Modulation of ADP-induced platelet activation by aspirin and pravastatin: role of lectin-like oxidized low-density lipoprotein receptor-1, nitric oxide, oxidative stress, and inside-out integrin signaling

Role of Thrombosis in Neurodegenerative Diseases: An Intricate Mechanism of Neurovascular Complications

Thrombosis, the formation of blood clots in arteries or veins, poses a significant health risk by disrupting the blood flow. It can potentially lead to major cardiovascular complications such as acute myocardial infarction or ischemic stroke (arterial thrombosis) and deep vein thrombosis or pulmonary embolism (venous thrombosis). Nevertheless, over the course of several decades, researchers have observed an association between different cardiovascular events and neurodegenerative diseases, which progressively harm and impair parts of the nervous system, particularly the brain. Furthermore, thrombotic complications have been identified in numerous clinical instances of neurodegenerative diseases, particularly Alzheimer's disease, Parkinson's disease, multiple sclerosis, and Huntington's disease. Substantial research indicates that endothelial dysfunction, vascular inflammation, coagulation abnormalities, and platelet hyperactivation are commonly observed in these conditions, collectively contributing to an increased risk of thrombosis. Thrombosis can, in turn, contribute to the onset, pathogenesis, and severity of these neurological disorders. Hence, this concise review comprehensively explores the correlation between cardiovascular diseases and neurodegenerative diseases, elucidating the cellular and molecular mechanisms of thrombosis in these neurodegenerative diseases. Additionally, a detailed discussion is provided on the commonly employed antithrombotic medications in the context of these neuronal diseases.

Flow Cytometry and Platelets

Clinical assessment of platelet activation by flow cytometry is useful in the characterization and diagnosis of platelet-specific disorders and as a measure of risk for thrombosis or bleeding. Platelets circulate in a resting, "unactivated" state, but when activated they undergo alterations in surface glycoprotein function and/or expression level, exposure of granule membrane proteins, and exposure of procoagulant phospholipids. Flow cytometry provides the means to detect these changes and, unlike other platelet tests, is appropriate for measuring platelet function in samples from patients with low platelet counts. The present review will focus on flow cytometric tests for platelet activation markers.

Abacavir causes leukocyte/platelet crosstalk by activating neutrophil P2X7 receptors thus releasing soluble lectin-like oxidized low-density lipoprotein receptor-1

BACKGROUND AND PURPOSE

Abacavir, an antiretroviral drug used in HIV therapy associated with myocardial infarction, promotes thrombosis through P2X7 receptors. The role of platelets as pro-thrombotic cells is acknowledged whereas that of neutrophils-due to their secretory capacity-is gaining recognition. This study analyses the role of neutrophils-specifically the secretome of abacavir-treated neutrophils (SN_ABC )-in platelet activation that precedes thrombosis.

EXPERIMENTAL APPROACH

Effects of abacavir or SN_ABC on platelet activation and platelet-leukocyte interactions and expression of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) were analysed by flow cytometry. The secretome was analysed by proteomics. The role of leukocytes in the actions of abacavir was evaluated in a mouse model of thrombosis.

KEY RESULTS

Abacavir induced platelet-leukocyte interactions, not directly via effects of abacavir on platelets, but via activation of neutrophils, which triggered interactions between platelet P-selectin and neutrophil P-selectin glycoprotein ligand-1 (PSGL-1). SN_ABC stimulated platelet activation and platelet-leukocyte interactions through a process that was dependent on LOX-1, neutrophil P2X7 and platelet P2Y1, P2Y12 and P2X1 receptors. Abacavir induced the expression of LOX-1 on neutrophils and of the soluble form of LOX-1 (sLOX-1) in SN_ABC . Neutrophils, LOX-1, P2X7, P2Y1, P2Y12 and P2X1 receptors were required for the pro-thrombotic actions of abacavir in vivo.

CONCLUSION AND IMPLICATIONS

Neutrophils are target cells in abacavir-induced thrombosis. Abacavir released sLOX-1 from neutrophils via activation of their P2X7 receptors, which in turn activated platelets. Hence, sLOX-1 could be the missing link in the cardiovascular risk associated with abacavir.

The structural basis of effective LOX-1 inhibition

Along with other scavenger receptors, splice variants of LOX-1 play an important role in modulating numerous subcellular mechanisms such as normal cell development, differentiation and growth in response to physiological stimuli. Thus, LOX-1 activity is a key regulator in determining the severity of many genetic, metabolic, cardiovascular, renal, and neurodegenerative diseases and/or cancer. Increased expression of LOX-1 precipitates pathological disorders during the aging process. Therefore, it becomes important to develop novel LOX-1 inhibitors based on its ligand binding polarity and/or affinity and disrupt the uptake of its ligand: oxidized low-density lipoproteins (ox-LDL). In this review, we shed light on the presently studied and developed novel LOX-1 inhibitors that may have potential for treatment of diseases characterized by LOX-1 activation.

PCSK9 Promotes Cardiovascular Diseases: Recent Evidence about Its Association with Platelet Activation-Induced Myocardial Infarction

Cardiovascular diseases are the leading cause of death worldwide, with the majority of the cases being heart failure due to myocardial infarction. Research on cardiovascular diseases is currently underway, particularly on atherosclerosis prevention, to reduce the risk of myocardial infarction. Proprotein convertase subtilisin/kexin type 9 (PCSK9) has been reported to play a role in lipid metabolism, by enhancing low-density lipoprotein (LDL) receptor degradation. Therefore, PCSK9 inhibitors have been developed and found to successfully decrease LDL plasma levels. Recent experimental studies have also implicated PCSK9 in platelet activation, having a key role during atherosclerosis progression. Although numerous studies have addressed the role of PCSK9 role in controlling hypercholesterolemia, studies and discussions exploring its involvement in platelet activation are still limited. Hence, here, we address our current understanding of the pathophysiological process involved in atherosclerosis-induced myocardial infarction (MI) through platelet activation and highlight the molecular mechanisms used by PCSK9 in regulating platelet activation. Undoubtedly, a deeper understanding of the relationship between platelet activation and the underlying molecular mechanisms of PCSK9 in the context of MI progression will provide a new strategy for developing drugs that selectively inhibit the most relevant pathways in cardiovascular disease progression.

