Sphingolipids in adipose tissue: What's tipping the scale?

The impacts of dietary sphingomyelin supplementation on metabolic parameters of healthy adults: a systematic review and meta-analysis of randomized controlled trials

Background

Studies have shown that sphingomyelin (SM) and its metabolites play signaling roles in the regulation of human health. Endogenous SM is involved in metabolic syndrome (MetS), while dietary SM supplementation may maintain lipid metabolism and prevent or alleviate MetS. Therefore, we hypothesized that dietary SM supplementation is beneficial for human health.

Aims

In order to examine the impacts of dietary SM on metabolic indexes in adults without MetS, we performed a meta-analysis to test our hypothesis.

Methods

A comprehensive search was performed to retrieve randomized controlled trials that were conducted between 2003 and 2023 to examine the effects of dietary SM supplementation on metabolic parameters in the Cochrane Library, PubMed, Web of Science, Embase, and ClinicalTrials.gov databases. RevMan 5.4 and Stata 14.0 software were used for meta-analysis, a sensitivity analysis, the risk of bias, and the overall quality of the resulted evidence.

Results

Eventually, 10 articles were included in this meta-analysis. Dietary SM supplementation did not affect the endline blood SM level. When compared to the control, SM supplementation reduced the blood total cholesterol level [MD: -12.97, 95% CI: (-14.57, -11.38), p < 0.00001], low-density lipoprotein cholesterol level [MD: -6.62, 95% CI: (-10.74, -2.49), p = 0.002], and diastolic blood pressure [MD: -3.31; 95% CI (-4.03, -2.58), p < 0.00001] in adults without MetS. The supplementation also increased high-density lipoprotein level [MD:1.41, 95% CI: (0.94, 1.88), p < 0.00001] and muscle fiber conduction velocity [MD: 95% 1.21 CI (0.53, 1.88), p = 0.0005]. The intake of SM had no effect on the blood phospholipids and lyso-phosphatidylcholine, but slightly decreased phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol concentrations. Dietary SM supplementation reduced insulin level [MD: -0.63; 95% CI (-0.96, -0.31), p = 0.0001] and HOMA-IR [MD: -0.23; 95% CI (-0.31, -0.16), p < 0.00001] without affecting blood levels of glucose and inflammatory cytokines.

Conclusion

Overall, dietary SM supplementation had a protective effect on blood lipid profiles and insulin level, but had limited impacts on other metabolic parameters in adults without MetS. More clinical trials and basic research are required.

Systematic review registration

PROSPERO, identifier CRD42023438460.

Genome-Wide Association (GWAS) Applied to Carcass and Meat Traits of Nellore Cattle

The meat market has enormous importance for the world economy, and the quality of the product offered to the consumer is fundamental for the success of the sector. In this study, we analyzed a database which contained information on 2470 animals from a commercial farm in the state of São Paulo, Brazil. Of this total, 2181 animals were genotyped, using 777,962 single-nucleotide polymorphisms (SNPs). After quality control analysis, 468,321 SNPs provided information on the number of genotyped animals. Genome-wide association analyses (GWAS) were performed for the characteristics of the rib eye area (REA), subcutaneous fat thickness (SFT), shear force at 7 days' ageing (SF7), and intramuscular fat (IMF), with the aid of the single-step genomic best linear unbiased prediction (ssGBLUP) method, with the purpose of identifying possible genomic windows (~1 Mb) responsible for explaining at least 0.5% of the genetic variance of the traits under analysis (≥0.5%). These genomic regions were used in a gene search and enrichment analyses using MeSH terms. The distributed heritability coefficients were 0.14, 0.20, 0.18, and 0.21 for REA, SFT, SF7, and IMF, respectively. The GWAS results indicated significant genomic windows for the traits of interest in a total of 17 chromosomes. Enrichment analyses showed the following significant terms (FDR ≤ 0.05) associated with the characteristics under study: for the REA, heat stress disorders and life cycle stages; for SFT, insulin and nonesterified fatty acids; for SF7, apoptosis and heat shock proteins (HSP27); and for IMF, metalloproteinase 2. In addition, KEGG (Kyoto encyclopedia of genes and genomes) enrichment analysis allowed us to highlight important metabolic pathways related to the studied phenotypes, such as the growth hormone synthesis, insulin-signaling, fatty acid metabolism, and ABC transporter pathways. The results obtained provide a better understanding of the molecular processes involved in the expression of the studied characteristics and may contribute to the design of selection strategies and future studies aimed at improving the productivity of Nellore cattle.

