Cytosolic phospholipase A2 (PLA2), but not secretory PLA2, potentiates hydrogen peroxide cytotoxicity in kidney epithelial cells

Unravelling oncosis: morphological and molecular insights into a unique cell death pathway

Programmed cell death (PCD) is a fundamental biological process for maintaining cellular equilibrium and regulating development, health, and disease across all living organisms. Among the various types of PCD, apoptosis plays a pivotal role in numerous diseases, notably cancer. Cancer cells frequently develop mechanisms to evade apoptosis, increasing resistance to standard chemotherapy treatments. This resistance has prompted extensive research into alternative mechanisms of programmed cell death. One such pathway is oncosis, characterized by significant energy consumption, cell swelling, dilation of the endoplasmic reticulum, mitochondrial swelling, and nuclear chromatin aggregation. Recent research suggests that oncosis can impact conditions such as chemotherapeutic cardiotoxicity, myocardial ischemic injury, stroke, and cancer, mediated by specific oncosis-related proteins. In this review, we provide a detailed examination of the morphological and molecular features of oncosis and discuss various natural or small molecule compounds that can induce this type of cell death. Additionally, we summarize the current understanding of the molecular mechanisms underlying oncosis and its role in both normal physiology and pathological conditions. These insights aim to illuminate future research directions and propose innovative strategies for leveraging oncosis as a therapeutic tool against human diseases and cancer resistance.

Whole transcriptome sequencing reveals the activity of the PLA2 family members in Androctonus crassicauda (Scorpionida: Buthidae) venom gland

Phospholipase A2 is the most abundant venom gland enzyme, whose activity leads to the activation of the inflammatory response by accumulating lipid mediators. This study aimed to identify, classify, and investigate the properties of venom PLA2 isoforms. Then, the present findings were confirmed by chemically measuring the activity of PLA2. The sequences representing PLA2 annotation were extracted from the Androctonus crassicauda transcriptome dataset using BLAS searches against the local PLA2 database. We found several cDNA sequences of PLA2 classified and named by conducting multiple searches as platelet-activating factor acetylhydrolases, calcium-dependent PLA2s, calcium-independent PLA2s, and secreted PLA2s. The largest and smallest isoforms of these proteins range between approximately 70.34 kDa (iPLA2) and 17.75 kDa (cPLA2). Among sPLA2 isoforms, sPLA2GXIIA and sPLA2G3 with ORF encoding 169 and 299 amino acids are the smallest and largest secreted PLA2, respectively. These results collectively suggested that A. crassicauda venom has PLA2 activity, and the members of this protein family may have important biological roles in lipid metabolism. This study also revealed the interaction between members of PLA2s in the PPI network. The results of this study would greatly help with the classification, evolutionary relationships, and interactions between PLA2 family proteins in the gene network.

Cytosolic phospholipase A2 regulates lipid homeostasis under osmotic stress through PPARγ

Physiologically, renal medullary cells are surrounded by a hyperosmolar interstitium. However, different pathological situations can induce abrupt changes in environmental osmolality, causing cell stress. Therefore, renal cells must adapt to survive in this new condition. We previously demonstrated that, among the mechanisms involved in osmoprotection, renal cells upregulate triglyceride biosynthesis (which helps preserve glycerophospholipid synthesis and membrane homeostasis) and cyclooxygenase-2 (which generates prostaglandins from arachidonic acid) to maintain lipid metabolism in renal tissue. Herein, we evaluated whether hyperosmolality modulates phospholipase A2 (PLA2 ) activity, leading to arachidonic acid release from membrane glycerophospholipid, and investigated its possible role in hyperosmolality-induced triglyceride synthesis and accumulation. We found that hyperosmolality induced PLA2 expression and activity in Madin-Darby canine kidney cells. Cytosolic PLA2 (cPLA2) inhibition, but not secreted or calcium-independent PLA2 (sPLA2 or iPLA2 , respectively), prevented triglyceride synthesis and reduced cell survival. Inhibition of prostaglandin synthesis with indomethacin not only failed to prevent hyperosmolality-induced triglyceride synthesis but also exacerbated it. Similar results were observed with the peroxisomal proliferator activated receptor gamma (PPARγ) agonist rosiglitazone. Furthermore, hyperosmolality increased free intracellular arachidonic acid levels, which were even higher when prostaglandin synthesis was inhibited by indomethacin. Blocking PPARγ with GW-9662 prevented the effects of both indomethacin and rosiglitazone on triglyceride synthesis and even reduced hyperosmolality-induced triglyceride synthesis, suggesting that arachidonic acid may stimulate triglyceride synthesis through PPARγ activation. These results highlight the role of cPLA2 in osmoprotection, since it is essential to provide arachidonic acid, which is involved in PPARγ-regulated triglyceride synthesis, thus guaranteeing cell survival.

A novel bactericidal homodimeric PLA2 group-I from Walterinnesia aegyptia venom

A novel non-toxic phospholipase A₂ was purified to homogeneity in a single chromatography step from the venom of Walterinnesia aegyptia, a monotypic elapid snake caught in Saudi Arabia, and its antimicrobial and hemolytic properties were evaluated as well. This enzyme, namely WaPLA₂, is a homodimer with an estimated molecular mass of 30 kDa, and its NH₂-terminal sequence exhibits a significant degree of similarity with PLA₂ group-I. At optimal pH (8.5) and temperature (45 °C), the purified PLA₂ exhibited a specific activity of 2100 U/mg, and it requires bile salts and Ca²⁺ for its activity. However, other cations such as Cd²⁺ and Hg²⁺ diminished the enzyme activity remarkably, thereby suggesting that the catalytic site arrangement has an exclusive structure for Ca²⁺ binding. Furthermore, WaPLA₂ maintained almost 100% and 60% of its full activity in a pH range of 6.0-10 after 24 h incubation or after 60 min treatment at 70 °C, respectively. In the biological activity assays, WaPLA₂ displayed potent indirectly hemolytic and antimicrobial activities that were strongly correlated. These promising findings encourage further in-depth research to understand the molecular mechanism of WaPLA₂'s antimicrobial properties for its possible use as a potential therapeutic lead molecule for treating infections.

Bradykinin-potentiating PEPTIDE-10C, an argininosuccinate synthetase activator, protects against H2O2-induced oxidative stress in SH-SY5Y neuroblastoma cells

Bradykinin-potentiating peptides (BPPs - 5a, 7a, 9a, 10c, 11e, and 12b) of Bothrops jararaca (Bj) were described as argininosuccinate synthase (AsS) activators, improving l-arginine availability. Agmatine and polyamines, which are l-arginine metabolism products, have neuroprotective properties. Here, we investigated the neuroprotective effects of low molecular mass fraction from Bj venom (LMMF) and two synthetic BPPs (BPP-10c, <ENWPHPQIPP; BPP-12b, <EWGRPPGPPIPP) in the SH-SY5Y cell line against H₂O₂-induced oxidative stress. The neuroprotective effects against H₂O₂-induced were analyzed by reactive oxygen species (ROS - DCFH) production; lipid peroxidation (TBARS); intracellular GSH; AsS, iNOS, and NF-kB expressions; nitrite levels (Griess); mitochondrial membrane potential (TMRM); and antioxidant activity (DPPH). Analysis of variance followed by Tukey's post hoc test were calculated for statistical comparisons. Pre-treatment with both BPPs significantly reduced cell death induced by H₂O₂, but BPP-10c showed higher protective capacity than BPP-12b. LMMF pretreatment was unable to prevent the reduction of cell viability caused by H₂O₂. The neuroprotective mechanism of BPP-10c against oxidative stress was investigated. BPP-10c reduced ROS generation and lipid peroxidation in relation to cells treated only with H₂O₂. BBP-10c increased AsS expression and was not neuroprotective in the presence of MDLA, a specific inhibitor of AsS. BPP-10c reduced iNOS expression and nitrate levels but decreased NF-kB expression. Furthermore, BPP-10c protected the mitochondrial membrane against oxidation. Overall, we demonstrated for the first time neuroprotective mechanisms of BPPs against oxidative stress, opening new perspectives to the study and application of these peptides for the treatment of neurodegenerative diseases.

