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Biomedical subjects

R W Giese

Publications and source records attributed to R W Giese.

At least 37 records · Page 2Linked to original sources
PubMed1993

Chemical transformation/derivatization of O6-methyl- and O6-(hydroxyethyl)guanine for detection by GC-EC/MS.

In this project we set out to make an important class of DNA adducts, comprising O6-alkyl and O6-(hydroxyalkyl)guanines, susceptible to sensitive detection by GC-EC/MS. While existing literature indicated that pentafluorobenzylation would be useful for the ring NH site on these compounds, how to best overcome the polarity of the exocyclic NH2 and OH groups, without losing the O6-alkyl moiety, was less clear. Working with O6-methylguanine and O6-(2'-hydroxyethyl)guanine as representative analytes, we found that the NH2 group could be converted into fluoro without loss of the O6 substituent. For the OH group, a comparison of several derivatives (OR') led to R' = tert-butyl as the best choice at this stage. The latter work, especially via NMR, also allowed exact structural assignments to be made for the N7 and N9 pentafluorobenzyl isomeric derivatives that formed. Of these R' derivatives, the N7 isomers migrated slower on silica-TLC, had higher GC retention times, had lower responses by GC-EC/MS, and were preferentially destroyed as the GC column aged. However, the N9 isomer was slower on TLC when the OH was not derivatized. This behavior was rationalized using a concept of "polar footprint" for the derivatives. The concept also seemed to explain the puzzling GC-EC/MS behavior of some related compounds in our laboratory. Apparently the polar footprint should be minimized in designing derivatives for trace detection by GC-EC/MS.

Chromatography, Thin Layer↗
PubMed1993

"Chitin Leash": a polysaccharide heterobifunctional cross-linking agent which can be cleaved by lysozyme.

6-O-[(2-Hydroxyethyl)poly(2-oxyethyl)]chitosan ("glycolchitosan") was oxidatively cleaved with nitrous acid and then partly acetylated with acetic anhydride, reacted with bromoacetyl-N-hydroxysuccinimide, and reacted further with acetic anhydride. Conditions were selected, including fractionation by size-exclusion chromatography, so that the resulting "Chitin Leash" had an estimated, average molecular weight of 10,000 (dextran standards), corresponding to a length of approximately 40 sugar residues. It possessed 0.9 terminal aldehyde and 2.6 random (presumably) side-chain bromoacetyl reactive groups per chain (average values). As a model system, the Chitin Leash was used to crosslink staphylococcal nuclease (SNase) to ribonuclease A (RNase) with retention of 75 and 78%, respectively, of the starting enzyme activities. For this coupling, the Nase was first converted to a sulfhydryl SNase derivative which retained 74% of the activity of starting enzyme. The yields in this synthesis were: 13% Chitin Leash from glycolchitosan, 24% Chitin Leash-RNase from Chitin Leash and 45% SNase-Chitin Leash-RNase from the latter conjugate. The ratio of SNase to RNase in this conjugate was 1.0:0.94. In a second preparation, in which [14C]acetic anhydride was used, a longer reaction time was employed for the coupling of Chitin Leash to RNase. This gave a 1.0:1.8:0.95 molar ratio of Nase: [14C]Chitin Leash: RNase, revealing multiple attachment of the [14C]Chitin Leash to RNase. The activity of the RNase in the final conjugate was 20%. The latter conjugate was approximately 70% hydrolyzed by diaminooctyl-succinyl-lysozyme, disconnecting the two enzymes while not affecting their activities.

Carbohydrate Sequence↗
PubMed1993

4-(Trifluoromethyl)-2,3,5,6-tetrafluorobenzyl bromide as a new electrophoric derivatizing reagent.

4-(Trifluoromethyl)-2,3,5,6-tetrafluorobenzyl bromide (TTBB) was synthesized in a single step from alpha,alpha,alpha,2,3,5,6-heptafluoro-p-xylene. The purpose of TTBB is to function as an analogue of pentafluorobenzyl bromide (PFBB) in electrophoric derivatization reactions prior to detection by gas chromatography-electron-capture negative ion mass spectrometry (GC-ECNI-MS). In more detail, it was anticipated that TTBB could be used along with, or as a substitute for, PFBB to help control some interferences and confirm results. This is because a TTBB-product (of an analyte) would have different retention and sometimes m/z characteristics than a corresponding PFBB product in GC-ECNI-MS, while the two products should be similar in their ease of formation and yields. Results demonstrating these expectations were achieved by derivatizing and detecting two analytes with these reagents: N7-(2-hydroxyethyl)xanthine, and 2,3-pyrenedicarboxylic acid.

