Regulation and metabolism of arachidonic acid

Protective Effect of Berberine on Acute Gastric Ulcer by Promotion of Tricarboxylic Acid Cycle-Mediated Arachidonic Acid Metabolism

Background and Objective

Peptic ulcer is a high incidence gastrointestinal disease in China. Berberine (BBR) is a natural product isolated from the Chinese herb Coptis chinensis Franch that has protective effects in digestive diseases. We aimed to evaluate the ability of BBR to attenuate acute gastric ulcer induced by one-time administration of ethanol in the rat.

Methods

Tissue pathological morphology, macroscopic score, ulcer healing rate, and serum levels of the inflammatory cytokines nitric oxide (NO), interleukin-6 (IL-6), and prostaglandin E2 (PGE2), and anti-inflammatory interleukin-10 (IL-10) were used to determine the efficacy of BBR and evaluated to identify the optimal dosage. Subsequently, transcriptome and metabolome sequencing were conducted in Control, Model, and optimal dosage groups to explore the pathogenesis of the disease and the mechanism of action of the drug. The levels of malondialdehyde (MDA), myeloperoxidase (MPO), as well as those of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were determined by enzyme-linked immunosorbent assay to verify the results of transcriptomics and metabolomics analyses.

Results

BBR significantly improved the pathological morphology of gastric ulcers, increased the macroscopic score and healing rate, decreased serum levels of NO, IL-6, and PGE2, and increased serum levels of IL-10, thus effectively alleviating gastric ulcer severity. Transcriptome results showed that the therapeutic effect of BBR was mainly mediated by the arachidonic acid metabolism pathway at the gene level, which is closely associated with inflammation and increased levels of reactive oxygen species (ROS). The differentially accumulated metabolite prostaglandin E1, which is a negative regulator of ROS, was significantly up-regulated after BBR administration. The validation results indicated that BBR pretreatment increased SOD and GSH-Px enzyme activities, while reducing levels of the oxidative products MDA and MPO.

Conclusion

This study demonstrated that BBR exerts a protective effect on acute gastric ulcer by promoting tricarboxylic acid cycle-mediated arachidonic acid metabolism.

Pterostilbene could alleviate diabetic cognitive impairment by suppressing TLR4/NF-кB pathway through microbiota-gut-brain axis

Diabetic cognitive impairment (DCI) is a serious neurodegenerative disorder caused by diabetes, with chronic inflammation being a crucial factor in its pathogenesis. Pterostilbene is a well-known natural stilbene derivative that has excellent anti-inflammatory activity, suggesting its potential medicinal advantages for treating DCI. Therefore, this study is to explore the beneficial effects of pterostilbene for improving cognitive dysfunction in DCI mice. A diabetic model was induced by a high-fat diet plus streptozotocin (40 mg·kg-1 ) for consecutive 5 days. After the animals were confirmed to be in a diabetic state, they were treated with pterostilbene (20 or 60 mg·kg-1 , i.g.) for 10 weeks. Pharmacological evaluation showed pterostilbene could ameliorate cognitive dysfunction, regulate glycolipid metabolism disorders, improve neuronal damage, and reduce the accumulation of β-amyloid in DCI mice. Pterostilbene alleviated neuroinflammation by suppressing oxidative stress and carbonyl stress damage, astrocyte and microglia activation, and dopaminergic neuronal loss. Further investigations showed that pterostilbene reduced the level of lipopolysaccharide, modulated colon and brain TLR4/NF-κB signaling pathways, and decreased the release of inflammatory factors, which in turn inhibited intestinal inflammation and neuroinflammation. Furthermore, pterostilbene could also improve the homeostasis of intestinal microbiota, increase the levels of short-chain fatty acids and their receptors, and suppress the loss of intestinal tight junction proteins. In addition, the results of plasma non-targeted metabolomics revealed that pterostilbene could modulate differential metabolites and metabolic pathways associated with inflammation, thereby suppressing systemic inflammation in DCI mice. Collectively, our study found for the first time that pterostilbene could alleviate diabetic cognitive dysfunction by inhibiting the TLR4/NF-κB pathway through the microbiota-gut-brain axis, which may be one of the potential mechanisms for its neuroprotective effects.

WFDC12-overexpressing contributes to the development of atopic dermatitis via accelerating ALOX12/15 metabolism and PAF accumulation

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by eczema-like skin lesions, dry skin, severe itching, and recurrent recurrence. The whey acidic protein four-disulfide core domain gene WFDC12 is highly expressed in skin tissue and up-regulated in the skin lesions of AD patients, but its role and relevant mechanism in AD pathogenesis have not been studied yet. In this study, we found that the expression of WFDC12 was closely related to clinical symptoms of AD and the severity of AD-like lesions induced by DNFB in transgenic mice. WFDC12-overexpressing in the epidermis might promote the migration of skin-presenting cells to lymph nodes and increase Th cell infiltration. Meanwhile, the number and ratio of immune cells and mRNA levels of cytokines were significantly upregulated in transgenic mice. In addition, we found that ALOX12/15 gene expression was upregulated in the arachidonic acid metabolism pathway, and the corresponding metabolite accumulation was increased. The activity of epidermal serine hydrolase decreased and the accumulation of platelet-activating factor (PAF) increased in the epidermis of transgenic mice. Collectively, our data demonstrate that WFDC12 may contribute to the exacerbation of AD-like symptoms in DNFB-induced mouse model by enhancing arachidonic acid metabolism and PAF accumulation and that WFDC12 may be a potential therapeutic target for human atopic dermatitis.

The Improved Milk Quality and Enhanced Anti-Inflammatory Effect in Acetylserotonin-O-methyltransferase (ASMT) Overexpressed Goats: An Association with the Elevated Endogenous Melatonin Production

Background: Transgenic animal production is an important means of livestock breeding and can be used to model pharmaceutical applications. Methods: In this study, to explore the biological activity of endogenously produced melatonin, Acetylserotonin-O-methyltransferase (ASMT)-overexpressed melatonin-enriched dairy goats were successfully generated through the use of pBC1-ASMT expression vector construction and prokaryotic embryo microinjection. Results: These transgenic goats have the same normal phenotype as the wild-type goats (WT). However, the melatonin levels in their blood and milk were significantly increased (p < 0.05). In addition, the quality of their milk was also improved, showing elevated protein content and a reduced somatic cell number compared to the WT goats. No significant changes were detected in the intestinal microbiota patterns between groups. When the animals were challenged by the intravenous injection of E. coli, the ASMT-overexpressed goats had a lower level of pro-inflammatory cytokines and higher anti-inflammatory cytokines compared to the WT goats. Metabolic analysis uncovered a unique arachidonic acid metabolism pattern in transgenic goats. Conclusions: The increased melatonin production due to ASMT overexpression in the transgenic goats may have contributed to their improved milk quality and enhanced the anti-inflammatory ability compared to the WT goats.

Emerging roles of ferroptosis in the tumor immune landscape: from danger signals to anti-tumor immunity

Regulated cell death (RCD) is a vital event in various physiological and pathological processes. Ferroptosis is a newly described RCD, which is driven by iron accumulation and unrestricted lipid peroxidation. The interaction between ferroptosis and immunity has been a topic of substantial interest since its discovery in 2012. It has become increasingly evident that ferroptosis is critically involved in the regulation of antitumor immunity and may provide potential strategies in immunotherapy. Ferroptosis could release various damage-associated molecular patterns (DAMPs) or lipid metabolites to regulate the cellular immune response, validating its role as a form of immunogenic cell death (ICD). Specifically, the oxygenated membrane lipids on ferroptotic cells could mediate the phagocytosis by macrophages to maintain the immune responses. Additionally, immune checkpoint inhibitor therapy may sensitize cancer cells to ferroptosis, while ferroptosis might contribute to tumor immune evasion by directly interfering with the function of various immune cells. Based on these insights, we provided a comprehensive review on the interaction patterns between ferroptosis and immunity, which may not only offer insight into the underlying regulatory mechanisms but also facilitating the development of ferroptosis-based antitumor therapeutics.

Does NLRP3 Inflammasome and Aryl Hydrocarbon Receptor Play an Interlinked Role in Bowel Inflammation and Colitis-Associated Colorectal Cancer?

