Measurement of platelet-activating factor in a canine model of coronary thrombosis and in endarterectomy samples from patients with advanced coronary artery disease

The Roles of Platelet-Activating Factor and Magnesium in Pathophysiology of Hypertension, Atherogenesis, Cardiovascular Disease, Stroke and Aging

Hypertension and atherosclerosis are debilitating diseases that affect millions each year. Long-term consequences include but are not limited to stroke, myocardial infarction, and kidney failure. Platelet-activating factor (PAF) is a proinflammatory mediator synthesized from a subclass of phosphatidylcholines that increases platelet activation, leukocyte adhesion, infiltration of macrophages, and intracellular lipid accumulation, thereby contributing to atherosclerosis. Magnesium, a key micronutrient and free radical scavenger, is a water-soluble mineral that regulates peripheral vasodilation and calcium, phosphate, and hydroxyapatite homeostasis. Magnesium’s antihypertensive ability stems from its role as a natural calcium antagonist and promoter of vasodilatory mediators, such as nitric oxide. Platelet-activating factor and magnesium share an inverse relationship, and elevated magnesium levels have been shown to have protective effects against plaque formation as well as antihypertensive and antiarrhythmic effects, all of which allow for healthier aging. The purpose of this literature review is to investigate the role of platelet-activating factor and magnesium in the pathophysiology of hypertension, atherosclerosis, cardiovascular disease, stroke, and aging. Since the pathophysiology of the platelet-activating factor biomolecule is underexplored, further research studies are warranted in order to navigate the putative signaling pathways involved in the cardioprotective effects of dietary magnesium as a natural anti-PAF agent.

Direct Growth Inhibitory Effect of Platelet Activating Factor C-16 and Its Structural Analogs on Mycobacteria

Mycobacterium tuberculosis, the causative agent of tuberculosis, is one of the leading causes of human deaths due to a single infectious agent. M. tuberculosis infection of the host initiates a local inflammatory response, resulting in the production of a range of inflammatory factors at the site of infection. These inflammatory factors may come in direct contact with M. tuberculosis and immune cells to activate different signaling pathways. One such factor produced in excess during inflammation is a phospholipid compound, Platelet Activating Factor C-16 (PAF C-16). In this study, PAF C-16 was shown to have a direct inhibitory effect on the growth of Mycobacterium bovis BCG (M. bovis BCG) and Mycobacterium smegmatis (M. smegmatis) in a dose- and time-dependent manner. Use of a range of PAF C-16 structural analogs, including the precursor form Lyso-PAF, revealed that small modifications in the structure of PAF C-16 did not alter its mycobacterial growth inhibitory properties. Subsequent experiments suggested that the attachment of aliphatic carbon tail via ether bond to the glycerol backbone of PAF C-16 was likely to play a vital role in its growth inhibition ability against mycobacteria. Fluorescence microscopy and flow cytometry using Propidium iodide (PI) indicated that PAF C-16 treatment had a damaging effect on the cell membrane of M. bovis BCG and M. smegmatis. Furthermore, the growth inhibitory effect of PAF C-16 was partially mitigated by treatment with membrane-stabilizing agents, α-tocopherol and Tween-80, which further suggests that the growth inhibitory effect of PAF C-16 was mediated through bacterial cell membrane damage.

Dogs cast NETs too: Canine neutrophil extracellular traps in health and immune-mediated hemolytic anemia

Neutrophil extracellular traps (NETs) are webs of DNA and protein with both anti-microbial and pro-thrombotic properties which have not been previously reported in dogs. To confirm dog neutrophils can form NETs, neutrophils were isolated from healthy dogs, and stimulated in vitro with 2μM, 8μM, 31μM, and 125μM platelet activating factor (PAF) or 0.03μM, 0.1μM, 0.4μM, 1.6μM and 6.4μM phorbol-12-myristate-13-acetate (PMA). Extracellular DNA was measured using the cell impermeable dye Sytox Green every hour for 4h. At 4h, extracellular DNA was significantly greater than non-stimulated cells at concentrations ≥31μM and ≥0.1μM for PAF and PMA, respectively. Cells stimulated with 31.25μM PAF reached maximal fluorescence by 1h, whereas maximal fluorescence was not achieved until 2h for cells stimulated with 0.1μM PMA. Immunofluorescent imaging using DAPI and anti-elastase antibody confirmed that extracellular DNA is released as NETs. As NETs have been implicated in thrombosis, nucleosomes, a marker correlated with NET formation, were measured in the serum of dogs with the thrombotic disorder primary immune-mediated hemolytic anemia (IMHA) (n=7) and healthy controls (n=20) using a commercially available ELISA. NETs were significantly higher in IMHA cases than controls (median 0.12 and 0.90, respectively, p=0.01), but there were large positive interferences associated with hemolysis and icterus. In summary, the study is the first to describe NET generation by canine neutrophils and provides preliminary evidence that a marker associated with NETs is elevated in IMHA. However, this apparent elevation must be interpreted with caution due to the effect of interference, emphasizing the need for a more specific and robust assay for NETs in clinical samples.

Hen egg yolk lipid fractions with antiatherogenic properties

Three different types of hen egg yolk, cage-free, organic and daily fresh, were tested for their antiatherogenic properties. Total lipids (TL) of all hen egg yolk samples were extracted by the method of Bligh and Dyer and further separated into total polar lipids (TPL) and total neutral lipids (TNL) by counter current distribution chromatography. TPL and TNL were further separated by preparative thin-layer chromatography (TLC). TL, TPL, TNL and the obtained polar and neutral lipid fractions after TLC separation were tested to determine whether they induce platelet activation or inhibit platelet activating factor (PAF)-induced platelet activation. All three hen egg yolk TL samples possessed strong inhibitory activity against PAF-induced platelet activation that was mainly attributed to TPL, especially to PL fraction 4. Cage-free hen egg yolk exhibited the most potent anti-PAF activity in all lipid classes (TL, TPL and TNL). Thus hen egg yolk contains PAF inhibitors that reinforce their nutritional value in terms of protection against cardiovascular diseases, since PAF is a crucial inflammatory phospholipid mediator that is implicated in the mechanism of atherogenesis.

Platelet-activating factor levels of serum and gingival crevicular fluid in nonsmoking patients with periodontitis and/or coronary heart disease

The purpose of the present study was to investigate systemic and local levels of platelet-activating factor (PAF), a potent proinflammatory mediator implicated in cardiovascular pathophysiology in adult nonsmoking patients with periodontitis with or without coronary heart disease (CHD). Eighty-seven volunteers, 25 periodontitis patients, 19 periodontitis with CHD patients, 19 CHD patients, and 24 healthy controls were included, and periodontal conditions were assessed. Gingival crevicular fluid (GCF) and venous blood were collected, and PAF levels were measured by enzyme-linked immunosorbent assay. PAF levels in serum (303.3 ± 204 pg/ml) and in GCF (26.3 ± 6 pg/μl) of the periodontitis group with CHD, the periodontitis group (serum, 302.4 ± 241 pg/ml and GCF, 26.3 ± 8 pg/μl) and the CHD group (serum, 284.7 ± 192 pg/ml and GCF, 20.8 ± 6 pg/μl) were significantly higher than the healthy control group (serum, 65.4 ± 35 pg/ml and GCF, 7.7 ± 3 pg/μl; p < 0.05). In summary, the present study could demonstrate that in patients with periodontitis, the inflammatory mediator PAF is released into serum at least in the same range as for patients with coronary heart disease. However, no additive effects were seen when both conditions were present.

