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J A Cortner

Publications and source records attributed to J A Cortner.

At least 37 records · Page 2Linked to original sources
PubMed1989

Measurement of apolipoprotein B synthesis in perfused rat liver using stable isotopes: [15N]hippurate as a measure of the intracellular [15N]glycine precursor enrichment.

Rat livers were perfused by the nonrecirculating technique with medium containing [15N]glycine and sodium benzoate. At various times, the isotopic enrichment of hepatic free glycine, hepatic glycyl-tRNA, and perfusate hippurate was measured by GLC-MS. After 60 min, these parameters had reached approximately maximal values. At 90 min, the perfusate hippurate had a 30% greater enrichment of 15N than the intracellular glycine or glycyl-tRNA. Hippurate enrichment was half that of the medium glycine. The rat livers secreted apolipoprotein B (B-100 plus B-48) at a rate of 22 micrograms/g per h. From the 15N enrichment and the secretion rate, an intrahepatic pool size of 86 micrograms/g of apoB was calculated. From the minimal intracellular transit time of 30 min, an apoB fractional synthetic rate (FSR) of 2 pools/h was indicated, whereas the FSR estimated from the 15N-enrichment was 0.26/h. A possible explanation for the discrepancy is that apoB may recycle within the hepatocyte. On the basis of the present experiments, when hippurate enrichment is used as a measure of the enrichment of intrahepatic glycine in in vivo studies with 15N-labeled glycine, a correction should be applied, under normal metabolic circumstances, of approximately 20-30%.

Animals↗
PubMed1987

Transcriptional activity of the genes for apoproteins A-I and E in neonatal rat liver.

The expression of the genes for apoproteins A-I and E (apoA-I, apoE) in fetal and neonatal rat livers was quantitated by measurement of steady-state levels of mRNA and by assays of relative transcriptional activity using the nuclear 'run-on' technique. From the last day of gestation (day -1) to day 5 after birth (day 5), for apoE there was a 2.2-fold increase in relative transcriptional activity and a 2.6-fold increase in steady-state mRNA. For apoA-I, from day -1 to 3 there was a 1.25-fold increase in both transcription and steady-state mRNA levels. We conclude that the increase in steady-state mRNA for the apoE gene which occurs during liver development in the rat is facilitated primarily by transcriptional control.

Animals↗
PubMed1987

Kinetics of chylomicron remnant clearance in normal and in hyperlipoproteinemic subjects.

The kinetics of chylomicron metabolism have been studied by measuring retinyl palmitate in chylomicrons and their remnants for 10-12 hr following oral administration of vitamin A and Lipomul in three groups of adult male subjects: A) normal plasma triglyceride levels (n = 7); B) endogenous hypertriglyceridemia (n = 12); C) apolipoprotein E (apoE) phenotype E2/2, with Type 3 hyperlipoproteinemia (n = 4) or normal plasma lipids (n = 1). A multicompartmental model was developed using SAAM 27 to characterize the appearance, intravascular metabolism, and clearance from the plasma of retinyl palmitate-labeled dietary lipoproteins. The half-times for retinyl palmitate clearance from the chylomicron remnant fraction (T1/2 REMNANT) were 14.1 +/- 9.7 min in Group A; they were prolonged in Group B (50.7 +/- 20.8 min) and were extremely prolonged for Type 3 subjects in Group C (611.9 +/- 419.9 min). One subject with the apoE 2/2 phenotype and normal plasma triglycerides had a T1/2 REMNANT of 66.8 min. T1/2 REMNANT was highly correlated with fasting plasma triglycerides in Group A and B (r = 0.77, slope = 0.15), and in Group C (r = 0.97, slope = 0.85). These results support the interpretation that delayed chylomicron remnant clearance in subjects with endogenous hypertriglyceridemia may be largely secondary to overproduction of VLDL particles, whose remnants compete with chylomicron remnants for removal by the liver via apoE receptor-mediated endocytosis. The subjects with apoE 2/2 have an additional defect in the removal of chylomicron remnants presumably due to the structural abnormality in their apoE.

