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Biomedical subjects

Y Mao

Publications and source records attributed to Y Mao.

At least 217 records · Page 12Linked to original sources
PubMed1996

Cervical cancer screening: are the 1989 recommendations still valid? National Workshop on Screening for Cancer of the Cervix.

Although screening for cervical cancer has been shown to be effective in reducing the morbidity and mortality associated with this disease, and despite many attempts to encourage the development of provincial programs, as of 1995 no province had a comprehensive screening program for cervical cancer. Participants at the Interchange '95 workshop, held in Ottawa in November 1995, reviewed the recommendations of the 1989 National Workshop on Screening for Cancer of the Cervix and identified factors that have impeded their implementation. Participants discussed the need for comprehensive information systems, quality control and strategies to increase recruitment of unscreened and underscreened women. They concluded that the formation of a Cervical Cancer Prevention Network involving key stakeholders will facilitate the development and implementation of provincial programs to ensure optimal screening. They agreed that, in the interim, recommendations for practising physicians should remain as they were following the 1989 workshop.

Canada↗
PubMed1996

Vanadium(IV)-mediated free radical generation and related 2'-deoxyguanosine hydroxylation and DNA damage.

Free radical generation, 2'-deoxyguanosine (dG) hydroxylation and DNA damage by vanadium(IV) reactions were investigated. Vanadium(IV) caused molecular oxygen dependent dG hydroxylation to form 8-hydroxyl-2'-deoxyguanosine (8-OHdG). During a 15 min incubation of 1.0 mM dG and 1.0 mM VOSO4 in phosphate buffer solution (pH 7.4) at room temperature under ambient air, dG was converted to 8-OHdG with a yield of about 0.31%. Catalase and formate inhibited the 8-OHdG formation while superoxide dismutase enhanced it. Metal ion chelators, DTPA and deferoxamine, blocked the 8-OHdG formation. Incubation of vanadium(IV) with dG in argon did not generate any significant amount of 8-OHdG, indicating the role of molecular oxygen in the mechanism of vanadium(IV)-induced dG hydroxylation. Vanadium(IV) also caused molecular oxygen-dependent DNA strand breaks in a pattern similar to that observed for dG hydroxylation. ESR spin trapping measurements demonstrated that the reaction of vanadium(IV) with H2O2 generated OH radicals, which were inhibited by DTPA and deferoxamine. Incubation of vanadium(IV) with dG or with DNA in the presence of H2O2 resulted in an enhanced 8-OHdG formation and substantial DNA double strand breaks. Sodium formate inhibited 8-OHdG formation while DTPA had no significant effect. Deferoxamine enhanced the 8-OHdG generation by 2.5-fold. ESR and UV measurements provided evidence for the complex formation between vanadium(IV) and deferoxamine. UV-visible measurements indicate that dG, vanadium(IV) and deferoxamine are able to form a complex, thereby, facilitating site-specific 8-OHdG formation. Reaction of vanadium(IV) with t-butyl hydroperoxide generated hydroperoxide-derived free radicals, which caused 8-OHdG formation from dG and DNA strand breaks. DTPA and deferoxamine attenuated vanadium(IV)/t-butyl-OOH-induced DNA strand breaks.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1996

Reduction of extracellular dehydroascorbic acid by K562 cells.

K562 erythroleukaemic cells produced ascorbate when incubated with dehydroascorbic acid. The reduction depended on the number of cells and on the concentration of dehydroascorbic acid. The observed rate consists of a high affinity (apparent Km 7 mu M, Vmax 3 center dot 25 pmol min-1 (10(6) cells)-1 and a low affinity component, which was non-saturable up to 1 mM of DHA (rate increase of 0 center dot 1 pmol min-1 (10(6) cells)-1 (1 mu M of DHA-1). The rate was dependent on temperature and was stimulated by glucose and inhibited by phloretin, N-ethylmaleimide, parachloro-mercuribenzoate and the noyltrifluoroacetone. Although uptake of DHA proceeded at a higher rate than its extracellular reduction, the generation of extracellular ascorbate from DHA cannot be accounted for by intracellular reduction and the release of ascorbate, since the latter was not linear with time and had an initial rate of approximately 3 pmol min-1 (10(6) cells-1). At a concentration of DHA of 100 mu M this is 25 per cent of the observed reduction.

Ascorbic Acid↗
PubMed1996

The Phytophthora sojae genome contains tandem repeat sequences which vary from strain to strain.

