In vivo approaches to quantifying and imaging brain arachidonic and docosahexaenoic acid metabolism

Measuring brain docosahexaenoic acid turnover as a marker of metabolic consumption

Docosahexaenoic acid (DHA, 22:6n-3) accretion in brain phospholipids is critical for maintaining the structural fluidity that permits proper assembly of protein complexes for signaling. Furthermore, membrane DHA can by released by phospholipase A₂ and act as substrate for synthesis of bioactive metabolites that regulate synaptogenesis, neurogenesis, inflammation, and oxidative stress. Thus, brain DHA is consumed through multiple pathways including mitochondrial β-oxidation, autoxidation to neuroprostanes, as well as enzymatic synthesis of bioactive metabolites including oxylipins, synaptamide, fatty-acid amides, and epoxides. By using models developed by Rapoport and colleagues, brain DHA loss has been estimated to be 0.07-0.26 μmol DHA/g brain/d. Since β-oxidation of DHA in the brain is relatively low, a large portion of brain DHA loss may be attributed to synthesis of autoxidative and bioactive metabolites. In recent years, we have developed a novel application of compound specific isotope analysis to trace DHA metabolism. By the use of natural abundance in ¹³C-DHA in food supply, we are able to trace brain phospholipid DHA loss in free-living mice with estimates ranging from 0.11 to 0.38 μmol DHA/g brain/d, in reasonable agreement with previous methods. This novel fatty acid metabolic tracing methodology should improve our understanding of the factors that regulate brain DHA metabolism.

Cyclooxygenases as Potential PET Imaging Biomarkers to Explore Neuroinflammation in Dementia

The most frequently studied target of neuroinflammation using PET is 18-kDa translocator protein, but its limitations have spurred the molecular imaging community to find more promising targets. This article reviews the development of PET radioligands for cyclooxygenase (COX) subtypes 1 and 2, enzymes that catalyze the production of inflammatory prostanoids in the periphery and brain. Although both isozymes produce the same precursor compound, prostaglandin H₂, they have distinct functions based on their differential cellular localization in the periphery and brain. For example, COX-1 is located primarily in microglia, a resident inflammatory cell in the brain whose role in producing inflammatory cytokines is well documented. In contrast, COX-2 is located primarily in neurons and can be markedly upregulated by inflammatory and excitatory stimuli, but its functions are poorly understood. This article reviews these 2 isozymes as biomarkers of neuroinflammation, as well as the radioligands that have recently been developed to image them in animals and humans. To place this work into context, the properties of COX-1 and COX-2 are compared with 18-kDa translocator protein, with special consideration of their application in Alzheimer disease as a representative neurodegenerative disorder.

Different patterns of association between white matter microstructure and plasma unsaturated fatty acids in those with high risk for psychosis and healthy participants

Background

Disrupted white matter (WM) microstructure has been commonly identified in youth at clinical high risk (CHR) for psychosis. Several lines of evidence suggest that fatty acids, especially unsaturated fatty acids (UFAs), might play a crucial role in the WM pathology of early onset psychosis. However, evidence linking UFA and WM microstructure in CHR is quite sparse.

Aims

We investigated the relationship between the plasma UFA level and WM microstructure in CHR participants and healthy controls (HC).

Methods

Plasma fatty acids were assessed and diffusion tensor imaging (DTI) data were performed with tract-based spatial statistics (TBSS) analysis for 66 individuals at CHR for psychosis and 70 HC.

Results

Both the global and regional diffusion measures showed significant between-group differences, with decreased fractional anisotropy (FA) but increased mean diffusivity (MD) and radial diffusivity (RD) found in the CHR group compared with the HC group. On top of that, we found that in the HC group, plasma arachidic acid showed obvious trend-level associations with higher global FA, lower global MD and lower global RD, which regionally spread over the corpus callosum, right anterior and superior corona radiata, bilateral anterior and posterior limb of the internal capsule, and bilateral superior longitudinal fasciculus. However, there were no associations between global WM measures and any UFA in the CHR group. Conversely, we even found negative associations between arachidic acid levels and regional FA values in the right superior longitudinal fasciculus and right retrolenticular part of the internal capsule in the CHR group.

Conclusions

Compared with the HC group, CHR subjects exhibited a different pattern of association between WM microstructure and plasma UFA, with a neuroprotective effect found in the HC group but not in the CHR group. Such discrepancy could be due to the excessively upregulated UFAs accumulated in the plasma of the CHR group, highlighting the role of balanced plasma-membrane fatty acids homeostasis in WM development.

The intermediary role of the central cyclooxygenase / lipoxygenase enzymes in intracerebroventricular injected nesfatin-1-evoked cardiovascular effects in rats

That nesfatin-1 is a neuromodulatory peptide for the cardiovascular system is well documented. Several central receptors have been shown to mediate the cardiovascular effects of nesfatin-1. Immunohistochemistry and Western blot studies showed that nesfatin-1 activated the expression of the central cyclooxygenase (COX) -1, -2 and lipoxygenase (LOX). In addition, microdialysis study showed that nesfatin-1 increased the release of total prostaglandins and leukotrienes from the hypothalamus. The present study investigated whether the central COX and LOX enzymes have a direct mediating role in the MAP and HR responses of nesfatin-1. Intracerebroventricularly administered nesfatin-1 produced dose-dependent pressor and phasic HR responses in normotensive conscious rats Sprague Dawley. Central pretreatment with a COX1/2 inhibitor, ibuprofen, completely blocked the nesfatin-1-induced responses. However, central pretreatment with a nonselective LOX inhibitor, nordihydroguaiaretic acid, partially attenuated the cardiovascular responses induced by nesfatin-1. The results suggest that centrally administered nesfatin-1 activates the central enzymes COX and LOX, which may be involved in the cardiovascular responses as a novel central mechanism for nesfatin-1.

Docosahexaenoic Acid-Loaded Polylactic Acid Core-Shell Nanofiber Membranes for Regenerative Medicine after Spinal Cord Injury: In Vitro and In Vivo Study

Spinal cord injury (SCI) is associated with disability and a drastic decrease in quality of life for affected individuals. Previous studies support the idea that docosahexaenoic acid (DHA)-based pharmacological approach is a promising therapeutic strategy for the management of acute SCI. We postulated that a nanostructured material for controlled delivery of DHA at the lesion site may be well suited for this purpose. Toward this end, we prepare drug-loaded fibrous mats made of core-shell nanofibers by electrospinning, which contained a polylactic acid (PLA) shell for encapsulation of DHA within the core, for delivery of DHA in situ. In vitro study confirmed sustained DHA release from PLA/DHA core-shell nanofiber membrane (CSNM) for up to 36 days, which could significantly increase neurite outgrowth from primary cortical neurons in 3 days. This is supported by the upregulation of brain-derived neurotropic factor (BDNF) and neurotrophin-3 (NT-3) neural marker genes from qRT-PCR analysis. Most importantly, the sustained release of DHA could significantly increase the neurite outgrowth length from cortical neuron cells in 7 days when co-cultured with PLA/DHA CSNM, compared with cells cultured with 3 μM DHA. From in vivo study with a SCI model created in rats, implantation of PLA/DHA CSNM could significantly improve neurological functions revealed by behavior assessment in comparison with the control (no treatment) and the PLA CSNM groups. According to histological analysis, PLA/DHA CSNM also effectively reduced neuron loss and increased serotonergic nerve sprouting. Taken together, the PLA/DHA CSNM may provide a nanostructured drug delivery system for DHA and contribute to neuroprotection and promoting neuroplasticity change following SCI.

