Determination of the cell lytic properties of amphiphilic inhibitors of the cytosolic phospholipase A2 against human platelets by measuring the liberation of serotonin with high-performance liquid chromatography and fluorescence detection

Evaluation of inhibitors of the arachidonic acid cascade with intact platelets using an on-line dilution and on-line solid phase extraction HPLC-MS method

An automatic on-line dilution/on-line solid phase extraction (SPE) system has been developed for the detection of metabolites of the arachidonic acid cascade in platelets. The method allows the direct injection of larger quantities of centrifugates from cell suspensions previously treated with an equal volume of an acetonitrile/methanol mixture for protein precipitation. The method was used to study the effect of inhibitors of platelet arachidonic acid cascade enzymes (cytosolic phospholipase A2α, cyclooxygenase-1, thromboxane synthase, 12-lipoxygenase) and related targets (cyclooxygenase-2, microsomal prostaglandin E synthase-1, 5-lipoxygenase) in intact platelets after stimulation with calcium ionophore A23187. In addition to enzyme inhibition, the cell-damaging properties of the test compounds was determined by measuring the release of serotonin from the platelets into the incubation buffer.

Mechanism of glutamine inhibition of cytosolic phospholipase a2 (cPLA2 ): Evidence of physical interaction between glutamine-Induced mitogen-activated protein kinase phosphatase-1 and cPLA2

Non-essential amino acid L-glutamine (Gln) possesses anti-inflammatory activity via deactivating cytosolic phospholipase A2 (cPLA2 ). We showed previously that Gln deactivated cPLA2 indirectly via dephosphorylating p38 mitogen-activated protein kinase (MAPK), the major kinase for cPLA2 phosphorylation, through inducing MAPK phosphatase-1 (MKP-1). In this study, we investigated the precise mechanism underlying Gln deactivation of cPLA2 . In lipopolysaccharide (LPS)-treated mice, Gln injection resulted in dephosphorylation of phosphorylated cPLA2 (p-cPLA2 ), which coincided with rapid Gln induction of MKP-1. MKP-1 small interfering RNA (siRNA) abrogated the ability of Gln to induce MKP-1 as well as the dephosphorylation of cPLA2 . Co-immunoprecipitation and in-situ proximity ligation assay revealed a physical interaction between MKP-1 and p-cPLA2 . In a murine model of allergic asthma, we also demonstrated the physical interaction between MKP-1 and p-cPLA2 . Furthermore, Gln suppressed various allergic asthma phenotypes, such as neutrophil and eosinophil recruitments into the airway, airway levels of T helper type 2 (Th2) cytokines [interleukin (IL)-4, IL-5 and IL-13], airway hyperresponsiveness, mucin production and metabolites (leukotriene B4 and platelet-activating factor) through inhibiting cPLA2 in a MKP-1-dependent manner. These data suggest that MKP-1 uses cPLA2 , in addition to p38, as a substrate, which further potentiates the anti-inflammatory action of Gln.

The ω3-polyunsaturated fatty acid derivatives AVX001 and AVX002 directly inhibit cytosolic phospholipase A(2) and suppress PGE(2) formation in mesangial cells

BACKGROUND AND PURPOSE

ω3-polyunsaturated fatty acids (ω3-PUFAs) are known to exert anti-inflammatory effects in various disease models although their direct targets are only poorly characterized.

EXPERIMENTAL APPROACH

Here we report on two new cPLA(2) inhibitors, the ω3-derivatives AVX001 and AVX002, and their effects on inflammatory PGE(2) production in cultures of renal mesangial cells.

KEY RESULTS

AVX001 and AVX002 dose-dependently inhibited the group IVA cytosolic phospholipase A(2) (cPLA(2) ) in an in vitro activity assay with similar IC(50) values for AVX001 and AVX002, whereas the known cPLA(2) inhibitor AACOCF(3) was less potent and docosahexaenoic acid (DHA) was inactive. In renal mesangial cells, AVX001 and AVX002 suppressed IL-1β-induced PGE(2) synthesis. Mechanistically, this effect occurred by a down-regulation of IL-1β-induced group IIA-sPLA(2) protein expression, mRNA expression and promoter activity. A similar but less potent effect was seen with AACOCF(3) and no effect was seen with DHA. As gene expression of sPLA(2) is known to be regulated by the transcription factor NF-κB, we further investigated NF-κB activation. Both compounds prevented NF-κB activation by blocking degradation of the inhibitor of κB.

CONCLUSIONS AND IMPLICATIONS

These data show for the first time that the novel cPLA(2) inhibitors AVX001 and AVX002 exert an anti-inflammatory effect in cultures of renal mesangial cells and reduce the pro-inflammatory mediator PGE(2) through an inhibitory effect on NF-κB activation. Therefore, these compounds may represent promising novel drugs for the treatment of inflammatory disorders.

