An improved method for tissue long-chain acyl-CoA extraction and analysis

Comparison of colorimetric, fluorometric, and liquid chromatography-mass spectrometry assays for acetyl-coenzyme A

Acetyl-Coenzyme A is a central metabolite in catabolic and anabolic pathways as well as the acyl donor for acetylation reactions. Multiple quantitative measurement techniques for acetyl-CoA have been reported, including commercially available kits. Comparisons between techniques for acetyl-CoA measurement have not been reported. This lack of comparability between assays makes context-specific assay selection and interpretation of results reporting changes in acetyl-CoA metabolism difficult. We compared commercially available colorimetric ELISA and fluorometric enzymatic-based kits to liquid chromatography-mass spectrometry-based assays using tandem mass spectrometry (LC-MS/MS) and high-resolution mass spectrometry (LC-HRMS). The colorimetric ELISA kit did not produce interpretable results even with commercially available pure standards. The fluorometric enzymatic kit produced comparable results to the LC-MS-based assays depending on matrix and extraction. LC-MS/MS and LC-HRMS assays produced well-aligned results, especially when incorporating stable isotope-labeled internal standards. In addition, we demonstrated the multiplexing capability of the LC-HRMS assay by measuring a suite of short-chain acyl-CoAs in a variety of acute myeloid leukemia cell lines and patient cells.

Recent developments in the analytical approaches of acyl-CoAs to assess their role in mitochondrial fatty acid oxidation disorders

Fatty acid oxidation disorders (FAOD) are inborn errors of metabolism that occur due to deficiency of specific enzyme activities and transporter proteins involved in the mitochondrial metabolism of fatty acids, causing a deficiency in ATP production. The identification of suitable biomarkers plays a crucial role in predicting the future risk of disease and monitoring responses to therapies. Acyl-CoAs are directly involved in the steps of fatty acid oxidation and are the primary biomarkers associated with FAOD. However, acyl-CoAs are not used as diagnostic biomarkers in hospitals and clinics as they are present intracellularly with low endogenous levels. Additionally, the analytical method development of acyl-CoAs is quite challenging due to diverse physicochemical properties and instability. Hence, secondary biomarkers such as acylcarnitines are used for the identification of FAOD. In this review, the focus is on the analytical techniques that have evolved over the years for the identification and quantitation of acyl-CoAs. Among these techniques, liquid chromatography-mass spectrometry clearly has an advantage in terms of sensitivity and selectivity. Stable isotope labeling by essential nutrients in cell culture (SILEC) enables the generation of labeled internal standards. Each acyl-CoA species has a distinct pattern of instability and degradation, and the use of appropriately matched internal standards can compensate for such issues. Although significant progress has been made in measuring acyl-CoAs, more efforts are needed for bringing these technical advancements to hospitals and clinics. This review also highlights the difficulties involved in the routine use of acyl-CoAs as a diagnostic biomarker and some of the measures that can be adopted by clinics and hospitals for overcoming these limitations.

Comparison of colorimetric, fluorometric, and liquid chromatography-mass spectrometry assays for acetyl-coenzyme A

Acetyl-Coenzyme A is a central metabolite in catabolic and anabolic pathways as well as the acyl donor for acetylation reactions. Multiple quantitative measurement techniques for acetyl-CoA have been reported, including commercially available kits. Comparisons between techniques for acetyl-CoA measurement have not been reported. This lack of comparability between assays makes context-specific assay selection and interpretation of results reporting changes in acetyl-CoA metabolism difficult. We compared commercially available colorimetric ELISA and fluorometric enzymatic-based kits to liquid chromatography-mass spectrometry-based assays using tandem mass spectrometry (LC-MS/MS) and high-resolution mass spectrometry (LC-HRMS). The colorimetric ELISA kit did not produce interpretable results even with commercially available pure standards. The fluorometric enzymatic kit produced comparable results to the LC-MS-based assays depending on matrix and extraction. LC-MS/MS and LC-HRMS assays produced well-aligned results, especially when incorporating stable isotope-labeled internal standards. In addition, we demonstrated the multiplexing capability of the LC-HRMS assay by measuring a suite of short-chain acyl-CoAs in a variety of acute myeloid leukemia cell lines and patient cells.

Techniques for the Measurement of Molecular Species of Acyl-CoA in Plants and Microalgae

The acyl-CoA pool is pivotal in cellular metabolism. The ability to provide reliable estimates of acyl-CoA abundance and distribution between molecular species in plant tissues and microalgae is essential to our understanding of lipid metabolism and acyl exchange. Acyl-CoAs are typically found in low abundance and require specific methods for extraction, separation and detection. Here we describe methods for acyl-CoA extraction and measurement in plant tissues and microalgae, with a focus on liquid chromatography hyphenated to detection techniques including ultraviolet (UV), fluorescence and mass spectrometry (MS). We address the resolution of isobaric species and the selection of columns needed to achieve this, including the analysis of branched chain acyl-CoA thioesters. For MS analyses, we describe diagnostic ions for the identification of acyl-CoA species and how these can be used for both discovery of new species (data dependent acquisition) and routine quantitation (triple quadrupole MS with multiple reaction monitoring).

