Increased levels of blood platelet-activating factor (PAF) and PAF-like lipids in patients with ischemic stroke

Associations between healthy food groups and platelet-activating factor, lipoprotein-associated phospholipase A2 and C-reactive protein: a cross-sectional study

PURPOSE

To investigate the association between pro-inflammatory markers platelet-activating factor (PAF), lipoprotein-associated phospholipase A2 (Lp-PLA2), hsCRP, and intake of core food groups including fruit, cruciferous and other vegetables, grains, meat and poultry, fish and seafood, nuts and legumes, and dairy.

METHODS

A cross-sectional study was conducted. 100 adults (49 ± 13 years, 31% male) with variable cardiovascular disease risk were recruited. Data were collected in 2021 and 2022. Fasting PAF, Lp-PLA2 activity, hsCRP and usual dietary intake (via a validated food frequency questionnaire) were measured. Intake of foods were converted into serves and classified into food groups. Correlations and multiple regressions were performed with adjustment for confounders.

RESULTS

A one-serve increase in cruciferous vegetables per day was associated with 20-24% lower PAF levels. An increase of one serve per day of nuts and legumes was associated with 40% lower hsCRP levels. There were small correlations with PAF and Lp-PLA2 and cheese, however, these were not significant at the Bonferroni-adjusted P < 0.005 level.

CONCLUSION

The lack of associations between PAF and Lp-PLA2 and other healthy foods may be due to confounding by COVID-19 infection and vaccination programs which prevents any firm conclusion on the relationship between PAF, Lp-PLA2 and food groups. Future research should aim to examine the relationship with these novel markers and healthy food groups in a non-pandemic setting.

The association between dietary quality scores with C-reactive protein and novel biomarkers of inflammation platelet-activating factor and lipoprotein-associated phospholipase A2: a cross-sectional study

Healthy dietary patterns are associated with lower inflammation and cardiovascular disease (CVD) risk and adherence can be measured using diet quality scores. Inflammation is traditionally measured with C-reactive protein (hsCRP), however there is interest in novel pro-inflammatory markers platelet-activating factor (PAF) and lipoprotein-associated phospholipase A2 (Lp-PLA2) that are specifically involved in endothelial dysfunction and inflammation. This cross-sectional study investigated the association between PAF, Lp-PLA2, hsCRP, and six diet scores. One hundred adults (49 ± 13 years, 31% male) with variable CVD risk were recruited. Fasting PAF, Lp-PLA2 and hsCRP and usual dietary intake were measured. Adherence to Dietary Approaches to Stop Hypertension (DASH), Dairy-adjusted DASH, Vegetarian Lifestyle Index, Healthy Eating Index for Australians (HEIFA), Mediterranean Diet Adherence Screener (MEDAS) and PREDIMED-Plus (erMedDiet) scores were calculated. Correlations and multiple regressions were performed. hsCRP, but not PAF, independently correlated with several diet scores. Lp-PLA2 independently correlated with Vegetarian Lifestyle Index only in unadjusted models. A one-point increase in adherence to the DASH Index, the Dairy-adjusted DASH Index and the Vegetarian Lifestyle Index was associated with a 30%, 30%, and 33% reduction in hsCRP levels, respectively. Smaller effects were seen with the other diet scores with a one-point increase in adherence resulting in a 19%, 22% and 16% reduction in hsCRP with HEIFA, MEDAS, erMedDiet scores, respectively. The lack of stronger associations between the novel markers of inflammation and diet scores may be due to confounding by COVID-19 infection and vaccination programs, which prevents any firm conclusion on the relationship between PAF, Lp-PLA2 and healthy dietary patterns. Future research should aim to examine the relationship with these novel markers and healthy dietary patterns in a non-pandemic setting.

Chronic inflammation, neuroglial dysfunction, and plasmalogen deficiency as a new pathobiological hypothesis addressing the overlap between post-COVID-19 symptoms and myalgic encephalomyelitis/chronic fatigue syndrome

After five waves of coronavirus disease 2019 (COVID-19) outbreaks, it has been recognized that a significant portion of the affected individuals developed long-term debilitating symptoms marked by chronic fatigue, cognitive difficulties ("brain fog"), post-exertional malaise, and autonomic dysfunction. The onset, progression, and clinical presentation of this condition, generically named post-COVID-19 syndrome, overlap significantly with another enigmatic condition, referred to as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Several pathobiological mechanisms have been proposed for ME/CFS, including redox imbalance, systemic and central nervous system inflammation, and mitochondrial dysfunction. Chronic inflammation and glial pathological reactivity are common hallmarks of several neurodegenerative and neuropsychiatric disorders and have been consistently associated with reduced central and peripheral levels of plasmalogens, one of the major phospholipid components of cell membranes with several homeostatic functions. Of great interest, recent evidence revealed a significant reduction of plasmalogen contents, biosynthesis, and metabolism in ME/CFS and acute COVID-19, with a strong association to symptom severity and other relevant clinical outcomes. These bioactive lipids have increasingly attracted attention due to their reduced levels representing a common pathophysiological manifestation between several disorders associated with aging and chronic inflammation. However, alterations in plasmalogen levels or their lipidic metabolism have not yet been examined in individuals suffering from post-COVID-19 symptoms. Here, we proposed a pathobiological model for post-COVID-19 and ME/CFS based on their common inflammation and dysfunctional glial reactivity, and highlighted the emerging implications of plasmalogen deficiency in the underlying mechanisms. Along with the promising outcomes of plasmalogen replacement therapy (PRT) for various neurodegenerative/neuropsychiatric disorders, we sought to propose PRT as a simple, effective, and safe strategy for the potential relief of the debilitating symptoms associated with ME/CFS and post-COVID-19 syndrome.