Lipopolysaccharide (LPS)-mediated priming of toll-like receptor 4 enhances oxidant-induced prostaglandin E2 biosynthesis in primary murine macrophages

Agonists and pseudo-agonists for toll-like receptor 4 (TLR4) are common in our environment. Thus, human exposure to these agents may result in "priming or sensitization" of TLR4. A body of evidence suggests that LPS-mediated sensitization of TLR4 can increase the magnitude of responses to exogenous agents in multiple tissues. We have previously shown that reactive oxygen and nitrogen species (RONS) stimulate TLR4. There is no evidence that LPS-primed TLR4 can influence the magnitude of responses to oxidants from either endogenous or exogenous sources. In the present study, we directly tested the hypothesis that LPS-primed TLR4 will sensitize primary murine peritoneal macrophages (pM) to oxidant-mediated prostaglandin E2 (PGE₂) production. We used potassium peroxychromate (PPC) and potassium peroxynitrite (PPN) as direct in vitro sources of exogenous RONS. Our results showed that a direct treatment with PPC or PPN alone as sources of exogenous oxidants had a limited effect on PGE₂ biosynthesis. In contrast, pM sensitized by prior incubation with LPS-EK, a TLR4-specific agonist, followed by oxidant stimulation exhibited increased transcriptional and translational expression of cyclooxygenase-2 (COX-2) with enhanced PGE₂ biosynthesis/production only in pM derived from TLR4-WT mice but not in TLR4-KO mice. Thus, we have shown a critical role for LPS-primed TLR4 in oxidant-induced inflammatory phenotypes that have the potential to initiate, propagate and maintain many human diseases.

Cytosolic phospholipase A2 (cPLA2) IVA as a potential signature molecule in cigarette smoke condensate induced pathologies in alveolar epithelial lineages

BACKGROUND

Smoking is one of the leading causes of millions of deaths worldwide. During cigarette smoking, most affected and highly exposed cells are the alveolar epithelium and generated oxidative stress in these cells leads to death and damage. Several studies suggested that oxidative stress causes membrane remodeling via Phospholipase A2s but in the case of cigarette smokers, mechanistically study is not yet fully defined. In view of present perspective, we evaluated the involvement of cytosolic phospholipase A2 (cPLA2) IVA as therapeutic target in cigarette smoke induced pathologies in transformed type I and type II alveolar epithelial cells.

METHODS

Transformed type I (WI26) and type II (A549) alveolar epithelial cells were used for the present study. Cigarette smoke condensate (CSC) was prepared from most commonly used cigarette (Gold Flake with filter) by the Indian population. CSC-induced molecular changes were evaluated through cell viability using MTT assay, reactive oxygen species (ROS) measurement using 2,7 dichlorodihydrofluorescin diacetate (DCFH-DA), cell membrane integrity using fluorescein diacetate (FDA) and ethidium bromide (EtBr) staining, super oxide dismutase (SOD) levels, cPLA2 activity and molecular involvement of specific cPLA2s at selected 24 h time period.

RESULTS

CSC-induced response on both type of epithelial cells shown significantly reduction in cell viability, declined membrane integrity, with differential escalation of ROS levels in the range of 1.5-15 folds and pointedly increased cPLA2 activity (p < 0.05). Likewise, we observed distinction antioxidant potential in these two types of lineages as type I cells had considerably higher SOD levels when compared to type II cells (p < 0.05). Further molecular expression of all cPLA2s increased significantly in a dose dependent manner, specifically cytosolic phospholipase A2 IVA with maximum manifestation of 3.8 folds. Interestingly, CSC-induced ROS levels and cPLA2s expression were relatively higher in A549 cells as compared to WI26 cells.

CONCLUSIONS

The present study indicates that among all cPLA2s, specific cPLA2 IVA are the main enzymes involved in cigarette smoke induced anomalies in type I and type II lung epithelial cells and targeting them holds tremendous possibilities in cigarette smoke induced lung pathologies.

Immobilization of Lipid Substrates: Application on Phospholipase A2 Determination

The purpose of the study was to assess a fluorimetric assay for the determination of total phospholipase A(2) (PLA(2)) activity in biological samples introducing the innovation of immobilized substrates on crosslinked polymeric membranes. The immobilized C(12)-NBD-PtdCho, a fluorescent analogue of phosphatidylcholine, exhibited excellent stability for 3 months at 4 °C and was not desorbed in the aqueous reaction mixture during analysis. The limit of detection was 0.5 pmol FA (0.2 pg) and the linear part of the response curve extended from 1 up to 190 nmol FA/h/mL sample. The intra- and inter-day relative standard deviations (%RSD), were ≤6 and ≤9 %, respectively. Statistical comparison with other fluorescent methods showed excellent correlation and agreement. Semiempirical calculations showed a fair amount of electrostatic interaction between the NBD-labeled substrate and the crosslinked polyvinyl alcohol with the styryl pyridinium residues (PVA-SbQ) material, from the plane of which, the sn-2 acyl chain of the phospholipid stands out and is accessible by PLA(2). Atomic Force Microscopy revealed morphological alterations of the immobilized substrate after the reaction with PLA(2). Mass spectrometry showed that only C(12)-NBD-FA, the PLA(2 )hydrolysis product, was detected in the reaction mixture, indicating that PLA(2) recognizes PVA-SbQ/C(12)-NBD-PtdCho as a surface to perform catalysis.

Group IVA Cytosolic Phospholipase A2 Regulates the G2-to-M Transition by Modulating the Activity of Tumor Suppressor SIRT2

The G2-to-M transition (or prophase) checkpoint of the cell cycle is a critical regulator of mitotic entry. SIRT2, a tumor suppressor gene, contributes to the control of this checkpoint by blocking mitotic entry under cellular stress. However, the mechanism underlying both SIRT2 activation and regulation of the G2-to-M transition remains largely unknown. Here, we report the formation of a multiprotein complex at the G2-to-M transition in vitro and in vivo. Group IVA cytosolic phospholipase A2 (cPLA2α) acts as a bridge in this complex to promote binding of SIRT2 to cyclin A-Cdk2. Cyclin A-Cdk2 then phosphorylates SIRT2 at Ser331. This phosphorylation reduces SIRT2 catalytic activity and its binding affinity to centrosomes and mitotic spindles, promoting G2-to-M transition. We show that the inhibitory effect of cPLA2α on SIRT2 activity impacts various cellular processes, including cellular levels of histone H4 acetylated at K16 (Ac-H4K16) and Ac-α-tubulin. This regulatory effect of cPLA2α on SIRT2 defines a novel function of cPLA2α independent of its phospholipase activity and may have implications for the impact of SIRT2-related effects on tumorigenesis and age-related diseases.

Low concentration of a dioxin (2, 3, 7, 8 TCDD) affects the glycosidases and Acid phosphatase activity in mice hepatocytes

Present communication reports the effects of environmentally available, low doses of tetra chloro di benzo-p-dioxin (2,3,7,8 TCDD) to lysosomal enzymes in mice liver. The study tests the hypothesis, in vivo exposure of low dose TCDD provokes dose and duration dependent toxic effects to key lysosomal enzymes and thereby causes cellular apoptotic changes. Three groups of female Swiss albino mice were subjected to two doses of TCDD (0.004 mg/kg bw/d, 0.04 mg/kg bw/d) for 2, 4 and 6 days of exposure durations. The results indicated significant exposure duration dependent effects of TCDD in mice liver cells. The results suggested that TCDD possibly induced an increase in intracellular ions or ROS which in turn altered different physiological activities by affecting different metabolic pathway of the liver cells. The altered functions of key lysosomal enzymes by TCDD may also evoke the process of cellular apoptosis.

Anti-bactericidal properties of stingray Dasyatis pastinaca groups V, IIA, and IB phospholipases A2: a comparative study

Group IIA secreted phospholipase A2 (group IIA sPLA2) is known to display potent Gram-positive bactericidal activity in vitro and in vivo. We have analyzed the bactericidal activity of the full set of native stingray and dromedary groups V, IIA, and IB sPLA2s on several Gram-positive and Gram-negative strains. The rank order potency among both marine and mammal sPLA2s against Gram-positive bacteria is group IIA > V > IB, whereas Gram-negative bacteria exhibited a much higher resistance. There is a synergic action of the sPLA2 with lysozyme when added to the bacteria culture prior to sPLA2.The bactericidal efficiency of groups V and IIA sPLA2s was shown to be dependent upon the presence of calcium ions and to a less extent Mg(2+) ions and then a correlation could be made to its hydrolytic activity of membrane phospholipids. Importantly, we showed that stingray and dromedary groups V, IIA, and IB sPLA2s present no cytotoxicity after their incubation with MDA-MB-231cells. stingray groups V and IIA sPLA2s, like mammal ones, may be considered as future therapeutic agents against bacterial infections.