A dry immersion model of microgravity modulates platelet phenotype, miRNA signature, and circulating plasma protein biomarker profile

Ground based research modalities of microgravity have been proposed as innovative methods to investigate the aetiology of chronic age-related conditions such as cardiovascular disease. Dry Immersion (DI), has been effectively used to interrogate the sequelae of physical inactivity (PI) and microgravity on multiple physiological systems. Herein we look at the causa et effectus of 3-day DI on platelet phenotype, and correlate with both miRomic and circulating biomarker expression. The miRomic profile of platelets is reflective of phenotype, which itself is sensitive and malleable to the exposome, undergoing responsive transitions in order to fulfil platelets role in thrombosis and haemostasis. Heterogeneous platelet subpopulations circulate at any given time, with varying degrees of sensitivity to activation. Employing a DI model, we investigate the effect of acute PI on platelet function in 12 healthy males. 3-day DI resulted in a significant increase in platelet count, plateletcrit, platelet adhesion, aggregation, and a modest elevation of platelet reactivity index (PRI). We identified 15 protein biomarkers and 22 miRNA whose expression levels were altered after DI. A 3-day DI model of microgravity/physical inactivity induced a prothrombotic platelet phenotype with an unique platelet miRNA signature, increased platelet count and plateletcrit. This correlated with a unique circulating protein biomarker signature. Taken together, these findings highlight platelets as sensitive adaptive sentinels and functional biomarkers of epigenetic drift within the cardiovascular compartment.

Increased Circulating Malondialdehyde-Modified Low-Density Lipoprotein Level Is Associated with High-Risk Plaque in Coronary Computed Tomography Angiography in Patients Receiving Statin Therapy

Objective: To evaluate the association of serum malondialdehyde low-density lipoprotein (MDA-LDL), an oxidatively modified LDL, with the prevalence of high-risk plaques (HRP) determined with coronary computed tomography angiography (CTA) in statin-treated patients. Methods: This study was a single-center retrospective cohort comprising 268 patients (mean age 67 years, 58% men) with statin therapy and who underwent coronary CTA for suspected stable coronary artery disease. Patients were classified into two groups according to median MDA-LDL level or median LDL-C level. Coronary CTA-verified HRP was defined when two or more characteristics, including positive remodeling, low-density plaques, and spotty calcification, were present. Results: Patients with HRP had higher MDA-LDL (p = 0.011), but not LDL-C (p = 0.867) than those without HRP. High MDA-LDL was independently associated with HRP (odds ratio 1.883, 95% confidential interval 1.082–3.279) after adjustment for traditional risk factors. Regarding incremental value of MDA-LDL for predicting CTA-verified HRP, addition of serum MDA-LDL levels to the baseline model significantly increased global chi-square score from 26.1 to 32.8 (p = 0.010). Conclusions: A high serum MDA-LDL level is an independent predictor of CTA-verified HRP, which can lead to cardiovascular events in statin-treated patients.

Lipoprotein receptor signalling in atherosclerosis

The founding member of the lipoprotein receptor family, low-density lipoprotein receptor (LDLR) plays a major role in the atherogenesis through the receptor-mediated endocytosis of LDL particles and regulation of cholesterol homeostasis. Since the discovery of the LDLR, many other structurally and functionally related receptors have been identified, which include low-density lipoprotein receptor-related protein (LRP)1, LRP5, LRP6, very low-density lipoprotein receptor, and apolipoprotein E receptor 2. The scavenger receptor family members, on the other hand, constitute a family of pattern recognition proteins that are structurally diverse and recognize a wide array of ligands, including oxidized LDL. Among these are cluster of differentiation 36, scavenger receptor class B type I and lectin-like oxidized low-density lipoprotein receptor-1. In addition to the initially assigned role as a mediator of the uptake of macromolecules into the cell, a large number of studies in cultured cells and in in vivo animal models have revealed that these lipoprotein receptors participate in signal transduction to modulate cellular functions. This review highlights the signalling pathways by which these receptors influence the process of atherosclerosis development, focusing on their roles in the vascular cells, such as macrophages, endothelial cells, smooth muscle cells, and platelets. Human genetics of the receptors is also discussed to further provide the relevance to cardiovascular disease risks in humans. Further knowledge of the vascular biology of the lipoprotein receptors and their ligands will potentially enhance our ability to harness the mechanism to develop novel prophylactic and therapeutic strategies against cardiovascular diseases.

Effect of Statins on Platelet Activation and Function: From Molecular Pathways to Clinical Effects

Purpose

Statins are a class of drugs widely used in clinical practice for their lipid-lowering and pleiotropic effects. In recent years, a correlation between statins and platelet function has been unveiled in the literature that might introduce new therapeutic indications for this class of drugs. This review is aimed at summarizing the mechanisms underlying statin-platelet interaction in the cardiologic scenario and building the basis for future in-depth studies.

Methods

We conducted a literature search through PubMed, Embase, EBSCO, Cochrane Database of Systematic Reviews, and Web of Science from their inception to June 2020.

Results

Many pathways could explain the interaction between statins and platelets, but the specific effect depends on the specific compound. Some could be mediated by enzymes that allow the entry of drugs into the cell (OATP2B1) and others by enzymes that mediate their activation (PLA2, MAPK, TAX2, PPARs, AKT, and COX-1), recruitment and adhesion (LOX-1, CD36, and CD40L), or apoptosis (BCL2). Statins also appear to have a synergistic effect with aspirin and low molecular weight heparins. Surprisingly, they seem to have an antagonistic effect with clopidogrel.

Conclusion

There are many pathways potentially responsible for the interactions between statins and platelets. Their effect appears to be closely related, and each single effect can be barely measured. Also, the same compound might have complex downstream signaling with potentially opposite effects, i.e., beneficial or deleterious. The multiple clinical implications that can be derived as a result of this interaction, however, represent an excellent reason to develop future in-depth studies.

LDL-Cholesterol and Platelets: Insights into Their Interactions in Atherosclerosis

Atherosclerosis and its complications, including acute coronary syndromes, are the major cause of death worldwide. The two most important pathophysiological mechanisms underlying atherosclerosis include increased platelet activation and increased low-density lipoproteins (LDL) concentration. In contrast to LDL, oxidized (ox)-LDL have direct pro-thrombotic properties by functional interactions with platelets, leading to platelet activation and favoring thrombus formation. In this review, we summarize the currently available evidence on the interactions between LDL-cholesterol and platelets, which are based on (i) the presence of ox-LDL-binding sites on platelets, (ii) generation of ox-LDL by platelets and (iii) the role of activated platelets and ox-LDL in atherosclerosis. In addition, we elaborate on the clinical implications of these interactions, including development of the new therapeutic possibilities. The ability to understand and modulate mechanisms governing interactions between LDL-cholesterol and platelets may offer new treatment strategies for atherosclerosis prevention.

Association of circulating soluble lectin-like oxidized low-density lipoprotein receptor-1 with inflammatory markers and urinary albumin excretion in patients with type 2 diabetes

OBJECTIVES

The main purpose of the study was to study the association between circulating soluble lectin-like oxidized low-density lipoprotein receptor-1 levels and various markers, including inflammatory markers such as high-sensitivity C-reactive protein and fibrinogen, serum lipids, and renal function, in patients with poorly controlled type 2 diabetes.

