Plasma folate levels are associated with the lipoprotein profile: a retrospective database analysis

BACKGROUND: Several studies demonstrated an association of homocysteine plasma levels and the plasma lipoprotein profile. This cross-sectional pilot study aimed at analyzing whether blood levels of the two important cofactors of homocysteine metabolism, folate and vitamin B12, coincide with the lipoprotein profile. METHODS: In a retrospective single center approach, we analyzed the laboratory database (2003-2006) of the University Hospital Bonn, Germany, including 1743 individuals, in whom vitamin B12, folate and at least one lipoprotein parameter had been determined by linear multilogistic regression. RESULTS: Higher folate serum levels were associated with lower serum levels of low density lipoprotein cholesterol (LDL-C; Beta = -0.164; p < 0.001), higher levels of high density lipoprotein cholesterol (HDL-C; Beta = 0.094; p = 0.021 for trend) and a lower LDL-C-C/HDL-C-ratio (Beta = -0.210; p < 0.001). Using ANOVA, we additionally compared the individuals of the highest with those of the lowest quartile of folate. Individuals of the highest folate quartile had higher levels of HDL-C (1.42 +/- 0.44 mmol/l vs. 1.26 +/- 0.47 mmol/l; p = 0.005), lower levels of LDL-C (3.21 +/- 1.04 mmol/l vs. 3.67 +/- 1.10 mmol/l; p = 0.001) and a lower LDL-C/HDL-C- ratio (2.47 +/- 1.18 vs. 3.77 +/- 5.29; p = 0.002). Vitamin B12 was not associated with the lipoprotein profile. CONCLUSION: In our study sample, high folate levels were associated with a favorable lipoprotein profile. A reconfirmation of these results in a different study population with a well defined status of health, diet and medication is warranted

Modulation of calcification of vascular smooth muscle cells in culture by calcium antagonists, statins, and their combination

Background Vascular calcification is an organized process in which vascular smooth muscle cells (VSMCs) are implicated primarily. The purpose of the present study was to assess the effects of calcium antagonists and statins on VSMC calcification in vitro. Methods VSMC calcification was stimulated by incubation in growth medium supplemented with 10 mmol/l β-glycerophosphate, 8 mmol/l CaCl2, 10 mmol/l sodium pyruvate, 1 μmol/l insulin, 50 μg/ml ascorbic acid, and 100 nmol/l dexamethasone (calcification medium). Calcification, proliferation, and apoptosis of VSMCs were quantified. Results Calcium deposition was stimulated dose-dependently by β-glycerophosphate, CaCl2, and ascorbic acid (all P < 0.01). Addition of amlodipine (0.01–1 μmol/l) to the calcification medium did not affect VSMC calcification. However, atorvastatin (2–50 μmol/l) stimulated calcium deposition dose-dependently. Combining treatments stimulated calcification to a degree similar to that observed with atorvastatin alone. Both atorvastatin and amlodipine inhibited VSMC proliferation at the highest concentration used. Only atorvastatin (50 μmol/l) induced considerable apoptosis of VSMCs. Conclusion In vitro calcification of VSMCs is not affected by amlodipine, but is stimulated by atorvastatin at concentrations ≥10 μmol/l, which could contribute to the plaque-stabilizing effect reported for statins

Triglyceride Blisters in Lipid Bilayers: Implications for Lipid Droplet Biogenesis and the Mobile Lipid Signal in Cancer Cell Membranes

Triglycerides have a limited solubility, around 3%, in phosphatidylcholine lipid bilayers. Using millisecond-scale course grained molecular dynamics simulations, we show that the model lipid bilayer can accommodate a higher concentration of triolein (TO) than earlier anticipated, by sequestering triolein molecules to the bilayer center in the form of a disordered, isotropic, mobile neutral lipid aggregate, at least 17 nm in diameter, which forms spontaneously, and remains stable on at least the microsecond time scale. The results give credence to the hotly debated existence of mobile neutral lipid aggregates of unknown function present in malignant cells, and to the early biogenesis of lipid droplets accommodated between the two leaflets of the endoplasmic reticulum membrane. The TO aggregates give the bilayer a blister-like appearance, and will hinder the formation of multi-lamellar phases in model, and possibly living membranes. The blisters will result in anomalous membrane probe partitioning, which should be accounted for in the interpretation of probe-related measurements