Cardiovascular friendly natural products: a promising approach in the management of CVD

Natural products play an important role as nutritional supplements and provide potential health benefits in cardiovascular diseases (CVD). Compiling data from experimental, epidemiological and clinical studies indicates that dietary nutrients have profound cardioprotective effects in the primary as well as secondary prevention of coronary heart disease, hence they are considered as cardiovascular friendly natural products. The mechanism of cardioprotection produced by dietary nutritional supplements such as flavonoids (citrus fruits, pulses, red wine, tea and cocoa), olive oil, omega-3 (omega-3) fatty acids (fish oil and fish-based products), lycopene (tomato and tomato-based products), resveratrol (grapes and red wine), coffee, and soy in the prevention and treatment of cardiovascular disorders have been discussed in the present review, with the emphasis of epidemiological and clinical studies. Based on the intriguing results of various studies, prophylactic and therapeutic potential of cardiovascular friendly natural products have been suggested. The supplementation of cardiovascular friendly natural products needs to be considered in all populations who have high prevalence of CVD.

Platelet-activating factor acetylhydrolase and transacetylase activities in human aorta and mammary artery

Platelet-activating factor (PAF), the potent phospholipid mediator of inflammation, is involved in atherosclerosis. Platelet-activating factor-acetylhydrolase (PAF-AH), the enzyme that inactivates PAF bioactivity, possesses both acetylhydrolase and transacetylase activities. In the present study, we measured acetylhydrolase and transacetylase activities in human atherogenic aorta and nonatherogenic mammary arteries. Immunohistochemistry analysis showed PAF-AH expression in the intima and the media of the aorta and in the media of mammary arteries. Acetylhydrolase and transacetylase activities were (mean +/- SE, n = 38): acetylhydrolase of aorta, 2.8 +/- 0.5 pmol/min/mg of tissue; transacetylase of aorta, 3.3 +/- 0.7 pmol/min/mg of tissue; acetylhydrolase of mammary artery, 1.4 +/- 0.3 pmol/min/mg of tissue (P < 0.004 as compared with acetylhydrolase of aorta); transacetylase of mammary artery, 0.8 +/- 0.2 pmol/min/mg of tissue (P < 0.03 as compared with acetylhydrolase of mammary artery). Lyso-PAF accumulation and an increase in PAF bioactivity were observed in the aorta of some patients. Reverse-phase HPLC and electrospray ionization mass spectrometry analysis revealed that 1-O-hexadecyl-2 acetyl-sn glycero-3-phosphocholine accounted for 60% of the PAF bioactivity and 1-O-hexadecyl-2-butanoyl-sn-glycerol-3-phosphocholine for 40% of the PAF bioactivity. The nonatherogenic properties of mammary arteries may in part be due to low PAF formation regulated by PAF-AH activity. In atherogenic aortas, an imbalance between PAF-AH and transacetylase activity, as well as lyso-PAF accumulation, may lead to unregulated PAF formation and to progression of atherosclerosis.

Repair of separated coronary segments resulting from a complicated coronary endarterectomy

Cardiac surgeons are treating an increasing number of patients with diffuse coronary artery disease that requires the use of alternative surgical techniques. We present a patient who had a technically unsatisfactory endarterectomy of the left anterior descending coronary artery. We were left with only 3 segments of properly endarterectomized coronary bed areas, separated with totally disintegrated coronary bed portions. These 3 segments were incorporated into the venous graft, with the inflow obtained from the left internal thoracic artery. We believe that this approach may be the rescue technique for complicated coronary artery endarterectomy.

Effect of traditional Greek Mediterranean meals on platelet aggregation in normal subjects and in patients with type 2 diabetes mellitus

Patients with type 2 diabetes mellitus have increased risk of cardiovascular disease. Epidemiological studies have shown a correlation between diet and incidence of coronary heart disease. The aim of the study is to determine the effect of a traditional Greek Mediterranean diet on platelet aggregation induced by ADP, arachidonic acid (AA), and especially platelet-activating factor (PAF) on patients with type 2 diabetes mellitus as well as on healthy volunteers. The patients were randomized into two subgroups, A and B. The lipid extracts from traditional Greek Mediterranean-type meals were tested in in vivo for their ability to reduce PAF- or thrombin-induced platelet aggregation. The meals with the most potent anti-aggregating activity were chosen for the diet of both subgroup A and healthy subjects and consumed for a period of 28 days, whereas subgroup B kept to their regular diet that was followed before entering the study. Platelet-rich plasma was isolated before and after the diet, and the ability of platelets to aggregate under the aggregating factors was tested. One-month consumption of diet resulted in a significant reduction in PAF- and ADP-induced aggregation of platelets in both groups of healthy volunteers (PAF and ADP, P < .05) and subgroup A (PAF, P < .001; ADP, P < .05), whereas the AA-induced aggregation was not affected. No effect was observed in subgroup B, which followed the standard diet. Thus the consumption of a traditional Greek Mediterranean diet even for a short period can reduce platelet activity in patients suffering from type 2 diabetes mellitus and in healthy subjects.

Nupafant, a PAF-antagonist prototype for suppression of ventricular fibrillation without liability for QT prolongation?

BACKGROUND AND PURPOSE

PAF antagonists inhibit ischaemia-induced ventricular fibrillation (VF) in animals. However, unfavourable ancillary actions (on QT interval and coronary flow) have been reported with the PAF antagonist, BN-50739. If these are class actions, they would preclude development of PAF antagonists as novel anti-VF drugs. Our purpose was to examine this proposition using the hitherto untested PAF antagonist, nupafant.

EXPERIMENTAL APPROACH

Two rat heart preparations (Langendorff and 'dual coronary' perfusion) were used to assay nupafant's effects on ischaemia-induced VF, coronary flow and QT interval, and to test for the site-selectivity necessary if any effects on VF are caused by PAF antagonism.

KEY RESULTS

Global (whole-heart) delivery of 10 microM nupafant, reduced the incidence of ischaemia-induced VF and widened QT interval without affecting coronary flow. Importantly, lower concentrations (0.1 and 1 microM) had no effect on VF, yet widened QT almost identically to 10 microM nupafant. When nupafant was delivered selectively to (and entrapped within) the involved region it partially protected against VF (P<0.05). This occurred without change in QT interval. Selective nupafant delivery to the uninvolved region was without effect.

CONCLUSIONS AND IMPLICATIONS

Nupafant protects against ischaemia-induced VF primarily by site-selective actions in the ischaemic region but, unlike BN-50739, the effect is unrelated to its QT widening action, and is not compromised by any effect on coronary flow. This establishes proof of concept that VF suppression by PAF antagonism need not invariably be associated with QT prolongation or vasodilatation, justifying further development of this drug class.