Inflammation is a hallmark in many forms of cancer; with colitis-associated colorectal cancer (CAC) being a progressive intestinal inflammation due to inflammatory bowel disease (IBD). While this is an exemplification of the negatives of inflammation, it is just as crucial to have some degree of the inflammatory process to maintain a healthy immune system. A pivotal component in the maintenance of such intestinal homeostasis is the innate immunity component, inflammasomes. Inflammasomes are large, cytosolic protein complexes formed following stimulation of microbial and stress signals that lead to the expression of pro-inflammatory cytokines. The NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome has been extensively studied in part due to its strong association with colitis and CAC. The aryl hydrocarbon receptor (AhR) has recently been acknowledged for its connection to the immune system aside from its role as an environmental sensor. AhR has been described to play a role in the inhibition of the NLRP3 inflammasome activation pathway. This review will summarise the signalling pathways of both the NLRP3 inflammasome and AhR; as well as new-found links between these two signalling pathways in intestinal immunity and some potential therapeutic agents that have been found to take advantage of this link in the treatment of colitis and CAC.

Vitamin B12 Status Upon Short-Term Intervention with a Vegan Diet-A Randomized Controlled Trial in Healthy Participants

Vegans are at an increased risk for certain micronutrient deficiencies, foremost of vitamin B₁₂. Little is known about the short-term effects of dietary change to plant-based nutrition on vitamin B₁₂ metabolism. Systemic biomarkers of vitamin B₁₂ status, namely, serum vitamin B₁₂ and holotranscobalamin, may respond quickly to a reduced intake of vitamin B₁₂. To test this hypothesis, 53 healthy omnivore subjects were randomized to a controlled unsupplemented vegan diet (VD, n = 26) or meat-rich diet (MD, n = 27) for 4 weeks. Vitamin B₁₂ status was examined by measurement of serum vitamin B₁₂, holotranscobalamin (holo-TC), methylmalonic acid (MMA) and total plasma homocysteine (tHcy). Holo-TC decreased significantly in the VD compared to the MD group after four weeks of intervention, whereas metabolites MMA and tHcy were unaffected. Body weight remained stable in both groups. VD intervention led to a significant reduction of cholesterol intake, and adequate profiles of nutrient and micronutrient status. Lower intake of vitamin B₁₂ was observed in VD, which was mirrored by a lower concentration of serum vitamin B₁₂ and reduced holo-TC after 4 weeks. Plasma holo-TC may be a fast-responding biomarker to monitor adequate supply of vitamin B₁₂ in plant-based individuals.

Arachidonic Acid and Nitroarachidonic: Effects on NADPH Oxidase Activity

Arachidonic acid (AA) is a polyunsaturated fatty acid that participates in the inflammatory response mainly through bioactive-lipids formation in macrophages and also in the phagocytic NADPH oxidase 2 (NOX2) activation. NOX2 is the enzyme responsible for a huge superoxide formation in macrophages, essential to eliminate pathogens inside the phagosome. The oxidase is an enzymatic complex comprised of a membrane-bound flavocytochrome b ₅₅₈ (gp91^phox/p22^phox), three cytosolic subunits (p47^phox, p40^phox and p67^phox) and a Rac-GTPase. The enzyme becomes active when macrophages are exposed to appropriate stimuli that trigger the phosphorylation of cytosolic subunits and its migration to plasmatic membrane to form the active complex. It is proposed that AA stimulates NOX2 activity through AA interaction with different components of the NADPH oxidase complex. In inflammatory conditions, there is an increase in reactive oxygen and nitrogen species that results in the production of nitrated derivatives of AA, such as nitroarachidonic acid (NO₂-AA). NO₂-AA is capable to inhibit NOX2 activity by interfering with p47^phox migration to the membrane without affecting phosphorylation of cytosolic proteins. Also, NO₂-AA is capable to interact with protein disulfide isomerase (PDI), which is involved on NOX2 active complex formation. It has been demonstrated that NO₂-AA forms a covalent adduct with PDI that could prevent the interaction with NOX2 and it would explain the inhibitory effects of the fatty acid upon NOX2. Together, current data indicate that AA is an important activator of NOX2 formed in the early events of the inflammatory response, leading to a massive production of oxidants that may, in turn, promote NO₂-AA formation and shutting down the oxidative burst. Hence, AA and its derivatives could have antagonistic roles on NOX2 activity regulation.

Anti-inflammatory signaling actions of electrophilic nitro-arachidonic acid in vascular cells and astrocytes

Nitrated derivatives of unsaturated fatty acids (nitro-fatty acids) are being formed and detected in human plasma, cell membranes and tissue, triggering signaling cascades via covalent and reversible post-translational modifications of nucleophilic amino acids in transcriptional regulatory proteins. Arachidonic acid (AA) represents a precursor of potent signaling molecules, i.e., prostaglandins and thromboxanes through enzymatic and non-enzymatic oxidative pathways. Arachidonic acid can be nitrated by reactive nitrogen species leading to the formation of nitro-arachidonic acid (NO₂-AA). A critical issue is the influence of NO₂-AA on prostaglandin endoperoxide H synthases, modulating inflammatory processes through redirection of AA metabolism and signaling. In this prospective article, we describe the key chemical and biochemical actions of NO₂-AA in vascular and astrocytes. This includes the ability of NO₂-AA to mediate unique redox signaling anti-inflammatory actions along with its therapeutic potential.

Hyperhomocysteinemia activates the aryl hydrocarbon receptor/CD36 pathway to promote hepatic steatosis in mice

Hyperhomocysteinemia (HHcy) is associated with liver diseases such as fatty liver and hepatic fibrosis; however, the underlying mechanism is still largely unknown. The current study aimed to explore the signaling pathway involved in HHcy-induced hepatic steatosis (HS). C57BL/6 mice were fed a high-methionine diet (HMD) for 4 and 8 weeks to establish the HHcy mouse model. Compared to a chow diet, the HMD induced hepatic steatosis and elevated hepatic expression of CD36, a fatty acid transport protein. The increased CD36 expression was associated with activation of the aryl hydrocarbon receptor (AHR). In primary cultured hepatocytes, high levels of homocysteine (Hcy) treatment up-regulated CD36 and increased subsequent lipid uptake; both were significantly attenuated by small interfering RNA (siRNA) knockdown of CD36 and AHR. Chromatin immunoprecipitation assay revealed that Hcy promoted binding of AHR to the CD36 promoter, and transient transfection assay demonstrated markedly increased activity of the AHR response element by Hcy, which was ligand dependent. Mass spectrometry revealed significantly increased hepatic content of lipoxin A4 (LXA4 ), a metabolite of arachidonic acid, in HMD-fed mice. Furthermore, overexpression of 15-oxoprostaglandin 13-reductase 1, a LXA4 inactivation enzyme, inhibited Hcy-induced AHR activation, lipid uptake, and lipid accumulation. Moreover, LXA4 -induced up-regulation of CD36 and lipid uptake was inhibited by AHR siRNA in vitro in hepatocytes. Finally, treatment with an AHR antagonist reversed HHcy-induced lipid accumulation by inhibiting the AHR-CD36 pathway in mice.

CONCLUSION

HHcy activates the AHR-CD36 pathway by increasing hepatic LXA4 content, which results in hepatic steatosis. (Hepatology 2016;64:92-105).

n-3 Fatty acids and asthma

Asthma is one of the most common and prevalent problems worldwide affecting over 300 million individuals. There is some evidence from observational and intervention studies to suggest a beneficial effect of n-3 PUFA in inflammatory diseases, specifically asthma. Marine-based n-3 PUFA have therefore been proposed as a possible complementary/alternative therapy for asthma. The proposed anti-inflammatory effects of n-3 fatty acids may be linked to a change in cell membrane composition. This altered membrane composition following n-3 fatty acid supplementation (primarily EPA and DHA) can modify lipid mediator generation via the production of eicosanoids with a reduced inflammatory potential/impact. A recently identified group of lipid mediators derived from EPA including E-series resolvins are proposed to be important in the resolution of inflammation. Reduced inflammation attenuates the severity of asthma including symptoms (dyspnoea) and exerts a bronchodilatory effect. There have been no major health side effects reported with the dietary supplementation of n-3 fatty acids or their mediators; consequently supplementing with n-3 fatty acids is an attractive non-pharmacological intervention which may benefit asthma.

