International Journal of Radiation Oncology Biology Physics, Aug 1, 2009
Purpose-Current biodosimetric techniques for determining radiation exposure have inherent delays,... more Purpose-Current biodosimetric techniques for determining radiation exposure have inherent delays, and quantitation and interpretation limitations. We have identified a new technique with the advantage of directly measuring circulating DNA by amplifying inter-B1 regions in the mouse genome, providing a sensitive method for quantitating plasma DNA. Methods and Materials-Real-time quantitative PCR was used to detect levels of DNA by amplifying inter-B1 genomic DNA in plasma samples collected at 0-48 hrs from mice receiving 0-10 Gy total-or partial-body irradiation [ 137 Cs γ-ray source at ≈1.86 Gy/min (homogeneity: ±6.5%)]. Results-The correlation coefficient between DNA levels and the threshold cycle value (C T ) was 0.996, and the average recoveries of DNA in the assay were 87%. This assay revealed that when BALB/c mice were exposed to 10 Gy TBI, plasma DNA levels gradually increased beginning at 3 hours after irradiation, peaked at 9 hours, and returned to baseline within 48 hours. Increased plasma DNA levels were also detected following upper-torso or lower-torso partial-body irradiation; however, TBI approximately doubled those plasma DNA levels at the same radiation dose. This technique therefore reflects total body cell damage. The advantages of this assay are that DNA extraction is not required, the assay is highly sensitive (0.002 ng), and results can be obtained within 2.5 hours after collection of plasma samples. Conclusions-A radiation dose-dependent increase of plasma DNA was observed in the dose range from 2-10 Gy, suggesting that plasma DNA may be a useful radiation biomarker and adjunct to existing cell-based assays.
An atomistic biophysical model permitting the calculation of initial attacks to a 38-bp represent... more An atomistic biophysical model permitting the calculation of initial attacks to a 38-bp representation of B-DNA base moieties by water radicals is presented. This model is based on a previous radiation damage model developed by Aydogan et al. (Radiat. Res. 157, 38-44, 2002). Absolute efficiencies for radical attack to the 38-bp DNA molecule are calculated to be 41, 0.8 and 15% for hydroxyl radical ( • OH), hydrogen radical (H • ), and hydrated electron ( ) , respectively. Among the e aq nucleobases, guanine is found to have the highest percentage • OH attack probability at 36%. Adenine, cytosine and thymine moieties have initial attack probabilities of 24, 18 and 22%, respectively. A systematic study is performed to investigate • OH attack probabilities at each specified attack site in four molecular models including free bases, single nucleotides, single base pairs, and the central eight base pairs of the 38-bp DNA molecule. Cytosine is the free base moiety for which the closest agreement is observed between the model prediction and the experimental data. The initial • OH attack probabilities for cytosine as the free base are calculated to be 72 and 28%, while experimental data are reported at 87 and 13% for the C5 and C6 positions on the base, respectively. In this study, we incorporated atomic charges to scale the site-specific • OH reaction rates at the individual atomic positions on the pyrimidine and purine bases. Future updates to the RIDNA model will include the use of electron densities to scale the reaction rates. With respect to reactions of the aqueous electron with DNA, a comparison of the initial distribution of electron attack sites calculated in this study and experimental results suggests an extremely rapid and extensive redistribution of the after their initial reactions with DNA. ᭧ 2008 by Radiation Ϫ e aq Research Society
Little computational or experimental information is available on site-specific hydroxyl attack pr... more Little computational or experimental information is available on site-specific hydroxyl attack probabilities to DNA. In this study, an atomistic stochastic model of OH radical reactions with DNA was developed to compute relative OH attack probabilities at individual deoxyribose hydrogen atoms. A model of the self-complementary decamer duplex d(CCAACGTTGG) was created including Na ؉ counter ions and the water molecules of the first hydration layer. Additionally, a method for accounting for steric hindrance from nonreacting atoms was implemented. The model was then used to calculate OH attack probabilities at the various C-H sites of the sugar moiety. Results from this computational model show that OH radicals exhibit preferential attack at different deoxyribose hydrogens, as suggested by their corresponding percentage solvent-accessible surface areas. The percentage OH attack probabilities for the deoxyribose hydrogens [1H(5)؉2H(5), H(4), H(3), 1H(2)؉2H(2), H(1)] were calculated as approximately 54.6%, 20.6%, 15.0%, 8.5% and 1.3%, respectively, averaged across the sequence. These results are in good agreement with the latest experimental site-specific DNA strand break data of Balasubramanian et al. [Proc. Natl. Acad. Sci. USA 95, 9738-9742 (1998)]. The data from this stochastic model suggest that steric hindrance from nonreacting atoms significantly influences site-specific hydroxyl radical attack probabilities in DNA. A number of previous DNA damage models have been based on the assumption that C(4) is the preferred site, or perhaps the only site, for OHmediated DNA damage. However, the results of the present study are in good agreement the experimental results of Balasubramanian et al. in which OH radicals exhibit preferential initial attack at sugar hydrogen atoms in the order 1H(5)؉2H(5) Ͼ H(4) Ͼ H(3) Ͼ 1H(2)؉2H(2) Ͼ H(1).
