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Biomedical subjects

S Lam

Publications and source records attributed to S Lam.

At least 163 records · Page 9Linked to original sources
PubMed1986

Structural and functional studies of insertion element IS200.

The nucleotide sequence of the insertion element IS200 has been determined partially, including the junctions between the element and the host chromosome at the insertion site. At most, two bases (A-A) are found repeated at the junctions and could be duplications of host sequences generated by the insertion of the element. No obvious sequence repeats, either direct or inverted, have been detected between the sequences just within the two ends of the element. The element is an extremely strong block to host transcription across the insertion site. A sequence similar to known transcription termination signals was found just within the element near the right end. Removal of less than 50 base-pairs at the right end of the element abolishes the transcription block. The putative terminator sequence is located within this 50 base-pair region. Genetic studies suggest that the element contains a promoter located more than 93 base-pairs from its left end. The proposed promoter and terminator are in proper orientation to form an internal transcription unit.

Autoradiography↗
PubMed1986

HPLC of trazodone in serum after microscale protein precipitation.

Trazodone, an anti-depressant medication, is found in serum in the 500-1000 ng/mL range in patients taking therapeutic doses. Because of this relatively high concentration, it has been possible to devise an HPLC assay system using the rapid, convenient microscale procedure described previously by Lam et al. (Clin. Chem. 26, 963 1980) to prepare the sample for chromatography. To 0.1 mL serum were added 0.1 mL acetonitrile and 10 microL of 10% zinc sulfate in water. The mixture was centrifuged and 50 microL of the clear supernatant was injected into a reversed-phase column which was eluted with 65% 0.05 M potassium phosphate-35% acetonitrile, with detection by ultraviolet absorbance at 210 nm. The trazodone elutes in 6 min, clearly resolved from endogenous interferences. The recovery of trazodone added to serum was better than 90%. Peak height was proportional to concentrations in the serum sample from 125 ng/mL to 3000 ng/mL.

Blood Proteins↗
PubMed1986

QT prolongation and the antiarrhythmic efficacy of amiodarone.

Amiodarone is an antiarrhythmic agent known to cause prolongation of action potential duration which is reflected in the electrocardiogram as a prolongation of the QT interval. Prolongation of the QT interval in patients dying suddenly was compared with that in patients who remained alive to determine whether a difference existed between these two groups. The electrocardiogram and amiodarone levels were evaluated in 33 patients who presented with cardiac arrest and symptomatic ventricular tachycardia in whom no other antiarrhythmic agent was found effective in preventing induction of ventricular tachycardia during electrophysiologic studies. There were 30 men and 3 women (mean age 52 +/- 10 years). Twenty-three are alive after a mean follow-up period of 12 +/- 7 months. Ten died: six suddenly, three of non-cardiac causes and one of congestive heart failure. Using a two-way analysis of variance, the percent change in QT, QTc, JT and JTc intervals before and after amiodarone therapy was analyzed. Marked prolongation in the QT interval was present in patients who remained alive with amiodarone therapy. A significant difference in percent QT prolongation was seen between the latter patients and those who died suddenly (p less than 0.005). No difference was observed in the percent change in QRS interval between the two groups. The levels of amiodarone (2.5 versus 3.2 micrograms/ml) and its metabolite (desethylamiodarone) were not significantly different between the living patients and those who died suddenly. These findings suggest that a prolongation of the QT interval may be a marker for the therapeutic antiarrhythmic effect of amiodarone.

Aged↗
PubMed1986

Deep venous thrombosis: detection by probe compression of veins.

The sonographic detection of echogenic, soft-tissue mass within the veins of the lower extremities assures the diagnosis of deep venous thrombosis (DVT). However, the sonographic diagnosis remains inconclusive when fresh thrombus and/or artifacts are present within the lumen of the vein. The present study attempts to augment the clinical utility of real-time sonography in the detection of DVT, based on the premise that total obliteration of the vein lumen by probe compression should not be possible in the presence of venous thrombi. Sonography and contrast venography of the lower extremity were performed in 20 patients with clinical suspicion of DVT. The presence of thrombi was confirmed in 14 patients. Probe compression failed to obliterate the lumen of the veins containing thrombi. The authors conclude that the technique of probe compression is useful for rapid and noninvasive detection of venous thrombi.

Humans↗
PubMed1985

Radioimmunoassay of the attack complex of complement in serum from patients with systemic lupus erythematosus.

We developed a radioimmunoassay to measure the attack complex of complement (SC5b-9) in serum from patients with systemic lupus erythematosus. The radioimmunoassay used a monoclonal antibody to an antigen of C9, which is absent from native C9 but present on SC5b-9. SC5b-9 was detectable in 13 of 63 normal subjects, with a mean value of 0.5 unit (range, 0 to 4.8), and elevated in 13 of 14 patients with active lupus. Analysis of 108 samples from the patients with lupus revealed a mean value of 10.1 units (range, 0 to 35) when the disease was active and 1.0 unit (range, 0 to 433) when it was clinically stable. SC5b-9 was a more sensitive measure of disease activity than C3, C4, or CH50; its specificity was equivalent to that of C3 and C4. SC5b-9 was elevated in serum from 6 of 49 patients with other forms of glomerulonephritis. Our study documents the presence of SC5b-9 in abnormal serum and correlates its elevation with clinical disease activity in patients with active systemic lupus erythematosus.

