The lectin-like oxidized low-density-lipoprotein receptor: a pro-inflammatory factor in vascular disease

Radical Oxygen Species, Oxidized Low-Density Lipoproteins, and Lectin-like Oxidized Low-Density Lipoprotein Receptor 1: A Vicious Circle in Atherosclerotic Process

Atherosclerosis is a complex condition that involves the accumulation of lipids and subsequent plaque formation in the arterial intima. There are various stimuli, cellular receptors, and pathways involved in this process, but oxidative modifications of low-density lipoprotein (ox-LDL) are particularly important in the onset and progression of atherosclerosis. Ox-LDLs promote foam-cell formation, activate proinflammatory pathways, and induce smooth-muscle-cell migration, apoptosis, and cell death. One of the major receptors for ox-LDL is LOX-1, which is upregulated in several cardiovascular diseases, including atherosclerosis. LOX-1 activation in endothelial cells promotes endothelial dysfunction and induces pro-atherogenic signaling, leading to plaque formation. The binding of ox-LDLs to LOX-1 increases the generation of reactive oxygen species (ROS), which can induce LOX-1 expression and oxidize LDLs, contributing to ox-LDL generation and further upregulating LOX-1 expression. This creates a vicious circle that is amplified in pathological conditions characterized by high plasma levels of LDLs. Although LOX-1 has harmful effects, the clinical significance of inhibiting this protein remains unclear. Further studies both in vitro and in vivo are needed to determine whether LOX-1 inhibition could be a potential therapeutic target to counteract the atherosclerotic process.

The involvement of soluble epoxide hydrolase in the development of cardiovascular diseases through epoxyeicosatrienoic acids

Arachidonic acid (AA) has three main metabolic pathways: the cycloxygenases (COXs) pathway, the lipoxygenases (LOXs) pathway, and the cytochrome P450s (CYPs) pathway. AA produces epoxyeicosatrienoic acids (EETs) through the CYPs pathway. EETs are very unstable in vivo and can be degraded in seconds to minutes. EETs have multiple degradation pathways, but are mainly degraded in the presence of soluble epoxide hydrolase (sEH). sEH is an enzyme of bifunctional nature, and current research focuses on the activity of its C-terminal epoxide hydrolase (sEH-H), which hydrolyzes the EETs to the corresponding inactive or low activity diol. Previous studies have reported that EETs have cardiovascular protective effects, and the activity of sEH-H plays a role by degrading EETs and inhibiting their protective effects. The activity of sEH-H plays a different role in different cells, such as inhibiting endothelial cell proliferation and migration, but promoting vascular smooth muscle cell proliferation and migration. Therefore, it is of interest whether the activity of sEH-H is involved in the initiation and progression of cardiovascular diseases by affecting the function of different cells through EETs.

Combined Effect of Omega-3 Fatty Acid and Vitamin D 3 on Oxidized LDL-C and Non-HDL-C Levels in People With Vitamin D Deficiency: A Randomized Controlled Trial

ABSTRACT

The present randomized clinical trial (RCT) was conducted on Jordanian participants with vitamin D deficiency (VDD) with no other medical conditions, to evaluate the combined effect of 1,25-dihydroxy vitamin D 3 (Vit.D 3 ) and omega-3 fatty acid (n-3FA) supplements (D+) on oxidized low-density lipoprotein (Ox-LDL) and non-high-density lipoprotein cholesterol (non-HDL-C) levels as common predictors of cardiovascular diseases (CVDs). Participants were randomized into 4 groups as follows: a control group (C) that received no supplementations, a Vit.D 3 group that received 50,000 IU of Vit.D 3 every week, an n-3FA group that received 300 mg of omega-3 fatty acid every day, and a D+ group that received a combination of both supplements, with the same dosage administered by the previous groups but with a 4-6-hour time interval between Vit.D 3 and n-3FA administration to avoid any possible interaction. All supplementations were administered orally for 8 weeks. Forty-seven participants were allocated to each group. Twenty-six in the control group, 37 participants in the Vit.D 3 group, 37 participants in the n-3FA group, and 46 participants in the D+ group completed the study to the end. The D+ supplementations significantly increased non-HDL-C (118.99 ± 60.98 to 155.26 ± 43.36 mg/dL, P << 0.05) but decreased Ox-LDL-C levels (69.29 ± 37.69 to 52.81 ± 17.30 pg/mL, P = 0.03). The stepwise regression showed that the serum LDL-C level was the main independent variable involved in the elevation of non-HDL levels (R 2 = 0.837) observed at the end of the trial in the D+ group. The groups that were supplemented with either Vit.D 3 alone or n-3FA alone had an insignificant decrease in the level of Ox-LDL-C. In conclusion, despite the observed hyperlipidemic effect, the combination treatment is recommended by the research team because the decrease in Ox-LDL may offset the hyperlipidemic effect.

The Regulation of Neutrophil Migration in Patients with Sepsis: The Complexity of the Molecular Mechanisms and Their Modulation in Sepsis and the Heterogeneity of Sepsis Patients

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Common causes include gram-negative and gram-positive bacteria as well as fungi. Neutrophils are among the first cells to arrive at an infection site where they function as important effector cells of the innate immune system and as regulators of the host immune response. The regulation of neutrophil migration is therefore important both for the infection-directed host response and for the development of organ dysfunctions in sepsis. Downregulation of CXCR4/CXCL12 stimulates neutrophil migration from the bone marrow. This is followed by transmigration/extravasation across the endothelial cell barrier at the infection site; this process is directed by adhesion molecules and various chemotactic gradients created by chemotactic cytokines, lipid mediators, bacterial peptides, and peptides from damaged cells. These mechanisms of neutrophil migration are modulated by sepsis, leading to reduced neutrophil migration and even reversed migration that contributes to distant organ failure. The sepsis-induced modulation seems to differ between neutrophil subsets. Furthermore, sepsis patients should be regarded as heterogeneous because neutrophil migration will possibly be further modulated by the infecting microorganisms, antimicrobial treatment, patient age/frailty/sex, other diseases (e.g., hematological malignancies and stem cell transplantation), and the metabolic status. The present review describes molecular mechanisms involved in the regulation of neutrophil migration; how these mechanisms are altered during sepsis; and how bacteria/fungi, antimicrobial treatment, and aging/frailty/comorbidity influence the regulation of neutrophil migration.

Biomarker Development in Cardiology: Reviewing the Past to Inform the Future

Cardiac biomarkers have become pivotal to the clinical practice of cardiology, but there remains much to discover that could benefit cardiology patients. We review the discovery of key protein biomarkers in the fields of acute coronary syndrome, heart failure, and atherosclerosis, giving an overview of the populations they were studied in and the statistics that were used to validate them. We review statistical approaches that are currently in use to assess new biomarkers and overview a framework for biomarker discovery and evaluation that could be incorporated into clinical trials to evaluate cardiovascular outcomes in the future.

Longitudinal Imaging-Based Clusters in Former Smokers of the COPD Cohort Associate with Clinical Characteristics: The SubPopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS)

PURPOSE

Quantitative computed tomography (qCT) imaging-based cluster analysis identified clinically meaningful COPD former-smoker subgroups (clusters) based on cross-sectional data. We aimed to identify progression clusters for former smokers using longitudinal data.

PATIENTS AND METHODS

We selected 472 former smokers from SPIROMICS with a baseline visit and a one-year follow-up visit. A total of 150 qCT imaging-based variables, comprising 75 variables at baseline and their corresponding progression rates, were derived from the respective inspiration and expiration scans of the two visits. The COPD progression clusters identified were then associated with subject demography, clinical variables and biomarkers.

RESULTS

COPD severities at baseline increased with increasing cluster number. Cluster 1 patients were an obese subgroup with rapid progression of functional small airway disease percentage (fSAD%) and emphysema percentage (Emph%). Cluster 2 exhibited a decrease of fSAD% and Emph%, an increase of tissue fraction at total lung capacity and airway narrowing over one year. Cluster 3 showed rapid expansion of Emph% and an attenuation of fSAD%. Cluster 4 demonstrated severe emphysema and fSAD and significant structural alterations at baseline with rapid progression of fSAD% over one year. Subjects with different progression patterns in the same cross-sectional cluster were identified by longitudinal clustering.

