The critical role of phosphatidylcholine and phosphatidylethanolamine metabolism in health and disease

Prospective metabolomics study identifies potential novel blood metabolites associated with pancreatic cancer risk

Using a metabolomics approach, we systematically searched for circulating metabolite biomarkers for pancreatic cancer risk in a case-control study nested within two prospective Shanghai cohorts. Included in our study were 226 incident pancreatic cancer cases and their individually-matched controls. Untargeted mass spectrometry platforms were used to measure metabolites in blood samples collected prior to cancer diagnosis. Conditional logistic regression was performed to assess the associations of metabolites with pancreatic cancer risk. We identified 10 metabolites associated with pancreatic cancer, after accounting for multiple comparisons (the Benjamini-Hochberg false discovery rate <0.05). The majority of the identified metabolites were glycerophospholipids (ORs per SD increase: 0.44-2.32; p values: 7.2 × 10^-4 to 1.0 × 10^-6 ), six of which were associated with decreased risk and one with increased risk. Additionally, levels of coumarin (OR = 1.96, p = 3.7 × 10^-6 ) and picolinic acid (OR = 2.53, p = 5.0 × 10^-5 ) were positively associated with pancreatic cancer risk, while tetracosanoic acid was inversely associated with risk (OR = 0.48, p = 7.16 × 10^-7 ). Four metabolites remained statistically significant after mutual adjustment. Our study provides novel evidence that the dysregulation of glycerophospholipids may play an important role in pancreatic cancer development.

Intestinal de novo phosphatidylcholine synthesis is required for dietary lipid absorption and metabolic homeostasis

De novo phosphatidylcholine (PC) synthesis via CTP:phosphocholine cytidylyltransferase-α (CTα) is required for VLDL secretion. To determine the precise role of de novo PC synthesis in intestinal lipid metabolism, we deleted CTα exclusively in the intestinal epithelium of mice (CTα^IKO mice). When fed a chow diet, CTα^IKO mice showed normal fat absorption despite a ∼30% decrease in intestinal PC concentrations relative to control mice, suggesting that biliary PC can fully support chylomicron secretion under these conditions. However, when fed a high-fat diet, CTα^IKO mice showed impaired passage of FAs and cholesterol from the intestinal lumen into enterocytes. Impaired intestinal lipid uptake in CTα^IKO mice was associated with lower plasma triglyceride concentrations, higher plasma glucagon-like peptide 1 and peptide YY, and disruption of intestinal membrane lipid transporters after a high-fat meal relative to control mice. Unexpectedly, biliary bile acid and PC secretion was enhanced in CTα^IKO mice due to a shift in expression of bile-acid transporters to the proximal intestine, indicative of accelerated enterohepatic cycling. These data show that intestinal de novo PC synthesis is required for dietary lipid absorption during high-fat feeding and that the reacylation of biliary lyso-PC cannot compensate for loss of CTα under these conditions.

Plasma metabolites and lipids predict insulin sensitivity improvement in obese, nondiabetic individuals after a 2-phase dietary intervention

Background

Weight loss in obese individuals aims to reduce the risk of type 2 diabetes by improving glycemic control. Yet, significant intersubject variability is observed and the outcomes remain poorly predictable.

Objective

The aim of the study was to predict whether an individual will show improvements in insulin sensitivity above or below the median population change at 6 mo after a low-calorie-diet (LCD) intervention.

Design

With the use of plasma lipidomics and metabolomics for 433 subjects from the Diet, Obesity, and Genes (DiOGenes) Study, we attempted to predict good or poor Matsuda index improvements 6 mo after an 8-wk LCD intervention (800 kcal/d). Three independent analysis groups were defined: "training" (n = 119) for model construction, "testing" (n = 162) for model comparison, and "validation" (n = 152) to validate the final model.