Interrelationships among platelet-activating factor and lipoprotein-associated phospholipase A2 activity and traditional cardiovascular risk factors

Traditionally cardiovascular disease (CVD) risk has been assessed through blood lipids and inflammatory marker C-reactive protein (hsCRP). Recent clinical interest in novel pro-inflammatory markers platelet-activating factor (PAF) and lipoprotein-associated phospholipase A₂ (Lp-PLA₂ ) recognizes that vascular damage can exist in the absence of traditional risk factors. This cross-sectional study investigated the potential relationship between circulating PAF, Lp-PLA₂ , hsCRP, and traditional risk factors for CVD. One hundred adults (49 ± 13 years, 31% male) with variable CVD risk were recruited. Fasting inflammatory markers PAF, Lp-PLA₂ and hsCRP and total, high-density lipoprotein (HDL), low-density lipoprotein (LDL) cholesterol, and triglycerides were measured. Blood pressure, body mass index, and waist circumference were measured. Medical and physical activity data were self-reported. Linear and multiple regressions were performed. PAF, Lp-PLA₂ , and hsCRP independently correlated with several CVD risk factors. PAF was correlated significantly with risk factors in an unexpected way; there was a medium positive correlation between PAF and HDL cholesterol (r = 0.394, p < 0.001) and medium negative correlations with Total:HDL cholesterol; (r = -0.436, p < 0.001) systolic blood pressure; (r = -0.307, p = 0.001); BMI (r = -0.381, p < 0.001); and waist circumference (r = -0.404, p < 0.001). There were large positive correlations between Lp-PLA₂ and LDL (r = 0.525, p < 0.001) and non-HDL cholesterol (r = 0.508, p < 0.001). There were large positive correlations between hsCRP and Total:HDL cholesterol (r = 0.524, p < 0.001); BMI (r = 0.668, p < 0.001); and waist circumference (r = 0.676, p < 0.001). PAF, Lp-PLA₂ , and hsCRP are implicated in the pathophysiology of inflammation in CVD; however, the relationships between each marker and traditional risk factors were different suggesting they may be involved in different atherogenic pathways.

An Integrated Metabolomic Screening Platform Discovers the Potential Biomarkers of Ischemic Stroke and Reveals the Protective Effect and Mechanism of Folic Acid

Folic acid has a protective effect against ischemic stroke. However, the protective pharmacological mechanism remains unclear. The aim of this study is to explore the protective effect of folic acid on ischemic stroke animals by an integrated metabolomic biomarker screening platform. Based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC/MS) coupled with multivariate data analysis, the changes in metabolites and pathways were characterized. We found that the metabolic alteration involved a total of 37 metabolites, of which 26 biomarkers such as γ-aminobutyric acid, lysine, glutamate, ribose, and valine can be regulated by folic acid via metabolic pathways of amino acid metabolism, carbohydrate metabolism, fatty acid metabolism, citrate cycle, and pyruvate metabolism, which may be the potential therapeutic targets of folic acid against ischemic stroke. Folic acid as an emerging potential natural anti-fibrosis agent has significant activity in protecting against middle cerebral artery occlusion-induced rat ischemic stroke model by delaying pathological development, reversing the metabolic biomarkers, and mainly regulating the perturbation in amino acid metabolism, carbohydrate metabolism, fatty acid metabolism, citrate cycle, and pyruvate metabolism. It also showed that the integrated metabolic biomarker screening platform could provide a better understanding of the therapeutic effect and mechanism of drugs.

The association between dietary patterns and the novel inflammatory markers platelet-activating factor and lipoprotein-associated phospholipase A2: a systematic review

CONTEXT

Atherosclerosis is a disease of chronic inflammation. Recent research has identified 2 novel inflammatory biomarkers: platelet-activating factor (PAF) and lipoprotein-associated phospholipase A2 (Lp-PLA2). Diet has been proposed as a mediator of inflammation, but to date, the focus for these novel biomarkers has been on individual foods and nutrients rather than overall dietary patterns.

OBJECTIVE

To systematically review the literature on the association between dietary patterns and PAF and Lp-PLA2.

DATA SOURCES

The PubMed, Embase, CINAHL, and Cochrane CENTRAL literature databases were searched.

DATA ANALYSIS

Study quality was evaluated using the Quality Criteria Checklist. Sixteen studies (n = 4 observational and n = 12 interventional) were included and assessed for associations between dietary patterns and PAF and Lp-PLA2.

CONCLUSION

Study quality varied from neutral (n = 10) to positive (n = 6). Mediterranean, heart healthy, and vegetarian dietary patterns were associated with improved levels of PAF and Lp-PLA2. Conversely, Western dietary patterns were less favorable. A range of well-established, healthier dietary patterns may lower inflammation and the risk of atherosclerosis. More well-designed studies are needed to confirm these findings and identify other dietary patterns that improve inflammation.

