Myeloperoxidase induces monocyte migration and activation after acute myocardial infarction.

Introduction: Myocardial infarction (MI) is a significant contributor to morbidity and mortality worldwide. Many individuals who survive the acute event continue to experience heart failure (HF), with inflammatory and healing processes post-MI playing a pivotal role. Polymorphonuclear neutrophils (PMN) and monocytes infiltrate the infarcted area, where PMN release high amounts of the heme enzyme myeloperoxidase (MPO). MPO has numerous inflammatory properties and MPO plasma levels are correlated with prognosis and severity of MI. While studies have focused on MPO inhibition and controlling PMN infiltration into the infarcted tissue, less is known on MPO's role in monocyte function. Methods and results: Here, we combined human data with mouse and cell studies to examine the role of MPO on monocyte activation and migration. We revealed a correlation between plasma MPO levels and monocyte activation in a patient study. Using a mouse model of MI, we demonstrated that MPO deficiency led to an increase in splenic monocytes and a decrease in cardiac monocytes compared to wildtype mice (WT). In vitro studies further showed that MPO induces monocyte migration, with upregulation of the chemokine receptor CCR2 and upregulation of inflammatory pathways identified as underlying mechanisms. Conclusion: Taken together, we identify MPO as a pro-inflammatory mediator of splenic monocyte recruitment and activation post-MI and provide mechanistic insight for novel therapeutic strategies after ischemic injury.

Myeloperoxidase is a critical mediator of anthracycline-induced cardiomyopathy.

Cardiotoxicity is a major complication of anthracycline therapy that negatively impacts prognosis. Effective pharmacotherapies for prevention of anthracycline-induced cardiomyopathy (AICM) are currently lacking. Increased plasma levels of the neutrophil-derived enzyme myeloperoxidase (MPO) predict occurrence of AICM in humans. We hypothesized that MPO release causally contributes to AICM. Mice intravenously injected with the anthracycline doxorubicin (DOX) exhibited higher neutrophil counts and MPO levels in the circulation and cardiac tissue compared to saline (NaCl)-treated controls. Neutrophil-like HL-60 cells exhibited increased MPO release upon exposition to DOX. DOX induced extensive nitrosative stress in cardiac tissue alongside with increased carbonylation of sarcomeric proteins in wildtype but not in Mpo-/- mice. Accordingly, co-treatment of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) with DOX and MPO aggravated loss of hiPSC-CM-contractility compared to DOX treatment alone. DOX-treated animals exhibited pronounced cardiac apoptosis and inflammation, which was attenuated in MPO-deficient animals. Finally, genetic MPO deficiency and pharmacological MPO inhibition protected mice from the development of AICM. The anticancer efficacy of DOX was unaffected by MPO deficiency. Herein we identify MPO as a critical mediator of AICM. We demonstrate that DOX induces cardiac neutrophil infiltration and release of MPO, which directly impairs cardiac contractility through promoting oxidation of sarcomeric proteins, cardiac inflammation and cardiomyocyte apoptosis. MPO thus emerges as a promising pharmacological target for prevention of AICM.

Myeloid leukocytes' diverse effects on cardiovascular and systemic inflammation in chronic kidney disease.

Chronic kidney disease's prevalence rises globally. Whereas dialysis treatment replaces the kidney's filtering function and prolongs life, dreaded consequences in remote organs develop inevitably over time. Even milder reductions in kidney function not requiring replacement therapy associate with bacterial infections, cardiovascular and heart valve disease, which markedly limit prognosis in these patients. The array of complications is diverse and engages a wide gamut of cellular and molecular mechanisms. The innate immune system is profoundly and systemically altered in chronic kidney disease and, as a unifying element, partakes in many of the disease's complications. As such, a derailed immune system fuels cardiovascular disease progression but also elevates the propensity for serious bacterial infections. Recent data further point towards a role in developing calcific aortic valve stenosis. Here, we delineate the current state of knowledge on how chronic kidney disease affects innate immunity in cardiovascular organs and on a systemic level. We review the role of circulating myeloid cells, monocytes and neutrophils, resident macrophages, dendritic cells, ligands, and cellular pathways that are activated or suppressed when renal function is chronically impaired. Finally, we discuss myeloid cells' varying responses to uremia from a systems immunology perspective.

