Isolation and structural elucidation of biologically active phospholipids from Scytonema julianum (cyanobacteria)

The role of platelet-activating factor (PAF) as a mediator appeared in rather primitive organisms like protozoans and was maintained in more evolved organisms. No reports exist for the presence of PAF or PAF analogues - or even compounds that exhibit PAF-like activity - in cyanobacteria, even though they belong to a a group of organisms at a low evolutionary level where the content of alkylacyl forms of ether lipids is expected to be high. In addition, cyanobacteria serve as a rich source of novel bioactive metabolites. In the present study the total lipids of a strain of Scytonema julianum, a filamentous cyanobacterium isolated from a Greek cave, were separated into neutral lipids and phospholipids, the latter being further fractionated by HPLC. Each phospholipid fraction was tested in vitro for its ability to inhibit PAF-, arachidonic acid- and ADP-induced washed-rabbit-platelet aggregation and/or to cause platelet aggregation. Two types of phospholipids causing platelet aggregation were detected and shown to be an acetylsphingomyelin and an acylacetylglycerol phosphoacetylated glycolipid. The existence of the sphingomyelin analogues is very important, since ceramides, cerebrosides and related lipids are intracellular second messengers. The identification of the phosphoglycoglycerolipid demonstrates a new type of lipid in cyanobacteria, namely one that exhibits a biological activity very similar to that of PAF. Its presence reinforces the concept that PAF is a member of a large family of lipid mediators, apparently having different physiological roles in prokaryotic and eukaryotic organisms. In addition, Scytonema julianum contains a phosphatidylcholine (C(16:0)/(18:2)), even though bacteria in general seldom contain choline-containing phosphoacylglycerols.

Is platelet-activating factor produced during hemodialysis with AN-69 polyacrylonitrile membrane?

BACKGROUND

Platelet-activating factor (PAF) production during hemodialysis (HD) with cuprophane (CU) membrane has previously been demonstrated, while the results regarding PAF production during HD with AN-69 polyacrylonitrile membrane are dubious. In this study an attempt is made to show that PAF is produced during HD using AN-69 membrane while comparing this production with the corresponding one from HD with CU. Since previous studies have indicated that PAF, like the complement system, could also be implicated in HD-related leukopenia and thrombocytopenia (especially when CU membrane is used), the circulating leukocyte and platelet counts as well as the C3a-desArg and SC5b-9 (soluble, nonlytic form of the terminal complement complex) levels were measured.

METHODS

Ten hemodialyzed patients were subjected to HD with CU and AN-69 membranes for 2 consecutive weeks (first week with CU and second with AN-69). During the third HD session of each week and at different times (0, 2, 5, 15, 30, 60, 180 and 240 min), the PAF levels in the blood as well as the leukocyte and platelet counts were measured, while the circulating levels of the C3a-desArg and SC5b-9 were measured at 0, 5, 15, 60 and 240 min. PAF was detected by ethanol extraction, followed by purification by column chromatography and high-pressure liquid chromatography and finally quantified by bioassay. The C3a-desArg and SC5b-9 fractions of the complement were measured by immunoassay while an autoanalyzer gave the leukocyte and platelet counts.

RESULTS

Circulating PAF levels were detected at all time intervals during HD with AN-69 (PAF(AN-69)) and CU (PAF(CU)) membranes. At all time intervals PAF(AN-69) < PAF(CU), however, statistically significant differences (s) between the two membranes existed only at 15, 30, 60, 180 and 240 min. The highest PAF(AN-69) and PAF(CU) occurred at 5 and 15 min into dialysis, respectively. The same observations were made for circulating C3a-desArg levels (s existed additionally at 5 min as well). The reduction of the circulating leukocytes had almost a mirror image with the C3a-desArg as well as PAF levels while the maximal reduction of platelets was observed after 2 min into dialysis with both membranes (i.e., simultaneously with the first increase in PAF secretion).

CONCLUSIONS

PAF is indeed produced during HD with AN-69 membrane, as it is during HD with CU. At all time intervals during the HD procedure, PAF(AN-69) < PAF(CU). PAF seems to contribute to HD-related leukopenia and thrombocytopenia with both membranes.

