Sphingolipid regulators of cellular dysfunction in Type 2 diabetes mellitus: a systems overview

The impact of overweight and obesity on health outcomes in the United States from 1990 to 2021

AIM

Elevated body mass index (BMI) presents a significant public health challenge in the United States, contributing to considerable morbidity, mortality and economic burden. This study investigates the health burden of overweight and obesity in the United States from 1990 to 2021, leveraging the Global Burden of Disease data set to analyse trends, disparities and potential determinants of high BMI-related health outcomes.

MATERIALS AND METHODS

Our study focused on the United States, analysing trends in disability-adjusted life years (DALY) and deaths attributable to high BMI, defined as a BMI of 25 kg/m2 or higher for adults. Statistical analyses included estimated annual percentage change (EAPC) in age-standardized DALY rates and age-standardized death rates. Pearson correlation was performed between EAPCs and the socio-demographic index (SDI), with significance set at p < 0.05.

RESULTS

From 1990 to 2021, age-standardized DALY rates attributable to high BMI increased by 24.9%, whereas the age-standardized death rates increased by 5.2%. Age disparities showed DALYs peaking at 60-64 years for males and 65-69 years for females, with deaths peaking at 65-69 years for males and 90-94 years for females. A strong negative correlation was found between the EAPC in age-standardized DALY and death rates and the SDI.

CONCLUSIONS

Overweight and obesity significantly impact public health in the United States, especially among older adults and lower socio-demographic regions. Comprehensive public health strategies integrating behavioural, technological and environmental interventions are crucial. Future research should focus on longitudinal studies, personalized interventions and policy-driven approaches to address the multifaceted influences on high BMI.

Sphingosine kinase 1 is induced by glucocorticoids in adipose derived stem cells and enhances glucocorticoid mediated signaling in adipose expansion

Sphingosine kinase 1 (SphK1) plays a crucial role in regulating metabolic pathways within adipocytes and is elevated in the adipose tissue of obese mice. While previous studies have reported both pro- and inhibitory effects of SphK1 and its product, sphingosine-1-phosphate (S1P), on adipogenesis, the precise mechanisms remain unclear. This study explores the timing and downstream effects of SphK1/S1P expression and activation during in vitro adipogenesis. We demonstrate that the synthetic glucocorticoid dexamethasone robustly induces SphK1 expression, suggesting its involvement in glucocorticoid-dependent signaling during adipogenesis. Notably, the activation of C/EBPδ, a key gene in early adipogenesis and a target of glucocorticoids, is diminished in SphK1-/- adipose-derived stem cells (ADSCs). Furthermore, glucocorticoid administration promotes adipose tissue expansion via SphK1 in a depot-specific manner. Although adipose expansion still occurs in SphK1-/- mice, it is significantly reduced. These findings indicate that while SphK1 is not essential for adipogenesis, it enhances early gene activation, thereby facilitating adipose tissue expansion.

Metabolic impairments associated with type 2 diabetes mellitus and the potential effects of exercise therapy: An exploratory randomized trial based on untargeted metabolomics

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a common condition that is characterized by metabolic impairments. Exercise therapy has proven effective in improving the physiological and psychological states of patients with T2DM; however, the influence of different exercise modalities on metabolic profiles is not fully understood. This study first aimed to investigate the metabolic changes associated with T2DM among patients and then to evaluate the potential physiological effects of different exercise modalities (Tai Chi and brisk walking) on their metabolic profiles.

METHODS

This study included 20 T2DM patients and 11 healthy subjects. Patients were randomly allocated to either the Tai Chi or walking group to perform Dijia simplified 24-form Tai Chi or brisk walking (80-100 m/min), with 90 minutes each time, three times per week for 12 weeks, for a total of 36 sessions. The healthy group maintained daily living habits without intervention. Glycemic tests were conducted at the baseline and after 12 weeks. Serum and urine samples were collected for untargeted metabolomic analyses at baseline and 12 weeks to examine the differential metabolic profiles between T2DM and healthy subjects, and the metabolic alterations of T2DM patients before and after exercise therapy.

RESULTS

Compared to the healthy group, T2DM patients exhibited metabolic disturbances in carbohydrates (fructose, mannose, galactose, glycolysis/gluconeogenesis), lipids (inositol phosphate), and amino acids (arginine, proline, cysteine, methionine, valine, leucine, and isoleucine) metabolism, including 20 differential metabolites in the serum and six in the urine. After exercise, the glycemic results showed insignificant changes. However, patients who practiced Tai Chi showed significant improvements in their post-treatment metabolic profiles compared to baseline, with nine serum and six urine metabolites, including branch-chained amino acids (BCAAs); while those in the walking group had significantly altered nine serum and four urine metabolites concerning steroid hormone biosynthesis and arachidonic acid metabolism compared to baseline.

