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Biomedical subjects

L Chan

Publications and source records attributed to L Chan.

At least 469 records · Page 26Linked to original sources
PubMed1982

Intestinal Biosynthesis of apolipoproteins in the rat: apoE and apoA-I mRNA translation and regulation.

Rat intestinal poly(A) RNA was translated in wheat germ and reticulocyte lysate systems in vitro. ApoA-I and apoE were demonstrated to be specific products by immunoprecipitation and fractionation on sodium dodecyl sulfate acrylamide gels. They were identical in size to the respective products from rat liver. In pulse-labeling studies, apoE was shown to be synthesized by slices of rat intestine in situ. Furthermore, a high cholesterol diet stimulated the synthesis of apoE and apoA-I at the pretranslational level.

Animals↗
PubMed1982

Antibody and complement in the stimulation of neutrophil chemiluminescence by Neisseria meningitidis: studies in a patient with complete deficiency of C7.

When an eight-year-old boy with a syndrome compatible with disseminated neisseria infection was found to lack C7, studies on the role of antibody and complement in the interaction of polymorphonuclear leukocytes (PMNLs) and Neisseria were initiated with use of a luminol-enhanced chemiluminescence assay. The chemiluminescent response to opsonized Neisseria meningitidis was markedly lower than the response to opsonized zymosan or Streptococcus pneumoniae but was similar to that obtained with Haemophilus influenzae type b. IgG antibody to N. meningitidis was shown to enhance the chemiluminescent response. The chemiluminescent response of PMNLs to N. meningitidis was normal when the bacteria were incubated with sera deficient in C5, C6, or C7 but was absent in serum lacking C2. Thus, both antibody and the early-acting proteins of the classical complement pathway appear to be essential for maximal stimulation of PMNL oxidative metabolism by N. meningitidis, although the late-acting components of complement are not.

Animals↗
PubMed1982

Revision of the Ontario phenylalanine equivalency system and development of a low protein equivalency system.

The Phenylalanine Content of Foods, an equivalency system used in the dietary treatment of phenylketonuria, was prepared in 1975. Recently this system was revised to include a total of 372 food items in various raw and processed states. Food lists are available in a simple version for parents listing the serving size per phenylalanine equivalent, and in a more comprehensive version for dietitians providing weights for the serving sizes as well as values for phenylalanine, protein, and energy per equivalent. Subsequently, the system was modified to form a low protein equivalency system for use in designing low protein diets for a number of other inherited metabolic disorders.

Diet Therapy↗
PubMed1982

Use and design of low protein diets for children with inborn metabolic disorders.

Low protein diets are used to treat infants and children with hyperammonemia due to urea cycle and other metabolic disorders as well as a number of amino and organic acidopathies. The incidence of these disorders is small and many are life-threatening. As a result, there is little in the literature on the dietary management of these patients. This paper draws on 10 years of clinical experience at the Hospital for Sick Children in Toronto, Ontario and presents a guide to the preparation of infant formulas providing levels of protein intake from 0.5 to 2.0 g per kg. Also described is a low protein equivalency system that is a useful guide for measuring both baby foods and table foods for affected children up to about six years of age. This dietary information is accompanied by a description of the disorders amenable to low protein diets, some of the adjunctive therapies employed and the nutritional concerns associated with severe restriction of protein.

Child↗
PubMed1982

Pneumococcal polysaccharide immunization of children with sickle cell disease. I. Clinical reactions to immunization and relationship to preimmunization antibody.

Vaccine reaction data were obtained from 154 patients with sickle cell disease immunized with tetradecavalent pneumococcal polysaccharide vaccine. There was a high rate (70%) of mild reactions, primarily at the site of injection. Fever over 100 degrees F was uncommon and precipitation of symptoms similar to sickling crisis was rare. Development of local reactions was associated with the level of preimmunization pneumococcal antibody titer.

Anemia, Sickle Cell↗
PubMed1982

Pneumococcal polysaccharide immunization of children with sickle cell disease. II. Serologic response and pneumococcal disease following immunization.

