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Biomedical subjects

J Tan

Publications and source records attributed to J Tan.

At least 19 recordsLinked to original sources
PubMed2007

Excision and meshed skin grafting for leg ulcers resistant to compression therapy.

BACKGROUND: The aim of this study was to determine the success of excision and meshed skin grafting for chronic leg ulcers. The effects of different ulcer aetiology and ulcer size on outcome were also assessed. METHODS: All patients who had excision and mesh grafting for chronic leg ulceration between January 1996 and December 2004 at St Thomas' Hospital were reviewed. Recurrence was classified as any breakdown of the ulcer during follow-up. RESULTS: Sixty-two patients with 100 chronic leg ulcers underwent operation. Seventy-two of the ulcers were venous and the median ulcer size was 36 (range 1.5-192) cm2. Only three patients left the hospital with their ulcers unhealed, but ulcers had recurred in 28 (28 per cent) by 2 months. A further 17 ulcers recurred later, with just over half (55 per cent) remaining healed by 5 years. There was no difference between the recurrence rates of venous ulcers and ulcers of other aetiologies (P=0.980), or large (more than 10 cm2) and small ulcers (P=0.686). CONCLUSION: Wide local excision and meshed skin grafting benefitted over half of these patients with refractory leg ulcers. Recurrence was most likely to occur in the first 2 months and, provided that ulcers were healed at this time, there was a low rate of further breakdown.

Adult↗
PubMed2007

Effect of placement of calcium sulphate when used for the repair of furcation perforations on the seal produced by a resin-based material.

AIM: To evaluate the sealing ability of calcium sulphate when used under composite resin for the repair of furcation perforations having different diameters. METHODOLOGY: Perforations of different diameter were created in the floors of pulp chambers in 60 extracted human molar teeth with either a number 3 (1 mm diameter) or 5 (1.5 mm diameter) round bur. The specimens of each group were divided into four sub-groups which were repaired with composite resin either alone or in combination with calcium sulphate that created an artificial floor (15 teeth group(-1)). Eight teeth without furcation perforations served as negative controls. In the leakage detection device, 1 mol L(-1) glucose solution was forced under a pressure of 1.5 KPa from the crown towards the pulp chamber floor. The concentration of leaked glucose was measured at 1, 2, 4, 7, 10, 15 and 20 days using a glucose oxidase method and the data evaluated using the rank sum test. RESULTS: The specimens with larger perforations repaired with composite resin alone had significantly more leakage (P < 0.05). Using calcium sulphate as an artificial floor significantly decreased leakage of smaller perforations (P < 0.05). In groups repaired with calcium sulphate under composite resin, leakage in smaller perforations was markedly lower than that in larger ones (P < 0.05). No significant difference was found between the specimens with 1 or 1.5 mm perforations repaired with resin alone (P > 0.05). CONCLUSIONS: Calcium sulphate significantly improved the sealing ability of 1 mm perforations repaired with composite resin but not for 1.5 mm perforations.

Calcium Sulfate↗
PubMed2006

A painless method of ultrasonically assisted debridement of chronic leg ulcers: a pilot study.

OBJECTIVES: Devitalized tissue in a recalcitrant leg ulcer is common and may impede healing. The aim of this study was to evaluate the use of a non-invasive low frequency ultrasound device to debride chronic leg ulcers as an adjunct to compression bandages therapy. METHODS: 19 patients with leg ulceration of at least 6 months were recruited. Low frequency ultrasound at 25kHz was delivered by a portable Sonaca--180 via a handheld probe, using normal saline as the irrigation/coupling medium. The ultrasound was applied for 10-20 seconds per probe head area onto the ulcer. Each leg underwent treatment at an interval of 2-3 weeks with compression bandages reapplied at the end of the treatment. Serial colour photographs were taken to evaluate the response at each visit. RESULTS: Each patient received on average 5.7 treatments each ranged from 5-20 minutes depending on the ulcer size. Symptomatic relief (pain and odour reduction) was achieved in 6 patients. 7 patients achieved complete ulcer healing (mean ulcer size=4.72+/-SD 1.872cm(2)) but no response was observed in 8 patients. There were no major complications of the treatment which was relatively painless. CONCLUSIONS: The application of low frequency ultrasound debridement may heal some recalcitrant ulcers when standard compression regimens have failed. It is cheap and does not require admission. The role of simple wound cleansing requires further investigation.

