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Biomedical subjects

M J Charles

Publications and source records attributed to M J Charles.

9 recordsLinked to original sources
PubMed2002

Comparison of methods for extraction, storage, and silylation of pentafluorobenzyl derivatives of carbonyl compounds and multi-functional carbonyl compounds.

The employment of O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) derivatization along with bis-(trimethylsilyl)trifluoroacetamide (BSTFA) or N, N-( tert-butyldimethylsilyl)trifluoroacetamide (MTBSTFA) derivatization is a popular method for measurement of oxygenated organics in environmental and biological samples. Most notably, the derivatization method enables the measurement of atmospheric photooxidation products not detected by using other methods. PFBHA derivatization is often conducted in an aqueous solution. Accordingly, experiments were performed to compare the efficiency of hexane, methyl- tert-butyl ether (MTBE), and dichloromethane (CH(2)Cl(2)) for extraction of O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) derivatives of carbonyl compounds from water. Further, the stability of these compounds when stored at 4 degrees C in CH(2)Cl(2) was determined, and commonly used methods for silylation of -OH and -COOH groups on the PFBHA derivatives were compared. Overall, CH(2)Cl(2)was the most efficient solvent for extraction of PFBHA derivatives of hydroxycarbonyl compounds, dicarbonyl compounds, and keto-acids from water. Derivatives of carbonyl compounds that do not have secondary functional groups were extracted with approximately equal efficiency by each of the three solvents examined. The PFBHA derivatives of aromatic and saturated aliphatic carbonyl compounds and hydroxycarbonyl compounds were stable in CH(2)Cl(2) at 4 degrees C for > or = 66 days whereas the derivatives of keto-acids and unsaturated aliphatic aldehydes begin to degrade after approximately 38 days. Comparison of four procedures for bis-(trimethylsilyl)trifluoroacetamide (BSTFA) derivatization of -OH and -COOH groups on PFBHA derivatives revealed that primary -OH groups react efficiently in 20-100% BSTFA in CH(2)Cl(2), and do not require a catalyst. Secondary -OH groups also react efficiently in 20-100% BSTFA, but the reaction yield improves slightly when trimethylchlorosilane (TMCS) is added as a catalyst. Reaction of tertiary -OH groups with BSTFA was very inefficient, but improved with addition of 10% TMCS to the BSTFA solution. Finally, -COOH groups seemed to react most efficiently and consistently in 100% BSTFA, without catalyst.

Chromatography, Liquid↗
PubMed2001

Organochlorines and 8-hydroxy-2'-deoxyguanosine (8-OHdG) in cancerous and noncancerous breast tissue: do the data support the hypothesis that oxidative DNA damage caused by organochlorines affects breast cancer?

A study was conducted to test the hypothesis that oxidative DNA damage caused by exposure to organochlorines is an important risk factor in breast cancer. This is the first study that evaluates this hypothesis by measuring 8-hydroxy-2'-deoxyguanosine (8-OHdG), a biomarker of oxidative DNA damage, polychlorinated biphenyl (PCB) congeners, and isomers of bis (4-chlorophenyl)-1,1,1-trichloroethane (DDT) and bis (4-chlorophenyl)-2,2,2-dichloroethane (DDE) in cancerous and noncancerous tissue. We measured these compounds in 44 primary tumors (cancerous) and 21 benign breast biopsy (noncancerous) tissues. Overall, no significant differences were observed in the level of the organochlorines between the tissues. The median concentration for 8-OHdG was 10.5 fmol/mg DNA (1.7/10(5) deoxyguanosine residues), and 8.5 fmol/mg DNA (1.4/10(5) deoxyguanosine residues) in cancerous and noncancerous tissue, respectively. These values are similar to background levels. No significant differences were observed in 8-OHdG levels in cancerous versus noncancerous tissue, and no correlation was demonstrated between the organochlorines and 8-OHdG. The data thus do not support the hypothesis that oxidative DNA damage caused by exposure to organochlorines is an important risk factor in breast cancer.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed2001

A reproducible approach to the reporting of organochlorine compounds in epidemiologic studies.