Antibacterial properties of intestinal phospholipase A2 from the common stingray Dasyatis pastinaca

Stingray phospholipase A(2) group IIA (SPLA(2)-IIA) was recently isolated and purified to homogeneity from the intestine of the common stingray Dasyatis pastinaca, suggesting that this enzyme plays an important role in systemic bactericidal defense. The present study showed that SPLA(2)-IIA was highly bactericidal against Gram-positive bacteria with inhibition zones and minimal inhibitory concentration values in the range of 13-25 mm and 2-8 μg/ml, respectively, whereas Gram-negative bacteria exhibited a much higher resistance. The bactericidal efficiency of SPLA(2)-IIA was shown to be unaffected by high protein and salt concentrations, but dependent upon the presence of calcium ions, and then correlated to the hydrolytic activity of membrane phospholipids. Importantly, we showed that stingray phospholipase A(2) group IIA presents no cytotoxicity after its incubation with MDA-MB-231 cells. SPLA(2)-IIA may be considered as a future therapeutic agent against bacterial infections.

Inhibition of cytosolic phospholipase A(2) alpha protects against focal ischemic brain damage in mice

It is postulated that inhibition of cytosolic phospholipase A(2) alpha (cPLA(2)α) can reduce severity of stroke injury. This is supported by the finding that cPLA(2)α-deficient mice are partially protected from transient, focal cerebral ischemia. The object of this study was to determine the effect of cPLA(2)α inhibition with arachidonyl trifluoromethyl ketone (ATK) on stroke injury in mice. Male C57BL/6 mice were subjected to 1h of focal cerebral ischemia followed by 24 or 72 h of reperfusion. Mice were treated with ATK or vehicle by intermittent intraperitoneal injection or continuous infusion via an implanted infusion pump. ATK injections 1h before and then 1 and 6h after the start of reperfusion significantly reduced infarction volumes in striatum and hemisphere after 24h of reperfusion. ATK did not reduce injury if it was not administered before onset of ischemia or was not administered after 6h of reperfusion. Intermittent doses of ATK failed to reduce infarct volume after 72 h of reperfusion. Continuous infusion with ATK throughout 72h of reperfusion significantly reduced cortical and whole hemispheric infarct volume compared to vehicle treatment. Following ischemia and reperfusion, ATK treatment significantly reduced brain PLA(2) activity. These results are the first to demonstrate a therapeutic effect of cPLA(2)α inhibition on ischemia and reperfusion injury and define a therapeutic time window. cPLA(2)α activity augments injury in the acute and delayed phases of cerebral ischemia and reperfusion injury. We conclude that cPLA(2)α inhibition may be clinically useful if started before initiation of cerebral ischemia.

Cytosolic phospholipase A(2)α protects against Fas- but not LPS-induced liver injury

BACKGROUND & AIMS

Cytosolic phospholipase A(2)α (cPLA(2)α) is a rate-limiting key enzyme controlling the release of arachidonic acid (AA) substrate for the synthesis of prostaglandins and leukotrienes. This study was designed to explore the role of hepatocyte cPLA(2)α in Fas-mediated liver injury, in vivo.

METHODS

Transgenic mice with targeted expression of cPLA(2)α under control of the albumin-promoter enhancer and wild-type mice were injected intraperitoneally with anti-Fas antibody Jo2 or lipopolysaccharide plus d-galactosamine and monitored for liver injury and survival at various time points.

RESULTS

The cPLA(2)α Tg mice resist Fas-induced liver failure, as reflected by the lower serum transaminase levels, fewer apoptotic hepatocytes, reduced caspase activation, and reduced PARP cleavage when compared to the matched wild type mice. Inhibition of cPLA(2)α by its pharmacological inhibitor, pyrrolidine, enhanced Jo2-induced liver injury in both cPLA(2)α Tg and wild type mice. Hepatic overexpression of cPLA(2)α increases the expression of EGFR in the liver and the EGFR inhibitor, AG1478, exacerbated Jo2-mediated liver injury. The cPLA(2)α transgenic mice develop more prominent liver tissue damage than wild-type mice after LPS/d-galactosamine injection.

CONCLUSIONS

Hepatocyte cPLA(2)α protects against Fas-induced liver injury and this effect is mediated at least in part through the upregulation of EGFR.

Arachidonic acid inhibits neuronal nitric oxide synthase elicited by proinflammatory stimuli and promotes astrocyte survival with both exogenous and endogenous peroxynitrite via different mechanisms

Cytosolic phospholipase A(2)-inhibited astrocytes respond to the cocktail lipopolysaccharide/interferon-gamma with an immediate formation of peroxynitrite (ONOO(-)) and a delayed lethal response. Low concentrations of arachidonic acid (ARA; i.e., <0.1 microM) cause tyrosine kinase-dependent inhibition of neuronal nitric oxide synthase (nNOS) activity, thereby suppressing formation of ONOO(-) and the ensuing lethal response. ARA promoted its effects only when given to the cultures just prior to, or in parallel with, the proinflammatory mixture. High concentrations of ARA, i.e., >3 microM, promoted cytoprotection when applied to the cultures up to 50 min after the formation of endogenous ONOO(-) had been completed or up to 30 min after addition of exogenous ONOO(-). The mechanism(s) involved in these responses was, however, independent of tyrosine kinase activation and was in fact mediated by ARA metabolites of the lipoxygenase pathway. These results are consistent with a scenario in which astrocytes respond to low or high amounts of ARA with the triggering of different pathways involved in the inflammatory response. Early nNOS inhibition mediated by very low levels of ARA is indeed critical for nuclear factor-kappaB activation, which is otherwise effectively inhibited by constitutive nitric oxide, and for preventing early formation of ONOO(-). Greater ARA concentrations promote survival in astrocytes committed to death by ONOO(-), a species extensively released under inflammatory conditions, via a mechanism dependent on lipoxygenase metabolism and inhibition of downstream events leading to cell demise.

Arachidonic acid: a key molecule for astrocyte survival to peroxynitrite

Nontoxic concentrations of peroxynitrite (ONOO(-)) nevertheless commit rat astrocytes to mitochondrial permeability transition-dependent toxicity, however prevented by a signaling response driven by arachidonic acid (ARA). The lipid messenger was released upon ONOO(-)-dependent activation of cytosolic phospholipase A(2) and its pharmacological inhibition, or knock-down, was invariably associated with a prompt apoptotic response sensitive to exogenous ARA, but insensitive to other polyunsaturated fatty acids, as eicosapentaenoic or linoleic acid. Interestingly, while microglia also used ARA to cope with ONOO(-), cerebellar granule cells were killed by the same concentrations of ONOO(-) employed in astrocyte/microglia experiments via a mechanism sensitive to inhibition of ARA release. These results collectively support the notion that resistance of glial cells to ONOO(-), a species extensively produced under neuroinflammatory conditions, is largely based on a critical survival signaling triggered by the inflammatory product ARA. In remarkable contrast with these results, the lipid messenger appears to mediate toxicity in neuronal cells.