Results

Initial modeling with baseline clinical variables (body mass index, Matsuda index, total lipid concentrations, sex, age) showed limited performance [area under the curve (AUC) on the "testing dataset" = 0.69; 95% CI: 0.61, 0.77]. Significantly better performance was achieved with an omics model based on 27 variables (AUC = 0.77; 95% CI: 0.70, 0.85; P = 0.0297). This model could be greatly simplified while keeping the same performance. The simplified model relied on baseline Matsuda index, proline, and phosphatidylcholine 0-34:1. It successfully replicated on the validation set (AUC = 0.75; 95% CI: 0.67, 0.83) with the following characteristics: specificity = 0.73, sensitivity = 0.68, negative predictive value = 0.60, and positive predictive value = 0.80. Marginally lower performance was obtained when replacing the Matsuda index with homeostasis model assessment of insulin resistance (AUC = 0.72; 95% CI: 0.64, 0.80; P = 0.08).

Conclusions

Our study proposes a model to predict insulin sensitivity improvements, 6 mo after LCD completion in a large population of overweight or obese nondiabetic subjects. It relies on baseline information from 3 variables, accessible from blood samples. This model may help clinicians assessing the large variability in dietary interventions and predict outcomes before an intervention. This trial was registered at www.clinicaltrials.gov as NCT00390637.

Gamma-tocotrienol attenuates the aberrant lipid mediator production in NLRP3 inflammasome-stimulated macrophages

The activation of NLRP3 inflammasome in innate immune cells is associated with enhanced production of pro-inflammatory lipid mediator eicosanoids that play a crucial role in propagating inflammation. Gamma-tocotrienol (γT3) is an unsaturated vitamin E that has been demonstrated to attenuate NLRP3-inflammasome. However, the role of γT3 in regulating eicosanoid formation is unknown. We hypothesized that γT3 abolishes the eicosanoid production by modulating the macrophage lipidome. LPS-primed bone marrow-derived macrophages (BMDM) were stimulated with saturated fatty acids (SFA) along with γT3, and the effects of γT3 in modulating macrophage lipidome were quantified by using mass spectrometry based-shotgun lipidomic approaches. The SFA-mediated inflammasome activation induced robust changes in lipid species of glycerolipids (GL), glycerophospholipids (GPL), and sphingolipids in BMDM, which were distinctly different in the γT3-treated BMDM. The γT3 treatment caused substantial decreases of lysophospholipids (LysoPL), diacylglycerol (DAG), and free arachidonic acid (AA, C20:4), indicating that γT3 limits the availability of AA, the precursor for eicosanoids. This was confirmed by the pulse-chase experiment using [³H]-AA, and by diminished prostaglandin E₂ (PGE₂) secretion by ELISA. Concurrently, γT3 inhibited LPS-induced cyclooxygenases 2 (COX2) induction, further suppressing prostaglandin synthesis. In addition, γT3 attenuated ceramide synthesis by transcriptional downregulation of key enzymes for de novo synthesis. The altered lipid metabolism during inflammation is linked to reduced ATP production, which was partly rescued by γT3. Taken together, our work revealed that γT3 induces distinct modification of the macrophage lipidome to reduce AA release and corresponding lipid mediator synthesis, leading to attenuated cellular lipotoxicity.

Do inositol supplements enhance phosphatidylinositol supply and thus support endoplasmic reticulum function?

This review attempts to explain why consuming extra myoinositol (Ins), an essential component of membrane phospholipids, is often beneficial for patients with conditions characterised by insulin resistance, non-alcoholic fatty liver disease and endoplasmic reticulum (ER) stress. For decades we assumed that most human diets provide an adequate Ins supply, but newer evidence suggests that increasing Ins intake ameliorates several disorders, including polycystic ovary syndrome, gestational diabetes, metabolic syndrome, poor sperm development and retinopathy of prematurity. Proposed explanations often suggest functional enhancement of minor facets of Ins Biology such as insulin signalling through putative inositol-containing 'mediators', but offer no explanation for this selectivity. It is more likely that eating extra Ins corrects a deficiency of an abundant Ins-containing cell constituent, probably phosphatidylinositol (PtdIns). Much of a cell's PtdIns is in ER membranes, and an increase in ER membrane synthesis, enhancing the ER's functional capacity, is often an important part of cell responses to ER stress. This review: (a) reinterprets historical information on Ins deficiency as describing a set of events involving a failure of cells adequately to adapt to ER stress; (b) proposes that in the conditions that respond to dietary Ins there is an overstretching of Ins reserves that limits the stressed ER's ability to make the 'extra' PtdIns needed for ER membrane expansion; and (c) suggests that eating Ins supplements increases the Ins supply to Ins-deficient and ER-stressed cells, allowing them to make more PtdIns and to expand the ER membrane system and sustain ER functions.

