The Microecology of Gastric Cancer - ACS Symposium Series (ACS

22 The Microecology of Gastric Cancer PELAYO CORREA Department of Pathology, Louisiana State University Medical Center, New Orleans, LA 70112

Downloaded by UNIV LAVAL on July 13, 2016 | http://pubs.acs.org Publication Date: December 9, 1981 | doi: 10.1021/bk-1981-0174.ch022

STEVEN R. TANNENBAUM Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, MA 02139 Evidence is reviewed supporting the proposition that stomach cancer etiologic factors operate by modifying the microenvironment of the gastric mucosa. Three main components of the gastric microecology probably related to gastric carcinogenesis are reviewed: the progressive histological lesions of the mucosa, the altered gastric secretions and the dietary items which apparently have an overriding influence in the process. A discussion and an update of the etiologic hypothesis based on intragastric synthesis of N-nitroso compounds are presented. Introduction The present state of our knowledge concerning the etiology of gastric cancer has focused on the microecology of the gastric mucosa. This point has been reached after decades of research by s c i e n t i s t s working i n different d i s c i p l i n e s and different parts of the world. Epidemiologic observations on the d i s t r i bution of cancer and precancerous conditions of the stomach throughout the world and observations of the pathology of gastric cancer and related lesions have been correlated with biochemical observations and led to the formulation of an etiologic hypoth esis which i s being tested i n different ways. The acceptance or rejection of this hypothesis hinges mainly on the results of the work on the chemistry of the process. We w i l l b r i e f l y review the basic data related to the evolution of these ideas. Geographic Distribution Marked contrasts i n the frequency of gastric cancer have been recognized for a long time, as shown i n Figure 1 which gives the rank order of the magnitude of the incidence rate for popu lations throughout the world ÇL, 2). I t i s immediately apparent that some populations i n Japan, Chile, Colombia, Iceland and 0097-6156/81 / 0 1 7 4 - 0 3 1 9 $ 0 5 . 0 0 / 0 © 1981 American Chemical Society

Scanlan and Tannenbaum; N-Nitroso Compounds ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


Figure 1. Map showing the ranks of the age-adjusted (world population) incidence rates for gastrie cancer taken from "Cancer Incidence in Five Continents." All rates are from Volume III (I) except the rate for Chile, which is from Volume I (2). The following regions are represented by more than one racial group: Singapore (Chinese rank 5, Malay rank 37); New Zealand (Maori rank 10, nonMaori rank 27); Hawaii (Japanese rank 11, Caucasian rank 22); California Bay area (black rank 18, white rank 34); New Mexico (Indian rank 19, Spanish rank 21, other white rank 38).


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Europe have rates that are several times greater than those found i n A f r i c a or India. Geography by i t s e l f cannot explain these differences. People of Chinese extraction l i v i n g i n Singapore (rank 5) have several times the rates of Malays i n the same c i t y (rank 37). Similar contrasts are found between whites and Maori l i v i n g i n New Zealand (ranks 10 and 27), blacks and whites i n Detroit and California (ranks 18 and 34), or Indians and whites i n New Mexico (ranks 19 and 38). Race by i t s e l f does not explain this geographic d i s t r i b u t i o n . Nonmigrating Japanese have several times the rate of people of Japanese extraction l i v i n g i n Hawaii, especially the second generation. Whites i n eastern and northern Europe have consider ably higher rates than whites i n New Zealand and the United States. Chinese i n Singapore have rates approximately f i v e times greater than those of Chinese i n Hawaii. Blacks i n Jamaica and Louisiana have rates much higher than those of African blacks. These observations clearly indicate that the disease i s determined mostly by the environment and not by the race of the population. Since the geographic environment per se i s ruled out, it seems that the c u l t u r a l environment i s the one that matters. The most obvious component of the c u l t u r a l environment i s the d i e t , and it may explain the interpopulation d i s t r i b u t i o n . A carcinogen i n the diet has been sought for decades. As i s often the case when carcinogens are looked for i n the d i e t , they are found and that was the case i n several countries, especially i n Iceland where Dungall and others isolated 3,4-benzpyrene from smoked salmon (3). Those findings, however, remain unconvincing i f not linked to epidemiologic or other biologic observations which indicate their relevance to the human cancer s i t u a t i o n . A c r u c i a l observation concerning the d i s t r i b u t i o n of gastric cancer has been that the populations migrating from a high-risk area (such as Russia, Norway, Japan, Latin America) to a low-risk area (such as the United States or Australia) keep their o r i g i n a l high r i s k i n the host country (4). They continue to have high rates of incidence and mortality i n spite of the fact that they l i v e p r a c t i c a l l y a l l of their adult l i v e s i n a country whose indigenous population displays low rates. This migration effect cannot be adequately explained by dietary patterns, and it has led to the idea that gastric cancer i s the result of forces set i n motion many years before cancer becomes c l i n i c a l l y evident. Abundant support for this idea has come from the studies of the pathology and c e l l kinetics of the neoplastic process. F u j i t a , studying the rate of growth (doubling time) of gastric c e l l popu l a t i o n s , estimates that the early (intramucosal) phase of gastric cancer lasts from 16 to 24 years (5). The multistage nature of the carcinogenic process has been well documented i n experimental gastric cancer, especially with the MNNG model which can be accelerated with well-known promoters such as croton o i l (6). Whether the process of carcinogenesis can be inhibited or slowed down by chemopreventive agents s t i l l needs to be demonstrated,


