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Biomedical subjects

L Chan

Publications and source records attributed to L Chan.

At least 289 records · Page 16Linked to original sources
PubMed1992

The effect of repeated chemotherapy on age-related predisposition to Ascaris lumbricoides and Trichuris trichiura.

This study examines the persistence of predisposition to Ascaris lumbricoides and Trichuris trichiura during repeated chemotherapy in an urban community in Kuala Lumpur, Malaysia. Significant predisposition was observed over 2 periods of reinfection with and without age-standardization of data. Analysis of different age groups indicated that predisposition was most strongly detectable in the younger age classes. The intensities of infection with both parasites were strongly correlated at each cycle of intervention, suggesting that individuals were similarly predisposed to both species.

Adolescent↗
PubMed1992

Segregation of human T cell lymphotropic virus type I and II infections by antibody reactivity to unique viral epitopes.

A recombinant protein of the human T cell lymphotropic virus type I (HTLV-I) gp46 outer membrane envelope, MTA-4 (residues 129-203), reacted by Western blot with sera from HTLV-I-infected individuals from the United States and Jamaica but not with 24 (10%) of 242 Japanese sera. A related gp46 recombinant protein, MTA-1 (residues 162-209), reacted with all 58 sera from HTLV-I-infected US and Jamaican individuals and 238 of 242 sera from infected Japanese (combined sensitivity of 99%). Neither recombinant showed reactivity to sera from HTLV-II-infected individuals or uninfected controls. The reactivity of recombinant proteins containing the region of HTLV-II gp46 analogous to MTA-1 was also evaluated by Western blot: GH2-K15 (residues 157-205) and GH2-K55 (residues 162-205) reacted with 88 (98%) and 89 (99%), respectively, of 90 sera from HTLV-II-infected individuals but not with sera from HTLV-I-infected individuals or uninfected controls. These recombinant proteins should permit the development of assays to unambiguously confirm and differentiate HTLV-I and HTLV-II infections.

Amino Acid Sequence↗
PubMed1992

Immune responsiveness to the immunodominant recombinant envelope epitopes of human T lymphotropic virus types I and II in diverse geographic populations.

The heterogeneity of immune responsiveness to the immunodominant epitopes of human T lymphotropic virus (HTLV) types I (MTA-1(162-209)) and II (K-55(162-205)) were determined in natural infections with HTLV-I and -II from diverse geographic areas (n = 285). Of the HTLV-I specimens confirmed by polymerase chain reaction (PCR), all North American (n = 37) and Peruvian (n = 19) specimens reacted with MTA-1. Of HTLV-II specimens confirmed by PCR, 44 (96%) of 46 from North American blood donors, 28 (97%) of 29 from native Americans, and all from intravenous drug users (n = 29) reacted with K-55. Specimens from other geographic areas (Peru, 30; Brazil, 4; Mexico, 10; Italy, 5; Somalia, 13; Ethiopia, 17; Japan, 32; and Jamaica, 15) all reacted either with MTA-1 or K-55. By synthetic peptide-based serologic typing, all of these specimens could be typed as HTLV-I or -II. In addition to the direct implications of these findings for diagnostic purposes, these data provide indirect evidence for the conservation of immunodominant HTLVenv epitopes in diverse geographic populations.

Africa↗
PubMed1992

Serologic confirmation of simian T-lymphotropic virus type I infection by using immunoassays developed for human T-lymphotropic virus antibody detection.

Serum specimens from diverse species of Old World monkeys, categorized as seropositive (n = 97) or seronegative (n = 23) for human T-lymphotropic virus (HTLV) infection, were tested by using recombinant env-spiked Western immunoblot assays and synthetic peptide assays for simultaneous detection and discrimination of simian T-lymphotropic virus (STLV) infection. Of the 97 seropositive specimens, 93 reacted with the recombinant transmembrane (r21env) protein and 90 reacted with a recombinant, MTA-1, derived from the central region of the external glycoprotein of HTLV-I (rgp46env), thus yielding test sensitivities of 96 and 93%, respectively. While 1 of the 23 negative monkey specimens reacted with r21env, none reacted with rgp46env, for overall specificities of 96 and 100%, respectively. Analysis of synthetic peptide-based immunoassays demonstrated that while 85 of 97 (88%) seropositive specimens reacted with HTLV-I-specific epitope (p19gag), none of the specimens reacted with HTLV-II-specific epitope (gp52env). These results show that recombinant envelope-spiked Western blots provide a simple means for serologic confirmation of STLV-I infection and that type-specific synthetic peptides can be used to confirm the virus type in seropositive monkey specimens.

