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PubMed1983

[Effect of short- or medium-chain fatty acids on cholesterol dynamics in the rat].

The effects of a diet consisting of 10% medium-chain triglycerides (C8:0, C10:0) or 10% homogeneous triglycerides of 6- to 14-carbon chain saturated fatty acids on cholesterol turnover processes were studied in rats using the isotope equilibrium method. Cholesterol absorption was not significantly affected by the type of dietary fatty acid ingested. In contrast, lengthening of the fatty acid chain caused a moderate increase in the rates of cholesterol secretion (internal and external) and of transformation into bile acids. Thus, cholesterol synthesis was 80% higher in rats fed trimyristin (25.7 mg/day) than in those receiving tricaproin (14.6 mg/day). This increase seems essentially due to stimulated liver cholesterogenesis, as shown by in vivo incorporation of 14C-acetate.

Animals↗
PubMed1976

Cholesterol dynamics in autoimmune hyperlipidemia.

A 69-year-old white male with autoimmune hyperlipidemia for 19 years characterized by high serum levels (1,5000 to 3,400 mg. per deciliter) of IgA firmly bound to very-low- and low-density lipoproteins (serum total cholesterol 852 +/- 51 mg./dl., free cholesterol 340 +/- 52, triglyceride 1638 +/- 411, phospholipid 934 +/- 84) received intravenously a tracer dose of cholesterol-4-14C. Serum cholesterol specific activity was followed for 337 days and analyzed by two methods: (1) compartmental analysis which revealed the best fit of a two-compartment model with rapidly exchangeable pool 710 gm. (2,563 per cent of the mean of 15 normal subjects), slowly exchangeable pool 317 gm. (651 per cent), mean transit time 92.5 days (167 per cent), turnover rate 9.23 gm. per day (654 per cent), and excretory coefficient 0.013 (25 per cent); (2) a simulated five-compartment model involving serum free, esterified, red blood cell, and rapidly and slowly exchangeable tissue cholesterols for which pool sizes of 17, 25, 2.4, 674, and 350 gm., respectively, were calculated and a turnover rate of 9.44 gm./day agreed well with that of the two-compartment model. The extreme hyperlipoproteinemia and expanded body cholesterol pools were primarily due to the impairment of feedback control of cholesterol synthesis as a consequence of the complexing of lipoprotein and IgA.

Aged↗
PubMed1996

Recent advances in membrane cholesterol domain dynamics and intracellular cholesterol trafficking.

Cholesterol is distributed nonrandomly in and between biological membranes. Despite over two decades' investigation of these phenomena, the origin, regulation, and function of membrane cholesterol asymmetry are not known. Likewise, although pathways of cellular cholesterol absorption/utilization as well as de novo synthesis have been investigated in depth, parallel progress in elucidating pathways of intracellular cholesterol trafficking and final deposition of cholesterol within membranes remains undefined. Understanding the nature and regulation of these processes is essential to resolving molecular mechanisms of cholesterol uptake, reverse cholesterol transport, steroidogenesis, and modulation of membrane function. Based on the fundamental observation that cholesterol is not distributed uniformly in the cell, three key concepts have contributed to recent advances in this field: First, cholesterol is asymmetrically distributed across the cell surface plasma membrane, wherein it translocates rapidly. Second, cholesterol is distributed within the plane of biomembrane bilayers into dynamic and static domains, with the latter predominating. The exact nature and physiological functions of such cholesterol domains or pools remain an enigma. Third, regulation of the size and kinetics of biomembrane cholesterol domains may be determining factors in intracellular cholesterol trafficking, targeting, and efflux. Contributions of both cytosolic carrier proteins and vesicular processes are recognized.

Animals↗
PubMed2004

Structure and cholesterol domain dynamics of an enriched caveolae/raft isolate.