This study demonstrates that mice, similar to humans, have a common mitochondrial DNA deletion (3... more This study demonstrates that mice, similar to humans, have a common mitochondrial DNA deletion (3,860 bp) that encodes 5 transfer RNA genes and 5 polypeptide genes that is related to aging, tissue type and radiotoxicity. Our research indicates that the deletion ratio in the liver was significantly higher than in the brain and gut tissues of 8-month-old mice, as compared to 8-week-old mice. Our results also demonstrate that tissue type, oxidative metabolic capacity and radiosensitivity influence the 3,860-bp deletion level. Therefore, this 3,860-bp deletion content may serve as a biomarker of aging and oxidative damage in mice.
Advances in Experimental Medicine and Biology, Nov 2, 2011
Genomic background helps determine sensitivity to TBI. Since the LD50/30 (the dose that causes de... more Genomic background helps determine sensitivity to TBI. Since the LD50/30 (the dose that causes death in half of exposed mice within 30 days) following TBI varies between murine strains, we tested four murine strains to determine whether TBI sensitivity was associated with different levels of circulating DNA after radiation. The LD50/30 for the mice we tested – BALB/c, NIH Swiss, C3H/HeN, and C57BL/6 – is approximately 5.8 ± 0.3, 7.3 ± 0.2, 7.4 ± 0.3, and 8.5 ± 0.3 Gy, respectively. We estimated the radiation dose at which circulating DNA reached a peak level (peakGy), and mice were subjected to different doses at 1.84 Gy/min. The peakGy was 6, 7, 9, and 9 Gy for BALB/c, NIH Swiss, C3H/HeN, and C57BL/6, which corresponds to each strain’s respective LD50/30. BALB/c, the most sensitive strain, had the lowest DNA concentration at peakGy, while C57BL/6, the most resistant strain, had the highest concentration at peakGy. At 7 Gy, the plasma DNA was approximately 3,754 ± 636, 8,238 ± 2,704, 9,773 ± 2,821, and 22,733 ± 5,914 ng/ml for BALB/c, NIH Swiss, C3H/HeN, and C57BL/6, respectively. These findings support our hypothesis that plasma DNA level is associated with genomic background.
The reactions of free and DNA-bound 2,2,5,5-tetramethylpyrrolidine-N-oxyl (PROXYL) probes with ra... more The reactions of free and DNA-bound 2,2,5,5-tetramethylpyrrolidine-N-oxyl (PROXYL) probes with radicals generated during radiolysis of dilute aqueous solutions of DNA were examined. For the free PROXYL probe in deaerated solution with each of the four nucleotides (dAMP, dCMP, dGMP, and TMP) it was found that the pyrimidine radicals were more reactive toward the probe than were the purine radicals. Reactions of the electron adduct of TMP and the hydroxyl radical adducts of dAMP, dGMP, and TMP with the probe resulted in little or no reduction of the probe. For TMP these results are consistent with the fact that both the protonated electron and hydroxyl radical adducts of TMP will covalently bind to the nitroxide function of the probe. Reduction of the PROXYL probe was observed in reactions with the hydroxyl radical adduct of dCMP and with the electron adducts of dAMP, dCMP, and dGMP. Results of the radiolysis of the free PROXYL probe in deaerated dilute solution of DNA suggest that the PROXYL probe protects the DNA from water radical attack as the ratio of DNA bases to PROXYL probe increases above 50:1. Reactions of DNA-bound probes are dependent on the depth of the nitroxide function in relation to the major groove of the DNA helix. Two probes with tether lengths which are less than the depth of the major groove show an expected increase in reactions with DNA base radicals as compared to a probe with a tether that extends beyond the groove. The longer probe is involved largely in reactions with sugar and water radicals along the periphery of the DNA helix. In the presence of oxygen, there is a dramatic decrease in the loss of both the free and DNA-bound probes due to the lack of reaction of these probes with peroxyl radicals formed by the addition of molecular oxygen to DNA radicals.
