Biomedical subjects
Publications and source records attributed to S W Li.
This is a report of a Chinese male, aged 67, who had been ill for 6 months and who was admitted with left hemiparesis and dementia. The diagnosis of Creutzfeldt-Jakob disease (CJD) was confirmed by serial electroencephalographic (EEG), computed tomographic (CT) and neuropathological studies. This is the first formal report of CJD occurring in Hong Kong.
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The nitroxyl-labeled analogues of N,N:N',N':N",N"-tri-1,2-ethanediylphosphoric triamide (TEPA), N,N:N',N'-bis(1,2-ethanediyl)-N"-[[(2,2,6,6-tetramethyl-1-oxypiperidi n-4- yl)amino]carbonyl]phosphoric triamide (5a) and N,N:N',N'-bis(1,2-ethanediyl)-N"-[[(2,2,5,5-tetramethyl-1-oxypyrrolid in-3- yl)amino]carbonyl]phosphoric triamide (11a), possess therapeutic indexes that are 8-12 times higher than those of thio-TEPA (1) and TEPA (2). The introduction of methyl groups into the aziridine ring, or the replacement of the nitroxyl moiety with hydroxylamine or amine derivatives, or with an adamantane moiety, results in compounds of lesser activity. An attempt is made to rationalize these results using a lipophilicity scale. A predictive design pattern is established.
The proton relaxation enhancement characteristics of seven potential MRI contrast agents containing two nitroxyl spin labels per molecule (diradicals) were compared with eight similar agents with only one spin label per molecule (monoradicals). Diradical nitroxyls were evaluated to test the hypothesis that multiple paramagnetic centers in one molecule will result in stronger proton relaxation enhancement characteristics, allowing effective contrast enhancement at lower molar concentrations and thus a reduced osmotic load and greater safety. The acute toxicity of these agents is believed to be largely related to osmotic load. Five of seven diradical nitroxyls tested had spin-lattice relaxivities that were substantially greater than all eight of the monoradicals tested. The spin-spin relaxation properties of these agents and other pertinent characteristics are favorable for contrast enhancement. The results indicate that diradical nitroxyl spin labels may be used advantageously for the design of safer, more effective MRI contrast agents.
A new nitroxyl labeled TEPA derivative 5 containing the urea bridge between the phosphorus and the nitroxyl moiety, and the congeners containing the NOH and NH groups instead of the nitroxyl function were synthesized, and tested in vivo on CD2F1 mice for anticancer activity against P388 and L1210. The nitroxyl compound is more active than the reduced forms. The nitroxyl compound 5 elicits 170% ILS at 90 mg/kg after 30 days and 439% ILSmax after 60 days against P388, and has a higher therapeutic ratio (26.4) than the clinically used Thio-TEPA (2.75). The LD50 of 5 is 270 mg/kg, while that of Thio-TEPA is 18 mg/kg. Consequently, the nitroxyl compound 5 is a promising new anticancer drug.
The spin labeled nitrosourea 1-(2-chloroethyl)-3-(1-oxyl-2,2,6,6- tetramethyl-piperidinyl)-1-nitrosourea (SLCNU, 4) and its analogues 5-7 were synthesized either by a regio-selective method or by a conventional route via the nitrosation of the spin labeled intermediates (11a-e). Nitrosation of the ureas 11a-e with dinitrogen tetraoxide resulted in better yields than those obtained with sodium nitrite. The nitrosoureas 4-8 were tested for their anticancer activity against the lymphocytic leukemia P388 in mice. Thus, either at the equal molar dose or at the dose of equal toxicity level, the SLCNU (4) was found to be more active than the clinically used CCNU (1). Unlike CCNU (1) whose LD50 is 56 mg/kg, the SLCNU (4) possesses a low toxicity (LD50 123 mg/kg). Therefore, SLCNU (4) is a promising new entry into the nitrosourea class of anticancer drugs.
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In order to further evaluate the effect of the nitroxyl moiety on the anticancer activity of nitroxyl labeled analogues of phosphoric N,N;N',N';N",N"-tris[1,2-ethanediyl]triamide (TEPA) and phosphorothioic N,N;N',N';N",N"-tris[1,2-ethanediyl]triamide (thio-TEPA), the activity of these compounds was compared in vivo, using murine lymphoid leukemia L1210, with the reduced forms of the drugs, i.e. the hydroxylamines and amine congeners. At optimum dose, all compounds were active. However, the nitroxyl containing compounds were more active than the corresponding reduced forms. An admixture of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl had no effect on the activity of thio-TEPA. Consequently, the nitroxyl moiety must be an integral part of the anticancer drug's structure in order to influence that drug's performance.
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The iron ore tailings located on the coastal area of Tolo Harbour impose severe pollution problems to the environment. Two grass species, Paspalum distichum and Sporobolus virginicus, were found extensively on the excavated tailings, with the former found in waterlogged areas and the latter in dry areas. These plants may have a potential use in reclaiming the tailings. The present experiment is aimed at studying the reclamation ability of the two local species. Samples of the grass species collected from the tailings were cultured in a series of concentrations of manganese, iron, and copper, separately. Heavy metal tolerance was found to be species specific. S. virginicus collected from the tailings had the higher index of tolerance (0.9) and ED50 (0.85 ppm) to copper whereas P. distichum had the higher index of tolerance and ED50 to manganese (0.98 and 9.2 ppm, respectively) and iron (0.66 and 41 ppm, respectively). Plants of the two species collected from uncontaminated sites showed low index of tolerance and ED50 values for all three metals.
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The losses of benzoic acid and a homologous series of both mono- and dibasic aliphatic acids in oil shale retort water were monitored with time (21 days) in liquid culture (4% retort water, vol/vol) inoculated with soil. The organic acids constituted approximately 12% of the dissolved organic carbon in retort water, which served as the sole source of carbon and energy in these studies. The levels of the acids in solution were reduced by 80 to 90% within 9 days of incubation. From mass balance calculations, the decrease in dissolved organic carbon with time of incubation was equal to the formation of CO(2) and bacterial cell carbon. The decrease in the level of the acid components, either from degradation to CO(2) or incorporation into bacteria, would account for approximately 70% of the loss in dissolved organic carbon within the first 9 days of incubation and would account for approximately 50% of the loss over the entire 21-day incubation period.