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Biomedical subjects

H L Tan

Publications and source records attributed to H L Tan.

At least 37 records · Page 2Linked to original sources
PubMed2001

A sodium-channel mutation causes isolated cardiac conduction disease.

Cardiac conduction disorders slow the heart rhythm and cause disability in millions of people worldwide. Inherited mutations in SCN5A, the gene encoding the human cardiac sodium (Na+) channel, have been associated with rapid heart rhythms that occur suddenly and are life-threatening; however, a chief function of the Na+ channel is to initiate cardiac impulse conduction. Here we provide the first functional characterization of an SCN5A mutation that causes a sustained, isolated conduction defect with pathological slowing of the cardiac rhythm. By analysing the SCN5A coding region, we have identified a single mutation in five affected family members; this mutation results in the substitution of cysteine 514 for glycine (G514C) in the channel protein. Biophysical characterization of the mutant channel shows that there are abnormalities in voltage-dependent 'gating' behaviour that can be partially corrected by dexamethasone, consistent with the salutary effects of glucocorticoids on the clinical phenotype. Computational analysis predicts that the gating defects of G514C selectively slow myocardial conduction, but do not provoke the rapid cardiac arrhythmias associated previously with SCN5A mutations.

Action Potentials↗
PubMed2001

Laparoscopic Anderson-Hynes dismembered pyeloplasty in children using needlescopic instrumentation.

The technique of needlescopic Anderson-Hynes dismembered pyeloplasty is discussed. The recent development of robust 3-mm needlescopic instruments designed to perform dismembered pyeloplasties has added a new dimension to laparoscopic suturing and will significantly enhance the ability to perform microanastomosis--the limiting factor preventing many surgeons from performing this technically demanding operation. The use of such fine instrumentation also reduces the size of instrument cannulae necessary, further reducing the postoperative pain and results in spectacular postoperative cosmetic appearance.

Child↗
PubMed2001

Adenosine induced ventricular arrhythmias in the emergency room.

While adenosine effectively terminates most supraventricular tachycardias (SVT), rare case reports have demonstrated its proarrhythmic potential, including induction of ventricular tachycardia (VT). The aim of this study was to define the proarrhythmic effects of adenosine in a large, unselected population. During a 5-year period, adenosine was used (average dose 9.7 mg) in the emergency room to manage 187 episodes of tachycardia in 127 patients. In two thirds of the cases, adenosine induced ventricular ectopy following successful termination of SVT, including premature ventricular complexes (PVC) and nonsustained VT. The adenosine induced PVCs and VT were transient and self-terminating. More than half had a right bundle branch block morphology with a superior axis that suggested an origin in the inferior left ventricular septum. In conclusion, although adenosine is commonly used in clinical practice to treat SVTs, we found that it induced PVCs and VT in two thirds of the patients. The high incidence of ventricular arrhythmias following adenosine infusion was surprising but did not require further intervention. These arrhythmias appeared to frequently originate from the inferior left ventricular septum, suggesting that this area may be particularly susceptible to the proarrhythmic effects of adenosine.

Adenosine↗
PubMed2000

RANK is the intrinsic hematopoietic cell surface receptor that controls osteoclastogenesis and regulation of bone mass and calcium metabolism.

We have generated RANK (receptor activator of NF-kappaB) nullizygous mice to determine the molecular genetic interactions between osteoprotegerin, osteoprotegerin ligand, and RANK during bone resorption and remodeling processes. RANK(-/-) mice lack osteoclasts and have a profound defect in bone resorption and remodeling and in the development of the cartilaginous growth plates of endochondral bone. The osteopetrosis observed in these mice can be reversed by transplantation of bone marrow from rag1(-/-) (recombinase activating gene 1) mice, indicating that RANK(-/-) mice have an intrinsic defect in osteoclast function. Calciotropic hormones and proresorptive cytokines that are known to induce bone resorption in mice and human were administered to RANK(-/-) mice without inducing hypercalcemia, although tumor necrosis factor alpha treatment leads to the rare appearance of osteoclast-like cells near the site of injection. Osteoclastogenesis can be initiated in RANK(-/-) mice by transfer of the RANK cDNA back into hematopoietic precursors, suggesting a means to critically evaluate RANK structural features required for bone resorption. Together these data indicate that RANK is the intrinsic cell surface determinant that mediates osteoprotegerin ligand effects on bone resorption and remodeling as well as the physiological and pathological effects of calciotropic hormones and proresorptive cytokines.

Animals↗
PubMed2000

Osteoprotegerin inhibits tumor-induced osteoclastogenesis and bone tumor growth in osteopetrotic mice.