Selective Visualization of Administrated Arachidonic and Docosahexaenoic Acids in Brain Using Combination of Simple Stable Isotope-Labeling Technique and Imaging Mass Spectrometry

We developed a new method for monitoring the distribution of administrated fatty acids in the body by combination of a stable isotope-labeling technique and imaging mass spectrometry (IMS). The developed stable isotope-labeling technique is very simple and able to adapt to all the fatty acid species. In this study, we synthesized stable isotope-labeled arachidonic acid (AA) and docosahexaenoic acid (DHA), and they were simultaneously administrated to mice to examine their migrations and distributions in the brain. The administrated AA and DHA have two more molecular weights compared to the originals and apparently were distinguished from the originally accumulated AA and DHA in the brain using IMS. As a result, we reveal that the administered AA and DHA first accumulated in the hippocampus and cerebellar cortex in the brain. This technique does not use radio isotopes and would appear to elucidate the role of all kinds of fatty acid species in the body.

Modulation of arachidonic acid-evoked cardiorespiratory effects by the central lipoxygenase pathway

We previously reported that intracerebroventricularly (ICV) injected arachidonic acid (AA) could produce pressor and bradycardic responses on the cardiovascular system and hyperventilation effect on the respiratory system by activating cyclooxygenase (COX). We also demonstrated that centrally injected AA-induced cardiovascular and respiratory responses were mediated by COX-metabolites, such as thromboxane A₂ (TXA₂), prostaglandin (PG) D, PGE, and PGF_2α. Brain tissue is also able to express the lipoxygenase (LOX) enzyme and LOX-induced AA-metabolites. The current study was designed to investigate the possible mediation of the central LOX pathway in AA-induced cardiorespiratory effects in anesthetized rats. Central pretreatment with different doses of a non-selective LOX inhibitor, nordihydroguaiaretic acid (NDGA) (500 and 1000 μg; ICV) partially blocked the AA (0.5 μmol; ICV)-evoked pressor and bradycardic cardiovascular responses in male anesthetized Sprague Dawley rats. Pretreatment with different doses of NDGA (500 and 1000 μg; ICV) also reduced AA-induced hyperventilation responses, with an increase in tidal volume, respiratory rate and minute ventilation, in the rats. Moreover, AA-induced increasing pO₂ and decreasing pCO₂ responses were diminished by central NDGA pretreatment. In summary, our findings show that the central LOX pathway might mediate, at least in part, centrally administered AA-evoked cardiorespiratory and blood gases responses.

Intracerebroventricularly injected nesfatin-1 activates central cyclooxygenase and lipoxygenase pathways

Nesfatin-1 is a multifunctional neuropeptide having crucial autonomic roles. It is well known that nesfatin-1 collaborates with other central neuromodulatory systems, such as central corticotropin-releasing hormone, melanocortin, oxytocin, and cholinergic systems to show its autonomic effects. Central arachidonic acid cascade plays an important role to provide the homeostasis by exhibiting similar autonomic effects to nesfatin-1. Based on these similarities, the current study was designed to show the effects of intracerebroventricularly (ICV) injected nesfatin-1 on the hypothalamic arachidonic acid (AA) cascade. Immunochemistry and western blot approaches demonstrated that ICV administration of nesfatin-1 provokes an increase in the hypothalamic cyclooxygenase (COX) -1, -2 and lipoxygenase (LOX) protein expression. Moreover, the microdialysis study demonstrated that centrally injected nesfatin-1 increased the posterior hypothalamic extracellular AA products. In conclusion, these findings report that while nesfatin-1 is generating its autonomic effects, it also might be using central prostaglandins and leukotrienes by activating central COX and LOX pathways.

Combining a high DHA multi-nutrient supplement with aerobic exercise: Protocol for a randomised controlled study assessing mobility and cognitive function in older women

There is a complex interplay between cognition and gait in older people, with declines in gait speed coexisting with, or preceding cognitive decline. Omega-3 fatty acids, B vitamins, vitamin E, phosphatidylserine, and Ginkgo Biloba show promise in preserving mobility and cognitive function in older adults. Exercise benefits mobility and there is evidence suggesting positive interactions between exercise and omega-3 fatty acids on physical and cognitive function in older adults. Non-frail or pre-frail females aged ≥60 years are included in a randomized placebo controlled study. Intervention groups are: high DHA multi-nutrient supplement and exercise, placebo supplement and exercise, high DHA multi-nutrient supplement, and placebo supplement. Dietary supplementation is 24 weeks. The exercise intervention, two cycle ergometer classes per week, is for the final 12 weeks. The primary outcome is habitual walking speed, secondary outcomes include gait variables under single and dual task, five times sit to stand, verbal and spatial memory, executive function, interference control and health related quality of life. Blood fatty acids, serum homocysteine, dietary intake, physical activity, and verbal intelligence are measured to assess compliance and control for confounding factors. The study is registered at www.clinicaltrials.gov (NCT03228550).

Functional fluxolipidomics of polyunsaturated fatty acids and oxygenated metabolites in the blood vessel compartment

Synthesis of bioactive oxygenated metabolites of polyunsaturated fatty acids and their degradation or transformation products are made through multiple enzyme processes. The kinetics of the enzymes responsible for the different steps are known to be quite diverse, although not precisely determined. The location of the metabolites biosynthesis is diverse as well. Also, the biological effects of the primary and secondary products, and their biological life span are often completely different. Consequently, phenotypes of cells in response to these bioactive lipid mediators must then depend on their concentrations at a given time. This demands a fluxolipidomics approach that can be defined as a mediator lipidomics, with all measurements done as a function of time and biological compartments. This review points out what is known, even qualitatively, in the blood vascular compartment for arachidonic acid metabolites and number of other metabolites from polyunsaturated fatty acids of nutritional value. The functional consequences are especially taken into consideration.