A growing body of research indicates that the most biologically active PCB congeners and organochlorines are not the most abundant components in human and wildlife samples. As researchers attempt measurement on a wider pool of less abundant compounds, they inevitably face quantification problems. To address this problem and enhance comparability across studies, we propose a standardized approach to report organochlorines that is based on a reproducible method to determine the limit of quantification (LQ). Two statistical methods are incorporated into our approach, one by Gibbons termed the Alternative Minimum Level (AML), and one based on determining a region of stable relativestandard deviation in instrument response (RSD). We illustrate our approach using historical samples collected during the 1960s from a cohort of pregnant women enrolled in the Child Health and Development Study. The results are applicable to determining the LQ of any method, and are of utmost importance to environmental scientists conducting trace organic analyses of complex mixtures. Our results demonstrate that: (1) precision as measured by RSD is the most important criterion in determining LQ; (2) the AML routinely isolates a region of constant RSD; and (3) the precision of the instrument detector response as measured with pure standards locates the LQ applicable for real samples - that is, the true limits of quantification reside in the detector, not the matrix effects or analyte recoveries associated with real samples. A corollary of these findings is that bias due to matrix effects and analyte recoveries can be assessed separately from precision and LQdetermination. Previous approaches involved spiking matrix blanks to determine LQ, a problematic strategy for real world, complex matrices. We have now validated the use of pure standards in LQ determination, an approach that is practical and accessible to most analysts.

Animals↗
PubMed1996

Quantitative analysis of the DNA adduct N2,3-ethenoguanine using liquid chromatography/electrospray ionization mass spectrometry.

The need for specificity and sensitivity in the analysis of DNA adducts has led the development of GC/MS methods. Such methods require chemical derivatization (i.e. silylation, electrophore labelling), which can also bring its own sets of problems, including the production of artifacts, interferences and sample to sample variability in derivatization. To obviate such problems, a liquid chromatographic/electrospray ionization mass spectrometric (LC/ESI-MS) method was developed to quantify N2,3-ethenoguanine (epsilon Gua), a promutagenic DNA adduct of vinyl chloride exposure. The response of epsilon Gua to isotopically labelled internal standard [13C4]epsilon Gua was linear (r2 = 0.999) and reproducible from 0.027 to 0.538 pmol microliter-1. We obtained an accuracy of 86 +/- 14% by analyzing chloroethylene oxide (CEO)-treated calf thymus DNA enriched with authentic epsilon Gua. The analysis of CEO-treated calf thymus DNA samples not enriched with authentic epsilon Gua provided a precision of 15%. The detection limits with a signal-to-noise ratio (S/N) 2.5:1 were obtained in the determination of authentic epsilon Gua at 5 fmol per injection. The detection limit obtained in the routine analysis of the biological samples was 50 fmol epsilon Gua with S/N = 3:1. The applicability of the method was established by determining epsilon Gua in rats treated with CEO by portal vein injection and an unexposed human liver. It was observed that the concentration of epsilon Gua in the rat livers increased with increase in dose and was inversely related to the time after, CEO exposure. This trend suggests rapid repair of the adduct in rat livers. In the human liver DNA sample, epsilon Gua was quantitated at 0.06 +/- 0.01 pmol mg-1 DNA.

Animals↗
PubMed1993

Formation and characterization of bacterial mutagens from reaction of the alternative disinfectant monochloramine with model aqueous solutions of fulvic acid.

