Biomedical subjects

John Chan

Publications and source records attributed to John Chan.

At least 19 recordsLinked to original sources

PubMed2006

N-staging by magnetic resonance imaging for patients with nasopharyngeal carcinoma: pattern of nodal involvement by radiological levels.

BACKGROUND AND PURPOSE: To study the pattern of lymphatic spread for patients with nasopharyngeal carcinoma (NPC), the significance of retropharyngeal node (RP-LN) involvement, and the possibility of replacing the supraclavicular fossa (SCF) by Levels IV and Vb (LL) as a demarcating criterion for N3-category. PATIENTS AND METHODS: The magnetic resonance imagings (MRI) of 202 consecutive patients with NPC treated during 2001-2002 were retrospectively reviewed. Distribution in terms of radiological level (using the same criteria as other head and neck cancers) was mapped, and the size of individual node measured. Prognostic significance of RP-LN and LL was analyzed. RESULTS: Only 4% of patients were node-negative on presentation. The nodal involvement occurred predominately at II (94%), III (85%) and RP-LN (80%). The presence of RP-LN affected the N-category in 3.5% of patients, and had no significant impact on tumor control. Replacing SCF by LL as one of the criteria for defining N3 is predictive for both distant control and overall survival. CONCLUSIONS: With sensitive detection by MRI, the incidence of nodal involvement was very high for patients with NPC. It was difficult to isolate the prognostic significance of RP-LN. The current criterion for defining N3-category by extension into SCF or nodal size > 6 cm is the recommended standard, however replacing SCF with LL could be potentially useful and further validation is warranted.

Adult↗

PubMed2006

The treatment of erectile dysfunction study: focus on treatment satisfaction of patients and partners.

OBJECTIVE: To assess patient and partner preferences for, and satisfaction with, tadalafil or sildenafil (phosphodiesterase type 5 inhibitors) in routine clinical practice for treating erectile dysfunction (ED), as these are important outcomes that might influence treatment adherence. PATIENTS AND METHODS: In a multicentre, prospective observational trial in Canada, patients with ED were eligible if they planned to change treatment from tadalafil to sildenafil or vice versa. Data were collected at baseline and 4-12 weeks later (endpoint). Satisfaction was assessed using patient and partner versions of the Erectile Dysfunction Inventory of Treatment Satisfaction (EDITS) questionnaire. EDITS index scores range from 0 (extremely low treatment satisfaction) to 100 (extremely high treatment satisfaction). RESULTS: Of 2425 patients, approximately 98% completed the study and 295 partners participated. When patients changed from sildenafil to tadalafil (1722 men) the mean EDITS index scores increased significantly for both patients (from 61.6 to 78.3) and partners (from 65.0 to 82.6; both P < 0.001). When patients changed from tadalafil to sildenafil (703 men), the mean EDITS index scores increased slightly but significantly for patients (from 68.8 to 70.2; P = 0.007) but not partners (from 76.8 to 68.9; P = 0.066). For the individual EDITS questions, mean scores increased significantly from baseline to endpoint on all questions for patients (all 11 questions; P < 0.001) and partners (all five questions; P < 0.001) in the sildenafil-to-tadalafil group, and in the tadalafil-to-sildenafil group, mean scores for patients decreased on nine of 11 questions (seven of nine significantly; P < 0.041) and mean scores for partners decreased on all five (two significantly; P < 0.049). For treatment preference, regardless of the change in treatment (i.e. sildenafil-tadalafil or tadalafil-sildenafil), a significantly higher percentage of patients and partners preferred tadalafil to sildenafil. CONCLUSIONS: These data indicate that patients with ED (and their partners) who changed from sildenafil to tadalafil treatment or vice versa in a routine clinical practice setting had higher treatment satisfaction when taking tadalafil than sildenafil, as assessed by most measures of EDITS. The higher treatment satisfaction with tadalafil might help to explain the greater preference for tadalafil compared with sildenafil in both patients and partners in this observational study.

Carbolines↗

PubMed2006

Brassica napus Rop GTPases and their expression in microspore cultures.

