Biomedical subjects

Y Mao

Publications and source records attributed to Y Mao.

At least 19 recordsLinked to original sources

PubMed1992

Herbicides and cancer.

Herbicides are a heterogeneous class of chemicals used in agriculture, forestry, and urban settings to kill weeds, shrubs, and broad-leaved trees. The role of herbicides in the etiology of cancer is controversial. Potential studies for review were identified through a MEDLINE search and from a check of references in related review articles. This review of the literature shows reasonable evidence suggesting that occupational exposure to phenoxy herbicides results in increased risk of developing non-Hodgkin's lymphoma. Several studies have noted large increases in risk of soft-tissue sarcomas with phenoxy herbicide exposure. In contrast, others have failed to observe increased risks, and evidence of an exposure-risk relationship is lacking. Although there have been too few appropriate studies for adequate assessment of risk of cancer at other sites, some findings have linked herbicide exposure with cancers of the colon, lung, nose, prostate, and ovary as well as to leukemia and multiple myeloma. Future studies must better identify and quantify the nature of herbicide exposures. In the interim, it seems only prudent to monitor and promote safety practices among persons occupationally exposed to phenoxy herbicides, particularly farmers and professional sprayers.

Animals↗

PubMed1992

Increasing incidence of primary malignant brain tumors: influence of diagnostic methods.

BACKGROUND: The incidence of brain cancer has increased dramatically over the last decades in most developed countries. Whether these trends can be attributed to improved diagnosis is not clear. PURPOSE: To determine the effect of new imaging technology on increased rates of brain cancer, we assessed the level of detection for neurological disorders when computed tomography (CT) and magnetic resonance imaging (MRI) results were not available. METHODS: A neurologist performed a blind review of hospital charts from 356 randomly selected patients, hospitalized between 1985 and 1989 for neurological disorders, including brain cancer. All prediagnosis information except CT and MRI results was used as a basis for diagnostic re-evaluation. Also, a random sample of 151 brain cancer patients diagnosed between 1960 and 1965 was selected for a description of diagnostic methods used during that period. RESULTS: A comparison between the original diagnoses and the re-evaluations for patients in the 1985-1989 sample indicated that there was, among the diseases selected, a 24% misclassification when CT scans and MRI were not available. In particular, 20% of brain tumors were undetected (95% confidence interval = 15%-25%), and 10% of non-tumor disorders were inaccurately labeled as brain tumors in the absence of these tests. The repeatability of the re-evaluations was 86%. CONCLUSIONS: Among elderly North Americans, at least twofold increases in brain cancer incidence were observed over the last two decades. Since our findings show that CT scans and MRI are responsible for the detection of about 20% of brain tumors, we conclude that other factors also are responsible for the observed trends.

Adolescent↗

PubMed1992

Risk assessment of physical activity and physical fitness in the Canada Health Survey mortality follow-up study.

The effect of physical fitness and physical activity on all-cause mortality and mortality due to cardiovascular disease (CVD), cancer and other causes was examined using a population-based representative sample of the Canadian population. A total of 691 deaths occurred among persons age 30-69 during the 7-year follow-up period. Of these, 37, 33 and 30% died of CVD, cancer and other causes, respectively. The effect of each risk factor on mortality was assessed using logistic regression analysis. Adjustment was made for age, sex, smoking and body mass index in the case of mortality due to CVD, all causes and causes other than CVD and cancer. Models for mortality due to cancer included adjustment for age, sex, smoking and alcohol consumption. For all cause mortality, those individuals who did not pass the physical fitness tests had significantly higher risks of death than those that passed. For CVD mortality, subjects whose physical activity was moderate were protected, and those who did not pass the physical fitness tests had substantially higher risks of death due to CVD. The risk of death due to cancer was not significantly related to physical activity or physical fitness. Persons who failed the physical fitness tests had significantly elevated risks of death due to causes other than CVD or cancer. Our findings support the conclusion that persons who are physically fit have an overall reduced risk of death independent of other major risk factors. Moderate levels of physical activity appear to be protective against cardiovascular disease.

