Biomedical subjects

W Chu

Publications and source records attributed to W Chu.

At least 55 records · Page 3Linked to original sources

PubMed2003

The dose and ratio effects of Fe(II) and H2O2 in Fenton's process on the removal of atrazine.

The degradation of pesticide, atrazine (ATZ), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine, by Fenton's reagent (FR) was investigated as a function of reagents' concentrations and ratios in a batch reactor. The degradation of ATZ was effectively achieved by hydroxyl radicals, which were generated in the FR process. The decay rates of ATZ and the oxidation capacities of FR were found to depend on the concentrations of hydrogen peroxide and ferrous ion. The removal kinetics of ATZ are initiated by a rapid decay and then followed by a much slower one. After an extended reaction time (5 to 10 minutes), the reactions ceased because the Fe2+ and H2O2 were consumable and would be deactivated in the process. The oxidation capacity of FR was found to have a nonlinear correlation to the doses of [Fe2+] and [H2O2] due to the involvement of some unwanted side reactions at both high and low FR ratios. In addition, it was also found that the FR ratio has little effect on the oxidation capacity at high [Fe2+] concentration, but it becomes more critical at lower [Fe2+], which is justified by the involvement of two parallel pathways for the oxidation of ATZ, i.e. the catalyzed oxidation of ATZ induced by FR and the direct oxidation of ATZ by H2O2.

Atrazine↗

PubMed2002

Evaluation of apolipoprotein A-II as a positional candidate gene for familial Type II diabetes, altered lipid concentrations, and insulin resistance.

AIMS/HYPOTHESIS: We hypothesized that apolipoprotein A-II sequence variation was responsible for the observed linkage of Type II (non-insulin-dependent) diabetes mellitus to the apolipoprotein A-II region in Northern European families ascertained for multiple diabetic siblings, and might also influence insulin sensitivity and secretion, non-esterified fatty acids, and lipids. METHODS: We recruited 698 members of 63 families for pedigree studies and additional unrelated people providing 117 diabetic and 130 control subjects. We screened the apolipoprotein A-II gene by single strand conformation polymorphism analysis and fluorescent sequence analysis. Variants were typed by oligonucleotide ligation assay, restriction digest of amplification products, or radioactive fragment analysis for the microsatellite polymorphism. Association of each variant with Type II diabetes was tested in the case-control population by chi-square analysis, or using transmission disequilibrium test in families. Haplotypes were established in families using SIMWALK and tested for association with diabetes and quantitative traits. RESULTS: No detected variant altered the coding sequence of the gene. Three single nucleotide polymorphisms showed modest evidence for an association, but no variant or haplotype was associated with diabetes in families. Similarly, we found no association with non-esterified fatty acid concentrations, HDL concentrations, or fasting insulin. In contrast, we found evidence for an association of some haplotypes and individual variants with 2-h post-challenge glucose and measures of insulin secretion. CONCLUSION/INTERPRETATION: Apolipoprotein A-II is not likely to explain the observed linkage of Type II diabetes, but variation in this gene could alter insulin secretion and post-challenge glucose.

Apolipoprotein A-II↗

PubMed2002

Modeling the sequential photodechlorination of hexachlorobenzene in surfactant micelles.

A five-stage consecutive irreversible model is derived to predict the photodegradation of hexachlorobenzene (HCB) in a surfactant solution, which was proven to be a useful treatment process following the surfactant-aided soil washing or remediation. The photodegradation of HCB in surfactant micelles is dominated by photodechlorination, which sequentially removes chlorides one at a time. The minor pathways of photoisomerization and photochlorination were neglected in the kinetic model. The results show that the derived consecutive irreversible model can accurately predict the decay of HCB and the formation (and decay) of its less-chlorinated congeners. The initial rate approach was used to identify the proper range of decay rate of each chlorinated benzene; so the overall rate constants can be determined easier by trial. The decreased performance of a completely mixed flow reactor (CMFR) with continuous input is also quantified compared to a batch reactor.