Androgenesis in plants involves a shift in development that causes cultured microspore cells to form embryos rather than continue to develop pollen. In Brassica napus microspore culture a mild heat stress is used to switch on embryo development. An early hallmark of embryogenesis in this system is a symmetrical division of the nucleus instead of the asymmetric division that occurs during pollen formation. ROP GTPases act as molecular switches in a variety of developmental processes; therefore, the current study was initiated to examine whether they might be involved in androgenesis. Five distinct Rop genes with nucleic acid similarities ranging from 82 to 93% to Arabidopsis Rop1 were isolated from B. napus cv Topas. A Southern blot hybridization with a BnRop sequence probe suggested that there are 11-15 ROP gene family members in B. napus. RT-PCR reactions with PCR primers specific to BnRop5, BnRop6, BnRop9 and BnRop10 showed that expression of the BnRop5 was restricted to pollen but the others were detected in leaf, root, stem and pollen tissue. Pollen-like cells obtained from 3-day-old cultures by flow cytometric sorting had BnRop5 transcript levels that were 2.8 times higher than in flow sorted embryogenic microspores. Conversely, the BnRop9 transcript levels were 2.5-fold higher in the embryogenic cells than in the pollen-like cells. The potential involvement of specific ROPs in early stage microspore culture responses is discussed.

Amino Acid Sequence↗

PubMed2006

Mycobacterium tuberculosis DeltaRD1 DeltapanCD: a safe and limited replicating mutant strain that protects immunocompetent and immunocompromised mice against experimental tuberculosis.

The global epidemic of tuberculosis (TB), fueled by the growing HIV pandemic, warrants the development of a safe and effective vaccine against TB. We report the construction and characterization of an unlinked double deletion mutant of Mycobacterium tuberculosis H37Rv that deletes both the primary attenuating mutation of BCG (DeltaRD1) and two genes required for the synthesis of pantothenate (DeltapanCD). The M. tuberculosis DeltaRD1 DeltapanCD (mc(2)6030) mutant undergoes limited replication in mice, and yet is both significantly safer than BCG in immunocompromised mice and also safe in guinea pigs. Additionally, the mc(2)6030 strain does not reactivate in a mouse chemo-immunosuppression model. Importantly, long-lived protective immune responses following immunization with the mc(2)6030 strain prolong the survival of wild type mice, and CD4-deficient mice against an aerosol challenge with virulent M. tuberculosis. Given its overall safety and effectiveness, the mc(2)6030 live attenuated strain should be considered as a human vaccine candidate for protecting both healthy and HIV-infected individuals against TB.

Animals↗

PubMed2006

Subjective memory and mood of Hong Kong Chinese adults with epilepsy.

Clinicians are often confronted with the self-report of memory difficulties by patients. This study explored the possible correlates of subjective memory in 67 adult Chinese patients with epilepsy in Hong Kong. These correlates include epilepsy-related factors, mood state, and actual performance on neuropsychological tests. Results suggested that there exists no significant systematic relationship between subjective and illness-related factors such as seizure frequency, age at onset, and medication. Instead, stepwise regression analysis revealed that mood (anxiety) explained about 17% of the variance of subjective memory difficulties, whereas performance on a memory test accounted for only 8% of the variance. Findings are discussed in the light of the need to attend to the anxiety of patients with epilepsy in the process of rehabilitation.

Adult↗

PubMed2006

11q22.3 deletion in B-chronic lymphocytic leukemia is specifically associated with bulky lymphadenopathy and ZAP-70 expression but not reduced expression of adhesion/cell surface receptor molecules.

