Search PubMed⌕ Search

Biomedical subjects

K C Lam

Publications and source records attributed to K C Lam.

At least 37 records · Page 2Linked to original sources
PubMed2000

Synthetic models for the zinc sites in the methionine synthases.

The syntheses and molecular structures of a series of tetrahedral zinc complexes designed to model the active sites in Escherichia coli methionine synthases are reported. [PhTttBu]ZnBr (PhTttBu = phenyltris((tert-butylthio)-methyl)borate) was prepared and characterized crystallographically to provide entry into [S3]ZnX complexes. Metathesis with KSPh yielded the phenylthiolato complex, [PhTttBu]Zn(SPh), which represents a structural mimic of the homocysteine ligated form of the enzyme. Alternatively, [S2N]ZnX (X = Br, CH3, SPh) species were prepared using the new mixed-donor ligands, [Ph(pz)BttBu] (phenyl(pyrazolyl)bis((tert-butylthio)methyl)borate) and [Ph(pztBu)BttBu] (phenyl(3-tert-butylpyrazolyl)bis((tert- butylthio)methyl)borate). Protonolysis of [Ph(pztBu)-BttBu]Zn(CH3) by PhSH in toluene yielded [Ph(pztBu)BttBu]Zn(SPh), a synthetic analogue of the homocysteine ligated form of cobalamin-independent methionine synthase (Met E). The average Zn-S bond distance in [Ph-(pztBu)BttBu]Zn(SPh) of 2.37 A compares well with the EXAFS-derived distance of 2.31 A found in the homocysteine-bound form of Met E.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed2000

Formation of a tetranuclear copper (II) cluster assembled by metal-assisted hydrolysis and desulfurization of bis(3,5-dimethylpyrazolyl)methylphosphine sulfide, MeP(S)(3,5-Me2Pz)2.

The reaction of methylphosphine sulfide, MeP(S)(3,5-Me2Pz)2, 1, with anhydrous CuCl2 affords a tetranuclear copper cluster[Cu2Cl2(3,5-Me2Pz)3(MePO3)]2, 2, and a dinuclear compound Cu2Cl4(3,5-Me2Pz)4, 3. This reaction involves a metal-assisted desulfurization along with concomitant hydrolysis of P-N bonds. The X-ray structures of 1-3 have been determined, and the crystal parameters for these are the following. 1: space group = C2/c, a = 15.2552(1) A, b = 8.7364(2) A, c = 21.4490(3) A, beta = 93.349(1) degrees, V = 2853.74(8) A3, and Z = 8. 2: space group = P2(1)/n, a = 12.5964(4) A, b = 15.7773(4) A, c = 13.9781(4) A, beta = 116.6280(10) degrees, V = 2483.32(12) A3, and Z = 2. 3: space group = P2(1)/c, a = 8.7137(8) A, b = 13.5493(14) A, c = 11.8847(12) A, beta = 106.179(2) degrees, V = 1347.6(2) A3, and Z = 2. The structure of 2 shows that it comprises two dinuclear copper cores bridged together by two tripodal methylphosphinate, MePO3, ligands. 2 is weakly antiferromagnetically coupled, as revealed by variable temperature magnetic susceptibility measurements.

Journal Article↗
PubMed2000

Home sweet home? A case study of household dust contamination in Hong Kong.

