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PubMedDate not supplied

[The effect of hemosorption repeated three times on activity of lecithin cholesterol acyltransferase].

Activity of lecithine-cholesterol acyltransferase (LCAT) was studied in blood of 26 patients with atherosclerosis of various localization after course of treatment involving three-fold hemosorption. The initial activity of the enzyme, decreased distinctly as compared with normal state, was dissimilarly altered during hemosorption. The system LCAT-HDLP was stabilized after the third hemosorption. These results relevant to programming hemosorption therapy of patients with atherosclerosis.

Adult↗
PubMed1989

Reaction of lecithin cholesterol acyltransferase with water-soluble substrates.

To separate the interfacial and catalytic reactions of lecithin cholesterol acyltransferase (LCAT), we carried out the first investigation of its reaction with water-soluble substrates. We used a continuous spectrophotometric assay for the hydrolysis of p-nitrophenyl esters of fatty acids to determine the chain length specificity of the enzyme and its modulation by anions and apolipoproteins in solution. By chemical modification of amino acid residues, we demonstrated that the active site serine and histidine residues participate in both the esterase and acyltransferase reactions but that cysteine residues are not involved in the esterase reaction. The kinetics of the LCAT reaction were measured for p-nitrophenyl esters of fatty acids having up to six (C-6) carbons in length. With increasing acyl chain lengths the optimal reaction rates occurred for the C-5 ester and Km and Vmax values decreased progressively, while the specificity constant, kcat/Km, increased. The same series of substrates and longer chain esters, up to C-16, were also reacted with LCAT in the presence of Triton X-100 in order to determine the general trends for the reaction rates as a function of chain length. The observed trends for the reaction rates and kinetic constants were attributed to an increasing binding affinity for the longer acyl chains in a large hydrophobic cavity, with a concomitant restriction in the motions of the substrates and a decreased probability for the correct positioning of the ester bond for hydrolysis, resulting in a decreased substrate turnover. Since the kinetics of the interfacial reactions of LCAT are very sensitive to the presence of anions and apolipoproteins, in particular apoA-I, we investigated the effects of these modulators on the reactions of LCAT in solution. Unlike the interfacial reactions, the hydrolysis of the p-nitrophenyl esters was not affected by 0.1 M concentrations of anions nor by water-soluble apolipoproteins (apoA-I, apoA-II, and apoCs). Thus the regulation of the activity of LCAT is mediated largely by the interfaces on which it acts.

Apolipoprotein C-II↗
PubMed1989

Significance of lecithin:cholesterol acyltransferase activity as a prognostic indicator of early allograft function in clinical liver transplantation.

Rapid and accurate assessment of allograft function in the early postoperative period is critical for successful liver transplantation. This study evaluated the efficacy of lecithin:cholesterol acyltransferase (LCAT) activity as an indicator of early allograft function in human orthotopic liver transplantation (OLTx). During a three-month period between September and November 1987, 9 of 11 adult OLTx recipients whose graft exhibited poor function were studied. Poor graft function was defined as primary nonfunction, need for retransplantation within a week after OLTx, or elevation of the prothrombin time over 20 sec early after OLTx. Plasma LCAT activities (measured pretransplant and at 0, 6, 12, 18, and 24 hr, as well as 3 days, after OLTx) and pretransplant clinical variables were compared with those of 15 control patients whose graft exhibited good function. A significant correlation was found between mean LCAT activities during the first 24-hr after OLTx and early allograft function (P less than 0.05, chi 2 = 5.23). When pretransplant histological findings of the 6 grafts with poor function and the 15 controls together were correlated with the mean LCAT activity within 24 hr following OLTx, a significant association was demonstrated (P less than 0.05). This study suggests that plasma LCAT activity is an effective and practical method for assessing early allograft function following OLTx.

Humans↗
PubMedDate not supplied

[Changes in the rate of lecithin cholesterol acyltransferase reaction and lipid indicators of serum under the effect of cathergene in acute experimental liver damage].

Fractional and molar rates of lecithin:cholesterol aminotransferase (LCAT)-catalyzed reaction were decreased, while free cholesterol fraction was increased in blood serum of rats within 24 hrs after single administration of CCl4 I mg/kg. Cathergene, contributing to a decrease in hepatocyte necrosis, affected positively the blood lipid spectrum in CCl4 treated rats. The cathergene protective effect, observed also after acute ethanol poisoning (6 g/kg), involved an increase by about 30% of the fractional and molar rates of LCAT-reactions; it also normalized the cholesterol esterification coefficient in blood serum. The drug did not prevent the postalcohol dystrophy of hepatocytes, hypertriglyceridemia, hypercholesterolemia.