PCYT1A Regulates Phosphatidylcholine Homeostasis from the Inner Nuclear Membrane in Response to Membrane Stored Curvature Elastic Stress

Cell and organelle membranes consist of a complex mixture of phospholipids (PLs) that determine their size, shape, and function. Phosphatidylcholine (PC) is the most abundant phospholipid in eukaryotic membranes, yet how cells sense and regulate its levels in vivo remains unclear. Here we show that PCYT1A, the rate-limiting enzyme of PC synthesis, is intranuclear and re-locates to the nuclear membrane in response to the need for membrane PL synthesis in yeast, fly, and mammalian cells. By aligning imaging with lipidomic analysis and data-driven modeling, we demonstrate that yeast PCYT1A membrane association correlates with membrane stored curvature elastic stress estimates. Furthermore, this process occurs inside the nucleus, although nuclear localization signal mutants can compensate for the loss of endogenous PCYT1A in yeast and in fly photoreceptors. These data suggest an ancient mechanism by which nucleoplasmic PCYT1A senses surface PL packing defects on the inner nuclear membrane to control PC homeostasis.

Metabolomic responses to lumacaftor/ivacaftor in cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) is a life-limiting disease caused by a defect in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Lumacaftor/Ivacaftor is a novel CFTR modulator approved for patients that are homozygous for Phe508del CFTR, but its clinical effectiveness varies amongst patients, making it difficult to determine clinical responders. Therefore, identifying biochemical biomarkers associated with drug response are clinically important for follow-up studies.

METHODS

Serum metabolomics was performed on twenty patients with CF pre- and 6-month post-Lumacaftor/Ivacaftor response via Ultrahigh Performance Liquid Chromatography-Tandem Mass Spectroscopy (UPLC-MS/MS). Correlation with clinical variables was performed.

RESULTS

Metabolomics analysis demonstrated 188 differentially regulated metabolites between patients pre- and post-Lumacaftor/Ivacaftor initiation, with a predominance of lipid and amino acid alterations. The top 30 metabolites were able to differentiate pre- and post-Lumacaftor/Ivacaftor status in greater than 90% of patients via a random-forest confusion matrix. Alterations in bile acids, phospholipids, and bacteria-associated metabolites were the predominant changes associated with drug response. Importantly, changes in metabolic patterns were associated with clinical responders.

CONCLUSIONS

Selected key lipid and amino acid metabolic pathways were significantly affected by Lumacaftor/Ivacaftor initiation and similar pathways were affected in clinical responders. Targeted metabolomics may provide useful and relevant biomarkers of CFTR modulator responses.

Historical perspective: phosphatidylserine and phosphatidylethanolamine from the 1800s to the present

This article provides a historical account of the discovery, chemistry, and biochemistry of two ubiquitous phosphoglycerolipids, phosphatidylserine (PS) and phosphatidylethanolamine (PE), including the ether lipids. In addition, the article describes the biosynthetic pathways for these phospholipids and how these pathways were elucidated. Several unique functions of PS and PE in mammalian cells in addition to their ability to define physical properties of membranes are discussed. For example, the translocation of PS from the inner to the outer leaflet of the plasma membrane of cells occurs during apoptosis and during some other specific physiological processes, and this translocation is responsible for profound life-or-death events. Moreover, mitochondrial function is severely impaired when the PE content of mitochondria is reduced below a threshold level. The discovery and implications of the existence of membrane contact sites between the endoplasmic reticulum and mitochondria and their relevance for PS and PE metabolism, as well as for mitochondrial function, are also discussed. Many of the recent advances in these fields are due to the use of isotope labeling for tracing biochemical pathways. In addition, techniques for disruption of specific genes in mice are now widely used and have provided major breakthroughs in understanding the roles and metabolism of PS and PE in vivo.

