Biomedical subjects

Karen Wong

Publications and source records attributed to Karen Wong.

13 recordsLinked to original sources

PubMed2006

Boc is a receptor for sonic hedgehog in the guidance of commissural axons.

In the spinal cord, sonic hedgehog (Shh) is secreted by the floor plate to control the generation of distinct classes of ventral neurons along the dorsoventral axis. Genetic and in vitro studies have shown that Shh also later acts as a midline-derived chemoattractant for commissural axons. However, the receptor(s) responsible for Shh attraction remain unknown. Here we show that two Robo-related proteins, Boc and Cdon, bind specifically to Shh and are therefore candidate receptors for the action of Shh as an axon guidance ligand. Boc is expressed by commissural neurons, and targeted disruption of Boc in mouse results in the misguidance of commissural axons towards the floor plate. RNA-interference-mediated knockdown of Boc impairs the ability of rat commissural axons to turn towards an ectopic source of Shh in vitro. Taken together, these data suggest that Boc is essential as a receptor for Shh in commissural axon guidance.

Animals↗

PubMed2006

Bacterial expression of functional, biotinylated peripheral cannabinoid receptor CB2.

A biotin-protein ligase recognition site (BRS) was inserted into a polypeptide comprised of the maltose-binding protein, the peripheral cannabinoid receptor (CB2), thioredoxin A, and a polyhistidine tag at the carboxy terminus. Expression levels of the recombinant receptor in Escherichia coli BL21(DE3) cells were approximately 1mg per liter of bacterial culture. The biotinylated CB2-fusion fully retained its ligand-binding capacity. Introduction of the BRS at the C-terminus of the CB2 fusion protein (construct CB2-109) resulted in its complete in vivo biotinylation; the biotinylated protein was streptavidin-binding competent. Positioning of the BRS near the N-terminus of CB2 (CB2-112) resulted in a very low level of biotinylation in vivo. However, the detergent solubilized and purified CB2-112 fusion protein were successfully biotinylated in vitro by action of a BirA biotin-protein ligase. The biotinylated CB2-112 fusion protein was cleaved by the tobacco etch virus protease at specifically inserted sites, and deposited onto monomeric avidin agarose beads. Biotinylation of the recombinant CB2 receptor enabled not only purification but also immobilization of the GPCR on a solid support in homogeneous orientation which is beneficial for subsequent structural characterization.

Binding, Competitive↗

PubMed2006

Assessing cognitive function in cancer patients.

GOALS OF WORK: Some patients with cancer suffer cognitive impairment after chemotherapy. A brief, sensitive instrument is required to screen patients for cognitive impairment. In this study, we compare three possible screening instruments. MATERIALS AND METHODS: Cancer patients (n=31) who had received adjuvant chemotherapy within 2 years underwent cognitive evaluation on three occasions. Fluent English speakers (n=20) completed the High Sensitivity Cognitive Screen (HSCS), the computer-based Headminder and CogHealth, and the Functional Assessment of Cancer Therapy-cognitive function (FACT-COG) questionnaire. Patients not fluent in English (NESB) (n=11) performed CogHealth and Headminder. RESULTS: The patients were aged 31-65 years, and 94% were women with breast cancer. At baseline, 6 of 20 (30%) had moderate-severe cognitive impairment on HSCS, 17 of 31 (55%) had scores greater than one standard deviation (SD) below the mean for normative data in one to two of three domains on Headminder, and on CogHealth, 8 of 31 (26%) were greater than one SD below the mean in at least two of six domains. A large practice effect was seen for the HSCS, with moderate-severe cognitive impairment decreasing from 30 to 5% between the first and second assessment. On FACT-COG, 9 of 19 patients (47%) rated their cognition as greater than one SD below that of a pre-chemotherapy breast cancer control group, with impact on quality of life greater than one SD below for 10 of 19 (53%) patients. No correlation was seen between objective cognitive testing and the FACT-COG. CONCLUSIONS: CogHealth and Headminder were suitable for NESB patients. The HSCS is not recommended for longitudinal studies with short intervals between testing due to practice effect. There is poor correlation between the patients' perception of their cognitive impairment and the objective tests.

