Rapid measurement of plasma free fatty acid concentration and isotopic enrichment using LC/MS

Deletion of sphingosine 1-phosphate receptor 1 in myeloid cells reduces hepatic inflammatory macrophages and attenuates MASH

BACKGROUND

Immune cell-driven inflammation is a key mediator of metabolic dysfunction-associated steatohepatitis (MASH) progression. We have previously demonstrated that pharmacological sphingosine 1-phosphate (S1P) receptor modulation ameliorates MASH and is associated with attenuated accumulation of intrahepatic macrophage and T-cell subsets. Although S1P receptors are expressed on several immune cell types, given the prominent role of monocyte-derived recruited macrophages in the sterile inflammation of MASH, we hypothesized that deletion of S1P receptor 1 (S1P1) on myeloid cells may ameliorate MASH by reducing the accumulation of proinflammatory monocyte-derived macrophages in the liver.

METHODS

The LyzMCre approach was used to generate myeloid cell-specific knockout mice, termed S1pr1MKO. Littermate S1pr1loxp/loxp mice were used as wild-type controls. MASH was established by feeding mice a high-fat, -fructose, and -cholesterol (FFC) diet for 24 weeks, which led to the development of steatohepatitis and MASH-defining cardiometabolic risk factors. Liver injury and inflammation were determined by histological and gene expression analyses. Intrahepatic leukocyte populations were analyzed by mass cytometry and immunohistochemistry.

RESULTS

Histological examination demonstrated a reduction in liver inflammatory infiltrates and fibrosis in high-fat, -fructose, and -cholesterol-fed S1pr1MKO compared to wild-type. There was a corresponding reduction in alanine aminotransferase, a sensitive marker for liver injury. As determined by mass cytometry, a significant decrease in recruited macrophages was noted in the livers of high-fat, -fructose, and -cholesterol-fed S1pr1MKO mice compared to wild-type. Gene ontology pathway analysis revealed significant suppression of the peroxisome proliferator-activated receptor gamma and mitogen-activated protein kinase pathways in S1pr1MKO consistent with attenuated MASH in mice.

CONCLUSIONS

Deletion of S1P1 in myeloid cells is sufficient to attenuate intrahepatic accumulation of monocyte-derived macrophages and ameliorate murine MASH.

Impaired Suppression of Plasma Lipid Extraction and its Partitioning Away from Muscle by Insulin in Humans with Obesity

CONTEXT

Humans with obesity and insulin resistance exhibit lipid accumulation in skeletal muscle, but the underlying biological mechanisms responsible for the accumulation of lipid in the muscle of these individuals remain unknown.

OBJECTIVE

We investigated how plasma insulin modulates the extraction of circulating triglycerides (TGs) and non-esterified fatty acids (NEFAs) from ingested and endogenous origin in the muscle of lean, insulin-sensitive humans (Lean-IS) and contrasted these responses to those in humans with obesity and insulin resistance (Obese-IR).

METHODS

The studies were performed in a postprandial state associated with steady-state plasma TG concentrations. The arterio-venous blood sampling technique was employed to determine the extraction of circulating lipids across the forearm muscle before and after insulin infusion. We distinguished kinetics of TGs and NEFAs from ingested origin from those from endogenous origin across muscle by incorporating stable isotope-labeled triolein in the ingested fat.

RESULTS

Insulin infusion rapidly suppressed the extraction of plasma TGs from endogenous, but not ingested, origin in the muscle of the Lean-IS, but this response was absent in the muscle of the Obese-IR. Furthermore, in the muscle of the Lean-IS, insulin infusion decreased the extraction of circulating NEFAs from both ingested and endogenous origin; however, this response was absent for NEFAs from ingested origin in the muscle of the Obese-IR subjects.

CONCLUSIONS

Partitioning of circulating lipids away from the skeletal muscle when plasma insulin increases during the postprandial period is impaired in humans with obesity and insulin resistance.

A near-complete assembly of the Houttuynia cordata genome provides insights into the regulatory mechanism of flavonoid biosynthesis in Yuxingcao

Houttuynia cordata, also known as Yuxingcao in Chinese, is a perennial herb in the Saururaceae family. It is highly regarded for its medicinal properties, particularly in treating respiratory infections and inflammatory conditions, as well as boosting the human immune system. However, a lack of genomic information has hindered research on the functional genomics and potential improvements of H. cordata. In this study, we present a near-complete assembly of H. cordata genome and investigate the biosynthetic pathway of flavonoids, specifically quercetin, using genomics, transcriptomics, and metabolomics analyses. The genome of H. cordata diverged from that of Saururus chinensis around 33.4 million years ago; it consists of 2.24 Gb with 76 chromosomes (4n = 76) and has undergone three whole-genome duplication (WGD) events. These WGDs played a crucial role in shaping the H. cordata genome and influencing the gene families associated with its medicinal properties. Through metabolomics and transcriptomics analyses, we identified key genes involved in the β-oxidation process for biosynthesis of houttuynin, one of the volatile oils responsible for the plant's fishy smell. In addition, using the reference genome, we identified genes involved in flavonoid biosynthesis, particularly quercetin metabolism, in H. cordata. This discovery has important implications for understanding the regulatory mechanisms that underlie production of active pharmaceutical ingredients in traditional Chinese medicine. Overall, the high-quality genome assembly of H. cordata serves as a valuable resource for future functional genomics research and provides a solid foundation for genetic improvement of H. cordata for the benefit of human health.

Impaired Suppression of Plasma Lipid Extraction and its Partitioning Away from Muscle by Insulin in Humans with Obesity

Context

Humans with obesity and insulin resistance exhibit lipid accumulation in skeletal muscle, but the underlying biological mechanisms responsible for the accumulation of lipid in the muscle of these individuals remain unknown.

Objective

We investigated how plasma insulin modulates the extraction of circulating triglycerides (TGs) and non-esterified fatty acids (NEFAs) from ingested and endogenous origin in the muscle of lean, insulin-sensitive humans (Lean-IS) and contrasted these responses to those in humans with obesity and insulin resistance (Obese-IR).

Methods

The studies were performed in a postprandial state associated with steady-state plasma TG concentrations. The arterio-venous blood sampling technique was employed to determine the extraction of circulating lipids across the forearm muscle before and after insulin infusion. We distinguished kinetics of TGs and NEFAs from ingested origin from those from endogenous origin across muscle by incorporating stable isotope-labeled triolein in the ingested fat.

Results

Insulin infusion rapidly suppressed the extraction of plasma TGs from endogenous, but not ingested, origin in the muscle of the Lean-IS, but this response was absent in the muscle of the Obese-IR. Furthermore, in the muscle of the Lean-IS, insulin infusion decreased the extraction of circulating NEFAs from both ingested and endogenous origin; however, this response was absent for NEFAs from ingested origin in the muscle of the Obese-IR subjects.

Conclusions

Partitioning of circulating lipids away from the skeletal muscle when plasma insulin increases during the postprandial period is impaired in humans with obesity and insulin resistance.

Dyslipidemia-induced renal fibrosis related to ferroptosis and endoplasmic reticulum stress

Dyslipidemia may induce chronic kidney disease and trigger both ferroptosis and endoplasmic reticulum (ER) stress, but the instigating factors are incompletely understood. We tested the hypothesis that different models of dyslipidemia engage distinct kidney injury mechanisms. Wild-type (WT) or proprotein-convertase subtilisin/kexin type-9 (PCSK9)-gain-of-function (GOF) Ossabaw pigs were fed with a 6-month normal diet (ND) or high-fat diet (HFD) (n = 5-6 each). Renal function and fat deposition were studied in vivo using CT, and blood and kidney tissue studied ex-vivo for lipid profile, systemic and renal vein FFAs levels, and renal injury mechanisms including lipid peroxidation, ferroptosis, and ER stress. Compared with WT-ND pigs, both HFD and PCSK9-GOF elevated triglyceride levels, which were highest in WT-HFD, whereas total and LDL cholesterol levels rose only in PCSK9-GOF pigs, particularly in PCSK9-GOF/HFD. The HFD groups had worse kidney function than the ND groups. The WT-HFD kidneys retained more FFA than other groups, but all kidneys developed fibrosis. Furthermore, HFD-induced ferroptosis in WT-HFD indicated by increased free iron, lipid peroxidation, and decreased glutathione peroxidase-4 mRNA expression, while PCSK9-GOF induced ER stress with upregulated GRP94 and CHOP protein expression. In vitro, pig kidney epithelial cells treated with palmitic acid and oxidized LDL to mimic HFD and PCSK9-GOF showed similar trends to those observed in vivo. Taken together, HFD-induced hypertriglyceridemia promotes renal FFA retention and ferroptosis, whereas PCSK9-GOF-induced hypercholesterolemia elicits ER stress, both resulting in renal fibrosis. These observations suggest different targets for preventing and treating renal fibrosis in subjects with specific types of dyslipidemia.

shRNA-mediated down-regulation of Acsl1 reverses skeletal muscle insulin resistance in obese C57BL6/J mice

Prolonged consumption of diet rich in fats is regarded as the major factor leading to the insulin resistance (IR) and type 2 diabetes (T2D). Emerging evidence link excessive accumulation of bioactive lipids such as diacylglycerol (DAG) and ceramide (Cer), with impairment of insulin signaling in skeletal muscle. Until recently, little has been known about the involvement of long-chain acyl-CoAs synthetases in the above mechanism. To examine possible role of long-chain acyl-coenzyme A synthetase 1 (Acsl1) (a major muscular ACSL isoform) in mediating HFD-induced IR we locally silenced Acsl1 in gastrocnemius of high-fat diet (HFD)-fed C57BL/6J mice through electroporation-delivered shRNA and compared it to non-silenced tissue within the same animal. Acsl1 down-regulation decreased the content of muscular long-chain acyl-CoA (LCACoA) and both the Cer (C18:1-Cer and C24:1-Cer) and DAG (C16:0/18:0-DAG, C16:0/18:2-DAG, C18:0/18:0-DAG) and simultaneously improved insulin sensitivity and glucose uptake as compared with non-silenced tissue. Acsl1 down-regulation decreased expression of mitochondrial β-oxidation enzymes, and the content of both the short-chain acylcarnitine (SCA-Car) and short-chain acyl-CoA (SCACoA) in muscle, pointing towards reduction of mitochondrial FA oxidation. The results indicate, that beneficial effects of Acsl1 partial ablation on muscular insulin sensitivity are connected with inhibition of Cer and DAG accumulation, and outweigh detrimental impact of decreased mitochondrial fatty acids metabolism in skeletal muscle of obese HFD-fed mice.

