Modulations of bioactive lipids and their receptors in postmortem Alzheimer's disease brains

Integrated Proteomics and Lipidomics Analysis of Hippocampus to Reveal the Metabolic Landscape of Epilepsy

Epilepsy encompasses a spectrum of chronic brain disorders characterized by transient central nervous system dysfunctions induced by recurrent, aberrant, synchronized neuronal discharges. Hippocampal sclerosis (HS) is identified as the predominant pathological alteration in epilepsy, particularly in temporal lobe epilepsy. This study investigates the metabolic profiles of epileptic hippocampal tissues using proteomics and lipidomics techniques. An epilepsy model was established in Sprague-Dawley (SD) rats via intraperitoneal injection of pentylenetetrazole (PTZ), with hippocampal tissue samples subsequently extracted for histopathological examination. Proteomics analysis was conducted using isobaric tags for relative and absolute quantitation (iTRAQ) combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS), while lipidomics analysis employed ultrahigh-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC Q-TOF/MS). Proteomic analysis identified 144 proteins with significant differential expression in acute epileptic hippocampal tissue and 83 proteins in chronic epileptic hippocampal tissue. Key proteins, including neurofilament heavy (Nefh), vimentin (Vim), gelsolin (Gsn), NAD-dependent protein deacetylase (Sirt2), 2',3'-cyclic-nucleotide 3'-phosphodiesterase (Cnp), myocyte enhancer factor 2D (Mef2d), and Cathepsin D (Ctsd), were pivotal in epileptic hippocampal tissue injury and validated through parallel reaction monitoring (PRM). Concurrently, lipid metabolomics analysis identified 32 metabolites with significant differential expression in acute epileptic hippocampal tissue and 61 metabolites in chronic epileptic hippocampal tissue. Bioinformatics analysis indicated that glycerophospholipid (GP) metabolism, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, and glycerolipid (GL) metabolism were crucial in epileptic hippocampal tissue injury. Integrated proteomics and lipidomics analysis revealed key protein-lipid interactions in acute and chronic epilepsy and identified critical pathways such as sphingolipid signaling, autophagy, and calcium signaling. These findings provide deeper insights into the pathophysiological mechanisms of epileptic hippocampal tissue damage, potentially unveiling novel therapeutic avenues for clinicians.

Lipid mediators in post-mortem brain samples from patients with Alzheimer's disease: A systematic review

A proposed contributor to Alzheimer's disease (AD) pathology is the induction of neuroinflammation due to tau and beta-amyloid protein accumulation causing neuronal injury and dysfunction. Dysregulation of lipid mediators derived from polyunsaturated fatty acids may contribute to this inflammatory response in the brain of patients with AD, yet the literature has not yet been systematically reviewed. A systematic search was conducted in Medline, Embase and PsychINFO for articles published up to April 22, 2024. Papers were included if they measured levels of lipid mediators and/or enzymes involved in their production in post-mortem brain samples from patients with AD and control without neurological disease. A total of 50 relevant studies were identified. Despite heterogeneity in the results, pro-inflammatory lipid mediators, including 5-, 11-, 12- and 15-hydroxyeicosatetraenoic acid oxylipins and prostaglandin D2, were significantly higher, while anti-inflammatory lipoxin A4 and DHA-derived docosanoids were significantly lower in brains of patients with AD compared to control (16 studies). Thirty-seven articles reported on enzymes, with 32 reporting values for enzyme level changes between AD and controls. Among the 32 articles, the majority reported on levels of cyclooxygenase (COX) (18/32), with fewer studies reporting on phospholipase (8/32), lipoxygenase (LOX) (4/32) and prostaglandin E synthase (4/32). Enzyme levels also exhibited variability in the literature, with a trend towards elevated expression of enzymes involved in the pro-inflammatory response, including COX and LOX enzymes. Overall, these results are consistent with the involvement of neuroinflammation in the pathogenesis of AD measured by lipid mediators. However, the specific contribution of each lipid metabolite and enzymes to either the progression or persistence of AD remains unclear, and more research is required.

