Regulation of phosphatidylcholine biosynthesis

Proteomic analysis revealed gender-related differences in the skin mucus proteome of discus fish (Symphysodon haraldi) during the parental and non-parental care periods

The discus fish, Symphysodon spp., a South American cichlid, has a unique parental care behavior where fry bite on parental skin mucus after hatching. In this study, we used LC-MS/MS technique to compare the skin mucus proteome composition of male or female discus fish during parental and non-parental care periods. By multivariate statistical analysis, we found clear separations between different periods and between different sexes of mucus proteome. Compared with non-parental female fish, parental female fish had 283 up-regulated and 235 down-regulated expressed proteins. Compared with non-parental male fish, parental male fish had 169 up-regulated and 120 down-regulated expressed proteins. The differentially expressed proteins for male fish were enriched in sulfur relay system, mucin type O-glycan biosynthesis and antigen processing and presentation pathways, while those for female fish were enriched in sulfur relay system, steroid biosynthesis and complement and coagulation cascades pathways. During the parental care, both male and female discus showed an enhanced lipid metabolism, producing more phospholipids and cholesterol. The difference is that male discus had increased tricarboxylic acid cycle producing more energy during the parental care, while females produced more nucleotides especially guanylic acid. Our study could provide new insights into the understanding of the unique mucus supply behavior of discus fish based on proteomic change.

Phospholipase D1 promotes astrocytic differentiation through the FAK/AURKA/STAT3 signaling pathway in hippocampal neural stem/progenitor cells

Phospholipase D1 (PLD1) plays a crucial role in cell differentiation of different cell types. However, the involvement of PLD1 in astrocytic differentiation remains uncertain. In the present study, we investigate the possible role of PLD1 and its product phosphatidic acid (PA) in astrocytic differentiation of hippocampal neural stem/progenitor cells (NSPCs) from hippocampi of embryonic day 16.5 rat embryos. We showed that overexpression of PLD1 increased the expression level of glial fibrillary acidic protein (GFAP), an astrocyte marker, and the number of GFAP-positive cells. Knockdown of PLD1 by transfection with Pld1 shRNA inhibited astrocytic differentiation. Moreover, PLD1 deletion (Pld1^-/-) suppressed the level of GFAP in the mouse hippocampus. These results indicate that PLD1 plays a crucial role in regulating astrocytic differentiation in hippocampal NSPCs. Interestingly, PA itself was sufficient to promote astrocytic differentiation. PA-induced GFAP expression was decreased by inhibition of signal transducer and activation of transcription 3 (STAT3) using siRNA. Furthermore, PA-induced STAT3 activation and astrocytic differentiation were regulated by the focal adhesion kinase (FAK)/aurora kinase A (AURKA) pathway. Taken together, our findings suggest that PLD1 is an important modulator of astrocytic differentiation in hippocampal NSPCs via the FAK/AURKA/STAT3 signaling pathway.

Effects of insufficient serine on health and selenoprotein expression in rats and their offspring

Objective

To observe the impact of insufficient exogenous and/or endogenous serine on selenoprotein expression and health of pregnant rats and their offspring.

Method

Experiment 1 was conducted in male rats, in which the dose-dependent effects of serine on selenoprotein expression and thyroid hormones (T3, T4 and TSH) were investigated by feeding either a serine adequate diet (20C), serine-deprived diet (20CSD) or 20CSD with different serine levels (0.5, 1.0, and 2.0 times the amount of serine in 20C). In experiment 2, a PHGDH inhibitor was administrated to pregnant rats fed either 20C or 20CSD. Blood and organ tissues of pregnant rats and offspring were subjected to the analyses of thyroid hormone, serine and homocysteine and GPx3 and SELENOP in plasma and expression of GPx1 and DIO1, 2 in tissues respectively.

Result

In experiment 1, plasma SELENOP and GPx3 levels in adult male rats increased with the increasing dose of serine. Immunohistochemical results showed that GPx1 expression in liver and kidney of male rats also increased with increasing serine supplementation. Amongst all diet groups, only male rats fed 20CSD had significantly lower plasma TSH and T4 levels (P < 0.05). In experiment 2, GPx1 and DIO2 expression in the liver and kidney were suppressed in pregnant rats administered with a PHGDH compared to those who were not (P < 0.05). There were no significant differences in plasma T4 and T3 amongst all diet groups (P > 0.05). Also, offspring born to pregnant rats administered with a PHGDH inhibitor exhibited slower growth rates and hyperhomocysteinemia compared to offspring from mothers not administered with the inhibitor (P < 0.05). Conclusions: Insufficient exogenous serine through the diet decreased selenoprotein synthesis in adult male rats. However, this was not observed in pregnant rats, whereby exogenous or endogenous serine deficiency had no effect on the selenoprotein levels. A possible explanation is that dams may have an adaptive mechanism to limit maternal serine utilization and ensure adequate supply to the fetus.

Choline chloride attenuates the allergic airway disease by inhibiting the lysophosphatidylcholine induced response in mouse model

Aims

Allergic airway disease manifestation is induced by lysophosphatidylcholine (LPC) through CD1d-restricted Natural killer T (NKT) cells. Choline chloride (ChCl) and LPC both have the “choline” moiety in their structure and this may interplay the effect in allergic airway disease pathway.

Main methods

To test the hypothesis, mice were sensitized with cockroach extract (CE); challenged with CE or exposed to LPC and were given ChCl 1hr later.

Key findings

A significant increase in Airway hyperresponsiveness (AHR), total and differential cell count, Th2 cytokines, 8-isoprostanes level in bronchoalveolar lavage fluid (BALF) and inflammation score based on lung histology were observed on challenge with CE or exposure to LPC (p ​< ​0.05) indicating LPC induced airway disease manifestation in mice. These parameters were reduced significantly after administering mice with ChCl (p ​< ​0.05). The inflammatory parameters were significantly increased in LPC exposed mice, not sensitized with CE, which were significantly decreased when mice were administered with ChCl demonstrating its role in the inhibition of LPC induced allergic airway disease manifestation. Docking of CD1d with LPC and ChCl indicated the competitive inhibition of LPC induced effect by ChCl. This was validated in vivo in the form of decreased CD1d-restricted NKT cells in BALF and lung of the immunized mice on ChCl administration. There was no effect of ChCl administration on CD1d expression in BALF and lung cells.

Significance

This study shows that ChCl attenuates the allergic response by inhibiting the LPC induced- NKT cell mediated AHR, inflammation and oxidative stress by competitive inhibition to LPC in binding to CD1d.

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ChCl down regulates LPC (critical for allergic manifestation) induced response.

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Results were validated in cockroach extract immunized mice model.

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In silico studies indicate competitive inhibition to LPC by ChCl in binding to CD1d.

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In silico results were also validated in vivo in terms of CD1d-restricted NKT cells.

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Study explains the mechanism of ChCl action against allergic disease.

Fundamentals of Membrane Lipid Replacement: A Natural Medicine Approach to Repairing Cellular Membranes and Reducing Fatigue, Pain, and Other Symptoms While Restoring Function in Chronic Illnesses and Aging

Membrane Lipid Replacement (MLR) uses natural membrane lipid supplements to safely replace damaged, oxidized lipids in membranes in order to restore membrane function, decrease symptoms and improve health. Oral MLR supplements contain mixtures of cell membrane glycerolphospholipids, fatty acids, and other lipids, and can be used to replace and remove damaged cellular and intracellular membrane lipids. Membrane injury, caused mainly by oxidative damage, occurs in essentially all chronic and acute medical conditions, including cancer and degenerative diseases, and in normal processes, such as aging and development. After ingestion, the protected MLR glycerolphospholipids and other lipids are dispersed, absorbed, and internalized in the small intestines, where they can be partitioned into circulating lipoproteins, globules, liposomes, micelles, membranes, and other carriers and transported in the lymphatics and blood circulation to tissues and cellular sites where they are taken in by cells and partitioned into various cellular membranes. Once inside cells, the glycerolphospholipids and other lipids are transferred to various intracellular membranes by lipid carriers, globules, liposomes, chylomicrons, or by direct membrane-membrane interactions. The entire process appears to be driven by 'bulk flow' or mass action principles, where surplus concentrations of replacement lipids can stimulate the natural exchange and removal of damaged membrane lipids while the replacement lipids undergo further enzymatic alterations. Clinical studies have demonstrated the advantages of MLR in restoring membrane and organelle function and reducing fatigue, pain, and other symptoms in chronic illness and aging patients.