Adult↗
PubMed1986

Genetic variation of human mononuclear leukocyte lysosomal acid lipase activity. Relationship to atherosclerosis.

Lysosomal acid lipase activity was measured in mononuclear leukocytes of patients selected on the basis of premature cardiovascular disease, with or without hyperlipidemia. Enzyme activity was significantly lower in the patient population (4.8 +/- 1.3 nmol/min/mg protein, n = 190 males) than in an age-matched control population (5.4 +/- 1.3 nmol/min/mg protein, n = 124 males). There was no effect of hypercholesterolemia or hypertriglyceridemia on the enzyme activity. In the group of patients with normal plasma lipids (n = 77), 18% had mononuclear leukocyte acid lipase activity which fell below the control population 5th percentile, and in the range of enzyme activity observed in cells from obligate heterozygotes for inherited acid lipase deficiency (Wolman disease and cholesteryl ester storage disease). Studies of acid lipase activity in families of our patients provided evidence that an autosomal mutation is associated with (or responsible for) this reduced enzymatic activity and may represent an independent risk factor for the premature development of atherosclerosis.

Adult↗
PubMed1986

Genetic polymorphism of esterase B3 in human leukocytes.

Human tissues contain an esterase activity called ESB3, detectable by starch gel electrophoresis followed by staining with alpha-naphthyl butyrate. Using mononuclear leukocytes, we demonstrated an electrophoretic variant of ESB3. Family studies suggest that the variant is inherited as a simple Mendelian trait; individuals with the ESB3 2-1 phenotype are heterozygotes, designated ESB3(1)ESB3(2), to distinguish them from the more common homozygotes, ESB3(1)ESB3(1). The frequency of the ESB3(2) allele is estimated to be 0.035 in U.S. Whites. No homozygotes for this allele have yet been found. Our studies suggest that the enzyme from ESB3 1 individuals exists primarily as a trimer of three identical subunits with a molecular weight of approximately 58,000 daltons. The genetic variant (ESB3(2) allele) appears to be the result of a mutation that does not affect the charge of the subunit, but rather reduces its ability to form and maintain the trimeric structure.

Chromatography, Gel↗
PubMed1986

Direct measurement of apolipoprotein B synthesis in human very low density lipoprotein using stable isotopes and mass spectrometry.

Stable isotope methodology has been adapted to the study of lipoprotein turnover in human subjects. Using endogenous [15N]glycine labeling and gas-liquid chromatographic-mass spectrometric analysis, synthesis of apolipoprotein B in very low density lipoprotein (VLDL) was measured directly in five normal and two hyperlipidemic subjects. An isotopic precursor steady state was achieved during the studies by utilizing a priming dose and constant infusion containing [15N]glycine. Measurement of the plateau in 15N enrichment in the urinary hippurate produced during each study was used to estimate the 15N enrichment of the hepatic glycine precursor pool. The range of values for the fractional synthetic rate of VLDL apoB in the normal subjects obtained by this method was 5.9 to 11.5 day-1, with a mean of 9.2 +/- 2.4 (SD). This value agrees with the results of previous investigations which have utilized other methods. The method was also tested in two hypertriglyceridemic subjects and gave fractional synthetic rates of VLDL apoB that were significantly lower than in normals (1.5 and 2.8 day-1). This stable isotope method allows calculation of the fractional synthetic rate of VLDL apoB by maintaining an isotopic steady state throughout the study. It makes possible repeated studies in the same individual since no risk of exposure to radioisotopes is involved.

Apolipoproteins B↗
PubMed1985

Genetic deficiency of medium-chain acyl coenzyme A dehydrogenase: studies in cultured skin fibroblasts and peripheral mononuclear leukocytes.