CONCLUSION

qCT imaging-based metrics at two visits for former smokers allow for the derivation of four statistically stable clusters associated with unique progression patterns and clinical characteristics. Use of baseline variables and their progression rates enables identification of longitudinal clusters, resulting in a refinement of cross-sectional clusters.

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.

Matrix Metalloproteinase 9 is Regulated by LOX-1 and erk1/2 Pathway in Dental Peri-Implantitis

BACKGROUND AND OBJECTIVE

Dental peri-implantitis, which can be caused by several different microbial factors, is characterized by inflammatory lesions of the surrounding hard and soft tissues of an oral implant. Matrix Metalloproteinase 9 (MMP9) is thought to be involved in the pathogenesis of peri-implantitis. However, the regulatory mechanism of MMP9 in peri-implantitis has not been fully elucidated. In this study, we tried to evaluate the regulatory mechanism of MMP9 in peri-implantitis.

METHODS

We collected Peri-Implant Crevicular Fluid (PICF) from ten healthy implants and ten periimplantitis patients and compared their expression level of MMP9. We also cultured macrophages from the peripheral blood of healthy volunteers infected by Porphyromonas gingivalis to reveal the regulatory mechanism of MMP9 in peri-implantitis. Western blot, immunofluorescence staining and quantitative Polymerase Chain Reaction (RT-PCR) were used to better characterize the mechanism of MMP9.

RESULTS

The expression of MMP9 was up-regulated in peri-implantitis patient PICF and P. gingivalis infected human macrophages. LOX-1, not dectin-1, was found to mediate MMP9 expression in human macrophages with P. gingivalis infection. Expression of Erk1/2 was responsible for infection-induced MMP9 expression. Finally, use of a broad-spectrum metalloproteinase inhibitor impaired LOX-1 expression in infected macrophages.

CONCLUSION

Our results demonstrate that MMP9 is involved in dental peri-implantitis and is regulated by LOX-1 and Erk1/2. This LOX-1/MMP9 signaling pathway may represent a potential drug target for peri-implantitis.

Physiological functions of SPP/SPPL intramembrane proteases

Intramembrane proteolysis describes the cleavage of substrate proteins within their hydrophobic transmembrane segments. Several families of intramembrane proteases have been identified including the aspartyl proteases Signal peptide peptidase (SPP) and its homologues, the SPP-like (SPPL) proteases SPPL2a, SPPL2b, SPPL2c and SPPL3. As presenilin homologues, they employ a similar catalytic mechanism as the well-studied γ-secretase. However, SPP/SPPL proteases cleave transmembrane proteins with a type II topology. The characterisation of SPP/SPPL-deficient mouse models has highlighted a still growing spectrum of biological functions and also promoted the substrate discovery of these proteases. In this review, we will summarise the current hypotheses how phenotypes of these mouse models are linked to the molecular function of the enzymes. At the cellular level, SPP/SPPL-mediated cleavage events rather provide specific regulatory switches than unspecific bulk proteolysis. By this means, a plethora of different cell biological pathways is influenced including signal transduction, membrane trafficking and protein glycosylation.

A small-molecule inhibitor of lectin-like oxidized LDL receptor-1 acts by stabilizing an inactive receptor tetramer state

The C-type lectin family member lectin-like oxidized LDL receptor-1 (LOX-1) has been object of intensive research. Its modulation may offer a broad spectrum of therapeutic interventions ranging from cardiovascular diseases to cancer. LOX-1 mediates uptake of oxLDL by vascular cells and plays an important role in the initiation of endothelial dysfunction and its progression to atherosclerosis. So far only a few compounds targeting oxLDL-LOX-1 interaction are reported with a limited level of characterization. Here we describe the identification and characterization of BI-0115, a selective small molecule inhibitor of LOX-1 that blocks cellular uptake of oxLDL. Identified by a high throughput screening campaign, biophysical analysis shows that BI-0115 binding triggers receptor inhibition by formation of dimers of the homodimeric ligand binding domain. The structure of LOX-1 bound to BI-0115 shows that inter-ligand interactions at the receptor interfaces are key to the formation of the receptor tetramer thereby blocking oxLDL binding.

Nerolidol inhibits the LOX-1 / IL-1β signaling to protect against the Aspergillus fumigatus keratitis inflammation damage to the cornea

PURPOSE

Nerolidol, a naturally occurring sesquiterpene has both anti-microbial and anti-inflammatory properties. The current study aims to investigate the antifungal and the anti-inflammatory effects of nerolidol against mouse Aspergillus fumigatus (A. fumigatus) keratitis.

METHODS

The minimum inhibitory concentration (MIC) and cytotoxicity tests were used to study the antifungal ability. For in vivo and in vitro studies, the mouse corneas and the human corneal epithelial cells (HCECs) infected with A. fumigatus spores were intervented with nerolidol or phosphate buffer saline (PBS). Thereafter, the effect of the nerolidol on the response against inflammation was analyzed using the following parameters: recruitment of the neutrophils or macrophages and the expression of the lectin-type oxidized low density lipoprotein receptor-1 (LOX-1) and interleukin 1β (IL-1β). Techniques used were the slit lamp, immunofluorescence, myeloperoxidase (MPO) detection, quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot.

RESULTS

Nerolidol directly inhibits the growth of A. fumigatus. The administration of nerolidol reduced the severity of fungal keratitis with infiltration of fewer inflammatory cells and reduced levels of the LOX-1, as well the anti-inflammatory cytokines such as IL-1β were reduced compared with the PBS group. Additionally, in vitro studies showed that treatment with nerolidol inhibited the production of the LOX-1 / IL-1β levels in A. fumigatus stimulated HCECs.

CONCLUSION

Nerolidol attenuated the A. fumigatus keratitis inflammatory response by inhibiting the growth of A. fumigatus, reducing the recruitment of the neutrophils and the macrophages, and inhibiting the LOX-1/ IL-1β signaling.

Targeting Foam Cell Formation in Atherosclerosis: Therapeutic Potential of Natural Products

Foam cell formation and further accumulation in the subendothelial space of the vascular wall is a hallmark of atherosclerotic lesions. Targeting foam cell formation in the atherosclerotic lesions can be a promising approach to treat and prevent atherosclerosis. The formation of foam cells is determined by the balanced effects of three major interrelated biologic processes, including lipid uptake, cholesterol esterification, and cholesterol efflux. Natural products are a promising source for new lead structures. Multiple natural products and pharmaceutical agents can inhibit foam cell formation and thus exhibit antiatherosclerotic capacity by suppressing lipid uptake, cholesterol esterification, and/or promoting cholesterol ester hydrolysis and cholesterol efflux. This review summarizes recent findings on these three biologic processes and natural products with demonstrated potential to target such processes. Discussed also are potential future directions for studying the mechanisms of foam cell formation and the development of foam cell-targeted therapeutic strategies.

LOX-1 is involved in TLR2 induced RANKL regulation in peri-implantitis

PURPOSE

To explore whether receptor activator of nuclear factor kappa-B ligand (RANKL) is involved in the nosogenesis of peri-implantitis and to reveal the regulatory mechanism in Porphyromonas gingivalis induced RANKL production.

METHODS

Therefore, we collected peri-implant crevicular fluid (PICF) and gingival tissues from healthy implants and peri-implantitis patients. The expression of RANKL in samples was tested by ELISA, Western blot and immunofluorescence staining. The production of RANKL in THP-1 macrophages stimulated with P. gingivalis was detected by qRT-PCR and Western blot. Then macrophages were pre-treated with neutralizing antibodies of Toll-like receptor 2 (TLR2) or lectin-type oxidized LDL receptor 1 (LOX-1) and inhibitors of TLR2, LOX-1 or Erk1/2 before P. gingivalis stimulation to evaluate the roles of TLR2, LOX-1 and Erk1/2 in RANKL production by qRT-PCR and Western blot.