METHODS

The subjects were 70 patients (men 45, women 25) who were hospitalized for treatment of poor glycemic control. Plasma soluble lectin-like oxidized low-density lipoprotein receptor-1 levels were assayed using a sandwich chemiluminescence enzyme immunoassay.

RESULTS

Circulating soluble lectin-like oxidized low-density lipoprotein receptor-1 was significantly positively correlated with lectin-like oxidized low-density lipoprotein-1 ligands containing apolipoprotein B, reflecting modified low-density lipoprotein, and with inflammatory markers such as high-sensitivity C-reactive protein and fibrinogen. In addition, there was a significant positive correlation between soluble lectin-like oxidized low-density lipoprotein receptor-1 and urinary albumin excretion.

CONCLUSIONS

Soluble lectin-like oxidized low-density lipoprotein receptor-1 may serve as a marker reflecting the degrees of inflammation and albuminuria in patients with poorly controlled type 2 diabetes.

From Classical to Unconventional: The Immune Receptors Facilitating Platelet Responses to Infection and Inflammation

Platelets have long been recognized for their role in maintaining the balance between hemostasis and thrombosis. While their contributions to blood clotting have been well established, it has been increasingly evident that their roles extend to both innate and adaptive immune functions during infection and inflammation. In this comprehensive review, we describe the various ways in which platelets interact with different microbes and elicit immune responses either directly, or through modulation of leukocyte behaviors.

Platelets and Their Role in the Pathogenesis of Cardiovascular Events in Patients With Community-Acquired Pneumonia

Community-acquired pneumonia (CAP) remains an important cause of morbidity and mortality throughout the world with much recent and ongoing research focused on the occurrence of cardiovascular events (CVEs) during the infection, which are associated with adverse short-term and long-term survival. Much of the research directed at unraveling the pathogenesis of these events has been undertaken in the settings of experimental and clinical CAP caused by the dangerous, bacterial respiratory pathogen, Streptococcus pneumoniae (pneumococcus), which remains the most common bacterial cause of CAP. Studies of this type have revealed that although platelets play an important role in host defense against infection, there is also increasing recognition that hyperactivation of these cells contributes to a pro-inflammatory, prothrombotic systemic milieu that contributes to the etiology of CVEs. In the case of the pneumococcus, platelet-driven myocardial damage and dysfunction is exacerbated by the direct cardiotoxic actions of pneumolysin, a major pore-forming toxin of this pathogen, which also acts as potent activator of platelets. This review is focused on the role of platelets in host defense against infection, including pneumococcal infection in particular, and reviews the current literature describing the potential mechanisms by which platelet activation contributes to cardiovascular complications in CAP. This is preceded by an evaluation of the burden of pneumococcal infection in CAP, the clinical features and putative pathogenic mechanisms of the CVE, and concludes with an evaluation of the potential utility of the anti-platelet activity of macrolides and various adjunctive therapies.

Clinical Significance of Electronegative Low-Density Lipoprotein Cholesterol in Atherothrombosis

Despite the numerous risk factors for atherosclerotic cardiovascular diseases (ASCVD), cumulative evidence shows that electronegative low-density lipoprotein (L5 LDL) cholesterol is a promising biomarker. Its toxicity may contribute to atherothrombotic events. Notably, plasma L5 LDL levels positively correlate with the increasing severity of cardiovascular diseases. In contrast, traditional markers such as LDL-cholesterol and triglyceride are the therapeutic goals in secondary prevention for ASCVD, but that is controversial in primary prevention for patients with low risk. In this review, we point out the clinical significance and pathophysiological mechanisms of L5 LDL, and the clinical applications of L5 LDL levels in ASCVD can be confidently addressed. Based on the previously defined cut-off value by receiver operating characteristic curve, the acceptable physiological range of L5 concentration is proposed to be below 1.7 mg/dL. When L5 LDL level surpass this threshold, clinically relevant ASCVD might be present, and further exams such as carotid intima-media thickness, pulse wave velocity, exercise stress test, or multidetector computed tomography are required. Notably, the ultimate goal of L5 LDL concentration is lower than 1.7 mg/dL. Instead, with L5 LDL greater than 1.7 mg/dL, lipid-lowering treatment may be required, including statin, ezetimibe or PCSK9 inhibitor, regardless of the low-density lipoprotein cholesterol (LDL-C) level. Since L5 LDL could be a promising biomarker, we propose that a high throughput, clinically feasible methodology is urgently required not only for conducting a prospective, large population study but for developing therapeutics strategies to decrease L5 LDL in the blood.

LOX-1 en las afecciones cardiovasculares, perspectivas terapéuticas futuras

El receptor de la lipoproteína de baja densidad oxidado tipo lectina 1 (LOX-1), también conocido como OLR-1, es un receptor scavenger (SR) clase E, que media la absorción del colesterol LDL en su forma oxidada, por las células vasculares. LOX-1 está involucrado en la disfunción endotelial, la adhesión de monocitos, la proliferación, migración y apoptosis de las células del músculo liso, la formación de células espumosas, la activación de plaquetas, así como la inestabilidad a nivel del endotelio vascular; todos eventos críticos en la patogénesis de la aterosclerosis. LOX-1 contribuyen a la inestabilidad de la placa ateroesclerótica y a las últimas secuelas clínicas de ruptura endotelial e isquemia tisular cardíaca potencialmente mortal. No existe en la actualidad ningún fármaco aprobado o en desarrollo clínico a partir de LOX-1, debido a sus complejos mecanismos biológicos no dilucidados completamente. Se han utilizado diversas terapias con el objetivo de inhibir la acción de LOX-1; medicamentos como: antioxidantes, estatinas, agentes antinflamatorios naturales, que actúen sobre su expresión, pero todos con eficacia moderada. También se ha evaluado la administración de anticuerpos anti-LOX-1 inhibe la aterosclerosis al disminuir eventos celulares. El diseño de fármacos enfocados en el conocimiento de las vías de señalización de LOX-1 y la aplicación de herramientas biotecnológicas permite el desarrollo de nuevas dianas terapéuticas basadas en la potencialidad que tienen los anticuerpos monoclonales. Con estos antecedentes el, receptor LOX-1, representa un objetivo terapéutico atractivo para el tratamiento de enfermedades ateroscleróticas humanas. La evidencia reciente indica que la acción sobre este SR es una posible estrategia para el tratamiento de la enfermedad vascular, explorando en esta revisión su papel y posibles futuras aplicaciones en el diagnóstico y la terapéutica.