Chlorine↗

PubMed2002

The direct and indirect photolysis of 4,4'-dichlorobiphenyl in various surfactant/solvent-aided systems.

Surfactant and organic solvents have individually been shown useful in assisting the solubilization of hydrophobic organics out of contaminated soil and promoting UV-induced photodecay at a succeeding treatment process. A newly proposed process is to use the mixtures of surfactant and solvents together in achieving better performance. This study was to explore some basic variables and conditions that may be useful in optimizing the performance of surfactant/solvent-aided UV systems through the selection of surfactant micelles, the adjustment of the reaction pH levels, and the addition of photosensitizer and hydrogen sources. A PCB monomer 4,4'-dichlorobiphenyl (DCB) was used as the target compound for this study; about 1.3 to 2.3 times greater DCB photodecay rate enhancements were observed by using surfactant/acetone or surfactant/triethylamine (TEA) combinations at their optimal conditions. Overdose of these additives (acetone and TEA) will result in retardation of the reactions. However, the use of surfactant with a multisolvents system (surfactant/acetone/TEA) shows an add-on effect in amplifying the overall decay rate for more than 12%, suggesting that a more complicated mechanism is involved than the simple parallel-reaction assumption.

Hydrogen-Ion Concentration↗

PubMed2002

The mechanisms of rate enhancing and quenching of trichloroethene photodecay in the presence of sensitizer and hydrogen sources.

The reaction mechanisms and rates of trichloroethene (TCE) photodecay in the presence of photosensitizer (acetone, ACE) and hydrogen sources (surfactant and triethylamine, TEA) were investigated. Quantum yields of TCE photodecay in solution with surfactant Brij 35 and optimal ACE dosage are about 25 times higher than in Brij 35 alone. However, with an excess ACE dosage, ACE will act as a light barrier and attenuate the light intensity available for TCE photodegradation. TCE photodegradation follows a two-stage kinetics, in which a lag-phase is followed by a fast decay. The lag-phase distribution depends on initial pH levels and ACE concentrations. The overall TCE removal was found to be higher at high pH level, suggesting that free radical reaction is dominant at high pH levels. The use of additional hydrogen source (TEA) in the reaction can further accelerate the reaction, but overdosing of TEA would quench the reaction. The possible reaction mechanisms of TCE photodecay involving ACE and TEA were proposed, and rateenhancing and rate-quenching models at low and high TEA concentrations respectively were derived based on the proposed mechanism, they were found useful for predicting the TEC decay quantum yields.

Acetone↗

PubMed2002

Modeling of photodecoloration of azo dye in a cocktail photolysis system.

The modeling of photodecoloration of a nonbiodegradable azo dye, Reactive Red 2 (RR2), in a cocktail mixture of acetone (ACE) and triethylamine (TEA) solution, was investigated. It was found that the cocktail photolysis system was capable of completely decolorizing the azo dye in a very short treatment time, and the overall dye degradation followed pseudo-first-order decay kinetic. Three distinct stages were observed in the cocktail photolysis profiles. A lag phase was observed at the commencement of the degradation, but its duration was gradually reduced with the increment of the TEA concentration and the incident light intensity. Subsequently, a fast decay of RR2 was observed, in which over 80% of the dyes were reduced and it was interesting to find a tailing stage after 90-95% of the color was removed. A quantitative estimation of RR2 in the cocktail photolysis system was also studied. The differential equation consisting of two parallel reactions was solved to predict the concentration of RR2 at any reaction time with very good agreements. Furthermore, the sensitivity analysis indicated that the photosensitization process (contributed by ACE) was the dominant mechanism in the cocktail photolysis system, while the presence of a hydrogen source (TEA) did not contribute a major decay pathway but promoted the reaction rate of photosensitization by offering an add-on effect.