RESULTS

The protein level of RANKL was higher in PICF of peri-implantitis patients than healthy implants. We observed increased RANKL expression in P. gingivalis infected macrophages compared to controls. RANKL induced by P. gingivalis stimulation was mediated by TLR2 and Erk1/2 signaling pathway in THP-1 macrophages. LOX-1 is involved in TLR2 induced RANKL expression.

CONCLUSION

RANKL was involved in peri-implantitis, and regulated by TLR2, LOX-1 and Erk1/2 signaling against P. gingivalis infection. As the novel inflammation pathway triggers, TLR2 and LOX-1 which mediate RANKL production seems to be potential drug targets of peri-implantitis.

Inhibition of β-amyloid-induced neurotoxicity by planar analogues of procyanidin B3

Reactive oxygen species (ROS) are known to be produced during the amyloid beta (Aβ) aggregation process. Both ROS production and Aβ fibril formation can result in nerve cell injury. Proanthocyanidins are oligomers of catechin that can act as inhibitors of Aβ aggregation. Procyanidin B3 (Cat-Cat), the dimer of (+)-catechin, can easily cross the blood-brain barrier. Previously, we synthesized two derivatives of Cat-Cat, namely Cat-PCat and PCat-PCat, in which the geometry of one or both catechin molecules in Cat-Cat was constrained to be planar. The antioxidative activities of Cat-PCat and PCat-PCat were found to be stronger than that of Cat-Cat, with PCat-PC at exhibiting the most potent activity. These compounds are predicted to protect against Aβ-induced neurotoxicity via inhibition of Aβ aggregation as well as by antioxidative effects toward Aβ-induced intracellular ROS generation. PCat-PCat exhibited the most potent neuroprotective effects against Aβ-induced cytotoxicity, which resulted from inhibition of β-sheet structure formation during the Aβ aggregation process. PCat-PCat may be a promising lead compound for the treatment of Alzheimer's disease.

Health Effects of Phenolic Compounds Found in Extra-Virgin Olive Oil, By-Products, and Leaf of Olea europaea L

Olea europaea L. fruit is a peculiar vegetal matrix containing high levels of fatty acids (98–99% of the total weight of extra-virgin olive oil, EVOO) and low quantities (1–2%) of phenolics, phytosterols, tocopherols, and squalene. Among these minor components, phenolics are relevant molecules for human health. This review is focused on their beneficial activity, in particular of hydroxytyrosol (HT), oleuropein (OLE), oleocanthal (OLC), and lignans found in EVOO, olive oil by-products and leaves. Specifically, the cardioprotective properties of the Mediterranean diet (MD) related to olive oil consumption, and the biological activities of polyphenols recovered from olive oil by-products and leaves were described. Recent European projects such as EPIC (European Prospective Investigation into Cancer and Nutrition) and EPICOR (long-term follow-up of antithrombotic management patterns in acute coronary syndrome patients) have demonstrated the functional and preventive activities of EVOO showing the relation both between cancer and nutrition and between consumption of EVOO, vegetables, and fruit and the incidence of coronary heart disease. The data reported in this review demonstrate that EVOO, one of the pillars of the MD, is the main product of Olea europaea L. fruits; leaves and by-products are secondary but precious products from which bioactive compounds can be recovered by green technologies and reused for food, agronomic, nutraceutical, and biomedical applications according to the circular economy strategy.

The effect of alpha-lipoic acid on expression of VCAM-1 in type 2 diabetic rat

Macrovascular diabetes complications are generally caused by a process called atherosclerosis. Evidences suggest that to initiate atherosclerosis, oxidated low-density lipoprotein (oxLDL) has to promote the expression of adhesion molecule. Several studies have evidenced the relevance of oxidative stress and atherosclerosis. However, the protective effect of alpha-lipoic acid (ALA) at atherosclerosis still needs to be explored. This study is aimed at investigating the concentration of plasma oxLDL and the expression of adhesion molecule of type 2 diabetes mellitus (DM) using rat model. Eighteen male rats were segregated into three groups labeled as control group, DM group and DM+ALA group. Type 2 diabetes was induced by intraperitoneal injection of streptozotocin (50 mg/kg) followed by nicotinamide (110 mg/kg). ALA was administered at a dose of 60 mg/kg body weight/day throughout the feeding period of 3 weeks. Plasma oxLDL concentration was measured by enzyme-linked immunosorbent assays and expression of vascular cell adhesion molecule-1 (VCAM-1) was measured by immunohistochemistry. Expression of abdominal aortic adhesion molecule was assessed by calculation with Adobe Photoshop CS3. Analysis of variance test was used to compare the concentration of plasma oxLDL and expression of adhesion molecule. A P-value of 0.05 was considered statistically significant. Plasma oxLDL was lower in diabetic rat+ALA compared with the diabetic rat. Percentage of area VCAM-1 in DM+ALA group was lower than DM group. There were no significant differences between groups in intensity of VCAM-1. In conclusion, ALA showed protective effects against early atherosclerosis in diabetic rats.

LOX-1 and atherosclerotic-related diseases

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), a scavenger receptor of oxidized low-density lipoprotein (ox-LDL) found in various cells, plays a crucial role in the formation and progression of atherosclerotic plaques. Animal studies have suggested that LOX-1 mediates the balance between internalization and degeneration of endothelial cells, thereby contributing to various steps in the atherosclerotic process, from initiation to plaque rupture. Under pathological conditions, the extracellular domain of membrane bound LOX-1 can be largely proteolytically cleaved into a soluble form (sLOX-1), which is proportional and linked to the LOX-1 expression level. Circulating levels of sLOX-1 are regarded as a risk biomarker for plaque rupture and acute coronary syndrome (ACS). Recently, studies have shown that sLOX-1 is also elevated in patients with acute stroke and can be a predictive biomarker for acute stroke. With the discovery of the vital role of LOX-1 in atherosclerosis, there is growing focus on the influence of LOX-1 in atherosclerotic-related diseases, including coronary arterial disease(CAD), stroke, and other cardiovascular events. Genetic polymorphisms of LOX-1 have been investigated and have been found to modulate the risk of these diseases. Most polymorphisms have been found to be risk factors, except for the splicing isoform LOXIN. This review concludes with a discussion of the potential future applications of LOX-1 for atherosclerotic-related diseases.

C-terminus of heat shock protein 60 can activate macrophages by lectin-like oxidized low-density lipoprotein receptor 1

Immune responses against antigens generally require an efficient activation of antigen-presenting cells (APCs). Currently, the targeting of vaccine antigens to APCs has emerged as a promising strategy for boosting vaccine immunogenicity. Here, we reported that the C-terminus of heat shock protein 60 (HSP60C) can activate mouse peritoneal macrophages to secret a series of cytokines, and phosphorylation of p38 mitogen-activated protein kinase (MAPK) and NF-κB p65 was involved in the pathway. We showed that the activation effect of HSP60C on macrophages was independent of toll-like receptor (TLR) 4 and the TLR-associated myeloide differentiation factor 88 (MyD88). Knockdown of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) reduced the activation of HSP60C-induced macrophage p38 MAPK, NF-κB p65 and cytokine secretion to some extent. Finally, we found that HSP60C up-regulated the expression of LOX-1 on macrophages and ovalbumin (OVA) model antigen fused with HSP60C markedly enhanced OVA-specific IgG responses. Thus, our results unravel a novel LOX-1-dependent pathway by which HSP60C can effectively activate macrophages and APCs targeting based on LOX-1 interaction is a promising approach to improve vaccines.

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.

