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Biomedical subjects

M C Cheung

Publications and source records attributed to M C Cheung.

At least 91 records · Page 5Linked to original sources
PubMed1985

The thyroglobulin gene resides on chromosome 8 in man and on chromosome 7 in the rat.

Human chromosomes were separated by a dual laser FACS sorter and their DNA hybridized with a thyroglobulin gene probe. A strong hybridization signal was obtained with DNA from chromosome 8. A panel of mouse-rat cell hybrids was used to determine the chromosomal localization of the rat thyroglobulin gene by the Southern blotting method. Comparison of the cytogenetic data with the hybridization signals obtained with the rat thyroglobulin probe allowed assignment of this gene to rat chromosome 7. It is concluded that the synteny relationship between the thyroglobulin gene and the c-myc oncogene has been conserved in rat and man.

Animals↗
PubMed1984

Characterization of lipoprotein particles isolated by immunoaffinity chromatography. Particles containing A-I and A-II and particles containing A-I but no A-II.

Two populations of A-I-containing lipoprotein particles: A-I-containing lipoprotein with A-II (Lp (A-I with A-II], and A-I-containing lipoprotein without A-II (Lp (A-I without A-II] have been isolated from plasma of 10 normolipidemic subjects by immunoaffinity chromatography and characterized. Both types of particles possess alpha-electrophoretic mobility and hydrated density in the range of plasma high-density lipoproteins (HDL). Lp (A-I without A-II) and Lp (A-I with A-II) are heterogeneous in size. Lp (A-I without A-II) comprised two distinct particle sizes with mean apparent molecular weight and Stokes diameter of 3.01 X 10(5), and 10.8 nm for Lp (A-I without A-II)1, and 1.64 X 10(5), and 8.5 nm for Lp (A-I without A-II)2. Lp (A-I with A-II) usually contained particles of at least three distinct molecular sizes with mean apparent molecular weight and Stokes diameter of 2.28 X 10(5) and 9.6 nm for Lp (A-I with A-II)1, 1.80 X 10(5) and 8.9 nm for Lp (A-I with A-II)2, and 1.25 X 10(5) and 8.0 nm for Lp (A-I with A-II)3. Apoproteins C, D, and E, and lecithin:cholesterol acyltransferase (LCAT) were detected in both Lp (A-I without A-II) and Lp (A-I with A-II) with most of the apoprotein D, and E, and LCAT (EC 2.3.1.43) in Lp (A-I with A-II) particles. Lp (A-I without A-II) had a slightly higher lipid/protein ratio than Lp (A-I with A-II). Lp (A-I with A-II) had an A-I/A-II molar ratio of approximately 2:1. The percentage of plasma A-I associated with Lp (A-I without A-II) was highly correlated with the A-I/A-II ratio of plasma (r = 0.96, n = 10). The variation in A-I/A-II ratio of HDL density subfractions therefore reflects different proportions of two discrete types of particles: particles containing A-I and A-II in a nearly constant ratio and particles containing A-II but no A-II. Each type of particle is heterogeneous in size and in apoprotein composition.

Animals↗
PubMed1984

High-resolution chromosome sorting and DNA spot-blot analysis assign McArdle's syndrome to chromosome 11.

A rapid gene-mapping system uses a high-resolution, dual-laser sorter to identify genes from separate human chromosomes prepared with a new stain combination. This system was used to sort 21 unique chromosome types onto nitrocellulose filter papers. Several labeled gene probes hybridized to the sorted chromosomal DNA types predicted by their previous chromosome assignments. The skeletal muscle glycogen phosphorylase gene was then mapped to a portion of chromosome 11 by spot blotting normal and translocated chromosomes.

Animals↗
PubMed1984

The inheritance of high density lipoprotein cholesterol and apolipoproteins A-I and A-II.

A large pedigree was ascertained through cases of early myocardial infarction. High density lipoprotein cholesterol and apolipoproteins A-I and A-II were measured on family members. Likelihood analysis, using the polygenic/major gene mixed model, provided no evidence that major loci play a role in determining the levels of any of the three measurements. Heritability estimates, assuming polygenic inheritance, were 0.59 and 0.26 for HDL-C level and A-II level, respectively. No evidence of genetic transmission of A-I level was found.

Adult↗
PubMed1983

Recombination within and between the human insulin and beta-globin gene loci.

