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

Synthesis and Preclinical Evaluation of 22-[18F]Fluorodocosahexaenoic Acid as a Positron Emission Tomography Probe for Monitoring Brain Docosahexaenoic Acid Uptake Kinetics

Docosahexaenoic acid [22:6(n-3), DHA], a polyunsaturated fatty acid, has an important role in regulating neuronal functions and in normal brain development. Dysregulated brain DHA uptake and metabolism are found in individuals carrying the APOE4 allele, which increases the genetic risk for Alzheimer's disease (AD), and are implicated in the progression of several neurodegenerative disorders. However, there are limited tools to assess brain DHA kinetics in vivo that can be translated to humans. Here, we report the synthesis of an ω-radiofluorinated PET probe of DHA, 22-[18F]fluorodocosahexaenoic acid (22-[18F]FDHA), for imaging the uptake of DHA into the brain. Using the nonradiolabeled 22-FDHA, we confirmed that fluorination of DHA at the ω-position does not significantly alter the anti-inflammatory effect of DHA in microglial cells. Through dynamic PET-MR studies using mice, we observed the accumulation of 22-[18F]FDHA in the brain over time and estimated DHA's incorporation coefficient (K*) using an image-derived input function. Finally, DHA brain K* was validated using intravenous administration of 15 mg/kg arecoline, a natural product known to increase the DHA K* in rodents. 22-[18F]FDHA is a promising PET probe that can reveal altered lipid metabolism in APOE4 carriers, AD, and other neurologic disorders. This new probe, once translated into humans, would enable noninvasive and longitudinal studies of brain DHA dynamics by guiding both pharmacological and nonpharmacological interventions for neurodegenerative diseases.

Marine Algae-Derived Bioactive Compounds: A New Wave of Nanodrugs?

Marine algae are rich in bioactive nutraceuticals (e.g., carbohydrates, proteins, minerals, fatty acids, antioxidants, and pigments). Biotic (e.g., plants, microorganisms) and abiotic factors (e.g., temperature, pH, salinity, light intensity) contribute to the production of primary and secondary metabolites by algae. Easy, profitable, and sustainable recovery methods include novel solid-liquid and liquid-liquid extraction techniques (e.g., supercritical, high pressure, microwave, ultrasound, enzymatic). The spectacular findings of algal-mediated synthesis of nanotheranostics has attracted further interest because of the availability of microalgae-based natural bioactive therapeutic compounds and the cost-effective commercialization of stable microalgal drugs. Algal extracts can serve as stabilizing/capping and reducing agents for the synthesis of thermodynamically stable nanoparticles (NPs). Different types of nanotherapeutics have been synthesized using physical, chemical, and biological methods. Marine algae are a fascinating source of lead theranostics compounds, and the development of nanotheranostics has been linked to enhanced drug efficacy and safety. Indeed, algae are remarkable nanobiofactories, and their pragmatic properties reside in their (i) ease of handling; (ii) capacity to absorb/accumulate inorganic metallic ions; (iii) cost-effectiveness; and (iv) capacity of eco-friendly, rapid, and healthier synthesis of NPs. Preclinical and clinical trials shall enable to really define effective algal-based nanotherapies. This review aims to provide an overview of the main algal compounds that are nutraceuticals and that can be extracted and purified for nanotheranostic purposes.

Brain PUFA Concentrations Are Differentially Affected by Interactions of Diet, Sex, Brain Regions, and Phospholipid Pools in Mice

BACKGROUND

PUFAs play vital roles in the development, maintenance, and functioning of circuitries that regulate reward and social behaviors. Therefore, modulations in PUFA concentrations of these brain regions may disrupt reward and social circuitries contributing to mood disorders, developmental disabilities, and addictions. Though much is known about regional and phospholipid-pool-specific PUFA concentrations, less is known about the effects of dietary interventions that concurrently lowers n-6 PUFA and supplements n-3 PUFA, on brain PUFA concentrations. There is even less knowledge on the effects of sex on brain PUFA concentrations.

OBJECTIVE

This study aimed to comprehensively examine the interaction effects of diet (D), sex (S), brain regions (BR), and phospholipid pools (PL) on brain PUFA concentrations.