One-hundred seventy-four children with sickle cell disease (SCD) were immunized with a single dose of tetradecavalent pneumococcal vaccine. Preimmunization and postimmunization antibody against 13 of the 14 pneumococcal capsular antigens was measured by indirect hemagglutination (IHA). The ability of each antigen to stimulate antibody following immunization was characterized by one of three types of responses: (1) poor antibody response regardless of the age at immunization (capsular types 6A, 14, and 19F); (2) improving antibody response with advancing age at immunization (capsular types 1, 4, 9N, 12F, 18C, and 23F); and (3) good antibody response regardless of age at immunization (capsular types 2, 3, 7F, and 8). An increase in antibody following immunization was significantly correlated (P less than 0.0005) with an increasing level of preimmunization antibody titer for all 13 antigens. Through the first 24 months of study, two episodes of pneumococcal sepsis caused by group 23 pneumococci were documented in two children immunized prior to 24 months of age (incidence rate, 4.40/100 patient-years in children less than 5 years of age), and one additional episode caused by a group 23 pneumococcus occurred in a 5 7/12-year-old child (incidence rate, 0.66/100 patient-years in children greater than 5 years of age). These observations suggest that anamnestic immune response significantly contributed to the enhanced antibody response observed in older children and adults. Only modest vaccine efficacy may be expected among children with SCD who receive a single dose of pneumococcal vaccine.

Adolescent↗
PubMed1981

A simple, efficient method for coupling DNA to cellulose. Development of the method and application to mRNA purification.

A simple, efficient method to couple covalently DNA to cellulose is described. It utilizes the bifunctional oxirane 1,4-butanediol diglycidyl ether to activate cellulose and subsequently to link DNA to the cellulose. The optimal conditions for the latter reaction included use of a dehydration technique whereby DNA and activated cellulose were allowed to react on a glass slide in 0.1 N NaOH. Initial volume of the reaction was important; less than or equal to 250 microliters/50 mg cellulose was necessary for maximum efficiency. At DNA concentrations of less than or equal to 4 micrograms/mg cellulose, efficiency of binding was 90%. Binding studies using nucleotide homopolymers indicated that the order of the relative efficiencies of binding was poly(dT) greater than poly(dC) = poly(dA) greater than poly(dG). DNAs subjected to the binding conditions had an average of 0-1 breaks/molecule (for a 915-base DNA). A cloned double-stranded cDNA was coupled to cellulose by this technique. The cDNA was coupled to cellulose by this technique. The DNA-cellulose matrix was successfully used to purify the complementary mRNA from total poly(A)-enriched RNA by affinity chromatography. This method is very simple and highly efficient and can be conveniently adapted for the covalent coupling of various DNA species to cellulose for affinity chromatography.

Animals↗
PubMed1981

Pneumococcal septicemia in children with sickle cell anemia. Changing trend of survival.

Streptococcus pneumoniae infection has been the predominant cause of death among children with sickle cell anemia (SS). We report our observed change in the pattern of progression of septicemia to meningitis and death in nonimmunized SS children who were not receiving prophylactic penicillin in the face of a persistently high incidence of pneumococcal disease. Of 233 SS children less than ages 6 years observed for 781 person-years, the overall incidence rate of pneumococcal septicemia was 5.9 episodes per 100 person-years. Prior to July 1972, of 23 children who had pneumococcal septicemia, eight (35%) died and meningitis developed in 15 (65%), whereas since July 1972, 11 children have had pneumococcal septicemia, but no children died and meningitis developed in only two (18%). This decrease in major morbidity is attributed to the establishment of a clinical program that provides close medical supervision of the SS child with fever and the rapid institution of parenteral antibiotic therapy.

Anemia, Sickle Cell↗
PubMed1981

Characterization, cell-free synthesis, and processing of apolipoprotein A-I of rat high-density lipoproteins.

