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Biomedical subjects

C Chu

Publications and source records attributed to C Chu.

At least 19 recordsLinked to original sources
PubMed1999

Protein conjugates of synthetic saccharides elicit higher levels of serum IgG lipopolysaccharide antibodies in mice than do those of the O-specific polysaccharide from Shigella dysenteriae type 1.

Our development of vaccines to prevent shigellosis is based on the hypothesis that a critical (protective) level of serum IgG to the O-specific polysaccharide (O-SP) domain of Shigella lipopolysaccharide (LPS) confers immunity. The O-SP is a hapten and must be conjugated to a protein to induce serum antibodies. The O-SP of Shigella dysenteriae type 1 (approximately 27 tetrasaccharide repeat units), prepared by acid hydrolysis of the LPS, was bound to human serum albumin (HSA) by multiple point attachment (O-SP-HSA): The molar ratio of HSA to O-SP was 1.0. Synthetic saccharides, composed of one or multiples of the O-SP tetrasaccharide, equipped with a spacer at their reducing end, were bound to HSA by a single point attachment: The average molar ratios of the saccharides to HSA ranged from 4 to 24. Serum IgG anti-LPS, elicited in mice by O-SP-HSA or synthetic tetra-, octa-, dodeca-, and hexadecasaccharide fragments, was measured by ELISA. Outbred 6-week-old female mice were injected s.c. three times at biweekly intervals with 2.5 micrograms of saccharide as a conjugate and were bled 7 days after the second and third injections. Excepting the tetramer, conjugates of the octamer, dodecamer and hexadecamer elicited IgG LPS antibodies after the second injection, a statistically significant rise (booster) after the third injection, and higher levels than those vaccinated with O-SP-HSA (P = 0.0001). The highest geometric mean levels of IgG anti-LPS were elicited by the hexadecamer with 9 chains or 9 moles of saccharide/HSA (15.5 ELISA units) followed by the octamer with 20 chains (11.1 ELISA units) and the dodecamer with 10 chains (9.52 ELISA units). Clinical evaluation of these synthetic saccharides bound to a medically useful carrier is planned.

Animals↗
PubMed1999

Prognostic value of plasma HIV RNA in the natural history of Pneumocystis carinii pneumonia, cytomegalovirus and Mycobacterium avium complex. Multicenter AIDS Cohort Study.

OBJECTIVES: To use follow-up on untreated HIV-positive men to assess the prognostic information provided by baseline data on plasma HIV RNA, CD4 cell count, age, and HIV-related symptom status, separately for three specific AIDS-defining illnesses: Pneumocystis carinii pneumonia (PCP), cytomegalovirus (CMV), and Mycobacterium avium complex (MAC). METHODS: The study population were 734 HIV-positive homosexual men enrolled in the Multicenter AIDS Cohort Study, with follow-up (1984-1985 through mid-1988) restricted to the antiretroviral treatment-free and prophylaxis-free era. Baseline marker values were categorized and assessed as predictor variables in separate time-to-event analyses for each of the three specific outcomes. RESULTS: A total of 138 cases of PCP, 25 cases of CMV, and 25 cases of MAC were observed. For PCP and CMV, higher categories of HIV RNA and lower categories of CD4 cell count were associated with increased risk relative to the respective reference groups. For MAC, oral candidiasis or fever and elevated HIV RNA at baseline were the primary risk factors. Further analysis highlighted the importance of monitoring HIV RNA levels in addition to CD4 cell counts when evaluating patients' risk of developing PCP. CONCLUSIONS: In the absence of treatment, plasma HIV RNA levels provide prognostic information about the risk of these three specific AIDS-defining illnesses, independently of the CD4 cell count. These data provide a useful reference as researchers investigate changing patterns in the incidence and predictors of opportunistic infections in the era of increasingly active antiretroviral therapies.

AIDS-Related Opportunistic Infections↗
PubMed1999

Myocardial oxygenation during high work states in hearts with postinfarction remodeling.

