Separation and Detection of Plasmalogen in Marine Invertebrates by High-Performance Liquid Chromatography with Evaporative Light-Scattering Detection

A comparative lipid profile of four fish species: From muscle to industrial by-products based on RPLC-Q-TOF-MS/MS

Fish are crucial for the fishing industry and essential nutrient provision, including lipids. This study employed a high-throughput lipidomic approach to evaluate and contrast the lipid profiles of three marine fish species (P. crocea, S. fuscens, and C. saira) and one freshwater species (H. molitrix) across head, muscle, and viscera. Over 1000 molecular lipid species across 17 subclasses were identified. Notably, acylated monogalactosyldiacylglycerol (acMGDG) was detected for the first time in these species, with a high prevalence of saturated fatty acids (44.7 %-87.7 %). Glycerolipids (67.7 - 86.3 %) and PLs (10.7 - 31.8 %) were identified as the dominant lipid classes. Marine fish muscles displayed higher PL content than freshwater species, and P. crocea viscera contained over 30 % PLs of total lipids. In particular, ether phosphatidyl ethanolamine incorporated more DHA than ether phosphatidylcholine. The viscera of four fish species also exhibited a significant abundance of diacylglycerol (DG), indicating their potential as functional lipid sources. Multivariate analysis identified triglyceride (TG) (59:13), DG (16:1/22:5), and MGDG (16:0/18:2) as potential biomarkers for differentiating among fish anatomical parts. This study deepens the understanding of the nutritional values of these fish, providing guidance for consumer dietary choices and paving the way for transforming previously underutilized by-products into resources with high-value potential.

Temperature effects on plasmalogen profile and quality characteristics in Pacific oyster (Crassostrea gigas) during depuration

The quality of Pacific oyster (Crassostrea gigas) can be affected by many factors during depuration, in which temperature is the major element. In this study, we aim to determine the quality and plasmalogen changes in C. gigas depurated at different temperatures. The quality was significantly affected by temperature, represented by varying survival rate, glycogen content, total antioxidant capacity, alkaline phosphatase activity between control and stressed groups. Targeted MS analysis demonstrated that plasmalogen profile was significantly changed during depuration with PUFA-containing plasmalogen species being most affected by temperature. Proteomics analysis and gene expression assay further verified that plasmalogen metabolism is regulated by temperature, specifically, the plasmalogen synthesis enzyme EPT1 was significantly downregulated by high temperature and four plasmalogen-related genes (GPDH, PEDS, Pex11, and PLD1) were transcriptionally regulated. The positive correlations between the plasmalogen level and quality characteristics suggested plasmalogen could be regarded as a quality indicator of oysters during depuration.

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.

Ethanolamine plasmalogens derived from scallops stimulate both follicle-stimulating hormone and luteinizing hormone secretion by bovine gonadotrophs

Brain ethanolamine plasmalogens (EPls) are the only known ligands of G-protein-coupled receptor 61, a novel receptor that stimulates follicle-stimulating hormone (FSH), but not luteinizing hormone (LH), secretion by bovine gonadotrophs. We hypothesized that the recently developed neuroprotective EPls extracted from scallop (Pecten yessoensis) (scallop EPls) could stimulate FSH secretion by gonadotrophs. To test this hypothesis, bovine gonadotrophs were cultured for 3.5 days and treated with increasing concentrations of scallop EPls. FSH secretion was stimulated by all tested concentrations of scallop EPls (P < 0.05). Surprisingly, LH secretion was stimulated by both 0.5 (P < 0.05) and 5 (P < 0.01) ng/mL of scallop EPls. To clarify the important differences between bovine brain and scallop EPls, we utilized two-dimensional liquid chromatography–mass spectrometry, which revealed 44 peaks, including 10 large peaks. Among them, eight were scallop-specific EPl molecular species, occupying approximately 58% of the total area percentage of scallop EPls. Almost all large peaks contained 4, 5, or 6 unsaturated double bonds in the carbon chain at the sn-2 position of the glycerol backbone. Our results showed that EPls from scallops, lacking pituitary glands, stimulated both FSH and LH secretion by bovine gonadotrophs.

