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Biomedical subjects

M L Cheng

Publications and source records attributed to M L Cheng.

At least 19 recordsLinked to original sources
PubMed1995

Changes of protein kinase C subspecies in staphylococcal enterotoxin-B-induced thymocyte apoptosis.

Our previous studies demonstrated that intravenous administration of staphylococcal enterotoxin B (SEB) to BALB/c mice resulted in thymocyte apoptosis. In the present study, we evaluated the role of protein kinase C (PKC) in thymocyte apoptosis induced by SEB. Our results showed that the level of protein phosphorylation in the thymocytes was reduced after the in vivo SEB treatment for 24 h. The activity of classical PKC subspecies was decreased in both cytosolic and membrane fractions of thymocytes following SEB administration. The lowest level of PKC activity was reached by 24 and 48 h, then was recovered gradually after 72 h. Furthermore, the mRNA expression of PKC-beta and, to a much less extent, PKC-alpha, but not PKC-sigma, in thymocytes was reduced by SEB. The decrease of mRNA level of PKC-beta showed good correlation with the pattern of PKC activity. These results provide direct evidence showing the changes in PKC subspecies mRNA expression during the process of apoptosis.

Animals↗
PubMed1992

Distribution of specific apolipoproteins determined by immunoblotting of baboon lipoproteins resolved by polyacrylamide gradient gel electrophoresis.

A method for the quantitative assessment of apolipoprotein distributions among baboon serum lipoproteins is described. The method combines the precise and reproducible separation of lipoproteins by polyacrylamide gradient gel electrophoresis with the specificity of immunoblotting. The method permits the measurement of distributions for any apolipoprotein for which there are antibodies available. Radioactive secondary antibodies are used to expose X-ray film, and distributions are determined by densitometry. Absorbance is linearly related to both antigen and antibody concentrations. The method is reproducible, with the mean coefficient of variation calculated to be 0.118, and has a high repeatability (r2 = 0.97). The immunoblotting method can be employed to measure the fine details of lipoprotein phenotypes as they are influenced by genotype and environment.

Animals↗
PubMed1988

Method for quantitating cholesterol in subfractions of serum lipoproteins separated by gradient gel electrophoresis.

Extensive heterogeneity in particle size distribution of serum lipoproteins of baboons was resolved by a procedure that combined Sudan black B prestaining, polyacrylamide gradient gel electrophoresis (GGE), and quantitative densitometry. Each densitometric scan represented a continuous distribution of the relative amount of cholesterol in a serum sample, as a function of the lipoprotein particle size. For analytical purposes, each scan was divided into 12 fractions, representing 12 particle size ranges. The relationship between the estimated cholesterol concentrations in the summed GGE/densitometric fractions corresponding to very low-density lipoproteins (VLDL) + low-density lipoproteins (LDL) and those corresponding to high-density lipoproteins (HDL) and concentrations measured by the heparin-Mn2+ precipitation/enzymatic procedure was linear over a broad range. However, a systematic overestimation of HDL cholesterol concentration and an underestimation of VLDL + LDL cholesterol concentration was apparent. Therefore, correction factors were developed for adjusting the estimates of VLDL + LDL and HDL cholesterol concentrations obtained by the GGE/densitometric method. This analytical method is rapid, repeatable, economical, and useful for genetic and dietary research in which cholesterol concentrations in multiple particle size ranges of lipoproteins must be measured in large numbers of samples. It also is adaptable to immunoblotting procedures for detecting the distribution of specific apolipoproteins among the size-resolved lipoproteins.

Centrifugation, Density Gradient↗
PubMed1988

Functional response of healthy and diseased glomeruli to a large, protein-rich meal.

Differential solute clearances and hormone assays were used to characterize the effect of a large, protein-rich meal (1.5 g/kg) on glomerular function in 12 healthy volunteers (group I) and 12 patients with chronic glomerular disease (group II). Changes from baseline during 3 h after the meal included an elevation of plasma osmolality, progressive urinary concentration, and increasingly positive fluid balance. Plasma renin activity and arginine vasopressin levels (measured in group II only) increased significantly. Nevertheless, the rate of peak postmeal renal plasma flow became elevated by 13 and 33% in groups I and II, respectively. Corresponding peak increases in postmeal glomerular filtration rate exceeded baseline by 10 and 16%. In the proteinuric subjects of group II the fractional clearances of albumin, IgG and uncharged dextrans in the radius interval 36-54 A, declined significantly after the meal. A similar depression of the fractional dextran-clearance profile was observed also in group I. Applying the fractional clearances of relatively permeant dextrans (radii less than or equal to 44 A) to a model of hindered solute transport through an isoporous membrane, we estimate that transmembrane hydraulic pressure difference increased by 12% in group I and by between 0 to 12% in group II after protein ingestion. We conclude (i) that oral protein ingestion increases glomerular ultrafiltration pressure and rate in both normal and diseased glomeruli, (ii) that this hemodynamic response may be mediated in part by the glomerulopressor hormones angiotensin II and arginine vasopressin, and (iii) that the foregoing hemodynamic changes exert no acute adverse effect on glomerular barrier size-selectivity.

Adult↗
PubMed1987

Detecting genetic effects on lipoprotein phenotypes in baboons: a review of methods and preliminary findings.

