Lisa R. Karam

Generation of oxy radicals in biosystems.

Many recent lines of evidence indicate that endogenous free radicals contribute to spontaneous mutagenesis through the direct induction of DNA damage. However, the mechanisms underlying this process are not yet fully understood. A brief overview of the knowledge that is currently available is provided here, with emphasis on the generation of oxy radicals in biosystems, the reactions of those radicals with biomolecules, and the induction of oxidative DNA base damage that might lead to mutation.

OH Radical-induced Products of Tyrosine Peptides

Reactions of radiation-generated OH radicals with tyrosine and its homopeptides, i.e. L-Tyr-L-Tyr and L-Tyr-L-Tyr-L-Tyr, in N2O saturated solutions were shown to give crosslinks between the peptide chains with high yields. High-performance liquid chromatography, capillary gas chromatography and mass spectrometry were used for isolation and identification of the monomeric and dimeric products. Evidence is presented for the crosslinking to occur through C-C and C-O-C bonds. To the best of our knowledge, the formation of the ether type of crosslink is demonstrated for the first time. Mechanisms of product formation are also discussed, which involve radicals that were described in previous pulse radiolysis studies.

Biomarkers of oh Radical Damage In Vivo

Mechanisms of formation of o-tyrosine (o-Tyr) and thymine glycol (TG), the two possible markers of OH radical generation in biosystems and in vivo are described. The o-Tyr measurements require invasive approaches, while TG detection may be accomplished by noninvasive analysis in the urine.

Intramolecular H atom abstraction from the sugar moiety by thymine radicals in oligo- and polydeoxynucleotides.

Hydroxyl radical addition to uracil (U) has been suggested to lead to strand breaks in polyuridylic acid, an occurrence attributed in part to H atom abstraction by .U-OH radicals from the ribose moiety [D.G.E. Lemaire et al., Int. J. Radiat. Biol. 45, 351-358 (1984)]. We have investigated this particular reaction by means of the hydroxyl radical-induced products of thymine (T), pT, TpT, TpTpT, polythymidylic acid (poly-T), (T + dR) poly-dA.poly-T, and a mixture of T and 2-deoxyribose (dR). The major monomeric product of .T-OH in TpT, TpTpT, poly-T, and poly-dA.poly-T was found to be 5-hydroxy-6-hydrothymine (H-T-OH), while that in T, pT, and T plus dR was thymine glycol (HO-T-OH). These results indicated that the intramolecular H atom abstraction from a nearby sugar (in this case, deoxyribose) moiety by base radicals, i.e., .T-OH, occurs in oligo- and polydeoxynucleotides of T. In poly-T, the yield of H-T-OH is not much greater than in TpT or TpTpT, indicating that the abstraction of an H atom from the sugar moiety of a nucleotide subunit further than two nucleotides along the chain may not be significant. Additionally, a corresponding decrease in the yield of HO-T-OH with an increase in the yield of H-T-OH suggests that the formations of these two types of thymine products are competitive.

Modeling energy deposition and cellular radiation effects in human bronchial epithelium by radon progeny alpha particles.

Energy deposition and cellular radiation effects arising from the interaction of single 218Po and 214Po alpha particles with basal and secretory cell nuclei were simulated for different target cell depths in the bronchial epithelium of human airway generations 2, 4, 6, and 10. To relate the random chord lengths of alpha particle tracks through spherical cell nuclei to the resulting biological endpoints, probabilities per unit track length for different cellular radiation effects as functions of LET were derived from in vitro experiments. The radiobiological data employed in the present study were inactivation and mutation (mutant frequency at the HPRT gene) in V79 Chinese hamster cells and inactivation and transformation in C3H 10T1/2 cells. Based on computed LET spectra and relative frequencies of target cells, probabilities for transformation, mutation, and cell killing in basal and secretory cells were computed for a lifetime exposure of 20 WLM. While predicted transformation probabilities were about two orders of magnitude higher than mutation probabilities, they were still about two orders of magnitude lower than inactivation probabilities. Furthermore transformation probabilities for basal cells are generally higher than those for secretory cells, and 214Po alpha particles are primarily responsible for transformations in bronchial target cells.

