Dietary Omega-6/Omega-3 and Endocannabinoids: Implications for Brain Health and Diseases

Omega-3 (omega-3) and omega-6 (omega-6) are polyunsaturated fatty acids (PUFAs) that play critical role in human health and have to be provided by food. In the brain, PUFAs are also precursors of endocannabinoids. The aim of this chapter is to review the existing literature on how dietary PUFAs impact on the endocannabinoid system in the brain and what are the consequences for brain function and dysfunction. In this chapter, we will first describe how PUFAs enter the brain, what are their metabolism processes and roles in brain function. We will describe the pathways from PUFAs to endocannabinoid production. Then, we will review the literature on how dietary omega-6/omega-3 ratio impacts the endocannabinoid system, in terms of endocannabinoid levels, proteins and endocannabinoid-dependent synaptic plasticity. In the next part, we will describe what we know about the interactions between PUFAs and endocannabinoids in neurological and neuropsychiatric disorders. Finally, we will conclude on the possible implications of the interactions between dietary PUFAs and endocannabinoids in the normal and pathological brain. In particular, we will discuss how dietary PUFAs, as homeostatic regulators of endocannabinoids, can constitute interesting therapeutic strategies for the prevention and/or treatment of neurological disorders with endocannabinoids impairment.FP7-267196-MSCA-COFUND-AgreenSkill

Dietary Long‐Chain n‐3 Polyunsaturated Fatty Acid Supplementation Alters Electrophysiological Properties in the Nucleus Accumbens and Emotional Behavior in Naïve and Chronically Stressed Mice

Long‐chain (LC) n‐3 polyunsaturated fatty acids (PUFAs) have drawn attention in the field of neuropsychiatric disorders, in particular depression. However, whether dietary supplementation with LC n‐3 PUFA protects from the development of mood disorders is still a matter of de-bate. In the present study, we studied the effect of a two‐month exposure to isocaloric diets containing n‐3 PUFAs in the form of relatively short‐chain (SC) (6% of rapeseed oil, enriched in α‐linolenic acid (ALA)) or LC (6% of tuna oil, enriched in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)) PUFAs on behavior and synaptic plasticity of mice submitted or not to a chronic social defeat stress (CSDS), previously reported to alter emotional and social behavior, as well as synaptic plasticity in the nucleus accumbens (NAc). First, fatty acid content and lipid metabolism gene expression were measured in the NAc of mice fed a SC (control) or LC n‐3 (supplemented) PUFA diet. Our results indicate that LC n‐3 supplementation significantly increased some n‐3 PUFAs, while decreasing some n‐6 PUFAs. Then, in another cohort, control and n‐3 PUFA‐supplemented mice were subjected to CSDS, and social and emotional behaviors were assessed, together with long‐term depression plasticity in accumbal medium spiny neurons. Overall, mice fed with n‐3 PUFA supple-mentation displayed an emotional behavior profile and electrophysiological properties of medium spiny neurons which was distinct from the ones displayed by mice fed with the control diet, and this, independently of CSDS. Using the social interaction index to discriminate resilient and suscep-tible mice in the CSDS groups, n‐3 supplementation promoted resiliency. Altogether, our results pinpoint that exposure to a diet rich in LC n‐3 PUFA, as compared to a diet rich in SC n‐3 PUFA, influences the NAc fatty acid profile. In addition, electrophysiological properties and emotional behavior were altered in LC n‐3 PUFA mice, independently of CSDS. Our results bring new insights about the effect of LC n‐3 PUFA on emotional behavior and synaptic plasticity. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Memory deficits in a juvenile rat model of type 1 diabetes are due to excess 11β-HSD1 activity, which is upregulated by high glucose concentrations rather than insulin deficiency

