Increased activity of the platelet-activating factor acetylhydrolase in plasma low density lipoprotein from patients with essential hypertension

Gene Expression Profile in Different Age Groups and Its Association with Cognitive Function in Healthy Malay Adults in Malaysia

The mechanism of cognitive aging at the molecular level is complex and not well understood. Growing evidence suggests that cognitive differences might also be caused by ethnicity. Thus, this study aims to determine the gene expression changes associated with age-related cognitive decline among Malay adults in Malaysia. A cross-sectional study was conducted on 160 healthy Malay subjects, aged between 28 and 79, and recruited around Selangor and Klang Valley, Malaysia. Gene expression analysis was performed using a HumanHT-12v4.0 Expression BeadChip microarray kit. The top 20 differentially expressed genes at p < 0.05 and fold change (FC) = 1.2 showed that PAFAH1B3, HIST1H1E, KCNA3, TM7SF2, RGS1, and TGFBRAP1 were regulated with increased age. The gene set analysis suggests that the Malay adult's susceptibility to developing age-related cognitive decline might be due to the changes in gene expression patterns associated with inflammation, signal transduction, and metabolic pathway in the genetic network. It may, perhaps, have important implications for finding a biomarker for cognitive decline and offer molecular targets to achieve successful aging, mainly in the Malay population in Malaysia.

Fetal High-Density Lipoproteins: Current Knowledge on Particle Metabolism, Composition and Function in Health and Disease

Cholesterol and other lipids carried by lipoproteins play an indispensable role in fetal development. Recent evidence suggests that maternally derived high-density lipoprotein (HDL) differs from fetal HDL with respect to its proteome, size, and function. Compared to the HDL of adults, fetal HDL is the major carrier of cholesterol and has a unique composition that implies other physiological functions. Fetal HDL is enriched in apolipoprotein E, which binds with high affinity to the low-density lipoprotein receptor. Thus, it appears that a primary function of fetal HDL is the transport of cholesterol to tissues as is accomplished by low-density lipoproteins in adults. The fetal HDL-associated bioactive sphingolipid sphingosine-1-phosphate shows strong vasoprotective effects at the fetoplacental vasculature. Moreover, lipoprotein-associated phospholipase A2 carried by fetal-HDL exerts anti-oxidative and athero-protective functions on the fetoplacental endothelium. Notably, the mass and activity of HDL-associated paraoxonase 1 are about 5-fold lower in the fetus, accompanied by an attenuation of anti-oxidative activity of fetal HDL. Cholesteryl ester transfer protein activity is reduced in fetal circulation despite similar amounts of the enzyme in maternal and fetal serum. This review summarizes the current knowledge on fetal HDL as a potential vasoprotective lipoprotein during fetal development. We also provide an overview of whether and how the protective functionalities of HDL are impaired in pregnancy-related syndromes such as pre-eclampsia or gestational diabetes mellitus.

Platelet activating factor levels and metabolism in Tangier disease: a case study

Background

Tangier disease (TD) is a phenotypic expression of rare familial syndrome with mutations in the ABCA1 transporter. The risk of coronary artery disease in patients with TD is variable. On the other hand the pivotal role of Platelet-Activating Factor (PAF) mediator in atheromatosis was found. Plasma lipoproteins are transporters of the PAF acetylhydrolase (PAF-AH) in cells and known as lipoprotein-phospholipase A₂ (Lp-PLA₂) in plasma and regulators of PAF levels in blood. In addition, PAF can be biosynthesized from the remodeling and the de novo pathways in which Lyso-platelet activating factor-acetyltransferase (Lyso-PAF-AT) and platelet activating factor-cholinephosphotransferase (PAF-CPT) are the regulatory enzymes. The aim of this study is to investigate in a TD patient with a unique mutation (C2033A), the concentration of PAF in blood, the Equivalent Concentration for 50% aggregation (EC₅₀) values of platelet rich plasma (PRP) toward PAF, adenosine diphosphate (ADP) and thrombin, and the activities of PAF metabolic enzymes Lp-PLA₂, PAF-AH, Lyso-PAF-AT and PAF-CPT.

Methods

The EC₅₀ value of PRP was measured by an aggregometer. The determination of the specific activity of PAF-CPT and Lyso-PAF-AT was made after in vitro enzymatic assay, chromatographic separation and measurement of the produced PAF in a biological assay with washed rabbit platelets. The determination of PAF-AH and Lp-PLA₂ was made after an in vitro enzymatic assay from the decay of radioactive PAF.

Results

The TD patient had lower bound-PAF values in blood, decreased specific activity of PAF-CPT and Lyso-PAF-AT, increased specific activity of PAF-AH in platelets and leukocytes and Lp-PLA₂ activity in plasma compared to healthy women. The EC₅₀ of PAF and Thrombin were higher compared to healthy women.

Conclusion

The increased Lp-PLA₂ activity, as well as, the decreased activities of PAF-CPT and Lyso-PAF-AT, explain the decreased bound-PAF level in TD patient and the EC₅₀ of PAF. However, total PAF is in a normal range and this probably can explain one of the reasons this TD patient has no CAD.

Variation of lipoprotein associated phospholipase A2 across demographic characteristics and cardiovascular risk factors: a systematic review of the literature

BACKGROUND

Lipoprotein association phospholipase A2 (Lp-PLA(2)), an enzyme which has been found in atherosclerotic plaque is currently under investigation in large Phase III clinical trials of vascular disease prevention. We assessed in a variety of different population settings variation of Lp-PLA(2) mass and activity across gender, ethnicity, diabetes, kidney disease and metabolic syndrome. We also assessed correlations with measures of circulating lipids, systemic inflammation and adiposity.

METHODS

Systematic review of studies measuring Lp-PLA(2) and at least one of the relevant characteristics in >50 participants.

RESULTS

We identified a total of 77 studies involving 102,499 participants meeting the inclusion criteria. Lp-PLA(2) mass and activity were consistently approximately 10% higher in males than females and 15% higher in Caucasians than African Americans or Hispanics. There were no clear associations of Lp-PLA(2) mass or activity with type II diabetes, markers of systemic inflammation (C-reactive protein, fibrinogen) or with body mass index. Correlations of Lp-PLA(2) mass or activity with low density lipoprotein cholesterol and apolipoprotein B were moderate and positive, whilst correlations with high density lipoprotein cholesterol were negative and moderate to weak. There was no clear differences in associations with any of the above characteristics in groups defined based upon prevalent cardiovascular disease or its risk factors.

