Current Pharmaceutical Design

ISSN: 1381-6128

Current Pharmaceutical Design
Volume 13, Number 17, 2007

Contents

Trends in Vascular Biology; Functional Restoration of Damaged Endothelium
Executive Editors: J.A. Rodriguez-Feo and G. Pasterkamp


Editorial: Pp. 1723-1725


Understanding eNOS for Pharmacological Modulation of Endothelial Function: A Translational View Pp. 1727-1740
B. Braam and M.C. Verhaar
[Abstract]


Endothelial Function: A Surrogate Endpoint in Cardiovascular Studies Pp. 1741-1750
M. Frick and F. Weidinger
[Abstract]


The Dialogue Between Endothelial Cells and Monocytes/Macrophages in Vascular Syndromes Pp. 1751-1759
J. Martin, S. Collot-Teixeira, L. McGregor and J.L. McGregor
[Abstract]


Caveolae and Caveolin-1: Novel Potential Targets for the Treatment of Vascular Disease Pp. 1761-1769
P.G. Frank, G.S. Hassan, J.A. Rodriguez-Feo and M.P. Lisanti
[Abstract]


Influence of Statin Use on Endothelial Function: From Bench to Clinics Pp. 1771-1786
J. Martínez-González and L. Badimon
[Abstract]


Matrix Metalloproteinases: New Routes to the Use of MT1-MMP As A Therapeutic Target in Angiogenesis-Related Disease Pp. 1787-1802
A.G. Arroyo, L. Genís, P. Gonzalo, S. Matías-Román, A. Pollán and B.G. Gálvez
[Abstract]


Growth Factor Therapy in Atherosclerotic Disease–Friend or Foe Pp. 1803-1810
I.E. Hoefer, L. Timmers and J.J. Piek
[Abstract]


The Importance of Reendothelialization After Arterial Injury Pp. 1811-1824
D. Versari, L. O. Lerman and A. Lerman
[Abstract]




Abstracts


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Editorial: Trends in Vascular Biology; Functional Restoration of Damaged Endothelium

Endothelial injury and dysfunction are early alterations in vessel wall biology preceding atherosclerotic plaque formation. In the presence of established cardiovascular risk factors, endothelial cells are constantly injured and repaired by the proliferation of resident cells and circulating endothelial progenitor cells. The maintenance of the endothelial layer physical continuity and function represents a major target for the prevention of vascular disease. This special issue covers key aspects of endothelial cell biology and potential therapeutic approaches that may restore the function of the endothelium. Basic and clinical researchers have reviewed the current state of art in endothelial dysfunction, endothelium-monocyte cross-talk, angiogenesis, arteriogenesis and the potentiality of bone-marrow derived progenitor cells to achieve a successful re-endothelization of arterial segments.

The vascular endothelium is a continuous monolayer of thin, flat cells that lines the interior surface of small and large blood vessels, forming an interface between circulating blood and the subnendothelial matrix [1] (Fig. 1). Endothelial cells line the entire circulatory system, from the heart to the smallest capillary. In small blood vessels and capillaries, endothelial cells (ECs) are often the only cell-type present. For many years ECs were seen as a mere barrier that passively participated in the transport of substances from the blood to the rest of the arterial wall [1]. However, nowadays there are no doubts that the vascular endothelium acts as a key integrator and modulator of many important functions of the arterial wall (Fig. 1) [2;3].



Fig. (1). Schematic representation of vascular endothelium and its opposite roles under normal (Top right) and pathological conditions (Bottom right). Under non-pathological conditions, ECs produce and release vasoactive substances that regulate among others vascular permeability, anti-inflammatory, anti-adhesive and anti-proliferative properties Injury of endothelial cells (ECs) by classical risk factors, mechanical forces and others, promote alterations in the normal function of ECS. NO= Nitric Oxide.

Endothelial dysfunction is a commonly used phrase but that encompasses many different biological processes or diagnostic measures of vascular disease. Expression of selectins and integrins and subsequent enhanced monocyte adhesion, disturbed vasodilating responses and increased permeability of the endothelial layer are all features that can be observed in atherosclerotic disease and are used as a measure for endothelial dysfunction. Early in atherogenesis measures of endothelial dysfunction are detectable before other structural and/or compositional changes in the blood vessels [4]. Subsequent steps following vascular injury imply recruitment of inflammatory cells, accumulation of lipid into foam cells, oxidation of LDL, intimal growth, atherosclerotic plaque expansion and/or remodeling [5;6].