We detected a large number of polymorphic insulin restriction fragments in black Americans. These different size fragments were probably generated by unequal recombination on both sides of the human insulin gene. Population genetic analysis indicates that recombination occurred 33 times more frequently than expected to generate this large number of polymorphic fragments. Specific properties of the unique repeated 14- to 16-base-pair sequences 5' to the insulin gene suggest that this sequence would promote increased unequal recombination. Additional pedigree analysis showed that the recombination rate between the structural insulin and beta-globin gene loci was 14% with strong evidence for linkage. Since both insulin and beta-globin have been mapped to the short arm of human chromosome 11, this study establishes that the genetic map distance between these genes is 14.2 centimorgans.

Base Composition↗
PubMed1983

Ultrastructural immunolocalization of apolipoprotein B within human jejunal absorptive cells.

Apolipoprotein B (apoB) was localized by electron microscopy within absorptive cells of human jejunal biopsy specimens taken fasting and after micellar fat infusion. Nakane's double antibody immunoperoxidase technique was used to label apoB near open cut surfaces of 60-Micrometers fixed tissue slices sectioned by a Ralph knife in a Vibratome. In fasting tissue, apoB label was found within structurally intact peri-mitochondrial rough endoplasmic reticulum (RER) and within Golgi cisternae of absorptive cells covering the tips of jejunal villi. After fat infusion, apoB label was found adjacent to very low density lipoproteins (VLDL) and chylomicrons within apical smooth endoplasmic reticulum (SER). Less label was seen within RER than in fasting absorptive cells, and RER-SER connections containing apoB label were occasionally seen. Expanded Golgi vesicles and cisternae contained VLDL, chylomicrons, and apoB label. Vesicles containing chylomicrons and apoB label were occasionally visualized bordering the lateral plasma membrane in a configuration suggesting exocytosis. Specific apoB label was regularly seen within intercellular spaces and capillaries, but the in vivo significance of this Localization was problematical. These observations suggest that apoB is synthesized in RER, transfers to SER where it is incorporated into new VLDL and chylomicrons, and moves to Golgi cisternae and vesicles to be prepared for exocytosis through the plasma membrane.

Apolipoproteins↗
PubMed1982

Assigning the polymorphic human insulin gene to the short arm of chromosome 11 by chromosome sorting.

We have determined the subchromosomal location of the human insulin gene by analyzing DNA isolated from sorted human metaphase chromosomes. Metaphase chromosome suspensions were sorted into fractions according to relative Hoechst fluorescence intensity by the fluorescence activated chromosome sorter. The chromosomal DNA in each fraction was characterized by restriction endonuclease analysis. Initial sorts indicated that the insulin gene-containing fragment resided in a fraction containing chromosomes 9, 10, 11, and 12. Studies of cell lines that contained chromosome translocations permitted the assignment of the insulin gene to a derivative chromosome that contains portions of the short arm of chromosome II. Simultaneous sorting of the normal homolog from this small derivative chromosome separated the two different sized insulin gene-containing restriction fragments in this individual. These data indicate that the two restriction fragments represent insulin gene polymorphism and not duplicate gene loci.

Alleles↗
PubMed1982

Reduction in high density lipoproteins by anabolic steroid (stanozolol) therapy for postmenopausal osteoporosis.

The effects of stanozolol, 17-methyl-2H-5 alpha-androst-2-eno [3,2-c] pyrazol-17 beta-ol, on lipoprotein levels were assessed in a short-term (6 wk) prospective study of 10 normolipidemic, postmenopausal, osteoporotic women. While total cholesterol and triglyceride levels remained constant, equal and offsetting responses were seen in low density lipoprotein (LDL) cholesterol (+30.9 +/- 28.1 mg/dl [mean +/- S.D.], p less than 0.01, a 21% increase) and high density lipoprotein (HDL) cholesterol (-32.5 +/- 11.9 mg/dl [mean +/- S.D.], p less than 0.001, a 53% decline). Hence the LDL/HDL ratio increased dramatically, from 2.5 +/- 0.7 to 6.8 +/- 2.5. Within HDL, stanozolol was associated with a greater decline in HDL2 (from 26.0 +/- 7.4 mg/dl to 3.8 +/- 1.9 mg/dl, p less than 0.001, an 85% decrease) than HDL3 (which diminished from 35.7 +/- 3.2 to 24.1 +/- 5.8 mg/dl. p less than 0.001, a 35% decrease). The major HLD apolipoproteins also declined (A-I by a mean of 41% and A-II by 24%, both p less than 0.001). Postheparin hepatic triglyceride lipase increased (off treatment 74 +/- 42 nmole free fatty acid min-1 mole-1, on treatment 242 +/- 110, n = 6, p = 0.06). All changes were reversed by 5 wk following termination of the drug. These lipoprotein changes suggest caution in the long term prescription of stanozolol, particularly in those without overriding clinical indications for its use.

Aged↗
PubMed1982

Distribution of high density lipoprotein particles with different apoprotein composition: particles with A-I and A-II and particles with A-I but no A-II.

