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T C Yeung

Publications and source records attributed to T C Yeung.

11 recordsLinked to original sources
PubMed1997

The spectrum of chronic lymphoproliferative disorders in Hong Kong. A prospective study.

We report the incidence of the chronic lymphoproliferative disorders evolving with leukaemia in Hong Kong. Our findings demonstrate that B cell malignancies are significantly more frequent than mature T cell neoplasms, a picture similar to that seen in Western countries but different from other Eastern countries, eg Japan, where T cell malignancies are more frequent. In contrast to the West, where chronic lymphocytic leukaemia (CLL) is the most common disorder, in Hong Kong there is a clear predominance of B cell lymphomas in leukaemic phase accounting for two-thirds of the cases and particularly those displaying lymphoplasmacytic features or with villous lymphocytes. CLL in Hong Kong has similar clinical and laboratory features to the disease in patients from the West. Distinct disease categories, rare in the West such as the variant form of hairy cell leukaemia and T cell prolymphocytic leukaemia, are also documented. It is unclear whether the differences in prevalence of disease subtypes between Hong Kong and the West relate to different genetic background or environmental factors determinant of the development or progression of the leukaemia. Further studies investigating the genetic/molecular lesions may help to clarify whether the aetiopathogenesis of the lymphoid disorders in Hong Kong is similar to that of Western countries.

Adult↗
PubMed1984

Interaction of metronidazole with DNA repair mutants of Escherichia coli.

It has been proposed that one of metronidazole's partially reduced intermediates interacts either with DNA to exert a bactericidal effect or with water to form acetamide. To test this hypothesis we have examined the effect of metronidazole on several mutants of Escherichia coli that are defective in DNA repair. UV-susceptible RecA- and UvrB- point mutants have an increased susceptibility to metronidazole as manifested by both a decreased minimal inhibitory concentration and a greater bactericidal response to metronidazole in resting cultures. By these criteria, however, we find that UvrB- deletion mutants, which lack the ability to reduce nitrate and chlorate, are no more susceptible to metronidazole than is the wild type. We find, however, that these deletion mutants also lack the ability to reduce metronidazole and thus possibly to form its reactive species. When metronidazole's bactericidal effect is expressed in terms of the concurrent accumulation of acetamide derived from metronidazole, then all RecA- and UvrB- mutants are killed more efficiently than their wild types. The data are consistent, therefore, with metronidazole's lethal effect being mediated by a partially reduced intermediate on the metabolic pathway between metronidazole and acetamide. Defects in other aspects of the DNA repair system do not confer this increased susceptibility to the proposed intermediate. A Tag- mutant, for example, which is defective in 3-methyl-adenine-DNA glycosylase, does not have this increased susceptibility to the presumed precursor of acetamide. Thus, these results provide further support for the hypothesis that the bactericidal effect of metronidazole is mediated by a partially reduced intermediate in the metabolic conversion of metronidazole to acetamide and suggest that this intermediate interacts with DNA to produce a lesion similar to that caused by UV light.

Acetamides↗
PubMed1983

Role of sulfhydryl compounds in the bactericidal effect of metronidazole.

The bactericidal effect of metronidazole on Escherichia coli and Bacteroides fragilis can be partially reversed by cysteamine under conditions that lead to the formation of an adduct, the thioether, 4-(2-aminoethyl)thio-2-methylimidazole-1-ethanol (4-ATME). This adduct, which is not mutagenic for the Ames histidine auxotrophs of Salmonella typhimurium, forms at a rate that is independent of live bacterial cells and, therefore, can not be shown to relate to the biological effect of cysteamine. When treated with Raney nickel, this adduct yields 2-methylimidazole-1-ethanol. To determine whether a structurally related adduct forms with bacterial protein, a culture of B. fragilis was incubated with radiolabelled metronidazole and then treated with 5% trichloroacetic acid. That the radiolabel in the precipitate did not yield 2-methylimidazole-1-ethanol when treated with Raney nickel suggests that binding of metronidazole to cellular macromolecules does not involve thioether formation.

Bacteria↗
PubMed1983

Reduction of nitroheterocyclic compounds by mammalian tissues in vivo.

To determine whether nitro group reduction occurs in mammalian tissues, metronidazole (0.021, 0.064 and 10 mg/kg), misonidazole (0.015 mg/kg) and nitrofurazone (0.13 mg/kg), respectively, were administered to germfree rats. A reduced metabolite [1-(2-aminoimidazol-1-yl)-3-methoxypropan-2-ol] and two of its hydrolysis products, urea and (2-hydroxy-3-methoxypropyl)-guanidine, were found in the urines of germfree rats that received misonidazole. When nitrofurazone was administered, a reduced metabolite, 4-cyano-2-oxobutyraldehyde semicarbazone, was detected in the urines. However, acetamide and N-(2-hydroxyethyl)oxamic acid, fragmentation products from the reduction of metronidazole, were not found in significant concentrations in the urine when germfree rats received metronidazole. Apparently metronidazole is reduced so much more slowly than misonidazole and nitrofurazone in the tissues of germfree rats that its reductive metabolites are not detectable. This observation may be explained by the one-electron reduction potentials (E1 7) of these drugs, that of metronidazole (E1 7 = -486 mV) being lower than those of either misonidazole (E1 7 = -389 mV) or nitrofurazone (E1 7 = -257 mV). Under these circumstances, metronidazole reduction is not detected, either because its radical anion forms more slowly than that of the other nitroheterocyclic compounds or because its radical anion interacts more rapidly with oxygen to restore the parent compound.

Acetamides↗
PubMedDate not supplied

Wettability of nonaqueous elastomeric impression materials.

The wettability of eight nonaqueous elastomeric impression materials was studied by comparing their contact angles. The materials included three polyethers (one of which was light activated), three hydrophilic poly(vinyl siloxanes), one conventional poly(vinyl siloxane), and one poly(vinyl siloxane) putty. Extracted teeth were prepared to approximate the roughness of a tooth preparation. Contact angles were measured at different time intervals after the start of mixing but were not shown to be significant. The nonhydrophilic poly(vinyl siloxane) materials and the poly(vinyl siloxane) putty were found to be significantly less wettable.

Analysis of Variance↗