Immunotherapeutic Strategies in Cancer and Atherosclerosis-Two Sides of the Same Coin.

The development and clinical approval of immunotherapies has revolutionized cancer therapy. Although the role of adaptive immunity in atherogenesis is now well-established and several immunomodulatory strategies have proven beneficial in preclinical studies, anti-atherosclerotic immunotherapies available for clinical application are not available. Considering that adaptive immune responses are critically involved in both carcinogenesis and atherogenesis, immunotherapeutic approaches for the treatment of cancer and atherosclerosis may exert undesirable but also desirable side effects on the other condition, respectively. For example, the high antineoplastic efficacy of immune checkpoint inhibitors, which enhance effector immune responses against tumor cells by blocking co-inhibitory molecules, was recently shown to be constrained by substantial proatherogenic properties. In this review, we outline the specific role of immune responses in the development of cancer and atherosclerosis. Furthermore, we delineate how current cancer immunotherapies affect atherogenesis and discuss whether anti-atherosclerotic immunotherapies may similarly have an impact on carcinogenesis.

Nanoparticle-encapsulated siRNAs for gene silencing in the haematopoietic stem-cell niche.

Bone-marrow endothelial cells in the haematopoietic stem-cell niche form a network of blood vessels that regulates blood-cell traffic as well as the maintenance and function of haematopoietic stem and progenitor cells. Here, we report the design and in vivo performance of systemically injected lipid-polymer nanoparticles encapsulating small interfering RNA (siRNA), for the silencing of genes in bone-marrow endothelial cells. In mice, nanoparticles encapsulating siRNA sequences targeting the proteins stromal-derived factor 1 (Sdf1) or monocyte chemotactic protein 1 (Mcp1) enhanced (when silencing Sdf1) or inhibited (when silencing Mcp1) the release of stem and progenitor cells and of leukocytes from the bone marrow. In a mouse model of myocardial infarction, nanoparticle-mediated inhibition of cell release from the haematopoietic niche via Mcp1 silencing reduced leukocytes in the diseased heart, improved healing after infarction and attenuated heart failure. Nanoparticle-mediated RNA interference in the haematopoietic niche could be used to investigate haematopoietic processes for therapeutic applications in cancer, infection and cardiovascular disease.

Imaging Cardiovascular and Lung Macrophages With the Positron Emission Tomography Sensor 64Cu-Macrin in Mice, Rabbits, and Pigs.

BACKGROUND: Macrophages, innate immune cells that reside in all organs, defend the host against infection and injury. In the heart and vasculature, inflammatory macrophages also enhance tissue damage and propel cardiovascular diseases. METHODS: We here use in vivo positron emission tomography (PET) imaging, flow cytometry, and confocal microscopy to evaluate quantitative noninvasive assessment of cardiac, arterial, and pulmonary macrophages using the nanotracer 64Cu-Macrin-a 20-nm spherical dextran nanoparticle assembled from nontoxic polyglucose. RESULTS: PET imaging using 64Cu-Macrin faithfully reported accumulation of macrophages in the heart and lung of mice with myocardial infarction, sepsis, or pneumonia. Flow cytometry and confocal microscopy detected the near-infrared fluorescent version of the nanoparticle (VT680Macrin) primarily in tissue macrophages. In 5-day-old mice, 64Cu-Macrin PET imaging quantified physiologically more numerous cardiac macrophages. Upon intravenous administration of 64Cu-Macrin in rabbits and pigs, we detected heightened macrophage numbers in the infarcted myocardium, inflamed lung regions, and atherosclerotic plaques using a clinical PET/magnetic resonance imaging scanner. Toxicity studies in rats and human dosimetry estimates suggest that 64Cu-Macrin is safe for use in humans. CONCLUSIONS: Taken together, these results indicate 64Cu-Macrin could serve as a facile PET nanotracer to survey spatiotemporal macrophage dynamics during various physiological and pathological conditions. 64Cu-Macrin PET imaging could stage inflammatory cardiovascular disease activity, assist disease management, and serve as an imaging biomarker for emerging macrophage-targeted therapeutics.

Bone Marrow Endothelial Cells Regulate Myelopoiesis in Diabetes Mellitus.

