In vivo approaches and rationale for quantifying kinetics and imaging brain lipid metabolic pathways

The Emerging Role of the Double-Edged Impact of Arachidonic Acid- Derived Eicosanoids in the Neuroinflammatory Background of Depression

Eicosanoids are arachidonic acid (AA) derivatives belonging to a family of lipid signalling mediators that are engaged in both physiological and pathological processes in the brain. Recently, their implication in the prolonged inflammatory response has become a focus of particular interest because, in contrast to acute inflammation, chronic inflammatory processes within the central nervous system (CNS) are crucial for the development of brain pathologies including depression. The synthesis of eicosanoids is catalysed primarily by cyclooxygenases (COX), which are involved in the production of pro-inflammatory AA metabolites, including prostaglandins and thromboxanes. Moreover, eicosanoid synthesis is catalysed by lipoxygenases (LOXs), which generate both leukotrienes and anti-inflammatory derivatives such as lipoxins. Thus, AA metabolites have double- edged pro-inflammatory and anti-inflammatory, pro-resolving properties, and an imbalance between these metabolites has been proposed as a contributor or even the basis for chronic neuroinflammatory effects. This review focuses on important evidence regarding eicosanoid-related pathways (with special emphasis on prostaglandins and lipoxins) that has added a new layer of complexity to the idea of targeting the double-edged AA-derivative pathways for therapeutic benefits in depression. We also sought to explore future research directions that can support a pro-resolving response to control the balance between eicosanoids and thus to reduce the chronic neuroinflammation that underlies at least a portion of depressive disorders.

Safflower Seed Oil, Containing Oleic Acid and Palmitic Acid, Enhances the Stemness of Cultured Embryonic Neural Stem Cells through Notch1 and Induces Neuronal Differentiation

Embryonic neural stem cells (eNSCs) could differentiate into neurons, astrocytes and oligodendrocytes. This study was aimed to determine the effect of safflower seed oil, which contains linoleic acid (LA), oleic acid (OA), and palmitic acid (PA), on cultured eNSC proliferation and differentiation, in comparison to linoleic acid alone. Results showed that safflower seed oil, but not LA, increased significantly the viability and proliferation of eNSCs. Moreover, treatment of NSCs by safflower seed oil, but not LA, resulted in a significant increase in mRNA levels of notch1, hes1, and Ki-67, and protein levels of notch intracellular domain (NICD), in comparison to controls, indicating an enhancement of stemness. Finally, safflower seed oil, but not LA, caused an increase in the number of oligodendrocytes (MBP+), astrocytes (GFAP+) and neurons (β-III tubulin+) of which only the increase in β-III tubulin positive cells was statistically significant. In summary, OA and PA, present in safflower seed oil may prove beneficial for the enhancement of eNSCs and their neuronal differentiation.

Synthesis and preliminary evaluation of N-(16-18F-fluorohexadecanoyl)ethanolamine (18F-FHEA) as a PET probe of N-acylethanolamine metabolism in mouse brain

N-Acylethanolamines are lipid signaling molecules found throughout the plant and animal kingdoms. The best-known mammalian compound of this class is anandamide, N-arachidonoylethanolamine, one of the endogenous ligands of cannabinoid CB1 and CB2 receptors. Signaling by N-acylethanolamines is terminated by release of the ethanolamine moiety by hydrolyzing enzymes such as fatty acid amide hydrolase (FAAH) and N-acylethanolamine-hydrolyzing amidase (NAAA). Herein, we report the design and synthesis of N-(16-(18)F-fluorohexadecanoyl)ethanolamine ((18)F-FHEA) as a positron emission tomography (PET) probe for imaging the activity of N-acylethanolamine hydrolyzing enzymes in the brain. Following intravenous administration of (18)F-FHEA in Swiss Webster mice, (18)F-FHEA was extracted from blood by the brain and underwent hydrolysis at the amide bond and incorporation of the resultant (18)F-fluorofatty acid into complex lipid pools. Pretreatment of mice with the FAAH inhibitor URB-597 (1 mg/kg IP) resulted in significantly slower (18)F-FHEA incorporation into lipid pools, but overall (18)F concentrations in brain regions were not altered. Likewise, pretreatment with a NAAA inhibitor, (S)-N-(2-oxo-3-oxytanyl)biphenyl-4-carboxamide (30 mg/kg IV), did not significantly affect the uptake of (18)F-FHEA in the brain. Although evidence was found that (18)F-FHEA behaves as a substrate of FAAH in the brain, the lack of sensitivity of brain uptake kinetics to FAAH inhibition discourages its use as a metabolically trapped PET probe of N-acylethanolamine hydrolyzing enzyme activity.