Structure and Mechanism of a Unique Diiron Center in Mammalian Stearoyl-CoA Desaturase

Stearoyl-CoA desaturase 1 (SCD1) is a membrane-embedded metalloenzyme that catalyzes the formation of a double bond on a saturated acyl-CoA. SCD1 has a diiron center and its proper function requires an electron transport chain composed of NADH (or NADPH), cytochrome b5 reductase (b5R), and cytochrome b5 (cyt b5). Since SCD1 is a key regulator in fat metabolism and is required for survival of cancer cells, there is intense interest in targeting SCD1 for various metabolic diseases and cancers. Crystal structures of human and mouse SCD1 were reported recently; however, both proteins have two zinc ions instead of two iron ions in the catalytic center, and as a result, the enzymes are inactive. Here we report a general approach for incorporating iron into heterologously expressed proteins in HEK293 cells. We produced mouse SCD1 that contains a diiron center and visualized its diiron center by solving its crystal structure to 3.5 Å. We assembled the entire electron transport chain using the purified soluble domains of cyt b5 and b5R, and the purified mouse SCD1, and we showed that three proteins coordinate to produce proper products. These results established an in vitro system that allows precise perturbations of the electron transport chain for the understanding of the catalytic mechanism in SCD1.

Inhibition of Endothelial Notch Signaling Impairs Fatty Acid Transport and Leads to Metabolic and Vascular Remodeling of the Adult Heart

BACKGROUND

Nutrients are transported through endothelial cells before being metabolized in muscle cells. However, little is known about the regulation of endothelial transport processes. Notch signaling is a critical regulator of metabolism and angiogenesis during development. Here, we studied how genetic and pharmacological manipulation of endothelial Notch signaling in adult mice affects endothelial fatty acid transport, cardiac angiogenesis, and heart function.

METHODS

Endothelial-specific Notch inhibition was achieved by conditional genetic inactivation of Rbp-jκ in adult mice to analyze fatty acid metabolism and heart function. Wild-type mice were treated with neutralizing antibodies against the Notch ligand Delta-like 4. Fatty acid transport was studied in cultured endothelial cells and transgenic mice.

RESULTS

Treatment of wild-type mice with Delta-like 4 neutralizing antibodies for 8 weeks impaired fractional shortening and ejection fraction in the majority of mice. Inhibition of Notch signaling specifically in the endothelium of adult mice by genetic ablation of Rbp-jκ caused heart hypertrophy and failure. Impaired heart function was preceded by alterations in fatty acid metabolism and an increase in cardiac blood vessel density. Endothelial Notch signaling controlled the expression of endothelial lipase, Angptl4, CD36, and Fabp4, which are all needed for fatty acid transport across the vessel wall. In endothelial-specific Rbp-jκ-mutant mice, lipase activity and transendothelial transport of long-chain fatty acids to muscle cells were impaired. In turn, lipids accumulated in the plasma and liver. The attenuated supply of cardiomyocytes with long-chain fatty acids was accompanied by higher glucose uptake, increased concentration of glycolysis intermediates, and mTOR-S6K signaling. Treatment with the mTOR inhibitor rapamycin or displacing glucose as cardiac substrate by feeding a ketogenic diet prolonged the survival of endothelial-specific Rbp-jκ-deficient mice.

CONCLUSIONS

This study identifies Notch signaling as a novel regulator of fatty acid transport across the endothelium and as an essential repressor of angiogenesis in the adult heart. The data imply that the endothelium controls cardiomyocyte metabolism and function.

Lipidomics analysis of long-chain fatty acyl-coenzyme As in liver, brain, muscle and adipose tissue by liquid chromatography/tandem mass spectrometry

RATIONALE

Long-chain fatty acyl-coenzyme As (FA-CoAs) are important bioactive molecules, playing key roles in biosynthesis of fatty acids, membrane trafficking and signal transduction. Development of sensitive analytical methods for profiling theses lipid species in various tissues is critical to understand their biological activity. A high-pressure liquid chromatography/tandem mass spectrometry method has been developed for the quantitative analysis and screening of long-chain FACoAs in liver, brain, muscle and adipose tissue.

METHODS

The sample preparation method consists of tissue homogenization, extraction with organic solvent and reconstitution in an ammonium hydroxide buffer. Extracts are separated by liquid chromatography (LC) on a reversed-phase column and detected by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in positive mode. An additional neutral loss scan allows for untargeted FA-CoAs screening.

