Plasmalogens, the Vinyl Ether-Linked Glycerophospholipids, Enhance Learning and Memory by Regulating Brain-Derived Neurotrophic Factor

Unlocking nature's antioxidants: a novel method for synthesising plasmalogens

Plasmalogens are glycerophospholipids distinguished by their O-(Z)-vinyl ether at the sn-1 position. These lipids are implicated in several disease states requiring analytical, diagnostic and therapeutic interventions, which demand synthetic availability for a variety of structural types. By deploying the new O-protecting group 1,4-dimethoxynaphthyl-2-methyl ('DIMON') and a new stereospecific method for accessing Z-vinyl ethers, a reproducible, versatile synthetic route to plasmalogens [plasmenyl phosphocholines] has been developed. A key intermediate is (S,Z)-1-((1,4-dimethoxynaphthalen-2-yl)methoxy)-3-(hexadec-1-en-1-yloxy)propan-2-ol, which in principle, permits plasmalogen synthesis 'à la carte' at scale. The methodology compares favourably with all previous synthetic routes by virtue of the very high configurational (>99% Z) and optical purity (>99% ee), including the ability to incorporate polyunsaturated fatty acyl chains (e.g. all Z docosahexaenoic acid) reliably at the sn-2 position.

KIT-13, a novel plasmalogen derivative, attenuates neuroinflammation and amplifies cognition

Plasmalogens (Pls) are specialized phospholipids integral to brain health, whose decline due to aging and stress contributes to cognitive impairment and neuroinflammation. This study explores the potential of a novel Pls derivative, KIT-13 (1-O-octadecyl-2-arachidonoyl-sn-glycerol-3-phosphoethanolamine), in mitigating neuroinflammation and enhancing cognition. When administered to mice, KIT-13 exhibited potent memory enhancement attributed to upregulated brain-derived neurotrophic factor (BDNF), a key player in cognitive processes. In vitro experiments with neuronal cells revealed KIT-13's ability to induce robust cellular signaling, surpassing natural plasmalogens. KIT-13 also promoted neurogenesis and inhibited apoptosis of neuronal-like cells, highlighting its potential in fostering neuronal growth and plasticity. Additionally, KIT-13 treatments reduced pro-inflammatory cytokine expression and attenuated glial activation in the brain. KIT-13's superior efficacy over natural Pls positions it as a promising therapeutic candidate for neurodegenerative conditions such as Alzheimer's disease, characterized by cognitive decline and neuroinflammation. This study presents KIT-13 as an innovative approach for addressing cognitive impairment and neuroinflammatory pathologies.

Effects of miR-204-5p and Target Gene EphB2 on Cognitive Impairment Induced by Aluminum Exposure in Rats

Aluminum is a common environmental neurotoxin. Aluminum ions can cross the blood-brain barrier and accumulate in different brain regions, damage brain tissue, and cause cognitive impairment, but the molecular mechanism of aluminum neurotoxicity is not precise. This study investigated the effects of miR-204-5p, target gene EphB2, and downstream signaling pathway NMDAR-ERK-CREB-Arc on cognitive dysfunction induced by aluminum exposure. The results showed that the learning and memory of the rats were impaired in behavior. The accumulation of aluminum in the hippocampus resulted in the damage of nerve cell morphology in the CA1 region of the hippocampus. The expression level of miR-204-5p was increased, and the mRNA and protein expressions of EphB2, NMDAR2B, ERK1/2, CREB, and Arc were decreased. The results indicated that the mechanism of impaired learning and memory induced by aluminum exposure might promote the expression of miR-204-5P and further inhibit the expression of the target gene EphB2 and its downstream signaling pathway NMDAR-ERK-CREB-Arc.

Advances in the composition, efficacy, and mimicking of human milk phospholipids

Phospholipids are the essential components of human milk, contributing to the enhancement of cognitive development, regulation of immune functions, and mitigation of elevated cholesterol levels. Infant formulas supplemented with phospholipids can change the composition, content, and globule membrane structure of milk lipids, improving their digestive properties and nutritional value. However, mimicking phospholipids in infant formulas is currently limited, and the supplemented standards of phospholipid species and amounts in infant formulas are unknown. Consequently, there is a significant difference between the phospholipids in infant formulas and those in human milk. This article reviews the recent progress in human milk phospholipid research, aiming to describe the composition, content, and positive effects of human milk phospholipids, as well as summarises the dietary sources of phospholipid supplementation and the current state of human milk phospholipid mimicking in infant formulas. This review provides clear directions for research on mimicking human milk phospholipids and evaluating the nutritional functions of phospholipids in infants.