Impact of lipid nutrition on neural stem/progenitor cells

The neural system originates from neural stem/progenitor cells (NSPCs). Embryonic NSPCs first proliferate to increase their numbers and then produce neurons and glial cells that compose the complex neural circuits in the brain. New neurons are continually produced even after birth from adult NSPCs in the inner wall of the lateral ventricle and in the hippocampal dentate gyrus. These adult-born neurons are involved in various brain functions, including olfaction-related functions, learning and memory, pattern separation, and mood control. NSPCs are regulated by various intrinsic and extrinsic factors. Diet is one of such important extrinsic factors. Of dietary nutrients, lipids are important because they constitute the cell membrane, are a source of energy, and function as signaling molecules. Metabolites of some lipids can be strong lipid mediators that also regulate various biological activities. Recent findings have revealed that lipids are important regulators of both embryonic and adult NSPCs. We and other groups have shown that lipid signals including fat, fatty acids, their metabolites and intracellular carriers, cholesterol, and vitamins affect proliferation and differentiation of embryonic and adult NSPCs. A better understanding of the NSPCs regulation by lipids may provide important insight into the neural development and brain function.

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.

Fifteen weeks of dietary n-3 polyunsaturated fatty acid deprivation increase turnover of n-6 docosapentaenoic acid in rat-brain phospholipids

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-(14)C]DPAn-6 was infused intravenously for 5min 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. (196 words).

Regulation of complement factor H (CFH) by multiple miRNAs in Alzheimer's disease (AD) brain

Human brain cells rely on a specific subset of microRNAs (miRNAs or miRs) to shape their gene expression patterns, and this is mediated through microRNA effects on messenger RNA (mRNA) speciation and complexity. In recent studies (a) in short post-mortem interval Alzheimer's disease (AD) brain tissues versus age-matched controls, and (b) in pro-inflammatory cytokine- and Aβ42 peptide-stressed human neuronal-glial (HNG) cells in primary culture, we have identified several brain-abundant miRNA species found to be significantly up-regulated, including miR-125b and miR-146a. Both of these nuclear factor kappa B (NF-κB)-activated, 22 nucleotide small non-coding RNAs (sncRNAs) target the mRNA of the key, innate-immune- and inflammation-related regulatory protein, complement factor-H (CFH; chr 1q32), resulting in significant decreases in CFH expression (p < 0.01, ANOVA). Our results further indicate that HNG cells respond to IL-1β + Aβ42-peptide-induced stress by significant NF-κB-modulated up-regulation of miRNA-125b- and miRNA-146a. The complex interactive signaling of NF-κB, miR-125b, miR-146a, and perhaps other miRNAs, further illustrate interplay between inducible transcription factors and multiple pro-inflammatory sncRNAs that regulate CFH expression. The novel concept of miRNA actions involving mRNA target convergence and divergence are proposed and discussed. The combinatorial use of NF-кB inhibitors with anti-miRNAs (AMs; antagomirs) may have potential against CFH-driven pathogenic signaling in neurodegenerative disease, and may redirect our therapeutic perspectives to novel treatment strategies that have not yet been considered.

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.

Docosahexaenoic acid: brain accretion and roles in neuroprotection after brain hypoxia and ischemia

PURPOSE OF REVIEW

With important effects on neuronal lipid composition, neurochemical signaling and cerebrovascular pathobiology, docosahexaenoic acid (DHA), a n-3 polyunsaturated fatty acid, may emerge as a neuroprotective agent against cerebrovascular disease. This paper examines pathways for DHA accretion in brain and evidence for possible roles of DHA in prophylactic and therapeutic approaches for cerebrovascular disease.

