Diet and Colon Cancer Prevention: Insight into Phytochemicals and Flavonoids

1. Diet and Colon Cancer Prevention Nancy D. Turner Nutrition & Food Science Department Faculty of Toxicology Faculty of Genetics Vegetable and Fruit Improvement Center Texas A&M University College Station, TX 77843-2253

2. Overview of Talk • Quick review of colon cancer • Evidence from our lab • Discussion of potentials/pitfalls in use of phytochemicals • Summary

3. What is Carcinogenesis • Multistep process • Cellular • Molecular • Typically takes many years to develop • Colon cancer can take up to 40 years

4. Stages of Carcinogenesis • Initiation • Exposure to carcinogenic agents • Changes at the DNA level - selective growth advantage • Promotion • Expansion of initiated cells • Progression • Tumors • Metastasis

5. Normal Growth and Function • Cell number determined by • Proliferation • Apoptosis • Cell phenotype determined by • Differentiation

6. Apoptosis Differentiation Proliferation Normal Colon Architecture Goblet cells Epithelial cells

7. Cancerous Growth • Loss of cell cycle controls • Increased proliferation • Decreased apoptosis • Results from • Genetic changes - mutations/deletions • Epigenetic changes - altered gene expression

8. Cartoon of Cancer Development Proliferation Apoptosis

9. Genetic Changes • DNA is damaged by exogenous and endogenous: • Reactive oxygen species • Reactive nitrogen species • Alkylating agents • Lipid peroxidation products

10. Exogenous vs Endogenous • Exogenous sources of oxidants and carcinogens are found in the diet • Component of food • Result of food processing/cooking • Endogenous sources derived from metabolism • Conversion of pro-carcinogens to ultimate carcinogen • Reactive oxygen species generation

11. Chemoprevention Opportunities • Reduce formation/uptake of carcinogens • Modification of carcinogen metabolism • Scavenge activated carcinogens • Inhibit DNA adduct formation • Antioxidant activity • Cell cycle activity regulation • Normalize cellular signal transduction

12. Epidemiological Results • Cancer prevalence is higher in cultures where intake of plant-foods is low • Cancer incidence increases as people migrate from low to high incidence rate environments • More of an effect of environment (e.g., diet) than genetic predisposition

13. Questions on Colon Carcinogenesis • Chemicals that promote colon cancer are derived from….? • Cancer growth differs from normal growth in what ways? • What are the stages of carcinogenesis and what characterizes the events of that stage?

14. So What Is in the Diet that Can Protect Us from Colon Cancer?

15. Quercetin • Quercetin is present in many plant-based foods • Level depends on food source • High plant food diets would provide a reasonable mass of the compound

16. Quercetin Inhibits Colon Cancer • We demonstrated • Reduction in early colon cancer lesions • Proliferation and apoptosis effects • Lower expression of COX-1, COX-2 Warren et al., 2009; J. Nutrition 139:101

17. Quercetin Conclusions • Suppresses development of early lesions • Beneficially affects proliferation and apoptosis to return cell numbers to normal levels • Has a small impact on pro-inflammatory mediators

18. Flavonoids and Limonoids • Citrus contains many different compounds with potential • Evaluated relative protection in 5 diets • Basal • Rio Red grapefruit pulp powder (GFPP, ~1.5/day) • Irradiated Rio Red grapefruit pulp powder (IGFPP) • Isolated Naringin (same level in GFPP) • Isolated Limonin (~10-15 times higher than GFPP, but same level as Naringin)

19. Early Lesions HMACF Number (% of Basal) P = 0.01 a b b b b All diets reduce formation of these early lesions. Vanamala et al., 2006; Carcinogenesis 27:1257

20. Proliferative Index Proliferative Index (% of Basal) a P = 0.02 b b b b All diets reduce proliferation with the maximum reduction occurring with the GFPP and limonin diets.

