Extracellular vesicles and endothelial dysfunction in infectious diseases

Cardiovascular diseases (CVDs) remain the leading cause of mortality and morbidity globally. Studies have shown that infections especially bacteraemia and sepsis are associated with increased risks for endothelial dysfunction and related CVDs including atherosclerosis. Extracellular vesicles (EVs) are small, sealed membrane-derived structures that are released into body fluids and blood from cells and/or microbes and are critically involved in a variety of important cell functions and disease development, including intercellular communications, immune responses and inflammation. It is known that EVs-mediated mechanism(s) is important in the development of endothelial dysfunction in infections with a diverse spectrum of microorganisms including Escherichia coli, Candida albicans, SARS-CoV-2 (the virus for COVID-19) and Helicobacter pylori. H. pylori infection is one of the most common infections globally. During H. pylori infection, EVs can carry H. pylori components, such as lipopolysaccharide, cytotoxin-associated gene A, or vacuolating cytotoxin A, and transfer these substances into endothelial cells, triggering inflammatory responses and endothelial dysfunction. This review is to illustrate the important role of EVs in the pathogenesis of infectious diseases, and the development of endothelial dysfunction in infectious diseases especially H. pylori infection, and to discuss the potential mechanisms and clinical implications.

The Role of Omega-3 Fatty Acids in the Setting of Coronary Artery Disease and COPD: A Review

Chronic obstructive pulmonary disease (COPD) is a growing healthcare concern and will represent the third leading cause of death worldwide within the next decade. COPD is the result of a complex interaction between environmental factors, especially cigarette smoking, air pollution, and genetic preconditions, which result in persistent inflammation of the airways. There is growing evidence that the chronic inflammatory state, measurable by increased levels of circulating cytokines, chemokines, and acute phase proteins, may not be confined to the lungs. Cardiovascular disease (CVD) and especially coronary artery disease (CAD) are common comorbidities of COPD, and low-grade systemic inflammation plays a decisive role in its pathogenesis. Omega-3 polyunsaturated fatty acids (n-3 PUFAs) exert multiple functions in humans and are crucially involved in limiting and resolving inflammatory processes. n-3 PUFAs have been intensively studied for their ability to improve morbidity and mortality in patients with CVD and CAD. This review aims to summarize the current knowledge on the effects of n-3 PUFA on inflammation and its impact on CAD in COPD from a clinical perspective.

Induction of cardiovascular pathology in a novel model of low-grade chronic inflammation

OBJECTIVE

Epidemiological and clinical evidence indicate that inflammatory processes play a pivotal role in a number of conditions associated with aging, including osteoporosis and cardiovascular diseases. The purpose of this study was to evaluate cardiovascular pathology and select inflammatory mediators of interest in a model of low-grade inflammation-induced osteopenia.

METHODS

Slow-release pellets were subcutaneously implanted in male rats to deliver 0, 3.3, or 33.3 microg of lipopolysaccharide (LPS)/day for 90 days. Tail blood was collected at 1, 2, and 3 months for differential white cell counts, and at the end of the study, hearts were harvested for histological and immunohistochemical evaluation.

RESULTS

The low-grade inflammatory response was characterized by elevated peripheral blood neutrophils and monocytes. Histological examination of heart cross sections revealed increased fibrous tissue, infiltration of lymphocytes, accumulation of mast cells, and roughened intimal borders within the arteries and arterioles, consistent with vascular disease. Inflammatory mediators (cyclooxygenase-2, tumor necrosis factor-alpha, and interleukin-1 beta) were up-regulated, and increased expression of platelet endothelial cell adhesion molecule-1 and receptor activator for NF-kappaB ligand was localized to the microvasculature endothelium.

CONCLUSIONS

These findings suggest that inflammation induced by chronic exposure to LPS produces cardiovascular pathology in the smaller intramural arteries and arterioles and support the utility of this model for further mechanistic and therapeutic studies focused on the role of chronic inflammation in cardiovascular disease.

Systemic bone loss and induction of coronary vessel disease in a rat model of chronic inflammation

Clinically, osteopenia or low bone mass has been observed in a variety of chronic inflammatory diseases, and elevated proinflammatory mediators have implicated this process. The purpose of this study was to develop an in vivo model of bone loss induced by chronic systemic inflammation. Time-release pellets designed to deliver one of three doses of LPS: Low (3.3 microg/day), High (33.3 microg/day), or Placebo over 90 days, were implanted subcutaneously in 3-month-old male Sprague-Dawley rats (n = 8/group). Neutrophil counts, indicative of ongoing inflammation, were elevated (P < 0.05) in both LPS groups at 30 days post-implant and remained significantly elevated in the High dose throughout the 90-day study period. At the end of the study, bone loss occurred in the femur as indicated by decreased bone mineral density (BMD) in both LPS-treated groups, but vertebral BMD was reduced in the High dose animals only. Microcomputed tomography revealed that trabecular bone volume (BV/TV) of the proximal tibial metaphysis tended to be reduced in the High dose LPS group. Deleterious effects on trabecular number (TbN) and trabecular separation (TbSp) were observed in both LPS-treated groups, but only the High dose group reached statistical significance. These alterations in trabecular microarchitecture resulted in compromised biomechanical properties. No changes in cortical thickness, porosity, or area of the tibia midshaft were evident at either dose of LPS. Up-regulation of the proinflammatory mediators, cyclooxygenase (COX)-2, interleukin (IL)-1, and tumor necrosis factor (TNF)-alpha was demonstrated in the metaphyseal region where the deleterious effects of LPS were observed. In addition to these alterations in bone, trichrome staining indicated changes in the coronary arterioles, consistent with vascular disease. Utilization of a LPS time-release pellet appears to provide an in vivo model of chronic inflammation-induced bone loss and a potentially novel system to study concurrent development of osteopenia and vascular disease.

Homocysteine at pathophysiologic concentrations activates human monocyte and induces cytokine expression and inhibits macrophage migration inhibitory factor expression

OBJECTIVE

Homocystinemia is an important independent risk factor for atherosclerosis. Inflammatory cytokines play key roles in the development of atherogenesis. This study investigated the effect of homocysteine on inflammatory cytokine expression.

