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Biomedical subjects

J C Tan

Publications and source records attributed to J C Tan.

34 records · Page 2Linked to original sources
PubMed1995

Factors that influence the choice of infant feeding.

UNLABELLED: To consider some of the many factors that influence the choice to initiate and continue breast-feeding. CONCLUSION: There is increasing recognition of the nutritional value and related health outcomes of breast-fed infants. Further research is essential to appraise the medical and social determinants of infant feeding practices, particularly the early discontinutation of breast-feeding. Paediatricians are in an ideal position to foster, encourage and support such research and to accept a wider role in advocacy of the infant's right to obtain optimal nutrition.

Advertising↗
PubMed1993

Characterization of interleukin-10 receptors on human and mouse cells.

Human interleukin (IL)-10 is a pleiotropic cytokine acting on a variety of immune cells. Here we show that the protein can be enzymatically iodinated to high specific radioactivity with retention of biological activity. The radiolabeled ligand binds specifically to its receptor in several mouse and human cell lines, notably human B-lymphoma line JY and mouse mast cell line MC/9. Human IL-10 apparently binds as a dimer to a single class of receptor in both the JY and MC/9 cell lines with a Kd in the 50-200 pM range. Interestingly, mouse IL-10 was capable of blocking binding of human IL-10 to mouse but not human cells. There appears to be at most only a few hundred IL-10 receptors/cell for both mouse and human cell lines examined. Chemical cross-linking of the radioiodinated hIL-10 to JY and MC/9 cells revealed a common protein complex with an apparent molecular mass of about 97 kDa. Additional high molecular weight complexes were detected with JY but not MC/9 cells.

Animals↗
PubMed1993

Isometric maximal and submaximal trunk extension at different flexed positions in standing. Triaxial torque output and EMG.

Thirty-one healthy men were tested for the effects of trunk-flexion positions (0 degrees, 15 degrees, and 35 degrees) in standing on triaxial torques and electromyogram of 10 trunk muscles during voluntary maximal and submaximal isometric trunk extension. At a more flexed position, both erector spinae and latissimus dorsi showed significantly higher RMS-EMG. The abdominal obliques were coactivated only during 100% maximum voluntary exertion at each posture. In all tests, the rectus abdomini were quiet. Mean maximum extension torque increased significantly at 15 degrees and 35 degrees of trunk flexion. The ratio of extension torque over RMS-EMG of the trunk extensor muscles, called the neuromuscular efficiency ratio (NMER), also increased in the more flexed posture. However, NMER has to be interpreted with caution because it is affected both by posture and exertion levels. The effects of posture on the torque generation capability of the trunk question the validity of the current lifting recommendations.

Abdominal Muscles↗
PubMed1992

Role of physical therapy in the treatment of cervical disk disease.

Table 4 summarizes how physical therapy should be implemented during the acute and chronic phase of cervical disk disease. From the outset of treatment, the patient should be encouraged to return to work or other productive activities and should be taught how to be responsible for their own recovery. If passive modalities are used, they must be an adjunct to the active modalities. As soon as the patient is able to continue with an active program without unbearable pain, the passive modalities should be discontinued gradually. If neck pain becomes chronic, the accompanying psychosocial dysfunction must be addressed through behavioral modification techniques, preferably in a multidisciplinary setting. Modification of the work place, work habits, and lifestyles must be emphasized at both the acute and chronic stages. The modalities presented in this article are commonly used by physical therapists. Unfortunately, the clinical efficacy of most of these modalities has yet to be proved. A literature search on the effectiveness of various physical therapy modalities by Sievers et al showed that only 4% of the studies published from 1979 to 1985 were controlled clinical trials. This scientific output of physical therapists needs to be corrected.

Acupuncture Therapy↗
PubMed1991

Ectopic expression of a c-kitW42 minigene in transgenic mice: recapitulation of W phenotypes and evidence for c-kit function in melanoblast progenitors.

The proto-oncogene c-kit encodes a transmembrane tyrosine kinase receptor that is allelic with the murine white-spotting locus (W). W mutations affect melanogenesis, gametogenesis, and hematopoiesis during development and adult life, and they result from the partial or complete loss of c-kit function. The W42 allele is a W mutation with severe effects in both the homozygous and the heterozygous states. Previous analysis of the W42 allele identified a missense mutation in an essential amino acid of the c-kitW42 kinase domain that abolishes the in vitro kinase activity of the c-kitW42 protein but does not affect its normal expression. These results suggested that the c-kitW42 allele was a dominant negative mutation within the context of c-kit-mediated signal transduction. To further explore the dominant negative characteristics of the W42 mutation, we have generated transgenic mice in which ectopic expression is driven by the human beta-actin promoter (hAP). Two mouse lines carrying the hAP-c-kitW42 transgene show an effect on pigmentation and the number of tissue mast cells. The patchy coat color pattern of the line 695 mice may reflect variable expression of the transgene in melanoblast progenitors and their descendants and, consequently, is indicative of a function for c-kit in early melanoblasts. Germ cell development and erythropoiesis, however, do not appear to be affected by the transgene. Mice expressing the c-kitW42 transgene therefore recapitulate some of the phenotypes of mice with W mutations. These results are therefore in agreement with the molecular basis of the W42 mutation and the dominant-negative characteristics of the c-kitW42 protein product.