Adolescent↗
PubMed2006

Precancerous changes in the cervix and risk of subsequent preterm birth.

OBJECTIVE: The aims of this study were (i) to examine whether women referred for assessment of precancerous changes in the cervix had higher rates of preterm birth compared with those in the general population and (ii) to compare preterm birth rates for treated and untreated women adjusting for possible confounding factors. DESIGN: Retrospective cohort design. SETTING: Teaching hospital. POPULATION: All women referred to the Royal Women's Hospital, Melbourne (1982-2000), who subsequently had a birth recorded on the Victorian Perinatal Data Collection system (n = 5548). METHODS: Record linkage of hospital dysplasia clinic records and population-based birth records. MAIN OUTCOME MEASURES: Total preterm delivery (<37 weeks of gestation) and subtypes. RESULTS: Both treated and untreated women were at a significantly increased risk for preterm birth compared with those in the general population: treated--standardised prevalence ratio (SPR) 2.0, 95% CI 1.8-2.3 and untreated--SPR 1.5, 95% CI 1.4-1.7. Within the cohort, the treated women were significantly more likely to give birth preterm (adjusted OR 1.23, 95% CI 1.01-1.51). An increased risk of preterm birth was also associated with a history of induced or spontaneous abortions, illicit drug use during pregnancy or a major maternal medical condition. Cone biopsy, loop electrosurgical excision procedure and diathermy were associated with preterm birth. After adjusting for possible confounding factors, only diathermy remained significant (adjusted OR 1.72, 95% CI 1.36-2.17). Women treated using laser ablation were not at an increased risk for preterm birth (adjusted OR 1.1, 95% CI 0.8-1.4). CONCLUSIONS: Diagnosis of precancerous changes in the cervix (regardless of the treatment) was associated with an increased risk of preterm birth. Consideration should be given to the preferential use of ablative treatments.

Adult↗
PubMed2006

Controllable preparation of monodisperse O/W and W/O emulsions in the same microfluidic device.

This letter presents a simple way to prepare monodisperse O/W and W/O emulsions in the same T-junction microfluidic device just by changing the wetting properties of the microchannel wall with different surfactants. Highly uniform droplets ranging from 50 to 400 mum with a polydispersity index (sigma) value of less than 2% were successfully prepared. With the change in surfactants and surfactant concentrations, the interfacial tension and the wetting properties varied, and disordered or ordered two-phase flow patterns could be controllable. Monodisperse O/W and W/O emulsions were prepared under the action of a cross-flowing shear force or a perpendicular shear force by using an oil solution with 0.1-2.0 wt % Span 80 and an aqueous solution with 0.1-2.0 wt % Tween 20 as a continuous-phase flow, respectively. It gives a controllable method of preparing O/W and W/O emulsions in the same microfluidic device.

Emulsions↗
PubMed2006

Caffeine protects Alzheimer's mice against cognitive impairment and reduces brain beta-amyloid production.

A recent epidemiological study suggested that higher caffeine intake over decades reduces the risk of Alzheimer's disease (AD). The present study sought to determine any long-term protective effects of dietary caffeine intake in a controlled longitudinal study involving AD transgenic mice. Caffeine (an adenosine receptor antagonist) was added to the drinking water of amyloid precursor protein, Swedish mutation (APPsw) transgenic (Tg) mice between 4 and 9 months of age, with behavioral testing done during the final 6 weeks of treatment. The average daily intake of caffeine per mouse (1.5 mg) was the human equivalent of 500 mg caffeine, the amount typically found in five cups of coffee per day. Across multiple cognitive tasks of spatial learning/reference memory, working memory, and recognition/identification, Tg mice given caffeine performed significantly better than Tg control mice and similar to non-transgenic controls. In both behaviorally-tested and aged Tg mice, long-term caffeine administration resulted in lower hippocampal beta-amyloid (Abeta) levels. Expression of both Presenilin 1 (PS1) and beta-secretase (BACE) was reduced in caffeine-treated Tg mice, indicating decreased Abeta production as a likely mechanism of caffeine's cognitive protection. The ability of caffeine to reduce Abeta production was confirmed in SweAPP N2a neuronal cultures, wherein concentration-dependent decreases in both Abeta1-40 and Abeta1-42 were observed. Although adenosine A(1) or A(2A) receptor densities in cortex or hippocampus were not affected by caffeine treatment, brain adenosine levels in Tg mice were restored back to normal by dietary caffeine and could be involved in the cognitive protection provided by caffeine. Our data demonstrate that moderate daily intake of caffeine may delay or reduce the risk of AD.