Adult↗

PubMed2006

The diversity of liver diseases among outpatient referrals for an elevated serum ferritin.

BACKGROUND: The aim of the present study was to examine the diversity of liver diseases in outpatients referred because of elevated serum ferritin. METHODS: A retrospective review was performed of outpatient referrals for serum ferritin elevations made to a tertiary care centre liver clinic between 1999 and 2005. Information regarding serum ferritin, transferrin saturation, liver biopsy, liver iron concentration and final diagnosis was extracted. Patients were stratified into two groups based on ferritin concentration: ferritin concentration 300 microg/L to 1000 microg/L, and ferritin concentration greater than 1000 microg/L. RESULTS: A total of 482 charts were reviewed, of which 119 (25%) had ferritin concentrations greater than 1000 microg/L. HFE-linked hemochromatosis, nonalcoholic steatohepatitis and alcohol-related liver disease were the top three diagnoses. HFE-linked hemochromatosis accounted for 28% to 42% of the diagnoses in all subgroups. The percentage of patients diagnosed with HFE-linked hemochromatosis was similar in the ferritin 300 microg/L to 1000 microg/L and the ferritin greater than 1000 microg/L groups (P = 0.067). Among patients with ferritin greater than 1000 microg/L, 63% underwent a liver biopsy. Of those with an elevated liver iron concentration (greater than 35 micromol/g dry weight), 71% had a transferrin saturation greater than 50% (88% of C282Y homozygotes and 43% of non-C282Y homozygotes). In non-C282Y homozygotes with an elevated serum ferritin concentration greater than 1000 microg/L, 64% did not have iron overload on liver biopsy. CONCLUSION: HFE-linked hemochromatosis accounted for less than one-half of the diagnoses in an outpatient population referred for elevated ferritin, suggesting a need to search further for an alternate cause.

Ambulatory Care↗

PubMed2006

Colour contrast influences perceived shape in combined shading and texture patterns.

The 'colour-shading effect' describes the phenomenon whereby a chromatic pattern influences perceived shape-from-shading in a luminance pattern. Specifically, the depth corrugations perceived in sinusoidal luminance gratings can be enhanced by spatially non-aligned, and suppressed by spatially aligned sinusoidal chromatic gratings. Here we examine whether colour contrast can influence perceived shape in patterns that combine shape-from-shading with shape-from-texture. Stimuli consisted of sinusoidal modulations of texture (defined by orientation), luminance and colour. When the texture and luminance modulations were suitably combined, one obtained a vivid impression of a corrugated depth surface. The addition of a colour grating to the texture-luminance combination was found to enhance the impression of depth when out-of-phase with the luminance modulation, and suppress the impression of depth when in-phase with the luminance modulation. The degree of depth enhancement and depth suppression was approximately constant across texture amplitude when measured linearly. In the absence of the luminance grating however, the colour grating had no phase-dependent affect on perceived depth. These results show that colour contrast modulates the contribution of shading to perceived shape in combined shading and texture patterns.

Color Perception↗

PubMed2006

A comparison of continuous and bi-level positive airway pressure non-invasive ventilation in patients with acute cardiogenic pulmonary oedema: a meta-analysis.