Fluorobenzenes↗
PubMed1993

KO2 chemical transformation/mass spectrometry detection of covalent damage to the DNA of cultured human lymphocytes exposed to benzo[a]pyrene.

Cultured human lymphocytes were exposed to benzo[a]pyrene (B[a]P), and diol epoxide-type DNA adducts arising from this chemical were detected by a method consisting of the following sequence of steps: (1) isolate the DNA; (2) subject the DNA to mild acid hydrolysis to release the polyaromatic moiety as a tetrahydrotetrol; (3) add an internal standard; (4) oxidize the tetrahydrotetrol with potassium superoxide to pyrene-2,3-dicarboxylic acid; (5) derivatize the latter with pentafluorobenzyl bromide; (6) purify the diester product on a silica cartridge; and (7) detect this product by gas chromatography electron capture negative ion mass spectrometry. From the dose (1 microgram/mL) of B[a]P applied, five adducts in 10(7) normal nucleotides were found. Largely because steps 2-5 of the method take place sequentially in a single vial, the procedure is convenient and affords precise results. To demonstrate the potential of the method to detect KO2-susceptible polyaromatic hydrocarbon DNA adducts in general, including unknowns, it was also applied to picomole and femtomole amounts of a standard of chrysene-1,4-quinone using scanning and selected ion monitoring conditions, respectively, in the MS. Since standard products can be detected with selected ion monitoring at levels 10(4) below those encountered here (prior work), it should be possible in the future to extend the method to samples containing smaller amounts of such adducts.

Animals↗
PubMed1993

Primary contribution of the injector to carryover of a trace analyte in high-performance liquid chromatography.

When a low-nanogram amount of N1,N3-bis-(pentafluorobenzyl)-N7-(2- [pentafluorobenzyloxy]ethyl)xanthine was subjected to HPLC, low-picogram amounts of the compound could be detected subsequently (off-line by gas chromatography-electron-capture negative-ion mass spectrometry) after injection of pure mobile phase. This was in spite of significant, intermediate washing of the injector and column. It was determined that essentially 99.9% of this analyte contamination came from the injector. Use of two injectors is a practical remedy for this problem.

Artifacts↗
PubMed1993

High-performance liquid chromatography versus solid-phase extraction for post-derivatization cleanup prior to gas chromatography-electron-capture negative-ion mass spectrometry of N1,N3-bis-(pentafluorobenzyl)-N7- (2-[pentafluorobenzyloxy]ethyl)xanthine, a product derived from an ethylene oxide DNA adduct.

N7-(2-Hydroxyethyl)xanthine (N7-HEX), as a standard, has been measured at the low picomole level by the following sequence of steps: (1) derivatization with pentafluorobenzyl bromide; (2) post-derivatization sample cleanup by reversed-phase high-performance liquid chromatography (HPLC) or silica solid-phase extraction; and (3) separation/detection by gas chromatography electron-capture negative-ion mass spectrometry (GC-ECNI-MS). The average yield of product from the two sample cleanup procedures applied to 95 pg (0.48 pmol) of N7-HEX was comparable: 60% for HPLC; 56% for solid-phase extraction. The reaction blanks (0 pg N7-HEX) showed an interfering GC-ECNI-MS peak after HPLC cleanup. This problem was not encountered with solid-phase extraction, which, along with its greater convenience, made it the preferred technique for post-derivatization sample cleanup.

Chromatography, High Pressure Liquid↗
PubMed1993

Methods development toward the measurement of polyaromatic hydrocarbon-DNA adducts by mass spectrometry.

