Serum sphingolipids and inflammatory mediators in adolescents at risk for metabolic syndrome

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.

Blood-Derived Lipid and Metabolite Biomarkers in Cardiovascular Research from Clinical Studies: A Recent Update

The primary prevention, early detection, and treatment of cardiovascular disease (CVD) have been long-standing scientific research goals worldwide. In the past decades, traditional blood lipid profiles have been routinely used in clinical practice to estimate the risk of CVDs such as atherosclerotic cardiovascular disease (ASCVD) and as treatment targets for the primary prevention of adverse cardiac events. These blood lipid panel tests often fail to fully predict all CVD risks and thus need to be improved. A comprehensive analysis of molecular species of lipids and metabolites (defined as lipidomics and metabolomics, respectively) can provide molecular insights into the pathophysiology of the disease and could serve as diagnostic and prognostic indicators of disease. Mass spectrometry (MS) and nuclear magnetic resonance (NMR)-based lipidomics and metabolomics analysis have been increasingly used to study the metabolic changes that occur during CVD pathogenesis. In this review, we provide an overview of various MS-based platforms and approaches that are commonly used in lipidomics and metabolomics workflows. This review summarizes the lipids and metabolites in human plasma/serum that have recently (from 2018 to December 2022) been identified as promising CVD biomarkers. In addition, this review describes the potential pathophysiological mechanisms associated with candidate CVD biomarkers. Future studies focused on these potential biomarkers and pathways will provide mechanistic clues of CVD pathogenesis and thus help with the risk assessment, diagnosis, and treatment of CVD.

Sphingolipid Levels and Signaling via Resveratrol and Antioxidant Actions in Cardiometabolic Risk and Disease

Resveratrol (RSV) is a phenolic compound with strong antioxidant activity, which is generally associated with the beneficial effects of wine on human health. All resveratrol-mediated benefits exerted on different systems and pathophysiological conditions are possible through resveratrol's interactions with different biological targets, along with its involvement in several key cellular pathways affecting cardiometabolic (CM) health. With regard to its role in oxidative stress, RSV exerts its antioxidant activity not only as a free radical scavenger but also by increasing the activity of antioxidant enzymes and regulating redox genes, nitric oxide bioavailability and mitochondrial function. Moreover, several studies have demonstrated that some RSV effects are mediated by changes in sphingolipids, a class of biolipids involved in a number of cellular functions (e.g., apoptosis, cell proliferation, oxidative stress and inflammation) that have attracted interest as emerging critical determinants of CM risk and disease. Accordingly, this review aimed to discuss the available data regarding the effects of RSV on sphingolipid metabolism and signaling in CM risk and disease, focusing on oxidative stress/inflammatory-related aspects, and the clinical implications of this relationship.

Physical activity as a promising alternative for young people with juvenile idiopathic arthritis: Towards an evidence-based prescription

Juvenile idiopathic arthritis (JIA) is the most common rheumatic disease in young people. Although biologics now enable most children and adolescents with JIA to enjoy clinical remission, patients present lower physical activity and spend more time in sedentary behavior than their healthy counterparts. This impairment probably results from a physical deconditioning spiral initiated by joint pain, sustained by apprehension on the part of both the child and the child's parents, and entrenched by lowered physical capacities. This in turn may exacerbate disease activity and lead to unfavorable health outcomes including increased risks of metabolic and mental comorbidities. Over the past few decades, there has been growing interest in the health benefits of increased overall physical activity as well as exercise interventions in young people with JIA. However, we are still far from evidence-based physical activity and / or exercise prescription for this population. In this review, we give an overview of the available data supporting physical activity and / or exercise as a behavioral, non-pharmacological alternative to attenuate inflammation while also improving metabolism, disease symptoms, poor sleep, synchronization of circadian rhythms, mental health, and quality of life in JIA. Finally, we discuss clinical implications, identify gaps in knowledge, and outline a future research agenda.

The Impact of Phytochemicals in Obesity-Related Metabolic Diseases: Focus on Ceramide Metabolism

The prevalence of obesity and related metabolic diseases has increased dramatically worldwide. As obesity progresses, various lipid species accumulate in ectopic tissues. Amongst them, ceramides-a deleterious sphingolipid species-accumulate and cause lipotoxicity and metabolic disturbances. Dysregulated ceramide metabolism appears to be a key feature in the pathogenesis of obesity-related metabolic diseases. Notably, dietary modification might have an impact on modulating ceramide metabolism. Phytochemicals are plant-derived compounds with various physiological properties, which have been shown to protect against obesity-related metabolic diseases. In this review, we aim to examine the impact of a myriad of phytochemicals and their dietary sources in altering ceramide deposition and ceramide-related metabolism from in vitro, in vivo, and human clinical/epidemiological studies. This review discusses how numerous phytochemicals are able to alleviate ceramide-induced metabolic defects and reduce the risk of obesity-related metabolic diseases via diverse mechanisms.

The mitophagy receptor BNIP3 is critical for the regulation of metabolic homeostasis and mitochondrial function in the nucleus pulposus cells of the intervertebral disc

The contribution of mitochondria to the metabolic function of hypoxic NP cells has been overlooked. We have shown that NP cells contain networked mitochondria and that mitochondrial translocation of BNIP3 mediates hypoxia-induced mitophagy. However, whether BNIP3 also plays a role in governing mitochondrial function and metabolism in hypoxic NP cells is not known. BNIP3 knockdown altered mitochondrial morphology, and number, and increased mitophagy. Interestingly, BNIP3 deficiency in NP cells reduced glycolytic capacity reflected by lower production of lactate/H⁺ and lower ATP production rate. Widely targeted metabolic profiling and flux analysis using 1-2-¹³C-glucose showed that the BNIP3 loss resulted in redirection of glycolytic flux into pentose phosphate and hexosamine biosynthesis as well as pyruvate resulting in increased TCA flux. An overall reduction in one-carbon metabolism was noted suggesting reduced biosynthesis. U¹³C-glutamine flux analysis showed preservation of glutamine utilization to maintain TCA intermediates. The transcriptomic analysis of the BNIP3-deficient cells showed dysregulation of cellular functions including membrane and cytoskeletal integrity, ECM-growth factor signaling, and protein quality control with an overall increase in themes related to angiogenesis and innate immune response. Importantly, we observed strong thematic similarities with the transcriptome of a subset of human degenerative samples. Last, we noted increased autophagic flux, decreased disc height index and aberrant COL10A1/collagen X expression, signs of early disc degeneration in young adult bnip3 knockout mice. These results suggested that in addition to mitophagy regulation, BNIP3 plays a role in maintaining mitochondrial function and metabolism, and dysregulation of mitochondrial homeostasis could promote disc degeneration.Abbreviations: ECAR extracellular acidification rate; HIF hypoxia inducible factor; MFA metabolic flux analysis; NP nucleus pulposus; OCR oxygen consumption rate; ShBnip3 short-hairpin Bnip3.