Animals↗
PubMed1986

Lecithin-sphingomyelin ratios in amniotic fluid of pregnancies with an anencephalic fetus.

As many investigators have shown that surfactant production in the developing human lung is subject to multihormonal regulation, the present authors determined the lecithin-sphingomyelin (L/S) ratio in amniotic fluid of pregnancies with an anencephalic fetus, in which there was known to be aberrant production of fetal pituitary, adrenal, and consequently, placental hormones. The L/S ratio in amniotic fluid from seven of eight pregnancies with an anencephalic fetus was substantially lower than that in amniotic fluids of pregnancies with a normal fetus at the same stage of gestation. The L/S ratio in amniotic fluid of an anencephalic fetus of a twin pregnancy (monochorionic diamniotic) at 34 weeks' gestation was low; the L/S ratio of the amniotic fluid of the normal fetus was high. These data are supportive of the view that fetal lung maturation is dependent, in part, upon normal function of the fetal pituitary and adrenal.

Amniotic Fluid↗
PubMed1986

Cold labelled substrate and estimation of cholesterol esterification rate in lecithin cholesterol acyltransferase radioassay.

A simple and reproducible radioassay of lecithin cholesterol acyltransferase (LCAT E.C. 2.3.1.43) activity is described. The method is based on cold labelling of the serum, plasma or other LCAT and lipoproteins containing fluids with a trace of 14C-cholesterol spread in ready made sorbent discs. Since the procedure minimizes the chemical, heating and time consuming steps, it may be particularly suitable for routine investigation of the defects of cholesterol kinetics and also for experimental studies.

Animals↗
PubMed1986

Factors influencing the cholesterol esterification rate in lecithin cholesterol acyltransferase radioassay.

Factors affecting the esterification rate of cholesterol by lecithin cholesterol acyltransferase (LCAT E.C. 2.3.1.43) in native cold labelled substrates (human, rabbit, rat serum, plasma, VLDL, LDL depleted serum, rabbit intraocular fluids) repaired by use of ready-made 14C-cholesterol discs (Cholesterol kinetics LCAT-test, UVVVR, Czechoslovakia) were investigated. EDTA added to the serum during the cold incubation (18 h, 0 degrees C-4 degrees C) increased the rate of esterification due to elimination of Ca2+ ions. The similar stimulating effect was found in the presence of mercaptoethanol (ME) in the serum, while in the plasma already stimulated by EDTA no additional effect by ME could be noticed. Freezing and thawing did not affect the fractional esterification rate (FER-per cent of total serum unesterified cholesterol esterified per hour) in normolipidaemic sera, whereas in hyperlipidaemic sera, particularly those with high levels of VLDL, FER was stimulated. Esterification partially proceeded during the cold incubation of serum or plasma with 14C-cholesterol ready-to-use discs, attaining the values of about 0.3%/h and 2-6%/h, respectively, in human sera and in rabbit and rat sera. The starting level of esterification did not affect the linearity of LCAT reaction during warm incubation (30 min at 37 degrees C), neither was the absolute value of FER changed as compared with cold labelled sera with those inhibited by DTNB and reactivated by ME. Substantial LCAT activity was also detected in extremely diluted substrates--such as intraocular fluid collected from rabbits with induced uveitis or after preceding paracentesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Effect of polyenoic phospholipid therapy on lecithin cholesterol acyltransferase activity in the human serum.

The effect of polyenoic phospholipids on the concentration of serum lipids and the activity of lecithin cholesterol acyltransferase (LCAT, E.C. 2.3.1.43) was investigated in 18 patients with chronic glomerulonephritis accompanied by hyperlipaemia and reduced rate of cholesterol esterification in the plasma. The effects of therapy were evaluated immediately after a 2-month period of treatment and again after a 3-month drug free interval following termination of the therapy. An immediate effect of the treatment was reflected in a significant increase in the fractional esterification rate (FER % .h-1) and a marked reduction of the concentration of triglycerides (TG). Discontinuation of the drug resulted in the return of TG and FER values to the initial levels and in a rise of total (TCH) and unesterified cholesterol (UCH), HDL-cholesterol (HDL-TCH) and the molar esterification rate (MER mumol.1-1.h-1). The activity of LCAT estimated by radioassay in common and endogenous substrates varied in parallel.

