Ceramides are fuel gauges on the drive to cardiometabolic disease

Ceramides are signals of fatty acid excess that accumulate when a cell's energetic needs have been met and its nutrient storage has reached capacity. As these sphingolipids accrue, they alter the metabolism and survival of cells throughout the body including in the heart, liver, blood vessels, skeletal muscle, brain, and kidney. These ceramide actions elicit the tissue dysfunction that underlies cardiometabolic diseases such as diabetes, coronary artery disease, metabolic-associated steatohepatitis, and heart failure. Here, we review the biosynthesis and degradation pathways that maintain ceramide levels in normal physiology and discuss how the loss of ceramide homeostasis drives cardiometabolic pathologies. We highlight signaling nodes that sense small changes in ceramides and in turn reprogram cellular metabolism and stimulate apoptosis. Finally, we evaluate the emerging therapeutic utility of these unique lipids as biomarkers that forecast disease risk and as targets of ceramide-lowering interventions that ameliorate disease.

Adiponectin overexpression improves metabolic abnormalities caused by acid ceramidase deficiency but does not prolong lifespan in a mouse model of Farber Disease

Farber Disease is a debilitating and lethal childhood disease of ceramide accumulation caused by acid ceramidase deficiency. The potent induction of a ligand-gated neutral ceramidase activity promoted by adiponectin may provide sufficient lowering of ceramides to allow for the treatment of Farber Disease. In vitro, adiponectin or adiponectin receptor agonist treatments lowered total ceramide concentrations in human fibroblasts from a patient with Farber Disease. However, adiponectin overexpression in a Farber Disease mouse model did not improve lifespan or immune infiltration. Intriguingly, mice heterozygous for the Farber Disease mutation were more prone to glucose intolerance and insulin resistance when fed a high-fat diet, and adiponectin overexpression protected from these metabolic perturbations. These studies suggest that adiponectin evokes a ceramidase activity that is not reliant on the functional expression of acid ceramidase, but indicates that additional strategies are required to ameliorate outcomes of Farber Disease.

Phospholipid isotope tracing suggests β-catenin-driven suppression of phosphatidylcholine metabolism in hepatocellular carcinoma

Activating mutations in the CTNNB1 gene encoding β-catenin are among the most frequently observed oncogenic alterations in hepatocellular carcinoma (HCC). Profound alterations in lipid metabolism, including increases in fatty acid oxidation and transformation of the phospholipidome, occur in HCC with CTNNB1 mutations, but it is unclear what mechanisms give rise to these changes. We employed untargeted lipidomics and targeted isotope tracing to measure phospholipid synthesis activity in an inducible human liver cell line expressing mutant β-catenin, as well as in transgenic zebrafish with activated β-catenin-driven HCC. In both models, activated β-catenin expression was associated with large changes in the lipidome including conserved increases in acylcarnitines and ceramides and decreases in triglycerides. Lipid isotope tracing analysis in human cells revealed a reduction in phosphatidylcholine (PC) production rates as assayed by choline incorporation. We developed lipid isotope tracing analysis for zebrafish tumors and observed reductions in phosphatidylcholine synthesis by both the CDP-choline and PEMT pathways. The observed changes in the β-catenin-driven HCC phospholipidome suggest that zebrafish can recapitulate conserved features of HCC lipid metabolism and may serve as a model for identifying future HCC-specific lipid metabolic targets.

Integrating molecular and clinical variables to predict myocardial recovery

Mechanical unloading and circulatory support with left ventricular assist devices (LVADs) mediate significant myocardial improvement in a subset of advanced heart failure (HF) patients. The clinical and biological phenomena associated with cardiac recovery are under intensive investigation. Left ventricular (LV) apical tissue, alongside clinical data, were collected from HF patients at the time of LVAD implantation (n=208). RNA was isolated and mRNA transcripts were identified through RNA sequencing and confirmed with RT-qPCR. To our knowledge this is the first study to combine transcriptomic and clinical data to derive predictors of myocardial recovery. We used a bioinformatic approach to integrate 59 clinical variables and 22,373 mRNA transcripts at the time of LVAD implantation for the prediction of post-LVAD myocardial recovery defined as LV ejection fraction (LVEF) ≥40% and LV end-diastolic diameter (LVEDD) ≤5.9cm, as well as functional and structural LV improvement independently by using LVEF and LVEDD as continuous variables, respectively. To substantiate the predicted variables, we used a multi-model approach with logistic and linear regressions. Combining RNA and clinical data resulted in a gradient boosted model with 80 features achieving an AUC of 0.731±0.15 for predicting myocardial recovery. Variables associated with myocardial recovery from a clinical standpoint included HF duration, pre-LVAD LVEF, LVEDD, and HF pharmacologic therapy, and LRRN4CL (ligand binding and programmed cell death) from a biological standpoint. Our findings could have diagnostic, prognostic, and therapeutic implications for advanced HF patients, and inform the care of the broader HF population.

Association between pre-diagnostic circulating lipid metabolites and colorectal cancer risk: a nested case-control study in the European Prospective Investigation into Cancer and Nutrition (EPIC)

BACKGROUND

Altered lipid metabolism is a hallmark of cancer development. However, the role of specific lipid metabolites in colorectal cancer development is uncertain.

METHODS

In a case-control study nested within the European Prospective Investigation into Cancer and Nutrition (EPIC), we examined associations between pre-diagnostic circulating concentrations of 97 lipid metabolites (acylcarnitines, glycerophospholipids and sphingolipids) and colorectal cancer risk. Circulating lipids were measured using targeted mass spectrometry in 1591 incident colorectal cancer cases (55% women) and 1591 matched controls. Multivariable conditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for associations between concentrations of individual lipid metabolites and metabolite patterns with colorectal cancer risk.

FINDINGS

Of the 97 assayed lipids, 24 were inversely associated (nominally p < 0.05) with colorectal cancer risk. Hydroxysphingomyelin (SM (OH)) C22:2 (ORper doubling 0.60, 95% CI 0.47-0.77) and acylakyl-phosphatidylcholine (PC ae) C34:3 (ORper doubling 0.71, 95% CI 0.59-0.87) remained associated after multiple comparisons correction. These associations were unaltered after excluding the first 5 years of follow-up after blood collection and were consistent according to sex, age at diagnosis, BMI, and colorectal subsite. Two lipid patterns, one including 26 phosphatidylcholines and all sphingolipids, and another 30 phosphatidylcholines, were weakly inversely associated with colorectal cancer.

INTERPRETATION

Elevated pre-diagnostic circulating levels of SM (OH) C22:2 and PC ae C34:3 and lipid patterns including phosphatidylcholines and sphingolipids were associated with lower colorectal cancer risk. This study may provide insight into potential links between specific lipids and colorectal cancer development. Additional prospective studies are needed to validate the observed associations.

FUNDING

World Cancer Research Fund (reference: 2013/1002); European Commission (FP7: BBMRI-LPC; reference: 313010).

A Retrospective Chart Review Suggests That Coordinated, Multidisciplinary Treatment for Patients with Anorexia Nervosa Improves Odds of Weight Restoration

Purpose

The objective of this study was to conduct a secondary data analysis of clinical information documented in the electronic medical record to assess the clinical outcomes of patients who received three different treatment approaches on clinical outcomes for treatment of patients with anorexia nervosa (AN).