Aims/hypothesis: Children with diabetes may display cognitive alterations although vascular disorders have not yet appeared. Variations in glucose levels together with relative insulin deficiency in treated type 1 diabetes have been reported to impact brain function indirectly through dysregulation of the hypothalamus-pituitary-adrenal axis. We have recently shown that enhancement of glucocorticoid levels in children with type 1 diabetes is dependent not only on glucocorticoid secretion but also on glucocorticoid tissue concentrations, which is linked to 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) activity. Hypothalamus-pituitary-adrenal axis dysfunction and memory alteration were further dissected in a juvenile rat model of diabetes showing that excess 11β-HSD1 activity within the hippocampus is associated with hippocampal-dependent memory deficits. Here, to investigate the causal relationships between diabetes, 11β-HSD1 activity and hippocampus-dependent memory deficits, we evaluated the beneficial effect of 11β-HSD1 inhibition on hippocampal-related memory in juvenile diabetic rats. We also examined whether diabetes-associated enhancement of hippocampal 11β-HSD1 activity is due to an increase in brain glucose concentrations and/or a decrease in insulin signalling. Methods: Diabetes was induced in juvenile rats by daily i.p. injection of streptozotocin for 2 consecutive days. Inhibition of 11β-HSD1 was obtained by administrating the compound UE2316 twice daily by gavage for 3 weeks, after which hippocampal-dependent object location memory was assessed. Hippocampal 11β-HSD1 activity was estimated by the ratio of corticosterone/dehydrocorticosterone measured by LC/MS. Regulation of 11β-HSD1 activity in response to changes in glucose or insulin levels was determined ex vivo on acute brain hippocampal slices. The insulin regulation of 11β-HSD1 was further examined in vivo using virally mediated knockdown of insulin receptor expression specifically in the hippocampus. Results: Our data show that inhibiting 11β-HSD1 activity prevents hippocampal-related memory deficits in diabetic juvenile rats. A significant increase (53.0±9.9%) in hippocampal 11β-HSD1 activity was found in hippocampal slices incubated in high glucose conditions (13.9 mmol/l) vs normal glucose conditions (2.8 mmol/l) without insulin. However, 11β-HSD1 activity was not affected by variations in insulin concentration either in the hippocampal slices or after a decrease in hippocampal insulin receptor expression. Conclusions/interpretation: Together, these data demonstrate that an increase in 11β-HSD1 activity contributes to memory deficits observed in juvenile diabetic rats and that an excess of hippocampal 11β-HSD1 activity stems from high glucose levels rather than insulin deficiency. 11β-HSD1 might be a therapeutic target for treating cognitive impairments associated with diabetes

Essential omega-3 fatty acids tune microglial phagocytosis of synaptic elements in the mouse developing brain

AbstractOmega-3 fatty acids (n-3 PUFAs) are essential for the functional maturation of the brain. Westernization of dietary habits in both developed and developing countries is accompanied by a progressive reduction in dietary intake of n-3 PUFAs. Low maternal intake of n-3 PUFAs has been linked to neurodevelopmental diseases in Humans. However, the n-3 PUFAs deficiency-mediated mechanisms affecting the development of the central nervous system are poorly understood. Active microglial engulfment of synapses regulates brain development. Impaired synaptic pruning is associated with several neurodevelopmental disorders. Here, we identify a molecular mechanism for detrimental effects of low maternal n-3 PUFA intake on hippocampal development in mice. Our results show that maternal dietary n-3 PUFA deficiency increases microglia-mediated phagocytosis of synaptic elements in the rodent developing hippocampus, partly through the activation of 12/15-lipoxygenase (LOX)/12-HETE signaling, altering neuronal morphology and affecting cognitive performance of the offspring. These findings provide a mechanistic insight into neurodevelopmental defects caused by maternal n-3 PUFAs dietary deficiency.Infrastructure de Recherche Translationnelle pour les Biothérapies en NeurosciencesProgram Initiative d’Excellenc

Implication of vitamin A in neuroprotection of dopaminergic neurons in a rat model of Parkinson's disease