The Role of Sphingolipids in the Pathogenesis of Psoriasis

Psoriasis is a complex, chronic, immunologically mediated disease which involves skin and joints. Psoriasis is commonly connected with numerous other diseases such as liver diseases, metabolic syndrome, impaired glucose tolerance, diabetes mellitus, atherosclerosis, hypertension, and ischemic heart disease. Interestingly, comorbidities of psoriasis are an attention-grabbing issue. Additionally, it can cause impairment of quality of life and may be associated with depressive disorders. Altered levels of ceramides in psoriatic skin may lead to anti-apoptotic and pro-proliferative states, consequently leading to an over-proliferation of keratinocytes and the development of skin lesions. The pathophysiology of psoriasis and its comorbidities is not fully understood yet. Sphingolipids (including ceramides) and their disturbed metabolism may be the link between psoriasis and its comorbidities. Overall, the goal of this review was to discuss the role of sphingolipid disturbances in psoriasis and its comorbidities. We searched the PubMed database for relevant articles published before the beginning of May 2022. The systematic review included 65 eligible original articles.

To Be or Not to Be: The Divergent Action and Metabolism of Sphingosine-1 Phosphate in Pancreatic Beta-Cells in Response to Cytokines and Fatty Acids

Sphingosine-1 phosphate (S1P) is a bioactive sphingolipid with multiple functions conveyed by the activation of cell surface receptors and/or intracellular mediators. A growing body of evidence indicates its important role in pancreatic insulin-secreting beta-cells that are necessary for maintenance of glucose homeostasis. The dysfunction and/or death of beta-cells lead to diabetes development. Diabetes is a serious public health burden with incidence growing rapidly in recent decades. The two major types of diabetes are the autoimmune-mediated type 1 diabetes (T1DM) and the metabolic stress-related type 2 diabetes (T2DM). Despite many differences in the development, both types of diabetes are characterized by chronic hyperglycemia and inflammation. The inflammatory component of diabetes remains under-characterized. Recent years have brought new insights into the possible mechanism involved in the increased inflammatory response, suggesting that environmental factors such as a westernized diet may participate in this process. Dietary lipids, particularly palmitate, are substrates for the biosynthesis of bioactive sphingolipids. Disturbed serum sphingolipid profiles were observed in both T1DM and T2DM patients. Many polymorphisms were identified in genes encoding enzymes of the sphingolipid pathway, including sphingosine kinase 2 (SK2), the S1P generating enzyme which is highly expressed in beta-cells. Proinflammatory cytokines and free fatty acids have been shown to modulate the expression and activity of S1P-generating and S1P-catabolizing enzymes. In this review, the similarities and differences in the action of extracellular and intracellular S1P in beta-cells exposed to cytokines or free fatty acids will be identified and the outlook for future research will be discussed.

Serum and aqueous humor adiponectin levels correlate with diabetic retinopathy development and progression

PURPOSE

To compare adiponectin (APN) levels in the serum and aqueous humor (AH) and evaluate their association with the development/progression of diabetic retinopathy (DR).

METHODS

Diabetic patients with (group 3; n = 59) and without (group 2; n = 39) DR and age- and sex-matched normal subjects (group 1; n = 35) were compared. Duration of diabetes, body mass index, serum HbA1c, vascular endothelial growth factor (VEGF), APN, pentraxin 3 (PTX3), platelet derived growth factor (PDGF), intercellular adhesion molecule-1 (ICAM-1), and APN were measured and analyzed.

RESULTS

One hundred and thirty-three participants were included. Compared to patients without diabetes, diabetic patients with DR had significantly elevated average serum APN levels (5.99±3.89 μg/ml versus 3.51±1.44 μg/ml, P = 0.002) and average AH APN levels (10.94±11.74 ng/ml versus 3.65±3.33 ng/ml, P<0.001). Serum APN was significantly correlated with AH APN (R = 0.512, P<0.001) and AH VEGF (R = 0.202, P = 0.020). The log serum APN was significantly correlated with intraocular cytokines, including log APN, log VEGF, log ICAM, log leptin, log PTX3, log PDGF, angiopoietin, C-reactive protein, and interleukins (IL)-5 and IL-10 (P<0.001, P = 0.020, P<0.001, P<0.001, P = 0.001, P<0.001, P = 0.008, P = 0.009, P<0.001, and P = 0.046, respectively). Log serum VEGF showed a significant correlation only with log AH VEGF (P = 0.001). Multivariate logistic analysis was performed to evaluate the association of DR progression and cytokine concentrations; log Serum APN and log AH APN showed good correlation with the DR progression in each model.

CONCLUSIONS

AH APN levels correlated well with DR development and progression. Serum APN could be a better marker for estimating intraocular cytokines, including both intraocular APN and VEGF concentrations in clinical field, than serum VEGF in DR patients.

Lipid regulation of NLRP3 inflammasome activity through organelle stress

Inflammation driven by the NLRP3 inflammasome in macrophages is an important contributor to chronic metabolic diseases that affect growing numbers of individuals. Many of these diseases involve the pathologic accumulation of endogenous lipids or their oxidation products, which can activate NLRP3. Other endogenous lipids, however, can inhibit the activation of NLRP3. The intracellular mechanisms by which these lipids modulate NLRP3 activity are now being identified. This review discusses emerging evidence suggesting that organelle stress, particularly involving mitochondria, lysosomes, and the endoplasmic reticulum, may be key in lipid-induced modification of NLRP3 inflammasome activity.

Circulating ceramides as biomarkers of cardiovascular disease: Evidence from phenotypic and genomic studies

There is a need for new biomarkers of atherosclerotic cardiovascular disease (ACVD), the main cause of death globally. Ceramides, a class of potent bioactive lipid mediators, have signalling roles in apoptosis, cellular stress and inflammation. Recent studies have highlighted circulating ceramides as novel biomarkers of coronary artery disease, type-2 diabetes and insulin resistance. Ceramides are highly regulated by enzymatic reactions throughout the body in terms of their activity and metabolism, including production, degradation and transport. The genetic studies that have been completed to date on the main ceramide species found in circulation are described, highlighting the importance of DNA variants in genes involved in ceramide biosynthesis as key influencers of heritable, circulating ceramide levels. We also review studies of disease associations with ceramides and discuss mechanistic insights deriving from recent genomic studies. The signalling activities of ceramides in vascular inflammation and apoptosis, associations between circulating ceramides and coronary artery disease risk, type-2 diabetes and insulin resistance, and the potential importance of ceramides with regard to ACVD risk factors, such as blood pressure, lipoproteins and lifestyle factors, are also discussed.

Lipid profile disturbances may predispose psoriatic patients to liver dysfunction

INTRODUCTION

Psoriasis is a chronic inflammatory disease associated with metabolic disturbances and liver dysfunction. Both serum fatty acids (FA) and ceramides (Cer) have structural functions but also are signal molecules that could be involved in the pathogenesis of liver dysfunction.

AIM

To assess the concentration of the circulating FA and Cer in correlation with the alanine aminotransferase (ALT) blood level in psoriatic patients. In addition, we have examined the relationship between ALT concentration and severity of the disease and inflammation markers.

MATERIAL AND METHODS

Eighty-five patients with psoriasis and 32 healthy controls were enrolled in the study. Patients were divided into 2 groups according to ALT blood levels. Serum concentration of 14 FA and 14 Cer were measured by gas-liquid chromatography. The results were correlated with the Psoriasis Area and Severity Index (PASI), serum lipid profile, and inflammatory markers.

RESULTS

We observed higher PASI score (p = 0.01) and higher C-reactive protein (p = 0.02) concentration in the group of psoriatic patients with high ALT. Serum ALT positively correlated with saturated fatty acids (SFA) (p = 0.01, r = 0.27) and SFA/unsaturated fatty acids (UFA) ratio (p = 0.01, r = 0.26). ALT negatively correlated with UFA level (p = 0.008, r = -0.28). Lignoceric ceramide positively correlated with ALT level (r = 0.22; p = 0.045) in psoriatic patients.