Nervonic acid and its sphingolipids: Biological functions and potential food applications

Nervonic acid, a 24-carbon fatty acid with only one double bond at the 9th carbon (C24:1n-9), is abundant in the human brain, liver, and kidney. It not only functions in free form but also serves as a critical component of sphingolipids which participate in many biological processes such as cell membrane formation, apoptosis, and neurotransmission. Recent studies show that nervonic acid supplementation is not only beneficial to human health but also can improve the many medical conditions such as neurological diseases, cancers, diabetes, obesity, and their complications. Nervonic acid and its sphingomyelins serve as a special material for myelination in infants and remyelination patients with multiple sclerosis. Besides, the administration of nervonic acid is reported to reduce motor disorder in mice with Parkinson's disease and limit weight gain. Perturbations of nervonic acid and its sphingolipids might lead to the pathogenesis of many diseases and understanding these mechanisms is critical for investigating potential therapeutic approaches for such diseases. However, available studies about this aspect are limited. In this review, relevant findings about functional mechanisms of nervonic acid have been comprehensively and systematically described, focusing on four interconnected functions: cellular structure, signaling, anti-inflammation, lipid mobilization, and their related diseases.

The nutritional functions of dietary sphingomyelin and its applications in food

Sphingolipids are common structural components of cell membranes and are crucial for cell functions in physiological and pathophysiological conditions. Sphingomyelin and its metabolites, such as sphingoid bases, ceramide, ceramide-1-phosphate, and sphingosine-1-phosphate, play signaling roles in the regulation of human health. The diverse structures of sphingolipids elicit various functions in cellular membranes and signal transduction, which may affect cell growth, differentiation, apoptosis, and maintain biological activities. As nutrients, dietary sphingomyelin and its metabolites have wide applications in the food and pharmaceutical industry. In this review, we summarized the distribution, classifications, structures, digestion, absorption and metabolic pathways of sphingolipids, and discussed the nutritional functioning of sphingomyelin in chronic metabolic diseases. The possible implications of dietary sphingomyelin in the modern food preparations including dairy products and infant formula, skin improvement, delivery system and oil organogels are also evaluated. The production of endogenous sphingomyelin is linked to pathological changes in obesity, diabetes, and atherosclerosis. However, dietary supplementations of sphingomyelin and its metabolites have been shown to maintain cholesterol homeostasis and lipid metabolism, and to prevent or treat these diseases. This seemly paradoxical phenomenon shows that dietary sphingomyelin and its metabolites are candidates for food additives and functional food development for the prevention and treatment of chronic metabolic diseases in humans.

Distinct Effects of Cannabidiol on Sphingolipid Metabolism in Subcutaneous and Visceral Adipose Tissues Derived from High-Fat-Diet-Fed Male Wistar Rats

Available data suggest that cannabidiol (CBD) may ameliorate symptoms of insulin resistance by modulating the sphingolipid concentrations in particular organs. However, it is not entirely clear whether its beneficial actions also involve adipose tissues in a state of overnutrition. The aim of the study was to evaluate the effect of CBD on sphingolipid metabolism pathways and, as a result, on the development of insulin resistance in subcutaneous (SAT) and visceral (VAT) adipose tissues of an animal model of HFD-induced insulin resistance. Our experiment was performed on Wistar rats that were fed with a high-fat diet and/or received intraperitoneal CBD injections. We showed that CBD significantly lowered the ceramide content in VAT by reducing its de novo synthesis and increasing its catabolism. However, in SAT, CBD decreased the ceramide level through the inhibition of salvage and de novo synthesis pathways. All of these changes restored adipose tissues’ sensitivity to insulin. Our study showed that CBD sensitized adipose tissue to insulin by influencing the metabolism of sphingolipids under the conditions of increased availability of fatty acids in the diet. Therefore, we believe that CBD use may be considered as a potential therapeutic strategy for treating or reducing insulin resistance, T2DM, and metabolic syndrome.

