Lipolysis generates platelet dysfunction after in vivo heparin administration

Heparin, when administered to patients undergoing operations using cardiopulmonary bypass, induces plasma changes that gradually impair platelet macroaggregation, but heparinization of whole blood in vitro does not have this effect. The plasma changes induced by heparin in vivo continue to progress in whole blood ex vivo. Heparin releases several endothelial proteins, including lipoprotein lipase, hepatic lipase, platelet factor-4 and superoxide dismutase. These enzymes, which remain active in plasma ex vivo, may impair platelet macroaggregation after in vivo heparinization and during cardiopulmonary bypass

Maternal obesity is associated with the formation of small dense LDL and hypoadiponectinemia in the third trimester

Context: Maternal obesity is associated with high plasma triglyceride, poor vascular function, and an increased risk for pregnancy complications. In normal-weight pregnant women, higher triglyceride is associated with increased small, dense low-density lipoprotein (LDL). Hypothesis: In obese pregnancy, increased plasma triglyceride concentrations result in triglyceride enrichment of very low-density lipoprotein-1 particles and formation of small dense LDL via lipoprotein lipase. Design: Women (n = 55) of body mass index of 18–46 kg/m2 were sampled longitudinally at 12, 26, and 35 weeks' gestation and 4 months postnatally. Setting: Women were recruited at hospital antenatal appointments, and study visits were in a clinical research suite. Outcome Measures: Plasma concentrations of lipids, triglyceride-rich lipoproteins, lipoprotein lipase mass, estradiol, steroid hormone binding globulin, insulin, glucose, leptin, and adiponectin were determined. Results: Obese women commenced pregnancy with higher plasma triglyceride, reached the same maximum, and then returned to higher postnatal levels than normal-weight women. Estradiol response to pregnancy (trimester 1–3 incremental area under the curve) was positively associated with plasma triglyceride response (r2 adjusted 25%, P < .001). In the third trimester, the proportion of small, dense LDL was 2-fold higher in obese women than normal-weight women [mean (SD) 40.7 (18.8) vs 21.9 (10.9)%, P = .014], and 35% of obese, 14% of overweight, and none of the normal-weight women displayed an atherogenic LDL subfraction phenotype. The small, dense LDL mass response to pregnancy was inversely associated with adiponectin response (17%, P = .013). Conclusions: Maternal obesity is associated with an atherogenic LDL subfraction phenotype and may provide a mechanistic link to poor vascular function and adverse pregnancy outcome

Lipoprotein-associated phospholipase A2 as a biomarker for coronary disease and stroke

Lipoprotein-associated phospholipase A2 (Lp-PLA2), also known as platelet-activating factor acetylhydrolase, is a plasma enzyme that circulates bound to lipoproteins. The association between Lp-PLA2 and atherosclerosis is ambiguous, as it can both degrade and generate potentially damaging vasoactive molecules. In this article, we speculate that Lp-PLA2 associated with HDL might have cardioprotective properties, whereas the same enzyme bound to LDL might contribute directly to atherosclerosis at all stages, from lipoprotein oxidation to endothelial dysfunction, and plaque initiation and growth. Genetic and animal model studies give varying indications as to the contribution of Lp-PLA2 to atherogenesis and tend to support the view that higher Lp-PLA2 levels are cardioprotective. By contrast, a series of population studies point clearly to a positive association between plasma Lp-PLA2 levels or activity levels and risk of coronary heart disease or stroke. Typically, people with Lp-PLA2 levels in the highest quintile of the population have about a twofold greater risk than those in the lowest quintile. It is, perhaps, too early to introduce Lp-PLA2 as a population-wide biomarker for coronary heart disease risk; however, with accumulating evidence, it might find a place in a stepwise risk assessment of individuals who require more aggressive intervention to prevent vascular disease