INTRODUCTION: We conducted the present study to investigate the potential beneficial and adverse effects of continuous positive airway pressure (CPAP) compared with bi-level positive airway pressure (BiPAP) noninvasive ventilation in patients with cardiogenic pulmonary oedema. METHOD: We included randomized controlled studies comparing CPAP and BiPAP treatment in patients with cardiogenic pulmonary oedema from the Cochrane Controlled Trials Register (2005 issue 3), and EMBASE and MEDLINE databases (1966 to 1 December 2005), without language restriction. Two reviewers reviewed the quality of the studies and independently performed data extraction. RESULTS: Seven randomized controlled studies, including a total of 290 patients with cardiogenic pulmonary oedema, were considered. The hospital mortality (relative risk [RR] 0.76, 95% confidence interval [CI] 0.32-1.78; P = 0.52; I2 = 0%) and risk for requiring invasive ventilation (RR 0.80, 95% CI 0.33-1.94; P = 0.62; I2 = 0%) were not significantly different between patients treated with CPAP and those treated with BiPAP. Stratifying studies that used either fixed or titrated pressure during BiPAP treatment and studies involving patients with or without hypercapnia did not change the results. The duration of noninvasive ventilation required until the pulmonary oedema resolved (weighted mean difference [WMD] in hours = 3.65, 95% CI -12.12 to +19.43; P = 0.65, I2 = 0%) and length of hospital stay (WMD in days = -0.04, 95% CI -2.57 to +2.48; P = 0.97, I2 = 0%) were also not significantly different between the two groups. Based on the limited data available, there was an insignificant trend toward an increase in new onset acute myocardial infarction in patients treated with BiPAP (RR 2.10, 95% CI 0.91-4.84; P = 0.08; I2 = 25.3%). CONCLUSION: BiPAP does not offer any significant clinical benefits over CPAP in patients with acute cardiogenic pulmonary oedema. Until a large randomized controlled trial shows significant clinical benefit and cost-effectiveness of BiPAP versus CPAP in patients with acute cardiogenic pulmonary oedema, the choice of modality will depend mainly on the equipment available.

Acute Disease↗

PubMed2005

Gene targeting using a promoterless gene trap vector ("targeted trapping") is an efficient method to mutate a large fraction of genes.

A powerful tool for postgenomic analysis of mammalian gene function is gene targeting in mouse ES cells. We report that homologous recombination using a promoterless gene trap vector ("targeting trapping") yields targeting frequencies averaging above 50%, a significant increase compared with current approaches. These high frequencies appear to be due to the stringency of selection with promoterless constructs, because most random insertions are silent and eliminated by drug selection. The promoterless design requires that the targeted gene be expressed in ES cells at levels exceeding a certain threshold (which we estimate to be approximately 1% of the transferrin receptor gene expression level, for the secretory trap vector used here). Analysis of 127 genes that had been trapped by random (nontargeted) gene trapping with the same vector shows that virtually all are expressed in ES cells above this threshold, suggesting that targeted and random trapping share similar requirements for expression levels. In a random sampling of 130 genes encoding secretory proteins, about half were expressed above threshold, suggesting that about half of all secretory genes are accessible by either targeted or random gene trapping. The simplicity and high efficiency of the method facilitate systematic targeting of a large fraction of the genome by individual investigators and large-scale consortia alike.

Animals↗

PubMed2005

Generalized seizure and toxic epidermal necrolysis following levofloxacin exposure.

OBJECTIVE: To report the case of a ciprofloxacin-allergic patient who developed a generalized tonic-clonic seizure and toxic epidermal necrolysis (TEN) following a single dose of levofloxacin. CASE SUMMARY: An 87-year-old white woman was admitted to the hospital following a transient episode of unresponsiveness that had been accompanied by flailing of her limbs. Approximately 4 hours earlier, she had developed a pruritic rash on her trunk and limbs, and 3 hours before this had taken a first dose of levofloxacin. The fluoroquinolone had been prescribed for treatment of an upper respiratory tract infection. She had developed a skin rash approximately 3 years earlier following ciprofloxacin prescribed for a urinary tract infection. On admission, the patient had a normal neurologic examination. She was mildly hypomagnesemic (serum magnesium 1.7 mg/dL), with no other electrolyte imbalances present. Skin biopsy confirmed TEN. The lesions progressed to involve 30% of the body surface area and were managed with polymyxin B and gramicidin cream. Levofloxacin was discontinued on admission, and no anticonvulsants were prescribed. The woman remained seizure-free at discharge one week later. DISCUSSION: Generalized tonic-clonic seizures are a rare complication of levofloxacin therapy. TEN following levofloxacin use has, to our knowledge, as of March 28, 2005, been previously reported only once. The seizure and TEN were probably induced by levofloxacin as corroborated by the Naranjo probability scale. We believe that the previous adverse dermatologic reaction to ciprofloxacin sensitized our patient to levofloxacin. CONCLUSIONS: These rare adverse reactions to levofloxacin, involving disparate organ systems, can occur simultaneously. A previous dematologic adverse reaction to a fluoroquinolone can sensitize a patient to more severe adverse reactions (with onset after only a single dose of the subsequent fluoroquinolone). Further fluoroquinolone use should be avoided in such patients.