The role of polyunsaturated fatty acids and GPR40 receptor in brain

Polyunsaturated fatty acids (PUFAs) are found in abundance in the nervous system. They perform significant functions for example boosting synaptogenesis, neurogenesis, inducing antinociception, stimulating gene expression and neuronal activity, preventing apoptosis and neuroinflammation. G-protein-coupled receptor 40 (GPR40), also called free fatty acid receptor 1 (FFA1), is ubiquitously expressed in various regions of the human brain including the olfactory bulb, midbrain, medulla oblongata, hippocampus, hypothalamus, cerebral cortex, cerebellum and in the spinal cord. GPR40, when binding with polyunsaturated fatty acids (PUFAs) has shown promising therapeutic potential. This review presents current knowledge regarding the pharmacological properties of GPR40 and addresses its functions in brain, with a focus on neurodevelopment & neurogenesis. Furthermore, the demonstration of GPR40 involvement in several neuropathological conditions such as apoptosis, inflammatory pain, Alzheimer's disease and Parkinson's disease. Although the results are encouraging, further research is needed to clarify their role in the treatment of inflammatory pain, Alzheimer's disease and Parkinson's disease. This article is part of the Special Issue entitled 'Lipid Sensing G Protein-Coupled Receptors in the CNS'.

Role of TRP channels in the cardiovascular system

The transient receptor potential (TRP) superfamily consists of a large number of nonselective cation channels with variable degree of Ca(2+)-permeability. The 28 mammalian TRP channel proteins can be grouped into six subfamilies: canonical, vanilloid, melastatin, ankyrin, polycystic, and mucolipin TRPs. The majority of these TRP channels are expressed in different cell types including both excitable and nonexcitable cells of the cardiovascular system. Unlike voltage-gated ion channels, TRP channels do not have a typical voltage sensor, but instead can sense a variety of other stimuli including pressure, shear stress, mechanical stretch, oxidative stress, lipid environment alterations, hypertrophic signals, and inflammation products. By integrating multiple stimuli and transducing their activity to downstream cellular signal pathways via Ca(2+) entry and/or membrane depolarization, TRP channels play an essential role in regulating fundamental cell functions such as contraction, relaxation, proliferation, differentiation, and cell death. With the use of targeted deletion and transgenic mouse models, recent studies have revealed that TRP channels are involved in numerous cellular functions and play an important role in the pathophysiology of many diseases in the cardiovascular system. Moreover, several TRP channels are involved in inherited diseases of the cardiovascular system. This review presents an overview of current knowledge concerning the physiological functions of TRP channels in the cardiovascular system and their contributions to cardiovascular diseases. Ultimately, TRP channels may become potential therapeutic targets for cardiovascular diseases.

Radiolabeled COX-2 inhibitors for non-invasive visualization of COX-2 expression and activity--a critical update

Cyclooxygenase-2 (COX-2) is a key player in inflammation. Its overexpression is directly associated with various inflammatory diseases and, additionally, with several processes of carcinogenesis. The development of new selective COX-2 inhibitors (COXIBs) for use in cancer treatment is in the focus of the medicinal chemistry research field. For this purpose, a set of methods is available to determine COX-2 expression and activity in vitro and ex vivo but it is still a problem to functionally characterize COX-2 in vivo. This review focusses on imaging agents targeting COX-2 which have been developed for positron emission tomography (PET) and single photon emission computed tomography (SPECT) since 2005. The literature reveals that different radiochemical methods are available to synthesize COXIBs radiolabeled with fluorine-18, carbon-11, and isotopes of radioiodine. Unfortunately, most of the compounds tested did not show sufficient stability in vivo due to de[¹⁸F]fluorination or de[¹¹C]methylation or they failed to bind specifically in the target region. So, suitable stability in vivo, matching lipophilicity for the target compartment and both high affinity and selectivity for COX-2 were identified as prominent criteria for radiotracer development. Up to now, it is not clear what approach and which model is the most suited to evaluate COX-2 targeting imaging agents in vivo. However, for proof of principle it has been shown that some radiolabeled compounds can bind specifically in COX-2 overexpressing tissue which gives hope for future work in this field.

Omega-3 fatty acids and brain resistance to ageing and stress: body of evidence and possible mechanisms

The increasing life expectancy in the populations of rich countries raises the pressing question of how the elderly can maintain their cognitive function. Cognitive decline is characterised by the loss of short-term memory due to a progressive impairment of the underlying brain cell processes. Age-related brain damage has many causes, some of which may be influenced by diet. An optimal diet may therefore be a practical way of delaying the onset of age-related cognitive decline. Nutritional investigations indicate that the ω-3 poyunsaturated fatty acid (PUFA) content of western diets is too low to provide the brain with an optimal supply of docosahexaenoic acid (DHA), the main ω-3 PUFA in cell membranes. Insufficient brain DHA has been associated with memory impairment, emotional disturbances and altered brain processes in rodents. Human studies suggest that an adequate dietary intake of ω-3 PUFA can slow the age-related cognitive decline and may also protect against the risk of senile dementia. However, despite the many studies in this domain, the beneficial impact of ω-3 PUFA on brain function has only recently been linked to specific mechanisms. This review examines the hypothesis that an optimal brain DHA status, conferred by an adequate ω-3 PUFA intake, limits age-related brain damage by optimizing endogenous brain repair mechanisms. Our analysis of the abundant literature indicates that an adequate amount of DHA in the brain may limit the impact of stress, an important age-aggravating factor, and influences the neuronal and astroglial functions that govern and protect synaptic transmission. This transmission, particularly glutamatergic neurotransmission in the hippocampus, underlies memory formation. The brain DHA status also influences neurogenesis, nested in the hippocampus, which helps maintain cognitive function throughout life. Although there are still gaps in our knowledge of the way ω-3 PUFA act, the mechanistic studies reviewed here indicate that ω-3 PUFA may be a promising tool for preventing age-related brain deterioration.

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.

Supplementation with DHA and the psychological functioning of young adults

The grey matter of the brain contains high levels of the essential nutrient DHA. Although the role of DHA in the developing brain and in dementia has attracted attention, its influence on the brain of the healthy adult has been little considered. A total of 285 young adult females took 400 mg of DHA, in a double-blind, placebo-controlled trial, for 50 d. After 50 d, recently acquired information was more likely to be forgotten by those who had consumed DHA. No significant differences in mood, reaction times, vigilance or visual acuity were found.

The utility of (11)C-arachidonate PET to study in vivo dopaminergic neurotransmission in humans

We developed a novel method to study dopaminergic neurotransmission using positron emission tomography (PET) with [1-(11)C]arachidonic acid ([1-(11)C]AA). Previous preclinical studies have shown the utility of [1-(11)C]AA as a marker of signal transduction coupled to cytosolic phospholipase A(2) (cPLA(2)). Using [1-(11)C]AA and [(15)O]water PET, we measured regional incorporation coefficients K(*) for AA and regional cerebral blood flow (rCBF), respectively, in healthy male volunteers given the D(1)/D(2) 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 D(2)-like receptors coupled to cPLA(2). Changes in rCBF are consistent with previous studies showing net functional effects of D(1)/D(2) activation. [1-(11)C]AA PET may be useful for studying disturbances of dopaminergic neurotransmission in conditions such as Parkinson's disease and schizophrenia.