Apolipoproteins: metabolic role and clinical biochemistry applications

Lipoprotein metabolism is dependent on apolipoproteins, multifunctional proteins that serve as templates for the assembly of lipoprotein particles, maintain their structure and direct their metabolism through binding to membrane receptors and regulation of enzyme activity. The three principal functions of lipoproteins are contribution to interorgan fuel (triglyceride) distribution (by means of the fuel transport pathway), to the maintenance of the extracellular cholesterol pool (by means of the overflow pathway) and reverse cholesterol transport. The most important clinical application of apolipoprotein measurements in the plasma is in the assessment of cardiovascular risk. Concentrations of apolipoprotein B and apolipoprotein AI (and their ratio) seem to be better markers of cardiovascular risk than conventional markers such as total cholesterol and LDL-cholesterol. Apolipoprotein measurements are also better standardized than the conventional tests. We suggest that measurements of apolipoprotein AI and apolipoprotein B are included as a part of the specialist lipid profile. We also suggest that lipoprotein (a) should be measured as part of the initial assessment of dyslipidaemias because of its consistent association with cardiovascular risk. Genotyping of apolipoprotein E isoforms remains useful in the investigation of mixed dyslipidaemias. Lastly, the role of postprandial metabolism is increasingly recognized in the context of atherogenesis, obesity and diabetes. This requires better markers of chylomicrons, very-low-density lipoproteins and remnant particles. Measurements of apolipoprotein B48 and remnant lipoprotein cholesterol are currently the key tests in this emerging fiel

Effects of moderate exercise on VLDL1 and Intralipid kinetics in overweight/obese middle-aged men

Prior moderate exercise reduces plasma triglyceride (TG)-rich lipoprotein concentrations, mainly in the large very low-density lipoprotein (VLDL1) fraction, but the mechanism responsible is unclear. We investigated the effects of brisk walking on TG-rich lipoprotein kinetics using a novel method. Twelve overweight/obese middle-aged men underwent two kinetic studies, involving infusion of Intralipid to block VLDL1catabolism, in random order. On the afternoon prior to infusion, subjects either walked on a treadmill for 2 h at ∼50% maximal oxygen uptake or performed no exercise. Multiple blood samples were taken during and after infusion for separation of Intralipid (Sf400) and VLDL1(Sf60–400). VLDL1-TG and -apoB production rates were calculated from their linear rises during infusion; fractional catabolic rates (FCR) were calculated by dividing linear rises by fasting concentrations. Intralipid-TG FCR was determined from the postinfusion exponential decay. Exercise reduced fasting VLDL1-TG concentration by 30% ( P = 0.007) and increased TG enrichment of VLDL1particles [30% decrease in cholesteryl ester (CE)/TG ratio ( P = 0.007); 26% increase in TG/apoB ratio ( P = 0.059)]. Exercise also increased VLDL1-TG, VLDL1-apoB, and Intralipid-TG FCRs by 82, 146, and 43%, respectively (all P &lt; 0.05), but had no significant effect on VLDL1-TG or -apoB production rates. The exercise-induced increase in VLDL1-apoB FCR correlated strongly with the exercise-induced changes in VLDL1CE/TG ( r = −0.659, r = 0.020) and TG/apoB ( r = 0.785, P = 0.002) ratios. Thus, exercise-induced reductions in VLDL1concentrations are mediated by increased catabolism, rather than reduced production, which may be facilitated by compositional changes to VLDL1particles that increase their affinity for clearance from the circulation.</jats:p

Energy replacement attenuates the effects of prior moderate exercise on postprandial metabolism in overweight/obese men