Deregulation of Lipid Homeostasis: A Fa(c)t in the Development of Metabolic Diseases

Lipids are important molecules for human health. The quantity and quality of fats consumed in the diet have important effects on the modulation of both the natural biosynthesis and degradation of lipids. There is an important number of lipid-failed associated metabolic diseases and an increasing number of studies suggesting that certain types of lipids might be beneficial to the treatment of many metabolic diseases. The aim of the present work is to expose an overview of de novo biosynthesis, storage, and degradation of lipids in mammalian cells, as well as, to review the published data describing the beneficial effects of these processes and the potential of some dietary lipids to improve metabolic diseases.

Recent advances in the design of choline kinase α inhibitors and the molecular basis of their inhibition

Upregulated choline metabolism, characterized by an increase in phosphocholine (PCho), is a hallmark of oncogenesis and tumor progression. Choline kinase (ChoK), the enzyme responsible for PCho synthesis, has consequently become a promising drug target for cancer therapy and as such a significant number of ChoK inhibitors have been developed over the last few decades. More recently, due to the role of this enzyme in other pathologies, ChoK inhibitors have also been used in new therapeutic approaches against malaria and rheumatoid arthritis. Here, we review research results in the field of ChoKα inhibitors from their synthesis to the molecular basis of their binding mode. Strategies for the development of inhibitors and their selectivity on ChoKα over ChoKβ, the plasticity of the choline-binding site, the discovery of new exploitable binding sites, and the allosteric properties of this enzyme are highlighted. The outcomes summarized in this review will be a useful guide to develop new multifunctional potent drugs for the treatment of various human diseases.

De novo phosphatidylcholine synthesis is required for autophagosome membrane formation and maintenance during autophagy

Macroautophagy/autophagy can enable cancer cells to withstand cellular stress and maintain bioenergetic homeostasis by sequestering cellular components into newly formed double-membrane vesicles destined for lysosomal degradation, potentially affecting the efficacy of anti-cancer treatments. Using 13C-labeled choline and 13C-magnetic resonance spectroscopy and western blotting, we show increased de novo choline phospholipid (ChoPL) production and activation of PCYT1A (phosphate cytidylyltransferase 1, choline, alpha), the rate-limiting enzyme of phosphatidylcholine (PtdCho) synthesis, during autophagy. We also discovered that the loss of PCYT1A activity results in compromised autophagosome formation and maintenance in autophagic cells. Direct tracing of ChoPLs with fluorescence and immunogold labeling imaging revealed the incorporation of newly synthesized ChoPLs into autophagosomal membranes, endoplasmic reticulum (ER) and mitochondria during anticancer drug-induced autophagy. Significant increase in the colocalization of fluorescence signals from the newly synthesized ChoPLs and mCherry-MAP1LC3/LC3 (microtubule-associated protein 1 light chain 3) was also found on autophagosomes accumulating in cells treated with autophagy-modulating compounds. Interestingly, cells undergoing active autophagy had an altered ChoPL profile, with longer and more unsaturated fatty acid/alcohol chains detected. Our data suggest that de novo synthesis may be required to increase autophagosomal ChoPL content and alter its composition, together with replacing phospholipids consumed from other organelles during autophagosome formation and turnover. This addiction to de novo ChoPL synthesis and the critical role of PCYT1A may lead to development of agents targeting autophagy-induced drug resistance. In addition, fluorescence imaging of choline phospholipids could provide a useful way to visualize autophagosomes in cells and tissues.

ABBREVIATIONS

AKT: AKT serine/threonine kinase; BAX: BCL2 associated X, apoptosis regulator; BECN1: beclin 1; ChoPL: choline phospholipid; CHKA: choline kinase alpha; CHPT1: choline phosphotransferase 1; CTCF: corrected total cell fluorescence; CTP: cytidine-5'-triphosphate; DCA: dichloroacetate; DMEM: dulbeccos modified Eagles medium; DMSO: dimethyl sulfoxide; EDTA: ethylenediaminetetraacetic acid; ER: endoplasmic reticulum; GDPD5: glycerophosphodiester phosphodiesterase domain containing 5; GFP: green fluorescent protein; GPC: glycerophosphorylcholine; HBSS: hanks balances salt solution; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; LPCAT1: lysophosphatidylcholine acyltransferase 1; LysoPtdCho: lysophosphatidylcholine; MRS: magnetic resonance spectroscopy; MTORC1: mechanistic target of rapamycin kinase complex 1; PCho: phosphocholine; PCYT: choline phosphate cytidylyltransferase; PLA2: phospholipase A2; PLB: phospholipase B; PLC: phospholipase C; PLD: phospholipase D; PCYT1A: phosphate cytidylyltransferase 1, choline, alpha; PI3K: phosphoinositide-3-kinase; pMAFs: pancreatic mouse adult fibroblasts; PNPLA6: patatin like phospholipase domain containing 6; Pro-Cho: propargylcholine; Pro-ChoPLs: propargylcholine phospholipids; PtdCho: phosphatidylcholine; PtdEth: phosphatidylethanolamine; PtdIns3P: phosphatidylinositol-3-phosphate; RPS6: ribosomal protein S6; SCD: stearoyl-CoA desaturase; SEM: standard error of the mean; SM: sphingomyelin; SMPD1/SMase: sphingomyelin phosphodiesterase 1, acid lysosomal; SGMS: sphingomyelin synthase; WT: wild-type.

Symposium review: One-carbon metabolism and methyl donor nutrition in the dairy cow

The present review focuses on methyl donor metabolism and nutrition in the periparturient and lactating dairy cow. Methyl donors are involved in one-carbon metabolism, which includes the folate and Met cycles. These cycles work in unison to support lipid, nucleotide, and protein synthesis, as well as methylation reactions and the maintenance of redox status. A key feature of one-carbon metabolism is the multi-step conversion of tetrahydrofolate to 5-methyltetrahyrofolate. Homocysteine and 5-methyltetrahyrofolate are utilized by vitamin B₁₂-dependent Met synthase to couple the folate and Met cycles and generate Met. Methionine may also be remethylated from choline-derived betaine under the action of betaine hydroxymethyltransferase. Regardless, Met is converted within the Met cycle to S-adenosylmethionine, which is universally utilized in methyl-group transfer reactions including the synthesis of phosphatidylcholine. Homocysteine may also enter the transsulfuration pathway to generate glutathione or taurine for scavenging of reactive oxygen metabolites. In the transition cow, a high demand exists for compounds with a labile methyl group. Limited methyl group supply may contribute to inadequate hepatic phosphatidylcholine synthesis and hepatic triglyceride export, systemic oxidative stress, and compromised milk production. To minimize the perils associated with methyl donor deficiency, the peripartum cow relies on de novo methylneogenesis from tetrahydrofolate. In addition, dietary supplementation of rumen-protected folic acid, vitamin B₁₂, Met, choline, and betaine are potential nutritional approaches to target one-carbon pools and improve methyl donor balance in transition cows. Such strategies have merit considering research demonstrating their ability to improve milk production efficiency, milk protein synthesis, hepatic health, and immune response. This review aims to summarize the current understanding of folic acid, vitamin B₁₂, Met, choline, and betaine utilization in the dairy cow. Methyl donor co-supplementation, fatty acid feeding strategies that may optimize methyl donor supplementation efficacy, and potential epigenetic mechanisms are also considered.

Choline Is an Intracellular Messenger Linking Extracellular Stimuli to IP3-Evoked Ca2+ Signals through Sigma-1 Receptors

Sigma-1 receptors (Sig-1Rs) are integral ER membrane proteins. They bind diverse ligands, including psychoactive drugs, and regulate many signaling proteins, including the inositol 1,4,5-trisphosphate receptors (IP3Rs) that release Ca2+ from the ER. The endogenous ligands of Sig-1Rs are unknown. Phospholipase D (PLD) cleaves phosphatidylcholine to choline and phosphatidic acid (PA), with PA assumed to mediate all downstream signaling. We show that choline is also an intracellular messenger. Choline binds to Sig-1Rs, it mimics other Sig-1R agonists by potentiating Ca2+ signals evoked by IP3Rs, and it is deactivated by metabolism. Receptors, by stimulating PLC and PLD, deliver two signals to IP3Rs: IP3 activates IP3Rs, and choline potentiates their activity through Sig-1Rs. Choline is also produced at synapses by degradation of acetylcholine. Choline uptake by transporters activates Sig-1Rs and potentiates Ca2+ signals. We conclude that choline is an endogenous agonist of Sig-1Rs linking extracellular stimuli, and perhaps synaptic activity, to Ca2+ signals.

