Palmitoleate is a mitogen, formed upon stimulation with growth factors, and converted to palmitoleoyl-phosphatidylinositol

Rapid Movement of Palmitoleic Acid from Phosphatidylcholine to Phosphatidylinositol in Activated Human Monocytes

This work describes a novel route for phospholipid fatty acid remodeling involving the monounsaturated fatty acid palmitoleic acid. When administered to human monocytes, palmitoleic acid rapidly incorporates into membrane phospholipids, notably into phosphatidylcholine (PC). In resting cells, palmitoleic acid remains within the phospholipid pools where it was initially incorporated, showing no further movement. However, stimulation of the human monocytes with either receptor-directed (opsonized zymosan) or soluble (calcium ionophore A23187) agonists results in the rapid transfer of palmitoleic acid moieties from PC to phosphatidylinositol (PI). This is due to the activation of a coenzyme A-dependent remodeling route involving two different phospholipase A2 enzymes that act on different substrates to generate free palmitoleic acid and lysoPI acceptors. The stimulated enrichment of specific PI molecular species with palmitoleic acid unveils a hitherto-unrecognized pathway for lipid turnover in human monocytes which may play a role in regulating lipid signaling during innate immune activation.

Dynamics of Docosahexaenoic Acid Utilization by Mouse Peritoneal Macrophages

In this work, the incorporation of docosahexaenoic acid (DHA) in mouse resident peritoneal macrophages and its redistribution within the various phospholipid classes were investigated. Choline glycerophospholipids (PC) behaved as the major initial acceptors of DHA. Prolonged incubation with the fatty acid resulted in the transfer of DHA from PC to ethanolamine glycerophospholipids (PE), reflecting phospholipid remodeling. This process resulted in the cells containing similar amounts of DHA in PC and PE in the resting state. Mass spectrometry-based lipidomic analyses of phospholipid molecular species indicated a marked abundance of DHA in ether phospholipids. Stimulation of the macrophages with yeast-derived zymosan resulted in significant decreases in the levels of all DHA-containing PC and PI species; however, no PE or PS molecular species were found to decrease. In contrast, the levels of an unusual DHA-containing species, namely PI(20:4/22:6), which was barely present in resting cells, were found to markedly increase under zymosan stimulation. The levels of this phospholipid also significantly increased when the calcium-ionophore A23187 or platelet-activating factor were used instead of zymosan to stimulate the macrophages. The study of the route involved in the synthesis of PI(20:4/22:6) suggested that this species is produced through deacylation/reacylation reactions. These results define the increases in PI(20:4/22:6) as a novel lipid metabolic marker of mouse macrophage activation, and provide novel information to understand the regulation of phospholipid fatty acid turnover in activated macrophages.

Mediterranean diet and olive oil, microbiota, and obesity-related cancers. From mechanisms to prevention

Olive oil (OO) is the main source of added fat in the Mediterranean diet (MD). It is a mix of bioactive compounds, including monounsaturated fatty acids, phytosterols, simple phenols, secoiridoids, flavonoids, and terpenoids. There is a growing body of evidence that MD and OO improve obesity-related factors. In addition, obesity has been associated with an increased risk for several cancers: endometrial, oesophageal adenocarcinoma, renal, pancreatic, hepatocellular, gastric cardia, meningioma, multiple myeloma, colorectal, postmenopausal breast, ovarian, gallbladder, and thyroid cancer. However, the epidemiological evidence linking MD and OO with these obesity-related cancers, and their potential mechanisms of action, especially those involving the gut microbiota, are not clearly described or understood. The goals of this review are 1) to update the current epidemiological knowledge on the associations between MD and OO consumption and obesity-related cancers, 2) to identify the gut microbiota mechanisms involved in obesity-related cancers, and 3) to report the effects of MD and OO on these mechanisms.

Desaturation of sebaceous-type saturated fatty acids through the SCD1 and the FADS2 pathways impacts lipid neosynthesis and inflammatory response in sebocytes in culture

Sebum is a lipid-rich mixture secreted by the sebaceous gland (SG) onto the skin surface. By penetrating through the epidermis, sebum may be involved in the regulation of epidermal and dermal cells in both healthy and diseased skin conditions. Saturated and monounsaturated fatty acids (FAs), found as free FAs (FFAs) and in bound form in neutral lipids, are essential constituents of sebum and key players of the inflammatory processes occurring in the pilosebaceous unit in acne-prone skin. Little is known on the interplay among uptake of saturated FFAs, their biotransformation, and induction of proinflammatory cytokines in sebocytes. In the human SG, palmitate (C16:0) is the precursor of sapienate (C16:1n-10) formed by insertion of a double bond (DB) at the Δ6 position catalysed by the fatty acid desaturase 2 (FADS2) enzyme. Conversely, palmitoleate (C16:1n-7) is formed by insertion of a DB at the Δ9 position catalysed by the stearoyl coenzyme A desaturase 1 (SCD1) enzyme. Other FFAs processed in the SG, also undergo these main desaturation pathways. We investigated lipogenesis and release of IL-6 and IL-8 pro-inflammatory cytokines in SZ95 sebocytes in vitro after treatment with saturated FFAs, that is, C16:0, margarate (C17:0), and stearate (C18:0) with or without specific inhibitors of SCD1 and FADS2 desaturase enzymes, and a drug with mixed inhibitory effects on FADS1 and FADS2 activities. C16:0 underwent extended desaturation through both SCD1 and FADS2 catalysed pathways and displayed the strongest lipoinflammatory effects. Inhibition of desaturation pathways proved to enhance lipoinflammation induced by SFAs in SZ95 sebocytes. Palmitate (C16:0), margarate (C17:0), and stearate (C18:0) are saturated fatty acids that induce different arrays of neutral lipids (triglycerides) and dissimilar grades of inflammation in sebocytes.

