The Emerging Role of the Double-Edged Impact of Arachidonic Acid- Derived Eicosanoids in the Neuroinflammatory Background of Depression

Unraveling the link between neuropathy target esterase NTE/SWS, lysosomal storage diseases, inflammation, abnormal fatty acid metabolism, and leaky brain barrier

Mutations in Drosophila Swiss cheese (SWS) gene or its vertebrate orthologue neuropathy target esterase (NTE) lead to progressive neuronal degeneration in flies and humans. Despite its enzymatic function as a phospholipase is well established, the molecular mechanism responsible for maintaining nervous system integrity remains unclear. In this study, we found that NTE/SWS is present in surface glia that forms the blood-brain barrier (BBB) and that NTE/SWS is important to maintain its structure and permeability. Importantly, BBB glia-specific expression of Drosophila NTE/SWS or human NTE in the sws mutant background fully rescues surface glial organization and partially restores BBB integrity, suggesting a conserved function of NTE/SWS. Interestingly, sws mutant glia showed abnormal organization of plasma membrane domains and tight junction rafts accompanied by the accumulation of lipid droplets, lysosomes, and multilamellar bodies. Since the observed cellular phenotypes closely resemble the characteristics described in a group of metabolic disorders known as lysosomal storage diseases (LSDs), our data established a novel connection between NTE/SWS and these conditions. We found that mutants with defective BBB exhibit elevated levels of fatty acids, which are precursors of eicosanoids and are involved in the inflammatory response. Also, as a consequence of a permeable BBB, several innate immunity factors are upregulated in an age-dependent manner, while BBB glia-specific expression of NTE/SWS normalizes inflammatory response. Treatment with anti-inflammatory agents prevents the abnormal architecture of the BBB, suggesting that inflammation contributes to the maintenance of a healthy brain barrier. Considering the link between a malfunctioning BBB and various neurodegenerative diseases, gaining a deeper understanding of the molecular mechanisms causing inflammation due to a defective BBB could help to promote the use of anti-inflammatory therapies for age-related neurodegeneration.

Alterations of endogenous pain-modulatory system of the cerebral cortex in the neuropathic pain

Neuropathic pain (NeP) remains a significant clinical challenge owing to insufficient awareness of its pathological mechanisms. We elucidated the aberrant metabolism of the cerebral cortex in NeP induced by the chronic constriction injury (CCI) using metabolomics and proteomics analyses. After CCI surgery, the values of MWT and TWL markedly reduced and maintained at a low level. CCI induced the significant dysregulation of 57 metabolites and 31 proteins in the cerebral cortex. Integrative analyses showed that the differentially expressed metabolites and proteins were primarily involved in alanine, aspartate and glutamate metabolism, GABAergic synapse, and retrograde endocannabinoid signaling. Targeted metabolomics and western blot analysis confirmed the alterations of some key metabolites and proteins in endogenous pain-modulatory system. In conclusion, our study revealed the alterations of endocannabinoids system and purinergic system in the CCI group, and provided a novel perspective on the roles of endogenous pain-modulatory system in the pathological mechanisms of NeP.

The antidepressant effects and serum metabonomics of bifid triple viable capsule in a rat model of chronic unpredictable mild stress

Background

Probiotics have shown potential antidepressant effects. This study evaluated the effect and probable mechanisms of bifid triple viable capsules (BTVCs) on a rat model of chronic unpredictable mild stress (CUMS).

Materials and methods

Rats were randomly divided into Normal, CUMS model, fluoxetine hydrochloride (FLX), BTVCs, and FLX+BTVCs groups. Depressive-like behaviours, pathological changes in the hippocampus, changes in serum metabolites and potential biomarkers, and metabolic pathways were detected via behavioural tests, haematoxylin-eosin staining, nissl staining, non-targetted metabolomics, and ingenuity pathway analysis (IPA).

