Inhibition Of Cytosolic Phospholipase Research Articles

Taxifolin prevents β-amyloid-induced impairments of synaptic formation and deficits of memory via the inhibition of cytosolic phospholipase A2/prostaglandin E2 content.

Taxifolin is a potent flavonoid with anti-inflammatory activity. Taxifolin has been reported to decrease the accumulation of β-amyloid (Aβ), and reduce Aβ-induced neurotoxicity. However, the detail molecular mechanism of taxifolin against Aβ-induced neurotoxicity is largely unknown. In this study, we revealed the protective effects and the underlying mechanisms of taxifolin on the impairments of cognitive function and synapse formation induced by soluble Aβ oligomers. Our results showed that taxifolin prevented neuronal cell death in a concentration-dependent manner. The recognition memory in novel object recognition tasks and the spatial memory in Morris water maze tests are significantly lower in the Alzheimer's disease (AD) model mice induced by hippocampal injection of Aβ42. Taxifolin treatment prevented the recognitive and spatial memory deficits of the AD mice. 10mg/kg taxifolin treatment also significantly prevented the decreased expression levels of PSD 95 induced by Aβ42. Live cell imaging study showed that 2h pre-treatment of taxifolin prevented the decrease in the number of filopodium and spine induced by Aβ42 oligomers. Aβ42 oligomers significantly increased the production of cytosolic phospholipase A2 (cPLA2), a crucial enzyme of pro-inflammatory mediator, and prostaglandin E2 (PGE2), a neuroinflammatory molecule. Taxifolin significantly reduced the content of cPLA2 and PGE2 induced by Aβ42 both in the primary hippocampal neurons and hippocampal tissues. These results indicated that taxifolin might prevent Aβ42 oligomer-induced synapse and cognitive impairments through decreasing cPLA2 and PGE2. Our study provided novel insights into the cellular mechanisms for the protective effects of taxifolin on AD.

Inhibition of Cytosolic Phospholipase A2 Has Neuroprotective Effects on Motoneuron and Muscle Atrophy after Spinal Cord Injury.

Surviving motoneurons undergo dendritic atrophy after spinal cord injury (SCI), suggesting an important therapeutic target for neuroprotective strategies to improve recovery of function after SCI. Our previous studies showed that cytosolic phospholipase A2 (PLA2) may play an important role in the pathogenesis of SCI. In the present study, we investigated whether blocking cytosolic PLA2 (cPLA2) pharmacologically with arachidonyl trifluoromethyl ketone (ATK) or genetically using cPLA2 knockout (KO) mice attenuates motoneuron atrophy after SCI. C57BL/6 mice received either sham or contusive SCI at the T10 level. At 30 min after SCI, mice were treated with ATK or vehicle. Four weeks later, motoneurons innervating the vastus lateralis muscle of the quadriceps were labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed in three dimensions. Soma volume, motoneuron number, lesion volume, and tissue sparing were also assessed, as were muscle weight, fiber cross-sectional area, and motor endplate size and density. ATK administration reduced percent lesion volume and increased percent volume of spared white matter, compared to the vehicle-treated control animals. SCI with or without ATK treatment had no effect on the number or soma volume of quadriceps motoneurons. However, SCI resulted in a decrease in dendritic length of quadriceps motoneurons in untreated animals, and this decrease was completely prevented by treatment with ATK. Similarly, vastus lateralis muscle weights of untreated SCI animals were smaller than those of sham surgery controls, and these reductions were prevented by ATK treatment. No effects on fiber cross-sectional areas, motor endplate area, or density were observed across treatment groups. Remarkably, genetically deleting cPLA2 in cPLA2 KO mice attenuated dendritic atrophy after SCI. These findings suggest that, after SCI, cord tissue damage and regressive changes in motoneuron and muscle morphology can be reduced by inhibition of cPLA2, further supporting a role for cPLA2 as a neurotherapeutic target for SCI treatment.