METHODS

Male and female C57BL/6J mice were fed 1 of 4 custom-designed diets varying in linoleic acid (LNA) (8 en% or 1 en%) and eicosapentaenoic acid/docosahexaenoic acid (EPA/DHA) (0.4 en% or 0 en%) concentrations from in utero to 15 weeks old. At 15 weeks old, the prefrontal cortex, dorsal striatum, and cerebellum were collected. Fatty acids of 5 major PL were quantified by GC-flame ionization detection. Repeated measures ANOVA was used to test for differences among the groups for D, S, BR, and PL.

RESULTS

No significant 4-way interactions on PUFA concentrations. DHA, predominant n-3 PUFA, concentrations were dependent on significant D × BR × PL interactions. DHA concentration was not affected by sex. Arachidonic acid (ARA; predominant n-6 PUFA) concentrations were not dependent on 3-way interactions. However, significant 2-way D × PL, BR × PL, and D × Sinteractions affected ARA concentrations. Brain fatty acid concentrations were differentially affected by various combinations of D, S, BR, and PL interactions.

CONCLUSION

Though DHA concentrations are not affected by sex, ARA concentrations are affected by interactions of the 4 variables examined. This study provides comprehensive references in the investigation of complex interactions between factors that affect brain PUFA concentrations in mice.

ω-3 and ω-6 Polyunsaturated Fatty Acids, Obesity and Cancer

Recently, nutraceutical bioactive compounds in foods have been discovered for their potential health benefits regarding the prevention of chronic disorders, such as cancer, and inflammatory, cardiovascular, and metabolic diseases. Dietary omega-3 polyunsaturated fatty acids (ω-3PUFAs), including alpha-linolenic acid, docosapentaenoic acid, and eicosapentaenoic acid, are mostly attractive. They are available for the customers worldwide from commonly used foods and/or as components of commercial food supplements. The anti-inflammatory and hypotriglyceridemic effects of these fatty acids are well known, whereas pro-inflammatory properties have been recognized in their dietary counterparts, the ω-6PUFAs. Both ω-3 and ω-6PUFAs contribute to the production of lipid mediators such as endocannabinoids that are notably involved in control of food intake, energy sensing, and food-related disorders. In this review, we present ω-3 and ω-6PUFAs and their derivatives, endocannabinoids; discuss the anti-obesity effects of ω-3PUFAs; their roles in inflammation and colorectal cancer development; and how their action can be co-preventative and co-therapeutic.

Genetic variants in FADS1 and ELOVL2 increase level of arachidonic acid and the risk of Alzheimer's disease in the Tunisian population

Polyunsaturated fatty acids (PUFAs) are closely related to various physiological conditions. In several age-related diseases including Alzheimer's disease (AD) altered PUFAs metabolism has been reported. However, the mechanism behind PUFAs impairment and AD developpement remains unclear. In humans, PUFAs biosynthesis requires delta-5 desaturase (D5D), delta-6 desaturase (D6D) and elongase 2 activities; which are encoded by fatty acid desaturase 1 (FADS1), fatty acid desaturase 2 (FADS2), and elongation of very-long-chain fatty acids-like 2 (ELOVL2) genes, respectively. In the present work, we aim to assess whether genetic variants in FADS1, FADS2 and ELOVL2 genes influence plasma and erythrocyte PUFA composition and AD risk. A case-control study was carried out in 113 AD patients and 161 healthy controls.Rs174556, rs174617, and rs3756963 of FADS1, FADS2, and ELOVL2 genes, respectively were genotyped using PCR-RFLP. PUFA levels were quantified using Gas Chromatography. Genotype distributions of rs174556 (FADS1) and rs3756963 (ELOVL2) were different between case and control groups. The genotype TT of rs174556 and rs3756963 single nucleotide polymorphism (SNP) increases significantly the risk of AD in our population. PUFA analysis showed higher plasma and erythrocyte arachidonic acid (AA) level in patients with AD, whereas only plasma docosahexaenoic acid (DHA) was significantly decreased in AD patients. The indexes AA/Dihomo-gamma-linolenic acid (DGLA) and C24:4n-6/Adrenic acid (AdA) were both higher in the AD group. Interestingly, patients with TT genotype of rs174556 presented higher AA level and AA/DGLA index in both plasma and erythrocyte. In addition, higher AA and AA/DGLA index were observed in erythrocyte of TT genotype ofrs3756963 carrier's patients. Along with, positive correlation between AA/DGLA index, age or Gamma-linolenic acid (GLA)/ Linoleic acid (LA) index was seen in erythrocyte and /or plasma of AD patients. After adjustment for confounding factors, the genotype TT of rs174556, erythrocyte AA and AA/DGLA index were found to be predictive risk factors for AD while plasma DHA was found associated with lower AD risk. Both rs174556 and rs3756963 influence AD risk in the Tunisian population and they are likely associated with high AA level. The combination of the two variants increases further the susceptibility to AD. We suggest that FADS1 and ELOVL2 variants could likely regulate the efficiency of AA biosynthesis which could be at the origin of inflammatory derivate.

