atorvastatin on tetrahydrobiopterin-mediated endothelial nitric oxide (NO) synthase coupling in patients with coronary artery disease. Methods and Results— We first examined the association of statin treatment with vascular NO bioavailability and arterial superoxide (O2·−) in 492 patients undergoing coronary artery bypass graft surgery. Then, 42 statin-naïve patients undergoing elective coronary artery bypass graft surgery were randomized to atorvastatin 40 mg/d or placebo for 3 days before surgery to examine the impact of atorvastatin on endothelial function and O2·− generation in internal mammary arteries. Finally, segments of internal mammary arteries from 26 patients were used in ex vivo experiments to evaluate the statin-dependent mechanisms regulating the vascular redox state. Statin treatment was associated with improved vascular NO bioavailability and reduced O2·− generation in internal mammary arteries. Oral atorvastatin increased vascular tetrahydrobiopterin bioavailability and reduced basal and N-nitro-L-arginine methyl ester–inhibitable O2·− in internal mammary arteries independently of low-density lipoprotein lowering. In ex vivo experiments, atorvastatin rapidly improved vascular tetrahydrobiopterin bioavailability by upregulating GTP-cyclohydrolase I gene expression and activity, resulting in improved endothelial NO synthase coupling and reduced vascular O2·−. These effects were reversed by mevalonate, indicating a direct effect of vascular hydroxymethylglutaryl-coenzyme A reductase inhibition. Conclusions— This study demonstrates for the first time in humans the direct effects of statin treatment on the vascular wall, supporting the notion that this effect is independent of low-density lipoprotein lowering. Atorvastatin directly improves vascular NO bioavailability and reduces vascular O2·− through tetrahydrobiopterin-mediated endothelial NO synthase coupling. These findings provide new insights into the mechanisms mediating the beneficial vascular effects of statins in humans. Clinical Trial Registration— URL: http://www.clinicaltrials.gov. Unique identifier: NCT01013103.

Preoperative Atorvastatin Treatment in CABG Patients Rapidly Improves Vein Graft Redox State by Inhibition of Rac1 and NADPH-Oxidase Activity

Background— Statins improve clinical outcome of patients with atherosclerosis, but their perioperative role in patients undergoing coronary artery bypass grafting (CABG) is unclear. We hypothesized that short-term treatment with atorvastatin before CABG would improve the redox state in saphenous vein grafts (SVGs), independently of low-density lipoprotein cholesterol (LDL)-lowering. Methods and Results— In a randomized, double-blind controlled trial, 42 statin-naïve patients undergoing elective CABG received atorvastatin 40 mg/d or placebo for 3 days before surgery. Circulating inflammatory markers and malondialdehyde (MDA) were measured before and after treatment. SVG segments were used to determine vascular superoxide (O2·−) and Rac1 activation. For ex vivo studies, SVG segments from 24 patients were incubated for 6 hours with atorvastatin 0, 5, or 50 &mgr;mol/L. Oral atorvastatin reduced vascular basal and NADPH-stimulated O2·− in SVGs (P<0.05 for all versus placebo) and reduced plasma MDA (P<0.05), independently of LDL-lowering and of changes in inflammatory markers. In SVGs exposed to atorvastatin ex vivo, without exposure to LDL, basal and NADPH-stimulated O2·− were significantly reduced (P<0.01 for both concentrations versus 0 &mgr;mol/L) in association with a striking reduction in Rac1 activation and 1 membrane-bound Rac1 and p67phox subunit. The antioxidant effects of atorvastatin were reversed by mevalonate, implying a dependence on vascular HMG-CoA reductase inhibition. Conclusions— Short-term treatment with atorvastatin 40 mg/d before CABG improves redox state in SVGs, by inhibiting vascular Rac1-mediated activation of NADPH-oxidase. These novel findings suggest that statin therapy should be maintained or initiated in patients undergoing CABG, independently of LDL levels. Clinical Trial Registration— URL: http://www.clinicaltrials.gov. Unique identifier: NCT01013103.

Role of asymmetrical dimethylarginine in inflammation-induced endothelial dysfunction in human atherosclerosis.

