Valnoctamide, a non-teratogenic amide derivative of valproic acid, inhibits arachidonic acid activation in vitro by recombinant acyl-CoA synthetase-4.

OBJECTIVE: Valproic acid (VPA), a mood stabilizer used for treating bipolar disorder (BD), uncompetitively inhibits acylation of arachidonic acid (AA) by recombinant AA-selective acyl-CoA synthetase 4 (Acsl4) at an enzyme inhibition constant (Ki ) of 25 mM. Inhibition may account for VPA's ability to reduce AA turnover in brain phospholipids of unanesthetized rats and to be therapeutic in BD. However, VPA is teratogenic. We tested whether valnoctamide (VCD), a non-teratogenic amide derivative of a VPA chiral isomer, which had antimanic potency in a phase III BD trial, also inhibits recombinant Acsl4. METHODS: Rat Acsl4-flag protein was expressed in Escherichia coli. We used Michaelis-Menten kinetics to characterize and quantify the ability of VCD to inhibit conversion of AA to AA-CoA by recombinant Acsl4 in vitro. RESULTS: Acsl4-mediated activation of AA to AA-CoA by Acsl4 was inhibited uncompetitively by VCD, with a Ki of 6.38 mM. CONCLUSIONS: VCD's ability to uncompetitively inhibit AA activation to AA-CoA by Acsl4, at a lower Ki than VPA, suggests that, like VPA, VCD may reduce AA turnover in rat brain phospholipids. If so, VCD and other non-teratogenic Acsl4 inhibitors might be considered further for treating BD.

Transient postnatal fluoxetine leads to decreased brain arachidonic acid metabolism and cytochrome P450 4A in adult mice.

Fetal and perinatal exposure to selective serotonin (5-HT) reuptake inhibitors (SSRIs) has been reported to alter childhood behavior, while transient early exposure in rodents is reported to alter their behavior and decrease brain extracellular 5-HT in adulthood. Since 5-HT2A/2C receptor-mediated neurotransmission can involve G-protein coupled activation of cytosolic phospholipase A2 (cPLA2), releasing arachidonic acid (ARA) from synaptic membrane phospholipid, we hypothesized that transient postnatal exposure to fluoxetine would alter brain ARA metabolism in adult mice. Brain ARA incorporation coefficients k* and rates Jin were quantitatively imaged following intravenous [1-(14)C]ARA infusion of unanesthetized adult mice that had been injected daily with fluoxetine (10mg/kg i.p.) or saline during postnatal days P4-P21. Expression of brain ARA metabolic enzymes and other relevant markers also was measured. On neuroimaging, k* and Jin was decreased widely in early fluoxetine- compared to saline-treated adult mice. Of the enzymes measured, cPLA2 activity was unchanged, while Ca(2+)-independent iPLA2 activity was increased. There was a significant 74% reduced protein level of cytochrome P450 (CYP) 4A, which can convert ARA to 20-HETE. Reduced brain ARA metabolism in adult mice transiently exposed to postnatal fluoxetine, and a 74% reduction in CYP4A protein, suggest long-term effects independent of drug presence in brain ARA metabolism, and in CYP4A metabolites. These changes might contribute to reported altered behavior following early SSRI in rodents.

Propylisopropylacetic acid (PIA), a constitutional isomer of valproic acid, uncompetitively inhibits arachidonic acid acylation by rat acyl-CoA synthetase 4: a potential drug for bipolar disorder.

BACKGROUND: Mood stabilizers used for treating bipolar disorder (BD) selectively downregulate arachidonic acid (AA) turnover (deacylation-reacylation) in brain phospholipids, when given chronically to rats. In vitro studies suggest that one of these, valproic acid (VPA), which is teratogenic, reduces AA turnover by inhibiting the brain long-chain acyl-CoA synthetase (Acsl)4 mediated acylation of AA to AA-CoA. We tested whether non-teratogenic VPA analogues might also inhibit Acsl4 catalyzed acylation, and thus have a potential anti-BD action. METHODS: Rat Acsl4-flag protein was expressed in Escherichia coli, and the ability of three VPA analogues, propylisopropylacetic acid (PIA), propylisopropylacetamide (PID) and N-methyl-2,2,3,3-tetramethylcyclopropanecarboxamide (MTMCD), and of sodium butyrate, to inhibit conversion of AA to AA-CoA by Acsl4 was quantified using Michaelis-Menten kinetics. RESULTS: Acsl4-mediated conversion of AA to AA-CoA in vitro was inhibited uncompetitively by PIA, with a Ki of 11.4mM compared to a published Ki of 25mM for VPA, while PID, MTMCD and sodium butyrate had no inhibitory effect. CONCLUSIONS: PIA's ability to inhibit conversion of AA to AA-CoA by Acsl4 in vitro suggests that, like VPA, PIA may reduce AA turnover in brain phospholipids in unanesthetized rats, and if so, may be effective as a non-teratogenic mood stabilizer in BD patients.

