Lipoprotein separation in a novel iodixanol density gradient, for composition, density, and phenotype analysis.

Separation of lipoproteins by traditional sequential salt density floatation is a prolonged process ( approximately 72 h) with variable recovery, whereas iodixanol-based, self-generating density gradients provide a rapid ( approximately 4 h) alternative. A novel, three-layered iodixanol gradient was evaluated for its ability to separate lipoprotein fractions in 63 subjects with varying degrees of dyslipidemia. Lipoprotein cholesterol, triglycerides, and apolipoproteins were measured in 21 successive iodixanol density fractions. Iodixanol fractionation was compared with sequential floatation ultracentrifugation. Iodixanol gradient formation showed a coefficient of variation of 0.29% and total lipid recovery from the gradient of 95.4% for cholesterol and 84.7% for triglyceride. Recoveries for VLDL-, LDL-, and HDL-cholesterol, triglycerides, and apolipoproteins were approximately 10% higher with iodixanol compared with sequential floatation. The iodixanol gradient effectively discriminated classic lipoproteins and their subfractions, and there was evidence for improved resolution of lipoproteins with the iodixanol gradient. LDL particles subfractionated by the gradient showed good correlation between density and particle size with small, dense LDL (<25.5 nm) separated in fractions with density >1.028 g/dl. The new iodixanol density gradient enabled rapid separation with improved resolution and recovery of all lipoproteins and their subfractions, providing important information with regard to LDL phenotype from a single centrifugation step with minimal in-vitro modification of lipoproteins.

Sustained endogenous glucose production, diminished lipolysis and non-esterified fatty acid appearance and oxidation in non-obese women at high risk of type 2 diabetes.

OBJECTIVE: To evaluate early defects in glucose production, lipolysis and fatty acid oxidation in non-obese, normally glucose tolerant women, who are nevertheless at risk of type 2 diabetes. METHODS: Ten women with previous gestational diabetes (pGDM) and ten controls were studied in two 4 h infusions of stable isotopes 6,6-(2)H(2)-glucose, 1-(13)C-palmitate, and 1,1,2,3,3-(2)H(5)-glycerol with and without infusion of adrenaline. Fatty acid oxidation was quantified using indirect calorimetry and (13)CO(2) measurements. Insulin sensitivity was evaluated using the short insulin tolerance test. RESULTS: The pGDM and control women were non-obese and carefully matched for body mass index and fat mass. Whole body insulin sensitivity and basal insulin concentrations did not differ significantly but basal glucose concentrations were increased in women with pGDM. During a 0.9% saline infusion, glucose appearance was not significantly different at the first (90-120 min) and second (210-240 min) steady states. However, glucose appearance decreased in controls but was maintained in the pGDM women (-0.33 +/- 0.02 vs -0.03 +/- 0.08 mg/kg per min; P = 0.004). Basal glycerol appearance (0.27 +/- 0.02 vs 0.38 +/- 0.03 mg/kg per min; P = 0.02), palmitate appearance (0.74 +/- 0.09 vs 1.05 +/- 0.09 mg/kg per min; P = 0.03) and palmitate oxidation (0.07 +/- 0.01 vs 0.10 +/- 0.01 mg/kg per min; P = 0.03) were lower in the pGDM women. During the adrenaline infusion, changes in glucose, glycerol and palmitate concentrations and kinetics were similar in both groups. CONCLUSIONS: Sustained glucose production during fasting is an early abnormality in non-obese subjects at risk of type 2 diabetes. Lipolysis and non-esterified fatty acid appearance and oxidation are diminished, suggesting an increased tendency to store fat. The observations are not readily attributable to differences in insulin or catecholamine sensitivity.

Effects of short- and long-term growth hormone replacement on lipoprotein composition and on very-low-density lipoprotein and low-density lipoprotein apolipoprotein B100 kinetics in growth hormone-deficient hypopituitary subjects.

In this study, we concurrently examined the effects of 8 and 40 weeks of growth hormone replacement (GHR) on lipids, lipoprotein composition, low-density lipoprotein (LDL) size, very-low-density lipoprotein (VLDL) apolipoprotein (apo)B kinetics and LDL apoB kinetics. Eight weeks of GHR did not alter lipid profiles. Forty weeks of GHR increased high-density lipoprotein-cholesterol (HDL-C) concentration (P =.01), nonsignificantly reduced LDL-C (P =.06), and reduced the HDL/LDL-C ratio (P =.04). Forty weeks of GHR increased HDL free cholesterol (P =.03), total cholesterol (P =.01), and cholesterol ester (P <.01) concentrations. No other significant changes in VLDL, LDL, or HDL composition or LDL size were noted at any time. Eight weeks of GHR reduced VLDL apoB absolute secretion rate (ASR, P =.03), with nonsignificant reductions in fractional secretion rate (FSR, P =.09) and pool size (P =.09). After 40 weeks of GHR, the VLDL apoB ASR, FSR, and pool size were not significantly different from baseline. Forty weeks of GHR increased both LDL apoB FSR (P =.02) and LDL apoB ASR (P =.04), with a small decrease in pool size. Thus, GHR may have important antiatherogenic effects; HDL-C increased, LDL-C was nonsignificantly reduced, the total/HDL-C ratio was reduced, VLDL apoB production was reduced, and LDL apoB turnover was increased.