Neuroinflammation plays a critical role in the progression of many neurodegenerative diseases and neuropsychiatric illnesses. It is evident that microglia in particular are central to mediating the effects of neuroinflammation. Activated microglia release a number of cytokines and chemokines, which in turn activate many signal transduction pathways. For instance, interleukin-1 beta and tumor necrosis factor alpha regulate transcription of a number of genes within the brain including proinflammatory products of the arachidonic acid (AA) cascade. Co-activation of pro-inflammatory markers and associated cytotoxic products during neuroinflammation process are detrimental to neurons by altering the synaptic proteins. In this review, we discuss both neuroinflammation as well as excitotoxicity insults reduce synaptic markers such as synaptophysin and drebrin in rat brain. Further we discuss here, neurodegenerative and neuropsychiatric illness are associated with increased neuroinflammatory and excitotoxicity markers as well as upregulated brain arachidonic acid markers and the loss of synaptic markers. The decrease in synaptic markers might contribute to reported cognitive defects in neurodegenerative and neuropsychiatric illnesses.
Linoleic acid (LA) is the most abundant polyunsaturated fatty acid in human diets, a major component of human tissues, and the direct precursor to the bioactive oxidized LA metabolites (OXLAMs), 9- and 13 hydroxy-octadecadienoic acid (9- and 13-HODE) and 9- and 13-oxo-octadecadienoic acid (9- and 13-oxoODE). These four OXLAMs have been mechanistically linked to pathological conditions ranging from cardiovascular disease to chronic pain. Plasma OXLAMs, which are elevated in Alzheimer’s dementia and non-alcoholic steatohepatitis, have been proposed as biomarkers useful for indicating the presence and severity of both conditions. Because mammals lack the enzymatic machinery needed for de novo LA synthesis, the abundance of LA and OXLAMs in mammalian tissues may be modifiable via diet. To examine this issue in humans, we measured circulating LA and OXLAMs before and after a 12-week LA lowering dietary intervention in chronic headache patients. Lowering dietary LA significantly reduced the abundance of plasma OXLAMs, and reduced the LA content of multiple circulating lipid fractions that may serve as precursor pools for endogenous OXLAM synthesis. These results show that lowering dietary LA can reduce the synthesis and/or accumulation of oxidized LA derivatives that have been implicated in a variety of pathological conditions. Future studies evaluating the clinical implications of diet-induced OXLAM reductions are warranted.
Linoleic acid; HODE; hydroxy-octadecadienoic acid; oxoODE; oxo-octadecadienoic acid; oxidation; OXLAM; PUFA; polyunsaturated fatty acid
HIV-1 transgenic rat; fatty acid; brain; liver; heart; plasma; arachidonic; docosahexaenoic; polyunsaturated fatty acids (PUFA); concentration; composition; metabolism
Docosapentaenoic acid (DPAn-6, 22:5n-6) is an n-6 polyunsaturated fatty acid (PUFA) whose brain concentration can be increased in rodents by dietary n-3 PUFA deficiency, which may contribute to their behavioral dysfunction. We used our in vivo intravenous infusion method to see if brain DPAn-6 turnover and metabolism also were altered with deprivation. We studied male rats that had been fed for 15 weeks post-weaning an n-3 PUFA adequate diet containing 4.6% alpha-linolenic acid (α-LNA, 18:3n-3) or a deficient diet (0.2% α-LNA), each lacking docosahexaenoic acid (22:6n-3) and arachidonic acid (AA, 20:4n-6). [1-14C]DPAn-6 was infused intravenously for 5 min in unanesthetized rats, after which the brain underwent high-energy microwaving, and then was analyzed. The n-3 PUFA deficient compared with adequate diet increased DPAn-6 and decreased DHA concentrations in plasma and brain, while minimally changing brain AA concentration. Incorporation rates of unesterified DPAn-6 from plasma into individual brain phospholipids were increased 5.2–7.7 fold, while turnover rates were increased 2.1–4.7 fold. The observations suggest that increased metabolism and brain concentrations of DPAn-6 and its metabolites, together with a reduced brain DHA concentration, contribute to behavioral and functional abnormalities reported with dietary n-3 PUFA deprivation in rodents.