Aged↗

PubMed2005

12-hour versus 24-hour creatinine clearance in critically ill pediatric patients.

Measurement of renal function is important to optimize drug dosing in critically ill pediatric patients and to prevent dose-related toxicities caused by medications that are eliminated or metabolized by the kidney. In clinical practice, the 24-h creatinine clearance (CrCl) is used as a surrogate marker of renal function. However, a 24-h urine collection period delays the availability of the result and increases the potential for collection errors. This prospective, observational study was performed to determine whether a 12-h CrCl is comparable to the traditional 24-h CrCl and to assess whether CrCl could be reliably predicted by the Schwartz equation, which mathematically estimates a child's GFR. A 24-h urine sample was collected in two 12-h aliquots from 60 catheterized critically ill children (age 2 d to 18 y). CrCl and Schwartz glomerular filtration rate (GFR) estimates were determined for each 12- and 24-h period. Agreement between 12- and 24-h CrCl and between CrCl and Schwartz GFR estimates was assessed using intraclass correlation coefficients (ICCs). An ICC > or =0.8 was considered to indicate excellent agreement. The ICC between the first 12-h CrCl and 24-h CrCl was 0.9605. The ICC between the second 12-h CrCl and 24-h CrCl was 0.9602. The ICC between the 24-h CrCl and Schwartz GFR was only 0.7046. All comparisons of 12- and 24-h CrCl indicated excellent agreement. In summary, the Schwartz equation was not a reliable estimate of renal function in critically ill children, and a 12-h CrCl is just as accurate as the standard 24-h CrCl to assess renal function and guide drug dosing.

Adolescent↗

PubMed2005

A point mutation in the iron-responsive element of the L-ferritin in a family with hereditary hyperferritinemia cataract syndrome.

BACKGROUND: Hereditary hyperferritinemia cataract syndrome is an autosomal dominant condition that is characterized by a high serum ferritin level and bilateral early-onset cataracts in the absence of iron overload. The genetic abnormality is identified as a mutation in the 5' regulatory region of the L-ferritin messenger RNA known as the iron-responsive element (IRE). The IRE controls ferritin synthesis in response to cytoplasmic iron pools by interacting with regulatory proteins called iron responsive proteins. Mutations in the IRE decrease its affinity for iron responsive proteins, leading to the constitutive synthesis of L-ferritin which results in hyperferritinemia and the intracellular accumulation of ferritin in the lens and eventual cataract formation. PATIENTS AND METHODS: A 22-year-old woman who was being investigated for hyperferritinemia was diagnosed with hereditary hyperferritinemia cataract syndrome after an extensive workup, including genetic testing for hemochromatosis and a liver biopsy to rule out iron overload. She developed anemia with phlebotomy treatments and subsequently developed symptomatic cataracts. The pedigree of her family affected with cataracts was consistent with an autosomal dominant transmission pattern. DNA was extracted from peripheral leukocytes of eight family members, four of whom were affected by cataracts. Polymerase chain reaction amplification of the 5' region of the L-ferritin gene was performed and a heterozygous point mutation (G32T) was identified in the bulge region of the IRE. CONCLUSION: The combination of early-onset cataracts and an elevated ferritin level should suggest this genetic syndrome.

Adult↗

PubMed2004

Comparing gene discovery from Affymetrix GeneChip microarrays and Clontech PCR-select cDNA subtraction: a case study.