Compositional Study of Phospholipids from the Dried Big Head and Opossum Shrimp, Mussel, and Sea Cucumber Using 31P NMR Spectroscopy: Content and Fatty Acid Composition of Plasmalogen

Herein, we present a qualitative and quantitative analysis of the compositions of plasmalogens and phospholipids (PLs) in dried big head shrimp (Solenocera melantho), opossum shrimp (Neomysis awatschensis), mussel (Mytilus galloprovincialis), and sea cucumber (Apostichopus japonicus). We also analyze the fatty acid composition of the extracted lipids, phosphatidyl choline (PtdCho), and plasmalogen choline (PlsCho) from each sample. In big head shrimp, opossum shrimp, and mussel, phosphatidyl choline (PtdCho) was the most abundant PL at 1677.9, 1603, and 1661.6 mg/100 g of dried sample, respectively, whereas the most abundant PL in sea cucumber was PlsCho (206.9 mg/100 g of dried sample). In all four samples, plasmalogen ethanolamine (PlsEtn) was higher than phosphatidyl ethanolamine (PtdEtn). The content (mg/100 g of dried sample) of PlsCho was highest in mussel (379.0), and it was higher in big head shrimp (262.3) and opossum shrimp (245.6) than sea cucumber (206.9). The contents (mg/100 g of dried sample) of PlsEtn were in the order of mussel (675.4) > big head shrimp (629.5) > opossum shrimp (217.9) > sea cucumber (51.5). For analyzing the fatty acids at the sn-2 position of PlsCho, the consecutive treatment with phospholipase A1, solid phase extraction, thin-layer chromatography (TLC), and GC-FID were applied. The most abundant fatty acid was eicosapentaenoic acid (EPA, C20:5, n-3) in big head shrimp and sea cucumber, palmitoleic acid (C16:1, n-7) in opossum shrimp, and docosadienoic acid (C22:2, n-6) in mussel.

Structural Characterization of Mono- and Dimethylphosphatidylethanolamines from Various Organisms Using a Complex Analytical Strategy Including Chiral Chromatography

Two minor phospholipids, i.e., mono- and/or dimethylphosphatidylethanolamines, are widespread in many organisms, from bacteria to higher plants and animals. A molecular mixture of methyl-PE and dimethyl-PE was obtained from total lipids by liquid chromatography and further identified by mass spectrometry. Total methyl-PE and dimethyl-PE were cleaved by phospholipase C, and the resulting diacylglycerols, in the form of acetyl derivatives, were separated into alkyl-acyl, alkenyl-acyl, and diacylglycerols. Reversed-phase LC/MS allowed dozens of molecular species to be identified and further analyzed. This was performed on a chiral column, and identification by tandem positive ESI revealed that diacyl derivatives from all four bacteria were mixtures of both R and S enantiomers. The same applied to alkenyl-acyl derivatives of anaerobic bacteria. Analysis thus confirmed that some bacteria biosynthesize phospholipids having both sn-glycerol-3-phosphate and sn-glycerol-1-phosphate as precursors. These findings were further supported by data already published in GenBank. The use of chiral chromatography made it possible to prove that both enantiomers of glycerol phosphate of some molecular species of mono- and dimethylphosphatidylethanolamines are present. The result of the analysis can be interpreted that the cultured bacteria do not have homochiral membranes but, on the contrary, have an asymmetric, i.e., heterochiral membranes.

Effects of Dietary Food Components on Cognitive Functions in Older Adults

Population aging has recently been an important issue as the number of elderly people is growing worldwide every year, and the extension of social security costs is financially costly. The increase in the number of elderly people with cognitive decline is a serious problem related to the aging of populations. Therefore, it is necessary to consider not only physical care but also cognitive patterns in the future care of older adults. Since food contains a variety of bioactive substances, dietary patterns may help improve age-related cognitive decline. However, the relationship between cognitive function and individual food components remains ambiguous as no clear efficacy or mechanism has been confirmed. Against this background, this review summarizes previous reports on the biological process of cognitive decline in the elderly and the relationship between individual compounds in foods and cognitive function, as well as the role of individual components of food in cognitive function, in the following order: lipids, carotenoids, vitamins, phenolic compounds, amino acids, peptides, and proteins. Based on the research presented in this review, a proper diet that preserves cognitive function has the potential to improve age-related cognitive decline, Alzheimer's disease, and Parkinson's disease. Hopefully, this review will help to trigger the development of new foods and technologies that improve aging and cognitive functions and extend the healthy life span.