Osteoprotegerin and osteoprotegerin ligand have recently been identified as novel proteins that inhibit and stimulate, respectively, osteoclast formation. We examined the possibility that osteoprotegerin would inhibit cancer-induced osteoclastogenesis and cancer growth in bone. An experimental model was used in which osteolytic tumors are known to stimulate osteoclastogenesis and grow in femora of osteoclast-deficient mice (op/op). Osteoprotegerin treatment decreased the number of osteoclasts by 90% (p < 0.0007) at sites of tumor in a dose-dependent manner and decreased bone tumor area by greater than 90% (p < 0.003). The mechanisms through which osteoprotegerin decreased osteoclast formation in tumor-bearing animals included (a) an osteoprotegerin-mediated, systemic reduction in the number of splenic and bone marrow-residing osteoclast precursor cells, (b) a decrease in the number of osteoclast precursor cells at sites of tumor as detected by cathepsin K and receptor activator of NFkappaB mRNA expression, and (c) a decrease in osteoprotegerin ligand mRNA at sites of tumor. These findings suggest that osteoprotegerin treatment, in addition to having direct antagonistic effects on endogenous osteoprotegerin ligand, decreases the number of osteoclast precursors and reduces production of osteoprotegerin ligand at sites of osteolytic tumor.

Animals↗
PubMed2000

Ectopic pancreatic rests: a rare cause of persistent umbilical discharge.

Ectopic pancreatic rests are rare. We report two cases discovered in infants who underwent surgical exploration of the umbilicus for persistent umbilical discharge with peri-umbilical excoriation. A shallow sinus leading to a firm cyst was excised in both infants, and histopathological study confirmed the presence of exocrine and endocrine pancreatic tissue. There is only one other case of ectopic umbilical pancreatic tissue reported, and this was in a patient presenting with an umbilical mass.

Choristoma↗
PubMed2000

Osteoprotegerin ligand modulates murine osteoclast survival in vitro and in vivo.

Osteoprotegerin ligand (OPGL) targets osteoclast precursors and osteoclasts to enhance differentiation and activation, however, little is known about OPGL effects on osteoclast survival. In vitro, the combination of OPGL + colony-stimulating factor-1 (CSF-1) is required for optimal osteoclast survival. Ultrastructurally, apoptotic changes were observed in detached cells and culture lysates exhibited elevated caspase 3 activity, particularly in cultures lacking CSF-1. DEVD-FMK (caspase 3 inhibitor) partially protected cells when combined with OPGL, but not when used alone or in combination with CSF-1. CSF-1 maintained NF-kappaB activation and increased the expression of bcl-2 and bcl-X(L) mRNA, but had no effect on JNK activation. In contrast, OPGL enhanced both NF-kappaB and JNK kinase activation and increased the expression of c-src, but not bcl-2 and bcl-X(L) mRNA. These data suggest that aspects of both OPGL's and CSF-1's signaling/survival pathways are required for optimal osteoclast survival. In mice, a single dose of OPG, the OPGL decoy receptor, led to a >90% loss of osteoclasts because of apoptosis within 48 hours of exposure without impacting osteoclast precursor cells. Therefore, OPGL is essential, but not sufficient, for osteoclast survival and endogenous CSF-1 levels are insufficient to maintain osteoclast viability in the absence of OPGL.

Animals↗
PubMed2000

Economic cost of male erectile dysfunction using a decision analytic model: for a hypothetical managed-care plan of 100,000 members.

OBJECTIVE: This paper examined the economic cost of male erectile dysfunction (ED) for a hypothetical managed-care (MC) model. DESIGN AND SETTING: A prevalence-based cost-of-illness approach was used to estimate the direct medical cost for ED treatment. A treatment plan algorithm was developed from a MC perspective to model the initial treatment selection of various patient groups [vacuum erection device, intracavernosal injection (ICI) therapy, transurethral alprostadil suppository, sildenafil, testosterone replacement therapy, penile prosthesis] and their therapy outcomes during a 3-year period. Overall cost was based on 1998 US dollars. Total direct medical cost of ED considered in this model included the cost of initial physician consultation and evaluation, the cost incurred by patients from various treatment groups (pharmacological and surgical options), as well as the cost related to patients' follow-up for treatment within the 3-year period. Consideration for therapy switches made by patients who failed initial therapy was included as part of the clinical assumptions for this model. Treatment response and expected outcomes (dropouts) were considered for the various treatment options. PARTICIPANTS: A total of 100,000 enrolled members were included in the study. MAIN OUTCOME MEASURES AND RESULTS: The total cost of ED was $US3,204,792 for the 3-year period in the hypothetical MC plan. The treatment portion accounted for approximately 80% of the total cost while the cost of medical services and diagnostic tests were minimal in comparison. The 3 year total cost of nonsurgical treatment was $US2,473,045. Costs associated with each treatment alternative were $US81,866 (testosterone transdermal patch), $US51,930 (vacuum erection device), $US384,624 (ICI therapy), $US226,483 (transurethral alprostadil suppository) and $US1,728,142 (sildenafil citrate). Results from the model showed a noticeable trend of decreasing cost patterns over time and reflected the attrition observed for many of the standard medical therapies for ED. CONCLUSIONS: Sildenafil and the vacuum erection device should be considered as first-line management strategies for ED whereas ICI therapy, transurethral alprostadil suppository and penile prosthesis implant should be reserved for second- or third-line therapy. Because costs associated with switches related to successive treatment failures can be high, treatment considerations should, therefore, focus on achieving long term patient satisfaction. The patient's preferred treatment choice, using goal-directed therapy during the initial consultation and evaluation visit, should be used.