CONCLUSIONS

Despite considerable variability in absolute levels of Lp-PLA(2) across studies, the variability of Lp-PLA(2) across gender, ethnicity, and levels of circulating lipids and markers of systemic inflammation are more consistent and appear not to vary importantly across categories defined by CVD or its risk factors.

Differential expression of platelet-activating factor acetylhydrolase in lung macrophages

Platelet-activating factor (PAF) acetylhydrolase plays a crucial role inactivating the potent inflammatory mediator, PAF. PAF is implicated in the initiation and propagation of acute lung injury. Although PAF acetylhydrolase is a constitutively active plasma protein, increased PAF production during inflammatory events may necessitate an increase in PAF acetylhydrolase activity in the local environment. A series of experiments were conducted to determine whether the systemic administration of LPS to Sprague-Dawley rats resulted in enhanced expression of PAF acetylhydrolase in lung tissue. Ribonuclease protection assays revealed a dramatic increase in PAF acetylhydrolase mRNA, which peaked at 24 h following in vivo LPS administration. The increase in PAF acetylhydrolase mRNA was dose dependent and was detected when as little as 10 microg/kg of LPS was administered. Western blot analyses of lung tissue homogenates confirmed an increased production of PAF acetylhydrolase protein in response to LPS. In addition, Western blot analyses revealed the rat PAF acetylhydrolase protein exhibited heterogeneous molecular weights with predominant species migrating at 63 and 67 kDa. Some of the molecular weight heterogeneity likely resulted from extensive glycosylation of the secreted protein. Immunohistochemical analyses of lung tissue sections and colocalization experiments revealed a heterogenous population of cells that express the plasma-type PAF acetylhydrolase. Lung interstitial macrophages were PAF acetylhydrolase positive, but surprisingly, alveolar macrophages did not increase expression of PAF acetylhydrolase in response to systemic LPS administration. In addition, rat granulocytes consisting primarily of neutrophils were strongly positive for PAF acetylhydrolase in the LPS-exposed lung tissue. The absence of immunoreactive PAF acetylhydrolase in alveolar macrophages obtained from bronchial alveolar lavage confirmed that systemic LPS administration resulted in enhanced PAF acetylhydrolase expression only in a subset of lung macrophages.

Lipoprotein-associated PAF-acetylhydrolase activity in subjects with the metabolic syndrome

Plasma- and lipoprotein-associated activity of the platelet activating factor acetylhydrolase (PAF-acetylhydrolase, PAF-AH) plays an important role in inflammation and in atherosclerotic process, which are present in the metabolic syndrome (MS). Paraoxonase 1 (PON1) is an esterase associated with high-density lipoprotein (HDL) which contributes to the anti-atherogenic effects of this lipoprotein. We investigated the activities of both enzymes in 60 patients with MS and 110 age- and sex-matched subjects without it (non-MS group). Plasma PAF-AH activity was higher in the MS compared to the non-MS group, while HDL-PAF-AH and serum PON1 activities were lower in the MS compared to the non-MS group. Univariate regression analysis in the MS group showed that plasma PAF-AH activity was positively associated with systolic blood pressure, whereas HDL-PAF-AH activity was inversely associated with the homeostasis model assessments (HOMA) index. Both associations remained significant in the multivariate regression analysis, suggesting that insulin resistance and systolic hypertension are major determinants for the alterations in plasma and HDL-associated PAF-AH activity among those observed in MS patients.

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.

Lp-PLA2: an emerging biomarker of coronary heart disease

Cardiovascular disease is the leading cause of death in most industrialized countries. However, the diagnosis and management of coronary heart disease is far from optimal. Lipoprotein-associated phospholipase A2 (Lp-PLA2), also known as platelet-activating factor acetylhydrolase, is an enzyme that hydrolyses oxidized phospholipids and is primarily associated with low-density lipoprotein. Discussed in this review is the accumulating evidence supporting the view that Lp-PLA2 is a potential biomarker of coronary heart disease and plays and an important proinflammatory role in the progression of atherosclerosis. A new ELISA method for the quantitative measurement of Lp-PLA2 mass in human plasma developed by diaDexus, Inc. is presented. Furthermore, potential clinical applications of Lp-PLA2 mass measurements are proposed.

The effect of 3-month ingestion of Ginkgo biloba extract (EGb 761) on pancreatic beta-cell function in response to glucose loading in individuals with non-insulin-dependent diabetes mellitus

In the first report (Journal of Clinical Pharmacology 2000; 40:647-654), it was shown that ingestion of 120 mg of Ginkgo biloba extract (EGb 761) daily for 3 months by normal glucose-tolerant individuals caused a significant increase in pancreatic beta-cell insulin and C-peptide response, measured as the area under the curve (AUC0-->120) during a 2-hour standard (75 g) oral glucose tolerance test (OGTT). This follow-up study was designed to determine the effect of the same Ginkgo biloba treatment on glucose-stimulated pancreatic beta-cell function in non-insulin-dependent diabetes mellitus (NIDDM) subjects. In diet-controlled subjects (fasting plasma glucose [FPG], 117 +/- 16 mg/dl; fasting plasma insulin [FPI], 29 +/- 8 microU/ml; n = 6), ingestion of Ginkgo biloba produced no significant effect on the insulin AUC0-->120 (193 +/- 53 vs. 182 +/- 58 microU/ml/h, before and after ingesting Ginkgo biloba, respectively). In hyperinsulinemic NIDDM subjects taking oral hypoglycemic medications (n = 6) (FPG 143 +/- 48 mg/dl; FPI 46 +/- 13 microU/ml), ingestion of Ginkgo biloba caused blunted plasma insulin levels from 30 to 120 minutes during the OGTT, leading to a reduction of the insulin AUC0-->120 (199 +/- 33 vs. 147 +/- 58 microU/ml/h, before and after Ginkgo biloba, respectively). The C-peptide levels increased, and so the AUC0-->120 did not parallel the insulin AUC0-->120, creating a dissimilar insulin/C-peptide ratio indicative of an enhanced hepatic extraction of insulin relative to C-peptide. Thus, in pancreatic beta-cells that are already maximally stimulated, ingestion of Ginkgo biloba may cause a reduction in plasma insulin levels. Only in NIDDM subjects with pancreatic exhaustion (FPG 152 +/- 46 mg/dl; FPI 16 +/- 8 microU/ml; n = 8), who also took oral hypoglycemic agents, did Ginkgo biloba ingestion significantly increase pancreatic beta-cell function in response to glucose loading (insulin AUC0-->120 increased from 51 +/- 29 to 98 +/- 20 microU/ml/h, p < 0.0001), paralleled by a C-peptide AUC0-->120 increase from 7.2 +/- 2.8 to 13.7 +/- 6.8 (p < 0.0001). Whether this increase is due to "resuscitation" of previously exhausted islets or increased activity of only the remaining functional islets is unclear. However, not even in this group did increased pancreatic beta-cell activity cause a reduction of blood glucose during the OGTT. It is concluded that ingestion of Ginkgo biloba extract by an NIDDM subject may increase the hepatic metabolic clearance rate of not only insulin but also the hypoglycemic agents. The result is reduced insulin-mediated glucose metabolism and elevated blood glucose.