Animals↗
PubMed1992

The largest subunit of RNA polymerase II in Dictyostelium: conservation of the unique tail domain and gene expression.

cDNAs encoding the largest subunit of RNA polymerase II were isolated from a Dictyostelium cDNA library. A total of 2.9 kilobases (kb) of cDNA was sequenced and the amino acid sequence of the carboxyl-terminal half of the protein was deduced. Similar to other eukaryotic RNA polymerases II, the largest subunit of Dictyostelium RNA polymerase II contains a unique repetitive tail domain at its carboxyl-terminal region. It consists of 24 highly conserved heptapeptide repeats, with a consensus sequence of Tyr-Ser-Pro-Thr-Ser-Pro-Ser. In addition to the tail domain, five segments of the deduced primary structure show > 50% sequence identity with either yeast or mouse protein. RNA blots show that cDNA probes hybridized with a single mRNA species of approximately 6 kb and immunoblots using a monoclonal antibody raised against the tail domain lighted up a single protein band of 200 kilodaltons. Interestingly, expression of the largest subunit of RNA polymerase II appears to be under developmental regulation. The accumulation of its mRNA showed a 60% increase during the first 3 h of development, followed by a steady decrease during the next 6 h. Cells began to accumulate a higher level of the RNA polymerase II mRNA after 9 h of development. When cells were treated with low concentrations of cAMP pulses to stimulate the developmental process, the pattern of mRNA accumulation moved 3 h ahead, but otherwise remained similar to that of control cells.

Amino Acid Sequence↗
PubMed1992

Localization of prostatic glycoconjugates by the lectin-gold method.

The glycoconjugates of the lateral prostate were examined ultrastructurally by lectin-gold histochemistry in combination with a low-temperature embedding technique using Lowicryl K4M. The binding patterns of concanavalin A, wheat germ agglutinin, Griffonia simplicifolia, soybean agglutinin, peanut agglutinin, Ricinus communis agglutinin isolectin I, Griffonia simplicifolia isolectin B4, Ulex europaeus isolectin I and Phaseolus vulgaris agglutinin P have been documented in the subcellular compartments of the lateral prostate. The results show that the granular endoplasmic reticulum (GER) is rich in glycoproteins with mannosyl residues while the Golgi cisternae, secretory granules and microvilli are less so. The mannose (Man) and N-acetylglucosamine (GlcNAc) residues present in the GER of the epithelial cells may be associated with the initial assembly of the N-linked oligosaccharides of glycoproteins. The secretory granules exhibited different reactivities to lectins. Most of the lectin-binding sites confined to the limiting membranes may play a role in the transport of plasmalemma glycoconjugates to the apical plasma membrane. The epithelial Golgi stack is rich in GlcNAc, galactose (Gal), N-acetylgalactosamine (GalNAc) and sialic acid residues, and a compartmental organization of the Golgi stack is apparent which might be associated with the sequential addition of sugar residues to the oligosaccharides. The plasma membrane contains abundant Man, GlcNAc, Gal, GalNAc and complex carbohydrates, especially in the microvilli, and a differential lectin labelling was noted between the apical and basolateral plasma membrane. The present study showed that fucose-containing glycoconjugates were detected in the apical plasma membrane of the lateral prostate. The stromal extracellular matrices as well as the epithelial basement membranes demonstrated weak lectin reaction. Man, GlcNAc, Gal residues and complex sugars were also noted in the stromal tissues of the lateral prostate including the extracellular matrix, capillaries and smooth muscle.

Animals↗
PubMed1992

Flumazenil reversal of conscious sedation for minor oral surgery.