Adult↗
PubMed1985

Detection of lecithin: cholesterol acyltransferase (LCAT) in a human hepatoma cell line.

A human hepatoma cell line (HepG-2) was probed for the presence of lecithin: cholesterol acyltransferase (LCAT) using an antiserum to human plasma LCAT. Double immunodiffusion analysis using antiserum to human plasma LCAT revealed a single precipitin line in the sonicated cell homogenate. This precipitin line showed a reaction of identity with highly purified plasma LCAT. The presence of LCAT within the hepatoma cells was also confirmed by an immunofluorescence test. In contrast, the cell culture supernate showed a weak and inconsistent precipitin line. These data suggest that HepG-2 cells synthesize LCAT but secretion of the enzyme by these cells into the culture medium may be partially or totally impaired.

Carcinoma, Hepatocellular↗
PubMed1985

Serum activity and hepatic secretion of lecithin:cholesterol acyltransferase in experimental hypothyroidism and hypercholesterolemia.

Lecithin:cholesterol acyltransferase (LCAT), the major cholesterol esterifying enzyme in plasma, plays an important role in the removal of cholesterol from peripheral tissues. This study in rat focuses upon the effects of hypothyroidism and cholesterol feeding on serum activity and hepatic LCAT secretion. To obviate the effect that inclusion of high concentrations of cholesterol in the rat serum may have on the proteoliposome used in the assay of LCAT, very low and low density lipoproteins (VLDL and LDL) were removed by ultracentrifugation at d 1.063 g/ml. The molar esterification rate in the euthyroid VLDL + LDL-free serum was found to be 0.94 +/- 0.06 compared to 0.67 +/- 0.05 in hypothyroid rats and 1.56 +/- 0.14 in hypercholesterolemic rats. LCAT secretion by suspension cultures of hepatocytes from hypercholesterolemic rats was found to be significantly depressed when compared to that for euthyroid and hypothyroid animals. Secretion by hepatocytes from hypothyroid rats was depressed for the first 0-4 hr, but rapidly recovered. The depressed secretion of LCAT by hepatocytes from hypercholesterolemic rats correlates with the appearance in the media of apoE-rich, discoidal HDL. Discoidal HDL was six times more effective as a substrate for purified human LCAT than HDL from hypercholesterolemic serum, and twice as effective as serum and nascent HDL from euthyroid animals. It is concluded that the depressed LCAT activity in serum from hypothyroid rats is due to a depressed hepatic secretion of the enzyme and that the elevated serum activity of hypercholesterolemic rats may be related to a defect in LCAT clearance. Finally, the appearance of discoidal HDL in the medium upon culture of hepatocytes from hypercholesterolemic rats appears to be due to an inhibition of LCAT secretion by these cells.

Animals↗
PubMed1987

Reaction of discoidal complexes of apolipoprotein A-I and various phosphatidylcholines with lecithin cholesterol acyltransferase. Interfacial effects.

Complexes of phospholipids-apolipoprotein A-I-cholesterol, containing various bulk phosphatidylcholines or a matrix of the ether analog of 1-palmitoyl 2-oleoyl phosphatidylcholine including test phosphatidylcholines were used as substrates for human lecithin-cholesterol acyltransferase. The enzymatic reaction rates for both series of complexes were determined as a function of temperature, particle concentration, neutral salt concentration, and the type of anion present in solution. The kinetic results support the hypothesis that phospholipids, in discoidal complexes, modulate the reaction rates by molecular effects at the active site, but also by interfacial effects on the interaction of the enzyme with the particles. The relevant interfacial parameters are the lipid packing at the interface and the structure of apolipoprotein A-I.

Anions↗
PubMed1986

Distribution and localization of lecithin:cholesterol acyltransferase and cholesteryl ester transfer activity in A-I-containing lipoproteins.