Excipient-related impurities in liposome drug products

Liposomes are widely used in the pharmaceutical industry as drug delivery systems to increase the efficacy and reduce the off-target toxicity of active pharmaceutical ingredients (APIs). The liposomes are more complex drug delivery systems than the traditional dosage forms, and phospholipids and cholesterol are the major structural excipients. These two excipients undergo hydrolysis and/or oxidation during liposome preparation and storage, resulting in lipids hydrolyzed products (LHPs) and cholesterol oxidation products (COPs) in the final liposomal formulations. These excipient-related impurities at elevated concentrations may affect liposome stability and exert biological functions. This review focuses on LHPs and COPs, two major categories of excipient-related impurities in the liposomal formulations, and discusses factors affecting their formation, and analytical methods to determine these excipient-related impurities.

Palmitate and group B Streptococcus synergistically and differentially induce IL-1β from human gestational membranes

Introduction

Rupture of the gestational membranes often precedes major pregnancy complications, including preterm labor and preterm birth. One major cause of inflammation in the gestational membranes, chorioamnionitis (CAM) is often a result of bacterial infection. The commensal bacterium Streptococcus agalactiae, or Group B Streptococcus (GBS) is a leading infectious cause of CAM. Obesity is on the rise worldwide and roughly 1 in 4 pregnancy complications is related to obesity, and individuals with obesity are also more likely to be colonized by GBS. The gestational membranes are comprised of several distinct cell layers which are, from outermost to innermost: maternally-derived decidual stromal cells (DSCs), fetal cytotrophoblasts (CTBs), fetal mesenchymal cells, and fetal amnion epithelial cells (AECs). In addition, the gestational membranes have several immune cell populations; macrophages are the most common phagocyte. Here we characterize the effects of palmitate, the most common long-chain saturated fatty acid, on the inflammatory response of each layer of the gestational membranes when infected with GBS, using human cell lines and primary human tissue.

Results

Palmitate itself slightly but significantly augments GBS proliferation. Palmitate and GBS co-stimulation synergized to induce many inflammatory proteins and cytokines, particularly IL-1β and matrix metalloproteinase 9 from DSCs, CTBs, and macrophages, but not from AECs. Many of these findings are recapitulated when treating cells with palmitate and a TLR2 or TLR4 agonist, suggesting broad applicability of palmitate-pathogen synergy. Co-culture of macrophages with DSCs or CTBs, upon co-stimulation with GBS and palmitate, resulted in increased inflammatory responses, contrary to previous work in the absence of palmitate. In whole gestational membrane biopsies, the amnion layer appeared to dampen immune responses from the DSC and CTB layers (the choriodecidua) to GBS and palmitate co-stimulation. Addition of the monounsaturated fatty acid oleate, the most abundant monounsaturated fatty acid in circulation, dampened the proinflammatory effect of palmitate.

Discussion

These studies reveal a complex interplay between the immunological response of the distinct layers of the gestational membrane to GBS infection and that such responses can be altered by exposure to long-chain saturated fatty acids. These data provide insight into how metabolic syndromes such as obesity might contribute to an increased risk for GBS disease during pregnancy.

Identification of circulating plasma ceramides as a potential sexually dimorphic biomarker of pancreatic cancer-induced cachexia

Background

Cancer patients who exhibit cachexia lose weight and have low treatment tolerance and poor outcomes compared to cancer patients without weight loss. Despite the clear increased risk for patients, diagnosing cachexia still often relies on self-reported weight loss. A reliable biomarker to identify patients with cancer cachexia would be a valuable tool to improve clinical decision making and identification of patients at risk of adverse outcomes.

Methods

Targeted metabolomics, that included panels of amino acids, tricarboxylic acids, fatty acids, acylcarnitines, and sphingolipids, were conducted on plasma samples from patients with confirmed pancreatic ductal adenocarcinoma (PDAC) with and without cachexia and control patients without cancer (n=10/group, equally divided by sex). Additional patient samples were analyzed (total n=95) and Receiver Operating Characteristic (ROC) analyses were performed to establish if any metabolite could effectively serve as a biomarker of cachexia.

Results

Targeted profiling revealed that cachectic patients had decreased circulating levels of three sphingolipids compared to either non-cachectic PDAC patients or patients without cancer. The ratio of C18-ceramide to C24-ceramide (C18:C24) outperformed a number of other previously proposed biomarkers of cachexia (area under ROC = 0.810). It was notable that some biomarkers, including C18:C24, were only altered in cachectic males.

Conclusions

Our findings identify C18:C24 as a potentially new biomarker of PDAC-induced cachexia that also highlight a previously unappreciated sexual dimorphism in cancer cachexia.

A Randomized Trial of ω-3 Fatty Acid Supplementation and Circulating Lipoprotein Subclasses in Healthy Older Adults

BACKGROUND

Omega-3 (n-3) PUFAs are recognized for triglyceride-lowering effects in people with dyslipidemia, but it remains unclear if n-3-PUFA intake influences lipoprotein profiles in older adults without hypertriglyceridemia.

OBJECTIVES

The objective was to determine the effect of n-3-PUFA supplementation on plasma lipoprotein subfractions in healthy older men and women in the absence of cardiovascular disease (CVD) or hypertriglyceridemia. This was a secondary analysis and considered exploratory.

METHODS

Thirty young (20-35 y old) and 54 older (65-85 y old) men and women were enrolled in the study. Fasting plasma samples were collected. After baseline sample collection, 44 older adults were randomly assigned to receive either n-3-PUFA ethyl esters (3.9 g/d) or placebo (corn oil) for 6 mo. Pre- and postintervention plasma samples were used for quantitative lipoprotein subclass analysis using high-resolution proton NMR spectroscopy.

RESULTS

The number of large, least-dense LDL particles decreased 17%-18% with n-3 PUFAs compared with placebo (<1% change; P < 0.01). The number of small, dense LDL particles increased 26%-44% with n-3 PUFAs compared with placebo (∼11% decrease; P < 0.01). The cholesterol content of large HDL particles increased by 32% with n-3 PUFAs and by 2% in placebo (P < 0.01). The cholesterol content of small HDL particles decreased by 23% with n-3 PUFAs and by 2% in placebo (P < 0.01).

CONCLUSIONS

Despite increasing abundance of small, dense LDL particles that are associated with CVD risk, n-3 PUFAs reduced total triglycerides, maintained HDL, reduced systolic blood pressure, and shifted the HDL particle distribution toward a favorable cardioprotective profile in healthy older adults without dyslipidemia. This study suggests potential benefits of n-3-PUFA supplementation to lipoprotein profiles in healthy older adults without dyslipidemia, which should be considered when weighing the potential health benefits against the cost and ecological impact of widespread use of n-3-PUFA supplements.This trial was registered at clinicaltrials.gov as NCT03350906.

Increased Expression of Syncytin-1 in Skeletal Muscle of Humans With Increased Body Mass Index

Obesity negatively impacts skeletal muscle protein metabolism, and also impairs skeletal muscle maintenance and regeneration. We analyzed muscle biopsy samples from humans with increased body mass index (BMI) (i.e. > 30 kg/m²) and controls (i.e., BMI < 25 kg/m²) for expression of syncytin-1, a fusogenic protein regulating skeletal muscle regeneration. When compared to controls, humans with increased BMI and concomitant reduction in muscle protein synthesis had higher expression of syncytin-1 in skeletal muscle (p < 0.05). Across human subjects, muscle protein synthesis correlated inversely (r = −0.51; p = 0.03) with syncytin-1 expression in muscle. Using a C2C12 cell line we found that expression of syncytin-A (i.e, corresponding protein in murine tissue) is increased by insulin, and that this response is impaired in the presence of fatty acids, whose metabolism is altered within the metabolic environment induced by increased BMI. In C2C12 cells, the response of the protein 4E-BP1, which signals increase in protein synthesis in muscle, resembled that of syncytin-A. These findings provide novel insights into the expression of syncytin-1 in skeletal muscle of humans with increased BMI, as well as its basic regulation by insulin and fatty acids in muscle. The findings signify the need for further research into the regulation of syncytin-1 in skeletal muscle of humans with increased BMI, as well as its biological implications for altering muscle protein metabolism and regeneration.

