Improvement of retinal function in Alzheimer disease-associated retinopathy by dietary lysophosphatidylcholine-EPA/DHA

Alzheimer disease (AD) is the most prevalent cause of dementia in the elderly. Although impaired cognition and memory are the most prominent features of AD, abnormalities in visual functions often precede them, and are increasingly being used as diagnostic and prognostic markers for the disease. Retina contains the highest concentration of the essential fatty acid docosahexaenoic acid (DHA) in the body, and its deficiency is associated with several retinal diseases including diabetic retinopathy and age related macular degeneration. In this study, we tested the hypothesis that enriching retinal DHA through a novel dietary approach could ameliorate symptoms of retinopathy in 5XFAD mice, a widely employed model of AD. The results show that 5XFAD mice have significantly lower retinal DHA compared to their wild type littermates, and feeding the lysophosphatidylcholine (LPC) form of DHA and eicosapentaenoic acid (EPA) rapidly normalizes the DHA levels, and increases retinal EPA by several-fold. On the other hand, feeding similar amounts of DHA and EPA in the form of triacylglycerol had only modest effects on retinal DHA and EPA. Electroretinography measurements after 2 months of feeding the experimental diets showed a significant improvement in a-wave and b-wave functions by the LPC-diet, whereas the TAG-diet had only a modest benefit. Retinal amyloid β levels were decreased by about 50% by the LPC-DHA/EPA diet, and by about 17% with the TAG-DHA/EPA diet. These results show that enriching retinal DHA and EPA through dietary LPC could potentially improve visual abnormalities associated with AD.

Encapsulation of Docosahexaenoic Acid Oil Substantially Improves the Oxylipin Profile of Rat Tissues

Docosahexaenoic acid (DHA) is a major n-3 polyunsaturated fatty acid (PUFA) particularly involved in cognitive and cardiovascular functions. Due to the high unsaturation index, its dietary intake form has been considered to improve oxidation status and to favor bioaccessibility and bioavailability as well. This study aimed at investigating the effect of DHA encapsulated with natural whey protein. DHA was dietary provided as triacylglycerols to achieve 2.3% over total fatty acids. It was daily supplied to weanling rats for four weeks in omelet as food matrix, consecutively to a 6-hour fasting. First, when DHA oil was encapsulated, consumption of chow diet was enhanced leading to promote animal growth. Second, the brain exhibited a high accretion of 22.8% DHA, which was not improved by dietary supplementation of DHA. Encapsulation of DHA oil did not greatly affect the fatty acid proportions in tissues, but remarkably modified the profile of oxidized metabolites of fatty acids in plasma, heart, and even brain. Specific oxylipins derived from DHA were upgraded, such as Protectin Dx in heart and 14-HDoHE in brain, whereas those generated from n-6 PUFAs were mainly mitigated. This effect did not result from oxylipins measured in DHA oil since DHA and EPA derivatives were undetected after food processing. Collectively, these data suggested that dietary encapsulation of DHA oil triggered a more efficient absorption of DHA, the metabolism of which was enhanced more than its own accretion in our experimental conditions. Incorporating DHA oil in functional food may finally improve the global health status by generating precursors of protectins and maresins.

Why Have the Benefits of DHA Not Been Borne Out in the Treatment and Prevention of Alzheimer's Disease? A Narrative Review Focused on DHA Metabolism and Adipose Tissue

Docosahexaenoic acid (DHA), an omega-3 fatty acid rich in seafood, is linked to Alzheimer's Disease via strong epidemiological and pre-clinical evidence, yet fish oil or other DHA supplementation has not consistently shown benefit to the prevention or treatment of Alzheimer's Disease. Furthermore, autopsy studies of Alzheimer's Disease brain show variable DHA status, demonstrating that the relationship between DHA and neurodegeneration is complex and not fully understood. Recently, it has been suggested that the forms of DHA in the diet and plasma have specific metabolic fates that may affect brain uptake; however, the effect of DHA form on brain uptake is less pronounced in studies of longer duration. One major confounder of studies relating dietary DHA and Alzheimer's Disease may be that adipose tissue acts as a long-term depot of DHA for the brain, but this is poorly understood in the context of neurodegeneration. Future work is required to develop biomarkers of brain DHA and better understand DHA-based therapies in the setting of altered brain DHA uptake to help determine whether brain DHA should remain an important target in the prevention of Alzheimer's Disease.