Two types of A-I-containing lipoproteins are found in human high density lipoproteins (HDL): particles with A-II (Lp(A-I with A-II] and particles without A-II (Lp(A-I without A-II]. We have studied the distribution of lecithin:cholesterol acyltransferase (LCAT) and cholesteryl ester transfer (CET) activities in these particles. Lp(A-I with A-II) and Lp(A-I without A-II) particles were isolated from ten normolipidemic subjects by anti-A-I and anti-A-II immunosorbents. Most plasma LCAT mass (70 +/- 15%), LCAT (69 +/- 16%), and CET (81 +/- 15%) activities were detected in Lp(A-I without A-II). Some LCAT (mass: 16 +/- 7%, activity: 17 +/- 8%) and CET activities (7 +/- 8%) were detected in Lp(A-I with A-II). To determine the size subspecies that contain LCAT and CET activities, isolated Lp(A-I with A-II) and Lp(A-I without A-II) particles of six subjects were further fractionated by gel filtration column chromatography. In Lp(A-I without A-II), most LCAT and CET activities were associated with different size particles, with the majority of the LCAT and CET activities located in particles with hydrated Stokes diameters of 11.6 +/- 0.4 nm and 10.0 +/- 0.6 nm, respectively. In Lp(A-I with A-II), most of the LCAT and CET activities were located in particles similar in size: 11.1 +/- 0.4 nm and 10.6 +/- 0.3 nm, respectively. Ultracentrifugation of A-I-containing lipoproteins resulted in dissociation of both LCAT and CET activities from the particles. Furthermore, essentially all CET and LCAT activities were recovered in the non-B-containing plasma obtained by anti-LDL immunoaffinity chromatography. This report, therefore, provides direct evidence for the association of LCAT and CET protein with A-I-containing lipoproteins. Our conclusions pertain to fasting normolipidemic subjects and may not be applicable to hyperlipidemic or nonfasting subjects.

Apolipoprotein A-I↗
PubMed1987

Formation of mixed micelles and vesicles of human apolipoproteins A-I and A-II with synthetic and natural lecithins and the bile salt sodium taurocholate: quasi-elastic light scattering studies.

We employed quasi-elastic light scattering to systematically study the interactions of human apolipoproteins A-I and A-II (apo A-I and apo A-II) with synthetic and natural lecithins, analogues of the major membrane lipids found in high-density lipoproteins (HDL). Equilibrium values of the mean hydrodynamic radius (Rh) of systems with varying concentrations of dimyristoylphosphatidylcholine (DMPC) to apolipoprotein showed that as the percentage of DMPC was increased, three distinct regions were observed. At low DMPC to apolipoprotein ratios, Rh values either increased, remained constant, or decreased, depending upon the total apolipoprotein concentration, which influenced the size of pure apolipoprotein micelles [Donovan, J. M., Benedek, G. B., & Carey, M. C. (1987) Biochemistry (preceding paper in this issue)]. When the percentage of DMPC approached the micellar phase boundary, Rh values uniformly diverged (50 to approximately 150 A); with the percentage of DMPC in excess of the micellar phase boundary, large Rh values (200-300 A) were observed that were consistent with unilamellar apo A-I/DMPC or apo A-II/DMPC vesicles. Decreases in total solute concentration (1.0-0.25 mg/mL) and/or elevations in temperature (25-37 degrees C) shifted micellar phase limits to lower percentages of DMPC in the case of both apolipoproteins. Although apo A-I interacted spontaneously with DMPC at 25 degrees C, it was necessary to dilute mixed micellar solutions of sodium taurocholate (TC) and egg yolk phosphatidylcholine (EYPC) with apo A-I solutions to form apo A-I/EYPC mixed micelles. Despite the presence of submicellar concentrations of TC (below 3 mM, the lower limit of its critical micellar concentration), Rh values of apo A-I/EYPC mixed micelles were similar to those observed for the apo A-I/DMPC system. Dilution of micellar TC/EYPC solutions with low concentrations of apo A-I (0.001-0.10 mg/mL) influenced the width of the mixed micellar zone, the kinetics of micelle-to-vesicle transitions, and the size of metastable vesicles. Dilution with higher apo A-I concentrations (0.05 and 0.1 mg/mL) resulted in the transformation of bile salt rich EYPC micelles into apo A-I rich EYPC micelles with an intervening zone of metastable vesicles. The micelle-to-vesicle transition was abolished by dilution with an apo A-I concentration of 0.5 mg/mL, suggesting that bile salts and apo A-I can directly interchange in micellar solubilization of EYPC.(ABSTRACT TRUNCATED AT 400 WORDS)

Apolipoprotein A-I↗
PubMed1988

[HDL2b lipoproteins as an acceptor of cholesterol from erythrocyte membrane and the role of lecithin-cholesterol-acyltransferase during this process].