METHODS

Human monocytes were treated in vitro with a variety of DL-homocysteine concentrations that ranged from physiologic concentration to higher than pathophysiologic concentration, and we analyzed their expressions of inflammatory cytokines, including tumor necrosis factor-alpha, interleukin-1beta, interleukin-6, interleukin-8, interleukin-12, and migration inhibitory factor.

RESULTS

DL-homocysteine at a marginal physiologic concentration of 2 microg/mL (15 microM) activated monocytes. In addition, DL-homocysteine at the pathophysiologic dose of 25 microg/mL (185 microM) induced mRNA and protein expressions of inflammatory cytokines tumor necrosis factor-alpha, IL-1beta, interleukin-6, interleukin-8, and interleukin-12. Moreover, at the larger dose of 50 microg/mL (370 microM) DL-homocysteine decreased expression of migration inhibitory factor at the mRNA and protein levels.

CONCLUSION

These findings suggest that homocysteine may contribute to the initiation and progression of vascular disease by activating monocytes, resulting in the secretion of cytokines that amplify the inflammatory response.

High density lipoprotein can modulate the inhibitory effect of oxLDL on prostacyclin generation by rat aorta in vitro

To examine the effect of oxidized low density lipoprotein (oxLDL) on prostacyclin (PGI2) generation by rat aorta in vitro and whether high density lipoprotein (HDL) has any protective effect against the inhibition of PGI2 generation induced by oxLDL is the objective of this study. Preincubation of aortas with oxLDL resulted in significant inhibition of PGI2 generation compared to preincubation with normal low density lipoprotein (nLDL) or buffer only. The inhibitory effect of oxLDL resided in its lipid moiety while the lipid fraction of nLDL showed no effect. Aortas preincubated with 10 microg/ml of lyso phosphatidycholine (lyso PC) also showed 30% inhibition of PGI2 generation, indicating that lyso PC was among the lipid components of oxLDL which inhibited PGI2 generation. Preincubation of aortas with a mixture of HDL and oxLDL at a ratio of 10:1 showed a significant recovery of PGI2 generation compared to aortas preincubated with only oxLDL, indicating a protective role for HDL. When HDL was incubated with oxLDL the transfer of lyso PC from oxLDL to HDL suggested that HDL trapped lyso PC from oxLDL thus preventing it from acting on the aorta. However, when a mixture of HDL and oxLDL at a ratio of 3:1 was preincubated with aortas, no protective effect of HDL was observed. Preincubation of aortas with a mixture of HDL plus oxLDL at a ratio of 8:1, which was incubated for 1 h at 37 degrees C, produced significantly less PGI2 than aortas preincubated only with oxLDL, indicating that HDL under these conditions was not protective but even enhanced the inhibitory effect of oxLDL. Similarly, aortas preincubated with HDL plus whole oxLDL (at a ratio of 10:1); containing all the small molecular weight oxidation products and characterized by high levels of thiobarbituric acid reactive substance (TBARS) and lipid hydroperoxides; produced significantly less PGI2 than aortas preincubated with whole oxLDL. These results were evaluated in light of possible modification of HDL by oxLDL and its lipid oxidation products such as aldehydes and lipid peroxides. The modified HDL can add more lipid peroxides and increase the effectiveness of lipid peroxides originally present in oxLDL.

Organosulfur compounds from alliaceae in the prevention of human pathologies

A strong association between elevated plasma low-density-lipoprotein (LDL) and the development of cardiovascular diseases (CVD) has been established. Oxidation of LDL (Ox-LDL) promotes vascular dysfunction, enhances the production and release of inflammatory mediators such as reactive oxygen species and contribute to the initiation and progression of atherosclerosis. In addition, Ox-LDL enhances the production and release of tumor necrosis factor (TNF-alpha), interleukin (IL)-6, arachidonic acid metabolites and nitric oxide (NO) that are responsible for various human pathologies including cancer. Organosulfur compounds (OSC) from alliaceae modulate the glutathione (GSH) redox cycle and inhibits NFkappa-B activation in human T cells. Furthermore, OSC bioactivities include antioxidant, antibacterial, anticarcinogenic, antiatherogenic, immunostimulatory, and liver protection potential.

The role of estrogen in cardiovascular disease

Cardiovascular disease is the number one cause of death among women, accounting for nearly 50% of female deaths. Statistics show that women on average develop cardiovascular disease 10 to 15 years later in life than men, and that the risk may increase after menopause. This observation has led to much speculation as to what physiological change(s) associated with menopause is responsible for the higher risk of atherosclerosis. Estrogen, with its potential as a cardioprotective agent and as an immunomodulator of the inflammatory response in atherosclerosis, has received the most attention. Understanding the mechanisms that lead to these differences may allow beneficial therapeutic intervention to enhance this effect in females and evoke this protection in males. This review will do the following: (1) characterize mechanisms of atherosclerosis, (2) explore the role of estrogen-replacement therapy, (3) define the effect of gender on inflammation, (4) compare and contrast the effects of estrogen and testosterone on endothelial functional, and (5) suggest mechanistic based therapeutic opportunities.

Monocyte/macrophage regulation of vascular calcification in vitro

BACKGROUND

Calcification is a common complication of atherosclerosis and other chronic inflammatory processes that involves infiltration of monocytes and accumulation of macrophages.

METHODS AND RESULTS

To determine whether these cells modulate vascular calcification in vitro, calcifying vascular cells (CVCs), a subpopulation of osteoblast-like cells derived from the artery wall, were cocultured with human peripheral blood monocytes for 5 days. Results showed that alkaline phosphatase (ALP) activity, a marker of osteoblastic differentiation, was significantly greater in cocultures than in cultures of CVCs or monocytes alone. Both ALP activity and matrix mineralization increased in proportion to the number of monocytes added. Activation of monocyte/macrophages (M/Ms) by oxidized LDL further increased ALP activity in cocultures. However, neither conditioned medium from oxidized-LDL-activated M/Ms or transwell coculture had this effect on CVCs, which suggests a need for cell-to-cell contact. In contrast, conditioned medium from lipopolysaccharide-activated M/Ms increased ALP activity of CVCs. ELISA showed that lipopolysaccharide-activated M/Ms secreted tumor necrosis factor-alpha, and neutralizing antibody to tumor necrosis factor-alpha attenuated the induction of ALP activity by the conditioned media.