Regulation of rat plasma and cerebral cortex oxylipin concentrations with increasing levels of dietary linoleic acid

Linoleic acid (LA, 18:2n-6) is the most abundant polyunsaturated fatty acid in the North American diet and is a precursor to circulating bioactive fatty acid metabolites implicated in brain disorders. This exploratory study tested the effects of increasing dietary LA on plasma and cerebral cortex metabolites derived from LA, its elongation-desaturation products dihomo-gamma linolenic (DGLA, 20:3n-6) acid and arachidonic acid (AA, 20:4n-6), as well as omega-3 alpha-linolenic (α-LNA, 18:3n-3), eicosapentaenoic (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). Plasma and cortex were obtained from rats fed a 0.4%, 5.2% or 10.5% energy LA diet for 15 weeks and subjected to liquid chromatography tandem mass spectrometry analysis. Total oxylipin concentrations, representing the esterified and unesterified pool, and unesterified oxylipins derived from LA and AA were significantly increased and EPA metabolites decreased in plasma at 5.2% or 10.5% energy LA compared to 0.4% energy LA. Unesterified plasma DHA metabolites also decreased at 10.5% energy LA. In cortex, total and unesterified LA and AA metabolites increased and unesterified EPA metabolites decreased at 5.2% or 10.5% LA. DGLA and α-LNA metabolites did not significantly change in plasma or cortex. Dietary LA lowering represents a feasible approach for targeting plasma and brain LA, AA, EPA or DHA-derived metabolite concentrations.

Fatty acid transporting proteins: Roles in brain development, aging, and stroke

Polyunsaturated fatty acids are required for the brain development and significantly impact aging and stroke. Due to the hydrophobicity of fatty acids, fatty acids transportation related proteins that include fatty acid binding proteins (FABPs), long chain acyl-coA synthase (ACS), fatty acid transportation proteins (FATPs), fatty acid translocase (FAT/CD36) and newly reported major facilitator superfamily domain-containing protein (Mfsd2a) play critical roles in the uptake of various fatty acids, especially polyunsaturated fatty acids. They are not only involved in neurodevelopment, but also have great impact on neurological disease, such as aging related dementia and stroke.

Therapeutic Potentials of Microalgae in the Treatment of Alzheimer's Disease

Current research is geared towards the discovery of new compounds with strong neuroprotective potential and few or no side effects compared to synthetic drugs. This review focuses on the potentials of extracts and biologically active compounds derived from microalgal biomass for the treatment and management of Alzheimer’s disease (AD). Microalgal research has gained much attention recently due to its contribution to the production of renewable fuels and the ability of alga cells to produce several secondary metabolites such as carotenoids, polyphenols, sterols, polyunsaturated fatty acids and polysaccharides. These compounds exhibit several pharmacological activities and possess neuroprotective potential. The pathogenesis of Alzheimer’s disease (AD) involves complex mechanisms that are associated with oxidative stress, cholinergic dysfunction, neuronal damage, protein misfolding and aggregation. The antioxidant, anticholinesterase activities as well as the inhibitory effects of some bioactive compounds from microalgae extracts on β-amyloid aggregation and neuronal death are discussed extensively. Phytochemical compounds from microalgae are used as pharmaceuticals, nutraceuticals and food supplements, and may possess neuroprotective potentials that are relevant to the management and/or treatment of AD.

