Nutraceutical approaches to non-alcoholic fatty liver disease (NAFLD): A position paper from the International Lipid Expert Panel (ILEP)

Non-Alcoholic Fatty Liver Disease (NAFLD) is a common condition affecting around 10-25% of the general adult population, 15% of children, and even > 50% of individuals who have type 2 diabetes mellitus. It is a major cause of liver-related morbidity, and cardiovascular (CV) mortality is a common cause of death. In addition to being the initial step of irreversible alterations of the liver parenchyma causing cirrhosis, about 1/6 of those who develop NASH are at risk also developing CV disease (CVD). More recently the acronym MAFLD (Metabolic Associated Fatty Liver Disease) has been preferred by many European and US specialists, providing a clearer message on the metabolic etiology of the disease. The suggestions for the management of NAFLD are like those recommended by guidelines for CVD prevention. In this context, the general approach is to prescribe physical activity and dietary changes the effect weight loss. Lifestyle change in the NAFLD patient has been supplemented in some by the use of nutraceuticals, but the evidence based for these remains uncertain. The aim of this Position Paper was to summarize the clinical evidence relating to the effect of nutraceuticals on NAFLD-related parameters. Our reading of the data is that whilst many nutraceuticals have been studied in relation to NAFLD, none have sufficient evidence to recommend their routine use; robust trials are required to appropriately address efficacy and safety.

A specific tongue microbiota signature is found in patients displaying an improvement of orosensory lipid perception after a sleeve gastrectomy

Introduction

A preferential consumption of low-fat foods is reported by most of the patients after a vertical sleeve gastrectomy (VSG). The fact that a recent study shed light on a relationship between oral microbiota and fat taste sensitivity in obese patients prompted us to explore whether such a connection also exists in the context of a VSG.

Methods

Thirty-two adult female patients with a severe obesity (BMI = 43.1 ± 0.7 kg/m²) and candidates for a VSG were selected. Oral microbiota composition surrounding the gustatory circumvallate papillae (CVP) and the lipid perception thresholds were explored before and 6 months after surgery.

Results

VSG was found to be associated both with a qualitative (compositional changes) and quantitative (lower gene richness) remodeling of the peri-CVP microbiota. Analysis of the lipid perception allowed us to distinguish two subgroups: patients with a post-operative improvement of the fat taste sensitivity (i.e., with a lower threshold, n = 14) and unimproved patients (n = 18). Specific peri-CVP microbiota signatures also discriminated these two subgroups, unimproved patient being characterized by higher levels of Porphyromonas, Fusobacterium, and Haemophilus genera associated with lower levels of Atopobium and Prevotella genera as compared to the lipid-improved patients.

Conclusion

Collectively, these data raise the possibility that the microbial environment surrounding gustatory papillae might play a role in the positive changes of fat taste sensitivity observed in some patients after VSG.

Step-by-step diagnosis and management of the nocebo/drucebo effect in statin-associated muscle symptoms patients: a position paper from the International Lipid Expert Panel (ILEP)

Statin intolerance is a clinical syndrome whereby adverse effects (AEs) associated with statin therapy [most commonly statin-associated muscle symptoms (SAMS)] result in the discontinuation of therapy and consequently increase the risk of adverse cardiovascular outcomes. However, complete statin intolerance occurs in only a small minority of treated patients (estimated prevalence of only 3-5%). Many perceived AEs are misattributed (e.g. physical musculoskeletal injury and inflammatory myopathies), and subjective symptoms occur as a result of the fact that patients expect them to do so when taking medicines (the nocebo/drucebo effect)-what might be truth even for over 50% of all patients with muscle weakness/pain. Clear guidance is necessary to enable the optimal management of plasma in real-world clinical practice in patients who experience subjective AEs. In this Position Paper of the International Lipid Expert Panel (ILEP), we present a step-by-step patient-centred approach to the identification and management of SAMS with a particular focus on strategies to prevent and manage the nocebo/drucebo effect and to improve long-term compliance with lipid-lowering therapy.

Wnt5a Promotes Lysosomal Cholesterol Egress and Protects Against Atherosclerosis

BACKGROUND

Impairment of cellular cholesterol trafficking is at the heart of atherosclerotic lesions formation. This involves egress of cholesterol from the lysosomes and 2 lysosomal proteins, the NPC1 (Niemann-Pick C1) and NPC2 that promotes cholesterol trafficking. However, movement of cholesterol out the lysosome and how disrupted cholesterol trafficking leads to atherosclerosis is unclear. As the Wnt ligand, Wnt5a inhibits the intracellular accumulation of cholesterol in multiple cell types, we tested whether Wnt5a interacts with the lysosomal cholesterol export machinery and studied its role in atherosclerotic lesions formation.

METHODS

We generated mice deleted for the Wnt5a gene in vascular smooth muscle cells. To establish whether Wnt5a also protects against cholesterol accumulation in human vascular smooth muscle cells, we used a CRISPR/Cas9 guided nuclease approach to generate human vascular smooth muscle cells knockout for Wnt5a.

RESULTS

We show that Wnt5a is a crucial component of the lysosomal cholesterol export machinery. By increasing lysosomal acid lipase expression, decreasing metabolic signaling by the mTORC1 (mechanistic target of rapamycin complex 1) kinase, and through binding to NPC1 and NPC2, Wnt5a senses changes in dietary cholesterol supply and promotes lysosomal cholesterol egress to the endoplasmic reticulum. Consequently, loss of Wnt5a decoupled mTORC1 from variations in lysosomal sterol levels, disrupted lysosomal function, decreased cholesterol content in the endoplasmic reticulum, and promoted atherosclerosis.

CONCLUSIONS

These results reveal an unexpected function of the Wnt5a pathway as essential for maintaining cholesterol homeostasis in vivo.

Lipoprotein(a): Pathophysiology, measurement, indication and treatment in cardiovascular disease. A consensus statement from the Nouvelle Société Francophone d'Athérosclérose (NSFA)

Lipoprotein(a) is an apolipoprotein B100-containing low-density lipoprotein-like particle that is rich in cholesterol, and is associated with a second major protein, apolipoprotein(a). Apolipoprotein(a) possesses structural similarity to plasminogen but lacks fibrinolytic activity. As a consequence of its composite structure, lipoprotein(a) may: (1) elicit a prothrombotic/antifibrinolytic action favouring clot stability; and (2) enhance atherosclerosis progression via its propensity for retention in the arterial intima, with deposition of its cholesterol load at sites of plaque formation. Equally, lipoprotein(a) may induce inflammation and calcification in the aortic leaflet valve interstitium, leading to calcific aortic valve stenosis. Experimental, epidemiological and genetic evidence support the contention that elevated concentrations of lipoprotein(a) are causally related to atherothrombotic risk and equally to calcific aortic valve stenosis. The plasma concentration of lipoprotein(a) is principally determined by genetic factors, is not influenced by dietary habits, remains essentially constant over the lifetime of a given individual and is the most powerful variable for prediction of lipoprotein(a)-associated cardiovascular risk. However, major interindividual variations (up to 1000-fold) are characteristic of lipoprotein(a) concentrations. In this context, lipoprotein(a) assays, although currently insufficiently standardized, are of considerable interest, not only in stratifying cardiovascular risk, but equally in the clinical follow-up of patients treated with novel lipid-lowering therapies targeted at lipoprotein(a) (e.g. antiapolipoprotein(a) antisense oligonucleotides and small interfering ribonucleic acids) that markedly reduce circulating lipoprotein(a) concentrations. We recommend that lipoprotein(a) be measured once in subjects at high cardiovascular risk with premature coronary heart disease, in familial hypercholesterolaemia, in those with a family history of coronary heart disease and in those with recurrent coronary heart disease despite lipid-lowering treatment. Because of its clinical relevance, the cost of lipoprotein(a) testing should be covered by social security and health authorities.