RECENT FINDINGS

DHA is a major n-3 fatty acid in the mammalian central nervous system and enhances synaptic activities in neuronal cells. DHA can be obtained through diet or to a limited extent via conversion from its precursor, α-linolenic acid (α-LNA). DHA attenuates brain necrosis after hypoxic ischemic injury, principally by modulating membrane biophysical properties and maintaining integrity in functions between presynaptic and postsynaptic areas, resulting in better stabilizing intracellular ion balance in hypoxic-ischemic insult. Additionally, DHA alleviates brain apoptosis, by inducing antiapoptotic activities such as decreasing responses to reactive oxygen species, upregulating antiapoptotic protein expression, downregulating apoptotic protein expression, and maintaining mitochondrial integrity and function.

SUMMARY

DHA in brain relates to a number of efficient delivery and accretion pathways. In animal models DHA renders neuroprotection after hypoxic-ischemic injury by regulating multiple molecular pathways and gene expression.

Infection risk by dermatophytes during storage and after domestic laundry and their temperature-dependent inactivation

In the developed countries infections of the feet (tinea pedis, athlete's foot) and nails (onychomycosis) with the anthropophile fungus Trichophyton rubrum are most common. We examined the propagation of dermatophytes before and during domestic laundering. About 10% of the infectious material was transferred from contaminated textiles to sterile textiles during storage in a clothes basket simulation indicating a high infection risk during storage. This was evaluated with two quantification techniques: cultivation with subsequent colony counting and tracing of radioactively labelled propagating units. Both approaches reliably revealed similar results with the latter method reducing experimental time to few minutes compared to 2 weeks with the traditional method. The tracer technique allowed favourably to directly reflect the textile-bound infectious material at the moment of skin contact. To address the infection risk during domestic laundry, bioindicators with T. rubrum or the yeast Candida albicans were introduced into common domestic washing procedures with different temperature courses. While C. albicans did not survive any of the tests, T. rubrum could be recovered after washing at 30°C, indicating the risk potential of dermatophyte infections at home. Up to 16% of the initial fungus load was detected in the rinsing water. Washing at 60°C however, eliminated both pathogens, T. rubrum and C. albicans.

HSV-1 infection of human brain cells induces miRNA-146a and Alzheimer-type inflammatory signaling

Herpes simplex virus type-1 (HSV-1) infection of human brain cells induces changes in gene expression favorable to the propagation of the infecting agent and detrimental to the function of the host cells. We report that infection of human primary neural cells with a high phenotypic reactivator HSV-1 (17syn+) induces upregulation of a brain-enriched microRNA (miRNA)-146a that is associated with proinflammatory signaling in stressed brain cells and Alzheimer's disease. Expression of cytoplasmic phospholipase A2, the inducible prostaglandin synthase cyclooxygenase-2, and the neuroinflammatory cytokine interleukin-1beta were each upregulated. A known miRNA-146a target in the brain, complement factor H, was downregulated. These data suggest a role for HSV-1-induced miRNA-146a in the evasion of HSV-1 from the complement system, and the activation of key elements of the arachidonic acid cascade known to contribute to Alzheimer-type neuropathological change.

Synapse formation is enhanced by oral administration of uridine and DHA, the circulating precursors of brain phosphatides

OBJECTIVE

The loss of cortical and hippocampal synapses is a universal hallmark of Alzheimer's disease, and probably underlies its effects on cognition. Synapses are formed from the interaction of neurites projecting from "presynaptic" neurons with dendritic spines projecting from "postsynaptic" neurons. Both of these structures are vulnerable to the toxic effects of nearby amyloid plaques, and their loss contributes to the decreased number of synapses that characterize the disease. A treatment that increased the formation of neurites and dendritic spines might reverse this loss, thereby increasing the number of synapses and slowing the decline in cognition.

DESIGN SETTING, PARTICIPANTS, INTERVENTION, MEASUREMENTS AND RESULTS

We observe that giving normal rodents uridine and the omega-3 fatty acid docosahexaenoic acid (DHA) orally can enhance dendritic spine levels (3), and cognitive functions (32). Moreover this treatment also increases levels of biochemical markers for neurites (i.e., neurofilament-M and neurofilament-70) (2) in vivo, and uridine alone increases both these markers and the outgrowth of visible neurites by cultured PC-12 cells (9). A phase 2 clinical trial, performed in Europe, is described briefly.