Patients and methods

Historical electronic medical record (EMR) data on patients aged 6 to 80 years diagnosed with AN seen in a healthcare system between 2007 and 2017 were stratified, according to services received, into three groups: Group A (n = 48) received hospital-based services; Group B (n = 290) saw one or two provider types; Group C (n = 26) received outpatient coordinated multidisciplinary care from three provider types. Clinical outcomes [body mass index for adults (BMI), body mass index percentile (BMI%ile) for pediatric patients] defined AN severity and weight restoration. EMR data were analyzed using a generalized mixed-effects model and a Markov Transition model to examine the odds of weight restoration and the change in odds of weight restoration across the number of provider visits, respectively.

Results

Patients receiving coordinated multidisciplinary care had significantly higher odds of weight restoration compared with patients receiving hospital-based services only (OR = 3.76, 95% CI [1.04, 13.54], p = 0.042). In addition, patients receiving care from 1 to 2 providers (OR = 1.006, 95% CI [1.003, 1.010], p = 0.001) or receiving coordinated multidisciplinary care (OR = 1.005, 95% CI [1.001, 1.011], p = 0.021) had significantly higher odds of weight restoration per provider visit day compared with patients receiving hospital-based services only.

Conclusion

This retrospective chart review supports the coordinated, multidisciplinary care model for the weight restoration in patients with AN in an outpatient setting.

HAF Prevents Hepatocyte Apoptosis and Hepatocellular Carcinoma through Transcriptional Regulation of the NF-κB pathway

Background

Hepatocellular carcinoma (HCC) incidence is increasing worldwide due to the obesity epidemic, which drives metabolic dysfunction-associated steatohepatitis (MASH) that can lead to HCC. However, the molecular pathways that lead to MASH-HCC are poorly understood. We have previously reported that male mice with global haploinsufficiency of hypoxia-associated factor, HAF ( SART1 +/ - ) spontaneously develop MASH/HCC. However, the cell type(s) responsible for HCC associated with HAF loss are unclear.

Results

SART1 -floxed mice were crossed with mice expressing Cre-recombinase within hepatocytes (Alb-Cre; hepS -/- ) or macrophages (LysM-Cre, macS -/- ). Only hepS -/- mice (both male and female) developed HCC suggesting that HAF protects against HCC primarily within hepatocytes. HAF-deficient macrophages showed decreased P-p65 and P-p50 and in many major components of the NF-κB pathway, which was recapitulated using HAF siRNA in vitro . HAF depletion increased apoptosis both in vitro and in vivo , suggesting that HAF mediates a tumor suppressor role by suppressing hepatocyte apoptosis. We show that HAF regulates NF-κB activity by controlling transcription of TRADD and RIPK1 . Mice fed a high-fat diet (HFD) showed marked suppression of HAF, P-p65 and TRADD within their livers after 26 weeks, but manifest profound upregulation of HAF, P-65 and TRADD within their livers after 40 weeks of HFD, implicating deregulation of the HAF-NF-κB axis in the progression to MASH. In humans, HAF was significantly decreased in livers with simple steatosis but significantly increased in HCC compared to normal liver.

Conclusions

HAF is novel transcriptional regulator of the NF-κB pathway that protects against hepatocyte apoptosis and is a key determinant of cell fate during progression to MASH and MASH-HCC.

Identification of genetic drivers of plasma lipoprotein size in the Diversity Outbred mouse population

Despite great progress in understanding lipoprotein physiology, there is still much to be learned about the genetic drivers of lipoprotein abundance, composition, and function. We used ion mobility spectrometry to survey 16 plasma lipoprotein subfractions in 500 Diversity Outbred mice maintained on a Western-style diet. We identified 21 quantitative trait loci (QTL) affecting lipoprotein abundance. To refine the QTL and link them to disease risk in humans, we asked if the human homologs of genes located at each QTL were associated with lipid traits in human genome-wide association studies. Integration of mouse QTL with human genome-wide association studies yielded candidate gene drivers for 18 of the 21 QTL. This approach enabled us to nominate the gene encoding the neutral ceramidase, Asah2, as a novel candidate driver at a QTL on chromosome 19 for large HDL particles (HDL-2b). To experimentally validate Asah2, we surveyed lipoproteins in Asah2-/- mice. Compared to wild-type mice, female Asah2-/- mice showed an increase in several lipoproteins, including HDL. Our results provide insights into the genetic regulation of circulating lipoproteins, as well as mechanisms by which lipoprotein subfractions may affect cardiovascular disease risk in humans.

Ceramides Increase Fatty Acid Utilization in Intestinal Progenitors to Enhance Stemness and Increase Tumor Risk

BACKGROUND & AIMS

Cancers of the alimentary tract, including esophageal adenocarcinomas, colorectal cancers, and cancers of the gastric cardia, are common comorbidities of obesity. Prolonged, excessive delivery of macronutrients to the cells lining the gut can increase one's risk for these cancers by inducing imbalances in the rate of intestinal stem cell proliferation vs differentiation, which can produce polyps and other aberrant growths. We investigated whether ceramides, which are sphingolipids that serve as a signal of nutritional excess, alter stem cell behaviors to influence cancer risk.

METHODS

We profiled sphingolipids and sphingolipid-synthesizing enzymes in human adenomas and tumors. Thereafter, we manipulated expression of sphingolipid-producing enzymes, including serine palmitoyltransferase (SPT), in intestinal progenitors of mice, cultured organoids, and Drosophila to discern whether sphingolipids altered stem cell proliferation and metabolism.

RESULTS

SPT, which diverts dietary fatty acids and amino acids into the biosynthetic pathway that produces ceramides and other sphingolipids, is a critical modulator of intestinal stem cell homeostasis. SPT and other enzymes in the sphingolipid biosynthesis pathway are up-regulated in human intestinal adenomas. They produce ceramides, which serve as prostemness signals that stimulate peroxisome-proliferator activated receptor-α and induce fatty acid binding protein-1. These actions lead to increased lipid utilization and enhanced proliferation of intestinal progenitors.

CONCLUSIONS

Ceramides serve as critical links between dietary macronutrients, epithelial regeneration, and cancer risk.

Phospholipid isotope tracing reveals β-catenin-driven suppression of phosphatidylcholine metabolism in hepatocellular carcinoma

Background and Aims

Activating mutations in the CTNNB1 gene encoding β-catenin are among the most frequently observed oncogenic alterations in hepatocellular carcinoma (HCC). HCC with CTNNB1 mutations show profound alterations in lipid metabolism including increases in fatty acid oxidation and transformation of the phospholipidome, but it is unclear how these changes arise and whether they contribute to the oncogenic program in HCC.

Methods

We employed untargeted lipidomics and targeted isotope tracing to quantify phospholipid production fluxes in an inducible human liver cell line expressing mutant β-catenin, as well as in transgenic zebrafish with activated β-catenin-driven HCC.

Results

In both models, activated β-catenin expression was associated with large changes in the lipidome including conserved increases in acylcarnitines and ceramides and decreases in triglycerides. Lipid flux analysis in human cells revealed a large reduction in phosphatidylcholine (PC) production rates as assayed by choline tracer incorporation. We developed isotope tracing lipid flux analysis for zebrafish and observed similar reductions in phosphatidylcholine synthesis flux accomplished by sex-specific mechanisms.

Conclusions

The integration of isotope tracing with lipid abundances highlights specific lipid class transformations downstream of β-catenin signaling in HCC and suggests future HCC-specific lipid metabolic targets.