Platelet-activating factor acetylhydrolases in health and disease

The platelet-activating factor (PAF) acetylhydrolases catalyze hydrolysis of the sn-2 ester bond of PAF and related pro-inflammatory phospholipids and thus attenuate their bioactivity. One secreted (plasma) and four intracellular isozymes have been described. The intracellular isozymes are distinguished by differences in primary sequence, tissue localization, subunit composition, and substrate preferences. The most thoroughly characterized intracellular isoform, Ib, is a G-protein-like complex with two catalytic subunits (alpha1 and alpha2) and a regulatory beta subunit. The beta subunit is a product of the LIS1 gene, mutations of which cause Miller-Dieker lissencephaly. Isoform II is a single polypeptide that is homologous to the plasma PAF acetylhydrolase and has antioxidant activity in several systems. Plasma PAF acetylhydrolase is also a single polypeptide with a catalytic triad of amino acids that is characteristic of the alpha/beta hydrolases. Deficiency of this enzyme has been associated with a number of pathologies. The most common inactivating mutation, V279F, is found in >30% of randomly surveyed Japanese subjects (4% homozygous, 27% heterozygous). The prevalence of the mutant allele is significantly greater in patients with asthma, stroke, myocardial infarction, brain hemorrhage, and nonfamilial cardiomyopathy. Preclinical studies have demonstrated that recombinant plasma PAF acetylhydrolase can prevent or attenuate pathologic inflammation in a number of animal models. In addition, preliminary clinical results suggest that the recombinant enzyme may have pharmacologic potential in human inflammatory disease as well. These observations underscore the physiological importance of the PAF acetylhydrolases and point toward new approaches for controlling pathologic inflammation.

The expression and localization of plasma platelet-activating factor acetylhydrolase in endotoxemic rats

The production of platelet-activating factor (PAF) and PAF-like phospholipids that also bind the PAF receptor are implicated in numerous pathological situations including bacterial endotoxemia and injury-induced oxidative damage. PAF and PAF-like phospholipids are hydrolyzed and inactivated by the enzyme PAF acetylhydrolase. In the intact rat, infusion of lipopolysaccharide (LPS) into a mesenteric vein served as an acute, liver-focused model of endotoxemia. We determined that the liver responds to LPS exposure with the production of plasma-type PAF acetylhydrolase mRNA and protein expression specifically in the resident macrophages of the liver. Liver macrophages, defined immunohistochemically using antibodies against ED1, present in livers from saline-treated animals contained no detectable PAF acetylhydrolase. Twenty-four hours following in vivo LPS administration, immunohistochemistry detected a slight increase in the number of ED1 staining cells and the ED1-positive cells now contained an abundance of PAF acetylhydrolase. The systemic administration of LPS resulted in increased expression of PAF acetylhydrolase in several tissues. Of the tissues examined, the greatest increase in PAF acetylhydrolase expression was observed in lung followed by increases in spleen, liver, kidney, and thymus. Additionally, the expression of PAF acetylhydrolase mRNA increased in circulating leukocytes and in peritoneal macrophages in response to systemic exposure to LPS. We examined the regulation of PAF acetylhydrolase expression and demonstrated the administration of the PAF receptor antagonists, BN 50739 and WEB 2170, inhibited by 50% the increase in PAF acetylhydrolase expression in response to LPS. The up-regulation of the plasma-type PAF acetylhydrolase expression constitutes an important mechanism for elevating the local and systemic ability to inactivate PAF and oxidized phospholipids in order to minimize PAF-mediated pathophysiology consequent from exposure to endotoxin. The abundance of PAF acetylhydrolase production in the liver lobule likely limits endotoxin-mediated tissue damage due to PAF synthesis.

Lipoprotein-associated phospholipase A(2), platelet-activating factor acetylhydrolase: a potential new risk factor for coronary artery disease

A specific and robust immunoassay for the lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), platelet-activating factor acetylhydrolase, is described for the first time. The immunoassay was used to evaluate possible links between plasma Lp-PLA(2) levels and atherosclerosis risk amongst susceptible individuals. Such an investigation was important because Lp-PLA(2) participates in the oxidative modification of low density lipoprotein by cleaving oxidised phosphatidylcholines, generating lysophosphatidylcholine and oxidised free fatty acids. The majority of Lp-PLA(2) was found associated with LDL (approximately 80%) and, as expected, enzyme levels were significantly positively correlated to LDL cholesterol. Plasma Lp-PLA(2) levels were significantly elevated in patients with angiographically proven coronary artery disease (CAD) when compared with age-matched controls, even though LDL cholesterol levels did not differ significantly. Indeed, when included in a general linear model with LDL cholesterol and other risk factors, Lp-PLA(2) appeared to be an independent predictor of disease status. We propose, therefore, that plasma Lp-PLA(2) mass should be viewed as a potential novel risk factor for CAD that provides information related to but additional to traditional lipoprotein measurements.