DISCUSSION AND CONCLUSION

Uridine and DHA are circulating precursors for the phosphatides in synaptic membranes, and act in part by increasing the substrate-saturation of enzymes that synthesize phosphatidylcholine from CTP (formed from the uridine, via UTP) and from diacylglycerol species that contain DHA: the enzymes have poor affinities for these substrates, and thus are unsaturated with them, and only partially active, under basal conditions. The enhancement by uridine of neurite outgrowth is also mediated in part by UTP serving as a ligand for neuronal P2Y receptors. Moreover administration of uridine with DHA activates many brain genes, among them the gene for the m-1 metabotropic glutamate receptor [Cansev, et al, submitted]. This activation, in turn, increases brain levels of that gene's protein product and of such other synaptic proteins as PSD-95, synapsin-1, syntaxin-3 and F-actin, but not levels of non-synaptic brain proteins like beta-tubulin. Hence it is possible that giving uridine plus DHA triggers a neuronal program that, by accelerating phosphatide and synaptic protein synthesis, controls synaptogenesis. If administering this mix of phosphatide precursors also increases synaptic elements in brains of patients with Alzheimer 's disease, as it does in normal rodents, then this treatment may ameliorate some of the manifestations of the disease.

Rapid sample preparation and simultaneous quantitation of prostaglandins and lipoxygenase derived fatty acid metabolites by liquid chromatography-mass spectrometry from small sample volumes

BACKGROUND

Fatty acid metabolites play a key role in numerous physiological and pathological processes. A rapid liquid chromatography-mass spectrometry assay for the simultaneous determination of prostanoids, isoprostane and lipoxygenase (LOX) derived fatty acid metabolites in a small biological sample of only 20 microL was developed.

METHODS

Human plasma samples were applied to a filter spot, extracted without prior derivatization and analyzed within 13 min. Detection of metabolites was performed on a triple quadrupole mass spectrometer in negative multiple-reaction monitoring detection mode. Application of this assay to various biological matrices was performed.

RESULTS

The validated assay was linear over the concentration range of 5-500 nmol/L for prostanoids and isoprostane, 50-5000 nmol/L for LOX-derived metabolites and 400-40,000 nmol/L for fatty acids. Limits of quantitation were 0.4-233 nmol/L, depending on the metabolite. Plasma samples from diabetic patients and controls showed significant increases in (+/-)9-HODE and 15(S)-HETE with p-values of 0.019 and 0.024, respectively.

CONCLUSIONS

The small amount of 20 microL sample volume used in this assay and the demonstrated application to various sample types makes it an ideal routine analysis method for fatty acid metabolites. The resulting values for LOX-derived metabolites in diabetes mellitus type 2 samples support earlier findings about the role of lipid oxidation products in diabetes.

Fatty acid binding protein: localization and functional significance in the brain

Long chain fatty acids are important nutrients for brain development and function. However, the molecular basis of their actions in the brain is still to be clarified. Fatty acid-binding proteins (FABPs) belong to the multigene family of the intracellular lipid-binding protein. FABPs bind to long chain fatty acids, being involved in the promotion of cellular uptake and transport of fatty acids, the targeting of fatty acids to specific metabolic pathways, and the regulation of gene expression. FABPs are widely expressed in mammalian tissues, with distinct expression patterns for the individual protein. Although FABPs have been implicated to serve as regulators in systemic cellular metabolic pathways, recent studies have demonstrated the ability of FABPs to regulate functions of the brain, one of the most fat-enriched tissues in the body. This review summarizes the localization of FABPs in the brain, and recent progress in elucidating the function of FABPs in the brain.

