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Biomedical subjects

C K Lim

Publications and source records attributed to C K Lim.

At least 73 records · Page 4Linked to original sources
PubMed1994

Altered urinary porphyrin excretion in a human population chronically exposed to arsenic in Mexico.

1. A detailed study of the urinary excretion pattern of porphyrins in humans chronically exposed to As via drinking water was performed using high performance liquid chromatography (HPLC) 2. Thirty-six individuals (15 men and 21 women) were selected from a town which had 0.400 mg L-1 of As in drinking water. The control group consisted of thirty-one individuals (13 men and 18 women) whose As concentration in drinking water was 0.020 mg L-1. 3. The major abnormalities in the urinary porphyrin excretion pattern observed in arsenic-exposed individuals were: (a) significant reductions in coproporphyrin III excretion resulting in decreases in the COPRO III/COPRO I ratio, and (b) significant increases in uroporphyrin excretion. Both alterations were responsible for the decrease in the COPRO/URO ratio. 4. No porphyrinogenic response was found in individuals with urinary As concentrations below 1,000 micrograms of As g-1 of creatinine. However, as arsenic concentrations exceeded this value, the excretion of porphyrins (except coproporphyrin III) increased proportionally. 5. The prevalence of clinical signs of arsenicism showed a direct relationship to both As concentration in urine and time-weighted exposure to As. A direct relationship between time-weighted exposure and alterations in urinary porphyrin excretion ratios was also observed. 6. The alterations found are compatible with a lower uroporphyrinogen decarboxylase activity in arsenic-exposed individuals. However, the similarities in the urinary porphyrin excretion pattern between As-exposed individuals and Dubin-Johnson syndrome patients suggest that impairments in the excretion of coproporphyrin isomers may also contribute to the pattern observed.

Adult↗
PubMed1993

Photodynamic therapy with m-tetrahydroxyphenylchlorin in vivo: optimization of the therapeutic index.

The therapeutic index of meta-tetrahydroxyphenylchlorin-mediated photodynamic therapy (mTHPC-PDT) was assessed in BALB/c nude mice bearing human malignant mesothelioma xenografts. Equal doses of 650 nm laser light were delivered to the tumour and to an equal-sized area of the hind leg (control site) after i.p. administration of mTHPC. Twenty-one groups of 6 animals each were treated under various drug-light conditions and at drug-light intervals ranging from 4 hr to 6 days. After light delivery the extent of tumour necrosis and the depth of alterations in normal tissue were assessed by light microscopy of standardized histological sections. A therapeutic index (TI) of mTHPC-PDT was defined as the cross-sectional area of tumour necrosis per depth of visible tissue injury at the control site. This TI was strongly related to the conditions of treatment. In particular, it was increased by prolonging the drug-light interval up to 5 days and by increasing the dose of light for any dose of drug. The most profound increase of TI was obtained by increasing the intensity of light administered at the chosen interval while reducing the dose of drug. Our findings suggest that threshold conditions operate in PDT and have important implications for clinical application of the treatment.

Animals↗
PubMed1993

Order of uroporphyrinogen III decarboxylation on incubation of porphobilinogen and uroporphyrinogen III with erythrocyte uroporphyrinogen decarboxylase.

The isomeric compositions of the heptacarboxylic, hexacarboxylic and pentacarboxylic porphyrinogens formed by incubation of porphobilinogen with human red-cell haemolysates have been analysed and compared with those derived from incubation with chemically prepared uroporphyrinogen III as substrate. The results indicated that when supplied with an excess (3.7 microM) of exogenous uroporphyrinogen III, uroporphyrinogen decarboxylase utilized the substrate at random and a mixture of isomers was produced; whereas with uroporphyrinogen III generated enzymically from porphobilinogen as substrate a clockwise decarboxylation sequence was observed, resulting in the formation of intermediates mainly with the ring-D, rings-AD and rings-ABD acetate groups decarboxylated. Using [14C]uroporphyrinogen III as substrate at low concentrations (0.01-0.5 microM) also led to preferential decarboxylation of the ring-D acetate group. It was concluded that the order of uroporphyrinogen III decarboxylation is substrate-concentration-dependent, and under normal physiological conditions enzymic decarboxylation is most probably orderly and clockwise, starting at the ring-D acetate group.

Chromatography, High Pressure Liquid↗
PubMed1993

Effect of drug-light interval on photodynamic therapy with meta-tetrahydroxyphenylchlorin in malignant mesothelioma.