Despite the importance of cholesterol in the formation and function of caveolar microdomains in plasma membranes, almost nothing is known regarding the structural properties, cholesterol dynamics or intracellular factors affecting caveolar cholesterol dynamics. A non-detergent method was employed to isolate caveolae/raft domains from purified plasma membranes of murine fibroblasts. A series of fluorescent lipid probe molecules or a fluorescent cholesterol analogue, dehydroergosterol, were then incorporated into the caveolae/raft domains to show that: (i) fluorescence polarization of the multiple probe molecules [diphenylhexatriene analogues, DiI18 (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), parinaric acids and NBD-stearic acid [12-(N-methyl)-N-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-octadecanoic acid] indicated that acyl chains in caveolae/raft domains were significantly less 'fluid' (i.e. more rigid) and the transbilayer 'fluidity gradient' was 4.4-fold greater than in plasma membranes; (ii) although sterol was more ordered in caveolae/raft domains than plasma membranes, spontaneous sterol transfer from caveolae/raft domains was faster (initial rate, 32%; half-time, t(1/2), 57%) than from the plasma membrane; (iii) although kinetic analysis showed similar proportions of exchangeable and non-exchangeable sterol pools in caveolae/raft domains and plasma membranes, addition of SCP-2 (sterol carrier protein-2) 1.3-fold more selectively increased sterol transfer from caveolae/raft domains by decreasing the t(1/2) (50%) and increasing the initial rate (5-fold); (iv) SCP-2 was also 2-fold more selective in decreasing the amount of non-exchangeable sterol in caveolae/raft domains compared with plasma membranes, such that nearly 80% of caveolar/raft sterol became exchangeable. In summary, although caveolae/raft lipids were less fluid than those of plasma membranes, sterol domains in caveolae/rafts were more spontaneously exchangeable and more affected by SCP-2 than those of the bulk plasma membranes. Thus caveolae/raft domains isolated without the use of detergents display unique structure, cholesterol domain kinetics and responsiveness to SCP-2 as compared with the parent plasma membrane.

Animals↗
PubMed1993

13C-NMR determination of the molecular dynamics of cholesterol in dimyristoylphosphatidylcholine vesicles.

Using 13C-NMR measurements of T1, T2 and the nuclear Overhauser enhancement factor at 50.32, 90.56 and 150.87 MHz, we have measured the dynamics of cholesterol in dimyristoylphosphatidylcholine (DMPC) vesicles from 28 to 50 degrees C. Using the model-free approach of Lipari and Szabo, we have found that at 37 degrees C the motion of the rigid steroid ring can be described by an equal contribution from two effective motions with correlation times of 63 and 0.85 ns. The C26 and C27 carbon atoms of cholesterol were found to have an effective correlation time of 8 +/- 2 ps and a value for the square of the generalised order parameter of 0.03 +/- 0.01. The corresponding values for the C25 carbon atom were 17 +/- 4 ps and 0.09 +/- 0.02, showing slower motion and greater order for this carbon atom, which is nearer to the rigid steroid ring. Apart from the effect of vesicle size on T2, no concentration dependence of the dynamics of cholesterol was detected over the cholesterol concentration range 2-30 mol%. The order parameters and correlation times from the present 13C-NMR experiments are shown to be compatible with those from 2H-NMR experiments. This establishes the validity of the present approach, which we are currently extending to low concentrations of cholesteryl oleate in DMPC vesicles.

Carbon Isotopes↗
PubMed2002

Anisotropic motion and molecular dynamics of cholesterol, lanosterol, and ergosterol in lecithin bilayers studied by quasi-elastic neutron scattering.