Adult↗

PubMed1992

Genetic dissection of autoimmune type I diabetes in the BB rat.

The BB rat is among the best models of insulin-dependent diabetes mellitus--with onset and pathogenesis closely resembling the human disease. One unusual feature is a severe T-cell lymphopenia, which appears to be inherited as a recessive trait controlled by a single gene, Lyp. Based on genetic analysis of several crosses, we show that development of diabetes involves at least three genes: Lyp, which is tightly linked to the neuropeptide Y (Npy) gene on chromosome 4, a gene linked to the major histocompatibility complex (MHC) on chromosome 20, and a third unmapped gene for which the Fischer rat strain carries an allele conferring resistance.

Animals↗

PubMed1992

Discrimination of clenches at varied jaw positions using autoregressive model coefficients of myoelectrical activities of anterior temporal and masseter muscles.

During 10% maximum clenching at intercuspal, protruded, retruded contact and lateral positions, the surface electromyograms (EMG) of bilateral anterior temporal and masseter muscles of 20 normal subjects with intact natural dentitions were recorded. The autoregressive (AR) model of the sampled EMG was then built and the obtained coefficients of the AR model were accepted as featured parameters of the EMG. Finally Bayes' stepwise discriminant analysis was used for establishing discriminant functions of estimating low level clenches at varied jaw positions. It was found that total conformation rates of internal and external sample substitution (15 and 5 subjects) were 82.67% and 78% respectively; the discriminant effect between intercuspal and retruded contact position was not up to predicted standard. The results indicate that AR model coefficients may describe the characteristics of surface EMG of masticatory muscles and easily be used in multiple statistical analysis, from which the classification and diagnosis may be taken.

Adult↗

PubMed1992

Brain cancer and farming in western Canada.

A cohort study of the mortality experience (1971-1987) of male Canadian prairie farmers has been conducted. This involved linking the records of 156,242 male Alberta, Saskatchewan and Manitoba farmers identified on the 1971 Census of Agriculture and the corresponding Census of Population to mortality records. Exposure indices for individual farm operators were derived from 1971 Census of Agriculture records. Cancer histologies for brain cancer cases were obtained from the Canadian National Cancer Incidence Database and from Provincial Cancer Registries. A statistically significant association was noted between risk of dying of glioblastomas and increasing fuel/oil expenditures (test for trend p = 0.03, top quartile relative risk = 2.11, 95% confidence interval = 0.89-5.01). No significant association was found between brain cancer and either education or mother tongue. However, low income was associated with a significantly reduced risk of brain cancer mortality.

Agricultural Workers' Diseases↗

PubMed1992

In vivo fluoride concentrations measured for two hours after a NaF or a novel two-solution rinse.

The concentrations of fluoride in various samples from the oral environment were measured at timed intervals after a novel rinse or a NaF rinse, both containing a total of 12 mmol/L (228 ppm) fluoride. The novel rinse consisted of two solutions mixed just before application: Part A contained calcium chloride and sodium acetate; part B contained a hydrolyzable source of fluoride (sodium hexafluorosilicate) and sodium phosphate. Samples were obtained as follows: Single-site plaque-fluid samples were obtained by centrifugation of first-molar plaque; pooled whole-plaque samples were collected from second molars; centrifuged, pooled whole-saliva was collected by vacuum. All samples were analyzed by micro-analytical methods. Results showed that, compared with NaF, the two-solution rinse produced significantly higher salivary fluoride concentrations, plaque-fluid fluoride concentrations, and acid-extractable fluoride in the whole plaque by factors of about 4, 2, and 6, respectively, at 120 min. The results of this study suggest that the new rinse may provide a greater cariostatic effect at the same fluoride dosage than does a NaF rinse.

Adult↗

PubMed1992

An investigation of the increase in preschool-age asthma in Manitoba, Canada.