Compartmentalized regulation of lipid signaling in oxidative stress and inflammation: Plasmalogens, oxidized lipids and ferroptosis as new paradigms of bioactive lipid research

Perturbations in lipid homeostasis combined with conditions favoring oxidative stress constitute a hallmark of the inflammatory response. In this review we focus on the most recent results concerning lipid signaling in various oxidative stress-mediated responses and inflammation. These include phagocytosis and ferroptosis. The best characterized event, common to these responses, is the synthesis of oxygenated metabolites of arachidonic acid and other polyunsaturated fatty acids. Major developments in this area have highlighted the importance of compartmentalization of the enzymes and lipid substrates in shaping the appropriate response. In parallel, other relevant lipid metabolic pathways are also activated and, until recently, there has been a general lack of knowledge on the enzyme regulation and molecular mechanisms operating in these pathways. Specifically, data accumulated in recent years on the regulation and biological significance of plasmalogens and oxidized phospholipids have expanded our knowledge on the involvement of lipid metabolism in the progression of disease and the return to homeostasis. These recent major developments have helped to establish the concept of membrane phospholipids as cellular repositories for the compartmentalized production of bioactive lipids involved in cellular regulation. Importantly, an enzyme classically described as being involved in regulating the homeostatic turnover of phospholipids, namely the group VIA Ca²⁺-independent phospholipase A₂ (iPLA₂β), has taken center stage in oxidative stress and inflammation research owing to its key involvement in regulating metabolic and ferroptotic signals arising from membrane phospholipids. Understanding the role of iPLA₂β in ferroptosis and metabolism not only broadens our knowledge of disease but also opens possible new horizons for this enzyme as a target for therapeutic intervention.

Roles of Palmitoleic Acid and Its Positional Isomers, Hypogeic and Sapienic Acids, in Inflammation, Metabolic Diseases and Cancer

In the last few years, the monounsaturated hexadecenoic fatty acids are being increasingly considered as biomarkers of health with key functions in physiology and pathophysiology. Palmitoleic acid (16:1n-7) and sapienic acid (16:1n-10) are synthesized from palmitic acid by the action of stearoyl-CoA desaturase-1 and fatty acid desaturase 2, respectively. A third positional isomer, hypogeic acid (16:1n-9) is produced from the partial β-oxidation of oleic acid. In this review, we discuss the current knowledge of the effects of palmitoleic acid and, where available, sapienic acid and hypogeic acid, on metabolic diseases such as diabetes, cardiovascular disease, and nonalcoholic fatty liver disease, and cancer. The results have shown diverse effects among studies in cell lines, animal models and humans. Palmitoleic acid was described as a lipokine able to regulate different metabolic processes such as an increase in insulin sensitivity in muscle, β cell proliferation, prevention of endoplasmic reticulum stress and lipogenic activity in white adipocytes. Numerous beneficial effects have been attributed to palmitoleic acid, both in mouse models and in cell lines. However, its role in humans is not fully understood, and is sometimes controversial. Regarding sapienic acid and hypogeic acid, studies on their biological effects are still scarce, but accumulating evidence suggests that they also play important roles in metabolic regulation. The multiplicity of effects reported for palmitoleic acid and the compartmentalized manner in which they often occur, may suggest the overlapping actions of multiple isomers being present at the same or neighboring locations.

PI(18:1/18:1) is a SCD1-derived lipokine that limits stress signaling

Cytotoxic stress activates stress-activated kinases, initiates adaptive mechanisms, including the unfolded protein response (UPR) and autophagy, and induces programmed cell death. Fatty acid unsaturation, controlled by stearoyl-CoA desaturase (SCD)1, prevents cytotoxic stress but the mechanisms are diffuse. Here, we show that 1,2-dioleoyl-sn-glycero-3-phospho-(1’-myo-inositol) [PI(18:1/18:1)] is a SCD1-derived signaling lipid, which inhibits p38 mitogen-activated protein kinase activation, counteracts UPR, endoplasmic reticulum-associated protein degradation, and apoptosis, regulates autophagy, and maintains cell morphology and proliferation. SCD1 expression and the cellular PI(18:1/18:1) proportion decrease during the onset of cell death, thereby repressing protein phosphatase 2 A and enhancing stress signaling. This counter-regulation applies to mechanistically diverse death-inducing conditions and is found in multiple human and mouse cell lines and tissues of Scd1-defective mice. PI(18:1/18:1) ratios reflect stress tolerance in tumorigenesis, chemoresistance, infection, high-fat diet, and immune aging. Together, PI(18:1/18:1) is a lipokine that links fatty acid unsaturation with stress responses, and its depletion evokes stress signaling.

Fatty acid unsaturation by stearoyl-CoA desaturase 1 (SCD1) protects against cellular stress through unclear mechanisms. Here the authors show 1,2-dioleoyl-sn-glycero-3-phospho-(1’-myo-inositol) is an SCD1-derived signaling lipid that regulates stress-adaption, protects against cell death and promotes proliferation.

Complex Alterations of Fatty Acid Metabolism and Phospholipidome Uncovered in Isolated Colon Cancer Epithelial Cells

The development of colon cancer, one of the most common malignancies, is accompanied with numerous lipid alterations. However, analyses of whole tumor samples may not always provide an accurate description of specific changes occurring directly in tumor epithelial cells. Here, we analyzed in detail the phospholipid (PL), lysophospholipid (lysoPL), and fatty acid (FA) profiles of purified EpCAM⁺ cells, isolated from tumor and adjacent non-tumor tissues of colon cancer patients. We found that a number of FAs increased significantly in isolated tumor cells, which also included a number of long polyunsaturated FAs. Higher levels of FAs were associated with increased expression of FA synthesis genes, as well as with altered expression of enzymes involved in FA elongation and desaturation, including particularly fatty acid synthase, stearoyl-CoA desaturase, fatty acid desaturase 2 and ELOVL5 fatty acid elongase 5 We identified significant changes in ratios of specific lysoPLs and corresponding PLs. A number of lysophosphatidylcholine and lysophosphatidylethanolamine species, containing long-chain and very-long chain FAs, often with high numbers of double bonds, were significantly upregulated in tumor cells. Increased de novo synthesis of very long-chain FAs, or, altered uptake or incorporation of these FAs into specific lysoPLs in tumor cells, may thus contribute to reprogramming of cellular phospholipidome and membrane alterations observed in colon cancer.