Inflammasome Activation and Pyroptosis via a Lipid-regulated SIRT1-p53-ASC Axis in Macrophages From Male Mice and Humans

Obesity-linked diabetes is associated with accumulation of proinflammatory macrophages into adipose tissue leading to inflammasome activation and pyroptotic secretion of interleukin (IL)-1β and IL-18. Targeting fatty acid binding protein 4 (FABP4) uncouples obesity from inflammation, attenuates characteristics of type 2 diabetes and is mechanistically linked to the cellular accumulation of monounsaturated fatty acids in macrophages. Herein we show that pharmacologic inhibition or genetic deletion of FABP4 activates silent mating type information regulation 2 homolog 1 (SIRT1) and deacetylates its downstream targets p53 and signal transducer and activator of transcription 3 (STAT3). Pharmacologic inhibition of fatty acid synthase or stearoyl-coenzyme A desaturase inhibits, whereas exogenous addition of C16:1 or C18:1 but not their saturated acyl chain counterparts, activates SIRT1 and p53/STAT3 signaling and IL-1β/IL-18 release. Expression of the p53 target gene ASC [apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (CARD)] required for assembly of the NLR family pyrin domain containing 3 (NLRP3) inflammasome is downregulated in FABP4 null mice and macrophage cell lines leading to loss of procaspase 1 activation and pyroptosis. Concomitant with loss of ASC expression in FABP4-/- macrophages, inflammasome activation, gasdermin D processing, and functional activation of pyroptosis are all diminished in FABP4 null macrophages but can be rescued by silencing SIRT1 or exogenous expression of ASC. Taken together, these results reveal a novel lipid-regulated pathway linking to SIRT1-p53-ASC signaling and activation of inflammasome action and pyroptosis.

Serine Palmitoyltransferase Gene Silencing Prevents Ceramide Accumulation and Insulin Resistance in Muscles in Mice Fed a High-Fat Diet

Skeletal muscles account for ~80% of insulin-stimulated glucose uptake and play a key role in lipid metabolism. Consumption of a high-fat diet (HFD) contributes to metabolic changes in muscles, including the development of insulin resistance. The studies carried out to date indicate that the accumulation of biologically active lipids, such as long-chain acyl-CoA, diacylglycerols and ceramides, play an important role in the development of insulin resistance in skeletal muscles. Unfortunately, it has not yet been clarified which of these lipid groups plays the dominant role in inducing these disorders. In order to explore this topic further, we locally silenced the gene encoding serine palmitoyltransferase (SPT) in the gastrocnemius muscle of animals with HFD-induced insulin resistance. This enzyme is primarily responsible for the first step of de novo ceramide biosynthesis. The obtained results confirm that the HFD induces the development of whole-body insulin resistance, which results in inhibition of the insulin pathway. This is associated with an increased level of biologically active lipids in the muscles. Our results also demonstrate that silencing the SPT gene with the shRNA plasmid reduces the accumulation of ceramides in gastrocnemius muscle, which, in turn, boosts the activity of the insulin signaling pathway. Furthermore, inhibition of ceramide synthesis does not significantly affect the content of other lipids, which suggests the leading role of ceramide in the lipid-related induction of skeletal muscle insulin resistance.

Adipose Tissue Inflammation Is Not Related to Adipose Insulin Resistance in Humans

The role of adipose tissue (AT) inflammation in AT function in humans is unclear. We tested whether AT macrophage (ATM) content, cytokine gene expression, and senescent cell burden (markers of AT inflammation) predict AT insulin resistance measured as the insulin concentration that suppresses lipolysis by 50% (IC50). We studied 86 volunteers with normal weight or obesity at baseline and a subgroup of 25 volunteers with obesity before and after weight loss. There was a strong positive relationship between IC50 and abdominal subcutaneous and femoral fat cell size (FCS). The positive, univariate relationships between IC50 and abdominal AT inflammatory markers CD68, CD14, CD206 ATM/100 adipocytes, senescent cells, IL-6, and TNF-α mRNA were not significant after adjustment for FCS. A 10% weight loss significantly reduced IC50; however, there was no reduction in adipose ATM content, senescent cells, or cytokine gene expression. Our study suggests that commonly used markers of AT inflammation are not causally linked to AT insulin resistance, whereas FCS is a strong predictor of AT insulin resistance with respect to lipolysis.

CerS1 but Not CerS5 Gene Silencing, Improves Insulin Sensitivity and Glucose Uptake in Skeletal Muscle

Skeletal muscle is perceived as a major tissue in glucose and lipid metabolism. High fat diet (HFD) lead to the accumulation of intramuscular lipids, including: long chain acyl-CoA, diacylglycerols, and ceramides. Ceramides are considered to be one of the most important lipid groups in the generation of skeletal muscle insulin resistance. So far, it has not been clearly established whether all ceramides adversely affect the functioning of the insulin pathway, or whether there are certain ceramide species that play a pivotal role in the induction of insulin resistance. Therefore, we designed a study in which the expression of CerS1 and CerS5 genes responsible for the synthesis of C18:0-Cer and C16:0-Cer, respectively, was locally silenced in the gastrocnemius muscle of HFD-fed mice through in vivo electroporation-mediated shRNA plasmids. Our study indicates that HFD feeding induced both, the systemic and skeletal muscle insulin resistance, which was accompanied by an increase in the intramuscular lipid levels, decreased activation of the insulin pathway and, consequently, a decrease in the skeletal muscle glucose uptake. CerS1 silencing leads to a reduction in C18:0-Cer content, with a subsequent increase in the activity of the insulin pathway, and an improvement in skeletal muscle glucose uptake. Such effects were not visible in case of CerS5 silencing, which indicates that the accumulation of C18:0-Cer plays a decisive role in the induction of skeletal muscle insulin resistance.

Influence of Free Fatty Acid Concentrations and Weight Loss on Adipose Tissue Direct Free Fatty Acid Storage Rates

CONTEXT

The factors that determine the recycling of free fatty acids (FFA) back into different adipose tissue depots via the direct storage pathway are not completely understood.

OBJECTIVE

To assess the interactions between adipocyte factors and plasma FFA concentrations that determine regional FFA storage rates.

DESIGN

We measured direct adipose tissue FFA storage rates before and after weight loss under high FFA (intravenous somatostatin and epinephrine) and low (intravenous insulin and glucose) FFA concentrations.

SETTING

Mayo Clinic Clinical Research Unit.

PATIENTS

Sixteen premenopausal women, body mass index 30 to 37 kg/m2.

INTERVENTION

Comprehensive lifestyle weight loss program.

MAIN OUTCOME MEASURE

Direct FFA storage rates in upper and lower body subcutaneous fat.

RESULTS

Over the entire range of FFA and under isolated conditions of elevated FFA concentrations, the storage rates of FFA into upper and lower body subcutaneous fat per unit lipid were associated with concentrations, not adipocyte fatty acid storage factors. Under low FFA conditions, direct FFA storage rates were related to adipocyte CD36 content, not tissue level content of fatty acid storage factors. Weight loss did not change these relationships.

CONCLUSIONS

The regulation of direct FFA storage under low FFA concentration conditions appears to be at the level of the cell/adipocyte content of CD36, whereas under high FFA concentration conditions, direct FFA storage at the tissue level is predicted by plasma FFA concentrations, independent of adipocyte size or fatty acid storage factors. These observations offer novel insights into how adipose tissue regulates direct FFA storage in humans.

Red blood cell triglycerides - a unique pool that incorporates plasma free fatty acids and relates to metabolic health

Most research into red blood cell (RBC) lipids focuses on membrane phospholipids and their relationships to metabolic conditions and diet. Triglycerides (TGs) exist in most cells; the TG-fatty acids serve as readily available fuel for oxidative phosphorylation. Because RBCs lack mitochondria, they would not be expected to store fatty acids in TG. We followed up on a previous in vitro study that found FFA can be incorporated into RBC-TG by testing whether intravenously infused [U-¹³C]palmitate could be detected in RBC-TG. We also quantified RBC-TG fatty acid concentrations and profiles as they relate to plasma FFA and lipid concentrations. We found that 1) RBC-TG concentrations measured by glycerol and LC/MS were correlated (r = 0.77; P < 0.001) and averaged <50 nmol/ml RBC; 2) RBC-TG concentrations were stable over 18 h; 3) [U-¹³C]palmitate was detectable in RBC-TG from half the participants; 4) RBC-TGs were enriched in saturated fatty acids and depleted in unsaturated fatty acid compared with plasma FFA and previously reported RBC membrane phospholipids; 5) RBC-TG fatty acid profiles differed significantly between obese and nonobese adults; 6) weight loss altered the RBC-TG fatty acid profile in the obese group; and 7) the RBC-TG fatty acid composition correlated with plasma lipid concentrations. This is the first report showing that plasma FFA contributes to RBC-TG in vivo, in humans, and that the RBC-TG fatty acid profile is related to metabolic health. The storage of saturated fatty acids in RBC-TG stands in stark contrast to the highly unsaturated profile reported in RBC membrane phospholipids.

Adipocyte Proteins and Storage of Endogenous Fatty Acids in Visceral and Subcutaneous Adipose Tissue in Severe Obesity

OBJECTIVE

This study tested whether substrate concentrations or fatty acid storage proteins predict storage of endogenous lipids in visceral adipose tissue (VAT) and upper body subcutaneous adipose tissue (UBSQ) fat.

METHODS

The day prior to surgery, 25 patients undergoing bariatric procedures received an infusion of autologous [1-¹⁴ C]triolein-labeled very low-density lipoprotein (VLDL) particles, and during surgery, they received a continuous [U-¹³ C]palmitate infusion/bolus [9,10-³ H]palmitate tracer. VAT and UBSQ fat were collected to measure VLDL-triglyceride (TG) storage, direct free fatty acid (FFA) storage rates, CD36 content, lipoprotein lipase (LPL), acyl-CoA synthetase, diacylglycerol acetyl-transferase, and glycerol-3-phosphate acyltransferase activities.

RESULTS

Storage of VLDL-TG and FFA-palmitate in UBSQ and VAT was not different. Plasma palmitate concentrations correlated with palmitate storage rates in UBSQ and VAT (r = 0.46, P = 0.02 and r = 0.46, P = 0.02, respectively). In VAT, VLDL-TG storage was correlated with VLDL concentrations (r = 0.53, P < 0.009) and LPL (r = 0.42, P < 0.05). In UBSQ, VLDL-TG storage was correlated with LPL (r = 0.42, P < 0.05). CD36, acyl-CoA synthetase, glycerol-3-phosphate acyltransferase, and diacylglycerol acetyl-transferase were not correlated with VLDL-TG or palmitate storage.