Plasma platelet-activating factor acetylhydrolase activity in human immunodeficiency virus infection and the acquired immunodeficiency syndrome

Platelet-activating factor (PAF) acetylhydrolase (PAF-AH) catalyzes the hydrolysis of PAF, a mediator of inflammation, as well as other biologically active oxidized phospholipids. In humans, plasma PAF-AH activity is bound to low-density lipoprotein (LDL) and high-density lipoprotein (HDL). Higher levels of plasma PAF-AH activity have been found in a variety of diseases, and are thought to be a defense mechanism against the toxic effects of PAF and oxidized phospholipids. We studied plasma PAF-AH activity in patients with human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS), a disease characterized by chronic HIV infection and a systemic host response. Plasma PAF-AH activity was significantly greater in AIDS patients compared with control subjects (25.2 +/- 2.0 v 17.0 +/- 0.8 nmol/min/mL, P < .001). The higher levels of plasma PAF-AH activity were found in LDL (28.2 +/- 2.2 v 18.3 +/- 1.0 nmol/min/mL for AIDS v controls, respectively, P = .0005), but not in HDL. Plasma PAF-AH activity in AIDS correlated with circulating interferon alfa (r = .575, P = .005) and plasma triglycerides (r = .556, P < .0025). The presence of secondary infection in AIDS did not significantly change plasma PAF-AH activity. The initiation of a new antiretroviral regimen with either a protease inhibitor or the nucleoside analog lamivudine did not significantly decrease plasma PAF-AH activity, despite successful suppression of HIV RNA levels. Plasma PAF-AH activity may be a sensitive marker of the host response to infection, and the higher levels of plasma and LDL-associated PAF-AH activity in patients with HIV infection and AIDS may be a physiological response to protect the host against oxidative injury from PAF and oxidized phospholipids.

Plasma and Lp(a)-associated PAF-acetylhydrolase activity in uremic patients undergoing different dialysis procedures

Plasma and Lp(a)-associated PAF-acetylhydrolase activity in uremic patients undergoing different dialysis procedures.

BACKGROUND

Platelet-activating factor (PAF) is a potent inflammatory mediator associated with several physiopathological conditions, including renal diseases. PAF is degraded to the inactive metabolite lyso-PAF by PAF-acetylhydrolase (PAF-AH), which is considered as a potent anti-inflammatory and anti-atherogenic enzyme associated with lipoproteins. In this study, we evaluated the plasma- and lipoprotein(a) [Lp(a)]-associated PAF-AH activity in relationship to plasma lipid parameters and Lp(a) isoform size in patients with mild/moderate chronic renal failure (CRF), as well as in hemodialysis (HD) and chronic ambulatory peritoneal dialysis (CAPD) patients.

METHODS

We studied 74 patients undergoing maintenance HD, 44 patients undergoing CAPD, 56 patients with mild/moderate CRF, and 98 healthy subjects whose lipid profile, as well as plasma and high-density lipoprotein (HDL)-associated PAF-AH activity, was determined. Moreover, the effect of Lp(a) plasma levels on the distribution of PAF-AH among plasma lipoproteins, as well as the specific activity and kinetic properties of PAF-AH on two different Lp(a) isoforms, was measured in each studied group.

RESULTS

The plasma PAF-AH activity in all studied groups was significantly higher than in controls, and the increase was more profound in CAPD patients. The HDL-associated PAF-AH activity, expressed per milliliter of plasma, was similar among all studied groups; however, when it was expressed as either per milligrams of HDL cholesterol or per milligrams of plasma apolipoprotein (apo) AI, the PAF-AH activity was significantly higher in all patient groups compared with controls. All patient groups had significantly elevated plasma Lp(a) levels, which altered the distribution of PAF-AH among the plasma lipoproteins compared with that observed in subjects with very low plasma Lp(a) levels (<8 mg/dl). Additionally, in each studied group, the specific activity as well as the apparent Km and Vmax values of the 19K4 apo(a) isoform were significantly higher (P < 0.01) compared with the values of the 23K4 isoform. However, the specific activity, as well as the Km and Vmax values on either the 19K4 apo(a) isoform or the 23K4 isoform, was significantly higher in CAPD patients compared with the other three groups.

CONCLUSIONS

Plasma PAF-AH activity is increased in uremic patients. This elevation is more profound in CAPD patients, who also exhibit a more atherogenic lipid profile and more pronounced alterations in the specific activity and the kinetic constants of Lp(a)-associated PAF-AH.

Cellular source(s) of platelet-activating-factor acetylhydrolase activity in plasma

Platelet activating factor (PAF) is immediately degraded and inactivated in the bloodstream by plasma PAF acetylhydrolase (PAF-AH). Although plasma PAF-AH-like activity was secreted in vitro from various cell types such as macrophages and hepatocytes, the exact cellular source(s) of this enzyme activity in vivo remains unclear. There is a naturally-occurring missense mutation (V279F) in the plasma PAF-AH gene in the Japanese population which results in complete loss of the enzyme activity. We analyzed 52 Japanese who had received an allogeneic bone marrow transplant and maintained donor-derived hematopoiesis. Ten recipients had chimeric plasma PAF-AH genotypes between the donor-derived peripheral blood leukocytes and the recipient-derived epithelial cells of buccal mucosa. Multiple regression analysis demonstrated that PAF-AH activity in plasma depended on the donor's genotype (standardized regression coefficient = 0.68, P < 0.0001), but not on the recipient's genotype (p = 0.48). One recipient who was a V279F homozygote in leukocytes and wild type homozygote in buccal mucosa had undetectable PAF-AH activity in plasma. We conclude that most of the PAF-AH activity in human plasma originates from hematopoietic lineage cells.

Regulation of platelet-activating factor (PAF) activity in human diseases by phospholipase A2 inhibitors, PAF acetylhydrolases, PAF receptor antagonists and free radical scavengers

The aim of this review is to present recent findings indicating the likely involvement of platelet-activating factor (PAF) in human diseases, and possible ways of alleviating its harmful effects. PAF is a potent proinflammatory mediator and promotes adhesive interactions between leukocytes and endothelial cells, leading to transendothelial migration of leukocytes, by a process of juxtacrine intercellular signalling. This process leads to activation of leukocytes and the release of reactive oxygen radicals, lipid mediators, cytokines and enzymes. These reaction products subsequently contribute to the pathological features of various inflammatory diseases. The reactive oxygen radicals cause low density lipoprotein (LDL) oxidation which mediates the development of atherosclerosis. Oxidized LDL may damage cellular and subcellular membranes, leading to tissue injury and cell death. Among the therapeutic approaches considered are agents that inhibit/degrade proinflammatory mediators and thereby have anti-inflammatory and/or anti-atherogenic potential. These include inhibitors of phospholipase A2 activity, PAF-acetylhydrolases, PAF antagonists and free radical scavengers/antioxidants, the latter protecting against oxidized LDL-induced cytotoxicity.

