Platelet-Activating Factor Acetylhydrolase Prevents Myocardial Ischemia-Reperfusion Injury

Serum from the Human Fracture Hematoma Contains a Potent Inducer of Neutrophil Chemotaxis

A controlled local inflammatory response is essential for adequate fracture healing. However, the current literature suggests that local and systemic hyper-inflammatory conditions after major trauma induce increased influx of neutrophils into the fracture hematoma (FH) and impair bone regeneration. Inhibiting neutrophil chemotaxis towards the FH without compromising the hosts' defense may therefore be a target of future therapies that prevent impairment of fracture healing after major trauma. We investigated whether chemotaxis of neutrophils towards the FH could be studied in vitro. Moreover, we determined whether chemotaxis of neutrophils towards the FH was mediated by the CXCR1, CXCR2, FPR, and C5aR receptors. Human FHs were isolated during an open reduction internal fixation (ORIF) procedure within 3 days after trauma and spun down to obtain the fracture hematoma serum. Neutrophil migration towards the FH was studied using Ibidi™ Chemotaxis3D μ-Slides and image analysis of individual neutrophil tracks was performed. Our study showed that the human FH induces significant neutrophil chemotaxis, which was not affected by blocking CXCR1 and CXCR2. In contrast, neutrophil chemotaxis towards the FH was significantly inhibited by chemotaxis inhibitory protein of Staphylococcus aureus (CHIPS), which blocks FPR and C5aR. Blocking only C5aR with CHIPSΔ1F also significantly inhibited neutrophil chemotaxis towards the FH. Our finding that neutrophil chemotaxis towards the human FH can be blocked in vitro using CHIPS may aid the development of therapies that prevent impairment of fracture healing after major trauma.

Anti-ischaemic effects of bilobalide on neonatal rat cardiomyocytes and the involvement of the platelet-activating factor receptor

Terpene trilactones from Ginkgo biloba have been investigated extensively for their antioxidant and anti-ischaemic activities on the brain and the heart, but the mechanisms of these effects remain unclear. For the present study, a terpenoid constituent from G. biloba, bilobalide, was screened for protective effects on the ischaemic heart and the involvement of the PAFR [PAF (platelet-activating factor) receptor] and the enzyme that degrades PAF, PAF-AH (PAF acetylhydrolase) during hypoxia. The PAF pathway is supposed to play a role in hypoxia and its regulation may prevent or alleviate MI (myocardial infarction). Cardiomyocytes from neonatal rat hearts were cultured and treated with different concentrations of bilobalide (500–0.5 ng/ml). After being subjected to a hypoxic environment, the cells' viability was evaluated and proteins as well as RNA were extracted for analysis by Western blotting and RT–PCR (reverse transcription PCR) respectively. With the MI model we tested for bilobalide's cardioprotective effects and the involvement of PAFR and PAF-AH. Bilobalide (5 ng/ml) significantly decreased the mortality of cells in a concentration-dependent way. mRNA expression of PAFR was up-regulated in hypoxic cells but in the groups treated with bilobalide, its expression was down-regulated to the level of the normal control. In hypoxic tissue, PAFR protein expression was also up-regulated, but was reduced in the bilobalide (10 mg/kg of body weight) treated group. Our results indicate that PAF and its receptor may be involved in the cellular response of cardiomyocytes to hypoxia and that bilobalide may interact with this receptor to exert its cardioprotective effects.

Modulation of oxidative stress, inflammation, and atherosclerosis by lipoprotein-associated phospholipase A2