BACKGROUND: Postinfarction left ventricular remodeling (LVR) is associated with reductions in myocardial high-energy phosphate (HEP) levels, which are more severe in animals that develop overt congestive heart failure (CHF). During high work states, further HEP loss occurs, which suggests demand-induced ischemia. This study tested the hypothesis that inadequate myocyte oxygen availability is the basis for these HEP abnormalities. METHODS AND RESULTS: Myocardial infarction was produced by left circumflex coronary artery ligation in swine. Studies were performed in 20 normal animals, 14 animals with compensated LVR, and 9 animals with CHF. Phosphocreatine (PCr)/ATP was determined with 31P NMR and deoxymyoglobin (Mb-delta) with 1H NMR in myocardium remote from the infarct. Basal PCr/ATP tended to be decreased in postinfarct hearts, and this was significant in animals with CHF. Infusion of dobutamine (20 microg x kg-1 x min-1 IV) caused doubling of the rate-pressure product in both normal and LVR hearts and resulted in comparable significant decreases of PCr/ATP in both groups. This decrease in PCr/ATP was not associated with detectable Mb-delta. In CHF hearts, rate-pressure product increased only 40% in response to dobutamine; this attenuated response also was not associated with detectable Mb-delta. CONCLUSIONS: Thus, the decrease of PCr/ATP during dobutamine infusion is not the result of insufficient myocardial oxygen availability. Furthermore, in CHF hearts, the low basal PCr/ATP and the attenuated response to dobutamine occurred in the absence of myocardial hypoxia, indicating that the HEP and contractile abnormalities were not the result of insufficient oxygen availability.

Adenosine Triphosphate↗
PubMed1999

Epitopic overload at the site of injection may result in suppression of the immune response to combined capsular polysaccharide conjugate vaccines.

Capsular polysaccharide (CP) conjugate vaccines targeting a variety of bacterial infections are currently under development and clinical evaluation. The inclusion of multiple CP serotypes combined in a single injection is an important maneuver being evaluated. The combination of CP conjugate vaccines into a single multivalent injection may result in competition among the different components and adversely affect the immunogenicity of any individual conjugate. We observed a reduction of 30-90% in antibody responses to several serotypes in mice when immunogenicity of a 12-valent Escherichia coli (E. coli) lipopolysaccharide (LPS) conjugate vaccine was compared to the immunogenicity of each monovalent vaccine evaluated separately. A reduction of 30% was observed in the Staphylococcus aureus (S. aureus) type 8 CP antibodies when a type 8-rEPA conjugate was combined with a type 5-rEPA conjugate. S. aureus types 5 and 8-rEPA conjugates were combined with 100 micrograms of either rEPA (homologous) or diphtheria toxoid (DT) (heterologous) carrier proteins, and evaluated in rEPA or DT primed mice. The addition of the homologous protein resulted in a 64% reduction in type 5 CP antibodies. The heterologous protein did not affect the immunogenicity of the type 5. We postulate that the free protein competed with the conjugate and recruited most of the rEPA primed T cells. In the case of the DT conjugates, the DT targeted different populations of the T cells, thus interference was not observed. These data suggested that the epitopic load rather than the antigenic load at the site of injection caused reduced immunogenicity of the conjugates. We theorize that individual components of multivalent CP vaccines conjugated to the same carrier proteins would compete for a limited number of specific carrier protein primed T cells. This would result in one or more components being unavailable in eliciting a sufficient immune response. The use of multiple carrier proteins should be considered as an approach to reduce interference when multivalent conjugate vaccines are to be formulated into a single injection.

Animals↗
PubMed1999

Comparative physical and genetic maps of the virulence plasmids of Salmonella enterica serovars typhimurium, enteritidis, choleraesuis, and dublin.

Using fragment profiling, PCR, and Southern hybridization, we found that Salmonella enterica serovar Choleraesuis harbored virulence plasmids of various sizes, whereas serovars Typhimurium, Enteritidis, and Dublin carried a plasmid of a unique size. Also, the virulence plasmid of Typhimurium contained genes in the same order detected in the other three plasmids, all of which contained deletions.

Base Sequence↗
PubMed1998

Molecular identification of a role for tyrosine 167 in the function of the human intestinal proton- coupled dipeptide transporter (hPepT1).

hPepT1 is a proton-coupled peptide transporter that mediates the absorption of di- and tripeptides. Here we show that tyrosine 167 (Y167) in transmembrane domain 5 (TMD5) of this 12-transmembrane spanning protein contributes to its transport function. We identified this particular amino acid by a computer model of the arrangement of the TMDs of hPepT1 and investigated its role by site-directed mutagenesis and dipeptide uptake studies. [3H]Gly-sar uptake in cells transiently transfected with Y167A-hPepT1 was abolished completely, even though the level of Y167A-hPepT1 expression by Western blot analysis and cell surface expression by immunofluorescence microscopy was similar to those of the wild type. Therefore, mutation affected transport function, but apparently not the steady-state protein level or trafficking of the transporter to the plasma membrane. Moreover, mutation of Y167 into phenylalanine, serine, or histidine all abolished gly-sar uptake in transfected HEK 293 cells. Taken together, these findings suggest that Y167 plays an essential role in hPepT1 function, perhaps due to the unique chemistry of its phenolic side chain.