docosapentaenoic; docosahexaenoic; deficient; turnover; kinetics; brain; diet; n-6; PUFA; arachidonic; rat; phospholipase A2
Calcium-independent phospholipase A2 group VIA (iPLA2β) releases docosahexaenoic acid (DHA) from phospholipids in vitro. Mutations in the iPLA2β gene, PLA2G6, are associated with dystonia-parkinsonism and infantile neuroaxonal dystrophy. To understand the role of iPLA2β in brain, we applied our in vivo kinetic method using radiolabeled DHA in 4 to 5-month-old wild type (iPLA2β+/+) and knockout (iPLA2β−/−) mice, and measured brain DHA kinetics, lipid concentrations, and expression of PLA2, cyclooxygenase (COX), and lipoxygenase (LOX) enzymes. Compared to iPLA2β+/+ mice, iPLA2β−/− mice showed decreased rates of incorporation of unesterified DHA in plasma into brain phospholipids, reduced concentration of several fatty acid residues (including DHA) esterified in ethanolamine- and serine-glycerophospholipids, and increased lysophospholipid fatty acid concentrations. DHA turnover rates in brain phospholipids did not differ between genotypes. In iPLA2β−/− mice, brain levels of iPLA2β mRNA, protein, and activity were decreased, as was the iPLA2γ (Group VIB PLA2) mRNA level. Brain levels of secretory sPLA2-V mRNA, protein, and activity and cytosolic cPLA2-IVA mRNA were increased in iPLA2β−/− mice. Levels of COX-1 protein were decreased in brain, while COX-2 protein and mRNA were increased. Levels of 5-, 12-, and 15-LOX proteins did not differ significantly between genotypes. Thus, genetic iPLA2β deficiency in mice is associated with profound reorganization of lipid-metabolizing enzyme expression and of phospholipid fatty acid content of brain (particularly of DHA), which may be relevant to the neurologic abnormalities in humans with iPLA2β mutations.
iPLA2; knockout; mice; docosahexaenoic acid; brain; turnover; incorporation; lipid; PLA2G6; phospholipid metabolism
In rats, FDA-approved mood stabilizers used for treating bipolar disorder (BD) selectively downregulate brain markers of the arachidonic acid (AA) cascade, which are upregulated in postmortem BD brain. Phase III clinical trials show that gabapentin (GBP) is ineffective in treating BD. We hypothesized that GBP would not alter the rat brain AA cascade. Chronic GBP (10 mg/kg body weight, injected i.p. for 30 days) compared to saline vehicle did not significantly alter brain expression or activity of AA-selective cytosolic phospholipase A2 (cPLA2) IVA or secretory (s) PLA2 IIA, activity of cyclooxygenase-2, or prostaglandin or thromboxane concentrations. Plasma AA concentration was unaffected. These results, taken with evidence of an upregulated AA cascade in the BD brain and that approved mood stabilizers downregulate rat brain AA cascade, support the hypothesis that effective anti-BD drugs act by targeting the AA cascade, and suggest that the rat model might be used for drug screening
gabapentin; arachidonic acid; bipolar disorder; mood stabilizer; drug screening
Docosahexaenoic acid (DHA) is required for normal brain function. The concentration of DHA in the brain depends on both diet and liver metabolism.
To determine rat brain DHA concentration and consumption in relation to dietary n-3 (omega-3) polyunsaturated fatty acid (PUFA) content and liver secretion of DHA derived from circulating α-linolenic acid (α-LNA).
Following weaning, male rats were fed for 15 weeks either: (1) a diet with a high DHA and α-LNA content, (2) an n-3 PUFA “adequate” diet containing 4.6% α-LNA but no DHA, or (3) an n-3 PUFA “deficient” diet containing 0.2% α-LNA and no DHA. Brain DHA consumption rates were measured following intravenous infusion in unanesthetized rats of [1-14C]DHA, whereas liver and brain DHA synthesis rates were measured by infusing [1-14C]α-LNA.
Brain DHA concentrations equaled 17.6 μm/g, 11.4 μm/g and 7.14 μm/g in rats on diets 1, 2 and 3, respectively. With each diet, the rate of brain DHA synthesis from α-LNA was much less than the brain DHA consumption rate, whereas the liver synthesis-secretion rate was 5-10 fold higher. Higher elongase 2 and 5 and desaturase Δ5 and Δ6 activities in liver than in brain accounted for the higher liver DHA synthesis rates; these enzymes were transcriptionally upregulated in liver but not in brain of rats fed the deficient diet.