An effective medical response to a large-scale radiation event requires prompt and effective init... more An effective medical response to a large-scale radiation event requires prompt and effective initial triage so that appropriate care can be provided to individuals with significant risk for severe acute radiation injury. Arguably, it would be advantageous to use injury rather than radiation dose for the initial assessment, i.e., use bioassays of biological damage. Such assays would be based on changes in intrinsic biological response elements, e.g., up- or down-regulation of genes, proteins, metabolites, blood cell counts, chromosomal aberrations, micronuclei, micro-RNA, cytokines, or transcriptomes. Using a framework to evaluate the feasibility of biodosimetry for triaging up to a million people in less than a week following a major radiation event, Part 1 analyzes the logistical feasibility and clinical needs for ensuring that biomarkers of organ-specific injury could be effectively utilized in this context. We conclude that the decision to use biomarkers of organ-specific injury would greatly benefit by first having independent knowledge of whether the person’s exposure was heterogeneous and, if so, what was the dose distribution (to determine which organs were exposed to high doses). In Part 2 we describe how these two essential needs for prior information (heterogeneity and dose distribution) could be obtained by using in vivo nail dosimetry. This novel physical biodosimetry method can also meet the needs for initial triage, providing non-invasive, point-of-care measurements made by non-experts with immediate dose estimates for 4 separate anatomical sites. Additionally, it uniquely provides immediate information as to whether the exposure was homogeneous and, if not, can estimate the dose distribution. We conclude that combining the capability of methods such as in vivo EPR nail dosimetry with bioassays to predict organ-specific damage would together allow effective use of medical resources to save lives.
I am extremely proud and grateful that so many outstanding scientists have contributed to this sp... more I am extremely proud and grateful that so many outstanding scientists have contributed to this special issue highlighting the contributions of my laboratory to magnetic resonance, especially in electron paramagnetic resonance. The articles in the two parts of the special issue highlight how advances in both instrumentation and concepts have made EPR of biological systems so productive. This raises my optimism that, where there are current limitations, further technical and scientific progress will make EPR of biological systems even more productive in the future. While I am of course both proud and humbled by the many senior colleagues with whom I have the privilege of collaborating and exchanging knowledge, I am especially proud of my 'academic children', i.e., those who worked with me in their formative years as students, post-docs, visiting fellows, or young academics in my laboratories. This group includes many very bright and energetic men and women who went on to have very impressive careers, including many who have established their own research groups and produced additional excellent science as well as nextgeneration scientists. This talented group encompasses
Rapid and accurate retrospective dosimetry is of critical importance and strategic value for the ... more Rapid and accurate retrospective dosimetry is of critical importance and strategic value for the emergency medical response to a large-scale radiological/nuclear event. One technique that has the potential for rapid and accurate dosimetry measurements is electron paramagnetic resonance (EPR) spectroscopy of relatively stable radiation-induced signals (RIS) in fingernails and toenails. Two approaches are being developed for EPR nail dosimetry. In the approach using ex vivo measurements on nail clippings, accurate estimation of the dose-dependent amplitude of the RIS is complicated by the presence of mechanically-induced signals (MIS) that are generated during the nail clipping. Recent developments in ex vivo nail dosimetry, including a thorough characterization of the MIS and an appreciation of the role of hydration and the development of effective analytic techniques, have led to improvements in the accuracy and precision of this approach. An in vivo nail dosimetry approach is also very promising, as it eliminates the problems of MIS from the clipping and it has the potential to be an effective and efficient approach for field deployment. Two types of EPR resonators are being developed for in vivo measurements of fingernails and toenails.
A new resonant geometry for X-band in vivo electron paramagnetic resonance (EPR) nail dosimetry h... more A new resonant geometry for X-band in vivo electron paramagnetic resonance (EPR) nail dosimetry has been developed, fabricated, and tested. The dielectricbacked aperture resonator (DAR) was specifically designed for depth-limited surface spectroscopy. The DAR improves EPR sensitivity of surface samples with sub-millimeter thicknesses by at least a factor of 20 compared to other aperture resonator designs. The increase in EPR sensitivity was achieved using a non-resonant dielectric slab which is placed on the aperture inside the cavity. The dielectric slab provides an increased microwave magnetic field, while minimizing the problematic resonance conditions of the aperture. It has been shown that the DAR provides sufficient sensitivity to make biologically-relevant measurements both in vitro and in vivo. This work demonstrates that in vivo tests with an equivalent dosimetry sensitivity of approximately 1.4 Gy are feasible. Plausible ways to further increase the sensitivity are discussed, such as, the introduction and simulations of a DAR based on a semi-spherical TE 011 geometry.
Objectives-The aim of this paper is to delineate characteristics of biodosimetry most suitable fo... more Objectives-The aim of this paper is to delineate characteristics of biodosimetry most suitable for assessing individuals who have potentially been exposed to significant radiation from a nuclear device explosion, when the primary population targeted by the explosion and needing rapid assessment for triage is civilians vs. deployed military personnel. Methods-We first carry out a systematic analysis of the requirements for biodosimetry to meet the military's needs to assess deployed troops in a warfare situation, which include accomplishing the military mission. We then systematically compare and contrast the military's special capabilities to respond and carry out biodosimetry for deployed troops in warfare, in contrast to those available to respond and conduct biodosimetry for civilians who have been targeted, e.g., by terrorists. We then compare the effectiveness of different biodosimetry methods to address military vs. civilian needs and capabilities in these scenarios and, using five representative types of biodosimetry with sufficient published data to be useful for the simulations, we estimate the number of individuals who could be assessed by military vs. civilian responders within the timeframe needed for triage decisions.
A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic... more A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarterwave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human fingernails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg 2+ doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 coaxial input. Agreement between simulated and experimental results is shown.
