Marked elevation of vascular endothelial growth factor and basic fibroblast growth factor in pericardial fluid of patients with angina pectoris

Ischemic heart disease: Cellular and molecular immune contributions of the pericardium

Ischemic heart disease promotes complex inflammatory and remodeling pathways which contribute to the development of chronic heart failure. Although blood-derived and local cardiac mediators have traditionally been linked with these processes, the pericardial space has more recently been noted as alternative contributor to the injury response in the heart. The pericardial space contains fluid rich in physiologically active mediators, and immunologically active adipose tissue, which are altered during myocardial infarction. Key immune cells in the pericardial fluid and adipose tissue have been identified which act as mediators for cell recruitment and function after myocardial infarction have been identified in experimental models. Here, we provide an overview of the current understanding of the inflammatory mechanisms of the pericardial space and their role in post-myocardial infarction remodeling and the potential for the use of the pericardial space as a delivery vehicle for treatments to modulate heart healing.

An overview of human pericardial space and pericardial fluid

The pericardium is a double-layered fibro-serous sac that envelops the majority of the surface of the heart as well as the great vessels. Pericardial fluid is also contained within the pericardial space. Together, the pericardium and pericardial fluid contribute to a homeostatic environment that facilitates normal cardiac function. Different diseases and procedural interventions may disrupt this homeostatic space causing an imbalance in the composition of immune mediators or by mechanical stress. Inflammatory cells, cytokines, and chemokines are present in the pericardial space. How these specific mediators contribute to different diseases is the subject of debate and research. With the advent of highly specialized assays that can identify and quantify various mediators we can potentially establish specific and sensitive biomarkers that can be used to differentiate pathologies, and aid clinicians in improving clinical outcomes for patients.

Gata6+ Pericardial Cavity Macrophages Relocate to the Injured Heart and Prevent Cardiac Fibrosis

Macrophages play an important role in structural cardiac remodeling and the transition to heart failure following myocardial infarction (MI). Previous research has focused on the impact of blood-derived monocytes on cardiac repair. Here we examined the contribution of resident cavity macrophages located in the pericardial space adjacent to the site of injury. We found that disruption of the pericardial cavity accelerated maladaptive post-MI cardiac remodeling. Gata6⁺ macrophages in mouse pericardial fluid contributed to the reparative immune response. Following experimental MI, these macrophages invaded the epicardium and lost Gata6 expression but continued to perform anti-fibrotic functions. Loss of this specialized macrophage population enhanced interstitial fibrosis after ischemic injury. Gata6⁺ macrophages were present in human pericardial fluid, supporting the notion that this reparative function is relevant in human disease. Our findings uncover an immune cardioprotective role for the pericardial tissue compartment and argue for the reevaluation of surgical procedures that remove the pericardium.

Technologies for intrapericardial delivery of therapeutics and cells

The pericardium, which surrounds the heart, provides a unique enclosed volume and a site for the delivery of agents to the heart and coronary arteries. While strategies for targeting the delivery of therapeutics to the heart are lacking, various technologies and nanodelivery approaches are emerging as promising methods for site specific delivery to increase therapeutic myocardial retention, efficacy, and bioactivity, while decreasing undesired systemic effects. Here, we provide a literature review of various approaches for intrapericardial delivery of agents. Emphasis is given to sustained delivery approaches (pumps and catheters) and localized release (patches, drug eluting stents, and support devices and meshes). Further, minimally invasive access techniques, pericardial access devices, pericardial washout and fluid analysis, as well as therapeutic and cell delivery vehicles are presented. Finally, several promising new therapeutic targets to treat heart diseases are highlighted.

Is it time to change how we think about incomplete coronary revascularization?

