Endothelial lipase mediates efficient lipolysis of triglyceride-rich lipoproteins.

Triglyceride-rich lipoproteins (TRLs) are circulating reservoirs of fatty acids used as vital energy sources for peripheral tissues. Lipoprotein lipase (LPL) is a predominant enzyme mediating triglyceride (TG) lipolysis and TRL clearance to provide fatty acids to tissues in animals. Physiological and human genetic evidence support a primary role for LPL in hydrolyzing TRL TGs. We hypothesized that endothelial lipase (EL), another extracellular lipase that primarily hydrolyzes lipoprotein phospholipids may also contribute to TRL metabolism. To explore this, we studied the impact of genetic EL loss-of-function on TRL metabolism in humans and mice. Humans carrying a loss-of-function missense variant in LIPG, p.Asn396Ser (rs77960347), demonstrated elevated plasma TGs and elevated phospholipids in TRLs, among other lipoprotein classes. Mice with germline EL deficiency challenged with excess dietary TG through refeeding or a high-fat diet exhibited elevated TGs, delayed dietary TRL clearance, and impaired TRL TG lipolysis in vivo that was rescued by EL reconstitution in the liver. Lipidomic analyses of postprandial plasma from high-fat fed Lipg-/- mice demonstrated accumulation of phospholipids and TGs harboring long-chain polyunsaturated fatty acids (PUFAs), known substrates for EL lipolysis. In vitro and in vivo, EL and LPL together promoted greater TG lipolysis than either extracellular lipase alone. Our data positions EL as a key collaborator of LPL to mediate efficient lipolysis of TRLs in humans and mice.

Dietary lysophosphatidylcholine-EPA enriches both EPA and DHA in the brain: potential treatment for depression.

EPA and DHA protect against multiple metabolic and neurologic disorders. Although DHA appears more effective for neuroinflammatory conditions, EPA is more beneficial for depression. However, the brain contains negligible amounts of EPA, and dietary supplements fail to increase it appreciably. We tested the hypothesis that this failure is due to absorption of EPA as triacylglycerol, whereas the transporter at the blood-brain barrier requires EPA as lysophosphatidylcholine (LPC). We compared tissue uptake in normal mice gavaged with equal amounts (3.3 µmol/day) of either LPC-EPA or free EPA (surrogate for current supplements) for 15 days and also measured target gene expression. Compared with the no-EPA control, LPC-EPA increased brain EPA >100-fold (from 0.03 to 4 µmol/g); free EPA had little effect. Furthermore, LPC-EPA, but not free EPA, increased brain DHA 2-fold. Free EPA increased EPA in adipose tissue, and both supplements increased EPA and DHA in the liver and heart. Only LPC-EPA increased EPA and DHA in the retina, and expression of brain-derived neurotrophic factor, cyclic AMP response element binding protein, and 5-hydroxy tryptamine (serotonin) receptor 1A in the brain. These novel results show that brain EPA can be increased through diet. Because LPC-EPA increased both EPA and DHA in the brain, it may help in the treatment of depression as well as neuroinflammatory diseases, such as Alzheimer's disease.

Molecular-Scale Biophysical Modulation of an Endothelial Membrane by Oxidized Phospholipids.

The influence of two bioactive oxidized phospholipids on model bilayer properties, membrane packing, and endothelial cell biomechanics was investigated computationally and experimentally. The truncated tail phospholipids, 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC) and 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphocholine (PGPC), are two major oxidation products of the unsaturated phospholipid 1-palmitoyl-2-arachidonoyl-sn-glycero-phosphocholine. A combination of coarse-grained molecular dynamics simulations, Laurdan multiphoton imaging, and atomic force microscopy microindentation experiments was used to determine the impact of POVPC and PGPC on the structure of a multicomponent phospholipid bilayer and to assess the consequences of their incorporation on membrane packing and endothelial cell stiffness. Molecular simulations predicted differential bilayer perturbation effects of the two oxidized phospholipids based on the chemical identities of their truncated tails, including decreased bilayer packing, decreased bilayer bending modulus, and increased water penetration. Disruption of lipid order was consistent with Laurdan imaging results indicating that POVPC and PGPC decrease the lipid packing of both ordered and disordered membrane domains. Computational predictions of a larger membrane perturbation effect by PGPC correspond to greater stiffness of PGPC-treated endothelial cells observed by measuring cellular elastic moduli using atomic force microscopy. Our results suggest that disruptions in membrane structure by oxidized phospholipids play a role in the regulation of overall endothelial cell stiffness.