Platelet-activating factor (PAF) increase intracellular lipid accumulation by increasing both LDL and scavenger receptors in human mesangial cells

Intra- and extracellular lipid accumulation and the production of inflammatory mediators by renal and accessory cells may play an important role in the initiation and progression of these lesions. Platelet activating factor (PAF) is a biologically active phospholipid that is produced by various cells upon activation by different stimuli. It has been suggested that PAF plays a role in atherogenesis, and several studies indicated its participation in the pathogenesis of renal diseases. The aim of this study is to investigate the role of PAF on intracellular lipid accumulation and gene regulation of lipoprotein receptors in human mesangial cells (HMCs). A human mesangial cell line (HMC) was used to study the effects of PAF on foam cell formation by Oil red O staining and on the expression of LDLr, SR-AI, and PAF-R mRNA using RT-PCR. Native LDL caused foam cell formation in HMC in the presence of PAF. PAF enhanced LDLr expression and overrode LDL receptor suppression induced by a high concentration of LDL. Moreover, it enhanced SR-AI expression. PAF also caused increase in PAF-R expression. The above data suggest that PAF enhances its own receptor expression and then increases lipid accumulation by dysregulating LDL receptor regulation and inducing scavenger receptor expression in HMCs. These results suggest that PAF has a potential role in lipid mediated renal injury.

PAF-receptor is preferentially expressed in a distinct synthetic phenotype of smooth muscle cells cloned from human internal thoracic artery: functional implications in cell migration

Platelet-activating-Factor (PAF) and its structural analogues formed upon low density lipoprotein oxidation are involved in atherosclerotic plaque formation and may signal through PAF-receptor (PAF-R) expressed in human macrophages and in certain smooth muscle cells (SMCs) in the media, but rarely in the intima of human plaques. Our aim was to determine which SMC phenotype expresses PAF-R and whether this receptor is functional in cell migration. Circulating SMC progenitors and two phenotypically distinct clones of proliferative, epithelioid phenotype vs contractile, spindle-shaped SMCs from the media of adult internal thoracic artery were studied for the presence of PAF-receptor (PAF-R). The levels of specific mRNA were obtained by reverse transcription/real-time PCR, the protein expression was deduced from immunohistochemistry staining, and the functional transmigration assay was performed by Boyden chamber-type chemotaxis assay. Only SMCs of spindle-shape and synthetic phenotype expressed both mRNA and PAF-R protein and in the functional test migrated at low concentrations of PAF. Two unrelated, specific PAF-R antagonists inhibited PAF-induced migration, but did not modify the migration initiated by PDGF. The presence of functional PAF-R in arterial spindle-shaped SMCs of synthetic phenotype may be important for their migration from the media into the intima and atherosclerotic plaques formation.

A single nucleotide polymorphism in the plasma PAF acetylhydrolase gene and risk of atherosclerosis in Japanese patients with peripheral artery occlusive disease

BACKGROUND

Plasma PAF-acetylhydrolase (PAF-AH) gene polymorphisms (G994 --> T in exon 9) and the resulting deficiency of enzyme activity were identified in the Japanese population. The objective of this study was to assess the joint effect of the polymorphism and hypercholesterolemia on risk of atherosclerosis.

METHODS AND RESULTS

We performed a case-control study including 150 patients who underwent operation for peripheral arterial occlusive disease (PAOD) and 158 controls matched for age and sex. Genomic DNA was analyzed for the mutant allele by a specific polymerase-chain reaction. Plasma PAF-AH activity was measured in both groups. The patients with multiple atherosclerotic diseases showed higher levels of PAF-AH activities than the patients with only peripheral artery occlusive disease among normal genotypes. PAOD patients were assessed either with or without polymorphism or hypercholesterolemia in regard to accompanying coronary artery disease or stroke. The prevalence of the polymorphism was significantly more frequent in the patients with PAOD. The plasma PAF-AH activity was correlated with total cholesterol and LDL level, and inversely related with HDL in normal genotype (GG) PAOD patients. However, neither the correlation nor the inverse relation was found in patients with the polymorphism. Patients with both hypercholesterolemia and the polymorphisms revealed a relative risk for other atherosclerotic disease of 11.5 (6.0-40.3) compared with normal genotype and normal lipid level.

CONCLUSION

The plasma PAF-AH gene polymorphism and hypercholesterolemia may interact and increase the risk of atherosclerosis.

Effect of fast-food Mediterranean-type diet on type 2 diabetics and healthy human subjects' platelet aggregation

OBJECTIVE

The aim of our work was to carry out a randomized clinical trial with a fast-food Mediterranean type diet rich in platelet activating factor (PAF) antagonist to investigate the effect on type 2 diabetics and healthy human subject's platelet aggregation.

RESEARCH DESIGN AND METHODS

We extracted lipids from fast-food Mediterranean type foodstuffs, and tested them in vitro for their ability to inhibit or antagonize PAF towards washed rabbit platelets. We chose the foodstuffs that exerted the most potent in vitro anti-PAF activity and fed 22 healthy (group A) and 23 type 2 diabetics (group B) subjects on a diet containing the chosen foodstuffs. The 22 type 2 diabetics (group C) subjects were kept on their regular diet that was being followed before entering the study. Before and after a 4-week diet, all enrolled subjects underwent the following examinations; measurement of total cholesterol, low density lipoprotein (LDL-cholesterol), high density lipoprotein (HDL-cholesterol), triglycerides, glucose, HbA(1c), body mass index (BMI), and platelet aggregation in response to PAF, adenosine 5' diphosphate (ADP) and arachidonic acid (AA).

RESULTS

The chosen diet significantly increased the EC(50) values of PAF and ADP to groups A and B (p<0.05). No statistical difference was observed on the EC(50) value of group C. No statistical differences were detected among Cholesterol, LDL-cholesterol, triglycerides, glucose, HBA(1c), BMI, and EC(50) for AA values, for any of the three groups.

CONCLUSIONS

Consumption of a fast-food Mediterranean type diet rich in PAF antagonist improved platelet response of type 2 diabetics and healthy human subjects against thrombotic, inflammatory and proatherogenic factors.

Oxidized phospholipid: POVPC binds to platelet-activating-factor receptor on human macrophages. Implications in atherosclerosis

Atherosclerosis as a chronic inflammatory disease resulting from the imbalance of the pro- and anti-inflammatory factors in the vessel wall. PAF and PAF-like oxidized phospholipids generated upon LDL oxidation in the intima of the arteries may interact with infiltrated monocytes/macrophages and lead to the alteration of gene expression patterns accompanied by an impaired production of chemokines, interleukins and proteolytic and lipolytic enzymes. The aim of this study was to evaluate the binding capacity of the major component of PAF-like oxidized phospholipids, namely the 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphorylcholine (POVPC) to PAF-receptor (PAF-R) on the surface of human monocytes/macrophages and to further characterize the gene expression induced by such binding. We show that, POVPC binds to cultured human macrophages via PAF-R and transduces the signals leading to the intracellular Ca(2+) fluxes and modifies the transcription levels of numerous pro-inflammatory and pro-atherogenic genes. Although a some similarity of the gene expression patterns was observed when macrophages were activated with POVPC versus PAF, we observed that only POVPC treatment induced a several-fold activation of IL-8 gene. In turn, only PAF activated PAF-R, matrix metalloproteinase-13 and 15-lipoxygenase mRNA accumulation. Thus, we suggest, that POVPC signals in mature macrophages only in part through the PAF-R, a part of its effects may involve other receptors.