Asthma has long been a major cause of illness and disability among young Canadians. From 1970-71 to 1987-88, hospital admissions for asthma increased significantly among Canadian children under the age of fourteen. Many hypotheses may explain this increase in asthma prevalence. There could be a true increase in the number of people developing symptoms of the disease or increased asthma rates could be an artifact due to changes in detection, diagnosis, treatment, or coding. This study reviews hypotheses put forward to explain the increase in asthma prevalence, and tests some of them in Manitoba for children aged 0-4. Physician claims data and hospital separation data were merged to create unique person oriented medical records. These records were used to estimate the number of children seeking medical services for asthma during a five-year period (1984-85 to 1988-89) and the change in rates over this time period. From 1984-85 to 1988-89, both prevalence and incidence rates for children less than five years of age increased. Prevalence rates showed strong seasonal peaks in the spring and the fall. There is no indication that asthma increased in severity. The hospitalization rate (the number visiting a hospital for asthma divided by the total number seeking medical care for asthma), the average number of hospital admissions per year, and the average number of days spent in a hospital per year did not increase. Levels of ozone (O3) and nitrogen dioxide (NO2) in downtown Winnipeg increased over the study period and asthma prevalence increased twice as fast in Winnipeg as in the rest of the province. For Manitoba, the increase in preschool-aged asthma does not appear to be due to increased use of medical services, a change in ICD coding, an increase in the severity of the cases, or a decrease in income levels. The increases appear to be at least partly due to changes in diagnostic practices. The relationship between asthma and air pollution needs more detailed study as pollution is likely to be an important factor, particularly during the spring. Other areas for further investigation are changes in allergy and virus precursors, maternal smoking, and increased levels of pollens, molds and dust mites.

Abstracting and Indexing↗

PubMed1992

[Multi-origin usage for chromosome replication of suppressive integration strain of dnaA46 mutant of Escherichia coli integrated with R6K].

The chromosome of temperature sensitive initiation mutant dnaA46 of Escherichia coli K-12 fails to replicate at 42 degrees C. Suppressive integration (Sin) strain integrated with the R6K plasmid was screened at 42 degrees C. Marker frequency determination of the Sin strain reveals that replication was initiated at the normal site of initiation at 30 degrees C, while at three different sites at 42 degrees C. Two of the sites have been reported in the stable DNA replication mutant, one of them is a novel site. Inhibition of chromosome replication was not observed for the recA derivative of Sin initiated at two of the initiation sites close to the normal initiation site. Inhibition was observed for chromosome replication initiated near the site where chromosome replication normally terminates. It indicates that chromosome replication initiated at sites close to the terminus is recA gene dependent.

Chromosomes, Bacterial↗

PubMed1991

A totally synthetic histidine-2 ferredoxin: thermal stability and redox properties.

The entire polypeptide of Clostridium pasteurianum ferredoxin (Fd) with a site-substituted tyrosine-2----histidine-2 was synthesized using standard t-Boc procedures, reconstituted to the 2[4Fe-4S] holoprotein, and compared to synthetic C. pasteurianum and native Fds. Although histidine-2 is commonly found in thermostable clostridial Fds, the histidine-2 substitution into synthetic C. pasteurianum Fd did not significantly increase its thermostability. The reduction potential of synthetic histidine-2 Fd was -343 and -394 mV at pH 6.4 and 8.7, respectively, versus standard hydrogen electrode. Similarly, Clostridium thermosaccharolyticum Fd which naturally contains histidine-2 was previously determined to have a pH-dependent reduction potential [Smith, E.T., & Feinberg, B.A. (1990) J. Biol. Chem. 265, 14371-14376]. An electrostatic model was used to calculate the observed change in reduction potential with pH for a homologous ferredoxin with a known X-ray crystal structure containing a hypothetical histidine-2. In contrast, the reduction potential of both native C. pasteurianum Fd and synthetic Fd with the C. pasteurianum sequence was -400 mV versus standard hydrogen electrode and was pH-independent [Smith, E.T., Feinberg, B.A., Richards, J.H., & Tomich, J.M. (1991) J. Am. Chem. Soc. 113, 688-689]. On the basis of the above results, we conclude that the observed pH-dependent reduction potential for both synthetic and native ferredoxins that contain histidine-2 is attributable to the electrostatic interaction between histidine-2 and iron-sulfur cluster II which is approximately 6 A away.

