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Biomedical subjects

M N Nguyen

Publications and source records attributed to M N Nguyen.

15 recordsLinked to original sources
PubMed2005

Two-stage multi-class support vector machines to protein secondary structure prediction.

Bioinformatics techniques to protein secondary structure (PSS) prediction are mostly single-stage approaches in the sense that they predict secondary structures of proteins by taking into account only the contextual information in amino acid sequences. In this paper, we propose two-stage Multi-class Support Vector Machine (MSVM) approach where a MSVM predictor is introduced to the output of the first stage MSVM to capture the sequential relationship among secondary structure elements for the prediction. By using position specific scoring matrices, generated by PSI-BLAST, the two-stage MSVM approach achieves Q3 accuracies of 78.0% and 76.3% on the RS126 dataset of 126 nonhomologous globular proteins and the CB396 dataset of 396 nonhomologous proteins, respectively, which are better than the highest scores published on both datasets to date.

Computational Biology↗
PubMed2002

Extremely low vertical-emittance beam in the accelerator test facility at KEK.

Electron beams with the lowest, normalized transverse emittance recorded so far were produced and confirmed in single-bunch-mode operation of the Accelerator Test Facility at KEK. We established a tuning method of the damping ring which achieves a small vertical dispersion and small x-y orbit coupling. The vertical emittance was less than 1% of the horizontal emittance. At the zero-intensity limit, the vertical normalized emittance was less than 2.8 x 10(-8) rad m at beam energy 1.3 GeV. At high intensity, strong effects of intrabeam scattering were observed, which had been expected in view of the extremely high particle density due to the small transverse emittance.

Journal Article↗
PubMed2001

exo1-Dependent mutator mutations: model system for studying functional interactions in mismatch repair.

EXO1 interacts with MSH2 and MLH1 and has been proposed to be a redundant exonuclease that functions in mismatch repair (MMR). To better understand the role of EXO1 in mismatch repair, a genetic screen was performed to identify mutations that increase the mutation rates caused by weak mutator mutations such as exo1Delta and pms1-A130V mutations. In a screen starting with an exo1 mutation, exo1-dependent mutator mutations were obtained in MLH1, PMS1, MSH2, MSH3, POL30 (PCNA), POL32, and RNR1, whereas starting with the weak pms1 allele pms1-A130V, pms1-dependent mutator mutations were identified in MLH1, MSH2, MSH3, MSH6, and EXO1. These mutations only cause weak MMR defects as single mutants but cause strong MMR defects when combined with each other. Most of the mutations obtained caused amino acid substitutions in MLH1 or PMS1, and these clustered in either the ATP-binding region or the MLH1-PMS1 interaction regions of these proteins. The mutations showed two other types of interactions: specific pairs of mutations showed unlinked noncomplementation in diploid strains, and the defect caused by pairs of mutations could be suppressed by high-copy-number expression of a third gene, an effect that showed allele and overexpressed gene specificity. These results support a model in which EXO1 plays a structural role in MMR and stabilizes multiprotein complexes containing a number of MMR proteins. A similar role is proposed for PCNA based on the data presented.

Adenosine Triphosphate↗
PubMed2001

An improved GC/MS-based procedure for the quantitation of the isoprostane 15-F2t-IsoP in rat plasma.

This article describes a procedure for the quantitation of the isoprostane 15-F2t-IsoP (9a,11a,15S-trihydroxy-(8b)-prosta-5Z,13E-dien-1-oic acid [CAS#27415-26-5] formerly known as 8-epi-PGF2a or 8-iso-PGF2a, and also as iPF2a-III). We have combined features from several earlier methods for 15-F2t-IsoP and prostaglandins, and identified and modified those steps that may lead to poor recoveries. The resulting protocol is precise and reliable, and was validated by a blind time-course study of plasma levels in rats treated with 120 and 1200 mg CCl4/kg body weight. Plasma levels of 15-F2t-IsoP, as measured according to the procedure described above, are good indicators of acute oxidative stress as induced by CCl4. The precision of the measurements allows detection of elevated plasma 15-F2t-IsoP levels as long as 16 h after an acute exposure of 120 mg CCl4/kg body weight, and 2 h after an exposure of 1 mg CCl4/kg body weight. The results of this low-dose, pilot study suggest that this method has sufficient analytical precision to allow the detection of the small changes in plasma isoprostane levels, which result from chronic and/or lower-level exposures to agents causing oxidative stress.

Animals↗
PubMed2000

Myeloperoxidase and protein oxidation in cystic fibrosis.