While DHA is essential to normal brain function, this need might be covered by dietary α-LNA when liver metabolic conversion machinery is intact and the diet has a high α-LNA content.
docosahexaenoic acid; liver; brain; rat; n-3; omega-3; PUFA; imaging; metabolism; diet; synthesis; α-linolenic acid
We developed a novel method to study dopaminergic neurotransmission using positron emission tomography (PET) with [1-11C]arachidonic acid ([1-11C]AA). Previous preclinical studies have shown the utility of [1-11C]AA as a marker of signal transduction coupled to cytosolic phospholipase A2 (cPLA2). Using [1-11C]AA and [15O]water PET, we measured regional incorporation coefficients K* for AA and regional cerebral blood flow (rCBF), respectively, in healthy male volunteers given the D1/D2 agonist (10 or 20 μg/kg subcutaneous) apomorphine. We confirmed a robust central dopaminergic response to apomorphine by observing significant increases in the serum concentration of growth hormone. We observed significant increases, as well as decreases in K* and increases in rCBF in response to apomorphine. These changes remained significant after covarying for handedness and apomorphine dosage. The magnitude of increases in K* was lower than those in our previous animal experiments, likely reflecting the smaller dose of apomorphine used in the current human study. Changes in K* may reflect neuronal signaling downstream of activated D2-like receptors coupled to cPLA2. Changes in rCBF are consistent with previous studies showing net functional effects of D1/D2 activation. [1-11C]AA PET may be useful for studying disturbances of dopaminergic neurotransmission in conditions such as Parkinson's disease and schizophrenia.
apomorphine; cPLA2; D1/D2 receptors; [1-11C]arachidonate PET; regional cerebral blood flow
Dietary n-6 polyunsaturated fatty acid (PUFA) deprivation in rodents reduces brain arachidonic acid (20:4n-6) concentration and 20:4n-6-preferring cytosolic phospholipase A2 (cPLA2-IVA) and cyclooxygenase (COX)-2 expression, while increasing brain docosahexaenoic acid (DHA, 22:6n-3) concentration and DHA-selective Ca2+-independent iPLA2-VIA expression. We hypothesized that these changes are accompanied by upregulated brain DHA metabolic rates. Using a fatty acid model, brain DHA concentrations and kinetics were measured in unanesthetized male rats fed, for 15 weeks post-weaning, an n-6 PUFA “adequate” (31.4 wt% linoleic acid) or “deficient” (2.7 wt% linoleic acid) diet, each lacking 20:4n-6 and DHA. [1-14C]DHA was infused intravenously, arterial blood was sampled, and the brain was microwaved at 5 min and analyzed. Rats fed the n-6 PUFA deficient compared with adequate diet had significantly reduced n-6 PUFA concentrations in brain phospholipids but increased eicosapentaenoic acid (EPA, 20:5n-3), docosapentaenoic acidn-3 (DPAn-3, 22:5n-3) and DHA (by 9.4%) concentrations, particularly in ethanolamine glycerophospholipid. Incorporation rates of unesterified DHA from plasma, which represent DHA metabolic loss from brain, were increased 45% in brain phospholipids, as was DHA turnover. Increased DHA metabolism following dietary n-6 PUFA deprivation may increase brain concentrations of antiinflammatory DHA metabolites, which with a reduced brain n-6 PUFA content, likely promote neuroprotection. (199 words)
linoleic acid; arachidonic PUFA; diet; turnover; metabolism; docosahexaenoic; kinetics; brain; alpha-linolenic; rat
The polyunsaturated fatty acids (PUFAs), arachidonic acid (AA, 20:4n-6) and docosahexaenoic acid (DHA, 22:6n-3), important second messengers in brain, are released from membrane phospholipid following receptor-mediated activation of specific phospholipase A2 (PLA2) enzymes. We developed an in vivo method in rodents using quantitative autoradiography to image PUFA incorporation into brain from plasma, and showed that their incorporation rates equal their rates of metabolic consumption by brain. Thus, quantitative imaging of unesterified plasma AA or DHA incorporation into brain can be used as a biomarker of brain PUFA metabolism and neurotransmission. We have employed our method to image and quantify effects of mood stabilizers on brain AA/DHA incorporation during neurotransmission by muscarinic M1,3,5, serotonergic 5-HT2A/2C, dopaminergic D2-like (D2, D3, D4) or glutamatergic N-methyl-D-aspartic acid (NMDA) receptors, and effects of inhibition of acetylcholinesterase, of selective serotonin and dopamine reuptake transporter inhibitors, of neuroinflammation (HIV-1 and lipopolysaccharide) and excitotoxicity, and in genetically modified rodents. The method has been extended for the use with positron emission tomography (PET), and can be employed to determine how human brain AA/DHA signaling and consumption are influenced by diet, aging, disease and genetics.
arachidonic acid; bipolar disorder; brain imaging; docosahexaenoic acid; mood stabilizers; neuroinflammation
Background and Objective
Hyperdopaminergic signaling and an upregulated brain arachidonic acid (AA) cascade may contribute to bipolar disorder (BD). Lithium and carbamazepine, FDA-approved for the treatment of BD, attenuate brain dopaminergic D2-like (D2, D3, and D4) receptor signaling involving AA when given chronically to awake rats. We hypothesized that valproate (VPA), with mood-stabilizing properties, would also reduce the D2-like-mediated signaling via AA.