Endothelial dysfunction is a common feature in subjects suffering from diabetes mellitus, hypertension or other vascular disorders [4]. It is independently related with adverse cardiovascular events, including myocardial infarction, coronary death, and the need for revascularization. One of the main mechanisms of endothelial dysfunction is the diminishing of actions of nitric oxide (NO) [7]. The importance of NO is here documented by Braam et al. [23] who summarized several aspects regarding NO biology with a special emphasis in its numerous actions and different pharmacologic approaches leading to increase the production of endothelial-derived NO. The clinical significance and the limitations of the current methods to test endothelial functionality in human beings will be critically reviewed by Frick et al. [24].

Dysfunctional endothelial cells express more adhesion molecules and as a consequence circulating monocytes are captured by activated endothelium promoting an inflammatory reaction [8]. Monocyte adhesion to activated endothelial cells is a multistep process [5,6]. First, L-selectin and the P-selectin glycoprotein ligand-1 (PSGL-1) expressed on monocytes [7,8] and E-selectin and P-selectin expressed on activated endothelial cells [9,10] mediate the initial tethering of leukocytes, also called rolling adhesion. When a rolling monocyte encounters chemokines presented by the activated endothelial cells, integrins get activated, a process called inside-out signalling [11]. Not only chemokines, but also other stimuli like growth factors, cytokines, and bacterial-derived products such as lipopolysaccharide (LPS)³, a Toll-like receptor 4 ligand [12], and R-848, a Toll-like receptor 7 ligand [13], are able to activate integrins on monocytes. In this issue, Martin et al. [25], discuss potential pharmacological targets for the modulation of endothelial cell-monocyte cross-talk.

Subsequently lipids are accumulated into the sub-endothelial space [6]. In vitro and in vivo studies have shown that caveolae (“small caves”) rather abundant in ECs and their major protein Caveolin-1 play an important role in atherosclerosis. In the cardiovascular system, Caveolin-1 participates in the regulation of important signaling cascades involved in atherosclerotic plaque formation, and disease progression might be modulated by caveloae number and or Caveolin 1 levels [18,19]. Mice lacking caveolin-1 in an atherosclerotic background show less lipid content in the aorta consistent with a pro-atherogenic role of this protein. In contrast, however, absence of caveolin-1 promotes smooth muscle cell proliferation and promotes intimal thickening, suggesting an anti-atherogenic role for Caveolin 1 [20]. Frank et al. give an overview about the dual role of Caveolin-1 main protein Caveolae in atherosclerosis [26].

Management of cholesterol levels has an impact in the vascular function. The beneficial effects of cholesterol lowering drugs on hard clinical endpoints is beyond any doubt. The beneficial effects of statins are not only explained by the effect of the lipid profile in peripheral blood but also by pleiotrophic effects on the atherosclerotic plaque. Statins may have a stabilizing effect on atherosclerotic vulnerable lesions that are prone to rupture. Also the restoration of the dysfunctional endothelium may be part of this anti-inflammatory pleiotrophic effect of statins as described by Martínez-González et al. [27].

Stimulation of neovascularization (angiogenesis, arteriogenesis) represents a therapeutic approach to treat patients with coronary disease. These strategies aim to improve cardiac function by ensuring myocardial perfusion and to reduce the risk of myocardial infarction. Angiogenesis, the formation of new vessels from pre-existing capillaries, is a fundamental physiological process which also plays a role in disease. In this issue Arroyo et al. [28] reviews the importance of MT1-MMP as a target in angiogenesis-related disease while Hoefer et al. [29] focused on arteriogenesis.

The last decade, after the discovery of the potential of the bone-marrow derived stem cells [21,22], many researches have searched for “the magic bullets” to rescue arterial segments in which endothelial cells are absent or dysfunctional. The research field on the function of the endothelial progenitor cell is emerging and therefore in this issue Versari et al. [30] reviews the current state of art in cell-mediated re-endothelization.

