Search PubMed⌕ Search

Biomedical subjects

E J Schaefer

Publications and source records attributed to E J Schaefer.

At least 253 records · Page 14Linked to original sources
PubMed1988

Differences in low density lipoprotein subfractions and apolipoproteins in premenopausal and postmenopausal women.

Postmenopausal or oophorectomized women are at higher risk for the development of coronary artery disease than are premenopausal women. These differences in risk may be due to alternations in plasma lipoproteins modulated by hormonal changes. Plasma cholesterol, triglyceride, lipoprotein cholesterol, and apolipoprotein A-I and B (apoB) concentrations, as well as low density lipoprotein (LDL) particle size (LDL 1-7), as assessed by 2-16% polyacrylamide-agarose gradient gel electrophoresis, were determined in 87 premenopausal and 43 postmenopausal women. All were participants in the Framingham Offspring Study, were gynecologically normal, and were not taking any hormones. The postmenopausal women had significantly (P less than 0.05) higher plasma LDL cholesterol concentrations than did the premenopausal women. Plasma triglyceride, total cholesterol, very low density lipoprotein cholesterol, and apoB levels were higher, and apoA-I and high density lipoprotein cholesterol were lower in the postmenopausal group, but these differences were not significant at P less than 0.05. The postmenopausal women were likely to have small LDL particles compared to premenopausal women. Controlling for age and body mass index effects significantly reduced the differences in total cholesterol, LDL cholesterol, apoB, and LDL particle size and broadened the differences in apoA-I and high density lipoprotein cholesterol. These data indicate that menopause is positively correlated with LDL cholesterol (P less than 0.05) and decreased LDL particle size (P less than 0.05) after adjusting for significant covariates.

Aging↗
PubMed1988

Coronary artery disease, lipid disorders and genetic polymorphisms.

Coronary artery disease (CAD) is the leading cause of morbidity and mortality in most industrialized countries, accounting for one out of every two deaths in the United States. Disorders of the lipid transport system resulting from complex interactions among nutritional, environmental and genetic factors, play a very important role in the development of this disease. It has been proposed that low density lipoproteins (LDL) cause cholesterol deposition in the arterial wall, whereas high density lipoproteins (HDL) promote efflux of cholesterol from this site. Thus, low levels of HDL and/or high levels of LDL, have been associated with increased risk of CAD. Apolipoprotein A-I (Apo A-I) is the major protein component of HDL, and it has been proposed that the levels of this protein are a better predictor of risk of CAD than the level of cholesterol in HDL. The human Apo A-I gene has been characterized, and it has been found to be adjacent to the genes for apolipoproteins C-lll and A-lV on the long arm of chromosome 11. The cloning of these genes provides the appropriate tools to apply molecular genetic techniques to find differences between individuals at the gene level (restriction fragment length polymorphisms, RFLP) and to identify specific alleles at this particular gene locus which may be associated with a clinical phenotype, more specifically, premature CAD and familial hypoalphalipoproteinemia. In a preliminary study we have identified a Pst I restriction-endonuclease site flanking the human apolipoprotein A-I gene at its 3' end that is polymorphic.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein A-I↗
PubMed1988

Lipoprotein cholesterol concentrations in the plasma of human subjects as measured in the fed and fasted states.

Lipoprotein cholesterol concentrations in plasma are routinely estimated by using the Friedewald formula, whereby very-low-density lipoprotein cholesterol (VLDL-C) is estimated to be one-fifth the plasma triglyceride concentration. Ordinarily, this formula is applied only to plasma sampled from patients in the fasted state. To determine whether lipoprotein cholesterol measurements are altered substantially in plasma sampled from nonfasting subjects, we obtained postprandial blood samples from 22 healthy subjects (nine men, 13 women, ages 22-79 years) fed a fat-rich meal (1 g fat per kilogram body wt.). The plasma triglyceride concentration increased postprandially in all subjects (233 +/- 16% of baseline at 3 h). The mean cholesterol concentration in plasma was essentially unchanged. High-density lipoprotein cholesterol (HDL-C) was significantly decreased (94 +/- 2% at 3 h, P less than 0.001). VLDL-C and low-density lipoprotein cholesterol (LDL-C), estimated by the Friedewald formula, were compared with measurements obtained by modified Lipid Research Clinics (LRC) methodology. As measured by either method, VLDL-C increased and LDL-C decreased significantly after the fat-rich meal. These postprandial changes were significantly greater (P less than 0.01) when estimated by the Friedewald formula than by LRC methodology. We conclude that (a) lipoprotein cholesterol concentrations measured in the fed subject differ significantly from those measured in the fasted subject, and (b) plasma must be obtained after at least a 12-h fast if an individual's risk of coronary heart disease is to be accurately assessed.