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), also known as platelet-activating factor acetylhydrolase (PAF-AH), is a unique member of the phospholipase A(2) superfamily. This enzyme is characterized by its ability to specifically hydrolyze PAF as well as glycerophospholipids containing short, truncated, and/or oxidized fatty acyl groups at the sn-2 position of the glycerol backbone. In humans, Lp-PLA(2) circulates in active form as a complex with low- and high-density lipoproteins. Clinical studies have reported that plasma Lp-PLA(2) activity and mass are strongly associated with atherogenic lipids and vascular risk. These observations led to the hypothesis that Lp-PLA(2) activity and/or mass levels could be used as biomarkers of cardiovascular disease and that inhibition of the activity could offer an attractive therapeutic strategy. Darapladib, a compound that inhibits Lp-PLA(2) activity, is anti-atherogenic in mice and other animals, and it decreases atherosclerotic plaque expansion in humans. However, disagreement continues to exist regarding the validity of Lp-PLA(2) as an independent marker of atherosclerosis and a scientifically justified target for intervention. Circulating Lp-PLA(2) mass and activity are associated with vascular risk, but the strength of the association is reduced after adjustment for basal concentrations of the lipoprotein carriers with which the enzyme associates. Genetic studies in humans harboring an inactivating mutation at this locus indicate that loss of Lp-PLA(2) function is a risk factor for inflammatory and vascular conditions in Japanese cohorts. Consistently, overexpression of Lp-PLA(2) has anti-inflammatory and anti-atherogenic properties in animal models. This thematic review critically discusses results from laboratory and animal studies, analyzes genetic evidence, reviews clinical work demonstrating associations between Lp-PLA(2) and vascular disease, and summarizes results from animal and human clinical trials in which administration of darapladib was tested as a strategy for the management of atherosclerosis.

Clinical significance of circulating platelet-activating factor acetylhydrolase levels in systemic sclerosis

Platelet-activating factor acetylhydrolase (PAF-AH) has been demonstrated to be one of anti-inflammatory and anti-apoptotic factors, suggesting the potential to be involved in the development of systemic sclerosis (SSc). The aim of this study is to determine serum PAF-AH levels and their clinical associations in patients with SSc. Serum PAF-AH levels were examined by enzyme-linked immunosorbent assay in 57 patients with SSc and 24 healthy individuals. Serum PAF-AH levels were significantly elevated in SSc patients (130.4 ± 69.5 ng/ml) compared with healthy individuals (81.6 ± 34.8 ng/ml; P < 0.001). Among SSc patients, there were no differences in serum PAF-AH levels between those with diffuse cutaneous SSc (135.5 ± 79.3 ng/ml; n = 29) and those with limited cutaneous SSc (125.1 ± 58.6 ng/ml; n = 28). Patients with SSc who had raised PAF-AH levels less often had digital ulcers and arthritis/arthralgias than those with normal PAF-AH levels. The results show that serum PAF-AH levels were increased in patients with SSc and associated with a lower frequency of pitting scars/digital ulcers and arthritis/arthralgias. PAF-AH could be a protective factor against the development of digital ulcers and arthritis/arthralgia in this disease and as such would be a useful serological marker for disease severity.

Plasma lipoprotein-associated phospholipase A2 in patients with metabolic syndrome and carotid atherosclerosis

Background

Lipoprotein-associated phospholipase A₂ (Lp-PLA₂) is a recently identified and potentially useful plasma biomarker for cardiovascular and atherosclerotic diseases. However, the correlation between the Lp-PLA₂ activity and carotid atherosclerosis remains poorly investigated in patients with metabolic syndrome (MetS). The present study aimed to evaluate the potential role of Lp-PLA₂ as a comprehensive marker of metabolic syndrome in individuals with and without carotid atherosclerosis.

Methods

We documented 118 consecutive patients with MetS and 70 age- and sex-matched healthy subjects served as controls. The patients were further divided into two groups: 39 with carotid plaques and 79 without carotid plaques to elucidate the influence of Lp-PLA₂ on carotid atherosclerosis. The plasma Lp-PLA₂ activity was measured by using ELISA method and carotid intimal-media thickness (IMT) was performed by ultrasound in all participants.

Results

Lp-PLA₂ activity was significantly increased in MetS subgroups when compared with controls, and was higher in patients with carotid plaques than those without plaques (P < 0.05). Furthermore, we found that significant difference in Lp-PLA₂ was obtained between patients with three and four disorders of metabolic syndrome (P < 0.01). Age (β = 0.183, P = 0.029), LDL-cholesterol (β = 0.401, P = 0.000) and waist-hip ratio (β = 0.410, P = 0.000) emerged as significant and independent determinants of Lp-PLA₂ activity. Multiple stepwise regression analysis revealed that LDL-cholesterol (β = 0.309, P = 0.000), systolic blood pressure (β = 0.322, P = 0.002) and age (β = 0.235, P = 0.007) significantly correlated with max IMT, and Lp-PLA₂ was not an independent predictor for carotid IMT.