Plasma phospholipid arachidonic acid and lignoceric acid are associated with the risk of cardioembolic stroke

Cardioembolic (CE) stroke is the most severe subtype of ischemic stroke with high recurrence and mortality. However, there is still little information on the association of plasma fatty acid (FA) with CE stroke. The objective of this study was to test the hypothesis whether the composition of plasma phospholipid FA is associated with the risk of CE stroke. The study subjects were collected from the Korea University Stroke Registry. Twenty-one subjects were selected as CE stroke group, and 39 age- and sex-matched subjects with non-CE stroke were selected as controls. Sociodemographic factors, clinical measurements, and plasma phospholipid FA compositions were compared between the groups. Logistic regression was used to obtain estimates of the associations between the relevant FAs and CE stroke. The result showed that the CE stroke group had higher levels of free FA and lower levels of triglycerides before and after adjustment (all P < .05). In the regression analysis, elaidic acid (18:1Tn9) and arachidonic acid (20:4n6) were positively related, but lignoceric acid (24:0) was negatively related to CE stroke in all constructed models (all P < .05). In conclusion, plasma phospholipid FA composition was associated with CE stroke risk in Korean population, with higher proportions of elaidic acid and arachidonic acid and lower proportion of lignoceric acid in CE stroke.

Induction of an altered lipid phenotype by two cancer promoting treatments in rat liver

Changes in lipid metabolism have been associated with tumor promotion in rat liver. Similarities and differences of lipid parameters were investigated using the mycotoxin fumonisin B1 (FB1) and the 2-acetylaminofluorene/partial hepatectomy (AAF/PH) treatments as cancer promoters in rat liver. A typical lipid phenotype was observed, including increased membranal phosphatidylethanolamine (PE) and cholesterol content, increased levels of C16:0 and monounsaturated fatty acids in PE and phosphatidylcholine (PC), as well as a decrease in C18:0 and long-chained polyunsaturated fatty acids in the PC fraction. The observed lipid changes, which likely resulted in changes in membrane structure and fluidity, may represent a growth stimulus exerted by the cancer promoters that could provide initiated cells with a selective growth advantage. This study provided insight into complex lipid profiles induced by two different cancer promoting treatments and their potential role in the development of hepatocyte nodules, which can be used to identify targets for the development of chemopreventive strategies against cancer promotion in the liver.

An update on adding docosahexaenoic acid (DHA) and arachidonic acid (AA) to baby formula

Human milk is the ideal food providing optimal nutrition for healthy term infants. Its complex lipid composition is critical for infant growth and serves as a golden standard for baby formula development. Docosahexaenoic acid (C22:6 n- 3, DHA) and arachidonic acid (C20:4 n- 6, AA) are the two major long chain polyunsaturated fatty acids (PUFAs) in human milk. In humans, they are fundamental components of the cell membrane and play an important role in neurite growth and signal transmission. Their importance for both preterm and term infants has been demonstrated by various clinical trials. DHA and AA supplementation shows desirable influences on visual and cognitive development in early life and is additionally associated with potential benefits on later health. Further clinical data revealed that supplementing both DHA and AA instead of DHA alone during infancy is important to deliver the optimal outcome. In this review, we summarize current research and scientific evidence of DHA and AA on baby development.

Roles of acidic phospholipids and nucleotides in regulating membrane binding and activity of a calcium-independent phospholipase A2 isoform

Phospholipase A(2) activity plays key roles in generating lipid second messengers and regulates membrane topology through the generation of asymmetric lysophospholipids. In particular, the Group VIA phospholipase A(2) (GVIA-iPLA(2)) subfamily of enzymes functions independently of calcium within the cytoplasm of cells and has been implicated in numerous cellular processes, including proliferation, apoptosis, and membrane transport steps. However, mechanisms underlying the spatial and temporal regulation of these enzymes have remained mostly unexplored. Here, we examine the subset of Caenorhabditis elegans lipases that harbor a consensus motif common to members of the GVIA-iPLA(2) subfamily. Based on sequence homology, we identify IPLA-1 as the closest C. elegans homolog of human GVIA-iPLA(2) enzymes and use a combination of liposome interaction studies to demonstrate a role for acidic phospholipids in regulating GVIA-iPLA(2) function. Our studies indicate that IPLA-1 binds directly to multiple acidic phospholipids, including phosphatidylserine, phosphatidylglycerol, cardiolipin, phosphatidic acid, and phosphorylated derivatives of phosphatidylinositol. Moreover, the presence of these acidic lipids dramatically elevates the specific activity of IPLA-1 in vitro. We also found that the addition of ATP and ADP promote oligomerization of IPLA-1, which probably underlies the stimulatory effect of nucleotides on its activity. We propose that membrane composition and the presence of nucleotides play key roles in recruiting and modulating GVIA-iPLA(2) activity in cells.

Application of comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry method to identify potential biomarkers of perinatal asphyxia in a non-human primate model

Perinatal asphyxia is a leading cause of brain injury in infants, occurring in 2-4 per 1000 live births. The clinical response to asphyxia is variable and difficult to predict with current diagnostic tests. Reliable biomarkers are needed to help predict the timing and severity of asphyxia, as well as response to treatment. Two-dimensional gas chromatography-time-of-flight-mass spectrometry (GC×GC-TOFMS) was used herein, in conjunction with chemometric data analysis approaches for metabolomic analysis in order to identify significant metabolites affected by birth asphyxia. Blood was drawn before and after 15 or 18 min of cord occlusion in a Macaca nemestrina model of perinatal asphyxia. Postnatal samples were drawn at 5 min of age (n=20 subjects). Metabolomic profiles of asphyxiated animals were compared to four controls delivered at comparable gestational age. Fifty metabolites with the greatest change pre- to post-asphyxia were identified and quantified. The metabolic profile of post-asphyxia samples showed marked variability compared to the pre-asphyxia samples. Fifteen of the 50 metabolites showed significant elevation in response to asphyxia, ten of which remained significant upon comparison to the control animals. This metabolomic analysis confirmed lactate and creatinine as markers of asphyxia and discovered new metabolites including succinic acid and malate (intermediates in the Krebs cycle) and arachidonic acid (a brain fatty acid and inflammatory marker) as potential biomarkers. GC×GC-TOFMS coupled with chemometric data analysis are useful tools to identify acute biomarkers of brain injury. Further study is needed to correlate these metabolites with severity of disease, and response to treatment.

Prostaglandin E2 and the pathogenesis of pulmonary fibrosis

Prostaglandin (PG)E(2) is a bioactive eicosanoid that regulates many biologically important processes in part due to its ability to signal through four distinct G-protein-coupled receptors with differential signaling activity and unique expression patterns in different cell types. Although PGE(2) has been linked to malignancy in many organs, it is believed to play a beneficial role in the setting of fibrotic lung disease. This is in part due to the ability of PGE(2) to limit many of the pathobiologic features of lung fibroblasts and myofibroblasts, including the ability of PGE(2) to limit fibroblast proliferation, migration, collagen secretion, and, as originally reported in the Journal by us in 2003, the ability to limit transforming growth factor (TGF)-β-induced myofibroblast differentiation. In the setting of lung fibrosis, PGE(2) production and signaling is often diminished. In the last 8 years, significant advances have been made to better understand the dysregulation of PGE(2) production and signaling in the setting of lung fibrosis. We also have a clearer picture of how PGE(2) inhibits myofibroblast differentiation and the receptor signaling pathways that can influence fibroblast proliferation. This review highlights these recent advances and offers new insights into the potential ways that PGE(2) and its downstream signals can be regulated for therapeutic benefit in a disease that has no validated treatment options.

Inhibitory effect of hot-water extract of quince (Cydonia oblonga) on immunoglobulin E-dependent late-phase immune reactions of mast cells

We evaluated the effect of a crude hot-water extract (HW) of quince (Cydonia oblonga Miller) fruit on immunoglobulin E (IgE)-dependent late-phase immune reactions of mast cells using in vitro system. Mast cell-like RBL-2H3 cells were treated with quince HW and late-phase reaction was then induced by stimulation with IgE + Antigen. Quince HW reduced the elevation of interleukin-13 and tumor necrosis factor-α expression level. Furthermore, quince HW suppressed these cytokine expressions of mouse bone marrow-derived mast cells (BMMCs), a normal mast cell model. Leukotriene C(4) and prostaglandin D(2) production in BMMCs after 1 and 6 h of stimulation, respectively, were also reduced by treating the cells with quince HW. We found that the induction of intracellular cyclooxygenase (COX)-2 expression but not COX-1 expression in BMMCs was reduced by quince HW. These results suggest that quince HW has an inhibitory effect on broad range of the late-phase immune reactions of mast cells.