Inhibition of cPLA2 activation by Ginkgo biloba extract protects spinal cord neurons from glutamate excitotoxicity and oxidative stress‐induced cell death

Ginkgo biloba extract (EGb761) has been shown to be neuroprotective; however, the mechanism by which EGb761 mediates neuroprotection remains unclear. We hypothesized that the neuroprotective effect of EGb761 is mediated by inhibition of cytosolic phospholipase A(2) (cPLA(2)), an enzyme that is known to play a key role in mediating secondary pathogenesis after acute spinal cord injury (SCI). To determine whether EGb761 neuroprotection involves the cPLA(2) pathway, we first investigated the effect of glutamate and hydrogen peroxide on cPLA(2) activation. Results showed that both insults induced an increase in the expression of phosphorylated cPLA(2) (p-cPLA(2)), a marker of cPLA(2) activation, and neuronal death in vitro. Such effects were significantly reversed by EGb761 administration. Additionally, EGb761 significantly decreased prostaglandin E(2) (PGE(2)) release, a downstream metabolite of cPLA(2). Moreover, inhibition of cPLA(2) activity with arachidonyl trifluromethyl ketone improved neuroprotection against glutamate and hydrogen peroxide-induced neuronal death, and reversed Bcl-2/Bax ratio; notably, EGb761 produced greater effects than arachidonyl trifluromethyl ketone. Finally, we showed that the extracellular signal-regulated kinase 1/2 signaling pathway is involved in EGb761's modulation of cPLA(2) phosphorylation. These results collectively suggest that the protective effect of EGb761 is mediated, at least in part, through inhibition of cPLA(2) activation, and that the extracellular signal-regulated kinase 1/2 signaling pathway may play an important role in mediating the EGb761's effect.

Moxifloxacin Alleviates Oleic Acid-provoked Neutrophilic Respiratory Burst in the Rat Lung through the Inhibition of Cytosolic Phospholipase A2

Background: According to the notion of the immunoregulatory functions of moxifloxacin (MFX), the effect of MFX on the neutrophilic respiratory burst in conjunction with the expression of cytosolic phospholipase A(2) (cPLA(2)) was investigated. Methods: The effects and possible mechanisms of MFX on neutrophilic respiratory burst in oleic acid (OA)-induced acutely injured rats lung and OA-stimulated, isolated murine neutrophils were probed, associated with the expression of cytosolic phospholipase A(2) in vivo and in vitro. Results: In the OA-induced acutely-injured lungs, neutrophils were accumulated, which was attenuated by MFX. The parameters denoting a neutrophilic respiratory burst, such as nitro blue tetrazolium reaction, cytochrome-c reduction, neutrophil aggregation, H(2)O(2) production in neutrophils revealed increased neutrophilic respiratory burst by OA, and MFX decreased all of these parameters. In addition, the enhanced expression of cPLA(2) in the lung and isolated murine neutrophils by OA were decreased by MFX. Conclusion: MFX suppresses the OA-induced neutrophilic respiratory burst by the suppression of cPLA(2) in neutrophils.

Coupling factor 6 as a novel vasoactive and proatherogenic peptide in vascular endothelial cells

Coupling factor 6 (CF6) is composed of 76 amino acids and is present in the peripheral stalk of mitochondrial ATP synthase. The generation of CF6 is positively regulated by tumor necrosis factor alpha and shear stress via nuclear factor kappaB, and by high glucose via protein kinase C and p38 mitogen-activated protein kinase. CF6 is released outside of the cells from vascular endothelial cells, and binds to the beta-subunit of the plasma membrane-bound ATP synthase in vascular endothelial cells and leads to intracellular acidosis. CF6 produces vasoconstriction, and the biological active site resides at the C-terminal portion. CF6 suppresses prostacyclin generation via inhibition of cytosolic phospholipase A(2). CF6 also suppresses nitric oxide synthase activity via an increase in asymmetric dimethylarginine and a decrease in platelet/endothelial cell adhesion molecule-1. CF6 induces the gene and protein expression of proatherogenic molecules such as endothelin 2, urokinase type plasminogen activator receptor, estrogen receptor beta, a soluble short form of vascular endothelial growth factor receptor-1, and lectin-like oxidized low-density lipoprotein receptor-1. The plasma level of CF6 is elevated in patients with essential hypertension, diabetes mellitus, end-stage renal disease, acute myocardial infarction, and coronary heart disease. It is likely that CF6 contributes to the pathogenesis of cardiovascular diseases, but further intensive investigation is needed.