Conclusions

Lp-PLA₂ may be a modulating factor for carotid IMT via age and LDL-cholesterol, not independent predictor in the pathophysiological process of carotid atherosclerosis in patients with MetS.

Lipoprotein-associated phospholipase A2: a cardiovascular risk predictor and a potential therapeutic target

Lipoprotein-associated phospholipase A2 (Lp-PLA2), present in the circulation and in atherosclerotic plaque, is an inflammatory marker with potential use as a predictor of cardiovascular risk and as a therapeutic target. Although Lp-PLA2 is associated with both LDL and HDL, it is important to determine whether Lp-PLA2 has a predominantly pro- or anti-atherogenic effect. Increasing evidence suggests a proatherogenic role for Lp-PLA2. ©iEpidemiologic and clinical evidence suggests Lp-PLA2 is an independent predictor of risk and may be superior to other inflammatory markers owing to its specificity and minimal biovariation. Lp-PLA2 inhibitors currently being investigated in clinical trials are promising novel anti-inflammatory agents with a specificity for the vascular bed and a potential for decreasing plaque vulnerability.

Role of lipoprotein-associated phospholipase A2 in atherosclerosis

Lipoprotein-associated phospholipase A(2)(Lp-PLA(2)) is a biomarker that can be used to assess the risk for cardiovascular disease and events. In addition to being a useful marker of a risk factor, several studies suggest that Lp-PLA(2) has a pathophysiologic role in the atherosclerotic disease process. In this article, we review this aspect and its therapeutic implications.

Increased serum creatine kinase is a reliable marker for acute transplanted heart rejection diagnosis in rats

Different molecules have been studied as biochemical markers in heart transplantation. However, their utility is under discussion as results in human and animal models are controversial. In this work, lactate dehydrogenase (LDH), creatine kinase (CK) and cardiac troponin I (TnI) were studied as serologic markers of acute rejection after heterotopical heart transplantation in rats. In predictable rejection experiments, animals were divided into three groups: nonoperated (Lewis rats), control group (Lewis-Lewis isografts) and rejection group (Brown Norway-Lewis allografts). Nonpredictable rejection experiments were performed using nonconsanguineous Sprague-Dawley allografts. In predictable rejection experiments, LDH activity was similar between control and rejection groups. TnI values were heterogeneous in control and rejection groups. In contrast, the rejection group showed CK activity increased 4.5-fold compared with the control group. In addition to these predictable studies, we also presented novel nonpredictable experiments in which rats were divided into groups based on low and high CK activity. Histologic studies in these rats showed that none of those with low CK activity presented rejection signs, while all animals with high CK levels showed grade 2R rejection. These results suggest that CK might be an excellent marker for prediction of rejection in heart transplantation.

Modifications of plasma platelet-activating factor (PAF)-acetylhydrolase/PAF system activity in patients with chronic hepatitis C virus infection

Hepatitis C virus (HCV) chronically infects about 200 million individuals worldwide and leads to severe liver and lymphatic diseases. HCV circulates in the serum, associated with apoB-containing lipoproteins. Platelet-activating factor (PAF), a pro-inflammatory mediator, is mainly modulated by plasma PAF-acetylhydrolase (pPAF-AH), associated with ApoB100-containing low-density lipoproteins (LDL). The aim of the study was to evaluate the potential effects of chronic HCV infection on the PAF/pPAF-AH system. HCV-RNA was detected in plasma, peripheral blood mononuclear cells (PBMC) and liver samples. Plasma PAF levels, pPAF-AH activity, ApoB100 serum titres and pPAF-AH mRNA levels in cultured macrophages were determined. Plasma PAF levels were significantly higher and pPAF-AH activity was significantly lower in HCV patients than in controls. No significant modifications of pPAF-AH mRNA in macrophages or in ApoB100 values were observed in HCV patients compared with controls. Patients who cleared HCV after antiviral treatment showed a complete restoration of pPAF-AH activity and significant decrease of PAF levels during the follow-up. No data exist about the PAF/pPAF-AH system behaviour during HCV infection. This study shows that in HCV patients modifications of pPAF-AH activity/PAF levels take place and that HCV clearance restored pPAF-AH activity. This suggests that circulating viral particles play a role in PAF/pPAF-AH system modifications and such an alteration could be involved in HCV-related damage.

