Temporal changes in sphingolipids and systemic insulin sensitivity during the transition from gestation to lactation

<div><p>Reduced insulin action develops naturally during the peripartum to ensure maternal nutrient delivery to the fetus and neonate. However, increased insulin resistance can facilitate excessive lipolysis which in turn promotes metabolic disease in overweight dairy cattle. Increased fatty acid availability favors the accumulation of the sphingolipid ceramide and is implicated in the pathogenesis of insulin resistance, however, the relationship between sphingolipid metabolism and insulin resistance during the peripartum remains largely unknown. Our objectives were to characterize temporal responses in plasma and tissue sphingolipids in lean and overweight peripartal cows and to establish the relationships between sphingolipid supply and lipolysis, hepatic lipid deposition, and systemic insulin action. Twenty-one multiparous lean and overweight Holstein cows were enrolled in a longitudinal study spanning the transition from gestation to lactation (d -21 to 21, relative to parturition). Plasma, liver, and skeletal muscle samples were obtained, and sphingolipids were profiled using LC/MS/MS. Insulin sensitivity was assessed utilizing intravenous insulin and glucose challenges. Our results demonstrated the following: first, insulin resistance develops postpartum concurrently with increased lipolysis and hepatic lipid accumulation; second, ceramides and glycosylated ceramides accumulate during the transition from gestation to lactation and are further elevated in overweight cows; third, ceramide accrual is associated with lipolysis and liver lipid accumulation, and C16:0- and C24:0-ceramide are inversely associated with systemic insulin sensitivity postpartum; fourth, plasma sphingomyelin, a potential source of ceramides reaches a nadir at parturition and is closely associated with feed intake; fifth, select sphingomyelins are lower in the plasma of overweight cows during the peripartal period. Our results demonstrate that dynamic changes occur in peripartal sphingolipids that are influenced by adiposity, and are associated with the onset of peripartal insulin resistance. These observations are in agreement with a putative potential role for sphingolipids in facilitating the physiological adaptations of peripartum.</p></div

Skeletal muscle content of C16:0-ceramide increases progressively during peripartum.

<p>(<b>A</b>) Ceramide profile of skeletal muscle (μg/mg of wet skeletal muscle), concentrations of (<b>B</b>) C16:0-ceramide, (<b>C</b>) C24:0-ceramide, and (<b>D</b>) total ceramide. Data are represented as least squares means and their standard errors. †, <i>P</i> < 0.10. Total ceramide was calculated by summation of C16:0-, C18:0-, C20:0-, C22:0-, C24:0-, and C26:0-ceramide.</p

Plasma ceramide content is quadratically associated with hepatic ceramide accumulation postpartum.

<p>Regression analysis of plasma and liver concentrations of (<b>A</b>) total and (<b>B</b>) C24:0-ceramide in lean and overweight dairy cows at d 4 postpartum. No associations were detected prepartum. Total ceramide was calculated by summation of C16:0-, C18:0-, C20:0-, C22:0-, C24:0-, C24:1-, and C26:0-ceramide.</p

Animal performance and metabolic responses during peripartum.

<p>Animal performance and metabolic responses during peripartum.</p

Plasma sphingomyelins decrease toward parturition and increase postpartum.

<p>Plasma concentrations (μg/mL) of (<b>A</b>) C16:0-, (<b>B</b>) C16:1-, (<b>C</b>) C18:0-, (<b>D</b>) C18:1-, (<b>E</b>) C20:0-, (<b>F</b>) C22:0-, (<b>G</b>) C24:0-, and (<b>H</b>) C24:1-sphingomyelin in lean and overweight peripartal dairy cows. Data are represented as least squares means and their standard errors. *, <i>P</i> < 0.05; †, <i>P</i> < 0.10.</p

Plasma ceramides are elevated in overweight cows during the transition from gestation to lactation.