Restoration of the dysfunctional endothelium is considered one of the primary objectives to maintain the integrity of the vascular wall and prevent local inflammatory responses and subsequent atherosclerotic plaque formation. This issue will provide an excellent overview of the different experimental approaches that are being considered to achieve that objective.

References

[1] Marsden PA, Goligorsky MS, Brenner BM. Endothelial cell biology in relation to current concepts of vessel wall structure and
function. J Am Soc Nephrol 1991; 1: 931-48.

[2] Furchgott RF, Zawadzki JV. The obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine. Nature 1980; 288: 373-76.

[3] Luscher TF, Richard V, Tschudi M, Yang ZH, Boulanger C. Endothelial control of vascular tone in large and small coronary arteries. J Am Coll Cardiol 1990; 15: 519-27.

[4] Forgione MA, Leopold JA, Loscalzo J. Roles of endothelial dysfunction in coronary artery disease. Curr Opin Cardiol 2000; 15: 409-15.

[5] Falk E, Shah PK, Fuster V. Coronary plaque disruption. Circulation 1995; 92: 657-71.

[6] Ross R. Atherosclerosis--an inflammatory disease. N Engl J Med 1999; 340: 115-26.

[7] Palmer RM, Ferrige AG, Moncada S. Nitric oxide release accounts for the biological activity of endothelium-derived relaxing factor. Nature 1987; 327: 524-26.

[8] Krieglstein CF, Granger DN. Adhesion molecules and their role in vascular disease. Am J Hypertens 2001; 14: 44S-54S.

[9] Beekhuizen H, van Furth R. Monocyte adherence to human vascular endothelium. J Leukoc Biol 1993; 54: 363-78

[10] Jang Y, Lincoff AM, Plow EF, Topol EJ. Cell adhesion molecules in coronary artery disease. J Am Coll Cardiol 1994; 24: 1591-601.

[11] McEver RP. Selectins. Curr Opin Immunol 1994; 6: 75-84.

[12] Moore KL, Patel KD, Bruehl RE, Li F, Johnson DA , Lichenstein HS, Cummings RD, Bainton DF, McEver RP. P-selectin glycoprotein ligand-1 mediates rolling of human neutrophils on P-selectin. J Cell Biol 1995; 128: 661-71.

[13] Foxall C, Watson SR, Dowbenko D, Fennie C, Lasky LA, Kiso M, Hasegawa A, Asa D, Brandley BK. The three members of the selectin receptor family recognize a common carbohydrate epitope, the sialyl lewis(x) oligosaccharide. J Cell Biol 1992; 117: 895-902

[14] Asa D, Raycroft L, Ma L, Aeed PA, Kaytes PS, Elhammer AP, Geng JG. The P-selectin glycoprotein ligand functions as a common human leukocyte ligand for P- and E-selectins. J Biol Chem 1995; 270: 11662-70.

[15] Ginsberg MH, Du X, Plow EF. Inside-out integrin signalling. Curr Opin Cell Biol 1992; 4: 766-71.

[16] Haugen TS, Skjonsberg OH, Nakstad B, Lyberg T. Modulation of adhesion molecule profiles on alveolar macrophages and blood leukocytes. Respiration 1999; 66: 528-37.

[17] Nagase H, Okugawa S, Ota Y, Yamaguchi M, Tomizawa H, Matsushima K, Ohta K, Yamamoto K, Hirai K. Expression and function of Toll-like receptors in eosinophils: activation by Toll-like receptor 7 ligand. J Immunol 2003; 171: 3977-82

[18] Gratton JP, Bernatchez P, Sessa WC. Caveolae and caveolins in the cardiovascular system. Circ Re. 2004; 94: 1408-17.

[19] Hnasko R, Lisanti MP. The biology of caveolae: lessons from caveolin knockout mice and implications for human disease. Mol Interv 2003; 3: 445-64.

[20] Hassan GS, Jasmin JF, Schubert W, Frank PG, Lisanti MP. Caveolin-1 deficiency stimulates neointima formation during vascular injury. Biochemistry 2004; 43: 8312-21.

[21] Xu Q. The impact of progenitor cells in atherosclerosis. Nat Clin Pract Cardiovasc Med 2006; 3: 94-101.