CONCLUSIONS

Adipose storage of VLDL-TG is predicted by VLDL-TG concentrations and LPL; FFA concentrations predict direct adipose tissue FFA storage rates.

Binahong (Anredera cordifolia (Tenore) Steen.) Leaf Extract Modulates Fatty Acids and Amino Acids to Lower Blood Glucose in High-Fat Diet-Induced Diabetes Mellitus Rats

Patients with diabetes are 1.6 times more likely to use complementary alternative medicine than nondiabetic patients. Previous studies have shown that Anredera cordifolia (Tenore) Steen. (A. cordifolia) leaf extract has the capacity to lower blood glucose, but the actual mechanisms are unclear. Therefore, in this study, we explored the effect of A. cordifolia leaf extract on the metabolism of fatty acids and amino acids. Six-week-old male Wistar rats were randomly divided into six experimental groups (n = 5 per group). Two groups were fed with a regular diet or a high-fat diet (HFD) for six weeks. The regular diet and HFD groups were administered with 0.5% carboxymethylcellulose as a vehicle, and HFD rats were also fed with a suspension of glibenclamide (0.51 mg/kg body weight (BW)) or A. cordifolia leaf extract (25, 50, and 100 mg/kg BW). During the whole treatment, BW and food intake were recorded weekly. The rats were euthanized seven weeks after treatment. Blood glucose was evaluated by spectrophotometry, while fatty acids and amino acids were evaluated using a gas chromatography/flame ionization detector (GC/FID). All doses of A. cordifolia administration reduced blood glucose significantly, and 50 mg/kg BW was most effective in lowering blood glucose, similar to the effects of glibenclamide. A. cordifolia leaf extract affected the levels of medium-chain fatty acids, especially at 50 mg/kg BW. In contrast, glibenclamide affected long-chain fatty acids (LCFAs) to lower blood glucose. Based on the analysis conducted, we conclude that administration of A. cordifolia leaf extract can decrease blood glucose levels by regulating fatty acid metabolism and that a dose of 50 mg/kg BW in rats was the optimal dose.

Regulation of direct adipose tissue free fatty acid storage during mixed meal ingestion and high free fatty acid concentration conditions

We found that direct free fatty acid (FFA) storage (fatty acid cycling back into adipose tissue) in leg vs. abdominal subcutaneous fat is related to regional differences in adipose tissue diacylglycerol acyltransferase (DGAT) activity under high-FFA conditions and to differences in adipose tissue acyl-CoA synthetase (ACS)activity under meal ingestion conditions. We also found that direct FFA storage rates in leg fat were significantly less in physically active than sedentary adults. Direct FFA storage into adipocytes relates to body fat distribution. Adipose tissue CD36, ACS, and DGAT may account for some of the between-depot and interindividual variability in FFA storage. These studies were to test whether CD36, ACS, or DGAT might be important for direct palmitate storage under meal ingestion or high-FFA conditions. We measured upper (UBSQ) and lower body subcutaneous (LBSQ) adipose tissue FFA storage rates by infusing palmitate tracers intravenously and performing adipose biopsies under hypoinsulinemic (high-FFA) and mixed-meal conditions. We recruited five postmenopausal women, physically active males (5) and females (5), and sedentary males (5) and females (5). We found that 1) the ratio of UBSQ to LBSQ DGAT activity predicted the ratio of palmitate storage [adjusted R = 0.25, F = 8.0, P = 0.01, 95% CI (0.07, 0.48)] under high-FFA conditions; 2) the ratio of UBSQ to LBSQ ACS activity predicted the ratio of palmitate storage under meal conditions [adjusted R = 0.18, F = 6.3, P = 0.02, 95% CI (0.12, 1.28)]; 3) LBSQ direct palmitate storage rates were significantly less in physically active than sedentary and 4) adipose tissue CD36 protein content, ACS, or DGAT activities did not independently predict palmitate storage rates. We conclude that physically active adults have lesser fatty acid cycling back into adipose tissue and that adipose ACS and DGAT may affect competition between UBSQ and LBSQ adipose for direct palmitate storage.

The Influence of Obesity and Associated Fatty Acids on Placental Inflammation

PURPOSE

Maternal obesity, affecting nearly 1 in 4 pregnancies, is associated with increased circulating saturated fatty acids, such as palmitate. These fatty acids are implicated in placental inflammation, which may in turn exacerbate both maternal-fetal tolerance and responses to pathogens, such as group B Streptococcus. In this review, we address the question, "How do obesity and associated fatty acids influence placental inflammation?"

METHODS

In this narrative review, we searched PubMed and Google Scholar using combinations of the key words placental inflammation or pregnancy and lipids, fatty acids, obesity, palmitate, or other closely related search terms. We also used references found within these articles that may have been absent from our original search queries. We analyzed methods and key results of these articles to compare and contrast their findings, which were occasionally at odds with each other.

FINDINGS

Although obesity can be studied as a whole, complex phenomena with in vivo mouse models and human samples from patients with obesity, in vitro modeling often relies on the treatment of cells or tissues with ≥1 fatty acids and occasionally other compounds (eg, glucose and insulin). We found that palmitate, most commonly used in vitro to recreate hallmarks of obesity, induces apoptosis, oxidative stress, mitochondrial dysfunction, autophagy defects, and inflammasome activation in many placental cell types. We compare this to in vivo models of obesity wherever possible. We found that obesity as a whole may have more complex regulation of these phenomena (apoptosis, oxidative stress, mitochondrial dysfunction, autophagy defects, and inflammasome activation) compared with in vitro models of fatty acid treatment (primarily palmitate) because of the presence of unsaturated fatty acids (ie, oleate), which may have anti-inflammatory effects.

IMPLICATIONS

The interaction of unsaturated fatty acids with saturated fatty acids may ameliorate many inflammatory effects of saturated fatty acids alone, which complicates interpretation of in vitro studies that focus on a particular fatty acid in isolation. This complication may explain why certain studies of obesity in vivo have differing outcomes from studies of specific fatty acids in vitro.

In Vivo Optical Metabolic Imaging of Long-Chain Fatty Acid Uptake in Orthotopic Models of Triple-Negative Breast Cancer

Simple Summary

A dysregulated metabolism is a hallmark of cancer. Once understood, tumor metabolic reprogramming can lead to targetable vulnerabilities, spurring the development of novel treatment strategies. Beyond the common observation that tumors rely heavily on glucose, building evidence indicates that a subset of tumors use lipids to maintain their proliferative or metastatic phenotype. This study developed an intra-vital microscopy method to quantify lipid uptake in breast cancer murine models using a fluorescently labeled palmitate molecule, Bodipy FL c16. This work highlights optical imaging’s ability to both measure metabolic endpoints non-destructively and repeatedly, as well as inform small animal metabolic phenotyping beyond in vivo optical imaging of breast cancer alone.

Abstract

Targeting a tumor’s metabolic dependencies is a clinically actionable therapeutic approach; however, identifying subtypes of tumors likely to respond remains difficult. The use of lipids as a nutrient source is of particular importance, especially in breast cancer. Imaging techniques offer the opportunity to quantify nutrient use in preclinical tumor models to guide development of new drugs that restrict uptake or utilization of these nutrients. We describe a fast and dynamic approach to image fatty acid uptake in vivo and demonstrate its relevance to study both tumor metabolic reprogramming directly, as well as the effectiveness of drugs targeting lipid metabolism. Specifically, we developed a quantitative optical approach to spatially and longitudinally map the kinetics of long-chain fatty acid uptake in in vivo murine models of breast cancer using a fluorescently labeled palmitate molecule, Bodipy FL c16. We chose intra-vital microscopy of mammary tumor windows to validate our approach in two orthotopic breast cancer models: a MYC-overexpressing, transgenic, triple-negative breast cancer (TNBC) model and a murine model of the 4T1 family. Following injection, Bodipy FL c16 fluorescence increased and reached its maximum after approximately 30 min, with the signal remaining stable during the 30–80 min post-injection period. We used the fluorescence at 60 min (Bodipy₆₀), the mid-point in the plateau region, as a summary parameter to quantify Bodipy FL c16 fluorescence in subsequent experiments. Using our imaging platform, we observed a two- to four-fold decrease in fatty acid uptake in response to the downregulation of the MYC oncogene, consistent with findings from in vitro metabolic assays. In contrast, our imaging studies report an increase in fatty acid uptake with tumor aggressiveness (6NR, 4T07, and 4T1), and uptake was significantly decreased after treatment with a fatty acid transport inhibitor, perphenazine, in both normal mammary pads and in the most aggressive 4T1 tumor model. Our approach fills an important gap between in vitro assays providing rich metabolic information at static time points and imaging approaches visualizing metabolism in whole organs at a reduced resolution.

Stearoyl-CoA Desaturase-Mediated Monounsaturated Fatty Acid Availability Supports Humoral Immunity

Immune cells can metabolize glucose, amino acids, and fatty acids (FAs) to generate energy. The roles of different FA species and their impacts on humoral immunity remain poorly understood. Here, we report that proliferating B cells require monounsaturated FAs (MUFAs) to maintain mitochondrial metabolism and mTOR activity and to prevent excessive autophagy and endoplasmic reticulum (ER) stress. Furthermore, B cell-extrinsic stearoyl-CoA desaturase (SCD) activity generates MUFA to support early B cell development and germinal center (GC) formation in vivo during immunization and influenza infection. Thus, SCD-mediated MUFA production is critical for humoral immunity.