Lipidome disruption in Alzheimer's disease brain: detection, pathological mechanisms, and therapeutic implications

Alzheimer's disease (AD) is among the most devastating neurodegenerative disorders with limited treatment options. Emerging evidence points to the involvement of lipid dysregulation in the development of AD. Nevertheless, the precise lipidomic landscape and the mechanistic roles of lipids in disease pathology remain poorly understood. This review aims to highlight the significance of lipidomics and lipid-targeting approaches in the diagnosis and treatment of AD. We summarized the connection between lipid dysregulation in the human brain and AD at both genetic and lipid species levels. We briefly introduced lipidomics technologies and discussed potential challenges and areas of future advancements in the lipidomics field for AD research. To elucidate the central role of lipids in converging multiple pathological aspects of AD, we reviewed the current knowledge on the interplay between lipids and major AD features, including amyloid beta, tau, and neuroinflammation. Finally, we assessed the progresses and obstacles in lipid-based therapeutics and proposed potential strategies for leveraging lipidomics in the treatment of AD.

The Octadecanoids: Synthesis and Bioactivity of 18-Carbon Oxygenated Fatty Acids in Mammals, Bacteria, and Fungi

The octadecanoids are a broad class of lipids consisting of the oxygenated products of 18-carbon fatty acids. Originally referring to production of the phytohormone jasmonic acid, the octadecanoid pathway has been expanded to include products of all 18-carbon fatty acids. Octadecanoids are formed biosynthetically in mammals via cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) activity, as well as nonenzymatically by photo- and autoxidation mechanisms. While octadecanoids are well-known mediators in plants, their role in the regulation of mammalian biological processes has been generally neglected. However, there have been significant advancements in recognizing the importance of these compounds in mammals and their involvement in the mediation of inflammation, nociception, and cell proliferation, as well as in immuno- and tissue modulation, coagulation processes, hormone regulation, and skin barrier formation. More recently, the gut microbiome has been shown to be a significant source of octadecanoid biosynthesis, providing additional biosynthetic routes including hydratase activity (e.g., CLA-HY, FA-HY1, FA-HY2). In this review, we summarize the current field of octadecanoids, propose standardized nomenclature, provide details of octadecanoid preparation and measurement, summarize the phase-I metabolic pathway of octadecanoid formation in mammals, bacteria, and fungi, and describe their biological activity in relation to mammalian pathophysiology as well as their potential use as biomarkers of health and disease.

Comprehensive metabolic modulations of sphingolipids are promising severity indicators in COVID-19

The COVID-19 pandemic, caused by SARS-CoV-2, has had a significant worldwide impact, affecting millions of people. COVID-19 is characterized by a heterogenous clinical phenotype, potentially involving hyperinflammation and prolonged tissue damage, although the exact underlying mechanisms are yet to be fully understood. Sphingolipid metabolites, which govern cell survival and proliferation, have emerged as key players in inflammatory signaling and cytokine responses. Given the complex metabolic pathway of sphingolipids, this study aimed to understand their potential role in the pathogenesis of COVID-19. We conducted a comprehensive examination of sphingolipid modulations across groups classified based on disease severity, incorporating a time-course in serum and urine samples. Several sphingolipids, including sphingosine, lactosylceramide, and hexosylceramide, emerged as promising indicators of COVID-19 severity, as validated by correlation analyses conducted on both serum and urine samples. Other sphingolipids, such as sphingosine 1-phosphate, ceramides, and deoxy-dihydroceramides, decreased in both COVID-19 patients and individuals with non-COVID infectious diseases. This suggests that these sphingolipids are not specifically associated with COVID-19 but rather with pathological conditions caused by infectious diseases. Our analysis of urine samples revealed elevated levels of various sphingolipids, with changes dependent on disease severity, potentially highlighting the acute kidney injury associated with COVID-19. This study illuminates the intricate relationship between disturbed sphingolipid metabolism, COVID-19 severity, and clinical factors. These findings provide valuable insights into the broader landscape of inflammatory diseases.

