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Biomedical subjects

Y L Lau

Publications and source records attributed to Y L Lau.

At least 55 records · Page 3Linked to original sources
PubMed2000

An efficient method of generating transgenic mice by pronuclear microinjection.

Genetic transformation of mice using pronuclear microinjection was demonstrated by a number of groups in rapid succession in the early 1980's. Since that time, studies using transgenic animals have produced major advances in biomedical sciences and molecular genetics. More important, it is possible to study the molecular basis for tissue and stage-specific expression of genes. We recently used this method to generate transgenic mice. DNA fragment (transgene) was injected into the pronucleus of one-cell embryos. We describe this simplified protocol, which is reliable. With the use of buffered medium M2 for the whole process, it is not mandatory to have a CO2 incubator.

Animals↗
PubMed2000

Testicular sperm extraction and intracytoplasmic sperm injection in non-obstructive azoospermia.

OBJECTIVE: To report the experience in sperm extraction from testicular biopsies (TESE) performed from March 1996 to July 1998 in men with non-obstructive azoospermia (NOA). METHODS: Comparisons of age, volume of both testes, serum FSH and testosterone in men, and histology of testicular samples in the first cycles between cycles with spermatozoa found and those without spermatozoa found were performed. Comparisons of fertilization, cleavage and pregnancy rates between cycles with spermatozoa injected and those with spermatids injected were performed. RESULTS: Spermatozoa were found in only 12 out of 26 first TESE cycles (46.2%) and other cycles had spermatids (round cells) only. Age of men, history of mumps orchitis/oligozoospermia, volume of both testes and serum FSH/testosterone levels in men were not significantly different between cycles with and without spermatozoa. The fertilization rate was significantly higher in cycles with spermatozoa injected than those with round cell injections (63.3% vs 23.2%, P < 0.0001, Chi-squared test). The pregnancy rate was 14.3% per cycle when spermatozoa were injected. CONCLUSIONS: TESE followed by intracytoplasmic sperm injection (ICSI) is an effective treatment in patients with NOA. Less than half of the patients undergoing TESE had spermatozoa recovered. Age of men, volume of both testes and serum FSH/testosterone levels in men were not useful in predicting successful recovery. Compared to using ejaculated and epididymal spermatozoa, fertilization and pregnancy rates were achieved when testicular spermatozoa were used for ICSI.

Adult↗
PubMed1999

Mannose binding lectin gene mutations are associated with progression of liver disease in chronic hepatitis B infection.

Mannose-binding lectin (MBL) plays an important role in immune defense. We examined the MBL gene mutations and MBL levels in Chinese hepatitis B and hepatitis C patients with and without symptomatic cirrhosis. We recruited 190 hepatitis B and C patients, and 117 normal Chinese as controls. Serum MBL levels were measured by enzyme-linked immunosorbent assay. MBL gene mutation at codons 52, 54, and 57 was detected by polymerase chain reaction (PCR) assay. In asymptomatic hepatitis B and C patients, there was no increase in codons 52, 54, and 57 mutation, but the MBL levels were significantly lower than those in the controls. Codon 54 mutation rate was increased to 44.4% (P =.007) in symptomatic hepatitis B cirrhosis and 64.3% (P =.0026) in patients with spontaneous bacterial peritonitis (SBP). There was no increase in codon 54 mutation rate in hepatitis B-related hepatocellular carcinoma (HCC). In chronic hepatitis B infection, the odds ratio for an individual with codon 54 mutation to develop cirrhosis was 1.84 (95% CI: 1.21-2. 81) and to develop SBP was 4.58 (95% CI: 1.73-12.16). Chronic hepatitis B and hepatitis C infection lowered the MBL levels, probably by suppressing MBL production. Codon 54 mutation of MBL was associated with progression of disease in chronic hepatitis B infection.

Adolescent↗
PubMed1999

Effect of insulin-like growth factor 1 on PHA-stimulated cord blood mononuclear cell telomerase activity.

Telomerase may contribute to the capacity for cell replication by compensating for the loss of telomere length. Exploring the use of biological modifiers in increasing cellular replicative potential through telomerase activity may be useful for in vitro expansion of haemopoietic stem cells for transplantation or lymphoid cells for adoptive immunotherapy. In this study we showed for the first time that insulin-like growth factor 1 (IGF-1) modulated telomerase activity in human cord blood mononuclear cells (MNC) and some of the known functional determinants of telomerase activity. We found that cord blood MNC expressed constitutively a low level of telomerase activity and human telomerase reverse transcriptase (hTRT) mRNA, and a high level of human telomerase RNA component (hTR) and telomerase-associated protein-1 (TP1) mRNA. Interestingly, IGF-I alone did not increase the telomerase activity of cord blood MNC but could enhance the PHA-induced increase in telomerase activity. These alterations in telomerase activity were not completely in phase with those of proliferation response. On the other hand, IGF-I did not alter hTRT mRNA expression but enhanced the PHA-induced increase in hTRT whereas TP1 mRNA expression was stimulated by either IGF-I or PHA but showed no additive increase when stimulated by both IGF-1 and PHA. Neither IGF-1 nor PHA altered hTR expression. Finally, the temporal dynamics of hTRT mRNA expression and telomerase activity in cord blood MNC over 5 d in culture were not totally concordant. suggesting that key factors other than hTRT were involved in regulating telomerase activity in cord blood MNC. The modulatory effect of IGF-1 on telomerase activity supports its potential role in increasing replicative potential of cord blood lymphoid cells or haemopoietic stem cells.