BACKGROUND: Diabetes mellitus is a prevalent public health problem that affects about one-third of the US population and leads to serious vascular complications with increased risk for coronary artery disease. How bone marrow hematopoiesis contributes to diabetes mellitus complications is incompletely understood. We investigated the role of bone marrow endothelial cells in diabetic regulation of inflammatory myeloid cell production. METHODS: In 3 types of mouse diabetes mellitus, including streptozotocin, high-fat diet, and genetic induction using leptin-receptor-deficient db/db mice, we assayed leukocytes, hematopoietic stem and progenitor cells (HSPC). In addition, we investigated bone marrow endothelial cells with flow cytometry and expression profiling. RESULTS: In diabetes mellitus, we observed enhanced proliferation of HSPC leading to augmented circulating myeloid cell numbers. Analysis of bone marrow niche cells revealed that endothelial cells in diabetic mice expressed less Cxcl12, a retention factor promoting HSPC quiescence. Transcriptome-wide analysis of bone marrow endothelial cells demonstrated enrichment of genes involved in epithelial growth factor receptor (Egfr) signaling in mice with diet-induced diabetes mellitus. To explore whether endothelial Egfr plays a functional role in myelopoiesis, we generated mice with endothelial-specific deletion of Egfr (Cdh5CreEgfrfl/fl). We found enhanced HSPC proliferation and increased myeloid cell production in Cdh5CreEgfrfl/fl mice compared with wild-type mice with diabetes mellitus. Disrupted Egfr signaling in endothelial cells decreased their expression of the HSPC retention factor angiopoietin-1. We tested the functional relevance of these findings for wound healing and atherosclerosis, both implicated in complications of diabetes mellitus. Inflammatory myeloid cells accumulated more in skin wounds of diabetic Cdh5CreEgfrfl/fl mice, significantly delaying wound closure. Atherosclerosis was accelerated in Cdh5CreEgfrfl/fl mice, leading to larger and more inflamed atherosclerotic lesions in the aorta. CONCLUSIONS: In diabetes mellitus, bone marrow endothelial cells participate in the dysregulation of bone marrow hematopoiesis. Diabetes mellitus reduces endothelial production of Cxcl12, a quiescence-promoting niche factor that reduces stem cell proliferation. We describe a previously unknown counterregulatory pathway, in which protective endothelial Egfr signaling curbs HSPC proliferation and myeloid cell production.

Tissue-Specific Macrophage Responses to Remote Injury Impact the Outcome of Subsequent Local Immune Challenge.

Myocardial infarction, stroke, and sepsis trigger systemic inflammation and organism-wide complications that are difficult to manage. Here, we examined the contribution of macrophages residing in vital organs to the systemic response after these injuries. We generated a comprehensive catalog of changes in macrophage number, origin, and gene expression in the heart, brain, liver, kidney, and lung of mice with myocardial infarction, stroke, or sepsis. Predominantly fueled by heightened local proliferation, tissue macrophage numbers increased systemically. Macrophages in the same organ responded similarly to different injuries by altering expression of tissue-specific gene sets. Preceding myocardial infarction improved survival of subsequent pneumonia due to enhanced bacterial clearance, which was caused by IFNÉ£ priming of alveolar macrophages. Conversely, EGF receptor signaling in macrophages exacerbated inflammatory lung injury. Our data suggest that local injury activates macrophages in remote organs and that targeting macrophages could improve resilience against systemic complications following myocardial infarction, stroke, and sepsis.

Imaging the Vascular Bone Marrow Niche During Inflammatory Stress.