Chuanxiong Renshen Decoction Inhibits Alzheimer's Disease Neuroinflammation by Regulating PPARγ/NF-κB Pathway

Background and Aim

Previous studies of our research group have shown that Chuanxiong Renshen Decoction (CRD) has the effect of treating AD, but the exact mechanism of its effect is still not clarified. The aim of this study was to investigate the effect and mechanism of CRD on AD neuroinflammation.

Materials and Methods

Morris Water Maze (MWM) tests were employed to assess the memory and learning capacity of AD mice. HE and Nissl staining were used to observe the neural cells of mice. The expression of Iba-1 and CD86 were detected by immunohistochemical staining. Utilize UHPLC-MS/MS metabolomics techniques and the KEGG to analyze the metabolic pathways of CRD against AD. Lipopolysaccharide (LPS) induced BV2 microglia cells to construct a neuroinflammatory model. The expression of Iba-1 and CD86 were detected by immunofluorescence and flow cytometry. The contents of TNF-α and IL-1β were detected by ELISA. Western blot assay was used to detect the expression of PPARγ, p-NF-κB p65, NF-κB p65 proteins and inflammatory cytokines iNOS and COX-2 in PPARγ/NF-κB pathway with and without PPARγ inhibitor GW9662.

Results

CRD ameliorated the learning and memory ability of 3×Tg-AD mice, repaired the damaged nerve cells in the hippocampus, reduced the area of Iba-1 and CD86 positive areas in both the hippocampus and cortex regions, as well as attenuated serum levels of IL-1β and TNF-α in mice. CRD-containing serum significantly decreased the expression level of Iba-1, significantly reduced the levels of TNF-α and IL-1β, significantly increased the protein expression of PPARγ, and significantly decreased the proteins expression of iNOS, COX-2 and p-NF-κB p65 in BV2 microglia cells. After addition of PPARγ inhibitor GW9662, the inhibitory effect of CRD-containing serum on NF-κB activation was significantly weakened.

Conclusion

CRD can activate PPARγ, regulating PPARγ/NF-κB signaling pathway, inhibiting microglia over-activation and reducing AD neuroinflammation.

Diet Supplemented with Special Formula Milk Powder Promotes the Growth of the Brain in Rats

This investigation was to study the effects of different formula components on the brain growth of rats. Fifty male SD rats were randomly divided into five groups: a basic diet group; a 20% ordinary milk powder group; a 20% special milk powder group; a 30% ordinary milk powder group; and a 30% special milk powder group by weight. LC-MS was used to detect brain lipidomics. After 28 days of feeding, compared with the basic diet group, the brain/body weights of rats in the 30% ordinary milk powder group were increased. The serum levels of 5-HIAA in the 30% ordinary milk powder group were lower than in the 20% ordinary milk powder group. Compared with the basic diet group, the expressions of DLCL, MePC, PI, and GM1 were higher in the groups with added special milk powder, while the expressions of LPE, LdMePE, SM, and MGTG were higher in the groups with added ordinary milk powder. The expression of MBP was significantly higher in the 20% ordinary group. This study found that different formula components of infant milk powder could affect brain growth in SD rats. The addition of special formula infant milk powder may have beneficial effects on rat brains by regulating brain lipid expression.

Unveiling the "hidden quality" of the walnut pellicle: a precious source of bioactive lipids

Tree nut consumption has been widely associated with various health benefits, with walnuts, in particular, being linked with improved cardiovascular and neurological health. These benefits have been attributed to walnuts' vast array of phenolic antioxidants and abundant polyunsaturated fatty acids. However, recent studies have revealed unexpected clinical outcomes related to walnut consumption, which cannot be explained simply with the aforementioned molecular hallmarks. With the goal of discovering potential molecular sources of these unexplained clinical outcomes, an exploratory untargeted metabolomics analysis of the isolated walnut pellicle was conducted. This analysis revealed a myriad of unusual lipids, including oxylipins and endocannabinoids. These lipid classes, which are likely present in the pellicle to enhance the seeds' defenses due to their antimicrobial properties, also have known potent bioactivities as mammalian signaling molecules and homeostatic regulators. Given the potential value of this tissue for human health, with respect to its "bioactive" lipid fraction, we sought to quantify the amounts of these compounds in pellicle-enriched waste by-products of mechanized walnut processing in California. An impressive repertoire of these compounds was revealed in these matrices, and in notably significant concentrations. This discovery establishes these low-value agriculture wastes promising candidates for valorization and translation into high-value, health-promoting products; as these molecules represent a potential explanation for the unexpected clinical outcomes of walnut consumption. This "hidden quality" of the walnut pellicle may encourage further consumption of walnuts, and walnut industries may benefit from a revaluation of abundant pellicle-enriched waste streams, leading to increased sustainability and profitability through waste upcycling.

