Biomedical subjects
Raymond W M Ng
Publications and source records attributed to Raymond W M Ng.
Elimination of palatal fistula after the maxillary swing procedure.
BACKGROUND: The maxillary swing procedure has been used as an anterolateral approach to expose the nasopharynx, the central skull base, and its vicinity. The reported incidence of postoperative palatal fistula has ranged from 20% to 25%. The oronasal incompetence especially associated with a large fistula has adversely affected normal speech, eating, and swallowing functions. We describe a modified palatal incision to reduce the incidence of palatal fistula associated with the maxillary swing procedure. METHODS: Fifteen consecutive patients who underwent maxillary swing procedures for salvage resection of recurrent nasopharyngeal carcinoma after radiotherapy had the modified palatal incision. The flap was raised as described, and the outcome was analyzed. RESULTS: Fourteen patients' palatal wound healed uneventfully. One patient experienced partial flap necrosis, which healed with conservative treatment. All 15 patients tolerated oral feeding 1 week after the surgery. No palatal fistulas occurred. CONCLUSION: The modified palatal incision as described has effectively prevented palatal fistula formation after the maxillary swing procedure.
Endoscopic sural nerve harvesting for facial nerve reconstruction.
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Insertion of Provox2 voice prosthesis using the anterograde technique immediately after the secondary tracheoesophageal puncture.
Insertion of a voice prosthesis through the tracheoesophageal puncture (TEP) is one way to restore the voice after total laryngectomy. The second generation Provox voice prosthesis is presently one of the most popular devices. Although TEP can be done primarily, there are many centres that prefer it to be done at a second stage for various reasons. However, secondary TEP for retrograde replacement of prosthesis can be difficult and general anaesthesia is very often necessary. Moreover, the presence of neck stiffness and fibrosis from the surgery or previous radiotherapy could affect the neck extension for proper positioning of the trocar. Similarly, it is difficult to insert the prosthesis if there is stenosis at the pharyngoesophageal segment. We describe a technique in which creation of secondary TEP and insertion of Provox2 is done with local anaesthesia under the same setting. The procedure is well tolerated and can be safely performed on an out-patient basis.
Quantitative analysis of plasma cell-free Epstein-Barr virus DNA in nasopharyngeal carcinoma after salvage nasopharyngectomy: a prospective study.
BACKGROUND: The quantity of circulating cell-free Epstein-Barr virus (EBV) DNA in patients with nasopharyngeal carcinoma (NPC) managed by radiotherapy has prognostic relevance. We measured the copy number of EBV DNA in patients with early recurrent NPC before and after salvage nasopharyngectomy. METHODS: Nasopharyngectomy with the maxillary swing approach was performed for 28 patients. Serum blood samples were taken prospectively before nasopharyngectomy and on postoperative day 7. Plasma cell-free EBV DNA copies were measured with a real-time quantitative polymerase chain reaction for the BamHI-W fragment of the EBV genome. RESULTS: Cell-free EBV DNA was detected in 17 patients before nasopharyngectomy. Surgical resection reduced the copy number of EBV DNA significantly (p = .016). Negative surgical margins achieved during nasopharyngectomy is associated with a zero EBV DNA copy postoperatively (p = .022). CONCLUSION: Cell-free EBV DNA was detected in 61% of patients with recurrent NPC, and its quantity postoperatively reflects whether the salvage nasopharyngectomy has achieved a negative surgical margin.
Pharyngeal entry through the vallecula.
The authors describe a technique of entry into the vallecula with the guide of a small Deaver retractor inserted transorally, beyond the tongue base, into the vallecula. The tip of the Deaver directs the surgeon to the pharyngotomy site and allows pharyngeal entry and access without damaging structures in the region. This technique is particularly useful in total laryngectomy with or without pharyngectomy and is applicable whenever entry to the pharynx through the vallecula is indicated.
Differential expression, localization and activity of two alternatively spliced isoforms of human APC regulator CDH1.