Promising Strategies to Reduce the SARS-CoV-2 Amyloid Deposition in the Brain and Prevent COVID-19-Exacerbated Dementia and Alzheimer's Disease

The COVID-19 pandemic, caused by infection with the SARS-CoV-2 virus, is associated with cognitive impairment and Alzheimer's disease (AD) progression. Once it enters the brain, the SARS-CoV-2 virus stimulates accumulation of amyloids in the brain that are highly toxic to neural cells. These amyloids may trigger neurological symptoms in COVID-19. The meningeal lymphatic vessels (MLVs) play an important role in removal of toxins and mediate viral drainage from the brain. MLVs are considered a promising target to prevent COVID-19-exacerbated dementia. However, there are limited methods for augmentation of MLV function. This review highlights new discoveries in the field of COVID-19-mediated amyloid accumulation in the brain associated with the neurological symptoms and the development of promising strategies to stimulate clearance of amyloids from the brain through lymphatic and other pathways. These strategies are based on innovative methods of treating brain dysfunction induced by COVID-19 infection, including the use of photobiomodulation, plasmalogens, and medicinal herbs, which offer hope for addressing the challenges posed by the SARS-CoV-2 virus.

High coverage of targeted lipidomics revealed lipid changes in the follicular fluid of patients with insulin-resistant polycystic ovary syndrome and a positive correlation between plasmalogens and oocyte quality

Background

Polycystic ovary syndrome with insulin resistance (PCOS-IR) is the most common endocrine and metabolic disease in women of reproductive age, and low fertility in PCOS patients may be associated with oocyte quality; however, the molecular mechanism through which PCOS-IR affects oocyte quality remains unknown.

Methods

A total of 22 women with PCOS-IR and 23 women without polycystic ovary syndrome (control) who underwent in vitro fertilization and embryo transfer were recruited, and clinical information pertaining to oocyte quality was analyzed. Lipid components of follicular fluid (FF) were detected using high-coverage targeted lipidomics, which identified 344 lipid species belonging to 19 lipid classes. The exact lipid species associated with oocyte quality were identified.

Results

The number (rate) of two pronuclear (2PN) zygotes, the number (rate) of 2PN cleaved embryos, and the number of high-quality embryos were significantly lower in the PCOS-IR group. A total of 19 individual lipid classes and 344 lipid species were identified and quantified. The concentrations of the 19 lipid species in the normal follicular fluid (control) ranged between 10-3 mol/L and 10-9 mol/L. In addition, 39 lipid species were significantly reduced in the PCOS-IR group, among which plasmalogens were positively correlated with oocyte quality.

Conclusions

This study measured the levels of various lipids in follicular fluid, identified a significantly altered lipid profile in the FF of PCOS-IR patients, and established a correlation between poor oocyte quality and plasmalogens in PCOS-IR patients. These findings have contributed to the development of plasmalogen replacement therapy to enhance oocyte quality and have improved culture medium formulations for oocyte in vitro maturation (IVM).

Solitary and Synergistic Effects of Different Hydrophilic and Hydrophobic Phospholipid Moieties on Rat Behaviors

Glycerophospholipids have hydrophobic and hydrophilic moieties. Previous studies suggest that phospholipids with different moieties have different effects on rodent behavior; however, the relationship between chemical structures and behavioral effects remains unclear. To clarify the functions of phospholipid moieties, we injected male rats with phospholipids with different moieties and conducted behavioral tests. Exploratory activity was reduced by phosphatidylethanolamine (PE)(18:0/22:6) but not PE(18:0/18:0) or PE(18:0/20:4). Conversely, exploratory activity was increased by plasmanyl PE(16:0/22:6), which harbors an alkyl-ether linkage, but not by phosphatidylcholine (PC)(16:0/22:6) or plasmanyl PC(16:0/22:6). Docosahexaenoic acid (DHA)(22:6) and an alkyl-ether linkage in PE were thus postulated to be involved in exploratory activity. Anxiety-like behavior was reduced by plasmenyl PC(18:0/20:4), which harbors a vinyl-ether linkage, but not by PC(18:0/20:4) or plasmanyl PC(18:0/20:4), suggesting the anxiolytic effects of vinyl-ether linkage. The activation of social interaction was suppressed by PE(18:0/18:0), PE(18:0/22:6), PC(16:0/22:6), plasmanyl PE(16:0/22:6), and plasmanyl PC(16:0/22:6) but not by PE(18:0/20:4), plasmenyl PE(18:0/20:4), or plasmanyl PC(18:0/22:6). DHA may suppress social interaction, whereas arachidonic acid(20:4) or a combination of alkyl-ether linkage and stearic acid(18:0) may restore social deficits. Our findings indicate the characteristic effects of different phospholipid moieties on rat behavior, and may help to elucidate patterns between chemical structures and their effects.