Dietary n-6 polyunsaturated fatty acid deprivation increases docosahexaenoic acid metabolism in rat brain

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 A(2) (cPLA(2) -IVA) and cyclooxygenase (COX)-2 expression, while increasing brain docosahexaenoic acid (DHA, 22:6n-3) concentration and DHA-selective calcium-independent phospholipase A(2) (iPLA(2) )-VIA expression. We hypothesized that these changes are accompanied by up-regulated 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-(14) C]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 acid n-3 (DPAn-3, 22:5n-3), and DHA (by 9.4%) concentrations, particularly in ethanolamine glycerophospholipid (EtnGpl). 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 promotes neuroprotection and alters neurotransmission.

Effects of zinc and DHA on the epigenetic regulation of human neuronal cells

Dietary intake of zinc and omega-3 fatty acids (DHA) have health benefits for a number of human diseases. However, the molecular basis of these health benefits remains unclear. Recently, we reported that zinc and DHA affect expression levels of histones H3 and H4 in human neuronal M17 cells. Here, using immunoblotting and densitometric analysis, we aimed to investigate the effect of zinc and DHA on post-translational modifications of histone H3 in M17 cells. In response to increase in zinc concentration, we observed increase in deacetylation, methylation and phosphorylation of H3 and decrease in acetylation. We also investigated the role of zinc in apoptosis, and found that zinc reduced the levels of the anti-apoptotic marker Bcl-2 while increasing the apoptotic marker caspase-3 levels, correlating with cell viability assays. Conversely, DHA treatment resulted in increase in acetylation of H3 and Bcl-2 levels and decrease in deacetylation, methylation, phosphorylation of H3 and caspase-3 levels, suggesting that DHA promotes gene expression and neuroprotection. Our novel findings show the opposing effects of zinc and DHA on the epigenetic regulation of human neuronal cells and highlight the potential benefit of dietary intake of DHA for management of neurodegenerative diseases.

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.

Sex differences in the relationship of dietary Fatty acids to cognitive measures in american children

Because the first neurons evolved in an environment high in the n−3 (omega-3) fatty acid docosahexaenoic acid (DHA), this fatty acid became a major component of neural structure and function and makes up 10% of the dry weight of the human brain. Since n−3 fatty acids must come from the diet, this suggests a possible positive role for dietary n−3 fatty acids in cognition and a possible negative role for n−6 fatty acids, which compete with n−3 for access to critical enzymes. Because human females must provide DHA for the growth of the unusually large brains of their offspring from maternal fat stored during childhood, their need for DHA is especially great. We used stepwise regression to determine whether particular dietary fatty acids and other nutrients were related to cognitive performance in over 4000 American children aged 6–16 from the Third National Health and Nutrition Examination Survey; a variety of possible biological, social, and environmental risk factors were statistically controlled. In this context the only dietary factors related to cognitive performance were n−3 and n−6 fatty acids. Dietary n−3 fatty acids were positively related to cognitive test scores in male and female children, while n−6 showed the reverse relationship, significantly so in females. In female children the positive effects of n−3 intake were twice as strong as in males and exceeded the negative effects of lead exposure. This suggests that increasing dietary intake of n−3 and decreasing n−6 fatty acids may have cognitive benefits in children, especially in females.

Ginger phenylpropanoids inhibit IL-1beta and prostanoid secretion and disrupt arachidonate-phospholipid remodeling by targeting phospholipases A2

The rhizome of ginger (Zingiber officinale) is employed in Asian traditional medicine to treat mild forms of rheumatoid arthritis and fever. We have profiled ginger constituents for robust effects on proinflammatory signaling and cytokine expression in a validated assay using human whole blood. Independent of the stimulus used (LPS, PMA, anti-CD28 Ab, anti-CD3 Ab, and thapsigargin), ginger constituents potently and specifically inhibited IL-1β expression in monocytes/macrophages. Both the calcium-independent phospholipase A(2) (iPLA(2))-triggered maturation and the cytosolic phospholipase A(2) (cPLA(2))-dependent secretion of IL-1β from isolated human monocytes were inhibited. In a fluorescence-coupled PLA(2) assay, most major ginger phenylpropanoids directly inhibited i/cPLA(2) from U937 macrophages, but not hog pancreas secretory phospholipase A(2). The effects of the ginger constituents were additive and the potency comparable to the mechanism-based inhibitor bromoenol lactone for iPLA(2) and methyl arachidonyl fluorophosphonate for cPLA(2), with 10-gingerol/-shogaol being most effective. Furthermore, a ginger extract (2 μg/ml) and 10-shogaol (2 μM) potently inhibited the release of PGE(2) and thromboxane B2 (>50%) and partially also leukotriene B(4) in LPS-stimulated macrophages. Intriguingly, the total cellular arachidonic acid was increased 2- to 3-fold in U937 cells under all experimental conditions. Our data show that the concurrent inhibition of iPLA(2) and prostanoid production causes an accumulation of free intracellular arachidonic acid by disrupting the phospholipid deacylation-reacylation cycle. The inhibition of i/cPLA(2), the resulting attenuation of IL-1β secretion, and the simultaneous inhibition of prostanoid production by common ginger phenylpropanoids uncover a new anti-inflammatory molecular mechanism of dietary ginger that may be exploited therapeutically.

LC/MS/MS method for analysis of E₂ series prostaglandins and isoprostanes

15-series prostaglandins (PGE₂s) and isoprostanes (isoPGE₂s) are robust biomarkers of oxidative stress, possess potent biological activity, and may be derived through cyclooxygenase or free radical pathways. Thus, their quantification is critical in understanding many biological processes where PG, isoPG, or oxidative stress are involved. LC/MS/MS methods allow a highly selective, sensitive, simultaneous analysis for prostanoids without derivatization. However, the LC/MS/MS methods currently used do not allow for simultaneous separation of the major brain PGE₂/D₂) and isoPGE₂ without derivatization and multiple HPLC separations. The developed LC/MS/MS method allows for the major brain PGE₂/PGD₂/isoPGE₂ such as PGE₂, entPGE₂, 8-isoPGE₂, 11β-PGE₂, PGD₂, and 15(R)-PGD₂ to be separated and quantified without derivatization. The method was validated by analyzing free and esterified isoPGE₂ in mouse brains fixed with head-focused microwave irradiation before or after global ischemia. Using the developed method, we report for the first time the esterified isoPGE₂ levels in brain tissue under basal conditions and upon global ischemia and demonstrate a nonreleasable pool of esterified isoPG upon ischemia. In addition, we demonstrated that PGE₂s found esterified in the sn-2 position in phospholipids are derived from a free radical nonenzymatic pathway under basal conditions. Our method for brain PG analysis provides a high level of selectivity to detect changes in brain PG and isoPG mass under both basal and pathological conditions.

