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Biomedical subjects

K C Chan

Publications and source records attributed to K C Chan.

At least 73 records · Page 4Linked to original sources
PubMed1995

Separation and detection of amino acids and their enantiomers by capillary electrophoresis: a review.

Since its introduction as an analytical technique capillary electrophoresis has been used for the separation of amino acids and their enantiomers; over 150 studies have been published to date. This review deals with their separation and detection. Amino acids have been resolved using both capillary zone electrophoresis and micellar electrokinetic chromatography. Pre-column derivatization schemes which are employed for the sensitive detection of amino acids are discussed. Criteria for the selection of the pre- or post-column derivatizing agent, chromophore or fluorophore, are presented. Detection systems, direct and indirect, that have been used are given with emphasis on fluorogenic reagents and laser induced fluorescence detection. Also, procedures for the separation of amino acid enantiomers are discussed and illustrated.

Amino Acids↗
PubMed1995

Enantiomeric separation of amino acids using micellar electrokinetic chromatography after pre-column derivatization with the chiral reagent 1-(9-fluorenyl)-ethyl chloroformate.

Direct enantiomeric separations of some racemic amino acids derivatized with 9-fluorenylmethyl chloroformate were obtained using cyclodextrin-modified micellar electrokinetic chromatography (CD/MEKC) with a buffer made up of 5 mM sodium borate (pH 9.2), 150 mM sodium dodecyl sulfate (SDS) and 40 mM gamma-CD. Alternatively, enantiomeric separations were also achieved indirectly using MEKC after pre-column derivatization with (+)-1-(9-fluorenyl) ethyl chloroformate (FLEC). Using either a 10 mM sodium phosphate (pH 6.8) or a 5 mM sodium borate buffer (pH 9.2), each of which contained 25 mM SDS and 10-15% of acetonitrile, FLEC-derivatized serine, alanine, valine, methionine, leucine, phenylalanine, tryptophan, and their diastereomeric pairs were all separated: the L-isomers migrated faster than the corresponding D-isomers. However, when (-)-FLEC was used for derivatization, the D-isomers migrated faster than the corresponding L-isomers. Also, the diastereomers of aspartic acid, glutamic acid, and proline were resolved using a 10 mM sodium citrate buffer (pH 4.4). Using KrF (248 nm) laser-induced fluorescence, the detection limit of (+)-FLEC derivatized DL-amino acids was obtained at the nM level, which was about 100 x more sensitive than UV absorption at 200 nm. Analyte concentrations as low as 3 x 10(-8) M (DL-Val) could be derivatized with (+)-FLEC.

Acetonitriles↗
PubMed1995

Extracorporeal membrane oxygenation and the treatment of critical pulmonary hypertension in congenital heart disease.

Certain forms of congenital heart disease (CHD) confer a high risk for the development of severe pulmonary hypertension before and after corrective cardiac surgery. Extracorporeal membrane oxygenation (ECMO) has theoretical benefits in the treatment of this complication in that it assures oxygenation, corrects acid-base balance and provides haemodynamic support at the same time as allowing lung rest from ventilation. We examined our experience of the 117 children and neonates supported with ECMO between November 1989 and July 1993. Of these, five received support for critical pulmonary hypertension associated with congenital heart disease. They comprised three who had undergone surgical repair of CHD, one whose total anomalous pulmonary venous drainage was diagnosed and corrected whilst on ECMO and one neonate with functional pulmonary atresia. Pulmonary artery pressure (PAP) was estimated by Doppler echocardiography in all patients and confirmed invasively in two. The median systolic PAP was 46 (range 42-65) mmHg prior to ECMO. The median ratio of pulmonary to systemic arterial pressure (PAP/SAP) was 0.75 (0.70-0.92). Following ECMO of 16-120 h duration, the median systolic PAP was 34 (30-49) mmHg with PAP/SAP 0.50 (0.35-0.60). All patients survived and there were no complications related to ECMO. Extracorporeal membrane oxygenation is an effective treatment in critical pulmonary hypertension and should be considered in all patients in whom this is refractory to conventional measures.

Acid-Base Equilibrium↗
PubMed1994

Analysis of nitrate and nitrite in water and urine by capillary zone electrophoresis.