Lyso-PAF, a biologically inactive phospholipid, contributes to RAF1 activation

Phospholipase A2, group VII (PLA2G7) is widely recognized as a secreted, lipoprotein-associated PLA2 in plasma that converts phospholipid platelet-activating factor (PAF) to a biologically inactive product Lyso-PAF during inflammatory response. We report that intracellular PLA2G7 is selectively important for cell proliferation and tumor growth potential of melanoma cells expressing mutant NRAS, but not cells expressing BRAF V600E. Mechanistically, PLA2G7 signals through its product Lyso-PAF to contribute to RAF1 activation by mutant NRAS, which is bypassed by BRAF V600E. Intracellular Lyso-PAF promotes p21-activated kinase 2 (PAK2) activation by binding to its catalytic domain and altering ATP kinetics, while PAK2 significantly contributes to S338-phosphorylation of RAF1 in addition to PAK1. Furthermore, the PLA2G7-PAK2 axis is also required for full activation of RAF1 in cells stimulated by epidermal growth factor (EGF) or cancer cells expressing mutant KRAS. Thus, PLA2G7 and Lyso-PAF exhibit intracellular signaling functions as key elements of RAS-RAF1 signaling.

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.

New Insights Into the Pathologic Roles of the Platelet-Activating Factor System

Described almost 50 years ago, the glycerophosphocholine lipid mediator Platelet-activating factor (PAF) has been implicated in many pathologic processes. Indeed, elevated levels of PAF can be measured in response to almost every type of pathology involving inflammation and cell damage/death. In this review, we provide evidence for PAF involvement in pathologic processes, with focus on cancer, the nervous system, and in photobiology. Importantly, recent insights into how PAF can generate and travel via bioactive extracellular vesicles such as microvesicle particles (MVP) are presented. What appears to be emerging from diverse pathologies in different organ systems is a common theme where pro-oxidative stressors generate oxidized glycerophosphocholines with PAF agonistic effects, which then trigger more enzymatic PAF synthesis via the PAF receptor. A downstream consequence of PAF receptor activation is the generation and release of MVP which provide a mechanism to transmit PAF as well as other bioactive agents. The knowledge gaps which when addressed could result in novel therapeutic strategies are also discussed. Taken together, an enhanced understanding of the PAF family of lipid mediators is essential in our improved comprehension of the relationship amongst the diverse cutaneous, cancerous, neurologic and systemic pathologic processes.

Untargeted metabolomics predicts the functional outcome of ischemic stroke

BACKGROUND/PURPOSE

Metabolites in blood have been found associated with the occurrence of vascular diseases, but its role in the functional recovery of stroke is unclear. The aim of this study is to investigate whether the untargeted metabolomics at the acute stage of ischemic stroke is able to predict functional recovery.

METHODS

One hundred and fifty patients with acute ischemic stroke were recruited and followed up for 3 months. Fasting blood samples within 7 days of stroke were obtained, liquid chromatography and mass spectrometry were applied to identify outcome-associated metabolites. The patients' clinical characteristics and identified metabolites were included for constructing the outcome prediction model using machine learning approaches.

RESULTS

By using multivariate analysis, 220 differentially expressed metabolites (DEMs) were discovered between patients with favorable outcomes (modified Rankin Scale, mRS ≤ 2 at 3 months, n = 77) and unfavorable outcomes (mRS ≥ 3 at 3 months, n = 73). After feature selection, 63 DEMs were chosen for constructing the outcome prediction model. The predictive accuracy was below 0.65 when including patients' clinical characteristics, and could reach 0.80 when including patients' clinical characteristics and 63 selected DEMs. The functional enrichment analysis identified platelet activating factor (PAF) as the strongest outcome-associated metabolite, which involved in proinflammatory mediators release, arachidonic acid metabolism, eosinophil degranulation, and production of reactive oxygen species.

CONCLUSION

Metabolomics is a potential method to explore the blood biomarkers of acute ischemic stroke. The patients with unfavorable outcomes had a lower PAF level compared to those with favorable outcomes.

Coagulopathy induced by traumatic brain injury: systemic manifestation of a localized injury

Traumatic brain injury (TBI)-induced coagulopathy is a common and well-recognized risk for poor clinical outcomes, but its pathogenesis remains poorly understood, and treatment options are limited and ineffective. We discuss the recent progress and knowledge gaps in understanding this lethal complication of TBI. We focus on (1) the disruption of the brain-blood barrier to disseminate brain injury systemically by releasing brain-derived molecules into the circulation and (2) TBI-induced hypercoagulable and hyperfibrinolytic states that result in persistent and delayed intracranial hemorrhage and systemic bleeding.

From peroxisomal disorders to common neurodegenerative diseases - the role of ether phospholipids in the nervous system

The emerging diverse roles of ether (phospho)lipids in nervous system development and function in health and disease are currently attracting growing interest. Plasmalogens, a subgroup of ether lipids, are important membrane components involved in vesicle fusion and membrane raft composition. They store polyunsaturated fatty acids and may serve as antioxidants. Ether lipid metabolites act as precursors for the formation of glycosyl-phosphatidyl-inositol anchors; others, like platelet-activating factor, are implicated in signaling functions. Consolidating the available information, we attempt to provide molecular explanations for the dramatic neurological phenotype in ether lipid-deficient human patients and mice by linking individual functional properties of ether lipids with pathological features. Furthermore, recent publications have identified altered ether lipid levels in the context of many acquired neurological disorders including Alzheimer's disease (AD) and autism. Finally, current efforts to restore ether lipids in peroxisomal disorders as well as AD are critically reviewed.

