Evidence of the Role of Omega-3 Polyunsaturated Fatty Acids in Brain Glucose Metabolism.

In mammals, brain function, particularly neuronal activity, has high energy needs. When glucose is supplemented by alternative oxidative substrates under different physiological conditions, these fuels do not fully replace the functions fulfilled by glucose. Thus, it is of major importance that the brain is almost continuously supplied with glucose from the circulation. Numerous studies describe the decrease in brain glucose metabolism during healthy or pathological ageing, but little is known about the mechanisms that cause such impairment. Although it appears difficult to determine the exact role of brain glucose hypometabolism during healthy ageing or during age-related neurodegenerative diseases such as Alzheimer's disease, uninterrupted glucose supply to the brain is still of major importance for proper brain function. Interestingly, a body of evidence suggests that dietary n-3 polyunsaturated fatty acids (PUFAs) might play significant roles in brain glucose regulation. Thus, the goal of the present review is to summarize this evidence and address the role of n-3 PUFAs in brain energy metabolism. Taken together, these data suggest that ensuring an adequate dietary supply of n-3 PUFAs could constitute an essential aspect of a promising strategy to promote optimal brain function during both healthy and pathological ageing.

Very low inadequate dietary intakes of essential n-3 polyunsaturated fatty acids (PUFA) in pregnant and lactating French women: The INCA2 survey.

BACKGROUND: The French National survey INCA2 pointed out that the majority of the French population (children, adolescents, adults and elderly) ingest low quantities of n-3 polyunsaturated fatty acid (PUFA) in the form of both precursor (alpha-linolenic acid, ALA) and long-chain (mainly docosahexaenoic acid, DHA). However, we don't know whether such inadequate n-3 PUFA consumption is also found again in pregnant and lactating women. METHODS: Dietary lipid and PUFA intakes were determined from 28 pregnant and 21 lactating French women by using the most recent set of national robust data on food (National Survey INCA2 performed in 2006 and 2007), and compared with that of 742 women of childbearing age. RESULTS: Main results showed that mean daily intakes of n-3 PUFA were very low in this French woman population because no pregnant and lactating women met recommended dietary intakes (RDIs). Moreover, some of them ingested quantities 4 times (ALA) to 10 times (DHA) lower than RDIs. Very similar dietary intakes were observed in women of childbearing age. CONCLUSION: French pregnant and lactating women did not change their dietary habits to favor ALA and n-3 long-chain PUFA consumption via rich-ALA vegetable oils and fish and oily fish consumption, and have low n-3 PUFA dietary consumption typical of French women of childbearing age. Such PUFA intakes could have adverse impact on long-chain n-3 PUFA incorporation in brain membranes of fetus and infants, but also on cognitive and visual development of infants during the first years of life.

Long-chain n-3 PUFAs from fish oil enhance resting state brain glucose utilization and reduce anxiety in an adult nonhuman primate, the grey mouse lemur.

Decreased brain content of DHA, the most abundant long-chain n-3 polyunsaturated fatty acid (n-3 LCPUFA) in the brain, is accompanied by severe neurosensorial impairments linked to impaired neurotransmission and impaired brain glucose utilization. In the present study, we hypothesized that increasing n-3 LCPUFA intake at an early age may help to prevent or correct the glucose hypometabolism observed during aging and age-related cognitive decline. The effects of 12 months' supplementation with n-3 LCPUFA on brain glucose utilization assessed by positron emission tomography was tested in young adult mouse lemurs (Microcebus murinus). Cognitive function was tested in parallel in the same animals. Lemurs supplemented with n-3 LCPUFA had higher brain glucose uptake and cerebral metabolic rate of glucose compared with controls in all brain regions. The n-3 LCPUFA-supplemented animals also had higher exploratory activity in an open-field task and lower evidence of anxiety in the Barnes maze. Our results demonstrate for the first time in a nonhuman primate that n-3 LCPUFA supplementation increases brain glucose uptake and metabolism and concomitantly reduces anxiety.

Perinatal high-fat diet increases hippocampal vulnerability to the adverse effects of subsequent high-fat feeding.

