Dr. Bryant C. Nelson, a bioanalytical chemist, received his undergraduate degree in chemistry from The University of Texas at Austin and his doctoral degree in bioanalytical chemistry from The University of Massachusetts at Amherst. He pursued postdoctoral training in clinical mass spectrometry at the National Institute of Standards and Technology (NIST) in 1996 and became a staff member in 1999. He is currently the nanogenotoxicology project leader in the DNA Science Group. His current research interests include investigating and characterizing the biological mechanisms of oxidatively induced DNA damage and its repair as they relate to the incidence and progression of age-related diseases such as cancer and metabolic syndrome. He is currently developing novel measurement platforms and mass spectrometry-based approaches for evaluating the impact of engineered nanomaterials on the induction of oxidative damage to DNA.
Member of Sigma Xi
Research in my laboratory addresses problems at the interface of chemistry, biology and materials science that are mainly focused on understanding the fundamental interactions between engineered nanomaterials and DNA. We are interested in developing measurement strategies and analytical methods for assessing the environmental health and safety of engineered nanomaterials with a specific emphasis on characterizing the toxicological impacts on DNA (nanogenotoxicology) in humans, plants, animals and other important ecological targets. The formation and accumulation of nanomaterial induced DNA lesions is biologically deleterious because they can adversely affect DNA replication and transcription. In order to characterize the mechanisms involved in nanomaterial induced lesion formation, we develop and apply new tandem mass spectrometry (LC/MS/MS, GC/MS/MS, etc.) approaches for both the identification and quantification of DNA lesions in both simple and complex biological models. A variety of experimental protocols/tools, such as kinetics, enzyme and isotope labeling studies and electron paramagnetic resonance studies, in addition to mass spectrometry, are necessary for our research.
Interactions of Nanomaterials with DNA and DNA Repair Proteins
Engineered nanoparticles have many unique electrical, mechanical and catalytic properties and are being used in an increasing number of commercial applications ranging from health care to consumer products. A major concern impeding the commercialization of nanoparticle-based technologies is the potential of intentional or inadvertent release of nanoparticles from products and their adverse impact on human health and the environment. Much research is currently directed towards addressing these health and safety concerns; however, a fundamental understanding of the general toxicity of nanoparticles with respect to oxidative damage to DNA has yet to be achieved. For example, studies have shown that metal- and metal oxide-based nanomaterials can act as mediators of DNA damage in mammalian cells, organisms and even in bacteria, but the molecular mechanisms through which this occurs remain poorly understood. In work that sheds light on fundamental reaction mechanisms of DNA damage, our group in concert with collaborators at the University of Massachusetts Amherst, have found compelling evidence that copper oxide nanoparticles (CuO NPs) induce DNA damage in agricultural (radish) and grassland (annual and perennial ryegrass) plants under controlled laboratory conditions. This study is the first of its kind to report multiple DNA lesion formation and accumulation in plants as a result of exposure to engineered nanoparticles. Parallel efforts are now focused on understanding the mechanisms of titanium dioxide nanoparticle (TiO2 NP) uptake and DNA damage in other terrestrial plant models.
One primary challenge in nanotoxicology studies is the lack of well-characterized nanoparticle reference materials which could be used as positive or negative nanoparticle controls. NIST is in the midst of developing and characterizing the physicochemical properties of several metal- and metal oxide-based nanoparticle reference materials such as AuNPs, AgNPs, TiO2 NPs and also carbon-based reference materials such SWCNTs and Buckypaper. Our group is currently investigating the biological mechanisms that could potentiate the NIST citrate-stabilized AuNPs to induce oxidative stress and oxidative DNA damage in cultured HepG2 cells. Thus far, neither significantly elevated, dose-dependent DNA damage nor the evolution of reactive oxygen species have been detected when the AuNPs are dosed at biomedically relevant concentrations (≤ 0.2 µg/mL gold atoms). Our collected data suggests that the AuNPs could potentially serve as suitable negative-control nanoparticle reference materials for in vitro and in vivo genotoxicity studies. NIST AuNPs thus hold substantial promise for improving the reproducibility and reliability of nanoparticle genotoxicity studies. Further cytotoxicity and genotoxicity studies on the other NIST nanoparticle reference materials are forthcoming.