An acute dose of quinpirole (1 mg/kg) or saline was administered to unanesthetized rats that had been treated for 30 days with a therapeutically relevant dose of VPA (200 mg/kg/day) or vehicle. Regional brain AA incorporation coefficients, k*, and incorporation rates, Jin, markers of AA signaling and metabolism, were measured by quantitative autoradiography after intravenous [1-14C]AA infusion. Whole brain concentrations of prostaglandin (PG)E2 and thromboxane (TX)B2 also were measured.
Quinpirole compared to saline significantly increased k* in 40 of 83 brain regions, and increased brain concentrations of PGE2 in chronic vehicle-treated rats. VPA treatment by itself reduced concentrations of plasma unesterified AA and whole brain PGE2 and TXB2, and blocked the quinpirole-induced increments in k* and PGE2.
These results further support our hypothesis that similar to lithium and carbamazepine, VPA downregulates brain dopaminergic D2-like receptor-signaling involving AA.
arachidonic acid; phospholipase A2; valproate; D2-like receptor; quinpirole; bipolar disorder
Knowing threshold changes in brain lipids and lipid enzymes during dietary n-3 polyunsaturated fatty acid deprivation may elucidate dietary regulation of brain lipid metabolism. To determine thresholds, rats were fed for 15 weeks DHA-free diets having graded reductions of α-linolenic acid (α-LNA). Compared with control diet (4.6% α-LNA), plasma DHA fell significantly at 1.7% dietary α-LNA while brain DHA remained unchanged down to 0.8% α-LNA, when plasma and brain docosapentaenoic acid (DPAn-6) were increased and DHA-selective iPLA2 and COX-1 activities were downregulated. Brain AA was unchanged by deprivation, but AA selective-cPLA2, sPLA2 and COX-2 activities were increased at or below 0.8% dietary α-LNA, possibly in response to elevated brain DPAn-6. In summary, homeostatic mechanisms appear to maintain a control brain DHA concentration down to 0.8% dietary DHA despite reduced plasma DHA, when DPAn-6 replaces DHA. At extreme deprivation, decreased brain iPLA2 and COX-1 activities may reduce brain DHA loss.
n-3 PUFA deprivation; rat brain; phospholipase A2; docosapentaenoic acid
Arachidonic acid (AA) is found in high concentrations in brain phospholipids and is released as a second messenger during neurotransmission and much more so during neuroinflammation and excitotoxicity. Upregulated brain AA metabolism associated with neuroinflammation has been imaged in rodents using [1-14C]AA and with PET in Alzheimer disease patients using [1-11C]AA. Radiotracer brain AA uptake is independent of cerebral blood flow, making it an ideal tracer despite altered brain functional activity. However, the 20.4-min radioactive half-life of 11C-AA and challenges of routinely synthesizing 11C fatty acids limit their translational utility as PET biomarkers.
As a first step to develop a clinically useful 18F-fluoroarachidonic acid (18F-FAA) with a long radioactive half-life of 109.8 min, we report here a high-yield stereoselective synthetic method of non-radioactive 20-19F-FAA. We tested its in vivo pharmacokinetics by infusing purified nonradioactive 19F-FAA intravenously for 5 min at 2 doses in unanesthetized mice and measured its plasma and brain distribution using gas chromatography–mass spectrometry.
Incorporation coefficients of injected 19F-FAA into brain phospholipids (ratio of brain 19F-FAA concentration to plasma input function) were 3- to 29-fold higher for choline glycerophospholipid and phosphatidylinositol than for ethanolamine glycerophospholipid and phosphatidylserine at each of the 2 tested doses. The selectivities and values of incorporation coefficients were comparable to those reported after [1-14C]AA (the natural arachidonate) infusion in mice.
These results suggest that it would be worthwhile to translate our stereoselective synthetic method for 19F-FAA to synthesize positron-emitting 18F-FAA for human brain AA metabolism in neuroinflammatory disorders such as Alzheimer disease.
positron emitting tomography (PET); fluorinated arachidonic acid; fluoroarachidonic acid; brain; phospholipids; arachidonic acid signaling; imaging; neuroinflammation; excitotoxicity; biomarker; Alzheimer’s disease; cancer
In animal models, the metabolic syndrome elicits a cerebral response characterized by altered phospholipid and unesterified fatty acid concentrations and increases in pro-apoptotic inflammatory mediators that may cause synaptic loss and cognitive impairment. We hypothesized that these changes are associated with phospholipase (PLA2) enzymes that regulate arachidonic (AA, 20:4n-6) and docosahexaenoic (DHA, 22:6n-6) acid metabolism, major polyunsaturated fatty acids in brain. Male Wistar rats were fed a control or high-sucrose diet for 8 weeks. Brains were assayed for markers of AA metabolism (calcium-dependent cytosolic cPLA2 IVA and cyclooxygenases), DHA metabolism (calcium-independent iPLA2 VIA and lipoxygenases), brain-derived neurotrophic factor (BDNF), and synaptic integrity (drebrin and synaptophysin). Lipid concentrations were measured in brains subjected to high-energy microwave fixation.