The oömycete Phytophthora sojae causes root and stem rot of soybean. In P. sojae, 37 cultivarspecific physiological races have been reported with different reactions against 13 single dominant resistance genes in soybean. Recent genetic studies have demonstrated that the P. sojae-soybean interaction follows Flor's gene-for-gene model. Genomic subtraction was carried out to isolate race-specific DNA sequences possibly including avirulence genes. DNA from a race 1 isolate was subtraction-enriched with the DNAs from race 19 and race 22 isolates. The enriched DNAs were used to differentially screen a P. sojae genomic library. Characterization of the clones obtained identified repetitive sequences with variable copy numbers among isolates. Five of these repetitive sequences were tandemly repeated and were localized on single chromosomes. The sixth corresponded to the ribosomal RNA genes. These observations suggest that gene amplification could contribute to the generation of genetic diversity in P. sojae. Enriched sequences corresponding to avirulence genes were not detected.

Base Sequence↗
PubMed1996

Cloning and sequence analysis of elicitin genes of Phytophthora sojae.

A gene, Sojein2, has been cloned that encodes an elicitin from Phytophthora sojae with 81.6-92.9% identity with other elicitins. DNA hybridization analysis indicated that elicitins are encoded by a multigene family in P. sojae. Necrosis tests and elicitin production suggest that elicitins do not contribute to race-specificity in P. sojae.

Amino Acid Sequence↗
PubMed1996

Role of chromium(IV) in the chromium(VI)-related free radical formation, dG hydroxylation, and DNA damage.

A reactive Cr(IV) ester was synthesized from a reaction of CrO3 with 2,4-dimethyl-2,4-pentanediol as verified by electron spin resonance (ESR) and magnetic susceptibility measurements. ESR spin trapping studies demonstrate that the Cr(IV) ester is capable of generating hydroxyl free radical (.OH) through a Fenton-like mechanism (Cr(IV)+H2O2-->Cr(V)+.OH+OH-) with a concomitant generation of Cr(V) species (g = 1.9787). Cr(IV) caused DNA strand breaks as measured by electrophoretic assays. H2O2 enhanced the DNA strand breaks via .OH formation by a Cr(IV)-mediated Fenton-like reaction. In the Cr(IV)/H2O2 system, formate did not block Cr(V) formation, but prevented DNA damage, indicating that .OH radicals, and not Cr(V), caused the DNA damage. Reaction of Cr(VI) with ascorbate was also used as a source of Cr(IV). Incubation of Cr(VI), ascorbate, and DNA caused DNA strand breaks. A free radical trap, 5,5-dimethyl-1-pyrroline (DMPO), only slightly inhibited the DNA damage. Addition of Mn(II), which inhibited Cr(IV), caused significant protection. H2O2 enhanced the DNA damage via Cr(IV)-mediated .OH radical generation and Mn(II) inhibited the damage, again showing that Cr(IV) and its related .OH generation caused DNA strand breaks. HPLC measurements showed that .OH radicals generated by a Cr(IV)-mediated Fenton-like reaction generated 8-hydroxy-2'-deoxyguanosine from 2'-deoxyguanosine. The results demonstrate that Cr(IV) and its generated .OH radicals are capable of damaging DNA. Moreover, in comparison with Cr(V), Cr(IV) is a more potent DNA damaging agent.

Chromium↗
PubMed1996

The effects of Lactobacillus strains and oat fiber on methotrexate-induced enterocolitis in rats.

BACKGROUND & AIMS: Administration of methotrexate to rats on an elemental diet results in severe enterocolitis and death. Lactobacilli, an integral part of the healthy gastrointestinal microecology, may provide therapeutic benefits to help the recovery from enterocolitis. The purpose of this study was to evaluate the effects of lactobacilli and oatbase on methotrexate-induced enterocolitis in rats. METHODS: Rats received continuous intragastric infusion of elemental diet or with supplementation of oatbase, Lactobacillus reuteri R2LC, and Lactobacillus plantarum DSM 9843, with and without fermentation, from the beginning of the study. Methotrexate (20 mg/kg) was injected intraperitoneally on day 3, and the sampling was performed on day 6. RESULTS: Lactobacilli and oatbase decreased body weight loss and intestinal permeability and increased bowel mucosal mass in enterocolitic rats. Administration of lactobacilli, but not oatbase, decreased the intestinal myeloperoxidase level, reestablished intestinal microecology, and reduced bacterial translocation to extraintestinal sites. Both lactobacilli and oatbase reduced plasma endotoxin levels. The effects of lactobacilli were greater with fermentation than without fermentation or oatbase alone, and L. plantarum was more effective in reducing intestinal pathogens than L. reuteri. CONCLUSIONS: Exogenous administration of lactobacilli, especially L. plantarum with fermentation, is helpful in reducing the severity of enterocolitis in rats.