PosterParkinson’s disease (PD) is a brain disease caused by a loss of dopaminergic neurons in the substantia nigra pars compacta (SNc), leading to strong motor impairments. Vitamin A, through the action of its active metabolite retinoic acid (RA), is involved in the development, differentiation and protection of SNc dopaminergic neurons. However, the bioavailability of retinoic acid in the brain decreases with aging. Prior reports suggest that altered vitamin A signaling is implicated in the etiology of Parkinson’s disease, though the mechanisms are poorly understood. Here we hypothesize that nutritional supplementation with vitamin A may reduce dopaminergic cells loss by increasing RA levels in the brain, thus delaying the progression of the disease. We showed that rats deprived of vitamin A became progressively impaired in their motor functions and were unable to perform correctly the rotarod test after thirteen weeks of deprivation. However, locomotor functions were improved after just three weeks of vitamin A supplementation. To assess the effect of vitamin A supplementation, we modeled Parkinson’s disease in rat. Dopaminergic neurons were selectively deleted with unilateral injection of 6-hydroxydopamine (6-OHDA) toxin into rat’s striatum. Rats fed a vitamin A supplemented diet (20UI/g) for five weeks prior to the toxin injection exhibited an improvement in rotarod test compared to rats fed with control diet (5UI/g). Degeneration of dopaminergic terminals was assessed with stereological analysis of tyrosine hydroxylase staining in the striatum. Finally, dopamine levels in striatum were measured with HPLC. These preliminary data established the link between dietary vitamin A and dopaminergic system in PD. Future work will focus on establishing its underlying mechanisms and molecular basis

Implication of vitamin A in survival of dopaminergic neurons in a rat model of Parkinson's disease

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Implication of vitamin A in neuroprotection of dopaminergic neurons in a rat model of Parkinson's disease

PosterParkinson's disease (PD) is caused by a loss of dopaminergic neurons in the substantia nigra pars compacta (SNc), leading to strong motor impairments. Dopaminergic neurons from the SNc project to the striatum which allow the control of voluntary movements. Vitamin A, through the action of its active metabolite, retinoic acid (RA), is involved in the development, differentiation and neuroprotection of SNc dopaminergic neurons. Additionally, retinaldehyde dehydrogenase (RALDH), the synthesis enzyme of retinoic acid, is involved in cellular detoxification. However, the cerebral bioavailability of retinoic acid decreases with aging, which downregulates RALDH expression. This may precipitate neurodegenerative processes such as those observed in Parkinson's disease. Here we hypothesize that nutritional supplementation with vitamin A normalizes brain levels of retinoic acid and thus RALDH, which exhibit a neuroprotective effect on dopaminergic neurons, to delay the progression of the disease. To test our hypothesis, we modeled Parkinson's disease with unilateral injection of 6-hydroxydopamine (6-OHDA), a toxin that selectively destroys dopaminergic neurons, into rats' striatum. Rats were supplemented or not with dietary vitamin A (20 UI/g) for 5 weeks before the lesion. Motor impairments induced by 6-OHDA and protective effect of vitamin A were quantified with the step test, cylinder test and rotarod. Extend of dopaminergic neurons degeneration was assessed with stereological analysis of tyrosine hydroxylase, the production enzyme of dopamine, staining in the striatum. To evaluate the functionality of the dopaminergic system, levels of dopamine and its metabolites were measured in the striatum with HPLC. Finally, to precisely interrogate the impact of vitamin A supplementation on RALDH enzyme, its expression and localization will be assessed with immunostaining, western blot and RT-qPCR analyses. These experiments that are still in progress will allow a precise assessment of the neuroprotective effects of vitamin A supplementation on dopaminergic neurons in a rat model of Parkinson's disease. This work may open therapeutic strategies to prevent neurodegeneration