Blotting, Western↗
PubMed1998

Caveolin-mediated regulation of signaling along the p42/44 MAP kinase cascade in vivo. A role for the caveolin-scaffolding domain.

The p42/44 mitogen-activated protein (MAP)-kinase cascade is a well-established signal transduction pathway that is initiated at the cell surface and terminates within the nucleus. More specifically, receptor tyrosine kinases can indirectly activate Raf, which in turn leads to activation of MEK and ERK and ultimately phosphorylation of Elk, a nuclear transcription factor. Recent reports have suggested that some members of p42/44 MAP kinase cascade can be sequestered within plasmalemmal caveolae in vivo. For example, morphological studies have directly shown that ERK-1/2 is concentrated in plasma membrane caveolae in vivo using immunoelectron microscopy. In addition, constitutive activation of the p42/44 MAP kinase cascade is sufficient to reversibly down-regulate caveolin-1 mRNA and protein expression. However, the functional relationship between the p42/44 MAP kinase cascade and caveolins remains unknown. Here, we examine the in vivo role of caveolins in regulating signaling along the MAP kinase cascade. We find that co-expression with caveolin 1 dramatically inhibits signaling from EGF-R, Raf, MEK-1 and ERK-2 to the nucleus. Using a variety of caveolin-1 deletion mutants, we mapped this in vivo inhibitory activity to caveolin-1 residues 32-95. Peptides derived from this region of caveolin 1 also inhibit the in vitro kinase activity of purified MEK-1 and ERK-2. Thus, we show here that caveolin-1 expression can inhibit signal transduction from the p42/44 MAP kinase cascade both in vitro and in vivo. Taken together with previous data, our results also suggest that a novel form of reciprocal negative regulation exists between p42/44 MAP kinase activation and caveolin-1 protein expression, i.e. up-regulation of caveolin-1 protein expression down-modulates p42/44 MAP kinase activity (this report) and up-regulation of p42/44 MAP kinase activity down-regulates caveolin-1 mRNA and protein expression.

Animals↗
PubMed1998

Decline in total T cell count is associated with onset of AIDS, independent of CD4(+) lymphocyte count: implications for AIDS pathogenesis.

We previously reported that blind T cell homeostasis, in which the total T cell count is maintained but the CD4(+) and CD8(+) subset composition of the T cells can vary, fails approximately 1.5 to 2.5 years before the onset of AIDS. The present study was premised on the hypothesis that if failure of T cell homeostasis (i.e., a decline in total T cell counts) is important in the pathogenesis of AIDS, it should be a significant predictor of AIDS after controlling for the CD4(+) lymphocyte count. Data from 1556 homosexual men with sufficient sequential T cell subset measurements were evaluated, representing 11,988 person-visits in men with known clinical outcomes over a period of more than 10 years. Using regression models that incorporated CD4(+) lymphocyte count and HIV-related symptoms (fever, thrush), it was determined that a yearly decline of more than 300 T cells/microliter of peripheral blood was an independent predictor of the onset of AIDS for subjects with CD4(+) lymphocyte counts of <500 cells/microliter. The results support an important role for failure of T cell homeostasis in the pathogenesis of AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Equilibration of air temperature inside the thimble of a Farmer-type ion chamber.

Ionization chambers are frequently moved from one environment to another, sometimes with significant differences in temperature between the chamber and measurement phantom. To obtain reliable ionization data, the temperature of the air in the chamber must be allowed to equilibrate with the measuring phantom. The air temperature inside a thimble of a Farmer-type ion chamber was measured as a function of time for various phantom materials (air, water, and plastic). Equilibration rates for the various conditions are presented. Heat-diffusion theory is presented to explain the characteristics of the measured data. Waiting times for temperature equilibration down to 10% of the initial temperature difference ranges from 1 to 18 min, depending on the phantom material and use of bare or covered thimble. Radiation measurements confirm the temperature data.

Equipment Design↗
PubMed1997

MyoD functions as a transcriptional repressor in proliferating myoblasts.

The myogenic basic helix-loop-helix (myo-bHLH) proteins are a family of transcriptional regulators expressed in myoblasts and differentiated skeletal muscle. Ectopic expression of myo-bHLH regulators transdetermines some fibroblast cell lines into myoblasts, which exit the cell cycle and differentiate into skeletal muscle when cultured in low mitogen medium. While members of the myo-bHLH family have been shown to function as transcriptional activators in differentiating muscle, the molecular basis of their function in proliferating myoblasts has not been elucidated. In this report, we present evidence that MyoD functions as a transcriptional repressor in myoblasts. We show that transcription from a cyclin B1 promoter construct is repressed in proliferating myoblasts and that repression is mediated by a pair of MyoD binding sites. We also show that transcription from the cyclin B1 promoter is repressed in proliferating C3H10T1/2 cells by ectopic expression of MyoD. These results demonstrate that MyoD can repress transcription of specific genes in proliferating cells, a novel function that may be important to maintenance of the myogenic phenotype and to cell cycle regulation in myoblasts.