High density lipoproteins (HDL) were subfractionated by equilibrium CsCl gradient centrifugation of the d 1.063-1.21 g/ml HDL fraction isolated from two men and two women. The various HDL subfractions were analyzed for their apoproteins (apo) A-I, A-II, B, D, and E and the major lipid contents. ApoA-I and A-II were found throughout the density gradient with the maximum concentration between the d 1.105 and 1.120 g/ml fractions. ApoE was found in all HDL fractions with the higher concentration in the lower density fractions. Conversely, the concentration of apoD increased as the density of the HDL fraction increased. Each density subfraction underwent quantitative precipitation with anti-A-I and anti-A-II immunoglobulin. Essentially all A-II in all density subfractions was precipitated with either immunoglobulin. Particles from each density subfraction precipitated with anti-A-II immunoglobulin had an A-I/A-II molar ratio of approximately 2.0 (range 1.9-2.3). However, particles precipitated with anti-A-I immunoglobulin had A-I/A-II molar ratios identical to the A-I/A-II ratio of the subfraction (range 2.1-7.1). The subfractions (d 1.105-1.149 g/ml fractions) with A-I/A-II molar ratios of about 2 had the least proportion of A-I in particles containing A-I but not A-II. Conversely, the subfractions (d 1.063-1.075 g/ml fractions) with the highest A-I/A-II molar ratio had the greatest proportion of apoA-I in particles containing A-I but not A-II. These data indicate that HDL contains at least two types of particles: particles with both A-I and A-II in a 2:1 molar ratio, and particles containing A-I but no A-II. The variation in A-I/A-II ratio observed in different HDL density subfractions was due to the different proportions of these two types of particles.

Apolipoprotein A-I↗
PubMed1981

High density lipoprotein composition in insulin-dependent diabetes mellitus.

Although atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death in insulin-dependent diabetics, plasma levels of high density lipoprotein (HDL) cholesterol (an independent "negative" risk factor for ASCVD) have been reported to be normal or high. To test whether alterations in HDL composition might increase potential risk of insulin-dependent diabetics to ASCVD, their major constituent apolipoproteins, A-I and A-II, were measured and compared with levels in controls. HDL cholesterol levels were slightly higher (P = NS) in diabetics than in controls. The HDL cholesterol/LDL cholesterol ratio (an inverse index of relative risk of developing ASCVD) was significantly higher in diabetic men than in controls (P less than 0.02). HDL composition differed markedly in diabetics and controls: the apolipoprotein A-I/A-II ratio was significantly higher (P less than 0.001) in both diabetic men and women (diabetic men--4.1 +/- 0.5, mean +/- SD, controls 3.6 +/- 0.4; diabetic women--4.6 +/- 0.4, controls 3.9 +/- 0.5). Subsequent analysis of plasma from four patients by analytic ultracentrifugation demonstrated a high correlation (r = 0.993, P less than 0.01) between the apolipoprotein A-I/A-II ratio and HDL2, the cholesterol-rich lighter subclass of HDL thought to be the group of particles involved in reduced risk of ASCVD. Therefore, the alteration of HDL composition in insulin-dependent diabetics appears similar to that associated with reduced risk in nondiabetics. Thus, whether a genetic or acquired abnormality, the high apolipoprotein A-I/A-II ratio in insulin-dependent diabetics does not appear to counteract their increased risk of developing ASCVD.

Adolescent↗
PubMed1981

Cholesterol and apoprotein quantitation in lipoproteins.

Lipids are solubilized and transported by associating with carrier proteins (apoproteins) to form lipoproteins. Their physical and chemical properties allow separation, quantification and characterization by both the lipid and protein portions of these macromolecules. Separation and quantitation methods based on the lipid-protein content include ultracentrifugation, electrophoresis and precipitation. Measurements of LDL cholesterol and HDL cholesterol and the associated methodological variations and errors are discussed. As the physiological roles of apoproteins are elucidated, their quantitative values, determined by immunochemical methods, can be used for describing and diagnosing disorders of lipoprotein metabolism.

Apoproteins↗
PubMed1980

High density lipoproteins during hypolipidemic therapy. A comparative study of four drugs.