Adult↗
PubMed1988

Postprandial plasma lipoprotein changes in human subjects of different ages.

Plasma lipoprotein changes were monitored for 12 hr after a fat-rich meal (1 g of fat/kg body weight) in 22 subjects (9 males, 13 females, 22-79 yr old). Plasma triglyceride, measured hourly, peaked once in some subjects, but twice or three times in others. The magnitude of postprandial triglyceridemia varied considerably between subjects (range: 650-4082 mg.hr/dl). Males tended to have greater postprandial triglyceridemia than females, and elderly subjects had significantly (P less than 0.05) greater postprandial triglyceridemia than younger subjects. Total plasma cholesterol, measured every three hr, increased significantly (6.0 +/- 2.1%) in 7 subjects, decreased significantly (7.1 +/- 1.2%) in 10 subjects, and remained unchanged in the remainder. Single spin ultracentrifugation and dextran sulfate precipitation procedures were used to quantitate triglyceride and cholesterol in triglyceride-rich lipoproteins (TRL, d less than 1.006 g/ml), low density lipoproteins (LDL), and high density lipoproteins (HDL). Plasma TRL and HDL triglyceride increased after the fat meal, while LDL triglyceride decreased at 3 hr but increased at 9 and 12 hr. TRL cholesterol increased postprandially, while LDL and HDL cholesterol decreased. Phospholipid (PL), free (FC) and esterified (EC) cholesterol measurements were carried out on the plasma and lipoprotein fractions of 8 subjects. Plasma PL increased significantly at 3, 6, and 9 hr after the fat-rich meal, due to increases in TRL and HDL PL. TRL CE increased postprandially, but a greater decrease in LDL and HDL CE caused plasma CE to be decreased. Plasma FC increased, predominantly due to an increase in TRL FC. Plasma concentrations of apolipoprotein A-I and apolipoprotein B both decreased after the fat-rich meal. The magnitude of postprandial triglyceridemia was inversely correlated with HDL cholesterol levels (r = -0.502, P less than 0.05) and positively correlated with age (r = -0.449, P less than 0.05), fasting levels of plasma triglyceride (r = 0.636, P less than 0.01), plasma apoB (r = 0.510, P less than 0.05), TRL triglyceride (r = 0.564, P less than 0.01), TRL cholesterol (r = 0.480, P less than 0.05) and LDL triglyceride (r = 0.566, P less than 0.01). Change in postprandial cholesterolemia was inversely correlated with fasting levels of HDL cholesterol (r = -0.451, P less than 0.05) and plasma apoA-I (r = -0.436, P less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1988

Plasma apolipoprotein changes in the triglyceride-rich lipoprotein fraction of human subjects fed a fat-rich meal.

Twenty two subjects (9 males, 13 females) were fed a fat-rich meal (1 g of fat/kg body weight). Triglyceride-rich lipoproteins (TRL) were isolated by ultracentrifugation (d less than 1.006 g/ml) from blood drawn 0, 3, 6, 9, and 12 hr after the meal. Plasma triglyceride increased then decreased postprandially, while plasma apoA-I and apoB concentrations decreased. TRL triglyceride, TRL total protein, and TRL apoB concentrations all increased then decreased after the fat-rich meal. Postprandial rise in plasma triglyceride was significantly correlated with fasting plasma triglyceride levels (r = 0.66, P less than 0.001); postprandial rise in TRL triglyceride was significantly correlated with fasting TRL triglyceride levels (r = 0.58, P less than 0.01); postprandial rise in TRL apoB was not, however, significantly correlated with fasting TRL apoB levels (r = 0.37, N.S.). TRL apolipoproteins were separated by polyacrylamide gradient (4-22.5%) gel electrophoresis and protein bands were scanned in two dimensions with a laser densitometer. Relative postprandial changes in the concentration of the TRL apolipoproteins were determined. TRL apoB-100, apoB-48, apoE, and apoC increased then decreased postprandially. The increase in TRL apoB-100 after the fat-rich meal was confirmed in 8 subjects by direct measurement of apoB-100 with a monoclonal antibody ELISA assay. ApoA-I concentration in TRL was unchanged. Albumin in the TRL fraction was significantly increased 12 hr after the meal. Subjects with a greater magnitude of postprandial triglyceridemia had a greater increase in TRL triglyceride and TRL apoB, but their TRL apoB-100/apoB-48 ratios were not different from subjects with less pronounced triglyceridemia. Assuming that plasma TRL containing apoB-100 are predominantly derived from the liver, our data suggest that triglyceride-rich lipoproteins from both the liver and intestine make a significant contribution to postprandial triglyceridemia.

