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Biomedical subjects

C C Yip

Publications and source records attributed to C C Yip.

At least 19 recordsLinked to original sources
PubMed2003

Traumatic eye injuries due to large unusual foreign bodies: a Singapore case series.

PURPOSE: Traumatic eye injuries due to large foreign bodies (FB) are rare. The visual prognosis is often poor in these cases because of severe ocular damage. Staged surgical procedures with eventual enucleation or evisceration are often indicated. METHODS: Case series. RESULTS: The authors describe two patients with eye injury due to large FB with visual acuity of no light perception at presentation. Both had initial repair of the ocular injuries and removal of the FB. One patient with an intraocular FB eventually underwent enucleation; the other, with intraorbital FB, had evisceration as a secondary procedure. Orbital implantations were done in both. Neither of the patients had developed sympathetic ophthalmia at the last review. CONCLUSIONS: The visual outcome of eye injuries due to large FB is poor. Both enucleation and evisceration can be performed with low risk of sympathetic ophthalmia. Prevention remains the best approach to such devastating injuries.

Adult↗
PubMed2002

Lacrimal sac tumour presenting with blood-stained ocular discharge.

Malignant epithelial tumours of the lacrimal sac are uncommon. They can mimic chronic dacryocystitis or dacryostenosis to cause a delay in diagnosis. The presence of a medial canthal lump with blood-stained ocular discharge should arouse the suspicion of this diagnosis. The prognosis of lacrimal sac tumour is often guarded especially following tumour recurrence after incomplete resection. We report a patient with squamous cell carcinoma of the lacrimal sac to highlight its presentation and clinical course.

Adult↗
PubMed2001

A randomized double-masked crossover study comparing latanoprost 0.005% with unoprostone 0.12% in patients with primary open-angle glaucoma and ocular hypertension.

PURPOSE: To compare the intraocular pressure)-lowering effect and side effects of latanoprost 0.005% once daily with unoprostone 0.12% twice daily. METHODS: Sixty patients with primary open-angle glaucoma or ocular hypertension were randomized to receive either latanoprost once daily in the evening and placebo once daily in the morning, or unoprostone twice daily in the morning and evening. The study was double masked and followed a crossover design with two treatment periods of 1 month separated by a 3-week washout period. The intraocular pressure was measured at 9 AM and 5 PM on the baseline and day 28 visits, and at 9 AM on day 2 and day 14 visits of each treatment period. The 9 AM measurement was taken 2 hours and 13 hours after the last drop of unoprostone and latanoprost, and the 5 PM measurement was at 10 and 21 hours, respectively. The mean of the measurements was calculated. Safety parameters were also recorded. RESULTS: Fifty-six patients completed both treatment periods and had intraocular pressure data available for evaluation. After 1 month of treatment, latanoprost significantly reduced intraocular pressure (mean +/- SEM) by 6.1 +/- 0.5 mm Hg (P <.001) and unoprostone by 4.2 +/- 0.4 mm Hg (P <.001) adjusted from an overall baseline of 22.3 +/- 0.5 mm Hg and 23.2 +/- 0.4 mm Hg, respectively. The difference of 1.9 mm Hg between treatments was statistically significant in favor of latanoprost [P =.003, analysis of covariance (ANCOVA)]. Unadjusted analysis of responders using the percentage decrease in intraocular pressure showed that the proportion of responders in the latanoprost-treated group was greater than in the unoprostone-treated group. Adverse ocular symptoms and findings were mild in both treatment groups. Eye redness and ocular irritation were the most frequently reported events. CONCLUSIONS: Latanoprost once daily was significantly more effective in reducing intraocular pressure compared with unoprostone twice daily after 1 month of treatment in patients with primary open-angle glaucoma and ocular hypertension. Both drugs were well tolerated with few ocular adverse events.

Adult↗
PubMed2001

Herpes zoster ophthalmicus and the superior orbital fissure syndrome.