Biologically active lipids with antiatherogenic properties from white wine and must

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

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

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

Separation of biologically active lipids from red wine

A number of lines of evidence suggest that red wine exerts a protective effect against coronary heart disease, but the nature of the protective compounds is unclear and the mechanism is incompletely understood. In this study, total lipids of a Greek red wine were separated into neutral and polar lipids. Polar lipids were further separated into glyco- and phospholipids, which were fractionated by HPLC. Each lipid fraction was tested in vitro for its ability to inhibit platelet-activating factor (PAF) and thrombin-induced washed rabbit platelet aggregation and/or to cause platelet aggregation. A significant number of glyco- and phospholipids that exerted the above biological activities were detected. Structural data of an active phosphoglycolipid are also provided. trans-Resveratrol demonstrated also a dose-dependent inhibition of PAF-induced platelet aggregation along with the already reported inhibitory activity against thrombin and adenosine-5'-diphosphate. Because it has already been reported that PAF is involved in atheromatosis generation, the existence of PAF inhibitors in red wine may contribute to the protective role of red wine against atherosclerosis.

Identification of a new endogenous platelet-activating factor-like molecule in gingival crevicular fluid

Periodontal disease is an inflammatory disease and the major cause of tooth loss in adults. Bacteria and their products are the causative agents of this disease. Endogenous molecules mediate the inflammatory process and play a major role in its amplification and perpetuation as well as in the ensuing tissue destruction. The relationship between platelet-activating factor (PAF) and periodontal disease has not so far been examined thoroughly. We have isolated a phospholipid molecule with PAF-like activity from gingival crevicular fluid. This molecule, purified on HPLC, causes washed platelet aggregation with EC50 value 0.1 microM, based on phosphorus determination. It acts through PAF-receptors and is inactivated by PAF-acetylhydrolase. In addition, this phospholipid presents biological activity towards human platelets. The combination of the results obtained from the chemical and enzymic treatments, the biological assays as well as results from the electrospray analysis, leads to the conclusion that this phospholipid is a hydroxyl-PAF analogue with relative molecular mass 703. This PAF-like molecule may be implicated in periodontal disease.

Synthesis of a new phosphoglycolipid with biological activity towards platelets

Various synthetic as well as naturally occurring compounds have been found to exhibit platelet-activating factor (PAF)-like activity or to act as specific PAF inhibitors. In this work we have synthesized a new phosphoglycolipid, methyl 2,3,4-tri-O-acetyl-6-(1'-O-stearoyl-2'-O- acetyl-DL-glycero-3'-phosphoryl)-alpha-D-glucopyranoside ammonium salt, using a combination of known synthetic steps. This phosphoglycolipid was first purified on TLC (Rf 0.7, using chloroform/methanol/water, 65:25:4, v/v/v as solvent system). It was further purified onto a high performance liquid chromatography silica column with an elution system that contained acetonitrile and methanol (retention time 13.5 min). Its identification was based on chemical determinations and electrospray mass spectrometry analysis. The above compound induced washed platelet aggregation with an EC50 value at 2 x 10(-4) M. The aggregation curve was biphasic, the first wave of which was through the PAF way while the second one was through the ADP way. Treatment with acetylhydrolase resulted in a rapid decrease of the first wave of aggregation and in a slow decrease of the second wave. In lower concentrations, the phosphoglycolipid inhibited PAF- and thrombin-induced aggregation with IC50 values of the order of 10(-7) M. In conclusion, this phosphoglycolipid has a diverse biological activity. The PAF-like activity of this new lipid enforces the conception that PAF is a member of a large family consisting of lipid mediators.

Blood cardiolipin in haemodialysis patients. Its implication in the biological action of platelet-activating factor