Enhanced incorporation of dietary DHA into lymph phospholipids by altering its molecular carrier.

Several previous studies indicated that for optimal uptake by the brain, docosahexaenoic acid (DHA) should be present as phospholipid in the plasma. However most of dietary DHA is absorbed as triacylglycerol (TAG) because it is released as free fatty acid during digestion of either TAG-DHA (fish oil) or sn-2-DHA phospholipid (krill oil), and subsequently incorporated into TAG of chylomicrons. We tested the hypothesis that the absorption of DHA as phospholipid can be increased if it is present in the sn-1 position of dietary phospholipid or in lysophosphatidylcholine (LPC), because it would escape the hydrolysis by pancreatic phospholipase A2. We infused micelle containing the DHA either as LPC or as free acid, into the duodenum of lymph cannulated rats, and analyzed the chylomicrons and HDL of the lymph for the DHA-containing lipids. The results show that while the total amount of DHA absorbed was comparable from the two types of micelle, the percentage of DHA recovered in lymph phospholipids was 5 times greater with LPC-DHA, compared to free DHA. Furthermore, the amount of DHA recovered in lymph HDL was increased by 2-fold when LPC-DHA micelle was infused. These results could potentially lead to a novel strategy to increase brain DHA levels through the diet.

Regulation of hepatic lipase activity by sphingomyelin in plasma lipoproteins.

Hepatic lipase (HL) is an important enzyme in the clearance of triacylglycerol (TAG) from the circulation, and has been proposed to have pro-atherogenic as well as anti-atherogenic properties. It hydrolyzes both phospholipids and TAG of lipoproteins, and its activity is negatively correlated with HDL levels. Although it is known that HL acts preferentially on HDL lipids, the basis for this specificity is not known, since it does not require any specific apoprotein for activity. In this study, we tested the hypothesis that sphingomyelin (SM), whose concentration is much higher in VLDL and LDL compared to HDL, is an inhibitor of HL, and that this could explain the lipoprotein specificity of the enzyme. The results presented show that the depletion of SM from normal lipoproteins activated the HL roughly in proportion to their SM content. SM depletion stimulated the hydrolysis of both phosphatidylcholine (PC) and TAG, although the PC hydrolysis was stimulated more. In the native lipoproteins, HL showed specificity for PC species containing polyunsaturated fatty acids at sn-2 position, and produced more unsaturated lyso PC species. The enzyme also showed preferential hydrolysis of certain TAG species over others. SM depletion affected the specificity of the enzyme towards PC and TAG species modestly. These results show that SM is a physiological inhibitor of HL activity in lipoproteins and that the specificity of the enzyme towards HDL is at least partly due to its low SM content.

ApoE derived from adipose tissue does not suppress atherosclerosis or correct hyperlipidemia in apoE knockout mice.

The synthesis of apoE by adipocytes has profound effects on adipose tissue lipid flux and gene expression. Using adipose tissue transplantation from wild-type (WT) to apoE knockout (EKO) mice, we show that adipose tissue also contributes to circulating apoE. Different from circulating apoE produced by bone marrow transplantation (BMT), however, adipose tissue-derived apoE does not correct hyperlipidemia or suppress atherosclerosis. ApoE secreted by macrophages has a more acidic isoform distribution, and it increases binding of reconstituted VLDL particles to hepatocytes and fibroblasts more effectively than apoE secreted by adipocytes. The incremental binding can be entirely accounted for by binding to the LDL receptor. After BMT into EKO hosts, plasma cholesterol and macrophage-derived apoE are largely within IDL/LDL- and HDL-sized particles. After adipose tissue transplantation, most cholesterol and adipocyte apoE remain in VLDL. After BMT, circulating apoE no longer demonstrates predominance of acidic isoforms compared with that circulating after fat transplantation. In conclusion, fat transplantation provides circulating apoE levels similar to those provided by bone marrow transplantation, but it does not suppress hyperlipidemia or atherosclerosis. A potential mechanism contributing to this difference is differential binding to cell surface lipoprotein receptors.