In order to find out whether resedation occurred following antagonism with flumazenil of sedation for minor oral surgery, in a double-blind randomised cross-over study thirty healthy Hong Kong Chinese patients undergoing bilateral third molar surgery at two visits were sedated with midazolam. Following surgery they received either flumazenil or placebo at one visit and the alternative at the other visit. Recovery was monitored by observation and objective tests. Following recovery they were monitored for resedation for a total period of two hours from the injection of the reversal agent. Resedation, sufficient to prevent a patient from being discharged to be accompanied home with an escort, did not occur provided the patient responded to verbal command following sedation.

Adolescent↗
PubMed1992

Cytochemical localisation and characterisation of proteoglycans (glycosaminoglycans) in the epithelial-stromal interface of the seminal vesicle of the guinea pig.

The proteoglycans (PGs) in the guinea pig seminal vesicle were demonstrated ultrastructurally by both cuprolinic blue (CB) and ruthenium red (RR) staining. The PGs appeared as electron-dense granules with RR, but were filamentous following CB staining using the critical electrolyte concentration method. Three major types of PGs (T1, T2, T3) have been described according to their different locations and sizes. T1 filaments were short and were found mostly on both sides of the lamina densa of the basal lamina of the glandular epithelium (40-60 nm long) and also on the basal laminae of smooth muscle cells and capillary endothelial cells (20-30 nm long). In the epithelial basal lamina they were regularly spaced at an interval of 40-60 nm. T1 filaments in the lamina densa were smaller and more randomly distributed. Cytochemical characterisation of these PGs by various GAG degrading enzymes showed that T1 PGs are rich in heparan sulphate. T2 filaments were 30-40 nm long and closely associated with the collagen fibrils. They were arranged perpendicular to the long axis of collagen fibrils, also at intervals of about 60 nm. T2 filaments were removed by chondroitinase (Ch)-ABC, Ch-ABC plus Streptomyces (S)-hyaluronidase and pronase, but resistant to nitrous acid, heparitinase, heparinase, neuraminidase and S-hyaluronidase. These show that T2 filaments are rich in dermatan sulphate. T3 filaments (60-100 nm) were widely distributed in the stroma at sites such as the interstitial spaces of the lamina propria, the reticular layer below the basal lamina, around individual collagen fibrils or bundles of such fibres, and on the cell surfaces of fibroblasts. The T3 filaments were removed by Ch-ABC, Ch-AC and pronase but were resistant to heparitinase, heparinase, S-hyaluronidase, neuraminidase and nitrous acid. They are therefore rich in chondroitin sulphate.

Animals↗
PubMed1992

HTLV-I antibody study in normal individuals and unselected hospital patients in Malaysia.

A serological investigation for human T cell leukemia virus I (HTLV-I) infection was carried out at the University Hospital, Kuala Lumpur. A total of 626 sera from a non-patient population and 1,038 sera from unselected in-patients were screened for HTLV-I antibodies using an enzyme-linked immunosorbent assay (ELISA). 27/1664 (1.6%) were found to be reactive. However, on Western blotting, only 2 sera were confirmed positive, both showing reactions for the major core (p19 and p24) and the envelope (gp46) proteins. Both of the serum samples were from unselected hospital patients. Most of the remaining sera which were reactive on screening showed indeterminate results on Western blotting. These were further tested by radioimmunoprecipitation assay (RIPA) and none of these sera gave a positive reaction. Therefore, only 2/1038 (0.19%) unselected patients could be confirmed to have antibodies to HTLV-I. None of the normal individuals screened showed a positive Western blot result. Our data indicate that HTLV-I infection is present in our population, but at a low prevalence rate.

Adult↗
PubMed1992

The effect of repeated chemotherapy on the prevalence and intensity of Ascaris lumbricoides and Trichuris trichiura infection.

The prevalence and intensity of intestinal nematode infections were assessed during 3 anthelminthic interventions in an urban community in Malaysia. The prevalence levels of Ascaris lumbricoides at Interventions 1, 2 and 3 were 30.6%, 18.9% and 15.5%, respectively and the mean intensities were 1.9, 0.75 and 0.81 worms per person. For Trichuris trichiura, the prevalence levels at Interventions 1, 2 and 3 were 46.9%, 21.6% and 15.7%, respectively. The mean intensities for T. trichiura at Interventions 1, 2 and 3 were 3.30, 0.92 and 0.07 worms per person. No gender-related prevalence and intensity were observed for the two geohelminths in this community. Prevalences and intensity had convex age profiles. Although repeated chemotherapeutic intervention reduced both prevalence and intensity levels, intensity was a more sensitive indicator than prevalence. The results indicate that age-targetting treatment at school children of 7-12 years of age would be an appropriate strategy for this community.