BACKGROUND: Several high throughput technologies have been employed to identify differentially regulated genes that may be molecular targets for drug discovery. Here we compared the sets of differentially regulated genes discovered using two experimental approaches: a subtracted suppressive hybridization (SSH) cDNA library methodology and Affymetrix GeneChip technology. In this "case study" we explored the transcriptional pattern changes during the in vitro differentiation of human monocytes to myeloid dendritic cells (DC), and evaluated the potential for novel gene discovery using the SSH methodology. RESULTS: The same RNA samples isolated from peripheral blood monocyte precursors and immature DC (iDC) were used for GeneChip microarray probing and SSH cDNA library construction. 10,000 clones from each of the two-way SSH libraries (iDC-monocytes and monocytes-iDC) were picked for sequencing. About 2000 transcripts were identified for each library from 8000 successful sequences. Only 70% to 75% of these transcripts were represented on the U95 series GeneChip microarrays, implying that 25% to 30% of these transcripts might not have been identified in a study based only on GeneChip microarrays. In addition, about 10% of these transcripts appeared to be "novel", although these have not yet been closely examined. Among the transcripts that are also represented on the chips, about a third were concordantly discovered as differentially regulated between iDC and monocytes by GeneChip microarray transcript profiling. The remaining two thirds were either not inferred as differentially regulated from GeneChip microarray data, or were called differentially regulated but in the opposite direction. This underscores the importance both of generating reciprocal pairs of SSH libraries, and of real-time RT-PCR confirmation of the results. CONCLUSIONS: This study suggests that SSH could be used as an alternative and complementary transcript profiling tool to GeneChip microarrays, especially in identifying novel genes and transcripts of low abundance.

Dendritic Cells↗

PubMed2003

Dose surgical sub-specialization influence survival in patients with colorectal cancer?

AIM: To perform a review of patients with colorectal cancer to a community hospital and to compare the risk-adjusted survival between patients managed in general surgical units versus a colorectal unit. METHODS: The study evaluated all patients with colorectal cancer referred to either general surgical units or a colorectal unit from 1/1996 to 6/2001. These results were compared to a historical control group treated within general surgical units at the same hospital from 1/1989 to 12/1994. A Kaplan-Meier survival analysis compared the overall survivals (all-cause mortality) between the groups. A Cox proportional hazards model was used to determine the influence of a number of independent variables on survival. These variables included age, ASA score, disease stage, emergency surgery, adjuvant chemotherapy and/or radiotherapy, disease location, and surgical unit. RESULTS: There were 974 patients involved in this study. There were no significant differences in the demographic details for the three groups. Patients in the colorectal group were more likely to have rectal cancer and Stage I cancers, and less likely to have Stage II cancers. Patients treated in the colorectal group had a significantly higher overall 5-year survival when compared with the general surgical group and the historical control group (56 % versus 45 % and 40 % respectively, P<0.01). Survival regression analysis identified age, ASA score, disease stage, adjuvant chemotherapy, and treatment in a colorectal unit (Hazards ratio: 0.67; 95 % CI: 0.53 to 0.84, P =0.0005), as significant independent predictors of survival. CONCLUSION: The results suggest that there may be a survival advantage for patients with colon and rectal cancers being treated within a specialist colorectal surgical unit.

Adult↗

PubMed2002

An RBCC protein implicated in maintenance of steady-state neuregulin receptor levels.

Despite numerous recent advances in our understanding of the molecular mechanisms underlying receptor tyrosine kinase down-regulation and degradation in response to growth factor binding, relatively little is known about ligand-independent receptor tyrosine kinase degradation mechanisms. In a screen for proteins that might regulate the trafficking or localization of the ErbB3 receptor, we have identified a tripartite or RBCC (RING, B-box, coiled-coil) protein that interacts with the cytoplasmic tail of the receptor in an activation-independent manner. We have named this protein Nrdp1 for neuregulin receptor degradation protein-1. Northern blotting reveals ubiquitous distribution of Nrdp1 in human adult tissues, but message is particularly prominent in heart, brain, and skeletal muscle. Nrdp1 interacts specifically with the neuregulin receptors ErbB3 and ErbB4 and not with epidermal growth factor receptor or ErbB2. When coexpressed in COS7 cells, Nrdp1 mediates the redistribution of ErbB3 from the cell surface to intracellular compartments and induces the suppression of ErbB3 and ErbB4 receptor levels but not epidermal growth factor receptor or ErbB2 levels. A putative dominant-negative form of Nrdp1 potentiates neuregulin-stimulated Erk1/2 activity in transfected MCF7 breast tumor cells. Our observations suggest that Nrdp1 may act to regulate steady-state cell surface neuregulin receptor levels, thereby influencing the efficiency of neuregulin signaling.

Amino Acid Sequence↗