CONCLUSIONS

Patients with severe psoriasis are predisposed to the development of liver dysfunction. We have demonstrated disturbances of serum fatty acid and sphingolipid profile in psoriatic patients, which may trigger liver disease.

Obesity-Related Changes in High-Density Lipoprotein Metabolism and Function

In obese individuals, atherogenic dyslipidemia is a very common and important factor in the increased risk of cardiovascular disease. Adiposity-associated dyslipidemia is characterized by low high-density lipoprotein cholesterol (HDL-C) levels and an increase in triglyceride-rich lipoproteins. Several factors and mechanisms are involved in lowering HDL-C levels in the obese state and HDL quantity and quality is closely related to adiponectin levels and the bioactive lipid sphingosine-1-phosphate. Recent studies have shown that obesity profoundly alters HDL metabolism, resulting in altered HDL subclass distribution, composition, and function. Importantly, weight loss through gastric bypass surgery and Mediterranean diet, especially when enriched with virgin olive oil, is associated with increased HDL-C levels and significantly improved metrics of HDL function. A thorough understanding of the underlying mechanisms is crucial for a better understanding of the impact of obesity on lipoprotein metabolism and for the development of appropriate therapeutic approaches. The objective of this review article was to summarize the newly identified changes in the metabolism, composition, and function of HDL in obesity and to discuss possible pathophysiological consequences.

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.

Lipid deposition and metaflammation in diabetic kidney disease

A critical link between metabolic disorders and a form of low-grade systemic and chronic inflammation has been recently established and named 'Metaflammation'. Metaflammation has been recognized as a key mediator of both microvascular and macrovascular complications of diabetes and as a significant contributor to the development of diabetic kidney disease (DKD). The goal of this review is to summarize the contribution of diabetes-induced inflammation and the related signaling pathways to diabetic complications, with a particular focus on how innate immunity and lipid metabolism influence each other.

Ceramides in Adipose Tissue

Adipose tissue is a key nutrient-sensing depot that regulates excess energy storage and consumption. Adipocytes, the key components of the adipose tissue, have unique ability to store excess energy in the form of triglycerides, sense systemic energy demands, and secrete factors (lipids, peptides, cytokines, and adipokines) to regulate other metabolic tissues. The presence of various types of adipocytes (white, brown, and beige) characterized by the number/size of lipid droplets, mitochondrial density, and thermogenic capacity, further highlights how intricate is the communication of these cell-types with other metabolic tissues to sense nutrients. In obesity the inherent capacity of adipose tissue to store and sense nutrients is compromised, causing spillover of the intermediate lipid metabolites into circulation and resulting in their ectopic deposition in tissues not suitable for lipid storage, a phenomenon known as lipotoxicity. This results in a spectrum of cellular dysfunction, that underlies various metabolic diseases. Of the numerous lipid classes implicated in eliciting lipotoxicity, sphingolipid: ceramides are among the most deleterious as they modulate signaling pathways involved in regulating glucose metabolism, triglyceride synthesis, apoptosis, and fibrosis. Notably, recent experimental studies have strongly implicated ceramides in the development of numerous metabolic diseases such as insulin resistance, diabetes, cardiomyopathy, hepatic-steatosis, and atherosclerosis. Herein we discuss and summarizes recent findings that implicate ceramides as a key contributor to adipocyte dysfunction underlying metabolic diseases and how depletion of ceramides can be exploited to improve metabolic health.

Sphingolipid Metabolism and Signaling in Skeletal Muscle: From Physiology to Physiopathology

Sphingolipids represent one of the major classes of eukaryotic lipids. They play an essential structural role, especially in cell membranes where they also possess signaling properties and are capable of modulating multiple cell functions, such as apoptosis, cell proliferation, differentiation, and inflammation. Many sphingolipid derivatives, such as ceramide, sphingosine-1-phosphate, and ganglioside, have been shown to play many crucial roles in muscle under physiological and pathological conditions. This review will summarize our knowledge of sphingolipids and their effects on muscle fate, highlighting the role of this class of lipids in modulating muscle cell differentiation, regeneration, aging, response to insulin, and contraction. We show that modulating sphingolipid metabolism may be a novel and interesting way for preventing and/or treating several muscle-related diseases.

Serum sphingolipid level in psoriatic patients with obesity

Introduction

Psoriasis is a chronic inflammatory disease associated with metabolic syndrome, including obesity. Ceramides (CER) and sphingosine-1-phosphate (S1P), which belongs to sphingolipids, have both biological and structural functions in the human epidermis.

Aim

To evaluate serum concentrations of selected CER in psoriatic patients in different weight ranges, the impact of obesity on the concentration of circulating CERs, their association with the course of psoriasis and selected inflammatory markers.

Material and methods

Eigthy-five patients with active plaque-type psoriasis and 32 healthy controls were enrolled in the study. Patients were divided into 3 groups: normal weight, overweight and obese. Serum concentrations of 14 ceramides were measured by gas-liquid chromatography. The results were correlated with the Psoriasis Area and Severity Index (PASI), serum lipid profile and inflammatory markers.

Results

There were no significant differences in total serum CER concentration between psoriatic groups of patients. The S1P concentration was higher in psoriatic patients with normal body weight and overweight than in the control group (p = 0.002 and p = 0.04, respectively). In psoriatic patients with normal body weight, nervonic ceramide (C24:1) correlated with PASI (r = 0.38; p = 0.042) and CRP (C-reactive protein) (r = 0.42; p = 0.023). In overweight patients, the concentration of lignoceric ceramide (C24:0) correlated inversely with the severity of the disease (r = -0.41; p = 0.022) and CRP (r = -0.6; p = 0.0004).

Conclusions

We have demonstrated an abnormal sphingolipid profile in psoriatic patients in different weight groups. Selected CER might be the biomarkers of psoriasis severity and inflammation, may reflect lipid disturbances and contribute to the development of metabolic syndrome.

Sphingolipids in Obesity and Correlated Co-Morbidities: The Contribution of Gender, Age and Environment

This paper reviews our present knowledge on the contribution of ceramide (Cer), sphingomyelin (SM), dihydroceramide (DhCer) and sphingosine-1-phosphate (S1P) in obesity and related co-morbidities. Specifically, in this paper, we address the role of acyl chain composition in bodily fluids for monitoring obesity in males and females, in aging persons and in situations of environmental hypoxia adaptation. After a brief introduction on sphingolipid synthesis and compartmentalization, the node of detection methods has been critically revised as the node of the use of animal models. The latter do not recapitulate the human condition, making it difficult to compare levels of sphingolipids found in animal tissues and human bodily fluids, and thus, to find definitive conclusions. In human subjects, the search for putative biomarkers has to be performed on easily accessible material, such as serum. The serum “sphingolipidome” profile indicates that attention should be focused on specific acyl chains associated with obesity, per se, since total Cer and SM levels coupled with dyslipidemia and vitamin D deficiency can be confounding factors. Furthermore, exposure to hypoxia indicates a relationship between dyslipidemia, obesity, oxygen level and aerobic/anaerobic metabolism, thus, opening new research avenues in the role of sphingolipids.