The timely destruction of key regulators through ubiquitin-mediated proteolysis ensures the orderly progression of the cell cycle. The APC (anaphase-promoting complex) is a major component of this degradation machinery and its activation is required for the execution of critical events. Recent studies have just begun to reveal the complex control of the APC through a regulatory network involving WD40 repeat proteins CDC20 and CDH1. In the present paper, we report on the identification and characterization of human CDH1beta, a novel alternatively spliced isoform of CDH1. Both CDH1alpha and CDH1beta can bind to the APC and stimulate the degradation of cyclin B1, but they are differentially expressed in human tissues and cells. CDH1alpha contains a nuclear localization signal which is absent in CDH1beta. Intracellularly, CDH1alpha appears in the nucleus whereas CDH1beta is a predominantly cytoplasmic protein. The forced overexpression of CDH1alpha in cultured cells correlates with the reduction of nuclear cyclin A, but the steady-state amount of cyclin A does not change noticeably in CDH1beta-overexpressed cells. In Xenopus embryos, ectopic overexpression of human CDH1alpha, but not of CDH1beta, induces cell-cycle arrest during the first G(1) phase at the mid-blastula transition. Taken together, our findings document the differential expression, subcellular localization and cell-cycle-regulatory activity of human CDH1 isoforms.
Aesthetic considerations in the cervicofacial management of Madelung syndrome.
The most common concern in patients with Madelung syndrome who are seeking cosmetic improvement is the deposition of fat in the cervicofacial region. Surgical experience in a series of 15 patients was summarised to provide guidelines for a rational approach to a better aesthetic outcome. The records and clinical photographs of these patients were reviewed. Outcome was assessed in terms of adequacy of debulking, final overall symmetry, smoothness of contour, prominence of scar, and necessity for multiple sessions. Open excision was the preferred primary treatment. A long mid-neck, transverse skin crease incision provided good exposure and was superior to multiple local incisions. Other surgical details worth noting include subplatysmal dissection, thick skin flaps, dissection around instead of into lipomas, appropriate removal of redundant skin, adequate reduction of tumour size instead of total excision, haemostasis, suction drainage, and layered skin closure. Liposuction was a useful adjunct for contouring the sides of the jaws in selected patients.
Safe tracheostomy for patients with severe acute respiratory syndrome.
OBJECTIVES/HYPOTHESIS: Severe acute respiratory syndrome (SARS) caused by coronavirus has become an epidemic affecting many regions worldwide. Fourteen percent to 20% of patients require endotracheal intubation and ventilator support. Some of these patients may require tracheostomy subsequently. This procedure, when performed without protection, may lead to infection of the medical and nursing staff taking care of the patient. STUDY DESIGN: Based on clinical information of three patients. METHODS: The authors carried out an emergency tracheostomy and changed the tracheostomy tube for one patient and performed elective tracheostomy in another two patients. RESULTS: No medical or nursing staff member was infected after carrying out the procedure while taking all the precautions and wearing the appropriate protective apparel. CONCLUSION: The authors have prepared guidelines for performing a safe tracheostomy under both elective and emergency conditions. Surgeons who might be involved in performing the tracheostomy should become familiar with these guidelines and the appropriate protective apparel.
Post-activation turn-off of NF-kappa B-dependent transcription is regulated by acetylation of p65.
NF-kappaB represents a family of eukaryotic transcription factors participating in the regulation of various cellular genes involved in the immediate early processes of immune, acute-phase, and inflammatory responses. Cellular localization and consequently the transcriptional activity of NF-kappaB is tightly regulated by its partner IkappaBalpha. Here, we show that the p65 subunit of NF-kappaB is acetylated by both p300 and PCAF on lysines 122 and 123. Both HDAC2 and HDAC3 interact with p65, although only HDAC3 was able to deacetylate p65. Acetylation of p65 reduces its ability to bind kappaBeta-DNA. Finally, acetylation of p65 facilitated its removal from DNA and consequently its IkappaBetaalpha-mediated export from the nucleus. We propose that acetylation of p65 plays a key role in IkappaBetaalpha-mediated attenuation of NF-kappaBeta transcriptional activity which is an important process that restores the latent state in post-induced cells.
The APC regulator CDH1 is essential for the progression of embryonic cell cycles in Xenopus.