Spatial lipidomics maps brain alterations associated with mild traumatic brain injury

Traumatic brain injury (TBI) is a global public health problem with 50-60 million incidents per year, most of which are considered mild (mTBI) and many of these repetitive (rmTBI). Despite their massive implications, the pathologies of mTBI and rmTBI are not fully understood, with a paucity of information on brain lipid dysregulation following mild injury event(s). To gain more insight on mTBI and rmTBI pathology, a non-targeted spatial lipidomics workflow utilizing high resolution mass spectrometry imaging was developed to map brain region-specific lipid alterations in rats following injury. Discriminant multivariate models were created for regions of interest including the hippocampus, cortex, and corpus callosum to pinpoint lipid species that differentiated between injured and sham animals. A multivariate model focused on the hippocampus region differentiated injured brain tissues with an area under the curve of 0.99 using only four lipid species. Lipid classes that were consistently discriminant included polyunsaturated fatty acid-containing phosphatidylcholines (PC), lysophosphatidylcholines (LPC), LPC-plasmalogens (LPC-P) and PC potassium adducts. Many of the polyunsaturated fatty acid-containing PC and LPC-P selected have never been previously reported as altered in mTBI. The observed lipid alterations indicate that neuroinflammation and oxidative stress are important pathologies that could serve to explain cognitive deficits associated with rmTBI. Therapeutics which target or attenuate these pathologies may be beneficial to limit persistent damage following a mild brain injury event.

Spatial Lipidomics Maps Brain Alterations Associated with Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is a global public health problem with 50-60 million incidents per year, most of which are considered mild (mTBI) and many of these repetitive (rmTBI). Despite their massive implications, the pathologies of mTBI and rmTBI are not fully understood, with a paucity of information on brain lipid dysregulation following mild injury event(s). To gain more insight on mTBI and rmTBI pathology, a non-targeted spatial lipidomics workflow utilizing ultrahigh resolution mass spectrometry imaging was developed to map brain region-specific lipid alterations in rats following injury. Discriminant multivariate models were created for regions of interest including the hippocampus, cortex, and corpus callosum to pinpoint lipid species that differentiated between injured and sham animals. A multivariate model focused on the hippocampus region differentiated injured brain tissues with an area under the curve of 0.994 using only four lipid species. Lipid classes that were consistently discriminant included polyunsaturated fatty acid-containing phosphatidylcholines (PC), lysophosphatidylcholines (LPC), LPC-plasmalogens (LPC-P) and PC potassium adducts. Many of the polyunsaturated fatty acid-containing PC and LPC-P selected have never been previously reported as altered in mTBI. The observed lipid alterations indicate that neuroinflammation, oxidative stress and disrupted sodium-potassium pumps are important pathologies that could serve to explain cognitive deficits associated with rmTBI. Therapeutics which target or attenuate these pathologies may be beneficial to limit persistent damage following a mild brain injury event.

Ether-lipids and cellular signaling: A differential role of alkyl- and alkenyl-ether-lipids?

Ether-lipids (EL) are specific lipids bearing a characteristic sn-1 ether bond. Depending on the ether or vinyl-ether nature of this bond, they are present as alkyl- or alkenyl-EL, respectively. Among EL, alkenyl-EL, also referred as plasmalogens in the literature, attract most of the scientific interest as they are the predominant EL species in eukaryotic cells, thus less is known about alkyl-EL. EL have been implicated in various signaling pathways and alterations in their quantity are frequently observed in pathologies such as neurodegenerative and cardiovascular diseases or cancer. However, it remains unknown whether both alkyl- and alkenyl-EL play the same roles in these processes. This review summarizes the roles and mechanisms of action of EL in cellular signaling and tries to discriminate between alkyl- and alkenyl-EL. We also focus on the involvement of EL-mediated alterations of cellular signaling in diseases and discuss the potential interest for EL in therapy.

