Ceramide concentrations in liver, plasma, and very low-density lipoproteins of humans with severe obesity.

We 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.

Adipocyte Proteins and Storage of Endogenous Fatty Acids in Visceral and Subcutaneous Adipose Tissue in Severe Obesity.

OBJECTIVE: This 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. METHODS: The day prior to surgery, 25 patients undergoing bariatric procedures received an infusion of autologous [1-14 C]triolein-labeled very low-density lipoprotein (VLDL) particles, and during surgery, they received a continuous [U-13 C]palmitate infusion/bolus [9,10-3 H]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. RESULTS: Storage 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. CONCLUSIONS: Adipose storage of VLDL-TG is predicted by VLDL-TG concentrations and LPL; FFA concentrations predict direct adipose tissue FFA storage rates.

Hepatic Fatty Acid Balance and Hepatic Fat Content in Humans With Severe Obesity.

OBJECTIVE: Nonalcoholic 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. DESIGN: We 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. RESULTS: Among 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). CONCLUSION: We 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.

Contribution of very low-density lipoprotein triglyceride fatty acids to postabsorptive free fatty acid flux in obese humans.

OBJECTIVE: In the fasting state, plasma free fatty acids (FFA) are thought to derive almost exclusively from adipose tissue lipolysis. However, there are mixed reports as to whether the spillover of fatty acids (FA) from very low-density lipoprotein triglyceride (VLDL-TG) hydrolysis contributes significantly to the plasma FFA pool. Because substantial VLDL-TG fatty acid spillover into the plasma FFA pool would profoundly impact the interpretation of isotope dilution measures of FFA flux, we investigated the contribution of VLDL-TG spillover to plasma FFA appearance. MATERIALS/METHODS: Eighteen obese adults (15 women) participated in these studies. Each volunteer received a primed, continuous infusion of their own ex-vivo labeled ([1-(14)C]triolein) VLDL-TG and a continuous infusion of [U-(13)C]oleate (8 nmol · kg fat free mass(-1) · min(-1)) to measure VLDL-TG and FFA rate of appearance (Ra), respectively. The presence of (14)C-oleate in the plasma FFA-oleate pool was used to calculate the contribution of spillover from VLDL-TG-oleate to the plasma FFA-oleate Ra. RESULTS: The spillover rate of VLDL-TG-oleate into plasma FFA-oleate was 6 ± 2 µmol/min (7% ± 2% of [(14)C]oleate from VLDL-TG) and FFA-oleate flux was 240 ± 61 µmol/min. Thus, only 3% ± 1% of total plasma FFA-oleate appearance could be accounted for by VLDL-TG spillover. CONCLUSION: The contribution of VLDL-TG spillover to the total plasma FFA pool is negligible and will not materially affect the interpretation of FFA flux measures as an index of adipose tissue lipolysis.

Pancreatic volume is reduced in adult patients with recently diagnosed type 1 diabetes.

CONTEXT: Pancreatic atrophy is common in longstanding type 1 diabetes, but there are limited data concerning pancreas size at diagnosis. OBJECTIVE: Our objective was to determine whether pancreatic size was reduced in patients with recently diagnosed type 1 diabetes and assess whether pancreatic volume was related to residual ß-cell function or islet autoantibodies. DESIGN AND SETTING: We conducted a controlled cohort study with strict inclusion criteria, recruiting from hospital diabetes clinics between 2007 and 2010. PATIENTS AND HEALTHY CONTROLS: Participants included 20 male adult patients (median age 27 yr) with recent-onset type 1 diabetes (median duration 3.8 months) and 24 male healthy controls (median age 27 yr). INTERVENTION: Interventions included noninvasive magnetic resonance imaging, collection of fasting blood samples, and glucagon stimulation testing in patients. MAIN OUTCOME MEASURES: We compared pancreatic volume estimates between patients with recent-onset type 1 diabetes and healthy controls as planned a priori. RESULTS: Scans were analyzed by an experienced radiologist blinded to diabetes status. Pancreatic volume correlated with body weight in patients and controls (P = 0.007). After adjustment for body weight, mean pancreatic volume index was 26% less in patients (1.19 ml/kg, se 0.07 ml/kg) than in controls (1.61 ml/kg, se 0.08 ml/kg) (P = 0.001). No correlation was seen between pancreatic volume index in patients and diabetes duration, glucose or C-peptide levels, glycated hemoglobin, and islet autoantibodies. CONCLUSIONS: Pancreatic volume is reduced by 26% in patients with type 1 diabetes within months of diagnosis, suggesting that atrophy begins years before the onset of clinical disease. Pancreatic atrophy within individuals is therefore a potential clinical marker of disease progression.