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.

Brain arachidonic acid uptake and turnover: implications for signaling and bipolar disorder

PURPOSE OF REVIEW

Arachidonic acid was first detected in the brain in 1922. Although earlier work examined the role of arachidonic acid in growth and development, more recent advancements have elucidated roles for arachidonic acid in brain health and disease.

RECENT FINDINGS

In this review, we summarize evidence demonstrating that unesterified arachidonic acid in the plasma pool, which is supplied in part from adipose, is readily taken up and incorporated into brain phospholipids. By labeling plasma unesterified arachidonic acid, it is possible to trace the subsequent release of arachidonic acid from brain phospholipids upon neuroreceptor-mediated release by phospholipase A2 in response to drugs and neuroinflammation in rodents. With the synthesis of 11C labeled fatty acids, brain arachidonic acid signaling can now be measured in humans with position emission tomography. Arachidonic acid signals are known to regulate important biological functions, including neuroinflammation and excitotoxicity, and we focus on how the brain arachidonic acid cascade is a common target of drugs used to treat bipolar disorder (e.g. lithium, carbamazepine and valproate).

SUMMARY

A better understanding of the regulation of arachidonic acid uptake into the brain and the brain arachidonic acid cascade could lead to new imaging techniques and the identification of novel therapeutic targets in excitotoxicity, neuroinflammation and bipolar disorder.

Can the rat liver maintain normal brain DHA metabolism in the absence of dietary DHA?

BACKGROUND

Docosahexaenoic acid (DHA) is required for normal brain function. The concentration of DHA in the brain depends on both diet and liver metabolism.

OBJECTIVE

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 alpha-linolenic acid (alpha-LNA).

DESIGN

Following weaning, male rats were fed for 15 weeks either: (1) a diet with a high DHA and alpha-LNA content, (2) an n-3 PUFA "adequate" diet containing 4.6% alpha-LNA but no DHA, or (3) an n-3 PUFA "deficient" diet containing 0.2% alpha-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]alpha-LNA.

RESULTS

Brain DHA concentrations equaled 17.6, 11.4 and 7.14 microm/g in rats on diets 1, 2 and 3, respectively. With each diet, the rate of brain DHA synthesis from alpha-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 Delta5 and Delta6 activities in liver than in brain accounted for the higher liver DHA synthesis rates. Furthermore, these enzymes were transcriptionally upregulated in liver but not in brain of rats fed the deficient diet.

CONCLUSIONS

While DHA is essential to normal brain function, this need might be covered by dietary alpha-LNA when liver metabolic conversion machinery is intact and the diet has a high alpha-LNA content.

Bipolar disorder and mechanisms of action of mood stabilizers

Bipolar disorder (BD) is a major medical and social burden, whose cause, pathophysiology and treatment are not agreed on. It is characterized by recurrent periods of mania and depression (Bipolar I) or of hypomania and depression (Bipolar II). Its inheritance is polygenic, with evidence of a neurotransmission imbalance and disease progression. Patients often take multiple agents concurrently, with incomplete therapeutic success, particularly with regard to depression. Suicide is common. Of the hypotheses regarding the action of mood stabilizers in BD, the "arachidonic acid (AA) cascade" hypothesis is presented in detail in this review. It is based on evidence that chronic administration of lithium, carbamazepine, sodium valproate, or lamotrigine to rats downregulated AA turnover in brain phospholipids, formation of prostaglandin E(2), and/or expression of AA cascade enzymes, including cytosolic phospholipase A(2), cyclooxygenase-2 and/or acyl-CoA synthetase. The changes were selective for AA, since brain docosahexaenoic or palmitic acid metabolism, when measured, was unaffected, and topiramate, ineffective in BD, did not modify the rat brain AA cascade. Downregulation of the cascade by the mood stabilizers corresponded to inhibition of AA neurotransmission via dopaminergic D(2)-like and glutamatergic NMDA receptors. Unlike the mood stabilizers, antidepressants that increase switching of bipolar depression to mania upregulated the rat brain AA cascade. These observations suggest that the brain AA cascade is a common target of mood stabilizers, and that bipolar symptoms, particularly mania, are associated with an upregulated cascade and excess AA signaling via D(2)-like and NMDA receptors. This review presents ways to test these suggestions.

Temporal changes in mouse brain fatty acid amide hydrolase activity

Fatty acid amide hydrolase (FAAH) activity is known to mediate the tone of endogenous fatty acid amides including the endocannabinoid anandamide. FAAH is a potential therapeutic target because genetic or pharmacological ablation of FAAH promotes analgesia and anxiolytic effects without disrupting motor coordination. Little is known about the endogenous temporal fluctuations of brain FAAH activity. This is the first comprehensive study examining temporal fluctuations in mouse brain FAAH activity. Regional mouse brain homogenates were generated at the midpoint of the light ("noon") and dark ("midnight") cycles. While immunoblots revealed no significant changes (P>0.05) in regional activity between these two time points, in vitro activity assays detected a subtle 10% reduction (P<0.05) in cerebellar FAAH activity at midnight. A novel ex vivo autoradiography technique permitted the study of 11 different brain regions, many of which cannot be studied using traditional in vitro methods. The cerebellum and the periaqueductal gray both exhibited significant (P<0.05) reductions in regional FAAH activity in "midnight" brains. These data confirm the need to account for temporal changes in FAAH activity when therapeutically targeting FAAH.

Acute but not chronic donepezil increases muscarinic receptor-mediated signaling via arachidonic acid in unanesthetized rats

Donepezil, an acetylcholinesterase (AChE) inhibitor used for treating Alzheimer's disease patients, is thought to act by increasing brain extracellular acetylcholine (ACh), and ACh binding to cholinergic receptors. Muscarinic receptors are coupled to cytosolic phospholipase A2 (cPLA2) activation and arachidonic acid (AA) release from synaptic membrane phospholipid. This activation can be imaged in rodents as an AA incorporation coefficient k*, using quantitative autoradiography. Acute and chronic effects of donepezil on the AA signal, k* for AA, were measured in 81 brain regions of unanesthetized rats. Twenty min after a single oral dose (3.0 mg/kg) of donepezil, k* was increased significantly in 37 brain regions, whereas k* did not differ from control 7 h afterwards or following chronic (21 days) of donepezil. Pretreatment with atropine prevented the 20-min increments in k* following donepezil. Donepezil also increased the brain ACh concentration and reduced brain AChE activity, but did not change cPLA2 activity, regardless of administration regimen. These results show that donepezil acutely increases the brain AA signal that is mediated by ACh acting at muscarinic receptors, but that this signal is rapidly desensitized despite continued elevated brain ACh concentration. In contrast, the AA signal in response to arecoline was not altered following donepezil.