CONCLUSIONS

These results suggest that M/Ms enhance in vitro vascular calcification via 2 independent mechanisms: cell-cell interaction and production of soluble factors such as tumor necrosis factor-alpha.

Oxidized low density lipoprotein inhibits prostacyclin generation by rat aorta in vitro: a key role of lysolecithin

The objective of this study was to examine the effect of oxLDL on prostacyclin (PGI2) generation by rat aortic segments and to see whether the lipid fraction of oxLDL or its components are responsible for that effect. We also tested if antioxidants have any protective role. LDL oxidized by copper was characterized by higher TBARS, conjugated diene, lysophosphatidylcholine (lyso PC), oxysterols and less polyunsaturated fatty acids (PUFA) than nLDL. Preincubation of aortas with oxLDL caused a significant inhibition of PGI2 generation compared to aortas preincubated with nLDL or buffer only. The percent inhibition was dependent on the concentration of oxLDL. Most of the inhibitory effect of oxLDL resided in its lipid moiety while the lipid fraction of nLDL, as well as native LDL had no effect. Preincubation of aortas with 10 microg/ml of 7-ketocholesterol the major oxysterol in oxLDL reduced the amount of PGI2 generated by aorta at all times tested; however that decrease did not reach a significant level. Aortas preincubated with 10 microg/ml of lyso PC showed a 21-36% inhibition of PGI2 generation which was comparable to the inhibition produced by preincubating the aortas with 50 microg protein/ml of oxLDL (containing about 7.5 microg lyso PC). This indicated that most of the inhibitory effect of oxLDL was due to its lyso PC. The small molecular weight fraction (< 10 kDa) with a high level of TBARS (TBARS solution) also significantly decreased the PGI2 generation by aorta. Addition of superoxide dismutase (SOD) + catalase or vitamin E simultaneously with oxLDL or TBARS solution in the preincubation medium did not reverse their inhibitory effects. This indicated that oxygen free radicals are not a contributing factor to the inhibitory effect of oxLDL but lyso PC and the lipid peroxides and probably other components already present within oxLDL are the important inhibitors.

Garlic compounds minimize intracellular oxidative stress and inhibit nuclear factor-kappa b activation

Oxidative modification of LDL has been recognized as playing an important role in the initiation and progression of atherosclerosis. In this study, we determined the effects of aged garlic extract (AGE) and its major compound, S-allylcysteine (SAC), on oxidized LDL (Ox-LDL)-induced injury in endothelial cells (EC). Lactate dehydrogenase (LDH) release as an index of membrane damage, methylthiazol tetrazoium (MTT) assay for cell viability and thiobarbituric acid reactive substances (TBARS) indicating lipid peroxidation were measured. Ox-LDL caused an increase of LDH release, loss of cell viability and TBARS formation. Both AGE and SAC prevented all of these changes. To elucidate the mechanism, effects of AGE or SAC on intracellular glutathione (GSH) level in EC, and release of peroxide from EC and macrophages (M Phi) were determined. Ox-LDL depleted intracellular GSH and increased release of peroxides. Both AGE and SAC inhibited these changes. Effects of SAC on hydrogen peroxide (H(2)O(2)) or tumor necrosis factor (TNF)-alpha-induced nuclear factor (NF)-kappa B activation were determined. Pretreatment of EC with SAC inhibited NF-kappa B activation. We demonstrated that both AGE and SAC can protect EC from Ox-LDL-induced injury by preventing intracellular GSH depletion in EC and by minimizing release of peroxides from EC and M Phi. SAC also inhibited H(2)O(2)- or TNF-alpha-induced NF-kappa B activation. Our data suggest that AGE and its main compound, SAC, may be useful for prevention of atherosclerosis.

Oxidizability of atherogenic low-density lipoprotein subspecies in severe familial hypercholesterolemia: impact of long-term low-density lipoprotein apheresis

BACKGROUND

Oxidative modification of low-density lipoprotein (LDL) plays a key role in the pathophysiology of atherosclerosis. LDL-apheresis, which involves direct removal of plasma LDL from circulating blood, is an efficient treatment of homozygous familial hypercholesterolemia (FH).

METHODS

We evaluated impact of long-term LDL apheresis treatment on the atherogenicity of the major LDL subclasses (light, LDL1, and LDL2, density [d] 1.018-1.030 g/mL; intermediate, LDL3, d 1.030-1.040 g/mL, and dense LDL, LDL4 and LDL5, d 1.040-1.065 g/mL) separated by density gradient ultracentrifugation in severe FH patients. Therefore, we compared the oxidative resistance as well as the chemical and physical properties of each LDL subpopulation in the FH group with those in the corresponding LDL subfractions from normocholesterolemic control subjects.

RESULTS

Both intermediate and dense LDL subfractions were significantly more resistant to copper-mediated oxidation in FH patients treated regularly by LDL-apheresis than their counterpart controls. The lag phases for LDL3, LDL4, and LDL5: 63.9+/-11.6, 55.8+/-1.2, and 47.2+/-6.5 min. in FH patients were significantly longer than those of the corresponding subfractions in normocholesterolemic controls (P <.01 for LDL3 and LDL5, P<.005 for LDL4). This protective effect was reflected in the delayed formation of biologically active lipid oxidation products such as oxysterols, lipid hydroperoxides, dienes, and dienals in the intermediate and dense LDL subfractions of FH patients. These findings may result from lower "seed" contents of lipid hydroperoxide (LOOH) detected as dienes in plasma LDL from apheresis-treated FH patients; indeed, baseline LOOH/diene contents in all 5 LDL subclasses from FH patients were significantly lower than those of the corresponding subclasses in normolipidemic subjects (P<.0005). On the other hand, the enhanced oxidative resistance of both intermediate (LDL3) and dense (LDL4 and LDL5) LDL subpopulations in FH patients could not be accounted for by any consistent modification in chemical composition or in lipophilic antioxidant content, although minor differences were observed between patients and controls in unsaturated fatty acid profile. In contrast, sphingomyelin content was enriched in FH LDL subclasses, potentially resulting in reduced penetration of the hydrophilic surface layer of LDL by oxygen radicals.