Amino Acid Sequence↗

PubMed1991

Increasing brain cancer rates in Canada.

OBJECTIVE: To analyse brain cancer patterns in Canada, particularly according to age and sex distributions, temporal patterns and regional variations. Changes in diagnostic techniques, survival rates and trends by tumour type were also examined. DESIGN: Descriptive epidemiologic study based on Canada-wide population data for 1959-88. OUTCOME MEASURES: Rates of death, incidence and admission to hospital because of brain cancer, as well as survival time and methods of diagnosis. SUBJECTS: Incidence and death rates and time trends were examined for Canada as a whole, by province and by census division. RESULTS: The rates of death from brain cancer increased rapidly among Canadians aged 55 years or more from 1959 to 1988. In particular, age-adjusted death rates increased by 117%, 797% and 118% among men 65 to 74 years, 75 to 84 and 85 or more respectively. The corresponding increases among women were 138%, 535% and 400%. The incidence rates also increased substantially. The trends in incidence rates by tumour type indicated that the increase was more pronounced for glioblastomas. The incidence rates of cases detected histologically, radiologically and clinically all increased. CONCLUSIONS: Because glioblastomas are generally easier to diagnose than astrocytomas and because the incidence rates of glioblastomas were found to increase substantially, the increased brain cancer rates among elderly people may not be entirely attributable to improved diagnostic techniques. However, analytic investigations of the impact of changes in diagnostic procedures on brain cancer trends are needed to clarify this issue.

Adolescent↗

PubMed1991

Properties of matrix-assisted laser desorption. Measurements with a time-to-digital converter.

Some properties of matrix-assisted laser desorption have been studied using single-ion-counting methods and a time-to-digital converter. The methods allow examination of the process for irradiances near the reported threshold for observation with a transient recorder. All measurements were made using bovine insulin as a test compound. We present direct evidence that an irradiance threshold near 10(6) W cm-2 exists for ion production, and that the process is a collective effect, either involving a large number of molecular ions (approximately 10(4) in a successful event or none at all. Above the threshold, the yield is found to scale with a high power (4th to 6th) of the irradiance. Measurements of initial velocity distributions indicate an axial velocity spread corresponding to approximately 50 eV and a radial velocity spread corresponding to approximately 2.4 eV. Thus the ejection or extraction mechanism appears to be strongly asymmetric.

Animals↗

PubMed1991

The relationship of suicide rates to sociodemographic factors in Canadian census divisions.

The correlates of suicide rates were determined by conducting a multivariate study of sociodemographic indicators and suicide rates of 261 Canadian census divisions. Twenty-one sociodemographic variables were entered into a stepwise multiple linear regression to develop a model for suicide rates. The important variables were mortality rate for all causes of death, the age of the population, average family income, population density, proportion with no religious affiliation, proportion of Francophones, unemployment, immigration, proportion of Native people, a regional effect for British Columbia and the north, and growth by mobility, explaining 62% of the observed variation. This spatial ecologic analysis highlights the importance of cultural differences in explaining the variation of suicide rates. The analysis supports the previously found negative relationship between income and suicide while contrasting from previous studies in determining a inverse relationship with unemployment and an inverse relationship with the age distribution.

Canada↗

PubMed1991

[The effect of plaque fluid on demineralization of enamel powder].

The aim of this study was to explore any substance in dental plaque which might affect the demineralization of enamel. Plaque fluid was prepared by centrifugation of pooled plaque from 56 young adults without periodontal diseases. Enamel was separated from healthy teeth of adolescents and crushed into powder. The enamel powder was treated separately by plaque fluid and synthetic plaque fluid (as a control, with similar calcium, fluoride content and pH as the natural). After this, the enamel powder was washed with PBS. Both the plaque fluid-treated and synthetic plaque fluid-treated enamel powder were demineralized by mixed organic acid (pH 4.5). The calcium content in both plaque fluids, PBS and organic acid after treatment with enamel powder was analysed by atomic absorption spectrophotometer. The results showed that there was no promoting effect in plaque fluid on demineralization of enamel, but, on the other hand, some protecting action was observed which might contribute to the presence of proteins in plaque fluid.