The transparent, multicellular eukaryotic nematode, Caenorhabditis elegans (C. elegans), possesses a genetic sequence that is ~70% homologous with the human genetic sequence. The remarkable genetic similarity between C. elegans and humans allows scientists to utilize C. elegans as surrogates for studying the development, progression and mechanisms of human diseases, such as diabetes and cancer. Scientists also have the ability to prepare C. elegans mutant strains in which single or multiple genes are knocked out or knocked down. C. elegans mutant strains in which specific DNA base excision or nucleotide excision repair genes are knocked out allow us to study the specific function of those genes in the repair of DNA damage. Our laboratory utilizes both C. elegans wildtype and DNA repair knockout strains to investigate and characterize the biological effects of engineered nanomaterials, such as silver and gold nanoparticles, on the mechanisms of formation and accumulation of oxidatively induced DNA damage. We are also performing parallel studies to understand the nanoparticle uptake mechanisms in C. elegans with a focus on understanding the significance of nanoparticle size and dispersity on the resulting uptake and toxicity. The goal is to establish the C. elegans model as a preferred in vivo surrogate for assessing the environmental health and human safety risks of engineered nanomaterials. Part of this research is being performed in collaboration with the FDA – Division of Toxicology.
The rapidly expanding use of ferrofluids in nanomedicine (as MRI contrast agents, drug delivery vehicles and anticancer hyperthermia probes) necessitates a rigorous understanding of their potential risks to patient health. Our laboratory, in conjunction with collaborators at the Swansea University School of Medicine (Wales), is currently investigating the potential of dextran-coated maghemite (γ-Fe2O3) nanoparticles to induce genotoxicity (oxidatively induced DNA damage and chromosomal damage) in human lymphoblastoid B cells (MCL-5: human white blood cells). Preliminary findings indicate that these ultrafine superparamagnetic nanoparticles are preferentially uptaken into endosomes, induce a variety of DNA lesions and induce binucleated micronuclei via clastrogenic processes, however the γ-Fe2O3 nanoparticles themselves are not cytotoxic to the cells at the tested doses. This work is rapidly advancing our understanding of the toxic mechanisms of iron-based nanoparticles and also of nanoparticle-protein interactions. Further toxicity studies on the nanoparticle coating as well as studies on other types of types of iron oxide nanoparticles used in medicine are on-going.
Commercial grade, low iron MWCNTs can readily enter mouse liver cells (AML12) and lead to reduced cellular viability, upregulation of heme oxygenase 1 and cycling of glutathione. These are all positive indicators of CNT mediated oxidative stress. However, when these same low iron (≤ 0.2 % mass fraction Fe) CNTs enter the nuclei, there is no significant accumulation of oxidatively induced DNA damage. In concert with our colleagues in the Department of Pathology and Laboratory Medicine at Brown University, we are trying to unravel the potential mechanisms for the lack of accumulated DNA damage in this well characterized cell model even in the presence of inordinately high, non-environmentally relevant CNT levels (≥ 40 mg/L based on carbon surface area).
This is an emerging area of ecological research that is new to our nanogenotoxicology portfolio. The potential genotoxic effects of introducing nanoparticles, nanowires and quantum dots into commercial fishing environments is unknown. However, it is important to determine and understand the long-term effects of nanomaterials on the health and sustainability of food grade shellfish. In this effort, we are at the initial stages of designing projects in collaboration with Virginia Tech, to evaluate the DNA damaging effects of AgNPs on clams.
Wrapping SWCNTs with ssDNA is an effective way of producing monodisperse solution preparations of SWCNTs. Additionally, the wrapping procedure allows the SWCNTs to be efficiently separated and sorted using HPLC based upon the differential chiral or electronic properties (i.e., metallic vs. semiconductor) of the dispersed CNTs. However, the DNA wrapping procedure involves the use of high energy probe ultrasonication and we have determined that the ultrasonication protocol induces the formation of high levels of oxidatively induced DNA lesions. What effects do the CNTs have on the formation of the DNA lesions? Does the formation of the DNA lesions affect the structure and/or properties of the DNA-wrapped CNTs? Does the formation of the lesions reduce the yield of the chirality-based or the electronic-based sorting protocols? These are open questions and quantifying the levels of DNA damage induced by sonication and the factors that control the lesions levels are therefore important. This ongoing research is being conducted in collaboration with the NIST Polymers Division.