Orosensory Perception of Fat/Sweet Stimuli and Appetite-Regulating Peptides before and after Sleeve Gastrectomy or Gastric Bypass in Adult Women with Obesity

The aim of this study was to explore the impact of bariatric surgery on fat and sweet taste perceptions and to determine the possible correlations with gut appetite-regulating peptides and subjective food sensations. Women suffering from severe obesity (BMI > 35 kg/m²) were studied 2 weeks before and 6 months after a vertical sleeve gastrectomy (VSG, n = 32) or a Roux-en-Y gastric bypass (RYGB, n = 12). Linoleic acid (LA) and sucrose perception thresholds were determined using the three-alternative forced-choice procedure, gut hormones were assayed before and after a test meal and subjective changes in oral food sensations were self-reported using a standardized questionnaire. Despite a global positive effect of both surgeries on the reported gustatory sensations, a change in the taste sensitivity was only found after RYGB for LA. However, the fat and sweet taste perceptions were not homogenous between patients who underwent the same surgery procedure, suggesting the existence of two subgroups: patients with and without taste improvement. These gustatory changes were not correlated to the surgery-mediated modifications of the main gut appetite-regulating hormones. Collectively these data highlight the complexity of relationships between bariatric surgery and taste sensitivity and suggest that VSG and RYGB might impact the fatty taste perception differently.

Identification of an oral microbiota signature associated with an impaired orosensory perception of lipids in insulin-resistant patients

AIMS

Type 2 diabetes leads to multiple sensory dysfunctions affecting notably the gustatory sensitivity. Although this sensory defect, by impacting food choices, might lead to unhealthy eating behavior, underlying mechanisms remains poorly studied. We have recently reported that the composition of microbiota in contact with circumvallate gustatory papillae might affect the orosensory perception of lipids in lean and normoglycemic obese subjects. This finding has prompted us to explore whether such a phenomenon also occurs in diabetic obese patients.

METHODS

The composition of microbiota surrounding the circumvallate papillae was analyzed in combination with the linoleic acid perception thresholds in male insulin-resistant patients and weight-matched healthy controls. Two complementary comparisons were performed: (1) controls vs diabetic and (2) diabetic low-lipid tasters versus diabetic high-lipid tasters.

RESULTS

Despite subtle modifications in the oral microbiota composition, comparison of orosensory lipid perception in controls and diabetic subjects did not lead to discriminating data due to the large inter-individual variability of linoleic acid perception thresholds. In contrast, specific bacterial signatures were found by comparing diabetic low- and high-lipid tasters leading to differential molecular pathways. Surprisingly, a lower fatty taste perception was mainly found in patients treated with metformin and/or statins, suggesting a possible side effect of these antidiabetic and/or hypolipidemic drugs on taste acuity.

CONCLUSIONS

Collectively, these data show that the diabetic patients with defective fatty taste detection are characterized by a specific microbiota metabolism at the circumvallate papillae levels, this occurrence seeming amplified by drugs commonly used to counteract the damaging metabolic effects of T2D. Trial registration for original previous studies: ClinicalTrials.gov #NCT02028975.

Obesity of mice lacking VAP-1/SSAO by Aoc3 gene deletion is reproduced in mice expressing a mutated vascular adhesion protein-1 (VAP-1) devoid of amine oxidase activity

The product of Aoc3 gene is known as vascular adhesion protein-1 (VAP-1), a glycoprotein contributing to leukocyte extravasation and exhibiting semicarbazide-sensitive amine oxidase activity (SSAO). Regarding the immune functions of VAP-1/SSAO, it is known that mice bearing Aoc3 gene knock-out (AOC3KO) exhibit defects in leukocyte migration similar to those of mice expressing a mutated VAP-1 lacking functional SSAO activity (knock-in, AOC3KI). However, it has not been reported whether these models differ regarding other disturbances. Thus, we further compared endocrine-metabolic phenotypes of AOC3KO and AOC3KI mice to their respective control. Special attention was paid on adiposity, glucose and lipid handling, since VAP-1/SSAO is highly expressed in adipose tissue (AT). In both mouse lines, no tissue SSAO activity was found, while Aoc3 mRNA was absent in AOC3KO only. Although food consumption was unchanged, both AOC3KO and AOC3KI mice were heavier and fatter than their respective controls. Other alterations commonly found in adipocytes from both lines were loss of benzylamine insulin-like action with unchanged insulin lipogenic responsiveness and adiponectin expression. A similar downregulation of inflammatory markers (CD45, IL6) was found in AT. Glucose handling and liver mass remained unchanged, while circulating lipid profile was distinctly altered, with increased cholesterol in AOC3KO only. These results suggest that the lack of oxidase activity found in AOC3KI is sufficient to reproduce the metabolic disturbances observed in AOC3KO mice, save those related with cholesterol transport. Modulation of SSAO activity therefore constitutes a potential target for the treatment of cardiometabolic diseases, especially obesity when complicated by low-grade inflammation.

ABCB1 (P-glycoprotein) regulates vitamin D absorption and contributes to its transintestinal efflux

Efficient intestinal absorption of dietary vitamin D is required in most people to ensure an adequate status. Thus, we investigated the involvement of ATP binding cassette subfamily B member 1 (ABCB1) in vitamin D intestinal efflux. Both cholecalciferol (D₃) and 25-hydroxycholecalciferol [25(OH)D₃] apical effluxes were decreased by chemical inhibition of ABCB1 in Caco-2 cells and increased by ABCB1 overexpression in Griptites or Madin-Darby canine kidney type II cells. Mice deficient for the 2 murine ABCB1s encoded by Abcb1a and Abcb1b genes ( Abcb1^-/-) displayed an accumulation of 25(OH)D₃ in plasma, intestine, brain, liver, and kidneys, together with an increased D₃ postprandial response after gavage compared with controls. 25(OH)D₃ efflux through Abcb1^-/- intestinal explants was markedly decreased compared with controls. This reduction of 25(OH)D₃ transfer from plasma to lumen was further confirmed in vivo in intestine-perfused mice. Docking experiments established that both D₃ and 25(OH)D₃ could bind with high affinity to Caenorhabditis elegans P-glycoprotein, used as an ABCB1 model. Finally, in a group of 39 healthy male adults, a single-nucleotide polymorphism (SNP) in ABCB1 (rs17064) was significantly associated with the fasting plasma 25(OH)D₃ concentration. Thus, we showed here for the first time that ABCB1 is involved in neo-absorbed vitamin D efflux by the enterocytes and that it also contributes to vitamin D transintestinal excretion and likely impacts vitamin D status.-Margier, M., Collet, X., le May, C., Desmarchelier, C., André, F., Lebrun, C., Defoort, C., Bluteau, A., Borel, P., Lespine, A., Reboul, E. ABCB1 (P-glycoprotein) regulates vitamin D absorption and contributes to its transintestinal efflux.