Cell Division↗
PubMed1999

IGF-I increases interferon-gamma and IL-6 mRNA expression and protein production in neonatal mononuclear cells.

Neonates are vulnerable to infections because of their immature immunity. IGF-I has been reported to have profound positive effects on immune function. In this study, we investigated the effects of IGF-I on neonatal immunity. The production of IL-2, IL-4, and interferon-gamma in phytohemagglutinin (PHA)-stimulated neonatal mononuclear cells (MNC) was significantly decreased when compared with that of adults. IGF-I alone induced a high level of IL-6 mRNA expression and protein production in neonatal MNC. IGF-I significantly increased mRNA expression and protein production of both IL-6 and interferon-y but had no influence on that of IL-2 and IL-4 in PHA-stimulated neonatal MNC. Moreover, it increased neonatal interferon-gamma production in PHA-stimulated MNC to a level similar to that of adults. IGF-I could further enhance the mRNA expression of lymphocyte-activation gene 3, which is associated with interferon-gamma production and differentiation of T-helper 1 lymphocytes, in PHA-stimulated neonatal MNC. These results suggest IGF-I could promote maturation of neonatal T cells, and its potential use to enhance neonatal immunity deserves further study.

Adult↗
PubMed1998

Clinical significance of alimentary tract microbes in bone marrow transplant recipients.

A prospective study on the microbes isolated from the alimentary tract in 120 bone marrow transplant (BMT) recipients (1991-1993) was undertaken to define the spectrum of organisms isolated under antimicrobial prophylaxis, their temporal sequence of emergence, and the associated morbidity and mortality. Clostridium difficile (n = 20), isolated in the pre-engraftment and early post-engraftment periods (day 2-45 post-BMT), was the most common microbe recovered from stool of patients with diarrhea. In contrast to previous reports, no significant difference in mortality was observed between patients with and without C. difficile isolated in stool. Two patients had neutropenic ileocecitis with concomitant bacteremia due to Escherichia coli and Klebsiella pneumoniae. One patient was found to have astrovirus gastroenteritis (day 7), and Giardia lamblia was recovered from the stool of another (day -7). Heavy growth of Staphylococcus aureus from direct smear-positive specimens was found from the upper airway of two patients with severe mucositis and complete dysphagia (day 12 and 23). Salmonella spp. of groups B and E were found in the stool of five asymptomatic patients at the time of conditioning. No specific organisms was recovered from the endoscopic brushing of two patients with lower end esophagitis, three patients with upper gastrointestinal bleeding, and three patients with perirectal cellulitis. During the post-engraftment period, five patients had documented cytomegalovirus gastroenterocolitis (days 34-97), one had Mycobacterium chelonae colitis (day 70), and another had nodular gastritis due to Acremonium falciforme (day 270). Overall, only 28% of patients with alimentary tract symptoms/syndrome had specific pathogens isolated from clinical specimens. Differentiation of the causation of alimentary tract symptoms was often difficult because noninfectious complications such as conditioning toxicity, graft-versus-host disease, and its treatment often caused alimentary tract symptoms in addition to predisposed BMT patient to infection. The reluctance of obtaining tissue biopsy for ascertaining the importance of those potential alimentary tract pathogens often dictate the use of empirical treatment.

Adolescent↗
PubMed1998

Primary human herpes virus 6 infection transmitted from donor to recipient through bone marrow infusion.

An 8.5-month-old boy with Wiskott-Aldrich syndrome received a sibling matched bone marrow transplant from his healthy non-identical twin brother. The donor had primary human herpes virus 6 (HHV-6) infection around the time of bone marrow donation. The recipient had hepatitis in the first week and then developed fever and rash on day 18. Skin biopsy was shown to have HHV-6 antigen and his peripheral blood leukocytes were HHV-6 DNA positive. He engrafted on day 18 but the ANC dropped from 5.5 x 10(9)/l (day 23) to 0.48 x 10(9)/l (day 34) with persistent HHV-6 DNAemia. Bone marrow on day 35 was positive for HHV-6 DNA. He was treated with G-CSF and ganciclovir with good response. He later had pneumonitis which was treated empirically with foscarnet, ceftazidime and clarithromycin.

