Spinal phospholipase A2 in inflammatory hyperalgesia: role of group IVA cPLA2

PLA2G4A and ACHE modulate lipid profiles via glycerophospholipid metabolism in platinum-resistant gastric cancer

BACKGROUND

Bioactive lipids involved in the progression of various diseases. Nevertheless, there is still a lack of biomarkers and relative regulatory targets. The lipidomic analysis of the samples from platinum-resistant in gastric cancer patients is expected to help us further improve our understanding of it.

METHODS

We employed LC-MS based untargeted lipidomic analysis to search for potential candidate biomarkers for platinum resistance in GC patients. Partial least squares discriminant analysis (PLS-DA) and variable importance in projection (VIP) analysis were used to identify differential lipids. The possible molecular mechanisms and targets were obtained by metabolite set enrichment analysis and potential gene network screened. Finally, verified them by immunohistochemical of a tissue microarray.

RESULTS

There were 71 differential lipid metabolites identified in GC samples between the chemotherapy-sensitivity group and the chemotherapy resistance group. According to Foldchange (FC) value, VIP value, P values (FC > 2, VIP > 1.5, p < 0.05), a total of 15 potential biomarkers were obtained, including MGDG(43:11)-H, Cer(d18:1/24:0) + HCOO, PI(18:0/18:1)-H, PE(16:1/18:1)-H, PE(36:2) + H, PE(34:2p)-H, Cer(d18:1 + hO/24:0) + HCOO, Cer(d18:1/23:0) + HCOO, PC(34:2e) + H, SM(d34:0) + H, LPC(18:2) + HCOO, PI(18:1/22:5)-H, PG(18:1/18:1)-H, Cer(d18:1/24:0) + H and PC(35:2) + H. Furthermore, we obtained five potential key targets (PLA2G4A, PLA2G3, DGKA, ACHE, and CHKA), and a metabolite-reaction-enzyme-gene interaction network was built to reveal the biological process of how they could disorder the endogenous lipid profile of platinum resistance in GC patients through the glycerophospholipid metabolism pathway. Finally, we further identified PLA2G4A and ACHE as core targets of the process by correlation analysis and tissue microarray immunohistochemical verification.

CONCLUSION

PLA2G4A and ACHE regulated endogenous lipid profile in the platinum resistance in GC patients through the glycerophospholipid metabolism pathway. The screening of lipid biomarkers will facilitate earlier precision medicine interventions for chemotherapy-resistant gastric cancer. The development of therapies targeting PLA2G4A and ACHE could enhance platinum chemotherapy effectiveness.

DADLE promotes motor function recovery by inhibiting cytosolic phospholipase A2 mediated lysosomal membrane permeabilization after spinal cord injury

BACKGROUND AND PURPOSE

Autophagy is a protective factor for controlling neuronal damage, while necroptosis promotes neuroinflammation after spinal cord injury (SCI). DADLE (D-Ala2 , D-Leu5 ]-enkephalin) is a selective agonist for delta (δ) opioid receptor and has been identified as a promising drug for neuroprotection. The aim of this study was to investigate the mechanism/s by which DADLE causes locomotor recovery following SCI.

EXPERIMENTAL APPROACH

Spinal cord contusion model was used and DADLE was given by i.p. (16 mg·kg-1 ) in mice for following experiments. Motor function was assessed by footprint and Basso mouse scale (BMS) score analysis. Western blotting used to evaluate related protein expression. Immunofluorescence showed the protein expression in each cell and its distribution. Network pharmacology analysis was used to find the related signalling pathways.

KEY RESULTS

DADLE promoted functional recovery after SCI. In SCI model of mice, DADLE significantly increased autophagic flux and inhibited necroptosis. Concurrently, DADLE restored autophagic flux by decreasing lysosomal membrane permeabilization (LMP). Additionally, chloroquine administration reversed the protective effect of DADLE to inhibit necroptosis. Further analysis showed that DADLE decreased phosphorylated cPLA2 , overexpression of cPLA2 partially reversed DADLE inhibitory effect on LMP and necroptosis, as well as the promotion autophagy. Finally, AMPK/SIRT1/p38 pathway regulating cPLA2 is involved in the action DADLE on SCI and naltrindole inhibited DADLE action on δ receptor and on AMPK signalling pathway.

CONCLUSION AND IMPLICATION

DADLE causes its neuroprotective effects on SCI by promoting autophagic flux and inhibiting necroptosis by decreasing LMP via activating δ receptor/AMPK/SIRT1/p38/cPLA2 pathway.

Early upregulation of cytosolic phospholipase A2α in motor neurons is induced by misfolded SOD1 in a mouse model of amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal multifactorial neurodegenerative disease characterized by the selective death of motor neurons. Cytosolic phospholipase A₂ alpha (cPLA₂α) upregulation and activation in the spinal cord of ALS patients has been reported. We have previously shown that cPLA₂α upregulation in the spinal cord of mutant SOD1 transgenic mice (SOD1^G93A) was detected long before the development of the disease, and inhibition of cPLA₂α upregulation delayed the disease's onset. The aim of the present study was to determine the mechanism for cPLA₂α upregulation.

METHODS

Immunofluorescence analysis and western blot analysis of misfolded SOD1, cPLA₂α and inflammatory markers were performed in the spinal cord sections of SOD1^G93A transgenic mice and in primary motor neurons. Over expression of mutant SOD1 was performed by induction or transfection in primary motor neurons and in differentiated NSC34 motor neuron like cells.

RESULTS

Misfolded SOD1 was detected in the spinal cord of 3 weeks old mutant SOD1^G93A mice before cPLA₂α upregulation. Elevated expression of both misfolded SOD1 and cPLA₂α was specifically detected in the motor neurons at 6 weeks with a high correlation between them. Elevated TNFα levels were detected in the spinal cord lysates of 6 weeks old mutant SOD1^G93A mice. Elevated TNFα was specifically detected in the motor neurons and its expression was highly correlated with cPLA₂α expression at 6 weeks. Induction of mutant SOD1 in primary motor neurons induced cPLA₂α and TNFα upregulation. Over expression of mutant SOD1 in NSC34 cells caused cPLA₂α upregulation which was prevented by antibodies against TNFα. The addition of TNFα to NSC34 cells caused cPLA₂α upregulation in a dose dependent manner.

CONCLUSIONS

Motor neurons expressing elevated cPLA₂α and TNFα are in an inflammatory state as early as at 6 weeks old mutant SOD1^G93A mice long before the development of the disease. Accumulated misfolded SOD1 in the motor neurons induced cPLA₂α upregulation via induction of TNFα.

Genetic Factors Associated With Pain Severity, Daily Opioid Dose Requirement, and Pain Response Among Advanced Cancer Patients Receiving Supportive Care

BACKGROUND

Current understanding of genetic factors associated with pain severity, and improvement of pain with opioids in advanced cancer patients (AC) is inadequate for delivery of personalized pain therapy (PPT). Therefore, the aim of this study was to determine the genetic factors associated with pain severity, daily opioid dose, and pain response in AC patients receiving supportive care.

METHODS

In this prospective study, AC patients were eligible if they had cancer pain ≥4/10 on Edmonton Symptom Assessment Scale (ESAS) - Pain Item and needed opioid rotation for pain control by specialist at the outpatient supportive care center. Association of genetic factors with pain phenotype was assessed using logistic regression models and SKATO (Gene-block) analysis.

RESULTS

About 174/178 (98%) patient samples were analyzed. After adjustment for demographic and clinical variables, pain severity was negatively associated with intron variant alleles in OPRM1 rs9322446, P = 0.02; rs2270459, P = 0.038; rs62052210, P = 0.038. Opioid daily dose was positively associated NFKBIA rs2233419, P = 0.008; rs2233417, P = 0.007; rs3138054, P = 0.008; rs1050851, P = 0.015; ORPM1 rs9479759, P = 0.046; rs2003185, P = 0.047; rs636433, P = 0.044; COMT (rs9306234, P = 0.014; rs165728, P = 0.014; rs2020917, P = 0.036; rs165728, P = 0.034); ARRB2 (rs1045280, P = 0.045); and pain response to opioids was negatively associated OPRM1 rs1319339, P = 0.024; rs34427887, P = 0.048; and COMT rs4646316, P = 0.03; rs35478083, P = 0.028, respectively. SKATO analysis showed association between pain severity and CXCL8 (P = 0.0056), and STAT6 (P = 0.0297) genes respectively, and pain response with IL-6 (P = 0.00499).