Lysophosphatidylserine: A Signaling Lipid with Implications in Human Diseases

Lysophosphatidylserine (lyso-PS) has emerged as yet another important signaling lysophospholipid in mammals, and deregulation in its metabolism has been directly linked to an array of human autoimmune and neurological disorders. It has an indispensable role in several biological processes in humans, and therefore, cellular concentrations of lyso-PS are tightly regulated to ensure optimal signaling and functioning in physiological settings. Given its biological importance, the past two decades have seen an explosion in the available literature toward our understanding of diverse aspects of lyso-PS metabolism and signaling and its association with human diseases. In this Review, we aim to comprehensively summarize different aspects of lyso-PS, such as its structure, biodistribution, chemical synthesis, and SAR studies with some synthetic analogs. From a biochemical perspective, we provide an exhaustive coverage of the diverse biological activities modulated by lyso-PSs, such as its metabolism and the receptors that respond to them in humans. We also briefly discuss the human diseases associated with aberrant lyso-PS metabolism and signaling and posit some future directions that may advance our understanding of lyso-PS-mediated mammalian physiology.

Alzheimer's disease manifests abnormal sphingolipid metabolism

Introduction

Alzheimer's disease (AD) is associated with disturbed metabolism, prompting investigations into specific metabolic pathways that may contribute to its pathogenesis and pathology. Sphingolipids have garnered attention due to their known physiological impact on various diseases.

Methods

We conducted comprehensive profiling of sphingolipids to understand their possible role in AD. Sphingolipid levels were measured in AD brains, Cerad score B brains, and controls, as well as in induced pluripotent stem (iPS) cells (AD, PS, and control), using liquid chromatography mass spectrometry.

Results

AD brains exhibited higher levels of sphingosine (Sph), total ceramide 1-phosphate (Cer1P), and total ceramide (Cer) compared to control and Cerad-B brains. Deoxy-ceramide (Deoxy-Cer) was elevated in Cerad-B and AD brains compared to controls, with increased sphingomyelin (SM) levels exclusively in Cerad-B brains. Analysis of cell lysates revealed elevated dihydroceramide (dhSph), total Cer1P, and total SM in AD and PS cells versus controls. Multivariate analysis highlighted the relevance of Sph, Cer, Cer1P, and SM in AD pathology. Machine learning identified Sph, Cer, and Cer1P as key contributors to AD.

Discussion

Our findings suggest the potential importance of Sph, Cer1P, Cer, and SM in the context of AD pathology. This underscores the significance of sphingolipid metabolism in understanding and potentially targeting mechanisms underlying AD.

Mass Spectrometric Imaging of Anionic Phospholipids Desorbed from Human Hippocampal Sections: Discrimination between Temporal and Nontemporal Lobe Epilepsies

Temporal lobe epilepsy (TLE) is one of the most common neurological disorders, often accompanied by hippocampal sclerosis. The molecular processes underlying this epileptogenesis are poorly understood. To examine the lipid profile, 39 fresh frozen sections of the human hippocampus obtained from epilepsy surgery for TLE (n = 14) and non-TLE (control group; n = 25) patients were subjected to desorption electrospray ionization mass spectrometry imaging in the negative ion mode. In contrast to our earlier report that showed striking downregulation of positively charged phospholipids (e.g., phosphatidylcholine and phosphatidylethanolamine, etc.) in the TLE hippocampus, this study finds complementary upregulation of negatively charged phospholipids, notably, phosphatidylserine and phosphatidylglycerol. This result may point to an active metabolic pool in the TLE hippocampus that produces these anionic phospholipids at the expense of the cationic phospholipids. This metabolic shift could be due to the dysregulation of the Kennedy and CDP-DG pathways responsible for biosynthesizing these lipids. Thus, this study further opens up opportunities to investigate the molecular hallmarks and potential therapeutic targets for TLE.