Coagulopathy associated with traumatic brain injury

Coagulopathy is often observed after traumatic brain injury (TBI), but the pathogenic mechanisms of this phenomenon remain elusive. Brain injury is the leading cause of trauma deaths, and the development of coagulopathy after TBI is associated with increased morbidity and mortality in these patients. The coagulopathy after TBI comprises a hypocoagulable and a hypercoagulable state with hemorrhagic and thrombotic phenotypes that are both associated with worse outcome. Some theories of its pathogenesis include massive release of tissue factor, altered protein C homeostasis, microparticle upregulation, and platelet hyperactivity. This article aims to examine the coagulopathy associated with blunt head injury, to review its effect on progression of hemorrhagic injury, and to discuss the possible relevant pathophysiological mechanisms.

Platelet activating factors in depression and coronary artery disease: a potential biomarker related to inflammatory mechanisms and neurodegeneration

The persistence of a depressive episode in coronary artery disease (CAD) patients not only heightens the risk of acute ischemic events, but it is also associated with accelerated cognitive decline. Antidepressant interventions for depression in CAD have only modest effects and novel approaches are limited by a poor understanding of etiological mechanisms. This review proposes that the platelet activating factor (PAF) family of lipids might be associated with the persistence of a depressive episode and related neurodegenerative pathology in CAD due to their association with leading etiological mechanisms for depression in CAD such as inflammation, oxidative and nitrosative stress, vascular endothelial dysfunction, and platelet reactivity. The evidence implicating PAFs in CAD, vascular pathology, and neurodegenerative processes is also presented. We also propose future directions for the investigation of PAFs as mediators of persistent depression. In summary, PAFs are implicated in leading mechanisms associated with depression in CAD. PAFs may therefore be associated with the persistence of depression in CAD and related to neurodegenerative and cognitive sequelae.

Traumatic brain injury-associated coagulopathy

Traumatic injury is a common cause of coagulopathy, primarily due to blood loss and hemodilution secondary to fluid resuscitation. Traumatic injury-associated coagulopathy often follows a course of transition from hyper- to hypocoagulable state exemplified in disseminated intravascular coagulation. The incidence of coagulopathy is significantly higher in patients with traumatic brain injury (TBI), especially those with penetrating trauma compared to injury to the trunk and limbs. This occurs despite the fact that patients with isolated TBI bleed less and receive restricted volume load of fluids. TBI-associated coagulopathy is extensively documented to associate with poor clinical outcomes, but its pathophysiology remains poorly understood. Studies in the past have shown that brain tissue is highly enriched in key procoagulant molecules. This review focuses on the biochemical and cellular characteristics of these molecules and pathways that could make brain uniquely procoagulant and prone to coagulopathy. Understanding this unique procoagulant environment will help to identify new therapeutic targets that could reverse a state of coagulopathy with minimal impacts on hemostasis, a critical requirement for neurosurgical treatments of TBI.

Circulating platelet-activating factor is primarily cleared by transport, not intravascular hydrolysis by lipoprotein-associated phospholipase A2/ PAF acetylhydrolase

RATIONALE

The phospholipid platelet-activating factor (PAF) stimulates all cells of the innate immune system and numerous cardiovascular cells. A single enzyme (plasma PAF acetylhydrolase [PAF-AH] or lipoprotein-associated phospholipase [Lp-PL]A(2)) in plasma hydrolyzes PAF, but significant controversy exists whether its action is pro- or antiinflammatory and accordingly whether its inhibition will slow cardiovascular disease.

OBJECTIVE

We sought to define how PAF and related short-chain oxidized phospholipids turnover in vivo and the role of PAF acetylhydrolase/Lp-PLA(2) in this process.

METHODS AND RESULTS

[(3)H-acetyl]PAF was hydrolyzed by murine or human plasma (t(1/2), 3 and 7 minutes, respectively), but injected [(3)H-acetyl]PAF disappeared from murine circulation more quickly (t(1/2), <30 seconds). [(3)H]PAF clearance was unchanged in PAF receptor(-/-) animals, or over the first 2 half-lives in PAF-AH(-/-) animals. [(3)H]PAF turnover was reduced by coinjecting excess unlabeled PAF or an oxidatively truncated phospholipid, and [(3)H]PAF clearance was slowed in hyperlipidemic apolipoprotein (apo)E(-/-) mice with excess circulating oxidatively truncated phospholipids. [(3)H]PAF, fluorescent NBD-PAF, or fluorescent oxidatively truncated phospholipid were primarily accumulated by liver and lung, and were transported into endothelium as intact phospholipids through a common mechanism involving TMEM30a.

CONCLUSIONS

Circulating PAF and oxidized phospholipids are continually and rapidly cleared, and hence continually and rapidly produced. Saturable PAF receptor-independent transport, rather than just intravascular hydrolysis, controls circulating inflammatory and proapoptotic oxidized phospholipid mediators. Intravascular PAF has access to intracellular compartments. Inflammatory and proapoptotic phospholipids may accumulate in the circulation as transport is overwhelmed by substrates in hyperlipidemia.

Age-related increase of plasma platelet-activating factor concentrations in Chinese

BACKGROUND

Platelet-activating factor (PAF) is a potent bioactive phospholipid, which may be one of the determinants of atherogenesis. The purpose of this study was to investigate the relationship between the concentrations of plasma platelet-activating factor and age in a common Chinese population.