Ramadan intermittent fasting is associated with ameliorated inflammatory markers and improved plasma sphingolipids/ceramides in subjects with obesity: lipidomics analysis

Intermittent fasting (IF) is associated with enormous metabolic alterations that underpin its diverse health effects. Changes in lipid metabolism, particularly ceramides, and other sphingolipids, are among the most notable of these alterations. This study investigated the lipidomic alterations associated with 29-30 days of Ramadan diurnal intermittent fasting (RIF) in metabolically healthy overweight and obese subjects. A prospective cohort of 57 overweight and obese adults (70% males, 38.4 ± 11.2 years), with an age range of 18-58 years was observed prior to and at the conclusion of Ramadan. At both time points, anthropometric, biochemical (lipid profile, glycemic, and inflammatory markers), and dietary intake measurements were taken. Using liquid chromatography-mass spectrometry, a lipidomic analysis of ceramides and other sphingolipids was conducted. Using paired sample t-tests, pre- and post-Ramadan anthropometric, biochemical, and dietary values were compared. RIF was associated with improved levels of lipid profile compartments and inflammatory markers. In addition, RIF was associated with a decrease in plasma sphingosine and sphinganine, which was accompanied by a decrease in sphingosine 1-phosphate and sphinganine 1-phosphate. In addition, RIF was associated with decreased C17, C22, and C24 sphingomyelin, but not C14, C16, C18, C20, and C24:1 sphingomyelin, as well as C20, C22, C24, and C24:1 dihydrosphingomyelin, but not C16 and C18 dihydrosphingomyelin. This study demonstrates that RIF is associated with improvements in plasma sphingosine, sphinganine sphingomyelin, and dihydrosphingomyelin lipid species, as well as improved lipid profile and inflammatory markers, which may confer short-term protection against cardiometabolic problems in patients with overweight/obesity.

New-Onset Diabetes after an Obesity-Related Cancer Diagnosis and Survival Outcomes in the Women's Health Initiative

BACKGROUND

Individuals diagnosed with an obesity-related cancer (ORC survivors) are at an elevated risk of incident diabetes compared with cancer-free individuals, but whether this confers survival disadvantage is unknown.

METHODS

We assessed the rate of incident diabetes in ORC survivors and evaluated the association of incident diabetes with all-cause and cancer-specific mortality among females with ORC in the Women's Health Initiative cohort (N = 14,651). Cox proportional hazards regression models stratified by exposure-risk periods (0-1, >1-3, >3-5, >5-7, and >7-10 years) from ORC diagnosis and time-varying exposure (diabetes) analyses were performed.

RESULTS

Among the ORC survivors, a total of 1.3% developed diabetes within ≤1 year of follow-up and 2.5%, 2.3%, 2.3%, and 3.6% at 1-3, 3-5, 5-7, and 7-10 years of follow-up, respectively, after an ORC diagnosis. The median survival for those diagnosed with diabetes within 1-year of cancer diagnosis and those with no diabetes diagnosis in that time frame was 8.8 [95% confidence interval (CI), 7.0-14.5) years and 16.6 (95% CI, 16.1-17.0) years, respectively. New-onset compared with no diabetes as a time-varying exposure was associated with higher risk of all-cause (HR, 1.27; 95% CI, 1.16-1.40) and cancer-specific (HR, 1.17; 95% CI, 0.99-1.38) mortality. When stratified by exposure-risk periods, incident diabetes in ≤1 year of follow-up was associated with higher all-cause (HR, 1.76; 95% CI, 1.40-2.20) and cancer-specific (HR0-1, 1.82; 95% CI, 1.28-2.57) mortality, compared with no diabetes diagnosis.

CONCLUSIONS

Incident diabetes was associated with worse cancer-specific and all-cause survival, particularly in the year after cancer diagnosis.

IMPACT

These findings draw attention to the importance of diabetes prevention efforts among cancer survivors to improve survival outcomes.

Palmitate-Induced Inflammation and Myotube Atrophy in C2C12 Cells Are Prevented by the Whey Bioactive Peptide, Glycomacropeptide

BACKGROUND

Metabolic diseases are often associated with muscle atrophy and heightened inflammation. The whey bioactive compound, glycomacropeptide (GMP), has been shown to exhibit anti-inflammatory properties and therefore may have potential therapeutic efficacy in conditions of skeletal muscle inflammation and atrophy.

OBJECTIVES

The purpose of this study was to determine the role of GMP in preventing lipotoxicity-induced myotube atrophy and inflammation.

METHODS

C2C12 myoblasts were differentiated to determine the effect of GMP on atrophy and inflammation and to explore its mechanism of action in evaluating various anabolic and catabolic cellular signaling nodes. We also used a lipidomic analysis to evaluate muscle sphingolipid accumulation with the various treatments. Palmitate (0.75 mM) in the presence and absence of GMP (5 μg/mL) was used to induce myotube atrophy and inflammation and cells were collected over a time course of 6-24 h.

RESULTS

After 24 h of treatment, GMP prevented the palmitate-induced decrease in the myotube area and myogenic index and the increase in the TLR4-mediated inflammatory genes tumor necrosis factor-α and interleukin 1β. Moreover, phosphorylation of Erk1/2, and gene expression of myostatin, and the E3 ubiquitin ligases, FBXO32, and MuRF1 were decreased with GMP treatment. GMP did not alter palmitate-induced ceramide or diacylglycerol accumulation, muscle insulin resistance, or protein synthesis.

CONCLUSIONS

In summary, GMP prevented palmitate-induced inflammation and atrophy in C2C12 myotubes. The GMP protective mechanism of action in muscle cells during lipotoxic stress may be related to targeting catabolic signaling associated with cellular stress and proteolysis but not protein synthesis.

Vitamin B2 enables regulation of fasting glucose availability

Flavin adenine dinucleotide (FAD) interacts with flavoproteins to mediate oxidation-reduction reactions required for cellular energy demands. Not surprisingly, mutations that alter FAD binding to flavoproteins cause rare inborn errors of metabolism (IEMs) that disrupt liver function and render fasting intolerance, hepatic steatosis, and lipodystrophy. In our study, depleting FAD pools in mice with a vitamin B2-deficient diet (B2D) caused phenotypes associated with organic acidemias and other IEMs, including reduced body weight, hypoglycemia, and fatty liver disease. Integrated discovery approaches revealed B2D tempered fasting activation of target genes for the nuclear receptor PPARα, including those required for gluconeogenesis. We also found PPARα knockdown in the liver recapitulated B2D effects on glucose excursion and fatty liver disease in mice. Finally, treatment with the PPARα agonist fenofibrate activated the integrated stress response and refilled amino acid substrates to rescue fasting glucose availability and overcome B2D phenotypes. These findings identify metabolic responses to FAD availability and nominate strategies for the management of organic acidemias and other rare IEMs.

Writing and erasing ceramides to alter liver disease

M6A RNA modifications mediate RNA processing and stability. Ceramides are lipid metabolites containing an amino acid-based backbone, which promote metabolic dysfunction. Wang et al. describe a novel m6A-dependent regulatory node that tunes ceramide-generating enzymes.

Metabolic dysfunction and obesity-related cancer: Results from the cross-sectional National Health and Nutrition Examination Survey

BACKGROUND

Metabolic syndrome (MetS), a group of risk factors that define metabolic dysfunction in adults, is strongly associated with obesity and is an emerging risk factor for cancer. However, the association of MetS and degree of metabolic dysfunction with obesity-related cancer is unknown.

METHODS

Using National Health and Nutrition Examination Survey data from 1999 to 2018, we identified 528 obesity-related cancer cases and 18,972 cancer-free participants. MetS was defined as the presence of or treatment for ≥3 of hyperglycemia, hypertension, hypertriglyceridemia, low HDL-cholesterol, and abdominal obesity. A metabolic syndrome score (MSS) was computed as the total number of abnormal MetS parameters to determine the severity of metabolic dysfunction. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using multivariable logistic regression models, adjusting for sociodemographic and lifestyle factors.