RESULTS

Extraction was optimized for low sample load (10 mg) of four tissue types (liver, brain, muscle and adipose tissue) with recoveries between 60-140% depending on the analyte and tissue type. Targeted quantification was validated for ten FA-CoAs in the range 0.1-500 ng/mL with accuracies between 85-120%.

CONCLUSIONS

We have developed and validated a LC/MS/MS method for the quantifications and screening of long-chain FA-CoAs in four different types of mammalian tissue. The extraction method is straightforward and long-chain FA-CoA species can be quantified using only minimum amount of tissue. Copyright © 2016 John Wiley & Sons, Ltd.

Fasting-induced liver GADD45β restrains hepatic fatty acid uptake and improves metabolic health

Recent studies have demonstrated that repeated short‐term nutrient withdrawal (i.e. fasting) has pleiotropic actions to promote organismal health and longevity. Despite this, the molecular physiological mechanisms by which fasting is protective against metabolic disease are largely unknown. Here, we show that, metabolic control, particularly systemic and liver lipid metabolism, is aberrantly regulated in the fasted state in mouse models of metabolic dysfunction. Liver transcript assays between lean/healthy and obese/diabetic mice in fasted and fed states uncovered “growth arrest and DNA damage‐inducible” GADD45β as a dysregulated gene transcript during fasting in several models of metabolic dysfunction including ageing, obesity/pre‐diabetes and type 2 diabetes, in both mice and humans. Using whole‐body knockout mice as well as liver/hepatocyte‐specific gain‐ and loss‐of‐function strategies, we revealed a role for liver GADD45β in the coordination of liver fatty acid uptake, through cytoplasmic retention of FABP1, ultimately impacting obesity‐driven hyperglycaemia. In summary, fasting stress‐induced GADD45β represents a liver‐specific molecular event promoting adaptive metabolic function.

Advanced Shotgun Lipidomics for Characterization of Altered Lipid Patterns in Neurodegenerative Diseases and Brain Injury

Multi-dimensional mass spectrometry-based shotgun lipidomics (MDMS-SL) is a powerful technology platform among current lipidomics practices due to its high efficiency, sensitivity, and reproducibility, as well as its broad coverage. This platform has been widely used to determine the altered lipid profiles induced by diseases, injury, genetic manipulations, drug treatments, and aging, among others. Herein, we summarize the principles underlying this platform and present a protocol for analysis of many of the lipid classes and subclasses covered by MDMS-SL directly from lipid extracts of brain samples. We believe that this protocol can aid researchers in the field to determine altered lipid patterns in neurodegenerative diseases and brain injury.

Methods for measuring CoA and CoA derivatives in biological samples

CoA (coenzyme A) is a ubiquitous and essential cofactor that acts as an acyl group carrier in biochemical reactions. Apart from participating in numerous metabolic pathways as substrates and intermediates, CoA and a number of its thioester derivatives, such as acetyl-CoA, can also directly regulate the activity of proteins by allosteric mechanisms and by affecting protein acetylation reactions. Cellular levels of CoA and CoA thioesters change under various physiological and pathological conditions. Defective CoA biosynthesis is implicated in NBIA (neurodegeneration with brain iron accumulation). However, the exact role of CoA in the pathogenesis of NBIA is not well understood. Accurate and reliable assays for measuring CoA species in biological samples are essential for studying the roles of CoA and CoA derivatives in health and disease. The present mini-review discusses methods that are commonly used to measure CoA species in biological samples.

A fast one-step extraction and UPLC-MS/MS analysis for E2/D 2 series prostaglandins and isoprostanes

Prostaglandins (PG) and isoprostanes (iso-PG) may be derived through cyclooxygenase or free radical pathways and are important signaling molecules that are also robust biomarkers of oxidative stress. Their quantification is important for understanding many biological processes where PG, iso-PG, or oxidative stress are involved. One of the common methods for PG and iso-PG quantifications is LC-MS/MS that allows a highly selective, sensitive, simultaneous analysis for prostanoids without derivatization. However, the currently used LC-MS/MS methods require a multi-step extraction and a long (within an hour) LC separation to achieve simultaneous separation and analysis of the major iso-PG. The developed and validated for brain tissue analysis one-step extraction protocol and UPLC-MS/MS method significantly increases the recovery of the PG extraction up to 95 %, and allows for a much faster (within 4 min) major iso-PGE2 and -PGD2 separation with 5 times narrower chromatographic peaks as compared to previously used methods. In addition, it decreases the time and cost of analysis due to the one-step extraction approach performed in disposable centrifuge tubes. All together, this significantly increases the sensitivity, and the time and cost efficiency of the PG and iso-PG analysis.