Adult↗
PubMed1987

Similarity of cruzin, an inhibitor of Trypanosoma cruzi neuraminidase, to high-density lipoprotein.

A specific inhibitor of the neuraminidase of the protozoan parasite Trypanosoma cruzi was isolated recently and named cruzin. It is now shown that cruzin is similar to high-density lipoprotein by amino acid homology, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, by immunoblot analysis, and by isoelectric focusing. Cruzin purified by ion exchange chromatography and high-density lipoprotein isolated by density gradient ultracentrifugation inhibited Trypanosoma cruzi neuraminidase to the same extent. Cruzin or high-density lipoprotein restores to normal the decreased multiplication rate of Trypanosoma cruzi epimastigotes grown in a medium depleted of lipoproteins, suggesting that it may be important for survival of the parasite in nature.

Amino Acid Sequence↗
PubMed1987

Secretion of apolipoprotein A-I in lipoprotein particles following transfection of the human apolipoprotein A-I gene into 3T3 cells.

Apolipoprotein A-I (apoA-I) is the major protein constituent of plasma high density lipoproteins (HDL). To examine apoA-I processing and secretion, the human apoA-I gene (2.2-kilobase PstI-PstI fragment) linked to the mouse metallothionein promoter was transfected by electroporation into NIH 3T3 fibroblasts along with the plasmid pSV2 neo, which confers neomycin resistance. Transfected cells were selected for neomycin resistance and screened for the ability to produce apoA-I by enzyme-linked immunosorbent assay. In the absence of lipids in the medium, selected 3T3 cells secreted apoA-I, mainly in the proprotein form, at density greater than 1.25 g/ml. Following incubation of cells with lipids, and subsequent washing with lipid-free medium, apoA-I was recovered in the HDL region (1.063-1.21 g/ml) as well as in the 1.21 g/ml infranatant. Examination of the HDL fraction by electron microscopy revealed round particles, 10-21 nm in diameter. These data indicate that human apoA-I secreted by transfected 3T3 fibroblasts can assemble into lipoprotein particles under the appropriate conditions.

Animals↗
PubMed1987

Automated enzymatic standardized lipid analyses for plasma and lipoprotein fractions.

Excellent normal ranges for plasma lipid and lipoprotein cholesterol levels have been developed by the Lipid Research Clinics program, standardized by the Centers for Disease Control (CDC). However these values were generated by methods not currently in use in most clinical chemistry laboratories. Automated enzymatic methods for cholesterol, triglycerides and free glycerol determinations, as well as a dextran sulfate-Mg2+ procedure for separation of high density lipoproteins (HDL) with standardization are described. Similar methods for the measurement of unesterified cholesterol and phospholipids are also given. Serum pools for total cholesterol with values ranging from 1220-3490 mg/l produced coefficients of variation (CV) less than or equal to 2.85%; reference values for low total cholesterol samples in a range of 280-727 mg/l gave CV of 4.35% or less; HDL cholesterol reference values of 265-640 mg/l yielded CV less than or equal to 3.70%; and values for triglycerides between 0.74 and 3.05 mmol/l gave CV of 4.22% or less through three to eight testing cycles (9-24 mth). These data indicate that long term CDC standardization of total cholesterol, triglycerides, and HDL cholesterol can be obtained with automated enzymatic methods utilizing commercially available reagents.

Blood Chemical Analysis↗
PubMed1987

A novel cell line (Caco-2) for the study of intestinal lipoprotein synthesis.