Epidemiological observations report an increase in fat consumption associated with low intake of n-3 relative to n-6 polyunsaturated fatty acids (PUFAs) in women of childbearing age. However, the impact of these maternal feeding habits on cognitive function in the offspring is unknown. This study aims to investigate the impact of early exposure to a high-fat diet (HFD) with an unbalanced n-6/n-3 PUFAs ratio on hippocampal function in adult rats. Furthermore, we explored the effects of perinatal HFD combined with exposure to HFD after weaning. Dams were fed a control diet (C, 12% of energy from lipids, n-6/n-3 PUFAs ratio: 5) or HFD (HF, 39% of energy from lipids, n-6/n-3 PUFAs ratio: 39) throughout gestation and lactation. At weaning, offspring were placed either on control (C-C, HF-C) or high-fat (HF-HF) diets. In adulthood, hippocampus-dependent memory was assessed using the water-maze task and potential hippocampal alterations were determined by studying PUFA levels, gene expression, neurogenesis and astrocyte morphology. Perinatal HFD induced long-lasting metabolic alterations and some changes in gene expression in the hippocampus, but had no effect on memory. In contrast, spatial memory was impaired in animals exposed to HFD during the perinatal period and maintained on this diet. HF-HF rats also exhibited low n-3 and high n-6 PUFA levels, decreased neurogenesis and downregulated expression of several plasticity-related genes in the hippocampus. To determine the contribution of the perinatal diet to the memory deficits reported in HF-HF animals, an additional experiment was conducted in which rats were only exposed to HFD starting at weaning (C-HF). Interestingly, memory performance in this group was similar to controls. Overall, our results suggest that perinatal exposure to HFD with an unbalanced n-6/n-3 ratio sensitizes the offspring to the adverse effects of subsequent high-fat intake on hippocampal function.

Gene expression of fatty acid transport and binding proteins in the blood-brain barrier and the cerebral cortex of the rat: differences across development and with different DHA brain status.

Specific mechanisms for maintaining docosahexaenoic acid (DHA) concentration in brain cells but also transporting DHA from the blood across the blood-brain barrier (BBB) are not agreed upon. Our main objective was therefore to evaluate the level of gene expression of fatty acid transport and fatty acid binding proteins in the cerebral cortex and at the BBB level during the perinatal period of active brain DHA accretion, at weaning, and until the adult age. We measured by real time RT-PCR the mRNA expression of different isoforms of fatty acid transport proteins (FATPs), long-chain acyl-CoA synthetases (ACSLs), fatty acid binding proteins (FABPs) and the fatty acid transporter (FAT)/CD36 in cerebral cortex and isolated microvessels at embryonic day 18 (E18) and postnatal days 14, 21 and 60 (P14, P21 and P60, respectively) in rats receiving different n-3 PUFA dietary supplies (control, totally deficient or DHA-supplemented). In control rats, all the genes were expressed at the BBB level (P14 to P60), the mRNA levels of FABP5 and ACSL3 having the highest values. Age-dependent differences included a systematic decrease in the mRNA expressions between P14-P21 and P60 (2 to 3-fold), with FABP7 mRNA abundance being the most affected (10-fold). In the cerebral cortex, mRNA levels varied differently since FATP4, ACSL3 and ACSL6 and the three FABPs genes were highly expressed. There were no significant differences in the expression of the 10 genes studied in n-3 deficient or DHA-supplemented rats despite significant differences in their brain DHA content, suggesting that brain DHA uptake from the blood does not necessarily require specific transporters within cerebral endothelial cells and could, under these experimental conditions, be a simple passive diffusion process.

Fatty acid composition of the brain, retina, liver and adipose tissue of the grey mouse lemur (Microcebus murinus, primate).