CONCLUSIONS

This study identified that SNPs of OPRM1, COMT, NFKBIA, CXCL8, IL-6, STAT6, and ARRB2 genes were associated with pain severity, opioid daily dose, and pain response in AC receiving supportive care. Additional studies are needed to validate our findings for PPT.

Plasma Lipolysis and Changes in Plasma and Cerebrospinal Fluid Signaling Lipids Reveal Abnormal Lipid Metabolism in Chronic Migraine

Background

Lipids are a primary storage form of energy and the source of inflammatory and pain signaling molecules, yet knowledge of their importance in chronic migraine (CM) pathology is incomplete. We aim to determine if plasma and cerebrospinal fluid (CSF) lipid metabolism are associated with CM pathology.

Methods

We obtained plasma and CSF from healthy controls (CT, n = 10) or CM subjects (n = 15) diagnosed using the International Headache Society criteria. We measured unesterified fatty acid (UFA) and esterified fatty acids (EFAs) using gas chromatography-mass spectrometry. Glycerophospholipids (GP) and sphingolipid (SP) levels were determined using LC-MS/MS, and phospholipase A₂ (PLA₂) activity was determined using fluorescent substrates.

Results

Unesterified fatty acid levels were significantly higher in CM plasma but not in CSF. Unesterified levels of five saturated fatty acids (SAFAs), eight monounsaturated fatty acids (MUFAs), five ω-3 polyunsaturated fatty acids (PUFAs), and five ω-6 PUFAs are higher in CM plasma. Esterified levels of three SAFAs, eight MUFAs, five ω-3 PUFAs, and three ω-6 PUFAs, are higher in CM plasma. The ratios C20:4n-6/homo-γ-C20:3n-6 representative of delta-5-desaturases (D5D) and the elongase ratio are lower in esterified and unesterified CM plasma, respectively. In the CSF, the esterified D5D index is lower in CM. While PLA₂ activity was similar, the plasma UFA to EFA ratio is higher in CM. Of all plasma GP/SPs detected, only ceramide levels are lower (p = 0.0003) in CM (0.26 ± 0.07%) compared to CT (0.48 ± 0.06%). The GP/SP proportion of platelet-activating factor (PAF) is significantly lower in CM CSF.

Conclusions

Plasma and CSF lipid changes are consistent with abnormal lipid metabolism in CM. Since plasma UFAs correspond to diet or adipose tissue levels, higher plasma fatty acids and UFA/EFA ratios suggest enhanced adipose lipolysis in CM. Differences in plasma and CSF desaturases and elongases suggest altered lipid metabolism in CM. A lower plasma ceramide level suggests reduced de novo synthesis or reduced sphingomyelin hydrolysis. Changes in CSF PAF suggest differences in brain lipid signaling pathways in CM. Together, this pilot study shows lipid metabolic abnormality in CM corresponding to altered energy homeostasis. We propose that controlling plasma lipolysis, desaturases, elongases, and lipid signaling pathways may relieve CM symptoms.

Calcium-independent phospholipase A2 inhibitor produces an analgesic effect in a rat model of neuropathic pain by reducing central sensitization in the dorsal horn

OBJECTIVE

Phospholipase A2 (PLA2) plays an important role in regulating the production of arachidonic acid and various eicosanoids. The aim of our study was to investigate the analgesic mechanisms of calcium-dependent cytosolic phospholipase A2 and calcium-independent PLA2 (iPLA2) inhibitors in the spinal cord in a rat model of neuropathic pain.

METHODS

Lumbar 5 spinal nerve ligation was performed in male Sprague-Dawley rats to develop a peripheral neuropathic pain model. Paw withdrawal thresholds in response to von Frey filaments, brush, pressure, and pinch were measured. Lumbar wide dynamic range neuronal firing rates and iPLA2 subtype expression were measured by in vivo extracellular recording and double immunofluorescence staining, respectively.

RESULTS

In our rat models, oral administration of prednisolone, a non-selective PLA2 inhibitor, and intrathecal injection of bromoenolactone, a iPLA2 inhibitor, significantly increased the ipsilateral hindpaw withdrawal thresholds in response to von Frey filament stimulation, but intrathecal injection of arachidonyl trifluoromethyl ketone, a selective cytosolic PLA2 inhibitor, did not show significant changes. In spinal dorsal horn neurons, bromoenolactone reduced neuronal firing rates in response to withdrawal stimulation and spontaneous firing rates in the ipsilateral side of the spinal dorsal horn. In addition, the expression of iPLA2 was co-localized with astrocytes and neurons on the ipsilateral side of the dorsal horn in rats that underwent spinal nerve ligation.

DISCUSSION

These data suggest that selective iPLA2 inhibitor produce analgesia in neuropathic rats by reducing central sensitization in the dorsal horn.

Long-lasting analgesia via targeted in situ repression of NaV1.7 in mice

Current treatments for chronic pain rely largely on opioids despite their substantial side effects and risk of addiction. Genetic studies have identified in humans key targets pivotal to nociceptive processing. In particular, a hereditary loss-of-function mutation in NaV1.7, a sodium channel protein associated with signaling in nociceptive sensory afferents, leads to insensitivity to pain without other neurodevelopmental alterations. However, the high sequence and structural similarity between NaV subtypes has frustrated efforts to develop selective inhibitors. Here, we investigated targeted epigenetic repression of NaV1.7 in primary afferents via epigenome engineering approaches based on clustered regularly interspaced short palindromic repeats (CRISPR)-dCas9 and zinc finger proteins at the spinal level as a potential treatment for chronic pain. Toward this end, we first optimized the efficiency of NaV1.7 repression in vitro in Neuro2A cells and then, by the lumbar intrathecal route, delivered both epigenome engineering platforms via adeno-associated viruses (AAVs) to assess their effects in three mouse models of pain: carrageenan-induced inflammatory pain, paclitaxel-induced neuropathic pain, and BzATP-induced pain. Our results show effective repression of NaV1.7 in lumbar dorsal root ganglia, reduced thermal hyperalgesia in the inflammatory state, decreased tactile allodynia in the neuropathic state, and no changes in normal motor function in mice. We anticipate that this long-lasting analgesia via targeted in vivo epigenetic repression of NaV1.7 methodology we dub pain LATER, might have therapeutic potential in management of persistent pain states.

Changes in transcriptome profiling during the acute/subacute phases of contusional spinal cord injury in rats

Background

Spinal cord injuries (SCIs), along with subsequent secondary injuries, often result in irreversible damage to both sensory and motor functions. However, a thorough view of the underlying pathological mechanisms of SCIs, especially in a temporal-spatial manner, is still lacking.

Methods

To obtain a comprehensive, real-time view of multiple subsets of the cellular mechanisms involved in SCIs, we applied RNA-sequencing technology to characterize the temporal changes in gene expression around the lesion site of contusion SCI in rats. First, we identified the differentially expressed genes (DEGs) in contrast to sham controls at 1, 4, and 7 days post SCI. Through bioinformatics analysis, including Pathway analysis, Gene-act-net, and Pathway-act-net, we screened and verified potential key pathways and genes associated with either the acute or subacute stages of SCI pathology.

Results

The top three overrepresented pathways were associated with cytokine-cytokine receptor interaction, TNF signaling pathway, and cell cycle at day 1; lysosome, cytokine-cytokine receptor interaction, phagosome at day 4; and phagosome, lysosome, cytokine-cytokine receptor interaction at day 7 post injury. Further, we identified uniquely enriched genes at each time point, such as Ccr1 and Nos2 at day 1; as well as Mgst2, and Pla2g3 at 4 and 7 days post-injury.