The optimal degree of revascularization for patients with chronic multivessel coronary artery disease remains an unsolved issue. Intuitively, complete revascularization decreases cardiovascular events and improves outcomes compared to incomplete procedures, but in recent years the concept of incomplete revascularization moved from a sub-optimal or a defective treatment towards the most appropriate revascularization technique in some categories of patients. A reasonable level of incomplete anatomic revascularization has been shown to be safe and achievable with both percutaneous (PCI) and surgical procedures (CABG), despite with different long-term outcomes. What are the mechanisms underlying the clinical benefits of an incomplete revascularization and what are the factors explaining the discrepancy in the long-term clinical outcomes between the two modes of revascularization PCI and CABG? The biological consequences of coronary reperfusion might provide valuable hints in this context and at the same time cast new light on the way we think about incomplete revascularization.

High molecular weight fibroblast growth factor-2 in the human heart is a potential target for prevention of cardiac remodeling

Fibroblast growth factor 2 (FGF-2) is a multifunctional protein synthesized as high (Hi-) and low (Lo-) molecular weight isoforms. Studies using rodent models showed that Hi- and Lo-FGF-2 exert distinct biological activities: after myocardial infarction, rat Lo-FGF-2, but not Hi-FGF-2, promoted sustained cardioprotection and angiogenesis, while Hi-FGF-2, but not Lo-FGF-2, promoted myocardial hypertrophy and reduced contractile function. Because there is no information regarding Hi-FGF-2 in human myocardium, we undertook to investigate expression, regulation, secretion and potential tissue remodeling-associated activities of human cardiac (atrial) Hi-FGF-2. Human patient-derived atrial tissue extracts, as well as pericardial fluid, contained Hi-FGF-2 isoforms, comprising, respectively, 53%(±20 SD) and 68% (±25 SD) of total FGF-2, assessed by western blotting. Human atrial tissue-derived primary myofibroblasts (hMFs) expressed and secreted predominantly Hi-FGF-2, at about 80% of total. Angiotensin II (Ang II) up-regulated Hi-FGF-2 in hMFs, via activation of both type 1 and type 2 Ang II receptors; the ERK pathway; and matrix metalloprotease-2. Treatment of hMFs with neutralizing antibodies selective for human Hi-FGF-2 (neu-AbHi-FGF-2) reduced accumulation of proteins associated with fibroblast-to-myofibroblast conversion and fibrosis, including α-smooth muscle actin, extra-domain A fibronectin, and procollagen. Stimulation of hMFs with recombinant human Hi-FGF-2 was significantly more potent than Lo-FGF-2 in upregulating inflammation-associated proteins such as pro-interleukin-1β and plasminogen-activator-inhibitor-1. Culture media conditioned by hMFs promoted cardiomyocyte hypertrophy, an effect that was prevented by neu-AbHi-FGF-2 in vitro. In conclusion, we have documented that Hi-FGF-2 represents a substantial fraction of FGF-2 in human cardiac (atrial) tissue and in pericardial fluid, and have shown that human Hi-FGF-2, unlike Lo-FGF-2, promotes deleterious (pro-fibrotic, pro-inflammatory, and pro-hypertrophic) responses in vitro. Selective targeting of Hi-FGF-2 production may, therefore, reduce pathological remodelling in the human heart.

The roles of natriuretic peptides in pericardial fluid in patients with heart failure

BACKGROUND

It is well known that the plasma concentrations of atrial and brain natriuretic peptides, as cardiac hormones, are elevated in heart failure.

HYPOTHESIS

Pericardial fluid in patients with various heart diseases contains both natriuretic peptides that are released into the pericardial fluid. However, it is unknown whether these peptides reflect cardiac function in patients with various heart diseases, more than both the peptides in blood.

METHODS

Plasma and pericardial fluid samples were obtained from 22 patients undergoing cardiac surgery for the measurement of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) levels in plasma and pericardial fluid.

RESULTS

The ANP levels in pericardial fluid were higher in patients with impaired left ventricular systolic function (ejection fraction<50% versus>or=50%; 77.0+/-4.9 versus 14.0+/-50.9, p=0.017), but not BNP.However, BNP levels in pericardial fluid were significantly higher in patients with left ventricle dilatation (left ventricular diastolic dimension<or=54 mm versus>54 mm; 130.3+/-68.9: 709.7+/-324.7, p=0.0168). Moreover, BNP levels in pericardial fluid were significantly higher in Grade III than Grade II and I (Grade I: echo-free space<5 mm, Grade II: 5-10 mm, Grade III: >10 mm).