METHODS

Two-hundred seventy-nine Han nation subjects (male: n=162; female: n=117) who had visited two hospitals for overall health survey, as an annual medical check-up or for other reasons by clinical examinations were recruited and divided into six age groups (21-30, 31-40, 41-50, 51-60, 61-70, 71-80 years). PAF was extracted from their plasma and purified by thin-layer chromatography (TLC). The PAF concentrations were detected by radioimmunoassay.

RESULTS

The PAF concentrations (pg/ml) in plasma showed significantly age-related increase (r=0.3348, P<0.01, n=279). In the 21-30-year group, the PAF concentration was 338+/-96 pg/ml. Except for the 31-40-year group, the PAF concentrations in other four groups were all higher than that of the 21-30-year group (P<0.05, P<0.01, P<0.001 and P<0.001, respectively).

CONCLUSIONS

Considering PAF is one of the key factors relevant to progression of atherogenesis, and the high concentrations of plasma PAF may therefore serve as a marker for the risk of atherosclerosis. Adjustment of the concentrations of plasma PAF correlated with aging may be helpful to reducing the prevalence rate of multi-senile arteriosclerosis occlusive diseases.

Neuroprotection during cardiac surgery: a randomised trial of a platelet activating factor antagonist

OBJECTIVE

To assess platelet activating factor (PAF) antagonists, potent neuroprotective agents in experimental cerebral dysfunction, in clinical practice.

DESIGN

Double blind, minimised, placebo controlled trial of low and high dose PAF antagonist (lexipafant).

SETTING

Cardiac surgery unit.

PATIENTS

150 patients undergoing coronary artery bypass graft (CABG) surgery using cardiopulmonary bypass.

INTERVENTIONS

Randomisation to placebo, low dose (10 mg) or high dose (100 mg) lexipafant.

MAIN OUTCOME MEASURES

Incidence of impairment on four established cognitive tests, undertaken before, five days, and three months after CABG, examined by three methods for defining impairment.

RESULTS

The three groups were similar with respect to preoperative and intraoperative factors. Observed levels of cognitive impairment were less than had been predicted from previous studies. There was no difference in the groups in cognitive change scores at five days or three months. Group mean analysis showed significant time factors for all four tests but not for interactions or for the lexipafant group. A composite cognitive index, based on the aggregate of four normally distributed tests, showed a significant effect for timing of the test but not for the lexipafant group or interaction. Age, but not duration of bypass, was the most important determinant of postoperative cognitive impairment.

CONCLUSIONS

The neuroprotective PAF antagonist lexipafant did not differentially reduce the level of cognitive impairment after CABG as determined by power estimates derived from published studies. The strongest predictors of cognitive impairment were age and timing of the test after operation.

Plasma PAF-acetylhydrolase in patients with coronary artery disease: results of a cross-sectional analysis

Inflammation underlies both onset and perpetuation of atherosclerosis. Plasma lipoproteins transport the platelet-activating factor-acetylhydrolase (PAF-AH) with potentially anti-inflammatory activities. Our aim was to determine whether PAF-AH activity was associated with inflammatory markers and with coronary artery disease (CAD). PAF-AH activity and a panel of inflammatory mediators were measured in plasma of 496 patients with CAD and in 477 controls; 276 patients presented with stable angina pectoris and 220 with acute coronary syndrome (ACS). Individuals within the highest quartile of PAF-AH activity had an 1.8-fold increase in CAD risk [95% confidence interval (CI), 1.01 to 3.2; P = 0.048] compared with those in the first quartile (adjusted for clinical and metabolic factors). When excluding individuals receiving statin and angiotensin-converting enzyme-inhibitor medication, individuals within the highest quartile of PAF-AH activity revealed a 3.9-fold increase in CAD risk (95% CI, 2.0 to 7.7; P < 0.0001). In these subjects, the plasma PAF-AH activity increased gradually in stable angina and in ACS both in men (P < 0.0001) and in women (P < 0.001), as compared with controls. No correlation was found between PAF-AH levels and those of common markers of inflammation. This study and the previous ones raise the important issue of whether PAF-AH is simply a marker of risk or directly promotes atherosclerosis.

MgATP may depress de novo neuronal nuclear PAF generation by promoting the formation of alkylacylglycerophosphate, an inhibitor of alkylglycerophosphate acetyltransferase

MgATP substantially inhibited 1-alkyl-sn-glycero-3-phosphate (AGP) acetyltransferase found in neuronal nuclei. Other nucleotides and the ATP analogue AMP-PNP did not show a comparable inhibition. MgATP inhibition decreased in the presence of bovine serum albumin or the fatty acyl CoA synthetase inhibitor, Triacsin C. MgATP inhibition increased when nuclei were preincubated in 50 mM Tris-HCl (pH 7.4)/1 mM MgCl(2) at 37 degrees C, and preincubations elevated levels of nuclear free fatty acid. Exogenous free fatty acid, added to the acetylation incubations, increased the inhibition seen in the presence of MgATP. Oleoyl CoA, in the absence of MgATP, also inhibited AGP acetylation. These results suggested that MgATP supported the conversion of nuclear free fatty acids to fatty acyl CoA. Fatty acyl CoA may directly inhibit nuclear AGP acetyltransferase, but inhibition brought about by MgATP was competitive for the AGP substrate, suggesting an inhibitor close in structure to AGP. 1-Hexadecyl-2-arachidonoyl-sn-glycero-3-phosphate was identified as a competitive inhibitor for AGP in the acetylation reaction. Neuronal nuclei can convert AGP to 1-alkyl-2-acyl-sn-glycero-3-phosphate (AAcylGP), a reaction dependent upon MgATP and the presence of acetyl CoA or free CoA. This nuclear acylation was increased by free fatty acid addition and was seen using oleoyl CoA in the absence of MgATP. Nuclear AAcylGP formation was inhibited by bovine serum albumin and by Triacsin C. Thus, nuclear AGP acetyltransferase may be regulated by AGP acyltransferase activity and the availability of MgATP, a nucleotide that is rapidly lost during brain ischemia.