The Hypoxic Microenvironment Induces Stearoyl-CoA Desaturase-1 Overexpression and Lipidomic Profile Changes in Clear Cell Renal Cell Carcinoma

Simple Summary

Clear cell renal cell carcinoma (ccRCC) is characterized by a high rate of cell proliferation and an extensive accumulation of lipids. Uncontrolled cell growth usually generates areas of intratumoral hypoxia that define the tumor phenotype. In this work, we show that, under these microenvironmental conditions, stearoyl-CoA desaturase-1 is overexpressed. This enzyme induces changes in the cellular lipidomic profile, increasing the oleic acid levels, a metabolite that is essential for cell proliferation. This work supports the idea of considering stearoyl-CoA desaturase-1 as an exploitable therapeutic target in ccRCC.

Abstract

Clear cell renal cell carcinoma (ccRCC) is the most common histological subtype of renal cell carcinoma (RCC). It is characterized by a high cell proliferation and the ability to store lipids. Previous studies have demonstrated the overexpression of enzymes associated with lipid metabolism, including stearoyl-CoA desaturase-1 (SCD-1), which increases the concentration of unsaturated fatty acids in tumor cells. In this work, we studied the expression of SCD-1 in primary ccRCC tumors, as well as in cell lines, to determine its influence on the tumor lipid composition and its role in cell proliferation. The lipidomic analyses of patient tumors showed that oleic acid (18:1n-9) is one of the major fatty acids, and it is particularly abundant in the neutral lipid fraction of the tumor core. Using a ccRCC cell line model and in vitro-generated chemical hypoxia, we show that SCD-1 is highly upregulated (up to 200-fold), and this causes an increase in the cellular level of 18:1n-9, which, in turn, accumulates in the neutral lipid fraction. The pharmacological inhibition of SCD-1 blocks 18:1n-9 synthesis and compromises the proliferation. The addition of exogenous 18:1n-9 to the cells reverses the effects of SCD-1 inhibition on cell proliferation. These data reinforce the role of SCD-1 as a possible therapeutic target.

Release of Anti-Inflammatory Palmitoleic Acid and Its Positional Isomers by Mouse Peritoneal Macrophages

Positional isomers of hexadecenoic acid are considered as fatty acids with anti-inflammatory properties. The best known of them, palmitoleic acid (cis-9-hexadecenoic acid, 16:1n-7), has been identified as a lipokine with important beneficial actions in metabolic diseases. Hypogeic acid (cis-7-hexadecenoic acid, 16:1n-9) has been regarded as a possible biomarker of foamy cell formation during atherosclerosis. Notwithstanding the importance of these isomers as possible regulators of inflammatory responses, very little is known about the regulation of their levels and distribution and mobilization among the different lipid pools within the cell. In this work, we describe that the bulk of hexadecenoic fatty acids found in mouse peritoneal macrophages is esterified in a unique phosphatidylcholine species, which contains palmitic acid at the sn-1 position, and hexadecenoic acid at the sn-2 position. This species markedly decreases when the macrophages are activated with inflammatory stimuli, in parallel with net mobilization of free hexadecenoic acid. Using pharmacological inhibitors and specific gene-silencing approaches, we demonstrate that hexadecenoic acids are selectively released by calcium-independent group VIA phospholipase A₂ under activation conditions. While most of the released hexadecenoic acid accumulates in free fatty acid form, a significant part is also transferred to other phospholipids to form hexadecenoate-containing inositol phospholipids, which are known to possess growth-factor-like-properties, and are also used to form fatty acid esters of hydroxy fatty acids, compounds with known anti-diabetic and anti-inflammatory properties. Collectively, these data unveil new pathways and mechanisms for the utilization of palmitoleic acid and its isomers during inflammatory conditions, and raise the intriguing possibility that part of the anti-inflammatory activity of these fatty acids may be due to conversion to other lipid mediators.

The n-10 Fatty Acids Family in the Lipidome of Human Prostatic Adenocarcinoma Cell Membranes and Extracellular Vesicles

A new pathway leading to the n-10 fatty acid series has been recently evidenced, starting from sapienic acid, a monounsaturated fatty acid (MUFA) resulting from the transformation of palmitic acid by delta-6 desaturase. Sapienic acid has attracted attention as a novel marker of cancer cell plasticity. Here, we analyzed fatty acids, including the n-10 fatty acid contents, and for the first time, compared cell membranes and the corresponding extracellular vesicles (EV) of two human prostatic adenocarcinoma cell lines of different aggressiveness (PC3 and LNCaP). The n-10 components were 9-13% of the total fatty acids in both cancer cell lines and EVs, with total MUFA levels significantly higher in EVs of the most aggressive cell type (PC3). High sapienic/palmitoleic ratios indicated the preference for delta-6 versus delta-9 desaturase enzymatic activity in these cell lines. The expressions analysis of enzymes involved in desaturation and elongation by qRT-PCR showed a higher desaturase activity in PC3 and a higher elongase activity toward polyunsaturated fatty acids than toward saturated fatty acids, compared to LNCaP cells. Our results improve the present knowledge in cancer fatty acid metabolism and lipid phenotypes, highlighting EV lipidomics to monitor positional fatty acid isomer profiles and MUFA levels in cancer.

