Increased brain docosahexaenoic acid has no effect on the resolution of neuroinflammation following intracerebroventricular lipopolysaccharide injection

Involvement of Microglia in Neurodegenerative Diseases: Beneficial Effects of Docosahexahenoic Acid (DHA) Supplied by Food or Combined with Nanoparticles

Neurodegenerative diseases represent a major public health issue and require better therapeutic management. The treatments developed mainly target neuronal activity. However, an inflammatory component must be considered, and microglia may constitute an important therapeutic target. Given the difficulty in developing molecules that can cross the blood–brain barrier, the use of food-derived molecules may be an interesting therapeutic avenue. Docosahexaenoic acid (DHA), an omega-3 polyunsaturated fatty acid (22:6 omega-3), has an inhibitory action on cell death and oxidative stress induced in the microglia. It also acts on the inflammatory activity of microglia. These data obtained in vitro or on animal models are corroborated by clinical trials showing a protective effect of DHA. Whereas DHA crosses the blood–brain barrier, nutritional intake lacks specificity at both the tissue and cellular level. Nanomedicine offers new tools which favor the delivery of DHA at the cerebral level, especially in microglial cells. Because of the biological activities of DHA and the associated nanotargeting techniques, DHA represents a therapeutic molecule of interest for the treatment of neurodegenerative diseases.

The effects of n-6 polyunsaturated fatty acid deprivation on the inflammatory gene response to lipopolysaccharide in the mouse hippocampus

Background

Neuroinflammation is thought to contribute to psychiatric and neurological disorders such as major depression and Alzheimer’s disease (AD). N-6 polyunsaturated fatty acids (PUFA) and molecules derived from them, including linoleic acid- and arachidonic acid-derived lipid mediators, are known to have pro-inflammatory properties in the periphery; however, this has yet to be tested in the brain. Lowering the consumption of n-6 PUFA is associated with a decreased risk of depression and AD in human observational studies. The purpose of this study was to investigate the inflammation-modulating effects of lowering dietary n-6 PUFA in the mouse hippocampus.

Methods

C57BL/6 male mice were fed either an n-6 PUFA deprived (2% of total fatty acids) or an n-6 PUFA adequate (23% of total fatty acids) diet from weaning to 12 weeks of age. Animals then underwent intracerebroventricular surgery, in which lipopolysaccharide (LPS) was injected into the left lateral ventricle of the brain. Hippocampi were collected at baseline and following LPS administration (1, 3, 7, and 14 days). A microarray (n = 3 per group) was used to identify candidate genes and results were validated by real-time PCR in a separate cohort of animals (n = 5–8 per group).

Results

Mice administered with LPS had significantly increased Gene Ontology categories associated with inflammation and immune responses. These effects were independent of changes in gene expression in any diet group. Results were validated for the effect of LPS treatment on astrocyte, cytokine, and chemokine markers, as well as some results of the diets on Ifrd2 and Mfsd2a expression.

Conclusions

LPS administration increases pro-inflammatory and lipid-metabolizing gene expression in the mouse hippocampus. An n-6 PUFA deprived diet modulated inflammatory gene expression by both increasing and decreasing inflammatory gene expression, without impairing the resolution of neuroinflammation following LPS administration.

The Effects of Doxorubicin-based Chemotherapy and Omega-3 Supplementation on Mouse Brain Lipids

Chemotherapy-induced cognitive impairment affects ~30% of breast cancer survivors, but the effects on how chemotherapy impacts brain lipids, and how omega-3 polyunsaturated fatty acid supplementation may confer protection, is unknown. Ovariectomized mice were randomized to two rounds of injections of doxorubicin + cyclophosphamide or vehicle after consuming a diet supplemented with 2% or 0% EPA+DHA, and sacrificed 4, 7, and 14 days after the last injection (study 1, n = 120) or sacrificed 10 days after the last injection (study 2, n = 40). Study 1 whole brain samples were extracted and analyzed by UHPLC-MS/MS to quantify specialized pro-resolving mediators (SPMs). Lipidomics analyses were performed on hippocampal extracts from study 2 to determine changes in the brain lipidome. Study 1 results: only resolvin D1 was present in all samples, but no differences in concentration were observed (P > 0.05). Study 2 results: chemotherapy was positively correlated with omega-9 fatty acids, and EPA+DHA supplementation helped to maintain levels of plasmalogens. No statistically significant chemotherapy*diet effect was observed. Results demonstrate a limited role of SPMs in the brain post-chemotherapy, but a significant alteration of hippocampal lipids previously associated with other models of cognitive impairment (i.e., Alzheimer's and Parkinson's disease).

N-3 Polyunsaturated Fatty Acids and the Resolution of Neuroinflammation

In the past few decades, as a result of their anti-inflammatory properties, n-3 long chain polyunsaturated fatty acids (n-3 LC-PUFAs), have gained greater importance in the regulation of inflammation, especially in the central nervous system (in this case known as neuroinflammation). If sustained, neuroinflammation is a common denominator of neurological disorders, including Alzheimer’s disease and major depression, and of aging. Hence, limiting neuroinflammation is a real strategy for neuroinflammatory disease therapy and treatment. Recent data show that n-3 LC-PUFAs exert anti-inflammatory properties in part through the synthesis of specialized pro-resolving mediators (SPMs) such as resolvins, maresins and protectins. These SPMs are crucially involved in the resolution of inflammation. They could be good candidates to resolve brain inflammation and to contribute to neuroprotective functions and could lead to novel therapeutics for brain inflammatory diseases. This review presents an overview 1) of brain n-3 LC-PUFAs as precursors of SPMs with an emphasis on the effect of n-3 PUFAs on neuroinflammation, 2) of the formation and action of SPMs in the brain and their biological roles, and the possible regulation of their synthesis by environmental factors such as inflammation and nutrition and, in particular, PUFA consumption.

Acyl-CoA synthetase 6 enriches the neuroprotective omega-3 fatty acid DHA in the brain

Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is highly abundant in the brain and confers protection against numerous neurological diseases, yet the fundamental mechanisms regulating the enrichment of DHA in the brain remain unknown. Here, we have discovered that a member of the long-chain acyl-CoA synthetase family, Acsl6, is required for the enrichment of DHA in the brain by generating an Acsl6-deficient mouse (Acsl6^-/-). Acsl6 is highly enriched in the brain and lipid profiling of Acsl6^-/- tissues reveals consistent reductions in DHA-containing lipids in tissues highly abundant with Acsl6. Acsl6^-/- mice demonstrate motor impairments, altered glutamate metabolism, and increased astrogliosis and microglia activation. In response to a neuroinflammatory lipopolysaccharide injection, Acsl6^-/- brains show similar increases in molecular and pathological indices of astrogliosis compared with controls. These data demonstrate that Acsl6 is a key mediator of neuroprotective DHA enrichment in the brain.