<p>Peripartal plasma concentrations of (<b>A</b>) C16:0-, (<b>B</b>) C18:0-, (<b>C</b>) C20:0-, (<b>D</b>) C22:0-, (<b>E</b>) C24:0-ceramide, and (<b>F</b>) total ceramide in lean and overweight dairy cows. Data are represented as least squares means and their standard errors. *, <i>P</i> < 0.05; †, <i>P</i> < 0.10. Total ceramide was calculated by summation of C16:0-, C18:0-, C20:0-, C22:0-, C22:1-, C24:0-, and C26:0-ceramide.</p

Glycosylated ceramides increase during peripartum and are elevated in overweight cows.

<p>Peripartal plasma concentrations (ng/mL) of monohexosylceramides (GlcCer), and lactosylceramides (LacCer) in lean and overweight cows. Plasma (<b>A</b>) C16:0-GlcCer, (<b>B</b>) C24:0-GlcCer, (<b>C</b>) total GlcCer, (<b>D</b>) C16:0-LacCer, (<b>E</b>) C24:0-LacCer, and (<b>F</b>) total LacCer. Data are represented as least squares means and their standard errors. *, <i>P</i> < 0.05; †, <i>P</i> < 0.10. Total GlcCer was calculated by summation of C16:0-, C16:1-, C18:0-, C18:1-, C20:0-, C22:0-, C22:1-, C24:0-, C24:1-, and C26:0-GlcCer. Total LacCer was calculated by summation of C16:0-, C18:0-, C22:0-, C24:0-, and C24:1-LacCer.</p

Plasma sphingomyelins reach nadir at parturition.

<p>(<b>A</b>) Plasma profile of sphingomyelin and (<b>B</b>) peripartal changes of plasma total sphingomyelin in lean and overweight cows. Data are represented as least squares means and their standard errors. (<b>C</b>) Global changes in plasma sphingomyelins during peripartum. For visualization purposes, the heat map represents fold-change of log2 transformed data. The main effect of day relative to parturition was significant for all sphingolipids shown (<i>P</i> < 0.01). The main effect of adiposity (BCS) was significant for C20:1-sphingomyelin (<i>P</i> < 0.01). BCS × Day interaction significant for C18:1-sphingomyelin. DH: dihydro.</p

Total ceramide and C24:0-ceramide accumulate progressively in the liver of peripartal overweight cows.

<p>(<b>A</b>) Hepatic ceramide profile, and concentrations (μg/mg of wet liver) of (<b>B</b>) C16:0-, (<b>C</b>) C24:0-ceramide, and (<b>D</b>) total ceramide in peripartal lean and overweight cows. Data are represented as least squares means and their standard errors. *, <i>P</i> < 0.05; †, <i>P</i> < 0.10. Total ceramide was calculated by summation of C16:0-, C18:0-, C20:0-, C22:0-, C24:0-, C24:1-, and C26:0-ceramide.</p

Use of a Glycolipid Inhibitor to Ameliorate Renal Cancer in a Mouse Model

<div><p>In a xenograft model wherein, live renal cancer cells were implanted under the kidney capsule in mice, revealed a 30-fold increase in tumor volume over a period of 26 days and this was accompanied with a 32-fold increase in the level of lactosylceramide (LacCer). Mice fed D- threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP), an inhibitor of glucosylceramide synthase and lactosylceramide synthase (LCS: β-1,4-GalT-V), showed marked reduction in tumor volume. This was accompanied by a decrease in the mass of lactosylceramide and an increase in glucosylceramide (GlcCer) level. Mechanistic studies revealed that D-PDMP inhibited cell proliferation and angiogenesis by inhibiting p44MAPK, p-AKT-1 pathway and mammalian target for rapamycin (mTOR). By linking glycosphingolipid synthesis with tumor growth, renal cancer progression and regression can be evaluated. Thus inhibiting glycosphingolipid synthesis can be a bonafide target to prevent the progression of other types of cancer.</p></div