The high-sucrose compared with control diet induced insulin resistance, and increased phosphorylated-cPLA2 protein, cPLA2 and iPLA2 activity and 12-lipoxygenase mRNA, but decreased BDNF mRNA and protein, and drebrin mRNA. The concentration of several n-6 fatty acids in ethanolamine glycerophospholipids and lysophosphatidylcholine was increased, as was unesterified AA concentration. Eicosanoid concentrations (prostaglandin E2, thromboxane B2 and leukotriene B4) did not change.
These findings show upregulated brain AA and DHA metabolism and reduced BDNF and drebrin, but no changes in eicosanoids, in an animal model of the metabolic syndrome. These changes might contribute to altered synaptic plasticity and cognitive impairment in rats and humans with the metabolic syndrome.
Arachidonic acid; Docosahexaenoic acid; BDNF; Brain; Polyunsaturated fatty acids (PUFA); Metabolic syndrome; Drebrin; Sucrose; Insulin resistance
The mode of action of clozapine, an atypical antipsychotic approved for treating schizophrenia and bipolar disorder (BD) mania, remains unclear. We tested for overlap with the actions of the mood stabilizers, lithium, carbamazepine and valproate, which downregulate arachidonic acid (AA) cascade markers in rat brain and upregulate BDNF. AA cascade markers are upregulated in the postmortem BD brain in association with neuroinflammation and synaptic loss, while BDNF is decreased. Rats were injected intraperitoneally with a therapeutically relevant dose of clozapine (10 mg/kg/day) or with saline for 30 days, and AA cascade and synaptic markers and BDNF were measured in the brain. Compared with saline-injected rats, chronic clozapine increased brain activity, mRNA and protein levels of docosahexaenoic acid (DHA)-selective calcium-independent phospholipase A2 type VIA (iPLA2), mRNA and protein levels of BDNF and of the postsynaptic marker, drebrin, while decreasing cyclooxygenase (COX) activity and concentration of prostaglandin E2 (PGE2), a proinflammatory AA metabolite. Activity and expression of AA-selective calcium-dependent cytosolic cPLA2 type IVA and of secretory sPLA2 Type II were unchanged. These results show overlap with effects of mood stabilizers with regard to downregulation of COX activity and PGE2 and to increased BDNF, and suggest a common action against the reported neuropathology of BD. Additionally, the increased iPLA2 expression following clozapine suggests increased production of anti-inflammatory DHA metabolites, consistent with reports that dietary n-3 polyunsaturated fatty acid supplementation is beneficial in BD.
atypical; antipsychotic; arachidonic acid; BDNF; bipolar disorder; drebrin; cyclooxygenase; rat; clozapine; brain; docosahexaenoic; schizophrenia; mood stabilizer; iPLA2; PGE2
HIV-1 transgenic (Tg) rats, a model for human HIV-1 associated neurocognitive disorder (HAND), show upregulated markers of brain arachidonic acid (AA) metabolism with neuroinflammation after 7 months of age. Since lithium decreases AA metabolism in a rat lipopolysaccharide model of neuroinflammation, and may be useful in HAND, we hypothesized that lithium would dampen upregulated brain AA metabolism in HIV-1 Tg rats.
Regional brain AA incorporation coefficients k* and rates Jin, markers of AA signaling and metabolism, were measured in 81 brain regions using quantitative autoradiography, after intravenous [1-14C] AA infusion in unanesthetized 10-month-old HIV-1 Tg and age-matched wildtype rats that had been fed a control or LiCl diet for 6 weeks.
k* and Jin for AA were significantly higher in HIV-1 Tg than wildtype rats fed the control diet. Lithium feeding reduced plasma unesterified AA concentration in both groups and Jin in wildtype rats, and blocked increments in k* (19 of 54 regions) and Jin (77 of 81 regions) in HIV-1 Tg rats.
These in vivo neuroimaging data indicate that lithium treatment dampened upregulated brain AA metabolism in HIV-1 Tg rats. Lithium may improve cognitive dysfunction and be neuroprotective in HIV-1 patients with HAND through a comparable effect.