The measurement of DNA adducts in human samples is at an early stage. The accuracy of some of the current measurements is not defined, the structures are unknown for a significant number of the adducts that have been detected, and there is little information about how many adducts remain to be discovered. This is due largely to the trace amounts of human DNA adducts in any sample. A consequence of this is that the true potential of DNA adducts as indicators of exposure and risk in human toxicology is far from realized. Mass spectrometry, a powerful technique for organic analysis, is the key to exploiting fully the usefulness of human DNA adducts as biomarkers of human exposure and risk. Mass spectrometry can make accurate measurements, discover unknown compounds, and determine the structures of these unknown compounds. However, the trace (very small) amounts of human DNA adducts have limited mass spectrometry's usefulness in analyzing such samples. This project focused on increasing the sensitivity of mass spectrometry for measuring human DNA adducts. Advances in sensitivity have been achieved for two modes of mass spectrometry applied to standards related to DNA adducts: gas chromatography with electron-capture negative ion mass spectrometry, and fast-atom-bombardment mass spectrometry. These advances involve both sample preparation and instrument conditions.

2-Acetylaminofluorene↗
PubMed1992

Purification of DNA-derived deoxynucleotides from leukocytes involving nuclease elution of an ion-exchange column.

A method has been developed in which the DNA of leukocytes (as the buffy coat from blood) is isolated in the form of its constituent deoxynucleotides. The steps in this method are as follows: (1) lyse the leukocytes with sodium dodecyl sulfate (SDS) and enzymatically digest the proteins and RNA, (2) remove the SDS on a non-polar adsorbent (Bio-Beads SM-4) and then trap the DNA on a quaternary amine silica cartridge, (3) wash the column with 1 M NaCl-buffer, (4) digest the DNA on the column with staphylococcal nuclease and (5) elute the digested DNA with 0.5 M NaCl-buffer and digest it further with bovine spleen phosphodiesterase II to deoxynucleotide-3'-monophosphates. From a 40-microliters sample of butty coat was obtained 126 +/- 14 micrograms (two experiments, eight sample total) of deoxynucleotides. Reversed-phase high-performance liquid chromatography, which removed the added enzymes, showed only peaks for deoxynucleotides. For comparison, the amount of deoxynucleotides obtained from the leukocytes by an automated phenol extraction procedure was 101 +/- 5.4 micrograms (one experiment in triplicate).

Chromatography, High Pressure Liquid↗
PubMed1991

Superoxide chemical transformation of diolepoxide polyaromatic hydrocarbon DNA adducts. Determination of benzo[a]pyrene-r-7,t-8,9,c-10-tetrahydrotetrol by gas chromatography.

Benzo[a]pyrene-r-7,t-8,9,c-10-tetrahydrotetrol (100 pg, 342 fmol) was measured using the following sequence of steps: (1) chemical transformation with potassium superoxide to 2,3-pyrenedicarboxylic acid; (2) electrophore derivatization with pentafluorobenzyl bromide; (3) sample clean-up by high-performance liquid chromatography and (4) measurement by gas chromatography with electron-capture detection and by gas chromatography with electron-capture negative-ion mass spectrometry. The overall, absolute yields obtained by the two procedures were 69% and 60%, respectively. This work completes the first stage towards the establishment of a general method for detecting diolepoxide polyaromatic hydrocarbon DNA adducts by gas chromatography.

Benzo(a)pyrene↗
PubMed1990

Detection and structural characterization of amino polyaromatic hydrocarbon-deoxynucleoside adducts using fast atom bombardment and tandem mass spectrometry.

Fast atom bombardment (FAB) and tandem mass spectrometry (MS/MS) are shown to be useful methods for the detection and structural characterization of nanogram amounts of amino polyaromatic hydrocarbon-nucleoside DNA adducts. The positive ion spectra of four aromatic amine guanosine adducts were studied in detail. The FAB spectra of these adducts exhibit an [MH]+ ion and a more abundant aglycon fragment ion, [AH2]+, which results from the loss of the deoxyribose sugar. The sensitivity of the adducts to FAB was enhanced by preparing trimethylsilyl (TMS) ether derivatives. High-quality full-scan spectra could be obtained on less than 70 ng of the derivatized adducts without signal averaging. With a B/E-linked scan of the [MH]+ ion for the TMS2 species, these same adducts could be detected by examination of their metastable ion spectra at levels as low as 4-5 ng (S/N greater than 10). Collision-induced dissociation (CID) of the [MH]+ ion yields the aglycon fragment and an ion, S1, which results from cleavage through the sugar. The CID spectrum of the aglycon [AH2]+ ion is much more useful, providing structural information relating to the base, the polyaromatic hydrocarbon, and, possibly, the site of covalent attachment. Differentiation of isomeric aminophenanthrene-guanine adducts was demonstrated on the basis of the CID spectra of their respective [AH2]+ ions. The use of TMS derivatives also improves the sensitivity of these methods.

