Biomedical subjects

E Prenner

Publications and source records attributed to E Prenner.

8 recordsLinked to original sources

PubMed2000

Lateral microheterogeneity of diphenylhexatriene-labeled choline phospholipids in the erythrocyte ghost membrane as determined by time-resolved fluorescence spectroscopy.

Choline phospholipids are the major constituents of the outer layer of the erythrocyte membrane. To investigate their lateral membrane organization we determined the fluorescence lifetime properties of diphenylhexatriene analogues of phosphatidylcholine, choline plasmalogen, (the respective enolether derivative), and sphingomyelin inserted into the outer layer of hemoglobin-free ghosts. Fluorescence lifetimes were recorded by time-resolved phase and modulation fluorometry and analyzed in terms of Continuous Lorentzian distributions. To assess the influence of membrane proteins on the fluorescence lifetime of the labeled lipids in the biomembrane, lipid vesicles were used as controls. In general, the lifetime distributions in the ghost membranes are broad compared to vesicles. Phosphatidylcholine and sphingomyelin exhibit very similar lifetime distributions in contrast to an increased plasmalogen lifetime heterogeneity in both systems. Orientational effects of side chain mobilities on the observed lifetimes can be excluded. Fluorescence anisotropies revealed identical values for all three labeled phospholipids in the biomembrane.

Choline↗

PubMed1994

Reversible reduction of phospholipid bound arachidonic acid after low density lipoprotein apheresis. Evidence for rapid incorporation of plasmalogen phosphatidylethanolamine into the red blood cell membrane.

In order to evaluate whether acute changes in fatty acids bound to phospholipids in plasma are transmitted into red blood cell membrane (RBCM) phospholipids, molecular species of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were analyzed after reduction of apo B containing lipoproteins through low density lipoprotein (LDL) apheresis in patients with severe hypercholesterolemia. As compared to the control, increases and decreases in molecular species with arachidonic acid (20:4) and with linoleic acid (18:2), respectively, at sn-2 of plasma diacyl-PC were seen in the patients before the apheresis. Directly after the procedure, the sum of species of plasma and RBCM PC plus PE with 20:4 were reduced. Two days after apheresis major species of plasma diacyl-PC reapproached preapheresis values while, in contrast, the composition of plasma alkenylacyl(plasmalogen)-PE was distinctly altered. In plasmalogen-PE of RBCM similar modifications were induced by the apheresis as in the same subgroup in plasma. In vitro experiments using vesicles with plasmalogen-PE labeled at sn-2 with either [14C]20:4 or a fluorescent pyrenedecanoyl residue indicated fast incorporation of the subgroup into the RBCM. In contrast, diacyl-PE was not taken up by the RBCM. In conclusion, apo B containing lipoproteins are partially responsible for the supply of phospholipids with arachidonic acid to RBCM, in particular by means of the fast incorporation of plasmalogen-PE. The transmission of changes induced by apheresis in plasma into those of the RBCM suggest that erythrocytes play an important role in the homeostasis of fatty acids bound to plasma phospholipids in vivo.

Arachidonic Acid↗

PubMed1994

Phase behavior of the antineoplastic ether lipid 1-O-octadecyl-2-O-methyl-glycero-3-phosphochloline.

The physicochemical properties of the antineoplastic etherphospholipid 1-O-octadecyl-2-O-methyl-glycero-3-phosphochline were examined in the concentration range 1-35% (w/w) lipid, as a function of temperature (range -10 degrees C to 40 degrees C) and of different aqueous solvents by dynamic light scattering, small- and wide-angle X-ray scattering, differential scanning calorimetry and ultrasonic speed measurements. On cooling the lipid dispersion undergoes a phase transition near 6 degrees C, transforming slowly from a micellar into a lamellar gel phase with interdigitating hydrocarbon chains. The lamellar repeat distance is nearly constant over the hydration range 65-90% buffer (d = 5.09-5.14 nm). The size of the micelles in terms of the hydrodynamic radius is 3.8 +/- 0.1 nm, the polydispersity is low. Their average shape is spherical. The electron density distribution across the micelle gives 2.5 nm for the extension of the hydrocarbon chains and 1.5 nm for the polar moiety. The existence of micelles was verified up to a concentration of 35% lipid. Throughout this concentration range size and shape do not change significantly. The kinetics of formation of the low-temperature phase is slow on cooling, increasing with increasing concentration. Upon heating the phase behavior shows a hysteresis. The extended lamellar organizations start to break down into smaller aggregates near 3 degrees C. The micellar phase is reformed near 20 degrees C.