A Specific Gut Microbiota Dysbiosis of Type 2 Diabetic Mice Induces GLP-1 Resistance through an Enteric NO-Dependent and Gut-Brain Axis Mechanism

Glucagon-like peptide-1 (GLP-1)-based therapies control glycemia in type 2 diabetic (T2D) patients. However, in some patients the treatment must be discontinued, defining a state of GLP-1 resistance. In animal models we identified a specific set of ileum bacteria impairing the GLP-1-activated gut-brain axis for the control of insulin secretion and gastric emptying. Using prediction algorithms, we identified bacterial pathways related to amino acid metabolism and transport system modules associated to GLP-1 resistance. The conventionalization of germ-free mice demonstrated their role in enteric neuron biology and the gut-brain-periphery axis. Altogether, insulin secretion and gastric emptying require functional GLP-1 receptor and neuronal nitric oxide synthase in the enteric nervous system within a eubiotic gut microbiota environment. Our data open a novel route to improve GLP-1-based therapies.

Exposure to dietary lipid leads to rapid production of cytosolic lipid droplets near the brush border membrane

Background

Intestinal absorption of dietary lipids involves their hydrolysis in the lumen of proximal intestine as well as uptake, intracellular transport and re-assembly of hydrolyzed lipids in enterocytes, leading to the formation and secretion of the lipoproteins chylomicrons and HDL. In this study, we examined the potential involvement of cytosolic lipid droplets (CLD) whose function in the process of lipid absorption is poorly understood.

Methods

Intestinal lipid absorption was studied in mouse after gavage. Three populations of CLD were purified by density ultracentrifugations, as well as the brush border membranes, which were analyzed by western-blots. Immunofluorescent localization of membranes transporters or metabolic enzymes, as well as kinetics of CLD production, were also studied in intestine or Caco-2 cells.

Results

We isolated three populations of CLD (ranging from 15 to 1000 nm) which showed differential expression of the major lipid transporters scavenger receptor BI (SR-BI), cluster of differentiation 36 (CD-36), Niemann Pick C-like 1 (NPC1L1), and the ATP-binding cassette transporters ABCG5/G8 but also caveolin 2 and fatty acid binding proteins. The enzyme monoacylglycerol acyltransferase 2 (MGAT2) was identified in the brush border membrane (BBM) in addition to the endoplasmic reticulum, suggesting local synthesis of triglycerides and CLD at both places.

Conclusions

We show a very fast production of CLD by enterocytes associated with a transfer of apical constituents as lipid transporters. Our findings suggest that following their uptake by enterocytes, lipids can be partially metabolized at the BBM and packaged into CLD for their transportation to the ER.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0107-9) contains supplementary material, which is available to authorized users.

Cholesterol and Sphingomyelin-Containing Model Condensed Lipid Monolayers: Heterogeneities Involving Ordered Microdomains Assessed by Two Cholesterol Derivatives

Lipid monolayers are often considered as model membranes, but they are also the physiologic lipid part of the peripheral envelope of lipoproteins and cytosolic lipid bodies. However, their structural organization is still rather elusive, in particular when both cholesterol and sphingomyelin are present. To investigate such structural organization of hemimembranes, we measured, using alternative current voltammetry, the differential capacitance of condensed phosphatidylcholine-based monolayers as a function of applied potential, which is sensitive to their lipid composition and molecular arrangement. Especially, monolayers containing both sphingomyelin and cholesterol, at 15% w/w, presented specific characteristics of the differential capacitance versus potential curves recorded, which was indicative of specific interactions between these two lipid components. We then compared the behavior of two cholesterol derivatives (at 15% w/w), 21-methylpyrenyl-cholesterol (Pyr-met-Chol) and 22-nitrobenzoxadiazole-cholesterol (NBD-Chol), with that of cholesterol when present in model monolayers. Indeed, these two probes were chosen because of previous findings reporting opposite behaviors within bilayer membranes regarding their interaction with ordered lipids, with only Pyr-met-Chol mimicking cholesterol well. Remarkably, in monolayers containing sphingomyelin or not, Pyr-met-Chol and NBD-Chol presented contrasting behaviors, and Pyr-met-Chol mimicked cholesterol only in the presence of sphingomyelin. These two observations (i.e., optimal amounts of sphingomyelin and cholesterol, and the ability to discriminate between Pyr-met-Chol and NBD-Chol) can be interpreted by the existence of heterogeneities including ordered patches in sphingomyelin- and cholesterol-containing monolayers. Since such monolayer lipid arrangement shares some properties with the raft-type lipid microdomains well-described in sphingomyelin- and cholesterol-containing bilayer membranes, our data thus strongly suggest the existence of compact and ordered microdomains in model lipid monolayers.

The Gut Microbiota Regulates Intestinal CD4 T Cells Expressing RORγt and Controls Metabolic Disease

A high-fat diet (HFD) induces metabolic disease and low-grade metabolic inflammation in response to changes in the intestinal microbiota through as-yet-unknown mechanisms. Here, we show that a HFD-derived ileum microbiota is responsible for a decrease in Th17 cells of the lamina propria in axenic colonized mice. The HFD also changed the expression profiles of intestinal antigen-presenting cells and their ability to generate Th17 cells in vitro. Consistent with these data, the metabolic phenotype was mimicked in RORγt-deficient mice, which lack IL17 and IL22 function, and in the adoptive transfer experiment of T cells from RORγt-deficient mice into Rag1-deficient mice. We conclude that the microbiota of the ileum regulates Th17 cell homeostasis in the small intestine and determines the outcome of metabolic disease.

Specific cellular incorporation of a pyrene-labelled cholesterol: lipoprotein-mediated delivery toward ordered intracellular membranes

In the aim of testing tools for tracing cell trafficking of exogenous cholesterol, two fluorescent derivatives of cholesterol, 22-nitrobenzoxadiazole-cholesterol (NBD-Chol) and 21-methylpyrenyl-cholesterol (Pyr-met-Chol), with distinctive chemico-physical characteristics, have been compared for their cell incorporation properties, using two cell models differently handling cholesterol, with two incorporation routes. In the Caco-2 cell model, the cholesterol probes were delivered in bile salt micelles, as a model of intestinal absorption. The two probes displayed contrasting behaviors for cell uptake characteristics, cell staining, and efflux kinetics. In particular, Pyr-met-Chol cell incorporation involved SR-BI, while that of NBD-Chol appeared purely passive. In the PC-3 cell model, which overexpresses lipoprotein receptors, the cholesterol probes were delivered via the serum components, as a model of systemic delivery. We showed that Pyr-met-Chol-labelled purified LDL or HDL were able to specifically deliver Pyr-met-Chol to the PC-3 cells, while NBD-Chol incorporation was independent of lipoproteins. Observations by fluorescence microscopy evidenced that, while NBD-Chol readily stained the cytosolic lipid droplets, Pyr-met-Chol labelling led to the intense staining of intracellular structures of membranous nature, in agreement with the absence of detectable esterification of Pyr-met-Chol. A 48 h incubation of PC-3 cells with either Pyr-met-Chol-labelled LDL or HDL gave same staining patterns, mainly colocalizing with Lamp1, caveolin-1 and CD63. These data indicated convergent trafficking downwards their respective receptors, LDL-R and SR-BI, toward the cholesterol-rich internal membrane compartments, late endosomes and multivesicular bodies. Interestingly, Pyr-met-Chol staining of these structures exhibited a high excimer fluorescence emission, revealing their ordered membrane environment, and indicating that Pyr-met-Chol behaves as a fair cholesterol tracer regarding its preferential incorporation into cholesterol-rich domains. We conclude that, while NBD-Chol is a valuable marker of cholesterol esterification, Pyr-met-Chol is a reliable new lipoprotein fluorescent marker which allows to probe specific intracellular trafficking of cholesterol-rich membranes.