Bone Marrow Transplantation↗
PubMed1998

Near-haploid common acute lymphoblastic leukaemia of childhood with a second hyperdiploid line: a DNA ploidy and fluorescence in-situ hybridization study.

Near-haploidy is a rare cytogenetic finding in childhood acute lymphoblastic leukaemia (ALL) and is associated with a poor prognosis. A second hyperdiploid line, occurring presumably by endoreduplication of the near-haploid stemline, is often observed. We present a case of common ALL in relapse characterized morphologically by a dual population of small and large lymphoblasts. Cytogenetic analysis supplemented with fluorescence in-situ hybridization (FISH) studies localized near-haploidy and hyperdiploidy to the small and large blast population respectively. DNA ploidy determination confirmed two abnormal clones with near-haploidy as the predominant one. A novel t(9;12)(q11;q13) was present in the near-haploid clone and was duplicated in the hyperdiploid clone. This finding identified cells bearing near-haploidy to be the clonogenic population following malignant transformation and confirmed endoreduplication as the mechanism for the presence of associated hyperdiploidy.

Child↗
PubMed1998

Prevalence and risk factors of childhood asthma, rhinitis and eczema in Hong Kong.

OBJECTIVE: To assess the prevalence and risk factors of childhood asthma and allergies in Hong Kong and compare with that in Singapore and Great Britain. METHODOLOGY: Parents of 3618 randomly selected 6- to 7-year-old children responded to a questionnaire prepared by the International Study of Asthma and Allergies in Childhood (ISAAC) together with supplementary questions on risk factors. RESULTS: The 12-month prevalences of wheezing, rhinitis symptoms and itchy rash were 9.2%, 35.1% and 4.2%, respectively. Wheezing in the past year was significantly associated with rhinitis symptoms in the past year, itchy rash in the past year, rhinitis interfering with daily activities moderately or severely, kept awake by itchy rash in the past year, parental wheezing (one or both parents), frequent upper respiratory tract infections (URTI), born in Hong Kong and male sex. For girls, the prevalence of wheezing in the past year was lowest when they were born in July/August and highest when born in January/February. CONCLUSIONS: The prevalence of allergic disorders in Hong Kong was comparable to that in Singapore and Great Britain. Several potential risk factors such as parental wheezing, frequent URTI, born in Hong Kong, male sex and month of birth in girls were identified.

Asthma↗
PubMed1998

End tidal carbon monoxide concentration in childhood haemolytic disorders.

OBJECTIVES: Endogenous carbon monoxide (CO) is produced mainly by heme catabolism. As CO is excreted solely by the lung, a simple technique for measuring the end tidal carbon monoxide (ETCO) level was assessed as a method for screening for haemolytic disease in children. METHODS: Two end expiratory breath samples were collected from normal children and from children with haemolytic disease using a one way valve connector between a mouth piece and an anaesthetic bag. The samples were analysed by gas chromatography for CO and carbon for dioxide (CO2). The CO2 value was used to normalise the CO value to an alveolar concentration. Carboxyhaemoglobin (HbCO) also was measured in the patient group for correlation analysis with ETCO. RESULTS: A total of 21 children with beta thalassaemia major, 15 children with other haemolytic diseases (hereditary spherocytosis n=8, haemoglobin H disease n=3 and thalassaemia intermedia n=4) and 23 normal children were studied. The mean ETCO concentrations in the three groups were 3.21 p.p.m., 7.41 p.p.m. and 0.69 p.p.m., respectively, which were significantly different from each other (P<0.0001). There was a significant correlation between ETCO and HbCO in the patient groups (r=0.85; P<0.0001). CONCLUSIONS: The end expiratory breath collection device is a simple and feasible sample collection method. The results confirm that ETCO can be used clinically to distinguish children with a variety of haemolytic disorders from normal subjects.

Adolescent↗
PubMed1998

Microbial adsorption of cyanazine and metolachlor.

A laboratory experiment was performed to study the role of microorganisms in producing the non-extractable residues by anaerobically incubating cyanazine (2-[[4-chloro-6-(ethylamino)-1,3,5,-triazin-2-yl]-amino]-2-methoxy -l- methylethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methoxy-l- methylethyl)acetamide] in culture media that had been inoculated with sewage bacteria from anaerobic sludge. Based on the gas chromatographic analyses of extracts from the degradation, adsorption, and abiotic controls for the parent herbicide and its possible metabolites, this study provided the first direct evidence that bacterial biomass, rather than metabolism, was mainly involved in the formation of bound residues with cyanazine. Anaerobic bacteria appeared to be incapable of forming bound residues with metolachlor. The common phenomenon of age-dependent extractability for bound residues was observed with cyanazine. These results imply that bacteria may adsorb pesticides selectively with preference for certain chemical structures over others.

Acetamides↗