Zhou et al. show that monounsaturated fatty acids (MUFAs), generated by stearoyl-CoA desaturase (SCD), support B cell mitochondrial metabolism and mTOR activity and promote B cell development and humoral immune responses. These data establish MUFA availability as a key regulator for humoral immunity and a potential therapeutic target.

Reliability of LipidSearch software identification and its application to assess the effect of dry salting on the long-chain free fatty acid profile of tilapia muscles

Dry salting has important effects on food lipids. In this work, the reliability of LipidSearch software identification and its application to assess the effect of dry salting on the long-chain free fatty acid profile of tilapia muscles were studied by ultra-high-performance liquid chromatography-Q-Extractive Orbitrap mass spectrometry and LipidSearch software. Compared with the standard reference identification method, the LipidSearch software identification method was suggested to be a reliable identification method for long-chain free fatty acid identification. During the dry salting process, tilapia muscles with low muscle-to-salt mass ratios of 3-8 might have stable and similar free fatty acid profile changes, and the free fatty acid amounts decreased and then increased with time. This work could provide useful information to evaluate the development and application of LipidSearch software as well as a way to analyze the effect of dry salting on the free fatty acids change of aquatic products.

GPAT Gene Silencing in Muscle Reduces Diacylglycerols Content and Improves Insulin Action in Diet-Induced Insulin Resistance

Skeletal muscle is an important tissue responsible for glucose and lipid metabolism. High-fat diet (HFD) consumption is associated with the accumulation of bioactive lipids: long chain acyl-CoA, diacylglycerols (DAG) and ceramides. This leads to impaired insulin signaling in skeletal muscle. There is little data on the involvement of DAG in the development of these disorders. Therefore, to clarify this enigma, the gene encoding glycerol-3-phosphate acyltransferase enzyme (GPAT, responsible for DAG synthesis) was silenced through shRNA interference in the gastrocnemius muscle of animals with diet-induced insulin resistance. This work shows that HFD induces insulin resistance, which is accompanied by an increase in the concentration of plasma fatty acids and the level of bioactive lipids in muscle. The increase in these lipids inhibits the insulin pathway and reduces muscle glucose uptake. GPAT silencing through electroporation with shRNA plasmid leads to a reduction in DAG and triacylglycerol (TAG) content, an increase in the activity of the insulin pathway and glucose uptake without a significant effect on ceramide content. This work clearly shows that DAG accumulation has a significant effect on the induction of muscle insulin resistance and that inhibition of DAG synthesis through GPAT modulation may be a potential target in the treatment of insulin resistance.

Mass spectrometry-based determination of lipids and small molecules composing adipose tissue with a focus on brown adipose tissue

Adipose tissue has been the subject of research for a very long time. Many studies perform a comprehensive analysis of different types of adipose tissue with an emphasis on brown adipose tissue. Mass spectrometry-based approaches are particularly useful in the exploration not only of the metabolic composition of adipose tissue but also its function. In the presented review, a complex and critical overview of publications devoted to the analysis of adipose tissue by means of mass spectrometry was performed. Detailed investigation of analytical aspects related to either untargeted or targeted analysis of adipose tissue was performed, leading to the formation of a collection of hints at the available analytical methods. Moreover, a profound analysis of the metabolic composition of brown adipose tissue was performed. Brown adipose tissue metabolome was characterized on structural and functional levels, providing information about its exact metabolic composition but also connecting these molecules and placing them into biochemical pathways. All our work resulted in a very broad picture of the analysis of adipose tissue, starting from the analytical aspects and finishing on the current knowledge about its composition.

Unique Metabolic Features of Adults Discordant for Indices of Insulin Resistance

PURPOSE

Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) and Adipose Insulin Resistance index (ADIPO-IR) values are often concordant. In this study we evaluated whether there are groups discordant for HOMA-IR and ADIPOpalmitate-IR and, if so, what are their defining characteristics.

METHODS

The body composition, basal metabolic rate (BMR), fasting plasma lipids, insulin, glucose, and free fatty acid (FFA) palmitate concentrations data of 466 volunteers from previous research studies were abstracted and analyzed. The middle 2 population quartiles for HOMA-IR and Adipose Insulin Resistance index palmitate concentration (ADIPOpalmitate-IR) defined medium HOMA-IR and ADIPOpalmitate-IR (MH and MA), the top and bottom quartiles were defined as high/low HOMA (HH/LH), and high/low ADIPOpalmitate as HA/LA. Because ADIPOpalmitate-IR was significantly greater in women than in men, we established sex-specific quartiles for each index. We identified groups discordant for HOMA-IR and ADIPO-IR (HHMA, LHMA, MHHA, and MHLA).

RESULTS

Body fat and fasting triglycerides (TGs) were significantly greater with higher indices in the concordant groups (HHHA > MHMA > LHLA). MHHA differed from MHLA by visceral fat (P < .01) and fasting TGs (P < .05), whereas HHMA differed (P < .01) from LHMA by BMR. By multivariate regression, the group factor contributed to BMR (P < .01) and visceral fat (P < .05).

CONCLUSIONS

Adults discordant for HOMA-IR and ADIPO-IR have unique features including differences in visceral fat, TGs, and BMR. This suggests different forms of insulin resistance are present, which should be considered when studying insulin resistance in the future.

Adipose tissue macrophage burden, systemic inflammation, and insulin resistance

Adipose tissue inflammation, as defined by macrophage accumulation, is proposed to cause insulin resistance and systemic inflammation. Because the strength of this relationship for humans is unclear, we tested whether adipose tissue macrophage (ATM) burden is correlated with these health indicators. Using immunohistochemistry, we measured abdominal subcutaneous CD68+ (total ATM), CD14+ (proinflammatory/M1), and CD206+ (anti-inflammatory/M2) ATM in 97 volunteers (BMI 20-38 kg/m², in addition to body composition, adipocyte size, homeostasis model assessment of insulin resistance, ADIPO-IR, adipose tissue insulin resistance measured by palmitate, plasma lipids, TNF, and IL-6 concentrations. There were several significant univariate correlations between metabolic parameters to IL-6 and ATM per 100 adipocytes, but not ATM per gram tissue; adipocyte size was a confounding variable. We used matching strategies and multivariate regression analyses to investigate the relationships between ATM and inflammatory/metabolic parameters independent of adipocyte size. Matching approaches revealed that the groups discordant for CD206 but concordant for adipocyte size had significantly different fasting insulin and IL-6 concentrations. However, groups discordant for adipocyte size but concordent for ATM differeded in that visceral fat, plasma triglyceride, glucose, and TNF concentrations were greater in those with large adipocytes. Multivariate regression analysis indicated that indexes of insulin resistance and fasting triglycerides were predicted by body composition; the predictive value of ATM per 100 adipocytes or per gram tissue was variable between males and females. We conclude that the relationship between ATM burden and metabolic/inflammatory variables is confounded by adipocyte size/body composition and that ATM do not predict insulin resistance, systemic inflammation, or dyslipidemia. ATM may primarily play a role in tissue remodeling rather than in metabolic pathology.

Sex and Depot Differences in Palmitoleic Acid Content of Human Blood and Fat

Palmitoleic acid has been classified as an insulin-sensitizing lipokine, but evidence for this from human studies has been inconsistent. We hypothesized that this is related to either the types of samples or conditions under which samples are collected. We measured plasma palmitoleic acid and total free fatty acids (FFA) using ultra-performance liquid chromatography in blood samples collected from 34 adults under a variety of conditions. We collected duplicate samples of adipose (n = 10), FFA (n = 9), and very low density lipoprotein triacylglycerol (VLDL-TAG) (n = 7) to measure the palmitoleic acid as a percentage of total fatty acids. We tested whether the percentage of palmitoleic acid was correlated with insulin resistance, as measured by homeostatic model of insulin resistance (HOMA-IR). Adipose stearoyl-coenzyme A desaturase 1 (SCD-1) protein was measured by capillary Western blotting. FFA-palmitoleic acid percentage increased as a function of total FFA and was greater (p < 0.005) in females than males. Adipose palmitoleic acid percentage was greater in females than males (p < 0.001), as was adipose SCD-1. Palmitoleic acid was greater in femoral fat than in abdominal fat in both females and males (p < 0.001), and correlated positively with HOMA-IR only in females. The test-retest reliability values for percentage palmitoleic acid were 7 ± 10% for adipose, 24 ± 26% for VLDL, and 53 ± 31% for FFA. Because FFA-palmitoleic acid percentage varies as a function of total FFA, investigators should re-evaluate how palmitoleic acid data is presented. The positive relationship between adipose palmitoleic acid and HOMA-IR in females suggests that it is not a potent insulin-sensitizing lipokine in humans.

Hepatic Fatty Acid Balance and Hepatic Fat Content in Humans With Severe Obesity

OBJECTIVE

Nonalcoholic fatty liver disease can lead to hepatic inflammation/damage. Understanding the physiological mechanisms that contribute to excess hepatic lipid accumulation may help identify effective treatments.

DESIGN

We recruited 25 nondiabetic patients with severe obesity scheduled for bariatric surgery. To evaluate liver export of triglyceride fatty acids, we measured very-low-density lipoprotein (VLDL)-triglyceride secretion rates the day prior to surgery using an infusion of autologous [1-14C]triolein-labeled VLDL particles. Ketone body response to fasting and intrahepatic long-chain acylcarnitine concentrations were used as indices of hepatic fatty acid oxidation. We measured intraoperative hepatic uptake rates of plasma free fatty acids using a continuous infusion of [U-13C]palmitate, combined with a bolus dose of [9,10-3H]palmitate and carefully timed liver biopsies. Total intrahepatic lipids were measured in liver biopsy samples to determine fatty liver status. The hepatic concentrations and enrichment from [U-13C]palmitate in diacylglycerols, sphingolipids, and acyl-carnitines were measured using liquid chromatography/tandem mass spectrometry.