Mycobacterium tuberculosis activates human macrophage peroxisome proliferator-activated receptor gamma linking mannose receptor recognition to regulation of immune responses

Mycobacterium tuberculosis enhances its survival in macrophages by suppressing immune responses in part through its complex cell wall structures. Peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear receptor superfamily member, is a transcriptional factor that regulates inflammation and has high expression in alternatively activated alveolar macrophages and macrophage-derived foam cells, both cell types relevant to tuberculosis pathogenesis. In this study, we show that virulent M. tuberculosis and its cell wall mannose-capped lipoarabinomannan induce PPARgamma expression through a macrophage mannose receptor-dependent pathway. When activated, PPARgamma promotes IL-8 and cyclooxygenase 2 expression, a process modulated by a PPARgamma agonist or antagonist. Upstream, MAPK-p38 mediates cytosolic phospholipase A(2) activation, which is required for PPARgamma ligand production. The induced IL-8 response mediated by mannose-capped lipoarabinomannan and the mannose receptor is independent of TLR2 and NF-kappaB activation. In contrast, the attenuated Mycobacterium bovis bacillus Calmette-Guérin induces less PPARgamma and preferentially uses the NF-kappaB-mediated pathway to induce IL-8 production. Finally, PPARgamma knockdown in human macrophages enhances TNF production and controls the intracellular growth of M. tuberculosis. These data identify a new molecular pathway that links engagement of the mannose receptor, an important pattern recognition receptor for M. tuberculosis, with PPARgamma activation, which regulates the macrophage inflammatory response, thereby playing a role in tuberculosis pathogenesis.

Glucocorticoid-regulated crosstalk between arachidonic acid and endocannabinoid biochemical pathways coordinates cognitive-, neuroimmune-, and energy homeostasis-related adaptations to stress

Arachidonic acid and its derivatives constitute the major group of signaling molecules involved in the innate immune response and its communication with all cellular and systemic aspects involved on homeostasis maintenance. Glucocorticoids spread throughout the organism their influences over key enzymatic steps of the arachidonic acid biochemical pathways, leading, in the central nervous system, to a shift favoring the synthesis of anti-inflammatory endocannabinoids over proinflammatory metabolites, such as prostaglandins. This shift modifies local immune-inflammatory response and neuronal activity to ultimately coordinate cognitive, behavioral, neuroendocrine, neuroimmune, physiological, and metabolic adjustments to basal and stress conditions. In the hypothalamus, a reciprocal feedback between glucocorticoids and arachidonate-containing molecules provides a mechanism for homeostatic control. This neurochemical switch is susceptible to fine-tuning by neuropeptides, cytokines, and hormones, such as leptin and interleukin-1beta, assuring functional integration between energy homeostasis control and the immune/stress response.

Glucocorticoids shift arachidonic acid metabolism toward endocannabinoid synthesis: a non-genomic anti-inflammatory switch

Glucocorticoids are capable of exerting both genomic and non-genomic actions in target cells of multiple tissues, including the brain, which trigger an array of electrophysiological, metabolic, secretory and inflammatory regulatory responses. Here, we have attempted to show how glucocorticoids may generate a rapid anti-inflammatory response by promoting arachidonic acid-containing endocannabinoids biosynthesis. According to our hypothesized model, non-genomic action of glucocorticoids results in the global shift of membrane lipid metabolism, subverting metabolic pathways toward the synthesis of the anti-inflammatory endocannabinoids, anandamide (AEA) and 2-arachidonoyl-glycerol (2-AG), and away from arachidonic acid production. Post-transcriptional inhibition of cyclooxygenase-2 (COX(2)) synthesis by glucocorticoids assists this mechanism by suppressing the synthesis of pro-inflammatory prostaglandins as well as endocannabinoid-derived prostanoids. In the central nervous system (CNS) this may represent a major neuroprotective system, which may cross-talk with leptin signaling in the hypothalamus allowing for the coordination between energy homeostasis and the inflammatory response.

The search for endogenous activators of the aryl hydrocarbon receptor

The primary design of this perspective is to describe the major ligand classes of the aryl hydrocarbon receptor (AHR). A grander objective is to provide models that may help define the physiological activator or "endogenous ligand" of the AHR. We present evidence supporting a developmental role for the AHR and propose mechanisms by which an endogenous ligand and consequent AHR activation might be important during normal physiology and development. From this vista, we survey the known xenobiotic, endogenous, dietary, and "unconventional" activators of the AHR, including, when possible, information about their induction potency, receptor binding affinity, and potential for exposure. In light of the essential function of the AHR in embryonic development, we discuss the candidacy of each of these compounds as physiologically important activators.

Phospholipase A2 as targets for anti-cancer drugs

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

Expression and mechanism of spleen tyrosine kinase activation by angiotensin II and its implication in protein synthesis in rat vascular smooth muscle cells

Syk, a 72-kDa tyrosine kinase, is involved in development, differentiation, and signal transduction of hematopoietic and some non-hematopoietic cells. This study determined if Syk is expressed in vascular smooth muscle cells (VSMC) and contributes to angiotensin II (Ang II) signaling and protein synthesis. Syk was found in VSMC and was phosphorylated by Ang II through AT1 receptor. Ang II-induced Syk phosphorylation was inhibited by piceatannol and dominant negative but not wild type Syk mutant. Syk phosphorylation by Ang II was attenuated by cytosolic phospholipase A(2) (cPLA(2)) inhibitor pyrrolidine-1 and retrovirus carrying small interfering RNAs (shRNAs) of this enzyme. Arachidonic acid (AA) increased Syk phosphorylation, and AA- and Ang II-induced phosphorylation was diminished by inhibitors of AA metabolism (5,8,11,14-eicosatetraynoic acid) and lipoxygenase (LO; baicalein) but not cyclooxygenase (indomethacin). AA metabolites formed via LO, 5(S)-, 12(S)-, and 15(S)-hydroxyeicosatetraenoic acids, which activate p38 MAPK, increased Syk phosphorylation. p38 MAPK inhibitor SB202190, and dominant negative p38 MAPK mutant attenuated Ang II- and AA-induced Syk phosphorylation. Adenovirus dominant negative c-Src mutant abolished Ang II - and AA-induced Syk phosphorylation and SB202190, and dominant negative p38 MAPK mutant inhibited Ang II-induced c-Src phosphorylation. Syk dominant negative mutant but not epidermal growth factor receptor blocker AG1478 also inhibited Ang II-induced VSMC protein synthesis. These data suggest that Syk expressed in VSMC is activated by Ang II through p38 MAPK-activated c-Src subsequent to cytosolic phospholipase A(2) and generation of AA metabolites via LO, and it mediates Ang II-induced protein synthesis independent of epidermal growth factor receptor transactivation (Ang II --> cPLA(2) --> AA metabolites of LO --> p38 MAPK --> c-Src --> Syk --> protein synthesis).

Arachidonic and docosahexaenoic acids reduce the growth of A549 human lung-tumor cells increasing lipid peroxidation and PPARs

Polyunsaturated fatty acids (PUFAs) play an important role in both induction and prevention of carcinogenic process. It is well known that several types of neoplastic cells show decreased total PUFA content, contributing to their resistance to chemotherapy and lipid peroxidation. In the light of this, human lung cancer A549 cells, with low PUFA content, were exposed to arachidonic or docosahexaenoic acid to investigate the effect of n-6 and n-3 PUFAs on growth and elucidate underlying mechanisms. The bulk of the results showed that both n-6 PUFAs and n-3 PUFAs decrease human lung-tumor cell growth in a concentration-dependent manner, inducing cell death mainly evident at 100microM concentration. The mechanism underlying the antiproliferative effect of n-6 and n-3 PUFAs appeared to be the same, involving changes in fatty acid composition of biomembranes, production of cytostatic aldehydes derived from lipid peroxidation and able to affect DNA-binding activity of AP-1, and induction of PPAR. From these results it may be hypothesized that n-6 PUFAs, like n-3 PUFAs, are able to inhibit tumor growth.