Adult↗
PubMed1999

Tumor necrosis factor receptor family member RANK mediates osteoclast differentiation and activation induced by osteoprotegerin ligand.

A receptor that mediates osteoprotegerin ligand (OPGL)-induced osteoclast differentiation and activation has been identified via genomic analysis of a primary osteoclast precursor cell cDNA library and is identical to the tumor necrosis factor receptor (TNFR) family member RANK. The RANK mRNA was highly expressed by isolated bone marrow-derived osteoclast progenitors and by mature osteoclasts in vivo. Recombinant OPGL binds specifically to RANK expressed by transfected cell lines and purified osteoclast progenitors. Transgenic mice expressing a soluble RANK-Fc fusion protein have severe osteopetrosis because of a reduction in osteoclasts, similar to OPG transgenic mice. Recombinant RANK-Fc binds with high affinity to OPGL in vitro and blocks osteoclast differentiation and activation in vitro and in vivo. Furthermore, polyclonal Ab against the RANK extracellular domain promotes osteoclastogenesis in bone marrow cultures suggesting that RANK activation mediates the effects of OPGL on the osteoclast pathway. These data indicate that OPGL-induced osteoclastogenesis is directly mediated through RANK on osteoclast precursor cells.

Animals↗
PubMed1999

OPGL is a key regulator of osteoclastogenesis, lymphocyte development and lymph-node organogenesis.

The tumour-necrosis-factor-family molecule osteoprotegerin ligand (OPGL; also known as TRANCE, RANKL and ODF) has been identified as a potential osteoclast differentiation factor and regulator of interactions between T cells and dendritic cells in vitro. Mice with a disrupted opgl gene show severe osteopetrosis and a defect in tooth eruption, and completely lack osteoclasts as a result of an inability of osteoblasts to support osteoclastogenesis. Although dendritic cells appear normal, opgl-deficient mice exhibit defects in early differentiation of T and B lymphocytes. Surprisingly, opgl-deficient mice lack all lymph nodes but have normal splenic structure and Peyer's patches. Thus OPGL is a new regulator of lymph-node organogenesis and lymphocyte development and is an essential osteoclast differentiation factor in vivo.

Animals↗
PubMed1999

Laparoscopic Anderson-Hynes dismembered pyeloplasty in children.

PURPOSE: The feasibility and results of laparoscopic Anderson-Hynes dismembered pyeloplasty in children were evaluated. MATERIALS AND METHODS: All laparoscopic Anderson-Hynes pyeloplasties performed by the author were retrospectively reviewed. A total of 18 children 3 months to 15 years old (mean age 17 months) with proved ureteropelvic junction obstruction underwent laparoscopic Anderson-Hynes dismembered pyeloplasty between August 1994 and June 1998. Of the 18 pyeloplasties 15 were performed in children who had not undergone previous upper tract surgery, and 3 had undergone previous upper tract surgery, including laparoscopic pyeloplasty in 2 and emergency percutaneous nephrostomy drainage of pyonephrosis 6 weeks earlier in 1. All operations were performed via a transperitoneal route. RESULTS: Postoperative evaluation is complete in 16 patients and pending in 2. Of the 16 patients 14 (87%) have no demonstrable evidence of obstruction. Two patients with persistent obstruction underwent repeat laparoscopic pyeloplasty. There was no conversion to open surgery. Mean operative time was 89 minutes. In 1 patient trocar hematoma resolved with bed rest. In another case the stent was misplaced with its distal end reaching the lower ureter, and was removed via ureteroscopy 6 weeks postoperatively. There was no other operation related morbidity. CONCLUSIONS: Laparoscopic Anderson-Hynes pyeloplasty represents an attractive alternative to conventional open pyeloplasty. It is technically challenging but with practice it may be completed in the same time as conventional open pyeloplasty. It offers results approaching those of conventional dismembered pyeloplasty.

