Role of myeloperoxidase in inflammation and atherosclerosis (Review).

Myeloperoxidase (MPO) belongs to the heme peroxidase family, which includes a set of enzymes with potent oxidoreductase activity. MPO is considered an important part of the innate immune system's microbicidal arm and is secreted by neutrophils and macrophages. Interestingly, this enzyme has been implicated in the pathogenesis of several diseases including atherosclerosis. MPO is ubiquitous in atherosclerotic lesions and contributes to the initiation and progression of the disease primarily by oxidizing low-density lipoprotein (LDL) particles. MPO is the only human enzyme with the ability to produce hypochlorous acid (HOCl) at physiological chloride concentrations and HOCl-LDL epitopes were shown to be present inside atheromatous lesions making it a physiologically relevant model for the oxidation of LDL. It has been shown that MPO modified LDL is not able to bind to the native LDL receptor and is recognized instead by scavenger receptors on both endothelial cells and macrophages, which can lead to endothelial dysfunction and foam cell formation, respectively; both of which are instrumental in the progression of the disease. Meanwhile, several studies have proposed MPO as a biomarker for cardiovascular diseases where high levels of this enzyme were linked to an increased risk of developing coronary artery disease. Overall, there is sufficient evidence supporting the value of MPO as a crucial player in health and disease. Thus, future research should be directed towards investigating the still unknown processes associated with this enzyme. This may assist in better understanding the pathophysiological role of MPO, as well in the development of therapeutic strategies for protecting against the deleterious effects of MPO in numerous pathologies such as atherosclerosis.

The effect of myeloperoxidase-oxidized LDL on THP-1 macrophage polarization and repolarization.

Macrophages (Mφs) play a crucial role in the development of atherosclerosis by engulfing modified LDL particles and forming foam cells, the hallmark of atherosclerosis. Many studies suggest that myeloperoxidase-oxidized LDL (Mox-LDL) is an important pathophysiological model for LDL modification in vivo. Classically (M1) and alternatively activated (M2) Mφs are both implicated in the process of atherogenesis. Mφs are highly plastic cells whereby they undergo repolarization from M1 to M2 and vice versa. Since little is known about the effects of Mox-LDL on Mφ polarization and repolarization, our study aimed at evaluating the in vitro effects of Mox-LDL at this level through making use of the well-established model of human THP-1-derived Mφs. Resting M0-Mφs were polarized toward M1- and M2-Mφs, then M0-, M1- and M2-Mφs were all treated with physiological concentrations of Mox-LDL to assess the effect of Mox-LDL treatment on Mφ polarization and repolarization. Treatment of M0-Mφs with a physiological concentration of Mox-LDL had no significant effects at the level of their polarization. However, treatment of M1-Mφs with Mox-LDL resulted in a significant reduction in their IL-10 cytokine secretion. Our results point to a potential role of Mox-LDL in increasing the pro-inflammatory state in Mφs through reducing the release of the anti-inflammatory cytokine, IL-10.

Myeloperoxidase-Oxidized LDL Activates Human Aortic Endothelial Cells through the LOX-1 Scavenger Receptor.

Cardiovascular disease as a result of atherosclerosis is a leading cause of death worldwide. Atherosclerosis is primarily caused by the dysfunction of vascular endothelial cells and the subendothelial accumulation of oxidized forms of low-density lipoprotein (LDL). Early observations have linked oxidized LDL effects in atherogenesis to the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) scavenger receptor. It was shown that LOX-1 is upregulated by many inflammatory mediators and proatherogenic stimuli including cytokines, reactive oxygen species (ROS), hemodynamic blood flow, high blood sugar levels and, most importantly, modified forms of LDL. Oxidized LDL signaling pathways in atherosclerosis were first explored using LDL that is oxidized by copper (Cuox-LDL). In our study, we used a more physiologically relevant model of LDL oxidation and showed, for the first time, that myeloperoxidase oxidized LDL (Mox-LDL) may affect human aortic endothelial cell (HAEC) function through the LOX-1 scavenger receptor. We report that Mox-LDL increases the expression of its own LOX-1 receptor in HAECs, enhancing inflammation and simultaneously decreasing tubulogenesis in the cells. We hypothesize that Mox-LDL drives endothelial dysfunction (ED) through LOX-1 which provides an initial hint to the pathways that are initiated by Mox-LDL during ED and the progression of atherosclerosis.

Endothelial dysfunction and COVID-19 (Review).