Adenosine↗
PubMed2006

The major 8p22 tumor suppressor DLC1 is frequently silenced by methylation in both endemic and sporadic nasopharyngeal, esophageal, and cervical carcinomas, and inhibits tumor cell colony formation.

Identification of tumor suppressor genes (TSG) silenced by methylation uncovers mechanisms of tumorigenesis and identifies new epigenetic tumor markers for early cancer detection. Both nasopharyngeal carcinoma (NPC) and esophageal carcinoma are major tumors in Southern China and Southeast Asia. Through expression subtraction of NPC, we identified Deleted in Liver Cancer 1 (DLC1)/ARHGAP7 (NM_006094)--an 8p22 TSG as a major downregulated gene. Although expressed in all normal tissues, DLC1 was silenced or downregulated in 11/12 (91%) NPC, 6/15 (40%) esophageal, 5/8 (63%) cervical and 3/9 (33%) breast carcinoma cell lines. No genetic deletion of DLC1 was detected in NPC although a hemizygous deletion at 8p22-11 was found by 1-Mb array-CGH in some cell lines. We then located the functional DLC1 promoter by 5'-RACE and promoter activity assays. This promoter was frequently methylated in all downregulated cell lines and in a large collection of primary tumors including 89% (64/72) NPC (endemic and sporadic types), 51% (48/94) esophageal, 87% (7/8) cervical and 36% (5/14) breast carcinomas, but seldom in paired surgical marginal tissues and not in any normal epithelial tissue. The transcriptional silencing of DLC1 could be reversed by 5-aza-2'-deoxycytidine or genetic double knock-out of DNMT1 and DNMT3B. Furthermore, ectopic expression of DLC1 in NPC and esophageal carcinoma cells strongly inhibited their colony formation. We thus found frequent epigenetic silencing of DLC1 in NPC, esophageal and cervical carcinomas, and a high correlation of methylation with its downregulation, suggesting a predominant role of epigenetic inactivation. DLC1 appears to be a major TSG implicated in the pathogenesis of these tumors, and should be further tested as a molecular biomarker in patients with these cancers.

Base Sequence↗
PubMed2006

Yisheng injection decreases the expression of H60 and RAE-1 genes in ischemic mice liver.

OBJECTIVE: Major histocompatability complex class I chain-related antigen A, B (MICA, B) functions as ligands for human NKG2D receptors, which may play a role in graft rejection and cellular stress. In this study we explored the effect of ischemia/reperfusion injury (IRI) on the expression of H60 and RAE-1 (MICA, B homologues) in mice to study the protective effect of Yisheng injection (YS), an herbal preparation developed from traditional Chinese medicine. METHODS: Male BALB/c mice were divided into sham, ischemic, and YS-treated groups using 90 minutes of left liver lobe ischemia. Sham control mice underwent the same operation, but without vascular occlusion. In the treated group, YS (20 mg/kg) was given before ischemia and after reperfusion for 7 days. Liver samples collected at 7 days postoperation were used for real-time quantitative polymerase chain reaction analysis, Western blotting, and immunohistochemical assays. RESULTS: Compared with the sham group, H60 and RAE-1 mRNA levels were increased by sevenfold and 4.5-fold in the ischemic group, respectively. After YS treatment, they were reduced by 76% and 70%, respectively. Western blotting and immunohistochemical assays showed that there was absent or faint H60 and RAE-1 expression in sham liver, but they were apparently increased in ischemic liver; however, the expressions were significantly decreased in the presence of YS. CONCLUSIONS: Hepatic IRI significantly increased H60 and RAE-1 expression in mouse liver. YS treatment effectively reduced this increase, seeming to attenuate NKG2D-ligand-mediated immune responses caused by IRI. This may suggest a new concept to prevent IRI and graft rejection.