RESULTS

About 45.7% of obesity-related cancer cases were classified as having MetS compared with only 33.0% of cancer-free participants. Overall, MetS and MSS were not associated with obesity-related cancer. However, MSS was associated with higher obesity-related cancer risk among participants under 50 years of age (OR [95% CI] = 1.28 [1.08-1.52]). When evaluating MSS categorically, compared with healthy participants with no abnormal MetS parameters (MSS = 0), participants with one or two abnormal parameters had a statistically significant higher risk of obesity-related cancer (OR [95% CI] = 1.73 [1.06-2.83]).

CONCLUSIONS

Metabolic dysfunction is associated with a higher risk of obesity-related cancer, particularly in young adults under 50 years of age, and among participants with one or two abnormal metabolic parameters. A more accurate indicator of metabolic dysfunction, beyond metabolic syndrome, is needed to better assist in stratifying individuals for obesity-related cancer risk.

The Use of Ceramides to Predict Metabolic Response to Metformin in Women With PCOS

Context

Polycystic ovarian syndrome (PCOS) is a complex disorder in which metabolic abnormalities are associated with reproductive dysfunction. Women with PCOS have increased ceramide concentrations. Previous studies demonstrated that treating metabolic abnormalities of PCOS with metformin improved glucose effectiveness after 12 weeks.

Objective

We evaluated whether, in women with PCOS, lower baseline ceramide, diacylglycerol (DAG), and triacylglycerol (TAG) concentrations were associated with improved metabolic response to metformin.

Methods

Women (n = 29), aged 29 ± 5 years and diagnosed with PCOS by the NIH criteria underwent an intravenous glucose tolerance test (IVGTT) before and after 12-week treatment with metformin (1500 mg per day). Metabolic responders were defined by improved glucose effectiveness, specifically, the ability of glucose to stimulate uptake and suppress production, after metformin treatment.

Results

Twelve weeks of metformin resulted in weight loss (-1.7 ± 2.6 kg, P < 0.01) and a reduction in BMI (-0.6 ± 0.9 kg/m², P < 0.01) with no change in HbA1c. The concentrations of Cer(d18:1/22:0), Cer(d18:1/24:0), total ceramides, total Cer(d16:0), total Cer(d18:2), DAG, dihydrosphingomyelin (DHSM), and TAG decreased after metformin treatment (P < 0.05). Baseline total Cer(d16:0) concentration <204.1 pmol/mL was 82% sensitive (AUC 0.72, P = 0.03) and total DHSM concentration <32237 pmol/mL was 100% specific (AUC 0.73, P = 0.03) in predicting improved metabolic response to metformin, as measured by IVGTT.

Conclusion

Lower total Cer(16:0) and DHSM concentrations are associated with a beneficial metabolic response to metformin in women with PCOS. Based on the known association between higher ceramide levels and type 2 diabetes, the data suggest that metformin improves metabolic parameters in women with mild metabolic derangements.

The Lard Works in Mysterious Ways: Ceramides in Nutrition-Linked Chronic Disease

Diet influences onset, progression, and severity of several chronic diseases, including heart failure, diabetes, steatohepatitis, and a subset of cancers. The prevalence and clinical burden of these obesity-linked diseases has risen over the past two decades. These metabolic disorders are driven by ectopic lipid deposition in tissues not suited for fat storage, leading to lipotoxic disruption of cell function and survival. Sphingolipids such as ceramides are among the most deleterious and bioactive metabolites that accrue, as they participate in selective insulin resistance, dyslipidemia, oxidative stress and apoptosis. This review discusses our current understanding of biochemical pathways controlling ceramide synthesis, production and action; influences of diet on ceramide levels; application of circulating ceramides as clinical biomarkers of metabolic disease; and molecular mechanisms linking ceramides to altered metabolism and survival of cells. Development of nutritional or pharmacological strategies to lower ceramides could have therapeutic value in a wide range of prevalent diseases.

A dominant negative ADIPOQ mutation in a diabetic family with renal disease, hypoadiponectinemia, and hyperceramidemia

Adiponectin, encoded by ADIPOQ, is an insulin-sensitizing, anti-inflammatory, and renoprotective adipokine that activates receptors with intrinsic ceramidase activity. We identified a family harboring a 10-nucleotide deletion mutation in ADIPOQ that cosegregates with diabetes and end-stage renal disease. This mutation introduces a frameshift in exon 3, resulting in a premature termination codon that disrupts translation of adiponectin's globular domain. Subjects with the mutation had dramatically reduced circulating adiponectin and increased long-chain ceramides levels. Functional studies suggest that the mutated protein acts as a dominant negative through its interaction with non-mutated adiponectin, decreasing circulating adiponectin levels, and correlating with metabolic disease.

Metabolic dysfunction and obesity-related cancer: Beyond obesity and metabolic syndrome

OBJECTIVES

The metabolic dysfunction driven by obesity, including hyperglycemia and dyslipidemia, increases risk for developing at least 13 cancer types. The concept of "metabolic dysfunction" is often defined by meeting various combinations of criteria for metabolic syndrome. However, the lack of a unified definition of metabolic dysfunction makes it difficult to compare findings across studies. This review summarizes 129 studies that evaluated variable definitions of metabolic dysfunction in relation to obesity-related cancer risk and mortality after a cancer diagnosis. Strategies for metabolic dysfunction management are also discussed.

METHODS

A comprehensive search of relevant publications in MEDLINE (PubMed) and Google Scholar with review of references was conducted.

RESULTS

Metabolic dysfunction, defined as metabolic syndrome diagnosis or any number of metabolic syndrome criteria out of clinical range, inflammatory biomarkers, or markers of metabolic organ function, has been associated with risk for, and mortality from, colorectal, pancreatic, postmenopausal breast, and bladder cancers. Metabolic dysfunction associations with breast and colorectal cancer risk have been observed independently of BMI, with increased risk in individuals with metabolically unhealthy normal weight or overweight/obesity compared with metabolically healthy normal weight.

CONCLUSION

Metabolic dysfunction is a key risk factor for obesity-related cancer, regardless of obesity status. Nonetheless, a harmonized definition of metabolic dysfunction will further clarify the magnitude of the relationship across cancer types, enable better comparisons across studies, and further guide criteria for obesity-related cancer risk stratification.

Short-term exposure to a clinical dose of metformin increases skeletal muscle mitochondrial H2O2 emission and production in healthy, older adults: A randomized controlled trial

BACKGROUND AND AIMS

Metformin is the most commonly prescribed medication to treat diabetes. Emerging evidence suggests that metformin could have off target effects that might help promote healthy muscle aging, but these effects have not been thoroughly studied in glucose tolerant older individuals. The purpose of this study was to investigate the short-term effects of metformin consumption on skeletal muscle mitochondrial bioenergetics in healthy older adults.

METHODS

We obtained muscle biopsy samples from 16 healthy older adults previously naïve to metformin and treated with metformin (METF; 3F, 5M), or placebo (CON; 3F, 5M), for two weeks using a randomized and blinded study design. Samples were analyzed using high-resolution respirometry, immunofluorescence, and immunoblotting to assess muscle mitochondrial bioenergetics, satellite cell (SC) content, and associated protein markers.