Sphingolipid serum profiling in vitamin D deficient and dyslipidemic obese dimorphic adults

Recent studies on Saudi Arabians indicate a prevalence of dyslipidemia and vitamin D deficiency (25(OH)D) in both normal weight and obese subjects. In the present study the sphingolipid pattern was investigated in 23 normolipidemic normal weight (NW), 46 vitamin D deficient dyslipidemic normal weight (-vitDNW) and 60 vitamin D deficient dyslipidemic obese (-vitDO) men and women by HPTLC-primuline profiling and LC-MS analyses. Results indicate higher levels of total ceramide (Cer) and dihydroceramide (dhCers C18–22) and lower levels of total sphingomyelins (SMs) and dihydrosphingomyelin (dhSM) not only in -vitDO subjects compared to NW, but also in –vitDNW individuals. A dependency on body mass index (BMI) was observed analyzing specific Cer acyl chains levels. Lower levels of C20 and 24 were observed in men and C24.2 in women, respectively. Furthermore, LC-MS analyses display dimorphic changes in NW, -vitDNW and –vitDO subjects. In conclusion, LC-MS data identify the independency of the axis high Cers, dhCers and SMs from obesity per se. Furthermore, it indicates that long chains Cers levels are specific target of weight gain and that circulating Cer and SM levels are linked to sexual dimorphism status and can contribute to predict obese related co-morbidities in men and women.

Metabolic Messengers: ceramides

Ceramides are products of metabolism that accumulate in individuals with obesity or dyslipidaemia and alter cellular processes in response to fuel surplus. Their actions, when prolonged, elicit the tissue dysfunction that underlies diabetes and heart disease. Here, we review the history of research on these enigmatic molecules, exploring their discovery and mechanisms of action, the evolutionary pressures that have given them their unique attributes and the potential of ceramide-reduction therapies as treatments for cardiometabolic disease.

Beyond adiponectin and leptin: adipose tissue-derived mediators of inter-organ communication

The breakthrough discoveries of leptin and adiponectin more than two decades ago led to a widespread recognition of adipose tissue as an endocrine organ. Many more adipose tissue-secreted signaling mediators (adipokines) have been identified since then, and much has been learned about how adipose tissue communicates with other organs of the body to maintain systemic homeostasis. Beyond proteins, additional factors, such as lipids, metabolites, noncoding RNAs, and extracellular vesicles (EVs), released by adipose tissue participate in this process. Here, we review the diverse signaling mediators and mechanisms adipose tissue utilizes to relay information to other organs. We discuss recently identified adipokines (proteins, lipids, and metabolites) and briefly outline the contributions of noncoding RNAs and EVs to the ever-increasing complexities of adipose tissue inter-organ communication. We conclude by reflecting on central aspects of adipokine biology, namely, the contribution of distinct adipose tissue depots and cell types to adipokine secretion, the phenomenon of adipokine resistance, and the capacity of adipose tissue to act both as a source and sink of signaling mediators.

Current Progress of Lipid Analysis in Metabolic Diseases by Mass Spectrometry Methods

BACKGROUND

Obesity, insulin resistance, diabetes, and metabolic syndrome are associated with lipid alterations, and they affect the risk of long-term cardiovascular disease. A reliable analytical instrument to detect changes in the composition or structures of lipids and the tools allowing to connect changes in a specific group of lipids with a specific disease and its progress, is constantly lacking. Lipidomics is a new field of medicine based on the research and identification of lipids and lipid metabolites present in human organism. The primary aim of lipidomics is to search for new biomarkers of different diseases, mainly civilization diseases.

OBJECTIVE

We aimed to review studies reporting the application of mass spectrometry for lipid analysis in metabolic diseases.

METHOD

Following an extensive search of peer-reviewed articles on the mass spectrometry analysis of lipids the literature has been discussed in this review article.

RESULTS

The lipid group contains around 1.7 million species; they are totally different, in terms of the length of aliphatic chain, amount of rings, additional functional groups. Some of them are so complex that their complex analyses are a challenge for analysts. Their qualitative and quantitative analysis of is based mainly on mass spectrometry.

CONCLUSION

Mass spectrometry techniques are excellent tools for lipid profiling in complex biological samples and the combination with multivariate statistical analysis enables the identification of potential diagnostic biomarkers.

Obesity and dyslipidemia

Obesity, a pandemic of the modern world, is intimately associated with dyslipidemia, which is mainly driven by the effects of insulin resistance and pro-inflammatory adipokines. However, recent evidence suggests that obesity-induced dyslipidemia is not a unique pathophysiological entity, but rather has distinct characteristics depending on many individual factors. In line with that, in a subgroup of metabolically healthy obese (MHO) individuals, dyslipidemia is less prominent or even absent. In this review, we will address the main characteristics of dyslipidemia and mechanisms that induce its development in obesity. The fields, which should be further investigated to expand our knowledge on obesity-related dyslipidemia and potentially yield new strategies for prevention and management of cardiometabolic risk, will be highlighted. Also, we will discuss recent findings on novel lipid biomarkers in obesity, in particular proprotein convertase subtilisin/kexin type 9 (PCSK9), as the key molecule that regulates metabolism of low-density lipoproteins (LDL), and sphingosine-1-phosphate (S1P), as one of the most important mediators of high-density lipoprotein (HDL) particles function. Special attention will be given to microRNAs and their potential use as biomarkers of obesity-associated dyslipidemia.

Maternal obesity leads to long-term altered levels of plasma ceramides in the offspring as revealed by a longitudinal lipidomic study in children

BACKGROUND/OBJECTIVES

Maternal obesity is associated with increased risk of obesity and other symptoms of the metabolic syndrome in the offspring. Nevertheless, the molecular mechanisms and cellular factors underlying this enhanced disease susceptibility remain to be determined. Here, we aimed at identifying changes in plasma lipids in offspring of obese mothers that might underpin, and serve as early biomarkers of, their enhanced metabolic disease risk.

SUBJECTS/METHODS

We performed a longitudinal lipidomic profiling in plasma samples from normal weight, overweight, and obese pregnant women and their children that participated in the Prenatal Omega-3 Fatty Acid Supplementation, Growth, and Development trial conducted in Mexico. At recruitment women were aged between 18 and 35 years and in week 18-22 of pregnancy. Blood samples were collected at term delivery by venipuncture from mothers and from the umbilical cord of their newborns and from the same infants at 4 years old under non-fasting conditions. Lipidomic profiling was done using ultra-performance liquid chromatography high-resolution mass spectrometry.

RESULTS

Analysis of the lipidomic data showed that overweight and obese mothers exhibited a significant reduction in the total abundance of ceramides (Cer) in plasma, mainly of Cer (d18:1/20:0), Cer (d18:1/22:0), Cer (d18:1/23:0), and Cer (d18:1/24:0), compared with mothers of normal body weight. This reduction was confirmed by the direct quantification of these and other ceramide species. Similar quantitative differences in the plasma concentration of Cer (d18:1/22:0), Cer (d18:1/23:0), and Cer (d18:1/24:0), were also found between 4-year-old children of overweight and obese mothers compared with children of mothers of normal body weight. Noteworthy, children exhibited equal daily amounts of energy and food intake independently of the BMI of their mothers.

CONCLUSIONS

Maternal obesity results in long-lasting changes in plasma ceramides in the offspring suggesting that these lipids might be used as early predictors of metabolic disease risk due to maternal obesity.

