Biomedical subjects

H Tan

Publications and source records attributed to H Tan.

At least 127 records · Page 7Linked to original sources

PubMed1994

[Pathological study of enamel caries produced by oral bacteria in vitro].

The authors used the bacterial culture method to study early enamel caries-like lesions in vitro. Pathologic changes in the lesions were observed under polarized light microscope and scanning electron microscope. The results showed that this method could simulate the destructive procedures in carious development. The destructive way and pathologic changes of the caries-like lesions were very similar to those of natural caries. Under microscope, the ultrastructures of the relatively intact layer of the enamel surfaces were already changed. The prisms in the enamel surfaces were destroyed, and dissolved to form small pores. The pores could be an important path of the carious development.

Actinomyces viscosus↗

PubMed1994

[The effect of a promoter P28-1 of Bacillus subtilis on Streptomyces differentiation].

A 1.1kb promoter P28-1 was inserted into pUC19. After then, the P28-1 was subcloned into the HindIII-EcoRI sites of the high copy number Streptomyces promoter probe plasmid pIJ4083 containing xy1E reporter gene. This recombinant plasmid was designated as pIJ4498. When pIJ4498 was introduced into Streptomyces coelicolor J1501 protoplasts, transformants conferred a white phenotype, whereas the vector pIJ4083 gave rise to colonies of normal, dark grey appearance which is the same as that of J1501 itself. After confirming pIJ4498 structure with some restriction enzymes, it was also introduced into whiG mutant (C71). Crude enzyme extracts were isolated from J1501/pIJ4498, J1501/pIJ4083 and C71/pIJ4498 respectively, the crude enzyme extract from J1501/pIJ4498 could oxidize catechol (colourless) to 2-hydroxy muconic semialdehyde (yellow colour), but crude enzyme extracts from J1501/pIJ4083 and C71/pIJ4498 could not oxidize catechol to 2-hydroxymuconic semialdehyde. The results indicated that P28-1 might be recognised by sigma whiG RNA polymerase, and activated the xylE reporter gene expression and reduced J1501 sporulation.

Bacillus subtilis↗

PubMed1993

Genomic rearrangement of the alpha-globin gene complex during mammalian evolution.

In man, the gene for hydroxyacyl glutathione hydrolase (HAGH; glyoxalase II) is closely linked to the alpha-globin locus (HB alpha) on Chromosome 16. HAGH polymorphism in the mouse has now enabled the mapping of the murine homologue. Deletion mapping, congenic strain studies, and characterization of 41 recombinant inbred strains establish that the mouse Hagh locus lies very close to the alpha-globin pseudogene (Hba-ps4) in the vicinity of the major histocompatibility locus (H-2) on chromosome 17. Several other loci have been identified previously that are also closely linked to the human alpha-globin locus but near the alpha-globin pseudogene Hba-ps4 in the mouse. These linkage relationships suggest that during the evolution of mice a translocation occurred that subdivided the alpha-globin locus, leaving one inactive alpha-globin gene still associated with the Hagh locus and linked sequences, while moving and inserting the active alpha-globin locus and all distal sequences into an internal location on another autosome, the predecessor to mouse chromosome 11.

Animals↗

PubMed1993

Two developmentally controlled promoters of Streptomyces coelicolor A3(2) that resemble the major class of motility-related promoters in other bacteria.

Experiments were designed to allow isolation of Streptomyces coelicolor promoters that depend on the whiG sporulation gene, which encodes a putative sigma factor important in the sporulation of aerial hyphae. The strategy, based on earlier evidence that sigma WhiG is limiting for sporulation (K. F. Chater, C. J. Burton, K. A. Plaskitt, M. J. Buttner, C. Méndez, and J. Helmann, Cell 59:133-143, 1989) was to seek DNA fragments that inhibit sporulation in aerial hyphae when present at a high copy number. In a suitable Sau3AI-generated library of DNA from S. coelicolor A3(2), two inserts were found to inhibit sporulation. Both inserts caused expression of the adjacent xylE reporter gene present in the vector in a developmentally normal strain of S. coelicolor, but there was no xylE expression in an otherwise isogenic whiG mutant. S1 nuclease protection experiments were done with RNAs isolated from these plasmid-bearing strains or from the wild-type strain lacking either recombinant plasmid. In each case, an apparent transcription start site was found upstream of an apparent open reading frame (ORF) and just downstream of sequences that resemble consensus features of promoters for motility-related genes in Bacillus subtilis and coliform bacteria. Such promoters depend on sigma factors (sigma D and sigma F, respectively) particularly similar to the deduced whiG gene product. Each of the putative whiG-dependent promoters is within an ORF that is upstream of, and potentially translationally coupled to, the putative whiG-dependent ORF (although use of one of the promoters would necessitate the use of a different start codon, further downstream). Thus, in unknown circumstances, the whiG-dependent ORFs may be expressed from a more remote promoter as part of a complex transcription unit.