Phospholipid mediators in the vessel wall: involvement in atherosclerosis

PURPOSE OF REVIEW

This review provides a brief update on the involvement of major phospholipid mediators, with the emphasis on platelet-activating factor and its analogues generated upon the oxidation of lipoproteins in vascular pathology, including atherogenesis.

RECENT FINDINGS

Phospholipid mediators are produced during inflammation by various enzymes, mostly from pre-existing membrane phospholipids, and trigger cellular signaling via G-coupled receptors. A short description of lysophosphatidic acid, lysophosphocholine and sphingosine-1 phosphate receptors and their actions is given, but attention is focused mainly on platelet-activating factor and its analogues. The majority of these mediators participate in leukocyte adhesiveness to the endothelium, leukocyte transmigration into the vessel wall and the subsequent formation of various chemokines leading to foam cell formation and smooth muscle cell proliferation and dedifferentiation. Platelet-activating factor and platelet-activating factor-like phospholipids are degraded in plasma by the lipoprotein-bound enzyme of myeloid origin, PAF-acetylhydrolase, also known as LDL-PLA2. Although the overexpression of PAF-acetylhydrolase shows marked anti-atherogenic properties in animal models, epidemiological data in the Caucasian population have demonstrated that its level might be a risk factor for cardiovascular disease. Recent genetic studies have shown, however, that the A379V polymorphism of this gene, responsible for slightly higher enzymatic activity, exerts a protective effect, probably by modifying the enzyme function towards a less atherogenic form.

SUMMARY

Phospholipid-borne mediators are certainly key players in inflammation and thus in atherosclerosis. The generation of such biologically active molecules is possibly dependent on nutritional habits and the availability of antioxidants, including enzymes protective against oxidative damage, including PAF-acetylhydrolase.

Inhibition of platelet activating factor (PAF)-induced aggregation of human thrombocytes by ginkgolides: considerations on possible bleeding complications after oral intake of Ginkgo biloba extracts

The special Ginkgo biloba leaf extract EGb 761 is marketed for more then two decades. During this time its therapeutic efficacy and favorable safety profile have been proven in numerous clinical trails as well as by postmarketing surveillance in accordance with German drug regulations. During recent years, however, several cases of hemorrhage have been reported to occur in coincidence with the use of Ginkgo products. Although a clear causality between Ginkgo intake and bleeding could not be established, these observations have generally been explained by the platelet-activating factor (PAF)-antagonistic action of ginkgolides, which represent characteristic constituents of Ginkgo extracts. PAF was originally characterized by inducing aggregation and secretion of serotonin and histamine from rabbit platelets. We now confirmed that induction of aggregation of human platelets by PAF requires at least 200 times higher concentration when compared to rabbit cells. Under the chosen experimental conditions, PAF-mediated aggregation of human platelets was half-maximally inhibited by ginkgolide B, A, C and J at concentrations of 2.5, 15.8, 29.8 and 43.5 microg/ml, respectively. These concentrations are generally more than 100 times higher as the peak plasma values measured after oral intake of EGb 761 at recommended doses between 120 and 240 mg. As PAF is a 'weak' platelet activator, which does not appear to be of importance for primary hemostasis, our results rise serious doubts that the PAF antagonistic effect of ginkgolides could be responsible for hemorrhage in patients taking EGb 761.

Reduced PAF-acetylhydrolase activity associated with Lp(a) in patients with coronary artery disease

Lipoprotein(a) [Lp(a)] may be an independent risk factor for coronary artery disease (CAD). Lp(a) is enriched in platelet activating factor acetylhydrolase (PAF-AH), an enzyme which hydrolyzes and inactivates platelet activating factor (PAF) and oxidized phospholipids that are implicated in atherogenesis. We determined the mass and catalytic properties of the Lp(a)-associated PAF-AH in 28 CAD patients in relation to the LDL-associated enzyme ones. Results were then compared to those of 30 control subjects and 16 unrelated patients with primary hypercholesterolemia (Type IIA dyslipidemia) before and after atorvastatin therapy. The mass, the specific activity and kinetic constants of the Lp(a)-associated PAF-AH were significantly lower in CAD patients compared to those of either controls or hypercholesterolemic patients, a phenomenon not observed for LDL-associated PAF-AH. The enzyme specific activity and kinetic constants were significantly increased after removal of apo(a) from Lp(a) by reductive cleavage, which was not found in the control population, suggesting that the apo(a) moiety of Lp(a) from CAD patients may play an important role in the observed lower catalytic efficiency of PAF-AH. The reduced PAF-AH mass and specific activity on Lp(a) is a feature characteristic of this lipoprotein in CAD patients and may lead to a diminished capability of Lp(a) to degrade proinflammatory phospholipids. The consequences of this phenomenon as regards the pathophysiological role of Lp(a) in atherosclerosis remain to be established.

Adenovirus-mediated gene transfer of Lp-PLA2 reduces LDL degradation and foam cell formation in vitro

Oxidation of LDL generates biologically active platelet-activating factor (PAF)-like phospholipid derivatives, which have potent proinflammatory activity. These products are inactivated by lipoprotein-associated phospholipase A2 (Lp-PLA2), an enzyme capable of hydrolyzing PAF-like phospholipids. In this study, we generated an adenovirus (Ad) encoding human Lp-PLA2 and injected 10(8), 10(9), and 10(10) plaque-forming unit doses of Adlp-PLA2 and control AdlacZ intra-arterially into rabbits to achieve overexpression of Lp-PLA2 in liver and in vivo production of Lp-PLA2-enriched LDL. As a result, LDL particles with 3-fold increased Lp-PLA2 activity were produced with the highest virus dose. Increased Lp-PLA2 activity in LDL particles decreased the degradation rate in RAW 264 macrophages after standard in vitro oxidation to 60-80% compared with LDL isolated from LacZ-transduced control rabbits. The decrease was proportional to the virus dose and Lp-PLA2 activity. Lipid accumulation and foam cell formation in RAW 264 macrophages were also decreased when incubated with oxidized LDL containing the highest Lp-PLA2 activity. Inhibition of the Lp-PLA2 activity in the LDL particles led to an increase in lipid accumulation and foam cell formation. It is concluded that increased Lp-PLA2 activity in LDL attenuates foam cell formation and decreases LDL oxidation and subsequent degradation in macrophages.