A capillary zone electrophoresis method for the separation and analysis of nitrate and nitrite in water and urine was developed. No interference in the electropherogram from other anions is observed by using a polyacrylamide-coated column with a modified phosphate buffer at pH 3 for the separation, and UV absorption at 214 nm for the detection. The method does not require sample pretreatment or the use of organic solvents. The limit of detection for each analyte (S/N = 3), using a 75 microns I.D. capillary, is 0.5 microgram/ml. Urine samples require 40-fold dilution in order to maintain migration time reproducibility to within 1% relative standard deviation.

Electrophoresis↗
PubMed1994

High-performance liquid chromatography and micellar electrokinetic chromatography of taxol and related taxanes from bark and needle extracts of Taxus species.

High-performance liquid chromatography (HPLC) and micellar electrokinetic chromatography (MEKC) were applied for the separation of taxol, cephalomannine, and baccatin III in crude extracts from the needle and bark of Taxus species. The chromatogram of the bark extract was cleaner than that of the needle allowing a more reliable detection of taxol and cephalomannine in the bark extract. However, HPLC quantitation of taxol in the needle extract would be difficult due to coeluting taxinines. Nevertheless, this was not a problem in the MEKC experiment. In comparison to HPLC, MEKC offered baseline resolution of taxol from taxinines in the needle extract, less solvent waste, a smaller sample requirement, and the simultaneous detection of taxol, cephalomannine and baccatin III in a relatively simpler electrophoretic run.

Alkaloids↗
PubMed1994

Micellar electrokinetic chromatography of the anti-human immunodeficiency virus (HIV) agent michellamine B with absorption and laser-induced fluorescence detection.

Micellar electrokinetic chromatography (MEKC) was applied to the separation of the anti-HIV agents, michellamines A and B, and two other structurally related monomers found in the extract of the Ancistrocladus plants. Using buffers containing either 10 mM sodium phosphate (pH 7.0), 50 mM sodium deoxycholate and 10-20% acetonitrile or 5 mM sodium phosphate (pH 7.0), 20 mM sodium dodecyl sulfate and 25% acetonitrile allowed baseline separations of the four components in the mixture in less than 10 min. The MEKC methods gave sharper peaks and better resolution compared to high-performance liquid chromatography. For MEKC separation of the plant extracts, UV absorption detection provided adequate sensitivity; however, higher sensitivity could be achieved with UV laser-induced fluorescence detection (LIF). Using the sodium dodecyl sulfate-containing buffer and LIF, the limit of detection for michellamine B was approximately 2 ng/mL. The sensitivity was degraded approximately 100-fold when using the deoxycholate buffer because of high background fluorescence. Preliminary results show that MEKC with LIF is feasible for the sensitive detection of michellamine B in serum.

Antiviral Agents↗
PubMed1994

Marginal seal of new-generation dental bonding agents.

This in vitro study evaluated microleakage of three new adhesive systems--All-Bond 2, Gluma 2000, and Scotchbond Multi-Purpose. Enamel was removed from the buccal surfaces of 40 extracted molars, and cavity preparations were made on both the buccal and lingual surfaces of each tooth. Buccal cavities were entirely in dentin, and the lingual cavities had enamel margins. Specimens were randomly assigned to three groups for treatment with All-Bond 2, Gluma 2000, or Scotchbond Multi-Purpose adhesive systems. A fourth group of specimens was untreated to serve as the control. All cavity preparations were restored with a visible light-cured microfilled composite resin. Specimens were thermocycled and subjected to a crystal violet staining technique to detect marginal microleakage. Microleakage was recorded as ordinal data and analyzed with nonparametric statistical tests. Each of the adhesives tested significantly reduced microleakage at the enamel and dentin margins. The extent of leakage at dentin margins was only slightly greater than at enamel margins in each treatment group.

Adhesives↗
PubMed1994

Right ventricular outflow reconstruction with cryopreserved homografts in pediatric patients: intermediate-term follow-up with serial echocardiographic assessment.