Medium-chain acyl coenzyme A (CoA) dehydrogenase deficiency was demonstrated in fibroblasts and/or mononuclear leukocytes from 14 patients, most of whom initially presented early in childhood with a Reye-like syndrome associated with hypoketotic hypoglycemia, dicarboxylic aciduria, and low levels of plasma carnitine. Parents of these patients had intermediate levels of medium-chain acyl CoA dehydrogenase activity, consistent with their being heterozygous for an autosomal recessive trait. All patients had normal levels of long-chain acyl CoA dehydrogenase activity, but had reduced short-chain acyl CoA dehydrogenase activity. Fatty acid oxidation was examined in cultured fibroblasts from five of the patients, using a series of 14C-labeled fatty acids of different chain length (palmitic, octanoic, and butyric). Oxidation of [1-14C]-octanoic acid was less than 20% of control levels: [1-14C], [6-14C]-, [16(14)C]-, and [14C(U)]-palmitic acid oxidation rates were 88, 51, 13, and 42% of control rates, respectively. [1-14C]-butyric acid was oxidized normally. These data extend our previous findings of medium-chain acyl CoA dehydrogenase deficiency in liver tissue from three of these patients. They demonstrate the value of cultured fibroblasts and leukocytes in the diagnosis and evaluation of inherited disorders of fatty acid oxidation.

Acyl-CoA Dehydrogenase, Long-Chain↗
PubMed1982

Hormone-sensitive lipase in human adipose tissue, isolated adipocytes, and cultured adipocytes.

Employing a perifusion technique, the activity of hormone-sensitive lipase (HSL) in human adipose tissue and isolated adipocytes was found to be significantly stimulated by 5 microM epinephrine (5-fold. P less than 0.001) or 0.5 mM theophylline (2-fold, P less than 0.03). The stimulatory effect of both, however, was not cumulative; instead, theophylline appeared to blunt the epinephrine effect. The two effectors together produced a 3-fold increase in activity over basal (P less than 0.01). Basal lipolysis was highly and significantly correlated with epinephrine and/or theophylline stimulated lipolysis in the tissue as well as in the isolated cells. The activity of the enzyme was examined in cultured human adipocytes using a cell-free system. The basal activity of HSL in the 20,000 X g supernatant (S20) fraction of cultured cells grown in fat-enriched medium was significantly higher than the value in the same fraction of cells grown in regular medium (6.06 +/- 1.49 versus 2.78 +/- 0.89 nmole glycerol/min/mg protein, mean +/- S.D., P less than 0.01), an was similar in the S20 fractions of cells grown in the enriched medium and the original tissue (6.06 +/- 1.49 versus 5.44 +/- 2.73 nmole glycerol/Min/mg protein, mean +/- S.D., P greater than 0.83). When the tissue and cells were stimulated in vitro before fractionation, the HSL activity in the S20 fraction of the original tissue increased 4-fold over basal (P less than 0.001), whereas that in the cultured cells increased 2-fold (P less than 0.01) regardless of the culture medium employed. In the S20 fractions derived from basally incubated samples, but not in those derived from the epinephrine-stimulated samples, the HSL enzyme was slightly but significantly (P less than 0.002) activated by exogenous addition of ATP, cyclic AMP, and protein kinase. The data suggest that the activity of HSL is retained in cultured human adipocytes and could be enhanced under conditions of culture which favor lipid accumulation and adipose conversion.

Adipose Tissue↗
PubMed1979

Acid lipase activity of human lymphocytes.

Acid lipase activity was examined in human leukocytes using 4-methylumbelliferyl esters in a fluorimetric assay. Mononuclear leukocytes had 10--15 times the acid lipase activity of polymorphonuclear leukocytes. The enzyme activity was highest using the oleate ester of 4-methylumbelliferone at pH 4.0, in the presence of L-alpha-phosphatidylcholine and taurodeoxycholic acid (sodium salt). Acid lipase activity was inhibited by diethylaminoethoxyhexestrol, sodium chloride and fluoride, potassium chloride, calcium chloride and albumin, but was unaffected by diethyl p-nitrophenyl phosphate or sulphydryl reagents. There were at least two forms of acid lipase activity: one (A form) was sensitive to heart inactivation (56 degrees C) and corresponded to the enzyme deficient in patients with Wolman's disease; the other (B form) was resistant to heat inactivation and corresponded to the residual enzyme activity found in Wolman's disease.

