Brett Shaw and Dr. Merrill Christensen, Department of Nutrition, Dietetics and Food Science
Introduction
This project utilized histology in determining whether dietary supplementation of selenium and/or isoflavones (a component of soy) had a preventative effect on the development of prostate cancer. Additionally, we explored the timing of introduction of these supplements and observed their individual and combinational effects on cancer progression.
Methodology
For the project we used the TRAMP (TRansgenic Adenocarcinoma of the Mouse Prostate) mouse model, where mice are genetically modified to develop prostate cancer in a manner similar to human development (1). In a 2X2 factorial design, groups of mice were each provided one of four different supplementations of dietary treatment. There were 2 basal stock diets – one with high soy content, and the other lacking in soy. Additionally, one of these diets had selenium, while the other did not. Effect of timing of supplementation was examined by introducing mice to their dietary treatment from conception and at 6 weeks of age and then we sacrificed the mice at 18 weeks of age.
The prostate tissues were harvested (the ventral and dorsal-lateral lobes of the prostate) for histological examination. The tissues were fixated for 20 hours in 4% paraformaldehyde, embedded in a paraffin wax, cut into 6 μm sections, and placed on microscope slides. We then histologically determined the development of cancer by staining the microscope slides with Hematoxylin and Eosin (H&E). This staining technique allowed us to examine the cell morphology and lesion progression of the cells, which are indicative of cancer progression. Using a microscope and camera, pictures of each prepared slide were taken and scored by myself and two other independent student researchers. All researchers were blinded to the type of diet the tissues came from to avoid any bias.
To score the tissues, we adapted the Gleason system (used in human clinical pathology) by assigning a representative number ranging from 1 to 6, based on morphological characteristics of the developing stages of tumorigenesis. As multiple scores may be represented by each tissue (one section of a tissue may be a “1” while another section is a “3”), we then assigned the percentage of tissue of each score. One overall number is then calculated for each tissue that accounts for both scores and percentage of tissue. In brief summary – the lower the assigned number, the less the cancer has progressed.
Results
The following graph shows the average histological scores among the varying diets the mice were fed from conception. There were positive trends and cancer progression was slowed in diets containing isoflavones, selenium, and both in combination.
We used the Sigma Plot software to determine statistical significance. Regarding the ventral prostate, the difference in the mean values among the different levels of selenium was greater than would be expected by chance after allowing for effects of differences in isoflavones (P = <0.001). There seemed to be a synergistic effect between selenium and isoflavones, and the progression of cancer was slowed when used in combination. In addition, the effect of Selenium depended on what level of time was present (P = <0.001). When selenium was introduced to the mice from birth as opposed to 6 weeks of age, it was more efficacious in preventing the progression of the cancer.
Discussion and Conclusion
Selenium proved to be effective in reducing the progression of prostate cancer in the ventral prostate in mice that were sacrificed at 18 weeks of age. However, selenium was most efficacious when introduced in the diet from birth as opposed to 6 weeks of age. Further research will be done to confirm these results and to merit possible clinical intervention. Our results and current understanding imply that men would need to include both selenium and isoflavones in their diet from an early age to maximize effectiveness in the prevention of prostate cancer.
Scholarly Sources
- Hurwitz AA, Foster BA, Allison JP, Greenberg NM, Kwon ED. The TRAMP mouse as a model for prostate cancer. Curr Protoc Immunol Chapter 20: Unit 20. 2001