Statistical methods for detecting the contribution of major genes to quantitative phenotypes have been widely applied in human family studies. Some of these methods are reviewed, and their application to analysis of an animal model for a human disease is described. Analysis of lipoprotein concentrations in pedigreed baboons provides evidence for genetic effects on specific lipoprotein components that have been associated with reduced susceptibility to atherosclerosis in humans.

Animals↗
PubMed1987

Pregnancy-associated esterase in sera of baboons.

Baboon serum samples were resolved by starch gel electrophoresis and polyacrylamide gradient gel electrophoresis and stained with naphthol substrates for esterase activity. An esterase that hydrolyzed alpha-naphthyl butyrate in preference to alpha-naphthyl acetate was found in very high activities in some individuals but not others. It migrated just cathodal of the albumin band in starch gels. In polyacrylamide gradient gels, it co-migrated with albumin and had an apparent molecular weight of approximately 65,000 daltons. Electrophoretic analysis by gel electrophoresis of random serum samples from male and female baboons indicated that this esterase was present only in the sera of pregnant baboons. Further investigation of serial samples collected from carefully monitored baboons confirmed that the amount of activity of this esterase was correlated with stage of pregnancy. Therefore, it was named pregnancy esterase (PE). PE was detectable by gel electrophoresis and chromogenic staining techniques as early as day 30 of pregnancy; its activity gradually increased with progressive pregnancy and reached maximum activity near full term (182 days). Soon after parturition, the activity of PE decreased rapidly and was not detected in maternal sera by day 14 postpartum. No evidence of PE was detected in sera of pregnant humans.

Animals↗
PubMed1986

A novel system for storage of sera frozen in small aliquots.

A novel sample storage system involves the storage of frozen sera and other fluids within small heat-sealed segments of Tygon tubing. Each series of attached segments comprises one sample divided into small aliquots and protected by a cellulose acetate butyrate tube situated in a specially constructed rack in a low-temperature freezer. This storage system offers several benefits including elimination of repeated freezing and thawing, protection against contamination of bulk samples, simplicity in keeping inventory records, ease of retrieving samples, and elimination of the need to return samples to storage. It is efficient, economical and applicable to a variety of liquid specimens, and greatly increases the length of potential storage life.

Animals↗
PubMed1985

A versatile technique for drying polyacrylamide slab gels.

Slab gels of different thickness, and of various homogeneous or gradient concentrations of acrylamide, can be dried rapidly and consistently using a newly developed drying procedure. After drying, stained gels retain excellent resolution of electrophoretic patterns, and unstained gels are suitable for use in autoradiography and fluorography.

Animals↗
PubMed1985

Biological and biophysical properties of the tumor-localizing component of hematoporphyrin derivative.

Reverse-phase chromatography, aqueous gel exclusion, and nonaqueous gel exclusion were assessed as procedures for preparative fractionation of the tumor-localizing product hematoporphyrin derivative. Porphyrin accumulation, fluorescence, and photodynamic cytotoxicity were monitored using the murine Sarcoma 180 tumor. Aqueous gel exclusion chromatography can provide a hematoporphyrin derivative fraction enriched in the tumor-localizing component. A further enrichment occurs when this procedure is carried out at 55 degrees C, but nonlocalizing porphyrins could not be eliminated. While providing a better separation, reverse-phase chromatography cannot provide a tumor-localizing fraction free from contaminating protoporphyrin. However, this and other contaminants can be eliminated from the tumor-localizing fraction via nonaqueous gel exclusion chromatography. This latter separation provides two tumor-localizing products: a fast-eluting fraction enriched in the major photosensitizing component(s); and a more complex slowly eluting fraction enriched in fluorescence localizers.

Animals↗
PubMed1982

Role of a modified ovitrap in the control of Aedes aegypti in Houston, Texas, USA.

A modified ovitrap from which larvae could not escape was employed for one year for the control of Aedes aegypti at Blossom Heights, Houston, Texas. At the end of this period, the Breteau index in the ovitrap area had declined by 36%, in contrast to a sharp increase of nearly 500% in the non-ovitrap area. The premises index in the ovitrap area remained unchanged, while the index in the non-ovitrap area increased by 440%. The problems associated with this control campaign and the use of these "autocidal" ovitraps are discussed.Annual fluctuations in the egg populations of A. aegypti and A. triseriatus were studied by weekly collections of eggs from the ovitrap paddles. The weekly fluctuations of egg numbers, the percentage of ovitraps with eggs of Aedes mosquitos, as well as the ovitrap premises index (i.e., percentage of premises with at least one ovitrap positive) all exhibited a similar fluctuation pattern, with a distinct peak extending from June to October.

Aedes↗
PubMed1979

The genetics of hexokinase in a mosquito, Culex pipiens.

The genetics of hexokinase (HK) variants in a mosquito, Culex pipiens L., was studied using starch gel electrophoresis. Three isozymic forms of HK, all migrating anodally, were present in all three body regions, but in differing proportions. No obvious differences in specificity for three hexose sugars was detected among the three isozymic bands. However, qualitative differences in staining intensity indicate the following order of substrate affinity: glucose greater than fructose greater than mannose. The inheritance of the HK variants is controlled by a pair of co-dominant alleles at a single genetic locus.

Alleles↗