Amino Acid Sequence↗

PubMed1993

[Antithrombotic effect of Gynostemma pentaphyllum].

Human blood samples were investigated in vitro to observe the antithrombotic effect of water extract of Gynostemma pentaphyllum (GP). The results showed that GP could inhibit significantly the platelet aggregation induced by ADP and compound agonists (P < 0.05), accelerate obviously the disaggregation (P < 0.05) and inhibit effectively the experimental thrombosis (P < 0.05). The delayed effects of GP on KPTT, PT, TT, AT, RVV-RT, RVV-CT suggested that this drug could decrease the activity of multiple coagulation factors. And it showed that GP could accelerate the erythrocyte electrophoresis rate. This study revealed that GP is an antithrombotic agent affecting the links of thrombotic chain which is worthwhile to be studied further.

Adult↗

PubMed1993

Altered immunity in haemophiliacs treated exclusively with cryoprecipitate.

Sixty-five patients with haemophilia A from Singapore General Hospital, treated within the last 15 years exclusively with cryoprecipitate, were studied for the effect of the total number of exposures to random blood donors on their immune system. These haemophiliacs were aged 4 to 71 years (median 24 years) and were all apparently healthy with no clinical evidence of viral infection. None of them was a homosexual or intravenous drug user. All of them tested negative for human immuno-deficiency virus antibody and hepatitis B surface antigen. Analysis of the T-lymphocyte subset population showed 20 out of 65 haemophiliacs or 30.8% had reversal of T4/T8 ratio, ie. less than 1.00. There was no significant difference in the mean age of the 20 patients with abnormal T4/T8 ratios compared with the 45 with normal T4/T8 ratios. The mean age of the former group was 23 and the latter was 25. The group with reversal of T4/T8 ratio had exposure to 827.4 +/- 137.3 (mean +/- SEM) random blood donors, which is significantly higher than 402.5 +/- 64.1 in the group with normal T4/T8 ratio (p < 0.05). The reversal of T4/T8 ratio is predominantly due to the suppression of absolute T4 cell counts, with slightly raised absolute T8 cell counts. This abnormality may be transient or permanent. Interestingly, all the six out of 65 haemophiliacs with factor VIII inhibitor did not show any reversal of T4/T8 ratio in this study.

Adolescent↗

PubMed1992

Laterality in the vestibulo-cerebellar mossy fiber projection to flocculus and caudal vermis in the rabbit: a retrograde fluorescent double-labeling study.

The vestibular nuclear input into the flocculus and the uvula and nodulus of the caudal vermis was studied in rabbits by means of retrograde transport of the fluorescent tracers Fast Blue and Diamidino Yellow. Through simultaneous injection of the tracers in the homonymous lobules at either side of the midline, the distribution, the preference in laterality and the degree of collateralization of vestibulo-cerebellar neurons could be studied. The nucleus prepositus hypoglossi was included in the analysis. In the nucleus prepositus hypoglossi and in the medial vestibular nucleus 6% of the number of labeled neurons contained both tracers, against 4% in the descending vestibular nucleus. In the superior vestibular nucleus a statistically significant difference in the proportion of double-labeled neurons was found between cases with injections in the flocculus (1%) and the caudal vermis (9%). The relative distribution of single-labeled neurons projecting to either the flocculus or the caudal vermis was similar in most of the vestibular nuclei. A statistically significant preference for a projection to the flocculus in favor of one to the caudal vermis, was found for neurons in the medial vestibular nucleus and the prepositus hypoglossal nucleus. Statistically significant laterality preferences were found in the superior vestibular nucleus for the contralateral flocculus.

