Astronauts on long-duration spaceflights are exposed to higher levels and different types of radiation than are found on Earth, which can lead to cancer. The primary goal of Dr. Joanne R. Lupton’s research is to develop a set of gene expression profiles that accurately characterize the colon cancer-causing properties of radiation and the protective effect of dietary countermeasures, using an animal model of the disease. With this research, scientists will have sets of gene expression profiles that can be used to monitor astronauts before, during and after spaceflight in order to detect exposure and response to a radiation event so that appropriate intervention strategies can be prescribed
Nutritional Countermeasures to Radiation-Enhanced Colon Cancer
Joanne R. Lupton, Ph.D.
Texas A&M University
From the global transcriptional profile (analyzed by microarray technology) in samples isolated from colonic mucosa, determine which sets of gene expression profiles best characterize the initiation stage, the promotion stage (aberrant crypt development) and the final tumor stage of colon cancer development using a 2 x 4 x 4 experimental design (+ or radiation; four time points and four diets).
The second goal, addressed by Specific Aim 2 is to compare gene expression profiles developed from exfoliated cells to those from colonic mucosal cells to determine how well they reflect in vivo events. This information is important for our short-term future goal of using fecal material from humans as a noninvasive method to monitor changes in gene expression patterns over time.
Our long-term future goal is to have sets of gene expression profiles that can be used to monitor astronauts before, during and after spaceflight to detect exposure and response to a radiation event so that appropriate intervention strategies (e.g., dietary countermeasures) can be implemented as needed.
Data generated from this research program will support the NASA/NSBRI goals of:
- Gaining greater understanding of the mechanisms involved in the synergy of radiation and other environmental insults on carcinogenesis;
- Developing a system to monitor the need for countermeasure administration during or after flight; and
- Development of countermeasures that can be applied before, during and after flight.
Analysis of fecal samples collected over time indicated there was a variety of genes with differences in expression in response to diet, radiation treatment, stage of disease progression and their interactions. Radiation exposure caused changes in expression for 125 genes; time of sampling affected the expression of 369 genes; and diet caused differential expression in 387 genes. Of the differentially expressed genes with a known function in the two radiation exposure groups, there were diverse functional activities represented. Expression of genes involved in metabolism, regulation of cell proliferation and differentiation, and signaling cascades in colonocytes were affected by radiation exposure.
After pathway analyses, many genes were identified that were over-represented for their respective biological processes. There were more than 300 genes for which differences in gene expression were observed for the diet time interaction, indicating the transformations occurring in the colon during tumor development were sensitive to dietary intervention. These proteins are important in buffering cellular redox status, immune function, regulation of nutrient and xenobiotic metabolism, and signaling through protein kinase pathways. Gene expression in mucosal samples collected at termination for the initiation, promotion and tumor stages identified treatment-induced differential expression patterns that were reflective of the particular endpoint being measured and treatment groups. For example, 10 days after radiation exposure, genes known to be affected by radiation in cell culture studies that are involved in the regulation of cell cycle activity were differentially expressed. Similarly, we have previously demonstrated a reduction in aberrant crypt foci of rats consuming pectin diets and that this effect was paralleled by an increase in apoptosis. In the mucosal gene expression patterns, we have noted large numbers of genes differentially expressed in rats consuming the two fiber types, several of which are involved in apoptosis regulation.
We are in the final stages of establishing gene sets that best reflect/describe the animal phenotypes. These genes can then be used to diagnose radiation exposure, monitor disease development and target appropriate dietary interventions. Because these genes are the subjects of a patent application, we are not able to disclose their identities. However, upon submission of the patent application this information will be published.
Impact of Findings on Project Goals
The observations support the feasibility of using fecal polyA+ RNA as a noninvasive measure of colonocyte gene expression in Earth-based medicine and to monitor in-flight radiation exposure and cell responses. It would be possible to identify interventions for astronauts in order to slow disease progression until their return to Earth. This work also indicates dietary modifications influence gene expression in colonocytes and the pattern of changes in expression that occur during disease progression. It is therefore possible to use diet as a mediator in colon carcinogenesis in order to reduce the enhancement of cancer risk posed by exposure to galactic cosmic radiation. We have identified genes that are most indicative of radiation exposure and of each stage of disease progression, which was the overall goal of the project.
Proposed Research Plan for the Coming Year
We will complete the final statistical analyses and prepare the list of genes that are most predictive of radiation exposure and disease progression. The data will be incorporated into publications, which will be submitted once the patent application has been submitted.