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J C Gibson

Publications and source records attributed to J C Gibson.

At least 37 records · Page 2Linked to original sources
PubMed1985

Immunoaffinity isolation of apolipoprotein E-containing lipoproteins.

Discrete apolipoprotein E-containing lipoproteins can be identified when EDTA plasma is fractionated on columns of 4% agarose. The present study has demonstrated, by physical and metabolic criteria, that these apolipoprotein E-containing lipoprotein subclasses may be further isolated by immunoaffinity chromatography. Whole plasma was first bound to an anti-apolipoprotein E immunoadsorbent prior to gel filtration on 4% agarose. After elution from the affinity column and dialysis, the bound fraction was chromatographed on 4% agarose. Discrete subfractions of apolipoprotein E could be demonstrated within elution volumes similar to those observed in the original plasma. When whole plasma was first submitted to gel filtration and the apolipoprotein E-containing lipoproteins of either intermediate- or of high-density lipoprotein (HDL) size were subsequently bound to anti-apolipoprotein E columns, the bound eluted fractions maintained their size and physical properties as shown by electron microscopy and by rechromatography on columns of 4% agarose. The metabolic integrity of apolipoprotein E-containing very-low-density lipoproteins (VLDL) was examined by coinjection into a cynomolgus monkey of 125I-labeled apolipoprotein E-rich and 131I-labeled apolipoprotein E-deficient human VLDL which had been separated by immunoaffinity chromatography. The plasma specific activity time curves of the apolipoprotein B in VLDL, intermediate-density (IDL) and low-density (LDL) lipoproteins demonstrated rates of decay and precursor-product relationships similar to those obtained after injection of whole labeled VLDL, supporting the metabolic integrity of VLDL isolated by immunoaffinity chromatography.

Animals↗
PubMed1985

Plasma apolipoprotein secretion by human monocyte-derived macrophages.

Apolipoprotein E has been demonstrated to be a major secretory protein of human monocyte macrophages. The synthesis of the other plasma apolipoproteins by these cells has not been documented. Human monocyte macrophages cultured for 17-76 days were preincubated for 24 h in RPMI 1640/0.2% bovine serum albumin with or without malondialdehyde-LDL (100 micrograms/ml), followed by an additional 24 h incubation in RPMI 1640/0.2% bovine serum albumin. The media from the two incubation periods were analyzed for apolipoproteins A-I, B, C-II, C-III and E by specific radioimmunoassays. No apolipoprotein B mass was detected with a specific radioimmunoassay capable of detecting 10 ng apolipoprotein B. No apolipoproteins A-I, C-II or C-III mass was detected, even though the radioimmunoassays for these apolipoproteins were as sensitive as that for apolipoprotein E (detection limit of 0.2 ng). In contrast, significant levels of macrophage-secreted apolipoprotein E were quantified. Baseline apolipoprotein E production ranged from 0.64 to 2.82 micrograms/mg cell protein per 24 h. Preincubation in the presence of malondialdehyde-LDL (100 micrograms/ml) stimulated a 1.6-3.0-fold increase in apolipoprotein E secretion. The identification of the immunoreactive material as apolipoprotein E was confirmed by labelling the cells with [35S]methionine, followed by fractionation of the 35S-labelled secretory products by anti-apolipoprotein E affinity chromatography and SDS-gel electrophoresis. We thus report the absence of synthesis of apolipoproteins A-I, B, C-II and C-III by cultured human monocyte macrophages. These cells, however, can synthesize microgram levels of apolipoprotein E on a per mg protein basis.

Apolipoprotein A-I↗
PubMed1985

Plasma lipoprotein abnormalities associated with acquired hepatic triglyceride lipase deficiency.