Oral administration of circulating precursors for membrane phosphatides can promote the synthesis of new brain synapses

Although cognitive performance in humans and experimental animals can be improved by administering omega-3 fatty acid docosahexaenoic acid (DHA), the neurochemical mechanisms underlying this effect remain uncertain. In general, nutrients or drugs that modify brain function or behavior do so by affecting synaptic transmission, usually by changing the quantities of particular neurotransmitters present within synaptic clefts or by acting directly on neurotransmitter receptors or signal-transduction molecules. We find that DHA also affects synaptic transmission in mammalian brain. Brain cells of gerbils or rats receiving this fatty acid manifest increased levels of phosphatides and of specific presynaptic or postsynaptic proteins. They also exhibit increased numbers of dendritic spines on postsynaptic neurons. These actions are markedly enhanced in animals that have also received the other two circulating precursors for phosphatidylcholine, uridine (which gives rise to brain uridine diphosphate and cytidine triphosphate) and choline (which gives rise to phosphocholine). The actions of DHA aere reproduced by eicosapentaenoic acid, another omega-3 compound, but not by omega-6 fatty acid arachidonic acid. Administration of circulating phosphatide precursors can also increase neurotransmitter release (acetylcholine, dopamine) and affect animal behavior. Conceivably, this treatment might have use in patients with the synaptic loss that characterizes Alzheimer's disease or other neurodegenerative diseases or occurs after stroke or brain injury.

Chronic administration of docosahexaenoic acid or eicosapentaenoic acid, but not arachidonic acid, alone or in combination with uridine, increases brain phosphatide and synaptic protein levels in gerbils

Synthesis of phosphatidylcholine, the most abundant brain membrane phosphatide, requires three circulating precursors: choline; a pyrimidine (e.g. uridine); and a polyunsaturated fatty acid. Supplementing a choline-containing diet with the uridine source uridine-5'-monophosphate (UMP) or, especially, with UMP plus the omega-3 fatty acid docosahexaenoic acid (given by gavage), produces substantial increases in membrane phosphatide and synaptic protein levels within gerbil brain. We now compare the effects of various polyunsaturated fatty acids, given alone or with UMP, on these synaptic membrane constituents. Gerbils received, daily for 4 weeks, a diet containing choline chloride with or without UMP and/or, by gavage, an omega-3 (docosahexaenoic or eicosapentaenoic acid) or omega-6 (arachidonic acid) fatty acid. Both of the omega-3 fatty acids elevated major brain phosphatide levels (by 18-28%, and 21-27%) and giving UMP along with them enhanced their effects significantly. Arachidonic acid, given alone or with UMP, was without effect. After UMP plus docosahexaenoic acid treatment, total brain phospholipid levels and those of each individual phosphatide increased significantly in all brain regions examined (cortex, striatum, hippocampus, brain stem, and cerebellum). The increases in brain phosphatides in gerbils receiving an omega-3 (but not omega-6) fatty acid, with or without UMP, were accompanied by parallel elevations in levels of pre- and post-synaptic proteins (syntaxin-3, PSD-95 and synapsin-1) but not in those of a ubiquitous structural protein, beta-tubulin. Hence administering omega-3 polyunsaturated fatty acids can enhance synaptic membrane levels in gerbils, and may do so in patients with neurodegenerative diseases, especially when given with a uridine source, while the omega-6 polyunsaturated fatty acid arachidonic acid is ineffective.

Docosahexaenoic acid synthesis from α-linolenic acid by rat brain is unaffected by dietary n-3 PUFA deprivation

Rates of conversion of alpha-linolenic acid (alpha-LNA, 18:3n-3) to docosahexaenoic acid (DHA, 22:6n-3) by the mammalian brain and the brain's ability to upregulate these rates during dietary deprivation of n-3 polyunsaturated fatty acids (PUFAs) are unknown. To answer these questions, we measured conversion coefficients and rates in post-weaning rats fed an n-3 PUFA deficient (0.2% alpha-LNA of total fatty acids, no DHA) or adequate (4.6% alpha-LNA, no DHA) diet for 15 weeks. Unanesthetized rats in each group were infused intravenously with [1-(14)C]alpha-LNA, and their arterial plasma and microwaved brains collected at 5 minutes were analyzed. The deficient compared with adequate diet reduced brain DHA by 37% and increased brain arachidonic (20:4n-6) and docosapentaenoic (22:5n-6) acids. Only 1% of plasma [1-(14)C]alpha-LNA entering brain was converted to DHA with the adequate diet, and conversion coefficients of alpha-LNA to DHA were unchanged by the deficient diet. In summary, the brain's ability to synthesize DHA from alpha-LNA is very low and is not altered by n-3 PUFA deprivation. Because the liver's reported ability is much higher, and can be upregulated by the deficient diet, DHA converted by the liver from circulating alphaLNA is the source of the brain's DHA when DHA is not in the diet.