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but there i s suggestive epidemiologic evidence that this may occur i n humans (7) .


Microenvironment Epidemiologic studies of the macroenvironment focused on the diet and the long incubation period have led us to postulate that long-lasting disturbances i n the normal gastric mucosa may determine the f i n a l outcome of the neoplastic transformation (8). This explains the present interest i n precursor lesions rather than i n cancer i t s e l f . We, therefore, need to scrutinize the gastric microenvironment and attempt to point out the components that may be relevant to neoplasia. The microenvironment could be considered to be determined by three basic elements: A. What i s the structure of the gastric mucosa B. What i s secreted into the cavity C. What i s ingested into the stomach We w i l l analyze these components basing our discussions mostly on our observations i n Narino, Colombia, where gastric cancer i s extremely frequent (9, 10, 11). Mucosal Lesions The gastric mucosa surrounding most gastric carcinomas (those of " i n t e s t i n a l " or "epidemic" type) i s the s i t e of profound changes which take many years to develop. The normal glands disappear and are replaced by new glands which resemble those found normally i n the intestine. This process i s called intes t i n a l metaplasia and i s considered a result of chronic inflamma t i o n leading to loss of glands and abnormal regeneration, a l l components of the so-called chronic atrophic g a s t r i t i s . These lesions are found i n the majority of adults i n populations at high gastric cancer r i s k . I t i s c h a r a c t e r i s t i c a l l y a focal process starting around the union of the antrum and the corpus of the stomach. The independent small f o c i of metaplasia gradually expand and coalesce u n t i l extensive areas of the surface are covered. Only rarely the metaplasia covers a l l the surface so that most of the time there are atrophic and normal areas coexisting side by side. The metaplastic c e l l s i n most patients are "mature" i n that they have a l l the characteristics of normal adult small i n t e s t i n a l c e l l s . In some patients, groups of metaplastic c e l l s begin to lose some of the "differentiated" characteristics, produce less mucus and increase their mitotic a c t i v i t y . These changes are usually called dysplasia, which includes distortions of the architecture of the glands (12). As this process becomes more advanced, the gastric mucosa more closely resembles cancer tissues. The f i n a l transformation consists of the loss of dependency of the dysplastic c e l l s on other tissues, which enables them to invade the neighboring structures, the hallmark of cancer.



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The process of cancerization i n the stomach mucosa, there fore, seems to be a continuum of changes which turns a normal c e l l into a metaplastic c e l l and then to a progressively dysplastic c e l l and f i n a l l y a cancerous c e l l . The changes usually take several decades, are gradual, and the change from one c e l l type to the other does not seem obligatory. They seem to r e f l e c t sequential mutations or c e l l transformations. The morphologic changes just described are accompanied by profound histochemical alterations especially related to glycoproteins and cytoplasmic enzymes. The normal surface e p i t h e l i a l c e l l of the stomach accumulates i n i t s cytoplasm multiple droplets of a neutral glycoprotein which constitutes the gastric mucus (13). This i s changed i n metaplastic mucosa which accumulates i n their cytoplasm a large globus (goblet) of acid glycoproteins (mucin). I t appears that i n the early stages of metaplasia the mucin resembles small i n t e s t i n a l mucin i n that it stains with Alcian Blue but not with HID (high-iron diamine) which c l a s s i f i e s it as a sialomucin (14). This type of meta p l a s i a has been called complete metaplasia. In later stages the mucin resembles that of the colon i n that the mucin stains with HID and, therefore, corresponds to sulfomucin. This type of metaplasia has been called incomplete (15-18). Intestinal meta p l a s i a brings to the gastric mucosa enzymes which are foreign to it. In complete metaplasia, sucrase, trehalase, leucine aminopeptidase (LAP) and alkaline phosphatase (ALP) are present; i n incomplete metaplasia, sucrase but not trehalase i s present i n the surface: LAP i s found i n the tissue sections and ALP i s present but only i n very small amounts (16). Cancer i s mostly surrounded by "incomplete" metaplasia, probably another indication of the progressive loss of d i f f e r entiation of the metaplastic c e l l s (19). Secretions The gastric juice i s a mixture of compounds mostly secreted by the different compartments of the gastric mucosa and it varies i n composition according to the physiologic needs and other circumstances. Changes i n the mucus and enzyme secretions which take place i n cancer precursor states have already been described. Fasting gastric juice i n normal persons has a pH of 1 to 2 as a result of the secretion of HC1 by the p a r i e t a l c e l l s . In chronic atrophic g a s t r i t i s the progressive loss of p a r i e t a l c e l l s gradually decreases HC1 secretion but for a long time this i s compensated by overstimulation due to an excess of gastrin secretion and G c e l l hyperplasia (20). When the loss of p a r i e t a l c e l l s i s i n s u f f i c i e n t to respond to the excessive stimulation by gastrin, the secretion of HC1 i s decreased and the pH of the gastric juice becomes elevated. Most patients with chronic atrophic g a s t r i t i s have a pH of 5 or above i n their fasting gastric j u i c e . Whatever HC1 i s secreted comes from islands of