Association of gene polymorphisms with coronary artery disease in individuals with or without nonfamilial hypercholesterolemia

A substantial proportion of individuals with coronary artery disease (CAD) has concomitant hypercholesterolemia. A large-scale association study was performed to identify separately genes that confer susceptibility to CAD in the absence or presence of nonfamilial hypercholesterolemia. The study population comprised 5248 unrelated Japanese individuals, including 3085 subjects with CAD (2350 men, 735 women) and 2163 controls (1329 men, 834 women). Among all study subjects, 2541 individuals (1688 men, 853 women) had nonfamilial hypercholesterolemia, and 2707 individuals (1991 men, 716 women) did not have this condition. The genotypes for 33 polymorphisms of 27 candidate genes were determined with a fluorescence- or colorimetry-based allele-specific DNA primer-probe assay system. Multivariate logistic regression analysis with adjustment for age, body mass index, and the prevalence of smoking, hypertension, diabetes mellitus, and hyperuricemia revealed that three polymorphisms [994G --> T (Val279Phe) in the platelet-activating factor acetylhydrolase gene, 242C --> T (His72Tyr) in the NADH/NADPH oxidase p22 phox gene, and 1100C --> T in the apolipoprotein C-III gene] were significantly associated with CAD in men with hypercholesterolemia. Genotyping of these three polymorphisms may prove informative for prediction of the genetic risk for CAD in men with nonfamilial hypercholesterolemia.

Structure elucidation of phenolic compounds from red/white wine with antiatherogenic properties

The oxidative modification of low-density lipoproteins (LDL) is supposed to play a critical role in atherogenesis. During this oxidation a potent inflammatory phospholipid mediator named platelet activating factor (PAF) is produced, and it is believed to be the key for the initiation of the inflammation and therefore for the process of atherogenesis. From many studies, it is established that wine has beneficial effects on health, including protection against cardiovascular diseases. According to our point of view, the cardioprotective effect of wine may be attributed partly to the existence of PAF antagonists in red or white wine and partly to the existence of antioxidants that reduce the oxidation of LDL and therefore the production of PAF. In this study, wine compounds that antagonize PAF were isolated and purified via chromatographic procedures, and determined structurally using chemical, enzymatic and spectroscopic methods.

Plasma platelet activating factor-acetylhydrolase (PAF-AH)

The platelet-activating factor-acetylhydrolase (PAF-AH) is an enzyme which catalyzes the hydrolysis of acetyl ester at the sn-2 position of PAF. The family of PAF-AHs consists of two intracellular isoforms (Ib and II), and one secreted isoform (plasma). These PAF-AHs show different biochemical characteristics and molecular structures. Plasma PAF-AH and intracellular isoform, II degrade not only PAF but also oxidatively fragmented phospholipids with potent biological activities. Among these PAF-AHs, plasma PAF-AH has been the target of many clinical studies in inflammatory diseases, such as asthma, sepsis, and vascular diseases, because the plasma PAF-AH activity in the patients with these diseases is altered when compared with normal individuals. Finding a genetic deficiency in the plasma PAF-AH opened the gate in elucidating the protecting role of this enzyme in inflammatory diseases. The most common loss-of-function mutation, V279F, is found in more than 30% of Japanese subjects (4% homozygous, 27% heterozygous). This single nucleotide polymorphism in plasma PAF-AH and the resulting enzymatic deficiency is thought to be a genetic risk factor in various inflammatory diseases in Japanese subjects. Administration of recombinant plasma PAF-AH or transfer of the plasma PAF-AH gene improves pathology in animal models. Therefore, substitution of plasma PAF-AH would be an effective in the treatment of the patients with the inflammatory diseases and a novel clinical approach. In addition, the detection of polymorphisms in the plasma PAF-AH gene and abnormalities in enzyme activity would be beneficial in the diagnosis of the inflammatory diseases.

Reduction in the extent of atherosclerosis in apolipoprotein E-deficient mice induced by electroporation-mediated transfer of the human plasma platelet-activating factor acetylhydrolase gene into skeletal muscle

The effect of increasing the activity of plasma platelet-activating factor (PAF) acetylhydrolase (AH) (PAF-AH) on the progression of atherosclerosis in apolipoprotein E-deficient (apoE(-/-)) mice was examined by gene delivery to skeletal muscle. The expression vector pcDNA3.1 containing either human PAF-AH cDNA (pcDNA/PAF-AH) or green fluorescent protein cDNA (pcDNA/GFP) was introduced into the skeletal muscle of both hind legs of 6-week-old apoE(-/-) mice by electroporation. The activity of PAH-AH in plasma was significantly increased 4-16 weeks after electroporation of apoE(-/-) mice with 120 microg of pcDNA/PAF-AH; the maximal (2.5-fold) increase was apparent after 8 weeks. The mean thickness of the aortic wall, determined by 160 measurements in each mouse, was significantly reduced in apoE(-/-) mice 8-16 weeks after exposure to pcDNA/PAF-AH compared with that in corresponding control animals that received pcDNA/GFP. These results suggest that the electrotransfer of the plasma PAF-AH gene to skeletal muscle reduces the extent of atherosclerosis in apoE(-/-) mice.

Biologically active lipids with antiatherogenic properties from white wine and must

Wine can be considered an integral part of the Mediterranean diet. Evidence from epidemiological and experimental studies suggests a protective effect against the development of coronary heart disease with moderate consumption of wine and especially red wine. The exact nature of the protective effect remains to be established. However, mechanisms including low-density lipoproteins oxidation, inhibition of platelet aggregation, modification of eicosanoid metabolism, and endothelium-dependent relaxation of blood vessels are recognized as contributory. In this study, a new approach has been examined, based on previous reports that platelet-activating factor (PAF) is involved in atherogenesis. An attempt was made to detect key components in wine/must that through inhibition of PAF action may contribute to the protective role of white wine/must against atherosclerosis. More specifically, polar lipids from four wines and three musts were fractionated by thin-layer chromatography, and fractions were tested in vitro for their ability to inhibit PAF and thrombin-induced washed rabbit platelet aggregation and/or to cause platelet aggregation. On the basis of the above results, a white wine from the principal Greek grape Rompola and its respective must with and without extra yeast were chosen for further high-performance liquid chromatography separation. A significant number of biological active lipids were detected, and structural data for the most active lipids are provided.

Antithrombotic lipid minor constituents from vegetable oils. Comparison between olive oils and others

Many epidemiological studies suggest that vegetable oils and especially olive oil present a protective effect against atherosclerosis. In this study, total lipids (TL) of Greek olive oils and seed oils of four kinds, namely, soybean, corn, sunflower, and sesame oil, were separated into total polar lipids (TPL) and total neutral lipids (TNL) via a novel extraction procedure. TPL and TNL of olive oil were fractionated by HPLC for further study. Each lipid fraction from HPLC separation along with TL, TPL, and TNL lipid samples from oils were tested in vitro for their capacity to induce or to inhibit washed rabbit platelet aggregation. Comparison between olive and seed oils supports the superiority of olive oil as high levels of platelet activating factor (PAF) antagonists have been detected, mainly in TPL. In addition, the structure of the most active fraction from olive oil was elucidated, as a glycerol-glycolipid. Because it has already been reported that PAF plays a pivotal role in atherogenesis, the existence of PAF agonists and antagonists in vegetable oils may explain their protective role against atherosclerosis.