Intestinal scavenger receptors are involved in vitamin K1 absorption

Vitamin K1 (phylloquinone) intestinal absorption is thought to be mediated by a carrier protein that still remains to be identified. Apical transport of vitamin K1 was examined using Caco-2 TC-7 cell monolayers as a model of human intestinal epithelium and in transfected HEK cells. Phylloquinone uptake was then measured ex vivo using mouse intestinal explants. Finally, vitamin K1 absorption was compared between wild-type mice and mice overexpressing scavenger receptor class B type I (SR-BI) in the intestine and mice deficient in cluster determinant 36 (CD36). Phylloquinone uptake by Caco-2 cells was saturable and was significantly impaired by co-incubation with α-tocopherol (and vice versa). Anti-human SR-BI antibodies and BLT1 (a chemical inhibitor of lipid transport via SR-BI) blocked up to 85% of vitamin K1 uptake. BLT1 also decreased phylloquinone apical efflux by ∼80%. Transfection of HEK cells with SR-BI and CD36 significantly enhanced vitamin K1 uptake, which was subsequently decreased by the addition of BLT1 or sulfo-N-succinimidyl oleate (CD36 inhibitor), respectively. Similar results were obtained in mouse intestinal explants. In vivo, the phylloquinone postprandial response was significantly higher, and the proximal intestine mucosa phylloquinone content 4 h after gavage was increased in mice overexpressing SR-BI compared with controls. Phylloquinone postprandial response was also significantly increased in CD36-deficient mice compared with wild-type mice, but their vitamin K1 intestinal content remained unchanged. Overall, the present data demonstrate for the first time that intestinal scavenger receptors participate in the absorption of dietary phylloquinone.

21-Methylpyrenyl-cholesterol stably and specifically associates with lipoprotein peripheral hemi-membrane: a new labelling tool

Lipoproteins are important biological components. However, they have few convenient fluorescent labelling probes currently reported, and their physiological reliability can be questioned. We compared the association of two fluorescent cholesterol derivatives, 22-nitrobenzoxadiazole-cholesterol (NBD-Chol) and 21-methylpyrenyl-cholesterol (Pyr-met-Chol), to serum lipoproteins and to purified HDL and LDL. Both lipoproteins could be stably labelled by Pyr-met-Chol, but virtually not by NBD-Chol. At variance with NBD-Chol, LCAT did not esterify Pyr-met-Chol. The labelling characteristics of lipoproteins by Pyr-met-Chol were well distinguishable between HDL and LDL, regarding dializability, associated probe amount and labelling kinetics. We took benefit of the pyrene labelling to approach the structural organization of LDL peripheral hemi-membrane, since Pyr-met-Chol-labelled LDL, but not HDL, presented a fluorescence emission of pyrene excimers, indicating that the probe was present in an ordered lipid micro-environment. Since the peripheral membrane of LDL contains more sphingomyelin (SM) than HDL, this excimer formation was consistent with the existence of cholesterol- and SM-enriched lipid microdomains in LDL, as already suggested in model membranes of similar composition and reminiscent to the well-described "lipid rafts" in bilayer membranes. Finally, we showed that Pyr-met-Chol could stain cultured PC-3 cells via lipoprotein-mediated delivery, with a staining pattern well different to that observed with NBD-Chol non-specifically delivered to the cells.

Intestinal SR-BI does not impact cholesterol absorption or transintestinal cholesterol efflux in mice

Reverse cholesterol transport (RCT) can proceed through the classic hepatobiliary route or through the nonbiliary transintestinal cholesterol efflux (TICE) pathway. Scavenger receptor class B type I (SR-BI) plays a critical role in the classic hepatobiliary route of RCT. However, the role of SR-BI in TICE has not been studied. To examine the role of intestinal SR-BI in TICE, sterol balance was measured in control mice and mice transgenically overexpressing SR-BI in the proximal small intestine (SR-BI(hApoCIII-ApoAIV-Tg)). SR-BI(hApoCIII-ApoAIV-Tg) mice had significantly lower plasma cholesterol levels compared with wild-type controls, yet SR-BI(hApoCIII-ApoAIV-Tg) mice had normal fractional cholesterol absorption and fecal neutral sterol excretion. Both in the absence or presence of ezetimibe, intestinal SR-BI overexpression had no impact on the amount of cholesterol excreted in the feces. To specifically study effects of intestinal SR-BI on TICE we crossed SR-BI(hApoCIII-ApoAIV-Tg) mice into a mouse model that preferentially utilized the TICE pathway for RCT (Niemann-Pick C1-like 1 liver transgenic), and likewise found no alterations in cholesterol absorption or fecal sterol excretion. Finally, mice lacking SR-BI in all tissues also exhibited normal cholesterol absorption and fecal cholesterol disposal. Collectively, these results suggest that SR-BI is not rate limiting for intestinal cholesterol absorption or for fecal neutral sterol loss through the TICE pathway.

Transintestinal cholesterol excretion is an active metabolic process modulated by PCSK9 and statin involving ABCB1

OBJECTIVE

Transintestinal cholesterol excretion (TICE) is an alternate pathway to hepatobiliary secretion. Our study aimed at identifying molecular mechanisms of TICE.

APPROACH AND RESULTS

We studied TICE ex vivo in mouse and human intestinal explants, and in vivo after bile diversion and intestinal cannulation in mice. We provide the first evidence that both low-density lipoprotein (LDL) and high-density lipoprotein deliver cholesterol for TICE in human and mouse jejunal explants at the basolateral side. Proprotein convertase subtilisin kexin type 9 (PCSK9)(-/-) mice and intestinal explants show increased LDL-TICE, and acute injection of PCSK9 decreases TICE in vivo, suggesting that PCSK9 is a repressor of TICE. The acute repression was dependent on the LDL receptor (LDLR). Further, TICE was increased when mice were treated with lovastatin. These data point to an important role for LDLR in TICE. However, LDLR(-/-) mice showed increased intestinal LDL uptake, contrary to what is observed in the liver, and tended to have higher TICE. We interpret these data to suggest that there might be at least 2 mechanisms contributing to TICE; 1 involving LDL receptors and other unidentified mechanisms. Acute modulation of LDLR affects TICE, but chronic deficiency is compensated for most likely by the upregulation of the unknown mechanisms. Using mice deficient for apical multidrug active transporter ATP-binding cassette transporter B1 a and b, and its inhibitor, we show that these apical transporters contribute significantly to TICE.

CONCLUSIONS

TICE is operative in human jejunal explants. It is a metabolically active process that can be acutely regulated, inversely related to cholesterolemia, and pharmacologically activated by statins.

Lipidomic and spatio-temporal imaging of fat by mass spectrometry in mice duodenum during lipid digestion

Intestinal absorption of dietary fat is a complex process mediated by enterocytes leading to lipid assembly and secretion of circulating lipoproteins as chylomicrons, vLDL and intestinal HDL (iHDL). Understanding lipid digestion is of importance knowing the correlation between excessive fat absorption and atherosclerosis. By using time-of-flight secondary ion mass spectrometry (TOF-SIMS), we illustrated a spatio-temporal localization of fat in mice duodenum, at different times of digestion after a lipid gavage, for the first time. Fatty acids progressively increased in enterocytes as well as taurocholic acid, secreted by bile and engaged in the entero-hepatic re-absorption cycle. Cytosolic lipid droplets (CLD) from enterocytes were originally purified separating chylomicron-like, intermediate droplets and smaller HDL-like. A lipidomic quantification revealed their contents in triglycerides, free and esterified cholesterol, phosphatidylcholine, sphingomyelin and ceramides but also in free fatty acids, mono- and di-acylglycerols. An acyl-transferase activity was identified and the enzyme monoacylglycerol acyl transferase 2 (MGAT2) was immunodetected in all CLD. The largest droplets was also shown to contain the microsomal triglyceride transfer protein (MTTP), the acyl-coenzyme A-cholesterol acyltransferases (ACAT) 1 and 2, hormone sensitive lipase (HSL) and adipose triglyceride lipase (ATGL). This highlights the fact that during the digestion of fats, enterocyte CLD contain some enzymes involved in the different stages of the metabolism of diet fatty acids and cholesterol, in anticipation of the crucial work of endoplasmic reticulum in the process. The data further underlines the dual role of chylomicrons and iHDL in fat digestion which should help to efficiently complement lipid-lowering therapy.