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well-preserved mucosa which l i e side by side with the atrophic mucosa. The gastric juice pH, therefore, represents well the contents of the gastric cavity but not the microecology of the gastric mucosa. The well-preserved areas of the mucosa, with their normal or exaggerated HC1 secretion, probably have a low pH at their surface. In the immediate v i c i n i t y , the atrophic metaplastic mucosa, deprived of HC1 secretion, has a much higher pH. This type of microenvironment, therefore, lends i t s e l f for chemical reactions that may take place i n a wide range of pHs, from 1 to 7. Alterations i n other gastric secretions, such as pepsinogens and blood group substances also take place i n chronic atrophic g a s t r i t i s . The secretion of pepsinogen I has been used as an indicator of i n t e s t i n a l metaplasia and gastric cancer (21, 22). Ingested Materials An important component of gastric microecology derives from ingested materials: food items, bacteria, s a l i v a and the large series of chemical compounds ingested with our foods and our drinking water. There have been many attempts to characterize the diet of populations at high gastric cancer r i s k and of patients with gastric cancer (23). No individual food item has been found universally associated with gastric cancer. This probably should have been anticipated when considering dietary habits i n high-risk areas as d i s i m i l a r as those of England, Finland, Japan, Iceland, Hawaii and Latin America. The s i m i l a r i t i e s of these diets can only be described i n general terms. Most diets associated with high gastric cancer r i s k have the following characteristics: - They are low i n animal f a t and animal protein - They are high i n complex carbohydrates - They obtain a substantial part of their proteins from vegetable sources, mostly grains - They are low i n salads and fresh, green, leafy vegetables - They are low i n fresh f r u i t s , especially citrus - They are high i n s a l t content Exactly how this type of diet predisposes to gastric cancer has not been determined. I t s high bulk obviously influences the gastric microenvironment, and i t s low fat content probably interferes with the absorption of l i p i d soluble substances such as vitamin A and vitamin E. The scarcity of fresh, green leafy vegetables and of c i t r i c f r u i t s may also point to some vitamin deficiencies. The high s a l t content may damage the mucous barrier that protects the mucosa from food items, as well as from the acid-pepsin secretions. There are many populations i n the world with high bulk diet and low gastric cancer rates, and i n some populations such as Finland, the gastric cancer rate has been steadily declining without apparently drastic changes i n the bulk or the vegetable content of the diet. The epidemiologic