Lipoprotein synthesis by the colonic adenocarcinoma cell line Caco-2 was investigated to assess the utility of this cell line as a model for the in vitro study of human intestinal lipid metabolism. Electron micrographic analysis of conditioned medium revealed that under basal conditions of culture post-confluent Caco-2 cells synthesize and secrete lipoprotein particles. Lipoproteins of density (d) less than 1.063 g/ml consist of a heterogeneous population of particles (diameter from 10 to 90 nm). This fraction consists of very low density lipoproteins (d less than 1.006 g/ml) and low density lipoproteins (d = 1.019-1.063 g/ml). Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of [35S]methionine-labeled Caco-2 lipoproteins revealed that very low density lipoproteins contain apolipoprotein E (apoE) and C apolipoproteins, while low density lipoproteins contained apoB-100, apoE, apoA-I, and C apolipoproteins. The 1.063-1.21 g/ml density fraction contained two morphological entities, discoidal (diameter 15.6 +/- 3.9 nm) and round high density lipoprotein particles (diameter 10.2 +/- 2.3 nm). The high density lipoproteins contained apoA-I, apoB-100, apoB-48, apoE, and the C apolipoproteins. Using isoelectric focusing polyacrylamide gel electrophoresis newly secreted apoA-I was identified as pro-apoA-I. ApoE and apoC-III released by Caco-2 cells were highly sialylated. mRNA species for apoA-I, apoC-III, and apoE, but not apoA-IV were identified by Northern blot analysis. ApoA-I, apoB, and apoE were visualized in Caco-2 cells by immunolocalization analysis. This intestinal cell line may be useful for in vitro studies of nutritional and hormonal regulation of lipoprotein synthesis.

Adenocarcinoma↗
PubMed1987

Effect of menstrual cycle phase on plasma lipids.

The effect of endogenous sex hormone fluctuations on plasma lipoprotein levels was studied in 15 young women. Plasma samples were taken during the follicular, ovulatory, and luteal phases of the menstrual cycle while the women were consuming a defined diet, similar to the average American diet. No significant effect of menstrual cycle phase on plasma total cholesterol or cholesterol lipoprotein subfraction levels was found; however, a 34% increase in total plasma triglycerides associated with an increased very low density lipoprotein triglyceride fraction was found during the ovulatory phase. These data indicate that menstrual cycle phase can have a significant effect on plasma triglyceride levels, but not on plasma cholesterol or lipoprotein fractions.

Adult↗
PubMed1987

Apolipoprotein E isoform phenotyping methodology and population frequency with identification of apoE1 and apoE5 isoforms.

Minigel methodology has been utilized for apolipoprotein (apo) E isoform phenotyping and criteria for distinguishing the apoE4/4 phenotype (mean apoE4/apoE3 ratio: 5.81) from the apoE4/3 phenotype (mean ratio: 1.01) and the apoE3/3 phenotype (mean apoE3/apoE2 ratio: 2.67) from the apoE3/2 phenotype (mean ratio: 0.76) based on gel scanning were developed. ApoE allele frequencies in 1209 subjects were: apoE3, 0.786; apoE4, 0.135; apoE2, 0.075; apoE5, 0.002; and apoE1, 0.002. Subjects with the apoE2 allele tended to have higher plasma very low density lipoprotein (VLDL) cholesterol and lower low density lipoprotein (LDL) cholesterol concentrations than subjects with the apoE3 allele, while the converse was true for subjects with the apoE4 allele. Subjects with the rare apoE1 allele had values similar to those with the apoE2 allele, while subjects with the rare apoE5 allele had values similar to those with the apoE4 allele.

Adult↗
PubMed1987

Criteria for essential fatty acid deficiency in plasma as assessed by capillary column gas-liquid chromatography.

To develop criteria for deficiency of essential fatty acids (EFA), we used capillary-column gas-liquid chromatography to determine fatty acids (percentage of total fatty acids) in plasma obtained in the fasting state from 56 reference subjects and from 10 patients with intestinal fat malabsorption and suspected EFA deficiency. Fatty acid evaluations (percentage of total fatty acids) that allowed for a clear distinction (P less than 0.01) between reference subjects and patients, based on values two standard deviations below or above the reference mean, included values for linoleic acid (18:2w6) below 27%, and values for palmitic acid (16:0), palmitoleic acid (16:1w7), oleic acid (18:1w9), vaccenic acid (18:1w7), and Mead acid (20:3w9) exceeding 21%, 2.6%, 23.3%, 2.1%, and 0.21%, respectively. Ratios of total EFA to total non-EFA of less than 0.60 and of Mead acid to arachidonic acid of greater than 0.025 also served to identify patients, and were not found in reference subjects. Significant inverse correlations between percentages of plasma EFA and plasma mono-unsaturated fatty acids were noted. Our reference-interval data can be used to assess normality of plasma EFA status.