Coloring Agents↗

PubMed2001

Bcl-2 expression in F-MuLV-induced erythroleukemias: a role for the anti-apoptotic action of Bcl-2 during tumor progression.

Erythroleukemias induced by various strains of Friend virus are multistage malignancies that result from the accumulation of genetic mutations, including the activation of proto-oncogenes and the inactivation of tumor suppressor genes. In this study, we demonstrate that Bcl-2 expression is activated in the majority of F-MuLV-induced erythroleukemia cell lines. In contrast, Bcl-2 was not expressed in any of the FV-P-induced erythroleukemia cell lines and protein levels were low or negligible in FV-A-induced erythroleukemia cell lines examined. In vivo, Bcl-2 expression levels gradually increased in F-MuLV-induced erythroleukemic cells prior to adaptation to culture. High expression of Bcl-2 in F-MuLV-induced erythroleukemic cells was shown to proceed the emergence of p53 mutation suggesting that Bcl-2 expression may delay p53 mutation in the leukemic cells. This is further supported by the demonstration that the majority of F-MuLV-induced erythroleukemia cell lines established from primary tumors induced in p53 mutant mice express low to negligible levels of Bcl-2. We have shown that the high levels of Bcl-2 expression in FV-P-induced erythroleukemic cells inhibited apoptosis induced by etoposide, low serum and p53 expression. Similarly, ectopic Bcl-2 expression within these cells also provided protection from apoptosis induced by etoposide and growth in low serum. These results suggest that the anti-apoptotic action of Bcl-2 may confer a selective in vivo and in vitro growth advantage to F-MuLV-induced erythroleukemic cells, which is not shared by FV-P/FV-A-induced erythroleukemic cells. The observed induction of Bcl-2 expression in vivo constitutes a novel but late oncogenic event associated with the progression of F-MuLV-induced erythroleukemias.

Animals↗

PubMed2001

Genetic factors related to racial variation in plasma levels of insulin-like growth factor-1: implications for premenopausal breast cancer risk.

The oral contraceptive pill is associated with a modest increase in the risk of early-onset breast cancer in the general population, but it is possible that the risk is higher in certain subgroups of women. The relative risk of breast cancer associated with oral contraceptive use has been reported to be higher for African-American women than for white women. African-American women also have a higher incidence of premenopausal breast cancer than white women. Circulating levels of insulin-like growth factor-1 (IGF-I) vary between ethnic groups and are positively associated with the risk of premenopausal breast cancer. In general, the plasma level of IGF-I is lower in women who take oral contraceptives than in women who do not. In an attempt to explain the observed ethnic difference in IGF-I levels with oral contraceptive use, we sought to identify polymorphic variants of genes that are associated with IGF-I levels and estrogen metabolism. We measured IGF-I and IGFBP-3 plasma levels in 503 nulligravid women between the ages of 17 and 35. All women filled out a questionnaire that included information about ethnic background and oral contraceptive use. Samples of DNA were used to genotype the women for known polymorphic variants in the IGF1, AIB1, and CYP3A4 genes. Black women had significantly higher mean IGF-I levels than white women (330 ng/ml versus 284 ng/ml; P = 0.001, adjusted for age and oral contraceptive use). IGF-I levels were significantly suppressed by oral contraceptives in white women (301 ng/ml versus 267 ng/ml; P = 0.0003), but not in black women. Among oral contraceptive users, the IGF-I level was positively associated with the absence of the IGF1 19-repeat allele (338 ng/ml versus 265 ng/ml; P = 0.00007), with the presence of the CYP3A4 variant allele (320 ng/ml versus 269 ng/ml; P = 0.01), and with the presence of the AIB1 26-repeat allele (291 ng/ml versus 271; P = 0.08). After adjusting for genotypes, ethnic group was no longer a significant predictor of the IGF-I level. IGF-I levels are higher among black than white women. Polymorphic variants in the CYP3A4, IGF1, and AIB1 genes are associated with increases in the plasma levels of IGF-I among oral contraceptive users and the variant alleles are much more common in black women than in white women. The high incidence of premenopausal breast cancer among black women may be mediated through genetic modifiers of circulating levels of IGF-I.