Secretory phospholipase A2 plays an essential role in microglial inflammatory responses to Mycobacterium tuberculosis

In previous studies, we have shown that reactive oxygen species (ROS)-mediated inflammatory signaling is essential for microglial proinflammatory responses to Mycobacterium tuberculosis (Mtb). To further investigate the molecular mechanisms governing these processes, we sought to describe the role of phospholipase A(2) (PLA(2)) in Mtb-induced ROS generation and inflammatory mediator release by microglia. Inhibition of secretory PLA(2) (sPLA(2)), but not cytosolic PLA(2) (cPLA(2)), profoundly abrogated Mtb-mediated ROS release, the generation of various inflammatory mediators (tumor necrosis factor, interleukin-6, cyclooxygenase-2, inducible nitric oxide synthase, and matrix metalloproteinase-2 and -9), and the activation of nuclear factor (NF)-kappaB and MAPKs (ERK1/2, p38, and JNK/SAPK) by murine microglial BV-2 cells or primary mixed glial cells. Interruption of the Ras/Raf-1/MEK1/ERK1/2 pathway abolished Mtb-induced sPLA(2) activity, whereas the blockage of JNK/SAPK or p38 activity had no effect. Specific inhibition of sPLA(2), but not cPLA(2), suppressed the upregulation of ERK1/2 phosphorylation by Mtb stimulation, suggesting the existence of a mutual dependency between the ERK1/2 and sPLA(2) pathways. Moreover, examination of the protein kinase C (PKC) family revealed that classical PKCs are involved in Mtb-induced sPLA(2) activation by microglia. Taken together, our results demonstrate for the first time that sPLA(2), either through pathways comprising Ras/Raf-1/MEK1/ERK1/2 or the classical PKC family, plays an essential role in Mtb-mediated ROS generation and inflammatory mediator release by microglial cells.

The identification of a phospholipase B precursor in human neutrophils

A phospholipase B (PLB) precursor was purified from normal human granulocytes using Sephadex G-75, Mono-S cation-exchange and hydroxyapatite columns. The molecular mass of the protein was estimated to be approximately 130 kDa by gel filtration and 22 and 42 kDa by SDS/PAGE. Tryptic peptide and sequence analyses by MALDI-TOF and tandem mass spectrometry (MS/MS) identified the protein as a FLJ22662 (Homo sapiens) gene product, a homologue of the amoeba Dictyostelium discoideum PLB. The native protein needed modifications to acquire deacylation activity against phospholipids including phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine and lysophospholipids. Enzyme activity was associated with fragments derived from the 42 kDa fragment. The enzyme revealed a PLB nature by removing fatty acids from both the sn-1 and sn-2 positions of phospholipids. The enzyme is active at a broad pH range with an optimum of 7.4. Immunoblotting of neutrophil postnuclear supernatant using antibodies against the 42 kDa fragment detected a band at a molecular mass of 42 kDa, indicating a neutrophil origin of the novel PLB precursor. The existence of the PLB precursor in neutrophils and its enzymatic activity against phospholipids suggest a role in the defence against invading microorganisms and in the generation of lipid mediators of inflammation.

Phospholipid-mediated signaling and heart disease

Cardiac hypertrophy, congestive heart failure, diabetic cardiomyopathy and myocardial ischemia-reperfusion injury are associated with a disturbance in cardiac sarcolemmal membrane phospholipid homeostasis. The contribution of the different phospholipases and their related signaling mechanisms to altered function of the diseased myocardium is not completely understood. Resolution of this issue is essential for both the understanding of the pathophysiology of heart disease and for determining if components of the phospholipid signaling pathways could serve as appropriate therapeutic targets. This review provides an outline of the role of phospholipase A2, C and D and subsequent signal transduction mechanisms in different cardiac pathologies with a discussion of their potential as targets for drug development for the prevention/treatment of heart disease.

Role of calcium-independent phospholipase A2 in complement-mediated glomerular epithelial cell injury

In experimental membranous nephropathy, complement C5b-9-induced glomerular epithelial cell (GEC) injury leads to morphological changes in GEC and proteinuria, in association with phospholipase A2 (PLA2) activation. The present study addresses the role of calcium-independent PLA2 (iPLA2) in GEC injury. iPLA2β short and iPLA2γ were expressed in cultured rat GEC and normal rat glomeruli. To determine whether iPLA2 is involved in complement-mediated arachidonic acid (AA) release, GEC were stably transfected with iPLA2γ or iPLA2β cDNAs (GEC-iPLA2γ; GEC-iPLA2β). Compared with control cells (GEC-Neo), GEC-iPLA2γ and GEC-iPLA2β demonstrated greater expression of iPLA2 proteins and activities. Complement-mediated release of [3H]AA was augmented significantly in GEC-iPLA2γ compared with GEC-Neo, and the augmented [3H]AA release was inhibited by the iPLA2-directed inhibitor bromoenol lactone (BEL). For comparison, overexpression of iPLA2γ also amplified [3H]AA release after incubation of GEC with H2O2, or chemical anoxia followed by reexposure to glucose (in vitro ischemia-reperfusion injury). In parallel with release of [3H]AA, complement-mediated production of prostaglandin E2 was amplified in GEC-iPLA2γ. Complement-mediated cytotoxicity was attenuated significantly in GEC-iPLA2γ compared with GEC-Neo, and the cytoprotective effect of iPLA2γ was reversed by BEL, and in part by indomethacin. Overexpression of iPLA2β did not amplify complement-dependent [3H]AA release, but nonetheless attenuated complement-mediated cytotoxicity. Thus iPLA2γ may be involved in complement-mediated release of AA. Expression of iPLA2γ or iPLA2β induces cytoprotection against complement-dependent GEC injury. Modulation of iPLA2 activity may prove to be a novel approach to reducing GEC injury.

Phospholipase A2 as targets for anti-cancer drugs

Phospholipase A(2) (PLA(2)) are esterases that cleave glycerophospholipids to release fatty acids and lysophospholipids. Inhibition of PLA(2) alters cancer cell growth and death in vitro and PLA(2) expression is increased in breast, lung, and prostate cancers compared to control tissues. Thus, PLA(2) may be novel targets for chemotherapeutics. However, PLA(2) are a diverse family of enzymes, encompassing 19 members. The selectivity of these individual PLA(2) for phospholipids varies, as does their location within the cell, and tissue expression. Thus, their role in cancer may also vary. This review summarizes the expression of individual PLA(2) in cancers, focuses on the potential mechanisms by which these esterases mediate carcinogenesis, and suggests that select PLA(2) isoforms may be targets for anti-cancer drugs.

Involvement of p38 MAP kinase in burn-induced degradation of membrane phospholipids and upregulation of cPLA2 in cardiac myocytes

This study was aimed to evaluate the role of p38 mitogen-activated protein (MAP) kinase in the degradation of membrane phospholipids and the regulation of cytosolic phospholipase A2 (cPLA2) in cardiac myocytes after burn trauma. In an in vivo study, rats were randomized into four groups: (1) sham-burn group, (2) burn group (40% total body surface area full-thickness burn), (3) burn + SB203580 group, and (4) burn + vehicle group. The rats from each group were killed at varying times after burn to examine the p38 MAP kinase activation (by means of Western blot analysis and immunohistochemical assay), the expression of cPLA2 (by means of reverse transcriptase polymerase chain reaction), the level of cardiac membrane phospholipids, and the level of the remaining creatine kinase-MB (CK-MB) isoenzyme in the heart. These studies showed that burn resulted in a significant decrease in the level of cardiac membrane phospholipids from 3 to 24 h after burn, which was paralleled with a persistent activation of p38 MAP kinase and an increased expression of cPLA2 in the heart. SB203580, a selective inhibitor of p38 MAP kinase, inhibited the activation of cardiac p38 MAP kinase, suppressed the burn-induced upregulation of cPLA2 and the increased PLA2 activity, and prevented burn-induced decrease in the levels of the cardiac membrane phospholipids and the remaining creatine kinase-MB isoenzyme. In addition, the in vitro treatment of cardiac myocytes with SB203580 also abolished the upregulation of cPLA2 and the disturbance of phospholipid homeostasis elicited by hypoxia and burn serum challenge. Taken together, these results have demonstrated for the first time that p38 MAP kinase is involved in burn-induced membrane phospholipids degradation in cardiac myocytes, at least in part through the regulation of cPLA2.

Phospholipid-mediated signaling systems as novel targets for treatment of heart disease

The phospholipases associated with the cardiac sarcolemmal (SL) membrane hydrolyze specific membrane phospholipids to generate important lipid signaling molecules, which are known to influence normal cardiac function. However, impairment of the phospholipases and their related signaling events may be contributory factors in altering cardiac function of the diseased myocardium. The identification of the changes in such signaling systems as well as understanding the contribution of phospholipid-signaling pathways to the pathophysiology of heart disease are rapidly emerging areas of research in this field. In this paper, I provide an overview of the role of phospholipid-mediated signal transduction processes in cardiac hypertrophy and congestive heart failure, diabetic cardiomyopathy, as well as in ischemia-reperfusion. From the cumulative evidence presented, it is suggested that phospholipid-mediated signal transduction processes could serve as novel targets for the treatment of the different types of heart disease.