Comprehensive Analysis of Metabolites in Postmortem Brains of Patients with Alzheimer's Disease

BACKGROUND

Disturbed metabolism has been proposed as being involved in the pathogenesis of Alzheimer's disease (AD), and more evidence from human AD brains is required.

OBJECTIVE

In this study, we attempted to identify or confirm modulations in the levels of metabolites associated with AD in postmortem AD brains.

METHODS

We performed metabolomics analyses using a gas chromatography mass spectrometry system in postmortem brains of patients with confirmed AD, patients with CERAD score B, and control subjects.

RESULTS

Impaired phosphorylation of glucose and elevation of several tricarboxylic acid (TCA) metabolites, except citrate, were observed and the degree of impaired phosphorylation and elevation in the levels of the TCA cycle metabolites were negatively and positively correlated, respectively, with the clinical phenotypes of AD. The levels of uronic acid pathway metabolites were modulated in AD and correlated positively with the amyloid-β content. The associations of nucleic acid synthesis and amino acid metabolites with AD depended on the kinds of metabolites; in particular, the contents of ribose 5-phosphate, serine and glycine were negatively correlated, while those of ureidosuccinic acid and indole-3-acetic acid were positively modulated in AD. Comprehensive statistical analyses suggested that alterations in the inositol pathway were most closely associated with AD.

CONCLUSIONS

The present study revealed many novel associations between metabolites and AD, suggesting that some of these might serve as novel potential therapeutic targets for AD.

EP1 receptor: Devil in emperors coat

EP1 receptor belongs to prostanoid receptors and is activated by prostaglandin E2. The receptor performs contrasting functions in central nervous system (CNS) and other tissues. Although the receptor is neurotoxic and proapoptotic in CNS, it has also been reported to act in an antiapoptotic manner by modulating cell survival, proliferation, invasion, and migration in different types of cancers. The receptor mediates its neurotoxic effects by increasing cytosolic Ca2+ levels, leading to the activation of its downstream target, protein kinase C, in different neurological disorders including Alzheimer's disease, Parkinson's disease, stroke, amyotrophic lateral sclerosis, and epilepsy. Antagonists ONO-8713, SC51089, and SC51322 against EP1 receptor ameliorate the neurotoxic effect by attenuating the neuroinflammation. The receptor also shows increased expression in different types of cancers and has been found to activate different signaling pathways, which lead to the development, progression, and metastasis of different cancers. The receptor stimulates the cell survival pathway by phosphorylating the AKT and PTEN (phosphatase and tensin homolog deleted on chromosome 10) signaling pathways. Although there are limited studies about this receptor and not a single clinical trial has been targeting the EP1 receptor for different neurological disorders or cancer, the receptor is appearing as a potential candidate for therapeutic targets. The aim of this article is to review the recent progress in understanding the pathogenic roles of EP1 receptors in different pathological conditions.

The Expression of the Endocannabinoid Receptors CB2 and GPR55 Is Highly Increased during the Progression of Alzheimer's Disease in AppNL-G-F Knock-In Mice

BACKGROUND

The endocannabinoid system (ECS) and associated lipid transmitter-based signaling systems play an important role in modulating brain neuroinflammation. ECS is affected in neurodegenerative disorders, such as Alzheimer's disease (AD). Here we have evaluated the non-psychotropic endocannabinoid receptor type 2 (CB2) and lysophosphatidylinositol G-protein-coupled receptor 55 (GPR55) localization and expression during Aβ-pathology progression.

METHODS

Hippocampal gene expression of CB2 and GPR55 was explored by qPCR analysis, and brain distribution was evaluated by immunofluorescence in the wild type (WT) and APP knock-in App^NL-G-F AD mouse model. Furthermore, the effects of Aβ42 on CB2 and GPR55 expression were assessed in primary cell cultures.