Urinary platelet-activating factor excretion is elevated in non-insulin dependent diabetes mellitus

Proteinuria is currently considered a very sensitive predictor of diabetic nephropathy, but 20-25% of all diabetic patients with negative Albustix reaction excrete higher than normal (< 20 mg/24 h) amounts of albumin in their urine. It is our hypothesis that platelet-activating factor (PAF), a potent glycerophospholipid that acts as a chemical mediator for a wide spectrum of biological activities, including increased vascular permeability, may be produced in significant amounts during periods preceding microalbuminuria. In this study, we compared urinary PAF excretion in Mexican-American subjects who were diagnosed with non-insulin dependent diabetes mellitus (NIDDM) with their healthy control counterparts. The age of the NIDDM subjects (45.9 +/- 2.1 years) was not significantly different from the healthy control group, which was 39.4 +/- 2.7 years (P < 0.0672). The NIDDM subjects (body mass index, 29.9 +/- 1.1 compared to 26.1 +/- 0.9 kg/m2 in healthy controls) were characterized by significantly increased (P < 0.05) fasting plasma glucose (192 +/- 11 vs. 97 +/- 4 mg/dl in healthy controls), fasting insulin (20.9 +/- 2.4 vs. 12.3 +/- 1.6 microU/ml), fasting C-peptide (2.93 +/- 1.26 vs. 1.48 +/- 0.51 ng/ml), and hemoglobin A1c (10.3 +/- 0.7 vs. 5.6 +/- 0.3%), respectively. The urine output for the NIDDM and control subjects were 1942 +/- 191 ml/24 h and 1032 +/- 94 ml/24 h, respectively, and urinary albumin excretion (UAE) rates were estimated to be 38 +/- 7 micrograms/min and 11 +/- 1 micrograms/min, respectively. The NIDDM subjects produced significantly increased levels of urinary PAF (2606.3 +/- 513.1 ng/24 h compared with 77.9 +/- 14.1 ng/24 h in controls (or 1706.3 +/- 420.8 ng/ml compared with 85.4 +/- 17.8 pg/ml of urine, in NIDDM and control subjects, respectively). We found that urinary PAF excretion was significantly correlated with microalbumin excretion (r = 0.7) especially at UAE rates greater than 30 mg/day and more importantly, some NIDDM patients with negative Albustix reaction (i.e. normal UAE) produced significantly more PAF, suggesting that PAF excretion may precede microalbuminuria and that subtle injury to the kidneys are present in NIDDM long before overt albuminuria ensues, urinary PAF measurements could potentially therefore serve as a sensitive indicator of renal injury in diabetes mellitus. These results lend further credence to our hypothesis that PAF may be the biochemical compound linking the various members of the insulin resistance syndrome.

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.

A mutation in plasma platelet-activating factor acetylhydrolase (Val279-->Phe) is a genetic risk factor for stroke

BACKGROUND AND PURPOSE

Platelet-activating factor (PAF) is a phospholipid with multiple actions that include thrombosis and inflammation. It is inactivated by a plasma enzyme, PAF acetylhydrolase. Deficiency of this enzyme in plasma is caused by a missense mutation in the gene (Val279-->Phe). We have studied a possible association of this mutation with the risk of stroke.

SUBJECTS AND METHODS

We studied 120 consecutive patients with cerebral thrombosis. The control group consisted of 134 patients matched for age and sex with minor complaints but without stroke. Genomic DNA was analyzed for the mutant allele by a specific polymerase-chain reaction. Plasma PAF acetylhydrolase activity was determined by the method of Stafforini et al.

RESULTS

The prevalence of the mutant gene was 43.4% in stroke patients (39.2% heterozygotes and 4.2% homozygotes), which was significantly higher than the 25.4% in control subjects (22.4% heterozygotes and 3.0% homozygotes) (chi 2 = 9.22, P < .01). The prevalence was slightly higher in stroke patients without hypertension than those with hypertension, but the difference was not significant. The patients with family histories of stroke had a slightly higher but not a significant prevalence of the mutant gene as compared with those without family histories of stroke. Plasma PAF acetylhydrolase activity was higher in patients than in control subjects, in normal subjects, or patients with a heterozygous genotype.

CONCLUSIONS

These results suggest that plasma PAF acetylhydrolase deficiency may be a risk factor for stroke. This may explain the relatively high prevalence of stroke in Japan, as the mutation is more common among Japanese than Caucasians.

Plasma PAF acetylhydrolase in non-insulin dependent diabetes mellitus and obesity: effect of hyperinsulinemia and lovastatin treatment