Electron paramagnetic resonance (EPR) spectroscopy has been well established as a viable techniqu... more Electron paramagnetic resonance (EPR) spectroscopy has been well established as a viable technique for measurement of free radicals and oxygen in biological systems, from in vitro cellular systems to in vivo small animal models of disease. However, the use of EPR in human subjects in the clinical setting, although attractive for a variety of important applications such as oxygen measurement, is challenged with several factors including the need for instrumentation customized for human subjects, probe and regulatory constraints. This paper describes the rationale and development of the first clinical EPR systems for two important clinical applications, namely, measurement of tissue oxygen (oximetry), and radiation dose (dosimetry) in humans. The clinical spectrometers operate at 1.2 GHz frequency and use surface loop resonators capable of providing topical measurements up to 1 cm depth in tissues. Tissue pO 2 measurements can be carried out noninvasively and repeatedly after placement of an oxygen-sensitive paramagnetic material (currently India ink) at the site of interest. Our EPR dosimetry system is capable of measuring radiation-induced free radicals in the tooth of irradiated human subjects to determine the exposure dose. These developments offer potential opportunities for clinical dosimetry and oximetry, which include guiding therapy for individual patients with tumors or vascular disease, by monitoring of tissue oxygenation. Further work is in progress to translate this unique technology to routine clinical practice.
International Journal of Radiation Biology, Nov 17, 2021
PURPOSE Based on the experience of biodosimetry laboratories during the COVID-19 pandemic, the pu... more PURPOSE Based on the experience of biodosimetry laboratories during the COVID-19 pandemic, the purpose of this paper is to describe the challenges of providing biodosimetry service in the event of a major radiation incident during a pandemic. This includes describing some of the preparations and planning made by biodosimetry laboratories and special challenges in maintaining a state of readiness while adhering to safety protocols and balancing the need to assist with the COVID-19 response where possible. Experiences of several biodosimetry laboratories will be described and lessons learned will be outlined that could be applied to any large population-scale emergencies. CONCLUSIONS There are many challenges that arise when maintaining capacity and capabilities for biodosimetry when faced with a global pandemic such as COVID-19. The key is to be prepared for anything within reason. This includes, but is not limited to, maintaining flexibility, shifting and reorganizing deployment of staff between pandemic response and biodosimetry needs, strengthening networks to be able to provide assistance to other laboratories, managing staff in the face of possible infections and preparing protocols for the handling of potentially infected biological samples according to regulatory requirements. By implementing these recommendations, international biodosimetry networks can be prepared to address large-scale radiological incidents within the context of a pandemic and ensure the safety of biodosimetry personnel as well as victims in such dual emergencies.
As COVID-19 emerged, there are parallels between the responses needed for managing SARS-CoV-2 inf... more As COVID-19 emerged, there are parallels between the responses needed for managing SARS-CoV-2 infections and radiation injuries. While some SARS-CoV-2-infected individuals present as asymptomatic, others exhibit a range of symptoms including severe and rapid onset of high-risk indicators of mortality. Similarly, a variety of responses are also observed after a radiological exposure depending on radiation dose, dose heterogeneity, and biological variability. The impact of acute radiation syndrome (ARS) has guided the identification of many biomarkers of radiation exposure, the establishment of medical management strategies, and development of medical countermeasures in the event of a radiation public health emergency. Biodosimetry has a prominent role for identifying exposed persons during a large scale radiological emergency situation. Identifying exposed individuals is also critical in the case of pandemics such as COVID-19, with the additional goal of controlling the spread of disease. Conclusions and significance: IABERD has taken advantage of its competences in biodosimetry to draw lessons from current practices of managing the testing strategy for nuclear accidents to improve responses to SARS-CoV-2. Conversely, lessons learned from managing SARS-CoV-2 can be used to inform best practices in managing radiological situations. Finally, the potential need to deal with testing modalities simultaneously and effectively in both situations is considered.
Background: Hemorrhagic cystitis from chemical or radiation bladder injury can cause life-threate... more Background: Hemorrhagic cystitis from chemical or radiation bladder injury can cause life-threatening bleeding and/or urothelial cancer. Fibroblast growth factor 7 (FGF7) blocks urothelial apoptosis induced by cyclophosphamide (CPP) or radiation, but there are limitations to its use in patients, including an inability to apply it by direct bladder infusion and the high cost due to the large size of the protein (18.8 kDa). Purpose: We previously identified a small peptide that equaled or exceeded the mitigation effect of full length FGF2 on acute radiation syndrome. Benefits of developing a similar FGF7 biomimetic peptide include lower likelihood of inflammation, longer shelf life, higher purity, and lower cost than the full-length protein. Methods: Based on the 3-dimensional structure of FGF2 peptide, a corresponding FGF7 peptide (FGF7p) consisting of 19 amino acids was identified and synthesized. FGF7p or vehicle was given subcutaneously (SQ) to female mice subjected to sham injury...