Adolescent↗
PubMed1985

Ceftriaxone therapy in bacteremic typhoid fever.

The efficacy and safety of ceftriaxone in the treatment of bacteremic typhoid fever was studied in 14 patients. Ceftriaxone at a dosage of 50 to 60 mg/kg per day was administered intravenously in two divided doses in 13 patients and as a single dose in 1 patient. When the two patients with medical complications causing persistent fever and the patient who was febrile during therapy were excluded from the calculations, the mean period of defervescence was 4 days. Five to eight days of ceftriaxone therapy was adequate for the patients who were cured. The 14 patients treated with ceftriaxone included 13 patients who were considered cured, although 1 was a convalescent carrier, and one patient who was a treatment failure. There were no relapses in the 11 patients who were monitored for 1 to 8 months. Both peak and trough concentrations of ceftriaxone were well above the ceftriaxone MICs for the Salmonella typhi strains isolated from the patients. We have demonstrated that ceftriaxone can be used successfully in the treatment of typhoid fever in some patients. The advantages of its use include rapid clinical response, short course of treatment, and lack of serious adverse drug reactions.

Adolescent↗
PubMed1985

Predictors of bronchial hyperexcitability in grainhandlers.

We have studied bronchial hyperexcitability to methacholine (defined as a fall of at least 20 percent in FEV1 at 8 mg/ml or lower) in 504 white male grainhandlers working in terminal elevators in the Port of Vancouver. There was a significant association between bronchial hyperexcitability and level of FEV1; for a 10 percent decrease in percent of predicted FEV1, bronchial hyperexcitability was twice as common. Among those with bronchial hyperexcitability, the PC20 was significantly related to the FEV1. Grainhandlers with immediate skin reactivity to common allergens were twice as likely to have bronchial hyperexcitability. There was a significant increase in the prevalence of bronchial hyperexcitability with increasing duration of employment. Grainhandlers with chest tightness and breathlessness were over twice as likely to have bronchial hyperexcitability. We did not observe an increased prevalence of bronchial hyperexcitability in smokers, and there was no difference between age groups. We conclude that the determinants of bronchial hyperexcitability in this population include baseline FEV1, immediate skin reactivity to common allergens, some respiratory symptoms, and cumulative exposure to grain dust.

Adult↗
PubMed1985

Effect of filtration and concentration on the composition of bronchoalveolar lavage fluid.

The effects of filtration and concentration on the cellular and protein composition of bronchoalveolar lavage fluids were examined in ten normal subjects and 11 patients with asthma. Filtration of lavage fluid preferentially removed bronchial epithelial cells, resulting in a relative increase in the proportion of alveolar macrophages. Concentration of the lavage fluid results in a significant loss of proteins, with a greater loss of large molecular weight proteins. A similar loss was not observed when diluted sera form the same subjects were concentrated in the same manner. Our results suggest that when studying the cellular composition of bronchoalveolar lavage fluid, the aspirated fluid should not be filtered through cotton gauze if changes in the bronchial epithelium may be of importance because it will remove a significant proportion of these cells. Proteins in lavage fluids should be quantitated in unconcentrated lavage fluid whenever possible.

Adult↗
PubMed1985

Effect of bronchial lavage volume on cellular and protein recovery.

To investigate the optimal lavage technique to study the airway response in patients with asthma, differential volume lavage was carried out in 22 normal subjects and 18 patients with red cedar asthma. Ten ml of fluid was instilled into a main-stem bronchus followed by 5, 10, 20, 50 and 100 ml into different segmental bronchi. Small volume lavage (less than 20 ml) in a main stem bronchus or a segmental bronchus recovered more epithelial cells and neutrophils while a lavage volume of 20-100 ml in a segmental bronchus recovered more lymphocytes, alveolar macrophages, albumin, IgG and alpha 1-antitrypsin. In patients with asthma, a higher proportion of epithelial cells was observed in the 20 ml segmental bronchus lavage 24 to 48 hours after bronchial challenge with plicatic acid, the chemical compound responsible for red cedar asthma. There was an increase in eosinophils and IgG with all volume lavages, but the changes were most marked in the 10 ml main bronchus lavage and the 10 and 20 ml segmental bronchus lavage. The results show the importance of using a systematic lavage protocol to characterize the cellular and protein changes in the airways of patients with asthma. A single volume lavage in one site may not encompass all the changes observed.

Adolescent↗
PubMed1984

High-performance liquid chromatography of amino acids in urine and cerebrospinal fluid.