Biological activity of total lipids from red and white wine/must

Wine is an essential component of the Mediterranean diet, and it is thought to exert a protective effect against coronary heart disease. Although many efforts have been made to determine the protective compounds in wines, their exact nature and how they are involved in the protection mechanisms are still unclear. In this study, total lipids, total polar lipids, and total neutral lipids of five wines and three musts were tested in vitro for their ability to induce washed rabbit platelet aggregation and/or to inhibit platelet activating factor (PAF) induced aggregation. The results showed that the biological activity of wine/must total lipids can be attributed mainly to total polar lipids. In the red wine Cabernet Sauvignon, we fractionated total neutral lipids, total polar lipids, and pigments by HPLC. Each fraction was tested in vitro for its biological activity. Structural data of the most active fractions, based on biological, chemical, and spectral methods, are also presented.

Oxidized low density lipoproteins downregulate LPS-induced platelet-activating factor receptor expression in human monocyte-derived macrophages: implications for LPS-induced nuclear factor-kappaB binding activity

Monocytes/macrophages play a key role in atherogenesis due to their inflammatory properties including formation of lipid mediators such as platelet-activating-factor (PAF). We investigated the effect of oxidized low-density lipoprotein (oxLDL) on lipopolysaccharide (LPS)-induced PAF receptor (PAF-R) expression in human macrophages and the implication of the nuclear factor (NF)-kappaB in this regulation. LPS-treatment (1 microg.mL(-1)) of macrophages increased PAF binding and PAF-R mRNA expression by 56% (P < 0.05) and twofold (P < 0.01), respectively. In contrast, highly oxidized low-density lipoprotein [ox24hLDL; 100 microg.mL(-1); thiobarbituric acid reacting substances: 31 +/- 3 nmol equiv. malondialdehyde (MDA).mg protein LDL-1] diminished PAF-R expression (-69%; P < 0.05) and mRNA level (- 45%; P < 0.01). LPS pretreatment induced the activated form of p65 in the nuclear compartment of macrophages (detected by Western blotting) and NF-kappaB binding activity (by electrophoretic mobility shift assay). Treatment of macrophages with ox24hLDL suppressed the LPS-induced binding of NF-kappaB to DNA. In addition, treatment of macrophages with lysophosphatidylcholine (2 and 10 microM), a major component of oxLDL, inhibited the LPS-induced NF-kappaB binding to DNA and reduced PAF binding by 30 and 70%, respectively. In conclusion, oxLDL may downregulate PAF-R expression in human macrophages by inhibiting LPS-induced NF-kappaB binding to DNA.

Is tranexamic acid safe in patients undergoing coronary endarterectomy?

BACKGROUND

Patients undergoing coronary endarterectomy during coronary artery bypass grafting (CABG) are at increased risk of perioperative myocardial infarction due to coronary intimal disruption. Data assessing the safety of the antifibrinolytic drug tranexamic acid (TA) in patients undergoing this procedure are lacking.

METHODS

From September 1997 to December 1999, 221 patients underwent nonemergency primary CABG with endarterectomy of the right coronary artery alone in 149, the left anterior descending in 35, or both right and left anterior descending in 27. TA was administered intraoperatively to 87 patients (TA group: average total dose 62 +/- 4.4 mg/kg; range 20 to 109 mg/kg), and was not administered to 134 patients (No TA group).

RESULTS

The patient characteristics of the 2 groups were similar. In-hospital mortality consisted of 2 patients in the TA group and 4 patients in the No TA group. Perioperative myocardial infarction rates were 2% and 5% in the TA and No TA groups, respectively (p = 0.49). The relative risk for any type of perioperative cardiac ischemic event in the TA group versus the No TA group was 0.77 (95% CI; 0.4, 1.2). Patients in the TA group had a significant reduction in postoperative chest tube drainage (685 versus 894 mL in the TA versus No TA groups, respectively) and in the use of fresh-frozen plasma (p = 0.03).

CONCLUSIONS

These results suggest that the clinical effectiveness of tranexamic acid in reducing postoperative blood loss in patients undergoing coronary endarterectomy is not associated with a higher incidence of myocardial ischemia-related complications.

Oxidized low-density lipoprotein and peroxisome-proliferator-activated receptor alpha down-regulate platelet-activating-factor receptor expression in human macrophages

Regulation of the expression of platelet-activating factor (PAF) receptor by atherogenic lipoproteins might contribute to atherogenesis. We show that progressive oxidation of low-density lipoprotein (LDL) gradually inhibits PAF receptor expression on the macrophage cell surface. We tested the effect of oxidized LDL (oxLDL) on PAF receptor expression in human monocytes that do not contain peroxisome-proliferator-activated receptor gamma (PPARgamma), a nuclear receptor activated by oxLDL. OxLDL decreased by 50% (P < or = 0.001) and by 29% (P < or = 0.05) the binding of PAF and the expression of PAF receptor mRNA respectively. Next we demonstrated that progressive oxidation of LDLs significantly activated PPARalpha-dependent transcription in transfected mouse aortic endothelial cells. Finally we demonstrated, in mature macrophages, that fenofibrate (20 microM), a specific PPARalpha agonist, but not the specific PPARgamma agonist BRL49653 (20 nM), significantly decreased both PAF binding and PAF receptor mRNA expression, by 65% and 40% (P < or = 0.001) respectively. Additionally, another PPARalpha agonist, Wy14,643, decreased PAF receptor promoter activity by 70% (P < or = 0.05) in transfected THP-1 cells, suggesting the involvement of the proximal promoter region (-980 to -500) containing a series of four nuclear factor (NF)-kappaB motifs. Thus PPARalpha might be involved in the down-regulation of PAF receptor gene expression by oxLDLs in human monocytes/macrophages. The oxidation of one or more lipid components of LDLs might result in the formation of natural activators of PPARalpha. It is hypothesized that such activators might modulate inflammation and apoptosis upon atherogenesis by decreasing the expression of PAF receptor.

Role of platelet-activating factor in cardiovascular pathophysiology

Platelet-activating factor (PAF) is a phospholipid mediator that belongs to a family of biologically active, structurally related alkyl phosphoglycerides. PAF acts via a specific receptor that is coupled with a G protein, which activates a phosphatidylinositol-specific phospholipase C. In this review we focus on the aspects that are more relevant for the cell biology of the cardiovascular system. The in vitro studies provided evidence for a role of PAF both as intercellular and intracellular messenger involved in cell-to-cell communication. In the cardiovascular system, PAF may have a role in embryogenesis because it stimulates endothelial cell migration and angiogenesis and may affect cardiac function because it exhibits mechanical and electrophysiological actions on cardiomyocytes. Moreover, PAF may contribute to modulation of blood pressure mainly by affecting the renal vascular circulation. In pathological conditions, PAF has been involved in the hypotension and cardiac dysfunctions occurring in various cardiovascular stress situations such as cardiac anaphylaxis and hemorrhagic, traumatic, and septic shock syndromes. In addition, experimental studies indicate that PAF has a critical role in the development of myocardial ischemia-reperfusion injury. Indeed, PAF cooperates in the recruitment of leukocytes in inflamed tissue by promoting adhesion to the endothelium and extravascular transmigration of leukocytes. The finding that human heart can produce PAF, expresses PAF receptor, and is sensitive to the negative inotropic action of PAF suggests that this mediator may have a role also in human cardiovascular pathophysiology.