The particular interest in supplementing human foods with n-3 fatty acids has arisen from the findings that this series of polyunsaturated fatty acids (PUFA) have an impact on neuronal functions. Indeed vertebrates, including humans, preferentially use docosahexaenoic acid (DHA, 22:6n-3) over other long-chain n-3 PUFA for the genesis of their neuronal and retinal membranes. The grey mouse lemur is a nocturnal prosimian primate originating from Madagascar. The increased use of this omnivorous primate in nutritional studies (chronic caloric restriction, n-3 fatty acids supplementation), justifies the interest of determining their fatty acids body composition. In the present study, we report the fatty acid composition in lipid classes from the main target tissues (brain, retina, liver and adipose tissue) of six adult mouse lemurs raised under laboratory nutritional conditions. Among the main findings, n-6-docosapentaenoic acid (n-6-DPA; 22:5n-6) is very low in the brain cortex and retina, whereas there is a very high accumulation of docosahexaenoic acid (DHA, 22:6n-3) in the neural tissues compared to liver and plasma. In particular, DHA accounts for about one half of the total fatty acids in the retina ethanolamine glycerophospholipids. This high concentration clearly indicates that DHA is efficiently transferred from blood lipids to the outer segment of the mouse lemur retina. We conclude that the mouse lemur n-3 PUFA metabolism efficiently drives DHA to neural tissues, through the blood-brain barrier and the blood-retina barrier.

n-3 PUFA status affects expression of genes involved in neuroenergetics differently in the fronto-parietal cortex compared to the CA1 area of the hippocampus: effect of rest and neuronal activation in the rat.

n-3 Polyunsaturated fatty acids (PUFA) support whole brain energy metabolism but their impact on neuroenergetics in specific brain areas and during neuronal activation is still poorly understood. We tested the effect of feeding rats as control, n-3 PUFA-deficient diet, or docosahexaenoic acid (DHA)-supplemented diet on the expression of key genes in fronto-parietal cortex and hippocampal neuroenergetics before and after neuronal stimulation (activated) by an enriched environment. Compared to control rats, n-3 deficiency specifically repressed GLUT1 gene expression in the fronto-parietal cortex in basal state and also during neuronal activation which specifically stimulated GLUT1. In contrast, in the CA1 area, n-3 deficiency improved the glutamatergic synapse function in both neuronal states (glutamate transporters, Na(+)/K(+) ATPase). DHA supplementation induced overexpression of genes encoding enzymes of the oxidative phosphorylation system and the F1F0 ATP synthase in the CA1 area. We conclude that n-3 deficiency repressed GLUT1 gene expression in the cerebral cortex, while DHA supplementation improved the mitochondrial ATP generation in the CA1 area of the hippocampus.

Oleate metabolism in pig enterocytes is characterized by an increased oxidation rate in the presence of a high esterification rate within two days after birth.

Oleate (OLE) is the principle fatty acid (FA) in mammalian colostrum, but its role in the energy supply in enterocytes after birth remains unknown. We investigated the metabolic fate of OLE in pig enterocytes at birth (d0) and after 2 d of suckling (d2). Cellular TG and phospholipids (PL) and FA composition were analyzed. Metabolic end-products of [1-¹4C]OLE were measured in enterocyte incubations. We characterized intestinal carnitine palmitoyltransferase 1 (CPT1), the key enzyme of mitochondrial FA oxidation. The TG content was 6.6-fold higher in enterocytes from pigs on d 2 than in those obtained on d 0, whereas the PL content did not differ. The level of OLE in TG and PL increased from 15 and 11% of total FA, respectively, in enterocytes from newborn piglets to 30 and 17%, respectively, in those from d2 pigs. The capacity for OLE utilization was 2.8-fold greater in d2 than in d0 pig enterocytes. The oxidation and esterification rates were enhanced in enterocytes from piglets on d 2 compared to those obtained on d 0, by 4- and 2.6-fold, respectively. The predominant OLE fate was the esterification pathway, representing >85% of OLE metabolized in both groups. The limited OLE oxidation observed at d 2 may result from the presence of a highly malonyl-CoA-sensitive CPT1A, because the half maximal inhibitory concentration for malonyl-CoA was 162 ± 25 nmol/L. This study highlighted the high esterification capacity for OLE in the newborn pig intestine, which may preserve this major colostrum FA for delivery to other tissues.

Influence of gender on DHA synthesis: the response of rat liver to low dietary α-linolenic acid evidences higher ω3 ∆4-desaturation index in females.