Altered lipid concentrations of liver, heart and plasma but not brain in HIV-1 transgenic rats.

Disturbed lipid metabolism has been reported in antiretroviral-naive HIV-1-infected patients suggesting a direct effect of the virus on lipid metabolism. To test that the HIV-1 virus alone could alter lipid concentrations, we measured these concentrations in an HIV-1 transgenic (Tg) rat model of human HIV-1 infection, which demonstrates peripheral and central pathology by 7-9 months of age. Concentrations were measured in high-energy microwaved heart, brain and liver from 7-9 month-old HIV-1 Tg and wildtype rats, and in plasma from non-microwaved rats. Plasma triglycerides and liver cholesteryl ester and total cholesterol concentrations were significantly higher in HIV-1 Tg rats than controls. Heart and plasma fatty acid concentrations reflected concentration differences in liver, which showed higher n-3 and n-6 polyunsaturated fatty acid (PUFA) concentrations in multiple lipid compartments. Fatty acid concentrations were increased or decreased in heart and liver phospholipid subfractions. Brain fatty acid concentrations differed significantly between the groups for minor fatty acids such as linoleic acid and n-3 docosapentaenoic acid. The profound changes in heart, plasma and liver lipid concentrations suggest a direct effect of chronic exposure to the HIV-1 virus on peripheral lipid (including PUFA) metabolism.

Chronic lithium feeding reduces upregulated brain arachidonic acid metabolism in HIV-1 transgenic rat.

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 J ( in ), markers of AA signaling and metabolism, were measured in 81 brain regions using quantitative autoradiography, after intravenous [1-(14) C]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 J ( in ) 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 J ( in ) in wildtype rats, and blocked increments in k* (19 of 54 regions) and J ( in ) (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.

Dose-dependent changes in neuroinflammatory and arachidonic acid cascade markers with synaptic marker loss in rat lipopolysaccharide infusion model of neuroinflammation.

BACKGROUND: 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. RESULTS: 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. CONCLUSIONS: 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.

Knocking out the dopamine reuptake transporter (DAT) does not change the baseline brain arachidonic acid signal in the mouse.

BACKGROUND: 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 D(2) receptors. One aspect of neurotransmission involves DA binding to postsynaptic D(2)-like receptors coupled to cytosolic phospholipase A(2) (cPLA(2)), which releases the second messenger, arachidonic acid (AA), from synaptic membrane phospholipid. We hypothesized that tonic overactivation of D(2)-like receptors in DAT(-/-) mice due to the excess DA would not increase brain AA signaling, because of compensatory downregulation of postsynaptic DA signaling mechanisms. METHODS: [1-(14)C]AA was infused intravenously for 3 min in unanesthetized DAT(+/+), heterozygous (DAT(+/-)), and DAT(-/-) mice. AA incorporation coefficients k* and rates J(in), markers of AA metabolism and signaling, were imaged in 83 brain regions using quantitative autoradiography; brain cPLA(2)-IV activity also was measured. RESULTS: Neither k* nor J(in) for AA in any brain region, or brain cPLA(2)-IV activity, differed significantly among DAT(-/-), DAT(+/-), and DAT(+/+) mice. CONCLUSIONS: These results differ from reported increases in k* and J(in) for AA, and in brain cPLA(2) 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.

Imaging brain signal transduction and metabolism via arachidonic and docosahexaenoic acid in animals and humans.

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 A(2) (PLA(2)) 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 M(1,3,5), serotonergic 5-HT(2A/2C), dopaminergic D(2)-like (D(2), D(3), D(4)) 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.

Lamotrigine blocks NMDA receptor-initiated arachidonic acid signalling in rat brain: implications for its efficacy in bipolar disorder.