RATIONALE: Inflammatory stress induced by exposure to bacterial lipopolysaccharide causes hematopoietic stem cell expansion in the bone marrow niche, generating a cellular immune response. As an integral component of the hematopoietic stem cell niche, the bone marrow vasculature regulates the production and release of blood leukocytes, which protect the host against infection but also fuel inflammatory diseases. OBJECTIVE: We aimed to develop imaging tools to explore vascular changes in the bone marrow niche during acute inflammation. METHODS AND RESULTS: Using the TLR (Toll-like receptor) ligand lipopolysaccharide as a prototypical danger signal, we applied multiparametric, multimodality and multiscale imaging to characterize how the bone marrow vasculature adapts when hematopoiesis boosts leukocyte supply. In response to lipopolysaccharide, ex vivo flow cytometry and histology showed vascular changes to the bone marrow niche. Specifically, proliferating endothelial cells gave rise to new vasculature in the bone marrow during hypoxic conditions. We studied these vascular changes with complementary intravital microscopy and positron emission tomography/magnetic resonance imaging. Fluorescence and positron emission tomography integrin αVß3 imaging signal increased during lipopolysaccharide-induced vascular remodeling. Vascular leakiness, quantified by albumin-based in vivo microscopy and magnetic resonance imaging, rose when neutrophils departed and hematopoietic stem and progenitor cells proliferated more vigorously. CONCLUSIONS: Introducing a tool set to image bone marrow either with cellular resolution or noninvasively within the entire skeleton, this work sheds light on angiogenic responses that accompany emergency hematopoiesis. Understanding and monitoring bone marrow vasculature may provide a key to unlock therapeutic targets regulating systemic inflammation.

E-Selectin Inhibition Mitigates Splenic HSC Activation and Myelopoiesis in Hypercholesterolemic Mice With Myocardial Infarction.

OBJECTIVE: Atherosclerosis is a chronic disease characterized by lipid accumulation in the arterial wall. After myocardial infarction (MI), atherosclerotic plaques are infiltrated by inflammatory myeloid cells that aggravate the disease and increase the risk of secondary myocardial ischemia. Splenic myelopoiesis provides a steady flow of myeloid cells to inflamed atherosclerotic lesions after MI. Therefore, targeting myeloid cell production in the spleen could ameliorate increased atherosclerotic plaque inflammation after MI. APPROACH AND RESULTS: Here we show that MI increases splenic myelopoiesis by driving hematopoietic stem and progenitor cells into the cell cycle. In an atherosclerotic mouse model, E-selectin inhibition decreased hematopoietic stem and progenitor cell proliferation in the spleen after MI. This led to reduced extramedullary myelopoiesis and decreased myeloid cell accumulation in atherosclerotic lesions. Finally, we observed stable atherosclerotic plaque features, including smaller plaque size, reduced necrotic core area, and thicker fibrous cap after E-selectin inhibition. CONCLUSIONS: Inhibiting E-selectin attenuated inflammation in atherosclerotic plaques, likely by reducing leukocyte recruitment into plaques and by mitigating hematopoietic stem and progenitor cell activation in the spleen of mice with MI.

Myeloid-Specific Deletion of Diacylglycerol Lipase α Inhibits Atherogenesis in ApoE-Deficient Mice.

BACKGROUND: The endocannabinoid 2-arachidonoylglycerol (2-AG) is a known modulator of inflammation. Despite its high concentration in vascular tissue, the role of 2-AG in atherogenesis has not yet been examined. METHODS: ApoE-deficient mice were sublethally irradiated and reconstituted with bone marrow from mice with a myeloid-specific knockout of the 2-AG synthesising enzyme diacylglycerol lipase α (Dagla) or control bone marrow with an intact 2-AG biosynthesis. After a cholesterol-rich diet for 8 weeks, plaque size and plaque morphology were examined in chimeric mice. Circulating inflammatory cells were assessed by flow cytometry. Aortic tissue and plasma levels of endocannabinoids were measured using liquid chromatography-multiple reaction monitoring. RESULTS: Mice with Dagla-deficient bone marrow and circulating myeloid cells showed a significantly reduced plaque burden compared to controls. The reduction in plaque size was accompanied by a significantly diminished accumulation of both neutrophil granulocytes and macrophages in atherosclerotic lesions of Dagla-deficient mice. Moreover, CB2 expression and the amount of oxidised LDL within atherosclerotic lesions was significantly reduced. FACS analyses revealed that levels of circulating inflammatory cells were unaltered in Dagla-deficient mice. CONCLUSIONS: Myeloid synthesis of the endocannabinoid 2-AG appears to promote vascular inflammation and atherogenesis. Thus, myeloid-specific disruption of 2-AG synthesis may represent a potential novel therapeutic strategy against atherosclerosis.

Macrophages retain hematopoietic stem cells in the spleen via VCAM-1.

