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Biomedical subjects

M C Cheung

Publications and source records attributed to M C Cheung.

98 records · Page 6Linked to original sources
PubMed1979

Distribution of cholesterol and apolipoprotein A-I and A-II in human high density lipoprotein subfractions separated by CsCl equilibrium gradient centrifugation: evidence for HDL subpopulations with differing A-I/A-II molar ratios.

The purpose of this experiment was to characterize the high density lipoproteins (HDL) as a function of hydrated density. HDL was subfractionated on the basis of hydrated density by CsCl density gradient centrifugation of whole serum or the d 1.063-1.25 g/ml HDL fraction isolated from three men and three women. Apolipoprotein A-I and A-II quantitation by radial immunodiffusion showed that the A-I/A-II ratio varied with the lipoprotein hydrated density. The A-I/A-II molar ratio of HDL lipoproteins banding between d 1.106 and 1.150 g/ml was nearly constant at 2.2 +/- 0.2. In the density range 1.151-1.25 g/ml the A-I/A-II ratio increased as the density increased. On the other hand, in the density range between 1.077 and 1.105 the A-I/A-II ratio increased as the density decreased, ranging from 2.8 +/- 0.5 for the d 1.093-1.105 g/ml fraction to 5.6 +/- 1.3 for the d 1.077-1.082 g/ml fraction. The d 1.063-1.076 g/ml fraction and the d 1.077-1.082 g/ml fractions had comparable A-I/A-II ratios. Serum and the d 1.063-1.25 g/ml HDL fraction exhibited similar trends. The cholesterol/(A-I + A-II) ratio decreased as the density increased in all 12 samples (six serum and six HDL) examined. Gradient gel electrophoresis of the density gradient fractions showed that as the density increased from 1.063 to 1.200 g/ml the apparent molecular weight decreased from 3.9 x 10(5) to 1.1 x 10(5). HDL subfractions with the same hydrated densities had comparable molecular weights and A-I/A-II and cholesterol/(A-I + A-II) ratios when isolated from men or women. HDL contains subpopulations that differ in the A-I/A-II molar ratio.-Cheung, M. C., and J. J. Albers. Distribution of cholesterol and apolipoprotein A-I and A-II in human high density lipoprotein subfractions separated by CsCl equilibrium gradient centrifugation: evidence for HDL subpopulations with differing A-I/A-II molar ratios.

Apolipoproteins↗
PubMed1979

Comparison of current methods for high-density lipoprotein cholesterol quantitation.

We compared six precipitation methods for high-density-lipoprotein cholesterol quantitation with an ultracentrifugation method, the accuracy of which was improved by correcting for 4% manipulative loss in the d greater than 1.063 fractions. For purposes of comparison, the apoprotein B-associated cholesterol (average 56 mg/L) measured by immunoassay in the d greater than 1.063 fractions was subtracted. In 65 plasma samples from men, women, and children, a heparin-Mn2+ procedure with Mn2+ at 46 mmol/L produced results slightly higher (+16 mg/L), while results with Mn2+ at 92 mmol/L averaged slightly lower (-8 mg/L) than the comparison ultracentrifuge method. Results that were about 5% low were obtained by the dextran sulfate 500-Mg2+ (-25 mg/L) and phosphotungstate-Mg2+ (-31 mg/L) methods. A heparin-Ca2+ method produced results 10% high (+58 mg/L). Results by a polyethylene glycol-6000 precipitation method were 12% low (-64 mg/L). Precision was better with the two heparin-Mn2+ and the dextran sulfate 500-Mg2+ procedures, with CVs of 4%, intermediate with phosphotungstate-Mg2+ and polyethylene glycol-6000 (CV 6-7%), and poorest with heparin-Ca2+ (CV 10%). Precipitation by phosphotungate-Mg2+ appeared more sensitive to reagent concentration and temperature variations than either the heparin-Mn2+ or dextran sulfate 500-Mg2+ methods. We conclude that these precipitation methods are not equivalent, but give rise to significant systematic differences in high-density-lipoprotein cholesterol quantitation.

Adult↗
PubMed1977

The measurement of apolipoprotein A-I and A-II levels in men and women by immunoassay.