HIV-1; lithium; arachidonic acid; brain imaging; phospholipase A2; metabolism
Brain lipid metabolism was studied in rats following permanent bilateral common carotid artery ligation (BCCL), a model for chronic cerebral hypoperfusion. Unesterified (free) fatty acids (uFA) and acyl-CoA concentrations were measured 6 h, 24 h, and 7 days after BCCL or sham surgery, in high energy-microwaved brain. In BCCL compared to sham rats, cPLA2 immunoreactivity in piriform cortex, and concentrations of total uFA and arachidonoyl-CoA, an intermediate for arachidonic acid reincorporation into phospholipids, were increased only at 6 h. At 24 h, immunoreactivity for secretory phospholipase A2 (sPLA2), which may regulate blood flow, was increased near cortical and hippocampal blood vessels. BCCL did not affect difference brain IB4+ microglia, glial fibrillary acidic protein (GFAP)+ astrocytes, cyclooxygenase-2 (COX-2) immunoreactivity at any time, but increased cytosolic cPLA2 immunoreactivity in one region at 6 h. Thus, BCCL affected brain lipid metabolism transiently, likely because of compensatory sPLA2-mediated vasodilation, without producing evidence of neuroinflammation.
arachidonic acid; ischemia; carotid; ligation; acyl-CoA; brain; cPLA2; sPLA2; rat; brain; neuroinflammation
Dopamine transporter (DAT) homozygous knockout (DAT−/−) mice have a 10-fold higher extracellular DA concentration in the caudate-putamen and nucleus accumbens than do wildtype (DAT+/+) mice, but show reduced presynaptic DA synthesis and fewer postsynaptic D2 receptors. One aspect of neurotransmission involves DA binding to postsynaptic D2-like receptors coupled to cytosolic phospholipase A2 (cPLA2), releasing second messenger arachidonic acid (AA) from synaptic membrane phospholipid. We hypothesized that tonic overactivation of D2-like receptors in DAT−/− mice due to elevated DA would not increase brain AA signaling, because of compensatory downregulation of postsynaptic signaling mechanisms.
[1-14C]AA was infused intravenously for 3 min in unanesthetized DAT+/+, heterozygous (DAT+/−) and DAT−/− mice. AA incorporation coefficients k* and rates Jin, markers of AA metabolism and signaling, were imaged in 83 brain regions using quantitative autoradiography brain cPLA2-IV activity also was measured.
Neither k* nor Jin for AA in any brain region, or in brain cPLA2-IV activity, differed significantly between DAT−/−, DAT+/− and DAT+/+ mice.
These results differ from reported increases in k* and Jin for AA, and brain cPLA2 expression, in serotonin reuptake transporter (5-HTT) knockout mice, and suggest that postsynaptic dopaminergic neurotransmission mechanisms involving AA are downregulated despite elevated DA in DAT−/− mice.
arachidonic acid; phospholipase A2; dopamine; dopamine transporter; knockout; mouse
Olanzapine (OLZ) is used to treat bipolar disorder, but its therapeutic mechanism of action is not clear. Arachidonic acid (AA, 20:4n-6) plays a critical role in brain signaling and an upregulated AA metabolic cascade was reported in postmortem brains from bipolar disorder patients. Here we tested whether, similar to the action of the mood stabilizers lithium, carbamazepine and valproate, chronic OLZ treatment would reduce AA turnover in rat brain. We administered OLZ (6 mg/kg/day) or vehicle i.p. to male rats once daily for 21 days. A washout group received 21 days of OLZ followed by vehicle on day 22. Two hours after the last injection, [1-14C]AA (170 µCi/kg) was infused intravenously for 5 min, and timed arterial blood samples were taken. After the rat was euthanized at 5 min, its brain was microwaved, removed and analyzed. Chronic OLZ decreased plasma unesterified AA concentration, AA incorporation rates and AA turnover in brain phospholipids. These effects were absent after washout. Consistent with reduced AA turnover, OLZ decreased brain cyclooxygenase activity and the brain concentration of the proinflammatory AA-derived metabolite, prostaglandin E2. In view of upregulated brain AA metabolic markers in bipolar disorder, the abilities of OLZ and the mood stabilizers to commonly decrease prostaglandin E2 and AA turnover in rat brain phospholipids, albeit by different mechanisms, may be related to their efficacy against the disease.
