Measurement of platelet-activating factor acetylhydrolase activity by quantitative high-performance liquid chromatography determination of coumarin-derivatized 1-O-alkyl-2-sn-lysoglyceryl-3-phosphorylcholine

Rifampicin Nanoformulation Enhances Treatment of Tuberculosis in Zebrafish

Mycobacterium tuberculosis, the etiologic agent of tuberculosis, is an intracellular pathogen of alveolar macrophages. These cells avidly take up nanoparticles, even without the use of specific targeting ligands, making the use of nanotherapeutics ideal for the treatment of such infections. Methoxy poly(ethylene oxide)- block-poly(ε-caprolactone) nanoparticles of several different polymer blocks' molecular weights and sizes (20-110 nm) were developed and critically compared as carriers for rifampicin, a cornerstone in tuberculosis therapy. The polymeric nanoparticles' uptake, consequent organelle targeting and intracellular degradation were shown to be highly dependent on the nanoparticles' physicochemical properties (the cell uptake half-lives 2.4-21 min, the degradation half-lives 51.6 min-ca. 20 h after the internalization). We show that the nanoparticles are efficiently taken up by macrophages and are able to effectively neutralize the persisting bacilli. Finally, we demonstrate, using a zebrafish model of tuberculosis, that the nanoparticles are well tolerated, have a curative effect, and are significantly more efficient compared to a free form of rifampicin. Hence, these findings demonstrate that this system shows great promise, both in vitro and in vivo, for the treatment of tuberculosis.

NB 06: From a simple lysosomotropic aSMase inhibitor to tools for elucidating the role of lysosomes in signaling apoptosis and LPS-induced inflammation

Ceramide generation is involved in signal transduction of cellular stress response, in particular during stress-induced apoptosis in response to stimuli such as minimally modified Low-density lipoproteins, TNFalpha and exogenous C₆-ceramide. In this paper we describe 48 diverse synthetic products and evaluate their lysosomotropic and acid sphingomyelinase inhibiting activities in macrophages. A stimuli-induced increase of C₁₆-ceramide in macrophages can be almost completely suppressed by representative compound NB 06 providing an effective protection of macrophages against apoptosis. Compounds like NB 06 thus offer highly interesting fields of application besides prevention of apoptosis of macrophages in atherosclerotic plaques in vessel walls. Most importantly, they can be used for blocking pH-dependent lysosomal processes and enzymes in general as well as for analyzing lysosomal dependent cellular signaling. Modulation of gene expression of several prominent inflammatory messengers IL1B, IL6, IL23A, CCL4 and CCL20 further indicate potentially beneficial effects in the field of (systemic) infections involving bacterial endotoxins like LPS or infections with influenza A virus.

Stereospecific induction of apoptosis in tumor cells via endogenous C16-ceramide and distinct transcripts

Concentration and distribution of individual endogenous ceramide species is crucial for apoptosis induction in response to various stimuli. Exogenous ceramide analogs induce apoptosis and can in turn modify the composition/concentrations of endogenous ceramide species and associated signaling. In this study, we show here that the elevation of endogenous C₁₆-ceramide levels is a common feature of several known apoptosis-inducing triggers like mmLDL, TNF-alpha, H₂O₂ and exogenous C₆-ceramide. Vice versa apoptosis requires elevation of endogenous C₁₆-ceramide levels in cells. Enantiomers of a synthetic ceramide analog HPL-1RS36N have been developed as probes and vary in their capacity to inducing apoptosis in macrophages and HT-29 cells. Apoptosis induction by the two synthetic ceramide analogs HPL-39N and HPL-1R36N correlates with generation of cellular C₁₆-ceramide concentration. In contrast to the S-enantiomer HPL-1S36N, the R-enantiomer HPL-1R36N shows significant effects on the expression of distinct genes known to be involved in cell cycle, cell growth and cell death (CXCL10, CCL5 and TNF-alpha), similarly on apoptosis induction. Enantioselective effects on transcription induced by metabolically stable synthetic probes provide clues on molecular mechanisms of ceramide-induced signaling, as well as leads for future anti-cancer agents.

HPLC separation and ultrasensitive optical quantification of ceramide species applying 7-(diethylamino)coumarin-3-carbonyl azide derivatisation

Ceramides are derivatised using 7-(diethylamino)coumarin-3-carbonyl azide; subsequent gradient HPLC separation allows sensitive optical quantification of individual cellular ceramides. Compared to 9-anthracenecarbonyl cyanide (9-anthroyl nitrile) as derivatisation agent, the limit of detection could be improved 415-fold, respectively 10,000-fold (detection limit 0.6 pmol labelled ceramide/sample) when compared to benzoyl chloride-labelling. Acidic or alkaline catalysts are not required, enabling drying and storing of the labelled samples and a free choice of solvents for subsequent HPLC-separation. The quantitative method is characterised by high sensitivity, linearity and robustness in the pico- to nanomolar concentration range and does not require mass-spectrometry for quantification of cellular ceramides.