Dietary calories and lipids synergistically shape adipose tissue cellularity during postnatal growth

Objective

The susceptibility to abdominal obesity and the metabolic syndrome is determined to a substantial extent during childhood and adolescence, when key adipose tissue characteristics are established. Although the general impact of postnatal nutrition is well known, it is not clear how specific dietary components drive adipose tissue growth and how this relates to the risk of metabolic dysfunction in adulthood.

Methods

Adipose tissue growth including cell proliferation was analyzed in juvenile mice upon dietary manipulation with in vivo nucleotide labeling. The proliferative response of progenitors to specific fatty acids was assayed in primary cultures. Long-term metabolic consequences were assessed through transient dietary manipulation post-weaning with a second obesogenic challenge in adulthood.

Results

Dietary lipids stimulated adipose tissue progenitor cell proliferation in juvenile mice independently of excess caloric intake and calorie-dependent adipocyte hypertrophy. Excess calories increased mitogenic IGF-1 levels systemically, whereas palmitoleic acid was able to enhance the sensitivity of progenitors to IGF-1, resulting in synergistic stimulation of proliferation. Early transient consumption of excess lipids promoted hyperplastic adipose tissue expansion in response to a second dietary challenge in adulthood and this correlated with abdominal obesity and hyperinsulinemia.

Conclusions

Dietary lipids and calories differentially and synergistically drive adipose tissue proliferative growth and the programming of the metabolic syndrome in childhood.

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Dietary fat accelerates adipose tissue progenitor proliferation in juvenile mice.

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Lipid-mediated proliferation is independent of excess calorie intake.

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Excess calories elevate IGF-1 levels and adipocyte hypertrophy.

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Palmitoleic acid enhances the proliferative response of progenitors to IGF-1.

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Lipids and calories in childhood program features of the adult metabolic syndrome.

Hexadecenoic Fatty Acid Positional Isomers and De Novo PUFA Synthesis in Colon Cancer Cells

Palmitic acid metabolism involves delta-9 and delta-6 desaturase enzymes forming palmitoleic acid (9cis-16:1; n-7 series) and sapienic acid (6cis-16:1; n-10 series), respectively. The corresponding biological consequences and lipidomic research on these positional monounsaturated fatty acid (MUFA) isomers are under development. Furthermore, sapienic acid can bring to the de novo synthesis of the n-10 polyunsaturated fatty acid (PUFA) sebaleic acid (5cis,8cis-18:2), but such transformations in cancer cells are not known. The model of Caco-2 cell line was used to monitor sapienic acid supplementation (150 and 300 μM) and provide evidence of the formation of n-10 fatty acids as well as their incorporation at levels of membrane phospholipids and triglycerides. Comparison with palmitoleic and palmitic acids evidenced that lipid remodelling was influenced by the type of fatty acid and positional isomer, with an increase of 8cis-18:1, n-10 PUFA and a decrease of saturated fats in case of sapienic acid. Cholesteryl esters were formed only in cases with sapienic acid. Sapienic acid was the less toxic among the tested fatty acids, showing the highest EC₅₀s and inducing death only in 75% of cells at the highest concentration tested. Two-photon fluorescent microscopy with Laurdan as a fluorescent dye provided information on membrane fluidity, highlighting that sapienic acid increases the distribution of fluid regions, probably connected with the formation of 8cis-18:1 and the n-10 PUFA in cell lipidome. Our results bring evidence for MUFA positional isomers and de novo PUFA synthesis for developing lipidomic analysis and cancer research.

Therapeutic targeting of lipid synthesis metabolism for selective elimination of cancer stem cells

Cancer stem cells (CSCs) are believed to have an essential role in tumor resistance and metastasis; however, no therapeutic strategy for the selective elimination of CSCs has been established. Recently, several studies have shown that the metabolic regulation for ATP synthesis and biological building block generation in CSCs are different from that in bulk cancer cells and rather similar to that in normal tissue stem cells. To take advantage of this difference for CSC elimination therapy, many studies have tested the effect of blocking these metabolism. Two specific processes for lipid biosynthesis, i.e., fatty acid unsaturation and cholesterol biosynthesis, have been shown to be very effective and selective for CSC targets. In this review, lipid metabolism specific to CSCs are summarized. In addition, how monounsaturated fatty acid and cholesterol synthesis may contribute to CSC maintenance are discussed. Specifically, the molecular mechanism required for lipid synthesis and essential for stem cell biology is highlighted. The limit and preview of the lipid metabolism targeting for CSCs are also discussed.

Caryocar brasiliense oil improves cardiac function by increasing Serca2a/PLB ratio despite no significant changes in cardiovascular risk factors in rats

Background

Caryocar brasiliense (pequi) oil is high in monounsaturated fat acids (MUFA), especially oleic, and in carotenoids, which have been associated with protection against cardiovascular disease. However, this food is poorly studied in this context, especially in the cardiac function. Therefore, we investigated the effects of a long-term intake of pequi oil in systemic cardiovascular risk factors and in the ex vivo cardiac function of rats.

Methods

Previously, we determined fatty acids and carotenoids in pequi oil. Next, male rats were divided in C – control group feed a standard diet, and PO – pequi oil group fed the same diet added pequi oil (+2.25 g.100 g⁻¹). After 15 weeks, plasma lipids, glucose, insulin, blood pressure, heart rate, hepatic lipids were accessed and visceral fat pads were harvested. Hearts were used for the ex vivo cardiac function, histologic assays, SERCA2a and phospholanban (PLB) determinations.

Results

In agreement with scientific data, pequi oil had expressive amounts MUFA, especially oleic acid, and carotenoids. Hepatic triglycerides (TG) were reduced by pequi oil intake (p < 0.05). All others cardiovascular risk factors were not changed. The intrinsic heart rate was lower in PO group (p < 0.05). SERCA2a content was higher in this group (p < 0.05), without affecting PLB. Also, SERCA2a/PLB ratio increased in PO group (p < 0.05).

Conclusion

Pequi oil intake improved cardiac function ex vivo, despite no significant changes in systemic cardiovascular risk factors. The higher lipid offer in pequi oil diet, its composition in oleic acid and carotenoids could be related to those effects.

