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Biomedical subjects

M Krieger

Publications and source records attributed to M Krieger.

At least 163 records · Page 9Linked to original sources
PubMed1978

Receptor-mediated uptake of low density lipoprotein reconstituted with 25-hydroxycholesteryl oleate suppresses 3-hydroxy-3-methylglutaryl-coenzyme A reductase and inhibits growth of human fibroblasts.

The free and esterified cholesterols of plasma low density lipoprotein (LDL) were extracted with heptane and replaced with 25-hydroxycholesteryl oleate. The resulting particle, designated r-[25-HC oleate]LDL, bound to LDL receptors on human fibroblasts, was taken up by adsorptive endocytosis and was hydrolyzed in lysosomes in a manner similar to that of native LDL. The r-[25-HC oleate]LDL suppressed 3-hydroxy-3-methylglutaryl-coenzyme A reductase [mevalonate:NADP(+) oxidoreductase (CoA-acylating), EC 1.1.1.34], the enzyme catalyzing the rate-limiting step in cholesterol biosynthesis. This suppression did not occur when lysosomal hydrolysis of r-[25-HC oleate]LDL was inhibited by chloroquine. When fibroblasts were incubated with r-[25-HC oleate]LDL in the absence of a source of cholesterol, the cells developed an abnormal morphology, their growth was inhibited, and the cells died. The toxic effects of r-[25-HC oleate]LDL were prevented when the growth medium was supplemented with cholesterol in ethanol or with mevalonate, the product of the reductase reaction. These data suggest that the toxicity of r-[25-HC oleate]LDL was due to its suppression of reductase, which in turn caused cellular cholesterol deficiency. The r-[25-HC oleate]LDL did not suppress reductase activity nor did it alter the growth or morphology of mutant fibroblasts lacking LDL receptors, which were obtained from a patient with homozygous familial hypercholesterolemia. These experiments demonstrate the feasibility of using reconstituted LDL to selectively deliver hydrophobic compounds other than typical cholesteryl esters to cells possessing LDL receptors.

Cholesterol↗
PubMed1978

Synovial cysts in juvenile rheumatoid arthritis.

In a case of juvenile rheumatoid arthritis with large synovial cysts, cyst fluid aspiration was performed to relieve pain, but recurrence was prevented with salicylate therapy alone. The mechanism of formation of synovial cysts is discussed.

Arthritis, Juvenile↗
PubMed1977

The effect of pre-incubation on trypsin kinetics at low pH.

A possible source of discrepancy between kinetic and spectroscopic studies of the active site ionizations in the enzyme trypsin (EC 3.4.21.4) could arise if a slow pH-dependent conformational change affected the rates at low pH. No such effect is observed within the time range of 1 min- 3 h when pre-incubation of trypsin at pH 2.0 or at pH 6.9 precedes the enzymatic hydrolysis of Nalpha-carbobenzoxy-L-lysine-p-nitrophenyl ester. The deacylation rate of this hydrolysis depends on a single pKa on the enzyme between pH 3 and pH 7.

Animals↗
PubMed1976

pH dependence of tritium exchange with the C-2 protons of the histidines in bovine trypsin.

At pH 8.9 and 37 degrees C the half-times for tritium exchange with the C-2 protons of the histidines of trypsin are 73 days for His-57, and greater than 1000 days for His-40 and His-91. These half-times are much longer than the half-life of exchange for the C-2 proton of free histidine (2.8 days at pD 8.2), and longer than any previously reported half-time of exchange at pH greater than 8. These very low rates of exchange are discussed with reference to the refined structure of trypsin. The tritium exchange of His-57 depends on an apparent pKa of 6.6. This pKa may represent the pKa of the imidazole of His-57 in an inactive conformation of the enzyme.

Amino Acid Sequence↗
PubMedDate not supplied

Regulation of low density lipoprotein receptor function in a human hepatoma cell line.