Improvement of retinal function in Alzheimer disease-associated retinopathy by dietary lysophosphatidylcholine-EPA/DHA.

Alzheimer disease (AD) is the most prevalent cause of dementia in the elderly. Although impaired cognition and memory are the most prominent features of AD, abnormalities in visual functions often precede them, and are increasingly being used as diagnostic and prognostic markers for the disease. Retina contains the highest concentration of the essential fatty acid docosahexaenoic acid (DHA) in the body, and its deficiency is associated with several retinal diseases including diabetic retinopathy and age related macular degeneration. In this study, we tested the hypothesis that enriching retinal DHA through a novel dietary approach could ameliorate symptoms of retinopathy in 5XFAD mice, a widely employed model of AD. The results show that 5XFAD mice have significantly lower retinal DHA compared to their wild type littermates, and feeding the lysophosphatidylcholine (LPC) form of DHA and eicosapentaenoic acid (EPA) rapidly normalizes the DHA levels, and increases retinal EPA by several-fold. On the other hand, feeding similar amounts of DHA and EPA in the form of triacylglycerol had only modest effects on retinal DHA and EPA. Electroretinography measurements after 2 months of feeding the experimental diets showed a significant improvement in a-wave and b-wave functions by the LPC-diet, whereas the TAG-diet had only a modest benefit. Retinal amyloid ß levels were decreased by about 50% by the LPC-DHA/EPA diet, and by about 17% with the TAG-DHA/EPA diet. These results show that enriching retinal DHA and EPA through dietary LPC could potentially improve visual abnormalities associated with AD.

The role of oxysterols in control of endothelial stiffness.

Endothelial dysfunction is a key step in atherosclerosis development. Our recent studies suggested that oxLDL-induced increase in endothelial stiffness plays a major role in dyslipidemia-induced endothelial dysfunction. In this study, we identify oxysterols, as the major component of oxLDL, responsible for the increase in endothelial stiffness. Using Atomic Force Microscopy to measure endothelial elastic modulus, we show that endothelial stiffness increases with progressive oxidation of LDL and that the two lipid fractions that contribute to endothelial stiffening are oxysterols and oxidized phosphatidylcholines, with oxysterols having the dominant effect. Furthermore, endothelial elastic modulus increases as a linear function of oxysterol content of oxLDL. Specific oxysterols, however, have differential effects on endothelial stiffness with 7-ketocholesterol and 7α-hydroxycholesterol, the two major oxysterols in oxLDL, having the strongest effects. 27-hydroxycholesterol, found in atherosclerotic lesions, also induces endothelial stiffening. For all oxysterols, endothelial stiffening is reversible by enriching the cells with cholesterol. oxLDL-induced stiffening is accompanied by incorporation of oxysterols into endothelial cells. We find significant accumulation of three oxysterols, 7α-hydroxycholesterol, 7ß-hydroxycholesterol, and 7-ketocholesterol, in mouse aortas of dyslipidemic ApoE⁻/⁻ mice at the early stage of atherosclerosis. Remarkably, these are the same oxysterols we have identified to induce endothelial stiffening.

Incorporation profiles of conjugated linoleic acid isomers in cell membranes and their positional distribution in phospholipids.