RESULTS

We found that metformin treatment did not alter maximal mitochondrial respiration rates in muscle compared to CON. In contrast, mitochondrial H2O2 emission and production were elevated in muscle samples from METF versus CON (METF emission: 2.59 ± 0.72 SE Fold, P = 0.04; METF production: 2.29 ± 0.53 SE Fold, P = 0.02). Furthermore, the change in H2O2 emission was positively correlated with the change in type 1 myofiber SC content and this was biased in METF participants (Pooled: R2 = 0.5816, P = 0.0006; METF: R2 = 0.674, P = 0.0125).

CONCLUSIONS

These findings suggest that acute exposure to metformin does not impact mitochondrial respiration in aged, glucose-tolerant muscle, but rather, influences mitochondrial-free radical and SC dynamics.

CLINICAL TRIAL REGISTRATION

NCT03107884, clinicaltrials.gov.

Following Roux-en-Y gastric bypass surgery, serum ceramides demarcate patients that will fail to achieve normoglycemia and diabetes remission

BACKGROUND

Obesity is a prevalent health threat and risk factor for type 2 diabetes. In this study, we evaluate the relationship between ceramides, which inhibit insulin secretion and sensitivity, and markers of glucose homeostasis and diabetes remission or recursion in patients who have undergone a Roux-en-Y gastric bypass (RYGB).

METHODS

The Utah Obesity Study is a prospective cohort study, with targeted ceramide and dihydroceramide measurements performed on banked serum samples. The Utah Obesity Study consists of 1,156 participants in three groups: a RYGB surgery group, a non-surgery group denied insurance coverage, and severely obese population controls. Clinical examinations and ceramide assessments were performed at baseline and 2 and 12 years after RYGB surgery.

FINDINGS

Surgery patients (84% female, 42.2 ± 10.6 years of age at baseline) displayed lower levels of several serum dihydroceramides and ceramides at 2 and 12 years after RYGB. By contrast, neither the control group (77% female, 48.7± 6.4 years of age at baseline) nor the non-surgery group (95% female, 43.0± 11.4 years of age at baseline) experienced significant decreases in any species. Using a linear mixed effect model, we found that multiple dihydroceramides and ceramides positively associated with the glycemic control measures HOMA-IR and HbA1c. In surgery group participants with prevalent diabetes, ceramides inversely predict diabetes remission, independent of changes in weight.

CONCLUSIONS

Ceramide decreases may explain the insulin sensitization and diabetes resolution observed in most RYGB surgery patients.

FUNDING

Funded by the National Institutes of health (NIH), The Juvenile Diabetes Research Foundation, and the American Heart Association.

Very-Long-Chain Unsaturated Sphingolipids Mediate Oleate-Induced Rat β-Cell Proliferation

Fatty acid (FA) signaling contributes to β-cell mass expansion in response to nutrient excess, but the underlying mechanisms are poorly understood. In the presence of elevated glucose, FA metabolism is shifted toward synthesis of complex lipids, including sphingolipids. Here, we tested the hypothesis that sphingolipids are involved in the β-cell proliferative response to FA. Isolated rat islets were exposed to FA and 16.7 mmol/L glucose for 48-72 h, and the contribution of the de novo sphingolipid synthesis pathway was tested using the serine palmitoyltransferase inhibitor myriocin, the sphingosine kinase (SphK) inhibitor SKI II, or knockdown of SphK, fatty acid elongase 1 (ELOVL1) and acyl-CoA-binding protein (ACBP). Rats were infused with glucose and the lipid emulsion ClinOleic and received SKI II by gavage. β-Cell proliferation was assessed by immunochemistry or flow cytometry. Sphingolipids were analyzed by liquid chromatography-tandem mass spectrometry. Among the FAs tested, only oleate increased β-cell proliferation. Myriocin, SKI II, and SphK knockdown all decreased oleate-induced β-cell proliferation. Oleate exposure did not increase the total amount of sphingolipids but led to a specific rise in 24:1 species. Knockdown of ACBP or ELOVL1 inhibited oleate-induced β-cell proliferation. We conclude that unsaturated very-long-chain sphingolipids produced from the available C24:1 acyl-CoA pool mediate oleate-induced β-cell proliferation in rats.

Cordyceps inhibits ceramide biosynthesis and improves insulin resistance and hepatic steatosis

Ectopic ceramide accumulation in insulin-responsive tissues contributes to the development of obesity and impairs insulin sensitivity. Moreover, pharmacological inhibition of serine palmitoyl transferase (SPT), the first enzyme essential for ceramide biosynthesis using myriocin in rodents reduces body weight and improves insulin sensitivity and associated metabolic indices. Myriocin was originally extracted from fruiting bodies of the fungus Isaria sinclairii and has been found abundant in a number of closely related fungal species such as the Cordyceps. Myriocin is not approved for human use but extracts from Cordyceps are routinely consumed as part of traditional Chinese medication for the treatment of numerous diseases including diabetes. Herein, we screened commercially available extracts of Cordyceps currently being consumed by humans, to identify Cordyceps containing myriocin and test the efficacy of Cordyceps extract containing myriocin in obese mice to improve energy and glucose homeostasis. We demonstrate that commercially available Cordyceps contain variable amounts of myriocin and treatment of mice with a human equivalent dose of Cordyceps extract containing myriocin, reduces ceramide accrual, increases energy expenditure, prevents diet-induced obesity, improves glucose homeostasis and resolves hepatic steatosis. Mechanistically, these beneficial effects were due to increased adipose tissue browning/beiging, improved brown adipose tissue function and hepatic insulin sensitivity as well as alterations in the abundance of gut microbes such as Clostridium and Bilophila. Collectively, our data provide proof-of-principle that myriocin containing Cordyceps extract inhibit ceramide biosynthesis and attenuate metabolic impairments associated with obesity. Moreover, these studies identify commercially available Cordyceps as a readily available supplement to treat obesity and associated metabolic diseases.

Ceramides and Acute Kidney Injury

Altered lipid metabolism is a characteristic feature and potential driving factor of acute kidney injury (AKI). Of the lipids that accumulate in injured renal tissues, ceramides are potent regulators of metabolism and cell fate. Up-regulation of ceramide synthesis is a common feature shared across several AKI etiologies in vitro and in vivo. Furthermore, ceramide accumulation is an early event in the natural history of AKI that precedes cell death and organ dysfunction. Emerging evidence suggests that inhibition of ceramide accumulation may improve renal outcomes in several models of AKI. This review examines the landscape of ceramide metabolism and regulation in the healthy and injured kidney. Furthermore, we discuss the body of literature regarding ceramides as therapeutic targets for AKI and consider potential mechanisms by which ceramides drive kidney pathogenesis.

Ceramide signaling in the gut

Sphingolipids are essential lipid components in the intestinal epithelial cells (IEC) along the intestinal tract. They play crucial roles in maintaining barrier integrity, regulating nutrient absorption, and acting as signaling molecules to regulate regeneration and differentiation of intestinal mucosa (Kurek et al., 2012). Ceramide is the central sphingolipid species and the precursor of all complex sphingolipids and other downstream simple intermediates like sphingosine (SPH), ceramide-1-phosphate (C-1-P), and sphingosine-1-phosphate (S-1-P). It is also a critical signaling molecule regulating numerous physiologic and pathologic processes. This review will summarize the metabolism of ceramides in the gut and their regulation in inflammatory bowel diseases and colorectal cancer.