Animals↗
PubMed1996

Generation of reactive oxygen species by Co(II) from H2O2 in the presence of chelators in relation to DNA damage and 2'-deoxyguanosine hydroxylation.

The generation of reactive oxygen species by Co(II) from H2O2 in the presence of chelators and related DNA damage was investigated by electron spin resonance (ESR), electrophoretic assays, and high-performance liquid chromatography (HPLC). Incubation of Co(II) with beta-alanyl-3-methyl-L-histidine (anserine) and H2O2 generated .OH radicals. Omission of any one component sharply reduced the amount of .OH radicals generated, indicating that anserine modulated the oxidation potential of Co(II) to enhance its capability to generate .OH radicals from H2O2. Formate only moderately decreased the .OH radical generation, while ethanol had no observable effect, indicating that the generation of .OH radical is site specific. The metal ion chelator 1,10-phenanthroline reduced the .OH radical generation, and deferoxamine suppressed it with the formation of deferoxamine nitroxide radical. Electrophoretic assays using both lambda Hind III linear DNA and PM2 supercoiled DNA showed that .OH radicals generated from a mixture of Co(II), H2O2, and anserine caused DNA strand breaks. A mixture of Co(II), H2O2, and 1,10-phenanthroline also caused DNA strand breaks, which were inhibited by sodium azide, indicating that 1O2 was involved in DNA damage. HPLC measurements showed that .OH radicals and 1O2 generated by Co(II) reactions caused 2'-deoxyguanosine hydroxylation to form 8-hydroxy-2'-deoxyguanosine. ESR spin trapping measurements provided evidence for 1O2 generation by Co(II) from H2O2 in the presence of 1,10-phenanthroline. The results indicate that the oxidation potential of Co(II) can be modulated by chelators to facilitate its generation of reactive oxygen species from H2O2. These species may be involved in Co(II)-induced cellular damage.

Anserine↗
PubMed1996

Acoustically enhanced bubble growth at low frequencies and its implications for human diver and marine mammal safety.

Computations are made of the conditions necessary to obtain bubble growth by rectified diffusion under a variety of conditions associated with low-frequency sonar propagation in the ocean. The complex issue of microbubble nuclei stabilization is treated by assuming either a sufficient level of supersaturation to stabilize the initial bubble size, or by examining a microbubble nucleus with zero surface tension. The bubble growth rates and thresholds are obtained for a ranged of sound-pressure levels (re: 1 microPa) from 150-220 dB, for initial bubble radii from 1-10 microns, and for levels of the dissolved gas concentration from 100% to 223% of saturation. It was determined that for the range of conditions examined, it was necessary to utilize three different formulations of the equations for bubble growth. The results of these calculations (and assumptions concerning nuclei stabilization) indicate that for SPL's in excess of 210 dB, significant bubble growth can be expected to occur, and divers and marine mammals exposed to these conditions could be at risk. For SPL's below about 190 dB, however, except under relatively extreme conditions of supersaturation, significant bubble growth is unexpected.

Acoustics↗
PubMed1996

Pectin-supplemented enteral diet reduces the severity of methotrexate induced enterocolitis in rats.

BACKGROUND: Administration of methotrexate (MTX) to rats fed an elemental diet results in a high mortality from severe enterocolitis. Previous studies have shown that pectin is an important precursor of substrates for intestinal structure and function and may facilitate intestinal recovery after enterocolitis. The aim of this study is to evaluate the effect of pectin on MTX-induced enterocolitis in rats. METHODS: Rats received intragastric infusion of either 1% pectin-supplemented or pectin-free elemental diet from the beginning of the study via a gastrostomy. On the 4th day animals received either MTX, 20 mg/kg intraperitoneally, or saline injection and were killed on the 7th day for sampling. RESULTS: Pectin supplementation significantly decreased body weight loss, organ water content, and intestinal myeloperoxidase levels and increased mucosal protein, DNA, and RNA content in enterocolitis rats. The intestinal permeability was increased by administration of MTX, and pectin supplementation significantly reversed the increased permeability in the distal small bowel and colon. Pectin supplementation also lowered the magnitude of bacterial translocation, decreased plasma endotoxin levels, and restored bowel microecology. CONCLUSIONS: Pectin significantly decreased MTX-induced intestinal injury and improved bowel integrity.

Animals↗
PubMed1996

Risk of preschool asthma: incidence, hospitalization, recurrence, and readmission probability.