Herpes Zoster Ophthalmicus (HZO) is not an uncommon condition in the elderly and the immunocompromised. The common ocular manifestations include blepharoconjunctivitis, keratitis and uveitis. Dramatic presentations like orbital apex syndrome and superior orbital fissure syndromes occur rarely in patients with herpes zoster meningo-encephalitis. We report a patient with herpes zoster meningo-encephalitis and the superior orbital fissure syndrome (SOFS).

Anisocoria↗
PubMed2000

Mechanism of transmembrane signaling: insulin binding and the insulin receptor.

Transmembrane signaling via receptor tyrosine kinases generally requires oligomerization of receptor monomers, with the formation of ligand-induced dimers or higher multimers of the extracellular domains of the receptors. Such formations are expected to juxtapose the intracellular kinase domains at the correct distances and orientations for transphosphorylation. For receptors of the insulin receptor family that are constitutively dimeric, or those that form noncovalent dimers without ligands, the mechanism must be more complex. For these, the conformation must be changed by the ligand from one that prevents activation to one that is permissive for kinase phosphorylation. How the insulin ligand accomplishes this action has remained a puzzle since the discovery of the insulin receptor over 2 decades ago, primarily because membrane proteins in general have been refractory to structure determination by crystallography. However, high-resolution structural evidence on individual separate subdomains of the insulin receptor and of analogous proteins has been obtained. The recently solved quaternary structure of the complete dimeric insulin receptor in the presence of insulin has now served as the structural envelope into which such individual domains were fitted. The combined structure has provided answers on the details of insulin/receptor interactions in the binding site and on the mechanism of transmembrane signaling of this covalent dimer. The structure explains many observations on the behavior of the receptor, from greater or lesser binding of insulin and its variants, point and deletion mutants of the receptor, to antibody-binding patterns, and to the effects on basal and insulin-stimulated autophosphorylation under mild reducing conditions.

Cell Communication↗
PubMed2000

Comparison of the intraocular pressure-lowering effect of latanoprost and timolol in patients with chronic angle closure glaucoma: a preliminary study.

OBJECTIVE: To compare the intraocular pressure (IOP)-reducing effect and side effects of 0.005% latanoprost once daily to 0.5% timolol twice daily in patients with primary chronic angle closure glaucoma (CACG). DESIGN: Randomized, double-masked two-center clinical trial. PARTICIPANTS: Thirty-two Asian patients with CACG, defined as glaucomatous optic neuropathy with a compatible visual field defect and at least 6 clock hours of synechial angle closure on gonioscopy were recruited. All patients had previous peripheral iridotomy (PI) with IOP >21 mmHg after PI and were thereafter controlled (IOP <22 mmHg) with one or two pressure-reducing drugs. INTERVENTION: After a washout period, the patients were randomized to a 2-week treatment period with either placebo in the morning and 0.005% latanoprost in the evening or 0.5% timolol twice daily. MAIN OUTCOME MEASURES: The short-term IOP reduction of latanoprost and timolol in patients with CACG. IOP was measured at baseline, and after 2, 7, and 14 days of treatment. In addition, the short-term ocular and systemic adverse events of the two drugs were evaluated. RESULTS: Thirty patients completed the study. Two patients in the timolol group were withdrawn because of inadequate IOP control. Compared with baseline, the IOP after 2 weeks of treatment was statistically significantly reduced by 8.8 +/- 1.1 mmHg (mean +/- SEM, P < 0.001) in the latanoprost group, and by 5.7 +/- 0.9 mmHg (P < 0.001) in the timolol group. The difference in IOP reduction between the two treatment groups was 3.1 +/- 1.5 mm Hg in favor of latanoprost (P = 0.04). The main ocular adverse events reported in both treatment groups were conjunctival hyperemia and discomfort. CONCLUSIONS: In this preliminary study, a significantly greater IOP reduction was achieved with 0.005% latanoprost once daily compared with 0.5% timolol twice daily in patients with CACG. The results suggest that latanoprost may be a therapeutic choice for the medical treatment of primary CACG.