LOX-1 (Lectin-Like Oxidized Low-Density Lipoprotein Receptor-1) Deletion Has Protective Effects on Stroke in the Genetic Background of Stroke-Prone Spontaneously Hypertensive Rat

Background and Purpose- oxLDL (oxidized low-density lipoprotein) has been known for its potential to induce endothelial dysfunction and used as a major serological marker of oxidative stress. Recently, LOX-1 (lectin-like oxidized low-density lipoprotein receptor-1), a lectin-like receptor for oxLDL, has attracted attention in studies of neuronal apoptosis and stroke. We aim to investigate the impact of LOX-1-deficiency on spontaneous hypertension-related brain damage in the present study. Methods- We generated a LOX-1 deficient strain on the genetic background of stroke-prone spontaneously hypertensive rat (SHRSP), an animal model of severe hypertension and spontaneous stroke. In this new disease model with stroke-proneness, we monitored the occurrence of brain abnormalities with and without salt loading by multiple procedures including T₂ weighted magnetic resonance imaging and also explored circulatory miRNAs as diagnostic biomarkers for cerebral ischemic injury by microarray analysis. Results- Both T₂ weighted magnetic resonance imaging abnormalities and physiological parameter changes could be detected at significantly delayed timing in LOX-1 knockout rats compared with wild-type SHRSP, in either case of normal rat chow and salt loading (P<0.005 in all instances; n=11-20 for SHRSP and n=13-23 for LOX-1 knockout rats). There were no significant differences in the form of magnetic resonance imaging findings between the strains. A number of miRNAs expressed in the normal rat plasma, including rno-miR-150-5p and rno-miR-320-3p, showed significant changes after spontaneous brain damage in SHRSP, whereas the corresponding changes were modest or almost unnoticeable in LOX-1 knockout rats. There appeared to be the lessening of correlation of postischemic miRNA alterations between the injured brain tissue and plasma in LOX-1 knockout rats. Conclusions- Our data show that deficiency of LOX-1 has a protective effect on spontaneous brain damage in a newly generated LOX-1-deficient strain of SHRSP. Further, our analysis of miRNAs as biomarkers for ischemic brain damage supports a potential involvement of LOX-1 in blood brain barrier disruption after cerebral ischemia. Visual Overview- An online visual overview is available for this article.

Effects of Antiplatelet and Nonsteroidal Anti-inflammatory Medications on Platelet-Rich Plasma: A Systematic Review

Background:

Platelet-rich plasma (PRP) has wide applications in orthopaedic care. Its beneficial effects are attributed to the growth factor profile from the platelet secretome. In theory, these effects would be diminished by medications that inhibit platelet activation and/or the subsequent release of growth factors.

Purpose:

To determine whether commonly used antiplatelets, nonsteroidal anti-inflammatory drugs (NSAIDs), or anticoagulant medications affect platelet growth factor release in PRP.

Study Design:

Systematic review; Level of evidence, 2.

Method:

A systematic review of the literature related to antiplatelet, anti-inflammatory, and anticoagulant drugs was performed following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. We used the Downs and Black objective quality scoring system. The literature search consisted of PubMed and Cochrane Library databases. Search terms consisted of 1 item selected from “platelet-rich plasma,” “platelet-derived growth factor,” and “platelet-rich plasma AND growth factor” combined with 1 item from “antiplatelet,” “aspirin,” “anticoagulant,” and “NSAID.” Only studies published within the past 25 years were included.

Results:

A total of 15 studies met the inclusion criteria: 7 studies detected no significant decrease in growth factors or mitogenesis, whereas 6 detected a decrease with antiplatelet agents, 1 detected mixed results with an antiplatelet agent, and 1 had mixed results with an antiplatelet agent/vasodilator. In terms of PRP activation, all 3 studies assessing collagen, the 2 studies analyzing adenosine diphosphate alone, and the 1 study investigating arachidonic acid found a decrease in growth factor concentration.

Conclusion:

Antiplatelet medications may decrease the growth factor release profile in a cyclooxygenase 1– and cyclooxygenase 2–dependent manner. Eight of 15 studies found a decrease in growth factors or mitogenesis. However, more studies are needed to comprehensively understand antiplatelet effects on the PRP secretome.

LOX-1: Regulation, Signaling and Its Role in Atherosclerosis

Atherosclerosis has long been known to be a chronic inflammatory disease. In addition, there is intense oxidative stress in atherosclerosis resulting from an imbalance between the excess reactive oxygen species (ROS) generation and inadequate anti-oxidant defense forces. The excess of the oxidative forces results in the conversion of low-density lipoproteins (LDL) to oxidized LDL (ox-LDL), which is highly atherogenic. The sub-endothelial deposition of ox-LDL, formation of foamy macrophages, vascular smooth muscle cell (VSMC) proliferation and migration, and deposition of collagen are central pathophysiologic steps in the formation of atherosclerotic plaque. Ox-LDL exerts its action through several different scavenger receptors, the most important of which is LOX-1 in atherogenesis. LOX-1 is a transmembrane glycoprotein that binds to and internalizes ox-LDL. This interaction results in variable downstream effects based on the cell type. In endothelial cells, there is an increased expression of cellular adhesion molecules, resulting in the increased attachment and migration of inflammatory cells to intima, followed by their differentiation into macrophages. There is also a worsening endothelial dysfunction due to the increased production of vasoconstrictors, increased ROS, and depletion of endothelial nitric oxide (NO). In the macrophages and VSMCs, ox-LDL causes further upregulation of the LOX-1 gene, modulation of calpains, macrophage migration, VSMC proliferation and foam cell formation. Soluble LOX-1 (sLOX-1), a fragment of the main LOX-1 molecule, is being investigated as a diagnostic marker because it has been shown to be present in increased quantities in patients with hypertension, diabetes, metabolic syndrome and coronary artery disease. LOX-1 gene deletion in mice and anti-LOX-1 therapy has been shown to decrease inflammation, oxidative stress and atherosclerosis. LOX-1 deletion also results in damage from ischemia, making LOX-1 a promising target of therapy for atherosclerosis and related disorders. In this article we focus on the different mechanisms for regulation, signaling and the various effects of LOX-1 in contributing to atherosclerosis.

Targeting LOX-1 in atherosclerosis and vasculopathy: current knowledge and future perspectives

LOX-1 (lectin-like oxidized low-density lipoprotein receptor-1; also known as OLR1) is the dominant receptor that recognizes and internalizes oxidized low-density lipoproteins (ox-LDLs) in endothelial cells. Several genetic variants of LOX-1 are associated with the risk and severity of coronary artery disease. The LOX-1-ox-LDL interaction induces endothelial dysfunction, leukocyte adhesion, macrophage-derived foam cell formation, smooth muscle cell proliferation and migration, and platelet activation. LOX-1 activation eventually leads to the rupture of atherosclerotic plaques and acute cardiovascular events. In addition, LOX-1 can be cleaved to generate soluble LOX-1 (sLOX-1), which is a useful diagnostic and prognostic marker for atherosclerosis-related diseases in human patients. Of therapeutic relevance, several natural products and clinically used drugs have emerged as LOX-1 inhibitors that have antiatherosclerotic actions. We hereby provide an updated overview of role of LOX-1 in atherosclerosis and associated vascular diseases, with an aim to highlighting the potential of LOX-1 as a novel theranostic tool for cardiovascular disease prevention and treatment.