Animals↗
PubMed2006

The impact of spirometry on pediatric asthma diagnosis and treatment.

Research has shown that spirometry is underutilized in the clinical setting. This study profiles the use of spirometry in an asthma management program at an inner-city community health clinic. Eligible subjects included 56 children who presented with an acute asthma exacerbation. Physicians recorded patient diagnosis before and after viewing spirometry. Bivariate and multivariate analysis was used to determine associations between symptoms and forced expiratory volume in 1 second (FEV1). Physicians changed 30.4% of patients' treatment plans after viewing spirometry results. Wheezing was significantly associated with FEV1 in bivariate analysis; however, multivariate modeling failed to identify significant relationships. The use of spirometry influenced patient diagnosis and treatment.

Acute Disease↗
PubMed2006

Henoch Schönlein purpura with nephritis in adults: adverse prognostic indicators in a UK population.

BACKGROUND: Henoch Schönlein purpura with nephritis (HSN) in adults may cause severe organ injury, but its rarity has contributed to a lack of data. AIM: To evaluate clinical outcomes and risk factors in adult HSN patients. DESIGN: Retrospective analysis. METHODS: Thirty-seven patients with adult HSN attending the Regional Vasculitis Clinic between 1974 and 2004 were assessed. For inclusion, a renal biopsy showing predominant mesangial IgA immune deposits was required, plus at least two of: purpuric rash, arthralgia, abdominal pain. RESULTS: Ten patients (27%) progressed to end-stage renal failure (ESRF). Renal failure rates were highest in the first decade, with survival rate 72% at 5 years, 68% at 10 years and 46% at final review. Risk factors for ESRF were: proteinuria > or =1 g/day during follow-up (RR 83.8, p = 0.0006); hypertension at presentation (RR = 53.3, p = 0.0045) and during follow-up (RR = 5.9, p = 0.05); renal impairment at presentation (RR 8.0, p = 0.0015); age <30 years (RR 7.6, p = 0.02); and male sex (RR = 6.0, p = 0.05). Biopsies frequently showed crescents, mostly affecting <50% of glomeruli; their presence predicted ESRF, as did interstitial fibrosis and tubular atrophy. Renal remission, in contrast, was also high (43%). Cytotoxics were used in 32%, with no clear effect on outcome. Relapses affecting the classical extra-renal systems were common, but were not associated with declines in renal function. A high proportion of patients (41%) also suffered vasculitic organ injuries outside the classical systems. DISCUSSION: HSN in adults is a serious relapsing disease, causing renal failure as frequently as in small-vessel ANCA-positive vasculitides. Prognosis and risks differed in this series from those in other countries, including a higher risk of ESRF than in previous series. Distinct groups developed either ESRF, or remitted. The absence of clear benefit suggests that corticosteroids should be reserved for patients with serious disease, and that cytotoxics may not be merited for those at high risk of renal failure.

Adolescent↗
PubMed2006

Assessment of 2 cervical screening methods in Mongolia: cervical cytology and visual inspection with acetic acid.

OBJECTIVE: The aim of the study was to evaluate the test parameters of visual inspection with acetic acid (VIA) and cervical cytology in 3 Mongolian aimags. METHODS: From February 18, 2002, to December 12, 2004, sexually active women, 30 years or older who had never been screened, underwent cervical cytology and VIA in the aimags' central hospital. Women with abnormal test results and 5% of women with normal results were recommended to have colposcopy with or without biopsy. RESULTS: Two thousand nine women underwent both tests. Visual inspection with acetic acid was abnormal in 254 (12.6%); Pap smear showed atypical squamous cells of undetermined significance or worse in 3%. Using cervical intraepithelial neoplasia 2 or higher disease on biopsy as the end point, the test parameters for VIA are sensitivity of 82.9% (95% CI = 81.3%-84.5%), specificity of 88.6% (95% CI = 87.2%-90.0%), positive predictive value of 12.2% (95% CI = 10.8%-13.6%), and negative predicative value of 99.7% (95% CI = 99.5%-99.9%). The test parameters for Pap smear are sensitivity of 88.6% (95% CI = 87.2%-90.0%), specificity of 98.5% (95% CI = 98.0%-99.0%), positive predictive value of 51.7% (95% CI = 49.5%-53.9%), and negative predicative value of 99.8% (95% CI = 99.6%-100%). CONCLUSION: Visual inspection with acetic acid has an acceptable test parameter for population-based cervical screening in Mongolia.