It is well recognized that many heavy metals have chronic effects on humans and as such, they are potential environmental health hazards, particularly to young children (see, for example, Body P, Inglis G, Dolan P, Mulcahy D. Environmental lead: a review. Crit Rev Environ Control 1991;20:299-310). Considerable attention has been paid to the study of metal pollution in city air, roadside dusts and soils. However, there is a lack of concern of the presence of trace metals in house dust in the populous city of Hong Kong, where it has traditionally been assumed that such pollutants are rapidly dispersed by ocean breezes. This research aims at quantifying the concentrations of heavy metals within the home environment in Hong Kong and their relationships with environmental factors. The results of this study seem to suggest that traffic and the age of the building and neighborhood are more important factors than the types of industry and socioeconomic status in affecting household dust contamination. The metal burdens in Kwung Tong, an old area with heavy traffic, are significantly higher than other districts. When a Kruskal-Wallis one-way analysis of variance was performed on the ranked metal concentrations in different housing districts, the Chi-square values are all significant at a probability level of < 0.001. This might be attributable to the fact that there is no highly contaminating industries (such as metal smelters, battery plants and petrochemicals) in Hong Kong. The dust metals may travel from the roads, through the windows and balconies, into the houses, as those homes that do not have their windows opened often had a lower level of contaminants in their house dust (median Cd= 3.6 microg/g; median Cu = 313.2 microg/g; median Pb = 144.6 microg/g; median Mn = 211.6 microg/g; and median Zn = 1,333.7 microg/g). Moreover, those occupants who sweep their floors or dust their furniture on daily bases, or use vacuum cleaners, had a lower level of metals inside their houses. Another finding of interest is that the color of the wall paint used in the house may be another factor influencing the contamination levels.

Air Pollution, Indoor↗
PubMed2000

Titanium alkoxide complexes: condensed phase and gas phase comparisons.

The complex [Ti(2,4-dimethyl-2,4-pentanediolate)2]2 (1) has been synthesized from [Ti(OiPr)4] by transesterification with a stoichiometric amount of 2,4-dimethyl-2,4-pentanediol. We have characterized complex 1 in the solid state by single-crystal X-ray diffraction and in the gas phase by desorption chemical ionization mass spectrometry (DCI-MS). The structural and mass spectrometric data show complex 1 to be stable as a dimer in both the solid and gas phases. The retention of dimeric nuclearity in the gas phase sets complex 1 apart from other simple titanium alkoxide complexes [Ti(OiPr)4] and [Ti(OMe)4]4 that give rise to respective families of molecular ions in the DCI-MS experiment. The highest mass molecular ions for Ti alkoxide complexes in the gas phase may reveal the highest nuclearity that these complexes achieve in condensed phases. According to this interpretation the complex [Ti(OiPr)4] is principally dimeric in the gas phase and probably also in the pure liquid phase and should be represented by the formula [Ti(OiPr)4]2.

Journal Article↗
PubMed2000

Fish uptake of inorganic and mucus complexes of lead.

Carassius auratus were exposed to lead in synthetic water. Mucus secreted from the fish was measured and characterized for its lead binding capacity. The increase in mucus concentration in the water depended on secretion and degradation rates and the former was speeded up by lead. The complexation between mucus and lead can be described based on a single-site interaction model. Lead speciation in the system with or without mucus was calculated using chemical equilibrium modeling. The dominant species of lead was PbCO(3)(0). Other major species included Pb(OH)(+), Pb(OH)(2)(0), Pb(CO(3))(2)(2-), Pb-mucus, and Pb(2+), among which free lead and lead hydroxo complexes were available to fish uptake.

Animals↗
PubMed2000

Management of building services. Procurement for highly serviced healthcare facilities.

The question of whether design and build is the best procurement system is hard to tell as other procurement alternatives (main-contractor and principal services contractor coupled with project management team, and construct management method plus good building team) can also give satisfactory results. Besides, it is also known that there is no standard solution or best buy amongst procurement systems. Indeed, there is no single method of procurement which can be suitable for every project for all time. It is also accepted that the choice and use of an inappropriate procurement system is not the only reason for inefficient project management, people and experience are far more important than strategy. Coordination of building services has a direct bearing on the success of a hospital project. Services must be fully integrated and coordinated. One thing is clear, as far as building services coordination is concerned, the traditional procurement system is not conducive to effect coordination process, however, the integrated nature of D&B has relieved all the burdens on the client's design team, and, from the face of this procurement path, all coordination problems that the client would normally encounter from the traditional method will no longer exist. Of course, the technical and managerial problems in relation to coordination still exist but they would all be passed to the contractor side. To protect the contractor's interest, all coordination problems would still have to be managed and controlled by D&B contractor and his specialist contractors expeditiously. Indeed, if design is not fully integrated, and construction and services are not completely coordinated, no matter how integrated is the team, D&B method will not work. To sum up, the author's discussions can be summarized as follows: Project success can be enhanced by engendering a team spirit and a high degree of cooperation between project participants. This can be achieved by the use of non-traditional procurement systems. Building services and hospital engineering systems must be properly coordinated at both design and installation stages. Coordination must be seen as both technical and managerial issues. A professional building team can manage the complex issues of services coordination. But it is known that an integrated building team can give better result. D&B is not a panacea, other procurement paths with adequate project management can provide a better alternative than either the traditional or the design and build system.