Nervonic acid limits weight gain in a mouse model of diet-induced obesity

Lipid perturbations contribute to detrimental outcomes in obesity. We previously demonstrated that nervonic acid, a C24:1 ω-9 fatty acid, predominantly acylated to sphingolipids, including ceramides, are selectively reduced in a mouse model of obesity. It is currently unknown if deficiency of nervonic acid-sphingolipid metabolites contribute to complications of obesity. Mice were fed a standard diet, a high fat diet, or these diets supplemented isocalorically with nervonic acid. The primary objective was to determine if dietary nervonic acid content alters the metabolic phenotype in mice fed a high fat diet. Furthermore, we investigated if nervonic acid alters markers of impaired fatty acid oxidation in the liver. We observed that a nervonic acid-enriched isocaloric diet reduced weight gain and adiposity in mice fed a high fat diet. The nervonic acid enrichment led to increased C24:1-ceramides and improved several metabolic parameters including blood glucose levels, and insulin and glucose tolerance. Mechanistically, nervonic acid supplementation increased PPARα and PGC1α expression and improved the acylcarnitine profile in liver. These alterations indicate improved energy metabolism through increased β-oxidation of fatty acids. Taken together, increasing dietary nervonic acid improves metabolic parameters in mice fed a high fat diet. Strategies that prevent deficiency of, or restore, nervonic acid may represent an effective strategy to treat obesity and obesity-related complications.

Sphingolipids in food and their critical roles in human health

Sphingolipids (SLs) are ubiquitous structural components of cell membranes and are essential for cell functions under physiological conditions or during disease progression. Abundant evidence supports that SLs and their metabolites, including ceramide (Cer), ceramide-1-phosphate (C1P), sphingosine (So), sphingosine-1-phosphate (S1P), are signaling molecules that regulate a diverse range of cellular processes and human health. However, there are limited reviews on the emerging roles of exogenous dietary SLs in human health. In this review, we discuss the ubiquitous presence of dietary SLs, highlighting their structures and contents in foodstuffs, particularly in sea foods. The digestion and metabolism of dietary SLs is also discussed. Focus is given to the roles of SLs in both the etiology and prevention of diseases, including bacterial infection, cancers, neurogenesis and neurodegenerative diseases, skin integrity, and metabolic syndrome (MetS). We propose that dietary SLs represent a "functional" constituent as emerging strategies for improving human health. Gaps in research that could be of future interest are also discussed.

Developing a Robust Assay to Monitor and Quantify Key Players of Metabolic Pathways during Adipogenesis by Targeted Proteomics

Targeted data acquisition using nano liquid chromatrography (nano-LC) coupled mass spectrometry is an emerging approach when there is a need to quantify proteins with high accuracy, sensitivity, and reproducibility. Nevertheless, creating assays meeting all those criteria still remains a laborious task, especially when investigating low abundant proteins and small concentration changes. In this work a targeted data acquisition workflow is developed reducing time and effort to target and investigate key players of metabolic pathways during the process of adipocyte differentiation. This leads to accurate and sensitive quantification of proteins involved in the synthesis of fatty acids, glycerolipids, glycerophospholipids, sphingolipids, the production of energy and reduction equivalents. Additionally low abundant signaling molecules part of the peroxisome proliferator-activated receptor gamma (PPARγ) and insulin signaling pathway with ≈400 for the insulin receptor substrate and 1100 copies per cell for PPARγ are determined.