Biomedical subjects

T M Forte

Publications and source records attributed to T M Forte.

At least 37 records · Page 2Linked to original sources

PubMed1997

Cryo-electron microscopy of low density lipoprotein and reconstituted discoidal high density lipoprotein: imaging of the apolipoprotein moiety.

Cryo-electron microscopy was used to analyze the structure of low density lipoprotein from normolipidemic subjects (N-LDL), phospholipid-depleted N-LDL (PD-LDL), small dense LDL from hypertriglyceridemic subjects (SD-LDL), and reconstituted discoidal high density lipoproteins (rHDL). In different projections of N-LDL, a high density component of the particle was visible as two parallel bands or as a single ring. Projections of PD-LDL were very similar to those of N-LDL, indicating that the contribution of phospholipid headgroups to the observed high density structure is minor. In preparations of SD-LDL, projections with two high density bands or a single high density ring were rare. Instead, triangular and diamond-shaped projections were recognized. In different projections of discoidal rHDL, a high density component was visible as a single band or as a single ring. The present results indicate that cryo-electron microscopy reveals the distribution of apolipoproteins within lipoprotein particles. Thus, apolipoprotein B-100 (apoB) in N-LDL appears to be organized as a double ring around the particle, while apoB in SD-LDL is indicated to have a different conformation. Cryo-electron micrographs of rHDL are consistent with the presence of apolipoprotein A-I on the periphery of the lipoprotein disc.

Apolipoprotein A-I↗

PubMed1997

High density lipoprotein particle size restriction in apolipoprotein A-I(Milano) transgenic mice.

Human carriers of apolipoprotein A-I(Milano) (Arg173 --> Cys substitution in apolipoprotein A-I) are characterized by an HDL deficiency in which small, dense HDL accumulate in plasma. Because affected individuals are heterozygous for this mutation, the full impact of apolipoprotein A-I(Milano) (apoA-I(Milano)) on HDL-cholesterol metabolism is unknown. In this study, apoA-I(Milano) transgenic mice were used to evaluate the extent of apoA-I(Milano) dimerization and HDL particle size restriction in the absence of wild-type apoA-I. Murine apoA-I knockout mice were utilized to express apoA-I(Milano) and human apoA-II in the presence of wild-type, human apoA-I (apoA-IMilano/A-Iwt/A-II) and in its absence (apoA-IMilano/A-II). Plasma HDL-cholesterol concentrations were similar (30 mg/dl) in both lines of apoA-I(Milano) transgenic mice. In the apoA-IMilano/A-Iwt/A-II phenotype, 14% of the apoA-I(Milano) formed homodimers and 33% formed heterodimers with apoA-II. ApoA-I(Milano) homodimers increased by 71% in the apoA-IMilano/A-II transgenics and was associated with an abundance of small, 7.6-nm HDL3-sized particles compared to the 9.5, 8.3, and 7.6-nm-sized particles in apoA-IMilano/A-Iwt/A-II mice. The unesterified cholesterol/cholesteryl ester mole ratio of HDL was elevated by 45% in apoA-IMilano/A-Iwt/A-II mice and by 90% in apoA-IMilano/A-II transgenics compared to wild-type (human apoA-I/A-II). Both apoA-I(Milano) transgenics possessed normal levels of plasma LCAT activity, but endogenous cholesterol esterification rates were reduced by 50% compared to controls. Thus, HDL particle size restriction was not the result of impaired LCAT activation; rather, dimerization of apoA-I(Milano) limited the esterification of cholesterol on endogenous HDL. In the absence of wild-type apoA-I, the more extensive dimerization of apoA-I(Milano) severely limited cholesteryl ester accumulation on plasma HDL accounting for the abundance of small, 7.6-nm HDL3 particles in apoA-IMilano/A-II mice.

Animals↗

PubMed1996

Minimally oxidized LDL is a potent inhibitor of lecithin:cholesterol acyltransferase activity.