Analysis of mammalian fatty acyl-coenzyme A species by mass spectrometry and tandem mass spectrometry

Acyl-CoAs are intermediates of numerous metabolic processes in eukaryotic cells, including beta-oxidation within mitochondria and peroxisomes, and the biosynthesis/remodeling of lipids (e.g. mono-, di-, and triglycerides, phospholipids and sphingolipids). Investigations of lipid metabolism have been advanced by the ability to quantitate acyl-CoA intermediates via liquid chromatography coupled to electrospray ionization-tandem mass spectrometric detection (LC-ESI-MS/MS), which is presently one of the most sensitive and specific analytical methods for both lipids and acyl-CoAs. This review of acyl-CoA analysis by mass spectrometry focuses on mammalian samples and long-chain analytes (i.e. palmitoyl-CoA), particularly reports of streamlined methodology, improved recovery, or expansion of the number of acyl chain-lengths amenable to quantitation.

Reversible high affinity inhibition of phosphofructokinase-1 by acyl-CoA: a mechanism integrating glycolytic flux with lipid metabolism

The enzyme phosphofructokinase-1 (PFK-1) catalyzes the first committed step of glycolysis and is regulated by a complex array of allosteric effectors that integrate glycolytic flux with cellular bioenergetics. Here, we demonstrate the direct, potent, and reversible inhibition of purified rabbit muscle PFK-1 by low micromolar concentrations of long chain fatty acyl-CoAs (apparent Ki∼1 μM). In sharp contrast, short chain acyl-CoAs, palmitoylcarnitine, and palmitic acid in the presence of CoASH were without effect. Remarkably, MgAMP and MgADP but not MgATP protected PFK-1 against inhibition by palmitoyl-CoA indicating that acyl-CoAs regulate PFK-1 activity in concert with cellular high energy phosphate status. Furthermore, incubation of PFK-1 with [1-(14)C]palmitoyl-CoA resulted in robust acylation of the enzyme that was reversible by incubation with acyl-protein thioesterase-1 (APT1). Importantly, APT1 reversed palmitoyl-CoA-mediated inhibition of PFK-1 activity. Mass spectrometric analyses of palmitoylated PFK-1 revealed four sites of acylation, including Cys-114, Cys-170, Cys-351, and Cys-577. PFK-1 in both skeletal muscle extracts and in purified form was inhibited by S-hexadecyl-CoA, a nonhydrolyzable palmitoyl-CoA analog, demonstrating that covalent acylation of PFK-1 was not required for inhibition. Tryptic footprinting suggested that S-hexadecyl-CoA induced a conformational change in PFK-1. Both palmitoyl-CoA and S-hexadecyl-CoA increased the association of PFK-1 with Ca2+/calmodulin, which attenuated the binding of palmitoylated PFK-1 to membrane vesicles. Collectively, these results demonstrate that fatty acyl-CoA modulates phosphofructokinase activity through both covalent and noncovalent interactions to regulate glycolytic flux and enzyme membrane localization via the branch point metabolic node that mediates lipid flux through anabolic and catabolic pathways.

Long-chain acyl-CoA synthetase 4 modulates prostaglandin E₂ release from human arterial smooth muscle cells

Long-chain acyl-CoA synthetases (ACSLs) catalyze the thioesterification of long-chain FAs into their acyl-CoA derivatives. Purified ACSL4 is an arachidonic acid (20:4)-preferring ACSL isoform, and ACSL4 is therefore a probable regulator of lipid mediator production in intact cells. Eicosanoids play important roles in vascular homeostasis and disease, yet the role of ACSL4 in vascular cells is largely unknown. In the present study, the ACSL4 splice variant expressed in human arterial smooth muscle cells (SMCs) was identified as variant 1. To investigate the function of ACSL4 in SMCs, ACSL4 variant 1 was overexpressed, knocked-down by small interfering RNA, or its enzymatic activity acutely inhibited in these cells. Overexpression of ACSL4 resulted in a markedly increased synthesis of arachidonoyl-CoA, increased 20:4 incorporation into phosphatidylethanolamine, phosphatidylinositol, and triacylglycerol, and reduced cellular levels of unesterified 20:4. Accordingly, secretion of prostaglandin E₂ (PGE₂) was blunted in ACSL4-overexpressing SMCs compared with controls. Conversely, acute pharmacological inhibition of ACSL4 activity resulted in increased release of PGE₂. However, long-term downregulation of ACSL4 resulted in markedly reduced PGE₂ secretion. Thus, ACSL4 modulates PGE₂ release from human SMCs. ACSL4 may regulate a number of processes dependent on the release of arachidonic acid-derived lipid mediators in the arterial wall.