bipolar disorder; antipsychotic; washout; phospholipid; cyclooxygenase; prostaglandin E2
An upregulated brain arachidonic acid (AA) cascade and a hyperglutamatergic state characterize bipolar disorder (BD). Lamotrigine (LTG), a mood stabilizer approved for treating BD, is reported to interfere with glutamatergic neurotransmission involving N-methyl-D-aspartate receptors (NMDARs). NMDARs allow extracellular calcium into the cell, thereby stimulating calcium-dependent cytosolic phospholipase A2 (cPLA2) to release arachidonic acid (AA) from membrane phospholipid. We hypothesized that LTG, like other approved mood stabilizers, would reduce NMDAR-mediated AA signaling in rat brain. An acute subconvulsant dose of NMDA (25 mg/kg) or saline was administered intraperitoneally to unanesthetized rats that had been treated p.o. daily for 42 days with vehicle or a therapeutically relevant dose of LTG (10 mg/kg/.d). Regional brain AA incorporation coefficients k* and rates Jin, AA signals, were measured using quantitative autoradiography after intravenous [1-14C]AA infusion, as were other AA cascade markers. In chronic vehicle-treated rats, acute NMDA compared to saline increased k* and Jin in widespread regions of the brain, as well as prostaglandin (PG)E2 and thromboxane B2 concentrations. Chronic LTG treatment compared to vehicle reduced brain cyclooxygenase (COX) activity, PGE2 concentration, and DNA binding activity of the COX-2 transcription factor, NF-κB. Pretreatment with chronic LTG blocked the acute NMDA effects on AA cascade markers. In summary, chronic LTG like other mood stabilizers blocks NMDA-mediated signaling involving the AA metabolic cascade. Since markers of the AA cascade and of NMDAR signaling are up-regulated in the postmortem BD brain, mood stabilizers generally may be effective in BD by dampening NMDAR signalling and the AA cascade.
arachidonic acid; cyclooxygenase; mood stabilizer; NMDA receptor; phospholipase A2
Neuroinflammation, caused by six days of intracerebroventricular infusion of bacterial lipopolysaccharide (LPS), stimulates rat brain arachidonic acid (AA) metabolism. The molecular changes associated with increased AA metabolism are not clear. We examined effects of a six-day infusion of a low-dose (0.5 ng/h) and a high-dose (250 ng/h) of LPS on neuroinflammatory, AA cascade, and pre- and post-synaptic markers in rat brain. We used artificial cerebrospinal fluid-infused brains as controls.
Infusion of low- or high-dose LPS increased brain protein levels of TNFα, and iNOS, without significantly changing GFAP. High-dose LPS infusion upregulated brain protein and mRNA levels of AA cascade markers (cytosolic cPLA2-IVA, secretory sPLA2-V, cyclooxygenase-2 and 5-lipoxygenase), and of transcription factor NF-κB p50 DNA binding activity. Both LPS doses increased cPLA2 and p38 mitogen-activated protein kinase levels, while reducing protein levels of the pre-synaptic marker, synaptophysin. Post-synaptic markers drebrin and PSD95 protein levels were decreased with high- but not low-dose LPS.
Chronic LPS infusion has differential effects, depending on dose, on inflammatory, AA and synaptic markers in rat brain. Neuroinflammation associated with upregulated brain AA metabolism can lead to synaptic dysfunction.
Arachidonic acid; Cytokine; Synapse; Drebrin; Lipopolysaccharide; Synaptophysin; Phospholipase A2; Neuroinflammation; NF-κB
The ability of chronic valproate (VPA) to reduce arachidonic acid (AA) turnover in brain phospholipids of unanesthetized rats has been ascribed to its inhibition of acyl-CoA synthetase (Acsl)-mediated activation of AA to AA-CoA. Our aim was to identify a rat Acsl isoenzyme that could be inhibited by VPA in vitro.
Rat Acsl3-, Acsl6v1- and Acsl6v2-, and Acsl4-flag proteins were expressed in E. coli, and the ability of VPA to inhibit their activation of long-chain fatty acids to acyl-CoA was estimated using Michaelis-Menten kinetics.
VPA uncompetitively inhibited Acsl4-mediated conversion of AA and of docosahexaenoic (DHA) but not of palmitic acid to acyl-CoA, but did not affect AA conversion by Acsl3, Acsl6v1 or Acsl6v2. Acsl4-mediated conversion of AA to AA-CoA showed substrate inhibition and had a 10-times higher catalytic efficiency than did conversion of DHA to DHA-CoA. Butyrate, octanoate, or lithium did not inhibit AA activation by Acsl4.