We explored the role of asymmetrical dimethylarginine (ADMA) as a cause of endothelial dysfunction induced by systemic inflammation. In vitro data suggest that ADMA bioavailability is regulated by proinflammatory stimuli, but it is unclear whether ADMA is a link between inflammation and endothelial dysfunction in humans. In study 1 we recruited 351 patients with coronary artery disease (CAD) and 87 healthy controls. In study 2 we recruited 69 CAD, 69 healthy, and 10 patients with rheumatoid arthritis, whereas in study 3, 22 healthy and 70 CAD subjects were randomly assigned to Salmonella typhii vaccination (n=11 healthy and n=60 CAD) or placebo (n=11 healthy and n=10 CAD). Circulating interleukin 6/ADMA and flow-mediated dilation (FMD) were measured at 0 and 8 hours. In study 1, ADMA was inversely correlated with FMD in healthy individuals and CAD patients (P<0.0001 for both). However, interleukin 6 was inversely correlated with FMD (P<0.0001) in healthy subjects but not in CAD patients. The positive correlation between ADMA and interleukin 6 was stronger in healthy (r=0.515; P<0.0001) compared with CAD (r=0.289; P=0.0001) subjects. In study 2, both patients with rheumatoid arthritis and CAD had higher interleukin 6 (P<0.0001) and ADMA (P=0.004) but lower FMD (P=0.001) versus healthy subjects. In study 3, vaccination increased interleukin 6 in healthy (P<0.001) and CAD (P<0.001) subjects. FMD was reduced in healthy subjects (P<0.05), but its reduction in CAD was borderline. Vaccination increased ADMA only in healthy subjects (P<0.001). Systemic, low-grade inflammation leads to increased ADMA that may induce endothelial dysfunction. This study demonstrated that ADMA may be a link between inflammation and endothelial dysfunction in humans.

Induction of Vascular GTP-Cyclohydrolase I and Endogenous Tetrahydrobiopterin Synthesis Protect Against Inflammation-Induced Endothelial Dysfunction in Human Atherosclerosis

Background— The endothelial nitric oxide synthase cofactor tetrahydrobiopterin (BH4) is essential for maintenance of enzymatic function. We hypothesized that induction of BH4 synthesis might be an endothelial defense mechanism against inflammation in vascular disease states. Methods and Results— In Study 1, 20 healthy individuals were randomized to receive Salmonella typhi vaccine (a model of acute inflammation) or placebo in a double-blind study. Vaccination increased circulating BH4 and interleukin 6 and induced endothelial dysfunction (as evaluated by brachial artery flow-mediated dilation) after 8 hours. In Study 2, a functional haplotype (X haplotype) in the GCH1 gene, encoding GTP-cyclohydrolase I, the rate-limiting enzyme in biopterin biosynthesis, was associated with endothelial dysfunction in the presence of high-sensitivity C-reactive protein in 440 coronary artery disease patients. In Study 3, 10 patients with coronary artery disease homozygotes for the GCH1 X haplotype (XX) and 40 without the haplotype (OO) underwent S Typhi vaccination. XX patients were unable to increase plasma BH4 and had a greater reduction of flow-mediated dilation than OO patients. In Study 4, vessel segments from 19 patients undergoing coronary bypass surgery were incubated with or without cytokines (interleukin-6/tumor necrosis factor-&agr;/lipopolysaccharide) for 24 hours. Cytokine stimulation upregulated GCH1 expression, increased vascular BH4, and improved vasorelaxation in response to acetylcholine, which was inhibited by the GTP-cyclohydrolase inhibitor 2,4-diamino-6-hydroxypyrimidine. Conclusions— The ability to increase vascular GCH1 expression and BH4 synthesis in response to inflammation preserves endothelial function in inflammatory states. These novel findings identify BH4 as a vascular defense mechanism against inflammation-induced endothelial dysfunction.