The presence of chromosome abnormalities promotes tumor progression in B-chronic lymphocytic leukemia (CLL). However, the molecular pathways that are relevant to tumor progression remain unclear. In this study, we screened for common chromosome abnormalities [13q14 del, 11q22.3 (ATM) del, 17p13 (p53) del and trisomy 12] by fluorescent in situ hybridization in 40 B-CLL patients. Each of the four chromosome abnormality groups was compared to several clinical factors related to lymphocyte behaviour in CLL. The 11q22.3 (ATM) deletion group was significantly associated with the presence of bulky abdominal/mediastinal lymphadenopathy (P = 0.014). We hypothesized that this phenotype would be associated with an altered transcription pattern of genes. Class comparison analysis by significance analysis of microarrays on a subset of CLL samples (n = 14) indicated that a number of cell surface receptor and adhesion related genes were under-expressed in the 11q22.3 deletion group (CD44, CD11a, PTPRC, CD79a, chemokine ligand 17 and chemokine receptor type 6). The presence of additional prognostic factors, such as CD38 and immunoglobulin heavy chain variable region mutational status, may also influence the transcriptional pathways between the two groups. Therefore, we employed a novel analysis technique for the correlation of log(2) gene expression ratios with the percentage of each tumor that carried the 11q22.3 deletion. Using Spearman's correlation, ZAP-70, chemokine ligand 17, BSAP (PAX5), CD7, LAG3 and PTPR6 were significantly correlated with the percentage of cells with the 11q22.3 deletion. However, the down-regulation of cell surface receptors and adhesion molecules observed by class comparison could not be confirmed to be specific for the 11q22.3 deletion by this method.

Cell Adhesion Molecules↗

PubMed2006

5'-Adenosinephosphosulphate reductase (CysH) protects Mycobacterium tuberculosis against free radicals during chronic infection phase in mice.

A major obstacle to tuberculosis (TB) control is the problem of chronic TB infection (CTBI). Here we report that 5'-adenosinephosphosulphate reductase (CysH), an enzyme essential for the production of reduced-sulphur-containing metabolites, is critical for Mycobacterium tuberculosis (Mtb) survival in chronic infection phase in mice. Disruption of cysH rendered Mtb auxotrophic for cysteine and methionine, and attenuated virulence in BALB/c and C57BL/6 immunocompetent mice. The mutant and wild-type Mtb replicated similarly during the acute phase of infection, but the mutant showed reduced viability during the persistent phase of the infection. The cysH mutant caused disease and death after 4-7 weeks of infection in four different groups of mice - Rag1(-/-), NOS2(-/-), gp91phox(-/-) NOS2(-/-) and gp91phox(-/-) mice given aminoguanidine [to suppress the effects of nitric oxide synthase 2 (NOS2)]- indicating minimal metabolic effect on the cysH mutant survival in these mice. The cysH mutant was also susceptible to peroxynitrite and hydrogen peroxide in vitro. These results show that CysH is important for Mtb protection during the chronic infection phase, and that resistance to nitrosative and oxidative stress may be the mechanism of this protection. Thus, this metabolic gene of an intracellular pathogen could have a secondary role in protection against the host immune response. Finally the lack of an endogenous human orthologue of cysH and its possible role in defence against adaptive immunity renders CysH an attractive enzyme for further studies as a target for therapeutics active against CTBI.

Animals↗

PubMed2006

Characterization of the tuberculous granuloma in murine and human lungs: cellular composition and relative tissue oxygen tension.

The granulomatous reaction is the hallmark of the host response to infection with Mycobacterium tuberculosis. Despite its apparent importance to host defence against the tubercle bacillus, the granulomatous response remains to be completely defined. The present study used histological, immunohistochemical and flow-cytometric analyses to characterize pulmonic granulomatous tissues of tuberculous mice and humans. The kinetics of recruitment of neutrophils, macrophages, dendritic cells, and T and B lymphocytes into the lungs of mice infected aerogenically with the virulent Erdman strain of M. tuberculosis was evaluated in detail in both the acute and persistent phase of infection. A hypoxia-sensing compound based on the 2-nitroimidazole structure (EF5), together with immunohistochemical studies targeting endothelial cells were used to examine the relative oxygen tension in tuberculous granulomatous tissues in mice. The results have provided evidence that: (i) the granulomatous tissues are a highly organized structure whose formation is regulated by orderly recruitment of specific immune cells exhibiting distinct spatial relationship with one another; (ii) the granulomatous reaction, at least in the mouse, may represent an exaggerated response to the tubercle bacillus that can play a role in the development of immunopathology; (iii) B lymphoid aggregates are a prominent feature in both murine and human granulomatous tissues, although the immune cells that are most prominently associated with these clusters vary among the two species; (iv) murine tuberculous granulomatous tissues are relatively aerobic, suggesting that mouse models of persistent tuberculosis may not be suitable for the study of any hypoxic response of M. tuberculosis.