Membranes are not just rafts

A new definition for lipid rafts was coined at the Keystone Symposium of Lipid Rafts and Cell Function based on recent advances in the field. The revised definition lumps all membrane heterogeneities that are not rafts into a single class of "non-raft". In this commentary, we suggest that "non-raft" domains encompass a variety of membrane heterogeneities and are quite diverse in composition and origin. A good starting point for the study of this diversity would be phospholipids with unsaturated acyl chains, which display little affinity for cholesterol; these lipids are abundant in membranes such as the endoplasmic reticulum and that may form their own macro- or microdomains.

Decrease of human hepatoma cell growth by arachidonic acid is associated with an accumulation of derived products from lipid peroxidation

We showed that the metabolism of arachidonic acid (AA) in HepG2 cells generates reactive oxygen species (ROS), which activate the p38 mitogen-activated protein kinase (MAPK) pathway and the redox-sensitive transcription factors AP-1 and NF-kappaB, leading to the induction of the antioxidant manganese superoxide dismutase gene. The present study reports that AA decreases the HepG2 cell growth by 40% and 55% after a treatment for 24 and 48 h, respectively. This effect was blocked by an inhibitor of lipoxygenase/cytochrome P450 monooxygenase pathways and by the antioxidants. In addition, AA induced an oxidative stress, as an accumulation of malondialdehyde (MDA)-modified proteins, resulting to a generation of MDA and H(2)O(2) was observed after 24 h. This AA-induced oxidative stress was associated with the lack of an increase in the H(2)O(2)-degrading enzyme level. In contrast, 5,8,11,14-eicosatetraynoic acid, a nonmetabolizable analog of AA, had not effect. The peroxisome proliferator-activated receptor gamma (PPARgamma) with AA metabolites as ligands was upregulated by the fatty acid but was not involved in the AA effect because its transcriptional activity estimated by reporter gene assays was negatively controlled by p38 MAPK pathway. These findings suggest that the effect of AA on human hepatoma cell growth by inducing an oxidative stress may present a clinical interest in the treatment of the liver cancer.

The role of carotenoids in the prevention of human pathologies

Reactive oxygen species (ROS) and oxidative damage to biomolecules have been postulated to be involved in the causation and progression of several chronic diseases, including cancer and cardiovascular diseases, the two major causes of morbidity and mortality in Western world. Consequently dietary antioxidants, which inactivate ROS and provide protection from oxidative damage are being considered as important preventive strategic molecules. Carotenoids have been implicated as important dietary nutrients having antioxidant potential, being involved in the scavenging of two of the ROS, singlet molecular oxygen (1O2) and peroxyl radicals generated in the process of lipid peroxidation. Carotenoids are lipophilic molecules which tend to accumulate in lipophilic compartments like membranes or lipoproteins. Chronic ethanol consumption significantly increases hydrogen peroxide and decreases mitochondrial glutathione (GSH) in cells overexpressing CYP2E1. The depletion of mitochondrial GSH and the rise of hydrogen peroxide are responsible for the ethanol-induced apoptosis. Increased intake of lycopene, a major carotenoid in tomatoes, consumed as the all-trans-isomer attenuates alcohol induced apoptosis in 2E1 cells and reduces risk of prostate, lung and digestive cancers. Cancer-preventive activities of carotenoids have been associated as well as with their antioxidant properties and the induction and stimulation of intercellular communication via gap junctions which play a role in the regulation of cell growth, differentiation and apoptosis. Gap junctional communication between cells which may be a basis for protection against cancer development is independent of the antioxidant property.

Cyclooxygenase-2 contributes to dysmotility and enhanced excitability of myenteric AH neurones in the inflamed guinea pig distal colon

We have previously demonstrated that trinitrobenzene sulphonic acid (TNBS)-induced colitis in guinea pig is associated with hyperexcitability of myenteric AH neurones, enhanced synaptic activity in the myenteric plexus, increased serotonin (5-HT) availability in the mucosa, and decreased propulsive motor activity. The current study tested the hypothesis that the activation of cyclooxygenase (COX) contributes to these alterations in bowel functions. DFU inhibition of COX-2, but not SC-560 inhibition of COX-1, restored to normal levels the electrical properties of myenteric AH neurones, the proportion of S neurones exhibiting slow EPSPs, and the rate of propulsive motor activity. Neither inhibitor was effective in altering the level of inflammation, the increased availability of mucosal 5-HT, or the enhanced fast EPSPs in myenteric AH and S neurones. COX-2 expression is enhanced in the myenteric plexus and cells within the smooth muscle layers during colitis, possibly reflecting the site at which COX-2 inhibition acts to allow recovery of motor function. In support of this concept, COX-1, but not COX-2, inhibition was effective in restoring normal mucosal prostaglandin levels. These results indicate that the various changes that occur in the motor neural pathways of the distal colon in TNBS-induced colitis do not involve a single neuroimmune mechanism. COX-2 activation is a critical step in the enhanced excitability of AH neurones as well as diminished propulsive motility in TNBS colitis, whereas other yet to be resolved pathways, that do not involve COX-1 or COX-2 activation, lead to altered 5-HT content in the mucosa and an augmentation of fast EPSPs.

Dihomo-gamma-linolenic acid inhibits tumour necrosis factor-alpha production by human leucocytes independently of cyclooxygenase activity

Dietary oils (such as borage oil), which are rich in gamma-linolenic acid (GLA), have been shown to be beneficial under inflammatory conditions. Dihomo-GLA (DGLA) is synthesized directly from GLA and forms a substrate for cyclooxygenase (COX) enzymes, resulting in the synthesis of lipid mediators (eicosanoids). In the present study, the immunomodulatory effects of DGLA were investigated and compared with those of other relevant fatty acids. Freshly isolated human peripheral blood mononuclear cells (PBMC) were cultured in fatty acid (100 microm)-enriched medium for 48 hr. Subsequently, cells were stimulated with lipopolysaccharide (LPS) for 20 hr and the cytokine levels were measured, in supernatants, by enzyme-linked immunosorbent assay (ELISA). Phospholipids were analysed by gas chromatography. Fatty acids were readily taken up, metabolized and incorporated into cellular phospholipids. Compared with the other fatty acids tested, DGLA exerted pronounced modulatory effects on cytokine production. Tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-10 levels were reduced to 60% of control levels, whereas IL-6 levels were not affected by DGLA. Kinetic studies showed that peak levels of TNF-alpha, occurring early after LPS addition, were inhibited strongly, whereas IL-10 levels were not affected until 15 hr after stimulation. Both the reduction of cytokine levels and the decrease in arachidonic acid levels in these cells, induced by DGLA, were dose dependent, suggesting a shift in eicosanoid-subtype synthesis. However, although some DGLA-derived eicosanoids similarly reduced TNF-alpha levels, the effects of DGLA were probably not mediated by COX products, as the addition of indomethacin did not alter the effects of DGLA. In conclusion, these results suggest that DGLA affects cytokine production by human PBMC independently of COX activation.

CYP2U1, a novel human thymus- and brain-specific cytochrome P450, catalyzes omega- and (omega-1)-hydroxylation of fatty acids

Long chain fatty acids have recently emerged as critical signaling molecules in neuronal, cardiovascular, and renal processes, yet little is presently known about the precise mechanisms controlling their tissue distribution and bioactivation. We have identified a novel cytochrome P450, CYP2U1, which may play an important role in modulating the arachidonic acid signaling pathway. Northern blot and real-time PCR analysis demonstrated that CYP2U1 transcripts were most abundant in the thymus and the brain (cerebellum), indicating a specific physiological role for CYP2U1 in these tissues. Recombinant human CYP2U1 protein, expressed in baculovirus-infected Sf9 insect cells, was found to metabolize arachidonic acid exclusively to two region-specific products as determined by liquid chromatography-mass spectrometry. These metabolites were identified as 19- and 20-hydroxy-modified arachidonic acids by liquid chromatography-tandem mass spectrometry analysis. In addition to omega/omega-1 hydroxylation of arachidonic acid, CYP2U1 protein also catalyzed the hydroxylation of structurally related long chain fatty acid (docosahexaenoic acid) but not fatty acids such as lauric acid or linoleic acid. This is the first report of the cloning and functional expression of a new human member of P450 family 2, CYP2U1, which metabolizes long chain fatty acids. Based on the ability of CYP2U1 to generate bioactive eicosanoid derivatives, we postulate that CYP2U1 plays an important physiological role in fatty acid signaling processes in both cerebellum and thymus.