The oxidation of low density lipoproteins (LDL) has been implicated in the development of atherosclerosis. As a variety of highly reactive lipid peroxidation products can transfer from oxidized LDL to HDL, we evaluated the potential deleterious effects of LDL oxidation on HDL-cholesterol metabolism. To address this issue, we exposed the HDL-containing d > 1.063 g/ml fraction of human plasma to copperoxidized LDL and assessed lecithin:cholesterol acyltransferase (LCAT) activity and apolipoproteinA-I (apoA-I) structure. To determine whether LCAT was directly affected by oxidized LDL, independent of crosslinking of apoA-I, we used an exogenous, [14C]cholesterol-labeled proteoliposome substrate to measure plasma LCAT activity. We observed an inhibition of LCAT activity where copper-oxidized LDL possessing only 2.3 +/- 0.1 and 7.3 +/- 1.4 TBARS produced 24 +/- 3% and 47 +/- 10% reductions in [14C]cholesterol esterification by 1 h, respectively. Copper-oxidized LDL that had been passed through a GF-5 desalting column, while retaining only one-third of its original TBARS, possessed nearly all of its LCAT inhibitory capacity suggesting that the LCAT inhibitory factor(s) was a lipophilic oxidation product. Analysis of polarlipids isolated from copper-oxidized LDL indicated that phospholipid and sterol fractions effectively inhibited LCAT. Copper-oxidized LDL, with as little as 6.3 TBARS, also produced intermolecular crosslinking of apoA-I molecules. Taken together, these data suggest that products of LDL oxidation may adversely affect HDL-cholesterol metabolism by two separate mechanisms: 1) a direct inhibitory effect on LCAT activity and 2) through crosslinking of apoA-I. If occurring in vivo, minimally oxidized LDL may impair cholesteryl ester formation on HDL thereby limiting the ability of HDL to function efficiently in the putative antiatherogenic reverse cholesterol transport pathway.

Apolipoprotein A-I↗

PubMed1996

Structural relationships between nascent apoA-I-containing particles that are extracellularly assembled in cell culture.

Apolipoprotein A-I (apoA-I) incubated with CHO cells assembles three major nascent lipid complexes with diameters of 7.3, 9, and 11 nm. Previous studies suggested that the smaller nascent particles were precursors for the larger nascent ones. To test this hypothesis, the 7.3, 9, and 11 nm apoA-I-lipid complexes formed by incubating CHO cells with lipid-free apoA-I were isolated and subsequently each subpopulation was re-incubated with cells in the absence of other subpopulations. The physical-chemical characteristics of each subpopulation were examined before and after re-incubation in an effort to understand relationships. if any, between the different nascent complexes. The 7.3, 9, and 11 nm complexes were unique in that each of the particles had pre-alpha mobility on agarose gels: this rapid migration was not altered by re-incubation with cells. Protein crosslinking studies indicated that the 7.3, 9, and 11 nm complexes possessed 2, 3, and 4 apoA-I molecules per complex, respectively; it is unlikely that the size of the particle and number of apoA-I molecules per particle played a role in the increased negative charge of the particles. The present study shows that smaller particles did not give rise to larger ones upon re-incubation with cells. Rather, the 11 and 9 nm particles both generated smaller discs (the 11 nm giving rise primarily to 9 nm discs and the 9 nm complex giving rise to 7.3 nm discs) suggesting that, during incubation with cells, the complexes are destabilized and remodeled into smaller, not larger, complexes. Surprisingly, the 7.3 nm complexes during re-incubation with cells were extremely stable and did not undergo size alteration. When the 7.3 nm particles were incubated with additional small quantities of lipid-free apoA-I (1-2 microgram/ml), larger discoidal complexes were generated suggesting that the formation of larger particles may be driven by the availability of lipid-free apoA-I.