Localization and expression of CTP: Phosphocholine cytidylyltransferase in rat brain following cocaine exposure

Phosphatidylcholine (PC) is a primary phospholipid and major source of secondary lipid messengers and also serves as a biosynthetic precursor for other membrane phospholipids. Phosphocholine cytidylyltransferase (CCT) is the rate-limiting enzyme responsible for catalyzing the formation of PC. Changes in CCT activity have been associated with lipid dysregulation across various neurological disorders. Additionally, intermediates in PC synthesis, such as CDP-choline, have been suggested to attenuate drug craving during cocaine addiction. Recent work from our group demonstrated that cocaine exposure and conditioning alter the level of PC in the brain, specifically in the cerebellum and hippocampus. The present study examines the role of CCT expression in the brain and determines the effect of cocaine exposure on CCT expression. Immunohistochemical analysis (IHC) was performed to assess region-specific expression of CCT, including both of its isoforms; alpha (CCTα) and beta (CCTβ). IHC did not detect any staining of CCTα throughout the rat brain. In contrast, CCTβ expression was detected in the Purkinje cells of the cerebellum with decreases in expression following cocaine exposure. Collectively, these data demonstrate the region- and cell-specific localization of CCTα and CCTβ in the rat brain, as well as the altered expression of CCTβ in the cerebellum following cocaine exposure.

Fluorocholine Transport Mediated by the Organic Cation Transporter 2 (OCT2, SLC22A2): Implication for Imaging of Kidney Tumors

[18F]fluorocholine is the fluorinated analog of [11C]choline and is used in positron emission tomography to monitor tumor metabolic activity. Although important to optimize its use and expand the clinical indications, the molecular determinants of fluorocholine cellular uptake are poorly characterized. In this work, we described the influx kinetics of fluorocholine mediated by the organic cation transporter 2 (OCT2, SLC22A2) and compared with that of choline. Then we characterized the expression pattern of OCT2 in renal cell carcinoma (RCC). In HEK293 cells stably transfected with OCT2 fluorocholine influx, kinetics was biphasic, suggesting two independent binding sites: a high-affinity (Km = 14 ± 8 µM, Vmax = 1.3 ± 0.5 nmol mg-1 min-1) and a low-affinity component (Km = 1.8 ± 0.3 mM, Vmax = 104 ± 4.5 nmol mg-1 min-1). Notably, choline was found to be transported with sigmoidal kinetics typical of homotropic positive cooperativity (h = 1.2, 95% confidence interval 1.1-1.3). OCT2 mRNA expression level was found significantly decreased in primary but not in metastatic RCC. Tissue microarray immunostaining of 216 RCC biopsies confirmed that the OCT2 protein level was consistent with that of the mRNA. The kinetic properties described in this work suggest that OCT2 is likely to play a dominant role in [18F]fluorocholine uptake in vivo. OCT2-altered expression in primary and metastatic cancer cells, as compared with the surrounding tissues, could be exploited in RCC imaging, especially to increase the detection sensitivity for small metastatic lesions, a major clinical challenge during the initial staging of RCC.

Neuronal Cholesterol Accumulation Induced by Cyp46a1 Down-Regulation in Mouse Hippocampus Disrupts Brain Lipid Homeostasis

Impairment in cholesterol metabolism is associated with many neurodegenerative disorders including Alzheimer's disease (AD). However, the lipid alterations underlying neurodegeneration and the connection between altered cholesterol levels and AD remains not fully understood. We recently showed that cholesterol accumulation in hippocampal neurons, induced by silencing Cyp46a1 gene expression, leads to neurodegeneration with a progressive neuronal loss associated with AD-like phenotype in wild-type mice. We used a targeted and non-targeted lipidomics approach by liquid chromatography coupled to high-resolution mass spectrometry to further characterize lipid modifications associated to neurodegeneration and cholesterol accumulation induced by CYP46A1 inhibition. Hippocampus lipidome of normal mice was profiled 4 weeks after cholesterol accumulation due to Cyp46a1 gene expression down-regulation at the onset of neurodegeneration. We showed that major membrane lipids, sphingolipids and specific enzymes involved in phosphatidylcholine and sphingolipid metabolism, were rapidly increased in the hippocampus of AAV-shCYP46A1 injected mice. This lipid accumulation was associated with alterations in the lysosomal cargoe, accumulation of phagolysosomes and impairment of endosome-lysosome trafficking. Altogether, we demonstrated that inhibition of cholesterol 24-hydroxylase, key enzyme of cholesterol metabolism leads to a complex dysregulation of lipid homeostasis. Our results contribute to dissect the potential role of lipids in severe neurodegenerative diseases like AD.

Membrane Lipid Replacement for chronic illnesses, aging and cancer using oral glycerolphospholipid formulations with fructooligosaccharides to restore phospholipid function in cellular membranes, organelles, cells and tissues

Membrane Lipid Replacement is the use of functional, oral supplements containing mixtures of cell membrane glycerolphospholipids, plus fructooligosaccharides (for protection against oxidative, bile acid and enzymatic damage) and antioxidants, in order to safely replace damaged, oxidized, membrane phospholipids and restore membrane, organelle, cellular and organ function. Defects in cellular and intracellular membranes are characteristic of all chronic medical conditions, including cancer, and normal processes, such as aging. Once the replacement glycerolphospholipids have been ingested, dispersed, complexed and transported, while being protected by fructooligosaccharides and several natural mechanisms, they can be inserted into cell membranes, lipoproteins, lipid globules, lipid droplets, liposomes and other carriers. They are conveyed by the lymphatics and blood circulation to cellular sites where they are endocytosed or incorporated into or transported by cell membranes. Inside cells the glycerolphospholipids can be transferred to various intracellular membranes by lipid globules, liposomes, membrane-membrane contact or by lipid carrier transfer. Eventually they arrive at their membrane destinations due to 'bulk flow' principles, and there they can stimulate the natural removal and replacement of damaged membrane lipids while undergoing further enzymatic alterations. Clinical trials have shown the benefits of Membrane Lipid Replacement in restoring mitochondrial function and reducing fatigue in aged subjects and chronically ill patients. Recently Membrane Lipid Replacement has been used to reduce pain and other symptoms as well as removing hydrophobic chemical contaminants, suggesting that there are additional new uses for this safe, natural medicine supplement. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

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

Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are the most abundant phospholipids in all mammalian cell membranes. In the 1950s, Eugene Kennedy and co-workers performed groundbreaking research that established the general outline of many of the pathways of phospholipid biosynthesis. In recent years, the importance of phospholipid metabolism in regulating lipid, lipoprotein and whole-body energy metabolism has been demonstrated in numerous dietary studies and knockout animal models. The purpose of this review is to highlight the unappreciated impact of phospholipid metabolism on health and disease. Abnormally high, and abnormally low, cellular PC/PE molar ratios in various tissues can influence energy metabolism and have been linked to disease progression. For example, inhibition of hepatic PC synthesis impairs very low density lipoprotein secretion and changes in hepatic phospholipid composition have been linked to fatty liver disease and impaired liver regeneration after surgery. The relative abundance of PC and PE regulates the size and dynamics of lipid droplets. In mitochondria, changes in the PC/PE molar ratio affect energy production. We highlight data showing that changes in the PC and/or PE content of various tissues are implicated in metabolic disorders such as atherosclerosis, insulin resistance and obesity. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Impact of Organic Cation Transporters (OCT-SLC22A) on Differential Diagnosis of Intrahepatic Lesions

Positron emission tomography (PET) using the cationic compound [18F]fluoromethylcholine (FCH) enhances the sensitivity for noninvasive classification of hepatic tumors due to peculiar patterns of accumulation. The underlying transporters are not known. We aim to identify the carriers mediating uptake of FCH in liver and to correlate their expression pattern with PET intrahepatic signal distribution to clarify the role of membrane transporters in FCH accumulation. FCH transport was characterized in cells overexpressing organic cation transporters (OCTs). OCT mRNA levels were determined in different types of hepatic lesions and correlated with FCH PET signal intensity. Additionally, OCT1 and OCT3 protein was analyzed in a subset of patients by Western blotting. HEK293 cells overexpressing OCT1, OCT2, or OCT3 showed higher intracellular levels of FCH in comparison with wild-type cells. mRNA levels of OCT1 paralleled protein levels and were significantly downregulated in hepatocellular carcinoma (HCC), hepatocellular adenoma (HCA), and, to a lesser extent, in focal nodular hyperplasia compared with matched nontumor tissues. In three patients with HCA, the FCH PET signal intensity was reduced relative to normal liver. This correlated with the simultaneous downregulation of OCT1 and OCT3 mRNA. In another patient with HCA, lesion and surrounding tissue did not show a difference in signal, coinciding with downregulation of OCT1 and upregulation of OCT3. Therefore, OCT1 is very likely a key transporter for the accumulation of FCH in the liver. The data support the hypothesis that the varying expression levels of OCT1 and OCT3 in focal liver lesions determine FCH PET signal intensity.