Sustained CREB phosphorylation by lipid-peptide liquid crystalline nanoassemblies

Cyclic-AMP-response element-binding protein (CREB) is a leucine zipper class transcription factor that is activated through phosphorylation. Ample CREB phosphorylation is required for neurotrophin expression, which is of key importance for preventing and regenerating neurological disorders, including the sequelae of long COVID syndrome. Here we created lipid-peptide nanoassemblies with different liquid crystalline structural organizations (cubosomes, hexosomes, and vesicles) as innovative nanomedicine delivery systems of bioactive PUFA-plasmalogens (vinyl ether phospholipids with polyunsaturated fatty acid chains) and a neurotrophic pituitary adenylate cyclase-activating polypeptide (PACAP). Considering that plasmalogen deficiency is a potentially causative factor for neurodegeneration, we examined the impact of nanoassemblies type and incubation time in an in vitro Parkinson's disease (PD) model as critical parameters for the induction of CREB phosphorylation. The determined kinetic changes in CREB, AKT, and ERK-protein phosphorylation reveal that non-lamellar PUFA-plasmalogen-loaded liquid crystalline lipid nanoparticles significantly prolong CREB activation in the neurodegeneration model, an effect unattainable with free drugs, and this effect can be further enhanced by the cell-penetrating peptide PACAP. Understanding the sustained CREB activation response to neurotrophic nanoassemblies might lead to more efficient use of nanomedicines in neuroregeneration.

Marine Plasmalogens: A Gift from the Sea with Benefits for Age-Associated Diseases

Aging increases oxidative and inflammatory stress caused by a reduction in metabolism and clearance, thus leading to the development of age-associated diseases. The quality of our daily diet and exercise is important for the prevention of these diseases. Marine resources contain various valuable nutrients, and unique glycerophospholipid plasmalogens are found abundantly in some marine invertebrates, including ascidians. One of the major classes, the ethanolamine class (PlsEtn), exists in a high ratio to phospholipids in the brain and blood, while decreased levels have been reported in patients with age-associated diseases, including Alzheimer's disease. Animal studies have shown that the administration of marine PlsEtn prepared from marine invertebrates improved PlsEtn levels in the body and alleviated inflammation. Animal and human studies have reported that marine PlsEtn ameliorates cognitive impairment. In this review, we highlight the biological significance, relationships with age-associated diseases, food functions, and healthcare materials of plasmalogens based on recent knowledge and discuss the contribution of marine plasmalogens to health maintenance in aging.

Asymmetric Distribution of Plasmalogens and Their Roles-A Mini Review

Plasmalogens are a unique family of cellular glycerophospholipids that contain a vinyl-ether bond. The synthesis of plasmalogens is initiated in peroxisomes and completed in the endoplasmic reticulum. Plasmalogens are transported to the post-Golgi compartment, including endosomes and plasma membranes, in a manner dependent on ATP, but not vesicular transport. Plasmalogens are preferentially localized in the inner leaflet of the plasma membrane in a manner dependent on P4-type ATPase ATP8B2, that associates with the CDC50 subunit. Plasmalogen biosynthesis is spatiotemporally regulated by a feedback mechanism that senses the amount of plasmalogens in the inner leaflet of the plasma membrane and controls the stability of fatty acyl-CoA reductase 1 (FAR1), the rate-limiting enzyme for plasmalogen biosynthesis. The physiological consequences of such asymmetric localization and homeostasis of plasmalogens are discussed in this review.