Adolescent↗
PubMed1992

Structure and evolution of the lipase superfamily.

The lipase superfamily includes three vertebrate and three invertebrate (dipteran) proteins that show significant amino acid sequence similarity to one another. The vertebrate proteins are lipoprotein lipase (LPL), hepatic lipase (HL), and pancreatic lipase (PL). The dipteran proteins are Drosophila yolk proteins 1, 2, and 3. We review the relationships among these proteins that have been established according to gene structural relatedness and introduce our findings on the phylogenetic relationships, distance relationships, and evolutionary history of the lipase gene superfamily. Drosophila yolk proteins contain a 104 amino acid residue segment that is conserved with respect to the lipases. We have used the yolk proteins as an outgroup to root a phylogeny of the lipase family. Our phylogenetic reconstruction suggests that ancestral PL diverged earlier than HL and LPL, which share a more recent root. Human and bovine LPL are shown to be more closely related to murine LPL than to guinea pig LPL. A comparison of the distance (a measure of the number of substitutions between sequences) between mammalian and avian LPL reveals that guinea pig LPL has the largest distance from the other mammals. Human, rodent, and rabbit HL show marked divergence from one another, although they have similar relative rates of amino acid substitution when compared to human LPL as an outgroup. Human and porcine PL are not as divergent as human and rat HL, suggesting that PL is more conserved than HL. However, canine PL demonstrates an unusually rapid rate of substitution with respect to the other pancreatic lipases. The lipases share several structurally conserved features. One highly conserved sequence (Gly-Xaa-Ser-Xaa-Gly) contains the active site serine. This feature, which agrees with that found in serine esterases and proteases, is found within the entire spectrum of lipases, including the evolutionarily unrelated prokaryotic lipases. We review the location and possible activity of putative lipid binding domains. We have constructed a conservation index (CI) to display conserved structural features within the lipase gene family, a CI of 1.0 signifying perfect conservation. We have found a correlation between a high CI and the position of conserved functional structures. The putative lipid-binding domains of LPL and HL, the disulfide-bridging cysteine residues, catalytic residues, and N-linked glycosylation sites of LPL, HL, and PL all lie within regions having a CI of 0.8 or higher. A number of amino acid substitutions have been identified in familial hyperchylomicronemia which result in loss of LPL function.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1992

A missense mutation (Trp86----Arg) in exon 3 of the lipoprotein lipase gene: a cause of familial chylomicronemia.

We have investigated a patient of English ancestry with familial chylomicronemia caused by lipoprotein lipase (LPL) deficiency. DNA sequence analysis of all exons and intron-exon boundaries of the LPL gene identified two single-base mutations, a T----C transition for codon 86 (TGG) at nucleotide 511, resulting in a Trp86----Arg substitution, and a C----T transition at nucleotide 571, involving the codon CAG encoding Gln106 and producing Gln106----Stop, a mutation described by Emi et al. The functional significance of the two mutations was confirmed by in vitro expression and enzyme activity assays of the mutant LPL. Linkage analysis established that the patient is a compound heterozygote for the two mutations. The Trp86----Arg mutation in exon 3 is the first natural mutation identified outside exons 4-6, which encompass the catalytic triad residues.

Amino Acid Sequence↗
PubMed1992

Effect of long-acting calcium entry blocker (anipamil) on blood pressure, renal function and survival of uremic rats.