RESULTS

CB2 and GPR55 mRNA levels were significantly upregulated in App^NL-G-F mice at 6 and 12 months of age, compared to WT. CB2 was highly expressed in the microglia and astrocytes surrounding the Aβ plaques. Differently, GPR55 staining was mainly detected in neurons and microglia but not in astrocytes. In vitro, Aβ42 treatment enhanced CB2 receptor expression mainly in astrocytes and microglia cells, whereas GPR55 expression was enhanced primarily in neurons.

CONCLUSIONS

These data show that Aβ pathology progression, particularly Aβ42, plays a crucial role in increasing the expression of CB2 and GPR55 receptors, supporting CB2 and GPR55 implications in AD.

Measuring brain docosahexaenoic acid turnover as a marker of metabolic consumption

Docosahexaenoic acid (DHA, 22:6n-3) accretion in brain phospholipids is critical for maintaining the structural fluidity that permits proper assembly of protein complexes for signaling. Furthermore, membrane DHA can by released by phospholipase A₂ and act as substrate for synthesis of bioactive metabolites that regulate synaptogenesis, neurogenesis, inflammation, and oxidative stress. Thus, brain DHA is consumed through multiple pathways including mitochondrial β-oxidation, autoxidation to neuroprostanes, as well as enzymatic synthesis of bioactive metabolites including oxylipins, synaptamide, fatty-acid amides, and epoxides. By using models developed by Rapoport and colleagues, brain DHA loss has been estimated to be 0.07-0.26 μmol DHA/g brain/d. Since β-oxidation of DHA in the brain is relatively low, a large portion of brain DHA loss may be attributed to synthesis of autoxidative and bioactive metabolites. In recent years, we have developed a novel application of compound specific isotope analysis to trace DHA metabolism. By the use of natural abundance in ¹³C-DHA in food supply, we are able to trace brain phospholipid DHA loss in free-living mice with estimates ranging from 0.11 to 0.38 μmol DHA/g brain/d, in reasonable agreement with previous methods. This novel fatty acid metabolic tracing methodology should improve our understanding of the factors that regulate brain DHA metabolism.

Quantitative Lipidomic Analysis of Serum Phospholipids Reveals Dissociable Markers of Alzheimer's Disease and Subcortical Cerebrovascular Disease

BACKGROUND

Circulating phospholipid species have been shown to predict Alzheimer's disease (AD) prognosis but the link between phospholipid disturbances and subcortical small vessel cerebrovascular disease (CeVD) common in AD patients is not known.

OBJECTIVE

This study used quantitative lipidomics to measure serum diacyl, alkenyl (ether), alkyl, and lyso phospholipid species in individuals with extensive CeVD (n = 29), AD with minimal CeVD (n = 16), and AD with extensive CeVD (n = 14), and compared them to age-matched controls (n = 27). Memory was assessed using the California Verbal Learning Test. 3.0T MRI was used to assess hippocampal volume, atrophy, and white matter hyperintensity (WMH) volumes as manifestations of CeVD.

RESULTS

AD was associated with significantly higher concentrations of choline plasmalogen 18:0_18:1 and alkyl-phosphocholine 18:1. CeVD was associated with significantly lower lysophospholipids containing 16:0. Phospholipids containing arachidonic acid (AA) were associated with poorer memory in controls, whereas docosahexaenoic acid (DHA)-containing phospholipids were associated with better memory in individuals with AD+CeVD. In controls, DHA-containing phospholipids were associated with more atrophy and phospholipids containing linoleic acid and AA were associated with less atrophy. Lysophospholipids containing 16:0, 18:0, and 18:1 were correlated with less atrophy in controls, and of these, alkyl-phosphocholine 18:1 was correlated with smaller WMH volumes. Conversely, 16:0_18:1 choline plasmalogen was correlated with greater WMH volumes in controls.

CONCLUSION

This study demonstrates discernable differences in circulating phospholipids in individuals with AD and CeVD, as well as new associations between phospholipid species with memory and brain structure that were specific to contexts of commonly comorbid vascular and neurodegenerative pathologies.