Two enzymes, lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL), are released into human plasma after intravenous injection of heparin. LPL is the major enzyme responsible for initiating catabolism of chylomicrons and very-low-density lipoproteins (VLDL). The physiological role of HTGL is less certain. HTGL has been postulated to be an alternate enzyme to LPL in hydrolysis of triglyceride in VLDL and to be an important enzyme for removal of phospholipid from both low-density lipoproteins (LDL) and high-density lipoproteins (HDL). In this latter role, this enzyme would convert larger, lighter lipoprotein particles to smaller denser particles. HTGL deficiency has been found in severe liver disease and with a genetic deficiency of this enzyme. A unique patient is described with acquired hepatic triglyceride lipase deficiency and vitamin A intoxication. This patient developed hypercholesterolemia with an increase in both LDL and HDL. An increased proportion of lighter LDL (LDL1) and HDL (HDL2) was noted. In addition, after administration of heparin there was no shift in the distribution of apoE in plasma fractionated using a column containing 4% agarose. These findings are consistent with a postulated role of HTGL in metabolism of light LDL and HDL particles and some classes of apoE containing lipoproteins.

Chromatography, Agarose↗
PubMed1985

Regulation of the production and catabolism of plasma low density lipoproteins in hypertriglyceridemic subjects. Effect of weight loss.

In subjects with hypertriglyceridemia, plasma concentrations of low density lipoprotein (LDL) cholesterol are often normal or reduced. Perturbations that alter plasma very low density lipoprotein (VLDL) concentrations are associated with opposite changes in plasma LDL levels. To determine the mechanisms regulating plasma LDL levels, we used 131I-VLDL and 125I-LDL to measure the fractional catabolic rates (FCR), production rates (PR), and rates of interconversion of apoprotein B (apo B) in VLDL, intermediate density lipoprotein, and LDL in six hypertriglyceridemic subjects pre- and post-weight reduction. [2-3H]glycerol was used to quantitate VLDL triglyceride PR. All data are presented as mean +/- SD. Percent ideal body weight fell from 132 +/- 17.9 to 119 +/- 15.9% in the group, P less than 0.05. After weight loss, plasma VLDL triglyceride (486.0 +/- 364.1 vs. 191.3 +/- 65.4 mg/dl, P less than 0.05) and VLDL apo B (32.2 +/- 12.0 vs. 14.8 +/- 6.8 mg/dl, P less than 0.05) concentrations were reduced. VLDL triglyceride PR also fell after weight reduction (56.6 +/- 39.0 vs. 28.6 +/- 23.1 mg/kg per h, P less than 0.05), as did VLDL apo B PR (47.9 +/- 41.4 vs. 19.0 +/- 14.1 mg/kg per d, P less than 0.05). Pre-weight loss, plasma LDL cholesterol and apo B levels were low-normal or reduced (64.0 +/- 12.6 and 58.4 +/- 11.9 mg/dl, respectively) despite normal or elevated LDL apo B PR (17.4 +/- 7.2 mg/kg per d). The reduced cholesterol and apo B levels were associated with increased FCRs (0.68 +/- 0.29 d-1) and reduced cholesterol/protein ratios (1.01 +/- 0.18) in LDL. The plasma levels of LDL cholesterol and apo B rose after weight reduction (84.8 +/- 24.9, P less than 0.05; and 69.5 +/- 14.3 mg/dl, P less than 0.05, respectively, vs. base line). These increased concentrations resulted from a combination of events. First, the FCR for LDL apo B fell in five of six subjects with a significant reduction for the group as a whole (0.48 +/- 0.11 d-1, P less than 0.05 vs. base line). Second, the cholesterol/protein ratio increased in all six subjects with a significantly greater mean after weight loss (1.25 +/- 0.27, P less than 0.05 vs. base line). In contrast, the LDL apo B PR fell or was essentially unchanged in the six subjects after weight loss (mean, 14.4 +/- 2.8 mg/kg per d; NS vs. pre-weight loss). The changes in LDL catabolism and composition were associated with changes in the source of LDL apo B. Pre-weight loss, 73.3% of LDL was derived from VLDL, while 26.7% was directly secreted into plasma. Post-weight reduction, VLDL-derived LDL fell to 46.8% of total, while direct secretion accounted for 53.2% of LDL production. These changes were significant; P < 0.95. Thus, all subjects had direct secretion of LDL apo B and the magnitude of this source of VLDL triglyceride secretion. These results indicate that the regulation of plasma LDL levels in hypertriglyceridemic subjects is quite complex and that the rise in LDL levels after weight loss results from reduction in the fractional catabolism of this lipoprotein. The fall in the FCR is associated with changes in the source of LDL and in its composition.