Conclusions

Our pathway analysis suggested a transition from inflammatory responses to multiple forms of cell death processes from the acute to subacute stages of SCI. Further, our results revealed a continuous transformation from a more inflammatory to an apoptotic/self-repairing transcriptome following the time-course of SCIs. Our research provides novel insights into the molecular mechanisms of SCI pathophysiology and identifies potential targets for therapeutic intervention after SCI.

Oxidized Lipids in Persistent Pain States

Chemotherapy, nerve injuries, or diseases like multiple sclerosis can cause pathophysiological processes of persistent and neuropathic pain. Thereby, the activation threshold of ion channels is reduced in peripheral sensory neurons to normally noxious stimuli like heat, cold, acid, or mechanical due to sensitization processes. This leads to enhanced neuronal activity, which can result in mechanical allodynia, cold allodynia, thermal hyperalgesia, spontaneous pain, and may initiate persistent and neuropathic pain. The treatment options for persistent and neuropathic pain patients are limited; for about 50% of them, current medication is not efficient due to severe side effects or low response to the treatment. Therefore, it is of special interest to find additional treatment strategies. One approach is the control of neuronal sensitization processes. Herein, signaling lipids are crucial mediators and play an important role during the onset and maintenance of pain. As preclinical studies demonstrate, lipids may act as endogenous ligands or may sensitize transient receptor potential (TRP)-channels. Likewise, they can cause enhanced activity of sensory neurons by mechanisms involving G-protein coupled receptors and activation of intracellular protein kinases. In this regard, oxidized metabolites of the essential fatty acid linoleic acid, 9- and 13-hydroxyoctadecadienoic acid (HODE), their dihydroxy-metabolites (DiHOMEs), as well as epoxides of linoleic acid (EpOMEs) and of arachidonic acid (EETs), as well as lysophospholipids, sphingolipids, and specialized pro-resolving mediators (SPMs) have been reported to play distinct roles in pain transmission or inhibition. Here, we discuss the underlying molecular mechanisms of the oxidized linoleic acid metabolites and eicosanoids. Furthermore, we critically evaluate their role as potential targets for the development of novel analgesics and for the treatment of persistent or neuropathic pain.

Electroacupuncture for pain relief in labour inhibits spinal p38 MAPK-mediated prostaglandin E2 release and uterine prostaglandin E2 receptor expression in rats

BACKGROUND

p38 mitogen-activated protein kinase (p38 MAPK) activation involves the release of prostaglandin E2 (PGE2) and hyperalgesia. We have previously reported that electroacupuncture (EA) relieves labour pain, but the potential mechanisms remain unclear.

OBJECTIVE

To observe the effects of EA on labour pain intensity, serum PGE2 levels and the p38 MAPK signalling pathway in rats during labour.

METHODS

Female rats copulated with male rats to induce pregnancy, and then received castor oil to trigger labour. During labour, rats remained untreated (Control group, n=30) or were treated with remifentanil (n=30) or EA at Jiaji (n=30) or SP6+LI4 (n=30), respectively. The warm water tail-flick test was used to assess labour pain. Serum PGE2 levels were measured by ELISA. Protein expression of prostaglandin E2 receptor (PGER2), p38 MAPK and phospholipase A2 (PLA2) were analysed by Western blotting, and mRNA levels were measured by real-time PCR.

RESULTS

EA treatment at Jiaji or SP6+LI4 significantly relieved labour pain, decreased serum PGE2 levels and inhibited protein and gene expression of PGER2 in the myometrium. Moreover, EA reduced protein expression of PLA2 and p38 MAPK, and inhibited phosphorylation of p38 MAPK in the lumbar spinal cord but not in the cerebral grey matter. Additionally, EA markedly decreased mRNA levels of p38 MAPK in the lumbar spinal cord and significantly reduced PLA2-IV mRNA levels in both the lumbar spinal cord and cerebral grey matter.

CONCLUSIONS

This study indicates that EA relieves labour pain through, at least in part, inhibition of spinal p38 MAPK-mediated PGE2 release and uterine PGER2 expression in rats.

Secreted Phospholipases A₂ from Animal Venoms in Pain and Analgesia

Animal venoms comprise a complex mixture of components that affect several biological systems. Based on the high selectivity for their molecular targets, these components are also a rich source of potential therapeutic agents. Among the main components of animal venoms are the secreted phospholipases A₂ (sPLA₂s). These PLA₂ belong to distinct PLA₂s groups. For example, snake venom sPLA₂s from Elapidae and Viperidae families, the most important families when considering envenomation, belong, respectively, to the IA and IIA/IIB groups, whereas bee venom PLA₂ belongs to group III of sPLA₂s. It is well known that PLA₂, due to its hydrolytic activity on phospholipids, takes part in many pathophysiological processes, including inflammation and pain. Therefore, secreted PLA₂s obtained from animal venoms have been widely used as tools to (a) modulate inflammation and pain, uncovering molecular targets that are implicated in the control of inflammatory (including painful) and neurodegenerative diseases; (b) shed light on the pathophysiology of inflammation and pain observed in human envenomation by poisonous animals; and, (c) characterize molecular mechanisms involved in inflammatory diseases. The present review summarizes the knowledge on the nociceptive and antinociceptive actions of sPLA₂s from animal venoms, particularly snake venoms.

Articular inflammation induced by an enzymatically-inactive Lys49 phospholipase A2: activation of endogenous phospholipases contributes to the pronociceptive effect

BACKGROUND

Arthritis is a set of inflammatory conditions that induce aching, stiffness, swelling, pain and may cause functional disability with severe consequences to the patient's lives. These are multi-mediated pathologies that cannot be effectively protected and/or treated. Therefore, the aim of this study was to establish a new model of acute arthritis, using a Lys49-PLA₂ (Bothrops asper myotoxin II; MT-II) to induce articular inflammation.

METHODS

The articular inflammation was induced by MT-II (10 μg/joint) injection into the left tibio-tarsal or femoral-tibial-patellar joints. Cellular influx was evaluated counting total and differential cells that migrated to the joint. The plasma extravasation was determined using Evans blue dye. The edematogenic response was evaluated measuring the joint thickness using a caliper. The articular hypernociception was determined by a dorsal flexion of the tibio-tarsal joint using an electronic pressure-meter test. The mediators involved in the articular hypernociception were evaluated using receptor antagonists and enzymatic inhibitors.

RESULTS

Plasma extravasation in the knee joints was observed 5 and 15 min after MT-II (10 μg/joint) injection. MT-II also induced a polymorphonuclear cell influx into the femoral-tibial-patellar joints observed 8 h after its injection, a period that coincided with the peak of the hyperalgesic effect. Hyperalgesia was inhibited by the pretreatment of the animals with cyclooxygenase inhibitor indomethacin, with type-2 cyclooxygenase inhibitor celecoxib, with AACOCF₃ and PACOCF_3, inhibitors of cytosolic and Ca²⁺-independent PLA₂s, respectively, with bradykinin B₂ receptor antagonist HOE 140, with antibodies against TNFα, IL-1β, IL-6 and CINC-1 and with selective ET-A (BQ-123) and ET-B (BQ-788) endothelin receptors antagonists. The MT-II-induced hyperalgesia was not altered by the lipoxygenase inhibitor zileuton, by the bradykinin B₁ receptor antagonist Lys-(Des-Arg9,Leu8)-bradykinin, by the histamine and serotonin antagonists promethazine and methysergide, respectively, by the nitric oxide inhibitor LNMMA and by the inhibitor of matrix 1-, 2-, 3-, 8- and 9- metalloproteinases GM6001 (Ilomastat).

CONCLUSION

These results demonstrated the multi-mediated characteristic of the articular inflammation induced by MT-II, which demonstrates its relevance as a model for arthritis mechanisms and treatment evaluation.