Physiologic and pathophysiologic roles of lipid mediators in the kidney

Small lipids such as eicosanoids exert diverse and complex functions. In addition to their role in regulating normal kidney function, these lipids also play important roles in the pathogenesis of kidney diseases. Cyclooxygenase (COX)-derived prostanoids play important role in maintaining renal function, body fluid homeostasis, and blood pressure. Renal cortical COX2-derived prostanoids, particularly (PGI2) and PGE2 play critical roles in maintaining blood pressure and renal function in volume contracted states. Renal medullary COX2-derived prostanoids appear to have antihypertensive effect in individuals challenged with a high salt diet. 5-Lipoxygenase (LO)-derived leukotrienes are involved in inflammatory glomerular injury. LO product 12-hydroxyeicosatetraenoic acid (12-HETE) is associated with pathogenesis of hypertension, and may mediate angiotensin II and TGFbeta induced mesengial cell abnormality in diabetic nephropathy. P450 hydroxylase-derived 20-HETE is a potent vasoconstrictor and is involved in the pathogenesis of hypertension. P450 epoxygenase derived epoxyeicosatrienoic acids (EETs) have vasodilator and natriuretic effect. Blockade of EET formation is associated with salt-sensitive hypertension. Ceramide has also been demonstrated to be an important signaling molecule, which is involved in pathogenesis of acute kidney injury caused by ischemia/reperfusion, and toxic insults. Those pathways should provide fruitful targets for intervention in the pharmacologic treatment of renal disease.

Roles of Lipid Mediators in Kidney Injury

Small lipids such as eicosanoids exert diverse and complex functions. In addition to their role in regulating normal kidney function, these lipids also play important roles in the pathogenesis of kidney diseases. Increased glomerular cyclooxygenase (COX)1 or COX2 expression has been reported in patients with nephritis and in animal models of nephritis. COX inhibitors have shown beneficial effects on lupus nephritis and passive Heymann nephritis, but not anti-Thy1.1-induced nephritis. 5-Lipoxygenase-derived leukotrienes are involved in inflammatory glomerular injury. Lipoxygenase product 12-hydroxyeicosatetraenoic acid may mediate angiotensin II and transforming growth factor beta-induced mesangial cell abnormality in diabetic nephropathy. P450 arachidonic acid mono-oxygenase-derived 20-hydroxyeicosatetraenoic acid and epoxyeicosatrienoic acids are involved in several forms of kidney injury, including renal injury in metabolic syndrome. Ceramide also has been shown to be an important signaling molecule that is involved in the pathogenesis of acute kidney injury caused by ischemia/reperfusion and toxic insults. Those pathways should provide fruitful targets for intervention in the pharmacologic treatment of renal disease.

Cytosolic phospholipase A(2) alpha mediates electrophysiologic responses of hippocampal pyramidal neurons to neurotoxic NMDA treatment

The arachidonic acid-generating enzyme cytosolic phospholipase A(2) alpha (cPLA(2)alpha) has been implicated in the progression of excitotoxic neuronal injury. However, the mechanisms of cPLA(2)alpha toxicity have yet to be determined. Here, we used a model system exposing mouse hippocampal slices to NMDA as an excitotoxic injury, in combination with simultaneous patch-clamp recording and confocal Ca(2+) imaging of CA1 pyramidal neurons. NMDA treatment caused significantly greater injury in wild-type (WT) than in cPLA(2)alpha null CA1 neurons. Bath application of NMDA evoked a slow inward current in voltage-clamped neurons (composed of both NMDA receptor-mediated and other conductances) that was smaller in cPLA(2)alpha null than in WT slices. This was not due to down-regulation of NMDA receptor function because NMDA receptor-mediated currents were equivalent in each genotype following brief photolysis of caged glutamate. Current-clamp recordings were made during and following NMDA exposure by eliciting a single action potential with a brief current injection. After NMDA exposure, WT CA1 neurons developed a spike-evoked plateau potential and an increased spike-evoked dendritic Ca(2+) transient. These effects were absent in CA1 neurons from cPLA(2)alpha null mice and WT neurons treated with a cPLA(2)alpha inhibitor. The Ca-sensitive K-channel toxins, apamin and paxilline, caused spike broadening and Ca(2+) enhancement in WT and cPLA(2)alpha null slices. NMDA application in WT and arachidonate applied to cPLA(2)alpha null cells occluded the effects of apamin/paxilline. These results indicate that cPLA(2)alpha activity is required for development of aberrant electrophysiologic events triggered by NMDA receptor activation, in part through attenuation of K-channel function.

Cytosolic phospholipase A alpha modulates NMDA neurotoxicity in mouse hippocampal cultures

The arachidonic acid-specific cytosolic phospholipase A(2) alpha (cPLA(2)alpha) has been implicated in the generation of neurological injuries. cPLA(2)alpha-dependent neurological injury has been postulated to be mediated through inflammatory and eicosanoid pathways. We determined if cPLA(2)alpha amplifies the injury of a non-inflammatory, excitotoxic stimulus by modifying a well-described toxicity assay to measure the toxicity of N-methyl-d-aspartate (NMDA) in the CA1 region of organotypic, mouse hippocampal cultures. Hippocampal cultures from wild-type and cPLA(2)alpha knockout mice were exposed to 5, 7.5 or 10 microm NMDA for 1 h. Toxicity was measured 23 h later. Cultures derived from cPLA(2)alpha(-/-) mice and cultures treated with the selective inhibitor AACOCF(3) were significantly protected from NMDA toxicity, as compared with wild-type cultures. To determine if cPLA(2)alpha-dependent toxicity is cyclooxygenase (COX)-2 dependent, COX-2 and PGE(2) levels were measured 7 and 25 h after NMDA treatment. NMDA treatment failed to induce COX-2 protein or increase PGE(2) in the culture media in either genotype at either time. In contrast, phorbol 12-myristate 13-acetate and ionophore treatment caused robust induction of COX-2 and PGE(2) in both genotypes. We conclude that cPLA(2)alpha may have a hitherto unrecognized direct effect on excitatory neurotoxicity, suggesting that cPLA(2)alpha inhibition is a therapeutic candidate for treatment of the early, excitotoxic injury observed in stroke.

Differential behavior of sPLA2-V and sPLA2-X in human neutrophils

Neutrophils and differentiated PLB-985 cells contain various types of PLA(2)s including the 85 kDa cytosolic PLA(2) (cPLA(2)), Ca(2+)-independent PLA(2) (iPLA(2)) and secreted PLA(2)s (sPLA(2)s). The present study focuses on the behavior of sPLA(2)s in neutrophils and PLB cells and their relationship to cPLA(2)alpha. The results of the present research show that the two types of sPLA(2) present in neutrophils, sPLA(2)-V and sPLA(2)-X, which are located in the azurophil granules, are differentially affected by physiological stimuli. While sPLA(2)-V is secreted to the extacellular milieu, sPLA(2)-X is detected on the plasma membranes after stimulation. Stimulation of neutrophils with formyl-Met-Leu-Phe (fMLP), opsonized zymosan (OZ) or A23187 resulted in a different kinetics of sPLA(2) secretion as detected by its activity in the neutrophil supernatants. Neutrophil priming by inflammatory cytokines or LPS enhanced sPLA(2) activity detected in the supernatant after stimulation by fMLP. This increased activity was due to increased secretion of sPLA(2)-V to the supernatant and not to release of sPLA(2)-X. sPLA(2) in granulocyte-like PLB cells exhibit identical characteristics to neutrophil sPLA(2), with similar activity and optimal pH of 7.5. Granulocyte-like cPLA(2)alpha-deficient PLB cells serve as a good model to study whether sPLA(2) activity is regulated by cPLA(2)alpha. Secretion and activity of sPLA(2) were found to be similar in granulocyte-like PLB cells expressing or lacking cPLA(2)alpha, indicating that they are not under cPLA(2)alpha regulation.