Adrenergic beta-Antagonists↗
PubMed2000

Ocular decompression retinopathy after resolution of acute primary angle closure glaucoma.

A patient presented with acute primary angle closure glaucoma with markedly elevated intraocular pressure. Two weeks after laser peripheral iridotomy and resolution of the acute attack, the patient was noted to have developed scattered retinal haemorrhages. The haemorrhages resolved over time with no visual sequelae. This is the first reported case of ocular decompression retinopathy after resolution of acute primary angle closure glaucoma.

Acute Disease↗
PubMed2000

The correction of oriental lower lid involutional entropion using the combined procedure.

INTRODUCTION: Involutional entropion is a common lid malposition problem in the Chinese geriatric population. The major contributing factors of involutional entropion include disinsertion of the lower lid retractors and horizontal lid laxity. The combined procedure (lower lid retractor repair and lateral tarsal strip procedure) is a useful technique that tackles both the horizontal and vertical aetiologic components of this condition. The surgical technique of this procedure is described and the results and complications presented. MATERIALS AND METHODS: A retrospective non-randomised study on 41 lower eyelids of 38 Chinese patients. The combined procedure was performed by a single surgeon over a 2 years 11 months period. Nine patients had bilateral lid surgeries. The clinical charts and operative notes were reviewed by an observer. RESULTS: The mean age of the patients was 74.7 years (range 51 to 92 years). There were 14 males (36.8%) and 24 females (63.2%). The cases were followed up postoperatively for a mean duration of 13 months (range 3 to 48 months). Twelve lids had early postoperative overcorrection but the majority (8 lids) resolved spontaneously with good lid-globe apposition. Of the remaining 4 eyelids, 3 lids had persistent mild asymptomatic ectropion that did not require surgical treatment and only one required re-operation. CONCLUSION: The combined procedure is an effective means of repair for oriental lower lid entropion with low complication rates.

Age Factors↗
PubMed1999

Quaternary structure of the insulin-insulin receptor complex.

The three-dimensional (3D) structure of the intrinsically dimeric insulin receptor bound to its ligand, insulin, was determined by electron cryomicroscopy. Gold-labeled insulin served to locate the insulin-binding domain. The 3D structure was then fitted with available known high-resolution domain substructures to obtain a detailed contiguous model for this heterotetrameric transmembrane receptor. The 3D reconstruction indicates that the two alpha subunits jointly participate in insulin binding and that the kinase domains in the two beta subunits are in a juxtaposition that permits autophosphorylation of tyrosine residues in the first step of insulin receptor activation.

Binding Sites↗
PubMed1998

Direct force measurements of insulin monomer-monomer interactions.

Direct measurement of the forces involved in protein-protein and protein-receptor interactions can, in principle, provide insight necessary for the advancement of structural biology, molecular biology, and the development of therapeutic proteins. The protein insulin is illustrative in this respect as the mechanisms of insulin dimer dissociation and insulin-insulin receptor binding are crucial to the efficacy of insulin medications for the control of diabetes. Insulin molecules, modified with a photochemically active azido functionality on specific residues, were attached to force microscope tips and opposing mica surfaces in configurations that would either favor or disfavor dimer formation. Force curve measurements performed in buffer solution revealed the complexity of the insulin monomer-monomer interaction with multiple unbinding events occurring upon tip retraction, suggesting disruption of discrete molecular bonds at the monomer-monomer interface. Furthermore, the force curves exhibit long-range unbinding events, consistent with considerable elongation of the insulin molecule prior to dissociation. The unbinding forces observed in this study are the result of a combination of molecular disentanglement and dimer dissociation processes.

Aluminum Silicates↗
PubMed1998

High-pressure paint gun injury to the orbit and ocular adnexa.