Arachidonic acid and the brain

Kinetic methods in unanesthetized rodents have shown that turnover rates of arachidonic acid (AA) and docosahexaenoic acid (DHA) in brain membrane phospholipids are rapid and energy consuming and that phospholipase A(2) (PLA(2)) and acyl-CoA synthetase enzymes that regulate turnover are specific for one or the other PUFA. Thus, AA turnover in brain phospholipids was reduced, and AA-selective cytosolic cPLA(2) or acyl-CoA synthetase, as well as cyclooxygenase (COX)-2, were downregulated in brains of rats given drugs effective against bipolar disorder, whereas DHA turnover and expression of DHA-selective calcium-independent iPLA(2) were unchanged. Additionally, the brain AA and DHA cascades can be altered reciprocally by dietary or genetic conditions. Thus, following 15 wk of dietary (n-3) PUFA deprivation, DHA loss from rat brain was slowed because of reduced iPLA(2) and COX-1 expression, whereas AA-selective cPLA(2), sPLA(2), and COX-2 were upregulated, as were AA and docosapentaenoic acid concentrations. Measured rates of AA and DHA incorporation into brain represent their respective rates of metabolic consumption, because these PUFA are not synthesized de novo or converted significantly from their precursors in brain. In healthy human volunteers, positron emission tomography (PET) was used to show that the brain consumes AA and DHA at respective rates of 17.8 and 4.6 mg/d, whereas in patients with Alzheimer disease, AA consumption is elevated. In the future, PET could be used to relate human brain rates of AA and DHA consumption to liver PUFA metabolism and dietary PUFA intake.

Brain arachidonic and docosahexaenoic acid cascades are selectively altered by drugs, diet and disease

Metabolic cascades involving arachidonic acid (AA) and docosahexaenoic acid (DHA) within brain can be independently targeted by drugs, diet and pathological conditions. Thus, AA turnover and brain expression of AA-selective cytosolic phospholipase A(2) (cPLA(2)), but not DHA turnover or expression of DHA-selective Ca(2+)-independent iPLA(2), are reduced in rats given agents effective against bipolar disorder mania, whereas experimental excitotoxicity and neuroinflammation selectively increase brain AA metabolism. Furthermore, the brain AA and DHA cascades are altered reciprocally by dietary n-3 polyunsaturated fatty acid (PUFA) deprivation in rats. DHA loss from brain is slowed and iPLA(2) expression is decreased, whereas cPLA(2) and COX-2 are upregulated, as are brain concentrations of AA and its elongation product, docosapentaenoic acid (DPA). Positron emission tomography (PET) has shown that the normal human brain consumes 17.8 and 4.6 mg/day, respectively, of AA and DHA, and that brain AA consumption is increased in Alzheimer disease patients. In the future, PET could help to determine how human brain AA or DHA consumption is influenced by diet, aging or disease.

Dose-dependent anticonvulsant effects of linoleic and alpha-linolenic polyunsaturated fatty acids on pentylenetetrazol induced seizures in rats

PURPOSE

Linoleic and alpha-linolenic polyunsaturated fatty acids, derived from plant oils, have been reported to reduce neuronal excitability ex vivo and in cell culture. The evidence derived from animal seizure models, however, has been contradictory. The goal of the present study was to assess the dose-dependent anticonvulsant effects of a fatty acid mixture containing linoleic and alpha-linolenic acids in a 4 to 1 ratio (the "SR-3" compound).

METHODS

The maximal pentylenetetrazol seizure model and Long-Evans hooded rats were used.

RESULTS

Daily intraperitoneal injection of SR-3 for 21 consecutive days raised omega-3 polyunsaturated fatty acid (n-3 PUFA) composition in the unesterified fatty acid fraction of brain lipids (p < 0.05), and increased latency to seizure onset when administered at 200 mg/kg (p < 0.05), but not at 40 mg/kg (p > 0.05). There were no significant effects of SR-3 on seizure occurrence or on seizure severity (p > 0.05). A toxic effect of the SR-3 compound on peristalsis was observed at a dose of 400 mg/kg and above.

CONCLUSION

Linoleic and alpha-linolenic polyunsaturated fatty acids in a 4 to 1 ratio raises n-3 PUFA composition of unesterified fatty acids in the brain and increases resistance to pentylenetetrazol-induced seizures.

Chronic carbamazepine administration attenuates dopamine D2-like receptor-initiated signaling via arachidonic acid in rat brain

Observations that dopaminergic antagonists are beneficial in bipolar disorder and that dopaminergic agonists can produce mania suggest that bipolar disorder involves excessive dopaminergic transmission. Thus, mood stabilizers used to treat the disease might act in part by downregulating dopaminergic transmission. In agreement, we reported that dopamine D2-like receptor mediated signaling involving arachidonic acid (AA, 20:4n-6) was downregulated in rats chronically treated with lithium. To see whether chronic carbamazepine, another mood stabilizer, did this as well, we injected i.p. saline or the D2-like receptor agonist, quinpirole (1 mg/kg), into unanesthetized rats that had been pretreated for 30 days with i.p. carbamazepine (25 mg/kg/day) or vehicle, and used quantitative autoradiography to measure regional brain incorporation coefficients (k*) for AA, markers of signaling. We also measured brain prostaglandin E2 (PGE2), an AA metabolite. In vehicle-treated rats, quinpirole compared with saline significantly increased k* for AA in 35 of 82 brain regions examined, as well as brain PGE2 concentration. Affected regions belong to dopaminergic circuits and have high D2-like receptor densities. Chronic carbamazepine pretreatment prevented the quinpirole-induced increments in k* and in PGE2. These findings are consistent with the hypothesis that effective mood stabilizers generally downregulate brain AA signaling via D2-like receptors, and that this signaling is upregulated in bipolar disorder.

Arachidonic acid and ion channels: an update

Arachidonic acid (AA), a polyunsaturated fatty acid with four double bonds, has multiple actions on living cells. Many of these effects are mediated by an action of AA or its metabolites on ion channels. During the last 10 years, new types of ion channels, transient receptor potential (TRP) channels, store-operated calcium entry (SOCE) channels and non-SOCE channels have been studied. This review summarizes our current knowledge about the effects of AA on TRP and non-SOCE channels as well as classical ion channels. It aims to distinguish between effects of AA itself and effects of AA metabolites. Lipid mediators are of clinical interest because some of them (for example, leukotrienes) play a role in various diseases, others (such as prostaglandins) are targets for pharmacological therapeutic intervention.