RESULTS

Among study participants with fatty liver disease, intrahepatic lipid was negatively correlated with VLDL-triglyceride secretion rates (r = -0.92, P = 0.01) but unrelated to hepatic free fatty acid uptake or indices of hepatic fatty acid oxidation. VLDL-triglyceride secretion rates were positively correlated with hepatic concentrations of saturated diacylglycerol (r = 0.46, P = 0.02) and sphingosine-1-phosphate (r = 0.44, P = 0.03).

CONCLUSION

We conclude that in nondiabetic humans with severe obesity, excess intrahepatic lipid is associated with limited export of triglyceride in VLDL particles rather than increased uptake of systemic free fatty acids.

EUS-guided core liver biopsy sampling using a 22-gauge fork-tip needle: a prospective blinded trial for histologic and lipidomic evaluation in nonalcoholic fatty liver disease

BACKGROUND AND AIMS

Diagnostic tools for nonalcoholic fatty liver disease (NAFLD) detection and prognostication are limited, with histology remaining the criterion standard. We evaluated the feasibility and safety of EUS-guided liver biopsy (EUS-LB) sampling in NAFLD staging.

METHODS

In a prospective cohort of NAFLD patients with steatohepatitis and early liver fibrosis based on magnetic resonance elastography (MRE), EUS-LB sampling procedures were performed using a 22-gauge fork-tip core biopsy needle. Samples were evaluated by a blinded pathologist. Total aggregate sample length (TASL), number of complete portal triads, ability to calculate NAFLD activity score, ability to stage liver fibrosis, and ability to provide enough core liver tissue for lipidomics analysis were evaluated. Performance of EUS-LB sampling was compared with MRE.

RESULTS

Forty-one EUS-LB samples were obtained. The median TASL was 2.4 cm (interquartile range, 2.00-2.75). The median number of complete portal triads per TASL was 26 (interquartile range, 7-62). Of the samples, 100% were adequate to convey NAFLD activity score and fibrosis stage. All samples provided enough core liver tissue to allow the application of lipidomics testing. A significant positive linear association between EUS-LB sampling-detected fibrosis and MRE-detected fibrosis was observed (r = .469, P < .005). Compared with MRE, EUS-LB sampling established early fibrosis in 13 cases that MRE classified as normal. EUS-LB sampling-related adverse events occurred in 7% and were restricted to postprocedural pain.

CONCLUSIONS

EUS-LB sampling is a viable technique for full NAFLD evaluation and may be superior to MRE in establishing the diagnosis of nonalcoholic steatohepatitis with early fibrosis. (Clinical trial registration number: NCT02880189.).

DNA variants affecting the expression of numerous genes in trans have diverse mechanisms of action and evolutionary histories

DNA variants that alter gene expression contribute to variation in many phenotypic traits. In particular, trans-acting variants, which are often located on different chromosomes from the genes they affect, are an important source of heritable gene expression variation. However, our knowledge about the identity and mechanism of causal trans-acting variants remains limited. Here, we developed a fine-mapping strategy called CRISPR-Swap and dissected three expression quantitative trait locus (eQTL) hotspots known to alter the expression of numerous genes in trans in the yeast Saccharomyces cerevisiae. Causal variants were identified by engineering recombinant alleles and quantifying the effects of these alleles on the expression of a green fluorescent protein-tagged gene affected by the given locus in trans. We validated the effect of each variant on the expression of multiple genes by RNA-sequencing. The three variants differed in their molecular mechanism, the type of genes they reside in, and their distribution in natural populations. While a missense leucine-to-serine variant at position 63 in the transcription factor Oaf1 (L63S) was almost exclusively present in the reference laboratory strain, the two other variants were frequent among S. cerevisiae isolates. A causal missense variant in the glucose receptor Rgt2 (V539I) occurred at a poorly conserved amino acid residue and its effect was strongly dependent on the concentration of glucose in the culture medium. A noncoding variant in the conserved fatty acid regulated (FAR) element of the OLE1 promoter influenced the expression of the fatty acid desaturase Ole1 in cis and, by modulating the level of this essential enzyme, other genes in trans. The OAF1 and OLE1 variants showed a non-additive genetic interaction, and affected cellular lipid metabolism. These results demonstrate that the molecular basis of trans-regulatory variation is diverse, highlighting the challenges in predicting which natural genetic variants affect gene expression.

Differences in the DNA sequence of individual genomes contribute to differences in many traits, such as appearance, physiology, and the risk for common diseases. An important group of these DNA variants influences how individual genes across the genome are turned on or off. In this paper, we describe a strategy for identifying such “trans-acting” variants in different strains of baker’s yeast. We used this strategy to reveal three single DNA base changes that each influences the expression of dozens of genes. These three DNA variants were very different from each other. Two of them changed the protein sequence, one in a transcription factor and the other in a sugar sensor. The third changed the expression of an enzyme, a change that in turn caused other genes to alter their expression. One variant existed in only a few yeast isolates, while the other two existed in many isolates collected from around the world. This diversity of DNA variants that influence the expression of many other genes illustrates how difficult it is to predict which DNA variants in an individual’s genome will have effects on the organism.

Preliminary evidence for reduced adipose tissue inflammation in vegetarians compared with omnivores

Background

There are links between obesity and inflammation that may relate activation of pro-inflammatory pathways by dietary factors. Because dietary fat intake of vegetarians is thought to be more beneficial than that of omnivores, we hypothesized that obese vegetarians would have less adipose tissue inflammation and lower intramyocellular ceramide concentrations than equally obese omnivores.

Methods

Eight obese vegetarian (1 male) and 8 obese omnivore volunteers (1 male) completed a Food Frequency Questionnaire, underwent body composition measures, subcutaneous adipose tissue and muscle biopsies. We used immunohistochemistry to measure adipose macrophage (ATM) and senescent cells. Plasma free fatty acid (FFA), adipose FA and muscle ceramide profiles were measured using liquid chromatography/mass spectrometry. Student t tests were used for the comparison of primary outcomes; univariate regression analysis was used to test for associations between dietary patterns and ATMs (secondary analysis).

Results

There were no differences in age (38 ± 8 vs. 39 ± 8 years), BMI (32.2 ± 2.6 vs. 33.3 ± 1.9 kg/m²) or percent body fat (44 ± 8 vs. 45 ± 4) between the vegetarians and omnivores. Vegetarians consumed 42% (P = 0.02) less saturated fat and 50% (P = 0.04) less cholesterol than the omnivores. Plasma FFA of vegetarians had lesser proportions of palmitic acid (24 ± 3 vs. 29 ± 4%, P = 0.02) and vegetarians had fewer femoral pro-inflammatory ATMs than omnivores (3.6 ± 2.8 vs. 7.9 ± 4.4 per 100 adipocytes, respectively; P = 0.02). Omnivores had 50% greater (P = 0.01) expression of TNF mRNA in abdominal fat. We found no significant between group differences in muscle ceramide concentrations.

Conclusions

Although the sample size is small, these results may indicate that dietary patterns play a role in adipose tissue inflammation, as reflected by reduced number of femoral ATMs in obese vegetarians than obese omnivores.

Subcutaneous adipose tissue free fatty acid uptake measured using positron emission tomography and adipose biopsies in humans

Positron emission tomography (PET) radiopharmaceuticals can noninvasively measure free fatty acid (FFA) uptake into adipose tissue. We studied 29 volunteers to test whether abdominal and femoral subcutaneous adipose tissue FFA uptake measured using [1-¹¹C]palmitate PET agrees with FFA storage rates measured using an intravenous bolus of [1-¹⁴C]palmitate and adipose biopsies. The dynamic left ventricular cavity PET images combined with blood sample radioactivity corrected for the ¹¹CO₂ content were used to create the blood time activity curve (TAC), and the constant (K_i) was determined using Patlak analysis of the TACs generated for regions of interest in abdominal subcutaneous fat. These data were used to calculate palmitate uptake rates in abdominal subcutaneous adipose tissue (µmol·kg^-1·min^-1). Immediately after the dynamic imaging, a static image of the thigh was taken to measure the standardized uptake value (SUV) in thigh adipose tissue, which was scaled to each participant's abdominal adipose tissue SUV to calculate thigh adipose palmitate uptake rates. Abdominal adipose palmitate uptake using PET [1-¹¹C]palmitate was correlated with, but significantly (P < 0.001) greater than, FFA storage measured using [1-¹⁴C]palmitate and adipose biopsy. Thigh adipose palmitate measured using PET calculation was positively correlated (R² = 0.44, P < 0.0001) with and not different from the biopsy approach. The relative differences between PET measured abdominal subcutaneous adipose tissue palmitate uptake and biopsy-measured palmitate storage were positively correlated (P = 0.03) with abdominal subcutaneous fat. We conclude that abdominal adipose tissue FFA uptake measured using PET does not equate to adipose FFA storage measured using biopsy techniques.

Trial analysis of drug profiling by liquid chromatography/mass spectrometry and inductively coupled plasma mass spectrometry to establish the origin of ephedrines used as precursors for illicit production of methamphetamine

RATIONALE

We investigated whether chemical information on the origin of ephedrine and pseudoephedrine (ephedrines) can be acquired by liquid chromatography/mass spectrometry (LC/MS) as a substitute method for stable isotope ratio mass spectrometry (IRMS), which is not routinely available in forensic laboratories. We examined the characteristic inorganic elemental contaminants of ephedrines as a preliminary study.

METHODS

The stable isotope ratios measured by IRMS analysis are expressed relative to the stable isotope ratios of conventional standards. Referring to the method using validated standard samples in IRMS, we selected a standard sample for acquiring stable isotopic ratio by LC/MS. The abundance ratio of the [M + 2H]⁺ ion to the [M + H]⁺ ion was measured by means of selected ion monitoring. We carried out qualitative analysis of inorganic elements contained in ephedrines produced by different manufacturing methods with ICPMS.