Adolescent↗
PubMed1999

Effects of adenosine A1-receptor activation on torsade de pointes in rabbits.

PURPOSE: We tested whether the adenosine A1 receptor agonist, R-PIA, suppressed torsade de pointes (TdP) induced by the delayed rectifier potassium channel blocker clofilium. Furthermore, we studied the underlying mechanism: beta-adrenergic antagonism or ATP-sensitive K+ channel (IK-ATP) opening. METHODS: In anesthetized rabbits, TdP was induced by simultaneous infusion of clofilium and the alpha1-adrenoceptor agonist methoxamine. Four groups were studied: (1) saline infusion after TdP induction; (2) R-PIA (1.3 mg/kg) infusion; (3) R-PIA infusion after propranolol (2 micromol/kg) pretreatment; (4) R-PIA infusion after glibenclamide (10 micromol/kg) pretreatment. RESULTS: TdP suppression rate was 0% in group 1, 78% in group 2 (p<0.01 vs. group 1), 67% in group 3 (p<0.05 vs. group 1, p = NS vs. group 2), 33% in group 4 (p = NS vs. group 1, p = 0.08 vs. group 2). TdP induction coincided with increased QT/QTc duration and QT dispersion. TdP suppression coincided with reduced QT dispersion, but further QT/QTc lengthening. CONCLUSIONS: R-PIA suppressed TdP, not by beta-adrenergic antagonism, but mostly by IK-ATP opening. QT dispersion correlated better with TdP induction/suppression than QT/QTc duration.

Adenosine↗
PubMed1999

Risk of gonadoblastoma in female patients with Y chromosome abnormalities and dysgenetic gonads.

We report two female patients with gonadal dysgenesis and sex chromosome mosaicism involving the Y chromosome. Conventional karyotyping was supplemented with fluorescent in situ hybridisation techniques in order to confirm the presence of Y chromosomes. One patient is a phenotypic female with karyotype 45,X/46,X,idic(Y)(q11.2). She underwent a laparoscopic gonadectomy at which streak ovaries without evidence of gonadoblastoma were removed. The second patient presented as a virilised female with karyotype 45,X/47,XYY. At laparoscopy, she was found to have mixed gonadal dysgenesis with a gonadoblastoma in situ. We recommend early gonadectomy in female children presenting with gonadal dysgenesis and the presence of a Y chromosome although once the gonadoblastoma locus on Y chromosome gene has been cloned it may be possible to identify those patients who have a low risk of developing gonadoblastoma.

Child, Preschool↗
PubMed1999

Laparoscopy as the investigation and treatment of choice for urinary incontinence caused by small 'invisible' dysplastic kidneys with infrasphincteric ureteric ectopia.

OBJECTIVE: To report our experience of using laparoscopy for the accurate location and simultaneous removal of small dysplastic kidneys with ectopic ureteric insertion causing urinary incontinence and that were not detected by conventional imaging modalities. PATIENTS AND METHODS: Seven girls (mean age 7.9 years, range 3.5-13) presented with urinary leakage occurring between normal voids. Imaging studies including ultrasonography, renal scintigraphy, intravenous urography, computed tomography and/or magnetic resonance imaging in six of the seven patients revealed a single normal functioning kidney, but failed to detect the contralateral nonfunctioning dysplastic kidney. All patients were examined under anaesthesia, followed by transperitoneal laparoscopy for the simultaneous localization and removal of the dysplastic kidneys under the same setting. RESULTS: Laparoscopy in all seven patients revealed a small dysplastic kidney that could always be easily located by first finding the draining ureter over the iliac vessels and then following it upwards. Four dysplastic kidneys were found in the renal fossa (two left, two right). One kidney was found at the left iliac fossa just above the pelvic brim, one at the left lumbar region, and the other at the right iliac fossa. Laparoscopic nephroureterectomy was successful in all seven girls and the patients were discharged 48 h after surgery. The follow-up (mean 2.7 years, range 3 months-5.4 years) showed excellent cosmetic results and all the patients have remained completely dry. CONCLUSIONS: In patients with a classical picture of urinary incontinence caused by infrasphincteric ureteric ectopia associated with a small nonfunctioning kidney, video-laparoscopy, with its magnifying effect, can reliably confirm the diagnosis, locate the dysplastic kidney and allow its removal in the same setting. We propose that laparoscopy should be considered the investigation and treatment of choice in such patients, and should be undertaken without delay even if the dysplastic kidney or the ectopic ureteric orifice cannot be identified with all other conventional means.

Adolescent↗