BACKGROUND. Sphingolipids (SPs) are ubiquitous, structurally diverse molecules that include ceramides, sphingomyelins (SMs), and sphingosines. They are involved in various pathologies, including obesity and type 2 diabetes mellitus (T2DM). Therefore, it is likely that perturbations in plasma concentrations of SPs are associated with disease. Identifying these associations may reveal useful biomarkers or provide insight into disease processes. METHODS. We performed a lipidomics evaluation of molecularly distinct SPs in the plasma of 2302 ethnically Chinese Singaporeans using electrospray ionization mass spectrometry coupled with liquid chromatography. SP profiles were compared to clinical and biochemical characteristics, and subjects were evaluated with follow-up visits for 11 years. RESULTS. We found that ceramides correlated positively but hexosylceramides correlated negatively with BMI and homeostatic model assessment of insulin resistance (HOMA-IR). Furthermore, SPs with a d16:1 sphingoid backbone correlated more positively with BMI and HOMA-IR, while d18:2 SPs correlated less positively, relative to canonical d18:1 SPs. We also found that higher concentrations of 2 distinct SMs were associated with a higher risk of T2DM (HR 1.45 with 95% CI 1.18-1.78 for SM d16:1/18:0 and HR 1.40 with 95% CI 1.17-1.68 for SM d18:1/18:0). CONCLUSIONS. We identified significant associations between SPs and obesity/T2DM characteristics, specifically, those of hexosylceramides, d16:1 SPs, and d18:2 SPs. This suggests that the balance of SP metabolism, rather than ceramide accumulation, is associated with the pathology of obesity. We further identified 2 specific SPs that may represent prognostic biomarkers for T2DM.

Meibomian gland (MG) dysfunction is the leading cause of evaporative dry eye and it leads to inflammation of the ocular surface. Eicosanoids may be involved in inflammation of dry eye. This study aimed to profile tear eicosanoid levels in healthy individuals and those with MG dysfunction, and to examine if these levels are associated with clinical factors and expressibility of MG. Forty participants with MG dysfunction and 30 healthy controls were recruited in this study. Clinical signs of MG dysfunction were assessed, and tear lactoferrin concentration was evaluated. Tear eicosanoids were extracted from Schirmer’s strips and analyzed using mass spectrometry. We were able to quantify 38 tear eicosanoids and levels were increased in older individuals. In participants with MG dysfunction, higher 5-HETE, LTB4, 18-HEPE, 12-HEPE and 14-HDoHE were associated with poorer MG expressibility. The eicosanoids PGF2α, 18-HEPE, 20-HDoHE and 17-HDoHE were elevated with increased corneal staining; higher 5-HETE, LTB4 were associated with lower tear lactoferrin levels. The receiver-operating-characteristics analysis shows higher levels of 5-HETE, LTB4 and 18-HEPE were able to predict poor expressibility of MGs. In conclusion, tear eicosanoid levels are age-dependent and specific eicosanoids may be indicators of clinical obstruction of MG or the severity of ocular surface damage.

Highlights d Sphingolipids atlas of 21 tissues from C57BL/6 mice d Quantitative differences of sphingolipids across tissues d Sex-specific differences in the sphingolipidome of 21 mouse tissues d Effect of high-fat diet on the sphingolipidome

Lipids in breastmilk play a critical role in infant growth and development. However, few studies have investigated sources of variability of both high- and low-abundant milk lipids. The objective of our study was to investigate individual and morning–evening differences in the human milk lipidome. In this study, a modified two-phase method (MTBE: Methanol 7:2) was validated for the extraction of lipids from human breastmilk. This method was then applied to samples from a group of 20 healthy women to measure inter- and intra-individual (morning versus evening) variability of the breastmilk lipidome. We report here the levels of 237 lipid species from 13 sub-classes using reversed-phase liquid chromatography mass spectrometry (RP-LCMS) and direct-infusion mass spectrometry (DI-MS). About 85% of lipid species showed stable inter-individual differences across time points. Half of lipid species showed higher concentrations in the evening compared with the morning, with phosphatidylethanolamines (PEs) and triacylglycerols (TAGs) exhibiting the largest changes. In morning and evening samples, the biological variation was greater for diacylglycerols (DAGs) and TAGs compared with phospholipids and sphingolipids, and the variation in DAGs and TAGs was greater in evening samples compared with morning samples. These results demonstrate that variation in the milk lipidome is strongly influenced by individual differences and time of day.

Background Lipids play a vital role in health and disease, but changes to their circulating levels and the link with obesity remain poorly characterized in expecting mothers and their offspring in early childhood. Methods LC-MS/MS-based quantitation of 480 lipid species was performed on 2491 plasma samples collected at 4 time points in the mother-offspring Asian cohort GUSTO (Growing Up in Singapore Towards healthy Outcomes). These 4 time points constituted samples collected from mothers at 26–28 weeks of gestation (n=752) and 4–5 years postpartum (n=650), and their offspring at birth (n=751) and 6 years of age (n=338). Linear regression models were used to identify the pregnancy and developmental age-specific variations in the plasma lipidomic profiles, and their association with obesity risk. An independent birth cohort (n=1935), the Barwon Infant Study (BIS), comprising mother-offspring dyads of Caucasian origin was used for validation. Results Levels of 36% of the profiled lipids were significantly higher (absolute fold change > 1.5 and Padj < 0.05) in antenatal maternal circulation as compared to the postnatal phase, with phosphatidylethanolamine levels changing the most. Compared to antenatal maternal lipids, cord blood showed lower concentrations of most lipid species (79%) except lysophospholipids and acylcarnitines. Changes in lipid concentrations from birth to 6 years of age were much higher in magnitude (log2FC=−2.10 to 6.25) than the changes observed between a 6-year-old child and an adult (postnatal mother) (log2FC=−0.68 to 1.18). Associations of cord blood lipidomic profiles with birth weight displayed distinct trends compared to the lipidomic profiles associated with child BMI at 6 years. Comparison of the results between the child and adult BMI identified similarities in association with consistent trends (R2=0.75). However, large number of lipids were associated with BMI in adults (67%) compared to the children (29%). Pre-pregnancy BMI was specifically associated with decrease in the levels of phospholipids, sphingomyelin, and several triacylglycerol species in pregnancy. Conclusions In summary, our study provides a detailed landscape of the in utero lipid environment provided by the gestating mother to the growing fetus, and the magnitude of changes in plasma lipidomic profiles from birth to early childhood. We identified the effects of adiposity on the circulating lipid levels in pregnant and non-pregnant women as well as offspring at birth and at 6 years of age. Additionally, the pediatric vs maternal overlap of the circulating lipid phenotype of obesity risk provides intergenerational insights and early opportunities to track and intervene the onset of metabolic adversities. Clinical trial registration This birth cohort is a prospective observational study, which was registered on 1 July 2010 under the identifier NCT01174875.