Differential gene expression patterns in cyclooxygenase-1 and cyclooxygenase-2 deficient mouse brain

Microarray analysis of gene expression in the cerebral cortex and hippocampus of mice deficient in cyclooxygenase-1 or cyclooxygenase-2 reveals that the two enzymes differentially modulate brain gene expression.

Background

Cyclooxygenase (COX)-1 and COX-2 produce prostanoids from arachidonic acid and are thought to have important yet distinct roles in normal brain function. Deletion of COX-1 or COX-2 results in profound differences both in brain levels of prostaglandin E₂ and in activation of the transcription factor nuclear factor-κB, suggesting that COX-1 and COX-2 play distinct roles in brain arachidonic acid metabolism and regulation of gene expression. To further elucidate the role of COX isoforms in the regulation of the brain transcriptome, microarray analysis of gene expression in the cerebral cortex and hippocampus of mice deficient in COX-1 (COX-1^-/-) or COX-2 (COX-2^-/-) was performed.

Results

A majority (>93%) of the differentially expressed genes in both the cortex and hippocampus were altered in one COX isoform knockout mouse but not the other. The major gene function affected in all genotype comparisons was 'transcriptional regulation'. Distinct biologic and metabolic pathways that were altered in COX^-/- mice included β oxidation, methionine metabolism, janus kinase signaling, and GABAergic neurotransmission.

Conclusion

Our findings suggest that COX-1 and COX-2 differentially modulate brain gene expression. Because certain anti-inflammatory and analgesic treatments are based on inhibition of COX activity, the specific alterations observed in this study further our understanding of the relationship of COX-1 and COX-2 with signaling pathways in brain and of the therapeutic and toxicologic consequences of COX inhibition.

Inflammation and skin cholesterol in LDLr-/-, apoA-I-/- mice: link between cholesterol homeostasis and self-tolerance?

Diet-fed low density lipoprotein receptor-deficient/apolipoprotein A-I-deficient (LDLr-/-, apoA-I-/-) mice accumulate a 10-fold greater mass of cholesterol in their skin despite a 1.5- to 2-fold lower plasma cholesterol concentration compared with diet-fed LDLr-/- mice. The accumulation of cholesterol predominantly in the skin has been shown to occur in a growing number of other hypercholesterolemic double knockout mouse models sharing deficits in genes regulating cellular cholesterol homeostasis. Exploring the relationship between cholesterol balance and inflammation, we have examined the time course of cholesterol accumulation in a number of extrahepatic tissues and correlated with the onset of inflammation in diet-fed LDLr-/-, apoA-I-/- mice. After 4 weeks of diet, LDLr-/-, apoA-I-/- mice showed a significant increase in skin cholesterol mass compared with LDLr-/- mice. In addition, after 4 weeks on the diet, cholesterol accumulation in the skin was also found to be associated with macrophage infiltration and accompanied by increases in tumor necrosis factor-alpha, cyclooxygenase-2, and langerin mRNA, which were not seen in the liver. Overall, these data suggest that as early as 4 weeks after starting the diet, the accumulation of skin cholesterol and the onset of inflammation occur concurrently. In summary, the use of hypercholesterolemic LDLr-/-, apoA-I-/- mice may provide a useful tool to investigate the role that apoA-I plays in maintaining cholesterol homeostasis and its relationship to inflammation.

Upregulated liver conversion of alpha-linolenic acid to docosahexaenoic acid in rats on a 15 week n-3 PUFA-deficient diet