Bile Acids and Salts↗
PubMed1978

Prenatal diagnosis of Wolman disease.

Two pregnancies at risk for Wolman disease were monitored by assay and electrophoresis of acid lipase in cultured amniotic-fluid cells. Cells from patient 1 had 5% of control levels of acid lipase, using 14C-triolein as substrate; however, when artificial substrates (esters of 4-methylumbelliferone and p-nitrophenol) were used to measure acid lipase, these cells had 30% of control levels. Electrophoresis of cell extracts revealed the absence of the A form of acid lipase, consistent with the diagnosis of Wolman disease. Analysis of fetal tissues following prostaglandin termination of this pregnancy confirmed the diagnosis. Assay of fetal-skin fibroblasts with 14C-triolein, as well as with artificial substrates, showed marked deficiency of acid lipase activity. Electrophoresis of fetal-tissue extracts also demonstrated the absence of the A form of acid lipase. Amniotic-fluid cells from patient 2 showed normal levels of acid lipase with all substrates tested; the electrophoretic pattern of acid lipase was normal. The results suggest that the prenatal diagnosis of Wolman disease be made using the radioassay of acid lipase and/or electrophoresis.

Acetylglucosaminidase↗
PubMed1978

Acid and neutral lipases of cultured adipocytes of infants and children.

In order to determine whether the mobilization of intracellular triglycerides observed in cultured human adipocytes is associated with changes in the activities of acid and neutral lipases, the activities of both enzymes were measured weekly on cultured adipocytes for several months. The activity of acid lipase was initially very low, but rose to levels 40 times the original activity within 3 months. The activity of neutral lipase decreased rapidly within the first 2-4 weeks and remained at approximately 25% of original levels thereafter.

Adipose Tissue↗
PubMed1977

Neutral and acid lipase of mouse 3T3 fibroblasts with increased adipose conversion.

In the resting state, 3T3-L1 fibroblasts become adipose converted and increase their fatty acid and triglyceride synthetase. We have found that they contain four times the neutral lipase activity and 1.5 times the acid lipase activity of logarithmically dividing cells. The activities of lysosomal acid beta-galactosidase and N-acetyl-beta-D-glucosaminidase were the same in the adipose converted and logarithmically dividing cells. The data suggest a possible relation between the increased neutral lipase activity in 3T3-L1 cells and their adipose conversion and demonstrates that the adipose converted 3T3-L1 fibroblasts, unlike true adipose cells, contain high levels of lysosomal acid hydrolases.

Acetylglucosaminidase↗
PubMed1976

Genetic variation of lysosomal acid lipase.

Lysosomal acid lipase (LAL) activity was measured using a new fluorometric assay in cultured skin fibroblasts from eight control subjects, two obligate heterozygotes for Wolman's disease (WD), one patient with WD, and one patient with cholesteryl ester storage disease (CESD). The LAL activities (mean+/-SD) were 25.8+/-8.2, 13.2+/-0.1,1.1, and 1.4 nmol 4-methylumbelliferyl oleate (4-MUO) hydrolyzed/min/mg protein, respectively. These results compare favorably with those obtained using standard radioassays. The LAL activities of two cultures of amniotic fluid cells were 12.1 and 10.5. The LAL activity (mean+/-SD) of peripheral leukocytes obtained from 34 laboratory volunteers (19 females, 15 males) was 4.0+/-1.8. Partially purified lymphocytes contained about 25 times as much LAL activity as did granulocytes. Cellogel electrophoresis, followed by staining with 4-MUO, showed at least two bands of LAL (A and B) from normal fibroblasts, amniotic fluid cells, and lymphocytes. Band A was absent from WD and CESD fibroblasts and was reduced in fibroblasts of the WD heterozygotes.

Cholesterol Esters↗