Dietary Linoleic Acid Lowering Reduces Lipopolysaccharide-Induced Increase in Brain Arachidonic Acid Metabolism

Linoleic acid (LA, 18:2n-6) is a precursor to arachidonic acid (AA, 20:4n-6), which can be converted by brain lipoxygenase and cyclooxygenase (COX) enzymes into various lipid mediators involved in the regulation of brain immunity. Brain AA metabolism is activated in rodents by the bacterial endotoxin, lipopolysaccharide (LPS). This study tested the hypothesis that dietary LA lowering, which limits plasma supply of AA to the brain, reduces LPS-induced upregulation in brain AA metabolism. Male Fischer CDF344 rats fed an adequate LA (5.2 % energy (en)) or low LA (0.4 % en) diet for 15 weeks were infused with LPS (250 ng/h) or vehicle into the fourth ventricle for 2 days using a mini-osmotic pump. The incorporation rate of intravenously infused unesterified ¹⁴C-AA into brain lipids, eicosanoids, and activities of phospholipase A₂ and COX-1 and 2 enzymes were measured. Dietary LA lowering reduced the LPS-induced increase in prostaglandin E₂ concentration and COX-2 activity (P < 0.05 by two-way ANOVA) without altering phospholipase activity. The ¹⁴C-AA incorporation rate into brain lipids was decreased by dietary LA lowering (P < 0.05 by two-way ANOVA). The present findings suggest that dietary LA lowering reduced LPS-induced increase in brain markers of AA metabolism. The clinical utility of LA lowering in brain disorders should be explored in future studies.

Threshold changes in rat brain docosahexaenoic acid incorporation and concentration following graded reductions in dietary alpha-linolenic acid

BACKGROUND

This study tested the dietary level of alpha-linolenic acid (α-LNA, 18:3n-3) required to maintain brain (14)C-Docosahexaenoic acid (DHA, 22:6n-3) metabolism and concentration following graded α-LNA reduction.

METHODS

Fischer-344 (CDF) male rat pups (18-21 days old) were randomized to the AIN-93G diet containing as a % of total fatty acids, 4.6% ("n-3 adequate"), 3.6%, 2.7%, 0.9% or 0.2% ("n-3 deficient") α-LNA for 15 weeks. Rats were intravenously infused with (14)C-DHA to steady state for 5 min, serial blood samples collected to obtain plasma, and brains excised following microwave fixation. Labeled and unlabeled DHA concentrations were measured in plasma and brain to calculate the incorporation coefficient, k*, and incorporation rate, J(in).

RESULTS

Compared to 4.6% α-LNA controls, k* was significantly increased in ethanolamine glycerophospholipids in the 0.2% α-LNA group. Circulating unesterified DHA and brain incorporation rates (J(in)) were significantly reduced at 0.2% α-LNA. Brain total lipid and phospholipid DHA concentrations were reduced at or below 0.9% α-LNA.

CONCLUSION

Threshold changes for brain DHA metabolism and concentration were maintained at or below 0.9% dietary α-LNA, suggesting the presence of homeostatic mechanisms to maintain brain DHA metabolism when dietary α-LNA intake is low.

Chronic dietary n-6 PUFA deprivation leads to conservation of arachidonic acid and more rapid loss of DHA in rat brain phospholipids

To determine how the level of dietary n-6 PUFA affects the rate of loss of arachidonic acid (ARA) and DHA in brain phospholipids, male rats were fed either a deprived or adequate n-6 PUFA diet for 15 weeks postweaning, and then subjected to an intracerebroventricular infusion of (3)H-ARA or (3)H-DHA. Brains were collected at fixed times over 128 days to determine half-lives and the rates of loss from brain phospholipids (J out). Compared with the adequate n-6 PUFA rats, the deprived n-6-PUFA rats had a 15% lower concentration of ARA and an 18% higher concentration of DHA in their brain total phospholipids. Loss half-lives of ARA in brain total phospholipids and fractions (except phosphatidylserine) were longer in the deprived n-6 PUFA rats, whereas the J out was decreased. In the deprived versus adequate n-6 PUFA rats, the J out of DHA was higher. In conclusion, chronic n-6 PUFA deprivation decreases the rate of loss of ARA and increases the rate of loss of DHA in brain phospholipids. Thus, a low n-6 PUFA diet can be used to target brain ARA and DHA metabolism.