Abstract 22: LDLR Promotes and PCSK9 Inhibits LDL-Derived Transintestinal Cholesterol Excretion

Direct transintestinal cholesterol excretion (TICE) is an alternative path to biliary secretion and accounts for 33% of fecal cholesterol excretion in mice.

Objectives: We aimed at identifying i) the lipoproteins involved in TICE ii) the role of intestinal LDL receptor (LDLR) and of its natural inhibitor, circulating proprotein convertase subtilisin kexine type 9 (PCSK9) at the basolateral pole iii) the implication of ATP binding cassette transporter ABCB1ab, a cholesterol floppase localized at the enterocytes apical side.

Methods: We labelled human lipoproteins with free 3H cholesterol (free3H) or with 3H-cholesteryl oleate (3HCO). We measured lipoprotein-derived 3H-cholesterol TICE ex vivo in intestinal explants mounted in Ussing chambers. Human explants were obtained from 4 patients undergoing bariatric surgery with their informed consent. In vivo, TICE was measured in mice i.v. injected with radiolabelled lipoproteins, by cannulation of the proximal intestine and concomitant surgical bile diversion, counting radioactivity in intestinal perfusates over 120 minutes.

Results: For the first time, we showed direct evidence of TICE in human duodenal explants, from both LDL and HDL. Both lipoproteins (labelled with free3H or 3HCO ) contributed to TICE in mouse explants; TICE was highly responsive to changes in temperature and medium oxygenation. LDL-derived TICE was decreased by 58% (p<0.05) in explants from LDLR knockout mice (LDLR KO), compared with control C57Bl6J. In vivo free3H- or 3HCO-LDL-derived-TICE was conserved in LDLRKO mice, suggestive of a compensatory mechanism. LDL-derived TICE was increased by 62% (p<0.01) in PCSK9KO that present with ∼300% more intestinal LDLR. Acute depletion of intestinal LDLR with purified recombinant PCSK9 (i.v.) led to 40% (p<0.05) less TICE in PCSK9KO but had no effect in LDLRKO, confirming the implication of this receptor. Lovastatin (0.02% W/W 10d) increased TICE by 71% (p < 0.05) in C57Bl6J but not in LDLRKO. Interestingly, using 3H-cholesterol diluted in intralipid as a source, we showed that ABCB1 plays an important role in TICE. Indeed ABCB1ab -/- mice presented with 26% (p<0.05) less TICE than FVB controls in vivo and ABCB1 inhibitor PSC-833 (5mircoM) decreased TICE by 64% in an ABCB1 dependent fashion in explants.

Collectively, these results provide the first molecular understanding of TICE.

P-glycoprotein dysfunction contributes to hepatic steatosis and obesity in mice

Although the main role of P-glycoprotein (Pgp) is to extrude a broad range of xenochemicals and to protect the organism against xenotoxicity, it also transports a large range of endogenous lipids. Using mice lacking Pgp, we have investigated the possible involvement of Pgp in lipid homeostasis in vivo. In a long term study, we have followed the food intake, body status and lipid markers in plasma and liver of wild-type and mdr1ab(-/-) mice over 35 weeks. Pgp-deficient mice showed excess weight, hypertrophy of adipose mass, high insulin and glucose levels in plasma. Some of these metabolic disruptions appeared earlier in Pgp-deficient mice fed high-fat diet. Moreover, hepatosteatosis with increased expression of genes involved in liver detoxification and in de novo lipid synthesis occurred in Pgp-deficient mice. Overall, Pgp deficiency clearly induced obesity in FVB genetic background, which is known to be resistant to diet-induced obesity. These data reinforce the finding that Pgp gene could be a contributing factor and possibly a relevant marker for lipid disorder and obesity. Subsequent to Pgp deficiency, changes in body availabilities of lipids or any Pgp substrates may affect metabolic pathways that favour the occurrence of obesity. This is of special concern because people are often facing simultaneous exposition to many xenochemicals, which inhibits Pgp, and an excess in lipid dietary intake that may contribute to the high prevalence of obesity in our occidental societies.

Vitamin D intestinal absorption is not a simple passive diffusion: evidences for involvement of cholesterol transporters

SCOPE

It is assumed that vitamin D is absorbed by passive diffusion. However, since cholecalciferol (vitamin D(3) ) and cholesterol display similar structures, we hypothesized that common absorption pathways may exist.

METHODS AND RESULTS

Cholecalciferol apical transport was first examined in human Caco-2 and transfected Human embryonic kidney (HEK) cells. Cholecalciferol uptake was then valuated ex vivo and in vivo, using either wild-type mice, mice overexpressing Scavenger Receptor class B type I (SR-BI) at the intestinal level or mice treated or not with ezetimibe. Cholecalciferol uptake was concentration-, temperature- and direction-dependent, and was significantly impaired by a co-incubation with cholesterol or tocopherol in Caco-2 cells. Moreover Block Lipid Transport-1 (SR-BI inhibitor) and ezetimibe glucuronide (Niemann-Pick C1 Like 1 inhibitor) significantly decreased cholecalciferol transport. Transfection of HEK cells with SR-BI, Cluster Determinant 36 and Niemann-Pick C1 Like 1 significantly enhanced vitamin D uptake, which was significantly decreased by the addition of Block Lipid Transport-1, sulfo-N-succinimidyl oleate (Cluster Determinant 36 inhibitor) or ezetimibe glucuronide, respectively. Similar results were obtained in mouse intestinal explants. In vivo, cholecalciferol uptake in proximal intestinal fragments was 60% higher in mice overexpressing SR-BI than in wild-type mice (p<0.05), while ezetimibe effect remained non-significant.

CONCLUSION

These data show for the first time that vitamin D intestinal absorption is not passive only but involves, at least partly, some cholesterol transporters.

P2Y13 receptor is critical for reverse cholesterol transport

A major atheroprotective functionality of high-density lipoproteins (HDLs) is to promote "reverse cholesterol transport" (RCT). In this process, HDLs mediate the efflux and transport of cholesterol from peripheral cells and its subsequent transport to the liver for further metabolism and biliary excretion. We have previously demonstrated in cultured hepatocytes that P2Y(13) (purinergic receptor P2Y, G protein-coupled, 13) activation is essential for HDL uptake but the potential of P2Y(13) as a target to promote RCT has not been documented. Here, we show that P2Y(13)-deficient mice exhibited a decrease in hepatic HDL cholesterol uptake, hepatic cholesterol content, and biliary cholesterol output, although their plasma HDL and other lipid levels were normal. These changes translated into a substantial decrease in the rate of macrophage-to-feces RCT. Therefore, hallmark features of RCT are impaired in P2Y(13)-deficient mice. Furthermore, cangrelor, a partial agonist of P2Y(13), stimulated hepatic HDL uptake and biliary lipid secretions in normal mice and in mice with a targeted deletion of scavenger receptor class B type I (SR-BI) in liver (hypomSR-BI-knockout(liver)) but had no effect in P2Y(13) knockout mice, which indicate that P2Y(13)-mediated HDL uptake pathway is independent of SR-BI-mediated HDL selective cholesteryl ester uptake.