Results

The rats displayed depressive-like behaviours after CUMS exposure, but BTVCs ameliorated the depressive-like behaviours. In addition, the pathological results showed that the hippocampal tissue was damaged in rats after CUMS exposure and that the damage was effectively alleviated by treatment with BTVCs. A total of 20 potential biomarkers were identified. Treatment with BTVCs regulated D-phenylalanine, methoxyeugenol, (±)-myristoylcarnitine, 18:3 (6Z, 9Z, 12Z) /P-18:1 (11Z), propionyl-L-carnitine, and arachidonic acid (AA) concentrations, all compounds that are involved with biosynthesis of unsaturated fatty acids, glycerophospholipid metabolism, linoleic acid metabolism and AA metabolism. The IPA demonstrated that endothelin-1 signalling and cyclic adenosine monophosphate response element binding protein (CREB) signalling in neurons may be involved in the development of depression.

Conclusion

Our findings suggest that BTVCs can alleviate depressive-like behaviours, restore damage to the hippocampus in CUMS rats and regulate serum metabolism, which may be related to endothelin-1 signalling or CREB signalling in neurons.

Study of Antidepressant-Like Effects of Albiflorin and Paeoniflorin Through Metabolomics From the Perspective of Cancer-Related Depression

Mental health has become a new challenge in cancer treatment, with a high prevalence of depression in patients with cancer. Albiflorin (AF) and paeoniflorinn (PF) are isomers extracted from the root of Paeoniae Radix Alba (Baishao in Chinese), belonging to the monoterpene glycosides, and multiple studies have been conducted on their antidepression and anti-cancer effects. However, the effects of AF and PF on cancer-related depression are unclear. Therefore, the current study aims to investigate whether the two isomers are able to exert antidepressant-like effects and understand the underlying mechanisms in a rat model, established by combining irradiation with chronic restraint stress and solitary confinement. Our results demonstrate a significant regulation of AF and PF in the pharmacodynamic index, including the peripheral blood, organ index, behavioral traits, and HPA axis, relative to control rats. In serum and cerebral cortex metabonomics analysis, AF and PF showed a significantly restorative trend in abnormal biomarkers and regulating ether lipid metabolism, alanine, aspartate, glutamate metabolism, tryptophan metabolism, carnitine metabolism, arachidonic acid metabolism, arginine and proline metabolism pathway. Eight potential biomarkers were further screened by means of receiver operating characteristic (ROC) analysis. The data indicate that AF and PF could effectively ameliorate a depression-like state in the model rats, and the mechanism may be associated with the regulation of the neuroendocrine immune system and disrupted metabolic pathways. Further experiments are warranted to comprehensively evaluate the antidepressant effects of AF and PF in cancer-related depression. This study provides a better insight into the action mechanisms of antidepression of TCM, and provides a new perspective for the therapy of cancer-related depression.

Sex-specific differences in plasma lipid profiles are associated with Gulf War Illness

Background

Nearly 250,000 veterans from the 1990–1991 Gulf War have Gulf War Illness (GWI), a condition with heterogeneous pathobiology that remains difficult to diagnose. As such, availability of blood biomarkers that reflect the underlying biology of GWI would help clinicians provide appropriate care to ill veterans. In this study, we measured blood lipids to examine the influence of sex on the association between blood lipids and GWI diagnosis.

Methods

Plasma lipid extracts from GWI (n = 100) and control (n = 45) participants were subjected to reversed-phase nano-flow liquid chromatography-mass spectrometry analysis.

Results

An influence of sex and GWI case status on plasma neutral lipid and phospholipid species was observed. Among male participants, triglycerides, diglycerides, and phosphatidylcholines were increased while cholesterol esters were decreased in GWI cases compared to controls. In female participants, ceramides were increased in GWI cases compared to controls. Among male participants, unsaturated triglycerides, phosphatidylcholine and diglycerides were increased while unsaturated cholesterol esters were lower in GWI cases compared to controls. The ratio of arachidonic acid- to docosahexaenoic acid-containing triglyceride species was increased in female and male GWI cases as compared to their sex-matched controls.

Conclusion

Differential modulation of neutral lipids and ratios of arachidonic acid to docosahexaenoic acid in male veterans with GWI suggest metabolic dysfunction and inflammation. Increases in ceramides among female veterans with GWI also suggest activation of inflammatory pathways. Future research should characterize how these lipids and their associated pathways relate to GWI pathology to identify biomarkers of the disorder.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03272-3.