Cholesterol - the devil you know; ceramide - the devil you don't

Ectopic lipids play a key role in numerous pathologies, including heart disease, stroke, and diabetes. Of all the lipids studied, perhaps the most well understood is cholesterol, a widely used clinical biomarker of cardiovascular disease and a target of pharmacological interventions (e.g., statins). Thousands of studies have interrogated the regulation and action of this disease-causing sterol. As a growing body of literature indicates, a new class of lipid-based therapies may be on the horizon. Ceramides are cholesterol-independent biomarkers of heart disease and diabetes in humans. Studies in rodents suggest that they are causative agents of disease, as lowering ceramides through genetic or pharmacological interventions prevents cardiovascular disease and diabetes. Herein, we discuss the evidence supporting the potential of therapeutics targeting ceramides to treat cardiometabolic disease, contrasting it with the robust datasets that drove the creation of cholesterol-lowering pharmaceuticals.

Ceramides and other sphingolipids as drivers of cardiovascular disease

Increases in calorie consumption and sedentary lifestyles are fuelling a global pandemic of cardiometabolic diseases, including coronary artery disease, diabetes mellitus, cardiomyopathy and heart failure. These lifestyle factors, when combined with genetic predispositions, increase the levels of circulating lipids, which can accumulate in non-adipose tissues, including blood vessel walls and the heart. The metabolism of these lipids produces bioactive intermediates that disrupt cellular function and survival. A compelling body of evidence suggests that sphingolipids, such as ceramides, account for much of the tissue damage in these cardiometabolic diseases. In humans, serum ceramide levels are proving to be accurate biomarkers of adverse cardiovascular disease outcomes. In mice and rats, pharmacological inhibition or depletion of enzymes driving de novo ceramide synthesis prevents the development of diabetes, atherosclerosis, hypertension and heart failure. In cultured cells and isolated tissues, ceramides perturb mitochondrial function, block fuel usage, disrupt vasodilatation and promote apoptosis. In this Review, we discuss the body of literature suggesting that ceramides are drivers - and not merely passengers - on the road to cardiovascular disease. Moreover, we explore the feasibility of therapeutic strategies to lower ceramide levels to improve cardiovascular health.

Characterizing a Common CERS2 Polymorphism in a Mouse Model of Metabolic Disease and in Subjects from the Utah CAD Study

CONTEXT

Genome-wide association studies have identified associations between a common single nucleotide polymorphism (SNP; rs267738) in CERS2, a gene that encodes a (dihydro)ceramide synthase that is involved in the biosynthesis of very-long-chain sphingolipids (eg, C20-C26) and indices of metabolic dysfunction (eg, impaired glucose homeostasis). However, the biological consequences of this mutation on enzyme activity and its causal roles in metabolic disease are unresolved.

OBJECTIVE

The studies described herein aimed to characterize the effects of rs267738 on CERS2 enzyme activity, sphingolipid profiles, and metabolic outcomes.

DESIGN

We performed in-depth lipidomic and metabolic characterization of a novel CRISPR knock-in mouse modeling the rs267738 variant. In parallel, we conducted mass spectrometry-based, targeted lipidomics on 567 serum samples collected through the Utah Coronary Artery Disease study, which included 185 patients harboring 1 (n = 163) or both (n = 22) rs267738 alleles.

RESULTS

In-silico analysis of the amino acid substitution within CERS2 caused by the rs267738 mutation suggested that rs267738 is deleterious for enzyme function. Homozygous knock-in mice had reduced liver CERS2 activity and enhanced diet-induced glucose intolerance and hepatic steatosis. However, human serum sphingolipids and a ceramide-based cardiac event risk test 1 score of cardiovascular disease were not significantly affected by rs267738 allele count.

CONCLUSIONS

The rs267738 SNP leads to a partial loss-of-function of CERS2, which worsened metabolic parameters in knock-in mice. However, rs267738 was insufficient to effect changes in serum sphingolipid profiles in subjects from the Utah Coronary Artery Disease Study.

Gutting out Myc to decrease ceramides

MYC is a transcription factor controlling growth and nutrient metabolism. Luo et al. now link intestinal expression of MYC to impairments in glucose, lipid and body-weight homeostasis by uncovering novel roles of MYC in regulating the glucagon-like peptide GLP1 and the ceramide-biosynthesis regulator CERS4. Myc deletion in the intestinal epithelium prevents or reverses diet-induced obesity and hepatic steatosis in mice. Critically, people with obesity display elevated MYC and CERS4 expression in the ileum, thus further supporting the clinical relevance of these findings.

Gain of 'FAOnction', Loss of Fibrosis

Recent research by Miguel et al. and Dhillon et al. reveals associations between impaired lipid metabolism and kidney fibrosis. Kidney tubule fatty acid oxidation (FAO) gain-of-function in mouse models of kidney disease stimulated cellular respiration, mitochondrial dynamics, and tubular epithelial cell (TEC) differentiation, while upregulation of FAO in kidney tubules provided protection from kidney fibrosis and functional decline.

Ceramide Biomarkers Predictive of Cardiovascular Disease Risk Increase in Healthy Older Adults After Bed Rest

Acute bed rest places older adults at risk for health complications by disrupting homeostasis in many organ systems, including the cardiovascular system. Circulating ceramides are emerging biomarkers predictive of cardiovascular and metabolic health and have recently been shown to be sensitive indices of cardiovascular (CV) risk. Therefore, the purpose of this study was to characterize the time course of changes in circulating ceramides in healthy younger and older adults after 5 days of bed rest and to determine whether short-term bed rest alters CV-related circulating ceramides. We hypothesized that circulating ceramides predictive of poor cardiometabolic outcomes would increase following 5 days of bed rest. Thirty-five healthy younger and older men and women (young: n = 13, old: n = 22) underwent 5 days of controlled bed rest. Fasting blood samples collected daily during the course of bed rest were used to measure circulating ceramides, lipoproteins, adiponectin, and fibroblast growth factor 21 (FGF21) levels. The primary findings were that circulating ceramides decreased while ceramide ratios and the cardiac event risk test 1 score were increased primarily in older adults, and these findings were independent of changes in circulating lipoprotein levels. Additionally, we found that changes in circulating adiponectin, FGF21 and the 6-minute walk test (6MW) inversely correlated with CV-related circulating ceramides after bed rest. The results of this study highlight the sensitivity of circulating ceramides to detect potential CV dysfunction that may occur with acute physical disuse in aging.

Ceramides are necessary and sufficient for diet-induced impairment of thermogenic adipocytes

Objective

Aging and weight gain lead to a decline in brown and beige adipocyte functionality that exacerbates obesity and insulin resistance. We sought to determine whether sphingolipids, such as ceramides, a class of lipid metabolites that accumulate in aging and overnutrition, are sufficient or necessary for the metabolic impairment of these thermogenic adipocytes.

Methods

We generated new mouse models allowing for the conditional ablation of genes required for ceramide synthesis (i.e., serine palmitoyltransferase subunit 2, Sptlc2) or degradation (i.e., acid ceramidase 1, Asah1) from mature, thermogenic adipocytes (i.e., from cells expressing uncoupling protein-1). Mice underwent a comprehensive suite of phenotyping protocols to assess energy expenditure and glucose and lipid homeostasis. Complementary studies were conducted in primary brown adipocytes to dissect the mechanisms controlling ceramide synthesis or action.

Results

Depletion of Sptlc2 increased energy expenditure, improved glucose homeostasis, and prevented diet-induced obesity. Conversely, depletion of Asah1 led to ceramide accumulation, diminution of energy expenditure, and exacerbation of insulin resistance and obesity. Mechanistically, ceramides slowed lipolysis, inhibited glucose uptake, and decreased mitochondrial respiration. Moreover, β-adrenergic receptor agonists, which activate thermogenesis in brown adipocytes, decreased transcription of enzymes required for ceramide synthesis.