The high density lipoprotein HDL) response of 14 hyperlipidemic subjects to four hypolipidemic agents was studied through serial measurement of HDL cholesterol and apolipoproteins A-I and A-II before and during 3 months each (separated by 2 months off drug) of clofibrate (2 g/day, n = 14), colestipol (20 g/day, n = 12), para-amino salicylic acid--ascorbate (PAS-C, 6--8 g/day, n = 14) taken in random sequence and oxandrolone (7.5 mg/day, n = 11) as the final drug. The maximal effect of each drug appeared by the first monthly evaluation, and A-1, A-II and HDL cholesterol levels returned to pretreatment levels by one month after discontinuation of each agent. With clofibrate, HDL cholesterol increased by 16 +/- 20% from baseline (mean +/- SD) (P less than 0.05), A-I by 11 +/- 13% (P less than 0.05) and A-II by 39 +/- 17% (P less than 0.01). During oxandrolone HDL cholesterol declined by 36 +/- 20% from baseline (P less than 0.01), A-I by 21 +/- 13% (P less than 0.01), and A-II by 16 +/- 11% (P less than 0.025). Neither PAS-C nor colestipol exerted major effects on HDL, or any of the variables although both were associated with a slight rise in the A-I/A-II ratio (11 +/- 15% and 12 +/- 12%, respectively).

Adult↗
PubMed1980

The effect of a high cholesterol and saturated fat diet on serum high-density lipoprotein-cholesterol, apoprotein A-I, and apoprotein E levels in normolipidemic humans.

The effects of a high cholesterol, high saturated fat diet on serum high density lipoprotein cholesterol, apo A-I, and apo E levels were studied in six normolipidemic subjects. The study was done on an outpatient basis and mixed natural foods normally consumed by humans were used. When compared with a low cholesterol (98 mg/day) high polyunsaturated fat (P/S ratio 1.6) diet, the high cholesterol (1021 mg/day), high saturated fat (P/S ratio 0.4) diet increased serum cholesterol (23%) by raising the cholesterol concentration in very low-density lipoproteins (59%), low-density lipoproteins (15%), and high-density lipoproteins (30%). The low-density lipoprotein-cholesterol/high-density lipoprotein-cholesterol ratio fell significantly from 1.78 to 1.58. The increased high-density lipoprotein-cholesterol was associated with an elevation of serum apo A-I but not apo E. Serum triglycerides did not change significantly.

Adult↗
PubMed1980

Effect of storage on the measurement of apolipoproteins A-I and A-II by radial immunodiffusion.

We studied the effect of storage time and conditions on the measurement of apolipoprotein A-I and A-II by radial immunodiffusion. Purified A-I and A-II standards were stable for at least 6 months before any change in immunoreactivity was detected if stored at 4 degrees C at concentrations of 0.06-0.24 mg/ml for A-I and 0.016-0.064 mg/dl for A-II in 0.84 M tetramethylurea, 6.4 M urea, and 8 mM Tris-hydrocholoride, pH 8.0. Purified A-I (0.8-1.6 mg/ml) and A-II (0.5-1.0 mg/ml) were stable for 1 year if stored at -60 degrees C in 5 mM NH4HCO3 with or without 4.2 M tetramethylurea. Serum or plasma could be stored at 4 degrees C (under conditions where evaporation and bacterial growth were minimized) for at least 46 days or at -20 degrees C for up to 3 years without any change in A-I or A-II levels. For four serum samples stored at -20 degrees C for 2 to 3 years, the coefficient of variation of measurement ranged from 6.3 to 9.8% for A-I and from 6.7 to 10.6% for A-II. Samples stored at 4 degrees C had comparable apolipoprotein levels to those stored at -20 degrees C. However, apolipoprotein levels in serum samples were 3-5% higher than those obtained on plasma samples. We conclude that purified A-I or A-II and serum and plasma can be stored for long periods without any change in the measurement of the A-I or A-II by radial immunodiffusion.

Apolipoprotein A-I↗
PubMed1979

Short-term egg yolk feeding in humans. Increase in apolipoprotein B and low density lipoprotein cholesterol.

In animal studies, hypercholesterolemia induced by cholesterol feeding results in the plasma cholesterol being transported by lipoproteins of lower densities. Little information is available for humans. To determine the specific lipoprotein responses to dietary cholesterol challenge in humans, four volunteer subjects ingested a liquid formula diet containing 5000 mg of egg yolk cholesterol per day for 30 days and the changes in their lipoprotein fractions were examined. The high dietary cholesterol (above the range of normal diet) was associated with marked increases in apolipoprotein B and low density lipoprotein (LDL) cholesterol levels. An elevated cholesterol : triglyceride ratio in the LDL fraction indicated that the diet altered both LDL level and composition. High density lipoprotein cholesterol and apolipoprotein AI increased slightly. Very low and intermediate density lipoprotein cholesterol and apolipoprotein E levels did not increase during the diet. Thus, high dietary cholesterol was associated with major changes in LDL level and composition, but only minor changes in the other lipoprotein fractions and suggested only minor accumulation of remnant particles.

Adult↗