Adult↗
PubMed1985

Effect of heparin-induced lipolysis on the distribution of apolipoprotein e among lipoprotein subclasses. Studies with patients deficient in hepatic triglyceride lipase and lipoprotein lipase.

In normal subjects, apolipoprotein E (apo E) is present on very low density lipoproteins (VLDL) (fraction I) and on particles of a size intermediate between VLDL and low density lipoproteins (LDL) (fraction II). The major portion of apo E is, however, on particles smaller than LDL but larger than the average high density lipoproteins (HDL) (fraction III). To investigate the possible role of the vascular lipases in determining this distribution of apo E among the plasma lipoproteins, we studied subjects with primary deficiency of either hepatic lipase or of lipoprotein lipase and compared them with normal subjects. Subjects with familial hepatic triglyceride lipase deficiency (n = 2) differ markedly from normal in that fraction II is the dominant apo E-containing group of lipoproteins. When lipolysis of VLDL was enhanced in these subjects upon release of lipoprotein lipase by intravenous heparin, a shift of the apo E from VLDL into fractions II and III was observed. In contrast, apolipoproteins CII and CIII (apo CII and CIII, respectively) did not accumulate in intermediate-sized particles but were shifted markedly from triglyceride rich lipoproteins to HDL after treatment with heparin. In subjects with primary lipoprotein lipase deficiency (n = 4), apo E was confined to fractions I and III. Release of hepatic triglyceride lipase by heparin injection in these subjects produced a shift of apo E from fraction I to III with no significant increase in fraction II. This movement of apo E from large VLDL and chylomicron-sized particles occurred with little hydrolysis of triglyceride and no significant shift of apo CII or CIII into HDL from triglyceride rich lipoproteins. When both lipoprotein lipase and hepatic triglyceride lipase were released by intravenous heparin injection into normal subjects (n = 3), fraction I declined and the apo E content of fraction III increased by an equivalent amount. Either moderate or no change was noted in the intermediate sized particles (fraction II). These data strongly support the hypothesis that fraction II is the product of the action of lipoprotein lipase upon triglyceride rich lipoproteins and is highly dependent on hepatic triglyceride lipase for its further catabolism. In addition, the hydrolysis by hepatic triglyceride lipase of triglyceride rich lipoproteins in general results in a preferential loss of apo E and its transfer to a specific group of large HDL.

Adult↗
PubMed1985

Evidence for non-equilibrating pools of apolipoprotein C-III in plasma lipoproteins.

Using immunoaffinity chromatography to isolate apoC-III from radiolabeled lipoproteins for direct determination of specific radioactivity, we have studied the metabolism of human apoC-III in VLDL and in HDL following the bolus injection of 125I-labeled VLDL. Transfer of apoC-III radioactivity from VLDL to HDL was detected in the plasma sample drawn 5 min after injection of the tracer. However, the specific radioactivity of apoC-III in VLDL was found to be higher than that in HDL, with this difference being maintained throughout the sampling period (48-72 hr). The ratios of the respective specific activities ranged from 1.2 to 1.9 in six subjects studied (two normolipidemics and four hypertriglyceridemics). When 125I-labeled HDL was injected as the tracer, however, the higher apoC-III specific radioactivity was associated with the HDL fraction. This lack of complete equilibration of apoC-III between VLDL and HDL in vivo was further characterized by in vitro studies using either 125I-labeled VLDL or 125I-labeled HDL. All incubations were carried out for 3 hr at 37 degrees C followed by 16 hr at 4 degrees C and the apoC-III specific activity in each lipoprotein fraction was directly determined after immunoaffinity chromatography. In a study of plasma from a mildly hypertriglyceridemic subject in which 125I-labeled VLDL was incubated with unlabeled HDL, apoC-III specific activities in VLDL remained 30% greater than that in HDL. When 125I-labeled HDL (from the same subject) was incubated with unlabeled VLDL of apoC-III, final specific activity in VLDL was less than 10% of that of HDL apoC-III. Differences in specific activities were also demonstrated when radiolabeled purified apoC-III was exchanged onto VLDL prior to its incubation with HDL. A consistent difference in apoC-III specific activities in VLDL and HDL was observed after isolation of the particles either by molecular sieve chromatography or by ultracentrifugation. These studies demonstrated that, while the exchange of apoC-III between VLDL and HDL may be very rapid, this equilibration is not complete. Pools of apoC-III that do not participate in the equilibration process are present in both the VLDL and HDL fractions and could account for 30-60% of the total apoC-III mass in each lipoprotein fraction.

