Modification of milk formula to enhance accretion of long-chain n-6 and n-3 polyunsaturated fatty acids in artificially reared infant rats

Lowering dietary n-6 polyunsaturated fatty acids: interaction with brain arachidonic and docosahexaenoic acids

PURPOSE OF REVIEW

Arachidonic (ARA) and docosahexaenoic (DHA) acids are the most abundant polyunsaturated fatty acids (PUFA) in the brain, where they have many biological effects, including on inflammation, cell-signaling, appetite regulation, and blood flow. The Western diet contains a high ratio of n-6: n-3 PUFA. Although interest in lowering this ratio has largely focused on increasing intake of n-3 PUFA, few studies have examined lowering dietary n-6 PUFA. This review will evaluate the effect of lowering dietary n-6 PUFA on levels and metabolism of ARA and DHA in animal models and in humans, with a primary focus on the brain.

RECENT FINDINGS

In animal models, lowering dietary ARA or linoleic acid generally lowers levels of brain ARA and raises DHA. Lowering dietary n-6 PUFA can also modulate the levels of ARA and DHA metabolizing enzymes, as well as their associated bioactive mediators. Human studies examining changes in plasma fatty acid composition following n-6 PUFA lowering demonstrate no changes in levels of ARA and DHA, though there is evidence of alterations in their respective bioactive mediators.

SUMMARY

Lowering dietary n-6 PUFA, in animal models, can alter the levels and metabolism of ARA and DHA in the brain, but it remains to be determined whether these changes are clinically meaningful.

Hempseed Products Fed to Hens Effectively Increased n-3 Polyunsaturated Fatty Acids in Total Lipids, Triacylglycerol and Phospholipid of Egg Yolk

Hempseed products represent potential alternative feed ingredients for poultry. However, their usage is not currently approved due to a lack of data to support their safety and efficacy. In this regard, the current study was conducted to assess the impact of dietary concentration of hempseed (HS) products and duration of their feeding to hens on the polyunsaturated fatty acid (PUFA) composition of egg yolk lipids. In the current study, 48 Lohmann LSL-Classic hens were individually housed in metabolism cages, in a completely randomized design, and provided one of six diets (wheat-barley-soybean-based) containing either HS (10, 20 and 30 %), hempseed oil (HO; 4.5 and 9.0 %) or no hempseed product (control) over 12 weeks. Increasing alpha-linolenic acid (ALA) intake via increasing dietary hempseed product inclusion, significantly (p < 0.0001) increased the n-3 PUFA contents of yolk total lipid. The values of ALA increased by 12-fold (152 ± 3.56 and 156 ± 2.42 mg/yolk) and docosahexaenoic acid (DHA) by twofold to threefold (41.3 ± 1.57 and 43.6 ± 1.61 mg/yolk) over the control, for the highest levels of HS and HO inclusion, respectively. Increasing levels of hemp products in laying hen diets proved effective in manipulating the fatty acid profile of the total lipid, triacylglycerol (TAG) and total phospholipid (PL) fractions of yolks, enhancing the n-3 fatty acids and reducing the n-6/n-3 ratio. The latter benefit was achieved within 4 weeks of feeding hens either HS- or HO-containing diets.

Long-chain polyunsaturated fatty acids modulate interleukin-1beta-induced changes in behavior, monoaminergic neurotransmitters, and brain inflammation in rats

Recent evidence has suggested that an imbalance between membrane (n-3) and (n-6) fatty acids may contribute to the etiology of autoimmune and neurodegenerative diseases. In this study, the mechanisms by which eicosapentaenoic acid (EPA), gamma-linolenic acid (GLA), and arachidonic acid (AA) modulate neurotransmitters, behavior, and brain inflammation were evaluated in rats that received central saline or interleukin-1beta (IL-1) administrations. In rats treated with saline, only the AA-enriched diet significantly increased anxiety-like behavior in the elevated plus maze, which was associated with increased corticosterone secretion. AA also increased the turnover of dopamine (DA), noradrenaline (NA), and serotonin (5-HT) in the amygdala and increased the prostaglandin (PG)E(2) level in the hippocampus. IL-1 administration slowed rat learning in the water maze and increased anxiety-like behavior, changes which were associated with increased homovanillic acid and 5-HT turnover, decreased NA in the hippocampus and amygdala, decreased DA in the frontal cortex, and decreased IL-10 in limbic brain regions. Increased corticosterone secretion following IL-1 administration was accompanied by increased NA turnover in the hippocampus (P < 0.05) and increased PGE(2) concentration (P < 0.01) in the limbic brain regions. Of the 3 diets tested, only EPA attenuated IL-1-induced behavioral changes (P < 0.05 or 0.01), which was associated with the modulation of EPA on the neuroendocrine and immune changes induced by IL-1. GLA reduced hippocampal PGE(2) concentration in rats given IL-1 (P < 0.01). AA did not counteract any of the changes induced by IL-1. These results suggest that EPA, GLA, and AA play different roles in the neuroendocrine-immune network.

