Niels P. Riksen

Acute and long-term cardiovascular effects of coffee: implications for coronary heart disease.

Despite decades of research, the question as to whether coffee intake increases the risk of coronary heart disease (CHD) remains controversial. In the current paper, we discuss the acute and long-term cardiovascular effects of coffee, and its major constituents, which could underlie such an association. Experimental studies have shown that administration of coffee or caffeine acutely raises blood pressure, circulating concentrations of (nor)epinephrine, increases arterial stiffness, impairs endothelium dependent vasodilation and inhibits ischemic preconditioning. The adverse effects of chronic coffee consumption on traditional risk factors for CHD are less consistent: although coffee intake slightly increases blood pressure, and plasma concentrations of homocysteine and cholesterol, there is no association with the incidence of hypertension, and a strong negative association with the incidence of type 2 diabetes mellitus. Moreover, common polymorphisms in genes involved in the metabolism of caffeine, catecholamines, homocysteine, and cholesterol can modulate the effect of coffee intake on cardiovascular parameters. Many epidemiological studies have explored the association between coffee drinking and CHD. Most prospective studies have not shown a positive association, whereas case-control studies in general have reported such an association. This discrepancy could be explained by an acute adverse effect of coffee, rather than a long-term adverse effect. We postulate that coffee drinking may have an acute detrimental effect in triggering coronary events and increasing infarct size in selected patient groups, rather than promoting the development of atherosclerosis in the general population, and we propose an alternative approach to explore such an effect in epidemiological studies.

Oxidized Low-Density Lipoprotein Induces Long-Term Proinflammatory Cytokine Production and Foam Cell Formation via Epigenetic Reprogramming of Monocytes

Objective— Although the role of monocytes in the pathogenesis of atherosclerosis is well established, the persistent vascular inflammation remains largely unexplained. Recently, our group reported that stimulation of monocytes with various microbial products can induce a long-lasting proinflammatory phenotype via epigenetic reprogramming, a process termed trained immunity. We now hypothesize that oxidized low-density lipoprotein (oxLDL) also induces a long-lasting proinflammatory phenotype in monocytes, which accelerates atherosclerosis by proinflammatory cytokine production and foam cell formation. Approach and Results— Isolated human monocytes were exposed for 24 hours to medium or oxLDL. After washing and resting for 6 days, the cells were exposed to toll-like receptor 2 and 4 agonists. Pre-exposure to oxLDL increased mRNA expression and protein formation on toll-like receptor 2 and 4 stimulation of several proatherogenic proteins, including interleukin-6, interleukin-18, interleukin-8, tumor necrosis factor-&agr;, monocyte chemoattractant protein 1, and matrix metalloproteinase 2 and 9. In addition, foam cell formation was enhanced after oxLDL exposure, which was associated with an upregulation of scavenger receptors CD36 and scavenger receptor-A and downregulation of ATP-binding cassette transporters, ABCA1 and ABCG1. Chromatin immunoprecipitation performed 6 days after oxLDL stimulation demonstrated increased trimethylation of lysine 4 at histone 3 in promoter regions of tnf&agr;, il-6, il-18, mcp-1, mmp2, mmp9, cd36, and sr-a. Finally, pretreatment of the monocytes with the histone methyltransferase inhibitor methylthioadenosine completely prevented the oxLDL-induced long-lasting proinflammatory phenotype. Conclusions— Brief exposure of monocytes to a low concentration of oxLDL induces a long-lasting proatherogenic macrophage phenotype via epigenetic histone modifications, characterized by increased proinflammatory cytokine production and foam cell formation.

The cardioprotective effects of metformin

Purpose of review In patients with type 2 diabetes mellitus, treatment with metformin is associated with a lower cardiovascular morbidity and mortality, compared with alternative glucose-lowering drugs. It has been suggested that metformin might exert direct protective effects on the heart. Recent findings This review appraises recent experimental animal studies on the effect of metformin on myocardial ischaemia-reperfusion injury and remodeling. In murine models of myocardial infarction, the administration of metformin potently limits infarct size. Activation of adenosine monophosphate-activated protein kinase, increased formation of adenosine, and the prevention of opening of the mitochondrial permeability transition pore at reperfusion all contribute to this cardioprotective effect. In addition, metformin therapy attenuates postinfarction cardiac remodeling. There is evidence that activation of adenosine monophosphate-activated protein kinase and endothelial nitric oxide synthase, and a reduced collagen expression are crucial for this effect. Summary The finding that metformin limits myocardial infarct size and remodeling in animal models of myocardial infarction suggests that patients suffering from myocardial ischaemia could benefit from treatment with metformin, even when these patients do not have diabetes. Currently, several clinical trials are being performed to test this hypothesis.