Recombinant Human Thioredoxin-1 Protects Macrophages from Oxidized Low-Density Lipoprotein-Induced Foam Cell Formation and Cell Apoptosis

Oxidized low-density lipoprotein (ox-LDL)-induced macrophage foam cell formation and apoptosis play critical roles in the pathogenesis of atherosclerosis. Thioredoxin-1 (Trx) is an antioxidant that potently protects various cells from oxidative stress-induced cell death. However, the protective effect of Trx on ox-LDL-induced macrophage foam cell formation and apoptosis has not been studied. This study aims to investigate the effect of recombinant human Trx (rhTrx) on ox-LDL-stimulated RAW264.7 macrophages and elucidate the possible mechanisms. RhTrx significantly inhibited ox-LDL-induced cholesterol accumulation and apoptosis in RAW264.7 macrophages. RhTrx also suppressed the ox-LDL-induced overproduction of lectin-like oxidized LDL receptor (LOX-1), Bax and activated caspase-3, but it increased the expression of Bcl-2. In addition, rhTrx markedly inhibited the ox-LDL-induced production of intracellular reactive oxygen species (ROS) and phosphorylation of p38 mitogen-activated protein kinases (MAPK). Furthermore, anisomycin (a p38 MAPK activator) abolished the protective effect of rhTrx on ox-LDL-stimulated RAW264.7 cells, and SB203580 (a p38 MAPK inhibitor) exerted a similar effect as rhTrx. Collectively, these findings indicate that rhTrx suppresses ox-LDL-stimulated foam cell formation and macrophage apoptosis by inhibiting ROS generation, p38 MAPK activation and LOX-1 expression. Therefore, we propose that rhTrx has therapeutic potential in the prevention and treatment of atherosclerosis.

Cerebrovascular Gene Expression in Spontaneously Hypertensive Rats After Transient Middle Cerebral Artery Occlusion

Hypertension is a major risk factor for stroke, which is one of the leading global causes of death. In the search for new and effective therapeutic targets in stroke research, we need to understand the influence of hypertension in the vasculature following stroke. We used Affymetrix whole-transcriptome expression profiling as a tool to address gene expression differences between the occluded and non-occluded middle cerebral arteries (MCAs) from spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto (WKY) rats after transient middle cerebral artery occlusion (tMCAO), to provide clues about the pathological mechanisms set in play after stroke. Verified by quantitative PCR, expression of Ccl2, Edn1, Tgfβ2, Olr1 and Serpine1 was significantly increased in the occluded compared to non-occluded MCAs from both SHRs and WKY rats. Additionally, expression of Mmp9, Icam1, Hif1α and Timp1 was increased in the occluded compared to non-occluded MCAs isolated from WKY rats. In comparison between occluded MCAs from SHRs versus occluded MCAs from WKY rats, expression of Ccl2, Olr1 and Serpine1 was significantly increased in SHR MCAs. However, the opposite was observed regarding expression of Edn1. Thus these data suggest that Ccl2, Edn1, Tgfβ2, Olr1 and Serpine1 may be possible mediators of the vascular changes in the occluded MCAs from both SHRs and WKY rats after tMCAO. The aforementioned genes possess biological functions that are consistent with early stroke injuries. In conclusion, these genes may be potential targets in future strategies for acute stroke treatments that can be used in patients with and without hypertension.

Enhanced radical scavenging activity of a procyanidin B3 analogue comprised of a dimer of planar catechin

Proanthocyanidins are oligomers of catechins that exhibit potent antioxidative activity and inhibit binding of oxidized low-density lipoprotein (OxLDL) to the lectin-like oxidized LDL receptor (LOX-1), which is involved in the onset and development of arteriosclerosis. Previous attempts aimed at developing proanthocyanidin derivatives with more potent antioxidative activity and stronger inhibition for LOX-1 demonstrated the synthesis of a novel proanthocyanidin derivative (1), in which the geometry of one catechin molecule in procyanidin B3 was constrained to a planar orientation. The radical scavenging activity of 1 was 1.9-fold higher than that of procyanidin B3. Herein, we synthesized another procyanidin B3 analogue (2), in which the geometries of both catechin molecules in the dimer were constrained to planar orientations. The radical scavenging activity of 2 was 1.5-fold higher than that of 1, suggesting that 2 may be a more effective candidate than 1 as a therapeutic agent to reduce oxidative stress induced in arteriosclerosis or related cerebrovascular disease.

Electronegative L5-LDL induces the production of G-CSF and GM-CSF in human macrophages through LOX-1 involving NF-κB and ERK2 activation

BACKGROUND AND AIMS

Circulating levels of granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage colony-stimulating factor (GM-CSF) are associated with the severity of acute myocardial infarction (AMI). However, what causes increases in G-CSF and GM-CSF is unclear. In this study, we investigated whether L5-low-density lipoprotein (LDL), a mildly oxidized LDL from AMI, can induce G-CSF and GM-CSF production in human macrophages.

METHODS

L1-LDL and L5-LDL were isolated through anion-exchange chromatography from AMI plasma. Human macrophages derived from THP-1 and peripheral blood mononuclear cells were treated with L1-LDL, L5-LDL, or copper-oxidized LDL (Cu-oxLDL) and G-CSF and GM-CSF protein levels in the medium were determined. In addition, the effects of L5-LDL on G-CSF and GM-CSF production were tested in lectin-type oxidized LDL receptor-1 (LOX-1), CD36, extracellular signal-regulated kinase (ERK) 1, and ERK2 knockdown THP-1 macrophages.

RESULTS

L5-LDL but not L1-LDL or Cu-oxLDL significantly induced production of G-CSF and GM-CSF in macrophages. In vitro oxidation of L1-LDL and L5-LDL altered their ability to induce G-CSF and GM-CSF, suggesting that the degree of oxidation is critical for the effects. Knockdown and antibody neutralization experiments suggested that the effects were caused by LOX-1. In addition, nuclear factor (NF)-κB and ERK1/2 inhibition resulted in marked reductions of L5-LDL-induced G-CSF and GM-CSF production. Moreover, knockdown of ERK2, but not ERK1, hindered L5-LDL-induced G-CSF and GM-CSF production.

CONCLUSIONS

The results indicate that L5-LDL, a naturally occurring mild oxidized LDL, induced G-CSF and GM-CSF production in human macrophages through LOX-1, ERK2, and NF-κB dependent pathways.

LOX-1 is involved in IL-1β production and extracellular matrix breakdown in dental peri-implantitis

PURPOSE

To explore whether lectin-type oxidized LDL receptor 1 (LOX-1), interleukin 1 beta (IL-1β), matrix metalloproteinase 2 (MMP2) and matrix metalloproteinase 9 (MMP9) are involved in the nosogenesis of human dental peri-implantitis and determine the role of LOX-1 in IL-1β, MMP2 and MMP9 production in response to Porphyromonas gingivalis.

METHODS

Peri-implant crevicular fluid (PICF) was collected from ten patients with healthy implants and ten patients with peri-implantitis. The LOX-1 protein in PICF was detected by Western-blot, and the expression of LOX-1 in superficial gingiva of peri-implantitis patients was detected by immunofluorescence staining. The IL-1β, MMP2 and MMP9 proteins in PICF were detected by enzyme-linked immunosorbent assay (ELISA). THP-1 macrophages were pretreated with neutralizing antibody (LOX-1) and inhibitors (LOX-1 and c-Jun N-terminal kinase, JNK) to evaluate the role of LOX-1 and JNK in IL-1β production, as well as the role of LOX-1 in MMP2 and MMP9 production in response to P. gingivalis by quantitative polymerase chain reaction (RT-PCR) and Western-blot.

RESULTS

LOX-1, IL-1β, MMP2 and MMP9 increased in PICF of peri-implantitis patients and in THP-1 macrophages on P. gingivalis stimulation. IL-1β, MMP2 and MMP9 production in response to P. gingivalis in THP-1 macrophages was dependent on LOX-1. JNK was responsible for LOX-1 induced IL-1β production as a result of P. gingivalis infection.

CONCLUSION

LOX-1 is involved in IL-1β production and extracellular matrix breakdown is a novel inflammatory pathway trigger and potential drug target in human dental peri-implantitis.