Glutamine preferentially inhibits T‐helper type 2 cell‐mediated airway inflammation and late airway hyperresponsiveness through the inhibition of cytosolic phospholipase A2 activity in a murine asthma model

The non-essential amino acid, l-glutamine (Gln), is abundant in the human body. Gln exhibits beneficial effects on endotoxic shock through the inhibition of cytosolic phospholipase A(2) (cPLA(2)) activity. cPLA(2) has been reported to be implicated in the pathogenesis of asthma, but the effects of Gln on asthma have not yet been defined. To investigate the effects of Gln on allergic bronchial inflammation and airway hyperresponsiveness (AHR), and to determine the possible action mechanisms of Gln in a murine model of asthma. cPLA(2) phosphorylation was assessed by immunoprecipitation and Western blotting. Smears of bronchoalveolar lavage cells were stained with Diff-Quik solution for differential cell counting. Airway levels of the proteins [T-helper type-1 (Th1) and Th2 cytokines, and mucin] were measured by ELISA. mRNA expression of cytokines was assessed by real-time RT-PCR. AHR was assessed as a change in airway resistance (RL). Histological studies were performed to assess the levels of mucin and pulmonary inflammation. Systemic Gln administration inhibited cPLA(2) phosphorylation and its enzymatic activity in the lungs. Additionally, Gln effectively suppressed the key features of Th2-dependent asthmatic features, such as airway eosinophilia, mucus formation, and airway type 2 cytokine production, as well as late AHR. Gln was found to be effective in the suppression of Th2-dependent phenotypes and late AHR, and this effect of Gln appeared to be at least partially attributable to its ability to suppress cLPA(2) activity in the airway. Our results suggest that clinical use of Gln for patients with asthma may be beneficial.

Normal-phase HPLC and HPLC–MS studies of the metabolism of a cytosolic phospholipase A 2α inhibitor with activated ketone group by rat liver microsomes

Inhibition of cytosolic phospholipase A 2α (cPLA 2α) is assumed to provide a novel therapeutic approach for the treatment of many inflammatory diseases. 1-[3-(4-Octylphenoxy)-2-oxopropyl]indole-5-carboxylic acid ( 2) is a potent inhibitor of cPLA 2α. An important part of the pharmacophore of 2 is its activated electrophilic ketone moiety. Since it is known that activated ketones may be metabolically unstable, the metabolism of 2 by rat liver microsomes was investigated. For quantification of the metabolites normal-phase HPLC/UV on a cyano column was used, because under reversed-phase conditions with aqueous solvents 2 was partly transformed into its hydrate resulting in chromatograms with splitted peaks. Under the conditions applied about 30% of 2 were metabolized. The main metabolite was the alcohol 4 as shown by LC/MS n.