Acute Disease↗

PubMed2006

Physician-rated patient preference and patient- and partner-rated preference for tadalafil or sildenafil citrate: results from the Canadian 'Treatment of Erectile Dysfunction' observational study.

OBJECTIVE: To determine physician-based ratings of patient preference, patient preference, partner preference and physician-based assessment of the reasons for patient preference for tadalafil or sildenafil citrate (sildenafil) as a treatment for erectile dysfunction (ED) in routine clinical practice. Phosphodiesterase type 5 inhibitors (PDE5i) are effective and well-tolerated therapies for ED, but patient and partner preferences for these treatments might be determined by many factors, both medical and nonmedical. PATIENTS AND METHODS: The Treatment of ED (TED) observational trial was a multicentre study conducted in Canada to determine patient and partner preferences for the PDE5i tadalafil or sildenafil in routine clinical practice. Patients who planned to change treatment from tadalafil or sildenafil to the alternative drug were invited to participate in the study. The study duration was 4-12 weeks. At visit 1 (baseline), patient background information was collected. At visit 2, physicians answered the physician-rated patient-treatment preference questionnaire, patients answered the treatment preference question (TPQ) and the global assessment question (GAQ), and partners answered the partner TPQ. RESULTS: The TED study was conducted at 266 sites across Canada and involved 2425 patients who used the allowed study medications, and 295 sexual partners who attended clinic visits. More than 98% of patients completed the study. Responses to the preference questionnaires showed that physician-rated patient preference, patient preference, and partner preference had a similar pattern preference, with a significantly higher proportion preferring tadalafil over sildenafil regardless of the change in treatment (i.e. sildenafil to tadalafil or tadalafil to sildenafil). Responses to the GAQ showed that nearly 90% of the patients who took either PDE5i said that the treatment had improved erections. CONCLUSIONS: TED is the first study to assess physician-based ratings of patient preference, patient preference, and partner preference for tadalafil or sildenafil in a routine clinical practice settings. Most participants preferred tadalafil over sildenafil. Understanding the underlying reasons influencing the preference might improve patient compliance and satisfaction with treatment.

Aged↗

PubMed2006

Deletion of the Mycobacterium tuberculosis resuscitation-promoting factor Rv1009 gene results in delayed reactivation from chronic tuberculosis.

Approximately one-third of the human population is latently infected with Mycobacterium tuberculosis, comprising a critical reservoir for disease reactivation. Despite the importance of latency in maintaining M. tuberculosis in the human population, little is known about the mycobacterial factors that regulate persistence and reactivation. Previous in vitro studies have implicated a family of five related M. tuberculosis proteins, called resuscitation promoting factors (Rpfs), in regulating mycobacterial growth. We studied the in vivo role of M. tuberculosis rpf genes in an established mouse model of M. tuberculosis persistence and reactivation. After an aerosol infection with the M. tuberculosis Erdman wild type (Erdman) or single-deletion rpf mutants to establish chronic infections in mice, reactivation was induced by administration of the nitric oxide (NO) synthase inhibitor aminoguanidine. Of the five rpf deletion mutants tested, one (deltaRv1009) exhibited a delayed reactivation phenotype, manifested by delayed postreactivation growth kinetics and prolonged median survival times among infected animals. Immunophenotypic analysis suggested differences in pulmonary B-cell responses between Erdman- and deltaRv1009-infected mice at advanced stages of reactivation. Analysis of rpf gene expression in the lungs of Erdman-infected mice revealed that relative expression of four of the five rpf-like genes was diminished at late times following reactivation, when bacterial numbers had increased substantially, suggesting that rpf gene expression may be regulated in a growth phase-dependent manner. To our knowledge, deltaRv1009 is the first M. tuberculosis mutant to have a specific defect in reactivation without accompanying growth defects in vitro or during acute infection in vivo.