An anatomical and temporal portrait of physiological substrates for fatty acid amide hydrolase

Fatty acid amide hydrolase (FAAH) regulates amidated lipid transmitters, including the endocannabinoid anandamide and its N-acyl ethanolamine (NAE) congeners and transient receptor potential channel agonists N-acyl taurines (NATs). Using both the FAAH inhibitor PF-3845 and FAAH(-/-) mice, we present a global analysis of changes in NAE and NAT metabolism caused by FAAH disruption in central and peripheral tissues. Elevations in anandamide (and other NAEs) were tissue dependent, with the most dramatic changes occurring in brain, testis, and liver of PF-3845-treated or FAAH(-/-) mice. Polyunsaturated NATs accumulated to very high amounts in the liver, kidney, and plasma of these animals. The NAT profile in brain tissue was markedly different and punctuated by significant increases in long-chain NATs found exclusively in FAAH(-/-), but not in PF-3845-treated animals. Suspecting that this difference might reflect a slow pathway for NAT biosynthesis, we treated mice chronically with PF-3845 for 6 days and observed robust elevations in brain NATs. These studies, taken together, define the anatomical and temporal features of FAAH-mediated NAE and NAT metabolism, which are complemented and probably influenced by kinetically distinguishable biosynthetic pathways that produce these lipids in vivo.

A review of lipidomic technologies applicable to sphingolipidomics and their relevant applications

Sphingolipidomics, a branch of lipidomics, focuses on the large-scale study of the cellular sphingolipidomes. In the current review, two main approaches for the analysis of cellular sphingolipidomes (i.e. LC-MS- or LC-MS/MS-based approach and shotgun lipidomics-based approach) are briefly discussed. Their advantages, some considerations of these methods, and recent applications of these approaches are summarized. It is the authors' sincere hope that this review article will add to the readers understanding of the advantages and limitations of each developed method for the analysis of a cellular sphingolipidome.

C75 is converted to C75-CoA in the hypothalamus, where it inhibits carnitine palmitoyltransferase 1 and decreases food intake and body weight

Central nervous system administration of C75 produces hypophagia and weight loss in rodents identifying C75 as a potential drug against obesity and type 2 diabetes. However, the mechanism underlying this effect is unknown. Here we show that C75-CoA is generated chemically, in vitro and in vivo from C75 and that it is a potent inhibitor of carnitine palmitoyltranferase 1 (CPT1), the rate-limiting step of fatty-acid oxidation. Three-D docking and kinetic analysis support the inhibitory effect of C75-CoA on CPT1. Central nervous system administration of C75 in rats led to C75-CoA production, inhibition of CPT1 and lower body weight and food intake. Our results suggest that inhibition of CPT1, and thus increased availability of fatty acids in the hypothalamus, contribute to the pharmacological mechanism of C75 to decrease food intake.

Shotgun lipidomics reveals the temporally dependent, highly diversified cardiolipin profile in the mammalian brain: temporally coordinated postnatal diversification of cardiolipin molecular species with neuronal remodeling

Large-scale neuronal remodeling through apoptosis occurs shortly after birth in all known mammalian species. Apoptosis, in large part, depends upon critical interactions between mitochondrial membranes and cytochrome c. Herein, we examined the hypothesis that the large-scale reorganization of neuronal circuitry after birth is accompanied by profound alterations in cardiolipin (CL) content and molecular species distribution. During embryonic development, over 100 CL molecular species were identified and quantitated in murine neuronal tissues. The embryonic CL profile was notable for the presence of abundant amounts of relatively short aliphatic chains (e.g., palmitoleic and oleic acids). In sharp contrast, after birth, the CL profile contained a remarkably complex repertoire of CL molecular species, in which the signaling fatty acids (i.e., arachidonic and docosahexaenoic acids) were markedly increased. These results identify the rapid remodeling of CL in the perinatal period with resultant alterations in the physical properties of the mitochondrial membrane. The complex distribution of aliphatic chains in the neuronal CL pool is separate and distinct from that in other organs (e.g., heart, liver, etc.), where CL molecular species contain predominantly only one major type of aliphatic chain (e.g., linoleic acid). Analyses of mRNA levels by real-time quantitative polymerase chain reactions suggested that the alterations in CL content were due to the combined effects of both attenuation of de novo CL biosynthesis and decreased remodeling of CL. Collectively, these results provide a new perspective on the complexity of CL in neuronal signaling, mitochondrial bioenergetics, and apoptosis.

Alkaline methanolysis of lipid extracts extends shotgun lipidomics analyses to the low-abundance regime of cellular sphingolipids

Sphingolipids that contain a sphingoid base are composed of hundreds to thousands of distinct compounds, many of which serve as lipid regulators of biological functions. The global analysis of the large number of low-abundance sphingolipid molecular species has been hampered in many cases by the sphingolipid molecular species being overwhelmed by the quantity of other classes of lipid (e.g., glycerophospholipid) molecular species present, thereby imposing severe restrictions on the dynamic range of their measurement using shotgun lipidomics. Herein, we developed a facile approach in which the sphingolipids of cellular extracts were dramatically enriched by direct alkaline methanolysis of lipid extracts followed by extraction to remove the large majority of other endogenous lipid classes. Through direct infusion of the resultant enriched solution, we identified and quantitated a variety of very-low-abundance sphingolipid classes (e.g., sphingosine, psychosine, and lysosphingomyelin) and molecular species (e.g., sphingomyelin) using electrospray ionization mass spectrometry (i.e., shotgun sphingolipidomics). Accordingly, through utilization of these facile enrichment techniques, direct penetrance into the sphingolipidomes has been greatly extended, facilitating new insights into their metabolism and signaling functions in biological systems.