Triglycerides Revisited to the Serial

This review discusses the role of triglycerides (TGs) in the normal cardiovascular system as well as in the development and clinical manifestation of cardiovascular diseases. Regulation of TGs at the enzymatic and genetic level, in addition to their possible relevance as preclinical and clinical biomarkers, is discussed, culminating with a description of available and emerging treatments. Due to the high complexity of the subject and the vast amount of material in the literature, the objective of this review was not to exhaust the subject, but rather to compile the information to facilitate and improve the understanding of those interested in this topic. The main publications on the topic were sought out, especially those from the last 5 years. The data in the literature still give reason to believe that there is room for doubt regarding the use of TG as disease biomarkers; however, there is increasing evidence for the role of hypertriglyceridemia on the atherosclerotic inflammatory process, cardiovascular outcomes, and mortality.

In vivo Magnetic Resonance Metabolic and Morphofunctional Fingerprints in Experimental Models of Human Ovarian Cancer

Epithelial ovarian cancer (EOC) is the gynecological malignancy with the highest death rate, characterized by frequent relapse and onset of drug resistance. Disease diagnosis and therapeutic follow-up could benefit from application of molecular imaging approaches, such as magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS), able to monitor metabolic and functional alterations and investigate the underlying molecular mechanisms. Here, we overview the quantitative alterations that occur during either orthotopic or subcutaneous growth of preclinical EOC models. A common feature of (1)H MR spectra is the presence of a prominent peak due to total choline-containing metabolites (tCho), together with other metabolic alterations and MRI-detected morphofunctional patterns specific for different phenotypes. The tCho signal, already present at early stages of tumor growth, and changes of diffusion-weighted MRI parameters could serve as markers of malignancy and/or tumor response to therapy. The identification by MRS and MRI of biochemical and physiopathological fingerprints of EOC disease in preclinical models can represent a basis for further developments of non-invasive MR approaches in the clinical setting.

The hepatic circadian clock regulates the choline kinase α gene through the BMAL1-REV-ERBα axis

The circadian timing system adapts most of the mammalian physiology and behaviour to the 24 h light/dark cycle. This temporal coordination relies on endogenous circadian clocks present in virtually all tissues and organs and implicated in the regulation of key cellular processes including metabolism, transport and secretion. Environmental or genetic disruption of the circadian coordination causes metabolic imbalance leading for instance to fatty liver, dyslipidaemia and obesity, thereby contributing to the development of a metabolic syndrome state. In the liver, a key metabolic organ, the rhythmic regulation of lipid biosynthesis is known, yet the molecular mechanisms through which the circadian clock controls lipogenesis, in particular, that of phospholipids, is poorly characterised. In this study, we show that the wild-type mice display a rhythmic accumulation of hepatic phosphatidylcholine with a peak at ZT 22-0 while clock-deficient Bmal1(-/-) mice show elevated phosphatidylcholine levels in the liver associated with an atherogenic lipoprotein profile. Profiling of the mRNA expression of enzymes from the Kennedy and phosphatidylethanolamine N-methyltransferase pathways which control the production of hepatic phosphatidylcholine revealed a robust circadian pattern for Chkα while other mRNA showed low amplitude (Chkβ and Pemt) or no rhythm (Cctα and Chpt1). Chkα mRNA expression was increased and no longer rhythmic in the liver from clock-deficient Bmal1(-/-) mice. This change resulted in the upregulation of the CHKα protein in these animals. We further show that the robust circadian expression of Chkα is restricted to the liver and adrenal glands. Analysis of the Chkα gene promoter revealed the presence of a conserved response element for the core clock transcription factors REV-ERB and ROR. Consistent with the antiphasic phase relationship between Chkα and Rev-erbα expression, in cotransfection experiments using HepG2 cells we show that RORα4-dependent transactivation of this element is repressed by REV-ERBα· Correspondingly, Rev-erbα(-/-)mice displayed higher Chkα mRNA levels in liver at ZT 12. Collectively, these data establish that hepatic phosphatidylcholine is regulated by the circadian clock through a Bmal1-Rev-erbα-Chkα axis and suggest that an intact circadian timing system is important for the temporal coordination of phospholipid metabolism.

Cytosolic lipid droplets: from mechanisms of fat storage to disease

The lipid droplet (LD) is a phylogenetically conserved organelle. In eukaryotes, it is born from the endoplasmic reticulum, but unlike its parent organelle, LDs are the only known cytosolic organelles that are micellar in structure. LDs are implicated in numerous physiological and pathophysiological functions. Many aspects of the LD has captured the attention of diverse scientists alike and has recently led to an explosion in information on the LD biogenesis, expansion and fusion, identification of LD proteomes and diseases associated with LD biology. This review will provide a brief history of this fascinating organelle and provide some contemporary views of unanswered questions in LD biogenesis.

Suppression effects of betaine-enriched spinach on hyperhomocysteinemia induced by guanidinoacetic acid and choline deficiency in rats

Betaine is an important natural component of rich food sources, especially spinach. Rats were fed diets with betaine or spinach powder at the same level of betaine for 10 days to investigate the dose-dependent effects of spinach powder supplementation on hyperhomocysteinemia induced by guanidinoacetic acid (GAA) addition and choline deprivation. The GAA-induced hyperhomocysteinemia in rats fed 25% casein diet (25C) was significantly suppressed by supplementation with betaine or spinach, and it was completely suppressed by taking 11.0% spinach supplementation. The choline deprivation-induced enhancement of plasma homocysteine concentration in rats fed 25% soybean protein diet (25S) was markedly suppressed by 3.82% spinach. Supplementation with betaine or spinach partially prevented the effects of GAA on hepatic concentrations of methionine metabolites. The decrease in activity of betaine-homocysteine S-methyltransferase (BHMT) and cystathionine β-synthase (CBS) in GAA-induced hyperhomocysteinemia was recovered by supplementation with betaine or spinach. Supplementation with betaine or spinach did not affect BHMT activity, whereas it partially restored CBS activity in choline-deprived 25S. The results indicated that betaine or spinach could completely suppress the hyperhomocysteinemia induced by choline deficiency resulting from stimulating the homocysteine removal by both remethylation and cystathionine formation.

Studies on the regulation of lipid biosynthesis in plants: application of control analysis to soybean

Although there is much knowledge of the enzymology (and genes coding the proteins) of lipid biosynthesis in higher plants, relatively little attention has been paid to regulation. We have demonstrated the important role for cholinephosphate cytidylyltransferase in the biosynthesis of the major extra-plastidic membrane lipid, phosphatidylcholine. We followed this work by applying control analysis to light-induced fatty acid synthesis. This was the first such application to lipid synthesis in any organism. The data showed that acetyl-CoA carboxylase was very important, exerting about half of the total control. We then applied metabolic control analysis to lipid accumulation in important oil crops - oilpalm, olive, and rapeseed. Recent data with soybean show that the block of fatty acid biosynthesis reactions exerts somewhat more control (63%) than lipid assembly although both are clearly very important. These results suggest that gene stacks, targeting both parts of the overall lipid synthesis pathway will be needed to increase significantly oil yields in soybean. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Lipid Replacement Therapy: a natural medicine approach to replacing damaged lipids in cellular membranes and organelles and restoring function