Sol Sherry lecture in thrombosis: molecular events in acute inflammation

The inflammatory response is characterized by a multistep molecular interaction between "signaling" cells, such as endothelial cells, and "responding" cells, such as neutrophils and monocytes. In the first step, selectins produced by signaling cells mediate the tethering of responding cells at sites of inflammation. Subsequently, an additional mediator expressed by signaling cells activates the tethered responding cells. Under pathological conditions, the same mechanism is invoked in inappropriate ways: (1) by prolonged presentation of selectins on the cell surface and (2) by the unregulated production of oxidized phospholipids that mimic the normal secondary signaling molecule, platelet-activating factor (PAF). The enzyme PAF acetylhydrolase (PAF-AH) inactivates PAF and oxidized phospholipids and constitutes an "off" switch that suppresses inflammation. Inhibition of normal PAF-AH function or inactivating mutations of the PAF-AH gene can lead to increased susceptibility to inflammatory disease. These studies have relevance to atherosclerosis and thrombosis, because inflammation is a central feature of both.

Platelet-activating factor in infants at risk for necrotizing enterocolitis

BACKGROUND

Platelet-activating factor (PAF) is a heterogeneous phospholipid that has been implicated as participating in a number of perinatal disease processes including necrotizing enterocolitis (NEC).

METHODS

Baseline blood levels of PAF and related lipids (PAF-LL) were measured for 164 infants at risk for NEC from 3 neonatal intensive care units. Serial levels were obtained from the 11 infants in whom NEC developed.

RESULTS

The mean peak PAF-LL in the infants without NEC was 2.03 +/- 1.96 ng/mL. Infants with stage II (n = 6) and III (n = 5) NEC had elevated peak PAF-LL values (mean peak value 13.6 +/- 6.9 ng/mL). No PAF-LL measurements obtained from infants during stage II or III NEC were <2.03 ng/mL. Three infants had PAF-LL elevations before the development of any clinical or radiographic evidence of NEC. PAF-LL level increased as the severity of NEC increased and decreased with its resolution. Setting a PAF-LL level of 10.2 ng/mL as a cutoff for NEC had a positive predictive value of 100%.

CONCLUSIONS

PAF-LL determinations can complement clinical and radiographic studies to diagnose and follow the progression of NEC. PAF-LL may have a role in the evolution of NEC.

Lipid acetylation reactions and the metabolism of platelet-activating factor

In this review properties of lipid acetyltransferase enzymes are outlined. The three activities of interest are lyso PAF acetyltransferase (acetyl CoA: 1-alkyl-sn-glycero-3-phosphocholine acetyltransferase), AGP acetyltransferase (acetyl CoA: 1-alkyl sn-glycero-3-phosphate acetyltransferase) and a transacetylase activity that can transfer acetyl groups from PAF to lipid acceptors in the formation of 1-alkenyl-2-acetyl-sn-glycero-3-phosphoethanolamine and N-acetyl sphingosine (C2 ceramide). This review focuses on the role of acetyltransferases and transacetylases within the metabolism of platelet-activating factor and specifically addresses characteristics of the enzymes, including subcellular localization, substrate selectivity, and enzymatic regulation.

Nafamostat mesilate modulates the release of platelet-activating factor during left ventricular assistance with hemofiltration in canine heart failure

OBJECTIVE

The enhanced generation of various chemical mediators is regarded as one of the mechanisms by which severe heart failure progresses to multiple organ failure. Platelet-activating factor is a phospholipid mediator which plays an important role in inflammatory reactions and circulatory shock. We studied the changes in platelet-activating factor levels in a canine heart failure model treated with a left ventricular assist device and hemofiltration, and assessed the effect of a protease inhibitor, nafamostat mesilate.

METHODS

Twenty dogs underwent multiple coronary ligations, and at 2 hours after the ligations they were maintained on left ventricular assist device support with continuous hemofiltration. The animals were divided into two groups: a nafamostat group (n = 10) that received nafamostat mesilate (2 mg/kg/hr), and a control group (n = 10) that received vehicle only.

RESULTS

The blood platelet-activating factor level, before coronary ligations, in the control and nafamostat groups was 2.3 +/- 0.4 and 2.0 +/- 0.7 ng/ml, respectively, and the coronary ligations had little effect on the platelet-activating factor. However, after the initiation of left ventricular assist device, the platelet-activating factor in the control group (5.6 +/- 2.2) was significantly higher (p < 0.05) than that in the nafamostat group (1.1 +/- 0.3). Nafamostat administration was also effective in controlling the increase in the blood lactate level. Hemofiltration did not change the platelet-activating factor.

CONCLUSIONS

We concluded that platelet-activating factor may play a critical role in the development of severe heart failure with left ventricular assistance, and nafamostat administration is likely to be beneficial in such a critical condition by suppressing the platelet-activating factor level.