RESULTS

We found that the ratio of stable isotope ion to molecular ion (stable isotope ratio) of ephedrines could be measured with LC/MS. The stable isotope ratio of ephedrines determined by LC/MS were confirmed to show relatively good correlations with the carbon and hydrogen stable isotope ratios found by IR-MS. We identified strontium as a characteristic inorganic element contained in ephedrines prepared by the semisynthetic method from molasses, or in the biosynthetic method from ephedra plants.

CONCLUSIONS

Our results suggest that useful chemical information can be obtained by LC/MS, which is easy to carry out, and is generally available in forensic laboratories. It would be worthwhile to investigate the usefulness of stable isotope ratio measurements of Sr in the future.

Metformin treatment affects adipocytokine secretion and lipid composition in adipose tissues of diet-induced insulin-resistant rats

OBJECTIVES

Adipose tissue plays a central role in the pathogenesis of insulin resistance (IR) and type 2 diabetes. However, the molecular changes that promote these diseases are not completely understood. Several studies demonstrated that ceramide (Cer) and diacylglycerol (DAG) accumulation in muscle is associated with IR. The aim of this study was to explain whether a high-fat diet (HFD) leads to bioactive lipid accumulation in adipose tissue and how metformin affects the lipid content in adipocytes and the concentration of plasma adipocytokines.

METHODS

The experiments were conducted on male Wistar rats divided into three groups: control, HFD-fed, and HFD-fed and treated with metformin. Cer and DAGs were analyzed by liquid chromatography tandem mass spectrometry. Phosphorylation of hormone-sensitive lipase (HSL) was analyzed by Western blot. Oral glucose tolerance and insulin tolerance tests were also performed. Plasma adiponectin and tumor necrosis factor (TNF)-α concentration were measured by enzyme-linked immunosorbent assay.

RESULTS

HFD induced IR and elevated DAGs and Cer content in subcutaneous and visceral adipose tissues, which was accompanied by an increased phosphorylation of HSL. Metformin improved insulin sensitivity, decreased Cer and DAG levels, and attenuated the phosphorylation of HSL in both fat depots. Furthermore, we observed a strong correlation between adiponectin (negative) and TNF-α (positive) and bioactive lipids in both fat tissues.

CONCLUSIONS

These results indicated that bioactive lipids accumulation in adipose tissue influences the induction of IR and, at least in part, answered the question of what the insulin-sensitizing effect of metformin at the level of adipose tissue is.

Errors in measuring plasma free fatty acid concentrations with a popular enzymatic colorimetric kit

OBJECTIVES

Our goal was to test whether an enzymatic, colorimetric assay, the WAKO NEFA kit, provides information equivalent to liquid chromatography (LC) LC-based measures of free fatty acid (FFA).

DESIGN & METHODS

We reanalyzed nadir FFA samples from 109 volunteers from a previous study where we demonstrated that maximal suppression of FFA concentrations predicts metabolic abnormalities in humans; the results from the WAKO NEFA kit, which has been widely used for over three decades, could not replicate our findings. We conducted additional studies to directly compare results from this kit to our LC-mass spectrometry (LC/MS) method that was validated by our LC-UV detection method.

RESULTS

Plasma samples with FFA concentrations ranging from 0.015 to 1.813 mmol/L were measured both by LC-mass spectrometry (LC/MS) and by the WAKO NEFA kit. Despite good overall agreement (R² = 0.86), the slope was significantly different from 1.0 and the intercept was significantly different from zero. The results from the kit were especially discrepant with FFA concentrations <0.200 and >1.000 mmol/L. Some of the discrepancy was related to the use of oleate as the standard solution for the kit and the substrate specificity of the kit enzymes for different fatty acids. Despite attempts to improve the kit by modifying the reaction time, sample volume and the types of standard solutions, we could not obtain a satisfactory agreement between the WAKO NEFA results and LC/MS.

CONCLUSIONS

The WAKO NEFA kit should not be used when high precision and accuracy of FFA concentrations over a wide range is required.

Development and Validation of a LC⁻MS/MS-Based Assay for Quantification of Free and Total Omega 3 and 6 Fatty Acids from Human Plasma

Few high-performance liquid chromatography⁻tandem mass spectrometry (LC-MS/MS) methods have been developed for the full quantitation of fatty acids from human plasma without derivatization. Therefore, we propose a method that requires fewer sample preparation steps, which can be used for the quantitation of several polyunsaturated fatty acids in human plasma. The method offers rapid, accurate, sensitive, and simultaneous quantification of omega 3 (α-linolenic, eicosapentaenoic, and docosahexaenoic acids) and omega 6 fatty acids (arachidonic and linoleic acids) using high-performance LC-MS/MS. The selected fatty acids were analysed in lipid extracts from both free and total forms. Chromatographic separation was achieved using a reversed phase C18 column with isocratic flow using ammonium acetate for improving negative electrospray ionization (ESI) response. Mass detection was performed in multiple reaction monitoring (MRM) mode, and deuterated internal standards were used for each target compound. The limits of quantification were situated in the low nanomolar range, excepting linoleic acid, for which the limit was in the high nanomolar range. The method was validated according to the U.S. Department of Health and Human Services guidelines, and offers a fast, sensitive, and reliable quantification of selected omega 3 and 6 fatty acids in human plasma.

Inhibition of Ceramide De Novo Synthesis Affects Adipocytokine Secretion and Improves Systemic and Adipose Tissue Insulin Sensitivity

Ceramide accumulation in muscle and in liver is implicated in the induction of insulin resistance. Much less in known about the role of ceramide in adipose tissue. The aim of the present study was to elucidate the role of ceramide in adipose tissue and to clarify whether lipids participate in the regulation of adipocytokine secretion. The experiments were performed on male Wistar rats divided into three groups: 1. Control, 2. fed high fat diet (HFD), and 3. fed HFD and treated with myriocin. Ceramide (Cer) and diacylglycerol (DAG) content were analyzed by LC/MS/MS. Hormone sensitive lipase (HSL) phosphorylation was analyzed by Western Blot. Plasma adiponectin and tumor necrosis factor alpha (TNF-α) concentration were measured by enzyme-linked immunosorbent assay. An oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) was also performed. In HFD group, total DAG and Cer content was elevated in both subcutaneous and visceral adipose tissue, which was accompanied by increased glucose, insulin, and HOMA-IR value. Myriocin treatment restored HOMA-IR as well as glucose and insulin concentration to control values. Moreover, myriocin decreased not only Cer, but also DAG levels in both fat depots. Furthermore, we observed a strong correlation between adiponectin (negative) and TNF-α (positive) and Cer in both fat tissues, which suggests that Cer is involved in the regulation of adipocytokine secretion.

Analytical Considerations of Stable Isotope Labelling in Lipidomics

Over the last two decades, lipids have come to be understood as far more than merely components of cellular membranes and forms of energy storage, and are now also being implicated to play important roles in a variety of diseases, with lipid biomarker research one of the most widespread applications of lipidomic techniques both in research and in clinical settings. Stable isotope labelling has become a staple technique in the analysis of small molecule metabolism and dynamics, as it is the only experimental setup by which biosynthesis, remodelling and degradation of biomolecules can be directly measured. Using state-of-the-art analytical technologies such as chromatography-coupled high resolution tandem mass spectrometry, the stable isotope label can be precisely localized and quantified within the biomolecules. The application of stable isotope labelling to lipidomics is however complicated by the diversity of lipids and the complexity of the necessary data analysis. This article discusses key experimental aspects of stable isotope labelling in the field of mass spectrometry-based lipidomics, summarizes current applications and provides an outlook on future developments and potential.

Mitochondrial ATP synthase β-subunit production rate and ATP synthase specific activity are reduced in skeletal muscle of humans with obesity

NEW FINDINGS

What is the central question of this study? Humans with obesity have lower ATP synthesis in muscle along with lower content of the β-subunit of the ATP synthase (β-F1-ATPase), the catalytic component of the ATP synthase. Does lower synthesis rate of β-F1-ATPase in muscle contribute to these responses in humans with obesity? What is the main finding and its importance? Humans with obesity have a lower synthesis rate of β-F₁ -ATPase and ATP synthase specific activity in muscle. These findings indicate that reduced production of subunits forming the ATP synthase in muscle may contribute to impaired generation of ATP in obesity.

ABSTRACT

The content of the β-subunit of the ATP synthase (β-F₁ -ATPase), which forms the catalytic site of the enzyme ATP synthase, is reduced in muscle of obese humans, along with a reduced capacity for ATP synthesis. We studied 18 young (37 ± 8 years) subjects of which nine were lean (BMI = 23 ± 2 kg m^-2 ) and nine were obese (BMI = 34 ± 3 kg m^-2 ) to determine the fractional synthesis rate (FSR) and gene expression of β-F₁ -ATPase, as well as the specific activity of the ATP synthase. FSR of β-F₁ -ATPase was determined using a combination of isotope tracer infusion and muscle biopsies. Gene expression of β-F₁ -ATPase and specific activity of the ATP synthase were determined in the muscle biopsies. When compared to lean, obese subjects had lower muscle β-F₁ -ATPase FSR (0.10 ± 0.05 vs. 0.06 ± 0.03% h^-1 ; P < 0.05) and protein expression (P < 0.05), but not mRNA expression (P > 0.05). Across subjects, abundance of β-F₁ -ATPase correlated with the FSR of β-F₁ -ATPase (P < 0.05). The specific activity of muscle ATP synthase was lower in obese compared to lean subjects (0.035 ± 0.004 vs. 0.042 ± 0.007 arbitrary units; P < 0.05), but this difference was not significant after the activity of the ATP synthase was adjusted to the β-F₁ -ATPase content (P > 0.05). Obesity impairs the synthesis of β-F₁ -ATPase in muscle at the translational level, reducing the content of β-F₁ -ATPase in parallel with reduced capacity for ATP generation via the ATP synthase complex.