1-O-alkyl-glycerols from Squid Berryteuthis magister Reduce Inflammation and Modify Fatty Acid and Plasmalogen Metabolism in Asthma Associated with Obesity

Asthma associated with obesity is considered the most severe phenotype and can be challenging to manage with standard medications. Marine-derived 1-O-alkyl-glycerols (AGs), as precursors for plasmalogen synthesis, have high biological activity, making them a promising substance for pharmacology. This study aimed to investigate the effect of AGs from squid Berryteuthis magister on lung function, fatty acid and plasmalogen levels, and cytokine and adipokine production in obese patients with asthma. The investigational trial included 19 patients with mild asthma associated with obesity who received 0.4 g of AGs daily for three months in addition to their standard treatment. The effects of AGs were evaluated at one and three months of treatment. The results of the study demonstrated that intake of AGs increased the FEV1 and FEV1/VC ratios, and significantly decreased the ACQ score in 17 of the 19 patients after three months of treatment. The intake of AGs increased concentration of plasmalogen and n-3 PUFA in plasma, and modified leptin/adiponectin production by adipose tissue. The supplementation of AGs decreased the plasma levels of inflammatory cytokines (TNF-α, IL-4, and IL-17a), and oxylipins (TXB2 and LTB4), suggesting an anti-inflammatory property of AGs. In conclusion, 1-O-alkyl-glycerols could be a promising dietary supplement for improving pulmonary function and reducing inflammation in obese asthma patients, and a natural source for plasmalogen synthesis. The study highlighted that the beneficial effects of AG consumption can be observed after one month of treatment, with gradual improvement after three months of supplementation.

The role of mitochondrial dynamics in cerebral ischemia-reperfusion injury

Stroke is one of the leading causes of death and long-term disability worldwide. More than 80 % of strokes are ischemic, caused by an occlusion of cerebral arteries. Without question, restoration of blood supply as soon as possible is the first therapeutic strategy. Nonetheless paradoxically, reperfusion can further aggravate the injury through a series of reactions known as cerebral ischemia-reperfusion injury (CIRI). Mitochondria play a vital role in promoting nerve survival and neurological function recovery and mitochondrial dysfunction is considered one of the characteristics of CIRI. Neurons often die due to oxidative stress and an imbalance in energy metabolism following CIRI, and there is a strong association with mitochondrial dysfunction. Altered mitochondrial dynamics is the first reaction of mitochondrial stress. Mitochondrial dynamics refers to the maintenance of the integrity, distribution, and size of mitochondria as well as their ability to resist external stimuli through a continuous cycle of mitochondrial fission and fusion. Therefore, improving mitochondrial dynamics is a vital means of treating CIRI. This review discusses the relationship between mitochondria and CIRI and emphasizes improving mitochondrial dynamics as a potential therapeutic approach to improve the prognosis of CIRI.

Plasmalogens inhibit neuroinflammation and promote cognitive function

Neuroinflammation (NF) is defined as the activation of brain glial cells that are found in neurodegenerative diseases including Alzheimer's disease (AD). It has been known that an increase in NF could reduce the memory process in the brain but the key factors, associated with NF, behind the dysregulation of memory remained elusive. We previously reported that the NF and aging processes reduced the special phospholipids, plasmalogens (Pls), in the murine brain by a mechanism dependent on the activation of transcription factors, NF-kB and c-MYC. A similar mechanism has also been found in postmortem human brain tissues with AD pathologies and in the AD model mice. Recent evidence showed that these phospholipids enhanced memory and reduced neuro-inflammation in the murine brain. Pls can stimulate the cellular signaling molecules, ERK and Akt, by activating the membrane-bound G protein-coupled receptors (GPCRs). Therefore, recent findings suggest that plasmalogens could be one of the key phospholipids in the brain to enhance memory and inhibit NF.

Gut brain interaction theory reveals gut microbiota mediated neurogenesis and traditional Chinese medicine research strategies

Adult neurogenesis is the process of differentiation of neural stem cells (NSCs) into neurons and glial cells in certain areas of the adult brain. Defects in neurogenesis can lead to neurodegenerative diseases, mental disorders, and other maladies. This process is directionally regulated by transcription factors, the Wnt and Notch pathway, the extracellular matrix, and various growth factors. External factors like stress, physical exercise, diet, medications, etc., affect neurogenesis and the gut microbiota. The gut microbiota may affect NSCs through vagal, immune and chemical pathways, and other pathways. Traditional Chinese medicine (TCM) has been proven to affect NSCs proliferation and differentiation and can regulate the abundance and metabolites produced by intestinal microorganisms. However, the underlying mechanisms by which these factors regulate neurogenesis through the gut microbiota are not fully understood. In this review, we describe the recent evidence on the role of the gut microbiota in neurogenesis. Moreover, we hypothesize on the characteristics of the microbiota-gut-brain axis based on bacterial phyla, including microbiota's metabolites, and neuronal and immune pathways while providing an outlook on TCM's potential effects on adult neurogenesis by regulating gut microbiota.