The Role of the Novel Lipokine Palmitoleic Acid in Health and Disease

The monounsaturated fatty acid palmitoleate (palmitoleic acid) is one of the most abundant fatty acids in serum and tissues, particularly adipose tissue and liver. Its endogenous production by stearoyl-CoA desaturase 1 gives rise to its cis isoform, cis-palmitoleate. Although trans-palmitoleate is also synthesized in humans, it is mainly found as an exogenous source in ruminant fat and dairy products. Recently, palmitoleate was considered to be a lipokine based on evidence demonstrating its release from adipose tissue and its metabolic effects on distant organs. After this finding, research has been performed to determine whether palmitoleate has beneficial effects on metabolism and to elucidate the underlying mechanisms. Thus, the aim of this work was to review the current status of knowledge about palmitoleate, its metabolism, and its influence on metabolic abnormalities. Results have shown mixed cardiovascular effects, direct or inverse correlations with obesity, and hepatosteatosis, but a significant amelioration or prevention of insulin resistance and diabetes. Finally, the induction of palmitoleate release from adipose tissue, dietary intake, and its supplementation are all interventions with a potential impact on certain metabolic diseases.

Metabolic interplay between white, beige, brown adipocytes and the liver

In mammalian evolution, three types of adipocytes have developed, white, brown and beige adipocytes. White adipocytes are the major constituents of white adipose tissue (WAT), the predominant store for energy-dense triglycerides in the body that are released as fatty acids during catabolic conditions. The less abundant brown adipocytes, the defining parenchymal cells of brown adipose tissue (BAT), internalize triglycerides that are stored intracellularly in multilocular lipid droplets. Beige adipocytes (also known as brite or inducible brown adipocytes) are functionally very similar to brown adipocytes and emerge in specific WAT depots in response to various stimuli including sustained cold exposure. The activation of brown and beige adipocytes (together referred to as thermogenic adipocytes) causes both the hydrolysis of stored triglycerides as well as the uptake of lipids and glucose from the circulation. Together, these fuels are combusted for heat production to maintain body temperature in mammals including adult humans. Given that heating by brown and beige adipocytes is a very-well controlled and energy-demanding process which entails pronounced shifts in energy fluxes, it is not surprising that an intensive interplay exists between the various adipocyte types and parenchymal liver cells, and that this influences systemic metabolic fluxes and endocrine networks. In this review we will emphasize the role of hepatic factors that regulate the metabolic activity of white and thermogenic adipocytes. In addition, we will discuss the relevance of lipids and hormones that are secreted by white, brown and beige adipocytes regulating liver metabolism in order to maintain systemic energy metabolism in health and disease.

SCD1 inhibition during 3T3-L1 adipocyte differentiation remodels triacylglycerol, diacylglycerol and phospholipid fatty acid composition

The conversion of saturated fatty acids (FAs) palmitate (16:0) and stearate (18:0) into monounsaturated FAs palmitoleate (16:1n-7) and oleate (18:1n-9) is catalyzed by stearoyl-CoA desaturase 1 (SCD1). These FAs represent the dominant constituents of adipocyte triacylglycerols (TAGs) and phospholipids (PLs). Given the critical role of SCD1 in lipid metabolism and the notable increase in its expression during adipogenesis, reductions in SCD1 activity have the potential to compromise the adipocyte's ability to accumulate lipid. The current study used thin-layer and gas chromatography to examine the content and FA composition of TAGs, PLs, cholesteryl esters, diacylglycerols and free fatty acids in SCD1-inhibited differentiating 3T3-L1 adipocyte cells. SCD1 inhibition reduced total cellular PL and TAG content concurrent with the down-regulation of genes involved in TAG and PL biosynthesis; however, the relative amount of PL was unaltered. While total DAG levels were increased ~2.7-fold in SCD1-inhibited adipocytes, this did not induce JNK activation; however, phosphorylated (Ser473) AKT was significantly reduced. As expected, total SFA and MUFA content were increased (~1.3-fold) and decreased (~4.0-fold). Further, SCD1 inhibition caused a ~2.2-fold increase and a ~8.3-fold decrease in total cellular 18:0 and 16:1n-7 levels, respectively. Similar changes were also seen in other lipid fractions. The levels of other FAs, including polyunsaturated FAs, were also changed in SCD1-inhibited adipocytes. Together, these results add to the existing body of knowledge regarding SCD1 function in adipocytes and highlight its important role in regulating global adipocyte lipid composition.

Perspective of microsomal prostaglandin E2 synthase-1 as drug target in inflammation-related disorders

Prostaglandin (PG)E2 encompasses crucial roles in pain, fever, inflammation and diseases with inflammatory component, such as cancer, but is also essential for gastric, renal, cardiovascular and immune homeostasis. Cyclooxygenases (COX) convert arachidonic acid to the intermediate PGH2 which is isomerized to PGE2 by at least three different PGE2 synthases. Inhibitors of COX - non-steroidal anti-inflammatory drugs (NSAIDs) - are currently the only available therapeutics that target PGE2 biosynthesis. Due to adverse effects of COX inhibitors on the cardiovascular system (COX-2-selective), stomach and kidney (COX-1/2-unselective), novel pharmacological strategies are in demand. The inducible microsomal PGE2 synthase (mPGES)-1 is considered mainly responsible for the excessive PGE2 synthesis during inflammation and was suggested as promising drug target for suppressing PGE2 biosynthesis. However, 15 years after intensive research on the biology and pharmacology of mPGES-1, the therapeutic value of mPGES-1 as drug target is still vague and mPGES-1 inhibitors did not enter the market so far. This commentary will first shed light on the structure, mechanism and regulation of mPGES-1 and will then discuss its biological function and the consequence of its inhibition for the dynamic network of eicosanoids. Moreover, we (i) present current strategies for interfering with mPGES-1-mediated PGE2 synthesis, (ii) summarize bioanalytical approaches for mPGES-1 drug discovery and (iii) describe preclinical test systems for the characterization of mPGES-1 inhibitors. The pharmacological potential of selective mPGES-1 inhibitor classes as well as dual mPGES-1/5-lipoxygenase inhibitors is reviewed and pitfalls in their development, including species discrepancies and loss of in vivo activity, are discussed.