[22] Asahara T, Murohara T, Sullivan A, Silver M, van der ZR, Li T et al. Isolation of putative progenitor endothelial cells for angiogenesis. Science 1997; 275: 964-67.

[23] Braam B, Verhaar MC. Understanding eNOS for Pharmacological Modulation of Endothelial Function: A Translational View. Curr Pharm Des 2007; 13(17): 1727-1740.

[24] Frick M, Weidinger F. Endothelial Function: A Surrogate Endpoint in Cardiovascular Studies. Curr Pharm Des 2007; 13(17): 1741-1750.

[25] Martin J, Collot-Teixeira S, McGregor L, McGregor J.L. The Dialogue Between Endothelial Cells and Monocytes/ Macrophages in Vascular Syndromes. Curr Pharm Des 2007; 13(17): 1751-1759.

[26] Frank PG, Hassan GS, Rodriguez-Feo JA, Lisanti MP. Caveolae and Caveolin-1: Novel Potential Targets for the Treatment of Vascular Disease. Curr Pharm Des 2007; 13(17): 1761-1769.

[27] Martínez-González J, Badimon L. Influence of Statin Use on Endothelial Function: From Bench to Clinics. Curr Pharm Des 2007; 13(17): 1771-1786.

[28] Arroyo AG, Genís L, Gonzalo P, Matías-Román S, Pollán A, Gálvez BG. Matrix Metalloproteinases: New Routes to the Use of MT1-MMP As A Therapeutic Target in Angiogenesis-Related Disease. Curr Pharm Des 2007; 13(17): 1787-1802.

[29] Hoefer IE, Timmers L, Piek JJ. Growth Factor Therapy in Atherosclerotic Disease–Friend or Foe. Curr Pharm Des 2007; 13(17): 1803-1810.

[30] Versari D, Lerman LO. Lerman A. The Importance of Reendothelialization After Arterial Injury. Curr Pharm Des 2007; 13(17): 1811-1824.


Juan A. Rodriguez-Feo


Gerard Pasterkamp


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Understanding eNOS for Pharmacological Modulation of Endothelial Function: A Translational View
B. Braam and M.C. Verhaar

Knowledge about the function of endothelial nitric oxide synthase (eNOS), and its regulation in pathophysiological states has tremendously increased. It is now clear that diminished activity of nitric oxide (NO) contributes to endothelial dysfunction, which is a characteristic of impeding atherosclerosis. This review aims to summarize the available knowledge about the impact of important cardiovascular risk factors on NO production by eNOS. There are 4 principle causes of diminished NO bio-activity: decreased expression and/or activity of the eNOS enzyme, eNOS uncoupling, enhanced breakdown or scavenging of NO and impaired transmission of NO-mediated signaling events (failure of the effector mechanisms). From the analysis, it becomes clear, that several aspects of eNOS functionality have only scarcely been tested under conditions of increased (experimental) cardiovascular risk. These aspects include palmitoylation, myristoylation and phosphorylation of the eNOS enzyme. Clear is that enhanced production of reactive oxygen species (ROS) and eNOS uncoupling are relatively important causes of reduced NO-bioactivity in cardiovascular disease states . Ideally, eNOS is sufficiently expressed, produces NO sufficiently and not abundantly, does not produce superoxide and is not scavenged by ROS; the produced NO then reaches its signaling target, mainly soluble guanylyl cyclase (sGC) and elicits a cellular response. Considering which aspects of eNOS are now assessable in a clinical setting and which therapeutic measures are available, there is a great challenge ahead.


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Endothelial Function: A Surrogate Endpoint in Cardiovascular Studies
M. Frick and F. Weidinger

Endothelial dysfunction is a well documented early phenomenon in atherosclerosis. Because it may precede structural changes and clinical manifestations, major research efforts have focused on the detection of endothelial dysfunction in humans. The utility of such tests in clinical practice critically depends on the proof of their prognostic value, their safety and reproducibility. First data supporting the prognostic impact of endothelial function have come from studies using intracoronary infusion of acetylcholine, a test clearly too invasive to be performed in asymptomatic subjects. Therefore, non-invasive techniques such as flow-mediated vasodilation of the brachial artery and strain-gauge venous plethysmography of the forearm have been developed. Numerous studies in a variety of patient populations have been performed to evaluate the prognostic value of these methods.