Role of monocytes in atherogenesis

This review focuses on the role of monocytes in the early phase of atherogenesis, before foam cell formation. An emerging consensus underscores the importance of the cellular inflammatory system in atherogenesis. Initiation of the process apparently hinges on accumulating low-density lipoproteins (LDL) undergoing oxidation and glycation, providing stimuli for the release of monocyte attracting chemokines and for the upregulation of endothelial adhesive molecules. These conditions favor monocyte transmigration to the intima, where chemically modified, aggregated, or proteoglycan- or antibody-complexed LDL may be endocytotically internalized via scavenger receptors present on the emergent macrophage surface. The differentiating monocytes in concert with T lymphocytes exert a modulating effect on lipoproteins. These events propagate a series of reactions entailing generation of lipid peroxides and expression of chemokines, adhesion molecules, cytokines, and growth factors, thereby sustaining an ongoing inflammatory process leading ultimately to lesion formation. New data emerging from studies using transgenic animals, notably mice, have provided novel insights into many of the cellular interactions and signaling mechanisms involving monocytes/macrophages in the atherogenic processes. A number of these studies, focusing on mechanisms for monocyte activation and the roles of adhesive molecules, chemokines, cytokines and growth factors, are addressed in this review.

Arachidonic acid activates a functional AP-1 and an inactive NF-kappaB complex in human HepG2 hepatoma cells

Exogenous arachidonic acid (AA) has been shown to induce the antioxidant manganese superoxide dismutase gene by reactive oxygen species (ROS) derived from AA metabolism and the participation of the p38 mitogen-activated protein kinase (MAPK) pathway in human HepG2 hepatoma cells. The goal of this study was to investigate the effect of AA on the activation of the two redox-sensitive transcription factors AP-1 and NF-kappaB in HepG2 cells. Using electrophoretic mobility shift assays, DNA-binding activities of AP-1 and NF-kappaB were markedly increased in AA-treated HepG2 cells. The c-Jun and c-Fos proteins were identified as components of the AA-induced AP-1 complex and their levels were increased. AA-activated NF-kappaB complex was constituted as a p50 homodimer resulting in a nuclear translocation for this protein only. Moreover, no degradation of IkappaBalpha was observed. These results were contrasted to the interleukin-1beta-activated p50/p65 complex used as a positive control. Using 5,8,11,14-eicosatetraynoic acid and inhibitors of AA metabolism, AP-1 and NF-kappaB activation required the lipoxygenase/cytochrome P450 monooxygenase pathways. In addition, antioxidants inhibited the AA-induced AP-1 and NF-kappaB activation, suggesting a role of ROS released from the AA metabolism. In reporter gene assays, AA induced the transcriptional activity of AP-1 but not that of NF-kappaB. Further investigations showed that the AA-induced transcriptional activity of AP-1 was regulated by protein kinase C and p38 MAPK pathways. These results suggest that the functional AP-1 activated by AA and coupled to that of p38 MAPK pathway may play an important role in response to ROS induced by AA metabolism in HepG2 cells without the involvement of the NF-kappaB pathway.

Lycopene attenuates arachidonic acid toxicity in HepG2 cells overexpressing CYP2E1

Arachidonic acid (AA) was shown to be toxic to HepG2 cells expressing cytochrome P4502E1 (CYP2E1) because of oxidative stress. The aim of this study was to investigate whether lycopene, a carotenoid with high anti-oxidant capacity, protects HepG2 cells expressing CYP2E1 against AA toxicity. In preliminary experiments, lycopene as well as placebo (vehicle) were not toxic in the three types of cells tested: HepG2 cells, HepG2 cells transfected with pCI-neo (Neo) or pCI-neo/2E1 (2E1). AA produced toxic effects, especially in the 2E1 cells, and caused a remarkable increase in hydrogen peroxide production and lipid peroxidation compared to the Neo and HepG2 cells. Lycopene had a protective effect whereas the placebo did not. This was due, at least in part, to inhibition of hydrogen peroxide production and of the resulting lipid peroxidation, confirming the potent anti-oxidant properties of lycopene and its suitability for clinical studies.

Lipids and the immune response: from molecular mechanisms to clinical applications

PURPOSE OF REVIEW

This review critically evaluates recent studies investigating the effects of fatty acids on immune and inflammatory responses in both healthy individuals and in patients with inflammatory diseases, with some reference to animal studies where relevant. It examines recent findings describing the cellular and molecular basis for the modulation of immune function by fatty acids. The newly emerging area of diet-genotype interactions will also be discussed, with specific reference to the anti-inflammatory effects of fish oil.

RECENT FINDINGS

Fatty acids are participants in many intracellular signalling pathways. They act as ligands for nuclear receptors regulating a host of cell responses, they influence the stability of lipid rafts, and modulate eicosanoid metabolism in cells of the immune system. Recent findings suggest that some or all of these mechanisms may be involved in the modulation of immune function by fatty acids.

SUMMARY

Human studies investigating the relationship between dietary fatty acids and some aspects of the immune response have been disappointingly inconsistent. This review presents the argument that most studies have not been adequately powered to take into account the influence of variation (genotypic or otherwise) on parameters of immune function. There is well-documented evidence that fatty acids modulate T lymphocyte activation, and recent findings describe a range of potential cellular and molecular mechanisms. However, there are still many questions remaining, particularly with respect to the roles of nuclear receptors, for which fatty acids act as ligands, and the modulation of eicosanoid synthesis, for which fatty acids act as precursors.

Reactive oxygen species in sustained airway constriction induced by citric acid aerosol inhalation

We tested if there is a direct relationship between reactive oxygen species and citric acid-induced airway constriction. Guinea pigs were divided into two groups: control and dimethylthiourea (a hydroxyl radical scavenger). The animals in each group were further separated into four subgroups: baseline, recovery 2-3 min, recovery 10 min, and recovery 20 min. Each animal was anesthetized, cannulated, paralyzed, and artificially ventilated. Citric acid aerosol inhalation caused the following significant changes in the control group during the recovery period: airway constriction for at least 20 min, increases in luminol-amplified t-butyl hydroperoxide-initiated chemiluminescence counts in the bronchoalveolar lavage samples at 2-3 and 20 min, an increase in bronchoalveolar lavage fluid substance P level at 2-3 min, and elevations in the bronchoalveolar lavage fluid total cell and neutrophil numbers at 20 min. All citric acid-induced alterations were prevented by dimethylthiourea pretreatment. These results suggest that citric acid inhalation induces the initial release of reactive oxygen species and tachykinins, which causes further cellular infiltration and sustained airway constriction.

85-kDa cytosolic phospholipase A2 mediates peroxisome proliferator-activated receptor gamma activation in human lung epithelial cells

The 85-kDa cytosolic phospholipase A(2) (cPLA(2)) plays an important role in the control of arachidonic acid metabolism. This study was designed to investigate the possible contributions of cPLA(2) and group IIA secretory phospholipase A(2) (sPLA(2)) in the regulation of peroxisome proliferator-activated receptor (PPAR)-mediated gene transcription in human airway epithelial cells. Primary normal human bronchial epithelial cells and human lung epithelial cell lines BEAS 2B, A549, and NCI-H292 all express PPARgamma and -beta. Overexpression of cPLA(2) in BEAS 2B cells and primary bronchial epithelial cells resulted in a significant increase of PPARgamma-mediated reporter activity. In contrast, overexpression of group IIA sPLA(2) had no effect on PPARgamma activation. The PPARgamma activity in A549 cells was significantly inhibited by the cPLA(2) inhibitor arachidonyltrifluoromethyl ketone but not by the sPLA(2) inhibitor LY311727 and the iPLA(2) inhibitor HELSS. Activation of cPLA(2) by the calcium ionophore, induced a dose-dependent increase of PPAR activity in normal human bronchial epithelial cells and in the A549 cells. Electrophoretic mobility shift assays show that the binding between PPAR isolated from A549 cells and peroxisome proliferator response element (PPRE) is enhanced by but partially blocked by the cPLA(2) inhibitors arachidonyltrifluoromethyl ketone and methyl arachidonyl fluorophosphate. Finally, NS 398, a COX-2 inhibitor, partially blocked the effect on PPAR activity and binding to the PPRE suggesting involvement of COX-2 metabolites in PPRE activation. The above results demonstrate a novel function of cPLA(2) in the control of PPARgamma activation in human lung epithelial cells.