Splenic myelopoiesis provides a steady flow of leukocytes to inflamed tissues, and leukocytosis correlates with cardiovascular mortality. Yet regulation of hematopoietic stem cell (HSC) activity in the spleen is incompletely understood. Here, we show that red pulp vascular cell adhesion molecule 1 (VCAM-1)(+) macrophages are essential to extramedullary myelopoiesis because these macrophages use the adhesion molecule VCAM-1 to retain HSCs in the spleen. Nanoparticle-enabled in vivo RNAi silencing of the receptor for macrophage colony stimulation factor (M-CSFR) blocked splenic macrophage maturation, reduced splenic VCAM-1 expression and compromised splenic HSC retention. Both, depleting macrophages in CD169 iDTR mice or silencing VCAM-1 in macrophages released HSCs from the spleen. When we silenced either VCAM-1 or M-CSFR in mice with myocardial infarction or in ApoE(-/-) mice with atherosclerosis, nanoparticle-enabled in vivo RNAi mitigated blood leukocytosis, limited inflammation in the ischemic heart, and reduced myeloid cell numbers in atherosclerotic plaques.

Inhibition of endocannabinoid-degrading enzyme fatty acid amide hydrolase increases atherosclerotic plaque vulnerability in mice.

The role of endocannabinoids such as anandamide during atherogenesis remains largely unknown. Fatty acid amide hydrolase (FAAH) represents the key enzyme in anandamide degradation, and its inhibition is associated with subsequent higher levels of anandamide. Here, we tested whether selective inhibition of FAAH influences the progression of atherosclerosis in mice. Selective inhibition of FAAH using URB597 resulted in significantly increased plasma levels of anandamide compared to control, as assessed by mass spectrometry experiments in mice. Apolipoprotein E-deficient (ApoE(-/-)) mice were fed a high-fat, cholesterol-rich diet to induce atherosclerotic conditions. Simultaneously, mice received either the pharmacological FAAH inhibitor URB597 1mg/kg body weight (n=28) or vehicle (n=25) via intraperitoneal injection three times a week. After eight weeks, mice were sacrificed, and experiments were performed. Vascular superoxide generation did not differ between both groups, as measured by L012 assay. To determine whether selective inhibition of FAAH affects atherosclerotic plaque inflammation, immunohistochemical staining of the aortic root was performed. Atherosclerotic plaque formation, vascular macrophage accumulation, as well as vascular T cell infiltration did not differ between both groups. Interestingly, neutrophil cell accumulation was significantly increased in mice receiving URB597 compared to control. Vascular collagen structures in atherosclerotic plaques were significantly diminished in mice treated with URB597 compared to control, as assessed by picro-sirius-red staining. This was accompanied by an increased aortic expression of matrix metalloproteinase-9, as determined by quantitative RT-PCR and western blot analysis. Inhibition of fatty acid amide hydrolase does not influence plaque size but increases plaque vulnerability in mice.

Impact of pulmonary vein isolation on obstructive sleep apnea in patients with atrial fibrillation.

BACKGROUND: Obstructive sleep apnea (OSA) has been identified as associated with the onset and propagation of atrial fibrillation (AF) and predicts recurrences of AF after pulmonary vein isolation (PVI). Vice versa, it has never been investigated whether PVI influences OSA. However, it has been controversial whether a restored atrial function can affect the course of OSA. There-fore, we have assessed whether PVI procedure modulates the prevalence and severity of OSA. METHODS AND RESULTS: We included 23 individuals with AF that were assigned to undergo PVI into this study. Patients were 65 ± 7 years old, obese (BMI 29.9 ± 5.4 kg/m²), white (100%) and had a normal left ventricular function (LVEF 64 ± 9%). Polygraphic assessment was carried out before and 6 months after PVI. The prevalence of OSA, defined as an apnea-hypopnea index (AHI) ≥ 5 per hour of sleep, was 74% before PVI compared to 70% 6 months after the procedure (p > 0.05). Severity of OSA did not differ (AHI before vs. after: 18 ± 18/h vs. 15 ± 17/h, p > 0.05) as well as further polygraphic parameters did not differ before and after the procedure. CONCLUSIONS: Prevalence and severity of OSA are not affected by PVI in patients suffering from AF.

Monocytic microparticles promote atherogenesis by modulating inflammatory cells in mice.