CONCLUSION

These results establish P2Y(13) as an attractive novel target for modulating RCT and support the emerging view that steady-state plasma HDL levels do not necessarily reflect the capacity of HDL to promote RCT.

F1-adenosine triphosphatase displays properties characteristic of an antigen presentation molecule for Vgamma9Vdelta2 T cells

Human Vgamma9Vdelta2 T lymphocytes are activated by phosphoantigens provided exogenously or produced by tumors and infected cells. Activation requires a contact between Vgamma9Vdelta2 cells and neighboring cells. We previously reported a role for cell surface F1-adenosine triphosphatase (ATPase) in T cell activation by tumors and specific interactions between Vgamma9Vdelta2 TCRs and purified F1-ATPase. 721.221 cells do not express surface F1-ATPase and do not support phosphoantigen responses unless they are rendered apoptotic by high doses of zoledronate, a treatment that promotes F1-expression as well as endogenous phosphoantigen production. By monitoring calcium flux in single cells, we show in this study that contact of T cells with F1-ATPase on polystyrene beads can partially replace the cell-cell contact stimulus during phosphoantigen responses. Triphosphoric acid 1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester, an adenylated derivative of isopentenyl pyrophosphate, can stably bind to F1-ATPase-coated beads and promotes TCR aggregation, lymphokine secretion, and activation of the cytolytic process provided that nucleotide pyrophosphatase activity is present. It also acts as an allosteric activator of F1-ATPase. In the absence of Vgamma9Vdelta2 cells, triphosphoric acid 1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester immobilized on F1-ATPase is protected from nucleotide pyrophosphatase activity, as is the antigenic activity of stimulatory target cells. Our experiments support the notion that Vgamma9Vdelta2 T cells are dedicated to the recognition of phosphoantigens on cell membranes in the form of nucleotide derivatives that can bind to F1-ATPase acting as a presentation molecule.

Role of P-glycoprotein in the disposition of macrocyclic lactones: A comparison between ivermectin, eprinomectin, and moxidectin in mice

Macrocyclic lactones (MLs) are lipophilic anthelmintics and substrates for P-glycoprotein (P-gp), an ATP-binding cassette transporter involved in drug efflux out of both host and parasites. To evaluate the contribution of P-gp to the in vivo kinetic disposition of MLs, the plasma kinetics, brain concentration, and intestinal excretion of three structurally different MLs (ivermectin, eprinomectin, and moxidectin) were compared in wild-type and P-gp-deficient [mdr1ab(-/-)] mice. Each drug (0.2 mg/kg) was administered orally, intravenously, or subcutaneously to the mice. Plasma, brain, and intestinal tissue concentrations were measured by high-performance liquid chromatography. The intestinal excretion rate after intravenous administration was determined at different levels of the small intestine by using an in situ intestinal perfusion model. P-gp deficiency led to a significant increase in the area under the plasma concentration-time curve (AUC) of ivermectin (1.5-fold) and eprinomectin (3.3-fold), whereas the moxidectin AUC was unchanged. Ivermectin and to a greater extent eprinomectin were both excreted by the intestine via a P-gp-dependent pathway, whereas moxidectin excretion was weaker and mostly P-gp-independent. The three drugs accumulated in the brains of the mdr1ab(-/-) mice, but eprinomectin concentrations were significantly lower. We concluded that eprinomectin disposition in mice is controlled mainly by P-gp efflux, more so than that of ivermectin, whereas moxidectin disposition appears to be mostly P-gp-independent. Given that eprinomectin and ivermectin have higher affinity for P-gp than moxidectin, these findings demonstrated that the relative affinity of MLs for P-gp could be predictive of the in vivo kinetic behavior of these drugs.

Effects of human follicular fluid and high-density lipoproteins on early spermatozoa hyperactivation and cholesterol efflux

The preovulatory human follicular fluid contains only HDLs as a lipoprotein class with a typically high proportion of prebeta HDL. We first examined the role of follicular fluid and HDL subfractions on human spermatozoa capacitation, a process characterized by a hyperactivation of the flagellar movement and a depletion of plasma membrane cholesterol. Whole follicular fluid and isolated HDL, used at constant free cholesterol concentration, were both able to promote an early flagellar hyperactivation. Moreover, incubation of [(3)H]cholesterol-labeled spermatozoa with follicular fluid induced a rapid cholesterol efflux from spermatozoa that was confirmed by mass measurements of cholesterol transfer. Using isolated HDL, the cholesterol efflux had a similar time course and represented 70% of that mediated by whole follicular fluid. We then analyzed the time course of radioactive labeling of HDL subfractions. In the first minute of incubation, we found that the prebeta HDL fraction incorporated the main part of the radioactivity (60%), with the rest being found in alpha-HDL, but strikingly, the labeling of alpha-HDL increased with time at the expense of prebeta HDL.Thus, our results indicate that HDLs are involved in both spermatozoa hyperactivation and cholesterol effl ux and suggest the role of prebeta-HDL particles as fi rst cellular cholesterol acceptors.

Specific requirements for Vgamma9Vdelta2 T cell stimulation by a natural adenylated phosphoantigen

Human Vgamma9Vdelta2 T lymphocytes recognize phosphorylated alkyl Ags. Isopentenyl pyrophosphate (IPP) was previously proposed as the main Ag responsible for Vgamma9Vdelta2 T cell activation by cancer cells. However, triphosphoric acid 1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester (ApppI), a metabolite in which the isopentenyl moiety is linked to ATP, was reported in cells activated with aminobisphosphonates. The contribution of this compound to tumor-stimulatory activity was thus examined. ApppI induces selective expansion of Vgamma9Vdelta2 T cells from PBMCs. In the absence of APCs, however, ApppI has little stimulatory activity on Vgamma9Vdelta2 T cells, and optimal activation with ApppI requires addition of a nucleotide pyrophosphatase releasing IPP plus AMP. Thus, ApppI has no intrinsic stimulatory activity. Nevertheless, stimulation by ApppI is strengthened by the presence of APCs. Moreover, in contrast to IPP, ApppI can be efficiently pulsed on dendritic cells as well as on nonprofessional APCs. Pulsed APCs display stable and phosphatase-resistant stimulatory activity, indicative of Ag modification. HPLC analysis of tumor cell extracts indicates that latent phosphoantigenic activity is stored intracellularly in the Vgamma9Vdelta2 cell-sensitive tumor Daudi and can be activated by a nucleotide pyrophosphatase activity. The presence of ApppI in Daudi cell extracts was demonstrated by mass spectrometry. Nucleotidic Ags such as ApppI are thus a storage form of phosphoantigen which may represent a major source of phosphoantigenic activity in tumor cells. The unique properties of ApppI may be important for the design of Ags used in anticancer immunotherapeutic protocols using Vgamma9Vdelta2 cells.