PURPOSE: The conversion rate of α-linolenic acid (ALA) into docosahexaenoic acid (DHA) is determined by dietary and non-dietary factors. Higher capacity of DHA synthesis has been evidenced in females, indicating that sex factors influence the conversion pathway. To evaluate the extent to which sexual dimorphism of DHA synthesis is subordinated to nutritional handling, we measured the ω3 ∆4-desaturation index in male and female rats receiving adequate or inadequate amounts of ALA. The ω3 ∆4-desaturation index was drawn from the DHA to docosapentaenoic acid (ω3DPA) ratio in liver phospholipids. METHODS: Male and female rats born to ω3-deficient dams were fed a supplemented diet supplying low, inadequate, intermediate, or adequate ALA (5, 20, 100, or 300 mg ALA/100 g diet, respectively). Control rats from both gender received the adequate diet from fetal life. RESULTS: Compared with control, low ALA feeding induced the ω3 ∆4-desaturation index to increase by 38 and 70% in the phosphatidylethanolamine fraction of males and females, respectively, and by 67% in phosphatidylcholine in females only. Supplementations with increased doses of ALA progressively smoothed this gender effect. Moreover, the analysis of our data from a previous study shows that ovariectomy decreased, whereas estradiol treatment increased the ω3 index to values comparable with those of diet-matched males and intact females, respectively. CONCLUSION: Females are more prone than males to increase their index of ω3 ∆4-desaturation, especially in response to low supplies in ALA. Estradiol supports the ω3 index, suggesting that this hormone plays a role in the effect of gender on DHA synthesis.

Omega-3 fatty acids enhance mitochondrial superoxide dismutase activity in rat organs during post-natal development.

The protection of the developing organism from oxidative damage is ensured by antioxidant defense systems to cope with reactive oxygen species (ROS), which in turn can be influenced by dietary polyunsaturated fatty acids (PUFAs). PUFAs in membrane phospholipids are substrates for ROS-induced peroxidation reactions. We investigated the effects of dietary supplementation with omega-3 PUFAs on lipid peroxidation and antioxidant enzyme activities in rat cerebrum, liver and uterus. Pups born from dams fed a diet low in omega-3 PUFAs were fed at weaning a diet supplying low α-linolenic acid (ALA), adequate ALA or enriched with eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA). Malondialdehyde (MDA), a biomarker of lipid peroxidation, and the activities of superoxide dismutase 1 (SOD1), SOD2, catalase (CAT) and glutathione peroxidase (GPX) were determined in the three target organs. Compared to low ALA feeding, supplementation with adequate ALA or with EPA+DHA did not affect the cerebrum MDA content but increased MDA content in liver. Uterine MDA was increased by the EPA+DHA diet. Supplementation with adequate ALA or EPA+DHA increased SOD2 activity in the liver and uterus, while only the DHA diet increased SOD2 activity in the cerebrum. SOD1, CAT and GPX activities were not altered by ALA or EPA+DHA supplementation. Our data suggest that increased SOD2 activity in organs of the growing female rats is a critical determinant in the tolerance to oxidative stress induced by feeding a diet supplemented with omega-3 PUFAs. This is may be a specific cellular antioxidant response to ROS production within the mitochondria.

Omega-3 fatty acids from fish oil lower anxiety, improve cognitive functions and reduce spontaneous locomotor activity in a non-human primate.