Lipid Replacement Therapy, the use of functional oral supplements containing cell membrane phospholipids and antioxidants, has been used to replace damaged, usually oxidized, membrane glycerophospholipids that accumulate during aging and in various clinical conditions in order to restore cellular function. This approach differs from other dietary and intravenous phospholipid interventions in the composition of phospholipids and their defense against oxidation during storage, ingestion, digestion and uptake as well as the use of protective molecules that noncovalently complex with phospholipid micelles and prevent their enzymatic and bile disruption. Once the phospholipids have been taken in by transport processes, they are protected by several natural mechanisms involving lipid receptors, transport and carrier molecules and circulating cells and lipoproteins until their delivery to tissues and cells where they can again be transferred to intracellular membranes by specific and nonspecific transport systems. Once delivered to membrane sites, they naturally replace and stimulate removal of damaged membrane lipids. Various chronic clinical conditions are characterized by membrane damage, mainly oxidative but also enzymatic, resulting in loss of cellular function. This is readily apparent in mitochondrial inner membranes where oxidative damage to phospholipids like cardiolipin and other molecules results in loss of trans-membrane potential, electron transport function and generation of high-energy molecules. Recent clinical trials have shown the benefits of Lipid Replacement Therapy in restoring mitochondrial function and reducing fatigue in aged subjects and patients with a variety of clinical diagnoses that are characterized by loss of mitochondrial function and include fatigue as a major symptom. This Article is Part of a Special Issue Entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Peculiarities of one-carbon metabolism in the strict carnivorous cat and the role in feline hepatic lipidosis

Research in various species has indicated that diets deficient in labile methyl groups (methionine, choline, betaine, folate) produce fatty liver and links to steatosis and metabolic syndrome, but also provides evidence of the importance of labile methyl group balance to maintain normal liver function. Cats, being obligate carnivores, rely on nutrients in animal tissues and have, due to evolutionary pressure, developed several physiological and metabolic adaptations, including a number of peculiarities in protein and fat metabolism. This has led to specific and unique nutritional requirements. Adult cats require more dietary protein than omnivorous species, maintain a consistently high rate of protein oxidation and gluconeogenesis and are unable to adapt to reduced protein intake. Furthermore, cats have a higher requirement for essential amino acids and essential fatty acids. Hastened use coupled with an inability to conserve certain amino acids, including methionine, cysteine, taurine and arginine, necessitates a higher dietary intake for cats compared to most other species. Cats also seemingly require higher amounts of several B-vitamins compared to other species and are predisposed to depletion during prolonged inappetance. This carnivorous uniqueness makes cats more susceptible to hepatic lipidosis.

Chronic ethanol consumption alters mammalian gastrointestinal content metabolites

Chronic ethanol consumption is associated with not only the alteration of metabolic profiles in biofluids but also the composition of the gut microbiome. Our understanding of the importance of the intestinal microbiota as well as the disturbances elicited by ethanol intervention is limited by the fact that previous analyses have primarily focused on biofluids and liver tissue metabolome; the metabolic profiles of the gastrointestinal (GI) contents are rarely investigated. In this study, we applied a metabonomics approach using a high performance liquid chromatography-time-of-flight mass spectrometry (HPLC-TOF MS) and gas chromatography-mass spectrometry (GC-MS) to characterize the metabolic alterations of the contents within the GI tract (stomach, duodenum, jejunum, ileum, cecum, colon, and rectum) in male Sprague-Dawley rats following 8 weeks of ethanol exposure. We obtained a snapshot of the distinct changes of the intestinal content metabolite composition in rats with ethanol exposure, which indicated a profound impact of ethanol consumption on the intestinal metabolome. Many metabolic pathways that are critical for host physiology were affected, including markedly altered bile acids, increased fatty acids and steroids, decreased carnitines and metabolites involved in lipid metabolism, a significant decrease of all amino acids and branched chain amino acids, and significantly decreased short chain fatty acids except for acetic acid, which rapidly elevated as a product of ethanol metabolism. These results provide an improved understanding of the systemic alteration of intestinal content metabolites in mammals and the interplay between the host and its complex resident microbiota and may aid in the design of new therapeutic strategies that target these interactions.

PLD1 Negatively Regulates Dendritic Branching

Neurons have characteristic dendritic arborization patterns that contribute to information processing. One essential component of dendritic arborization is the formation of a specific number of branches. Although intracellular pathways promoting dendritic growth and branching are being elucidated, the mechanisms that negatively regulate the branching of dendrites remain enigmatic. In this study, using gain-of-function and loss-of-function studies, we show that phospholipase D1 (PLD1) acts as a negative regulator of dendritic branching in cultured hippocampal neurons from embryonic day 18 rat embryos. Overexpression of wild-type PLD1 (WT-PLD1) decreases the complexity of dendrites, whereas knockdown or inhibition of PLD1 increases dendritic branching. We further demonstrated that PLD1 acts downstream of RhoA, one of the small Rho GTPases, to suppress dendritic branching. The restriction of dendritic branching by constitutively active RhoA (V14-RhoA) can be partially rescued by knockdown of PLD1. Moreover, the inhibition of dendritic branching by V14-RhoA and WT-PLD1 can be partially ameliorated by reducing the level of phosphatidic acid (PA), which is the enzymatic product of PLD1. Together, these results suggest that RhoA-PLD1-PA may represent a novel signaling pathway in the restriction of dendritic branching and may thus provide insight into the mechanisms of dendritic morphogenesis.

Factors contributing to the resistivity of a higher casein diet against choline deficiency-induced hyperhomocysteinemia in rats

The mechanism by which feeding a higher casein diet results in resistance to choline deprivation-induced hyperhomocysteinemia was investigated in rats. Plasma homocysteine concentration was significantly lower in rats fed a 30% casein diet (30C) than in rats fed a 10% casein diet (10C). Choline deprivation did not enhance plasma homocysteine concentration in rats fed 30C, while it significantly enhanced plasma homocysteine concentration in rats fed 10C. The choline deprivation-induced enhancement of plasma homocysteine concentration in rats fed 10C was significantly suppressed by methionine supplementation in a dose-dependent manner in the range of 0.1 to 0.3%, but the suppressive effect of methionine became smaller with an increase in supplementation level in the range of 0.3 to 0.5%. At a 0.5% supplementation level, methionine did not exhibit any suppressive effect on choline deprivation-induced hyperhomocysteinemia. The higher plasma homocysteine concentration in rats fed choline-deprived 10C+0.5% methionine was significantly decreased by concurrent supplementation with 0.32% glycine+0.94% serine to the level of rats fed 10C. Raising dietary total amino acid level by adding 3.61% branched-chain amino acids (BCAA)+4.5% acidic amino acids (AAA) to choline-deprived 10C+0.5% methionine+0.32% glycine+0.94% serine resulted in a further decrease in plasma homocysteine concentration to a level lower than the level in rats fed 10C. Choline deprivation-induced increases in hepatic S-adenosylhomocysteine and homocysteine concentrations were significantly suppressed by supplementation with glycine+serine and further suppressed by BCAA+AAA. Hepatic cystathionine β-synthase activity and its gene expression were significantly increased by BCAA+AAA. Hepatic triglyceride concentration changed in a manner similar to that of plasma homocysteine concentration. The results indicate that there are at least three factors contributing to the resistivity of rats fed a higher casein diet (30C) to choline deprivation-induced hyperhomocysteinemia, i.e., higher intake of methionine, higher intake of glycine and serine, and higher intake of other amino acids such as BCAA and AAA.

Age-related topographical metabolic signatures for the rat gastrointestinal contents

Symbiotic gut microbiota is essential for mammalian physiology and analyzing the metabolite compositions of gastrointestinal contents is vital for understanding the microbiome-host interactions. To understand the developmental dependence of the topographical metabolic signatures for the rat gastrointestinal contents, we systematically characterized the metabolite compositional variations of the contents in rat jejunum, ileum, cecum, and colon for two age-groups using (1)H NMR spectroscopy and multivariate analysis. Significant topographical metabolic variations were present for the jejunal, ileal, cecal, colonic contents, and feces, reflecting the absorption functions for each intestinal region and the gut microbiota therein. The concentrations of amino acids, lactate, creatine, choline, bile acids, uracil and urocanate decreased drastically from jejunal to ileal contents followed with steady decreases from cecal content to feces. Short-chain fatty acids (SCFAs) and arabinoxylan-related carbohydrates had highest levels in cecal content and feces, respectively. Such topographical metabolic signatures for the intestinal contents varied with animal age highlighted by the level changes for lactate, choline, taurine, amino acids, carbohydrates, keto-acids, and SCFAs. These findings provided essential information for the topographical metabolic variations in the gastrointestinal tract and demonstrated metabolic profiling as a useful approach for understanding host-microbiome interactions and functional status of the gastrointestinal regions.