Acyl-CoA synthetases as regulators of brain phospholipid acyl-chain diversity

Each individual cell-type is defined by its distinct morphology, phenotype, molecular and lipidomic profile. The importance of maintaining cell-specific lipidomic profiles is exemplified by the numerous diseases, disorders, and dysfunctional outcomes that occur as a direct result of altered lipidome. Therefore, the mechanisms regulating cellular lipidome diversity play a role in maintaining essential biological functions. The brain is an organ particularly rich in phospholipids, the main constituents of cellular membranes. The phospholipid acyl-chain profile of membranes in the brain is rather diverse due in part to the high degree of cellular heterogeneity. These membranes and the acyl-chain composition of their phospholipids are highly regulated, but the mechanisms that confer this tight regulation are incompletely understood. A family of enzymes called acyl-CoA synthetases (ACSs) stands at a pinnacle step allowing influence over cellular acyl-chain selection and subsequent metabolic flux. ACSs perform the initial reaction for cellular fatty acid metabolism by ligating a Coenzyme A to a fatty acid which both traps a fatty acid within a cell and activates it for metabolism. The ACS family of enzymes is large and diverse consisting of 25-26 family members that are nonredundant, each with unique distribution across and within cell types, and differential fatty acid substrate preferences. Thus, ACSs confer a critical intracellular fatty acid selecting step in a cell-type dependent manner providing acyl-CoA moieties that serve as essential precursors for phospholipid synthesis and remodeling, and therefore serve as a key regulator of cellular membrane acyl-chain compositional diversity. Here we will discuss how the contribution of individual ACSs towards brain lipid metabolism has only just begun to be elucidated and discuss the possibilities for how ACSs may differentially regulate brain lipidomic diversity.

Comparison of Fatty Acid Contents in Major Lipid Classes of Seven Salmonid Species from Siberian Arctic Lakes

Long-chain omega-3 polyunsaturated fatty acids (LC-PUFA) essential for human nutrition are mostly obtained from wild-caught fish. To sustain the LC-PUFA supply from natural populations, one needs to know how environmental and intrinsic factors affect fish fatty acid (FA) profiles and contents. We studied seven Salmoniformes species from two arctic lakes. We aimed to estimate differences in the FA composition of total lipids and two major lipid classes, polar lipids (PL) and triacylglycerols (TAG), among the species and to evaluate LC-PUFA contents corresponding to PL and TAG in muscles. Fatty acid profiles of PL and TAG in all species were characterized by the prevalence of omega-3 LC-PUFA and C16-C18 monoenoic FA, respectively. Fish with similar feeding spectra were identified similarly in multivariate analyses of total lipids, TAG and PL, due to differences in levels of mostly the same FA. Thus, the suitability of both TAG and total lipids for the identification of the feeding spectra of fish was confirmed. All species had similar content of LC-PUFA esterified as PL, 1.9–3.5 mg g⁻¹, while the content of the TAG form strongly varied, from 0.9 to 9.8 mg g⁻¹. The LC-PUFA-rich fish species accumulated these valuable compounds predominately in the TAG form.

Marine omega-3 (n-3) phospholipids: A comprehensive review of their properties, sources, bioavailability, and relation to brain health

For several decades, there has been considerable interest in marine-derived long chain n-3 fatty acids (n-3 LCPUFAs) due to their outstanding health benefits. n-3 LCPUFAs can be found in nature either in triglycerides (TAGs) or in phospholipid (PL) form. From brain health point of view, PL n-3 is more bioavailable and potent compared to n-3 in TAG form, as only PL n-3 is able to cross the blood-brain barrier and can be involved in brain biochemical reactions. However, PL n-3 has been ignored in the fish oil industry and frequently removed as an impurity during degumming processes. As a result, PL products derived from marine sources are very limited compared to TAG products. Commercially, PLs are being used in pharmaceutical industries as drug carriers, in food manufacturing as emulsifiers and in cosmetic industries as skin care agents, but most of the PLs used in these applications are produced from vegetable sources that contain less (without EPA, DPA, and DHA) or sometimes no n-3 LCPUFAs. This review provides a comprehensive account of the properties, structures, and major sources of marine PLs, and provides focussed discussion of their relationship to brain health. Epidemiological, laboratory, and clinical studies on n-3 LCPUFAs enriched PLs using different model systems in relation to brain and mental health that have been published over the past few years are discussed in detail.