Methylmercury-induced toxicity is mediated by enhanced intracellular calcium through activation of phosphatidylcholine-specific phospholipase C

Methylmercury (MeHg) is a ubiquitous environmental toxicant to which humans can be exposed by ingestion of contaminated food. MeHg has been suggested to exert its toxicity through its high reactivity to thiols, generation of arachidonic acid and reactive oxygen species (ROS), and elevation of free intracellular Ca(2+) levels ([Ca(2+)](i)). However, the precise mechanism has not been fully defined. Here we show that phosphatidylcholine-specific phospholipase C (PC-PLC) is a critical pathway for MeHg-induced toxicity in MDCK cells. D609, an inhibitor of PC-PLC, significantly reversed the toxicity in a time- and dose-dependent manner with concomitant inhibition of the diacylglycerol (DAG) generation and the phosphatidylcholine (PC)-breakdown. MeHg activated the group IV cytosolic phospholipase A(2) (cPLA(2)) and acidic form of sphingomyelinase (A-SMase) downstream of PC-PLC, but these enzymes as well as protein kinase C (PKC) were not linked to the toxicity by MeHg. Furthermore, MeHg produced ROS, which did not affect the toxicity. Addition of EGTA to culture media resulted in partial decrease of [Ca(2+)](i) and partially blocked the toxicity. In contrast, when the cells were treated with MeHg in the presence of Ca(2+) in the culture media, D609 completely prevented cell death with parallel decrease in [Ca(2+)](i). Our results demonstrated that MeHg-induced toxicity was linked to elevation of [Ca(2+)](i) through activation of PC-PLC, but not attributable to the signaling pathways such as cPLA(2), A-SMase, and PKC, or to the generation of ROS.

Up-regulation of cytosolic phospholipase A2α expression by N,N-diethyldithiocarbamate in PC12 cells; involvement of reactive oxygen species and nitric oxide

Disulfiram (an alcohol-aversive drug) and related compounds are known to provoke several side effects involving behavioral and neurological complications. N,N-diethyldithiocarbamate (DDC) is considered as one of the main toxic species of disulfiram and acts as an inhibitor of superoxide dismutase. Since arachidonic acid (AA) formation is regulated by reactive oxygen species (ROS) and related to toxicity in neuronal cells, we investigated the effects of DDC on AA release and expression of the alpha type of cytosolic phospholipase A(2) (cPLA(2)alpha) in PC12 cells. Treatment with 80-120 microM DDC that causes a moderate increase in ROS levels without cell toxicity stimulated cPLA(2)alpha mRNA and its protein expression. The expression was mediated by extracellular-signal-regulated kinase (ERK1/2), one of the mitogen-activated protein kinases. Treatment with N(G) nitro-L-arginine methyl ester (an inhibitor of nitric oxide synthase, 1 mM) and oxy-hemoglobin (a scavenger of nitric oxide, 2 mg/mL) abolished the DDC-induced responses (ERK1/2 phosphorylation and cPLA(2)alpha expression). We also showed DDC-induced up-regulation of the mRNA expression of lipocortin 1, an inhibitor of PLA(2). Furthermore, DDC treatment of the cells enhanced Ca(2+)-ionophore-induced AA release in 30 min, although the effect was limited. Changes in AA metabolism in DDC-treated cells may have a potential role in mediating neurotoxic actions of disulfiram. In this study, we show the first to demonstrate the up-regulation of cPLA(2)alpha expression by DDC treatment in neuronal cells.

On the differential lipolytic capabilities of rat spleen and cardiac muscle. An in vitro incubation in conjunction with chromatographic and densitometric analysis

The phospholipid profiles of newborn, young adult and aged rat heart and spleen and their in vitro response to endogenous phospholipases at pH 7.4 and 38 degrees C for 60 min were analysed by thin layer chromatography (TLC) technology and densitometry measurement. The noticeable high level of cardiolipin (CL) and its preferential deacylation, as detected by the formation of monolysocardiolipin (MLCL) and concurrent reduction of CL level were the most prevalent lipolytic events of rat cardiac muscle (newborn, young adult and aged) but the least prevalent in rat spleen. The level of ethanolamine plasmalogen (PE) was high in both the rat spleen and cardiac muscle (newborn, young adult and aged). Following in vitro incubation, the reduction in the level of PE and the high level of lyso alkenyl PE produced were most conspicuous in rat spleen (newborn, young adult and aged) and noticeably less in rat cardiac muscle. These data clearly illustrate the differential response of the endogenous substrates (phospholipids) to the endogenous phospholipases of these two tissues, and probably are related to their physiological activities in vivo.

Necrosis, a well-orchestrated form of cell demise: signalling cascades, important mediators and concomitant immune response

Necrosis has long been described as a consequence of physico-chemical stress and thus accidental and uncontrolled. Recently, it is becoming clear that necrotic cell death is as well controlled and programmed as caspase-dependent apoptosis, and that it may be an important cell death mode that is both pathologically and physiologically relevant. Necrotic cell death is not the result of one well-described signalling cascade but is the consequence of extensive crosstalk between several biochemical and molecular events at different cellular levels. Recent data indicate that serine/threonine kinase RIP1, which contains a death domain, may act as a central initiator. Calcium and reactive oxygen species (ROS) are main players during the propagation and execution phases of necrotic cell death, directly or indirectly provoking damage to proteins, lipids and DNA, which culminates in disruption of organelle and cell integrity. Necrotically dying cells initiate pro-inflammatory signalling cascades by actively releasing inflammatory cytokines and by spilling their contents when they lyse. Unravelling the signalling cascades contributing to necrotic cell death will permit us to develop tools to specifically interfere with necrosis at certain levels of signalling. Necrosis occurs in both physiological and pathophysiological processes, and is capable of killing tumour cells that have developed strategies to evade apoptosis. Thus detailed knowledge of necrosis may be exploited in therapeutic strategies.

Overexpression of Cytosolic Group IVA Phospholipase A2 Protects Cells from Ca2+-dependent Death

The calcium ionophore ionomycin induces apoptosis-like events in the human embryonic kidney cell line at early times. Plasma membrane blebbing, mitochondrial depolarization, externalization of phosphatidylserine, and nuclear permeability changes can all be observed within 15 min of treatment. However, there is no activation of caspases or chromatin condensation. Expression of a fusion protein containing the enhanced green fluorescent protein (EGFP) and human cytosolic Group IVA phospholipase A(2)alpha (EGFP-cPLA(2)alpha) in these cells prevents ionomycin-induced phosphatidylserine externalization and death. Cells expressing the cPLA(2)alpha mutant D43N, which does not bind calcium, retain their susceptibility to ionomycin-induced cell death. Both nonexpressing and EGFP-D43N-cPLA(2)alpha-expressing human embryonic kidney cells can be spared from ionomycin-induced cell death by pretreating them with exogenous arachidonic acid. Moreover, during calcium overload, mitochondrial depolarization is significantly lower in the EGFP-cPLA(2)alpha-expressing cells than in cells expressing normal amounts of cPLA(2)alpha. These results suggest that early cell death events promoted by an overload of calcium can be prevented by the presence of high levels of arachidonic acid.

Role of cytochrome P450 in phospholipase A2- and arachidonic acid-mediated cytotoxicity

Phospholipases A2 (PLA2) comprise a set of extracellular and intracellular enzymes that catalyze the hydrolysis of the sn-2 fatty acyl bond of phospholipids to yield fatty acids and lysophospholipids. The PLA2 reaction is the primary pathway through which arachidonic acid (AA) is released from phospholipids. PLA2s have an important role in cellular death that occurs via necrosis or apoptosis. Several reports support the hypothesis that unesterified arachidonic acid in cells is a signal for the induction of apoptosis. However, most of the biological effects of arachidonic acid are attributable to its metabolism by mainly three different groups of enzymes: cytochromes P450, cyclooxygenases, and lipoxygenases. In this review we will focus on the role of cytochrome P450 in AA metabolism and toxicity. The major pathways of arachidonic acid metabolism catalyzed by cytochrome P450 generate metabolites that are subdivided into two groups: the epoxyeicosatrienoic acids, formed by CYP epoxygenases, and the arachidonic acid derivatives that are hydroxylated at or near the omega-terminus by CYP omega-oxidases. In addition, autoxidation of AA by cytochrome P450-derived reactive oxygen species produces lipid hydroperoxides as primary oxidation products. In some cellular models of toxicity, cytochrome P450 activity exacerbates PLA2- and AA-dependent injury, mainly through the production of oxygen radicals that promote lipid peroxidation or production of metabolites that alter Ca2+ homeostasis. In contrast, in other situations, cytochrome P450 metabolism of AA is protective, mainly by lowering levels of unesterified AA and by production of metabolites that activate antiapoptotic pathways. Several lines of evidence point to the combined action of phospholipase A2 and cytochrome P450 as central in the mechanism of cellular injury in several human diseases, such as alcoholic liver disease and myocardial reperfusion injury. Inhibition of specific PLA2 and cytochrome P450 isoforms may represent novel therapeutic strategies against these diseases.