Animals↗

PubMed1995

Gas-phase cigarette smoke inhibits plasma lecithin-cholesterol acyltransferase activity by modification of the enzyme's free thiols.

Cigarette smoking is associated with an increased risk of premature atherosclerosis. The underlying mechanisms responsible for this association are unknown. Recent work from this laboratory has shown that ex vivo exposure to plasma to gas-phase cigarette smoke (CS) produces a rapid inhibition of lecithin-cholesterol acyltransferase (LCAT) activity and crosslinking of HDL-apolipoproteins. The goal of the present study was to investigate the mechanism(s) by which CS inhibited LCAT and modified HDL. When dialyzed human plasma (12 ml) was exposed to the gas-phase of an equivalent of 1/8 of a cigarette (one 'puff') at 15 min intervals for 3 h, LCAT activity was reduced by 76 +/- 1% compared to controls; supplementation of plasma with glutathione produced a dose-dependent protection of LCAT activity where at the highest concentration (1 mM) 78% protection was observed. A similar protection was obtained with N-acetyl cysteine (1 mM). In addition to LCAT inhibition, HDL-apolipoproteins were crosslinked after 3 h exposure of plasma to CS; crosslinking was reduced by the addition of either glutathione or N-acetyl cysteine to plasma. The amino compounds N-acetyl lysine, N-acetyl arginine, and aminoguanidine failed to protect LCAT and HDL indicating a specificity with regard to the ability of free thiols to buffer the deleterious components of CS which inhibited LCAT and crosslinked HDL-apolipoproteins. Since LCAT contains two free cysteine residues (Cys-31 and -184) near the active site of the enzyme, we tested whether pretreatment of plasma with the reversible sulfhydryl modifying compound, 5,5'-dithiobis-2-nitrobenzoic acid (DTNB), could protect LCAT from CS-induced inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcysteine↗

PubMed1995

Human apo A-I in transgenic mice is more efficient in activating lecithin:cholesterol acyltransferase than mouse apo A-I.

This study shows that, in control and transgenic mice, there is a parallel increase in LCAT activity and plasma apo A-I concentrations during postnatal development. We also demonstrate that human apo A-I is a much more efficient activator (1.6-fold) of mouse LCAT activity than mouse apo A-I. We propose that the differences in amino acid sequence between human and mouse apo A-I may account for the higher LCAT activity with human apo A-I.

Animals↗

PubMed1995

Inhibition of lecithin-cholesterol acyltransferase and modification of HDL apolipoproteins by aldehydes.

Experimental evidence suggests that aldehydes generated as a consequence of lipid peroxidation may be involved in the pathogenesis of atherosclerosis. It is well documented that aldehydes modify LDL: however, less is known concerning the effects of aldehydes on other plasma and interstitial fluid components. In the present study, we investigated the effects of five physiologically relevant aldehydes (acetaldehyde, acrolein, hexanal, 4-hydroxynonenal [HNE], and malondialdehyde [MDA]) on two key constituents of the antiatherogenic reverse cholesterol transport pathway, lecithin-cholesterol acyltransferase (LCAT) and HDL. Human plasma was incubated for 3 hours at 37 degrees C with each one of the five aldehydes at concentrations ranging from 0.16 to 84 mmol/L. Dose-dependent decreases in LCAT activity were observed. The short-chain (acrolein) and long-chain (HNE) alpha,beta-unsaturated aldehydes were the most effective LCAT inhibitors. Micromolar concentrations of these unsaturated aldehydes resulted in significant reductions in plasma LCAT activity. The short- and longer-chain saturated aldehydes acetaldehyde and hexanal and the dialdehyde MDA were considerably less effective at inhibiting LCAT than were acrolein and HNE. In addition to inhibiting LCAT, aldehydes increased HDL electrophoretic mobility and cross-linked HDL apolipoproteins. Cross-linking of apolipoproteins A-I and A-II required higher aldehyde concentrations than inhibition of LCAT. The alpha,beta-unsaturated aldehydes acrolein and HNE were fourfold to eightfold more effective cross-linkers of apolipoproteins A-I and A-II than the other aldehydes studied. These data suggest that products of lipid peroxidation, especially unsaturated aldehydes, may interfere with normal HDL cholesterol transport by inhibiting LCAT and modifying HDL apolipoproteins.