Dietary omega-6 fatty acid lowering increases bioavailability of omega-3 polyunsaturated fatty acids in human plasma lipid pools

BACKGROUND

Dietary linoleic acid (LA, 18:2n-6) lowering in rats reduces n-6 polyunsaturated fatty acid (PUFA) plasma concentrations and increases n-3 PUFA (eicosapentaenoic (EPA) and docosahexaenoic acid (DHA)) concentrations.

OBJECTIVE

To evaluate the extent to which 12 weeks of dietary n-6 PUFA lowering, with or without increased dietary n-3 PUFAs, alters unesterified and esterified plasma n-6 and n-3 PUFA concentrations in subjects with chronic headache.

DESIGN

Secondary analysis of a randomized trial. Subjects with chronic headache were randomized for 12 weeks to (1) average n-3, low n-6 (L6) diet; or (2) high n-3, low n-6 LA (H3-L6) diet. Esterified and unesterified plasma fatty acids were quantified at baseline (0 weeks) and after 12 weeks on a diet.

RESULTS

Compared to baseline, the L6 diet reduced esterified plasma LA and increased esterified n-3 PUFA concentrations (nmol/ml), but did not significantly change plasma arachidonic acid (AA, 20:4n-6) concentration. In addition, unesterified EPA concentration was increased significantly among unesterified fatty acids. The H3-L6 diet decreased esterified LA and AA concentrations, and produced more marked increases in esterified and unesterified n-3 PUFA concentrations.

CONCLUSION

Dietary n-6 PUFA lowering for 12 weeks significantly reduces LA and increases n-3 PUFA concentrations in plasma, without altering plasma AA concentration. A concurrent increase in dietary n-3 PUFAs for 12 weeks further increases n-3 PUFA plasma concentrations and reduces AA.

Adolescent behavior and dopamine availability are uniquely sensitive to dietary omega-3 fatty acid deficiency

BACKGROUND

Understanding the nature of environmental factors that contribute to behavioral health is critical for successful prevention strategies in individuals at risk for psychiatric disorders. These factors are typically experiential in nature, such as stress and urbanicity, but nutrition--in particular dietary deficiency of omega-3 polyunsaturated fatty acids (n-3 PUFAs)-has increasingly been implicated in the symptomatic onset of schizophrenia and mood disorders, which typically occurs during adolescence to early adulthood. Thus, adolescence might be the critical age range for the negative impact of diet as an environmental insult.

METHODS

A rat model involving consecutive generations of n-3 PUFA deficiency was developed on the basis of the assumption that dietary trends toward decreased consumption of these fats began 4-5 decades ago when the parents of current adolescents were born. Behavioral performance in a wide range of tasks as well as markers of dopamine-related neurotransmission was compared in adolescents and adults fed n-3 PUFA adequate and deficient diets.

RESULTS

In adolescents, dietary n-3 PUFA deficiency across consecutive generations produced a modality-selective and task-dependent impairment in cognitive and motivated behavior distinct from the deficits observed in adults. Although this dietary deficiency affected expression of dopamine-related proteins in both age groups in adolescents but not adults, there was an increase in tyrosine hydroxylase expression that was selective to the dorsal striatum.

CONCLUSIONS

These data support a nutritional contribution to optimal cognitive and affective functioning in adolescents. Furthermore, they suggest that n-3 PUFA deficiency disrupts adolescent behaviors through enhanced dorsal striatal dopamine availability.