Animals↗
PubMed1997

Delayed reperfusion alters matrix metalloproteinase activity and fibronectin mRNA expression in the infarct zone of the ligated rat heart.

Delayed reperfusion has a beneficial effect on prognosis, independent of infarct size. One potential mechanism to explain this observation may be an effect on infarct healing. In this study, the impact of delayed reperfusion on two aspects of the healing process was examined, the activity of matrix metalloproteinase (MMP) enzymes and the expression of fibronectin (FN) mRNA. The rat model of coronary artery ligation was used and rats were randomly assigned to delayed reperfusion (150 min following coronary ligation) or permanent ligation. Animals were subsequently killed 1, 2, 3 and 7 days following infarction. Infarct tissue was harvested for MMP activity (zymography), FN mRNA (RNase protection analysis) and protein (immunofluorescence microscopy and Western analysis), and collagen content (hydroxyproline concentration). Infarction produced marked activation of MMP-1, -2, and -9. Reperfusion significantly attenuated the activity of these enzymes (approximately 50% reduction in MMP-1, P=0.03 and ;60% reduction in MMP-2 at 7 days, P=0.001; approximately 55% reduction in MMP-9 at 24 h and 84% reduction at 48 h, P=0.01 and 0.002, respectively). Delayed reperfusion also produced a trend toward a greater increase in FN mRNA 24 h following infarction and immunofluorescent staining suggested the presence of more FN protein at this point. These data demonstrate that delayed reperfusion alters matrix metalloproteinase activity and fibronectin mRNA expression in the infarct zone. The impact of these changes on infarct healing and their association with the improved prognosis of a patent infarct vessel following infarction will require further study.

Animals↗
PubMed1997

Effect of delayed intervention with ACE-inhibitor therapy on myocyte hypertrophy and growth of the cardiac interstitium in the rat model of myocardial infarction.

The effectiveness of angiotensin-converting enzyme (ACE)-inhibitor therapy in attenuating ventricular remodeling when initiated immediately following myocardial damage is clearly established. Less information, however, is available on the impact of late therapy on the remodeling process, especially its influence on the cellular components of these structural changes. The purpose of this study was to examine the effects of converting enzyme inhibitor therapy commenced 28 days following infarction in the rat on changes in cardiac myocyte dimension and the interstitium. At 28 days following infarction, myocyte cell length (153.9+/-7.3 v 131.1+/-5.9 micron, P=0.0002) and cell volume in the free wall of the left ventricle (38. 5+/-5.0 x 10(3) v31.4+/-3.1 x 10(3), P=0.009) had increased compared with sham-operated rats. Similar changes were noted in the septum and right ventricle. Captopril therapy administered between 28 and 56 days attenuated a further increase in cell length noted in an untreated group in the left ventricle (153.5+/-15.3 v 167.3+/-13.7 micron, P=0.02), right ventricle (153.8+/-20.5 v 173.8+/-2.3 micron, P=0.01) and septum (158.0+/-20.2 v 179.1+/-16.6 micron, P=0.004). There was an increase in hydroxyproline content in the right ventricle and a similar trend in the left ventricle in the untreated myocardial infarction groups. These changes were not altered by captopril therapy. In summary, even late therapy with captopril attenuates progressive myocyte remodeling, which may contribute to the ability of ACE-inhibitor therapy to slow progressive chamber enlargement following infarction.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1997

The effect of delayed reperfusion following infarction in the rat on structural changes in viable myocardium.