High-pressure injection injury to the orbit and adnexa is a rare but potentially blinding type of trauma. Few cases of such injury have been reported in the literature. A 27-year-old Indian man accidentally injected paint material from a high-pressure nozzle gun into his left eye. Radiological investigation revealed the presence of paint material in the orbital tissues and the ethmoidal sinuses. The patient underwent two orbital surgeries to remove the paint material. He later developed signs suggestive of limbal stem cell failure and was treated with limbal stem cell autografting. He also has ophthalmoplegia with a compensatory anomalous head posture that was managed conservatively. We report the clinical course and outcome of this unfortunate patient to highlight the complexity of such an injury and the need for a multidisciplinary approach in its management.

Adult↗
PubMed1997

The surgical management of an advanced pterygium involving the entire cornea.

PURPOSE: Conjunctival autografting is a well-established surgical procedure to prevent recurrence after pterygium excision. We described a modified technique of harvesting an annular autograft to cover a large conjunctival defect after excision of an extensive primary pterygium that involved three quadrants of the limbus. METHODS: A 73-year-old Chinese farmer underwent an excision of an advanced right pterygium involving the entire cornea. A free donor graft was then harvested from the remaining superior bulbar conjunctiva to cover the conjunctival defect, which involved approximately-three quadrants of limbus. The undersized graft was split down the center to create an annular graft to cover the defect. RESULTS: Postoperatively, there has been no recurrence over a total follow-up period of 11 months. Six months after the initial pterygium surgery, he underwent a successful penetrating keratoplasty for residual deep stromal scarring. Visual acuity 5 months after the penetrating keratoplasty remained stable at 6/18. CONCLUSIONS: This case report shows that a modified technique of conjunctival autografting can be successful in preventing recurrence in an advanced pterygium after excision. Successful visual rehabilitation with a penetrating keratoplasty also was demonstrated in this patient.

Aged↗
PubMed1995

A novel guanylyl cyclase-A isoform: rat GC-A1 identification and mRNA localization to renal papilla and adrenal.

Natriuretic peptides modulate systemic blood pressure, diuresis and natriuresis through the stimulation of cGMP production by guanylyl cyclase-coupled natriuretic peptide receptor-A and -B (GC-A and GC-B). A novel isoform of GC-A, GC-A1, has been identified which is the result of differential splicing of a new exon, 5a. This 9 bp sequence is predicted to add proline-cysteine-glutamine to the extracellular juxtamembrane region of the receptor protein. Transcripts for GC-A1 are expressed primarily in the renal papilla and adrenal. In these tissues, its abundance relative to GC-A was 1-2.5% as assessed by quantitative PCR.

Adrenal Glands↗
PubMed1995

Functional characterization of hybrid receptors composed of a truncated insulin receptor and wild type insulin-like growth factor 1 or insulin receptors.

To assess the characteristics of hybrid receptors composed of one kinase-inactive alpha beta-insulin half-receptor and one endogenous alpha beta-insulin-like growth factor 1 (IGF-1) or insulin half-receptor, a cell line expressing an insulin receptor truncated by 365 amino acids (HIR delta 978) was studied, which lacks most of the cytoplasmic beta-subunit. Analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis under nonreducing conditions revealed four distinct receptor species: endogenous receptors, the more rapidly migrating HIR delta 978 homodimer, and two intermediate species representing HIR delta 978/IGF-1 hybrid receptors and HIR delta 978/IR hybrid receptors. In vivo ligand-binding affinity of the hybrid receptors was studied by receptor-ligand cross-linking, and the delta 978/IGF-1R hybrid receptor was found to have a high affinity for IGF-1, whereas its affinity for insulin was low. Autophosphorylation studies of lectin-purified receptors revealed that neither the HIR delta 978 holoreceptor nor the hybrid receptors underwent autophosphorylation in response to either ligand, despite the presence of intact IGF-1 or insulin half-receptors in the hybrids. Neither hybrid receptor underwent ligand-induced endocytosis, as assessed with the bioactive photoaffinity probes B2(2-nitro-4-azidophenylacetyl)-des-PheB1-insulin and N-epsilon B28-monoazidobenzoyl-IGF-1. In conclusion, the HIR delta 978/IGF-1R hybrid receptor has a high in vivo affinity for IGF-1 but not for insulin. Neither the delta 978/IGF-1R nor the delta 978/IR hybrids undergo autophosphorylation or ligand-induced endocytosis in response to either ligand, indicating that intramolecular trans-, rather than cis-, signal transduction is important in mediating autophosphorylation and endocytosis.