Oxidative Stress in Atherosclerosis

PURPOSE OF REVIEW

Atherosclerosis is now considered a chronic inflammatory disease. Oxidative stress induced by generation of excess reactive oxygen species has emerged as a critical, final common mechanism in atherosclerosis. Reactive oxygen species (ROS) are a group of small reactive molecules that play critical roles in the regulation of various cell functions and biological processes. Although essential for vascular homeostasis, uncontrolled production of ROS is implicated in vascular injury. Endogenous anti-oxidants function as checkpoints to avoid these untoward consequences of ROS, and an imbalance in the oxidant/anti-oxidant mechanisms leads to a state of oxidative stress. In this review, we discuss the role of ROS and anti-oxidant mechanisms in the development and progression of atherosclerosis, the role of oxidized low-density lipoprotein cholesterol, and highlight potential anti-oxidant therapeutic strategies relevant to atherosclerosis.

RECENT FINDINGS

There is growing evidence on how traditional risk factors translate into oxidative stress and contribute to atherosclerosis. Clinical trials evaluating anti-oxidant supplements had failed to improve atherosclerosis. Current studies focus on newer ROS scavengers that specifically target mitochondrial ROS, newer nanotechnology-based drug delivery systems, gene therapies, and anti-miRNAs. Synthetic LOX-1 modulators that inhibit the effects of Ox-LDL are currently in development. Research over the past few decades has led to identification of multiple ROS generating systems that could potentially be modulated in atherosclerosis. Therapeutic approaches currently being used for atheroslcerotic vascular disease such as aspirin, statins, and renin-angiotensin system inhibitors exert a pleiotropic antioxidative effects. There is ongoing research to identify novel therapeutic modalities to selectively target oxidative stress in atherosclerosis.

Carbamylated Low-Density Lipoproteins Induce a Prothrombotic State Via LOX-1: Impact on Arterial Thrombus Formation In Vivo

BACKGROUND

Carbamylation alters low-density lipoprotein (LDL) structure and is thought to promote vascular inflammation and dysfunction in patients with chronic kidney disease (CKD).

OBJECTIVES

This study sought to determine whether carbamylated LDL (cLDL) exerts prothrombotic effects in vascular cells and platelets and whether cLDL enhances arterial thrombus formation in vivo.

METHODS

LDL was isolated from healthy subjects or patients with CKD by sequential ultracentrifugation. Ex vivo carbamylation of LDL from healthy subjects was induced with potassium cyanate. Arterial thrombus formation was analyzed in a murine carotid artery photochemical injury model. Protein expression and mRNA levels were analyzed by Western blotting, flow cytometry, and real-time PCR. Platelet aggregation was measured by impedance aggregometry.

RESULTS

Intravenous administration of cLDL in mice accelerated arterial thrombus formation compared to treatment with native LDL (nLDL) or vehicle. Tissue lysates of mouse carotid arteries revealed that cLDL induced the expression of TF, PAI-1, and LOX-1 mRNA in vascular cells. In human aortic smooth muscle and endothelial cells, cLDL induced TF and PAI-1 expression. In contrast, nLDL had no effect on either cell type. While nLDL and cLDL had no aggregatory effect on resting platelets, cLDL enhanced platelet aggregation in response to different agonists. This effect was mediated by mitogen-activated protein kinase p38 phosphorylation and LOX-1 translocation to the surface. LDL isolated from patients with CKD mimicked the prothrombotic effects of cLDL on vascular cells, platelets, and thrombus formation in vivo.

CONCLUSIONS

We found that cLDL induces prothrombotic effects in vascular cells and platelets by activation of the LOX-1 receptor and enhances thrombus formation in vivo. This observation reveals a new mechanism underlying the increased incidence of acute thrombotic events observed in patients with CKD and may lead to the development of new lipid-targeting therapies in this population.

The Use of Statins and Risk of Community-Acquired Pneumonia

PURPOSE OF THE REVIEW

Community-acquired pneumonia (CAP) is still associated with a large burden and causes significant morbidity and mortality. Besides universal vaccination and antibiotic treatment, statins as adjunctive therapy may also have a beneficial role in the prevention and treatment of CAP. Our goal from this review is to discuss the epidemiology of CAP, and role of statins as adjunctive therapy in the development of CAP.

RECENT FINDINGS

Statins are lipid-lowering medications characterized by their ability to control hypercholesterolemia in addition to other pleiotropic effects that could explain their role in the pathogenesis of CAP. While most observational studies have shown that statins reduce risk of pneumonia in the general population, patients with diabetes, and recently in patients with myocardial infarction, no randomized controlled trial (RCT) to date has been conducted to assess the efficacy of statins to prevent development of CAP. Given the paucity of robust randomized evidence to assess statin use and the development of CAP, and considering conflicting results of the observational studies, we are not in favor of initiation of statins for either the prevention or treatment of CAP.

Atorvastatin protects cardiomyocytes from oxidative stress by inhibiting LOX-1 expression and cardiomyocyte apoptosis

Coronary artery disease (CAD) is a major health problem worldwide. The most severe form of CAD is acute coronary syndrome (ACS). Recent studies have demonstrated the beneficial role of atorvastatin in ACS; however, the mechanisms underlying this effect have not been fully clarified. Growing evidence indicates that activation of the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) plays an important role in oxidative stress-induced cardiomyocyte apoptosis during ACS. In this study, we examined whether atorvastatin inhibits H2O2-induced LOX-1 expression and H9c2 cardiomyocyte apoptosis, and investigated the underlying signaling pathway. Treatment of H9c2 cardiomyocytes with H2O2 resulted in elevated expression of LOX-1 mRNA and protein, as well as increased caspase-3 and -9 protein expression and cell apoptosis. H2O2-induced LOX-1 expression, caspase protein expression, and cardiomyocyte apoptosis were attenuated by pretreatment with atorvastatin. Atorvastatin activated H2O2-inhibited phosphorylation of Akt in a concentration-dependent manner. The Akt inhibitor, LY294002, inhibited the effect of atorvastatin on inducing Akt phosphorylation and on suppressing H2O2-mediated caspase up-regulation and cell apoptosis. These findings indicate that atorvastatin protects cardiomyocyte from oxidative stress via inhibition of LOX-1 expression and apoptosis, and that activation of H2O2-inhibited phosphorylation of Akt may play an important role in the protective function of atorvastatin.