This review summarizes the current status of endothelial dysfunction as an early parameter of atherosclerosis and its potential use in the clinical arena. The value of endothelial function as a surrogate endpoint in cardiovascular studies is critically reviewed.


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The Dialogue Between Endothelial Cells and Monocytes/Macrophages in Vascular Syndromes
J. Martin, S. Collot-Teixeira, L. McGregor and J.L. McGregor

The aim of this chapter is to present and identify potential pharmacological targets in endothelial cell-monocyte interactions leading to vascular syndrome and involving inflammation, coagulation, vascular remodelling and thrombosis. Increasing evidence is indicating that endothelial cells play a key role in atherothombosis by their capacity to attract, bind and allow the extravasation of monocytes to sites of inflammation. Surface expression and/or activation of constituent cell adhesion molecules (for e.g. P-selectin, E-selectin, ICAM-1, and VCAM-1) on endothelial cells together with chemokines such as CXCL8 (IL-8), Platelet-activating factor (PAF), CCL2 and CCL5 (Table 1) allow the rolling, adhesion and extravasation of monocytes. This review focuses on pharmacological targets implicated in endothelial cells interactions with monocytes/macrophages in vascular disease states and on cutting edge genomic tools for the identification and characterization of such targets.


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Caveolae and Caveolin-1: Novel Potential Targets for the Treatment of Vascular Disease
P.G. Frank, G.S. Hassan, J.A. Rodriguez-Feo and M.P. Lisanti

Caveolae are 50-100 nm cell surface plasma membrane invaginations that are highly enriched in cholesterol and sphingolipids and are characterized by the protein marker caveolin-1. Caveolin-1 is highly expressed in terminally differentiated cells. Among these cells, endothelial cells, smooth muscle cells, and macrophages have all been shown to play key roles in the development of vascular disease. Atherosclerosis and neointimal formation are two major processes that have been associated with arterial occlusion. In both cases, caveolin-1 has been shown to play an important role. However, depending on the cell type and the metabolic pathways regulated by this protein, caveolin-1 may positively or negatively influence the development of vascular disease. Both of these aspects will be discussed in this review.


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Influence of Statin Use on Endothelial Function: From Bench to Clinics
J. Martínez-González and L. Badimon

Endothelial dysfunction has been shown to be a prognostic factor for cardiovascular disease and improvement of endothelial dysfunction prevents cardiovascular event presentation. Endothelial dysfunction is associated to a reduced nitric oxide (NO) bioactivity, as a result of the impairment of NO synthesis/release by the endothelial NO synthase (eNOS) or by inactivation of NO. Endothelial dysfunction measurements are valuable surrogate markers to assess the effectiveness of interventions addressed to prevent o treat coronary heart disease (CHD). Dyslipemia and other cardiovascular risk factors promote endothelial dysfunction and life style changes and pharmacological treatment, particularly HMG-CoA reductase inhibitors (statins), have shown early improve of endothelial-dependent vasomotion. Statins efficiently reduce plasma LDL cholesterol, an effect that may account for their beneficial effect on endothelial function, but they also reduce cellular levels of isoprenoid compounds relevant for the bioavailability of NO. Statins restore NO production by several mechanisms, including up-regulation of eNOS mRNA and protein levels and preservation of NO inactivation by reactive oxygen species (ROS). These effects are mediated, at least in a part, through mechanisms independent of their lipid lowering effect (pleiotropic effects). In this article we discuss the relevance of endothelium-dependent effects on the early and delayed clinical benefit of statins, as well as the multiple ways by which statins may restore endothelial function acting not only on the endothelium but also on endothelial progenitor cells (EPC), which likely could contribute to both ischemia-induced neovascularization and endothelial regeneration after injury.