Liposomal formulations of magnesium sulfanyl tribenzoporphyrazines for the photodynamic therapy of cancer

Photodynamic therapy of cancer comprises the activation of photosensitizer molecules delivered to cancer cells, to generate reactive oxygen species that mediate cytotoxicity. In this study, previously synthesized dendritic magnesium tribenzoporphyrazines were incorporated into four types of liposomes containing either 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) as the zwitterionic lipids. The addition of either l-α-phosphatidyl-dl-glycerol (PG) or 1,2-dioleoyl-3-trimethylammoniumpropane (DOTAP) imparted a negative or positive charge, respectively. Novel formulations were tested in oral squamous cell carcinoma cell lines (CAL 27, HSC-3) as well as cervical adenocarcinoma cells (HeLa). Positively charged DOTAP:POPC liposomes were the most effective carriers for all tested tribenzoporphyrazines. Calculated IC₅₀ values for DOTAP:POPC liposomes indicated that the incorporation of tribenzoporphyrazines into these liposomes can improve photocytotoxicity up to 50-fold compared to the free forms of macrocycles. Oral cancer cells (CAL 27 and HSC-3) were more sensitive to liposomal photodynamic treatment than HeLa cells.

Reduction of Liver Span and Parameters of Inflammation in Nonalcoholic Fatty Liver Disease Patients Treated with Lycosome Formulation of Phosphatidylcholine: A Preliminary Report

Twenty-nine newly diagnosed individuals with Nonalcoholic Fatty Liver Disease (NAFLD) remaining on habitual dietary regimen were supplemented with regular or lycosome formulations of phosphatidylcholine (PC) during a pilot, randomized, double-blinded clinical study. After two months of oral PC intake (450 mg daily) the liver size as well as serum levels of hepatic enzymes and markers of inflammation were evaluated by ultrasonography and biochemical analysis. It was shown that there was a statistically significant reduction of medians for the Mid-Clavicular liver size from 16.0 cm (95/5% CI: 17.1/15.5) to 15.1 cm (95/5% CI: 17.2/14.4, P = 0.021) in participants ingesting the lycosome-formulated PC (L-PC) whereas regular formulation of PC (R-PC) had only a marginal effect on this parameter (P = 0.044). A similar tendency was observed in the Mid-Sternal liver size. Moreover, there was a reduction of medians for ALT values at the end point of the study (P = 0.026) after ingestion of L-PC, while R-PC had no statistically significant effect. On the other hand, ingestion of both formulations was accompanied by reductions in values for Inflammatory Oxidative Damage (IOD) and oxidized LDL in serum. However, L-PC had superior activity in these terms, presumably due to the presence of lycopene, a powerful antioxidant, in the L-PC-Lycosome structure. C-reactive protein level was moderately decreased (reduction of medians from 6.5 [95/5% CI: 7.7/5.8] mg/L to 5.1 [95/5% CI: 5.6/4.3] mg/L) only after ingestion of L-PC. The greater efficacy of L-PC seen in NAFLD volunteers may reflect improved bioavailability of PC owing to better protection of the microencapsulated PC from gastrointestinal enzymes and possibly enhanced hepatic delivery of L-PC particles.

Prospective study of blood metabolites associated with colorectal cancer risk

Few prospective studies, and none in Asians, have systematically evaluated the relationship between blood metabolites and colorectal cancer risk. We conducted a nested case-control study to search for risk-associated metabolite biomarkers for colorectal cancer in an Asian population using blood samples collected prior to cancer diagnosis. Conditional logistic regression was performed to assess associations of metabolites with cancer risk. In this study, we included 250 incident cases with colorectal cancer and individually matched controls nested within two prospective Shanghai cohorts. We found 35 metabolites associated with risk of colorectal cancer after adjusting for multiple comparisons. Among them, 12 metabolites were glycerophospholipids including nine associated with reduced risk of colorectal cancer and three with increased risk [odds ratios per standard deviation increase of transformed metabolites: 0.31-1.98; p values: 0.002-1.25 × 10^-10 ]. The other 23 metabolites associated with colorectal cancer risk included nine lipids other than glycerophospholipid, seven aromatic compounds, five organic acids and four other organic compounds. After mutual adjustment, nine metabolites remained statistically significant for colorectal cancer. Together, these independently associated metabolites can separate cancer cases from controls with an area under the curve of 0.76 for colorectal cancer. We have identified that dysregulation of glycerophospholipids may contribute to risk of colorectal cancer.