RhoA/ROCK I signalling downstream of the P2Y13 ADP-receptor controls HDL endocytosis in human hepatocytes

Cell surface receptors for high-density lipoprotein (HDL) on hepatocytes are major partners in the regulation of cholesterol homeostasis. We have previously demonstrated on human hepatocytes that apolipoprotein A-I binding to an ectopic F(1)-ATPase stimulates the production of extracellular ADP that activates a P2Y(13)-mediated high-density lipoprotein (HDL) endocytosis pathway. However, P2Y(13)-dependent signalling pathway has never been described yet. The current study demonstrates a major role of cytoskeleton reorganization in F(1)-ATPase/P2Y(13)-dependent HDL endocytosis under the control of the small GTPase RhoA and its effector ROCK I. Indeed human hepatocytes (HepG(2) cells) stimulated by ADP or AR-C69931MX (both P2Y(13) agonists) showed a high specific activation of RhoA; in addition, inhibition of Rho proteins by C3 exoenzyme impairs HDL endocytosis whereas a constitutively active form of RhoA stimulates HDL endocytosis at the same level as under F(1)-ATPase/P2Y(13) activation. Pharmacological inhibition of ROCK activity decreased HDL endocytosis following stimulation by apoA-I (F(1)-ATPase ligand), ADP or AR-C69931MX and specific siRNA ROCK I extinction prevented the stimulation of HDL endocytosis without effect of ROCK II extinction. The functional involvement of ROCK I downstream F(1)-ATPase/P2Y(13) was confirmed by the strong enrichment of the membrane fraction in ROCK I and by the requirement of actin polymerization in hepatocyte HDL endocytosis. These results allow the identification of the molecular events downstream P2Y(13) receptor activation for a better understanding of hepatocyte HDL endocytosis, the latest step in reverse cholesterol transport.

Lycopene absorption in human intestinal cells and in mice involves scavenger receptor class B type I but not Niemann-Pick C1-like 1

Cholesterol membrane transporters scavenger receptor class B type I (SR-BI) and (cluster determinant 36) are involved in intestinal uptake of lutein and beta-carotene, 2 of the 3 main carotenoids of the human diet. The aim of this work was therefore to determine whether SR-BI and NPC1L1 (Niemann-Pick C1-like 1), another cholesterol transporter, are implicated in absorption of lycopene, the 3rd main carotenoid of the human diet. Anti-human SR-BI antibody and block lipid transport 1 (BLT1) (a chemical inhibitor of lipid transport by SR-BI) impaired up to 60% (all-E) and (5Z)-lycopene uptake (P < 0.05) by Caco-2 cell monolayers, which were used as a model of human intestinal epithelium. The involvement of SR-BI in lycopene absorption in vivo was then verified by comparing plasma lycopene concentrations in wild-type and SR-BI transgenic mice that were fed a diet enriched with 0.25 g/kg (all-E)-lycopene for 1 mo. Plasma lycopene concentrations were approximately 10-fold higher (P < 0.001) in mice overexpressing SR-BI in the intestine than in wild-type mice, confirming the involvement of SR-BI in lycopene absorption. Further experiments showed that (all-E)-lycopene did not affect SR-BI mRNA levels in Caco-2 cells or mouse intestine. In contrast to SR-BI, neither anti-human NPC1L1 antibody nor ezetimibe, used as inhibitors of lycopene uptake via NPC1L1, significantly impaired (all-E) or (5Z)-lycopene uptake by Caco-2 monolayers. Thus, the present data show that lycopene absorption is, at least in part, mediated by SR-BI but not by NPC1L1.

Ecto-F1-ATPase and MHC-class I close association on cell membranes

Subunits of the mitochondrial ATP synthase complex are expressed on the surface of tumors, bind the TCR of human Vgamma9/Vdelta2 lymphocytes and promote their cytotoxicity. Present experiments show that detection of the complex (called ecto-F1-ATPase) at the cell surface by immunofluorescence correlates with low MHC-class I antigen expression. Strikingly, the alpha and beta chains of ecto-F1-ATPase are detected in membrane protein precipitates from immunofluorescence-negative cells, suggesting that ATPase epitopes are masked. Removal of beta2-microglobulin by mild acid treatment so that most surface MHC-I molecules become free heavy chains reveals F1-ATPase epitopes on MHC-I+ cell lines. Ecto-F1-ATPase is detected by immunofluorescence on primary fibroblasts which express moderate levels of MHC-I antigens. Up-regulation of MHC-I on these cells following IFN-gamma and/or TNF-alpha treatment induces a dose-dependent disappearance of F1-ATPase epitopes. Finally, biotinylated F1-ATPase cell surface components co-immunoprecipitate with MHC-I molecules confirming the association of both complexes on Raji cells. Confocal microscopy analysis of MHC-I and ecto-F1-ATPase beta chain expression on HepG2 cells shows a co-localization of both complexes in punctate membrane domains. This demonstrates that the TCR target F1-ATPase is in close contact with MHC-I antigens which are known to control Vgamma9/Vdelta2 T cell activity through binding to natural killer inhibitory receptors.

Neuronal conduction of excitation without action potentials based on ceramide production

Background

Action potentials are the classic mechanism by which neurons convey a state of excitation throughout their length, leading, after synaptic transmission, to the activation of other neurons and consequently to network functioning. Using an in vitro integrated model, we found previously that peripheral networks in the autonomic nervous system can organise an unconventional regulatory reflex of the digestive tract motility without action potentials.

Methodology/Principal Findings

In this report, we used combined neuropharmacological and biochemical approaches to elucidate some steps of the mechanism that conveys excitation along the nerves fibres without action potentials. This mechanism requires the production of ceramide in membrane lipid rafts, which triggers in the cytoplasm an increase in intracellular calcium concentration, followed by activation of a neuronal nitric oxide synthase leading to local production of nitric oxide, and then to guanosine cyclic monophosphate. This sequence of second messengers is activated in cascade from rafts to rafts to ensure conduction of the excitation along the nerve fibres.

Conclusions/Significance

Our results indicate that second messengers are involved in neuronal conduction of excitation without action potentials. This mechanism represents the first evidence—to our knowledge—that excitation is carried along nerves independently of electrical signals. This unexpected ceramide-based conduction of excitation without action potentials along the autonomic nerve fibres opens up new prospects in our understanding of neuronal functioning.

Lipid rafts: dream or reality for cholesterol transporters?

As a key constituent of the cell membranes, cholesterol is an endogenous component of mammalian cells of primary importance, and is thus subjected to highly regulated homeostasis at the cellular level as well as at the level of the whole body. This regulation requires adapted mechanisms favoring the handling of cholesterol in aqueous compartments, as well as its transfer into or out of membranes, involving membrane proteins. A membrane exhibits functional properties largely depending on its lipid composition and on its structural organization, which very often involves cholesterol-rich microdomains. Then there is the appealing possibility that cholesterol may regulate its own transmembrane transport at a purely functional level, independently of any transcriptional regulation based on cholesterol-sensitive nuclear factors controling the expression level of lipid transport proteins. Indeed, the main cholesterol "transporters" presently believed to mediate for instance the intestinal absorption of cholesterol, that are SR-BI, NPC1L1, ABCA1, ABCG1, ABCG5/G8 and even P-glycoprotein, all present privileged functional relationships with membrane cholesterol-containing microdomains. In particular, they all more or less clearly induce membrane disorganization, supposed to facilitate cholesterol exchanges with the close aqueous medium. The actual lipid substrates handled by these transporters are not yet unambiguously determined, but they likely concern the components of membrane microdomains. Conversely, raft alterations may provide specific modulations of the transporter activities, as well as they can induce indirect effects via local perturbations of the membrane. Finally, these cholesterol transporters undergo regulated intracellular trafficking, with presumably some relationships to rafts which remain to be clarified.