Adult↗
PubMed1984

Reduced plasma concentrations of total, low density lipoprotein and high density lipoprotein cholesterol in patients with Gaucher type I disease.

Plasma lipid and serum apoprotein concentrations were determined in twenty-nine individuals with Gaucher type I disease. Plasma total cholesterol, low density lipoprotein (LDL) cholesterol and high density lipoprotein (HDL) cholesterol were all significantly reduced in the patients with Gaucher disease compared to a group of matched control subjects. Total, LDL and HDL cholesterol were lower in males than in females with Gaucher disease. These sex differences appeared to be inversely correlated with the severity of disease manifestations which were greater in the males. Serum levels of apoprotein-B and apoprotein-AI, the major structural apoproteins of LDL and HDL, respectively, were decreased in the subjects with Gaucher disease. Thus, the reductions in LDL and HDL cholesterol were associated with reduced numbers of lipoprotein particles in plasma. In contrast, apoprotein-E, a protein which is secreted by several tissues, including activated macrophages and which may mediate hepatic catabolism of lipoproteins, was elevated in the patients. Since macrophages may also catabolize lipoproteins, Gaucher disease may serve as a model for the effect of activated macrophages upon human lipoprotein metabolism.

Adolescent↗
PubMed1984

Precipitation of apo E-containing lipoproteins by precipitation reagents for apolipoprotein B.

We measured the solubility of apolipoprotein E (apo E) after precipitation, with heparin-Mn2+ or dextran sulfate-Mg2+, of lipoproteins containing apo B. Data from 46 randomly selected subjects suggest that apo E is readily precipitated by dextran sulfate-Mg2+, but that heparin-Mn2+ preferentially precipitates apo E associated with apo B-containing lipoproteins while leaving the apo E-containing fraction of high-density lipoproteins (HDL) in solution. In a more detailed analysis of three subjects, we measured the lipoprotein association of apo E by column chromatography on agarose beads, before and after its precipitation from plasma. This study confirmed the preferential solubility of apo E associated with HDL lipoproteins. Using plasma from two normolipidemic subjects, we maintained the heparin concentration at 1.30 g/L and varied the manganese concentration from 9.2 to 184 mmol/L. A 46 mmol/L concentration best separated apo E-containing HDL from apo B-containing lipoproteins. Thus, at these final concentrations, heparin-Mn2+ appears to precipitate the apo E associated with apo B-containing lipoproteins, leaving soluble most of the apo E associated with lipoproteins of HDL size.

Apolipoprotein A-I↗
PubMed1984

Clinical and experimental methods for the determination of cholesterol absorption.