The modulatory effects of prostaglandin-E on cytokine production by human peripheral blood mononuclear cells are independent of the prostaglandin subtype

The production of inflammatory mediators, relevant to (auto)immune diseases and chronic inflammatory conditions, can be modulated by dietary intake of n-3 and n-6 long chain polyunsaturated fatty acids (PUFAs). It was suggested that these effects are related to the formation of different series of eicosanoids, in particular prostaglandin-E (PGE). In this study we investigated whether prostaglandin subtypes metabolized from arachidonic acid (PGE2), dihomo-gamma-linolenic acid (PGE1) or eicosapentaenoic acid (PGE3) have different effects on T-cell proliferation and cytokine production in vitro. Freshly isolated human peripheral blood mononuclear cells (PBMC) were stimulated with concanavalin A (ConA) or lipopolysaccharide (LPS) in the presence or absence of exogenous PGE1, PGE2 or PGE3. We found that tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma) and to a lesser extent interleukin (IL)-10 production was inhibited by all PGE-subtypes in ConA-stimulated PBMC concomitant with unaffected IL-2 levels. The modulated cytokine production of ConA stimulated cells was independent of T-cell proliferation. PGE2 and PGE1 moderately stimulated proliferation, while PGE3 inhibited the proliferative response to some extent. In LPS-stimulated PBMC, TNF-alpha production was inhibited by all PGE-subtypes, whereas IL-6 remained unaffected and IL-10 production was increased. Time course experiments on the effects of PGE-subtypes on cytokine production after ConA or LPS stimulation showed these effects to be time dependent, but indifferent of the prostaglandin subtype added. Overall, the modulatory effects of PGE on cytokine production were irrespective of the subtype. This may implicate that the immunomodulatory effects of PUFAs, with respect to cytokine production, are not caused by a shift in the subtype of PGE.

Endothelium-dependent hyperpolarization to acetylcholine in carotid artery of guinea pig: role of lipoxygenase

This study was designed to determine whether lipoxygenase-dependent metabolites of arachidonic acid are involved in the endothelium-dependent hyperpolarization of the guinea pig carotid artery. The membrane potential of vascular smooth muscle cells was measured with intracellular microelectrodes and potassium channels were studied on freshly isolated cells with the patch-clamp technique. Acetylcholine-induced hyperpolarizations were not affected by arachidonyl trifluoromethyl ketone (AACOCF3), quinacrine (phospholipase A inhibitors), or eicosatetraenoic acid (nonspecific inhibitor of lipoxygenase, cytochrome P450, and cyclooxygenase). In contrast, cinnamyl-3,4 dihydroxy-alpha-cyanocinnamate (CDC) and AA861 (lipoxygenase inhibitors) as well as 1-(6-(17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino) hexyl)-1H-pyrrole-2,5-dione (U-73122) (phospholipase C inhibitor) produced a significant inhibition of the hyperpolarization. An opener of intermediate conductance calcium-activated potassium channels, 1-ethyl-2-benzamidazolinone (1-EBIO), induced a hyperpolarization that was unaffected by AACOCF3, CDC, AA861, or U-73122 but was inhibited by charybdotoxin. (+/-)12-hydroxy-eicosatetraenoic acid (12-HETE) and 12(S)-hydroperoxy-eicosatetraenoic acid (12(S)-HpETE) did not induce any significant changes in membrane potential. CDC inhibited the voltage-gated potassium current and increased the large conductance calcium-activated potassium current whereas AA861 inhibited both potassium currents. These results confirm that, in the isolated carotid artery of the guinea pig, stimulation of endothelial muscarinic receptors involves phospholipase C activation and indicate that the activation of phospholipase A2 and the release of lipoxygenase metabolites is unlikely to explain endothelium-dependent hyperpolarization.

Angiotensin II receptor-independent antiinflammatory and antiaggregatory properties of losartan: role of the active metabolite EXP3179

Angiotensin II (Ang II) type 1 receptor (AT(1)) antagonists such as losartan (LOS) are widely used for the treatment of hypertension and elicit antiinflammatory and antiaggregatory in vitro and in patients, although the underlying mechanism are unclear. Following computer-based molecule similarity, we proposed that on cytochrome-P450 degradation, the LOS metabolite EXP3179 is generated, which shows molecule homology to indomethacin, a cyclooxygenase inhibitor with antiinflammatory and antiaggregatory properties. Subsequently, serum-levels of EXP3179 were determined for 8 hours in patients receiving a single oral dose of 100 mg LOS. High-performance liquid chromatography followed by liquid chromatography-mass spectrometry (GC-MS) [corrected] from serum samples revealed a maximum of 10(-7) mol/L for EXP3179 peaking between 3 to 4 hours. The increase in serum-EXP3179 levels was associated with a significant reduction in platelet aggregation in vivo (-35+/-4%, P<0.001 versus control). EXP3179 generation was investigated in a chemical reaction mimicking the liver cytochrome-P450-dependent LOS-degradation and human endothelial cells were exposed to Ang II or lipopolysaccharides (LPS) in the presence of EXP3179 (10(-7) mol/L). LPS- and Ang II-induced COX-2 transcription was abolished by EXP3179. Moreover, EXP3179 significantly reduced Ang II- and LPS-induced formation of prostaglandin F2alpha as determined by GC-MS [corrected]. Thus, antiinflammatory properties of LOS are mediated via its EXP3179 metabolite by abolishing COX-2 mRNA upregulation and COX-dependent TXA2 and PGF2alpha generation. Serum levels of EXP3179 are detectable in patients in concentrations that exhibit antiinflammatory and antiaggregatory properties in vitro.

85-kDa cPLA(2) plays a critical role in PPAR-mediated gene transcription in human hepatoma cells

In an effort to understand the role of key eicosanoid-forming enzymes in the activation of peroxisome proliferator-activated receptor (PPAR), this study was designed to evaluate the possible contributions of cytosolic phospholipase A(2) (cPLA(2)) and group IIA secretory phospholipase A(2) (sPLA(2)) in the regulation of PPAR-mediated gene transcription in a human hepatoma cell line (HepG2). The HepG2 cells express both PPAR-alpha and -gamma but not PPAR-beta. Overexpression of cPLA(2), but not group IIA sPLA(2) in the HepG2 cells, caused a significantly increased PPAR-alpha/gamma-mediated reporter activity. Antisense inhibition of cPLA(2) resulted in a significantly decreased PPAR-alpha/gamma activity. The PPAR-alpha/gamma-induced gene transcription in the HepG2 cells was inhibited by the cPLA(2) inhibitors methyl arachidonyl fluorophosphonate and arachidonyltrifluoromethyl ketone, but not by the sPLA(2) inhibitor LY311727. The expression of PPAR-alpha-mediated endogenous gene apolipoprotein A-II was increased in cells with overexpression of cPLA(2), decreased in cells with antisense inhibition of cPLA(2), but unaltered in cells with overexpression of group IIA sPLA(2). The above results demonstrated an important role of cPLA(2), but not group IIA sPLA(2) in the control of PPAR activation. The cPLA(2)-mediated PPAR activation was likely mediated by arachidonic acid and prostaglandin E(2). This study reveals a novel intracellular function of cPLA(2) in PPAR activation in HepG2 cells. The cPLA(2) thus may represent a potential therapeutic target for the control of PPAR-related liver and metabolic disorders such as obesity, lipid metabolic disorders, diabetes mellitus, and atherosclerosis.

Lysophosphatidic acid activates the 70-kDa S6 kinase via the lipoxygenase pathway

Many hormones are known to activate the 70-kDa S6 kinase (p70(S6K)). The signalling pathways mediating p70(S6K) activation are only partially characterized. We investigate, in this report, the mechanisms by which lysophosphatidic acid (LPA) activates p70(S6K). We observed that p70(S6K) activation was conventional, in that it was sensitive to both rapamycin and PI3 kinase inhibition. p70(S6K) activation appeared to be caused by the activation of several phospholipase pathways. LPA was an effective stimulus of phospholipase C induced intracellular calcium mobilization, which appeared to participate in p70(S6K) activation. Similarly, the effect of LPA on p70(S6K) activity was antagonized by butan-1-ol but not butan-2-ol suggesting the involvement of agonist stimulated phospholipase D activity. Further, antagonism of the phospholipase A(2) and lipoxygenase pathways attenuated p70(S6K) activation indicating a novel mechanism of p70(S6K) regulation. We conclude that in Swiss 3T3 cells LPA coordinates activation of several phospholipases to regulate p70(S6K).