Fatty acid composition of skeletal muscle and adipose tissue in Spanish infants and children

There is a relationship between the fatty acid profile in skeletal muscle phospholipids and peripheral resistance to insulin in adults, but similar data have not been reported in infancy and childhood. The objective of this study was to investigate the fatty acid composition of skeletal muscle and adipose tissue across the paediatric age range. The fatty acid profile of skeletal muscle phospholipids and adipose tissue triacylglycerols was analysed in ninety-three healthy Spanish infants and children distributed into four groups: group 1 (0 to <2 years,n10); group 2 (2 to <5 years,n41); group 3 (5 to <10 years,n24); group 4 (10 to 15 years,n18). In skeletal muscle phospholipids, oleic acid (18: 1n-9cis) content decreased significantly whereas that of linoleic (18: 2n-6) acid increased significantly with age (Pfor trend <0·01). In adipose tissue, the contents of triacylglycerol and linoleic acid increased significantly across the paediatric age range (Pfor trend <0·01), whereas dihomo-γ-linolenic (20: 3n-6) and arachidonic (20: 4n-6) showed significant differences between groups. The variations in fatty acid composition observed with age indicated an imbalance in dietaryn-3/n-6 long-chain PUFA.

Brain docosahexaenoic acid status and learning in young rats submitted to dietary long-chain polyunsaturated fatty acid deficiency and supplementation limited to lactation

N-3 fatty acid deficiency has been related to decreased docosahexaenoic acid (DHA) and increased docosapentaenoic acid (DPA) levels in brain and to learning disadvantages. The influence of n-3 deficiency and supplementation on brain fatty acids and learning were investigated in young rats. Newborn Wistar rats were assigned to three groups of cross-foster mothers. The control group (C) was nursed by mothers that received essential fatty acids during pregnancy and lactation, and the deficient group (D) was nursed by mothers that did not receive those fatty acids. The supplemental group (S) had the same conditions as D, receiving an additional DHA and arachidonic acid supplement during lactation. Cerebral cortex and hippocampus fatty acid composition was examined using thin-layer and capillary column gas chromatography, and learning was measured by passive-avoidance procedure. D brains showed low DHA and high DPA levels, but S brain composition was similar to C. Learning in the S group was unaffected, but in the D group, it was poorer than C. Learning was directly correlated with DHA levels and inversely with DPA levels in brain. Low DHA and high DPA brain levels both were correlated with poor learning. DPA seems not to be a suitable brain functional analogue of DHA, and DHA supplementation reversed both biochemical and learning adverse effects observed in n-3 deficiency.

Phosphorus magnetic resonance spectroscopy: its utility in examining the membrane hypothesis of schizophrenia

A novel approach to understanding the pathophysiology of schizophrenia has been the investigation of membrane composition and functional perturbations, referred to as the "Membrane Hypothesis of Schizophrenia." The evidence in support of this hypothesis has been accumulating in findings in patients with schizophrenia of reductions in phospholipids and essential fatty acids various peripheral tissues. Postmortem studies indicate similar reductions in essential fatty acids in the brain. However, the use of magnetic resonance spectroscopy (MRS) has provided an opportunity to examine aspects of membrane biochemistry in vivo in the living brain. MRS is a powerful, albeit complex, noninvasive quantitative imaging tool that offers several advantages over other methods of in vivo biochemical investigations. It has been used extensively in investigating brain biochemistry in schizophrenia. Phosphorus MRS (31P MRS) can provide important information about neuronal membranes, such as levels of phosphomonoesters that reflect the building blocks of neuronal membranes and phosphodiesters that reflect breakdown products. 31P MRS can also provide information about bioenergetics. Studies in patients with chronic schizophrenia as well as at first episode prior to treatment show a variety of alterations in neuronal membrane biochemistry, supportive of the membrane hypothesis of schizophrenia. Below, we will briefly review the principles underlying 31P MRS and findings to date. Magnetic resonance spectroscopy (MRS) is a powerful, albeit complex, imaging tool that permits investigation of brain biochemistry in vivo. It utilizes the magnetic resonance imaging hardware. It offers several advantages over other methods of in vivo biochemical investigations. MRS is noninvasive, there is no radiation exposure, does not require the use of tracer ligands or contrast media. Because of it is relatively benign, repeated measures are possible. It has been used extensively in investigating brain biochemistry in schizophrenia.