Correlations between plasma platelet-activating factor acetylhydrolase (PAF-AH) activity and PAF-AH genotype, age, and atherosclerosis in a Japanese population

Platelet-activating factor acetylhydrolase (PAF-AH), a plasma enzyme that hydrolyzes PAF and oxidized phospholipids, is thought to be involved in protecting cells against oxidative stress. A G(994) (M allele)-->T (m allele) mutation in the plasma PAF-AH gene, which results in a Val(279)-->Phe substitution in the mature protein, leads to a loss of catalytic activity. To elucidate the relationships among PAF-AH enzyme activity, genotype, age, and atherosclerosis, we assayed these parameters in a large Japanese population (n=3932) that consisted of three groups; a control group (healthy individuals; n=1684), a risk-factor group (individuals having at least one conventional risk factor for atherosclerosis; n=1398), and a diseased group (patients who had suffered a myocardial infarction or stroke; n=850). We observed a significantly increased frequency of the m allele in the diseased group as compared with the control or risk-factor groups. Plasma PAF-AH activity increased significantly with age in women in the control group with the MM and Mm genotypes, and in men in the control group with the MM genotype, but not in men with the Mm genotype. In both the risk-factor and diseased groups, however, no correlation was observed between plasma PAF-AH activity and age in subjects with either genotype. These results suggest that in individuals with the MM genotype, plasma PAF-AH activity may be increased in response to stresses induced by PAF and/or oxidized phospholipids that might accumulate with age, but that this response is not evident or reduced in healthy individuals with the m allele, or in subjects with atherosclerotic disease, or having risk factors. Together with our previous findings, the G(994)-->T mutation in the PAF-AH gene may be one of the genetic determinants for atherosclerotic disease in the Japanese population.

Coronary microembolization--its role in acute coronary syndromes and interventions

The diagnosis coronary artery disease is classically based on patient's symptoms and morphology, as analyzed by angiography. The importance of risk factors for the development of coronary atherosclerosis and disturbance of coronary vasomotion is clearly established. However, microembolization of the coronary circulation has also to be taken into account. Microembolization may occur as a single or as multiple, repetitive events, and it may induce inflammatory responses. Spontaneous microembolization may occur, when the fibrous cap of an atheroma or fibroatheroma (Stary i.v. and Va) ruptures and the lipid pool with or without additional thrombus formation is washed out of the atheroma into the microcirculation. Such events with progressive thrombus formation are known as cyclic flow variations. Plaque rupture occurs more frequently than previously assumed, i.e. in 9% of patients without known heart disease suffering a traffic accident and in 22% of patients with hypertension and diabetes. Also, in patients dying from sudden death microembolization is frequently found. Patients with stable and unstable angina show not only signs of coronary plaque rupture and thrombus formation, but also microemboli and microinfarcts, the only difference between those with stable and unstable angina being the number of events. Appreciation of microembolization may help to better understand the pathogenesis of ischemic cardiomyopathy, diabetic cardiomyopathy and acute coronary syndromes, in particular in patients with normal coronary angiograms, but plaque rupture detected by intravascular ultrasound. Also, the benefit from glycoprotein IIb/IIIa receptor antagonist is better understood, when not only the prevention of thrombus formation in the epicardial atherosclerotic plaque, but also that of microemboli is taken into account. Microembolization also occurs during PTCA, inducing elevations of troponin T and I and elevations of the ST segment in the EKG. Elevated baseline coronary blood flow velocity, as a potential consequence of reactive hyperemia in myocardium surrounding areas of microembolization, is more frequent in patients with high frequency rotablation than in patients with stenting and in patients with PTCA. The hypothesis of iafrogenic microembolization during coronary interventions is now supported by the use of aspiration and filtration devices, where particles with a size of up to 700 microns have been retrieved. In the experiment, microembolization is characterized by perfusion-contraction mismatch, as the proportionate reduction of flow and function seen with an epicardial stenosis is lost and replaced by contractile dysfunction in the absence of reduced flow. The analysis of the coronary microcirculation, in addition to that of the morphology and function of epicardial coronary arteries, and in particular appreciation of the concept of microembolization will further improve the understanding of the pathophysiology and clinical symptoms of coronary artery disease.

Protection against ventricular fibrillation by the PAF antagonist, BN-50739, involves an ischaemia-selective mechanism

The platelet-activating factor (PAF) antagonist BN-50739 can suppress certain cardiac arrhythmias. PAF is released from ischaemic myocardium and may contribute to initiation of ischaemia-induced ventricular fibrillation (VF). In this study we characterised the action of BN-50739 on left regional ischaemia-induced VF and examined whether effects are mediated within the ischaemic territory, or are nonspecific. In rat isolated Langendorff perfused hearts (n = 12/group), 10 microM BN-50739 reduced the incidence of ischaemia-induced VF from 75 to 17% (p<0.05). This was accompanied by QT widening and an increase in coronary flow. Heart rate and PR interval were not affected by the drug. In separate studies, isolated rat hearts were perfused by using a dual-lumen tube that allows independent delivery of solution to the left and right coronary beds. Successful regional localisation of drug delivery was confirmed by observing, before ischaemia, a regionally selective increase in coronary flow (p<0.05), measured by using two in-line flow meters. Protection against ischaemia-induced VF (p<0.05) was achieved by pretreatment with BN-50739, delivered selectively and entrapped within the involved region, but not when the drug was delivered to the uninvolved region. In conclusion, BN-50739 protects against ischaemia-induced VF by eliciting a pharmacologic action in the involved (ischaemic) myocardium. This supports the hypothesis that BN-50739 suppresses an arrhythmogenic effect of endogenous PAF released within the ischaemic tissue.

Roles of plasma platelet-activating factor acetylhydrolase in allergic, inflammatory, and atherosclerotic diseases

Platelet-activating factor (PAF) mediates a variety of physiologic and pathologic events by activating platelets, neutrophils, monocytes, macrophages, and smooth muscle cells. A strongly oxidizing environment induces fragmentation of the polyunsaturated fatty acids of membrane phospholipids, and the resulting oxidized phospholipids are structurally similar to PAF and mimic its biologic actions. The effects of PAF and oxidized phospholipids are abolished by hydrolysis of the sn-2 residue, a reaction catalyzed by PAF acetylhydrolase. Plasma and intracellular forms of PAF acetylhydrolase have been purified and characterized. The plasma form binds with high affinity to lipoproteins in plasma. Furthermore, changes in the activity of this enzyme are associated with various human diseases and animal models of human pathology, suggesting that it may play important roles in their pathogenesis. Studies that have defined the properties of this enzyme and its roles in physiologic and pathologic processes are reviewed. Such studies have provided insight into the functions of PAF and oxidized phospholipids as well as into the etiology of allergic, inflammatory, and atherosclerotic diseases.

