Radiation
exposure and erythropoiesis
James Palis MD • University of
Rochester
We synthesize 2 million red cells every second to maintain our steady-state numbers of circulating red cells. Red cell production is sustained by the continued generation of committed erythroid progenitors that give rise to nucleated erythroid precursors that progressively mature and enucleate before entering the bloodstream as reticulocytes. Acute anemia elicits a rapid recovery response of “stress” reticulocytes that are twice the size of normal adult erythrocytes and contain fetal hemoglobin. Thus, stress erythrocytes share many common features with fetal red cells, supporting the notion that “stress” erythropoiesis represents a reactivation of a fetal erythroid program that is distinct from adult steady-state erythropoiesis. While radiation is well known to cause acute bone marrow damage and anemia, the characteristics of erythroid recovery following irradiation have not been well characterized. In this pilot project we will test the hypothesis that external radiation exposure at U19-relevant doses elicits a stress erythroid response that is characterized by expanded erythropoiesis and rapid release of large reticulocytes. In initial studies, radiation doses will be correlated with the timing of erythroid recovery. Subsequent studies will focus on the characteristics of the erythroid recovery, including reticulocyte size and temporal patterns of the changes in erythroid progenitor numbers in marrow and spleen. The successful completion of this pilot study will have several important outcomes. First, these studies will identify in an animal model several potential erythroid lineage-specific biomarkers of radiation toxicity. Second, if radiation is found to elicit a stress erythroid response, then future studies will be directed at augmenting this response with known agents, including dexamthasone and erythropoietin, important for the stress erythroid response. Third, if radiation exposure fails to elicit a stress erythroid response, then future studies will be directed at understanding the underlying causes of this failure. Finally, by examining the response of the erythroid lineage to radiation, this pilot project synergizes with U19-Project 4 that is examining newly formed red cells for the presence of DNA damage following radiation exposure (S. Dertinger) and creating in vitro models of erythropoiesis (D. Wu). These projects in aggregate will ultimately lead to a better understanding and treatment of the hematopoietic diseases that result from radiation exposure.
Serum
amyloid P (SAP): A Molecular Target for
Radiation Induced Lung Damage
Elizabeth L. Travis PhD • University of Texas-MD Anderson
The
goal of this project is to determine if the serum protein, Serum amyloid
protein component P, SAP, mitigates and/or is a treatment for inflammation
in our well-characterized mouse models of lung damage after whole thoracic
irradiation. In humans and other mammals SAP is made by the liver and
is secreted into the blood. SAP has been suggested to be both anti-inflammatory
as well as anti-fibrotic, although the exact mechanism(s) is unknown.
Recently we found that SAP is a potent inhibitor of bleomycin induced
lung damage after intratracheal delivery of the drug. Using quantitative
morphometry we found a 3 fold reduction in the area of the lung involved
with organizing alveolitis in mice given SAP daily for 13 days after a
single IT instillation of bleomycin compared to bleomycin treated mice
not given SAP, p<0.01. In addition, constitutive serum SAP levels are
mouse strain dependent and correlate with susceptibility and resistance
to lung damage after radiation and bleomycin. Thus SAP may have a dual
function as a predictor and mitigator of radiation induced lung damage.
The specific aims are to determine if:
1. SAP mitigates the progression of alveolitis/fibrosis when given post
exposure; and,
2. this reduction is durable after SAP administration ceases.
We propose combining IT bleomycin, which damages the lung locally, with
external thoracic or whole body irradiation at non-lethal doses as a model
of the internal and external radiation exposures that would be characteristic
of a radiological and/or nuclear dispersion event.
Development
of Hair and Cuticles as Human Biodosimeters of Radiation Exposure
Steven G. Swarts PhD • University of Rochester
The overall objective of this pilot project is to demonstrate that the levels of specific radiation-induced alterations measured in the proteins making up human hair and cuticles (finger and toe nails) can be used as a biodosimeter of human exposures to ionizing radiation at clinically relevant doses. Specifically, we will demonstrate that protein damage products can be reliably measured in hair and cuticle within dose ranges of 0.1 to 8 Gy, a range relevant to the triage and treatment of victims of intentional or accidental exposures to ionizing radiation. Specific aim 1 is to analyze hair and cuticle cuttings x-irradiated to doses high enough to readily reveal radiation-specific end-products using gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS) techniques. Specific aim 2 is to determine the threshold for detection of select radiation-induced protein end-products in hair and cuticle cuttings irradiated to doses from 0.1 to 50 Gy. Specific aim 3 is to apply Q-band electron paramagnetic resonance spectrometry (EPR) for in vitro measurement of free radical trapping in hair and cuticles so as to extend the applicability of EPR-based methodologies to exposures below 1 Gy. Specific aim 4 is to use the free radical signal as measured by Q-band EPR and select radiation-induced protein end-products in cuticle and hair as dosimeters in patients undergoing total body radiation therapy and compare this dosimetry to that calculated through standard clinical dosimetric techniques. It is expected that through this pilot project, we will have sufficient data to support a large field study of the nail and hair biodosimeter assay that will provide the necessary statistical validation of the techniques for estimating dose in human populations exposed to ionizing radiation. The results obtained from the combined pilot and field studies will be important for providing rapid assessment of dose in human populations intentionally (through radiological terrorist activity) or accidentally exposed to radiation which is essential for determining the course of treatment for individuals involved in a radiological event.
Radiation
exposure detection using migration of skin dendritic cells
Edith Lord PhD • University of Rochester
There
is a need for simple assays to detect possible radiation exposure following
an accidental or deliberate radiation event. To be maximally useful,
such assays should be easily performed, minimally invasive, provide
results quickly and be capable of being performed on large numbers of
individuals. Fulfilling all of these criteria is not easily achievable
and may require considerable experimentation to establish an appropriate
assay. Assays utilizing cells of the immune system are a logical starting
point as these cells have been shown to be exquisitely sensitive to
ionizing radiation. To minimize invasiveness we are proposing to examine
populations of antigen presenting cells (APC), which are present in
the skin. These include Langerhans cells (LC) present in the outermost
layer of the skin, the epidermis and cells within the dermis known as
dermal or interstitial dendritic cells (DC). These cells are important
“policemen” in the skin as they pick up antigens that may
have penetrated this barrier, they then migrate out of the skin carrying
the antigens to the draining lymph nodes (DLN) where they stimulate
antigen specific T lymphocytes that will eventually traffic back to
the site and eliminate the offending pathogen. We are hypothesizing
that ionizing radiation may cause the same migration out of the skin,
and thus changes in the density of these cells could potentially be
used as an indication of radiation exposure. Initially we are assessing
the number of these APC identifiable in whole mount preparations of
ears removed at various times from mice treated with varying doses of
ionizing radiation. Eventually, we will use locally delivered fluorescent
antibodies to specifically label these APC and then image their density
in the skin of live mice using confocal microscopy.
We also will determine if immunosuppression occurs following exposure
to ionizing radiation as is found with UV radiation. Interestingly,
the cytokine IL-12 has been found to prevent UV induced damage to these
cells by a mechanism involving DNA repair. If this is also the case
with ionizing radiation, we will proceed to examine the possibility
that cytokines such as IL-12 could reverse the damage or altered function
of these important cells.