Methionine and serine synergistically suppress hyperhomocysteinemia induced by choline deficiency, but not by guanidinoacetic acid, in rats fed a low casein diet

The effects of dietary supplementation with 0.5% methionine, 2.5% serine, or both on hyperhomocysteinemia induced by deprivation of dietary choline or by dietary addition of 0.5% guanidinoacetic acid (GAA) were investigated in rats fed a 10% casein diet. Hyperhomocysteinemia induced by choline deprivation was not suppressed by methionine alone and was only partially suppressed by serine alone, whereas it was completely suppressed by a combination of methionine and serine, suggesting a synergistic effect of methionine and serine. Fatty liver was also completely prevented by the combination of methionine and serine. Compared with methionine alone, the combination of methionine and serine decreased hepatic S-adenosylhomocysteine and homocysteine concentrations and increased hepatic betaine and serine concentrations and betaine-homocysteine S-methyltransferase activity. GAA-induced hyperhomocysteinemia was partially suppressed by methionine alone, but no interacting effect of methionine and serine was detected. In contrast, GAA-induced fatty liver was completely prevented by the combination of methionine and serine. These results indicate that a combination of methionine and serine is effective in suppressing both hyperhomocysteinemia and fatty liver induced by choline deprivation, and that methionine alone is effective in suppressing GAA-induced hyperhomocysteinemia partially.

Uptake and utilization of arachidonic acid in infective larvae of Angiostrongylus cantonensis

Infective larvae of Angiostrongylus cantonensis may take up and incorporate exogenous arachidonic acid into their lipid pool. By scintillation counting, uptake and incorporation were determined to be time dependent. Arachidonic acid was mainly incorporated into phospholipid (56.8%) and neutral lipid (22.4%) pools. In the neutral lipids, 64.0% was diglyceride and 36.0% triglyceride. Phosphatidylcholine was the predominant fatty acid in the phospholipid pool. In addition to the release of leukotriene B4, the parasite was found to generate radiolabelled CO2 after incubation with [U-14C]arachidonate. Moreover, enzymatic analysis of crude extracts revealed the presence of acyl-CoA dehydrogenase (short and long chain), thiolase, enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase. These findings suggest that infective larvae of A. cantonensis not only take up and incorporate exogenous arachidonic acid into their lipid pool, but may also utilize the fatty acid through a functional β-oxidation pathway.

Involvement of human choline kinase alpha and beta in carcinogenesis: a different role in lipid metabolism and biological functions

We have summarized here the importance of ChoKα1 in human carcinogenesis. ChoKα1 displays its oncogenic activity through activation of specific signaling pathways that influence on cell proliferation and survival. It is overexpressed in a large number of human tumors with an incidence of 40-60% of all tumors investigated. Currently, there is an active effort in the development of strategies to knockdown the activity of ChoKα through specific siRNA or small molecules inhibitors. Results from genetic silencing or from treatment with MN58b, a well characterized ChoKα inhibitor showing antiproliferative and antitumoral effect in mice xenografts, provide strong support to this concept, indicating that the design of new antitumoral drugs must be selective against this isoform. However, affecting the other two known isoforms of ChoK may have also therapeutic consequences since the physiologically active form of ChoK may be constituted by homo or heterodimers. Furthermore, alteration of the ChoKβ activity might lead to a change in the lipid content of the cells of particular tissues such as skeletal muscle as described in the ChoKβ null mice (Sher et al., 2006). Finally, the identification of the ChoKα1 isoform as an excellent novel tool for the diagnosis and prognosis of cancer patients may have clinical consequences of immediate usefulness. On one hand, the use of specific monoclonal antibodies against ChoKα1 as a tool for diagnosis in paraffin embedded samples from patient biopsies, through standard immunohistochemistry techniques, can now be achieved (Gallego-Ortega et al., 2006). On the other hand, it has been recently described the prognostic value of determination of ChoKα1 expression levels in non-small cell lung cancer using real time quantitative PCR technology (Ramírez de Molina et al., 2007). Therefore, further research should be supported on the utility of ChoK isoforms as a promising area to improve cancer diagnosis and treatment.

Transport and metabolism of radiolabeled choline in hepatocellular carcinoma

Altered choline (Cho) metabolism in cancerous cells can be used as a basis for molecular imaging with PET using radiolabeled Cho. In this study, the metabolism of tracer Cho was investigated in a woodchuck hepatocellular carcinoma (HCC) cell line (WCH17) and in freshly derived rat hepatocytes. The transporter responsible for [(11)C]-Cho uptake in HCC was also characterized in WCH17 cells. The study helped to define the specific mechanisms responsible for radio-Cho uptake seen on the PET images of primary liver cancer such as HCC. Cells were pulsed with [(14)C]-Cho for 5 min and chased for varying durations in cold media to simulate the rapid circulation and clearance of [(11)C]-Cho. Radioactive metabolites were extracted and analyzed by radio-HPLC and radio-TLC. The Cho transporter (ChoT) was characterized in WCH17 cells. WCH17 cells showed higher (14)C uptake than rat primary hepatocytes. [(14)C]-Phosphocholine (PC) was the major metabolite in WCH17. In contrast, the intracellular Cho in primary hepatocytes was found to be oxidized to betaine (partially released into media) and, to a lesser degree, phosphorylated to PC. [(14)C]-Cho uptake by WCH17 cells was found to have both facilitative transport and nonfacilitative diffusion components. The facilitative transport was characterized by Na(+) dependence and low affinity (K(m) = 28.59 ± 6.75 μM) with partial energy dependence. In contrast, ChoT in primary hepatocytes is Na(+) independent and low affinity. Our data suggest that transport and phosphorylation of Cho are responsible for the tracer accumulation during [(11)C]-Cho PET imaging of HCC. WCH17 cells incorporate [(14)C]-Cho preferentially into PC. Conversion of [(14)C]-PC into phosphatidylcholine occurred slowly in vitro. Basal oxidation and phosphorylation activities in surrounding hepatic tissue contribute to the background seen in [(11)C]-Cho PET images.

Choline kinase overexpression increases invasiveness and drug resistance of human breast cancer cells

A direct correlation exists between increased choline kinase (Chk) expression, and the resulting increase of phosphocholine levels, and histological tumor grade. To better understand the function of Chk and choline phospholipid metabolism in breast cancer we have stably overexpressed one of the two isoforms of Chk-alpha known to be upregulated in malignant cells, in non-invasive MCF-7 human breast cancer cells. Dynamic tracking of cell invasion and cell metabolism were studied with a magnetic resonance (MR) compatible cell perfusion assay. The MR based invasion assay demonstrated that MCF-7 cells overexpressing Chk-alpha (MCF-7-Chk) exhibited an increase of invasion relative to control MCF-7 cells (0.84 vs 0.3). Proton MR spectroscopy studies showed significantly higher phosphocholine and elevated triglyceride signals in Chk overexpressing clones compared to control cells. A test of drug resistance in MCF-7-Chk cells revealed that these cells had an increased resistance to 5-fluorouracil and higher expression of thymidylate synthase compared to control MCF-7 cells. To further characterize increased drug resistance in these cells, we performed rhodamine-123 efflux studies to evaluate drug efflux pumps. MCF-7-Chk cells effluxed twice as much rhodamine-123 compared to MCF-7 cells. Chk-alpha overexpression resulted in MCF-7 human breast cancer cells acquiring an increasingly aggressive phenotype, supporting the role of Chk-alpha in mediating invasion and drug resistance, and the use of phosphocholine as a biomarker of aggressive breast cancers.

Crystal structures of human choline kinase isoforms in complex with hemicholinium-3: single amino acid near the active site influences inhibitor sensitivity

Human choline kinase (ChoK) catalyzes the first reaction in phosphatidylcholine biosynthesis and exists as ChoKalpha (alpha1 and alpha2) and ChoKbeta isoforms. Recent studies suggest that ChoK is implicated in tumorigenesis and emerging as an attractive target for anticancer chemotherapy. To extend our understanding of the molecular mechanism of ChoK inhibition, we have determined the high resolution x-ray structures of the ChoKalpha1 and ChoKbeta isoforms in complex with hemicholinium-3 (HC-3), a known inhibitor of ChoK. In both structures, HC-3 bound at the conserved hydrophobic groove on the C-terminal lobe. One of the HC-3 oxazinium rings complexed with ChoKalpha1 occupied the choline-binding pocket, providing a structural explanation for its inhibitory action. Interestingly, the HC-3 molecule co-crystallized with ChoKbeta was phosphorylated in the choline binding site. This phosphorylation, albeit occurring at a very slow rate, was confirmed experimentally by mass spectroscopy and radioactive assays. Detailed kinetic studies revealed that HC-3 is a much more potent inhibitor for ChoKalpha isoforms (alpha1 and alpha2) compared with ChoKbeta. Mutational studies based on the structures of both inhibitor-bound ChoK complexes demonstrated that Leu-401 of ChoKalpha2 (equivalent to Leu-419 of ChoKalpha1), or the corresponding residue Phe-352 of ChoKbeta, which is one of the hydrophobic residues neighboring the active site, influences the plasticity of the HC-3-binding groove, thereby playing a key role in HC-3 sensitivity and phosphorylation.