Use of resonance ionization mass spectrometry for determination of Cs ratios in solid samples

A method to quantitatively determine the radionuclidic content of complex samples with a minimum of chemical preparation has been under development at the National Institute of Standards and Technology (NIST). Based on earlier studies with resonance ionization mass spectrometry (RIMS), a graphite furnace was added to the RIMS system at NIST. Efficiency determinations for 133Cs in solution and isotopic ratio measurements of cesium (135Cs/137Cs) for an NIST nuclear burn-up sample using RIMS and for a sediment natural matrix standard using thermal ionization mass spectrometry are presented.

Evaluation of Handheld Radionuclide Identifiers

Characterization of commercially available instruments for measurement and identification of unknown radionuclides was carried out in support of the development and testing of the American National Standards Institute (ANSI) standard, N42.34, “Performance Criteria for Hand-held Instruments for the Detection and Identification of Radionuclides.” Measurements were based on the performance of the devices, i.e., the capability of the detectors to ensure a correct radionuclide identification in a given time interval for various radioactive sources.

Encapsulation of 99mTc within Fullerenes: a novel radionuclidic carrier

Abstract The nature of fullerenes as miniature ‘isolation chambers’ suggests the possibility of unstable atoms carried within the interior of the molecular cage forming endofullerenes which could isolate potentially reactive atoms from their environment. We have produced, characterized by various techniques including thin layer chromatography, and purified endofullerenes containing gamma-ray emitting 99m Tc, the first direct encapsulation of a radionuclide during fullerene formation. Identification of 99m Tc@C 60 and 99m Tc@C 70 has been accomplished by application of ultra-low level radiation detection methods. Appropriately derivatized, 99m Tc ‘radioendofullerenes’ could eventually be used as a radiopharmaceutical for medical imaging.

NIST Radiochemistry Intercomparison Program: a Summary of Four-year Performance Evaluation Study

This paper summarizes the methods currently applied by the National Institute of Standards and Technology (NIST) for the preparation and verification of environmental and radiobioaasay performance evaluation materials for the traceability testing of low-level radioactivity measurements. The evaluation of measurement quality of the all participants indicated that over 90% of the intercomparison results complied with ANSI N42.22 and/or HPS N13.30 standards. Overall, the differences from the NIST values observed for all test nuclides and matrices are less than -7%, with a typical measurement precision better than 10% (1 s). The dependency of measurement quality on the test radionuclides, sample matrices, and radiochemical methods is identified by statistical analyses.

A GC–MS study of the addition reaction of aryl amines with acrylic monomers

Previous studies have shown that the interaction of carboxylic acid groups with the amine functionalities of aryl amines, especially secondary and tertiary aryl amines, can lead to the free-radical polymerization of acrylic monomers such as methyl methacrylate. In this study, the Michael addition reaction of primary and secondary aryl amines with acrylic monomers such as acrylic acid (AA) was investigated. Equivalent amounts of either p-toluidine (PT) or N-phenylglycine (NPG) and AA were combined in polar solvents such as ethanol. The reactions were conducted at ambient (23°C) or near-ambient (37–60°C) temperatures. Samples (about 3–5 mg) of these products were then trimethylsilylated with a solution consisting of 0.4 mL of bis(trimethylsilyl)trifluoroacetamide (BSTFA) and 0.4 mL of acetonitrile by heating for 30 min at 140°C under N2. These derivatives were characterized by gas chromatography–mass spectrometry (GC–MS). The GC–MS analyses suggest that 1 mol of the primary amine PT had reacted with 2 mol of AA to yield the expected N-p-tolyliminodipropionic acid. Similarly, the secondary amine NPG added to 1 mol of AA yielded the corresponding mixed iminodiacid, N-phenyliminoacetic–propionic acid. It would appear that the Michael reaction of primary and secondary amines with acrylic monomers may offer a general, facile synthetic route to a variety of tertiary amines. Aryl amino acids of the type synthesized in this study may find use in a number of dental applications, e.g., as surface-active adhesive agents and as polymerization initiators or activators.