VPA’s ability to inhibit Acsl4 activation of AA and of DHA to their respective acyl-CoAs, related to the higher catalytic efficiency of AA than DHA conversion, may account for VPA’s selective reduction of AA turnover in rat brain phospholipids, and contribute to VPA’s efficacy against bipolar disorder.
bipolar disorder; valproate; arachidonic acid; acyl-CoA synthetase; mood stabilizer; Acsl4; brain; rat
Human immunodeficiency virus (HIV)-associated infection involves the entry of virus-bearing monocytes into the brain, followed by microglial activation, neuroinflammation, and upregulated arachidonic acid (AA) metabolism. The HIV-1 transgenic (Tg) rat, a noninfectious HIV-1 model, shows neurologic and behavioral abnormalities after 5 months of age. We hypothesized that brain AA metabolism would be elevated in older HIV-1 Tg rats in vivo. Arachidonic acid incorporation from the plasma into the brain of unanesthetized 7-to-9-month-old rats was imaged using quantitative autoradiography, after [1-14C]AA infusion. Brain phospholipase (PLA2) activities and eicosanoid concentrations were measured, and enzymes were localized by immunostaining. AA incorporation coefficients k* and rates Jin, measures of AA metabolism, were significantly higher in 69 of 81 brain regions in HIV-1 Tg than in control rats, as were activities of cytosolic (c)PLA2-IV, secretory (s)PLA2, and calcium independent (i)PLA2-VI, as well as prostaglandin E2 and leukotriene B4 concentrations. Immunostaining of somatosensory cortex showed elevated cPLA2-IV, sPLA2-IIA, and cyclooxygenase-2 in neurons. Brain AA incorporation and other markers of AA metabolism are upregulated in HIV-1 Tg rats, in which neurologic changes and neuroinflammation have been reported. Positron emission tomography with [1-11C]AA could be used to test whether brain AA metabolism is upregulated in HIV-1-infected patients, in relation to cognitive and behavioral disturbances.
arachidonic acid; brain imaging; eicosanoids; HIV-1; phospholipase A2
Dietary n-3 polyunsaturated fatty acid (PUFA) deprivation increases expression of arachidonic acid (AA 20:4n-6)-selective cytosolic phospholipase A2 (cPLA2) IVA and cyclooxygenase (COX)-2 in rat brain, while decreasing expression of docosahexaenoic acid (DHA 22:6n-3)-selective calcium-independent iPLA2 VIA. Assuming that these enzyme changes represented brain homeostatic responses to deprivation, we hypothesized that dietary n-6 PUFA deprivation would produce changes in the opposite directions.
Brain expression of PUFA-metabolizing enzymes and their transcription factors was quantified in male rats fed an n-6 PUFA adequate or deficient diet for 15 weeks post-weaning.
The deficient compared with adequate diet increased brain mRNA, protein and activity of iPLA2 VIA and 15-lipoxygenase (LOX), but decreased cPLA2 IVA and COX-2 expression. The brain protein level of the iPLA2 transcription factor SREBP-1 was elevated, while protein levels were decreased for AP-2α and NF-κB p65, cPLA2 and COX-2 transcription factors, respectively.
With dietary n-6 PUFA deprivation, rat brain PUFA metabolizing enzymes and some of their transcription factors change in a way that would homeostatically dampen reductions in brain n-6 PUFA concentrations and metabolism, while n-3 PUFA metabolizing enzyme expression is increased. The changes correspond to reported in vitro enzyme selectivities for AA compared with DHA. (198 words)
linoleic acid; arachidonic; essential fatty acid; deficient; turnover rate; cyclooxygenase; brain; PUFA; phospholipase; lipoxygenase; SREBP; transcription
Age-related differences in the regional recruitment of prefrontal cortex (PFC) during cognitive tasks suggests that aging is associated with functional reorganization. Cholinergic enhancement with physostigmine reduces activity in the PFC regions selectively recruited during working memory (WM) and increases activity in visual processing areas, suggesting that augmenting cholinergic function reduces task effort by improving the visual representation of WM stimuli. Here, we investigated how cholinergic enhancement influenced PFC and visual cortical activity in young and older subjects as WM difficulty was altered. Regional cerebral blood flow (rCBF) was measured using H215O-PET in 10 young and 10 older volunteers during a parametrically varied face WM task, following an i.v. infusion of saline and physostigmine. Reaction time decreased during physostigmine relative to placebo in both groups. Prefrontal brain regions selectively recruited in each age group that responded differentially to task demands during placebo, had no significant activity during physostigmine. Medial visual processing areas showed task-selective increases in activity during drug in both groups, while lateral regions showed decreased activity in young and increased activity in older participants at longer task delays. These results are consistent with our previous findings, showing that the modulatory role of the cholinergic system persists during aging, and that the effects of cholinergic enhancement are functionally specific rather than anatomically specific. Moreover, the use of the parametric design allowed us to uncover group specific effects in lateral visual processing areas where increasing cholinergic function produced opposite effects on neural activity in the two age groups.
Cholinergic modulation; Working memory; Aging; PET; Physostigmine; Visual cortex