Novel role of the nutraceutical bioactive compound berberine in lectin-like OxLDL receptor 1-mediated endothelial dysfunction in comparison to lovastatin

BACKGROUND AND AIMS

Oxidized LDL (oxLDL) or pro-inflammatory stimuli lead to increased oxidative stress linked to endothelial dysfunction and atherosclerosis. The oxLDL receptor-1 (LOX1) is elevated within atheromas and cholesterol-lowering statins inhibit LOX1 expression. Berberine (BBR), an alkaloid extracted from plants of gender Berberis, has lipid-lowering and anti-inflammatory activity. However, its role in regulating LOX1-mediated signaling is still unknown. The aim of this study was to investigate the effect of BBR on oxLDL- and TNFα-induced endothelial dysfunction in human umbilical vein endothelial cells (HUVECs) and to compare it with that of lovastatin (LOVA).

METHODS AND RESULTS

Cytotoxicity was determined by lactate dehydrogenase assay. Antioxidant capacity was measured with chemiluminescent and fluorescent method and intracellular ROS levels through a fluorescent dye. Gene and protein expression levels were assayed by qRT-PCR and western blot, respectively. HUVECs exposure to oxLDL (30 μg/ml) or TNFα (10 ng/ml) for 24 h led to a significant increase in LOX1 expression, effect abrogated by BBR (5 μM) and LOVA (5 μM). BBR but not LOVA treatment abolished the TNFα-induced cytotoxicity and restored the activation of Akt signaling. In spite of a low direct antioxidant capacity, both compounds reduced intracellular ROS levels generated by treatment of TNFα but only BBR inhibited NOX2 expression, MAPK/Erk1/2 signaling and subsequent NF-κB target genes VCAM and ICAM expression, induced by TNFα.

CONCLUSIONS

These findings demonstrated for the first time that BBR could prevent the oxLDL and TNFα - induced LOX1 expression and oxidative stress, key events that lead to NOX, MAPK/Erk1/2 and NF-κB activation linked to endothelial dysfunction.

CHEMICAL COMPOUNDS STUDIED IN THIS ARTICLE

Berberine (PubChem CID: 2353); Lovastatin (PubChem CID: 53232).

Highly electronegative low-density lipoprotein L5 evokes microglial activation and creates a neuroinflammatory stress via Toll-like receptor 4 signaling

Atherogenic risk factors, such as hypercholesterolemia, are associated with increased risk of neurodegeneration, especially Alzheimer's dementia. Human plasma electronegative low-density lipoprotein [LDL(-)], especially L5, may serve as an important contributing factor. L5 promoting an inflammatory action in atherosclerosis has been extensively studied. However, the role of L5 in inducing neuroinflammation remains unknown. Here, we examined the impact of L5 on immune activation and cell viability in cultured BV-2 microglia. BV-2 cells treated with lipopolysaccharide or human LDLs (L1, L5, or oxLDL) were subjected to molecular/biochemical assays for measuring microglial activation, levels of inflammatory factors, and cell survival. A transwell BV-2/N2a co-culture was used to assess N2a cell viability following BV-2 cell exposure to L5. We found that L5 enables the activation of microglia and elicits an inflammatory response, as evidenced by increased oxygen/nitrogen free radicals (nitric oxide, reactive oxygen species, and peroxides), elevated tumor necrosis factor-α levels, decreased basal interleukin-10 levels, and augmented production of pro-inflammatory proteins (inducible nitric oxide synthase and cyclooxygenase-2). L5 also triggered BV-2 cell death primarily via apoptosis. These effects were markedly disrupted by the application of signaling pathway inhibitors, thus demonstrating that L5 interacts with Toll-like receptor 4 to modulate multiple pathways, including MAPKs, PI3K/Akt, and NF-κB. Decreased N2a cell viability in a transwell co-culture was mainly ascribed to L5-induced BV-2 cell activation. Together, our data suggest that L5 creates a neuroinflammatory stress via microglial Toll-like receptor 4, thereby leading to the death of BV-2 microglia and coexistent N2a cells. Atherogenic L5 possibly contributes to neuroinflammation-related neurodegeneration.

Soluble lectin-like oxidized low density lipoprotein receptor-1 in metabolic syndrome

Background

Serum levels of soluble lectin-like oxidized low-density lipoprotein receptor-1 (sLOX-1) reflect increases in LOX-1 receptor expression associated with inflammation and metabolic disorders.

Objectives

To examine sLOX-1 levels in metabolic syndrome and association of sLOX-1 with classical risk factors, and with metabolic syndrome, a clustering of metabolic disorders associated with cardiovascular risk factors.

Methods

We selected 148 serum samples from patient participants with metabolic syndrome and 206 samples from patients with non-metabolic syndrome as controls, using the modified National Cholesterol Educational Program Adult Treatment Panel III (NCEP-ATP III) criteria.

Results

Levels of sLOX-1 were increased significantly in participants with metabolic syndrome (P < 0.001). Serum sLOX-1 was positively associated with body mass index (BMI), blood pressure, fasting plasma glucose, triglyceride, and total cholesterol, but negatively associated with high-density lipoprotein cholesterol. Analysis of serum sLOX-1 for metabolic syndrome showed 99.03% specificity and 100% sensitivity. The area under the receiver operating characteristic curve was 0.998 (95%CI 0.996-1.001, P < 0.001). A univariate analysis showed sLOX-1 was significantly correlated with metabolic syndrome, but was not after adjustment for sex, age, blood pressure, and BMI. Multivariate regression analysis found that being overweight (82.3; 95%CI 10.7–631.9), hyperglycemia (1.1; 95%CI 1.1–1.2), and hypertriglyceridemia (1.1; 95%CI 1.0–1.1) were significantly correlated with metabolic syndrome. HDL cholesterol was a protective factor (0.96; 95%CI: 0.93–0.99).

Conclusions

Serum sLOX-1 is a suitable biomarker for diagnosis of metabolic syndrome. However, univariate and multivariate analysis suggested that sLOX-1 may be a modulating factor, and not an independent risk factor.

Upregulation of OLR1 and IL17A genes and their association with blood glucose and lipid levels in femoropopliteal artery disease

Oxidized low-density lipoprotein receptor 1 (OLR1) and interleukin 17A (IL17A) have pro-inflammatory roles in the development of cardiovascular disorders. The present study evaluated the association of OLR1 and IL17A and their polymorphisms with the development of femoropopliteal (FP) artery disease. The mRNA expression of OLR1 and IL17A in peripheral blood mononuclear cells as well as the frequency of OLR1 rs11053646 and IL17A rs8193037 and rs3819025 polymorphisms were assessed by polymerase chain reaction in 70 patients with FP artery disease and 80 age-matched disease-free controls. Furthermore, the levels of plasma cytokines were assessed by multiplex immunoassay. OLR1 and IL17A mRNA expression was significantly higher in patients with FP artery disease compared with that in controls (P<0.001). No significant difference was observed in the genotypic frequencies of OLR1 rs11053646 (P=0.87) or in IL17A rs8193037 and rs3819025 (P=0.80 and 0.92, respectively) polymorphisms between patients with FP artery disease and controls. Plasma IL4, -6, -10, -22, -31 and -33 as well as soluble cluster of differentiation 40 ligand and tumor necrosis factor-α levels were significantly increased among FP artery disease patients compared with controls (P<0.05). Furthermore, OLR1 expression was positively correlated with triglyceride (r=0.463, P<0.001), low-density lipoprotein cholesterol (r=0.507, P<0.001) and total cholesterol levels (r=0.357, P=0.006) in patients with FP artery disease. To the best of our knowledge, the present study was the first to identify an association between OLR1 and IL17A genes and FP artery disease. OLR1 and IL17A mRNA transcripts may be associated with blood lipid parameters and with the development of FP artery disease.