Animals↗

PubMed2005

Induction of high levels of protective immunity in mice after vaccination using dendritic cells infected with auxotrophic mutants of Mycobacterium tuberculosis.

Adoptively transferred dendritic cells presenting antigens derived from different pathogens have been shown to elicit specific T cell responses and to induce protective antibacterial immunity. We describe here the induction of high levels of protective immunity in mice using dendritic cells infected with auxotrophic mutants of Mycobacterium tuberculosis. We provide evidence that protection is superior to BCG and that it is associated with increased priming of CD4+ and CD8+ T cells specific for mycobacterial antigens. This method for generating high levels of anti-bacterial protective immunity could be helpful in the design of novel vaccines against tuberculosis and other intracellular pathogens.

Adoptive Transfer↗

PubMed2005

What's good for the host is good for the bug.

Tuberculosis, caused by Mycobacterium tuberculosis, kills approximately two million people each year. The infection is characterized by an inflammatory response culminating in the formation of a granuloma, a collection of immune cells that controls the infection. However, the granuloma can be the source of immunopathology that encourages transmission. Recent data support the idea that mycobacterial products can positively and negatively regulate the inflammatory response. Our contention is that induction of the immune response and subsequent granuloma formation is beneficial to the host for control of infection, and is also beneficial to the bacillus, as a place to hide and as a means for transmitting the infection to naive hosts.

Humans↗

PubMed2005

responses of mycobacterium tuberculosis to growth in the mouse lung.

Using a promoter trap, we have identified 56 Mycobacterium tuberculosis genes preferentially expressed in the mouse lung. Quantitative real-time PCR showed that RNA levels of several genes were higher from bacteria growing in mouse lungs than from broth cultures. These results support the current hypothesis that Mycobacterium tuberculosis utilizes fatty acids as a carbon source in the mouse lung.

Animals↗

PubMed2004

TNF influences chemokine expression of macrophages in vitro and that of CD11b+ cells in vivo during Mycobacterium tuberculosis infection.

Granulomas, focal accumulations of immune cells, form in the lung during Mycobacterium tuberculosis infection. Chemokines, chemotactic cytokines, are logical candidates for inducing migration of T lymphocytes and monocytes to and within the lung. TNF influences chemokine expression in some models. TNF-deficient mice infected with M. tuberculosis are highly susceptible to disease, and granuloma formation is inhibited. Through in vitro assays, we demonstrate that neutralization of TNF in M. tuberculosis-infected macrophages led to a reduction in many inflammatory chemokines, such as C-C chemokine ligand 5, CXC ligand 9 (CXCL9), and CXCL10. In TNF-deficient mice, immune cells migrated to the lungs early after infection, but did not organize to form granulomas within the lung. Although chemokine expression, as measured in whole lung tissue, was not different, the expression of chemokines in the CD11b(+) subset of cells isolated ex vivo from the lungs of TNF-deficient mice had reduced expression of C-C chemokine ligand 5, CXCL9, and CXCL10 at early time points after TNF neutralization. Local expression of CXCR3-binding chemokines within the lungs, as determined by in situ hybridization, was also affected by TNF. Therefore, TNF affects the expression of chemokines by macrophages in vitro and CD11b(+) cells in vivo, which probably influences the local chemokine gradients and granuloma formation.

Animals↗

PubMed2004

The immunological aspects of latency in tuberculosis.

A unique feature of Mycobacterium tuberculosis is its ability to exist in the granuloma of an asymptomatic host in a latent state that can subsequently reactivate to cause active disease. The latent state of infection poses a major obstacle to eradicating tuberculosis. In latent tuberculosis, the host immune response is capable of controlling the infection and yet falls short of eradicating the pathogen. That the host immune response contributes to the maintenance of latent tuberculous infection is supported by the observation that certain immunodeficient states, including those associated with the human immunodeficiency virus and tumor necrosis factor neutralization therapy, are associated with increased risks for developing reactivation disease. Latent tuberculosis is the product of a complex set of interactions between M. tuberculosis and the host immune response. The molecular basis for the persistence phenotype of M. Tuberculosis and the pertinent host immune mechanisms that contribute to the maintenance of tuberculous latency are just beginning to be understood. This review discusses the interactions between M. tuberculosis and the macrophage, the primary host cell that the tubercle bacillus parasitizes.