International Journal of Radiation Oncology Biology Physics, Aug 1, 2009
Purpose-Current biodosimetric techniques for determining radiation exposure have inherent delays,... more Purpose-Current biodosimetric techniques for determining radiation exposure have inherent delays, and quantitation and interpretation limitations. We have identified a new technique with the advantage of directly measuring circulating DNA by amplifying inter-B1 regions in the mouse genome, providing a sensitive method for quantitating plasma DNA. Methods and Materials-Real-time quantitative PCR was used to detect levels of DNA by amplifying inter-B1 genomic DNA in plasma samples collected at 0-48 hrs from mice receiving 0-10 Gy total-or partial-body irradiation [ 137 Cs γ-ray source at ≈1.86 Gy/min (homogeneity: ±6.5%)]. Results-The correlation coefficient between DNA levels and the threshold cycle value (C T ) was 0.996, and the average recoveries of DNA in the assay were 87%. This assay revealed that when BALB/c mice were exposed to 10 Gy TBI, plasma DNA levels gradually increased beginning at 3 hours after irradiation, peaked at 9 hours, and returned to baseline within 48 hours. Increased plasma DNA levels were also detected following upper-torso or lower-torso partial-body irradiation; however, TBI approximately doubled those plasma DNA levels at the same radiation dose. This technique therefore reflects total body cell damage. The advantages of this assay are that DNA extraction is not required, the assay is highly sensitive (0.002 ng), and results can be obtained within 2.5 hours after collection of plasma samples. Conclusions-A radiation dose-dependent increase of plasma DNA was observed in the dose range from 2-10 Gy, suggesting that plasma DNA may be a useful radiation biomarker and adjunct to existing cell-based assays.
An atomistic biophysical model permitting the calculation of initial attacks to a 38-bp represent... more An atomistic biophysical model permitting the calculation of initial attacks to a 38-bp representation of B-DNA base moieties by water radicals is presented. This model is based on a previous radiation damage model developed by Aydogan et al. (Radiat. Res. 157, 38-44, 2002). Absolute efficiencies for radical attack to the 38-bp DNA molecule are calculated to be 41, 0.8 and 15% for hydroxyl radical ( • OH), hydrogen radical (H • ), and hydrated electron ( ) , respectively. Among the e aq nucleobases, guanine is found to have the highest percentage • OH attack probability at 36%. Adenine, cytosine and thymine moieties have initial attack probabilities of 24, 18 and 22%, respectively. A systematic study is performed to investigate • OH attack probabilities at each specified attack site in four molecular models including free bases, single nucleotides, single base pairs, and the central eight base pairs of the 38-bp DNA molecule. Cytosine is the free base moiety for which the closest agreement is observed between the model prediction and the experimental data. The initial • OH attack probabilities for cytosine as the free base are calculated to be 72 and 28%, while experimental data are reported at 87 and 13% for the C5 and C6 positions on the base, respectively. In this study, we incorporated atomic charges to scale the site-specific • OH reaction rates at the individual atomic positions on the pyrimidine and purine bases. Future updates to the RIDNA model will include the use of electron densities to scale the reaction rates. With respect to reactions of the aqueous electron with DNA, a comparison of the initial distribution of electron attack sites calculated in this study and experimental results suggests an extremely rapid and extensive redistribution of the after their initial reactions with DNA. ᭧ 2008 by Radiation Ϫ e aq Research Society
Little computational or experimental information is available on site-specific hydroxyl attack pr... more Little computational or experimental information is available on site-specific hydroxyl attack probabilities to DNA. In this study, an atomistic stochastic model of OH radical reactions with DNA was developed to compute relative OH attack probabilities at individual deoxyribose hydrogen atoms. A model of the self-complementary decamer duplex d(CCAACGTTGG) was created including Na ؉ counter ions and the water molecules of the first hydration layer. Additionally, a method for accounting for steric hindrance from nonreacting atoms was implemented. The model was then used to calculate OH attack probabilities at the various C-H sites of the sugar moiety. Results from this computational model show that OH radicals exhibit preferential attack at different deoxyribose hydrogens, as suggested by their corresponding percentage solvent-accessible surface areas. The percentage OH attack probabilities for the deoxyribose hydrogens [1H(5)؉2H(5), H(4), H(3), 1H(2)؉2H(2), H(1)] were calculated as approximately 54.6%, 20.6%, 15.0%, 8.5% and 1.3%, respectively, averaged across the sequence. These results are in good agreement with the latest experimental site-specific DNA strand break data of Balasubramanian et al. [Proc. Natl. Acad. Sci. USA 95, 9738-9742 (1998)]. The data from this stochastic model suggest that steric hindrance from nonreacting atoms significantly influences site-specific hydroxyl radical attack probabilities in DNA. A number of previous DNA damage models have been based on the assumption that C(4) is the preferred site, or perhaps the only site, for OHmediated DNA damage. However, the results of the present study are in good agreement the experimental results of Balasubramanian et al. in which OH radicals exhibit preferential initial attack at sugar hydrogen atoms in the order 1H(5)؉2H(5) Ͼ H(4) Ͼ H(3) Ͼ 1H(2)؉2H(2) Ͼ H(1).