Plasmalogens - Ubiquitous molecules occurring widely, from anaerobic bacteria to humans

Plasmalogens are a group of lipids mainly found in the cell membranes. They occur in anaerobic bacteria and in some protozoa, invertebrates and vertebrates, including humans. Their occurrence in plants and fungi is controversial. They can protect cells from damage by reactive oxygen species, protect other phospholipids or lipoprotein particles against oxidative stress, and have been implicated as signaling molecules and modulators of membrane dynamics. Biosynthesis in anaerobic and aerobic organisms occurs by different pathways, and the main biosynthetic pathway in anaerobic bacteria was clarified only this year (2021). Many different analytical techniques have been used for plasmalogen analysis, some of which are detailed below. These can be divided into two groups: shotgun lipidomics, or electrospray ionization mass spectrometry in combination with high performance liquid chromatography (LC-MS). The advantages and limitations of both techniques are discussed here, using examples from anaerobic bacteria to specialized mammalian (human) organs.

Ethanolamine Plasmalogen Suppresses Apoptosis in Human Intestinal Tract Cells in Vitro by Attenuating Induced Inflammatory Stress

Ethanolamine plasmalogen (PlsEtn) is a subtype of ethanolamine glycerophospholipids (EtnGpl). Recently, PlsEtn has attracted increasing research interest due to its beneficial effects in health and disease; however, its functional role in colonic health has not been well established. This study was conducted to determine the mechanism underlying the antiapoptotic effect of PlsEtn in human intestinal tract cells under induced inflammatory stress. Lipopolysaccharide induced apoptosis of differentiated Caco-2 cells, which was suppressed by EtnGpl in a dose-dependent manner. Cells treated with ascidian muscle EtnGpl containing high levels of PlsEtn demonstrated a lower degree of apoptosis, and downregulated TNF-α and apoptosis-related proteins compared to those treated with porcine liver EtnGpl containing low PlsEtn. This indicates that PlsEtn exerted the observed effects, which provided protection against induced inflammatory stress. Overall, our results suggest that PlsEtn with abundant vinyl ether linkages is potentially beneficial in preventing the initiation of inflammatory bowel disease and colon cancer.

Absorption Kinetics of Ethanolamine Plasmalogen and Its Hydrolysate in Mice

Ethanolamine plasmalogen (PlsEtn), a subclass of ethanolamine glycerophospholipid (EtnGpl), has been reported to have many biological and dietary functions. In terms of PlsEtn absorption, some studies have reported that PlsEtn is re-esterized at the sn-2 position using lymph cannulation and the everted jejunal sac model. In this study, we aimed to better understand the uptake kinetics of PlsEtn and increase its absorption. We thus compared the uptake kinetics of PlsEtn with that of the lyso-form, in which the fatty acid at the sn-2 position was hydrolyzed enzymatically. Upon administration of EtnGpl (extracted from oysters or ascidians, 75.4 mol% and 88.4 mol% of PlsEtn ratio, respectively), the plasma PlsEtn species in mice showed the highest levels at 4 or 8 hours after administration. In the contrast, administration of the EtnGpl hydrolysate, which contained lysoEtnGpl and free fatty acids, markedly increased the plasma levels of PlsEtn species at 2 h after administration. The area under the plasma concentration-time curve (AUC), especially the AUC0-4 h of PlsEtn species, was higher with hydrolysate administration than that with EtnGpl administration. These results indicate that EtnGpl hydrolysis accelerated the absorption and metabolism of PlsEtn. Consequently, using a different experimental approach from that used in previous studies, we reconfirmed that PlsEtn species were absorbed via hydrolysis at the sn-2 position, suggesting that hydrolysis in advance could increase PlsEtn uptake.