Adult↗

PubMed1991

[An analysis of chemical oxygen demand, carbohydrate, IgG and IgA in extracellular fluid of bacterial plaque].

The chemical oxygen demand (COD) of extracellular plaque fluid was measured by potassium dichromate method. Micro-anthrone method and high performance liquid chromatography were used for measuring the carbohydrate content in the fluid. Immunochemistry system was used for measuring IgG and IgA contents in it. The results showed: (1) a high value of COD was found in the extracellular fluid, and it further increased with sugar-intake; (2) during resting stage, the content of carbohydrate measured by microanthrone method or high performance chromatography was very low, and there was no free glucose, fructose or sucrose; (3) no difference of IgG and IgA contents in plaque fluid between caries active (CA) and caries free (CF) subjects was found.

Adolescent↗

PubMed1990

Mortality study of Canadian male farm operators: non-Hodgkin's lymphoma mortality and agricultural practices in Saskatchewan.

A cohort study of the mortality experience (1971-1985) of male Saskatchewan farmers has been conducted. This study involved linkage of records of the almost 70,000 male farmers identified on the 1971 Census of Agriculture and the corresponding Census of Population to mortality records. Pesticide exposure indices for individual farm operators for the year 1970 were derived from the 1971 Census of Agriculture records. Although the cohort as a whole had no excess mortality for any specific causes of death, including non-Hodgkin's lymphoma, significant dose-response relationships were noted between risk of non-Hodgkin's lymphoma and acres sprayed in 1970 with herbicides, as well as with dollars spent on fuel and oil for farm purposes in 1970. Using Poisson regression modeling, we found that relative risks for the highest level of herbicide use (greater than or equal to 250 acres sprayed) and fuel purchased in 1970 (greater than or equal to $900) on farms less than 1,000 acres total area were 2.2 (95% confidence interval = 1.0-4.6) and 2.3 (95% confidence interval = 1.1-4.7), respectively.

Adult↗

PubMed1990

[Study on Ha-ras RFLPs in gastric carcinoma and normal tissue DNAs of Chinese individuals].

By using recombinant plasmid PHS-49 as a probe, BamHI restriction fragment length polymorphisms (RFLPs) was studied in tumour DNAs of 36 gastric carcinoma patients and normal tissue DNAs of 25 unaffected Chinese individuals. Ten alleles and eighteen genotypes for Ha-ras gene were found. Four "rare" restriction fragments of size less than 6 kilobase pairs (kb) are first reported for Ha-ras locus in present paper, we inferred that these alleles might be one of the characteristics of genetic polymorphisms in Chinese population. Moreover, the frequency of some "rare" alleles and genotypes occurred in gastric carcinoma samples is significantly higher than that occurred in normal individuals. The results of pedigree analysis for two patients showed that some heterozygotes carried three or four alleles. It suggested that there may be more than one copy of Ha-ras gene sequence existed in a chromosome. The possible causes of the phenomenon mentioned above were discussed.

Alleles↗

PubMed1990

[Effects of proteolytic enzymes on demineralization of enamel].

Papain, trypsin and collagenase were used in the experiment for the study of their effects on the demineralization of enamel surface by organic acids in vivo. No effect of any of the enzymes was observed. The use of papain and trypsin in treating tooth surfaces in vitro, no matter whether sodium bisulfite was used, showed no effect on the demineralization of the enamel by mixed organic acids. But, by the analysis of amino acids in the enzyme solutions before and after treating tooth surface, it was shown that some proteinous substances were destroyed. Accordingly, it can be suggested that the enzyme takes no part in the destruction of the inorganic tooth substance.

Dental Enamel↗