Inhibition of Cytosolic Phospholipase A2α: Hit to Lead Optimization

Compound 1 was previously reported to be a potent inhibitor of cPLA(2)alpha in both artificial monomeric substrate and cell-based assays. However, 1 was inactive in whole blood assays previously used to characterize cyclooxygenase and lipoxygenase inhibitors. The IC(50) of 1 increased dramatically with cell number or lipid/detergent concentration. In an attempt to insert an electrophilic ketone between the indole and benzoic acid moieties, we discovered that increasing the distance between the two moieties gave a compound with activity in the GLU (7-hydroxycoumarinyl-gamma-linolenate) micelle assay, which contains lipid and detergent. Extensive structure-activity relationship work around this lead identified a potent pharmacophore for cPLA(2)alpha inhibition. The IC(50)s between the GLU micelle and rat whole blood assays correlated highly. No correlation was found for other parameters, including lipophilicity or acidity of the required acid functionality. Compounds 25, 39, and 94 emerged as potent, selective inhibitors of cPLA(2)alpha and represent well-validated starting points for further optimization.

Inhibition of cytosolic phospholipase A 2 mRNA expression: a novel mechanism for acetylsalicylic acid-mediated growth inhibition and apoptosis in colon cancer cells

Acetylsalicylic acid (ASA) has been confirmed to inhibit proliferation and to induce apoptosis in human colorectal cancer cells in vitro. However, the mechanism by which ASA exhibits antiproliferative and proapoptotic effects in cyclooxygenase 2 (COX-2)-negative cells remains to be further elucidated. In the present study, SW480, a COX-2-negative colon cancer cell line, was treated with various concentrations of ASA (0, 2.5, 5, and 10 mM). The antiproliferative and proapoptotic effects of ASA were confirmed by MTT assay, flow cytometry of propidium iodide (PI)-stained cells, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) assay. After treatment with ASA, intracellular cyclic AMP (cAMP) levels were increased and the production of prostaglandin E 2 (PGE 2) was decreased. RT-PCR analysis revealed that treatment of ASA induced a concentration-dependent downregulation of cytosolic phospholipase A 2 (cPLA 2) mRNA expression in SW480 cells and also in two other colorectal cancer cell lines, Colo320 and HT-29 cells. Intracellular calcium levels were unaffected by ASA treatment. Our results indicate that the ASA-induced downregulation of cytosolic phospholipase A 2 mRNA expression might be a novel mechanism for ASA-mediated growth inhibition and apoptosis in colon cancer cells.

Role of cytosolic phospholipase A 2 in cytokine-stimulated prostaglandin release by human gallbladder cells

Eicosanoids are involved in gallbladder inflammation, epithelial water transport, and mucous secretion. Phospholipase A 2 enzymes liberate arachidonic acid from membrane phospholipids for the synthesis of eicosanoids. The purpose of this study was to determine the effect of selective cytoplasmic and secretory phospholipase A 2 inhibitors on basal and stimulated arachidonic acid and prostaglandin E 2 release in gallbladder cells. Western immunoblotting was employed to evaluate both cytosolic and secretory phospholipase A 2 enzymes in human gallbladder cells. Cells were incubated for 22 hours with 3H-labeled arachidonic acid. Arachidonic acid and prostaglandin E 2 release was then measured in the supernate after 2 hours of exposure to human interleukin-1β, alone or after pretreatment for 1 hour with the inhibitors. Unstimulated gallbladder cells express both 85 kDa cytosolic and 14 kDa secretory phospholipase A 2. The 85 kDa phospholipase A 2 was induced by interleukin-1β, whereas there was no apparent change in secretory phospholipase A 2 enzyme concentrations. Both the secretory phospholipase A 2 inhibitor p-bromophenylacyl bromide and the cytosolic phospholipase A 2 inhibitor arachidonyl trifluoromethyl ketone decreased basal and interleukin-1β—stimulated arachidonic acid release. In contrast, only inhibition of cytosolic phospholipase A 2 led to a decrease in interleukin-1β—stimulated prostaglandin E 2 release. Basal and interleukin-1β—stimulated arachidonic acid release appears to be the result of the activity of both cytosolic and secretory phospholipase A 2. Interleukin-1β—stimulated prostaglandin E 2 release appears to be dependent on the activity of cytosolic phospholipase A 2.