Aldehydes↗

PubMed1995

Recruitment of cell phospholipids and cholesterol by apolipoproteins A-II and A-I: formation of nascent apolipoprotein-specific HDL that differ in size, phospholipid composition, and reactivity with LCAT.

Studies were carried out to determine whether apolipoprotein (apo) A-II, like apoA-I, can recruit phospholipid and cholesterol from cell membranes, thereby forming nascent apoA-II-specific HDL. ApoA-II and apoA-I were purified from plasma and each was incubated with CHO cells at a concentration of 10 micrograms/ml. Lipid-containing complexes were isolated from the medium in both cases; the composition of the apoA-II- and apoA-I-specific complexes were similar where percent protein, phospholipid, and cholesterol were 35 +/- 3, 38 +/- 2, and 25 +/- 1 for apoA-II, respectively, and 40 +/- 2, 35 +/- 1, and 24 +/- 2 for apoA-I, respectively. On a per mole of apolipoprotein basis, apoA-I recruited significantly more phospholipid and cholesterol than dimeric apoA-II suggesting that apoA-I with its greater number of alpha helices binds more lipid. By electron microscopy, nascent apoA-II- and apoA-I-specific particles were predominantly discoidal in morphology. ApoA-II complexes were unique in their nondenaturing polyacrylamide gradient gel size distribution as six distinct populations of particles with diameters of 8.1, 9.3, 10.4, 11.8, 13.1, and 14.6 nm were routinely noted, compared with apoA-I which formed only three major populations with diameters of 7.3, 9.2, and 11.0 nm. Nascent apoA-I complexes incubated with purified lecithin:cholesterol acyltransferase (LCAT) were transformed into predominantly 8.4 nm particles. The latter is similar in size to plasma HDL3a, LpA-I particles, suggesting that extracellularly assembled apoA-I-lipid complexes can directly give rise to a major plasma LpA-I subpopulation upon interaction with LCAT. Unlike apoA-I, apoA-II-lipid complexes could not serve as substrates for LCAT and did not undergo transformation. This study also demonstrates, for the first time, that apoA-II and apoA-I show a preference in phospholipid recruitment from membranes. Although phosphatidylcholine is the major phospholipid removed by both apolipoproteins, apoA-II preferentially recruits phosphatidylethanolamine (PE) as its second most abundant phospholipid while apoA-I recruits sphingomyelin. As PE is usually associated with the inner leaflet of the membrane, it is likely that dimeric apoA-II, compared with apoA-I, can penetrate farther into the membrane and extract PE. This ability of apoA-II to insert more deeply into the lipid milieu may explain the known ability of apoA-II to resist dissociation from the mature HDL particle.

Animals↗

PubMed1995

Copper and gas-phase cigarette smoke inhibit plasma lecithin:cholesterol acyltransferase activity by different mechanisms.