Amidines↗

PubMed1992

Diverse actions of 5-hydroxytryptamine on frog spinal dorsal horn neurons in vitro.

The effects of 5-hydroxytryptamine on the membrane potential and input resistance of 86 dorsal horn neurons were studied using intracellular recordings in isolated, hemisected spinal cords of adult frogs (Rana pipiens). Bath application of serotonin (5-100 microM) caused membrane depolarizations in 58 (67%) neurons, hyperpolarizations in 12 (14%) cells, biphasic responses in nine (11%) neurons, and no detectable change in seven (8%) cells. In some neurons depolarized by serotonin, the amine's responses could be mimicked by the selective 5-HT2 agonist (+/-)-1(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride and the 5-HT1C/2 agonist alpha-methyl-5-hydroxytryptamine, and blocked by the 5-HT1C/2 antagonists ketanserin and mianserin. In other neurons depolarized by serotonin, the 5-HT3 agonist 2-methyl-5-hydroxytryptamine mimicked, and the 5-HT3 antagonist, 3-tropanyl-3,5-dichlorobenzoate, blocked the serotonin-induced responses. Depolarizing responses due to activation of 5-HT1C/2 receptors were generally accompanied by increases in the membrane input resistance, whereas depolarizations mediated by 5-HT3 receptors were associated with a decreased membrane input resistance. Superfusion with tetrodotoxin or low-Ca2+/high-Mg(2+)-containing media abolished about half of the depolarizing responses. Hyperpolarizations caused by serotonin were associated with a decrease in membrane input resistance, and might have been due to activation of a potassium conductance. These responses persisted in bathing solutions containing tetrodotoxin or low-Ca2+/high-Mg2+. The 5-HT1A agonist 8-hydroxy-2-(di-N-propylamine)tetralin hydrobromide mimicked, whereas the 5-HT1A antagonist spiroxatrine blocked, these hyperpolarizing responses. Other antagonists selective for 5-HT1C/2 or 5-HT3 receptors were without effect. Serotonin-produced biphasic responses consisted of either an initial depolarization followed by a hyperpolarization or the reverse. The selective 5-HT2 agonist (+/-)-1(2,5-dimethyoxy-4-iodophenyl)-2-aminopropane hydrochloride could only mimic the depolarizations, whereas the 5-HT1A agonist 8-hydroxy-2-(di-N-propylamine)tetralin hydrobromide produced only the hyperpolarizations. Spiroxatrine, a 5-HT1A antagonist, blocked only the hyperpolarizations without affecting the depolarizations, and methysergide, a non-specific 5-HT receptor antagonist, depressed both the depolarizations and hyperpolarizations. Serotonin also appeared to affect spinal dorsal horn neurons indirectly because it produced excitatory postsynaptic potentials, inhibitory postsynaptic potentials, and a mixture of both.(ABSTRACT TRUNCATED AT 400 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1992

Mucormycosis of the neonatal gut: a "new" disease or a variant of necrotizing enterocolitis?

Mucormycosis is an opportunistic infection that has been mainly described in adults with preexisting disease affecting immune status, eg, diabetes, leukemia, lymphoma, and renal failure on peritoneal dialysis. Few cases have been described in neonates. The presentation of mucormycosis as a cause of neonatal necrotizing enterocolitis is an unusual phenomenon. Three fatal cases of mucormycosis of the gut in premature infants in the period 1990 to 1991 are described. It is not clear whether this should be considered a separate disease or a variant of necrotizing enterocolitis. All three patients died soon after laparotomy from septic shock and the histological diagnosis of mucormycosis was made too late for effective chemotherapy.

Enterocolitis↗

PubMed1992

[Histological study of the structure of artificial plaque].

Five cariogenic bacteria were used to produce a plaque, called artificial plaque, by sequential culture in vitro. The results showed that the artificial plaque is very similar to the natural one in morphology and structure. Artificial plaque may be taken as an excellent model in vitro for the studies on cariogenicity of dental plaque.

Dental Caries↗

PubMed1991

Cardiovascular mortality in Peninsular Malaysia: 1950-1989.