Alleles↗
PubMed1991

Coronary artery disease and apolipoprotein A-I/C-III gene polymorphism: a study of Saudi Arabians.

The infrequent band of 3.2-kb of the apolipoprotein A-I/C-III polymorphic region has previously been found to be associated with coronary artery disease and with hypertriglyceridaemia in Caucasians. We studied the apolipoprotein A-I/C-III gene cluster polymorphism in 97 Saudi Arabians in relation to coronary artery disease. Patients were categorized as being with or without coronary artery disease on the basis of coronary angiography. Genomic blotting of Sac I-digested chromosomal DNA with the use of an apolipoprotein A-I gene probe revealed 4.2-kb and 3.2-kb hybridization bands. The genotype frequency of patients with and without coronary artery disease was not different. The frequency of the 3.2-kb allele occurred in 16% of patients with coronary artery disease and in 21% of patients with normal coronary arteries (non-significant). In conclusion, we have not been able to confirm in Saudi Arabians associations previously reported in Caucasians of the 3.2-kb band and coronary artery disease.

Apolipoprotein A-I↗
PubMed1990

The dominant W42 spotting phenotype results from a missense mutation in the c-kit receptor kinase.

The murine white spotting locus (W) is allelic with the proto-oncogene c-kit, which encodes a transmembrane tyrosine protein kinase receptor for an unknown ligand. Mutations at the W locus affect various aspects of hematopoiesis and the proliferation and migration of primordial germ cells and melanoblasts during development to varying degrees of severity. The W42 mutation has a particularly severe effect in both the homozygous and the heterozygous states. The molecular basis of the W42 mutation was determined. The c-kit protein products in homozygous mutant mast cells were expressed normally but displayed a defective tyrosine kinase activity in vitro. Nucleotide sequence analysis of mutant complementary DNAs revealed a missense mutation that replaces aspartic acid with asparagine at position 790 in the c-kit protein product. Aspartic acid-790 is a conserved residue in all protein kinases. These results provide an explanation for the dominant nature of the W42 mutation and provide insight into the mechanism of c-kit-mediated signal transduction.

Amino Acid Sequence↗
PubMed1990

Molecular bases of dominant negative and loss of function mutations at the murine c-kit/white spotting locus: W37, Wv, W41 and W.

The proto-oncogene c-kit encodes a transmembrane tyrosine protein kinase receptor for an unknown ligand and is allelic with the murine white-spotting locus (W). Mutations at the W locus affect various aspects of hematopoiesis, the proliferation and migration of primordial germ cells and melanoblasts during development. The original W mutation and W37 are severe lethal mutations when homozygous. In the heterozygous state the W mutation has a weak phenotype while W37 has dominant characteristics. Wv and W41 are weak W mutations with dominant characteristics. We have characterized the molecular basis of these four W mutations and determined their effects on mast cell differentiation by using a fibroblast/mast cell co-culture assay. We show that W37, Wv and W41 are the result of missense mutations in the kinase domain of the c-kit coding sequence (W37 E----K at position 582; Wv T----M position 660 and W41 V----M position 831), which affect the c-kit associated tyrosine kinase to varying degrees. The c-kit protein products in homozygous mutant mast cells are expressed normally, although the 160 kd cell membrane form of the c-kitW37 protein displays accelerated turnover characteristics. The W mutation is the result of a 78 amino acid deletion which includes the transmembrane domain of the c-kit protein. A 125 kd c-kit protein was detected in homozygous W/W mast cells which lacks kinase activity and is not expressed on the cell surface.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1990

Comparison of baseline sister-chromatid exchanges (SCE), cyclophosphamide-, ethylnitrosourea (ENU)-induced SCE, ENU-induced cell-cycle delay and chromosome aberrations between Peru and laboratory mice.

The baseline sister-chromatid exchange (SCE) frequency and sensitivity to the effects of the mutagens cyclophosphamide (CPP) and ethylnitrosourea (ENU) in bone-marrow cells of descendants of wild mice trapped from Rimac valley in Peru (Peru mice) were studied and compared to the same effects in laboratory mice. Baseline SCE of the Peru mice were significantly higher than those of the C57BL/6J and DBA/2 mice. The average SCE/cell of 4 Peru mice was 5.4 (range 3.8-7.6), while the average of SCE/cell of either 4 C57BL or 5 DBA mice was 3.2 (range 3.0-3.4). The variation of SCE/cell among Peru mice studied was statistically significant whereas among C57BL or DBA mice it was not. SCE frequencies of primary cultures derived from the ear tissue of 10 Peru (mean SCE/cell = 8.5) were also significantly higher than those of 6 C57BL mice (mean SCE/cell = 7.4). CPP treatment resulted in a dose-dependent increase of SCE frequencies in bone-marrow cells of all the mice. However, some of Peru mice treated with CPP had significantly higher SCE than the other Peru mice and than all of the C57BL and DBA mice treated with equivalent dose. ENU induced increased SCE frequencies in Peru and C57BL mice. Again some of Peru mice either had significantly higher SCE, greater extent induced cell-cycle delay or chromosome aberrations (CA) than other Peru mice and than of all the C57BL mice treated with equivalent dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Apolipoprotein A-I/C-III gene cluster polymorphism in Saudi Arabians, Filipinos and Caucasians.