To assess more completely the long-term effect of a long-acting calcium channel blocker, anipamil was given p.o. to rats with subtotal (five-sixths) nephrectomy. The mortality rates in anipamil-treated and control groups were 5% and 20%, respectively, at 6 weeks after separation (P less than .01) and 10% and 55%, respectively, at 10 weeks after separation (P less than .01). Mean arterial blood pressure was also more well controlled in the anipamil-treated group (144 +/- 36 vs. 192 +/- 35 mm Hg; n = 20; P less than .05 at week 5). In paired experiments, the degree of renal impairment in the placebo- and anipamil-treated groups, just before the onset of preterminal azotemia, was determined. Rats that were treated with anipamil had lower serum creatinine concentrations, compared with the placebo controls, at 4 to 6 weeks after separation (0.55 +/- 0.02 vs. 0.87 +/- 0.02 mg/100 ml; P less than .05). To dissociate this beneficial effect of anipamil from mean arterial blood pressure control, experiments were also performed to assess the effects of hydralazine on the remnant kidney model of chronic renal failure. Rats with remnant kidneys were divided into three groups and treated with anipamil (2 mg/kg/day), hydralazine (80 mg/liter in drinking water) or control. The anipamil-treated group exhibited significantly greater protection of renal function than did the hydralazine-treated group for the same level of blood pressure control. Thus, a long-acting calcium channel entry blocker such as anipamil may afford an additional cytoprotective effect in the prevention of progression of chronic renal failure beyond the antihypertensive effects of the agent.

Animals↗
PubMed1991

Locating a low density lipoprotein-targeting domain of human apolipoprotein B-100 by expressing a minigene construct in transgenic mice.

Through its interaction with the low density lipoprotein (LDL) receptor, apolipoprotein (apo) B-100 is a major determinant of LDL metabolism and plasma cholesterol. Its receptor binding ability is conformation-dependent and requires its expression on the right lipoprotein particles. The structural signal that targets apoB-100 to LDL is unknown. We have microinjected a human apoB-100 minigene construct comprising less than 25% of the apoB-100 sequence driven by the natural apoB promoter to produce transgenic mice. The transgene product was expressed at a high level and was present exclusively in the LDL of these animals. Analysis of the responsible sequence (residues 2878-3925 of apoB-100) reveals unique structural features that may be important in its role as an LDL-targeting domain.

Animals↗
PubMed1991

Apolipoprotein B mRNA editing is an intranuclear event that occurs posttranscriptionally coincident with splicing and polyadenylation.

The subcellular compartment in which apolipoprotein (apo) B mRNA is edited is unknown. We studied the site of endogenous apoB mRNA editing and correlated the extent of editing with mRNA maturation in the rat liver. RNA editing activity was demonstrated in both nuclear and cytoplasmic extracts. The specific activity of the editing activity was 5.5-fold higher in the nuclear extract, which was not accounted for by activators, inhibitors, or modulators. However, the total editing activity was 3.1 times higher in the cytoplasmic extract. Highly purified rat liver nuclear apoB mRNA contained 17.3 +/- 1.45% edited sequences compared with 56 +/- 2.5% and 62.15 +/- 6.2% edited sequences in hepatic total and polysomal RNAs, respectively. Because of the significant extent of editing of total nuclear RNA, we fractionated it into a poly(A-) and poly(A+) fraction. While the poly(A-) nuclear fraction contained only 10.4 +/- 1.1% edited sequences, which represents a maximum estimate, the poly(A+) nuclear apoB mRNA contained 50 +/- 1.8% edited sequences, a value very similar to that for polysomal RNA. By direct sequencing of cDNA and genomic clones, we found that as in the case of the human apoB gene, the rat apoB gene contains an intron 25 immediately upstream of the edited exon 26. Using this information, we developed a method to examine in a highly selective manner apoB mRNA that is present in the nucleus before splicing of intron 25 and after splicing of this intron. The unspliced nuclear pre-mRNA contained 7.4 +/- 0.2% edited sequences compared with 51.0 +/- 0.9% edited sequences in the spliced nuclear apoB mRNA. Furthermore, in the poly(A-) pool of apoB pre-mRNA, unspliced nuclear pre-mRNA contained hardly any (1.56%) edited sequences, and the spliced nuclear pre-mRNA contained 7.8 +/- 0.6% edited mRNA. In the poly(A+) fraction, unspliced nuclear pre-mRNA had 25.4 +/- 0.05% and spliced nuclear mRNA 53 +/- 0.6% of its apoB mRNA in an edited form. We conclude that in the rat liver apoB mRNA editing is not a cotransciptional event. It occurs posttranscriptionally, but the process is essentially complete in the spliced polyadenylated apoB mRNA before it leaves the nucleus. Little, if any, additional editing occurs in the cytoplasmic compartment.

Animals↗