Although the conjugated linoleic acids (CLA) have several isomer-specific biological effects including anti-carcinogenic and anti-adipogenic effects, their mechanisms of action remain unclear. To determine their potential effects on membrane structure and function, we studied the incorporation profiles of four CLA isomers (trans-10 cis-12 (A), trans-9 trans-11 (B), cis-9 trans-11 (C), and cis-9 cis-11 (D)) in CHO and HepG2 cells. All four isomers were incorporated into cellular lipids as efficiently as linoleic acid (LA), with the majority of the incorporated CLA present in membrane rafts. Of the four isomers, only CLA-A increased the cholesterol content of the raft fraction. Over 50% of the incorporated CLAs were recovered in phosphatidylcholine of CHO cells, but in HepG2 the neutral lipids contained the majority of CLA. The desaturation index (18:1/18:0 and 16:1/16:0) was reduced by CLA-A, but increased by CLA-B, the effects being apparent mostly in raft lipids. The Δ9 desaturase activity was inhibited by CLAs A and C. Unlike LA, which was mostly found in the sn-2 position of phospholipids, most CLAs were also incorporated significantly into the sn-1 position in both cell types. These studies show that the incorporation profiles of CLA isomers differ significantly from that of LA, and this could lead to alterations in membrane function, especially in the raft-associated proteins.

Role of Lysocardiolipin Acyltransferase in Cigarette Smoke-Induced Lung Epithelial Cell Mitochondrial ROS, Mitochondrial Dynamics, and Apoptosis.

Cigarette smoke is the primary cause of Chronic Obstructive Pulmonary Disorder (COPD). Cigarette smoke extract (CSE)-induced oxidative damage of the lungs results in mitochondrial dysfunction and apoptosis of epithelium. Mitochondrial cardiolipin (CL) present in the inner mitochondrial membrane plays an important role in mitochondrial function, wherein its fatty acid composition is regulated by lysocardiolipin acyltransferase (LYCAT). In this study, we investigated the role of LYCAT expression and activity in mitochondrial oxidative stress, mitochondrial dynamics, and lung epithelial cell apoptosis. LYCAT expression was increased in human lung specimens from smokers, and cigarette smoke-exposed-mouse lung tissues. Cigarette smoke extract (CSE) increased LYCAT mRNA levels and protein expression, modulated cardiolipin fatty acid composition, and enhanced mitochondrial fission in the bronchial epithelial cell line, BEAS-2B in vitro. Inhibition of LYCAT activity with a peptide mimetic, attenuated CSE-mediated mitochondrial (mt) reactive oxygen species (ROS), mitochondrial fragmentation, and apoptosis, while MitoTEMPO attenuated CSE-induced MitoROS, mitochondrial fission and apoptosis of BEAS-2B cells. Collectively, these findings suggest that increased LYCAT expression promotes MitoROS, mitochondrial dynamics and apoptosis of lung epithelial cells. Given the key role of LYCAT in mitochondrial cardiolipin remodeling and function, strategies aimed at inhibiting LYCAT activity and ROS may offer an innovative approach to minimize lung inflammation caused by cigarette smoke.

Differential effects of conjugated linoleic acid isomers on the biophysical and biochemical properties of model membranes.

Conjugated linoleic acids (CLA) are known to exert several isomer-specific biological effects, but their mechanisms of action are unclear. In order to determine whether the physicochemical effects of CLA on membranes play a role in their isomer-specific effects, we synthesized phosphatidylcholines (PCs) with 16:0 at sn-1 position and one of four CLA isomers (trans 10 cis 12 (A), trans 9 trans 11 (B), cis 9 trans 11 (C), and cis 9 cis 11 (D)) at sn-2, and determined their biophysical properties in monolayers and bilayers. The surface areas of the PCs with the two natural CLA (A and C) were similar at all pressures, but they differed significantly in the presence of cholesterol, with PC-A condensing more than PC-C. Liposomes of PC-A similarly showed increased binding of cholesterol compared to PC-C liposomes. PC-A liposomes were less permeable to carboxyfluorescein compared to PC-C liposomes. The PC with two trans double bonds (B) showed the highest affinity to cholesterol and lowest permeability. The two natural CLA-PCs (A and C) stimulated lecithin-cholesterol acyltransferase activity by 2-fold, whereas the unnatural CLA-PCs (B and D) were inhibitory. These results suggest that the differences in the biophysical properties of CLA isomers A and C may partly contribute to the known differences in their biological effects.

Correction: Sugasini et al. Efficient Enrichment of Retinal DHA with Dietary Lysophosphatidylcholine-DHA: Potential Application for Retinopathies. Nutrients 2020, 12, 3114.