Reciprocal Effects of Systemic Inflammation and Brain Natriuretic Peptide on Adiponectin Biosynthesis in Adipose Tissue of Patients With Ischemic Heart Disease

Objective— To explore the role of systemic inflammation in the regulation of adiponectin levels in patients with ischemic heart disease. Approach and Results— In a cross-sectional study of 575 subjects, serum adiponectin was compared between healthy subjects, patients with coronary artery disease with no/mild/severe heart failure (HF), and patients with nonischemic HF. Adiponectin expression and release from femoral, subcutaneous and thoracic adipose tissue was determined in 258 additional patients with coronary artery bypass grafting. Responsiveness of the various human adipose tissue depots to interleukin-6, tumor necrosis factor-&agr;, and brain natriuretic peptide (BNP) was examined by using ex vivo models of human fat. The effects of inducible low-grade inflammation were tested by using the model of Salmonella typhi vaccine-induced inflammation in healthy individuals. In the cross-sectional study, HF strikingly increased adiponectin levels. Plasma BNP was the strongest predictor of circulating adiponectin and its release from all adipose tissue depots in patients with coronary artery bypass grafting, even in the absence of HF. Femoral AT was the depot with the least macrophages infiltration and the largest adipocyte cell size and the only responsive to systemic and ex vivo proinflammatory stimulation (effect reversible by BNP). Low-grade inflammation reduced circulating adiponectin levels, while circulating BNP remained unchanged. Conclusions— This study demonstrates the regional variability in the responsiveness of human adipose tissue to systemic inflammation and suggests that BNP (not systemic inflammation) is the main driver of circulating adiponectin in patients with advanced atherosclerosis even in the absence of HF. Any interpretation of circulating adiponectin as a biomarker should take into account the underlying disease state, background inflammation, and BNP levels.

Platelet activation in atherogenesis associated with low-grade inflammation.

Further to the established role of platelets in thrombosis and hemostasis, increasing evidence suggests that they also play a crucial role in atherogenesis. Platelets produce a number of agents contributing to the systemic low-grade inflammation implicated in atherogenesis. Platelet activation following inflammatory stimulus leads to the expression of surface receptors such as GPIb/IX/V, P-selectin, CD40, and to the release of several pro-inflammatory agents. Platelet receptors and released molecules play a critical role during the initiation and the progression of atherosclerosis by mediating leukocytes recruitment and adhesion to the vascular wall. Endothelial dysfunction, an early feature in atherosclerosis, is associated with low-grade inflammation within the vascular wall, and it leads to the reduced bioavailability of nitric oxide. Dysfunctional endothelium itself releases inflammatory molecules leading toward platelets activation and adhesion to the vascular wall. Platelets are no longer considered simply as cells participating in thrombosis. They are regulators of multiple processes in the human body, including inflammation, regulation of endothelial physiology and atherogenesis. The design of new therapeutic strategies targeting platelets and their impact in atherosclerosis-related low-grade inflammation are in the center of current cardiovascular research.

Novel Therapeutic Strategies Targeting Vascular Redox in Human Atherosclerosis

It is now widely accepted that redox signaling is a key feature in vascular homeostasis. Reactive oxygen species are generated by a wide range of enzymatic systems located in both vascular endothelium and vascular wall. Further, to their role as cytotoxic molecules produced by immune system, free radicals play critical signaling roles in the vascular wall. By regulating several redox-sensitive transcription pathways, free radicals play a key role in the synthesis of inflammatory mediators in both vascular endothelium and vascular wall, with important role in the overall vascular dysfunction. The well-established role of redox state in vascular disease mandates that development of newer therapeutic strategies should be able to alter redox-sensitive intracellular signaling events. Widely used cardiovascular agents like statins or angiotensin receptor blockers have well documented beneficial effects on vascular redox state, reflected also in clinical outcome improvement. Newer promising strategies along with recent patented inventions may also include thiazolidinediones, folates, tetrahydrobiopterin, cyclopentone prostaglandins and aldose reductase inhibitors with well known effects on vascular redox, but with still unclear results on clinical outcome. Better understanding of redox-sensitive intracellular signaling pathways could indicate the critical steps to intervene with newer agents to reverse vascular dysfunction, inhibiting atherosclerosis progression and potentially improve clinical outcome.