Increased serum concentration of ceramides in obese children with nonalcoholic fatty liver disease

Background

Hepatic lipid accumulation is closely related to the development of insulin resistance, which is regarded as one of the most significant risk factors of nonalcoholic fatty liver disease (NAFLD). Although the exact molecular pathway leading to impaired insulin signaling has not been definitively established, ceramides are suspected mediators of lipid induced hepatic insulin resistance. Therefore, the aim of the study was to evaluate the serum ceramides concentration in obese children with NAFLD.

Methods

The prospective study included 80 obese children (aged 7–17 years, median 12 years) admitted to our Department to diagnose initially suspected liver disease. Patients with viral hepatitis (HCV, HBV, CMV), autoimmune (AIH), toxic and metabolic (Wilson’s disease, alfa-1–antitrypsin deficiency) liver diseases and celiac disease were excluded. NAFLD was diagnosed based on pediatric diagnostic criteria in obese children with liver steatosis in ultrasound (US) as well as elevated alanine transaminase (ALT) serum activity after exclusion of other major liver diseases listed before. Ultrasonography was used as a screening method and for qualitative assessment of the steatosis degree (graded according to Saverymuttu scale). Advanced steatosis was defined as a score > 1. The total intrahepatic lipid content (TILC) was assessed by magnetic resonance proton spectroscopy (¹HMRS) which is the most accurate technique for assessment of ectopic fat accumulation. Fasting serum concentration of ceramides was measured in 62 children.

Results

NAFLD was diagnosed in 31 children. Significant, positive correlation was found between total serum concentration of ceramides and insulin (r = 0.3, p = 0.02) and HOMA-IR (r = 0.28, p = 0.03). Total ceramide concentration as well as specific fatty acid-ceramides (FA-ceramides) concentrations, namely: myristic, palmitic, palmitoleic, stearic, oleic, behenic and lignoceric were significantly higher (p = 0.004, p = 0.003, p = 0.007, p < 0.001, p = 0.035, p = 0.008, p = 0.003, p = 0.006, respectively) in children with NAFLD compared to controls (n = 14). Moreover, children with NAFLD had significantly higher activity of ALT (p < 0.001) and GGT (p < 0.001), HOMA-IR (p = 0.04), BMI (p = 0.046), waist circumference (p = 0.01) steatosis grade in ultrasound (p < 0.001) and TILC in ¹HMRS (p < 0.001) compared to children without NAFLD. We did not find significant differences in total and FA-ceramide species concentrations between children with mild (grade 1) and advanced liver steatosis in ultrasonography (grade 2–3).

Conclusion

Elevated ceramide concentrations in obese patients together with their significant correlation with insulin resistance parameters suggest their association with molecular pathways involved in insulin signaling impairment known to be strongly linked to pathogenesis of non-alcoholic fatty liver disease.

Feeding a slowly digestible carbohydrate diet during pregnancy of insulin-resistant rats prevents the excess of adipogenesis in their offspring

An obesogenic environment during pregnancy has been shown to increase the risk of dysregulation on adipogenesis and insulin resistance in the offspring. Being essential for the growing fetus, glucose supply is guaranteed by a number of modifications in the mother's metabolism, and thus, glucose control during pregnancy especially among obese or diabetic women is paramount to prevent adverse consequences in their children. Besides the election of low-glycemic-index carbohydrates, the rate of carbohydrate digestion could be relevant to keep a good glucose control. In the present study, we compared the effects of two high-fat diets with similar glycemic load but different rates of carbohydrate digestion given to pregnant insulin-resistant rats. After birth, all animals were fed a standard diet until age 14 weeks. We analyzed offspring body composition, plasma and adipocyte lipidomics, lipid metabolism in adipose tissue and insulin sensitivity. Those animals whose mothers were fed the rapid-digesting carbohydrate diet exhibited an excessive adipogenesis. Thus, these animals showed a marked lipidemia, increased lipid synthesis in the adipose tissue and reduced glucose transporter amount in the adipose. On the contrary, those animals whose mothers were fed the slow-digesting carbohydrate diet showed a profile in the measured parameters closer to that of the offspring of healthy mothers. These results support the hypothesis that not only glycemic index but the rate of carbohydrate digestion during gestation may be critical to regulate the programming of adipogenesis in the offspring.

Serum Metabolomics of Activity Energy Expenditure and its Relation to Metabolic Syndrome and Obesity

Modifiable lifestyle factors, including exercise and activity energy expenditure (AEE), may attenuate the unfavorable health effects of obesity, such as risk factors of metabolic syndrome (MetS). However, the underlying mechanisms are not clear. In this study we sought to investigate whether the metabolite profiles of MetS and adiposity assessed by body mass index (BMI) and central obesity are inversely correlated with AEE and physical activity. We studied 35 men and 47 women, aged 30-60 years, using doubly labeled water to derive AEE and the Sedentary Time and Activity Reporting Questionnaire (STAR-Q) to determine the time spent in moderate and vigorous physical activity. Proton nuclear magnetic resonance spectroscopy was used for serum metabolomics analysis. Serine and glycine were found in lower concentrations in participants with more MetS risk factors and greater adiposity. However, serine and glycine concentrations were higher with increasing activity measures. Metabolic pathway analysis and recent literature suggests that the lower serine and glycine concentrations in the overweight/obese state could be a consequence of serine entering de novo sphingolipid synthesis. Taken together, higher levels of AEE and physical activity may play a crucial part in improving metabolic health in men and women with and without MetS risk factors.

Obesity-related insulin resistance in adolescents: a systematic review and meta-analysis of observational studies

Insulin resistance is common among obese adolescents; however, the extent of this problem is not clear. We conducted a systematic review of PubMed-Medline, CINAHL, The Web of Science, EMBASE and Scopus for observational studies evaluating components defining insulin resistance (insulin, C-peptide and homeostatic model assessment-insulin resistance [HOMA-IR]) in obese adolescents (12-18 years) versus non-obese adolescents. Our systematic review and meta-analysis followed the PRISMA guidelines. Data were combined using a random-effects model and summary statistics were calculated using the mean differences (MDs). 31 studies were included (n = 8655). In 26 studies, fasting insulin levels were higher in obese adolescents when compared to non-obese adolescents (MD = 64.11 pmol/L, 95%CI 49.48-78.75, p < 0.00001). In three studies, fasting C-peptide levels were higher in obese adolescents when compared to non-obese adolescents (MD = 0.29 nmol/L, 95%CI 0.22-0.36, p < 0.00001). In 24 studies, HOMA-IR values were higher in obese adolescents when compared to non-obese adolescents (MD = 2.22, 95%CI 1.78-2.67, p < 0.00001). Heterogeneity of effects among studies was moderate to high. Subgroup analyses showed similar results to the main analyses. Circulating insulin and C-peptide levels and HOMA-IR values were significantly higher in obese adolescents compared to those non-obese.

Sphingolipids and phospholipids in insulin resistance and related metabolic disorders

Obesity, insulin resistance, type 2 diabetes mellitus and cardiovascular disease form a metabolic disease continuum that has seen a dramatic increase in prevalence in developed and developing countries over the past two decades. Dyslipidaemia resulting from hypercaloric diets is a major contributor to the pathogenesis of metabolic disease, and lipid-lowering therapies are the main therapeutic option for this group of disorders. However, the fact that dysfunctional lipid metabolism extends far beyond cholesterol and triglycerides is becoming increasingly clear. Lipidomic studies and mouse models are helping to explain the complex interactions between diet, lipid metabolism and metabolic disease. These studies are not only improving our understanding of this complex biology, but are also identifying potential therapeutic avenues to combat this growing epidemic. This Review examines what is currently known about phospholipid and sphingolipid metabolism in the setting of obesity and how metabolic pathways are being modulated for therapeutic effect.