Apurinic and apyrimidinic (AP) sites are highly mutagenic and are produced on the order of 10,000 – 50,000 lesions per cell per day. These lesions arise through the hydrolysis of both native and damaged DNA nucleotides. They are also generated during intermediate steps of base excision repair. Some engineered nanomaterials, because of their potential to generate free radicals, promote macromolecular crowding and/or interact directly with DNA or DNA repair proteins, can induce the formation of AP sites. Therefore, in addition to accurately identifying and measuring the level of oxidatively modified DNA bases and nucleosides, we are also interested in developing novel MS and MS/MS based methodology for the determination AP sites using either GC or LC on the front end. At the same time, we are currently evaluating the development and utilization of isotope dilution GC/tandem quadrupole mass spectrometry in order to improve the measurement sensitivity and accuracy of our established GC/single quadrupole methods for oxidatively modified bases.
DNA repair proteins can either be upregulated or downregulated in specific types of human cancers. In order to fundamentally understand how engineered nanomaterials enhance or inhibit the catalytic activity or the expression of DNA repair proteins, it is useful to be able to measure the DNA repair protein levels in vivo before and after human exposure to nanomaterials. We are using NIST established techniques to stably label (15N) and bacterially express DNA repair proteins for use as quantitative LC/MS/MS protein internal standards. Appropriate peptide fragments from tryptic digests will be utilized to evaluate nanomaterial induced alteration of DNA repair protein expression in noncancerous and cancerous human cells and eventually in human tissues. The goal of this project is to develop isotopically-labeled protein internal standards for the major human DNA glycosylases in the BER and NER protein pathways. This emerging research area is the brainchild of Miral Dizdaroglu at NIST.
Recent in vitro research has shown that Au55 clusters stabilized with TPPMS with a diameter of 1.4 nm (Au1.4MS) are highly toxic to both cancerous and noncancerous cell lines. There exists compelling computational and experimental evidence that the gold nanoparticles enter the nucleus of the cells and bind to the nuclear DNA. This data illustrates the fact that all gold nanoparticles are not without safety risks and that as the size of the gold nanoparticle decreases below approximately 2 nm, unknown "nanoparticle effects" come into action. Our laboratory has embarked on in vitro acellular studies to try to understand the origin of this gold nanoparticle cytotoxicity with a particular emphasis on trying to understand what types of oxidative damage occurs to the DNA and to DNA repair proteins in the microenvironment of the nanoparticles. Initial experimental results with an important BER protein, mNEIL-1, indicate that the gold particles inhibit the specific excision activity of the protein for FapyGua and FapyAde. This project has expanded to encompass a complete investigation of other DNA glycosylases that are homologous to the bacterial Fpg/Nth family. This project is being conducted in conjunction with collaborators at RWTH Aachen – Germany.
Nanosilver (colloidal silver, silver nanoparticles, etc.) is under strong scrutiny as of late because investigators have not been able to clarify the exact mechanisms driving its apparent biocidal activity. Complicating these investigations is the fact that silver nanoparticles (AgNPs) rapidly produce silver ions (Ag+) in solution and it is difficult to discriminate between the toxicological effects caused by Ag+ ions and those caused by AgNPs. Our laboratory is utilizing electron paramagnetic resonance (EPR) spectroscopy and atomic force microscopy (AFM) in combination with mass spectrometry to investigate the fundamental interactions of Ag+ ions and AgNPs with DNA in an acellular environment. The types and levels of free radicals that are produced by AgNPs and Ag+ ions are different when driven by the presence of exogenous H2O2 and the types and levels of oxidatively induced DNA base lesions are similarly different. These preliminary results indicate that even though AgNPs and Ag+ ions are both potentially genotoxic materials, the mechanisms of their toxicity are not the same.