Mortality statistics of Peninsular Malaysia for the period 1950-1989 have been studied in relation to cardiovascular diseases, with particular emphasis on coronary heart disease as an important cause of death. It was observed that among six major disease groups reviewed, cardiovascular diseases which occupied third place as a cause of death in 1950 emerged as the number one killer during the 1970s and has remained so since (with exception in 1980). In contrast, infectious diseases which ranked first in 1950 dropped to fourth position in 1980. Between 1960 and 1980, mortality due to cardiovascular diseases was higher in males than in females. This tendency became less apparent during 1985-1989. With reference to race, the incidence of cardiovascular deaths was highest in Indians followed by Chinese and Malays. Among the specific cardiovascular diseases, coronary heart and cerebrovascular diseases accounted for the main causes of mortality. Mortality due to coronary heart disease has increased by more than three fold over the last 40 years and is still rising. However, mortality incidence due to rheumatic heart disease and hypertension decreased during the same period. In 1965, mortality due to coronary heart disease was highest in the 55-59 age group. In recent years (1985 to 1989), it shifted to the older age group (i.e. 65-69). There was a tendency for higher mortality due to coronary heart disease in males compared to females. Indians had a higher mortality due to coronary heart disease than Chinese and Malays.

Age Factors↗

PubMed1990

A novel peroxisomal nonspecific lipid-transfer protein from Candida tropicalis. Gene structure, purification and possible role in beta-oxidation.

We have sequenced the nucleotides of the gene POX18 that encodes PXP-18, a major peroxisomal polypeptide inducible by oleic acid in the yeast Candida tropicalis. POX18 had a single open reading frame of 127 amino acids. Some 33% of the amino acid sequence of the predicted basic polypeptide (13,805 Da), was identical to that of the nonspecific lipid-transfer protein (sterol carrier protein 2) from rat liver. PXP-18, purified to near homogeneity from isolated peroxisomes, had an amino-terminal sequence identical to that of the predicted polypeptide except for the initiator methionine, and had nonspecific lipid-transfer activity comparable to that of its mammalian equivalents. Unexpectedly, PXP-18 lacked the cysteine residue thought to be essential for the activity of this protein in mammals. RNA blot analysis showed that the POX18 gene was expressed exclusively in cells grown on oleic acid, suggesting that PXP-18 has a role in the beta-oxidation of long-chain fatty acids. PXP-18 modulated acyl-coenzyme A oxidase activity at low pH.

Amino Acid Sequence↗

PubMed1990

The changes of BPA level in 31 cases of children with aplastic anaemia and its clinical significance.

Burst-promoting activity (BPA) was measured in the sera from 31 children with aplastic anaemia (AA). BPA levels were elevated in most of the children with AA (65.2%), the mean value (137.7 +/- 18.4%) being significantly higher than that in normal children (69.6 +/- 9.4%), in children in the recovery period and in children with non-aplastic anaemia. There was a negative relationship between the BPA level in children with AA and the peripheral haemoglobin concentration. The BPA level was higher in those whose duration of illness was shorter than 1 year. In three cases of AA caused by chloramphenicol and benzene hexachloride and one case of congenital pure red cell AA, the BPA level was not elevated. Eleven patients received fetal liver cell suspensions intravenously (FLI). After FLI the BPA level in their sera was significantly reduced. According to these results, it appears that the elevation of BPA level is a special phenomenon of AA. The measurement of BPA in serum is helpful for differentiation between AA and other kinds of anaemia. The elevation of the BPA level in serum is a biological compensation for the haematopoietic disorder, and the measurement of BPA in the serum of patients with AA may be helpful in evaluating the haematopoietic condition.

Adolescent↗

PubMed1990

[Life span and cercaria shedding of schistosome-infected snails in mountain region of Yunnan].

The life span and cercaria shedding of infected Oncomelania snails in a mountain region of Shitoudi village, Weishan County, Yunnan Province were observed in simulated local ecological environments. 135 infected snails were isolated for observation 3 months after exposure to miracidia in August, 1987. The snail survival rate from the day of initial cercaria shedding to next June, July, August and September was 27.4, 16.3, 13.3 and 11.9% respectively, and the average number of cercariae shed was 139.9, 29.6, 39.2 and 75 per month respectively. The average life span of infected snails was 171.6 days. The average number of cercariae shed per snail in its whole life was 673.0. It was estimated that the average patent period of infected snails was over half a year. As this is the first report in our country in respect to the life span and cercariae shedding of infected snails in a mountain region, the result might be useful for quantitative analysis of epidemiological factors of schistosomiasis in this kind of endemic areas as well as for formulation of control strategy.