It is hypothesized that several comorbidities increase the severity of COVID-19 symptoms. Cardiovascular disease including hypertension was shown to play a critical role in the severity of COVID-19 infection by affecting the survival of patients with COVID-19. Hypertension and the renin-angiotensin-aldosterone system are involved in increasing vascular inflammation and endothelial dysfunction (ED), and both processes are instrumental in COVID-19. Angiotensin-converting enzyme 2 is an essential component of the renin-angiotensin-aldosterone system and the target receptor that mediates SARS-CoV-2 entry to the cell. This led to speculations that major renin-angiotensin-aldosterone system inhibitors, such as angiotensin receptor blockers and angiotensin-converting enzyme inhibitors might affect the course of the disease, since their administration enhances angiotensin-converting enzyme (ACE)2 expression. An increase in ACE2 activity could reduce angiotensin II concentration in the lungs and mitigate virus-driven lung injury. This could also be associated with a reduction in blood coagulation, which plays a critical role in the pathogenesis of SARS-CoV-2; of note, COVID-19 is now regarded as a disorder of blood clotting. Therefore, there is an urgent need to better understand the effect of targeting ACE2 as a potential treatment for SARS-CoV-2 driven injury, and in alleviating COVID-19 symptoms by reversing SARS-CoV-2-induced excessive coagulation and fatalities. Ongoing therapeutic strategies that include recombinant human ACE2 and anti-spike monoclonal antibodies are essential for future clinical practice in order to better understand the effect of targeting ED in COVID-19.

Human apolipoprotein L1 interferes with mitochondrial function in Saccharomyces cerevisiae.

To the best of our knowledge, the vertebrate apolipoprotein L (APOL) family has not previously been ascribed to any definite pathophysiological function, although the conserved BH3 protein domain suggests a role in programmed cell death or an interference with mitochondrial processes. In the present study, the human APOL1 was expressed in the yeast Saccharomyces cerevisiae in order to determine the molecular action of APOL1. APOL1 inhibited cell proliferation in a non­fermentable carbon source, such as glycerol, while it had no effect on proliferation in fermentable carbon sources, such as galactose. APOL1, expressed in yeast, is localized in the mitochondrial fraction, as determined via western blotting. APOL1 induced a loss of mitochondrial function, demonstrated by a loss of respiratory index, and mitochondrial membrane potential. Green fluorescent protein tagging of mitochondrial protein revealed that APOL1 was associated with abnormal mitochondrial and lysosomal morphologies, observed by a loss of the normal mitochondrial tubular network. Thus, the results of the present study suggest that APOL1 could be a physiological regulator of mitochondrial function.

Effect of myeloperoxidase modified LDL on bovine and human aortic endothelial cells.

Cardiovascular disease associated with atherosclerosis is a leading cause of death worldwide. Atherosclerosis is primarily caused by the dysfunction of vascular endothelial cells and the subendothelial accumulation of oxidized forms of low-density lipoproteins (LDL). Early observations have associated fibrin deposition with atheroma plaque formation, which has led to the proposition that a decrease in endothelial cell fibrinolysis may negatively influence atherogenesis. It has been recently demonstrated that myeloperoxidase modified LDL (MoxLDL) decreases endothelial cell profibrinolytic capacity in real-time. The present study investigated the role of MoxLDL in endothelial cell dysfunction by determining the molecules that may be involved in decreasing the fibrinolysis of human aortic endothelial cells (HAEC). Accordingly, reverse transcription-quantitative PCR was performed to screen for the differential expression of major genes that are implicated in the fibrinolytic process. In addition, the response of the latter cell type to MoxLDL was compared with bovine aortic endothelial (BAE) cells. Furthermore, the effect of the treatment on the generation of reactive oxygen species (ROS) was also determined. Although the current study did not demonstrate an association between MoxLDL treatment and a change in the expression of any major fibrinolytic factor in HAEC, a discrepancy between HAEC and BAE cells with respect to their response to modified LDL treatment was observed. The result have also demonstrated that MoxLDL does not increase ROS generation in HAEC as opposed to the other major type of modified LDL, cupper oxidized LDL (CuoxLDL) that was reported to exhibit a positive effect at this level. The present study provided important insight into the different effects of MoxLDL and CuoxLDL in endothelial cells, which may aid future studies to determine the various signaling pathways that are promoted by these molecules. The results of the present study may be utilized to identify potential molecular drug targets for the treatment of atherosclerosis.

ApolipoproteinL1 is expressed in papillary thyroid carcinomas.

The apolipoprotein L (apoL) family has not yet been ascribed any definite patho-physiological function although the conserved BH3 protein domain suggests a role in programmed cell death. As repression of the regular apoptotic program is considered a hallmark of tumor progression, we investigated apoL expression in cancer. We show that the levels of one member of the family, apolipoprotein L1 (apoL1) is higher in papillary thyroid carcinoma compared to normal tissue. A combination of qRTPCR, immunohistochemistry and in situ hybridization allowed us to ascribe this increase to endogenous overexpression in carcinoma cells. Whether apoL1 plays an instrumental role in refraining cell death is the subject of ongoing molecular biology experiments.

Myeloperoxidase oxidized LDL interferes with endothelial cell motility through miR-22 and heme oxygenase 1 induction: possible involvement in reendothelialization of vascular injuries.