Conclusions

These studies support our hypothesis that ceramides are necessary and sufficient for the impairment in thermogenic adipocyte function that accompanies obesity. Moreover, they suggest that implementation of therapeutic strategies to block ceramide synthesis in thermogenic adipocytes may serve as a means of improving adipose health and combating obesity and cardiometabolic disease.

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β-Adrenergic agonists lower ceramide levels in brown adipocytes by decreasing expression of Sptlc2 and CerS6.

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Selective inhibition of ceramide synthesis in UCP1⁺ cells confers resistance to obesity and increases energy expenditure.

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Selectively inducing ceramide accumulation in UCP1⁺ cells impairs thermogenesis to exacerbate obesity and insulin resistance.

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Brown adipocyte ceramides alter mitochondrial ultrastructure and activity and influences rates of fatty acid uptake.

Ceramides in Metabolism: Key Lipotoxic Players

The global prevalence of metabolic diseases such as type 2 diabetes mellitus, steatohepatitis, myocardial infarction, and stroke has increased dramatically over the past two decades. These obesity-fueled disorders result, in part, from the aberrant accumulation of harmful lipid metabolites in tissues not suited for lipid storage (e.g., the liver, vasculature, heart, and pancreatic beta-cells). Among the numerous lipid subtypes that accumulate, sphingolipids such as ceramides are particularly impactful, as they elicit the selective insulin resistance, dyslipidemia, and ultimately cell death that underlie nearly all metabolic disorders. This review summarizes recent findings on the regulatory pathways controlling ceramide production, the molecular mechanisms linking the lipids to these discrete pathogenic events, and exciting attempts to develop therapeutics to reduce ceramide levels to combat metabolic disease.

Adipocyte Ceramides-The Nexus of Inflammation and Metabolic Disease

Adipose depots are heterogeneous tissues that store and sense fuel levels. Through the secretion of lipids, cytokines, and protein hormones (adipokines), they communicate with other organ systems, informing them of the organism's nutritional status. The adipose tissues include diverse types of adipocytes (white, beige, and brown) distinguished by the number/size of lipid droplets, mitochondrial density, and thermogenic capacity. Moreover, they include a spectrum of immune cells that modulate metabolic activity and tissue remodeling. The unique characteristics and interplay of these cells control the production of ceramides, a class of nutrient signals derived from fat and protein metabolism that modulate adipocyte function to regulate glucose and lipid metabolism. The excessive accumulation of ceramides contributes to the adipose tissue inflammation and dysfunction that underlies cardiometabolic disease. Herein we review findings on this important class of lipid species and discuss their role at the convergence point that links overnutrition/inflammation to key features of the metabolic syndrome.

Mitochondrial pyruvate carrier is required for optimal brown fat thermogenesis

Brown adipose tissue (BAT) is composed of thermogenic cells that convert chemical energy into heat to maintain a constant body temperature and counteract metabolic disease. The metabolic adaptations required for thermogenesis are not fully understood. Here, we explore how steady state levels of metabolic intermediates are altered in brown adipose tissue in response to cold exposure. Transcriptome and metabolome analysis revealed changes in pathways involved in amino acid, glucose, and TCA cycle metabolism. Using isotopic labeling experiments, we found that activated brown adipocytes increased labeling of pyruvate and TCA cycle intermediates from U¹³C-glucose. Although glucose oxidation has been implicated as being essential for thermogenesis, its requirement for efficient thermogenesis has not been directly tested. We show that mitochondrial pyruvate uptake is essential for optimal thermogenesis, as conditional deletion of Mpc1 in brown adipocytes leads to impaired cold adaptation. Isotopic labeling experiments using U¹³C-glucose showed that loss of MPC1 led to impaired labeling of TCA cycle intermediates. Loss of MPC1 in BAT increased 3-hydroxybutyrate levels in blood and BAT in response to the cold, suggesting that ketogenesis provides an alternative fuel source to compensate. Collectively, these studies highlight that complete glucose oxidation is essential for optimal brown fat thermogenesis.

Antioxidant Effects of N-Acetylcysteine Prevent Programmed Metabolic Disease in Mice

An adverse maternal in utero and lactation environment can program offspring for increased risk for metabolic disease. The aim of this study was to determine whether N-acetylcysteine (NAC), an anti-inflammatory antioxidant, attenuates programmed susceptibility to obesity and insulin resistance in offspring of mothers on a high-fat diet (HFD) during pregnancy. CD1 female mice were acutely fed a standard breeding chow or HFD. NAC was added to the drinking water (1 g/kg) of the treatment cohorts from embryonic day 0.5 until the end of lactation. NAC treatment normalized HFD-induced maternal weight gain and oxidative stress, improved the maternal lipidome, and prevented maternal leptin resistance. These favorable changes in the in utero environment normalized postnatal growth, decreased white adipose tissue (WAT) and hepatic fat, improved glucose and insulin tolerance and antioxidant capacity, reduced leptin and insulin, and increased adiponectin in HFD offspring. The lifelong metabolic improvements in the offspring were accompanied by reductions in proinflammatory gene expression in liver and WAT and increased thermogenic gene expression in brown adipose tissue. These results, for the first time, provide a mechanistic rationale for how NAC can prevent the onset of metabolic disease in the offspring of mothers who consume a typical Western HFD.

Too Much of a Good Thing? An Evolutionary Theory to Explain the Role of Ceramides in NAFLD

Non-alcoholic fatty liver disease (NAFLD), which ranges from the relatively benign and reversible fatty liver (NAFL) to the more advanced and deadly steatohepatitis (NASH), affects a remarkably high percentage of adults in the population. Depending upon severity, NAFLD can increase one's risk for diabetes, cardiovascular disease, and hepatocellular carcinoma. Though the dominant histological feature of all forms of the disease is the accumulation of liver triglycerides, these molecules are likely not pathogenic, but rather serve to protect the liver from the damaging consequences of overnutrition. We propose herein that the less abundant ceramides, through evolutionarily-conserved actions intended to help organisms adapt to nutrient excess, drive the cellular events that define NAFL/NASH. In early stages of the disease process, they promote lipid uptake and storage, whilst inhibiting utilization of glucose. In later stages, they stimulate hepatocyte apoptosis and fibrosis. In rodents, blocking ceramide synthesis ameliorates all stages of NAFLD. In humans, serum and liver ceramides correlate with the severity of NAFLD and its comorbidities diabetes and heart disease. These studies identify key roles for ceramides in these hepatic manifestations of the metabolic syndrome.

An Interpretive Description of Women's Experience in Coordinated, Multidisciplinary Treatment for an Eating Disorder

Coordinated, multidisciplinary treatment for women with eating disorders is consistently recommended as maximally effective, but few studies have considered the patient experience. This qualitative study examined the experiences of women receiving such care in an outpatient setting. Using an interpretive description methodology, we conducted 12 in-depth interviews with participants who were diagnosed with an eating disorder and were receiving team-based treatment. Patients uniformly advocated for the coordinated, multidisciplinary treatment approach. Analysis of participants’ experiences yielded four categories: relying on the lifeline of communication, supporting autonomy, drawing on individual strengths, and valuing synergy. These findings build on previous research emphasizing the importance of autonomy support and connectedness in the recovery process from an eating disorder. Findings highlight the importance of nurses to support a multidisciplinary care approach to working with this patient population; these women’s voices also support a treatment approach that, despite being widely recommended, is vastly understudied and underutilized.