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observations suggest that i n some populations a protective factor i s being added to the diet. Another ingested substance which has been linked to the diet i s n i t r a t e . I t has been found that i n some, but not a l l popu lations at high gastric cancer r i s k , the ingestion of nitrates i n the food and drinking water i s higher than i n similar populations with lower r i s k (9, 2Λ). The correlation of n i t r a t e intake and gastric cancer rates i s not observed i n some other populations. This i s not unexpected since n i t r a t e by i t s e l f has not been implicated i n carcinogenesis. Nitrate i s reduced to n i t r i t e i n the s a l i v a and may then be ingested into the stomach. Ingested nitrate i s probably not reduced to n i t r i t e to any s i g n i f i c a n t degree i n the gastric cavity of normal individuals. In patients with chronic g a s t r i t i s , however, a s i g n i f i c a n t amount of n i t r i t e i s detected i n the gastric j u i c e , especially when the pH i s above 5, as can be seen i n Figure 2. The elevated concentrations of n i t r i t e i n gastric juice may be a result of the multitude of bacteria ingested with the diet and the s a l i v a . Instead of being destroyed by the normal acid medium, these bacteria survive and proliferate at the higher pH. Many species of bacteria have been obtained from fasting gastric juice i n patients with chronic atrophic g a s t r i t i s and many of them have n i t r a t e reductases (25, 26). These surviving b a c t e r i a l colonies come i n contact with the gastric mucosa and would find a favorable environment for their survival i n the atrophic areas with t h e i r higher than normal pH. Since these areas are adjacent to the HCl-secreting areas with low pH, the microecology of the junction of the two areas provides the unusual circumstances of having n i t r a t e , n i t r i t e , abundant bacteria and a wide range of pHs. Etiologic Hypothesis Based on the above data and on other available experimental work showing that nitroso compounds can induce gastric cancer i n animals (6) and that nitrosation reactions leading to synthesis of carcinogens can take place i n the gastric cavity environment (27, 28, 29), we have formulated an e t i o l o g i c hypothesis for gastric cancer (8). We have proposed that gastric cancer may be the end result of a series of mutations (or similar c e l l transformations) begun many years before cancer becomes c l i n i c a l l y apparent. The mutagens could be nitroso compounds synthesized i n s i t u from n i t r i t e and naturally-occurring nitrogen-containing compounds. The n i t r i t e results from reduction of nitrate by bacteria abnormally present i n the gastric mucosa and the gastric cavity. The bacteria grow i n s i t u because the pH i s elevated as a result of loss of HC1 secretion secondary to the loss of p a r i e t a l c e l l s and their replacement by intestinal-type epithelium. P a r i e t a l c e l l s are l o s t as a result of chronic atrophic g a s t r i t i s . What


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Correlation between pH and gastric juice of patients in Colombia.


Narino,


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i n i t i a t e s chronic atrophic g a s t r i t i s i s not clear; it may be related to alterations i n the mucous barrier of the stomach brought about by abrasives or i r r i t a n t s such as hard grains, high concentrations of s a l t i n the d i e t , or surfactants. The process, once i n i t i a t e d , i s self-sustaining and may become more accelerated with time because the atrophy and intes t i n a l metaplasia are progressive lesions and lead to further loss of p a r i e t a l c e l l s and incrased bacterial colonization of the mucosa. The i n i t i a l mutations transform gastric c e l l s into mature intestinal-type c e l l s . Further superimposed mutations transform metaplastic c e l l s into progressively dysplastic c e l l s and eventually into neoplastic c e l l s . This i s a process of loss of d i f f e r e n t i a t i o n which implies a multihit phenomenon which could be explained on the basis of continued formation of minute amounts of nitroso compounds over many years. Recent Work After our formulation of the hypothesis i n 1975, many pieces of evidence have come to support the basic theme. A positive association of dysplasia, representing advanced stages of the process, with n i t r i t e levels i n the gastric juice has been reported i n England and Colombia (12, 30). Higher than expected rates of cancer have been reported i n patients with gastrectomy performed 5 or more years previously (31). Of special interest i s the type of gastrectomy called B i l r o t h I I i n which i n t e s t i n a l reflux to the gastric cavity i s f a c i l i t a t e d . In such patients, high levels of n i t r i t e are found i n the gastric cavity (26). The incomplete (less differentiated) f o c i of metaplasia surround f o c i of cancer, suggesting progressive loss of d i f f e r e n t i a t i o n (16, 19). High n i t r i t e levels i n the gastric cavity have been associated with acceleration of the gastric cancer induction with MNNG i n experimental animals (26). Gastric cancer has been induced i n experimental animals with products derived from n i t r o sated f i s h (32). So f a r , we have been considering the nitrosation to occur i n the lumen of the stomach. Recently, Stemmermann et a l . (33) have reported that nitrosation may occur within the gastric mucosa itself.