OBJECTIVE: Evidence indicates that patency of the infarct related artery following the completion of myocardial necrosis can attenuate ventricular remodeling. Data have also demonstrated that inhibition of infarct expansion contributes to the anti-remodeling effect of delayed reperfusion. However, the influence of a patent artery on components of the remodeling process in the viable myocardium is poorly understood. METHODS: Myocyte morphometrics (isolated cell technique) and collagen content (hydroxyproline analysis) were assessed 28 days following experimental myocardial infarction from rats with permanently ligated left coronary vessels (NRP; n = 10) compared with rats who underwent reperfusion 150 minutes after ligation (RP; n = 11) and a sham-operated group (n = 10). RESULTS: Analysis of infarct size (planimetry) in a separate group of rats demonstrated that reperfusion at this late time point did not reduce infarct size (NRP: 33 +/- 3 vs. RP: 35 +/- 5%). Myocyte length in RP rats was less than in NRP rats in viable, non-infarcted left ventricular tissue (155 +/- 3 vs. 167 +/- 4 microns, p = 0.02), in the right ventricle (154 +/- 4 vs. 167 +/- 3 microns, p = 0.02) and in the septum (158 +/- 4 vs. 169 +/- 4 microns, p = 0.05). Reperfusion also attenuated the expected increase in cell volume compared with NRP rats (left ventricle 39.4 +/- 1.7 x 10(3) vs. 44.1 +/- 1.6 x 10(3) micron 3, p = 0.06; right ventricle 36.7 +/- 1.6 x 10(3) vs. 42.7 +/- 2.0 x 10(3) micron 3, p = 0.02; septum 41.0 +/- 1.6 x 10(3) vs. 44.2 +/- 1.8 x 10(3) micron 3, p = 0.19). Hydroxyproline content increased in the viable left ventricular tissue in both the reperfused and non-reperfused groups. CONCLUSION: Reperfusion without myocardial salvage attenuates the increase in myocyte length and volume that occurs in remodeling myocardium following infarction in the rat, with no effect on the increase in collagen content. These data indicate that patency of the infarct vessel, which is known to have an inhibitory effect on infarct expansion, also has an anti-remodeling effect remote from the area perfused by this artery.

Animals↗
PubMed1997

Detection of infection with human immunodeficiency virus type 1 before seroconversion: correlation with clinical symptoms and outcome.

Early (pre-seroconversion) infection with human immunodeficiency virus type 1 (HIV-1) was identified in 50 of 267 participants in the Multicenter AIDS Cohort Study. These 50 men had a positive EIA result, which detected IgM antibody (n = 35), p24 antigen, or serum HIV RNA (n = 15) at their last "seronegative" visit. At that visit, the mean CD4 lymphocyte number (890/mm3 vs. 1038/mm3) was significantly lower than in men who subsequently seroconverted but had no evidence of early infection. The decline in CD4 cells was slower and the duration of AIDS-free time longer in the 19 men who were symptomatic in comparison to the 31 asymptomatic men with early infection, but differences were not significant.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Identification of functioning cortex using cortical optical imaging.

OBJECTIVE: The purpose of this study was to evaluate the technique of cortical optical imaging (COI) of intrinsic cortical optical signals related to neuronal activation. The specific goals of the study were to evaluate some of the technical aspects of COI and thus maximize the intensity of the image of this intrinsic signaling process and to determine the physiological reliability of COI in a well-defined animal system. METHODS: The intrinsic optical signal of activated whisker barrel cortex of rat was imaged using a computer-based technique for rapid acquisition of enhanced images. Single-unit microelectrode recordings of cortical neuronal responses to whisker movement were used to confirm the locations of the whisker barrels. RESULTS: Narrow band incident light at 600- to 610-nm wavelength was most effective for producing optical images. Images could be obtained during activation by a single long (40 s) stimulus or by averaging the signal generated by repeated shorter (1-8 s) stimuli. Focusing slightly below the cortical surface, minimizing movement, and abolishing extraneous light were all important in increasing the signal-to-noise ratio. The locations of whisker movement-evoked cortical activity determined using COI are consistent with the known functional anatomy of rat whisker barrel cortex. The images obtained with this experimental arrangement are shown to be accurate predictors of the location of neuronal activity determined by comparing the locations of active sites identified with COI with locations of areas of neuronal activity determined using single-cell recording techniques. CONCLUSIONS: COI is able to rapidly identify areas of cortex containing elicited neuronal activity. The technique allows cortical activation maps to be made rapidly with a very high degree of spatial resolution. COI is reliable and consistent over time. COI, if used carefully, holds promise as an intraoperative technique to study both human and experimental animal cortical function.

Animals↗
PubMed1997

The health-promoting workplace: an integrative perspective.

The workplace is an important setting, affecting the physical, mental, economic and social wellbeing of workers, and, in turn, their families. Health of workers has many determinants, and a multidisciplinary, integrated approach is important. An overview of trends in workplace health promotion shows that current thinking has changed from a narrowly based risk-factors approach aimed at individual behaviour changes, to an integrative approach aimed at creating health-promoting workplaces. The health-promoting workplace has 'an all-encompassing approach that empowers workers and employers to improve all facets of their health'. There are gaps in knowledge, at the state and national levels, relevant to the planning and assessment of workplace health. A national information network is needed to facilitate better links between public health practitioners and researchers in advancing the health of working Australians.

Adult↗