&lt;i&gt;Background&lt;/i&gt;: The extent to which exercise-induced changes to postprandial metabolism are dependant on the associated energy deficit is not known. &lt;i&gt;Objective&lt;/i&gt;: To determine the effects of exercise, with and without energy replacement, on postprandial metabolism. &lt;i&gt;Design&lt;/i&gt;: Each subject underwent three 2-day trials in random order. On day 1 of each trial subjects rested (control), walked at 50% maximal oxygen uptake to induce a net energy expenditure of 27 kJ kg(-1) body mass (energy-deficit) or completed the same walk with the net energy expended replaced (energy-replacement). On day 2 subjects completed an 8.5-h metabolic assessment. For 3 days prior to day 2, subjects consumed an isocaloric diet, avoided planned exercise (apart from exercise interventions) and alcohol. &lt;i&gt;Subjects&lt;/i&gt;: A total of 13 overweight/obese men (age: 40 +/- 8 years, body mass index: 31.1 +/- 3.0 kg m(-2)). &lt;i&gt;Measurements&lt;/i&gt;: Postprandial triglyceride, insulin, glucose, non-esterified fatty acid and 3-hydroxybutyrate concentrations and substrate utilization rates were determined. &lt;i&gt;Results&lt;/i&gt;: Energy-deficit lowered postprandial triglyceride concentrations by 14 and 10% compared with control and energy-replacement (P lt 0.05 for both). Energy-deficit increased postprandial 3-hydroxybutyrate concentrations by 40 and 19% compared with control and energy-replacement (P lt 0.05 for both). Postprandial insulin concentrations were 18 and 10% lower for energy-deficit and energy-replacement compared with control and 10% lower for energy-deficit than energy-replacement (P lt 0.05 for all). Postprandial fat oxidation increased by 30 and 14% for energy-deficit and energy-replacement compared to control and was 12% higher for energy-deficit than energy-replacement (P lt 0.05 for all). &lt;i&gt;Conclusion&lt;/i&gt;: Exercise with energy replacement lowered postprandial insulinaemia and increased fat oxidation. However an exercise-induced energy deficit augmented these effects and was necessary to lower postprandial lipaemia

Physical activity, dietary intake and metabolic risk factors in non-diabetic daughters of patients with type II diabetes

Background. It has been reported that the offspring of patients with type II diabetes have an adverse metabolic risk profile. This study aimed to investigate the impact of habitual physical activity and diet on metabolic risk factors in the daughters of patients with type II diabetes and control subjects.&lt;p&gt;&lt;/p&gt; Methods. Thirty-nine offspring and 39 age- and sex-matched controls completed physical activity and food intake diaries, during the week preceding a fasting blood sample.&lt;p&gt;&lt;/p&gt; Results. The offspring had higher body mass index, percentage body fat, and waist circumference than the control subjects (all P &#60; 0.01). Fasting glucose and insulin, and insulin sensitivity estimated by the homeostasis model assessment (HOMAIR) method, were also higher in the offspring group (all P &#60; 0.01). Daily energy expenditure was lower (P &#60; 0.0001) in the offspring than control group. Dietary profile was not different between the groups. Daily energy expenditure was significantly correlated with waist circumference, fasting insulin, and HOMAIR (all P &#60; 0.05) in offspring but not controls.&lt;p&gt;&lt;/p&gt; Conclusions. Offspring had a less favourable physical and metabolic profile and were less physically active than control subjects. In offspring, central adiposity and metabolic risk factors were influenced by habitual physical activity to a greater degree than in control subjects.&lt;p&gt;&lt;/p&gt

Fractionation of cholesteryl ester rich intermediate density lipoprotein subpopulations by chondroitin sulphate

IDL is considered an atherogenic lipoprotein but little progress has been made on methods to subfractionate this density class. Furthermore, previous work suggests that lipoproteins retained by the arterial wall, of which chondoitin sulphate is the major arterial wall proteoglycan, are potentially atherogenic. The aim of this study was to assess the subfractionation of IDL particles using chondroitin sulphate (CS). Forty healthy subjects were recruited from laboratory staff and/or their partners. Fasted plasma samples were obtained and IDL (1.006 g/ml &#60; d &#60; 1.030 g/ml) was isolated. Approximately 1 mg protein of IDL was allowed to interact with CS. The unbound and bound IDL particles were eluted using a low salt and high salt buffer, respectively. On average 70% of IDL bound to CS ranging from 56 to 92%. Total, unbound and bound IDL particles were analysed for lipid composition and particle size. The unbound IDL particles were larger (32 nm) and triglyceride rich (40% versus 33%, P &#60; 0.01), whereas the bound IDL particles were smaller (26–28 nm) and cholesterol rich (21% versus 14%, P &#60; 0.01). The unbound particles contain at least double the amount of apo C-II and apo C-III per IDL particle compared with the bound IDL particles. There are specific IDL particles that bind to CS in vitro, these being the cholesterol rich IDL particles. It remains to be determined if these cholesterol rich IDL particles are potentially more atherogenic than the triglyceride rich IDL particles