2-Acetylaminofluorene↗
PubMed1990

Chromatographic enzyme immunoassay for T-2 toxin.

Both the active ester and maleimide moieties of the cross-linking reagent, N-[(gamma-maleimidobutyryl)oxy]succinimide (GMBS), were found to react with the primary amino groups on ribonuclease (RNase). This largely inactivated RNase towards a polymeric (but not monomeric) substrate. Citraconylating the RNase first, so that essentially only a single primary amino group remained to react with GMBS, overcame this problem. The subsequent maleimido-citraconyl-RNase was used to prepare a 1:1.1 M conjugate of anti-T-2 toxin Fab' and RNase (Fab'-RNase) in a 76% yield. The conjugate was used to detect as little as 0.1 microgram of T-2 toxin based on the ability of T-2 toxin to specifically displace Fab'-RNase complexed to a T-2 agarose affinity gel.

Chromatography↗
PubMed1990

Preparation of ethylenediaminephosphoramidates of nucleotides and derivatization with fluorescein isothiocyanate.

Fluorescence post-labeling of nucleotides is a potentially useful technique for the detection of trace amounts of damaged DNA (DNA adducts). Towards this goal, we have studied a derivatization procedure starting with the four major 5'-deoxynucleotides as model compounds. The 5'-phosphate group was first labeled with ethylenediamine via a phosphorimidazolide intermediate in methanol with an organic-soluble carbodiimide. The resulting ethylenediaminephosphoramidate products were reacted in turn with fluorescein isothiocyanate. The reaction sequence has been characterised at all stages by high-performance liquid chromatography.

Chemical Phenomena↗
PubMed1990

Dissociative binding of alpha- and beta-sulphoxides of biotinylamidoethyl-3-(4-hydroxy-3-[125I]iodophenyl)propionamide to avidin.

Previously we reported the dissociative binding of biotinylamidoethyl-3-(4-hydroxy-3-[125I]iodophenyl)propionamide to avidin [Garlick & Giese (1988) J. Biol. Chem. 263, 210-215]. In the present paper we report the corresponding binding of the alpha- and beta-sulphoxides of this parent compound to avidin. The 1:1 complex (obtained with avidin in excess) of the alpha-sulphoxide derivative with avidin has a dissociation half-life (t1/2) of 25 days, only 1.6 times as fast as the parent compound (t1/2 41 days). However, the corresponding beta-sulphoxide dissociates 446 times faster (t1/2 0.092 day) than the parent compound, this apparently being due to a steric effect. The alpha-sulphoxide is attractive as a tracer reagent to facilitate studies and applications of the avidin-biotin system.

Avidin↗
PubMed1990

Selection of electrophoric derivatives of 1-aminopyrene and 2-aminofluorene for determination by gas chromatography with electron-capture negative-ion mass spectrometry.

Several electrophoric derivatives of 1-aminopyrene and 2-aminofluorene were prepared. Reagents such as heptafluorobutyryl chloride, pentafluorobenzoyl chloride, pentafluorobenzyl bromide and pentafluorobenzaldehyde, alone and in certain combinations, were employed. The ease of formation, yield, stability and fragmentation by gas chromatography with electron-capture negative-ion (ECNI) mass spectrometry of the derivatives were compared. This allowed the most promising ones to be selected for future work on the sensitive detection of aminopolyaromatics by this detection technique. Pentafluorobenzylidene (first choice) and N-pentafluorobenzyl-N-heptafluorobutyryl (second choice) derivatives emerged as the best ones. The origins of losses of HF and 2HF from some of the derivatives were elucidated in the ECNI mass spectra by studies of deuterium-labeled analogues.

Chemistry Techniques, Analytical↗