Contract Services↗
PubMed2000

[Uptake of particulate lead via gills of goldfish].

This paper studied the uptake of Pb absorbed on suspended gibbsite via gills of goldfish (Carassius auratus). Under conditions of the concentration of the particulate Pb varied while that of free Pb maintained at a constant level, the levels of both Pb and Al in the gills increased with increasing exposed Pb concentration. The increasing rate (slope 0.171) of Pb level in the blood with the Pb level in the gills was lower than that (slope 0.343) of soluble Pb exposure experiment. Partial Pb adhered on the gills did not transfer into blood. The ratio of Pb/Al in the gills was 1-2 orders of magnitude higher than that in the water, and on the microtome section of filament, the gibbsite particles adhered on gill mucus were observed, indicating the bioavailability of the particulate Pb uptake by the gills of goldfish. The major mechanism was: when the absorbed Pb on suspended particles was flowed into gill filaments, it was desorbed on the surface of gills, and then, passively diffused or transferred by carriers via gill cells into flood, and after the particles stayed on the surface of gill filaments for a short time, in company with sloughed mucus, they were released from the gills along with waterflow.

Absorption↗
PubMed1999

Lamivudine in the treatment of hepatitis B virus reactivation during cytotoxic chemotherapy.

Hepatitis B virus (HBV) reactivation has been described in cancer patients who received cytotoxic/immunosuppressive therapy and may result in liver damage of varying degrees of severity. There is no known effective treatment. Lamivudine, a nucleoside analogue, has been found to suppress HBV replication and to improve histology in chronic carriers of hepatitis B virus. The outcome of lamivudine therapy (at doses of 100 or 150 mg/day) in eight patients who developed HBV reactivation while receiving cytotoxic chemotherapy is described. Each of the eight patients had >98% suppression of the pretreatment HBV DNA levels. Three of the five patients who were initially HBeAg positive underwent seroconversion. Five patients had normalization of liver function tests and improvement in clinical condition. However, one patient died of hepatic failure due to HBV-related submassive liver necrosis, and two died of widespread metastases (including liver) from the primary malignancies. It is concluded that early commencement, i.e., at the onset of HBV reactivation before severe hepatic decompensation, of lamivudine may be effective in the control of HBV reactivation during chemotherapy. In Hong Kong, where hepatitis B infection is endemic, we propose to screen all cancer patients for hepatitis B surface antigen before immunosuppressive/cytotoxic therapy, and to closely monitor liver function of those who are found to be HBsAg seropositive.

Adult↗
PubMed1998

Multimodality treatment of primary lymphoepithelioma-like carcinoma of the lung.

BACKGROUND: Lymphoepithelioma-like carcinoma (LELC) of the lung occurs at a higher frequency in Asian compared with Western patients. Its association with Epstein-Barr virus varies among different ethnic groups. METHODS: Nine patients with primary LELC of the lung treated at a single institution with a multimodality approach comprised of surgery, chemotherapy, and radiotherapy are reported. Chemotherapy was comprised of cisplatin, 100 mg/m2, on Day 1 and 5-fluorouracil, 1 g/m2, on Days 2, 3, and 4. RESULTS: Five male and 4 female patients were treated over a 3-year period. Eight patients were non-smokers. Three patients had operable disease. Two of these patients received adjuvant radiotherapy or chemotherapy and remained free of recurrence at 18 and 20 months, respectively; 1 patient received no adjuvant treatment, and palliative chemotherapy was given for subsequent recurrent disease. Six patients had inoperable disease and received palliative chemotherapy +/- radiotherapy. Five patients had distant metastatic disease at presentation. Of the 7 patients who were evaluable for response to chemotherapy, 71.4% had a partial response and 28.6% had progressive disease. One patient who was evaluable for response to radiotherapy achieved a partial response. CONCLUSIONS: Primary LELC of the lung has a high rate of systemic metastasis and is highly chemosensitive. A multimodality approach to the management of this disease is recommended.

