Two weeks of docosahexaenoic acid (DHA) supplementation increases synthesis-secretion kinetics of n-3 polyunsaturated fatty acids compared to 8 weeks of DHA supplementation

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.jnutbio.2018.07.002 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Docosahexaenoic acid (DHA, 22:6n-3) must be consumed in the diet or synthesized from n-3 polyunsaturated fatty acid (PUFA) precursors. However, the effect of dietary DHA on the metabolic pathway is not fully understood. Presently, 21-day-old Long Evans rats were weaned onto one of four dietary protocols: 1) 8 weeks of 2% ALA (ALA), 2) 6 weeks ALA followed by 2 weeks of 2% ALA + 2% DHA (DHA), 3) 4 weeks ALA followed by 4 weeks DHA and 4) 8 weeks of DHA. After the feeding period, 2H5-ALA and 13C20-eicosapentaenoic acid (EPA, 20:5n-3) were co-infused and blood was collected over 3 h for determination of whole-body synthesis-secretion kinetics. The synthesis-secretion coefficient (ml/min, means ± SEM) for EPA (0.238±0.104 vs. 0.021±0.001) and DPAn-3 (0.194±0.060 vs. 0.020±0.008) synthesis from plasma unesterified ALA, and DPAn-3 from plasma unesterified EPA (2.04±0.89 vs. 0.163±0.025) were higher (P<.05) after 2 weeks compared to 8 weeks of DHA feeding. The daily synthesis-secretion rate (nmol/d) of DHA from EPA was highest after 4 weeks of DHA feeding (843±409) compared to no DHA (70±22). Liver gene expression of ELOVL2 and FADS2 were lower (P<.05) after 4 vs. 8 weeks of DHA. Higher synthesis-secretion kinetics after 2 and 4 weeks of DHA feeding suggests an increased throughput of the PUFA metabolic pathway. Furthermore, these findings may lead to novel dietary strategies to maximize DHA levels while minimizing dietary requirements.Natural Sciences and Engineering Research Council of Canada || 48259

N-3 Polyunsaturated Fatty Acids and Neuroinflammation in Alzheimer's Disease

Neuroinflammation may factor in the etiology of Alzheimer’s Disease (AD). n-3 polyunsaturated fatty acids (PUFA) and their bioactive lipid mediator derivatives have inflammation-modulating properties. Epidemiological and animal data suggests n-3 PUFA may be protective in AD, but whether this protection is conferred by modulating neuroinflammation is unknown. To determine how integral neuroinflammation is to AD pathology, a systematic review was conducted of studies comparing microglial markers in post-mortem human brain samples from patients with AD and controls. The analysis of 114 studies presented in Chapter 2 showed that markers of microglial activation are elevated in AD, suggesting that neuroinflammation is an important feature of the disease. A series of experiments were conducted to examine the effects of n-3 PUFA on neuroinflammation in an AD model. Fat-1 transgenic mice, animals that endogenously synthesize n-3 PUFA, and their wildtype littermates were fed either a n-3 PUFA deprived safflower oil diet, or a fish oil diet containing n-3 PUFA. In Chapter 3, we examined the time-course of neuroinflammation and its resolution following intracerebroventricular infusion of amyloid-β 1-40. Wildtype mice fed the n-3 PUFA-deprived diet exhibited a greater increase in microglia proliferation, more neuronal death, and alterations in microglia morphology consistent with activation, with no changes in the time-course of resolution. In Chapter 4, we show that fish oil-fed mice have a greater astrocyte activation response to amyloid-β than either the safflower-fed or fat-1 animals. Using a microarray in Chapter 5, we found that safflower oil-fed mice exhibited greater enrichment of gene categories associated with inflammation than fish oil-fed mice, independent of changes in levels of lipid mediators. Together, the data in this thesis show that neuroinflammation is a common pathological feature of AD that is modulated by brain n-3 PUFA. This does not seem to require detectable changes in bioactive lipid mediators.Ph.D.2018-06-19 00:00:0

Brain omega-3 polyunsaturated fatty acids modulate microglia cell number and morphology in response to intracerebroventricular amyloid-β 1-40 in mice