The authors wish to make the following corrections to their recently published paper [...].

LPC-DHA/EPA-Enriched Diets Increase Brain DHA and Modulate Behavior in Mice That Express Human APOE4.

Compared with APOE3, APOE4 is associated with greater age-related cognitive decline and higher risk of neurodegenerative disorders. Therefore, development of supplements that target APOE genotype-modulated processes could provide a great benefit for the aging population. Evidence suggests a link between APOE genotype and docosahexaenoic acid (DHA); however, clinical studies with current DHA supplements have produced negative results in dementia. The lack of beneficial effects with current DHA supplements may be related to limited bioavailability, as the optimal form of DHA for brain uptake is lysophosphatidylcholine (LPC)-DHA. We previously developed a method to enrich the LPC-DHA content of krill oil through lipase treatment (LT-krill oil), which resulted in fivefold higher enrichment in brain DHA levels in wild-type mice compared with untreated krill oil. Here, we evaluated the effect of a control diet, diet containing krill oil, or a diet containing LT-krill oil in APOE3- and APOE4-targeted replacement mice (APOE-TR mice; treated from 4 to 12 months of age). We found that DHA levels in the plasma and hippocampus are lower in APOE4-TR mice and that LT-krill oil increased DHA levels in the plasma and hippocampus of both APOE3- and APOE4-TR mice. In APOE4-TR mice, LT-krill oil treatment resulted in higher levels of the synaptic vesicle protein SV2A and improved performance on the novel object recognition test. In conclusion, our data demonstrate that LPC-DHA/EPA-enriched krill oil can increase brain DHA and improve memory-relevant behavior in mice that express APOE4. Therefore, long-term use of LT-krill oil supplements may on some level protect against age-related neurodegeneration.

Potential role of hepatic lipase in the accretion of docosahexaenoic acid (DHA) by the brain.

DHA (docosahexaenoic acid) is an essential fatty acid that is required for the normal development and function of the brain. Because of its inability to synthesize adequate amounts of DHA from the precursors, the brain has to acquire DHA from plasma through the blood brain barrier (BBB). Recent studies demonstrated the presence of a transporter at the BBB that specifically transports DHA into the brain in the form of lysophosphatidylcholine (LPC-DHA). However, the mechanism by which LPC-DHA is generated in the plasma is not known. Our previous studies showed that there are at least three different enzymes - lecithin cholesterol acyltransferase (LCAT), endothelial lipase (EL), and hepatic lipase (HL), which can generate LPC-DHA from sn-2 DHA phosphatidylcholine. Here we determined the relative contributions of these enzymes in the delivery of DHA to the brain by measuring the brain DHA levels in the mice deficient in each of these enzymes. The results show that the brain DHA levels of LCAT-deficient mice or EL-deficient mice were not significantly lower than those of their littermates. However, brain DHA was significantly decreased in HL deficient mice (13.5% of total fatty acids) compared to their littermates (17.1%) (p < 0.002), and further decreased to 8.3% of total fatty acids in mice deficient in both HL and EL. These results suggest that HL activity may be the major source for the generation of LPC-DHA in the plasma necessary for transport into the brain, and EL might contribute to this process in the absence of HL.

GH directly inhibits steatosis and liver injury in a sex-dependent and IGF1-independent manner.