Adolescent↗

PubMed2001

CYP gene polymorphisms and early menarche.

Early age at menarche is a risk factor for breast cancer. A previous study reported a significant positive association between the CYP3A4*1B variant allele and early puberty. We investigated whether polymorphisms of the CYP3A4, CYP17, CYP1B1, and CYP1A2 genes predict the age at onset of menarche. Five hundred eighty-three nulliparous women between ages 17 and 35, of various ethnic backgrounds, completed a questionnaire that included information about menstrual history. Samples of DNA were provided and used to genotype these women for polymorphic variants in the four genes. There was no significant difference in mean age at menarche between women who carried two variant CYP17 A2 alleles (12.5 years) and women who carried one or no variant allele (12.5 years) (P = 0.8, adjusted for ethnic group and year of birth). Similar results were found for the CYP1B1*3 variant allele and for the CYP1A2*1F variant allele. Women who carried two variant CYP3A4*1B alleles had an earlier mean age at menarche (12.0 years) than women who carried one or no variant allele (12.6 years) (P = 0.02). However, after adjusting for ethnic group and year of birth, no significant differences in mean age at menarche were found. The polymorphic variants of the CYP3A4, CYP17, CYP1B1, and CYP1A2 genes are unlikely to influence age of menarche.

Adolescent↗

PubMed2001

Modeling the two stages of surfactant-aided soil washing.

This paper provides new insights into modelling the distribution of hydrophobic compounds between soil and water phases in the presence of nonionic surfactant micelles. Experimental measurements were made of various systems comprising a non-ionic surfactant, five soils of different fractional organic carbon contents, and a hydrophobic (disperse) dye. Soil-washing performance was quantified using reciprocal surfactant-soil solubilization coefficients (1/Kd). Two stages of partitioning were identified. In stage 1, the dye concentration increased slightly with increasing surfactant dose until surfactant monomers saturated the bulk solution at the critical micelle concentration (cmc). The washing performance was 1:1 proportional to the surfactant monomer concentration. Most of the surfactant in this stage is sorbed. In stage 2, above the cmc, soil-washing performance increased linearly with increasing available surfactant micelles in the bulk solution. Reciprocal surfactant-soil solubilization coefficients (1/Kd), octanol-water partition coefficients (Kow), fractional organic carbon content of the soil (foc), and surfactant concentration were correlated for each stage in the soil-washing process using two simple equations.

Micelles↗

PubMed2001

Photodegradation mechanism and rate improvement of chlorinated aromatic dye in non-ionic surfactant solutions.

A typical insoluble chlorinated aromatic dye (CAD), disperse red (DR), was used to explore the reaction mechanism and kinetics of photodegradation in non-ionic surfactant solutions. The use of an additional hydrogen source and photosensitizer is also studied to improve the decay rates. The decay rate of dye in surfactants depends on the Km of surfactants and their ability to offering an effective hydrogen source. The photodegradation of CAD can be divided into three stages: the initial lag stage. the fast degradation stage and the final retardation stage. The lag stage will vanish and the decay rates of dye can be greatly improved by 2.5-3.6 times after adding an additional hydrogen source (NaBH4) or photosensitizer (acetone) to the surfactant micellar solution. However, the use of an additional hydrogen source or photosensitizer has dosage limitations in such applications. The photoreduction of DR is the main reaction mechanism, in which photodechlorination is observed first with the generation of HCI as the final product, then followed by photodecolorization by breaking the azo bond of the chromophore.

Acetone↗

PubMed2001

Dye removal from textile dye wastewater using recycled alum sludge.