Antineoplastic Agents↗

PubMed1994

Apoprotein-phospholipid interactions in Lp(a).

Lipoprotein (a) (Lp(a)) and low-density lipoprotein (LDL) are structurally related to each other. Both exhibit identical phospholipid compositions and possess one molecule of apoprotein B-100 (apoB). Lp(a) contains, in addition, apoprotein (a) (apo(a)), which localizes to the particle surface and interacts with the apoB component by non-covalent and covalent forces. Protein-protein interaction is probably interrelated with protein-lipid interaction. Fluorescent analogs of phosphatidylcholine and sphingomyelin were inserted into the surface layer of LDL and Lp(a). The obtained fluorescence data reflecting mobility and distributional heterogeneity of the labeled lipids provided evidence that apo-proteins discriminate between choline phospholipids and preferentially associate with phosphatidylcholine. This effect is enhanced in Lp(a) because of the presence of apolipoprotein (a). Higher affinity for Lp(a) as compared with LDL was also observed with a fluorescent diether analog of phosphatidylcholine in native serum. In contrast, the time-dependent transfer of the same lipid into Lp(a) was slower compared with LDL, probably as a consequence of the more rigid surface of the former lipoprotein.

Apolipoproteins↗

PubMed1993

Inequivalence of fluorescent choline and ethanolamine phospholipids in the erythrocyte membrane: fluorescence lifetime determination in the frequency and time domain.

The fluorescence decay of 1-palmitoyl-2-diphenyl-hexatrienyl-propionyl-sn-glycero-3-phosphocholine and the respective ethanolamine derivative were determined in human erythrocyte ghost membranes by phase and modulation fluorometry. The obtained bimodal distribution decay model could independently be confirmed by pulse fluorometry and data analysis by the exponential series method. Distributional widths of labeled choline and ethanolamine phospholipids were different in ghost membranes but identical in phospholipid vesicles. Thus, it is concluded that both lipid classes containing the same fluorophore experience environments of different heterogeneity in the biological system.

Erythrocyte Membrane↗

PubMed1992

Organization of phosphatidylcholine and sphingomyelin in the surface monolayer of low density lipoprotein and lipoprotein(a) as determined by time-resolved fluorometry.

Fluorescent analogs of phosphatidylcholine (PC) and sphingomyelin (SM) labeled with diphenylhexatrienylpropionic acid (DPH) were prepared and incorporated into the surface layer of human low density lipoprotein (LDL) and lipoprotein(a) (Lp(a)). Fluorescence anisotropy measurements of DPH-PC and DPH-SM in both lipoprotein classes were carried out at different temperatures ranging from 20 to 37 degrees C. DPH-PC as well as DPH-SM were shown to reside in more rigid domains in Lp(a) than in LDL according to higher anisotropy values in Lp(a). In both LDL and Lp(a), DPH-PC experienced a more rigid environment than DPH-SM, suggesting different environments of PC and SM in the surface shell of the lipoproteins. Fluorescence lifetimes of the labeled lipoproteins were determined by phase and modulation fluorometry. We found bimodal Lorentzian distributions for the decay times of DPH-PC and DPH-SM in LDL and Lp(a). Lifetime distribution centers for labeled lipids were very similar except for DPH-PC in Lp(a) which was shifted to longer lifetimes, suggesting a less polar environment of PC in Lp(a) than in LDL. The distributional width of DPH-PC in Lp(a) was broader than in LDL. Accordingly, phosphatidylcholine must be localized in a more homogeneous environment in LDL as compared with Lp(a). On the other hand, no difference in distributional widths was observed for DPH-SM in both lipoproteins, showing that SM organization in Lp(a) is unaffected by apo(a). From the obtained fluorescence data we propose that apoproteins discriminate between the choline phospholipids and preferentially associate with phosphatidylcholine. This effect is enhanced in Lp(a) due to the presence of apolipoprotein(a).