In-vitro and in-vivo immunomodulatory effects of syringin

Syringin was found to possess immunomodulatory activity by which it inhibited the in-vitro immunohaemolysis of antibody-coated sheep erythrocytes by guinea-pig serum through suppression of C3-convertase of the classical complement. In this study, we examined its in-vitro and in-vivo activity on tumour necrosis factor (TNF)-alpha and nitric oxide (NO) production, CD4+ T cell and CD8+ cytotoxic T cell (CTLL-2) proliferation, and croton oil-, arachidonic acid- and fluorescein-isothiocynate (FITC)-induced mouse ear oedema model. Syringin significantly inhibited both TNF-alpha production from lipopolysaccharide (LPS)-stimulated RAW264.7 cells and CD8+ T cell (CTLL-2) proliferation in a dose-dependent manner, whereas neither NO production nor CD4+ T cell proliferation were blocked even by high concentrations of syringin. In the invivo experiments, syringin also significantly suppressed FITC-induced ear oedema in mice but not the ear oedema induced by croton or arachidonic acid. These results suggest that syringin may be implicated as an immunomodulator having an anti-allergic effect rather than an anti-inflammatory effect. The anti-allergic effect of syringin seems to be due, in part, to inhibition of TNF-alpha production and cytotoxic T cell proliferation.

Modulation of cell-substrate adhesion by arachidonic acid: lipoxygenase regulates cell spreading and ERK1/2-inducible cyclooxygenase regulates cell migration in NIH-3T3 fibroblasts

Adhesion of cells to an extracellular matrix is characterized by several discrete morphological and functional stages beginning with cell-substrate attachment, followed by cell spreading, migration, and immobilization. We find that although arachidonic acid release is rate-limiting in the overall process of adhesion, its oxidation by lipoxygenase and cyclooxygenases regulates, respectively, the cell spreading and cell migration stages. During the adhesion of NIH-3T3 cells to fibronectin, two functionally and kinetically distinct phases of arachidonic acid release take place. An initial transient arachidonate release occurs during cell attachment to fibronectin, and is sufficient to signal the cell spreading stage after its oxidation by 5-lipoxygenase to leukotrienes. A later sustained arachidonate release occurs during and after spreading, and signals the subsequent migration stage through its oxidation to prostaglandins by newly synthesized cyclooxygenase-2. In signaling migration, constitutively expressed cyclooxygenase-1 appears to contribute approximately 25% of prostaglandins synthesized compared with the inducible cyclooxygenase-2. Both the second sustained arachidonate release, and cyclooxygenase-2 protein induction and synthesis, appear to be regulated by the mitogen-activated protein kinase extracellular signal-regulated kinase (ERK)1/2. The initial cell attachment-induced transient arachidonic acid release that signals spreading through lipoxygenase oxidation is not sensitive to ERK1/2 inhibition by PD98059, whereas PD98059 produces both a reduction in the larger second arachidonate release and a blockade of induced cyclooxygenase-2 protein expression with concomitant reduction of prostaglandin synthesis. The second arachidonate release, and cyclooxygenase-2 expression and activity, both appear to be required for cell migration but not for the preceding stages of attachment and spreading. These data suggest a bifurcation in the arachidonic acid adhesion-signaling pathway, wherein lipoxygenase oxidation generates leukotriene metabolites regulating the spreading stage of cell adhesion, whereas ERK 1/2-induced cyclooxygenase synthesis results in oxidation of a later release, generating prostaglandin metabolites regulating the later migration stage.

Enhanced cyclooxygenase-2 mRNA expression in human gingival fibroblasts induced by cell contact with human lymphocytes

Prostaglandins, especially prostaglandin E2 (PGE2), play a crucial role in the pathogenesis of periodontal disease. We have previously reported that inflammatory mediators interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha) increase the production of PGE2 in human gingival fibroblasts. In this study, we investigated the effect of cell-to-cell interactions between gingival fibroblasts and lymphocytes on PGE2 production by using co-culture technique. Cell-to-cell contact between gingival fibroblasts and lymphocytes synergistically enhanced the production of PGE2 in co-cultures. In contrast to lymphocytes, the cyclooxygenase-2 (COX-2) mRNA expression in gingival fibroblasts was strongly enhanced following cell contact between gingival fibroblasts and lymphocytes. The level of COX-1 mRNA expression, however, was not affected either in gingival fibroblasts or in lymphocytes by the interactions between fibroblasts and lymphocytes. The study demonstrates that cell contact between gingival fibroblasts and lymphocytes strongly stimulates PGE2 production partly due to enhanced COX-2 mRNA expression in gingival fibroblasts. The cell-to-cell contact between gingival fibroblasts and lymphocytes should be considered as an important regulatory aspect for the enhancement of PGE2 in periodontal disease.

Phospholipase from Trypanosoma brucei releases arachidonic acid by sequential sn-1, sn-2 deacylation of phospholipids

Previously, we showed that arachidonic acid (AA) stimulates Ca2+ currents in pathogenic Trypanosoma brucei (Eintracht J, Maathai R, Mellors A, Ruben L. Calcium entry in Trypanosoma brucei is regulated by phospholipase A2 and arachidonic acid. Biochem. J 1998;336:659-666). Here we examine the mechanism used by T. brucei to release AA from the sn-2 position of diacyl glycero-phospholipids. We report that T. brucei accomplishes this feat in the apparent absence of phospholipase A2 (PLA2). Instead, deacylation is initiated at the sn-1 position, followed by acyl migration and hydrolysis with LysoPLA. Neither whole cell homogenates nor enriched protein fractions could release AA from substrates whose sn-1 position contained a non-hydrolyzable alkyl ether linkage. These same fractions however, released AA from ester linked phospholipids, and TLC analysis of the reaction products supported the sequential deacylation process. The release of sn-2 AA from 1-palmitoyl-2-[1-14C]arachidonyl-sn-glycero-3-PC was linear up to 90 min at an average rate of 50 nmol x min(-1) x mg(-1). sn-2 AA was processed more efficiently than sn-2 palmitate. The reaction was also greatest for: LysoPC>diacyl-PC (sn-1 labeled)>diacyl-PC (sn-2 labeled). Product formation was sensitive to polar head group, and PI was processed at less than 10% the rate of PC or PE. The enzymatic deacylation was inhibited by the serine specific reagent, methyl arachidonyl fluorophosphonate (MAFP) and the cysteine reagent N-ethylmaleimide (NEM). Both NEM and MAFP inhibited LysoPLA activity under conditions where there was little effect on PLA1 activity. Overall, we conclude that T. brucei can release AA from diacyl glycero-phospholipids by a sequential deacylation process. Two independent active sites appear to be involved. Interestingly, a high percentage of inner leaflet phospholipids are protected from degradation since they occur in the non-hydrolyzable 1-alkyl ether form.

Increased 15-HPETE production decreases prostacyclin synthase activity during oxidant stress in aortic endothelial cells

Selenium (Se) is an integral component of glutathione peroxidase and is able to detoxify peroxides that can affect arachidonic acid (AA) metabolism, thereby influencing eicosanoid biosynthesis. This study investigated the effects of oxidant stress, a consequence of Se deficiency, on eicosanoid formation and important key enzyme expression in bovine aortic endothelial cells (BAEC). Bovine aortic endothelial cells cultured in Se-deficient media and stimulated with tumor necrosis factor alpha or H2O2 produced significantly less prostacyclin (PGI(2)) and more 15-hydroxyeicosatetraenoic acid, 15-hydroperoxyeicosatetraenoic acid (15-HPETE), and thromboxane than Se-supplemented BAEC. Additionally, reverse transcription polymerase chain reaction and immunoblotting determined that the mRNA and protein levels of the eicosanoid forming enzymes cyclooxygenase-1 (COX1), cyclooxygenase-2 (COX2), and PGI synthase were not significantly changed. The addition of 15-HPETE to Se-supplemented BAEC inhibited the production of PGI(2) suggesting that the accumulation of lipid hydroperoxides during Se-deficiency may be the underlying factor in the altered eicosanoid production during Se deficiency. Furthermore, inhibition of COX and addition of PGH(2) to Se-deficient or Se-supplemented BAEC still resulted in lower PGI(2) formation by Se-deficient cells. Together, these results suggest that Se deficiency modifies eicosanoid production by affecting the activity of key enzymes, particularly PGI synthase, rather than their transcription or translation.