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Biomedical subjects

T Kwan

Publications and source records attributed to T Kwan.

At least 19 recordsLinked to original sources
PubMed2002

Transplantation of EGF-responsive neurospheres from GFP transgenic mice into the eyes of rd mice.

The isolation of stem cells from various regions of the central nervous system has raised the possibility of using them as a donor cell source for cell transplantation, where they offer great promise for repair of the diseased brain, spinal cord, and retina. Here, we have studied the migration, integration, and differentiation of EGF-responsive neurospheres isolated from the brains of green fluorescent protein transgenic mice and transplanted into the eyes of mature rd mice, a model of retinitis pigmentosa. While grafts of freshly isolated postnatal day 8 retina expressed many markers characteristic of mature retina (e.g. rhodopsin, protein kinase C), very few of the grafted cells migrated into host retina. EGF-responsive neurospheres, conversely, readily migrated into and integrated with the remaining host retina, but showed a very limited ability to differentiate into mature retinal neurons. While the progenitor cells used here show remarkable ability to integrate with host retina and develop some attributes of retinal cells, the failure to fully differentiate into retinal cells suggests that they already express some level of terminal commitment that precludes using them to replace lost photoreceptors.

Animals↗
PubMed2001

The cell adhesion molecule BEN defines a prosensory patch in the developing avian otocyst.

The distribution of the cell adhesion molecule BEN in the developing chick inner ear is described. BEN is first detected in the otic placode at stage 11. As the placode begins to invaginate, BEN becomes concentrated in a ventromedial region extending from the anterior to the posterior end of the otic pit. BEN expression levels increase in this region as the pit closes to form the otocyst, and distinct boundaries become defined along the dorsal and ventral edges of the ventromedial band of BEN expression. BEN expression also becomes concentrated dorsally within the otic epithelium as the pit closes and is observed in the condensing otic ganglion. By stage 22, the ventromedial band of BEN expression splits into two distinct regions, a small caudal patch within which the posterior crista will develop, and a larger anterior patch. By stage 26, this larger anterior patch of cells expressing BEN becomes subdivided into five separate areas corresponding to the regions within which the anterior crista, the lateral crista, the utricle, the saccule, and both the basilar papilla and lagenar macula form. Hair cells only develop within these regions defined by BEN distribution. The data suggest that the ventromedial patch of BEN expression observed from stage 11 onwards defines a single sensory competent zone from which all sensory organs of the inner ear develop. BEN immunoreactivity in the inner ear declines after stage 38. In response to noise exposure, upregulation of BEN expression is mainly detected in regions of the posthatch papilla where the damage is severe and regenerating hair cells are not observed. The regenerating hair and supporting cells do not express BEN, highlighting a molecular difference between the processes of development and regeneration.

Activated-Leukocyte Cell Adhesion Molecule↗
PubMed2001

Giant cells in pyoderma gangrenosum.

It has been claimed that pyoderma gangrenosum (PG) lesions may contain granulomatous foci when associated with Crohn's disease. To test this assertion, we obtained clinical histories and archived cutaneous biopsies from 34 PG patients. Thirteen of these patients had inflammatory bowel disease (IBD). Immunostaining with PGM1, a macrophage marker, revealed well-formed giant cells with three or more nuclei in biopsies from 6 of 13 patients with IBD. Five of the 6 biopsies came from patients with Crohn's disease and one from a patient with ulcerative colitis. Two were peristomal. In the 21 patients who had PG without IBD, no giant cells were seen. Thus, PGM1+ histiocytic giant cells within a PG lesion may be indicative of associated IBD (p = 0.006), particularly Crohn's disease.

Crohn Disease↗
PubMed2000

Muscle-specific transcriptional regulation of the slowpoke Ca(2+)-activated K(+) channel gene.

Transcriptional regulation of the Drosophila slowpoke calcium-activated potassium channel gene is complex. To date, five transcriptional promoters have been identified, which are responsible for slowpoke expression in neurons, midgut cells, tracheal cells, and muscle fibers. The slowpoke promoter called Promoter C2 is active in muscles and tracheal cells. To identify sequences that activate Promoter C2 in specific cell types, we introduced small deletions into the slowpoke transcriptional control region. Using transformed flies, we asked how these deletions affected the in situ tissue-specific pattern of expression. Sequence comparisons between evolutionarily divergent species helped guide the placement of these deletions. A section of DNA important for expression in all cell types was subdivided and reintroduced into the mutated control region, a piece at a time, to identify which portion was required for promoter activity. We identified 55-, 214-, and 20-nucleotide sequences that control promoter activity. Different combinations of these elements activate the promoter in adult muscle, larval muscle, and tracheal cells.