Inhibitors of Cytosolic Phospholipase A2α as Anti-inflammatory Drugs

Arachidonic acid derivatives, like prostaglandins and leukotrienes, as well as the alkyl-ether phospholipid platelet-activating factor (PAF) are highly active substances with diverse biological actions. Elevated levels of these lipid mediators in response to a variety of stimuli have been implicated in the pathology of many inflammatory diseases. The rate-limiting step in the generation of prostaglandins, leukotrienes and PAF, respectively, is the cleavage of the sn-2-ester of membrane phospholipids by a phospholipase A2 (PLA2). Among the superfamily of PLA2 enzymes, cytosolic PLA2α (cPLA2α, also referred to as group IVA PLA2) is thought to play the primary role in this biochemical reaction. Therefore, inhibition of cPLA2α activity is an attractive approach to the control of inflammatory disorders.

In this chapter the main groups of cPLA2α inhibitors are described and the problems associated with the development of clinical active drug candidates are discussed. Furthermore, in-vivo data obtained with such compounds in pre-clinical animal models of inflammation will be presented.

Lipids as targets for novel anti-inflammatory therapies

Lipids serve important functions as membrane constituents and also as energy storing molecules. Besides these functions certain lipid species have now been recognized as signalling molecules that regulate a multitude of cellular responses including cell growth and death, and also inflammatory reactions. Bioactive lipids are generated by hydrolysis from membrane lipids mainly by phospholipases giving rise to fatty acids and lysophospholipids that either directly exert their function or are further converted to active mediators. This review will summarize the present knowledge about bioactive lipids that either promote or attenuate inflammatory reactions. These lipids include polyunsaturated fatty acids (PUFA), eicosanoids including the epoxyeicosatrienoic acids (EET), peroxisome proliferation activating receptor (PPAR) activators, cannabinoids and the sphingolipids ceramide, sphingosine 1-phosphate and sphingosylphosphorylcholine.

Synthesis of polyfluoro ketones for selective inhibition of human phospholipase A2 enzymes

The development of selective inhibitors for individual PLA(2) enzymes is necessary in order to target PLA(2)-specific signaling pathways, but it is challenging due to the observed promiscuity of known PLA(2) inhibitors. In the current work, we present the development and application of a variety of synthetic routes to produce pentafluoro, tetrafluoro, and trifluoro derivatives of activated carbonyl groups in order to screen for selective inhibitors and characterize the chemical properties that can lead to selective inhibition. Our results demonstrate that the pentafluoroethyl ketone functionality favors selective inhibition of the GVIA iPLA(2), a very important enzyme for which specific, potent, reversible inhibitors are needed. We find that 1,1,1,2,2-pentafluoro-7-phenyl-heptan-3-one (FKGK11) is a selective inhibitor of GVIA iPLA(2) (X(I)(50) = 0.0073). Furthermore, we conclude that the introduction of an additional fluorine atom at the alpha' position of a trifluoromethyl ketone constitutes an important strategy for the development of new potent GVIA iPLA(2) inhibitors.

Role of intracellular calcium and phospholipase A2 in arachidonic acid-induced toxicity in liver cells overexpressing CYP2E1

Liver cells (HepG2 and primary hepatocytes) overexpressing CYP2E1 and exposed to arachidonic acid (AA) were previously shown to lose viability together with enhanced lipid peroxidation. These events were blocked in cells pre-incubated with antioxidants (alpha-tocopherol, glutathione ethyl ester), or in HepG2 cells not expressing CYP2E1. The goal of the current study was to evaluate the role of calcium and calcium-activated hydrolases in these CYP2E1-AA interactions. CYP2E1-expressing HepG2 cells treated with AA showed an early increase in cytosolic calcium and partial depletion of ionomycin-sensitive calcium stores. These changes in calcium were blocked by alpha-tocopherol. AA activated phospholipase A2 (PLA2) in CYP2E1-expressing liver cells, and this was inhibited by PLA2 inhibitors or alpha-tocopherol. PLA2 inhibitors prevented the cell death caused by AA, without affecting CYP2E1 activity or lipid peroxidation. AA toxicity and PLA2 activation were inhibited in calcium-depleted cells, but not by removal of extracellular calcium alone. Removal of extracellular calcium inhibited the early increase in cytosolic calcium caused by AA. CYP2E1 overexpressing HepG2 cells exposed to AA showed a decrease in mitochondrial membrane potential, which was prevented by the PLA2 inhibitors. These results suggest that AA-induced toxicity to CYPE1-expressing cells: (i) is associated with release of Ca2+ from intracellular stores that depends mainly on oxidative membrane damage; (ii) is associated with activation of PLA2 that depends on intracellular calcium and lipid peroxidation; (iii) does not depend on increased influx of extracellular calcium, and (iv) depends on the effect of converging events (lipid peroxidation, intracellular calcium, activation of PLA2) on mitochondria to induce bioenergetic failure and necrosis. These interactions may play a role in alcohol liver toxicity, which requires polyunsaturated fatty acids, and involves induction of CYP2E1.