An up-regulated 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 AA from membrane phospholipid. We hypothesized that LTG, like other approved mood stabilizers, would reduce NMDAR-mediated AA signalling in rat brain. An acute subconvulsant dose of NMDA (25 mg/kg) or saline was administered intraperitoneally to unanaesthetized rats that had been treated p.o. daily for 42 d with vehicle or a therapeutically relevant dose of LTG (10 mg/kg.d). Regional brain AA incorporation coefficients k* and rates J in, and 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 J in 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 signalling involving the AA metabolic cascade. Since markers of the AA cascade and of NMDAR signalling are up-regulated in the post-mortem BD brain, mood stabilizers generally may be effective in BD by dampening NMDAR signalling and the AA cascade.

Chronic valproate treatment blocks D2-like receptor-mediated brain signaling via arachidonic acid in rats.

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 D(2)-like (D(2), D(3), and D(4)) receptor signaling involving AA when given chronically to awake rats. We hypothesized that valproate (VPA), with mood-stabilizing properties, would also reduce D(2)-like-mediated signaling via AA. METHODS: 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, J(in), markers of AA signaling and metabolism, were measured by quantitative autoradiography after intravenous [1-(14)C]AA infusion. Whole brain concentrations of prostaglandin (PG)E(2) and thromboxane (TX)B(2) also were measured. RESULTS: Quinpirole compared to saline significantly increased k* in 40 of 83 brain regions, and increased brain concentrations of PGE(2) in chronic vehicle-treated rats. VPA treatment by itself reduced concentrations of plasma unesterified AA and whole brain PGE(2) and TXB(2), and blocked the quinpirole-induced increments in k* and PGE(2). CONCLUSION: These results further provide evidence that mood stabilizers downregulate brain dopaminergic D(2)-like receptor signaling involving AA.

Increased neuroinflammatory and arachidonic acid cascade markers, and reduced synaptic proteins, in brain of HIV-1 transgenic rats.

BACKGROUND: Cognitive impairment has been reported in human immune deficiency virus-1- (HIV-1-) infected patients as well as in HIV-1 transgenic (Tg) rats. This impairment has been linked to neuroinflammation, disturbed brain arachidonic acid (AA) metabolism, and synapto-dendritic injury. We recently reported upregulated brain AA metabolism in 7- to 9-month-old HIV-1 Tg rats. We hypothesized that these HIV-1 Tg rats also would show upregulated brain inflammatory and AA cascade markers and a deficit of synaptic proteins. METHODS: We measured protein and mRNA levels of markers of neuroinflammation and the AA cascade, as well as pro-apoptotic factors and synaptic proteins, in brains from 7- to 9-month-old HIV-1 Tg and control rats. RESULTS: Compared with control brain, HIV-1 Tg rat brain showed immunoreactivity to glycoprotein 120 and tat HIV-1 viral proteins, and significantly higher protein and mRNA levels of (1) the inflammatory cytokines interleukin-1ß and tumor necrosis factor α, (2) the activated microglial/macrophage marker CD11b, (3) AA cascade enzymes: AA-selective Ca2+-dependent cytosolic phospholipase A2 (cPLA2)-IVA, secretory sPLA2-IIA, cyclooxygenase (COX)-2, membrane prostaglandin E2 synthase, 5-lipoxygenase (LOX) and 15-LOX, cytochrome p450 epoxygenase, and (4) transcription factor NF-κBp50 DNA binding activity. HIV-1 Tg rat brain also exhibited signs of cell injury, including significantly decreased levels of brain-derived neurotrophic factor (BDNF) and drebrin, a marker of post-synaptic excitatory dendritic spines. Expression of Ca2+-independent iPLA2-VIA and COX-1 was unchanged. CONCLUSIONS: HIV-1 Tg rats show elevated brain markers of neuroinflammation and AA metabolism, with a deficit in several synaptic proteins. These changes are associated with viral proteins and may contribute to cognitive impairment. The HIV-1 Tg rat may be a useful model for understanding progression and treatment of cognitive impairment in HIV-1 patients.

Docosahexaenoic acid (DHA) incorporation into the brain from plasma, as an in vivo biomarker of brain DHA metabolism and neurotransmission.