Role of prefrontal cortical calcium-independent phospholipase A2 in antinociceptive effect of the norepinephrine reuptake inhibitor antidepresssant maprotiline

The prefrontal cortex is essential for executive functions such as decision-making and planning. There is also accumulating evidence that it is important for the modulation of pain. In this study, we investigated a possible role of prefrontal cortical calcium-independent phospholipase A₂ (iPLA₂) in antinociception induced by the norepinephrine reuptake inhibitor (NRI) and tetracyclic (tricyclic) antidepressant, maprotiline. Intraperitoneal injections of maprotiline increased iPLA₂ mRNA and protein expression in the prefrontal cortex. This treatment also reduced grooming responses to von-Frey hair stimulation of the face after facial carrageenan injection, indicating decreased sensitivity to pain. The antinociceptive effect of maprotiline was abrogated by iPLA₂ antisense oligonucleotide injection to the prefrontal cortex, indicating a role of this enzyme in antinociception. In contrast, injection of iPLA₂ antisense oligonucleotide to the somatosensory cortex did not reduce the antinociceptive effect of maprotiline. Lipidomic analysis of the prefrontal cortex showed decrease in phosphatidylcholine species, but increase in lysophosphatidylcholine species, indicating increased PLA2 activity, and release of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) after maprotiline treatment. Differences in sphingomyelin/ceramide were also detected. These changes were not observed in maprotiline-treated mice that received iPLA₂ antisense oligonucleotide to the prefrontal cortex. Metabolites of DHA and EPA may help to strengthen a known supraspinal antinociceptive pathway from the prefrontal cortex to the periaqueductal gray. Together, results indicate a role of prefrontal cortical iPLA₂ and its enzymatic products in the antinociceptive effect of maprotiline.

Liberating Chiral Lipid Mediators, Inflammatory Enzymes, and LIPID MAPS from Biological Grease

In 1970, it was well accepted that the central role of lipids was in energy storage and metabolism, and it was assumed that amphipathic lipids simply served a passive structural role as the backbone of biological membranes. As a result, the scientific community was focused on nucleic acids, proteins, and carbohydrates as information-containing molecules. It took considerable effort until scientists accepted that lipids also "encode" specific and unique biological information and play a central role in cell signaling. Along with this realization came the recognition that the enzymes that act on lipid substrates residing in or on membranes and micelles must also have important signaling roles, spurring curiosity into their potentially unique modes of action differing from those acting on water-soluble substrates. This led to the creation of the concept of "surface dilution kinetics" for describing the mechanism of enzymes acting on lipid substrates, as well as the demonstration that lipid enzymes such as phospholipase A₂ (PLA₂) contain allosteric activator sites for specific phospholipids as well as for membranes. As our understanding of phospholipases advanced, so did the understanding that many of the lipids released by these enzymes are chiral information-containing signaling molecules; for example, PLA₂ regulates the generation of precursors for the biosynthesis of eicosanoids and other bioactive lipid mediators of inflammation and resolution underlying disease progression. The creation of the LIPID MAPS initiative in 2003 and the ensuing development of the lipidomics field have revealed that lipid metabolites are central to human metabolism. Today lipids are recognized as key mediators of health and disease as we enter a new era of biomarkers and personalized medicine. This article is my personal "reflection" on these scientific advances.

Phospholipase A₂-Generated Lipid Mediators in the Brain: The Good, the Bad, and the Ugly

Phospholipase A2 (PLA2) generates arachidonic acid, docosahexaenoic acid, and lysophospholipids from neural membrane phospholipids. These metabolites have a variety of physiological effects by themselves and also are substrates for the synthesis of more potent lipid mediators such as eicosanoids, platelet activating factor, and 4-hydroxynonenal (4-HNE). At low concentrations, these mediators act as second messengers. They affect and modulate several cell functions, including signal transduction, gene expression, and cell proliferation, but at high concentrations, these lipid mediators cause neurotoxicity. Among the metabolites generated by PLA2, 4-HNE is the most cytotoxic metabolite and is associated with the apoptotic type of neural cell death. Levels of 4-HNE are markedly increased in neurological disorders such as Alzheimer disease, Parkinson disease, ischemia, spinal cord trauma, and head injury. The purpose of this review is to summarize and integrate the vast literature on metabolites generated by PLA2 for a wider audience. The authors hope that this discussion will jump-start more studies not only on the involvement of PLA2 in neurological disorders but also on the importance of PLA2-generated lipid mediators in physiological and pathological processes.

Reduction of cytosolic phospholipase A2α upregulation delays the onset of symptoms in SOD1G93A mouse model of amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal multifactorial neurodegenerative disease characterized by selective death of motor neurons in the cortex, brainstem, and spinal cord. Cytosolic phospholipase A2 alpha (cPLA2α) upregulation and activation in the spinal cord of patients with sporadic ALS and in the spinal cord of human mutant SOD1G93A (hmSOD1) transgenic mice were recently reported.

METHODS

cPLA2α upregulation in the brainstem and spinal cord was reduced by brain infusion of a specific antisense oligonucleotide against cPLA2α (AS), and the effect was evaluated on disease progression and brain cell activation.

RESULTS

We found that the elevation of cPLA2α protein expression in the spinal cord was first detected at 6-week-old hmSOD1 mice and remained elevated during their whole life span. Reduction of the elevated expression of cPLA2α in the spinal cord of hmSOD1 mice by brain infusion of an AS at week 15 (shortly before the appearance of the disease symptoms), for a duration of 6 weeks, delayed the loss of motor neuron function in comparison with hmSOD1 mice and with sense brain-infused hmSOD1 mice. To characterize the effect of cPLA2α upregulation on different processes taking place at the appearance of the disease symptoms, mice were brain infused with AS or with sense at week 15 for 3-4 weeks. The AS treatment that reduced cPLA2α upregulation in the spinal cord of AS-treated hmSOD1 mice (as analyzed at week 18-19) prevented the reduction in the number of the neurons (detected by NeuN) and inhibited astrocyte activation (detected by GFAP) and microglia activation (detected by Iba-1 and by CD40). In addition, AS treatment blunted the upregulation of the proinflammatory enzyme-inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) detected in hmSOD1 mice.

CONCLUSIONS

Since specific reduction of cPLA2α in the brainstem and spinal cord significantly attenuated the development of the disease, cPLA2α may offer an efficient target for treatment of ALS.

Persistent Nociception Triggered by Nerve Growth Factor (NGF) Is Mediated by TRPV1 and Oxidative Mechanisms

Nerve growth factor (NGF) is elevated in certain chronic pain conditions and is a sufficient stimulus to cause lasting pain in humans, but the actual mechanisms underlying the persistent effects of NGF remain incompletely understood. We developed a rat model of NGF-induced persistent thermal hyperalgesia and mechanical allodynia to determine the role of transient receptor potential vanilloid 1 (TRPV1) and oxidative mechanisms in the persistent effects of NGF. Persistent thermal hypersensitivity and mechanical allodynia require de novo protein translation and are mediated by TRPV1 and oxidative mechanisms. By comparing effects after systemic (subcutaneous), spinal (intrathecal) or hindpaw (intraplantar) injections of test compounds, we determined that TRPV1 and oxidation mediate persistent thermal hypersensitivity via peripheral and spinal sites of action and mechanical allodynia via only a spinal site of action. Therefore, NGF-evoked thermal and mechanical allodynia are mediated by spatially distinct mechanisms. NGF treatment evoked sustained increases in peripheral and central TRPV1 activity, as demonstrated by increased capsaicin-evoked nocifensive responses, increased calcitonin gene-related peptide release from hindpaw skin biopsies, and increased capsaicin-evoked inward current and membrane expression of TRPV1 protein in dorsal root ganglia neurons. Finally, we showed that NGF treatment increased concentrations of linoleic and arachidonic-acid-derived oxidized TRPV1 agonists in spinal cord and skin biopsies. Furthermore, increases in oxidized TRPV1-active lipids were reduced by peripheral and spinal injections of compounds that completely blocked persistent nociception. Collectively, these data indicate that NGF evokes a persistent nociceptive state mediated by increased TRPV1 activity and oxidative mechanisms, including increased production of oxidized lipid TRPV1 agonists.