PPARγ Agonists Attenuate Palmitate-Induced ER Stress through Up-Regulation of SCD-1 in Macrophages

Background

Clinical trials have shown that treatment of patients with type 2 diabetes with pioglitazone, a peroxisome proliferator-activated receptor (PPAR)γ agonist, reduces cardiovascular events. However, the effect of PPARγ agonists on endoplasmic reticulum (ER) stress that plays an important role in the progression of atherosclerosis has not been determined. We sought to determine the effect of PPARγ agonists on ER stress induced by palmitate, the most abundant saturated fatty acid in the serum.

Methods and Results

Protein expression of ER stress marker was evaluated by Western blot analysis and stearoyl-CoA desaturase1 (SCD-1) mRNA expression was evaluated by qRT-PCR. Macrophage apoptosis was detected by flowcytometry. Pioglitazone and rosiglitazone reduced palmitate-induced phosphorylation of PERK, a marker of ER stress, in RAW264.7, a murine macrophage cell line. Pioglitazone also suppressed palmitate-induced apoptosis in association with inhibition of CHOP expression, JNK phosphorylation and cleavage of caspase-3. These effects of pioglitazone were reversed by GW9662, a PPARγ antagonist, indicating that PPARγ is involved in this process. PPARγ agonists increased expression of SCD-1 that introduces a double bond on the acyl chain of long-chain fatty acid. 4-(2-Chlorophenoxy)-N-(3-(3-methylcarbamoyl)phenyl)piperidine-1-carboxamide, an inhibitor of SCD-1, abolished the anti-ER stress and anti-apoptotic effects of pioglitazone. These results suggest that PPARγ agonists attenuate palmitate-induced ER stress and apoptosis through SCD-1 induction. Up-regulation of SCD-1 may contribute to the reduction of cardiovascular events by treatment with PPARγ agonists.

SCD5-induced oleic acid production reduces melanoma malignancy by intracellular retention of SPARC and cathepsin B

A proper balance between saturated and unsaturated fatty acids (FAs) is required for maintaining cell homeostasis. The increased demand of FAs to assemble the plasma membranes of continuously dividing cancer cells might unbalance this ratio and critically affect tumour outgrowth. We unveiled the role of the stearoyl-CoA desaturase SCD5 in converting saturated FAs into mono-unsaturated FAs during melanoma progression. SCD5 is down-regulated in advanced melanoma and its restored expression significantly reduced melanoma malignancy, both in vitro and in vivo, through a mechanism governing the secretion of extracellular matrix proteins, such as secreted protein acidic and rich in cysteine (SPARC) and collagen IV and of their proteases, such as cathepsin B. Enforced expression of SCD5 or supplementation of its enzymatic product, oleic acid, reduced the intracellular pH (pHe > pHi) and, in turn, vesicular trafficking across plasma membranes as well as melanoma dissemination. This intracellular acidification appears also to depend on SCD5-induced reduction of the C2 subunit of the vacuolar H(+) -ATPase, a proton pump whose inhibition changes the secretion profile of cancer cells. Our data support a role for SCD5 and its enzymatic product, oleic acid, in protection against malignancy, offering an explanation for the beneficial Mediterranean diet. Furthermore, SCD5 appears to functionally connect tumour cells and the surrounding stroma toward modification of the tumour microenvironment, with consequences on tumour spread and resistance to treatment.

Fatty acids and cardiac disease: fuel carrying a message

From the viewpoint of the prevention of cardiovascular disease (CVD) burden, there has been a continuous interest in the detrimental effects of the Western-type high-fat diet for more than half a century. More recently, this general view has been subject to change as epidemiological studies showed that replacing fat by carbohydrate may even be worse and that various polyunsaturated fatty acids (FA) have beneficial rather than detrimental effects on CVD outcome. At the same time, advances in lipid biology have provided insight into the mechanisms by which the different lipid components of the Western diet affect the cardiovascular system. In fact, this still is a rapidly growing field of research and in recent years novel FA derivatives and FA receptors have been discovered. This includes fish-oil derived FA-derivatives with anti-inflammatory properties, the so-called resolvins, and various G-protein-coupled receptors that recognize FA as ligands. In the present review, we will extensively discuss the role of FA and their metabolites on cardiac disease, with special emphasis on the role of the different saturated and polyunsaturated FA and their respective metabolites in cellular signal transduction and the possible implications for the development of cardiac hypertrophy and cardiac failure.

Diversity and function of membrane glycerophospholipids generated by the remodeling pathway in mammalian cells

Cellular membranes are composed of numerous kinds of glycerophospholipids with different combinations of polar heads at the sn-3 position and acyl moieties at the sn-1 and sn-2 positions, respectively. The glycerophospholipid compositions of different cell types, organelles, and inner/outer plasma membrane leaflets are quite diverse. The acyl moieties of glycerophospholipids synthesized in the de novo pathway are subsequently remodeled by the action of phospholipases and lysophospholipid acyltransferases. This remodeling cycle contributes to the generation of membrane glycerophospholipid diversity and the production of lipid mediators such as fatty acid derivatives and lysophospholipids. Furthermore, specific glycerophospholipid transporters are also important to organize a unique glycerophospholipid composition in each organelle. Recent progress in this field contributes to understanding how and why membrane glycerophospholipid diversity is organized and maintained.