Estimating the size of laterally phase separated cholesterol domains in model membranes with Förster resonance energy transfer: A simulation study

In this work, we use two vertically-coupled square two-dimensional lattices to simulate membrane bilayers containing a uniform size distribution of cholesterol immiscible domains of a predetermined size distribution. We substitute cholesterols and phospholipids with their fluorescent analogs and calculate the efficiency of energy transfer as a function of acceptor concentration for four membrane configurations. The simulated efficiency of energy transfer as a function of acceptor concentration data is then fit with an analytical FRET model to estimate the domain size, in the same manner in which experimental FRET data is analyzed. The fitted model parameters (domain size and donor partition coefficient) are compared to the simulation inputs to test the applicability of the FRET model to estimating the size of laterally phase separated cholesterol domains. We show that the FRET model yields good size estimates for domains that range between 1 and 25nm. We also find that the assumed fluorophore configuration in the FRET model leads to a constant under-prediction of these values. Finally, we demonstrate that when two parameters are open to the fit, the FRET model adequately predicts the donor partition coefficient in addition to the domain size. © 2003 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex

Detection and characterization of laterally phase separated cholesterol domains in model lipid membranes

We present evidence that laterally phase separated cholesterol domains constitute a new, equilibrium phase in biological membranes. The domains are characterized in multi-lamellar vesicles (MLV) made of cholesterol and dimyristoylphosphatidylcholine (DMPC) but are also shown to exist in biologically relevant, egg lecithin systems containing a mixture of phospholipids. This work utilizes the fluorescent membrane probes 1-acyl-2-[12-[(5-dimethylamino-1-naphthalenesufonyl)amino]dodecanoyl]-sn- glycero-3-phosphocholine (DANSYL), and ergosta-5,7,9(11),22-tetraen-3β-ol (ERGO), which have been shown to be minimally invasive mimics of native membrane lipids. The highlight of the work is a heating-induced alleviation of a DANSYL blue shift at relatively high (but undersaturated) cholesterol loadings, which is reversible through at least three heating and cooling cycles. Comparison of the DANSYL spectral shifts with published DMPC-cholesterol phase diagrams shows unequivocally that the spectral results cannot be explained in terms of previously understood phase behavior. Rather, a lateral phase separation occurs within the vesicle bilayer, giving rise to cholesterol micro-domains. The cholesterol domains appear to coexist with, and should not be confused with, the well-known liquid-order phase that arises because of the cholesterol condensation effect. Additional studies involving ERGO-DANSYL energy transfer show a sequestration of probes within the bilayer, confirming the DANSYL spectral data, and a model that includes domains provides the best description of measured energy transfer efficiencies. Best fits of the energy transfer data, using a mathematical model developed to account for the presence of domains, indicates the domain size to be in the range 10-20 nm. © 2003 Elsevier Science B.V. All rights reserved.link_to_subscribed_fulltex

Aggregation kinetics of low density lipoproteins upon exposure to sphingomyelinase

The response-to-retention hypothesis in atherosclerosis states that subendothelial retention of cholesterol-rich, atherogenic lipoproteins is the central pathogenic event that is both necessary and sufficient to provoke lesion initiation in an otherwise normal artery. Sphingomyelinase-induced aggregation of low density lipoproteins (LDL) is known to facilitate LDL retention, and the only available measurements of LDL aggregates suggest LDL aggregate size is approximately 100 nm. This study investigates the hypothesis that LDL aggregate size is determined by the relative rates of sphingomyelinase hydrolysis and LDL collisions. Using a combination of dynamic light scattering and UV-vis absorbance spectroscopy to measure aggregation kinetics and particle sizes, a mass action model was developed to describe the aggregation process. It is found that LDL aggregation is sensitive to the relative amounts of sphingomyelinase and LDL and to pH. Model rate parameters were fit to experimental data in vitro and used to predict LDL aggregate sizes in vivo. The value of 100 nm in vivo does not appear to be fixed; rather, it is the value expected for the prevailing enzyme-to-LDL molar ratio. © 2004 Elsevier Inc. All rights reserved.link_to_subscribed_fulltex