The orderly progression of cell cycle depends on timely destruction of key regulators through ubiquitin-mediated proteolysis. The anaphase-promoting complex (APC) is a major component of this degradation machinery and its activation is regulated by CDC20 and CDH1. We demonstrate here that CDH1 mRNA is ubiquitously expressed in Xenopus embryos of all developmental stages. Loss of CDH1 function during early embryonic cell cycles leads to an immediate and prolonged arrest with low cyclin-dependent kinase activity. In contrast, ectopic overexpression of CDH1 induces cell cycle arrest during the first G(1) phase at the midblastula transition. CDH1-dependent degradation of cyclin A is likely involved in this G(1) arrest. Our findings establish the essential roles of CDH1 in embryonic cell cycles.
Significance of MAD2 expression to mitotic checkpoint control in ovarian cancer cells.
Chromosome instability is a commonly observed feature in ovarian carcinoma. Mitotic checkpoint controls are thought to be essential for accurate chromosomal segregation, and MAD2 is a key component of this checkpoint. In this study, we investigated the competence of the mitotic checkpoint and its relationship to the expression of MAD2 protein in seven ovarian cancer cell lines. We found that a significant number (43%, three of seven cell lines) of the tested ovarian cancer cells failed to arrest in the G(2)-M phase of the cell cycle in response to microtubule disruption. This loss of mitotic checkpoint control was associated with reduced expression of the MAD2 protein. To additionally understand the significance of the MAD2 to mitotic checkpoint control, we established an inducible expression system in which MAD2 was induced by the addition of ponasterone A. Notably, the induced expression of MAD2 in two checkpoint-defective ovarian cancer cell lines led to the restoration of mitotic checkpoint response to spindle-disrupting agents. Taken together, our findings suggest that the steady-state amount of MAD2 inside cells may represent a molecular switch for mitotic checkpoint control. This provides a novel insight into the molecular basis of CIN in ovarian carcinoma and has implications for effective use of checkpoint-targeting drugs.
Microvascular free tissue reconstruction following extirpation of head and neck tumour: experience towards an optimal outcome.
Familiarity with four types of free tissues transfers allows appropriate reconstruction of most defects in the head and neck region functionally and aesthetically. These include jejunal graft, radial forearm, rectus abdominus myocutaneous and fibula osteocutaneous flaps. Free colonic and gastric patches were used occasionally. We report our experience of 215 free tissue transfers for reconstruction of defects in the head and neck region after tumour extirpation. The overall success rate was 94 per cent. The commonest cause of failure was related to arterial inflow (70 per cent). Three patients died in hospital, but their mortality was not related to the tissue transfers. Complications due to free tissue transfer at both the donor and recipient sites were few and manageable. The co-operation between the two surgical teams, together with the timely application of suitable salvage procedures, contribute to an optimal outcome.
Cooperation of yeast peroxiredoxins Tsa1p and Tsa2p in the cellular defense against oxidative and nitrosative stress.
Peroxiredoxins are a family of antioxidant enzymes conserved from bacteria to humans. In Saccharomyces cerevisiae, there exist five peroxiredoxins, among which Tsa2p shares striking homology with the well described Tsa1p but has not been extensively studied. Here we report on the functional characterization of yeast tsa2Delta mutants and the comparison of TSA1 with TSA2. The tsa2Delta and tsa1Delta tsa2Delta cells grew normally under aerobic conditions. However, the tsa1Delta tsa2Delta mutant yeast was more susceptible to oxidants than either tsa1Delta or tsa2Delta cells. Notably, the tsa1Delta tsa2Delta yeast was also hypersensitive to peroxynitrite and sodium nitroprusside. This phenotype was rescued by the expression of either the TSA1 or TSA2 gene. The demonstration of a peroxynitrite reductase activity of Tsa2p in vitro points to a pivotal role for peroxiredoxins in the protection against nitrosative stress. In yeast cells, Tsa1p and Tsa2p exhibited comparable antioxidant activity. While the basal expression level of TSA1 was significantly higher than that of TSA2, the transcription of TSA2 was stimulated more potently by various oxidants. In addition, TSA2 was activated in tsa1Delta cells in a Yap1p-dependent manner. Taken together, our findings implicate the cooperation of Tsa1p and Tsa2p in the cellular defense against reactive oxygen and nitrogen species.