CONCLUSION

These results suggest that BNP levels in pericardial fluid served as more sensitive and accurate indicators of left ventricular diastolic dysfunction, and that increased BNP levels in pericardial fluid may have an important pathophysiologic role in heart failure as a cardiocyte-derived antifibrotic factor.

Reduced pericardial levels of endostatin correlate with collateral development in patients with ischemic heart disease

OBJECTIVES

We investigated whether pericardial levels of a pro-angiogenic factor (vascular endothelial growth factor, VEGF) or an anti-angiogenic factor (endostatin) related to the presence of coronary collateral circulation in patients with significant coronary artery disease (CAD).

BACKGROUND

Coronary collateralization favorably alters the prognosis of patients with occlusive CAD. The specific factors that mediate and maintain collateral formation in coronary vessel occlusion are yet to be identified.

METHODS

Coronary angiograms from 39 patients undergoing coronary artery bypass surgery were evaluated for the absence of collaterals (n = 20) or the presence of Rentrop classification grade 3 collaterals (n = 19). Pericardial fluid samples were obtained at the time of surgery and were assayed for the VEGF and endostatin by enzyme-linked immunosorbent assay comparing the two groups of patients.

RESULTS

Vascular endothelial growth factor levels were not significantly different between the groups (28.86 +/- 4.67 pg/ml vs. 24.39 +/- 3.08 pg/ml, p = 0.43). However, pericardial fluid endostatin levels were nearly 40% lower in patients with grade 3 collateralization compared with those lacking angiographic evidence of collaterals (15.17 +/- 1.87 ng/ml vs. 24.25 +/- 2.08 ng/ml, p < 0.0025).

CONCLUSIONS

Pericardial fluid levels of endostatin, but not VEGF, are associated with the presence or absence of collaterals in patients with CAD. These data suggest that the angiogenesis inhibitor endostatin levels may locally modulate coronary collateral formation.

Concentrations of Hepatocyte Growth Factor, Basic Fibroblast Growth Factor, and Vascular Endothelial Growth Factor in Pericardial Fluid and Plasma

Some angiogenic factors, including hepatocyte growth factor (HGF), basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF), have been reported to promote angiogenesis and improve myocardial perfusion in experimental models of ischemic heart disease. These factors are produced in various tissues, including myocardium. We measured the concentrations of HGF, bFGF, and VEGF by enzyme-linked immunosorbent assay in plasma and in pericardial fluid sampled during open heart surgery (12 patients with ischemic heart disease and 17 with nonischemic heart disease). HGF levels were significantly higher in plasma than in pericardial fluid (12.0 +/- 1.8 versus 0.26 +/- 0.04 ng/mL, P < 0.0001). On the other hand, bFGF levels were significantly higher in pericardial fluid than in plasma (243.5 +/- 50.9 versus 49.6 +/- 7.8 pg/mL, P = 0.009). VEGF levels were not significantly different between pericardial fluid and plasma (47.2 +/- 17.6 versus 24.5 +/- 3.6 pg/mL, P = 0.23). Concentrations of angiogenic factors in pericardial fluid and in plasma were not significantly different between patients with ischemic and nonischemic heart disease. These results suggest that the production, secretion, and kinetics of HGF, bFGF, and VEGF are different. These angiogenic factors may have different pathophysiologic roles.

Redox signaling in vascular angiogenesis

Angiogenesis is thought to be regulated by several growth factors (EGF, TGF-alpha, beta-FGF, VEGF). Induction of these angiogenic factors is triggered by various stresses. For instance, tissue hypoxia exerts its pro-angiogenic action through various angiogenic factors, the most notable being vascular endothelial growth factor, which has been mainly associated with initiating the process of angiogenesis through the recruitment and proliferation of endothelial cells. Recently, reactive oxygen species (ROS) have been found to stimulate angiogenic response in the ischemic reperfused hearts. Short exposure to hypoxia/reoxygenation, either directly or indirectly, produces ROS that induce oxidative stress which is associated with angiogenesis or neovascularization. ROS can cause tissue injury in one hand and promote tissue repair in another hand by promoting angiogenesis. It thus appears that after causing injury to the cells, ROS promptly initiate the tissue repair process by triggering angiogenic response.