CONCLUSION

We conclude that low concentrations of preformed lipid hydroperoxides and dienes, together with surface sphingomyelin enrichment, can account for the enhanced oxidative resistance of intermediate (LDL3) and atherogenic dense LDL (LDL4, LDL5) induced by long-term LDL apheresis in severe FH patients.

Functional genomics and DNA array techniques in atherosclerosis research

DNA arrays are revolutionizing the analysis of gene expression and single nucleotide polymorphisms of genomic DNA. Currently, the expression of 10-15% of human genes can be analysed simultaneously in a single experiment using cDNA or oligonucleotide-based format of DNA array. Alternatively, smaller DNA arrays with a limited number of selected genes, such as cytokines, growth factors or transcription factors, can be used. In concordance with Human Genome Project, after a few years, the DNA arrays will allow the analysis of expression of the whole human genome and will have a great impact on basic research, drug development and diagnostics. It is important to characterise mechanisms of atherosclerosis-related diseases at the level of gene expression so that new therapeutic strategies can be identified. With the aid of DNA array it is possible to identify multiple, simultaneous, transcriptional events that ameliorate or contribute to atherogenesis. The results are non-physical maps of the function, hierarchy and interactions of genetic programs. In this review we focus on DNA array technology and its applications in atherosclerosis research.

Cholesterol-induced changes of type VIII collagen expression and distribution in carotid arteries of rabbit

Lipoproteins play a major role in cardiovascular disease and atherosclerosis. In the vascular wall, they strongly influence the organization of extracellular matrix. The present study set out to investigate the changes in the extracellular matrix of the vessel wall induced by atherogenic diet, focusing on type VIII collagen, a vascular collagen that has not previously been investigated in detail. The influence of cholesterol diet on the expression, distribution, and deposition of type VIII collagen was examined in carotid arteries of New Zealand White rabbits. Carotid arteries of rabbits receiving diet supplemented with 1% cholesterol for 6 weeks and those on the same regimen followed by normal chow for 1 day, 10 days, 5 weeks, and 12 weeks were studied and compared with controls not exposed to the cholesterol diet. Carotid arteries of normocholesterolemic rabbits contained type VIII collagen-expressing cells in all layers, with focal accumulations of expressing cells in the subendothelial areas, the outer medial zone, and the adventitia. In response to cholesterol diet, type VIII collagen synthesis was reduced in media and adventitia and the distribution patterns changed. Expressing cells were found predominantly in the endothelium, and type VIII collagen accumulated in the intimal space. Immunogold labeling for electron microscopy revealed that type VIII collagen in the intima is associated with microfibrils extending from the internal elastic lamina. Withdrawal of cholesterol resulted in reestablishment of the normal distribution pattern. Northern and Western blot analyses supported the immunoconfocal and in situ hybridization data, demonstrating decreased type VIII collagen expression in response to cholesterol diet and progressive recovery to normal levels with time after withdrawal of cholesterol. Our study demonstrates that type VIII collagen is modulated in the presence of cholesterol. The data indicate that type VIII collagen is specifically remodeled during early experimental atherosclerosis, implying a role for this extracellular matrix component in neointimal growth.

Aged garlic extract attenuates intracellular oxidative stress

Oxidation of low density lipoprotein (LDL) has been recognized as playing an important role in the initiation and progression of atherosclerosis. We recently reported that aged garlic extract (AGE) inhibited LDL oxidation and minimized oxidized LDL-induced cell injury. In this study, the antioxidant effects of AGE were further examined using bovine pulmonary artery endothelial cells (PAEC) and murine macrophages. Lactate dehydrogenase (LDH) release, as an index of membrane injury, and intracellular glutathione (GSH) levels were determined. Oxidized LDL (Ox-LDL) caused an increase of LDH release and depletion of GSH. Pretreatment with AGE prevented these changes. AGE exhibited an inhibition of Ox-LDL-induced peroxides in PAEC. AGE suppressed peroxides in murine Macrophage (J774 cells) dose-dependently. The J774 cells were also incubated with AGE, interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) and nitric oxide (NO) production was measured. AGE inhibited NO production in J774 cells. In a cell free system, AGE was shown to scavenge H2O2 dose-dependently. Our data demonstrate that AGE can protect the endothelial cells from oxidized LDL-induced injury by preventing depletion of intracellular GSH and by removing peroxides. AGE also reduces levels of NO and peroxides in macrophages. These data suggest that AGE is a useful protective agent against cytotoxicity associated with Ox-LDL and NO, and it may thus be useful for the prevention of atherosclerosis and cardiovascular diseases.

Oxidized LDL activates STAT1 and STAT3 transcription factors: possible involvement of reactive oxygen species

The effect of cupric ion-oxidized low density lipoprotein (Cu-LDL) or endothelial cell-oxidized LDL (E-LDL) on STAT1 and STAT3 (signal transducers and activators of transcription) DNA binding activity was investigated by electrophoretic mobility shift assay in human endothelial cells. Both oxidized LDL enhanced STAT1 and STAT3 binding to their respective consensus binding sites. Furthermore, the activation of STATs was proportional to the oxidation degree of LDL in that the highly oxidized Cu-LDL exhibited a more marked effect than E-LDL. Oxidized LDL induced an intracellular oxidative stress, as shown by the increase in the intracellular level of lipid peroxidation products (thiobarbituric acid-reactive substances) and in the level of reactive oxygen species, measured by the fluorescence of dichlorofluorescein diacetate. The binding activity of STAT1 and STAT3 paralleled these two parameters, which suggests that it is dependent upon the redox state of the cell. The activation of STATs by oxidized LDL was almost completely inhibited by the lipophilic antioxidant vitamin E, and partially antagonized by the hydrophilic thiol-containing compound N-acetylcysteine, suggesting that the oxidative stress induced by oxidized LDL is involved in the observed phenomenon. Furthermore, the lipid extract of Cu-LDL also activated STAT1 and STAT3. Since the STAT pathway plays a key role in cytokine and growth factor signal transduction, the activation of STATs by oxidized LDL might be related to their proinflammatory and fibroproliferative effect in the atherosclerotic plaque.