OBJECTIVES: This study was performed to assess by echocardiography the intermediate-term outcome of cryopreserved homografts employed in pulmonary outflow reconstruction in children and to validate the reliability of Doppler echocardiography in their evaluation. BACKGROUND: Cryopreserved homografts have become the most widely used pulmonary conduits. Previous reports have shown the occurrence of homograft regurgitation in the immediate postoperative period and the propensity of regurgitation to progress. Although Doppler echocardiography has been useful in assessing extracardiac valved conduit stenosis, its reliability in assessing a large series of cryopreserved homografts has not been documented. METHODS: Echocardiograms of 41 patients (43 homografts) who underwent operations between December 1986 and October 1992 were retrospectively reviewed. The median age of patients at operation was 37.5 months (range 3 to 333), and the median duration of follow-up was 28.5 months (range 1 to 68). Homograft regurgitation was classified on a scale of 0 to 4+. Pressure gradients across the homografts measured in 23 catheterizations were correlated with corresponding echocardiographic gradients. RESULTS: Regurgitation: Homograft regurgitation occurred in 100% of patients at follow-up. Progression of severity > 2 grades occurred during follow-up in 35% and was associated with operation before age 18 months (p < 0.002) and stenosis progression (p < 0.05) but not with homograft type (aortic or pulmonary). These data predict that 50% of patients operated on before 18 months of age will have severe regurgitation by 15 months postoperatively compared with only 15% operated on after 18 months. Stenosis: At follow-up, 51% of homografts had a stenotic gradient > or = 25 mm Hg predominantly at the distal anastomosis, and stenosis progression was related to young age at operation (< 18 months, p < 0.005) and small conduit size (p < 0.01). Fifty percent of conduits implanted before age 18 months could be predicted to stenose by 21.8 months compared with only 5% of those implanted after age 18 months. The gradient measured from Doppler echocardiography correlated well with the catheterization gradient (r = 0.86). CONCLUSIONS: Cryopreserved homograft dysfunction is frequent and progressive. Young age at operation (< 18 months) predicts more rapid deterioration. Doppler echocardiography is reliable in assessing the systolic gradients across homografts. Serial echocardiographic assessment in the follow-up of these patients accurately characterizes these problems.

Adolescent↗
PubMed1994

Characterization of rat serum insulin-like growth factor-binding proteins by two-dimensional gel electrophoresis: identification of a potentially novel form.

The insulin-like growth factor-binding proteins (IGFBPs) in rat serum were analyzed by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by Western ligand or immunoblotting. A ligand blot of adult female rat serum revealed at least 20 proteins that bound labeled IGF-I specifically. They ranged in size from about 24-50K, and their pI values ranged from approximately 5.5-8.0. Immuno- and ligand blots showed that IGFBP-3 appeared as a broad band composed of numerous individual spots of about 40-45K, with pI values ranging from about 5.5-7.7. Immunoblots showed that IGFBP-4 resolved into at least three spots of approximately 29K, with pI values of about 6.3-6.7 and an approximately 24K nonglycosylated form that usually appeared as a single spot with a pI of about 7, but occasionally it resolved into a doublet. Immunoblots of neonatal rat serum using antiserum to IGFBP-2 resulted in immunoreactivity of two sets of proteins: approximately 33K forms composed of two proteins and approximately 30K forms comprising at least five different variants with pI values of about 7.0-7.5. However, ligand analysis showed that only the 30K forms had binding activity. IGFBP-1, -5, and -6 were not detectable by immunoblotting. However, a set of about 29K IGFBPs with pI values of approximately 5.9, which appears in significant amounts in the serum of pups and diabetic rats and in placental tissue-conditioned medium, has been tentatively identified as IGFBP-1 by ligand blotting. One finding of particular interest is an approximately 50K BP with a pI of about 6 that comigrates with IGFBP-3. However, unlike IGFBP-3, which is glycosylated and undergoes proteolysis during gestation, this approximately 50K IGFBP is not susceptible to endoglycosidase-F treatment and persists throughout pregnancy. Immunoblotting analysis revealed weak cross-reactivity between the approximately 50K IGFBP and antiserum to IGFBP-4. These results show that the rat serum IGFBPs are more heterogeneous than was previously realized. The two-dimensional system will allow changes in these different forms to be evaluated critically in different physiological and experimental states.