Rat apolipoprotein A-I (apoA-I) was isolated from delipidated high-density lipoproteins by sequential chromatography on Sephacryl S-200 and Sephadex G-150 columns in guanidine buffer. The purified protein had an apparent Mr of 27 000 and was homogeneous by NaDodSO4 and urea gel electrophoresis. Its amino acid composition was similar to that previously reported by Swaney et al. [Swaney, J. B., Wraithwaite, F., & Eder, H. G. (1977) Biochemistry 16, 271-278]. Microsequencing yielded an N-terminal sequence of Asp-Glu-Pro-Pro-Val-(Ser)-Glu-. Rabbit antisera were generated against the purified rat apoA-I and were shown to be monospecific against the protein by immunodiffusion and immunoelectrophoresis. Total poly(A) RNA was isolated from the rat liver by extraction in guanidine hydrochloride buffer and oligo(dT)-cellulose chromatography. In vitro translation of the RNA was performed in both wheat germ and nuclease-treated reticulocyte lysate systems, using [35S]Met as the radioactive amino acid precursor. Immunoreactive 35S- labeled apoA-I synthesized in vitro was precipitated by a rabbit antirat apoA-I serum. It was analyzed on an NaDodSO4- acrylamide slab gel and visualized by fluorography. The in vitro product was found to have an apparent Mr of 28 500, being larger than the authentic plasma protein by approximately 1500 daltons. When translation was performed in the presence of dog pancreatic microsomal membranes, the immunoprecipitable material was cotranslationally cleaved to a product identical in size (Mr 27 000) with plasma apoA-I. Thus, we have synthesized in vitro a putative precursor to rat apoA-I, designated preapoA-I. The preapoA-I has been processed in a cell-free system to its mature plasma counterpart by the addition of exogenous microsomal membranes.

Amino Acid Sequence↗
PubMed1981

Synthesis and accumulation of mannose-containing glycopeptides in human fibroblast cells: possible separate pathways for neutral and acidic glycopeptides.

The normal human fibroblast, WI-38, was labelled with radioactive mannose and its incorporation, as well as the accumulation of acidic and neutral glycopeptides on the cell surface, was followed as a function of time. The transit time of newly made Pronase-released cell surface glycopeptides from their intracellular site of synthesis to the cell surface was slower in nongrowing cells than in a rapidly growing culture. When the surface glycopeptides were separated by high-voltage paper electrophoresis into neutral and acidic species, it was observed that the cell surface material was initially enriched with neutral glycopeptides. However, with time the relative proportion of acidic species increased so that by 3 h the ratio between the acidic and neutral species approached a constant value. Our data are consistent with the hypothesis that multiple pathways for asparagine-linked glycoprotein biosynthesis are possible.

Acids↗
PubMed1981

Comparison of the nucleotide sequence of cloned DNA coding for an apolipoprotein (apo VLDL-II) from avian blood and the amino acid sequence of an egg-yolk protein (apovitellenin I): equivalence of the two sequences.

We have compared the amino acid sequences of two low-molecular-weight avian apoproteins: apoVLDL-II from very low-density lipoproteins of hen plasma and apovitellenin I from hen egg yolk. The sequence of White Leghorn apoVLDL-II was derived from the nucleotide sequence of cloned apoVLDL-II DNA (Chan et al., 1980). The sequenator was used to determine the amino acid sequence of apovitellenin I from two breeds of hen (White Leghorn and Australorp). The sequences from the two breeds were not only identical, but they also completely matched the predicted sequence derived from the apoVLDL-II DNA sequence. The identity reported here establishes that this protein is transported intact from the blood to the egg yolk.

Amino Acid Sequence↗
PubMed1981

Estrogen regulation of yolk and non-yolk protein synthesis in the avian liver. An immunocytochemical study.

The effects of acute and chronic estrogen treatment on two egg yolk proteins, vitellogenin and apoVLDL-II, and two non-yolk proteins, ovalbumin and apoA-I, were studied by immunocytochemical techniques. Three groups of cockerels received either no treatment, or a single injection of diethylstilbestrol (DES, 2.5 mg) (acute stimulation) 24 h before killing, or 14 daily injections of 2.5 mg DES (chronic stimulation) before killing. The animals were killed at 4 weeks of age and their livers examined with respect to the distribution of the four different proteins by the indirect immunoperoxidase method. Vitellogenin was undetectable in the untreated cockerel liver. A single injection of DES resulted in the appearance of the protein in approximately 10%-15% of the hepatocytes. Chronic DES stimulation increased the number of positive cells to about 20%. In contrast, apoVLDL-II was present in 1%-2% of the hepatocytes in untreated animals. It was detected in an increased proportion (20%-25%) of cells after a single dose of DES. After chronic estrogen treatment, there was a very marked increase in the number of positive cells (less than 90%). Ovalbumin was undetectable in untreated cockerel liver, while apoA-I was detected in an extremely low proportion of cells (0.005%-0.01%). Neither ovalbumin nor apoA-I distribution seemed to be affected by a single dose of DES. However, chronic DES treatment resulted in the appearance of ovalbumin-containing cells (approximately 0.02%) and a marked increase in the number of cells containing apoA-I (10%-15%).

Animals↗