Insulin resistance is characterized principally by impaired insulin-mediated glucose uptake which provokes a compensatory increase in pancreatic beta-cell secretory activity. For a time this may produce well-controlled plasma glucose levels but as the insulin resistance worsens the augmented insulin production becomes inadequate to keep plasma glucose at euglycemia leading to the development of non-insulin dependent diabetes mellitus (NIDDM), accompanied by hyperinsulinemia and hyperglycemia. A number of metabolic defects are associated with NIDDM including obesity, hypercoagulability, cardiovascular disease risk factors such as hypertension and dyslipidemia and these constitute the insulin resistance syndrome. The identity of the biochemical factor that might link all these defects is not yet known. We have hypothesized that platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF) may be such a link. In this study, we measured plasma acetylhydrolase (EC.1.1.48), which degrades PAF to the inactive metabolise lyso-PAF, as a surrogate for PAF activity in three groups of hypercholesterolemic subjects: lean controls (n = 9), non-diabetic obese (n = 6) and NIDDM subjects (n = 6). The ages and body mass indices of the subjects were 46 +/- 3.1 and 24.2 +/- 2.2 for the lean controls, 52 +/- 2.5 and 28.7 +/- 0.9 for the NIDDM subjects and 60 +/- 2 and 27.6 +/- 2.1 for the obese, non-diabetic subjects (mean +/- S.E.M.). The measurements were made before and after therapy with the cholesterol-lowering drug lovastatin, a 3-hydroxy 3 methylglutaryl (HMG) coenzyme. A reductase inhibitor (40 mg/day) for 3 months. Fasting plasma glucose (FPG) levels were 91 +/- 11, 96 +/- 3 and 146 +/- 11 mg/dl, for the lean, obese and NIDDM subjects, respectively, before therapy began. Lovastatin did not affect FPG in any of the three subject groups. Before treatment, the fasting plasma insulin (FPI) levels were 6.1 +/- 0.92, 10.83 +/- 2.03 and 14.68 +/- 3.64 mU/l for the lean, non-diabetic obese and NIDDM subjects, respectively. After lovastatin therapy only the obese group exhibited a significant change in FPI (15.35 +/- 2.47 mU/l) (P < 0.05). Total cholesterol levels were similar in all three groups both before and after lovastatin therapy but within each group lovastatin therapy significantly reduced the total cholesterol by 32, 29 and 34% in the lean, obese and NIDDM subject groups respectively (P < 0.0001). Lovastatin therapy reduced LDL-cholesterol levels by 40, 32 and 46% in the lean, obese and NIDDM subjects, respectively, but produced no significant effect on HDL or triglyceride levels. Before therapy, the plasma acetylyhydrolase activities were 104 +/- 7, 164 +/- 7 and 179 +/- 7 nmol/ml per min in the lean, obese and NIDDM subjects, respectively. Lovastatin therapy reduced plasma acetylhydrolase levels to 70 +/- 7, 87 +/- 6 and 86 +/- 7 nmol/ml per min in the lean, obese and NIDDM subjects, respectively. Plasma acetylhydrolase activity was predominantly (> 80%) associated with LDL cholesterol both before and after lovastatin treatment. Also, plasma acetylhydrolase activity significantly correlated with fasting plasma insulin levels before lovastatin therapy but not after. Taken together, this study clearly implicates PAF metabolism in three defects associated with the insulin resistance syndrome: hypercholesterolemia, obesity and NIDDM. Additionally, we conclude that chronic hyperinsulinemia may play a significant role in the production of plasma acetylhydrolase.

Cell-specific regulation of expression of plasma-type platelet-activating factor acetylhydrolase in the liver

Platelet-activating factor (PAF) is a potent proinflammatory phospholipid mediator that causes hypotension, increases vascular permeability, and has been implicated in anaphylaxis, septic shock and several other inflammatory responses. PAF is hydrolyzed and inactivated by the enzyme PAF-acetylhydrolase. In the intact rat, a mesenteric vein infusion of lipopolysaccharide (LPS) served as an acute, liver-focused model of endotoxemia. Plasma PAF-acetylhydrolase activity increased 2-fold by 24 h following LPS administration. Ribonuclease protection experiments demonstrated very low levels of plasma-type PAF-acetylhydrolase mRNA transcripts in the livers of saline-infused rats; however, 24 h following LPS exposure, a 20-fold induction of PAF-acetylhydrolase mRNA was detected. In cells isolated from endotoxin-exposed rat livers, Northern blot analyses demonstrated that Kupffer cells but not hepatocytes or endothelial cells were responsible for the increased PAF-acetylhydrolase mRNA levels. In Kupffer cells, plasma-type PAF-acetylhydrolase mRNA was induced by 12 h, peaked at 24 h, and remained substantially elevated at 48 h. Induction of neutropenia prior to LPS administration had no effect on the increase in PAF-acetylhydrolase mRNA seen at 24 h. Although freshly isolated Kupffer cells contain barely detectable levels of plasma-type PAF-acetylhydrolase mRNA, when Kupffer cells were established in culture, PAF-acetylhydrolase expression became constitutively activated concomitant with cell adherence to the culture plates. Alterations in plasma-type PAF-acetylhydrolase expression may constitute an important mechanism for elevating plasma PAF-acetylhydrolase levels and an important component in minimizing PAF-mediated pathophysiology in livers exposed to endotoxemia.

Chronic hyperinsulinemia inhibits platelet-activating factor (PAF) biosynthesis in the rat kidney

A number of risk factors for cardiovascular disease, including hypertension, are associated with the insulin resistance syndrome. The hallmark of this syndrome is an impairment in insulin action which provokes a compensatory increase in pancreatic beta-cell insulin secretion leading to chronic hyperinsulinemia. Indirect studies show that platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphorylcholine, PAF), a potent antihypertensive lipid produced by the kidney, may be decreased by hyperinsulinemia. The present study was designed to evaluate the effect of chronic hyperinsulinemia on renal PAF metabolism, arterial blood pressure and whole body insulin sensitivity. Chronic catheterized, unstressed rats were infused with saline or insulin plus glucose to create a chronic condition of sustained euglycemic (approximately 130 mg/dl) hyperinsulinemia (approximately 90 mU 1. or 3-fold over basal levels). PAF is a metabolically unstable compound being susceptible to rapid degradation to the biologically inactive lyso-PAF, a metabolite which also serves as a precursor for PAF synthesis. PAF synthesis and counter-regulatory prostaglandins may be derived from the same arachidonate precursor. The enzymes which catalyze these reactions were measured in plasma and in the subcellular fractions of the kidneys. Compared to saline-treated rats, sustained physiologic hyperinsulinemia for 7 days: (i) decreased insulin-mediated glucose disposal by 30%; (ii) caused an increased plasma PAF:acetylhydrolase, which degrades PAF to lyso-PAF, without any change in cytosolic PAF:acetylhydrolase activity; and (iii) completely inhibited microsomal lyso-PAF:acetyl CoA acetyltransferase activity which catalyzes the conversion of lyso-PAF back to bioactive PAF. The increased catabolism of PAF in plasma, combined with decreased renal PAF biosynthesis, would be expected to decrease circulating PAF levels leading to a rise in blood pressure. However, blood pressure remained unchanged. The sustained hyperinsulinemia stimulated plasma membrane CoA-independent transacylase activity, which is responsible for the mobilization of arachidonates into lyso-PAF, to form l-alkylarchidonoyl-glycerophosphocholine. The latter is the stored precursor for the synthesis of PAF and vasodilatory prostaglandins, which may have offset the effect of decreased PAF. We hypothesize that hyperinsulinemia may alter the blood pressure only if the balance between the synthesis/catabolism of PAF and vasodilatory prostaglandins is disrupted.