We quantified incorporation rates of plasma-derived alpha-linolenic acid (alpha-LNA, 18:3n-3) into "stable" liver lipids and the conversion rate of alpha-LNA to docosahexaenoic acid (DHA, 22:6n-3) in male rats fed, after weaning, an n-3 PUFA-adequate diet (4.6% alpha-LNA, no DHA) or an n-3 PUFA-deficient diet (0.2% alpha-LNA, no DHA) for 15 weeks. Unanesthetized rats were infused intravenously with [1-14C]alpha-LNA, and arterial plasma was sampled until the liver was microwaved at 5 min. Unlabeled alpha-LNA and DHA concentrations in arterial plasma and liver were reduced >90% by deprivation, whereas unlabeled arachidonic acid (20:4n-6) and docosapentaenoic acid (22:5n-6) concentrations were increased. Deprivation did not change alpha-LNA incorporation coefficients into stable liver lipids but increased synthesis-incorporation coefficients of DHA from alpha-LNA by 6.6-, 8.4-, and 2.3-fold in triacylglycerol, phospholipid, and cholesteryl ester, respectively. Assuming that synthesized-incorporated DHA eventually would be secreted within lipoproteins, calculated liver DHA secretion rates equaled 2.19 and 0.82 micromol/day in the n-3 PUFA-adequate and -deprived rats, respectively. These rates exceed the published rates of brain DHA consumption by 6- and 10-fold, respectively, and should be sufficient to maintain normal and reduced brain DHA concentrations, respectively, in the two dietary conditions.

Low liver conversion rate of alpha-linolenic to docosahexaenoic acid in awake rats on a high-docosahexaenoate-containing diet

We quantified the rates of incorporation of alpha-linolenic acid (alpha-LNA; 18:3n-3) into "stable" lipids (triacylglycerol, phospholipid, cholesteryl ester) and the rate of conversion of alpha-LNA to docosahexaenoic acid (DHA; 22: 6n-3) in the liver of awake male rats on a high-DHA-containing diet after a 5-min intravenous infusion of [1-(14)C]alpha-LNA. At 5 min, 72.7% of liver radioactivity (excluding unesterified fatty acid radioactivity) was in stable lipids, with the remainder in the aqueous compartment. Using our measured specific activity of liver alpha-LNA-CoA, in the form of the dilution coefficient lambda(alpha-LNA-CoA), we calculated incorporation rates of unesterified alpha-LNA into liver triacylglycerol, phospholipid, and cholesteryl ester as 2,401, 749, and 9.6 nmol/s/g x 10(-4), respectively, corresponding to turnover rates of 3.2, 8.7, and 2.9%/min and half-lives of 8-24 min. A lower limit for the DHA synthesis rate from alpha-LNA equaled 15.8 nmol/s/g x 10(-4) (0.5% of the net in corporation rate). Thus, in rats on a high-DHA-containing diet, rates of beta-oxidation and esterification of alpha-LNA into stable liver lipids are high, whereas its conversion to DHA is comparatively low and insufficient to supply significant DHA to the brain. High incorporation and turnover rates likely reflect a high secretion rate by liver of stable lipids within very low density lipoproteins.

Characterizing the Phospholipid Profiles in Mammalian Tissues by MALDI FTMS

Discussed here is an analytical method for profiling lipids and phospholipids directly from mammalian tissues excised from Mus musculus (house mouse). Biochemical analysis was accomplished through the use of matrix-assisted laser desorption/ionization (MALDI) Fourier transform mass spectrometry, where whole tissue sections of mouse brain, heart, and liver were investigated. Lipid and phospholipid ions create complex MALDI mass spectra containing multiple ions with different m/z values corresponding to the same fundamental chemical species. When a computational sorting approach is used to group these ions, the standard deviation for observed relative chemical abundance can be reduced to 6.02%. Relative standard deviations of 10% are commonly accepted for standard chromatographic phospholipid analyses. Average mass measurement accuracy for 232 spectra representing three tissue types from 12 specimens was calculated to be 0.0053 Da. Further it is observed, that the data and the analysis between all the animals have near-identical phospholipid contents in their brain, heart, and liver tissues, respectively. In addition to the need to accurately measure relative abundances of phospholipid species, it is essential to have adequate mass resolution for complete and accurate overall analysis. It is reasonable to make mass composition assignments with spectral resolving power greater than 8000. However, results from the present study reveal 14 instances (C12 carbon isotope) of multiple m/z ions having the same nominal value that require greater resolution in order that overlap will not occur. Spectra measured here have an average resolving power of 12 000. It is established that high mass resolution and mass accuracy coupled with MALDI ionization provide for rapid and accurate phospholipid analysis of mammalian tissue sections.