Asthma is one of the most common chronic illnesses in childhood. Increases in hospitalization rates have occurred in several countries. The cumulative risk of asthma requiring medical attention was 11.7% for males and 7.0% for females aged 0-4 in Manitoba, Canada, for the cohort of children born in 1984/1985. The cumulative risk of hospitalization for males was nearly twice that of females (2.1% vs. 1.1%). Disease onset was most likely at age 1 year. The risk of rehospitalization or return physician visit for asthma increased significantly with the number of prior hospitalizations and physician visits, respectively, which may reflect both the persistence of asthma and the difficulty of developing an effective disease management strategy.

Age of Onset↗
PubMed1996

Neonatal characteristics as risk factors for preschool asthma.

Childhood asthma usually begins early in life. Neonatal characteristics are reportedly predictive of symptom onset. This investigation utilized data from a provincial health organization to evaluate the effect of several birth characteristics on asthma incidence and hospitalization for asthma during age 0-4. Using logistic regression, the odds ratios (OR) for the following variables indicate a significant (p < 0.05) association with physician-diagnosed preschool asthma: male gender (OR = 1.72), birthweight < 1500 g (OR = 2.11), prematurity (OR = 1.34), respiratory distress syndrome (RDS) in the presence (OR = 2.95) or absence (OR = 1.61) of bronchopulmonary dysplasia (BPD), and transient tachypnea of the newborn (TTN; OR = 1.36). Male gender (OR = 1.91), birthweight < 1500 g (OR = 2.56), RDS with and without BPD (OR = 3.35 and 2.50, respectively), TTN (OR = 2.08), and severe birth asphyxia (OR = 1.94) showed an important association with hospitalization due to asthma. Neonatal characteristics are important determinants for the risk of preschool asthma, even after mutual adjustment.

Asthma↗
PubMed1996

[Supra-aortic arch esophagogastrostomy through esophageal bed in treating patients with middle and lower esophageal carcinoma].

A new surgical procedure of esophagogastrostomy was carried out in 162 cases with middle or lower thoracic esophageal carcinoma in our department from January, 1992 to December, 1994. Esophagogastrostomy was performed at supra-aortic arch site by pulling the stomach along the esophageal bed instead of putting it before aortic arch in the thoracic cavity. The procedure may keep the normal physiological function of the organs in the chest. It may help fully distend the left lung so as to reduce impairement of pulmonary function because the thoracic stomach was kept within the mediastinum. No resection mortality or anastomotic leakage occurred in the series. Since the esophagus and the stomach were anastomosed in a linear fashion without angulation, the evenly distributed intracavitary pressure may help prevent anastomotic leakage from occurrence. It is also easy to be dilated if anastomotic stricture occurs. In addition, the new procedure may be helpful in promoting gastric emptying, preventing gastric reflux, depressing and stopping the blood oozing in the mediastinum and air leakage from the ruptured lungs, as well as in distinguishing pleural effusion from gastric retention. Compared with other procedures, it is more difficult to perform the anastomosis. Once anstomotic leakage occurs, drainage is not easy.

Adult↗
PubMed1996

[Results of initial surgery and adjuvant chemotherapy in treating small-cell lung cancer].

Results of initial surgery and postoperative chemotherapy in the treatment of 104 small-cell lung cancer (SCLC) were reported. The overall resectability rate was 84.6%. Operative modes include pneumonectomy in 16 cases, regular lobectomy (bilobectomy) in 62, and sleeve lobectomy in 10. There was no resection mortality. The clinical TNM staging was: stage I in 77 cases, stage II in 19, stage III a in 8. The pathological TNM staging was: stage II in 45 cases, stage I in 32, stage III a in 25, stage III b in 1, and stage IV in 1. A total of 54 cases was incorrectly staged, of which 46 cases were clinically understaged while 8 cases were overstaged. The follow-up rate reached 94.9%. The overall 5-yr survival rate was 27.5%. The modes of resection, surgica pathological staging and postoperative chemotherapy are three factors possibly related to long-term survival. The 5-yr survival rate for lobectomy and pneumonectomy was 30.9% and 12.5%, that for stage I, II, III was 33.3%, 14.3%, and 33.3%. The 5-yr survival rate with and without postoperative chemotherapy was 32.4% and 16.7%. The results suggest that for SCLC surgery is indicated in T3N0 and T3N1 among stoge I, II and III a patients. Correct preoperative staging and postoperative chemotherapy are indispensable for better prognosis.