Increase in circulating sphingosine-1-phosphate and decrease in ceramide levels in psoriatic patients

Psoriasis is characterized by hyperproliferation, deregulated differentiation and impaired apoptosis of keratinocytes. Mechanisms of lipid profile disturbances and metabolic syndrome in the psoriatic patients are still not fully understood. Sphingolipids, namely ceramides (CER) and sphingosine-1-phosphate (S1P) are signal molecules which can regulate cell growth, apoptosis and immune reactions. The aim of the study was to evaluate circulating CER and S1P levels in plaque-type psoriasis and their associations with the disease activity, inflammatory or metabolic markers and the presence of psoriatic comorbidities. Eighty-five patients with exacerbated plaque-type psoriasis and thirty-two healthy controls were enrolled. Serum CER and S1P concentrations before the treatment were examined. General patient characteristics included: PASI (Psoriasis Area and Severity Index), BMI (Body Mass Index), inflammatory and biochemical markers, lipid profile and presence of psoriatic comorbidities. Total serum concentration of CER was significantly decreased (p = 0.02) and concomitantly S1P levels significantly increased (p = 0.002) in psoriatic patients compared to the healthy control group. Among patients with psoriasis no significant correlations with the disease activity and inflammation markers were observed and only patients with psoriatic arthritis had significantly higher CER total concentration. Serum sphingolipid disturbances in psoriatic patients were observed. Decreased total CER and increased S1P serum levels may reflect their epidermal altered composition and metabolism. Patients with psoriatic arthritis have higher CER levels than psoriasis with skin involvement only. It might provide additional predictive value for psoriatic arthritis and may convey higher risk of metabolic and cardiovascular disease development in this group of patients.

From Molecules to the Clinic: Linking Schizophrenia and Metabolic Syndrome through Sphingolipids Metabolism

Metabolic syndrome (MS) is a prevalent and severe comorbidity observed in schizophrenia (SZ). The exact nature of this association is controversial and very often accredited to the effects of psychotropic medications and disease-induced life-style modifications, such as inactive lifestyle, poor dietary choices, and smoking. However, drug therapy and disease-induced lifestyle factors are likely not the only factors contributing to the observed converging nature of these conditions, since an increased prevalence of MS is also observed in first episode and drug-naïve psychosis populations. MS and SZ share common intrinsic susceptibility factors and etiopathogenic mechanisms, which may change the way we approach clinical management of SZ patients. Among the most relevant common pathogenic pathways of SZ and MS are alterations in the sphingolipids (SLs) metabolism and SLs homeostasis. SLs have important structural functions as they participate in the formation of membrane “lipid rafts.” SLs also play physiological roles in cell differentiation, proliferation, and inflammatory processes, which might be part of MS/SZ common pathophysiological processes. In this article we review a plausible mechanism to explain the link between MS and SZ through a disruption in SL homeostasis. Additionally, we provide insights on how this hypothesis can lead to the developing of new diagnostic/therapeutic technologies for SZ patients.

Sphingosine 1-phosphate in metabolic syndrome (Review)

Metabolic syndrome (MetS), a clustering of components, is closely associated with the development and prognosis of cardiovascular disease and diabetes. Sphingosine 1-phosphate (S1P) is a lysophospholipid with paracrine and autocrine effects, which is associated with obesity, insulin resistance, hyperglycemia, dyslipidemia and hypertension through extracellular and intracellular signals to achieve a variety of biological functions. However, there is controversy regarding the role of S1P in MetS; the specific role played by S1P remains unclear. It ameliorates abnormal energy metabolism and deviant adipogenesis and mediates inflammation in obesity. Despite the fact that sphingosine kinase (SphK)2/S1P increases the glucose‑stimulated insulin secretion of β-cells, more evidence showed that activation of the SphK1/S1P/S1P2R pathway inhibited the feedback loop of insulin secretion and sensitivity. The majority of S1P1R activation improves diabetes whereas S1P2R activation worsens the condition. In hyperlipidemia, S1P binds to high-density lipoprotein, low‑density lipoprotein and very low-density lipoprotein exerting different effects. Moreover, low concentrations of S1P lead to vasodilation whereas high concentrations of S1P result in vasocontraction of isolated arterioles. This review discusses the means by which different SphKs, S1P concentrations or S1P receptor subtypes results to diverse result in MetS, and then examines the role of S1P in MetS.

The association of obesity with hearing thresholds in women aged 18-40 years

An elevation in hearing thresholds and decrease in hearing sensitivity in adults, particularly due to aging, are quite common. Recent studies have shown that, apart from aging, various other factors also play a role in auditory changes. Studies on the association of hearing loss (HL) with obesity are limited in advanced age cases and present contradictions. In this study, the association between obesity and hearing thresholds in women aged 18-40 years has been assessed. Forty women diagnosed with obesity (mean age, 31.8 years) and 40 healthy non-obese female controls (mean age, 30.5 years) were included in this prospective study. Each subject was tested with low (250, 500, 1000 and 2000 Hz) and high (4000, 6000 and 8000 Hz) frequency audiometry. In the case and control groups, the average hearing thresholds at low frequencies were 16.03 ± 4.72 and 16.15 ± 2.72 (p = 0.885) for the right ear, respectively, and 16.15 ± 5.92 and 14.71 ± 3.18 (p = 0.180) for the left ear, respectively. The average hearing threshold levels at high frequencies were 20.70 ± 10.23 and 15.33 ± 3.87 (p = 0.003), respectively, for the right ear, and 22.91 ± 15.54 and 15.87 ± 4.35 (p = 0.007), respectively, for the left ear with statistical significance. This is the first report on the association of obesity with hearing threshold in women aged 18-40 years. We have demonstrated that obesity may affect hearing function, particularly that related to high frequencies. Hearing loss can be prevented by avoidance or control of obesity and its risk factors. Moreover, an auditory screening of obese cases at an early stage may provide early diagnosis of HL and may also contribute to their awareness in the fight against obesity.

A Role of the Inflammasome in the Low Storage Capacity of the Abdominal Subcutaneous Adipose Tissue in Obese Adolescents

The innate immune cell sensor leucine-rich-containing family, pyrin domain containing 3 (NLRP3) inflammasome controls the activation of caspase-1, and the release of proinflammatory cytokines interleukin (IL)-1β and IL-18. The NLRP3 inflammasome is implicated in adipose tissue inflammation and the pathogenesis of insulin resistance. Herein, we tested the hypothesis that adipose tissue inflammation and NLRP3 inflammasome are linked to the downregulation of subcutaneous adipose tissue (SAT) adipogenesis/lipogenesis in obese adolescents with altered abdominal fat partitioning. We performed abdominal SAT biopsies on 58 obese adolescents and grouped them by MRI-derived visceral fat to visceral adipose tissue (VAT) plus SAT (VAT/VAT+SAT) ratio (cutoff 0.11). Adolescents with a high VAT/VAT+SAT ratio showed higher SAT macrophage infiltration and higher expression of the NLRP3 inflammasome-related genes (i.e., TLR4, NLRP3, IL1B, and CASP1). The increase in inflammation markers was paralleled by a decrease in genes related to insulin sensitivity (ADIPOQ, GLUT4, PPARG2, and SIRT1) and lipogenesis (SREBP1c, ACC, LPL, and FASN). Furthermore, SAT ceramide concentrations correlated with the expression of CASP1 and IL1B. Infiltration of macrophages and upregulation of the NLRP3 inflammasome together with the associated high ceramide content in the plasma and SAT of obese adolescents with a high VAT/VAT+SAT may contribute to the limited expansion of the subcutaneous abdominal adipose depot and the development of insulin resistance.