Omega-3 (ω3) polyunsaturated fatty acids (PUFA) are major components of brain cells membranes. ω3 PUFA-deficient rodents exhibit severe cognitive impairments (learning, memory) that have been linked to alteration of brain glucose utilization or to changes in neurotransmission processes. ω3 PUFA supplementation has been shown to lower anxiety and to improve several cognitive parameters in rodents, while very few data are available in primates. In humans, little is known about the association between anxiety and ω3 fatty acids supplementation and data are divergent about their impact on cognitive functions. Therefore, the development of nutritional studies in non-human primates is needed to disclose whether a long-term supplementation with long-chain ω3 PUFA has an impact on behavioural and cognitive parameters, differently or not from rodents. We address the hypothesis that ω3 PUFA supplementation could lower anxiety and improve cognitive performances of the Grey Mouse Lemur (Microcebus murinus), a nocturnal Malagasy prosimian primate. Adult male mouse lemurs were fed for 5 months on a control diet or on a diet supplemented with long-chain ω3 PUFA (n = 6 per group). Behavioural, cognitive and motor performances were measured using an open field test to evaluate anxiety, a circular platform test to evaluate reference spatial memory, a spontaneous locomotor activity monitoring and a sensory-motor test. ω3-supplemented animals exhibited lower anxiety level compared to control animals, what was accompanied by better performances in a reference spatial memory task (80% of successful trials vs 35% in controls, p<0.05), while the spontaneous locomotor activity was reduced by 31% in ω3-supplemented animals (p<0.001), a parameter that can be linked with lowered anxiety. The long-term dietary ω3 PUFA supplementation positively impacts on anxiety and cognitive performances in the adult mouse lemur. The supplementation of human food with ω3 fatty acids may represent a valuable dietary strategy to improve behavioural and cognitive functions.

n-3 long-chain fatty acids and regulation of glucose transport in two models of rat brain endothelial cells.

Several in vivo studies suggest that docosahexaenoic acid (22:6 n-3), the main n-3 long-chain polyunsaturated fatty acids (LC-PUFA) of brain membranes, could be an important regulator of brain energy metabolism by affecting glucose utilization and the density of the two isoforms of the glucose transporter-1 (GLUT1) (endothelial and astrocytic). This study was conducted to test the hypothesis that 22:6 n-3 in membranes may modulate glucose metabolism in brain endothelial cells. It compared the impact of 22:6 n-3 and the other two main LC-PUFA, arachidonic acid (20:4 n-6) and eicosapentaenoic acid (20:5 n-3), on fatty acid composition of membrane phospholipids, glucose uptake and expression of 55-kDa GLUT1 isoform in two models of rat brain endothelial cells (RBEC), in primary culture and in the immortalized rat brain endothelial cell line RBE4. Without PUFA supplementation, both types of cerebral endothelial cells were depleted in 22:6 n-3, RBE4 being also particularly low in 20:4 n-6. After exposure to supplemental 20:4 n-6, 20:5 n-3 or 22:6 n-3 (15microM, i.e. a physiological dose), RBEC and RBE4 avidly incorporated these PUFA into their membrane phospholipids thereby resembling physiological conditions, i.e. the PUFA content of rat cerebral microvessels. However, RBE4 were unable to incorporate physiological level of 20:4 n-6. Basal glucose transport in RBEC (rate of [(3)H]-3-o-methylglucose uptake) was increased after 20:5 n-3 or 22:6 n-3 supplementation by 50% and 35%, respectively, whereas it was unchanged with 20:4 n-6. This increase of glucose transport was associated with an increased GLUT1 protein, while GLUT1 mRNA was not affected. The different PUFA did not impact on glucose uptake in RBE4. Due to alterations in n-6 PUFA metabolism and weak expression of GLUT1, RBE4 seems to be less adequate than RBEC to study PUFA metabolism and glucose transport in brain endothelial cells. Physiological doses of n-3 LC-PUFA have a direct and positive effect on glucose transport and GLUT1 density in RBEC that could partly explain decreased brain glucose utilization in n-3 PUFA-deprived rats.

Gender affects liver desaturase expression in a rat model of n-3 fatty acid repletion.

Dietary n-3 polyunsaturated fatty acids (PUFA) are major components of cell membranes and have beneficial effects on human health. Docosahexaenoic acid (DHA; 22:6n-3) is the most biologically important n-3 PUFA and can be synthesized from its dietary essential precursor, alpha-linolenic acid (ALA; 18:3n-3). Gender differences in the efficiency of DHA bioconversion have been reported, but underlying molecular mechanisms are unknown. We compared the capacity for DHA synthesis from ALA and the expression of related enzymes in the liver and cerebral cortex between male and female rats. Wistar rats, born with a low-DHA status, were supplied with a suboptimal amount of ALA from weaning to 8 weeks of age. Fatty acid composition was determined by gas chromatography, the mRNA expression of different genes involved in PUFA metabolism was determined by RT-PCR (low-density array) and the expression of proteins was determined by Western blot analysis. At 8 weeks, DHA content was higher (+20 to +40%) in each phospholipid class of female livers compared to male livers. The "Delta4," Delta5 and Delta6 desaturation indexes were 1.2-3 times higher in females than in males. The mRNA expression of Delta5- and Delta6-desaturase genes was 3.8 and 2.5 times greater, respectively, and the Delta5-desaturase protein was higher in female livers (+50%). No gender difference was observed in the cerebral cortex. We conclude that female rats replete their DHA status more readily than males, probably due to a higher expression of liver desaturases. Our results support the hypothesis on hormonal regulation of PUFA metabolism, which should be taken into account for specific nutritional recommendations.