Lipoxin A4 Receptor Stimulation Attenuates Neuroinflammation in a Mouse Model of Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is caused by the rupture of blood vessels in the brain. The excessive activation of glial cells and the infiltration of numerous inflammatory cells are observed during bleeding. Thrombin is a key molecule that triggers neuroinflammation in the ICH brain. In this study, we focused on lipoxin A₄ (LXA₄), an arachidonic acid metabolite that has been reported to suppress inflammation and cell migration. LXA₄ and BML-111, an agonist of the LXA₄ receptor/formyl peptide receptor 2 (ALX/FPR2), suppressed microglial activation; LXA₄ strongly inhibited the migration of neutrophil-like cells in vitro. ALX/FPR2 was expressed on neutrophils in the ICH mouse brain and the daily administration of BML-111 attenuated the motor coordination dysfunction and suppressed the production of proinflammatory cytokines in the ICH mouse brain. On the other hand, BML-111 did not show a significant reduction in the number of microglia and neutrophils. These results suggest that systemic administration of ALX/FPR2 agonists may suppress the neuroinflammatory response of microglia and neutrophils without a change in cell numbers. Additionally, their combination with molecules that reduce cell numbers, such as modulators of leukotriene B₄ signaling, may be required in future studies.

Time-Dependent Protective and Pro-Resolving Effects of FPR2 Agonists on Lipopolysaccharide-Exposed Microglia Cells Involve Inhibition of NF-κB and MAPKs Pathways

Prolonged or excessive microglial activation may lead to disturbances in the resolution of inflammation (RoI). The importance of specialized pro-resolving lipid mediators (SPMs) in RoI has been highlighted. Among them, lipoxins (LXA4) and aspirin-triggered lipoxin A4 (AT-LXA4) mediate beneficial responses through the activation of N-formyl peptide receptor-2 (FPR2). We aimed to shed more light on the time-dependent protective and anti-inflammatory impact of the endogenous SPMs, LXA4, and AT-LXA4, and of a new synthetic FPR2 agonist MR-39, in lipopolysaccharide (LPS)-exposed rat microglial cells. Our results showed that LXA4, AT-LXA4, and MR-39 exhibit a protective and pro-resolving potential in LPS-stimulated microglia, even if marked differences were apparent regarding the time dependency and efficacy of inhibiting particular biomarkers. The LXA4 action was found mainly after 3 h of LPS stimulation, and the AT-LXA4 effect was varied in time, while MR-39′s effect was mainly observed after 24 h of stimulation by endotoxin. MR-39 was the only FPR2 ligand that attenuated LPS-evoked changes in the mitochondrial membrane potential and diminished the ROS and NO release. Moreover, the LPS-induced alterations in the microglial phenotype were modulated by LXA4, AT-LXA4, and MR-39. The anti-inflammatory effect of MR-39 on the IL-1β release was mediated through FPR2. All tested ligands inhibited TNF-α production, while AT-LXA4 and MR-39 also diminished IL-6 levels in LPS-stimulated microglia. The favorable action of LXA4 and MR-39 was mediated through the inhibition of ERK1/2 phosphorylation. AT-LXA4 and MR39 diminished the phosphorylation of the transcription factor NF-κB, while AT-LXA4 also affected p38 kinase phosphorylation. Our results suggest that new pro-resolving synthetic mediators can represent an attractive treatment option for the enhancement of RoI, and that FPR2 can provide a perspective as a target in immune-related brain disorders.

The N-Formyl Peptide Receptor 2 (FPR2) Agonist MR-39 Exhibits Anti-Inflammatory Activity in LPS-Stimulated Organotypic Hippocampal Cultures