Influence of platelet-activating factor on cerebral microcirculation in rats: part 2. Local application

BACKGROUND AND PURPOSE

Platelet-activating factor (PAF) is involved in the development of secondary brain damage after ischemic and traumatic brain injury. On the basis of data from studies in peripheral organs, we hypothesized that PAF-mediated effects after cerebral injury could be secondary to alterations in cerebral microcirculation.

METHODS

Changes in cerebral microcirculation focusing on leukocyte-endothelium interactions were quantified with the use of a closed cranial window model in Sprague-Dawley rats (n=33) by means of intravital fluorescence microscopy. The brain surface was superfused with PAF in concentrations from 10(-3) (n=3) to 10(-12) mol/L (n=6) for 20 minutes (5 mL/h).

RESULTS

PAF 10(-4) mol/L (n=4) increased the number of rolling and adherent leukocytes in venules from 9.7+/-0.4 to 19.7+/-2.3 cells/100 mm. min (P=NS versus control) and from 2.2+/-0.5 to 4.3+/-0.7 cells/100 mm. min (P<0.05 versus control), respectively. Lower concentrations did not elicit leukocyte-endothelium interactions. Vessel diameters remained unchanged except for a transient increase of arteriolar diameters during superfusion with PAF 10(-4) and 10(-6) mol/L (n=6). Although only a limited area of the brain surface was exposed to PAF, the mediator induced a significant dose-dependent transitory arterial hypotension and caused irreversible circulatory shock at the high concentration (PAF 10(-3) mol/L). Arterial hypotension after administration of PAF 10(-3) mol/L could be attenuated by the intravenous pretreatment with the PAF antagonist WEB 2170BS.

CONCLUSIONS

PAF, when locally released after brain injury, can penetrate the blood-brain barrier and induce systemic effects, including arterial hypotension. Its role as a mediator in the development of secondary brain damage seems, at least in the initial phase, not to be associated with disturbances of cerebral microcirculation or activation of leukocytes.

Platelet-activating factor in the CNS

Platelet-activating factor (PAF) is a phospholipid synthesized in a variety of cells throughout the body. Platelet-activating factor has been identified in the CNS and has a number of diverse physiological and pathological functions. It has been shown to be a modulator of many CNS processes, ranging from long-term potentiation (LTP) to neuronal differentiation. Excessive levels of PAF appear to play an important role in neuronal cell injury, such as that resulting from ischaemia, inflammation, human immunodeficiency syndrome (HIV) and meningitis. The beneficial effects of PAF receptor antagonists are many and give rise to possible therapeutic strategies for neurotrauma.

Deficiency of plasma platelet-activating factor acetylhydrolase: roles of blood cells

Platelet-activating factor (PAF), a potent mediator of inflammation and circulatory shock, is inactivated by the enzyme PAF acetylhydrolase. Plasma PAF acetylhydrolase deficiency occurs even in healthy subjects. We hypothesized that erythrocyte PAF acetylhydrolase could play a supplementary role in this plasma acetylhydrolase deficiency. We examined 1,030 subjects who participated in mass checkups, and assayed plasma and erythrocyte PAF acetylhydrolase. We also investigated the degradation of exogenous PAF by erythrocytes or other blood cells obtained from subjects who exhibited the plasma enzyme deficiency. The incidence of the plasma enzyme deficiency in this general Japanese population was 4.7% (48/1,030). None of the subjects with the deficiency had a history of allergy, circulatory shock, or chronic inflammatory diseases. The mean values for erythrocyte cytosolic PAF acetylhydrolase activity in the normal and deficient subjects were 0.51 +/- 0.15 (SD) and 0.71 +/- 0.28 nkat (nmol/s)/g protein, respectively, and the difference was significant (P < 0.001, Mann-Whitney U-test). The half-life of 10 nmol/l [3H]PAF in plasma from normal subjects was about 5 min, and the half-life in whole blood or erythrocyte suspension in autologous plasma was almost the same as that in plasma. In plasma from deficient subjects, unchanged PAF virtually remained and the degradation in whole blood or erythrocyte suspension was a little faster than in plasma. We conclude that erythrocytes contribute only little to PAF metabolism in normal blood but they account for almost all of the slow PAF degradation in blood from subjects deficient in plasma PAF acetylhydrolase.

Activities of enzymes in platelet activating factor biosynthetic pathways in the gerbil model of cerebral ischemia

The activities of enzymes in platelet activating factor (PAF) biosynthetic pathways were analyzed in hippocampal and cerebral cortical regions of normal and ischemic gerbil brain to assess changes in enzyme activities and potential modulators that could explain the accentuated production of PAF seen in ischemia. Global forebrain ischemia was produced by bilateral carotid artery ligation, and the effectiveness of the ligation was shown by free fatty acid release and ATP depletion. Specific activities of 1-alkyl-2-acetyl-sn-glycerol (AAG) choline phosphotransferase, 1-alkyl-sn-glycero-3-phosphate (AGP) acetyl transferase, and 1-alkyl-sn-glycero-3-phosphocholine (lyso PAF) acetyl transferase in tissue homogenates were in the ratio 4:1:0.1, respectively. Sham-operated and ischemic or ischemic-reperfused tissues showed similar activities for individual enzymes, indicating that enzyme levels or activation states did not change in ischemic or reperfused tissues. However, small metabolites (relevant to ischemia) added to the in vitro assays did modify enzyme activities. Physiological concentrations of MgATP severely inhibited AGP acetyl transferase activity, and this resulted in the ratio of AGP acyl transferase to AGP acetyl transferase activities changing from 48:1 in the presence of 2.5 mM MgATP to 6:1 in the absence of MgATP. This suggests that falling ATP levels in cerebral ischemia may promote the de novo pathway of PAF biosynthesis by releasing inhibition of AGP acetyl transferase. Lyso PAF acetyl transferase was much less active than AGP acetyl transferase and was also inhibited by MgATP. AAG choline phosphotransferase was not inhibited by MgATP but was inhibited by calcium. However the superior specific activity of the choline phosphotransferase in comparison with the AGP acetyl transferase suggested that the lowered choline phosphotransferase activity in the presence of rising intracellular calcium would not seriously compromise the synthesis of PAF by the de novo route. Both acetyl transferase enzymes were also inhibited by oleoyl CoA.