This research project aims to rigorously investigate the feasibility of utilizing patterns of targeted intracellular energy molecules (acetyl coA, fumaric acid, glucose-6-phosphate, etc.,) and metabolites thereof, as predictive markers of oxidative DNA damage in representative in vivo models (i.e. C. elegans) that have been exposed to engineered nanomaterials (i.e. AgNPs). The hypothesis is that AgNPs will induce high and persistent levels of oxidative stress in the organism due to production of AgNP-induced superoxide radical. The presence of persistent oxidative stress will induce a quantifiable change in energy status of the organism that can be quantitatively assessed by collecting time-dependent profiles of targeted energy molecules/metabolites associated with both the glycolysis and Krebs metabolic cycles. AgNP mediated oxidative stress will not only induce formation of the superoxide radical, but also of the highly reactive hydroxyl radical which can directly damage both nuclear and mitochondrial chromatin. Additionally, AgNP induced perturbation or inhibition of the Krebs cycle will likely result in altered nucleotide synthesis and thus lead to further accumulation of DNA damage. By monitoring both the profiles of the energy molecules/metabolites and the accumulation of DNA base lesions in parallel, we will be able to establish the capacity and reliability for monitoring cytoplasmic energy molecules/metabolites in order to predict nanomaterial-driven nuclear DNA damage. Principal component analysis from AgNP exposed versus unexposed C. elegans strains will establish a "metabolic fingerprint" of AgNP toxicity that may be relevant for overall human safety risk assessment purposes. This research is being conducted in collaboration with the University of Minnesota.
The photocatalytic production and subsequent release of hydroxyl radicals from the surface of anatase titanium dioxide nanoparticles (TiO2 NPs) is a well-established phenomenon in aqueous environments that is considerably diminished for TiO2 particles above 100 nm in diameter. Nevertheless, numerous in vitro studies have reported NP induced DNA damage (strand breaks) both in the presence and absence of TiO2NP photoactivation. The observation of TiO2 NP induced DNA damage in both scenarios suggests either an uncontrolled measurement environment, a type B measurement error or a novel mechanism for TiO2 NP mediated DNA damage. In order to establish some clarity on this issue, we are critically evaluating the induction of TiO2 NP driven DNA damage under rigorously controlled illumination conditions (dark, ambient laboratory light, simulated sunlight – UVA @ 370 nm) in an acellular model using both electron paramagnetic resonance (EPR) spectroscopy and mass spectrometry. Parallel in vitro studies with human skin cells are being conducted to gain additional insight into alternative biological pathways for the apparent genotoxicity of TiO2 NPs in the absence of light. This ongoing research is being conducted in collaboration with Los Alamos National Laboratory.
Bryant C. Nelson, Elijah J. Petersen, and Bryce J. Marquis et al., NIST gold nanoparticle reference materials do not induce oxidative DNA damage. Nanotoxicology, 2011; Early Online, 1–9.
Neenu Singh, Gareth J.S. Jenkins, and Bryant C. Nelson et al., The role of iron redox state in the genotoxicity of ultrafine superparamagnetic iron oxide nanoparticles. Biomaterials 33 (2012) 163-170.
Reddy PT, Jaruga P, Nelson BC, Lowenthal M, Dizdaroglu M. Stable isotope-labeling of DNA repair proteins, and their purification and characterization. Protein Exp. Purif. 2011, Jul;78(1):94-101.
Jaruga P, Xiao Y, Nelson BC, Dizdaroglu M. Measurement of (5'R)- and (5'S)-8,5'-cyclo-2'-deoxyadenosines in DNA in vivo by liquid chromatography/isotope-dilution tandem mass spectrometry. Biochem. Biophys. Res. Commun. 2009 Sep 4;386(4):656-60.
Kim SK, Reddy SK, Nelson BC, Robinson H, Reddy PT, Ladner JE.A comparative biochemical and structural analysis of the intracellular chorismatemutase (Rv0948c) from Mycobacterium tuberculosis H(37)R(v) and the secretedchorismate mutase (y2828) from Yersinia pestis. FEBS J. 2008 Oct;275(19):4824-35. Epub 2008 Aug 22.
Nelson BC, Satterfield MB, Sniegoski LT, Welch MJ. Simultaneous quantification of homocysteine and folate in human serum or plasmausing liquid chromatography/tandem mass spectrometry. Anal Chem. 2005 Jun 1;77(11):3586-93.
Nelson BC, Pfeiffer CM, Margolis SA, Nelson CP. Affinity extraction combined with stable isotope dilution LC/MS for thedetermination of 5-methyltetrahydrofolate in human plasma. Anal Biochem. 2003 Feb 1;313(1):117-27.
Biochemical Science Division
DNA Science Group
2003 to present
2002 - 2003
1999 - 2002
1996 University of Massachusetts at Amherst, Ph.D. Analytical Chemistry
1990 University of Texas at Austin, BS, Chemistry