Kinetics of eicosapentaenoic acid in brain, heart and liver of conscious rats fed a high n-3 PUFA containing diet

Eicosapentaenoic acid (EPA, 20:5n-3), a precursor of docosahexaenoic acid (DHA), may benefit cardiovascular and brain health. Quantifying EPA's in vivo kinetics might elucidate these effects. [1-(14)C]EPA was infused i.v. for 5min in unanesthetized male rats fed a standard EPA-DHA diet. Plasma and microwaved tissue were analyzed. Kinetic parameters were calculated using our compartmental model. At 5min, 31-48% of labeled EPA in brain and heart was oxidized, 7% in liver. EPA incorporation rates from brain and liver precursor EPA-CoA pools into lipids, mainly phospholipids, were 36 and 2529nmol/s/g×10(-4), insignificant for heart. Deacylation-reacylation half-lives were 22h and 38-128min. Conversion rates to DHA equaled 0.65 and 25.1nmol/s/g×10(-4), respectively. The low brain concentration and incorporation rate and high oxidation of EPA suggest that, if EPA has a beneficial effect in brain, it might result from its suppression of peripheral inflammation and hepatic conversion to bioactive DHA.

Brain docosahexaenoic acid [DHA] incorporation and blood flow are increased in chronic alcoholics: a positron emission tomography study corrected for cerebral atrophy

OBJECTIVE

Chronic alcohol dependence has been associated with disturbed behavior, cerebral atrophy and a low plasma concentration of docosahexaenoic acid (DHA, 22∶6n-3), particularly if liver disease is present. In animal models, excessive alcohol consumption is reported to reduce brain DHA concentration, suggesting disturbed brain DHA metabolism. We hypothesized that brain DHA metabolism also is abnormal in chronic alcoholics.

METHODS

We compared 15 non-smoking chronic alcoholics, studied within 7 days of their last drink, with 22 non-smoking healthy controls. Using published neuroimaging methods with positron emission tomography (PET), we measured regional coefficients (K*) and rates (J(in)) of DHA incorporation from plasma into the brain of each group using [1-(11)C]DHA, and regional cerebral blood flow (rCBF) using [(15)O]water. Data were partial volume error corrected for brain atrophy. Plasma unesterified DHA concentration also was quantified.

RESULTS

Mean K* for DHA was significantly and widely elevated by 10-20%, and rCBF was elevated by 7%-34%, in alcoholics compared with controls. Unesterified plasma DHA did not differ significantly between groups nor did whole brain J(in), the product of K* and unesterified plasma DHA concentration.

DISCUSSION

Significantly higher values of K* for DHA in alcoholics indicate increased brain avidity for DHA, thus a brain DHA metabolic deficit vis-à-vis plasma DHA availability. Higher rCBF in alcoholics suggests increased energy consumption. These changes may reflect a hypermetabolic state related to early alcohol withdrawal, or a general brain metabolic change in chronic alcoholics.

Interaction of brain fatty acid-binding protein with the polyunsaturated fatty acid environment as a potential determinant of poor prognosis in malignant glioma

Malignant gliomas are the most common adult brain cancers. In spite of aggressive treatment, recurrence occurs in the great majority of patients and is invariably fatal. Polyunsaturated fatty acids are abundant in brain, particularly ω-6 arachidonic acid (AA) and ω-3 docosahexaenoic acid (DHA). Although the levels of ω-6 and ω-3 polyunsaturated fatty acids are tightly regulated in brain, the ω-6:ω-3 ratio is dramatically increased in malignant glioma, suggesting deregulation of fundamental lipid homeostasis in brain tumor tissue. The migratory properties of malignant glioma cells can be modified by altering the ratio of AA:DHA in growth medium, with increased migration observed in AA-rich medium. This fatty acid-dependent effect on cell migration is dependent on expression of the brain fatty acid binding protein (FABP7) previously shown to bind DHA and AA. Increased levels of enzymes involved in eicosanoid production in FABP7-positive malignant glioma cells suggest that FABP7 is an important modulator of AA metabolism. We provide evidence that increased production of eicosanoids in FABP7-positive malignant glioma growing in an AA-rich environment contributes to tumor infiltration in the brain. We discuss pathways and molecules that may underlie FABP7/AA-mediated promotion of cell migration and FABP7/DHA-mediated inhibition of cell migration in malignant glioma.

RETRACTED: Increased neuroinflammatory and arachidonic acid cascade markers, and reduced synaptic proteins, in the postmortem frontal cortex from schizophrenia patients

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editors. The National Institutes of Health has found that Dr. Jagadeesh S. Rao engaged in research misconduct by falsifying data. Data in Figures 1A, 1E, 3E and 3F were falsified. Dr. Rao was solely responsible for the falsification. None of the other authors are implicated in any way.