Disturbed phospholipid metabolism in serine biosynthesis defects revealed by metabolomic profiling

Serine biosynthesis defects are autosomal recessive metabolic disorders resulting from the deficiency of any of the three enzymes involved in de novo serine biosynthesis, specifically phosphoglycerate dehydrogenase (PGDH), phosphoserine aminotransferase (PSAT), and phosphoserine phosphatase (PSP). In this study, we performed metabolomic profiling on 4 children with serine biosynthesis defects; 3 with PGDH deficiency and 1 with PSAT deficiency. The evaluations were performed at baseline and with serine and glycine supplementation. Metabolomic profiling performed at baseline showed low phospholipid species, including glycerophosphocholine, glycerophosphoethanolamine, and sphingomyelin. All children had low serine and glycine as expected. Low glycerophosphocholine compounds were found in 4 children, low glycerophosphoethanolamine compounds in 3 children, and low sphingomyelin species in 2 children. Metabolic profiling with serine and glycine supplementation showed normalization of most of the low phospholipid compounds in the 4 children. Phospholipids are the major component of plasma and intracellular membranes, and phosphatidylcholine is the most abundant phospholipid of all mammalian cell types and subcellular organelles. Phosphatidylcholine is of particular importance for the nervous system, where it is essential for neuronal differentiation. The observed low phosphatidylcholine species in children with serine biosynthesis defects that improved after serine supplementation, supports the role of serine as a significant precursor for phosphatidylcholine. The vital role that phosphatidylcholine has during neuronal differentiation and the pronounced neurological manifestations in serine biosynthesis defects suggest that phosphatidylcholine deficiency occurring secondary to serine deficiency may have a significant contribution to the development of the neurological manifestations in individuals with serine biosynthesis defects.

Discovery of Phosphatidic Acid, Phosphatidylcholine, and Phosphatidylserine as Biomarkers for Early Diagnosis of Endometriosis

The sensitivity and specificity of clinical diagnostic indicators and non-invasive diagnostic methods for endometriosis at early stage is not optimal. Previous studies demonstrated that abnormal lipid metabolism was involved in the pathological development of endometriosis. Our cross-sectional study included 21 patients with laparoscopically confirmed endometriosis at stage I–II and 20 infertile women who underwent diagnostic laparoscopy combined with hysteroscopy from January 2014 to January 2015. Eutopic endometrium was collected by pipelle endometrial biopsy. Lipid metabolites were quantified by ultra-high performance liquid chromatography coupled with electrospray ionization high-resolution mass spectrometry (UHPLC-ESI-HRMS). Lipid profiles of endometriosis patients at early stage (I–II) was characterized by a decreased concentration of phosphatidylcholine (18:1/22:6), (20:1/14:1), (20:3/20:4), and phosphatidylserine (20:3/23:1) and an increased concentration of phosphatidic acid (25:5/22:6) compared with control. The synthesized predicting strategy with 5 biomarkers has a specificity of 75.0% and a sensitivity of 90.5%. Lipid profile of eutopic endometrium in endometriosis was effectively characterized by UHPLC-ESI-HRMS-based metabolomics. Our study demonstrated the alteration of phosphatidic acid, phosphatidylcholine, phosphatidylserine metabolites in endometriosis and provided potential biomarkers for semi-invasive diagnose of endometriosis at early stage.