Fluorescence Polarization↗

PubMed1991

Platelet membrane fluidity in type IIA, type IIB and type IV hyperlipoproteinemia.

Fluorescence spectroscopy, a very sensitive index for measuring the biophysical properties of living cell systems, was used to examine the structural order of intact, resting, gel-filtered platelets from hyperlipidemic subjects (n = 48, 25-70 years) and normolipemic subjects (n = 34, 19-68 years). Fluorescence anisotropy (r[s]), which is inversely related to membrane fluidity, was estimated using 3 different fluorescent dyes, DPH, TMA-DPH, and 6-AS, known to label different regions of biological membranes. Increased membrane fluidity was observed in type IIB (n = 24, 36-62 yrs; r[s] = 0.0692 +/- 0.09) and type IV (n = 10, 33-57 yrs; r[s] = 0.058 +/- 0.006) hyperlipidemics in comparison to type IIA (n = 14, 25-70 yrs; r[s] = 0.086 +/- 0.019) and control subjects (n = 24, 28-68 yrs; r[s] = 0.079 +/- 0.012). The temperature dependency of r[s]-DPH values was significantly different (P less than 0.01) in platelets from type IIB and type IV patients compared to type IIA and control subjects of similar age. A significant positive correlation (P less than 0.005) between membrane fluidity and age was found only in healthy control subjects (n = 34, 19-68 yrs). Despite significant (P less than 0.01) differences in plasma lipid concentrations in hyperlipidemic patients and controls, significant ex vivo relations between membrane fluidity and lipoprotein concentrations, free fatty acid distribution, and increased age were found only in healthy control subjects. Plasma levels of thromboxane as well as serum selenium concentrations did not significantly differ between hypercholesterolemic, hypertriglyceridemic, and control subjects.

Adult↗

PubMed1991

Effects of dietary fish oil supplementation on platelet aggregability and platelet membrane fluidity in normolipemic subjects with and without high plasma Lp(a) concentrations.

The purpose of this study was to compare the relative effect of n-3 fatty acids on plasma lipids and platelet function in normolipemic subjects (n = 8) with plasma Lp(a) levels greater than 30 mg/dl and normolipemic subjects (n = 7) without detectable plasma Lp(a) concentrations. Six weeks of dietary supplementation (3.8 g EPA and 2.9 g DHA/d) significantly reduced (P less than 0.005) plasma TGs in both groups whereas no changes of plasma TC, LDL-C, HDL-C, and Lp(a), respectively, were found. Collagen- or thrombin-stimulated platelet aggregation and collagen- or thrombin-induced TXB2 generation from platelets decreased by approx. 45% in Lp(a)-negative and Lp(a)-positive platelet donors after a 6 week dietary intake. Four more weeks without n-3 supplementation restored the pretreatment values of TGs, platelet aggregability and TXB2 release. The biophysical properties of platelets from normolipemics with and without high plasma Lp(a) concentrations revealed a similar structural order of platelets at 37 degrees C using DPH, TMA-DPH, or 6-AS as fluorescent probes. Also similar temperature-dependent changes in platelet fluidity from 37 degrees C to 17 degrees C were observed in platelet preparations from Lp(a)-positive and Lp(a)-negative subjects. However, no subtle changes in the structural order of platelets due to nutrient intakes were found in all subjects (n = 15, 19-28 yrs) using fluorescence polarization technique. The present data suggest a similar in vitro platelet behaviour from normolipemic subjects with and without high plasma levels of Lp(a) (which is considered a risk for premature atherosclerosis) in contrast to platelet aggregability and platelet fluidity in certain hyperlipidemic stages.

Adult↗