Ceramides - Lipotoxic Inducers of Metabolic Disorders

In obesity and dyslipidemia, the oversupply of fat to tissues not suited for lipid storage induces cellular dysfunction that underlies diabetes and cardiovascular disease (i.e., lipotoxicity). Of the myriad lipids that accrue under these conditions, sphingolipids such as ceramide or its metabolites are amongst the most deleterious because they disrupt insulin sensitivity, pancreatic β cell function, vascular reactivity, and mitochondrial metabolism. Remarkably, inhibiting ceramide biosynthesis or catalyzing ceramide degradation in rodents ameliorates many metabolic disorders including diabetes, cardiomyopathy, insulin resistance, atherosclerosis, and steatohepatitis. Herein we discuss and critically assess studies that identify sphingolipids as major contributors to the tissue dysfunction underlying metabolic pathologies, highlighting the need to further decipher the full array of benefits elicited by ceramide depletion.

Effect of pioglitazone on plasma ceramides in adults with metabolic syndrome

BACKGROUND

Metabolic syndrome (MetS) appears closely linked with ceramide accumulation, inducing insulin resistance and toxicity to multiple cell types. Animal studies demonstrate that thiazolidinediones (TZDs) reduce ceramide concentrations in plasma and skeletal muscle and support lowering of ceramide levels as a potential mediator of TZDs' mechanism of action in reducing insulin resistance; however, studies in humans have yet to be reported. This study investigated the effects of pioglitazone therapy on plasma ceramides to understand the mechanism by which TZDs improve insulin resistance in MetS.

METHODS

Thirty-seven subjects with MetS were studied in a single-centre, randomized, double-blind, placebo-controlled trial comparing pioglitazone to placebo. Data were collected at baseline and after 6 months of therapy. The primary endpoint was the change from baseline in plasma ceramide concentrations.

RESULTS

Treatment with pioglitazone for 6 months, compared with placebo, significantly reduced multiple plasma ceramide concentrations: C18:0 (p = 0.001), C20:0 (p = 0.0004), C24 : 1 (p = 0.009), dihydroceramide C18 :0 (p = 0.005), dihydroceramide C24:1 (p = 0.004), lactosylceramide C16:0 (p = 0.02) and the hexosylceramides C16:0 (p = 0.0003), C18 : 0 (p = 0.00001), C22:0 (p = 0.00002) and C24:1 (p = 0.0006). Additionally, significant reductions were found when ceramides were grouped by species: ceramides (p = 0.03), dihydroceramides (p = 0.02), hexosylceramides (p = 0.00001) and lactosylceramides (p = 0.02). The total of all measured ceramides was also significantly reduced (p = 0.001). Following treatment with pioglitazone, the decrease in some ceramide species correlated negatively with the change in insulin sensitivity (dihydroceramide C16:0, r = -0.54; p = 0.02) and positively with total (lactosylceramide C24:0, r = 0.53; p = 0.02) and high molecular weight (lactosylceramide C24:0, r = 0.48; p = 0.05) adiponectin measurements; however, significant associations with changes in liver fat and glycemic control reduction were not found.

CONCLUSIONS

Pioglitazone in individuals with MetS induces a potent decrease in plasma ceramides, and some of the changes correlate with changes in insulin resistance and adiponectin levels.

Recombinant murine fibroblast growth factor 21 ameliorates obesity-related inflammation in monosodium glutamate-induced obesity rats

The aim of this study is to investigate the role of FGF21 in obesity-related inflammation in livers of monosodium glutamate (MSG)-induced obesity rats. The MSG rats were injected with recombinant murine fibroblast growth factor 21(FGF21) or equal volumes of vehicle. Metabolic parameters including body weight, Lee's index, food intake, visceral fat and liver weight, intraperitoneal glucose tolerance, glucose, and lipid levels were dynamically measured at specific time points. Liver function and routine blood test were also analyzed. Further, systemic inflammatory cytokines such as glucose transporter 1 (GLUT-1), leptin, TNF-α, and IL-6 mRNAs were determined by real-time PCR. FGF21 independently decreased body weight and whole-body fat mass without reducing food intake in the MSG rats. FGF21 reduced blood glucose level, Lee's index, visceral fat, and liver weight, and improved glucose tolerance, lipid metabolic spectrum, and hepatic steatosis in the MSG-obesity rats. Liver function parameters including AST, ALT, ALP, TP, T.Bili, and D.Bili levels significantly reduced in the FGF21-treated obesity rats compared to the controls. Further, FGF21 ameliorated the total and differential white blood cell (WBC) count, serum C-reactive protein (CRP), IL-6, and TNF-α levels in adipose tissues of the obesity rats, suggesting inflammation amelioration in the in the obesity rats by FGF21. FGF21 improves multiple metabolic disorders and ameliorates obesity-related inflammation in the MSG-induced obesity rats.

Sphingolipid metabolites in inflammatory disease

Sphingolipids are ubiquitous building blocks of eukaryotic cell membranes. Progress in our understanding of sphingolipid metabolism, state-of-the-art sphingolipidomic approaches and animal models have generated a large body of evidence demonstrating that sphingolipid metabolites, particularly ceramide and sphingosine-1-phosphate, are signalling molecules that regulate a diverse range of cellular processes that are important in immunity, inflammation and inflammatory disorders. Recent insights into the molecular mechanisms of action of sphingolipid metabolites and new perspectives on their roles in regulating chronic inflammation have been reported. The knowledge gained in this emerging field will aid in the development of new therapeutic options for inflammatory disorders.

Serum acid sphingomyelinase is upregulated in chronic hepatitis C infection and non alcoholic fatty liver disease

Sphingolipids constitute bioactive molecules with functional implications in homeostasis and pathogenesis of various diseases. However, the role of sphingolipids as possible disease biomarkers in chronic liver disease remains largely unexplored. In the present study we used mass spectrometry and spectrofluorometry methods in order to quantify various sphingolipid metabolites and also assess the activity of an important corresponding regulating enzyme in the serum of 72 healthy volunteers as compared to 69 patients with non-alcoholic fatty liver disease and 69 patients with chronic hepatitis C virus infection. Our results reveal a significant upregulation of acid sphingomyelinase in the serum of patients with chronic liver disease as compared to healthy individuals (p<0.001). Especially in chronic hepatitis C infection acid sphingomyelinase activity correlated significantly with markers of hepatic injury (r=0.312, p=0.009) and showed a high discriminative power. Accumulation of various (dihydro-) ceramide species was identified in the serum of patients with non-alcoholic fatty liver disease (p<0.001) and correlated significantly to cholesterol (r=0.448, p<0.001) but showed a significant accumulation in patients with normal cholesterol values as well (p<0.001). Sphingosine, a further bioactive metabolite, was also upregulated in chronic liver disease (p<0.001). However, no significant correlation to markers of hepatic injury was identified.