Synthetic and natural inhibitors of phospholipases A2: their importance for understanding and treatment of neurological disorders

Phospholipases A2 (PLA2) are a diverse group of enzymes that hydrolyze membrane phospholipids into arachidonic acid and lysophospholipids. Arachidonic acid is metabolized to eicosanoids (prostaglandins, leukotrienes, thromboxanes), and lysophospholipids are converted to platelet-activating factors. These lipid mediators play critical roles in the initiation, maintenance, and modulation of neuroinflammation and oxidative stress. Neurological disorders including excitotoxicity; traumatic nerve and brain injury; cerebral ischemia; Alzheimer's disease; Parkinson's disease; multiple sclerosis; experimental allergic encephalitis; pain; depression; bipolar disorder; schizophrenia; and autism are characterized by oxidative stress, inflammatory reactions, alterations in phospholipid metabolism, accumulation of lipid peroxides, and increased activities of brain phospholipase A2 isoforms. Several old and new synthetic inhibitors of PLA2, including fatty acid trifluoromethyl ketones; methyl arachidonyl fluorophosphonate; bromoenol lactone; indole-based inhibitors; pyrrolidine-based inhibitors; amide inhibitors, 2-oxoamides; 1,3-disubstituted propan-2-ones and polyfluoroalkyl ketones as well as phytochemical based PLA2 inhibitors including curcumin, Ginkgo biloba and Centella asiatica extracts have been discovered and used for the treatment of neurological disorders in cell culture and animal model systems. The purpose of this review is to summarize information on selective and potent synthetic inhibitors of PLA2 as well as several PLA2 inhibitors from plants, for treatment of oxidative stress and neuroinflammation associated with the pathogenesis of neurological disorders.

Oral administration of cytosolic PLA2 inhibitor arachidonyl trifluoromethyl ketone ameliorates cauda equina compression injury in rats

BACKGROUND

Phospholipase A2 (PLA2)-derived proinflammatory lipid mediators such as prostaglandin E2 (PGE2), leukotrienes B4 (LTB4), lysophosphatidylcholine (LPC), and free fatty acids (FFA) are implicated in spinal cord injury (SCI) pathologies. Reducing the levels of these injurious bioactive lipid mediators is reported to ameliorate SCI. However, the specific role of the group IVA isoform of PLA2 cytosolic PLA2 (cPLA2) in lumbar spinal canal stenosis (LSS) due to cauda equina compression (CEC) injury is not clear. In this study, we investigated the role of cPLA2 in a rat model of CEC using a non-toxic cPLA2-preferential inhibitor, arachidonyl trifluoromethyl ketone (ATK).

METHODS

LSS was induced in adult female rats by CEC procedure using silicone blocks within the epidural spaces of L4 to L6 vertebrae. cPLA2 inhibitor ATK (7.5 mg/kg) was administered by oral gavage at 2 h following the CEC. cPLA2-derived injurious lipid mediators and the expression/activity of cPLA2, 5-lipoxygenase (5-LOX), and cyclooxygenase-2 (COX-2) were assessed. ATK-treated (CEC + ATK) were compared with vehicle-treated (CEC + VEH) animals in terms of myelin levels, pain threshold, and motor function.

RESULTS

ATK treatment of CEC animals reduced the phosphorylation of cPLA2 (pcPLA2) determined by Western blot, improved locomotor function evaluated by rotarod task, and reduced pain threshold evaluated by mechanical hyperalgesia method. Levels of FFA and LPC, along with PGE2 and LTB4, were reduced in CEC + ATK compared with CEC + VEH group. However, ATK treatment reduced neither the activity/expression of 5-LOX nor the expression of COX-2 in CEC + VEH animals. Increased cPLA2 activity in the spinal cord from CEC + VEH animals correlated well with decreased spinal cord as well as cauda equina fiber myelin levels, which were restored after ATK treatment.

CONCLUSION

The data indicate that cPLA2 activity plays a significant role in tissue injury and pain after LSS. Reducing the levels of proinflammatory and tissue damaging eicosanoids and the deleterious lipid mediator LPC shows therapeutic potential. ATK inhibits cPLA2 activity, thereby decreasing the levels of injurious lipid mediators, reducing pain, improving functional deficits, and conferring protection against LSS injury. Thus, it shows potential for preclinical evaluation in LSS.

Bromoenol Lactone, an Inhibitor of Calcium-Independent Phospholipase A2, Suppresses Carrageenan-Induced Prostaglandin Production and Hyperalgesia in Rat Hind Paw

Prostaglandin (PG) E₂ and PGI₂ are essential to hyperalgesia in inflammatory tissues. These prostaglandins are produced from arachidonic acid, which is cleaved from membrane phospholipids by the action of phospholipase A₂ (PLA₂). Which isozyme of PLA₂ is responsible for the cleavage of arachidonic acid and the production of prostaglandins essential to inflammation-induced hyperalgesia is not clear. In this study, we examined the effects of two PLA₂ isozyme-specific inhibitors on carrageenan-induced production of PGE₂ and PGI₂ in rat hind paw and behavioral nociceptive response to radiant heat. Local administration of bromoenol lactone (BEL), an inhibitor of calcium-independent PLA₂ (iPLA₂), significantly reduced carrageenan-induced elevation of prostaglandins in the inflamed foot pad 3 h after injection. It also ameliorated the hyperalgesic response between 1 h and 3 h after carrageenan injection. On the other hand, AACOCF₃, an inhibitor of cytosolic PLA₂, suppressed neither prostaglandin production nor the hyperalgesic response. BEL did not suppress the mRNA levels of iPLA₂β, iPLA₂γ, cyclooxygenase-2, microsomal prostaglandin E synthase, prostaglandin I synthase, or proinflammatory cytokines in the inflamed foot pad, indicating that BEL did not suppress inflammation itself. These results suggest that iPLA₂ is involved in the production of prostaglandins and hyperalgesia at the inflammatory loci.

Selective activation of microglia facilitates synaptic strength

Synaptic plasticity is thought to be initiated by neurons only, with the prevailing view assigning glial cells mere specify supportive functions for synaptic transmission and plasticity. We now demonstrate that glial cells can control synaptic strength independent of neuronal activity. Here we show that selective activation of microglia in the rat is sufficient to rapidly facilitate synaptic strength between primary afferent C-fibers and lamina I neurons, the first synaptic relay in the nociceptive pathway. Specifically, the activation of the CX3CR1 receptor by fractalkine induces the release of interleukin-1β from microglia, which modulates NMDA signaling in postsynaptic neurons, leading to the release of an eicosanoid messenger, which ultimately enhances presynaptic neurotransmitter release. In contrast to the conventional view, this form of plasticity does not require enhanced neuronal activity to trigger the events leading to synaptic facilitation. Augmentation of synaptic strength in nociceptive pathways represents a cellular model of pain amplification. The present data thus suggest that, under chronic pain states, CX3CR1-mediated activation of microglia drives the facilitation of excitatory synaptic transmission in the dorsal horn, which contributes to pain hypersensitivity in chronic pain states.

Epidural dexamethasone decreased inflammatory hyperalgesia and spinal cPLA₂ expression in a rat formalin test

PURPOSE

The aim of this study was to investigate the effect of epidural dexamethasone on analgesia and cytosolic phospholipase A₂ (cPLA₂) expression in the spinal cord in a rat formalin test.

MATERIALS AND METHODS

Epidural dexamethasone injection was performed to Sprague-Dawley rats with a 25 gauge needle under fluoroscopy. Following the epidural injection, a formalin induced pain behavior test was performed. Next, the spinal cords corresponding to L4 dorsal root ganglion was extracted to observe the cPLA₂ expression.

RESULTS

There were no differences in pain response during phase I among the groups. The phase II pain response in 300 μg of epidural dexamethasone group decreased as compared to control, 30 μg of epidural dexamethasone, 100 μg of epidural dexamethasone, and 300 μg of systemic dexamethasone groups. The expression of cPLA₂ decreased in Rexed laminae I-II in 300 μg of the epidural dexamethasone group compared with the ones in the control group.