Human endothelium as a source of multifunctional cytokines: molecular regulation and possible role in human disease

Endothelial cells, by virtue of their capacity to express adhesion molecules and cytokines, are intricately involved in inflammatory processes. Endothelial cells have been shown to express interleukin-1 (IL-1), IL-5, IL-6, IL-8, IL-11, IL-15, several colony-stimulating factors (CSF), granulocyte-CSF (G-CSF), macrophage CSF (M-CSF) and granulocyte-macrophage CSF (GM-CSF), and the chemokines, monocyte chemotactic protein-1 (MCP-1), RANTES, and growth-related oncogene protein-alpha (GRO-alpha). IL-1 and tumor necrosis factor-alpha (TNF-alpha) produced by infiltrating inflammatory cells can induce endothelial cells to express several of these cytokines as well as adhesion molecules. Induction of these cytokines in endothelial cells has been demonstrated by such diverse processes as hypoxia and bacterial infection. Recent studies have demonstrated that adhesive interactions between endothelial cells and recruited inflammatory cells can also signal the secretion of inflammatory cytokines. This cross-talk between inflammatory cells and the endothelium may be critical to the development of chronic inflammatory states. Endothelial-derived cytokines may be involved in hematopoiesis, cellular chemotaxis and recruitment, bone resorption, coagulation, and the acute-phase protein synthesis. As many of these processes are critical to the maturation of an inflammatory and reparative state, it appears likely that endothelial-derived cytokines play a crucial role in several diseases, including atherosclerosis, graft rejection, asthma, vasculitis, and sepsis. Genetic and pharmacologic manipulation of endothelial-derived cytokines provides an additional approach to the management of chronic inflammatory diseases.

Effect of uric acid and chemical analogues on oxidation of human low density lipoprotein in vitro

Oxidative modification of low density lipoprotein (LDL) is implicated in the early development of atherosclerosis. In the present study, attention has been focused toward the potential protective effects of uric acid and purine-based chemical analogues in copper-promoted oxidative changes to human LDL in vitro. Between 5-100 mumol/l uric acid protected LDL from oxidative degradation in a concentration dependent manner. However, 5 mumol/l were not capable of inhibiting the consumption of LDLs natural antioxidative components, alpha-tocopherol and beta-carotene, but led to a more than two-fold prolongation, up to 3 h, of the lag phase before onset of polyunsaturated acid (PUFA) oxidation. 100 mumol/l uric acid, which is still below the human serum level of 300 mumol/l, reduced consumption of alpha-tocopherol and beta-carotene by about 50% and largely suppressed PUFA oxidation for up to 4 h. A more lipophilic series of methyl analogues of uric acid exhibited less activity. Neither 1,3-dimethyl uric acid, nor the 1,3,7- or 1,7- or 3,7-methylated compounds, all at 100 mumol/l, exceeded the antioxidative potential of 10 mumol/l uric acid. At concentrations up to 100 mumol/l xanthine and its analogues lacked virtually any protective effects toward the LDL constituents. In conclusion, the present study indicates that uric acid at concentrations similar to its physiological levels, and also related analogues are able to suppress oxidative degradation of LDL components. In view of the various mechanisms underlying atherogenesis in vivo, the protective effect in terms of modulating redox reactions and oxidative events in the blood or at the arterial wall appears of potential importance.

Activity of free radical scavenging enzymes in red cells and plasma of patients undergoing extracorporeal low-density lipoprotein apheresis

There is evidence that reactive oxygen species (ROSs) are generated in extracorporeal circuits. Free radical scavenging enzymes (FRSEs) such as glutathione reductase (GSSG-R), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) protect against the damaging effect of ROSs. The influence of extracorporeal treatment on FRSE activity was investigated in the plasma and red blood cells (RBCs) of 21 patients undergoing regular low-density lipoprotein (LDL) apheresis. The FRSEs GSSG-R, GSH-Px, and SOD were measured. Determinations were made before and after a single treatment. Because all apheresis patients suffered from coronary heart disease (CHD), 201 CHD patients and 90 individuals without CHD, neither group undergoing apheresis, served as controls. In apheresis patients, GSH-Px (33.9+/-8.2 U/g Hb) and GSSG-R (7.6+/-0.9 U/g Hb) activities were increased whereas SOD activity (5.4+/-1.5 U/g Hb) was decreased in RBCs before a single treatment compared to controls. Plasma FRSEs of apheresis patients were not different from those of controls. There was no effect of a single treatment on FRSEs in RBCs. However, a significant decrease in plasma GSH-Px activity (209.9+/-24.9 U/ml) due to the extracorporeal treatment was observed. These data show that long-term extracorporeal therapy with LDL apheresis modulates the activity of antioxidant enzymes in RBCs whereas a single treatment was without major effect on FRSE activity in RBCs and plasma, except for plasma GSH-Px.

Evidence for the development of macrophage-like cells in long-term culture of bovine aortic endothelial cells

Macrophages are known to be derived from monocytes which proliferate in the bone marrow. The proliferation of monocytes may occur in other places as well. In the present study, we describe the morphological behaviour of macrophage-like cells in endothelial cell cultures obtained from bovine aorta. These cells resembled hemopoietic clones containing progenitor-like cells. Immature and mature macrophage-like cells were rich in acid phosphatase activity, and expressed the CD18 molecule using immunolocalisation. Mature cells contained intracellular lipid droplets. "Actin" globules were apparent only in the peripheral cell areas without lamellipodia or filipodia. At the ultrastructural level, the mature cells were crowded with granules which could be lysosomes, phagolysosomes, or endocytotic vesicles. Multinuclear giant cells which behaved in a different way to the macrophage-like cells were observed. The development and maintenance of macrophage-like cells appears to be dependent on the coculture with endothelial cells. It may signify that endothelial cells are involved in the proliferation of monocytes outside the bone marrow.