Transient Ca2+ entry by plasmalogen-mediated activation of receptor potential cation channel promotes AMPK activity

Ethanolamine-containing alkenyl ether glycerophospholipids, plasmalogens, are major cell membrane components of mammalian cells that activate membrane protein receptors such as ion transporters and G-protein coupled receptors. However, the mechanism by which plasmalogens modulate receptor function is unknown. Here, we found that exogenously added plasmalogens activate transient receptor potential cation channel subfamily C member 4 (TRPC4) to increase Ca²⁺ influx, followed by calcium/calmodulin-dependent protein kinase 2-mediated phosphorylation of AMP-activated protein kinase (AMPK). Upon topical application of plasmalogens to the skin of mice, AMPK activation was observed in TRPC4-expressing hair bulbs and hair follicles. Here, TRPC4 was co-localized with the leucine-rich repeat containing G protein-coupled receptor 5, a marker of hair-follicle stem cells, leading to hair growth. Collectively, this study indicates that plasmalogens could function as gate openers for TRPC4, followed by activating AMPK, which likely accelerates hair growth in mice.

The synaptic lipidome in health and disease

Adequate homeostasis of lipid, protein and carbohydrate metabolism is essential for cells to perform highly specific tasks in our organism, and the brain, with its uniquely high energetic requirements, posesses singular characteristics. Some of these are related to its extraordinary dotation of synapses, the specialized subcelluar structures where signal transmission between neurons occurs in the central nervous system. The post-synaptic compartment of excitatory synapses, the dendritic spine, harbors key molecules involved in neurotransmission tightly packed within a minute volume of a few femtoliters. The spine is further compartmentalized into nanodomains that facilitate the execution of temporo-spatially separate functions in the synapse. Lipids play important roles in this structural and functional compartmentalization and in mechanisms that impact on synaptic transmission. This review analyzes the structural and dynamic processes involving lipids at the synapse, highlighting the importance of their homeostatic balance for the physiology of this complex and highly specialized structure, and underscoring the pathologies associated with disbalances of lipid metabolism, particularly in the perinatal and late adulthood periods of life. Although small variations of the lipid profile in the brain take place throughout the adult lifespan, the pathophysiological consequences are clinically manifested mostly during late adulthood. Disturbances in lipid homeostasis in the perinatal period leads to alterations during nervous system development, while in late adulthood they favor the occurrence of neurodegenerative diseases.

Plasmalogen in the brain: Effects on cognitive functions and behaviors attributable to its properties

Ether phospholipid compositions are altered in the plasma or brain of patients with brain disorders, such as Alzheimer and Parkinson's disease, including those with psychiatric disorders like schizophrenia and bipolar disorders. Notably, plasmenyl ethanolamine has a unique chemical structure, i.e., a vinyl-ether bond at the sn-1 position, which mainly links with polyunsaturated fatty acids (PUFAs) at the sn-2 position. Those characteristic moieties give plasmalogen molecules unique biophysical and chemical properties that modulate membrane trafficking, lipid rafts, intramolecular PUFA moieties, and oxidative states. Previous reports suggested that a deficiency in plasmenyl ethanolamine leads to disturbances of the myelin structure, synaptic neurotransmission and intracellular signaling, apoptosis of neurons, and neuroinflammation, accompanied by cognitive disturbances and aberrant behaviors like hyperactivity in mice. Therefore, this review summarizes the relationship between the biological functions of plasmalogen. We also proposed biophysical properties that alter brain phospholipid compositions related to aberrant behaviors and cognitive dysfunction. Finally, a brief review of possible remedial plasmalogen replacement therapies for neurological, psychiatric, and developmental disorders attributable to disturbed plasmalogen compositions in the organs and cells was conducted.