Adult↗
PubMed1995

Survival experience among elderly end-stage renal disease patients. A controlled comparison of transplantation and dialysis.

Renal transplantation is a relatively recent treatment option among the elderly with end-stage renal disease (ESRD). Since little is known regarding the clinical benefits of transplantation relative to dialysis in this age group, this study compares transplantation and dialysis among the elderly with respect to patient survival. Data utilized in this investigation were obtained from the Canadian Organ Replacement Register (CORR). The study population consisted of the 6400 patients aged 60 and over at registration, diagnosed between 1987 and 1993, for whom data on comorbid conditions were available. Survival probability, death rates, age-standardized mortality ratios (SMRs) and Cox regression analysis were employed to evaluate the survival experience among the transplant and dialysis groups. Transplant recipients were matched (by age, underlying diagnosis leading to ESRD, and number of comorbid conditions) to 2 randomly selected patients who did not undergo transplantation. Using Cox regression, the time-dependent hazard ratio for transplantation versus dialysis patients was estimated at 0.47 (P < 0.0001), indicating that even after adjusting for other known prognostic factors, elderly patients who received a transplant experienced significantly greater survival probability than those who remained on dialysis. When transplant patients were matched to randomly selected dialysis patients with the constraint that the corresponding dialysis patient have at least as much follow-up time as the transplant patient had waiting time, five-year survival rates were 81% and 51% for the transplant and dialysis groups, respectively (P < 0.0001). These results support the potential advantage of transplantation among the elderly, and may have important implications for renal care in this age group.

Age Factors↗
PubMed1995

Trends in mortality from melanoma in Canada and prediction of future rates.

A long term increase in incidence of and mortality due to malignant melanoma has been observed in all well documented white populations. The major identified cause of melanoma is sun exposure. One would expect predictions of future atmospheric ozone depletion to lead to an increase in ultraviolet radiation (UVR) and in the effects of sun exposure. We consider age-period data for Canadian malignant malanoma mortality. We fit a multiplicative exponential/logistic (MEL) model to the data and extrapolate to AD 2010 hence yielding point estimates of future rates. We obtain total mortality forecasts by multiplying rates by population estimates. We present standard errors for forecasts. We forecast that melanoma will be a much larger burden on the health care system in the early years of the next century than it is at present. We obtain an age-cohort model by a simple transformation of the age-period model. Also, we obtain unconditional probabilities of death due to melanoma both for age-period and age-cohort models. We discuss the assumptions underlying the MEL model that suggest possible relationships between UVR and melanoma.

Adult↗
PubMed1995

DNA strand breakage, thymine glycol production, and hydroxyl radical generation induced by different samples of crystalline silica in vitro.

Five preparations of alpha-quartz [Min-U-Sil 5 (MQZ), MQZ pretreated with hydrofluoric acid (HFMQZ), Chinese standard alpha-quartz (CSQZ), and two German samples, DQ-12 and F600] and two preparations of the crystalline silica polymorphs, cristobalite and tridymite, previously characterized for surface area and surface charge, were evaluated for their relative activities in the following assays: (i) in vitro assays of short duration (< or = 15 min) for oxygen consumption and for generation of hydroxyl radicals (measured by electron spin resonance spin trapping), and (ii) in vitro assays of longer duration for DNA strand breakage (measured using linear DNA as a detector molecule) and for production of the oxidized DNA base, thymine glycol (measured by gas chromatography-mass spectrometry). Marked differences among the samples were found for their levels of oxygen consumption and of hydroxyl radicals' generation. All samples caused increased formation of thymine glycol, with wide variations in activity among samples. When normalized for equal surface area, the samples produced different levels of DNA strand breakage. Addition of hydrogen peroxide strongly accelerated DNA damage--more for cristobalite than for the alpha-quartz samples. DNA damage by quartz was enhanced by ferric chloride and inhibited by iron chelators. The order of relative activity of the samples varied with different types of in vitro assays and was not directly correlated to surface area. Electrophoretic mobility, as measured by zeta potential, was not significantly different among samples. The results suggest that the ability of different crystalline silica samples to generate a rapid burst of oxygen free radicals is distinct from their ability to induce DNA damage and DNA base oxidation over longer time periods. The relative activities of the samples in cellular assays (hemolysis of human erythrocytes; cytotoxicity and neoplastic transformation of BALB/3T3/A31-1-1 cells) were in turn markedly different from those listed above, suggesting a more critical role for surface area. The mechanisms of carcinogenesis by crystalline silica need to be further investigated in relation to the underlying physicochemical characteristics.

Animals↗