Glycated albumin induces lipid infiltration in mice aorta independently of DM and RAS local modulation by inducing lipid peroxidation and inflammation

AIMS

Advanced glycated albumin (AGE-albumin) adversely impairs macrophage lipid homeostasis in vitro, which may be prevented by angiotensin receptor blockers. In vivo studies are inconclusive whether AGE-albumin itself plays important role in early-stage atherogenesis. We aimed at investigating how AGE-albumin by itself drives atherosclerosis development in dyslipidemic non-diabetic mice and if its effects are due to the activation of renin-angiotensin system in the arterial wall and the expression of genes and proteins involved in lipid flux.

METHODS AND RESULTS

Murine albumin glycation was induced by incubation with 10mM glycolaldehyde and C-albumin with PBS alone. Twelve-week-old-male apoE knockout mice were submitted to a daily IP injection of control (C) or AGE-albumin (2mg/mL) during 30days with or without losartan (LOS: 100mg/L; C+LOS and AGE+LOS). Aortic arch was removed, and gene expression was determined by RT-PCR and protein content by immunofluorescence. Plasma lipid and glucose levels were similar among groups. Systolic blood pressure was similarly reduced in both groups treated with LOS. In comparison to C-albumin, aortic lipid infiltration was 5.3 times increased by AGE-albumin, which was avoided by LOS. LOS prevented the enhancement induced by AGE-albumin in Ager, Tnf and Cybb mRNA levels but did not reduce Olr1. Nfkb and Agt mRNA levels were unchanged by AGE-albumin. LOS similarly reduced Agtr1a mRNA level in both C and AGE-albumin groups. In AGE-albumin-treated mice, immunofluorescence for carboxymethyl-lysine, 4-hydroxynonenal and RAGE was respectively, 4.8, 2.6 and 1.7 times enhanced in comparison to C-albumin. These increases were all avoided by LOS.

CONCLUSIONS

AGE-albumin evokes a pre-stage of atherogenesis in dyslipidemic mice independently of the presence of diabetes mellitus or modulation in the RAS in part by the induction of lipid peroxidation and inflammation.

LOX-1 and TLR4 affect each other and regulate the generation of ROS in A. fumigatus keratitis

PURPOSE

To explore the relationship between LOX-1 and TLR4 in Aspergillus fumigatus (A. fumigatus) keratitis. To determine LOX-1 and TLR4 can affect each other and regulate inflammation through regulation of the generation of reactive oxygen species (ROS) in A. fumigatus keratitis.

METHODS

The cornea and abdominal cavity extracted neutrophils of susceptible C57BL/6 mice were infected with A. fumigatus. The cornea and neutrophils were pretreated with LOX-1 neutralizing antibody, Polyinosinic acid (Poly(I)) (the inhibitor of LOX-1) or CLI-095 (the inhibitor of TLR4) separately before infection. LOX-1, TLR4 and IL-1β expression were detected in normal and infected cornea by PCR and Western Blot, while ROS was detected in the neutrophils by flow cytometry.

RESULTS

LOX-1, TLR4, IL-1β mRNA and protein levels were up-regulated in C57BL/6 cornea after infection. LOX-1 neutralizing antibody or Poly(I) pretreatment decreased the expression of LOX-1, TLR4 and IL-1β in C57BL/6 cornea after infection and CLI-095 pretreatment decreased the expression of LOX-1, TLR4 and IL-1β in C57BL/6 cornea after infection. ROS generation was increased in C57BL/6 neutrophils after infection, however, ROS generation was decreased in C57BL/6 neutrophils after infection by LOX-1 neutralizing antibody or Poly(I) or CLI-095 pretreatment.

CONCLUSION

LOX-1, TLR4 and IL-1β expression and ROS generation are increased after infection. LOX-1 and TLR4 can affect each other and regulate the generation of ROS in A. fumigatus keratitis. Inhibition of LOX-1 and TLR4 can reduce ROS generation.

Efficacy and Safety of Loading-Dose Rosuvastatin Therapy in Elderly Patients with Acute Coronary Syndromes Undergoing Elective Percutaneous Coronary Intervention

OBJECTIVES

The aim of this work was to investigate the efficacy and safety of loading-dose rosuvastatin therapy in elderly patients with non-ST-segment elevation acute coronary syndromes (NSTEACS) undergoing elective percutaneous coronary intervention (PCI).

METHODS

A total of 126 patients (≥70 years old) with NSTEACS were randomly divided into two groups: (1) loading-dose rosuvastatin-treated group, treated with rosuvastatin 20 mg 12 h prior to PCI, with a second dose administered just before PCI (n = 62), and (2) control-treated group, treated with the standard method according to ACC/AHA guidelines in UAP/NSTEMI 2007 (n = 64). All patients were required to take rosuvastatin 10 mg once a day starting 24 h after the surgery irrespective of the initial randomization assignment. The serum soluble lectin-like oxidized low-density lipoprotein receptor-1 (sLox-1), high-sensitivity C-reactive protein (hs-CRP), creatinine kinase (CK)-MB, cardiac troponin I (cTnI), and brain natriuretic peptide (BNP) levels were measured prior to PCI and at 24 h and 30 days after PCI in both groups. The left ventricular ejection fraction (LVEF) levels were recorded prior to PCI and 30 days after PCI in both groups.

RESULTS

Compared to pre-PCI, the serum sLox-1, hs-CRP, CK-MB, and cTnI levels were increased at 24 h after PCI (all p < 0.05) in both groups. However, the increased sLox-1, hs-CRP, CK-MB, and cTnI values were significantly lower in the loading-dose rosuvastatin-treated group than in the control-treated group (p < 0.05). In addition the serum sLox-1 and hs-CRP levels were lower in the loading-dose rosuvastatin-treated group than in the control-treated group at 30 days after PCI. However, the decreased values of sLox-1and hs-CRP from 24 h after PCI to 30 days after PCI did not show any significant difference between the two groups. No significant difference was found in the serum ALT and Scr levels between the two groups before and after PCI. Compared to the control-treated group, the serum BNP level decreased (p < 0.05) and LVEF (p < 0.05) increased in the loading-dose rosuvastatin-treated group at 30 days after PCI.

CONCLUSION

The loading-dose rosuvastatin therapy in elderly patients with non-ST-segment elevation acute coronary syndromes undergoing elective PCI can attenuate the increase in serum hs-CRP, sLox-1, CK-MB, and cTnI levels, reduce myocardial injury and inflammatory reaction caused by PCI, and improve the LVEF level at 30 days after PCI, ensuring an effective and safe therapy.

Cryptotanshinone inhibits TNF-α-induced LOX-1 expression by suppressing reactive oxygen species (ROS) formation in endothelial cells

Cryptotanshinone (CPT) is a natural compound isolated from traditional Chinese medicine Salvia miltiorrhiza Bunge. In the present study, the regulatory effect and potential mechanisms of CPT on tumor necrosis factor alpha (TNF-α) induced lectin-like receptor for oxidized low density lipoprotein (LOX-1) were investigated. Human umbilical vein endothelial cells (HUVECs) were cultured and the effect of TNF-α on LOX-1 expression at mRNA and protein levels was determined by Real-time PCR and Western blotting respectively. The formation of intracellular ROS was determined with fluorescence probe CM-DCFH₂-DA. The endothelial ox-LDL uptake was evaluated with DiI-ox-LDL. The effect of CPT on LOX-1 expression was also evaluated with SD rats. TNF-α induced LOX-1 expression in a dose- and time-dependent manner in endothelial cells. TNF-α induced ROS formation, phosphorylation of NF-κB p65 and ERK, and LOX-1 expression, which were suppressed by rotenone, DPI, NAC, and CPT. NF-κB inhibitor BAY11-7082 and ERK inhibitor PD98059 inhibited TNF-α-induced LOX-1 expression. CPT and NAC suppressed TNF-α-induced LOX-1 expression and phosphorylation of NF-κB p65 and ERK in rat aorta. These data suggested that TNF-α induced LOX-1 expression via ROS activated NF-κB/ERK pathway, which could be inhibited by CPT. This study provides new insights for the anti-atherosclerotic effect of CPT.