Pericardial fluid as a new material for clinical heart research

This article will review the results of recent clinical studies relating to the pericardial fluid in patients with various heart diseases. In ischemic patients, several angiogenic growth factors are accumulated in a high concentration in pericardial fluid. These may contribute to the angiogenesis and arteriogenesis, which are self-protecting mechanisms of myocardial ischemia. In congestive heart failure, natriuretic peptides are released into the pericardial fluid in a higher concentration compared with plasma levels. This suggests that these peptides may act as autocrine and/or paracrine factors. Pericardial fluid from ischemic patients induces cell proliferation and apoptosis depending on the cell type. Intrapericardial drug administration may provide a reasonable therapeutic strategy for heart diseases. In conclusion, the analysis of pericardial fluid appears to be a logical approach for elucidation of the pathophysiology of the heart.

Pericardial fluid from patients with unstable angina induces vascular endothelial cell apoptosis

OBJECTIVES

The purpose of this study was to investigate whether pericardial fluid from patients with unstable angina (UA) would modulate vascular endothelial cell survival.

BACKGROUND

Apoptosis of vascular endothelial cells promotes the coagulation process, playing an important role in the formation of coronary arterial thrombi. However, little is known about the mechanisms of vascular endothelial cell death in acute coronary syndrome. We hypothesized that factors inducing apoptosis are produced by the ischemic heart and accumulated in high concentrations in pericardial fluid.

METHOD

Pericardial fluid was obtained during coronary artery bypass surgery from patients with UA (group A, n = 8) and those with stable angina (group B, n = 23). A survival assay of F2 cells from a mouse vascular endothelial cell line was performed in the presence of 10% pericardial fluid from each patient.

RESULTS

Pericardial fluid levels of vascular endothelial growth factor were significantly higher in group A than in group B, indicating that group A had more ischemic insults than group B. Pericardial fluid from group A, but not from group B, markedly induced F2 cell death (cell survival relative to fetal bovine serum; group A: 33 +/- 26% vs. group B: 91 +/- 22%, p < 0.01). Cell death was associated with internucleosomal DNA fragmentation, a hallmark of apoptosis. Fractionation of pericardial fluid using a Centricon C-100 demonstrated that apoptosis-inducible activities exist in the Centricon C-100 retentates but not in the filtrates.

CONCLUSIONS

Factors that induce vascular endothelial cell apoptosis are secreted into the pericardial space from the hearts of patients with UA. These factors are large complexes or unknown new proteins larger than 100 kDa.

Development of enzyme-linked immunosorbent assay for acidic fibroblast growth factor and its clinical application

We have developed, for the first time, an enzyme-linked immunosorbent assay (ELISA) system for the measurement of human acidic fibroblast growth factor (aFGF). Anti-bovine aFGF rabbit IgG was conjugated with N-hydroxysuccimidobiotin, and the resulting IgG-biotin conjugate was used as the second antibody. This assay was highly specific and reproducible, enabling us to detect aFGF at a concentration as low as 1 microg/l without any prior processing of samples. With this method, it was possible to determine human aFGF up to 833 x 10(3) ng/l, with the use of anti-bovine aFGF IgG as the first and second antibody. There was no significant cross-reactivity of the antibody with other growth factors, such as basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF). The aFGF concentration in pericardial fluid was significantly higher in patients with unstable angina than in those with other heart diseases, suggesting that the aFGF plays an important role(s) in the course of collateral growth in coronary artery disease. Therefore, our ELISA system may be useful in determining unknown biological function(s) or pathological role(s) of aFGF in various disease entities.