Animals↗

PubMed1990

[The construction of shuttle plasmid vector of Streptomyces and E. coli].

A shuttle plasmid vector, pSE-3 was constructed using the Streptomyces plasmid pIJ486 and E. coli plasmid pGEM-3 digested with BgIII and BamHI respectively. The shuttle plasmid pSE-3 could replicate and express its neomycin resistance in both Streptomyces and E. coli well. The pSE-3 has opposed promoters containing bacteriophage ST6 and T7, the restriction enzyme digestion showed that the pSE-3 has a single site with HindIII and EcoRI respectively, it is very useful for the cloning and expression of the valuable gene inserts. The pSE-3 is stable in both of Streptomyces and E. coli after re-transformed pSE-3 is re-transformed from Streptomyces into E. coli and some 50 generations are propagated.

Escherichia coli↗

PubMed1990

[A sero-epidemiological study on HBV infection in a farm].

A seroepidemiological study on HBV infection was carried out in a farm with a population of 777. HBsAg, anti-HBs and anti-HBc were tested with SPRIA; HBeAg and anti-HBe with ELISA and HBV DNA with spot hybridization. The results showed that: 1. in HBeAg negative individuals, the positive rate of HBV DNA was 9.33%, as a result, the infectivity of HBsAg carriers could not be estimated accurately with HBeAg examination only; 2. among the total HBV infected individuals, the positive rate of HBsAg of the males was significantly higher than that of the females (51.38% vs 38.89%, P less than 0.005), indicating the difference of response to HBV between males and females; 3. in anti-HBs positive individuals, 42.53% were anti-HBs positive alone, of which, 78.72% had evidence of HBV infection four years before the examination, indicating that the majority of persons who had anti-HBs alone were specifically responsive to HBV.

Antibodies, Viral↗

PubMed1989

[Antiplatelet aggregation effect of Andregraphis paniculata].

This article deals with the antiplatelet aggregation effect of Andregraphis paniculata (AP), 61 blood samples and 8 volunteers were investigated to observe the effect of AP on platelet function in vitro and in vivo respectively. The results showed that the crude extract of AP could inhibit significantly one-phase and two-phase platelet aggregation induced by ADP (P less than 0.001, 0.01). The potency of AP crude extract seemed to be somewhat stronger than Ligustrazine and Persantin injection in vitro, but the difference was not statistically significant (P greater than 0.05). A dose-effect relationship of AP was demonstrated also (r = 0.93). The rapid effect of this drug on platelet aggregation in vivo suggested that AP could be absorbed quickly, but the effect lasted for only a short time. 12 hours after with-drawing of AP, the 1 minute and 5 minutes aggregation rates increased by 18.67%, 36.63% respectively, as compared with the lowest aggregation rate after administration. The activating effect of AP on fibrinolysis was also detected by shortened euglobulinlysis time (211.50 vs 182.50 min in vitro, 219.38 vs 149.38 min in vivo, P less than 0.001). In addition, the influence of AP upon coagulation and thrombelastogram was determined. This study suggested that AP in a promising antithrombogenic agent. This drug might be beneficial in preventing and treating arterial thrombotic diseases.

Adult↗

PubMed1988

Iontophoretic application of calcitonin gene-related peptide produces a slow and prolonged excitation of neurons in the cat lumbar dorsal horn.

Calcitonin gene-related peptide (CGRP) was applied by iontophoresis onto physiologically characterized neurons. CGRP (20-100 nA) activated both wide-dynamic-range (5/8) and low-threshold mechanoreceptive units (3/12), but had no effect on nociceptive-specific neurons (0/4). The excitation was of slow onset (30 s to 3 min) and prolonged duration (up to 10 min). In none of the tested units did CGRP cause inhibition. The slow and prolonged action suggests a neuromodulatory role for CGRP in spinal cord sensory processes.

Animals↗