Monochloramine has been suggested as an alternative disinfectant to chlorine to reduce levels of trihalomethanes in treated drinking water, but little is known of the toxicological properties and potential health implications of by-products specific to the chloramination process. Model aqueous fulvic acid solutions (200-400 mg C/liter), serving as surrogates for humic surface waters, were chloraminated over a range of molar Cl:C ratios from 1:40 to 1:2. The resulting by-products were extracted into diethyl ether at pH 2 and investigated with the Ames plate incorporation assay. Extractable mutagenicity increased with increasing chlorine and carbon dose up to about 30,000 revertants/liter at Cl:C ratios of 1:2. Mutagenicity was higher in Salmonella typhimurium strain TA100 than in strain TA98, and was decreased in the presence of S9, indicating that the mutagens formed were direct-acting and induced predominantly base-pair substitutions. Bovine serum albumin decreased slightly, and glutathione reduced greatly, the mutagenic activity detected in extracts. HPLC fractionation of the by-products indicated that most of the mutagenic activity was found in the earliest-eluting (most polar) fraction. The mutagenic by-products appeared to be qualitatively similar to 3-chloro-4-dichloromethyl-5-hydroxy-2-(5H)-furanone (MX) in their chromatographic behavior and responses to glutathione and bovine serum albumin, but were less readily detoxified by S9 than was MX.

Benzopyrans↗
PubMed1979

Virus detection in soils: a comparison of four recovery methods.

Among nine eluents tested, 0.5% (w/v) isoelectric casein at pH 9.0 and 0.5% (w/v) non-fat dry milk (pH 9.0) were the most efficient in eluting poliovirus type 1 (Sabin) from Eustis fine sand. However, no significant difference was found between the overall (elution followed by concentration) virus recoveries by non-fat dry milk, isoelectric casein, beef extract, and glycine-EDTA methods. High overall recovery (75%) of low input (200 PFU) of viruses from 100 g of soil was achieved by the isoelectric casein method. It was found that the recovery efficiency of this method was not significantly affected by the soil type, following examination of four Florida soils. The mean overall recovery for the four soils was 50%. For other enteroviruses, the overall recovery for coxsackie B3 was 88% but was significantly lower (23%) for echovirus 4. Examination of the efficiency of the casein method under field conditions showed that it was possible to recovery low poliovirus numbers from soil (0.9-1.3 PFU/g soil).

Animals↗
PubMedDate not supplied

GC/ITMS measurement of carbonyls and multifunctional carbonyls in PM2.5 particles emitted from motor vehicles.

A method was developed and tested to identify and quantitate carbonyls and multifunctional carbonyls in fine particulate matter (PM2.5; <2.5 microm aerodynamic diameter). The method relies on ultrasonic extraction of particulate matter on filters at -8 degrees C; derivatization with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA), and PFBHA along with bis (trimethylsilyl) trifluoroacetamide (BSTFA); and detection of the derivatives by gas chromatography/ion trap mass spectrometry. Ultrasonic extraction of model compounds from enriched particles was affected by solvent polarity (water > methylene chloride > toluene-isopropanol (2 + 1, v/v). Water provided the highest recovery for dihydroxy acetone, pyruvic acid, and hydroxy acetone, compared to methylene chloride, and toluene-isopropanol. Lowering the ultrasonication bath temperature from 0 degrees to -8 degrees C improved the recoveries of the less water soluble and more volatile species-methacrolein, methyl vinyl ketone, 2,3-butanedione, and tolualdehyde. The power of the method was demonstrated by identification and quantitation of carbonyls and multifunctional carbonyls in sample extracts of fine particulate matter (PM2.5) collected in the Caldecott tunnel, CA. The identities of crotonaldehyde, 2,3-butanedione, glyoxal, 9H-fluoren-9-one, glycolaldehyde, glyoxylic acid, levulinic acid, and 3-hydroxybenzaldehyde were confirmed by comparing the relative retention time and mass spectra of the analyte in the sample extract with an authentic standard. Quantitation of crotonaldehyde, glyoxal, 2,3-butanedione, glyoxylic acid, and levulinic acid was accomplished. This is the first report of glyoxylic acid, levulinic acid, and 3-hydroxybenzaldheyde in PM2.5 particles sampled in a roadway tunnel. It is also the first report of a C10 carbonyl with the molecular formula of C10H16O2, a hydroxy carbonyl with the molecular formula of C17H21NO2, and a hydroxy or dihydroxy carbonyl with the molecular formula of C16H14O2 or C9H10O3. The high-molecular weight hydroxy carbonyls, which were found only in the heavy-duty (diesel) bore, may be tracers of diesel emissions in air.

Air Pollutants↗