Cystic fibrosis (CF) is associated with chronic pulmonary inflammation and progressive lung dysfunction, possibly associated with the formation of neutrophil myeloperoxidase (MPO)-derived oxidants. Expectorated sputum specimens from adult CF patients were analyzed for MPO characteristic protein modifications and found to contain large amounts of active MPO as well as high levels of protein-associated 3-chlorotyrosine and 3,3'-dityrosine, products that result from MPO activity, compared with expectorated sputum from non-CF subjects. Sputum levels of nitrite (NO(2)(-)) and nitrate (NO(3)(-)), indicating local production of nitric oxide (NO. ), were not elevated but in fact were slightly reduced in CF. However, there was a slight increase in protein-associated 3-nitrotyrosine in CF sputum compared with controls, reflecting the formation of reactive nitrogen intermediates, possibly through MPO-catalyzed oxidation of NO(2)(-). CF sputum MPO was found to contribute to oxidant-mediated cytotoxicity toward cultured tracheobronchial epithelial cells; however, peroxidase-dependent protein oxidation occurred primarily within sputum proteins, suggesting scavenging of MPO-derived oxidants by CF mucus and perhaps formation of secondary cytotoxic products within CF sputum. Our findings demonstrate the formation of MPO-derived oxidizing and possibly nitrating species within the respiratory tract of subjects with CF, which collectively may contribute to bronchial injury and respiratory failure in CF.

Adult↗
PubMed1997

Regular exercise in 30- to 60-year-old men: combining the stages-of-change model and the theory of planned behavior to identify determinants for targeting heart health interventions.

The theory of planned behavior and the stages-of-change model were used to gain a clearer understanding of the factors associated with regular exercise in order to plan more effective programs in heart disease prevention. The study was conducted using a self-administered postal questionnaire sent to a sample of 2,269 men 30 to 60 years of age. Nearly a quarter (23.3%) of respondents were physically inactive, of whom 10.5% were in the precontemplation and 12.8% in the contemplation stages; 42.1% exercised less than twice a week, of whom 22.4% were in the preparation I and 19.7% in the preparation II stages. Only 34.6% were in the action stage, exercising regularly for at least 20 minutes twice a week or more with the intention of continuing to do so. Logistic regression indicated that the variables derived from the theory of planned behavior, namely attitude, subjective norm and perceived behavioral control, were differently associated with the stages of behavior. Perceived behavioral control was strongly significant in all stages. Attitude was related with stages in which individuals have intention of exercising (contemplation and preparation II). In contrast, subjective norm seemed to be associated with stages in which individuals have no intention of doing so (precontemplation and preparation I). By identifying the specific needs of sub-groups, the results can help define programs most likely to accelerate men to the stage of regular exercise, part of an effective strategy for heart health promotion in this high-risk population.

Adult↗
PubMed1996

Diet and exercise profiles of 30- to 60-year-old male smokers: implications for community heart health programs.

The aim of this study was to estimate the prevalence of diet and exercise behaviors in middle-aged male smokers and identify their determinants of behaviors, with the ultimate goal of designing more effective interventions in a community heart health program. Self-administered, postal questionnaires produced a sample of n = 671 male smokers, 30 to 60 years of age residing in Laval, Quebec's second most populous city. Variables for the study were derived from the theory of planned behavior. Correspondence analysis explained 65% of the variance, classifying smokers into five groups based on diet and exercise behavior. Group 1, smokers with diet and exercise behaviors deemed inadequate for heart health, comprised 43% of the total. Groups 2 and 3, smokers with a diet deemed inadequate or needing improvement respectively, and Group 4, smokers with inadequate exercise, comprised 42% of the total. Group 5, smokers with neither of the other high-risk behaviors, comprised 15% of the total. Four significant variables contrasted Groups 1 to 4 with group 5: age, number of cigarettes smoked daily, and perceived behavioral control (PBC) in both diet and exercise. However, coefficients for age and smoking were weak for all groups. Coefficients for PBC in diet were high and negative only for smokers with an inadequate one. For PBC in exercise, they were high and negative only for smokers who exercised inadequately. Intervention groups based on specific deficiencies in diet and exercise behaviors were then identified. Therefore, the results suggest that smoking cessation programs may be made more effective by targeting specific sub-groups and by providing resources and opportunities to counteract the lack of perceived behavioral control in middle-aged male smokers vis-a-vis diet and exercise.

Adult↗
PubMed1996

Factors influencing the intention to use condoms in Quebec sexually-inactive male adolescents.

PURPOSE: The purpose of this study was to determine whether attitudes and other variables would be associated with intention to use condoms in sexually-inactive male adolescents. METHODS: The survey was conducted from April to June 1989 on a sample of 879 sexually-inactive boys aged 12-19 years registered in secondary schools in Laval, Quebec. RESULTS: The major findings of the study were that: (1) information on condoms provided by peers was significantly associated with the intention to use condoms; (2) information provided by schools, while not significant in the final model, was positively associated with younger adolescents' intention to use condoms; and (3) sexually-inactive male adolescents in a less committed couple relationship had a greater intention to use condoms. CONCLUSIONS: The results of this study highlight the importance of peer instructors as a source of information on condoms, as well as that of teachers and health professionals from the school environment. Other channels of communication, however, need to be developed particularly for older sexually-inactive adolescents who may be impervious to this latter source. The findings also underline the necessity to make sexually-inactive adolescents in stable couple relationships more aware of their potential vulnerability to STDs and AIDS should they commence sexual relations.

Adolescent↗
PubMed1995

Behavioral diagnosis of 30 to 60 year-old men in the Fabreville Heart Health Program.