Accumulating evidence indicates a pivotal role for chronic inflammatory processes in the pathogenesis of neurodegenerative and psychiatric disorders. G protein-coupled formyl peptide receptor 2 (FPR2) mediates pro-inflammatory or anti-/pro-resolving effects upon stimulation with biased agonists. We aimed to evaluate the effects of a new FPR2 ureidopropanamide agonist, compound MR-39, on neuroinflammatory processes in organotypic hippocampal cultures (OHCs) derived from control (WT) and knockout FPR2−/− mice (KO) exposed to bacterial endotoxin (lipopolysaccharide; LPS). Higher LPS-induced cytokine expression and basal release were observed in KO FPR2 cultures than in WT cultures, suggesting that a lack of FPR2 enhances the OHCs response to inflammatory stimuli. Pretreatment with MR-39 abolished some of the LPS-induced changes in the expression of genes related to the M1/M2 phenotypes (including Il-1β, Il-6, Arg1, Il-4, Cd74, Fizz and Cx3cr1) and TNF-α, IL-1β and IL-4 release in tissue derived from WT but not KO mice. Receptor specificity was confirmed by adding the FPR2 antagonist WRW4, which abolished the abovementioned effects of MR-39. Further biochemical data showed an increase in the phospho-p65/total p65 ratio after LPS stimulation in hippocampal tissues from both WT and KO mice, and MR-39 only reversed this effect on WT OHCs. LPS also increased TRAF6 levels, which are critical for the TLR4-mediated NF-κB pro-inflammatory responses. MR-39 attenuated the LPS-evoked increase in the levels of the NLRP3 and caspase-1 proteins in WT but not KO hippocampal cultures. Since NLRP3 may be involved in the pyroptosis, a lytic type of programmed cell death in which the main role is played by Gasdermin D (GSDMD), we examined the effects of LPS and/or MR-39 on the GSDMD protein level. LPS only increased GSDMD production in the WT tissues, and this effect was ameliorated by MR-39. Collectively, this study indicates that the new FPR2 agonist efficiently abrogates LPS-induced neuroinflammation in an ex vivo model, as evidenced by a decrease in pro-inflammatory cytokine expression and release as well as the downregulation of NLRP3 inflammasome-related pathways.

Regulation and role of Acyl-CoA synthetase 4 in glial cells

Acyl-CoA synthetase 4 (Acsl4), an enzyme involved in arachidonic acid (AA) metabolism, participates in physiological and pathological processes such as steroidogenesis and cancer. The role of Acsl4 in neurons and in nervous system development has also been documented but little is known regarding its functionality in glial cells. In turn, several processes in glial cells, including neurosteroidogenesis, stellation and AA uptake, are regulated by cyclic adenosine monophosphate (cAMP) signal. In this context, the aim of this work was to analyze the expression and functional role of Acsl4 in primary rat astrocyte cultures and in the C6 glioma cell line by chemical inhibition and stable silencing, respectively. Results show that Acsl4 expression was regulated by cAMP in both models and that cAMP stimulation of steroidogenic acute regulatory protein mRNA levels was reduced by Acsl4 inhibition or silencing. Also, Acsl4 inhibition reduced progesterone synthesis stimulated by cAMP and also affected cAMP-induced astrocyte stellation, decreasing process elongation and increasing branching complexity. Similar effects were observed for Acsl4 silencing on cAMP-induced C6 cell morphological shift. Moreover, Acsl4 inhibition and silencing reduced proliferation and migration of both cell types. Acsl4 silencing in C6 cells reduced the capacity for colony proliferation and neurosphere formation, the latter ability also being abolished by Acsl4 inhibition. In sum, this work presents novel evidence of Acsl4 involvement in neurosteroidogenesis and the morphological changes of glial cells promoted by cAMP. Furthermore, Acsl4 participates in migration and proliferation, also affecting cell self-renewal. Altogether, these findings provide insights into Acsl4 functions in glial cells.

Exploring the role of LC-PUFA metabolism in pregnancy complications

Maternal nutrition during pregnancy plays a significant role in growth and development of the placenta and influencing pregnancy outcome. Suboptimal nutritional status during early gestational period compromises the normal course of pregnancy leading to adverse maternal and fetal outcomes. Omega-3 and omega-6 long chain polyunsaturated fatty acids (LC-PUFA) are important for the growth and development of the placenta. Maternal fatty acids and their metabolites influence the normal course of pregnancy by regulating cell growth and development, cell signaling, regulate angiogenesis, modulate inflammatory responses and influence various structural and functional processes. Alterations in LC-PUFA and their metabolites may result in inadequate spiral artery remodeling or placental angiogenesis leading to structural and functional deficiency of the placenta which contributes to several pregnancy complications like preeclampsia, gestational diabetes mellitus, intrauterine growth restriction, and results in adverse birth outcomes. In this review, we summarize studies examining the role of fatty acids and their metabolites in pregnancy. We also discuss the possible molecular mechanisms through which LC-PUFA influences placental growth and development. Studies have demonstrated that omega-3 fatty acid supplementation lowers the incidence of preterm births, but its effect on reducing pregnancy complications are inconclusive.