The influence of the time interval (TI) between drug administration and laser activation on selectivity of meta-tetrahydroxyphenylchlorin(mTHPC)-mediated photodynamic therapy (PDT) for tumour tissue was assessed in BALB/c nude mice bearing human malignant mesothelioma xenografts. Following i.p. administration of 0.3 mg/kg mTHPC, a light dose of 10 J/cm2 and 0.1 W/cm2 was delivered at 650 nm on the tumour and an equal-sized area of the hind leg after 4, 12, 24 and 36 hr and 2, 3, 4, 5 and 6 days to groups of 6 animals (surface irradiance). Then, 72 hr after light delivery, the depth of necrosis was measured in the tumour and in the skin and underlying muscle of the hind leg. Photosensitized necrosis occurred in normal tissue at TI from 4 hr to 3 days and in the tumour at TI from 12 hr to 4 days. The therapeutic ratio of mTHPC-PDT varied significantly with the time interval between drug administration and laser activation and was greatest at an interval of 3 days. mTHPC concentration was measured in 3 control unirradiated animals at all time points in normal tissues and in tumour tissue, and found to be the same in both tissues. Thus the tissue concentration of mTHPC was of limited use as regards the prediction of photosensitizing effects in the tumour model.

Animals↗
PubMed1993

Absence of rhodamine 123-photochemotoxicity in human tumor xenografts.

Rhodamine 123 (R123)-photochemotoxicity was assessed in BALB/c nude mice bearing a xenografted human squamous cell carcinoma at various power densities and wavelengths and a given incident fluence of 150 Joules/cm2. One hour before light delivery, 1 mg R123/kg was injected i.p. in 20 animals. Surface irradiance was performed on the tumor and an equal size hind leg area of 40 animals. Three groups of 10 animals were treated at 514.5 nm and 0.1 W/cm2, 1 W/cm2, and 30 W/cm2, and one at 488 nm and 30 W/cm2. In each group, five animals received R123. The R123 concentration was measured in the tumor (0.023 +/- 0.007 micrograms/g) and tumor-free tissue (0.023 +/- 0.008 micrograms/g) in three additional animals by high performance liquid chromatography 1 hour after R123-administration. Histologic assessment 72 hours after light delivery revealed no tissue damage at nonthermal power densities, either in the tumor or in the tumor-free tissue, irrespective of R123-administration. At 30 W/cm2, neither in the tumor nor in tumor-free tissues was there any significant difference in the depth of necrosis, irrespective of R123-administration and the wavelength applied. Our results question the validity of R123 as a photosensitizer, at least in this rodent tumor model.

Animals↗
PubMed1993

Characterization of chromosomal homologs of the plasmid-borne copper resistance operon of Pseudomonas syringae.

Copper-resistant and copper-sensitive strains of Pseudomonas syringae, as well as many other pseudomonads, contain chromosomal DNA homologous to the plasmid-borne copper resistance operon (copABCD). cop homologs were cloned from the chromosome of P. syringae pv. tomato PT12.2, which had an elevated level of resistance to copper compared with typical copper-sensitive strains of other P. syringae pathovars and showed an unusually high frequency of spontaneous mutation to high levels of copper resistance. Two chromosomal cop homolog regions were cloned. Homolog 1 hybridized with copA and copB, and homolog 2 hybridized with copA, copB, copC, and the copper-responsive regulatory genes copRS. Homolog 1 had no detectable function when transferred to a copper-sensitive strain of P. syringae. However, homolog 2 conferred the low level of copper resistance observed with PT12.2 and produced proteins related to CopA and CopC. In addition, homolog 2 conferred a high frequency of mutation to full copper resistance. In a spontaneously mutated derivative of the cloned homolog 2 (pCOPH2R) that conferred copper resistance, an increased level of CopA was observed. pCOPH2R also supported a higher level of transcriptional activity of the cop promoter that was fused to lacZ and provided in trans (pCOP38), suggesting that the spontaneous mutation was regulatory, probably involving the copRS homologs. Homolog 2 was similar but not identical to the plasmid-borne cop operon, and it did not complement site-specific mutations in cop genes.

Bacterial Outer Membrane Proteins↗
PubMed1992

Molecular typing of Neisseria gonorrhoeae by restriction fragment length polymorphisms.