Chronic prehepatic portal hypertension in the rat: is it a type of metabolic inflammatory syndrome?

BACKGROUND

A progressive development of hepatic steatosis with an increase in the lipid hepatocyte content and the formation of megamitochondria have been demonstrated in rats with prehepatic portal hypertension. The aim of this study is to verify the existence of liver and serum lipid metabolism impairments in rats with long-term (2 years) portal hypertension.

METHODS

Male Wistar rats: Control (n = 10) and with prehepatic portal hypertension by triple partial portal vein ligation (n = 9) were used. Liver content of Triglycerides (TG), phospholipids (PL) and cholesterol and serum cholesterol, lipoproteins (HDL and LDL), TG, glucose and Lipid Binding Protein (LBP) were assayed with specific colorimetric commercial kits. Serum levels of insulin and somatostatin were assayed by RIA.

RESULTS

The liver content of TG (6.30 +/- 1.95 vs. 4.17 +/- 0.59 microg/ml; p < 0.01) and cholesterol (1.48 +/- 0.15 vs. 1.10 +/- 0.13 microg/ml; p < 0.001) increased in rats with portal hypertension. The serum levels of cholesterol (97.00+26.02 vs. 114.78 +/- 37.72 mg/dl), TG (153.41 +/- 80.39 vs. 324.39 +/- 134.9 mg/dl; p < 0.01), HDL (20.45 +/- 5.14 vs. 55.15 +/- 17.47 mg/dl; p < 0.001) and somatostatin (1.32 +/- 0.31 vs. 1.59 +0.37 mg/dl) decreased, whereas LDL (37.83 +/- 15.39 vs. 16.77 +/- 6.81 mg/dl; p < 0.001) and LBP (308.47 +/- 194.53 vs. 60.27 +/- 42.96 ng/ml; p < 0.001) increased.

CONCLUSION

Portal hypertension in the rat presents changes in the lipid and carbohydrate metabolisms similar to those produced in chronic inflammatory conditions and sepsis in humans. These underlying alterations could be involved in the development of hepatic steatosis and, therefore, in those described in the metabolic syndrome in humans.

Hypoxia regulates choline kinase expression through hypoxia-inducible factor-1 alpha signaling in a human prostate cancer model

The intensity of the total choline (tCho) signal in spectroscopic images of tumors is spatially heterogeneous. The likewise heterogeneous physiologic tumor microenvironment may contribute to this heterogeneity. We therefore investigated the relationship between hypoxia, choline metabolites, and choline kinase (Chk) in a human prostate cancer model. Human PC-3 prostate cancer cells were engineered to express enhanced green fluorescent protein (EGFP) under hypoxic conditions. These PC-3-5HRE-EGFP cells were characterized in culture and as tumors transplanted in mice using (1)H magnetic resonance spectroscopy (MRS) and MRS imaging (MRSI) combined with EGFP fluorescence microscopy and imaging. Hypoxic EGFP-fluorescing tumor regions colocalized with regions of high tCho in combined MRSI and optical imaging studies. Cellular phosphocholine (PC) and tCho concentrations as well as Chk expression levels significantly increased following exposure of PC-3 cells to hypoxia. A putative promoter region located 5' of the translation start site of the human chk-alpha gene was cloned and luciferase (Luc)-based reporter vector constructs were generated. Luc reporter assays provided evidence that some of the putative hypoxia response elements (HRE) within this putative chk-alpha promoter region functioned in vitro. Chromatin immunoprecipitation assays using an antibody against hypoxia-inducible factor (HIF)-1 alpha showed that HIF-1 can directly bind this region of the endogenous chk-alpha promoter in hypoxic PC-3-5HRE-EGFP cells. These data suggest that HIF-1 activation of HREs within the putative chk-alpha promoter region can increase Chk-alpha expression within hypoxic environments, consequently increasing cellular PC and tCho levels within these environments.

Hepatic lipid metabolism changes in short- and long-term prehepatic portal hypertensive rats

AIM: To verify the impairment of the hepatic lipid metabolism in prehepatic portal hypertension.

METHODS: The concentrations of free fatty acids, diacylglycerol, triglycerides, and phospholipids were assayed by using D-[U-¹⁴C] glucose incorporation in the different lipid fractions and thin-layer chromatography and cholesterol was measured by spectrophotometry, in liver samples of Wistar rats with partial portal vein ligation at short- (1 mo) and long-term (1 year) (i.e. portal hypertensive rats) and the control rats.

RESULTS: In the portal hypertensive rats, liver phospholipid synthesis significantly decreased (7.42 ± 0.50 vs 4.70 ± 0.44 nCi/g protein; P < 0.01) and was associated with an increased synthesis of free fatty acids (2.08 ± 0.14 vs 3.36 ± 0.33 nCi/g protein; P < 0.05), diacylglycerol (1.93 ± 0.2 vs 2.26 ± 0.28 nCi/g protein), triglycerides (2.40 ± 0.30 vs 4.49 ± 0.15 nCi/g protein) and cholesterol (24.28 ± 2.12 vs 57.66 ± 3.26 mg/g protein; P < 0.01).

CONCLUSION: Prehepatic portal hypertension in rats impairs the liver lipid metabolism. This impairment consists in an increase in lipid deposits (triglycerides, diacylglycerol and cholesterol) in the liver, accompanied by a decrease in phospholipid synthesis.

Adverse hepatic and cardiac responses to rosiglitazone in a new mouse model of type 2 diabetes: Relation to dysregulated phosphatidylcholine metabolism

Given the heterogeneous nature of metabolic dysfunctions associated with insulin resistance and type 2 diabetes (T2D), a single pharmaceutical cannot be expected to provide complication-free therapy in all patients. Thiazolidinediones (TZD) increase insulin sensitivity, reduce blood glucose and improve cardiovascular parameters. However, in addition to increasing fat mass, TZD have the potential in certain individuals to exacerbate underlying hepatosteatosis and diabetic cardiomyopathy. Pharmacogenetics should allow patient selection to maximize therapy and minimize risk. To this end, we have combined two genetically diverse inbred strains, NON/Lt and NZO/Lt, to produce a "negative heterosis" increasing the frequency of T2D in F1 males. As in humans with T2D, treatment of diabetic and hyperlipemic F1 males with rosiglitazone (Rosi), an agonist of peroxisome proliferator-activated gamma receptor (PPARgamma), reverses these disease phenotypes. However, the hybrid genome perturbed both major pathways for phosphatidylcholine (PC) biosynthesis in the liver, and effected remarkable alterations in the composition of cardiolipin in heart mitochondria. These metabolic defects severely exacerbated an underlying hepatosteatosis and increased levels of the adipokine, plasminogen activator inhibitor-1 (PAI-1), a risk factor for cardiovascular events. This model system demonstrates how the power of mouse genetics can be used to identify the metabolic signatures of individuals who may be prone to drug side effects.

Fundamental research is the basis for understanding and treatment of many human diseases

There are numerous examples of how fundamental research has been required to understand and treat human disease. This article focuses on three human diseases of lipid metabolism in which advancements in understanding and treatment would not have been possible without basic research. Fabry disease is an inherited metabolic disorder caused by the lack of a specific enzyme in glycosphingolipid catabolism. Cardiovascular disease is a complex and multifactorial disease but as many as half of the cases can be attributed to abnormal levels of plasma cholesterol. The incidence of liver disease is increasing due to the current epidemic of obesity. It is only recently that curiosity-driven research has yielded valuable insight into the mechanism by which liver disease evolves.