Translational studies on regulation of brain docosahexaenoic acid (DHA) metabolism in vivo

One goal in the field of brain polyunsaturated fatty acid (PUFA) metabolism is to translate the many studies that have been conducted in vitro and in animal models to the clinical setting. Doing so should elucidate the role of PUFAs in the human brain, and effects of diet, drugs, disease and genetics on this role. This review discusses new in vivo radiotracer kinetic and neuroimaging techniques that allow us to do this, with a focus on docosahexaenoic acid (DHA). We illustrate how brain PUFA metabolism is influenced by graded reductions in dietary n-3 PUFA content in unanesthetized rats. We also show how kinetic tracer techniques in rodents have helped to identify mechanisms of action of mood stabilizers used in bipolar disorder, how DHA participates in neurotransmission, and how brain DHA metabolism is regulated by calcium-independent iPLA₂β. In humans, regional rates of brain DHA metabolism can be quantitatively imaged with positron emission tomography following intravenous injection of [1-¹¹C]DHA.

Effects of chronic clozapine administration on markers of arachidonic acid cascade and synaptic integrity in rat brain

BACKGROUND

The mode of action of clozapine, an atypical antipsychotic approved for treating schizophrenia (SZ) and used for bipolar disorder (BD) mania, remains unclear. We tested for overlap with the actions of the mood stabilizers, lithium, carbamazepine and valproate, which downregulate arachidonic acid (AA) cascade markers in rat brain and upregulate BDNF. AA cascade markers are upregulated in BD and SZ postmortem BD brain in association with neuroinflammation and synaptic loss, while BDNF is decreased.

METHODS

Rats were injected intraperitoneally with a therapeutically relevant dose of clozapine (10 mg/kg/day) or with saline for 30 days, and AA cascade and synaptic markers and BDNF were measured in the brain.

RESULTS

Compared with saline-injected rats, chronic clozapine increased brain activity, mRNA and protein levels of docosahexaenoic acid (DHA)-selective calcium-independent phospholipase A₂ type VIA (iPLA₂), mRNA and protein levels of BDNF and of the postsynaptic marker, drebrin, while decreasing cyclooxygenase (COX) activity and concentration of prostaglandin E₂ (PGE₂), a proinflammatory AA metabolite. Activity and expression of AA-selective calcium-dependent cytosolic cPLA₂ type IVA and of secretory sPLA₂ Type II were unchanged.

CONCLUSIONS

These results show overlap with effects of mood stabilizers with regard to downregulation of COX activity and PGE₂ and to increased BDNF and suggest a common action against the reported neuropathology of BD and SZ. The increased iPLA₂ expression following clozapine suggests increased production of anti-inflammatory DHA metabolites, and, with increased BDNF and drebrin, clear neuroprotective action.

Effects of diet and/or exercise in enhancing spinal cord sensorimotor learning

Given that the spinal cord is capable of learning sensorimotor tasks and that dietary interventions can influence learning involving supraspinal centers, we asked whether the presence of omega-3 fatty acid docosahexaenoic acid (DHA) and the curry spice curcumin (Cur) by themselves or in combination with voluntary exercise could affect spinal cord learning in adult spinal mice. Using an instrumental learning paradigm to assess spinal learning we observed that mice fed a diet containing DHA/Cur performed better in the spinal learning paradigm than mice fed a diet deficient in DHA/Cur. The enhanced performance was accompanied by increases in the mRNA levels of molecular markers of learning, i.e., BDNF, CREB, CaMKII, and syntaxin 3. Concurrent exposure to exercise was complementary to the dietary treatment effects on spinal learning. The diet containing DHA/Cur resulted in higher levels of DHA and lower levels of omega-6 fatty acid arachidonic acid (AA) in the spinal cord than the diet deficient in DHA/Cur. The level of spinal learning was inversely related to the ratio of AA:DHA. These results emphasize the capacity of select dietary factors and exercise to foster spinal cord learning. Given the non-invasiveness and safety of the modulation of diet and exercise, these interventions should be considered in light of their potential to enhance relearning of sensorimotor tasks during rehabilitative training paradigms after a spinal cord injury.