The role of lectin-like oxidised low-density lipoprotein receptor-1 in vascular pathology

The lectin-like oxidised low-density lipoprotein receptor-1 (LOX-1) is a vascular scavenger receptor that plays a central role in the pathogenesis of atherothrombotic disease, which remains the main cause of mortality in the Western population. Recent evidence indicates that targeting LOX-1 represents a credible strategy for the management vascular disease and the current review explores the role of this molecule in the diagnosis and treatment of atherosclerosis. LOX-1-mediated pro-atherogenic effects can be inhibited by anti-LOX-1 monoclonal antibodies and procyanidins, whereas downregulation of LOX-1 expression has been achieved by antisense oligonucleotides and a specific pyrrole-imidazole polyamide. Furthermore, LOX-1 can be utilised for plaque imaging using monoclonal antibodies and even the selective delivery of anti-atherosclerotic agents employing immunoliposome techniques. Also, plasma levels of the circulating soluble form of LOX-1 levels are elevated in atherosclerosis and therefore may constitute an additional diagnostic biomarker of vascular pathology.

Oxidative stress level is not associated with survival in terminally ill cancer patients: a preliminary study

Background

While cancer patients have higher oxidative stress (OS) and lower antioxidant activity, evidence for the association of these parameters with survival in patients with terminally ill cancer is lacking.

Methods

We followed 65 terminal cancer patients prospectively. We assessed their performance status, some symptoms, and serum levels of vitamin C and OS level. The Gehan’s generalized Wilcoxon test was used to examine the association between survival times and variables.

Results

Subjects’ performance status was very poor and they had a high level of OS and a low level of vitamin C. No significant association of these two parameters with survival time was noted (p-value, 0.637 for high OS and 0.240 for low vitamin C). Poor performance status was independently related to high OS status after adjusting for potential confounders (adjusted OR, 4.45; p-value, 0.031).

Conclusions

In this study, OS was not associated with survival of terminally ill cancer patients and its prognostic role requires further study.

Highly electronegative LDL from patients with ST-elevation myocardial infarction triggers platelet activation and aggregation

Platelet activation and aggregation underlie acute thrombosis that leads to ST-elevation myocardial infarction (STEMI). L5-highly electronegative low-density lipoprotein (LDL)-is significantly elevated in patients with STEMI. Thus, we examined the role of L5 in thrombogenesis. Plasma LDL from patients with STEMI (n = 30) was chromatographically resolved into 5 subfractions (L1-L5) with increasing electronegativity. In vitro, L5 enhanced adenosine diphosphate-stimulated platelet aggregation twofold more than did L1 and induced platelet-endothelial cell (EC) adhesion. L5 also increased P-selectin expression and glycoprotein (GP)IIb/IIIa activation and decreased cyclic adenosine monophosphate levels (n = 6, P < .01) in platelets. In vivo, injection of L5 (5 mg/kg) into C57BL/6 mice twice weekly for 6 weeks shortened tail bleeding time by 43% (n = 3; P < .01 vs L1-injected mice) and increased P-selectin expression and GPIIb/IIIa activation in platelets. Pharmacologic blockade experiments revealed that L5 signals through platelet-activating factor receptor and lectin-like oxidized LDL receptor-1 to attenuate Akt activation and trigger granule release and GPIIb/IIIa activation via protein kinase C-α. L5 but not L1 induced tissue factor and P-selectin expression in human aortic ECs (P < .01), thereby triggering platelet activation and aggregation with activated ECs. These findings indicate that elevated plasma levels of L5 may promote thrombosis that leads to STEMI.

Scavenger receptors in homeostasis and immunity

Scavenger receptors were originally identified by their ability to recognize and to remove modified lipoproteins; however, it is now appreciated that they carry out a striking range of functions, including pathogen clearance, lipid transport, the transport of cargo within the cell and even functioning as taste receptors. The large repertoire of ligands recognized by scavenger receptors and their broad range of functions are not only due to the wide range of receptors that constitute this family but also to their ability to partner with various co-receptors. The ability of individual scavenger receptors to associate with different co-receptors makes their responsiveness extremely versatile. This Review highlights recent insights into the structural features that determine the function of scavenger receptors and the emerging role that these receptors have in immune responses, notably in macrophage polarization and in the pathogenesis of diseases such as atherosclerosis and Alzheimer's disease.

The lectin-like oxidized low-density lipoprotein receptor-1 as therapeutic target for atherosclerosis, inflammatory conditions and longevity

INTRODUCTION

The lectin-like oxidized LDL receptor-1 (LOX-1) is a scavenger receptor and is regarded as a central element in the initiation of endothelial dysfunction and its further progression to atherosclerosis. Increasing numbers of studies suggest that therapeutic strategies to modulate LOX-1 will have a broad spectrum of applications ranging from cardiovascular diseases to longevity.

AREAS COVERED

The dual role of LOX-1 as a culprit molecule in the process of atherosclerosis and as a danger signal in various tissues is introduced. The structure of the receptor, its ligands and its modulation by known drugs, by natural products (e.g., statins, imipramine, salicylate-based drugs, procyanidins, curcumin) and by new strategies (antisenseRNA, miRNA, pyrrole-imidazol-polyamides, LOX-1 antibodies, lipid apheresis) are described.

EXPERT OPINION

Therapeutic approaches via transcript regulation, allowing a modulation of LOX-1, may be an easier and safer strategy than a blockade of the receptor. Considering the wide distribution of LOX-1 on different tissues, research on the mechanisms of LOX-1 modulation by drugs and natural products applying "omic"-technologies will not only allow a better understanding of the role of LOX-1 in the processes of atherosclerosis, inflammation and longevity but also support the development of specific LOX-1 modulators, avoiding the initiation of molecular mechanisms which lead to adverse events.

LOX-1 in atherosclerosis: biological functions and pharmacological modifiers

Lectin-like oxidized LDL (oxLDL) receptor-1 (LOX-1, also known as OLR-1), is a class E scavenger receptor that mediates the uptake of oxLDL by vascular cells. LOX-1 is involved in endothelial dysfunction, monocyte adhesion, the proliferation, migration, and apoptosis of smooth muscle cells, foam cell formation, platelet activation, as well as plaque instability; all of these events are critical in the pathogenesis of atherosclerosis. These LOX-1-dependent biological processes contribute to plaque instability and the ultimate clinical sequelae of plaque rupture and life-threatening tissue ischemia. Administration of anti-LOX-1 antibodies inhibits atherosclerosis by decreasing these cellular events. Over the past decade, multiple drugs including naturally occurring antioxidants, statins, antiinflammatory agents, antihypertensive and antihyperglycemic drugs have been demonstrated to inhibit vascular LOX-1 expression and activity. Therefore, LOX-1 represents an attractive therapeutic target for the treatment of human atherosclerotic diseases. This review aims to integrate the current understanding of LOX-1 signaling, regulation of LOX-1 by vasculoprotective drugs, and the importance of LOX-1 in the pathogenesis of atherosclerosis.