Determination of phospholipase activity of PAF acetylhydrolase

This article presents a radiometric assay to determine the enzymatic activity of platelet-activating factor (PAF) acetylhydrolase (PAF-AH), also known as lipoprotein-associated phospholipase A2 and phospholipase A2 group 7A. The method is based on the release of radioactively labeled acetate from sn-2-labeled PAF and separation of substrate and product using reversed-phase column chromatography on octadecyl silica gel cartridges. The assay is fast, convenient, reproducible, sensitive, and inexpensive. The instrumentation required includes standard laboratory equipment and a liquid scintillation counter. The assay is also useful to determine the activity of intracellular PAF-AH (PAF-AH II), provided that a few modifications are included. The enzymatic activity determined using PAF as the substrate is a direct indication of the ability of plasma samples, purified preparations, and cellular and tissue lysates to hydrolyze short- and medium-chain phospholipids that may or may not harbor oxidized functionalities. In addition, the assay can be used to test the suitability of other phospholipids, including species containing oxidized, long-chain sn-2 fatty acyl groups, as PAF-AH substrates. This versatile assay can be used to accurately determine PAF-AH activity in biological samples and preliminarily assess affinity and efficiency of the hydrolysis of potential substrates present in complex mixtures.

Platelet-activating factor (PAF) in internal jugular venous blood of migraine without aura patients assessed during migraine attacks

The aim of the study was to verify the production of PAF and the activity of PAF acetyl-hydrolase (PAF-AH), the enzyme involved in the catabolism of this phospholipid mediator, in migraine attacks. Their levels were determined during migraine crises in serial samples of internal jugular venous blood taken from five migraine patients without aura, who were admitted to the hospital during the crises. Internal jugular venous blood samples were taken immediately after catheter insertion at 1, 2, and 4 h after attack onset, and within 2 h from its cessation. PAF was purified by high-performance liquid chromatography (HPLC) and determined by radioimmunoassay method. The enzymatic activity of PAF-AH was measured by reverse-phase HPLC, based on the derivatization with 7-diethylaminocoumarin-3-carbonylazide. In the internal jugular venous blood of migraine patients without aura (MO), an increase was observed in PAF levels, which was already evident at the time of catheter insertion (885.6 +/- 82.8) and at the first hour (868.4 +/- 65.24) (ANOVA: P < 0.0001). PAF levels remained elevated through the second (746.8 +/- 82.95), fourth (700.6 +/- 34.93) and sixth hours (644.4 +/- 42.85), and then decreased at the end of the attack, reaching levels significantly lower than those measured at the time of catheter insertion (565.5 +/- 38.34). The activity of PAF-AH showed an opposite trend with higher values at the first hour and significantly lower values at the second and fourth hours from the beginning of the migraine attack (ANOVA: P < 0.02). The increased production of PAF may account for persistent platelet activation during migraine crises, even in the presence of an increased production of nitric oxide (NO) end-products which, on the other hand, should instead intervene in counteracting and limiting platelet activation. Potential sources of PAF production are the endothelial cells from cerebral vessels, stimulated by trigeminal neuropeptides, platelets themselves, and mast cells, as suggested by the neurogenic inflammation model.

Cellular internalization of poly(ethylene oxide)-b-poly(epsilon-caprolactone) diblock copolymer micelles

Poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PEO-b-PCL) block copolymers self-assemble into micelles in aqueous solution. We have examined whether these micelles can internalize into P19 cells in vitro. Fluorescently labeled PEO(45)-b-PCL(23) block copolymer was prepared by conjugating a tetramethylrhodamine molecule to the end of the hydrophobic PCL block. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies yielded 24 +/- 2 and 25 +/- 2 nm, respectively, for the diameters of the micelles. The studies also showed that chemical labeling did not effect the morphology or size. When the rhodamine-labeled PEO(45)-b-PCL(23) block copolymer micelles were tested in vitro, time-, concentration-, and pH-dependence of the internalization process suggested that internalization proceeded by endocytosis. The results from these studies provide the first direct evidence for the internalization of PEO(45)-b-PCL(23) micelles. Future studies will utilize multiple labeling of these micelles, allowing questions to be addressed related to the fate of internalized micelles as drug carriers, the destination of the incorporated drugs or fluorescent probes released from micelles, and the identification of the subcellular localization of the whole drug-carrier system within cells, both in vitro and in vivo.

Fluorescent HPLC assay for 20-HETE and other P-450 metabolites of arachidonic acid

This study describes a fluorescent HPLC assay for measuring 20-hydroxyeicosatetraenoic acid (20-HETE) and other cytochrome P-450 metabolites of arachidonic acid in urine, tissue, and interstitial fluid. An internal standard, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid, was added to samples, and the lipids were extracted and labeled with 2-(2,3-naphthalimino)ethyl trifluoromethanesulfonate. P-450 metabolites were separated on a C18 reverse-phase HPLC column. Coelution and gas chromatography-mass spectrometry studies confirmed the identity of the 20-HETE peak. The 20-HETE peak can be separated from those for dihydroxyeicosatrienoic acids, other HETEs, and epoxyeicosatrienoic acids. Known amounts of 20-HETE were used to generate a standard curve (range 1-10 ng, r(2) = 0.98). Recovery of 20-HETE from urine averaged 95%, and the intra-assay variation was <5%. Levels of 20-HETE were measured in 100 microliter of urine and renal interstitial fluid or 0.1 mg of renal tissue. The assay was evaluated by studying the effects of 1-aminobenzotriazole (ABT) on the excretion of 20-HETE in rats. ABT reduced excretion of 20-HETE by >65% and inhibited the formation of 20-HETE by renal microsomes. The availability of this assay should facilitate work in this field.