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Literature Cited

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1. Waterhouse, J.; Muir, C.; Correa, P.; Powell, J., Eds.; "Incidence in Five Continents. Vol. III"; International Agency for Research on Cancer: Lyon, France, 1976. 2. Doll, R.; Payne, P.; Waterhouse, J., Eds.; "Cancer Incidence in Five Continents"; International Union Against Cancer: Springer Verlag, Berlin, 1966. 3. Dungal, N. J.A.M.A. 1961, 178, 789-98. 4. Haenszel, W. J. Natl. Cancer Inst. 1961, 26, 37-132. 5. Fujita, S.; Takanori, H. In: Pathophysiology of Carcinogenesis in Digestive Organs. University of Tokyo Press, 1977. 6. Sugimura, T.; Fujimura, S.; Baha, T. Cancer Res. 1970, 30, 455-65. 7. Bjelke, E. Scand. J. Gastroenterol. 1974, 9, 1-235. (Suppl.). 8. Correa, P.; Haenszel, W.; Cuello, C.; Tannenbaum, S.; Archer, M. Lancet 1975, 2, 58. 9. Cuello, C.; Correa, P.; Haenszel, W.; Gordillo, G.; Brown, C.; Archer, M.; Tannenbaum, S. J. Natl. Cancer Inst. 1976, 57, 1015-20. 10. Haenszel, W.; Correa, P.; Cuello, C.; Guzmán, N.; Burbano, L. C.; Lores, H.; Muñoz, J. J. Natl. Cancer Inst. 1976, 1021-6. 11. Correa, P.; Cuello, C.; Duque, E.; Burbano, L. C.; García, T.; Bolaño, O.; Brown, C.; Haenszel, W. J. Natl. Cancer Inst. 1976, 57, 1027-35. 12. Cuello, C.; Correa, P.; Zarama, G.; López, J.; Murray, J.; Gordillo, G. Am. J. Surg. Pathol. 1979, 3, 491-500. 13. Lev, R. Lab. Invest. 1965, 14, 2080-2100. 14. Spicer, S. S. J. Histochem. Cytochem. 1965, 13, 211-34. 15. Abe, M.; Ohuchi, N.; Sokano, H. Acta Histochem. Cytochem. 1974, 7, 282-9. 16. Matsukura, N.; Suzuki, K.; Kawachi, T.; Soyagi, M.; Sugimura, T.; Kitaoka, H.; Numajiri, H.; Slivota, Α.; Itahashi, M.; Hirota, T. J. Natl. Cancer Inst, 1980, 65, 231-40. 17. Jass, J. R.; Filipe, M. I. Histopathology 198, 4, 271-9. 18. Sipponen, P.; Seppala, K.; Varisk, L.; Ihamaki, T.; Kekki, M.; Siurala, M. Acta Pathol. Microbiol. Scand. 1980, Sect. A 88, 217-24. 19. Heilmann, K.;Hopker, W. Pathol. Res. Pract. 1979, 164, 249-58. 20. Correa, P. Front. Gastrointest. Res. 1980, 6, 98-108. 21. Nomura, Α.; Stemmermann, G. N.; Samloff, M. Ann. Intern. Med. 1980, 93, 537-40. 22. Stemmermann, G. N.; Ishidate, T.; Samloff, M.; Masuda, H.; Walsh, J.; Nomura, Α.; Yamakawa, H.; Glober, G. Am. J. Dig. Dis. 1978, 23, 815-20.



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23. Haenszel, W.; Correa, P. Cancer Res. 1975, 35, 3452-9. 24. Fraser, P.; Chilvers, C.; Beral, U.; Hill, M. Int. J. Epidemiol. 1980,9,3-11. 25. Hawksworth, G.; H i l l , M.; Gordillo, G.; Cuello, C. "N-nitroso Compounds in the Environment"; International Agency for Research on Cancer, Scientific Publication No. 9: Lyon, France, 1975. 26. Herfarth, C.; Schlag, P., Ed.; "Gastric Cancer"; Springer Verlag, Berlin, 1979; p 44, 120. 27. Druckery, H.; Steinhoff, D.; Beuthner, H.; Schneider, H.; Klarner, P. Arzneim. Forsch. 1963, 13, 320-5. 28. Sander,J.;Burkle, G.; Schweinsberg, F. "Topics in Chemical Carcinogenesis"; University Park Press: Baltimore, USA, 1973 ; p 297. 29. Endo, H.; Takahashi, K. Nature 1973, 245, 325. 30. Jones, S. M.; Davis, P. W.; Savage, A. Lancet 1978, 1, 1355. 31. Nichols, J. C. World J. Surg. 1979, 3, 731-6. 32. Weisburger, J. H.; Marquardt, H.; Hirota, N.; Mori, H.; Williams, G. M. J. Natl. Cancer Inst. 1980, 64, 163-7. 33. Stemmermann, G. N.; Mower, H.; Rice, S.; Ichinotosubo, D.; Tomiyasu, L.; Hayeshi, T.; Nomura, Α.; Mandel, M. "Gastrointestinal Cancer - Endogenous Factors"; Banbury Report No. 7: Cold Spring Harbor Laboratory, Ν. Y., 1981; p 175. RECEIVED August 10, 1981.


The Microecology of Gastric Cancer - ACS Symposium Series (ACS

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