Cigarette smokers have reduced levels of plasma high density lipoprotein (HDL) compared to nonsmokers and are at risk of premature cardiovascular disease. Previous work from this laboratory has shown that exposure of human plasma to gas-phase cigarette smoke (CS) inhibited the activity of lecithin:cholesterol acyltransferase (LCAT), the enzyme that catalyzes the formation of cholesteryl ester in HDL and thereby promotes HDL maturation. As CS contains free radicals that could potentially oxidize plasma lipoproteins, we examined the involvement of lipid peroxidation in LCAT inhibition. Results obtained with CS were compared with those obtained by initiating lipid peroxidation with copper ions. Exposure of dialyzed human plasma to an equivalent of one-eighth of a cigarette at 15-min intervals resulted in a progressive loss of LCAT activity (50 and 90% reductions by 1 and 6 h, respectively). A similar pattern of LCAT inhibition was produced with copper (0.5 mM) where 50 and 97% reductions were observed at 1 and 6 h, respectively. To determine whether LCAT inhibition was related to lipid peroxidation, lipoprotein fractions corresponding to VLDL-IDL, LDL, and HDL were isolated from plasma exposed to CS or copper and analyzed for changes in TBARS, the polyunsaturated fatty acid arachidonate relative to palmitate (20:4/16:0 ratio), and vitamin E concentrations. Exposure of plasma for 6 h to CS had no effect on the levels of TBARS and 20:4/16:0 ratio; however, 6 h copper treatment (0.5 mM) caused a 3.0-, 4.0-, and 1.4-fold increase in TBARS and a 17, 25, and 13% reduction in the 20:4/16:0 ratio in VLDL-IDL, LDL, and HDL fractions, respectively. In addition, a complete depletion of lipoprotein vitamin E was observed with CS, whereas copper decreased vitamin E levels by approximately 50% in each fraction. Supplementation of plasma with either vitamin C (85 microM) or butylated hydroxytoluene (BHT, 0.45 mM) was unable to protect LCAT from CS. In contrast, BHT completely protected LCAT activity from inhibition by copper. We conclude that unlike copper, CS-induced inhibition of plasma LCAT activity was unrelated to free radical-induced lipid peroxidation. The inhibition of LCAT activity by cigarette smoke may contribute to the development of atherosclerosis by impairing HDL metabolism and the reverse cholesterol transport process.

Ascorbic Acid↗

PubMed1994

Sodium oleate-facilitated reassembly of apolipoprotein A-I with phosphatidylcholine.

The influence of sodium oleate (oleate) on complexing of apolipoprotein A-I (apo A-I) with egg yolk phosphatidylcholine (EYPC) was evaluated. Without the use of additional detergent such as sodium cholate, oleate facilitates formation of a single complex of unique stoichiometry, approx. 76:2:20, molar ratio EYPC/apo A-I/oleate, and mean size 7.4 nm with round to ellipsoidal morphology. Near complete reassembly of apo A-I into the complex occurs when the stoichiometry of the mixture approximates that of the complex itself. With increasing content of EYPC in the mixture, the same complex is formed but in decreasing yield; larger complexes are not formed. The rate of complex formation decreases with increase of EYPC in the mixture. Reduction of pH in the reassembly mixture from 8.0 to 5.4 results in a marked reduction in complex formation indicating that ionized oleate facilitates lipidation. Removal of oleate by interaction of the complex with fatty acid-free human serum albumin does not degrade the complex. Incorporation of increasing amounts of unesterified cholesterol into the EYPC-sonicate progressively inhibits oleate-facilitated complex formation. This study shows that oleate, a physiologically relevant lipolysis-derived product, facilitates reassembly of apo A-I with EYPC and promotes formation of a small lipid-poor particle similar to that observed in nascent HDL and during in vivo or in vitro lipolysis of triacylglycerol-rich lipoproteins in the presence of HDL.

Apolipoprotein A-I↗

PubMed1994

Transgenic mice expressing human lipoprotein lipase driven by the mouse metallothionein promoter. A phenotype associated with increased perinatal mortality and reduced plasma very low density lipoprotein of normal size.