J Parkinsons Dis

Evidence shows that altered retinoic acid signaling may contribute to the pathogenesis and pathophysiology of Parkinson's disease (PD). Retinoic acid is the bioactive derivative of the lipophilic vitamin A. Vitamin A is involved in several important homeostatic processes, such as cell differentiation, antioxidant activity, inflammation and neuronal plasticity. The role of vitamin A and its derivatives in the pathogenesis and pathophysiology of neurodegenerative diseases, and their potential as therapeutics, has drawn attention for more than 10 years. However, the literature sits in disparate fields. Vitamin A could act at the crossroad of multiple environmental and genetic factors of PD. The purpose of this review is to outline what is known about the role of vitamin A metabolism in the pathogenesis and pathophysiology of PD. We examine key biological systems and mechanisms that are under the control of vitamin A and its derivatives, which are (or could be) exploited for therapeutic potential in PD: the survival of dopaminergic neurons, oxidative stress, neuroinflammation, circadian rhythms, homeostasis of the enteric nervous system, and hormonal systems. We focus on the pivotal role of ALDH1A1, an enzyme expressed by dopaminergic neurons for the detoxification of these neurons, which is under the control of retinoic acid. By providing an integrated summary, this review will guide future studies on the potential role of vitamin A in the management of symptoms, health and wellbeing for PD patients

Chemogenetic silencing of hippocampus and amygdala reveals a double dissociation in periadolescent obesogenic diet-induced memory alterations

In addition to numerous metabolic comorbidities, obesity is associated with several adverse neurobiological outcomes, especially learning and memory alterations. Obesity prevalence is rising dramatically in youth and is persisting in adulthood. This is especially worrying since adolescence is a crucial period for the maturation of certain brain regions playing a central role in memory processes such as the hippocampus and the amygdala. We previously showed that periadolescent, but not adult, exposure to obesogenic high-fat diet (HFD) had opposite effects on hippocampus- and amygdala-dependent memory, impairing the former and enhancing the latter. However, the causal role of these two brain regions in periadolescent HFD-induced memory alterations remains unclear. Here, we first showed that periadolescent HFD induced long-term, but not short-term, object recognition memory deficits, specifically when rats were exposed to a novel context. Using chemogenetic approaches to inhibit targeted brain regions, we then demonstrated that recognition memory deficits are dependent on the activity of the ventral hippocampus, but not the basolateral amygdala. On the contrary, the HFD- induced enhancement of conditioned odor aversion specifically requires amygdala activity. Taken together, these findings suggest that HFD consumption throughout adolescence impairs long-term object recognition memory through alterations of ventral hippocampal activity during memory acquisition. Moreover, these results further highlight the bidirectional effects of adolescent HFD on hippocampal and amygdala functions

Preventive Vitamin A Supplementation Improves Striatal Function in 6-Hydroxydopamine Hemiparkinsonian Rats

International audienceBackgroundThe mechanisms leading to a loss of dopaminergic (DA) neurons from the substantia nigra pars compacta (SNc) in Parkinson's disease (PD) have multifactorial origins. In this context, nutrition is currently investigated as a modifiable environmental factor for the prevention of PD. In particular, initial studies revealed the deleterious consequences of vitamin A signaling failure on dopamine-related motor behaviors. However, the potential of vitamin A supplementation itself to prevent neurodegeneration has not been established yet.Objective: The hypothesis tested in this study is that preventive vitamin A supplementation can protect DA neurons in a rat model of PD.Methods: The impact of a 5-week preventive supplementation with vitamin A (20 IU/g of diet) was measured on motor and neurobiological alterations induced by 6-hydroxydopamine (6-OHDA) unilateral injections in the striatum of rats. Rotarod, step test and cylinder tests were performed up to 3 weeks after the lesion. Post-mortem analyses (retinol and monoamines dosages, western blots, immunofluorescence) were performed to investigate neurobiological processes.Results: Vitamin A supplementation improved voluntary movements in the cylinder test. In 6-OHDA lesioned rats, a marked decrease of dopamine levels in striatum homogenates was measured. Tyrosine hydroxylase labeling in the SNc and in the striatum was significantly decreased by 6-OHDA injection, without effect of vitamin A. By contrast, vitamin A supplementation increased striatal expression of D2 and RXR receptors in the striatum of 6-OHDA lesioned rats.Conclusions: Vitamin A supplementation partially alleviates motor alterations and improved striatal function, revealing a possible beneficial preventive approach for PD