A reduction in hepatocyte growth hormone (GH)-signaling promotes non-alcoholic fatty liver disease (NAFLD). However, debate remains as to the relative contribution of the direct effects of GH on hepatocyte function vs indirect effects, via alterations in insulin-like growth factor 1 (IGF1). To isolate the role of hepatocyte GH receptor (GHR) signaling, independent of changes in IGF1, mice with adult-onset, hepatocyte-specific GHR knockdown (aHepGHRkd) were treated with a vector expressing rat IGF1 targeted specifically to hepatocytes. Compared to GHR-intact mice, aHepGHRkd reduced circulating IGF1 and elevated GH. In male aHepGHRkd, the shift in IGF1/GH did not alter plasma glucose or non-esterified fatty acids (NEFA), but was associated with increased insulin, enhanced systemic lipid oxidation and reduced white adipose tissue (WAT) mass. Livers of male aHepGHRkd exhibited steatosis associated with increased de novo lipogenesis, hepatocyte ballooning and inflammation. In female aHepGHRkd, hepatic GHR protein levels were not detectable, but moderate levels of IGF1 were maintained, with minimal alterations in systemic metabolism and no evidence of steatosis. Reconstitution of hepatocyte IGF1 in male aHepGHRkd lowered GH and normalized insulin, whole body lipid utilization and WAT mass. However, IGF1 reconstitution did not reduce steatosis or eliminate liver injury. RNAseq analysis showed IGF1 reconstitution did not impact aHepGHRkd-induced changes in liver gene expression, despite changes in systemic metabolism. These results demonstrate the impact of aHepGHRkd is sexually dimorphic and the steatosis and liver injury observed in male aHepGHRkd mice is autonomous of IGF1, suggesting GH acts directly on the adult hepatocyte to control NAFLD progression.

oxLDL-induced decrease in lipid order of membrane domains is inversely correlated with endothelial stiffness and network formation.

Oxidized low-density lipoprotein (oxLDL) is a major factor in development of atherosclerosis. Our earlier studies have shown that exposure of endothelial cells (EC) to oxLDL increases EC stiffness, facilitates the ability of the cells to generate force, and facilitates EC network formation in three-dimensional collagen gels. In this study, we show that oxLDL induces a decrease in lipid order of membrane domains and that this effect is inversely correlated with endothelial stiffness, contractility, and network formation. Local lipid packing of cell membrane domains was assessed by Laurdan two-photon imaging, endothelial stiffness was assessed by measuring cellular elastic modulus using atomic force microscopy, cell contractility was estimated by measuring the ability of the cells to contract collagen gels, and EC angiogenic potential was estimated by visualizing endothelial networks within the same gels. The impact of oxLDL on endothelial biomechanics and network formation is fully reversed by supplying the cells with a surplus of cholesterol. Furthermore, exposing the cells to 7-keto-cholesterol, a major oxysterol component of oxLDL, or to another cholesterol analog, androstenol, also results in disruption of lipid order of membrane domains and an increase in cell stiffness. On the basis of these observations, we suggest that disruption of lipid packing of cholesterol-rich membrane domains plays a key role in oxLDL-induced changes in endothelial biomechanics.

Efficient Enrichment of Retinal DHA with Dietary Lysophosphatidylcholine-DHA: Potential Application for Retinopathies.

Although decreased retinal docosahexaenoic acid (DHA) is a known risk factor for retinopathy, currently available omega-3 fatty acid supplements, which are absorbed as triacylglycerol (TAG), do not significantly enrich retinal DHA. We tested the hypothesis that lysophospahtidylcholine (LPC)-DHA which is absorbed as phospholipid, would efficiently increase retinal DHA because of the presence of LPC-specific transporter at the blood-retina barrier. In normal rats, LPC-DHA and di-DHA phosphatidylcholine (PC), which generates LPC-DHA during digestion, increased retinal DHA by 101% and 45%, respectively, but TAG-DHA had no significant effect at the same dose (40 mg/kg, 30 days). In normal mice, both sn-1 DHA LPC and sn-2 DHA LPC increased retinal DHA by 80%, but free DHA had no effect. Lipase-treated krill oil (which contains LPC-DHA and LPC-EPA (eicosapentaenoic acid), but not normal krill oil (which has little LPC), increased both retinal DHA (+76%) and EPA (100-fold). Fish oil, however, had no effect, whether lipase-treated or not. These studies show that retinal DHA can be efficiently increased by dietary LPC-DHA, but not by TAG-DHA or free DHA. Since DHA is known to be protective against retinopathy and other eye diseases, this study provides a novel nutraceutical approach for the prevention/treatment of these diseases.

Plasma BDNF is a more reliable biomarker than erythrocyte omega-3 index for the omega-3 fatty acid enrichment of brain.