OBJECTIVE: To characterise Neisseria gonorrhoeae isolates by restriction fragment length polymorphisms (RFLPs) in ribosomal RNA genes. DESIGN: Generation of RFLP patterns by HincII restriction of rRNA genes followed by hybridisation with a non-radioactive labelled broad spectrum 16 + 23S rRNA gene probe. This typing method was developed and compared with MAb based serotyping. SPECIMENS: Forty three randomly collected isolates from Bangkok (27 isolates) and Singapore (16 isolates) were studied. RESULTS: The RFLP patterns generated were reproducible and highly discriminatory between strains. Analysis of RFLPs produced by HincII restriction of rRNA genes established 9 patterns amongst the 43 isolates examined. Strains present within a common serovar could be further subdivided by RFLP typing. Identical RFLP patterns were found in some strains that belonged to various serovars. CONCLUSION: RFLP typing based on heterogeneities of rRNA gene restriction patterns could be advantageously used to complement monoclonal antibody based serotyping for further subdivision of serovars. Higher sensitivity of this combined approach would enable better differentiation of strains in epidemiological studies.

Electrophoresis, Agar Gel↗
PubMed1991

Determination of hydroxy and peroxy acid derivatives of uroporphyrin in the plasma of patients with congenital erythropoietic porphyria by high-performance liquid chromatography.

A reversed-phase high-performance liquid chromatographic method is described for the determination of hydroxy and peroxy acid derivatives of uroporphyrin in the plasma of patients with congenital erythropoietic porphyria. The porphyrins were extracted from the plasma with 20% trichloroacetic acid-dimethyl sulphoxide (1:1, v/v). The supernatant after centrifugation was chromatographed on a Hypersil-ODS column by gradient elution with 9% (v/v) acetonitrile in 1 M ammonium acetate buffer (pH 5.16) (solvent A) and 10% (v/v) acetonitrile in methanol (solvent B) as the gradient mixture. The method was also suitable for the preparative isolation of the porphyrins.

Chromatography, High Pressure Liquid↗
PubMed1991

High-performance liquid chromatographic assays for protoporphyrinogen oxidase and ferrochelatase in human leucocytes.

Rapid, sensitive and specific high-performance liquid chromatographic assays are described for protoporphyrinogen oxidase and ferrochelatase in human leucocytes. The enzyme reaction products were separated and quantitated by reversed-phase high-performance liquid chromatography with fluorescence detection. The optimal pH for the protoporphyrinogen oxidase assay was 8.6 and the Michaelis constant for protoporphyrinogen IX was 9.78 +/- 0.96 microM (mean +/- S.D.). The mean (+/- S.D.) activity of protoporphyrinogen oxidase in fourteen apparently healthy subjects was 0.146 +/- 0.023 nmol protoporphyrin IX per min per mg protein. In one patient with variegate porphyria, the activity was 0.028 nmol protoporphyrin IX per min per mg protein. The optimal pH for ferrochelatase was 7.4 and with protoporphyrin and Zn2+ as substrates, the Michaelis constants were 1.49 and 8.33 microM, respectively. The mean activity of ferrochelatase in ten control subjects was 0.24 nM Zn-protoporphyrin or 2.05 nM Zn-mesoporphyrin formed per h per mg protein.

Adult↗
PubMed1991

Random decarboxylation of uroporphyrinogen III by human hepatic uroporphyrinogen decarboxylase.

The type III heptacarboxylic porphyrinogens derived from enzymic decarboxylation of an acetic acid substituent on uroporphyrinogen III to a methyl group by human hepatic uroporphyrinogen decarboxylase has been analysed by reversed-phase high-performance liquid chromatography with electrochemical detection. The results showed that all four possible heptacarboxylic acid porphyrinogen isomers, with the methyl group attached to rings A, B, C and D of the tetrapyrrole macrocycle, respectively, were formed in almost equal proportions. It was concluded that the normal pathway of uroporphyrinogen III decarboxylation in human liver follows a random mechanism.

Chromatography, High Pressure Liquid↗
PubMed1991

Identification of peroxyacetic acid uroporphyrin I in the urine of patients with congenital erythropoietic porphyria by liquid chromatography and mass spectrometry.

A new porphyrin, peroxyacetic acid uroporphyrin I, has been isolated from the urine of patients with congenital erythropoietic porphyria by reversed phase high performance liquid chromatography. The porphyrin was characterized by high resolution mass spectrometry and by typical chemical reactions of a peroxyacid.

Chromatography, High Pressure Liquid↗
PubMed1991

Photodynamic therapy with chlorins for diffuse malignant mesothelioma: initial clinical results.