Bovine heart cardiolipin specifically inhibits platelet aggregation induced by PAF in vitro. In the past we have reported that patients with primary glomerulonephritis have increased PAF levels in plasma (Iatrou et al., 1995b). In this work we investigate the existence of cardiolipin in the blood of end-stage renal patients due to primary glomerulonephritis and we study its implication in the biological study of PAF. Lipids from blood samples of end-stage renal patients were extracted, fractionated onto silicic acid column and onto High Performance Liquid Chromatography (HPLC) cation exchange column. PAF fraction was removed and phospholipids were separated from the rest lipid fraction with current counter distribution and furthermore fractionated onto HPLC silica column. The results show: 1. cardiolipin is present in the blood of end-stage renal patients. 2. Blood cardiolipin specifically inhibits PAF-induced aggregation in washed rabbit platelets. 3. Scatchard plot analysis of PAF binding, in the presence of unlabelled PAF and in the presence of cardiolipin, shows that rabbit platelets possess two different types of binding sites. One of which is saturable and of high affinity, kD = 0.103 +/- 0.03 nM (SEM, n = 3) with 337 +/- 94 binding sites per platelet for PAF and kD = 0.087 +/- 0.02 nM with 371 +/- 92.7 binding sites per platelet for cardiolipin while the other one has almost infinite binding capacity. 4. Blood cardiolipin competes [3H]PAF binding in rabbit platelets. This work shows that cardiolipin exists in the blood of end-stage renal patients and specifically inhibits PAF-induced aggregation as well as PAF binding in rabbit platelets. The possible implication of the biological actions of cardiolipin in the anticardiolipin-antiphospholipid syndrome is also discussed.

Platelet-activating factor levels and PAF acetylhydrolase activities in patients with primary glomerulonephritis

Platelet-activating factor (PAF) belongs to a new class of lipid chemical inflammatory mediators described as acetyl glyceryl ether phosphorylcholine. Although PAF has been implicated in kidney injury, its role in renal immune injury has not been clearly defined yet. We studied the levels of PAF in the plasma and urine and acetylhydrolase (AH) activities in serum and in renal tissue (cortex, C and medulla, M) in patients with primary glomerulonephritis (PGN). PAF levels in the plasma and urine and AH activity in serum of normal volunteers as well as AH activities in normal renal parenchyma (C and M) from nephrectomized patients (served as control) were also measured. Our results demonstrate increased PAF levels in the plasma and urine as well as increased AH activity in serum in patients with PGN in comparison to normal volunteers. AH activity in cortex of those patients was diminished compared to normal kidney tissue. We propose that the enhanced AH activity in serum in patients with PGN could be due to hyperproduction and low degradation of PAF in nephritic tissue which on one hand results in enhanced PAF levels in the plasma and in urine and on the other hand results in enhanced serum AH activity by virtue of substrate (PAF) availability. These data provide new knowledge in the homeostasis of PAF and its degrative enzyme in the setting of PGN.

The production of platelet-activating factor (PAF) during hemodialysis with cuprophane membrane. Does the calcium concentration in the dialysate play any role on it?

There is evidence that PAF may be produced during hemodialysis (HD) mainly when using cuprophane membrane (CU). It is also known that PAF production is dependent on the amount of extracellular calcium (ECa2+). In the present study, we investigated the production of PAF during HD with CU as well as the role of the Ca2+ in the dialysate with respect to PAF production. Five hemodialyzed patients were studied in two consecutive HD sessions (the first performed using dialysate without Ca2+ and the second with a Ca2+ concentration of 3.25 mEq/L) and at different times during the sessions the circulating PAF levels as well as the leukocyte and platelet counts were measured. The results demonstrated that a) PAF was indeed produced during HD with CU, b) the highest PAF levels in blood were observed between 5 and 15 minutes from the beginning of HD, at which time the lowest circulating leukocyte and platelet count were measured and c) PAF levels in blood were inversely proportional to the Ca2+ concentration in the dialysate (with the exceptional case of the 15 minutes), although we expected the opposite results.

The influence of parathyroid hormone on platelet-activating factor (PAF) blood levels in hemodialysis patients