Calpain activation contributes to oxidative stress-induced pancreatic acinar cell injury

Oxygen radicals have been implicated as mediators in the pathogenesis of pancreatic acinar cell necrosis. However, the sequence of events between the oxidative insult and cell damage remains unclear. In the current study, we investigated whether the Ca(2+)-regulated cytosolic cysteine protease calpain is activated by oxidative stress and contributes to oxidant-induced acinar cell damage. Isolated rat pancreatic acinar cells were exposed to hydrogen peroxide (H(2)O(2))-generated oxidative stress in the presence or absence of the Ca(2+) chelator 1,2-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester (BAPTA-AM) and different calpain inhibitors including benzyloxycarbonyl-valyl-phenylalanine methyl ester. Calpain activation was studied by fluorescence spectrophotometry and immunoblotting. Cell injury was assessed by lactate dehydrogenase (LDH) release and characterization of the cellular ultrastructure including fluorescence-labeled actin filaments. Exposure of acinar cells to H(2)O(2) provoked a time- and dose-dependent increase in calpain proteolytic activity involving the ubiquitous isoforms mu- and m-calpain. The activation of calpain reflected the time course of developing cytotoxicity as demonstrated by increased LDH release. Inhibition of oxidant-induced calpain activity by BAPTA-AM and various calpain inhibitors provoked a decline in oxidant-induced cell injury. In particular, changes in the actin filament organization characterized by an increase in the basolateral actin and by a detachment of actin from the cell membrane in the region of membrane blebs were clearly reduced. In summary, our findings suggest that acinar cell damage through oxidative stress requires activation of calpain and that the actin cytoskeleton belongs to the cellular targets of the protease. The results support the hypothesis that calpain activation may play a role in the development of acute pancreatitis.

Nitric oxide alters arachidonic acid turnover in brain cortex synaptoneurosomes

Nitric oxide (NO) and arachidonic acid (AA) and also its metabolites are very important inter- and intracellular second messengers. They are involved in mechanisms of learning and memory. However, liberated in excessive amount in brain ischemia, Parkinson and Alzheimer diseases they are responsible for cell degeneration and death. Previously, we could show that Alzheimer disease's amyloid-beta protein enhanced nitric oxide liberation. The role of NO in AA metabolism is till now not well understood. Therefore, the aim of the present study was to investigate the mechanisms of NO-evoked activation of AA release and inhibition of AA incorporation into phospholipids of cortical rat brain synaptoneurosomes. The studies were carried out using NO donors, butyryl-cGMP (b-cGMP) and H2O2. All these compounds enhanced AA liberation from phosphatydilinositol (PI) and phosphatidylcholine (PC). Protein kinase ERK1/2, protein kinase C (PKC), cGMP-dependent protein kinase G (PKG) were involved in basal and NO-induced cytosolic phospholipase A2 (cPLA2) activation. Moreover, NO donors, b-cGMP and hydrogen peroxide (H2O2) exerted inhibitory effect on AA incorporation into PI and PC influencing arachidonyl-CoA transferase (AA-CoA-T) activity. AA-CoA synthase (AA-CoA-S) activity did not change. Specific inhibitors of protein kinase ERK1/2 (UO126), PKC (GF109203X), PKG (KT5823) had no effect on NO-mediated lowering of AA incorporation into PI and PC but inhibited the basal AA-CoA-S activity. Our data indicated that AA (10 microM) itself markedly decreased AA incorporation by about 50% into phospholipids of synaptoneurosomes membranes. Increasing release of AA and its metabolites causes the lowering of AA incorporation evoked by NO, b-cGMP and H2O2. Antioxidant, Resveratrol (100 microM) prevented NO- and cGMP-evoked inhibition of AA incorporation. These results suggest that NO affects the intracellular level of AA through alteration of cPLA2 and AA-CoA acyltransferase activities and may have an important implication in alterations of nerve endings properties and function.

Uteroglobin inhibits prostaglandin F2alpha receptor-mediated expression of genes critical for the production of pro-inflammatory lipid mediators

Prematurity is one of the leading causes of infant mortality. It may result from intrauterine infection, which mediates premature labor by stimulating the production of inflammatory lipid mediators such as prostaglandin F2alpha (PGF2alpha). The biological effects of PGF2alpha are mediated via the G protein-coupled receptor FP; however, the molecular mechanism(s) of FP signaling that mediates inflammatory lipid mediator production remains unclear. We reported previously that in the human uterus, a composite organ in which fibroblast, epithelial, and smooth muscle cells are the major constituents, an inverse relationship exists between the levels of PGF2alpha and a steroid-inducible anti-inflammatory protein, uteroglobin. Here we report that, in NIH 3T3 fibroblasts and human uterine smooth muscle cells, FP signaling is mediated via multi-kinase pathways in a cell type-specific manner to activate NF-kappaB, thus stimulating the expression of cyclooxygenase-2. Cyclooxygenase-2 is a critical enzyme for the production of prostaglandins from arachidonic acid, which is released from membrane phospholipids by phospholipase A2, the expression of which is also stimulated by PGF2alpha. Most importantly, uteroglobin inhibits FP-mediated NF-kappaB activation and cyclooxygenase-2 gene expression by binding and most likely by sequestering PGF2alpha into its central hydrophobic cavity, thereby preventing FP-PGF2alpha interaction and suppressing the production of inflammatory lipid mediators. We propose that uteroglobin plays important roles in maintaining homeostasis in organs that are vulnerable to inadvertent stimulation of FP-mediated inflammatory response.

Phospholipase A2 inhibitors in development

To date, three isoforms of phospholipase A2 (PLA2) have been identified. Of these, the two Ca2+-dependent isoforms, secretory (sPLA2) and cytosolic phospholipase A2 (cPLA2), are targets for new anti-inflammatory drugs. The catalytic mechanisms and functions of the third isoform, Ca2+-independent cytosolic phospholipase A2 (iPLA2), are unknown at present. sPLA2 and cPLA2 are both implicated in the release of arachidonic acid and prophlogistic lipid mediators. However, recent findings provide evidence that cPLA2 is the dominant isoform in various kinds of inflammation, such as T-cell-mediated experimental arthritis. A triple function of PLA2-derived lipid mediators has been suggested: causing immediate inflammatory signs, involvement in secondary processes, e.g., superoxide free radical (O2) generation, apoptosis, or tumour necrosis factor-alpha (TNF-alpha)-cytotoxicity, and controlling the expression and activation of pivotal proteins implicated in inflammation and cell development, e.g., cytokines, adhesion proteins, proteinases, NF-kappaB, fos/jun/AP-1, c-Myc, or p21ras. In the past, research predominantly focused on the development of sPLA2 inhibitors; however, present techniques enable discrimination of cPLA2, sPLA2, and iPLA2, and specific inhibitors of each of the three isoforms are likely to appear soon. Over the last decade, between 40 and 50 sPLA2 inhibitors have been described; and the list is growing. However, of these, few have the potential for clinical success, and those that do are predominantly active site-directed inhibitors, e.g., BMS-181162, LY311727, ARL-67974, FPL67047, SB-203347, Ro-23-9358, YM-26734, and IS-741. At present, there are no likely clinical candidates emerging from the ranks of cPLA2 and iPLA2 inhibitors in development. Indications for which PLA2 inhibitors are being pursued include, sepsis, acute pancreatitis, inflammatory skin and bowel diseases, asthma, and rheumatoid arthritis. The three main obstacles to the successful development of PLA2 inhibitors include, insufficient oral bioavailability, low affinity for the enzyme corresponding to low in vivo efficacy and insufficient selectivity.

cPLA2-interacting protein, PLIP, causes apoptosis and decreases G1 phase in mesangial cells

