Effects of meal ingestion on intramyocellular ceramide concentrations and fractional de novo synthesis in humans

Abstract

We investigated the effects of meal ingestion on intramyofibrillar (IMF) and subsarcolemmal (SS) ceramide metabolism in volunteers ranging from lean to obese. Thirty-eight women and men underwent a steady-state meal ingestion protocol that included a 6.5-h infusion of [U-¹³C]palmitate and muscle biopsies 1.5 and 6.5 h after starting the tracer infusion. We measured IMF and SS sphingolipid concentrations and the contribution of plasma palmitate to intramyocellular C16:0 ceramide by use of LC-MS-MS. In response to meal ingestion SS C24 ceramide concentrations, but not C14-C20 concentrations, increased significantly. IMF ceramide concentrations did not change. The increases in SS C24 ceramides were negatively related to parameters of insulin resistance. The fractional contribution of plasma palmitate to intramyocellular C16:0 ceramides in both IMF and SS fractions was inversely related to overweight status (β = -0.432, P = 0.0095 and β = -0.443, P = 0.0058, respectively). These data indicate that meal ingestion has differing effects on SS ceramide subspecies and suggest that the fractional de novo synthesis of intramyocellular ceramide from plasma palmitate in the postprandial condition is reduced in those who are overweight.

Keywords: insulin resistance; isotopic tracers; meals; obesity; skeletal muscle.

Fig. 1.

Schematic study design. Time denotes clock time. FFM, fat-free mass.

Fig. 2.

Relationships between metabolic parameters and the postprandial changes of intramyocellular very-long-chain ceramide species concentrations. A: correlation between postprandial insulin concentration and the change in subsarcolemmal (SS) C24:0 ceramide concentration (ρ = –0.553, P = 0.0004). B: correlation between fasting insulin concentration and the change in SS C24:0 ceramide concentration (ρ = –0.430, P = 0.0078). C: correlation between postprandial insulin concentration and the change in SS C24:1 ceramide concentration (ρ = –0.463, P = 0.0039). D: correlation between plasma HDL-cholesterol concentration and the change in SS C24:1 ceramide concentration (ρ = 0.434, P = 0.0072). ρ represents the Spearman’s rank correlation coefficient. Intramyocellular ceramide concentrations are normalized to per milligram of protein. The change (Δ) in intramyocellular ceramide concentrations was calculated as the data from the second biopsy minus that from the first biopsy.

Fig. 3.

Relationships between metabolic parameters and the postprandial changes of intramyocellular very-long-chain ceramide species concentrations. A: correlation between body mass index (BMI) and the change in SS C24:0 ceramide concentration (ρ = –0.439, P = 0.0065). B: correlation between visceral fat mass and the change in SS C24:0 ceramide concentration (ρ = –0.543, P = 0.0005). C: correlation between BMI and the change in SS C24:1 ceramide concentration (ρ = –0.461, P = 0.0041). D: correlation between visceral fat mass and the change in SS C24:1 ceramide concentration (ρ = –0.545, P = 0.0005). ρ represents the Spearman’s rank correlation coefficient. Intramyocellular ceramide concentrations are normalized to per milligram of protein. The change (Δ) in intramyocellular ceramide concentrations was calculated as the data from the second biopsy minus that from the first biopsy.

Fig. 4.

Relationships between body fat and the fractional contribution of plasma palmitate to intramyocellular ¹³C₁₆ 16:0 ceramide. A: correlation between BMI and fractional contribution of plasma palmitate to 16C-ceramide in intramyofibrillar (IMF) fraction (γ = –0.432, P = 0.010). B: correlation between BMI and fractional contribution of plasma palmitate to 16C-ceramide in SS fraction (γ = –0.417, P = 0.014).

Fig. 5.

Proposed ceramide regulations in intramyocellular SS fraction during meal ingestion. In postprandial conditions, there are differing effects on SS ceramide subspecies, and the de novo synthesis of intramyocellular ceramides from plasma palmitate is reduced in the overweight condition.