CONCLUSION

T2DM patients displayed impaired carbohydrate, lipid, and amino acid metabolism, and exercise therapy improved their metabolic health. Different modalities may act through different pathways. Tai Chi may improve disrupted BCAAs metabolism, whereas brisk walking mainly regulates steroid hormone biosynthesis and arachidonic acid metabolism.

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.

Circulating Sphingolipids in Insulin Resistance, Diabetes and Associated Complications

Sphingolipids play an important role in the development of diabetes, both type 1 and type 2 diabetes, as well as in the development of both micro- and macro-vascular complications. Several reviews have been published concerning the role of sphingolipids in diabetes but most of the emphasis has been on the possible mechanisms by which sphingolipids, mainly ceramides, contribute to the development of diabetes. Research on circulating levels of the different classes of sphingolipids in serum and in lipoproteins and their importance as biomarkers to predict not only the development of diabetes but also of its complications has only recently emerged and it is still in its infancy. This review summarizes the previously published literature concerning sphingolipid-mediated mechanisms involved in the development of diabetes and its complications, focusing on how circulating plasma sphingolipid levels and the relative content carried by the different lipoproteins may impact their role as possible biomarkers both in the development of diabetes and mainly in the development of diabetic complications. Further studies in this field may open new therapeutic avenues to prevent or arrest/reduce both the development of diabetes and progression of its complications.

Network Pharmacology- and Molecular Dynamics Simulation-Based Bioprospection of Aspalathus linearis for Type-2 Diabetes Care

The medicinal herb Aspalathus linearis (rooibos) is globally recognized in type-2 diabetes mellitus (T2DM) treatment due to its known and distinctive compounds. This work utilized network pharmacology (NP) coupled with molecular dynamics simulation in gaining new insight into the anti-diabetic molecular mechanism of action of rooibos teas. It looked at the interactions between rooibos constituents with various relevant protein receptors and signaling routes associated with T2DM progression. The initial analysis revealed 197 intersecting gene targets and 13 bioactive rooibos constituents linked to T2DM. The interactions between proteins and compounds to the target matrix were generated with the Cystoscope platform and STRING database. These analyses revealed intersecting nodes active in T2DM and hypoxia-inducible factor 1 (HIF-1) as an integral receptors target. In addition, KEGG analysis identified 11 other pathways besides the hub HIF-1 signaling route which may also be targeted in T2DM progression. In final molecular docking and dynamics simulation analysis, a significant binding affinity was confirmed for key compound-protein matrices. As such, the identified rooibos moieties could serve as putative drug candidates for T2DM control and therapy. This study shows rooibos constituents' interaction with T2DM-linked signaling pathways and target receptors and proposes vitexin, esculin and isovitexin as well as apigenin and kaempferol as respective pharmacologically active rooibos compounds for the modulation of EGFR and IGF1R in the HIF-1 signaling pathway to maintain normal homeostasis and function of the pancreas and pancreatic β-cells in diabetics.

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.

Type 2 Diabetes Mellitus Intersects With Pancreatic Cancer Diagnosis and Development

The relationship between type 2 diabetes mellitus (T2DM) and pancreatic cancer (PC) is complex. Diabetes is a known risk factor for PC, and new-onset diabetes (NOD) could be an early manifestation of PC that may be facilitate the early diagnosis of PC. Metformin offers a clear benefit of inhibiting PC, whereas insulin therapy may increase the risk of PC development. No evidence has shown that novel hypoglycemic drugs help or prevent PC. In this review, the effects of T2DM on PC development are summarized, and novel strategies for the prevention and treatment of T2DM and PC are discussed.

SSSPTA is essential for serine palmitoyltransferase function during development and hematopoiesis