The removal of dyes from textile dying wastewater by recycled alum sludge (RAS) generated by the coagulation process itself was studied and optimized. One hydrophobic and one hydrophilic dye were used as probes to examine the performance of this process. It was found that RAS is a good way of removing hydrophobic dye in wastewater, while simultaneously reducing the fresh alum dosage, of which one third of the fresh alum can be saved. The back-diffusion of residued dye from the recycling sludge is detected but is easily controlled as long as a small amount of fresh alum is added to the system. The use of RAS is not recommended for the removal of hydrophilic dyes, since the high solubility characteristics of such dyes can cause deterioration in the water quality during recycling.

Alum Compounds↗

PubMed2001

The modelling of trichloroethene photodegradation in Brij 35 surfactant by two-stage reaction.

Various clean-up technologies have been developed for the removal and/or destruction of trichloroethene (TCE) in the subsurface. Surfactant-aided soil washing followed by photodegradation could be a promising approach to such a task. The modelling of TCE photodegradation by UV in Brij 35 surfactant micelles is therefore investigated. Two stages of TCE degradation are observed in surfactant Brij 35 systems. A lag phase is observed at the commencement of the degradation, but the duration of the lag phase is significantly reduced as the initial pH increases. As the overall decay of TCE is also found to be faster at higher pH levels, it is suggested that the free radical reaction is dominant at high pH levels, and the formation of lag phases is mainly due to the deficiency of free radicals at lower pH levels. Since the period of the lag phase gradually decreases with the increase of initial pH level, and the two pseudo first-order reaction constants (one for the lag phase and one for the subsequent fast decay) for TCE decay in both stages are also pH dependent, a non-steady-state mathematical model is developed for the prediction of TCE photodegradation in Brij 35 solutions, in which the remaining fraction of TCE (C/C0) in the system can be determined at any instant by using a simple parameter of the initial system pH.

Detergents↗

PubMed2001

Quantum yield study of the photodegradation of hydrophobic dyes in the presence of acetone sensitizer.

The photodegradation of hydrophobic disperse dyes with different chromophores in the presence of acetone (ACE) was investigated. In this study, the photodecay of dyes was carried out in the Rayonet RPR-200 merry-go-round photoreactor, with 253.7 nm monochromatic ultraviolet (UV) lamps. A typical azo disperse dye (CI disperse yellow 7--DY7) and an anthraquinone disperse dye (CI disperse orange--DO11) were used as the probe compounds. The results demonstrate that the addition of acetone increases the solubility of hydrophobic disperse dyes and enhances the photosensitization reaction simultaneously. More than ten times of quantum yield enhancement is observed in the presence of ACE photosensitizer than in water alone. The photodegradation of DY7 and DO11 is dominated by photoreduction, which follows pseudo first-order decay, and the rate constants strongly depend on the solvent system (i.e., ACE/H2O ratios) and the initial pH levels. The decay quantum yields of dyes are normally observed with the increase of the ACE/H2O ratio. The optimum quantum yields of DY7 and DO11 were determined at 0.5 (v/v) and 0.25 (v/v), respectively, in alkaline conditions. A further increase in the ACE/H2O ratio reduces the quantum yields, possibly due to light attenuation by excess acetone.

Acetone↗

PubMed2001

The rate improvement and modeling of trichloroethene photodegradation by acetone sensitizer in surfactant solution.

The photodecay of trichloroethene (TCE) in surfactant solution by the help of photosensitizer (acetone, ACE) was investigated and modeled. Apart from the direct photodegradation, photosensitization is presumed to be one of the major mechanisms contributing to overall decay. Quantum yields of TCE photodecay in solution with surfactant Brij 35 and optimal ACE dosage are about 25 times higher than in Brij 35 alone. However, with an excess ACE dosage, ACE will act as a light barrier and attenuate the light intensity available for TCE photodegradation. TCE photodegradation follows a two-stage kinetics, in which a lag phase is followed by a fast decay. Mathematical models were developed for the prediction of the two-stage photodegradation, in which the remaining fraction of TCE (C/C0) in the system becomes predictable.