Topographic analysis of proliferative activity in carotid endarterectomy specimens by immunocytochemical detection of the cell cycle-related antigen Ki-67

BACKGROUND

On the basis of contradictory results found in animal experiments and coronary atherectomy tissue, there is an ongoing debate about the significance of cellular proliferation in human atherosclerosis. In the present prospective study, the cell cycle-related antigen Ki-67 was detected for topographic determination of cell turnover in distinct regions of human carotid endarterectomy specimens harvested en bloc by surgical biopsy.

METHODS AND RESULTS

After en bloc resection, serial sections of 26 consecutive carotid lesions were analyzed by histomorphological examination and immunohistochemistry. Thereby, 319 high-power fields were attributed to separate plaque regions defined as follows: distal boundary of the lesion with normal intima, plaque shoulder, core region, and diffuse intimal thickening. Endothelial cells, smooth muscle cells, T cells, and macrophages were identified by immunostaining of factor VIII-related protein, alpha-actin, CD68, and CD45R0. An overall proliferation index of 0.49+/-1.05% was yielded by positive anti-Ki-67 immunolabeling, predominantly in macrophage-rich areas characterized by high cell density (>1000 cells/mm2) as well as in reparative sites in the perimeter of atheroma, intramural thrombosis, plaque hemorrhage, and neovascularization (P<.01). Few or no signs of proliferation activity were found in normal intima, in areas of dense alpha-actin positivity, or adjacent media. As shown by double immunostaining, macrophages and unspecified mesenchymal cells represented the prevailing proliferating cell type.

CONCLUSIONS

Our results suggest that proliferation in advanced human carotid lesions is confined to the intima and focally concentrated in central plaque regions negative for alpha-actin. Furthermore, it apparently occurs primarily as part of inflammatory processes and structural repair predominantly involving macrophages, as well as unspecific mesenchymal cells.

Local application of LDL promotes intimal thickening in the collared carotid artery of the rabbit

Oxidized LDL (oxLDL) has been implicated in atherogenesis on the basis of in vitro studies and is present in atherosclerotic lesions. The aim of this study was to investigate the effects of LDL and oxLDL on intimal thickening in vivo. Intimal thickening was evoked by the placement of silicone collars around the carotid arteries of rabbits for 2 weeks. The collars were connected to osmotic minipumps containing LDL (7 micrograms h-1, n = 16 arteries), oxLDL (Cu2+ oxidized, 7 micrograms h-1, n = 16), or phosphate-buffered saline (5 microL h-1, n = 16). Segments proximal to the collars served as controls. Collar placement without lipoprotein application resulted in the appearance of alpha-SMC actin-immunoreactive cells in the intima, thereby increasing the intimal thickness from 5 +/- 1 to 26 +/- 5 microns. The perivascular infusion of LDL or oxLDL within the collar significantly enhanced the development of the intima ninefold and sevenfold, respectively. The large intimas resulting from lipoprotein exposure were infiltrated by macrophages and T lymphocytes, and the intimal collagen area was increased from 5 +/- 2% in the discrete collar-induced intima to approximately 20% in the lipoprotein-evoked lesions. In conclusion, the local vascular application of LDL, oxidized in vitro or possibly in vivo, elicited an inflammatory-fibroproliferative response characteristic of arteriosclerotic lesions, thereby demonstrating an active role for this class of lipoproteins in the disease process.

DNA fragmentation and ultrastructural changes of degenerating cells in atherosclerotic lesions and smooth muscle cells exposed to oxidized LDL in vitro

Degeneration of smooth muscle cells in the fibrous cap of atherosclerotic lesions is an important factor in plaque rupture. Recent studies have suggested that many plaque cells are in a process of apoptosis as determined by positive deoxyribonucleotide-transferase-mediated dUTP end labeling. In this study, we demonstrate the existence of a colocalization between deoxyribonucleotide-transferase-mediated dUTP end labeling-positive smooth muscle cells and oxidized LDL immunoreactivity in human carotid plaques. Oxidized LDL was found to induce deoxyribonucleotide-transferase-mediated dUTP end labeling positivity in cultured human smooth muscle cells, but only in the presence of tumor necrosis factor-alpha and interferon-gamma. Electron microscopic analysis of cultured smooth muscle cells exposed to oxidized LDL in the absence of cytokines demonstrated cytoplasmic swelling and disruption of the plasma membrane, suggesting cell death by oncosis. Cells exposed to both oxidized LDL and cytokines were characterized by chromatin and cytoplasmic condensation compatible with cell death by apoptosis. These findings further support the notion that oxidized lipids play a role in plaque cell death.

Direct copper reduction by macrophages. Its role in low density lipoprotein oxidation

Oxidation of low density lipoprotein (LDL) results in changes to the lipoprotein that are potentially atherogenic. Numerous studies have shown that macrophages cultured in vitro can promote LDL oxidation via a transition metal-dependent process, yet the exact mechanisms that are responsible for macrophage-mediated LDL oxidation are not understood. One contributing mechanism may be the ability of macrophages to reduce transition metals. Reduced metals (such as Fe(II) or Cu(I)) rapidly react with lipid hydroperoxides, leading to the formation of reactive lipid radicals and conversion of the reduced metal to its oxidized form. We demonstrate here the ability of macrophages to reduce extracellular iron and copper and identify a contributing mechanism. Evidence is provided that a proportion of cell-mediated metal reduction is due to direct trans-plasma membrane electron transport. Glucagon suppressed both macrophage-mediated metal reduction and LDL oxidation. Although metal reduction was augmented when cells were provided with a substrate for thiol production, thiol export was not a strict requirement for cell-mediated metal reduction. Similarly, while the metal-dependent acceleration of LDL oxidation by macrophages was augmented by thiol production, macrophages could still promote LDL oxidation when thiol export was minimized (by substrate limitation). This study identifies a novel mechanism that may contribute to macrophage-mediated LDL oxidation and may also reveal potential new strategies for the inhibition of this process.