Increased blood levels of platelet-activating factor in insulin-dependent diabetic patients with microalbuminuria

BACKGROUND

Platelet-activating factor (PAF), a phospholipid mediator of inflammation, may induce an enhanced size- and charge-dependent glomerular permeability in experimental animals. Studies on the role of PAF in enhanced glomerular permeability in the early phase of diabetic nephropathy are still lacking.

METHODS

We evaluated the intravascular levels of PAF and its main catabolic enzyme, the PAF-specific plasma acetyl-hydrolase (PAF-AH), in basal conditions and after exercise, in normo- or micro-albuminuric insulin-dependent diabetic (IDD) patients and in normal subjects.

RESULTS

The results obtained indicate that the concentration of PAF in whole blood was significantly enhanced in basal conditions, during and after exercise in all microalbuminuric IDD patients, but not in normoalbuminuric IDD or in control subjects. The increased concentration of PAF did not correlate with changes in the activity of PAF-AH, suggesting an enhanced production rather than a decreased catabolism of PAF.

CONCLUSIONS

These results indicate an association between increased production of PAF and enhanced glomerular permeability in microalbuminuric IDD patients.

Spectrophotometric assay for serum platelet-activating factor acetylhydrolase activity

We developed a spectrophotometric assay for serum platelet-activating factor acetylhydrolase (PAF-AH, EC 3.1.1.47.) activity using a platelet-activating factor (PAF) analogue with a 4-nitrophenyl group as substrate. PAF-AH hydrolyzes the sn-2 position of the substrate ¿1-myristoyl-2-(p-nitrophenylsuccinyl)phosphatidylcholine, producing p-nitrophenyl succinate. This liberation was spectrophotometrically monitored and the activity determined from the change in absorption. The assay does not require radioisotopes and is applicable to an automatic analyzer. Utilizing this assay with an automatic analyzer, it is possible to measure the activities of thousands of samples in a few hours with excellent precision (CV 0.5%, n=30) and high correlation (r=0.979, n=100) with the results of a conventional radioisotopic assay. The assay should be particularly useful for clinical diagnostics.

Intramolecularly quenched BODIPY-labeled phospholipid analogs in phospholipase A(2) and platelet-activating factor acetylhydrolase assays and in vivo fluorescence imaging

Phospholipase substrate analogs containing both a fluorescent BODIPY group and a quenching 2,4-dinitrophenyl (DNP) group were synthesized. They showed little fluorescence, but upon hydrolysis became fluorescent as the quenching group was removed. Two substrates were phosphatidylethanolamine analogs with a BODIPY-pentanoyl group at the sn-2 position and DNP linked to the amino head group. The third was a phosphatidylcholine analog with a BODIPY-labeled alkyl ether at the sn-1 position and a N-(DNP)-8-amino-octanoyl group at the sn-2 position. These compounds were evaluated as substrates for cytosolic (85 kDa) phospholipase A(2) (cPLA(2)) and plasma platelet-activating factor acetylhydrolase (rPAF-AH). Two were good substrates for cPLA(2) (specific activities: 18 and 5 nmol min(-1) mg(-1)) and all were good for rPAF-AH (specific activities: 17, 11, and 6 micro mol min(-1) mg(-1)). The minimal amount of enzyme detectable was 50 ng for cPLA(2) and 0.1 ng for rPAF-AH. These substrates were active in assays of PLA(2) in zebrafish embryo extracts and one was well suited for imaging of PLA(2) activity in living zebrafish embryos. Embryos were injected with substrate at the one- to four-cell stage and allowed to develop until early somitogenesis when endogenous PLA(2) activity increases dramatically; substrate persisted (12 h) and specifically labeled cells of the developing notochord.

Simultaneous determination of lysophospholipids by high-performance liquid chromatography with fluorescence detection

A high-performance liquid chromatography (HPLC) procedure for the separation of choline lysophospholipids including 1-acyl-lysophosphatidylcholines and 1-O-alkyl-lysophosphatidyl- cholines, like the lysoform of the platelet activating factor (2-lysoPAF), is described. The lysophospholipids are derivatized at the sn-2 position of the hydroxyl group by 7-diethylaminocoumarin-3-carbonylazide, which converts them into the corresponding carbamoyl derivatives. The derivatized compounds were well separated by reversed-phase HPLC and quantified by fluorimetric detection. This method shows a high sensitivity and allows the separation and quantification of mixtures of lysophospholipids at picomolar level. The method was applied to assay enzyme activities, like phospholipase A2 and PAF-acetylhydrolase, on single phospholipids or their mixtures.