Differential effects of steroids on the synthesis of polyunsaturated fatty acids by human neuroblastoma cells.

Polyunsaturated fatty acids (PUFA) are crucial for proper functioning of cell membranes, particularly in brain. Biologically important PUFA include docosahexaenoic acid (n-3 series) and arachidonic acid (n-6 series) which can be formed from their respective dietary essential precursors, alpha-linolenic acid (ALA) and linoleic acid (LA). Steroid hormones are thought to modulate PUFA synthesis in humans but whether they regulate PUFA status in brain and/or in neural membranes is unknown. In human neuroblastoma SH-SY5Y cells, we compared the effect of estradiol, testosterone, and progesterone on PUFA synthesis. Cells were incubated with ALA and/or LA 7 microM in combination with estradiol, testosterone, or progesterone at 10 nM without serum. The fatty acid composition was determined by gas chromatography and the mRNA expression of genes involved in PUFA metabolism by real-time RT-PCR. Estradiol affected both the n-3 and the n-6 PUFA conversion, the n-3 PUFA pathway being more sensitive to the estradiol treatment. In ALA-supplemented cells, estradiol increased while testosterone decreased the long-chain n-3 PUFA content (+17% and -15%, respectively) and the mRNA expression of the Delta5-desaturase (+11% and -9%), these two events being strongly correlated. Progesterone did not affect the PUFA composition. The positive effect of estradiol was blocked by the estrogen receptor antagonist ICI-182,780. We conclude that steroids have differential effects on PUFA synthesis and that their mode of action could involve the modulation of the Delta5-desaturase mRNA expression in neuroblastoma cells. These results help our understanding of the regulation of brain PUFA metabolism by steroid hormones.

Uncoupling of interleukin-6 from its signalling pathway by dietary n-3-polyunsaturated fatty acid deprivation alters sickness behaviour in mice.

Sickness behaviour is an adaptive behavioural response to the activation of the innate immune system. It is mediated by brain cytokine production and action, especially interleukin-6 (IL-6). Polyunsaturated fatty acids (PUFA) are essential fatty acids that are highly incorporated in brain cell membranes and display immunomodulating properties. We hypothesized that a decrease in n-3 (also known as omega3) PUFA brain level by dietary means impacts on lipopolysaccharide (LPS)-induced IL-6 production and sickness behaviour. Our results show that mice exposed throughout life to a diet containing n-3 PUFA (n-3/n-6 diet) display a decrease in social interaction that does not occur in mice submitted to a diet devoid of n-3 PUFA (n-6 diet). LPS induced high IL-6 plasma levels as well as expression of IL-6 mRNA in the hippocampus and cFos mRNA in the brainstem of mice fed either diet, indicating intact immune-to-brain communication. However, STAT3 and STAT1 activation, a hallmark of the IL-6 signalling pathway, was lower in the hippocampus of LPS-treated n-6 mice than n-3/n-6 mice. In addition, LPS did not reduce social interaction in IL-6-knockout (IL-6-KO) mice and failed to induce STAT3 activation in the brain of IL-6-KO mice. Altogether, these findings point to alteration in brain STAT3 as a key mechanism for the lack of effect of LPS on social interaction in mice fed with the n-6 PUFA diet. The relative deficiency of Western diets in n-3 PUFA could impact on behavioural aspects of the host response to infection.

An (n-3) polyunsaturated fatty acid-deficient diet disturbs daily locomotor activity, melatonin rhythm, and striatal dopamine in Syrian hamsters.