Pharmacological evidence of a role for platelet activating factor as a modulator of vasomotor tone and blood pressure

The purpose of the present study was to investigate the role of platelet-activating factor (PAF, 1-O-hexadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine), a phospholipid mediator synthesized by endothelial and smooth muscle cells, in the modulation of vascular tone and blood pressure. In pentobarbitone-anaesthetised rabbits, unloading of the carotid sinus baroreceptors by a bilateral carotid artery occlusion elicited a reflex rise in arterial pressure which was markedly potentiated by pretreating the animals with the PAF receptor antagonists WEB 2086 [3-4-(2-chlorphenyl)-9-methyl-6H-thieno-3,2f-1,2,4-triazolo-4, 3 a-1,4-diazepin-2-yl-(4-morpholinyl)-I-propanone; 2, 5 or 10 mg kg-1, i.v.] or BN 52021 (ginkgolide B; 0.1, 0.3 or 1.0 mg kg-1, i.v.). The increases in systemic vascular resistance induced by noradrenaline (30 micrograms kg-1, i.v.) or by the central activation of the sympathetic nervous system with glutamate (1 mg kg-1, intracerebroventricular) were also significantly potentiated in animals pretreated with WEB 2086 (5 mg kg-1, i.v.). In contrast, pretreatment with the cyclooxygenase inhibitor indomethacin (3 mg kg-1, i.v.) did not affect the haemodynamic actions of noradrenaline, thus excluding the possibility that prostacyclin may modulate the potentiating effect. To further confirm that PAF is released during systemic vasoconstriction, the cardiovascular PAF receptors were desensitized by the daily administration of PAF (3 micrograms kg-1, i.v.) for seven days. This procedure significantly reduced the intensity and duration of the hypotensive response to a subsequent PAF injection (3 micrograms kg-1, i.v.). In desensitized animals, the hypertensive response to bilateral carotid artery occlusion was potentiated to the same extent as in the animals treated with PAF receptor antagonists. Inhibition of PAF biosynthesis by pretreatment of the animals with the phospholipase A2 inhibitor mepacrine (5 mg kg-1, i.v.) also enhanced the increase in blood pressure elicited by carotid artery occlusion. We conclude that PAF is involved in the acute but not basal modulation of vasomotor tone and, hence, arterial pressure, probably by a negative feedback mechanism triggered by important increases in the vascular tone.

The biochemical role of platelet-activating factor in reproduction

The presence of Co-A independent transacylase activity in amnion cells and the preferential transfer of arachidonic acid to acceptor-ethanolamine plasmalogen provide a satisfactory explanation to the questions raised by the observation that arachidonate-enriched ethanolamine plasmalogen increases in amnion late in gestation without alteration in the total amount of ethanolamine glycerophospholipids. The proposed mechanism also serves as a link between the observed changes in glycerophospholipid composition and the generation of PAF. We have emphasized a role for PAF in fetal lung maturation, the initiation and maintenance of parturition, and in certain complications associated with a premature delivery. Although PAF is known to be the most potent lipid mediator yet described and its importance in reproductive biology is well documented, it is our view that these events cannot be attributed solely to PAF and in all likelihood a number of autacoids participate in these processes.

PAF and haematopoiesis: III. Presence and metabolism of platelet-activating factor in human bone marrow

Platelet-activating factor (PAF) is a phospholipid compound with major immunoregulatory activities. The present study shows that human bone marrow contains 576 +/- 39 pg PAF/ml (n = 35). Bone marrow-derived PAF exhibits the same biophysical and biological properties that synthetic PAF. PAF concentrations in bone marrow are correlated with the granulocyte (r = 0.4, P = 0.02) but not with the lymphocyte (r = 0.24, P = 0.17) and the monocyte (r = 0.12, P = 0.48) counts. In bone marrow PAF is inactivated by a plasma PAF acetylhydrolase activity (48.0 +/- 2.3 nmol/min per ml, n = 34). Experiments with [3H]PAF indicate that human bone marrow cells actively metabolize this potent molecule by the deacetylation-transacylation pathway. Results of this investigation indicate the permanent presence of significant amounts of PAF in bone marrow suggesting its putative involvement in the processes of bone marrow cell proliferation and maturation.

PAF and hematopoiesis. II. Elevated levels of plasma paf acetylhydrolase after rapid infusion of 5-fluorouracil in cancer patients

Blood platelet-activating factor (PAF) levels are regulated by a plasma PAF acetylhydrolase. We investigated its levels in cancer patients during the course of a 5-day 5-fluorouracil (5-FU) treatment. PAF acetylhydrolase increased in nine patients with daily bolus infusion of 0.4 g 5-FU per m2 of body surface (81.7 +/- 8.7 nmol PAF/min/ml vs. 66.6 +/- 7.0; P < 0.001 for day 5 as compared to day 1). By contrast PAF acetylhydrolase did not change in seven patients with continuous infusion of 5-FU. The meaning of these results is discussed in respect of the immunoregulatory role of PAF.

Hydrolysis and transesterification of platelet-activating factor by lecithin-cholesterol acyltransferase

Purified lecithin-cholesterol acyltransferase (LCAT, EC 2.3.1.43) from human plasma was found to hydrolyze platelet-activating factor (PAF) to lyso-PAF and acetate. In addition, it catalyzed the transfer of the acetate group from PAF to lysophosphatidylcholine, forming lyso-PAF and a 1-acyl analog of PAF. In contrast to the cholesterol-esterification reaction carried out by the enzyme, the hydrolysis and transacetylation of PAF by LCAT did not require an apoprotein activator and were not inhibited by sulfhydryl inhibitors but were inhibited by serum albumin. When added to a proteoliposome substrate of LCAT or to whole plasma, PAF inhibited cholesterol esterification by LCAT competitively. PAF acetylhydrolase (EC 3.1.1.47), purified from human plasma, also catalyzed the transfer of acetate from PAF to lysophosphatidylcholine. However, the LCAT-catalyzed reactions of PAF were not due to contamination with PAF acetylhydrolase, since the ratio of acetyl transfer to acetyl hydrolysis was 3 times greater for LCAT, when compared with PAF acetylhydrolase under identical conditions. Furthermore, recombinant human LCAT secreted by baby hamster kidney cells also catalyzed the hydrolysis and transacetylation of PAF. These results demonstrate that LCAT can inactivate PAF in plasma by transacetylation and suggest that it may have a role in the metabolism of PAF, and possibly of oxidized phospholipids, in plasma.

