Triay, Jessica

AbstractWe investigated the relationships between ceramide species concentrations in liver, plasma and very low‐density lipoproteins (VLDL) particles of humans with obesity as well as the relationships between hepatic fat content and hepatic ceramide concentrations and proportional distribution. Twenty‐five obese (body mass index >35 kg/m2) adults participated in this study. Plasma, VLDL and hepatocellular ceramide concentrations were measured by liquid chromatography/tandem mass spectrometry. The proportionate distribution of measured ceramide species differed between liver, whole plasma and the VLDL fraction. We found significant, positive correlations between the proportion of C14:0, C18:0, C20:0 and C24:1 ceramide in the liver and whole plasma (γ = 0.491, p = 0.013; γ = 0.573, p = 0.003; γ = 0.479, p = 0.015; γ = 0.716, p = 0.00006; respectively). In contrast, only the proportional contribution of C24:1 ceramide correlated positively between VLDL and liver (γ = 0.425, p = 0.013). The percent hepatic fat correlated positively with the proportion of C18:1, C18:0 and C20:0 hepatic ceramides (γ = 0.415, p = 0.039; γ = 0.426, p = 0.034; γ = 0.612, p = 0.001; respectively), but not with total hepatic ceramide concentration. The proportions of whole plasma ceramide subspecies, especially C14:0, C18:0, C20:0 and C24:1chain length, are reflective of those of hepatic ceramide subspecies in obese humans; these appear to be markers of hepatic ceramide species composition.

ObjectiveThis study tested whether substrate concentrations or fatty acid storage proteins predict storage of endogenous lipids in visceral adipose tissue (VAT) and upper body subcutaneous adipose tissue (UBSQ) fat.MethodsThe day prior to surgery, 25 patients undergoing bariatric procedures received an infusion of autologous [1‐14C]triolein‐labeled very low‐density lipoprotein (VLDL) particles, and during surgery, they received a continuous [U‐13C]palmitate infusion/bolus [9,10‐3H]palmitate tracer. VAT and UBSQ fat were collected to measure VLDL‐triglyceride (TG) storage, direct free fatty acid (FFA) storage rates, CD36 content, lipoprotein lipase (LPL), acyl‐CoA synthetase, diacylglycerol acetyl‐transferase, and glycerol‐3‐phosphate acyltransferase activities.ResultsStorage of VLDL‐TG and FFA‐palmitate in UBSQ and VAT was not different. Plasma palmitate concentrations correlated with palmitate storage rates in UBSQ and VAT (r = 0.46, P = 0.02 and r = 0.46, P = 0.02, respectively). In VAT, VLDL‐TG storage was correlated with VLDL concentrations (r = 0.53, P < 0.009) and LPL (r = 0.42, P < 0.05). In UBSQ, VLDL‐TG storage was correlated with LPL (r = 0.42, P < 0.05). CD36, acyl‐CoA synthetase, glycerol‐3‐phosphate acyltransferase, and diacylglycerol acetyl‐transferase were not correlated with VLDL‐TG or palmitate storage.ConclusionsAdipose storage of VLDL‐TG is predicted by VLDL‐TG concentrations and LPL; FFA concentrations predict direct adipose tissue FFA storage rates.

AbstractObjectiveNonalcoholic fatty liver disease can lead to hepatic inflammation/damage. Understanding the physiological mechanisms that contribute to excess hepatic lipid accumulation may help identify effective treatments.DesignWe recruited 25 nondiabetic patients with severe obesity scheduled for bariatric surgery. To evaluate liver export of triglyceride fatty acids, we measured very-low-density lipoprotein (VLDL)–triglyceride secretion rates the day prior to surgery using an infusion of autologous [1-14C]triolein-labeled VLDL particles. Ketone body response to fasting and intrahepatic long-chain acylcarnitine concentrations were used as indices of hepatic fatty acid oxidation. We measured intraoperative hepatic uptake rates of plasma free fatty acids using a continuous infusion of [U-13C]palmitate, combined with a bolus dose of [9,10-3H]palmitate and carefully timed liver biopsies. Total intrahepatic lipids were measured in liver biopsy samples to determine fatty liver status. The hepatic concentrations and enrichment from [U-13C]palmitate in diacylglycerols, sphingolipids, and acyl-carnitines were measured using liquid chromatography/tandem mass spectrometry.ResultsAmong study participants with fatty liver disease, intrahepatic lipid was negatively correlated with VLDL-triglyceride secretion rates (r = −0.92, P = 0.01) but unrelated to hepatic free fatty acid uptake or indices of hepatic fatty acid oxidation. VLDL-triglyceride secretion rates were positively correlated with hepatic concentrations of saturated diacylglycerol (r = 0.46, P = 0.02) and sphingosine-1-phosphate (r = 0.44, P = 0.03).ConclusionWe conclude that in nondiabetic humans with severe obesity, excess intrahepatic lipid is associated with limited export of triglyceride in VLDL particles rather than increased uptake of systemic free fatty acids.