Inhibition of stearoyl-CoA desaturase-1 in differentiating 3T3-L1 preadipocytes upregulates elongase 6 and downregulates genes affecting triacylglycerol synthesis

BACKGROUND

Stearoyl-CoA desaturase-1 (SCD1) is rate limiting for the conversion of saturated fatty acids palmitate (16:0) and stearate (18:0) to monounsaturated fatty acids palmitoleate (16:1n7) and oleate (18:1n9), respectively. Given that reduced SCD1 activity is associated with improved insulin sensitivity and decreased body weight, there is considerable interest to elucidate the role of this enzyme in adipocytes. During adipogenesis, SCD1 levels increase concomitantly with the accumulation of triacylglycerol (TG); however, the extent to which reduced SCD1 activity can influence TG synthesis and metabolic pathways in differentiating adipocytes remains relatively unexplored.

OBJECTIVE

The aim of this work was to delineate how reduced SCD1 activity affects gene expression, protein content and cellular fatty acids in differentiating murine preadipocytes.

METHODS

3T3-L1 preadipocytes were treated with an SCD1 inhibitor (10 nM) throughout differentiation. After 7 days, global gene expression, protein content and fatty acid profiles were examined using microarrays, western blotting and gas chromatography, respectively.

RESULTS

SCD1 inhibition increased the abundance of 16:0 and 18:0 (45% and 194%, respectively) and decreased 16:1n7 and 18:1n7 (61% and 35%, respectively) in differentiated preadipocytes. Interestingly, 18:1n9 levels increased by 61%. The augmented 18:0 suggested a possible increase in elongase activity. Elongase 6 (Elovl6) gene expression was increased 2.8-fold (P = 0.04); however, changes were not detected for ELOVL6 protein content. Microarray analysis revealed that genes affecting TG synthesis were downregulated with SCD1 inhibition, which coincided with a 33% decrease in cellular TG content.

CONCLUSION

These results provide new mechanistic insight into the role of SCD1 as a regulator of fatty acid profiles and TG synthesis in adipocytes, and reinforce that modulating SCD1 activity may help reduce the risk of obesity-related complications.

Molecular interplay between Δ5/Δ6 desaturases and long-chain fatty acids in the pathogenesis of non-alcoholic steatohepatitis

OBJECTIVE

The mechanisms underlying non-alcoholic steatohepatitis (NASH) are not completely elucidated. In the current study we integrated gene expression profiling of liver biopsies from NASH patients with translational studies in mouse models of steatohepatitis and pharmacological interventions in isolated hepatocytes to identify new molecular targets in NASH.

DESIGN AND RESULTS

Using oligonucleotide microarray analysis we identified a significant enrichment of genes involved in the multi-step catalysis of long-chain polyunsaturated fatty acids, namely, Δ-5 desaturase (Δ5D) and Δ6D in NASH. Increased expression of Δ5D and Δ6D at both mRNA and protein level were confirmed in livers from mice with high-fat diet-induced obesity and NASH. Gas chromatography analysis revealed impaired desaturation fluxes toward the ω-6 and ω-3 pathways resulting in increased ω-6 to ω-3 ratio and reduced ω-3 index in human and mouse fatty livers. Restoration of hepatic ω-3 content in transgenic fat-1 mice expressing an ω-3 desaturase, which allows the endogenous conversion of ω-6 into ω-3 fatty acids, produced a significant reduction in hepatic insulin resistance, steatosis, macrophage infiltration, necroinflammation and lipid peroxidation, accompanied by attenuated expression of genes involved in inflammation, fatty acid uptake and lipogenesis. These results were mostly reproduced by feeding obese mice with an exogenous ω-3-enriched diet. A combined Δ5D/Δ6D inhibitor, CP-24879, significantly reduced intracellular lipid accumulation and inflammatory injury in hepatocytes. Interestingly, CP-24879 exhibited superior antisteatotic and anti-inflammatory actions in fat-1 and ω-3-treated hepatocytes.

CONCLUSIONS

These findings indicate that impaired hepatic fatty acid desaturation and unbalanced ω-6 to ω-3 ratio play a role in the pathogenesis of NASH.

Hexadecenoic fatty acid isomers: a chemical biology approach for human plasma biomarker development

Hexadecenoic fatty acids are monounsaturated lipid components, which are interesting targets of plasma lipidomic studies and biomarker development. The main positional isomers, palmitoleic (9-cis-16:1) and sapienic acids (6-cis-16:1), have an endogenous origin from palmitic acid, the former being recognized as a component of adipose tissue with signaling activity, whereas the latter is mainly reported as a component of sebum. The trans 16:1 isomers are attributed so far to dietary sources of industrial and dairy fats, whereas the endogenous formation due to the free radical-mediated isomerization can represent an emerging, yet unexplored, pathway connected to cellular stress. Herein, we report a chemical biology approach for the development of hexadecenoic fatty acids as plasma biomarkers, with the first synthesis of 6-trans-16:1 and the efficient analytical setup with unambiguous assignment of 16:1 double bond position and geometry, which was applied to human commercial LDL and plasma cholesteryl esters. Sapienic acid was identified together with its geometrical trans isomer for the first time. The quantitation of hexadecenoic fatty acid isomers evidenced their different levels in the two lipid classes and LDL fractions, making us foresee interesting applications to the metabolic evaluation of fatty acid pathways. These findings open new perspectives for plasma lipidomics involving monounsaturated fatty acids, highlighting future developments for their evaluation in different health conditions including free radical stress.