Formation of eicosanoids, E2/D2 isoprostanes, and docosanoids following decapitation-induced ischemia, measured in high-energy-microwaved rat brain

Inflammatory lipid mediators derived from arachidonic acid (AA) and docosahexaenoic acid (DHA) modify the pathophysiology of brain ischemia. The goal of this work was to investigate the formation of eicosanoids and docosanoids generated from AA and DHA, respectively, during no-flow cerebral ischemia. Rats were subjected to head-focused microwave irradiation 5 min following decapitation (complete ischemia) or prior to decapitation (controls). Brain lipids were extracted and analyzed by reverse-phase liquid chromatography-tandem mass spectrometry. After complete ischemia, brain AA, DHA, and docosapentaenoic acid concentrations increased 18-, 5- and 4-fold compared with controls, respectively. Prostaglandin E(2) (PGE(2)) and PGD(2) could not be detected in control microwaved rat brain, suggesting little endogenous PGE(2)/D(2) production in the brain in the absence of experimental manipulation. Concentrations of thromboxane B(2), E(2)/D(2)-isoprostanes, 5-hydroxyeicosatetraenoic acid (5-HETE), 5-oxo-eicosatetraenoic acid, and 12-HETE were significantly elevated in ischemic brains. In addition, DHA products such as mono-, di- and trihydroxy-DHA were detected in control and ischemic brains. Monohydroxy-DHA, identified as 17-hydroxy-DHA and thought to be the immediate precursor of neuroprotectin D(1), was 6.5-fold higher in ischemic than in control brain. The present study demonstrated increased formation of eicosanoids, E(2)/D(2)-IsoPs, and docosanoids following cerebral ischemia. A balance of these lipid mediators may mediate immediate events of ischemic injury and recovery.

Imaging apomorphine stimulation of brain arachidonic acid signaling via D2-like receptors in unanesthetized rats

RATIONALE AND OBJECTIVE

Because of the important role of dopamine in neurotransmission, it would be useful to be able to image brain dopamine receptor-mediated signal transduction in animals and humans. Administering the D1-D2 receptor agonist apomorphine may allow us to do this, as the D2-like receptor is reported to be coupled to cytosolic phospholipase A2 activation and arachidonic acid (AA) release from membrane phospholipid.

METHODS

Unanesthetized adult rats were given intraperitoneally apomorphine (0.5 mg/kg) or saline, with or without pretreatment with 6 mg/kg intravenous raclopride, a D2/D3 receptor antagonist. [1-14C]AA was injected intravenously, then AA incorporation coefficients k*--brain radioactivity divided by integrated plasma radioactivity--markers of AA signaling, were measured using quantitative autoradiography in 62 brain regions.

RESULTS

Apomorphine significantly elevated k* in 26 brain regions, including the frontal cortex, motor and somatosensory cortex, caudate-putamen, thalamic nuclei, and nucleus accumbens. Raclopride alone did not change baseline values of k*, but raclopride pretreatment prevented the apomorphine-induced increments in k*.

CONCLUSIONS

A mixed D1-D2 receptor agonist, apomorphine, increased the AA signal by activating only D2-like receptors in brain circuits containing regions with high D2-like receptor densities. Thus, apomorphine might be used with positron emission tomography to image brain D2-like receptor-mediated AA signaling in humans in health and disease.

Essential fatty acid-deprived tube-fed adults synthesize arachidonic and docosahexaenoic acids: a pilot analysis of the fatty acid status of people with profound developmental disabilities

OBJECTIVE

Determine whether there are essential fatty acid abnormalities in arachidonic (AA) and docosahexaenoic acid (DHA)-deprived tube-fed individuals.

DESIGN AND METHODS

Plasma fatty acid concentrations were measured in eight tube-fed adults with profound developmental disabilities.

RESULTS

Mean plasma AA, DPAn-6, stearic, oleic, Mead, palmitoleic, and vaccenic acid concentrations were elevated but DHA was normal. Numerous fatty acid ratios were also elevated.

CONCLUSIONS

In this context, significant synthesis of both AA and DHA was apparent. However, abnormal fatty acid profiles were common.

n-3 Fatty acid erythrocyte membrane content, APOE varepsilon4, and cognitive variation: an observational follow-up study in late adulthood

BACKGROUND

Evidence for an inverse relation between dietary intake of n-3 polyunsaturated fatty acids (PUFAs) and age-related cognitive decline is inconsistent. This inconsistency may arise because the relation is present only in the absence of the apolipoprotein E epsilon4 (APOE epsilon4) allele.

OBJECTIVE

We aimed to determine the contribution of erythrocyte n-3 PUFA content to cognitive aging in the presence or absence of the APOE epsilon4 allele.

DESIGN

We followed up 120 volunteers, born in 1936, at approximate ages of 64, 66, and 68 y. Their intelligence quotient at 11 y old was available. At first follow-up, we determined APOE genotype and measured the PUFA composition of erythrocyte membranes. Six cognitive tests were administered at all follow-ups. We related cognitive performance at approximately 64 y old and cognitive changes from approximately 64 to approximately 68 y old to erythrocyte n-3 PUFA composition on recruitment and to APOE epsilon4 allele status.

RESULTS

Total n-3 PUFA and docosohexaenoic acid concentrations were associated with benefits for cognition at approximately 64 y old and from approximately 64 to approximately 68 y old. After adjustment for sex, APOE epsilon4 status, and intelligence quotient at 11 y old, the effects associated with total n-3 PUFA remained significant. Cognitive benefits were associated with higher erythrocyte n-3 PUFA content but were significant only in the absence of the APOE epsilon4 allele.

CONCLUSIONS

These data are evidence of a gene x environment interaction for cognitive aging. They are relevant to the analysis of trials of n-3 PUFA supplements in cognitive aging and dementia prevention, and they support heterogeneity in cognitive aging and, possibly, in Alzheimer disease.

A putative link of PUFA, GPR40 and adult-born hippocampal neurons for memory

Long chain polyunsaturated fatty acids (PUFA) such as docosahexaenoic and arachidonic acids, which are enriched in the brain, are important for multiple aspects of neuronal development and function including neurite outgrowth, signal transduction and membrane fluidity. Recent studies show that PUFA are capable of improving hippocampal long-term potentiation, learning ability of aged rats, and cognitive function of humans with memory deficits, although the underlying mechanisms are unknown. There have been several reports studying physiological roles of G-protein coupled receptor 40 (GPR40) in the pancreas, but no studies have focused on the function of GPR40 in the brain. As GPR40 was recently identified in neurons throughout the brain, it is probable that certain PUFA may act, as endogenous ligands, on GPR40 at their cell surface. However, the effects of PUFA upon neuronal functions are still not clearly understood. Here, although circumferential, a combination of in vitro and in vivo data is introduced to consider the effects of docosahexaenoic and arachidonic acids on brain functions. GPR40 was found in the newborn neurons of the normal and postischemic hippocampi of adult macaque monkeys, while the positive effects of PUFA upon Ca(2+) mobilization and cognitive functions were demonstrated in both GPR40 gene-transfected PC12 cells and human subjects with memory deficits. The purpose of this review is to propose a putative link among PUFA, GPR40, and hippocampal newborn neurons by discussing whether PUFA can improve memory functions through GPR40 activation of adult-born neurons. At present, little is known about PUFA requirements that make possible neurogenesis in the adult hippocampus. However, the idea that 'PUFA-GPR40 interaction might be crucial for adult neurogenesis and/or memory' should be examined in detail using various experimental paradigms.