CONCLUSION

Chronic hepatitis C virus infection and non-alcoholic fatty liver disease induce a significant upregulation of serum acid sphingomyelinase which appears as a novel biomarker in chronic hepatopathies. Further studies are required to elucidate the potential of the sphingolipid signaling pathway as putative therapeutic target in chronic liver disease.

Hematological parameters are associated with metabolic syndrome in Japanese community-dwelling persons

Hematological parameters including red blood cell (RBC) count, hematocrit (Hct), and hemoglobin (Hgb) are independently associated with insulin resistance. The aim of this study was to determine whether hematological parameters are associated with metabolic syndrome (MetS), and its components, independent of gender, body mass index (BMI) and other confounders of cardiovascular disease. A total of 692 men [60 ± 14 (mean ± standard deviation); 20-89 (range) years] and 1,004 women (63 ± 12; 21-88 years) participants without diabetes were recruited from a single community at the time of their annual health examination. We examined the relationship between hematological parameters and insulin resistance assessed by Homeostasis model assessment of insulin resistance (HOMA-IR), MetS, and its components. RBC count, Hct, and Hgb were all significantly associated with measures of HOMA-IR. Multiple linear regression analyses for HOMA-IR showed that RBC count, Hct, and Hgb were all shown to be independently and significantly associated with HOMA-IR as well as gender, BMI, alcohol consumption, current smoking status, γ-glutamyltransferase, high molecular weight adiponectin, and uric acid. Inclusion of hematological parameters into the model further increased the coefficient of determination (R (2)). Compared to participants with the lowest quartile of Hct, multivariate-adjusted odds ratio for insulin resistance (HOMA-IR ≥ 1.74) was 2.27 [95 % confidence interval (CI), 1.55-3.31] for the third quartile, and 3.78 (95 % CI, 2.38-5.99) for the highest quartile. Hct was significantly and strongly associated with increased HOMA-IR levels. Hematological parameters were positively associated with insulin resistance and prevalence of MetS in Japanese dwelling-community persons.

Ceramides contained in LDL are elevated in type 2 diabetes and promote inflammation and skeletal muscle insulin resistance

Dysregulated lipid metabolism and inflammation are linked to the development of insulin resistance in obesity, and the intracellular accumulation of the sphingolipid ceramide has been implicated in these processes. Here, we explored the role of circulating ceramide on the pathogenesis of insulin resistance. Ceramide transported in LDL is elevated in the plasma of obese patients with type 2 diabetes and correlated with insulin resistance but not with the degree of obesity. Treating cultured myotubes with LDL containing ceramide promoted ceramide accrual in cells and was accompanied by reduced insulin-stimulated glucose uptake, Akt phosphorylation, and GLUT4 translocation compared with LDL deficient in ceramide. LDL-ceramide induced a proinflammatory response in cultured macrophages via toll-like receptor-dependent and -independent mechanisms. Finally, infusing LDL-ceramide into lean mice reduced insulin-stimulated glucose uptake, and this was due to impaired insulin action specifically in skeletal muscle. These newly identified roles of LDL-ceramide suggest that strategies aimed at reducing hepatic ceramide production or reducing ceramide packaging into lipoproteins may improve skeletal muscle insulin action.

Plasma ceramides are elevated in female children and adolescents with type 2 diabetes

Accumulation of ceramides within tissues induces insulin resistance. Moreover, adiponectin exerts its beneficial metabolic effects at least partially through ceramide catabolism. We hypothesized that specific plasma ceramide subspecies are elevated in obese children and adolescents with type 2 diabetes (T2D), and that they inversely correlate with adiponectin and measures of insulin sensitivity. This was a cross-sectional study. Participants included 14 obese female subjects with T2D, ages 10-17, and 14 lean healthy controls of the same age and gender. Fasting plasma ceramide subspecies were measured by quantitative tandem mass spectrometry. Subjects with T2D had higher concentrations of C22:0 and C20:0 ceramides, with a 2-fold increase in C18:0 ceramide and C24:1 dihydroceramide (p<0.05). C22:0, C20:0 and C18:0 ceramide correlated with decreased adiponectin concentrations, increased HOMA-IR, BMI Z-score, triglyceride and fasting blood glucose concentrations (p<0.05). Plasma levels of C18:0, C20:0 and C22:0 ceramide, as well as C24:1 dihydroceramide, were elevated in obese female children and adolescents with T2D. This may be a reflection of tissue insulin resistance and could be a result of low adiponectin levels.

Targeting the sphingosine kinase/sphingosine 1-phosphate pathway in disease: review of sphingosine kinase inhibitors

Sphingosine 1-phosphate (S1P) is an important bioactive sphingolipid metabolite that has been implicated in numerous physiological and cellular processes. Not only does S1P play a structural role in cells by defining the components of the plasma membrane, but in the last 20 years it has been implicated in various significant cell signaling pathways and physiological processes: for example, cell migration, survival and proliferation, cellular architecture, cell-cell contacts and adhesions, vascular development, atherosclerosis, acute pulmonary injury and respiratory distress, inflammation and immunity, and tumorogenesis and metastasis [1,2]. Given the wide variety of cellular and physiological processes in which S1P is involved, it is immediately obvious why the mechanisms governing S1P synthesis and degradation, and the manner in which these processes are regulated, are necessary to understand. In gaining more knowledge about regulation of the sphingosine kinase (SK)/S1P pathway, many potential therapeutic targets may be revealed. This review explores the roles of the SK/S1P pathway in disease, summarizes available SK enzyme inhibitors and examines their potential as therapeutic agents. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Increased serum concentration of sphingosine-1-phosphate in juvenile-onset systemic lupus erythematosus

PURPOSE

Sphingosine-1-phosphate (S1P) is an active sphingolipid with chemotactic abilities and has been linked to inflammatory mediators and autoimmune disease. The aim of this study was to assess whether children with juvenile-onset systemic lupus erythematosus (JSLE) express increased systemic and/or urinary concentrations of S1P.

METHODS

A subgroup of patients participating in the UK JSLE Cohort Study, were invited to participate. Cross sectional serum and urine samples were prospectively collected along with demographic and standard clinical data. Results were compared to a cohort of disease controls (Henoch Schonlein Purpura; HSP) and healthy controls (HC).

RESULTS

The median age of JSLE patients (n = 15) was 13.6 years (7.2-16.9 years). The serum concentrations of S1P in JSLE patients (7.4 uM, IQR 6.3-12.3 uM) were statistically significantly increased when compared to patients with HSP (n = 10; 5.2 uM, IQR 4.0-7.9 uM; p = 0.016) and HCs (n = 10; 3.8 uM, IQR 2.1-5.8 uM; p = 0.003). There was a trend towards increased serum S1P concentrations between patients with active lupus nephritis (n = 8; 8.7 uM, IQR 6.2-15.3 uM) compared to lupus non-nephritis (n = 7; 6.6 uM, IQR 6.3-10.6 uM; p = 0.355). No relationship was found between disease activity markers and S1P. Urine S1P concentrations were no different between JSLE patients (56.0 nM, IQR 40.3-96.6 nM) and HCs (58.7 nM, IQR 0-241.9 nM; p = 0.889).

CONCLUSIONS

We have demonstrated, for the first time, an increased serum concentration of S1P in a cohort of JSLE patients. These findings highlight a role of S1P in the pathophysiology of JSLE that warrants further investigation.