21. Apoptotic Index Apoptotic Index (% of Basal) c P = 0.02 c b b a The GFPP and limonin diets caused the greatest level of apoptosis

22. Mechanisms? • Colon cancer is promoted by repeated bouts of inflammation. • Reducing proinflammatory proteins may be protective

23. Cyclooxygenase - 2 COX-2 Protein Level P < 0.032 a a ab b b COX-2 levels were lowest in rats consuming the GFPP and limonin diets.

24. What About Other Citrus Compounds • Not all compounds perform equally • Naringenin and Apigenin reduce early lesions • Naringenin reduced proliferation • Naringenin and Apigenin increased apoptosis Leonardi et al., 2010; Experimental Biology & Medicine 235:710

25. Conclusions for Citrus Flavonoids/Limonoids • Grapefruit and some bioactives reduce colon carcinogenesis • Not all citrus compounds have equal protective ability • Irradiation may negatively affect the chemoprotection provided by grapefruit.

26. Inflammation • Inflammation promotes colon cancer • Can bioactive compounds inhibit chronic inflammation and injury • Stonefruits • Bran from grains

27. Inflammation-Induced Injury

28. Activation of NF-kB

29. Intestinal Microbiota and IBD • Intestinal bacterial populations (dysbiosis) are tied to development and severity of colitis • Recurrent colitis is a promoter of colon cancer

30. Colon Microbial Differences • Distinct diet patterns • Brans contain • Anthocyanidins (black) • Condensed tannins (sumac) • Both (high tannin) Cellulose Black Sumac High Tannin Ritchie, Azcarate-Peril, and Turner, In Preparation

31. Inflammation and Injury Induction Pectin • Black and Sumac sorghum reduced activation of an inflammatory mediator (NF-kB) and resulting injury scores High-Tannin Black Sumac Cellulose Black p=0.01, R2=0.98 Ritchie et al. (unpublished data)

32. Inflammation Conclusions • During chronic inflammation, injury and inflammation induction are dependent on fiber type • Activation of NF-kB (inflammation regulator) is lowest in rats consuming chlorogenic acid or brans from black or sumac sorghums • Diet has a major impact on microbial populations

33. Interactions Between Substances • Studying a molecule in isolation ignores potential interactions with other diet components. • One molecule may affect absorption/ availability of another (ß-carotene reduces absorption of other carotenoids) • Compounds may oppose or enhance effects of other compounds

34. Prevailing Wisdom • Insoluble fiber more protective • Fish oil (omega 3 fatty acid source) would be protective • Hypothesis: • Combination of fish oil and cellulose would reduce tumor incidence

35. Fat and Fiber in Colon Cancer Rats with Colon Tumors, % a a,b a,b b Chang et al., 1997; Carcinogenesis 18:721

36. Human Studies Suggest Caution • In both the ATBC and CARET trial - ß-carotene promoted lung cancer • Dietary recommendations, or “treatments”, need to be tailored for the individual, not the population • Recommendations for someone without the disease or in the early stages may differ from those for someone with cancer • Vitamin E and prostate cancer trial (SELECT) was also stopped because of enhanced cancer rates

37. Supplement vs Functional Food • Supplements • Bolus of compound • Usually in a purified form • Functional food • Smaller amount of compound • Slows delivery • Competes/complements other molecules present in food

38. Is it Always a Chemoprotectant? • Although a molecule may protect against a certain type of cancer, it is not always beneficial to all systems • Need to evaluate multiple mechanisms • Need to study a variety of tissues/diseases • Will require more data • How does processing affect responses

39. Summary • Many potential chemoprotectants • More work is needed to identify individuals in populations that will benefit • Must be aware of potential interactions • Functional foods probably more desirable than nutraceutical supplements

40. Bioactive Questions • Are all bioactive compounds effective at preventing colon cancer? • What are the possible mechanisms of chemoprotection conferred by bioactive compounds? • What are the pros and cons of using a supplement vs getting compounds via the food?