Effect of 17 beta-estradiol on secretion of platelet-activating factor acetylhydrolase by HepG2 cells

Estrogen has been shown to decrease plasma platelet-activating factor (PAF) acetylhydrolase activity, but the precise mechanisms are not known. We examined the effect of estradiol on the secretion of PAF acetylhydrolase by HepG2 cells. In our previous study, we demonstrated the production of this enzyme by HepG2 cells, which we used as an experimental model of normal hepatocytes. 17 beta-Estradiol mildly but consistently inhibited the secretion of PAF acetylhydrolase by HepG2 cells in a concentration-dependent manner. Under basal conditions, HepG2 cells secreted 42.3 pmol/mg cell protein/min PAF acetylhydrolase in 24 hours (mean of 8 dishes), and the presence of 10(-7) mol/L 17 beta-estradiol decreased the secretion to 77% +/- 10.3% of control values (mean +/- SD, n = 8, P < .02). 17 beta-Estradiol treatment affected neither the secretion of apolipoprotein (apo) A-I nor cell-associated PAF acetylhydrolase activity. Electrophoretic separation of [35S]methionine-labeled PAF acetylhydrolase revealed a single band whose molecular weight was approximately 43,000 d. We conclude that estrogen decreases the secretion of PAF acetylhydrolase by the liver, and it may explain, at least in part, the effect of estrogen on plasma PAF acetylhydrolase.

Platelet-activating factor-acetylhydrolase activity in normotensive and hypertensive pregnancies

OBJECTIVE

The purpose of our study was to evaluate the hypothesis that pregnancy is associated with decreased platelet-activating factor-acetylhydrolase activity in women with normotension, but not in women with hypertension.

STUDY DESIGN

We evaluated plasma platelet-activating factor-acetylhydrolase activity in normal nonpregnant women (n = 10), normal pregnant women (n = 24), pregnant women with pregnancy-induced hypertension-preeclampsia (n = 7), and a group of men with normotension (n = 10).

RESULTS

Platelet-activating factor-acetylhydrolase activity was lower at 32 weeks of gestation during normal pregnancies compared with nonpregnant controls (p < 0.001); however, in women with pregnancy-induced hypertension-preeclampsia, platelet-activating factor-acetylhydrolase activity was not decreased. Platelet-activating factor-acetylhydrolase activity in men was higher than in all women (p < 0.01).

CONCLUSION

Pregnant women with normotension may be refractory to pressor agents such as angiotensin II in part because of the decrease in plasma platelet-activating factor-acetylhydrolase activity, which results in an increase in platelet-activating factor. In contrast, enzyme activity is not decreased in pregnant women with hypertension, who have increased sensitivity to various pressor agents.

Alteration of platelet activating factor (PAF) metabolism in rat pulmonary alveolar macrophages and plasma by cigarette smoking

The pathophysiological role of platelet activating factor (PAF) in smoking-induced disorders was examined in rats exposed daily to smoke for 10, 18 and 26 weeks. The concentration of PAF in bronchoalveolar lavage fluid and the activities of PAF biosynthetic and catabolic enzymes in alveolar macrophages and in plasma were determined. The concentration of PAF in lavage fluid of the smoke-exposed group was significantly lower than that in the sham group for each duration of smoke exposure. The PAF biosynthetic enzyme, acetyl transferase, activity in alveolar macrophages of smoked group was less than that in the sham group although the difference was not statistically significant. PAF catabolic enzyme, acetyl hydrolase, activities in alveolar macrophages and in plasma were all significantly higher in every smoked group than in the sham group. These data indicate that cigarette smoking alters PAF metabolism in the respiratory tract and in plasma and such an alteration may contribute, at least in part, to smoking induced cardiopulmonary disorders.

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

Levels of platelet-activating factor (PAF) in blood from patients with ischemic stroke were determined by radioimmunoassay (RIA). Using 2 ml of blood as a starting material, PAF was detected in 11 out of 17 stroke patients and 3 of 25 age-matched healthy controls. This implies that blood level of PAF is higher in stroke patients than in controls. Plasma levels of PAF-like lipid(s) (PAF-LL) were also estimated in the same subjects by a bioassay based on aggregation of human polymorphonuclear neutrophils. PAF-LL was detected in plasma samples of all subjects and the average values in patients and controls were 294 +/- 211 pg/ml and 140 +/- 122 pg/ml, respectively. There was a statistically significant difference between these two values (p less than 0.01). Separation of plasma lipids by HPLC gave a single peak in bioassay, which had the same elution volume as authentic PAF. When each fraction was subjected to RIA, the fractions corresponded to phosphatidylcholine (PC) or lysoPC also showed the immunoreactivity, however, the purification procedure using an octadecylsilica gel cartridge eliminated such cross-reacting compounds. We conclude that blood PAF is higher in patients with ischemic stroke than in healthy subjects. Besides, there may be bioactive phospholipid molecules other than PAF, which level in plasma is also higher in stroke patients.

Platelet activating factor acetylhydrolase activity in the urine of patients with renal disease

Platelet activating factor has been demonstrated in blood and urine and has a broad range of effects on kidney function. The kidney possesses the enzymes responsible for PAF synthesis as well as the specific acetylhydrolase which deactivates PAF. We used a radioactive assay to measure PAF-acetylhydrolase activity in urine samples obtained from normal individuals and patients with various nephropathies. Activity was detected in the majority of normal urines with a mean + 2 SD = 0.70 nmol/30 min/ml. Activity exceeding this value was measured in the urines of 11 of 14 patients with diabetes mellitus, 14 of 22 with glomerulonephritis, and 5 of 16 with hypertensive renal disease. Further study is necessary to relate urine hydrolase activity to specific functional and structural abnormalities of the kidney.