We have produced transgenic mice expressing human lipoprotein lipase (LPL) driven by the mouse metallothionein I promoter. We found that integration of the LPL gene construct was associated with a high perinatal mortality. Animals that survived the first 2 weeks of life grew normally afterwards. Compared with controls, transgenic animals had higher post-heparin plasma LPL and tissue LPL activities. Immunoreactive human LPL was detected in their post-heparin plasma but not in controls. Transgenic animals had significantly lower plasma very low density lipoprotein (VLDL) while on a regular laboratory chow. By electron microscopic analysis and nondenaturing polyacrylamide gradient gel electrophoresis, the size and morphology of the plasma VLDL were very similar in transgenic and control animals, which suggests that VLDL particles acted on by the increased tissue LPL in the transgenic animals were mostly taken up by the cell without being released back into circulation. The hypertriglyceridemia and elevated VLDL in response to sucrose feeding were completely abolished in transgenic animals. They also had lower VLDL lipids compared with control animals when they were fed a high-fat, high-cholesterol diet. Feeding the mother of transgenic mice a high-fat diet during pregnancy completely reversed the high perinatal mortality associated with the integrated transgene, which suggests that the deleterious effect of LPL overexpression may be related to the depletion of some essential lipid nutrient.

Animals↗

PubMed1994

Hypertriglyceridemia during late pregnancy is associated with the formation of small dense low-density lipoproteins and the presence of large buoyant high-density lipoproteins.

Late pregnancy is a unique metabolic state where there are transient increases in the concentrations of plasma triglyceride (TG), cholesterol, and apolipoprotein (apo) B. Despite the hypertriglyceridemic environment, we recently reported that there is an unusual shift in high-density lipoprotein (HDL) subclass distribution from smaller HDL subclasses to the largest, most buoyant HDL2b subclass. In the present investigation, we determined whether the subclasses of low-density lipoprotein (LDL) also change during this transient hyperlipidemic state and whether such changes were associated with plasma TG and apolipoprotein concentrations. Thirty-six Hispanic subjects at 35 to 36 weeks' gestation and at 6 weeks' postpartum were studied. At 35 to 36 weeks of gestation, plasma concentrations of TG, cholesterol, and apo B were increased (218 +/- 62, 234 +/- 48, and 130 +/- 35 mg/dL, respectively) over levels at 6 weeks' postpartum (112 +/- 69, 197 +/- 36, and 97 +/- 25 mg/dL respectively). However, lipoprotein(a) [Lp(a)] concentrations were not changed during pregnancy compared with postpartum. LDL subclass patterns (A, B, or I) were determined by nondenaturing polyacrylamide gradient gel electrophoresis in our group of 36 pregnant women. During late pregnancy, 97% of subjects were categorized as LDL subclass patterns B or I, indicating that small, dense LDL particles predominated. This predominance of small, dense LDL was associated with plasma TG concentration, where there was a significant inverse relationship (r = -.45, P < .01) between the LDL peak particle diameter and plasma TG concentration. In an apparent anomaly, there were significant increases in the concentrations of HDL cholesterol (HDL-C) and HDL2 mass, even though small, dense LDL particles predominated.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

The role of apolipoprotein A-I-containing lipoproteins in atherosclerosis.

The inverse relationship between HDL and apolipoprotein A-I concentrations and the risk for premature atherosclerosis is well established, but the mechanism whereby apolipoprotein A-I offers protection is still somewhat elusive. Recent studies suggest that a specific subpopulation within the lipoprotein (AI) subclass may be more effective than others in promoting cholesterol efflux from cells. In addition, it appears that the lipid-free form of apolipoprotein A-I may have an important role in the antiatherosclerotic process. Unique new functions of apolipoprotein A-I-containing particles in modulating cytokines and lipid hydroperoxide transport, together with their role in antiatherogenesis, are also discussed. Current research with transgenic mice, however, indicates that apolipoprotein A-II must be taken into consideration in understanding the development of atherosclerosis, because it appears to be a potent antagonist for the protective properties of apolipoprotein A-I.

Animals↗

PubMed1994

Modification of LCAT activity and HDL structure. New links between cigarette smoke and coronary heart disease risk.