Pravastatin and simvastatin improves acetylsalicylic acid-mediated in vitro blood platelet inhibition

BACKGROUND

Insight into the pathophysiology of atherothrombosis indicates that an integrated risk factor approach, focusing particularly on the management of dyslipidaemia (with statins) and thrombosis (with ASA), may constitute an optimal therapeutic approach. We investigated whether pravastatin, simvastatin and atorvastatin may directly modulate under in vitro conditions the reactivity of blood platelets originating from healthy volunteers. In addition, we analysed the influence of statins on the platelet sensitivity to ASA under such conditions.

MATERIALS AND METHODS

We monitored collagen- or ADP-induced platelet aggregation, CD36, PAC-1 and CD62 expression on platelet surface and thromboxane generation after incubation with pravastatin, simvastatin, atorvastatin and/or ASA.

RESULTS

The incubation of whole blood with simvastatin and pravastatin significantly decreased CD36 expression. In the presence of 50 μM ASA, simvastatin and pravastatin significantly reduced the PAC-1 expression (30% reduction for simvastatin, P < 0·01, and 15% reduction for pravastatin, P < 0·01), platelet aggregation (20% reduction for both statins, P < 0·01) and thromboxane generation (35% reduction for simvastatin, P < 0·001, and 30% reduction for pravastatin, P < 0·001) compared to ASA alone. Atorvastatin changed neither baseline platelet aggregation nor ASA-mediated platelet inhibition.

CONCLUSIONS

Our results suggested that statins may directly interact with platelet membranes or may modulate a signalling pathway in platelets (the pleiotropic effects of statins). It is possible that the statin effect on CD36 and ASA-mediated protein acetylation can be reached by the modulation of a distribution or a function of membrane-associated proteins. Further studies are certainly needed to better elucidate the mechanism(s) underlying the statins' effects on platelet sensitivity to ASA.

The discovery of LOX-1, its ligands and clinical significance

LOX-1 is an endothelial receptor for oxidized low-density lipoprotein (oxLDL), a key molecule in the pathogenesis of atherosclerosis.The basal expression of LOX-1 is low but highly induced under the influence of proinflammatory and prooxidative stimuli in vascular endothelial cells, smooth muscle cells, macrophages, platelets and cardiomyocytes. Multiple lines of in vitro and in vivo studies have provided compelling evidence that LOX-1 promotes endothelial dysfunction and atherogenesis induced by oxLDL. The roles of LOX-1 in the development of atherosclerosis, however, are not simple as it had been considered. Evidence has been accumulating that LOX-1 recognizes not only oxLDL but other atherogenic lipoproteins, platelets, leukocytes and CRP. As results, LOX-1 not only mediates endothelial dysfunction but contributes to atherosclerotic plaque formation, thrombogenesis, leukocyte infiltration and myocardial infarction, which determine mortality and morbidity from atherosclerosis. Moreover, our recent epidemiological study has highlighted the involvement of LOX-1 in human cardiovascular diseases. Further understandings of LOX-1 and its ligands as well as its versatile functions will direct us to ways to find novel diagnostic and therapeutic approaches to cardiovascular disease.

LOX-1: a new target for therapy for cardiovascular diseases

There is much interest in the role of oxidant stress in an ever-increasing list of disease states. However, the precise mediator of oxidant stress and the stressor molecule/s have not been identified. Accordingly, trials of inhibitors of oxidant stress in animal models of disease states have met only limited success. The trials of traditional anti-oxidant vitamins have been largely unsuccessful in the treatment of a wide array of disease states in humans. Recent identification of LOX-1 in vascular endothelial cells and its activation by oxidant species have led to a marked improvement in our understanding of the pathology of several cardiovascular disease states. Here, we review the disease states where therapy targeted at LOX-1 inhibition might be helpful.

Biomarkers of oxidative stress and risk of developing colorectal cancer: a cohort-nested case-control study in the European Prospective Investigation Into Cancer and Nutrition

Oxidative stress has been shown to play an important role in carcinogenesis, but prospective evidence for an association between biomarkers of oxidative stress and colorectal cancer (CRC) risk is limited. The authors investigated the association between prediagnostic serum levels of oxidative stress indicators (i.e., reactive oxygen metabolites (ROM) and ferric reducing ability of plasma (FRAP)) and CRC risk. This was examined in a nested case-control study (1,064 CRC cases, 1,064 matched controls) in the European Prospective Investigation Into Cancer and Nutrition cohort (1992-2003). Incidence rate ratios and 95% confidence intervals were calculated using conditional logistic regression analyses. ROM were associated with overall CRC risk (highest tertile vs. lowest: adjusted incidence rate ratio (IRR(adj)) = 1.91, 95% confidence interval (CI): 1.47, 2.48), proximal (IRR(adj) = 1.89, 95% CI: 1.06, 3.36) and distal (IRR(adj) = 2.31, 95% CI: 1.37, 3.89) colon cancer, and rectal cancer (IRR(adj) = 1.69, 95% CI: 1.05, 2.72). When results were stratified by tertile of follow-up time, the association remained significant only in participants with less than 2.63 years of follow-up (IRR(adj) = 2.28, 95% CI: 1.78, 2.94; P-heterogeneity < 0.01). FRAP was not associated with CRC risk. In conclusion, prediagnostic serum ROM levels were associated with increased risk of CRC. However, this association was seen only in subjects with relatively short follow-up, suggesting that the association results from production of reactive oxygen species by preclinical tumors.

Current Concepts of the Role of Oxidized LDL Receptors in Atherosclerosis

Atherosclerosis is characterized by accumulation of lipids and inflammatory cells in the arterial wall. Oxidized low-density lipoprotein (ox-LDL) plays important role in the genesis and progression of atheromatous plaque. Various scavenger receptors have been recognized in the past two decades that mediate uptake of ox-LDL leading to formation of foam cells. Inhibition of scavenger receptor A and CD36 has been shown to affect progression of atherosclerosis by decreasing foam cell formation. Lectin-type oxidized LDL receptor 1 (LOX-1) participates at various steps involved in the pathogenesis of atherosclerosis, and in experimental studies its blockade has been shown to affect the progression of atherosclerosis at multiple levels. In this review, we summarize the role of ox-LDL and scavenger receptors in the formation of atheroma with emphasis on effects of LOX-1 blockade.