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Matrix Metalloproteinases: New Routes to the Use of MT1-MMP As A Therapeutic Target in Angiogenesis-Related Disease
A.G. Arroyo, L. Genís, P. Gonzalo, S. Matías-Román, A. Pollán and B.G. Gálvez

Angiogenesis, the formation of new vessels from pre-existing capillaries, is a fundamental physiological process which is also critical for the development of several pathological conditions; thus a diminished angiogenic response is related to ischemic disorders, whereas increased angiogenesis is associated with tumorigenesis and chronic inflammatory diseases. New ways of modulating angiogenesis therefore have potential in the treatment of these diseases. During angiogenesis, normally quiescent endothelial cells (ECs) become migratory and invade the surrounding tissue. To do this, they require a specific enzyme machinery to degrade the tissue barriers presented by the basement membranes and the interstitial matrix. This function is supplied by matrix metalloproteinase (MMP) proteins, a large family of enzymes responsible for degrading a variety of extracellular matrix (ECM) components and for modulating the bioactivity of transmembrane receptors and soluble factors. In this review we examine the participation of MMPs – in particular membrane type 1-matrix metalloproteinase (MT1-MMP) – in the different steps of angiogenesis, and discuss the mechanisms of regulation of MT1-MMP in ECs. Finally, we explore the potential use of MMP inhibitors (MMPI) in the treatment of angiogenesis-related disease, with especial emphasis on novel approaches to the inhibition of MT1-MMP activity in ECs.


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Growth Factor Therapy in Atherosclerotic Disease–Friend or Foe
I.E. Hoefer, L. Timmers and J.J. Piek

Stimulation of neovascularization (angiogenesis, arteriogenesis) has emerged as a promising new strategy to treat patients with coronary disease. These strategies aim to improve cardiac function by ensuring myocardial perfusion and to reduce the risk of myocardial infarction. While angiogenesis describes a de-novo formation of small caliber capillary vessels, arteriogenesis leads to the outgrowth of pre-existing arterioles into large conductance collateral arteries. Inflammatory cells (e.g. monocytes), which can produce and secrete growth factors and cytokines, mediate both processes. Several trials have shown that intra-coronary infusion of growth factors or progenitor cells can improve left ventricular function after arterial occlusion. Despite these encouraging results, potential unfavorable effects on plaque progression and stability should not be neglected.

Destabilization of atherosclerotic plaques leads to plaque rupture, intravascular thrombosis and tissue infarction. Increased neovascularization of the plaque (e.g. by angiogenesis) is thought to arise from the adventitial vasa vasorum, leading to an abnormal vascular development. This network of immature vessels is a viable source of invading inflammatory cells that can contribute to plaque instability. Furthermore, intra-plaque hemorrhages can lead to accumulation of erythrocyte membranes in the plaque that are rich in phospholipids and free cholesterol, promoting lesion instability through necrotic core expansion.

Future angiogenic and arteriogenic approaches need to take these pitfalls into account and should focus on stimulation of vessel growth in combination with neutral or even beneficial effects on plaque formation and composition.

This review discusses the delicate balance between the benefits and the drawbacks of therapeutic strategies to influence angiogenesis and arteriogenesis.


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The Importance of Reendothelialization After Arterial Injury
D. Versari, L. O. Lerman and A. Lerman

Atherosclerosis is still the principal cause of morbidity and mortality in Western countries and although a significant progress has been made in the understanding of its pathophysiology, the determinants of atherosclerotic plaque instability are still poorly understood. The endothelium plays a pivotal role for the development, progression, and complication of atherosclerosis. Endothelial dysfunction is widely recognized as one of the early alteration in the vessel wall preceding the development of the plaque. However, considering the plethora of vascular functions which are regulated by endothelium, it plays a pivotal role throughout the atherosclerotic process and indeed the loss of endothelial cells, leading to plaque denudation, is one of the main causes of plaque complication. It is therefore conceivable that the maintenance of the endothelial layer physical continuity and function is crucial for the prevention of atherosclerosis. In the presence of cardiovascular risk factors, endothelial cells are continuously injured and repaired by the proliferation of resident cells and circulating endothelial progenitor cells. Indeed the number of circulating endothelial progenitor cells has been identified as an predictor of cardiovascular events. The increase in bone marrow release of endogenous progenitor cells or the enhancement of their homing in arterial denuded sites or in intravascular stent surface, are currently pursued to reduce atherosclerosis development/complication and intrastent restenosis, respectively. However, some challenges may arise from procedures enhancing endothelialization, including unwanted angiogenesis which may favor neoplasia progression and paradoxically atherosclerotic plaque expansion and complication.