Adult↗
PubMed1987

Enzyme-linked immunosorbent assay for human plasma apolipoprotein B.

A noncompetitive enzyme-linked immunosorbent assay (ELISA) has been developed for measuring total plasma apolipoprotein (apo) B using affinity purified polyclonal and monoclonal antibodies. Microtiter plates from different manufacturers were tested with regard to their IgG binding characteristics; only one plate yielded consistent coefficients of variation of less than 5%. The optimal plasma dilution in this assay was 1:3000. IgG anti-apoB antisera conjugated to alkaline phosphatase was used as a second antibody. p-Nitrophenyl phosphate was utilized as substrate for color development, and the absorbance (410 nm) was read utilizing an ELISA reader interfaced with a microcomputer for data processing. Plasma apoB levels in plasma have been determined in 1115 male and female participants in the Framingham Offspring Study. Mean (+/- SD) plasma concentrations were 89 +/- 28 mg/dl. Significant age and sex related differences in apoB levels were noted.

Adult↗
PubMed1986

Impaired hepatocyte binding, uptake and degradation of glucosylated low-density lipoproteins.

The catabolism of low-density lipoproteins (LDL), the major cholesterol-carrying lipoproteins in plasma, is mediated in part via a high-affinity uptake pathway in the liver. Non-enzymatic glucosylation of lysine residues of apolipoprotein B, the major protein of LDL, blocks receptor-mediated uptake of LDL by fibroblasts and endothelial cells. We investigated the effect of the degree of glucosylation on the binding, uptake and degradation of radioiodinated LDL by the human hepatoma cell line Hep G2. Human LDL was glucosylated with 250 mM glucose and 30 mM cyanoborohydride at 37 degrees C. Incubations ranging from 3 to 48 h in duration resulted in the formation of 6-27% of glucitol-lysine adducts as demonstrated by coincubation with [14C]glucose. The degree of glucose incorporation corresponded to the extent of inhibition of binding, uptake and degradation of LDL (10-90%). The data are consistent with the view that glucosylation of LDL markedly impairs their catabolism. This phenomenon may be related to the pathophysiology of the premature atherosclerosis observed in diabetes mellitus.

Arteriosclerosis↗
PubMed1986

Apolipoprotein A-I gene polymorphism associated with premature coronary artery disease and familial hypoalphalipoproteinemia.

Decreased plasma high-density-lipoprotein (HDL) cholesterol and apolipoprotein A-I levels have been associated with premature coronary artery disease. We identified a PstI restriction-endonuclease site flanking the human apolipoprotein A-I gene at its 3' end that is polymorphic. The absence and presence of this site, as determined by genomic blotting analysis of PstI-digested chromosomal DNA with the use of an apolipoprotein A-I gene probe, were associated with 3.3-kb and 2.2-kb hybridization bands, respectively. The 3.3-kb band appeared in 4.1 percent of 123 randomly selected control subjects and in 3.3 percent of 30 subjects with no angiographic evidence of coronary artery disease. In contrast, among 88 patients who had severe coronary disease before the age of 60, as documented by angiography, the 3.3-kb band occurred in 32 percent (P less than 0.0001). It was also found in 8 of 12 index cases (P less than 0.0001) of kindreds with familial hypoalphalipoproteinemia. In the two patient groups, the allele frequencies of the site that produced the 3.3-kb band were 17 and 42 percent, respectively, as compared with an allele frequency of only 2 percent in the control populations. Within kindreds with familial hypoalphalipoproteinemia and among first-degree relatives of patients with coronary artery disease, the 3.3-kb band was associated with decreased HDL cholesterol levels. Among all patients with coronary artery disease, 58 percent had HDL cholesterol levels below the 10th percentile of normal values; however, this frequency increased to 73 percent when patients with the 3.3-kb band were considered. These findings indicate that the polymorphism in the region between the apolipoprotein A-I and apolipoprotein C-III genes may be a useful marker for the risk of premature coronary artery disease and familial hypoalphalipoproteinemia.

Age Factors↗