Several studies suggest that (n-3) PUFA may play a role in the regulation of cognitive functions, locomotor and exploratory activity, and affective disorders. Additionally, (n-3) PUFA affect pineal function, which is implicated in the sleep-wake rhythm. However, no studies to our knowledge have explored the role of PUFA on the circadian system. We investigated the effect of an (n-3) PUFA-deficient diet on locomotor and pineal melatonin rhythms in Syrian hamsters used as model species in circadian rhythm research. To assess the possible relationship between voluntary wheel running activity and dopaminergic neurotransmission, we also measured endogenous monoamine concentrations in the striatum. Two-month-old male hamsters, fed either an (n-3) PUFA-deficient or an (n-3) PUFA-adequate diet, were housed individually in cages equipped with run wheels. At 3 mo, cerebral structures were extracted for biochemical and cellular analysis. In (n-3) PUFA-deficient hamsters, the induced changes in the pineal PUFA membrane phospholipid composition were associated with a reduction in the nocturnal peak level of melatonin that was 52% lower than in control hamsters (P < 0.001). The (n-3) PUFA-deficient hamsters also had higher diurnal (P < 0.01) and nocturnal (P = 0.001) locomotor activity than the control hamsters, in parallel with activation of striatal dopaminergic function (P < 0.05). The (n-3) PUFA-deficient hamsters exhibited several symptoms: chronic locomotor hyperactivity, disturbance in melatonin rhythm, and striatal hyperdopaminergia. We suggest that an (n-3) PUFA-deficient diet lessens the melatonin rhythm, weakens endogenous functioning of the circadian clock, and plays a role in nocturnal sleep disturbances as described in attention deficit/hyperactivity disorder.

Estradiol favors the formation of eicosapentaenoic acid (20:5n-3) and n-3 docosapentaenoic acid (22:5n-3) from alpha-linolenic acid (18:3n-3) in SH-SY5Y neuroblastoma cells.

Whether neurosteroids regulate the synthesis of long chain polyunsaturated fatty acids in brain cells is unknown. We examined the influence of 17-beta-estradiol (E2) on the capacity of SH-SY5Y cells supplemented with alpha-linolenic acid (ALA), to produce eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). Cells were incubated for 24 or 72 h with ALA added alone or in combination with E2 (ALA + E2). Fatty acids were analyzed by gas chromatography of ethanolamine glycerophospholipids (EtnGpl) and phosphatidylcholine (PtdCho). Incubation for 24 h with ALA alone increased EPA and DPA in EtnGpl, by 330 and 430% compared to controls (P < 0.001) and DHA by only 10% (P < 0.05). Although DHA increased by 30% (P < 0.001) in ALA + E2-treated cells, the difference between the ALA and ALA + E2 treatments were not significant after 24 h (Anova-1, Fisher's test). After 72 h, EPA, DPA and DHA further increased in EtnGpl and PtdCho of cells supplemented with ALA or ALA + E2. Incubation for 72 h with ALA + E2 specifically increased EPA (+34% in EtnGpl, P < 0.001) and DPA (+15%, P < 0.001) compared to ALA alone. Thus, SH-SY5Y cells produced membrane EPA, DPA and DHA from supplemental ALA. The formation of DHA was limited, even in the presence of E2. E2 significantly favored EPA and DPA production in cells grown for 72 h. Enhanced synthesis of ALA-elongation products in neuroblastoma cells treated with E2 supports the hypothesis that neurosteroids could modulate the metabolism of PUFA.

Docosahexaenoic acid (22:6n-3) enrichment of membrane phospholipids increases gap junction coupling capacity in cultured astrocytes.

