Rate Of Phospholipid Transfer Research Articles

DEVELOPMENTAL CHANGES IN PHOSPHATIDYLINOSITOL TRANSFER PROTEIN CONCENTRATION AND PHOSPHOLIPID TRANSFER ACTIVITIES IN RAT TYPE II CELLS

The phospholipid transfer proteins (PLTPs) are cytosolic proteins that have been characterized by their ability to facilitate the transfer of phospholipids between membranes in vitro. The goals of this study were to determine whether PITPalpha concentration and phospholipid transfer activities are enriched in type II cells compared with whole lung and to determine the developmental changes in PITPalpha concentration and phospholipid transfer activities during late gestation and newborn period. The concentration of PITPalpha in type II cell cytosol measured by enzyme-linked immunosorbent assay (ELISA) increased during late fetal gestation to 2.2-fold adult levels and declined 41% during the first postnatal day. However, compared to whole adult lung cytosol, type II cell cytosol was not significantly enriched with PITPalpha. Phospholipid transfer activities were determined by a vesicle-rat lung membrane transfer assay. In adult lung, transfer activities for all the phospholipids were enriched in adult type II cell cytosol compared to whole lung cytosol (phosphatidylglycerol [PG], 12.5-fold; phosphatidylinositol [PI], 9.2-fold; phosphatidylcholine [PC], 6.5-fold; and phosphatidylethanolamine [PE], 6.6-fold; P <. 05 in each case). The rate of phospholipid transfer in type II cell cytosol increased during late fetal gestation to levels 4.9 (PG), 3.7 (PI), and 2.8 (PC) times greater than adult levels. In cytosol from cells from different stages, the order of transfer rate was PG > PI > PC > PE. PITPalpha immunodepletion of adult type II cytosol did not significantly affect phospholipid transfer activities, suggesting that other PLTPs are responsible for the majority of the observed transfer activities in these cells. Developmental increases in PITPalpha concentration and other PLTPs parallel developmental changes in type II cell surfactant phospholipid metabolism, suggesting a possible role of these transfer proteins in the unique function of the type II cell.

Influence of the electrostatic charge of lipoprotein particles on the activity of the human plasma phospholipid transfer protein

The aim of the present study was to determine the effect of the electrostatic charge of lipoproteins on the phospholipid transfer activity of the plasma phospholipid transfer protein (PLTP). Progressive decreases in the PLTP-mediated phospholipid transfer rates were observed when the surface potential of isolated high density lipoproteins (HDL) was either reduced from –11.7 mV down to –15.7 mV by succinylation of apolipoprotein lysyl residues, or increased from –11.6 mV up to –10.9 mV by replacing apolipoprotein (apo) A-I by apoA-II. When succinylated low density lipoprotein (LDL) series with surface potentials ranging between –4.3 mV and –14.3 mV were used, successive increase and decrease in phospholipid transfer rates were observed along the electronegativity scale. When various plasma HDL subfractions with surface potentials ranging from –10.5 mV to –12.5 mV were separated by anion exchange chromatography, PLTP-mediated phospholipid transfer activity increased progressively with HDL electronegativity until maximal lipid transfer rates were reached for a mean HDL surface potential of –11.6 mV. As the electronegativity of plasma HDL subfractions kept increasing beyond the optimal value, a progressive decrease in PLTP activity was observed. Striking parallelism between cholesteryl ester transfer protein (CETP) and PLTP transfer activity curves obtained with each HDL series were noted, and the optimal HDL surface potential values were remarkably similar, approximating –11.6 mV in all the experiments. With isolated plasma LDL subfractions with surface potentials ranging from –3.5 mV to –5.0 mV, a linear rise in PLTP activity was observed. In conclusion, data of the present study indicate that, like CETP, the activity of PLTP is influenced by electrostatic interactions with lipoproteins.—Desrumaux, C., A. Athias, D. Masson, P. Gambert, C. Lallemant, and L. Lagrost. Influence of the electrostatic charge of lipoprotein particles on the activity of the human plasma phospholipid transfer protein. J. Lipid Res. 1998. 39: 131–142.