Quantitative and Comparative Investigation of Plasmalogen Species in Daily Foodstuffs

Plasmalogens are an animal-derived functional phospholipid increasingly known as a safe and effective nutritional ingredient, however, the quantitation and comparison of plasmalogen species in foods is limited. In the present work, determination methods for dietary plasmalogens using liquid chromatography-tandem mass spectroscopy under positive and negative ionization modes were compared. The negative-mode method, which showed better selectivity, sensitivity, and accuracy, was then applied in 14 kinds of livestock, poultry, and seafood samples. Livestock and poultry showed abundant total plasmalogen (530.83-944.94 nmol/g), higher than fish (46.08-399.75 nmol/g) and mollusk (10.00-384.76 nmol/g). While fish and mollusk samples expressed healthier fatty acyl composition, with higher eicosapentaenoyl and more beneficial n-6/n-3 ratio than the land animal meats, especially for squid and octopus, with eicosapentaenoyl of 98.4% and 94.5%, respectively. The correlations among plasmalogen species varied in different foodstuffs with distinguishing patterns, suggesting the customizable strategies for achieving targeted plasmalogen species. These findings not only provided fundamental comparison of plasmalogen among daily foodstuffs, but also contributed to extend the dietary plasmalogen sources for health food development.

Dietary PlsEtn Ameliorates Colon Mucosa Inflammatory Stress and ACF in DMH-Induced Colon Carcinogenesis Mice: Protective Role of Vinyl Ether Linkage

Ethanolamine plasmalogen (PlsEtn), a sub-class of ethanolamine glycerophospholipids (EtnGpl), is a universal phospholipid in mammalian membranes. Several researchers are interested in the relationship between colon carcinogenesis and colon PlsEtn levels. Here, we evaluated the functional role of dietary purified EtnGpl from the ascidian muscle (87.3 mol% PlsEtn in EtnGpl) and porcine liver (7.2 mol% PlsEtn in EtnGpl) in 1,2-dimethylhydrazine (DMH)-induced aberrant crypt foci (ACF) in vivo, and elucidated the possible underlying mechanisms behind it. Dietary EtnGpl-suppressed DMH-induced aberrant crypt with one foci (AC1) and total ACF formation (P < 0.05). ACF suppression by dietary ascidian muscle EtnGpl was higher compared with dietary porcine liver EtnGpl. Additionally, dietary EtnGpl decreased DMH-induced oxidative damage, overproduction of TNF-α, and expression of apoptosis-related proteins in the colon mucosa. The effect of dietary ascidian muscle EtnGpl showed superiority compared with dietary porcine liver EtnGpl. Our results demonstrate the mechanisms by which dietary PlsEtn suppress ACF formation and apoptosis. Dietary PlsEtn attained this suppression by reducing colon inflammation and oxidative stress hence a reduction in DMH-induced intestinal impairment. These findings provide new insights about the functional role of dietary PlsEtn during colon carcinogenesis.

Preparation and effects on neuronal nutrition of plasmenylethonoamine and plasmanylcholine from the mussel Mytilus edulis

Plasmenylethonoamine (pPE) and plasmanylcholine (aPC) are important phospholipid subclasses. Herein we explored optimum conditions for enzymatic purification and preparation of pPE and aPC from the mussel Mytilus edulis and bovine brain. Among them, pPE in Mytilus edulis PE was mainly p18:0-20:5 and p18:0-22:6, and its purity was 92.7%; aPC in PC was primarily a16:0-22:6 and a16:0-20:5, and aPC accounted for 90.2% of PC. We thereafter evaluated neurotrophic effects of Mytilus edulis pPE, aPC, and bovine brain pPE in a NGF-induced PC12 cell model. Morphologically, pPE and aPC could both promote differentiation, manifested in a significant increase in neurite length and number, due to increased expression of synaptophysin and growth protein GAP-43 in a dose-independent and structure-selective manner. Importantly, the effect on neuronal nutrition of pPE was better than aPC, and marine pPE was better than terrestrial pPE, which might be ascribed to vinyl-ether bond and differences in fatty acid composition.Abbreviations: AA: arachidonic acid; DHA: docosahexaenoic acid; EIC: extracted ion chromatogram; EPA: eicosapentanoic acid; GAP: growth-associated protein; HPLC: high-performance liquid chromatography; LC-MS/MS: liquid chromatography-tandem mass spectrometry; LPC: lyso-PC; LPE: lyso-PE; MS: mass spectrometry; NGF: nerve growth factor; PC: phosphatidylcholine; aPC: plasmanylcholine; PE: phosphatidylethanolamine; pPE: plasmenylethonoamine; PG: phosphoglycerols; PLs: phospholipids; PS: phosphoserines; TIC: total ion chromatogram.