This study demonstrates that mice, similar to humans, have a common mitochondrial DNA deletion (3... more This study demonstrates that mice, similar to humans, have a common mitochondrial DNA deletion (3,860 bp) that encodes 5 transfer RNA genes and 5 polypeptide genes that is related to aging, tissue type and radiotoxicity. Our research indicates that the deletion ratio in the liver was significantly higher than in the brain and gut tissues of 8-month-old mice, as compared to 8-week-old mice. Our results also demonstrate that tissue type, oxidative metabolic capacity and radiosensitivity influence the 3,860-bp deletion level. Therefore, this 3,860-bp deletion content may serve as a biomarker of aging and oxidative damage in mice.
Advances in Experimental Medicine and Biology, Nov 2, 2011
Genomic background helps determine sensitivity to TBI. Since the LD50/30 (the dose that causes de... more Genomic background helps determine sensitivity to TBI. Since the LD50/30 (the dose that causes death in half of exposed mice within 30 days) following TBI varies between murine strains, we tested four murine strains to determine whether TBI sensitivity was associated with different levels of circulating DNA after radiation. The LD50/30 for the mice we tested – BALB/c, NIH Swiss, C3H/HeN, and C57BL/6 – is approximately 5.8 ± 0.3, 7.3 ± 0.2, 7.4 ± 0.3, and 8.5 ± 0.3 Gy, respectively. We estimated the radiation dose at which circulating DNA reached a peak level (peakGy), and mice were subjected to different doses at 1.84 Gy/min. The peakGy was 6, 7, 9, and 9 Gy for BALB/c, NIH Swiss, C3H/HeN, and C57BL/6, which corresponds to each strain’s respective LD50/30. BALB/c, the most sensitive strain, had the lowest DNA concentration at peakGy, while C57BL/6, the most resistant strain, had the highest concentration at peakGy. At 7 Gy, the plasma DNA was approximately 3,754 ± 636, 8,238 ± 2,704, 9,773 ± 2,821, and 22,733 ± 5,914 ng/ml for BALB/c, NIH Swiss, C3H/HeN, and C57BL/6, respectively. These findings support our hypothesis that plasma DNA level is associated with genomic background.
The reactions of free and DNA-bound 2,2,5,5-tetramethylpyrrolidine-N-oxyl (PROXYL) probes with ra... more The reactions of free and DNA-bound 2,2,5,5-tetramethylpyrrolidine-N-oxyl (PROXYL) probes with radicals generated during radiolysis of dilute aqueous solutions of DNA were examined. For the free PROXYL probe in deaerated solution with each of the four nucleotides (dAMP, dCMP, dGMP, and TMP) it was found that the pyrimidine radicals were more reactive toward the probe than were the purine radicals. Reactions of the electron adduct of TMP and the hydroxyl radical adducts of dAMP, dGMP, and TMP with the probe resulted in little or no reduction of the probe. For TMP these results are consistent with the fact that both the protonated electron and hydroxyl radical adducts of TMP will covalently bind to the nitroxide function of the probe. Reduction of the PROXYL probe was observed in reactions with the hydroxyl radical adduct of dCMP and with the electron adducts of dAMP, dCMP, and dGMP. Results of the radiolysis of the free PROXYL probe in deaerated dilute solution of DNA suggest that the PROXYL probe protects the DNA from water radical attack as the ratio of DNA bases to PROXYL probe increases above 50:1. Reactions of DNA-bound probes are dependent on the depth of the nitroxide function in relation to the major groove of the DNA helix. Two probes with tether lengths which are less than the depth of the major groove show an expected increase in reactions with DNA base radicals as compared to a probe with a tether that extends beyond the groove. The longer probe is involved largely in reactions with sugar and water radicals along the periphery of the DNA helix. In the presence of oxygen, there is a dramatic decrease in the loss of both the free and DNA-bound probes due to the lack of reaction of these probes with peroxyl radicals formed by the addition of molecular oxygen to DNA radicals.
An effective medical response to a large-scale radiation event requires prompt and effective init... more An effective medical response to a large-scale radiation event requires prompt and effective initial triage so that appropriate care can be provided to individuals with significant risk for severe acute radiation injury. Arguably, it would be advantageous to use injury rather than radiation dose for the initial assessment, i.e., use bioassays of biological damage. Such assays would be based on changes in intrinsic biological response elements, e.g., up- or down-regulation of genes, proteins, metabolites, blood cell counts, chromosomal aberrations, micronuclei, micro-RNA, cytokines, or transcriptomes. Using a framework to evaluate the feasibility of biodosimetry for triaging up to a million people in less than a week following a major radiation event, Part 1 analyzes the logistical feasibility and clinical needs for ensuring that biomarkers of organ-specific injury could be effectively utilized in this context. We conclude that the decision to use biomarkers of organ-specific injury would greatly benefit by first having independent knowledge of whether the person’s exposure was heterogeneous and, if so, what was the dose distribution (to determine which organs were exposed to high doses). In Part 2 we describe how these two essential needs for prior information (heterogeneity and dose distribution) could be obtained by using in vivo nail dosimetry. This novel physical biodosimetry method can also meet the needs for initial triage, providing non-invasive, point-of-care measurements made by non-experts with immediate dose estimates for 4 separate anatomical sites. Additionally, it uniquely provides immediate information as to whether the exposure was homogeneous and, if not, can estimate the dose distribution. We conclude that combining the capability of methods such as in vivo EPR nail dosimetry with bioassays to predict organ-specific damage would together allow effective use of medical resources to save lives.