Docosahexaenoic acid (DHA) is critical for maintaining normal brain structure and function, and is considered neuroprotective. Its brain concentration depends on dietary DHA content and hepatic conversion from its dietary derived n-3 precursor, α-linolenic acid (α-LNA). We have developed an in vivo method in rats using quantitative autoradiography and intravenously injected radiolabeled DHA to image net incorporation into the brain of unesterified plasma DHA, and showed with this method that the incorporation rate of DHA equals the rate of brain metabolic DHA consumption. The method has been extended for use in humans with positron emission tomography (PET). Furthermore, imaging in unanesthetized rats using DHA incorporation as a biomarker in response to acute N-methyl-D-aspartate administration confirms that regional DHA signaling is independent of extracellular calcium, and likely mediated by a calcium-independent phospholipase A(2) (iPLA(2)). Studies in mice in which iPLA(2)-VIA (ß) was knocked out confirmed that this enzyme is critical for baseline and muscarinic cholinergic signaling involving DHA. Thus, quantitative imaging of DHA incorporation from plasma into brain can be used as an in vivo biomarker of brain DHA metabolism and neurotransmission.

Anti-inflammatory effects of chronic aspirin on brain arachidonic acid metabolites.

Pro-inflammatory and anti-inflammatory mediators derived from arachidonic acid (AA) modulate peripheral inflammation and its resolution. Aspirin (ASA) is a unique non-steroidal anti-inflammatory drug, which switches AA metabolism from prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) to lipoxin A4 (LXA4) and 15-epi-LXA4. However, it is unknown whether chronic therapeutic doses of ASA are anti-inflammatory in the brain. We hypothesized that ASA would dampen increases in brain concentrations of AA metabolites in a rat model of neuroinflammation, produced by a 6-day intracerebroventricular infusion of bacterial lipopolysaccharide (LPS). In rats infused with LPS (0.5 ng/h) and given ASA-free water to drink, concentrations in high-energy microwaved brain of PGE2, TXB2 and leukotriene B4 (LTB4) were elevated. In rats infused with artificial cerebrospinal fluid, 6 weeks of treatment with a low (10 mg/kg/day) or high (100 mg/kg/day) ASA dose in drinking water decreased brain PGE2, but increased LTB4, LXA4 and 15-epi-LXA4 concentrations. Both doses attenuated the LPS effects on PGE2, and TXB2. The increments in LXA4 and 15-epi-LXA4 caused by high-dose ASA were significantly greater in LPS-infused rats. The ability of ASA to increase anti-inflammatory LXA4 and 15-epi-LXA4 and reduce pro-inflammatory PGE2 and TXB2 suggests considering aspirin further for treating clinical neuroinflammation.

Valproate uncompetitively inhibits arachidonic acid acylation by rat acyl-CoA synthetase 4: relevance to valproate's efficacy against bipolar disorder.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: VPA's ability to inhibit Acsl4 activation of AA and of DHA to their respective acyl-CoAs, when 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.

Imaging upregulated brain arachidonic acid metabolism in HIV-1 transgenic rats.

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-(14)C]AA infusion. Brain phospholipase (PLA(2)) activities and eicosanoid concentrations were measured, and enzymes were localized by immunostaining. AA incorporation coefficients k* and rates J(in), 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)PLA(2)-IV, secretory (s)PLA(2), and calcium independent (i)PLA(2)-VI, as well as prostaglandin E(2) and leukotriene B(4) concentrations. Immunostaining of somatosensory cortex showed elevated cPLA(2)-IV, sPLA(2)-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-(11)C]AA could be used to test whether brain AA metabolism is upregulated in HIV-1-infected patients, in relation to cognitive and behavioral disturbances.

Imaging decreased brain docosahexaenoic acid metabolism and signaling in iPLA(2)ß (VIA)-deficient mice.