Inhibition of cytosolic phospholipase A 2 attenuates activation of mitogen-activated protein kinases in human monocytic cells

Eicosanoids and platelet-activating factor generated upon activation of cytosolic phospholipase A 2 enhance activity of transcription factors and synthesis of proinflammatory cytokines. Here, we show that selective inhibitors and antisense oligonucleotides against this enzyme suppressed expression of the interleukin-1β gene at the level of transcription and promoter activation in human monocytic cell lines. This inhibitory effect was due to failure of activation of mitogen-activated protein kinases (MAPK) through phosphorylation by upstream mitogen-activated protein kinase kinases (MKK). Consequently, phosphorylation and degradation of inhibitor-κBα (I-κBα) and subsequent cytoplasmic mobilization, DNA-binding and the transactivating potential of nuclear factor-κB (NF-kB), nuclear factor-interleukin-6 (NF-IL6), activation protein-1 (AP-1) and signal-transducer-and-activator-of-transcription-1 (STAT-1) were impaired. It is concluded, that lipid mediators promote activation of MAPKs, which in turn lead to phosphorylation and liberation of active transcription factors. Since inhibition of cytosolic phospholipase A 2 ameliorates inflammation in vivo, this potency may reside in interference with the MAPK pathway.

Inhibition of leukotriene synthesis by terfenadine in vitro

To determine the inhibitory mechanisms of terfenadine on the synthesis of leukotriene C 4 (LTC 4), an important mediator in allergic diseases, we evaluated the action of terfenadine on the IgE-dependent production of LTC 4 in rat basophilic leukaemia 2H3 cells. Rat IgE-loaded cells were stimulated with anti-IgE in the presence or absence of various concentrations of terfenadine and the level of LTC 4 released into the medium was measured by performing a specific radio immunoassay. Terfenadine inhibited the synthesis of LTC 4 to 67.2% at a concentration of 5 μg/ml. LT synthesis was directly suppressed by inhibition of 5-lipoxygenase (5-LO) through calcium ion-independent mechanisms, and was also possibly suppressed by inhibition of cytosolic phospholipase A 2 and 5-LO by blocking the influx of intracellular calcium ion that was initiated by IgE-related stimulation.

Distinctive inhibitory activity of docosahexaenoic acid against sphingosine-induced apoptosis

The effect of supplementation of docosahexaenoic acid (DHA) on the apoptosis of HL60 cells was examined using N-acetyl sphingosine (C 2-ceramide) and sphingosine as apoptosis-inducing agents. Although C 2-ceramide-induced apoptosis was not affected by DHA supplementation, sphingosine-induced apoptosis was reduced almost to the background level by preincubation with 10 μM DHA for 24 h. Among the fatty acids, only DHA appeared to be endowed with the ability to reduce sphingosine-induced apoptosis, whereas, other unsaturated fatty acids, such as arachidonic acid (AA) and eicosapentaenoic acid (EPA), did not show this activity. Incubation of HL60 with DHA within 6 h did not affect the apoptosis, suggesting that DHA probably expressed the inhibitory activity after modulation of the membrane fatty acid composition. DHA also attenuated the apoptosis induced by dimethylsphingosine and H-7, but not by calphostin C, indicating that enrichment of DHA in membranous phospholipid does not necessarily prevent all of the apoptosis associated with the inhibition of protein kinase C. The mechanism of the inhibition against sphingosine-induced apoptosis by DHA remains to be further explored. However, the inhibition of cytosolic phospholipase A 2 (cPLA 2) may be involved in the mechanism, because distinctive inhibitory activity of DHA against cPLA 2 has been demonstrated [M. Shikano, Y. Masuzawa, K. Yazawa, K. Takayama, I. Kudo, K. Inoue, Biochim. Biophys. Acta, 1212, 1994, 211–216], and arachidonyl trifluoromethylketone, a specific inhibitor of cPLA 2, attenuated the apoptosis induced by sphingosine.