Four patients underwent intraoperative photodynamic therapy after surgery with meso-tetra-(hydroxyphenyl)-chlorin (mTHPC-PDT) for diffuse malignant mesothelioma. Preliminary procedures were performed in two patients in order to establish the efficacy of mTHPC-PDT and to optimise its tumoricidal effect. The tumoricidal effect was related to the mTHPC dose, light dose and the time interval between sensitation and activation. 0.3 mg kg-1 mTHPC activated after 48 h with 10 Joules cm-2 of non-thermal laser light at 650 nm resulted in a 10 mm deep tumour infarction, due to tumour vessel necrosis and thrombosis. The mTHPC tissue concentration was up to 14 times higher in the tumour than in normal tissues. Skin photosensitivity was mild, dose dependent and occurred 3 to 10 days after administration of mTHPC. According to the results obtained, intraoperative mTHPC-PDT was performed following pleuropneumonectomy in two, pleurectomy and lobectomy in one and pleurectomy in one patient. Ten Joules cm-2 were delivered to the diaphragm and the costophrenic sulcus and 5 Joules cm-2 to the remaining thoracic cavity. The postoperative course was marked by loss of appetite, fluid retention, hypoproteinemia and severe chest pain. One patient succumbed from aspiration pneumonia. The remaining patients developed no neural or vascular alterations and no bronchial stump insufficiency during follow-up. mTHPC-PDT following surgical tumour resection deserves further evaluation in good risk patients with diffuse malignant mesothelioma.

Combined Modality Therapy↗
PubMed1990

Separation of anionic and cationic compounds of biomedical interest by high-performance liquid chromatography on porous graphitic carbon.

The separation of small, ionizable compounds of biomedical interest on porous graphitic carbon is described. The retention of anionic compounds is dominated by electronic interaction between the solute and the delocalized electron clouds on the graphitized carbon, while cationic compounds are mainly retained by reversed-phase interaction with the hydrophobic carbon surface. Anionic and cationic compounds can be separated simultaneously with a mobile phase containing an electronic modifier (e.g., trifluoroacetic acid) and an organic modifier (e.g., acetonitrile) for elution. Examples of applications include the measurement of oxalic acid in urine, the determination of creatine and creatinine in urine and in serum, the separation of basic drugs (remoxipride and FLA 981) and the simultaneous analysis of pertechnetate anion and the cationic technetium-amine complexes.

Anions↗
PubMed1990

Decarboxylation of uroporphyrinogen III by erythrocyte uroporphyrinogen decarboxylase. Evidence for a random decarboxylation mechanism.

The isomeric composition of type-III heptacarboxylic porphyrinogens derived from decarbosylation of uroporphyrinogen III by erythrocyte uroporphyringogen decarboxylase was analysed by h.p.l.c. with electrochemical detection. All four possible isomers were identified, and there were little differences in the proportion of isomers formed by erythrocytes from normal subjects and from patients with sporadic porphyria cutanea tarda. The results provide conclusive evidence that the normal decarboxylation pathway is random in nature, and the fourth isomer only increases when enzyme abnormality is found.

Carboxy-Lyases↗
PubMed1990

Isolation and characterization of beta-hydroxypropionic acid- and hydroxyacetic acid-uroporphyrin I in the urine of a patient with congenital erythropoietic porphyria by high performance liquid chromatography and liquid secondary ion mass spectrometry.

beta-Hydroxypropionic acid- and hydroxyacetic acid-uroporphyrin I have been isolated from the urine of a patient with congenital erythropoietic porphyria by reversed phase high performance liquid chromatography. The compounds were characterized by their chemical behaviour and confirmed by liquid secondary ion mass spectrometry.

Adult↗
PubMed1990

High performance liquid chromatographic studies of erythrocytes haem biosynthetic enzyme activities in alcoholic macrocytosis.

The activities of 5-aminolaevulinate dehydrase (ALA-D), hydroxymethylbilane synthase (HMB-S), uroporphyrinogen III synthase (URO-S) and uroporphyrinogen decarboxylase (URO-D) in the erythrocytes of alcoholics were assayed and compared with those in controls and abstaining alcoholics. The HMB-S and URO-S activities in alcoholics were significantly higher than the controls and there were significant correlations between enzyme activities and mean corpuscular volume (MCV). Alcoholics abstaining from alcohol over a nine-month period showed a return to normal enzyme activities in parallel with the normalization of their MCV. Abstaining alcoholics thus all had normal HMB-S and URO-S activities. The ALA-D and URO-D activities of alcoholics were not significantly different from controls or from abstaining alcoholics. Alcohol appears to have a selective effect on the haem biosynthetic enzymes in the erythron.

Adult↗