Regulation of plasmalogen metabolism and traffic in mammals: The fog begins to lift

Due to their unique chemical structure, plasmalogens do not only exhibit distinct biophysical and biochemical features, but require specialized pathways of biosynthesis and metabolization. Recently, major advances have been made in our understanding of these processes, for example by the attribution of the gene encoding the enzyme, which catalyzes the final desaturation step in plasmalogen biosynthesis, or by the identification of cytochrome C as plasmalogenase, which allows for the degradation of plasmalogens. Also, models have been presented that plausibly explain the maintenance of adequate cellular levels of plasmalogens. However, despite the progress, many aspects around the questions of how plasmalogen metabolism is regulated and how plasmalogens are distributed among organs and tissues in more complex organisms like mammals, remain unresolved. Here, we summarize and interpret current evidence on the regulation of the enzymes involved in plasmalogen biosynthesis and degradation as well as the turnover of plasmalogens. Finally, we focus on plasmalogen traffic across the mammalian body - a topic of major importance, when considering plasmalogen replacement therapies in human disorders, where deficiencies in these lipids have been reported. These involve not only inborn errors in plasmalogen metabolism, but also more common diseases including Alzheimer's disease and neurodevelopmental disorders.

Ether lipid transfer across the blood-brain and placental barriers does not improve by inactivation of the most abundant ABC transporters

Phospholipid transport from the periphery to the brain is an understudied topic. When certain lipid species are deficient due to impaired synthesis, though, transfer across the blood-brain barrier is essential for replenishing lipids in the brain. For example, the deficiency in plasmalogens, the most abundant ether lipids in mammals, has detrimental effects on the brain, which is a major issue in inherited peroxisomal disorders but also contributes to more common disorders like Alzheimer's disease. Oral administration of alkylglycerols like batyl alcohol, which carry a pre-formed ether bond, enables replenishment of ether lipids in various peripheral tissues. However, plasmalogen deficiency in the brain cannot be overcome by this approach. Here, we tried to increase cerebral plasmalogen uptake by modulating the efflux transport across the blood-brain barrier. We hypothesized, based on previous literature, that at least some ether lipid species readily enter endothelial cells of the barrier through the transporter MFSD2A but are re-exported by ATP-binding cassette (ABC) transporters. By crossbreeding Mdr1a^-/-/Mdr1b^-/-/Bcrp^-/- and ether lipid-deficient Gnpat^-/- mice as well as pharmacological inhibition with MK-571 to inactivate the major ABC transporters at the blood-brain barrier, we evaluated the potential of combined ABC transporter inhibition and oral batyl alcohol administration for the treatment of plasmalogen deficiency. We found that even in the absence of the most abundant ABC transporters, batyl alcohol supplementation did not restore plasmalogen levels in the brain, despite the presence of a wide spectrum of ether lipid subspecies in the plasma as demonstrated by lipidomic analysis. Surprisingly, batyl alcohol treatment of pregnant Gnpat^+/- dams had beneficial effects on the plasmalogen levels of Gnpat^-/- offspring with defective ether lipid biosynthesis, independently of ABC transporter status at the placental barrier. Our results underline the autonomy of brain lipid homeostasis and indicate that peripheral supplementation of ether lipids is not sufficient to supply the brain with larger amounts of plasmalogens. Yet, the findings suggest that alkylglycerol treatment during pregnancy may pose a viable option to ameliorate some of the severe developmental defects of inborn ether lipid deficiency.

Targeted Plasmalogen Supplementation: Effects on Blood Plasmalogens, Oxidative Stress Biomarkers, Cognition, and Mobility in Cognitively Impaired Persons

Plasmalogens are a specific type of glycerophospholipid found in especially high levels in neuronal membranes. Decreased blood and brain levels of docosahexaenoic acid (DHA) containing plasmalogens are associated with decreased cognition and neuromuscular function in humans. Administration of 1-O-alkyl-2-acylglycerol (AAG) plasmalogen precursors containing DHA at the sn-2 position dose-dependently increase blood DHA plasmalogens and are neuroprotective in animal models of neurodegeneration at doses between 10 and 50 mg/kg. We conducted an investigational clinical trial in 22 cognitively impaired persons to evaluate the effects of an escalating oral dosing regimen of DHA-AAG from 900 to 3,600 mg/day over a 4-month period on blood serum plasmalogen and non-plasmalogen phospholipids and oxidative stress biomarkers. Safety, tolerability and therapeutic effects on cognition and mobility were also evaluated. DHA plasmalogen levels increased with increasing dose and remained significantly elevated at all treatment doses and durations. DHA plasmalogen levels were positively associated with catalase activity and negatively associated with malondialdehyde (MDA) levels. DHA-AAG supplementation normalized catalase activity in persons with low baseline catalase activity, normalized MDA levels in persons with high baseline MDA levels, and normalized superoxide dismutase activity in persons with high baseline SOD activity. Cognition improved in nine participants, was unchanged in nine, and declined in four. Mobility improved in twelve, was unchanged in five and declined in four participants. Changes in cognition and mobility were statistically significant versus a random outcome. Baseline DHA-plasmalogen levels were not predictive of clinical response. DHA-AAG was well tolerated at all dosages and no adverse reactions were observed.