Antigen Presentation↗

PubMed2004

An optimal, cost-effective laparoscopic appendectomy technique for our surgical residents.

Since early 1999, we have implemented a standardized technique for laparoscopic appendectomy, which is simple, safe and easily learned and mastered by our residents. Besides superior ergonomics, it offers cosmetic advantages. It is inexpensive as only reusable instruments are used. It incorporates useful modifications, such as the use of suprapubic ports, inferior approach with repositioning of the videoscope from the umbilical port to the left suprapubic port, laparoscopic gauze swabs and instrument-assisted knotting, as well as skeletonization of the appendix. We analyze the outcome of this technique between January 2000 and December 2002. The overall conversion rate of 713 laparoscopic appendectomies was 8.7%, which is comparable with the "best" rates in international literature. Operative times (mean, 59.0 minutes) and the complication rate (6.7%) compared favorably with previous reports on resident training. In summary, our residents feel comfortable with our standardized approach, while producing acceptable results with low cost.

Adolescent↗

PubMed2004

Individual Mycobacterium tuberculosis resuscitation-promoting factor homologues are dispensable for growth in vitro and in vivo.

Mycobacterium tuberculosis possesses five genes with significant homology to the resuscitation-promoting factor (Rpf) of Micrococcus luteus. The M. luteus Rpf is a secreted approximately 16-kDa protein which restores active growth to cultures of M. luteus rendered dormant by prolonged incubation in stationary phase. More recently, the Rpf-like proteins of M. tuberculosis have been shown to stimulate the growth of extended-stationary-phase cultures of Mycobacterium bovis BCG. These data suggest that the Rpf proteins can influence the growth of mycobacteria; however, the studies do not demonstrate specific functions for the various members of this protein family, nor do they assess the function of M. tuberculosis Rpf homologues in vivo. To address these questions, we have disrupted each of the five rpf-like genes in M. tuberculosis Erdman, and analyzed the mutants for their growth in vitro and in vivo. In contrast to M. luteus, for which rpf is an essential gene, we find that all of the M. tuberculosis rpf deletion mutant strains are viable; in addition, all show growth kinetics similar to Erdman wild type both in vitro and in mouse organs following aerosol infection. Analysis of rpf expression in M. tuberculosis cultures from early log phase through late stationary phase indicates that expression of the rpf-like genes is growth phase-dependent, and that the expression patterns of the five M. tuberculosis rpf genes, while overlapping to various degrees, are not uniform. We also provide evidence that mycobacterial rpf genes are expressed in vivo in the lungs of mice acutely infected with virulent M. tuberculosis.

Animals↗

PubMed2004

A high-throughput turbidometric assay for screening inhibitors of protein disulfide isomerase activity.

Protein disulfide isomerase (PDI) plays a key role in protein folding by catalyzing rearrangements of disulfide bonds in substrate proteins following their synthesis in eukaryotic cells. Besides its major role in the processing and maturation of secretory proteins in the endoplasmic reticulum, this enzyme and its homologs have been implicated in multiple important cellular processes; however, they have not served as targets for the development of therapeutic agents. The authors developed a high-throughput screening assay for PDI and its homologous enzymes in 384-well microplates. The method is based on the enzyme-catalyzed reduction of insulin in the presence of dithiothreitol and measures the aggregation of reduced insulin chains at 650 nm. This kinetic assay was converted to an end-point assay by using hydrogen peroxide as a stop reagent. The feasibility of this high-throughput assay for screening chemical libraries was demonstrated in a pilot screen. The authors show that this homogenous turbidometric assay is robust and cost-effective and can be applied to identify PDI inhibitors from chemical libraries, opening this class of enzymes for therapeutic exploration.

Animals↗