Animals↗
PubMed1994

Incomplete forms of Beckwith-Wiedemann syndrome: report of a case.

Beckwith-Wiedemann syndrome is a rare disease characterized by a constellation of congenital and time-dependent abnormalities such as defects of the abdominal wall, gigantism, craniofacial dysmorphism, visceromegaly and hemihypertrophy. The syndrome is divided into complete and incomplete forms and, as it may only have subtle phenotypic features, it is easily neglected by clinicians. Patients with this syndrome, particularly those associated with hemihypertrophy, have a high risk of growing malignant tumors. This is a case report of a patient with an incomplete form of this syndrome with left hemihypertrophy, hepatosplenomegaly and a small right adrenal cystic lesion.

Adult↗
PubMed1993

Micellar electrokinetic chromatography of hydroxyproline and other secondary amino acids in biological samples with laser-induced fluorescence detection.

Micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence (LIF) was used for the rapid and sensitive detection of hydroxyproline in serum and hydrolyzed urine that were pre-column derivatized with 9-fluorenylmethyl chloroformate (FMOC). The application of the combined o-phthalaldehyde (OPA)/FMOC derivatization in MEKC for the selective detection of secondary amino acids in biological samples is investigated.

Amino Acids↗
PubMed1993

Separation of pyridinecarboxylic acid isomers and related compounds by capillary zone electrophoresis. Effect of cetyltrimethylammonium bromide on electroosmotic flow and resolution.

The effect of the addition of cetyltrimethylammonium bromide (CTAB) to the buffer system in capillary electrophoresis on electroosmotic flow (EOF) is examined. At a CTAB concentration of 2.5 x 10(-4) M, EOF is anodal (flow towards the positive detector column end). With bare silica columns, anodal EOF first increases with increasing pH, up to a maximum in the pH range 4-6 depending on CTAB concentration, then decreases as pH is further increased. Optimum resolution of pyridinecarboxylic acid isomers is obtained at pH 2.7 with a 10 mM phosphate buffer and 30 mM CTAB. Using the same buffer system, optimum resolution for hydroxy-substituted pyridinecarboxylic acid isomers is obtained at pH 7.5. The use of CTAB results in a dramatic improvement in peak shape. Preliminary results, using an excimer laser operated at 248 nm, show that the fluorescence intensity of isonicotinic acid is substantially enhanced with the addition of 0.3% hydrogen peroxide to the phosphate buffer system.

Cetrimonium↗
PubMed1993

Laser-induced fluorescence detection of 9-fluorenylmethyl chloroformate derivatized amino acids in capillary electrophoresis.

Laser-induced fluorescence (LIF) was applied to the detection of 9-fluorenylmethyl chloroformate (FMOC-Cl) derivatized amino acids separated by capillary electrophoresis. Fluorescence excitation was provided by a pulsed, KrF laser operating at 248 nm. A limit of detection of 5 x 10(-10) M was obtained for FMOC-alanine (S/N = 2). Separation of FMOC-derivatized proline, hydroxyproline, and sarcosine was achieved with a 20 mM borate buffer (pH 9.2), and the separation of FMOC-derivatized amino acid standard mixture was obtained using a 20 mM borate buffer (pH 9.2) containing 25 mM sodium dodecyl sulfate.

Amino Acids↗
PubMed1993

Fetal and neonatal outcome of exposure to anticoagulants during pregnancy.

We studied fetal and neonatal outcome of women maintained on anticoagulants (warfarin and/or heparin) during pregnancy. Among 22 Chinese families, 13 mothers (59%) had a history of recurrent abortion or stillbirth while being maintained on warfarin treatment. Twenty-nine liveborn children (17 boys, 12 girls), ages 0.6-11.3 years at follow-up, were analysed for evidence of embryopathy. These were subdivided into 2 groups. Group 1 consisted of 18 children (12 boys, 6 girls) whose mothers were only given warfarin during pregnancy. Five were small for gestational age, and 12 had features of warfarin embryopathy such as nasal hypoplasia. One had subependymal intraventricular hemorrhage shown on neonatal ultrasonography. Group 2 consisted of 11 children (5 boys, 6 girls) whose mothers were maintained on warfarin and heparin during pregnancy. Three were premature deliveries, and 4 had nasal hypoplasia. One had cleft lip, cleft palate, cataract, microphthalmia, intraventricular hemorrhage, and hydrocephalus. We found that despite the high risk of fetal wastage, there was a relative lower risk of major complications, except for some minor cosmetic defects such as nasal hypoplasia. This might lead to readjustment of advice concerning contraception given to pregnant women who were maintained on anticoagulant therapy.