Distinct patterns of heparin affinity chromatography VLDL1 and VLDL2 subfractions in the different dyslipidaemias

Very low density lipoprotein (VLDL) 1 and 2 were fractionated by heparin affinity chromatography into a bound and an unbound fraction and the different subtractions were quantified in 17 normolipidaemic (NL), 13 hypercholesterolaemic (HC), 10 hypertriglyceridaemic (HTG) and 11 combined hyperlipidaemic subjects (CHL). Unbound VLDL1 and VLDL2 were, respectively, 1.9- and 2.2-fold richer in triglycerides than bound VLDL1 and VLDL2. In HTG and CHL the concentration of all the VLDL subtractions was increased and plasma triglyceride level was correlated to unbound VLDL1 and to bound VLDL1 (respectively, r= 0.86 (p &lt; 0.001) and r= 0.77 (p &lt; 0.01) in HTG and r= 0.73 (p&lt;0.001) and r=0.62 (p&lt;0.05) in CHL). In HC unbound VLDL2 and bound VLDL2 concentration were increased compared to NL and in CHL, the concentration of bound VLDL2 was particularly increased (3.2-fold compared to NL (p&lt;0.001)). In both HC and CHL bound VLDL2 concentration was correlated to low density lipoprotein cholesterol (LDL-C) concentration (respectively, r=0.67 (P&lt;0.01) and r=0.62 (p &lt; 0.05)). In hypertriglyceridaemic states the intravascular accumulation of both unbound and bound VLDL1 appears as the determinant of plasma triglyceride concentration, whereas in moderately hypercholesterolaemic states the concentration of bound VLDL2 is strikingly correlated to LDL-C concentration, suggesting that these two species are linked metabolically, e.g. bound VLDL2 contain the precursor pool of LD

Lipoprotein-associated phospholipase A2 decreases oxidized lipoprotein cellular association by human macrophages and hepatocytes

We investigated whether the presence of endogenous or exogenous lipoprotein-associated phospholipase A2 (Lp-PLA2) can modify the cellular association of oxidized low density lipoprotein (oxLDL) and oxidized lipoprotein(a) (oxLp(a)) by human monocyte-derived macrophages (MDM) and hepatocytes (HepG2). Purified recombinant Lp-PLA2 was used as a source of exogenous enzyme whereas Pefabloc (serine esterase inhibitor) was used to inhibit the endogenous Lp-PLA2 activity associated with isolated lipoproteins. Cellular association studies were performed with Dil-labeled oxLDL or oxLp(a) and human monocyte-derived macrophages and HepG2 cells. Active Lp-PLA2 decreased the cellular association of oxLDL and oxLp(a) in macrophages and HepG2 cells by approximately 30-40%, whereas the inactive enzyme did not significantly change oxidized lipoprotein cellular association by either cell type. OxLDL pretreated by Pefabloc increased oxLDL cellular association by MDM and HepG2 cells compared to untreated oxLDL Therefore, unlike some lipases, Lp-PLA2 did not appear to have any catalytic independent function in oxLDL cellular association. To assess whether the reduced cellular association mediated by Lp-PLA2 was due to the hydrolysis of oxidized phosphatidylcholine (oxPC), we measured the concentration of lysophosphatidylcholine (lysoPC) in lipoprotein fractions after Lp-PLA2 treatment. LysoPC was increased by 20% (0.4 mu M) and 87% (0.7 mu M) by active Lp-PLA2 compared to inactive Lp-PLA2 for oxLDL and Lp(a), respectively. LysoPC at higher concentration dose-dependently increased the cellular association of oxLDL and oxLp(a) in MDM and HepG2 cells. We conclude that Lp-PLA2 mediates a decrease in oxidized lipoprotein cellular association in human macrophages and HepG2 cells by reducing the concentration of oxPC within these lipoproteins