Animals↗
PubMed2000

Successful percutaneous stenting of a right gastroepiploic coronary bypass graft using monorail delivery system: a case report.

The right gastroepiploic artery (RGEA) is being successfully used as an arterial conduit in a selected group of patients undergoing coronary artery bypass graft surgery. However, myocardial ischemia may result due to spasm, occlusion, and stenosis of this graft. The anastamosis site at distal right coronary artery (RCA) or posterior descending artery (PDA) is the most common location for stenosis of an in situ gastroepiploic coronary bypass graft. Balloon angioplasty of such stenoses has been reported with optimal short-term results. Stent deployment would decrease the restenosis rate, so that repeat procedures could be minimized for these technically challenging lesions. We describe a case of successful deployment of a stent with monorail delivery system at the anastamotic site stenosis of an in situ gastroepiploic right coronary artery bypass graft. This percutaneous coronary intervention could prevent redo coronary artery bypass graft surgery. Cathet. Cardiovasc. Intervent. 49:197-199, 2000.

Angioplasty, Balloon, Coronary↗
PubMed2000

Parotid oncocytoma in the Birt-Hogg-Dubé syndrome.

Birt-Hogg-Dubé syndrome consists of fibrofolliculomas, trichodiscomas, and acrochordons and has been associated with several noncutaneous tumors. We report the first case of Birt-Hogg-Dubé syndrome in association with a parotid oncocytoma, a rare salivary gland tumor.

Adenoma, Oxyphilic↗
PubMed2000

Functional analysis of a tryptophan-less P-glycoprotein: a tool for tryptophan insertion and fluorescence spectroscopy.

P-glycoprotein (Pgp) functions as an ATP-dependent drug efflux pump to confer multidrug resistance to tumor cells. In the absence of a high-resolution structure for this protein, several important and intriguing aspects of Pgp structure and function remain poorly understood. Fluorescence spectroscopy of endogenous or genetically engineered tryptophan residues represents a potentially powerful method to probe static and dynamic aspects of Pgp at high resolution. We have used site-directed mutagenesis to modify the wild-type (WT) mouse mdr3 Pgp for tryptophan fluorescence spectroscopy by replacement of all 11 tryptophan residues individually with phenylalanine. None of the 11 tryptophans were found to be absolutely essential for Pgp activity, because Chinese hamster ovary cells transfected and overexpressing this mutant Trp-less mdr3 cDNA (mdr3F(1-11)) become multidrug-resistant and can carry out active transport of vinblastine, colchicine, and Calcein-AM. The mdr3F(1-11) mutant has reduced activity compared with WT Mdr3, and shows a unique pattern of drug resistance clearly distinct from WT and, as opposed to the latter, can neither confer FK-506 resistance nor functionally complement ste6 in yeast. Studies with Pgp mutants containing either single or double tryptophan residues or with chimeric molecules constructed between wild-type Pgp and mdr3F(1-11) indicated that no single tryptophan residue was responsible for the reduced activity of the mdr3F(1-11) mutant. Likewise, all but one chimeric Pgp preserved the unique drug resistance profile of the mdr3F(1-11) mutant. Altogether, we show that a Trp-less Pgp is functionally active and can be used as a molecular backbone for insertion of tryptophans in strategic locations to probe various aspects of Pgp function.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2000

Successful percutaneous balloon mitral valvuloplasty using left ventricular pressure as a guide to cross the mitral valve--a case report.

Percutaneous balloon mitral valvuloplasty (PBMV) provides an effective alternative to surgery in a selective group of patients with symptomatic mitral stenosis. The Inoue balloon technique involves transseptal catheterization followed by catheter manipulation to cross the mitral valve. The authors describe a case of successful percutaneous balloon mitral valvuloplasty in a patient with severe mitral stenosis and pulmonary hypertension. Left ventricular systolic pressure was used as a guide to locate and to advance the balloon catheter across the mitral valve. This technique to cross the mitral valve has not been reported in the literature.