Animals↗
PubMed1994

Unusual insulin binding to cells expressing an insulin receptor mutated at cysteine 524.

The involvement of cysteine 524 of the insulin receptor in an intermolecular (class I) disulfide bond between the two alpha-subunits was investigated using site-directed mutagenesis. The oligomeric structure of the mutated receptor was partially disrupted, although a significant portion of the receptor remained in its heterotetrameric form. Interestingly, the mutated insulin receptor heterotetramer was more susceptible than the wildtype receptor to reduction to heterodimers by low concentrations of dithiothreitol. Insulin binding to solubilized mutant receptors was normal and the mutant receptors had normal affinity for insulin, but insulin binding to cells expressing mutant insulin receptors displayed positive cooperativity. Cysteine 524 is most likely involved in a class I disulfide bond and receptors mutated at this site displayed unusual insulin binding properties only in the cellular environment.

Amino Acids↗
PubMed1994

Dithiothreitol stimulates insulin receptor autophosphorylation at the juxtamembrane domain.

Autophosphorylation of insulin receptors from human placental membranes prepared with iodoacetamide was more than double that of control receptors prepared without iodoacetamide. Dithiothreitol (DTT) treatment of control receptors prepared without iodoacetamide resulted in increased autophosphorylation. However, DTT was without effect on insulin receptors prepared with iodoacetamide. Phosphopeptide analysis showed that while 32P-labeling of all of the phosphopeptides was increased in insulin receptors from membranes prepared with iodoacetamide, two additional phosphopeptides were detected and identified as deriving from the juxtamembrane domain, containing tyrosine residue 960. Similar results were produced by DTT treatment of control insulin receptors. These observations suggest that a thiol(s) may be involved in insulin receptor autophosphorylation in the juxtamembrane domain.

Dithiothreitol↗
PubMed1994

Rodent insulin receptors are immunologically different from other mammalian insulin receptors.

Four monoclonal antibodies (MA-5, MA-10, MA-20, and MA-51) and one polyclonal antibody (ARS-2) against human insulin receptor were used to immunoprecipitate the insulin receptor from several species which had been photolabeled with N epsilon B29-monoazido-benzoyl-[125I]iodoinsulin. All four monoclonal antibodies immunoprecipitated human insulin receptor from human placental membranes. MA-10 and MA-51, but not MA-5 or MA-20, immunoprecipitated insulin receptors from liver plasma membranes of rabbit, guinea pig, dog, cattle, pig, and chicken. None of the monoclonal antibodies immunoprecipitated insulin receptors of rat, mouse, hamster, or chinchilla. In contrast, all of the insulin receptors were immunoprecipitated by the polyclonal anti-insulin receptor antibody, ARS-2. MA-10 and MA-51 compared with [125I]iodoinsulin for binding to guinea pig and rabbit liver plasma membranes in a fashion similar to insulin, although less effectively. MA-51 also mimicked the action of insulin by stimulating lipogenesis and autophosphorylation of the insulin receptor beta subunit in isolated rabbit adipocytes. The results suggest that insulin receptors of mammals, other than rodent, share with human insulin receptor the same epitope(s) recognized by MA-10 and MA-51. Rodent insulin receptors, with the exception of guinea pig, are different. We speculate that the difference lies in the amino acid sequence 485-599 of the alpha subunit of the insulin receptor.

Adipose Tissue↗