I am extremely proud and grateful that so many outstanding scientists have contributed to this sp... more I am extremely proud and grateful that so many outstanding scientists have contributed to this special issue highlighting the contributions of my laboratory to magnetic resonance, especially in electron paramagnetic resonance. The articles in the two parts of the special issue highlight how advances in both instrumentation and concepts have made EPR of biological systems so productive. This raises my optimism that, where there are current limitations, further technical and scientific progress will make EPR of biological systems even more productive in the future. While I am of course both proud and humbled by the many senior colleagues with whom I have the privilege of collaborating and exchanging knowledge, I am especially proud of my 'academic children', i.e., those who worked with me in their formative years as students, post-docs, visiting fellows, or young academics in my laboratories. This group includes many very bright and energetic men and women who went on to have very impressive careers, including many who have established their own research groups and produced additional excellent science as well as nextgeneration scientists. This talented group encompasses
Rapid and accurate retrospective dosimetry is of critical importance and strategic value for the ... more Rapid and accurate retrospective dosimetry is of critical importance and strategic value for the emergency medical response to a large-scale radiological/nuclear event. One technique that has the potential for rapid and accurate dosimetry measurements is electron paramagnetic resonance (EPR) spectroscopy of relatively stable radiation-induced signals (RIS) in fingernails and toenails. Two approaches are being developed for EPR nail dosimetry. In the approach using ex vivo measurements on nail clippings, accurate estimation of the dose-dependent amplitude of the RIS is complicated by the presence of mechanically-induced signals (MIS) that are generated during the nail clipping. Recent developments in ex vivo nail dosimetry, including a thorough characterization of the MIS and an appreciation of the role of hydration and the development of effective analytic techniques, have led to improvements in the accuracy and precision of this approach. An in vivo nail dosimetry approach is also very promising, as it eliminates the problems of MIS from the clipping and it has the potential to be an effective and efficient approach for field deployment. Two types of EPR resonators are being developed for in vivo measurements of fingernails and toenails.
A new resonant geometry for X-band in vivo electron paramagnetic resonance (EPR) nail dosimetry h... more A new resonant geometry for X-band in vivo electron paramagnetic resonance (EPR) nail dosimetry has been developed, fabricated, and tested. The dielectricbacked aperture resonator (DAR) was specifically designed for depth-limited surface spectroscopy. The DAR improves EPR sensitivity of surface samples with sub-millimeter thicknesses by at least a factor of 20 compared to other aperture resonator designs. The increase in EPR sensitivity was achieved using a non-resonant dielectric slab which is placed on the aperture inside the cavity. The dielectric slab provides an increased microwave magnetic field, while minimizing the problematic resonance conditions of the aperture. It has been shown that the DAR provides sufficient sensitivity to make biologically-relevant measurements both in vitro and in vivo. This work demonstrates that in vivo tests with an equivalent dosimetry sensitivity of approximately 1.4 Gy are feasible. Plausible ways to further increase the sensitivity are discussed, such as, the introduction and simulations of a DAR based on a semi-spherical TE 011 geometry.
Objectives-The aim of this paper is to delineate characteristics of biodosimetry most suitable fo... more Objectives-The aim of this paper is to delineate characteristics of biodosimetry most suitable for assessing individuals who have potentially been exposed to significant radiation from a nuclear device explosion, when the primary population targeted by the explosion and needing rapid assessment for triage is civilians vs. deployed military personnel. Methods-We first carry out a systematic analysis of the requirements for biodosimetry to meet the military's needs to assess deployed troops in a warfare situation, which include accomplishing the military mission. We then systematically compare and contrast the military's special capabilities to respond and carry out biodosimetry for deployed troops in warfare, in contrast to those available to respond and conduct biodosimetry for civilians who have been targeted, e.g., by terrorists. We then compare the effectiveness of different biodosimetry methods to address military vs. civilian needs and capabilities in these scenarios and, using five representative types of biodosimetry with sufficient published data to be useful for the simulations, we estimate the number of individuals who could be assessed by military vs. civilian responders within the timeframe needed for triage decisions.
A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic... more A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarterwave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human fingernails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg 2+ doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 coaxial input. Agreement between simulated and experimental results is shown.