The Effect of n-3 PUFA Binding Phosphatidylglycerol on Metabolic Syndrome-Related Parameters and n-3 PUFA Accretion in Diabetic/Obese KK-Ay Mice

n-3 Polyunsaturated fatty acid binding phospholipids (n-3 PUFA-PLs) are known to be potent carriers of n-3 PUFAs and provide health benefits. We previously prepared n-3 PUFA binding phosphatidylglycerol (n-3 PUFA-PG) by phospholipase D-mediated transphosphatidylation. Because PG has excellent emulsifiability, n-3 PUFA-PG is expected to work as a functional molecule with properties of both PG and n-3 PUFAs. In the present study, the health benefits and tissue accretion of dietary n-3 PUFA-PG were examined in diabetic/obese KK-A^y mice. After a feeding duration over 30 days, n-3 PUFA-PG significantly reduced the total and non-HDL cholesterols in the serum of diabetic/obese KK-A^y mice. In the mice fed n-3 PUFA-PG, but not n-3 PUFA-TAG, hepatic lipid content was markedly alleviated depending on the neutral lipid reduction compared with the SoyPC-fed mice. Further, the n-3 PUFA-PG diet increased eicosapentaenoic acid and docosahexaenoic acid (DHA) and reduced arachidonic acid in the small intestine, liver, perirenal white adipose tissue, and brain, and the ratio of the n-6 PUFAs to n-3 PUFAs in those tissues became lower compared to the SoyPC-fed mice. Especially, the DHA level was more significantly elevated in the brains of n-3 PUFA-PG-fed mice compared to the SoyPC-fed mice, whereas n-3 PUFA-TAG did not significantly alter DHA in the brain. The present results indicate that n-3 PUFA-PG is a functional lipid for reducing serum and liver lipids and is able to supply n-3 PUFAs to KK-A^y mice.

Docosahexaenoic acid (22:6n-3) Ameliorated the Onset and Severity of Experimental Autoimmune Encephalomyelitis in Mice

Multiple sclerosis (MS) is a neurologic autoimmune disease, which is the leading cause of nontraumatic neurologic disability in young adults in United States and Europe. n-3 polyunsaturated fatty acids (PUFA) are reported to mitigate severity of this disease. Recent studies suggest that phospholipid (PL) form of dietary n-3 PUFA may lead to their higher tissue accretion than triacylglycerol (TAG) form. We compared efficacy of PL-docosahexaenoic acid (22:6n-3) (DHA) and TAG-DHA on onset and severity of experimental autoimmune encephalomyelitis (EAE) in a mouse model of MS. Female mice were fed low alpha-linolenic acid (18:3n-3) (ALA) diet (control) for 2 weeks and then fed either control, 0.3%, or 1.0% DHA (PL or TAG) for 4 weeks pre-EAE induction and 4 weeks post-EAE induction. The brain and spinal cord n-6:n-3 ratio was significantly lower in all mice fed DHA compared to control. EAE onset was delayed in mice fed both DHA forms and concentrations, except for 1% TAG-DHA. The inverse association between the EAE score and the brain DHA concentration was nonsignificant at the end of the study (p = 0.08). Daily EAE scores of mice fed different DHA diets did not differ from control, however, the score of all DHA groups combined during days 9-16 was lower (p = 0.028) compared to the control. During days 17-22, the EAE score trended lower in 0.3% TAG-DHA and during days 23-28, the EAE score trended lower in both PL-DHA groups than those in all other groups. These findings suggest that TAG-DHA may be more effective than PL-DHA in the early phases of EAE, and in the final outcome, PL-DHA may be more effective than TAG-DHA.