Blood levels of saturated and monounsaturated fatty acids as markers of de novo lipogenesis and risk of prostate cancer

De novo lipogenesis has been implicated in prostate carcinogenesis, and blood levels of specific saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs) could reflect activity of this pathway. We used gas chromatography to measure blood SFA and MUFA levels in prediagnostic samples from 476 incident prostate cancer cases (1982-1995) in the Physicians' Health Study and an equal number of controls matched on age and smoking status. Five tagging polymorphisms in the fatty acid synthase (FASN) gene (rs1127678, rs6502051, rs4246444, rs12949488, and rs8066956) were related to blood SFA and MUFA levels. Conditional logistic regression was used to estimate the rate ratios, with 95% confidence intervals, of prostate cancer across quintiles of blood fatty acid levels. The polymorphisms rs6502051 and rs4246444 were associated with lower levels of 14:1n-5, 16:1n-7, and 18:1n-9. Blood levels of 16:1n-7 were associated with higher prostate cancer incidence, with rate ratios for men in increasing quintiles of 1.00, 1.40, 1.35, 1.44, and 1.97 (95% confidence interval: 1.27-3.06; Ptrend = 0.003). Furthermore, 16:1n-7 levels were positively related to incidence of high-grade (Gleason score ≥7) tumors (rate ratioQ5-Q1 = 3.92; 95% confidence interval: 1.72-8.94) but not low-grade tumors (rate ratioQ5-Q1 = 1.51; 95% confidence interval: 0.87-2.62) (Pheterogeneity = 0.02). Higher activity of enzymes involved in de novo lipogenesis, as reflected in blood levels of 16:1n-7, could be involved in the development of high-grade prostate cancer.

A phosphatidylinositol species acutely generated by activated macrophages regulates innate immune responses

Activation of macrophages with stimuli of the innate immune response results in the intense remodeling of arachidonate-containing phospholipids, leading to the mobilization of large quantities of this fatty acid for conversion into biologically active eicosanoids. As a consequence of this process, the arachidonate levels in membrane phospholipids markedly decrease. We have applied mass spectrometry-based lipid profiling to study the levels of arachidonate-containing phospholipids under inflammatory activation of macrophages. We identify an unusual inositol phospholipid molecule, PI(20:4/20:4), the levels of which do not decrease but actually increase by 300% after activation of the macrophages. PI(20:4/20:4) is formed and degraded rapidly, suggesting a role for this molecule in regulating cell signaling events. Using a metabolipidomic approach consisting in exposing the cells to deuterium-labeled arachidonate at the time they are exposed to stimuli, we show that PI(20:4/20:4) biosynthesis occurs via the sequential incorporation of arachidonate, first into the sn-2 position of a preformed phosphatidylinositol (PI) molecule, followed by the rapid introduction of a second arachidonate moiety into the sn-1 position. Generation requires the participation of cytosolic phospholipase A2α and CoA-dependent acyltransferases. PI(20:4/20:4) formation is also detected in vivo in murine peritonitis exudates. Elevating the intracellular concentration of PI(20:4/20:4) by introducing the lipid into the cells results in enhancement of the microbicidal capacity of macrophages, as measured by reactive oxygen metabolite production and lysozyme release. These findings suggest that PI(20:4/20:4) is a novel bioactive inositol phospholipid molecule that regulates innate immune responses in macrophages.

Arachidonoyl-phosphatidylcholine oscillates during the cell cycle and counteracts proliferation by suppressing Akt membrane binding

The activity of protein kinase B (Akt)--a major kinase promoting cell proliferation and survival--oscillates during the cell cycle. To investigate whether membrane phospholipids may regulate Akt phosphorylation and thus activity, we monitored the lipid profile of nocodazole-synchronized mouse NIH 3T3 fibroblasts during the cell cycle by liquid chromatography electrospray ionization tandem mass spectrometry (LC-MS/MS). The proportion of sn-2-arachidonoyl-phosphatidylcholine (20:4-PC) inversely correlated with Akt activity. Increasing the cellular ratio of 20:4-PC by supplementation of 20:4-PC to the cell culture medium diminished Akt [serine (Ser)473] phosphorylation. Saturated and monounsaturated phosphatidylcholines, used as control had no effect; 20:4-PC reduced cell proliferation relative to controls, interfered with S-phase transition, and suppressed Akt downstream signaling and cyclin expression like LY294002, which is a specific inhibitor of the phosphatidylinositol-3-kinase/Akt pathway. Additive effects of 20:4-PC and LY294002 were not observed, underlining the critical role of Akt for 20:4-PC signaling; 20:4-PC suppressed Akt membrane translocation as shown by immunofluorescence microscopy but left the concentration of the anchor lipid phosphatidylinositol-3,4,5-trisphosphate unchanged. An in vitro binding assay suggests that 20:4-PC attenuates the interaction of Akt with its membrane binding site. We conclude that 20:4-PC oscillates during the cell cycle and delays cell cycle progression by inhibiting Akt membrane binding.

Simultaneous activation of p38 and JNK by arachidonic acid stimulates the cytosolic phospholipase A2-dependent synthesis of lipid droplets in human monocytes

Exposure of human peripheral blood monocytes to free arachidonic acid (AA) results in the rapid induction of lipid droplet (LD) formation by these cells. This effect appears specific for AA in that it is not mimicked by other fatty acids, whether saturated or unsaturated. LDs are formed by two different routes: (i) the direct entry of AA into triacylglycerol and (ii) activation of intracellular signaling, leading to increased triacylglycerol and cholesteryl ester formation utilizing fatty acids coming from the de novo biosynthetic route. Both routes can be dissociated by the arachidonyl-CoA synthetase inhibitor triacsin C, which prevents the former but not the latter. LD formation by AA-induced signaling predominates, accounting for 60-70% of total LD formation, and can be completely inhibited by selective inhibition of the group IVA cytosolic phospholipase A(2)α (cPLA(2)α), pointing out this enzyme as a key regulator of AA-induced signaling. LD formation in AA-treated monocytes can also be blocked by the combined inhibition of the mitogen-activated protein kinase family members p38 and JNK, which correlates with inhibition of cPLA(2)α activation by phosphorylation. Collectively, these results suggest that concomitant activation of p38 and JNK by AA cooperate to activate cPLA(2)α, which is in turn required for LD formation possibly by facilitating biogenesis of this organelle, not by regulating neutral lipid synthesis.