From yeast to humans - roles of the Kennedy pathway for phosphatidylcholine synthesis

The major phospholipid present in most eukaryotic membranes is phosphatidylcholine (PC), comprising ~ 50% of phospholipid content. PC metabolic pathways are highly conserved from yeast to humans. The main pathway for the synthesis of PC is the Kennedy (CDP-choline) pathway. In this pathway, choline is converted to phosphocholine by choline kinase, phosphocholine is metabolized to CDP-choline by the rate-determining enzyme for this pathway, CTP:phosphocholine cytidylyltransferase, and cholinephosphotransferase condenses CDP-choline with diacylglycerol to produce PC. This Review discusses how PC synthesis via the Kennedy pathway is regulated, its role in cellular and biological processes, as well as diseases known to be associated with defects in PC synthesis. Finally, we present the first model for the making of a membrane via PC synthesis.

Impact of Time-Restricted Feeding and Dawn-to-Sunset Fasting on Circadian Rhythm, Obesity, Metabolic Syndrome, and Nonalcoholic Fatty Liver Disease

Obesity now affects millions of people and places them at risk of developing metabolic syndrome, nonalcoholic fatty liver disease (NAFLD), and even hepatocellular carcinoma. This rapidly emerging epidemic has led to a search for cost-effective methods to prevent the metabolic syndrome and NAFLD as well as the progression of NAFLD to cirrhosis and hepatocellular carcinoma. In murine models, time-restricted feeding resets the hepatic circadian clock and enhances transcription of key metabolic regulators of glucose and lipid homeostasis. Studies of the effect of dawn-to-sunset Ramadan fasting, which is akin to time-restricted feeding model, have also identified significant improvement in body mass index, serum lipid profiles, and oxidative stress parameters. Based on the findings of studies conducted on human subjects, dawn-to-sunset fasting has the potential to be a cost-effective intervention for obesity, metabolic syndrome, and NAFLD.

Metabonomics analysis of serum from rats given long-term and low-level cadmium by ultra-performance liquid chromatography-mass spectrometry

1. This study evaluated the toxicity of chronic exposure to low-level cadmium (Cd) in rats using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Forty male Sprague-Dawley rats were randomly assigned to four groups, namely, the control group, low-dose group (0.13 mg/kg·bw), middle-dose group (0.8 mg/kg·bw) and high-dose group (4.89 mg/kg·bw). The rats continuously received CdCl₂ via drinking water for 24 weeks. Serum samples were collected for metabonomics analysis. The data generated from the UPLC-MS was analysed using principal components analysis (PCA) and partial least-squares discriminant analysis (PLS-DA). PLS-DA model with satisfactory explanatory and predictive ability is capable of discriminating the treatment groups from the control group. 2. Finally, the 10 metabolites were identified and showed significant changes in some treatment groups compared with that in the control group (p < 0.0167 or p < 0.003). Exposure to Cd resulted in increased intensities of lysophosphatidic acid (P-16:0e/0:0), glycocholic acid, bicyclo-prostaglandin E2, lithocholyltaurine, sulfolithocholylglycine, lysophosphatidylethanolamine (20:5/0:0) and lysophosphatidylcholine (20:0), as well as decreased intensities of 3-indolepropionic acid, phosphatidylcholine (18:4/18:0) and 15S-hydroxyeicosatrienoic acid in rat serum. 3. Results suggest that exposure to Cd can cause disturbances in the lipid metabolism, amino acid metabolism, nervous system, antioxidant defence system, liver and kidney function.

The ins and outs of endoplasmic reticulum-controlled lipid biosynthesis

Endoplasmic reticulum (ER)-localized enzymes synthesize the vast majority of cellular lipids. The ER therefore has a major influence on cellular lipid biomass and balances the production of different lipid categories, classes, and species. Signals from outside and inside the cell are directed to ER-localized enzymes, and lipid enzyme activities are defined by the integration of internal, homeostatic, and external information. This allows ER-localized lipid synthesis to provide the cell with membrane lipids for growth, proliferation, and differentiation-based changes in morphology and structure, and to maintain membrane homeostasis across the cell. ER enzymes also respond to physiological signals to drive carbohydrates and nutritionally derived lipids into energy-storing triglycerides. In this review, we highlight some key regulatory mechanisms that control ER-localized enzyme activities in animal cells. We also discuss how they act in concert to maintain cellular lipid homeostasis, as well as how their dysregulation contributes to human disease.