Cell surface adenylate kinase activity regulates the F(1)-ATPase/P2Y (13)-mediated HDL endocytosis pathway on human hepatocytes

We have previously demonstrated on human hepatocytes that apolipoprotein A-I binding to an ecto-F(1)-ATPase stimulates the production of extracellular ADP that activates a P2Y(13)-mediated high-density lipoprotein (HDL) endocytosis pathway. Therefore, we investigated the mechanisms controlling the extracellular ATP/ADP level in hepatic cell lines and primary cultures to determine their impact on HDL endocytosis. Here we show that addition of ADP to the cell culture medium induced extracellular ATP production that was due to adenylate kinase [see text] and nucleoside diphosphokinase [see text] activities, but not to ATP synthase activity. We further observed that in vitro modulation of both ecto-NDPK and AK activities could regulate the ADP-dependent HDL endocytosis. But interestingly, only AK appeared to naturally participate in the pathway by consuming the ADP generated by the ecto-F(1)-ATPase. Thus controlling the extracellular ADP level is a potential target for reverse cholesterol transport regulation.

Gliotoxin from Aspergillus fumigatus affects phagocytosis and the organization of the actin cytoskeleton by distinct signalling pathways in human neutrophils

Gliotoxin is a mycotoxin having a considerable number of immuno-suppressive actions and is produced by several moulds such as Aspergillus fumigatus. In this study, we investigated its toxic effects on human neutrophils at concentrations corresponding to those found in the blood of patients with invasive aspergillosis. Incubation of the cells for 10min with 30-100ng/ml of gliotoxin inhibited phagocytosis of either zymosan or serum-opsonized zymosan without affecting superoxide production or the exocytosis of specific and azurophil granules. Gliotoxin also induced a significant re-organization of the actin cytoskeleton which collapsed around the nucleus leading to cell shrinkage and the disappearance of filopodia. This gliotoxin-induced actin phenotype was reversed by the cAMP antagonist Rp-cAMP and mimicked by pCPT-cAMP indicating that it probably resulted from the deregulation of intracellular cAMP homeostasis as previously described for gliotoxin-induced apoptosis. By contrast, gliotoxin-induced inhibition of phagocytosis was not reversed by Rp-cAMP but by arachidonic acid, another member of a known signalling pathway affected by the toxin. This suggests that gliotoxin can affect circulating neutrophils and favour the dissemination of A. fumigatus by inhibiting phagocytosis and the consequent killing of conidia.

ApoO, a novel apolipoprotein, is an original glycoprotein up-regulated by diabetes in human heart

Obesity is an independent risk factor for cardiac failure. Obesity promotes excessive deposition of fat in adipose and nonadipose tissues. Intramyocardial lipid overload is a relatively common finding in nonischemic heart failure, especially in obese and diabetic patients, and promotes lipoapoptosis that contributes to the alteration of cardiac function. Lipoprotein production has been proposed as a heart-protective mechanism through the unloading of surplus cellular lipids. We previously analyzed the heart transcriptome in a dog nutritional model of obesity, and we identified a new apolipoprotein, regulated by obesity in heart, which is the subject of this study. We detected this new protein in the following lipoproteins: high density lipoprotein, low density lipoprotein, and very low density lipoprotein. We designated it apolipoprotein O. Apolipoprotein O is a 198-amino acid protein that contains a 23-amino acidlong signal peptide. The apolipoprotein O gene is expressed in a set of human tissues. Confocal immunofluorescence microscopy colocalized apolipoprotein O and perilipins, a cellular marker of the lipid droplet. Chondroitinase ABC deglycosylation analysis or cell incubation with p-nitrophenyl-beta-d-xyloside indicated that apolipoprotein O belongs to the proteoglycan family. Naringenin or CP-346086 treatments indicated that apolipoprotein O secretion requires microsomal triglyceride transfer protein activity. Apolipoprotein O gene expression is up-regulated in the human diabetic heart. Apolipoprotein O promoted cholesterol efflux from macrophage cells. To our knowledge, apolipoprotein O is the first chondroitin sulfate chain containing apolipoprotein. Apolipoprotein O may be involved in myocardium-protective mechanisms against lipid accumulation, or it may have specific properties mediated by its unique glycosylation pattern.

Role of apolipoproteins in gammadelta and NKT cell-mediated innate immunity

Recent findings reveal unanticipated connections between the fields of lipid metabolism and immunology. They concern gammadelta and NKT cells, nonconventional T cell populations that do not recognize protein antigens and are involved in immunity against cancer, defense against infections, or in regulation of classical immune responses. In this review, we summarize data linking perturbations of apolipoprotein levels and nonconventional T cells with inflammatory processes such as autoimmune diseases or atherosclerosis. We integrate and discuss recent findings on the implication of apolipoproteins in antigen recognition by gammadelta and NKT cells, with emphasis on apolipoproteins A-I and E. These findings also provide indications that apolipoproteins influence antitumor immunosurveillance.

Ecto-F1Fo ATP synthase/F1 ATPase: metabolic and immunological functions

PURPOSE OF REVIEW

Until recently, F1Fo ATP synthase expression was believed to be strictly confined to mitochondria where it generates most cellular ATP. This paper reviews the recent evidence for an extra-mitochondrial expression of its components by immunofluorescence, biochemistry and proteomics studies. It discusses its possible implications in an ecto-nucleotide metabolism and its pathophysiological role in normal and tumoral cells.

RECENT FINDINGS

F1Fo ATP synthase components have been identified as cell-surface receptors for apparently unrelated ligands in the course of studies carried out on angiogenesis, lipoprotein metabolism, innate immunity, hypertension, or regulation of food intake.

SUMMARY

F1Fo ATP synthase is expressed on endothelial cells where it binds angiostatin, regulates surface ATP levels, and modulates endothelial cell proliferation and differentiation. Through binding of apolipoprotein A-I, a similar complex, expressed on hepatocytes, regulates lipoprotein internalization. On tumors, it is recognized in association with apolipoprotein A-I by the antigen receptor of circulating cytotoxic lymphocytes of the gammadelta subtype and thus promotes an innate tumor cell recognition and lysis. It binds enterostatin on brain cells. Biochemistry and proteomics studies indicate an enrichment of F1Fo components in lipid rafts selectively with some other mitochondrial proteins, suggesting intracellular traffic connections between mitochondria and other membrane compartments. Finally, depending on cell type and environment, it can generate ATP or ADP which may transfer a downstream signal to purinergic receptors.

Accelerated lipid absorption in mice overexpressing intestinal SR-BI

Dietary cholesterol absorption contributes to a large part of the circulating cholesterol. However, the mechanism of sterol intestinal uptake is not clearly elucidated. Scavenger receptor class B type I (SR-BI), major component in the control of cholesterol homeostasis, is expressed in the intestine, but its role in this organ remains unclear. We have generated transgenic mice overexpressing SR-BI primarily in the intestine by using the mouse SR-BI gene under the control of intestinal specific "apoC-III enhancer coupled with apoA-IV promoter." We found SR-BI overexpression with respect to the natural protein along the intestine and at the top of the villosities. After a meal containing [(14)C]cholesterol and [(3)H]triolein, SR-BI transgenic mice presented a rise in intestinal absorption of both lipids that was not due to a defect in chylomicron clearance nor to a change in the bile flow or the bile acid content. Nevertheless, SR-BI transgenic mice showed a decrease of total cholesterol but an increase of triglyceride content in plasma without any change in the high density lipoprotein apoA-I level. Thus, we described for the first time a functional role in vivo for SR-BI in cholesterol but also in triglyceride intestinal absorption.