Microparticles (MP) are generated during a vast number of biological processes such as inflammation, cell activation and apoptosis. Increasing evidence points towards an important role of MP as intercellular messengers of biological information. During atherogenesis, monocytes infiltrate the vascular wall and foster inflammation, accompanied by the release of monocytic MP (mono-MP). To date, only little is known about the biological function of mono-MP in the vascular wall. Here, we investigated the role of mono-MP during atherogenesis. Mono-MP were generated by starvation of THP-1 monocytes and isolated by ultracentrifugation. To investigate whether mono-MP influence atherogenesis, ApoE(-/-) mice were fed a high-fat, cholesterol-rich diet for 8 weeks and simultaneously treated with mono-MP or vehicle twice a week. Mice treated with mono-MP showed significantly increased monocyte and T-cell infiltration into the vessel wall, as assessed by Moma-2 and CD3 staining, and enhanced plaque formation, as assessed by oil-red-O staining. However, atherosclerotic plaque composition was not influenced by mono-MP application. In vitro, incubation of mono-MP with murine macrophages and endothelial cells resulted in the uptake of calcein-labelled mono-MP. Mono-MP uptake initiated the generation of intracellular reactive oxygen species. Murine macrophages pre-treated with mono-MP showed significantly enhanced expression of CCR2, migration to MCP-1 and increased release of pro-inflammatory interleukin-6. Co-incubation of mono-MP with endothelial cells resulted in significantly increased expression of ICAM-1, as assessed by RT-PCR and ELISA. Mono-MP act as paracrine messengers that intensify inflammation during atherogenesis by stimulating vascular-bound and inflammatory cells in their vicinity.

Endothelial microparticle uptake in target cells is annexin I/phosphatidylserine receptor dependent and prevents apoptosis.

OBJECTIVE: Endothelial microparticles (EMP) are released from activated or apoptotic cells, but their effect on target cells and the exact way of incorporation are largely unknown. We sought to determine the uptake mechanism and the biological effect of EMP on endothelial and endothelial-regenerating cells. METHODS AND RESULTS: EMP were generated from starved endothelial cells and isolated by ultracentrifugation. Caspase 3 activity assay and terminal deoxynucleotidyl transferase dUTP nick end labeling assay showed that EMP protect target endothelial cells against apoptosis in a dose-dependent manner. Proteomic analysis was performed to identify molecules contained in EMP, which might be involved in EMP uptake. Expression of annexin I in EMP was found and confirmed by Western blot, whereas the corresponding receptor phosphatidylserine receptor was present on endothelial target cells. Silencing either annexin I on EMP or phosphatidylserine receptor on target cells using small interfering RNA showed that the uptake of EMP by human coronary artery endothelial cells is annexin I/phosphatidylserine receptor dependent. Annexin I-downregulated EMP abrogated the EMP-mediated protection against apoptosis of endothelial target cells. p38 activation was found to mediate camptothecin-induced apoptosis. Finally, human coronary artery endothelial cells pretreated with EMP inhibited camptothecin-induced p38 activation. CONCLUSIONS: EMP are incorporated by endothelial cells in an annexin I/phosphatidylserine receptor-dependent manner and protect target cells against apoptosis. Inhibition of p38 activity is involved in EMP-mediated protection against apoptosis.

Selective inhibition of leukotriene receptor BLT-2 reduces vascular oxidative stress and improves endothelial function in ApoE-/- mice.

Atherosclerosis is a chronic inflammatory disease and represents the main cause of death in the industrialized world. Metabolites of the arachidonic acid derived from the 5-lipoxygenase pathway are known as leukotrienes that mediate various inflammatory processes during atherogenesis. Leukotriene B4 elicits the overexpression of several proinflammatory proteins, promotes chemotaxis and foam cell formation via BLT receptors. Currently, little is known about the implications of the BLT2 receptor in atherogenesis. Here, we tested whether selective inhibition of this receptor influences the progression of atherosclerosis in mice. Apolipoprotein-E deficient mice were fed a high-fat, cholesterol-rich diet to create atherosclerotic conditions (each group n=9). Simultaneously, mice received the pharmacologic BLT2 inhibition (Ly) by intraperitoneal injection every second day 5 mg/kg bw or vehicle. After 8 weeks, mice were killed and experiments were performed. Vascular superoxide release was diminished in mice treated with Ly compared with the control group (68±15 vs 131±20 RLU, P=0.01), as measured by L012 assay. Next, endothelial function was assessed by organ chamber experiments. Endothelial-dependent relaxation was improved in mice treated with the BLT2 receptor antagonist. To determine whether selective inhibition of the BLT2 receptor affects the atherosclerotic plaque growth, immunohistochemical stainings of the aortic root were performed. Oil red O staining revealed no significant differences between both groups (36±3% vs 38±3%). Monocyte infiltration into the vessel wall was analyzed using Moma-2 staining. No significant differences were observed between both groups (31±3% vs 34±2%). Selective inhibition of the BLT2 receptor in mice reduces the release of vascular reactive oxygen species and improves endothelial function in mice. Further experiments are necessary in order to obtain tissue-specific and mechanistical insights.