Human monocytes/macrophages release TNF-alpha in response to Ox-LDL

The uptake of oxidatively modified low density lipoprotein (Ox-LDL) by intimal macrophages is believed to play a key role in the development of atherosclerosis. The present study demonstrates that Ox-LDL in low concentrations activates monocyte/macrophage release of factors that stimulate smooth muscle cell growth, whereas higher concentrations are inhibitory. Exposure of monocytes/macrophages to 8 micrograms/mL Ox-LDL increased expression of tumor necrosis factor-alpha (TNF-alpha) mRNA but had no effect on interleukin-1 beta, platelet-derived growth factor B and heparin-binding epidermal growth factor-like mitogen mRNA levels. Ox-LDL also stimulated monocyte/macrophage release of TNF-alpha in a dose-dependent manner, with maximal effect at an LDL concentration of 8 micrograms/mL. Addition of TNF-alpha-blocking antibodies to conditioned medium from monocytes/ macrophages already exposed to Ox-LDL reduced mitogenic activity by 44.7 +/- 8.4% (P < .005). Stimulation of TNF-alpha release by Ox-LDL was associated with activation of transcription factor AP-1, whereas the activity of transcription factor nuclear factor-kB remained unchanged. These findings suggest that enhanced secretion of TNF-alpha by macrophages exposed to Ox-LDL may be involved in the formation of atherosclerotic lesions.

Oxidative susceptibility of low density lipoprotein from rabbits fed atherogenic diets containing coconut, palm, or soybean oils

The oxidative susceptibilities of low density lipoproteins (LDL) isolated from rabbits fed high-fat atherogenic diets containing coconut, palm, or soybean oil were investigated. New Zealand white rabbits were fed atherogenic semisynthetic diets containing 0.5% cholesterol and either (i) 13% coconut oil and 2% corn oil (CNO), (ii) 15% refined, bleached, and deodorized palm olein (RBDPO), (iii) 15% crude palm olein (CPO), (iv) 15% soybean oil (SO), or (v) 15% refined, bleached, and deodorized palm olein without cholesterol supplementation [RBDPO(wc)], for a period of twelve weeks. Total fatty acid compositions of the plasma and LDL were found to be modulated (but not too drastically) by the nature of the dietary fats. Cholesterol supplementation significantly increased the plasma level of vitamin E and effectively altered the plasma composition of long-chain fatty acids in favor of increasing oleic acid. Oxidative susceptibilities of LDL samples were determined by Cu2(+)-catalyzed oxidation which provide the lag times and lag-phase slopes. The plasma LDL from all palm oil diets [RBDPO, CPO, and RBDPO(wc)] were shown to be equally resistant to the oxidation, and the LDL from SO-fed rabbits were most susceptible, followed by the LDL from the CNO-fed rabbits. These results reflect a relationship between the oxidative susceptibility of LDL due to a combination of the levels of polyunsaturated fatty acids and vitamin E.

Synthesis of an endogeneous lectin, galectin-1, by human endothelial cells is up-regulated by endothelial cell activation

The pattern of expression of an endogenous lectin, galectin-1, was examined in human lymphoid tissue. Galectin-1 was detected in the endothelial cells lining specialized vessels, termed high endothelial venules, in activated lymphoid tissue, but not in a resting lymph node. Cultured endothelial cells (human aortic and umbilical vein endothelial cells (HAECs and HUVECs)) expressed galectin-1. Activation of the cultured endothelial cells increased the level of galectin-1 expression, as determined by ELISA. Northern blot analysis and high throughput cDNA sequencing. These results suggest that galectin-1 expressed by endothelial cells may bind to and affect the trafficking of cells emigrating from blood into tissues.

The megakaryocyte platelet system and vascular disease

Platelets form a heterogeneous population of cells produced from the uniquely large polyploid cell found in the bone marrow, the megakaryocyte. The platelet megakaryocyte axis forms a dynamic equilibrium varying in normal biology and in disease. Prolonged platelet destruction leads to the production of large platelets from large, high ploidy megakaryocytes. In vivo and ex vivo studies show that such platelets have more haemostatic potential than smaller less dense platelets. The evidence suggesting that prothrombotic changes in the megakaryocyte platelet axis precede coronary artery thrombosis and the importance of platelet reactivity in atherosclerosis will be reviewed.

1 Acyl-2 acetyl-sn-glycero-3 phosphocholine decreases the susceptibility of low-density lipoprotein to oxidative modification by copper ions, monocytes or endothelial cells

The effects of platelet-activating factor (PAF) and its analogue, 1 acyl-2 acetyl-sn-glycero-3 phosphocholine (1 acyl-2 acetyl-GPC), were investigated on the oxidative modification of low-density lipoprotein (LDL) by copper ions, U937 monocyte-like cells or endothelial cells, by determination of the lipid peroxidation end products (TBARS) content and measurement of the electrophoretic mobility of the particle. 1 Acyl-2 acetyl-GPC, in the concentration range 1-5 micrograms/ml, inhibited LDL oxidation in a dose-dependent manner in the three systems, whereas PAF had no effect. The protective effect of 1 acyl-2 acetyl-GPC was markedly more important when oxidative modification was performed with endothelial cells, leading to total inhibition at 5 micrograms/ml. At the same concentration, the TBARS production was inhibited by 60% and 20% with monocytes and copper ions, respectively. The degradation by J774 macrophage-like cells of LDL modified by copper ions, U937 monocyte-like cells or endothelial cells was also inhibited when modification was performed in the presence of 1 acyl-2 acetyl-GPC. Furthermore, preincubation of the LDL particle with 1 acyl-2 acetyl-GPC before modification protected the lipoprotein against oxidation, whereas preincubation of the cultured cells with the phospholipid had no effect. Thus 1 acyl-2 acetyl-GPC decreases the susceptibility of the LDL particle to oxidative modification, possibly by intercalation within the lipid phase of the particle. Since LDL oxidation is believed to play an important role in the initiation and progression of atherosclerosis, this inhibitory effect of 1 acyl-2 acetyl-GPC might be of importance in view of the fact that this phospholipid is produced concomitantly with PAF in some inflammatory cells.