Although it is agreed that n-3 polyunsaturated fatty acids (PUFAs) are important for brain function, it has yet to be demonstrated how they are involved in precise cellular mechanisms. We investigated the role of enhanced n-3 PUFA in astrocyte membranes on the gap junction capacity of these cells. Astrocytes isolated from newborn rat cortices were grown in medium supplemented with docosahexaenoic acid (DHA), the main n-3 PUFA in cell membranes, or arachidonic acid (AA), the main n-6 PUFA, plus an antioxidant (alpha-tocopherol or N-acetyl-cystein) to prevent peroxidation. The resulting three populations of astrocytes differed markedly in their n-3:n-6 PUFA ratios in phosphatidylethanolamine and phosphatidylcholine, the main phospholipids in membranes. DHA-supplemented cells had a physiological high n-3:n-6 ratio (1.58), unsupplemented cells had a low n-3:n-6 ratio (0.66) and AA-supplemented cells had a very low n-3:n-6 ratio (0.36), with excess n-6 PUFA. DHA-supplemented astrocytes had a greater gap junction capacity than unsupplemented cells or AA-supplemented cells. The enhanced gap junction coupling of DHA-enriched cells was associated with a more functional distribution of connexin 43 at cell interfaces (shown by immunocytochemistry) and more of the main phosphorylated isoform of connexin 43. These findings suggest that the high n-3:n-6 PUFA ratio that occurs naturally in astrocyte membranes is needed for optimal gap junction coupling in these cells.

Temporal changes in dietary fats: role of n-6 polyunsaturated fatty acids in excessive adipose tissue development and relationship to obesity.

The importance of a high fat intake in the increasing prevalence of childhood and adult obesity remains controversial. Moreover, qualitative changes (i.e. the fatty acid composition of fats) have been largely disregarded. Herein is reviewed the role of polyunsaturated fatty acids (PUFAs) of the n-6 series in promoting adipogenesis in vitro and favouring adipose tissue development in rodents during the gestation/suckling period. Epidemiological data from infant studies as well as the assessment of the fatty acid composition of mature breast milk and infant formulas over the last decades in the Western industrialized world are revisited and appear consistent with animal data. Changes over decades in the intake of n-6 and n-3 PUFAs, with a striking increase in the linoleic acid/alpha-linolenic ratio, are observed. In adults, using a consumption model based upon production data, similar changes in the PUFA content of ingested lipids have been found for France, and are associated with an increase of fat consumption over the last 40 years. These profound quantitative and qualitative alterations can be traced in the food chain and shown to be due to changes in human dietary habits as well as in the feeding pattern of breeding stock. If prevention of obesity is a key issue for future generations, agricultural and food industry policies should be thoroughly reevaluated.

Changes of the transcriptional and fatty acid profiles in response to n-3 fatty acids in SH-SY5Y neuroblastoma cells.

Synthesis of docosahexaenoic acid (DHA) from its metabolic precursors contributes to membrane incorporation of this FA within the central nervous system. Although cultured neural cells are able to produce DHA, the membrane DHA contents resulting from metabolic conversion do not match the high values of those resulting from supplementation with preformed DHA. We have examined whether the DHA precursors down-regulate the incorporation of newly formed DHA within human neuroblastoma cells. SH-SY5Y cells were incubated with gradual doses of alpha-linolenic acid (alpha-LNA), EPA, or docosapentaenoic acid (DPA), and the incorporation of DHA into ethanolamine glycerophospholipids was analyzed as a reflection of synthesizing activity. The incorporation of EPA, DPA, and preformed DHA followed a dose-response saturating curve, whereas that of DHA synthesized either from alpha-LNA, EPA, or DPA peaked at concentrations of precursors below 15-30 microM and sharply decreased with higher doses. The mRNA encoding for six FA metabolism genes were quantified using real-time PCR. Two enzymes of the peroxisomal beta-oxidation, L-bifunctional protein and peroxisomal acyl-CoA oxidase, were expressed at lower levels than fatty acyl-CoA ligase 3 (FACL3) and delta6-desaturase (delta6-D). The delta6-D mRNA slightly increased between 16 and 48 h of culture, and this effect was abolished in the presence of 70 microM EPA. In contrast, the EPA treatment resulted in a time-dependent increase of FACL3 mRNA. The terminal step of DHA synthesis seems to form a "metabolic bottleneck," resulting in accretion of EPA and DPA when the precursor concentration exceeds a specific threshold value. We conclude that the critical precursor- concentration window of responsiveness may originate from the low basal expression level of peroxisomal enzymes.