Atheroprotection via cannabinoid receptor-2 is mediated by circulating and vascular cells in vivo.

Low-dose oral tetrahydrocannabinol (THC) reduces progression of atherosclerosis in mice. THC activates central cannabinoid-1 receptors (CB1) with subsequent psychoactive effects as well as peripheral cannabinoid-2 receptors (CB2). In order to dissect the underlying mechanisms, we performed experiments under selective CB2 stimulation as well as after genetic disruption of the CB2 receptor. Atherosclerosis prone apolipoprotein E-deficient mice were crossed with cannabinoid receptor-2 deficient mice to obtain ApoE -/- CB2 -/- double knockout mice. After 8weeks of a high-cholesterol diet, immunohistochemical stainings of the aortic root revealed that vascular leukocyte infiltration in atherosclerotic plaques was accelerated in ApoE -/- CB2 -/- mice compared with ApoE -/- mice. This was accompanied by increased release of reactive oxygen species as measured using L012-enhanced chemiluminescence, and by decreased endothelial function as assessed in isolated aortic rings in organ chamber experiments. ApoE -/- mice treated with the selective CB2 agonist JWH 133 during a high-cholesterol diet showed decreased atherosclerotic lesion formation, improved endothelial function and reduced levels of reactive oxygen species. To assess whether CB2 expression in circulating cells influences atherosclerosis, irradiated ApoE -/- mice were repopulated with bone marrow-derived cells from ApoE -/- and ApoE -/- CB2 -/- mice and were fed a high-cholesterol diet for 8weeks. CB2 deficiency in bone marrow-derived cells increased leukocyte infiltration into the vessel wall, but had no impact on plaque formation. Cell culture experiments revealed that CB2 activation diminishes ROS generation in vascular cells. Selective CB2 receptor stimulation modulates atherogenesis via impact on both circulating proinflammatory and vascular cells.

High prevalence of obstructive sleep apnea in patients with resistant paroxysmal atrial fibrillation after pulmonary vein isolation.

OBJECTIVES: To address the question whether obstructive sleep apnea (OSA) is associated with the recurrence of paroxysmal atrial fibrillation (AF) in patients treated with ≥2 pulmonary vein isolation procedures. PATIENTS AND METHODS: In this study, we included adults with therapy-resistant symptomatic paroxysmal AF, defined as AF recurring after ≥2 PV-isolation procedures (n = 23). For comparison, we selected another cohort of patients being successfully treated by one PV isolation without AF recurrence within 6 months (n = 23). PV isolation was performed by radiofrequency with an open irrigated tip catheter. Each of the 46 participants completed an overnight polygraphic study. The two groups were matched for age, gender, and ejection fraction. Patients were late middle-aged (65 ± 7 vs 63 ± 10 years, P = 0.23), white (100%), and overweight (BMI 27.3 ± 3.6 vs. 27.2 ± 4.6 kg/m(2), P = 0.97). RESULTS: The prevalence of sleep apnea, defined as an apnea-hypopnea index (AHI) of >5 per hour of sleep, was 87% in patients with therapy-resistant AF compared to 48% in the control cohort (P = 0.005). In addition, OSA was more severe in the resistant AF group indicated by a significantly higher AHI (27 ± 22 vs 12 ± 16, P = 0.01). CONCLUSION: The extraordinarily high prevalence of sleep apnea in patients with recurrent paroxysmal AF supports its presumable role in the pathogenesis of AF and demands further controlled prospective trials. Moreover, OSA should inherently be considered in patients with therapy-resistant AF.