A new method of purification and sensitive bioassay of platelet-activating factor (PAF) in human whole blood

There is no satisfactory assay procedure of PAF in human whole blood in terms of sensitivity, reproducibility and simplicity. This is due to coexisting lipids from plasma and cellular membranes which inhibit measurement of PAF in various assay procedures, including bioassay. In the present study, an attempt was made to eliminate these interfering lipid inhibitors from blood samples. Lipids in human whole blood were extracted according to the method of Bligh & Dyer and the organic layer was dried under a stream of nitrogen. Then, the dried organic layer was dissolved in diethyl-ether and the solution was kept at -20 degrees C which was then centrifuged. The resulting supernatant was then applied to an anion-exchange column and the PAF fraction was obtained by step-wise gradient elution. The fraction was further purified by normal phase HPLC. Then PAF in the final sample was determined by sensitive bioassay using rabbit platelets containing fibrinogen and epinephrine. The recovery rate of PAF throughout this procedure was constant and satisfactory (37.4 +/- 9.7%), which was confirmed using [3H]-PAF. The lower limit of the present assay was estimated to be 5pg in 1 ml of blood and it was sensitive enough to detect PAF in blood samples from healthy volunteers and patients with sepsis or liver cirrhosis. Furthermore, attempts were made to compare the sensitivity and the recovery of our method with these of a commercially available radioimmunoassay (RIA) kit for PAF. However, it was not possible to detect any amount of authentic PAF added to whole blood.

Release of proinflammatory and prothrombotic mediators in the brain and peripheral circulation in spontaneously hypertensive and normotensive Wistar-Kyoto rats

BACKGROUND AND PURPOSE

We reported previously that stroke risk factors prepared the brain stem for the development of ischemia and hemorrhage and induced the production of tumor necrosis factor following an intrathecal injection of lipopolysaccharide, a prototypic monocyte-activating stimulus. This study evaluates whether blood or brain cells of hypertensive rats produce more proinflammatory and prothrombotic mediators than do blood or brain cells of normotensive rats.

METHODS

Levels of tumor necrosis factor, platelet-activating factor, 6-ketoprostaglandin F1 alpha, and thromboxane B2 in the cerebrospinal fluid and blood of spontaneously hypertensive and normotensive Wistar-Kyoto rats were monitored before and after a challenge with lipopolysaccharide.

RESULTS

Little or no activity from these mediators was found in the cerebrospinal fluid or blood of saline-injected control animals. Intravenous administration of lipopolysaccharide (0.001, 0.1, and 1.8 mg/kg) produced dose-dependent increases in blood levels of all mediators in hypertensive rats. In normotensive rats the levels were less than in hypertensive rats and were not clearly dose-related. When lipopolysaccharide was injected intracerebroventricularly, more tumor necrosis factor was measured in the cerebrospinal fluid than in the blood, suggesting local synthesis of this cytokine. Levels of tumor necrosis factor and platelet-activating factor in the cerebrospinal fluid were higher in hypertensive than in normotensive rats. The thromboxane A2/prostacyclin ratio was not altered significantly between the two rat strains.

CONCLUSIONS

It is suggested that the higher incidence of brain stem ischemia and hemorrhage after the intrathecal injection of lipopolysaccharide in hypertensive rats than in normotensive rats might be related to the higher levels of the two cytotoxic factors tumor necrosis factor and platelet-activating factor produced in response to such challenge.

Platelet-activating factor acetylhydrolase in plasma lipoproteins from patients with ischemic stroke

BACKGROUND AND PURPOSE

Platelet-activating factor is a potent bioactive phospholipid and may play an important role in occlusive vascular diseases. To assess the inactivation of this autacoid in plasma, we measured platelet-activating factor acetylhydrolase activity in plasma low density and high density lipoproteins from patients with ischemic stroke.

METHODS

Low density and high density lipoproteins were separated by ultracentrifugation from plasma of 33 patients with cerebral thrombosis and 31 age-matched healthy control subjects, and platelet-activating factor acetylhydrolase activity in each fraction was assayed.

RESULTS

The average values of platelet-activating factor acetylhydrolase activity in low density lipoprotein from patients and control subjects were 41 +/- 18 and 29 +/- 17 nmol/ml per minute, respectively, and the difference was statistically significant (p less than 0.01 U test). There was no difference in activity in high density lipoprotein between the two groups (16 +/- 11 versus 14 +/- 9 nmol/ml per minute, respectively).

CONCLUSIONS

The increased plasma platelet-activating factor acetylhydrolase activity in stroke patients is primarily attributable to the increased binding to low density lipoprotein, and this increase may be an adaptation to the augmented generation of platelet-activating factor in ischemic stroke.