CONCLUSION

Taken together, these results suggest that 300 μg of epidural dexamethasone has an attenuating effect on the peripheral inflammatory tissue injury induced hyperalgesia and this effect is mediated through the inhibition of intraspinal cPLA₂ expression and the primary site of action is the laminae I-II of the spinal cord.

Bisgma stimulates prostaglandin E2 production in macrophages via cyclooxygenase-2, cytosolic phospholipase A2, and mitogen-activated protein kinases family

BACKGROUND

Bisphenol A-glycidyl-methacrylate (BisGMA) employs as a monomer in dental resins. The leakage of BisGMA from composite resins into the peripheral environment can result in inflammation via macrophage activation. Prostaglandin E2 (PGE2) is a key regulator of immunopathology in inflammatory reactions. Little is known about the mechanisms of BisGMA-induced PGE2 expression in macrophage. The aim of this study was to evaluate the signal transduction pathways of BisGMA-induced PGE2 production in murine RAW264.7 macrophages.

METHODOLOGY/PRINCIPAL FINDINGS

Herein, we demonstrate that BisGMA can exhibit cytotoxicity to RAW264.7 macrophages in a dose- and time-dependent manner (p<0.05). In addition, PGE2 production, COX-2 expression, and cPLA2 phosphorylation were induced by BisGMA on RAW264.7 macrophages in a dose- and time-dependent manner (p<0.05). Moreover, BisGMA could induce the phosphorylation of ERK1/2 pathway (MEK1/2, ERK1/2, and Elk), p38 pathway (MEK3/6, p38, and MAPKAPK2), and JNK pathway (MEK4, JNK, and c-Jun) in a dose- and time-dependent manner (p<0.05). Pretreatment with AACOCF3, U0126, SB203580, and SP600125 significantly diminished the phosphorylation of cPLA2, ERK1/2, p38, and JNK stimulated by BisGMA, respectively (p<0.05). BisGMA-induced cytotoxicity, cPLA2 phosphorylation, PGE2 generation, and caspases activation were reduced by AACOCF3, U0126, SB203580, and SP600125, respectively (p<0.05).

CONCLUSIONS

These results suggest that BisGMA induced-PGE2 production may be via COX-2 expression, cPLA2 phosphorylation, and the phosphorylation of MAPK family. Cytotoxicity mediated by BisGMA may be due to caspases activation through the phosphorylation of cPLA2 and MAPKs family.

Gene-centric association study of acute chest syndrome and painful crisis in sickle cell disease patients

Patients with sickle cell disease (SCD) present with a wide range of clinical complications. Understanding this clinical heterogeneity offers the prospects to tailor the right treatments to the right patients and also guide the development of novel therapies. Several environmental (eg, nutrition) and nonenvironmental (eg, fetal hemoglobin levels, α-thalassemia status) factors are known to modify SCD severity. To find new genetic modifiers of SCD severity, we performed a gene-centric association study in 1514 African American participants from the Cooperative Study of Sickle Cell Disease (CSSCD) for acute chest syndrome (ACS) and painful crisis. From the initial results, we selected 36 single nucleotide polymorphism (SNPs) and genotyped them for replication in 387 independent patients from the CSSCD, 318 SCD patients recruited at Georgia Health Sciences University, and 449 patients from the Duke SCD cohort. In the combined analysis, an association between ACS and rs6141803 reached array-wide significance (P = 4.1 × 10(-7)). This SNP is located 8.2 kilobases upstream of COMMD7, a gene highly expressed in the lung that interacts with nuclear factor-κB signaling. Our results provide new leads to gaining a better understanding of clinical variability in SCD, a "simple" monogenic disease.

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.

Phospholipase A₂ activity in first episode schizophrenia: associations with symptom severity and outcome at week 12

OBJECTIVES

Intracellular phospholipases A₂ (inPLA₂) are activated during monoaminergic neurotranismision and act as key enzymes in cell membrane repair and remodelling, neuroplasticity, neurodevelopment, apoptosis, synaptic pruning, neurodegenerative processes and neuroinflammation. Several independent studies found increased inPLA₂ activity in drug-naïve first episode and chronic schizophrenia. This study investigates if inPLA₂ activity is associated with symptoms severity and treatment response in first episode schizophrenia (FES).

METHODS

InPLA₂ activity was measured in serum of 35 young FES patients (mean age: 19.36 ± 3.32, mean duration of illness: 7.53 ± 6.28 months, 16 neuroleptic-naïve) before and after 12 weeks of treatment with second-generation antipsychotic medications (olanzapine, quetiapine or risperidone), as well as in 22 healthy controls matched for age. Psychopathology and social functioning were assessed at the same time points.

RESULTS

Baseline inPLA₂ activity was significantly increased in drug-naïve and treated FES patients compared to healthy controls. Baseline inPLA₂ activity was also associated with severity of negative symptoms and lower functioning at baseline. Furthermore, baseline inPLA₂ activity was associated with improvement in negative symptoms and functioning within the first 12 weeks of treatment.

CONCLUSIONS

Intracellular PLA₂ activity is increased in first episode schizophrenia and associated with symptom severity and outcome after 12 weeks of treatment. Future studies should investigate the implications of inPLA₂ activity as a potential predictor of treatment response for different antipsychotic agents.

A brief comparison of the pathophysiology of inflammatory versus neuropathic pain

PURPOSE OF REVIEW

The causes of inflammatory pain and neuropathic pain are fundamentally different. There are, however, common mechanisms underlying the generation of each pain state. We will discuss some specific elements observed in both tissue and nerve injury pain states and consider the hypothesis that these two states actually demonstrate a convergence over time.

RECENT FINDINGS

The increased pain sensation following tissue and nerve injury results from several mechanisms, including altered ion channel expression in dorsal root ganglion neurons, enhanced dorsal horn glutamate release from primary afferents, enhanced glutamate receptor function in second-order neurons, disinhibition in the dorsal horn and glia cell activation. The role of specific subtypes of receptors, ion channels and glutamate transporters is revealed at peripheral and central sites. Importantly over time, a number of changes, in the dorsal root ganglion and in dorsal horn observed after tissue injury resemble changes observed after nerve injury.

SUMMARY

Recognition of mechanisms common to both inflammatory pain and neuropathic pain might shed light on the understanding of the transition from acute pain to persistent pain.

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.

A phospholipase A₂ from Bothrops asper snake venom activates neutrophils in culture: expression of cyclooxygenase-2 and PGE₂ biosynthesis

In this study, the production of prostaglandin E₂ (PGE₂) and up-regulation in cyclooxygenase (COX) pathway induced by a phospholipase A₂ (PLA₂), myotoxin-III (MT-III), purified from Bothrops asper snake venom, in isolated neutrophils were investigated. The arachidonic acid (AA) production and the participation of intracellular PLA₂s (cytosolic PLA₂ and Ca(2+)-independent PLA₂) in these events were also evaluated. MT-III induced COX-2, but not COX-1 gene and protein expression in neutrophils and increased PGE₂ levels. Pretreatment of neutrophils with COX-2 and COX-1 inhibitors reduced PGE₂ production induced by MT-III. Arachidonyl trifluoromethyl ketone (AACOCF₃), an intracellular PLA₂ inhibitor, but not bromoenol lactone (BEL), an iPLA₂ inhibitor, suppressed the MT-III-induced AA and PGE₂ release. In conclusion, MT-III directly stimulates neutrophils inducing COX-2 mRNA and protein expression followed by production of PGE₂. COX-2 isoform is preeminent over COX-1 for production of PGE₂ stimulated by MT-III. PGE₂ and AA release by MT-III probably is related to cPLA₂ activation.