DES1: A Key Driver of Lipotoxicity in Metabolic Disease

Ceramides have emerged as important regulators of tissue metabolism that play essential roles in cardiometabolic disease. They are potent biomarkers of diabetes and heart disease and are now being measured clinically as predictors of major adverse cardiac events. Moreover, studies in rodents reveal that inhibitors of ceramide synthesis prevent or reverse the pathogenic features of type 2 diabetes, nonalcoholic fatty liver disease, atherosclerosis, and cardiomyopathy. Herein the authors discuss inhibition of dihydroceramide desaturase-1, the final enzyme in the ceramide biosynthesis pathway, as a potential therapeutic approach to lower ceramides and combat cardiometabolic disease.

Machine learning reveals serum sphingolipids as cholesterol-independent biomarkers of coronary artery disease

BACKGROUNDCeramides are sphingolipids that play causative roles in diabetes and heart disease, with their serum levels measured clinically as biomarkers of cardiovascular disease (CVD).METHODSWe performed targeted lipidomics on serum samples from individuals with familial coronary artery disease (CAD) (n = 462) and population-based controls (n = 212) to explore the relationship between serum sphingolipids and CAD, using unbiased machine learning to identify sphingolipid species positively associated with CAD.RESULTSNearly every sphingolipid measured (n = 30 of 32) was significantly elevated in subjects with CAD compared with measurements in population controls. We generated a novel sphingolipid-inclusive CAD risk score, termed SIC, that demarcates patients with CAD independently and more effectively than conventional clinical CVD biomarkers including serum LDL cholesterol and triglycerides. This new metric comprises several minor lipids that likely serve as measures of flux through the ceramide biosynthesis pathway rather than the abundant deleterious ceramide species that are included in other ceramide-based scores.CONCLUSIONThis study validates serum ceramides as candidate biomarkers of CVD and suggests that comprehensive sphingolipid panels should be considered as measures of CVD.FUNDINGThe NIH (DK112826, DK108833, DK115824, DK116888, and DK116450); the Juvenile Diabetes Research Foundation (JDRF 3-SRA-2019-768-A-B); the American Diabetes Association; the American Heart Association; the Margolis Foundation; the National Cancer Institute, NIH (5R00CA218694-03); and the Huntsman Cancer Institute Cancer Center Support Grant (P30CA040214).

Pharmacological inhibition of TLR4 ameliorates muscle and liver ceramide content after disuse in previously physically active mice

Toll-like receptor 4 (TLR4) is a proposed mediator of ceramide accumulation, muscle atrophy, and insulin resistance in skeletal muscle. It is currently unknown whether pharmacological inhibition of TLR4, using the TLR4-specific inhibitor TAK-242 during muscle disuse, is able to prevent changes in intracellular ceramide species and consequently preserve muscle size and insulin sensitivity in physically active mice. To address this question, we subjected running wheel-conditioned C57BL/6 male mice (13 wk old; ∼10/group) to 7 days of hindlimb suspension (HS), 7 days of continued wheel running (WR), or daily injections of TAK-242 during HS (HS + TAK242) for 7 days. We measured hindlimb muscle morphology, intramuscular and liver ceramide content, HOMA-IR, mRNA proxies of ceramide turnover and lipid trafficking, and muscle fatty acid and glycerolipid content. As a result, soleus and liver ceramide abundance was greater (P < 0.05) in HS vs. WR but was reduced with TLR4 inhibition (HS + TAK-242 vs. HS). Muscle mass declined (P < 0.01) with HS (vs. WR), but TLR4 inhibition did not prevent this loss (soleus: P = 0.08; HS vs. HS + TAK-242). HOMA-IR was impaired (P < 0.01) in HS versus WR mice, but only fasting blood glucose was reduced with TLR4 inhibition (HS + TAK-242 vs HS, P < 0.05). Robust decreases in muscle Spt2 and Cd36 mRNA and muscle lipidomic trafficking may partially explain reductions in ceramides with TLR4 inhibition. In conclusion, pharmacological TLR4 inhibition in wheel-conditioned mice prevented ceramide accumulation during the early phase of hindlimb suspension (7 days) but had little effect on muscle size and insulin sensitivity.

Reign in the membrane: How common lipids govern mitochondrial function

The lipids that make up biological membranes tend to be the forgotten molecules of cell biology. The paucity of data on these important entities likely reflects the difficulties of studying and understanding their biological roles, rather than revealing a lack of importance. Indeed, the lipid composition of biological membranes has a profound impact on a diverse array of cellular processes. The focus of this review is on the effects of different lipid classes on the function of mitochondria, particularly bioenergetics, in health and disease.

Influence of Exercise Training on Skeletal Muscle Insulin Resistance in Aging: Spotlight on Muscle Ceramides

Intramuscular lipid accumulation has been associated with insulin resistance (IR), aging, diabetes, dyslipidemia, and obesity. A substantial body of evidence has implicated ceramides, a sphingolipid intermediate, as potent antagonists of insulin action that drive insulin resistance. Indeed, genetic mouse studies that lower ceramides are potently insulin sensitizing. Surprisingly less is known about how physical activity (skeletal muscle contraction) regulates ceramides, especially in light that muscle contraction regulates insulin sensitivity. The purpose of this review is to critically evaluate studies (rodent and human) concerning the relationship between skeletal muscle ceramides and IR in response to increased physical activity. Our review of the literature indicates that chronic exercise reduces ceramide levels in individuals with obesity, diabetes, or hyperlipidemia. However, metabolically healthy individuals engaged in increased physical activity can improve insulin sensitivity independent of changes in skeletal muscle ceramide content. Herein we discuss these studies and provide context regarding the technical limitations (e.g., difficulty assessing the myriad ceramide species, the challenge of obtaining information on subcellular compartmentalization, and the paucity of flux measurements) and a lack of mechanistic studies that prevent a more sophisticated assessment of the ceramide pathway during increased contractile activity that lead to divergences in skeletal muscle insulin sensitivity.

Rotten to the Cortex: Ceramide-Mediated Lipotoxicity in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a prevalent and progressive comorbidity of diabetes mellitus that increases one's risk of developing renal failure. Progress toward development of better DKD therapeutics is limited by an incomplete understanding of forces driving and connecting the various features of DKD, which include renal steatosis, fibrosis, and microvascular dysfunction. Herein we review the literature supporting roles for bioactive ceramides as inducers of local and systemic DKD pathology. In rodent models of DKD, renal ceramides are elevated, and genetic and pharmacological ceramide-lowering interventions improve kidney function and ameliorate DKD histopathology. In humans, circulating sphingolipid profiles distinguish human DKD patients from diabetic controls. These studies highlight the potential for ceramide to serve as a central and therapeutically tractable lipid mediator of DKD.

Autophagy Ablation in Adipocytes Induces Insulin Resistance and Reveals Roles for Lipid Peroxide and Nrf2 Signaling in Adipose-Liver Crosstalk

Autophagy is a homeostatic cellular process involved in the degradation of long-lived or damaged cellular components. The role of autophagy in adipogenesis is well recognized, but its role in mature adipocyte function is largely unknown. We show that the autophagy proteins Atg3 and Atg16L1 are required for proper mitochondrial function in mature adipocytes. In contrast to previous studies, we found that post-developmental ablation of autophagy causes peripheral insulin resistance independently of diet or adiposity. Finally, lack of adipocyte autophagy reveals cross talk between fat and liver, mediated by lipid peroxide-induced Nrf2 signaling. Our data reveal a role for autophagy in preventing lipid peroxide formation and its transfer in insulin-sensitive peripheral tissues.