We studied the polymorphic locus in the A-I/C-III gene cluster on the long arm of chromosome 11 in 147 Saudi Arabian, in 84 Filipino and in 69 Caucasian blood donors. Digestion of DNA yielded two fragments 4.2 kb and 3.2 kb long. The genotype distribution was the same in Arabs and Filipinos, but both were significantly different from Caucasians (p = 0.005 and 0.0005). The 3.2-kb allele occurred in 18% of the Saudi Arabians, in 23% of the Filipinos and in 4% of Caucasians. The frequency of the 3.2-kb allele was significantly higher in Arabs and Filipinos compared to Caucasians (p = 0.0005).

Alleles↗
PubMed1984

Non-protein bound zinc concentration in human plasma and amniotic fluid measured by ultrafiltration.

Using an ultrafiltration technique, apparent non-protein bound (NPB) zinc concentrations in plasma were found to be 2.2 +/- 0.2 (SEM) microgram Zn/l (10 observations) in normal males, 1.6 +/- 0.3 (10) micrograms/l in normal females and 1.2 +/- 0.2 (10) micrograms/l in pregnant mothers during their 16th week of gestation. These values are about 0.2% of the total plasma zinc concentrations, at least five-fold less than previous estimates. In amniotic fluid, the NPB-zinc concentration was 12.6 +/- 0.4 (10) micrograms/l, 5-10 times that of normal plasma, though the total zinc concentration (100 +/- 30 micrograms/l) was only one tenth that of plasma. When plasma or amniotic fluid samples were ultrafiltered without precaution against CO2 loss, their NPB-zinc concentrations increased, suggesting that pH changes alter zinc binding. The low concentration of NPB-zinc in plasma explains the low urinary excretion of zinc observed by others and would be expected to restrict the entry of zinc into cells.

Adult↗
PubMed1982

Vitamin A concentration in amniotic fluid and maternal serum related to neural-tube defects.

The vitamin A concentration of amniotic fluid and maternal serum was measured during the second trimester of pregnancy in 106 women, 12 of whom had a baby with a neural-tube defect. In these 12 pregnancies the amniotic fluid vitamin A concentration was significantly higher than in 94 normal pregnancies. There was a highly significant correlation between amniotic fluid vitamin A and both zinc and alpha-fetoprotein (AFP) levels. The maternal serum vitamin A levels were also significantly related to serum zinc levels. Women with a raised serum AFP level, but a normal baby, had significantly higher amniotic fluid vitamin A levels and significantly lower serum vitamin A levels compared with those in women with normal serum AFP levels.

Adult↗
PubMed1978

Sister chromatid exchanges and growth inhibition induced by the flame retardant tris(2,3-dipromopropyl) phosphate in Chinese hamster cells.

The effects of the flame retardant tris(2,3-dibromopropyl) phosphate (Tris-BP) on growth, sister chromatid exchanges (SCE), and chromosome aberrations of Chinese hamster V79 cells cultured either in vitro or in diffusion chambers (DC) implanted into mice were studied. Tris-BP caused a dose- and time-dependent reduction of cell growth as measured by colony-forming activities. A significant dose-dependent increase in SCE was observed in V79 cells either in the cultures treated with Tris-BP or in DC in mice given injections of the chemical. In contrast, Tris-BP in V79 cells in culture, in V79 cells in DC in mice, in two human lymphoid cell lines, or in mouse bone marrow cells in vivo did not significantly increase chromosome aberrations.

Animals↗
PubMed1976

Effects of radiation and porphyrin on mitosis and chromosomes in human hematopoietic cell lines.

The effect on mitosis of a human hematopoietic cell line RPMI-1788 treated with a metal chelate (Zn++) of meso-tetra (p-carboxyphenyl) porphine (Zn-TCPP) alone at various concentrations or in combination with gamma-irradiation at various doses were studied. The results showed that both Zn-TCPP and radiation were effective in interfering with normal mitosis and that the effect of radiation was relatively more effective. Data also suggest interacting effects between Zn-TCPP and gamma-irradiation. At low doses of radiation, Zn-TCPP potentiated the effect of radiation. The reverse seemed to be true at a high dose of radiation. The effects of two porphyrins (Zn-TCPP and hematoporphyrin) and radiation on chromosomes were also studied. Chromosomal aberrations characteristic of radiation were observed. The porphyrins were found not to be effective chromosome-breaking agents under the experimental conditions tested.

Cell Division↗