RNA interference-mediated choline kinase suppression in breast cancer cells induces differentiation and reduces proliferation

Choline kinase is overexpressed in breast cancer cells and activated by oncogenes and mitogenic signals, making it a potential target for cancer therapy. Here, we have examined, for the first time, the effects of RNA interference (RNAi)-mediated down-regulation of choline kinase in nonmalignant and malignant human breast epithelial cell lines using magnetic resonance spectroscopy (MRS) as well as molecular analyses of proliferation and differentiation markers. RNAi knockdown of choline kinase reduced proliferation, as detected by proliferating cell nuclear antigen and Ki-67 expression, and promoted differentiation, as detected by cytosolic lipid droplet formation and expression of galectin-3. The functional importance of RNAi-mediated choline kinase down-regulation on choline phospholipid metabolism was confirmed by the significant reduction of phosphocholine detected by MRS. These results strongly support the targeting of choline kinase in breast cancer cells with RNAi and show the potential ability of noninvasive MRS to detect and evaluate future treatments incorporating such strategies.

Effect of S-adenosylmethionine on Age-induced Hepatocyte Damage in Old Wistar Rats

Aging is accompanied by changes in the morphology and physiology of organs and tissues, such as the liver. This process might be due to the accumulation of oxidative damage induced by reactive oxygen (ROS) and reactive nitrogen species (RNS). Hepatocytes are very rich in mitochondria and have a high respiratory rate, so they are exposed to large amounts of ROS and permanent oxidative stress. S-Adenosylmethionine (SAMe) is an endogenous metabolite that has shown to exert protective effects on different experimental pathological models in which free radicals are involved. The aim of this study was to investigate the effect of SAMe on age-induced damage in hepatocytes. For this purpose, male and female Wistar rats of 18 and 2 months of age were used. Cells were isolated and, after incubation in the presence or in the absence of SAMe, different parameters were measured. Aging induced a significant increase in nitric oxide, carbon monoxide and cGMP, and a reduction in reduced glutathione, ATP and phosphatidylcholine synthesis, as well as in methionine- adenosyl-transferase and methyl-transferase activities. Incubation of old cells with SAMe prevented all these age-related changes, reaching values in some of the parameters similar to those found in young animals. In conclusion, SAMe seems to have beneficial effects against age-induced damage in hepatocytes.

Review of the carcinogenic activity of diethanolamine and evidence of choline deficiency as a plausible mode of action

Diethanolamine (DEA) is a chemical used widely in a number of industries and is present in many consumer products. Studies by the National Toxicology Program (NTP) have indicated that lifetime dermal exposure to DEA increased the incidence and multiplicity of liver tumors in mice, but not in rats. In addition, DEA was not carcinogenic when tested in the Tg.Ac transgenic mouse model. Short-term genotoxicity tests have yielded negative results. In view of these apparent inconsistencies, we have critically evaluated the NTP studies and other data relevant to assessing the carcinogenic potential of DEA. The available data indicate that DEA induces mouse liver tumors by a non-genotoxic mode of action that involves its ability to cause choline deficiency. The following experimental evidence supports this hypothesis. DEA decreased the hepatic choline metabolites and S-adenosylmethionine levels in mice, similar to those observed in choline-deficient mice. In contrast, DEA had no effect in the rat, a species in which it was not carcinogenic at a maximum tolerated dose level. In addition, a consistent dose-effect relationship had been established between choline deficiency and carcinogenic activity since all DEA dosages that induced tumors in the NTP studies were also shown to cause choline deficiency. DEA decreased phosphatidylcholine synthesis by blocking the cellular uptake of choline in vitro, but these events did not occur in the presence of excess choline. Finally, DEA induced transformation in the Syrian hamster embryo cells, increased S-phase DNA synthesis in mouse hepatocytes, and decreased gap junctional intracellular communication in primary cultured mouse and rat hepatocytes, but all these events were prevented with choline supplementation. Since choline is an essential nutrient in mammals, this mode of action is qualitatively applicable to humans. However, there are marked species differences in susceptibility to choline deficiency, with rats and mice being far more susceptible than other mammalian species including humans. These differences are attributed to quantitative differences in the enzyme kinetics controlling choline metabolism. The fact that DEA was carcinogenic in mice but not in rats also has important implications for human risk assessment. DEA has been shown to be less readily absorbed across rat and human skin than mouse skin. Since a no observed effect level for DEA-induced choline deficiency in mice has been established to be 10 mg/kg/d, this indicates that there is a critical level of DEA that must be attained in order to affect choline homeostasis. The lack of a carcinogenic response in rats suggests that exposure to DEA did not reach this critical level. Since rodents are far more sensitive to choline deficiency than humans, it can be concluded that the hepatocarcinogenic effect of DEA in mice is not predictive of similar susceptibility in humans.

Effects of choline deficiency and methotrexate treatment upon rat liver

Choline deficiency and treatment with methotrexate (MTX) both are associated with fatty infiltration of the liver. Choline, methionine, and folate metabolism are interrelated and converge at the regeneration of methionine from homocysteine. MTX perturbs folate metabolism, and it is possible that it also influences choline metabolism. We fed rats a choline deficient diet for 2 weeks and/or treated them with methotrexate (MTX; 0.1 mg/kg daily). Choline deficiency lowered hepatic concentrations of choline (to 43% control), phosphocholine (PCho; to 18% control), glycerophosphocholine (GroPCho; to 46% control), betaine (to 30% control), phosphatidylcholine (PtdCho; to 62% control), methionine (to 80% control), and S-adenosylmethionine (AdoMet; to 57% control), while S-adenosylhomocysteine (AdoHcy) and triacylglycerol concentrations increased (to 126% and 319% control, respectively). MTX treatment alone lowered hepatic concentrations of PCho (to 48% control), GroPCho (to 69% control), betaine (to 55% control), and AdoMet (to 75% control). The addition of MTX treatment to choline deficiency resulted in a larger decrease in AdoMet concentrations (to 75% control) and larger increases in AdoHcy and triacylglycerol concentrations (to 150% and 500% control, respectively) than was observed in choline deficiency alone. Livers from MTX-treated animals used radiolabeled choline to make the same metabolites as did livers from controls (most of the label was converted to PCho and betaine). In choline deficient animals, most of the labeled choline was converted to PtdCho. Therefore, MTX depleted hepatic PCho, GroPCho, and betaine by a mechanism that was different from that of choline deficiency. MTX increased the extent of fatty infiltration of the liver in choline deficient rats, and choline deficiency and MTX treatment damaged hepatocytes as measured by leakage of alanine aminotransferase activity. Our data are consistent with the hypothesis that the fatty infiltration of the liver associated with MTX treatment occurs because of a disturbance in choline metabolism.

An integrative metabolism approach identifies stearoyl‐CoA desaturase as a target for an arachidonate‐enriched diet

Epidemiological studies have correlated diets containing higher intakes of PUFA with lower rates of chronic metabolic diseases. The molecular mechanisms regulated by the consumption of PUFA were examined by using an integrative metabolism approach assaying the liver transcriptome and lipid-metabolome of mice fed a control diet, an arachidonate (AA)-enriched fungal oil, an eicosapentaenoic (EPA)/docosahexaenoic (DHA)-enriched fish oil, or a combination of the two oils. Hepatic gene transcription and fatty acid (FA) metabolism were significantly altered by diets enriched with AA, as revealed by global error assessment and singular value decomposition (SVD) analysis, respectively. SVD analysis of the lipid data, reinforced with transcriptomics, suggests that the chronic feeding of AA modulates molecular endpoints similar to those previously reported in the obesity-resistant SCD1-/- mouse, namely, genes involved in lipid oxidation/synthesis and the significant changes in FA metabolism stemming from a repressed SCD1 activity. Specifically, the total levels and FA composition of several phospholipid (PL) species were significantly changed, with phosphatidylcholine (PC) demonstrating the greatest alterations. Reduced PC levels were linked to decreased expression of enzymes in PC biosynthesis (choline kinase, -2.2-fold; glycerol-3-phosphate acyltransferase, -2.0-fold). Alterations in PL-FA composition were related to decreased expression of FA biosynthetic genes [fatty acid synthetase, -3.7-fold; stearoyl-CoA desaturase-1 (SCD1), -1.8-fold]. Lower hepatic SCD1 gene expression levels were reflected in various aspects of FA metabolism through increased concentrations of palmitic (fungal oil, +45%; combination, +106%) and stearic acids (fungal oil, +60%; combination, +63%) in PC. Importantly, an integrated approach showed that these effects were not attenuated by the addition of an EPA/DHA-enriched fish oil, thereby identifying a previously unrecognized and distinct role for AA in the regulation of hepatic lipid metabolism.