Cardiovascular disease linked to atherosclerosis is the leading cause of death worldwide. Atherosclerosis is mainly linked to dysfunction in vascular endothelial cells and subendothelial accumulation of oxidized forms of LDL. In the present study, we investigated the role of myeloperoxidase oxidized LDL (Mox-LDL) in endothelial cell dysfunction. We studied the effect of proinflammatory Mox-LDL treatment on endothelial cell motility, a parameter essential for normal vascular processes such as angiogenesis and blood vessel repair. This is particularly important in the context of an atheroma plaque, where vascular wall integrity is affected and interference with its repair could contribute to progression of the disease. We investigated in vitro the effect of Mox-LDL on endothelial cells angiogenic properties and we also studied the signalling pathways that could be affected by analysing Mox-LDL effect on the expression of angiogenesis-related genes. We report that Mox-LDL inhibits endothelial cell motility and tubulogenesis through an increase in miR-22 and heme oxygenase 1 expression. Our in vitro data indicate that Mox-LDL interferes with parameters associated with angiogenesis. They suggest that high LDL levels in patients would impair their endothelial cell capacity to cope with a damaged endothelium contributing negatively to the progression of the atheroma plaque.

Membranes over the lateral window in sinus augmentation procedures: a two-arm and split-mouth randomized clinical trials.

OBJECTIVE: This study evaluates whether or not, among other factors, membrane-coverage of antrostomy defects improves implant survival in sinus augmentation procedures. MATERIALS AND METHODS: We performed a two-arm and split-mouth randomized controlled clinical trial on 104 and 5 patients respectively. In the two-arm study, antrostomy defects were membrane-covered in 66 procedures and uncovered in 69, before placing a total of 265 implants that were followed up for 1 year. In the split-mouth study, following bilateral sinus augmentation, antrostomy defects were membrane-covered on one side and left uncovered on the contra-lateral. Bone biopsies from each sinus were histologically analysed 6 months later. RESULTS: In the two-arm study, implant survival rates were similar (p = 0.08) in the membrane-covered (96.1%) and uncovered (94.2%) groups. In the split-mouth study, bone augmentation was similar in both groups (p = 0.52). Delayed implant placement (p = 0.04), thick Schneider's membrane (≥2 mm) (p < 0.01), treatment for hypertension (p = 0.04) and non-smoking (p = 0.01) seemed to be associated with lower risk of implant failure. CONCLUSIONS: Implant survival in sinus lifting procedures could be influenced significantly by timing of implant placement, Schneider's membrane thickness, antihypertensive treatment and smoking habits, but not by antrostomy membrane coverage.

Exposure of endothelial cells to physiological levels of myeloperoxidase-modified LDL delays pericellular fibrinolysis.

BACKGROUND: Blood fluidity is maintained by a delicate balance between coagulation and fibrinolysis. The endothelial cell surface is a key player in this equilibrium and cell surface disruptions can upset the balance. We investigated the role of pericellular myeloperoxidase oxidized LDLs (Mox-LDLs) in this balance. METHODS AND RESULTS: We designed a technical device that enabled us to monitor fibrinolysis in real-time at the surface of an endothelial cell line (EA.hy926), and showed that Mox-LDL decreased pericellular fibrinolysis. There were no changes in fibrinolysis when EA.hy926 endothelial cells were exposed to native LDL (24 hours) at doses of 10, 50, 100 and up to 1250 µg/ml. However, treatment of EA.hy926 endothelial cells with 10 and 50 µg/ml of Mox-LDL (physiological serum concentrations) increased the lysis time by 15 and 13%, respectively (p<0.001), although this effect was not present at higher concentrations of 100 µg/ml. This effect was not correlated with any changes in PAI-1 or t-PA or PA Receptor (PAR) expression. No effect was observed at the surface of smooth muscle cells used as controls. CONCLUSION: Our data link the current favorite hypothesis that modified LDL has a causal role in atheroma plaque formation with an old suggestion that fibrin may also play a causal role. Our data help complete the paradigm of atherosclerosis: Modified LDL locally enhances fibrin deposition (present work); fibrin deposits enhance endothelial permeability; this effect allows subendothelial accumulation of lipid and foam cells.

The Candida albicans Dse1 Protein Is Essential and Plays a Role in Cell Wall Rigidity, Biofilm Formation, and Virulence.

The fungal pathogen Candida albicans is one of the leading causative agents of death in immunocompromised individuals. It harbors an arsenal of cell wall anchored factors that are implicated in virulence such as filamentation inducing factors, adhesins, lipases, proteases, and superoxide dismutases. Dse1 is a cell wall protein involved in cell wall metabolism. The purpose of this study is to characterize the role Dse1 plays in virulence. Dse1 appears to be an essential gene as no homozygous null mutant was possible. The heterozygote mutant exhibited increased susceptibility to calcofluor white, a cell wall disrupting agent, with a subsequent reduction in cell wall chitin content, decreased oxidative stress tolerance, a 30% reduction in biofilm formation, and a delay in adhesion that was mirrored by a reduction in virulence in a mouse model of infection. Dse1 thus appears to be an important protein involved in cell wall integrity and rigidity.