Microglial activation mediates de novo lysophosphatidic acid production in a model of neuropathic pain

We recently demonstrated that de novo lysophosphatidic acid (LPA) production in the spinal cord occurs in the early phase after nerve injury or LPA injection, and underlies the peripheral mechanisms of neuropathic pain. In this study, we examined the possible involvement of spinal cord microglia in such LPA-mediated functions. Intrathecal LPA injection rapidly increased the gene expression of CD11b and protein expression of phosphor-p38, accompanied by a morphological change of microglia from a ramified to amoeboid shape. Although early treatment with minocycline significantly inhibited LPA-induced neuropathic pain-like behavior and microglial activation, late treatment did not. Early treatment with minocycline also blocked LPA-evoked de novo LPA production and the increased activation of cytosolic phospholipase A(2), an LPA synthesis-related enzyme. Similar results were observed when the sciatic nerve was partially injured: early, but not late, treatment with minocycline significantly inhibited the injury-induced neuropathic pain, microglial activation, de novo LPA production and the underlying increased activation of cytosolic phospholipase A(2) as well as calcium-independent phospholipase A(2), another LPA synthesis-related enzyme. These findings suggest that the early phase of microglial activation is involved in de novo LPA production, and that this underlies the initial mechanisms of nerve injury-induced neuropathic pain.

P2X4 receptors mediate PGE2 release by tissue-resident macrophages and initiate inflammatory pain

Prostaglandin E2 (PGE2) is a key mediator of inflammation and contributes to pain hypersensitivity by promoting sensory neurons hyperexcitability. PGE2 synthesis results from activation of a multi-step enzymatic cascade that includes cyclooxygenases (COXs), the main targets of non-steroidal anti-inflammatory drugs (NSAIDs). Although NSAIDs are widely prescribed to reduce inflammatory symptoms such as swelling and pain, associated harmful side effects restrict their long-term use. Therefore, finding new drugs that limit PG production represents an important therapeutic issue. In response to peripheral inflammatory challenges, mice lacking the ATP-gated P2X4 channel (P2X4R) do not develop pain hypersensitivity and show a complete absence of inflammatory PGE2 in tissue exudates. In resting conditions, tissue-resident macrophages constitutively express P2X4R. Stimulating P2X4R in macrophages triggers calcium influx and p38 MAPK phosphorylation, resulting in cytosolic PLA2 (cPLA2) activation and COX-dependent release of PGE2. In naive animals, pain hypersensitivity was elicited by transfer into the paw of ATP-primed macrophages from wild type, but not P2X4R-deficient mice. Thus, P2X4Rs are specifically involved in inflammatory-mediated PGE2 production and might therefore represent useful therapeutic targets.

Phospholipase A2 and its molecular mechanism after spinal cord injury

Phospholipases A(2) (PLA(2)s) are a diverse family of lipolytic enzymes which hydrolyze the acyl bond at the sn-2 position of glycerophospholipids to produce free fatty acids and lysophospholipids. These products are precursors of bioactive eicosanoids and platelet-activating factor which have been implicated in pathological states of numerous acute and chronic neurological disorders. To date, more than 27 isoforms of PLA(2) have been found in the mammalian system which can be classified into four major categories: secretory PLA(2), cytosolic PLA(2), Ca(2+)-independent PLA(2), and platelet-activating factor acetylhydrolases. Multiple isoforms of PLA(2) are found in the mammalian spinal cord. Under physiological conditions, PLA(2)s are involved in diverse cellular responses, including phospholipid digestion and metabolism, host defense, and signal transduction. However, under pathological situations, increased PLA(2) activity, excessive production of free fatty acids and their metabolites may lead to the loss of membrane integrity, inflammation, oxidative stress, and subsequent neuronal injury. There is emerging evidence that PLA(2) plays a key role in the secondary injury process after traumatic spinal cord injury. This review outlines the current knowledge of the PLA(2) in the spinal cord with an emphasis being placed on the possible roles of PLA(2) in mediating the secondary SCI.

Phospholipase A2 activity is associated with structural brain changes in schizophrenia

Regional structural brain changes are among the most robust biological findings in schizophrenia, yet the underlying pathophysiological changes remain poorly understood. Recent evidence suggests that abnormal neuronal/dendritic plasticity is related to alterations in membrane lipids. We examined whether serum activity of membrane lipid remodelling/repairing cytosolic phospholipase A(2) (PLA(2)) were related to regional brain structure in magnetic resonance images (MRI). The study involved 24 schizophrenia patients, who were either drug-naïve or off antipsychotic medication, and 25 healthy controls. Using voxel-based morphometry (VBM) analysis of T1-high-resolution MRI-images, we correlated both gray matter and white matter changes with serum PLA(2)-activity. PLA(2) activity was increased in patients, consistent with previous findings. VBM group comparison of patients vs. controls showed abnormalities of frontal and medial temporal cortices/hippocampus, and left middle/superior temporal gyrus in first-episode patients. Group comparison of VBM/PLA(2)-correlations revealed a distinct pattern of disease-related interactions between gray/white matter changes in patients and PLA(2)-activity: in first-episode patients (n=13), PLA(2)-activity was associated with structural alterations in the left prefrontal cortex and the bilateral thalamus. Recurrent-episode patients (n=11) showed a wide-spread pattern of associations between PLA(2)-activity and structural changes in the left (less right) prefrontal and inferior parietal cortex, the left (less right) thalamus and caudate nucleus, the left medial temporal and orbitofrontal cortex and anterior cingulum, and the cerebellum. Our findings demonstrate a potential association between membrane lipid biochemistry and focal brain structural abnormalities in schizophrenia. Differential patterns in first-episode vs. chronic patients might be related to PLA(2)-increase at disease-onset reflecting localized regenerative activity, whereas correlations in recurrent-episode patients might point to less specific neurodegenerative aspects of disease progression.

Inflammatory hyperalgesia induces essential bioactive lipid production in the spinal cord

Lipid molecules play an important role in regulating the sensitivity of sensory neurons and enhancing pain perception, and growing evidence indicates that the effect occurs both at the site of injury and in the spinal cord. Using high-throughput mass spectrometry methodology, we sought to determine the contribution of spinal bioactive lipid species to inflammation-induced hyperalgesia in rats. Quantitative analysis of CSF and spinal cord tissue for eicosanoids, ethanolamides and fatty acids revealed the presence of 102 distinct lipid species. After induction of peripheral inflammation by intra-plantar injection of carrageenan to the ipsilateral hind paw, lipid changes in cyclooxygenase (COX) and 12-lipoxygenase (12-LOX) signaling pathways peaked at 4 h in the CSF. In contrast, changes occurred in a temporally disparate manner in the spinal cord with LOX-derived hepoxilins followed by COX-derived prostaglandin E(2), and subsequently the ethanolamine anandamide. Systemic treatment with the mu opioid agonist morphine, the COX inhibitor ketorolac, or the LOX inhibitor nordihydroguaiaretic acid significantly reduced tactile allodynia, while their effects on the lipid metabolites were different. Morphine did not alter the lipid profile in the presence or absence of carrageenan inflammation. Ketorolac caused a global reduction in eicosanoid metabolism in naïve animals that remained suppressed following injection of carrageenan. Nordihydroguaiaretic acid-treated animals also displayed reduced basal levels of COX and 12-LOX metabolites, but only 12-LOX metabolites remained decreased after carrageenan treatment. These findings suggest that both COX and 12-LOX play an important role in the induction of carrageenan-mediated hyperalgesia through these pathways.

Expression genetics identifies spinal mechanisms supporting formalin late phase behaviors

Background

Formalin injection into rodent hind paws is one of the most commonly employed pain assays. The resulting nocifensive behaviors can be divided into two phases differing in timing, duration and underlying mechanisms. Spinal sensitization has long been felt to participate in the second phase of this response, although this sensitization is incompletely understood. By using correlative analysis between spinal gene expression and mouse strain-dependent intensity of late phase behavior, we hypothesized genes participating in variability of the response could be identified.