Adult↗
PubMed1998

Are nursery schools and kindergartens safe for our kids? The Hong Kong study.

Pediatric heavy metal (particularly lead) poisoning is a widespread, yet preventable problem in many parts of the world. Interior floor dust is found to be one of the major pathways of childhood exposure. However, school and health authorities in most countries do not have any stipulations nor guidelines in regulating heavy metal contamination in floor dusts in schools. This study attempts to examine the level of heavy metal contamination in 53 nursery schools and kindergartens in Hong Kong and study its relationship with the environmental factors. The results of this study reveal that the arithmetic mean level of lead in exterior dust is 280.01 mg/kg, with a minimum level of 48.80 mg/kg and a maximum of 2108.31 mg/kg, which is somewhat lower than other studies, such as those reported by Chan et al. (Biomed. Environ. Sci. 1989;2:131-140) and Akhter and Madany (Water Air Soil Pollut. 1993;66:111-119), but those of the manganese (mean = 532.16 mg/kg, range = 102.51-1736.25 mg/kg) and zinc levels (mean = 2694.23 mg/kg, range = 898.33-9899.85 mg/kg) are much higher. Out of the 10 districts examined, Kwun Tong and North Point are found to be the most polluted. They are older districts with polluting industries and heavy traffic. The results of the analysis of variance suggest that the heavy metal particulate may originate from the exterior. Auto-vehicles are a likely source. The toxins are blown inside through the opened windows. Other factors that may affect the content of metal in floor dusts are the time since the school was last painted, the age of the housing complex, the condition of the school and the use of vacuum cleaners.

Child, Preschool↗
PubMed1998

A synoptic climatological approach to forecast concentrations of sulfur dioxide and nitrogen oxides in Hong Kong.

The objective of this study is to develop an automated synoptic climatological procedure to forecast high air pollution concentrations in the most polluted synoptic categories. The procedure is able to identify air masses historically associated with high air pollution concentrations. The arrival of air mass can be predicted 24 or 48 h in advance with the use of the weather forecast data. The development and statistical basis of the procedure are discussed, and an analysis of the procedure's ability to forecast weather conditions associated with high air pollution concentrations is presented. In addition, the dataset of 24 weather variables from 1993 to 1995 is used to validate the procedure. The procedure predicts that 70.3 and 83.3% of total high and severe SO2 concentration days fall into the identified most polluted categories, and the corresponding figures for NOx are 47.8 and 73.7%. The agreement between observed and predicted values is generally good. The prediction models can explain about 58 and 45% of total variance for NOx and SO2 with RMSEs of 42.5 and 16.5 microg m(-3), respectively. They are smaller than 1 SD of the observations.

Journal Article↗
PubMed1996

Outmigration of U.S. immigrants.

"A methodology is devised for the empirical analysis of the determinants of outmigration of immigrants in a population. Empirical studies in this area have been hindered by a lack of longitudinal data on the characteristics of the immigrants. This problem is tackled by making use of cross-sectional data at two points in time. It is applied to the study of male immigrants in the United States. It is found that education is positively related to the rate of outmigration for immigrants from Canada, Asia and the pooled sample of immigrants. This finding suggests that the cross-sectional estimates of the growth in earnings of immigrants in the United States are underestimated for these groups of immigrants."

Americas↗
PubMed1983

Clear cell carcinoma of liver. An ultrastructural study.