PAF represents a new family of glycerophospholipids and possesses multiple biological activities including platelet aggregation. Production of PAF has been demonstrated in a number of different cell types and in response to various stimuli. In this work an attempt is made to study the effect of parathyroid hormone (PTH) on PAF production. In 13 hemodialysis patients with severe secondary hyperparathyroidism, PAF levels in blood as well as intact PTH (iPTH) and total calcium in serum (tCa), before and 10 days after parathyroidectomy (PTHx), were measured. Our results indicate that PAF levels in blood as well as iPTH and tCa were higher before PTHx than after [a) PAF before 1.10 x 10(-4) +/- 9 x 10(-5) gamma/ml and after 2 x 10(-5) +/- 1 x 10(-5) gamma/ml, p < 0.001; b) iPTH before 880 +/- 392.9 pm/ml and after 121.6 +/- 61.9 pm/ml, p < 0.001; c) tCa before 9.96 +/- 0.35 mg/dl and after 8.38 +/- 0.30 mg/dl, p < 0.001]. Using stepwise regression analysis it seems that PAF is dependent on calcium which is dependent mainly on iPTH. Since a) platelet dysfunction is among the factors which are incriminated for bleeding in uremia and b) PAF which induces platelet aggregation acts via specific receptors, we checked the response of platelets in terms of their ability to aggregate in vitro following increasing doses of exogenous PAF in 5 of the above patients in order to investigate whether the high levels of PAF before PTHx may desensitize platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet-activating factor acetylhydrolase (PAF-AH) in human kidney

1. PAF-AH activity in human kidney (cortex and medulla) has been demonstrated and shares the following properties. 2. Does not require the presence of Ca2+ and appears to be different from phospholipase A2. 3. The pH optimum shows a peak at 7-7.4. 4. It is stable for 4 days at -30 degrees C. 5. It is mainly distributed in the microsomal fraction. 6. The apparent Km values of the enzymes of cortex and medulla are 0.553 and 0.207 microM, respectively and distinct from serum PAF-AH (1.439 microM). 7. The apparent molecular weight values are 60,000 and 25,000 for medulla and cortex, respectively and distinct from serum PAF-AH (94,000).

Platelet-activating factor formation during oxidative modification of low-density lipoprotein when PAF-acetylhydrolase has been inactivated

A PAF aggregating activity corresponding to 427 +/- 91, 668 +/- 111 and 1319 +/- 217 pg/mg protein was detected when LDL was preincubated at pH 3.5 or with 4 mM PMSF or both for 30 min (treatments that inactivate PAF-AH) and then oxidized with 20 microM Cu2+ at 37 degrees C for 24 h. This molecule was characterized as PAF by its chromatographic behavior on TLC and other established methods and was further characterized as 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (C16: PAF) by its retention time on reverse phase HPLC and by fast atom bombardment-mass spectroscopy. Native LDL incubated under non oxidizing conditions, even when PAF-AH has been inactivated, or oxidized in the absence of PAF-AH inactivating agents or after pretreatment with 0.5 mM pBPB, does not produce detectable amounts of PAF. The kinetics of PAF formation in relation to PAF-AH activity, show that the apparent rate of PAF formation as well as its total amount depends on both the existence of oxidative conditions and the remaining PAF-AH activity the first hours following the onset of oxidation. Peroxidation of the phosphatidylcholine (PC) content of native LDL produces PAF-like aggregating activity much lower than that produced when intact LDL is oxidized and is not inhibited by BN 52021 as effectively as PAF produced by LDL peroxidation. Our results provide evidence that C16: PAF is formed during LDL peroxidation when PAF-AH has been inactivated and it does not result as a product of peroxidation of the LDL-PC content.

A simple and precise method for the routine determination of platelet-activating factor in blood and urine

A simple and precise method is described for the measurement of platelet-activating factor (PAF) in blood and urine. The method involves the isolation of PAF from blood samples by two successive steps. In the first step, blood proteins are precipitated with ethanol and the "free" PAF, i.e., the PAF which is extractable with ethanol, is recovered. In the second step, "bound" PAF, i.e., PAF not extractable with ethanol, is extracted from the protein precipitate with chloroform/methanol/water. The extraction of PAF from urine samples requires only the ethanol extraction step. "Free" and "bound" PAF are then each fractionated by silicic acid column chromatography, and the methanol/water eluent containing PAF is then further fractionated by high-performance liquid chromatography using an isocratic solvent system of acetonitrile/methanol/water. PAF is then quantitated by measuring its ability to induce platelet aggregation in an aggregometer. Application of the method to blood and urine samples from twenty-three healthy volunteers revealed PAF levels in blood of 140-480 pg/mL (630-254.4 pg "free" PAF/mL and 64-225.6 pg "bound" PAF/mL), and of 1.2-4.0 pg PAF/mL in urine. The method overcomes various technical problems and was shown to be very precise. It should prove useful for monitoring PAF levels in various disease conditions.