Acetic Acid↗
PubMed2005

Molecular characterization of marker-free transgenic lines of indica rice that accumulate carotenoids in seed endosperm.

A single Agrobacterium strain harbouring two binary plasmids was successfully used for the first time to develop a marker-free transgenic rice of improved nutritional value. Sixty-eight T0 co-transformants were obtained in three indica rice cultivars--two popular high-yielding Bangladeshi varieties (BR28 and BR29), and one high-iron rice cultivar (IR68144). Marker-free lines were obtained from 14 out of 24 selected co-transformants screened in the T1 generation. The accumulation of total carotenoids in polished T2 rice seeds of the primary transgenic VPBR29-17-37 reached levels of up to 3.0 microg/g, with the level of beta-carotene reaching 1.8 microg/g. In the cultivars BR28 and IR68144, total carotenoid levels in the transformants reached 2.0 microg/g of polished rice seeds. The levels of lutein and other carotenoids in the seeds were also significantly enhanced. T1 plants obtained from primary transgenics with simple gene-integration patterns tended to have a lower carotenoid content than the original parental lines. This study describes the development of marker-free transgenic rice lines containing high levels of carotenoids, and addresses the relationship between the rearrangement of transgenes and the presence of metabolic end products in transgenic rice.

Blotting, Southern↗
PubMed2005

Basiliximab (Simulect) reduces acute rejection among sensitized kidney allograft recipients.

AIMS: Our goal was to evaluate the efficacy and safety of basiliximab (Simulect) as immunosuppressive induction therapy for the prevention of acute allograft rejection among sensitized kidney recipients. METHODS: Fifty-six adult recipients receiving cadaveric kidney transplant with panel reactive antibody class I ranging from 30% to 50% and or class II 30% to 80% were randomized at about a 2:1 ratio to the Simulect group (36 patients) or matching control group (20 patients). All patients received baseline triple immunosuppressive therapy with cyclosporine (Neoral), mycophenolate mofetil, and steroids. Simulect was given in two doses of 20 mg each on day 0 (2 hours before operation) and day 4 after transplantation. RESULTS: There was no hyperacute rejection in either group and delayed graft function occurred in three control patients. The incidence of acute rejection during the first 3 months was 11.1% in the Simulect group compared with 50% in the placebo group (77.8% reduction, P < .01). No apparent adverse and toxic events were recorded in the Simulect group. The mean daily dose of steroids was significantly higher in the control group 2 to 4 weeks posttransplantation. No clinically meaningful differences in the mean dose of cyclosporine were observed between the two groups; in addition, there were no statistically significant differences in the rate of patient or graft survival. CONCLUSIONS: On the basis of appropriate selection of the donor and recipient, Simulect is effective and safety for the sensitized recipients as immunosuppressive induction therapy.

Acute Disease↗
PubMed2005

Birth defects in Singapore: 1994-2000.

INTRODUCTION: To study characteristics of birth defect cases among live births, stillbirths and abortions in Singapore between 1994 and 2000. METHODS: Index cases for the National Birth Defects Registry (NBDR) were obtained from all neonatal nurseries in Singapore, all hospital discharge summaries, cytogenetic and pathology reports from all pathology laboratories in Singapore, and from the compulsory reporting of all termination of pregnancy cases and stillbirths delivered. Further information was obtained from case notes retrieved from the medical record offices, antenatal clinics, cytogenetic laboratories, pathology departments and the Registry of Births and Deaths. The notified cases (live births, stillbirths and abortions) between 1994 and 2000 were extracted from the NBDR and analysed with regard to ethnicity, maternal age, trend over the seven years and types of birth defects using the British Paediatric Association Classification. RESULTS: Between 1994 and 2000, a total of 7,870 cases (6,278 births and 1,592 abortuses) were notified, giving a rate of 23.99 birth defect cases per 1000 live births. There was a decreasing trend in birth defect incidence (19.76 to 16.85 per 1,000 live births) among live births and stillbirths and an increasing trend of abortion (3.25 to 7.57 per 1,000 live births) for birth defects. Malays had a higher rate of congenital defects at birth (24.4/1,000 live births) compared to Chinese (18.4/1,000 births). The 25-29 years age group had the lowest overall rate (22.6/1,000 live births) compared to the 19 years and below group at 31.6/1,000 live births and the 45-49 years group at 126.6/1,000 live births. The five most common groups of anomalies (per 1,000 live births) were those of heart (9.07), musculoskeletal (4.98), chromosomal (4.35), urinary (3.12) and nervous systems (2.90). The five most common aborted anomalies (per 1,000 live births) were those of chromosomal (2.40), nervous (1.23), heart (0.95), musculoskeletal (0.85) and urinary systems (0.36). CONCLUSION: There was an increasing trend of abortion for birth defects, accompanied by a falling trend in the congenital anomalies of live births. Both extremes of maternal age were at higher risk of non-chromosomal birth defects while advanced maternal age was at higher risk of chromosomal defects.