Discovery of potent, selective, orally bioavailable stearoyl-CoA desaturase 1 inhibitors

Stearoyl-CoA desaturase 1 (SCD1) catalyzes the committed step in the biosynthesis of monounsaturated fatty acids from saturated, long-chain fatty acids. Studies with SCD1 knockout mice have established that these animals are lean and protected from leptin deficiency-induced and diet-induced obesity, with greater whole body insulin sensitivity than wild-type animals. In this work, we have discovered a series of potent, selective, orally bioavailable SCD1 inhibitors based on a known pyridazine carboxamide template. The representative lead inhibitor 28c also demonstrates excellent cellular activity in blocking the conversion of saturated long-chain fatty acid-CoAs (LCFA-CoAs) to monounsaturated LCFA-CoAs in HepG2 cells.

Alterations in myocardial cardiolipin content and composition occur at the very earliest stages of diabetes: a shotgun lipidomics study

Recently, we have identified the dramatic depletion of cardiolipin (CL) in diabetic myocardium 6 weeks after streptozotocin (STZ) injection that was accompanied by increases in triacylglycerol content and multiple changes in polar lipid molecular species. However, after 6 weeks in the diabetic state, the predominant lipid hallmarks of diabetic cardiomyopathy were each present concomitantly, and thus, it was impossible to identify the temporal course of lipid alterations in diabetic myocardium. Using the newly developed enhanced shotgun lipidomics approach, we demonstrated the dramatic loss of abundant CL molecular species in STZ-treated hearts at the very earliest stages of diabetes accompanied by a profound remodeling of the remaining CL molecular species including a 16-fold increase in the content of 18:2-22:6-22:6-22:6 CL. These alterations in CL metabolism occur within days after the induction of the diabetic state and precede the triacylglycerol accumulation manifest in diabetic myocardium. Similarly, in ob/ob mice, a dramatic and progressive redistribution from 18:2 FA-containing CL molecular species to 22:6 FA-containing CL molecular species was also identified. Collectively, these results demonstrate alterations in CL hydrolysis and remodeling at the earliest stages of diabetes and are consistent with a role for alterations in CL content in precipitating mitochondrial dysfunction in diabetic cardiomyopathy.

α-Synuclein gene ablation increases docosahexaenoic acid incorporation and turnover in brain phospholipids

Previously, we demonstrated that ablation of alpha-synuclein (Snca) reduces arachidonate (20:4n-6) turnover in brain phospholipids through modulation of an endoplasmic reticulum-localized acyl-CoA synthetase (Acsl). The effect of Snca ablation on docosahexaenoic acid (22:6n-3) metabolism is unknown. In the present study, we examined the effect of Snca gene ablation on brain 22:6n-3 metabolism. We determined 22:6n-3 uptake and incorporation into brain phospholipids by infusing awake, wild-type and Snca-/- mice with [1-14C]22:6n-3 using steady-state kinetic modeling. In addition, because Snca modulates 20:4n-6-CoA formation, we assessed microsomal Acsl activity using 22:6n-3 as a substrate. Although Snca gene ablation does not affect brain 22:6n-3 uptake, brain 22:6n-3-CoA mass was elevated 1.5-fold in the absence of Snca. This is consistent with the 1.6- to 2.2-fold increase in the incorporation rate and turnover in ethanolamine glycerophospholipid, phosphatidylserine, and phosphatidylinositol pools. Increased 22:6n-3-CoA mass was not the result of altered Acsl activity, which was unaffected by the absence of Snca. While Snca bound 22:6n-3, Kd = 1.0 +/- 0.5 micromol/L, it did not bind 22:6n-3-CoA. These effects of Snca gene deletion on 22:6n-3 brain metabolism are opposite to what we reported previously for brain 20:4n-6 metabolism and are likely compensatory for the decreased 20:4n-6 metabolism in brains of Snca-/- mice.