The mechanism(s) through which smoking influences the progression of atherosclerosis is poorly understood. Recent evidence suggests that oxidants present in the gas phase of cigarette smoke are involved. We exposed human plasma to the filtered gas phase of cigarette smoke to assess its effects on plasma components involved in the antiatherogenic reverse cholesterol transport pathway. In our model, freshly isolated plasma (24 mL) was exposed to filtered air or gas-phase cigarette smoke for up to 6 hours at 37 degrees C. Lecithin-cholesterol acyltransferase (LCAT) activity was dramatically inhibited by cigarette smoke. A single 15-minute exposure to the smoke from an eighth of a cigarette was sufficient to reduce LCAT activity by 7%; additional exposures resulted in further decreases in activity. At 6 hours, only 22% of control LCAT activity remained in plasma exposed to smoke. Compared with control, gas-phase cigarette smoke-exposed plasma possessed high-density lipoprotein (HDL) with increased (16%) negative charge and with cross-linked apolipoproteins AI and AII. These data demonstrate that gas-phase cigarette smoke can inhibit a key enzyme (LCAT) and modify an integral lipid transport particle (HDL) that are essential components for the normal function of the reverse cholesterol transport pathway. Gas-phase cigarette smoke-induced modification of the reverse cholesterol transport pathway may provide a new mechanistic link between cigarette smoke and coronary heart disease risk.

Adult↗

PubMed1994

Heparin-induced lipolysis in hypertriglyceridemic subjects results in the formation of atypical HDL particles.

This study reports on the characterization of high density lipoprotein (HDL) in normotriglyceridemic and hypertriglyceridemic (HTG) subjects, after a fat meal and heparin-induced release of lipases. Samples for detailed analysis of HDL by density gradient ultracentrifugation and nondenaturing gradient gel electrophoresis were collected at 0 h and 5 h after the meal and 15 min after the administration of heparin. The normotriglyceridemic subjects were subdivided into two groups: those who remained normotriglyceridemic 5 h after the meal (NTG) or those who were hypertriglyceridemic at this time point (NTG-HTG). At the outset of the study, mean triglyceride levels were significantly higher (P < 0.001) and HDL cholesterol levels lower (P < 0.02) in the HTG group. The HDL particles in this group were enriched with triglyceride (P < 0.001). Serum triglyceride levels rose in all three groups after the fat meal and this was associated with further triglyceride enrichment of the HDL particles. In all groups, rapid lipolysis induced by heparin caused a significant decrease in plasma triglycerides and increase in free fatty acid levels, these changes being greatest in the HTG group. HDL density profiles of the study groups prior to the administration of heparin demonstrated two distinct peaks at density 1.09 g/ml (HDL2) and 1.13 g/ml (HDL3). However, after the administration of heparin to the HTG group, only a single peak in the HDL profile was evident that was located at the density region corresponding to HDL2 (1.09 g/ml). Upon gradient gel electrophoresis of this peak, there was an increased number (P < 0.005 vs. NTG) of small particles (< 4.37 nm) whose size was similar to the size range normally associated with HDL3b and HDL3c. Similar changes in HDL density and size after the administration of heparin were observed in the NTG-HTG group who were also hypertriglyceridemic postprandially. By contrast, the density gradient profiles and sizes of the HDL particles did not change after the administration of heparin to NTG subjects. Thus, the activation of lipolysis in HTG subjects leads to the generation of atypical HDL particles that are small but of reduced density. Rapid clearance of such particles could account for the inverse relationship between triglyceride and HDL cholesterol in this population subgroup.

Body Mass Index↗

PubMed1993

Re-uptake of nascent low-density lipoproteins by HepG2 cells.