Acetone↗

PubMed2001

Modeling the quantum yields of herbicide 2,4-D decay in UV/H2O2 process.

The photodecay of herbicide 2,4-D in a hydrogen peroxide-aided photolysis process was studied and modeled. The decay rate of 2,4-D was known to be low in the natural environment, but rate improvement was achieved in an H2O2/UV system. The 2,4-D decay quantum yields under ultraviolet (UV) light at 253.7 nm increased from 4.86 x 10(-6) to 1.30 x 10(-4) as the ratio of [H2O2]/[2,4-D] increased from 0.05 to 12.5. Apparently, in the presence of UV light, the decay rate of 2,4-D could be greatly improved as the concentration of hydrogen peroxide increased. However, the efficiency of 2,4-D photodecay was retarded if the concentration of H2O2 was overdosed, because the excess hydrogen peroxide consumes the hydroxyl radicals (HO*) in the solution, resulting in a much weaker oxidant HO2*. The decay of 2,4-D was also pH dependent. A ranking of acid (highest), base (middle) and neutral (lowest) was observed owing to the property change of reactants and the shifting of dominant mechanisms among photolysis, photohydrolysis and chemical oxidation. Two mathematical models were proposed to predict the quantum yield for various [H2O2]/[2,4-D] ratios and initial pH levels, in which very good correlation was found for the ranges of regular application.

2,4-Dichlorophenoxyacetic Acid↗

PubMed2001

V89L polymorphism of type-2, 5-alpha reductase enzyme gene predicts prostate cancer presence and progression.

OBJECTIVES: The valine (V) to leucine (L) polymorphism of the SRD5A2 gene is associated with 5-alpha reductase-2 activity; patients with the V allele have high activity and patients with the L allele have low activity. We examined whether this polymorphism predicts the presence of prostate cancer in 320 men without cancer who underwent biopsy and cancer progression in 318 men who underwent radical prostatectomy. METHODS: The effect of the SRD5A2 gene in predicting the presence of prostate cancer was examined using logistic regression analysis, controlling for established risk factors. The effect of the SRD5A2 gene in predicting prostate cancer progression was examined using a nested, matched, case-control design. Most of the participants were white. RESULTS: Of the 320 men, 158 (49.4%) were found on biopsy to have prostate cancer. The overall distribution of the V/V, V/L, and L/L genotypes was 47.5%, 42.5%, and 10.0%, respectively. The adjusted odds ratio for having prostate cancer for patients with at least one V allele was 2.53 compared with patients with the L/L genotype (P = 0.03). Of the 318 patients with cancer, 80 had biochemically detected recurrence and 238 had no evidence of recurrence. The odds ratio for progression for patients with at least one V allele was 3.32 (95% confidence interval 1.67 to 6.62, P = 0.0006) compared with patients with the L/L genotype. CONCLUSIONS: Men who have the V allele of the SRD5A2 gene have a twofold increase in the risk of prostate cancer development and an additional twofold increase in the risk of progression compared with men with the L/L genotype.

Aged↗

PubMed2001

Lineage-specific mechanism of drug and radiation resistance in melanoma mediated by tyrosinase-related protein 2.

A major obstacle in the clinical management of malignant melanoma is its intrinsic resistance to chemotherapy and radiation therapy. Consequently, most patients with melanoma often do not respond to conventional anticancer therapy in a clinically significant manner. Recent advances in cancer research have provided new insights into the mechanisms of intrinsic resistance in melanomas. We have recently reported that the over-expression of tyrosinase-related protein 2 (TYRP2), an enzyme that is well characterized for its function in melanin synthesis, is associated specifically with resistance to DNA damaging drugs and radiation treatment. This review will summarize our findings as well as discuss the possible mechanisms by which TYRP2 over-expression contributes to intrinsic resistance in human malignant melanoma.

Antineoplastic Agents↗