Correlations between peripheral polyunsaturated fatty acid content and in vivo membrane phospholipid metabolites

BACKGROUND

There is evidence for membrane abnormalities in schizophrenia. It is unclear whether the observed membrane deficits in peripheral cells parallel central membrane phospholipid metabolism. To address this question we examined the relations between red blood cell polyunsaturated fatty acids and brain phospholipid metabolites from different regions of interest in schizophrenia and healthy subjects.

METHODS

Red blood cell membrane fatty acids were measured by capillary gas chromatography and in vivo brain phospholipid metabolite levels were measured using a multi-voxel (31)P Magnetic Resonance Spectroscopy technique on 11 first-episode, neuroleptic-naïve schizophrenic subjects and 11 normal control subjects.

RESULTS

Both the total polyunsaturated fatty acids and the individual 20:4(n-6) contents were significantly correlated with the freely-mobile phosphomonoester [PME(s-tau(c))] levels (r =.5643, p =.0062 and r =.6729, p =.0006, respectively). The 18:2(n-6) polyunsaturated fatty acids content correlated positively with freely-mobile phosphodiester [PDE(s-tau(c))] levels (r =.5573, p =.0071). The above correlations were present in the combined right and left prefrontal region of the brain, while other regions including the basal ganglia, occipital, inferior parietal, superior temporal and centrum semiovale yielded no significant correlations.

CONCLUSIONS

Our preliminary data support the association between the decreased red blood cell membrane phospholipid polyunsaturated fatty acids content and the decreased building blocks [PME(s-tau(c))] and breakdown products [PDE(s-tau(c))] of membrane phospholipids in the prefrontal region of first-episode, neuroleptic-naïve schizophrenic subjects.

Long-chain polyunsaturated fatty acids in rat maternal milk, offspring brain and peripheral tissues in essential fatty acid deficiency

Fatty acid status in humans is usually related to plasma or red blood cell fatty acid profiles. The aim of the study was to explore whether a maternal deficiency in dietary essential fatty acids would differentially affect lipid fractions in several tissues of the offspring, including brain. Female Wistar rats were fed an essential fatty acid-deficient diet during 3 months before mating. The fatty acid composition of different lipid fractions was examined in maternal milk, and in plasma, red blood cells, liver, adipose tissue, cerebral cortex and hippocampus of the offspring using thin layer and capillary column gas chromatography. Lipid fractions from most tissues of deprived offspring showed a common fatty acid profile characterized by elevated 20:3 omega9/20:4 omega6 ratio, and decreased docosahexaenoic acid and arachidonic acid. However, arachidonic acid was not affected in brain, even though 22:5 omega6 was increased in phospholipids of cerebral cortex and hippocampus. The present results demonstrate different degrees of resistance to essential fatty acid deficiency in lipid fractions and tissues. This suggests a priority distribution of arachidonic acid to preferential areas and shows that blood phospholipid fatty acids do not exactly reflect brain phospholipid status.

A combined subchronic (90-day) toxicity and neurotoxicity study of a single-cell source of docosahexaenoic acid triglyceride (DHASCO oil)

Docosahexaenoic acid (DHA), a 22-carbon long-chain polyunsaturated fatty acid of the omega-3 family, is a major structural component of neural membranes and is a particularly important nutrient during infant development. New safe and well-defined sources of DHA are required for infant formula fortification and dietary supplementation. DHASCO oil is an algal-derived triglyceride containing 40-50% DHA. Previous studies have shown that DHASCO oil is neither mutagenic nor toxic in acute or 28-day subchronic tests. To further establish the safety of this oil, a 90-day subchronic toxicity study in rats which included haematology, clinical chemistry, pathology and ophthalmologic, neurobehavioural and neuropathological assessments, using doses of 0.5 and 1.25g/kg body weight/day was performed. There were no treatment-related adverse effects in any of the parameters measured at either dose. Based on these results, the no-adverse-effect level (NOAEL) for DHASCO oil under the conditions of this study corresponds to the highest dose level. The DHA in the DHASCO oil was bioavailable, resulting in significant elevations in the levels of this fatty acid in liver, heart and brain after 90 days of administration. In conclusion, this 90-day subchronic toxicity study provides additional evidence that DHASCO oil is a safe and bioavailable source of dietary DHA.