Adult↗
PubMed2000

Percutaneous coronary intervention as a bridge to renal transplantation in a patient with end-stage renal disease--a case report.

Renal transplantation is one of the preferred modes of replacement therapy in patients with end-stage renal disease. Cardiovascular disease remains the leading cause of morbidity and mortality in patients with end-stage renal disease and renal transplant recipients. The authors describe a patient with end-stage renal disease who developed unstable angina before renal transplantation. Emergent cardiac catheterization and percutaneous coronary intervention served as a bridge to his successful renal transplantation without complications.

Angina, Unstable↗
PubMed2000

Paravalvular regurgitation: a rare complication following valve replacement surgery.

Paravalvular regurgitation is an uncommon but important complication, usually following valve replacement surgery. Early recognition and management are important for reoperations are associated with high morbidity and mortality rates. Presently, little data are available on this topic. The authors review the subject.

Aortic Valve Insufficiency↗
PubMed1999

ST-T alternans and myocardial ischemia.

Previous studies using intracoronary electrocardiography have demonstrated that ST-T alternans can develop during standard balloon coronary angioplasty. Total occlusion with a large amount of myocardium in jeopardy is the postulated prerequisite. In this study, the authors used perfusion balloons instead of standard balloons, so coronary perfusion was maintained and ischemia was minimized. Fourteen patients with standard balloon technique and 11 patients with perfusion balloon technique were studied. The ST segment was less elevated during perfusion angioplasty (0.15 +/- 0.05 mV vs 1.04 +/- 0.19 mV, p<0.001). There were six (43%) patients with ST-T alternans with standard balloon technique compared with none in the perfusion balloon group (p<0.001). In this study, the authors found that there was less ischemia, less ST segment elevation, and lack of ST-T alternans on the intracoronary electrocardiogram during perfusion balloon angioplasty. These findings support the postulate that a large amount of ischemic myocardium is a prerequisite for ST-T alternans.

Adult↗
PubMed1999

Successful percutaneous balloon mitral valvuloplasty in a patient with left atrial thrombus--a case report.

Percutaneous balloon mitral valvuloplasty (PBMV) described by Inoue et al, is a safe FDA (Food and Drug Administration) approved procedure in patients with severe mitral stenosis. One of the contraindications of the procedure is presence of a left atrial thrombus; however, it has been reported that intense warfarin therapy may led to dissolution of the thrombus. The authors report a patient who was referred for PBMV and was found to have a left atrial thrombus. After intense warfarin therapy, successful PBMV was undertaken without complications.

Anticoagulants↗
PubMed1999

Coronary artery aneurysms, aortic dissection, and hypertension secondary to primary aldosteronism: a rare triad. A case report.

Primary aldosteronism is a relatively uncommon etiology of hypertension. Plasma renin activity is suppressed in the majority of the cases but not always. Plasma renin activity has been associated with increased vascular injury. The occurrence of vascular complications has rarely been reported with low plasma renin activity. The authors report a case of long-standing secondary hypertension due to primary aldosteronism with coronary artery aneurysms and aortic dissection. Diagnosing is important, for therapeutic intervention can be curative.

Adrenal Cortex Neoplasms↗
PubMed1999

Successful transcatheter closure of a patent ductus arteriosus: using two Gianturco coils in a 41-year-old woman. A case report.

Patent ductus arteriosus (PDA) is a form of congenital heart disease uncommonly diagnosed in adult patients. Transcatheter closure of PDA has been widely used in children. However, the experience is limited in adults especially with use of Gianturco coils. The authors describe a case of successful transcatheter closure of a PDA, incidentally diagnosed in a 41-year-old woman, by successively deploying two coils by a transarterial approach. No residual shunting was seen angiographically after the procedure. A literature review of similar procedures in adult patients is discussed.

Adult↗
PubMed1999

Regression of large atrial thrombi and coronary neovascularizations with conventional anticoagulation in mitral stenosis--a case report.

The authors report a case of angiographically documented multiple coronary neovascularizations originating from the left circumflex artery (LCX) and coursing toward multiple thrombi located in the left atrium in a patient with severe mitral stenosis. The thrombi as well as the neovascularizations underwent near-complete resolution with 4 weeks' anticoagulation therapy with warfarin maintaining an international normalization ratio of 3.5. Percutaneous mitral balloon valvuloplasty was performed successfully without complications.

Anticoagulants↗