Acyl-CoA synthetase activity links wild-type but not mutant alpha-synuclein to brain arachidonate metabolism

Because alpha-synuclein (Snca) has a role in brain lipid metabolism, we determined the impact that the loss of alpha-synuclein had on brain arachidonic acid (20:4n-6) metabolism in vivo using Snca-/- mice. We measured [1-(14)C]20:4n-6 incorporation and turnover kinetics in brain phospholipids using an established steady-state kinetic model. Liver was used as a negative control, and no changes were observed between groups. In Snca-/- brains, there was a marked reduction in 20:4n-6-CoA mass and in microsomal acyl-CoA synthetase (Acsl) activity toward 20:4n-6. Microsomal Acsl activity was completely restored after the addition of exogenous wild-type mouse or human alpha-synuclein, but not by A30P, E46K, and A53T forms of alpha-synuclein. Acsl and acyl-CoA hydrolase expression was not different between groups. The incorporation and turnover of 20:4n-6 into brain phospholipid pools were markedly reduced. The dilution coefficient lambda, which indicates 20:4n-6 recycling between the acyl-CoA pool and brain phospholipids, was increased 3.3-fold, indicating more 20:4n-6 was entering the 20:4n-6-CoA pool from the plasma relative to that being recycled from the phospholipids. This is consistent with the reduction in Acsl activity observed in the Snca-/- mice. Using titration microcalorimetry, we determined that alpha-synuclein bound free 20:4n-6 (Kd = 3.7 microM) but did not bind 20:4n-6-CoA. These data suggest alpha-synuclein is involved in substrate presentation to Acsl rather than product removal. In summary, our data demonstrate that alpha-synuclein has a major role in brain 20:4n-6 metabolism through its modulation of endoplasmic reticulum-localized acyl-CoA synthetase activity, although mutant forms of alpha-synuclein fail to restore this activity.

Immediate no-flow ischemia decreases rat heart nonesterified fatty acid and increases acyl-CoA species concentrations

Tissues changes in FA metabolism can occur quite rapidly in response to ischemia and may require immediate microwave fixation to determine basal concentrations. The present study aimed to quantify the effects of immediate no-flow ischemia on concentrations of individual nonesterified FA (NEFA) and acyl-CoA species in the rat heart. Male CDF 344 rats were anesthetized and decapitated either 5 min prior to being microwaved (5.5 kW, 3.4 s, twice) to produce ischemia or microwaved prior to decapitation (nonischemic). Hearts were then removed and used to measure the concentrations of acyl-CoA species and FA in several lipid classes. The ischemic heart total NEFA concentration was significantly lower than that in the nonischemic heart (11.9 vs. 19.0 nmol/g). Several individual NEFA concentrations were decreased by 31-85%. Ischemic heart total long-chain acyl-CoA concentrations (21.0 nmol/g) were significantly higher than those in nonischemic hearts (11.4 nmol/g). Increased concentrations of individual acyl-CoA species occurred in palmitoyl-CoA, stearoyl-CoA, oleoyl-CoA, and linoleoyl-CoA. Concentrations of short-chain acetyl-CoA and beta-hydroxy-beta-methylglutaryl-CoA were also two- to three-fold higher in ischemic hearts than in nonischemic hearts. The FA concentration in TG and phospholipids generally did not differ between the groups. Decreases in concentrations of individual FA and increases in acyl-CoA species during no-flow ischemia occur very rapidly within the heart. Although it is not clear how these alterations contribute to the pathogenesis of ischemia, it is evident that future studies attempting to quantify basal levels of these metabolites could use microwave fixation.

Low liver conversion rate of alpha-linolenic to docosahexaenoic acid in awake rats on a high-docosahexaenoate-containing diet

We quantified the rates of incorporation of alpha-linolenic acid (alpha-LNA; 18:3n-3) into "stable" lipids (triacylglycerol, phospholipid, cholesteryl ester) and the rate of conversion of alpha-LNA to docosahexaenoic acid (DHA; 22: 6n-3) in the liver of awake male rats on a high-DHA-containing diet after a 5-min intravenous infusion of [1-(14)C]alpha-LNA. At 5 min, 72.7% of liver radioactivity (excluding unesterified fatty acid radioactivity) was in stable lipids, with the remainder in the aqueous compartment. Using our measured specific activity of liver alpha-LNA-CoA, in the form of the dilution coefficient lambda(alpha-LNA-CoA), we calculated incorporation rates of unesterified alpha-LNA into liver triacylglycerol, phospholipid, and cholesteryl ester as 2,401, 749, and 9.6 nmol/s/g x 10(-4), respectively, corresponding to turnover rates of 3.2, 8.7, and 2.9%/min and half-lives of 8-24 min. A lower limit for the DHA synthesis rate from alpha-LNA equaled 15.8 nmol/s/g x 10(-4) (0.5% of the net in corporation rate). Thus, in rats on a high-DHA-containing diet, rates of beta-oxidation and esterification of alpha-LNA into stable liver lipids are high, whereas its conversion to DHA is comparatively low and insufficient to supply significant DHA to the brain. High incorporation and turnover rates likely reflect a high secretion rate by liver of stable lipids within very low density lipoproteins.