Electron paramagnetic resonance (EPR) spectroscopy has been well established as a viable techniqu... more Electron paramagnetic resonance (EPR) spectroscopy has been well established as a viable technique for measurement of free radicals and oxygen in biological systems, from in vitro cellular systems to in vivo small animal models of disease. However, the use of EPR in human subjects in the clinical setting, although attractive for a variety of important applications such as oxygen measurement, is challenged with several factors including the need for instrumentation customized for human subjects, probe and regulatory constraints. This paper describes the rationale and development of the first clinical EPR systems for two important clinical applications, namely, measurement of tissue oxygen (oximetry), and radiation dose (dosimetry) in humans. The clinical spectrometers operate at 1.2 GHz frequency and use surface loop resonators capable of providing topical measurements up to 1 cm depth in tissues. Tissue pO 2 measurements can be carried out noninvasively and repeatedly after placement of an oxygen-sensitive paramagnetic material (currently India ink) at the site of interest. Our EPR dosimetry system is capable of measuring radiation-induced free radicals in the tooth of irradiated human subjects to determine the exposure dose. These developments offer potential opportunities for clinical dosimetry and oximetry, which include guiding therapy for individual patients with tumors or vascular disease, by monitoring of tissue oxygenation. Further work is in progress to translate this unique technology to routine clinical practice.
International Journal of Radiation Biology, Nov 17, 2021
PURPOSE Based on the experience of biodosimetry laboratories during the COVID-19 pandemic, the pu... more PURPOSE Based on the experience of biodosimetry laboratories during the COVID-19 pandemic, the purpose of this paper is to describe the challenges of providing biodosimetry service in the event of a major radiation incident during a pandemic. This includes describing some of the preparations and planning made by biodosimetry laboratories and special challenges in maintaining a state of readiness while adhering to safety protocols and balancing the need to assist with the COVID-19 response where possible. Experiences of several biodosimetry laboratories will be described and lessons learned will be outlined that could be applied to any large population-scale emergencies. CONCLUSIONS There are many challenges that arise when maintaining capacity and capabilities for biodosimetry when faced with a global pandemic such as COVID-19. The key is to be prepared for anything within reason. This includes, but is not limited to, maintaining flexibility, shifting and reorganizing deployment of staff between pandemic response and biodosimetry needs, strengthening networks to be able to provide assistance to other laboratories, managing staff in the face of possible infections and preparing protocols for the handling of potentially infected biological samples according to regulatory requirements. By implementing these recommendations, international biodosimetry networks can be prepared to address large-scale radiological incidents within the context of a pandemic and ensure the safety of biodosimetry personnel as well as victims in such dual emergencies.
As COVID-19 emerged, there are parallels between the responses needed for managing SARS-CoV-2 inf... more As COVID-19 emerged, there are parallels between the responses needed for managing SARS-CoV-2 infections and radiation injuries. While some SARS-CoV-2-infected individuals present as asymptomatic, others exhibit a range of symptoms including severe and rapid onset of high-risk indicators of mortality. Similarly, a variety of responses are also observed after a radiological exposure depending on radiation dose, dose heterogeneity, and biological variability. The impact of acute radiation syndrome (ARS) has guided the identification of many biomarkers of radiation exposure, the establishment of medical management strategies, and development of medical countermeasures in the event of a radiation public health emergency. Biodosimetry has a prominent role for identifying exposed persons during a large scale radiological emergency situation. Identifying exposed individuals is also critical in the case of pandemics such as COVID-19, with the additional goal of controlling the spread of disease. Conclusions and significance: IABERD has taken advantage of its competences in biodosimetry to draw lessons from current practices of managing the testing strategy for nuclear accidents to improve responses to SARS-CoV-2. Conversely, lessons learned from managing SARS-CoV-2 can be used to inform best practices in managing radiological situations. Finally, the potential need to deal with testing modalities simultaneously and effectively in both situations is considered.
Background: Hemorrhagic cystitis from chemical or radiation bladder injury can cause life-threate... more Background: Hemorrhagic cystitis from chemical or radiation bladder injury can cause life-threatening bleeding and/or urothelial cancer. Fibroblast growth factor 7 (FGF7) blocks urothelial apoptosis induced by cyclophosphamide (CPP) or radiation, but there are limitations to its use in patients, including an inability to apply it by direct bladder infusion and the high cost due to the large size of the protein (18.8 kDa). Purpose: We previously identified a small peptide that equaled or exceeded the mitigation effect of full length FGF2 on acute radiation syndrome. Benefits of developing a similar FGF7 biomimetic peptide include lower likelihood of inflammation, longer shelf life, higher purity, and lower cost than the full-length protein. Methods: Based on the 3-dimensional structure of FGF2 peptide, a corresponding FGF7 peptide (FGF7p) consisting of 19 amino acids was identified and synthesized. FGF7p or vehicle was given subcutaneously (SQ) to female mice subjected to sham injury...
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Papers by Steven Swarts