To study apolipoprotein A-II, a simple, precise, and accurate immunodiffusion assay was developed and applied in a population sample of industrial employees. Apolipoprotein A-II (A-II) did not increase with age in men (r = -0.20, n = 172), but showed a slight increase with age in women (0.1 mg/dl per yr, r = 0.20, n = 188). A-II correlated significantly with apolipoprotein A-I (A-I) (r = 0.71) and high density lipoprotein (HDL) cholesterol (men, r = 0.64; women, r = 0.49). The A-I/A-II ratio was significantly related to HDL cholesterol (men, r = 0.29; women, r = 0.44). Women on no medication (n = 92) had A-II levels similar to men (34+/-5 and 33+/-5 mg/dl, mean+/-SD, respectively), whereas women on oral contraceptives or estrogens had significantly higher levels (39+/-6 mg/dl, n = 75, P < 0.01). The plasma A-I/A-II weight ratio was 3.6+/-0.4 for men and 3.8+/-0.5 for women. In the d = 1.10-1.21 subfraction, both males and females had similar A-I, A-II, and HDL cholesterol levels (men: mean, 97, 27, and 32 mg/dl, respectively; women: mean, 104, 28, and 36 mg/dl, respectively). Women had approximately twice the amount of A-I, A-II, and HDL cholesterol than men in the d = 1.063-1.10 fraction (men: mean, 10, 2, and 10 mg/dl, respectively; women: mean, 24, 4, and 19 mg/dl, respectively). The A-I/A-II weight ratio in the d = 1.063-1.10 fraction (men, 5.1+/-0.7; women, 6.1+/-1.3) was significantly greater (P < 0.01) than that in the d = 1.10-1.21 fraction (men, 3.7+/-0.2; women, 3.8+/-0.2). Furthermore, the weight ratio of cholesterol to total apoprotein A in the d = 1.063-1.10 fraction (men, 0.75+/-0.09; women, 0.67+/-0.05) was significantly higher (P < 0.01) than that found in the d = 1.10-1.21 fraction (men, 0.26+/-0.04, women, 0.28+/-0.05). Thus, the compositions of HDL hydrated density subclasses are significantly different from each other. These results suggest that the differences in HDL between men and women are due primarily to differences in the relative proportions of HDL subclasses rather than to the intrinsic differences in HDL structure.

Adult↗
PubMed1976

Use of polyethylene glycol in separating bound from unbound ligand in radioimmunoassay of thyroxine.

In most rapid radioimmunoassay methods, absorbents are used that disturb the equilibrium of the ligand-antibody interaction; thus the separation process must be rigidly timed. We show here that polyethylene glycol (mol wt. 6000) abolishes this constant. We measured gamma-globulin precipitation by polyethylene glycol (150g/liter) in a thyroxine radioimmunoassay system involving use of a sheep anti-thyroxine antiserum, quantitatively and qualitatively, with either normal human serum or completely precipitated at pH 6-9 at 4 and 25 degrees C, but incompletely if salt concentration was high (1 mol/liter). Specificity of gamma-globulin precipitation increased with increasing pH and temperature. All gamma-globulin-bound thyroxine was precipitated, and also some not bound to gamma-globulin. This was taken into account by including "blank" tubes (no antibody, but with normal sheep serum) in all assays. Because this reaction is predominantly entropic and temperature independent, the entire procedure can be done at 37 degrees C and room temperature without rigid timing. The assay requires 10 mul of serum, its reproducibility is 4-8% (CV) in the euthyroid and hyperthyroid range, and its accuracy is close to 100%.

Evaluation Studies as Topic↗
PubMedDate not supplied

Nonseminomatous germ cell tumour of testis in Hong Kong Chinese patients.

Combination chemotherapy with multidisciplinary support results in excellent cure rate for nonseminomatous germ cell tumour of testis. 52 Chinese patients treated in two institutions in Hong Kong were reviewed retrospectively. 29 patients were stage I and IM and 3-year survival was 96% with a median follow-up of 49 months. 23 patients were stage II and above and 3-year survival was 54% with a median follow-up of 21 months. The patient details are compared with a Western population, factors influencing outcome are discussed, and provision of optimal care outlined.

Adult↗
PubMedDate not supplied

Plasma lipids and microangiopathy in insulin-dependent diabetes mellitus.

The relationship of plasma levels of high density lipoprotein (HDL) cholesterol, apolipoproteins A-I and A-II (the major apolipoproteins in HDL), low density lipoprotein (LDL) cholesterol, triglyceride, and glucose to microangiopathy was evaluated in 49 insulin-dependent diabetic subjects. Although the HDL cholesterol/LDL cholesterol ratio (a risk determinant for macroangiopathy) was lower in women with proteinuria, no other relationships between HDL cholesterol or the A apolipoproteins and renal microangiography were found. The only independent association between HDL and retinal microangiopathy was found in women, where an inverse correlation was found between the apo A-I/apo A-II ratio and the number of microaneurysms (rs = -0.561, P less than 0.05). Men showed strong relationships of glucose, triglyceride, cholesterol, and LDL cholesterol to renal microangiopathy whereas women, in general, had stronger correlations of these variables with retinal microangiopathy. Thus, several alterations in lipoprotein cholesterol distribution and HDL composition are associated with diabetic microangiopathy. In addition, differences between sexes suggest that previously undescribed hormonal factors may influence the severity of this process.

Adolescent↗