Low density lipoprotein (LDL) processing was investigated in a human hepatoma-derived cell line, Hep G2. Hep G2 cells bound, internalized and degraded LDL via a saturable, high affinity (Kd approximately 2 X 10(-8)M) pathway similar to that present in other mammalian cells. Although 80% of the uptake and degradation of 125I-LDL was inhibited by 40-fold excess native LDL, the same concentration of methylated LDL, which cannot bind to LDL receptors, had virtually no effect on processing. When added at low concentrations, the lysosomotropic agent, chloroquine, inhibited degradation (I50 approximately 15 microM) without affecting the rate of lipoprotein internalization. Receptor activity was decreased 60% by preincubation of the cells in medium containing a source of cholesterol (LDL or unesterified cholesterol) and increased 1.7-fold by preincubation with compactin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase. The Hep G2 cell line may prove a useful system both for the further study of hepatic lipoprotein metabolism and for the evaluation of new antihypercholesterolemic agents.

Carcinoma, Hepatocellular↗
PubMedDate not supplied

Expression and regulation of human low-density lipoprotein receptors in Chinese hamster ovary cells.

Low-density lipoprotein (LDL), the major cholesterol transport component of human plasma, delivers cholesterol to mammalian cells via the LDL pathway of receptor-mediated endocytosis. LDL receptor activity and cholesterol biosynthesis are coordinately regulated by cholesterol-mediated feedback suppression. We have developed methods for the isolation of mutant and revertant (M.K., unpublished data) Chinese hamster ovary (CHO) cells having alterations in cholesterol biosynthesis and in the receptor-mediated endocytosis of LDL. The defective locus of one LDL receptor-negative CHO mutant (clone 7a-1) is apparently the structural gene for the LDL receptor (D. Kingsley, M. Segal and M.K., unpublished data). Here we have transfected 7a-1 cells with human DNA and selected colonies which synthesize functional human LDL receptors whose expression is regulated normally. This selection may prove useful for cloning genes required for the receptor-mediated endocytosis of LDL and other ligands and thus for elucidating the molecular defects responsible for familial hypercholesterolaemia, one of the most common genetic diseases in humans.

Animals↗
PubMedDate not supplied

[Osteoneogenesis in callus and epiphyseal distraction].

X-rays were reviewed after callus distractions (50 cases) and distraction epiphysiolysis (10 cases) in 45 patients. With the aid of a computerized digitization system for analogue films, the relative x-ray density of the distraction area was determined in the medial, lateral, ventral and dorsal surface areas, and in the median line of the callus tissue. Bone formation became evident within 21.7 +/- 3.7 days post-distraction in the thigh and 25.4 +/- 4.9 days in the shank. The lowest density values were found at the end of the distraction phase followed by a continual increase in x-ray density in the fixation phase. There was a significant decrease in callus x-ray density in the shank from lateral to medial and from dorsal to ventral, and in the thigh from medial to lateral and from dorsal to ventral. When the corticotomized callus distraction is compared to the distraction epiphysiolysis without corticotomy it becomes apparent that the differences between lateral-medial x-ray densities and dorsal-ventral x-ray densities were significantly greater in the group with callus distraction. The deminished bone formation in the ventromedial area of the shank and the ventrolateral area of the thigh seems to be due to soft tissue damage and disturbances in local bone blood supply after the operative approach for corticotomy.

Adolescent↗
PubMedDate not supplied

Time course of osteocalcin, bone-specific alkaline phosphatase, and C-terminal procollagen peptide during callus distraction.

This study involved 15 patients who were undergoing extremity lengthening by callus distraction. Blood samples and radiographs of the callus distraction segment were obtained before surgery, every 2 weeks during the distraction phase, and every 4 weeks between the end of distraction and removal of the fixator. A digital radiograph analysis system was used to determine the radiographic density of the callus distraction segments. In addition, the serum parameters osteocalcin, bone-specific alkaline phosphatase, and C-terminal procollagen peptide (PICP) were evaluated. The radiographic density was constant during the distraction phase, but increased logarithmically during the consolidation period. Similar kinetics were observed for osteocalcin, with an average coefficient of correlation between these two parameters of 0.66+/-0.15. PICP levels rose rapidly after surgery and increased further during the consolidation period. Serum levels of bone-specific alkaline phosphatase were not uniform between patients, and there was no correlation to the kinetics of radiographic density or the other serum parameters. The similarity between radiographic density and osteocalcin kinetics, as well as the rapid postoperative increase in PICP, imply that further information may be obtained about osteoneogenesis from the study of these two serum parameters.

Adolescent↗