The following section summarizes this methodological treatment of cholesterol absorption by considering the advantages and disadvantages of the available methods. As outlined in Table 6, there are certain technical and interpretational disadvantages to all methods which should be weighed in deciding the appropriate method to use for a given experimental protocol. Direct methods are virtually the only ones capable of measuring the total flux of cholesterol between intestinal lumen and lymph. All the other methods allow interpretations relating only to the flux of exogenous cholesterol. On the other hand, the direct methods are invasive--involving surgery--in the case of experimental animals, and intubation, in the case of intestinal perfusion. This could potentially lead to unnatural conditions for the absorptive surface of the gut. Direct methods, balance methods, and the isotopic equilibrium method all measure a mass of cholesterol transferred. Method IV, the plasma isotope ratio method, and the continuous feeding method, on the other hand, only provide an estimate of the percent of an administered dose absorbed, although this can be converted to a mass estimate with an accurate knowledge of intake. The balance methods, continuous feeding, and isotopic equilibrium method all provide an estimate of absorption over time. The plasma isotope ratio method and method IV, however, rely on repeated measurements to measure fluctuations in absorption. In their favor, method IV and the isotope ratio technique have several advantages that make them the methods of choice for human and large-scale animal studies. These are simplicity, low isotope dosage, and the fact that they are readily done on an outpatient basis. In general, then, direct or balance methods are preferable for precise studies where absolute levels of absorbed cholesterol and fluctuations over time need to be assessed. Direct methods certainly provide the greatest interpretational flexibility in this regard by measuring endogenous and exogenous flux. Among balance methods, method II may be the most precise, but method I is the easiest to perform technically, may be used on an outpatient basis, and requires lower isotope dosage. For evaluating differences in percent cholesterol absorption in man and in all animals except the rabbit, the plasma isotope ratio technique is technically the easiest method both for the investigator and the subject. It also appears to compare very favorably with the more tedious balance methods and will undoubtedly be used in more and more experimental studies of cholesterol absorption.

Animals↗
PubMed1983

Apolipoprotein E-enriched lipoprotein subclasses in normolipidemic subjects.

This study was undertaken to objectively define the lipoprotein association of apoE without ultracentrifugation and represents a description of three distinct apoE-containing lipoprotein (LP) subclasses in normal human plasma. The lipoproteins of whole plasma were fractionated in a continuous manner by molecular sieve chromatography using 4% agarose and the elution profile of apoE was compared to that of apoB, apoA-I, cholesterol, and triglyceride. The data show that all apoE in normal subjects is LP-associated and is confined to three discrete LP subfractions of characteristic size. The largest (fraction I), appears to be a subclass of very low density lipoproteins (VLDL). The other two, however, are distinct in size from the major cholesterol-carrying LP; fraction II is intermediate in size between VLDL and the major apoB-containing lipoprotein, LDL; and fraction III is larger than the major apoA-I-containing lipoproteins, HDL, but smaller than LDL. Parallel chromatography of supernatant and infranatant fractions obtained after ultracentrifugation of serum at each of three different densities, 1.006, 1.019, and 1.063 g/ml confirmed that fraction I is of density less than 1.006 g/ml, but that fractions II and III overlap the conventional density intervals.

Apolipoproteins↗
PubMed1983

Direct measurement of apoprotein C-III specific activity in 125I-labeled very low density lipoproteins using immunoaffinity chromatography.

We have developed a technique for isolating apoprotein C-III by immunoaffinity chromatography, allowing the measurement of its specific radioactivity in lipoprotein fractions from small plasma samples. IgG specific for apoC-III was purified from goat antisera and bound to Sepharose. One ml of this gel (5 mg of IgG) bound 80-90 micrograms of apoC-III. The specific activity of apoC-III was determined by application of delipidated very low density lipoproteins to 1-ml columns and analysis of the protein eluted at pH 2.5 for mass and radio-activity. The coefficient fo variation for apoC-III specific activity determination from 125I-labeled VLDL was 4.3%. Minimal contamination of the eluates by apoproteins B, E, and C-II was confirmed by radioimmunoassay (0.3-1.2%). Following the injection of autologous 125I-labeled VLDL, specific activity decay curves for VLDL apoC-III were biexponential, with the clearance of apoC-III being slower in hypertriglyceridemic subjects. These affinity columns can be used repeatedly and yield reproducible results. This technique should be useful for simultaneous studies of the turnover of several apoproteins in the same individual following a single injection of labeled autologous lipoprotein.

Apolipoprotein C-III↗
PubMed1982

Increased low-density-lipoprotein catabolism in myeloproliferative disorders.