Serine palmitoyltransferase complex (SPT) mediates the first and rate-limiting step in the de novo sphingolipid biosynthetic pathway. The larger subunits SPTLC1 and SPTLC2/SPTLC3 together form the catalytic core while a smaller third subunit either SSSPTA or SSSPTB has been shown to increase the catalytic efficiency and provide substrate specificity for the fatty acyl-CoA substrates. The in vivo biological significance of these smaller subunits in mammals is still unknown. Here, using two null mutants, a conditional null for ssSPTa and a null mutant for ssSPTb, we show that SSSPTA is essential for embryogenesis and mediates much of the known functions of the SPT complex in mammalian hematopoiesis. The ssSPTa null mutants are embryonic lethal at E6.5 much like the Sptlc1 and Sptlc2 null alleles. Mx1-Cre induced deletion of ssSPTa leads to lethality and myelopoietic defect. Chimeric and competitive bone marrow transplantation experiments show that the defect in myelopoiesis is accompanied by an expansion of the Lin⁻Sca1⁺c-Kit⁺ stem and progenitor compartment. Progenitor cells that fail to differentiate along the myeloid lineage display evidence of endoplasmic reticulum stress. On the other hand, ssSPTb null mice are homozygous viable, and analyses of the bone marrow cells show no significant difference in the proliferation and differentiation of the adult hematopoietic compartment. SPTLC1 is an obligatory subunit for the SPT function, and because Sptlc1^−/− and ssSPTa^−/− mice display similar defects during development and hematopoiesis, we conclude that an SPT complex that includes SSSPTA mediates much of its developmental and hematopoietic functions in a mammalian model.

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.

The Intersection of Serine Metabolism and Cellular Dysfunction in Retinal Degeneration

In the past, the importance of serine to pathologic or physiologic anomalies was inadequately addressed. Omics research has significantly advanced in the last two decades, and metabolomic data of various tissues has finally brought serine metabolism to the forefront of metabolic research, primarily for its varied role throughout the central nervous system. The retina is one of the most complex neuronal tissues with a multitude of functions. Although recent studies have highlighted the importance of free serine and its derivatives to retinal homeostasis, currently few reviews exist that comprehensively analyze the topic. Here, we address this gap by emphasizing how and why the de novo production and demand for serine is exceptionally elevated in the retina. Many basic physiological functions of the retina require serine. Serine-derived sphingolipids and phosphatidylserine for phagocytosis by the retinal pigment epithelium (RPE) and neuronal crosstalk of the inner retina via D-serine require proper serine metabolism. Moreover, serine is involved in sphingolipid–ceramide balance for both the outer retina and the RPE and the reductive currency generation for the RPE via serine biosynthesis. Finally and perhaps the most vital part of serine metabolism is free radical scavenging in the entire retina via serine-derived scavengers like glycine and GSH. It is hard to imagine that a single tissue could have such a broad and extensive dependency on serine homeostasis. Any dysregulation in serine mechanisms can result in a wide spectrum of retinopathies. Therefore, most critically, this review provides a strong argument for the exploration of serine-based clinical interventions for retinal pathologies.

Sphingosine-1-phosphate analog FTY720 reverses obesity but not age-induced anabolic resistance to muscle contraction

Sarcopenia, the age-associated loss of skeletal muscle mass and function, is coupled with declines in physical functioning leading to subsequent higher rates of disability, frailty, morbidity, and mortality. Aging and obesity independently contribute to muscle atrophy that is assumed to be a result of the activation of mutual physiological pathways. Understanding mechanisms contributing to the induction of skeletal muscle atrophy with aging and obesity is important for determining targets that may have pivotal roles in muscle loss in these conditions. We find that aging and obesity equally induce an anabolic resistance to acute skeletal muscle contraction as observed with decreases in anabolic signaling activation after contraction. Furthermore, treatment with the sphingosine-1-phosphate analog FTY720 for 4 wk increased lean mass and strength, and the anabolic signaling response to contraction was improved in obese but not older animals. To determine the role of chronic inflammation and different fatty acids on anabolic resistance in skeletal muscle cells, we overexpressed IKKβ with and without exposure to saturated fatty acid (SFA; palmitic acid), polyunsaturated fatty acid (eicosapentaenoic acid), and monounsaturated fatty acid (oleic acid). We found that IKKβ overexpression increased inflammation markers in muscle cells, and this chronic inflammation exacerbated anabolic resistance in response to SFA. Pretreatment with FTY720 reversed the inflammatory effects of palmitic acid in the muscle cells. Taken together, these data demonstrate chronic inflammation can induce anabolic resistance, SFA aggravates these effects, and FTY720 can reverse this by decreasing ceramide accumulation in skeletal muscle.

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

Adipose tissue lies at the heart of obesity, mediating its many effects upon the rest of the body, with its unique capacity to expand and regenerate, throughout the lifespan of the organism. Adipose is appreciated as an endocrine organ, with its myriad adipokines that elicit both physiological and pathological outcomes. Sphingolipids, bioactive signaling molecules, affect many aspects of obesity and the metabolic syndrome. While sphingolipids are appreciated in the context of these diseases in other tissues, there are many discoveries yet to be uncovered in the adipose tissue. This review focuses on the effects of sphingolipids on various aspects of adipose function and dysfunction. The processes of adipogenesis, metabolism and thermogenesis, in addition to inflammation and insulin resistance are intimately linked to sphingolipids as discussed below.