Adolescent↗
PubMed2004

Galantamine and nicotine have a synergistic effect on inhibition of microglial activation induced by HIV-1 gp120.

Chronic brain inflammation is the common final pathway in the majority of neurodegenerative diseases and central to this phenomenon is the immunological activation of brain mononuclear phagocyte cells, called microglia. This inflammatory mechanism is a central component of HIV-associated dementia (HAD). In the healthy state, there are endogenous signals from neurons and astrocytes, which limit excessive central nervous system (CNS) inflammation. However, the signals controlling this process have not been fully elucidated. Studies on the peripheral nervous system suggest that a cholinergic anti-inflammatory pathway regulates systemic inflammatory response by way of acetylcholine acting at the alpha7 nicotinic acetylcholine receptor (alpha7nAChR) found on blood-borne macrophages. Recent data from our laboratory indicates that cultured microglial cells also express this same receptor and that microglial anti-inflammatory properties are mediated through it and the p44/42 mitogen-activated protein kinase (MAPK) system. Here we report for the first time the creation of an in vitro model of HAD composed of cultured microglial cells synergistically activated by the addition of IFN-gamma and the HIV-1 coat glycoprotein, gp120. Furthermore, this activation, as measured by TNF-alpha and nitric oxide (NO) release, is synergistically attenuated through the alpha7 nAChR and p44/42 MAPK system by pretreatment with nicotine, and the cholinesterase inhibitor, galantamine. Our findings suggest a novel therapeutic combination to treat or prevent the onset of HAD through this modulation of the microglia inflammatory mechanism.

Analysis of Variance↗
PubMed2004

Strongly magnetized antihydrogen and its field ionization.

Internal orbits of experimentally analyzed antihydrogen (H) atoms depend as much on an external magnetic field as on the Coulomb force. A circular "guiding center atom" model is used to understand their field ionization. This useful model, assumed in the theory of three-body H recombination so far, ignores the important coupling between internal and center-of-mass motion. A conserved pseudomomentum, effective potential, saddle point analysis, and numerical simulation show where the simple model is valid and classify the features of the general case, including "giant dipole states."

Journal Article↗
PubMed2004

Repairs of partial oblique tendon injuries: a biomechanical evaluation.

This study evaluated the tensile properties of oblique partial tendon lacerations and the effects of peripheral sutures on their strength. Seventy-four fresh pig flexor digitorum profundus tendons were divided into eight groups and were transected across 90% of their diameter. The lacerations in the tendons of five of the groups were at 0 degrees, 15 degrees, 30 degrees, 45 degrees, and 60 degrees to their transverse cross-section, respectively. In the other three groups the lacerations were 0 degrees, 45 degrees, and 60 degrees to the cross-section and were repaired with running peripheral sutures. The tendons were subjected to load-to-failure tests in a tensile testing machine to determine the initial, 1 and 2mm gap formation forces, and the ultimate strength. Obliquity of tendon lacerations affected the strength of partially lacerated tendons. The tendons with 45 degrees and 60 degrees oblique lacerations had a significantly lower ultimate strengths than those with transverse (0 degrees), or 15 degrees or 30 degrees oblique lacerations. Running peripheral sutures significantly increased both the gap formation forces and the ultimate strength of the tendons with oblique partial lacerations.

Animals↗