Glutaminolysis and Fumarate Accumulation Integrate Immunometabolic and Epigenetic Programs in Trained Immunity

Induction of trained immunity (innate immune memory) is mediated by activation of immune and metabolic pathways that result in epigenetic rewiring of cellular functional programs. Through network-level integration of transcriptomics and metabolomics data, we identify glycolysis, glutaminolysis, and the cholesterol synthesis pathway as indispensable for the induction of trained immunity by β-glucan in monocytes. Accumulation of fumarate, due to glutamine replenishment of the TCA cycle, integrates immune and metabolic circuits to induce monocyte epigenetic reprogramming by inhibiting KDM5 histone demethylases. Furthermore, fumarate itself induced an epigenetic program similar to β-glucan-induced trained immunity. In line with this, inhibition of glutaminolysis and cholesterol synthesis in mice reduced the induction of trained immunity by β-glucan. Identification of the metabolic pathways leading to induction of trained immunity contributes to our understanding of innate immune memory and opens new therapeutic avenues.

Oxidized Phospholipids on Lipoprotein(a) Elicit Arterial Wall Inflammation and an Inflammatory Monocyte Response in Humans

Background: Elevated lipoprotein(a) [Lp(a)] is a prevalent, independent cardiovascular risk factor, but the underlying mechanisms responsible for its pathogenicity are poorly defined. Because Lp(a) is the prominent carrier of proinflammatory oxidized phospholipids (OxPLs), part of its atherothrombosis might be mediated through this pathway. Methods: In vivo imaging techniques including magnetic resonance imaging, 18F-fluorodeoxyglucose uptake positron emission tomography/computed tomography and single-photon emission computed tomography/computed tomography were used to measure subsequently atherosclerotic burden, arterial wall inflammation, and monocyte trafficking to the arterial wall. Ex vivo analysis of monocytes was performed with fluorescence-activated cell sorter analysis, inflammatory stimulation assays, and transendothelial migration assays. In vitro studies of the pathophysiology of Lp(a) on monocytes were performed with an in vitro model for trained immunity. Results: We show that subjects with elevated Lp(a) (108 mg/dL [50–195 mg/dL]; n=30) have increased arterial inflammation and enhanced peripheral blood mononuclear cells trafficking to the arterial wall compared with subjects with normal Lp(a) (7 mg/dL [2–28 mg/dL]; n=30). In addition, monocytes isolated from subjects with elevated Lp(a) remain in a long-lasting primed state, as evidenced by an increased capacity to transmigrate and produce proinflammatory cytokines on stimulation (n=15). In vitro studies show that Lp(a) contains OxPL and augments the proinflammatory response in monocytes derived from healthy control subjects (n=6). This effect was markedly attenuated by inactivating OxPL on Lp(a) or removing OxPL on apolipoprotein(a). Conclusions: These findings demonstrate that Lp(a) induces monocyte trafficking to the arterial wall and mediates proinflammatory responses through its OxPL content. These findings provide a novel mechanism by which Lp(a) mediates cardiovascular disease. Clinical Trial Registration: URL: http://www.trialregister.nl. Unique identifier: NTR5006 (VIPER Study).

Metformin Prevents Myocardial Reperfusion Injury by Activating the Adenosine Receptor

Metformin improves cardiovascular outcomes in patients with type 2 diabetes compared with other glucose-lowering drugs. Experimental studies have shown that metformin can increase the intracellular concentration of adenosine monophosphate, which is a major determinant of the intracellular formation of adenosine. We hypothesize that metformin, given at reperfusion, can limit myocardial infarct size due to increased adenosine receptor stimulation. Isolated perfused hearts from Sprague-Dawley rats were subjected to 35 minutes of regional ischemia and 120 minutes of reperfusion. Perfusion with metformin (50 μM) for the first 15 minutes of reperfusion reduced infarct size (percent area at risk) from 42% ± 2% to 19% ± 4% (n ≥ 6; P < 0.01), which was blocked by a concomitant perfusion with the adenosine receptor antagonist 8-p-sulfophenyltheophylline (100 μM; 43% ± 3%) or nitrobenzylthioinosine (a blocker of transmembranous adenosine transport; 1 μM; 45% ± 5%). In addition, intravenous administration of metformin (5 mg/kg) reduced infarct size in a rat in situ model of myocardial infarction (34% ± 6% vs. 62% ± 5%; P < 0.01), which was completely abolished by 8-p-sulfophenyltheophylline (61% ± 3%). We conclude that metformin, given at reperfusion, reduces infarct size in a rat model of myocardial infarction, which is critically dependent on adenosine receptor stimulation, probably via increased intracellular formation of adenosine.