A light microscopic and ultrastructural study of ten consecutive cases each of the clear cell type and nonclear cell type of hepatocellular carcinoma (HCC) showed important differences between the two groups which may help to explain their different biological behavior. The clear cells contained substantial quantities of glycogen and lipid which partly substitute the usual cytoplasmic constituents. An analogy was made between these tumor cells with clear cytoplasm and the clear cells which occurred in the intermediary stages of hepatocellular carcinogenesis in animals in an attempt to explain the better outcome of clear cell HCC.

Adenocarcinoma↗
PubMed1983

Sitosterol and cholesterol metabolism in a patient with coexisting phytosterolemia and cholestanolemia.

Sitosterol and cholesterol metabolism were studied in a patient with coexisting phytosterolemia and cholestanolemia, and in a control subject, both on similar diets containing about 170 mg cholesterol and 135 mg phytosterols per day. The turnover of 22,23-3H-sitosterol and 4-14C-cholesterol, given intravenously, were followed for up to 372 days. The specific activity-time curves for both sterols were resolved into two exponentials and fitted into a two-pool model. The half-lives of both exponential curves for sitosterol, in the patient, were abnormally long. Equilibration of the tracer between the two pools, in the patient, occurred at about 30 days as compared to 10-15 days in the control subject. The daily turnover of sitosterol in the patient was estimated to be 10 times greater than that in the control subject. The patient's total body exchangeable pool of sitosterol was 9.6 g or about 80 times the amount found in the control. The patient's plasma phytosterol levels fell by 25% when he went on a diet containing only 10 mg phytosterols per day. During this period the specific activity of his plasma sitosterol with respect to an equilibrated dose of 3H-labeled tracer remained constant; this was compatible with the absence of endogenous synthesis. Cholesterol turnover in the patient showed prolonged half-lives for both exponential curves and reduced fractional daily loss from the fast-exchanging pool. The patient's xanthoma sterols underwent 16% and 55% exchange with plasma sitosterol and cholesterol, respectively, on day 60, indicating the presence of a third exchangeable pool.

Adult↗
PubMed1983

Ranitidine does not affect gonadal function in man.

We studied the effect of ranitidine on gonadal function in 20 male subjects with chronic duodenal ulcer. Eleven were treated with ranitidine 150 mg twice daily for 3 months and 150 mg at night for 9 months, nine with placebo for 3 months. Similar to placebo, treatment with ranitidine did not influence basal serum concentrations of testosterone (T), luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL). No significant changes were found in sperm concentration, motility or morphology. Ranitidine does not affect gonadal function in man.

Adolescent↗
PubMed1982

Spontaneous regression of hepatocellular carcinoma: a case study.

A Chinese patient with documented hepatocellular carcinoma (HCC) satisfied the criteria of Everson and Cole for spontaneous regression of malignant tumors. Subsequently he survived a tumor-free period of at least 13 years. During the period of regression, shrinkage of liver coincided with a rise of SGOT to a level comparable to that reported for patients with liver cancer during hepatic arterial ligation and cytotoxic therapy. Postregression liver biopsy from the site of the previous tumor revealed relatively uninflamed HBsAg-positive tissue without dysplasia. The case provided the positive end of the survival spectrum in HCC, evidence that regression of HCC might occur by involution rather than maturation, and histologic data suggesting that regressed HCC might be replaced by surrounding tissue instead of leaving behind dysplasia.

Aspartate Aminotransferases↗
PubMed1982

Effect of cimetidine on gonadal function in man.

1 To study the effect of cimetidine on gonadal function in man, eleven male subjects with chronic duodenal ulcer were given cimetidine orally at a dosage of 1000 mg per day 3 months and 400 mg nocte for the subsequent 3 months. 2 Testosterone levels were found to be elevated during therapy when compared to pre- and post-treatment periods. Serum LH remained unchanged but FSH was increased during therapy. In five out of eleven subjects serum PRL levels were increased. Mean sperm count was lower during cimetidine therapy when compared with that after drug withdrawal. The motility and morphology of the spermatozoa were not affected.

Adult↗