To develop effective interventions in the Fabreville Heart Health Program, a behavioral diagnosis was conducted on a sample of 1,600 men 30 to 60 years of age residing in the Fabreville district of Laval, Quebec's second most populous city. The response rate of the self-administered postal questionnaire was 73.5%. The results indicate that dietary fat consumption, smoking and a sedentary lifestyle were more prevalent among the younger respondents, particularly those less-educated. The results underline the importance of segmenting the target population so that heart health interventions can respond to the specific needs of each sub-population. Furthermore, the data seem to suggest the need to adapt educational messages to the target lifestyle habits. The results showed that in terms of diet, consumption of meat and dairy products contributed the most to fat intake. Of the 30% who were smokers, a large proportion would be reluctant to stop the habit; 20% smoked 26 cigarettes or more a day, and more than half had already tried once or more to stop. Although 60% of respondents indicated they engaged in physical activity, only 37.0% did it regularly. These results demonstrate the need to clearly target specific behaviours and subgroups in our promotion messages for a healthy heart.

Adult↗
PubMed1994

Influence of attitudes on the intention to use condoms in Quebec sexually active male adolescents.

PURPOSE: The purpose of this study was to determine the influence of attitudes and other variables on the intention to use condoms in sexually active male adolescents. METHODS: The survey was conducted from April to June 1989 on a sample of 433 sexually active boys aged 12-19 years registered in secondary schools in Laval, Quebec. RESULTS: Information on condoms provided by parents, peers, school, or media had no positive effect on male adolescents' intention to use condoms. Having a favorable attitude towards contraceptive responsibility, however, was significantly associated with the outcome variable. Endorsement of this responsibility seemed short-lived being replaced by the birth control pill in older adolescents. The study also found that in younger adolescents, intention to use condoms was significantly associated with supportive parental attitudes. CONCLUSIONS: The results of this study highlight the importance of developing strategies to encourage sexually active male adolescents to assume greater responsibility for using condoms, and suggest that in order for programs to be effective, STD and acquired immunodeficiency syndrome prevention should be done at younger ages while encouraging parents to take a greater role in sex education.

Adolescent↗
PubMedDate not supplied

Is the intention to quit smoking influenced by other heart-healthy lifestyle habits in 30- to 60-year-old men?

The aim of this study was to analyze whether the intention to quit smoking was associated with other lifestyle habits healthy for the heart, namely a low-fat diet and regular exercise, using variables suggested by the theory of planned behavior. Self-administered postal questionnaires were sent to 3,200 men 30 to 60 years of age residing in Laval, Quebec. With a response rate of 70.9%, 671 respondents (29.6%) were smokers. A significant proportion (43%) had all three risk behaviors--smoking, a high-fat diet, and sedentariness, and 42% had two--smoking and one of the other behaviors. The remaining had a single risk behavior, namely smoking. Regression analysis suggested that a healthy diet and exercise had no significant influence on the intention to quit smoking. However, men who had a stronger intention to quit smoking than others had a more favorable attitude toward the behavior, a stronger perception of approval in achieving it on the part of important referents, stronger perceived behavioral control, and were among those who smoked fewer cigarettes per day, but had made more attempts to quit. These results can assist in designing better heart-health intervention programs for this high-risk population.

Adult↗
PubMedDate not supplied

Determinants of intention to adopt a low-fat diet in men 30 to 60 years old: implications for heart health promotion.

PURPOSE: The purpose of the study was to identify the determinants of intention to have a low-fat diet in 30- to 60-year-old men. DESIGN: The survey design was cross-sectional and consisted of a self-administered questionnaire. The dependent variable was the intention to have a low-fat diet within the next 4 months, and the independent variables were those suggested by the theory of planned behavior. SETTING: The study population was drawn from three districts representing a modal sample of Laval, the second most populous city (N = 314,398) in the province of Quebec. SUBJECTS: The sample comprised 3200 people. Of the 3200 questionnaires sent out, 2583 were received and 2269 were eligible (i.e., were answered by 30- to 60-year-old men), giving a response rate of 70.9%. Of the 2269 questionnaires, 430 were incomplete, resulted in 1839 being usable for analysis. MEASURES: Multiple regression analysis was conducted to determine the influence of the independent variables on the dependent variable, the intention to have a low-fat diet. The independent variables were (1) direct and indirect determinants of intention as suggested in the theory of planned behavior and (2) sociodemographic and concomitant variables and their interactions. Discriminant analysis was used on the significant variables obtained in the regression to establish the cognitive profile of respondents' intention, strong or weak. RESULTS: In the final model, five variables 51% of the total variance. Respondents who had a stronger intention perceived that their important referents would approve them having a low-fat diet. They scored higher in seeing the advantages of adopting the target behavior and had a more positive attitude toward the behavior. They also perceived themselves as having control over the target behavior, and scored higher in terms of recognizing the perceived power of this control factor. CONCLUSIONS: The results suggests that the theory of planned behavior can be an effective tool in the planning of heart health promotion. They indicate that low-fat diet programs for men should target the work site and peer-group organizations, and place emphasis on adapting usual recipes. Though accenting the health and nutritional benefits of a low-fat diet, messages should appeal to emotion as well as reason.

Adult↗