The balance between proliferation and apoptosis of mesangial cells is a critical component of proliferative glomerulonephritis. The regulation of cell proliferation and apoptosis is linked at the level of the cell cycle (Shankland SJ. Kidney Int 52: 294-308, 199). cPLA2-interacting protein (PLIP), the Tip60 splice variant, interacts with cPLA2 and enhances the susceptibility of renal mesangial cells to serum deprivation-induced apoptosis (Sheridan AM, Force T, Yoon HJ, O'Leary E, Choukroun G, Taheri MR, and Bonventre JV. Mol Cell Biol 21: 4470-4481, 2001). We report that adenoviral-driven PLIP expression results in enhanced apoptosis of non-serum-deprived mesangial cells associated with a marked decrease in G0/G1 phase cells. The effect of PLIP on the cell cycle may be independent of its interaction with cPLA2 because a mutation of PLIP that does not interact with cPLA2 also causes a decrease in G0/G1 cells. Endogenous PLIP and Tip60 protein levels are increased in cells exposed to injurious stimuli including X-irradiation and H2O2, but the intracellular localization of the splice variants may differ. Whereas PLIP localizes in the nucleus of all mesangial cells, Tip60 localizes in the cytosol of untreated mesangial cells and of cells exposed to low concentrations (50-200 microM) of H2O2. Tip60 is targeted to the nucleus of cells exposed to high concentrations (1-2 mM) of H2O2. We conclude that PLIP may cause cells to exit from the cell cycle after the S phase and may function as part of a G2/M checkpoint mechanism. Tip60 splice variants may function in both cytosolic and nuclear signaling pathways in mesangial cells.

Indomethacin induces free radical-mediated changes in renal brush border membranes

Nonsteroidal anti-inflammatory drugs (NSAIDs) are used extensively in clinical medicine. One disadvantage of their use, however, is the occurrence of adverse effects in the kidneys. The side effects produced in this organ have been classically attributed to the inhibitory effect of these drugs on the activity of cyclooxygenase, a key enzyme in prostaglandin synthesis. Our earlier work with indomethacin, a commonly used NSAID, has shown that oxidative stress and mitochondrial dysfunction occur in the kidney in response to the drug. In view of this, this study looked into the effect of indomethacin on brush border membranes (BBM) from the kidney, as these biomembranes are prime targets of oxygen free radicals. Rats, fasted overnight, were dosed with indomethacin (20 mg/kg) by gavage and sacrificed 24 h later. BBM were isolated from the kidneys by polyethylene glycol precipitation. It was found that there was an increase in levels of products of peroxidation and a fall in the level of alpha-tocopherol in the BBM from indomethacin-dosed rats. These BBM also exhibited impaired glucose transport. The lipid composition of the membranes was also found to be altered. Alterations in lipids were associated with up-regulation of phospholipase A2. Pretreatment with L-arginine, a nitric oxide donor, protected against these effects of indomethacin. Thus, this study suggests that indomethacin induces impairment in structure and function of BBM in the kidney, with these effects possibly mediated by free radicals and activation of phospholipases. We postulate that such alterations may be important in the pathogenesis of NSAID-induced nephropathy.

Differential changes in phospholipase D and phosphatidate phosphohydrolase activities in ischemia–reperfusion of rat heart

Phospholipase D (PLD2) produces phosphatidic acid (PA), which is converted to 1,2 diacylglycerol (DAG) by phosphatidate phosphohydrolase (PAP2). Since PA and DAG regulate Ca(2+) movements, we examined PLD2 and PAP2 in the sarcolemma (SL) and sarcoplasmic reticular (SR) membranes from hearts subjected to ischemia and reperfusion (I-R). Although SL and SR PLD2 activities were unaltered after 30 min ischemia, 5 min reperfusion resulted in a 36% increase in SL PLD2 activity, whereas 30 min reperfusion resulted in a 30% decrease in SL PLD2 activity, as compared to the control value. SR PLD2 activity was decreased (39%) after 5 min reperfusion, but returned to control levels after 30 min reperfusion. Ischemia for 60 min resulted in depressed SL and SR PLD2 activities, characterized with reduced V(max) and increased K(m) values, which were not reversed during reperfusion. Although the SL PAP2 activity was decreased (31%) during ischemia and at 30 min reperfusion (28%), the SR PAP2 activity was unchanged after 30 min ischemia, but was decreased after 5 min reperfusion (25%) and almost completely recovered after 30 min reperfusion. A 60 min period of ischemia followed by reperfusion caused an irreversible depression of SL and SR PAP2 activities. Our results indicate that I-R induced cardiac dysfunction is associated with subcellular changes in PLD2 and PAP2 activities.

Increased calcium-independent phospholipase A2 activity in first but not in multiepisode chronic schizophrenia

BACKGROUND

Increased activity of calcium independent phospholipase A2 (iPLA2) has repeatedly been found in the serum of unmedicated first-episode schizophrenia patients and assumed to reflect a pertubation of phospholipid metabolism. Previous studies in chronic schizophrenia were less conclusive. To explore whether iPLA2 changes are stage dependent, we investigated serum iPLA2 activity in various stages of schizophrenia.

METHODS

iPLA2 activity was assessed in the serum of 30 first-episode and 23 multiepisode schizophrenia patients and 53 healthy control subjects matched for age and gender. A fluorimetric assay was applied using the PLA2 specific substrate NBDC6-HPC, thin-layer chromatography of reaction products, and digital image scanning for signal detection.

RESULTS

Group comparison between first-episode and multiepisode patients and corresponding control groups revealed significantly increased iPLA2 activity only in first-episode patients. Enzyme activity in first-episode patients was also markedly increased, compared with chronic patients. iPLA2 changes observed were irrespective of neuroleptic medication, age, or gender.

CONCLUSIONS

Our results suggest increased lipid turnover in the acute early phase of schizophrenia that is less obvious in chronic stages. Future longitudinal studies involving iPLA2 activity and phosphorous magnetic resonance spectroscopy need to address the relation between perturbed brain lipid metabolism and iPLA2 increment in the course of schizophrenia.

Hydrogen peroxide generated at the level of mitochondria in response to peroxynitrite promotes U937 cell death via inhibition of the cytoprotective signalling mediated by cytosolic phospholipase A2

We have studied the relationships existing between delayed formation of H2O2 and activation of cytosolic phospholipase A2 (cPLA2), events respectively promoting toxicity or survival in U937 cells exposed to peroxynitrite. The outcome of an array of different approaches using phospholipase A2 inhibitors, or cPLA2 antisense oligonucleotides, as well as specific respiratory chain inhibitors and respiration-deficient cells led to the demonstration that H2O2 does not mediate toxicity by producing direct molecular damage. Rather, the effects of H2O2 were found to be upstream to the arachidonic acid (AA)-mediated cytoprotective signalling and in fact causally linked to inhibition of cPLA2. Thus, it appears that U937 cells exposed to nontoxic concentrations of peroxynitrite are nevertheless committed to death, which however is normally prevented by the activation of parallel pathways resulting in cPLA2-dependent release of AA. A rapid necrotic response, however, takes place when high concentrations of peroxynitrite promote formation of H2O2 at levels impairing the cPLA2 cytoprotective signalling.

Studies on the endogenous phospholipids of mammalian kidney and theirin vitro hydrolysis by endogenous phospholipases: a thin layer chromatographic and densitometric study

The phosphoglycerides profile of six species of mammalian kidney (guinea pig, pig, cat, dog, mouse and rat) and their in vitro response to the endogenous phospholipases were determined by TLC technology in conjunction with densitometric measurements. Changes in their phospholipids profile subsequent to in vitro incubation of whole tissue homogenate of these kidneys for 60 min, at pH 7.4, 38 degrees C, and prior to phospholipids extraction have shown that the deacylation of the endogenous cardiolipin (CL) is the most prevalent lipolytic event of all mammalian kidneys studied. Concurrent with the deacylation of CL, there was also formation of monolysocardiolipin (MLCL) and a reduction in CL level. To a much lesser extent, lyso alkenyl phosphatidyl ethanolamine (LPE) was also produced concomitant with a decrease of the endogenous alkenyl phosphatidyl ethanolamine (PE) level. The deacylation of PE plasmalogen to its lyso form confirms the action of endogenous PLA(2) releasing sn-2 fatty acids.