Self-Assembled Nanoscale Materials for Neuronal Regeneration: A Focus on BDNF Protein and Nucleic Acid Biotherapeutic Delivery

Enabling challenging applications of nanomedicine and precision medicine in the treatment of neurodegenerative disorders requires deeper investigations of nanocarrier-mediated biomolecular delivery for neuronal targeting and recovery. The successful use of macromolecular biotherapeutics (recombinant growth factors, antibodies, enzymes, synthetic peptides, cell-penetrating peptide–drug conjugates, and RNAi sequences) in clinical developments for neuronal regeneration should benefit from the recent strategies for enhancement of their bioavailability. We highlight the advances in the development of nanoscale materials for drug delivery in neurodegenerative disorders. The emphasis is placed on nanoformulations for the delivery of brain-derived neurotrophic factor (BDNF) using different types of lipidic nanocarriers (liposomes, liquid crystalline or solid lipid nanoparticles) and polymer-based scaffolds, nanofibers and hydrogels. Self-assembled soft-matter nanoscale materials show favorable neuroprotective characteristics, safety, and efficacy profiles in drug delivery to the central and peripheral nervous systems. The advances summarized here indicate that neuroprotective biomolecule-loaded nanoparticles and injectable hydrogels can improve neuronal survival and reduce tissue injury. Certain recently reported neuronal dysfunctions in long-COVID-19 survivors represent early manifestations of neurodegenerative pathologies. Therefore, BDNF delivery systems may also help in prospective studies on recovery from long-term COVID-19 neurological complications and be considered as promising systems for personalized treatment of neuronal dysfunctions and prevention or retarding of neurodegenerative disorders.

Orally Administered Plasmalogens Alleviate Negative Mood States and Enhance Mental Concentration: A Randomized, Double-Blind, Placebo-Controlled Trial

Background: Plasmalogens have been shown to improve neurodegenerative pathology and cognitive function. We hypothesized that plasmalogens work in small amounts as a kind of hormone interacting with a G protein-coupled receptor, and then explored the effects of scallop-derived purified plasmalogens on psychobehavioral conditions in a randomized placebo-controlled trial of college athletes in Japan.

Methods and materials: Eligible participants were male students aged 18–22 years who belonged to university athletic clubs. They were randomly allocated to either plasmalogen (2 mg per day) or placebo treatment of 4 weeks’ duration. The primary outcome was the T-score of the Profile of Mood States (POMS) 2–Adult Short, and the secondary outcomes included the seven individual scales of the POMS 2, other psychobehavioral measures, physical performance, and laboratory measurements. The trial was registered at the Japan Registry of Clinical Trials (jRCTs071190028).

Results: Forty participants (20 in the plasmalogen group and 20 in the placebo group) completed the 4-week treatment. The Total Mood Disturbance (TMD) score of the plasmalogen group showed a greater decrease at 4 weeks than that of the placebo group while the between-group difference was marginally significant (p = 0.07). The anger-hostility and fatigue-inertia scores of the POMS 2 decreased significantly in the plasmalogen group, but not in the placebo group, at 4 weeks. Between-group differences in those scores were highly significant (p = 0.003 for anger-hostility and p = 0.005 for fatigue-inertia). The plasmalogen group showed a slight decrease in the Athens Insomnia Scale at 2 weeks, and the between-group difference was near-significant (p = 0.07). The elapsed time in minute patterns on the Uchida-Kraepelin test, which is a marker of mental concentration, revealed significantly greater performance in the plasmalogen group than in the placebo group. There were no between-group differences in physical and laboratory measurements.

Conclusion: It is suggested that orally administered plasmalogens alleviate negative mood states and sleep problems, and also enhance mental concentration.