Evidence for the presence of early vascular lesions in newborn Watanabe heritable hyperlipidemic (WHHL) rabbits

We have investigated the morphology of the aortic wall of newborn New Zealand White (NZW) (n = 10) and newborn Watanabe heritable hyperlipidemic (WHHL) (n = 10) rabbits. In both strains, lipid levels (cholesterol and triglycerides) were elevated above the concentrations expected. This was particularly evident in WHHL. The morphology of the aortas of NZW rabbits suggested an intensive biosynthetic and bioenergetic activity of endothelium. This was most evident in areas where blood flow underwent division. No major abnormalities were noted in the endothelium or subendothelium. In newborn WHHL rabbits, leucocyte adhesion (usually monocytes) to endothelium and migration into the subendothelium was apparent, particularly on the aortic arch and around areas of dividing blood flow in the thoracic aorta. Tuberous raised structures were present in low numbers and distributed randomly on the aortic wall. Endothelial cells had elevated nuclear zones projecting into the vessel lumen. At regions of blood flow division, endothelium was polygonal in shape and silver staining of cell borders was more intense. Fatty streaks were present at blood flow divisions and micro-plaque was seen. Transmission electron microscopy of fatty streak-like areas showed the presence of up to two layers of smooth muscle cells and in some areas, lipid-laden macrophages were seen. The presence of atherosclerotic lesions in newborn WHHL rabbits suggests that the process may commence in utero.

The pathogenesis of atherosclerosis: a perspective for the 1990s

Atherosclerosis, the principal cause of heart attack, stroke and gangrene of the extremities, is responsible for 50% of all mortality in the USA, Europe and Japan. The lesions result from an excessive, inflammatory-fibroproliferative response to various forms of insult to the endothelium and smooth muscle of the artery wall. A large number of growth factors, cytokines and vasoregulatory molecules participate in this process. Our ability to control the expression of genes encoding these molecules and to target specific cell types provides opportunities to develop new diagnostic and therapeutic agents to induce the regression of the lesions and, possibly, to prevent their formation.

Effects of doxazosin on atherosclerosis in cholesterol-fed rabbits

Doxazosin was administered to rabbits fed diets enriched in cholesterol and peanut oil for 7.5 or 12 weeks, in 2 separate experiments. Doxazosin suppressed the accumulation of cholesterol and formation of atherosclerotic plaques in the aortas of treated rabbits and prevented a diet-induced increase in aortic collagen and wall mass. Doxazosin was more effective in the thoracic and abdominal segments of the aorta than in the aortic arch. Pharmacokinetic analysis indicated that treated rabbits were exposed to concentrations of doxazosin, integrated over 24 h, which were consistent with the therapeutic range of doxazosin measured in patients treated for hypertension. Doxazosin did not alter serum levels of cholesterol or triglycerides, nor were there any consistent effects on glucose, free fatty acid or ketone levels. Hypotheses of the mechanism of action of doxazosin are discussed, including the possible involvement of alpha 1-adrenergic receptors in recruitment of smooth muscle cells by subintimal macrophages and nonadrenergic mechanisms of inhibition of lipid infiltration.

The role of lipid peroxidation and antioxidants in oxidative modification of LDL

The purpose of this study is to provide a comprehensive survey on the compositional properties of LDL (e.g., lipid classes, fatty acids, antioxidants) relevant for its susceptibility to oxidation, on the mechanism and kinetics of LDL oxidation, and on the chemical and physico-chemical properties of LDL oxidized by exposure to copper ions. Studies on the occurrence of oxidized LDL in plasma, arteries, and plaques of humans and experimental animals are discussed with particular focus on the use of poly- and monoclonal antibodies for immunochemical demonstration of apolipoprotein B modifications characteristic for lipid peroxidation. Apart from uptake of oxidized LDL by macrophages, studies describing biological effects of heavily or minimally oxidized LDL are only briefly addressed, since several reviews dealing with this subject were recently published. This article is concluded with a section on the role of natural and synthetic antioxidants in protecting LDL against oxidation, as well as some previously unpublished material from our laboratories.

Hypothesis: a damaging role in aging for reactive protein oxidation products?

This paper discusses our knowledge of protein oxidation and its relationship to aging. It also outlines new observations from our laboratories concerning reactive species produced during protein oxidation, and proposes that these may inflict damage on other molecules, and hence contribute to the progression of aging. Whereas it has previously been difficult to see how relatively inert protein oxidation products could possibly have any causal role in aging, the detection of these novel reactive species implies a potentially significant role.

Lipophilic β-blockers inhibit monocyte and endothelial cell-mediated modification of low density lipoproteins

The effects of propranolol, pindolol and metoprolol on the modification of low density lipoprotein (LDL) by U937 monocyte-like cells, endothelial cells and copper ions were studied by determination of the lipid peroxidation product content and measurement of the relative electrophoretic mobility of the particle. Propranolol and pindolol inhibited LDL oxidation by U937 cells in a dose-dependent manner from 10 to 100 microM, whereas metoprolol had no effect. In the case of LDL modification by endothelial cells, all the three beta-blockers were efficient within the same range of concentrations, and the order of potency was propranolol greater than pindolol greater than metoprolol. In vitro oxidation of LDL in the presence of copper ions was also inhibited by propranolol; pindolol and metoprolol had no significant protective effect in this system. These results concerning the inhibitory action of beta-blockers were confirmed by testing the degradation of modified LDL by J774 macrophages. Although the concentrations of the drugs utilized in this study are relatively high, in long-term treatment beta-blockers might accumulate in target tissues, and the protective effect of propranolol against LDL oxidation might be involved in its inhibitory action on atherosclerosis previously reported in animal models.