A polymorphism in plasma platelet-activating factor acetylhydrolase is involved in resistance to immunoglobulin treatment in Kawasaki disease

OBJECTIVE

To investigate whether reduced levels of plasma platelet-activating factor acetylhydrolase (PAF-AH) as a result of a genetic polymorphism are involved in the pathogenesis of Kawasaki disease (KD).

STUDY DESIGN

The frequency of a V279F polymorphism (G/T transversion) in the PAF-AH gene was quantified in 76 Japanese children with KD and 112 healthy Japanese adults using the allele-specific polymerase chain reaction (PCR). Associations between genotype, clinical features, and resistance to intravenous immunoglobulin (IVIG) were investigated in the patients with KD. Plasma PAF-AH activity was measured by using [3H]-acetyl-PAF.

RESULTS

There were no significant differences in genotype frequency between patients and controls (P = .51). Compared with the GG (normal genotype) group, significantly more patients in the GT (heterozygous) +TT (homozygous deficient) group required additional IVIG (52% vs 14%, P = .001). The duration of fever and maximum serum C-reactive protein (CRP) levels also were significantly increased in the GT+TT group (P = .012 and .036, respectively), whereas plasma PAF-AH activity was significantly lower (P <.0001).

CONCLUSION

We conclude that the V279F polymorphism in the plasma PAF-AH gene and consequent enzymatic deficiency is one of the factors for IVIG nonresponse in Japanese patients with acute KD.

The p38 MAPK pathway mediates transcriptional activation of the plasma platelet-activating factor acetylhydrolase gene in macrophages stimulated with lipopolysaccharide

Administration of lipopolysaccharide (LPS) to experimental animals results in the up-regulation of expression of the plasma form of platelet-activating factor acetylhydrolase (PAF AH) in tissue macrophages. To investigate the mechanism underlying induction of PAF AH by LPS we used murine RAW264.7 and human THP-1 macrophages as model systems. We found that the p38 mitogen-activated protein kinase (p38 MAPK) pathway mediates transcriptional activation of the PAF AH gene through the participation of nucleotides -68/-316 relative to the transcriptional initiation site. This promoter region spans two Sp1/Sp3 binding sites (SP-A and SP-B) and is necessary and sufficient for the observed effect. Disruption of these Sp binding sites significantly reduces promoter activity in LPS-stimulated cells. The ability of LPS to induce transcriptional activation of PAF AH is not due to enhanced Sp1/Sp3 binding to the promoter but involves enhanced transactivation function of Sp1 via p38 MAPK activation. These studies characterize the mechanism by which LPS modulates expression of PAF AH at the transcriptional level, and they have important implications for our understanding of responses that occur during the development of LPS-mediated inflammatory diseases.

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.

Detection and characterization of 45 kDa platelet activating factor acetylhydrolase in cerebrospinal fluid of children with meningitis

Platelet activating factor acetylhydrolase (PAF-AH) activity has been identified in cerebrospinal fluid (CSF) samples taken from children with meningitis. We reported that PAF-AH activity is significantly increased, by about 3 fold, in patients with meningitis compared to control subjects. Because of limited knowledge about this enzyme in CSF, we examined the biochemical properties of CSF PAF-AH. PAF-AH of CSF was calcium independent, showed a broad pH spectrum and was relatively heat stable. In addition, this enzyme activity was strongly inhibited by phenylmethanesulfonyl fluoride (PMSF), partially inhibited by p-bromophenacylbromide (p-BPB), uninhibited by iodoacetamide, and moderately stimulated by dithiothreitol (DTT). PAF-AH of CSF did not degrade phospholipid with a long chain fatty acyl group at sn-2 position. This enzyme hydrolyzed PAF and oxidatively modified phosphatidylcholine. Furthermore, we identified a monomeric polypeptide with a molecular weight of approximately 45 kDa by Western blot using human plasma PAF-AH antibody. These results suggested that plasma type PAF-AH activity exist in CSF taken from children with meningitis.