The role of lecithin-cholesterol-acyltransferase (LCAT) in net cholesterol transport from erythrocyte membranes to one of high density lipoprotein subclasses--HDL2b--was studied in vitro. It was shown that an addition of partially purified LCAT to the incubation medium containing human HDL2b and human erythrocytes triggers free cholesterol transport from erythrocyte membranes to HDL2b. In this case, the rise in HDL cholesterol occurs mainly due to the formation of cholesteryl esters produced by LCAT. The significance of cholesterol ecceptor properties of HDL2b in vivo is discussed.

Biological Transport↗
PubMedDate not supplied

[Interaction of aldolase A with lecithin liposomes].

The aldolase A binding to the lecithin liposomes (Kd = 2.4 +/- 0.1 X 10(-3) M) has been shown by the fluorescence and tryptophan phosphorescence at the room temperature. The interaction is accompanied by an increase in the phospholipid bilayer microviscosity, and some conformational changes in the hydrophobic part of the enzyme, pronouncing themselves in Trp-147 environment rigidity, decrease. The observation of membrane viscosity vs. incubation time revealed practically instant enzyme-membrane interaction and no gradual incorporation. The accessibility of the NAD-binding domain of aldolase for NADH in the liposome presence remains unaltered.

Fructose-Bisphosphate Aldolase↗
PubMed1988

Evidence for a lecithin-retinol acyltransferase activity in the rat small intestine.

Cellular retinol-binding protein, type II (CRBP (II] is an abundant protein of the mature enterocytes of the small intestine. It has been shown to direct retinol to an acyl-CoA-independent esterifying activity that utilizes an endogenous acyl donor (Ong, D.E., Kakkad, B., and MacDonald, P.N. (1987) J. Biol. Chem. 262, 2729-2736). Here we report that this activity in intestinal microsomes will catalyze the transfer of acyl moieties from exogenous phosphatidylcholine (PC) to retinol-CRBP(II) to produce retinyl esters. The microsomal activity displayed positional selectivity as only the sn-1-acyl moiety of PC was transferred to retinol-CRBP(II). The retinyl ester synthase was selective for PC substrates as acyl transfer from phosphatidylethanolamine, phosphatidic acid, or free fatty acid to retinol-CRBP(II) was not observed. Some formation of retinyl esters was observed with exogenous acyl-CoA, but the amount produced was considerably lower than ester formation from exogenous PC and could be shown to be due to a different enzyme activity. Inhibitor studies clearly distinguished between the enzyme activities responsible for the acyl-CoA-dependent esterification and the phosphatidylcholine-dependent esterification of retinol. The results provide strong evidence that retinol-CRBP(II) esterification in the intestine proceeds via a phosphatidylcholine-dependent transacylase mechanism similar to that established for the esterification of cholesterol by lecithin-cholesterol acyltransferase.

Acyl Coenzyme A↗
PubMed1987

Effects of some cyclic elements containing amphiphilic compounds on stability and transport properties of model lecithin membranes.

The paper presents results of studies on changes in model membrane properties induced by some single-chain amphiphilic quaternary ammonium salts with fungicidal activity, N-dodecyl-N-methylmorpholinium chloride (IVC), N-dodecyloxymethylene-N-methylmorpholinium chloride (IVD), N-dodecyl-N-methylpiperidinium chloride (VIC), N-dodecyloxymethylene-N-methylpiperidinium chloride (VID) and N-dodecyl-N,N-dimethyl-N-benzy-lammonium chloride (IB). Two different lipid systems were used, namely, unilamellar liposomes and black planar membranes (BLM). All the compounds studied interfered with sulphate ion transport across liposomal membranes as well as with calcium ion desorption from the membranes. The compounds were found also to change the stability of black lecithin membranes. Generally the sequence of effectiveness of the salts studied on both models used was: IB greater than VID greater than IVD greater than VIC greater than IVC, although there were some differences for particular processes. The results obtained are discussed in view of a possible mechanism of the interaction between the salts studied and the lipid model including the role the salt head group structure and charge distribution can play in this interaction.

Antifungal Agents↗