Ca(2+)-independent phospholipase A(2)ß (iPLA(2)ß) selectively hydrolyzes docosahexaenoic acid (DHA, 22:6n-3) in vitro from phospholipid. Mutations in the PLA2G6 gene encoding this enzyme occur in patients with idiopathic neurodegeneration plus brain iron accumulation and dystonia-parkinsonism without iron accumulation, whereas mice lacking PLA2G6 show neurological dysfunction and neuropathology after 13 months. We hypothesized that brain DHA metabolism and signaling would be reduced in 4-month-old iPLA(2)ß-deficient mice without overt neuropathology. Saline or the cholinergic muscarinic M(1,3,5) receptor agonist arecoline (30 mg/kg) was administered to unanesthetized iPLA(2)ß(-/-), iPLA(2)ß(+/-), and iPLA(2)ß(+/+) mice, and [1-(14)C]DHA was infused intravenously. DHA incorporation coefficients k* and rates J(in), representing DHA metabolism, were determined using quantitative autoradiography in 81 brain regions. iPLA(2)ß(-/-) or iPLA(2)ß(+/-) compared with iPLA(2)ß(+/+) mice showed widespread and significant baseline reductions in k* and J(in) for DHA. Arecoline increased both parameters in brain regions of iPLA(2)ß(+/+) mice but quantitatively less so in iPLA(2)ß(-/-) and iPLA(2)ß(+/-) mice. Consistent with iPLA(2)ß's reported ability to selectively hydrolyze DHA from phospholipid in vitro, iPLA(2)ß deficiency reduces brain DHA metabolism and signaling in vivo at baseline and following M(1,3,5) receptor activation. Positron emission tomography might be used to image disturbed brain DHA metabolism in patients with PLA2G6 mutations.

Extracellular-derived calcium does not initiate in vivo neurotransmission involving docosahexaenoic acid.

In vitro studies show that docosahexaenoic acid (DHA) can be released from membrane phospholipid by Ca(2+)-independent phospholipase A(2) (iPLA(2)), Ca(2+)-independent plasmalogen PLA(2) or secretory PLA(2 (sPLA2)), but not by Ca(2+)-dependent cytosolic PLA(2) (cPLA2), which selectively releases arachidonic acid (AA). Since glutamatergic NMDA (N-methyl-D-aspartate) receptor activation allows extracellular Ca(2+) into cells, we hypothesized that brain DHA signaling would not be altered in rats given NMDA, to the extent that in vivo signaling was mediated by Ca(2+)-independent mechanisms. Isotonic saline, a subconvulsive dose of NMDA (25 mg/kg), MK-801, or MK-801 followed by NMDA was administered i.p. to unanesthetized rats. Radiolabeled DHA or AA was infused intravenously and their brain incorporation coefficients k*, measures of signaling, were imaged with quantitative autoradiography. NMDA or MK-801 compared with saline did not alter k* for DHA in any of 81 brain regions examined, whereas NMDA produced widespread and significant increments in k* for AA. In conclusion, in vivo brain DHA but not AA signaling via NMDA receptors is independent of extracellular Ca(2+) and of cPLA(2). DHA signaling may be mediated by iPLA(2), plasmalogen PLA(2), or other enzymes insensitive to low concentrations of Ca(2+). Greater AA than DHA release during glutamate-induced excitotoxicity could cause brain cell damage.

Lithium modifies brain arachidonic and docosahexaenoic metabolism in rat lipopolysaccharide model of neuroinflammation.

Neuroinflammation, caused by 6 days of intracerebroventricular infusion of a low dose of lipopolysaccharide (LPS; 0.5 ng/h), stimulates brain arachidonic acid (AA) metabolism in rats, but 6 weeks of lithium pretreatment reduces this effect. To further understand this action of lithium, we measured concentrations of eicosanoids and docosanoids generated from AA and docosahexaenoic acid (DHA), respectively, in high-energy microwaved rat brain using LC/MS/MS and two doses of LPS. In rats fed a lithium-free diet, low (0.5 ng/h)- or high (250 ng/h)-dose LPS compared with artificial cerebrospinal fluid increased brain unesterified AA and prostaglandin E(2) concentrations and activities of AA-selective Ca(2+)-dependent cytosolic phospholipase A(2) (cPLA(2))-IV and Ca(2+)-dependent secretory sPLA(2). LiCl feeding prevented these increments. Lithium had a significant main effect by increasing brain concentrations of lipoxygenase-derived AA metabolites, 5- hydroxyeicosatetraenoic acid (HETE), 5-oxo-eicosatetranoic acid, and 17-hydroxy-DHA by 1.8-, 4.3- and 1.9-fold compared with control diet. Lithium also increased 15-HETE in high-dose LPS-infused rats. Ca(2+)-independent iPLA(2)-VI activity and unesterified DHA and docosapentaenoic acid (22:5n-3) concentrations were unaffected by LPS or lithium. This study demonstrates, for the first time, that lithium can increase brain 17-hydroxy-DHA formation, indicating a new and potentially important therapeutic action of lithium.