Choline and Ethanolamine Plasmalogens Prevent Lead-Induced Cytotoxicity and Lipid Oxidation in HepG2 Cells

Plasmalogens derived from dietary phospholipids are considered to be potential protectors against oxidation-related disorders, while lead (Pb) is an environmental contaminant worldwide and is known to induce oxidative stress. However, the protective and antilipid oxidative effects of individual plasmalogen species against Pb damage have received little attention. In this study, six plasmalogen species (with either choline or ethanolamine as the headgroup and p16:0/18:1, p16:0/18:2, or p16:0/20:5 as the side chains) were evaluated in human hepatoma cells. Plasmalogen species showed a remarkable recovery in cell viability as well as elimination of reactive oxygen species and suppressed the accumulation of phosphatidylcholine hydroperoxides (from 63.6 ± 1.8% to 80.3 ± 2.9%) and phosphatidylethanolamine hydroperoxides (from 25.7 ± 9.3% to 76.1 ± 3.7%). Moreover, plasmalogens significantly upregulated the gene expression levels of a series of antioxidant enzymes that are regulated via the Nrf-2-dependent pathway. This study suggested that choline and ethanolamine plasmalogens could prevent Pb-induced cytotoxicity and lipid oxidation in HepG2 cells.

Mechanism for Remodeling of the Acyl Chain Composition of Cardiolipin Catalyzed by Saccharomyces cerevisiae Tafazzin

Remodeling of the acyl chains of cardiolipin (CL) is responsible for final molecular composition of mature CL after de novo CL synthesis in mitochondria. Yeast Saccharomyces cerevisiae undergoes tafazzin-mediated CL remodeling, in which tafazzin serves as a transacylase from phospholipids to monolyso-CL (MLCL). In light of the diversity of the acyl compositions of mature CL between different organisms, the mechanism underlying tafazzin-mediated transacylation remains to be elucidated. We investigated the mechanism responsible for transacylation using purified S. cerevisiae tafazzin with liposomes composed of various sets of acyl donors and acceptors. The results revealed that tafazzin efficiently catalyzes transacylation in liposomal membranes with highly ordered lipid bilayer structure. Tafazzin elicited unique acyl chain specificity against phosphatidylcholine (PC) as follows: linoleoyl (18:2) > oleoyl (18:1) = palmitoleoyl (16:1) ≫ palmitoyl (16:0). In these reactions, tafazzin selectively removed the sn-2 acyl chain of PC and transferred it into the sn-1 and sn-2 positions of MLCL isomers at equivalent rates. We demonstrated for the first time that MLCL and dilyso-CL have inherent abilities to function as an acyl donor to monolyso-PC and acyl acceptor from PC, respectively. Furthermore, a Barth syndrome-associated tafazzin mutant (H77Q) was shown to completely lack the catalytic activity in our assay. It is difficult to reconcile the present results with the so-called thermodynamic remodeling hypothesis, which premises that tafazzin reacylates MLCL by unsaturated acyl chains only in disordered non-bilayer lipid domain. The acyl specificity of tafazzin may be one of the factors that determine the acyl composition of mature CL in S. cerevisiae mitochondria.

Extrinsic plasmalogens suppress neuronal apoptosis in mouse neuroblastoma Neuro-2A cells: importance of plasmalogen molecular species

Plasmalogen, especially those having 22:6, suppressed neuronal apoptosisviadeath receptor and mitochondrial pathways. These mechanisms of action of plasmalogen may be responsible for regulation of membrane functions and second messenger production.