Enriching brain DHA is believed to be beneficial for the prevention and treatment of several neurological diseases, including Alzheimer's disease. An impediment in assessing the effectiveness of the treatments is the lack of a reliable biomarker for brain DHA. The commonly used erythrocyte omega-3 index is not suitable for brain because of the involvement of unique transporter at the blood brain barrier (BBB). We recently showed that dietary lysophosphatidylcholine (LPC)-DHA significantly increases brain DHA, which results in increase of brain BDNF. Since there is bidirectional transport of BDNF through the BBB, we tested the hypothesis that plasma BDNF may be used as biomarker for brain DHA enrichment. We altered the brain DHA in rats and mice over a wide range using different dietary carriers of DHA, and the correlations between the increase in brain omega-3 index with the increases in plasma BDNF and the erythrocyte index were determined. Whereas the increase in brain omega-3 index positively correlated with the increase in plasma BDNF, it negatively correlated with the erythrocyte index. These results show that the plasma BDNF is more reliable than the erythrocyte index as biomarker for assessing the effectiveness of omega-3 supplements in improving brain function.

Lipase Treatment of Dietary Krill Oil, but Not Fish Oil, Enables Enrichment of Brain Eicosapentaenoic Acid and Docosahexaenoic Acid.

SCOPE: Currently available omega-3 fatty acid supplements do not enrich the docosahexaenoic acid (DHA) of the adult brain because they are absorbed as triacylglycerol, whereas the transporter at the blood brain barrier requires lysophosphatidylcholine (LPC)-DHA. The hypothesis that treatment of krill oil (KO), which contains DHA/eicosapentaenoic acid (EPA) at the SN2 position of phosphatidylcholine, with SN1-specific lipase will generate LPC-DHA/EPA and which can be absorbed intact and transported into the brain, is tested. METHODS: KO and fish oil (FO) are treated with Mucor meihei lipase, incorporated into AIN 93G diet, and fed to 2-month-old mice for 30 days. Fatty acid composition is analyzed by gas chromatography/mass spectroscopy. Brain derived neurotrophic factor (BDNF) is measured by ELISA. RESULTS: Lipase-treated (LT) KO increases brain DHA and EPA, respectively, 5-and 70-fold better than untreated (UT) KO. FO, whether lipase-treated or not, has no effect on brain DHA/EPA. LTKO is also more efficient in enriching liver DHA/EPA, but less efficient than UTKO and FO in enriching adipose tissue and heart. Brain BDNF is significantly increased by LTKO, but only marginally by other preparations. CONCLUSIONS: Pretreatment of dietary KO with lipase enables it to efficiently increase brain DHA/EPA because of the generation of LPC-DHA/EPA.

Opposing effects of platelet-activating factor and lyso-platelet-activating factor on neutrophil and platelet activation.

Platelet-activating factor (PAF) is a potent, bioactive phospholipid that acts on multiple cells and tissues through its G protein-coupled receptor (GPCR). PAF is not stored but is rapidly generated via enzymatic acetylation of the precursor 1-O-hexadecyl-2-hydroxy-sn-glycero-3-phosphocholine (lysoPAF). The bioactivity of PAF is effectively and tightly regulated by PAF acetylhydrolases, which convert PAF back to lysoPAF. Previous studies report that lysoPAF is an inactive precursor and metabolite of PAF. However, lysoPAF has not been carefully studied in its own context. Here we report that lysoPAF has an opposing effect of PAF in the activation of neutrophils and platelets. Whereas PAF potentiates neutrophil NADPH oxidase activation, lysoPAF dose-dependently inhibits this function. Inhibition by lysoPAF is not affected by the use of a PAF receptor antagonist or genetic deletion of the PAF receptor gene. The mechanism of lysoPAF-mediated inhibition of neutrophils involves an elevation in the intracellular cAMP level, and pharmacological blockade of adenylyl cyclase completely reverses the inhibitory effect of lysoPAF. In addition, lysoPAF increases intracellular cAMP levels in platelets and inhibits thrombin-induced platelet aggregation, which can be reversed by inhibition of protein kinase A. These findings identify lysoPAF as a bioactive lipid with opposing functions of PAF and suggest a novel and intrinsic regulatory mechanism for balance of the potent activity of PAF.