Stable Isotope Labeling Highlights Enhanced Fatty Acid and Lipid Metabolism in Human Acute Myeloid Leukemia

Background: In Acute Myeloid Leukemia (AML), a complete response to chemotherapy is usually obtained after conventional chemotherapy but overall patient survival is poor due to highly frequent relapses. As opposed to chronic myeloid leukemia, B lymphoma or multiple myeloma, AML is one of the rare malignant hemopathies the therapy of which has not significantly improved during the past 30 years despite intense research efforts. One promising approach is to determine metabolic dependencies in AML cells. Moreover, two key metabolic enzymes, isocitrate dehydrogenases (IDH1/2), are mutated in more than 15% of AML patient, reinforcing the interest in studying metabolic reprogramming, in particular in this subgroup of patients. Methods: Using a multi-omics approach combining proteomics, lipidomics, and isotopic profiling of [U-¹³C] glucose and [U-¹³C] glutamine cultures with more classical biochemical analyses, we studied the impact of the IDH1 R132H mutation in AML cells on lipid biosynthesis. Results: Global proteomic and lipidomic approaches showed a dysregulation of lipid metabolism, especially an increase of phosphatidylinositol, sphingolipids (especially few species of ceramide, sphingosine, and sphinganine), free cholesterol and monounsaturated fatty acids in IDH1 mutant cells. Isotopic profiling of fatty acids revealed that higher lipid anabolism in IDH1 mutant cells corroborated with an increase in lipogenesis fluxes. Conclusions: This integrative approach was efficient to gain insight into metabolism and dynamics of lipid species in leukemic cells. Therefore, we have determined that lipid anabolism is strongly reprogrammed in IDH1 mutant AML cells with a crucial dysregulation of fatty acid metabolism and fluxes, both being mediated by 2-HG (2-Hydroxyglutarate) production.

The effect of high-fat diet and inhibition of ceramide production on insulin action in liver

Liver, as one of the most important organs involved in lipids and glucose metabolism, is perceived as a key tissue for pharmacotherapy of insulin resistance (IRes) and type 2 diabetes. Ceramides (Cer) are biologically active lipids, which accumulation is associated with the induction of muscle IRes. We sought to determine the role of intrahepatic bioactive lipids production on insulin action in liver of insulin-resistant rats and after myriocin administration. The experiments were conducted on male Wistar rats divided into three groups: Control, fed high-fat diet (HFD), and fed HFD and treated with myriocin (HFD/Myr). Before sacrifice, the animals were infused with a [U-¹³ C]palmitate to calculate lipid synthesis rate by means of tracer incorporation technique in particular lipid groups. Liver Cer, diacylglycerols (DAG), acyl-carnitine concentration, and isotopic enrichment were analyzed by LC/MS/MS. Proteins involved in lipid metabolism and insulin pathway were analyzed by western blot analysis. An OGTT and ITT was also performed. HFD-induced IRes and increased both the synthesis rate and the content of DAG and Cer, which was accompanied by inhibition of an insulin pathway. Interestingly, myriocin treatment reduced synthesis rate not only of Cer but also DAG and improved insulin sensitivity. We conclude that the insulin-sensitizing action of myriocin in the liver is a result of the lack of inhibitory effect of lipids on the insulin pathway, due to the reduction of their synthesis rate. This is the first study showing how the synthesis rate of individual lipid groups in liver changes after myriocin administration.

Lower Fasted-State but Greater Increase in Muscle Protein Synthesis in Response to Elevated Plasma Amino Acids in Obesity

OBJECTIVE

Obesity alters protein metabolism in skeletal muscle, but consistent evidence is lacking. This study compared muscle protein synthesis in adults with obesity and in lean controls in the fasted state and during an amino acid infusion.

METHODS

Ten subjects with obesity (age: 36 ± 3 years; BMI: 34 ± 1 kg/m2 ) and ten controls (age: 35 ± 3 years; BMI: 23 ± 1 kg/m2 ) received an infusion of L-[2,3,3,4,5,5,5,6,6,6-2 H10 ]leucine (0.15 μmol/kg fat-free mass/min) to measure muscle protein synthesis after an overnight fast and during amino acid infusion.

RESULTS

Despite greater muscle mammalian target of rapamycin phosphorylation (P ≤ 0.05), fasted-state mixed-muscle and mitochondrial protein synthesis were lower in subjects with obesity (P ≤ 0.05). However, the change in mixed-muscle protein synthesis during the amino acid infusion was 2.7-fold greater in subjects with obesity (P ≤ 0.05), accompanied by a greater change in S6 kinase-1 phosphorylation (P ≤ 0.05). The change in mitochondrial protein synthesis did not differ between groups (P > 0.05).

CONCLUSIONS

Adults with obesity have reduced muscle protein synthesis in the fasted state, but this response is compensated for by a greater change in overall muscle protein synthesis during amino acid infusion.

The effect of high fat diet and metformin treatment on liver lipids accumulation and their impact on insulin action

We sought to determine whether metformin treatment reverses a high-fat diet (HFD)-induced hepatic insulin resistance (IRes) and to identify lipid intermediates involved in induction of liver IRes. The experiments were conducted on male Wistar rats divided into three groups: 1. Control, 2. fed HFD and 3. fed HFD and treated with metformin. The animals were infused with a [U-¹³C]palmitate to measure fractional lipid synthesis rate. This allowed for the calculation of fractional synthesis rate of signaling lipids (FSR) through the estimation of their isotopic enrichment. Liver ceramide (Cer), diacylglycerol (DAG) and acyl-carnitine concentration and enrichment were analyzed by LC/MS/MS. The content of proteins involved in lipid metabolism and insulin signaling were analyzed by Western Blot. HFD treatment increased the content and FSR of DAG and Cer in the liver which was accompanied by systemic insulin resistance and inhibition of hepatic insulin signaling pathway under insulin stimulation. Metformin treatment ameliorated systemic insulin resistance and augmented the hepatic insulin signaling cascade. It reduced both the concentration and FSR of Cer, DAG, and increased acyl-carnitine content and the expression of mitochondrial markers. We postulate, that in liver, the insulin sensitizing effect of metformin depends on augmentation of mitochondrial β-oxidation, which protects from hepatic accumulation of both the Cer and DAG and preserves insulin sensitivity under HFD consumption. Moreover, we showed that hepatic content of Cer and DAG corresponds with their respective FSR.

Free fatty acid flux measured using [1-11C]palmitate positron emission tomography and [U-13C]palmitate in humans

PET radiopharmaceuticals can noninvasively measure free fatty acid (FFA) tissue uptake. Investigators often use PET scan-derived data to calculate FFA flux. We tested whether the [1-¹¹C]palmitate PET measures of palmitate flux provide results equivalent to a continuous infusion of [U-¹³C]palmitate. Nine volunteers participated in study 1 to evaluate whether a rapidly (10-20 s) given bolus of [1-¹¹C]palmitate affects calculated flux results. Thirty volunteers participated in study 2, which was identical to study 1 except that the [1-¹¹C]palmitate bolus was given over 1 min. Volunteers in both studies also received a continuous intravenous infusion of [U-¹³C]palmitate. Plasma palmitate concentrations and enrichment were measured by liquid chromatography-mass spectrometry. The PET/CT images were analyzed on a workstation running PMOD. Palmitate flux was estimated using PET time-activity curve (TAC) data from regions of interest in the left ventricle (LV) and aorta both with and without hybrid TACs that employed the ¹¹CO₂-corrected data for the first 5 min and the ¹¹CO₂-corrected blood radioactivity for the remainder of the PET scan. Palmitate flux in study 1 measured with PET [1-¹¹C]palmitate and [U-¹³C]palmitate were not correlated, and the PET [1-¹¹C]palmitate flux was significantly less than the [U-¹³C]palmitate measured flux. In study 2, the palmitate flux using PET [1-¹¹C]palmitate hybrid LV models provided closer mean estimates of [U-¹³C]palmitate measured flux. The best PET calculation approaches predicted 64% of the interindividual variance in [U-¹³C]palmitate measured flux. Palmitate kinetics measured using [1-¹¹C]palmitate/PET do not provide the same palmitate kinetic results as the continuous infusion [U-¹³C]palmitate approach.

Effects of meal ingestion on intramyocellular ceramide concentrations and fractional de novo synthesis in humans

We investigated the effects of meal ingestion on intramyofibrillar (IMF) and subsarcolemmal (SS) ceramide metabolism in volunteers ranging from lean to obese. Thirty-eight women and men underwent a steady-state meal ingestion protocol that included a 6.5-h infusion of [U-¹³C]palmitate and muscle biopsies 1.5 and 6.5 h after starting the tracer infusion. We measured IMF and SS sphingolipid concentrations and the contribution of plasma palmitate to intramyocellular C16:0 ceramide by use of LC-MS-MS. In response to meal ingestion SS C24 ceramide concentrations, but not C14-C20 concentrations, increased significantly. IMF ceramide concentrations did not change. The increases in SS C24 ceramides were negatively related to parameters of insulin resistance. The fractional contribution of plasma palmitate to intramyocellular C16:0 ceramides in both IMF and SS fractions was inversely related to overweight status (β = -0.432, P = 0.0095 and β = -0.443, P = 0.0058, respectively). These data indicate that meal ingestion has differing effects on SS ceramide subspecies and suggest that the fractional de novo synthesis of intramyocellular ceramide from plasma palmitate in the postprandial condition is reduced in those who are overweight.