The kinetics and specificity of the interaction of nascent HepG2 LDL with the HepG2 LDL receptor were examined. 125I-Labeled HepG2 LDL and plasma LDL were bound by HepG2 cells in a specific and saturable manner at 4 degrees C. Competition studies with HepG2 LDL and plasma LDL indicated that both ligands bound to the same receptor. Scatchard analyses of the specific 4 degrees C-binding data revealed a Kd of 75 nM for HepG2 LDL and a Kd of 30 nM for plasma LDL suggesting that HepG2 LDL bind less efficiently to the HepG2 LDL receptor than plasma LDL. Binding, internalization and degradation studies carried out at 37 degrees C indicated that HepG2 cells are capable of catabolizing their own nascent LDL; however, under normal experimental conditions re-uptake of nascent LDL is quantitatively insignificant.

Binding, Competitive↗

PubMed1993

Unusual high-density lipoprotein subclass distribution during late pregnancy.

Plasma lipoprotein distribution during late pregnancy is unusual since high-density lipoprotein (HDL) levels are increased in the presence of hypertriglyceridemia; the latter is usually associated with decreases in HDL levels. To determine whether there is a relationship between late-pregnancy lipid levels and specific HDL subclasses, HDL size distribution was determined by nondenaturing gradient gel electrophoresis (GGE) in a group of 36 women at 35 to 36 weeks of gestation and again at 6 weeks' postpartum, and in a group of 10 nonpregnant women. At 35 to 36 weeks of gestation, plasma triglyceride (TG) and cholesterol concentrations were significantly increased over postpartum levels (218 +/- 62 v 112 +/- 69 mg/dL and 234 +/- 48 v 197 +/- 36 mg/dL, respectively). During late pregnancy, apolipoprotein A-I (apo A-I) and HDL cholesterol concentrations were also increased relative to postpartum levels (211 +/- 42 v 168 +/- 20 mg/dL and 63 +/- 13 v 53 +/- 11 mg/dL, respectively). GGE analysis indicated that at 35 to 36 weeks of gestation, 86% of the subjects had a substantial increase of the most buoyant and largest of the HDL species, HDL2b; postpartum and nonpregnant HDL subclass distribution was characterized by the predominance of HDL3a, which are smaller, more dense HDL. The shift in the HDL subclass distribution during late pregnancy was associated with significant positive correlations between HDL2b and apo A-I (r = .50, P < .05) and HDL cholesterol (r = .60, P < .001). There were significant elevations in the concentrations of cholesteryl ester transfer protein (CETP) and estrogen during late pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Apolipoprotein A-I-cell membrane interaction: extracellular assembly of heterogeneous nascent HDL particles.

The ability of lipid-free human apoA-I expressed by transfected Chinese hamster ovary (CHO) cells to form apoA-I-lipid complexes extracellularly when incubated with CHO cell monolayers was investigated. Lipid-free apoA-I was incubated with nontransfected CHO-C19 cells for 24 h and extracellular assembly products were isolated at d < or = 1.235 g/ml; approximately 12% of the incubated apoA-I floated at d < or = 1.235 g/ml when apoA-I was added at 10 micrograms/ml. The composition of the particles was 51.3% protein, 20.3% phospholipid, and 28.3% cholesterol. Electron microscopy of the apoA-I-lipid complexes revealed that discoidal particles 15.4 +/- 4.1 nm diameter predominated but some vesicular particles 34.7 +/- 16.8 nm diameter were also in evidence. Nondenaturing gradient gel electrophoresis of the extracellular assembly products formed after 24 h incubation with 10 micrograms/ml apoA-I showed particle size heterogeneity with major bands at 11.2 and 9.0 nm; additional minor components banded at 7.3, 17.7, and 19.5 nm. This size distribution, as well as composition and electron microscopic structure, is similar to that of complexes isolated from the medium of CHO cells transfected with the human apoA-I gene. The formation of extracellular assembly complexes was concentration-dependent such that at 2 micrograms apoA-I/ml for 24 h, primarily 7.3 nm complexes were formed; at 4 micrograms/ml the distribution was more heterogeneous and the major band peaked at 9.2 nm, while at 8 micrograms/ml the 7.3 nm component was greatly diminished and the 11.2 nm component was the major one.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