Identification of the G994--> T missense in exon 9 of the plasma platelet-activating factor acetylhydrolase gene as an independent risk factor for coronary artery disease in Japanese men

Platelet-activating factor (PAF) acetylhydrolase may play important roles in the pathophysiology of thrombosis and atherosclerosis related to its catalytic action in the degradation of PAF and oxidized phospholipids. A missense mutation (G--> T transversion at nucleotide 994) in the plasma PAF acetylhydrolase gene results in a Val--> Phe substitution at amino acid 279 of the mature protein and a consequent loss of catalytic activity. However, the role of a deficiency or low activity of this enzyme caused by the missense mutation in the etiology of coronary artery disease (CAD) has not been determined. The relation between this mutation and the incidence of CAD in the Japanese population is investigated herein. The genotype of plasma PAF acetylhydrolase (MM, normal; Mm, heterozygote; and mm, deficient homozygote) was determined with a polymerase chain reaction (PCR) assay for 454 patients with myocardial infarction (MI) and 602 control subjects. The frequency of the m allele was significantly higher in male patients with MI (odds ratio, 1.8) than in controls, an association that was more marked in a low-risk subgroup (odds ratio, 2.3). In contrast, the m allele was not associated with MI in women. These results indicate that the G994--> T missense mutation in exon 9 of the plasma PAF acetylhydrolase gene is an independent risk factor for CAD in Japanese men, especially low-risk individuals, but not in women.

Expression of the PAF receptor in human monocyte-derived macrophages is downregulated by oxidized LDL: relevance to the inflammatory phase of atherogenesis

Human monocyte-derived macrophages play a major role in the initiation and progression of atherosclerotic lesions as a result of the production of a wide spectrum of proinflammatory and prothrombotic factors. Among such factors is a potent inflammatory phospholipid, platelet-activating factor (PAF), which is produced after macrophage activation. Because the cells involved in PAF biosynthesis are typically targets for the bioactions of PAF via specific cell surface receptors, we evaluated the expression of the PAF receptor in human monocyte-derived macrophages. Oxidized LDL (oxLDL) exerts multiple cellular effects that enhance lesion progression; we therefore investigated the potential modulation of expression of the macrophage PAF receptor by oxLDL. [3H]PAF bound to adherent human macrophages with a K(d) of 2.1 nmol/L and a B(max) of 19 fmol/10(6) cells; approximately 5300 binding sites per cell were detected. OxLDL (100 microg protein per milliliter) induced a twofold decrease in cellular PAF binding after 3 hours at 37 degrees C. Analysis of macrophage mRNA by reverse transcription-polymerase chain reaction (RT-PCR) revealed two forms corresponding to the PAF receptor, of which the leukocyte type (type 1 promoter) predominated. Expression of PAF receptor mRNA, evaluated by quantitative RT-PCR using an actin or a GAPDH mimic, was progressively reduced (up to 70%) by oxLDL up to 6 hours and remained low for at least 24 hours. Such downregulation was reversible after incubation of the cells for 24 hours in oxLDL-free medium. Addition of forskolin (3 micromol/L) or dibutyryl cAMP (1 mmol/L) to macrophage cultures reproduced the oxLDL-mediated inhibition of PAF receptor expression; carbamyl PAF reduced PAF binding and PAF mRNA to a similar degree (approximately 50%). These data demonstrate that atherogenic oxLDL downregulates the expression of both cellular PAF receptors and PAF receptor mRNA in macrophages, consistent with both a diminished bioresponse to PAF and decreased cell motility. Such diminished bioresponse to a powerful antacoid reflects the suppression of an acute inflammatory reaction, thereby leading to chronic, low-level inflammation, such as that characteristic of fatty streaks and more advanced atherosclerotic plaques.

Phagocytic activation induces formation of platelet-activating factor in human monocyte-derived macrophages and in macrophage-derived foam cells. Relevance to the inflammatory reaction in atherogenesis

Monocyte-derived macrophages and macrophage-derived foam cells in arterial tissue may undergo phagocytic activation and thereby contribute to an inflammatory reaction. We have investigated the effect of phagocytic activation on the formation of platelet-activating factor (1-0-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF-acether, PAF), a proinflammatory phospholipid, in human monocyte-derived macrophages (macrophages) and in cholesterol-loaded macrophage foam cells (foam cells). Adherent human monocyte-derived macrophages were transformed into foam cells upon incubation with acetylated low-density lipoproteins (Ac-LDL). Such foam cells characteristically displayed a markedly increased content of cholesteryl esters compared with macrophages (4.3 +/- 1.3 microgram/microgram DNA and 0.2 +/- 0.3 microgram/microgram DNA, n = 5, respectively). After phagocytic stimulation with serum-opsonized zymosan (OPZ), both macrophages and foam cells synthesized PAF transiently with maximal production (0.5-1.1 pmol PAF/microgram DNA, n = 5, corresponding to 4.0-8.8 pmol PAF/10(6) cells, as assessed by bioassay) occurring approximately 15 min after stimulation. A major fraction of the synthesized PAF remained cell-associated; such PAF was composed mainly of the hexadecyl (16:0 PAF, approximately 75%) and the octadecenyl (18:1 PAF) species and of trace amounts of octadecyl (18:0 PAF), as assessed by reverse-phase liquid chromatography. Addition of exogenous 16:0 lyso-PAF alone triggered PAF formation (0.9-1.7 pmol PAF/microgram DNA, after 15 min of cellular stimulation); simultaneous cellular stimulation with OPZ and 16:0 lyso-PAF increased PAF formation in an additive manner. Acetyltransferase, the enzyme which acetylates the precursor lyso-PAF and transforms it into PAF, displayed elevated activity both in macrophages and in foam cells, attaining 83-240 pmol PAF formed per min per mg DNA (n = 4); such elevated activity was not increased by OPZ-stimulation. The activity of acetylhydrolase, the PAF-degrading enzyme, was similar in macrophages and in foam cells, and varied between 120 pmol and 320 pmol PAF degraded per min per mg DNA (n = 5). Cell-associated acetylhydrolase activity was increased significantly by 40+/-15 % (P < 0.003, n = 5) after 15 - 30 min of activation with OPZ compared with non-stimulated cells and may account for the rapid decrease in cellular PAF content observed approximately 30 min after stimulation. These studies have established that metabolism of PAF in foam cells closely resembles that in macrophages, and thus PAF metabolism is largely independent of cellular cholesterol content. Moreover our data are consistent with the hypothesis that both macrophages and macrophage-derived foam cells upon phagocytic-activation constitute a significant transient source of PAF at inflammatory sites in the arterial intima where this phospholipidic mediator may exert potent proatherogenic and prothrombotic effects.