Results

Late phase formalin behavior scores among 10 inbred mouse strains were correlated with a spinal cord gene expression database constructed using expression arrays. Messenger RNA levels for several genes were highly correlated with the late phase behavioral responses. Most of these genes had already been implicated in mechanisms regulating pain and analgesia. One of the most strongly correlated genes, Mapk8 coding for c-Jun N-terminal kinase 1 (JNK1), was chosen for further analysis. Studies using additional strains of mice confirmed that spinal cord mRNA expression levels of Mapk8 followed the pattern predicted by strain-specific levels of formalin behavior. Interestingly, spinal cord JNK1 protein levels displayed an inverse relationship with mRNA measurements. Finally, intrathecal injections of the selective JNK inhibitor, SP600125, selectively reduced late phase licking behavior.

Conclusions

Wide differences in pain behaviors, including those resulting from the injection of formalin, can be observed in inbred strains of mice suggesting strong genetic influences. Correlating levels of gene expression in tissues established to be mechanistically implicated in the expression of specific behaviors can identify genes involved in the behaviors of interest. Comparing formalin late phase behavior levels with spinal cord gene expression yielded several plausible gene candidates, including the Mapk8 gene. Additional molecular and pharmacologic evidence confirmed a functional role for this gene in supporting formalin late phase responses.

Expression profile of multiple secretory phospholipase A(2) isoforms in the rat CNS: enriched expression of sPLA(2)-IIA in brainstem and spinal cord

Phospholipases A(2) (PLA(2)) are enzymes which cleave the sn-2 ester bond in membrane phospholipids to release free fatty acids and lysophospholipids. The present study aimed to elucidate the expression profile of multiple secretory phospholipase A(2) (sPLA(2)) isoforms in the normal rat CNS with focus on sPLA(2)-IIA in the brainstem and spinal cord. Quantitative RT-PCR analysis showed that sPLA(2)-IB expression was low throughout the CNS, sPLA(2)-IIA expression was high in the brainstem and spinal cord, sPLA(2)-IIC expression was high in the cerebral neocortex, hippocampus and thalamus/hypothalamus, sPLA(2)-V expression was high in the olfactory bulb and cerebellum, and sPLA(2)-X was expressed at very low levels in the normal CNS. Of the isoforms, sPLA(2)-IIA mRNA expression was highest in the brainstem and spinal cord suggesting that this could be the most relevant isoform in the ascending pain pathway. Western blot analysis showed high level of sPLA(2)-IIA expression in the brainstem and cervical, thoracic and lumbar spinal segments but low level of expression in other parts of the brain. sPLA(2)-IIA was localized by immunohistochemistry to the spinal trigeminal and facial motor nuclei and dorsal- and ventral-horns of the spinal cord. The enzyme was found on the endoplasmic reticulum of neuronal cell bodies and small diameter dendrites or dendritic spines at electron microscopy. The expression of sPLA(2)-IIA in the dorsal horn and spinal trigeminal nucleus is consistent with previous results which showed an important role of CNS sPLA(2) in nociceptive transmission.

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.

Locomotor networks are targets of modulation by sensory transient receptor potential vanilloid 1 and transient receptor potential melastatin 8 channels

It is well recognized that proprioceptive afferent inputs can control the timing and pattern of locomotion. C and Adelta afferents can also affect locomotion but an unresolved issue is the identity of the subsets of these afferents that encode defined modalities. Over the last decade, the transient receptor potential (TRP) ion channels have emerged as a family of non-selective cation conductances that can label specific subsets of afferents. We focus on a class of TRPs known as ThermoTRPs which are well known to be sensor receptors that transduce changes in heat and cold. ThermoTRPs are known to help encode somatosensation and painful stimuli, and receptors have been found on C and Adelta afferents with central projections onto dorsal horn laminae. Here we show, using in vitro neonatal mouse spinal cord preparations, that activation of both spinal and peripheral transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential melastatin 8 (TRPM8) afferent terminals modulates central pattern generators (CPGs). Capsaicin or menthol and cooling modulated both sacrocaudal afferent (SCA) evoked and monoaminergic drug-induced rhythmic locomotor-like activity in spinal cords from wild type but not TRPV1-null (trpv1(-/-)) or TRPM8-null (trpm8(-/-)) mice, respectively. Capsaicin induced an initial increase in excitability of the lumbar motor networks, while menthol or cooling caused a decrease in excitability. Capsaicin and menthol actions on CPGs involved excitatory and inhibitory glutamatergic mechanisms, respectively. These results for the first time show that dedicated pathways of somatosensation and pain identified by TRPV1 or TRPM8 can target spinal locomotor CPGs.

Neuropathic pain in dogs and cats: if only they could tell us if they hurt

Neuropathic pain is difficult to diagnose in veterinary patients because they are unable to verbalize their pain. By assuming that neuropathic pain may exist based on the history of events that each patient has experienced, a focused client history and neurologic examination may identify a lesion resulting in persistent or spontaneous pain. Once neuropathic pain is diagnosed, a trial analgesic or acupuncture session(s) should be prescribed with instructions for owners to observe behavior. Dosing of the analgesic can be titrated to the patient's needs while avoiding adverse effects. When a particular analgesic may be ineffectual, an alternate class should be tried. As research into the neurobiologic mechanisms of neuropathic pain continues, specific therapies for its management should eventually appear in the human clinical setting and subsequently be investigated for veterinary clinical use.

Platelet-activating factor production in the spinal cord of experimental allergic encephalomyelitis mice via the group IVA cytosolic phospholipase A2-lyso-PAFAT axis

Platelet-activating factor (PAF; 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) plays a critical role in inflammatory disorders including experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis (MS). Although PAF accumulation in the spinal cord (SC) of EAE mice and cerebrospinal fluid of MS patients has been reported, little is known about the metabolic processing of PAF in these diseases. In this study, we demonstrate that the activities of phospholipase A(2) (PLA(2)) and acetyl-CoA:lyso-PAF acetyltransferase (LysoPAFAT) are elevated in the SC of EAE mice on a C57BL/6 genetic background compared with those of naive mice and correlate with disease severity. Correspondingly, levels of groups IVA, IVB, and IVF cytosolic PLA(2)s, group V secretory PLA(2), and LysoPAFAT transcripts are up-regulated in the SC of EAE mice. PAF acetylhydrolase activity is unchanged during the disease course. In addition, we show that LysoPAFAT mRNA and protein are predominantly expressed in microglia. Considering the substrate specificity and involvement of PAF production, group IVA cytosolic PLA(2) is likely to be responsible for the increased PLA(2) activity. These data suggest that PAF accumulation in the SC of EAE mice is profoundly dependent on the group IVA cytosolic PLA(2)/LysoPAFAT axis present in the infiltrating macrophages and activated microglia.

Role of secretory phospholipase a(2) in CNS inflammation: implications in traumatic spinal cord injury

Secretory phospholipases A(2) (sPLA(2)s) are a subfamily of lipolytic enzymes which hydrolyze the acyl bond at the sn-2 position of glycerophospholipids to produce free fatty acids and lysophospholipids. These products are precursors of bioactive eicosanoids and platelet-activating factor (PAF). The hydrolysis of membrane phospholipids by PLA(2) is a rate-limiting step for generation of eicosanoids and PAF. To date, more than 10 isozymes of sPLA(2) have been found in the mammalian central nervous system (CNS). Under physiological conditions, sPLA(2)s are involved in diverse cellular responses, including host defense, phospholipid digestion and metabolism. However, under pathological situations, increased sPLA(2) activity and excessive production of free fatty acids and their metabolites may lead to inflammation, loss of membrane integrity, oxidative stress, and subsequent tissue injury. Emerging evidence suggests that sPLA(2) plays a role in the secondary injury process after traumatic or ischemic injuries in the brain and spinal cord. Importantly, sPLA(2) may act as a convergence molecule that mediates multiple key mechanisms involved in the secondary injury since it can be induced by multiple toxic factors such as inflammatory cytokines, free radicals, and excitatory amino acids, and its activation and metabolites can exacerbate the secondary injury. Blocking sPLA(2) action may represent a novel and efficient strategy to block multiple injury pathways associated with the CNS secondary injury. This review outlines the current knowledge of sPLA(2) in the CNS with emphasis placed on the possible roles of sPLA(2) in mediating CNS injuries, particularly the traumatic and ischemic injuries in the brain and spinal cord.