Protein-mediated transfer of fluorescent-labeled phospholipids across brush border of rabbit intestine

Monoacyl and diacyl phospholipids labeled with the fluorescent probe 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) were used to measure the rate of phospholipid transfer between artificial large unilammelar vesicles and rabbit intestine brush-border membrane vesicles (BBMV). This assay demonstrated that transfer into and out of BBMV occurred in two kinetic phases. The fast rate of transfer resulted from interbilayer transfer between the outer membrane leaflets. The slower rate resulted from transmembrane transfer across the BBMV. Treatment of the BBMV with the protease pronase E and with the histidyl reagent diethylpyrocarbonate inhibited the rate of transmembrane transfer. Phospholipids containing one or two acyl chains and a wide range of head-group structures were transported across the membranes with rates that increased as a direct function of their water solubility. These data demonstrated the existence of a protein transporter in the intestinal brush border that functions to absorb slightly water-soluble lysophospholipids and short-chain diacyl phospholipids without redistributing the highly water-insoluble long-chain diacyl phospholipids between the outer and inner leaflets of the brush-border membrane.

Low concentrations of bile salts increase the rate of spontaneous phospholipid transfer between vesicles.

The rate of 1-palmitoyl-2-[12-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino] dodecanoyl] phosphatidylcholine (P-C12-NBD-PC) transfer between dioleoylphosphatidylcholine vesicles was measured by a technique based on resonance energy transfer between P-C12-NBD-PC and N-(lissamine rhodamine B sulfonyl)dioleoylphosphatidylethanolamine [Nichols, J. W., & Pagano, R. E. (1982) Biochemistry 21, 1720-1726]. Addition of bile salts at concentrations below their critical micelle concentrations increased the rate of spontaneous P-C12-NBD-PC transfer without disrupting the vesicles. The effectiveness in increasing the transfer rate was dependent on the structure of the bile salt. In general, conjugated bile salts were more effective than unconjugated, and mono- and dihydroxy bile salts were more effective than trihydroxy. The kinetics of intervesicular P-C12-NBD-PC transfer in the presence of cholate were found to be consistent with a mass action kinetic model based on the premise that bile salts bind to the vesicles, alter the dissociation and/or association rate constants for phospholipid monomer-vesicle interaction, and increase the rate of phospholipid transfer via the diffusion of soluble monomers through the aqueous phase. Temperature dependence studies indicated that cholate binding to vesicles is an entropy-driven process and that cholate binding lowers the free energy of activation for phospholipid monomer-vesicle dissociation by producing compensatory decreases in both the enthalpy and entropy of activation.

Measurement and prediction of the rates of spontaneous transfer of phospholipids between plasma lipoproteins

The purpose of this report is to develop a correlation between the hydrophobicity of a phospholipid as measured by reversed-phase high-performance liquid Chromatography and its rate of spontaneous transfer and to use this correlation to predict the rate of transfer of any homologous lipid from any lipoprotein. We have studied the mechanism of transfer of a series of fluorescent or radiolabeled phospholipids among natural and reassembled serum lipoproteins. Fluorescent phosphatidylcholines included those with 9-(1-pyrenyl)non-anoic acid in the sn-2 position and lauric, myristic, palmitic, stearic, oleic or linoleic acid at sn-1. The radioactive phosphatidylcholines contained [ 3H]oleic acid in the sn-2 position and lauric, myristic, or palmitic acid at sn-1. The kinetics of transfer of the pyrene-labeled lipid were followed by changes in the excimer fluorescence, and that of the radioactive lipids by separation of the donor (lipid-apolipoprotein recombinant) from the acceptor (single bilayer vesicles) on a column of Sephacryl S-200. The retention time of each lipid was measured by high-performance hydrophobic chromatography through a Waters radially compressed C 18 column eluted with 75% isopropanol and 25% triethylammonium phosphate (0.15 M). A linear relationship was observed between the rate-constant of transfer and the retention time which suggest that the rate of desorption of phosphatidylcholines from lipoproteins and vesicles is controlled predominately by the hydrophobic effect. For a homologous series of lipids, the rate of transfer can be predicted from retention times obtained from hydrophobic chromatography. The kinetics of transfer of 1-lauroyl-2-[9-(1-pyrenyl)non-anoyl] phosphatidylcholine between isolated human serum lipoproteins exhibits a linear correlation between the transfer half-time and the size of the donor lipoproteins. As a consequence, transfer from very-low-density lipoprotein is 10-times slower than that observed from high-density lipoproteins. The observed correlations between phospholipid transfer rates and both the Stokes radius of the donor and the retention time of the phospholipid on a hydrophobic column permit one to calculate the rate of transfer of homologous molecules between lipid-protein complexes. The results predict that the spontaneous transfer of phospholipids between plasma lipoproteins would be too slow to be a physiologically important phenomena.