RAPID, DIRECT EFFECTS OF STATIN TREATMENT ON ARTERIAL REDOX STATE AND NITRIC OXIDE BIOAVAILABILITY IN HUMAN ATHEROSCLEROSIS VIA TETRAHYDROBIOPTERIN-MEDIATED ENOS COUPLING

Methods: We recruited 492 patients undergoing CABG. During surgery segments of internal mammary arteries (IMA) were obtained. Arterial O2was determined by lucigenin chemiluminescence (+/-LNAME), while acetylcholine-induced vasorelaxations were assessed ex-vivo. In a 2nd study, IMA segments from 10 patients were incubated ex vivo with atorvastatin, for 6h (+/mevalonate (Mev)). Vascular tetrahydrobiopterin (BH4 was measured by HPLC, while GTP-cyclohydrolase I (GTPCH-I) gene expression was determined by qRT-PCR.

MYOCARDIAL O2-AND ONOO-GENERATION IN CHRONIC ATRIAL FIBRILLATION

Background: Myocardial redox state is a key feature for atrial fibrillation (AF). We examined the mechanisms regulating myocardial superoxide (O2-) and peroxynitrite (ONOO-) generation in patients with chronic AF. Methods: Samples of right atrium appendage were obtained from 113 patients undergoing elective cardiac surgery (98 in sinus rhythm (SR) and 15 with chronic AF). Myocardial O2- generation was determined by lucigenin chemiluminescence, while urate-inhibitable luminol chemiluminescence was used to estimate ONOO- generation. NADPH oxidase activity was estimated by the NADPH-stimulated O2- and its apocynin inhibitable fraction, uncoupled nitric oxide synthase (NOS) by using LNAME and mitochondrial oxidases by using rotenone. Results: Patients with chronic AF had slightly but not significantly higher resting O2- (A). However, NADPH-stimulated (B) and apocynin-inhibitable (C) O2- were significantly greater in AF compared to SR patients. There was no significant difference in rotenone-inhibitable O2- (D). However, LNAME-inhibitable (E) and ONOO- generation (F) were significantly greater in AF compared to SR patients (F). Left atrium diameter was significantly correlated with NADPH-stimulated O2- (r=0.294, p=0.025) and apocynin-inhibitable O2- (r=0.288, p=0.032). Conclusions: Chronic AF is characterized by greater NADPH-oxidase activity, NOS uncoupling and elevated ONOO- generation in atrial myocardium. Targeting these mechanisms provides new therapeutic strategies for AF.

Epicardial right ventricular lipoma presenting with sustained ventricular tachycardia

Cardiac lipomas are benign tumors but can be associated with septal infiltration, arrhythmias, and superior vena cava stenosis. We present images of an epicardial right ventricular lipoma presentingwith sustained ventricular tachycardia (VT). A 59-year-old female, with no previous medical history, presented with syncope and was found to have sustained VT with left bundle branch block morphology, which was successfully cardioverted to normal sinus rhythm (NSR). A transthoracic echocardiogram revealed a 6 × 4-cm mass compressing the right ventricle (RV), resulting in significant tricuspid regurgitation (Figure 1A). Cardiac magnetic resonance imaging confirmed these findings (Figure 1B). A coronary angiogram revealed no coronary stenosis. At the time of surgery, cardiopulmonary bypass (CPB) was established via a mediansternotomy and ascending aortic and bicaval cannulation. The aorta was crossclamped and the heart arrested with cold antegrade blood cardioplegia. The tumor was located on the anterior surface of the RV and extended from the atrioventricular groove to the tricuspid annulus (Figures 2A and 2B). The tumor, with its surrounding capsule, was resected (Figure 2C). The tricuspid annulus was repaired with a #30 annuloplasty ring (Carpentier-Edwards Physio Annuloplasty Ring, Edwards Lifesciences LLC, Irvine, CA) and the defect in the RV was reconstructed with a pericardial patch reinforced with pericardial strips (Figure 2D). The patient was weaned off CPB in NSR; the CPB and crossclamp times were 114 and 102min, respectively. The patient had an uncomplicated postoperative course and the histology was consistent with a benign lipoma. A month following surgery, a follow-up electrophysiology study showed sustained monomorphic VT associated with hemodynamic compromise. Therefore, an implantable cardioverterdefibrillator (EveraTM ICD, Medtronic, Minneapolis, MN) was inserted. She is now 2 years postsurgery and has had no further VT on beta-blocker therapy. Follow-up echocardiography showed no recurrent tumor development (Figure 3).