Two different methods for analyzing amino acids by reversed-phase high-performance liquid chromatography (HPLC), both of which can separate D- and L- stereoisomers, have been used for studying the amino acid composition of cerebrospinal fluid (CSF) and urine. One method, by which Dns derivatives of amino acids are separated as mixed chelate complexes with Cu(II) and a single stereoisomer of a second amino acid, was used to analyze CSF. CSF contains ca. 10 mumole/l per amino acid, compared to 100 mumole/l in serum. The high sensitivity of fluorescence detection enabled complete analysis, starting with 50 microliter of fluid. The second method, which uses lower concentrations of both the copper and the second amino acid and detects amino acids by the change in absorbance of the copper complex, was used to measure the urine concentration of the lysine metabolite, pipecolic acid (piperidine-2-carboxylic acid), a secondary amino acid that is difficult to detect by the more usual detection methods. Our procedure involves passing urine through a cation-exchange column, collecting the fraction containing pipecolic acid, and chromatographing it on a reversed-phase HPLC column with a mobile phase containing L-aspartame and Cu(II). To assess the utility of the method, urine samples from a patient given loading doses of D- or L-isomers were analyzed. When either isomer was administered, both D- and L-isomers were detected, but in different proportions. Varying proportions and concentrations of both isomers were also detected in the urines of patients with hyperpipecolatemia from different metabolic abnormalities.

Amino Acid Metabolism, Inborn Errors↗
PubMed1984

Stereoselective D- and L-amino acid analysis by high-performance liquid chromatography.

This paper describes a gradient system for separating D- and L-isomers of Dns-amino acids by mixed chelate complexation through the addition of histidine methyl ester and copper sulfate to the mobile phase. Most of the biologically important amino acids were separated in a single analysis. With a simple solvent gradient consisting of increasing concentrations of acetonitrile in L-histidine methyl ester buffer all the common amino acids were resolved except cysteine and all optical isomers were resolved except those of threonine, alanine and proline. Analysis time was 90 min. Use of this system for determining non-protein amino acids in human cerebrospinal fluid showed the amino acids to be L-isomers, as expected. The pattern in fluid from a patient with bacterial meningitis was different from that of most of the others.

Amino Acids↗
PubMed1984

Stereoselective analysis of D and L dansyl amino acids as the mixed chelate copper(II) complexes by HPLC.

This paper reviews the mixed chelation approach to resolution of the optical isomers of D and L dansyl amino acids by high performance liquid chromatography. The use of eluants containing Cu(II) complexes of L-proline, L-arginine, L-histidine, and L-histidine methyl ester effected the separation of many D and L amino acids, including those with aliphatic, polar, and aromatic substituents. The mechanism of separation, which is based on the preferential ternary complex formation of the analyte amino acid and the chiral chelate with Cu(II) in the mobile phase, is discussed. The stereoselectivity depends mainly on the different steric interactions between the alkyl side chains of the amino acid analytes and the chiral ligands coordinating around Cu(II), although such parameters as pH, temperature, organic modifier, and concentration of the chiral additive also affect the chromatographic separation. Among the chiral ligands studied, L-histidine methyl ester is unique in that it possesses both achiral selectivity for the dansyl amino acids and chiral selectivity for the respective D and L enantiomers. With a mobile phase gradient of acetonitrile in a buffer containing Cu(II) L-histidine methyl ester complex, a stereoselective procedure was devised for the analysis of D and L amino acid enantiomers, achieving the separation that the current amino acid analyzer could not perform. Finally, the use of the mixed chelation approach in two biomedical studies is described. In the first application, the histidine methyl ester gradient was adapted for analyzing amino acids in cerebrospinal fluid; in the second, an L-aspartame Cu(II) complex eluant was developed for measuring the urine concentration of D and L pipecolic acid (piperidine-2-carboxylic acid), a metabolite of lysine.

Amino Acids↗
PubMed1984

A common source foodborne outbreak of cholera in Singapore.

An epidemiological investigation of an outbreak of Vibrio cholerae 01, biotype El Tor, serotype Ogawa, phage type 1, confined to a group of foreign construction workers in Singapore is described. A total of 22 workers were confirmed to have cholera and another 15 had asymptomatic Vibrio cholerae 01 infection between 3 November and 11 November 1982. The source of infection was traced to contaminated seafood prepared at the construction site canteen where two food handlers were found to be infected with V. cholerae 01 (one symptomatic and the other asymptomatic). The incubation period of cholera in this outbreak ranged from 4 to 203 hours with a median of 38 hours. Only two workers had moderate to severe dehydration and required intravenous therapy. Early recognition of the outbreak and prompt implementation of control measures prevented the outbreak from spreading to other parts of Singapore.

Adolescent↗
PubMed1984

Isolation of mucoid Vibrio parahaemolyticus strains.

Mucoid strains of Vibrio parahaemolyticus were isolated from the stools of two asymptomatic carriers and a patient with gastroenteritis. The strains demonstrated biochemical reactions and antibiotic susceptibility typical of nonmucoid strains of V. parahaemolyticus isolated locally. The slime substance was typed by coagglutination and was antigenically similar to the capsular antigen of the same strain. Three different serotypes (O10:K24, O5:K17, and O5:K15) were involved.

Antigens, Bacterial↗