Aspirin suppresses cardiac fibroblast proliferation and collagen formation through downregulation of angiotensin type 1 receptor transcription

Aspirin (acetyl salicylic acid, ASA) is a common drug used for its analgesic and antipyretic effects. Recent studies show that ASA not only blocks cyclooxygenase, but also inhibits NADPH oxidase and resultant reactive oxygen species (ROS) generation, a pathway that underlies pathogenesis of several ailments, including hypertension and tissue remodeling after injury. In these disease states, angiotensin II (Ang II) activates NADPH oxidase via its type 1 receptor (AT1R) and leads to fibroblast growth and collagen synthesis. In this study, we examined if ASA would inhibit NADPH oxidase activation, upregulation of AT1R transcription, and subsequent collagen generation in mouse cardiac fibroblasts challenged with Ang II. Mouse heart fibroblasts were isolated and treated with Ang II with or without ASA. As expected, Ang II induced AT1R expression, and stimulated cardiac fibroblast growth and collagen synthesis. The AT1R blocker losartan attenuated these effects of Ang II. Similarly to losartan, ASA, and its SA moiety suppressed Ang II-mediated AT1R transcription and fibroblast proliferation as well as expression of collagens and MMPs. ASA also suppressed the expression of NADPH oxidase subunits (p22(phox), p47(phox), p67(phox), NOX2 and NOX4) and ROS generation. ASA did not affect total NF-κB p65, but inhibited its phosphorylation and activation. These observations suggest that ASA inhibits Ang II-induced NADPH oxidase expression, NF-κB activation and AT1R transcription in cardiac fibroblasts, and fibroblast proliferation and collagen expression. The critical role of NADPH oxidase activity in stimulation of AT1R transcription became apparent in experiments where ASA also inhibited AT1R transcription in cardiac fibroblasts challenged with H2O2. Since SA had similar effect as ASA on AT1R expression, we suggest that ASA's effect is mediated by its SA moiety.

Platelet dysfunction in vascular pathologies and how can it be treated

Cardiovascular diseases are one of the leading causes of morbidity and mortality in industrialized countries, and although many processes play a role in the development of vascular disease, thrombosis is the primary event that precipitates stroke and acute coronary syndromes. The blood platelets are of significant importance in medicine. These cells are involved in many physiological processes, particularly haemostasis through their ability to aggregate and form clots in response to activation. In addition, these dynamic cells display activities that extend beyond thrombosis, including an important role in initiating and sustaining vascular inflammation. The expansion of knowledge from basic and clinical research has highlighted the critical position of platelets in several inflammatory diseases such as arthritis and atherosclerosis. Platelets are emerging as important mediators of inflammation and provide important signals to mediate phenotype of other blood and vascular cells. The important role of platelets in arterial thrombosis and the onset of acute myocardial infarction after atherosclerotic plaque rupture make inhibition of platelet aggregation a critical step in preventing thrombotic events associated with stroke, heart attack, and peripheral arterial thrombosis. However, the use of platelet inhibitors for thrombosis prevention must seek a delicate balance between inhibiting platelet activation and an associated increased bleeding risk. The aim of this review is to up-date the knowledge on platelets physiology and dysfunction in pathologies, such as diabetes mellitus, hypercholesterolemia, and hypertension, emphasizing the link between platelets and the inflammation-related atherosclerosis. The review evaluates the opportunities offered by the novel platelet inhibitors to efficiently alleviate the thrombotic events.

Oxidative stress and lectin-like ox-LDL-receptor LOX-1 in atherogenesis and tumorigenesis

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) has been identified as a major receptor for oxidized low-density lipoprotein (ox-LDL) in endothelial cells, monocytes, platelets, cardiomyocytes, and vascular smooth muscle cells. Its expression is minimal under physiological conditions but can be induced under pathological conditions. The upregulation of LOX-1 by ox-LDL appears to be important for physiologic processes, such as endothelial cell proliferation, apoptosis, and endothelium remodeling. Pathophysiologic effects of ox-LDL in atherogenesis have also been firmly established, including endothelial cell dysfunction, smooth muscle cell growth and migration, monocyte transformation into macrophages, and finally platelet aggregation-seen in atherogenesis. Recent studies show a positive correlation between increased serum ox-LDL levels and an increased risk of colon, breast, and ovarian cancer. As in atherosclerosis, ox-LDL and its receptor LOX-1 activate the inflammatory pathway through nuclear factor-kappa B, leading to cell transformation. LOX-1 is important for maintaining the transformed state in developmentally diverse cancer cell lines and for tumor growth, suggesting a molecular connection between atherogenesis and tumorigenesis.

Review of the putative cell-surface receptors for alpha-fetoprotein: identification of a candidate receptor protein family

The identification of a receptor for alpha-fetoprotein (AFP) has long been sought in the field of medicine. The uptake and endocytosis of AFP by rat tumor cells in 1984 sparked a series of confirmatory reports and the original studies were then extended to include multiple tumor types in rats, mice, and humans. The following year, French investigators partially characterized the binding properties of the AFP receptor, but they were not able to purify the receptor. It was not until 1991-1992 that an AFP receptor was partially purified and characterized from both human monocytes and breast cancer cells. By 1993, a monoclonal antibody had been raised against the AFP receptor produced from a breast cancer extract with claims that the receptor was a widespread (universal) oncofetal biomarker for cancer. However, that receptor has yet to be cloned and/or purified due to its complex multimeric binding interactions and associations. The present report will review the literature of the multiple putative AFP receptors described to date, the cellular uptake and endocytosis of AFP, and the biochemical characterization of these putative cell-surface proteins. In addition, evidence derived from computer modeling, proteolytic degradation patterns, and amino acid sequence analysis will be presented in a proposed identification of a family of multi-ligand binding receptors; this family fits many, if not most, of the criteria required for an AFP receptor. The purposed receptor protein family is tentatively identified as the Scavenger receptors which comprise several classes of single- and double-pass integral transmembrane proteins. Present data do not support the concept that the AFP receptor is a "universal" tumor receptor and/or biomarker.

Aspirin resistance: Fact or fiction? A point of view

Aspirin is a wonder drug that has been used for well over 100 years for its analgesic and antipyretic effects. For the past three decades, it has increasingly been used for the prevention of primary and secondary cardiovascular events. Lately, it has been suggested that a significant number of individuals taking aspirin have become resistant to this drug. The phenomenon of "aspirin resistance" is based on the observation of clinical events in some patients taking aspirin, and/or a diminished platelet aggregation inhibitory response to aspirin therapy. Unfortunately, laboratory assays used to monitor the efficacy of aspirin are far from accurate and the results are not reproducible. Furthermore, results of different platelet function tests are often not congruent. In addition, platelet aggregation studies show marked inter-individual and intra-individual variability. Patients with coronary heart disease take many drugs that interfere with the effect of aspirin on platelet aggregation. Besides inhibiting formation of thromboxane A(2) from arachidonic acid, aspirin has a host of platelet-independent effects that complement its platelet inhibitory effects. Laboratory assays designed to measure platelet function do not take into account these pleiotropic effects of aspirin. In our view, use of the term "aspirin resistance" based on inadequate knowledge of imperfect laboratory tests does a disservice to physicians and patients.