Deletion of LOX-1 Protects against Heart Failure Induced by Doxorubicin

Oxidative stress is one of the major factors in doxorubicin (DOX)-induced cardiomyopathy. Lectin-like oxidized low-density lipoprotein (oxLDL) receptor-1 (LOX-1) plays an important role to regulate cardiac remodeling and oxidative stress after ischemia-reperfusion. Therefore, we examined whether or not LOX-1 contributes to the pathogenesis of DOX-induced cardiomyopathy. Cardiomyopathy was induced by a single intraperitoneal injection of DOX into wild-type (WT) mice and LOX-1 knockout (KO) mice. Echocardiography and catheter-based hemodynamic assessment apparently revealed preserved left ventricular (LV) fractional shortening (FS) and cavity size of LOX-1 KO mice compared with those of WT mice after DOX administration. Less production of tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1ß) was observed in LOX-1 KO mice than WT mice after DOX administration. Western blotting analysis also showed lower activation of nuclear factor κB (NF-κB) and p38 mitogen-activated protein kinase (MAPK) in LOX-1 KO mice treated with DOX than WT mice treated with DOX. In fact, NF-κB-dependent gene expressions of LOX-1 and vascular cell adhesion molecule-1 (VCAM-1) were suppressed in LOX-1 KO mice treated with DOX compared with WT mice treated with DOX. Therefore, histological analyses showed attenuation of leukocyte infiltration and cardiac fibrosis in LOX-1 KO mice compared with WT mice. Meanwhile, extracellular signal-regulated kinase MAPK (ERK) inactivation and decreased expression of sarcomeric proteins and related transcription factor GATA-4 in WT mice treated with DOX administration were not seen in LOX-1 KO mice treated with DOX administration and WT and LOX-1 KO mice treated with vehicle. Decreased expression of sarcometric proteins resulted in smaller diameters of cardiomyocytes in WT mice than in LOX-1 KO mice after DOX treatment. The expression of LOX-1 in cardiomyocytes was much more abundant than that in endothelial cells, fibroblasts and inflammatory cells. Endothelial cells, fibroblasts and inflammatory cells treated with DOX showed no elevated LOX-1 expression compared with those treated with vehicle. However, cardiomyocytes treated with DOX showed much more expression of LOX-1 than those treated with vehicle. Immunohistochemistry study also showed that LOX-1 expression was strongly elevated in cardiomyocytes in the heart tissue of mice treated with DOX in vivo. We conclude that LOX-1 in cardiomyocytes plays the most important roles in the pathology of DOX-induced cardiomyopathy. LOX-1 deletion altered the LOX-1-related signaling pathway, which led to improvements in cardiac function, myocardial inflammation, fibrosis and degenerative changes after DOX treatment.

Interplay between CRP, Atherogenic LDL, and LOX-1 and Its Potential Role in the Pathogenesis of Atherosclerosis

BACKGROUND

Studies have shown that the classic acute-phase protein C-reactive protein (CRP) has proinflammatory effects on vascular cells and may play a causal role in the pathogenesis of coronary artery disease. A growing body of evidence has suggested that interplay between CRP, lectin-like oxidized LDL receptor-1 (LOX-1), and atherogenic LDL may underlie the mechanism of endothelial dysfunction that leads to atherosclerosis.

CONTENT

We review the biochemical evidence for an association of CRP, LOX-1, and either oxidized LDL (OxLDL) or electronegative L5 LDL with the pathogenesis of coronary artery disease. Artificially oxidized OxLDL has been studied extensively for its role in atherogenesis, as has electronegative L5 LDL, which is present at increased levels in patients with increased cardiovascular risks. OxLDL and L5 have been shown to stimulate human aortic endothelial cells to produce CRP, indicating that CRP is synthesized locally in the endothelium. The ligand-binding face (B-face) of CRP has been shown to bind the LOX-1 scavenger receptor and increase LOX-1 expression in endothelial cells, thereby promoting the uptake of OxLDL or L5 by LOX-1 into endothelial cells to induce endothelial dysfunction.

SUMMARY

CRP and LOX-1 may form a positive feedback loop with OxLDL or L5 in atherogenesis, whereby increased levels of atherogenic LDL in patients with cardiovascular risks induce endothelial cells to express CRP, which may in turn increase the expression of LOX-1 to promote the uptake of atherogenic LDL into endothelial cells. Further research is needed to confirm a causal role for CRP in atherogenesis.

Macrophage-mediated cholesterol handling in atherosclerosis

Formation of foam cells is a hallmark at the initial stages of atherosclerosis. Monocytes attracted by pro-inflammatory stimuli attach to the inflamed vascular endothelium and penetrate to the arterial intima where they differentiate to macrophages. Intimal macrophages phagocytize oxidized low-density lipoproteins (oxLDL). Several scavenger receptors (SR), including CD36, SR-A1 and lectin-like oxLDL receptor-1 (LOX-1), mediate oxLDL uptake. In late endosomes/lysosomes of macrophages, oxLDL are catabolysed. Lysosomal acid lipase (LAL) hydrolyses cholesterol esters that are enriched in LDL to free cholesterol and free fatty acids. In the endoplasmic reticulum (ER), acyl coenzyme A: cholesterol acyltransferase-1 (ACAT1) in turn catalyses esterification of cholesterol to store cholesterol esters as lipid droplets in the ER of macrophages. Neutral cholesteryl ester hydrolases nCEH and NCEH1 are involved in a secondary hydrolysis of cholesterol esters to liberate free cholesterol that could be then out-flowed from macrophages by cholesterol ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 and SR-BI. In atherosclerosis, disruption of lipid homoeostasis in macrophages leads to cholesterol accumulation and formation of foam cells.

Oxidized low-density lipoprotein is a common risk factor for cardiovascular diseases and gastroenterological cancers via epigenomical regulation of microRNA-210

Hyperlipidemia, including the oxidized low-density lipoprotein (oxLDL) accumulation, is a risk and highly associated with the development of cancers and cardiovascular diseases. microRNA-210 (miR-210), a hypoxia-responsive microRNA regulated by HIF-1α, has been implicated in cancer and cardiovascular disease formation. Furthermore, Bioinformatics analysis revealed that the promoter of the miR-210 gene contains CpG-rich regions. It is unclear whether miR-210 expression could be epigenetically regulated in these disease progresses. The study aimed to explore the relationships between lipid and miR-210 in the context of cardiovascular disease and gastrointestinal cancer. We demonstrated oxLDL can decrease methylation in the miR-210 promoter to up-regulate miR-210. HIF-1α can bind to miR-210 promoter, but this HIF-1α binding site can be blocked by methylation. We showed that subjects of carotid atherosclerosis, stroke patients and cancer patients had hypomethylation in the miR-210 promoter, especially the HIF-1α binding site. Furthermore, miR-210 can directly inhibit sprouty-related EVH1 domain 2 (SPRED2) expressions, and SPRED2 reduces cell migration via ERK/c-Fos/MMPs pathways. Increased miR-210 and reduced SPRED2 levels were found in aorta of mice under high-fat diet and tumor tissues, which implied that miR-210 can be an underlying mechanism to explain oxLDL as a common risk factor for cardiovascular disease and gastrointestinal cancer.

Role of 4-hydroxynonenal-protein adducts in human diseases

SIGNIFICANCE

Oxidative stress provokes the peroxidation of polyunsaturated fatty acids in cellular membranes, leading to the formation of aldheydes that, due to their high chemical reactivity, are considered to act as second messengers of oxidative stress. Among the aldehydes formed during lipid peroxidation (LPO), 4-hydroxy-2-nonenal (HNE) is produced at a high level and easily reacts with both low-molecular-weight compounds and macromolecules, such as proteins and DNA. In particular, HNE-protein adducts have been extensively investigated in diseases characterized by the pathogenic contribution of oxidative stress, such as cancer, neurodegenerative, chronic inflammatory, and autoimmune diseases.