Hypocholesterolemia reported in patients with myeloproliferative disorders prompted our investigation of lipoprotein metabolism in these patients. The production and fractional catabolic rates of very-low-density lipoprotein (VLDL) apoprotein-B were measured using 131I-VLDL; those of VLDL triglyceride, using 3H-glycerol; and those of low-density lipoprotein (LDL) apoprotein-B, using 125I-LDL. Plasma total and LDL cholesterol levels (mean +/- SD) were significantly reduced in seven patients with myeloproliferative diseases, compared to five normal subjects (93.1 +/- 20.3 mg/dL versus 166.8 +/- 24.6 mg/dL and 50.3 +/- 14.8 mg/dL versus 107 +/- 20.8 mg/dL, respectively). The production rates of VLDL apoprotein-B and VLDL triglyceride were normal in the patients. The fractional catabolic rate of LDL apoprotein-B was increased in the patients with myeloproliferative diseases (0.89 +/- 0.32/d versus 0.52 +/- 0.10/d; p less than 0.05); this increased rate was associated with reduced plasma LDL apoprotein-B levels (41.7 +/- 7.1 mg/dL versus 57.0 +/- 11.3 mg/dL; p less than 0.05) despite normal or elevated LDL apoprotein-B production (16.7 +/- 5.3 mg/kg body weight . d versus 12.9 +/- 1.2 mg/kg body weight . d). The site (or sites) of increased LDL catabolism in these hypocholesterolemic patients with myeloproliferative disorders is under investigation.

Adult↗
PubMed1980

Impaired plasma triglyceride clearance as a feature of both uremic and posttransplant triglyceridemia.

After accurate plasma volume calculation, endogenous plasma very-low-density-lipoprotein (VLDL)-triglyceride turnover rates were measured in 20 undialyzed patients with chronic renal failure (CRF) and in 16 renal transplant recipients with stable graft function. When kinetic criteria were based on a group of healthy subjects (Vmax = 36.7 mumoles/hr/kg), it was clear that, on the whole, CRF patients had a reduced capacity for VLDL-triglyceride removal (Vmax = 14.0 mumoles/hr/kg), as did graft recipients (Vmax = 19.5 mumoles/hr/kg). In transplant recipients with impaired graft function, however, extremes of both under removal and over production of VLDL-triglycerides were observed. In CRF, defective clearance was accompanied by a reduction in postheparin lipoprotein and hepatic lipase activities, although there was no statistical relationship. Enzyme activities were not reduced, however, after transplantation, and the metabolic factors responsible for defective clearance were not clearly identified.

Adolescent↗
PubMed1980

Vascular disease risk factors in women with premature menopause.

The vascular disease risk factor profile was studied in 21 women who had experienced a premature menopause due to bilateral oophorectomy. Compared with age-matched menstruating control subjects, oophorectomized women did not differ appreciably with respect to the prevalence of major vascular risk factors other than hyperlipidaemia, nor did they exhibit an excessive prevalence of vascular disease. In oophorectomized women not receiving hormone replacement therapy, the total serum cholesterol and low density lipoprotein (LDL) cholesterol levels were increased, while high density lipoprotein (HDL) cholesterol was not significantly altered. In women receiving replacement with ethinyl oestradiol, the total and LDL cholesterol were significantly decreased while HDL cholesterol was significantly increased, relative to oophorectomized women not receiving hormone replacement. The increased proportion of LDL to HDL in those not receiving hormone replacement suggests that they may be exposed to an increased theoretical long-term vascular risk, and this might justify appropriate hormone replacement in all such women, subject to certain safeguards.

Adult↗
PubMed1980

Type I hyperlipoproteinaemia and recurrent scrotal pain.

A three-year-old boy is described with type I hyperlipoproteinaemia in association with recurrent scrotal pain and hepatosplenomegaly. His parents are consanguinous and it is likely that he is homozygous for an autosomal recessive trait, characterized by the absence of plasma lipoprotein lipase following intravenous injection of heparin. Studies have been performed in a number of first degree relatives, but the findings are inconclusive. He has responded well to a low fat diet with dramatic reductions in elevated plasma triglyceride concentrations.

Adult↗