Mitochondrial lipid abnormality and electron transport chain impairment in mice lacking alpha-synuclein

The presynaptic protein alpha-synuclein, implicated in Parkinson disease (PD), binds phospholipids and has a role in brain fatty acid (FA) metabolism. In mice lacking alpha-synuclein (Snca-/-), total brain steady-state mass of the mitochondria-specific phospholipid, cardiolipin, is reduced 22% and its acyl side chains show a 51% increase in saturated FAs and a 25% reduction in essential n-6, but not n-3, polyunsaturated FAs. Additionally, 23% reduction in phosphatidylglycerol content, the immediate biosynthetic precursor of cardiolipin, was observed without alterations in the content of other brain phospholipids. Consistent with these changes, more ordered lipid head group and acyl chain packing with enhanced rotational motion of diphenylhexatriene (DPH) about its long axis were demonstrated in time-resolved DPH fluorescence lifetime experiments. These abnormalities in mitochondrial membrane properties were associated with a 15% reduction in linked complex I/III activity of the electron transport chain, without reductions in mitochondrial number, complex II/III activity, or individual complex I, II, III, or IV activity. Reduced complex I activity is thought to be a critical factor in the development of PD. Thus, altered membrane composition and structure and impaired complex I/III function in Snca-/- brain suggest a relationship between alpha-synuclein's role in brain lipid metabolism, mitochondrial function, and PD.

Alpha-synuclein gene deletion decreases brain palmitate uptake and alters the palmitate metabolism in the absence of alpha-synuclein palmitate binding

Alpha-synuclein is an abundant protein in the central nervous system that is associated with a number of neurodegenerative disorders, including Parkinson's disease. Its physiological function is poorly understood, although recently it was proposed to function as a fatty acid binding protein. To better define a role for alpha-synuclein in brain fatty acid uptake and metabolism, we infused awake, wild-type, or alpha-synuclein gene-ablated mice with [1-(14)C]palmitic acid (16:0) and assessed fatty acid uptake and turnover kinetics in brain phospholipids. Alpha-synuclein deficiency decreased brain 16:0 uptake 35% and reduced its targeting to the organic fraction. The incorporation coefficient for 16:0 entering the brain acyl-CoA pool was significantly decreased 36% in alpha-synuclein gene-ablated mice. Because incorporation coefficients alone are not predictive of fatty acid turnover in individual phospholipid classes, we calculated kinetic values for 16:0 entering brain phospholipid pools. Alpha-synuclein deficiency decreased the incorporation rate and fractional turnover of 16:0 in a number of phospholipid classes, but also increased the incorporation rate and fractional turnover of 16:0 in the choline glycerophospholipids. No differences in incorporation rate or turnover were observed in liver phospholipids, confirming that these changes in lipid metabolism were brain specific. Using titration microcalorimetry, we observed no binding of 16:0 or oleic acid to alpha-synuclein in vitro. Thus, alpha-synuclein has effects on 16:0 uptake and metabolism similar to those of an FABP, but unlike FABP, it does not directly bind 16:0; hence, the mechanism underlying these effects is different from that of a classical FABP.

Acyl-coenzyme A binding protein expression alters liver fatty acyl-coenzyme A metabolism

Although studies in vitro and in yeast suggest that acyl-CoA binding protein ACBP may modulate long-chain fatty acyl-CoA (LCFA-CoA) distribution, its physiological function in mammals is unresolved. To address this issue, the effect of ACBP on liver LCFA-CoA pool size, acyl chain composition, distribution, and transacylation into more complex lipids was examined in transgenic mice expressing a higher level of ACBP. While ACBP transgenic mice did not exhibit altered body or liver weight, liver LCFA-CoA pool size increased by 69%, preferentially in saturated and polyunsaturated, but not monounsaturated, LCFA-CoAs. Intracellular LCFA-CoA distribution was also altered such that the ratio of LCFA-CoA content in (membranes, organelles)/cytosol increased 2.7-fold, especially in microsomes but not mitochondria. The increased distribution of specific LCFA-CoAs to the membrane/organelle and microsomal fractions followed the same order as the relative LCFA-CoA binding affinity exhibited by murine recombinant ACBP: saturated > monounsaturated > polyunsaturated C14-C22 LCFA-CoAs. Consistent with the altered microsomal LCFA-CoA level and distribution, enzymatic activity of liver microsomal glycerol-3-phosphate acyltransferase (GPAT) increased 4-fold, liver mass of phospholipid and triacylglyceride increased nearly 2-fold, and relative content of monounsaturated C18:1 fatty acid increased 44% in liver phospholipids. These effects were not due to the ACBP transgene altering the protein levels of liver microsomal acyltransferase enzymes such as GPAT, lysophosphatidic acid acyltransferase (LAT), or acyl-CoA cholesterol acyltransferase 2 (ACAT-2). Thus, these data show for the first time in a physiological context that ACBP expression may play a role in LCFA-CoA metabolism.