RECENT ADVANCES

In this review, we describe and discuss recent insights regarding the role played by covalent adducts of HNE with proteins in the development and evolution of those among the earlier mentioned disease conditions in which the functional consequences of their formation have been characterized.

CRITICAL ISSUES

Results obtained in recent years have shown that the generation of HNE-protein adducts can play important pathogenic roles in several diseases. However, in some cases, the generation of HNE-protein adducts can represent a contrast to the progression of disease or can promote adaptive cell responses, demonstrating that HNE is not only a toxic product of LPO but also a regulatory molecule that is involved in several biochemical pathways.

FUTURE DIRECTIONS

In the next few years, the refinement of proteomical techniques, allowing the individuation of novel cellular targets of HNE, will lead to a better understanding the role of HNE in human diseases.

Scavenger Receptors: Emerging Roles in Cancer Biology and Immunology

Scavenger receptors constitute a large family of evolutionally conserved protein molecules that are structurally and functionally diverse. Although scavenger receptors were originally identified based on their capacity to scavenge modified lipoproteins, these molecules have been shown to recognize and bind to a broad spectrum of ligands, including modified and unmodified host-derived molecules or microbial components. As a major subset of innate pattern recognition receptors, scavenger receptors are mainly expressed on myeloid cells and function in a wide range of biological processes, such as endocytosis, adhesion, lipid transport, antigen presentation, and pathogen clearance. In addition to playing a crucial role in maintenance of host homeostasis, scavenger receptors have been implicated in the pathogenesis of a number of diseases, e.g., atherosclerosis, neurodegeneration, or metabolic disorders. Emerging evidence has begun to reveal these receptor molecules as important regulators of tumor behavior and host immune responses to cancer. This review summarizes our current understanding on the newly identified, distinct functions of scavenger receptors in cancer biology and immunology. The potential of scavenger receptors as diagnostic biomarkers and novel targets for therapeutic interventions to treat malignancies is also highlighted.

Generation of Adducts of 4-Hydroxy-2-nonenal with Heat Shock 60 kDa Protein 1 in Human Promyelocytic HL-60 and Monocytic THP-1 Cell Lines

Heat shock 60 kDa protein 1 (HSP60) is a chaperone and stress response protein responsible for protein folding and delivery of endogenous peptides to antigen-presenting cells and also a target of autoimmunity implicated in the pathogenesis of atherosclerosis. By two-dimensional electrophoresis and mass spectrometry, we found that exposure of human promyelocytic HL-60 cells to a nontoxic concentration (10 μM) of 4-hydroxy-2-nonenal (HNE) yielded a HSP60 modified with HNE. We also detected adducts of HNE with putative uncharacterized protein CXorf49, the product of an open reading frame identified in various cell and tissue proteomes. Moreover, exposure of human monocytic THP-1 cells differentiated with phorbol 12-myristate 13-acetate to 10 μM HNE, and to light density lipoprotein modified with HNE (HNE-LDL) or by copper-catalyzed oxidation (oxLDL), but not to native LDL, stimulated the formation of HNE adducts with HSP60, as detected by immunoprecipitation and western blot, well over basal levels. The identification of HNE-HSP60 adducts outlines a framework of mutually reinforcing interactions between endothelial cell stressors, like oxLDL and HSP60, whose possible outcomes, such as the amplification of endothelial dysfunction, the spreading of lipoxidative damage to other proteins, such as CXorf49, the activation of antigen-presenting cells, and the breaking of tolerance to HSP60 are discussed.

Oxidized LDL (oxLDL) activates the angiotensin II type 1 receptor by binding to the lectin-like oxLDL receptor

The angiotensin II type 1 receptor (AT1) is a 7-transmembrane domain GPCR that when activated by its ligand angiotensin II, generates signaling events promoting vascular dysfunction and the development of cardiovascular disease. Here, we show that the single-transmembrane oxidized LDL (oxLDL) receptor (LOX-1) resides in proximity to AT1 on cell-surface membranes and that binding of oxLDL to LOX-1 can allosterically activate AT1-dependent signaling events. oxLDL-induced signaling events in human vascular endothelial cells were abolished by knockdown of AT1 and inhibited by AT1 blockade (ARB). oxLDL increased cytosolic G protein by 350% in Chinese hamster ovary (CHO) cells with genetically induced expression of AT1 and LOX-1, whereas little increase was observed in CHO cells expressing only LOX-1. Immunoprecipitation and in situ proximity ligation assay (PLA) assays in CHO cells revealed the presence of cell-surface complexes involving LOX-1 and AT1. Chimeric analysis showed that oxLDL-induced AT1 signaling events are mediated via interactions between the intracellular domain of LOX-1 and AT1 that activate AT1. oxLDL-induced impairment of endothelium-dependent vascular relaxation of vascular ring from mouse thoracic aorta was abolished by ARB or genetic deletion of AT1. These findings reveal a novel pathway for AT1 activation and suggest a new mechanism whereby oxLDL may be promoting risk for cardiovascular disease.

LOX-1 plays an important role in ischemia-induced angiogenesis of limbs

LOX-1, lectin-like oxidized low-density lipoprotein (LDL) receptor-1, is a single transmembrane receptor mainly expressed on endothelial cells. LOX-1 mediates the uptake of oxidized LDL, an early step in atherosclerosis; however, little is known about whether LOX-1 is involved in angiogenesis during tissue ischemia. Therefore, we examined the role of LOX-1 in ischemia-induced angiogenesis in the hindlimbs of LOX-1 knockout (KO) mice. Angiogenesis was evaluated in a surgically induced hindlimb ischemia model using laser Doppler blood flowmetry (LDBF) and histological capillary density (CD) and arteriole density (AD). After right hindlimb ischemia, the ischemic/nonischemic hindlimb blood flow ratio was persistently lower in LOX-1 KO mice than in wild-type (WT) mice. CD and AD were significantly smaller in LOX-1 KO mice than in WT mice on postoperative day 14. Immunohistochemical analysis revealed that the number of macrophages infiltrating ischemic tissues was significantly smaller in LOX-1 KO mice than in WT mice. The number of infiltrated macrophages expressing VEGF was also significantly smaller in LOX-1 KO mice than in WT mice. Western blot analysis and ROS production assay revealed that LOX- KO mice show significant decrease in Nox2 expression, ROS production and HIF-1α expression, the phosphorylation of p38 MAPK and NF-κB p65 subunit as well as expression of redox-sensitive vascular cell adhesion molecule-1 (VCAM-1) and LOX-1 itself in ischemic muscles, which is supposed to be required for macrophage infiltration expressing angiogenic factor VEGF. Reduction of VEGF expression successively suppressed the phosphorylation of Akt and eNOS, which accelerated angiogenesis, in the ischemic leg of LOX-1 KO mice. Our findings indicate that LOX-1 plays an important role in ischemia-induced angiogenesis by 1) Nox2-ROS-NF-κB activation, 2) upregulated expression of adhesion molecules: VCAM-1 and LOX-1 and 3) promoting macrophage infiltration, which expresses angiogenic factor VEGF.

Functional expression of the Fc-fused extracellular domains of group II membrane proteins

The complicated delivery mechanism of group II membrane proteins makes it difficult to decide the fusion pattern of their extracellular domains (ECDs) with Fc moiety. In this study, we compared the expression of ECDs of three group II membrane proteins including CLEC-2, Dectin-1, and LOX-1 by fusion of Fc moiety. We found that the pattern of ECD-Fc fusion order produced the functionally active recombinant proteins while the pattern of Fc-ECD fusion order led to the altered glycosylation which abolished the binding of these proteins with their ligands. Meanwhile, our results indicated that the secretion of mouse Fc (mFc)-fused ECD of CLEC-2 was more efficient than that of rabbit Fc (rFc)-fused protein, while rFc moiety was more sensitive for detection compared with mFc moiety. Altogether, we provide a favorable fusion pattern of Fc moiety with the ECDs of group II transmembrane proteins.