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

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

Sphingosine-1-phosphate controls endothelial sphingolipid homeostasis via ORMDL

Disruption of sphingolipid homeostasis and signaling has been implicated in diabetes, cancer, cardiometabolic, and neurodegenerative disorders. Yet, mechanisms governing cellular sensing and regulation of sphingolipid homeostasis remain largely unknown. In yeast, serine palmitoyltransferase, catalyzing the first and rate-limiting step of sphingolipid de novo biosynthesis, is negatively regulated by Orm1 and 2. Lowering sphingolipids triggers Orms phosphorylation, upregulation of serine palmitoyltransferase activity and sphingolipid de novo biosynthesis. However, mammalian orthologs ORMDLs lack the N-terminus hosting the phosphosites. Thus, which sphingolipid(s) are sensed by the cells, and mechanisms of homeostasis remain largely unknown. Here, we identify sphingosine-1-phosphate (S1P) as key sphingolipid sensed by cells via S1PRs to maintain homeostasis. The increase in S1P-S1PR signaling stabilizes ORMDLs, restraining SPT activity. Mechanistically, the hydroxylation of ORMDLs at Pro137 allows a constitutive degradation of ORMDLs via ubiquitin-proteasome pathway, preserving SPT activity. Disrupting S1PR/ORMDL axis results in ceramide accrual, mitochondrial dysfunction, impaired signal transduction, all underlying endothelial dysfunction, early event in the onset of cardio- and cerebrovascular diseases. Our discovery may provide the molecular basis for therapeutic intervention restoring sphingolipid homeostasis.