Seizure resistance in fat-1 transgenic mice endogenously synthesizing high levels of omega-3 polyunsaturated fatty acids

N-3 polyunsaturated fatty acids (PUFA), derived from marine oils, have been shown to protect against various neurological diseases. However, very little is known about their potential anticonvulsant properties. The objective of the present study was to determine whether enrichment of brain lipids with n-3 PUFA inhibits seizures induced by pentylenetetrazol. We demonstrate that increased brain levels of n-3 PUFA in transgenic fat-1 male mice, which are capable of de novo synthesis of n-3 PUFA from n-6 PUFA, increases latency to seizure onset by 45%, relative to wildtype controls (p = 0.08). Compared with wildtype littermates, transgenic fat-1 mice have significantly (p < 0.05) higher levels of docosahexaenoic acid and total n-3 PUFA in brain total lipid extracts and phospholipids. Levels of brain docosahexaenoic acid were positively correlated to seizure latency (p < 0.05). These findings demonstrate that n-3 PUFA have anticonvulsant properties and suggest the possibility of a novel, non-drug dietary approach for the treatment of epilepsy.

Plasma free polyunsaturated fatty acid levels are associated with symptom severity in acute mania

OBJECTIVES

Nutritionally essential polyunsaturated fatty acids (PUFAs) have been implicated as potentially important factors in mood disorders. For instance, n-3 PUFA supplementation is reported to improve outcomes in major depressive disorder and bipolar disorder. However, the role of PUFAs in acute mania has been minimally investigated. We performed a pilot study to compare plasma levels of free (non-esterified) and esterified PUFAs between patients in an acute manic episode and healthy volunteers, and to explore associations between symptom severity and levels of fatty acids and of the arachidonic acid metabolite, prostaglandin E2 (PGE2).

METHODS

Patients (n=10) who were medication-free for at least two weeks and seeking inpatient admission for an acute manic episode were compared with healthy volunteers (n=10). Symptom severity was assessed at admission and after six weeks of naturalistic treatment. Fasting baseline free and esterified plasma levels of docosahexaneoic acid (DHA, 22:6n-3), eicosapentaenoic acid (EPA, 20:5n-3), arachidonic acid (AA,20:4n-6) and the AA metabolite PGE2 were determined, and PGE2 levels were tested again at six weeks.

RESULTS

No between-group differences were found in levels of individual or total fatty acids, or of PGE2. Among subjects, manic symptom severity correlated negatively with levels of free AA and free EPA, and positively with the free AA:EPA ratio. PGE2 levels did not differ between groups or in subjects pre- and post-treatment.

CONCLUSIONS

Our preliminary results suggest that, in susceptible persons, low plasma levels of free EPA compared with AA are related to the severity of mania.

Brain metabolism of nutritionally essential polyunsaturated fatty acids depends on both the diet and the liver

Plasma alpha-linolenic acid (alpha-LNA, 18:3n-3) and linoleic acid (LA, 18:2n-6) do not contribute significantly to the brain content of docosahexaenoic acid (DHA, 22:6n-3) or arachidonic acid (AA, 20:4n-6), respectively, and neither DHA nor AA can be synthesized de novo in vertebrate tissue. Therefore, measured rates of incorporation of circulating DHA and AA into brain exactly represent their rates of consumption by brain. Positron emission tomography (PET) has been used to show, based on this information, that the adult human brain consumes AA and DHA at rates of 17.8 and 4.6 mg/day, respectively, and that AA consumption does not change significantly with age. In unanesthetized adult rats fed an n-3 PUFA "adequate" diet containing 4.6% alpha-LNA (of total fatty acids) as its only n-3 PUFA, the rate of liver synthesis of DHA was more than sufficient to maintain brain DHA, whereas the brain's rate of DHA synthesis is very low and unable to do so. Reducing dietary alpha-LNA in the DHA-free diet led to upregulation of liver but not brain coefficients of alpha-LNA conversion to DHA and of liver expression of elongases and desaturases that catalyze this conversion. Concurrently, brain DHA loss slowed due to downregulation of several of its DHA-metabolizing enzymes. Dietary alpha-LNA deficiency also promoted accumulation of brain docosapentaenoic acid (22:5n-6), and upregulated expression of AA-metabolizing enzymes, including cytosolic and secretory phospholipases A(2) and cyclooxygenase-2. These changes, plus reduced levels of brain derived neurotrophic factor (BDNF) and cAMP response element-binding protein (CREB) in n-3 PUFA diet deficient rats, likely render their brain more vulnerable to neuropathological insults.

Chronic carbamazepine administration reduces N-methyl-D-aspartate receptor-initiated signaling via arachidonic acid in rat brain

BACKGROUND

Lithium and carbamazepine (CBZ) are used to treat mania in bipolar disorder. When given chronically to rats, both agents reduce arachidonic acid (AA) turnover in brain phospholipids and downstream AA metabolism. Lithium in rats also attenuates brain N-methyl-D-aspartic acid receptor (NMDAR) signaling via AA. We hypothesized that, like chronic lithium, chronic CBZ administration to rats would reduce NMDAR-mediated signaling via AA.

METHODS

We used our fatty acid method with quantitative autoradiography to image the regional brain incorporation coefficient k* of AA, a marker of AA signaling, in unanesthetized rats that had been given 25 mg/kg/day I.P. CBZ or vehicle for 30 days, then injected with NMDA (25 mg/kg I.P.) or saline. We also measured brain concentrations of two AA metabolites, prostaglandin E(2) (PGE(2)) and thromboxane B(2) (TXB(2)).

RESULTS

In chronic vehicle-treated rats, NMDA compared with saline increased k* significantly in 69 of 82 brain regions examined, but did not change k* significantly in any region in CBZ-treated rats. In vehicle- but not CBZ-treated rats, NMDA also increased brain concentrations of PGE(2) and TXB(2).

CONCLUSIONS

Chronic CBZ administration to rats blocks increments in the AA signal k*, and in PGE(2) and TXB(2) concentrations that are produced by NMDA in vehicle-treated rats. The clinical action of antimanic drugs might involve inhibition of brain NMDAR-mediated signaling involving AA and its metabolites.