Docosahexaenoic and arachidonic acid prevent a decrease in dopaminergic and serotoninergic neurotransmitters in frontal cortex caused by a linoleic and alpha-linolenic acid deficient diet in formula-fed piglets

This study examined the effects of diets deficient (D) in linoleic [18:2(n-6)] and linolenic acid [18:3(n-3)] at 0.8 and 0.05% energy, respectively, or adequate (C) in 18:2(n-6) and 18:3(n-3) at 8.3 and 0.8% energy, respectively, without (-) or with (+) 0.2% energy arachidonic [20:4(n-6)] and 0.16% energy docosahexaenoic [22:6(n-3)] acid in piglets fed from birth to 18 d. Frontal cortex dopaminergic and serotoninergic neurotransmitters and phospholipid fatty acids were measured. Piglets fed the D- diet had significantly lower frontal cortex dopamine, 3,4-dihydroxyphenylacetic (DOPAC), homovanillic acid (HVA), serotonin and 5-hydroxyindoleacetic acid (5-HIAA) concentrations than did piglets fed the C- diets. Frontal cortex dopamine, norepinephrine, DOPAC, HVA, serotonin and 5-HIAA were higher in piglets fed the D+ compared to those fed the D- diet (P < 0.05) and not different between piglets fed the D+ and those fed the C- diets or the C- and C+ diets. Piglets fed the D- diet had lower frontal cortex phosphatidylcholine (PC) and phosphatidylinositol (PI) 20:4(n-6) and PC and phosphatidylethanolamine (PE) 22:6(n-3) than did piglets fed the C- diet (P < 0.05). Piglets fed the D+ diet had higher frontal cortex PC and PI 20:4(n-6) and PC, PE, PS and PI 22:6(n-3) than did piglets fed the D- diet. These studies show that dietary essential fatty acid deficiency fed for 18 d from birth affects frontal cortex neurotransmitters in rapidly growing piglets and that these changes are specifically due to 20:4(n-6) and/or 22:6(n-3).

Dietary supplementation with arachidonic and docosahexaenoic acids has no effect on pulmonary surfactant in artificially reared infant rats

Despite the potential use of long chain polyunsaturated fatty acid (LCPUFA) supplementation to promote growth and neural development of the infant, little is known about potential harmful effects of the supplementation. The present study determined whether supplementation with arachidonic acid (AA) and/or docosahexaenoic acid (DHA) in rat milk formula (RMF) affects saturation of pulmonary surfactant phospholipids (PL). Beginning at 7 d of age, infant rats were artificially fed for 10 d with RMF supplemented with AA at 0, 0.5, and 1.0% of total fatty acid, or supplemented with DHA at 0, 0.5, and 1.0%, or cosupplemented with AA and DHA at levels of 0:0, 0.5:0.3, and 1.0:0.6% of the fat blend. Lung tissue PL contained 43 weight percent palmitate (16:0) of total fatty acids in infant rats fed the unsupplemented RMF. The supplementation with AA at both 0.5 and 1.0% decreased the weight percentage of 16:0 and stearate (18:0), indicating a decrease in saturation of PL. The observed decreases were accompanied by increases in AA and linoleic acid (18:2n-6). Surfactant phosphatidylcholine (PC) consisted of 71 weight percent 16:0 in the unsupplemented group, and this highly saturated PC was not altered by the cosupplementation with AA and DHA although there was a slight increase in DHA. Similarly, the cosupplementation did not change fatty acid composition of surfactant PL when compared with the unsupplemented group. The cosupplementation slightly decreased the weight percentage of 16:0 with a proportional increase in 18:0 leading to an unchanged weight percentage of total saturated fatty acids. These results suggest that, unlike lung tissue PL, the composition of saturated fatty acids in surfactant PL, particularly PC, is resistant to change by dietary AA and DHA supplementation. This, together with the unchanged concentration of total fatty acids in surfactant PC, indicates that LCPUFA cosupplementation causes no effect on pulmonary surfactant.