Oral therapy with dipyridamole limits ischemia-reperfusion injury in humans

Adenosine receptor stimulation induces several effects that could limit ischemia‐reperfusion injury. We hypothesize that treatment with the nucleoside uptake inhibitor dipyridamole increases endogenous adenosine and limits ischemia‐reperfusion injury in humans.

Potential role for adenosine in the pathogenesis of the vascular complications of hyperhomocysteinemia.

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Most previous investigations focused on the role of homocysteine as direct pathogenetic factor for these adverse vascular events. However, the exact pathophysiological mechanism is still unknown. In this review we discuss the hypothesis that a decreased extracellular concentration of adenosine could contribute to the adverse cardiovascular effects of hyperhomocysteinemia. Fundamental to this hypothesis is that, in vivo, any increase in the plasma concentration of homocysteine reflects an increased intracellular homocysteine concentration, which inevitably will result in a decrease in the adenosine concentration. In this situation, the hydrolase reaction catalysed by S-adenosylhomocysteine hydrolase will reverse and S-adenosylhomocysteine will accumulate at the expense of adenosine. Stimulation of adenosine receptors by adenosine results in various cardio- and vasoprotective actions, like modulation of vascular resistance, presynaptic inhibition of norepinephrine release, ischaemic preconditioning, inhibition of platelet aggregation, modulation of inflammation and regulation of vascular cell proliferation and death. In this respect, a decrease in the adenosine concentration could contribute significantly to the cardiovascular effects of hyperhomocysteinemia.

Annexin A5 Scintigraphy of Forearm as a Novel In Vivo Model of Skeletal Muscle Preconditioning in Humans

Background—Nonlethal ischemia and reperfusion reduce ischemia-reperfusion–induced cell death, a phenomenon called ischemic preconditioning. In animal models, this potent endogenous protection is mimicked in vivo by administration of adenosine. In humans, exploitation of ischemic preconditioning is hindered by the lack of an appropriate in vivo model to study this phenomenon. To solve this problem, we aimed to set up an easy-to-use human in vivo model to study ischemic or pharmacological preconditioning. Methods and Results—Healthy male volunteers performed unilateral ischemic handgrip. At reperfusion, we intravenously injected technetium-99m–labeled Annexin A5, a presumed marker of ischemic injury, and we imaged both forearms and hands simultaneously with a gamma camera. Region of interest analysis (counts per pixel) and subsequent calculation of the percentage difference in radioactivity between experimental and control hands (thenar muscle; mean±SE) revealed significant uptake to the ischemically exercised tissue (26±3% at 4 hours after reperfusion; P<0.05). This selective localization of Annexin A5 was reduced by ischemic preconditioning (10 minutes of ischemia plus reperfusion before ischemic exercise) or by infusion of adenosine into the brachial artery to 6±1% and 10±3%, respectively (P<0.05 versus ischemic exercise alone), resembling observations in animal models with infarct size as an end point. Appropriate control experiments supported our conclusion. Conclusions—Annexin A5 scintigraphy can be applied to test pharmacological or physiological interventions for their ability to prevent ischemia-reperfusion injury.

Enhanced Cellular Adenosine Uptake Limits Adenosine Receptor Stimulation in Patients With Hyperhomocysteinemia

Objective— Endogenous adenosine has several cardioprotective effects. We postulate that in patients with hyperhomocysteinemia increased intracellular formation of S-adenosylhomocysteine decreases free intracellular adenosine. Subsequently, facilitated diffusion of extracellular adenosine into cells through dipyridamole-sensitive transporters is enhanced, limiting adenosine receptor stimulation. We tested this hypothesis in patients with classical homocystinuria (n=9, plasma homocysteine 93.1±24.7 &mgr;mol/L) and matched controls (n=8, homocysteine 9.1±1.0). Methods and Results— Infusion of adenosine (0.5, 1.5, 5.0, and 15.0 &mgr;g/min/dL forearm) into the brachial artery increased forearm blood flow, as measured with venous occlusion plethysmography, to 2.9±0.4, 4.3±0.5, 5.6±1.1, and 9.6±2.1 in the patients and to 2.8±0.6, 4.4±1.0, 9.0±1.7, and 17.0±3.1 mL/min/dL in controls (P<0.05). However, adenosine-induced vasodilation in the presence of dipyridamole (100 &mgr;g/min/dL) was similar in both groups (P=0.9). Additionally, in isolated erythrocytes, adenosine uptake was accelerated by incubation with homocysteine (half-time 6.4±0.3 versus 8.1±0.5 minutes, P<0.001) associated with increased intracellular formation of S-adenosylhomocysteine (P<0.0001). Conclusions— In hyperhomocysteinemia, adenosine-induced vasodilation is impaired but is restored by dipyridamole. Accelerated cellular adenosine uptake probably accounts for these observations. These impaired actions of adenosine could well contribute to the cardiovascular complications of hyperhomocysteinemia.