Quasi-elastic neutron scattering (QENS) was employed to study the molecular dynamics of three structurally related sterols, namely, cholesterol, lanosterol, and ergosterol. Oriented bilayers of dipalmitoylphosphatidylcholine (DPPC) were investigated at 40 mol % sterol content and at three temperatures (20, 36, and 50 degrees C) for two energy resolutions. Data analysis was concentrated on a direct comparison of the out-of-plane and the in-plane high-frequency motions of the three sterols in terms of their rates and amplitudes. The (spatially restricted) diffusive motion of the three sterols in the two directions was characterized by diffusion constants in the range of (5-30) x 10(-12) x m(2) x s(-1), with a significantly faster rate of diffusion along the membrane normal, resulting in a diffusional anisotropy, D(a). At low temperature (20 degrees C), cholesterol showed the highest value (D(a) = 4.5), while lanosterol gave the lowest one (D(a) = 2.0). At high temperature (50 degrees C), ergosterol diffusion had the highest diffusion anisotropy (D(a) = 2.0) compared to lanosterol (D(a) = 1.8) and cholesterol (D(a) = 1.6). Most interestingly, cholesterol showed at all three temperatures an amplitude of its out-of-plane-motion of 1.0-1.1 nm, more than a factor of 3 higher than measured for the other two sterols. This finding suggests that the short alkyl chain of the cholesterol molecule may cross at high frequency the bilayer midplane, while the other two sterols remain confined within the geometrical limits of each monolayer leaflet. The results provide an example of how slight structural alterations of sterols can affect their molecular dynamics in bilayers, which in turn may be relevant to the membrane micromechanical properties.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1982

Studies on the mechanism of antihypercholesterolemic action of soy protein and soy protein-type amino acid mixtures in relation to the casein counterparts in rats.

Given evidence of a hypocholesterolemic effect in rats, soy protein compared with casein showed the following effects on cholesterol dynamics: a) lower cholesterol absorption and greater fecal steroid excretion, b) more rapid turnover of serum cholesterol, c) a marked size reduction of the rapidly exchangeable cholesterol pool (pool A) through a significant increase in the removal rate in that compartment without influencing the production rate, and d) greater hepatic sterogenesis both in vitro and in vivo. In contrast, the amino acid mixture equivalent to soy protein compared with casein-type mixture showed: a) no effects on cholesterol absorption and fecal steroid excretion, b) no effects on the turnover of serum cholesterol, c) the reduction of pool A size as a result of decreased production, and d) the reduction of hepatic steroidogenesis in vitro, but not in vivo. These results indicate that decreased intestinal absorption of cholesterol, and increased fecal steroid excretion are primarily responsible for the antihypercholesterolemic effect of soy protein compared with casein. The fecal loss of steroids far outweighs the activation of hepatic steroidogenesis. In the case of the soy protein-type amino acid mixture, the depression of hepatic cholesterol synthesis seems accountable for reducing serum cholesterol levels.

Absorption↗
PubMed2005

Differences in the modulation of collective membrane motions by ergosterol, lanosterol, and cholesterol: a dynamic light scattering study.

A dynamic light scattering setup was used to study the undulations of freely suspended planar lipid bilayers, the so-called black lipid membranes, over a previously inaccessible range of frequency and wave number. A pure synthetic lecithin bilayer, 1,2-dielaidoyl-sn-3-glycero-phoshatidylcholine (DEPC), and binary mixtures of DEPC with 40 mol % of cholesterol, ergosterol, or lanosterol were studied. By analyzing the dynamic light scattering data (oscillation and damping curves) in terms of transverse shear motion, we extracted the lateral tension and surface viscosity of the composite bilayers for each sterol. Cholesterol gave the strongest increase in lateral tension (approximately sixfold) with respect to the DEPC control, followed by lanosterol (approximately twofold), and ergosterol (1.7-fold). Most interestingly, only cholesterol simultaneously altered the surface viscosity of the bilayer by almost two orders of magnitude, whereas the other two sterols did not affect this parameter. We interpret this unique behavior of cholesterol as a result of its previously established out-of-plane motion which allows the molecule to cross the bilayer midplane, thereby effectively coupling the bilayer leaflets to form a highly flexible but more stable composite membrane.

Anisotropy↗