Abstract Background Neuroinflammation is a proposed mechanism by which Alzheimer’s disease (AD) pathology potentiates neuronal death and cognitive decline. Consumption of omega-3 polyunsaturated fatty acids (PUFA) is associated with a decreased risk of AD in human observational studies and exerts protective effects on cognition and pathology in animal models. These fatty acids and molecules derived from them are known to have anti-inflammatory and pro-resolving properties, presenting a potential mechanism for these protective effects. Methods Here, we explore this mechanism using fat-1 transgenic mice and their wild type littermates weaned onto either a fish oil diet (high in n-3 PUFA) or a safflower oil diet (negligible n-3 PUFA). The fat-1 mouse carries a transgene that enables it to convert omega-6 to omega-3 PUFA. At 12 weeks of age, mice underwent intracerebroventricular (icv) infusion of amyloid-β 1-40. Brains were collected between 1 and 28 days post-icv, and hippocampal microglia, astrocytes, and degenerating neurons were quantified by immunohistochemistry with epifluorescence microscopy, while microglia morphology was assessed with confocal microscopy and skeleton analysis. Results Fat-1 mice fed with the safflower oil diet and wild type mice fed with the fish oil diet had higher brain DHA in comparison with the wild type mice fed with the safflower oil diet. Relative to the wild type mice fed with the safflower oil diet, fat-1 mice exhibited a lower peak in the number of labelled microglia, wild type mice fed with fish oil had fewer degenerating neurons, and both exhibited alterations in microglia morphology at 10 days post-surgery. There were no differences in astrocyte number at any time point and no differences in the time course of microglia or astrocyte activation following infusion of amyloid-β 1-40. Conclusions Increasing brain DHA, through either dietary or transgenic means, decreases some elements of the inflammatory response to amyloid-β in a mouse model of AD. This supports the hypothesis that omega-3 PUFA may be protective against AD by modulating the immune response to amyloid-β

Whole-body DHA synthesis-secretion kinetics from plasma eicosapentaenoic acid and alpha-linolenic acid in the free-living rat

AbstractWhole body docosahexaenoic acid (DHA, 22:6n-3) synthesis from α-linolenic acid (ALA, 18:3n-3) is considered to be very low, however, the daily synthesis-secretion of DHA may be sufficient to supply the adult brain. The current study aims to assess whether whole body DHA synthesis-secretion kinetics are different when comparing plasma ALA versus eicosapentaenoic acid (EPA, 20:5n-3) as the precursor. Male Long Evans rats (n=6) were fed a 2% ALA in total fat diet for eight weeks, followed by surgery to implant a catheter into each of the jugular vein and carotid artery and 3h of steady-state infusion with a known amount of 2H-ALA and 13C-eicosapentaenoic acid (EPA, 20:5n3). Blood samples were collected at thirty-minute intervals and plasma enrichment of 2H- and 13C EPA, n−3 docosapentaenoic acid (DPAn-3, 22:5n-3) and DHA were determined for assessment of synthesis-secretion kinetic parameters. Results indicate a 13-fold higher synthesis-secretion coefficient for DHA from EPA as compared to ALA. However, after correcting for the 6.6 fold higher endogenous plasma ALA concentration, no significant differences in daily synthesis-secretion (nmol/day) of DHA (97.6±28.2 and 172±62), DPAn-3 (853±279 and 1139±484) or EPA (1587±592 and 1628±366) were observed from plasma unesterified ALA and EPA sources, respectively. These results suggest that typical diets which are significantly higher in ALA compared to EPA yield similar daily DHA synthesis-secretion despite a significantly higher synthesis-secretion coefficient from EPA

Plasma non-esterified docosahexaenoic acid is the major pool supplying the brain : Plasma NEFA pool supplies the brain with DHA

Acknowledgements This project was funded by a NSERC and CIHR grant to R.P.B. and studentship to C.T.C. R.P.B. holds a Canada Research Chair in Brain Lipid Metabolism. R.P.B. acknowledges support and mass spectrometry equipment and solutions for lipidomics from Sciex. Computer programmable pump software was designed by Dr. Brian Scott. HPLC analyses were performed at the Analytical Facility at the Department of Nutritional Sciences by Dr. Zhen Liu. LC/MS/MS analyses of NEFA-DHA and LPC-DHA and MALDI imaging were performed at the Analytical Facility for Bioactive Molecules (AFBM) with the assistance of Michael Leadley. The AFBM is part of the Centre for the Study of Complex Childhood Diseases (CSCCD) at the Hospital for Sick Children, Toronto, Ontario. CSCCD was supported by Canadian Foundation for Innovation (CFI).Peer reviewedPublisher PD