Abortion, Habitual↗
PubMed1993

Salvage of postoperative pulmonary hypertensive crisis using ECMO via cervical cannulation in a case of truncus arteriosus.

The survival of patients with truncus arteriosus beyond one year of age is rare without surgical treatment [3 . Early surgery may be associated with a mortality but is still preferable, as the risks of established pulmonary hypertensive disease complicate delayed surgery [2]. We report the successful salvage of a pulmonary hypertensive crisis 24 h after corrective surgery in a late presenting patient using extracorporeal membrane oxygenation (ECMO) via cervical cannulation. Post-operative pulmonary hypertensive crises may present a difficult management problem. Extracorporeal membrane oxygenation is therapeutic in these circumstances in addition to providing life support. Cervical cannulation remains the method of choice in the postoperative cardiac patient.

Catheterization↗
PubMed1993

High casein-lactalbumin diet accelerates blood coagulation in rats.

This study investigates the influence of a high protein intake on normal hemostasis, fluid balance and organ growth. Adult rats were fed semipurified diets that contained either 18 or 56 g/100 g casein-lactalbumin for 2 wk, and the following functions were measured: food and water intake, weight gain, blood pressure, bleeding and clotting time, ADP-stimulated platelet aggregation, thrombin time, prothrombin time and partial thromboplastin time. Although food intake was depressed by the high protein diet, weight gain was not affected by the regimen. Water consumption, 24-h urine excretion and kidney weight were significantly greater in rats fed the high protein diet than in controls. High protein intake resulted in shorter barbiturate-induced sleeping time. Bleeding time and clotting time were significantly lower in rats fed the high protein diet for 7 d. However, heart rate, mean arterial pressure, plasma protein and osmolarity, platelet aggregation, prothrombin time, partial thromboplastin time and thrombin time did not differ significantly. Because a high protein intake caused rapid coagulation of blood in rats without affecting the activity of clotting factors, we suggest that this diet sensitized rats to factors that initiate clotting in vivo.

Animals↗
PubMed1993

Morphological variations of fossa ovalis atrial septal defects (secundum): feasibility for transcutaneous closure with the clam-shell device.

OBJECTIVE--To assess the morphology of fossa ovalis atrial septal defects (FOASD; secundum atrial septal defect) to determine in what proportion percutaneous closure with the clam-shell device might be feasible. DESIGN--Review of the intraoperative description of the morphology and size of FOASD. PATIENTS--106 consecutive patients with FOASD. SETTING--A regional children's cardiac referral centre. MAIN OUTCOME MEASURES--Determination of morphology and size of FOASD. RESULTS--Morphological variations in the FOASD were found: (1) central FOASD, 70 (66%); (2) superior FOASD, 4 (3.7%); (3) inferior FOASD, 8 (7.6%); (4) posterior FOASD, 2 (1.9%); (5) subtotal absence of atrial septum, 3 (2.8%); (6) completely fenestrated FOASD, 10 (9.4%); (7) partially fenestrated FOASD, 9 (8.5%). Depending on its site, the edge of the FOASD may be close to important atrial structures such as the orifices of the superior and inferior caval veins, coronary sinus, and right pulmonary veins. The shape of the FOASD was usually oval with the major diameter ranging from 10 to 50 mm with a mean (SD) of 27.8 (0.93) mm. The minor diameter ranged from 4 to 30 mm with a mean (SD) of 15.3 (5.9) mm. The ratio of the major to minor diameter ranged from 1.0 to 5.0 with a mean of 2.01. Based on intraoperative measurement and description, it is postulated that it should be possible to close about 50% of these defects with the clam-shell device.

Adolescent↗