Phospholipases during membrane dynamics in malaria parasites

Plasmodium parasites, the causative agents of malaria, display a well-regulated lipid metabolism required to ensure their survival in the human host as well as in the mosquito vector. The fine-tuning of lipid metabolic pathways is particularly important for the parasites during the rapid erythrocytic infection cycles, and thus enzymes involved in lipid metabolic processes represent prime targets for malaria chemotherapeutics. While plasmodial enzymes involved in lipid synthesis and acquisition have been studied in the past, to date not much is known about the roles of phospholipases for proliferation and transmission of the malaria parasite. These phospholipid-hydrolyzing esterases are crucial for membrane dynamics during host cell infection and egress by the parasite as well as for replication and cell signaling, and thus they are considered important virulence factors. In this review, we provide a comprehensive bioinformatic analysis of plasmodial phospholipases identified to date. We further summarize previous findings on the lipid metabolism of Plasmodium, highlight the roles of phospholipases during parasite life-cycle progression, and discuss the plasmodial phospholipases as potential targets for malaria therapy.

From masochistic enzymology to mechanistic physiology and disease

The pioneering work of Eugene Kennedy in the 1950s established the choline pathway for phosphatidylcholine (PC) biosynthesis. However, the regulation of PC biosynthesis was poorly understood at that time. When I started my lab at the University of British Columbia in the 1970s, this was the focus of my research. This article provides my reflections on these studies that began with enzymology and the use of cultured mammalian cells, and progressed to utilize the techniques of molecular biology and gene-targeted mice. The research in my lab and others demonstrated that the regulated and rate-limiting step in the choline pathway for PC biosynthesis was catalyzed by CTP:phosphocholine cytidylyltransferase. This enzyme is regulated by its movement from a soluble form (largely in the nucleus) to a membrane-associated form where the enzyme becomes activated. Gene targeting in mice subsequently demonstrated that this gene is essential for development of mouse embryos. The other mammalian pathway for PC biosynthesis is catalyzed by phosphatidylethanolamine N-methyltransferase (PEMT) that converts phosphatidylethanolamine to PC. Understanding of the regulation and function of the integral membrane protein PEMT was improved when the enzyme was purified (a masochistic endeavor) in 1987, leading to the cloning of the Pemt cDNA. Generation of knock-out mice that lacked PEMT showed that they were protected from atherosclerosis, diet-induced obesity, and insulin resistance. The protection from atherosclerosis appears to be due to decreased secretion of lipoproteins from the liver. We continue to investigate the mechanism(s) by which Pemt^-/- mice are protected from weight gain and insulin resistance.

Membrane-lipid therapy: A historical perspective of membrane-targeted therapies - From lipid bilayer structure to the pathophysiological regulation of cells

Our current understanding of membrane lipid composition, structure and functions has led to the investigation of their role in cell signaling, both in healthy and pathological cells. As a consequence, therapies based on the regulation of membrane lipid composition and structure have been recently developed. This novel field, known as Membrane Lipid Therapy, is growing and evolving rapidly, providing treatments that are now in use or that are being studied for their application to oncological disorders, Alzheimer's disease, spinal cord injury, stroke, diabetes, obesity, and neuropathic pain. This field has arisen from relevant discoveries on the behavior of membranes in recent decades, and it paves the way to adopt new approaches in modern pharmacology and nutrition. This innovative area will promote further investigation into membranes and the development of new therapies with molecules that target the cell membrane. Due to the prominent roles of membranes in the cells' physiology and the paucity of therapeutic approaches based on the regulation of the lipids they contain, it is expected that membrane lipid therapy will provide new treatments for numerous pathologies. The first on-purpose rationally designed molecule in this field, minerval, is currently being tested in clinical trials and it is expected to enter the market around 2020. However, it seems feasible that during the next few decades other membrane regulators will also be marketed for the treatment of human pathologies. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.